Motion Systems Handbook 2016 by WTWH Media LLC

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September 2016

MOTION

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MILES BUDIMIR SENIOR EDITOR

MOTION SYSTEMS; EVOLUTIONARY CHANGE... and then some EACH

year, the Design World motion editors prepare this special Motion Systems Handbook aiming to give our readers an overview of the basics of motion control systems. While it may be a truism that the fundamentals don’t change all that much from year to year, there is certainly evolutionary change taking place. Both tried and true technologies of yore, such as belts and pulleys, chains, and screws, as well as more sophisticated components like controllers and drives are changing in line with the evolving industrial landscape, a chief driver of which is the Internet of Things (IoT) and its grittier cousin the Industrial Internet of Things (IIoT). In fact, if anything can qualify as revolutionary, it may just be this proliferation of data in the increasingly interconnected world of devices. Most recent predictions for the motion industry focus overwhelmingly not on components themselves but rather on data. The vast amounts of data available promise an abundance of benefits to industrial machines and systems such as increased productivity, less machine downtime, and better efficiency. There are a lot of related concepts here, including the so-called “smart factory” or “smart manufacturing”, yesterday’s buzzwords that are becoming today’s reality. All of them rely on collecting and analyzing data and putting it

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to productive use. Collecting this data via sensors, making it available to control systems at both the machine level as well as the enterprise level is what is bringing about the next generation of intelligent manufacturing. Changes to motion system components reflect this. Some common examples include drives with auto-tuning capabilities for on-the-fly adjustments based on real-time conditions, and motors incorporating sensors collecting data on vibration which is then used to adjust performance or alert operators of any issues. As the motion industry continues to change, our hope is that this handbook will be informative and useful to you in your work. We always appreciate feedback from our readers and welcome more. Let us know how we’re doing as we look for ways to improve going forward. Tell us what you think.

Is there something we’ve missed? Do you want more detail or less? Is there some technology or component we’ve overlooked? You’re welcome to send any feedback directly to any of our motion editors. You can reach me at mbudimir@wtwhmedia.com or senior editor Lisa Eitel at leitel@wtwhmedia.com. You can also follow us on twitter at @DW_Motion, @DW_Lisa_Eitel, as well as our linear motion editor Danielle Collins at @DW_dcollins. Together we deliver the latest news and developments in motion control directly to you. And be sure to check out our specialized motion-themed websites at www. motioncontroltips.com, www.linearmotiontips.com as well as www.bearingtips.com and www.couplingtips. com for all the latest news, technical stories and industry trends.

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Line Voltage, Current, and Power – The Basics LINE VOLTAGE Three-phase line voltage consists of three voltage vectors. • By deﬁnition, the system is “balanced” • Vectors are separated by 120° • Vectors are of equal magnitude • Sum of all three voltages = 0 V at Neutral

Neutral

Line

At any given moment in time, the voltage magnitude is V * sin(α) • V = magnitude of voltage vector • α = angle of rotation, in radians

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Line

The resulting time-varying “rotating” voltage vector appears as a sinusoidal waveform with a ﬁxed frequency • 50 Hz in Europe • 60 Hz in US • Either 50 or 60 Hz in Asia • Other frequencies are sometimes used in non-utility supplied power, e.g. • 400 Hz • 25 Hz

Important to Know • Voltage is stated as “VAC”, but this is really VRMS • Rated Voltage is Line-Neutral • VPEAK = 2 * VAC (or 2 * VRMS ) • 169.7 V in the example below • VPK-PK = 2 * VPEAK • If rectiﬁed and ﬁltered • VDC = 2 * VAC = VPEAK AC Single-Phase “Utility” Voltage

120 VAC Example

Volts (Peak), Line-Neutral

200

teledynelecroy.com/staticdynamic-complete

At any given moment in time, the current magnitude is I*sin(α) • I = magnitude of current vector • α = angle of rotation, in radians

120VAC

150 100 50 0

THREE-PHASE

-100 -150 -200

800

Important to Know • Voltage is stated as “VAC”, but this is really VRMS • Rated Three-phase voltage is always Line-Line (VL-L) • Line-Line is A-B (VA-B), B-C (VB-C), and C-A (VC-A) • Line-Line is sometimes referred to as Phase-Phase • VPEAK(L-L) = 2 * VL-L • 679 V in the example to the right • VPK-PK(L-L) = 2 * VPEAK(L-L)

“True” RMS

400

VRMS =

1 V PK-PK 2 2

VRMS = VAC2 For one power cycle

-800

800

If a neutral wire is present, three-phase voltages may also be measured Line-Neutral • VL-N = VL-L/ 3 • 277 VAC (VRMS) in this example • VPEAK = 2 * VL-N • 392 V in the example to the right • VPK-PK = 2 * VPEAK

Time

AC Three-Phase “Utility” Voltage 480VAC , Measured Line-Neutral

600 400 200 0 -200

-400

-600 -800

Time

A-N Voltage B-N Voltage C-N Voltage Three-phase Rectiﬁed DC

AC Three-Phase "Line" Currents

9 6 3

Time A Current B Current C Current

Reactive Power • Q, in Volt-Amperes reactive, or VAr • Q = S2 - P2 • Does not “transfer” to load during a power cycle, just “moves around” in the circuit

10 ARMS Example

Period 1 Mi = 18 points

Period 2 Mi = 18 points

mi = point 7

mi = point 25

V B-N

N V A -N

P≠V*I

Capacitive load

• The digital samples are grouped into measurement cycles (periods) • For a given cycle index i…. • The digitally sampled voltage waveform is represented as having a set of sample points j in cycle index i • For a given cycle index i, there are Mi sample points beginning at mi and continuing through mi + Mi -1. • Voltage, current, power, etc. values are calculated on each cycle index i from 1 to N cycles.

PTO TA L = VA -N * IA + VB-N * IB + VC-N * IC

IA PTO TA L ≠ VA -N * IA + VB-N * IB + VC-N * IC

V C-N

teledynelecroy.com/motor-drive-analyzer

IRMS

Real Power for each Phase • P, in Watts • = instantaneous V * I for a given power cycle

VRMSi =

IRMSi =

Reactive Power for each Phase • Q, in Volt-Amperes reactive, or VAr • Q = S2 - P2

SB PA

• PTOTAL = PA + PB + PC • STOTAL = SA + SB + SC • QTOTAL = QA + QB + QC

φ φ

PC QC

Line-Line Voltage Sensing Case

B IB VB-C

Current is measured L-N

L-L voltages must be transformed to L-N reference:

VB-N

VA-B

VA-N IA

VC-A

Calculations are straightforward, as described above: • PTOTAL= PA + PB + PC • STOTAL = SA + SB + SC • QTOTAL = QA + QB + QC

VC-N

Two Wattmeter Method – 2 Voltages, 2 Currents with Wye (Y or Star) or Delta (∆) Winding

φ P

Real Power

Note: Any distortion present on the Line voltage and current waveforms will result in power measurement errors if real power (P) is calculated as |S|*cos(φ). To avoid measurement errors, a digital sampling technique for power calculations should be used, and this technique is also valid for pure sinusoidal waveforms.

Voltage is measured L-L on two phases • Note that the both voltages are measured with reference to C phase

mi + Mi - 1 1 V j2 Mi j=mi

mi + Mi - 1 1 I j2 Mi j=mi

PTOTAL = VA-C * IA + VB-C * IB STOTAL= VRMSA-C * IRMSA + VRMSB-C * IRMSB QTOTAL = STOTAL2 - PTOTAL2

Current is measured on two phases • The two that flow into the C phase Mathematical assumptions: • Σ(IA + IB + IC) = 0 • Σ(VA-B + VB-C + VC-A) = 0 This is a widely used and valid method for a balanced three-phase system

Formulas Used for Per-cycle Digitally Sampled Calculations

VRMS

V A -N

IC V C-N

Voltage is measured L-L • Neutral point may not be accessible, or • L-L voltage sensing may be preferred

Inductive load

-9

Delta (∆) 3-phase Connection • Neutral is not present in the winding (in most cases)

Real Power • P, in Watts • = instantaneous V * I for a given power cycle

0 -3 -6

-12 -15

A IC

Apparent Power • |S|, in Volt-Amperes, or VA • = VRMS * IRMS for a given power cycle

15 12

Digital Sampling Technique for Power Calculations�

Single-phase Real, Apparent and Reactive Power

Three-Phase Winding Connections

V I

• For inductive loads • The current vector “lags” the voltage vector angle φ • Purely inductive load has angle φ = 90° • Capacitive Loads • The current vector “leads” the voltage vector by angle φ • Purely capacitive load has angle φ = 90°

Important to Know • Current is stated as “lAC”, but this is really IRMS • Line currents can represent either current through a coil, or current into a terminal (see image below) depending on the three-phase winding connection • IPEAK = 2 * IRMS • 14.14A for a 10 ARMS current in the example to the right • IPK-PK = 2 * IPEAK

A-B Voltage B-C Voltage C-A Voltage

480 VAC Example

P≠V*I N

Line Current Measurements

-600

As with the single-phase case, Power is not the simple multiplication of voltage and current magnitudes, and subsequent summation for all three phases.

Apparent Power for each Phase • |S|, in Volt-Amperes, or VA • = VRMS * IRMS for a given power cycle

Single-phase, Non-resistive Loads For capacitive and inductive loads • P ≠ V * I since voltage and current are not in phase

-400

For one power cycle

120°

Current value = IX*sin(α) • IX = magnitude of line current vector • α = angle of rotation, in radians

200

-200

Line-Neutral Voltage Measurements

Wye (Y) 3-phase Connection • Neutral is present in the winding • But often is not accessible • Most common conﬁguration

VPK-PK

Neutral

Like voltage, the resulting time-varying “rotating” current vectors appear as three sinusoidal waveforms • Separated by 120° • Of equal peak amplitude for a balanced load

AC Three-Phase “Utility” Voltage 480VAC , Measured Line-Line

600

480 VAC Example

Time

“Not True” RMS

Power Factor (PF, or λ) • cos(φ) for purely sinusoidal waveforms • Unitless, 0 to 1, • 1 = V and I in phase, purely resistive load • 0 = 90° out of phase, purely capacitive or purely inductive load • Not typically “signed” – current either leads (capacitive load) or lags (inductive load) the voltage

Line-Line Voltage Measurements

Three-phase, Non-resistive Loads

For purely resistive loads • PA = VA-N * IA • PB = VB-N * IB • PC = VC-N * IC • PTOTAL = PA + PB + PC V B-N

Voltage Current

120°

VA-N

Resistive load

Three-phase, Resistive Loads

Three-phase, Any Load

ω (rad/s) or freq (Hz)

Like voltage, three-phase current has three different line current vectors that rotate at a given frequency • Typically, 50 or 60 Hz for utility-supplied voltage

By deﬁnition, the system is “balanced” • Vectors are separated by 120˚ • Vectors are of equal magnitude • Sum of all three currents = O A at neutral (provided there is no leakage of current to ground)

VA-B

Neutral

120°

P=V * I

Power Factor

Phase Angle (φ) • Indicates the angular difference between the current and voltage vectors • Degrees: - 90° to +90° • Or radians: -π/2 to + π/2

Line

Neutral

Voltage value = VX*sin(α) • VX = magnitude of phase voltage vector • α = angle of rotation, in radians

If all three phases are rectiﬁed and ﬁltered • VDC = 2 * VL-N * 3 = VPEAK * 3 = 679 V in the example to the right

-50

For purely resistive loads • P = I2R = V2/R = V * I • The current vector and voltage vector are in perfect phase

Phase Angle ω (rad/s) or freq (Hz)

The resulting time-varying “rotating” voltage vectors appear as three sinusoidal waveforms • Separated by 120° • Of equal peak amplitude

Voltages can be measured two ways: • Line-Line (L-L) • Also referred to as Phase-Phase • e.g. from VA to VB, or VA-B • Line-Neutral (L-N) • Neutral must be present and accessible • e.g. from VA to Neutral, or VA-N • VL-L conversion to VL-N • Magnitude: VL-N * 3 = VL-L • Phase: VL-N - 30° = VL-L

THREE-PHASE

Electric Power • “The rate at which energy is transferred to a circuit” • Units = Watts (one Joule/second)

The resulting time-varying “rotating” current vector appears as a sinusoidal waveform

120°

VB ω (rad/s) or freq (Hz) Neutral

to receive a Power Basics

Neutral

120°

The three voltage vectors rotate at a given frequency • Typically, 50 or 60 Hz for utility-supplied voltage The single-phase voltage vector rotates at a given frequency • Typically, 50 or 60 Hz for utility-supplied voltage

120°

ω (rad/s) or freq (Hz)

Typically, the three phases are referred to as A, B, and C, but other conventions are also used: • 1, 2, and 3 • L1, L2, and L3 • R, S, and T

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SINGLE-PHASE

Like voltage, the single-phase current vector rotates at a given frequency • Typically, 50 or 60 Hz

Imaginary Power

Typically, the single-phase is referred to as “Line” voltage, and is referenced to neutral.

LINE POWER

SINGLE-PHASE B

Line Current (Peak)

• Magnitude (voltage) • Angle (phase)

Volts (Peak), Line-Line

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THREE-PHASE

Single-phase line voltage consists of one voltage vector with:

Volts (Peak), Line-Neutral

Learn more about the

LINE CURRENT

SINGLE-PHASE

IB VB-C

IA VA-C

VB-C

VA-C

mi + Mi - 1

Real Power (P, in Watts)

Pi =

Apparent Power (S, in VA)

Reactive Power (Q, in VAR)

1 Mi

Vj * Ij

j=mi

Power Factor (λ)

λi =

Pi Si

Si = VRMSi * IRMSi

magnitude Qi =

S i2 - P i2

Sign of Qi is positive if the fundamental voltage vector leads the fundamental current vector

Phase Angle (φ)

magnitude Φi = cos-1λi Sign of Φi is positive if the fundamental voltage vector leads the fundamental current vector

MDA800 Series 8 ch, 12-bit, 1 GHz Oscilloscope tlec-mda-poster-designworld-Q3.indd 1 Commentary.Miles_MSHandbook8-16_V1.indd 7

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The downside of

PATENT PROTECTION LEE TESCHLER EXECUTIVE EDITOR

MUCH

angst has been expressed over patent trolls that buy up lowquality patents then sue the bejesus out of potential infringers to “enforce” IP rights. Lest you think patent suits by these guys are over money earned from patents, consider this: Scholars at the National Bureau of Economic Research have found that patent trolls often sue though the patent in question has earned little or no money. The suits gets filed, scholars say, simply because the “infringers” have a lot of cash; the cash often comes from other businesses that have nothing to do with the patent. The NBER scholars have also found that such shenanigans hamper innovation. They say firms targeted by patent trolls reduce their own R & D budgets by an average of more than 25%. The implication is that some of the funds normally spent on advancing technology instead go toward defending against nuisance lawsuits. The trolls frequently defend their actions with claims they benefit the small inventors whose patents they defend from “infringement.” Not true, according to the NBER scholars. Little of the money patent trolls receive in litigation passes through to the small inventors. And there is no evidence any of this court action has led to an upsurge in patent activity among independent inventors.

DESIGN WORLD — MOTION

Commentary.Lee_MSHandbook8-16_V1.indd 8

A number of observers have recently come around to that view that patents could be more trouble than they’re worth, and not just because of spurious patent suits. A review of history shows that the mere holding of a patent is no guarantee of commercial success. In fact, it is easy to uncover tales of inventors who were consumed with defending their patent rights while others founded industries related to the work of those pioneers. For an example, consider the case of Charles Goodyear. Goodyear received his patent for vulcanized rubber in 1844 but spent most of the rest of his life in patent disputes with Thomas Hancock and Stephen Moulton. Goodyear himself was never prosperous. The company bearing his name, Goodyear Tire & Rubber, wasn’t founded until almost four decades after his death, long after his patents had expired. Perhaps more notorious are the patent disputes surrounding the Wright brothers. It has been reported that the Wrights had such a reputation for lawsuits that aviator Glenn Curtiss and his colleagues mockingly suggested the brothers would sue anyone jumping in the air and waiving their arms. The Wright’s business was profitable but not overly so. And it didn’t last. Orville sold the company in 1915 after the death of his brother. The firm produced its last plane in 1916. 9 • 2016

A more modern example that invokes discussion about the value of patents is in 3D printing. The first patents for stereolithography and digital slicing strategies were filed in the 1980s. But the 3D printing industry didn’t really boom until 30 years later. So you have to wonder how much of an advantage it was to be the inventor of those early discoveries. There are ways to avoid the downside of patenting. One is counterintuitive: In 2014, Tesla Motors founder Elon Musk decided to make all Tesla patents open source. Tesla patents number in the hundreds. They cover everything from bumper mounting plates to battery pack safety. Musk’s rationale for the move: “I realized that receiving a patent really just meant that you bought a lottery ticket to a lawsuit.” Then, of course, there is the approach taken by Cicoil in Valencia, Calif. In the 1950s, this maker of motion cable came up with a special process for extruding continuous lengths of flat cable out of clear material. But don’t bother trying to find Cicoil’s patents on the technique. There aren’t any. The firm treats the process and anything related to it as a trade secret.

motioncontroltips.com | designworldonline.com

9/14/16 5:03 PM

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INSIDE

VOL 2 • NO 3

the motion systems handbook Actuators

Drives

Electrical ..................................................18

AC ...........................................................86

Pneumatic ............................................ 24

DC ...........................................................90

Rigid Chain ..............................................28

Encoders .......................................................92

Ballscrews .....................................................31

Gearing .........................................................98

Bearings ........................................................36

Gearmotors ............................................... 110

Belts & Pulleys ..............................................40 Brakes & Clutches .........................................45 Cable Management ......................................48

HMI Hardware ........................................... 114 HMI Software ............................................. 116 Leadscrews................................................. 119

Cabling .........................................................52

Linear Guides Rails, Slides & Systems ....... 122

Chain ............................................................57

Motors

Compression Springs ...................................59 Controllers ....................................................62 Conveyors .....................................................73 Couplings .....................................................76

AC ........................................................ 131 DC ........................................................ 132 Integrated ............................................ 134 Linear ................................................... 136

Servo .................................................... 142 Stepper ................................................ 148

Networks.................................................... 152 Rack and Pinion Sets ................................. 157 Retaining Rings .......................................... 161 Shock, Vibration Damping ......................... 162 Stages & Tables ......................................... 166 Transducers ................................................ 172 Wave Springs ............................................. 173

Cover photography by Miles Budimir

DESIGN WORLD — MOTION

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9 • 2016

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9/13/16 2:21 PM

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HANDBOOK

What are the main types of

Motion System

ELECTRIC ACTUATORS? ELECTRIC

actuators come in myriad configurations to suit almost any application, environment or industry. They’re primarily categorized by their drive mechanism. Then manufacturers use other features such guide and housing types to further differentiate them. Here’s an explanation of all the most common linear-actuator categories.

BELT-DRIVEN AND SCREW-DRIVEN LINEAR ACTUATORS Although belt and screw drives are different technologies, it makes sense to put them in the same category because they are the two most common types of electromechanical actuators. Most manufacturers of linear actuators offer both belt and screw-driven options. Belt-driven actuators pair with a variety of guide mechanisms — with plain bearings, cam-roller guides, and

recirculating bearings (riding a profiled rail or round shaft) most common. Because their strengths are high speed and long stroke, belt-driven systems are often housed in an aluminum extrusion or in open configurations without protective housing. Within the screw-driven category, there are ballscrew-driven and lead-screw-driven actuators. Ballscrew actuators have higher repeatability and thrust forces than lead-screw actuators, but both provide inherent gearing through the screw’s lead (pitch). The most common guide system for screw-driven actuators is profiled rail, although plain bearings sometimes guide lead-screw-driven actuators. Because screwdriven actuators need rigidly mounted end bearings, aluminum extrusions often enclose them. However, applications needing high travel accuracy benefit from ball-screw types with a machined steel housing. One design that doesn’t exist is a ball screw actuator with cam rollers as the guide mechanism. This is because the forte of cam-roller guides is high speed, whereas ball-screw actuators are primarily for high repeatability and high thrust force — with limited speed capabilities.

This Tolomatic MXB-S belt-driven actuator has a solid bearing design to boost performance in harsh environments — with load-carrying capacities up to 520 lb.

DESIGN WORLD — MOTION

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maxon control electronics for strong DC brushed and brushless motors.

maxon motor control

Power under control.

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maxon precision motors 101 Waldron Road, Fall River, MA 02720, USA Phone 508-677-0520 info@maxonmotorusa.com, www.maxonmotorusa.com

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HANDBOOK

Motion System

This LINAK electric linear actuator has an integrated controller to reduce wiring and eliminate the need for external controls. Basic, Advanced, Parallel and BUS options offer different functionalities.

carriages independently. A common application for rack-and-pinion actuators is overhead gantries in automotive production. Linear-motor actuators are also capable of long travel lengths with multiple carriages, but they’re primarily used for high-precision strokes and very dynamic motion. To complement the strengths of linear motors, these actuators use highprecision profiled rails, crossed roller guides, or even air bearings as their guidance. Linear-motor-based actuators can mount in an extruded housing or on a machined aluminum plate, but to meet the highest travel accuracy specifications, they can also mount on a machined steel plate or granite base.

USING TOOLS TO PICK FROM MULTIPLE ACTUATOR OPTIONS

PNEUMATICALLY DRIVEN ACTUATORS Pneumatically driven actuators aren’t electromechanical devices like the other actuator types, but their prevalence in automated equipment makes them important. For more information on two types — slider and rod-type offerings — see the section in this handbook covering pneumatic actuators.

RACK-AND-PINION DRIVEN ACTUATORS For extremely long lengths and robustness against contamination, rack-and-pinion-driven actuators are often the most suitable choice. However, finding a comparably suitable guide can sometimes be difficult. Joined profiled rails sometimes work for extremely long lengths. However, where contamination is a significant concern, metal wheels are usually preferred. A unique feature of rack-and-pinion-based actuators is their ability to drive multiple 20

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With so many options, choosing the best linear actuator is a complex task. There’s rarely one right way to make a selection. The easiest place to start is usually with a manufacturer’s sizing software or selection program. Results often include several choices, which can be narrowed down by considering non-quantitative criteria such as ease of maintenance, integration with existing components or systems, and space constraints. Usually, sizing and selection software will run through the traditional lineup of steps in selecting an electric actuator. The first step is to define the motion profile. This establishes the demands for velocity and time as well as force (or torque) and the required travel distance. This is also the place to determine maximum stroke needed as well as maximum and minimum speed requirements. The next step is to calculate the load. This can include inertial load, friction load, external applied load, as well as gravitational load. Load calculations also depend on the orientation of the actuator itself, whether it’s horizontal or vertical. Next define duty cycle. This the ratio of operating time to resting time expressed as a percentage. The cycling rate may be in seconds, minutes, hours or even days; knowing the operating hours per day may also be necessary. Knowing the duty cycle helps engineers estimate system life requirements and can eliminate problems such as overheating, faster wear and premature component failure due to incorrectly sized actuators. Know the positional accuracy and precision demanded by the application. The actuator’s precision should meet or exceed the application’s requirements for accuracy, backlash, motioncontroltips.com | designworldonline.com

9/9/16 4:57 PM

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HANDBOOK

Motion System

Actuator offerings in the Optimized Motion Series (OMS) of packaged linear and rotary designs from Festo lower OEM overhead by speeding specification, assembly, and commissioning of axes. Online tools help engineers in specification, and quick delivery reduces inventory requirements.

and straightness and flatness of linear motion. This directly impacts system cost. If the application doesn’t demand high accuracy or precision, then there is no need to buy a more expensive actuator when a less expensive one will satisfy the demands of the application. Aside from the technical specifications mentioned above, select the proper configuration for the actuator in the final design. This includes mounting considerations and the need for any other external components, such as holding brakes and communication and power cables. Lastly, consider the operating environment for the actuator. What are the temperature requirements? Are there any contaminants such as water, oil or abrasive chemicals? Contaminants can damage seals and shorten actuator life. Selecting an actuator with a sufficient IP rating can guard against contaminants.

CURRENT STATE OF ACTUATOR TECHNOLOGIES

These electric actuators from Warner Linear are tailored to light-duty, general-duty, or rugged-duty applications.

DESIGN WORLD — MOTION

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Electric actuators are more cost effective than ever, and that’s allowed new application uses. It’s a bit how servomotors are replacing some induction motors to boost performance and efficiency — and direct drives are replacing some traditional motor-gearbox combinations to impart more dynamic performance and precision. For the same reasons, electric actuators are replacing some pneumatic cylinders in applications. Electric actuators can be more complicated that fluid-power offerings to setup, but can integrate power, control and actuation in one device. What’s more, they can constantly monitor feedback from the motor and adjust performance accordingly. Though not necessary for every application, closed-loop operation lets some actuators adjust and correct variances in the operation to get repeatable and accurate motion. In fact, some of the most significant improvements in electric-actuator design have been in their controls. Faster bus systems such as industrial Ethernet (Ethernet IP, Modbus, TCP) and other realtime communications are making electric-actuator integration simpler than ever. That’s useful because servo-run actuators need fast communication and exchange of real-time data between the axis drive and machine control. The bus was always the bottleneck in these systems — until now. So today, many actuators work as fully integrated motion devices that deliver more precise control than ever.

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HANDBOOK

Motion System

Norgren’s ISO/VDMA actuators are interchangeable with other manufacturers’ cylinders and conform to ISO 15552 and 6431, VDMA 24562 and NFE 49-003-1. The series includes aluminum profile-barrel and traditional tie-rod construction.

Technical update on

PNEUMATIC ACTUATORS PNEUMATIC

actuator technology has existed for more than 50 years, but better piston seals and rod wiper seals (of modern materials) make pneumatic actuators more resilient and efficient than ever. These seals reduce leakage and withstand extreme temperatures to let engineers use the actuators in more environments. Likewise, surfaces with permanent lubrication, servo-pneumatic controls, improved corrosion resistance and air-cushioning features make pneumatic actuators more useful than ever.

Rodless cylinders are used in pneumatic applications requiring a compact installation with a wide range of stroke possibilities. They most often used for automation applications requiring positioning, and can run full stroke to index tooling, or position objects in material handing. The most common applications for rodless cylinders are packaging, cutting, material transfer, assembly and electronics manufacturing. They stroke length is nearly as long as their body length, where a standard piston rod cylinder extends entirely outside its retracted length. Some rodless cylinders use a reciprocating cable instead of a guided table, allowing unique results not possible with rods or guides.

WHERE ARE RODLESS CYLINDERS USED?

Pneumatics is the technology of compressed air. However, it’s commonly considered a type of automation control. Pressurized gas — generally air that is dry or lubricated — is used to actuate an end effector and do work. End effectors can range from the common cylinder to more applicationspecific devices such as grippers or air springs. Vacuum systems, also in the pneumatic realm, use vacuum generators and cups to handle delicate operations, such as lifting and

WHAT ARE THE BENEFITS OF PNEUMATIC ACTUATORS? A rodless cylinder has a piston activated from either side with compressed air. The piston is mechanically or magnetically coupled to the guided table, and as the piston moves, so does the table.

Airpel anti-stiction air cylinders from Airpot deliver accurate force control thanks to a graphite piston and borosilicate glass cylinder. The cylinder and piston mate with extremely close clearances, so the actuators respond to forces down to a few grams and pressures of less than 0.2 psi. One-foot strokes are standard, though longer versions in custom actuators are possible.

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Electric rod actuators

The shortest distance to linear motion solutions

Power and performance to replace pneumatic and hydraulic cylinders

ERD electric cylinders • USDA- and 3A-approved hygienic design • Ball- or roller-screw driven • IP69K/IP67 options • Force range to 7,868 lbf (35 kN)

High-force RSA actuator • Ball- or roller-screw driven • IP67 • High thrust up to 13,039 lbf (58 kN) • Guided options

Heavy-duty IMA linear servo actuator • Compact package • Ball- or roller-screw driven • IP67 • Force range to 6,875 lbf (30 kN)

Visit www.tolomatic.com/electric-rod

Tolomatic makes it easy to take your machine design from premise to production. Make your next machine everything you imagine it can be. Optimize cost and performance with our complete single-axis linear motion solutions—actuator, drive, motor and controls. We meet nearly any application requirement, and our online tools simplify specification. With over 60 years of product innovation and integrity, our technical and customer service support is unequaled. Great design ideas start on the back of a napkin. Contact us to help you get from point A to point B. Visit www.tolomatic.com or call 877-385-2234. Download our white paper comparing linear actuator solutions. www.tolomatic.com/Napkin

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HANDBOOK

Motion System

moving large sheets of glass or delicate objects such as eggs. Pneumatics is common in industries that include medical, packaging, material handling, entertainment and even robotics. By its nature, air is easily compressible, and so pneumatic systems tend to absorb excessive shock, a feature useful in some applications. Most pneumatic systems operate at a pressure of about 100 psi, a small fraction of the 3,000 to 5,000 psi that some hydraulic systems see. As such, pneumatics are generally used when much smaller loads are involved. A pneumatic system generally uses an air compressor to reduce the volume of the air, thereby increasing the pressure of the gas. The pressurized gas travels through pneumatic hoses and is controlled by valves on the way to the actuator. The air supply itself must be filtered and monitored constantly to keep the system operating efficiently and the various components working properly. This also helps to ensure long system life. In recent years, the control available within

Festo’s DDLI servo-pneumatic actuator makes precise dynamic movements, even when transporting loads to 180 kg horizontally and 60 kg vertically with 30% faster cycle times than comparable pneumatic actuators. It also features integrated position feedback which offers OEMs fast, controlled positioning and the capability to regulate feed forces on the fly.

pneumatic systems (thanks to advanced electronics and componentry) has increased a great deal. Where once pneumatic systems could not compete with many comparable electronic automation systems, the technology today is seeing a renaissance of sorts.

HOW DO THESE FLUID-POWER ACTUATORS WORK? Many industrial applications require linear motion during their operating sequence. One of the simplest and most cost effective ways to accomplish this is with a pneumatic actuator, often referred to as an air cylinder. An actuator is a device that translates a source of static power into useful output motion. It can also be used to apply a force. Actuators are typically mechanical devices that take energy and convert it into some kind of motion. That motion can be in any form, such as blocking, clamping or ejecting. Pneumatic actuators are mechanical devices that use compressed air acting on a piston inside a cylinder to move a load along a linear path. Unlike their hydraulic alternatives, the operating fluid in a pneumatic actuator is simply air, so leakage doesn’t drip and contaminate surrounding areas. There are many styles of pneumatic actuators, including diaphragm cylinders, rodless cylinders, telescoping cylinders and through-rod cylinders.

This RLSS Series linear locking device from Fabco-Air is spring-engaged (and air-released). It fits onto air cylinders and guide rods to hold loads during emergency stops.

DESIGN WORLD — MOTION

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ACTUATORS • PNEUMATIC

The most popular style of pneumatic actuator consists of a piston and rod moving inside a closed cylinder. This actuator style can be sub-divided into two types based on the operating principle: single acting and double acting. Single-acting cylinders use one air port to let compressed air enter the cylinder to move the piston to the desired position, as well as an internal spring to return the piston to the “home” position when the air pressure is removed. Double-acting cylinders have an air port at each end and move the piston forward and back by alternating the port that receives the high pressure air. In a typical application, the actuator body connects to a support frame and the end of the rod is connected to a machine element that is to be moved. An on/off control valve is used to direct compressed air into the extended port while opening the retract port to atmosphere. The difference in pressure on the two sides of the piston results in a force equal to the pressure differential multiplied by the surface area of the piston.

If the load connected to the rod is less than the resultant force, the piston and rod will extend and move the machine element. Reversing the valving and the compressed air flow will cause the assembly to retract back to the “home” position. Pneumatic actuators are at the working end of a fluid power system. Upstream of these units, which produce the visible work of moving a load, are compressors, filters, pressure regulators, lubricators, on/off control valves and flow controls. Connecting all of these components together is a network of piping or tubing (either rigid or flexible) and fittings. Pressure and flow requirements of the actuators in a system must be considered when selecting these upstream system components. Undersized upstream components can cause pneumatic actuators to perform poorly, or even make them incapable of moving their loads.

Pneumatic actuators often pair with mechanical guides to precisely apply force and transport objects.

Variations on how pneumatic actuators integrate into linear systems In some setups, load rides on a carriage.

Bearing block

Here the slide makes linear strokes. Guide shaft

Tool bar

Air cylinder

In some setups, load rides on a moving frame. Here, linear bearings support much of the load. The slide makes linear strokes.

Guide shaft The pneumatic cylinder is stationary.

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Motion System

HANDBOOK

Common rigid chains have two rows of link plates and shoulders, whereas duplex chains have three. Other options abound. Image courtesy iwis Drive Systems

Basics of

RIGID CHAIN ACTUATORS RIGID-CHAIN

actuators work by pairing a drive (usually an electric motor) with a length of chain sporting shoulders on each link. The motor output shaft—fitted with a specialty sprocket or pinion—applies tangential force to the chain. Then the chain comes out and straightens, and its links’ shoulders lock to form a rigid series. When the motor runs in the opposite direction, the chain shoulders disengage and allow for coiling. Inside the actuator body, reaction plates and guides counter thrust resistance and keep the chain on track. Links travel around the pinion to exit the actuator body along the stroke path. Here, the motor’s torque comes to act as forward thrust via the link shoulder to the rest of the links’ shoulders. The last link in the chain before the load has geometry

DESIGN WORLD — MOTION

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that puts the thrust higher than the articulation axis. This makes a moment that effectively locks the link shoulders. In reverse, pulling force acts along the links’ cross axes. Rigid-chain actuators have the mechanical benefits of conventional chain but can act in horizontal push setups or vertically as jacks. Plus they’re compact. In contrast, traditional chain drives can only pull, so need two drives for bidirectional motion. Traditional screw jacks for vertical power transmission need space for retraction that’s as long as the working stroke itself. Before specifying a rigid-chain actuator, determine the application’s total load, including the transported load, acceleration forces, external environmental forces, and that due to friction — with a coefficient between 0.05 and 0.5 for typical rigid-chain actuator setups. Next, determine what type of actuator body and chain-storage magazine the application can accommodate. Determine whether the chain will need to change direction on its way from the magazine to actuator body. Actuators usually feed chain around 90° or 180° turns. Note that rigid-chain actuators can work alone or in tandem. Twinchain setups deliver high positioning accuracy and stability where loads are large or bulky. Here, a pushing bar acts as a yoke to keep loads steady, with optional hooks for pulling as well. Optimized geometry has

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HANDBOOK

Motion System

the force vector act on the load’s center for balance. If twin-chain setups are impossible, consider adding framework to guide awkward loads. Guides on the chain also help maintain stability—even over very long strokes— because they address side and buckling forces. Such guides come in different shapes with different crampons and subcomponents to engage the chain. Where use of chain guides is impossible, most designs run the chain with link shoulders down for moderate stability. Some last design notes: Standard chain is carbon steel to withstand heat to 200°C, but stainless, high-temperature, and coated chain for long life are other options. The required length of chain is total design stroke plus a few links to engage the actuator pinions. As with any powertransmission setup, consult the manufacturer for tips and guidance on determining necessary drive power and other details.

Common rigid-chain arrangements Chain link shoulders

Unguided chain with shoulders up coils downwards ...

... but guided chain is most stable. Actuator body Pinion Input drive shaft Choose a rigid-chain actuator to satisfy the design geometry.

An unguided chain with shoulders up coils downwards, which is useful but not always stable enough for long strokes. A chain with shoulders down (here, at bottom) is slightly more stable. Use a guided chain wherever space permits.

SOLUTIONS FOR PRECISION MOVEMENT OF VERY HEAVY LOADS

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RollBeam Telescopic push-pull

LinearBeam guided push-pull Press-mounted dual push-pulls

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BALLSCREWS

Shown here is a metric ball screw made in the U.S. by Thomson Industries. FSI metric ball screws deliver smooth motion and are DIN 69051 compliant, so work in laboratory, medical and mechatronic applications (as well as large three-axis structures).

New technical information on

BALLSCREWS COMPARED

to similar actuation methods such as leadscrews, ballscrews typically cost a bit more, but are more accurate. They also boast higher efficiencies, though need more lubrication because of their use of recirculating balls. The basic components of a ballscrew are a nut, a screw with helical grooves, and balls (of steel, ceramic, or hard plastic material) that roll between the nut and screw grooves when either the screw or nut rotates. Balls run through ball-return system inside the nut and in a continuous path to the ball nut’s opposite end. Seals on either side of the nut prevent debris from compromising smooth motion.

FAQ: HOW TO AVOID MISTAKES BASED ON BALLSCREW LEAD ERROR? Accuracy is an important criterion in ballscrew selection. Four different standards define ballscrew accuracy — and these define four criteria for specifying ballscrew accuracy. Average lead deviation is the difference between the specified travel and the mean travel, where the mean travel is the best-fit line of the deviation curve over the useful length of the ballscrew. The second criteria defining accuracy is maximum deviation range — the maximum range of travel deviations (peak-to-valley) over the useful length of the ballscrew. This is shown by two parallel lines enclosing the full lead deviation curve. Maximum deviation of more than 300 mm is measured over any 300-mm section of the useful length. The V300 criteria is the most commonly used definition of lead accuracy. Maximum deviation range over one revolution is also known as lead wobble. (This specification is applicable only to positioning ballscrews.) motioncontroltips.com | designworldonline.com

Ballscrews_MSHandbook_V3.indd 31

Understanding the standards (and the differences between the two manufacturing methods) helps identify ballscrews that can meet specifications without forcing a design team to pay for higher accuracy than the application requires. Part of defining the intended purpose of a ballscrew is to determine whether it’s for positioning or load transport. For positioning screws, the maximum deviation over 300 mm (V300) can’t accumulate over the length of the screw. In contrast, it’s permissible for it to accumulate for transport screws. Maximum deviation range is most relevant to Grade 5 and (less often) Grade 3 screws, because these grades can fall under either positioning or transport designations. For more information, visit linearmotiontips.com and search for lead error.

This cutaway drawing from Nook Industries shows the inner workings of a ballscrew, including the recirculating balls and the deflector in relation to the screw assembly.

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HANDBOOK

Ballscrew nut using tube-type recirculation versus deﬂector-type ballscrew nut Return tube Bridge-type deﬂector

Motion System

Screw shaft

Ball nut

Screw shaft

Standard ballscrews use economical tube-type recirculation. Balls recirculate through a ball-return tube as shown on the left here. On the right, a deflector type uses a horseshoeshaped tube to bridge adjacent ball thread grooves (for a more compact nut). Image courtesy NSK

RECENT TECHNOLOGICAL ADVANCES IN BALLSCREW DESIGN

Ballscrews have a mechanical efficiency that’s only made better with precision finishes of the ball tracks within the nut. The ballscrews shown here are from NSK, a manufacturer of precision-ground ballscrews specializing in linear-motion components with high accuracy and durability.

DESIGN WORLD — MOTION

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New manufacturing methods and materials have improved ballscrew performance so machine designers today can get better linear motion with them at lower cost. Some improvements include the fact that the latest generation of ballscrews has more load density than ever, giving designers higher capacity from a smaller package. There is also a trend toward more miniaturization, but also faster ballscrews with rolled and ground screw manufacturing methods. Ballscrews suit applications needing light, smooth motion, applications requiring precise positioning, and when heavy loads must be moved. Examples include machine tools, assembly devices, X-Y motion, Z motion, and robots. Ballscrews are usually classified according to factors such as lead accuracy, axial play and preload, and life/ load relationship. Lead accuracy refers to the degree to which the shaft’s rotational movements are translated into linear movement. With lead accuracy and axial play determined by the manufacturing method of the ballscrew shaft and the assembly of the nut, high lead accuracy and zero axial play is generally associated with relatively higher-cost precision ground ballscrews, while lower lead accuracy and some axial play is associated with lower-cost rolled ballscrews. Fabricated by rolling or other means, their shafts yield a less precise but mechanically efficient and less expensive ballscrew.

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Linear motion made easy, find a solution today! • • • • • •

Easy installation and low maintenance Compact and lightweight Environment protection and energy saving Accuracy-speed-reliability High precision and high stiffness Complete linear motion system

HIWIN

Motion Control & System Technology

All components are Hiwin manufactured

Single and Multi-axis systems available

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Control your motion needs with a HIWIN D1 or D2 drive & servomotors HIWIN drive: • • • • • •

Accuracy enhancement Error compensation Vibration suppression filter Real-time oscilloscope Data collection Analysis tools

With its introduction into the North American market, HIWIN provides its customers with exceptional quality at the most competitive prices. HIWIN supplies many hi-tech industries with critical components for machine tools, medical equipment, vending machinery, material handling, and the automotive industry to name a few.

Ball Screws

Linear Guideways

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Linear Motors

Direct Drive Motors

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HANDBOOK

Motion System

Axial play is the degree to which a ball nut can be moved in the screw axis direction without any rotation of either nut or screw. Preload is applied to eliminate axial play. The process of preloading removes backlash and increases stiffness. Ball recirculation inside the ball nut can affect precision and repeatability. Thus, ball nuts are available with a range of preload options to reduce or remove the axial play as they rotate around the screw. Minimal axial play allows better accuracy, for example, because no motion is lost from the clearance in the balls as they reengage. There are several techniques for preloading. Some common methods include oversizing the balls inside the nut housing; using the so-called double-nut or tension nut method; or by using a manufactured offset in the raceway spiral to change the angle of ball engagement (the lead shift method) and deliberately force the balls into a preload

condition. Each method has its advantages and disadvantages, but all serve to minimize or eliminate backlash between the nut and screw. One drawback of ballscrews is that they require high levels of lubrication to prevent corrosion, reduce friction, extend operating life, and ensure efficient operation. That’s because ballscrews are a bearing system, so need lubrication to avoid metal-to-metal contact of the balls in the raceway. The lubrication choice can be either oil or grease, but avoid solid additives (such as graphite) as they clog the recirculation system in the nut. An NLGI Number2-type grease is recommended but food-grade or other special lubrication may be required. Ballscrews in machine tools generally require lubricants with EP additives to prevent excessive wear. The lubricant amount is fixed, but the needed frequency of lubrication depends on move-cycle characteristics and environmental contamination. Polluted lubrication can increase friction. In addition, ballscrews can fail if the balls travel over metal chips or dirt in the ball thread raceway. Using lubricants recommended by machine tool manufacturers can help prevent this effect. Here, telescopic covers or bellows can help keep ballscrews clean when used in environments with many contaminants.

Basic deﬁnitions of accuracy and lead error for transport and positioning ball screws I1 I1 = Axial thread length Iu = Usable travel V300p = Permissable travel variation within 300 mm travel I0 = Nominal travel V2πp = Permissible travel variation with 2π travel Cup = Travel compensation Vup = Permissible travel variation within useful travel Ie = Excess travel ep = Tolerance on useful travel

Positioning ball screw

Travel deviation

θp ν2

300 mm Actual mean travel line (Lm)

V300p

V2πp

Vup 2π rad

I1 Iu 300

Actual travel curve (La)

2π

Vup

Transport ball screw

Nominal travel line (L0)

ν300

Effective thread length (Le)

ν0

300

Travel deviation

Ball screw lead error 0 +

+ Travel deviation

V300p

Ie ep Io

Criteria for specifying ball screw accuracy include average lead deviation, which is the difference between specified and mean travel — where mean travel is the best-fit line of the deviation curve over the useful ball screw length. Another criteria defining accuracy is maximum deviation range shown by two parallel lines enclosing the full lead deviation curve (applicable only to positioning ball screws.) Ball screw lead error chart courtesy NOOK Industries, Inc.

DESIGN WORLD — MOTION

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100 YEARS OF INNOVATION.

For 100 years NSK has been proudly designing motion and control products that not only help increase productivity but also help make the world a more safe, reliable and comfortable place. Here’s to celebrating the past, innovating in the present and setting the future in motion. 877.994.6675

NSK_MSHandbook9-16.indd 35

www.nskamericas.com

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HANDBOOK

Technical update on

Motion System

ROTARY BEARINGS BEARINGS

are internal machine components that are crucial to motion applications. They reduce friction between moving parts by giving a surface something on which to roll rather than slide. Rotary bearings consist of smooth rollers or metal balls and inner and outer surfaces (races) against which the rollers or balls travel. These rollers or balls carry load carrier and let axes spin freely. Bearings typically encounter radial and axial load. Radial loads are perpendicular to the shaft, and axial loads occur parallel to the shaft. Depending on the application, some bearings must withstand both loads simultaneously.

WHAT’S THE DIFFERENCE BETWEEN BALL AND ROLLER BEARINGS? As the name implies, ball bearings use balls to provide a low friction means of motion between two bearing races. Because the contact area between the balls and races is so small, ball bearings can’t support as much load as other bearing types — so are suitable for light to moderate loads. However, the small areas of surface contact also minimize friction-generated heat, so ball bearings work well in high-speed applications.

Some ball bearings, like Koyo’s RSH2 Ball Bearing, have larger rolling elements to increase power density. In this case,15% more capacity while the envelope dimensions are unchanged.

DESIGN WORLD — MOTION

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BEARINGS

In contrast, roller bearings have cylindrical rollers. They’re common in applications such as conveyor belt rollers because their rolling elements make more surface contact with their races — so handle larger loads without deforming. Their shape also allows for a moderate amount of thrust load, as weight is distributed across cylinders instead of spheres.

WHAT KINDS OF APPLICATIONS USE NEEDLE ROLLER BEARINGS? Needle-roller bearings operate in tight spaces — for example, in automotive applications such as rocker-arm pivots and transmissions. In short, these are roller bearings with rollers having a length at least four times the roller diameter. The large surface area of the needle roller bearing lets them support extremely high radial loads. Usually a cage orients and contains the needle rollers. The outer race is sometimes machined into the a housing interior. Needle-roller bearings come in two different arrangements — a radial arrangement (in which the rollers run parallel to the shaft) and a thrust arrangement (in which the rollers are flat in a radial pattern and run perpendicular to the shaft).

bearings are the only bearing type that can concurrently handle large amounts of axial and radial loads. A single row taper bearing can only take high axial loads from one direction, but if adjusted against a second tapered roller bearing, that axial load is counteracted. This allows the bearings to accept high radial and axial loads from multiple directions. Tapered roller bearings can only accommodate slight angular misalignment of the inner ring in relation to the outer ring — just a few minutes of arc at the most. As with other roller bearings, tapered roller bearings must carry a minimum load, especially in high-speed applications where the inertial forces and friction can damage rollers and raceways should they come out of contact.

WHAT ARE THRUST BEARINGS? Thrust ball bearings go in applications with primarily axial loads and handle shaft misalignment. These bearings also work on highspeed axes in the aerospace and automotive industries. Thrust roller bearings also transmit load from one raceway to the other to resolve radial loads. Their self-aligning capability makes them immune to shaft deflection and alignment errors.

TAPERED ROLLER BEARINGS Tapered roller bearings have tapered inner and outer ring raceways with tapered rollers between them — angled so the rollers’ surface converge at the axis of the bearing. These motioncontroltips.com | designworldonline.com

Bearings_MSHandbook8-16_V1.indd 37

Bearings like these HPS spherical roller bearings from NSK are used in industrial machinery and have a cage and guide ring designed to suppress tilting in the rollers for 30% less heat generation.

9 • 2016

PLAIN BEARINGS EXCEL IN MEDICAL AND OTHER APPLICATIONS With no moving parts, plain bearings are the simplest type. They are often cylindrical, though the bearing design differs depending on the intended motion. Plain bearings come in journal, linear and thrust versions. Journal style bearings are designed to support radial motion where a shaft rotates within the bearing. Linear bearings often go into applications requiring slide plates for straight strokes. Plain thrust bearings do the same job as roller-based thrust bearings, but use pads arranged in a circle around the cylinder. These pads create wedgeshaped regions of oil inside the bearing to prevent hard component contact with the rotating disk supporting the application’s thrust. Out of all the bearing types available, plain bearings tend to be the least expensive. They’re often made of bronze, graphite, or plastics such as Nylon, PTFE and polyacetal. Material innovations have made plastic plain bearings more useful than ever, though plain bearings of all types are lightweight and compact and can carry substantial load. Growing use of plain plastic bearings and increasingly stringent industry standards means these bearings must increasingly meet FDA, RoHS, and other standards. Some bearings even meet EU directive 10/2011/EC standards, which holds material manufacturing processes to certain criteria. Note that a competing technology in some cases is dry bearings. These have rolling DESIGN WORLD — MOTION

9/12/16 9:26 AM

Replace your metal bearings

Motion System

HANDBOOK

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elements but go where designs can’t have lubrication — or where shortened design life is acceptable — in some medical devices, for example. In fact, some plain bearings are self-lubricating and some aren’t. Plain bearings made of bronze or polyacetal contain lubricant in their walls, but need additional lubrication to maximize performance. Other plain bearings use the material itself as the lubricant — those made from PTFE or metalized graphite, for example.

HOW TO PICK THE RIGHT LUBRICANT FOR A ROTARY BEARING? Rotary-bearing lubrication takes the form of oil or grease, but grease usually lasts longer, thanks to thickeners that sustain the lubrication layer between raceways and rolling elements. Grease with extreme-pressure additives also extends bearing life when subject to higher forces. Even so, oil is more common for open bearings or those subject to low torque or high speeds. Oils’ lower viscosity imparts less drag than greases as the balls move through the lubricant. Mode of oil delivery, application rpm and temperature, and potential environmental contaminants dictate which oil is most suitable. Case in point: Operating temperature dictates which oil viscosity will work in a given application. Overly thick oil increases required torque to make the rotary bearing spin; overly thin oil won’t maintain the protective layer needed to prevent mental-onmetal contact.

Reduce cost and increase technology with iglide® iglide® plastic bearings are 100% self-lubricating, maintenancefree, and available in a range of 40+ materials to suit even the most demanding applications. With product selection tools, reliable lifetime calculation, CAD downloads, and more available online. Thousands of dimensions in stock and ready to ship as early as same-day.

APPLICATIONS FOR ROTARY BEARINGS Bearings abound in industrial and consumer designs. For example, deep-groove ball bearings often go into in small to medium-sized electric motors because they can accommodate both

Free samples available at www.igus.com/drytechbox sales@igus.com 1.800.521.2747

For some applications like food processing lines, bearings prefilled with a solid polymeric lubricant are necessary. In this image we se a Solid Lube bearing bearing from Koyo. They are available as deep groove ball bearings or spherical roller bearings.

Bearings_MSHandbook8-16_V1.indd 38

DESIGN WORLD — MOTION

9 • 2016

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Reduce cost and increase technology with iglide®

iglide® plastic bearings are 100% self-lubricating, maintenancefree, and available in a range of 40+ materials to suit even the most demanding applications. With product selection tools, reliable lifetime calculation, CAD downloads, and more available online. Thousands of dimensions in stock and ready to ship as early as same-day.

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This ADAPT bearing from Timken is used as an alternative to traditional float position roller bearings on rotating shafts in applications like paper mill dryer rolls.

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DESIGN WORLD — MOTION

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Reduce downtime and increase service life with Chainflex® cables

Unmatched testing, widest selection, and a full guarantee for up to 36 months make Chainflex a world leader in continuousflex cable performance. More than 1,200 cables in a range of types available from stock and ready to ship in as little as 24 hours. Never any cutting costs or minimum orders. Free samples available at www.igus.com/cf-sample

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high speeds and radial and axial loads. Selfaligning ball bearings, on the other hand, are work well in fans. These bearings have two rows of balls with a common raceway in the outer ring. This design allows for angular misalignment while maintaining running accuracy. The only caveat is that they’re one of the most difficult bearings to install correctly. Tapered roller bearings go in needing support for axial and radial loads — as in a tire hub bearing vehicle weight and the axial loads associated with cornering. These bearings are also common in gearboxes where they mount with a second bearing of the same type in a face-to-face or back-toback orientation. They provide rigid shaft support to minimize deflection. This reduced shaft deflection minimizes gear backlash. Tapered bearings also have the advantage of being lightweight but efficient, even while maintaining good overall speed capabilities. In applications where the bearings mount vertically, they typically mount in a face-to-face setup. In horizontal applications, they mount back-to-back.

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Tapered roller bearings like these from Timken are designed to manage both thrust and radial loads on rotating shafts and in housings.

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9/14/16 9:26 AM

HANDBOOK

Motion System

New technical tips on using

BELTS & PULLEYS INDUSTRIAL

belt drives consist of rubber belts that wrap around drive pulleys, in turn driven by electric motors. In a typical setup, the belt also wraps around one or more idler pulleys that keep the belt taut and on track. The main reasons that engineers pick belt drives over other options is that modern varieties require little if no maintenance; they’re less expensive than chain drives; and they’re quiet and efficient, even up to 95% or more. In addition, the tensile members of today’s belts—cords embedded into the belt rubber that carry the majority of the belt load—are stronger than ever. Made of polyester, aramid, fiberglass or carbon fiber, these tensile cords make today’s belt drives thoroughly modern powertransmission devices. Manufacturers generally describe belts and pulleys with five main geometries. Pitch diameter is the drive pulley’s diameter. Center distance is the distance between the two pulleys’ centers. Minimum wrap angle is a measure of how much the belt wraps around the smallest pulley. Belt length is how long the belt would be if cut and laid flat. Finally, in the case of toothed belts (also called synchronous belts) the pitch is the number of teeth per some length—so a 3-mm pitch means that the belt has one tooth every 3 mm, for example.

BASICS ON HOW TO INTEGRATE SYNCHRONOUS BELTS Some general guidelines are applicable to all timing belts, including miniature and double-sided belts. First of all, engineers should always design these belt drives with a sufficient safety factor—in other words, with ample reserve horsepower capacity. Tip: Take note of overload service factors. Belt ratings are generally only 1/15 of the belt’s ultimate strength. These ratings are set so the belt will deliver at least 3,000 hours of useful life if the end user properly installs and maintains it. The pulley diameter should never be smaller than the width of the belt. As mentioned, belts are quieter than other power-transmission drive options … but they’re not silent. Noise frequency increases proportionally with belt speed, and noise amplitude increases with belt tension. Most belt noise arises from the way in which belt teeth entering the pulleys at high speed repeatedly compresses the trapped pockets of air. Other noise arises from belt rubbing against the flange; in some cases, this happens when the shafts aren’t parallel. Pulleys are metal or plastic, and the most suitable depends on required precision, price, inertia, color, magnetic properties and the engineer’s preference based on experience. Plastic pulleys with metal inserts or metal hubs are a good compromise. Tip: Make at least one pulley in the belt drive adjustable to allow for belt installation and tensioning. Also note that in a properly designed belt drive, there should be a minimum of six teeth in mesh and at least 60° of belt wrap around the drive pulley. Other tips: Pretension belts with the proper recommended tension. This extends life and prevents belt ratcheting or tooth jumping.

This Festo ELGA-RF is accurate enough to function as the main axis on a machine that produces printed circuit boards. Its robust roller bearings let it move to 10 m/sec — faster than designs using ball-bearing guides. Two synchronized belt drives extend the length of travel.

DESIGN WORLD — MOTION

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MPC

SYNCHRONOUS SPROCKETS

Direct drop-in for the most popular tooth profile

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Martin's MPC® Sprockets are manufactured in various sizes, dimensions and capacities to

meet a variety of industrial requirements. These include a wide range of loads, speeds, and demanding applications such as blowers, conveyors, pumps and mixers.

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Motion System

HANDBOOK

Manufacturers of Power Transmission and Motion Control Components

Concentric Maxi Torque

Stock and Custom Keyless Hub-to-Shaft Connection System Email or call to get your

CMT Stock Products Catalog Order today. Ships today!

Engineers at BKIN Technologies used Concentric Maxi Torque Systems — beltand-pulley sets — from Custom Machine and Tool (CMT) for the drives on their KINARM Exoskeleton Lab modules. These robotic exoskeletons analyze human limb kinematics with high precision. The Concentric Maxi Torque Systems have a low-profile design to allow direct coupling to the motor shaft, so the design doesn’t need a custom-length shaft or bellows coupler on the motor.

Custom Synchronous Drives

Precise. Reliable. Cost Effective.

Align shafts and pulleys to prevent belt-tracking forces and belt edge wear. Don’t crimp belts beyond the smallest recommended pulley radius for that belt section.

SELECT THE APPROPRIATE BELT FOR THE DESIGN TORQUE Select the appropriate belt material for the environment (temperature, chemical, cleaning agents, oils and weather). Belt-and-pulley systems are suitable for myriad environments, but some applications need special consideration. Topping this list are environmental factors. Dusty environments do not generally present serious problems as long as the particles are fine and dry. In contrast, particulate matter can act as an abrasive and accelerates belt and pulley wear. Debris should be prevented from falling into belt drives. Debris caught in the drive is generally either forced through the belt or makes the system stall. In either case, serious damage occurs to the belt and related drive hardware.

Timing Pulley Stock

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Precise. Reliable. Trusted.

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DESIGN WORLD — MOTION

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9/13/16 4:48 PM

BELTS & PULLEYS

Manufacturers of Power Transmission and Motion Control Components

Wedge Link Belting from Fenner Drives now includes narrow-wedge 3V and 5V profiles. The polyesterpolyurethane link design lets users set belts to any length on-site â&#x20AC;&#x201D; eliminating the need for large inventories of spares. The belts work on captive and fixed-center drives in metals production, cement, and forestry applications. As an upgrade to rubber wedge belts, they combine cost savings with the performance of rubber options.

Light and occasional contact with waterâ&#x20AC;&#x201D;during occasional washdowns, for exampleâ&#x20AC;&#x201D;has little serious effect. However, prolonged contact with constant spray or submersion can significantly reduce tensile strength in fiberglass belts and make aramid belts break down and stretch out. In the same way, occasional contact with oils doesnâ&#x20AC;&#x2122;t damage synchronous belts. But prolonged contact with oil or lubricants, either directly or airborne, significantly reduces belt service life. Lubricants cause the rubber compound to swell, break down internal adhesion systems and reduce felt tensile strength. While alternate rubber compounds may provide some marginal improvement in durability, itâ&#x20AC;&#x2122;s best to prevent oil from contacting synchronous belts. The presence of ozone can be detrimental to the compounds used in rubber synchronous belts. Ozone degrades belt materials in much the same way as excessive temperatures. Although the bumper materials used in belts are compounded to resist the effects of ozone, eventually chemical breakdown occurs and they become hard and brittle and begin cracking. The amount of degradation depends on the ozone concentration and generation of exposure. Rubber belts arenâ&#x20AC;&#x2122;t suitable for cleanrooms, as they risk shedding particles. Instead, use urethane timing belts here â&#x20AC;Ś keeping in mind that while urethane belts make significantly less debris, most can carry only light loads. Also, none have static conductive construction to dissipate electrical charges. Shown here are Dura-Belt powered rollers that transmit power and convey loads. Their round polyurethane belts can carry more load than comparable rubber belts.

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DESIGN WORLD â&#x20AC;&#x201D; MOTION

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BRAKES & CLUTCHES

Primer on

BRAKES, CLUTCHES, AND TORQUE LIMITERS

for motion designs

TORQUE

limiters, clutches, and brakes stop, hold or index loads. Especially over the last five years, a trend toward application-specific designs has quickened as several industries are pushing the performance envelope of stock components. Brakes stop loads (typically rotating loads) and go in applications that need accurate stopping of the load with motors that stop as well. Clutches transfer torque and go in applications where the machinery must engage or disengage a load and motor while letting the motor continuously run. With a clutch, the design usually lets the load coast to a stop. Clutch and brake combinations go where a machine stops and starts a load while the motor continues to rotate. In fact, both clutches and clutch-brake combinations can mount to a motor shaft or mount to a base and engage the drive shaft with a belt drive, chain drive or coupling.

A machine’s motor frame size and horsepower dictate brake and clutch types suitable for a given design. In the case of base-mounted units, the design engineer may need to define the rpm at that location. To this end, manufacturers provide quick-selection charts that list unit size (which engineers can find at the chart’s intersection of motor horsepower and speed at the clutch shaft). Manufacturers base most of these charts on the dynamic torque capacity for the product and the torque capacity for the motor … plus an overload factor of some value. The FEA0550 by Carlyle Johnson is a spring-set Using this method presumes that holding brake. Used in military ground-vehicle missile the design engineer has selected a systems, the brake controls the movement of the side motor that’s sized appropriately to the launcher — and features a manual release to override rotation and position in case of an emergency or for application. In applications where cycle maintenance. rates are considered aggressive for the inertia of the load, it’s a good idea to consult with the application support staff of the manufacturer regarding the heat dissipation capacity. In the case of electric varieties, coil voltage is another clutch and brake consideration. The most common options are 6, 24 and 90 Vdc. 90 V is most common in North American markets. Versions that use 24 V are more common in Europe. In both cases, power supplies exist to convert ac to dc if the application needs it.

Some designs have backup drives that engage if there’s an emergency and the main drive becomes inoperable. Traditional designs require something to manually or electrically decouple the main drive and connect the backup — for example, on military vehicles or platforms to let operators use manual auxiliary mechanisms when needed.

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Because brakes usually hold drive position, they must be manually disengaged for the manual system to begin driving. Now, Mechanical Torque Lock (MTL) products from Carlyle Johnson are a new option that automatically transfer motion to secondary drive systems. They include a spring-engaged electromagnetically released clutch for automatic braking when the motor drive is de-energized or if vehicle power is lost. So the MTL can be driven manually to any position. However, when the MTL is released it will hold the shaft from rotating from that specific rotational location, regardless of whether the load on the shaft is trying to drive the shaft clockwise or counterclockwise. Previous options made operators pull or push a pin or mechanism to disengage one drive and engage the other.

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DESIGN WORLD — MOTION

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HANDBOOK

Motion System

CUSTOM CLUTCHES AND BRAKES TO MEET EXACT REQUIREMENTS Motion systems in general are evolving thanks to advances in engineering analysis — and demand for custom products to meet tight specifications established by such analysis. For example, a clutch or brake in a flight-control application must have operational characteristics plus be light. Design engineers can no longer accept standard products that only meet some requirements at the expense of others. Another development is that smart technologies can now monitor equipment functions during operation, according to Tom Thiffault of Carlyle Johnson Co. Powertransmission manufacturers have developed sensors to gather this information — including speed, temperature, motion, and vibration. So now analysis of data serves to predict failures of specific components. Case in point: Smart clutches and brakes can tell controls if they’re on or off — and if they are worn and by how much. Some of this data overlaps with sensors monitoring other system features; with ongoing review for trend analysis, today’s systems can use these parallel data streams to predict component failures and establish typical rates so operators can schedule maintenance instead of risking unplanned downtime. Here, cloud computing is spurring more review and data sharing at multiple sites as well. Here are some other insights from Thiffault on custom designs.

Modular brakes from Twiflex of Altra Industrial Motion now include VSD Series brakes for use in conveyors, hoists, geared grinding mills, and lifts. They feature two spring-module assemblies on each side of a central mounting plate. As a spring-applied, hydraulically-released brake caliper, the VSD applies braking forces from 100 to 220 kN.

CHANGES IN MOTION AND POWER-TRANSMISSION DESIGN Clutch and brake suppliers assume more drive-design responsibilities than ever. What’s more, engineers graduating college today have analytical skills to develop extremely specific requirements — and expect products to meet these parameters. So today’s product catalogs list basic product offerings from manufacturers, but it’s increasingly common for engineers to request special products, according to Thiffault of Carlyle Johnson Co. That’s why most power-transmission component suppliers today are adapting their engineering knowledge and manufacturing to produce custom components with short lead times. BENEFITS AND CHALLENGES OF INCREASED AUTOMATION Today, automation only works when it’s flexible — but flexible operations demand that plant operators perform advanced operations analysis to keep factory floors running. So operators traditionally just worked specific machines, today they must analyze the interaction of components to be manufactured as they move through the factory floor. That means operators must also review holistic machine operations and maintenance requirements in detail …including the time required for all tasks.

DESIGN WORLD — MOTION

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Clockwise from top left are a Mach III slip clutch adapted to diameter restriction; a stainless-steel torque limiter coupling to connect square shafts; a water-resistant clutch for shaft-to-output flange connection; and a stainless-steel tensioning brake. These and other brakes and clutches from Mach III Clutch Inc. come in torque capacities to 62,000 lb-in., bore sizes to 3.625 in., and in myriad mounting configurations — including those for through-shaft, end-of-shaft, flange, NEMA frame, IEC frame, and custom-motor frame mounting.

motioncontroltips.com | designworldonline.com

9/12/16 9:31 AM

Highest Torque in the Smallest Space ... or the largest. Our Maxitorq® clutches and brakes deliver the highest torque in the smallest space, and are customized to meet the exact needs of your installation and application. Land, sea and air – CJM is everywhere.

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Clutches, Brakes & Power Transmission Products For over 100 years, The Carlyle Johnson Machine Co. has combined the latest technology and industry-leading expertise to solve the toughest design challenges. With standard products and custom solutions, we offer: • electrical, mechanical, pneumatic & hydraulic models • system design and integration • expert engineers working on every order

Engineering Solutions for Clutches & Brakes

www.cjmco.com CarlyleJohnson_MSHandbook9-16.indd 47

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Bolton, CT 06043

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Phone: 860-643-1531

9/12/16 1:31 PM

HANDBOOK

Motion System

SUMMARY OF TODAY’S CABLE-MANAGEMENT OPTIONS Cable trays and cable carriers

MOTION

control systems can vary from simple and straightforward single-axis direct drives with little wiring to large and complex multi-axis robotics with a hornet’s nest of cables. Especially where there are lots of cables and wiring, cable management becomes an issue. Low-cost twist-tie-type bundlers can hold together groups of wires and cables. But with large bundles, they become impractical and can pose weight problems, leading to sagging and undue strain on the cables.

CABLE TRAYS FOR STATIC RUNS OF CABLE For largely stationary applications or where cable ties have reached their limit, cable trays are an advanced option for cable management. Cable trays safely and cleanly route cables. These designs include proper ventilation, division among varying cable types and protection from contaminates. Traditional cable-tray systems are generally comprised of a U-shaped open channel into which cables lay. They can be open at the top or closed with a cover or lid. They’re available in solid, ventilated or perforated styles with knockouts for cable 48

DESIGN WORLD — MOTION

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9 • 2016

exits or ladder style with rungs. Cable trays can be manufactured from a variety of materials including various gauges of steel, including stainless steel, aluminum, plastic, and fiberglass. Some trays for ground installation even feature ultra-thick treaded covers to let personnel walk on them. When selecting a cable tray, consider the type of cable to be routed, including its diameter and weight; the span between supports; the distance of the cable run; specific environmental conditions; the need for complete enclosure and/or ventilation; and the ability to drop out at certain points along the run. motioncontroltips.com | designworldonline.com

9/9/16 10:33 AM

CABLE MANAGEMENT Cable trays, such as this Ladder Cable Tray System from Cope, are a cost effective alternative for buildings requiring multiple cable runs. These open designs in materials such as steel or aluminum allow for easy installation of cables by electricians as well as future access for adding or removing cable runs.

Dynatect Ad – “Innovation Set In Motion” Design World – February 2016 Motion Control Issue 1/2 Island: 4-5/8 x 7-7/8

INNOVATION SET IN MOTION CABLE CARRIERS FOR DYNAMIC TASKS Cable carriers are used to protect cables and hoses on moving machinery while preventing tangling. They are made of many materials such as plastic, steel, or a metal alloy. Carriers can house a large volume of cables and wires and support the weight of them all without sagging or putting stress on the cabling. They also make managing and routing the cables through a machine or factory much simpler and provide easy access for troubleshooting or maintenance as well. Steel and other metal alloy carriers are best suited for heavy mechanical loads that run long distances carrying large cables and hose. They can handle harsh environments with ease — even long-term exposure to temperatures above 600° without negative impact. Because they don’t require maintenance or lubrication, steel cable carriers are ideal in tough environments, such as heavy-duty machinery found in foundries, mills, refining, offshore, and construction and mining applications. Plastic cable carriers, made from highperformance polymer or nylon, are less expensive than their metal counterparts and offer reduced weights while being corrosion resistant in hostile environments. They are usually used in more light- and medium-duty applications. Some designs made of the polymers can resist seawater and mineral oils, making them suitable to similar applications as metal designs. Their modular design makes them easy to maintain and replace damaged or broken links.

motioncontroltips.com | designworldonline.com

CableManagement_MSHandbook8-16_V3.indd 49

From protective cable carriers to precision ball screws and slip clutches, Dynatect products protect people and equipment. We’ve met the challenge of over a half million tough-to-solve applications from customers around the world. Let us set in motion an innovative solution for you. CABLE & HOSE CARRIERS SLIP CLUTCHES

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FOR MORE INFORMATION: 800-298-2066 sales@dynatect.com dynatect.com

9 • 2016

DESIGN WORLD — MOTION

9/9/16 10:37 AM

HANDBOOK

Motion System

Cable carriers are available as open or closed designs. This closed energy tube design from igus extends the life of cables and hoses by preventing damage caused by chips and dirt. This enclosed plastic cable carrier is extremely easy to open.

Selecting the right kind of cable carrier for an application starts with a few simple guidelines. The most important points to consider are the specifics of the application. These include the length of travel, the number of cables or hoses, the size and weight of the cables, the required speed and acceleration, and environmental factors such as exposure to any debris, excessive heat or chemicals. Knowing the weight of the cables ensures that the carrier won’t fail by snapping in two. Cable carrier styles can be either open or closed. Open varieties allow for easy access to the cables and visible access as well, whereas closed carriers seal off the cables from the environment to protect from environmental contaminants such as metal filings. One of the most important factors in carrier selection is the bend radius. Bend radius is measured from the center of the curve loop to the center of the pivot pin on the side link. A larger bend radius means less stress on the cable and a longer service life. It’s important for the bend radius, with the exception of applications with space restrictions, to be larger than the recommended minimum bend radius of the cables and media that make up the fill package. All cable carriers have a predetermined radius stopping point on each link. When a number of links are assembled, these stopping points restrict the carrier from fully pivoting and form a curve loop, or minimum bend radius. 50

DESIGN WORLD — MOTION

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9 • 2016

All cable carriers also have multiple bending radii to choose from and every manufacturer suggests a minimum bend radius. The bending radius chosen for the cable carrier will depend on the cable or hose with the largest diameter. Selecting a considerably larger bend radius than required for the fill package will extend the lifespan of the cables and hoses. Here are a few general rules to keep in mind when selecting the bend radius: • Don’t exceed the manufacturer’s suggested minimum bend radius; however, using the largest bend radius possible is optimal. • If you don’t know the recommended minimum bend radius of the cables in the fill package, follow these guidelines from NFPA 79 2007: “Cables with flexible properties subject to movement shall be supported in such a way that there is neither mechanical strain on the connection points nor any sharp flexing. When this is achieved by the use of a loop, it shall provide motioncontroltips.com | designworldonline.com

9/9/16 10:38 AM

CABLE MANAGEMENT

• •

•

the cable with a bending radius of at least 10 times the diameter of the cable.” The larger the bend radius, the less stress is put on the cables and hoses, which will ensure longer service life. Keep in mind that the minimum bend radius is partly based on a temperature range for flexing. Special consideration is needed when the environment reaches or exceeds the temperature rating for the cable. This is especially true for low-temperature applications using thermoplastic cables, which tend to stiffen when exposed to the cold. Stiff cables can raise the radius of the cable carrier and lead to mechanical failures. Best practice is to use a cable with a low-temperature rated PUR or TPE jacket and/or consult the manufacturer for bend radius recommendations. In applications with severe space restrictions, the bend radius of the cable carrier may need to be smaller than the recommended minimum bend radius for the fill package. This is not ideal, but if it cannot be avoided, use cables specially designed for low bend radius installations or consult your cable carrier manufacturer for the best solution.

WHAT ARE THE TEMPERATURE LIMITATIONS OF PLASTIC CABLE CARRIERS? Metal cable carriers are ideal for harsh environments, such as those in mobile machinery. This MA Series openstyle metal cable carrier from Dynatect is manufactured with proven extrude technology for greater unsupported spans versus similar carriers. This lightweight design is strong and features a self-cleaning link function.

Cable-management systems are made of several types of plastic, but the most common is glass-filled nylon or nylon six. This material works in applications with ambient temperatures from -40° to 240° F. However, cable carriers can survive higher operating temperatures if they’re made of specialty plastics or materials with additives that increase longevity, durability and strength. One caveat: Even when using these special composites, operating a carrier at extremes beyond -40° to 240° F can reduce mechanical values and service life. Also consider the cables or hoses that the cable track will house. If the application uses standard cables or hose, assume standard cable tracks are acceptable. However, if the application demands hose or cables rated for extreme temperatures, find an equally resilient cable-management system. One last consideration is whether the application is indoors or outdoors. Some carriers consist of UV-resistant materials that help motion designs work longer in hot outdoor applications. Energy chains, such as this P4 e-chain from igus, are used in harsh environments, like building cranes, where they must be able to withstand increasing demands on travel distances, fill weights, special and high travel speeds while operating quietly at the same time.

motioncontroltips.com | designworldonline.com

CableManagement_MSHandbook8-16_V3.indd 51

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DESIGN WORLD — MOTION

9/9/16 10:41 AM

HANDBOOK

Motion System

Update on

SELECTING CABLES for motion applications

lot of industrial automation equipment today operates continuously, with multi-axis machines and robots that execute motions repeatedly, sometimes thousands of times a day. These applications stress moving machine parts as well as the electrical cabling. All too often, designers spend more time sizing components like motors, actuators, and controllers and give little thought to the cabling. Here, if standard cabling is used the cables aren’t designed to flex continuously, so can fail prematurely. In contrast, flexible or continuous-flex cables are those designed and manufactured to cope with the tight bending radii and physical stress associated with motion applications. These highly flexible cables extend their service life, especially when run inside cable carriers. A regular cable typically manages 50,000 cycles, but a flexible cable can complete between one and three million cycles. Flexible cables fall into two categories — those with conductors stranded in layers inside the cable and those with bundled or braided conductors. Cables with stranded layers are easier to produce so usually less expensive. The cable cores are stranded firmly and left relatively long in several layers around the center and are then enclosed in an extruded tube-shaped jacket. In the case of shielded cables, the cores are wrapped up with fleece or foils. However, this type of construction means that during the bending process the inner radius compresses and the outer radius stretches as the cable core moves. This can work quite well because the elasticity of the material is still sufficient, but material fatigue can set in and cause permanent deformations. The cores move and begin to make their own compressing and stretching zones, which can lead to a corkscrew shape and even core rupture.

DESIGN WORLD — MOTION

Cables_MSHandbook8-16_V3.indd 52

9 • 2016

Pictured here are Chainflex cables from igus inside a “ReadyChain” pre-harnessed energy supply system. The system is fully harnessed and tested by igus, and delivered on an optional “ReadyChain Rack,” which is a portable, modular racking system to allow for a true plug-and-play solution for all types of energy/ data/media supply.

motioncontroltips.com | designworldonline.com

9/9/16 10:49 AM

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SAB_MSHandbook9-16.indd 53

9/12/16 1:32 PM

Helukabel_MSHandbook9-16.indd 54

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CABLING

The other construction technique involves braiding conductors around a tension-proof center instead of layering them. Eliminating multiple layers guarantees a uniform bend radius across each conductor. At any point where the cable flexes, the path of any core moves quickly from the inside to the outside of the cable. The result is that no single core compresses near the inside of the bend or stretches near the outside of the bend, which reduces overall stresses. An outer jacket is still required to prevent the cores from untwisting. A pressure-filled jacket fills all the gussets around the cores and ensures that the cores cannot untwist. The resulting flexible cable is often stiffer than a standard cable, but lasts longer in applications where it must constantly flex. An alternative to flexible cabling in some motion applications are flat cables. These cables can incorporate any variety of power, signal, and video conductors in a single compact cable. In addition to every type of electrical conductor, flat cables can also include tubing for air or liquids, and even fiber optics. By incorporating all these elements into a single flat cable, motion equipment can be significantly smaller, quieter, and more energy efficient. Flat cables are best for continuous flexing. Their wire conductors can individually flex in a single plane, which provides optimum flex life. Some motion control systems may encase separate wires, cables, and tubes in a carrier track to contain and manage the separate elements and to constrain their motion. These tracks are usually made of plastic and have a rather large bend radius. These tracks do not add performance to the motion device or machine, as they are simply cable management devices. Cable tracks can add bulk, mass and inertia to the motion system, and moving this extra mass requires more energy. While certain motion systems such as robotic applications may require this type

When Size and Performance Matters Medical-Industrial Actual Micro-Coax cable bundle diameter compared to a penny.

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9 â&#x20AC;˘ 2016

Cables_MSHandbook8-16_V3.indd 55

DESIGN WORLD â&#x20AC;&#x201D; MOTION

Manchester, New Hampshire , USA Tel: +1.603.669.4347 www.hca.hitachi-cable.com

9/9/16 10:50 AM

Motion System

HANDBOOK

HELUKABEL’S Topflex VFD power cable features a threeconductor, three-symmetricalground configuration, which allows for a smaller cable diameter and reduced EMI.

HOW IMPORTANT IS SHIELDING DURING VFD CABLE SELECTION? Variable frequency drives (VFDs) emit electrical noise that interferes with other circuits. This interference can cause motor torque loss, stalls and failures; nuisance lockouts or controller errors; false trips of drive overcurrent; system inefficiency; and electrical hazards to personnel. VFD cable shielding prevents by containing electrical noise and providing low-impedance grounding. Shielding is either foil and tinned copper braid or a copper tape wound in overlapped layers around cable conductors. This contains the cable’s own noise to prevents interfering with other cables nearby. Cable shielding mitigates the effects of VFD-induced common mode noise. Such noise can damage motor bearings if allowed to run through them to ground. In a similar way, armored cables can provide low-impedance paths for common-mode noise back to the VFD. Tip: Here, limit VFD run lengths parallel to instrumentation cables to 10 feet or less. Frequency changes, pulsing, reflective-wave phenomena, and coupling effects are more likely to affect the cable than EMI. Properly grounded shielding that’s connected with a grounding gland at a metal drive enclosure or motor sheds noise. Thus, connecting shielding to terminals forms a Faraday Cage to contain noise and ground it. A comparison of typical insulation and capacitance values for standard THHN cables and SAB North America’s VFD cables with thicker insulation. SAB’s 30-mil VFD lean products are better at protecting against corona discharge, plus have lower capacitance. RHW-2 XLPE

THHN PVC (15 mil) and nylon (4 mil)

0.045 in.

0.019 in.

DESIGN WORLD — MOTION

Cables_MSHandbook8-16_V3.indd 56

XHHW-2 XLPE

SAB VFD lean PVC (22 mil) and nylon (8 mil)

0.030 in.

9 • 2016

of cabling design, other designs may not and can use standard flat cabling instead to save weight and cost. Some flat-cable manufacturers offer cables with silicone jacketing. These types of flat cables are durable and need no external armor for protection. They resist abrasion and will even self-heal minor nicks. Silicone encapsulation also provides protection against oils, acids, ozone, steam, and extreme temperatures. Selecting the right cable for an application starts with fundamental parameters. First, determine whether the cable will be stationary or moving. If the latter, does the motion induce cable flexing or twisting? Or does the application induce flexing and torsion? Cables exists for all three situations. If the application is only bending, determine the cable’s worst-case bend radius. Bend radius depends on the cable wire gauge and the kind of conductors in the cable. Cable size is determined by the gauge of wire in turn dependent on current requirements (and the number of conductors the application needs). As a general rule, finer conductor gauge allows tighter bend radii. Flat cables with PTFE jackets can have a larger bend radius than cables with silicone jacketing for a given number of conductors. For cabling in flexing applications, two key factors are wire conductors and the cable jacket. With continuous flexing, conductors containing multiple strands of fine-gauge wire generally last the longest. The most suitable choice of cable material depends on application needs, and can include PVC and halogenfree to Neoprene, rubber, silicone and other materials. Also, do the cables require electrical shielding? Tip: Consider any approvals that the cables may need to meet such as UL, CSA, CE, and RoHS. Chief environmental factors dictating the most suitable cable choice include exposure to harsh conditions such as temperature and humidity and required resistance to environmental contaminants such as aoil or corrosive materials. For instance, what is the operating temperature for the application? Will the cables be in cold (freezing and below freezing) or hot environments? Will the cables need to endure exposure to oil? Here, other cables can resist full immersion for days. In the same way, cables also have varying degrees of flame resistance. motioncontroltips.com | designworldonline.com

9/13/16 2:49 PM

CHAIN

This Rexnord HTX7748 MatTop chain illustrates two things — how chain can serve as a conveying axis and how chain drives are increasingly customized to specific applications. The one shown here is for shrink-wrap case packers in high temperature heat tunnels. These are common in facilities that package food and beverages.

WHEN TO for PICK CHAIN power transmission? CHAIN

drives actuate machinery axes and convey products with reliability. Now, advances in precision and technology let designers use chains in more applications than ever. Remote installations benefit from long-life chain that requires no lubrication, for example. Chain-based setups vary, but the most common industrial designs use roller chain. This type of chain consists of five basic components: pin, bushing, roller, pin link plate and roller link plate. Manufacturers make and assemble each of these subcomponents to precise tolerances and heat treat them to optimize performance. More specifically, modern roller chains exhibit high wear resistance, fatigue strength and tensile strength. Roller-chain applications generally fall into two categories: drives and conveyors.

motioncontroltips.com | designworldonline.com

Chain_MSHandbook8-16_V3.indd 57

Where chains operate as power-transmission components only (without doing double-duty as a conveyor) ASME/ANSI roller chain wraps around a driver sprocket (connected directly to the motor or reducer) and the driven sprocket (often connected to a machine’s conveyor head-shaft). This portion of the drive lets the designer build a system that’s either faster or slower by simply changing the ratio of teeth between the drive and driven sprocket. The ratio of the teeth determines the reduction in rpm … so to reduce rpm, the driven sprocket must be larger than the driver sprocket. For example, if the driver sprocket has 15 teeth and the driven sprocket has 30 teeth, the ratio is 2:1, so the rpm is halved at the driven sprocket. The simplest way to select a roller chain is using horsepower charts. First, obtain the motor horsepower and rpm of the small driver sprocket. From this, determine the chain size and number of teeth for the driver sprocket. Where roller chain must drive applications that need long life without contamination, pick chain with self-lubricating subcomponents. Where roller chain must drive applications that need high precision, pick chain with precision roller bearings at each link connection.

COMMON POWER-TRANSMISSION CHAIN CHALLENGES Chain drives are often picked for their ability to withstand harsh environments. Some require clean operation without the contamination risk of lubrication. Others expose chain-driven machinery to weather, water or chemicals. So, chain manufacturers offer several products to meet these challenges. Consider roller chain: One critical area where roller chains need lubrication is the pin-bushing contact zone. Self-lubricating chains stay cleaner because the exterior of the chain is free of excess lube. These chains also attract less

9 • 2016

DESIGN WORLD — MOTION

9/12/16 9:36 AM

CHAIN UPDATE FOR 2016

Motion System

HANDBOOK

Here are some insights into recent chain innovation from Michael Hogan, Senior Roller Chain Design & Application Engineer at U.S. Tsubaki. Chain manufacturers and OEMs are using more automation than ever. It’s key to having consistent cost-effective manufacturing, especially in the U.S. For example, advanced systems ensure that everything from chain fabrication, heat treatment, and assembly are controlled to the highest precision and accuracy. On the end-user side, even those applying robotics are finding that bearing-bushing chain extends life and boosts precision. To review, bearing-bushing conveyor chains feature needle bearings between pins and bushings. These eliminate wear elongation — helpful in indexing and other exacting applications such as precision machining. Positioning accuracy can be held to ±0.008 in. using a positioning pin. We have seen growth in specialty chains — mostly to satisfy specialty designs and the demand for high load capacities in small spaces. Case in point: Standard roller chain comes with many different attachments, but end users must often bolt a pusher or adapt to a given application. This necessitates costly machining of parts and labor to fasten to the chain. Now some manufacturers offer special attachments built into the chain that reduce overall cost for end users (and make the attachments stronger).

Roller-chain selection chart Chain strands 3

900 1,000 700 1,000 800 500 800 600 400 600 400 300 400 300 200 300 200 200 100 100 80 60 40 30

100 80 60

20 10 8 6 4 3

10 8 6

1 0.8

500 400 300 200 100 80 60 40 30 20

10 8 6 4 3

4 3

1 0.8 0.6

2 1 0.8

20 10 8 6 5 4 3

80 60

1 0.8 0.6

0.6

0.4

0.6

0.4

0.3

0.4

0.3

0.2

19 T 19 22 T T 2 2 25 1T 5T 22 19 T T T 21 25 25 T 2 T 23 23 5T T 2 17 T 21 25 T 1 20 40 T T T 25 1 9T 0 1 21 7T T 18 21 7T T 1 0 T 25 14 60 23 17 T 0 T T 12 2 15 25 1T 0 T 1 T 00 17 19 T T 19 80 T 23 6 T 0 15 50 T 40 35

Roller-chain drive capacity (horsepower)

0.4 0.3 0.2

10 20

30 50 80 200 500 1,000 3,000 7,000 40 60 100 300 700 2,000 5,000 10,000

Speed of roller chain’s small sprocket (rpm) 58

DESIGN WORLD — MOTION

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9 • 2016

dust and particulates than regular chains. Such roller chains are useful where oil contamination is a concern, including paper-product or wood-processing industries. Nickel-plated chains offer another alternative for chain coatings, providing some protection for mildly corrosive environments. Stainless-steel chains offer superior corrosion resistance; however, designers must be aware that regular stainless steels cannot be hardened in the same manner as carbon steel. Therefore, the load carrying capacity of stainless steel is lower than carbon steel. Proper chain maintenance requires periodic inspection. All chains must be checked for damage, wear and chemical attack on a regular basis. Another issue is wear elongation. Eventually roller chains wear so much that they necessitate replacement— typically at 1.5 to 2% (12.180 in./ft to 12.240 in./ ft) elongation. Chains may work until they reach 3% elongation, but are at increased risk for suboptimal performance. One final note: Besides chain strictly for power transmission, there are also conveyor chains that do double duty to accept a power input and move product horizontally, vertically or even around curved radii. The most common conveyor chains are ASME-style (ANSIstyle) attachment chains. These have pins or plates with tabs onto which parts or product-holding shoes can bolt. Common versions are single-pitch attachment, doublepitch attachment, hollow-pin, curved-attachment and plastic-sleeve chain. The attachments let engineers put special fixtures or blocks onto the chain to serve specific conveyor functions. One subtype — accumulating chain conveyors — stop discrete products even while the chain is still moving without a lot of friction. Accumulating conveyors are suitable for applications (such as assembly lines) that have products ride through several stations.

motioncontroltips.com | designworldonline.com

9/12/16 9:36 AM

COMPRESSION SPRINGS

Photo courtesy Lee Spring

How to specify

COMPRESSION SPRINGS ENGINEERS

incorporate compression springs in designs that need linear compressive forces and mechanical energy storage—designs such as pneumatic cylinders and pushbutton controls, for example. The most conventional compression spring is a round metallic wire coiled into a helical form. The most common compression spring, the straight metal coil spring, bends at the same diameter for its entire length, so has a cylindrical shape. Coneshaped metal springs are distinct in that diameter changes gradually from a large end to a small end; in other words, they bend at a tighter radius at one end. Coneshaped springs generally go into

motioncontroltips.com | designworldonline.com

CompressionSprings_MSHandbook8-16_V3.indd 59

applications that need low solid height (the total height when compressed) and higher resistance to surging. Whether cylindrical or cone shaped, helical compression springs often go over a rod or fit inside a hole that controls the spring’s movement. Other configuration types include hourglass (concave), barrel (convex), and magazine (in which the wire coils into a rectangular helix). Most compression springs have squared and ground ends. Ground ends provide flat planes and stability under load travel. Squareness is a characteristic that influences how the axis force produced by the spring can be transferred to adjacent parts. Although open ends may be suitable in some applications, closed ends afford a greater degree of squareness. Squared and ground end compression springs are useful for applications that specify high-duty springs; unusually close tolerances on load or rate; minimized solid height; accurate seating and uniform bearing pressures; and minimized buckling. The key physical dimensions and operating characteristics of these springs include their outside diameter (OD), inside diameter, wire diameter, free length, solid height, and spring rate or stiffness. • Free length is the overall length of a spring in the unloaded position. • Solid height is the length of a compression spring under sufficient load to bring all coils into contact with adjacent coils.  • Spring rate is the change in load per unit deflection in pounds per inch (lb/in.) or Newtons per millimeter (N/mm). 9 • 2016

DESIGN WORLD — MOTION

9/12/16 9:43 AM

HANDBOOK

Motion System

This compression spring has reduced ends.

This concave (hourglass-shaped) compression spring can stay centered, even in large-diameter bores.

The dimensions, along with the load and deflection requirements, determine the mechanical stresses in the spring. When the design loads a compression spring, the coiled wire is stressed in torsion and the stress is greatest at the wire surface. As the spring is deflected, the load varies, causing a range of operating stress. Stress and stress range affect the life of the spring. The higher the stress range, the lower the maximum stress must be to obtain comparable life. Relatively high stresses may be used when the stress range is low or if the spring is subjected to static loads only. The stress at solid height must be low enough to avoid permanent damage because springs are often compressed solid during installation.

FAQ: WHAT ARE PARAMETERS DICTATING HELICAL COMPRESSION-SPRING SELECTION? The OD of a spring expands under compression. Consider this if the spring goes into a tube or a bore during assembly. Also remember that the OD of a spring is subject to manufacturing tolerances, just as any mechanical part. If the tolerance range is positive, the spring’s dimensions may be slighter larger and can add to the overall assembly’s envelope size. Most spring suppliers specify work-in-hole diameters for their springs to factor in manufacturing tolerances and the OD’s expected expansion. Look for this information to quickly select from stock spring catalogs, or use this information to better communicate product needs when ordering custom-made springs. Consider loading or travel requirements on the compression spring. The spring rate (also called the spring constant) is the relationship of the force to compress a spring by a unit of length, typically pounds per inch. So with a given load, the product designer can calculate expected spring travel. The further the spring travels, the more stress it endures. So at a critical point, stress can yield the wire material … causing a phenomenon called spring set. After spring set, the spring can’t expand back to its original unloaded length. Even so, in some assemblies, such springs can still function. 60

DESIGN WORLD — MOTION

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9 • 2016

Stress formulas and online calculators predict spring set. Otherwise, a starting rule of thumb is to avoid solid height by at least 20% (so that there’s always 20% of the spring’s total travel left during the normal range of operation). Compression spring-end types are standard or special. Standard ends are either plain open or closed. Either can be ground or not ground. The ends actually affect the spring rate. So, springs with dissimilar ends that are otherwise identical (with the same total coils, wire size, and OD) have different spring rates. Ground ends require more manufacturing effort. However, combined with closed ends, round ends improve the squareness of the loading force and reduce spring-buckling tendencies. Some manufacturers include closed and ground ends in standard catalog stock design, while some don’t. Know the difference. Special end examples include reduced coil for screw mounting, offset legs to work as alignment pins, and enlarged coils to snap into ring grooves. Spring materials abound and include everything from carbon steel to exotic alloys. Music wire is a high-carbon spring steel and is the most widely used material. Stainless steel 302 has less strength than music wire, but adds general corrosion resistance. Nickel alloys make a lot of springs branded under various trademarks and are chosen for extreme high or low operating temperatures, specific corrosive environments, and non-magnetic qualities. Springs made of phosphor bronze and beryllium copper are copper alloys for good corrosion resistance and electrical conductivity.

motioncontroltips.com | designworldonline.com

9/13/16 2:33 PM

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HANDBOOK

Motion System

MICROMO MC3/MCS motion controls include FAULHABER V3.0 motion controllers —intelligent networked drives optimized for OEM and automation applications. These controllers feature 100-msec sample rates for velocity, position and current feedback. They network via Ethernet fieldbus technology, USB, CANopen and RS-232. They pair with FAULHABER coreless dc motors, brushless dc motors and linear dc servo motors (and offer high power matchup with other motors to 300 W). MC 5005 and MC 5010 versions go in switch cabinets or devices; an MC 5004 open card version goes into existing housings.

How did today’s range of

MOTION CONTROLS develop?

ELECTRONIC

controls were first designed about 70 years ago, when John Parson pioneered production manufacture of Sikorsky helicopter blades. His efforts to use early computer technology — to cut more precise aerodynamic shapes for blade profiles — led directly to the creation of computer numerically controlled (CNC) machine tools. By the early 1950s, such controls were standard for manufacturing. Then with the advent of transistor logic, solid-state memory, and the ability to program with CRT workstations, all the pieces were available for the creation of programmable controllers in 1968. The Third Industrial Revolution — automation — was about to begin. At about the same time came distributed control systems (DCSs) with unique control requirements for many individual analog controllers employing PID algorithms and sequential control. DCSs or SCADA systems ran chemical processes, nuclear power plants and steel mills. Here, with an array of minicomputers and engineered communications networks, the Texaco Port Arthur petrochemical refinery installed the first “modern” DCS in 1959. Honeywell launched its DCS product for process automation in the early 1960s.

DESIGN WORLD — MOTION

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These CNC, PLC and DCS designs were separate disciplines with distinct modes of application modeling. So during this period of control development, their fundamental difference necessitated creation of unique hardware and software. One controls’ subsystems were inapplicable to the others. Nowadays, industrial-control manufacturers benefit from computer processor power, memory and communications that offer almost boundless capabilities. It’s true that for those without direct experiences of historical control technologies, the existence of today’s disparate range of programming and hardware is confusing. But in reality, any of today’s processors (including those in PC-based controls) are capable of performing CNC, motion, PLC or DCS functions. They are different families of control based on their unique programming and tasking. So it may appear as a distinction without difference, but the difference is there when it comes to the application.

MOTION-CONTROL LANDSCAPE OF 2016 Motion controllers in feedback-based designs take an input command, compare it with a feedback signal at the motor, and trigger corrective action to make the output (or actual position) and input (target position) match—ideally, with minimal error. Motion controllers also calculate trajectories for the machine axes’ motors to follow to meet the target commands. These trajectories form

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Motion System

HANDBOOK

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Lexium Motion Modules are programmable motion controllers from Schneider Electric that are programmable via MCode (also used in MDrive products). The shared platform as well as development boards fast-track motion concepts to market. Motors in NEMA sizes 8, 11, 14, and 17 pair well with 1.5-A versions of the controller, and there are other versions.

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motion profiles, which are sequences of position commands (expressed as functions of time) that tell the motors where to position the load and how fast to do it. Common motion profiles are trapezoidal, ramp, triangular and complex polynomial profiles. Each of them satisfies certain motion conditions and tasks. For instance, a trapezoidal profile (with a velocity-versus-time profile in the shape of a trapezoid) delivers constant acceleration, then velocity, then deceleration. Such actions need copious signal processing, so motion controllers typically use digital signal processors (DSPs) to perform the mathematical operations. DSPs handle algorithmic processing better than standard microcontrollers incapable of heavy mathematical processing. To get the target motion profile out of the physical machine, the controller needs to track the profile and (in most cases) reject disturbances. Controllers track commands by commanding motor drives to follow positions, velocities, torques (or forces) and accelerations. Called feedforward control, this compensation relies on accurate machine and motor models. In contrast, disturbance-rejecting controls are more active, fixing output to correct for problems with sudden or unexpected loads on the machine or inaccurate feedforward models. The simplest of these is proportional (P) control for constant integer gain. Then programmers can add integral gain (I) and in some cases

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Your Machine’s Motion, Simplified

You wouldn’t believe the things we do. Mitsubishi Electric’s Motion Controllers make it easier than ever to replace complex mechanical systems with the flexibility of high-performance servo control. The Graphical Mechanical Editor software takes care of multi-axis synchronization automatically, eliminating the need for complex calculations and formulas in your programming code. Design your machine however you wish. Mitsubishi Electric makes the programming simple, so that you can go from concept to production in no time.

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HANDBOOK

Motion System

Sysmac Libraries are a new addition to Sysmac Studio’s integrated development environment designed for Omron Automation’s NJ/NX Machine Automation Controller. They include Vibration Suppression function blocks to make motion designs quieter, faster, steadier, and more accurate. Consider the application shown here: A single-axis chip handler needs to wait over a socket until vibration stops. So a function block called VSMoveParam1 calculates S-curve (velocity, acceleration, and jerk) parameters during positioning and then damps vibration at system resonant frequency for quicker handling.

either derivative (D) gain or velocity (V) gain to make PID or PIV loops to actively reject errors. The integral value integrates error over time and helps to drive it to zero. The derivative value helps to stabilize the P-I system. PID loops are particularly common and powerful algorithms to help machines track commanded trajectories. They work on the error signal—the difference between a commanded value and actual value of an output—and attempt to drive the error to zero while maintaining machine stability.

FAQ: WHICH OPTION IS BEST FOR GIVEN CONTROL REQUIREMENTS? On a physical level, most motion controllers are stand-alone controllers, PC-based controllers or microcontrollers. Stand-alone controllers are complete systems (including all electronics, power supplies and external connections) that mount in one physical enclosure. These controllers go into machines to command one application consisting of a single-motion axis or multiplemotion axes.

DESIGN WORLD — MOTION

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PC-based controllers include a motherboard of a basic personal computer or a ruggedized industrial PC, as well as PC-type hardware components and a high-speed dedicated bus that transmits information to and from the processor. The latter exists because using a PC for control requires the same inputs and outputs as a basic PC … as well as interfaces to factory-floor devices. Here, typical I/O includes the electric motors and fluid-power devices for actuation, as well as discrete sensors, pushbuttons, signaling lights and mechanical switches for feedback. One key advantage of PC-based controllers is that they provide a ready-made graphical user interface for easier programming and tuning. PC-based controller software includes some operating system to manage internal processing and resources. OS instability issues are a thing of the past thanks to proliferating real-time operating systems, professional grades of Windows, and Linux application software to trigger the target behavior in a machine or process.

9 • 2016

Control programming languages include computer-science offerings (such as C+, Visual Basic, and so on) to more application-specific languages— including IEC-61131-recognized Ladder Diagram, Instruction List, Function Block Diagram, Structured Texas and Sequential Function Chart languages. Lastly, there are microcontrollers. These are individual integrated chips (ICs) that manufacturers usually design on printed circuit boards with I/O for feedback and driving connected motors. While these controllers are relatively inexpensive and have the advantage of giving designers chiplevel access to their systems, the drawback is that some require good programming skills to configure and implement. Programmable logic controllers (or PLCs) are specialized microprocessorbased controllers to command specific machine or process tasks. They work in automation and manufacturing to control assembly lines and factoryfloor machinery as well as mechanical, electrical and electronic equipment in industrial applications. Design

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Integrated machine and plant control is on the rise with controllers such as the Mitsubishi Electric Automation iQ-R Series. The design incorporates sequence, motion, safety, process, and C language control into one platform. It lets machines or production lines consolidate control in one rack. The system allows four CPUs per rack and has a 0.98 nsec execution speed and a high-speed bus. It also uses a CC-Link IE field network with deterministic performance over industrial Ethernet.

CONTROLLER CHIPS FIT FOR EVERY APPLICATION Nippon Pulse manufactures a variety of servo/stepper controller chips, and they all have different strengths.

Some are ultra high-precision with a variety of interpolation functions. Some are simple and low-cost for basic motion control. Some feature pre-registers for smooth, seamless and continuous movement. Any of them will ease the burden on your CPU and allow for smoother, faster, more complicated motion profiles than an FPGA or CPU alone. All of them will impress you. Contact us today for a free consultation!

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engineers have used PLCs for automation since the 1960s, when they began to replace physical relays setup through ladder logic. Basic PLC hardware includes the processor, I/O modules (to handle inputs to the processor and outputs to controlled devices), and a user interface. The latter can be anything from a simple keypad or a touchscreen to an Ethernet connection to a PC for more complex programming. No matter its form, users program the PLC through the user interface. I/O modules bring input signals to the PLC’s CPU and output control signals to devices such as electric motors, sensors, and fluid-power valves and actuators. One key metric of PLC performance is scan time—the time the PLC takes to run through the program to collect data and update outputs. Scan time usually takes only a few milliseconds, but can take much longer if the program is long or the processor is slow. Faster scan times accommodate processes with more real-time demands. In contrast, fast scans aren’t necessary for traditional applications that run more slowly.

COMPLETE CONTROL WITH TODAY’S PACS PACs (programmable automation controllers) are similar to PLCs but include more hardware and software to satisfy a broader range of industrial functions. When manufacturers first introduced them in the early 2000s, their main strength was their ability to execute more complex automation. Today, their key advantage is that they help integrate other industrial tasks that surround motion setups in facilities.

DESIGN WORLD — MOTION

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THE PERFECT MOTION FOR ANY APPLICATION Platinum Maestro, “Best in Class” Multi-Axis Controller

Any Machine Any Kinematic Any Motion

Elmo’s most feature-rich motion controller, all included IEC61131-3 PLCopen Motion Control

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HANDBOOK

Motion System

Some motor drives include control functions. Case in point: These Groschopp ac controls reduce slip and increase efficiency when matched with Groschopp motors and gearmotors. The DA1230K-4X shown here with the black enclosure sports a die-cast aluminum case with hinged cover (NEMA 4X) with a motor hp selection jumper. Here with the red cover is the DA1230k-0. It has its own industrial mounting (chassis) with a finger-safe cover that is simple to operate and has MOV transient suppression. The one-horsepower ac controls have slip compensation; motor overload I2T; an electric inrush current limit; short-circuit protection; and input voltage options of 115, 208, or 230 at 50 or 60 Hz.

As a superset of PLCs, PACs excel where machines need multiple channels of communication, high data traffic and coordination with intelligent sub-systems. PACs work especially well here thanks to better real-time control of high-end automation tasks. More specifically, PACs help integrate management monitoring, HMI inputs and outputs, process control and analog I/O, and business enterprise-level functions. In fact, as high-performance PAC microprocessors are ever more affordable, PACs are an increasingly common alternative for complex control architectures. Though it’s true that most high-performance PLCs can host additional intelligent processors in their backplanes (such as Ethernet modules with multiple ports for expanded data and communications), such setups are usually more expensive that using PACs. That’s because vendors’ proprietary backplanes and internal operating systems are both additional overhead.

SERVO CONTROLLERS ARE CORE OF SERVO SYSTEMS Servo systems— controller, motor and feedback—run closed-loop to outperform open-loop systems. Namely, they improve transient response times and reduce steady state errors and system sensitivity to different load parameters. Servo-controller circuitry usually includes a motion controller that generates motion profiles for the motor to follow, and an interface with a motor drive that supplies power to the motor based on controller commands. These perform two tasks: They make a machine’s axes track a commanded input, and they improve system disturbance rejection (often through a PID loop). Refer to 70

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the previous section on motion controllers for more on PID loops. There are a few important factors to consider when selecting a servo controller for an application. The first task it to determine which type of motor the system will control. Is the servomotor an ac or dc motor? If it’s dc, is it brushless or brushed? This will help determine the kind of commutation the motor needs and if the controller can accommodate it. How many axes of motion does the application have? Is it a single axis of control or are there multiple axes? Some servo controllers control simple single-axis applications as well as more complex motion, such as multi-axis robotic workcells. Next, how many channels of I/O does the machine need? Are special input types needed beyond inputs for feedback signals such as speed and position? Be sure that the controller can accommodate all necessary feedback devices, whether they’re signals from encoders, resolvers, SSIs or Hall sensors. One factor designers sometimes overlook is controller setup. Is the controller easy to setup and program? Is programming done with a keypad or does the controller let designers program it from a computer screen? Also consider the available communication links. Are there basic RS232 or RS485 links? Does the controller include bus interfaces for common networks such as CAN, DeviceNet, Sercos or Ethernet? Answering these questions helps identify servo controllers that are most suitable for a given application. motioncontroltips.com | designworldonline.com

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Galil Motion Control

ALL THE RIGHT MOVES...

...for Ultimate Precision Galil Motion Controllers handle virtually any application Between our flexible product offering and our affordable custom solutions, we can accomodate all of your motion and I/O needs. Select one through eight axes. Choose internal multi-axis servo or stepper drives. Increase the number of axes and I/O by daisy-chaining through built-in Ethernet ports. Guaranteed low price per axis with driver included. Galil products are easy to program and use, backed by unparalleled technical support and both ISO 9000 and ISO 13485 certification.

• Process commands in as little as 31 microseconds • Handle all modes of motion, simple to complex • Handle ultra-high resolution systems • Support closed loop stepper motors • Up and running in minutes • Use virtually any encoder • EtherCAT master available

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1. Developing ideas 2. Drafting concepts 3. Implementing solutions 4. Manufacturing machines 5. Ensuring productivity

With increasing engineering tasks and ever shorter time frames, it’s good to know you have a drive and automation specialist at your side who can make many of these tasks easy for you. We work with you through the entire development process of your machine – from initial ideas all the way to after-sales, from the control system all the way to the drive shaft. Come discover the future of engineering with us, and you will find more freedom to explore what really counts – your ideas. Find out more at www.Lenze.com

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CONVEYORS

for simple to complex transport

Dorner’s 3200 Series Modular and Flat Belt conveyors, the 2200 Series Precision Move and the SmartFlex conveyor platforms have Ultraclean Products Approval Laboratory certification for use in ISO Standard 14644-1 Class 5 and Federal Standard 209 Class 100 rated cleanrooms. This means the four Dorner conveyors don’t contaminate cleanrooms conforming to those standards.

CONVEYORS

move bulk material or discrete products from one area to another, and serve as main material-handling arteries to improve efficiency and throughput. Advances in materials, controls and modular subcomponents have spurred new large conveyors for bulk material transport, miniature conveyors for discrete sorting, and everything in between. During manufacture, myriad products move on conveyors. So conveyors come in an array of shapes and widths of less than 2 in. (for moving extremely small parts) to several feet wide. Once viewed as an afterthought, conveyors have become an integral component in nearly all automated facilities and applications. Select a conveyor by first asking: What types of product is the application moving? Conveyors for material handling of bulk product are more rugged than those for moving discrete product. In contrast, the latter often requires conveyors that can advance product with more precision.

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How does surrounding equipment interact with the product riding on the conveyor? Conveyor Class 1 includes material-handling uses in which the conveyor serves as an artery to transport bulk or discrete product in a steady stream (with little interaction along the way). Class 2 includes conveyors that act as bridges to take product from one location or machine to another. Class 3 includes conveyors that take materials into or out of machines or stations. Class 4 includes conveyors that run right through machinery without break. The first two classes generally prioritize ruggedness or throughput. The last two classes need positioning and (in many cases) custom workpiece pucks to steady product while machines perform work on the product pieces. What is the maximum weight of the product being moved? Does the conveyor need to operate at a certain speed? Does the application require the conveyor system to have inclines, declines or curves? Look for conveyor features that secure or enclose material or product onto the conveyor. Will moisture be present in the application? Does the application need to be sanitary? Look for rugged or washdown-rated conveyors with open frames. 9 • 2016

DESIGN WORLD — MOTION

9/12/16 10:13 AM

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Most conveyors in light to medium-duty discrete-transport applications use belt that’s wrapped around two or more pulleys. A motor powers the pulleys that in turn engage the conveyor belt. Styles and materials abound to meet specific applications. Some belts are low friction, so product can slide a bit for accumulation. In contrast, highfriction belts have more grip to better hold products to the belt. Engineers can design such conveyors to meet exact application specifications. Magnetic conveyors are built with ceramic magnets for applications that need parts to adhere to the belt during processing, or for jobs that require elevation changes. The designer can specify higher magnet strength for use in inverted applications. In contrast, metal-free conveyors have Delrin bedplates (instead of the traditional steel bedplate) under sections where metal-scanning equipment checks product—usually food—for metal shavings. (Delrin is an inflexible polymer that works as a tough, heatresistant metal substitute.) This lets a device check passing product without getting false readings. Pivot conveyors mount to a pivot base to swing out of the way when workers need to walk through the line. Interlock switches and a timer let the conveyor clear before the gate opens. Some controls can automatically resume product flow after the conveyor returns to the inline position. Servo drives accurately start and stop belt conveyors to provide precise part location. They also let engineers control acceleration and deceleration, so are most suitable for conveyors used in assembly operations. Manufacturers mount encoders to a conveyor’s drive shaft to sense shaft rotation or count pulley revolutions for accurate control of the belt in feeding or indexing applications. Single-drive, multi-belt conveyors serve two or more lanes of product for the sake of efficiency. Here, two or more conveyors run off a single gearmotor on a common drive shaft or coupled shafts. In some arrangements, the belts even mount to a single conveyor frame. Timing-belt conveyors use toothed belts that engage synchronous drive pulleys while serving as the conveyor surface as well. These provide excellent belt-movement control for accurate part or fixture positioning. Vacuum conveyors work with a perforated belt that draws air through grooves in the conveyor bedplate to hold light or flimsy parts on inclines or during especially fast transport. 74

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Design

CONVEYORS

Conveyors that provide basic machine input and output can be fairly simple.

Conveyors that move product through a standalone machine can also use one-way conveyors with the most basic encoder feedback.

Conveyors that move product from one machine to another in a continuous manufacturing line must be precision setups — often with a servodrive and motor running a toothed pulley to (positively) engage a belt.

When a conveyor is a manufacturing line’s main artery, it needs a precision setup as well. Software setup helps facilitate drive sizing to accomodate distance moved, load, and startup inertia.

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Call or email to get started on your application 860.769.5500 • sales@mknorthamerica.com

7/7/2016 9/12/169:19:46 10:15 AM AM

HANDBOOK

COUPLINGS:

Motion System

Torque, misalignment and more

COUPLINGS

connect shafts on rotating equipment such as motors to transmit motion, velocity and torque. They should accommodate relative movement between the machine sections they join. Two types are available — rigid and flexible. Flexible couplings compensate for misalignment, while rigid designs join shafts already in alignment.

Clamped, or compression style, couplings come in two parts that completely wrap around the shaft. Like most coupling designs, this protects the shaft from damage while providing high torsional holding power. Their advantage comes from their two-piece design, which allows them to be removed for easy maintenance.

RIGID COUPLINGS

FLEXIBLE COUPLINGS

Rigid couplings are torsionally stiff and best used when shafts are already in proper alignment; parallel shaft misalignment ideally should be well below one thousandth of an inch. One drawback is that they are susceptible to vibration and cannot be run at high speeds. Sleeve-style rigid couplings are suitable for light- to medium-duty applications. The one-piece sleeve—essentially a tube with an inner diameter that is the same as the shafts it is joining together—has two set-screws to fasten it to the shaft. They are easy to use and offer high torque capacity, stiffness and zero backlash.

Flexible couplings can be used where there is a slight amount of misalignment between shafts. They accommodate misalignment while still transmitting torque. Misalignments can be one of several fundamental types, including lateral, axial, angular or skewed. The greater the misalignment, the less efficient the motor is in generating speed and torque. Misalignment also contributes to premature wear including broken shafts, failed bearings and excessive vibration.

R+W’s FIT/STB series of safety couplings are an example of torsionally stiff flexible bellows couplings. They have a fully enclosed modular balldetent system, for overload disengagement at high speeds and torques in excess of 1,000 Nm.

DESIGN WORLD — MOTION

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HANDBOOK

Motion System

Flexible couplings are typically the most compliant of components in mechanical motion systems, making torsional stiffness a critical factor in terms of maintaining positional control over a load. Many users of servomotors require the shaft to start and stop multiple times per second, which requires a torsionally stiff coupling to help diminish the settling time between cycles. However, torsionally flexible couplings frequently win out in terms of their torque capacity in a given body size. Torsionally flexible couplings are naturally better for vibration damping, which is needed just as frequently in continuous motion applications as in cyclic duty applications. Types of motion differ in applications as well. For instance, in manufacturing lines, motion may be either continuous or start and stop. With the latter type, couplings can help dampen all-too-common vibration, diminish the settling time of the system and improve throughput. In contrast, continuous motion applications give greater weight to torsional strength over damping capabilities. Motion applications that require precise motion control, such as in packaging and scanning and inspection, call for zero-backlash couplings. Bellows couplings are commonly used in motion control applications that require precision control and where shaft misalignment is present. If your application requires precision, then it is important to understand the performance factors that are critical for selecting the optimum bellows coupling for the task.

They are flexible with zero-backlash. There is a difference between backlash—which is a true mechanical clearance, such as that which is found between gear teeth—and torsional deflection, or wind-up, which everything on earth will exhibit to some degree. Most couplings are preloaded to eliminate backlash or are inherently backlash free, like the bellows coupling. But they all have different levels of torsional stiffness, which is often traded off for lateral flexibility during the coupling selection process. Bellows couplings tend to have the highest torsional stiffness of any servomotor coupling, do not handle quite as much misalignment as others, but also do not impose heavy reaction loads onto the shafts and bearings as they flex. Key benefits of bellows couplings include misalignment compensation and precise transmission of velocity, positioning and torque. Bellows couplings are known for their exceptional torsional rigidity, and flexibility in dealing with axial, angular and parallel shaft misalignment. Bellows couplings are typically made from a stainless-steel tube hydroformed to create deep corrugations that make them flexible across axial, angular and parallel shaft misalignments. When coupling shafts, bellows couplings absorb slight misalignments from perpendicularity and concentricity tolerances between the mounting surfaces of the two connected components.

Typical applications for a servo type coupling like this GWE 5112 from Ringfeder are encoders, machine tools, robotics, linear motion applications, test rigs, and packaging machines. The servo coupling consists of two “outer cone” connection type hubs and an elastomeric insert.

DESIGN WORLD — MOTION

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PRECISE. ROBUST. AVAILABLE. These new generation CD® Couplings feature zero backlash precision and high torsional stiffness. They answer today’s demanding needs in servo motor applications with high reverse loads and positioning requirements. New clamp style hubs handle increased torque on shafts without using keyways. Manufactured of RoHS compliant materials. Now size, select and see the right CD® Coupling solution for your coupling application with Zero-Max 3D CAD files. Check our FAST deliveries.

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Motion System

HANDBOOK

Here we see examples of single piece couplings with custom bores and attachment features from Helical. Features clockwise from left to right: threaded hub, flange and integral clamp, hex bore, turned down hub as spring pin, square bore and miniature coupling with set screws.

Jaw couplings feature two metal hubs and a spider insert, usually made of elastomer, which are fitted together to absorb vibration and shock. The elastomer is available in a variety of hardness and temperature ratings, so the spiders can be chosen for specific applications. Because they are not as torsionally stiff as other couplings, they are better suited to constant motion applications. They are available in two types: straight jaw and curved jaw with zero backlash. Because accuracy of torque transmission can be an issue, straight jaw couplings are not used in most servo applications. Curved jaw couplings, on the other hand, reduce deformation on the spider and the effects of centrifugal forces during high-speed (up to 40,000+ rpm) operation. Both types

In this image we see a variation of a standard coupling from Helical designed for a custom attachment and greater misalignment.

DESIGN WORLD — MOTION

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can easily handle axial motion. If a spider breaks, the driving jaws can still contact the driven jaws directly, maintaining operation, making jaw couplings fails-afe designs. Oldham couplings can be preloaded to eliminate backlash and can handle misalignment of all types depending on the disc material. They are being used more often as an alternative to straight jaw couplings on general industrial equipment such as pumps, valves, gearboxes and conveyor systems. They are versatile and offer long lives when misalignment is an issue. Their three-piece design—two hubs and a torque-transmitting center— makes them easy to install and disassemble. Oldham couplings can be specified in a variety of materials to meet the needs of different applications, for example, if zero backlash is required versus vibration reduction. They are best suited when parallel misalignment may be high. And because of their three-piece design, axial motion is limited. Disc couplings are a logical choice for servomotor and other

demanding applications because of their ability to transmit high torque, operate at high or changing speeds, and handle misalignment and system loads. While a coupling’s torque, misalignment and speed capacities need to be evaluated against a system’s requirements, the discpack usually is the most important aspect of the coupling’s construction because it will affect all critical performance aspects of the coupling and the system in which it is used. The most common type of discpack is made of metal and can be found in different shapes (straightsided, scalloped edges, square, and so on). In the case of metal disc couplings, double-flex designs need to be used if there is to be any parallel shaft misalignment. The single-flex variety of metal disc coupling is good for angular misalignment but not parallel. This can be quite advantageous in case a user needs to suspend a load between two single-flex couplings, because their lateral stiffness can support the weight of the intermediate component.

motioncontroltips.com | designworldonline.com

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THE COUPLING. ABSOLUTE PRECISION 0.1-100,000 NM.

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Here we see a regular and exploded view of GAM’s KSS coupling. The KSS is a compact coupling with reinforced bellow for higher torsional rigidity and conical hubs for higher torque capacity and clamping force.

Beam, or helical couplings are almost always manufactured of aluminum, but stainless-steel versions are also available for use in corrosive environments and increased torque and stiffness. Their one-piece design makes them easy to maintain. Offering zero backlash, they feature spiral cuts that transmit torque and can handle all types of misalignment and angular, parallel or axial motion. Parallel motion is more of a challenge for the single beam design because it must bend in two directions, which causes stress and possible failure. Two designs exist under this style—single and multiple beams. Single beams are best suited to low-torque applications where no parallel misalignment is present, while multiple-beam designs are stiffer, for higher maximum torque capabilities.

SPECIAL COUPLINGS Most disc couplings feature a metal disc-pack. However, some have composite disc-packs that are constructed of a special composite material rather than metal. This composite material provides an alternative to metal disc couplings. The advantages include its ability to absorb shock and vibration, its misalignment capacity, electrical isolation and elimination of fatigue and fretting. Whereas metal disc couplings may be less expensive initially, overall cost of composite disc couplings usually will be lower because they are maintenance free and are rated for long life. 82

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The ability to accommodate misalignment is a critical aspect of a flexible disc coupling. Misalignment between coupled shafts often exists due to manufacturing tolerances, improper installation or from loads on the system. Parallel, angular and axial misalignment between coupled shafts should all be examined to see if the coupling selected is up to the task. It is important to know a coupling’s misalignment rating as well as the stiffness rating. The stiffer a coupling, the higher the reaction load misalignment will transmit to the coupled items. These reaction loads will have a negative effect on the life of the system. To limit these reaction loads, composite disc couplings are less radially stiff than metal disc couplings. Therefore, they transmit lower reaction loads on the coupled equipment, thereby increasing the life of connected (and often expensive) components. The amount of misalignment that a system can experience will typically determine the selection between a single-flex (one flexible disc-pack) and a double-flex (two flexible disc-pack) coupling. While more compact in size than the double-flex variety, a single-flex coupling will have lower misalignment capacity and higher reaction loads. A common misconception is that single-flex disc couplings cannot accommodate parallel misalignment. Although this is true for metal disc couplings, the design of some disc-pack couplings allow single-flex CD couplings to accommodate limited parallel misalignment. This motioncontroltips.com | designworldonline.com

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THE COUPLING. SIMPLY UNBEATABLE 2-25,000 NM.

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HANDBOOK

permits designers to implement a single-flex disc coupling into designs that may not have space for a double-flex coupling. Gear couplings are a type of mechanical device that transmits torque between two shafts that are not collinear. The coupling typically consists of two flexible joints, one fixed to each shaft. These joints are often connected by a third shaft called the spindle. Each joint generally consists of a 1:1 gear ratio internal/external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth. Gear couplings are generally limited to angular misalignments of 4 to 5°. Gear couplings ordinarily come in flanged sleeve and continuous sleeve variations. Flanged gear couplings consist of short sleeves surrounded by a perpendicular flange. One sleeve on each shaft lets the two flanges line up face to face. A series of screws or bolts in the flanges hold them together. Continuous-sleeve gear couplings have shaft ends coupled together and abutted against each other, which are then enveloped by a sleeve. Generally, these sleeves are made of metal, but they can also be nylon.

Single-joint gear couplings connect two nominally coaxial shafts. In this application, the device is called a gear-type flexible, or flexible coupling. The single joint allows for minor misalignments, such as installation errors and changes in shaft alignment due to operating conditions. These types of gear couplings can accommodate 0.25° to 0.5° of angular misalignment at most. Magnetic couplings are designed to transfer torque from one shaft to another, but they do so without a physical mechanical connection. This makes them suitable for fluid pumping applications since the connection can be made through thin barriers, which help maintain a hermetically sealed rotary feed through. Since there are no contacting parts in the coupling, wear is virtually nonexistent and the use of permanent magnets means no external power source is needed. Magnetic couplings also have a built-in safety feature where, in the event of an overload on the coupling, it will shift to the next position and keep going. Magnetic couplings can typically only handle light torque loads and applications with either gradual starts, or low rotational inertia of the driven side of the system. They are also rather large in diameter, considering their relatively light torque load. The couplings also have moderate radial loads on support bearings.

HOW DO I ENSURE COUPLING ALIGNMENT FOR PRECISION MOTION CONTROL APPLICATIONS? Alignment is important in smaller devices, especially when the

Typical servo drive lines with linear modules use backlash-

application must output precision or dynamic motion. So it’s

free couplings tolerant of little shaft misalignment. With too

clear flexible couplings are for misalignment compensation.

much shaft offset in a precision coupling, failure modes range

Two bearing-supported shafts will never be perfectly aligned —

from noise and backlash over time, to complete failure, which

and in an imperfect world with external influences, those shafts

typically happens with metal couplings, normally used for

are probably not going to stay aligned forever.

higher torsional stiffness and shorter settling times. Obviously,

Even on newly assembled systems, the real priorities

engineers don’t want misalignment failure. So, in the world of

in terms of performance, extended bearing life, increased

precision motion control alignment features are everywhere.

efficiency and vibration reduction are important. In larger

Servo motors, stepper motors or even gear head outputs,

power transmission drive lines, there’s also been a widespread

almost always see some sort of alignment feature that’s

effort to improve alignment. It is also necessary in precision

concentric to the shaft and bearings machined directly into

applications because many couplings are not tolerant of

the frame. Almost all precision linear motion systems also have

large amounts of misalignment to begin with. In essence, all

them.

couplings should be aligned as well as possible regardless of how much offset a coupling is designed or rated to handle.

R+W America

Think of a typical coupling housing. Many suppliers of servo

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gear heads and linear modules and even some third-parties provide coupling housings that include alignment features.

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Motion System

An overview of

AC DRIVES MOTOR

drives control the speed of a motor. Some manufacturers refer to a controller and motor together as a drive system. However, from the electrical side of things, the drive is often specifically the electrical components that make up the variable frequency inverter itself. So drives are the interface between the control signals and the motor and include power electronic devices such as SCRs (silicon controlled rectifiers), transistors, and thyristors. Matching the correct drive to the type of motor in an application is critical for obtaining optimal performance. There are a wide range of drives available depending on the needs of the specific application and motor type. In general though, drive types typically fall into two categories; dc and ac drives. A basic dc drive is similar in operation to an ac drive in that the drive controls the speed of the motor. For dc motor control, a common method is a thyristor-based control circuit. These circuits consist of a thyristor bridge circuit that rectifies ac into dc for the motor armature; and varying the voltage to the armature controls the motor’s speed.

AC DRIVES AC drives control ac motors, such as induction and synchronous motors. AC drives convert ac to dc and then using a range of different switching techniques generate variable voltage and frequency outputs to drive the motor. An ac motor’s speed is determined by the number of poles and the frequency. Thus, as frequency is adjusted the motor’s speed can be controlled as well. A common way to control frequency is by the use of pulse width modulation (PWM). A PWM drive outputs a train of dc pulses to a motor and by modulating the pulse width, making it either narrower or wider, delivers an ac current waveform to the motor.

Motor drives like the Unidrive M from Control Techniques, an Emerson business, when paralleled together, can control asynchronous and permanent magnet motors in systems up to 2.8 MW (4,200 hp). A new Size 11 frame is a 250 kW (400 hp) module that lets designers create high power solutions with the smallest number of components, keeping both footprint and costs to a minimum.

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Motion System

Another drive feature, the ability to slow down or stop a motor, is known as regenerative braking or regen braking. Regen braking provides a way of stopping a motor’s rotation by using the same solid-state components that control the motor’s voltage. The energy generated from braking can be channeled back into the ac mains or into a braking resistor. Advantages of regen drives include the ability to stop a motor faster than it would normally coast down.

VFDs

AD 1000 and AD 700E variable frequency drives from Nidec Motor Corp. reduce energy consumption by automatically adjusting to changing operating conditions They work to 30 hp and run 50 different parameters for a wide range of open and closed-loop applications in food & beverage, packaging, and conveying.

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Variable frequency drives (VFDs) operate by switching their output devices, which can be transistors, IGBTs (insulated gate bipolar transistors), or thyristors, on and off. VFDs can be either constant voltage or constant current. Constant voltage types are the most common type of VFD. It uses PWM to control both the frequency and the voltage applied to the motor. Why use VFDs? They are a powerful way to control the speed of ac induction motors and are fairly simple and easy to use. Among the benefits of using a VFD for motor speed control is the actual energy savings. Controlling the amount of current drawn by the motor can decrease energy costs because the motor will not run at full load all of the time. This is more important as motor efficiency has become a top design priority. For instance, single-phase induction machines (specifically, permanent split-capacitor motors) and universal motors, widely used in industrial washers, are managed with simple voltage-control techniques. Contrast this with high-end, highperformance machines where three-phase motors are more common and which use VFDs. So for instance, an OEM using a universal motor with simple triac control may now find that a three-phase VFD control will provide better energy efficiency, while OEMs using three-phase/ VFD configurations may make the move to technologies like brushless dc motors. Another advantage of VFDs is seen on motor start-up. Without a VFD, an induction motor on start-up has to handle a high initial in-rush current. As the motor speeds up and approaches a constant speed, the current levels off from the peak in-rush values. So with a VFD, the motor’s input starts off with low voltage and a low frequency, avoiding the problem of high in-rush currents. motioncontroltips.com | designworldonline.com

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AC DRIVES

ACF Series open-chassis microprocessor-based VFDs from American Control Electronics offer the simplicity of a dc drive. ACF700 drives setup without programming and have trim pots to set speeds, slip, boost, torque limit, acceleration, and braking parameters. The 115 Vac/230 Vac single-phase input can provide single or three-phase outputs of 115 Vac or 230 Vac.

Another benefit of using a VFD for motor speed control is the reduction of mechanical wear on the motor components. Eliminating the in-rush currents upon start-up gets rid of the excessive torque on components, increasing the life of the motor and reducing maintenance costs and the need for repair. In addition to reducing wear, mechanical stresses on the entire system are greatly reduced. In many cases, mechanical controls such as throttles, valves, dampers and louvers can be completley removed, thereby reducing mechanical wear and maintenance costs. Further, with reduced mechanical wear, due to precise motor speed control, the system output quality may be improved and production times reduced. There are some drawbacks to using VFDs, however. The main one is the possibility of harmonic distortion which can effect the power quality as well as the operation of other machinery. However, VFD manufacturers have been developing solutions that mostly eliminate this problem.

SELECTING AN AC DRIVE There are several key factors to consider when selecting an ac drive. For starters, consider the elements of the power supply available to the application. These are the key criteria for the input power supply: • • • • • • •

Input voltage Number of phases (3 phase or 1 phase) Grounded or not grounded Input frequency (50 or 60 Hz) Drive enclosure (NEMA 1, NEMA 12 ventilated, etc.) Motor cable length (also, shielded or unshielded) Motor cable type (fixed or flexing in machine operation)

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Next, look at the type of motor used in the application. What are the motor’s voltage, current rating, and horsepower? These can be found on the motor’s nameplate. This will help in determining the right drive for the application. Important current parameters include base load current, peak current, and peak current duty cycle description. Also, determine what type of speed control is needed; i.e. servo, closed loop vector, open loop vector, volts/Hz. Another consideration is the type of motor feedback. For closed-loop systems, common feedback can be any number of types including HTL/TTL, resolver, sin/cos 1 Vpp, or multi-turn absolute value EnDat. Next, look at the interface needs of the application. Almost all drive applications have an interface need for some combination of digital control, analog control and communications. These interface requirements are a key ingredient in the specification of operator and machine interaction. Key factors include: • • • • • •

Number of digital inputs and outputs Number of analog inputs and outputs (and signal type such as 0-10 Vdc, 4-20 mA) Communications (PROFIBUS-DP, PROFINET, EtherNet/IP, or other) Interface ports (RS232, RS485) PLC HMI

Also be sure to consider any safety features that the drive may require. These can range from basic features such as brake control and stops to more advanced capabilities such as acceleration monitoring, speed monitoring and speed limits. Lastly, don’t overlook environmental factors such as temperature, humidity, as well as dust and pollutants.

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HANDBOOK

Motion System

DC DRIVE basics A

dc drive supplies voltage to a dc motor. The motor draws current from the power source in proportion to the torque (or load) applied to the motor shaft. A controller lets operators start, stop, and change the direction and speed of a motor. A typical drive converts a three-phase ac voltage to an adjustable dc voltage, which is then applied to a dc motor armature. One of the most common methods of dc motor control is a thyristor-based control circuit. These circuits consist of a thyristor bridge that rectifies ac into dc for the motor armature; varying the voltage to the armature controls the motor’s speed There are two basic types of dc motors; brushed and brushless (or BLDC). Each type of motor has different drive techniques. For instance, one can drive a brushed dc motor by applying a voltage or pulse width modulated (PWM) voltage and the motor will start running and increasing in speed (while reducing torque) until the torque and speed match the load. BLDC motors are a bit more complicated to drive compared with brushed dc motors.

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For example, a typical brushless motor will have three sets of windings connected in a star or “Y” or “Delta” configuration. The motor controller energizes each of the windings to turn the motor. The motor position has to be known to control the windings properly, energizing the correct winding or windings. The controller can be a sensorless type, meaning that it relies on detecting the back EMF (electromotive force) of the windings to detect position and provide the sequence information for the controller. A sensorless drive allows the use of a motor without Hall effect sensors on the motor, making the motor less expensive and requiring fewer connections. For most BLDC motor controllers, the control signal is a speed control signal, such as a PWM input signal rather than an analog signal. As for PWM drives, two common types are sinusoidal (or sine) and trapezoidal. A sine PWM drive increases and decreases the current to each winding to follow a sinusoidal curve in order to smooth the drive power and produce a smoother motor torque. Simple on/off control of the windings will tend to produce an uneven torque through the rotation of the motor and also tends to generate more audible noise due to the uneven torque. A trapezoidal PWM drive is similar to a sine PWM drive and will increase the current to each winding in a straight line based on the motor position and then decrease it in a straight line while increasing the current to the next winding. To use motioncontroltips.com | designworldonline.com

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DC DRIVES

a trapezoidal or sinusoidal PWM drive, motor controllers need to know where the motor rotor is to a higher degree of accuracy than a simple Hall effect switch position provides. They do this by monitoring the motor velocity and predicting the position with time. While this won’t be perfectly accurate it is considerably better than simple on-off drive. Also, a trapezoidal drive will be quieter and smoother than a simple on/ off drive but not as smooth or quiet as a sinusoidal drive. In actual practice, dc motors and drives are still among the most common types of motors and drives in many industrial as well as consumer applications including automotive designs and consumer appliances. The fact is that tried and true motors like brushed dc motors are capable of high peak torques. Also, the fact that they have a linear torquespeed relationship makes control easier, meaning they can be controlled using simple speed controllers and often cost less than other motor and control options. Manufactures are also finding that using existing dc motors and upgrading the dc drives is often a good option. This is because dc motors are usually well built and can offer many years of reliable service.

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DESIGN WORLD — MOTION

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HANDBOOK

Motion System

This PST-360 through shaft sensor from Piher wraps around a shaft to directly sense motion. The 9-mm-thick assembly contains a full circle magnet and electronics module.

The basics of

ENCODERS AN

encoder is a type of transducer that measures position. This position information provides a point of orientation for controlling the position of a motion system. There are several common ways to classify encoders. One is the method of sensing (i.e. capacitive, optical or magnetic sensing) and another is whether the position output from the encoder is absolute or incremental. Another parameter is how much force the encoder can handle on the shaft, so there are light duty, medium duty, and heavy-duty encoders. Another quite common way encoders are classified is either rotary or linear, depending on the type of position they measure, with rotary encoders measuring rotary position and linear encoders measuring linear position.

inch or millimeter. The scale typically has a fixed resolution with embedded markings which is read by the sensing head. For example, a linear encoder with 100 points per inch resolution would read 100 marks for every inch of movement. In contrast with linear encoders, a rotary encoder measures resolution in pulses per revolution. Similar to linear encoders, a typical rotary encoder contains an internal coded disk and a sensing head. (See sidebar.) Think of a linear encoder as a type of tape measure while a rotary encoder is more like a measuring wheel. For instance, a rotary encoder with a 100 point per revolution resolution would have 100 marks on its coded disk. Scale-based linear encoders can use different types of sensing technology. The most common type are optical encoders, but they can also be magnetic, capacitive and even inductive.

ABSOLUTE AND INCREMENTAL ENCODERS LINEAR ENCODERS Linear encoders typically are made up of a scale such as a coded strip, and a sensing head. Reading the space between the scale coding determines position. The resolution of linear encoders is measured in pulses per

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Encoders can also be either absolute or incremental. Absolute encoders have a unique code for each shaft position. Or in other words, every position of an absolute encoder is distinctive. The absolute encoder interprets a system of coded tracks to create position information where no two positions are identical. Another feature is that

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Motion System

Designing more compact drives is an enduring challenge for manufacturers and one piece of that equation is encoders such as the Sendix F5883 from Kübler. An optical hollowshaft encoder with a mounting depth of only 43 mm, it opens up new possibilities for installing encoders in tight mounting spaces.

absolute encoders do not lose position whenever power is switched off. Since each position is distinctive, the verification of true position is available as soon as power is switched on without the need for a homing routine. Absolute encoders can be either single-turn or multi-turn. Single-turn encoders are well suited to short travel motion control applications where position verification is needed within a single turn of the encoder shaft. Multiturn encoders, on the other hand, are better for applications that involve complex or lengthy positioning requirements. Absolute encoders have a number of advantages. First is the nonvolatility of memory. True position is not lost if power is lost or the system moves while power is switched off. A continuous reading of position is not needed. This is specifically useful in those applications, such as satellitetracking antennas, where position verification is key. Safety is another benefit. In some applications where a loss of position could lead to operator injury or machine damage, an absolute encoder automatically provides position verification when the power is switched on. Absolute encoders also have good immunity to electrical noise. The device determines position by frequently reading a coded signal. Stray pulses from electrical noise will not build up and accurate position is presented again on the next reading. Incremental encoders generally supply square-wave signals in two channels, A and B, which are offset (or out-of-phase) by 90 degrees. This helps in determining the direction of rotation.

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Motion System

HANDBOOK

The output signals of an incremental encoder only have information on relative position not absolute position like an absolute encoder. In order for the encoder to provide any useful position information, the position of the encoder has to be referenced in some way, traditionally using an index pulse. So the incremental encoder sends incremental position changes to electronic circuits that perform the counting function. One traditional limitation of an incremental encoder is that the number of pulses counted is stored in an external or buffer counter which can be lost if there is an interruption of power. For instance, if a machine with an encoder is turned off, the encoder will not know its position when switched on again. The encoder has to perform a homing routine in order to know its exact position, forcing the motor to move until a home limit switch is activated. Then, a counter or buffer will be zeroed and the system will determine where it is relative to fixed positional points. One way around this issue of loss of power is to use a battery backup system. Such a solution ensures that the memory is backed up and can store the count information and provide an absolute count once power is restored.

ENCODER PERFORMANCE The most critical performance parameter for encoders is their ability to accurately measure position. One of the main factors is that the encoder should have the necessary level of resolution required by the application. However, resolution and accuracy are not

the same. For instance, an encoder may have a high resolution but low accuracy, or vice versa. The ideal encoder has both the necessary resolution and is highly accurate. Accuracy depends on a number of factors. For starters, there are differences between optical and magnetic technologies. Generally speaking, magnetic encoders are more resistant to shock and vibration than optical encoders. They’re also better able to withstand environmental contaminants such as dust, grease and moisture. As far as electrical interference goes, optical encoders are fairly immune to it since position measurement is not electrical-based but optical. Also, magnetic technologies may be subject to strong magnetic fields that could impact readings.

ENCODER COMMUNICATION PROTOCOLS The advent of more sophisticated communication protocols means that users have a lot more control over encoder operation. For instance, encoder resolution can be programmed through a USB interface via computer. Other parameters can be changed on the fly through simple software commands. Some of the most common encoder communication protocols include SSI (Synchronous Serial Interface), BISS (bidirectional serial/synchronous), ProfiBus, DeviceNet and Ethernet I/P. These protocols are “open”, meaning they are non-proprietary and not tied to a specific manufacturer’s products. Closed or proprietary protocols include Hiperface (High Performance Interface) and EnDat (Encoder Data).

HOW TO CHOOSE BETWEEN ROTARY AND LINEAR ENCODERS? It may seem as though linear encoders and rotary encoders have strictly defined (and maybe even mutually exclusive) applications. Prevailing logic is that linear encoders track linear motion and rotary encoders track rotating shafts — but this isn’t always the case. Some motion designs can use linear or rotary encoders, so engineers can pick between the two. Elsewhere, designs with multiple kinds of motion might benefit from multiple encoders on both linear and rotary axes to monitor key machine sections. Some installations excel when a machine uses both linear and rotary encoders. Linear and rotary encoder applications overlap in other designs. Consider a conveyor belt driven by a motor. Here, a rotary encoder can track the motor even if the latter misses steps or stalls. One caveat: If the conveyor slips or breaks, the motor might continue operating as if nothing occurred. Here, a linear encoder keeps better track of the whole conveyor system, sending feedback to the controller indicating conveyor motor faults as well as conveyor belt faults. In a similar way, an application using a drive belt can use a rotary encoder on an idle roller to detect faults, as that location would let the encoder detect the ceasing of rotary motion. In contrast, a rotary encoder mounted on the drive roller of a similarly arranged conveyor might not work so well. That’s because if the belt failed, the roller to which the encoder mounts would still spin. Here, an alternative is a linear encoder to track the conveyor to detect any loss of motion.

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HANDBOOK

Summary of gearing:

Motion System

GENERAL GEAR DESIGN THE

main function of a gear is to mesh with other gears to transmit altered torque and rotation. In fact, gearing can change the speed, torque and direction of motion from a drive source. When two gears with an unequal number of teeth engage, the mechanical advantage makes their rotational speeds and torques different. In the simplest setups, gears are flat with spur teeth (with edges parallel to the shaft) and the input gear’s shaft is parallel to that of the output. Spur gears mostly roll through meshing, so can be 98% or more efficient per reduction stage. However, there is some sliding between tooth surfaces, and initial tooth-totooth contact occurs along the whole tooth width at once, causing small shock loads that induce noise and wear. Sometimes lubrication helps mitigate these issues.

In slightly more complex setups, parallel-axis gearsets have helical gears that engage at an angle between 90° and 180° for more tooth contact and higher torque capacity. Helical reducers are suitable for higher-horsepower applications where long-term operational efficiency is more important than initial cost. Helical gear teeth engage gradually over the tooth faces for quieter and smoother operation than spur gearsets. They also tend to have higher load capacities. One caveat: Angled tooth contact generates thrust that the machine frame must resolve. No matter the subtype, most parallel-axis gearsets have gear teeth with tailored involute profiles— customized versions of the rolled trace off a circle with an imaginary string. Here, mating gears have tangent pitch circles for smooth rolling engagement that minimizes slipping. A related value, the pitch point, is where one gear initially contacts its mate’s pitch point. Involute gearsets also have an action path that passes through the pitch point tangent to a base circle. Besides parallel-axis gearsets, there are non-parallel and rightangle gearsets. These have input and output shafts that protrude in different directions to give engineers more mounting and design options. The gear teeth of such gearsets are either bevel (straight, spiral or zerol), worm, hypoid, skew or crossed-axis helical gears. The most common are bevel gearsets with teeth cut on an angular or conical shape. Hypoid gears are much like spiral-bevel gearsets, but the input and output shaft axes don’t intersect, so it’s easier to integrate supports. In contrast, zerol gearsets have curved teeth that align with the shaft to minimize thrust loads.

Spur, helical bevel, and worm gear sets abound from KHK USA Inc.

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t material of SCM415. carburizing (case hardening), SCM415 is normally used. requirements for harder material, SNCM220 and/or SNCM420 y used. hardness is determined by production condition. pected hardness value is informed in a quotation of gears.

Gear precision grade table : entioned equivalent grades are for reference only. ades completely match each other.

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The DieQua Advantage We offer the widest range of servo gearheads and gearboxes along with the experience and expertise to help you select the best solution for your requirements. Right angle or inline, economy or precision, we have the gearhead to meet your needs.

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GEARING

Summary of gearing:

GEARBOXES, SPECIALTY GEARHEADS & SERVOGEARSETS SERVO

designs are precision-motion setups with feedback and (in most cases) fairly stringent accuracy demands. So for these designs, engineers should pick servogear reducers with good torsional stiffness, reliable output torque and minimal backlash. OEMs tasked with integrating servo systems should look for quiet reducers that easily mount to the motor and require little or (if possible) no maintenance. In fact, a lot of advanced machinery integrates servogears into application-specific electromechanical arrangements, and several of these arrangements are common enough to have specific labels. Here is a look at some of the most widespread. Gearmotor: This complete motion component is a gear reducer integrated with an ac or dc electric motor. Usually the motor includes the gears on its output (typically in the form of an assembled gearbox) to reduce speed and boost available output torque. Engineers use gearmotors in machines that must move heavy objects. Speed specifications for gearmotors are normal speed and stall-speed torque. Gearbox: This is a contained gear train … a mechanical unit or component consisting of a series of integrated gears. Planetary gears are common in integrated gearboxes. Planetary gears: Particularly common in servo systems, these gearsets consist of one or more outer planet gears that revolve about a central, or sun, gear. Typically, the planet gears mount on a movable arm or carrier that rotates relative to the sun gear. The sets often use an outer ring gear, or annulus, that meshes with the planet gears. The gear ratio of a planetary set requires calculation, because there are several ways they can convert an input rotation to an output rotation. Typically, one of these three gear wheels stays stationary; another is an input that provides power to the system, and the last acts as an output that receives power from the driving motor. The ratio of input rotation to output rotation depends on the number of teeth in each gear and on which

motioncontroltips.com | designworldonline.com

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component is held stationary. Planetary gearsets offer several advantages over other gearsets. These include high power density, the ability to get large reductions from a small volume, multiple kinematic combinations, pure torsional reactions and coaxial shafting. Another advantage to planetary gearbox arrangements is power-transmission efficiency. Losses are typically less than 3% per stage, so rather than waste energy on mechanical losses inside the gearbox, these gearboxes transmit a high proportion of the energy for productive motion output. Planetary gearbox arrangements distribute load efficiently, too. Multiple planets share transmitted load between them, which greatly increases torque density. The more planets in the system, the greater load ability and the higher the torque density. This arrangement is also very stable due to the even distribution of mass and increased rotational stiffness. Disadvantages include high bearing loads, inaccessibility and design complexity. In servo systems, besides boosting output torque, gearboxes impart another benefit—reducing settling time. Settling time is a problem when motor inertia is low compared to load inertia … an issue that’s the source of constant debate (and regular improvement) in the industry. Gearboxes reduce the reflected inertia at the controls by a factor equal to the gear reduction squared. 9 • 2016

This is a Spinea precision cycloidal reducer from DieQua Corp. Spinea TwinSpin (TS) reducers have a unique speed-reduction mechanism and radial-axial bearings to maintain precision. Thanks to their configuration, the reducers are more compact than cycloidal reducers. In smaller sizes they compete with harmonic flex spline designs on torque density and rigidity.

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Cone Drive Operations sells this right-angle drive to accommodate any output shaft configuration. It has a servomotor to deliver up to 7.5 kw, gear ratios ranging from 5 to 60, and a backlash-free servocoupling for fast and error-free moves. The drive is suitable for packaging, machine tool, and conveyor applications.

Summary of gearing:

STRAIN-WAVE GEARING STRAIN-WAVE

gearing is a special gear design for speed reduction. It uses the metal elasticity (deflection) of a gear to reduce speed. (Strain-wave gearing sets are also known as Harmonic Drives, a registered trademark term of Harmonic Drive Systems Inc.) Benefits of using strain-wave gearing include zero backlash, high torque, compact size and positional accuracy. A strain-wave gearset consists of three components: wave generator, flexspline and circular spline. The wave generator is an assembly of a bearing and steel disk called a wave generator plug. The outer surface of the wave generator plug has an elliptical shape machined to a precise specification. A

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specialty ball bearing goes around this plug to conform to the same elliptical shape of the wave generator plug. Designers typically use the wave generator as the input (attached to a servomotor). The flexspline— usually acting as the output—is a thin-walled steel cup. Its geometry makes the cup walls radially compliant but torsionally stiff (because the cup has a large diameter). Manufacturers machine the gear teeth into the outer surface near the open end of the cup (near the brim). The cup has a rigid boss at one end for mounting. The wave generator goes inside the flexspline so the bearing is at the same axial location as the flexspline teeth. The flexspline wall near the brim of the cup conforms to the same elliptical shape of the bearing. This conforms the teeth on the outer surface of the flexspline to the elliptical shape. That way, the flexspline effectively has an elliptical gear-pitch diameter on its outer surface. The circular spline is a rigid circular steel ring with teeth on the inside diameter. It is usually attached to the housing and does not rotate. Its teeth mesh with those of the flexspline. The tooth pattern of the flexspline engages the tooth profile of the circular spline

motioncontroltips.com | designworldonline.com

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Permanent Precision, Excellent Backlash Stability • Harmonic Drive® or Harmonic Planetary® gearheads • Zero backlash and low backlash versions • Ratios: 3:1 - 160:1 • Peak Torque: 3.9 N•m - 3940 N•m • Sizes: 40mm - 230mm • Output Conﬁgurations: Hollow Shaft, Flange, Keyed Shaft

247 Lynnfield Street, Peabody, MA • 800.921.3332 www.HarmonicDriveGearhead.com Harmonic Drive, Harmonic Planetary and Quick Connect are registered trademarks of Harmonic Drive LLC.

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Common gear options

HANDBOOK

Spur gearsets are simple ...

Motion System

along the major axis of the ellipse. This engagement is like an ellipse inscribed concentrically within a circle. Mathematically, an inscribed ellipse contacts a circle at two points. However, gear teeth have a finite height, so two regions (instead of two points) engage. The pressure angle of the gear teeth transforms the output torque’s tangential force into a radial force acting on the wavegenerator bearing. The teeth of the flexspline and circular spline engage near the ellipse’s major axis and disengage at the ellipse’s minor axis. The flexspline has two less teeth than the circular spline, so every time the wave generator rotates one revolution, the flexspline and circular spline shift by two teeth. The gear ratio is:

Pitch circle

Reaction force ... but helical gearsets are more efficient. Cross-axis sets are another option.

number of flexspline teeth ÷ (number of flexspline teeth - number of circular spline teeth) The tooth engagement motion (kinematics) of the strain wave gear is different than that of planetary or spur gearing. The teeth engage in a manner that lets up to 30% of the teeth (60 for a 100:1 gear ratio) engage at all times. This contrasts with maybe six teeth for a planetary gear, and one or two teeth for a spur gear. In addition, the kinematics enable the gear teeth to engage on both sides of the tooth flank. Backlash is the difference between the tooth space and tooth width, and this difference is zero in strain-wave gearing. As part of the design, the manufacturer preloads the gear teeth of the flexspline against those of the circular spline at the ellipse’s major axis. The preload is such that the stresses are well below the material’s endurance limit. As the gear teeth wear, this elastic radial deformation acts like a stiff spring to compensate for space between teeth that would otherwise increase in backlash. This lets the performance remain constant over the life of the gear. Strain-wave gearing offers high torque-to-weight and torqueto-volume ratios. Lightweight construction and single-stage gear ratios (to 160:1) let engineers use the gears in applications requiring minimum weight or volume ... especially useful for designs with small motors. Another tooth profile for strain-wave gearing is the S tooth design. This design lets more gear teeth engage for a doubling of torsional stiffness and peak torque rating, as well as longer life. The S tooth form doesn’t use the involute tooth curve of a tooth. Instead, it uses a series of pure convex and concave circular arcs that match the loci of engagement points dictated by theoretical and CAD analysis. The increased root filet radius makes the S tooth much stronger than an involute curve gear tooth. It resists higher bending (tension) loads while maintaining a safe stress margin.

Planetary gearsets are compact and run to 10,000 rpm. Here, a lightweight Schaeffler differential for a hybrid vehicle has an axial spline to boost efficiency. Zerol bevel gearsets are a special veriation of straight right-angle bevel sets.

Worm gearsets are rugged and don’t let designs backdrive ... which can eliminate the need for brakes. Note there’s some overlap between bevel and worm applications. Case in point: The MS-Graessner DynaGear below is a single-stage bevel gear with a 30:1 ratio.

The ratio of a helical or bevel gearset is simply the number of teeth in the larger gear divided by the number of teeth in the smaller gear. Other gear types such as planetary gears have more complex ratio relationships.

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Engineers used Graessner USA’s Gearfox software to develop and optimize the drivetrain on this KUKA KL 100 linear robot-transfer unit (RTU). Custom gear designs are increasingly common as software makes specialized builds easier than ever to devise.

Summary of gearing:

CONSULTATION, CUSTOM GEAR DESIGN & GEAR ANALYSIS CUSTOM

106

gearboxes are increasingly common, mainly because they’re easier than ever to manufacture to specification. That’s not to say that the design work isn’t challenging. However, modern manufacturing lets some suppliers make gearboxes and components to meet specific application requirements. New supplier approaches to giving engineering support as well as new machine tools, automation and design software now let OEMs and end users get reasonably priced gearing even in modest volumes. When enlisting help from a consultant or manufacturer, an engineer is more likely to get gearing that mounts properly and performs to specification after reviewing the following and answering as many of these questions as possible:

•

• •

•

What’s the input speed and horsepower? What’s the gearbox target output speed or output torque? This partially defines the required gear ratio.

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•

What are the characteristics of use? How many hours per day will the gearbox run? Will it need to withstand shock and vibration? How overhung is the load? Is there internal overhung load? Remember that bevel gears usually can’t accommodate multiple supports, as their shafts intersect … so one or more gears often overhang. This load can deflect the shaft which misaligns the gears, in turn degrading tooth contact and life. One potential fix here is straddle bearings on each side of the gear. Does the machine need a shaft or hollow-bore input ... or a shaft or hollow-bore output? motioncontroltips.com | designworldonline.com

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•

This chart (courtesy of KHK USA Inc.) lists 11 gear-efficiency ranges. The number of stages, mode of tooth meshing, and (mostly in the case of worm sets) the speed-reduction ratio dictate overall efficiency.

Efficiencies of gear categories and Spur gears Spur Rack Parallel-axis gears

Internal Gears Helical Gears Helical Rack Double Helical Straight bevel gears

Intersecting-Axis gears

Spiral bevel gears Zerol bevel gears

Nonparrallel and nonintersecting

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Screw gears Worm gears

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How will the gearing be oriented? For instance, if specifying a right-angle worm gearbox, does the machine need the worm over or under the wheel? Will the shafts protrude from the machine horizontally or vertically? Does the environment necessitate corrosion-resistant paints or stainless-steel housing and shafts?

Service factor: The starting point for most gearbox manufacturers is to define a service factor. This adjusts for such concerns as type of input, hours of use per day, and any shock or vibration associated with the application. An application with an irregular shock (a grinding application, for example) needs a higher service factor than one that’s uniformly loaded. Likewise, a gearbox that runs intermittently needs a lower factor than one used 24 hours a day. Class of service: Once the engineer determines the service factor, the next step is to define a class of service. A gearbox paired to a plain ac motor driving an evenly loaded, constant-speed conveyor 20 hours per day may have a service class 2, for example. This information comes from charts from gearbox manufacturers that list classes of service. To use these charts, the design engineer must know input horsepower, application type and target ratio. For instance, suppose that an application needs a subtypes 2-hp motor with a 15:1 ratio. To use the chart, find the point where 2 hp and 15:1 ratio intersect. In this case, that indicates a size 726 gearbox. According to one manufacturer’s product-number system, size 726 98-99.5% defines a gearbox that has a 2.62 center distance. Such charts also work in reverse, to let engineers confirm the torque or speed of a given gearbox size. Overhung load: After the designer picks a size, the gearbox manufacturer’s catalog or website 98-99% lists values for the maximum overhung load that is permissible for that sized unit. Tip: If the load in 70-95% an application exceeds the allowed value, increase the gearbox size to 30-90% withstand the overhung load.

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GEARING

This HDP parallel-shaft gearbox from Bonfiglioli USA has gear ratios from 7.1 to 500 and outputs torque from 5,000 to 210,000 Nm depending on the version. It allows foot, flange, or shaft mounting; the cast-iron housing withstands harsh environments and helps maintain precise and vibration-free operation.

Mounting: At this point, the designer or manufacturer has defined the gearbox size and capability. So, the next step is to pick the mounting. Common mounting configurations abound, and gearbox manufacturers offer myriad options for each unit size. A flanged input with hollow bore for a C-frame motor combined with an output shaft projecting to the left may be the most common mounting, but there are many other choices. Options such as mounting feet for either above or below the body of the gearbox, hollow outputs, and input and output configuration are all possible. All gearbox manufacturers list their mounting options as well as dimensional information in catalogs and websites. Lubricant, seals and motor integration: Most manufacturers can ship gearboxes filled with lubrication. However, most default to shipping units empty to let users fill them on site. For applications where there is a vertical shaft down, some manufacturers recommend a second set of seals. Because many gearboxes eventually mount to a C-frame motor, many manufacturers also offer to integrate motioncontroltips.com | designworldonline.com

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motors onto gearboxes and ship assemblies as single units. Work with consultants and even use custom gear designs if the application needs a unique motor-gearbox combination. Some combinations are more efficient. Getting a pre-engineered geamotor ensures that the motorgearbox combination will perform to specification. Also remember that today’s custom and standard gearing aren’t mutually exclusive. Where fully custom gearboxes aren’t feasible (if quantities aren’t high enough, for example) consider working with manufacturers that sell gearboxes built to order from modular subcomponents. Otherwise, look for manufacturers that leverage the latest CAD and CAM software and machine tools to streamline post-processing work and reduce the cost of one-offs. One final tip: Once the gearmotor has been chosen and installed in the application, perform several test runs in sample environments that replicate typical operating scenarios. If the design exhibits unusually high heat, noise or stress, repeat the gear-selection process or contact the manufacturer. DESIGN WORLD — MOTION

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Integrated gearmotors as this one from Parker Automation are often more compact than an assembly with a separate gearhead and motor.

An overview of

GEARMOTORS A GEARMOTOR

integrates a gear reducer and either an ac or dc electric motor into one physical unit. Thanks to its gearset, a gearmotor can deliver high torque at low horsepower or low speed. Most industrial gearmotors incorporate fixed-speed ac motors. However, some gearmotors use dc motors. These dc gearmotors are common in automotive applications — to electronically adjust side-view mirrors and make automatic seat adjustments, for example. Engineers can mix and match motors and gears as needed to best fit application requirements. However, housing design, assembly gearings, gear lubrication, and specific mode of integration of pinion gear and motor-output shaft all affect gearmotor performance. Motor and gear-reducer combinations abound. For example, right-angle wormgear, planetary and parallel shaft gears can combine with permanent-magnet dc, ac induction, or brushless dc motors to form a gearmotor unit. Though it’s possible to combine many different motors and gearsets, not just any one will work for every application, because certain combinations are more efficient and cost-effective than others. Knowing the application and getting an accurate estimation of its required torque and operating speeds is the foundation for successfully integrating a gearmotor into a system.

COMMON GEARMOTOR TYPES AND VARIATIONS As gearmotors can be built on either ac or dc motors, there are a number of choices for the gear reducer. There are five basic 110

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types of gears that can be paired with a motor to form a complete gearmotor. Those are bevel, helical, hypoid, spur and worm types. Another way to classify gearmotors is by the physical arrangement of the final complete unit. So for instance, there are so-called in-line gearmotors where the gear shaft is parallel with the motor shaft, also called a parallel shaft. These can either be offset from the output shaft or completely in line with the output shaft. The other configuration is the right-angle gearmotor, where the output shaft is at a 90-degree angle to the motor shaft.

BENEFITS Gearmotors give better performance than other motor-gear combinations. More importantly, gearmotors simplify design implementation because they save engineers from integrating motors with gears, which in turn reduces engineering costs. If the application requirements are known, engineers can order the right gearmotor from a supplier directly. What’s more, if a gearmotor is sized properly, having the right combination of motor and gearing can prolong operating life and boost overall design efficiency. Another benefit of gearmotors is that they eliminate the need for couplings and potential alignment problems that come with those components. Such problems are common when a design includes the connection of a separate motor and gear reducer — which in turn increases the potential for misalignment and bearing failure, and ultimately reduces useful life. motioncontroltips.com | designworldonline.com

9/12/16 10:34 AM

Control Freak? If you like being in control, then SEW-EURODRIVE is your perfect partner! We put you in charge of every move with our gearmotors and electronics. No headaches, no whining, and virtually no maintenance. You build it and we move it…simple!

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Brother Gearmotors sells subfractional ac gearmotors and reducers for food and beverage and material handling equipment. 3D CAD drawings of their 1 to 3-hp motors are at brother-usa.com/ gearmotors.

WHEN TO PICK A PRE-ENGINEERED GEARMOTOR AND WHEN TO DESIGN YOUR OWN? The answer is partly application specific, partly a matter of resources.

GEARMOTOR ACCESSORIES Gearmotors, like non-geared motors, come in versions with myriad options to satisfy specific application and environmental conditions. For instance, common options include shaft type, bearing choices, seals and lubrication, and mounting and housing options. Housing materials can include stainless steel or aluminum. Some common options for aluminum housings are billet aluminum, sand-cast aluminum, permanent mold aluminum casting, and die-cast aluminum. Other options are die-cast zinc and magnesium injection molding. Despite being a fairly well-established technology, advances in gearmotor technology continue. Some of these include the use of new specialty materials, coatings and bearings, and improved gear-tooth designs that reduce noise, increase strength and extend life, all of which boost performance and reduce overall design size.

One tool to simplify selection of a gearmotor is the performance curve. These plots relate torque and speed and sometimes efficiency. To help designers select a pre-engineered gearmotor, manufacturers do much of the heavy lifting to ensure that their motor-gearing combinations will work together. (See sidebar/FAQ) Because manufacturers make performance calculations and do testing in advance, gearmotor failures from miscalculations or improper component matching are rare. The speed and torque that a given application needs are critical factors in gearmotor selection. Use speed and torque measurements to identify manufacturer’s performance curves that match the application needs. Gearmotor curves unify information (such as speed, torque and efficiency) to summarize the performance of the motor-gearset combination. If an OEM or end user buys a complete gearmotor assembly from a manufacturer, the latter supplies its performance curve. After identifying gearmotors with performance curves that appear to meet the application needs, review all calculations and use the values to determine which of the chosen gearmotors will cause problems once installed. Remember to consider thermal characteristics, full-load gearbox torque, gearbox input speed, gearbox yield strength and intermittent-duty effects. Once the speed and torque requirements are identified, that may not be the end of the story. That is, proper selection of a gearmotor is not all science. The fact is that this is merely a beginning, a starting point. This is because often times the manufacturer’s data may not be derived from empirical testing, so there may be some variation between calculated requirements and the actual application. This is why it’s important to test a sample load under the actual operating conditions of the application. DESIGN WORLD — MOTION

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In either case, it helps to know as much about your specific application needs as possible. For example, speed and torque requirements as well as mechanical issues like mounting configuration and orientation, and thermal considerations too. There are a few key factors that typically determine when to go pre-engineered and when not to. Going the pre-engineered route is best if you lack time or engineering resources or if you need a quick solution, not a long selection process. One of the biggest advantages of selecting a pre-engineered gearmotor is that the manufacturer you purchase from has done most of the work

GEARMOTOR PERFORMANCE CURVE

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Regardless of which method you choose, there are some things common to both approaches.

9 • 2016

for you already. A lot of the uncertainty has been dealt with. So there’s no need to pick a motor and gearbox separately and assemble them together and hope that you’ve done your homework correctly. Going the pre-engineered route saves engineering time and resources, eliminates complexity, and reduces design risk. What about the alternate route, selecting a separate motor and gearing and assembling them together? There are a number of reasons to consider this route. One may be cost. That is, it may be less expensive than choosing a pre-engineered gearmotor from a manufacturer. Another reason may be that the application is unique and you believe you can best design the perfect gearmotor for the application. This would also give you the most control over the final design.

Gearmotors with worm reducers, such as the one shown here from DieQua, are cost effective and suitable for light-duty motion control applications.

motioncontroltips.com | designworldonline.com

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GEARMOTORS

FOR MORE DETAILS AND RESOURCES VISIT OUR WEBSITE AT WWW.GROSCHOPP.COM

712.722.4135 • 712.722.1445 (fax) • 420 15th St. NE, Sioux Center, IA 51250 USA • Registered ISO 9001:2008

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Advances in

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HUMAN MACHINE INTERFACE (HMI) HARDWARE HUMAN

machine interfaces or HMIs are terminals on machinery to give operators a way to monitor and adjust controls and functions. This interaction is through a graphical user interface that facilitates information exchange and communication between supervisory and machine-level HMIs. Where are HMIs useful? Everywhere. The buttons and knobs of yesterday’s interfaces are yielding to HMIs in even the humblest designs. Consider how even consumer-grade products such as office printers now include touchscreen controls to help users with common paper, ink, and networking tasks. In the same way, HMIs are increasingly common on more sophisticated industrial machinery but with the same user-friendly simplicity. Industrial HMI hardware consists of compact controllers with embedded functions, usually in the form of ruggedized touchscreens — for example, LCDs with tempered glass and cast-aluminum frames or even sealed enclosures for outdoor applications or indoor plant applications with a lot of oil, dirt, and machining byproducts, for example. Hardware standardization is increasingly common for HMI hardware on open-source and proprietary setups alike. In addition, HMI hardware options can make displays satisfy specific application requirements. Depending on the application’s complexity, myriad I/O options exist — including digital and analog. Advances in HMI technology have quickened with

increasingly affordable touchscreens and replacement of resistive displays with capacitive. In fact, these capacitive displays are particularly helpful in medical and food-and-beverage applications that need bezel-free designs, as they’re sleeker and let personnel clean and even sterilize machinery more easily. Solid-glass capacitive touchscreens also last longer than HMI hardware based on resistive technologies, because the screens don’t use pressure points to form circuits, so don’t wear or lose sensitivity over time. What’s more, many HMIs with capacitive displays have the multitouch capabilities of smartphones, which lets OEMs leverage user familiarity to offer intuitive interfaces. In fact, electronics innovation for consumer products — with everimproving wireless communications, displays, and portable processing power — is letting users connect to HMIs for industrial applications via tablets and smartphones for real controls as well.

Some Maple Systems HMIs divide industrial control and remote access functionality between separate Ethernet networks — an internal industrial communications network and an external wide area network (WAN). This offers IIoT functionality plus security. 10/100/1000 Base-T Ethernet ports and a 1-GHz processor maintain peak performance.

The H3 wired handheld from On3 is an HMI that connects to an array of interfaces for machinery and automation. It can connect without additional hardware to controllers via RS422 or Ethernet cables.

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New

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HUMAN MACHINE INTERFACE (HMI) SOFTWARE HUMAN

machine interface (HMI) software is programming that gives operators a way to manage machine command panels. Interaction is through a graphical user interface (GUI) that facilitates information exchange and communication between two types of HMI — supervisory and machine level. Generally, programmers write HMI software for either machine-level HMI or supervisory-level HMI, with applications suitable for both types. Such software has high upfront cost, but is inexpensive long-term thanks to the way it reduces redundancies.

Case in point: Even lower-tech applications (in which most machine interaction is via switches and pushbuttons) entry-level HMI offerings are making inroads — as they often reduce interface-part count and simplify controls. More sophisticated applications benefit in a different way: Pharmaceutical and medical machinery use the latest HMI features to differentiate from competitive offerings. But no matter the performance grade, selecting HMI software starts with an analysis of product specifications and features. What

This Opto 22 groov software is on a phone — and the groov Box hardware appliance GROOV-AR1. The web-based software brings data from sensors, drives, meters, and other industrial devices to smartphones, tablets, and PCs. It uses OPC Unified Architecture (OPC UA) and Modbus/TCP protocols to communicate with myriad plant-floor devices.

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HANDBOOK

kind of GUI will the machine operator need? Will operators need to view diagrams, digital photos and detailed system schematics? Other considerations include system architecture, performance requirements, integration, cost of procurement, and operations.

Motion System

HMI SOFTWARE EDITORS HMI software editors let designers add touch-screen functions and configure control functions for industrial automation. Usually, programming is through Windows-based software or screen-editor software. That lets designers quickly edit schematics and set the right communication protocols in a familiar programming environment. Standard HMI software satisfies the needs of simpler machinery that’s not task-intensive. High-performance HMIs run software that lets users customize the interface to meet specific operator requirements. Sometimes, HMI software lets users program advanced control functions as well — for editing servomotor parameters and issuing global commands to other control axes on a machine, for example. (For motion-control applications, the visual GUI can range from simple 4 line x 20 column text displays to color monitors with touchscreen controls.) Such motion functions go well beyond basic HMI tasks observing processes or making very simple changes to some individual variables or parameters or setpoints.

REMOTE HMI ACCESS One iteration of HMI software that’s increasingly common are programs that let users remotely monitor and control HMIs from smartphones, tablets, or offsite PCs. Traditional setups only let users get to the HMI on the factory floor, but this new cloud-based HMI software gives operators remote access lets them check machines from anywhere. Sometimes called web-based visualization, this is particularly helpful where machines run in hard-to-reach places. Related innovations in HMI software even let remote users make on-the-fly changes to machine functions (for variable production output).

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New mapp View software from B&R lets automation engineers create powerful web-accessible HMI setups without knowing HTML5, CSS and JavaScript. It also encapsulates GUI functionality in modular control elements called widgets that just drag and drop into place for configuration.

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LEADSCREWS

A wide range of leadscrews with variations in thickness, thread type and pitch, as well as screw coating material are illustrated in these leadscrews from Haydon Kerk.

LEADSCREWS;

linear motion mainstays

LEADSCREWS

are one of many linear actuator components that also include ballscrews as well as belt and pulley systems, linear motors and chaindrive systems. A leadscrew, also known as a power screw, is a threaded rod or bar that translates rotational motion into linear motion. Leadscrews generate sliding rather than rolling friction between a nut and the screw. Consequently, higher friction means a lower overall efficiency. And efficiency, when talking about leadscrews, is simply the ability to convert torque to thrust while minimizing mechanical losses. Leadscrews are a staple of motion designs on machines big and small alike. They usually sport higher ratings than comparable ballscrews thanks to more contact between the nut and screw load surfaces. However, innovations in materials and helix geometry address old issues associated with leadscrew friction, bringing it

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down to better than 0.10 in some cases—good for fast and dynamic applications. In fact, there’s also been an uptick in leadscrew use because of proliferating machines for 3D printing, manufacturing and medical applications. Industries across the board are adopting new leadscrew components and linear systems. Designers of kiosk and automated retail applications, for instance, are looking for ways to simplify machines, reduce design weight and simplify assembly and maintenance. In a similar way, both additive manufacturing (3D printing) and traditional subtractive processes—plasma cutter, laser and waterjet manufacturing—are driving new leadscrew uses. The same holds true for factory automation. Leadscrew manufacturing processes can determine the performance and cost of the leadscrew. For instance, there are three ways leadscrews can be manufactured; by machining, rolling, or grinding. Ground leadscrews are the most expensive and are generally considered to be the highest performing as well. Another determinant of efficiency is the thread type. Acme threads are the simplest to produce, the most inexpensive, but also among the least efficient. Other types include buttress threads and square threads, which generally have the least amount of friction and higher efficiencies.

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Motion System

HANDBOOK

Leadscrews have a number of advantages including a relatively high load carrying capacity. They are also compact and simple to design into a system with a minimal number of parts. The motion is also generally smooth and quiet and requires little maintenance. Leadscrews also work well in wash-down environments because the materials used and the lubricant-free operation allows total immersion in water or other fluids. On the other hand, leadscrews do not have high efficiencies. Because of lower efficiency ratings they’re not used in applications requiring continuous power transmission. There’s also a high degree of friction on the threads meaning that the threads can wear quickly. Because a leadscrew nut and screw mate with rubbing surfaces they have relatively higher friction and stiction compared to mechanical parts that mate with rolling surfaces and bearings. There are several parameters that help determine leadscrew performance. These include thrust, speed, accuracy and repeatability. The two most important factors in determining the performance of a leadscrew are the screw pitch and lead. The pitch is the linear distance between the threads while the lead is the linear distance the nut travels. Speed is another critical parameter. Leadscrews have a critical velocity, which is the rotational velocity limit of the screw. Reaching this limit induces vibrations in the leadscrew. Accuracy and repeatability are also important factors. The accuracy of a leadscrew is a measure of how close to a desired end point the assembly can move a load to within a given tolerance. The accuracy of the leadscrew will mostly determine the system’s accuracy. On the other hand, repeatability is a measure of how well a leadscrew assembly can repeatedly move a load to the same position.

coupling

bearing

motor The diagram for a basic leadscrew setup shows a typical leadscrew, with the shaft, nut and bearing, connected to a motor via coupling.

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shaft

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Accessibility doesn’t have to be one sided…

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HANDBOOK

Motion System

This high-speed Model TY THK actuator uses a timing-belt drive to deliver strokes to 4,749 mm. Caged balls in its table carriage ride on linear rails and boost precision.

Update on

LINEAR-MOTION RAILS, GUIDES & SYSTEMS LINEAR-MOTION

systems are essential in everything from manually operated industrial drawers to advanced Cartesian robots. Mechanisms that include the former operate without power, using inertia or manual power to move loads. Components to complete the latter include ready-to-install drive and guidance designs … in the form of self-contained actuators or linear-motion machinery subsections. Some designs simply rely on the rotary-to-linear mechanism or actuator structure for total load support. However, most industrial linear designs have pneumatics, linear motors or motor-driven, rotary-to-linear mechanisms to advance attached loads, as well as rails that guide and support the loads. Here, linear rails, rotary rails, guide rails, linear slides and linear ways are just a few

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options to facilitate single-axis motion. Their main function is to support and guide load with minimal friction along the way. Typical linear-motion arrangements consist of rails or shafts, carriages and runner blocks, and some type of moving element. Engineers differentiate these systems by the type of surface interaction (sliding or rolling), the type of contact points, and (if applicable) how the design’s rolling-element recirculation works. In fact, slides and rails are more advanced than ever, with advances in materials and lubrication setups (to help designs last longer in harsh applications), innovative rail geometries (to help designs withstand more misalignment and load than ever), and modular guide mounts (to boost load capacity and minimize deflection). No matter the ultimate installation, linear-motion rails, guides, and ways enable motion along an axis or rail either through sliding or rolling contact. Myriad moving elements can produce either sliding or rolling support: ball bearings, cam roller sliders, dovetail bearings, linear roller bearings, magnetic bearings, fluid bearings, X-Y tables, linear stages and machine slides. One classic rail with sliding contact is a dovetail slide, and one classic rail with

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Need some help getting your project moving?

Have questions about linear slide systems? Not sure what product can handle the load? Our experienced team will answer your questions, brainstorm with you and help solve your system challenges. It’s what we’ve been doing for more than 45 years—and why we’re the go-to partner for linear motion systems in aerospace, medical, automotive and other industries. Just pick up the phone and speak with a seasoned application engineer and get your motion moving.

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Motion System

rolling contact is a ball rail with a recirculating system. Sliding-contact bearings are the more straightforward type of linear-motion component. These consist of a carriage or slide that rides over a surface known as a rail, way or guide. Sliding contact occurs when the moving part directly contacts the rail section. Older versions of these sliding-contact rails generated considerable friction during movement, so were only suitable for basic applications. However, newer versions have selflubricating sleeves and other features to boost positioning accuracy and repeatability. In contrast, rolling-element linear-motion systems are either recirculating or non-recirculating. Non-recirculating types use rolling elements such as bearing balls, rollers and cam followers for movement. Recirculating types use some type of moving platform that houses a bearing block. This bearing block contains raceways with rolling elements that let the platform move along the rail with little friction. Recirculating types include linear guides and ball-bushing bearings. More specifically, rolling-element linear guides come in two basic versions—those with circular arc grooves and those with Gothic arc grooves. These groove choices are a result of industry evolution that’s enabled new geometries for better load handling. Circular arc grooves contact bearing balls

This Amacoil/Uhing Model RG rolling ring linear drive is integrated with a motion controller for precision linear motion applications. The Precision Motion Drive is fully programmable and meets application requirements for precision winding and spooling, pick-and-place machines, X-Y coordinate tool movement, metrology equipment and other machinery providing fast, accurate positioning and reciprocating linear motion. Depending on the size of the RG drive nut in the system, the Precision Motion Drive System provides from 7 to 800 lb of axial thrust.

LoPro is a guide wheel based linear actuator from BishopWisecarver Corp. featuring 90° steel guide tracks. The steel tracks can be up to 20 feet long and can be readily butt joined for longer lengths. A pair of opposing tracks are mounted to aluminum track plates in sections of about 10 feet long. Polyurethane belting provides very long mechanical actuation with good accuracy and very high speeds while exhibiting low noise generation.

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NEED A

CUSTOM ENGINEERED LINEAR SLIDE ASSEMBLY?

When a Medical Equipment Manufacturer needed a custom linear slide assembly, they came to Del-tron. Many linear motion applications require CUSTOM DESIGN. Del-Tron Linear Engineering has the products, knowledge and expertise to help you design and achieve the perfect linear motion solution for your specific needs. Based in the United States and more than 40 years of experience, we have been providing our customers with design assistance, product prototyping and full service manufacturing for custom linear ball slides, crossed roller slides, positioning stages and complete linear positioning systems. Ranging anywhere from a standard ball or crossed roller slide requiring custom holes or special materials to a complex positioning system, Del-Tron Linear Engineering can help. Utilizing our customized or standard slides, let one of our knowledgeable engineers provide you with immediate technical assistance, enabling you to find work-arounds to design and develop unique out-of-the-box solutions. Call us today. You’ll find we’re always ready to help and offer personalized attention that’s unparalleled in the industry. We expect you’ll experience a level of responsiveness you just won’t see anywhere else.

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HANDBOOK

Motion System

Linear Slide Kits (LSKs) from GAM Enterprises are mounting solutions that enable virtually any motor or gearbox to connect to any linear belt or ball screw product. As far as competitive products go, some actuator companies make similar motor mounts — but if the motor does not fall within their standard offering, they may not be able to provide one. Then it is up to the engineer to design this interface. GAM’s LSK saves engineers time on a relative simple but time consuming task.

HOW TO COMPENSATE FOR ALIGNMENT ERRORS WITH PROFILE RAIL GUIDES? When an application has uneven mounting surfaces or the potential

face design compensate for misalignment. This is especially useful

for misalignment, the typical linear-guide solution is to use round

in applications that use two rails in parallel but where there may be

shafting and ball bushings that tolerate these modes of imprecision. In

a height deviation between the carriage mounting surfaces. Because

contrast, profiled rail guides need precision mounting to ensure even

the face-to-face arrangement works on both two-row and four-row

load distribution on the recirculating balls — so are most common

bearings, miniature bearings — which are commonly two-row designs

in applications that have machined mounting surfaces and tight

— also have this self-aligning capability. There are caveats. Even though profiled rail bearings that use the

tolerances. But some applications require the load-carrying capacity and stiffness that only profiled rail linear guides can offer ... even if they

capability, there are ways to modify these bearings so they can

don’t allow for precision alignment or preparation of mounting

compensate for misalignment. For example, one manufacturer sells

surfaces. Here, self-aligning profiled rail linear guides are an option.

profiled rail bearings with back-to-back arrangement in self-aligning

Raceway arrangement is how the load-carrying balls and rail

versions. In the setup, the load plate (which is a precision steel strip

raceways are arranged relative to each other, and how the resulting

on which the load-bearing balls ride) pivots on its supporting surface

contact lines are positioned. The two raceway arrangements for

inside the housing. This ensures uniform loading on the balls that are

profiled rail guides are face-to-face (or an X arrangement) and back-

in the load zone, thus avoiding premature wear.

to-back (or an O arrangement). The primary difference between these

Another self-aligning profiled-rail design has a block made of cast

two designs is the length of the moment arm arising from reaction

iron and housing a cylindrical spline nut. The nut is partially cut away

forces when a moment load rides the bearing.

to conform to the profiled rail, and the cylindrical cross-section lets

Face-to-face arrangements have a much shorter moment arm

126

back-to-back (or O) arrangement don’t have an inherent self-aligning

the block self-align. This design’s main advantage is to compensate

(roughly half the length) than the back-to-back arrangement. This

for alignment errors between twin rails in parallel. It also excels in

means that its moment load rigidity is lower than that of a bearing with

assemblies that need mounting on unmachined surfaces or with rail

a back-to-back arrangement, but the lower rigidity lets the face-to-

misalignment.

DESIGN WORLD — MOTION

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Infinite Possibilities in Motion The global leader in Linear Actuators with the experience to deliver the right combination to suit your needs Infinite winding options Multiple encoder options

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HANDBOOK

Motion System

at two points. The Gothic arch contacts the balls at four points for bidirectional load capacity. Another option for rolling-element linear motion is ball bushings that have a bushing nut lined with recirculating bearing balls. This nut rides along a round shaft to allow axial movement. History lesson: In 1946, the manufacturer Thomson introduced ball bushings, and the technology established the basic mechanism of rolling-element linearmotion bearings. In today’s designs, the bushings may also have integral flanges to support axial loads.

•

SLIDING-CONTACT RAIL GEOMETRIES

Rolling-element linear systems need little force to initiate motion. In addition, friction-force variations due to speed are minimal, so these systems can position loads with small and precise steps. The low friction also lets these systems move at high speeds without generating too much heat. That minimizes wear to help machinery maintain a level accuracy for much of the linear system’s operating life.

One feature of sliding carriage-and-rail setups is that manufacturers typically incorporate a ground groove in a rectangular track’s geometry (to serve as a working surface). Manufacturers typically build these rails in one of three shapes.

•

Rails with a boxway shape or square shape are simplest. Square rails excel at carrying large loads without a lot of deflection. Manufacturers often preload square rails, and most linear systems based on square rails do not selfalign. Square rails often have a smaller envelope size; the boxway rails handle the highest loads in all directions. Rails with a dovetail shape (or twin rail) have male geometry that securely engages female saddle geometry. That boosts stability and load capacity, even in unusual orientations or applications with unsteady loads. Round rails deflect less under load. In addition, systems based on round rails are inherently self-aligning, so are easier to install than other options. No matter the type, rails come in myriad sizes and lengths.

ROLLING-CONTACT FUNCTIONS AND OPTIONS

New linear guides from igus excel in setups that need manual adjustments, such as the ball pretensioned predefined positional system and the compact preload prism slide.

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www.rollonmotionbox.com

PLUG AND PLAY 3-AXIS MOTION One vendor. One part number. Two engineering hours. Motion Box is a pre-configured 3-axis Cartesian robot system that allows you to focus on your core competancy while we handle the motion, assembly and controls. Including linear actuators, servo motor, a motion controller and HMI, Motion Box is completely pre-engineered to offer a true plug-and-play, 3-axis system compatible with most control systems. Eliminate the time, expense and risk in building your own Cartesian robot. Contact us today to learn more.

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Wrap around motor mount is an option. In-line mount is standard for each axis.

Gripper shown as concept. Not included.

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Motion System

Manufacturers produce rolling-contact guides in several variations. The differences are in rolling element shape (ball or roller); rolling element size; whether the rolling contact is two or fourpoint; conformity of ball contact; whether the design has two, four, six or some other number of rolling-element rows; contact angle; and how the rolling-element rows are arranged—in an X or O configuration. All these design factors determine load capacity, rigidity and friction. For example, O-shaped arrangements can withstand higher torque than X arrangements. In general, the number of load-bearing rolling-element rows influences the load capacity … so more rail rows means more load capacity and rigidity. However, more rows makes systems more complex and costly. Here are more details on these rollingcontact options: Rolling elements are either linear rollers or balls. Because the rolling elements recirculate in recirculating rolling-element guides, they have a nearly infinite stroke length. They are available on flat guide ways and guide way rails. Flat guide ways are available in single or double row rolling elements. Guide way rails are often square rails. Non-recirculating roller type units have limited stroke length. Flat guide ways are dominant here and have either a grooved race compatible with crossed rollers, or non-grooved race, which uses cage and roller-type rolling elements. Recirculating elements (ball or roller bearings) between the rail and the bearing block enable precise linear motion. The coefficient of friction with roller-element-based systems is much less than with slide based linear motion guides … about 1/50th that of non-recirculating systems. Ball-type rolling element units are also subdivided into recirculating and non-recirculating types. The flat guide ways here typically use double row recirculating rolling elements. The guide way rail can be either round or square. If the raceway is not grooved, the rolling element is typically a linear ball bushing. If the raceway is grooved, the unit usually uses a ball spline. For square rails, the raceway is usually grooved. For ball-type rolling element units that are non-recirculating, the flat guide ways are grooved and use linear ball guides. The guide ways are round rail, without a grooved raceway, and use stroke bearings.

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QUICK NOTE ON FLUID-FLOATED BEARINGS Less common types of linear systems include hydrostatic or aerostatic linear-motion bearings. Because these systems have no mechanical contact, they are suitable for applications that need extremely accurate or quiet operation. Here’s how they work: A pressure regulator sends pressurized fluid between the rail and carriage. That lifts the carriage off the guideway by about 0.01 mm or so. Aerostatic versions use air as the fluid; hydrostatic linear bearings use specially formulated hydraulic oil. This type of guide is difficult to manufacture and expensive, but damps vibrations and allows for moves to 120 m/min and 10 g—useful for ultraprecision machines.

FAQ: DO LINEAR RAILS NEED LUBRICATION? Many linear-motion designs need periodic application of lubricant, but many are available pre-lubricated. In addition, a number of systems use self-lubricated moving elements, eliminating the need for lubrication during the useful life. Note that the rails, ways and guides of linear motion systems tend to pick up dirt and debris from their application environment. For this reason, use carriages and slides with some kind of wiper system to keep the systems clean. When selecting linear systems, consider space limitations, accuracy needs, stiffness, travel length, magnitude and direction of loads, moving speed and acceleration, duty cycle, and the application’s environment. Note that an excessively large load or an impact load can permanently deform the raceway surface whether the linear guideway is at rest or in motion. Most manufacturers offer tables on the basic dynamic load rating, which can identify proper load ratings for a setup. Another caveat about friction: Friction measurements are carried out on all profiled rail systems. The friction values are given in tables in the manufacturers’ respective product catalogs. The level of friction depends on load, preload and sealing, taking into account travel speed, lubricant and runner block temperature. The total friction of a runner block includes the associated rolling or sliding friction, lubricant friction, and the friction of any seals.

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AC MOTORS

An overview of

AC MOTORS AC

motors are driven by an alternating current (ac), but differ from dc (direct current) motors in that there is no mechanical commutation involved, and can be single or multi-phase. A typical ac motor has two basic parts; a stationary stator with coils energized with alternating current which produce a rotating magnetic field, and a rotor attached to an output shaft which produces a second rotating magnetic field. The magnetic field in the rotor can be generated in several different ways including with dc or ac electrical windings, permanent magnets or via reluctance. Because ac motors have no commutators or brushes, they require less maintenance than brushed dc motors. With dc motors, control is done by varying voltage and current, while on ac motors the voltage and frequency (along with the number of magnetic poles) are used to control the motor. A common way to classify ac motors is based on the magnetic principle that produces rotation. So there are two fundamental types of ac motors; induction motors and synchronous motors. In induction motors, the key idea is the rotating magnetic field. The rotor turns in response to the induction of a rotating magnetic field within the stator. The most common source of this in ac motors is the squirrel cage configuration. The setup is essentially two rings, one at each end of the motor, with bars of aluminum or copper connecting the two ends. Induction motors have properties that make them especially well suited to a number of industrial as well as home appliance applications. For starters, they are simple and rugged motors that are easy to maintain. They also run at constant speed across a wide range of load settings, from zero to full-load. One drawback used to be that it was difficult to control the speed of induction motors. However, the availability of sophisticated variable-frequency drives means that even induction motors, usually three-phase induction motors, can be easily speed controlled as well. The other type of ac motor is a synchronous motor. Synchronous motors are so named because they run synchronously with whatever the frequency of the source is. The motor speed is fixed and

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The TMF 5000 programmable indexing table from Motion Index Drives has exceptional inertial load capability and a cast housing with a large center through-hole for running utilities and mounting equipment. Its programmability allows the use of just four oversized cam followers riding a barrel cam. A gearmotor (in the form of an ac motor with encoder or a servomotor) moves the table with accuracy of 10 arc-sec or better.

doesn’t change with changes to the load or voltage. These motors are primarily used where the requirement is precise and constant speed. Most synchronous motors are used in heavy industrial applications, with horsepower ratings ranging from hundreds up to tens of thousands of hp. Synchronous motors can be used in motion control applications, but there are some down sides to using these motors. Because of the rotor size, the motor’s response in incrementing applications is typically not good. Also, because acceleration of inertial loads may not be as high as other motor types, these motors may operate at irregular speeds and produce undesirable noise. And generally, synchronous motors are larger and more costly than other motors with the same horsepower rating. Sometimes terms used to describe motors can be a little confusing. For instance, it’s not uncommon to hear brushless dc motors referred to as ac motors because of the similarity of the moving magnetic field. However, the important point to remember is that the designation “ac” and “dc” refer to the type of current driving the motor. Comparing ac and dc brushed and brushless motors, all three have power losses in the form of I-R losses. Because dc motors use permanent magnets, none of their energy needs to be used to generate the magnetic field as in ac motors. The energy used by ac motors to create the magnetic field decreases the efficiency of an ac motor in comparison to dc motors. As for brushless dc motors, for the same mechanical work output they will usually be smaller than a brushed dc motor, and always smaller than an ac induction motor. The brushed dc motor is smaller because its body has less heat to dissipate. Also, brushed and brushless dc systems provide flat torque over a wide speed range while ac motors typically lose torque as speed increases. 9 • 2016

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DC MOTORS;

Motion System

brushed and brushless

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DIRECT

current (dc) motors generate a magnetic field, either via electromagnetic windings or permanent magnets. An armature, which is often a coil of wires, is placed between the north and south poles of a magnet. When current flows through the armature, the field produced by the armature interacts with the magnetic field from the magnets, generating torque. The most common dc motor types are the basic brushed dc motor, brushless dc motors, and permanent magnet (PM) motors. Some engineers call brushed dc motors wound-field motors, because a wound and lacquered coil of copper wire makes the electromagnetic field. There are permanent magnet, shunt, series, and compound-wound brushed dc motors. In a brushed dc motor, the magnet acts as the stator. The armature is integrated onto the rotor and a commutator switches the current flow. Brushed dc motors use commutators and brushes to pass current to the rotating rotor’s copper-wire windings. Speed is controlled by changing rotor voltage (and current with it) or by changing the magnetic flux between rotor and stator through adjustments of the fieldwinding current. This makes them suitable for applications that need simple and costeffective torque and speed control. Brushed dc motors have the advantage of generally low initial cost and simple control of the motor speed. However, there are some drawbacks. At certain periods during the dc motor rotation, the commutator must reverse the current, causing arcing and friction wear on the brushes. Because of this spark hazard, brushed dc motors aren’t suitable for explosive settings. Brushed dc motors also require more maintenance in the form of replacement of springs and brushes that carry the electric

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Some brushless dc motors, such as this six-pole DB43 from Nanotec, take advantage of design features such as sintered magnets to increase power output, in this case 30% more than a similar length motor.

current, and replacement or cleaning of the commutator. Brush particles also mean that the motors can’t be used in cleanroom applications. The same goes for applications that need high precision, as friction from brush-commutator engagement make for long position-settling times. A brushless dc (BLDC) motor is essentially a dc motor without the mechanical commutation of the brushed dc motor. BLDC motors are powered by direct current and have electronic commutation systems instead of the mechanical brushes and commutators used in brushed dc motors, eliminating mechanical wear issues. In BLDC motors, the permanent magnet is housed in the rotor and the coils are placed in the stator. The coil windings produce a rotating magnetic field because they’re separated from each other electrically, which enables them to be turned on and off. The BLDC’s commutator does not bring the current to the rotor. Instead, the rotor’s permanent magnet field trails the rotating stator field, producing the rotor field. For successful commutation, it’s important to have precise rotor position data, which is often achieved via magnetic sensing with a Hall effect sensor, which also allows for tracking of speed and torque. BLDC motors have quite a few advantages over their brushed counterparts. Compared to brushed dc motors, BLDC motors are typically more efficient due mainly to the elimination of the friction from the brushes. They’re also more reliable and typically have longer life spans. Getting rid of the brushes also means a decrease in EMI (electromagnetic interference) noise and no sparking from the brushes making contact with the commutator.

BRUSHED OR BRUSHLESS? Brushless motors typically last much longer than brushed motors, which rely on a mechanical connection for operation. And brushless motioncontroltips.com | designworldonline.com

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MOTORS • DC

motors run much faster as well. If you’re using a brushless motor for reliability, you won’t want to add a gearhead to the mix, though. The mechanical nature of a gearhead automatically means that it’ll have a shorter life cycle. Using a gearhead with a brushless motor will only negate the longevity of the combined system, and therefore reduce the longevity of the machine it was designed into. On the other hand, there are times when using a gearhead on a brushless motor is advised. For example, if the environment is such that noise is a concern or that a higher torque is needed, a gearhead will do the job. Don’t use gearheads to increase the speed of brush motors. Using a gearhead with a brushed motor won’t change the life cycle to any great extent. Both are mechanical components that are subject to wear and tear. A real issue in selecting between a brushed and brushless motor is the expertise of the machine

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builder. Brushless motors either come with built in electronics or with external electronics to operate the motor. It takes some experience to provide the custom electronics many machine builders choose to provide. But for high sales volumes, the costs are easily regained. Brushed motors, on the other hand, don’t need electronics to run the motor, offering a plug-and-play option to the designer. This means that if the machines are expected to sell in low quantities, a brushed motor will save on the overall cost of the system. Overall, many machine builders are electing to use brushless motors whenever possible. Long life and high speeds make these motors applicable to a broader array of applications.

Improved brushed dc motor designs, such as these Athlonix series motors from Portescap, allow motors to achieve efficiencies of up to 90%. A special coreless design along with a self-supporting coil and magnetic circuit boosts energy efficiency, making the motors suitable for battery-powered applications such as medical pumps, robotic systems, and power tools.

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HANDBOOK

Motion System

INTEGRATED MOTOR basics INTEGRATED

motors, sometimes called smart motors, are motors that integrate one or more motion system components. The motor part of the integrated motor can be any number of types including brushless dc motors, servomotors or stepper motors. Typical motion systems have a number of common components including the motor, controller, a drive and power for drive and control electronics, cabling, and feedback devices such as encoders. As a result, what constitutes an integrated motor can vary. For instance, the most basic type may consist of a motor and encoder or a motor and a drive and controller along with communication ports. Integrated motors are said to offer greater reliability mainly because there are fewer parts

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to connect together. Also, fewer external connections means less cabling and wiring. Less cabling and wiring reduces costs, as does the fact that the components that one would usually purchase separately such as the motion controller and the drive are integrated into one physical unit. Integrated motors are also designed to be programmed easily and quickly, which can help reduce development times. Communication options range from simple serial communication links such as RS232 or RS485 to more advanced network topologies suited to complex motion control tasks such as CANopen, DeviceNet, or Ethernet protocols. For machine builders, designing with integrated motors has a number of benefits including helping to reduce machine size, cost motioncontroltips.com | designworldonline.com

9/9/16 4:39 PM

MOTORS • INTEGRATED

This IP65-rated Lexium MDrive from Schneider Electric Motion USA is an integrated motor for machine builders to use in applications subject to tough environmental conditions. They include sealed M12 industrial connectors for power, communications and I/O interface.

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and complexity. In some cases, integrated motors can also eliminate external controllers such as PLCs. Such integrated systems can significantly reduce the amount of space required for a machine by consolidating components, eliminating cabling, and possibly the need for entire enclosures. Integrated motors became more prevalent with the advent of de-centralized motion control architectures. An alternative to centralized motion control, a de-centralized architecture distributes motion control to a number of individual motion axes (in this case, to individual integrated motors), eliminating the need for a central controller. This means that individual motors can execute the control closer to the actual axis of motion or load, thereby taking the computational burden off of a central controller and distributing it to individual integrated motors.

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SELECTING A MOTOR When selecting an integrated motor for an application, the most important step is determining the characteristics of the load. This is why properly calculating the load torque is such an important part of selecting the right motor and designing it into the application. A good rule of thumb to keep in mind is to try and keep the actual operating conditions below the published limits of the motor in order to ensure reliable and long-life operation. Motor sizing parameters are usually based on the torque curve and moment of inertia of the load. These two factors can help determine the motor’s operating bandwidth. Sets of torque curves depict limits of both continuous and peak torque for the given motor over its full range speed. There are different types of torque curves, dealing with peak torque and continuous torque as well. Peak torque curves can be derived from dyno testing and represent the point at which peak current limit hardware settings of the drive prevent further torque in an effort to protect drive stage components. For any mechanical system, if the motor is operating in its optimum range, then the system will be performing at its best. Beyond the motor itself, depending on the specifics of the application it may be necessary to adjust mechanical components such as gear reducers, belts, lead screw pitch or pinion gears in order to get optimal performance from the system. 9 • 2016

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Motion System

HANDBOOK

One classic analogy is that linear motors are conceptually similar to a rotary motor that someone’s cut open and flattened out. Instead of a rotating shaft for torque, the load connects to a flat moving forcer for linear movement and force. Depending on size, Tecnotion UXA series linear motors (as the one here) output 120 to 846 N continuous force and 615 to 4,200 N peak force.

Summary of

LINEAR MOTORS LINEAR

motors are a relatively new addition to the arsenal of motion components for designers building machinery. They consist of two main components: a stationary platform that manufacturers call a platen or secondary (with electromagnetic windings) and a moving forcer or primary that sometimes includes permanent magnets. Linear motors are fast and precise for positioning, but can move slowly and steadily for material processing. Depending on the type, linear motor speeds range from a few inches to thousands of inches per second. They’re capable of unlimited strokes and (with an encoder) accuracy to ±1 μm per 100 mm. Myriad inspection, medical, and material-handling applications use linear motors to boost throughput. As is the case with their rotary counterparts, linear motors use common drives and motion controllers. Linear-motor accessories also include cable carriers, feedback encoders, limit switches, and stages for multi-axis movement. But unlike rotary motors (which need mechanical rotary-to-linear devices to get

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MOTORS • LINEAR

straight strokes) linear motors are direct drive. So, they avoid the gradual wear of traditional rack-andpinion sets. Linear motors also avoid the drawbacks of a rotary motor with a belt and pulley for translation. These downsides are limited thrust because of tensilestrength limits; lengthy settling times; belt stretching, backlash and mechanical windup; and typical speed limits of 15 ft/sec or so. In the same way, linear motors avoid lead and ballscrew efficiencies (of 50% and 90%, respectively) as well as whip and vibration. They don’t force engineers to sacrifice speed (with higher pitches) for lower resolution, either. Multi-axis stages that use linear motors on each axis are more compact than traditional setups, and so fit into smaller spaces. Their lower component count also boosts reliability. Here, the motors connect to regular drives, and (in servo operation) a motion controller closes the position loop.

HOW LINEAR MOTORS WORK Linear motors use electromagnetic flux for their operation. Flux in this context is the rate of electromagnetic energy flow through the airgap, and flux density is the magnetic flux through the airgap area. In linear motors, the latter is proportional to magnetic and electrical loading — the vector quantity of flux lines between platen and forcer. Engineers express this value in Tesla or Gauss. Typical air-gap flux densities range from fractions to a few Tesla. Linear stepper motors — An older design, this type of linear motor has a toothed forcer consisting of laminated steel cores wound with coils. The platen also has teeth cut into a steel bar. Linear stepper-motor platens mount end-to-end for unlimited travel. Thrust originates from reluctance force. Linear stepper motors deliver speeds to 70 in./sec, suitable for relatively quick-acting pick-and-place and inspection machines. Other applications include part-transfer stations. Some manufacturers sell twin linear steppers with a common forcer to form X-Y stages. These stages mount in any orientation and have high stiffness and flatness to a few μm for every hundred mm to output accurate movement. Hybrid linear motors — Most of these have low-cost ferromagnetic platens. (Those with solid steel platens move to 3 m/sec; those with laminated platens move faster.) Much like linear stepper motors, they vary magnetic saturation from the platen to shape opposition to magnetic flow; in other words, thrust originates from reluctance force. Feedback plus a PID loop with positioning control helps the motor output servo-grade performance. motioncontroltips.com | designworldonline.com

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Key to hybrid linear-motor performance is a yoke on the platen that makes paths through which flux travels and closes flux loops between platen teeth and forcer. The moving forcer includes laminated stacks with three-phase coils wound into them. Some have permanent magnets on the platen for higher force output. Those that don’t rely solely on phase current in phase coils and the forcer’s magnets. These need coil current to electromagnetically balance magnet loading for optimal motor performance. Hybrid-motor drawbacks are limited output and cogging from reluctance coupling between the forcer and platen. Two solutions here are phase-teeth offset or driving to get partial saturation of platen teeth and sections of forcer teeth. Here, the drive only magnetically saturates working teeth sections. Some hybrid-core motors also use external cooling to get more output during continuous operation.

Linear Rotary half page.pdf

Industrial Linear Motors linmot.com linmot-usa.com usasales@linmot.com 262-743-2555

9/2/2016

This Electric Thrust Tubular (ETT) linear motor (from Parker’s Electromechanical Automation Div.) houses a motor stator with magnets in the moving rod to form a direct-drive, rodstyle thrust actuator. Acceleration reaches 200 m/sec2 and maximum speed is 4 m/sec.

3:05:34 PM

Linear Rotary Motors Two independent motions with only one component.

CMY

Standard options: Stainless Steel, hollow shaft, and gearbox

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MOTORS • LINEAR

Linear ac induction motors — Linear ac induction motors that run to 2,000 in./ sec work for people movers, rollercoasters, and large aerospace applications. General-purpose types can move a few inches to 150 ft/sec or faster to drive gates, people movers, and other material-handling conveyors. Linear ac synchronous motors — These are either iron-core or ironless-core motors. Ironless-core (or air-core) linear motors have an epoxy forcer plate holding copper coils. It slides inside a U-shaped magnetic platen to output up to 3,000 N and speeds to 230 in./sec or better. Sometimes called brushless cog-free linear motors, these are lighter motors with potentially unlimited travel and quick acceleration. However, their main benefit (particularly in semiconductor applications) is smooth output. Their speed is helpful in flying-shear applications and long-stroke pick-and place machines. Other applications exist for waterjet and laser cutting and robotics tasks. Iron-core motors have slotted steel lamination stacks (insulated to reduce Eddy currents) for output of 7,000 N or more. The forcer coil assemblies include steel laminations and windings in a single or three-phase configuration. This allows for control directly from a line or through an inverter or vector drive. Some such linear ac motors use water-cooling to boost force output — enough to let the motors drive large baggage handling and amusement-ride axes. Iron-core motors are suitable for certain machine-tool applications as well. Cylindrical linear motors — These have steel rods and a moving coil or rods filled with stacked magnets. With the same footprint as a traditional linear actuator, these work in myriad machines that need quick and accurate strokes.

Linear motors include a coil and stationary platform. Linear-motor subtypes include brushless ironcore and ironless designs as the ones from Chieftek Precision USA shown here.

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MOTORS • LINEAR

This LinMot PR01 linear-rotary motor comes in myriad sizes for different force and torque outputs. The motor integrates a linear motor with an attached rotary torque motor. Controls independently command the two.

HOW TO PICK A LINEAR MOTOR Besides the different speed capabilities listed above, a main specification factor is how much force the application needs to move the load. Linear stepper motors output to 50 lbf. Ironlesscore motors output to 560 lbf, and iron-core brushless motors to 3,100 lbf. Linear ac induction motors output to 500 lbf. Other factors include: Motion profile — This largely relates to how quickly the application needs the motor to accelerate the load. Form factor — Pieces of conveyor machinery often use linear ac induction motors for their lack of platen magnets and long strokes. Precision medical devices and motioncontroltips.com | designworldonline.com

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semiconductor lines make copious use of brushless cog-free linear motors for their accuracy. Accuracy — No matter the version, linear-motor accuracy is a design benefit: An axis running off a rotary stepper through a 6 rev/in. ballscrew positions to 0.005 in. or so assuming zero coupling or ballscrew backlash. The same setup with a servomotor positions to 0.0001 in. A linear motor driving the same load positions to 0.000007 in. Long life — Engineers often pick linear motors for the way they reduce maintenance and cost of ownership. Linear motors reduce maintenance, as they have fewer contacting subcomponents than other setups. The zero-backlash operation of linear motors also eliminates designbreaking shock loads. DESIGN WORLD — MOTION

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Motion System

So-called hybrid servomotors (based on a hybrid step motor), like the SilverMax line from QuickSilver Controls, provide superior continuous torque at low speeds transitioning to nearly constant power curves up to 4,000 rpm. They’re well suited to direct drive of lead screws and belt drives, typically eliminating the need for gear heads.

SERVOMOTORS: an overview

SERVOMOTORS

provide precise control of torque, speed or position using closedloop feedback. They also have the ability to operate at zero speed while maintaining enough torque to maintain a load in a given position. Servomotors have several distinct advantages over other types of motors. For starters, they offer more precise control of motion. This means they can accommodate complex motion patterns and profiles more readily. Also, because the level of precision is high, the position error is greatly reduced. All servo systems have essentially three components; an electric motor, a feedback device, and some type of electronic control.

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The electric motor can be either ac or dc, rotary or linear. Under the dc heading, brushed dc servomotors are generally less expensive than brushless servos, but do require more maintenance due to the brushes needed for motor commutation. Brushless servomotors are more expensive than brushed dc motors. Generally, these are used in applications requiring higher torque. Brushless dc servomotors are highly reliable and virtually maintenance free. However, the drives for brushless dc servomotors are more complex because the commutation is done electronically rather than mechanically as in the brushed dc motor. Servomotors also require a form of feedback, often with the feedback device, such as an encoder, built right into the motor frame. The feedback signal is needed by the control circuitry to close the control loop. Lastly, the control circuitry typically involves a motion controller, which generates the motion profile for the motor, and a motor drive (or servo amplifier) which supplies power to the motor based on the commands from the motion controller.

SIZING A SERVO MOTOR Correctly sizing a servomotor involves knowing some key parameters including different torque values, inertia values, and speed, among others. Here’s a more detailed look:

9 • 2016

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Motion System

HANDBOOK

LOAD

where JL is the moment of inertia of the load and JM is the moment of inertia of the motor. (See sidebar on inertia.)

to be made to determine the required continuous torque, peak torque, and maximum motor speed. This means the peak torque measurements must be calculated, usually during acceleration or deceleration, along with the running/normal torque. A motor’s continuous torque is its ability to produce the rated torque and speed without overheating. Intermittent torque indicates how much torque a motor can produce in a short period of time based on current limits of the drive and motor. The intermittent (or peak) torque of a motor can be much higher than its rated torque, and servo systems are usually designed to operate within that peak torque range when accelerating or decelerating the load. The required amount of continuous torque must fall inside the continuous operating region of the system torque-speed curve. The required amount of peak torque must also fall within the servo system’s intermittent operating region of the system torque-speed curve.

SPEED

GEARING

Another important factor is the speed or velocity. This involves knowing how far and how fast the load must travel. Knowing the inertia ratio can help with this as well as knowing the motion profile of the system. Figuring out what the motion profile is and knowing the system inertia helps determine the required speed, acceleration and torque.

The servomotor size directly affects other servo system components, so rightsizing the motor is critical. If a servomotor is oversized, it will need a larger amplifier than that required for a smaller motor. This means higher hardware costs as well as increased energy requirements. Servomotors generally run at speeds in the 3,000 to 5,000 rpm range, and in many applications the motor is paired with some type of gearing to increase output torque. Gearing increases the available torque by the amount of the gear ratio. Gearing will also lower the inertia mismatch ratio by the square of the gear ratio, so a 10:1 gearbox will reduce the reflected load inertia by a factor of 100. In many instances, gearing allows smaller motors to be used successfully, more than offsetting the cost of the gearing system. In many applications, adding gearing can allow the use of not only a smaller motor, but also a smaller drive. Downsizing the motor and drive can sometimes pay for the increased cost of additional gearing, particularly when operational costs are considered.

Correctly sizing a servomotor begins with knowing the load, which is also referred to in terms of inertia (or the load’s resistance to change in speed.) Generally speaking, the important figure is the inertia ratio, which is the ratio of the load inertia to the motor inertia, or Inertia Ratio = JL / JM

TORQUE Once the load and speed are known, calculate the required torque values. This can be determined from the motor’s torque-speed curve. Calculations need

Direct-drive servomotors, such as the P Series from Parker’s Electromechanical Automation Division, eliminate compliance in motion dystems and are an ideal fit for applications requiring high precision and accuracy such as robotics, indexing tables, and inspection equipment. P Series servomotors feature accuracy of +/- 30 arc sec and repeatability of +/- 1.3 arc sec.

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HANDBOOK

MORE ABOUT SERVOMOTOR INERTIA Inertia is an object’s resistance to a change in speed. To determine the inertia of an object, its mass is multiplied by the square of its distance from the axis of rotation. In an electromechanical system, both the motor and load have inertia, and how similar (or different)

Motion System

their inertias are will affect the performance of the system. The ratio of the load inertia to the motor inertia is one of the most important aspects of servomotor sizing. Motor inertia is given by the manufacturer, while the load inertia is calculated by adding the inertia of all rotating parts, which typically includes the actuator or drive (belt, ball screw, rack and pinion), the external load, and the coupling.

Motor Inertia Load: JL = JD + JE + JC JL = inertia of load reflected to motor JD = inertia of actuator or drive (ball screw, belt, rack & pinion) JE = inertia of external (moved) load JC = inertia of coupling For the motor to effectively and efficiently control the load during acceleration and deceleration, the motor and load inertias should, theoretically, be equal. But a 1:1 inertia match is rarely practical or achievable. Many factors influence what inertia ratio is acceptable for a given application, but one of the most important is the compliance, or wind-up, in the system. Mechanical components are not perfectly rigid, and the more components—belts, couplings, and gearboxes—in the drive train, the more compliance the system will have. In general, the higher the compliance, the lower the inertia ratio should be in order for the motor to effectively control the load. While there’s no formula for determining the best inertia ratio, some motor sizing guidelines stipulate that the inertia ratio should be 10:1 or lower. Higher mismatches cause the motor to draw more current than necessary, which decreases efficiency and increases operating costs. A higher ratio also increases resonance and can cause the system to overshoot the desired velocity and position, negatively affecting performance. If the inertia ratio is too high, there are two ways to reduce it: add a gearbox to the system, or use a larger motor. Gearboxes are frequently used in belt-driven systems to optimize the motor speed and torque. But they can also significantly reduce the inertia ratio of the system, since the gear ratio has an inverse square effect on the inertia of the load.

Motor Inertia with Gearbox: JL = [(JD + JE + JC )/i2 ] + JG JG = inertia of gearbox i = gear ratio The second method for reducing the inertia ratio is to use a larger motor with higher inertia. However, this is rarely a beneficial solution in the long term, since a larger motor costs more, requires more torque to overcome its own inertia, and consumes more energy, which increases the system’s total cost of ownership. On the other hand, an inertia ratio that is unnecessarily low, or even a “perfect” 1:1 match, can indicate that the motor is oversized, which results in unnecessary cost and energy consumption. Rather than striving for a perfect inertia ratio, designers should take into account the system dynamics and positioning requirements and strive for an inertia match that achieves these requirements with a servomotor that is neither over- nor under-sized.

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HANDBOOK

Motion System

Basics of

STEPPER MOTORS STEPPER

motors are commonly used in positioning applications and can be accurately controlled down to fractions of a degree without the use of feedback devices such as encoders or resolvers. They are operated in open-loop mode as opposed to closed loop like many other motor types. Stepper motors are typically classified by the number of allowable steps they can be commanded to move. For instance, a 1.8 degree step motor is capable of 200 steps/ revolution (1.8 x 200 = 360 degrees, or one full revolution) in full-step mode. If operated in half-step mode, each step becomes 0.9 degrees and the motor can then turn 400 steps/revolution. Another mode called microstepping subdivides the degrees per step even further, allowing for extremely precise movements. Several different stepper motor technologies exist including permanent magnet (PM) motors, variable reluctance (VR), and hybrid types. The principle of operation for stepper motors is fairly straightforward. Traditional VR stepper motors have a large number of electromagnets arranged around a central gear-shaped piece of iron. When

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This Amacoil/Uhing Model RG rolling-ring linear drive any individual integrates a motion controller and a stepper motor electromagnet is controlled by a Siemens S7 PLC. Applications include energized, the geared those on winding and spooling, pick-and-place, and iron tooth closest to metrology equipment. Depending on the size of the RG drive nut in the system, the Precision Motion Drive that electromagnet System outputs an axial thrust of 7 to 800 lb. will align with it. This makes them slightly offset from the next electromagnet so when it is turned on and the other switched off, the gear moves slightly to realign. This continues with the energizing and de-energizing of individual electromagnets, thus creating the individual steps of motion. Hybrid steppers combine the best features of both the PM and VR type stepper motors. The rotor is multi-toothed like the variable reluctance motor and contains an axially magnetized concentric magnet around its shaft. The teeth on the rotor provide a path to help guide the magnetic flux to preferred locations in the airgap. This further increases the detent, holding and dynamic torque characteristics of the motor when compared with both the variable reluctance and permanent magnet motor. Hybrid stepper motors are usually more expensive than PM stepper motors but can provide better performance with respect to step resolution, torque and speed. Control techniques such as half-stepping and microstepping let designers get even finer movements of rotation, which make for more exact output than that from VR stepper motors (which can’t usually be microstepped). Hybrid stepper motors also have higher torque-to-size ratios and higher output speeds than other stepper-

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Motion System

HANDBOOK

motor types, and are also quieter than VR stepper motors. When the current changes, the rotor can turn a small amount—an improvement over basic PM motors and VR motors. While stepper motors are capable of producing high torque at low speeds, they generally are well suited for lower power applications, not for applications requiring lots of torque to move heavier loads. A few other drawbacks include the possibility that not properly controlling the motor can produce undesired resonance in the system. Also, stepper motors are generally not easy to operate at extremely high speeds, and as the motor speed increases, torque decreases. For two-phase stepper motors, there are two basic kinds of winding structures; unipolor and bipolar. A

unipolar arrangement uses 6 wires but current can only flow in one direction. These types of motors also require a unipolar driver. A bipolar winding uses 4 wires and current can flow in 2 directions and it requires a bipolar drive. Bipolar motors are generally more efficient and can provide more torque than unipolar models, although they can heat up faster than unipolar motors. A stepper motor’s low-speed torque varies directly with current. How quickly the torque falls off at higher speeds depends on a number of factors such as the winding inductance and drive circuitry including the drive voltage. Steppers are generally sized according to torque curves, which are typically specified by the manufacturer.

WHAT IS PULLOUT TORQUE AND WHY IS IT A CRITICAL STEPPER MOTOR VALUE?

Pullout (mNm) Mechanical power output

0.3

0.2

0.1

2 3 Speed (1,000 rpm) 8

4 16

Speed (100 Steps/sec) This plot shows the pullout torque for a common stepper motor. The green line contains the area of slew rate or pullout curve. The dark blue line plots the pull-in curve or start/stop region, which shows the maximum frequency at which a loaded stepper can stop and start without losing steps. Lastly, the red line shows mechanical power output. Keep in mind that the curves change if there is inertial mismatch. (Graph courtesy of MICROMO)

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0.0

Power (W)

Torque (mNm)

Torque start/stop (mNm)

Two of the most critical stepper motor parameters are pullout torque and pull-in torque. (See sidebar) Sufficient documentation of a stepper motor includes a torque curve that shows pull-in and pullout curves, as well as several other factors. To sum up, before basing design specifications on a stepper motor torque curve alone, look for data on the following important criteria to ensure the best design fit; power input (which impacts current draw and the possibility of overheating), the drive type, as well as the relation between step angle and torque.

Stepper motor pullout torque is the highest torque a stepper motor can output at a given speed without losing steps. Manufacturers find a stepper motor’s pullout torque by accelerating the motor up to the target speed and then increasing the torque load until the motor starts missing steps or stalling. Performing this test over a range of speeds and torques lets the manufacturer plot the data in a complete torque or pullout curve, which designers use when evaluating different motor options. To put it another way, the pullout-torque plot (also called slew rate) for a stepper motor shows the maximum torque at various speeds that a stepper motor can generate. If the motor runs outside of this curve, it will stall. The drive must decelerate or accelerate out and into the stepper motor’s pullout curve. A related value is stepper motor pull-in curve — the maximum frequency at which a loaded stepper can start and stop without losing steps.) The torque-speed curve changes with inertial mismatch, so designers should aim for a 25% to 50% safety margin when sizing stepper motors. If this is impossible for the application at hand—not unusual for precision applications—other means of compensation may be in order.

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What’s Inside Matters The PITTMAN Difference ®

On the outside, this looks like an ordinary DC motor. In fact, this particular motor is not a standard off-the-shelf part, but designed exactly to a customer’s specific technical requirements. PITTMAN has an experienced team of engineers focused on providing the perfect motor assembly to our customers demanding motion applications. • • • • •

Special brush formulation for use in a very low humidity environment Bearing system to handle higher than normal axial loads Very tight balancing spec to minimize audible noise and vibration at high speeds Unique magnet charge pattern to minimize cogging at low speeds Specially chosen surface-mount components inside the motor to meet an aggressive EMC requirement • Numerous integrated spur and planetary gearboxes, encoders, brakes and drives

When evaluating DC motor choices, it’s what’s inside that matters.

www.Pittman–Motors.com 343 Godshall Drive, Harleysville, PA 19438 USA: +1 267 933 2105 Europe: +33 2 40 92 87 51 Asia: +86 21 5763 1258

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HANDBOOK

Motion System

The Lexium Motion Module (LMM) from Schneider Electric Motion USA is an ultra-compact programmable motion controller that now comes in a CANopen version. The CANopen interface supports CiA DS301: CANopen Application Layer/ Communication Profile and DSP402: Device Profile for Drives/Motion Control. A one-axis development board comes with isolated I/O, CAN communications transceivers, and locking pluggable connectors.

How to

NETWORK MOTION DESIGNS? MOST

multi-axis motion control uses event-based synchronization so only some network protocols are suitable. The Industrial Internet of Things won’t change motion systems much, because most motion systems already use sensor data to measure performance, and nearly all data transmits on some form of Ethernet — the basic backbone of the Internet, including wireless versions. The basic topology of a motion systems network includes a real-time version of Ethernet connected to the motion components (motors, drives, sensors, controllers.) These components send data to a higher level network, usually an IT version of Ethernet, which may then be sent through the Internet to dashboards, various storage media, or analytics software.

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Assuring real-time control is key. Event-based synchronization is scheduled and absolute hard delivery of time-critical cyclic data. Data must be delivered usually in less than 1 μsec. Slower delivery rates tend to result in jitter, which increases the chances of uncontrolled motion in a machine tool or other motion system. So it’s important to define the time delivery needs for the given application. Synchronized multi-axis motion has different timing needs than a divert actuator on a conveyor.

WHAT ARE COMMON NETWORKS FOR MOTION CONTROL? Ethernet for Control Automation Technology (EtherCAT) was developed by Beckhoff. It’s fast and deterministic, and processes data using dedicated hardware and software. It uses a full duplex, master-slave configuration, and accommodates any topology. It can process 1,000 I/O points in 30 μsec and communicate with 100 servo axes in 100 μs. Axes receive set values and control data and report actual position and status. A distributed clock technique that’s a simple version of IEEE 1588 synchronizes the axes with less than 1 μsec of jitter.

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Motion System

Opto 22 sells Node-RED nodes for industrial programmable automation controllers (PACs) to quicken IIoT application development. These Node-RED nodes for PACs simplify prototyping and connection of physical assets to cloud applications — an increasingly important mode of connectivity for motion designs.

This protocol can deliver fast throughput because messages are processed in hardware before they’re forwarded to the next slave. Slaves read data relevant to them as the data frame passes and they insert new data into that same data stream on the fly. This procedure does not depend on the run-time of the protocol stack, so processing delays are typically just a few nanoseconds. EtherNet/IP (EIP) is another option. Standard Ethernet cannot guarantee data delivery of less than 1 μsec because of the data layer’s use of Carrier Sense Multiple Access/Collision Detection (CSMA/CD) techniques to control packet transmission. To overcome this issue, ODVA developed EtherNet/IP, and it did so without changing any of the four lower layers of Ethernet. EtherNet/IP is an industrial application layer protocol operating over the Ethernet medium and used for communication between industrial control systems and their components, such as programmable automation controllers, programmable logic controllers or I/O systems. The IP stands for Industrial Protocol — Rockwell Automation’s adoption of Common Industrial Protocol (CIPTM) standards as EtherNet/IP came into being. EtherNet/IP with CIP Motion as the application layer removes the requirement for strict determinism from the network infrastructure and entrusts the end devices with the timing information necessary to handle the real-time control needs of the application. Thus, this network can deliver the high performance, deterministic control required for closed-loop drive operation using standard, unmodified Ethernet (complying with Ethernet standards, including IEEE 802.3 and TCP/IP). CIP is also used by DeviceNet and ControlNet, so these networks are interoperable. CIP Motion accomplishes real time data transmission through the application profiles that define the 154

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technology. Those profiles allow position, speed and torque loops to be set within a drive. This protocol makes use of CIP Sync technology, the IEEE-1588 compliant Precision Clock Synchronization, which is also mapped into the CIP object model, to coordinate precise, synchronized motion control. CIP Sync consists of a Time Sync object and associated services for synchronizing nodes to within ± 100 ns of one another. EtherNet/IP with CIP Motion allows 100 axes to be coordinated with a 1 ms network update to all axes. Sercos is a digital bus that interconnects motion controllers, drives, I/O, sensors and actuators for numerically controlled machines and systems. It’s designed for high-speed serial communication of standard closed-loop real-time data over a noise-immune, fiber optic ring (Sercos I & II) or Industrial Ethernet cable (Sercos III). In a Sercos interface system, all servo loops are normally closed in the drive to reduce the computational load on the motion controller and synchronize more motion axes than it otherwise could. In addition, closing all the servo loops in the drive reduces the effect of the transport delay between the motion control and drive. Sercos III is the open, IEC-standard thirdgeneration version that transmits data over Industrial Ethernet cabling and protocol for realtime control. It combines the best of both Ethernet and previous Sercos designs for deterministic bi-directional real time motion and I/O control. It delivers rich I/O communication capabilities while enabling all conventional protocols to be transmitted over the same Ethernet network efficiently in parallel with Sercos real-time communication. motioncontroltips.com | designworldonline.com

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Is Your Industrial Ethernet Network Ready for All Your IIoT Requirements?

Consider CC-Link IE Field as your open network solution.

GIGABIT INDUSTRIAL ETHERNET Enabling seamless data communication from the plant-level enterprise network to the production floor network

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CC-Link Partner Association – Americas Tel: (847) 478-2423 or (847) 478-2647 email: info@CCLinkAmerica.org I www.CCLinkAmerica.org

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HANDBOOK

Sercos III achieves cycle times as low as 31.25 μs. It supports up to 511 slave devices in one network, with multiple networks possible in a system.

HOW TO SELECT THE RIGHT NETWORK?

Motion System

With the vast range of motion control applications, no one-size-fitsall approach to selecting a motion control networks exists. However, a few key factors help narrow the choices. 1. Reaction time and precision depend on how the network executes scans and how fast the system can react. At the very least, networks should close motion loops back at the controller to each drive. This function is paramount if the application has any coordinated motion, as each axis must receive its own unique commands. Some network protocol promoters will insist that slave-to-slave communication is a substitute for closed-loop control, but this is only true in the simplest of applications such as conveyor drive applications where there is only one master command and the remainder of the drives simply follow that same command or some constant offset from it. Any application where there must be independent control should have a robust, relatively fast scan rate to each slave. Also, use of a single network for motion, I/O and data

necessitates a design that can react system-wide to an input in a timely fashion. This is the reaction time — directly related to network scan rate. 2. Determinism is unrelated to network speed and raw scan rate. It’s a feature of predictable data transmission; regardless of how fast or slow, you will know exactly when data come through. Many industrial Ethernet fieldbus systems available today actually have a poor scan rate, but the vendors behind each will promote their system as “deterministic,” which may be true. But determinism will not guarantee quick reactions to external events. 3. Ensure the chosen controller has an embedded PC hardware platform specified or requirements for a particular Real Time OS (RTOS). Also verify whether the system is closed with connectivity options that can only be supplemented through add-on cards from the PLC vendor. These difficulties may restrict viable network protocols. 4. Consider third-party device support. Consider whether the desired motion network has a number of third-party master controllers and slave devices available.

The degree to which a given offering is widespread shows how well the technology is accepted outside of the main promoting company that developed the protocol. Widely used options usually allow work with a wider library of devices and substitutions from which to choose. 5. Diagnostics are key. Modern industrial Ethernet protocols provide a wealth of builtin diagnostics to help track network status and where maintenance may be required. Motion networks have long offered the ability to pinpoint and diagnose issues down to the exact location and identify the cause, which increases reliability, decreases downtime, and facilitates smoother commissioning, resulting in easier initial setup. 6. System cost is also important. Ethernet-based motion networks have the advantage of using standard Ethernet media and hardware. With the right industrial setup, they eliminate expensive switches, hubs, and routers.

MICROMO now offers MC3/MCS motion controllers for use with FAULHABER motors. The V3.0 controllers are intelligent drives for OEM and automation applications with a 100-msec sample time for velocity, position and current feedback. They use industry-standard network and control interfaces — including Ethernet fieldbus technology, USB, network communication protocols, CANopen and RS-232.

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RACK-AND-PINION SETS

This roller-pinion system from Nexen Group acts as cam and follower. Its cycloidal contact curves mean there’s no slipping. Rack-tooth geometry minimizes backlash by loading pairs of pinion rollers in opposition.

Where do

RACK-AND-PINION SETS EXCEL? RACK-AND-PINION

sets are precision mechanical devices that in some cases deliver performance rivaling that of electromechanical alternatives for linear motion. First modernized 150 years ago to drive railway trains up steep passages, rack-and-pinion sets today are useful in everything from small consumer devices that move a few ounces to large industrial machinery that moves tons of load. That includes off-highway machinery, foodprocessing, packaging lines and other applications that involve reciprocating motion. In short, rack and pinions work off a parallel-axis gearset that converts rotary motion to linear motion. It does this through a motor-driven pinion (essentially a specialty spur gear or engineered roller) that engages the rack (which is essentially a gear of infinite diameter). In rare cases, an input moves the rack to get pinion rotation. Usually, rack-and-pinion sets get paired with servomotors or (less commonly) with step motors. One rack-and-pinion variation is based on a roller pinion. These ultra-quiet rack-and-pinion sets have a pinion of bearing-supported rollers instead of a spur gear. Rollers ride the rack-tooth surfaces for 99% and repeatability to about 2.5 μm from one direction (or better than 5.8 μm from both). Manufacturers also make the rollers with meshing geometry to trace paths tangent to tooth faces. So, the rollers glide into engagement with the rack teeth, which eliminates the wear and inaccuracy from sliding friction and tooth slap of some rack-and-pinion sets.

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This gripper setup from Festo uses a rack-and-pinion linkage.

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Motion System

This dynamic rackand-pinion system from Wittenstein can drive linear motion to unlimited travel lengths. Some preassembled versions run true to 10 µm; those with actuators and servogears exhibit less backlash than standard setups.

No matter the version, the benefits of rackand-pinion sets are that they can operate without enclosures or protective covers; they are efficient to 98% or better; and many exhibit backlash of 1 arcmin or less. Another strength is that they’re often less expensive than comparable linear motors when stroke lengths are long … so that a rack-and-pinion set may cost half of what a linear motor costs … especially for many-meter strokes. Rack-and-pinion sets sometimes perform better than ballscrew actuators because they’re not affected by adjacent bearings, couplings, or bores; they’re also immune to stiffness degradation, even over long lengths. What’s more, as with any gear-based power transmission, rack-and-pinion sets come in several gear versions to satisfy various application requirements. For example, some helical-toothed racks sport helix angles engineered for quiet operation (with a high toothcontact ratio) even under high loads at high speeds. Rack-and-pinion installation is straightforward. The racks mount on flat surfaces, and many versions sport forgiving designs and mounting features to maintain performance without perfect assembly. Even so, misaligned or improper mounting can damage sets

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and the attached gearmotor’s bearings. One common mistake is to put the motor-driven pinion too far from the rack. Here, design engineers should ensure that the pinion-to-rack distance is set to the manufacturer’s recommendation and that the rack and motor-driven pinion is perpendicular to the rack within tolerances.

HOW DO ENGINEERS AVOID BACKLASH WITH RACKAND-PINION SETS? Manufacturers often preload rack-and-pinion sets to boost stiffness and eliminate backlash. There are a few ways to do this. One option is to run twin pinions concurrently, with a slave pinion that gently opposes the drive force. This setup usually reduces efficiency, but boosts machine dynamics and stiffness. A more sophisticated variation of this approach is to use the motion controller to apply preload electronically. Such controls maximize preload but reduce opposing slavepinion force when the drive pinion accelerates. During constant-speed strokes, the slave pinion mirrors the action of master pinion, and the two drive in tandem. When the axis decelerates, the slave pinion engages the opposite tooth flank, increases force opposing drive force, and helps slow the load.

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HIGH SPEEDS. 11 m/s (36 ft./sec.)

INCREDIBLE ACCURACY. ± 30 µm (± 0.00118 in.)

ZERO BACKLASH. UNLIMITED LENGTH.

[

That’s the way we roll.

]

Introducing the patented Precision Roller Pinion System (RPS)

Make your machines run faster and more accurately with less maintenance. The new, patented RPS engages two teeth simultaneously to achieve unmatched accuracy with zero backlash—in any desired length! This amazing system is also extremely quiet, 99% efficient and can run without lubrication. Overcome the speed, accuracy, load and noise limitations of rack and pinion, ball screw and belt drive technologies with a lower maintenance, longer lasting solution.

Learn more at www.nexengroup.com Call 800.843.7445 NX-118 RPS Ad 43.0910.07_DesignWorld.indd 1

7/30/10 11:10 AM

OVERCOMING COMMON PROBLEMS Found in Traditional Drive Systems

INDUSTRY PROBLEMS

Ball Screws

Traditional Rack/Gear & Pinion Systems

Low Accuracy Backlash/Vibrations

High Cost

Dirty Operation

High Maintenance

Low Load Capacity 4

Low Speed

High Positional Accuracy

Near-Zero Backlash 4

Little to No Maintenance

High Load Capacity Quiet: Pinion Rollers Glide Smoothly Along Teeth

High Speeds (Up to 11 m/sec) 4

Limited System Length/Size

Economical, Efficient Components No Dust Emissions

Magnetic Field High Wear/Low Life

NEXEN ROLLER PINION SYSTEMS

Chain Drives

Noisy

Linear Motors Direct Rotary Stages Direct Drive Motors

Belt Drives

No Magnetic Field

Long Life (Up to 36 million meters)

Custom Rack Sizes & Modular Components

Discover the Nexen Advantage by going to www.nexengroup.com

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RETAINING RINGS

The basics of

RETAINING RINGS RETAINING

rings are fasteners that hold components together on a shaft or in a housing when engaging a groove. Three main types of retaining rings include tapered section, constant section and spiral. Tapered-section rings typically have decreasing thickness from the center of the ring out to the ends. They mount either axially or radially. The taper is there to ensure full contact with the groove when installed. Constant section retaining rings have a constant width around the circumference of the ring. When installed, these rings do not maintain uniform contact with the entire component. They take on an elliptical shape and make contact with the groove at three points. Spiral retaining rings are installed into the housing or onto the shaft, making full contact with the groove and component. Their grooves are relatively shallow, so their load bearing capability is reduced. Spiral rings are often selected when full contact with the retained component or a lower axial profile is required. Spiral rings have no protruding ears to interfere with mating components in an assembly. The ring has a uniform cross-section and no gap or lugs for a functional and aesthetically pleasing ring. Unlike traditional fasteners, retaining rings eliminate machining and threading, reducing costs and weight.

Bowed preloading ring

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•

Spiral retaining rings do not require special tools for removal and are supplied standard with removal notches for easy extraction from a groove. When selecting a retaining ring for an application, several factors dictate which is most suitable. The first question to ask: What kind of assembly does the application require? Is it a housing assembly or shaft assembly? Next, determine the main critical dimensions. These include the housing or shaft diameter, groove diameter and the groove width. Also, what is the rotational speed (usually in rpm) of the assembly? Next, determine the maximum thrust applied to the ring. Generally speaking, designers define this thrust as either a light, medium or heavy-duty load. It’s important that the design engineer define the maximum thrust because its value also helps determine if groove deformation or ring shear could be a problem. Basically, groove deformation occurs because the groove material is soft, which in turn limits maximum capacity. Ring shear, on the other hand, occurs when the groove material is hardened but the load exceeds the ring’s maximum capacity. Other factors, such as the temperature as well as the presence of any corrosive media, also dictate the most suitable choice for ring material.

Radial retaining ring

•

Internally mounted axial ring

9 • 2016

WHAT IS EDGE MARGIN? This is the distance from the groove (for the retaining ring) to the end of a shaft or housing. Edge margin depends partially on the groove’s depth. Rule of thumb: When edge margin is about triple (or more) the groove depth, the groove can withstand the same level of thrust load as the mating ring.

Bowed retaining rings eliminate play in assemblies. Radial rings widen during installation for an interference fit once in place. They only wrap a portion of the groove circumference so withstand lower forces than alternatives but are easy to install. Axial rings slide into internally machined grooves.

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Review of

Motion System

SHOCK ABSORPTION AND VIBRATION DAMPING technologies MOTION

is present in almost all industrial automation systems. Stopping or changing the direction of that motion releases kinetic energy, which can cause shock and vibration to occur. Any sudden shock in a system can cause immediate damage to the overall machine and the components it may be manufacturing or processing. And consistent vibration inputs can cause damaging fatigue over time. This is why it’s necessary to decelerate a system smoothly through the use of shock and vibration attenuation components. Based on the type of inputs present in the application, vibration and shock attenuation components

can be comprised of shock absorbers, linear dampers, wire rope or spring isolators, elastomeric isolators, air springs, or structural damping treatments. These devices help manufacturers reduce equipment downtime and costly cycle time limitations. These products can be used in a broad range of applications, from the rate control mechanisms slow the motion of the overhead luggage bin or seat recline on commercial aircraft, to the isolators that keep GPS systems from losing signal or becoming damaged on farm and construction equipment as they harvest crops or pave roadways. Most shock absorbers achieve their damping characteristics through the use of hydraulic fluids. The fluid is pushed by a piston and rod through small orifice holes to create damping, and this action compresses some type of gas. This in turn creates a spring force to return the rod back to its starting position when the load is removed. Shock absorbers and dampers are generally made of high-strength steel to handle the pressures from the internal hydraulic forces. Elastomeric seals prevent the fluid from leaking out of the cylinder, and special plating and coatings keep the units protected from harsh operating environments. Recent and ongoing developments in sealing technologies and in the internal designs of shock absorbers and dampers have allowed for

Industrial shock absorbers, such as the Magnum series from ACE Controls, are a standard in medium-size damping. This line offers the lowest braking force and shortest braking time. Six models in this family offer key features such as selfcompensation, low- and high-temperature ratings, stainless steel, adjustable designs and membrane accumulators with piston tube technology.

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Motion System

HOW ARE SHOCK ABSORBERS AND LINEAR DAMPERS DIFFERENT? Industrial shock absorbers and linear dampers provide smooth, linear deceleration of a given load. Hydraulic shock absorbers and linear dampers use a medium such as transmission fluid or silicone oil to control the deceleration of the load. Pneumatic linear dampers

Wire Rope Isolators from ITT Endine feature stainless steel cable and aluminum retaining bars, which provide excellent vibration isolation. They are corrosion resistant, which makes them environmentally stable while providing high-performance in a variety of applications. The isolators are completely unaffected by oil, chemicals, abrasives, ozone, and temperature extremes. The compact wire rope isolator is smaller than a traditional wire rope and can absorb shock and vibration in small spaces. Single point mounting offers flexibility for integration into existing products.

use air or nitrogen to achieve the same goal. A linear damper, or velocity controller, is used when a load is in constant contact with the damper and the operator wants a smooth deceleration in either the compression or tension direction. Common applications include garage and storm doors and tool feed units. Here, the load is in contact with the damper when the deceleration starts, so there is no impact of the damper by the load. On the other hand, an industrial shock absorber is designed to “capture and control” the load as it comes into contact with the shock. It is designed so that as the load makes contact, the shock accepts the load and gradually decelerates the load through its stroke. If properly sized, the shock absorber will “catch” the load and over the stroke of the shock, gradually “control” the load until it reaches the end of the shock’s stroke. During this stroke, the velocity of the mass is gradually decreased until it finally reaches a full and complete stop. The mass should not bounce at either the beginning or end of stroke. If a bounce occurs, then the shock absorber selected is either the wrong one or is adjusted incorrectly. The goal of the shock absorber is to maintain a constant reaction force throughout the stroke.

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longer service life and more compact designs. Ongoing research in the field of noise attenuation (high frequency, low amplitude vibration) has led to an increased effectiveness in noise reduction technologies. A unique application for these types of hydraulic damping devices has come with the increased awareness for seismic and environmental protection of our infrastructure (buildings and bridges, for example). By adding damping to these critical structures, energy is absorbed by the hydraulic devices instead of damaging the structure. Vibration isolation products rely generally on mechanical designs to achieve their isolation characteristics. A spring function provides support for the mounted equipment, while decoupling it from the vibration source. Friction and elastomeric material properties give the isolators their damping characteristics. Isolators can be made from a variety of materials. Wire rope and spring isolators can be made from carbon steel, stainless steel or aluminum. Elastomeric isolators generally have metallic components that function as mounting brackets, separated by an elastomeric material that provides the stiffness and damping desired. Common elastomeric compounds include natural rubber, neoprene and silicone; however, a vast selection of compounds and compound blends can be used to achieve different characteristics specific to the application. Air springs are comprised of metallic end fittings coupled by a composite elastomeric-based bladder that contains the compressed motioncontroltips.com | designworldonline.com

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SHOCK ABSORPTION Hydraulic dampers provide smooth deceleration of a load. This VC25 hydraulic damper from ACE Controls is easy to assemble. As the hydraulic oil is forced out through the throttle opening, a constant feed rate is achieved on the stroke, which also avoids the stick-slip effect.

More than just shock absorbers!

Motion Control Custom control of hand forces

air used to provide isolation. These single-acting designs are comprised of a pressurized bladder and two end plates. As air is directed into the air bladders, they are expanded linearly. All of these reusable designs are self-contained, offering a number of advantages over any other technology that may require outside componentry. For example, hydraulic systems may require plumbing while electrical systems may require wiring and power. Energy or power dissipation is key when selecting a damper or shock-absorbing device. The size and characteristics of the device are based on these inputs, so it is generally the first consideration to make. Dynamic spring rate and damping are the two biggest considerations when selecting an isolator. These characteristics will define the natural frequency (sometimes referred to as resonant frequency) of the isolation system and are important in achieving the desired performance. DESIGN WORLD â&#x20AC;&#x201D; MOTION

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Safety Products Protection for all machine designs under any condition

Vibration Control Isolate unwanted vibrations

Automation Control Optimum tuning for any design

www.acecontrols.com

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HANDBOOK

Aerotech’s PRO series industrial linear motor and ball-screw positioning stages come in multiple versions. Noncontact linear encoders enable minimum incremental motion to 5 nm and sub-mm repeatability. Optional HALAR factory calibration improves positioning accuracy to ±0.75 μm. Travels is 50 to 1,500 mm for standard models to 2 m/sec.

POSITIONING STAGES and tables

POSITIONING

stages as well as linear and rotary tables are integrated systems consisting of motors and mechanical power-transmission devices or linear or arc-shaped motors and actuators — complete with encoders, sensors and controllers. Consider the most common iteration: Traditional linear stages combine axes in X-Y-Z actuator combinations. Where serial kinematic designs are too bulky, integrated setups (in Cartesian or hexapod and Stewart platforms) are increasingly common. These output more accurate motion with no mechanical error accumulation.

WHAT ARE SOME NEW STAGE OPTIONS?

Shown here are piezosystems from PI (Physik Instrumente) for fast integration into OEM stages. The advanced and affordable nanopositioning controllers are for production automation, metrology, scientific research, and lab automation.

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Better mechanical components and feedback and control options are enabling stages capable of motion that’s more accurate than ever. So, positioning stages today can execute tasks with tighter synchronization than in the past — useful for complicated axis commands. One new option that leverages the speed of today’s motion controllers is positioning stages that fit a finer piezo-based axis to a courser and more traditional motion axis based on a rotary-to-linear mechanical devices and electric motor. Such tandem axes are useful

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Micromachining Shouldn’t be a Giant Task Linear Stages

Integrated Servo/ Scanner Systems

• Models with travels from 50 mm to 1.5 m

• Wide range of focal lengths and apertures

• Speeds up to 2 m/s • Side-seal design with hard-cover

• Industry best accuracy and thermal stability

• Low cost; high performance

• Laser firing based on real-time scanner/servo position

• Ball-screw or linearmotor-driven models

PRO and PRO-LM Series Nmark AGV-HP

Cylindrical Laser Machining Systems • Integrated linear/rotary motion platform • Advanced control architecture • Single- or dual-spindle configurations

Nmark AGV-HPO

Nmark GCL

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E PERFORMANCE

S MATTERS

for fast execution of tasks that need super-fine movements once workpieces (such as medical devices or semiconductor chips) are in place. Another example of leading stage technology is air bearings. These are useful on stages that must deliver high reliability and accuracy. Air bearings support a load with a thin film of pressurized air between the fixed and moving elements. Sometimes called aerostatic bearings, the source of pressure the air film. Unlike mechanical bearings, the surfaces of an air bearing make no physical contact, so don’t need lubrication. Surfaces don’t wear, so the systems don’t generate particulates. That makes them suitable for cleanroom applications. In fact, with a clean and filtered air supply, these linear bearings operate for years without fail.

Stages and tables work as industrial robots in fiber optics and photonics, machine tools, semiconductor equipment, medical component laser machining, vision systems, and micromachining. They are made with increasingly diverse actuators such as this — an Infinity Series arc-shaped motor segment from Applimotion. Here, modular construction allows for unlimited diameters and large through-holes not possible with conventional assemblies.

At Primatics, when we tell you that our precision

motion products will perform to specification, you can be certain they will do just that. And, we have the data to back it up. We build high performance motion solutions that integrate easily and function seamlessly with complex automated systems. Our clients experience a high correlation between the test data we provide and the performance they are measuring in the field.

When performance matters, Primatics delivers! The PXL33B is small form factor linear stage, optimized for higher accuracy, repeatability, and nanometer level minimum incremental motion.

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OP LA

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POSITIONING STAGES

IntelLiDrives sells rotary servo tables fitted with absolute encoders. Its direct drive has a low profile of 42 mm and a large center aperture of 145 mm. Resolution reaches 0.25 arc-sec. The incorporated absolute encoder has SSI, BISS-C, and FANUS connectivity. The low rotor inertia significantly improves the start-and-stop behavior as well as velocity control â&#x20AC;&#x201D; especially compared to conventional stages.

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Linear Stages

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XY Stages

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INSPECTION/CALIBRATION

Griffin Motion is your source for micron/submicron accuracy in modular and application-specific motion systems for linear, XY, rotary and vertical lift stages; as well as multi-axis, custom and semi-custom solutions for your most demanding precision motion applications.

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FAQ: HOW TO SELECT TABLES FOR ROTARY INDEXING?

Motion System

HANDBOOK

Stages output linear, rotary, or even lift-type motion in the case of Z-axis positioning stages. Output is in one or more coordinated directions. The drive mechanisms for positioning stages and tables vary with the design’s budget and target accuracy. Some stages are directdrive using linear servomotors or even dual-axis linear motors that float the forcer on a base. Other stages and tables combine motors and gearing with couplings linear or rotary actuators based on belts and pulleys and ballscrews or leadscrews. Tables for rotary indexing are a special design for repetitive moves around a platform. Assembly, machining, and bottling machines use indexers. Usually, they take one piece around to work areas or move arrays of relatively small parts around stations for sequential machining or assembly tasks. Common setups use electric motors for either cam drives or servo tables. Mechanical cam indexers are relatively low cost and only index to set angles — but are capable of precision moves. Other options are programmable servo tables for flexible motion output that’s not always at the same station positions — or even direct-drive arrangements.

Griffin Motion offers this high-speed LM3 Series 300-mm-travel platform for high duty cycles and longlife inspection, scanning, positioning, and marking applications. Accuracy is to 15 µm; repeatability is to 1 µm; flatness is to 5 µm; and straightness is to 5 µm at up to 900 mm/sec.

Nanometer Precision Automation ACTUATORS & MOTION SYSTEMS

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Microscopy

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Fiber Alignment

Rotary

Beam Steering

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ROBUST, RELIABLE, ROTARY REVOLUTION!

Ring-in fast dynamics, flexible, high precision, and low operating costs… They’re all on the table! More Information? Call Us! 888 WEISSNA

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Direct Drive Indexers – TO / TW / ST-SW TO Series: Fast, versatile, reusable: The TO torque series from WEISS marked a new passage in the history of the rotary table. Thanks to the diversity of sizes it comes in, the TO series can tackle virtually all tasks. TO 1300

TW Series: An integrated torque motor combined with high-accuracy gear reduction: The TW combines the dynamics, precision, flexibility, and ease of use of the direct drive with a high power density and the precise and robust WEISS mechanics. TW 150

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TW 300

SW / ST Series: The SW/ST rotating modules with absolute rotary encoder are just what you need when fast, precise, and highly dynamic rotating, swivelling, and gripping movements are called for. Compact profile, light weight, with various mounting-possibilities.

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Technology that inspires

Servo Index Tables – NR / CR / NC NR Series: Freely programmable rotary indexing ring with very large central opening, extremely flat design and a high level of parts accuracy. The ring-shaped design allows extra free design space. The rotating aluminium ring can be adjusted to your specifications in terms of diameter and thickness.

NC Series: The NC combines robustness and durability with the advantages of a freely programmable rotary table offering a high level of torque. The NC differentiates itself from the TC range through its use of a brushless AC servo motor drive. In addition, the drive curve has a constant rise.

CR Series: Flat heavy duty ring with large central opening. The extremely flat design frees up space and offers flexibility for creating ergonomically sound workplaces. Using the WAS control system, the ring is completely freely programmable.

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HANDBOOK

Motion System

Summary of

TRANSDUCERS

the most fundamental level, a transducer is a device that converts one form of energy into another. Common types of transducers used in industrial applications can include sensors to measure temperature, pressure, force, strain, liquid levels and flow rates, among others. These physical quantities are converted to electrical signals in either analog or digital form and can be used to gain information about or control some process. In motion control applications, transducers can refer to any one of a number of sensors such as rotary or linear encoders or resolvers for position feedback, sensors such as tachometers for speed sensing, and even proximity switches to initiate or halt some machine action. For motion control, the measured variable is typically position or speed. Depending on a number of factors, the right transducer may be an encoder or a resolver or a simple potentiometer. A common approach to measuring linear position is a magnetostrictive linear displacement transducer (MLDT). They are typically mounted inside cylinders used in hydraulic motion systems, for instance. MLDTs use moving magnets that don’t come in

Piher’s PSC-360 shaft driven sensor is completely sealed to IP67 protection. Accuracy over 360° reaches 0.5% because the permanent magnet securely fastens to the shaft and acts as the only moving sensor component.

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contact with the sensor tube, avoiding mechanical wear. They also provide an absolute position readout, requiring no homing step before beginning to work with the position information from the MLDT. Advances in MLDT technology have led to sensors with resolutions down to 1 μm and fast signal processing of up to 1.5 MHz. There are a few key factors to consider when selecting any transducer including the desired variable to be measured, the accuracy or resolution needed, the type of output, as well as any size or space restrictions, environmental factors, and product lifetime and cost. For starters, what kind of motion is involved, rotary or linear? Specific transducer types exist for each kind of motion. For instance, encoders or resolvers measure rotary position while a tachometer can provide speed data. For linear motion there are linear encoders using a variety of sensing technologies including optical, capacitive, inductive, and magnetic methods. Determine the accuracy needed for the application. This includes factors such as linearity, resolution, and repeatability. Generally speaking, the greater the accuracy, the more expensive the transducer. This is why knowing the needed accuracy can help in selecting the best type of transducer and lowering the design costs by not paying for more resolution than the application demands. What range must the transducer measure? For linear applications, is the range on the order of nanometers, a few millimeters, or several feet? For rotary applications, if measured in degrees, is the angular distance more or less than 360 degrees? Is the 9 • 2016

The heavy duty SIKO MSK320 ZM magnetic sensor boasts a metallic housing with IP67 protection and an extended operating temperature range from -40 up to 80 °C (optional). Its main use is for rotary measuring tasks, such as measuring the drive shaft speed on all kinds of processing machines including machine tools, woodworking machines and textile machines.

type of encoder needed a single turn or multi-turn device? Also, if selecting an encoder, should the output be absolute or incremental? Consider the type of output. Is it voltage or current? Digital or analog? Many transducers are programmable via a data connection, such as a PC-to-USB link. Other interface options can include encoder-specific communication links like SSI (synchronous serial interface), BiSS (bi-directional serial/synchronous), or PROFINET. Other considerations may include any physical size or weight restrictions or special installation or mounting requirements. Environmental conditions are another important consideration. The transducer should be able to withstand the environmental conditions of the application. Some of the most common conditions to consider are EMI/RFI noise, shock and vibration disturbances, extreme heat or cold, and environmental contaminants such as dirt, dust, moisture, and corrosive chemicals. motioncontroltips.com | designworldonline.com

9/9/16 4:52 PM

WAVE SPRINGS

Update on

WAVE SPRINGS THERE

are almost as many variations of wave springs as there are spring applications. Although often out of sight, these springs are essential in many motion-control applications—including gear assemblies, actuators, rotary unions and different kinds of clutches—and consumer applications. At its most basic level, a spring is a device that stores mechanical energy. Here’s some basic information about wavespring technologies used in engineered designs. For starters, there are three types of springs: tension, compression and torsion. Tension springs operate in tension with a load attached, so as the application applies load, this spring stretches out. Compression springs, as the name implies, operate under compression, so as the application applies load, this spring becomes shorter. Torsion springs operate under twisting loads, which means the application applies torque to the spring. Compression springs are the most common wave spring type. Manufacturers make these out of coiled flat wire with waves added along the coils for more spring effect. Such wave springs can replace conventional round-wire compression springs in applications that have minimal space but need tight load deflection. As an alternative to other coil springs, wave springs occupy 30 to 50% of the compressed height space of comparable round-wire springs with the same deflection and load specifications. Manufacturers typically make wave springs from a single filament of flat wire formed in continuous precise coils with uniform diameters and waves … most commonly out of 17-7pH hardened stainless steel. Manufacturers make the springs with either plain ends (for wavy) or squared-flat ends (with shim ends).

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Wave springs operate as load bearing devices. They take up play and compensate for dimensional variations within assemblies. They can produce a range of forces whereby loads build either gradually or abruptly to reach a predetermined working height. This establishes a precise spring rate in which load is proportional to deflection. Some manufacturers offer single, nested and multi-turn wave springs. A single-turn wave spring with overlapping ends saves axial space so that more space is given for travel. The spring clings to the bore, which saves more radial space. The overlapping ends prevent radial jamming because a circumferential movement is allowed. The spring ends could move against each other so that the specification load at work height is always given. Nested wave springs suit applications requiring higher forces to meet safety regulations, such as those in government or military applications. A nested wave spring provides a higher load than a singleturn wave spring (a stamped wave washer) and uses the same radial space as a single-turn design. Multiple-turn wave springs do not cling to the bore, because radial jamming affects the specified load at work height. If the design of the multi-turn wave spring results in peripheral movement of the turns against each other, this can render the spring unstable. Compared to a single-turn design, longer travel or deflection is possible because the deflection in total is split. Every turn must tolerate less deflection than a single-turn design. Use of a multiturn wave spring can also save 50% in axial space compared to a traditional coil spring. What’s more, these springs eliminate the

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risk of torsional movements during compression to work height … a real problem with coil springs. In contrast, a wave spring always applies its load in an axial direction. Wave springs also apply very consistent loads within a small tolerance range at different work heights. That lets design engineers easily adjust the application to meet given requirements when needed.

HOW TO SELECT A WAVE SPRING FOR A GIVEN APPLICATION? Although wave spring applications abound, there is a basic set of rules to define spring requirements and determine whether a design can use a stock or standard spring or needs a special wave spring. The first and most important consideration is the load the application will apply to the wave spring. Required load is defined as the amount of axial force the spring must produce when installed at its work height. Some applications require multiple working heights so that there are critical loads at two or more operating heights. Often minimum and maximum loads are satisfactory solutions, particularly where tolerance stack-ups are inherent in the application. In any case, remember to consider whether the spring will be subject to high temperature, dynamic loading (fatigue), corrosive media or other unusual operating conditions. Solutions to various environmental conditions typically call for special materials that withstand operating stresses. Wave springs install into working cavities. These usually consist of a bore (in which the spring operates) or a shaft that the spring clears. The spring stays positioned by piloting in the bore or on the shaft. The distance between the loading surfaces defines the axial working cavity or the spring’s work

height. This is where the spring’s material cross-section is important to the overall design. Four critical factors dictate the most suitable wave spring for a given application: physical design constraints (including bore geometry, shaft, ID, OD and so on), the application load, the working height at which the design applies load, and the spring material that will best withstand the application environment. If a spring is designed for a static application, make sure that the percent stress at working height is less than 100%. Springs will take a “set” or length loss in operation due to the high stress condition of the spring, if subjected to a higher stress. If a spring is designed for a dynamic application, make sure that the percent stress at working height is less than 80%. Springs will take a set if put under higher stress. If the work height per turn is less than twice the wire thickness, the spring operates in a non-linear range and actual loads may exceed calculated loads. Number of turns must be between 2 and 20 Number of waves per turn (N) must be in half-turn increments Minimum radial wall = (3 times the wire thickness) Maximum radial wall = (10 times the wire thickness) One caveat: It’s best to avoid situations that compress a wave spring to solid. In addition, account for the expansion of the OD as well as the OD tolerance when designing a spring to fit in a bore or over a shaft.

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9/12/16 11:46 AM

IS THE ANSWER TO MY DESIGN CHALLENGE ALWAYS A PART NUMBER? Ask Smalley. We know that there’s really no such thing as a standard design. So we deliver a level of technical collaboration and customization far beyond what you’d ﬁnd in a typical parts catalog. Smalley engineers are always ready to share their expertise with you—tailoring a highperformance Smalley wave spring, Spirolox® retaining ring or constant section ring to meet your unique application requirements. So don’t settle for ordinary. Talk to a Smalley engineer today. Stamped Ring Constant Section Ring Spirolox® Ring Smalley retaining rings eliminate the protruding ears that interfere with assemblies, while providing a 360-degree retaining surface. And their unique design means no special tools are required.

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AD INDEX

Motion System

HANDBOOK

Accuride .......................................................................................... 121 ACE Controls Inc. ............................................................................ 165 Aereotech, Inc. ................................................................................ 167 All Motion ............................................................................................ 4 Altech Corporation ............................................................................ 29 Altra Industrial Motion Corp. ............................................................. 17 AMETEK PMC ................................................................................... 15 AMETEK/DFS .................................................................................... 97 Applied Motion Products ................................................................ 147 AutomationDirect .............................................................................. 11 Beckhoff Automation ....................................................................... 153 BellowsTech, LLC. ................................................................................ 2 Bimba Mfg Co ..................................................................................... 5 Bison Gear & Engineering Corp. ..................................................... IBC Bodine Electric Company ................................................................ 105 Bosch Rexroth .................................................................................... 23 Brogan & Patrick Manufacturing ........................................................ 64 Carlyle Johnson ................................................................................. 47 CC Link ............................................................................................ 155 Chieftek Precision USA ...................................................... 137,139,141 CGI, Inc. ....................................................................................... 12,13 Clippard Instrument Labratory Inc. ................................................... BC Custom Machine and Tool Co. Inc. .............................................. 42,43 Delta Tau ........................................................................................... 63 Deltron ............................................................................................. 125 DIEQUA Corporation ...................................................................... 100 Dorner ............................................................................................... 74 Dunkermotoren, part of AMETEK ................................................... 145 Dynatect ............................................................................................ 49 Elmo Motion Control ......................................................................... 69 Encoder Products Company .............................................................. 94 Festo .................................................................................................. 87 Galil ................................................................................................... 71 GAM Gear ........................................................................................... 6 Griffin Motion .................................................................................. 169 Groschopp. Inc ................................................................................ 113 Harmonic Drive ................................................................................ 103 Haydon/Kerk, part of AMETEK ........................................................ 127 Helical Products Company .................................................................. 9 Helukabel, USA ................................................................................. 54 Hitachi Cable America ....................................................................... 55 HIWIN ................................................................................................ 33 IDEC .................................................................................................. 16 igus, inc. ....................................................................................... 38,39 Intech ............................................................................................... 109 ITT Enidine ...................................................................................... 163 KEB America, Inc. .............................................................................. 67

KHK USA Inc. ..................................................................................... 99 Kuebler Inc. ....................................................................................... 95 LEE Spring ......................................................................................... 61 Lenze Americas ................................................................................. 72 Lin Engineering ............................................................................... 149 LinMot ............................................................................................. 138 Maple Systems Inc. .......................................................................... 117 Martin Sprocket ................................................................................. 41 Master Bond ...................................................................................... 14 Maxon Motors ................................................................................... 19 MicroMo ................................................................................Cover,133 Mitsubishi Electric .............................................................................. 65 mk North America ............................................................................. 75 Moog Animatics .............................................................................. 135 Moog Components Group .................................................................. 1 NB Corporation ................................................................................... 3 NBK America LLC .............................................................................. 77 Neugart USA Corp. ......................................................................... 107 Nexen .............................................................................................. 159 Nippon Pulse America Inc. ................................................................ 68 Nook Industries ............................................................................... 123 NSK Precision .................................................................................... 35 OMS Motion ...................................................................................... 90 PBC Linear ......................................................................................... 21 Physik Instrumente .......................................................................... 170 PITTMAN, part of AMETEK ............................................................. 151 Primatics, Inc. .................................................................................. 168 Pro-Face America ............................................................................ 115 R+W America ............................................................................... 81,83 Renishaw Inc. ................................................................................... 140 Rollon .............................................................................................. 129 Rotor Clip Company, Inc. ................................................................ 160 Ruland Manufacturing ....................................................................... 85 SAB North America ........................................................................... 53 Serapid Inc. ....................................................................................... 30 Servometer® ....................................................................................... 2 SEW Eurodrive ................................................................................. 111 Smalley Steel Ring Company........................................................... 175 Stock Drive Products/Sterling Instrument ......................................... 44 Teledyne LeCroy .................................................................................. 7 THK America, Inc. ............................................................................ IFC Tolomatic ........................................................................................... 25 US Digital ........................................................................................... 93 WEISS North America, Inc ............................................................... 171 Yaskawa America, Inc...................................................................... 143 Zero-Max, Inc. .................................................................................... 79

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