Motion Systems Handbook 2021

AUGUST 2021

DESIGNWORLDONLINE.COM MOTIONCONTROLTIPS.COM

MOTION SYSTEMS HANDBOOK

Hollow Shaft Meets Solid Stepper Performance

Cover final — MC HB 08-21.indd 1

8/11/21 3:34 PM

THINK INSIDE THE BOX Exceptional designs deserve superior components.

The developer of the original world-class linear motion systems, THK continues to redefine industry standards and to meet an ever-growing range of needs. From aerospace and machine tool to packaging and medical, THK products play a vital role in the advancement of technology and capability.

To learn more, call us at 1-800-763-5459 or visit www.thk.com.

Step Up Your Game with great value in stepper components from AutomationDirect. ®

®

Stepper Drives

AC Step Systems

SureStep® Linear Actuators

Starting at: $25.50 (DM322E)

AC stepper drive accepts 90-240VAC input to power high-voltage bipolar stepping motors for high torque, especially at higher speeds.

Starting at: $96.00 (ASTP-LE17-2A06ANN)

These 2-phase digital stepper drives offer a basic feature set at an unbeatable value.

• Motor auto-configuration on power up • Wide range of input voltages supported (12-110 VDC, 18-80 VAC) • Pulse input frequency up to 200kHz • Soft-start at power on • Automatic idle-current reduction • Over-voltage and over-current protection • Optically-isolated inputs • No software required; DIP-switches for built-in self-test, microstep resolution selection, and current level selection • NEMA 11, 14, 17, 23, 24, 34 and 42 frame size step motors supported

These NEMA 17 or NEMA 23 frame stepper motors have a stainless-steel lead screw extension of the rotor (and a screw nut), which translate motor torque into linear thrust.

AC Stepper Drive Starting at $199.00 (STP-DRVAC-24025) • Auto-setup measures motor parameters, configures current control, and anti-resonance gain settings • Switch selectable microstep resolution • Switch configurable: running current, anti-resonance, input signal filter, step smoothing filter, and self-test

• Up to 193 lbs of thrust • Speeds up to 18 inch/sec • Three standard lengths: 6 in, 9 in, and 12 in • Nine standard leads (travel per rev): • 0.25 in/rev, 0.5 in/rev, or 1.0 in/rev • 1.25 mm/rev, 2 mm/rev, 3 mm/rev, 6 mm/rev, 8 mm/rev, or 10.5 mm/rev • Styles with bearing journal and snap-ring groove (at screw end) • Styles with rear motor shaft and mounting holes for encoder mounting • Long life, no-maintenance screw nuts • Extension cables available in 6ft, 10ft, and 20ft lengths

High-Voltage Step Motors Starting at $57.00 (STP-MTRAC-23044) • High torque at higher speeds • Single-shaft and dual-shaft designs • NEMA frame sizes: 23, 24 • Available torque from 75 to 1841 oz-in • 1.8° step angle, 200 steps per revolution • IP40 protection rating

STEPPER SYSTEM SELECTOR Use our new Stepper System Selector to size a stepper motor for your application, then walk through all the options for that motor; including encoders, drives, power supplies, cables, and more.

Research, price, buy at:

www.automationdirect.com/stepper-systems Also Available SureStep® Stepper Drives

Integrated Stepper Motor/Drives

Single or Dual Shaft and IP65 Stepper Motors

www.automationdirect.com/ selectors/steppers

Order Today, Ships Fast! * See our Web site for details and restrictions. © Copyright 2021 AutomationDirect, Cumming, GA USA. All rights reserved.

1-800-633-0405

the #1 value in automation

PRECISE. ROBUST. AVAILABLE.

CD® Couplings • Zero-Backlash & High Torsional Stiffness • Engineered Performance for Reliable 24/7 Operation • Servo-Rated for Reversing, Positioning & Precision • Single-Flex, Double-Flex, Floating-Shaft Solutions • Standard Models / Fully Customizable • Engineering Assistance / Fast Delivery

www.zero-max.com 800.533.1731

Zero-Max CD Ad r7 Design World March 2020.indd 1

2/18/20 10:37 AM

210702_AutoHybridStepper_DW_US.indd 1

7/1/21 2:33 PM

NEW!

4 AXIS SERVO from

2.25”

Motion Systems Handbook

ON BRITNEY SPEARS, ARTIFICIAL INTELLIGENCE, AND AUTOMATION RECENTLY, BRITNEY SPEARS has been in

the news concerning the court-ordered conservatorship imposed on her stemming from her infamous 2008 mental health breakdown. As details of the story emerged, the public reacted with astonishment at the setup that essentially limits her freedom to make her own choices and therefore live her

- brushed or bldc motors - 5 amps per axis - 16 analog inputs - 16 on/off drivers - home and limit in - live tech support - made in the USA See the

EZQUAD SERVO in action!

WWW.ALLMOTION.COM

(510) 471-4000 30097 Ahern Avenue Union City, CA 94587 Te c h n i c a l S u p p o r t

(408) 460-1345

life as she sees fit. Some of the key decisions that her conservators make on her behalf include deciding whether or not she can work, when she can leave her house, and even how she spends her own money.

Most people reacted to this news with disbelief and shock, partly at the measures themselves but also at how long they had been in place and how long she’d been subjected to them. People grasped the curtailment of her individual choices as inherently unfair and unjust. That’s because it strikes at a person’s individual autonomy or agency; the ability to make choices about their own lives, something that is rightly considered a fundamental human right.

Likewise, there has been a proliferation of stories about artificial intelligence (AI), highlighting both the promises as well as the perils it brings. It’s long been known that the most troubling moral problems associated with certain uses of AI revolve around privacy, bias and discrimination, and the role of human judgment. Perhaps the most commonly cited example of AI bias involves the algorithm known as COMPAS (Correctional Offender Management Profiling for Alternative Sanctions); it’s used in some U.S. court systems to help predict defendant recidivism rates.

Such uses of AI software, where it is essentially deciding the fate or future direction

4

DESIGN WORLD — MOTION

of individual human lives with little if any transparency with regard to the methods and algorithms used, is recognized to be morally problematic. This is because in the end we recognize it to be an infringement on individual autonomy, striking at the power to decide for ourselves. It’s the same sense of violation of individual agency that people recognize in the case of Britney Spears; in her case, it’s a courtappointed conservator, and in the COMPAS case it’s essentially AI software making decisions.

And yet, the uses of AI are potentially limitless. There are a growing number of legitimate uses for AI in manufacturing and automation. AI software can help identify patterns that humans can’t see or analyze massive data sets, helping to improve many manufacturing and industrial processes. For example, AI is helping robotic systems through better data collection and analysis, which can improve productivity and performance.

In the end, it’s up to the human designers and engineers and other stakeholders to figure out the proper uses of AI, and those that are not. To that end, industry groups such as the IEEE Global Initiative on Ethics of Autonomous and Intelligent Systems along with others have been doing the work of addressing these and other ethical considerations involving the design and implementation of AI systems.

Such work is necessary to guide design into the future, so that we can identify and avoid uses of AI with harmful social effects, such as those that arise from facial recognition software, or uses that contain a coercive or manipulative dimension that impacts human autonomy.

Ultimately AI, like fire, is a tool. So it’s up to us, its human caretakers, to make wise decisions on how best to use it and in what circumstances to do so. As well as what not to do with it.

MILES BUDIMIR • SENIOR EDITOR 8 • 2021

PLANETARY Brushless DC Gearmotors

High Performance.

Zero Maintenance.

Get even more torque, high efficiency and maintenance-free performance with our brushless DC planetary gearmotors. Ideal for industrial automation applications, packaging equipment, and for a wide range of solar- or battery-powered equipment. Metric and US models available from stock. Now available with new encoder shaft kit.

RATED SPEED 15 to 658 rpm

TORQUE 11 to 226 lb-in.

GEAR RATIOS 4:1 to 162:1

VOLTAGES 24, 130 VDC

bodine-electric.com

4

info@bodine-electric.com • 7 73.478.3 515

BOD 2021-08 22B-60P full page.indd 2

7/1/21 11:53 AM

CONTENTS V O L U M E

4 10 16 19 23 27 30 34 36 38 41 44 49 57 60 67 69 73 76 81

6

DESIGN WORLD — MOTION

7

N U M B E R

3

EDITORIAL LINEAR ACTUATORS BALL SCREWS BEARINGS BELTS & PULLEYS BRAKES & CLUTCHES CABLES CONTROLLERS CONVEYORS COUPLINGS DRIVES ENCODERS GEARING GEARMOTORS LINEAR COMPONENTS MOTORS - DC MOTORS - STEPPER SPRINGS STAGES VIBRATION

8 • 2021

motioncontroltips.com | designworldonline.com

Design World’s Motion Control Classroom An online reference series

for design engineers. Each

motion installment features current trends, videos, typical and emerging

applications and FAQs.

MC² installments include • Linear Guide And Slide Rails And Ways • Couplings • Encoders • DC Motors • Stepper Motors • Gearmotors • Vibration Damping + Shocks • Conveyors • + More

stay up-to-date Future MC² Classroom installments will cover topics including essential power-transmission and motion-control technologies for an array of OEM machines, powered end-user products, servo drives, and automated installations.

learn more at: www.designworldonline.com/mc2 MC Classroom house1ad.indd 7 MC2-FullPage.indd

8/11/21 8/26/19 3:42 2:59 PM PM

DESIGN WORLD F O L L O W T H E W H O L E T E A M O N T W I T T E R @ D E S I G N W O R L D EDITORIAL VP, Editorial Director Paul J. Heney pheney@wtwhmedia.com @wtwh_paulheney Senior Contributing Editor Leslie Langnau llangnau@wtwhmedia.com @dw_3Dprinting Executive Editor Leland Teschler lteschler@wtwhmedia.com @dw_LeeTeschler Executive Editor Lisa Eitel leitel@wtwhmedia.com @dw_LisaEitel Senior Editor Miles Budimir mbudimir@wtwhmedia.com @dw_Motion Senior Editor Mary Gannon mgannon@wtwhmedia.com @dw_MaryGannon Associate Editor Mike Santora msantora@wtwhmedia.com @dw_MikeSantora

IN-PERSON EVENTS Events Manager Jen Osborne jkolasky@wtwhmedia.com @wtwh_Jen

VP, Creative Services Mark Rook mrook@wtwhmedia.com @wtwh_graphics Art Director Matthew Claney mclaney@wtwhmedia.com @wtwh_designer Graphic Designer Allison Washko awashko@wtwhmedia.com @wtwh_allison

Graphic Designer Mariel Evans mevans@wtwhmedia.com @wtwh_mariel Director, Audience Development Bruce Sprague bsprague@wtwhmedia.com

PRODUCTION SERVICES Customer Service Manager Stephanie Hulett shulett@wtwhmedia.com Customer Service Representative Tracy Powers tpowers@wtwhmedia.com Customer Service Representative JoAnn Martin jmartin@wtwhmedia.com Customer Service Representative Renee Massey-Linston renee@wtwhmedia.com Customer Service Representative Cathy Anthony-Gudel canthonygudel@wtwhmedia.com

WO R L D

Event Marketing Specialist Olivia Zemanek ozemanek@wtwhmedia.com

CREATIVE SERVICES & PRINT PRODUCTION

VP, Digital Marketing Virginia Goulding vgoulding@wtwhmedia.com @wtwh_virginia

Web Development Manager B. David Miyares dmiyares@wtwhmedia.com @wtwh_WebDave

Digital Marketing Manager Taylor Meade tmeade@wtwhmedia.com @Taylor Meade

Senior Digital Media Manager Patrick Curran pcurran@wtwhmedia.com @wtwhseopatrick

Digital Marketing Specialist Sean Kwiatkowski skwiatkowski@wtwhmedia.com Digital Design Manager Samantha King sking@wtwhmedia.com

Front End Developer Melissa Annand mannand@wtwhmedia.com Software Engineer David Bozentka dbozentka@wtwhmedia.com

Graphic Designer Hannah Bragg hbragg@wtwhmedia.com

Digital Production Manager Reggie Hall rhall@wtwhmedia.com

Senior Manager Webinars/ Virtual Events Lisa Rosen lrosen@wtwhmedia.com

Digital Production Specialist Elise Ondak eondak@wtwhmedia.com

Webinar Coordinator Halle Kirsh hkirsh@wtwhmedia.com

Digital Production Specialist Nicole Johnson njohnson@wtwhmedia.com

Webinar Coordinator Kim Dorsey kdorsey@wtwhmedia.com

VP, Strategic Initiatives Jay Hopper jhopper@wtwhmedia.com

VIDEOGRAPHY SERVICES

FINANCE

Video Manager Bradley Voyten bvoyten@wtwhmedia.com @bv10wtwh

Controller Brian Korsberg bkorsberg@wtwhmedia.com

Videographer Garrett McCafferty gmccafferty@wtwhmedia.com

2011- 2019

2014 Winner

Accounts Receivable Specialist Jamila Milton jmilton@wtwhmedia.com

2014 - 2016

N

G @ D E SI

ONLINE DEVELOPMENT & PRODUCTION

MARKETING

8

DESIGN WORLD — MOTION

8 • 2021

motioncontroltips.com

|

designworldonline.com

IP67 RATED

I/O SYSTEM FIELD A MODERN APPROACH TO IP67 RATED DISTRIBUTED I/O • • • •

Fieldbus Communications – PROFINET, EtherNet/IP, EtherCAT, Modbus, IO-Link IIoT Protocols – MQTT, OPC UA, HTTP(S), Bluetooth Integrated Load Management – Monitor power consumption, set alarms, and adjust output current Ready for the Future – Made for TSN

www.wago.us/systemfield

IO Field Ad.indd 1

2/5/21 2:17 PM

Motion Systems Handbook

COMPARING CORE LINEAR-ACTUATOR TECHNOLOGIES LINEAR 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 as the type of guide and housing to further differentiate them. Below is an explanation of the most common linear actuator categories.

Belt and screw-driven 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 can use a variety of guide mechanisms ... plain bearings, the more advanced option of wheel-based linear guides, and recirculating bearings (riding on a profiled rail or round shaft) are most common.

Because their strengths are high speeds and long strokes, belt-driven systems are often housed in an aluminum extrusion or in an open configuration with no protective housing.

Screw-driven actuators: Within the linear-screw category, there are two subcategories — ballscrew and leadscrew drives. While ballscrew actuators have higher repeatability and thrust forces than leadscrew actuators, both provide inherent gearing through the lead (pitch) of the screw.

The most common guide system for screw-driven actuators is the profiled rail, although leadscrew types are sometimes guided by plain bearings. Because screw-driven actuators require end bearings that must be rigidly mounted, they are often enclosed in an aluminum extrusion. However, when high travel accuracy is required, ballscrew types are

10

DESIGN WORLD — MOTION

commonly offered with a machined steel housing.

Ballscrew actuators also pair with track-roller linear guide mechanisms on high-speed axes and those to deliver high thrust force.

Pneumatically driven linear actuators: Although they’re not electromechanical devices like the other actuator types, their prevalence in automated equipment makes pneumatic driven versions an important category of linear actuators.

Pneumatic actuators can be further divided into two sub-categories … slider-type and rod-type.

In slider-type actuators, the motion is contained within the limits of a housing and the load is mounted to a slider — also called a carriage, saddle, or table.

In rod-type actuators, the motion is produced by a rod that extends and retracts from a housing.

The load may be mounted to the end of the rod or the rod can be used to push the load. One common application is the pressing or stamping of labels onto cartons … or pushing defective products to a diverter lane along a conveyor.

8 • 2021

THE MONOCARRIER RODLESS LINEAR ACTUATOR SERIES COMBINES THREE CORE NSK AUTOMATION TECHNOLOGIES: PRECISION-GROUND BALL SCREWS, LINEAR GUIDES WITH K1 LUBRICATION, AND SUPPORT BEARINGS. THESE FULLY INTEGRATED COMPONENTS PROVIDE SMOOTH, NEAR-SILENT, HIGHACCURACY LINEAR POSITIONING FOR UP TO FIVE YEARS OR 10,000 KM OF TRAVEL WITHOUT MAINTENANCE. COURTESY OF NSK AMERICAS

motioncontroltips.com | designworldonline.com

Motion Control Solutions from Extra Large to Extra Small Configure Today at pbclinear.com and Make

Your Tailored Solution!

MUK Series bit.ly/Config-MUK

MTB Series bit.ly/Config-MT

PLA Series bit.ly/Config-PL

UG Series bit.ly/Config-UG

Compact Series bit.ly/Config-Compact

ML Series bit.ly/Config-ML

LSM Series bit.ly/Config-LeadScrew

6402 E. Rockton Road, Roscoe • Illinois 61073 USA • +1.800.962.8979 • pbclinear.com

PBC Linear - MC HB 08-21.indd 11

8/11/21 3:43 PM

Motion Systems Handbook

Slider-type pneumatic actuators can be guided by recirculating or plain bearings, depending on the load for which they’re designed.

In contrast, rod-style versions are not typically designed for radial (downward-upward-side) loads and use simple plain bearings to provide guidance to the rod without significantly contributing to loadcarrying capacity.

Note: Ballscrew-driven actuators also come in slider and rod-types, making the actuator family tree even more complex.

Chain and rack-and-pinion driven actuators: For extremely long lengths and robustness against contamination, chain drives and rackand-pinion drives are often the most suitable choices. Joined profile rails are sometimes used with these drives. However, in settings with a lot of debris, these actuation systems are best paired with guide wheel based options.

Linear-motor based actuators: Linear motor actuators are also capable of long travel lengths with multiple carriages. They’re primarily used for high precision and highly dynamic motion. To complement the strengths of the linear motor, these actuators use high precision profiled rails, crossed roller guides, linear guide wheels, or even air bearings as their guidance system.

Linear motor types can be mounted in an extruded housing or on a machined aluminum plate ... though to meet the highest travel accuracy specifications, they typically mount on a machined steel plate or granite base.

WHEN TO SPECIFY A PRE-INTEGRATED LINEAR ACTUATOR

You’re working on an application that requires linear motion — maybe it’s a pick-and-place assembly system, a packaging line, or a gantry for material transfer. It’s quite likely that designing your own actuator from scratch (and sourcing the various parts, mounting, and aligning the components, and implementing a maintenance system) is not an effective use of your time.

So you begin looking at predesigned and preassembled linear actuators. Trouble is there are so many actuator types, sizes, and geometries that it’s hard to know where to start in your selection.

The first step in narrowing down the field is to choose which drive mechanism is best for the application. Most manufacturers offer at least two drive options, with toothed belt and ballscrew being the most common ... and pneumatic and linear motor drives serving niche applications. Below are five factors that will help guide your choice between the two most common types of actuators — toothed belt and ballscrew.

Linear actuator stroke length: The distance the actuator needs to move in one direction — known as the stroke length — is the first requirement to consider in choosing between ballscrew or belt drive. Ballscrew actuators are commonly found at lengths of 1,000 mm or less although larger-diameter ballscrews can be used at lengths to 3,000 mm. This limit is governed by the screw’s critical speed.

As a screw’s length increases, its critical speed (the speed at which the screw begins to encounter bending vibrations) decreases. Simply put, as a screw gets longer and turns faster it begins to “whip” like a jump rope.

12

DESIGN WORLD — MOTION

8 • 2021

For actuators with toothed belt drive, the ability to tension the belt limits the maximum length. By using belts with larger width (more contact area) and higher tooth pitch, belt-driven actuators are commonly found in applications requiring a stroke length of 10 to 12 meters.

Speed required by the linear axis: The second critical factor in choosing an actuator is speed. The maximum speed for most belt drive actuators is 5 m/sec. This limit is influenced by the guide system, which most commonly employs recirculating bearings. For applications that require higher speeds (to 10 m/sec) a belt drive can be used in conjunction with preloaded wheel-based guide mechanisms rather than recirculating bearings.

As mentioned, in a ballscrew drive actuator, as the length increases, the critical speed decreases. In general, ballscrew actuators can reach speeds to 1.5 m/sec at stroke lengths less than one meter. Ballscrew supports can provide additional rigidity by reducing the unsupported length of the screw ... letting the actuator reach higher speeds and longer lengths. When considering ballscrew supports, consult the manufacturer for assistance in executing necessary speed and length calculations.

Accuracy: Accuracy is broadly used to mean either travel accuracy (where the carriage or saddle is in space during the movement) along with positioning accuracy (how closely the actuator reaches the target position) or repeatability — how closely the actuator achieves the same position with each stroke. While travel accuracy is heavily influenced by the actuator’s structure, base, and mounting, positioning accuracy and repeatability are primarily functions of the drive mechanism. Ballscrews, particularly if they are preloaded, have better positioning accuracy than belt drives due to their rigidity. However, the inaccuracy in positioning can be measured and compensated for in the actuator’s control system. For this reason, repeatability (the ability to reach the same position with each stroke) often becomes the most important factor in high-precision applications. For high repeatability, the rigidity of the drive mechanism is critical, making a preloaded ballscrew and nut assembly the better choice.

Linear-actuator mounting options: In some cases, the direction in which the actuator is mounted will dictate which drive mechanism is best. Both belt and ballscrew drives are suitable for horizontal and inclined mounting orientations, but applications that require vertical mounting need more careful evaluation.

While every system that is moving a load vertically needs built-in safety mechanisms, ballscrew drives are often seen as safer than belt drives for carrying vertical loads. This is because ballscrews, depending on the load, screw lead, and friction in the system, are reluctant to back drive or “free fall” if there’s a failure of the brake or catastrophic damage to the system.

When a belt drive actuator is required in a vertical application, an external brake or counterweight should be seriously considered.

Maintenance (or lack thereof) for actuator: The primary cause of failure for linear actuators is lack of lubrication.

Both ballscrew and belt drive actuators require that the guide system be lubricated periodically, but ballscrews introduce another component that must be monitored for

motioncontroltips.com | designworldonline.com

LINEAR ACTUATORS

proper lubrication. Some manufacturers have addressed this by providing systems that are lubricated for life (with life being defined as a set travel distance or number of revolutions, with a given load, speed, and environment) but many applications fall outside these specified parameters and will require lubrication at some point during their intended lifetime.

Although belt driven actuators have the benefit of fewer components to maintain, when the environment contains dust or chips, look for an actuator design that minimizes the potential for contamination to enter the pulley housings. This will ensure longer life for the pulley bearings and reduce wear on the belt itself.

Both belt drives and ballscrew drives have performance benefits. When making an initial selection, remember that belt drives are typically the better choice for long stokes and high speeds, while ballscrew drives are better for applications that require high repeatability or vertical mounting.

In some applications, either drive mechanism will meet the criteria outlined above. In these cases, the manufacturer can guide design engineers in choosing the right actuator based on more advanced factors — such as acceleration, settling time, or environmental conditions.

motioncontroltips.com | designworldonline.com

MORE ON MOTION-GRADE PNEUMATIC CYLINDERS

Pneumatic cylinders and actuators are commonly known as bang-bang devices, making quick moves from one end of their stroke to the other, with limited regulation of the force or the move profile.

On the other hand, electromechanical actuators with servo controls offer high levels of refinement in positioning, force-torque, and accuracy.

Generally speaking, pneumatics are a cost-effective solution for rather crude point-to-point moves, while electromechanical actuators provide high precision at a higher cost.

There’s a spot between these two solutions where a relatively high level of control is needed, but without the complexity and cost of electromechanical servo driven systems. Bridging this gap are pneumatics that operate in a closed-loop system — in other words, servo pneumatics.

Servo pneumatics versus traditional pneumatics: A servo system is one that uses a feedback device and a controller to monitor and correct the system’s error (in position, speed, or torque-force). Hence, integrating a pneumatic cylinder or actuator with a feedback system and a controller that can issue commands based on that feedback, gives us a servo pneumatic device. Another key component of a servo

8 • 2021

DESIGN WORLD — MOTION

13

RELIABLE LINEAR, ROTARY, AND COMPLEX PROFILE SOLUTIONS FOR ANY ENVIRONMENT

MOTION CONTROL AUTOMATION

Let us help you!

VISIT:

MULTI-AXIS

ROTARY

DEBRIS RESISTANT

SMOOTH MOTION

COMPACT

LONG LIFE

BWC.COM/MOTION-CONTROL LOPRO® LINEAR ACTUATORS

• Designed to excel in harsh and extreme environments • Debris-tolerant vee guide wheel technology • Drive options for any application: belt, chain, ballscrew, or leadscrew

LOPRO® GANTRY KITS

• Multi-axis assemblies extend working envelope • Pre-configured connections for a variety of actuator sizes, configurations, drive types, and orientations

PRT2 HEPCOMOTION® PRECISION RING & TRACK

• Fully adjustable, low maintenance, debris-tolerant design • Extensive range of ring diameters up to 1.5 m • Build carriage circuits into nearly any shape Bishop-Wisecarver is proud to be the exclusive North American distributor of HepcoMotion products since 1984.

EXPERTLY DESIGNED, DELIVERED TO PERFORM

CONTACT: sales@bwc.com or (925) 439-8272

linear actuators

THIS IS A BRUSHLESS-DC SERVO CYLINDER FROM ULTRA MOTION FEATURING THE SUPPLIER’S OWN PHASE INDEX HIGHRESOLUTION ABSOLUTE-POSITION SENSING. IN SHORT, PHASE INDEX SENSING TRACKS THE PHASE RELATIONSHIP BETWEEN TWO CYCLIC SIGNALS TO GET LINEAR-POSITION INFORMATION WITHIN THE COMBINED SIGNALS’ INTERFERENCE CYCLE.

pneumatic system is a proportional valve, which precisely regulates air delivery to ensure that the commanded position or force is achieved.

Traditional pneumatics enable rapid, highforce, point-to-point motion. Servo pneumatics provide the same speed and force capabilities, with the advantage of higher accuracy positioning, not only at the ends of the stroke, but also at intermediate points along the travel.

In addition to obtaining feedback on position, servo pneumatics also monitor and regulate air pressure, which enables precise control of the force that’s produced.

One drawback (real or perceived) to traditional pneumatics is air consumption.

Air preparation and delivery costs money, and pneumatics can use a significant amount of air even when they’re not working. Servo pneumatics, on the other hand, control air flow based on the required position and force. This leads to less air consumption than standard pneumatics, by as much as 30%. Note that servo pneumatics require higher quality air than standard pneumatics. In addition to industrystandard filtration, a 5-µm filter is typically recommended for servo pneumatic systems.

So why servo pneumatics instead of electromechanical actuators? Of course, electromechanical actuators can provide accurate position and force control, but servo pneumatics have a much higher power density—that is, force capability for a given size.

A servo pneumatic cylinder or actuator typically

motioncontroltips.com | designworldonline.com

provides many times the force capability of an electromechanical actuator of a similar body size, which is a significant advantage in pressing, inserting, and tightening applications. Servo pneumatics also operate with 24-Vdc power supplies, which allows them to be used in lowpower applications. Lower power also reduces heat generation and thermal buildup, so they perform well in continuous-duty applications and high-temperature environments.

While electromechanical servo systems have been in use for decades, the adoption of servo pneumatics in industrial applications hinged on advancements in controls and software. Air is compressible, and this variable is much more difficult to define and model than the compliance or backlash in an electromechanical system.

Before servo pneumatics could be commercialized, pneumatic control algorithms capable of considering this non-linearity had to be created. But the past ten years or so have seen the development and integration of high-response valves and digital signal processors (DSPs) that can perform high-speed computations, making servo pneumatic systems a reality … capable of providing accurate, highly responsive positioning and force control.

8 • 2021

DESIGN WORLD — MOTION

15

Motion Systems Handbook

OVERVIEW OF BALL SCREW DESIGNS MOTION APPLICATIONS use two primary types of screw drives: those that

rely on sliding contact (lead screws), for applications that require corrosionresistance, self-locking operation; and customizable nut designs, and those that use re-circulating balls (ball screws) or rollers, for applications that require high rigidity, excellent positioning accuracy, and high duty cycles.

Ball screws translate rotational motion to linear motion. There are three main components of a ball screw; a nut, a screw with grooves, and balls, which can be made of steel, ceramic, or hard plastic. The balls rotate between the nut, screw, and grooves when either the nut or screw rotates.

Among ball screws, there are two primary divisions based on the manufacturing method; ball screws with ground threads and ball screws with threads formed by rolling. Ground ball screws have traditionally been the choice for high-precision applications, whereas rolled screws offered an economical solution for general industrial and automation applications.

THE DIFFERENCE BETWEEN A BALL SCREW SPLINE AND A TRADITIONAL BALL SCREW

The basic ball screw design can be altered for specific uses and environments. One such special design is a ball screw spline. A ball screw spline is a combination of two components — a ball screw and a rotary ball spline. By combining a driving element (the ball screw) and a guiding element (the rotary ball spline), a ball screw spline can provide both linear and rotary motion, as well as spiral motion, in a highly rigid, compact design.

COMPONENTS OF A BALL SCREW SPLINE

A ball screw uses recirculating steel balls in a precisely machined nut to drive a load to an exact position. In most designs, the screw is fixed at one or both ends, and the nut is prevented from rotating via a keyed housing or other anti-rotation setup. A motor drives, or rotates, the screw.

But because the screw is constrained from moving linearly, the motion is transferred to the ball nut, which travels along the length of the screw shaft.

Another ball screw design incorporates radial angular contact bearings on the outer diameter of the nut, allowing the nut to be driven — typically via a belt and pulley assembly connected to a motor — while the screw remains completely stationary. When the motor turns, it rotates the nut, causing it to traverse the length of the screw. This setup is commonly known as a “driven nut” design.

A ball spline is a type of linear guide system similar to the

round shaft and recirculating ball bearing, but with spline grooves precisely machined along the length of the shaft. These grooves prevent the bearing — referred to as a spline nut — from rotating, while also allowing the ball spline to transfer torque.

One variation of the standard ball spline is the rotary ball spline, which adds a rotating element — gears, crossed rollers, or angular contact ball bearings — to the outer diameter of the spline nut. This allows the rotary ball spline to provide both linear and rotational movement.

THREE MOTIONS: LINEAR, SPIRAL, AND ROTARY

Ball screw spline assemblies constrain both the ball screw nut and the ball spline nut from moving linearly. By driving the ball nut and the spline nut together or separately, three different types of motion can be produced: linear, spiral, and rotary.

To create linear motion, the ball nut is driven and the spline nut is held stationary. Since the ball nut cannot traverse linearly, the shaft traverses through the ball nut. However, the stationary spline nut keeps the shaft from spinning, so that the motion of the shaft is purely linear, with no rotation.

Alternatively, when the spline nut is driven and the ball nut is held stationary, the ball spline causes rotational motion, while the screw threads traveling through the stationary ball nut cause the shaft to travel linearly as it rotates, resulting in a spiral motion.

When both nuts are driven, the rotation of the ball nut essentially counteracts the linear motion caused by the ball spline, so the shaft rotates without any linear travel.

OPTIONS FOR INTEGRATED MOTOR AND SCREW DESIGNS

Ball and lead screw assemblies are often driven by a motor connected inline with the screw shaft via a coupling. While this mounting arrangement is simple and easy to service, the addition of a non-rigid mechanical component (the coupling) can introduce windup, backlash, and hysteresis — all of which affect positioning accuracy and repeatability. The coupling

THIS EXAMPLE FROM NIPPON BEARING SHOWS THAT A BALL SCREW SPLINE HAS BOTH A BALL NUT AND A SPLINE NUT, EACH WITH A RADIAL BEARING ON ITS OUTER DIAMETER. 16

DESIGN WORLD — MOTION

8 • 2021

motioncontroltips.com

|

designworldonline.com

ROCKFORD BALL SCREW

IT’S YOUR MOVE NEW METRIC BALL SCREWS

STANDARD BALL SCREWS

LINEAR GUIDE RAILS ROCKFORD LINEAR MOTION

With a re-engineered bearing return system, metric ball screws minimize footprints for a quiet, smooth performance. In addition, RBS metric ball screws feature new and improved wiper technology for optimum cleaning performance.

Our standard ball screws are an integral part of what keeps manufacturing, production, and people on the move - proudly made in the USA, and one of the largest inventories including, acme screws, free-wheeling screws and accessories.

Linear guide rail solutions from RBS are found in countless industrial and consumer product manufacturing applications – providing the ability to transport, process, handle, position, and automate with accuracy and smoothness.

We service all brands, including (but not limited to) American Ball Screw, Beaver Precision Products, Cincinnati, Nook, NSK, Rockford Ball Screw, THK, Thomson/Saginaw, Tsubaki, Twentieth Century and Warner Electric.

Count on RBS for outstanding support, state-of-the-art manufacturing, and the fastest turn times in the industry to keep you at the forefront of solving linear motion challenges. Learn more at rockfordballscrew.com or call 800.475.9532.

STAY CONNECTED! RBS Metric Ball Screw Ad-Final.indd 1

6/30/21 1:27 PM

Motion Systems Handbook also adds length, reduces rigidity, and increases the inertia of the system. One way to eliminate these potential problems is to do away with the external coupling and integrate the screw directly into the motor.

Integrated motor and screw assemblies are available in various configurations and designs.

The motor can be either a servo or a stepper type, and the screw can be a ball screw or a lead screw, although the most common configurations pair a lead screw with a stepper motor or a ball screw with a servo motor.

EXTERNAL MOTOR-SCREW INTEGRATION

One of the most common integrated designs uses a motor with a hollow shaft and integrates the lead screw directly into the motor. The screw is machined so that one end that mates to the hollow bore of the motor, and the machined end is either permanently fixed to the motor bore via welding or an adhesive, or secured with a fastener. Connecting the screw shaft to the motor bore via a fastener allows the components to be disassembled for maintenance and makes it possible to replace either component (rather than replacing the entire assembly), but this method can also experience loss of alignment and rigidity over time.

Regardless of which method is used to connect the screw shaft to the motor, this method of motor-screw integration is typically referred to as an “external” design because the ball or lead screw nut remains external to the motor. Like a traditional screw-motor setup, the motor’s rotation causes the screw to turn, which advances the nut (and the load) along the length of the screw shaft.

Although applications with short strokes and light loads can sometimes operate without additional support for the screw (essentially a fixed-free arrangement) or without linear guides, most applications will require support for the opposite end of the screw and the use of linear guides to prevent radial loads on the screw.

NON-CAPTIVE MOTOR-SCREW INTEGRATION

In the non-captive method of integration, the ball or lead screw nut is integrated into the motor (or mounted to the face of the motor) and does not travel along the screw. Instead, the screw is prevented from rotating (typically by the attached load), and when the motor and nut turn, the screw travels linearly, back-and-forth “through” the motor-nut combination. In this configuration, the non-captive design provides a better stroke-to-overall length ratio, provided

Compact. Silent.

Precise. MBSA.

the design allows space for the screw to extend beyond the back of the motor.

Alternatively, if the screw is fixed so that it doesn’t travel, the assembly essentially becomes a driven nut design, where the motor’s rotation causes the motor-nut assembly to travel back-and-forth along the stationary screw. Like a conventional driven nut assembly, this configuration allows higher travel speeds, because screw whip is almost entirely eliminated. It also allows multiple motor-nut combinations to be mounted to the same screw shaft and driven independently.

CAPTIVE MOTOR-SCREW INTEGRATION

A variation of the above motor-screw combination is the captive design. Like the noncaptive design, the nut is integrated directly into the motor, but a spline shaft is attached to the screw, preventing the screw from rotating and creating linear motion when the motor turns.

In this design, the screw extends and retracts from one end of the assembly and is not supported. The captive design is essentially a more compact version of the thrust rod style actuator, making it best suited for pushing or pressing applications where the load is guided and there is no radial force on the screw.

NSK MBSA Motorized Ball Screw Actuator

Motorized Ball Screw Actuator Compact, high-accuracy positioning through seamless mechatronic integration.

For life-critical medical, imaging and laboratory applications, NSK integrates a highresolution motor with our precision-machined ball screw to create the MBSA Motorized Ball Screw Actuator. The result: smooth, near-silent, extremely reliable and ultra-accurate motion, improving efficiency and throughput while lowering costs.

Enabling Automation in Motion & Control.

Ball screws — MC HB 08-21.indd 18

WWW.NSKAUTOMATION.COM

8/11/21 3:43 PM

BEARINGS DEEP GROOVE HYBRID BALL BEARINGS FROM NKE IN VARIOUS CAGE DESIGNS: WITH BRASS CAGE (TOP LEFT), STEEL SHEET CAGE (TOP RIGHT), POLYAMIDE CAGE (BOTTOM RIGHT AND BOTTOM LEFT)

BEARINGS: A TECHNICAL REVIEW BEARINGS ARE CRITICAL MECHANICAL COMPONENTS for motion applications. Bearings reduce friction by giving moving parts something to roll on rather than slide. Rotary bearings are designed with either metal balls or rollers and inner and outer surfaces (races) against which the rollers or balls travel. These rolling elements carry load and allow axes to spin freely. Most commonly, bearings encounter radial and axial load. A motion system’s bearings experience axial loads parallel to the shaft, while radial loads are perpendicular to the shaft. In certain applications, some bearings must withstand radial and axial loads simultaneously. motioncontroltips.com | designworldonline.com

WHAT’S THE DIFFERENCE BETWEEN BALL AND ROLLER BEARINGS?

With a limited contact area between the balls and races, ball bearings are not designed to handle loads as high as other bearing types. Instead, ball bearings are typically specified for light to moderate loads. However, the small surface area contact also minimizes friction-generated heat, making ball bearings a good choice for high-speed applications.

Conversely, roller bearings have cylindrical rollers. They’re often found in applications like conveyor belt rollers because of their increased surface contact with their races. This design allows the bearing to handle larger loads without deformation.

Their shape also permits a moderate thrust load, as the weight is distributed across cylinders instead of spheres.

WHAT KINDS OF APPLICATIONS USE NEEDLE ROLLER BEARINGS?

Needle-roller bearings operate where space is limited, such as an automotive application’s rocker-arm pivots or transmissions. These are roller bearings where the rollers’ length is at least four times its diameter. The larger roller surface area allows them to support much 8 • 2021

DESIGN WORLD — MOTION

19

ai1627492501660_HIWIN_Linear Stages_Ad_9x10.875.pdf

1

7/28/21

12:15 PM

STANDARD AND CUSTOMIZED

PRECISION

15 22 23

LINEAR STAGES

SINGLE & MULTI-AXIS

LMSSA High Acceleration LMX1K Powerful Motor

24

NPS Nanometer Accuracy

KK BALLSCREW STAGE Perfect for General Automation

SAVE DESIGN TIME. SAVE ASSEMBLY TIME. PARTNER WITH THE EXPERTS.

COMPARE PERFORMANCE & DOWNLOAD CAD linearstages.hiwin.us 12455 Jim Dhamer Dr, Huntley IL 60142

HIWIN - MC HB 08-21.indd 20

Phone: (877) 804.4946 Fax: (847) 827-2291

www.hiwin.us

8/11/21 3:44 PM

BEARINGS TAPERED ROLLER BEARINGS

IGLIDE R PLASTIC PLAIN BEARINGS ARE DESIGNED WITH A LOW-COST, SELF-LUBRICATING MATERIAL THAT IS CHARACTERIZED BY LOW COEFFICIENTS OF FRICTION AND GOOD WEAR RESISTANCE. higher radial loads. Often, a cage contains needle rollers. In some designs, the outer race is machined into the housing interior. There are two different arrangements for needle roller bearings — a radial arrangement (rollers running parallel to the shaft) and a thrust arrangement (rollers are flat, in a radial pattern, and run perpendicular to the shaft).

WHAT ARE THRUST BEARINGS?

Thrust ball bearings are used in applications with primarily axial loads and handle shaft misalignment. These bearings are also found on high-speed axes in the aerospace and automotive industries. Thrust roller bearings also transmit load from one raceway to the other to resolve radial loads. In addition, self-aligning capabilities make thrust roller bearings immune to alignment errors and shaft deflection.

Tapered roller bearings have tapered rollers between tapered inner and outer ring raceways — the rollers are angled, so the rollers’ surfaces converge at the axis of the bearing. These bearings are the only bearing type that can concurrently handle significant axial and radial loads.

A single row tapered bearing only handles excessive axial loads from one direction; however, if adjusted against a second tapered roller bearing, that axial load is counteracted. This design function allows the bearings to handle increased radial and axial loads from several directions.

Tapered roller bearings can account for only a slight angular misalignment of the inner and outer ring — a few minutes of arc at the maximum. Like other roller bearings, tapered roller bearings always carry a minimum load, especially in high-speed applications. Highspeed applications create an environment where friction and inertial forces can damage rollers and raceways if they disengage.

PLAIN BEARINGS EXCEL IN MEDICAL AND OTHER APPLICATIONS

With no moving parts, plain bearings have the least complicated design. They are often cylindrical, but bearing designs can differ depending on the motion profile expected.

Plain thrust bearings provide the same functions as roller-based thrust bearings but use pads arranged in a circle around the cylinder. The pads create wedge-shaped areas of oil inside the bearing. This lubrication prevents hard component contact with the rotating disk that supports the application’s thrust.

Of all bearing types, plain bearings are often the least expensive. Frequently, they are made of graphite, bronze, or plastics like PTFE, polyacetal, and Nylon. Innovation in materials science has dramatically improved plastic plain bearing efficiency. As a result, all types of plain bearings are compact, lightweight, and can carry substantial load.

XIROS B180 RADIAL DEEP GROOVE BALL BEARINGS WITH STAINLESS STEEL BALLS ARE A COST-EFFECTIVE OPTION FOR SMOOTH, DRY-RUNNING OPERATION. THESE MAINTENANCEFREE BEARINGS ARE SELF-LUBRICATING AND RESISTANT TO DIRT, CHEMICALS, AND SEAWATER. motioncontroltips.com | designworldonline.com

8 • 2021

A TAPERED ROLLER BEARING FROM FERSA. Increasingly, the growing use of plain plastic bearings means this type of solution must meet FDA, RoHS, and other industry standards. Some bearings even meet EU directive 10/2011/EC standards for material manufacturing process criteria.

There is also competing technology in dry bearings. These components have rolling elements but are specifically designed for applications where lubrication is not an option or where shortened design life is acceptable — in some medical devices, for example. Some plain bearings self-lubricate, and some do not.

Plain bearings made of polyacetal or bronze keep lubricant in their walls. However, with this design, additional lubrication is needed to maximize performance. Other plain bearings use the material itself as the lubricant — such as those made of PTFE or metalized graphite.

HOW TO PICK THE PROPER LUBRICANT FOR A ROTARY BEARING

There are two basic types of lubricant for bearings: grease and oil. Grease lubricants are created through a process of mixing oil with various thickeners.

Typically, grease outlasts other lubricants in rotary bearing applications; the thickeners sustain the lubrication between rolling elements and raceways. Grease with extreme pressure additives can extend bearing life as well when subject to higher forces. Still, oil is more common for open bearings or bearings in applications where high speeds or low torque is expected. Oil lubricants’ lower viscosity also introduces less drag than grease as the rolling elements move through the lubricant.

Temperature, application rpm, mode of oil delivery, and environmental contaminants determine the best choice for a given application. For example, operating temperature is the primary factor in deciding which oil viscosity will work in a given application. Excessive oil thickness increases

DESIGN WORLD — MOTION

21

Motion Systems Handbook WITH THE GEOMETRY OF THEIR DESIGN, TAPERED ROLLER BEARINGS CAN WITHSTAND COMBINED LOADS (AXIAL AND RADIAL). IN ADDITION, THIS DESIGN ALLOWS ROLLING MOVEMENT WITHOUT THE ROLLERS SLIPPING OFF THE TRACKS OF THE OUTER AND INNER RINGS. FERSA HAS A WIDE RANGE OF TAPERED ROLLER BEARINGS CONSISTING OF DETACHABLE ELEMENTS THAT MAKE THEM EASILY ADJUSTABLE IN APPLICATIONS.

the torque needed to make the rotary bearing spin, while an oil that’s too thin will not maintain the protective layer necessary for metal-on-metal contact prevention.

Grease is often selected for its viscosity. Oils may drain or leak from a bearing, while greases are solid enough to remain where they are applied. This makes it a better option for applications that will be shut down occasionally, as the grease will stay in the part and prevent the potential for dry starts when the application is turned on again.

This leakage resistance is also crucial for applications in environments where contamination is not an option, such as food processing applications. Additionally, there are greases available that are specially designed for environments with food. Tightlypacked greases can also help block contaminants from entering a bearing, which is useful in environments with dirt or water. These contaminants can then be removed during regreasing.

APPLICATIONS FOR ROTARY BEARINGS

Bearings can be found in endless industrial and consumer designs. Case in point: deep groove ball bearings are often found in small to medium-sized electric motors because they can accommodate both high speeds and radial and axial loads. Self-aligning ball bearings, on the other hand, 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. Yet, it is essential to note that these bearings can be one of the most difficult to install.

Tapered roller bearings need support for axial and radial loads. These bearings can also be found in gearboxes where they mount with a second bearing of the same type in a face-to-face or back-to-back 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.

Leading Supplier of High Performance Engineered Components for the Fluid Power Industry

Specializing in Plastics Prototype to Short Run to Production Quantities

Fluid Handling Components Supplied to Your Specifications

Plastic & Metal CNC Turned Adapters

Custom Milled Flowmeters

High Performance Custom Seals

Custom Molded Caps & Housings

Machined Nozzles

Customer Machined Flanges

Supplying High Performance Components for the Fluid Power Industry in the following materials: ABS, Aluminum, Brass, Bronze. Acetal, DELRIN®, HDPE, KYNAR, NORYLTM, NYLON, Stainless Steel, PEEK, Polycarbonate, Polypropylene, Polysulfone, PPS, PCTFE, PTFE, PVC, Rulon®, TEFLON®, TorlonTM, UHMW, ULTEMTM

www.nextlevelmanufacturing.com • Phone: 608-975-7424 NLM Ad - FPW 7-21_Vs3.indd 1

7/12/21 3:34 PM

BELTS & PULLEYS

BELT DRIVE SYSTEMS AND BELT TEETH PROFILES ONE OF THE MOST COMMON and oldest methods of power transmission are belt drive systems. Industrial belt drives typically consist of belts that wrap around drive pulleys, that are in turn driven by electric motors.

Engineers still use belt drives primarily because modern belt drive systems require little if any maintenance. They’re also less expensive than chain drives and also quieter and quite efficient.

What’s more, the tensile members of today’s belts – cords embedded into the belt rubber that carry the majority of the belt load – are stronger. Made of polyester, aramid, fiberglass or carbon fiber, these tensile cords make contemporary belt drives thoroughly modern power-transmission devices. motioncontroltips.com | designworldonline.com

Belts & pulleys — MC HB 08-21.indd 23

Manufacturers generally describe belts and pulleys with five main geometries. Pitch diameter is the drive pulley’s diameter. Center distance is the distance between two pulley’s 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.

For toothed belts (also called synchronous belts), the pitch is the number of teeth per some length. So for instance, a 3-mm pitch means the belt has one tooth every 3 mm.

TIMING BELT TOOTH PROFILE FOR HIGH-SPEED APPLICATIONS

Synchronous belts (also referred to as timing belts) are used in a wide range of power transmission and transport applications that require good positioning accuracy. Tensile cords molded into the belt material help eliminate or minimize belt stretch, and positive engagement between the teeth of the belt and the pulley make synchronous belts less likely to experience slip than V-belts. In addition, synchronous belts excel in applications that require high operating speed — especially when high torque or thrust loads are involved.

One of the primary factors that allows a synchronous timing belt to operate under highspeed conditions is the belt’s tooth profile, which influences the strength of the teeth, the meshing characteristics between the belt and pulley, and the belt’s tendency to ratchet, or jump teeth.

Synchronous belt tooth profiles can be divided into three main categories — trapezoidal, curvilinear, and modified curvilinear — although manufacturers offer their own proprietary 8 • 2021

DESIGN WORLD — MOTION

23

8/11/21 3:44 PM

BELTS & PULLEYS variations on these types (especially the modified curvilinear shape) to provide specific operating characteristics such as low noise, high speed, or better accuracy.

The original — and still widely-used — tooth profile for synchronous belts is the trapezoidal profile. This tooth design offers better efficiency than V-belt drives, but the trapezoidal shape leads to high stresses at the points where the belt and pulley mesh, which can cause rapid wear in high-speed applications.

The curvilinear tooth profile has a rounded shape and deeper tooth profile than the trapezoidal design. These features reduce stresses at the belt-pulley interface, allowing curvilinear designs to transmit higher forces and withstand higher speeds. The deeper tooth profile also reduces the possibility of ratcheting. However, the required clearance between belt teeth and pulley grooves is larger than for trapezoidal designs, meaning curvilinear designs have higher backlash than trapezoidal profiles.

An historical note; the curvilinear tooth profile for synchronous belts was originally developed by Gates, and belts with this new profile were designated “HTD” belts. (HTD stands for “high torque drive.”) Although each manufacturer has its own name for belts with this tooth design, the HTD designation is still used to identify a timing belt with the curvilinear tooth profile.

Tooth profiles classified as modified curvilinear often have a design that is proprietary to the specific manufacturer, but these designs can be identified by a lower tooth depth and higher flank angle than standard curvilinear designs. The modified curvilinear profiles were developed to overcome some of the drawbacks of the curvilinear design, with the most noticeable improvements being lower backlash and higher torque and force capabilities, thanks to better tooth flank contact, lower stresses on belt teeth, and less tooth deformation. These characteristics also make modified curvilinear belt designs the least likely to experience ratcheting, even under high loads.

These performance improvements — especially higher torque/ force and reduced ratcheting tendency — mean that modified curvilinear designs are typically the best choice for high-speed applications, particularly when quick acceleration to maximum speed is required or when the belt is moving heavy loads.

Noise can be problematic in synchronous belt drives, especially in high-speed applications. This is due to two factors.

First, the action of the belt meshing with the pulley causes impact noise. Second, as the belt teeth engage with the pulley grooves, air is trapped between them and then evacuated, making a sound similar to air escaping from a balloon — a phenomenon that can be especially prominent at higher belt speeds.

The improved belt-pulley meshing characteristics and increased tooth contact of modified curvilinear belts typically make them the least noisy of the three designs. However, noise is not just a product of the belt and pulley dynamics. The amount of pre-tension applied to the belt and the materials of the belt and the pulley also play a role in how much noise a synchronous belt produces.

AN ILLUSTRATION SHOWS THE THREE MAIN CATEGORIES OF SYNCHRONOUS BELT TOOTH PROFILES— TRAPEZOIDAL, CURVILINEAR, AND MODIFIED CURVILINEAR.

POWER TRANSMISSION-PART CONVEYING

PYRATHANE® BELTS Lifetime Warranty Against Manufacturing Defects

LINE SHAFT CONVEYOR BELTS Original Equipment and Connectable

CUSTOM MADE IN INCH, METRIC & O-RING SIZES • Round, Flat and Connectable Polyurethane Belts • Very Clean Operation • Eliminates Tensioning Devices • Exceptional Abrasion Resistancexxxxxxxxxxxxxx AN ISO 9001 CERTIFIED COMPANY

641.792.2405 sales@pyramidbelts.com DESIGN WORLD — MOTION

pyramidbelts.com

25 19Pyramid_4x475_PC.indd 1

12/4/2018 4:56:13 PM

ISO 9001:2015 | AS9100D ITAR Compliant - DDTC Registered DFARS Compliant NIST SP 800-171 Compliant We deliver precision gears, high-quality machined parts, and molded components for thousands of applications.

• Prototype • High-Volume Production • Custom Design • Engineering Support • Precision Manufacturing • Assembly

CNC Swiss Turning l CNC Milling & Turning l Gear Cutting | Bevel Gear Cutting Rapid Tooth Cutting Only Capability As an online engineering resource, SDP/SI provides: Engineered Mechanical Solutions Design Tools and Calculations Product Specifications 3D CAD Models

Shop with us 24 / 7 87,000 Component Choices Gears, Timing Belts, Pulleys, Couplings, and More

For Metric Gears or Bearings, Check into our sister companies: SDP/SI looks forward to working with you!

Send an RFQ – we can quote from a 3D model or drawing

Supplying North America with Metric Gears https://qtcgears.com

The Bearing Marketplace https://qbcbearings.com

Stock Drive Products / Sterling Instrument - 250 Duffy Avenue, Hicksville NY | www.sdp-si.com | (516) 328-3300

BRAKES & CLUTCHES

BRAKES AND CLUTCHES IN MOTION SYSTEMS

IN POWER TRANSMISSION and motion systems, brakes stop rotating loads.

They’re used in applications that need accurate stopping of the load with motors that stop as well. A machine’s motor frame size and horsepower will dictate the brake type suitable for a given design.

But first, there are several key parameters that dictate whether a clutch or a brake is suitable for the application at hand. For starters, consider the mode of motion and whether the axis needs a brake or clutch.

motioncontroltips.com | designworldonline.com

Clutches generally bridge moving machine sections to shape relative motion, while a brake’s main job is to stop and hold rotating elements. Several design variations exist, and a main differentiating factor is the way in which a brake or clutch engages. Some options include mechanical, electric, and fluidic.

Brakes and clutches using fluid-power actuation usually include a piston to physically engage friction discs for torque transmission from an input to an output. Hydraulically and pneumatically actuated clutches and brakes are quick-response units that act on fluid pressure and piston mass, so engagement speed follows control pressure.

8 • 2021

AN EXAMPLE OF AN APPLICATION USING BRAKES COMES FROM CONVEYING. HERE, A BXW POWER-OFF ENGAGED BRAKE FROM MIKI PULLEY HALTS A MOTORIZED CONVEYOR ROLLER WHEN SYSTEM POWER IS DISENGAGED. THE BXW BRAKES USE INTERNAL COMPRESSION SPRINGS TO PROVIDE POWER-OFF, FAIL-SAFE BRAKING WITH THE PRIMARY MOVING PART BEING THE ARMATURE PLATE. WHEN ACTUATED, THE BRAKE COMPRESSION SPRINGS PUSH THE ARMATURE PLATE INTO THE FRICTION DISC WHEN POWER IS DISENGAGED. DESIGN WORLD — MOTION

27

Motion Systems Handbook

You don’t need to be an expert in clutches, brakes or torque limiters.

Because we are.

We Are Your One-Stop Shop For Motion Control Solutions.

When it comes to high-performance, custom-made clutches, brakes and torque limiters, we aim to please. Which is why you’ll find Engineering, Production, Sales, and Product Support all under one roof. All to put you at ease, knowing that we’ll deliver the perfect solution for your applications.

The Mach III Advantage: Rapid Custom Solutions From slight design modifications to unique, clean-sheet creations, we can present you with a customized design solution in about 48 hours.

Built To Order We specialize in high variation, low quantity production. All products are built-to-order, allowing even catalog models to be bored to fit the exact shaft and key size required.

Reliable Ship Dates Every purchase order we receive is confirmed with a ship date that we meet or beat 98% of the time. Lead times for Standard Products: 2–5 weeks and Custom: 3–6 weeks.

To learn more, contact us at 859–291–0849 or email us at engineering@machiii.com

A few caveats though: In many clutches, full piston force transmits through a bearing — effectively a wear point — to let the body rotate as the housing stays put. Here, the bearings and high loads also limit operating speed. Brakes using fluidpower actuation don’t need such bearings.

Brakes and clutches using mechanical actuation include a lever for mechanical advantage to trigger engagement and disengagement. This levering usually works to squeeze friction discs together for torque transmission. When the mechanism moves, the clutch or brake condition changes from engaged to disengaged or vice versa. Some such brakes and clutches have a locking mechanism to keep the unit as it is until repowering. Such clutches and brakes have no bearings to fail; are fairly speed tolerant; come in optional one-position setups; are unaffected by power failures; and offer automatic overload release during over-torqueing or locking.

On the other hand, many mechanically actuated clutches and brakes don’t automatically disengage during power loss — and most need adjustments to compensate for wear.

Clutches and brakes that are electromagnetically engaged (or disengaged, depending on the design) use a magnetic coil to generate a magnetic flux — either to move an armature from friction-disc contact or to move the armature for squeezing discs together. That’s because electromagnetic clutches and brakes are either electrically activated or spring-appliedelectrically-deactivated setups. The latter does double-duty as a failsafe during power loss.

SPOTLIGHT ON ELECTROMAGNETIC POWER-OFF BRAKES

A specific type of electromagnetic brake is a power-off brake. They’re commonly used in motion control applications for stopping or holding a load (or both), especially on vertical axes or for emergency stop functionality in servo applications. Power-off brakes are so named because the brake is engaged when power is removed from the system — either intentionally or accidentally. (Power-off brakes are also sometimes referred to as fail-safe brakes.)

While there are many types of power-off brakes, electromagnetic versions are typically used in servo applications. Two designs of

28

MACH III_1/2 Page ISLAND Ad_FINAL_12.21.20.indd 1

12/21/20 10:28 AM

DESIGN WORLD — MOTION

BRAKES & CLUTCHES

electromagnetic power-off brakes — spring-engaged and permanent magnet — are preferred for applications that require high torque, low backlash, and the ability to be customized to the application.

SPRING-ENGAGED POWER-OFF BRAKES

Spring-engaged (also referred to as spring-applied) brakes are disengaged electrically via electromagnetic force when power is applied and engaged mechanically via spring force when power is removed. Their construction is relatively simple, with a coil, an armature plate, a friction disc, a pressure plate, springs, and a hub. The hub is connected to the shaft of the motor or component to be braked.

To disengage the brake, for normal operation, voltage is applied to the coil. The coil creates an electromagnetic field, and the magnetic flux from this field attracts the armature plate to the coil, which compresses the springs. This releases the friction disc and allows it to rotate, along with the hub and the connected load.

To engage the brake, for stopping or holding, power is removed from the coil. The electromagnetic (attractive) force dissipates and the armature plate moves away from the coil. This decompresses the springs, so they push the armature plate against the friction disc, trapping the friction disc between the armature plate and the pressure plate. This stops (or holds stationary) the friction disc, hub, and load.

Spring-engaged electromagnetic power-off brakes are highly customizable, with the ability to use different spring forces, friction materials, and operating voltages. Some manufacturers of spring-engaged electromagnetic brakes tout their high efficiency, since the amount of power supplied to the brake can be reduced once the armature plate is engaged. (It takes much less power to hold the armature plate in place once it has been attracted to the coil and the springs have been compressed.) It’s also possible, for brakes that have been appropriately sized, to use over-excitation — the momentary application of voltage higher than rated voltage — to reduce the brake’s response time. However, spring-engaged designs typically exhibit some backlash, so may not be suitable in applications where precise stopping or holding is critical.

The key to permanent magnet brake operation is the use of magnetic forces from both the coil and the permanent magnets. When voltage is applied to the coil — to disengage the brake for normal operation — an electromagnetic field is created. This field opposes and negates the field of the permanent magnets. Since there is no magnetic field to attract the armature to the coil, an air gap is created between them. And with no contact (and, therefore, no friction) between the armature and the coil, the armature, hub, and connected load are free to rotate.

To engage the brake — for stopping or holding a load — power is removed. With no power to create an electromagnetic field to counteract that of the permanent magnets, the field produced by the permanent magnets acts on and attracts the armature to the coil, and this metal-onmetal contact creates the braking force.

Permanent magnet electromagnetic power-off brakes have a good torque-to-size ratio and can operate at the high speeds servo motors often require, since there are no moving parts. Permanent magnet versions also don’t exhibit backlash and are typically preferred in high-precision positioning applications. However, these brakes require a consistent, narrow range of current (and, therefore, voltage) to counteract the force of the permanent magnets and release the brake. Conditions that could cause fluctuations in current, such as temperature changes or extreme temperatures, aren’t suitable for permanent magnet power-off brakes.

PERMANENT MAGNET POWER-OFF BRAKES

Permanent magnet power-off brakes are disengaged electrically with the application of power and engaged magnetically when power is removed. These designs incorporate both an electromagnetic coil and permanent magnets, as well as an armature plate and a hub.

motioncontroltips.com | designworldonline.com

8 • 2021

DESIGN WORLD — MOTION

29

Motion Systems Handbook COURTESY OF HELUKABEL

FUNDAMENTALS OF INDUSTRIAL CABLING ELECTRICAL CABLING IS A critical component in motion control

system design. Premature failures can result if you use something other than continuous flex industrial cabling, which are designed to cope with the tight bending radii and physical stress associated with motion control applications. A regular cable typically manages 50,000 cycles, but a flexible cable can complete between one and three million cycles.

Flexible cables can be divided into two

COUR

TESY

OF NE

W EN

GLAN

D WIR

E TEC

HNOL

OGIES

types: those with conductors stranded in layers inside the cable, and those that have bundled or braided conductors.

Cables with stranded layers are easier to produce, and usually less expensive. The cable cores are stranded firmly and left relatively long in several layers around the center and are enclosed in an extruded tube-shaped jacket.

However, this design can lead to core rupture.

Bundled designs feature braided conductors that surround a tension-proof center. A pressure filled outer jacket ensures the cores cannot twist, so these cables are often stiffer than standard cables, but last longer in constant flex applications.

Flat cables can incorporate power, signal, and video conductors as well as air or liquid tubing and fiber optics in a single compact cable suitable for continuous flexing.

30

DESIGN WORLD — MOTION

Cables — MC HB 08-21.indd 30

8 • 2021

Flat cables with silicone jacketing resist abrasion and other harsh environmental impacts and will even self-heal minor nicks.

To select the right cables, determine the application type, such as whether it will be stationary or moving, and what type of movement it is — flexing, torsion, or both?

If there is bending or motion involved, the bend radius must be specified. The bend radius depends on the wire gauge and kind of conductors used. With continuous flexing, conductors containing multiple strands of fine-gauge wire generally last the longest.

MAKING THE CONNECTION

Most cable assemblies use some type of interconnect device to transmit the signals from the cable to the motor or drive. Commonly used connectors include M12 and M8 connectors, which are circular connectors with a 12- or 8-mm locking thread used for sensors, actuators, Fieldbus and industrial Ethernet, primarily in factory automation applications. Often with ratings of IP65, IP68 and IP69K, they are ideal for washdown and corrosive environments.

High-speed, miniature connectors are growing in use in industrial automation, where signal density, electrical performance, and mechanical dependability in smaller package sizes are critical for efficient, compact and accurate machines (see sidebar on page 32 on Single-Pair Ethernet for more on modern connectivity designs). Modular connectors, micro connectors, heavy-duty connectors with locking systems, and more are used to provide constant, reliable connectivity for high-vibration environments.

Where rotating motion is present, slip rings should be used.

These electromechanical connectors transmit electrical signals, power and data from a stationary structure to a rotating machine. motioncontroltips.com | designworldonline.com

8/11/21 3:46 PM

Material handling involves many different facets of the automation industry such as automated guided vehicles, storage and retrieval systems, conveyor systems, as well as palletizing and sorting systems. Its used in industries such as automotive, mining, food and beverage, medical, and e-commerce making it a fixture in industrial applications. – HELUKABEL® offers its customers a superior, cost-effective solution.

Motion Systems Handbook

WHAT IS SINGLE PAIR ETHERNET (SPE) AND HOW IS IT USED IN INDUSTRIAL APPLICATIONS? SINGLE PAIR ETHERNET (SPE) is a technology that provides Ethernet transmission over a single pair of copper wires, while also transmitting power to connected devices via Power over Data Line (PoDL).

Single Pair Ethernet was initially developed to meet the demands of the automotive industry — smaller, lighter cables and connectors for transmitting data from the numerous sensors involved in adaptive cruise control, parking-assist, autonomous driving, and other onboard systems. In fact, the lower data loads and shorter distances required in automotive applications were the perfect fit for early SPE developments.

But as the technology evolved, companies began seeing its potential in other applications — especially manufacturing and building automation — and the SPE Industrial Partner Network was developed. This association of manufacturers promotes Single Pair Ethernet as the “basis for establishing the IIoT” and also supports standards for transmission protocols, cabling, and device components.

Traditional Ethernet requires two pairs of wires for data transmission rates of 100 Mbps, or four pairs of wires for 1 Gbps transmission rates. Single Pair Ethernet uses just one pair of wires to transmit data at rates of 1 Gbps for distances up to 40 m, or at 10 Mbps up to 1000 m — offering a significant reduction in cable size, cost, and complexity. And although traditional Ethernet has been implemented all along the automation pyramid, devices at the

THE INTERFACES (CONNECTIONS) FOR SPE IN INDUSTRIAL APPLICATIONS ARE GOVERNED BY THE IEC 63171-6 STANDARD, WITH DATA SPEED AND TRANSMISSION LENGTHS BEING COVERED BY THE ETHERNET PROTOCOL STANDARDS LAID OUT IN IEEE802.3.

COURTESY OF SPE INDUSTRIAL PARTNER NETWORK lowest level — the field level — are still often controlled by fieldbus protocols. SPE offers an Ethernet solution that can be implemented at all levels — from the cloud to the field — eliminating the need for gateways and other hardware that are required for various networks to “talk” to each other.

Smaller cables also use smaller connectors — another benefit of SPE in space-constrained applications or those with numerous, small devices at the field level. And the smaller bend radius of a thinner cable makes installation, routing, and management less cumbersome and more flexible, both literally and figuratively.

With the ability to transmit power — up to 50 W — together with data, SPE is positioned to be an ideal solution for IIoT applications, in which many field-level devices require power along with fast, real-time communication to higher-level controls or to the cloud. And for applications that require more than 50 W of power, hybrid solutions using four conductors are available, taking power capabilities up to 96 W at 24 V or 392 W at 48 V.

HOW DOES SPE ACHIEVE FAST ETHERNET COMMUNICATION WITH JUST ONE PAIR OF WIRES WHEN TRADITIONAL ETHERNET REQUIRES FOUR PAIRS?

SINGLE PAIR ETHERNET ENABLES ETHERNET COMMUNICATION FROM THE TOP TO THE BOTTOM LEVEL OF THE AUTOMATION PYRAMID. COURTESY OF MIAC AUTOMATION

32

DESIGN WORLD — MOTION

8 • 2021

Classic 1 Gbps Ethernet uses a Cat 5 cable with four pairs of wires and operates at frequencies up to 100 MHz. Each pair can send and receive data, allowing transmission rates up to 1 Gbps. Single Pair Ethernet uses just one pair of wires, but operates at frequencies up to 600 MHz. In this wide frequency band, some frequencies send data and others receive data, enabling 1 Gbps transmission speeds with just one pair of wires.

motioncontroltips.com | designworldonline.com

Motion Systems Handbook

FUNDAMENTALS OF PROGRAMMING CONTROLLERS MOTION CONTROLLERS CALCULATE and generate a commands for the motor or actuator to move. These are known as motion trajectories and involve calculating the right speed and position. These commands can be sent to a drive that develops the necessary current to drive the

a more open architecture and modular design. They’re also more capable than PLCs at monitoring and controlling a large number of I/O, such as in a large processing plant or a complex automation system. They do this because data can be exchanged between devices and applications in different domains, such as motion and process control.

motor. In a closed-loop system, there will also be some type of feedback from the process that helps to adjust the commands in order to meet system requirements. Controllers can use a number of algorithms needed to generate commands including control loops, interpolators and step generators.

Controllers can be categorized in a number of different ways depending on what is prioritized. For instance, they can be divided by the physical format (plug-in board, stand-alone, embedded,) or by function (PLC, PAC, motion controller) or even by architecture (distributed or centralized).

Standalone controllers are complete systems that include all electronics, power supplies and external connections that mount to one physical enclosure.

These controllers fit into machines to command applications consisting of either a single motion axis or multiple motion axes.

PC-based controllers include a basic PC motherboard or ruggedized industrial PC as well as PC-type hardware components and a high-speed dedicated bus that transmits information to and from the processor.

PC control requires the same inputs and outputs as a basic PC, as well as interfaces to factory floor devices. Here, typical I/O includes electric motors and other actuators, as well as discrete sensors and other mechanical components.

Programmable logic controllers (PLCs) are microprocessor-based electronic components that serve as the programmable smarts for simple or isolated applications. Now they’re also finding increased use on integrated machines and more complex automation setups. PLCs have evolved from their early days into controllers with a reputation for unbeatable reliability.

A step beyond PLCs are programmable automation controllers or PACs. These industrial controllers combine the functionality of a PLC with the processing capability of a PC. However, because there is no industry-standard definition of a PAC, the distinction between PACs and PLCs can be a bit blurry. Higher-end PLCs now incorporate some of the features considered PAC territory. In fact, many PLCs now include standard programming languages, the ability to expand functionality through add-on modules, and connectivity to various bus systems.

However, PACs still differentiate themselves from PLCs by employing

PROGRAMMING CONTROLLERS

Manufacturers of motion controllers provide some way for users to program their devices. This usually takes the shape of some type of graphical user interface (GUI), sometimes integrated with other automation software. The interface lets users write and edit control programs as well as monitor progress of an operation. Options for programming include visual techniques such as a drag-and-drop method from a menu of options or writing programs in Visual Basic, C, C++ or other languages.

The GUI can be as simple as a few buttons on a controller or a more standard basic keyboard. For extremely simple and uncomplicated applications, some controllers allow programming right on the controller itself via buttons or an interactive touchscreen. Stand-alone or rack-mountable motion controllers often have keypad entry where users can program the controller in this way. Another common method is via computer and keyboard.

Many companies have motion APIs (application programming interface) that let designers program controllers. They can also feature sample programs along with libraries of functions and other tools for diagnostics and tuning.

PLC-based motion control has also become more common. Here, programming is via industry-defined standards such as IEC 61131 (PLCopen) which takes advantage of existing programming methods that many engineers are already familiar with such as ladder logic diagrams and function block diagrams, as well as structured text and sequential function chart languages.

PACs also use the IEC 61131-3 programming languages (ladder diagram, function block diagram, sequential function chart, instruction list, or structured text), and some include standard PC programming languages such as C/C++, so familiarity is retained and the learning curve for programming is low, regardless of prior experience or expertise.

DEEP DIVE: DUAL-LOOP CONTROL FOR SERVO SYSTEMS

Consider a special case; a dual-loop control for a servo system. In servodriven systems, feedback for position, velocity, and/or torque control is typically provided by a rotary encoder or resolver mounted to the motor.

But mechanical components and connections in the drivetrain — such as

AS THIS ILLUSTRATION FROM ABB SHOWS, DUAL-LOOP CONTROL IS OFTEN USED FOR PRECISE POSITIONING OF LINEAR AXES, WITH A ROTARY ENCODER ON THE MOTOR AND A LINEAR ENCODER ON THE LINEAR AXIS.

34

DESIGN WORLD — MOTION

8 • 2021

motioncontroltips.com

|

designworldonline.com

A TYPICAL DUAL-LOOP CONTROL SCHEME IS SHOWN HERE, COURTESY OF GALIL. NOTICE THAT THIS CONTROL METHOD ALSO USES VELOCITY FEED-FORWARD COMMANDS TO COMPENSATE FOR PHASE LAG BETWEEN THE INNER (VELOCITY) AND OUTER (POSITION) LOOPS. gearboxes, ball screws, and couplings — are not perfectly rigid and introduce backlash, compliance, and windup into the system. This lack of rigidity causes a discrepancy between where the load “should” be based on the position of the motor shaft, and where the load is actually located. If the servo control system is based only on the motor feedback, the desired position may never be reached, and the system can experience instabilities such as oscillations and hunting.

In systems that exhibit backlash, compliance, and windup (that is, virtually all motion systems) but that also need accurate position control, a second encoder is required to directly measure the position of the load. This method of using two feedback devices — one on the motor and one located at the load — is typically referred to as dual-loop control, or dual-loop feedback.

There are several methods of operation with dual-loop control, but in the most basic method, the controller first closes the inner loop, which is the velocity control loop. The velocity control loop receives feedback from the motor encoder, and this feedback determines the appropriate velocity feedback gain (Kv), which imparts a damping effect on the system to reduce oscillations.

Note that velocity feedback gain (Kv) is similar to derivative gain (Kd), except that velocity feedback scales only the velocity measured by the motor encoder, whereas derivative gain scales the derivative of the position error. Velocity feedback gain is often used in dual-loop control.

Next, the controller closes the outer loop, which is the position loop. Feedback from the load encoder is used to determine the appropriate proportional and integral gains (Kp and Ki). Recall that proportional gain is directly proportional to the positioning error and influences the system’s stiffness, while integral gain accumulates the position error over time and “pushes” the system to zero positioning error.

The servo control system may also include a current control loop, positioned inside the velocity loop. Although in this scenario there would be three control loops, the term “dual-loop control” simply refers to the two control loops — position and velocity — that receive direct feedback from the encoders.

Unlike traditional cascaded control loops, in dualloop control, the velocity loop response is independent of the feedback (and, therefore, the resolution) of the load encoder. Likewise, the position loop response is independent of the feedback from the motor encoder.

Dual-loop feedback systems can use two rotary encoders or one rotary and one linear encoder.

Rotary-linear combinations are most common on linear motion systems, where there is a rotary encoder (or resolver) located on the motor and a linear encoder mounted on the linear axis.

DESIGN WORLD — MOTION

One servo drive for any ethernet!

Seamless Connectivity

The new servo drive CMMT-AS offers connectivity of the hardware and software, great efficiency, compact design and easy operation.

• • •

For point-to-point and interpolated motion with focus on dynamic motion and precise positioning Direct fieldbus integration Quick and easy commissioning with the Festo Automation Suite festo.com/cmmt-as

35

EA Product Ads - CMMT-AS - Half Page-v2-wBleed-5.375x8.625.indd 1

7/8/2021 8:51:08 AM

Motion Systems Handbook THIS CONVEYOR’S GREEN BELTS TRANSFER PALLETS (CARRYING FLATSCREENS) TO THE ADJACENT LINE.

UPDATE ON VARIOUS MODULES FOR PALLET CONVEYORS PALLET CONVEYORS are those that move products on individual carriers or pallets for flexibility in assembly, automation, and inspection processes, with the ability to move products asynchronously in virtually any configuration imaginable, including curves, turns, and small elevation changes.

Beyond these basic movements, special modules for pallet conveyors can transfer products horizontally or vertically — to another conveyor or offline process — or reorient the pallet (and therefore the product) on the conveyor without changing the direction of transport. Note the conveyor units described here are often called conveyor modules because each one is essentially a complete section of conveyor — with its own drive mechanism, switches, stops, brakes, and (if necessary) enclosure.

36

DESIGN WORLD — MOTION

Conveyors — MC HB 08-21 V3.indd 36

HOW LIFT-AND-ROTATE MODULES WORK

Pallet conveyors are useful where product being transferred needs to be precisely located on the conveyor — typical for assembly or inspection operations. But if during the transfer some operations need to take place on different sides of the product, a lift-and-rotate module can facilitate this. These specialty conveyor modules lift the pallet slightly above the conveying media and rotate the pallet so that its orientation is changed ... but the original direction of transfer is maintained.

Lift and rotate modules are also useful on conveyors with rectangular layouts. Here, a lift and rotate unit placed at the corner (where the conveyor makes a 90° turn) ensures the pallet maintains the proper orientation relative to the direction of conveying, even after it turns the corner. In fact, typical lift and rotate designs allow for 90° and 180° pallet rotations, but some manufacturers offer turntable-style modules that can rotate the pallet in smaller, predetermined increments (provided there is no interference with the conveyor or other structures). Lift and rotate units are generally driven by pneumatic cylinders, but servo- and stepper-driven units are available when precise, controlled rotation is required.

LIFT-AND-TRANSFER CONVEYOR MODULES

Some operations require that the product be taken offline to a station separate from the conveyor line ... or to a secondary conveyor near the primary line. These include curing as well as buffering ... and inspection as well as processing. In these cases, a lift and transfer module (sometimes called a transverse conveyor) transversely moves 8 • 2021

motioncontroltips.com | designworldonline.com

8/11/21 3:46 PM

CONVEYORS VERTICAL TRANSFER UNIT EXAMPLE COURTESY MK NORTH AMERICA

better products. better solutions. the pallet. These conveyor modules lift the pallet a small distance above the conveyor and transfer it to a conveyor or workstation at right angles — 90° — to the direction of the primary conveyor. Transfer units are commonly bidirectional, meaning they can transfer pallets both to and from the primary conveyor.

Most lift-and-transfer units use pneumatic lifts to raise and lower the pallet and belt or chain conveying media to transfer the product horizontally. Standard units maintain the orientation of the pallet (meaning its orientation relative to the direction of conveying will change by 90° once it is transferred) although some manufacturers offer transfer units that can also rotate the pallet if necessary.

VERTICAL TRANSFER UNITS

Pallet conveyors were traditionally used to transport products in two, horizontal dimensions. But a type of conveyor module referred to as a vertical transfer unit or VTU allows pallets to be transferred vertically to a different elevation — above or below the primary conveyor. Elevation changes allow over-under conveyor designs, where a second conveyor segment runs above (or below) the main conveyor. They also allow automatic transfer of pallets to a workstation located at a higher or lower elevation than the conveyor.

Vertical transfer units can also be used for static operations that take place during product transport, such as temporary storage or buffering while a longer process – such as glue or adhesive curing – takes place. Vertical transfer units can be operated by pneumatic or electric lifts, with electric lifts allowing multiple, programmable stop positions and tight control over velocity.

DESIGN WORLD — MOTION

37

CONVEYOR EXPERTS. You’re an expert in what you do. So it only makes sense to work with an expert in conveyors. Whether it’s a single conveyor or a complete conveyor system, mk has the answer. mk North America is the conveyor expert you need. mk provides not only a better product, but also a better solution.

CONVEYORS

PALLET-HANDLING SYSTEMS

FLEXIBLE CHAIN CONVEYORS

www.mknorthamerica.com/DW

(860) 769-5500 info@mknorthamerica.com

Motion Systems Handbook

COUPLING SELECTION: ESSENTIAL CONSIDERATIONS COUPLINGS ARE near-ubiquitous motion system devices that connect two shafts.

Mechanical couplings are often found on rotating equipment like motors where they transmit angular position, velocity, and torque.

Here, we examine some of the most important parameters for selecting the right coupling for an application.

COUPLING SELECTION FUNDAMENTALS TEMPERATURE

The environment where the coupling will operate is one of the first questions that must be answered when selecting a coupling for an application. Understanding the myriad environmental variables a coupling might encounter is crucial during the early design stages of your motion system.

Environmental considerations include moisture, temperature, chemicals, vacuum — all important things to consider at the time of selection. What are we dealing with in all these different issues? For example, an aerospace application where engineers are using a coupling to control aperture on a telescope. In this situation, a coupling that can survive the vibration of an actual spacecraft during takeoff would be necessary.

38

DESIGN WORLD — MOTION

Additionally, other factors like handling the vacuum of space, extreme temperatures, and no outgassing would need to be examined.

Another application example would be a coupling in an autoclave’s environment. For an application like this, a coupling will need to survive high temperatures for short intervals.

A bellows coupling might be an option, but autoclave temperatures will often exceed the temperature capability of the epoxy in the Oldham. To work around this, an Oldham coupling with a PEEK disk might work. The disk not only does not outgas, but it can also withstand high temperatures.

SPEED

Certain applications are relatively easy to solve with most any coupling at 5,000 or even up to 10,000 RPM. Occasionally, though, couplings may get up near 25,000 RPM or even higher — 75,000, 80,000 RPM. The consideration engineers need to factor in is not just torque capacity, but how well balanced the coupling is for that type of speed they expect the coupling to encounter. If the coupling is not either balanced or symmetrical by nature, a vibration problem is likely because of the imbalance of the weight. This is an important, and often overlooked, consideration. As positioning devices are accelerating faster and faster, coupling balance is more important than ever.

8 • 2021

WINDUP

Often confused with backlash, windup is easy to overlook when selecting couplings for a motion system. But windup is an important consideration that can cause real problems if not factored in early in the design process.

First, windup and backlash are often confused. They are not the same. Windup is dampening. It’s dampening or cushioning. It is not an error in the coupling — It’s not ‘play.’ A jaw coupling provides a perfect example of windup: The spider compresses, and rebounds and it absorbs shock and dampens — that’s wind up, not error. Some couplings have different amounts of wind up. A bellows coupling or disc coupling, for example, has little windup. They are highly torsionally stiff.

Rigid couplings have almost no windup.

Windup is a good thing to have in your coupling design, especially for applications where frequent shock loads are expected, and a jaw coupling has been selected.

PICTURED HERE IS A RINGFEDER GWE 5117 SERVO-COUPLING EQUIPPED WITH AN EXPANDING MANDREL FOR FRICTIONLOCKED TORQUE TRANSMISSION. IT HAS A SPIDER ELEMENT AVAILABLE IN SOLID STANDARD FORM, MINIMIZING MOVEMENT AND ACHIEVING LONGER LIFE, OR DRILLED THROUGH THE CENTER.

motioncontroltips.com | designworldonline.com

TOOL-LESS ADJUSTMENT COMPONENTS • Adjustable handles and knobs replace standard hardware and can be used to torque components without tools.

• Levers can be used with Ruland shaft collars for quick installation and adjustment.

• Introductory offer: 10% off your next web order with code

DW202105

• Free 2-day shipping on all domestic web orders - no minimum value.

• Full product data, CAD files, technical information, and installation videos.

• Large stock on hand in our Marlborough, MA USA location.

EXPANDED COUPLING LINE • Stainless steel oldham couplings for high temperature and corrosion resistance.

• Controlflex couplings for encoders in single and double insert styles and speeds up to 25,000 RPM. • Slit couplings with bores starting at 1.5mm and speeds up to 70,000 RPM.

MODULAR MOUNTING SYSTEMS • Assortment of components that allow users to build small assemblies for mounting sensors, conveyor rails, machine guards, and more.

UNIVERSAL JOINTS • Friction bearing for high torque.

• Optional pre-designed kits make it easier to select the right system for your application.

• Needle bearing for accuracy and higher RPM. • Single and double styles available.

INDEXING PLUNGERS VIBRATION ISOLATING COMPONENTS • Rubber bumpers are ideal as end stops or mounting feet.

• Vibration isolation mounts can be sandwiched between components to dampen shock loads.

• Spring-loaded indexing plugers with or without lock-out.

• Designed to lock devices in-place for adjustable positioning.

• Both types can have studs or tapped holes.

www.ruland.com I sales@ruland.com

RULANDi)

Carefully Made Shaft Collars and Couplings

Motion Systems Handbook

SLIT COUPLINGS LIKE THIS FROM RULAND AND RELIANCE PRECISION ARE MANUFACTURED FROM 7075 ALUMINUM FOR LOW MASS AND INERTIA, AND ARE CAPABLE OF SPEEDS UP TO 70,000 RPM. DUTY CYCLE

Duty cycle is a critical but often overlooked consideration during the coupling selection process. Critical elements like types of motion, potential shock load scenarios, and start/stop situations should all be evaluated when selecting a coupling for your next motion system application.

Duty cycle, types of motion, continuous start/ stop and reversing, and asking, “how often is the system running?” These all come into play with selection. Selection error often occurs when the type of motion is not accounted for or when the number of cycles is not understood. Talk to the manufacturer, give them your duty cycle.

Here’s an application example of a duty cycle, hard start/stop, a system running at full speed and neither stops nor reverses abruptly. A jaw coupling is a good fit for these types of applications. Beam couplings can work well in these applications and also for many of the coupling types like the bellows type, and in most cases, the disc type.

This gradual start/stop cycle is a must, just for coupling life, because they can’t handle that hard stop and start shock loads.

On dampening, frequent starts and stops, high shock loads may require a coupling that can dampen the impulse load; again, jaw couplings are a good option. Selection error occurs when this is not accounted for. In that type of application, use a beam coupling. When asking for increased dampening, choose a jaw coupling.

Dampening application examples where there are different materials available, different hardness of material to change the dampening characteristics, are common in food processing OEM applications.

40

DESIGN WORLD — MOTION

DRIVES

DRIVES – POWERING MOTION SYSTEMS DRIVES SERVE AS the interface between control signals and an electric motor.

Matching the correct drive to the type of motor in an application is critical for getting the optimal performance out of a system. A wide range of drives are available depending on the needs of the specific application and motor type. In general though, drive types typically fall into two categories; ac and dc drives for ac and dc motors, respectively.

At the most basic level, an ac drive is used to control the speed of an ac motor. For an ac motor, speed is determined by the number of poles and the frequency. A typical way to control frequency is via pulse width modulation (PWM). A PWM drive outputs a train of pulses to a motor and by modulating the pulse width, making it either narrower or wider, delivers an ac current waveform to the motor.

One of the most common types of ac drives is the variable frequency drive (VFD). They operate by switching output devices on and off, which can be transistors, IGBTs (insulated gate bipolar transistors), or thyristors. VFDs can be either constant voltage or constant current, with constant voltage types being more common. They use PWM to control both the frequency and the voltage applied to the motor.

VFDs have a number of significant benefits including 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 becoming more important as motor efficiency continues to be a top design priority. Also, on motor start-up, VFDs can provide a crucial advantage. 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. With a VFD, the motor’s input starts off with low voltage and a low frequency, avoiding the motioncontroltips.com | designworldonline.com

REGENERATIVE DRIVES CAN RECOVER ENERGY AND FEED IT BACK INTO THE NETWORK SO THAT IT CAN BE USED BY OTHER EQUIPMENT. THESE ACS880 REGENERATIVE DRIVES FROM ABB ARE SUITABLE FOR APPLICATIONS WITH CYCLIC OR CONTINUOUS BRAKING, SUCH AS CRANES, ELEVATORS, CENTRIFUGES, DOWNHILL CONVEYERS AND TEST BENCHES. problem of high in-rush currents. Eliminating the in-rush currents upon start-up also gets rid of the excessive torque on components, increasing the life of the motor and reducing maintenance costs and the need for repair.

REGENERATIVE DRIVE BASICS

The main purpose of a motor is to convert electrical energy into mechanical energy. But when the motor’s synchronous speed is less than the rotor speed, the motor acts like a generator and converts mechanical energy into electrical energy. This energy is typically fed back into capacitors in the dc bus, but the bus can only handle a limited amount of voltage before the drive registers a bus overvoltage fault. Regeneration gives this energy somewhere to go.

Regenerative drives allow motors to 8 • 2021

produce positive torque or negative torque, in either forward or reverse rotation. This is referred to as “four-quadrant” operation. Regeneration takes place in quadrants II and IV, where the direction of the torque opposes the direction of motor rotation (clockwise rotation with counterclockwise torque, or counterclockwise rotation with clockwise torque).

When the motor operates in one of these two modes, a regenerative drive can take the electrical energy generated by the motor and feed it back to the ac power source or to a common bus that supplies two or more drives. A common bus provides additional energy savings in that the power is only converted from ac to dc one time. When it is regenerated to the bus and passed to another inverter, it doesn’t have to be converted. In either case—whether it is fed back to the source or to a common bus—the generated DESIGN WORLD — MOTION

41

POWER HAS COME FULL CIRCLE G A 8 0 0 A C D R I V E F O R I N D U S T R I A L A P P L I C AT I O N S

Your time is valuable. The new, easy-to-use GA800 AC Drive from Yaskawa gives you the power to make all of your operations better.

• Rest easy with legendary Yaskawa quality and embedded functional safety.

• Experience ultimate ease-of-use with DriveWizard® Mobile and optional Bluetooth® connectivity.

• Enjoy incredible torque production and network connectivity.

Your days are complicated enough. Let us help simplify them. To learn more, visit or call Yaskawa today at 1-800-YASKAWA.

FOR MORE INFORMATION: https://www.yaskawa.com/ga800

Yaskawa America, Inc. 1-800-YASKAWA Email: info@yaskawa.com | yaskawa.com

YAI-DW_08.2021.indd 1

7/30/2021 3:02:26 PM

DRIVES

energy is used again, rather than being completely lost to heat, as is the case with a traditional dynamic brake.

One key component that enables regeneration in ac drives is the IGBT. Traditional diodes used in the inverter bridge can only handle power in one direction (incoming to the motor) and aren’t able to transfer power back to the ac source. Including IGBTs in the bridge allows power to flow in both directions.

Applications that involve frequent starts and stops, constant deceleration, or overhauling loads are good candidates for the use of regenerative drives. Examples include downhill conveyors (constant deceleration), elevators, and flywheels. But in reality, most applications regenerate power during some phases of their operation.

Despite the energy and cost savings of regenerative drives, their capital cost is relatively high when compared to simple dynamic braking systems. Therefore, cost-justification for regeneration is strongest when the amount of energy to be recovered is large, or when the cost of the recovered energy is high.

CONFIGURING PID PARAMETERS FOR VARIABLE FREQUENCY DRIVES

Using proportional-integral-derivative (PID) control with VFDs is common when a process set point—such as temperature, pressure, flow, or speed—needs to be precisely controlled. In fact, many VFDs are now supplied with an integrated PID controller.

PID CONTROLLER TERMS

Configuring the PID parameters for fast response and minimum overshoot (referred to as tuning the drive) is typically an iterative process, as each variable has an effect not only on the system performance, but also on the other variables. Regardless of the tuning method used, the first step in configuring PID parameters is to understand what each parameter means and how it affects the system.

Buy a Solution Fast with ACE Motion & Vibration Control Products Industrial shock absorbers Industrial gas springs Vibration isolation

P = Proportional The proportional component of the PID controller determines how much the output will change, based on the error between the feedback and the set point. With the proportional component, there is a linear, immediate relationship between the error and the response (output).

Note that in servo tuning, the P component is often referred to as proportional gain, whereas in process applications, the P component is typically referred to as proportional band.

These two terms are the inverse of each other: Proportional Gain = 100 / Proportional Band.

An increase in the proportional gain will yield a larger output change for a given error. In contrast, increasing the proportional band yields a smaller output change for a given error.

I = Integral

Standard products available to buy online Tools

Where the proportional term considers only the current state of the error at the time of the controller calculation, the integral term monitors the error over time and uses the error history to determine how quickly the output should change. Integral control works to eliminate the offset that results from the proportional control.

Integral gain is given in repeats per minute, indicating how aggressive the integral action is. However, in process industries, the integral term is often referred to as “reset rate” or “repeat rate,” which is expressed in minutes per repeat. As the inverse of integral gain, a high value for the repeat rate decreases the aggressiveness of the integral component.

Note: The proportional and integral gains work in conjunction to quickly move the process variable to the set point without overshooting. As the process variable moves toward the set point, the proportional gain output decreases, but the integral gain output increases because the process variable has not fully reached the set point. Only as the process variable gets close to the set point does the integral gain output begin to decrease.

Sizing & specification ▪ Online calculations & product selection

▪ One-on-one

application assistance

Resources Online & downloadable ▪ ACE CAD database ▪ ACETips video tutorials ▪ Technical blog &

D = Derivative

case studies

Derivative control determines the output based on the rate of change of the error. Its purpose is to limit overshoot and dampen system oscillations. Derivative gain essentially anticipates errors or upsets as they begin and reacts quickly to correct them.

8 • 2021

DESIGN WORLD — MOTION

43

800-521-3320 www.acecontrols.com

Motion Systems Handbook

ABSOLUTE ENCODER INTERFACES — AN OVERVIEW ONE OF THE INDISPENSIBLE DEVICES in any motion system is an encoder, measuring and providing feedback for accurate motion control. Encoders can provide information on position, distance traveled, and speed. They’re typically grouped by a number of distinguishing features including operating principle, whether they are linear or rotary, or whether they are absolute or incremental encoders.

There are three major categories of encoder based on the operating principle; optical, magnetic, or capacitive.

Traditionally, optical encoders were some of the first types of encoders with fairly high resolution and work using a light source for detection. Next is magnetic technology, which doesn’t use any optical means and which can achieve resolutions down to a micron and compete with optical technology in a host of applications. Magnetic technology is also more robust than optical technology, making magnetic encoders more common in harsh industrial environments. Lastly there are capacitive encoders. They offer resolution comparable to optical devices, with the ruggedness of magnetic encoders. Their suitability for applications requiring high precision and durability make them a good choice for the semiconductor, electronics, medical, and defense industries.

Another fundamental division is between absolute and incremental encoders.

Absolute encoders have an encoder disc (sporting marks or slots) on a power-transmission shaft and a stationary pickup, but the disc marks output a unique code for each shaft position. Absolute encoders are either single-turn or multi turn encoders. Single turn absolute encoders can verify position within a single turn of the encoder shaft. This makes them useful for short travel situations. In contrast, multiple-turn absolute encoders are better for more complex or longer positioning situations.

Engineers generally classify absolute encoders by the number of their output bits, which correlates to the number of the disc’s tracks—and the maximum rotary angle the encoder registers.

On the other hand, rotary incremental encoders

44

DESIGN WORLD — MOTION

WITH PROPAGATION DELAY COMPENSATION, THE ENDAT 2.2 PROTOCOL FROM HEIDENHAIN CAN SUPPLY CLOCK FREQUENCIES UP TO 16 MHZ. work by generating a series of pulses during movement. The encoder disc (sporting marks or slots) attaches to a power-transmission shaft, and a stationary pickup device mounts nearby. When the shaft and disc turn, the pickup tracks the motion to output the relative position. Such encoders generally supply square-wave signals in two channels that are offset from each other by 90° — in other words, out of phase by 90°. Each increment of rotation spurs an output signal.

DATA TRANSMISSION: DIFFERENCES BETWEEN ABSOLUTE ENCODER INTERFACES

The rise of IoT and automation has shined a spotlight on the importance of networking.

Encoders play a vital role in this equation as they produce data that is transmitted from the source of measurement to a controller or drive for processing. As such, they are key to automation and motion control applications achieving high speed and optimal performance.

Below is an overview of some of the main communication protocols for absolute encoders.

Absolute encoders can communicate with controllers through parallel or serial wiring, over a fieldbus, or via an Ethernet-based protocol such as EtherCAT. Of these options, serial communication is a simpler solution than parallel wiring (which requires a twisted pair of wires for each bit of output) and is well suited for applications that aren’t complex enough to justify a fieldbus or Ethernet-based protocol. Here, we’ll look at the differences between four of the most common absolute encoder serial interfaces available today: SSI, BiSS, Hiperface DSL, and EnDat 2.2.

8 • 2021

motioncontroltips.com | designworldonline.com

NEW

QUANTIC

™

incremental encoder series Analogue output available

Easy installation

High speed

Optional ADT (Advanced Diagnostic Tool)

Made for manufacturing The QUANTiC encoder series integrates Renishaw’s filtering optics design and interpolation technology to create a high speed, super-compact, easy to install, incremental open optical encoder.

For information more information visit www.renishaw.com/quantic For more visit www.renishaw.com/quantic Renishaw Inc 1001 Wesemann Drive West Dundee, IL, 60118 T 847-286-9953 F 847-286-9974 E usa@renishaw.com

www.renishaw.com

Quantic Analgue Advert - USA.indd 1

2/23/2021 7:36:15 PM

ENCODERS

ABSOLUTE ENCODERS WITH IO-LINK

THE SSI ENCODER INTERFACE IS SIMPLE, WITH JUST FOUR WIRES FOR COMMUNICATION (A TWISTED PAIR FOR DATA AND A TWISTED PAIR FOR CLOCK SIGNALS) AND TWO WIRES FOR POWER. COURTESY OF ACCUCODER

SSI: SYNCHRONOUS SERIAL INTERFACE

As its name suggests, SSI is a synchronous protocol, meaning that data is transferred from the encoder to the controller synchronously via a clock signal, or pulse, provided by the controller.

The encoder output can be in binary or gray code, and one bit is transmitted per clock pulse, with standard word lengths of 13 bits for single-turn encoders and 25 bits for multi-turn encoders.

Synchronous Serial Interface uses two pairs of twisted wires for communication, per the RS-422 standard — one pair for differential data signals and one pair for differential clock signals. There are also two wires for power to the encoder. The clock frequency, or rate of data transmission, can be up to 1.5 MHz, depending on the length of the cable. To ensure data integrity, some SSI encoders support multiple transmission (also known as “multi-path” or “ringshift” transmission), in which the same data is sent multiple times and the controller compares the transmissions to ensure they match.

BISS: BIDIRECTIONAL SYNCHRONOUS SERIAL INTERFACE

The Bidirectional Synchronous Serial Interface is an open protocol and is similar to SSI in that data transmission is synchronized by clock signals from the controller, but with BiSS, clock speeds up to 10 MHz are possible. BiSS also uses two twisted pairs of wires — one pair for data signals and one pair for clock signals — plus two wires for power.

Unlike SSI, which only supports unidirectional communication, BiSS supports bidirectional communication, meaning the controller can read from and write to non-volatile memory in the encoder, where registers contain encoder identification information. BiSS encoders can also send data, such as temperature, to the controller on demand. Another unique feature of BiSS versus SSI is that within each data cycle, the master determines and compensates for any

Smart Encoder Ready for Industry 4.0

Simplify Your Communications System Magnetic Multiturn Sensing Without Gears or Batteries Perfect for Factory and Process Automation Applications Condition Monitoring via Vibration and Temperature Sensor

The Versatility Champs

HIPERFACE DSL, ORIGINALLY DEVELOPED BY SICK, INCLUDES CHANNELS FOR POSITION FEEDBACK, PARAMETER EXCHANGE, PROCESS DATA, SAFE POSITION, AND CONDITION MONITORING (SENSORHUB) DATA, ALL TRANSMITTED ON TWO WIRES WHICH CAN BE INTEGRATED INTO THE MOTOR CABLE. 8 • 2021

DESIGN WORLD — MOTION

47

www.posital.com

Motion Systems Handbook transmission delay, allowing data transmission rates up to 10 Mbps.

The most current version of BiSS is BiSS-C (C = Continuously), although the interface is typically referred to as simply “BiSS.” Unlike SSI encoders, BiSS encoders can be connected point-topoint or via bus. When connected via bus, the data from all the encoders is clocked (synchronized) to the master in one continuous frame rather than individually. BiSS also implements a cyclic redundancy check (CRC) for error checking — a more reliable method than multiple transmission.

There also exists a BiSS Safety interface, for safety applications up to SIL3 per IEC 61508.

HIPERFACE DSL

Hiperface DSL, the HIgh PERformance InterFACE Digital Servo Link, was originally a proprietary interface developed by SICK. However, in 2016, SICK “opened up” the interface with a licensing model that allows other manufacturers to integrate the technology into their product offering.

Unlike its predecessor, Hiperface, Hiperface DSL is an all-digital protocol that uses just two wires for bi-directional communication and encoder power, bundled with the motor power cable (although a transformer is required to improve the common mode noise rejection).

This gives the advantage of eliminating the need for separate encoder connections on the motor and the controller. Hiperface DSL complies with the RS-485 standard and has a data transmission rate of 9.375 Mbaud.

Data can be transmitted cyclically (as fast as possible) or synchronously with the controller clock.

The Hiperface DSL architecture also includes channels for the transfer of motor parameter data, condition monitoring data, and integrated safe motion, with data being transmitted over two digital communication wires. This redundancy and error-checking make the Hiperface DSL interface compliant with SIL3 safety standards.

ENDAT 2.2

The Encoder Data, or EnDat 2.2, interface from Heidenhain is a synchronous, bidirectional standard that uses four wires for communication — two wires each for differential data and differential clock signals — plus two wires for power and two for either battery buffering or parallel power supply. EnDat 2.2 can provide clock frequencies of up to 2 MHz, and on some models, additional compensation for propagation delay makes frequencies up to 16 MHz possible.

Since Hiperface DSL has become an “open” interface, EnDat is now the only serial interface for absolute encoders that remains proprietary (although it should be noted that the original Hiperface protocol also remains proprietary).

EnDat 2.2 can also read, write, or update information stored in the encoder and can transfer data such as sensor information or diagnostic information from the encoder to the controller. The type of data transmitted — for example, absolute position, diagnostics, or parameter information — is sent via mode commands from the controller to the encoder. Like BiSS and Hiperface DSL, EnDat 2.2 is also compliant with SIL3 safety standards.

Reliable Motion Feedback Encoders Designed for Packaging Automation Get the precision motion feedback that your packaging applications demand.

At EPC, you’ll talk to engineers and encoder experts who will help you spec the right encoder for your application.

Call us or visit our website to get started.

1-800-366-5412 | encoder.com Encoders — MC HB 08-21.indd 48 4 20210714_DW_halfPageBranding.indd

8/11/21 3:47 7/16/2021 10:20:05 AMPM

GEARING

PRECISION PLANETARY-GEAR COURTESY OF CGI MOTION

FUNDAMENTALS OF GEARING RECALL A BASIC PREMISE OF GEAR FUNCTION: When two gears with an unequal number of teeth or engaging elements mesh, the mechanical advantage makes their rotational speeds and torques different. In the simplest of 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-to-tooth 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, parallelaxis 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 higherhorsepower 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 is the pitch point, is where one gear initially contacts its mate’s pitch point. Involute gearsets

motioncontroltips.com | designworldonline.com

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 right-angle 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, skewed, 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.

GENERAL SPEED REDUCERS, SHAFT-MOUNT SETS, AND WORM DRIVES

Gear reducers (also called speed reducers) are commonly paired with electric motors. Essentially, these consist of gears combined in such a manner as to alter the motor’s output torque. Typically, the torque increases in direct proportion to the reduction of rotations per unit of time.

Speed reducers come in two varieties: base mounted and shaft mounted. Shaft-mounted types come in two versions. One is truly shaft mounted in that the input shaft of the drive motor supports it … with a special coupling to address torque reactions. The other mounts to the machine housing so the input shaft doesn’t support the reducer’s weight or address torque reactions.

By the American Gear Manufacturers Association (AGMA) definition, engineers apply the term speed reducer to units operating at pinion speeds below 3,600 rpm or pitch-line velocities below 5,000 fpm. Recall that the AGMA

8 • 2021

is an international group of gear manufacturers, consultants, academics, users and suppliers.

Reducers operating at speeds higher than these are called high-speed units. Manufacturers base catalog ratings and engineering specifications for speed reducers on these AGMA standards.

There are as many types of speed reducers as there are gear types. Consider reducers in which the input and output shafts are at different angles. The most common of these are wormgear reducers.

Worm-gear reducers are used in low to moderate-horsepower applications. They offer low initial cost, high ratios, and high output torque in a small package … along with a higher tolerance for shock loading than helical gear reducers. In a traditional setup, a cylindrical toothed worm engages a disk-shaped wheel gear with teeth on its circumference or face.

Most worm gears are cylindrical with teeth of consistent size. Some worm-gear reducers use a double-enveloping tooth geometry — with a pitch diameter that goes from deep into short and back to deep — so more teeth engage. No matter the version, most wheel gears in worm-based reducers sport cupped teeth edges that wrap around the worm shaft during engagement.

In many cases, the sliding engagement lowers efficiency but extends life, as worm-gear mating holds a film of lubricant during operation.

The ratio of a worm-gear is the number of wheel teeth to the number of threads (starts or leads) on the worm.

REDUCERS VERSUS GEARHEADS

Gearheads usually serve the same function as speed reducers. But the term gearhead often implies that another primary function of the gearing DESIGN WORLD — MOTION

49

YOUR CUSTOM SOLUTIONS ARE

CGI STANDARD PRODUCTS

Advanced Products for Robotics and Automation CGI Motion standard products are designed with customization in mind. Our team of experts will work with you on selecting the optimal base product and craft a unique solution to help differentiate your product or application. So when you think customization, think standard CGI assemblies.

Connect with us today to explore what CGI Motion can do for you.

copyright©2021 cgi inc. all rights reserved.

800.568.GEAR (4327) • www.cgimotion.com

GEARING is reduction of the load’s reflected mass inertia, which makes accelerating heavy loads easier ... enabling a given axis to run off a smaller motor. Such gearing (associated with motor-driven motion designs with speed control) can also simplify servotuning of especially dynamic axes and axes for positioning. Another difference between gearheads and speed reducers is that in rare instances, gearheads work to actually increase output speed.

Gearheads come in a variety of styles, from basic spur gearheads to more complex offerings — each with their own characteristics and applications. Where precision is top design objective, one or more of zerobacklash gear options may be suitable.

THE SPECIAL CASE OF GEARING FOR PRECISION MOTION DESIGNS

Servo systems are precision-motion setups with feedback and (in most cases) 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, advanced machinery often 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 fully integrated mechanical component consisting of a series of mating gears contained in a housing with shafts and bearings (to support and resolve loads) and in many cases a flange for motor mounting.

Gearhead: Most of the motion industry makes no differentiation between the terms gearhead and gearbox. But in a few contexts, the term gearbox specifically refers to housed gearing as described above while the more general term gearhead also refers to assemblies of otherwise open gearing that installs within some existing machine frame.

The latter are often targeted to compact, consumer-grade, or battery-powered mobile designs necessitating especially tight integration and omission of potentially redundant subcomponents. In one variation, a series of parallel plates might support gear-train shafts (and bearings) and allow bolting to a motor face.

Though beyond the scope of this Design Guide, note that other open gearing simply mounts to the electricmotor output and operates exposed to the environment. Some such open gearing is self-lubricating — constructed of dimensionally stable polyamides or similar

HIGH-PERFORMANCE H SERIES HELICAL INLINE SERVO REDUCER ON MOTOR COURTESY OF DIEQUA CORP. motioncontroltips.com | designworldonline.com

materials engineered to meet stringent cleanliness, vibration, weight, and cost requirements.

MORE ON PLANETARY GEARSETS

Particularly common in servo systems, planetary gearsets consist of one or more outer planet gears that revolve about a central 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 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 powertransmission 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, 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.

QUICK PRIMER ON HYPOID GEARING

Hypoid gearboxes are a type of spiral bevel gearbox — with the difference that hypoid gears have axes that are non-intersecting and not parallel. In other words, the axes of hypoid gears are offset from one another. The basic geometry of the hypoid gear is hyperbolic rather than having the conical geometry of a spiral bevel gear.

In a hypoid gearbox, the spiral angle of the pinion is larger than the spiral angle of the gear, so the pinion diameter can be larger than that of a bevel gear pinion. This provides more contact area and better tooth strength, which allows more torque to be transmitted and high gear ratios (up to 200:1) to be used.

Because the shafts of hypoid gears don’t intersect, bearings can be used on both sides of the gear to provide extra rigidity.

The difference in spiral angles between the pinion and the crown (larger gear) causes some sliding along the teeth, but the sliding is uniform, both in the direction of the tooth profile and longitudinally. This gives hypoid gearboxes very smooth running properties and quiet operation. But it also requires special extreme pressure (EP) gear oil to maintain effective lubrication due to the pressure between the teeth.

Hypoid gearboxes are generally used where speeds exceed 1,000 rpm ... although above 8,000 rpm ground gears are recommended.

However, hypoid gearing is also useful for lower speed applications that require extreme smoothness of motion or quiet operation. In multi-stage gearboxes, hypoid gears are often used for the output stage, where lower speeds and high torques are required.

8 • 2021

DESIGN WORLD — MOTION

51

Motion Systems Handbook The most common application for hypoid gearboxes is in the automotive industry, where they are used in rear axles — especially for large trucks. With a left-hand spiral angle on the pinion and a right-hand spiral angle on the crown, these applications have what is known as a below-center offset ... which allows the driveshaft to be located lower in the vehicle.

This lowers the vehicle’s center of gravity and in some cases reduces interference with the interior vehicle space.

WAVE AND CYCLOIDAL GEAR APPLICATIONS

WAVE AND CYCLOIDAL GEAR OPTIONS INCLUDE (FROM TOP TO BOTTOM) STRAIN-WAVE GEARING, PLANOCENTRIC AND CYCLOIDAL GEARING, PLANETARY GEARING, AND DYNAMIC THRUSTEDTOOTH GEARING. 52

Many of today’s precision applications necessitate gears capable of dramatic speed reductions, power densities, and transmission accuracies. Leading choices in these designs include trochoidal and cycloidal gearing as well as gearsets relying on wave-inducing subcomponents having an elliptical or Reuleaux or other polygonal shape.

Recall from geometry that trochoidal and cycloidal gearing includes elements that rotate and trace curves around some other element. More specifically, cycloids traced by a point on a rolling element’s circumference include epicycloids (for which the element rolls along the outside of a sun gear or other reference component) and hypocycloids for which the element rolls within a ring or other reference component. In contrast, trochoids (and their subtypes) are traced not by a point on the rolling element’s circumference but rather some point within or without. One particularly common subtype of epicyclic gearing is planetary gearing. Because we’ve covered planetaries in previous sections of this Design Guide, here we’ll review other variations that are increasingly common in high-end machine tool, aerospace, material handling, and robotic applications requiring precision servo motion.

Consider the latter — in a robotic joint employing a motor (running at a few thousand rpm) fitted with gearing for output speeds to 100 times slower. Gearing in such designs also serves to boost acceleration torque for top power density — a priority design objective for SCARAs and collaborative robotics for which the total assembly is essentially a cantilevered mass.

Recall that conventional gearing used in such designs (including some planetary gearsets) usually exhibit a very small amount backlash. This is often limited to only a few arc-min. (100ths of a degree) and serves to accommodate lubrication and thermal expansion.

However, this backlash can in some cases degrade system accuracy by unacceptable amounts. So let’s take a look at other gear options that avoid the issue.

Strain-wave gearing uses the metal elasticity (deflection) of a gear to reduce speed. Key benefits of strain-wave gearing include zero backlash and high power density 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 a steel disc with an elliptical shape machined to precise specifications. A specialty ball bearing fits around this disc and conforms to the elliptical shape. Most designs attach the wave generator to a servomotor — to serve as the motion input.

DESIGN WORLD — MOTION

8 • 2021

The flexspline is a thin-walled steel cup. These cup walls are radially compliant but remain 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 what one might call the brim.

The flexspline usually serves as the output.

The cup has a rigid boss at one end to provide a rugged mounting surface. The wave generator is 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 teeth of the flexspline engage the teeth of the circular spline along the major (long) axis of the ellipse.

So there are two areas of meshing made by the ellipse inscribed concentrically within the ring. Roughly 30% of the teeth are engaged at all times — in contrast with six or so teeth engaged at any time for an equivalent planetary-gear set, and one or two teeth for an equivalent spur-gear set.

Recall that backlash is the difference between the space to accommodate the teeth and the tooth width ... and this difference is zero in strain-wave gearing. Elastic radial deformation of the strain-wave flexpline (preloaded

by the manufacturer against those of the circular spline at the major axis) acts like a very stiff spring to compensate for space between the teeth that would otherwise cause backlash. Preload is set to keep stresses well below the material’s endurance limit.

The pressure angle of the gear teeth transforms the output torque’s tangential force into a radial force acting on the wave-generator bearing. The flexspline and circular spline teeth engage near the ellipse’s major axis and disengage at the 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 the number of flexspline teeth ÷ (number of flexspline teeth – number of circular spline teeth).

The lightweight construction and single-stage gear ratios (to 160:1) of strain-wave gearing let engineers use the gears in designs needing minimized weight and volume. Even small motors can leverage their large mechanical advantage. Certain tooth profiles (of convex and concave arcs) for strain-wave gearing let more teeth engage — for increased torsional stiffness and torque ... as well as a longer MTBF. Now let’s consider the thrusted-tooth design mentioned earlier. This newer high-torque gearbox offering offers extreme torsional rigidity and zero-backlash operation for applications that need superior precision in output motion. In contrast with other gear offerings that transmit power over lines of contact on gear teeth, meshing gears in the drive make almost full-surface contact. This allows for tooth contact that’s up to 6.5 times that of certain types of conventional involute teeth.

motioncontroltips.com | designworldonline.com

GEARBOXES | COUPLINGS | RACK & PINION FOR PRECISION MOTION CONTROL & ROBOTIC APPLICATIONS Articulated Robot Joints and 7th Axis

Zero-Backlash Robotic Flange Gearboxes and Helical Rack and Pinion Systems, customized to your application

Cartesian System Build your own with Linear Mount Products

designed to simplify the process of designing and building a cartesian system. Everything Between the Motor and the Actuator Hollow Output Gearboxes

GCL Cycloidal withstands shock loads of 5x nominal torque

Inline or Right Angle, include custom adapter to mount to any linear actuator

PMK Space-saving Parallel Mount Kit

GCL Cycloidal with integrated pre-stage

GSL Strain Wave with harmonic gearing for precise motion

Distance Coupling Connect actuators without additional external bearings

GSL Strain Wave Theta/Wrist Axis

Trunnion Headstock Drive

Zero-backlash gearboxes provide precision positioning

GCL Cycloidal 7th Axis/Robot Transfer: Dyna Series + Helical Rack & Pinion

Precise point-to-point motion

Designed for optimal system performance

GPL Planetary

Vibration-free, continuous coordinated motion between trunnion and robot

From zero-backlash gearboxes to rack & pinion, GAM has the flexibility and broad product range for all your motion control and robotic applications.

As a U.S. manufacturer with one of the broadest product offerings in the gearbox industry, as well as the in-house engineering design expertise and manufacturing capabilities to develop customized solutions, GAM can help with your application.

GAM Can. www.gamweb.com | info@gamweb.com | 888.GAM.7117

GAM Enterprises, Inc. | 901 E. Business Center Dr. | Mount Prospect IL 60056

© 2021 GAM. ALL RIGHTS RESERVED

Motion Systems Handbook How does it work? In short, the gearbox guides a large array of individual teeth along an internal ring gear. The tooth geometry follows a logarithmic spiral that lets multiple teeth transmit power at once through hydrodynamic contact — covering much larger surface areas than traditional line contact.

The result is a gearbox with zero backlash even at the zero crossing. The logarithmic spiral path of the teeth allows for synchronization accuracy that outperforms traditional hollow-shaft drives with comparable outer diameters.

The gearbox also boasts up to 91% efficiency — 18 to 29% better than traditional strain-wave and cycloidal geared arrangements.

As part of a drive system, hydrodynamic tooth contact of the gear drive also delivers high overload capability. Emergency stop torque is 150 to 300% better than comparable systems, and torsional rigidity is to 580% higher ... so gearboxes of other designs might need to be up to three times larger to deliver the same torque as a given thrusted-tooth gearbox. The gear design also allows for a very large hollow-shaft diameter in relation to the outer diameter — to 70% larger in some cases.

UPDATE ON GEARMOTORS

Especially over the last twenty years, there’s been more integration of gearboxes into servomotors — in addition to certain ac motor types often associated with gearmotor offerings. Demand for more flexibility and control has driven this trend. Brushless dc gearmotors in particular can satisfy applications for which high-voltage signals are unacceptable or minimal wiring is a top design objective.

COMPARISON OF AC AND DC GEARMOTORS

The most common industrial gearmotors employ ac motors to run fixedspeed axes. But gearmotors for motion control can be built around either ac or dc electric motors. The choice of motor type depends on several factors.

In general, dc gearmotors (particularly brushless dc motors) have excellent speed-regulation properties — so they’re usually preferred in applications requiring tight variable-speed control. But over the years, ac gearmotors and their drives have gotten better at speed control … so now many are competitive with their dc counterparts.

Another factor is maintenance. Most ac gearmotors require less maintenance that comparable dc-motor offerings — and so are better for applications involving hard-to-reach areas or where environmental factors are more of a concern. There’s also cost: Usually dc gearmotors are slightly more costly than comparable ac gearmotors, mostly because of their speed-regulation properties.

Recent technological evolution hasn’t just been in the use of servomotors: Advanced variable frequency drives (VFDs) of paired with inverter-duty ac motors can in many cases deliver motion profiles needed for a particular axis — at a cost that’s lower than that of geared servomotors.

STANDARD VERSUS INVERTER-DUTY GEARMOTORS

Standard gearmotors are designed to operate over a wide range of conditions producing a range of output speed and torque. However, there are special motor designs aimed at specific applications, such as washdown motors used in food and beverage processing or explosion-proof motors used in hazardous locations. Inverter-duty gearmotors are a bit like this.

As the name implies, inverter-duty motor refers to a gearmotor specifically designed for speed control by an inverter (also called a variable frequency drive or VFD). The difference between an inverter-duty gearmotor and a standard gearmotor is in the winding construction. More specifically, the windings in such motors include more rugged insulation than other motor types so are better able to withstand the voltage spikes of the fast-switching PWM signals generated by VFDs. Such signals can cause the degradation of

54

DESIGN WORLD — MOTION

8 • 2021

winding insulation that leads to motor failure in other designs.

The insulation of inverterduty gearmotors is also designed to resist breakdown from overheating when the motor is run at low speeds. For this reason, certain inverter-duty gearmotors can produce a wider constant-torque speed range than comparable gearmotors with standard construction.

So where are inverter-duty gearmotors used? The most common applications are in material handling, packaging equipment, and conveying — any application requiring adjustable speed and the use of a VFD.

INCREASINGLY COMMON: PERMANENT-MAGNET AC MOTORS

THIS GEARMOTOR ASSEMBLY INCLUDES AN INDUCTION MOTOR FITTED WITH A HELICAL GEARSET.

In addition, with construction and operation much like those of brushless dc (bldc) motors, synchronous ac motors — sometimes billed brushless ac, permanentmagnet (PM) ac motors, and even permanentmagnet synchronous motors (PMSMs) — are now spreading from the most sophisticated servomotor applications into other industrial-drive applications.

More specifically, PMSMs are seeing increased use on printing and packaging equipment; conveyors; vehicle hub drives for AGVs and robotics; hoists and cranes; and regenerative elevator drives.

These lightweight low-inertia motors typically deliver 5 to 150 hp at high torque and efficiency. In fact, many maintain efficiencies 10 to 15% better than comparable induction motors.

Synchronous ac motors’ variable-speed operation necessitates control via an inverter or VFD specially designed to start and synchronize the rotorstator interaction. Just as bldc motors, synchronous ac motors use electronics (typically Hall-effect sensors) to dictate the correct amount of current to the windings. Arrays of four or more permanent magnets on the rotor make for synchronous operation.

But unlike bldc motors with trapezoidally wound stator coils (and back-EMF output with trapezoidal waveform needing direct current input) synchronous ac motors are wound sinusoidally. That makes for sinusoidal back-EMF output (and the need for sinusoidal current input) as well as an audibly and electrically quieter motor. Read more about the difference between bldc and synchronous ac motors at motioncontroltips.com.

Continuous commutation avoids torque ripple and makes for a power factor that is high ... and well as super-premium efficiency even when accounting for controller losses.

Unlike induction motors that exhibit low efficiency and power factors at low speeds, PM synchronous motors also maintain performance without always necessitating a gearing or a gearmotor design. In fact, the power density of PM synchronous motors is often leveraged to eliminate mechanical components such as gears and chain drives, for example — which in turn boosts efficiency and minimizes service requirements. But where direct driving through a PMSM is inappropriate or impossible (as on conveyor applications) PM synchronous gearmotors are more compact than other options.

motioncontroltips.com | designworldonline.com

Motion Components

to Automate any Industry

Right Angle Precision Servo Gearheads with Single or DUAL Output Options

800-363-2145

diequa.com/dw

full page print ad.indd 1

2/27/19 2:13 PM

Geared Motor Solutions Over 70 years’ of expertise creating the perfect combination of motor and gearbox to match a wide range of applications. We offer thousands of standard options and can easily customize any motor or gearbox to meet your exact requirements.

Our product range includes AC, PMDC and BLDC options for applications in industrial automation, transport and healthcare industries.

Contact us today to see how Parvalux can help your products really start to motor!

GEARMOTORS

GEARMOTORS — A REVIEW OF BASICS GEARMOTORS COMBINE EITHER an ac or dc electric motor with a gear reducer, integrating them together into one physical unit.

Many manufacturers offer gearmotors as integrated units, saving designers the effort of integrating separately purchased motors with gear reducers. Gearmotors come in many different styles, with a

are important. So for instance, torque and speed matter in all cases.

Another way gearmotors are differentiated or classified is by the output shaft orientation, with two standard types being parallel and right-angle arrangements. Beyond shaft configuration itself, other factors such as the type of gears used in the gearmotor determine performance.

wide array of motor and gear combinations available to suit unique

HOW TO CALCULATE REQUIRED INPUT POWER FOR A GEARMOTOR

application requirements.

A typical way to classify gearmotors is according to their horsepower rating; as either fractional or integral. An integral horsepower gearmotor is any motor with a horsepower of 1 and above, as opposed to fractional horsepower motors that are less than 1 hp. The design considerations for integral horsepower motors are fairly similar to fractional horsepower motors because the same types of parameters

GEARMOTORS HELP ENGINEERS LEVERAGE THE BENEFITS OF AUTOMATION — NAMELY ACCURACY AND FLEXIBILITY FOR TOP THROUGHPUT.

TO WITHSTAND WASHDOWN-GRADE CHEMICALS AND PROCESSES (WHICH POSE ESPECIALLY CHALLENGING CONDITIONS) GEARMOTORS CAN INCLUDE COATED, CHEMICALLY PROCESSED, OR STAINLESS HOUSINGS.

THE CUTAWAY DRAWING OF A GEARMOTOR SHOWS THE MOTOR AND ELECTRICAL CONNECTIONS ON THE LEFT WITH THE MOTOR OUTPUT CONNECTED TO A SYSTEM OF GEARS WITH A 90-DEGREE HOLLOW-SHAFT OUTPUT. motioncontroltips.com | designworldonline.com

The first place to start when sizing a gearmotor is to determine the required output torque and speed. But once torque and speed are defined, you’ll also want to know the required input power for the motor — particularly if the gearmotor uses an ac induction motor, where the power rating (typically given in horsepower) is used as a key factor in sizing.

INTEGRATION OF THE MOTOR-ROTOR SHAFT AND GEARING WITHIN PRE-ENGINEERED GEARMOTORS CAN BE ESPECIALLY TIGHT — FOR SHORTER OVERALL LENGTH.

PRE-ENGINEERED GEARMOTORS ALSO REDUCE THE DESIGN TIME AND PROJECT RISK FOR THE DESIGNER BECAUSE THE MANUFACTURER HAS DONE MUCH OF THE HEAVY LIFTING TO ENSURE THAT THE MOTOR AND GEARBOX COMBINATION WORK WELL TOGETHER.

GEARMOTORS ALSO INCLUDE STANDARDIZED FLANGE AND MOUNTING OPTIONS (WITH THE APPROPRIATE SUPPORT GEOMETRIES) FOR SIMPLIFIED INSTALLATION ON MACHINE AXES.

8 • 2021

DESIGN WORLD — MOTION

57

Fed up?

Problem: You want to use the latest automation technology. However, the complexity is overwhelming.

Solution: MOVIKIT® software modules!

They empower you to perform complex automation tasks easily and without experience. No more long hours. No more complex programming.

Positioning? Synchronization? Torque sharing? Winders? Yes, and even more!

Simple is good...

seweurodrive.com / 864-439-7537

8/11/21 3:48 PM

-

SEW Eurodrive - MC HB 08-21.indd 58

GEARMOTORS RELATIONSHIP BETWEEN WORK AND POWER

Before calculating the power, let’s review the relationship between power and work.

Work is defined as force applied over a distance:

POWER EQUATIONS FOR ELECTRIC MOTORS: METRIC UNITS

Electric motors produce torque (rather than force) through rotational motion (rather than linear distance), so power is equal to torque multiplied by angular velocity:

When torque is given in lb-ft and speed in rpm:

P = mechanical power (hp) T = torque (lb-ft) ω = angular velocity (rpm)

P=Txω

W=FxD

W = work (J) F = force (N) d = distance, or displacement (m) Mechanical power is the time rate at which work is done, so work divided by time:

P = mechanical power (W) T = torque (Nm) ω = angular velocity (rad/s)

Mechanical power can also be written as:

P = (F x D) / t

Note that distance divided by time (d/t) is velocity, so power can be written as force times velocity:

P=W/t

P = mechanical power (watt) W = work (J) t = time (s)

P=Fxv

v = velocity (m/s)

rad/sec = (rot/min) x (2π/60)

CONVERTING FROM WATTS TO HORSEPOWER

Although the SI unit of power is the watt, in discussions of motor power, the Imperial unit of horsepower is often used.

In the 1780s, James Watt and Matthew Boulton defined 1 horsepower (hp) as 33,000 ft-lb/min, which, is 44,742 Nm/min.

Converting this from Nm/min to Nm/s gives us 746 Nm/s, or 746 Watts. Therefore, to convert power from watts to horsepower, divide the power in watts by 746.

POWER EQUATIONS FOR ELECTRIC MOTORS: IMPERIAL UNITS

In gearmotor applications, torque and speed are still often given in Imperial units. In these cases, horsepower can be calculated directly, with the use of a conversion factor:

GEARMOTORS ARE COMMONLY AVAILABLE FOR SPECIFIC APPLICATION USES AND ENVIRONMENTAL CONDITIONS. FOR INSTANCE, THESE EX-PROOF GEARMOTORS FROM BODINE ELECTRIC ARE UL LISTED FOR USE IN ENVIRONMENTS WHERE IGNITABLE CONCENTRATIONS OF FLAMMABLE GASES, VAPORS, OR LIQUIDS ARE LIKELY TO EXIST UNDER NORMAL OPERATING CONDITIONS. motioncontroltips.com | designworldonline.com

5,252 = 33,0000 ft-lb/min ÷ 2π rad/rot

When torque is given in lb-in and speed in rpm:

Note that angular velocity has units of radians per second. If speed is given in rotations per minute (rot/min or rpm), be sure to convert rotations per minute to radians per second:

P = T x ω / 5,252

8 • 2021

P = T x ω / 63,025

P = mechanical power (hp) T = torque (lb-in) ω = angular velocity (rpm)

63,025 = 33,000 ft-lb/min * 12 in/ft ÷ 2π rad/rot

INPUT POWER FOR GEARMOTORS

Each equation for mechanical power given above can apply when sizing a gearmotor, depending on what units of torque and speed are being used.

However, when determining the input power required for the motor, the efficiency of the gearmotor assembly at transmitting that power to the load must be taken into account. Therefore, regardless of which equation above is used to calculate the required output power, the required input power at the motor is calculated as: Pinput = Poutput/ η η = gearmotor efficiency Note that efficiency can vary greatly, depending on the motor, type of gearing used, and the gear ratio. For example, gearmotors that use hypoid gearing can have efficiencies of greater than 90 percent, while those that use worm gears can have efficiencies ranging from less than 40 percent up to about 80 percent.

DESIGN WORLD — MOTION

59

Motion Systems Handbook

TRACK-ROLLER LINEAR GUIDES AND BELT ALONG WITH SCREW DRIVES COMPLEMENT THIS SEMICONDUCTOR-MANUFACTURING MACHINERY.

SORTING OUT LINEAR-GUIDE TYPES LINEAR BEARINGS ARE included in linear actuators and

• A carriage or comparable table rides on a linear rail or track via plain (sliding) elements • A carriage rides on linear rail via wheel-type track rollers • A carriage rides on a profiled linear rail via carriagecontained arrays of ball bearings or cylindrical rollers • A bushing studded on its inner diameter with rolling elements rides on a round shaft

The interrelated functions of these linear-motion components to both support (bear) loads and guide loads is the core reason why they’re called both linear bearings and linear guides — depending on which function is being emphasized by the source. Both terms are so generic that they can refer to any products from the four categories listed above — including such disparate designs as plain linear bearings, ball bushings, and recirculating-roller linear bearings.

Confusing matters is the fact that industry makes inconsistent use of even more specific linear-motion terms. For example, the term slide is often used to refer to the carriages of linear bearings based on rolling (not sliding) bearing elements. The term rolling-contact guide is often used to refer to profiled-rail linear bearings even though track-roller linear guides also include rolling contact (at their track wheels).

That said, linear guide often indicates a standalone guide rod, ball slide, or mechanism solely for guiding loads. The term profiled rail nearly always indicates

60

8 • 2021

the axes of other motion systems to guide and support machine assemblies and payloads over the linear stroke.

All linear bearings fall into four categories:

DESIGN WORLD — MOTION

motioncontroltips.com | designworldonline.com

LINEAR COMPONENTS some linear bearing with roller or ball elements. Many manufacturers use the terms linear slide (whether based on rolling or sliding action) and linear rail (whether plain, track-roller, or profile) to indicate a linear-motion guide element that’s incorporated into a build complete with some mechanical drive. Though the terminology surrounding plain linear bearings is probably the most consistent, various manufacturers use plane bearing (as in one dimension in 3D space) instead plain bearing. While the two terms are often used interchangeably, the American Bearing Manufacturers Association encourages use of the term plain bearing.

The term linear stage generally implies a design has guided elements as well as some mode of mechanical linear actuation and reinforced body — often sans inclusion of the motor.

Motorized rails (more commonly called linear actuators) abound — though the distinction here is that there are countless linear actuators sold without any linear-guide element. That’s useful for OEMs aiming to employ some specialized linear guide or omit guides altogether.

APPLICATIONS FOR LINEAR GUIDES

Linear rails are linear assemblies that have tandem tracks (usually on one monolithic run) containing load-supporting balls or rollers. The backbone of many industrial applications, they provide low-friction guidance and high stiffness for loads that can range from just a few grams to thousands of kilograms. Their variety of sizes, accuracy classes, and preloads make linear rails suitable for virtually any performance requirement.

The reasons for using linear rails are numerous, but their most obvious benefits over other types of guides are load capacity, travel accuracy, and rigidity. For example, round shaft guides can withstand only downward or liftoff loads, whereas linear rail guides can withstand downward loads and liftoff loads … as well as moment loads. Unlike crossedroller guides for which travel is often limited to 1 meter or less, linear rails can provide very long travel lengths. When compared to plain bearing guides, linear rails also have higher stiffness and rigidity, and often have better load and life characteristics.

Linear guides also provide a high level of travel accuracy, thanks to precise machining of one or both edges of the rail, which act as reference surfaces. With two, four, or six rows of rolling elements — either spherical balls or cylindrical rollers — stiffness is also high … and deflection of the bearing block is minimal.

All these attributes combine to provide a linear guide system that is perfectly suited for applications that require high precision, high rigidity, and long life. So here we outline common applications for these linear components in typical sizes.

SINGLE-RAIL APPLICATIONS

Because profiled-rail linear rails have load-supporting balls (or rollers) on each side of the rail assembly, they can withstand overhung loads, even when just a single rail is used.

In contrast, round shaft linear guides must be used in pairs when overhung loads are present. Because of this feature, numerous applications use a single linear rail, to save space or to prevent issues with misalignment among other components in the system.

Here are a few examples of applications that use a single linear rail.

Linear actuators: Linear rails are often the guide mechanism of choice for actuators that are driven with belts, screws, or pneumatic cylinders, because of their ability to withstand moment loads. They can also accommodate travel speeds up to 5 m/sec, which is important in belt or pneumatically driven systems.

Overhead transport systems: When loads are centered below the rail and bearing block, as is often the case with overhead transport systems, linear rails are a good choice for guidance. Their high load capacity allows heavy loads to be transported, and the rigidity of the linear rail helps to stiffen the entire system.

Gantry robots: The defining feature of a gantry is that it has two X (and sometimes 8 • 2021

DESIGN WORLD — MOTION

61

Motion Systems Handbook SLIDING-ELEMENT LINEAR GUIDES BOXWAY PLAIN BEARING

BUSHING PLAIN BEARING

DOVETAIL PLAIN BEARING

two Y and two Z) axes. The individual axes typically incorporate a single linear rail and are driven by a screw or a belt and pulley system. With two axes working in parallel (X and X’, for example) very good moment capacities are realized, even though each axis has just one linear rail.

DUAL-RAIL APPLICATIONS ROLLING-ELEMENT LINEAR GUIDES 1. TRACK ROLLER LINEAR GUIDES

V-SHAPED TRACK-ROLLER WHEEL AND TRACK

GOTHIC-ARCH TRACK-ROLLER WHEEL AND ROUND TRACK

2. PROFILED RAIL LINEAR GUIDES RECIRCULATING ROLLING ELEMENTS

NON-RECIRCULATING ROLLING ELEMENTS

CARRIAGE

RECIRCULATING SET OF RETAINED BALLS

GUIDEWAY RAIL

3.

ROUND RAIL LINEAR GUIDES

LINEAR BUSHING BALL SPLINE

62

DESIGN WORLD — MOTION

Linear components — MC HB 08-21 V3.indd 62

When high moment loads are present, linear rails can be used in pairs, which allows the moment load to be resolved into forces on the bearing blocks. In this configuration, the drive mechanism can be mounted between the linear rails, making the overall system very compact. Dual linear rail applications include …

Linear stages: Stages are typically very high precision systems, meaning that high travel accuracy and minimal deflection are paramount. Even if the load is centered on the stage with little or no moment loading, dual linear rails are often used to ensure that stiffness and bearing life are maximized.

Machine tools: Like stages, machine tools require very high levels of travel accuracy and stiffness, to ensure that the tool produces high-quality parts. Using two rails in parallel — typically with two bearing blocks per rail — ensures that deflection is minimized. Machine tools also experience very high loads, so resolving the load over four bearing blocks helps to maximize bearing life.

Cartesian robots: Because Cartesian robots typically use just one linear system per axis, it’s important that each axis can withstand high moment loads. Therefore most Cartesian robot axes are constructed from linear actuators that incorporate two linear guides in parallel.

Robot transport units: Six-axis robots provide flexible motion for applications that require reach and rotation in many directions. But if the robot needs to move to another station or work area, dual-rail systems can act as a seventh axis, transporting the entire robot to a new location. A significant benefit of linear rails in these applications is the ability to join multiple rails for very long travel lengths — often exceeding 15 meters.

Of course, linear rails aren’t the perfect solution for every application. For example, linear rails aren’t generally suitable for applications in the consumer space — such as door guides and drawer slides — often due to cost. Plus linear rails require very precise mounting surfaces, not only to reap the benefits of their high travel accuracy ... but also to avoid binding of the bearing block, which can lead to reduced life.

They must also be fully supported, unlike linear shaft systems, which can be only end-supported. This means that not only is the upfront cost of a linear rail typically higher than that of a round shaft or plain bearing system, the cost of preparation and mounting is also higher.

Linear rails can also be perceived as less smooth or notchy in their running properties than other bearing types. This is because of the contact that occurs between the loadcarrying balls (or rollers) and the raceways. Preloading a linear rail system, which is often done to increase stiffness, can exacerbate the feeling of notchiness when the bearing block is moved along the rail. (This effect goes away as load is applied to the bearing, but the perception often remains.)

SHOWN HERE IS THE TREE OF LINEAR-GUIDE FAMILIES AND SUBTYPES. NOTE HOW THE LOAD-BEARING ELEMENTS IN TRACK-ROLLER LINEAR GUIDES ARE INSIDE THE COMPONENTS’ WHEELS — IN CONTRAST WITH THE LOAD-BEARING ELEMENTS IN PROFILED-RAIL LINEAR GUIDES WHICH HAVE DIRECT CONTACT WITH THE LINEAR RACEWAY. THIS ASPECT OF TRACK-ROLLER DESIGN (AMONG OTHER THINGS) MAKES THE LINEAR GUIDE TYPE PARTICULARLY ROBUST ... EVEN IN EXTREME ENVIRONMENTS.

8 • 2021

motioncontroltips.com | designworldonline.com

8/11/21 3:48 PM

LINEAR COMPONENTS For applications that don’t require the load capacity, stiffness, or travel accuracy of a linear rail, other linear guides such as round shaft systems, plain bearing guides, or even crossed roller slides may be suitable and less expensive.

MORE ON THE GEOMETRY OF DUAL-GUIDE RAILS

Profiled-rail linear guide rails and bearings offer high stiffness and good travel accuracy. They can support downward, upward, and side loads ... and they can also withstand overhung or moment loads. Of course, the larger the linear rail and bearing system, the more moment capacity it has. Besides size, the arrangement of the profiled-rail rolling elements — face-to-face or back-to-back — also influences the amount of overhung load that it can support.

While the face-to-face design (also known as the X arrangement) provides equal load capacities in all directions, it results in a shorter moment arm along which overhung loads are applied, which reduces moment load capacity. The back-to-back arrangement (also known as the O arrangement) provides a larger moment arm and gives higher moment load capacities.

Many linear actuator designs include two rails in parallel with the drive mechanism — belt, screw, or linear motor — incorporated between the rails. While it’s not imperative that the drive be centered between the guide rails, centering does help ensure even loading on all

motioncontroltips.com | designworldonline.com

the bearings — and reduces cogging ... the uneven drive forces on each rail and bearing set. This arrangement also reduces the height of the actuator, making it relatively compact given the high load and moment capacity provided by the dual guide rails.

Another linear-guide option — that of recirculating bearings (bushings) that ride on round shafts — are unable to handle roll moments. Therefore most linear bushing applications require that two shafts be used in parallel.

One last note on classifications: The categorization of profiled-rail linear guides as recirculating or non-recirculating is less relevant that it is for profiled rail linear guides, as the former have load-bearing elements that qualify as non-recirculating (as their wheels remain fixed at given attachment locations on the system carriage) or recirculating (as the bearings inside each wheel assembly course round and round).

MORE ON TRACK-ROLLER LINEAR GUIDES

There are several names for track-roller linear guides. Terms found to be predominant in a given technical reference or data sheet depend on the manufacturer and market. In addition, reorganization of linearmotion industry taxonomy is afoot as new distribution channels such as Amazon (as well as established distributors such as McMaster-Carr) have come to influence how young engineers in particular reference various technologies. For example, Amazon currently categorizes

8 • 2021

DESIGN WORLD — MOTION

63

Motion Systems Handbook VARIOUS CROSS SECTIONS of

EXTRUDED C-CHANNEL TRACK FOR CROWNED WHEELS

LINEAR GUIDE TRACKS

CURVED TRACK FOR GOTHIC-ARCH WHEELS ON CARRIAGE WITH BOGIES

ROUND STEEL RACEWAYS MOUNTED TO HOLLOW ALUMINUM TRACK

Sometimes tracks of different types are paired together on an axis to constrain (and allow) movement in complementary ways.

64

DESIGN WORLD — MOTION

assembled into hobby-grade CNC systems to serve as basic track-roller linear guides.

Profiled wheel or wheel-based linear system is a slightly less common term usually used to emphasize some beneficial aspect of the wheels’ radial geometry (and to a lesser extent the mating track geometry). The use of the word profiled also serves a marketing function emphasizing to design engineers that track-roller linear guides are a highly engineered and viable alternative to profiled rail linear guides.

Square linear-guide rail usually refers to flat-wheel track-roller designs that pair with C-channel tracks. Many such designs include arrays of wheels in different orientations on a carriage to engage multiple interior track surfaces.

Cam-roller guides and idler-roller guides are other names for track-roller linear guides. However, there is some ambiguity with the term cam roller, because it also refers to the cam-follower-based rollers found within large mechanical indexing tables so common in automotive assembly and beverage-bottling applications.

TRACK-ROLLER LINEAR GUIDE ERROR ABSORPTION

100

ADMISSIBLE TANDEM-TRACK HEIGHT DIFFERENTIAL (mm)

linear motion components into six different subcategories under the Power Transmission Products section of its Industrial & Scientific category. Linear track roller is a very common and unambiguous variation of the “track roller linear guide” term predominantly used here.

Guide wheel and linear guide wheel and roller guide are all common terms for track roller linear guide systems and their wheels. Some of these terms are used to emphasize the accommodation of misalignment as a primary function of the linear guide. Manufacturers will often indicate the wheel material or shape when using this convention — nylon-12 crowned guide wheels or steel wheels, for example.

Skate-wheel linear guide is a term that is specific to manual and gravity conveyors as well as the DIY CNC maker community.

It often (though not always) implies an arrangement for which the track is beneath a carriage’s load-bearing wheels. The term references the fact that these wheels either closely resemble or actually are consumer-grade components sold for use on products such as skateboards.

Though most are entirely inappropriate for industrial use, skate wheels provide surprisingly decent accuracy when

50

0

-50

-100

ERROR FROM MOUNTING-PLANE MISALIGNMENT 0

250

500

1,000

1,500

2,000

2,500

DISTANCE BETWEEN TWIN TRACKS ON A TANDEM-SUPPORTED AXIS (mm)

8 • 2021

motioncontroltips.com

|

designworldonline.com

Precision Linear Motion when you need it NOW! Standard And Custom Engineered Linear Motion Components Designed to Serve A Wide Variety of Markets

Del-Tron Precision, Inc. is now ISO 9001:2015/AS9100D CERTIFIED MADE IN USA

Order Today! 800.245.5013 Solid Models Available for all Del-Tron Model Numbers

www.d el t ro n.co m

DC MOTORS

SPOTLIGHT ON CORELESS DC MOTORS ELECTRIC MOTORS ARE CENTRAL TO mechanical power transmission. The range of motors is broad, including ac motors that power conveyor lines to dc motors, both brushed and brushless, to servo and stepper motors for precision motion.

Electric motors can be categorized in a number of different ways; as ac (alternating current) or dc (direct current) motors, or by the type of motion they produce, rotary or linear. Another common approach is to distinguish between commutation methods; for example, self-commutated or external, and by mechanical means (as brushes used in brushed dc motors) or electronic commutation (as in brushless dc motors.)

A dc motor works by generating a magnetic field via electromagnetic windings or permanent magnets. The most common industry naming conventions for dc motors recognize three subtypes: brush motors, permanent-magnet (PM) motors, and universal motors. Many dc motors still employ brushes and wound fields, but PM motors dominate fractional and integralhorsepower applications below 18 hp.

For brushed dc motors, the magnet acts as the stator. The armature is integrated onto the rotor and a commutator switches the current flow. It does this by transferring current from a fixed point to the rotating shaft. Brushed dc motors generate torque straight from the dc power supplied to the motor by using internal commutation, fixed permanent magnets, and rotating electromagnets.

Brushless dc (BLDC) motors, on the other hand, do away with mechanical commutation. They use electronic commutation that eliminates the mechanical wear and tear involved with brushed dc motioncontroltips.com | designworldonline.com

A CORELESS DC MOTOR DOES AWAY WITH THE IRON CORE IN THE ROTOR. INSTEAD, THE ROTOR WINDINGS ARE WOUND IN A SKEWED, OR HONEYCOMB FASHION TO FORM A SELFSUPPORTING HOLLOW CYLINDER. THE STATOR MAGNET SITS INSIDE THE CORELESS ROTOR. COURTESY OF MAXON MOTOR AG motors. In BLDC motors, the permanent magnet is housed in the rotor and the coils are located in the stator. These 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 rotor’s permanent magnet field trails the rotating stator field, producing the rotor field.

BASICS OF CORELESS DC MOTORS

A typical brushed dc motor consists of an outer stator, typically made of either a permanent magnet or electromagnetic windings, and an inner rotor made of iron laminations with coil windings. A segmented commutator and brushes control the sequence in which the rotor 8 • 2021

windings are energized, to produce continuous rotation.

Coreless dc motors do away with the laminated iron core in the rotor.

(Coreless dc motors are also referred to as “air core,” “slotless,” or “ironless” motors.) Instead, the rotor windings are wound in a skewed, or honeycomb, fashion to form a self-supporting hollow cylinder or “basket.” Because there is no iron core to support the windings, they are often held together with epoxy. The stator is made of rare-earth magnets, such as Neodymium, AlNiCo (aluminumnickel-cobalt), or SmCo (samariumcobalt), and sits inside the coreless rotor.

The brushes used in coreless dc motors can be made of precious metal or graphite. Precious metal brushes DESIGN WORLD — MOTION

67

STEPPER MOTORS

STEPPER MOTORS FOR PRECISION MOTION OF THE MOTORS COMMONLY USED IN motion

control applications, stepper motors are most often employed where precision motion is needed. Their compact size and high torque as well as greater controllability are common advantages as well.

Stepper motors are typically grouped according to three basic designs — permanent magnet (PM), variable reluctance, (VR), and hybrid. Of the three, hybrid stepper motors are arguably the most common in industrial applications, combining the best performance characteristics of permanent magnet and variable reluctance types.

Hybrid stepper motors are constructed with a rotor made of two sections, or cups, with a permanent magnet between them. This causes the cups to be magnetized axially — with one cup polarized north and the other cup polarized south. The surfaces of the rotor cups have precisely ground teeth (typically 50 or 100 teeth per cup), and the cups are aligned with an offset of ½ tooth pitch between the two sets of teeth.

In a hybrid stepper motor, the stator poles are also toothed, and when pulses are delivered to the stator by the stepper drive, these poles are magnetized, causing the rotor to turn so that the teeth of the rotor and stator align (N-S or S-N).

The hybrid design — with teeth on both the rotor and stator — allows the motor to optimize magnetic flux, and thus produce higher torque than permanent magnet or variable reluctance designs. Hybrid stepper motors can also achieve step angles as small as 0.72 degrees in full-step mode and operate at higher speeds than other designs.

Control techniques such as half-stepping

motioncontroltips.com | designworldonline.com

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-motor types. They are also quieter than VR stepper motors.

One caveat is that hybrid stepper motors are more expensive than other step motors. So, designers should weigh the higher cost against the advantages of quiet operation, smaller steps, and torque output before making a final stepmotor selection.

Although proprietary designs and production methods allow manufacturers to optimize the torque output (as well as step accuracy and speed characteristics) of their

8 • 2021

THE ROTOR OF A HYBRID STEPPER MOTOR IS MADE UP OF TWO CUPS, WHICH TYPICALLY HAVE 50 TEETH EACH. THE TWO CUPS ARE OFFSET BY 1/2 TOOTH PITCH, AND THE TEETH ON ONE CUP ARE POLARIZED NORTH, WHILE THE TEETH ON THE OTHER CUP ARE POLARIZED SOUTH, FOR A TOTAL OF 100 POLES, OR 50 POLE PAIRS. COURTESY OF MICROCHIP

DESIGN WORLD — MOTION

69

STEPPER MOTORS hybrid stepper motors, torque production is still closely tied to the frame size of the motor.

Stepper motors generally adhere to the NEMA ICS 16-2001 standard for frame sizes, which specifies mounting dimensions such as flange size and bolt circle diameter. However, one dimension not covered by the NEMA standard is motor length. And this flexibility in motor length for a given frame size provides manufacturers with another option for increasing the torque production of a particular NEMA size stepper motor — by creating motors with longer stack lengths. For example, double- and triplestack stepper motors are now common offerings from several manufacturers.

Double- and triple-stack hybrid stepper motors simply have multiple rotors and stators, stacked end-to-end. With multiple rotor and stator sections, the motor can produce more torque without the need to increase the frame size. Only the length of the motor increases.

However in double- and triple-stack (and quad-stack) stepper motor designs, torque falls off faster as speed increases than it does in single-stack designs. This is because the added rotor and stator sections also increase the motor’s inductance. And higher inductance means the electrical time constant of the motor — the amount of time it takes the current in the windings to reach 63 percent of its maximum value — is also increased. When a stepper motor operates at high speeds, a high electrical time constant means there isn’t enough time for the current (and, therefore, torque) to reach its maximum value at each motor step, resulting in a torque drop-off as speed increases.

STEPPER MOTOR STATOR (WITH WINDINGS) AND ROTOR (WITH TWO SETS OF TEETH). all south poles. With 50 teeth per rotor cup, the pitch, or distance between teeth, is 7.2° (360° ÷ 50 = 7.2°). The two rotor cups are offset by ½ tooth pitch, so the combination of the two cups acts as a 100-tooth rotor, with 50 pole pairs (50 sets of north-south teeth).

The stator is made up of toothed poles, and each pole has a winding. In the case of a 5-phase stepper motor, there are ten poles, so that each of the five phases consists of two poles, orientated at 180° to each other. When current is applied to a phase, the two poles in that phase are energized and magnetized as both north or both south.

The rotor and stator construction of a 5-phase stepper motor means that each pulse of current moves the rotor by 1/10 of a tooth pitch, for a step angle of 0.72°.

Step angle = 360° ÷ (2 x Number of stator phases x Number of rotor pole pairs) Step angle = 360° ÷ (2 x 5 x 50) = 0.72°

PERFORMANCE BENEFITS OF 5-PHASE STEPPER MOTORS

In addition to the classifications mentioned above, stepper motors are often categorized by the number of phases in their construction, with 2-phase and 5-phase versions being common designs. And although 2-phase versions are more widely adopted, 5-phase stepper motors offer performance advantages that make them the preferred choice in some applications.

As mentioned above, the basic construction of a hybrid stepper motor includes two rotor cups, each with 50 teeth. The rotor cups are magnetized axially by a permanent magnet, so that the teeth of one cup are all north poles and the teeth of the other cup are

motioncontroltips.com | designworldonline.com

the smaller the difference in the torque-versusdisplacement curves, and the lower the torque ripple. Lower torque ripple also means more usable torque, lower vibration, and less noise.

One of the drawbacks of stepper motors is that they can lose synchronism if they overshoot (take too many steps) or undershoot (miss steps). In other words, the motor can physically gain or lose steps in relation to the drive’s commands, and without a feedback device, the drive can’t detect the motor’s incorrect position.

But with 5-phase stepper motors, losing synchronism is much less likely, because it requires that the rotor either overshoot by more than ½ tooth pitch or undershoot by less than ½ tooth pitch. Since ½ tooth pitch is 3.6°, and the step angle of a 5-phase stepper motor is 0.72°, the motor would have to overshoot or undershoot by 5 steps (3.6° ÷ 0.72° = 5 steps) before it loses synchronism — an unlikely scenario in most properly sized applications.

This small step angle translates to higher resolution than 2-phase motors, which have a step angle, or resolution, of 1.8°. Microstepping can further reduce the resolution of a 5-phase stepper motor by 250 times, for a step angle as small as 0.00288°.

Five-phase stepper motors also have less torque ripple, and in turn, more usable torque than other designs. The torque produced by each phase contributes to the total output torque of the motor. As each phase is energized and the rotor moves, a sinusoidal torque-versus-displacement curve is produced.

The difference in the curves for each phase represents the torque ripple of the motor. The more phases that contribute to total torque,

8 • 2021

DESIGN WORLD — MOTION

71

Scalable Motion Solutions for Your High Performance Applications Emerson’s new PACMotion™ portfolio enables you to scale your motion capabilities without sacrificing performance. Our new family of servo motors, servo drives, software and motion controller easily integrates with our PACSystems portfolio for a complete solution for high-speed, high-precision processes in packaging, printing, material handling, semiconductors, food and beverage and manufacturing or other applications where a high number of axes are needed.

Emerson offers end-to-end automation solutions for your high-performance machinery applications. Visit www.emerson.com/PACMotion to learn more. Reach out to us directly at ContactUs@Emerson.com

The Emerson logo is a trademark and service mark of Emerson Electric Co. ©2020 Emerson Electric Co.

SPRINGS

EXTENSION SPRINGS VERSUS TORSION SPRINGS EXTENSION SPRINGS (also called tension springs) are springs that can stretch in length. When extended, these springs are under tension. Typically, each end of the extension spring is attached to a different component … and when the components separate, the spring force works to pull them back together. Most extension springs are coiled springs manufactured from sprung steel spring wire.

Extension springs can have a hook or an eye at each end to facilitate fastening. Variations on such ends include open hooks, extended hooks, side hooks, and double full loops.

Extension springs are often used to create a restoring force in mechanisms such as latches and counterbalances.

Because extension springs are under tension, they require no support along their length. This often makes for a mechanism that’s simpler than those based on compression springs.

Hooke’s law — F = kx — is often used as an approximation for elastic objects. It states that the force F required to extend or compress a spring by some distance x is proportional to that distance. The rate at which the force increases will depend on the stiffness of the spring stiffness k.

In fact, industrial-grade extension springs don’t strictly obey Hooke’s Law because they have some initial tension F1 that must be overcome before any extension takes place. Therefore, a better approximation for the force of an extension spring is F = F1 + kx. The initial

tension F1 can be difficult to control and may vary significantly between springs of the same part number.

The dimensions of extension springs are normally given in their relaxed state. They may be specified in terms of outside diameter and inside diameter or wire diameter. The length of the body coils may be given in addition to the unloaded length inside the hooks as well as the maximum extended length inside the hooks.

Typically a sprung steel spring wire is coated with zinc, but stainless-steel springs are also available. Rubber bands, elastic bands, or bungee cord can provide lowcost alternatives to steel extension springs.

Extension springs can be stretched to increase their length, causing tension force within the spring.

ANOTHER SPRING TYPE: TORSION SPRINGS

A torsion spring is a component made from elastic material that (when twisted) exerts a moment resisting the rotation.

Common types of torsion spring include helical torsion springs, torsion bars, and spiral wound torsion springs.

Helical torsion springs are made from a material, typically sprung steel spring wire, and formed into a helix. At each end, the helix extends to form two straight legs through which the torque is applied. A circular mandrill inside the coil or a circular housing around the coil retains the spring position.

The legs typically extend tangentially, which results in the lowest stresses … though radial and axial legs are also used at times.

motioncontroltips.com | designworldonline.com

8 • 2021

THIS IS A TENSION SPRING ON A PIECE OF AGRICULTURAL OFF-HIGHWAY EQUIPMENT.

DESIGN WORLD — MOTION

73

F O K C I S ?

S G N I SPR

Motion Systems Handbook

COIL

SHOWN HERE IS A TORSION SPRING MADE OF STEEL.

We were too.

That’s why we invented the wave spring.

• Optimize Application Space & Weight • Industry-Specialized Design Support • Large Selection from Stock • Easy to Customize

Crest-to-Crest® Wave Springs

Request Free Samples at 847-719-5900 or smalley.com

A single coil version has a single leg extending from each end of a single helix. A double coil version is, essentially, two single coil springs that mirror one another — with the coils concentric but of opposite-handed windings. Both coils are wound from a single length of wire with the two central legs joined in a 180° bend.

Helical torsion springs are used in a wide range of applications, with wire diameters ranging from fractions of a millimeter to over an inch. Light-duty torsion springs are typically used as return springs in electrical devices, whereas heavy-duty springs are used in applications such as folding seats and door returns.

Torsion bars are simply straight bars of elastic material that can be twisted to its elastic limit. Torsion bars of typically constructed from steel or rubber. They are often used for heavy-duty applications, such as the suspension of trucks and tanks.

Torsion bar suspension is extremely durable because of its mechanical simplicity. It is also compact and allows for easy adjustments. Very light-duty torsion bars may require tension to generate a restoring torque, which is referred to as a torsion fiber.

A spiral-wound torsion spring is formed from a spring wire or (more commonly) a thin strip of sprung steel, coiled into a flat spiral. This configuration allows large angular deflections of many revolutions with relatively little variation in torque during the movement. No wonder spiral-wound torsion springs are used in clockwork devices, clocks, and other devices that require energy to be stored and consistently released.

Power springs are a specialty type of spiral-wound spring that can exert a consistent torque over many revolutions, they are sometimes referred to as clock springs or motor springs. Power springs are wound tightly within a case to provide particularly high energy density.

74

DESIGN WORLD — MOTION

8 • 2021

25,000+

Catalog Springs

Plus!

Custom Springs

To Meet Your Specifications.

ISO 9001:2015 Registered Company

Visit the All-New Lee Spring Website Easily find the right spring every time. View multiple spring features, specifications, pricing and quantity breaks side by side for easy spring selection.

Call: 888-SPRINGS (888-777-4647) Visit: leespring.com Fax: 888-426-6655 Email: sales@leespring.com

Motion Systems Handbook

MINIATURE GANTRIES ARE INDISPENSABLE FOR SEMICONDUCTOR MANUFACTURE.

SMALL POSITIONING STAGES, GANTRIES, AND XY 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.

76

DESIGN WORLD — MOTION

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. 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.

8 • 2021

motioncontroltips.com | designworldonline.com

| AT11-19US |

: Take flight with flying motion technology!

Flying 2D product transport with up to 6 degrees of freedom

Levitating planar movers kg

Scalable payload

360°

360° rotation

5°

Tilting by up to 5° Lifting by up to 5 mm Velocities up to 2 m/s

XPlanar enables new dimensions of freedom in product and material handling: Levitating planar movers fly over flexibly arranged planar tiles accommodating nearly any track layout and path planning.

Individual 2D transport at up to 2 m/s Processing with up to 6 degrees of freedom Transport and processing in one system Wear-free, hygienic and easy to clean Free arrangement of planar tiles enabling totally customized machine and process layouts Multi-mover control enables parallel and individual product handling Fully integrated into the powerful and standardized PC-based Beckhoff control system (TwinCAT, PLC IEC 61131, Motion, Measurement, Machine Learning, Vision, Communication, HMI) For use across all industries: assembly, packaging, food/bev, pharma, laboratory, entertainment, …

See XPlanar live!

Booth SL-6149

Motion Systems Handbook 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 for fast execution of tasks that need super-fine movements once workpieces (such as medical devices or semiconductor chips) are in place. Note: When a gantry or XY stage is designated as a planar type, this indicates that the system has been designed to provide extremely high travel accuracy. Planar stages are typically constructed of air bearing guides and linear motor drives.

Aire bearings 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.

DIFFERENT OPTIONS FOR STAGE, TABLE, AND GANTRY INSTALLATIONS

There are myriad ways to build linear systems for motion in the X, Y, and Z directions — also known as Cartesian coordinates. The terms that industry uses to refer to these systems depend on how the axes are assembled, where the load is positioned, and (to some extent) the application for which the systems are designed. In many industrial applications, Cartesian and gantry-style robots are prevalent ... but in precision applications, XY tables are often the better choice because they have a compact and rigid structure — and very high travel and positioning accuracies as well.

Cartesian systems consist of two or three axes to for X-Y, X-Z, or X-Y-Z setups. They often incorporate an end effector with a rotational component for orienting the load or workpiece … and always provide linear motion in at least two of the three Cartesian coordinates.

Where Cartesian systems are used, the load is usually cantilevered from the outermost axis — Y or Z. For example, in an X-Y gantry the load is mounted to the Y axis — either to

78

DESIGN WORLD — MOTION

A STEWART PLATFORM IS A TYPE OF HEXAPOD ROBOT HAVING ACTUATORS CONNECTED IN PAIRS AT THE STATIONARY OR MOVING PLATFORM …

OR BOTH. SHOWN HERE IS ONE SUCH HEXAPOD PLATFORM. THESE MOTION DESIGNS ARE COMMONLY USED IN THE SIMULATION OF AIRPLANE, SHIP, AND AUTOMOTIVE CABINS.

the end of the axis or at a distance from the axis to creating a moment arm on the Y axis.

This can limit load capacity, particularly when the outermost axis has a very long stroke (and creating a large moment on the lower supporting axes).

Cartesian systems are suitable for a wide range of applications with maximum strokes on each axis typically one meter or less. The most common of these applications include pickand-place, dispensing, and assembly.

To address the issue of outer axes causing a moment load on the inner axes, gantry systems use two X axes or (in some cases) two Y and two Z axes. Gantries almost always have three axes … X, Y and Z. The load on a gantry system is located within the gantry’s footprint and the gantry is mounted over the working area. However, for parts that cannot be handled from above, gantries can be configured to work from below.

Gantry systems are suitable in applications with long strokes (greater than one meter) and can transport very heavy payloads that are not suitable for a cantilevered design. One of the most common uses for gantry systems is overhead transport, such as moving large

8 • 2021

automotive components from one station to another in an assembly operation.

XY tables are like XY Cartesian systems in that they have two axes (X and Y, as their name implies) mounted on top of each other — and typically have strokes of one meter or less. But the key difference between XY Cartesian systems and XY tables lies in how the load is positioned. Instead of being cantilevered, as in a Cartesian system, the load on an XY table is almost always centered on the Y axis, with no significant moment created on the Y axis by the load.

This is where application uses distinguish various types of multi-axis systems. XY tables generally work only within their own footprint, meaning the load does not extend beyond the Y axis. This makes them best suited for applications where a load needs to be positioned in the horizontal plane (X-Y). A typical example is a semiconductor wafer being positioned for inspection or a part being positioned for a machining operation to take place.

So-called open-frame or open-aperture designs have a clear opening through the center of the table. This allows them to be used in applications where light or objects need to pass through, such as backlit inspection applications and insertion processes.

Because XY tables are primarily used for very high precision applications, the guideway of choice is that based on crossed-roller slides, as these provide extremely smooth and flat travel. Drive mechanisms are typically ball screw or linear motor, although very fine pitch lead screws are also common.

motioncontroltips.com | designworldonline.com

stages & gantries SERIAL KINEMATICS VERSUS PARALLEL KINEMATICS Today’s positioning tables and stages include hardware and software that’s more customized than ever to satisfy specific output requirements. That’s made for motion designs that move accurately through even complicated multi-axis commands. Precision feedback is key to such functionality — often taking the form of optical or (electronicsaugmented) magnetic encoders for nanometerscale resolution and repeatability … even over many inches of travel. In fact, miniature stage design is spurring the most innovation from feedback and control algorithms to move even very large loads with sub-sub-micron precision.

Use of pre-engineered stages and Cartesian robots continues to rise with rapid prototyping, automated research applications, and tighter time-to-market pressures. That’s especially true for photonics, medical-device, and semiconductor R&D and manufacturing.

motioncontroltips.com | designworldonline.com

In the past, building multi-axis motion for automating or otherwise improving tasks meant design engineers had to source and combine linear stages into X-Y-Z combinations … in-house. Any more degrees of freedom necessitated the after addition of goniometers, rotary stages, and other end effectors.

Called serial kinematics, such machine builds sometimes result in bulky setups with accumulated error due to tolerance stackup.

In some cases, bearings also limit such assemblies to one rotational center. These are non-issues when the design satisfies its motion requirements ... but miniature motion designs aren’t so forgiving of such factors.

Contrast these builds with hexapod or Stewart platforms — forms of parallel kinematic actuators for motion. At least for miniature multi-axis motion assemblies, these outperform serial kinematics. That’s in part because hexapod output motion isn’t limited by bearing (linear and rotary) ratings. Instead, the motion controls execute algorithms to an application-

8 • 2021

defined pivot point (center of rotation) unencumbered by error accumulation. Lower component count, lower inertia, and higher stiffness are other benefits.

As detailed on linearmotiontips.com articles on the topic, traditional motion systems can often work in conjunction with positioning stages having parallel kinematics — and traditional electromagnetic motors with piezoelectric motors … even on common assemblies or installations.

Multi-axis systems can be designed and built with either serial kinematics or parallel kinematics. In systems built on the principle of serial kinematics, one axis sits on top of another axis, and each axis is driven individually, independent of the others. Cartesian robots are a good example of serial kinematic design.

In parallel kinematic systems, multiple axes work together to move a common platform or end effector. The movement of one axis is constrained by the other axes, forming a type of closed-loop kinematic chain. Delta robots use parallel kinematics.

DESIGN WORLD — MOTION

79

Motion Systems Handbook DEEPER DIVE ON HEXAPOD ROBOTS

The term hexapod translates from Latin as six feet — and the hexapod robot (fittingly) consists of six actuators (also referred to as legs) that connect a stationary platform (typically the base) with a moving platform (typically the top). The legs are extending-rod style actuators — also referred to as prismatic actuators — which can be driven by ball screws, roller screws, linear motors, or even piezo devices. Ball or universal joints connect the ends of the actuators to the stationary and moving platforms.

Some manufacturers and experts refer to hexapod robots as simply hexapods — but the term hexapod also refers to six-legged arthropods.

To avoid confusion, we use the more specific term hexapod robot.

The first practical applications for hexapod mechanisms were in tire testing and flight simulator equipment, both of which still use hexapod robots today. But hexapod mechanisms are also widely used in photonics and optical alignment, positioning for machine tool equipment, and inspection systems.

Hexapod robots are unique among multi-axis systems because they allow a user-defined center of rotation, or pivot point, for all six axes of motion. They also have much higher stiffness and load-carrying capability than serial kinematic robots (Cartesian, SCARA, or six-axis) because their actuators or legs work together to support the load. The parallel design also means that the errors of each actuator are averaged, rather than accumulating as they do in serial robots.

Because only the top platform moves — motors, gearboxes, and other transmission components are stationary — hexapod robots have much lower inertia that serial designs, making them very well-suited for highly

dynamic moves with large payloads, or for sub-micron precision with light loads. From an integration standpoint, hexapod robots are easier and faster to commission. Controllers typically allow a simple input for the pivot point, and hexapod robots often forego servo tuning, because there is only one moving platform and system stiffness is inherently high. And if tuning is required, the parameters for all six axes are identical, making the tuning process much easier and faster than with serial robots.

Hexapod devices are analyzed using reverse kinematics. In other words, rather than the displacement of the moving platform being determined by the actuator movements, the actuator movements are determined based on the displacement of the platform. Reverse kinematic analysis is necessary because a given set of actuator displacements can result in 40 different platform positions, but each unique platform position corresponds to only one set of actuator displacements.

The kinematics of hexapod devices also give rise to singularities, or positions where the platform becomes uncontrollable, and its position cannot be uniquely determined by fixing the displacements of the actuators. (In extreme cases, a singularity may cause the entire system to effectively collapse.) But users of hexapod robots rarely must deal with the issue of singularities, because manufacturers define the robot’s working area to a space including no points of singularity.

One final note: The term Stewart platform comes from Mr. D. Stewart, who proposed to the UK Institution for Mechanical Engineers in 1965 that hexapod mechanisms be used as flight simulators. However, Mr. Stewart was neither the inventor of hexapod mechanisms nor the first to put them to use in a practical application.

SHOCK AND VIBRATION MITIGATION

COMPONENTS FOR VIBRATION AND SHOCK MITIGATION MANY SHOCK ABSORBERS common in industry achieve their damping characteristics using 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 longer service life and more compact designs. Miniaturization is a growing trend in these devices, as systems require tighter tolerances and smaller machine footprints. In machine automation and robotics, motion stabilization requires the use of hydraulic dampers, particularly micro-hydraulic designs.

In contrast, most 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 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.

Gas springs, also called gas dampers, tension springs and gaspressure springs depending on the setup and context, are compressedmotioncontroltips.com | designworldonline.com

air or oil cylinders that install in motion designs to damp forces and return kinematic linkages and more complicated assemblies to default positions.

Gas springs work through a piston on the end of a rod that protrudes from a steel cylinder body; usually compressed gas (often nitrogen) within the cylinder exerts force on this piston to reassume and maintain set positions.

Nitrogen is common here because it’s inert and nonflammable. In such designs, oil or grease between the piston and other contacting parts minimize friction. In fact, the small amount of oil in these gas springs serves another function — to further damp and gently decelerate gas springs during full extension or compression. Some setups even include a fine hole in the piston for damping that’s still slower than with other designs; such slowdamper springs are common on safety gates and doors.

In contrast, extended-reach gas springs usually leverage telescoping mechanisms pairing multiple cylinders on one rod; then the smaller cylinder extends from within the larger cylinder. Consider one particularly long-stroke application: Passive heave compensators — systems on ships or offshore oilrig systems that reduce the effect of waves on engineered structures — use gas springs with strokes to many meters long.

Still other gas-spring applications include those for medical beds and hoists; industrial equipment such as machine-tool presses; off-highway and automotive equipment for hatches, hoods, and covers; office equipment and furniture; and general strut and support applications. Fast-acting gas springs find use in weaponry and aerospace design. Specific variations include gas springs with standard or fixed-height cylinders; spindle-only designs; and cable, return, adjustable auto-return, nonrotating, stage, and multi-mode cylinders.

Elastomer and other synthetic and rubber pads can also damp vibration and isolate shock loads. They are available in several shapes, including tubes, bushings, blocks, pads and washers. These components are commonly used in heavy-duty applications to create strong cushioning plates or foundations in heavy machinery such as cranes, presses, and for vibration reduction in lab and testing equipment, aerospace, and for pipelines and bridges.

VERTICAL VIBRATION DAMPERS ON THIS WOODWORKING OPERATION ARE KEY TO CONSISTENT OUTPUT PRODUCT DESPITE NATURAL VARIATIONS IN THE INPUT LUMBER.

8 • 2021

DESIGN WORLD — MOTION

81

Motion Systems Handbook The rubber-like materials with which they are designed allow these padding materials to meet specific requirements, such as natural frequency, load, and area. And because they are soft, they are forgiving in most environments.

Predicting the natural frequency of an application lets material manufacturers target known disturbance frequencies to dissipate energy.

The lower the ratio of natural system frequency to disturbance frequency, the more it’s possible to isolate problem vibrations.

These cushioning plates can protect machinery subsystems against impacts and isolate vibration and structure-borne noise. For example, PAD plates from ACE Controls withstand compressive loads to 10,000 psi (69 N/ mm2) depending on plate form and size.

Another custom product called Sorbothane (from a company with the same name) is a thermoset that attenuates shock with near-faultless memory. That means its deformation is elastic and not plastic, so pads of the material reliably return to their original shape. Custom pieces of the material work for vibration damping, acoustic damping and isolation.

Sorbothane works by turning mechanical energy into heat as the material is deformed. Molecular friction generates heat energy that translates perpendicularly away from the axis of incidence.

ARBORS ARE USED ON MACHINE TOOLS (AS THIS INTERNAL-GRINDING DESIGN) TO REDUCE VIBRATION.

Horizontal milling machines are often referred to as arbor milling machines because their design requires the use of an arbor to achieve the proper tool position.

In machining processes, vibration can cause poor surface finish and machining accuracy as well as noise and reduced tool life. But machining operations require high forces and high rotational speeds, which naturally induce vibration.

Short of changing the part requirements or modifying the machining setup — unrealistic solutions in most cases — the most common way to reduce vibration in machine tool operations is to slow the machining rate. But a slower machining rate means fewer parts produced in a given amount of time (parts per minute, day, or hour) and lower productivity.

However, one factor that affects the amount of vibration at the APPLICATION-SPECIFIC VIBRATION MITIGATION: THE CASE OF ARBORS IN MACHINE TOOLS tool is relatively easy to modify. This factor is the design of the arbor — On a typical machine tool, the tool that performs the machining operation particularly its rigidity. The arbor’s rigidity is especially important when the (cutting, milling, or boring, for example) is attached to a rotating spindle machining length is long and the arbor has a high length-to-diameter (L/d) that drives the tool. But on machines that require long machining lengths, ratio, also referred to as “overhang.” such as milling and boring, the tool is mounted to an arbor. The arbor is To address the problem of vibration in machine tools, some manufacturers driven by the spindle and provides the necessary length for the tool to have even developed vibration-damping arbors that significantly reduce reach the workpiece in these operations. vibration, allow longer machining lengths (L/d ratio of 8 or greater) and trim machining times.

While each manufacturer uses a proprietary damping technology, most vibration-damping PROVEN SHOCK, VIBRATION & arbors are based on passive tuned mass NOISE REDUCING SOLUTIONS damping systems, consisting of a mass, a set of springs, and a damper. Multiple springs (or, similarly, several materials with frequencydependent stiffness) are used to address various RIAL frequencies that occur during machining.

MATE The frequencies of the tuned mass damping system are designed to match the structural frequencies to be eliminated. So when any of the specified frequencies is excited, the damper resonates out of phase with the structure, absorbing or dissipating the kinetic energy caused by vibrations.

Connected versions of vibration-damping arbors have also recently become available. The connected arbor designs have embedded sensors and use Bluetooth or other wireless technology to transmit tool performance data — such as temperature or cutting status — to a dashboard.

This insight is especially helpful for internal machining processes that can’t easily be monitored or inspected, such as boring or internal turning.

Manufacturers indicate that machine tool vibration amplitudes are up to 1000 times lower when using a vibration-damping arbor versus a standard arbor. This allows machining rates to be increased — leading to significant productivity improvements without sacrificing machining SORBOTHANE® quality or tool life.

REDUCES VIBRATION & NOISE IN COMMERCIAL PRODUCTS 800.838.3906

sorbothane.com

MADE IN THE U.S.A.

82 Sorbothane_DesignWorldAd_E-6.indd 1

4/7/20 2:41 PM

DESIGN WORLD — MOTION

DON’T LET VIBRATION BLUR YOUR PRODUCTIVITY.

Leverage Inventive Features like Vibration Suppression to Improve Machine Uptime and Performance Mitsubishi Electric’s MELSERVO-J5 Series empowers users with cutting-edge technology, industry-leading performance, and advanced servo features. MELSERVO-J5 supports high-speed, high-accuracy motion control via CC-Link IE TSN®. Enhance machine performance by leveraging the benefits of a total drive solution: • Advanced vibration suppression algorithm • AI-based predictive maintenance • New Quick Tune capabilities • Industry-leading servo performance in a compact footprint • Flexible drive capacity • Reduced Total Cost of Ownership (TCO) over the lifetime of a product

Automation - Simplified!

AD-VH-00134

Learn more about our problemsolving servo solutions by visiting:

go.meau.com/MRJ5DW2108P

AD INDEX

MOTION SYSTEMS HANDBOOK 2021 Ace Controls................................................................... 43 AllMotion.......................................................................... 4 AutomationDirect............................................................. 1 Beckhoff Automation..................................................... 77 Bishop Wisecarver.......................................................... 14 Bodine Electric Company................................................. 5 CGI Inc............................................................................ 50 Chieftek Precision.......................................................... 63 Clippard......................................................................... BC CMT ............................................................................... 24 Del-tron.......................................................................... 65 Diequa............................................................................ 55 Digi-Key Corporation....................................................... 3 Emerson Machine Automation Solutions....................... 72 Encoder Products Company.......................................... 48 FAULHABER MICROMO............................. Cover, 70, IBC FESTO............................................................................ 35 GAM............................................................................... 53 HELUKABEL USA........................................................... 31 HIWIN............................................................................. 20 Intech.............................................................................. 61 Kuebler........................................................................... 46 Lee Spring Company...................................................... 75 Mach III........................................................................... 28 maxon ............................................................................ 66

Mitsubishi Electric Automation...................................... 83 mk North America, Inc................................................... 37 NBK................................................................................ 40 New England Wire & Tubing Technologies.................... 33 Next Level Manufacturing.............................................. 22 NSK................................................................................ 18 Parvalux.......................................................................... 56 PBC Linear...................................................................... 11 PI (Physik Instrumente) LP.............................................. 80 PM B.V............................................................................ 79 POSITAL FRABA............................................................. 47 Pyramid Inc..................................................................... 25 Renishaw........................................................................ 45 Rockford Ball Screw........................................................ 17 Ruland Manufacturing Co.............................................. 39 SEW Eurodrive............................................................... 58 Smalley Steel Ring.......................................................... 74 Sorbothane..................................................................... 82 Stock Drive Products/Sterling Instrument...................... 26 THK America, Inc...........................................................IFC Ultra Motion................................................................... 13 WAGO Corporation......................................................... 9 Yaskawa Electric America............................................... 42 Zero-Max, Inc................................................................... 2

SALES

LEADERSHIP TEAM

Jami Brownlee jbrownlee@wtwhmedia.com 224.760.1055

Mike Francesconi mfrancesconi@wtwhmedia.com 630.488.9029

Courtney Nagle cseel@wtwhmedia.com 440.523.1685

Jim Dempsey jdempsey@wtwhmedia.com 216.387.1916

Neel Gleason ngleason@wtwhmedia.com 312.882.9867 @wtwh_ngleason

Jim Powers jpowers@wtwhmedia.com 312.925.7793 @jpowers_media

WTWH Media, LLC 1111 Superior Ave., Suite 2600 Cleveland, OH 44114 Ph: 888.543.2447 FAX: 888.543.2447

Publisher Mike Emich memich@wtwhmedia.com 508.446.1823 @wtwh_memich

EVP Marshall Matheson mmatheson@wtwhmedia.com 805.895.3609 @mmatheson

Managing Director Scott McCafferty smccafferty@wtwhmedia.com 310.279.3844 @SMMcCafferty

DESIGN WORLD does not pass judgment on subjects of controversy nor enter into dispute with or between any individuals or organizations. DESIGN WORLD is also an independent forum for the expression of opinions relevant to industry issues. Letters to the editor and by-lined articles express the views of the author and not necessarily of the publisher or the publication. Every effort is made to provide accurate information; however, publisher assumes no responsibility for accuracy of submitted advertising and editorial information. Non-commissioned articles and news releases cannot be acknowledged. Unsolicited materials cannot be returned nor will this organization assume responsibility for their care.

DESIGN WORLD does not endorse any products, programs or services of advertisers or editorial contributors. Copyright© 2021 by WTWH Media, LLC. No part of this publication may be reproduced in any form or by any means, electronic or mechanical, or by recording, or by any information storage or retrieval system, without written permission from the publisher.

Subscription Rates: Free and controlled circulation to qualified subscribers. Non-qualified persons may subscribe at the following rates: U.S. and possessions: 1 year: $125; 2 years: $200; 3 years: $275; Canadian and foreign, 1 year: $195; only US funds are accepted. Single copies $15 each. Subscriptions are prepaid, and check or money orders only.

Subscriber Services: To order a subscription or change your address, please email: designworld@omeda.com, or visit our web site at www.designworldonline.com POSTMASTER: Send address changes to: Design World, 1111 Superior Ave., Suite 2600, Cleveland, OH 44114

84

DESIGN WORLD — MOTION

8 • 2021

motioncontroltips.com | designworldonline.com

Precision

Control Solutions Designing efficient systems involves much more than simply understanding a few basic principles. There is a true art to balancing the specific requirements of an application in order to achieve the desired goals in the best possible way. Help us understand the unique needs of your application and together, we’ll develop something that surpasses what any of us could have done alone.

Contact your distributor to learn more, or visit clippard.com to request a free catalog and capabilities brochure.

• • • •

Electronic Valves Proportional Valves Isolation Valves Precision Regulators

• • • •

Toggle & Stem Valves Needle Valves Electronic Pressure Controllers Pneumatic Assemblies

• • • •

Special Manifold Designs Pneumatic Circuit Design Cylinders Fittings, Hose & Tubing

877-245-6247 CINCINNATI • BRUSSELS • SHANGHAI