Motion Control Power Transmission Guide

MAY 2024

DESIGNWORLDONLINE.COM

MOTIONCONTROLTIPS.COM

CONSIDERING ROLLINGELEMENT BEARINGS

NORTH AMERICAN EV BATTERY PRODUCTION

power transmission guide

WORLD-CLASS LINEAR

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THK is committed to meeting the worldwide demand for linear motion products. We manufacture, assemble, and ship across North America from our location in Hebron, Ohio. We’ve also ramped up our automating processes at existing facilities, including our U.S. manufacturing plant, where over 70% of THK Robotics Components are manufactured. Automated processes at this state-of-the-art facility enable increased production while maintaining the high standard of precision associated with THK products.

To learn more, visit www.thk.com

THK Manufacturing in Hebron, Ohio

QUICK SHIP COMPONENTS

1–2 Week Delivery of Select LM Guides and Actuators

Stuck on a Job-site Waiting for a Motor?

We stock hundreds of motors so you can keep your project moving AutomationDirect carries a full line of AC and DC motors from trusted brands like Toshiba®, U.S. Motors®, WEG®, Leeson®, IronHorse® and Marathon®, at some of the best prices in the industry. In-stock motors are shipped quickly with free shipping on orders over $49*.

Toshiba EQP SD (Severe Duty Motors) Starting at $376.00

• 230/460 VAC 3-phase from 1/2 - 100 hp • 1200, 1800, 3600 rpm • Inverter duty • Oversized 300-series bearings • Heavy-duty cast iron construction

• TEFC enclosure with IP55 protection • Class I, Division 2, Groups A, B, C, D • NEMA premium efficiency • UL, UR, CSA • 3-year warranty

U.S. Motors ACCU-Torq Motors

IronHorse MTS Stainless Steel Washdown-Duty

Starting at $370.00 • 230/460 VAC 3-phase from 1/4 - 10 hp • 1800 rpm • Constant torque operation; zero to base speed on vector drives • 5000:1 speed range • Constant horsepower operation to 2X base speed

• Optimized for operation with variable speed drives (VFDs) • Compatible with encoder installation • NEMA premium efficiency ratings on certain models • 3-year warranty (1hp and larger)

Starting at $401.00 • Three-phase 208-230/460 VAC from 1/3 to 20 hp • 1200, 3600 and 1800 RPM • TEFC or TENV enclosure • IP69K protection • Premium Efficiency (EISA Compliant)

WEG S-Series Rolled Steel Motors and Brake Motors

IronHorse MTRJ Series Jet Pump Motors

Starting at $194.00

• Three-phase 208- 230/460 VAC and single-phase 120/240 VAC from 1/4 to 3 hp • 1200, 3600 and 1800 RPM • TEFC enclosure with IP55 rating • Class F insulation • Premium and Standard Efficiency available • Certified Class I, Div 2,

Groups A,B,C,D • Brake motors include spring set, solenoid actuated AC brake with manual release lever • UL, CSA • 18 month warranty

• BISSC Certified • 304 stainless steel frame, end bracket, junction box and hardware • Class I, Div 2 hazardous locations • In accordance with NEMA, CSA, UL, and CE • 2 year warranty

Starting at $167.00 • TEFC enclosure • Class F winding insulation • Single-phase 120/230 VAC from 1/3 to 2 hp • Three-phase 208- 230/460 VAC from 1/3 to 3 hp

• 3600rpm • Built-in thermal protection on single-phase models • 56J frame with threade shaft for connection to a jet pump • 2 year warranty

Also Available Soft Starters and AC Drives

DC Motors

DC Drives

Research, price, buy at:

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Order Today, Ships Fast! * See our Web site for details and restrictions. © Copyright 2024 AutomationDirect, Cumming, GA USA. All rights reserved.

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power transmission guide

POWER TRANSMISSION IN A DIGITAL WORLD Each spring, the editors at Design World prepare a special

Here, we cover rotary bearings that are based on rolling

issue devoted to power transmission, which we call our

elements, including their manufacture and use in a range of

Power Transmission Guide. It covers the basics of power

applications. There’s also coverage of plastic bearings and

transmission by spotlighting key components such as gears,

how they compare with bearings made of more traditional

actuators, motors and other mechanical components.

materials, including some of the benefits of plastic bearings

In a world that is growing more digital by the day, these tried-and-true components remain at the heart of systems and machines that involve motion of any kind.

over these more traditional types.

One of the mainstays of power transmission systems are belt drives. Here we also take a look at some basics of belt and

The fast-paced nature of today’s automation systems,

pulley systems including some critical inertia calculations.

and the rate at which they are being installed in applications

New industries are also seeing the use of power

all over the spectrum, means that engineers designing these

transmission components as they are central to many newer

mechanical systems must ensure that they satisfy ever-

applications. This issue highlights one such application; the

changing application needs.

manufacture of batteries and battery components. With the

In this issue, we spotlight several key power transmission

rise of the EV industry and demand growing for more EV

components, including gears and gearing systems, paying

applications and uses, batteries are the components that power

particular attention to matching gearmotors to specific

it all.

application requirements. This includes considerations of

Automation in this sector involves the use of pneumatic

the type of motor used, whether brushless dc or permanent

as well as electric automation components. Such components

magnet synchronous ac or others, and how they match up with

are used across the entire range of the manufacturing process

different types of gears and gearsets.

from material handling to battery cell production, to assembly

Other key power transmission components include bearings. How

of battery packs and modules and even the recycling of used batteries.

critical are bearings to motion

To keep up with all the latest developments in

applications? Just consider

motion control and power transmission, be sure to follow

what a bearing failure

motioncontroltips.com, linearmotiontips.com, as well as

can mean in terms of

bearingtips.com and couplingtips.com. And don’t forget our

system reliability and

flagship site designworldonline.com.

performance — things grind to a halt, not metaphorically, but literally.

4

DESIGN WORLD — MOTION

05 • 2024

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Precise. Powerful. Modular.

Servo motors and gear units from SEW-EURODRIVE Servo motors and gear units from SEWEURODRIVE offer a high degree of dynamics and performance with a compact design, making them excellent for confined spaces. Multiple frame sizes and torque ratings makes them the perfect fit in material handling, hoist and gantry applications, and a wide variety of

machine automation applications. Their modular design allows for direct gear unit mounting without adapters or couplings. Pair that with the option of single-cable technology and you’ve got a flexible, precise servo drive solution.

www.seweurodrive.com

power transmission guide

37 08

CONTENTS v o l u m e

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n u m b e r

2

04 EDITORIAL 07 STAFF & AD INDEX 08 CONSIDERING ROLLING-ELEMENT BEARINGS 16 MATCHING GEARMOTORS TO APPLICATION REQUIREMENTS 24 NORTH AMERICAN EV BATTERY PRODUCTION 34 LINEAR TRACK-ROLLER WHEEL DESIGN 40 WINDUP

On the cover: Cleveland-based electric mobility and portable battery manufacturer LAND recently received a $3M anchor investment to help scale production of its cloud-connected CORE battery system featured in its The District electric motorcycles.

Most of the company’s offerings retail for less than $7,000.

For more information, visit LandMoto.io.

24 6

DESIGN WORLD — MOTION

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AD INDEX v o l u m e

1 0

n u m b e r

2

Ace Controls......................................................................29

EDITORIAL

Altech Corp......................................................................BC

VP, Editorial Director Paul J. Heney pheney@wtwhmedia.com

Automation Direct...............................................................1 Bodine Electric Company .................................................14 CGI Inc...............................................................................18 CMT ..................................................................................32 Diequa...............................................................................22 DigiKey................................................................................3 Harmonic Drive.................................................................20 iNTECH Power-Corp.........................................................27 KHK USA Inc....................................................................IBC NB Corp............................................................................12 NBK America.....................................................................23 PBC Linear.........................................................................39 Pyramid Inc. ......................................................................13 Quality Bearings & Components......................................30 Regal Rexnord...................................................................38 Renishaw...........................................................................26 SEW-Eurodrive....................................................................5 Sorbothane........................................................................15 THK America, Inc............................................................. IFC Whittet-Higgins.................................................... 25, 27, 29 Zero-Max, Inc......................................................................2

Executive Editor Lisa Eitel leitel@wtwhmedia.com Managing Editor Mike Santora msantora@wtwhmedia.com

CREATIVE SERVICES & PRINT PRODUCTION VP, Creative Director Matthew Claney mclaney@wtwhmedia.com Graphic Designer Shannon Pipik spipik@wtwhmedia.com Director, Audience Development Bruce Sprague bsprague@wtwhmedia.com

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power transmission guide

Because plastic generates none of the sounds of metal subcomponents, plastic bearings of various types are useful in medical-device and consumer designs that must be quiet. Their nonmagnetic nature is indispensable in magnetic resonance imaging (MRI) machines. 3D rendering: Dreamstime

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rotary bearings

CONSIDERING ROLLING-ELEMENT BEARINGS Rotary bearings based on rolling elements abound … and include designs made for specific mounting configurations, environments, and applications. That said, most all rolling-element rotary bearings are categorized by whether they use balls rollers or cylindrical rollers … and then by the type of load they’re designed to support — whether radial or axial (thrust).

Further classification of roller-based rotary bearings is based on the shape of the rollers — whether cylindrical (having a rectangular cross-section) or tapered (having a trapezoidal crosssection) or spherical (having a barrel or hourglass cross-section).

Sometimes the geometries and other features are concurrently specified in an iterative process.

Radial-load rotary bearings with ball elements

Within the ball-bearing family, deep-groove ball bearings are the simplest type. They have raceways that nearly match or conform to the balls’ common diameter. This bearing type is suitable to bear radial loads and axial loads in either direction … though load capacity is modest compared to that of other bearing types.

Single-row deep-groove ball bearings are perhaps the most common of all rolling-element bearings — and the design hasn’t changed much over the decades. That said, advances in materials and lubrication have extended their average efficiency and life … which is particularly helpful when they’re installed on high-speed axes.

For higher load capacity in a relatively small footprint, deep-groove ball bearings are also available in a double-row

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design with two rows of balls instead of one.

Angular-contact ball bearings have geometry such that an imaginary line through the contact points between inner ring, ball, and outer ring runs at an angle radially to the assembly’s primary axis.

Larger contact angle makes for larger load capacity but renders the bearing incapable of withstanding axial load in more than one direction. That’s why angular-contact ball bearings are often found in pairs or double-row designs — which is essentially two angular contact bearings mounted back-to-back. These ganged bearing arrangements withstand axial loads in both directions.

Four-point contact ball bearings are single angularcontact rolling-element rotary bearings that are designed to withstand high axial loads in both directions. They can also withstand combined axial and radial loads, as long as the axial component is predominant.

Thrust-load rotary bearings with ball elements

These are made of two relatively thin bearing rings (sometimes called bearing plates or washers) with raceways designed to take axial loads, in either one direction or both directions. Radial loads are typically not permissible for thrust bearings, and speed capabilities are limited — as low as 20 to 30% of their radial bearing counterparts in some cases.

Radial-load rotary bearings with cylindrical rollers

With rollers supporting the load, these have higher load capacities and higher rigidity than ball bearings of similar sizes. The type of load they can support depends primarily on the shape of the roller.

Cylindrical roller bearings can withstand high radial loads, while double-row cylindrical versions having extremely high radial load capacity and high

05 • 2024

DESIGN WORLD — MOTION

9

power transmission guide

Image: Dreamstime

angular segments called minutes.

A minute of arc is a unit of angular measurement equal to 1/60 of one degree … with 21,600 minutes in a circle.

The special case of slewing rings

rigidity in the radial direction. Although standard cylindrical roller bearings are not capable of taking axial loads, some designs include internal ribs or collars that allow them to handle relatively small axial loads in one or both directions.

Needle-roller rotary bearings use long, thin rollers, with a length that is anywhere between three and ten times the diameter. They have good radial load capacity, but the primary benefit of the needle design is that it has a thin cross-section, for applications where high radial capacity is required but space is limited.

Unlike cylindrical and needle roller bearings, tapered roller bearings (which use conical rolling elements to support the load) can withstand axial loads in one direction. In fact, a tapered roller bearing can be thought of as the roller version of an angular-contact ball bearing. Like their ball-bearing counterparts, tapered roller bearings often gang in pairs or double-row designs to counteract axial forces produced in the bearing upon radial loading. The tapered design also improves rolling properties and reduces internal bearing friction.

Spherical roller bearings use barrel-shaped rollers and have two inner raceways (inclined at an angle to the bearing axis) and one sphericalshaped outer raceway. This gives these bearings a self-alignment capability as well as very high radial load capacities … and the ability to withstand axial loads in both directions.

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DESIGN WORLD — MOTION

Thrust-load rotary bearings with cylindrical rollers

Tapered thrust roller bearings have pure rolling motion, so they produce less heat and wear than other options.

Thrust versions of roller bearings generally follow the strengths of their radial counterparts but with thrust (axial) load capabilities.

These roller bearings can accommodate high thrust loads and can withstand impact loads, although without additional design features, radial loads are not permissible.

Similarly, needle thrust roller bearings can withstand high axial loads … albeit in a much smaller form factor due to the use of needle bearings.

Tapered thrust roller bearings can be single-direction or doubledirection type, indicating whether they can accommodate axial loads in one direction or in both directions. Like their radial counterparts, the rolling elements in these bearings move with pure rolling for less heat and wear than other bearing options.

Spherical thrust roller bearings can carry very high axial loads (and small to moderate radial loads) and withstand some misalignment. For the latter capability, one common expression is minute of arc or MOA — expressed as 3 minutes of maximum allowable misalignment, for example. This expression derives from how a circle is divided into 360° (angular segments) around the circumference — and each degree is further divided into 60 smaller

05 • 2024

Slewing rings (also called slewing bearings) are large-diameter bearings with thin cross sections (in other words, large bores) as well as flanges or even teeth for tight integration into the designs they complement. They usually install on large rotary axes (direct-drive or geared) in wind turbines, the bases of construction cranes, spinning offhighway equipment such as excavators, research-grade telescopes, and the turrets of military tank vehicles.

Based on either ball or crossed cylindrical rolling elements, they include geometries to bear axial and radial loads while simultaneously resolving the loads associated with tipping.

A few more words on plastic rotary bearings

Not all plastic rotary bearings are plain bearings. Some plastic rotary bearings are rolling-element bearings with balls to bear the axis loads. Others are adapted bearing designs that integrate rollers (embedded over an internal working surface) to serve as deep-groove, thrust, angular-contact, and miniature rolling-element rotary bearings.

In the past, some engineers (especially those most familiar with bronze and steel options) hesitated to specify these various types of plastic bearings.

However, that’s changed with increased market familiarity with engineered plastics over the last couple decades and exhaustive documentation of industrial-grade plastics’ capabilities.

There’s also more engineering support than ever from manufacturers specializing in supplying plastic bearings — so OEMs needn’t start from scratch with mechanical components from injection-molding service providers.

Material-science foundations of plastic bearings motioncontroltips.com

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rotary bearings

Plastic bearings (whether plain or combined with steel or ceramic ball arrays for rolling-element bearing designs) incorporate elements made of a wide range of polymers in various grades as well as hybrid polymer blends. Many proprietary materials (engineered to satisfy specific design objectives related to load and speed ratings as well as heat, chemical, moisture, and even radiation resistance) are typically sold under trademarked names.

Polyacetal — sometimes just called acetal — and polyoxymethylene or POM are all-purpose semicrystalline polymers with excellent chemical, impact, and cold resistance. The opaque white material can be injection molded into even complex shapes with accuracy … and colorized and blended for aesthetic as well as performance objectives. Some thrust washers and flanged plain bearings are made of engineered POM formulations.

Polyamides or PAs classified as nylons (a DuPont trademark though now widely used as a generic term) come in various grades and formulas that are particularly useful in rotary-bearing applications.

The International Organization for Standardization (ISO) 1043-1 standard defines how base formulations are labeled. For example, PA66-GF40 is a heatstabilized nylon 66 — which indicates a molecular structure having two six-carbon-atom monomers — that’s reinforced by glass fibers constituting 40% of the material by weight. Many PA formulas are a dull greyish color and recognized for their bending stiffness and high tensile strength … even beyond 200 MPa in some instances.

Polyimides or PIs (not to be confused with polyamides) are imide monomers … with imide being a chemistry term indicating two acyl groups (C=O) bound to nitrogen. This chemical makeup is suitable for ball bearings with plastic bodies (and plastic plain bearings) that excel on robotics and other mobile automation.

Complicating classifications somewhat are proprietary polymers that are actually polyamideimide or PAI plastics — so designated for their alternating imide links and amide links. Bearings made of some such PAIs can survive impact loading and temperatures to 250° C though at the design tradeoff of vulnerability to moisture absorption.

Polysulfone (PSU) as well as the newer polyethersulfone (PES or PESU) and polyphenylsulfone (PPSU) polymers are amorphous (non-crystalline) plastics — so clear or pale yellow in common formulations. Though more brittle and delivering less tensile strength than some other alternatives, bearings made of these thermoformable plastics can also maintain high stiffness even in hot settings to 160° C and beyond.

DESIGN WORLD — MOTION

11

POWER TRANSMISSION

RETAINING DEVICES & maintenance & assembly tools BEARLOK

SHOELOK

BEARLOK Shrink Disc

BEARHUG

CLAMPNUT

TANGENTLOK

PRECISION NUTS & WASHERS

INCH and METRIC THREADS LEFT HANDED as well as RIGHT -HANDED

ADAPTER SLEEVE ASSEMBLIES

Materials of: CARBON, ALLOY and HARDENED ALLOY STEELS Materials of: ALLUMINUM and CORROSION RESISTANT STEEL NUTS & WASHERS

HARDENED TONGUE WASHERS

SPLIT COLLAR

RETHREADING DIES

ADJUSTABLE SPANNER WRENCH

BEARING ASSEMBLY SOCKET

W

HI

TT

ET

-H

IG

GI

NS US

A

WHITTET-HIGGINS manufactures quality oriented, stocks abundantly and delivers quickly the best quality and largest array of adjustable, heavy thrust bearing, and torque load carrying retaining devices for bearing, power transmission and other industrial assemblies; and specialized tools for their careful assembly.

Visit our website–whittet-higgins.com–to peruse the many possibilities to improve your assemblies. Much technical detail delineated as well as 2D and 3D CAD models for engineering assistance. Call your local

or a good distributor.

33 Higginson Avenue, Central Falls, Rhode Island 02863 Telephone: (401) 728-0700 • FAX: (401) 728-0703 E-mail: info@whittet-higgins.com Web: www.whittet-higgins.com

End Your Machining Headaches …With Tapped or Threaded Shafts Off-The-Shelf.

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rotary bearings

RACEWAY GEOMETRIES TO ACCOMMODATE ROTARY-BEARING ROLLING ELEMENTS Type A (for angular) ball bearings carry axial and radial loads ... and they’re often designed to hold a full complement of balls for higher load capacity.

Radii centers are offset from the ball plane.

RADIAL LOAD OFFSET CIRCULAR ARCH

Line of contact normal to ring faces.

AXIAL LOAD

Groove depth is about 25% of ball radius.

CIRCULAR ARCH TWO CONTACT POINTS

OFFSET GOTHIC ARCH

Type C ball bearings have one row of balls that ride deep grooves to carry radial loads.

GOTHIC ARCH FOUR CONTACT POINTS

Type X ball bearings carry axial and radial loads ... and in some cases, moment loads as well. Some can replace two bearings of simpler geometry.

SIMILARITIES WITH THE GEOMETRIES OF RACEWAYS ON LINEAR-MOTION COMPONENTS ...

TFAHS LEETS

The raceway geometries related to rotary bearings have (in many cases) similarities to those found in the profiled rail, linear spline shaft, and track-roller guides of the linear-bearing world.

Benefits of plastic bearings

NEEDLE-SHAPED ROLLERS

Bearings incorporating plastic elements offer still other advantages.

Of course, ball bearings are only one variation. Other rotary bearings based on rolling elements include ...

TAPERED ROLLERS

TWO SPHERICAL BEARING OPTIONS HOURGLASS-SHAPED ROLLERS

CYLINDRICAL ROLLERS

BARREL-SHAPED ROLLERS

There’s a lot of coverage of ball-element and race-contact arrangements in linear bearings … and in fact, these geometries are relevant to rotary bearings as well.

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Polytetrafluoroethylene or PTFE is a synthetic flurocarbon polymer with exceptionally low static and dynamic friction coefficients than only decrease under compressive stress. Sometimes PTFE is compounded with pigmented additives when used in rotarybearing construction for enhanced wear resistance. Glass-filled PTFE is also common where stiffness is a design objective.

One challenge with PTFE is that it can necessitate special cold molding, sintering, or extruding manufacturing processes. Another challenge is temperature-related dimensional changes even to 1.5% or more in drastic cases.

Polyether etherketone or PEEK is a thermoplastic that’s colorless until formulated into blends for mechanical applications. It’s most common in rotary ball bearings (with either ceramic or stainless balls) that need to withstand steamy or otherwise hot settings that may damage components made of standard acetal or other materials.

Such bearings usually include inner ring, outer ring, and ball-roller cage made of some engineered version of PEEK. Certain highperformance bearings needing high stiffness and load capacity are made of carbon-fiber-reinforced PEEK.

05 • 2024

1. Bearings incorporating plastic elements leverage how plastic is far lighter than the metals typically used in bearing construction. That in turn can trim machine weight and (in mobile designs such as warehouse robotics or other batterypowered vehicles) can trim energy consumption too.

DESIGN WORLD — MOTION

13

Stainless Steel Gearmotors.

Throw your worst at it.

Then wash it off.

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TORQUE

GEAR RATIO

VOLTAGES

29 to 176 rpm

158 to 638 lb-in

10:1 to 60:1

230/460 VAC

Powered by an AC inverter-duty motor with stainless steel, corrosion resistant housing, our new IP-69K rated hollow shaft gearmotors are fully watertight and can withstand rigorous daily washdowns. These geared motors deliver maintenance-free performance where standard gearmotors can’t survive.

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rotary bearings

2. Plastic bearings are more corrosion resistant than metal to better survive food-processing washdown and semiconductormanufacturing cleanroom conditions. Some settings even allow the water present on a machine axis to serve as the plastic bearing’s lubricant.

3. Most plastic bearings can also function sans added lubricant because of plastic’s low coefficient of friction and minimal wear during normal use. This can be helpful for applications that are either difficult to maintain or unlikely to receive maintenance.

Just consider how a plain plastic bearing might outperform a steel bearing with a porous bronze sinter layer impregnated and overlaid with polytetrafluoroethylene (PTFE) material. The linings on such layered bearings can sustain damage upon impact or wear off … especially if abrasive contaminants get between the bearing’s inner lining and shaft.

In contrast, self-lubricating plastic plain bearings in such settings — especially monolithic offerings constructed of a homogeneously blended base, fiber, and solid-lubricant materials — induce no shaft wear and maintain the specified coefficient of friction over the entire design life. That’s true even on reciprocating or oscillating axes. Such plain bearings carry solid lubricant in the fiberreinforced material of their inner lining to transfer onto the shaft, no matter the axis rpm or shaft type.

5. Plastic bearings are maximally configurable with materials, geometries, and treatments to satisfy very specific design life, speed, load, temperature, and shaft requirements. Decades of testing mean that even customized plastic bearings often come with extensive documentation regarding material performance.

Shown here is a magnetically detectable rolling-element xiros M180 rotary bearing and a spherical-bearing rod end from igus. Neither require additional lubrication.

SHO

LU ION SO T A R B I CK & V

NEED A STANDARD VIBRATION ISOLATOR?

4. Bearings incorporating plastic elements don’t conduct electricity and are nonmagnetic.

This is extremely important for any market where the bearings will be near sensitive electronic components or electromagnetic operations.

We Have A Solution for That!

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power transmission guide

Gearboxes and ac motors pair to drive bottling equipment in the food and beverage industry.

Standard gearmotors are designed to operate over a wide range of

MATCHING GEARMOTORS TO APPLICATION REQUIREMENTS 16

DESIGN WORLD — MOTION

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 05 • 2024

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gearing

Image: Dreamstime

winding insulation that leads to motor failure in other designs.

The insulation of inverter-duty 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.

Permanent-magnet ac motors

In addition, with construction and operation much like those of brushless dc (bldc) motors, synchronous ac motors — sometimes billed brushless ac, permanent-magnet (PM) ac motors, and even permanent-magnet synchronous motors (PMSMs) — are now motioncontroltips.com

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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 rotor-stator 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 05 • 2024

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gearing

(and back-EMF output with trapezoidal waveform needing direct current input) synchronous ac motors are wound sinusoidally. That makes for sinusoidal backEMF 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 designworldonline.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.

The limits of a gearmotor include those related to unusual loads, load arrangements, and duty cycles.

Durability and (gear) strength ratings are the limiting factors when a gearmotor is subject to cyclical loads. Note however that these load types differ from the rapid stops or reversals that can damage most gearmotors … especially inertial-load plug reversals — rapid switches in rotational direction sans intermediate stopping. That’s why properly designed gearmotor axes will either bring attached loads to a full stop before reversing ... or will fully disengage load attached to the gearmotor before such changes.

One common solution is to include a clutch or brake in the assembly to prevent large inertial loads from driving the gearmotor backward through axis backlash … or forward after de-energization.

Another common solution is the employ drives and controls capable of electronic compensation to prevent such backdriving and overrunning, which can otherwise damage gearmotors as mentioned … as motioncontroltips.com

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well as attached system components and workpieces.

Sudden or erratic and large peaks in torque called shock loading present similar modes of potential gearmotor damage.

Such loading is in some cases unavoidable. After all, punches, presses, and extruders subject their components to necessarily powerful strokes during normal operation; professional-grade crushers and power tools must sometimes power past temporary obstacles and jams; debarking, grinding, and chopping axes must sometimes drive through unusually dense material volumes; and hoists and conveyors must sometimes overcome sudden additions of payload — as when unexpectedly large products are dropped on conveyances, for example.

Shock loading is generally quantified by its severity as well as its switching duty — the frequency with which the torque peaks occur. Most gearmotor manufacturers publish figures on maximum gearmotor shock-loading capabilities according to a grading system or as a percentage of running load.

For example, a heavily ruggedized unit

05 • 2024

may be capable of withstanding shock that is 300% greater than the typical continuousrunning load for the axis. However, especially challenging inertia ratios and duty along with significant shock-load conditions (as well as shock-amplifying mechanical components such as chain in the drivetrain) can often necessitate further upsizing of the gearmotor.

Yet another extenuating condition is that of overhung loads — those which occur when some load exerts a perpendicular force (or hangs off) a gearmotor’s output shaft.

These loads can be: • (Most commonly) attached powertransmission components (including cable, belt-drive pulley, or chain sprocket) • (Less commonly) the payload itself • Shaft misalignment, often addressed with the addition of a flexible coupling.

Overhung loading can cause detrimental bending in the gearmotor output shaft — necessitating resistance to this force by both the shaft itself as well as its support bearings. In fact, any mechanical belt, cable, or chain drive directly mounted on the gearmotor’s shaft will exert some bending

DESIGN WORLD — MOTION

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force. Mounting such drives as close as possible to the gearmotor body helps minimize the effects of overhung load on the bearings and shaft.

Overhung load equals the ratio of torque to the radius of mechanical outputshaft component multiplied by a power-transmission adjustment factor.

In some rating Here, temperature sensors are systems, the latter embedded in the motor stator windings is unity for chain to communicate unacceptable thermal drives, 1.3 for conditions to a motor-protection relay. timing-belt drives, and 2.5 for flat-belt drives. down or completely fail. This is why many Once the motors and gearmotors — especially those (unavoidable) overhung load requirement used in motion-control applications — have for a given axis is calculated, the design thermistors or silicon-resistive sensors (also engineer should consult overhung-load called KTY sensors) integrated into the motor limits in charts supplied by gearmotor manufacturers ... or communicate the details windings.

Note the KTY designation was assigned by of the overhung load during the specification Philips Semiconductors, the sensors’ original process. manufacturer. KTY sensors directly monitor winding temperature (instead of measurements Thermistors and KTY sensors in of current) and work in conjunction with gearmotors protective circuits to prevent damage due to One of the most important parameters of motor excessive temperature. and gearmotor operation is the temperature of Another important caveat is that here the motor windings. we cover how some gearmotor designs Motor heating is caused by mechanical, rely on thermistors (in conjunction with electrical, and copper losses, as well as heat complementary circuitry) for current limiting transferred to the motor from external sources, and other motor-protection functions. Another including the ambient temperature and option for compensation of increased (but surrounding equipment. If the temperature of within the range of normal) motor temperature the motor windings surpasses the maximum is based on drive electronics. Some of these rated temperature, the windings can be track motor-resistance changes through damaged ... or the motor insulation can break associated declines in voltage.

Then field flux is modulated to prompt tighter regulation of the motor output. Otherwise, vector drives with direct torque control over motors

may modulate input carrier frequency to profile the motor as a way to improve torque and speed control accuracy (even at slow rpm).

PTC and NTC thermistors

One alternative for temperature monitoring in motors is thermistors.

Thermistors are devices that exhibit a predictable and precise change in resistance when they experience a change in temperature — regardless of whether the temperature change is caused by conduction or radiation from the surrounding environment or by selfheating due to power dissipation.

Thermistors are divided into two primary types: • Those with a positive temperature coefficient (PTC) • Those with a negative temperature coefficient (NTC) Positive temperature-coefficient thermistors experience an increase in resistance as temperature rises while negative temperature coefficient devices experience a decrease in resistance as temperature rises.

Positive temperature coefficient thermistors are typically made of ceramic

Thermistors are devices that exhibit a predictable and precise change in resistance when they experience a change in temperature — regardless of whether the temperature change is caused by conduction or radiation from the surrounding environment or by self-heating due to power dissipation.

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material that has been doped to create a semiconductor. These semiconductor PTC sensors have a nonlinear resistancetemperature curve, and at a critical temperature (sometimes called the switch temperature or Curie temperature) resistance increases significantly. This sharp spike in resistance can be used to trigger protective relays that switch off current to the motor, preventing damage to the windings and insulation.

NTC thermistors experience a nonlinear decrease in resistance with an increase in temperature, while PTC thermistors experience a slight decrease up to a critical temperature (Tc) at which point resistance increases significantly.

Negative temperature coefficient thermistors are made from a type of ceramic (polycrystalline oxide ceramic) that exhibits a very precise change in resistance as temperature changes.

Where PTC thermistors exhibit a “switching point” at a critical temperature, NTC thermistors are better suited for precise temperature monitoring over a wide temperature range and are often used for monitoring and limiting inrush current.

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More on silicon resistive sensors

Another type of positive temperature coefficient sensor is the silicon resistive sensor — the KTY sensors mentioned earlier.

These PTC sensors are made of doped silicone and manufactured with a process referred to as spreading resistance, which makes resistance nearly independent of manufacturing tolerances.

Unlike PTC thermistors, which experience a sharp rise in resistance at a critical temperature, KTY sensors have a nearly linear resistance-temperature curve.

KTY sensors have a high degree of stability (low thermal drift) and nearly constant temperature coefficient and are also typically lower cost than PTC thermistors.

While both PTC thermistors and KTY sensors are commonly used for monitoring winding temperature in motors and gearmotors, KTY sensors are more prevalent in large or high-value motors such as ironcore linear motors due to their high accuracy and linear behavior.

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power transmission guide

Volvo Trucks’ latest addition to its electric truck program – Volvo FM Low Entry – is a heavy-duty truck specifically developed to handle a wide variety of transport assignments in city areas. It’s also the first truck model ever developed by Volvo which is available only with an electric drive.

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ev battery production

NORTH AMERICAN EV BATTERY PRODUCTION By 2028, the 40-plus electric vehicle (EV) battery-manufacturing sites in the U.S. could annually output products capable of 1,037 GWh ... tracking to increase by twentyfold from the size of the industry just a few years ago, according to the U.S. Dept. of Energy. One geographical corridor running from Michigan to Alabama currently dominates the industry, benefitting from a $2.8B federal infrastructure investment to (among other things) develop commercial-scale facilities for extracting, processing, and recycling battery materials including lithium and graphite.

In fact, Tesla, Toyota, General Motors, Honda, Hyundai, MercedesBenz, Stellantis, and Volkswagen all have invested in North American battery-making facilities; Ford and Mazda have

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also made moves (albeit tentative and rescaled) to leverage such facilities.

So, Design World asked several industry experts about the efforts they’re seeing to make the energy and automotive industries (and their support of EVs) more domestically reliant.

Here’s what those experts had to say.

What’s the latest in North American EV battery manufacture?

Lin: The U.S. and Canada have significantly enhanced their competitiveness in EV battery manufacturing through government initiatives, technology advancements, and industry collaborations.

Policymakers in both countries have implemented a range of incentives, tax credits, and regulations to promote widespread adoption of electric vehicles. They’ve also supported domestic development in upstream and midstream processes through the Inflation Reduction Act’s battery rules.

Continued collaborations among automakers, technology companies, and battery manufacturers to develop increasingly efficient and cost-effective EV

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power transmission guide

batteries (and scale manufacturing to mass production) remains vital. Creating a sustainable electric mobility ecosystem in the U.S. and Canada will necessitate development of upstream, midstream, and downstream battery-production efforts — and successful scaling to meet EV market demands.

from targeting early adopters (attracting only those willing to pay a premium for an EV) to having broader appeal. These new customers are more price-sensitive … so the best way to ensure competitively priced

vehicles is to establish reliable large-scale supply chains that are local. Significant investments and the leveraging of incentives offered by the Inflation Reduction Act have provided a strong foundation for

Caldwell: Technological advancements and manufacturing changes in the automotive industry continue to drive innovation. To accommodate rising demand for affordable eco-friendly modes of transportation with less moving parts, EVs equipped with highcapacity batteries are now the focus of future U.S. and Canadian transportation — as well as automation.

Garbe: Given all the uncertainty geopolitically and in the global economy, it’s extremely important to establish strong North American supply chains to support the battery and EV market. The latter has moved

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the sustainable growth of the U.S. and Canadian EV market.

Here, a COGNEX D900 assists in the inspection of an EV battery cell pouch surface.

battery-powered electric vehicles as the only EVs, it’s actually hybrid vehicles as well as e-bikes, e-scooters, and e-motorcycles that will continue to expand the market. Top objectives are quality, short lead times, and reduced costs for components and sub-assemblies — all arguments to use automation during production.

In fact, mobility electrification has only increased the need for electronics in the past only used on traditional two and four-wheel internal-combustion vehicles.

Leath: Many automotive companies are trying to figure out where they want to offer advantages in the EV space. The experience of the EV vehicles from manufacturers such as Tesla prove to be a green initiative and one that saves consumers both money and maintenance effort — not to mention an enjoyable driving experience. Because these vehicles don’t need the exhaust and engine components of How is automation used in this specialized internal-combustion vehicles but do need to bear heavy market? batteries, manufacturers are looking for new processes to produce them.

Marks: With various global goals around electrification For example, gigacasting entire frames eliminates and sustainability, the demand for lithium-ion batteries separate forming and joining processes but requires (both for EVs and battery storage) is continuing to grow preparation and finishing processes that differ from those of traditional casting approaches before the cast parts are ready for assembly with the rest of the vehicle. New Aaron Donlon | Product manager • Epson Robots materials are also being used for further Chris Caldwell | Product manager — material handling • Yaskawa Motoman lightweighting efforts while increasing Gian Sachdev | Marketing head — Americas demand generation • Cognex vehicles’ strength and safety. U.S. Jarod Garbe | Industry segment manager — e-mobility • Festo manufacturer Tesla is leading the way with Josh Leath | Senior product manager — thermal • Yaskawa Motoman their processes, and companies such as Kenny Marks | Process systems and solutions business development manager • Emerson GM and Toyota are taking notice.

Lawrence Lin | Business development manager • Festo Patrick Varley | Product marketing manager — robotics • Mitsubishi Electric Automation Inc. Donlon: Demand for e-mobility has Rashid Farahati, Ph.D. | Director — corporate competence center • Schaeffler Americas been expanding in North America.

Yugi Ikeuchi | GM — Engineering and app development • IKO International While many people traditionally think of

MEET THE EXPERTS

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power transmission guide

at a rapid pace. The world will need a lot more batteries than today’s supply, capacity, and operations can support. North America is in a strong position to contribute to that global supply.

Automation will be key to meeting this need. The battery manufacturing drive is coming right at a time where companies cannot find the experienced people needed to perform battery manufacturing operations manually. Moreover, best-in-class automation will be critical to safely achieving the high purity and quality necessary to produce EV batteries.

Ikeuchi: EV markets are seeing substantial growth thanks to increased demand and new global policies. As EV advancements drive investments in automated production infrastructure, some aspects of EV manufacturing necessitate careful consideration of the most appropriate motion systems.

Lin: From the initial handling of raw materials to the final stage of recycling used batteries, our automation solutions cover the entire spectrum of battery production. We provide pneumatic and electric automation components as well as process valves to meet the rigorous specifications required for the cost-effective mass production of EV batteries. These automation components are well-suited to various stages of the manufacturing process, including handling raw materials, producing battery cells, assembling modules and packs, and recycling used batteries.

Marks: EV battery manufacture involves a very complex and involved supply chain.

Emerson supports the entire supply chain —from the mine to the Gigafactory — in extraction, lithium processing, precursor and active-material production, battery assembly, and even battery recycling. There’s a lot of built-in advanced functionality (especially between the DeltaV Automation Platform and advanced control from Emerson-supported AspenTech) to improve end users’ ability to drive processes and eliminate supply-chain variabilities.

Within the lithium-battery value chain, companies use our systems because they can scale and grow. After all, when companies aim to engineer better batteries, they need

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supporting technologies for research and development efforts as well as scale production efforts.

Many innovators start in small facilities and focus on testing and validation. With any success, these innovators must then quickly scale in facility size and functionality.

Using our vast and integrated portfolio, such innovators can easily mature while still maintaining the quality and compliance needed to achieve commercial production.

What specific components and systems are used in battery manufacture?

Sachdev: As EVs continue to grow in popularity, one of the biggest challenges for manufacturers is scaling quickly while meeting extremely high quality standards.

There’s no room for error when producing EV batteries, as even small holes, scratches, or dents can degrade efficiency and compromise safety.

To help battery manufacturers meet these challenges, we offer a powerful combination of: • Software (VisionPro deep learning) • Smart cameras (In-Sight 3D-L4000) • Lighting (Trevista CI dome).

Together, these can accurately differentiate between superficial and functional flaws in welds, cell surfaces, and glue seams.

Lin: In the handling of raw materials and recycling processes, we offer customizable process valves equipped with sensors and energy-efficient positioners featuring analog or digital feedback. These components ensure reliable and secure processes of the electrolyte and black mass. For sensitive production processes before the battery cell is sealed for testing, Festo offers an extensive range of copper-free, zinc-free, and dry-room compatible components, addressing the specific requirements to manufacture quality batteries.

We also provide the convenience of configuring multi-axis Cartesian gantries online for adhesive dispensing, cell placement, and module assembly in battery-pack production. The gantries provide high speed and accuracy ... and help optimize the use of floor space in the manufacturing plant.

Leath: This year we’re releasing two arms 05 • 2024

specific to this market. One is a limited-axis large-payload arm made for manipulating battery trays. The other is a high-rigidity robotic arm made for use with friction stir welding — a process commonly used in battery tray production and finding its place in other applications involving dissimilar metals or airtight components. motioncontroltips.com

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ev battery production

Varley: At Mitsubishi Electric Automation, we’re heavily involved with global EV battery manufacturing. Our robotic focus is for smaller robots — those with 20 kg or smaller payload — and this type of robot is widely used in EV battery production. Our other automation products fit well with this industry as well.

Garbe: Festo’s product portfolio has been tailored to meet the specific needs of the battery ecosystem. This includes solutions for material extraction, cell production, EV integration, and the emerging batteryrecycling industry. For example, we have a full line of process automation products (including corrosion-resistant ball and butterfly valve assemblies, for example) that excel in raw-material battery manufacturing processes. For battery assembly, we offer copper and zinc-free and dryroom-compatible variations of many automation components.

Case in point: Festo’s multi-axis Cartesian handling systems are widely used in battery-module assembly processes. Cartesian systems allow for high speed, high accuracy, and reduced footprints compared to other solutions.

Plus we’re constantly developing new custom solutions to satisfy this dynamic market and encourage customers to challenge us with their most demanding applications.

Cleveland-based electric mobility and portable battery manufacturer LAND recently received a $3M anchor investment to help scale production of its cloud-connected CORE battery system featured in its The District electric motorcycles. Most of the company’s offerings retail for less than $7,000. For more information, visit LandMoto.io.

05 • 2024

Farahati: Today’s top EV challenges include limited driving range on a single battery charge; fire risks associated with liquid electrolytes in used in today’s batteries; and long charging times, especially in cold settings.

Within the specialized market of next-generation EV battery production, Schaeffler’s components and systems play a crucial role in advancing the emerging battery technology known as all-solid-state electrolyte batteries or ASSBs. ASSBs are essential to the future of EVs due to their inherent advantages, which include: • Higher energy density than current state-of-the-art batteries (resulting in longer range on a single charge) • Faster charging times due to the

DESIGN WORLD — MOTION

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ev battery production

unique anode design • The ability to operate in higher temperatures without fire hazards (thereby improving reliability) and • Increased safety (as ASSBs eliminate the use of flammable organic electrolytes present in current batteries).

Schaeffler is developing a next-generation ASSB that benefits from our company’s extensive engineering and manufacturing know-how to help overcome current challenges faced by ASSB production.

Because there is no liquid electrolyte between the anode and cathode, maintaining low ionic impedance during charge and discharge is essential.

Here, special manufacturing techniques such as isostatic pressing apply high pressure and eliminate voids or gaps between grains and interfaces.

During the charge and discharge cycles, the anode and cathode of ASSBs expand and shrink, potentially causing cracks between grains and interfaces. To address this issue, we are designing an active-pressure battery module that constantly applies proper pressure to prevent crack initiation.

Moreover, Schaeffler has partnered with The Ohio State University to create a 25,000-squarefoot battery research and development center on the university’s campus. Slated to open in April 2025, the facility’s areas of focus will include further development of ASSB technology.

A Festo controller and automated process valves simulate the automated extraction process of precious materials from a slurry of shredded EV batteries.

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Ikeuchi: IKO offers several solutions for EV battery manufacture, including linear guides and precision positioning tables for repeatable linear motion — key for equipment to move batteries or subcomponents from one workcell to another.

Here, rolling-element linear guides with cylindrical rollers provide a large raceway contact area to deliver high load capacities and rigidity.

IKO positioning tables feature mechatronics suited to both the production and inspection of precision EV battery components; linear and rotary actuators deliver a wide range of load capacities and high positioning accuracy and repeatability as well as the ability to satisfy the high duty cycles associated with EV-component production. Other copper-free linear products with stainless steel parts abound.

For example, IKO also offers a cleanroomrated actuator that is suitable for the production of sensitive EV-related components .. and linearmotion guides and various actuators to deliver the precise motion that EV systems require — along with stainless-steel options and other protective accessories to properly handle sensitive lithium-ion elements.

DESIGN WORLD — MOTION

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ev battery production

Electric-actuator market trends

These insights are based on a recent Fact. MR report titled, Automotive Actuators Market.

Automotive electric actuators adjust engine settings; manage safety features; and impart precise control fuel efficiency.

Many such actuators are compact and light, fitting well in modern cars and requiring less maintenance. Some can be programmed to execute different tasks.

The market for these automotive actuators is likely to grow at a moderate pace and reach U.S. $38.3B by 2032 thanks in part to a few key drivers.

Growing vehicle production: The automotive actuators market is experiencing growth primarily due to the increased production of vehicles worldwide to satisfy rising demand for cars. That’s especially true in China and India, where growing incomes and urbanization are causing more people to purchase vehicles.

The rise of EVs: With the growing adoption of EVs, the need for actuators is expanding, fueling market growth in the automotive actuators segment.

Case in point: During last year’s Battery Show in Michigan, Marelli presented a smart actuator for EV transmission and thermal management systems. The actuators include a flexible and scalable mechanical design, an electronic control and networking module, and software to support easy integration.

Stringent emission regulations: Another growth driver is increasingly stringent emission regulations that are compelling internal-combustion car makers to adopt clean-engine technologies such as variable valve timing and exhaustgas recirculation. These advanced engine systems need precise control with actuators to regulate exhaust flow and timing, reduce emissions, and maximize engine efficiency..

Advancement of safety functions: Advanced driver assistance systems (ADASs) include features such as adaptive cruise control, lane-keeping assist, and emergency braking. These ADAS features heavily rely on actuators for adjusting speed, steering, and braking in response to changing traffic conditions. As ADASs

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become increasingly common, there’s a growing demand for the advanced actuators to support their functions.

Autonomous vehicles: Actuators are at the core of autonomous steering, braking, and throttle control — translating electronic signals into mechanical actions for safe navigation without human intervention. Their precise and reliable operation is essential for ensuring the safety of passengers and pedestrians alike.

As self-driving technology advances and becomes more mainstream, the demand for advanced actuators capable of supporting autonomous driving functionalities will continue to grow. This increasing demand is expected to drive innovation in the automotive industry as manufacturers strive to develop actuators that meet the stringent requirements of autonomous vehicle systems.

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A cantilever handling system based on Festo ELGT spindle axes ensures dynamic and safe loading and unloading of the process chamber.

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power transmission guide

LINEAR TRACK-ROLLER WHEEL DESIGN

Track-roller wheels can be customized to the application at hand through their internal bearing-element arrangements; sealing; and outer tread geometry and material makeup. In this context, the term treads refers to the wheels’ thick OD working surface, just as in automobile tires. The environment dictates which trackroller wheel-sealing options are most suitable.

Wheel treads and internal subcomponents are typically manufactured out of carbon steel, high-alloy steel, stainless steel, performance polymers, and even aluminum in some cases. Consumer-grade and simple medical-device applications may benefit from polymer track-roller wheels to minimize noise. Where a linear axis is subject to light debris or washdowns, sealed bearings are necessary — as are stainless-steel wheel sections. Steel track-roller wheels (and even heat-treated variations with engineered high-temperature lubricant) may also be necessary in or near ovens and other hot applications exposing linear axes to 200° C and beyond. Machine-tool applications and

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linear motion

Cam followers and track-roller linear guides are two technologies from the same origin. However, track-roller linear guides rely on advanced wheel arrangements and track integration for maximal linearmotion accuracy and reliability.

other designs subjecting the track-roller wheels to more copious or detrimental debris (such as metal shavings) may necessitate track-roller wheels with fully sealed and shielded bearings to prevent brinelling, spalling, and premature failure.

Some track-roller wheels are supplied from the manufacturer lubricated with lithium grease. Larger variations may have a relubrication port at their inner ring.

Regarding their geometries, track-roller linear guides include variations employing flat track rollers, crowned (rounded) track rollers, vee-shaped (notched) track rollers, chamfered track rollers, and flanged track rollers.

Flat track-roller wheels are just as they sound — simple flattreaded wheels. Many of these wheels also include treads machined of alloy steel and case hardened to Rockwell hardness of Rc 55 and beyond for tread wear resistance complemented by a softer (and tough) inner core.

Flat track-roller wheels pair with various linear tracks — including simple bar and square tracks as well as hollow-box tracks.

They are indispensable in heavy-duty automation, energy, and material handling applications.

Crowned (rounded) track-roller wheels include a slightly rounded radial profile on their OD. This geometric feature incurs

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additional cost but compensates for modest misalignment between the track-roller wheel and the track on which it rides. Such accommodation in turn helps avoid corner loading that would otherwise occur on the sharp shoulders of flat wheel profiles — and that minimizes thrust loading on the load-bearing elements contained inside the wheel. Crowned track-roller wheels (which are usually hardened steel) also minimize thrust loading during circular motion, such as that which can occur on curved sections of specialty track-roller linear guides. Speed is limited to a meter per second or so.

Note that crowned wheels can be ganged into concentric trackroller wheel pairs (to bear load) with one eccentrically mountable track-roller wheel to complete the carriage. The eccentrically mountable wheels are adjustable to impart preload and hold the load-bearing wheels firmly against the working track — so all the wheels on a carriage thus outfitted will roll without skidding or slipping. In fact, wheels accepting eccentric adjustment can also serve to compensate for wheel or track wear over time. Key to this arrangement are the designs of fixed bushings (for the load-bearing wheels for the radial load direction) and adjustable bushings (for the adjustable wheel).

Crowned track-roller wheels are most common in designs with

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linear motion

modest accuracy requirements — often paired with tracks that are simply welded onto the machine frame. These designs include those in certain office equipment as well as packaging and HVAC applications.

Elsewhere (in exceptionally rugged powertransmission applications) crowned wheels setup to ride on the surfaces of structural beams. Slightly more precise designs may pair the wheels with generic metal framing — long sheet metal or bar sections formed into C and U-channel tracks — such as those standardized by metal-framing supplier Unistrut USA of Atkore International Inc. Chamfered track-roller wheels are wheels that often include other geometries described here (such as V-shaped profiles) or tapered profiles. Chamfering serves the same purpose of crowning — avoidance of corner loading — which is useful in heavyduty applications such as fork trucks and other lifts.

V-shaped (sometimes called notched) track-roller wheels include a V-shaped radial cutout to mate with a track having a male V-shaped protrusion. These wheels are often wide enough to incorporate ground double-row or deep-groove angular contact ball bearings … or (in even larger iterations) tapered roller-bearing elements. V-shaped track-roller wheels operate on low to very high-accuracy axes; mounting greatly influences their overall precision. Benefits of these V-shaped wheels include the ability to

resolve radial and thrust loads as well as the tendency to shed debris — especially when the contaminants first land on the sloped sides of male V-shaped track. Track-roller linear guides with steep side angles are especially good at clearing debris.

Just like crowned track-roller wheels, V-shaped track-roller wheels also lend themselves to mounting in sophisticated arrays on their carriages … including eccentric adjustment to compensate for system wear. Or some designs may include tandem linear guides with one employing V-shaped track-roller geometry … and its parallel twin employing crowned trackroller geometry to resolve other loads and machine-frame imperfections.

As mentioned, V-notched trackroller wheels ride on ridged tracks having sloped angles matching their own notch angles. Tracks and wheels from different manufacturers aren’t designed to be interchangeable.

Where the raceway ridge is simply machined onto an extruded bar and plate, the design’s parallelism, flatness, and straightness tolerances are not particularly tight … so deliver accuracy to about ±100 µm … though such designs do make for exceptionally cost-effective solutions. Some manufacturers offer V-tracks that are induction hardened and polished on the surfaces destined to serve as the working raceways, but then leave the rest of the track untreated to make it easier to drill with holes for mounting.

At the other end of the spectrum, track-roller linear guides with V-shaped wheels on precision engineered raceways with drawn,

hardened, and ground steel surfaces can deliver accuracies to ±0.025 mm or better.

Professional installation is necessary to maintain this and other precision values.

Such tracks are offered in various grades of stainless steel to withstand harsh environments.

Note that there are other linear guides that leverage the benefits of V-shaped geometry. Instead of V-shaped track-roller wheels, these designs employ flat trackroller wheels mounted on V-shaped carriage to ride the two sides of a larger V-shaped track.

On flanged track-roller wheels, one or both axial sides have a wide flare. This serves as yet another mode of centering (tracking) the wheels on the linear raceway.

U-groove track-roller wheels have a scooped (rounded) channel around their treads’ radial profile to securely ride on round-profile shaft. Most of those for motion applications are made of high-carbon chromium alloy steel that is hardened and ground — and sealed and lubricated for life.

In fact, the exact geometry of this U groove is highly engineered for secure and smooth traversal of the track races. Though not typically suitable for heavy-duty applications, U-groove track track-roller wheels maintain exceptionally reliable guidance on reciprocating axes as well as vertical lifts and those subject to shock loading.

U-groove track-roller wheels are also called Gothic rollers. They’re often paired with hardened and ground steel raceways having a round profile and securely press fit into engineered receptacles on aluminumalloy extrusions. Lengths are to several meters.

One final note: Beyond profile geometries, track-roller wheels also allow customization in how they’re arranged and mounted on their carriages and other movable machine sections. Above we Shown here are the track-roller linear carriage wheels for several different linear guides. Image: Dreamstime

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linear motion

briefly covered how gangs of wheels sometimes include a track-roller wheel that serves as an eccentrically-mounted take-up wheel. Elsewhere, carriages with gangs of four, five, or even more wheels per side deliver exceptional linear-guide accuracy.

Mounting track-roller linear guides

For profiled rails with recirculating bearing elements, error in alignment degrades bearing preload accuracy and induces uneven loading as well as premature wear. This is not the case for track-roller linear guides, because carriage preload is adjustable — making mounting requirements for track-roller assemblies much less stringent than those for profiled rails. In most cases, mounting a track-roller linear guide rail doesn’t require a reference edge, even when mounting two guide rails in parallel.

Because many track-roller linear guide rails are aluminum, mounting them to aluminum substructures (such as extruded profiles, requires no special preparation or machining for flatness or straightness.

This makes track-roller linear guides a good choice for self-assembled linear actuators.

Taking this forgiving mounting feature a step further are some track-roller linear guides in large-scale printing and slicing applications. Many of these can even accommodate imperfect machine-frame geometry. Here, track-roller linear guide pairs with complementary geometry to accommodate the changing direction of the force vectors resulting from machine-frame misalignments.

More specifically, such track-roller linear guide pairs might include: • One guide with a C-shaped track having a flat raceway surface — to impart lateral freedom to a couple millimeters or more • Another guide with a track that constrains the track-roller wheels on one flank while permitting slight rotation on the other flank — to impart angular freedom to a couple degrees or more Together the linear guides work well even on nonmachined out-of-parallel surfaces for linear strokes sans excessive friction.

In contrast, traditional linear guides in such applications register misalignment as additional load that (due to no DOFs in the mounting surface or linear guides) causes tensile force within the guide assembly — even to the point of binding. That’s an especially distinct possibility on very long machine axes where even small assembly errors cause rather dramatic effects over the course of strokes that are multiple meters long.

Track-roller linear guides are indispensable on extendedstroke applications, where they can compensate for slight geometrical inconsistencies that are quickly magnified into significant errors by lengthy axis stretches.

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BELT AND PULLEY INERTIA found by multiplying the mass per unit length by the total length of the belt.

In calculations, just be sure to use the full circular belt length — not just the length of the stroke. Also remember that the applied load is typically mounted to the belt via a carriage or table, so the mass of this part should be included in the mass of the applied load.

The pulleys and coupling can be treating as solid cylinders that rotate about their own axes, and their inertia can be calculated as:

Where Jp = Inertia of solid cylinder — pulley and coupling, kgm2 m = Mass of cylinder, kg r = Radius of cylinder, m

Belt-driven linear systems are common in applications that require long travel and high speed, such as gantry robots and material handling and transport. The motors of choice for these systems are often servomotors, for their ability to accurately control position, speed, and torque.

For a motor to accelerate or decelerate a load, it must overcome the load’s inertia or resistance to change in motion, as defined in Newton’s First Law. In belt-driven linear motion systems, the motor must overcome not only the inertia of the applied load but also the inertia of the belt, pulleys, and motor coupling.

The inertia of each component can typically be estimated with sufficient accuracy by using the standard inertia equations for simple shapes.

Because inertia depends upon the axis around which the component rotates, we can start by considering the applied load and the belt together, since they both rotate around the axis of the driven pulley.

The applied load and the belt can be modeled as a point mass that rotates around the driven pulley, and their inertia can be calculated as:

Where JL = Inertia of belt and applied load, kg·m2 m = Mass of belt and applied load, kg r = Radius of driven pulley, m Belt manufacturers typically provide mass (or weight) information per unit length, so the mass of the belt can be

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Keep in mind that although the pulleys may have the same diameters (and radii) if one pulley is toothed (driven) and the other is smooth (idler) … as is the case in many belt-driven actuators, they will have different masses and therefore different inertias.

Although the solid cylinder approximation shown above is typically sufficient, more accurate inertia values for the pulleys and coupling can be found by considering that these components have a center bore and using the inertia equation for a hollow cylinder:

Where Jph = Inertia of hollow cylinder — pulleys and coupling, kg·m2 m = Mass of cylinder, kg ro = Outer radius, m ri = Inner radius, m.

It’s common for belt driven systems to use a gearbox to increase torque, reduce speed, and reduce the inertia of the load reflected to the motor. In this case, the total inertia of the moved mass (applied load, belt, pulleys, and coupling) should be divided by the square of the gear reduction, and then the inertia of the gearbox should be added. This will give the total inertia reflected back to the motor, which can be used for motor sizing and selection.

Where Jtotal = Total inertia reflected to motor, kg·m2 JL = Inertia of belt and applied load, kg·m2 Jp1 = Inertia of first pulley, kg·m2 Jp2 = Inertia of second pulley, kg·m2 Jc = Iinertia of coupling, kg·m2 i = Gear reduction Jg = Inertia of gearbox, kg·m2 05 • 2024

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