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How to specify motion components for cleanroom environments: Part 2

September 5, 2018 By Danielle Collins Leave a Comment

In this two-part article, we cover the products, materials, and features that designers and engineers should specify when choosing motion components for cleanroom environments.

In part 1, we looked at how to reduce particle generation due to friction between moving components. In this second part, we’ll look at another source of contamination — outgassing — and how to minimize it.

Objective #2: Minimize outgassing

Silicon wafer processing is extremely sensitive to contamination, including both particulates and outgassing.
Image credit: WaferPro

In cleanroom applications that involve the manufacture of LEDs, optics, or glass, or the processing of silicon wafers, a second type of contamination can damage the process or the product: outgassing.

Outgassing is the desorption of vapors or gasses, either from within a material or from the surface of a material. ISO standard 14644-8 addresses outgassing in cleanroom environments and specifically refers to airborne molecular contamination (AMC) as:

The presence in the atmosphere of a cleanroom or controlled environment of molecular (chemical, non-particulate) substances in the gaseous or vapor state that may have a deleterious effect on the product, process, or equipment in the cleanroom or controlled environment.

These types of airborne molecular contaminants take the form of molecular vapor. They’re smaller than particles and easily pass through HEPA and ULPA filters, making them particularly difficult to control once released.

Minimize outgassing through material selection

The first criteria when choosing motion components for cleanroom environments where outgassing is a concern is to ensure the material has a smooth surface, which makes it more difficult for airborne molecular contaminants to adhere to the surface. Stainless steel and anodized aluminum are the preferred materials, although some epoxy paints are suitable for environments where low-outgassing is required.

Fortunately, numerous motion control components, such as linear guides, motors, and gearboxes, can be made of stainless steel. When possible, plastic end caps on linear guides and screws should also be replaced with stainless steel versions to further minimize the use of plastics. And standard steel fastening hardware, such as screws or pins, should be replaced with stainless steel versions.

Although epoxy paint is sometimes suitable for motor and gearbox housings, stainless steel versions are better options.
Image credit: Wittenstein

When the required material has a high outgassing tendency, other solutions exist. For example, epoxy paint is suitable in some cleanroom environments and can be applied to the housings of linear actuators, motors, and gearboxes. And when steel is required — to maintain hardness, durability or load-carrying capacity — nickel plating can reduce the tendency of steel to outgas. (Note: Some nickel-plating formulas include a PTFE, or Teflon^®, top coat. The use of Teflon is generally advised against, so be sure to choose a nickel plating formula that does not include Teflon.)

Good: Nickel-plated steel, epoxy coated aluminum
Better: Stainless steel or anodized aluminum; minimal use of plastics
Look for: Smooth surfaces (no textured paints)

Reduce outgassing from lubricants

A wide variety of cleanroom-rated lubricants are suitable for bearings, motors, gearboxes, and other motion components.
Image credit: NSK

When it comes to outgassing, lubricants are one of the major offenders, readily spewing molecules of water and oil vapor into the atmosphere. Unfortunately, in the majority of motion systems, the use of components that require lubrication simply can’t be avoided. When lubrication is required, ensure the lubricant is suitable for cleanroom environments. Cleanroom compatible formulas that minimize outgassing while protecting bearing surfaces from rust and friction are widely available.

Good: Cleanroom-rated lubricants
Look for: Opportunities to minimize the need for lubrication through component selection

Feature image credit: Lin Engineering, Inc.

How to specify motion components for cleanroom environments: Part 1

August 29, 2018 By Danielle Collins Leave a Comment

In this two-part article, we cover the products, materials, and features that designers and engineers should specify when choosing motion components for cleanroom environments. In part 1, we look at how to reduce particle generation due to friction between moving components.

Designers of automation systems are tasked with many competing demands, such as balancing cost and performance, fitting motion components and systems into existing machine or process layouts, and designing for ease of manufacturing and assembly — to name a few. But when the system is to be used in a cleanroom, an additional layer of complexity is added, requiring designers to choose products that won’t degrade or compromise the cleanroom environment.

The level of “cleanliness” of a cleanroom is determined by the number of particles, broken down into six size ranges, that are present in a specified volume of air. In the United States, Federal Standard 209E is often used for cleanroom ratings, although it was officially canceled in 2001. This standard specifies cleanroom levels from 1 (best) to 100,000 (worst) in multiples of 10.

The current, and more universally-accepted, standard is ISO 14644-1, which defines cleanrooms on a scale from 1 (best) to 9 (worst). Each of the ISO classifications has a corresponding FS 209E level, with the exceptions of ISO classes 1 and 2, which are higher (better) than the highest FS 209E classification, and ISO class 9, which is lower (worse) than the lowest FS 209E classification.

ISO standard 14664-1 rates cleanrooms on a scale from 1 (best) to 9 (worst). Federal Standard 209E uses a scale from 1 (best) to 100,000 (worst) based on the number of allowable particles greater than or equal to 0.5 micron.
Image credit: Mecart Inc.

Objective #1: Reduce friction

One of the two primary sources of contamination, or particles, that can degrade a cleanroom environment is friction from moving components. (The other source is people.)

Virtually every motion system involves some amount of friction between sliding or rolling surfaces — whether from linear bearings, rotary bearings, or meshing gears. And when there is friction, particles are generated. Therefore, when specifying motion components for cleanroom environments, reducing friction should be the foremost objective.

Linear guides and drives

To minimize friction from linear guides, choose rolling contact rather than sliding contact and, when possible, avoid systems with high preload. For example, a non-preloaded miniature rail guide that uses two rows of recirculating balls emits significantly fewer particles than a preloaded standard guide with four rows of recirculating balls. And because there’s little chance of the bearing experiencing contamination in a cleanroom environment, use linear guides with low-friction or non-contact type seals.

Air bearings are another, although less common, method for guiding and supporting loads. In cleanroom applications, however, air bearings are often the best choice for low particle generation, since they are completely non-contact devices.

When it comes to linear drives, belts and chains should be avoided in cleanroom applications, due to the significant contact and wear they experience. Similarly, the meshing of gears in rack and pinion systems cause high friction and wear, so these should also be avoided. This means that ball screws are typically the default choice for linear drives in cleanroom applications.

However, ball screws require lubrication, and the rotation of the screw can cause lubrication to “sling” or “splatter,” contaminating the cleanroom environment. Using low-friction or non-contact seals (see above) will help keep the lubrication inside the ball nut and protect the cleanroom.

Like air bearings for linear guidance, linear motors provide a completely non-contact option for driving the load. But in their traditional setup, linear motors operate with the forcer (primary part) moving. This means the cables must move as well, and as we’ll discuss below, cables are another source of particle generation. A better configuration for cleanroom applications is to keep the forcer (primary part) and its cables stationary and allow the magnet track (secondary part) to move.

The combination of air bearing guides and a linear motor drive in this ABL 2000 stage from Aerotech provides completely non-contact movement, ideal for cleanroom applications.

Good: Rolling contact (rather than sliding contact) guides and drives
Better: Air bearing guides and linear motors
Look for: Low-friction or non-contact seals; cleanroom lubrication

Cables and cable management

Another source of friction and, therefore, particle generation, is the cable management system, including the cables themselves. Traditional round cables can generate particles when they rub against each other or against parts of the cable track. The best way to reduce particulates from cables and cable management systems is to use components and system design practices that reduce the amount of cabling required — for example, using an integrated motor-drive system instead of separate motor and drive components.

Cable carriers used in cleanrooms should have low vibration, low-abrasion fastening, and smooth interior surfaces to prevent abrasion of cables.
Image credit: igus Inc.

For the power, feedback, and data cables that are necessary in a motion control system, manufacturers offer cable designs with special low-friction coatings to minimize particulates and reduce outgassing. Similarly, several cable track manufacturers offer systems that reduce wear between chain sections through the use of abrasion-resistant joints. And for shorter lengths, so-called “trackless cables” are self-supporting flat cables that don’t require a cable track or carrier.

Trackless cables are self-supporting and don’t require cable carriers.
Image credit: W.L. Gore & Associates, Inc.

Good: Round cables with anti-friction coatings; cable carriers with abrasion-resistant joints
Better: Self-supporting flat cables
Look for: Opportunities to reduce cabling

Rotating equipment: motors and gearboxes

When it comes to rotating equipment in motion applications, the bad news is, motors and gearboxes use rotary bearings, and gearboxes require meshing teeth — all of which are sources of friction and particle generation. The good news is that these components are enclosed, so particles are less likely to “escape” and contaminate the cleanroom environment. And there is a wide range of cleanroom-compatible lubricants that can be used in the high-speed, high-load conditions found in motors and gearboxes.

To improve cleanroom compatibility, it is also possible to add a slight vacuum to the motor or gearbox housing. The vacuum serves to extract and remove particulates so they don’t have an opportunity to contaminate the cleanroom. Note that vacuum purge is also a good option for enclosed actuators that have a static (non-moving) seal. Although the enclosed design tends to keep particles inside the actuator, adding vacuum purge helps to achieve higher levels (class 100, 10, or 1) of cleanroom compatibility.

Vacuum purge is an effective way to ensure particulates from closed systems, such as this linear actuator, don’t have a chance to escape and degrade the cleanroom environment.
Image credit: THK Co., Ltd.

Good: Fully enclosed housings
Better: Vacuum purge
Look for: Cleanroom grease options

In part 2 of this article, we’ll look at another source of contamination — outgassing — and how to minimize it.

New igus robolink Apiro is modular kinematics system for automation

May 9, 2018 By Lisa Eitel Leave a Comment

igus now sells components as part of a modular motion system called robolink Apiro. The systems could soon make designing and using individual automation setups more cost effective and much easier.

With robolink Apiro, design engineers can choose from three lubrication-free worm gears for standard, inverted and linear movement. For users, the device offers setups ranging from the simple linear robot to complex humanoid and animatronic robots. The manufacturer introduced the robolink concept at Hannover Messe in Germany in April.

New igus robolink Apiro is modular kinematics system for automation of robotic design

The Apiro system allows for motion designs capable of movements like those of a spider … with only three new worm gears for standard, linear and inverted motion. Image courtesy igus GmbH

Apiro, which derives from the Greek word unlimited, was developed with a focus on decoupling the motor and gearbox while also introducing new kinds of worm gears that can be installed in up to six axes, such as an articulated robot. A gearbox with linear motion, inverted and conventional robolink worm gears in four sizes come in Apiro. They can also be combined.

The new modular system will allow even complicated movements to be implemented. For example, designers needing parts for individual SCARA robots and linear robots as well as sprue pickers used in removing products from injection molding machines will see benefit in Apiro. Designers of transport and handling systems, as well as humanoid and animatronic robots which can perform movements like those of a spider, will also recognize the benefits of the new modular motion system.

The new robolink series is also suitable for training, development and research as different kinematics can be set easily and quickly.

Modular motion system leads to flexible kinematics design

The multi-functional profile enables users to connect the different gearboxes of the robolink Apiro series. Placing several Apiro joints side by side also allows for the possibility of parallel joint connections, which creates endless possibilities for many different automation applications.

High-quality tribo-polymers are used in the worm gears of the new Apiro series. The corrosion-free and chemical-resistant high-performance plastics ensure a high degree of stability, low weight, long service life and maintenance freedom.

The joints are combined by a multi-functional profile made of aluminum that makes it possible to insert drive shafts through a hollow space in the middle of the unit. The inverted worm gear makes use of that hollow space.

The gearbox allows the aluminum piece to rotate, which makes it applicable for use in robotics and rotating applications. In the case of the new worm gear with linear movement, the aluminum profile can travel linearly through the worm gear, and vice versa. Worm gears also have very little clearance.

Rotary bearings: Summary of types and variations

March 14, 2018 By Danielle Collins Leave a Comment

The basic components of a radial ball bearing are the outer ring, inner ring, cage, and balls.
Image credit: NTN Corporation

Rotary bearings are common components in motion systems. They’re used in gearboxes, motors, pulleys, fans, pumps—virtually any time a shaft is rotating, rotary bearings are there to reduce friction and support radial or axial loads.

The classification of rotary bearings begins with the type of bearing that supports the load—ball or roller. Within the ball and roller types, the next distinguishing feature is the primary load direction that the bearing can withstand—radial or axial (aka thrust). Then, ball bearings are further classified by the configuration of the outer ring, while roller bearings are further categorized by the shape of the rollers.

While there are dozens of variations of rotary bearings—including designs made for specific environments, mounting configurations, and applications—the most common categories are covered here.

Rotary Bearings

Rotary bearings are categorized by whether they use balls or rollers, and then by the type of load they’re designed to support: radial or axial (thrust). Further classification for ball bearings is based on the configuration of the outer ring, whereas roller bearings are further classified by the shape of the rollers.

Ball Bearings—Radial

Angular contact ball bearings are typically used in pairs or in a double-row design (shown here) to withstand axial loads in both directions.
Image credit: SKF

Within the ball bearing family, deep groove ball bearings are the simplest type, with raceways that nearly match, or conform, to the diameter of the balls. This type is suitable for radial loads and for axial loads in either direction, although their load capacity is relatively small compared to other bearing types. For higher load capacity in a relatively small footprint, deep groove ball bearings are commonly available in a double-row design, with two rows of balls instead of one.

Angular contact ball bearings are designed so that the line that connects the points of contact of the inner ring, ball, and outer ring runs at an angle radially to the bearing. The contact angle increases load capacity, but it means the bearing can withstand an axial load only in one direction, so these bearings are typically used in pairs or in a double-row design (essentially two angular contact bearings mounted back-to-back) in order to withstand axial loads in both directions.

Four-point contact ball bearings are single angular contact 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.

Ball Bearings—Thrust

Thrust ball bearings are made of two relatively thin bearing rings (sometimes referred to as 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 percent of their radial bearing counterparts in some cases).

Roller Bearings—Radial

Roller bearings, such as the cylindrical roller bearing shown here, have higher radial load capacities than ball bearings, due to the use of rollers to support the load.
Image credit: NSK Ltd.

With rollers supporting the load, roller bearings 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 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 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 rollers to support the load, can withstand axial loads in one direction. Tapered roller bearings can be thought of as the roller version of the angular contact ball bearing, and like their ball bearing counterparts, tapered roller bearings are often used in pairs or in a double-row design, to counteract axial forces that are produced in the bearing when a radial load is applied. The tapered design also improves rolling properties and reduces friction within the bearing.

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

Roller Bearings—Thrust

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

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

Cylindrical thrust roller bearings can accommodate high axial loads and are able to withstand impact loads, although radial loads are not permissible.

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

Tapered thrust roller bearings can be single-direction or double-direction type, indicating whether they can accommodate axial loads in one direction or in both directions. Like their radial counterparts, tapered thrust roller bearings have “pure” rolling motion, which means less heat generation and less wear.

Spherical thrust roller bearings can take very high axial loads and small to moderate radial loads, with the ability to withstand some misalignment.

For more information on rotary bearings, visit our sister site: bearingtips.com.

7 linear motion principles that electrical engineers should know

August 22, 2017 By Danielle Collins Leave a Comment

Image credit: NSK Americas

Electrical and controls engineers are normally tasked with selecting and integrating the electronic components that go into a motion control system, such as motors, drives, controls, feedback devices, and HMIs. In doing so, their primary concerns tend to be on making the various components communicate with each other, working through complex equations for drive tuning, and programming HMIs to ensure the user can operate and troubleshoot the system with relative ease.

And while some of these tasks require a fundamental knowledge of mechanical principles – particularly torque, speed, and inertia – rarely do they go into the nuances of how linear guides and drives (ball screws, belts, rack and pinions) work and their impact on the electrical side of the system. But even if you never have to size or select them, it’s helpful to understand the basic principles and equations for linear motion components that are common in motion control systems.

L10 bearing life – Bearing life (or L10 life) is a fundamental concept for sizing any recirculating bearing. This article explains what L10 life is and how to calculate it.

How to calculate move profiles – The type of move profile an application uses determines the maximum speed and acceleration, which affects motor sizing and drive tuning. This tutorial describes the two most common move profiles and how to calculate velocity and acceleration for each.

Image credit: Womack Machine Supply Co.

How to calculate acceleration – More information (and equations) specifically dealing with acceleration.

How to calculate drive torque for ball screws – Continuous and intermittent torque values are key to motor sizing. This article explains how to calculate torque during constant speed, torque during acceleration, and torque during deceleration.

Torque considerations for keyed shafts – This article demonstrates the disparity between the torque that can be transmitted by a solid shaft versus a keyed shaft, including equations for calculating when shear failure and crushing failure will occur.

Image credit: 4mechtech.com

Ball screw back driving – Screws are often used in vertical applications because they prevent the load from catastrophically crashing if the motor loses power. But if the load is too heavy, it can still cause the screw to back drive. This application note provides equations for calculating back driving torque.

Ball screw buckling – When a screw is used in a vertical application, it’s important that the load doesn’t exceed the column strength of the screw, which depends on the screw length and the end bearings used. This tutorial explains why buckling occurs and how to calculate the buckling load for a given screw.

Image credit: NOOK Industries, Inc.

If you’re new to linear guides and drives, you may also want to check out the linear guide and ball screw glossaries. They include descriptions of each technology, including technical specifications and details on construction.

Image credit: tools-n-gizmos.com

Six FAQs about bearings and choosing between oil and grease

July 16, 2016 By Lisa Eitel Leave a Comment

Rotary bearings consist of smooth rollers or metal balls and inner and outer surfaces (races) against which the rollers or balls travel. These rollers or balls carry load carrier and let axes spin freely. Bearings typically encounter radial and axial load. Radial loads are perpendicular to the shaft, and axial loads occur parallel to the shaft. Depending on the application, some bearings must withstand both loads simultaneously.

Here is another batch of articles from motioncontroltips.com Design World sister site bearingtips.com. This site covers rotary bearings that take the form of ball and roller bearings as well as thrust bearings — in addition to the issues of bearing lubrication and integration.

The following are bearing features our colleague Mike Santora has posted there recently. Click on the headlines to read more.

What is a “floating” bearing arrangement?

Two bearings support and locate a shaft axially and radially in relation to the housing, which is stationary. There is “fixed” side and a “floating” side. The fixed side controls the shaft axially. The floating side has more freedom of movement (floating) to help compensate for misalignment and thermal expansion or contraction …

Bearing Lubrication: Oil vs. Grease

Rotary-bearing lubrication takes the form of oil or grease, but grease usually lasts longer, thanks to thickeners that sustain the lubrication layer between raceways and rolling elements. Grease with extreme-pressure additives also extends bearing life when subject to higher forces. Even so, oil is more common for open bearings or those subject to low torque or high speeds. Oils’ lower viscosity imparts less drag than greases …

Why is preload necessary in some bearing applications?

One of the final steps in the bearing manufacturing process is the assembly of the individual bearing components: the outer ring, inner ring, balls and retainer (or ball separator).

When the bearings are assembled, it is necessary to have a controlled amount of internal clearance, or looseness between the rings and balls … However, in certain applications, this internal clearance must be removed for a pair of bearings to operate properly. The application of an axial load across a pair of bearings for the purpose of removing free internal clearances is preload.

When should oil be used for bearings?

Sean P. Kelly, Field Applications Engineer for NMB Technologies Corporation says that Grease is preferred when longer life is needed.

“This is due to the grease thickener slowly releasing a base oil providing a lubrication layer between the raceways and rolling elements … ”

Why you should consider air bearings

It’s easy to overlook air bearings. Most of the time, mechanical bearings work well enough for a motion application. Most, but not all. Submicron bearing rumble not an option? Is geometric performance and angular repeatability paramount? Here are tips that will smooth out the specification process …

What are minimum loads and why are they important for bearings?

Eric Phaneuf, Applications Engineer, Industrial Market for SKF USA Inc. explains that for many radial bearings, it is common to provide a certain amount of space between the rolling elements and the raceways to allow for thermal expansion and prevent bearing seizure …

What’s being done about counterfeit bearings?

In this interview, Sr. VP, General Council & Secretary for SKF USA Timothy D. Gifford shares some insights into the current counterfeit bearing situation. Specifically, Gifford tells us how the bearing industry is fighting back against the global counterfeiting market …

Series of new bearings FAQs and interviews on bearingtips.com

July 9, 2016 By Lisa Eitel Leave a Comment

If you’re looking for information on bearings, then check out the latest from motioncontroltips.com Design World sister site bearingtips.com. This site covers rotary bearings that take the form of ball and roller bearings as well as thrust bearings — in addition to the issues of bearing lubrication and integration.

The following is a sampling of bearing features we’ve posted there recently.

A conversation with NSK Canada’s Dale Woitte

Recently our own Paul Heney talked with Dale Woitte of NSK Canada at the PTDA Canadian Conference in Ottawa. Heney asked Woitte a little about the company’s current focus and what the future holds. Woitte said that the OEM and automotive markets are strong segments for the company.

“But obviously we’re being hurt right now with mining, with the prices, nickel prices, steel … it’s in turmoil, shall we say …” Read the rest of Heney’s chat with Woitte here.

What is a pillow block bearing?

This is one FAQ from a series by editor Mike Santora. A pillow block bearing consists of a mounting bracket (pillow block) that houses a bearing and is used in low-torque, light load applications.

With this configuration, the pillow block is bolted to a foundation, securing it, while the shaft and the inner ring of the bearing are free to rotate … read the rest …

Are bearings with fluoro-rubber seals safe?

Fluoro rubbers have high thermal, chemical, ageing, ozone, wear and gas permeability resistance, and are safe as long as the material is not overheated. But there are some other caveats … read the rest …

What are self-aligning ball bearings?

This piece by Joyce Laird, contributing editor on bearingtips.com, outlines how the inner ring on a self-aligning bearing has two raceways and the outer ring has a single spherical raceway with its center of curvature coincident with the bearing axis.

This allows the axis of the inner ring, balls, and cage to deflect around the bearing center to automatically correct misalignment caused by housing and shaft machining or installation error.

“In contrast, a ball bearing only has one raceway groove on both the inner and outer ring and is the most common type of rolling bearing,” explains Paul Brda, Application Engineer at NSK Americas. Read this bearings piece — including a section on mounting and handling procedures — here.

Tips for selecting the proper bearing radial shaft seal

Another piece from Joyce Laird, contributing editor on bearingtips.com, explains the primary function of a radial shaft seal and how one matches the proper radial shaft seal for a bearing. Application conditions to consider include temperature, speed of the shaft, and environmental concerns — including exposure to chemicals.

igus motion plastics car ends 20,000 mile tour across North America

June 23, 2016 By Miles Budimir Leave a Comment

For nearly a year, the igus motion plastics tour has traveled across North America, visiting with more than 4,000 current and potential customers in all industries at more than 160 companies from Mexico City to Toronto. It has now returned to its home base in Rhode Island.

igus staff members show off a robotic retraction system at the last visit on the motion plastics tour.

After completing a worldwide tour in 2014, the car, retrofit with 56 igus plastic bearings, was deconstructed at HMI 2015 (Hannover Messe), and put back on the road for a second tour, this time with a focus on North America. Thousands of visitors stopped to see the car and chat with igus team members about their applications, and how plastic technology and components can increase the service life and reduce the cost of applications ranging from automotive design to medical components, and everything in between.

The car’s last day of visits took place in Connecticut, the 42nd US state visited on this leg of the tour alone. More than 80 engineers, purchasing staff, and other visitors stopped by the last day of visits to see the car and learn about igus motion plastic products.

The orange igus car, which has driven 34,281 miles around the world, will be based at igus’ North American headquarters in Rhode Island, making smaller trips throughout the New England area.

The igus car made a visit to our offices here at Design World back in 2014, where our editorial staff got a chance to learn more about the company’s plastic bearing offerings.

For more about the use of igus’ plastic bearings in automotive applications, check out editor Mike Santora’s piece here.

Motion control technologies you missed at MD&M West

February 20, 2016 By Lisa Eitel Leave a Comment

Last week, many of us with motioncontroltips.com and Design World headed to MD&M West 2016 colocated with the ATX West show in Anaheim, Calif. The Internet of Things (IoT) still leads much industry buzz, as does the idea of increasingly smart and connected components and the unabated rise of automation — in the medical industry and elsewhere.

My colleagues Paul Heney, Mary Gannon, and Danielle Collins covered many key items of robotics, fluid-power, and linear-motion news at the show …

Just check out this item from Paul — Live from MD&M West: Festo talks automation safety … or this from Danielle — Things are moving at ATX West 2016: Rollon in Cartesian robots.

I also visited some industry leaders in linear motion. Check it out: Recap of top linear-motion technologies at MD&M West

Following are some other new things I saw at MD&M West 2016 — motion-control technologies from AllMotion, Altech, Applied Motion, Beckhoff, Changzhou Motors, Herrmann Ultrasonics, KHK Gears, maxon motor, MICROMO, Neugart Precision, Opto-22, Suhner, and Wittenstein.

The biggest developments at MD&M West — multi-axis driving and controlling off of increasingly tiny boards; motors that communicate and get power over Power over Ethernet (PoE); and one major manufacturer putting all of its chips on IoT for all future automation. Enjoy!

In an early booth visit with AllMotion accompanied by our own Scott McCafferty, I got the chance to visit engineer and president David Goodin (in the picture to the left below). He explained how more engineers than ever are using his company’s four-axis drive-controller board in super-compact designs. In the center picture below (click to enlarge) the daisy-chained setup with multiple single-axis boards. In the image to the right, there’s an equivalent design that uses just one board for multiple axes … for a setup with a lower cost per axis.

Here’s tiny fluid-sample-processing machine AllMotion showed at MD&M. In this case, one of the company’s four-axis drive-controller boards (flat and tightly integrated) drives all the axes.

Click next: Visit with Altech — on automation components

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How to prevent false brinelling in rolling-element bearings

January 20, 2015 By Lisa Eitel Leave a Comment

This piece comes to us from Charles E. Harris, Partner at Plymouth Machine Integration LLC.

False brinelling is a kind of damage from fretting — wavy, chipped, or corroded damage on metal contact surfaces of power-transmission devices subject to wearing from repeated surface motion. It’s a problem in assemblies with mechanical subsections that move slowly but are subject to high vibration, and it’s especially common in large bearings with rolling elements in rolling-element bearing applications — in wind turbines, for example.

First some basics:
Explanation of false versus true brinelling

False-brinelling damage leaves series of divots that resemble those of true brinelling, which is permanent indentation of a component’s hard surfaces. However, true brinell damage is permanent material deformation (without loss of material) and occurs during one load event. In contrast, false brinelling is material wear or removal that happens over time because of vibration and light loads.

More specifically, true brinelling, named after the Brinell hardness scale, leaves repetitive series of indents on the working surfaces of mechanical parts. Most common on hydraulic pistons and bearings, it happens when a material surface failure caused by Hertz contact stress that exceeds the material limit — as when a heavy load impacts a small surface area, for example. Ultimately, brinelling causes chattering, vibration, and other forms of wear.

In contrast, false brinelling happens when a bearing design only redistributes lubricant during large rotations of all bearing raceway surfaces. When such bearings only move a little bit, small oscillations or vibrations can squeeze lubricant out of loaded spaces. Then wear begins and only accelerates with move vibrations. What’s more, sometimes small bits of material break off the raceway and oxidize. This material further abrades the damaged surface and accelerates wear.

False brinelling on wind-turbine bearings

False brinelling often develops on wind-turbine parts where bearings in pitch-control mechanisms can remain in one set position for long periods of time. In such situations, the lubricant film is gradually displaced, allowing metal to metal contact. The vibration in the joint causes this contact to produce physical damage. Purposely inducing small amounts of relative motion can be helpful, but the benefit is limited since the lubricant can be pushed aside in either direction.

For example, consider the blade pitch control on a wind turbine. Here, blade pitch angle is set to match aerodynamic force with wind speed and load demand. Changes to the pitch are infrequent and small, leading to damage to the bearings supporting the blade. Intentional motion can be imposed on the system to promote lubricant flow. This motion is called dither. The minimum motion required is a function of the spacing of rolling elements within the bearing. Dither puts the blade off of the preferred angle, and therefore decreases the efficiency of the turbine. Minimizing the required dither helps to maximize overall system efficiency.

Shown here is the bearing in a blade pitch control on a wind turbine. Its raceway surfaces are prone to false brinelling.

Plymouth Machine Integration has made a provisional patent application for a design that uses two concentric one-way bearings, installed such that their actions are opposed. With a modest amount of oscillatory motion, it induces large movements of the intermediate race — and both sets of rollers. That evenly distributes the lubricant.

How does it work? The motion in the intermediate race is from a one-way clutch in one of the two bearings holding that race motionless with respect to first the inner, then the outer race, depending on the direction of rotation within the period.

In this way, the design avoids false brinelling by maintaining a lubricant film and preventing adhesion of surface asperities.

This setup from Plymouth Machine Integration includes two concentric bearing rings fitted with one-way sprag clutches oriented in opposite directions. Small relative oscillatory motions of the inner race alternately lock and unlock the two clutches, in opposite phase. The middle (common) race is advanced in a single direction, by an angle equal to the amplitude of the oscillatory motion. The average motion within each bearing is non-zero, promoting movement of the lubricant within the rolling elements.

One caveat: This design doesn’t resolve issues from assemblies that lie motionless for substantial periods of time between uses — on spare electric motors, for example. This needs oscillatory motion of a magnitude large enough to engage the one-way clutch … oscillatory motion that’s either natural to the operation of the machine or imposed on the controls.

For further information, visit plymouthmachineintegration.com.

Also download the classic resource, Tribological Challenges in Wind Turbine Technology.

About the source: Charles E. Harris has twenty years of experience in the design, testing, and development of powertrain components and systems. Seventeen of those years were at Ilmor Engineering, Inc., a high-level engineering company for motorsports and marine pleasure-craft powertrains. According to Harris, experience in these fields meant study to bearings operating under difficult conditions … both on engines, such as engine throttle shafts, and in test equipment, such as dynamometer trunnion bearings.