Featured - Motion Control Tips

NORD launches next generation two-stage bevel gear motors

September 18, 2018 By Miles Budimir Leave a Comment

NORD’s new SK 920072.1 two-stage helical bevel gear motor (mounted with a NORD motor) is a drive solution for a wide range of light duty conveying, processing and manufacturing applications. Identified by its high-strength and light-weight design, NORD’s newest aluminum gear motor is a cost-effective replacement for cast iron units. Two housing styles offer options for multiple applications and environmental conditions.

The next size of premium efficient two-stage bevel gearboxes features a new compact, more efficient modular design. Covering applications for torques up to 443 in.-lb (50 Nm) and offering up to 97 percent gear efficiency, the SK 920072.1 and SK 930072.1 are superior alternatives to worm gear units in light conveying and processing applications, as well as for food and beverage industries.

Like other NORD gearmotors, the new size comes in two housing designs – the SK 920072.1 has optimized thermal properties due to its large surface area. The SK 930072.1 is ideal for washdown applications because of its closed housing design.

The new NORD size has a power range of 0.16 to 1.50 hp (0.12 to 1.1 kW) and speed ratios from 3.03 to 47.67. They provide exceptional adaptability for all mounting positions as far as input, output and motor options. Available with either NEMA or IEC input, a NORD motor or brake motor, both the SK 920072.1 and SK 930072.1 gear units are well suited for use in the material handling industry, car wash, as well as for sanitary and hygienic environments.

Available for the SK 930072.1 model is NORD’s NSD TUPH surface conversion, a revolutionary process only offered by NORD. The aluminum alloy reducer housing and modular accessories are electrically catalyzed producing a strong corrosion resistant base layer (or molecular surface conversion). The additional top layer provides enhanced sealing, additional corrosion protection and a brighter finish.

Unlike painted cast iron gear units, the extremely strong base layer (six to seven times harder than the original aluminum alloy) provides superior corrosion resistance and scratch resistance, and it will not chip, flake or rust.

With NORD’s leak-free design, longer gear and bearing life, quiet operation, and precise output torque capabilities, SK 920072.1 and SK 930072.1 helical bevels deliver high efficiency operations, low maintenance, and longer service life.

For more information, visit www.nord.com.

Advanced manufacturing and materials have made an highly efficient traction drive possible

September 14, 2018 By Lisa Eitel Leave a Comment

Rolling Motion Industries (RMI) has released two high-efficiency traction drives — the MAR-17-1-2.1 Traction Drive and the MAR-23-1-2.1 Traction Drive. These are 1-Way traction drives with only six moving parts and use an engineered traction fluid with a coefficient of friction of just 0.1 to 0.12. These traction drives typically last three times longer than conventional gearboxes and with no metal to metal contact these high efficiency drives generate up to 72% less heat after 24 hours of continuous operation, Additionally they create up to 38% lower dB at 3000 rpm (less than a home refrigerator) than conventional gearboxes. Even though there’s no metal to metal contact there’s no slippage or lost motion between the input and output shafts.

The MAR17-1-2.1 Traction Drive is designed for speeds to 3,600 rpm with 10 to 20 in/lb of torque, and the MAR-23-1-2.1 Traction Drive is rated for 3,600 rpm with 20 to 30 in/lb of torque. Operating at temperatures that are lower than a motor’s, with low vibration, and no torque losses from 10 to 3,000 rpm, these traction drives permit a motor to operate at peak efficiency. Applications for these 1-Way traction drives which can operate in explosive environments (ie. zone 1 and 21) include: Pumps, blowers, fans, turbo and super chargers, conveyers, HVAC systems, medical applications, and other power transmission and motion applications.

These revolutionary drives are available with an optional overriding clutch. Incorporating standard NEMA mounting dimensions, these drives can be easily integrated into new and existing applications.

In 1993 John Pawloski and his brother Ray took over the family business, Jewelers Machinist Co. They realized they needed to switch from outdated conventional thread grinders to CNC thread grinders. As a result, Jewelers Machinist Co is a source of some of the most complex thread grinding in the industry. The concept for the RMI traction drive came from John in 2007. Working in that high precision industry aided John in the development of the RMI Traction Drive.

In the years that followed, the design of the individual components and formula of the engineered traction fluid were finalized, testing was completed, a patent granted, and production begun. The RMI Traction Drive is one of the most efficient ways to transmit power from one point to another. Using rolling motion, RMI is able to transfer power at various ratios with minimal energy loss. Tested against V-belt, direct drive, chain, and gearbox setups, RMI Traction Drives offer energy saving benefits through true efficiency rating percentages up to 98%. The high efficiency of the traction drive allows electric motors to run at their peak efficiency ranges.

There are many applications where it can be used from automotive to industrial to medical. The RMI traction drive can be used in the electric vehicle market and precision applications. Offering benefits such as low backlash and no back driving, it set a new standard for high efficiency.

For more information, call (860)846-0530, email info@RMIDrive.com, or visit RMIDrive.com.

Galaxie Gearbox from WITTENSTEIN nominated as finalist for Germany’s Deutscher Zukunftspreis 2018

September 13, 2018 By Miles Budimir Leave a Comment

WITTENSTEIN’s Galaxie gearbox has been chosen as a finalist for the 2018 Federal President’s Award for Innovation in Science and Technology, recognized as “A radically new gearbox class – productivity leaps in the engineering industry”.

The jury for the Deutscher Zukunftspreis 2018 announced the three finalists for this year’s award. Galaxie inventors Dr. Manfred Wittenstein (Chairman of the Supervisory Board) and Thomas Bayer (Manager Innovation Lab) attended the ceremony and were officially recognized as part of the Deutscher Zukunftspreis “Circle of Excellence”.

The team of inventors nominated for the Deutscher Zukunftspreis 2018 (from left to right): Thomas Bayer (Manager Innovation Lab at WITTENSTEIN SE) and Dr. Manfred Wittenstein (Chairman of the Supervisory Board of WITTENSTEIN SE).

The new gearbox class has already won two prestigious awards: the Hermes Award in 2015 and the Innovation Award of the German Economy in 2016.

Dr. Wittenstein noted that “Germany’s prosperity is built on its engineering skills. The engineering industry is our country’s core competency and the biggest industrial employer. It is vital that this marketability be preserved for the future. We believe that our invention makes a significant and valuable contribution here.”

Originally unveiled at the Hannover Messe in 2015, the Galaxie Drive System is based on a novel, scientifically proven gearbox class. The principle of the innovative Galaxie gearbox is founded on several pillars: forces and torques are transmitted not by rigid gear wheels but by separate teeth which can be moved independently of one another. Rather than rolling against each other, these teeth slide to and fro in a ring gear. Furthermore, a very large number of teeth engage with one another at any given time, leading to full-surface contact because they are designed as a logarithmic spiral. This concept inspired the nominated team of inventors – Thomas Bayer and Dr. Manfred Wittenstein – to develop a completely new gearbox class which was radically different from anything that had gone before. “We weren’t happy with the state of the art at the time. Although we could probably have improved certain aspects, we were convinced that there must be another way,” said Dr. Wittenstein.

The Galaxie gearbox from WITTENSTEIN is a completely new gearbox concept with separate teeth instead of rigid gear wheels.

Mechatronic drive systems like Galaxie are employed in all kinds of automated production machinery. From food and packaging through medical devices, vehicles and wind turbines to robots or machine tools – almost all daily commodities are manufactured with the help of motor-gearbox units or make use of similar drive systems.

Deutscher Zukunftspreis 2018
The Federal President’s Award for Innovation in Science and Technology was instituted and presented for the first time in 1997; the intention is to encourage world-class scientific achievements that are simultaneously marketable and a source of employment. The Deutscher Zukunftspreis is not an award that is applied for, in other words projects must be nominated by one of the institutions entitled to propose worthy candidates. Once a year, a jury comprised of 10 independent experts from academia and industry then selects three teams for the final round.

The announcement of the winning team will take place on November 28, 2018. For all further information, see www.wittenstein.de and www.deutscher-zukunftspreis.de.

Danfoss acquires Finnish manufacturer of large electric motors

September 12, 2018 By Paul Heney Leave a Comment

Danfoss has expanded its electrification capability with acquisition of world-leading expert in large electric motors and generators, AXCO-Motors. AXCO-Motors is a technology leader in large electric solutions (from 250 kW and up to 6 MW) for applications like maritime vessels and off-highway vehicles. Danfoss said it is responding to the growing customer demand for electric solutions to reduce emissions and benefit from the efficiency and productivity gains that these solutions bring.

“Electrification is a global megatrend and holds very strong potential in fighting pollution and climate change. This acquisition is another commitment to broaden our mobile electrification capability as a core competency for Danfoss. It gives us the total package for serving our global markets with optimal solutions, and fully supports our customers’ needs — regardless of the chosen technologies. This will enable further growth in the markets we serve, and I’m really looking forward to welcoming the highly experienced and knowledgeable team from AXCO-Motors,” said Eric Alström, President, Danfoss Power Solutions.

AXCO-Motors, headquartered in Lappeenranta, Finland, will be integrated into Danfoss Editron — a business within the Danfoss Power Solutions segment.

Kimmo Rauma, VP, Danfoss Editron, said, “Several of our markets, such as off-highway, marine and distribution, are being challenged to reduce emissions and pollution. Mobile electric solutions are a highly relevant technology to this challenge, and AXCO-Motors is the leading expert in the large-scale power range up to 6 MW and thus an important and complementary technology to our current product range, and our mission to end pollution.”

“We have a passion for quality and for customer-focused products that fully meet the needs and requirements of each particular client, so joining Danfoss is great for us, because we have the same focus,” said Juhana Ylikojola, CEO at AXCO-Motors. “Being part of Danfoss means bigger capacity, a broader client base and possibilities for investment in innovation and market opportunities.”

Danfoss
www.danfoss.com

Power and free conveyors: Where do they excel?

September 11, 2018 By Danielle Collins Leave a Comment

Power and free conveyors are designed for manufacturing environments where products need to be transported in a non-linear fashion — that is, where materials aren’t necessarily delivered in the order they were loaded or at the same pace. Traditional “linear” conveyors, on the other hand, lack the flexibility to handle manufacturing environments where different production processes run at different cadences or where various materials have different flow paths.

Because of their flexibility in handling and delivering products, power and free conveyors are also referred to as “asynchronous” or “non-linear” conveyors.

The defining feature of a power and free conveyor is that it consists of two tracks — an upper track and a lower track. The upper track is powered by a chain, and the lower track is unpowered. Trolleys, which carry the load, run on the lower track, supported by rolling wheels. Mechanical devices — often referred to as “pusher dogs” — on the powered track engage with the trolleys to move them and disengage with the trolleys to stop them. The pusher dogs are engaged and disengaged by cam action caused by a trolley in front or by a stop blade positioned along the powered chain. Air-activated stops, triggered by switches, can also be used to control the movement of trolleys.

In a power and free conveyor, the upper track is powered by a chain and the lower track is unpowered. Trolleys (two of which are shown here) ride on the lower track and are driven by devices on the powered track called “pusher dogs” that engage and disengage with the trolleys.
Image credit: Cisco-Eagle

Much like cars on a road, conveyor “traffic” can also be merged or diverted among multiple conveyor lines, and both sharp turns and elevation changes can be executed. And unlike traditional linear conveyors, power and free versions can allow products to accumulate, or “stack up” by holding trolleys stationary while other trolleys “catch up” and join them. The trolleys can then be released in the required sequence. All of this is accomplished through mechanical linkages via the pusher dogs and trolleys, without requiring complex automation.

To maximize space, especially during accumulation, trolleys can be connected via rigid load bars that set the spacing between trolleys at as little as 6 inches (depending on the size and shape of the load). And storage density can be maximized with trolleys that hold the load diagonally relative to the conveyor path.

Trolleys positioned diagonally can maximize space and increase storage density.
Image credit: Ultimation Industries, LLC

Circuits of conveyors up to 300 feet can be controlled with just one motor, and complex “traffic” patterns and timing sequences can be controlled via sensors triggered by a PLC or PC-based controller. In addition, bar codes or RFID tags on the trolleys can be used to identify individual loads and carry instructions for sequencing.

This video from Caldan Conveyor A/S demonstrates how power and free conveyors work, including their ability to accumulate, stage, merge, and divert products.

While most power and free conveyors are mounted overhead, above the working area, and carry products below the tracks, floor-mounted designs are available that carry the product above the tracks. This is especially useful when overhead space is a concern, or when potential contamination from the conveyor or product is an issue, as is often the case in cleanroom environments. And when overhead space is limited but floor-mounting is not an option, some manufacturers offer overhead versions with powered and non-powered tracks positioned side-by-side, rather than in a top-and-bottom configuration.

A floor-mounted power and free conveyor is useful when overhead space is limited, or when contamination from the conveyor or the product is an issue.
Image credit: Richards-Wilcox

Power and free conveyors are custom-designed for each application and can carry loads from just a few pounds to several hundred pounds. They’re used extensively in the automotive industry, where robot cells are sometimes used to load/unload products from the trolleys or to perform work on the parts being conveyed as they’re held stationary. And power and free designs are available in heat- and corrosion-resistant versions, so they can transport loads through processes such as washing and painting or through ovens.

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.

Frameless brushless dc motors in hybrid solid-state LIDAR Applications

August 31, 2018 By Lisa Eitel Leave a Comment

Edited by Terry Persun || Use of light detection and ranging (LiDAR) in the automotive industry is growing exponentially. The two most common variations are solid-state LiDAR and hybrid spinning LiDAR.

Solid-state LiDAR are non-spinning systems. Some employ a phased array to steer the laser beam sans moving parts; others include a tiny mirror to steer the laser beam. Still another solid-state design called flash LiDAR illuminates entire scenes in a single flash to allow detection of returned light via a two-dimensional array of sensors — similar to the operation of a digital camera. With few moving parts, these methods provide cost-effective LiDAR functionality.

Vehicles with long-range LiDAR can anticipate the need to brake earlier — to reduce the necessary deceleration to a rate less likely to injure occupants. Frameless dc motors can make these LiDAR designs more compact.

Sometimes manufacturers put all the LiDAR electronics on a single chip, including the laser, any beam-steering circuitry, detectors for the return signal, and supporting computer power. But single-chip solutions for solid-state LiDAR are vulnerable to environmental challenges such as heat, cold, humidity, rain, and corrosive substances. End users needing to repair systems often find replacement ICs costly. What’s more, manufacturers are increasingly looking to offer lower-cost modular options that allow individual component swap-outs.

The latter is significant because a typical solid-state LiDAR setup provides a single fixed-in-place field of view of 120° or less. That means it takes at least four units to cover a full 360° safety zone. That contrasts with spinning LiDAR systems, which cover 360° operation with no blind spots due to gaps or overlapping … problems inherent to solid-state systems.

In addition, safety rules dictate that LiDAR must not generate laser output capable of damaging a person’s eyesight — even if that person were to look directly at the LiDAR unit for a number of seconds.

Reasons for solid-state hybrid LiDAR

Leveraging the advantages of both solid-state and spinning LiDAR is hybrid LiDAR. These designs have a field of view that is seamless and repeatable. Plus safety regulations permit moving laser sources to emit higher-power beams than stationary ones. So more powerful lasers let hybrid spinning LiDAR units map wide ranges and (when incorporated into systems for autonomous operation) help vehicles avoid the need to make short stops — and avoid the increased risk of body trauma to passengers. So even while solid-state LiDAR becomes increasingly common, demanding applications (including self-driving cars) will employ robust hybrids with superior long-range operation, higher resolution, and broader fields of view than other systems.

As we’ll see, trimming the cost and footprint of these LiDAR designs sometimes means using alternatives to the usual brushless dc (BLDC) motors employed for their spinning action.

Motors parts that LiDAR systems don’t need

Recall that brushless dc motors are more powerful than brushed motors — and avoid the friction and voltage drop associated with brushes for commutation. That’s why brushless dc motors are used in LiDAR systems. Spinning LiDAR designs usually turn at 200 to 500 rpm. The mirror assembly the motor turns is very light, so torque isn’t typically an issue. But many of today’s LiDAR systems use off-the-shelf (OtS) NEMA 17 and NEMA 23 motors — which can make for unnecessarily bulky builds.

Brushless dc motors are essential to hybrid LiDAR systems. But as the automotive industry works to miniaturize LiDAR systems, the built-in components of standard motor offerings (which are useful in other designs) are sometimes a detriment.

That’s because most OtS brushless dc motors are structurally and mechanically self-supporting. Endcaps suspend the rotor inside the stator; then the LiDAR’s moving assembly couples to an output shaft. In fact, motor ends can easily account for up to 50% of a motor’s overall length.

In contrast, frameless motors omit additional mounting supports, plates, brackets, and couplings to let design engineers directly integrate loads into the rotor design; in addition, the stator can be seamlessly incorporated into the system for a smaller design that doesn’t sacrifice performance.

Sleeker automobiles with compact LiDAR motors

Aerodynamics and visual styling are paramount in automotive design. It’s easier for engineers to incorporate wider flatter shapes to car exteriors than tall narrow shapes. Frameless motors can deliver this kind of geometry — with large diameters and less height than comparable OtS brushless dc motors. In addition, a portion of the LiDAR mirror load can sink down into the frameless design’s stator. Both of these options help reduce the overall LiDAR height for a streamlined shape.

Frameless motors — as these from Lin Engineering — integrate into designs to reduce waste and redundant mounting supports, plates, and brackets. They also omit endcaps that can easily account for up to 50% of overall motor overall length.

Frameless motors aren’t constrained to standard sized motors, so give design engineers more freedom to tailor motor shape and size to the application. This makes for LiDAR systems with the smallest footprint possible. When paired with the lightweight sensors of solid-state technologies, the motors have less mass to move and lower torque requirements to satisfy — allowing for a much smaller motor to do the job.

Off-the-shelf motors may be oversized for LiDAR systems. In contrast, custom motors are often more compact and (if supplied in high volumes) save thousands of dollars in manufacturing and production over the long run. For more information, visit Lin Engineering at linengineering.com.

Oriental Motor 60-mm DG II rotary actuator with AlphaStep AZ Series absolute encoder stepper motor

August 29, 2018 By Lisa Eitel Leave a Comment

Oriental Motor is pleased to expand the DGII Series product lineup and AlphaStep hybrid control system with the introduction of the new 60 mm DGII rotary actuator.

The DGII Series is a line of products that combine a high rigidity hollow rotary table with an AlphaStep absolute encoder AZ series closed loop stepper motor and driver. It retains the ease of use of a stepper motor, while also allowing for highly accurate positioning of large inertia loads.

The new DG II retains the ease of use of a stepper motor while allowing for highly accurate positioning of large inertia loads.

The smaller 60 mm frame size is equipped with an AlphaStep AZ Series absolute encoder stepper motor. This new rotary actuator is available to be used with 4 types of AZ Series DC input drivers … stored data type, pulse input driver with built-in RS-485 communications, pulse input type and multi-axis driver with EtherCAT communication.

It is a complete cost-effective accurate rotary actuator system that help eliminate the need for additional sensors. This new combination can work in traditional applications where step and direction are required, or, in applications where PLC or Touch Screens (HMI) are being used, without the need for additional modules connected to the PLC. The end result is a more efficient and energy efficient product that is compatible with a wider range of master controller types and control methods.

For more information about the Oriental Motor 60-mm DGII Series rotary actuator, call (800) 468-3982 or visit this deep link on orientalmotor.com.

Since its founding in Japan in 1885, Oriental Motor has been a world leader in motion control systems. For over a century, we have concentrated on technological advancement and product design improvement — an emphasis evident in the sophisticated devices we market today.

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.

What are slip rings and why do some motors use them?

August 21, 2018 By Danielle Collins Leave a Comment

Slip rings — also referred to as rotary electrical joints, electric swivels, and collector rings — are devices that can transmit power, electrical signals, or data between a stationary component and a rotating component. The design of a slip ring will depend on its application — transmitting data, for example, requires a slip ring with higher bandwidth and better EMI (electromagnetic interference) mitigation than one that transmits power — but the basic components are a rotating ring and stationary brushes.

A complete slip ring assembly includes end caps, bearings, and other structural features. But the basic components of a slip ring are the ring and the brushes.
Image credit: Moog Inc.

If the rotation of one component involves a fixed number of revolutions, it may be possible to use spools with sufficient cable length and rotating speed to allow for the required revolutions, although cable management in this setup can be quite complex. But if one component rotates continuously, using cables to transmit signals between the rotating and stationary components isn’t practical or reliable in many cases.

Slip rings in AC motors

Image credit: brighthubengineering.com

In a version of the AC induction motor referred to as a wound rotor motor, slip rings are used not for transferring power, but for inserting resistance into the rotor windings. A wound rotor motor uses three slip rings — typically made of copper or a copper alloy — mounted to (but insulated from) the motor shaft. Each slip ring is connected to one of the three phases of rotor windings. The slip ring brushes, made of graphite, are connected to a resistive device, such as a rheostat. As the slip rings turn with the rotor, the brushes maintain constant contact with the rings and transfer the resistance to the rotor windings.

Slip rings on a wound rotor AC motor. Once the motor reaches operating speed, the brushes are lifted via the springs and the slip rings are short-circuited via the sliding contact bar.
Image credit: Wikipedia

Adding resistance to the rotor windings brings the rotor current more in-phase with the stator current. (Recall that wound rotor motors are a type of asynchronous motor, in which the rotor and stator electrical fields rotate at different speeds) The result is higher torque production with relatively low current. The slip rings are only used at start-up, however, due to their lower efficiency and drop-off of torque at full running speed. As the motor reaches its operating speed, the slip rings are shorted out and the brushes lose contact, so the motor then acts like a standard AC induction (aka “squirrel cage”) motor.

The slip rings in a wound rotor motor form a secondary, external circuit. Inserting resistance to this circuit allows the motor to produce very high torque at start-up, which is necessary for moving loads with high inertia.

Slip ring or commutator?

You may have noticed that the design and function of a slip ring sounds very similar to that of a commutator. While there are similarities between the two, there are critical distinctions between slip rings and commutators. Physically, a slip ring is a continuous ring, whereas a commutator is segmented. Functionally, slip rings provide a continuous transfer of power, signals, or data. Specifically, in AC motors, they transfer resistance to the rotor windings.

Commutators, on the other hand, are used in DC motors to reverse the polarity of current in the armature windings. The ends of each armature coil are connected to commutator bars located 180 degrees apart. As the armature spins, brushes supply current to opposing segments of the commutator and, therefore, to opposing armature coils.

Slip rings are used in virtually any application that includes a rotating base or platform, from industrial equipment such as index tables, winders, and automated welders, to wind turbines, medical imaging machines (CT, MRI), and even amusement park rides that have a turntable-style operation. Although the traditional application for slip rings was to transmit power, they can also transmit analog and digital signals from devices such as temperature sensors or strain gauges, and even data via Ethernet or other bus networks.

Feature image credit: Rotary Systems Inc.