Actuators for Motion Control Applications

Keeping the elements at bay

February 12, 2019 By Miles Budimir Leave a Comment

Keep these five key factors in mind when selecting mechanical components for harsh environments.

Chad Carlberg
Product Line Manager for Industrial Actuators
Thomson Linear

As electromechanical actuators and other mechanical motion components expand in capability for heavy duty applications, so does their capability to resist harsh conditions. Extreme temperatures, high particulate levels, chemical exposure, high-pressure washdowns, vibration and shock, radiation, and electromagnetic interference are among the threats to reliable motion control. System designers can mitigate these threats when selecting motion control components for such applications through careful evaluation of five design elements that contribute to robust operation: material selection, coatings, sealing strategy, vibration/shock resistance and maintainability.

Electrak HD actuators from Thomson Linear use stainless steel, e-coated zinc, and anodized aluminum materials to provide protection in heavy duty environments. Advanced sealing features with the added benefit of IP66 dynamic protection keep internal components free of ingress.

Factor one: Material selection
Material selection is the first line of defense against challenging environmental conditions. Advances in material science are leading to the creation of new alloys and hybrid materials that can withstand temperature extremes, exposure to chemicals or abrasive materials, frequent washdown, and other environmental forces. Stainless steel, hard-anodized aluminum and resistant polymers are among the most common materials used to ruggedize motion control components.

Poor material selection can result in premature failures, expensive in-field service and repair, and lost productivity. Maximum protection comes when all motion control components – from the actuator housing to the smallest bearing – are selected with worst case operating scenarios in mind.

Factor two: Coatings
Motion control components used in extremely corrosive environments, such as those characterized by exposure to hydrocarbons, urea and fertilizers, should also be coated with high-performance materials. This improves operation and reduces downtime, especially in environments where corrosive chemicals, salt spray or submersion will require additional protection. The right coating and material combination can significantly extend component life.

Ruggedized electromechanical actuators can function in applications where once hydraulic actuators dominated, such as in agricultural equipment.

Testing chemical resistance
The most widely applied standard for chemical resistance is ISO 15003, which provides design requirements and guidance for the manufacturers of electrical and electronic equipment used in mobile agricultural machinery, forestry machinery, landscaping and gardening machinery. It provides test protocols for specific environmental conditions and defines severity levels for extreme conditions that might occur during typical operation. Testing for chemical resistance, for example, requires the ability to withstand three days of operation amidst the following chemical concentrations:

Diesel Fuel – 100%
Hydraulic Oil – 100%
Brake Oil – 100%
Ethylene Glycol – 50% aqueous solution
Urea Nitrogen – saturated solution
NPK Fertilizer*9 (7.5% each N, P, K) – saturated solution

Other standards applied to corrosion resistance, particularly Diesel Exhaust Fluid (DEF), are DIN 70070-05, AUS 32 and ISO 22241-1.

Factor three: Sealing strategies
After materials and coatings, the next line of defense in harsh environments is the sealing strategy. Unless a component is adequately sealed, chemicals and particulates can make their way to internal component mechanisms, causing damage, buildup and clogging, and creating fertile ground for bacterial and other microbial growth. Using inadequately sealed motion control components in harsh environments will require additional cost of enclosures and maintenance, and potentially more frequent maintenance.

Every component should be sealed, including motor mounts. Wipers, seals and gaskets are integral to success. The wiper brushes off contaminants from the extension tube during operation and prevents water intrusion. The seals back up the wipers to complete the protection. Lastly, gaskets provide sealing between housings, cover tubes, motors and rear mounting components.

One of the best indicators of a system’s sealing effectiveness is the International Protection Marking, or IP Code. Its ingress protection (IP) rating is the global standard for measuring protection from the ingress of solid objects and liquids. The IP rating specifies the degree of environmental protection an enclosure provides against foreign materials that could impact operation.

The IP rating is composed of two numbers (see Table 1). The first number represents resistance to solids and the second to liquids. An IP rating of 00, for example, means there is no protection from solids or liquids. An IP rating of 11 means protection from ingress by objects larger than 50 mm and from rain or condensation. An IP rating of 66 means protection from penetration by particulates the size of dust and from high-pressure water jets from any direction. This rating is also considered the minimum for use in harsh environments today.

Factor four: Vibration and shock resistance
Materials, coatings and sealing can all be compromised by shock and vibration. Components must be tough enough to withstand the extremes of machines operating in harsh conditions. Often this translates into heavy loads or intense vibration or forces acting on the components – sometimes in near constant operation. The constant torque and movement can weaken a component over time and cause failure. By incorporating design features that account for high vibration or shock load, manufacturers eliminate the need for product accommodations.

For example, planetary gear designs provide more shock resistance than parallel gearing, and stiffness can be improved further by cutting one of the internal gears directly into the output housing. Leveraging a single-piece housing and ring gear, in this way, eliminates the chance of the gear slipping inside the housing, offering higher peak torque. Avoiding bushings with rolling elements can also help systems handle the constant stress environments as can depth/through case hardening of shafting. Proper mating of all components is also critical to shock protection.

Testing shock resistance
Compliance with industry standards is one of the best ways to ensure the right level of shock protection needed. Table 2 compares the three most common standards applied to motion control equipment: MIL- S -901, EN60068-2-27 and EN60068-2-32.

Testing vibration resistance
To ensure that common vibration profiles can be completed without damage to the product, test protocols, usually OEM specific, are run on multiple components and planes, including protocols for testing housings, structural bolts and any included printed circuit assemblies or sensors. Testing is conducted with the unit not powered or operating and mounted on a vibration machine guided by the power spectral density (PSD) levels shown in Table 3. The device being tested should extend half of design maximum and be tested in three orthogonal axes for 24 hours each.

Factor five: Maintainability
Harsh environments present risks to human safety from extreme temperatures, toxic/harsh chemicals or inhalation hazards – even radiation. Besides lost productivity and downtime, maintenance or replacement presents risk of injury or illness – especially if frequently done. Components that offer little to no maintenance improve employee safety and minimize potential for workplace accidents, while reducing costs.

Lubrication issues are one of the main maintenance drivers for linear motion components. Smooth, reliable motion is a hallmark of a well-designed system and is ensured by maintaining the proper level of lubrication for moving components. Products that use oil for lubrication require routine maintenance and are predisposed to leaks. Components that pre-lubricate with grease or self-lubricate can greatly reduce or eliminate ongoing maintenance demands.

The right stuff
A few examples from Thomson illustrate how motion components can be designed for operation in harsh environments. For instance, Thomson’s Max Jac heavy duty electric linear actuators are made of stainless steel, hard anodized aluminum or a highly resistant polymer. The seals are made of materials that withstand both organic and nonorganic chemicals and abrasive materials. They’re also designed to operate in a wide temperature range from -40 to + 85°C. The actuators are also rated for IP66/IP69K and have been tested for 500 hours of salt spray, withstand dirt, dust and water, and resist aggressive substances such as fertilizers, acid, oil, grease and cleaning agents.

Light to medium-duty applications, such as this hood lift on an earth mover, can benefit from using electromechanical actuators.

Another example is the Electrak HD, which also uses stainless steel, e-coated zinc, and anodized aluminum materials to provide protection in heavy duty environments. It also features advanced sealing features with the added benefit of IP66 dynamic protection to keep the internal components free of ingress – even while the actuator is operating. The internal components themselves are protected from drops, shocks, and interference from other electrical sources to ensure proper operation, regardless of external application demands.

As long as harsh and hazardous environments require extended presence by humans, many opportunities to improve productivity will remain untapped. Motion control technology can reduce the need for human exposure, while at the same time enabling performance of operations beyond human capability.

But mechanical components require protection too, and careful consideration of materials, coatings, sealing strategies, vibration and shock resistance, and maintainability can help system designers ensure they will get maximum performance and life out of the systems they intend to deploy in challenging environments.

Thomson Linear
www.thomsonlinear.com

Direct-drive, high-resolution electric cylinders with integrated encoder

January 18, 2019 By Miles Budimir Leave a Comment

The SDLM-025-070-01-01 and SDLM-025-070-01-05 direct drive linear motors from Moticont, also known as electric cylinders, have built-in encoders, and feature high acceleration, high speed, high resolution, zero backlash, and zero cogging. These compact direct-drive linear motors with quiet linear plain bearings are just 1.00 in. (25.4 mm) in diameter and 2.75 in. (69.9 mm) long. Protected inside the motor housings are linear optical quadrature encoders that directly connect to the non-rotating shaft for the greatest possible accuracy.

Select only the degree of precision your application requires as the SDLM-025-070-01-01 has a resolution of 1.25 microns and the SDLM-025-070-01-05 has a resolution of 5.0 microns with a 10% savings in cost.

Each of these direct-drive linear motors has a stroke length of 0.500 in. (12.7 mm) and a continuous force rating of 22.2 oz (5.9 N) and peak force of 67.2 oz (18.7 N). Non-commutated, they feature direct coupling of the load or stage which eliminates backlash and allows for high acceleration/deceleration. Both ends of the motor and shaft ends are drilled and tapped for easy integration into new and existing applications. Some common applications include assembly, manufacturing, sorting, semiconductor handling, inspection, medical equipment and procedure tables, antenna positioning, dampers, door & valve actuators, agricultural equipment, and adjustable office furniture.

Inexpensive alternatives to hydraulic and pneumatic systems, these direct-drive linear actuators or electric cylinders are also available as a complete plug-and-play linear motion system with matching motion controllers.

For more information, visit www.moticont.com.

Finalists announced for Motion Control category of LEAP Awards

November 9, 2018 By Lisa Eitel Leave a Comment

Finalists were announced on Friday, November 2nd for the inaugural LEAP Awards Motion Control Category. The competition was scored by a panel of independent engineering judges. The judges below were responsible for the Motion Control category.

Dan Jones • President | Incremotion Associates

Dan Jones started as a production worker at a motor company in the late 1950s, balancing ac squirrel cage rotors and pressing shafts into rotors. He earned his BSEE from Hofstra University in 1965 and a Master’s in Math from Adelphi University in 1969. He has more than 50 years’ experience as a motor design engineer, manager, chief engineer, marketing director, vice president of marketing, and consultant.

Jones is experienced in custom motion marketing activities, surveys and strategic planning meetings and is a Life member of IEEE. He employs SPEED and MotorCAD for the design of all types of linear, radial, flux, and axial flux machines, PM brushless, switched reluctance and induction machines. Jones is the author of more than 250 seminars, papers and technical articles on a wide range of motion control subjects. He was project manager for the design and development of six specialty DC motors used on the two Mars Viking Landers in 1976.

Karl H. Schultz • President | Schultz Associates

Karl Schultz is the President of Schultz Associates, specializing in manufacturing and technical management consulting in the electric motor industry. He is also considered an expert in implementing lean/world class business processes.

Schultz is an experienced hands-on manufacturing management consultant who has had both line and staff positions in the electric motor industry. He was the division Director of Manufacturing Engineering for Emerson Electric for 10 years, supporting four plants in the U.S. and Mexico. He was then the Business Director of Manufacturing Engineering at GE Motors for three years. Consulting has taken him worldwide in many various successful projects. He has more than 25 years in the electric motor industry.

Schultz holds a BSME in Machine Design from Western Michigan University. He was a member of the Electrical Manufacturing and Coil Winding Association, serving as the VP and a Board member. He is a senior member of the Society of Manufacturing Engineers and a past member of the Society of Automotive Engineers. He has received numerous awards such as Best Industry award (General Signal), Most Valuable Player award (BMI), performance awards (GE Corporate & Motors), and others. He is an adjunct instructor at the Oregon Institute of Technology – Wilsonville … teaching junior and senior level management courses such as Lean/6 Sigma and Organizational Behavior.

Tom Solon | RH Murphy Co. Inc.

Tom Solon has a diverse engineering background in roles as both an OEM and supplier, spanning many industries, from housewares and consumer products, to semiconductor manufacturing and medical equipment technology. A recognized authority in linear motion products, plastics, and semiconductor handling, Tom has authored numerous articles and technical papers.

Tom earned his BSME in Machine Design and BA in Economics from Brown University and is a licensed Professional Engineer. He devotes much of his free time to public education as a school board member and technical education advisory board member.

Michael Torres • Chief Avionics Support Equipment Engineer | Naval Air Warfare Center, Weapons Div. Point Mugu

Michael Torres’ technical expertise is the design, development, and testing of advanced avionics (flyable electronics) that meet speed, size, weight, and power requirements of these systems. He focuses on the development of software mathematical algorithms to facilitate design solutions that meet these requirements.

Torres has developed and patented automated test systems for avionic systems and their test equipment. He holds nine Navy patents and is an expert in the development of manufacturing fixtures that simply the manufacturing of components, reducing the manpower requirements and producing better and more repeatable results.

Torres holds a Master of Science in Electrical Engineering specializing in Electronic Warfare from the Naval Post Graduate School, a Master of Science in Electrical and Computer Engineering from University of California at Santa Barbara, and a Bachelor of Science in Electrical Engineering from UCLA.

Below are descriptions of the Motion Control finalists. The overall winner of the Industrial Automation category will be announced at an awards dinner on December 11th in Costa Mesa, Calif.

ElectroCraft • RPX and LRPX

The ElectroCraft RPX and LRPX family of brushless DC motors and integrated gear motors are designed to optimize motion applications across markets where high torque is needed from a quiet, small, but powerful motor form factor. The RPX is powerful, energy efficient, highly controllable, and durable. It is a powerhouse of a motor that offers more torque density than other BLDC motors in relation to its small size. The RPX family offers a broad range of options from the RPX22, a 22-mm diameter motor that offers 25.2 oz.in of torque, to the RPX52, offering a whopping 184 oz-in. torque from a 52-mm diameter motor that is only 57 mm in length.

For even more demanding high torque applications, ElectroCraft presents the LRPX family which offer an integrated planetary gearbox optimized to work with the multi-pole RPX technology. While traditional BLDC motors spin too fast to work effectively with traditional gearboxes, the LRPX is designed for peak operation at relatively low BLDC speed that pairs perfectly with the integrated gearbox. The integrated LRPX gearmotor is also quiet due to its construction and relatively low speed of operation. Learn more at this deep link on electrocraft.com.

GAM Enterprises • Zero backlash gearbox

The GPL Series is a zero-backlash planetary gearbox. It has a high ratio helical spur input driving a conical spur gear planetary stage. A unique, patented mechanism on the conical planet gears continuously presses the planet gears into the ring gear to maintain zero backlash for the lifetime of the gearbox.

High torsional rigidity results in < 0.6 arc-min. of lost motion at start up. The GPL comes in seven sizes with either a solid flanged output (GPL-F) or a hollow flanged output (GPL-H). The GPL-H uses five planet gears to achieve a through hole for feeding power or air lines to the output. The GPL has a high torque density of 58-73 Nm/kg for high performance in a small gearbox. The gearbox is rated for a fully-loaded life of 20,000 operating hours.

Haydon Kerk Motion Solutions • 15-mm Linear Actuator

The Haydon Kerk Motion Solutions LE15 can-stack actuator offers precision linear motion in a compact and powerful package with the ease of use of a stepper motor. The base of the actuator is a 15mm diameter can-stack style stepper motor with integrated precision lead screw. The construction of the motor is such that it can sustain axial loads not typically seen with standard rotary motors, and still achieve industry leading power density for a can-stack style motor. The lead screw is offered in a 2 mm diameter with several lead options. For increased efficiency and life Kerkote TFE low friction coating is applied to the lead screw. The ZBM anti-backlash lead nut compensates for wear and backlash to provide a high degree of bidirectional linear precision. The result is a highly compact precision linear actuator.

A common trend is a need to reduce overall package size while maintaining a certain level of force output within a linear motion application. There are several drivers for this, but generally the need is the same, facilitating precise linear motion in smaller spaces. The manufacturer has addressed this need by miniaturizing an existing can-stack actuator line and its radially compensated line of lead nuts. The result is the world’s smallest commercially available linear actuator with the world’s smallest commercially available anti-backlash nut.

The LE15 linear actuator is a great choice for linear motion applications where space is at a premium and precise motion control is required. In addition to having high force density compared to other similarly sized products such as piezoelectric motors, the LE15 actuator is low cost and simple to use. Typical applications include medical equipment, semiconductor handling, valve control, optics focusing, X-Y tables, handheld instruments, and many more. In addition to standard configurations, Haydon Kerk Motion Solutions can, and often will customize the design of the actuators to meet specific application requirements.

The LE15 linear actuator is an enabling technology, without it some products would never make it to market. Often miniaturization of motion components comes at a high cost which can kill a project or product budget before the design gets off the ground.

Kinitics Automation • KLA05 Linear Actuator

The KLA05 Linear Actuator is a shape memory alloy-based actuator that uses proprietary Bundled Wire technology to deliver high force and actuation speed in a small package. The product is the first commercially available linear actuator using shape memory alloy to provide precise linear motion without the use of motors and requires only electrical power to operate. This breakthrough product allows users to upgrade and improve existing systems, while also enabling the automation and control of processes that were previously unfeasible using conventional equipment.

The new Kinitics KLA05 Linear Actuator provides forces up to 650 N (146 lbf) and strokes up to 6.7 mm, can be easily configured to supply a pushing or pulling force, and fits in a variety of applications. Position control is possible through the addition of a linear sensor while force control is possible through use of a strain gauge. Due to its use of shape memory alloy and Kinitics’ proprietary Bundled Wire technology, the KLA05 Linear Actuator offers a number of features and benefits that distinguish it from other types of actuators, including: positional accuracy of ±5 µm; requires minimal infrastructure to operate; and has only one moving part and no backlash.

Built inside a frame that conforms to the ISO 21287 standard, the KLA05 is compatible with a wide variety of rod-end attachments and mounting brackets. The frame features industry-standard 5 mm T-slots that permit easy mounting of proximity switches and non-contact position sensors. The product is both watertight and dustproof, making it suitable for use in harsh environments, and can be powered with standard 120 VAC power or sub-50 VDC power which can be delivered through flying leads or SJOOW cable hook-up.

Lin Engineering • Miniature Hybrid Step Motor

Lin Engineering’s new PT106 Hybrid Step Motor measures just 16 mm (0.63 in.) in width. In the past, this frame size was only possible to achieve with a less accurate, and less powerful permanent magnet (PM) motor. PT106 offers all of the benefits of a hybrid stepper, and none of the drawbacks of a PM motor. PT106 outperforms PM motors in all metrics: it’s more powerful, more accurate, offers higher speeds, and wider dynamic torque range.

The PT106 is able to achieve up to 2.1 oz-in of holding torque without the aid of a gearbox, which is 70% more holding torque of the closest competing design, or 4x more torque than a conventional PM motor of similar size. When paired with the manufacturer’s gearbox, the motor is capable of producing up to 8 oz-in of holding torque.

maxon precision motors • Exoskeleton Joint Actuator

The global Exoskeleton market is growing in both market share and technological developments at a rapid rate each year. Maxon motor worked with several global customers to design and develop brushless DC motor solutions for use in robotic limbs. The Exoskeleton joint actuator is for use in hip and knee exoskeletons. A complete joint actuation unit includes a pancake brushless DC motor (EC90 flat) with inertia optimized rotor, an

Internal high-resolution 4096 MILE Encoder, a planetary gearhead with absolute encoder and an EPOS4 position controller with CAN and RS232interface.

Fitting the 17bit SSI absolute encoder directly at the joint rotation to a degree will negate the effect of gearhead backlash … giving designers increased positioning accuracy. The unit will deliver54Nm of continuous torque and 120Nm on a 20% duty cycle. The system can be operated on supplies between 10 and 50V DC and the actuation speed is up to 22 rpm. The wide variety of different operating modes provides high flexibility in testing and optimizing of the entire exoskeleton system.

AMETEK • Windjammer Pro Brushless Blowers

The Windjammer PRO solves many customer issues related to temperature. The unique cooling design allows customer to run the blower fast resulting in increased performance. The blower also had a new bearing protection design to enhance the life of the blower. It Also has a decreased sound level due to the redesign in cooling. From the manufacturer:

Currently, we have several units sent to customers globally. We initially began design work after hearing about the problems listed above. Once we developed our first prototype, we were able to then work with a few select customers to test and understand the nuances of their products and how to adapt our new design to meet customer needs. We are still developing new designs to fit all of the needs of our customers. These designs are evolutions of the original Windjammer PRO and can be used in the same manner as the original.

To design this new blower, we used 3D printing and modeling for testing out our new designs. This helped us to reduce the amount of raw materials needed and find the right design to meet our customer needs. We also did several tests before our product was released to our beta customers.

End users are seeing value in drop-in replacements to their current blower model, a decrease in the number of SKUs purchased because the manufacturer can tune these blowers to work with generally accepted voltages around the world. There are also several electronic enhancements that allow the customer to easily have the blower retuned on site while still in their product.

Oriental Motor USA • Battery-Free Multi-Rotation Absolute Mechanical Encoder

In recent years, greater accuracy, better reliability, and safety are demanded of motors, especially motors used in critical positioning applications. Such systems typically utilize servo motors with encoder feedback along with battery backup, allowing it to perform closed loop absolute control. From these requirements, a battery-free, multi-rotation absolute mechanical encoder was developed. The AlphaStep AZ Series, a closed loop system, adopted this type of sensor and is currently on the market today.

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.

How does stiffness affect piezo output force and displacement?

August 15, 2018 By Danielle Collins Leave a Comment

Piezo actuators operate on the inverse piezoelectric effect: when voltage is applied, the actuator contracts or expands. But when the actuator is blocked from moving (by a load applied in the direction of travel), it generates a force. This relationship between displacement and force in piezo materials is an inverse relationship. In other words, the more force an actuator must generate against a load, the less travel it can produce. A “free” actuator — one that experiences no resistance to movement — will produce its maximum displacement, often referred to as “free stroke,” and generate zero force.

Conversely, when an actuator is blocked from moving, it will produce its maximum force, which is referred to as the blocked, or blocking, force. Theoretically, when the actuator is blocked, it is working against a load with infinitely high stiffness. But materials with infinite stiffness don’t occur in the real world, so the blocking force is determined by applying a voltage to the actuator, with no load applied. This “free” operation, as described above, generates the actuator’s maximum displacement, or free stroke. A force is then applied to return the actuator to its original length. This force is measured and recorded as the blocking force.

The stiffness of the actuator is the ratio of blocking force to free stroke.

k_p = stiffness of piezo actuator

F_block = blocking force

ΔL_fs = free stroke (nominal displacement) with no external load

In piezo actuators, force and displacement are inversely related. Maximum, or blocked, force (F_block) occurs when there is no displacement. Likewise, at maximum displacement, or free stroke, (ΔL_fs) no force is generated. When an external load is applied (A), the stiffness of the load (k_e) determines the displacement (ΔL_A) and force (ΔF_A) that can be produced.
Image credit: APC International, Ltd.

There are two types of load that can be applied to a piezo actuator: a spring load, which increases as the actuator moves, or a constant load, which does not vary. The actuator’s ability to produce displacement and force depends on the type of load.

Piezo output force and displacement with a non-constant (spring) load

Many piezo applications, such as valve operation, introduce loads that vary with the piezo’s stroke — in other words, spring loads. When the stiffness of the applied spring load is low compared to the piezo stiffness, the piezo output force (F_eff) is small. In other words, a spring (load) with low stiffness provides very little “blocking” for the piezo to work against in order to generate a force. Therefore, the piezo output force is greatly reduced from its maximum, or blocking, force.

F_eff = force produced with spring load

k_e = stiffness of applied load

On the other hand, the spring reduces the actuator’s displacement only slightly:

ΔL = displacement 0f actuator with spring load

Performance of a piezo actuator with no load (A) versus an actuator with a low-stiffness spring load (B). Note that the displacement (ΔL) with the spring load is slightly less than the maximum displacement, or free stroke, (ΔL_fs), but the force produced (F_eff) is much less than the maximum, or blocked, force (F_block). The stiffness of the spring load (k_e) is shown by the blue line.
Image credit: PI Ceramic GmbH

A low-stiffness spring load — typically no more than 10 percent of the piezo stiffness — is generally recommended for preloading a piezo actuator to ensure the displacement is not severely reduced.

Piezo output force and displacement with constant load

When a constant load is applied, there is an initial deflection, or compression, of the actuatordue to the load. This means the zero point of the working curve is offset, or shifted, but the actuator’s stroke is unaffected.

ΔL_N = offset of the zero point with constant load

F = applied load

Some force is generated when the load is applied, causing the initial deflection, but once the actuator responds to the application of the load, its remaining work goes into generating the displacement. The zero point of the blocking force (maximum force) is also shifted, but is magnitude is not affected.

When a constant load is applied, the zero point of the actuator’s displacement is shifted, but its total displacement, or free stroke, is not affected: ΔL’_fs = ΔL_fs
Image credit: PI Ceramic GmbH

Feature image credit: Noliac

How do rotary voice coil actuators work?

July 17, 2018 By Danielle Collins Leave a Comment

Most linear motion devices have a rotary equivalent, and voice coil actuators are no exception. While the versions depicted in most product images and videos are linear, rotary voice coil actuators fill a need for smooth, arc-shaped motion and torque production with fast response times. But unlike the design relationship between rotary and linear motors, developing a rotary voice coil actuator isn’t simply a matter of taking the linear version and rolling it into a cylinder. While their components are the same, the configurations of linear and rotary voice coil actuators are quite different.

Voice coil actuators work on the principle of the Lorentz force, which is the force generated when a current-carrying conductor is placed in a magnetic field. In the case of a voice coil actuator, the magnetic field is created by permanent magnets and the conductor is a coil of wire. When current is applied to the coil, a force is generated, and the magnitude of the force is proportional to the applied current. (All other variables in the force production, such as magnetic flux and length of wire, are fixed for a given voice coil design.)

F = k*B*L*I*N

F = force (N)

k = force constant

B = magnetic flux density (tesla)

L = length of wire (m)

I = current (amps)

N = number of conductors

The most common linear voice coil actuator design features a moving coil, although the actuator can be constructed so that either the coil or the magnet is the moving part. In the moving coil design, a stationary cylindrical permanent magnet produces a radial magnetic field. Housed inside the permanent magnet cylinder is a coil that is wrapped around a non-conducting structure, or holder. The permanent magnet is housed in a ferromagnetic cylinder that is open at one end and has a “core” through its middle, which is necessary for completing the magnetic circuit. The coil assembly rides in the air gap between this core and the interior surfaces of the permanent magnet. Although it sounds complicated, the construction is actually quite simple, as shown below.

The construction of a linear voice coil actuator is relatively simple. In this example, the magnet is stationary and the coil moves.

A rotary voice coil actuator is sometimes referred to as a “flattened” version of the linear design described above. In other words, to transform a linear voice coil actuator into a rotary version, place the linear voice coil actuator lengthwise on a table (as it would sit if it were operating horizontally) and flatten it into an essentially 2-D object. Then bend the ends so that it forms an arc (like a piece of macaroni). Now you have a rotary voice coil actuator.

In this rotary voice coil actuator, the permanent magnet segments are on the top and bottom (white) and the coil (gold) rides in the air gap between them.
Image credit: BEI Kimco

Rotary versions provide torque rather than force. Similar to their linear counterparts, the amount of torque generated is proportional to the applied current, and the direction of the current determines the direction of motion. Excursion angles are typically less than 180 degrees, and commonly fall between 15 and 60 degrees.

Voice coil actuators are, technically, non-commutated DC motors. The term “voice coil” is often used because one of their first applications was to vibrate the paper cones in loudspeakers. Rotary voice coil actuators are also referred to as “arc segment” actuators or “limited angle torque motors” because they produce arc-shaped motion.

One of the strengths of voice coil actuators is their extremely smooth, cog-free motion with no torque ripple. This makes rotary versions ideal for applications that require high torque and quick response, such as gimbal positioners. They are also well-suited for moving optics and for controlling stabilization devices.

This gimbal assembly design uses two rotary voice coil actuators. The inner axis moves 40 degrees in 32 milliseconds, and the outer axis moves 20 degrees in 140 milliseconds.
Image credit: BEI Kimco

Feature image credit: H2W Technologies, Inc.

Electric motors: Trends in stepper, battery-powered, and integrated motion designs

March 2, 2018 By Lisa Eitel Leave a Comment

From induction motors in electric vehicles to tiny coreless dc motors in drug-delivery equipment, electric motors continue to proliferate. Last year we saw consumer products, implantable medical devices, and automation of previously manual tasks spur the most innovation in motor design and use. This year those trends continue — and now we see increased use of servo and stepper motors in robotics.

maxon precision motors EC 4 brushless dc motors (which can be fitted with GP 4 planetary gearheads) are 4 mm in diameter with an ironless winding; ISO 13485 certified; and suitable for use in laboratory robots, micropumps, and diagnostic devices. Two lengths deliver power to 0.5 and 1 W. “We also want to offer more value-add services, as more companies than ever in the U.S. want finished motor and motion systems — so-called drop-in designs,” said McGrath of maxon. “So to that end, our expanding U.S. factory will have the capacity to supply custom assemblies and PCBs.”

In fact, whether it’s basic tin-can motors for low-cost custom actuation or integrated motors that output servo-like performance, overall use of stepper motors is growing. On the latter, a study by P&S Market Research projects a CAGR of 6.3% through 2023 for the global closed-loop stepper motor market. P&S cites the well-known benefits of control-feedback signals and power-adjusted current control as key reasons for the technology’s steady adoption.

Low-current dc motors from ISL Products Intl. Ltd. come in myriad mechanical and electrical configurations. Sometimes gearmotor modifications help the dc motors meet exacting OEM application specifications. In other cases, the motor must have special construction to avoid inducing EMI and RFI interference (Here, raw materials in the motor components are a main consideration, said to Kawaller of ISL.) Designs with reduced power consumption benefit from motors with specialized internal construction and nontraditional component materials.

Warren Osak, CEO of Toronto-based distributor Electromate Inc., sees this trend for integrated stepper motors, even while the middle of the stepper-motor market (actuated by standalone 1.8° hybrid stepper motors) recedes. Technology is either migrating upward (and taking the form of integrated motors or smart motors) or migrating downward — to lower-cost motors with less sophisticated structures, according to Osak.

“The use of traditional hybrid stepper motors has been yielding to integrated products … while in lower-end applications, we see more use of less-sophisticated motors with customer-provided integrated chips (ICs) to drive them,” he added.

Full interview with Osak: Motion-control trends distributor insight

Some closed-loop stepper manufacturers we surveyed for the Design World Trends issue include Schneider Electric Motion USA, Applied Motion Products Inc., Lin Engineering, MICROMO of Faulhaber, Oriental Motor Co., and Nippon Pulse America Inc. — with commentary from the latter in our actuator trends coverage. All detail pre-integrated or application-specific motor offerings. Case in point: Automation in the oil and gas industry has created numerous opportunities for motion control products, but stringent requirements for hazardous location ratings rule out most standard motor and drive solutions.

Use of tin-can stepper motors is on the rise, and now some new tools let engineers check their programming on the little motors more easily. Consider the Motion Checker 5 controller from Nippon Pulse America Inc. — a standalone handheld controller with an integrated driver circuit. Using it is as simple as plugging it into a normal outlet and connecting a stepper motor to run through motion sequences.

“To serve engineers in this industry, we’ve released the world’s only ATEX-rated stepper drive for hazardous locations … and this year we’ll introduce our first explosion-proof step motor to pair with it,” said Eric Rice of Applied Motion Products. “The drive is already being used on rigs in the oil field for applications where accurate braking and speed control of drill strings are required.”

Motors in (proliferating) battery-powered designs

Battery-powered designs such as ATVs, mobile robotics (including AGVs), scooters, ebikes, and drones present unique motion-system challenges. Motors that integrate into these designs might need to accept 48, 24, or 12-V input, and nearly all of them must meet tough efficiency requirements … NEXT PAGE →

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SERAPID supplies Meridian Lift for XXIII Olympic Winter games opening ceremony

February 9, 2018 By Miles Budimir Leave a Comment

The SERAPID solution has once again been chosen to provide dynamic stage action for the opening ceremony of the 2018 Olympic Winter Games in Pyeongchang, South Korea. SERAPID had previously provided an extensive stage lift system for the 2008 Summer Games in Beijing, China.

The opening ceremony took place in the Pyeongchang Olympic main stadium, and was broadcast globally with pre-show estimates of nearly 400 million viewers, 35,000 of which watched live in the stadium.

Center-stage at the ceremony was the SERAPID Meridian Lift, an impressive circular lifting platform, totally supported by the robust and reliable SERAPID LinkLift actuators. “We are proud to provide the Olympic games opening ceremony a system resistant to harsh climate (-20°C approximate with wind) and safe for moving people“, said Eric Michaut, Project Manager at SERAPID Group. “We used 15 LinkLift 100 telescopic actuators rising up to 5.5 m in height to lift two different platforms, one with a diameter of 24 m and another in its center with a diameter of 9 m.“

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About SERAPID
SERAPID produces customised solutions for moving heavy loads by use of our Rigid Chain Technology (RCT). This durable, low maintenance, eco-friendly technology has found applications in diverse industries including architecture, nuclear, medical, defense, automation, manufacturing, theatre and entertainment. SERAPID has a longstanding commitment to continued innovation in product design as well as to providing leadership in the advancement of engineering applications worldwide.

For more information, visit www.serapid.com.

SERAPID Group (lift and transfer-system supplier) launches new website

January 20, 2018 By Lisa Eitel Leave a Comment

SERAPID Group — a leading supplier of lifts, quick die change, and horizontal transfer systems — has launched its new website at www.serapid.com.

“We are proud to provide customers with a new and improved website,” said SERAPID Group Chief Operating Officer Guillaume Davies. “With this new site we aim to create an exciting experience for visitors … so that in discovering products and original designs, they’re [inspired to contact our team] …”

Davies continued, saying that the team is excited about the important release, and will continue to strive for perfection through a continuous improvement project — “taking into account comments and suggestions.”

SERAPID produces customized setups for moving heavy loads by use of Rigid Chain Technology (RCT). This durable, low maintenance, eco-friendly technology has found applications in diverse industries including architecture, nuclear, medical, defense, automation, engineering, manufacturing, theater, and entertainment. SERAPID has a longstanding commitment to continued innovation in product design as well as to providing leadership in the advancement of engineering practices worldwide.