Linear Motors - Motion Control Tips

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.

Hybrid linear stepper motors: Operation and applications

September 27, 2017 By Danielle Collins Leave a Comment

Like servo motors, stepper motors are available in both rotary and linear designs. When an application requires force (rather than torque) output and can operate in open loop control, a linear stepper motor is often the preferred solution. Although linear stepper motors are available in both variable reluctance and hybrid designs, the more common version is hybrid linear stepper motors.

In a hybrid linear stepper motor, the base, or platen, is a passive steel or stainless steel plate with slots milled into it. The forcer contains motor windings, permanent magnets, and laminations with slotted teeth that serve to concentrate the flux that’s created when current is applied to the coils. The teeth of the forcer and the platen are staggered by ¼ tooth pitch in relation to one another to ensure that constant attraction is maintained and that the next set of teeth will come into alignment as current is switched in the coils. This means that for each full step of the motor, the forcer moves along the platen by ¼ tooth pitch.

In a hybrid linear stepper motor, the platen is passive and the forcer contains laminations with slotted teeth, windings, and permanent magnets.
Image credit: Parker Compumotor

Whereas variable reluctance linear stepper motors can only operate in full step mode, hybrid versions can operate in either full step or microstepping modes. Microstepping, which divides the step angle into smaller increments, enables higher resolution motion and better control of speed and force. Because each phase of the motor is driven with (theoretically) ideal sine waves, 90 degrees apart, microstepping also allows the current to increase in one winding as it decreases in the other, providing smoother operation at low speeds than can be achieved with full- or half-step operation.

Microstepping makes the current waveform more sinusoidal and provides smoother motion at low speeds.
Image credit: Servo-drive LLC.

For guiding the load on hybrid linear stepper motors, either mechanical roller bearings or air bearings are typically used. (Because the platen in a hybrid linear stepper motor is passive, it can serve as the air bearing surface.) The magnetic flux between the forcer and platen creates a strong magnetic attraction, so these support bearings actually serve two purposes – to guide and support the load and to maintain the correct air gap between the forcer and the platen.

Like other linear motor designs, hybrid linear stepper motors can incorporate multiple forcers onto one platen, with each forcer moving independently. In addition to smooth low-speed operation (obtained with microstepping control), they are also able to achieve very high speeds and accelerations with high resolution and low to moderate force generation.

With simple mechanical construction and easy setup (no servo tuning required), hybrid linear stepper motors are ideal for applications that can operate in open-loop mode and that require either high speed with low force production or very smooth motion at low speed.

Featured image credit: H2W Technologies, Inc.

Five key electrical design concepts for mechanical engineers

March 11, 2016 By MCTips Staff Leave a Comment

Edited by: Paul J. Heney, Editorial Director

Mechanical engineers often overlook important electrical issues when specifying their respective parts of an electromechanical system. This targeted advice will help you design your next electromechanical system.

Mechatronic systems are the state-of-the-art technology in automation systems, intelligently integrating mechanical and electrical elements to perform increasingly complex and demanding functions. When designing electromechanical systems, mechanical engineers and electrical engineers may tend to emphasize the technologies, components and design principles from their single area of expertise—which can lead to systems with higher operating costs, increased maintenance demands and less than optimal performance. Electrical engineers involved in helping design and build mechatronic systems often see how inefficiencies and unnecessary complexity can be unintentionally designed into machines.

Better mechatronic systems can be created when mechanical engineers consider five crucial concepts when designing manufacturing systems, to derive the greatest value and efficiency electronics systems can offer to the manufacturing process.

1. Create a clean design
Good mechatronics design starts with good mechanical design—the best electronics and electrical systems can’t compensate for poor mechanical design. The most successful designs are clean; they feature a strong, rigid frame, using materials and structural principles to ensure that, whatever motion the machine undergoes, its long-term stability is engineered-in. Make sure that rigid bearings and support are used where motors are mounted on machines; this helps prevent shafts being sheared off due to microfractures that occur because the motor shaft is mounted out of alignment with a pillow block bearing or gearbox input planetary gear.

A clean design makes the largest contribution to a machine’s longevity, robustness and lowest overall cost of ownership.

Place motors on the machine in the best location so that operators aren’t accidentally stepping on cables and connectors causing damage, and design machine guarding with easy access points to get to motors mounted under the wing base of the machine while still protecting them against harsh environments. Most importantly, a clean design balances mass and motion: sturdy, durable framing that withstands years of vibration and shock, combined with lighter-weight components for the moving parts of the machine. This helps reduce mass, provides more energy-efficient motion, and makes it easier to size-up smaller motor/drive components for the machine. We’ve seen a lot of innovative mechanical machine designs over the years, and a clean design makes the largest contribution to a machine’s longevity, robustness, and lowest overall cost of ownership.

A clean design balances mass and motion: sturdy, durable framing withstands years of vibration and shock, combined with lighter-weight components helps reduce mass and enable the use of smaller motor/drive components.

2. Directly couple the motor to the load
Effective mechatronics starts with a clean slate design. In the past, machines were often built around a single ac motor powering a machine line shaft, to which were attached gearboxes, pulleys, sprockets, chain drives and other mechanical devices for moving individual areas of the machine in synchronization—an approach to powering manufacturing that literally can be traced back to the dawn of the Industrial Revolution.

Consider replacing this architecture with individual servomotors coupled directly to the load you are moving. There are multiple design, machine cost and operational advantages to this solution (which a surprising number of machine designs do not use). First, consider cost: Every time you add a gearbox, you add multiple costs; it’s an additional point of failure, it has to be lubricated, and it needs spare parts. Plus, you add mechanical backlash that needs to be compensated for during machine commissioning and every time you have a product changeover—motion and axes synchronization complexity that today’s intelligent drives and servomotors eliminate.

When you strategically locate servomotors as close as possible to the area of motion they are serving, the incremental cost of electric drive components is almost completely offset by eliminating the cost of mechanical components and labor that must be purchased, machined, assembled and configured. In particular, not having to stock multiple sets of sprockets, gears and cams, as well as the time involved in changeovers with mechanical drives, can really drive down the total cost of ownership for the machine.

direct-drive-direct-motors-linear-motors

Using direct drive, direct motors and linear motors versus mechanical couplings allows machine designers to run higher gains and improve machine performance.

Ultimately, this design approach greatly reduces windup and backlash, improves machine commissioning time, and current state-of-the-art direct drives, direct motors and linear motors allow machine designers to run higher gains and improve the machine’s performance.

Electromechanical design architecture (top) versus an older mechanical line shaft design (bottom).

3. Use electronic gearing and camming
Today’s electronic drives and motion control platforms give the mechanical engineer a powerful, flexible tool to improve the accuracy and performance of the machines you design. This technology lets you create a virtual “electronic line shaft” that can electronically synchronize all the drives and motors on the machine, eliminating the mechanical line shaft. In the process, you can dramatically improve axes synchronization and accuracy—from 1/16 or 1/32 in. typical with mechanical line shafts, down to motion precision closer to hundredths or even thousandths of an inch with electronic line shafting.

Using electronic gearing and camming allows for better machine synchronization while eliminating the mechanical line shaft.

And this synchronization can be accomplished with zero mechanical backlash—and fewer product jams. It also eliminates a host of mechanical adjustments to bring the machine online, as well as the operator adjustments each time the machine is stopped and restarted.

Electronic gearing and camming makes machine changeover completely programmable. Using FlexProfile technology, with the touch of a button on the HMI screen, you can load a machine recipe, and the changes are made in the control and servo system to run the next product.

This new FlexProfile camming technology makes it possible to build multi-segmented cam profiles based on position, velocity or time-based motion profiles. When you change a section of the electronic cam through a recipe change through the HMI, the control platform will automatically optimize the rest of the cam profile across all of the machine’s motion elements. This enables the machine to run a shorter cycle time, or provide smoother dynamics for the machine, even though a change has occurred, such as a different bag seal time or flap tucking cam position on a cartoning machine.

4. Incorporate energy-efficient technology
One of the fastest growing costs for any manufacturing operation is energy—and good mechatronic design can help control these costs through the application of electric drive and motor systems designed to save energy.

In machines that use servomotors directly coupled to critical axes of motion on the machine, and also use electronic synchronization and camming, the proper sizing of the servo system can create a highly energy-efficient machine.

Proper sizing requires an accurate assessment of several motion factors (motor by motor): how fast the axis needs to accelerate, the size of the mass you’re trying to move, and how precise the acceleration and deceleration needs to be. Undersizing will lead to strains on the drives and motors; oversizing will draw too much power to do too little work.

Some of today’s most cutting edge systems, such as the Rexroth IndraDrive Mi integrated drive/motor systems, include a highly energy-efficient feature: bus sharing. Multiple drives are daisy-chained together and share power from the same bus; in many multi-axis machines, as some motors are accelerating up to speed (drawing power), others are decelerating (regenerating power). With bus sharing, rather than having to deliver maximum power to the accelerating motors and bleed off the decelerating motors into heat across a bleeder resistor, power is shared, so the machine’s power consumption is significantly reduced.

Regenerative power supplies feed power back through a shared bus to re-use on the machine rather than dissipating excess power as heat.

A further energy-efficient technology is called regenerative power supplies. In many machines, multiple servomotors will decelerate at the same time, boosting the voltage to excess levels on the power bus. Older generation electrical drives would bleed that excess electrical energy as heat—wasting the power and adding to the factory floor’s heat production, requiring additional cabinet cooling. With regenerative power supplies coupled to a shared bus system, what was once wasted power can now be fed back through the shared bus and sold back to the electric company.

5. Use HMIs for better troubleshooting
The computer revolution has spread to today’s machine control panel, replacing knobs and pushbuttons with sophisticated PC-based and embedded HMIs with advanced programming and Windows-based operating systems.

Consider your typical office copier: when there’s a paper jam, a touchscreen control indicates where the jam is, what door to open, how to correct the problem, and prompts you what to do next once you’ve cleared the jam. The same user-friendly intelligence is now available to machine designers through today’s touchscreen HMIs featuring the latest graphical user interfaces. Machine layout drawings and schematics can be incorporated into control menus and diagnostic tools, to better manage the machine’s day-to-day operation and troubleshooting ease. Drawings and interactive instructional tools can not only show the precise point where a problem is—they can also show how to open enclosures and what steps an operator can take to put the machine in safe mode for initial maintenance, and other support resources to resolve a problem and step the operator back through the tasks to restart production.

HMI-intelligent-predictive-maintenance-alerts

Intelligent predictive maintenance alerts can be displayed via the HMI to the operator, along with next steps necessary to correct the issue.

Advanced graphics like this can be combined with the distributed intelligence inherent in servomotor-driven machines, to prevent machine failures or faults before they happen. Called predictive maintenance, this capability lets machine designers set fault tolerance bands in drives and then monitor drive performance. Electric drives and motors, such as IndraDrive systems, allow a broad range of conditions to be monitored—conditions that are directly associated with mechanical performance: variations in load, temperature, vibration, torque, belt tightness and gear meshing are all mechanical events that generate changes in the torque profile of an electric drive and motor moving those machine elements. Mechanical engineers can set tolerance bands for these components, and if they exceed them, then predictive maintenance alerts can be clearly and intelligently displayed over the HMI to operators, along with specific advice about next steps to take to correct the issue before it becomes a serious production problem or something that can damage the machine.

Blending technologies for optimal value
Every electromechanical system should perform its designed function with the minimal use of energy, motion and components required to get the job done—that’s the fundamental goal of any manufacturing engineer. Electrical drive and servomotor systems now offer a wealth of reliable, energy-efficient, digitally intelligent platforms to power the integrated vision of mechatronics to greater value and more innovative manufacturing and automation solutions. Hopefully, the five considerations described here demonstrate the advantages that today’s electric drives and controls offer, helping simplify certain mechanical design and engineering challenges and provide new resources for driving innovation and creativity in machine design.

Reprint info >>

Bosch Rexroth
www.boschrexroth-us.com

FAQ: What’s the difference between variable-reluctance linear and hybrid linear steppers?

July 21, 2015 By Zak Khan Leave a Comment

Shown here are true (not threaded-rod) linear stepper motors from H2W Technologies. They’re able to output up to 12 lb (53 N) of continuous force.

Linear motors come in different mechanical and electromechanical arrangements to satisfy the requirements of different applications. For example, brushless linear motors (capable of forces to 2,600 N or more) work well in heavy robotics or material-handing applications. Linear ac-induction motors output 2,000 N to satisfy heavy-conveyor parameters. In contrast, iron-core brushless linear motors deliver a whopping 15,000 N or more to satisfy the most grueling machine-tool tasks.

But the type of linear motor of focus here are linear stepper motors. True linear stepper motors (and not threaded-rod actuators driven by rotary stepper motors) come in two subtypes that output forces to 250 N—suitable for small robotics and part-transfer motors. For more on this, read:

The two subtypes—variable-reluctance and hybrid—operate much like the equivalent rotary versions.

Variable-reluctance linear stepper motors

A variable-reluctance linear stepper motor resembles a hybrid linear stepper motor, but without permanent magnets. Current into the coils switches on and off to the motor phases, which in turn generates electromagnetic reluctance … and linear force with it.

Variable-reluctance linear steppers usually run under three-phase closed-loop control. In short, a forcer with laminated magnetic steel stacks and coils engages a platen when a drive energizes the coils with pulse trains. Each branch (or phase) has one or more teeth; coils wind between the teeth. With no permanent magnets in the setup, the sole input is current.

Variable-reluctance linear stepper motors are an older technology than hybrid motors. Like rotary variable-reluctance stepper motors, variable-reluctance linear steppers can be noisy and are usually only run in full-step mode. But the motors have their own benefits:

Their platen-forcer electromagnetic coupling minimizes core losses.
They exhibit less torque drop at higher speeds.
They are less costly than hybrid linear steppers.

Hybrid linear stepper motors

A classic analogy is that a hybrid linear stepper resembles a hybrid rotary stepper unrolled and laid flat. These motors use electromagnetic reluctance to generate linear force, but include permanent magnets to magnify maximum overall thrust.

Hybrid linear stepper motors have a carriage-like moving piece (which manufacturers call the forcer) and a stationary track (which manufacturers call the platen). The platen is like that in a variable-reluctance linear stepper. The forcer has permanent magnets, phase coils around magnetic U-shaped stacks, and a magnetic yoke. Each stack has two tooth bodies acting as forcer poles. Coils wind between the teeth. Each tooth body can have one or more teeth. A small gap separates forcer and platen.

Hybrid linear stepper motors have a high detent torque and can operate at high speeds. They drive linear axes in automation, computer peripherals, and robots because they’re accurate and accelerate rapidly. They’re also mechanically simple and reliable—usually with low inertia as well. Hybrid linear steppers usually run under two-phase open-loop control. Their main drawback compared to other types is a higher price point.

For more information, read:

Industrial-Electronics.com: Linear Electric Motors

H2W Technologies: Single-axis linear stepper motors

U.S. patent for variable-reluctance linear stepper motor

HIS Engineering 360: Chapter 3: AC and DC Motors – Servomotors: Linear Motors

Anaheim Automation: Stepper Actuator Guide

Motion Control Tips: Linear Stepper Motors from H2W Technologies

More information from Mark Wilson of H2W Technologies

FAQ: How do linear stepper motors compare to familiar rotary types?

July 20, 2015 By Zak Khan Leave a Comment

Stepper motors go into linear actuators in two different ways:

Stepper motors that are traditional rotary motors couple to mechanical rotary-to-linear motion devices (often in the form of a threaded shaft that mates with traversing nut or carriage) to produce linear motion. In this actuator setup, the motor output shaft usually couples to the screw to turn it … and advance the nut (or carriage) and attached load. These are usually small designs that go into consumer products or small-stroke applications in industrial machines.

In contrast, true linear stepper motors—which this FAQ covers in more depth—function much like linear-motor types but leverage the same mode of operation as rotary stepper motors to produce linear motion. More specifically, traditional linear-stepper motors (using variable-reluctance operation) have a moving carriage called a forcer with a permanent magnet, laminated steel cores (which the manufacturer cuts into teeth) and coils around the laminated cores. This forcer engages a straight and stationary track called a platen. This linear-stepper part is mostly steel bar cores (which the manufacturer cuts into teeth and plates with nickel). For super-long strokes, installers can put multiple platens end-to-end and have the forcer ride on all of them.

Summary of linear stepper motors

Engineers most commonly use these linear actuators in larger installations; on axes that move heavier loads; and in high-end medical or material-handling applications such as pick-and-place machinery that require extremely high precision. Like rotary equivalents, linear stepper motors either use a variable reluctance (just described) or a hybrid mode of operation. A hybrid linear-stepper platen is like that of a variable-reluctance linear stepper. In contrast, the forcer has multiple permanent magnets, magnetic U-shaped cores (with coils around them) and a steel yoke.

Linear stepper motors are stiff and reliable linear actuators that output smooth motion. Putting platens end-to-end makes for potentially unlimited stroke.

Whether run open or closed loop, linear stepper motors output motion with repeatability and resolution. What’s more, linear steppers aren’t subject to wear. Nor does stalling damage them. The attractive force from the magnet preloads the assembly and lets engineers use these in myriad orientations. Linear stepper motors can also use changes in switched excitation (in one more phases) to get precise steps.

Summary of rotary-stepper-driven axes

When engineers use rotary-stepper-driven axes instead of linear stepper motors, they face a different set of design considerations. For starters, the engineer must pick the leadscrew’s lead and pitch. Lead defines the distance a screw thread advances in one revolution. Pitch is the distance between adjacent threads. A small lead with more threads per inch outputs higher force and resolution; large leads (or fewer threads) output lower force but higher speed.

Screws also have their own inertia. In setups where the motor body houses the screw-engaging nut, this inertia increases as the screw extends … which in turn reduces maximum design speed. In fact, it’s fairly common for stepper-driven leadscrews to have embedded drive nuts. Even where the setup takes a more traditional arrangement—with the nut outside the motor, and fixed to rails that bear the loads the axis advances—nut material selection is another design consideration. Engineers must ask: will this axis experience heat and the effects of friction? Plastic exhibits low friction but cannot withstand high heat; bronze nuts resist heat but have a high coefficient of friction.

One final note on rotary-stepper-driven axes: Because these actuators incorporate mechanical components, they exhibit wear and life limitations. That said, when engineers properly size for the load and create a forgiving operating environment (with low humidity, protection from harsh chemicals and dirt, and controlled temperature) rotary-stepper-driven exhibit long life—to millions of cycles.

For more information, read:

Sparkfun’s consumer-grade rotary-stepper-driven actuator for sale

PDF: BSA reference on linear motors

PDF: AMETEK’s Haydon Kerk linear-actuator primer

Google Books: Variable-reluctance linear motors

Google Books: More on linear motors

New trends in electric motors: Efficiency, power density, torque

March 4, 2015 By Miles Budimir Leave a Comment

Fractional-Horsepower-Motor-From-Groschopp

This is a sampling of fractional horsepower motors (motors
with rated output power of 746 W, or 1 hp, or less)
from Groschopp.

If there’s one trend that’s prevalent in motors of all kinds, it’s the theme of increasing performance, more specifically a trio of highers: higher efficiency, higher power density and higher torque density.

These are incremental improvements in motor performance that are at least partly driven by the Department of Energy (DOE) energy efficiency requirements, said Dan Jones, consulting motor designer and president of Incremotion. For instance, the DOE has been pressing the ac induction motors ranging from 1 to 500 hp. The DOE did not increase the efficiency requirements beyond premium efficiency (IE3) in their recent review last year, but a number of U.S., Brazilian and European motor manufacturers have moved to brushless PM motor types to achieve higher motor efficiencies in the IE4 category, added Jones.

ABB provided the market with a different solution. They developed a family of synchronous motors with which they’ve achieved the IE4 motor efficiency levels. The major problem for brushless PM motors has been competitive pricing against the similar sized ac induction motor. The ground rules for achieving a range of higher motor efficiencies requires a Variable Frequency Drive (VFD) to achieve good efficiencies over a range of application loads. While a large number of smaller HVAC applications can use plug-in-the-wall power, a major trend in industrial applications is using VFDs with the induction motors.

As far as higher power density goes, axial flux motors (PM brushless) are high-power density motors that have been used in hybrid cars primarily because of their high power capability. Part of their secret to success is that they operate at load speeds approaching 10,000 rpm. The axial flux motor also develops about 30 to 40% more torque than a similar sized radial flux motor. The combination of the two aforementioned elements determines the axial flux motor’s high power density.

The best motor type for torque density is the transverse flux motor, said Jones. It uses a 3D magnetic circuit, and only a few motor companies are currently building this brushless PM configuration. It’s a complicated machine that can double the shaft torque normally achieved by a conventional brushless PM motor. There is a speed limitation of most current models under 1,500 rpm and some as low as 300 rpm load speed.

Another trend is the increasing call for specialization of motors for specific applications. “It has become increasingly important for motor designers to get as close as possible to the end application to optimize design and manufacturing,” stated Matt Morrow, business development manager with Portescap. “Examples of this include new materials, construction, magnets and manufacturing processes, each of which deliver a better product to the application, and ultimately to the end customer,” he added.

One area where specialization is especially important is the medical industry. “Medical device manufacturers are helping drive change in motor design,” said Walter Hock, director of product management at Portescap. Patient comfort and discretion is driving wearable insulin and drug delivery systems design. “Motor manufacturers help meet this market need by delivering high-precision motion from smaller, more efficient motor solutions that minimize device size and weight and improve battery life,” he added. To do this, they have to change the way they design miniature motor coils, transmission components and high-accuracy feedback devices that deliver required accuracy and efficiency.

Furthermore, said Hock, “healthcare providers are focused on reducing the overall cost of care. This places an intensified emphasis on total cost of ownership of surgical instruments, which pushes motor design in two seemingly opposing directions.” Cost conscience healthcare providers want longer device life and therefore a motor designed to withstand more sterilization cycles. But, new device designs expose the motor to harsher, more diverse environments during the surgical procedure. In both cases, this has challenged motor design teams to innovate improvements in material selection, motor sealing and over-molding techniques.

As far as motor manufacturing goes, the single biggest change in manufacturing, particularly in the medical industry, has been a strengthening of processes and controls, providing ongoing traceability and accountability for quality. As the FDA has placed more stringent requirements on medical device manufacturers to control and monitor second and third-tier suppliers, there has been an increase in regulatory scrutiny on motor manufacturers. Based on this increased scrutiny, motor manufacturers are incorporating further process controls into the design process. This translates into better process controls on the manufacturing side, which allows it to become an extension of the medical device manufacturer. The output is a superior manufactured product.

Beyond general technology trends for motors of all kinds, we asked some top manufacturers of specific motor types what trends they’re seeing in particular motors, such as servomotors and steppers, among others. Below are their responses to our query.

Technology trends in servomotors

AKMH Series servomotors from Kollmorgen are built to withstand the most rigorous washdown conditions, thanks to a combination of IP69K construction and the use of corrosionresistant
materials.ervomotors

Bill Sutton • Strategic Sales Manager • Kollmorgen

1) What are some of the key technological advances that have taken place in the area of servomotors?

We’ve developed a servomotor and associated cables that can be used in washdown environments without any restrictions on cleaning methods. Cleaning solutions ranging from 2 to 12 pH can be applied to the motor, cables and connectors without restriction. High-pressure spray up to 1,500 psi can be used on the motors and associated cables and connectors without restriction, as well. The technical advances that allow this are the application of compatible materials that can handle the tough environment without degradation; development of a venting design that allows for motor heating and cooling cycles without creating relative pressure differences between the inside and outside of the motor, making the motor much more resistant to ingress of moisture or cleaning solutions; and a little bit of motor design magic that keeps the motor from being too big and expensive. In addition to being durable, the motors are designed to meet hygienic machine design standards making them easier to clean. The primary hygienic features are a 32-µ surface finish including laser annealed nameplate, no metal-to-metal seams, no external hardware, no flat surfaces and no nooks to harbor pathogens.

2) What industries are directly spurring changes in the design of servomotors?

The food processing industry is driving the design of motors that better fit their needs. We surveyed more than 80 food processing companies, and the overwhelming response that we received was the need for electric motors that could be cleaned without failure and that were easier to clean, requiring less time and effort to ensure sanitation was achieved. The need for a more durable and cleanable design has existed for a while, but existing designs for stainless-steel servomotors were big and expensive and many times were not significantly more reliable than standard servomotors. So, the pent up demand plus the anticipation of the effect that the Food Safety Modernization Act (FSMA) will have on sanitation standards and machinery design is driving this market.

Technology trends in stepper motors

Here are a few examples of both brushed and brushless, slotless dc motors from Portescap.

Clark Hummel • Director of Product Management • Schneider Electric Motion USA

1) What technological advances in the last few years would you say have improved the performance of stepper motors and helped foster their use in new kinds of applications?

First, the advent of integrated motion. Combining the stepper motor, drive, controller and encoder into one package that is easy to mount, wire and configure has proven to be a great advantage to machine builders. It reduces machine size, cost and complexity, while increasing the ease by which a system can be integrated.

Second is the creation of advanced control techniques, such as Hybrid Motion Technology (hMT). These controls maintain stepper motor advantages—high torque density, lack of jitter at standstill, no tuning requirements, cost effectiveness and more—while delivering typical servomotor advantages, such as no loss of synchronization, torque control capabilities, reduced heating and energy use.

2) Have any particular industries been responsible for improvements or changes in stepper motors in recent years? Are any particular industries increasing their use of motor drives? If so, can you say why?

Stepper’s strong position in biomedical/life science markets is longstanding. With recent improvements in integrated motors—including industrial connectors, IP ratings, hMT and the ability to reside on popular fieldbuses—steppers can proliferate in more industrial markets, such as packaging, food and beverage, and automotive.

3) Is there any particular motion control application you’ve seen recently that would have been impractical, say, five years ago?

Torque Control, a feature of Hybrid Motion Technology, was not previously possible with stepper motors. Torque Control supports applications such as winding, capping and clamping that were previously impossible to implement due to the motor’s loss of synchronization and stalling. Steppers are now being used in these applications every day.

Technology trends in linear motors

This linear motor from LinMot is an electromagnetic direct drive in tubular form. Because the motor components are
encapsulated, the motor is optimally protected even for intensive applications.

Peter Zafiro • LinMot USA

1) What are some of the key technological advances that have taken place in the area of linear motors?

Continued improvements in communication interfaces, the desire for better position control and the need for greater plant efficiencies are the key market drivers to using more electric actuators. These trends are definitely true for linear motor direct drive systems and now even in applications where induction motors and pneumatic cylinders were predominantly used.

The advent of Ethernet communications is driving the desire to put servo axes on the plant network. This provides significant data that plant managers can use to improve their productivity and throughput. Once this occurs, the next step is to get more flexibility in positioning and drive up productivity. Thus the drive to introduce servo axes in traditional induction motors and pneumatic applications. The last step in this process is to drive out cost and increase efficiency, which leads toward direct drive technologies, like linear motor driven actuators.

Eliminating belts, screws, cams and gears increases efficiency and reliability while providing higher throughput. In the end, it is all about up time and what a plant manager can do to decrease his weaker points in the production process. Mechanical drive systems bring limitations due to wear and have decreased performance characteristics. Decreasing the number of mechanical connections in almost all cases increases throughput and uptime.

There is a lasting benefit with direct-drive linear motor systems: energy savings. This is being taken advantage of heavily in Europe, and is just in its infancy here in North America. Even in some very traditional pneumatic applications, like a point-to-point positioning application, the direct drive tubular linear motor system can provide significant return on investment. The savings then flow to the bottom line in reduced energy costs and increased uptime.

2) What industries are you seeing that are spurring changes in the design of linear motors? Also, what industries are contributing to changes in linear motors?

The packaging industry has been a key driver in tubular linear motor development. Many pick-and-place applications are being upgraded to direct drive technologies simultaneously increasing productivity and decreasing energy costs. Another industry that is starting to affect linear motor development is the medical industry. The advantages of less mechanical connections mean cleaner running production lines. The ability to handle tough environmental requirements have driven significant developments into all stainless-steel IP69k tubular linear motor technologies. Many of the tough food processing and manufacturing environments are also a key player in this clean direct drive technology.

3) Are there any notable changes in manufacturing and/or distribution that have impacted linear motors? If so, what are they and how have they impacted designs?

Over the last ten years, many linear motor production processes have gone to mainstream production and thus allow for lower cost plant implementation. Another area that has evolved is logistics. Just shipping product from anywhere on the globe has gotten easier.

In North America, there has been a big push by the key automation distribution partners to increase their network and control knowledge, allowing the end customers and OEMs to concentrate on their core competences: producing the end product and/or manufacturing machines. These automation distributors are able to provide significant assistance to the plants and OEMs helping them achieve higher production goals and more efficient plant operations.

Technology trends in fractional-horsepower motors

Ed Tullars • Sales Manager • Groschopp

1) What are some of the key technological advances that have taken place in the area of fractional horsepower motors?

Mostly, the controls, electronics and sensors have come down in price, which has increased the demand for electric motors. As for changes in the motors themselves, one of the most prominent is that the cost of rare-earth material has improved, making different motor types easier to manufacture with more power.

2) What industries are you seeing that are spurring changes in the design of fractional horsepower motors? What industries are contributing to changes in fractional horsepower motors?

Really, a lot of industries are switching to electric power. You see this in the cars that GM and Ford and others are designing. There’s also a conversion from, let’s say, hydraulic systems to electric systems. Electric power is cleaner, easier and sometimes safer to use. Electric power equipment is also more accurate for robotics applications. Wherever we look, we’re seeing demand for more electric and automated products.

3) Are there any notable changes in manufacturing and/or distribution that have impacted fractional horsepower motors? If so, what are they and how have they impacted designs?

One notable change we see is more competition in the market driving a more competitive market place. It’s also harder and harder for some customers to find the correct motor for their application. It truly takes a trained person to get the correct motor speced for the correct application, based on speed, torque, stall startup torque, IP rating, duty cycle, current draw, and so no. In the past, you speced a motor that would not blow the fuse. Today we have to work with all the parameters to match the customer desired equipment needs.

Technology trends in DC Motors

Chad Hammerly • Motion Control Solutions • Business Unit Manager Rotary Products (Pittman)

1) What are some technological advances that have improved the performance of brushed and brushless dc motors or helped them get into new applications over the last few years?

One of the biggest and ongoing changes we’re seeing is the integration of controls in brushless motors.

2) What industries are spurring changes in the design of dc motors?

Ac motors, like this model from Baldor,
with permanent magnet (PM) rotor
technology provide a direct drive solution,
replacing conventional mechanical gear or
belt drive speed reduction designs.

Medical and dental instrumentation, power tools, autonomous robots, drones and unmanned aircraft. Also, general factory automation is using a great deal of smart dc communications controls. High flexibility reduces costs and allows for faster installations.

3) Has the manufacture or distribution of dc motors, linear motors and integrated actuators changed over the last few years?

Yes. The Internet has allowed convenient features, such as web-based configurations. For instance, our Pittman Express program allows customers to go online and order a selection of products that are available to ship within 24 hours.

4) The range of miniature applications is expanding, with the use of miniature motors expanding with it. Why do you think miniature designs are so promising from a design standpoint?

Invasive surgeries and remote surgical robotics are applications where miniature motors are expanding due to the need for power and precision in a small package.

Also, evolutionary trends are requiring products to be lighter, more powerful and portable. We’re also seeing trends where smaller motors are being requested to aid in ergonomics for applications. For instance, smaller hand drills to fit smaller hands.

ETEL to Showcase New Vibration Isolation System

June 16, 2014 By Garrett Harmon Leave a Comment

ETEL is very proud to announce the release of its new QuiET – Active Isolation System at SEMICON West in San Francisco, CA from July 8-10 (Booth # 1217). From now on, an advanced motion platform from ETEL does not only include the motion system and its associated motion controllers, but can also benefit from its proprietary active isolation system. This makes ETEL the only motion system supplier designing and offering a complete solution!

QuiET is a 6 Degrees Of Freedom (DOF) module cancelling both stage-born and ground-born vibrations resulting in:

Higher throughput thanks to shorter move and settle times
Higher process stability thanks to lower jitter and better position stability at motion stage level
Lower cost of ownership thanks to a single supplier for the complete advanced motion platform

Vibrations in the machine?
High-end applications in the semiconductor industry always require tighter performances in terms of position stability, vertical jitter, move and settle times and tracking error, to name but a few. Complex machine equipment is, in one way or another, connected to the granite of the motion platform. As such, any vibration at the granite level translates into inaccuracies and longer settle times at the process tool level. Thanks to ETELs solution, getting rid of those vibrations has never been so efficient.

Pushing Motion Performance to the next level!
Enhancing the synergies between its proprietary state-of-the-art components including motors, encoders, bearings, controllers, cable solutions and precision mechanics, ETEL was able to design a high performance active damping solution. Through a homogeneous, fully-digital and deterministic motion control architecture, acceleration feed forward accuracy has been brought to outstanding levels: higher than 99%! This makes move and settle times and residual vibration levels shrink to unprecedented values, which directly brings stability to the customers process.

Modular, scalable, and compatible with any footprint!
The QuiET Series has been designed to be highly modular and scalable. Thanks to a list of preselected active and passive components, ETEL can very quickly find the optimized solution to accommodate the customers needs. Spring elements, Lorentz actuators and proprietary sensors are embedded within a sandwich-based architecture that is then customized to fulfill specific footprint requirements.

ETEL taking full responsibility of overall performance
The QuiET series is pushing ETELs Forward Integration Strategy one step further. When using the QuiET module as part of an advanced motion platform, ETEL becomes the sole point-of-contact for everything relating to performance: eliminating the need to coordinate between different suppliers, ensuring optimization of communication channels, and allowing easier servicing and commissioning.

Etel
www.etelusa.com

Festo Introduces the EGSL Series Electric Slide

October 4, 2012 By Motion Control Tips Editor Leave a Comment

Whenever there is a need for precise pushing motion or handling of work pieces, the electric slide series EGSL from Festo is the right choice for pick and place systems or planar surface and 3D gantries. Even with heavy loads, these slide units operate with linearity and parallelism to an accuracy of + .0006 inches (+ 0.015 mm). The EGSL sliding electric guide also offers exceptional energy efficiency.

The EGSL electric slide provides an economical positioning function for strokes of up to 11.8 inches (300 mm). The enclosed ball screw prevents dirt or small work pieces from entering the guide area. Based on the high-precision guide of the DGSL, the pneumatic equivalent of the EGSL, these electric slides are available in four sizes as measured in slide width: 1.4, 1.8, 2.2, and 3 inches (35, 45, 55, and 75 mm).

The motor, which is matched perfectly to the mechanical components, does not project beyond the slide. It can be mounted axially or in parallel. This results in a rectangular slide that can be easily integrated into an application. The sensors on the slide itself are also easy to install and make position sensing simple. The intuitive Festo Configuration Tool provides help with commissioning.

To select the best possible solution and matching components, engineers can use Festo’s online engineering software Positioning Drives to calculate the characteristic load values for the selected drives quickly and reliably – in a maximum of four steps. Engineers simply enter the application parameters and required cycle times, edit the motion cycles, and select the desired solution package. The program then outputs the detailed results such as motor characteristic curve, system data, product data, and parts list. Engineers can then use this information for ordering and machine documentation. The software ensures that motors, gears, and axes are neither over- nor under-dimensioned.

Festo
www.festo.com/us

Nippon Pulse’s S605 Linear Shaft Motor offers 3100N of Force

April 24, 2012 By Miles Budimir 1 Comment

Radford, Va. – The S605 Linear Shaft Motor from Nippon Pulse offers up to 3100N of acceleration force and a continuous force of 780N. The S605 is ideal for industrial applications requiring high force, high precision, energy efficiency, and/or high precision. The motor is also capable of sub-micron resolution.

Available with one of three types of windings (double, triple, quadruple), the S605 has an acceleration force range between 1000N and 3100N and an acceleration current between 34 and 35A, and acceleration force and current can be maintained for up to 40 sec.

The S605 has a shaft diameter of 60.5mm and is available with effective strokes between 200 and 2000mm. Other features of the S605 include continuous forces between 420 and 780N, continuous currents between 8.4 and 8.8A, a non-critical air gap of 1.75mm, and a rated voltage of 240V.

The first linear servomotor designed for the ultra-high precision market, the Linear Shaft Motor is available in 18 different sizes, ranging from 4mm to 60.5mm. Because of its simple structure, the Linear Shaft Motor has no cogging issues, offers stiffness up to 100 times greater than similar motors, uses all magnetic flux, and minimizes heat generation. As a result, independent studies have proven the Linear Shaft Motor to be 50 percent more energy efficient than competing linear motors, including u-shaped motors.

For more information, visit www.nipponpulse.com.