• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Linear Motion Tips

Covering Linear Motion Systems, Components and Linear Motion Resources

  • New
    • Editor’s blog
    • Industry news
    • Motion Casebook
    • Video
  • Applications
  • Slides + guides
    • Ball + roller guides
    • Track roller (cam + wheel) guides
    • Crossed-roller slides
    • Linear bearings
    • Plastic + composite guides
  • Drives
    • Ball + lead + roller screws
    • Belt + chain drives for linear
    • Rack + pinion sets
  • Actuators
    • Ball + leadscrew driven
    • Belt + chain driven
    • Linear motors
    • Mini + piezo + voice coil
    • Rack + pinion driven
    • Rigid-chain actuators
  • Encoders + sensors (linear) + I/O
  • Stages + gantries
  • Suppliers

Where do linear motors make sense?

September 12, 2016 By Patrick Curran Leave a Comment

by Tony Chou, General Manager, Chieftek Precision USA

Linear motors deliver superior output, so excel in medical equipment, industrial automation, packaging, and semiconductor manufacturing. What’s more, new linear motors address the cost, heat, and integration complexity of early versions. To review, linear motors include a coil (primary part or forcer) and stationary platform sometimes called a platen or secondary. Subtypes abound, but the two most common for automation are brushless ironcore and ironless linear motors.

chieftek-linear-motor-lineup

Linear motors generally outperform mechanical drives. They have unlimited lengths. Without the elasticity and backlash of mechanical setups, accuracy and repeatability are high and stay that way over the life of the machine. In fact, only the guide bearings of a linear motor need maintenance; all other sub-components are wear-free.

chieftek-application
Linear motors outperform mechanical drives because they don’t exhibit elasticity and backlash. Accuracy and repeatability stay high for the whole design life.

Where ironcore linear motors excel
Ironcore linear motors have primary coils around an iron core. The secondary is usually a stationary magnet track. Ironcore linear motors work well in injection molding, machine tool, and press machines because they output high continuous force. One caveat is that ironcore linear motors can cog, because the magnetic pull of the secondary on the primary varies as it traverses the magnet track. Detent force is to blame here. Manufacturers address cogging in several ways, but it’s problematic where smooth strokes are the main objective.

ironcore-linear-motor-options
Shown here are ironcore linear-motor options.

Even so, ironcore linear-motor advantages abound. Stronger magnetic coupling (between iron core and stator magnets) makes for high force density. So, ironcore linear motors have higher force output than comparable ironless linear motors. In addition, these motors dissipate a lot of heat because the iron core sheds coil-generated heat during operation — reducing coil-to-ambient thermal resistance better than ironless motors. Finally, these motors are easy to integrate because the forcer and stator directly face each other.

chieftek-current-versus-force
When an ironcore motor operates in its linear region, the force constant is fixed and thrust output is directly proportional to input current. When operating in the saturation region, output thrust depends on magnetic saturation, so there’s less thrust increase for a given current increase.

Ironless linear motors for quick strokes
Ironless linear motors have no iron in their primary, so are lighter to output more dynamic motion. The coils are embedded in an epoxy plate. Most ironless linear motors have U-shaped tracks lined on the inner surfaces with magnets. Heat buildup can limit thrust forces to less than those of comparable ironcore motors, but some manufacturers address this issue with innovative channel and primary geometry.

chieftek-ironless-patented-core
Chieftek ironless motors have Y-beam geometry to dissipate waste heat from the forcer coils more easily. Overlapping forcer coils further boost power density. Chieftek also supplies values for continuous current, force, and thermal resistance for setups with and without heat sinks. Shown here is a test setup that Chieftek uses to get its values. Evenly cycled three-phase current is injected into the coils and increased until the coils reach 110° C. Chieftek also makes dynamic system measurements to account for the effect of airflow.

Short settling times further boost the dynamics of ironless linear motors to make quick and accurate moves. No inherent attractive forces between the primary and secondary means ironless linear motors are also easier to assemble than ironcore motors. Plus their support bearings aren’t subject to magnetic forces, so usually last longer.

chieftek-linear-motor-application
Actuators that use linear motors have high dynamic motion for demanding industrial applications.

Note that linear motors have trouble on vertical axes and in harsh environments. That’s because without some braking or counterweight, linear motors (which are inherently non-contact) let loads fall during power-off situations.

chieftek-iron-core-motor-features
Ironcore motor capabilities are defined by a force constant (force from an ampere of current) or motor constant (force from one Watt). The latter accounts for motor efficiency, so some manufacturers prefer it. In fact, simulation software demonstrates how some motors have a higher motor constant for a given dimension than other offerings. Notice how skewed magnets minimize cogging force from the magnetic pull on the iron core during transitions across magnetic poles on the stator.

In addition, some harsh environments can generate dust and shavings that stick to linear motors, especially in operations machining metal parts. Here, ironcore linear motors (and their magnet-filled track) are most vulnerable. Some actuators incorporate ironcore or ironless linear motors and a dustproof design to work in such environments. The latter eliminates the problems associated with bellows that traditionally protect linear axes.

chieftek-enclosed-ironcore-motors-for-harsh-applications
Dustproof enclosures on some linear-motor actuators (such as the Chieftek CLMS actuators shown here) resist challenging environments.

When to pick integrated linear-motor actuators
The direct-drive nature of linear-motor actuators boosts productivity and system dynamics for myriad industrial applications. Some linear-motor based actuators also include encoders for position feedback … to make linear motors easy to use, even compared to belt and ballscrew-based systems. Some of these actuators tightly integrate the linear motor, guide, and optical (or magnetic) encoder to further boost power density.

cls-series-compared-to-ballscrew-actuators
Chieftek CLS series actuators outperform those that pair a rotary electric motor with a ballscrew. They come in versions with various thrust outputs.

The encoder in some actuators installs horizontally so its position is unaffected by external impact. Some such arrangements can run to 6 m/sec with acceleration to 60 m/sec2 using a 230-Vac input. Modules with travel exceeding two meters are possible. Standard offerings usually include a magnetic encoder for position feedback, though optical encoders are available for higher precision. Other options include multi-slider setups as well as complete X-Y and gantry systems.

Compared to traditional ballscrew modules, linear-motor-based actuators offer better precision and velocity — even under many thrust output conditions — thanks to direct driving. Tighter integration also boosts productivity and reliability. Some such actuators include the linear motor itself, a base, and wide linear guide supporting an aluminum slider and optical scale for position feedback. Where the linear motor is ironless, it can pair with an aluminum slider to form a lightweight design that quickly accelerates.

Some compact linear-motor actuators also include sliders with built-in lubrication pads for environmentally friendly lubrication. Here, the runner-block ends sport hermetically sealed grease injectors to deliver raceway lubrication via steel ball circulation. In some cases, optional lubrication pads add lubrication for long-term operation with less maintenance, especially on axes that make short strokes.

chieftek-cls-linear-motor-stage
Compact-linear-actuator (CLS) setups are precise and fast because they directly drive loads.

Ironless linear motors inside some actuators also exhibit no cogging, so the axis can make stable moves when moving slowly or quickly. With some designs, repeatability with an optical linear encoder is 2 mm. Some actuators are even available in strokes from 152 to 1,490 mm with straightness from 6 to 30 mm.

Special example: Cleanroom applications
One last option particularly suitable for applications with short strokes and high cycle rates are linear-motor actuators in which the moving parts are the magnets and rail. Here, there aren’t issues with moving cables causing disconnections. Nor are there problems with dusty environments. In fact, the actuators work well in vacuum environments and cleanrooms. That’s because the coils are fixed, so heat easily dissipates to mounting structures. Some such linear-motor actuators output continuous force to 94.2 or 188.3 N and peak force to 242.1 or 484.2 N — accepting continuous current of 3.5, 7, or 14 A depending on the version. Strokes reach 430 mm.

Parameters to specify linear-motor stages
When specifying actuators or stages based on linear motors, consider the following criteria for each portion of the design’s motion profile:

• What is the known motion condition?
• What is the load’s mass, system mass, effective stroke, moving time, and dwell time?
• What’s the drive condition, maximum output voltage, continuous and peak current?
• What kind of encoder resolution does the setup need? Should it be analog or digital?
• Into what kind of working environment will the actuator or stage work? What will be the room temperature? Will the machine be subject to vacuum or clean room conditions?
• What are the application’s requirements for motion precision and positioning accuracy?
• Will the linear-motor actuator or stage move loads horizontally, vertically, or at an angle? Will the setup mount to a wall? Is it subject to space constraints?

Answering these questions will help design engineers identify the most appropriate linear-motor iteration for a given piece of machinery.

Reprint info >>

Chieftek Precision
www.chieftek.com

Filed Under: Linear actuators (all), Linear motors Tagged With: Chieftek

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

DESIGN GUIDE LIBRARY

“motion
Subscribe Today

RSS Featured White Papers

  • Evaluating actuators for washdown in food & beverage applications
  • Identifying Best-Value Linear Motion Technologies
  • Introduction to accuracy and repeatability in linear motion systems

RSS Motion Control Tips

  • Schneider Electric launches Universal Automation Discovery Packs to foster industrial innovation
  • Encoders from SIKO support Industrial Ethernet
  • Draw-wire encoders from SIKO measure position, speed and inclination
  • Incremental encoders configurable via NFC (near-field communication)
  • Low-cost motion control offered with CLICK PLUS PLCs from AutomationDirect

Footer

Linear Motion Tips

Design World Network

Design World Online
The Robot Report
Coupling Tips
Motion Control Tips
Bearing Tips
Fastener Engineering

Linear Motion Tips

Subscribe to our newsletter
Advertise with us
Contact us
About us

Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy