Can linear motors replace ball screws?

A reader of Control Engineering recently asked, “When I hear the sound of a ball screw that’s beginning to fail on a CNC milling center, I have to wonder: Isn’t there a better way to get that kind of linear movement? Are there other technologies?” We put that question to John Meyer at Siemens Motion Control Group, and he suggests linear motor technology.

08/01/2009


A reader of Control Engineering recently asked, “When I hear the sound of a ball screw that’s beginning to fail on a CNC milling center, I have to wonder: Isn’t there a better way to get that kind of linear movement? Are there other technologies?” We put that question to John Meyer at Siemens Motion Control Group, and he suggests linear motor technology.

Linear motors have not been part of the progression of modern machine design that has seen quantum leaps in control technology, says Meyer. Rather, modern machines still, for the most part, use slide propulsion that was designed in your grandfather’s day. We have gone from tape-driven NC machines driven by dc servo motors and ball screws, to sophisticated CNC controls that can take a CAD file and produce a machine program at the touch of a button, right on the machine. To drive the slides on this modern machine, we have progressed to ac servo motors driving ball screws. And maybe we also updated the slides from box way to truck and rail, but how are we driving these slides? Servo motors and ball screws.

Linear motors enable maximum precision and dynamic performance in various motion control tasks. These include not only rapid traverse, but slow constant speed traverse of machine heads, spindle slides, tool management systems, part handling devices and more. There are considerable cost savings when various mechanical components are replaced by simple and efficient linear motors. These motors provide a total drive system, offering reliability, precision, high dynamic stability, low maintenance, and improved production time.

What is a linear motor?

The rotary electric motors with which we are so familiar contain a circular electro-magnet called a stator. In a linear motor, the electromagnet is built the same way, only flat as if it were unrolled. The rotor is also built the same way, unrolled or flat. When the electromagnets of the primary are energized, they attract the secondary sections and push the motor along. The more current applied, the stronger the magnetic field and the more force the motor generates.

Visualize a wooden roller coaster at your favorite amusement park. To get the train up the first hill for that “big drop,” we roll to the base of the hill where a chain drive, driven by an electric motor, gearbox, and sprocket, clanks and jerks the train to the top of the hill. Now, imagine a ride a modern roller coaster with linear motors. Feel that sudden burst of acceleration as you leave the station? Enough force can be generated to propel the train over the first hill and through that first scary loop. Booster “shots” of force can be used at various points to maintain the train’s speed, as it rolls through loops and turns never before possible with older designs. Finally, you feel the braking action at the station by a linear motor. What stopped the wooden roller coaster? Remember the guy at the station pulling a big lever?

Linear motors are simple. Two main components, the primary containing electro-magnets and the secondary, with either permanent magnets or magnet-free, drive the moving member. Gone are servo motors, resolvers, tachometers, couplings, pulleys, timing belts, ball screws and nuts, support bearings, lubrication systems, and cooling systems. Gone also are systems that used hollow ball screws with coolant systems for thermal stabilization. Gone are rack and pinion systems that used expensive torque motors and/or gear boxes. Gone also are chain drive systems requiring high torque hydraulic motors with associated power units.

Linear motors are proven, available and economical. As more linear motors are produced, they will become even more economical. In short, it is time for the mechanical systems of these machines to catch up to the control technology.


Author Information

John Meyer is with Siemens Motion Control Group. To help the machine builder in the design and application process, Siemens has developed tools to configure the right size motor for the slide design application. Visit www.siemenscnc.com for more information.

Author Information

John Meyer is with Siemens Motion Control Group. To help the machine builder in the design and application process, Siemens has developed tools to configure the right size motor for the slide design application. Visit www.siemenscnc.com for more information.




No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Hannover Messe 2016: Taking hold of the future - Partner Country status spotlights U.S. manufacturing; Honoring manufacturing excellence: The 2015 Product of the Year Winners
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
Improving flowmeter calibration; Selecting flowmeters for natural gas; Case study: Streamlining assembly systems using PC-based control; CLPM: Improving process efficiency, throughput
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Warehouse winter comfort: The HTHV solution; Cooling with natural gas; Plastics industry booming

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me