Permanent magnet motors outperform induction motors in many applications

Permanent magnet synchronous motors offer significant advantages on high-energy-consuming and high-dynamic applications, compared to induction motors. See table, photo gallery.


This torque motor significantly reduces system components and wear: Permanent magnet motors offer various design integration options coupled with advanced performance features for greater energy-efficiency, substantial component reduction, and significantPermanent magnetic synchronous motors have been in use on machine tools and other production machinery for many years, owing to their reliable performance, durability, relatively low cost, and electrical stability. These motors have been the standard in the machine tool industry for many decades, used on the spindle, worktable rotation, ways and part articulation, in both rotary and linear applications of controlled motion. With the advent of the machine tool robot for materials handling, workpiece and tooling changes, high-precision load and unload functions, and more, the use of these motors has grown exponentially over the years. Behind the cutting theater, they’re also found on the chip conveyor, hydraulic manifold, oil reservoir, and coolant pumps.

Likewise, in the production machine realm, plastics and rubber molding and extrusion, papermaking, packaging, textiles, ceramic, glass, woodworking, and countless other pieces of equipment have utilized these motors for motion control.

Table compares features of a permanent magnet spindle motor and induction (asynchronous) motor. Courtesy: Siemens

Courtesy: Siemens, Control Engineering

Compact, high torque density

Further, the essential operational principle of a permanent magnet in the rotor assembly, generating a steady magnetic field instead of the short-circuit current found on asynchronous induction motor designs, has yielded many advantages for the machine designer, builder, and aftermarket. These advantages include compact form with high torque density and less weight, higher continuous torque over a wider range of speeds, lower rotor inertia, higher dynamic performance under load, higher operational efficiencies with no magnetizing current, and the corresponding absence of heat due to current in the rotor, low torque ripple effect, more robust performance compared to dc motors, good cos phi (a European term for power factor) and ultimately, better drive utilization.

Water-cooled torque motor: Permanent magnet motors offer various design integration options coupled with advanced performance features for greater energy-efficiency, substantial component reduction, and significantly smaller footprints in today’s machine

The challenges have been, of course, escalating costs of raw materials due to certain economic factors in the world market, though recent discoveries of rare earth magnets (REM) in the U.S. and elsewhere may impact that situation greatly in the future. Plus, more technical aspects such as limited speed ranges in field applications and degradation due to counter voltage created by the magnets, where normally an encoder for commutation is deemed necessary, along with the inevitable limit overload condition, are being continuously addressed by the manufacturers.

New PM motor applications

New market areas are emerging, however, where the use of permanent magnet (PM) motors is showing great promise. These applications involve the use of PM motors for increasing machine productivity with better operational efficiencies.

Air-cooled torque motor: Permanent magnet motors offer various design integration options coupled with advanced performance features for greater energy-efficiency, substantial component reduction, and significantly smaller footprints in today’s machine dr

One PM motor example is the servo pump, where a mechatronic analysis concluded substantial energy savings and operational improvements could be realized, with the additional benefit of environmental upsides, from the application of a PM motor on the hydraulic oil reservoir, replacing a variable capacity pump with a servo. Essentially, the pump motor runs only when the conditions of the machine mechanics warrant. No more was the long-standing presumption of continuous motor operation necessary. By use of a PM motor and direct drive technology, up to 50% savings are being realized on new and retrofit machines, with the obvious additional advantage of eliminating mechanical components, such as the gearbox.

Exploded view of rotary torque motor. Such a motor is ideal for high torque at low speed on various machinery: Permanent magnet motors offer various design integration options coupled with advanced performance features for greater energy-efficiency, substPermanent magnet synchronous torque motors typically have 30%-60% higher torque capacity and 30% better torque utilization with faster acceleration and deceleration, compared to asynchronous induction type motors, and this has proven advantageous in the field, particularly with machine tools and other metalworking production equipment where the rapid traverse function is critical to maintaining higher productivity.

The German word “Nebenzeit” describes the concept of downtime and, in today’s fast-paced, often unattended machining applications, elimination of that condition is an absolute must. There is also significantly higher response and the absence of the “slip” phenomenon with PM motors.

Among applications for advanced permanent magnetic motors are printing presses. Courtesy: SiemensIn the higher power ranges today, these motors are also showing a significantly longer use life, owing to the greater degree of rotor tension compensation. In other words, the reduction of backlash (hysteresis) and the maintaining of precise position are better achieved, whether under load or not. From the magnetic perspective, this condition derives from the combination of a larger air gap and smaller radial magnetic forces, with lower inertia moment and high short-term overload capacity with maintenance of desired torque.

Converting equipment uses advanced permanent magnetic motors. Courtesy: SiemensDrive technology improvements have likewise lobbied for increased use of PM motors in applications, as spindle motion precision and accuracy in a machine tool, for example, are directly dependent on the intelligence in the drive. Likewise, the complex current calculations for higher speed and rotor pole pair position identification are being made in the drive for use with simpler encoders or even encoderless configurations in the machine.

Harald Poesch, product manager for motion control motors in the USA for Siemens Industry, holds a degree in communications engineering from the University of Applied Science in Cologne, Germany, and has worked for Siemens since 1999, serving as an applicaUse of the asynchronous induction motor is far from obsolete, especially with the advancements in motor system elements, such as variable frequency drives and inverters, used on various phase configurations. Even so, advancements in magnetics configuration and the higher levels of intelligence in drives technology are opening new applications for PM magnets daily.

Somewhere, both Farraday and Tesla are smiling.

- Harald Poesch is product manager for motion control motors, USA, Siemens Industry Inc. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering and Plant Engineering, 

Applications for advanced permanent magnetic motors include machine tool rotary tables. Courtesy: SiemensSchematics show the configuration of asynchronous (induction) motor (on left) and permanent magnetic synchronous motor designs. As the technology has evolved, larger motors are being produced in the PM design. Table above compares the two designs. Courtesy: SiemensNewly developed mechatronic applications such as this integrated electrohydraulic pump motor, as used on a plastics injection molding machine, are yielding significant energy savings, short payback, and quieter operational conditions.

No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 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...
The true cost of lubrication: Three keys to consider when evaluating oils; Plant Engineering Lubrication Guide; 11 ways to protect bearing assets; Is lubrication part of your KPIs?
Contract maintenance: 5 ways to keep things humming while keeping an eye on costs; Pneumatic systems; Energy monitoring; The sixth 'S' is safety
Transport your data: Supply chain information critical to operational excellence; High-voltage faults; Portable cooling; Safety automation isn't automatic
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Maintaining low data center PUE; Using eco mode in UPS systems; Commissioning electrical and power systems; Exploring dc power distribution alternatives
Synchronizing industrial Ethernet networks; Selecting protocol conversion gateways; Integrating HMIs with PLCs and PACs
Why manufacturers need to see energy in a different light: Current approaches to energy management yield quick savings, but leave plant managers searching for ways of improving on those early gains.

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

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.