Innovation Keeps Motors Humming

Machine Designers and Builders Strive to Find New Methods and Materials to Give Them an Edge

By Jim Montague

Driven by unrelenting pressure to gain efficiency, improve reliability and save energy, motor designers and builders strive to find new methods and materials to give them an edge.

"Everyone is seeking greater energy density and efficiency in their motors, mostly by using permanent magnets, but they also want to simplify and avoid using controls requiring extra feedback devices and positioning applications," says Alby King, mechanical applications team lead at Lenze Americas. "So we developed controllers that can manage sensorless motors, and we're also working on an inverter that can handle sensorless devices. In fact, our controller can run induction motors and synchronous servo motors, so users only need one controller, and can keep the same controls as they move up the efficiency scale from induction to servos. Also, we've added a dedicated-frequency induction motor that has a 120 Hz base frequency, but its balanced winding design allows it to run at double traditional speeds with an inverter."

(Motor Designs Get Moving)

Sam Harris, business manager for large drive technologies at Siemens Industry, adds, "Increases in motor efficiency are driven mostly by government efficiency regulations, such as Energy Policy Act (EPAct) and Energy Independence and Security Act (EISA), and by end-user demands for reduced total cost of ownership. The fairly recent introduction of die-cast copper rotors by Siemens and a few other motor manufacturers have yielded higher efficiencies than mandated by the present EISA. Currently, the U.S. Dept. of Energy (DoE) is looking at additional energy savings potential, and will amend EISA to include even higher efficiency standards."

The DoE is working on a follow-up to EISA that will require even more efficient motors, perhaps by 2015, and add frame sizes beyond the 200 hp and less motors it covers now, reports Steve Evon, engineering manager for variable-speed and custom medium-ac motors at Baldor Electric. This will require builders to further optimize motor designs with finite analysis tools and models to identify power losses more easily.

"We're still using aluminum rotors with copper windings, but now we're using punched lamination stacks, which are thinner and easier to cool, and don't need the usual cast iron frame, so they allow more room for active components," Evon says. "We've really reached the physical limit of how much wire we can get into our winding slots, which is why PM and synchronous reluctance motors are so popular. The key to the future is finding lower-cost magnetic materials."

John Petro, founder and CTO at NovaTorque, adds, "We've designed a PM motor with a unique geometry that uses low-cost ferrite magnets, but achieves the performance of a PM motor with more expensive, rare earth-type magnets. This is done with a 3D geometry for the motor that provides magnetic flux concentration. This flux concentration is what allows low-cost, lower-performance ferrite magnets to achieve far greater performance."

Beyond pushing for energy efficiency, many motors and motion systems integrate discrete components to simplify and save time and labor, according to David Hansen, marketing manager at Exlar. "This integration includes joining gears with motors, and more recently combining drive electronics with motors and mechanics to simplify wiring and minimize panel space," Hansen says. "The outcome for us has been bigger PM servo motors replacing induction motors."

Users want motors that are easier to inventory and install in different applications, and so Rockwell Automation developed its VPL motor that's aligned to one cable for power and feedback instead of two or four, according to Chris Gottlieb, Rockwell's product manager for low-inertia servo motors. "VPL also has special windings for lower-speed profiles, which still maintain expected torque, but need less current," Gottlieb adds. "Previously, there was a lot of oversizing of motors. Users would buy 6,000–8,000 rpm motors with 16 A drives and 14-gauge cables, but only run them at 1,500–2,000 rpm, which only needs a 5 A drive and 18-gauge cable. Now they can save a lot of this power."