How to Raise Motor Efficiency

Striving for More Efficiency Can Entail Examining Everything From Motors to Entire Systems

By Hank Hogan

To paraphrase the Duchess of Windsor, a motor can never be too efficient. However, striving for more efficiency can entail examining everything from motors to entire systems.

For instance, the key to greater motor efficiency is focus, says Alan Crapo, vice president of engineering at NovaTorque. The company's motors feature a conical air gap that focuses magnetic flux in three dimensions and a design optimized to minimize losses. That configuration allows less-expensive materials to perform like more costly ones.

"We can use low-cost ferrite magnets, focus the flux, and operate with magnetic fields in the air gap and magnetic fields going through the windings that are similar to what you would get with rare-earth magnets," Crapo says.

NovaTorque's latest products, due out this year, are 94% efficient at the 3 hp motor size. A drawback of this focused approach is that the motors have greater inertia, making them a less likely choice when a fast response is needed.

The question of efficiency shouldn't be tackled simply by making changes to the motor, notes Peter Fischbach, industry manager for assembly and handling at Bosch Rexroth. For example, he says there might be more value in right-sizing a motor to make it more appropriate for a task.

That sort of analysis can be done on the entire mechanism. For that reason, Bosch Rexroth has been developing modeling tools that can simulate the actions of gearboxes, machine cycles, ramp times, etc. The model encompasses everything from the motor to the transmission that transforms the power the motor generates into useful work.

"You can modify the mechanics, you can change the gear ratio, and it spits out a performance curve or RMS power or things like that, so you can more easily optimize the machine," Fischbach says.

A systems approach can be seen in an offering from Kollmorgen. The company's software is designed to easily translate an old line shaft system to a software representation. This conversion enables the designer to optimize the motion engine and application.

The benefit is most evident when mechanical engineers are confronted with the task of converting a pneumatic or hydraulic system into one driven by servo motors controlled by PLCs. In such a situation, both the control system and the motion engine are foreign. "It makes the task of the electrification process of their machine much less daunting," says Kevin Liu, product line manager for industrial automation at Kollmorgen.

Right-sizing the motor and mechanical elements helps ensure maximum efficiency, he says. What also helps is using the correct motor technology.

Michael Cromheecke, marketing manager for mechatronic products and software tools at Rockwell Automation, also advocates looking at more than just the motor when considering efficiency. He cites a manufacturer that had a setup to punch out garage doors. The mechanical elements included a transmission, line shafts, belt-and-pulley systems, and a press. Using the company's motion analysis software and linear products, Rockwell was able to do the same task with a lower-power drive with far fewer wear points, without an increase in cost. The electricity usage was cut in half, which translates into lower operating expenses.

The key to achieving this improved efficiency is to start from basics, Cromheecke says. "Start with asking what energy is required to just move the load in your application. Take out all the other stuff that you think you need to do to get there."

Many of the motors from Portescap need to be efficient because they're in battery-operated applications, such as surgical hand tools. Others are found in heavy-industrial hand tools. Even here, efficiency is important because greater efficiency cuts down on the heat produced. No matter where they're going, the motors are designed using magnetic finite element analysis, says Jerry Vitale, principal design engineer.

 

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