Machinedesign 1512 106msdmedical 0 0

Gearmotor minimizes noise in medical settings

June 1, 2011
Specialized medical procedures such as joint replacement surgery call for automated operating tables that can be positioned with pinpoint accuracy. Equally

Specialized medical procedures such as joint replacement surgery call for automated operating tables that can be positioned with pinpoint accuracy. Equally important to positioning accuracy are high torque output and quiet operation from a motor housed within the table base that can handle up to a 500-lb load. When a leading medical device manufacturer was tasked with designing such a table, the company selected Groschopp Inc., Sioux Center, Iowa, to supply a suitable gearmotor.

With this particular table, two hinged arms must be driven so that their positional alignment and movement are completely synchronized. A traditional solution using link chains, belts, and pulleys exhibits operational error that renders precisely synchronized arm movement impossible. Another idea was to use one motor for each hinged arm, but using a single motor instead — with two outputs — provides greater accuracy and saves costs. Compounding the design challenge was a 24-V power supply specification.

Groschopp's engineers chose a 24-V permanent magnet dc gearmotor, which provides the needed output given the intermittent operation. The motor is customized for high torque, and its shaft drives two planetary speed reducer outputs. Because the same motor drives both outputs, there is both mechanical and electrical linkage. If two separate motors had been used, a more complex control scheme would be required. The planetary reducers' high efficiency allows the necessary torque while staying below the 20-A current limit.

Once the gearmotor was determined, the team went into extensive prototyping and testing to reduce noise. Engineers analyzed all potential sources - motor, gearbox, and gearmotor assembly - and then worked to subdue noise in each. For example, low-noise planetary speed reducers are incorporated into the design, with a combination of non-metallic and metallic gears that deliver high torque and minimize sound. For more information, visit

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