Machine Design

Eliminating gears makes traction drive more accurate

In many industrial settings, engineers want highly accurate output speeds from a high-speed servomotor. The usual solution is a speed reducer that uses precision gears or worm screws. Unfortunately, these don't handle changes in servomotor output very well, and they generate noise. An alternative solution from Mitsubishi Heavy Industries Ltd. of Japan combines a planetary traction transmission with a special U-shaped traction ring.

The U-shaped ring surrounds the sun and planetary rollers and exerts a uniform press-fitting force, thanks to a preload force applied to the entire circumference of both sides of the ring. A special "traction oil" lets the ring transfer torque from the smoothly rolling rollers. The ring reduces backlash and speed deviations which are common in worm-gear drives. And since there are no gears to mesh, noise and vibration are minimized.

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