Linear drive works without power-transmission components

April 5, 2001
The MHS 40 drive from Rexroth Star, Charlotte, NC, has its nut directly connect to a hollow-shaft motor.

Motor-driven ball screws are a mainstay in linear positioning. Many of these ball screws have the screw driven by an ac motor or v-belt, while a nut carries out the actual feed movements, turning rotary motion into linear motion. In this set up, axial rigidity needed for positional accuracy is limited by screw length and end bearings.

An alternate approach is to have the motor turn the nut with a toothed belt so that the nut and screw carry out the feed movement relative to each other. A new drive takes this second approach one step further. The screw of the ball-screw assembly passes through the servomotor's hollow shaft. There are no other transmission components such as drive belts or clutches.

This design puts the motor and ball screw on the same axis and saves space. The same housing also encloses an integrated brake. This compact arrangement makes it possible to add more than one motor on a spindle to handle independent motions.

Users can adjust the screw lead to alter speeds and loads or change motors to vary the power output.

The drive is extremely accurate, using positioning information derived from the ball screw, and can be combined with a rail-based measuring system for direct-travel measurement.

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