When it’s necessary to convert motion from rotary to linear, engineers usually use ball or leadscrews. But planetary roller screws, such as those from INA, a brand of the Schaeffler Group USA, Fort Mill, S. C. (www.schaeffler.us), can do the same task with less vibration, greater stiffness, and higher rotational speeds and accelerations.

The device consists of a screw and nut with several planetary rollers parallel to the axis between the screw and nut. The rollers have many points of contact with the screw and roller nut, providing two to three times the stiffness of similarly sized ball screws without significantly increasing friction or decreasing efficiency. The contact geometry also improves shock resistance and increases static and dynamic thrust-load capacities by a factor of 3 to 5 over comparable ball screws.

The rollers in the planetary roller screw are always in contact and do not circulate in and out of the nut. This lets the screw accelerate faster and reach speeds up to 6,500 rpm. Ball screws are typically limited to around 3,000 rpm. Standard lead accuracy is 10 μm/300 mm, with 5 μm/300 mm available as an option.

Edited by Stephen J. Mraz

© 2010 Penton Media, Inc.