Machining, Measurement, and Control Laboratory

A Study on the Friction Torque Variation of a Ball Screw at Motion Direction Change
- Friction Torque Variation due to the Change in Ball Contact Points -
Mizuho NINOMIYA (NSK, Ltd.)
Yasumi WATANABE (NSK, Ltd.)
Satoru ARAI (NSK, Ltd.)
Minoru HAMAMURA (Toshiba Machine Co., Ltd.)
Yoshiaki KAKINO (Kyoto University)

The friction torque on a double nut preloaded ball screw dynamically varies after motion direction change. The transient friction torque after motion direction change is less than that in the steady state. Although this friction torque variation is often mistaken for the backlash, the theoretical analysis shows that it is caused by the change in ball contact points. Experimental results coincide well with simulation results. This paper discusses the effect of the axial play, the preload, and the lead on the friction torque. Furthermore, this paper clarifies the difference of friction torque characteristics between a double nut preloaded ball screw and an over-size ball preloaded ball screw.

Key words: ball screw, friction torque, ball contact points, over-size ball, double nut