Kinematical analyses and transmission efficiency of a preloaded ball screw operating at high rotational speeds

High rotational speeds in ball screws (greater than 1000 rpm) cause more slip motion between balls and raceways than slower speeds. This increase in the slip motion increases the friction at the contact area, thus increasing the driving torque required for a high-speed ball screw. Theoretical analyses of the kinematics of a preloaded single-nut, double-cycle ball screw operating at high rotational speeds are presented in this study. The mechanical efficiency obtained from the theoretical driving torque, axial load and the orbital angular speeds of the ball was confirmed with experimental data. The slipping-rolling behaviour of each contact area was well developed from the distribution of stagnation lines consisting of pure-rolling points. Increasing the initial contact angle can significantly reduce the distance between the pure-rolling point and contact centre and decrease the driving torque, especially when the operating axial load approaches the applied preload. The mechanical efficiency can thus be increased, and wear may also be avoided by reducing the slip motion occurring at contact areas between balls and raceways. (C) 2011 Elsevier Ltd. All rights reserved.