ボールねじの球挙動の研究(第1報)

Abstract

Active balls in ball screws should be taken sliding motions, which are called "wedge sliding", in the normal direction to helicoid of ball center, because lead angles of shaft and nut raceways are not the same respectively. Ball slip may also be produced in the rolling direction of active balls, because they contact each other with some slip. It is well known that these slips will significantly affect the friction and wear characteristics and also the rolling fatigue lives of ball screws. The ball motion in the ball screws must be therefore investigated in order to make clear these characteristics. In this paper, the authors carried out some experiment using a magnetized ball and wound coil on the nut in order to measure the ball slip ratio in the rolling direction of active balls. The results are summarized as follows: (1) Active balls in the ball screw make complicated motion with sliding and spinning and their rotating periods vary widely. (2) Rapid spinning occurs more frequently in the back driving of the ball screw than the normal driving. (3) The slip ratio of ball revolution in the ball screw is about 1% at the shaft speed range of 60-600rpm. (4) The slip ratio of ball rotation increases as the shaft speed increases in the normal driving. The slip ratio of the back driving remarkably differs from the normal one in relation to the shaft speed.