Dynamic behaviour of ball motion and its effect on oil film formation in ball screw

Abstract

Using a magnetized ball and hall elements arranged on the nut and the return tube, the authors tried to measure the actual ball motion in a ball screw rotating at various shaft speed conditions. As test screws, a conventional ball screw and its improved type which incorporates resin retaining pieces between the balls were used, and by means of an electric resistance method, the state of oil film formation between balls and raceways was also measured in the grease lubricated condition. As a result of these experiments, a significant effect of retaining pieces on the ball motion and the oil film formation was found. Namely, owing to the retaining pieces which prevent direct contact or skirmishes of balls, the ball motion in the improved ball screw became smooth and the oil film was built up rapidly not only in the steady process but also in the acceleration or the deceleration phase.