| 摘要 |
PROBLEM TO BE SOLVED: To improve the service life of a ball screw while restricting the fatigue of a ball screw. SOLUTION: This ball screw has three or more ball trains 4a, 4b, 4c respectively formed of a set of balls 3 circulating around a screw shaft 1. In the ball trains 4a, 4b, 4c arranged in series, ball diameter of the ball trains 4a, 4b in both ends is formed smaller than the ball diameter of the ball train 4b at a central part. In the case where diameter of the balls 3 in each ball train is formed same with each other, load distribution in both ends of a nut 2 becomes high because of the force to be applied in the axial direction of a screw shaft 1, and the stress becomes uneven. This unevenness of the stress and the unevenness of the load are relaxed by reducing the ball diameter of the ball trains 4a, 4c in both ends. With this structure, concentration of the stress is relaxed so as to delay the breakdown of a screw shaft and a nut due to the fatigue by the use for a long time, and service life of the ball screw is prolonged.
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