| 摘要 |
In a ball groove profile of a ball screw, an outer diameter portion of a screw shaft of the ball screw and a substantially semi-circular ball rolling portion of a ball groove of the ball screw are connected to each other through arcuate portions. The radius of curvature of each arcuate portion ranges from a value half a radius of a rolling ball or more to twice the radius of the ball or less. The arcuate portions are connected at least to the ball rolling portion continuously and smoothly. The outer diameter of the screw shaft is set to a value equal to or slightly smaller than the diameter of the central circle of the ball fitted with the ball groove arranged on the outer diameter of the screw shaft, and the difference between the outer diameter of the screw shaft and the diameter of the central circle of the ball is set to 10% of the diameter of the ball or less. The ball groove profile can reduce the stress concentration even if impact derived from the collision of the ball is applied to land shoulder portions of the screw shaft, so that the land shoulder portions are not damaged under high-speed operation.
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