Patent ID: 7080571

Claim:
A ball screw comprising: a screw shalt including a spiral-shaped ball rolling groove formed in an outer peripheral surface thereof; a nut including a spiral-shaped ball rolling groove formed in an inner peripheral surface thereof; a plurality of balls disposed in a raceway formed by the two rolling grooves; and, a return path for moving the balls from the terminal point of the raceway to the start point of the raceway, the two end portions of the return path respectively including a rising surface rising from the ball rolling groove of the nut and a stopper portion disposed opposed to the rising surface to form the end portion of the raceway, wherein a boundaiy portion between the rising surface and the ball rolling groove of the nut is formed as a convex shaped portion towards the screw shaft having the radius of curvature 0.05 times the diameter of the ball or more, wherein the return path is partially formed by a tube including the stopper portion, and the rising surface is formed on the inner peripheral surface of the nut so as to form the return path.