Patent ID: 7207235

Claim:
A ball screw mechanism to transform from rotational movement into linear movement and from linear movement into rotational movement comprising: a shaft formed with a screw groove on an outer surface thereof, wherein turns of the screw groove are separated by a step; a nut formed with a screw groove on an inner surface thereof; a ball-roll path created spirally by the turns of the screw groove of the shaft and the screw groove of the nut being opposite each other; a plural number of balls contained in the ball-roll path; a ball-return path comprising a deflector that deflects a ball in the ball-roll path over the step from one turn to an adjacent turn to form a circulation path comprising the ball-roll path and the ball-return path, in which the balls move endlessly; and a plural number of separators of equal width arranged between the balls respectively in order to prevent balls from contacting each other; wherein a number of the balls is fewer from one ball to three balls than a maximum number of the balls which can be contained into the circulation path, and wherein a width of the separators is equal to a clearance between the balls which are next to each other when the balls are located at equal intervals, wherein an outer surface of each separator is chamfered so that a proportion of a maximum diameter at the center of the axial direction of the separator and a minimum diameter at the ends of the axial direction of the separator is in a range from 0.8 to 0.9.