Ball screw with inner ball circulation and linear actuator equipped with the ball screw

Abstract

A ball screw with inner ball circulation whose transfer displacement to size ratio is large, resulting in a device which has an optimized size with a positioning accuracy measured in microns, and a linear actuator equipped with the ball screw, are disclosed. The ball screw includes a plurality of balls arranged in a space between a hemispherical groove formed on a cylindrical inner surface of a housing and a hemispherical groove of a rotating male screw. The ball screw also includes a ball circulation tube with its cylindrical outer surface formed with the hemispherical groove of the male screw and with the groove corresponding to the hemispherical groove of the housing. The ball circulation tube is formed with ball openings penetrating from both ends of the male screw toward the inner part. The ball screw also includes a ball circulation section, which fits inside the ball circulation tube, and has a hemispherical inner return path formed on its outer cylindrical surface. By coupling the ball circulation section to the ball circulation tube, the inner return path has a start point and end point which are matched with the ball openings of the ball circulation tube and the ball circulation tube and the ball circulation section can rotate together as a fixed unit with the balls circulating along the inner return path of the ball circulation section.