Patent ID: 6860827

Claim:
An actuator device for manipulating a movable member, comprising: a screw shaft having a ball screw groove formed on an outer peripheral surface thereof; a nut member located on the outer periphery of the screw shaft and having a ball screw groove formed on an inner peripheral surface thereof; and a plurality of balls housed between the ball screw groove of the screw shaft and the ball screw groove of the nut member, wherein the nut member moves relatively to the screw shaft in a first axial direction and a second axial direction opposite thereto in a manner such that the nut member is continually subjected to a load in the first axial direction; the ball screw groove of the screw shaft has a loaded surface, which is formed on a groove base thereof, which extends in the first axial direction and which is pressed against the balls by the load in the first axial direction, and an unloaded surface which is formed on the groove base and which extends in the second axial direction; the ball screw groove of the nut member has a loaded surface, which is formed on a groove base thereof, which extends in the second axial direction and which is pressed against the balls by the load in the first axial direction, and an unloaded surface which is formed on the groove base and which extends in the first axial direction, the respective loaded surfaces and unloaded surfaces of the ball screw grooves, only the loaded surfaces are finished so that the surface roughness thereof is lower than that of the unloaded surfaces.