Patent ID: 7771307

Claim:
A rolling element screw device comprising: a screw member formed, in an outer peripheral surface thereof, with a screw side spiral groove; a nut member formed, in an inner peripheral surface thereof, with a nut side spiral groove; a plurality of rolling elements disposed to be rollable between the screw side spiral groove and the nut side spiral groove; a retainer ring disposed in an annular space between the screw member and the nut member opposing to each other and adapted to retain the plurality of rolling elements at predetermined positions to be rollable; and a power transmission mechanism for moving, in a condition that either one of the screw member and the nut member is constructed as a rotating side member, the retainer ring in an axial direction in accordance with the lead angles of the screw side spiral groove and the nut side spiral groove while rotating the retainer ring with a constant relation being maintained with respect to a rotational phase of the rotating side member according to rotation of the rotating side member, the power transmission mechanism comprising: an external tooth formed to the screw member; an internal tooth formed to the nut member; and a plurality of planetary gears held, to be rotatable, at circumferentially predetermined positions of the retainer ring in a condition to be meshed with the external tooth and the internal tooth, respectively, wherein the external tooth is formed to an area separated in an axial direction of the screw side spiral groove so as not to overlap with the screw side spiral groove formed to the screw member, and the internal tooth is formed to an area separated in an axial direction of the nut side spiral groove so as not to overlap with the nut side spiral groove formed to the nut member.