Patent ID: 8166838

Claim:
An actuator comprising: a hollow track member having a slit extending in an axial direction thereof and having a first length extending in the axial direction; a movable member disposed inside the track member to be movable along the track member and having a second length extending in the axial direction, wherein the second length is shorter than the first length; and a drive mechanism for moving the movable member along the axial direction of the track member, wherein an entire exposed outer periphery of the track member has a substantially circular-arc shape in a section perpendicular to the axial direction of the track member, wherein an inner periphery of the track member has a substantially circular-arc shape, wherein an outer periphery of the movable member has a substantially polygon shape in the section, wherein the track member is formed with a plurality of rolling member rolling grooves extending in the axial direction thereof as the guide portion, the movable member is formed with a plurality of loaded rolling member rolling grooves opposing to the rolling member rolling grooves, respectively, and the movable member has two side surfaces to each of which two rows of the loaded rolling member rolling grooves are formed, and a number of rolling members are interposed between the rolling member rolling grooves of the track member and the opposing loaded rolling member rolling grooves of the movable member, respectively, to be rollable therebetween, wherein the two rows of the loaded rolling member rolling grooves extend in the axial direction of the track member, and wherein a first row of the two rows of the loaded rolling member rolling grooves is positioned in vertical direction with respect to a second row of the two rows of the loaded rolling member rolling grooves.