Patent ID: 8449232

Claim:
An indexing device for a machine tool, comprising: a frame having a through hole; a rotary shaft provided in the through hole and rotatably supported by the frame; a shaft provided coaxially and integrally with the rotary shaft; a ring-shaped clamp sleeve configured to surround an outer peripheral portion of the shaft, the clamp sleeve configured to provide a clamping force to act on the shaft and prevent the rotary shaft from rotating; and a cylindrical pressure-receiving member fixed to the frame through a plurality of clamp members, wherein the cylindrical pressure-receiving member is configured such that an outer peripheral surface of the cylindrical pressure-receiving member faces an inner peripheral surface of the through hole of the frame, wherein the clamp sleeve has a cylindrical portion coaxially inserted into the cylindrical pressure-receiving member, a flange portion extending outward in a radial direction from an end portion of the cylindrical portion and integrally formed with the cylindrical portion, and an annular groove formed over an outer peripheral portion of the cylindrical portion and having a bottom portion that defines a thin-wall section, wherein the frame has an attachment portion accommodating the flange portion of the clamp sleeve and having an engagement surface extending outward in the radial direction from the through hole, wherein the cylindrical pressure-receiving member is attached to the flange portion through the plurality of clamp members respectively screwed into a plurality of screw holes provided in the flange portion of the clamp sleeve while a shaft end of the cylindrical pressure-receiving member engages with the flange portion of the clamp sleeve, and the cylindrical pressure-receiving member is attached to the frame by fixing the flange portion of the clamp sleeve to the attachment portion of the frame, wherein a space surrounded by a bottom surface of the annular groove of the clamp sleeve and the inner peripheral surface of the cylindrical pressure-receiving member forms a pressure chamber communicating with a fluid control circuit, pressure fluid being supplied to the pressure chamber, the pressure fluid causing the thin-wall section of the clamp sleeve to be deformed in a diameter-decreasing direction to generate the clamping force against the shaft, and wherein a predetermined gap is provided between the inner peripheral surface of the through hole in the frame and the outer peripheral surface of the cylindrical pressure-receiving member.