Patent ID: 8235370

Claim:
A clamp device, comprising an annular grip member capable of expanding and shrinking in a radial direction and moreover of being inserted into a hole in a workpiece and of gripping an inner circumferential surface of the hole, a clamp rod having a tapered shaft portion fitted into and engaged with the grip member, and a fluid pressure cylinder for driving the grip member and the clamp rod forwards and backwards in an axial direction, comprising: an upper main body member and a lower main body member to which the grip member, the clamp rod, and the fluid pressure cylinder are attached; a seating surface formed on the upper main body member for seating the workpiece; a pressurized air ejection hole for a seating sensor that opens in the seating surface; a workpiece mounting surface formed on the grip member, the work-piece mounting surface that, when the grip member is at an advanced position in which the grip member is shifted towards the workpiece, can receive and stop the workpiece at a position that is more advanced than the seating surface; and that, during clamp operation in which the grip member and the clamp rod are shifted towards retraction, shifts integrally with the grip member in a direction that is parallel to an axis of the clamp rod; the fluid pressure cylinder comprises: a cylinder bore; a piston member that is installed in the cylinder bore and is linked operatively to the clamp rod; a tubular piston rod that is formed on the piston member; a clamping fluid chamber that is defined within the cylinder bore on a side of the tubular piston rod, and an unclamping fluid chamber that is defined within the cylinder bore on an opposite side to the clamping fluid chamber relative to a piston portion of the piston member; and an annular pressure receiving member fitted on the exterior of the tubular piston rod and is movable in a direction parallel to the axis of the clamp rod while being capable of receiving the fluid pressure in the clamping fluid chamber, and that receives and stops a base end surface of the grip member; and the grip member and the clamp rod are disposed so as to be movable as one unit in directions orthogonal to the axis of the fluid pressure cylinder; and an elastic ring member is provided in a compressed state between the tubular piston rod and the clamp rod, and that, in order for a common axis of the grip member and the clamp rod to coincide with the axis of the fluid pressure cylinder, the elastic ring member elastically biasing the clamp rod in directions orthogonal to the axis of the fluid pressure cylinder.