Patent ID: 8246029

Claim:
A clamp device comprising an annular grip member capable of expanding and shrinking in a radial direction and 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, a fluid pressure cylinder for driving the grip member and the clamp rod forwards and backwards in an axial direction, and a main body member to which the grip member, the clamp rod, and the fluid pressure cylinder are attached, comprising: a seating surface formed on the main body member for seating the workpiece; a poor clamping detection means for detecting poor clamping in a state where the grip member is driven by the fluid pressure cylinder via the clamp rod in the direction parallel to an axis of the clamp rod, and the workpiece is seated on the seating surface, a co-operating member is provided that shifts integrally with the grip member in the direction parallel to the axis of the fluid pressure cylinder; and the poor clamping detection means comprises a valve mechanism that is actuated by the co-operating member to open when the grip member has been shifted to a grip member lower limit position in the clamping direction or to a position in the vicinity thereof, an air passage that supplies pressurized air to an input side of the valve mechanism, and a pressure switch that detects that a pressure of pressurized air in the air passage is greater than or equal to a predetermined pressure value used for determining whether clamping is poor.