Patent ID: 8302947

Claim:
A clamping apparatus comprising: a clamp rod ( 6 ) inserted into a guide hole ( 5 ) of a housing ( 4 ), the clamp rod ( 6 ) having a clamping member ( 10 ) provided at a leading end side of the clamp rod ( 6 ) in an axial direction, an inner piston ( 12 ), and a pressure receiving surface ( 13 ) approaching an axis toward a base end, which are arranged in this order in the axial direction; one outer piston ( 23 ) inserted into a first annular space ( 21 ) between the inner piston ( 12 ) and the guide hole ( 5 ), the outer piston ( 23 ) having an output portion ( 26 ) for locking and releasing on an inner periphery of a base end portion of the outer piston ( 23 ); a collet ( 33 ) inserted into a second annular space ( 32 ) between the pressure receiving surface ( 13 ) and the guide hole ( 5 ) and having a plurality of divided members ( 34 ) arranged circumferentially at substantially regular intervals, wherein an input portion ( 36 ) driven by the output portion ( 26 ) is provided in an outer periphery portion of each divided member ( 34 ), and a pressing surface ( 40 ) which makes a wedge-engagement with the pressure receiving surface ( 13 ) from a base end side is provided on an inner periphery portion of each divided member ( 34 ); and a lock chamber ( 42 ) and a release chamber ( 47 ) which apply/release fluid pressure to/from a base end surface and a leading end surface of the outer piston ( 23 ), respectively.