Clamping device

A clamping device for fixing a clamping object to a base by releasably engaging with an inner wall of a hole or a side wall formed in the clamping object, the clamping device comprising:

• a clamping main body fixed to the base and which is communicatingly formed with a rod insertion hole and a piston receiving cavity;
• a clamping rod which is inserted through the rod insertion hole of the clamping main body, a top-end portion of the clamping rod protruding from the clamping main body, the top-end portion being provided with an engagement portion engageable with the inner wall of the hole or the side wall;
• a piston member movably mounted in the piston receiving cavity of the clamping main body;
• a rod support mechanism which includes a pivot about which said clamping rod is movable and which moves the engagement portion of the clamping rod in a direction roughly rectangular to the longitudinal direction of the clamping rod and switchably supports the clamping rod in the clamping main body or the piston member between a clamping position of the clamping rod and a clamp release position of the clamping rod;
• a piston driving mechanism for driving the piston member between a first position corresponding to the clamping position of the clamping rod and a second position corresponding to the clamp release position of the clamping rod, the piston driving mechanism being provided with a spring which urges the piston member to the first position corresponding to the clamping position of the clamping rod and with a hydraulic chamber for driving the piston member to the second position corresponding to the clamp release position of the clamping rod by hydraulic pressure, said spring being mounted around the clamping rod between the clamping main body and the piston member;
• and
• a cam mechanism for driving the engagement portion of the clamping rod in a clamping direction roughly rectangular to the longitudinal direction of the clamping rod by a driving force of the piston driving mechanism driving the piston member to the first position, said cam mechanism being provided with a sphere or a roller rotatably mounted on a base end portion of the clamping rod, and an inclined portion being formed in the piston member so that the sphere or the roller makes contact therewith, said inclined portion being inclined so as to press the sphere or the roller toward the clamping rod when the piston member moves toward the hydraulic chamber by the urging force of the spring.