Opening and closing chuck

An opening and closing chuck, wherein:

• a guide rail, which is linear, is provided on an outer surface of a chuck body, a pair of fingers that grasp a workpiece is provided on the guide rail, and at least one of the pair of fingers is a movable finger that is movable along the guide rail;
• the movable finger includes a rail fitting groove into which the guide rail fits, a first concave groove is formed in right and left side surfaces of the guide rail and a second concave groove is formed in inner surfaces of right and left side walls of the rail fitting grooves, the first concave groove on the same side as the guide rail and the second concave groove on the same side as the rail fitting grooves being at positions at which the first concave groove and the second concave groove face each other, a rolling element is provided between the first concave groove and the second concave groove, and the movable finger is movable along the guide rail due to rolling of the rolling element;
• as many cylinder apparatuses as there are movable fingers are provided in the chuck body, each cylinder apparatus including a piston and a rod that advance and retract by an action of air pressure in directions of an axial line of a cylinder hole, a top end of the rod extends from an end of the chuck body to an outside, and an end block, which faces the end of the chuck body, is attached to the top end of the rod so as to move toward and away from the end of the chuck body according to forward and backward movements of the rod;
• the movable finger is linked to the end block, and opening and closing of the movable finger is driven by the rod through the end block;
• and
• a position at which the rod is linked to the end block is a position near one end side of the end block in a width direction, and a position at which the finger is linked to the end block is a position near the other end side of the end block in the width direction,
• wherein the guide rail is formed separately from the chuck body and is fixed to an outer surface of the chuck body, at least one of both ends of the guide rail in the longitudinal direction extends from the chuck body to within a moveable range of the block, and a clearance hole, into which the one end of the guide rail fits, is formed in the end block.