| 摘要 |
An annular piston (13) is inserted between a cylinder hole (6) of a housing (2) and a clamp rod (7) so as to be vertically movable and rotatable. A guide groove (18) is provided in an outer peripheral portion of the annular piston (13), and an engaging ball (19) to be fitted into the guide groove (18) is provided on an inner peripheral wall of the cylinder hole (6). A transmission mechanism (26) which prevents the clamp rod (7) and the annular piston (13) from rotating relatively to each other and permits them to move relatively to each other in a vertical direction is provided between the clamp rod (7) and the annular piston (13). When the clamp rod (7) is moved from a released raised position to a locked lowered position, the annular piston (13) descends while rotating via a rotational groove (23) and the engaging ball (19), and thereby the annular piston (13) causes, via the transmission mechanism (26), the clamp rod (7) to rotate, and thereafter, the annular piston (13) causes the clamp rod (7) to descend straight down. Descent of the clamp rod (7) during its rotation is prevented by a peripheral wall (52a) of a fitting hole (52). |
