PROBLEM TO BE SOLVED: To immediately release the locked condition of a rotor by arranging around the periphery of a coil spring, a cylindrical body which is brought in contact with the coil spring in its locking released condition and regulates the enlarging rate of the coil spring while being opposed to the coil spring in its locked condition having a clearance. ;SOLUTION: When pushing/pressing force F is applied to a cover wall 17 on the periphery of a cylindrical body 15A, the cylindrical body 15A is rotated in the same direction while being slid on a circular arc guide surface 19a. At the same time, the other end 4b of a twist coil spring 4 is also rotated in the same direction by the same distance so as to be enlarged and displaced, however, only a narrow clearance is sectioned between the cylindrical body 15A and the twist coil spring 4, therefore a first coil continued to the other end 4b is immediately brought in pressure contact with the inner circumferential surface of the cylindrical body 15A so that the twist coil spring 4 is regulated not to be enlarged any more. Hereupon, the enlarging phenomenon of this first coil is sequentially and rapidly transmitted to one end 4a side being a fixed end through a second coil..., therefore the locked condition of a rotor 2 is immediately released.;COPYRIGHT: (C)1997,JPO
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