Patent ID: 7707924

Claim:
A linear actuator capable of generating thrust in a direction back and forth, comprising: a cylinder having an overall cylindrical space with an inner wall S of a prescribed internal diameter D and being provided with a groove G disposed rearwardly of the inner wall S and having an internal dimension larger than the internal diameter D; a piston, sealing a gap with the inner wall S, supported so as to be capable of freely sliding back and forth; a cam rod, constituting an axial body supported inside the piston so as to be capable of freely sliding back and forth with a rear end exposed at a rear of the piston, having a profile changing at one location from a small diameter part of outer diameter D 1 to a large diameter part of a outer diameter D 2 larger than D 1 in accordance with a transition from a rear to a front of the cam rod; a locking ram constituting a block supported at the piston in a manner freely slidable in a radial direction, with an outer end of the locking ram constituting an end on the outside in a radial direction and being capable of projecting out from or being pulled into a line for a distance of D/ 2 from a center of the piston so that an inner end of the locking ram constituting an end on the inside in the radial direction is capable of coming into contact with the profile of the cam rod; a spring built-into the piston urging the cam rod rearwardly; a push rod, constituting an axial body supported in a freely sliding manner in a direction back and forth at the cylinder so that a rear end of the push rod is exposed at the rear part of the cylinder and a front end of the push rod is exposed at the rear part of the overall cylindrical space and faces a rear end of the cam rod; and a release lever supported on an outer part of the cylinder, the release lever capable of pushing the push rod and the cam rod forwardly, wherein, while the piston moves to a rear part of the overall cylindrical space, the inner end of the locking ram presses against the large diameter part so that the outer end of the locking ram fits into the groove G, and in this state, the front end of the push rod is able to press the cam rod, wherein said cam rod includes a projection having an outer diameter Dp smaller than the outer diameter D 1 of the small diameter part and a ring portion extending radially inward directly from the outer diameter D 1 at a rear end of the small diameter part to the outer diameter Dp at a front end of the projection, and wherein a flat end surface of said push rod engages directly with a flat end surface of said projection for selectively imparting reciprocation thereto for permitting said locking ram to selectively engage the small diameter part of the cam rod for releasing said locking ram.