Involute cam actuator with piston drive

DETAILED DESCRIPTION We claim: 1.
A mechanism for producing a linear relationship between angular movement of a shaft and axial movement of a piston comprising: a piston operating along an axis of a cylinder and having first and second fluid pressure faces at opposite ends thereof; a recess in a central portion of said piston; a shaft mounted for rotation about an axis that extends transversely to said cylinder axis and having fixed thereto a cam member which is mounted for angular movement about the shaft axis in said recess; cam engaging surfaces mounted on said piston with an invariant spacing at opposite sides of the recess and in constant engagement with opposed sides of said cam member; and said cam member having a shape such that linear movement of the piston has a linear relationship with the angular movement of said shaft through a stroke which extends from both sides of a central position of said piston whereby, upon an application of a fluid pressure on one of said first and second fluid pressure faces of said piston, the piston is linearly moved causing an associated cam engaging surface to engage the cam member and rotate said shaft.
2.
A mechanism as defined in claim 1 wherein the cam surface has the shape of a pair of involute curves which each extend from a base circle of said involute.
3.
A mechanism as defined in claim 2 wherein said involute curves are symmetrical, opposite and identical and the center of a base circle of the involute curves is coincident with the rotational axis of said shaft.
4.
A mechanism as defined in claim 1 further including means for applying a differential fluid pressure to the opposite faces of said piston for controlling the linear movement of the piston from a central position in said cylinder to thereby produce the rotation of said shaft.
5.
A mechanism as defined in claim 1, wherein the rotational axis of said shaft is perpendicular to the axis of said cylinder and located so that a line extending through points of engagement between the cam engaging surfaces and involute curves of the cam member is substantially tangent to a base circle of the involute curves