Abstract: A strong helical compression spring biases the plunger of a unidirectional actuator to an extended position. The actuator is a self contained unit having an integral travel stop to limit extension of the plunger and an integral down lock mechanism which locks the plunger when the maximum extended position is reached.

Abstract: An overcenter mechanism (10) includes a housing (12) and a first shaft (14) mounted on the housing. The first shaft has a first axis (34). A second shaft (20) is mounted on the housing and the second shaft has a second axis (41) that parallels the first axis. A lever (16) is attached to the first shaft, and the lever pivots about the first axis in response to a force (F.sub.op) applied to the lever. A cam (18) is attached to the first shaft, and the cam pivots about the first axis. The cam has a cam surface including a first surface portion (58) and a second surface portion (60). The first and second surface portions form a cusp (62) therebetween. A cam follower (21) has a cam follower surface, and the cam follower pivots about the second axis. A biasing member (26) urges the cam follower surface against the cam surface in pressure contact. The cam follower and the pressure contact cooperate with the cam to generate torque (.tau..sub.roller) on the cam until the cam follower surface contacts the cusp.