US Patent 7819198 Friction spring release mechanism

A one-shot thermally activated release mechanism, the release mechanism including a spiral or helically wound spring wrapped around a set of jaws in a manner that prevents the jaws from expanding; held in this tightened position by two wires, with one wire fixed to the body of a member of the jaws and the second wire attached to the spring, the wires bonded together by a solder or other fusible material. The jaws restrict the movement of a plunger. Heating the solder causes release of the spring and enables expansion of the jaws, allowing movement of the plunger. A bias force on the plunger assists in movement of the plunger past the expanding jaws.