Patent ID: 7481055

Claim:
An actuator comprising: a housing having a part with a generally cylindrical interior surface surrounding a longitudinal axis and including a plurality of helical grooves; a chamber within the housing and containing a working fluid that changes phase upon heating; an electrical heater disposed within the chamber for heating the working fluid upon application of electrical power to the electrical heater; a first piston slidably disposed within the housing and movable along and rotatable about the longitudinal axis between first and second positions; a rolling diaphragm, separating the chamber from the first piston, driven by the working fluid, and sliding the first piston toward the second position upon expansion of the working fluid, wherein the first piston is driven and slides from the first position to the second position in response to heating of the working fluid by the electrical heater, and the first piston includes a piston body having a plurality of partially spherical recesses; a piston rod extending from the piston body in a direction opposite the chamber and protruding from and moving relative to the housing; a plurality of balls, each ball being rotationally disposed in and captured between one of the helical grooves and one of the partially spherical recesses; a spring biasing the first piston toward the first; and a second piston interposed between the first piston and the rolling diaphragm, inhibiting transmission of torsion to the rolling diaphragm.