A linear actuator incorporates a DC motor whose stator is secured to a frame. A shaft is coupled to the rotor of the DC motor one end of which is circumferentially coupled to the inside of a torsion spring and the outer section of the torsion spring is coupled to the frame. The center section of the...http://www.google.de/patents/US6734582?utm_source=gb-gplus-sharePatent US6734582 - Linear actuator using a rotating motor
