Shape memory alloy device and control method

Abstract

A preferred rotary actuator includes an actuator assembly having a torque tube formed of a shape memory alloy (SMA), a superelastic NiTinol return spring associated with the torque tube and adapted to bias the torque tube toward an initial position, and a torque tube heating element, especially a thermoelectric device, for switching the SMA to cause rotation to an object connected to the actuator or to generate a torque upon that object. The torque tube ( ) includes a proximal end ( ) and a distal end ( ). The return spring and torque tube are connected at their ends, with the torque tube being pretwisted while in a martensitic state relative to the spring. Activation of the heating element causes the torque tube to enter an austenitic state in which it returns to its previous untwisted configuration. Removal of heat allows the torque tube to return to a martensitic state, when the return spring retwists the torque tube. A unique locking assembly is used with the preferred actuator assembly. A helicopter blade twist rotation system for a rotorcraft blade having a blade root and a tip includes a SMA rotary actuator located within the blade near the blade root, and a passive torque tube ( ) located within the blade and having a proximal end connected to the rotary actuator and a distal end connected to the blade near to the blade tip.