Shape memory alloy rotary actuator

A method for producing rotary actuator motion including the steps of supporting first and second pulleys for conjoint rotation about a common axis, said pulleys including sectors having arcuate circumferential edges, said sector of the first pulley having a radius of length r.sub.1 and said sector of the second pulley having a radius of length r.sub.2 which is less than r.sub.1 by a predetermined amount, attaching one end of a first elongate element of shape memory alloy material to the circumferential edge of the first pulley and attaching the opposite end of the element to the circumferential edge of the second pulley, heating the shape memory alloy material through its phase change transition temperature to cause contraction of the length of the element toward its memory shape, and holding the portion of the element intermediate its ends in tension to apply differential torque forces of opposite rotational senses against the pulleys with the resultant net torque urging the pulleys to rotate about the axis in a first direction.

A rotary actuator comprising means forming first and second moment arms which project in generally opposite directions from a common axis, said first moment arm having a radial length r.sub.1 and said second moment arm having a radial length r.sub.2 which is less than r.sub.1 by a predetermined amount, a reference structure, means mounting said moment arms for conjoint rotation relative to the reference structure about the common axis, an elongate element of shape memory alloy material, means for mounting one end of the element to the outer radial end of the first arm, means for mounting the other end of the element to the outer radial end of the second arm, means for heating the shape memory alloy material of the element through its phase change transition temperature to cause contraction of the length of the element toward its memory shape, and idler means for conducting portions of the shape memory alloy material of the element along a path which extends in a loop from the outer end of the first arm to the outer end of the second arm, said idler means holding the ends of the element under tension forces during contraction of the element with the tension forces applying torques on the respective moment arms whereby the resulting net torque causes relative rotation between the moment arms and reference structure.

A rotary actuator comprising the combination of a first pulley, a second pulley, a reference base, means for mounting the first and second pulleys conjointly together for rotation relative to the base, an elongate element of shape memory alloy material which undergoes a change in length between a memory shape and a trained shape when thermally cycled through the phase change transition temperature of the material, means for mounting one end of the element on the first pulley at a first radius r.sub.1 and the other end of the element to the second pulley at a second radius r.sub.2 on a side thereof which is opposite the side at which said first end is mounted, said first radius r.sub.1 exceeding the second radius r.sub.2 by a predetermined differential distance, idler means for conducting portions of the shape memory alloy along a path between the first and second pulleys during said change in length, said idler means constraining the path at a predetermined distance from the first and second pulleys whereby contraction in length of the element causes the opposite ends of the element to apply tension forces to the pulleys at the respective radii r.sub.1 and r.sub.2 whereby a resultant differential torque is applied to the pulleys for urging the pulleys and base to undergo relative rotation.