A micro rotary actuator using shape memory alloys.

A thin (0.1mm diameter) rod of shape memory alloy (Nitinol) wire was clamped at two ends under torsional strain and used as micro, rotary actuator. Using three electrical connections (two ends of the wire and a contact in the middle of the wire), the two halves of the wire were differentially heated which caused repeatable, continuous and directional angular deflections of the wire about its longitudinal axis. In addition, this configuration allows the shape memory alloy to serve as both the actuating mechanism and the mechanical bias (which restores the deformation in the wire after shape recovery). Thus, the reforming takes place with the activation time constant of the wire and not with the thermal cooling time constant as in previous designs. This present actuator to achieve operating bandwidths of approximately 4 Hz; a factor of 3 to 4 higher bandwidth over actuators of similar size which rely on bias springs. A micro fluid-valve and a pair of micro-tongs are presented as some applications of such an actuator.