Millimeter size joint actuator using shape memory alloy

A millimeter-size actuator to drive a rotary joint for a small robot was designed and fabricated using shape memory alloy (SMA), which has the merits of large force/weight and extendability to micron size. The actuator is of the push-pull type, composed of two SMA sheets of 0.05 mm×0.5 mm×3 mm. The theoretical model of the dynamics of the SMA actuator was derived based on an experimental analysis of the dynamics of the larger SMA sheets. Using this model, the design method of the SMA actuator was established. Finally, the theoretical torque vs. angular displacement characteristic of a millimeter-size rotary joint driven by the above millimeter-size SMA actuator was obtained, which shows a maximum of 4 gf-mm