Millimeter-sized joint actuator using a shape memory alloy

A millimeter-sized actuator for driving a rotary joint for a small robot is designed and fabricated using a shape memory alloy ( SMA); it has the advantages of a strong force/weight ratio and can be extended down to micron size. The actuator is of push-pull type composed of two 0.05 mm × 0.5 mm × 3 mm SMA sheets. First, a theoretical model of the dynamics of the SMA actuator is derived based on an experimental analysis of the dynamics of large SMA sheets. Using this model, the design method of the above type of SMA actuator is established. Finally, the theoretical torque versus angular displacement of a millimeter-sized rotary joint driven by the above millimeter-sized SMA actuator is obtained, with a maximum torque of 4 gf mm.