A linear SMA motor as direct-drive robotic actuator

A push-pull actuator for commanding the motion of the interphalangeal joints of anthropomorphic robotic hands is proposed. The actuator, based on coil springs, made of the shape-memory alloy Nitinol, is compact enough to be easily incorporated into the phalangeal structure of a robotic finger, thus eliminating the complex routing of the cables and tendons usually adopted for transmitting motion from conventional actuators (e.g. DC servomotors) to the joints. The performance of the SMA actuator is illustrated, and the concepts of temperature, strain, and stress limits for the control of the whole push-pull actuating system are emphasized. The methods adopted to improve the usually limited frequency response of SMA actuators are also described. Finally, the control of the whole system and some experimental results demonstrating promising actuator performance are discussed