Lightweight prosthetic hand with five fingers using SMA actuator

This paper proposes a lightweight prosthetic hand with five fingers that are driven by contraction force of shape memory alloy (SMA). Each finger is composed of SMA-wire mechanism similar to the muscle-tendon structure of human. Finger flexion is performed by contraction force of SMA, but its extension is carried out by a restoring force of a spring mounted on the backside of finger. The developed hand has five fingers, but its total DOF is six due to an under-actuated mechanism. Each finger posture is achieved by control of the SMA length using the electric resistance characteristics of SMA. Therefore the developed hand is possible to perform dexterous hand motions such as tip grasp, precision grasp and lateral hip. Based on a statics analysis of finger mechanism, we estimate the hand grip force. In experiments, we measured the grip force and then compared it to the simulation results. As a result, the maximum grip force was 4.52N by the constant input force, 13N, when the MCP joint angle was 90 degrees.