Synergistic design of a humanoid hand with hybrid DC motor - SMA array actuators embedded in the palm

A new approach to the design and control of multi-fingered hands using hybrid DC motor - shape memory alloy (SMA) array actuators is presented in this paper. The fundamental design concept is based on the principle of motor control "synergy", a biomechanics terminology of coordinated motion generation. A couple of DC motors are used for driving multiple fingers with a particular velocity distribution over a vast number of finger joints corresponding to the direction of the most significant synergy. Principal component analysis is used for determining the most significant direction and the residual directions. SMA array actuators are used for driving the fingers in the residual directions. Although many actuator axes are needed for spanning the residual space, the required strokes are much shorter than the most significant direction. Compact and high energy-density SMA actuators meet these requirements. The paper presents synergistic integration of these two types of actuators having diverse characteristics. This allows us to embed all the actuators and transmission mechanisms in the palm, eliminating a bundle of tendons crossing over the wrist joints. An initial prototype hand is designed and built.