Biomimetic myoelectric hand with voluntary control of finger angle and compliance

The purpose of this study was to develop a new type of myoelectrically controlled biomimetic prosthetic hand which has almost the same dynamics as that of the neuromuscular control system of the finger muscles, and in mechanical properties of the muscles and of the stretch reflex. One of the characteristic features of the neuromuscular control system in man is the increase in the compliance around the joint with decreasing activity of the muscle. Our prosthetic hand consisted of two surface EMG signal processing units, a digital servo system for a DC motor and 1 d.o.f. mechanical hand with three fingers. The dynamics of the neuromuscular control system including variation of the compliance around the joint was realized by using a position control system of the finger movement, force feedback and a variable gain which was modulated by the amplitude of IEMGs (rectified and smoothed EMG signals). EMG signals recorded from a pair of antagonistic muscles used to flex or to extend the wrist were used as control signals. It was shown that the finger angle and the compliance of the prosthetic hand could be controlled voluntarily with EMG signals, and that an amputee could grasp a soft object easily with the prosthetic hand. Utility of the biomimetic prosthetic hand was shown by executing myoelectric control experiments in one healthy subject and one amputee.