ヒトの運動制御機構を模擬した義手の制御方式および筋電位処理方式の開発

Abstract

The purpose of the present study is to develop a new type of myoelectrically controlled hand prosthesis (bio-mimetic prosthetic hand) which has the fundamental dynamic properties of the neuromuscular control system of finger muscles, in particular, the mechanical properties of the muscle and of the stretch reflex. The present work attempts particularly to design and implement both a servo mechanism of the prosthesis and a myoelectric signal processor (rectification and smoothing). The neuromuscular system dynamics are estimated by performing stretch experiments with flexor muscles in the human thumb. A key feature of the system is an increase in mechanical impedance (elasticity and viscosity) with an increase in activities of the muscle. A one-degree-of-freedom prosthetic hand with these properties is implemented by utilizing a position control system of DC motor, force feedback and variable gain. The sum of and the difference between rectified and smoothed EMG signals of two antagonistic muscles are used as control signals. The optimal smoothing filter of the myoelectric processor is determined so as to meet the following criteria: (1) the output of the processor agrees closely with the isometric torque exerted by the muscle, and (2) the subject can smoothly control movements of the developed prosthesis with the processor. First, frequency response between the torque and the rectified surface EMG signal is estimated from the isometric contractions of human finger muscles. Three Second-order transfer functions are selected by applying three different criteria of data fitting to the frequency response. Then, the best is determined among these transfer functions by carrying out myoelectric control experiments (pursuit tracking experiments) with normal human subjects. The determined filter has a damping constant of 1.29 and a resonance frequency of 10.9/sec. Usefulness of the developed prosthesis was indicated by myoelectric experiments executed with normal subjects; the prosthesis was smoothly controlled, and behaved softly like a natural limb, in response to disturbance torque.