オンオフ型およびバイオミメティック型筋電義手の3D-CGシミュレータの開発

Abstract

Some kinds of myoelectric prosthetic hand, which use myoelectric signals (EMGs) of muscles as control signals for opening and closing, are used to replace the functions of a natural hand lost by amputation. Chances for an amputee to watch, touch, and use a myoelectric hand are very rare in Japan, because few hospitals give information on them and are provided with actual myoelectric hands. A simulator of a myoelectric hand can enable an amputee to use myoelectric hands virtually. The purpose of this study is to develop a 3 D-CG (three-dimensional computer graphics) simulator of an on-off control myoelectric hand and a biomimetic myoelectric hand. The former is produced by Otto Bock, and the latter was developed by our group. Both prosthetic hands are one-degree-of-freedom units with simultaneous opening and closing of thumb, index, and middle fingers. In the on-off control hand, either opening or closing is determined by the EMG amplitudes of flexor and extensor muscles. In the biomimetic hand, both the finger angle and the compliance are controlled by the EMGs. First, in this simulator, the EMGs are detected with special surface electrodes used for each hand. Second, the finger angle of the prosthetic hand is calculated from the EMGs with the model. Third, positions of the subject's upper limb are measured. Finally, the hand and the upper limb are displayed with 3 D-CG. It was found, in the on-off control hand, that the rate of change of finger angle was dependent on the finger angle. We constructed a model of the on-off control hand; the rate of angle change was determined from the output of the EMG electrode and the present finger angle. Using this model, the finger angle was calculated from the EMG electrode output and the initial finger angle. In the model of the biomimetic hand, an ideal relation between EMG input and finger angle output was utilized, although the real biomimetic myoelectric hand had complex nonlinear properties, such as friction and saturation. Using the model, the finger angle was calculated from the EMG output of the surface electrode. The positions of shoulder, elbow, and wrist were observed with a three-dimensional position sensor, and the posture of the upper limb was calculated. In this simulator, the posture of the upper limb was drawn with a stick picture and the orientation of the prosthetic hand was displayed with 3 D-CG. The experiment was conducted on normal subjects. Watching the 3D-CG of the simulator, they could easily control the finger angle and orientation of the hand.