DEVELOPMENT OF EMG CONTROLLED PROSTHETIC FOREARM USING ULTRASONICMOTORS

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In developing an artificial device, eg. a prosthetic forearm, which is used by a person to overcome disability, the following points have to be considered : (1) its manipulability should be simple and casy ; (2) its appearance should be physically similar to the actual limb ; (3) its weight should be light ; (4) its operating noise should be negligible, or nearly negligible ; and, (5) its power supply should be small and lightweight, In addition, the capability of the prosthctic device to mimic the response of the actual limb with respect to voluntary motor commands and to environmental loads should be addressed.We developed an EMG controlled prosthetic forearm with three degrees of freedom actuated by small size ultrasonic motors. Its weight is less than 700 g and the size is the same as the adult's forearm. The conventional prosthetic arm using DC motors produces a motion noise. So the reduction of the motion noise was one of the big problems to be soleved. Since our prosthetic forearm uses ultrasonic motors, it produces no motion noise. In addtion, the amputee can control six kinds of motions i. e. pronation and supnation of the forarm, flection and extension of the wrist, and grasping and hand-opening. The interface between the amputee and the prosthetic forearm was designed on the basis of the fact that the amputee still preserves the phantom limb motor map after amputation. It can discriminate the amputee's intended motion among six kinds of motions using the EMG signals from the remained muscles and also produce the command signals to control the prosthetic arm. Consequently, the amputee is able to manipulate the prosthetic arm as he intends and hes control load is relieved sharply.