Development of artificial muscle having characteristics of human skeletal muscle

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We have developed artificial muscles made of helically colled shape memory alloy (SMA) wires. this SMA was made by diffusion method in order to reduce metal fatigue and to increase force of during transition. The transition temperature of this SMA for the artificial muscle was 75ﾟC(Af point). As feasible study of control of the SMA muscle, we made a dynamic model of the artificial hand where sophisticated duplicated skeleton system of the forarm and hand was used. Universal joints for robotics were used as joints for connecting each bone. A stainless steel rope was used as an artificial tendon and attached to the prescribed point of the bone where the tendon of each muscle is originally inserted in human. For applying current to each SMA muscle, a multichannel functional electrical stimulation (FES) system which we developed was used. Patterns of current application to SMA muscles were created from EMG data during hand motion recorded from normal volunteers. By using this system, hand motions such as cylindrical grasp and key grip were achieved in the artificial dynamic hand model.Then we have developed a muscle unit by a hellically colled SMA wire. Diameter of this wire was 0.1mm and D/d=5. Number of coiling was 100. Force of transition (contractile force) of this muscle unit was 6 kg/cm2 at 63ﾟC. This value was almost the same as that of human skeletal muscle during maximum contraction. An agonistantagonist system acting to the rabbit elbow joint with the above mentioned FES system was made by connecting the muscle units. It was found that flextion and extension of the elbow was basically controlled by this system.