Servo Control of Finger MP Joint by Functional Electrical Stimulation of Lumbrical and Extensor Digitorum Muscle

Functional Electrical Stimulation (FES) is a technique to present functional movements by applying electric current to nerve-muscles to induce muscle contraction. In the presentation of hand movements by FES, the flexor digitorum profundus muscle located in the forearm has been used as the muscle that causes flexion. However, the musculature of the forearm is intricate, making it difficult to stimulate arbitrary muscles, and therefore, highly accurate joint angle control has not been achieved. In this study, we aim to realize high-precision servo control of the hand joints by focusing on and stimulating lumbrical located in the hand to increase their independence as a system The performance of tracking the index finger metacarpophalangeal (MP) joint angle was compared when the flexor muscle were flexor digitorum superficialis and lumbrical. Step wave and sinusoidal wave were given as the command values for verification. The root mean square error (RMSE) results showed that the tracking accuracy was higher when the lumbrical was used. In addition, the shape comparison shows that the joints tracked more stably with less vibration when lumbrical was used. In this paper, we proposed a hand joint control system using the lumbrical as flexors. This method is effective for servo control of the hand MP joint angle. Experiments verified the effectiveness of the proposed system.