FESによる関節角制御システムの改善と負荷問題(1部神経・筋・制御)

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Control of joint angle or muscle force using functional electrical stimulation (FES) should be carried out with a feedback controller to obtain better performance of paralyzed extremities since the feedback system provides less tracking error and better command response than using open-loop system. Some FES systems involving the feedback controller have ever been proposed for assistance of exercise of the paralyzed lower extremities. We proposed a new joint angle control system using FES with the digital PID controller for the bidirectional movement of flexion and extension, some problems in the joint angle control were discussed and the controller was improved in this study. The design method of the digital PID controller was as follows: (1) the transfer function of the controlled subject in discrete time was obtained by the system identification using least squares algorithm, (2) the transfer function was converted into continuous time region, and (3) optimal parameters of the controller were determined with the transfer function using a model matching design method. Two different controllers for the flexor and the extensor were designed from each set of open-loop characteristics. Using the PID controller designed by this method, joint angle control of ankle and knee joint in the free state was carried out with normal subjects. Although some problems remained, a response was obtained to the command angle. One of the problems was oscillatory behavior or large overshoot in the step response of the joint. A command filter consisted of third-order Butterworth LPF with unit gain offered less overshoot and good stability in the step response. Another problem was due to stimulus electrode and stimulating position. We stimulated efferent nerves at the motor-point since the surface electrode was easier to use than an implantable electrode. Although the surface electrode could not apply stimulation to the nerves in the deep region, muscle stimulation was made at the optimal point with carbon-rubber electrodes. In addition, joint angle movement was investigated by stimulating the antagonist with constant stimulus amplitude. The result did not provide fine control of the joint movement so that further improvement of the stimulation method of the antagonist must be studied to obtain a better response. In order to improve the FES joint angle control for further applications, the effect of the load change on the joint response was investigated on the basis of the experimental results of open-loop and closed-loop controls. When the load was changed from zero to 5kg, the joint angle was best controlled (with some larger time constant) with the controller which was designed with the open-loop characteristic obtained at the load state. Since actual load was changed by various factors of the subject conditions and was unmeasurable, the load change should be estimated only from the actual nonlinear relation between stimulus amplitude and joint angle. In order to make a linear approximation of the object, adaptive control of the threshold amplitude is most desirable. We are currently studying adaptive control of the joint movement. In conclusion, joint angle control in the free state was attained by using the closed-loop system with a command filter. The effect of load change on the joint movement is discussed and a method of compensation for undesirable behavior is given.
バイオメカニズム学会の論文
1988-06-15

FESによる関節角制御システムの改善と負荷問題(1部神経・筋・制御)

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FESによる関節角制御システムの改善と負荷問題(1部 神経・筋・制御)

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FESによる関節角制御システムの改善と負荷問題(1部神経・筋・制御)