Research On The Motion Control Method Of Knee Joint Based On Functional Electrical Stimulation

In recent years,the number of stroke patients and spinal cord injury patients has been increasing year by year,and the number of patients with lower limb dyskinesia has also increased.Therefore,it is urgent to use devices to assist the recovery of walking.Functional electrical stimulation is a therapy that uses low frequency electrical pulse sequences to manually activate paralyzed muscles.Due to its advantages of simple operation and portability,it has been widely used in the rehabilitation of limb functions.However,exercise rehabilitation based on electrical stimulation is susceptible to factors such as muscle fatigue and external interference,and it is difficult to produce a quantitative joint motion output,thus limiting its application in gait rehabilitation.In this paper,the law of joint motion output under muscle stimulation and the influence of the change of stimulation parameters on muscle output are studied,a feed-forward feedback closed-loop control method based on Hill-Huxley inverse model and PID feedback control is proposed to realize the motion control of lower limb knee joint.Experiments prove that this method can reduce the influence of muscle fatigue and external interference on the control effect,and prove its feasibility in gait control.The specific research contents of this paper are as follows:(1)Improved design of electrical stimulation system based on array electrodes.Firstly,the basic principles of electrical stimulation are analyzed based on the physiological basis of electrical stimulation.The generation process of muscle action potential and the mechanism of muscle contraction force are elaborated.Secondly,in order to solve the problem of low output angle in the existing electrical stimulation system,array electrodes are adopted to improve the design of the electrical stimulation system.Finally,the electrical stimulation experiments are carried out with the improved electrical stimulation system.The experimental results show that the multi-electrode combination stimulation mode using array electrodes improves the experimenter's stimulation comfort and the stimulation output angle compared with the single electrode stimulation system before improvement.(2)Analysis of muscle fatigue under electrical stimulation.Firstly,the mechanism of muscle fatigue during electrical stimulation is analyzed.Secondly,muscle fatigue is analyzed by electromyographic signals.Finally,the effect of stimulation parameters on muscle fatigue is analyzed.The results show that the stimulation pulse width has the least effect on muscle fatigue,and the stimulation amplitude has the greatest effect on muscle fatigue.This result provides a basis for the follow-up study of knee joint electrical stimulation control methods.(3)Research on knee joint motion control method based on electrical stimulation.Firstly,the passive pendulum experiment and the electrical stimulation experiment are designed.Based on Hill-Huxley model,the relationship between stimulation pulse width parameters and knee joint motion angle is obtained.Then,the inverse of the model is calculated,and the relationship between knee joint motion angle and stimulation pulse width parameters is obtained,which provides a theoretical basis for knee joint angle control.Finally,in order to reduce the influence of nonlinear characteristics of human lower limb muscle system,a feed-forward control system for knee joint motion control is established based on Hill-Huxley inverse model,and combined with PID feedback control to form a feed-forward feedback controller,which improves the accuracy of knee joint motion control under electrical stimulation.(4)Experimental study on knee joint motion control based on electrical stimulation.The experimental system of knee joint motion control based on electrical stimulation is established,and control method comparison experiments,external interference experiments and muscle fatigue experiments are carried out.The results show that compared with the feed-forward control using Hill-Huxley inverse model alone or PID feedback control,the proposed feed-forward feedback control method has weaker time delay phenomenon(the average time delay error of 10 subjects is 1.59s),and more accurate joint motion control(the average root mean square error of knee joint angle of 10 subjects is 4.457°).At the same time,it can automatically adjust the stimulation pulse width to improve the tracking accuracy of knee joint angle during external interference and muscle fatigue.The research in this paper realizes the control of knee joint based on electrical stimulation,and also provides a research foundation for lower limb rehabilitation training such as lower limb gait control under electrical stimulation.