Design And Research On Posture Control Loop For FES Unsupported Standing

Function Electrical Stimulation (FES) is a cross-area advanced technology that generally refers to the artificial electrical stimulation of muscles which lost nervous control with surface or implanted electrodes in order to provide muscular contraction and produce a functionally useful movement. FES includes many application forms in the area of rehabilitation engineering and unsupported standing technology with FES is one kind of rehabilitation systems for paraplegic lower limbs. It's a challenging research direction in the area of rehabilitation engineering. Currently, for clinical application, people often apply open-loop function electrical stimulation to knee extensor and such balancing is feasible under the support of both intact arms. In this thesis, a closed-loop posture control system for paraplegic ankle joints was designed with the aim of realizing unsupported standing without the support of both arms which is known as"Unsupported Standing".Foreign and domestic research background and current state were discussed in detail in this thesis. With referring to former research achievements, simulation research on posture control for unsupported standing was carried out primarily. Firstly, the mechanism and effect of spinal cord injury were introduced briefly and that which kind of patients is appropriate for research interest was determined from above introduction. In addition, such paraplegic subject was conceptualized as an under actuated double inverted pendulum structure with two degrees of freedom and the dynamic model was developed utilizing Lagrange theory. Then, torque equations for both upper trunk joint and ankle joint were deduced. Secondly, an optimal controller was designed with the optimal control theory and the optimal control criteria is that it minimizes a cost function that estimates the effort of ankle joints via observation of ground reaction force position, relative to ankle joint axis. Finally, a PD controller, utilizing a random reference input, was used to simulate the intact upper body task. Considering the optimal controller and the Kalman state observer which was used to estimate the system state, the whole posture control system was designed. Then a young Chinese man who is 162 centimeter tall and weights 55 kilogram was taken as a sample, all data were calculated and simulation research was performed on the whole control system. The simulation results indicate that only a small torque in the ankle joint can maintain the paraplegic human body's balance. Thus the paraplegic subject is able to achieve a relative long-time standing in theory level without the support of both arms. All research results here contain a certain theoretic meaning for clinical application of unsupported standing with FES.