Research On Compound Anti-interference Control Of Electro-hydraulic Driven Lower Limb Exoskeleton

With the aging of population,the incidence rate of stroke increases gradually.Stroke is one of the main diseases leading to hemiplegia and losing athletic ability.Medicine shows that reasonable rehabilitation training can enable patient s to gain exercise ability again.The lower extremity exoskeleton is a kind of special robot that assists the rehabilitation training of patients.Model-based control is an effective method to improve the control performance of exoskeleton.However,due to the inaccurate modeling and unknown interference of the lower limb exoskeleton,it has a great impact on the precise control of exoskeleton trajectory.In this paper,the following exoskeleton is the research object,aiming at improving the track tracking performance in the case of modeling error and external interference,the following research work is carried out:(1)Design a kind of lower limb exoskeleton,including mechanical structure,hydraulic system,data acquisition and control system.ABAQUS is used to analyze the stress and strain of the leg connecting rod,so as to improve the structural rigidity under the premise of ensuring the strength.Design the hydraulic system of exoskeleton based on the principle of power matching.For the purpose of easy programming,the control scheme based on rapid control prototype technology is determined.(2)Kinematics and dynamics model of lower extremity exoskeleton based on geometric relation and Lagrange method.Solving the transfer relationship between the displacement of hydraulic cylinder and the joint angle.The natural frequency of valve controlled asymmetric cylinder is derived,and then the mathematical model of hydraulic power components of valve controlled asymmetric cylinder is established.The whole dynamic model of the lower limb exoskeleton is established by combining the dynamic model of the mechanism,and the simulation is carried out by using MATLAB/Simulink software.(3)Considering the model uncertainty and external interference of lower extremity exoskeleton.The parameter model of exoskeleton is identified by recursive least square method,and then an improved sliding mode controller is designed and its stability is analyzed.The observability of exoskeleton system is studied and an extended observer is designed.Analysis of disturbance rejection mechanism and robust stability of observer.(4)Experimental verification of the proposed control method.Firstly,the PI controller is used to verify the influence of load disturbance on trajectory tr acking performance,and then the interference suppression performance of sliding mode controller is compared and verified.The nominal model error is obtained by frequency sweep technique,and the filter bandwidth of the observer is determined.Based on the PI controller,the disturbance suppression effect of the observer is verified.Finally,the chattering reduction of the output of the sliding mode controller by the observer is verified.