Analysis And Compensation For Position And Force Control Of Electrohydrostatic System

The exoskeleton robot can greatly improve the strength of the human body under while ensuring the coordination between various human actions and machinery.In other words,the exoskeleton robot can help people realize long-distance marching and load carrying,complete the tasks of investigation,combat and transportation,etc.And it can also assist those with insufficient physical strength in sports and rehabilitation.So the exoskeleton robot has broad prospects for application.Because the hydraulic system has the advantages of large power-weight ratio and fast response speed,the hydraulic-driven exoskeleton robot can better adapt to the requirements of heavy load and high dynamic capacity.The exoskeleton robots have multiple joint degrees of freedom,and each degree of freedom is usually equipped with a highly integrated hydraulic drive unit,which is used for high performance motion control.Hydraulic drive unit can be generally divided into valvecontrolled cylinder system and pump-controlled cylinder system.Compared with the valvecontrolled cylinder system,the pump-controlled cylinder system adopts electro-hydrostatic system.although the control accuracy and response ability are poor,its energy efficiency is higher,which can greatly improve the endurance of the hydraulic exoskeleton robot.However,the electro-hydrostatic system brings pressure-flow nonlinearity,friction nonlinearity,dead zone and other problems.If it can compensate and improve its position and force control performance,it will be helpful to further promote the application of electro-hydrostatic system in exoskeleton robot field.In order to improve the position and force control performance of electro-hydrostatic system,this paper focuses on the following work:(1)The position control and force control systems of electro-hydrostatic system are modeled and analyzed.The composition and working principle of the system are introduced,and the nonlinear mathematical model of position and force control is established with the consideration of pressure-flow nonlinearity.The simulation model is built in MATLAB/Simulink,and the control performance of the position and force control system is analyzed under multiple working conditions.(2)The position control experiment,force control experiment and anti-interference performance test experiment for electro-hydrostatic system are conducted.The Experiment table of electro-hydrostatic system is built,and the hardware and software composition of the electro-hydrostatic system test bench are analyzed.The position control experiment and force control experiment are carried out by using the experiment table to analyze the reason of the poor control performance of its position and force control system.The antiinterference performance test bench of the electro-hydrostatic control system is built,and the anti-interference experiment of the electro-hydrostatic control system is carried out to research the anti-interference performance of the force control system and the adaptability of multiple working conditions.(3)The composite control method of electro-hydrostatic position control system is studied.Firstly,the changes characteristics of friction in the electro-hydrostatic control system are analyzed and the stribeck friction model is established.In view of the influence of friction on the control performance of the position control system,two control methods of nonlinear PID independent of the friction model and friction compensation based on disturbance observer are studied,and the control performance of the two control methods is simulated and analyzed under multiple working conditions.The two control methods are combined to form a composite controller for electro-hydrostatic position control system.The effectiveness of the composite controller is verified by simulation and experiment.The results show that the composite controller can greatly improve the control performance of the position control system.(4)The composite control method of electro-hydrostatic control system is studied.Aiming at the wave distortion phenomenon in the force control system,a harmonic suppression control method based on the least mean square error(LMS)adaptive filtering is studied,and the control effect of the control method is simulated to reduce the interference of harmonic signals to the force control system.Aiming at the phenomenon of flat top in force control system,the nonlinear PID control method of force control system is studied.It and the harmonic suppression control method based on LMS adaptive filter are combined to as the electro-hydrostatic control system composite controller.Simulation analysis and experimental verification are carried out under various working conditions.The results show that the composite controller can improve the control performance of the force control system.Finally,under the interference of different position signals,the anti-interference ability of the force composite controller is simulated,and the anti-interference performance of the force control system is tested on the test bench to verify the simulation results.The results show that the composite controller has certain anti-interference ability.