Research On Position/Force Control Strategy Of Pump-valve Compound Electro-hydraulic Servo System

For large hydraulic control systems such as hydraulic presses and straighteners,in order to meet the requirements of the molding process,it is necessary to simultaneously control the position and pressure of the working mechanism.At present,large hydraulic control systems at home and abroad use valve control systems,which has the problem of energy waste.In this paper,the valve-controlled open and pump-controlled closed parallel drive hydraulic actuator circuits are applied to the application of position / force composite control.The research work is carried out from three aspects :coordinated control strategy,position and force composite control strategy and loop control algorithm,and the AMEsim-MATLAB joint simulation model is established.A coordinated control strategy of pump control and valve control loop is designed for position force compound control.Based on the analysis of the principle of pump-valve compound drive hydraulic circuit,a position-force compound control scheme is proposed.The coordination strategy of pump control and valve control loop is designed.The working loop is switched according to the running state of the system.The pump control loop works in the dynamic operation process,and the valve control loop works in the position and force control stage.The simulation shows that the system efficiency is improved compared with the single valve control system.Aiming at the impact problem during position force switching and the parameter perturbation of electro-hydraulic system,an impedance control strategy based on force internal model is proposed.A double-loop control scheme with force control as the inner loop and impedance control as the outer loop is designed.Based on the mathematical model of valve-controlled cylinder force,the force internal model controller is designed.The simulation shows that the simultaneous control and smooth switching of position and force are realized,and the dynamic response performance is good and the robustness is strong.Aiming at the slow dynamic response of the pump control loop and the different characteristics of the asymmetric cylinder when extending and retracting,a fuzzy PID controller with compensation factor is designed.The fuzzy PID control is the main controller,which is compensated by the bidirectional operation characteristics of the compensation factor.The fuzzy PID controller and the fuzzy inferencer of the compensation factor are designed.The simulation shows that the response speed of the pump control position control system is improved,and the two-way operation characteristics of the asymmetric cylinder are the same.