Research On Force-Position Switching Control Of Electro-Hydraulic Servo System

Switching between position control and force control is more and more in the electro-hydraulic servo system. The system will produce adverse effects when both switching, such as parameters transition and jitter, having a serious impact on the performance of the electro-hydraulic servo system. Therefore, Research on the control method of the smooth switching between force and position is one of the problems to be solved of the servo control technology. In order to achieve the smooth switching between force and position of the electro-hydraulic servo system, a force-position switching control method used in the electro-hydraulic servo comprehensive testbed is mainly studied.Based on the servo control theory, for the electro-hydraulic servo comprehensive testbed, the mathematical models of servo valve, hydraulic cylinder, servo amplifier, and the sensor are established, and thus the transfer functions of position servo system and force servo system are obtained, which provides a prerequisite for the smooth switching between force and position.In order to solve the problem of the conversion between multiple control variables, a fuzzy-PID controller based on fuzzy switching is put forward, when the hydraulic cylinder contacts with the mechanical objects, fuzzy controller is designed to achieve the control requirements of the nonlinear and time-varying systems; when the hydraulic cylinder is far away from the mechanical objects, the PID controller is designed to achieve precise control of the position; meanwhile, according to the variation of the feedback force, the correction factor is controlled to achieve the fuzzy switching to ensure a smooth transition between the two controllers.In order to verify the feasibility of the algorithm, PID position controller, fuzzy force controller and fuzzy switching controller are established, and these controllers are applied to electro-hydraulic servo system, meanwhile the simulation analysis is performed.The experiments are carried out under the MATLAB/SIMULINK, and the real-time control is performed on the electro-hydraulic servo testbed through the Real Time Windows Target. The proposed control method is applied to the electro-hydraulic servo comprehensive testbed to verify that the control strategys of fuzzy switching controller are feasible and the mathematical models of the electro-hydraulic servo system are accurate.