Research On Load Stiffness Adaptive Control Method Of Electro-hydraulic Servo Testing Machine

The electro-hydraulic servo testing machine can test the performance of specimens,and in research of dynamic and static analysis,design,control strategy and simulation,the theoretical model of control system is changing as the differences among test subjects.The dynamic characteristic of the electro-hydraulic servo system can be different according to the variation of loading and controlling.In the case of elastic loading,particularly in the force control system,the variation of testing stiffness act as a vital role in the electro-hydraulic servo testing system.In this article,the elastic loading force control system of electro-hydraulic servo testing machine is taken as the study object,and considering the problem that theoretical model always changes with different specimen in controlling system,a solution of model reference adaptive control with minimum deadbeat response is proposed.Through setting appropriate adjustable parameters,the controller can make the actual output of the electro-hydraulic servo testing machine have a good tracking effect on the output of the reference model when the test pieces are changed.so that the system can achieve fast response and the overshoot is2%,which reduces the influences of testing stiffness variation on dynamic performance of the system.The main contents of this article includes:(1)Taking the electro-hydraulic servo testing machine as study object,and through the overall analysis of the system,the theoretical model of flexible loading force control system whose performance vary greatly as the stiffness variation is modeled.Based on the foundation an analysis is carried out qualitatively to find out the influence against different specimen stiffness.(2)Aiming at the problem of variable stiffness in electro-hydraulic servo testing machine,the model reference adaptive control strategy is proposed and make a description on the control system that utilizing I/O model reference adaptive.Based on the Lyapunov stability theory,the adaptive controller structure,parameter adaptive regulation rule,adaptive control law and control algorithm are deduced detailedly when the relative order of the controlled object is 1 and 2.(3)Through determining the parameters of electro-hydraulic servo testing machine,the specific structure of the transfer function about the control system is obtained.By selectingstiffness values of five different test pieces,the influence of different stiffness on the dynamic performance of the system is analyzed quantitatively,and through the conventional PID controller to simulate the control system.(4)Based on the principles of minimum deadbeat response system and strict positive real function,the third-order minimum deadbeat control system with minimum overshoot and fast response is selected as the reference model.According to the structure of electro-hydraulic servo testing machine's transfer function,the simulation model of model reference adaptive control system with relative order of 1 is established by using MATLAB /Simulink,and the simulation experiments are carried out through the step signal and sine signal input.(5)Through designing the hardware and software of control system,the model reference adaptive platform of 10 KN electro-hydraulic servo testing machine is built,and the field debugging test is carried out to verify the model reference adaptive controller based on the minimum deadbeat response which have good validity and feasibility to solve the variable stiffness problem of the electro-hydraulic servo testing machine.