| The thesis is focused both on a valve-controlled asymmetric cylinder system and a valve-controlled symmetric cylinder system, which are widely used in electro-hydraulic servo systems. The influence of system friction on electro-hydraulic servo system is analyzed. A dynamic friction compensation method is proposed to compensate the system friction force. A hydraulic control system is designed, and the experiment study of the system is done.Based on numerous related literatures and reference materials at home and abroad, the mathematical models of position system about valve-controlled asymmetric cylinder actuator and valve-controlled symmetric cylinder actuator are built and the correlative parameters of system model are calculated. Then the simulation study of the two system mathematical models is carried out, and furthermore, the stability and controllability of the two systems are analyzed.The friction of the two valve-controlled hydraulic systems is measured, and the friction-velocity relationship of the two systems is obtained. Both velocity observer and friction observer are designed, which compose an online friction observer, through which the real time data of the two systems' friction and velocity can be gained, and then the dynamic compensation can be made for the two valve-controlled hydraulic systems friction.Experiment study for the dynamic friction compensation method is performed at last. According to the structure invariance principle, a friction compensation controller is designed by choosing load pressure as the observed value. The experiment results show that by using the dynamic friction compensation method, compared with the PID control strategy, two valve-controlled hydraulic systems have rapid response and high positional accuracy, which proves that the friction compensation is quite efficient in electro-hydraulic servo position system. |
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