Research And Application On The Position Control System Of The Electro-Hydraulic Proportional Valve-Controlled Cylinder

In recent years, with the development of the electro-hydraulic proportional control technique, the electro-hydraulic proportional valve gradually replaced the servo valve because of its low cost, good anti-contamination capacity. Due to its simple structure , excellent reliability, the electro-hydraulic proportional valve controlled hydraulic cylinder of the position servo controlled system has abroad application in different fields, especially the industry.According to the requirements of the numerical control hydraulic bending machine, a single-rod hydraulic cylinder, whose cylinder barrel is fixed, is selected as the actuator, but it's more difficult to carry out servo control because the asymmetric single-rod hydraulic cylinder is controlled by the symmetry valve port direct-acting electro-hydraulic proportional direction-valve. According to these characters, high quality controllers are designed to focus on both point-to-point and continuous tracking control. The main contents are shown as follows:Firstly, the hardware experiment platform is established on the basis of analysis about the system structure and working principle. The real-time controller is carried out by the software Labview and Matlab. According to the electro-hydraulic proportional control characters, the mathematic models on the different parts of system is established by detailed analysis and then simplified, the model shows that the system is high order and nonlinear. The voltage of the proportional valve middle position and the system acting dead band is also determined during the experiments. The I/O characters are well understood, which is the basis of the controller design.Secondly, a PID controller is designed for the system, during the experiments of responding the step signal, square wave signal and sine signal, it is found that there are some disadvantages of the PID controller in this nonlinear system. In the step signal, square wave trajectory tracking experiment, the error is very small on the point-to-point control in single direction. But for the continuous tracking control experiment, the error is a little big, especially in the direction reversing process. The PID controller with subsection is developed and some effects are obtained . But generally, the error is still big and the response is unstable.In order to solve the above problems, a general fuzzy controller and a self-adaptive fuzzy-PID controller are developed and a mass of experiments are carried out. The result shows that the general fuzzy controller isn't able to eliminate the stable error, although which has a fast square wave response. That is decided by the essence of the fuzzy controller. So the self-adaptive fuzzy-PID controller is adopted, the result shows that the precision of sine wave response in a certain frequency bound is improved and the adaptive ability is enhanced. So the fuzzy controller is stable and effective.Finally, for the shortages and disadvantages still existing in this study, some suggestions and expectations are put forward for further research.