Research And Application Of Hydraulic Servo System Control Algorithm

With the development of hydraulic servo control technology and wide use in more areas, the higher capability of hydraulic servo control system is required more and more. The hydraulic servo control system is a complex system with time-delay and nonlinearity, and usually is affected by unpredictable disturbance, so it is important to research an appropriate control strategy to improve the control precision.This paper is based on hydraulic servo control in injection molding machine of Shanghai B&R Company, firstly the servo valve model and the valve controlled hydraulic cylinder model based on the Hydrodynamics and the classical control theory are built, then the models of the position servo system and the velocity servo system are deduced, and then the stability of the system and the influencing factors of the system error are analyzed. Combining with the hydraulic system of injection molding machine, the concepts of mold opening and clamping, mold locking, injection and holding pressure are introduced. In mold opening and clamping section, the speed close-loop control and the method of the speed sectional control are analyzed. In injection section, the variations of the injection speed and pressure, the mutual influences, and the method of the pressure switching are analyzed. And also, this paper gives the implementation method of the step injection. Since the speed and the pressure are influenced by time-delay and nonlinearity, researching a control strategy not depending on the model completely is necessary, and has practical significance.The conventional PID Controller is suitable for the linear system, but not for the injection molding machine system, because of the nonlinearities and model changes. In this paper, combining with the advantages of PID Control, and on the base of the PID Controller and the Fuzzy Control Theory, the Fuzzy Control is used to modify the three parameters of the PID Controller. The hydraulic system of the injection molding machine always changes with time, so the control performance and precision will be affected. Whereas the Quantization Factors and the Membership Functions (MF) in conventional Fuzzy-PID Controller are fixed, the real-time performance and the applicability will be limited. So adjustable parameters are introduced to Fuzzy-PID Controller, by this, the Quantization Factors and the MF can be regulated with the system changing.The Fuzzy-PID Controller with adjustable parameters designed in this paper, not only remedies the lack that PID Controller can't adjust the parameters on-line, but also reduces the static error in Fuzzy Controller, and also enhances the adaptability. Simulations in Matlab and the experiments in injection molding machine showed that the stability of the system is better, the accuracy is higher and also the applicability is stronger, compared with PID Controller.