Design And Implementation Of Injection Molding Machine Hydraulic Servo System

With the development of injection molding technology, the application of plastic product is expanding. The control system of injection molding system needs to meet the higher demand. Cost control plays an important role in injection molding machine manufacturing industry. So making the cost as little as possible is one of the biggest features. Improving the control precision becomes extremely important while maintain the same hardware system.This paper is on the base of injection molding machine of B&R Company. Firstly, introduce the concepts of mold opening and closing, mold locking, injection and holding pressure. Analyze the composition of the injection molding machine and working principle, through introducing the process of injection molding machine, analyze the objectives and requirements which the control system should meet. Then build the servo valve model and the valve controlled hydraulic cylinder model based on the hydrodynamics and the classical control theory. With the models, the speed close-loop control and the method of the speed sectional control in injecting and keeping pressure are analyzed. Besides, the variations of the injection speed and the system pressure, the mutual influence between the two variables and the method of the pressure switching are also analyzed. Finally, the detailed scheme of control system and control algorithm is given. And the scheme is tested by experiments.Conventional PID controller in industrial control has good effect, but the injection molding machine hydraulic servo system requires high precision, fast response of the control. PID controller can't satisfy the requirement. In this paper, feedforward control is added to PID controller to improve the speed and precision of control. The advantage of PID is used enough. Because of the fast and simple characters of feedforward, feedforward control can compensate the disadvantage of PID control. In the feedforward control of injection molding machine, prediction algorithm is used to improve the reaction speed of controller. The signal of switching speed is not given by position feedback. Estimate the time switching point according to the current speed and set speed. The switching signal is given by controller own timer to improve the speed of response. At the same time, decide when the PID control is in operation according to the results of control. Then PID control can be made good use of. In this paper, the design of automatic switching function not only makes up the speed disadvantagement of the traditional PID controller, but also eliminates the static error of PID controller. Use Matlab software to compare the effectiveness of different control algorithms and make better the algorithm. Finally, use B&R control panel and IO devices to build on the injection molding machine control system and test the algorithms. The results show that the proposed scheme is effective.