The Application Study Of Electro-Hydraulic Control Systems For Injection Molding Machine Based On Fuzzy PID Controller

Injection molding is a machine which can mould some product of some special shapes quickly. It contains four working process, melting, injecting, keeping pressure and cooling. Injecting process is electro-hydraulic displacement serve control system, and keeping pressure process is electro-hydraulic force serve control system.Because of different mould pattern, elastic load is constantly changing in the keeping pressure process, and when system switch from injecting process to keeping pressure process which is actual switching from electro-hydraulic displacement serve control system to electro-hydraulic force serve control system, there maybe wallop, so it is impossible that system can have a good performance using PID controllers. Base on this character, this paper will use fuzzy controller to apply some parameter varieties. However, because of fuzzy controller's structure, it can't have a good precision. So this paper absorb the advantages of fuzzy and PID controller's, it use a control methods of fuzzy PID controller (FPC). FPC has some structure forms, such as fuzzy turning PID controllers, fuzzy and PID controller combination, and optimizing fuzzy controller so on. The paper refers the working principle and decision of this FPC in keeping pressure process for injection molding.Fuzzy turning PID controller is the controller which changes the three parameters of PID controller by the error and error's varieties of systems, so it can adapt some parameters'varieties for system. Fuzzy and PID controller combination also can adapt some parameters'varieties by corporate output of fuzzy controller and PID controller, and it improves system's precision and response. The fuzzy controller with a fitted modifying factor adjust the weight of error and error change in the control rules with mutative error. According to the mutative error, the fuuzy congtroller parameters can be adjusted online using the tuning factors.By simulating of MATLAB for system and doing experiment with RTW toolbox applied in this system, we can get the performance of system by PID controller and FPIDC.In injecting process and keeping pressure process and switch of two process, compare FPIDC with PID controller when two methods control the system indivisually, and confirm the best controller.