PID Controller With Variable Parameters For Packing Pressure Of The Injection Molding Process

Injection molding is a widely applicable polymer processing technique for manufacturing plastic products. Controlling of the key variables in the process is very important which affects the quality of injection molding products. Packing pressure, which has obvious nonlinear and time-varying characteristics, is a key variable in the packing stage. Therefore, the modeling for injection packing stage, which can accurately describe the process, has a positive effect on the control of process variables. PID control method, with a simple structure and good robustness, is frequently used in the modern industrial production such as the injection molding. To deal with the complex properties of the packing stage, this work studies the design of a PID controller with variable parameters for the packing pressure of the injection molding.The original contribution of this thesis is summarized as follows:1. Developing the LPV (Linear Parameter Variable) model of packing stage based on the characteristics of the process. The precision of the model has been tested and the results reveal that the model can accurately describe the packing stage of injection molding process and the model can be applied to the close-loop control of PID controller effectively.2. Combining the LPV model of injection packing stage with internal model PID parameter tuning methods, the tuning for PID controller has been implemented. A PID controller with variable parameters of closed loop has been designed and validated on an industrial injection molding machine. The results indicate the performance and the practicability of the control method proposed in this work.