Injection Molding Machine (IMM) is one of the most important equipment in plastic industry. As a cyclic process, injection molding can be divided into three main stages: filling, packing-holding, and cooling, among which filling and packing are both most important phases for the quality of part, and the corresponding crucial process variables are injection velocity and packing pressure in filling and packing phases. Moreover the determining a suitable injection time, screw position and cavity pressure for transfer from injection velocity control to packing pressure control which is commonly called filling to packing switchover point is also critical for high quality part. This study is concerned with two research aspects: double servomotors synchronization control for injection unit, and filling to packing switchover methods. Two servomotors are synchronized by a hybrid control structure that is a master slave structure with a synchronous controller. Two systems, one is the master, the other is the slave are designed separately and then the synchronous controller is designed. The control system for the master motor includes a feedback controller and a feedforward controller. For slave motor, only velocity is controlled. In order to reduce synchronized motion error, two servomotors are synchronized by a synchronous controller. The relationship between pressure command and velocity command is found by a mathematics way. With proportional controller for pressure controller but the performance can be accepted. The simulation result of switching method based on injection time and ball screw position those are similar, and the result of switching method based on the cavity pressure that is better.

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