Fuzzy logic controller for a retrofitted closed-loop injection moulding machine

Abstract For the purposes of producing precise products and providing the flexibility for products variation, an open-loop control commercial injection moulding machine is retrofitted into a closed-loop control system for monitoring the filling and post-filling phases of the injection processes. The hydraulic control unit, control and interface circuits, safety limit switches and personal-computer-based controller were redesigned and constructed. Since the injection moulding processes have complicated non-linear dynamics and model uncertainty, the application of a classical proportional-integral-derivative controller has adaptivity and robustness problems, especially with regards to the pressure control during compression phase. Here, an intelligent fuzzy controller is employed to adjust the injection speed of the filling phase and to control the nozzle pressure of the post-filling phase. The experimental results show that this controller has good performance in actual injection moulding processes.