Development of a servo-hydraulic system with a self-tuning fuzzy PID controller to simulate injection molding process

This study designs an experimental system to simulate two controlling stages, namely injection and packing, in the injection molding process. During the injection stage, injection speed is the main concern while during the packing stage, packing pressure is the main concern. A servo-hydraulic system that uses servo motors and hydraulic pumps to provide energy for injection molding, which combines the advantages of a hydraulic injection molding machine (e.g., small volume but high working force) and an all-electric injection molding machine (e.g., quiet, energy efficiency, stable working performance), is investigated in the experimental system. Hence, the experimental system includes a servo motor and a pump. Because of the fast response requirements of hydraulic systems, it is necessary to apply a microcontroller unit (MCU) in the servo-hydraulic system with a proper sampling rate and a good control algorithm in order to meet the expected performance specifications. In order to determine the optimal sampling rate, MCUs with different sampling rates were applied in the experiment. Additionally, it is difficult to use a proportional–integral–derivative (PID) controller to meet the expected performance specifications for non-linear systems such as hydraulic systems. Thus, a self-tuning fuzzy PID controller is designed so as to provide the experiment system with a better response and more stable packing pressure control. The self-tuning fuzzy PID controller with a high sampling rate was applied in the experimental system in order to meet the performance requirements of a servo-hydraulic system for an injection molding machine.