Robust pressure control of electric injection molding machine using automatic parameter switching reaction force observer

The force control system of a typical injection molding machine obtains force information from the machine's environment via a force sensor. However, because of Force sensors often have disadvantages such as signal noise, high cost, and a narrow bandwidth, a reaction force observer was developed for electric injection molding machines. This method has a steady-state error owing to the influence of nonlinear friction. We realized sensorless force feedback control based on a friction compensation element, dither signal inserting method, and high order reaction force observer (HORFO). The HORFO does not influence either the inserted dither signal or the nonlinear friction phenomenon. However, as the desired parameters of the HORFO cannot be fixed at each driving point, the sensorless force feedback control method cannot always be used for fine pressure control. To overcome this problem, we propose new sensorless force control system based on HORFO in this paper. Experimental results confirmed the robustness of the proposed sensorless force control system.