Fine force control based on reaction force observer for electric injection molding machine

Currently, most plastic products are manufactured by using injection molding machines. The quality of plastic products depends largely on the injection force. In a typical force control system of an injection molding machine, force information from the machine environment is obtained by a force sensor. However, force sensors have a few disadvantages in terms of signal noise, sensor cost and narrow bandwidth. So, a sensor-less force detection method is desirable for electric injection molding machines. We have proposed the use of a reaction force observer based on the two-inertia resonant model. However, this method has some estimated error because of the influence of nonlinear characteristics of the holding process and the screw back-pressure process. This paper proposes a new injection force estimation method based on a proposed high-order reaction force observer (HORFO), which is not influenced by the nonlinear friction phenomenon significantly. This paper evaluates the possibility and versatility of the proposed sensor-less force control system by using proposed HORFO through experiments.