High-performance sensorless injection force control based on nonlinear friction phenomenon

Currently, most plastic products are manufactured 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, narrow bandwidth, etc. 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. The estimation accuracy of the reaction force observer depends on parameter variations and the non-linear friction phenomenon. This paper proposes a new injection force estimation method based on a proposed high-order reaction force observer, which is not influenced by the nonlinear friction phenomenon significantly. This paper evaluates the effectiveness and the sensorless feedback control of the proposed method through experiments.