Force sensorless pressure control considering nonliner friction phenomenon for electric injection molding machine

Currently, most plastic products are manufactured using injection molding machines. The quality of products produced this way depends largely on the injection force. In the force control system of a typical injection molding machine, force information from the machine´s environment is obtained by a force sensor. However, these sensors have several disadvantages, which include signal noise, sensor cost, and a narrow bandwidth. Thus, sensorless force detection methods are desirable. The use of a reaction force observer, based on the two-inertia resonant model, has been proposed. However, this method is inaccurate due to the influence of nonlinear friction phenomenon. We have previously proposed a new injection force estimation method based on a high-order reaction force observer (HORFO), which is not significantly influenced by the nonlinear friction phenomenon. In this paper, an automatic parameter-switching HORFO (APS-RFO) is proposed to improve the estimation accuracy of HORFO. Moreover, this paper evaluates the possibility of a sensorless force control system using the proposed APS-RFO.