Development of sensorless force control system based on nonlinear friction phenomenon for electric injection molding machine

Abstract

Currently, most of the plastic products are manufactured by using injection molding machines. The quality of the products depends largely on the injection force. In a typical force control system of an injection molding machine, the information about the force in the machine environment is obtained by a force sensor. However, force sensors have a few disadvantages such as signal noise, high sensor cost and narrow bandwidth. We have proposed the use of a reaction force observer based on the two-inertia resonant model. However, this method has some estimated error caused by a static friction in the holding process and a Coulomb friction in 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 the proposed high-order reaction force observer (HORFO), which is not influenced significantly by the nonlinear friction phenomenon. The effectiveness of the proposed method is confirmed by experimental results. © 2011 The Institute of Electrical Engineers of Japan.