Actuators for Motion Control: Fine Actuator Force Control for Electric Injection Molding Machines

Currently, most plastic products are manufactured using injection molding machines, where the product quality largely depends on the injection force. In a typical injection molding machines force control system, force information from the machine environment is obtained by a force sensor. However, these sensors have a few disadvantages in terms of signal noise, sensor cost, and narrow bandwidth, and thus a sensorless force detection method is desirable. The use of a reaction force observer, based on the two-inertia resonant model, has been proposed, but this method suffers from some estimation errors due to the influence of nonlinear characteristics in the holding process and the screw back-pressure process. This article proposes a new injection force estimation method based on a high-order reaction force observer (HORFO) with Coulomb friction compensation, which is not significantly influenced by the nonlinear friction phenomenon. Moreover, this article evaluates the possibility and versatility of a sensorless force control system using the proposed HORFO with Coulomb friction compensation.