Reaction Force Estimation for Injection Unit by Disturbance Observer

A force sensor is a very important element of the injection molding machines, because the injection pressure detected by the force sensor is especially important in the injection process. Therefore, such a fault detection method that is independent of the sensor is required. In this paper, an estimation method of reaction force is proposed for the drive system of the injection unit composed of a servo motor and a ball screw. We use a disturbance observer, and its structure is determined for the two-mass damper model. We construct a simplified low dimensional observer and its coefficients are identified from experimental data by the least square method