Investigation of an Appropriate Nominal Model and High-Precision Positioning of Large-Scale Stage Using Perfect Tracking Control

Abstract

Stages are widely used as positioning devices in industrial fields. One of the applications of these stages is the precise manufacture or accurate measurement of large-scale parts. For improving the production efficiency, it is necessary to increase the stage size as well as the positioning speed. In the vertical drive of such a stage, an air spring covered by high-polymer materials is used for supporting heavy weights. This spring is viscoelastic with low-frequency resonance modes. Moreover, the stage has many mechanical high-frequency resonance modes. Therefore, a high-bandwidth feedback controller cannot be realized, and the low resonance modes hinder fast and precise positioning. Hence, realization of an accurate feedforward controller by using an appropriate model is of utmost importance.
In this study, we designed three nominal models and identified the model which is the most appropriate for the vertical drive of a large-scale stage. Then, we show the advantages of the vibration suppression perfect tracking control (VSPTC) by using the fourth-order Maxwell model. Furthermore, we confirmed that a combination of a VSPTC and a disturbance observer using the same nominal model delivers a good performance by performing simulations and experiments.