Evaluation of positioning control system using relative displacement observer for precise positioning stages

Precise positioning technologies are widely used for industrial machines such as device manufacturing equipment. There have been many studies on state feedback control systems for precise positioning stages that improve accuracy by using sensor feedback. However, the sensor information cannot always indicate the performance of industrial machines directly because the final requirement of a stage system is generally to adjust a movable table to a target structure. Therefore, the relative relationship between the stage and the target structure must be controlled. However, the stage and other structures must be considered to be elastic elements, especially for precise positioning devices. Thus, this study aims to achieve high-precision relative positioning between flexible structures. The authors had proposed a relative displacement observer which estimated the relative displacement between the stage and the target structure by using only the stage displacement. However, in industrial applications, robustness against disturbances such as modeling errors and aging changes are required. In this paper, we show evaluation results of robustness against accuracy of model identification and aging change in resonant frequency of plant. Results of a numerical simulation show that the proposed control system improves relative positioning performance. And also, we confirm that it has enough robustness against aging change of the stage system.