Perfectly matched closed-loop dynamics based on IP controller for bi-axial contour following

Abstract

This article aims to achieve high contour following performance for bi-axial systems. First, the effects of closed-loop dynamics on the contour following performance are analyzed and it is determined that perfectly matched closed-loop dynamics is preferable. Next, the Integral-Proportional (IP) controller is utilized to control each axis and the parameters tuning method is proposed to achieve perfect matching. The tuning method contains two main parts. One primary part is to establish the relations between the two controller parameters by setting both axes to have the same closed-loop transfer functions. The other primary part is to determine the individual IP controller parameters loop by loop according to the bandwidth index. The design process is correspondingly implemented in two steps. First, the smaller bandwidth axis controller parameters are tuned, and then the other axis is tuned according to the above relations. In applications, feedforward controllers are usually added to enhance the motion performance, whose parameters depend on the individual closed-loop dynamics and can be directly determined. The novelty of this article is that no coupling mechanism is required to perfectly match the closed-loop dynamics and the contour following performance is improved via individual controller design alone. Both the controller and the tuning method are simple and easy to implement, which are of interest to control engineers. Experiments are carried out on an X-Y motion stage, which is commanded to follow diamond and circle contours. Results show that the proposed method can match closed-loop dynamics perfectly and significantly improve the contour following performance.