Robust Control of a High-precision Positioning Stage Using an Integrated H∞ and QFT Controller

Abstract

A new three-axis high precision stage is developed in this article, which consists of an X-Y moving platform and a rotational stage on the top of the platform. Piezoelectric actuators embedded in the flexure hinge are utilized to drive the stage and the displacements are measured by laser displacement sensors. To facilitate the design of the device, dynamic models are developed using the Lagrangian approach. The natural frequency of the system is analyzed and compared with the finite element model. Due to the installation and fabrication errors, it is found that the dynamics of the X-Y moving platform is coupled. To achieve better performance, the H_∞ controller for the MIMO system is developed first to eliminate the coupling effects. Variable payloads are considered in the design process to achieve system robustness. Then, the H_∞ controller is then reshaped using the QFT. The noise and control efforts are reduced significantly after applying the QFT technique. The results demonstrate that the coupling between the X-Y axes can be reduced with the integrated H_∞ and QFT controller. Moreover, the settling time and positioning accuracy for a 10-µm step input are less than 0.1 s and 0.3 µm, respectively.

Keywords

flexural Hinge positioning stage H∞ controller QFT control loop shaping.

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