Enhanced Observer-Based Repetitive Control for Tip-Tilt Disturbance Rejections Beyond Control Bandwidth in Optical-Stabilized Systems

Abstract

The stabilization and tracking performance of an image-based tip-tilt system is usually deteriorated by tip-tilt vibrations and beam jitter in optical links due to a limited tip-tilt correction bandwidth. This paper proposes an enhanced observer-based repetitive control (OBRC) method to break the bandwidth limitation of the time delay tip-tilt stabilized loop, which achieves high-frequency disturbance rejections beyond control bandwidth even up to Nyquist frequency. The enhanced repetitive controller is fused with the optimized observer based on Youla parameterization, which improves the stability of the closed-loop and reduces the waterbed effect in non-repetitive frequency. Furthermore, the time delay of the closed-loop system could be compensated by the OBRC. Therefore, disturbance suppressions can be transformed into the design of a repetitive controller, which is effective and easy to be used for tip-tilt vibrations and beam jitter suppression. Finally, simulation and experimental results show that the OBRC effectively suppresses the high-frequency disturbance beyond the control bandwidth of the optical-stabilized system.