Optimal design of Youla controller for vibration rejection in telescopes

Niu Shuaixu; Jiang Jing; Tang Tao; Yang Tao; Bao Qiliang

doi:10.12086/oee.2020.190547

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Niu S X, Jiang J, Tang T, et al. Optimal design of Youla controller for vibration rejection in telescopes[J]. Opto-Electron Eng, 2020, 47(9): 190547. doi: 10.12086/oee.2020.190547

Citation:

Niu S X, Jiang J, Tang T, et al. Optimal design of Youla controller for vibration rejection in telescopes[J]. Opto-Electron Eng, 2020, 47(9): 190547. doi: 10.12086/oee.2020.190547

Optimal design of Youla controller for vibration rejection in telescopes

1.
Key Laboratory of Optical Engineering, Chinese Academy of Sciences, Chengdu, Sichuan 610209, China
2.
Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu, Sichuan 610209, China
3.
University of Chinese Academy of Sciences, Beijing 100049, China

Fund Project: Supported by Youth Innovation Promotion Association CAS

More Information

Corresponding author: Tang Tao, E-mail:prettang@gmail.com

Received Date 17 September 2019

Revised Date 29 November 2019

Published Date 15 September 2020

Abstract

Abstract

Vibration rejection is a key technology of telescopes with stable accuracy of μrad level. Due to the low-rate sample and large time delay of the image sensor, the conventional control loop cannot well mitigate vibrations, especially the wideband vibrations with wide range and large energy. On the concept of optimal force design, an improved wideband vibration rejection method based on Youla parameterization is proposed to mitigate vibrations for improving the closed-loop performance of telescopes. In the case that the disturbances frequency can be obtained, this method can mitigate wideband vibrations by designing an appropriate Q-filter to accommodate to the wideband vibrations. The simulation and experimental results show that the proposed method greatly improves the wideband vibration rejection ability and closed-loop performance of the system compared with the traditional proportional-integral control method. In addition, this method can be extended to many engineering projects because of its low dependence and easy implementation.
- telescopes /
- Youla parameterization /
- Q-filter /
- wide-band vibrations rejection

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References

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Overview

Overview

Overview: Vibration rejection is a key technology of telescopes with stable accuracy of μrad level. Because the image sensor has the characteristics of low sampling rate and large delay time, the bandwidth of the control system is limited, and the control system cannot well mitigate vibrations, especially the wideband vibrations with wide range and large energy. Therefore, some new methods of vibration rejections have been developed, such as disturbance feed-forward control, as well as some improved control structures and optimized controls. Although these methods have the advantage of the control loop bandwidth without the limitation of the low sampling rate and large delay time of image sensor, they inevitably have some disadvantages: the closed-loop performance of the system is not only affected by the low-frequency drift and high-frequency noise of the measurement link, but also by the accuracy of the disturbance and the precision of the dynamic model. Therefore, an improved wideband vibration rejection method based on Youla parameterization is proposed to reduce these problems for improving the vibration rejection ability of the system. In the case that the disturbances frequency can be obtained, this method can mitigate wideband vibrations by designing an appropriate Q-filter to accommodate to the wideband vibrations. Considering the stability and closed-loop performance of the system, this paper proposes a novel design method of Q-filter to mitigate wideband vibrations, which is based on that wideband vibrations can be viewed as the multiple narrow-band vibrations with similar central frequencies so that multiple notch filters can be designed to act simultaneously to mitigate wideband vibrations. In this paper, we focus on introduction of the improved wideband vibration rejection method and its stability, and the design of the Q-filter. What's more, experiments are carried out to verify the correctness and feasibility of the method. Because this improved EDOB controller has a low dependence on the system model, the vibration rejection ability of the control system won't be restricted by the noise in the loop. The theoretical and experimental results show that this method can effectively mitigate wideband vibrations and improve the vibrations rejection ability of the system. Furthermore, this control method only utilizes an image sensor that only provide position deviation, which is not only economical, but also convenient to implement. Moreover, this method can be used not only in the tip-tilt mirror system but also in other servo control systems because of its simple structure and design process. Next work will concentrate on automatically designing for the parameters of the Q-filter, so we need to do the online identification of disturbances firstly.