Research On Control And Simulation Technology Of Large- Aperture FSM Mechanism In Space Telescope

In order to ensure the dynamic stabilization imaging of the space Telescope in astronomical observation,the spacecraft platform of the telescope is complete with the attitude control,and the telescope itself needs to take vibration suppression and precise stabilization control measures,so that the influence of the external disturbances and the system control deviation on the telescope visual axis is within the target range.The Precision image stabilization system can restrain the low-frequency disturbance while it completes the fast and accurate tracking of the observation target,which requires the precise image stabilization control system to have sufficient bandwidth and strong restraining disturbance ability at low frequency under the limitation of structure base frequency.This paper mainly focuses on the high precision image stabilization requirement of large aperture space telescope,carries out the research on the control method of the fast sweeping mirror(FSM)with a diameter of 400mm×400mm and a structure base frequency of 70 Hz,which is driven by a piezoelectric ceramic(PZT)in a precision image stabilization system.The main tasks accomplished are:Firstly,a survey was conducted on the advanced space telescopes using FSM image stabilization in the world,and the working principle and technical development of the large-aperture FSM were analyzed and compared.Secondly,the disturbance characteristics are obtained by analyzing the disturbance data of the telescope,the image stabilization scheme composed of the vibration isolation system,the attitude tracking system and the precision image stabilization system is proposed in combination with the structural characteristics of the system.Thirdly,the hysteresis of PZT was modeled by the Duhem model and the control system was designed to eliminate the hysteresis effect of PZT.The RMS error of the actual displacement and target displacement of PZT was 83.6nm under the signal driven by 10 Hz frequency.Fourthly,used sweep method to obtain the mathematical model of the large-aperture FSM system identification,then used the optimal Hankel norm approximation algorithm to reduce the transfer function to facilitate the subsequent controller design.Fifthly,Based on the optimal PID,linear quadratic Gaussian(LQG)and H? algorithm,the FSM controller was designed and simulated,and the simulation results show that the bandwidth of the system reaches above 20 Hz and the error suppression bandwidth reaches above 10 Hz.Sixthly,combined with Adams,a mechanical dynamics software,an integrated simulation system was built in Simulink to simulate the precision image stabilization system.The simulation results show that the designed control system has a good effect on the disturbance caused by the platform and the system bandwidth reaches 20 Hz.The disturbance suppression bandwidth reaches 8Hz,and the image stabilization accuracy reaches 0.043 arcseconds.Seventhly,the proposed controller is verified on a large-aperture FSM hardware-inthe-loop simulation platform.The sinusoidal signal with a frequency of 8 Hz is used as the excitation signal.The RMS error of the actual swing displacement of the FSM and the target swing displacement is 0.077 arcsec.The subject has conducted a comprehensive and in-depth study of the space telescope image stabilization system,completed the design of the control system for the large-aperture FSM.The main innovations of the project:Firstly,aiming at the large swing angle range and high-control bandwidth technical requirements of large-aperture FSM systems,a high-precision control research scheme of "model identification + controller design + semi-physical simulation" is proposed.The PZT drive mechanism and FSM parameter identification and control methods were systematically analyzed and studied.The hysteresis characteristics of PZT are modeled and compensated by the Duhem model;The system identification of large-aperture FSM is accomplished by sweep-frequency method;The optimal PID,linear quadratic Gaussian(LQG)and H? algorithm are used to design the controller for FSM and the simulation of the large-aperture FSM system is done.Secondly,based on the dynamic simulation,optical simulation and control simulation,a precise image stabilization system model is established to verify the tracking performance and disturbance rejection ability of the controller subsequently designed.A power spectral density(PSD)disturbance analysis model is established for the platform perturbation,and the envelope curve is designed according to the distribution characteristics of the disturbance,which can be used to analyze the disturbance suppression ability of large-aperture FSM system.Thirdly,a hardware-in-the-loop simulation platform is built to verify the designed controller,and the tracking accuracy is 0.077 arcsec.The integrated simulation results show that the designed control system has a good inhibitory effect on the platform disturbance,the system bandwidth reaches 20 Hz,the disturbance suppression bandwidth reaches 8Hz,and the image stabilization accuracy reaches 0.043 arcsec.