| With the gradual development of cosmic discoveries and deep space exploration projects in China,to develop space telescopes with high resolution and large field of view is very urgent.The working conditions of the space telescope in orbit is so complicated that the detection accuracy will be affected by many factors,such as the attitude change of spacecraft and the vibration inside and outside the telescope,and the opto-electronic compound-axis control is an important means to realize the highprecision tracking and high-quality imaging of space telescope.As the actuator unit of compound axis control system of space telescope,the performance of accurate image stabilization is determined directly by fast steering mirror mechanism.In this dissertation,a closed-loop control scheme of large-aperture fast steering mirror(LAFSM)mechanism consisting of dynamic hysteresis compensation of Piezoelectric Actuators(PZT),piezoelectric creep inhibition and FSM tracking control,based on the investigation of FSM at home and abroad and the performance requirement of the precision image stabilization system in space telescope,and the experimental system is established to verify the performance of control system.The specific contributions are as follows:(1)The system scheme and structure model of large-aperture fast steering mirror are determined,and the closed-loop control scheme of large-aperture fast steering mirror is put forward based on the analysis of technical parameters of the LAFSM mechanism closed-loop control system,according to the requirements of current astronomical observation and precision image stabilization system performance in space telescope.(2)The asymmetric PI inverse model based on the generalized Stop operator is directly built,according to the problems that the reversibility of PI model based on Play operator is limited by the constraint condition and the estimation error accumulation of model parameters in the inverse process.On the basis of this model,the Hammerstein feedforward compensator for dynamic hysteresis is directly set up to eliminate the dynamic hysteresis nonlinearity of PZT,and LQG optimal controller is designed to further improve the PZT positioning accuracy.The CADE algorithm is used to identify and tune the model and controller parameters in the process of modeling and the controller design.The simulation and experiment results verify the effectiveness and superiority of the compound control strategy combining the PI inverse model based on generalized Stop operator and LQG control algorithm.(3)The RBF piezoelectric creep prediction network is built based on the piezoelectric creep characteristics,aiming at the limitation of existing mathematical models for creep properties.And the CADE algorithm is adopted to improve the convergence rate by determining the learning rate,momentum factor and initial values of structural parameters with RBF network.The results of model comparison verify the effectiveness and superiority of CADE_RBF creep prediction model on the creep prediction for PZT.(4)The LAFSM open-loop system model is built by the F-test and recursive least square(RLS)methods in the light of the input and output datas.And the conventional IMC closed-loop controller is designed according to the identified open-loop system model of LAFSM mechanism,and the concept of supporting indirect Fuzzy control is adopted to tune IMC controller parameters self-adaptively.The simulation and actual verification results show the strong anti-jamming capability and robustness of this control algorithm.(5)A verification platform of LAFSM closed-loop control system is designed and established according to the technical parameters of the closed-loop control system of LAFSM mechanism.The x-axis and y-axis tracking accuracy can respectively reach 0.0887 " and 0.0847",in the real-time tracking for variable-frequency and variableamplitude target input signal with-35 "~35" angles and 1~20Hz frequencies;the x-axis and y-axis tracking accuracy can respectively reach 0.0469 " and 0.0497",in the realtime tracking for disturbance signal of spacecraft platform passing through vibration isolation system,which both obtain the expected experimental results of the algorithm.(6)The application of LAFSM mechanism's closed-loop control system in the optical close-loop experimental system of precise image stabilization in space telescope is completed.When the 2-D variable-frequency and variable-amplitude disturbances of simulation star within 6.25 Hz are compensated,the disturbance degrees of the star detected by FGS in the direction of x-axis and y-axis decrease by 71.72% and 73.65% respectively,and the energy concentration of star image imaged by the CCD longexposure camera which is used to simulate the celestial observation increases by 53.13% compared with the uncompensated diffuse star spot.The experimental results verify the ability of the line-of-sight deviation compensation for space telescope by the LAFSM closed-loop control system designed in this dissertation. |
PDF Full Text Request