| As an important means of information acquisition,spatial remote sensing technology is widely used in various fields such as meteorological observation,map mapping,resource investigation and military reconnaissance.The high resolution,high efficiency and high reliability of the low earth orbit space camera have made it a research focus of spatial remote sensing technology.However,during the imaging of the space camera,the image motion caused by high-speed flight of the satellite platform,scanning motion of the scanning mirror and earth rotation will seriously reduce the resolution of the image,so an image motion compensation system must be provided.This paper designs and studies the Fast Steering Mirror(FSM)mechanism in the image motion compensation system of low earth orbit space camera.Firstly,the working mode of space camera scanning imaging is introduced.The imaging coordinate system of typical structure space camera is established,and the mathematical model of image motion is established by homogeneous coordinate transformation method.The function of the compensation angle of the FSM and the exposure time is derived,which provides a basis for the technical indicators of the FSM in the structural design process.The performance index and main structure of the FSM are listed,and the influence of the parameters of each component on the performance of the whole machine is analyzed.Combined with the working conditions of the space camera,the structural design idea is clarified.The lightweight structure of the mirror and the holder was designed by theoretical analysis and topology optimization.The finite element software MSC.Patran was used to analyze the two mirror support schemes,lateral support and rear support with central point,the analysis results show that,the latter is more conducive to the high precision and lightweight design of the mirror.In order to achieve the better overall performance of the FSM,a multi-objective optimization of the main structural parameters of the mirror was executed.The Quality Index(QI)was defined to describe the overall performance of the mirror,and the variation trend of QI with the main structural parameters of the mirror is analyzed by finite element simulation.The results showed that the rib height and the adapter thickness contributed the most to the overall performance of the mirror.Under the optimized scheme,the overall light weight ratio of the mirror is 44.1%,and the RMS of the mirror surface under the condition of-8°C temperature load is only 2.2 nm.Based on the cross-shaped flexible hinge,the two-axis flexible link of the FSM is designed.The formula for calculating the rotational stiffness of the flexible hinge and the flexible support structure is theoretically derived.According to the moment of inertia of the structure and the resonant frequency requirement of the FSM mechanism,the main structural parameters of the cross-shaped flexible hinge were proposed.The arrangement of the voice coil motor is determined,the simplified dynamic model of the FSM mechanism and the corresponding dynamic balance equation are established,and the model of the voice coil motor is selected according to the compensation angle requirement of the FSM.The working principle of Position Sensitive Detector(PSD)is introduced.The deflection angle measuring mechanism based on two-dimensional PSD is designed,and the relationship between the measured voltage and the deflection angle of the mirror is derived.The modal analysis of the FSM mechanism based on finite element simulation shows that the resonant frequency of the mechanism meets the design requirements,and the overall structural scheme of the FSM is finally determined.The experimental prototype of the FSM was machined,and the mechanical performance such as the two-axis rotational stiffness,the mirror surface accuracy and the resonance frequency of the mechanism were tested.The experimental results and the theoretical calculation results were consistent within the allowable error range. |
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