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Research On The Structure Of Multiband Shared Aperture Imaging System Based On The Consistency Of The Fields Of View

Posted on:2017-02-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H LiFull Text:PDF
GTID:1108330482991335Subject:Mechanical Manufacturing and Automation
Abstract/Summary:PDF Full Text Request
Because of the large differences of optic characters while target is in different spectral band, multiband imaging is used to get more accurate information, then to achieve target detection with all time, wide coverage and high resolution. The purpose of multiband imaging system is the fusion of feature information of each band image, then to make a comprehensive analysis to target. This requires that the detector of each band images a same target at the same time, which means pixels among images of each band are strict alignment in space coordinate, in other words,the FOV of each band should be unanimous.To some extent, the bigger the relative shift of FOV is, the larger the search range in the image registration process. This implies that more calculation amount of image registration is required. In order to enhance the real-time performance, reduce the calculation of image fusion, a consideration at various factors to improve the consistency of FOV in structure design phase is very necessary.In this paper, the consistency of FOV is taken as evaluation standard.Considering the affects of adjustment error, structural distortion, temperature variation and other factors comprehensively, finite element method, topological optimization, athermalization and thermal compensation are used to achieve the prototype development and the structure improvement of multiband commonaperture imaging system.The operational environment and the technical specification are summarized.The overall structure of optical system and the design project of there optical subsystems are introduced. The imaging quality analysis of optical subsystem is completed. The overall mechanical structure is designed which includes three cam focusing mechanisms, bracing structure of reflectors and fixed structure of prisms.Then the principle prototype of multiband imaging system is developed on this basis.Room temperature stability test, high/low temperature storage test and high temperature operation test are completed. Test results show that the shift of FOV exists among the there optical subsystems, which beyond the technical index requirements, so structure improvement is needed.The effect of the position error of the main optical element on the consistency of FOV of the system is analyzed, including prisms, reflector lens and CCD cameras,etc. The error compensation principle of the shift of FOV by adjusting the reflector lens during assembling and alignment is explained briefly. The static analysis of focusing structure, reflector structure, prisms structure and the overall structure are completed. The results show that the main factor affecting the consistency of FOV is the static deformation of support frame, therefore the structural stiffness of support frame needs to be enhanced. The thermal deformation analysis of focusing structure,reflector structure, prisms structure and the overall structure are completed, and the conclusion is that the shift of FOV caused by the thermal deformation of reflector structure is extremely significant. Therefore technical means such as athermalization and thermal compensation need to be adopt to improve it.The topological optimization method considering the consistency of FOV as objective function is proposed. The concrete steps includes: firstly, the objective function, the constraint condition and the design space are determined; Secondly, the deflection angle equations of optical axis and the reflectors are established, based on weighted square sum method, the general objective function of the shift of FOV is constructed; finally, the topological optimization is implement, then based on theoptimization results, the support structure topology optimization model which is suitable for processing is extracted. Sizing optimization is carried on the topology optimization model to further improve the performance of the support structure.Simulations show that the shift of FOV cause by the deformation of supporting structure after sizing optimization is about 0.5 and 0.7 pixels. Compared with the original structure, the shift of FOV of optimization structure is reduced about by50%~60%. The effect of the pitching motion of the elevated platform on the consistency of FOV is analyzed, and we conclude that the pitch motion will deteriorate the consistency of FOV.The thermal-mechanical coupled analysis to the original structure is completed,and the surface figure accuracy RMS of visible and ultraviolet reflectors are obtained about 599.5nm and 366.7nm at uniform temperature elevation among +35°C. In order to enhance surface figure accuracy of reflector, the bonding way is adopt to fix reflector and the athermalization of reflector structure is achieved by adjusting the thickness of the rubber; the material and the connection way of reflector structure is changed to further improve the surface figure accuracy of reflectors, meanwhile it is also beneficial for realizing thermal compensation of the shift of FOV. The analysis result indicates that the RMS is about 107.2nm and 64.34 nm, which meet the requirements basically. Thermal compensation principle of reflector structure is elaborated. The thermal deformation analysis of optical mechanical structure in different temperature is completed, and the deflection angle data of optical axis and the reflector are obtained, then the curve about deflection angle with the temperature is fitted. Coefficient of thermal expansion of gasket is estimated to fulfill thermal compensation of reflector structure. Through the simulation contrast, the material combination of gasket is determined finally. We remodel and develop the prototype,then complete the thermal compensation experiment and the results show that the shift of FOV of visible subsystem after several high and low temperature tests is about(-2, 2) pixels, the shift of FOV in the work condition of high temperature is about(-4, 3) pixels, and the shift of FOV in the work condition of low temperature isabout(-2, 5) pixels, which meet the technical requirements, and reach the expected goal.
Keywords/Search Tags:multiband, consistency of FOV, error analysis, topological optimization, athermalization, thermal compensation
PDF Full Text Request
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