| The two-mirror optical systems(TMOSs),which consist of coaxial two-mirror optical systems(CaTMOSs)and off-axis two-mirror optical systems(Oa TMOSs),are dominant in the family of reflective optical systems.They are widely used in space cameras,telescopes,seekers,and other precision opto-mechanical systems,and their manufacturing capability is an important symbol to measure the level of national science and technology.With the development demand of "Made in China 2025",the assembly process of such systems is developing towards the direction of digitization,automation and intelligence,and misalignment computation is one of the important technologies to achieve this goal.However,due to the lack of systematic analysis of coma-free pivot point(CFPP),misalignment,surface figure error(SFE),field of view(FoV)and engineering application analysis of FoV positioning error,surface figure fitting error(SFFE),measurement error and other factors,the existing methods can not function well in the assembly process.In addition,the measurement requirement of wavefront aberration(WFE)in multi-FoVs and the demand for wavefront sensors also make the application inconvenient.Therefore,it is of great scientific significance and engineering value to research the misalignment computation methods for precision assembly of twomirror optical systems,which can promote the intelligent manufacturing of such optical systems and the optical systems with more mirrors.Four key technical problems,which are "lack of systematic analysis","dependence on WFE in Multi-FoVs","lack of engineering application analysis" and "dependence on wavefront sensors",in the process of precision assembly and misalignment computation,are the dominant research work needed to be solved in this dissertation.By taking TMOSs as the research object,the influence of the CFPP,misalignment and SFE on the WFE is analyzed based on the nodal aberration theory(NAT),and misalignment computation methods which combine theoretical analysis and engineering application are developed,and the systematic theoretical models,methods and assembly processes are formed.The specific research content includes the following aspects:(1)The influence of misalignment on WFE for different optical systems is summarized,and the analytical position formula of the third-order astigmatic double nodes under the influence of CFPP is established.The analysis of WFE is the premise of misalignment computation.Based on the NAT,the influence of misalignment on thirdorder WFE of different optical systems is analyzed,which can provide the selection guidance of aberration terms in misalignment computation.On this basis,the influence of the CFPP on the WFE characteristics of the CaTMOS is analyzed.The research shows that one node of the third-order astigmatism will locate near the center of FoV and reveals the reason why the existing methods cannot be used to evaluate the system is aligned well based on the single-FoV WFE.(2)The influence of SFE on WFE of optical systems is studied,an analytical aberration calculation model for precision assembly of CaTMOSs is established,and a new misalignment computation method based on single-FoV WFE is proposed.Under the framework of NAT,the influence of SFE which is located at or away from the aperture stop on WFE is analyzed by vectorizing the WFE represented by Zernike polynomials.Based on the superposition principle of aberration,the analytical aberration calculation model of CaTMOSs is established.The influence of SFE,misalignment and FoV on WFE can be derived analytically based on the established model.On this basis,the effective information of WFE is increased by introducing the quantitative misalignments rather than changing the FoV,and the misalignment robust calculation under the condition of single-FoV is realized.The accuracy of the established model and method is verified by simulation.(3)The WFE characteristics of Oa TMOSs are analyzed,and an application criterion of the sensitivity matrix method(STM)based on matrix condition number and an application model of merit function regression(MFR)method based on digital twin are proposed.Based on the established model in this paper,it is revealed that the effect of misalignment on the WFE of Oa TMOSs is coupled and the misalignment cannot be separated in the calculation process.Three common misalignment computation methods are studied in the application of TMOSs,a judging method based on the matrix condition number is proposed to solve the ill-posed problem in the application of STM,and an optical model based on the digital twin is proposed to solve the modeling accuracy problem in the application of MFR.The two methods are tested and validated respectively.(4)The common image quality evaluation methods of optical systems are summarized,and two kinds of misalignment computation methods based on image sensors are proposed.The essence of misalignment computation is based on the image quality difference between the actual system and the ideal system.By summarizing the common evaluation methods of image quality,the advantages of image sensors in the application of optical system precision assembly are revealed.On this basis,the influence of misalignment on the imaging quality of the system is quantitatively analyzed with the ellipticity distribution of stellar image as the evaluation index,and a method of misalignment computation method based on the ellipticity distribution of stellar image is proposed;The problem of misalignment calculation for optical system is turned into a multi-objective optimization problem by taking the centroid deviation information of lattice spot as evaluation index,and another misalignment computation method is proposed.The effectiveness of the two proposed methods is verified by simulation.(5)The influence of various engineering errors on the misalignment computation accuracy in the assembly process is studied,and the assembly adjustment strategy of "coma and astigmatism are corrected in two steps" is proposed,and the misalignment computation experiments for precision assembly of TMOS are carried out.WFE introduced by FoV positioning error,SFFE and measurement noise is uniformly described as the amount of noise subject to a normal distribution,and its influence on the calculation accuracy of misalignment is analyzed,which reveals that the fluctuation of the measured WFE coefficient is the main reason for the instability of the misalignment calculation accuracy;According to the CFPP characteristics of Co TMOSs,the method of misalignment computation method based on single FoV WFE is optimized,and a test device for precise assembly of TMOS is developed.Based on the Zygo interferometer,misalignment sampling test and misalignment computation test are carried out to verify the accuracy of the analytical model and method. |
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