| To meet the demands of space applications and deep space exploration,astronomers need to build telescopes with larger aperture for greater light-gather power and spatial resolution.The study from National Aeronautics and Space Administration(NASA)shows that the discovery speed of earth-like planets is directly proportional to the 1.8th power of the aperture diameter and the 0.4th power of the time,and that the aperture of telescopes should be larger than 8m to meet the basic requirements of exploring the origin of life.Due to the limitation of the launch fairing,space-based telescope with aperture larger than 4m should adopt the deployable optical system,which means the telescope must be folded before launch and deployed or assembled on orbit to achieve the imaging capability of the equivalent design aperture.How to ensure that the segmented mirrors can achieve co-phasing is a very challenging task.Firstly,it is must to analyze the impacts of the segment six degree of freedom pose-phasing errors on the deployable optical system,so as to reasonably allocate the tolerances of pose-phasing accuracy.Then,design a reasonable co-phasing adjustment device to complete the segments co-phasing adjustment,according to the tolerance indexes.Finally,in order to effectively verify the co-phasing device,it is necessary to quickly and accurately interpret the finite element simulation analysis results,extract effective parameters,and guide the design optimization.These technologies are not only the basic technologies to ensure the segmented mirror development,but also the key technologies.In order to ensure that the segmented primary mirror can complete co-phasing,this paper studies the co-phasing technology.Firstly,a coordinate-free mathematical model of the aspheric surface is established.According to the ray tracing theory,the formulas of the exiting wavefront deformation produced by incident wavefront deformation,segment pose errors and aspheric parameter errors are derived,and the transfer formula of the segment co-phasing errors in optical system is given.Using this model,the influence of the segment primary mirror co-phasing error with definite value can be evaluated,which provides a theoretical basis for further analysis the effects of the random co-phasing errors.Based on the model,the influence of a 8m segmented primary mirror co-phasing errors is completed,and the impact of different types of fixed value co-phasing error on the wavefront deformation is numerically simulated.The co-phasing error is random.In order to accurately predict this error impact on the optical system,and to reasonably allocate the co-phasing accuracy tolerance,the error sources and its distribution law are deeply analyzed.The prediction formula of the random co-phasing errors influence on wavefront deformation is derived.The method of weighted tolerance allocation based on equal contribution principle is proposed.The calculation method of co-phasing error weight coefficient is deduced in detail.In order to further reduce the system's requirement for co-phasing precision,the method using segment pose adjustment to compensate the aspheric parameter errors is presented,and the prediction formula of the modified residual is given.The numerical simulation test results show that this method can reduce the influence of aspheric parameter error by one to two orders of magnitude.In order to achieve the segments co-phasing adjustment,the phasing adjustment platform technology is studied.Firstly,based on the weighted tolerance allocation theory the phasing platform configuration optimization method is proposed,the platform configuration optimization is realized,and the improved 6PSS parallel platform is obtained.The forward kinematics and the inverse kinematics mathematical models of the platform are established.According to the kinematics equation and the closed-loop characteristics of the parallel mechanism,the platform error model is established,and the mapping between pose error and platform structural parameter error is derived.An error correction method based on the platform positioning accuracy detection data is proposed through the platform configuration optimization technology,the precision requirement of the platform execution component can be reduced by more than 40% without reducing the rigidity of the system.Using the error correction technology,the platform machining and assembly accuracy can be greatly relaxed,so as to significantly save the manufacturing cost and shorten the development cycle.The phasing platform needs to be verified whether the design performance can meet the co-phasing requirements through finite element analysis,and design iteration is performed rapidly according to the analysis results feedback.The finite element analysis results can only give the nodes deformation,and can not separate the important parameters required for the design of the optical machine structure,such as rigid body displacement,aspheric parameters and surface distortion.In order to solve the interpretation technique of the simulation analysis results under the condition of large rigid body displacement,a rigid body displacement parameter extraction algorithm based on homogeneous coordinate transformation is proposed,the node discrete error removal technology under the condition of large rigid body displacement is broken,and the aspheric parameter analysis method based on least squares Newton iteration method for complex node deformation is derived.The above theory can be applied to both static analysis and nonlinear analysis,can be applied to both segmented system and monolithic system,and have universal applicability.The co-phasing adjustment and testing for a segmented verification system is completed.Firstly,according to the co-phasing accuracy tolerance allocated,the segments manufacturing tolerance and positioning tolerance are completed.A co-phasing adjustment platform is developed,and an accuracy test system is built to test this co-phasing platform positioning precision.According to the test data,the control model is corrected by using error correction algorithm.The co-phasing adjustment and testing for the verification system is corrected out,and the wave aberration interference test is obtained.The experimental results show that the kinematics model can drive the co-phasing platform for specified motion,and the error correction algorithm can significantly improve the platform control accuracy.The co-phasing error impact prediction and the co-phasing accuracy tolerance allocation theory can effectively guide the co-phasing precision tolerance allocation. |
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