Research On Topology Optimization Design And Kinematic Supporting Techniques For A Large Aperture Space Mirror

With the continuous improvement of resolution requirement of space optical system,the aperture of the space telescope also increases.As an important component of space telescope,the positional accuracy and surface shape accuracy of large aperture space mirror has direct impact on the imaging quality of optical systems.However,an increase in the aperture of the mirror results in an increase in the quality of the telescope system,and the deformation of the mirror under gravity and temperature loads also increase.In order to reduce the launch cost,also the rigid body displacement and surface error of the mirror under the gravity load,the mirror must be lightweight.The absolute stiffness of the light weight design mirror is lower than that of the initial mirror blank,and its sensitivity to the supporting force is increased.Therefore,in order to ensure that the large aperture mirror has a good surface shape accuracy,a reasonable supporting structure must be designed.The high degree lightweight design of the mirror and the realization of high precision,high stability and high reliability support are the key and difficult points of space large aperture mirror research,and it’s very important scientific significance.This paper relies on a Φ1.42 m diameter primary mirror of a space telescope project to carry out research on lightweight design and kinematic supporting techniques for large aperture mirrors.The main research contents are as follows:(1)On the basis of summarizing the development status and design method of large aperture space mirror assembly,the design idea and design principle of passive support of large aperture space mirror are introduced.According to the kinematic support principle,the compound support scheme with peripheral support and back support is selected of the primary mirror of this subject.(2)In this paper,an optimization method based on neural network model for the axial support position of the mirror is proposed.The traditional method for solving the axial support position of the mirror is mainly solved by empirical formula or finite element analysis method.However,the traditional method can’t evaluate the surface shape error,and the result has a large optimization space.In this paper,the isight integrated analysis method combined with nural network approximation model is used to establish a comprehensive mapping relationship between structural parameters,axial support position and mirror surface RMS value of 1.4 m to 2 m aperture mirror.The neural network is trained by known sample points to make the network have the prediction function.Finally,the optimization algorithm is combined to minimize the surface shape RMS value as the objective function,and the axial optimal support position of the mirror can be solved quickly.(3)Aiming at the defects of the traditional lightweight design method for large aperture mirror,this paper proposes a topology optimization method based on the mirror with stiffener structure.By applying uniform density constraint,the mirror lightweight ratio can be further improved without changing the initial lightweight configuration.At the same time,this topology method can also provide a new grouping method for the size optimization of the mirror stiffener structure.In order to improve the manufacturability of 3d solid mirror topology optimization results,this paper also proposes a topology optimization method for flat and open back mirrors.In the topology optimization,processing manufacturing constraints are added to control the characteristics of topology results,and ensure that the mirror can be demoulded smoothly during the molding process.(4)Complete the kinematic support structure design of the large aperture mirror.According to the function distribution and index distribution results,the sensitivity analysis and parameter optimization are used to design the peripheral A-frame support structure.The topology optimization method is used to design the lightweight structure of the rigid parts in the whiffletree support,and the softness analysis method was used to design the flexible parts of the whiffletree support.The existing parasitic motion in each flexible link is analyzed in detail,and a triangular plate flexure and a lever flexure without parasitic motion are designed by adding the compensation module and the symmetric arrangement method respectively,thereby improving the positional accuracy and surface shape accuracy of the mirror under the back support.(5)Using the simulation analysis combined the test verification to investigate the deign results of the mirror assembly.The decoupling effect of the peripheral support and the back support was investigated by simulation analysis.And an equivalent temperature method is proposed to investigate the freedom release effect of the back flexible parts by simulating the machining error existing in the whiffletree support assembly.By detecting the mirror shape under the inspection support and the peripheral working support,the deign results of the mirror assembly can meet the optical requirements.Also the feasibility and effectiveness of the mirror support scheme and related design methods are demonstrated.