Design And Analysis Of TMT Tertiary Mirror System Support Structure

Thirty meter telescope(Thirty Meter Telescope,TMT)Tertiary Mirror system has very complicated working conditions during the observation.And the mirror's ratio of diameter-to-thickness is very large,which is difficult to design of its support structure.At the same time,tertiary mirror system also has extremely strict limitations on quality and volume,which further increases the difficulty of supporting structure design.In this paper,the support structure of TMT Tertiary Mirror is studied in terms of support plan optimization,structural optimization design and analysis,error analysis and prototype construction.First,based on the parametric model and simulated annealing optimization algorithm,the global optimization of the support point layout of the axial support of the mirror was realized.The mirror deformation Slope RMS was improved by 5.2%compared with the initial manual optimization design results.And according to the dynamics and statics principle,the theoretical model of multi-objective optimization of the lateral support layout was established.The Pareto solution set of the lateral support point layout was obtained by using the Neighborhood Cultivation Genetic Algorithm,which reduces the maximum tangential load of the side support by 5.77%relative to the initial design.The first-order resonant frequency was increased by4.55%.Secondly,the analysis of Tertiary Mirror system and the key areas of the supporting structure are carried out.The maximum mirror deformation Slope RMS under gravity conditions is 0.68?rad,and the maximum Plate Scale is 1.13 mas,which meets the system requirements.The first-order resonance frequency of system is12.82 Hz,which meets the system requirement after evaluation.It is necessary to further optimize the structural design to improve the rigidity of york and reduce the structural mass.The parametric modeling was used to analyze the relationship between the stiffness,stress safety factor and stability and the parameters of the flexible hinge.The parameters of the flexible hinge were selected according to the requirements.Based on the Hertz contact theory and Hale's interface repeatability theory,Tertiary Mirrors' repeated positioning interface was designed so that its maximum contact stress and repeatability accuracy met the requirements.In addition,the effects of various error sources during the assembling on the optical performance were analyzed and synthesized.The Slope RMS of the mirror deformation caused by the assembling error was 0.043?rad and the Plate Scale was0.284 mas,which met the system requirements.After combining all the error sources of mirror surface,the Slope RMS is 0.681?rad and the Plate Scale is 1.13 mas,which are both better than the system requirements.Finally,a prototype system of 1/4 scale was built to verify the design,analysis and assembling methods of Tertiary Mirror system were built.The actual positioning error of the axial support was 0.22 mm.The position and direction errors of the lateral support pads were less than 0.07°.And the positioning error of the mirror is 0.14 mm.The mirror deformation Slope RMS detected by the prototype under the vertical optical axis condition is consistent with the Finite Element Analysis results.In this paper,new methods were proposed in the optimizing the axial support and lateral support of Tertiary Mirror system and the installation and the system assembling.The completed research content laid the foundation for the Final Design Phase of the TMT Tertiary Mirror system and provided reference for the support design of the large aperture large-caliber telescope.