Design And Test Method Study Of TMT Tertiary Mirror Whiffletree Axial Support System

With the continuous development of modern astronomy and military technology,we hope to see father and father,and to see more and more faint goals.As the larger the optical aperture,the stronger the light collecting ability and resolution,so people continue to build more and more large-caliber telescopes.Thirty meter telescope(TMT)is on behalf of today's highest technical level of astronomical telescope development.TMT tertiary mirror is one of the main components directly involved in optical system imaging,and the accuracy of its surface shape is a key factor affecting the image quality of the telescope.In order to ensure the surface accuracy of TMT tertiary mirror at work,the Whiffletree axial support system is designed,and the parameter sensitivity and balance adjustment test method of the support structure are analyzed and studied.The specific research contents are as follows.Firstly,the structural forms and basic principles of the axial support system of the large aperture mirror are analyzed and summarized.The working principle of the Whiffletree structure is analyzed and studied emphatically.Considering all factors,the axial support scheme of Whiffletree structure with 18 support points and two levels is determined.The RMS value of the mirror surface is taken as the objective function to optimize the position of the axial support points.According to the finite element analysis results of the optimal solution,the RMS value of the mirror surface is 105.6nm.Secondly,the parametric finite element model of the TMT tertiary mirror support system is established by using APDL.In order to solve the problem that the supporting effect of the Whiffletree structure directly used in the elliptical mirror is poor,corrective moments are used to correct the support forces.The corrective moments are optimized,and the mirror surface RMS value is 107.6nm after correcting.It basically achieves the surface accuracy when the support points are optimized.Then,taking into account the effect of the errors introduced in the actual machining and assembling process,the local sensitivity analysis and global sensitivity analysis for the main parameters of the support structure are processed.The sensitivity of the position errors and balance errors are assessed.Finally,a new balance adjustment and test method for Whiffletree structure is designed according to the balance requirement of Whiffletree structure.A set of Whiffletree structure is adjusted and tested using this method and achieves good result.