Research Of Precise Positioning Method Of 2-m SiC Primary Mirror In Opto-Mechanical System

In an opto-mechanical system,the collimation and spacing between the optical components must be strictly ensured so as to avoid degradation of the imaging quality due to the introduction of aberrations.The primary mirror is the key optical component of the ground-based large aperture telescope,and its overall performance will have an important impact on the overall performance of the telescope such as imaging effect,working time and reliability.The factors influencing the image quality of the optomechanical system are mainly composed of the surface profile and positioning accuracy of the primary mirror.With the increasing in the aperture to thickness ratio of the primary mirror,and the using of new materials in mirror blank and the application of new structures such as concave mirrors and meniscus mirrors,the precise positioning method of large aperture primary mirrors in opto-mechanical systems has become more complex and more important.This issue studied the precise positioning method of the primary mirror in the telescope for a 2-meter-class ground-based telescope project,and designed the primary mirror's assembling positioning system,axial positioning system and radial positioning system.Each positioning system should be able to limit the total freedom of the primary mirror without disturbing the primary mirror's support system and can simultaneously ensure the position accuracy of the primary mirror,the resonant frequency of the primary mirror system,and the precision of the surface profile and other technical indicators.The specific research content is as follows:Firstly,the development history of the telescope is briefly introduced.Some commonly materials used primary mirror are listed and the performance parameters of various materials are compared.Silicon carbide has the advantage in these materials.The research background and significance of the subject are discussed.And some representative telescopes at home and abroad were introduced the basic parameters of its primary mirror and positioning methods.The content provided guidance and reference methods for the next research and design work.Secondly,the basic principles of kinematics constraints and the characteristics of kinematic interfaces are described.The influence of elastic deformation on the positioning and surface profile of the primary mirror is analyzed.It provided the theoretical basis for the precise positioning of the primary mirror in the opto-mechanical system.Thirdly,the basic situation of the primary mirror and support system model were briefly introduced.Based on the principle of kinematics constraints,a set of positioning system for large aperture primary mirrors is proposed.The scheme includes three aspects for the primary mirror: the assembling position system,the effect of the axial support system on the positioning,and the radial positioning system.Focusing on the comparison and comparison of the mandrel center positioning method and the kinematic constrained radial multi-point positioning method,the design of the primary mirror's radial positioning system was selected.Fourthly,for the primary mirror radial positioning system,the process of selecting and optimizing the point positions are mainly described.Using the matlab,UG,Patran/Nastran and other computer software,a specific positioning system structure was designed.The key points included the parametric design of the flexible struts and the structural design of the bidirectional buffer base.The finite element model of the primary mirror system was built by using UG,Hypermesh,Patran/Nastran and other software.And the influence of the radial positioning system on the position,resonant frequency and mirror surface profile of the large aperture primary mirror system was analyzed.The results show that the resonant frequency of the whole primary mirror system using this radial positioning system reaches 13.6Hz,the average displacement of the primary mirror along the Y-axis when the optical axis is horizontal is-356 nm,and the mirror surface profile is not affected;all the indicators meet the design requirements.Finally,a radial positioning assembly prototype was manufactured and tested.The actual stiffness of the flexible supporting rod and the pre-tightening force of the buffer spring in the designed radial positioning assembly were tested.The experimental data shows that the actual performance of the radial positioning assembly meets the design requirements.The precise positioning method of the large aperture primary mirror in the optomechanical system can effectively position the primary mirror.The designed primary mirror positioning system can ensure the position accuracy of the primary mirror and provide the resonant frequency of the primary mirror system without affecting the accuracy of the surface profile of the primary mirror.For the engineering application of the support and positioning technology of the 2-meter-class silicon carbide primary mirror,it has certain reference value.