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《Optics and Precision Engineering》 2017-10
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Hydrostatic support system for in-situ optical testing of a 4 m aperture SiC mirror

HU Hai-fei;ZHAO Hong-wei;LIU Zhen-yu;LUO Xiao;ZHANG Xue-jun;Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences;School of Mechanical Science and Engineering,Jilin University;  
A set of hydrostatic support system for a 4m SiC mirror in-situ testing was designed to reduce the risk of ultra-large mirror off-line testing and to improve fabrication efficiency.Firstly,the analytical formula for calculating support stiffness was derived,and its main factor was found.Then,some support samples were tested,and the support stiffness of a single support unit in different groups was predicted by combining the sample results and analytical formula.Finally,the stability of the support system was evaluated by pressurization test and in-situ testing,and the mirror surface precision with its gravity offloaded by the support system was calculated by finite element simulation.Results show that the average stiffness is about 1.9kN/mm with a relative difference among support units about 3% when 5 units are linked together,the stiffness for a single unit isolated is as high as 15kN/mm,and 3 kinds of unit stiffness in the support system are 1.7,1.1 and 0.8kN/mm respectively.Moreover,pressurization test shows a slow pressure change,which indicates that the system is well sealed.When the hydrostatic system was used for a 4m mirror,the height changes rise up and down within 50μm in 11 days,and the relative change is less than 20μm.When the mirror is supported on 54 units with stiffness difference by 3% randomly,the surface RMS is less than 20 nm.The proposed system meets the requirement of in-situ optical testing for precision and stability.
【Fund】: 国家自然科学基金资助项目(No.61210015 No.61605202)
【CateGory Index】: TH743
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