Research On Composite Support Technology In Manufacturing Of Large Aperture Optical Mirror

In the processing and manufacturing of large caliber reflector,in order to improve the machining efficiency and precision of gravity discharge,this paper puts forward a new type of hydraulic support structure,when the hydraulic support unit support stiffness between the presence of dispersion will significantly reduce the unloading accuracy and machining accuracy,the gravity of the mirror which may affect the precision of mirror surface shape.In this paper,the new hydraulic support as the research object,using theoretical analysis,finite element analysis and test to study the support stiffness dispersion,and put forward the measures to reduce the stiffness dispersion,so as to improve the mirror shape accuracy.The specific research work is as follows:The first part mainly introduces the structure of 4M mirror and the gravity unloading support modes of different mirrors.By comparing different support modes,hydraulic Whiffletree structure is finally selected as the gravity unloading support of 4M mirror.In Hyper Mesh software,a spring element is used to simulate the passive support of the mirror at 54 points,and the RMS values of the Z-direction(optical axis direction)gravity surface of the mirror with exactly the same support stiffness,3% difference and 5% difference are6.5nm,13.3nm and 19.0nm,respectively.The analysis results show that the dispersion of support stiffness has a negative effect on the unloading accuracy.The second part introduces the load unloading end,support structure and rolling diaphragm structure of in-situ inspection support system from system level,component level and component level respectively.The key material parameters of fiber sandwich rubber were measured by tensile test.Based on the force analysis of the hydraulic support unit,the analytic formula of the support stiffness of the support unit is derived from hydromechanics,elasticity and solid mechanics,and the conclusion that the support stiffness is related to the size parameters of the support structure,hydraulic medium parameters and oil pressure is obtained.The derivation of stiffness analytical formula provides a theoretical basis for the follow-up work of this paper,and also provides guidance for the design of other hydraulic support units.The third part studies the influence of various parameters and actual working conditions on the stiffness and stiffness dispersion.Firstly,through finite element analysis,it is concluded that the influences of the size parameters and material parameters on the support stiffness are as follows: diaphragm thickness,diaphragm convolution height,diaphragm convolution width and diaphragm elastic modulus from large to small.Then three group tests were carried out to test the effects of working pressure,workpiece pressing speed and bubble content on stiffness dispersion.The test results show that the stiffness dispersion decreases with the increase of working pressure and workpiece compression speed,and the bubble has a very adverse effect on reducing the dispersion of support stiffness.Finally,the effective measures to reduce the dispersion of stiffness are proposed.The fourth part is the performance verification of the hydraulic support system.In the case of the implementation of measures to reduce the dispersion of stiffness,the performance verification is carried out from two aspects of stability and gravity unloading accuracy.In order to test the stability of the system,the sealing test of single hydraulic support unit and hydraulic combined group was carried out under the loading condition.The test results show that the pressure inside the pipeline changes slowly and the pressure relief speed is low when the single hydraulic support unit is loaded.The pressure change of the pipeline is not obvious under the loading condition of hydraulic units.To test and verify the accuracy of gravity discharge of hydraulic support system,to 4 m in situ testing platform of 500 mm caliber reflector mirror systems than model for process integration,the introduction of measures to reduce stiffness dispersivity,eventually support the gravity of the situation at 9 points actual unloading surface shape accuracy of the RMS value of 10.4nm,with the results of analysis and calculation error is less than 5%,The effectiveness of the measures proposed in this paper to reduce stiffness dispersion is verified.