Study On The Design And Manufacturing Technology Of Silicon-based Aspheric Mirror

For the reflective optical remote-sensing camera,the primary mirror of the optical system is often an aspheric mirror with the largest aperture,the most difficult technical requirements,the longest development cycle and the highest cost in the optical system.Therefore,in the process of developing and exploring new materials and technologies for aspheric mirror,the material with high precision,low cost,excellent performance,and rapid manufacturing is an inevitable development trend.Single crystal silicon has excellent mechanical and thermal properties,such as low density,low coefficient of linear expansion,high homogeneity,and high thermal conductivity.In terms of the manufacturing cycle and the cost,the single crystal silicon aspheric mirror has more advantages than other common optical materials.Thus,it is an ideal material for medium or small aperture mirror.The development and application of silicon-based aspheric mirror in the field of optical imaging are still in the initial stage in China.In view of the current domestic research in this field is insufficient,this paper deeply studies the design and manufacture of single crystal silicon mirror.To explore the design and manufacturing technology of silicon-based aspheric mirror,this paper which takes single crystal silicon as the research object discusses the performance and connection method of silicon-based mirror,and then systematically optimizes a single crystal silicon mirror with a diameter of ?200mm.Furthermore,a flexible support structure,which can adapt to a large-span temperature range,is developed.Moreover,the single point diamond processing technology of the mirror is studied.Finally,a series of experiments on silicon-based aspheric mirror are carried out.The specific contents include:Firstly,this paper elaborates the performance evaluation method of mirror materials in detail,calculates the comprehensive evaluation results of common mirror materials,and discusses the advantages of silicon-based aspheric mirror in the field of medium or small aperture mirror.According to the brittle and hard characteristics of single crystal silicon,it conducts the experimental research on the material performance of single crystal silicon,sets the strength check standard for the design and optimization process of single crystal silicon mirror,studies the thermal characteristics of single crystal silicon mirror,and verifies that single crystal silicon has good characteristics of temperature maintenance and temperature stability.Then,according to the processing mode of the mirror,this paper proposes a lightweight design structure suitable for the single crystal silicon mirror,and investigates the influence of different lightweight curves on the surface accuracy.On this basis,the lightweight scheme of the mirror is preliminarily determined.Then,the training samples and support vector machine regression model are constructed by using the surrogate model method.Besides,the corresponding optimization algorithm is developed by using Matlab,and the structural parameters of the preliminary lightweight scheme are iteratively optimized.The optimized mirror weight is 0.564 kg,and the surface shape root mean square of the two directions is 0.54 nm and 2.6nm,respectively.Furthermore,the analysis and calculation of the temperature adaptability for the traditional mirror bonding structure show that the traditional structure can not adapt to a wide temperature range.In order to solve the problem of the temperature adaptability of the mirror,this paper studies the influence of the adhesive layer on the surface accuracy and determines the thickness of the adhesive layer.According to the principle of a heat-shrinkable mechanism,a non thermal connection structure of the mirror is proposed,and the geometric parameters of the structure are deduced.The final finite element analysis results of the non thermal structure indicate that the performance of the mirror is better under the condition of the temperature drop of 50?.The surface root mean square of the mirror is changed by 4.25 nm.The athermalized bonding technology proposed in this paper has a good thermal adaptability in a wide temperature range.Then,according to the accurate positioning principle of the mirror,the theoretical model of the mirror support structure is established.As for the mirror support structure,the form of Bipod is selected.The geometric parameters of the support structure are determined according to the structure space,and the initial structure is optimized.Firstly,the sensitivity analysis of the optimization variables is carried out,and the parameters with less influence on the objective function are ignored.Then,ISIGHT software,Patran,Nastran,Matlab and other software are used to optimize the variables automatically and iteratively.Finally,the optimization results are rounded,and the finite element analysis is conducted.Under 13 working conditions,the root mean square value of surface error of the mirror is less than 12 nm,the displacement in X and Z directions is less than 0.02 mm,and the rotation angle is less than 10?.Based on the optimization result,dynamic analysis of the mirror assembly is conducted.The analysis contents mainly include modal analysis,sinusoidal response analysis,random response analysis,and overload response analysis.Through calculation and experiential study,this paper finds that the mirror assembly has good mechanical properties,and can resist external excitation without structural damage.Finally,the research and manufacture of silicon-based aspheric mirror have been carried out.Specifically,it analyzes the influence of SPDT precision in the manufacturing process of mirror,environmental control factors in the actual processing,cutting tools,centrifugal force,and other factors on the surface figure accuracy.According to the general optical mirror manufacturing process and SPDT technical characteristics,this paper formulates the technological route for the development of silicon-based aspheric mirror,and gets the single crystal silicon aspheric mirror with surface root mean square of ?/50(?=632.8nm).The study on the optical properties of silicon mirror shows that the medium and high frequency surface errors formed by the residual turning tool lines on the surface of the mirror exert a great influence on the imaging quality.Aiming at the surface defects of the silicon mirror,this paper improves the surface quality of the silicon mirror through magnetorheological polishing technology.The surface roughness is improved from 5.2 nm to 1.1 nm,and the turning tool lines are obviously removed.Through the comparison of imaging experiments,this study found that the optical performance of the silicon mirror with improved surface quality is significantly enhanced.The success of the development and test of siliconbased aspheric mirror provides a new idea for the rapid manufacture and application of small and medium aperture mirror,which has a high promotion value.