| With the continuous improvement of optical system performance,the surface shape accuracy requirements of important optical components such as lithography objective and synchrotron radiation focusing mirror have reached sub-nanometer level.Ion beam figuring(IBF)technology is recognized as the most accurate optical processing method at present due to its outstanding advantages such as non-contact processing method,high stability removal function,and atomic-scale material removal resolution.It has become the ultimate means of precision generation of sub-nanometer precision optical components.With the in-depth study of this technology,researchers have accumulated more perfect equipment and process development experience.However,the research on motion system configuration,motion precision requirements,dynamic performance,and sub-nano precision generation of IBF equipment is not deep enough.In the process of using IBF equipment to process ultra-high precision optical components in China,there are still some problems,such as low convergence ratio,difficulty in suppressing medium and high-frequency errors,and low production efficiency.The paper studies the influence of IBF equipment performance on sub-nanometer precision generation.The influence of motion precision and dynamic characteristics of IBF equipment on different types of optical elements is studied by error modeling of ion beam motion mechanism with different configurations,and the error-sensitive direction in the figuring process is determined.According to the requirements of sub-nanometer figuring accuracy,the static and dynamic performance requirements of the equipment are theoretically derived.Further,combined with the existing equipment accuracy and performance measured data,an optimized process scheme is proposed.The stable convergence of surface sub-nanometer accuracy is verified by experiments.The research work mainly includes :1.The influence of equipment static performance on machining accuracy is analyzed.Based on the theory of multi-body system error modeling,the motion error model of IBF equipment with a five-axis configuration and three-axis configuration is established.Combined with the actual measurement of important motion error terms,the influence of various errors(such as angle error,target distance error,and tangential error)on removal function and dwell time in figuring process is studied.The influence of motion accuracy on figuring accuracy is established.2.The influence of equipment dynamic performance on machining accuracy is studied.The sensitive direction of the dynamic performance of IBF is clarified based on the analysis of the realization of the dwell time of computer controlled optical surfacing(CCOS).The dynamic performance models of the scanning axis and the target distance axis are established.Based on this model,the influences of beam diameter,peak removal rate,error frequency and initial surface steepness on the accuracy generation are analyzed.3.The sub-nano precision machining method based on equipment performance is explored.Based on the influence law of the motion accuracy and dynamic performance of the IBF equipment on the machining accuracy,the dynamic and static performance requirements of the equipment in the sub-nanometer precision machining process are comprehensively analyzed.Combined with the existing motion accuracy of the equipment and the initial shape characteristics of the workpiece,the sub-nano precision rapid manufacturing process as well as parameter optimization strategy are proposed.4.Sub-nano precision machining method based on equipment performance is used for experimental verification.The experiment was carried out on the microcrystalline plane mirror.By optimizing the process parameters,the high convergence ratio processing results with a single processing convergence ratio of 9.5 and the high-precision processing results with low-frequency surface shape accuracy better than0.3 nm RMS were obtained respectively,which verified the correctness of the method. |
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