Measurement And Evaluation Of Three Dimensional Surface Profile Of Large-Diameter Aspheric Optical Elements

The application of large-diameter aspheric optical element improves the imaging resolution of optical system and simplifies the system structure.Therefore,it has been widely used in the fields of national defense,aerospace,lithography laser and so on.However,During the process of machining high-precision large diameter aspheric mirrors,the development of aspheric optical element manufacturing is restricted by the detection technology.Therefore,the establishment of ultra-precision testing technology is the focus of modern optical manufacturing engineering research.Different testing techniques are needed for large-diameter aspheric lens in different manufacturing stages.In this paper,the measurement technology of large-diameter aspheric lens in grinding stage is mainly studied and discussed.In this stage,the surface roughness of optical elements is large,so the interference method is not suitable for detection.The coordinate detection technology has excellent measurement flexibility,reliable measurement data,and can meet the detection accuracy requirements of large-diameter aspheric surface optical components in the grinding stage.Therefore,the coordinate detection technology is the main detection method applied in the grinding stage at present.However,the detection process is faced with many problems,such as: detection path planning,high-precision fitting method and pose error correction and other problems,so the establishment of a reasonable detection technology is to improve the detection accuracy of the premise and foundation.The research work mainly includes the following aspects: a reasonable path planning for a large-diameter aspheric optical element with a diameter of 350 mm was carried out,and the three-dimensional surface shape of the optical element was measured by the Global Classic SR0575CMM;The nonlinear least square fitting method with high fitting accuracy was used to process the measured data,and the surface profile parameters of the large-diameter aspheric optical element were obtained,and the surface reconstruction of the aspheric mirror was realized by the above parameters.Based on the proposed fitting algorithm,the surface profile precision of the aspheric mirror was obtained by different detection paths was analyzed.The experimental results show that the proposed squirrel cage detection path can achieve high precision surface profile measurement and has high fitting accuracy.The influence of pose error on the measurement results was analyzed,and the pose error correction model was established.The reliability of the proposed algorithm was verified by comparing the UPMF900 calibration instrument with the ultra-precision measuring instrument PGI 3D.The results show that the high precision machining measurement can be achieved by using a reasonable testing path,a high-precision fitting algorithm and a reliable pose error correction system for large-diameter aspheric optical elements.