面向精密制造的光学自由曲面在位偏折测量技术  

In-situ deflectometric measurement of optical surfaces for precision manufacturing

作　　者：张祥朝[1] 徐敏[1] Zhang Xiangchao;Xu Min(Shanghai Engineering Research Centre of Ultra-Precision Optical Manufacturing,Fudan University,Shanghai 200438,China)

机构地区：[1]复旦大学上海超精密光学制造工程技术研究中心,上海200438

出　　处：《光电工程》2020年第8期70-79,共10页Opto-Electronic Engineering

基　　金：国家自然科学基金资助项目(51875107);国防基础科研科学挑战专题(JCKY2016212A506-0106)。

摘　　要：复杂光学曲面的在位测量是当前精密工程领域面临的重要难题。偏折术对光学曲面的测量精度可与干涉仪相比,而且拥有更高的测量效率、稳定性及动态范围,因此具有广阔的应用前景。但是偏折测量本质上是一个标定问题,其测量精度直接取决于几何标定的可靠性。本文结合单点金刚石切削机床设计了原位偏折测量系统,采用机床中自带的气浮转台安装辅助反射镜,在两个姿态下进行光线追迹,通过数值优化计算各元件之间的相对位置,将标定精度提高一个数量级。根据反向投影偏差的统计规律,可有效分离工件的面形偏差与位姿误差。该方法有效利用了工件的名义面形信息,将传统的位置-面形单向映射转变为双向映射,显著提高了在位测量的灵活性与效率。对于复杂的自由曲面,采用子孔径拼接测量方法,对待测的局部区域发展了精准定位技术,有效保证了迭代重构过程的正确收敛。采用离轴抛物镜等光学曲面进行实验验证,所提出的偏折测量方法的精度优于150 nm RMS。The in-situ measurement of complex optical surfaces is a challenging task in precision engineering.The phase measuring deflectometry is a powerful measuring method for complex specular surfaces,and it has higher measuring efficiency,stability and dynamic range compared to interferometry.Consequently it is promising to widespread applications in various fields.Deflectometry is essentially a calibration problem,and the measuring accuracy is directly determined by the quality of geometrical calibration.An in-situ deflectometric measuring system is designed based on the single point diamond turning machine.A self-calibration method is developed to specify the relative positions of the camera and screen.Ray tracing is conducted at two positions of an auxiliary reflecting mirror,which is mounted on an air bearing spindle.The accuracy of the geometrical positions can be improved by an order of magnitude by minimizing the deviations of the traced points with respect to the true correspondences.According to the statistical properties of the deviations in reverse ray tracing,the form errors and the position errors can be separated,and the positioning error of the workpiece can be corrected accordingly.Henceforth,the nominal shape of the fabricated workpiece can be fully utilized, and the conventional one-way position-form mapping can be convertedinto a two-way mapping problem. As for the complex shapes, the whole surface can be covered by sub-aperturemeasurement. Precise localization of a local region under test is achieved by multi-position imaging, so that correctconvergence of the iterative reconstruction process can be guaranteed. Several typical optical surfaces including anoff-axis paraboloid mirror are measured, and the measuring accuracy of the proposed method is proved better than150 nm RMS.

关 键 词：光学制造 在位测量 偏折术 几何标定 光线追迹 

分 类 号：TH741[机械工程—光学工程] TH247[机械工程—仪器科学与技术]