基于立体相位测量偏折术的预应力薄镜面形检测

Shape measurement of stressed mirror based onstereoscopic phase measuring deflectometry

应力抛光技术通过在镜面上施加预定载荷,将包括自由曲面在内的非球面转化为球面进行加工,对加工镜面的形变进行精准检测是实现高精度应力抛光的关键。利用立体相位测量偏折术对预应力薄镜进行镜面面形和形变检测,获得被测镜表面的连续相位分布,结合表面法线唯一性与梯度分布积分,最终得到被测镜的高度分布和面形。模拟了系统误差成分,同时采用旋转平均法对系统误差进行标定去除,保证和提高了测量精度。对一块口径320 mm,球面半径5200 mm的预应力薄镜面形和变形量进行测量,静态测量结果与三坐标机测量结果对比,动态应变测量结果与有限元仿真结果对比,分别一致吻合,表明本文方法具备微米级的测量精度,相比于干涉仪和三坐标机更适用于大面形变化的预应力薄镜检测。

Stressed polishing technology transforms aspheric fabrication into spherical fabrication by applying predetermined loads on the surface of the mirror.The key to achieve high precision of stressed polishing is to test the surface deformation with high precision.Stereoscopic phase measuring deflectometry was used to test the surface topography and the deformation of stressed mirror.After obtained unwrapped phase distribution,and combined with normal consistency constraint and gradient integral algorithm,the height distribution was finally obtained.Composition of systematic errors were simulated.Also,the errors were calibrated and removed by N-step averaging method in this system,which improved the measuring precision.In this paper,the surface topography and the deformation of a stressed mirror with a diameter of 320 mm,spherical radius of 5200 mm were measured.The measuring results were consistent with the corresponding result of CMM and finite element simulation, indicating that this proposedmethod is on the level of micron in terms of accuracy and more suitable for the test of stressed mirror compared withinterferometer and CMM.