Enhancement of measurement accuracy of discontinuous specular objects with stereo vision deflectometer

Phase measurement deflectometry (PMD) is widely used for specular surface measurement. However, when the measured surface is discontinuous, its measurement accuracy will decrease due to the slope integration process in PMD model. This paper proposes a method to realize high-precision measurement of discontinuous specular object using stereo vision deflectometer (SVD). The discontinuous surface is separated into continuous areas by region segmentation method to avoid the integration error of PMD. Then, slope integration is conducted in each continuous surface region to achieve high measurement accuracy. The absolute position of a height reference point (HRP) of each continuous surface is calculated to evaluate the relative positions between different surfaces. The performance of the proposed method is verified by measuring two sample specular objects with discontinuous surfaces. The experimental results show that the continuous surfaces can achieve nanometer level form measurement accuracy, while the absolute height measurement accuracy is in micrometer level.