High Accurate Three-dimensional Shape Measurement of Discontinuous Specular Surfaces by Stereo Direct Phase-Measuring Deflectometry

With the fast development of integrated circuits, photovoltaics, automobile industry, advanced manufacturing, and astronomy, it is particularly important to obtain the three-dimensional (3D) shape data of specular objects quickly and accurately. Owing to the advantages of large dynamic range, non-contact operation, full-field and fast acquisition, high accuracy, and automatic data processing, phase-measuring deflectometry (PMD, also called fringe reflection profilometry) has been widely studied and applied in many fields. Direct PMD (DPMD) can directly establish the relationship between phase and depth data without gradient integration process, so it can be used for 3D shape measurement of specular objects having discontinuous surfaces. However, compared with gradient data, depth data is more sensitive to measurement noise, so the measurement accuracy obtained by gradient field integration is higher. In order to make use of the anti-noise property of gradient measurement structure, some PMD techniques usually abandon the height data obtained from the intermediate process and use the gradient data to complete the surface reconstruction. Stereo deflectometry is a typical representative to retrieve 3D shape of the measured object according to the gradient integration. It calculates the gradient field based on the uniqueness of the normal vector of the object points by using two cameras. Although obtaining high-precision measurement results, this method cannot be used for the measurement of discontinuous objects. In this paper, a new stereo DPMD method is proposed to obtain 3D shape of specular objects having discontinuous surfaces. Some experimental results on measuring discontinuous specular objects verify the high precision of the proposed stereo DPMD method.