Three-dimensional shape measurement of specular object with discontinuous surfaces by direct phase measuring deflectometry

Abstract

Phase measuring deflectometry (PMD) has been widely studied to obtain three-dimensional (3D) shape of specular surfaces. Due to the procedure of slope integration, complicated specular components having discontinuous surfaces cannot be measured by the existing PMD methods. This paper presents a novel Direct PMD (DPMD) method to solve this problem of measuring discontinuous specular objects. A mathematical model is established to directly relate the absolute phase and depth data. Then a hardware measuring system has been set up. The system parameters are calibrated by using a plane mirror and a translating stage. 3D shape of an artificial specular step, a monolithic multi-mirror array having multiple specular surfaces and a reflected diamond distribution surface has been measured. The experimental results verified that the proposed method based on DPMD successfully measured full-field 3D shape of specular objects having discontinuous surfaces accurately and effectively.