One-shot deflectometry for high-speed inline inspection of specular quasi-plane surfaces

Deflectometry is a non-contact optical technique which uses a simple system setup to measure and inspect specular surfaces. Conventional deflectometry methods usually need very complicated system calibration and time-consuming phase-shifting methods, which are not practical for high-speed measurement. But if the measurement target is a quasi-plane surface where the local slope is directly modulated by phase, the complicated system calibration can be neglected. In this study, to reduce error, we investigated and analyzed error contribution when measuring quasi-plane surfaces. A simple and high speed one-shot phase retrieval method is proposed for quickly measuring surface phase. We used a single high carrier-frequency composite pattern for pattern projection, and derivation of the captured fringe pattern for phase retrieval. A phase-related slope is obtained for slope calculation and the 3D shape is reconstructed by integrating the surface slopes. We verified our proposed method by measuring representative quasi-plane surfaces and comparing results with conventional methods.