Real-time 3D measurement of freeform surfaces by dynamic deflectometry based on diagonal spatial carrier-frequency pattern projection

Deflectometry is a three-dimensional optical technique based on structured light projection for measuring and inspecting specular freeform surfaces. Conventional deflectometry method needs complicated calibration and time-consuming phase-extraction algorithm, which are not suitable for industrial metrology requiring dynamic and high-speed measurement. In this paper, a novel dynamic deflectometry method with a simple system setup and calibration is proposed for the three-dimensional measurement of specular freeform surfaces with high speed and high accuracy. We developed a very simple calibration method using a reference flat mirror which helps to save calibration time and computer resources. We also proposed a one-shot method by using a spatial carrier -frequency diagonal fringe pattern for screen projection along with an algorithm to separate a diagonal phase into vertical and horizontal phases. We extensively evaluated the feasibility of proposed calibration and one-shot method by different simulations and measuring several specular surfaces experimentally. Our novel deflectometry gives similar measurement accuracy compared to traditional contact measurement technique while offering much higher measurement speed. Dynamic surface shape measurement of silicon wafer due to tem-perature's variation proved the real-time measurement ability of our proposed method.