Automated High-Dynamic-Range Three-Dimensional Optical Metrology Technique

Measuring three-dimensional (3D) surfaces with extremely high contrast (e.g., partially shiny surfaces) is extremely difficult with optical metrology methods. Conventional techniques, which involve measurement from multiple angles or camera aperture adjustments, pose issues for high accuracy measurement in the manufacturing industry because they are difficult to automate and often induce undesirable vibrations in the calibrated measurement system. This paper presents a framework for optically capturing high-contrast 3D surfaces via flexible exposure time variation. This technique leverages the binary defocusing technique that was recently developed at Iowa State University to allow digital fringe projection with a camera exposure time far shorter than the projector’s projection period. Since the camera exposure time can be rapidly adjusted in software, the proposed technique could be automated without mechanical adjustments to the measurement system. Moreover, the exposure times are sufficiently short as to be efficiently packed into a projection period, giving this technique the potential for high speed applications. Experimental results will be presented to demonstrate the success of the proposed method.