Development of a high-precision surface metrology system using structured light projection

In this paper, we present a high-precision surface metrology system based on structured light projection. Gray code patterns are projected onto the object surface by a DMD projection device and a CCD camera captures the distorted pattern images. For the purpose of precision measurement, a 3D mathematical model is proposed for the system and a calibration process is developed to obtain system parameters. The pattern is encoded with a unique ID and correspondence pairs between the CCD and DMD can be found. The surface profile can be computed by the calibrated model. In order to acquire higher measurement resolution, we propose a correspondence matching method which combines Gray codes encoding and sub-pixel edge detection. With a line-shifting procedure, the measurement resolution is elevated four times higher. Experiment results demonstrate the system has measurement area of 12 × 9 mm2, with lateral resolution about 10 μm and vertical resolution about 3 μm.