Temperature fringe method with phase-shift for the 3D shape measurement

Linear laser fast scanning thermography technology has a good application prospect in the nondestructive detection of defects. Meanwhile, due to the modulation of the surface topography, the thermal response fringes excited by the line laser are distorted in the scanning process, whereby the three-dimensional topography of the specimen can be reconstructed. However, the accuracy of this method is currently limited by unfavorable factors, such as background noise of the specimen surface and the extraction error of the deformed temperature fringes. In this paper, by optimizing the initial position difference during line laser scanning and converting the laser fringes with specific position difference into temperature fringes with specific phase difference, the phase shift technique is combined with the temperature fringe method. What's more, some post-processing algorithms were developed to further develop the temperature fringe method and greatly improve the accuracy of the method. By measuring some specimens with different shapes and different colors, the results show that the technology and algorithms developed here can obtain the three-dimensional shape of the measured specimen with high accuracy while having a non-destructive testing function, without interference from the surface color of the specimen.