3D Shape Measurement Based On Digital Fringe Projection

During recent years, because of the development of digital photography andprojection, a3D shape measurement system based on digital fringe projection isincreasing popular. With the advantage of high precision, whole-field, non-contact,automatic, nondestructive feature, the technique has found various applications indiverse fields, such as security systems, mechanical engineering, virtual reality andreverse engineering. In this thesis project, a3D scanner based on digital fringeprojection has been constructed and developed. In order to improve the systemaccuracy performance, it is necessary to research the prime technologies:phase-shifting method, Fourier-transform method, gray code, system calibration.Phase-shifting method and the Fourier transform method are both fringe analysismethods. This thesis research focuses on utilizing these two methods to extract3Dshape information encoded in fringe patterns. For the ordinary Phase-shifting method,the fringe patterns on the projection surface are generated by a computer. The fringe patterns cycle is uniform, and use computer to extract the phase from these fringepatterns. Because of the Fourier transform method only use one fringe pattern toextract the phase, so it is suit for real-time3D shape measurement of dynamic objects.In contrast, the Phase-shifting method is more accurate than it. In this paper, we alsoselected representative encoding methods, their advantages and disadvantages werepresented. Based on the analysis results, the approach of the common coding methodgray code is studied. The advantages of gray code are optimized high stability andreduced error; it is very reliable and less sensitive to the surface characteristics, sinceonly binary values exist in all pixels. However, to achieve high spatial resolution, alarge number of sequential patterns need to be projected.According to these requires of3D surface measurement, we designed a low-cost3Dscanner based on digital fringe projection which adopts an improved Phase-shiftingmethod and Gray code approach. We present the scanner architecture, the softwaretechnologies adopted, and the first results of its use in a project regarding the3Dacquisition of a measuring workpiece and a black flat. Reconstruction results areincluded to demonstrate the attained quality.