Second- and first-order phase-locked loops in fringe profilometry and application of neural networks for phase-to-depth conversion

Second- and first-order phase-locked loops (PLLs) are applied to recover phase information from projected fringes recorded experimentally. The phase recovery is studied in terms of loop gain coefficients for both PLLs. Second-order loop compared to first-order loop recovers larger phase changes. Values of the phases thus recovered are compared with phases recovered by Fourier transform method. Neural networks are used to obtain depth information from phase planes and their known positions. The spatial period of the projected grating is calculated using Fourier transform of the image of the grating. An analysis is presented of second- and first-order loops in terms of performance comparison for extracting the phase information from fringe patterns. The use of neural network and automatic calculation of spatial period brings the measuring system closer to complete automation. (C) 2003 Elsevier Science B.V. All rights reserved.