Application of FTP in Rail Profile and Surface Flaw Detection Based on Orthogonal Two-Frequency Composite Grating

摘要

In order to reconstruct the rail profile and flaws on the rail surface, we aim to use the improved Fourier Transform Profilometry (FTP) based on the orthogonal two-frequency composite grating. The different modulation information caused by the rail profile and surface flaws can be obtained by the same frame of deformed fringe pattern of composite grating. After a basic process of FTP, the rail profile and flaws on the surface can be respectively reconstructed from the wrapping phase of the low frequency and high frequency. It is easier to perform the phase unwrapping from the spectrum with a lower frequency and longer equivalent wavelength, but the accuracy of measurement is inversely proportional to the equivalent wavelength. Accordingly, the accuracy of the image recovered with high frequency is higher than that recovered with the low one. So the rail shape is reconstructed from the low frequency part of the composite grating and the surface flaws are reconstructed from the high part, both with high accuracy. Simulations, error analysis and experiments were made. Results show that FTP based on the orthogonal two-frequency composite grating can meet the need of the actual measurement in the detection of the rail profile and surface flaws.