The Improvement Of Fourier Transform Method For 3D Shape Measurement

As technology and industrial production evolves, there have been more and more demands for 3D shape measurement in practical applications, including CAD/CAM, industrial inspection, quality control, reverse engineering, machine vision and biomedical engineering. Presently, with the features of non-contact, fast speed and high accuracy, the active 3D optical measurement has been one of the research hot spots.Fourier transform profilometry is one of the most popular active 3D optical measurement methods, with the advantage of high accuracy and fast acquisition speed. After the intensity distribution of the reference plane captured, this method requires only one more frame of the deformed fringe pattern to retrieve the surface of measured object, through a process of calculating Fourier transformation, filtering in frequency domain, calculating inverse Fourier transformation and phase unwrapping.This paper aims to improve the traditional Fourier transform profilometry. And the improvements are mainly reflected in the following aspects.(1) In the process of extracting the fundamental frequency component of deformed fringe pattern, there exists a problem of selecting filter windows in the traditional filtering methods. Therefore, a time-frequency analysis method based on smoothing is presented and successfully implemented into the extraction of the fundamental frequency component.(2) Since the phase calculated by conventional Fourier transform methods are wrapped phase, the phase unwrapping step is essential to gain the actual phase, which is a complex and time-consuming process. To solve this problem, a novel method utilizing a color fringe pattern is presented. Using the color information to calculate the phase shift range, the actual phase can be obtained directly without phase unwrapping. Therefore it can highly accelerate the calculation speed of 3-D profile measurement.(3) In the conventional phase-to-height model, there are so many constraints that make the 3D shape measurement hard to carry out in general cases. Therefore, we present a novel model with fewer constraints. The proposed technique requires neither a specific and precise experimental setup nor a manual measurement of geometric parameters. It can highly improve the measurement accuracies and thus broadens the application range of the fringe projection 3D shape measurement methods.