Studies On Fourier Transform Profilometry (FTP) Technology

Three dimensional surface measurement has been widely used for machine vision, industry monitoring, biomedicine, real object visualization etc. Fourier transform profilometry (FTP) based on fringe projection is one of the popular non-contact full-field 3-D measurement methods. This method requires only one frame of deformed fringe pattern reflected by a diffuse object surface, so it is very suitable for real time data acquisition and 3-D measurement of dynamic process. It consists of the following contents:The mathematical model of FTP phase measurement method is analyzed. The relationship between the phase and the height is researched. At the same time, the basis theory of wavelet transform is introduced.A phase demodulation technique in frequency domain based on Wavelet transform is investigated. Handling the original modulated grating image with wavelet transform, the object background image is created. And subtracting these Two images, a relative distorted grating image is obtained. The back ground components in spectrum of the relative image are basically removed and the useful one is leached easily. The steep gradient and complex object shapes can be measured automatically with this technique.After the algorithms of phase unwrapping is studied, a new phase unwrapping method — binary mask of surface features blocks is proposed. First of all, Image segmentation technique based on iterative calculation for threshold deal with the invalid measure-area due to local shadows, unlighted background, fringe discontinuities, etc. The first mask can effectively segment the object from its background. Second using the method of directional wavelet transform to get the distorted blocks in which many poles appear. and to construct the binary control mask, the control mask identifies valid and invalid discrete phase distribution, and remains the errors of phase unwrapping within the local confines successfully.A new calibration method for 3D machine vision, which combines height calibration with position calibration, is expounded. And Applying GeoMagic processed the spots cloud data and produces completed surface by shape integration.Finally, This thesis presents the structure of the measuring system and put forward the front subsystem (computer major control unit).