Research And Improvement On Measurement Method For The Three-Dimensional Shape Of Object Surface With Grating Projection

Three-dimensional shape measurement of object surface is now widely applied in different areas, such as reverse engineering, computer vision, online product inspection and medical diagnosis. A measurement method for the three-dimensional shape of object surface with grating projection is researched in this dissertation theoretically and practically. The basic principle of this method is to project a grating pattern on the surface of the measured object, and then a distorted strip pattern caused by the object height is recorded from another angle. Finally surface 3-D shape of the object is restructured by processing the pattern in computer and demodulating the phase information. The main contributions of this dissertation are as follows:The principle of three-dimensional shape measurement using the method of grating projection is stated based on a typical crossed-optical-axes geometry. The hardware in this measurement system of three-dimensional profilometry that consists of projecting light, CCD camera, image card and computer is designed. At the same time, a software package for measurement system is developed with Visual C++ 6.0 and MATLAB 7.0; and the system containing optical module, image collecting and image processing module has been calibrated.In the dissertation, the key techniques of measurement, such as pretreatment, phase demodulation, phase unwrapping for strip pattern and system calibration are investigated: advanced"normalized"algorithm is posed to demodulate the phase information of simply object successfully; all kinds of improved Fourier transform profilometry (FTP) is three times wider than traditional FTP in measure scope, and the measure precision has been improved obviously; new noise-immune phase unwrapping algorithm can check the location of the noise spot of phase wrapped map, reduce the noise impact on phase unwrapping, and raise the accuracy of it. It is proved that this measurement method for three-dimensional shape of object surface with grating projection presented in this dissertation can obtain good results.