Three-Dimensional Profile Measurement Using Structured Light Method

Three-dimensional profile measurement is now widely applied in different areas, such as reverse engineering, computer vision, on-line product inspection and medical diagnosis. A non-contact, simple and rapid method for three-dimensional profile measurement is presented in this paper, which is based on structured light projection. The principle of this method is to project a computer-generated structured light pattern on the surface of the measured object, and then a distorted pattern caused by the object height is recorded from another angle. Finally surface profile of the object is obtained by demodulating the phase information from the deformed image.What is contained in the thesis is as following:(1) The mathematical model of three-dimensional profile measurement using structured light method is introduced based on a typical crossed-optical-axes geometry, and then discuss the problems faced in phase demodulation using Fourier transform method. A p phase shifting method is proposed to increase measurement range which is confined by object gradient.(2) The principle of phase unwrapping and main phase unwrapping methods is introduced, and a new phase unwrapping algorithm which is based on reliability ordering is proposed to overcome the phase error propagation problem caused by noise. The core of the method is that pixel with higher reliability value will be phase unwrapped earlier according to reliability criteria and queue ordering. In this way it can bypass noise automatically, and solve problem of error propagation, and the experimental results of phase unwrapping show that this algorithm is effective for noise.(3) A system calibration method is presented firstly, and then the system error is analyzed theoretically. Based on the theoretical analysis and computer simulation, we design an experimental system for three-dimensional profile measurement. The system is fulfilled with a computer controlled projector to display structured light and a CCD camera to detect the deformed image, and the hardware and software of the system are designed also.The key techniques like phase unwrapping and system calibration are investigated in this paper, and experiments show that it can obtain good results using structured light method to measure three-dimensional profile.