Applied Study On Modulation Measurement Profilometry

With the fast development of non-contact optical three-dimensional (3D) sensing, three-dimension sensing methods with structured illumination, such as phase measurement profilometry (PMP), Fourier transform profilometry (FTP), and modulation measurement profilometry (MMP), have received great attention in recent years.Modulation measuring profilometry depends on the modulation distribution of the sinusoidal fringes projected on objects. The depth information is encoded into the fringe modulation patterns, instead of the deformed fringe patterns. The main advantage of this method is no shading problem, which is inherent to all triangulation techniques. Until now two techniques based on MMP principle have been developed, including MMP based on phase shifting technique and MMP based on Fourier fringe analysis. Contrary to phase shifting technique, Fourier fringe analysis is a faster technique of calculating modulation distribution. To calculate one frame of modulation pattern, only one frame of fringe pattern is needed. This dissertation is focus on the applied study on MMP based on Fourier analysis. The main results obtained can be summarized as follows:1. Method of design for measurement system of MMP is systematically established based on depth-of-modulation and the parameters of the measurement system have been designed and the measurement system has been set up.2. Method of calibration of the measurement system based on MMP is proposed. According to the method, several parallel planes have been measured and a look-table is made to reduce the system error of every CCD pixel.3. Several algorithms of depth retrieval from the modulation distribution are discussed carefully. A new depth retrieval algorithm based on the model of Gaussian point spread function is proposed, which uses the Gaussian distribution to interpolate the modulation to obtain the accurate depth map.4. Depth of modulation, an important system parameter, is to be presented and discussed in detail. It not only affects the measurement accuracy, but also decides other system parameters. A smaller depth-of-modulation causes modulation peaks more sharply, which means the high resolving capability of modulation. Other system parameters, which influence the accuracy of the measurement system, are discussed also.5. Two practical vertical scanning techniques and video image capture technique is used to set up more practical measurement system based on MMP. The new system is smaller and robust.6. The influence of the phase-shift miscalibration and the harmonic content of the fringe image to the measurement accuracy of MMP based on phase-shift technique is discussed in detail. An algorithm is proposed to eliminate the effects of both the phase-shift miscalibration and the second harmonic.This work will be important to the application of modulation measurement profilometry.