Research On Three-dimensional Profilometry Based On Temporal Phase Unwrapping

Optical three-dimensional (3D) sensing is a very important research direction. The 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. The profilometry based on fringe phase analysis such as PMP, FTP can only return phase ranging from -π to +π by phase extraction methods(phase shifting, Fourier transforming). Phase unwrapping is necessary to recover the object shape. On a practical wrapped phase map, there are usually (?)oises, shadows and discontinuities, witch can often make spatial phase unwrapping based on spatial coordinate fail. The difficulty in phase unwrapping has become the largest obstacle that prevents grating projection profilometry from automation and practical applications.The basic idea of temporal phase unwrapping is that the pitch of projected gratings is (?)aried over time. Compared with the spatial phase unwrapping, the temporal phase (?)nwrapping can unwrap at each pixel independently of all the other pixels in the image. The elimination of cross talk between pixels means that spatial propagation of the phase errors is prevented. The outstanding advantage of the method is that it can measure the shapes of discontinuous object, and it can unwrap the discontinuous object easily as the continuous object. So temporal phase unwrapping is an important methods in the field of phase measurement, and it has been applied widely in interferometry and structured illumination, ncluding speckle interferometry, shearography, wavelenth scanning interferometry, photoelasticity, PMP, FTP and et al. This dissertation focuses on the three-dimensional profilometry based on temporal phase unwrapping. The main results obtained can be summarized as follows:1. Based on an intuitionistic physical model, we discussed the basic principle and the phase unwrapping algorithm designing. Then we also compared several main temporal phase unwrapping on the aspects of data acquisition time, computation time and standard deviation. At last we analyzed and gave comments on the new development and its application.2. Several typical temporal phase unwrapping are analyzed by experiment. From the analysis we proposed a different method of height coordinates calibration based on temporal phase unwrapping. To recover the continuous phase distribution of all steps with the same height, and tu adjust the fitted phase surfaces of three virtual calibration planes to their ideal positions relative to the reference plane, reversal exponential temporal phase unwrapping is adopted. The propose method avoid the complicated iterative process of the former method. The experimental results prove that the proposed method is effective and feasible.3. The method of determining the proper frequency range of low-frequency grating was proposed. Frequency-Optimize of two-frequency phase measuring profilometry with low-frequency grating of different frequency and temporal- noise was analyzed theoretically and simulated numerically. It is significant especially for the reconstruction of discontinued objects.4. We have a further study about composite phase measuring profilometry(CPMP) which only one such composite grating can recover the depth. And we compare CPMP with PMP on the aspects of experiments and theories. The measurement precision and application range of CPMP is illuminated It is significant for the application of composite phase measuring profilometry.5. A novel method is proposed, in which a composite grating is projected. The composite grating is formed by modulating two separate fringe patterns with π phase difference along the orthogonal direction of the two distinct carrier frequencies. The method can eliminate zero frequency by using only one fringe pattern. The experiments show that there is no distinct decrease in the precisionof the novel method compared with the traditional π phase shifting technique. So, the novel method can allow for real time and high-speed...