Study On Phase-shift Algorithms And Analysis Of Errors In PMP

Phase Measuring Profilometry (PMP) is an important technique of 3-D shape measurement, which is based on fringe patterns projection and phase measurement. It has been widely used in industrial inspection, machine vision, inverse engineering etc because of the merits of noncontact, full-field, high-precision and high-speed.The measuring accuracy of PMP is influenced by the factors such as phase-shifting miscalibration, nonsinusoidal fringe patterns, detector nonlinearity, rationality of phase-shift algorithm and digital camera focusing-error etc. This dissertation focuses on the study of phase-shift algorithms and phase-measuring errors. The main results obtained can be summarized as follows:1. Detector nonlinearity is the main source of measuring-error in PMP . This dissertation gives the theoretical analysis and the computer simulation of this error, and compares the capability of tolerance for detector nonlinearity while N-frame phase-shift algorithms are used. The conclusion that N-frame algorithm is insensitive to less than (N-1)th order detector nonlinearity is drawn.2. A method is introduced that used the characteristic polynomials to design phase-shift algorithms. Three novel algorithms are proposed to eliminate the effectof phase-shift miscalibration and harmonics or detector nonlinearity. Computer simulation tests the tolerant capability of novel algorithms for these errors.3. As a new type of spatial-light modulator, digital micro-mirror device(DMD) will have a wide prospect in optical information processing and structured illumination 3-D sensing. In this dissertation, the Spatio-temporal characteristic of DMD is introduced and the effect on PMP due to the Spatio-temporal characteristic of DMD is discussed by computer simulation. The result can give the guidance for the application of DMD in structured illumination 3-D sensing.4. In PMP, the deformed fringe patterns are sometimes captured by an autofocus digital camera. The measuring accuracy of PMP will be influenced by the digital camera focusing-error. In this dissertation, the experiment phenomenon is presented, which verified the digital camera focusing error. The statistical analysis and computer simulation are performed, and an expression of statistical relationship between the phase-measuring error and the focusing-error is given. Several factors influencing the phase-measuring error are discussed and a method to decrease or avoid this error is put forward.