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In three-dimensional (3D) shape measurement based on phase analysis, the phase analysis process usually produces a wrapped phase map ranging from − π to π with some 2 π discontinuities, and thus a phase unwrapping algorithm is necessary to recover the continuous and nature phase map from which 3D height distribution can be restored. Usually, the minimum discontinuity phase unwrapping algorithm can be used to solve many different kinds of phase unwrapping problems, but its main drawback is that it requires a large amount of computations and has low efficiency in searching for the improving loop within the phase’s discontinuity area. To overcome this drawback, an improvement to speedup of the minimum discontinuity phase unwrapping algorithm by using the phase distribution on reference plane is proposed. In this improved algorithm, before the minimum discontinuity phase unwrapping algorithm is carried out to unwrap phase, an integer number K was calculated from the ratio of the wrapped phase to the nature phase on a reference plane. And then the jump counts of the unwrapped phase can be reduced by adding 2 K π , so the efficiency of the minimum discontinuity phase unwrapping algorithm is significantly improved. Both simulated and experimental data results verify the feasibility of the proposed improved algorithm, and both of them clearly show that the algorithm works very well and has high efficiency. [ABSTRACT FROM AUTHOR]

Phase-measuring deflectometry (PMD)-based methods have been widely used in the measurement of the three-dimensional (3D) shape of specular objects, and the existing PMD methods utilize visible light. However, specular surfaces are sensitive to ambient light. As a result, the reconstructed 3D shape is affected by the external environment in actual measurements. To overcome this problem, an infrared PMD (IR-PMD) method is proposed to measure specular objects by directly establishing the relationship between absolute phase and depth data for the first time. Moreover, the proposed method can measure discontinuous surfaces. In addition, a new geometric calibration method is proposed by combining fringe projection and fringe reflection. The proposed IR-PMD method uses a projector to project IR sinusoidal fringe patterns onto a ground glass, which can be regarded as an IR digital screen. The IR fringe patterns are reflected by the measured specular surfaces, and the deformed fringe patterns are captured by an IR camera. A multiple-step phase-shifting algorithm and the optimum three-fringe number selection method are applied to the deformed fringe patterns to obtain wrapped and unwrapped phase data, respectively. Then, 3D shape data can be directly calculated by the unwrapped phase data on the screen located in two positions. The results here presented validate the effectiveness and accuracy of the proposed method. It can be used to measure specular components in the application fields of advanced manufacturing, automobile industry, and aerospace industry.

Large components are widely used in aerospace, shipbuilding, automobile, and other fields. The accuracy of three-dimension (3D) measurement is an important standard to measure the quality of production and assembly of the whole equipment. Due to the large-scale and difficulty in measuring complex surfaces, some optical methods for measuring 3D shapes are difficult to apply. Optical 3D shape measurement technology based on the main theoretical basis such as close-range industrial photogrammetry and stereo vision 3D shape measurement technology based on fringe structure light projection has developed rapidly. Currently, there is no review paper to comprehensively introduce these technical methods. To fill this gap and stimulate further research, we conducted a comprehensive investigation on the 3D shape measurement methods of large-scale complex surfaces, including the basic principles, application scope, measurement instruments, and systems of various methods, discussed the tasks and challenges faced by the current research, and provided potential solutions. [ABSTRACT FROM AUTHOR]

Phase-measuring deflectometry (PMD)-based methods have been widely used in the measurement of the three-dimensional (3D) shape of specular objects, and the existing PMD methods utilize visible light. However, specular surfaces are sensitive to ambient light. As a result, the reconstructed 3D shape is affected by the external environment in actual measurements. To overcome this problem, an infrared PMD (IR-PMD) method is proposed to measure specular objects by directly establishing the relationship between absolute phase and depth data for the first time. Moreover, the proposed method can measure discontinuous surfaces. In addition, a new geometric calibration method is proposed by combining fringe projection and fringe reflection. The proposed IR-PMD method uses a projector to project IR sinusoidal fringe patterns onto a ground glass, which can be regarded as an IR digital screen. The IR fringe patterns are reflected by the measured specular surfaces, and the deformed fringe patterns are captured by an IR camera. A multiple-step phase-shifting algorithm and the optimum three-fringe number selection method are applied to the deformed fringe patterns to obtain wrapped and unwrapped phase data, respectively. Then, 3D shape data can be directly calculated by the unwrapped phase data on the screen located in two positions. The results here presented validate the effectiveness and accuracy of the proposed method. It can be used to measure specular components in the application fields of advanced manufacturing, automobile industry, and aerospace industry. [ABSTRACT FROM AUTHOR]