Abstract
When phase-shifting (PS) and temporal-phase-unwrapping algorithms are employed for three-dimensional (3D) shape measurement, the measured object must be kept static during the projection and acquisition. If the measured object is moving, deviation among multiple fringe images will inevitably occur, which results in the 3D measurement error. In this paper, a novel 3D measurement technique for rigid moving objects obtained by using the PS algorithm and the three-pitch heterodyne-unwrapping (TPHU) algorithm is proposed, which consists of six steps. First, the pixel offset is estimated based on a centroid deviation calculation. Second, the phase offsets among multiple fringes are calculated. Third, a novel set of fringes for the projection is generated. Fourth, we offset the captured fringe images according to the pixel offsets to generate a new set of captured fringe images for the phase calculation. Fifth, the wrapped phase is calculated by the PS algorithm. Finally, the unwrapped phase is calculated by the TPHU algorithm. The proposed method can be applied to the 3D shape reconstruction of a rigid movement object with a determined movement trajectory and constant movement speed. This approach not only greatly improves the measurement efficiency but also inherits the high accuracy and robustness of the PS and TPHU algorithms.
Highlights
Fringe pattern profilometry (FPP) has become an important noncontact measurement method with full-field inspection, high resolution and accuracy.1–8 At present, it is a commonly used technique to calculate the absolute phase information by combining the phase-shifting (PS) algorithm9–11 with the three-pitch heterodyneunwrapping (TPHU) algorithm.12–18 it requires multiple fringes for the projection and acquisition
The measured object is carried to the 3D measurement station by a robot
The proposed method requires the movement trajectory and speed to be constant, it inherits the advantages of high accuracy and robustness of the PS and TPHU algorithms
Summary
Fringe pattern profilometry (FPP) has become an important noncontact measurement method with full-field inspection, high resolution and accuracy. At present, it is a commonly used technique to calculate the absolute phase information by combining the phase-shifting (PS) algorithm with the three-pitch heterodyneunwrapping (TPHU) algorithm. it requires multiple fringes for the projection and acquisition. Zuo et al. demonstrated a new 3D dynamic imaging technique, micro Fourier transform profilometry (μFTP), which can realize an acquisition rate up to 20000 3D frame per second (fps) They focused on improving the phase recovery, phase-unwrapping, and error compensation algorithms, which enabled the reconstruction of a 3D point cloud with every two projected patterns. They developed a high-frame-rate fringe projection hardware by pairing a high-speed camera and a DLP projector, which enabled binary pattern switching and precisely synchronized image capture at a maximum frame rate of 20000 fps Based on this system, they realized the 3D shape measurement of dynamic objects. Combined with two-step phaseshifting (TPS), Fourier transform profilometry (FTP), and optimum three-frequency selection method, the 3D shape measurement of complex surfaces, such as discontinuous objects, can be performed with a single measurement This method has been applied to simulations and experiments on static and dynamic objects with promising results.
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