Real-Time 3-D Measurement Based on Dual-Frequency Hierarchical and Time-Interleaved Fringe Projection

Real-time 3-D measurement is valued for its practicality. However, achieving high algorithmic robustness and high reconstructing efficiency simultaneously remains a challenge due to their mutual constraint. Therefore, an innovative dual-frequency hierarchical phase-measuring profilometry (DFH-PMP) is proposed to achieve high algorithmic robustness and less computation time. While three high-frequency phase-shifting gratings and a couple of low-frequency complementary gratings are projected onto the measured object at a high refresh rate, by establishing two brand-new phase resolving model, the high-frequency and low-frequency phases just caused by the measured object itself are directly obtained from the five deformed patterns. By removing redundant phase components, DFH-PMP increases the frequency of low-frequency gratings, leading to improved low-frequency phase accuracy and reduced high-to-low frequency ratio, thus achieving high algorithmic robustness. Also, it simplifies the computational flow, reducing computation time. Furthermore, two innovative time-interleaved fringe projection (TIFP) strategies are also proposed to improve reconstructing efficiency. By interleaving the projection of two designed sequences, these strategies improve reconstructing efficiency from one reconstruction for every five patterns in normal strategy to an equivalent of one reconstruction for every three patterns and an equivalent of one reconstruction for every two patterns, respectively. Rigorous mathematical analyses are conducted to evaluate the motion-induced error of proposed strategies. Experimental results demonstrate proposed method achieves high algorithmic robustness and high reconstructing efficiency simultaneously and has prospective application in real-time 3-D measurement.