Chinese Optics Letters

Research background

 

Structured light three-dimensional (3D) reconstruction has been widely used in medicine, aerospace and other industrial fields. As one of the 3D reconstruction methods of structured light, phase-shifting profilometry (PSP) has attracted much attention due to its high accuracy and robustness. PSP is used to obtain the 3D shape of objects by collecting and solving the fringe patterns projected onto the object surface with phase information. The phase information of PSP has periodic phase ambiguity of (0-2π). The traditional method requires additional fringe patterns to determine the fringe period, which undoubtedly increases the time cost and limits the area of usage scenarios. With the increased of application scenarios such as dynamic object reconstruction and real-time object scanning in industry, traditional PSP cannot meet the requirements.

 

Research progress

 

In recent years, researchers have proposed lots of methods to improve the dynamic measurement capability of PSP. However, it is always difficult to ensure both accuracy and measurement efficiency simultaneously. In order to solve this problem, Dr. Liu Fei's group in Chongqing University proposed an inner shifting-phase coding fringe projection profilometry. Related research results were published in Chinese Optics Letters Vol. 20, Issue 11 in 2022, under the title of "Shichao Yang, Fei Liu, et al. High-speed three-dimensional shape measurement with inner shifting-phase fringe projection profilometry", and was selected as the cover.

 

This method embeds fringe order decoding information and wrapped phase information into three fringe patterns. The wrapped phase and fringe order are obtained only by 3 fringe patterns, which are needed 12 patterns in the traditional method. The flow chart of the 3D reconstruction of inner shifting-phase coding fringe projection profilometry is shown as follows:

 

Fig. 1 Reconstruction process of the inner shifting-phase coding fringe projection profilometry

 

It is seen from the flow chart that there are mainly four steps: acquiring the wrapped phase, calculating the background intensity and shifting phase, unwrapping the phase, and reconstructing the 3D model. Compared with the traditional method, which requires additional multiple fringe patterns to unwrap the phase, this method simultaneously obtains the wrapped phase and fringe order from three patterns. The number of projected patterns is only one-third of that of the traditional method. A standard sphere precision measurement experiment has been conducted in the paper. the experimental result proves that the two methods have the same precision.

 

In order to verify the performance of the proposed method in measuring dynamic objects, a 3D measurement experiment of high-speed vibration of aircraft models was prepared. The aircraft wing vibrates at high speed under the blowing of the fan. The real-time 3D data of the aircraft model and the dynamic trajectory information of the three points on the wing are given by the inner shifting-phase coding fringe projection profilometry proposed in this paper. The experimental results show that the proposed method is applied to high-speed dynamic 3D measurement. This method is simple and effective, which provides a new idea for 3D dynamic measurement research.

 

Fig. 2 Real time three-dimensional measurement of aircraft model with high-speed vibration

 

Future outlook

 

The inner shifting-phase fringe projection profilometry proposed by researchers has solved the contradiction between high accuracy and high dynamics of 3D measurement, but it is still insufficient for the measurement of reflective parts such as metals. In the future work, researchers will conduct in-depth research on the 3D measurement of highly reflective objects.