Error Analysis Of Three-dimensional Reconstruction For Dynamic Objects With Asynchronous Cameras

Aircraft, ships, trains have become an indispensable tool for people to travel since the advance development in machinery manufacturing from 1990s, which contributes to the rapid development in the field of vehicle and aerospace. Structural vibration widespread exists in the field of machinery manufacturing, civil engineering, aerospace and so on, which causes potential threat for structure security, while vibration test is an effective way to evaluate its dynamic performance. Vibration test includes contact and non-contact method. And contact method includes mechanical measurement and electrical measuring method, non-contact method includes photoelectric measurement method. Electrical measuring method is the generally applicable method, but load will be generated and the accuracy and objectivity of measurement results will be affected. And this method is not suitable to vibration test for large structures or flexible structures. Photoelectric measurement method has been gradually become the trend for vibration test because of low cost, no loading mass, simple operation and high accuracy. Representative photoelectric measurement is laser Doppler method, which optical design is very strict and generally used in isolation sistuation. With the rapid development of high-speed industrial cameras and digital image processing technology, computer vision gradually applied to vibration test. Binocular stereo vision technology is a branch of computer vision, which object’s 3-D information can be reconstructed by 2-D images on the left and right image planes. Because the majority of vibration test in engineering is to measure small displacement, the precision of 3-D reconstruction of binocular stereo vision is extremely important. However, the research on error of binocular stereo vision currently focuses on static error, dynamic error analysis of binocular stereo vision is very rare. Therefore, it’s meaningful to establish and analyze the dynamic error model of binocular stereo vision.In this paper, binocular stereo vision technology is applied to vibration test. Parallel and non-parallel imaging models of 3-D reconstruction based on binocular stereo vision are established and 3-D reconstruction formulas of spatial point are derivated detailly. In order to analyze the accuracy of dynamic 3-D reconstruction, two non-synchronous 3-D reconstruction error model based on binocular stereo vision on the basis of the previous two imaging models are established.3-D reconstruction error induced by dual camera angle, unsynchronized time and parameters of sinusoidal motion such as amplitude, frequency is calculated assuming that spatial point respectively does uniform motion, random motion and sinusoidal motion in each axis. To verify the established error model, high-speed industrial cameras, capture cards, signal generator, electric vibration test platform, computer are used to bulit binocular stereo vision system. One single point tracking method is used in experiment, which circular feature points are attached on vibrating platform and these features can reflect the movement of vibrating platform. This paper presents an improved center detection algorithm, which reaches to subpixel accuracy and improves the accuracy of 3-D reconstruction. Experimental results indicate theoretical error trends are correct. The established error model can be helpful to guide how to place cameras and evaluate cameras’synchronization requirement according to object’s motion when binocular stereo vision is applied to vibration test in the future.