Mr. Xi Xu Profile

Xi Xu

at Beijing Institute of Technology

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Publications (2)

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Proceedings Article | 21 December 2022 Presentation + Paper

Defect and deformation comprehensive measurement method based on dual-wavelength speckles

Tianshuang Han, Yao Hu, Xi Xu, Qun Hao

Proceedings Volume 12315, 123150H (2022) https://doi.org/10.1117/12.2641994

KEYWORDS: Speckle, Cameras, Speckle interferometry, Imaging systems, 3D metrology, Defect detection, 3D vision, Calibration

Read Abstract +

Composite materials are widely used in aviation, aerospace, and other fields. Poor service conditions, insufficient stiffness or strength of materials and other problems can cause deformation and defects of composite materials, affecting their service life and safety. Optical detection methods can measure composite materials' surface deformation and internal defects separately. However, there is a lack of comprehensive measurement methods for defects and deformation in these optical detection methods. It causes the problems of complicated detection steps, inefficiency in engineering, and is not conducive to in-depth analysis of the detection results. This paper proposes a comprehensive defect and deformation measurement method based on dual-wavelength speckles, which is beneficial for solving the above problems. The measurement system includes four parts: the control module, the speckle binocular vision module for 3D morphology measurement, the speckle interferometry module for internal defect detection, and the data processing module. Firstly, the system should perform trinocular calibration. Then, the control module controls the speckle interferometry module and the speckle binocular vision module to emit lasers with different wavelengths. Speckles of different colors and sizes are formed on the surface of the composite material specimen. The cameras corresponding to the two modules are controlled to capture speckle images. The data processing module processes the speckle images separately to obtain defect and morphology information. It then uses the information fusion algorithm to integrate the 2D defect and 3D morphology information to complete the measurement. Composite material specimens with internal defects of different sizes and shapes were measured. Finally, the comprehensive detection of both internal defects and 3D morphology of composite materials was realized with this method.

Proceedings Article | 8 July 2022 Paper

Three-dimensional measurement with stereo polarization digital image correlation method insensitive to ambient light

Xi Xu, Yao Hu, Shaohui Zhang, Qun Hao

Proceedings Volume 12282, 1228202 (2022) https://doi.org/10.1117/12.2615100

KEYWORDS: Polarization, Cameras, Speckle, 3D metrology, 3D modeling, Digital image correlation, Image fusion, Calibration, 3D image processing, Optical testing

Read Abstract +

The measurement of the external topography and deformation of large industrial equipment is important. Photoelectric measurement technology can quickly obtain three-dimensional (3D) topography information of components and equipment. Among them, stereo digital image correlation (stereo-DIC) is a 3D measurement method which combines binocular stereo vision system and digital image cross-correlation matching technology. This method has many advantages such as non-contact, wide measuring range, high speed and single frame reconstruction. However, this passive optical measurement method is prone to the interference of ambient light and the impact of high reflective surface, resulting in data loss, which limits the application scenarios of this method. This paper proposes a method of 3D reconstruction against ambient light based on stereo polarization digital image correlation (stereo-PDIC). In this method, speckle is generated by a laser beam irradiating a ground glass and is then projected onto the surface of the target. The polarization speckle image in single frame and multiple polarization channels is collected by binocular polarizing cameras. The influence of the reflected stray light and ambient light is eliminated and the contrast of speckle image is improved. Stereo matching of the speckle images with the corresponding angle of polarization captured by the binocular polarizing cameras is carried out, and finally the 3D reconstruction of the target is completed. The feasibility of this method is verified by both simulation and experiment.

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