Research On Key Technologies Of Blade Profile 3D Measurement Based On Digital Grating Projection

As the key core of an aero engine,aero-engine blades become more and more important for high efficiency and high precision inspection of blades.The traditional three-coordinate measurement method is difficult to efficiently measure the complex contours of blades,so it is an important trend to use structured light methods with rapid measurement characteristics to detect blades.However,the existing blade high-precision structured light measurement system is mostly monopolized by foreign products,which is difficult to be popularized by blade-related manufacturing enterprises.Under this background,this paper combines binocular vision theory and structured grating projection method to study the key technology of three-dimensional blade profile measurement.The main research contents of this paper include:(1)The measurement theory of the binocular vision system is studied,the epipolar line constraint conditions and the stereo correction theory of the binocular camera are respectively deduced,the parallax solution model under different optical axes is analyzed,and the principle of point cloud solution in the case of crossed optical axes is mainly studied.Then,the coordinate relationship transformation between the camera and the three-dimensional space in the system is deduced,and the left and right cameras and the projector are calibrated using the Zhang Zhengyou calibration method and the inverse camera method respectively.Finally,through analysis of Zhang Zhengyou's method,the remaining problems of system calibration optimization are found,and a system calibration optimization method based on external parameter constraints is proposed according to the calibration error model.(2)The research and analysis of Gray Code structured light and sinusoidal grating structured light projection principle are conducted,and the phase-unwrapping principle of the four-step phase shift method are further deduced.This paper mainly focuses on the research of phase-unwrapping algorithm based on sorting by reliability following a noncontinuous path.On this basis,a fast phase unwrapping algorithm based on multiple pigeonhole adaptive sorting is proposed,which not only effectively avoids the wrong solution in the phase unwrapping process,but also greatly improves the efficiency of phase unwrapping.(3)The principle of phase-based stereo matching under grating projection is studied.After studying and improving of the SAD matching algorithm,an improved SAD algorithm based on difference matrix is proposed,which is applied to absolute phase matching.Then,the efficiency and accuracy of disparity map solving under different size matching windows are analyzed and compared to further verify the effect of the improved SAD matching algorithm.Finally,the stitching method of blade poinst cloud obtained from different perspectives is studied,and the mosaic method of blade point cloud obtained from multiple perspectives can be realized adaptively.(4)An experimental platform for the 3D reconstruction system of binocular structured light is built,which can perform system calibration,phase unwrapping,disparity solving,blade point cloud computing and mosaicking with high efficiency and precision.The profile reconstruction and accuracy analysis of the calculated blade point cloud are carried out.According to the solution of disparity map,the method to improve the accuracy of the point cloud is studied,the sub-pixel phase matching optimization method is proposed,and the precision of the blade point cloud before and after optimization is compared and analyzed.Experiments show that the 3D reconstruction system of blade structured light developed in this paper can achieve the point cloud acquisition of blades with high precision and efficiency.