Research On Surface Defect Detection Of Wind Turbine Blade Based On Three-Dimensional Reconstruction

As a safe and reliable renewable clean energy,wind energy plays a vital role in optimizing the global energy structure.Wind turbine blade is the critical component to obtain wind energy,owing to prolonged exposure to severe outdoor working conditions,its surface will inevitably produce a variety of defects,if it cannot be repaired in time will cause serious impacts.For the rapid nondestructive testing of the wind turbine blade,especially the initial detection of blade surface defects can quickly find these defects to prevent secondary failures,thereby improving the safety of wind turbine.The three-dimensional reconstruction and defect detection based on structured light projection technology is extensively used in the field of three-dimensional detection due to its advantages of non-contact,large amount of information and high detection accuracy.For the purpose of achieving the three-dimensional defect detection on the surface of wind turbine blade,this thesis investigates the three-dimensional defect detection method based on structured light three-dimensional reconstruction technology,and the main work and research contents of this thesis are as follows:(1)The wrapped phase solution based on the four-step phase shift method and the phase unwrapping method based on the three-frequency heterodyne principle are studied,and the phase unwrapping method of modifying fringe orders is proposed to reduce the phase jump error and improve the phase accuracy in view of the factors such as noise and nonlinear response affecting the phase unwrapping accuracy based on the three-frequency heterodyne principle in the actual measurement.(2)The calibration accuracy of camera and projector determines the accuracy of structured light three-dimensional reconstruction.The monocular structured light system model is introduced,and the conversion relationship between two-dimensional pixel coordinates and three-dimensional spatial coordinates is derived.The principles and processes of camera calibration and projector calibration are depicted in detail,and calibration experiments are conducted.(3)The three-dimensional surface defect detection method based on point cloud data is studied.The pre-processing method of point cloud data is introduced,the surface reconstruction method based on greedy projection triangulation for visualization of surface defects is described,and the principle and process of three-dimensional point cloud defect detection based on ICP accurate registration algorithm are illustrated.(4)The experimental system of three-dimensional reconstruction based on monocular structured light is built,and the experiments of three-dimensional reconstruction of wind turbine blade and three-dimensional defect detection on wind turbine blade surface are completed,and the corresponding experimental results are given.