| Over the recent years nuclear power plants motivate the need for more challenging scenes with the automation and intellectualization reactor operation detection due to the national pays more attention to zero emissions of nuclear power and other clean energy.3D underwater measurement is a significant part of security inspection in nuclear power engineering.The structured light 3d measurement is implemented in high-precision fields and has many advantages such as high imaging efficiency,great real-time performance,and high accuracy so as to meet most requirements.In this paper,the 3D underwater measurement based on grating projection was studied deep,and the underwater measurement system for nuclear fuel assembly was developed by combining image technology and point cloud processing technology,which is vital for thesafe and reliable operation of nuclear reactor.The main contents are as follows:This paper presented an overview of two different time coding methods including phase shift method and Gray code method by studying the principle of structured light3 D imaging.The error source of grating projection technology applied in underwater environment was analyzed,and the error model of phase solution and expansion were constructed.The four-step phase-shifting principal value solving algorithm and multi-frequency heterodyne phase unwrapping algorithm were proposed to correct the phase unwrapping error of phase-shifting grating and the non-sinusoidal distribution of underwater grating.Further,a phase fusion method based on multi-brightness was presented to improve the quality of image to handle different reflection regions on the image of objects.The comparative results confirmed that the method can correct efficiently the error,so as to improve the accuracy of underwater phase solution and the integrity of 3D model.The imaging model and calibration method were presented by using expansion and erosion to improve the efficiency of system calibration and realize automatic calibration without manual interference.The segmentation of different checkerboard images and the automatic positioning and extraction of internal corner points were realized.The correspondences between different coordinate systems wered obtained by accurately computing the homography transformation matrix and counting coplanar property between the actual checkerboard pattern and the projection checkerboard pattern.The system parameter calibration was completed by introducting of the underwater equal-focal length model and automatic parameter calibration of the underwater grating projection measurement system including camera calibration and projector calibration was realized.The model between different tube seats was established to detect vertical distance and horizontal distance in underwater nuclear fuel elements measurement by considering the 3D model characteristics.The noise was removed and the feature region location and extraction were realized by applying the point cloud segmentation algorithm.The vertical distance measurement method of pipe base based on RANSAC algorithm was designed by comparing and analyzing the performance of the point cloud model plane fitting algorithm.In order to improve the number of effective points of model,a 3D plane projection method was introduced,and the horizontal spacing of tube base was measured based on Euclidean point cloud segmentation algorithm.Since the real-time requirements was considered,an optimization algorithm based on boundary extraction was extracted to improve the efficiency.A 3D measurement system with raster projection which took the underwater nuclear fuel elements as the measurement object was designed by considering object-oriented hierarchical architecture and the functional requirements.Windows10 and VS 2013 were selected and Qt,Open CV,PCL and SQLite were used to realize the function development of measurement software.The experiment proves the feasibility and the accuracy of the grating projection 3D underwater measurement system. |
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