The large-size blade is the core component of nuclear power and ultra-supercritical steam turbine, and its existing dimension detection methods generally have the problems of low detection efficiency or insufficient accuracy. So, an efficient and high-precision measurement technology of full profile based on multi view structured light 3D measurement is proposed in this paper. And several key factors affecting the measurement accuracy are analyzed. Then a highlight elimination technology combining multi view and phase shift is proposed to eliminate the effect of specular on the smooth metal surface of the blade. A non-overlapping point cloud registration method based on feature constraints is presented to solve the difficulty caused by the lack of overlapping point cloud on the thin inlet and outlet edges of blade and other areas. Finally, a platform for the whole profile of large-size turbine blade is constructed to realize the full profile measurement and evaluation of large-size turbine blades. The measurement results show that the full surface point cloud of an about 900mm long blade is completely obtained by the measurement platform, and the measurement accuracy of 70μm is achieved through the comparison test of high-precision gauge blocks and some standard balls.
Against the overall data layering problem caused by the different precision of each component in the multi-visual structured light measurement system, a compensation method based on spatial interpolation with an error library composed of 3D point clouds is proposed. First, the corresponding relationship between each monocular structured light system and the reference binocular structured light system is established by the unique code value, which is determined by the orthogonal coded fringe patterns projected by different systems. And an error library is constructed by comparing the measuring coordinate values of datum points in different measurement systems. Then an Inverse Distance Weighted method (IDW) based on the K-D tree neighborhood is proposed to complete the error compensation of measuring points in the measurement space, so as to improve the data quality of the whole system after complementary fusion. Different from the traditional error compensation method, this paper focuses on the multi-view structured light measurement system, from the point cloud data end for the measurement end compensation, to achieve the comprehensive compensation of complex error. Finally, experimental results show that the proposed method has outstanding effect and practicability.
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