Currently, advanced aero engines are developing towards high rotational speed, efficiency, thrust weight ration, reliability and turbine inlet temperature, which needs measuring and inspection technology of high level to support the design and manufacturing procedure. Along with the development of measurement technology and other related disciplines, as a kind of non-contact measuring method, optical measuring technology could be used to cope with so many problems which may be difficult or un-solvable for those traditional inspecting manners. Further, as a branch of the optical measuring technology, machine vision uses industrial cameras etc. to distinguish, measure and locate the target and 2D of the target to derive information, which possesses such advantages as compact structure, rich information and flexible application etc. Under this background, fruitful research has been carried out in the aspect of machine vision measuring and inspecting technology of key geometrical features of aero engine such as film cooling hole, blade-shaped hole and blade defect. Also, related special equipments have been developed to realize the efficient inspection of those key geometrical features.
In view of the characteristics of low precision, unstable quality and high rejection rate of the current gas film hole molding, there is no universal and engineered gas film hole detection equipment in China. A set of image detection equipment based on machine vision is developed to improve the efficiency and accuracy of the gas film hole detection. According to the depth of field synthesis and three-dimensional reconstruction technology, the resolution of pixels of different pictures in the same location is analyzed. Thus, the evaluation function of the pixel is obtained, and then each pixel is calculated, and the depth information of the pixel is given to complete the three-dimensional reconstruction. This paper proposes a method for evaluating the pixel clarity of gas film holes in turbine blades. Since the edge detection algorithm of traditional Sobel operator is poor, this paper proposes four-direction and eight-direction Sobel operators to evaluate the pixel clarity of standard measure blocks with the same material of gas film holes by giving different weights. Then, according to the experimental results, the window size of pixel sharpness evaluation was discussed, and the clarity ratio, steepness, local extreme factor and sensitivity of different window sizes were calculated respectively. Finally, the window size suitable for the evaluation of pixels in the air film hole was obtained. Finally, all the pixels were calculated, and the calculation results were compared with the real situation to verify the correctness of the proposed algorithm.
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