METHOD FOR AUTOMATICALLY DETECTING CASTING DEFECTS IN A TESTPIECE

摘要

The invention relates to a novel method for automatically inspecting e.g., aluminium cast parts using a monocular sequence of X-ray images taken of the test piece in different positions. Known methods for the automatic detection of casting defects use modified median filters which estimate X-ray images that are free of defects using recorded X-ray images. These images are compared with each other and casting defects are detected when a particularl y great difference exists between them. However, the configuration of each filter depends to a considerable extent on the size, shape and position of t he constructional structure of the test piece. These characteristics of the tes t piece therefore have to be considered a priori. The invention provides a method enabling casting defects to be automatically detected in two steps. T he method uses a single filter and no a priori knowledge of the structure of th e test piece. Aside from calibration, the first step of the method segments hypothetical casting defects in each image in the sequence. The second step entails trying to trace the hypothetical casting defects in the image sequence. The basic idea behind the inventive method is the assumption that the hypothetical casting defects that cannot be traced in the sequence are detection errors. By usingthis method it is possible to detect true casting defects with maximum probability and eliminate detection errors. The process of tracing the hypothetical casting defects in the image sequence is carried out according to the principles of multiple image analysis. Bifocal, trifoca l and quadrifocal tensors are used to reduce the calculation time. A 3D- reconstruction is produced of the hypothetical casting defects traced in the image sequence, enabling those which do not belong to the test piece space t o then be eliminated. The robustness and reliability of the method are checked with semi-synthetic and real X-ray image sequences taken of an aluminium rim with known material defects. The true casting defects are detected and the detection errors are eliminated.