Automatic 3D measurement and classification
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An important task in quality assurance is to identify, whether a part that has been exposed to corrosive atmospheres is free of relevant three dimensional surface corroded areas such as deep or shallow pits. We demonstrate a 3D metrology device which contains special modules for fully automatic measurement and classification of small scale surface corroded areas. The device is based on the focus variation technology to obtain both dense 3D data even for large areas and perfectly registered true color information. In contrast to other systems that only perform a 2D classification of corrosive areas the proposed system entirely relies on 3D information for corrosion detection. First the surface is scanned laterally and vertically to obtain the depth data and the true color information. Then special filtering stages are performed to restrict the classification to relevant area details with corrosion. Afterwards the depth information is analyzed to detect the corroded areas, which are then listed in a table together with parameters such as their depth, area or volume. Among additional information, a true color image of the whole surface with all marked corrosions is created. The measurement system is especially designed to allow fast corrosion measurement over large scan areas up to 200x200mm at high resolution. The measurement is not restricted to planar surfaces, however also parts with cylindrical or arbitrary form can be measured. Recent improvements include the increase of the scan speed by a factor of ten and the design of a special ringlight illumination with controllable segments that is ideally suited for the measurement of difficult samples with large corrosive areas. Examples are provided for different applications including the automatic measurement and classification of corrosions on aluminum plates with corrosion depths of a few micrometers and on curved parts. A comparison between manual corrosion segmentation and the automatic system demonstrates the accuracy of the proposed device. In the field of corrosion and erosion the system has already been applied to several applications including corrosion evaluation on steel samples.