Multispectral imaging system for the structural analysis of highly transparent technical surfaces

Modern surfaces are often used as technical design elements. The high-quality appearance of these surfaces is crucial. Depending on the application, different requirements such as colour, reflectivity and resistance have to be met by the surfaces. Surface defects in highly transparent materials such as cover glasses, windows and displays affect long-term stability and distract the user. This paper shows the development of a camera-based measurement system for the investigation of structural defects in highly transparent materials. The requirements for a system like the one presented here are comparable to solution qualities of the human eye. The system is particularly suitable for the detection of surface imperfections with depths in the single μm range and widths below 50 μm as well as lengths in the mm range. At the same time, however, it can also be used to evaluate the gloss, scatter and contrast of the surface for rating the appearance quality of those. For this purpose, the setup was designed in which a sample in darkfield configuration is illuminated with an angled, multispectral LED array that can be individually switched sectorally and also uses the usual reflection approaches