At the moment foreign substances in food are detected mainly by using
mechanical and optical methods as well as ultrasonic technique and than they are removed from the further process. These techniques detect a large portion of the foreign substances due to their different mass (mechanical sieving), their different colour (optical method) and their different surface density (ultrasonic detection). Despite the numerous different methods a considerable portion of the foreign substances remain undetected. In order to recognise materials still undetected, a complementary detection method would be desirable removing the foreign substances not registered by the a.m. methods from the production process. In a project with 13 partner from the food industry, the Fraunhofer - Institut für Holzforschung (WKI) and the Technische Unsiversität are trying to adapt thermography for the detection of foreign bodies in the food industry. After the initial tests turned out to be very promising for the differentiation of food stuffs and foreign substances, more and detailed investigation were carried out to develop suitable algorithms for automatic detection of foreign bodies. In order to achieve -besides the mere visual detection of foreign substances- also an automatic detection under production conditions, numerous experiences in image processing and pattern recognition are exploited. Results for the detection of foreign bodies will be presented at the conference showing the different advantages and disadvantages of using grey - level, statistical and morphological image processing techniques.
This paper gives a short introduction into the possibility of detecting foreign bodies in food by using IR thermography. The first results shown for combinations of cherries and chocolate and berries contaminated with leaves, stalks, pedicel and thorns could be easily evaluated manually. Therefore the differing emissivity coefficients or the different heat conductivities and/or capacities are used for differentiation. Applying pulse thermography, first heat conductivity measurements of different food materials are performed. Calculating the contrast of possible food / contaminant combinations shows the difficulty of differentiating certain materials. A possible automatic evaluation for raisins contaminated with wooden sticks and almonds blended with stones could be shown. The power of special adapted algorithms using statistical or morphological analysis is shown to distinguish the foreign bodies from the foodstuff.
Two remote and nondestructive testing techniques for the study of the decay mechanism of stone and plaster surfaces are presented. While electronic speckle pattern interferometer (ESPI) measures the 3-D-microdeformations of the surface, transient thermography shows at the same time invisible defects and structural faults as a reaction to the impact of short heat pulses. The combination of these two different techniques demonstrates its feasibility to detect restorative work and shows the compatibility of classical and modern substitutes and restoration techniques to historical materials.
A double shear speckle interferometer is presented that can provide information about the
curvature, i.e., the second order derivative of the out of plane displacement of an object under study.
Here, two shear interferometers are kept in sequence or tandem. The sheared images formed by the
first interferometer are sheared once again by the second interferometer. The shears at the image
plane can be adjusted for the required magnitude and orientation. A double exposure record is made
on a photographic plate before and after the object deformation. When the processed plate is
subjected to Fourier filtering, the curvature information is seen as a Moire of the two sheared slope
fringe patterns. The results for a centrally loaded diaphragm are presented. The advantages of the
present technique over the existing methods are discussed.
Deterioration of historical murals often leads to partial detachments of the paint carrying plaster layers. To identify such regions an acousto-optical method is described. Loose portions of the plaster are excited by sound waves and the resulting vibrations are detected by sensitized analog TV-holography.
Holograms of a particle field illuminated by a set of light sheets are made simultaneously on one recording material differing each in reference beam direction and coherence properties. Each sheet can thus be evaluated separately by ordinary PlY techniques. 2.