Thermal imaging & vision systems

Hyperspectral imaging C

Hyperspectral imaging provides its users with a high-performance possibility to determine differences in the chemical composition of test objects. This technology opens up interesting applications in areas such as recycling or food production, as Stemmer Imaging explains

onventional machine vision systems use parameters such as size, colour and shape to search for defects or

contaminants in the objects whose quality is to be checked. Systems that operate on the basis of hyperspectral imaging (HSI) take a different approach: they enable a spectroscopic analysis of the inspected materials to be carried out along with the coloured marking of the chemical composition of the substances. In this way both organic and inorganic contaminants can be detected with a single system. In the food industry, amongst others, this

capability allows a wide range of possibilities to find contaminants in foodstuffs. Even in high- speed production lines, hyperspectral imaging systems identify foreign matter such as shell fragments or other substances in the production of nuts as well as stones or earth when sorting potatoes; they classify meat, fat and cartilage contents in meat production or identify substances that barely look any different to the human eye at first glance, such as sugar, salt and citric acid. “The range of applications for hyperspectral imaging is extremely varied,” stresses Gerhard Stanzel, who specialises in this technology at Stemmer Imaging and has helped numerous customers with the successful implementation of such systems in recent years. “Apart from the detection of foreign matter, the task in food production is often one of detecting rotten or unripe goods or goods infested by pests such as fungi. A further area of application in which this technology is very often used is the recycling of plastics. Apart from these two fields, however, there are many more areas of application, among others mining or the pharmaceutical industry, in which HSI systems could offer a cost-effective solution.”

More THan 100 wavelengTHS Hyperspectral imaging mainly differs from image processing in the visible, UV or IR range in that more than 100 different wavelengths are frequently used for the analysis of the results. Depending on the technology in use, a spectrograph is required for this that splits the light into its spectrum and projects it onto the sensor of the camera. These images are then combined to form a three-dimensional data cube, which can contain very large quantities of data. In this way a “chemical fingerprint” of the pictured substance is created, allowing an exact


Jelly beans - their different shapes and colours, but similar density, make it hard to identify them by conventional methods

Hyperspectral imaging reveals the jelly beans

analysis of the test objects. A special evaluation software thereby enables each chemical component in the captured image to be given its own colour marking. “This allows even the different chemical compositions of substances that look very similar to be reliably detected and illustrated. Chemically identical substances in objects that look different can also be determined with the help of HSI systems,” says Stanzel.

InSpecTIon THrougH THe packagIng

One aspect of this technology is particularly interesting for various applications of hyperspectral systems: infrared light can penetrate through certain substances that are non-transparent to visible light. This property can thus be used to check the chemical composition of packaged contents even through correspondingly designed packaging. As one example of a specific application from

the food industry, Stanzel mentions the inspection of heat-sealed joints in cheese

April 2019 Instrumentation Monthly

packaging at the cheese manufacturer Bergader: “Such heat-sealed joints ensure the absolute airtight packaging of cheese or sausages. Even the tiniest contamination or damage can lead to leaking packaging and thus to the perishing of the foodstuffs before the calculated sell-by date. Possible consequences are unsaleable products or expensive recall actions.” With the support of Stemmer Imaging, Minebea Intec, a leading manufacturer of weighing and inspection solutions, implemented a heat-sealed joint inspection system for the cheese manufacturer Bergader that achieves almost 100 per cent reliability in the detection of

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