Fraunhofer Agriculture and Food Industry AllianceTea promises enjoyment and well-being, which is also confirmed by the consumption in Germany of about 70 liters per capita and year
To ensure that the tea remains enjoyable, high quality standards are required during product processing. One important quality feature is the purity of the tea, which is ensured by removing foreign bodies. A large number of foreign bodies that enter the tea on its long journey from the producer in distant countries to the processor must be removed by modern process technology. Despite modern technology, however, it is not possible to sort out all foreign bodies from the products.
The new opto-electronic FoodControl sorting system reliably removes foreign bodies of all kinds from a wide variety of dried foods. A prototype was developed together with the tea processor Salus-Haus in Bruckmühl near Munich and has been successfully in operation since June 2005. Further sorting systems have since been delivered to tea and dried vegetable processors in Germany.
SalusHaus has been operating a second IOSB sorting plant. Additional trials with dried vegetables and dried fruits have also been successful, so that an expansion of the industrial use of FoodControl is also expected in the corresponding product areas.
Process description
A vibratory conveyor ensures uniform distribution of the foodstuffs, which then slide onto a conveyor belt and are discharged at the end of the belt at a speed of approx. 2.9 m/s, well separated. Directly behind the discharge roller, an endless image is recorded over a width of 700 mm by a high-aufl lution color line scan camera with over 4000 pixels. The resolution is thus approx. 0.18 x 0.18 mm2/pixel or around 3000 pixels/cm2. Image background is a self-adapting illumination (chameleon), which assumes the color of the product.
Image evaluation guarantees reliable identification of foreign bodies by means of eight classificators. One classificator combines:
- a discrimination of 2.1 million colors,
- an area and length analysis, and
- up to 4 morphological operations.
A valve block with 256 nozzles shoots the detected foreign bodies out of the product stream. Depending on the product, the by-catch, i.e. the unwanted good product that is shot out, is only 0.5 - 3 %.