Grading potatoes with laser and mathematics. CULT IVAT ION AND T ECHNIQUE Because the belt has a controlled steady speed of 0.5 m per second, length is easy to calculate: divide belt speed by time and this will automatically result in the tuber’s length. The computer simultaneously determines the tuber’s width on the basis of the intensity of the light. The light is most intense in the middle of the tuber, the intensity gradually diminishes along the sides of the tuber, as a result of which the width and shape of the tuber can be calculated. The rounder the tuber, the faster the intensity diminishes. Because the tubers are not turning, the machine doesn’t make a 3-D image of the tuber. This means that they are only exposed from above. By measuring the angle between the beam on the potato and the beam on the belt, the height of the tuber can be calculated. The height, length, width and shape have now been established, this means that the volume can also be calculated. The square size is maximum width multiplied by maximum length, so, here we are, this parameter is also known. With the aid of mathematical calculations of the computer, the user can give the machine all kinds of grading instructions. In total, the machine can subdivide the potato flow into three different grades. To do this, two rows of rubber ejectors have been mounted beyond the laser beam. Depending on the outlet, the hollow pneumatically-driven mechanism pushes the potato into the desired direction. Practical test by customers After emptying the bag filled with around 5 kg of tubers up to 50 mm, the grading machine starts to run. Wepfer adjusts the machine for tubers shorter than 50 mm, tubers between 50 and 80 mm and tubers longer than 80 mm. The results are re-measured by customers from the Dutch potato trading company Korteweg, and their nodding heads indicate that the results have been accepted. Subsequently, more potatoes are added to the lot, after which a large field crop passes through the The results are checked by customers from the Dutch potato trading company Korteweg. machine with a speed of about 7.5 tonnes an hour. What catches the eye is that the process of pushing tubers in a different direction does not always go smoothly. The bigger tubers in particular tend to bump against the division strips and consequently do not end up in the correct flow. There are two reasons for this, according to Wepfer. “The optionally mounted transport belts have not been adjusted properly and the air pressure of the Climax compressor is a bit too low. This is approx. 6.5 and should be 7 bar.” Many possibilities Grading undersized chip potatoes on length can contribute to a better return on a potato lot. Moreover, such a machine can optimise the supply to the factory according to detailed specifications. As the tubers can also be counted, there are now numerous possibilities for the various markets. Precise grading on shape for consumption potatoes can improve the presentation in the bag. For microwave usage, four potatoes with exactly the same shape can be packaged. For seed potatoes, a grower would be able to indicate both weight and number. There are countless possible applications. The Samso machine, which can grade up to 15 to 20 tonnes an hour, costs 72,900 euros; this excludes VAT and the necessary transport systems. ● Jaap Delleman Hollow, rubber pneumatically-driven ejectors push the potatoes into the desired direction. Potatoworld 2006 27 Pagina 26
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