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The use of optical shape sorting in the bulk food industry

02/15/2012 In the bulk food industry, we often refer to optical sorting machines as ‘colour sorters’. This convention reflects the fact that the first models sorted solely on the basis of colour. Today colour sorting still covers the majority of sorting applications. The term ‘colour sorting’ is used rather loosely in the industry and includes sorting with monochromatic (greyscale) and colour cameras (e.g. bi-chromatic) as well as using visible or infra-red wavelengths of light. However, there is an increasing number of applications where the ability to sort by shape is an essential function. The term ‘shape sorting’ refers to the detection of defects either by shape alone or by some combination of shape and colour.

Brief history
One of the main drivers for the introduction of shape sorting technology into optical sorting machines was the so-called ‘killer application’ of detecting stalks on fine green beans. Once shape sorting was well-established in sorting green beans, the technology was soon adapted to other applications in the fruit and vegetable sectors. The next major innovation in shape sorting was the transfer of the technology from the fruit and vegetable sectors to applications in the dry commodities sector, such as coffee, nuts and pulses.

The transfer of shape sorting to dry commodities brought new challenges, which required further enhancements to the technology. For example, dry products tend to be sorted at comparatively greater throughputs per width of machine, resulting in more clumping of the product stream. One of the main enhancements was the addition of an image processing technique known as ‘object separation’, which enabled the sorting by shape of individual items even when some of these were touching other product pieces.

Today, shape sorting is one of the core technologies of Bühler’s SORTEX optical sorters and is available on the company’s entire range of bi-chromatic optical sorters.

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