In many processes we accept input material indiscriminately and continue to sift through it looking for the materials we are interested in. For example when processing harvested produce we wish to separate any foreign objects that might have been added to the mix from the actual produce we want to process or when recycling garbage we would like to be able to separate different type of garbage to different processing units – paper, plastic, glass etc.
Sorting by hand is costly in labor, inconsistent in results, limited in its ability to assess the material at hand and often can only cover a portion of the processed material. Optical sorting on the other hand is non-destructive, consistent in results, often allows 100% inspection of material volume and with increasing sophistication of both optical technology and image processing tools has an ever-increasing pool of inspection abilities.
Though there are numerous industries where optical sorting is used by far the two biggest industries are in food processing and in recycling, each with its own distinct needs and problems.
When recycling for plastics, for example, the aim is to remove foreign materials such as wood or polymeric materials, parts with unwanted colors and other more specific elements while grouping the accepted material granules based on individual color.
Food sorting is commodity dependent as the process with which you sort apples in different from the one you’d use for oranges and even when with grains and seeds every species and type need a different sorting mechanism. Luckily for us the properties that we need to measure are usually the same – color, size, shape etc. and we only need to change to model to which our system is referring to.
At the forefront of optical sorting technology are the hyperspectral cameras which allows us to image the materials over a large portion of the electromagnetic spectrum into narrow continuous bands and in essence allows us to analyze the material locally at the chemical level to find hidden defects that would have otherwise eluded us. This technology also allows us to create ever more sophisticated and precise models of the products we are trying to sort.