Optical sorting

Screening Used to separate solid waste components hy Trommels and horizontal and vibrating screens for Optical sorting Used to separate plastics... 

High-speed drop sorters may continue to increase in speed, although the high pressures required in these sorters may have reached their limit in terms of the viability of the sorted cells. Optical sorting (by using a laser to inactivate unwanted cells or chromosomes) may... 

A. S. Zelenina, R. Qnidant, G. Badenes, and M. Nieto-Vesperinas, Tunable optical sorting and manipulation of nanoparticles via plasmon excitation. Optics Letters 31 p. 2054-2056 (2006). 

Figme 6.1 shows a typical layout for an optical sorting machine. 

The term colour sorting arises from the effect on the overall product appearance as a result of optical sorting. Unfortunately, the term is misleading. 

Monochromatic sorting is based on the measurement of reflectance at a single isolated band of wavelengths. For optical sorting to be effective, there must be a distinct difference in reflectance within the selected waveband, between all the acceptable particles and all the reject particles (see Fig. 6.4). Removal of dark, rotten items from product like peanuts, or dried peas and removal of black peck from rice are typical applications of monochromatic sorting. 

An optical filter is essentially a piece of coloured glass. An extensive range of optical filters are readily available as off-the-shelf components. Alternatively, custom filters can be made at a higher cost. Four basic types of filter are used for optical sorting applications ... 

To detect small blemishes on frait and vegetables reliably, it is necessary to inspect the product from two sides. The traditional architecture of an optical sorting machine is to feed the product along a horizontal conveyor and then observe the product from top and bottom views as the product flies off the end of the conveyor. The drawback with this approach is that the bottom camera is soon covered in product. The Sortex Niagara machine overcomes this problem with the PowerShde feed system (Fig. 6.14). The belt conveyor on the Niagara is inclined at 60° to the horizontal, such that the cameras can view the product from either side, and remain clean. This novel feed mechanism is known as the PowerSlide and is patented by Sortex. 

A sophisticated optical sorting machine will track the average colour of the product so that, even though the average product colour may change with time, the machine will continue to remove only the predefined abnormal particles. Optical sorting machines are often provided with a white calibration plate which is either manually or automatically placed in the optical view at user-defined intervals. The machine is then able to correct for any measurement drift that has occurred. 

A major part of setting up an optical sorting machine is to achieve the best overall accept/reject ratio for the product being sorted. The operator can do this by using the user interface to adjust the shape and size of the map contour (Figs. 

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