New color sorting technology

by Roger Cook
Share This:

Used for many years in rice milling, color sorters have in recent years become a vital component in the wheat flour milling process.

Color sorters first became common in non-rice grain mills 10 years ago. Their use prior to that can be traced to only a few very selective installations such as low capacity removal of black tip from durum wheat and some oat mills. By 2005, capacities and prices had just brought machines within the range of flour and semolina millers. Referring to Moore’s Law, the observation that computing power doubles every two years, it’s not surprising that in the eight years that have since past, electronic sorting technology has also grown at an extremely rapid rate.

The machines that were available in 2005 were just starting to evolve from analogue-based systems to digital processing. Almost all the units sold were monochromatic, that is, depending on the manufacturer, an optical system consisting of colored lamps and/or lens filters. These colors, normally red or pink for wheat sorting, serve the purpose of “hiding” the color of the good grain from the camera’s sensor and enhancing the signal that is coming from lighter or darker material passing through the machine. Monochromatic sorting therefore is also well described as a “contrast” or “black and white” sort, since the machine has no understanding of the actual color of the material.

From monochromatic sorting, machines using additional NIR or InGaAs cameras have been widely promoted, though the claims by some companies that they’re introducing “new technology” are not perhaps sustainable as these systems were available in nut and special commodity sorters for many years prior to their popularity in grain processing. Machines with additional NIR or InGaAs cameras were generally referred to as “bi-chromatic.” This definition has lost relevance because manufacturers have also given this name to dual wavelength visible spectrum sorters.

The progression of sorting systems has led more and more to the reconsideration of the generic term “color sorter.” Monochromatic machines don’t actually see real color and NIR/InGaAs cameras are able to see differences in materials of the same color. In addition, some suppliers have offered shape or size recognition as a bolt-on to their normal sorting software. Therefore, we should better refer to the process as “optical sorting.”

The future of optical sorting lies in the development of machines with real full color imaging. These machines are able to capture red, green and blue (RGB) colors as combined photographic type images. This higher level technology is able to “see” as the human eye and recognize 16 million individual colors. Full color or RGB sorting technology is creating new possibilities and levels of accuracy unimaginable 10 years ago.

Mono and bi-chromatic sorters with their simple darker or lighter sensitivity settings are generally not too tough for even an inexperienced operator to understand. Asking that same person to comprehend the core principles of a three dimensional RGB system with 16 million values is a lot harder.

ROEber optoselector

German equipment specialist PETKUS Technologie GmbH addressed this issue with the launch of its ROEBER OptoSelector at the Agritechnica tradeshow in November.

ROEBER’s new OptoSelector uses an intuitive system called “TeachNSort” to self-learn the full RGB color range of the good material. When setting the machine for the first time, the operator simply feeds in a sample of around 20 kilograms of good grain. Within a second or two, the color profile is automatically generated. Material that does not match this good color profile is rejected. Those familiar with optical sorting will realize the key point of difference here. Conventional sorting relies on setting the parameters of the material to be rejected. OptoSelector recognizes the good material and rejects the rest. A practical example of the benefits of this would be comparing what happens when a monochromatic machine set to remove dark black and brown defects encounters a piece of orange plastic. It would be unlikely for the plastic to be recognized and therefore it would not be rejected. OptoSelector’s software knows that the orange plastic is not good grain and will reject it also.

Next appears another sophisticated feature of the OptoSelector. Each individual grain is recognized, whether it is good or bad, allowing a complete geometric analysis to be made. The parameters of area, length, width, stretch, compactness and symmetry can be checked and values for acceptance or rejection of the material configured. Sorting based on shape characteristics allows oats and barley to be removed from wheat, strengthening the case for making indented cylinders redundant in mill screenrooms. The recognition of each grain allows accurate data acquisition and statistical reporting of both good grain and contamination levels. The cumulative area measurements can be used to make an accurate estimation of flow rates and capacities.

Illumination systems have also significantly advanced in the last 10 years. The florescent tubes normally used to illuminate the product viewing area are being replaced with LED systems. The problem with fluorescent tubes is their change in lighting qualities after around 2,500 hours of use and differences caused by high and low temperatures. While not always significant in expense terms, regular replacement of fluorescent tubes is a necessary maintenance task on older style machines. LED’s provide almost limitless life and lower power consumption. However, not all LED systems are the same. OptoSelector uses a specially developed ultra-high density LED array and diffuser system for very even illumination.

PETKUS Technologie GmbH, the sole distributor of ROEBER in the seed and grain areas, provides full service and support for OptoSelector through its network of global offices. A full internet-based online service is also available, and because OptoSelector displays in real-time the color image of the material being sorted, remote technicians can make assessments and optimizations without having to visit the mill.

The demand for cleaner grain, higher levels of product security, improved energy efficiency and reduced good grain lost in the wheat screening process are driving the development of optical sorters. Full color RGB technology with geometric analysis opens up many new and exciting possibilities for the milling world.

Roger Cook is optical sorting applications manager for PETKUS Technologie GmbH. He can be reached at