February 2021

T he German manufacturer Sesotec specialises in product inspection and material sorting systems that help the food industry to produce food safely and profitably, and to cut waste. For example, it offers detectors that spot metal contaminants – such as wires or shavings – and X-ray systems that can identify non-metallic contaminants, such as glass or plastics. The food industry has become a complex, globally networked operation with many participants. Raw materials at various price and quality levels are bought internationally and are often sold, stored and processed far from where they were originally produced. The extended transport paths and multiple loading processes increase the risk of contamination. "Manufacturers need precise technologies to comply with the legal standards regarding food safety," explains Sesotec’s r&d director, Hermann Sammer. “However, an increasing degree of automation means fewer personnel and fewer inspections by employees in the production chain. The risk of any foreign objects present in the food not being detected thereby increases.” One problem faced when monitoring food products is the wide variety of colours, shapes and materials that may be encountered. In particular, packaging materials may be flat, glossy or transparent, and may have openings. They are not easy to detect using conventional sensors which typically scan from the side and cannot always detect the front edges of packaged products reliably. “The problem often manifests itself in the form of multiple triggering – especially at high conveyor speeds,” Sammer explains. This problem is especially acute with irregularly- shaped items such as fish and meat where individual pieces have differing dimensions. The same is true for the plastic outer packaging materials used for fruit and vegetables. In attempt to deal with such variations, Sesotec is testing a novel switching sensor that promises to detect every type of object and product packaging reliably, independent of its colour, shape and surface structure. The sensor – a device based on a new technology called Contrast Adaptive Teach (Cat) developed by Leuze – views objects from above. It uses the object’s environment as a teachable reference surface rather than the object itself. In packaging systems, the conveyor belt acts as this reference. Once the diffuse sensor has been taught contrast information about the conveyor belt, it only needs to be smart enough to adapt this knowledge to possible changes in the environment. The sensor learns the signal parameters of the conveyor belt at the press of a button and stores them as a “standard zero”. Any item carried on the conveyor belt then generates a signal. If this deviates from the zero state, the device detects this. The teach level can be chosen to optimise the performance of the device. For example, there is a teach routine for conveyor belts that are likely become heavily soiled over time. Another teach level is designed to detect flat or transparent objects. Once the sensor has been taught, no other settings or adjustments are needed, even if the object is changed, because the sensor is using the conveyor belt as a reference. Sesotec is has been testing Leuze’s DRT 25C sensor at its technical centre, using a variety of objects and packaging. These items travel on a conveyor belt into a metal detector. Before entering the detector, the new sensor identifies the front edge and the entire product length from above. “The view from above is a big advantage,” Sammer reports. “Irregular shapes can be detected significantly better. The sensor solutions currently on the market have so far only been able to perform this task to a limited extent.” As part of the tests, Sesotec has tried wetting, soiling or gumming up the conveyor belts, as might happen in the real world if labels become stuck, or if foodstuffs such as chocolate leave residues. To date, the test results are reported to have been “very positive”, even in difficult working conditions, such as fast-moving or vibrating conveyor belts. Leuze, which is working on more products based on the Cat technology, says it plans to use Sesotec’s test results to make possible adjustments and improvements to its products, and to guide further developments. n 34 n SENSORS AND ENCODERS February 2021 www.drivesncontrols.com A new angle on food inspection A novel sensor is helping a German manufacturer of food inspection systems to detect odd-shaped items and packaging reliably as they move along conveyors. Sesotec’s Unicon metal detection system, which consists of conveyor belt, detector coil, controller and ejector. The novel sensor is mounted above the belt before it enters the detector and can identify the front edges of oddly-shaped items and their entire lengths.