Case Study: Strelen – Nuts, and certainly nothing else but nuts
Nuts, and certainly nothing else but nuts
Strelen Control Systems GmbH uses a hyperspectral camera from the Finnish manufacturer Specim to check nuts before processed in the food industry. High-precision nozzles shoot faulty parts and foreign bodies out of the process in flight. There is only a little time left for reliable image processing.
One of the most critical food manufacturers' tasks is to avoid contamination in their products to minimize the risk of damage to health, expensive product recalls, and the associated loss of reputation. Of course, this also applies to foods that contain nuts as components, such as muesli, muesli bars, trail mixes, or biscuits.
"Because of the visual similarity, reliably differentiating nuts from their shells or other contamination at high speed is an extremely demanding task," says Dr. Stephan Strelen, Managing Director of Strelen Control Systems GmbH based in Büttelborn near Darmstadt, Germany. His company has been developing solutions for inspection and analysis and the automation and control of production processes in various industries for many years. They have already collected a lot of experience with applications from the food industry. "We have been dealing with machine vision since the company was founded and have our specialist department with six specially trained opto-engineers and employees who have specialized in this technology. Machine vision is our focus, and many of the projects we have implemented contain solutions that are based on the evaluation of images."
Strelen felt that his company was well equipped for a food producer request for a system for sorting nuts, especially since Strelen Control Systems had already implemented various other sorting systems. "The machine vision systems used were based on conventional RGB color cameras that, like the human eye, work with the three primary colors red, green, and blue and display all colors of human vision in a corresponding mixture. However, there's only little variation in the brown tones of nuts and their shells, which is why it was practically impossible to differentiate them reliably with such a camera."
The solution is hyperspectral
Hyperspectral cameras work on a different principle and analyze a recording spectrum of up to 250 spectral bands in the wavelength range from the visible to the near-infrared range. This allows individual spectra of the light to be recognized. On this basis, a hyperspectral system can distinguish whether the same shade of brown is created from one or more superimposed wavelengths.
The nuts to be processed, such as almonds, hazelnuts, walnuts, cashews, macadamia nuts, peanuts, and other types of nuts, each has identifiable spectra. With the use of suitable software, the hyperspectral images can be analyzed quickly and reliably. The system recognizes all spectra that do not correspond to the expected types of nuts, such as shells, remains of shells, plastic parts, nuts infected with mold, or any contamination, and assigns each recognized particle as good or not good. "To guarantee the purity of the end product, the sorting only recognizes perfect parts as good parts and rejects all objects that do not meet the requirements," Strelen emphasizes.
Sorted out in flight
Safe-Ident Sort is the name of the machine Strelen Control Systems has developed for nut sorting, which has been in use since autumn 2020. It works with a conveyor belt where the unsorted bulk material is transported at a speed of 150 mm per second under an FX10 hyperspectral camera from the Finnish manufacturer Specim. This camera continuously records images and forwards them to the Halcon-based image processing software, specially developed for that application.
The conveyor belt ends at a pulley where the bulk material falls over an edge to remove defective parts and all kinds of contamination. Based on the image evaluation results, the system controls 32 high-precision nozzles, which catapult detected objects not meeting the expectations out of the trajectory and into a reject container with targeted air blasts while falling. On the other hand, faultless parts land undisturbed in a collecting container and can be processed further.
Sophisticated system design
To enable this process and achieve the required speed and accuracy, a sophisticated design of the entire system, the machine vision part, and the communication between all components are required. "The Specim FX10 hyperspectral camera is the central element of the machine vision system and has convinced us for various reasons," explains Strelen. "The main argument was that it covers a large number of wavelengths in the spectrum relevant for this task. Also, it is the only hyperspectral camera that is also suitable for the visible range of the light spectrum. Besides, there is compatibility with the LuxFlux software libraries used for the classification and preprocessing of the image data and the Halcon software for the OK / NOK decision based on the LuxFlux results, the compact size, and, last but not least, the fair price of the camera." On top of that, Strelen was also impressed by the competent support provided by the Finnish manufacturer.
Optimal illumination is an essential requirement for the performance of a hyperspectral system. Hyperspectral cameras require a broad spectrum of light to identify the spectral responses of different materials reliably. The illumination has to get brighter as the inspection speed increases. Strelen Control Systems solved this requirement with in-house development, indirect homogeneous halogen illumination with a broad wavelength spectrum from 400 to 1000 nm. A special heat sink for this illumination dissipates the generated heat.
The first Safe-Ident Sort system has been running for Ortlieb Organic in Bensheim, Germany, since autumn 2020 and can do more than conventional sorting machines from established manufacturers. Strelen emphasizes: "Sorting systems are usually designed for a certain type of nuts. A change to a different nut requires the exchange of components, which can only be done with relatively great effort. However, Ortlieb Organic needed a system that can be quickly and easily converted to different nuts and shell products."
This is where the Specim hyperspectral camera, in combination with the software used, shows its particularity, explains the Managing Director: "Safe-Ident Sort can be converted to different products simply by reprogramming and does not require any retrofitting or replacement of components. For a program change, only a parameter change in the software programming is necessary. Even this step can be handled without the slightest effort due to the clear and user-friendly interface of the software."
Ortlieb Organic is extremely satisfied with the performance of the finished system, reports Founder and CEO Eberhard Ortlieb: "Since we have been working with Safe-Ident Sort, we have saved two workers per shift who previously checked the incoming goods manually on a sorting belt. Safe-Ident Sort enables the processing of approximately 900 kg nuts per hour and detects all good nut portions with a very high level of reliability in real-time. This gives us a high guarantee that our goods are free of defects concerning the nuts used. That hawse has therefore installed good protection against recalls or claims for damages. The reliable image recognition by the Specim FX10 hyperspectral camera and the simple conversion of the system to different types of nuts are the main reasons for this development's success. Without this system, 100% quality control would not even be economically feasible given the high production speeds in the production of food according to the strict requirements of the food industry."
About Specim and Strelen Control Systems:
Specim (www.specim.fi) is a globally leading supplier in hyperspectral imaging and a true pioneer and forerunner in this field. An international team of more than 70 professionals, with expertise in optics, electronics, software, and machine vision, serves the market with the broadest range of hyperspectral cameras, imaging spectrographs, systems, and accessories. SPECIM is a trusted partner for industrial OEMs, machine builders, and integrators.
Strelen Control Systems GmbH (www.strelen.de) is a technology software company based in Büttelborn near Darmstadt, Germany. The solutions developed by Strelen are suitable for inspection and analysis as well as for the automation and control of production processes. Many of the projects contain solutions that are based on the evaluation of images using methods from industrial machine vision. The company's solutions are used in various industries, mainly in the pharmaceutical, food, and automotive supplier industries.