Optical Sorting System enables the Inspection of Sausages in Flight
Wolf Wurstspezialitäten GmbH is one of the most important sausage manufacturers in Germany and produces, among other things, Berner sausages. Together with BT-Anlagenbau, STEMMER IMAGING developed and implemented a sorting system for the sausage maker to enable 360° quality checks of Berner sausages. With the help of machine vision, the sausages are inspected in flight to identify synthetic intestine residues.
The task
Feasibility studies, component selection and design support for a fully automated system to inspect and sort Berner sausages.
The challenge
Reliable 360° inspection of all sausages at high speeds complying with hygiene regulations.
The solution
Based on in-house feasibility studies and product tests the experts at STEMMER IMAGING worked with BT-Anlagenbau to design the innovative inspection system. Key elements of this system are machine vision components from STEMMER IMAGING as well as sophisticated machine vision software and a precise sorting system from BT-Anlagenbau, which enable the sausages to be inspected and rejected in flight.
- High-performance 360° camera technology
- Detecting synthetic intestine residues as small as 1 mm² in size
- Reliable inspection at maximum processing speed
- Error detection rate of up to 99.999%
- Sorting defective sausages in less than 195 ms
Reliable 360° inspection of sausage with varying sizes
In order to manufacture the basic sausage, a synthetic intestine is filled with sausage meat and then smoked and cooked before the intestine is removed. To ensure there is no intestine residue left on the sausages after the removal process, Wolf Wurstspezialitäten GmbH wanted to implement an automated quality control system in which the sausages are reliably inspected from all sides - despite the non-homogeneous shape and varying sausage sizes.
Another challenge is posed by the ultra-high production speed. Up to 30 sausages per second need to be inspected for synthetic intestine residues, some of which no larger than 1 mm². The cameras and lenses used have to be protected from contamination by intestine residues over long production shifts while the entire inspection system has to meet the strict regulations for food production.
„We initially considered scanning the sausages with a line scan camera as they passed by on a conveyor belt. It quickly transpired that in this way a large part of the underside of the sausages could not be captured by the camera and thus couldn't be checked. Intestine residues on the side facing away from the camera would therefore not have been reliably detectable.“
Matthias Seeger, Wolf Wurstspezialitäten
The solution: An optical sorting system for in-flight inspection
After another provider failed, STEMMER IMAGING took on the project, carried out several feasibility studies and product tests and finally developed a spectacular optical sorting system together with engineering specialist BT-Anlagenbau from Austria, which can inspect all sausages in flight, thus meeting all requirements for 100% quality control:
- 100% inspection of the sausages from all sides
- Detecting synthetic intestine residues as small as 1 mm² in size
- Reliable inspection at maximum processing speed
- Error detection rate of up to 99.999%
- Sorting out defective sausages in less than 195 ms
Optical sorting system – Step 1: Aligning and accelerating the sausages
For smoking and cooking, the sausages are wrapped in a synthetic casing, which is later removed by an automatic peeling machine. The peeled sausages are aligned via a conveyor belt and cascading flexible guides so that they lie longitudinal to the direction of transport of the conveyor belt and cannot roll around. The sausages are then accelerated to about 2 m/s on the belt and, at the end of the belt, fly past the cameras integrated above and below, which inspect the sausages in free flight.
Optical sorting system – Step 2: Quality checks with 360° camera technology
The vision station uses high-quality machine vision components from STEMMER IMAGING and sophisticated machine vision software. At the end of the conveyor belt, the sausages fly past the cameras integrated above and below, which simultaneously inspect the sausages in free flight. The two greyscale line scan cameras are equipped with additional heat sinks and matching red LED lights. Optics equipped with polarising and bandpass filters optimise the images captured to ensure the image quality and speed of image acquisition is achieved.
Computing power for this task is provided by a high-performance industrial PC with a real-time operating system, which is operated by a touch screen. If necessary, individual images or statistical overviews can be displayed and system settings can be adjusted.
The solution’s key success factors
As an independent technology provider, STEMMER IMAGING was able to select and optimally match the most suitable components for the application - without supplier lock-in. Combined with the solutions from BT-Anlagenbau, we developed a machine vision system that guarantees fully automated 100 % quality control of the processed sausages without restricting the production speed.
Powerful components
In addition to two Linea greyscale line scan cameras from Teledyne DALSA with additional heat sinks, red LED lights from Metaphase and lenses from Kowa equipped with polarising and bandpass filters provide the quality and speed needed for image capture.
Highest hygiene standards
Defective sausages with intestine residues are precisely blown out of the production line by compressed air. For this purpose, 80 ultra-fast special valves operating with sterilised air guarantee compliance with all hygiene regulations for food production.
Maximum processing speed
The sausages fly past the line scan cameras mounted above and below at a speed of approx. 2 m/s. The high production speed and powerful machine vision software enable the system to inspect up to 30 sausages per second.
More than 99 % error detection rate
The machine vision system developed by STEMMER IMAGING and BT-Anlagenbau reliably detects synthetic intestine residues as small as 1 mm². Depending on the defect size, a purity of up to 99.999 % of the processed sausages can be achieved after sorting.
Impressive computing power
After image capture, only 70 or, in the case of the larger sausages, 35 milliseconds remain for the detection of intestine residues and the pinpoint blowing of the contaminated sausages out of the production stream. Adequate computing power for this task is provided by a high-performance industrial PC with a real-time operating system.
High system availability
The cameras are mounted in housings exceeding IP 65 protection rating and kept clear of contamination by the use of a special air curtain in front of the housing. In this way, contamination by sausage residue is reliably prevented and also ensures the daily cleaning also does not affect the optical performance.
„The system reliably detects undesired intestine residues from a size of 1 mm². After sorting, the good products have a purity of 99.999% depending on the defect size, which means that STEMMER IMAGING and BT-Anlagenbau have far exceeded our specifications. We can thus put our trust in a compact, inexpensive and highly precise solution that fully meets all our requirements.“
Matthias Seeger, Wolf Wurstspezialitäten
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