Two machine vision systems secure quality of aluminium trays
Aluminium trays are used worldwide in a wide range of shapes for packaging food. Novelis Deutschland GmbH, with the help of the system integrator, Industrielle Sensorsysteme Wichmann GmbH (ISW), and based on machine vision components from STEMMER IMAGING, has produced a two-stage inspection system to check the quality of the trays.
We are familiar with them from meals on aeroplanes, our favourite Asian takeaway, pre-cooked ready meals at the supermarket and in many other forms: aluminium trays used as containers for food are present everywhere. On around 50 presses at its Plettenberg site in Sauerland, Novelis Deutschland GmbH makes countless types of trays with and without dividers as well as in the widest variety of shapes and sizes. What they all have in common is that the products must be leak-proof and have the required contours.
“Due to the high cycle speeds, we produce such large quantities on our presses every day that a manual check could only be carried out on a random sample basis,” says Novelis production engineer Julian Schmidt, describing the situation. At the beginning of 2017 Novelis invested in a two-stage imaging system and other machinery, further automating the complete production process on one line. “Due to the outstanding results and the significantly improved cost-effectiveness on the first installation, we set up several press lines featuring identical automation systems,” says Schmidt. The imaging systems used are critical for ensuring the quality of each aluminium container.
Two machine vision systems in series
The containers are checked in a two-stage system, with which the trays produced are 100% inspected for any leaks or contour defects. During the first stage, two Line Scan Bars (LSB) produced by Mitsubishi Electric inspect the trays’ contours and detect target deviations of +/- 100 µm. One Line Scan Bar with a CoaXPress interface and a sensor width of 400 mm is used per line, each illuminated by a line light made by CCS, which is fitted above the containers passing by as background lighting.
“This station detects geometry errors such as so-called noses or chads on the containers. The tolerance for checking the contours can be parametrised,” says Schmidt describing the technical possibilities of this sub-process. Containers outside the specified tolerances are rejected at the end of the vision system in order to collect the aluminium material from the detected trays and recycle it.
Four cameras for hole inspection
At the second machine vision system, directly after the contour checking station, the trays are checked for leaks. “The material thickness of the aluminium strips, from which the trays are pressed, is between 40 and 180 µm depending on the type of container. When deep drawing challenging container shapes, there is always the risk of material cracks even when processes run smoothly. Such defects must be detected in any event to ensure that the food is subsequently packaged hygienically without leaks and to rule out customer complaints,” says Schmidt underlining the importance of this inspection process.
Images are taken at this point by four Genie Nano area scan cameras supplied by Teledyne Dalsa, each capturing one half of the trays. To detect leaks it is best to work with background lighting, as any light shining through can be reliably detected and identified as a defect. Containers which have leak points are also sorted and fed to a recycling process.
A monitor is used to check and visualise the inspections, the results of the image analysis from both machine vision systems can be combined into a single view. The staff have the option of retrieving images of defects to check whether the system is working correctly. Based on this, good/bad decisions made by the system can be tracked and necessary settings corrected if required.
The trays identified by the machine vision system as defect-free are automatically stacked, shrink-wrapped and packaged. The tasks of the employees responsible for looking after the automated lines in the Novelis production building are limited to placing the aluminium coil at the entrance to the press line, providing the packaging materials and taking away the pallets with the stacked, packaged trays.
For the production engineer Schmidt, the machine vision system is clearly the key element to the whole facility: “Due to the high production speeds, without this system, it would have been impossible to replace the former random checks with a reliable 100% inspection of the contours as well as checking for leaks. Thus increasing the cost-effectiveness of our processes to the current level.”
According to Schmidt, the decisive factor for the fast, successful implementation of the fully automated solution is working together with experienced partners, to whom Novelis was able to rely on: “Industrielle Sensorsysteme Wichmann GmbH took care of all elements competently from the initial tests and design studies through to the integration and commissioning process. This made an important contribution to making this project a reality.”
The company based in Kölln-Reisiek near Elmshorn has specialised in complete machine vision based solutions, explains ISW authorised officer, Stefan Tukac: “To start with we were active in the packaging and automotive industry above all, then came orders from the pharmaceutical sector, and in the meantimewe have gathered lots of experience across all sectors in producing even complex machine vision solutions in 2D and 3D.” Several thousand cameras and overall solutions installed by ISW are successfully being operated in countless systems worldwide.
As a special feature of the Novelis facilities, Tukac highlights the required user-friendly conversion of the press lines to other types of trays. “We were faced with the challenge that both operating the facility and teaching new trays had to be made as quick and easy as possible. By using suitable teach software, it is sufficient to show the system ten good parts and confirm these, after which it is possible to start the production and inspection of new containers.”
For almost two decades, ISW has been procuring the machine vision components for its solutions from STEMMER IMAGING, which Tukac calls a key ISW supplier for this technology.
In Tukac’s words, this is also true of the collaboration whilst implementing the facilities at Novelis, where machine vision components that ISW purchased from the German company headquarters are used almost exclusively. “Just as important to us, however, is the support when it comes to selecting the best components, whose process reliability for the respective application is often checked beforehand in intensive feasibility studies. This was also the case for the Novelis systems, as the Line Scan Bars, in particular, were developed for a completely different concept.”
Further automation planned
Everyone at Novelis is very satisfied with the results of the collaboration and the automated production facilities that emerged from it, as Schmidt illustrates: “The present facilities work very reliably and the vision systems used were tailored specially to our requirements. Allowing us to detect errors reliably and cost-effectively with every individual tray.” These positive experiences have already led to the decision by Novelis to gradually carry out more automation measures in the years to come and to rely on the partners, ISW and STEMMER IMAGING, here once again.
Industrielle Sensorsysteme Wichmann GmbH has been a competent partner for sophisticated machine vision solutions for over 25 years. ISW GmbH provides support for overall projects and analyses and creates individual solutions for these, also including the required mechanical engineering, selects the right solution and has already implemented around 9,000 systems and high-performance facilities around the world.
Novelis Inc. is a worldwide leader in the manufacture of innovative aluminium products and in the provision of services as well as in aluminium recycling. The company is spearheaded by its drive to create a sustainable world together. Alongside its customers from the automotive industry, the drinks can manufacturing sector and the industries for many special products in North America, Europe, Asia and South America, Novelis works on product solutions that maximise the benefits of the lightweight and sustainable material, aluminium.