Packaging Technology How Cameras Seamlessly Inspect Package Labeling

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Around three years ago, Knauf automated the inspection of print quality on its packaging with camera sensors. Meanwhile, several plants are using image processing from IPF Electronic to seamlessly inspect the quality of package labeling—with consistently positive experiences.

The building materials and systems manufacturer Knauf has recently started using image processing from IPF in several of its plants. One of these plants is located in Lauterhofen, about 31 miles east of Nuremberg, Germany. "We produce several thousand tons of lime-cement plaster per month. And every single bag of finished product is labeled on the two production lines for base coat and finish coat plaster," explains Josef Geitner, plant manager at the Lauterhofen site. The labeling takes place at the respective conveyor belts of the two production lines using a printer that applies the markings to the packaging with inkjet heads. This amounts to approximately 1,500 bags per production line per hour.

Failures Prevent A Secure Process

Immediately afterward, it is checked whether the labeling is complete and, above all, easily readable. "This is not about whether the information is correct, as this is already checked before printing, but exclusively about print quality," emphasizes Thomas Schötz, master electrician and head of maintenance in Lauterhofen, Germany.

In the early days, this was done through visual inspection by employees, during which the two conveyor belts had to be stopped regularly.

About three years ago, the inspection of print quality on the packaging was automated using two camera sensors. One of the reasons for this was the labeling requirement with the so-called UFI code (Unique Formula Identifier) in accordance with the EU regulation for seamless traceability of chemical products, CLP (Classification, Labelling and Packaging).

However, the two devices failed to meet expectations, as Thomas Schötz reports: "The cameras stopped functioning several times a day. Since the cause could not be reproduced, we had to restart the devices more frequently, which was quite frustrating and nerve-wracking. As a result, a reliable process flow with consistently dependable inspection of print quality could not be ensured in the long term."

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A Lot of Flexibility With Variable Solutions

As there was already contact with IPF at the time, the company's application specialist, Christian Büttner, was consulted. He ultimately recommended an industrial camera from the OC53 series. It consists of variable camera sensors in different designs, ranging from a compact device with a lens, image sensor, and lighting, to highly flexible solutions with a C-mount lens mount and integrated flash controller for lighting control. The cameras are complemented by a free, powerful parameterization software that offers a very extensive range of graduated inspection features, allowing the devices to be used in a variety of applications with very different tasks.

From High Precision to Easy Operation

Of course, the plant manager and maintenance manager at Knauf had very specific expectations for the new solution, given their previous experiences. Josef Geitner elaborates: "The devices needed to enable a process-reliable, consistently error-free capture of the print on the packaging with high reading accuracy. Additionally, the solutions had to integrate seamlessly into the two production lines for base and finish coat plaster and communicate smoothly with the plant's control systems. Furthermore, we wanted simple operation so that we could make our own adjustments and optimizations. The demanding operating conditions also had to be taken into account—that is, a relatively dusty environment with comparatively high temperatures in summer and low temperatures in winter."

Compact Camera Plus Industrial Light

In an initial step, a test system was installed in the fall of 2024 on the production line for the finish coat plaster, specifically a compact camera with white light, type OC539E24, featuring an integrated lens, as well as a robust industrial LED light from the EM51 series by IPF, to exclude poor lighting conditions or ambient light from the outset when evaluating print quality. The camera, installed directly behind the printer and connected to the PLC, is triggered by a photoelectric sensor that detects the individual packages as soon as they are within the detection range of the camera lens.

Evaluation Based on A Test Feature

For the actual inspection, only one feature needs to be checked: the print quality. Due to production conditions, the position of the three-line print varies in the camera image. To remain independent of this, the software function "position tracking" is used. By teaching this function, the camera software automatically tracks the three relevant inspection areas to ensure that the respective relevant print is fully captured during inspection. This has the crucial advantage of being able to select only the truly important inspection areas of an object, thereby specifically ignoring other potentially disruptive influences on the object's surface during inspection.

Subsequently, monitoring of print quality is carried out using the "area size" feature inspection, with its "sensitivity" set to the grayscale values of the prints. Finally, in the area function, the reference value for the number of pixels present in the previously defined inspection areas is established via teach-in, ensuring that the print is assessed as complete and legible.

Seamless Automated Inspection

As the tests with different packaging on the finishing plaster line were extremely successful, two cameras were installed at the beginning of 2025, one replacing the test system and another on the production line for base plaster.

If the prints on at least three consecutive packages on one of the two production lines are evaluated as NIO, the conveyor belt is stopped via a PLC signal along with an additional acoustic alarm. The system operator can then recheck the respective bags and decide, for example, whether the print is still legible or if the printer is running low on ink or the print heads need cleaning.

Josef Geitner, Operations Manager at the Lauterhofen plant

To document the process, the images of the bags classified as defective are stored in the internal camera memory, and after more than 38 images, the oldest are deleted. "Based on the images, we check the readability of the prints afterward so that we can adjust the camera's software parameters if the print quality is still acceptable from our perspective. The software is so easy to use that even our shift supervisors can make minor adjustments without any issues," says Thomas Schötz.

Meanwhile, a total of 12 camera systems have been ordered for installation in other Knauf plants. In one of these plants, there was a request not only to assess the quality of the print on the bags but also to check the lettering itself using the OCR function of the camera sensors. "Additionally, a camera has been installed in another plant where the print is inspected at even higher process speeds. And here, too, the reliability of the system is highly satisfactory," concludes Josef Geitner.

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