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Erhardt+Leimer: Maximum quality control for RFID stickers and labels

Erhardt+Leimer: Maximum quality control for RFID stickers and labels

Improved inspection creates new capabilities

In the age of digitalization, there is increasing demand for the traceability of products and product supply chains. Transparent, reliable, unambiguous tracing is essential during the lifecycles of products, particularly in sectors such as the clothing and food industry, as well as in logistics, the automation industry and in health care. Labels with so-called RFID inlays and tags are often affixed to products or product packages for this process documentation. The RFID labels designed for the related frequencies, e.g. UHF or also HF and NFC, can be identified by means of RFID inlays and tags embedded in the label and in this way correspondingly dependable product information read using suitable devices such as RFID readers, as well as using smartphones for NFC applications.

Together with Alexander Thomalla, product manager at Erhardt+Leimer (Germany), we took a look at
the quality control for such an RFID label and also talked to a user. Here our focus was not so much
on electronic inspection, but instead on the visual inspection of RFID inlays as well as the visual
inspection of the embedded RFID chips. The challenge is that the chips are often not visible to the
human eye or a camera because they are embedded in the inlay or final label.

To begin with, let us take a closer look at a classic RFID label. As an example, we will use a self- adhesive label made of paper removed from the matrix and applied to a carrier. An RFID inlay is embedded in this label; at first glance this inlay is not visible from the exterior. The RFID inlay is to be checked for the following criteria:

  • Chip present
  • Chip positioned correctly
  • Chip free of defects
  • Inlay punched correctly
  • Inlay free of damage or soiling

Ideally, all these criteria are to be checked using only one camera system. Relevant defects must be detected reliably and faulty labels ejected.

Question for Alexander Thomalla: so what exactly is the challenge for a camera system?

“In principle, a camera system works like the human eye. We observe something and we can see or possibly not see details depending on the light source. This issue is easy to explain using our example label. If we illuminate it from above, we can make damage to the surface visible. This damage could be material defects, scratches, soiling or also printing errors. The disadvantage: the embedded chip and the related inlay cannot be seen.

If we now remove the incident light source and instead place a light source behind the label, the chip becomes visible. In this way the presence and positioning of the chip, as well as any damage, can be detected. The disadvantage with this transmitted light method is that surface defects are practically invisible without incident light. As such, the part of an RFID label visible to the human eye cannot be inspected. However, visible defects are immediately visible to anyone and would immediately result in a complaint.

Consequently, you could now think that if we use both light sources at the same time, we would be able to see all relevant details. However, this is precisely not the case. Using the two forms of lighting at the same time would reduce the contrast required to make defects visible. Positive effects are therefore counteracted by the brighter light source. The contrast is then insufficient to detect defects reliably and automatically.”

How does the camera system from Erhardt+Leimer tackle this task?

“The inspection system SMARTSCAN provides a special 200% inspection. SMARTSCAN is equipped with a high-resolution camera and has two lighting variants for the inspection of RFID labels. Both background lighting and incident lighting are incorporated. The special feature of SMARTSCAN is the way it processes images. During the inspection, SMARTSCAN continuously changes back and forth between the lighting variants. The labels are illuminated once from above and once from below, one after the other. Depending on the light source activated, the individual elements become visible and defects are detected.

The switching of the light sources, the related image acquisition and the evaluation of the images for defects are undertaken in real time. Speeds of over 400 m/min can be implemented due to this high- performance process. Defects can also be ejected reliably at these speeds such that faulty labels can be corrected immediately.

A further advantage of SMARTSCAN is that the machine operator also sees immediately on the monitor an image of the label inspected; this aspect is particularly important for the indication of faulty labels. It is possible to switch the display between the images acquired with the different forms of lighting. The operator can therefore view the image with illumination by means of transmitted light, or change directly to the data acquired with incident light for a clear image of the surface of the label.”

Quality assurance already during production

The company Tageos in Montpellier, France, is a market leader and specialist for the manufacture of highly-sensitive RFID inlays and tags; the company produces and supplies these inlays all over the world. While 100% electronic reading (inspection) of the chips has been a fixed element of its quality control for some time, 200% inspection using SMARTSCAN is now safeguarding further important quality criteria. The comprehensive quality control of its products is a vital element of the production process at Tageos and is equally important for all production sites. The company already has extensive experience with camera-based 100% inspection systems. Here the choice of the “correct” light source was an important factor. “We are pleased that with SMARTSCAN we have found a high-quality, easy-to-operate, all-in-one solution that meets our high requirements in quality management and that, in the meantime, is now in daily use on many of our machines.” says Alexandre Vautravers, industrial process manager at Tageos.

Alexander Thomalla also highlights a further advantage. SMARTSCAN is used during the actual production of the RFID inlays at Tageos. As such, the organization profits from the 200% inspection concept already during this stage. Defects can be detected immediately. This aspect is extremely important so that it is possible to react immediately to any defects that occur in the production process and tackle the source of the defect.

Alexandre Vautravers from Tageos can but agree with this statement in its entirety. “With our high production volumes, it is immensely important that we always maintain our quality at the same high standard and in this way keep the time and costs for any defect rectification as low as possible. We can already meet all these goals today using SMARTSCAN.”

SMARTSCAN in use for quality control on RFID labels
Incident light image for the detection of defects on the surface
Transmitted light image. Chip and antenna are visible with optimal contrast

Defects typically detected with illumination by means of transmitted light

  • Discontinuities in the antenna
  • Incorrect positioning of the chip
  • Hidden inclusions / damage

CHAD KUCHLER 864-764-4745

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