Complex inspection system helps overcome printing errors

Watchful eye of electronics aids German film processor in assuring customers of quality.

Imagine the product liability issues that could occur on a pharmaceutical product if the instruction printed on the plastics film were imperfect. The number ’3’ might appear as the number ’8’ because of gels, black specs, bubbles, holes, or other film impurities when the ink is applied.

That is something film processor Kobusch-Sengewald (Warburg, Germany), a subsidiary of U.S.-based Pregis, cannot afford and has taken steps to see it isn’t confronted with such problems. “We don’t sell quality ’A’ at one price and quality ’B’ at another. The entire product range [of processed films] has to be a single top quality throughout,” says Detlef Kaase, manufacturing manager at the company’s plant in Halle/Westphalia, Germany.

Kaase says the company first decided in 2003 to trial a web inspection system on a six-layer blown-film line and installed a multi-camera unit with self-teaching classification from Isra Surface Vision (Herten, Germany). This was done because customer quality demands increased and higher output of its processing equipment made human inspection impossible. Christian Schaefer, project engineer at the plant, says by adding optical inspection, the company had a better control of its own process.

The good experience it developed with this system on the extrusion line led to the decision to install an inspection system on its eight-color rotogravure printing equipment running at 200 m/min. The prerequisite was that the printing inspect has to be 100% of the repeating image patterns printed on the web surface with no gaps at any film width or speed. Defects had to be automatically reported without operator intervention.

In March a Print Inspection System was delivered. Schaefer says this system is a considerably more complex analysis system than that on the film line. Gels and black spots in an extruded film can cause ink to dissipate around it making the error appear even larger than it really is. Between March and July Kobusch-Sengewald gained the necessary expertise in handling the system as well as building up a databank of possible errors.

The company has more than 1000 print designs as well as barcodes requiring checking. Each label with print and illustrations is fed into an electronic library and the cameras compare each on any production width for checking color, print quality, and positioning. It can also determine if the printing on a film has been stretched out of shape. The system’s four high-resolution, digital color, line-scan cameras are water-cooled and provide a picture overlap, but software in the print inspection system compensates for this. The entire unit is enclosed, to prevent dust ingress, and located just after the final printing station and before the winder.

Schaefer says inspecting metallized, laminated film can be tricky since it acts like a mirror and reflects the light back, which, on a different system or location, could mask errors. Here, the vendor’s experience in dealing with inspection systems for various kinds of substrates helped to provide a solution with an optimized illumination system particularly suitable for dealing with glossy surfaces. Rudolf Krampe, managing director at Isra Surface Vision says there is no downtime for maintenance on the unit since it is pre-calibrated before installation and only requires an occasional wipe of the glass protecting the camera sets to clean off dust.

Schaefer says the system, which after the trial period is in full operation, has helped operators determine when printing equipment needs checking to prevent unnecessary cleaning downtime. During the trial phase both Isra and Kobusch-Sengewald exchanged usage information, updated software, or checked operations using the system’s remote diagnostics via the Internet.

Following error messages the inaccuracy is automatically flagged by a device controlled by the inspection system and the processor can decide whether to provide a defect label on the film for his customer, who can simply skip over the errors during conversion. Kobusch-Sengewald can also opt to cut out the mistakes and re-splice the film before distribution.