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System spots faulty sheets

One of the first Roland 700 systems equipped with a new sheet inspection system is operating at the Busche cigarette package printing company in Dortmund, Germany. Says Karl-Heinz Petzoldt, head of operations: “The system on our new six colour Roland 700 gives us the assurance that we’re delivering only quality, error-free product to our customers.”

Most of the errors the system detects are in the printing material. A strip inserting device marks the defective sheets, making it easy to sort them out in subsequent quality control steps. The press operator is also shown the precise position and type of defect on a dedicated display, with the position enlarged for easier visual inspection.

If problems occur in the printing process itself, the operator can take immediate action, reacting to scumming, for example, with additional dampener. Previously, such defects were detected only when the next inspection sheet was removed – meaning that anywhere from 200-500 sheets could be faulty, depending on the frequency of inspections. This kind of waste and high materials cost is now avoided, says MAN Roland.

The system can detect errors starting at a size of 0.6 x 0.6mm, including impurities in the printing material, as well as scratches, creases, and streaks. It also recognizes defects that occur during the printing process, such as hickeys, splashing, scumming, or prominent colour deviations that can occur if an inking unit runs out of ink.

A camera located above the last printing unit scans each sheet as it moves line by line through a narrow gap. One line is scanned per impression cylinder rotation of 0.5mm. The scanning process takes place while the sheet is still on the impression cylinder because here the sheet is fixed and register is precise.

The data generated from each and every sheet during the scanning process is compared with reference sheet data in the process computer. Deviations trigger acoustic and visual warnings. Defects are logged and the defective sheets are marked accordingly.

More information from MAN Roland Great Britain – TEL: +44 (0)20 8648 7090. WEBSITE: www.man-roland-gb.com