Dynamic registers gain ground

When Bobst premiered a dynamic register system on its SPrintera range of die cutters at drupa 2000, it seemed that the technology might be restricted to high performance machines. But in the intervening period the Swiss company has trickled the technology through its ranges and has seen increasing take-up from solid board, litho laminate and corrugated converters.

“As die cutters got faster we found we needed a new way to register the sheet,” says Stuart Taylor, die cutter product manager for Bobst in the UK and Ireland. “There's a limit to how quickly mechanical 'lays' can react and they would have been next to useless on a machine like the SPrintera, which runs at 12,000 sheets an hour. So our designers developed Power Register, the first dynamic register system.”

The Power Register system uses camera technology to identify the position of the incoming sheet accurately relative to the die cutting tools in the machine. The system then uses linear motors to move the sheet into the correct alignment before transferring control to the gripper bar.

The use of linear motors is said to give a much wider correction range than standard joggers and means that the sheet can be moved in two directions, rather than just towards the stop. This wider, more versatile, correction gave rise to an unexpected benefit, says Stuart Taylor.

“All die cutters suffer feed stops, whether because the pile isn't quite vertical or perhaps because a sheet has hung back slightly. Our designers found that not only could the Power Register keep up with the higher running speed of the SPrintera, but it also reduced the number of stops in production by something like 70 per cent.”

But Bobst says the system is more than just an improved way of positioning the sheet. It also relays information back to the feeder, telling it to adjust the pile tray if it has sensed that the pile is not vertical. It also automatically adjusts sheet synchronization of the feeder to match the rest of the machine.

Unrestricted

Because dynamic systems rely on video technology, they are not restricted to using the edge of the sheet as a reference point. A specially printed mark on the sheet, or the print itself, can be used as a reference and this means that not only can cut-to-sheet register be assured, but so can cut-to-print register. The result is that any errors in print register are resolved at the die cutting stage and Bobst says it can guarantee the print-to-cut register of each sheet through a machine with Power Register.

The company has now introduced an adapted version, offering solely transverse location, on its SPanthera 106LER die cutter, which is its most popular machine among carton manufacturers needing blank separation, and on its new Foilmaster 104FR foiling press. Power Register itself is now also available within the Bobst corrugated die cutter range.

But it is users of litho laminated board that have been particularly surprised by the benefits from Power Register systems, says Stuart Taylor. “One of the problems in die cutting litho lam has always been crushing of the printed liner if it has not been perfectly applied to line up with the carrier flute. Because Power Register systems don't use stops, this crushing can't happen and there are several plants in Europe running litho lam at very high speeds on Size VI machines with Power Register.”