Drives speed offline finishing

A high-speed offline finishing line at Howard Hunt Direct in Dartford has had such a dramatic effect on production capability of the company that a second line is already being considered.

A high-speed offline finishing line recently installed at Howard Hunt Direct in Dartford has had such a dramatic effect on production capability of the company that a second line is already being considered.

The 11-section Scheffer offline finishing line featuring APS real-time registration and shaftless web-tensioning control has increased their finishing capacity by at least 25%.

The line is one of the largest in the UK and, with a throughput potential of 1800ft/min, certainly one of the fastest.

"Many printers don't even consider offline finishing because of the problems of coping with continuous registration errors", explains APS Managing Director Per Lutteman.

"Traditionally it has meant large wastage and considerable downtime.

But, using our control system in conjunction with the dynamic control and accuracy of Control Techniques Unidrives (and using standard AC induction motors), we are able to bring offline finishing up to a comparable speed and productivity to an inline finishing system.

Many print lines are limited to often little more than a third of their potential speed by the capability of their inline finishing.

So by installing an APS shaftless registration system offline, the potential productivity gains are enormous".

The APS system allows the operator to restore both registration and web tension in real time, either locally at a manual station, or at the master touch-screen controller.

"Our system is totally digital and very fast", says Per Lutteman.

"Restoring registration can take several minutes on a conventional system - ours takes less than a second and provides resolutions down to 0.01mm! This would not have been possible without the speed and positioning accuracy of the Unidrives - and bear in mind that this is using standard AC motors, not expensive servos".

Each of the 19 Unidrives on the finishing line at Howard Hunt is fitted with additional plug-in coprocessors to give distributed control and networking capability via Control Techniques own high-speed CT-Net as well as high speed serial communications.

The bespoke software, written by APS, is programmed into each module, eliminating the need for costly PLCs.

At each station, the APS registration control, the DRS200, receives signals from a registration encoder and scanner, and transmits a correction signal via a high-speed RS485 serial link to the Unidrive, running in closed loop vector mode for speed or torque control and in servo mode for positioning.

Registration can be adjusted at each station or centrally from the master control.

All of the Unidrives are also fitted with plug-in Sin/Cos modules for processing of the feedback signals from the line.

Localised control allows the manual real time registration adjustment and there is a master touch-screen controller for overall centralised control.

The finishing line at Howard Hunt comprises eleven stations, all driven by Unidrives ranging from 0.75kW up to 15kW (the finishing line drive, which is digitally locked to the press speed, taking its signal from an encoder mounted on the press line-shaft).

An unwind feeds into a festoon and into an in-feed roll under tension control.

The first process is the 5.5kW perforator followed via the web-guide into a portable die-cutter featuring two 1.5kW and one 5.5kW Unidrives in closed loop vector control with 2 million pulse encoder feedback.

The angle-bar section splits the web into up to four ribbons, with a coating and personalising line running at right angles, before feeding back to the main line.

A compensator, with two 5.5kW motor-driven rolls on entry and exit, realigns the ribbons, which then feed through a wet-flap gluer and plow tower, both sections under 5.5kW vector control.

The line is completed with a 5.5kW shear slitter, a 4kW draw and a 15kW rotary cutter.

The line features the APS virtual mastering system (VMS).

The master control communicates via a high-speed serial link to each Unidrive's encoder input, providing the reference for the entire system to be digitally locked together.

The APS true sheet length (TSL) system provides a measure of true sheet length.

Software in each drive's plug-in processor takes the speed reference from the VMS and the true sheet length signal and generates an error signal for each digital registration system, which corrects the Unidrive speed to compensate.

Since errors are immediately corrected, in a fraction of a second, no cumulative error can build up due to stretching of the web.

Nine stations along the line are equipped with APS SUC100T single user tension control units.

These provide local adjustment of web tensioning, once again via the UD75 modules on the Unidrives, or centrally from the APS touch-screen controller.

"This would not have been possible without the local processing power of the Unidrives", explains Per Lutteman.

"Since we switched from DC to AC some 10 years ago and first used Control Techniques' Vector drive in the world's first shaftless system, we have worked closely with them to develop what we believe is the best registration and web tension control in the world.

Our first shaftless system was installed in Washington DC and is still working successfully.

Their support has been crucial and the design of the Unidrive, with its plug-in processors, is fundamental to the flexibility of the systems we offer today".

The new line is installed at the finishing department of Howard Hunt Direct in Dartford.

Installed in the autumn of 2000, the new finishing line helps to keep the company in the forefront of technology, enabling them to give customers an efficient service with quick turn around times.

The company currently has the capacity to produce 9 million leaflets per day.

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