Distributed I/O reduces manufacturing costs

Edited by the Engineeringtalk editorial team Apr 26, 2006

Distributed I/O systems used on commercial web presses instead of point-to-point wiring, reducing the costs associated with manufacturing, maintenance and upgrades.

Heidelberg is using Profibus-based distributed I/O systems on its commercial web presses, enabling best-in-class components to be used and costs to be reduced.

It is using the I/O systems instead of point-to-point wiring, reducing the costs associated with manufacturing, maintenance and upgrades.

Profibus was selected over alternative industrial Fieldbus systems because of its technological capabilities and its global acceptance.

With over 150 years or manufacturing experience behind it and having been supplying automatic sheet feed and delivery systems to the printing industry for more than 90 years, Heidelberg is highly regarded around the world, especially for its commercial web offset printing presses.

These use the latest technologies in motion control and computer interfaces to deliver high-quality, high-volume colour printing.

Engineers at the web systems division in Dover, New Hampshire, USA, recently updated the commercial web presses to the Profibus system to reduce the kilometres of field wiring typically required for these large machines.

The decision to use Profibus reflected the company's interest in incorporating a Fieldbus standard that has worldwide acceptance, including in Europe, which is a key market for the firm's presses.

Heidelberg's commercial web presses are the size of several city buses, averaging 42m long.

The presses use large rolls of paper that run at speeds of up to 15m/s to print large-volume publications such as catalogues, newspaper inserts and magazines.

The paper rolls range from 0.9 to 1.7m wide so that multiple pages can be printed simultaneously across the width of the paper.

At the end of the press, the paper is slit into ribbons of the appropriate final width, then the ribbons are stacked, cut and folded.

An industrial PC controls the overall system and HMI functions control everything from press speed to ink concentration and equipment such as the paper slitter.

Whereas previous paper-slitting systems had been expensive and based on proprietary hardware, the new paper slitting system uses an open-systems approach based on a Siemens S7 PLC and RMC100 motion controllers from Delta Computer Systems.

The Delta RMCs control up to ten axes of revolving blades and anvils that make up the paper slitters, and the motion controllers are connected to the PLC and industrial PC via a Profibus network.

Importantly, the Delta RMCs support direct Profibus interfaces without requiring any special interface modules and they communicate directly with the PLC.

In the past, the commercial web presses relied on VME-based communications that required kilometres of field wiring that was expensive to install and maintain.

As well as reducing the wiring costs, the distributed I/O system eases the problem of connecting the industrial computer to multiple system elements simultaneously; the Profibus is simply daisy-chained between the computer and control systems on the press.

Each system has a unique address on the bus, which the computer references when it writes instruction sequences or interrogates the status of that particular system.

Positional accuracy is key for the slitters.

Because the slitters are at the end of the process, any error will increase waste and therefore cost.

The slitters must thus be easily and accurately positioned to adjust for different page sizes and to reduce paper waste.

The printer also has the option of saving slitter settings for a certain job and recalling them later when running a similar job, so the slitters must be able to be accurately repositioned.

One reason why the Heidelberg engineers chose the Delta controllers was because of their accuracy of positioning.

But Profibus compatibility was also a requirement, and - using Delta's RMCWin graphical programming tool - their ease of programming and tuning resulted in a shorter development time and easier troubleshooting.