A manufacturing company for over 150 years, Heidelberg introduced its first printing press with an automatic sheet feed and delivery system in 1914. Today, Heidelberg's commercial web offset printing presses use the latest technologies in motion control and computer interfaces for high quality, high volume color printing. Engineers at Heidelberg's Web Systems Division (headquartered in Dover, New Hampshire) recently updated the company's line of commercial web presses to a PROFIBUS-based distributed I/O system in order to reduce the miles of field wiring typically required for one of these large machines. The PROFIBUS choice reflected Heidelberg's interest in incorporating a fieldbus standard that has worldwide acceptance, including broad acceptance in Europe, a key market for Heidelberg's presses.
Heidelberg's commercial web presses are the size of several city buses, averaging 137 feet long. The presses use large rolls of paper that are run through the press at speeds of up to 3,000 feet per minute to print large volume publications such as catalogs, newspaper inserts, and magazines. The paper rolls range from 35 inches to 66 inches wide so that multiple pages can be printed simultaneously across the width of the paper. At the end of the press, the continuous paper is slit into ribbons of the appropriate final paper width, then the ribbons are stacked, cut, and folded into their final size.
An industrial PC performs overall system control and human machine interface (HMI) functions to control everything from press speed to ink concentration to equipment such as the paper slitter. Other paper-slitting solutions have 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 (Vancouver, WA). The Delta RMCs control up to ten axes of revolving blades and anvils that make up the paper slitters. PROFIBUS connects the motion controllers to the Siemens PLC and to the industrial PC. The Delta RMC supports direct PROFIBUS interfaces without requiring any special interface modules, and communicates directly with the Siemens PLC.
Previously, these commercial web presses were VME-based systems that required miles of field wiring that was expensive to install and maintain. The new distributed I/O system eases the challenge of connecting the industrial computer to multiple system elements simultaneously. The PROFIBUS is "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 status from that particular system. Accuracy of position is key for the slitters. Because this is at the end of the process, any error will increase waste and therefore cost. The slitters must be easily and accurately positioned to adjust for different page sizes and to reduce paper waste. The printer also has the option of saving the position of the slitters for a certain job and recalling that position at a later date when running a similar job, so the slitters must be able to be accurately repositioned for this option. The Heidelberg engineers chose the Delta controllers because of their accuracy of positioning, PROFIBUS compatibility, and ? using Delta's RMCWin graphical programming tool ? their ease of programming and tuning that resulted in shorter development time and easier troubleshooting.
In addition to greatly simplifying system wiring compared to I/O-intensive point-to-point wired systems, the use of PROFIBUS allowed the Heidelberg engineers to design a system using best-of-class components, contributing to lower system manufacturing costs and easier system assembly, maintenance, and upgrades by worldwide staff.