Design News for Mechanical and Design Engineers

Slow to change for most of its nearly 600-year existence, the printing industry you spawned in that shop in Mainz, Germany, has changed dramatically in the last 20 years. The most recent revolution to surface: Use of servo drives to replace the highly reliable, but somewhat sloppy, inaccurate, and hard-to-maintain mechanical drive shaft systems that have been powering printing presses for the past decades.

"We're talking about a great leap forward in the evolution of printing," says Kurt Flathmann, vice president of flexographic press manufacturer Fischer & Krecke, Inc., Fairfield NJ. "Press manufacturers can now start their designs with a clean sheet of paper. They are no longer bound to previous designs."

Indeed, servo technology is providing fundamental change to machine design, not just incremental improvements. "Most new technologies being offered today monitor and adjust unstable processes," notes Jim Hulman, senior account executive for the printing and converting industry at Bosch Rexroth (www.bosch rexroth-us.com). "Shaftless drive technology eliminates the fundamental design flaws of the original printing press by removing transmission error and mechanical windup associated with a mechanical drive train. In addition, you automatically receive electronic job setup to increase manufacturing efficiency, unmatched accuracy, and the lowest waste possible."

The new servo-powered machines cost less to build and are more easily changed from one job to another. One new machine may now operate as efficiently as two or three older ones, in terms of throughput and improved print quality. "Also, these machines tend to be more efficient because the energy loss associated with transferring energy through a mechanical gearbox is eliminated," says Hulman, who cites possible energy savings between 7 and 21%.

Even installation costs can drop by 20 to 30% because the machines can be shipped in modules that are connected at the customer's site, rather than built at the factory, torn apart, shipped, and reassembled at the destination.

Flexographic printing is actually the last segment of the industry to embrace servo technology.

Flexographic presses print the consumer packages on supermarket shelves, plastic grocery bags to heavy cardboard soft drink boxes.

In the past, flexo presses were driven from a large motor on the drum that was linked through various gears to the print cylinders. A major disadvantage to this was that the repeat length increments were constrained to the size of the gear teeth. When printing on expensive substrates, minimizing the repeat length is important in order to conserve material.

A new servo-based design enabled Fischer & Krecke to create lightweight print sleeves and intermediate mandrels that slide out. A single operator can change them in just minutes, whereas previous machines required special hoists to lift out the 500-lb print rollers.