University of Rochester

Stalking the Paper Jam, the Curse of Modern Office Life

January 25, 1994

There's a little sound that office workers all over the world know and dread: the tell-tale crinkle of paper jamming, shearing, and wrinkling as it gets stuck in copiers, fax machines, or printers.

Richard Benson is out to ease such frustrations of modern life. Benson, chair of the Department of Mechanical Engineering at the University of Rochester, heads the Mechanics of Flexible Structures Project, where students are examining some of the mechanisms that can cause such minor annoyances. His students are frequently called on as trouble shooters to solve problems with everything from copiers to contact lenses.

"Flexible mechanical structures are everywhere," says Benson. "Think of the copier. Many people think of it as an electronic device, or an optical device, or even a chemical device. But what's the biggest problem in copiers, or for that matter in fax machines or printers? Paper jams -- a mechanical problem. Mechanical limitations often set the strictest limits on how fast or reliably these machines can operate."

Flexible structures include such things as clothing, plastic wrap and even skin. Benson and his research group of seven students put their effort toward technologically relevant flexible structures: paper, contact lenses, magnetic tape and disks found in computers and VCRs, and, in a project with Professor Stephen Burns, the shrink-wrap material used in digital color printers.

Recently a Texas company turned to graduate student Ken Stack to clear up the smeared images coming from its thermal printers. Stack has also designed an IV bag that deflates at a constant rate, and helped a major copier manufacturer transport paper through copiers with fewer jams. Two other students are working on ways to keep contact lenses thin and flexible to allow the cornea to absorb oxygen, yet rigid enough so they don't just crumple up in, literally, the blink of an eye.

Much of the group's work falls under the recent term mechatronics -- mechanics applied to electronic devices -- a term that describes most office technology and much of our lives.

Imagine a day where the mechatronics of your life are not in sync. You might wake up to find that the write-up of the Super Bowl is impossible to read because of a giant wrinkle down the middle of the newspaper. Unfazed, you play Mozart on your Walkman as you ride the bus to work, but the tape breaks and unravels, destroying your peace of mind.

You arrive at work -- grumbling -- only to find that your computer hard disk crashed, taking weeks of work with it. Luckily, you have a backup, so you print out that report for the boss -- who may or may not notice that giant ink smear. You race to the copier, turn your back for just an instant, only to hear the sound of an electronic machine gnawing and shredding your report as your supervisor walks through the door.

To keep flexible structures working smoothly, Benson's group does extensive mathematical modeling, running computer simulations and then checking the results with real-life scenarios at area companies. Simulations are critical in taking into account the thousands of variations in constructing a versatile and reliable machine.

The paper jam problem is a good example of the complexity of a flexible structure problem, says Stack. First, there's the material itself. "Paper is a terrible engineering material. Each piece is different. Even in one ream of paper, characteristics such as bending stiffness, density, or friction can vary by as much as 50 percent from sheet to sheet."

Benson likens the challenge to what confronts the designers of agricultural machinery. "An apple picker has to handle apples of all types of shapes and sizes. A copier has to do the same thing, but with paper: the paper could be heavy, or tissue-thin, or even glossy. The paper comes in different sizes, and the material might not even be paper -- it could be transparencies, for example. And the machine has to be able to handle thousands of sheets a day."

Then comes the transport: Paper pathway geometry, size of trays, types of rollers, reliability, expense, speed of transport, and a host of other factors can vary widely.

During thousands of computer simulations Stack learned that rapid acceleration is crucial for avoiding multifeeds, when more than one sheet is sent into the copier. "It's just like pulling a tablecloth out from under a set of dishes: The faster, the better," says Stack, whose work has been incorporated into several top-of-the-line copiers of a local firm.

"They found that my models matched up well to reality," he says. "We write specialized software that companies can use as design tools."

Benson's group is supported by Eastman Kodak, Bausch & Lomb, and Hewlett-Packard, and has also worked closely with Xerox and 3-M. "I especially enjoy our integration with the local industrial community," says Benson. "The first-rate engineers and scientists at local companies give my students and myself a huge base of support. We have a close partnership with all of our sponsors -- often my students spends summers working at the site of the sponsor, or conduct experiments in their laboratories."

Benson's group includes students Sinan Muftu, John LaFleche, Ted Diehl, Ming Tian, Guy Olive, Frank Duver and Stack. The group has included several Kodak engineers who have pursued their Ph.D.s on a part-time basis, most recently Jim Cain, who monitors the paper transport activity and plans to pursue doctoral studies in nonlinear dynamics. tr




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