The astounding science and engineering of printer jams

Anil Dash's third law holds that "Three things never work: Voice chat, printers and projectors." But Joshua Rothman's long, fascinating, even poetic profile of the Xerox engineers who work on paper-path process improvements is such a bit of hard-science whimsy that it almost makes me forgive every hour I've spent swearing over jammed paper.

Paper paths are remarkable things, "paper torture chambers" and "a Tough Mudder—a multistage obstacle course that must be run in hostile conditions" — while paper path engineers have to grapple with an interdisciplinary mix of "physics, chemistry, mechanical engineering, computer programming, and interface design" that can handle the heterogeneous mix of plant fibers that are "processed" not "manufactured" and have enormous regional variation: "In Spain, paper is made from eucalyptus; in Kentucky, from Southern pine; in the Northwest, from Douglas fir."

Rothman describes sitting in on a kind of war-room where a group of engineers are trying to figure out how to improve a printer that's just hit a new bug: the printer, sited somewhere in Asia, is jamming while trying to run a whole-book printout on Bible-like, onionskin paper that had absorbed more moisture from the humid air than the printer could manage. It's a beautiful rundown of the engineering methods available to move paper along a path while it is saturated with precision ink or sizzling with huge amounts of electric charge.

The team began to consider their options. The most obvious fix would have been to buffet the paper upward from below using a device called an air knife. This was off limits, however, because the bottom side was coated with loose toner. "An air knife will just blow the toner right off," Ruiz said. Another possibility was to place "fingers"—small, projecting pieces of plastic—where they could support the corners as they began to droop. "That might create a higher jam rate on different paper shapes," an engineer said—it could be a "stub point." A mystified silence descended.

A mechanical engineer named Dave Breed pointed toward the upside-down conveyor belt. "The vacuum pump actually works by pulling air through holes in the belts," he said. "So what is the pattern of those holes relative to the corners? Maybe there's no suction there."

On the whiteboard, Ruiz sketched a diagram of the conveyor belt—the V.P.T., or vacuum-paper transport—showing the holes through which the suction operated. "Optimize belt pattern," he wrote.

"If my understanding of air systems is right," Breed went on, "then the force that gets a sheet moving isn't really pressure—it's flow."

Why Paper Jams Persist [Joshua Rothman/The New Yorker]

(via /.)