February 1997

Virtual Assembly

By Larry Krumenaker

"Some assembly required." This phrase strikes fear into the heart of every parent faced with putting together a bicycle on the eve of a kid's birthday. But it's also an intimidating fact of life for manufacturing firms-perhaps none more so than aircraft makers, whose employees must often piece together bewildering assortments of parts using volumes of jumbled instructional verbiage. Wouldn't it be nice if these complex transportation systems could tell an assembler how to put them together?

For some airplane-factory workers, certain plane parts can do just that, with the aid of augmented reality (AR). This technology melds virtual-reality viewers or other visual displays with positional trackers and ever smaller and faster computers to provide real-time assembly instruction. Unlike virtual reality, in which the user is completely immersed in an artificial world, AR lets you see the real world as well as an additional overlay of information that appears attached to the workpiece itself.

Seeing instructions and diagrams superimposed onto a workpiece beats "lining things up by sight, measuring, or trying to figure out what to do from a blueprint," says Ulrich Neumann, a professor of computer science at the University of Southern California, who designs augmented-reality units for use in assembly operations. The technique is ideal, he says, for any jobs that are so complex that the operator is continually looking for instructions.

Anthony Majoros, a senior engineering scientist at McDonnell Douglas Aerospace in Long Beach, Calif., recently began testing one of Neumann's prototype systems. Pointing to small sections of the fuselage of a DC-10 aircraft, he explains that the AR device can aid assembly workers by highlighting intended drilling locations or displaying explanations of where and how a particular sealant should be applied.

The prototype system consists of a video camera on a tripod that is connected to a Silicon Graphics workstation with a flat-panel color monitor, all on a roll-around cart. When a worker wheels the cart to certain sections of the aircraft and aims the camera, the computer looks for fiducial markings-pre-placed dots, targets, crosses, or natural features like holes, seams, or bumps-and uses pattern-recognition software to determine the particular unit under construction and establish the correct spatial relationship between the camera and the object. The computer then calls up the appropriate graphics and instructions, which have been preprogrammed into the system, and superimposes them in the proper orientation over the assembly on the computer screen. Once an assembly step is accomplished, the operator triggers the next procedure using a keypad.

Farther up the coast in Bellevue, Wash., aircraft maker Boeing is also exploring the potential of augmented reality but with more portable, "wearable" systems. Boeing project manager David Mizell believes that these "garments" would be perfect for a number of complex manufacturing and assembly jobs, particularly those that require two free hands to reach inaccessible places.

Users of Mizell's system wear a modular, 2.75-pound Honeywell computer around the waist like a skin diver wears a weight belt. They also don a see-through visor from Digital Vision Corp. that swivels down from a headband over one eye, and a head-mounted camera from TriSen Corp. that looks for fiducial landmarks on the assembly. When the user's head moves side to side or back and forth, Mizell explains, the computer keeps track of the position of the fiducial markings and automatically realigns the overlaid information.