R. Winn Hardin
Juggling takes skill and focus. Imagine, then, juggling sections of airplanes that weigh 100,000 lb and that must be matched to within thousandths of an inch.
That was the situation Ed Chalupa and two fellow engineers faced when in 1993 they formed Advanced Integration Technology in Plano, Texas. The goal was to assemble airplanes with zero alignment defects, reducing the time and money spent correcting problems. Zero defects have other benefits, Chalupa added, such as improved aerodynamics. The more smoothly a plane goes through the air, the less fuel it consumes and the more money an airline saves.Chalupa's first project was assembling the US Army's C-17 cargo plane, including attachment of the wings to the aircraft's body for a total span of 195 ft. Fitting several of the giant parts around a single connecting hole with position variances to thousandths of an inch posed a problem until Chalupa began consulting with laser manufacturers. Although many lasers can measure such precise tolerances, he said the list quickly dwindles when manufacturers learn that the measurements have to be made from up to 80 ft away.
After an exhaustive search, Chalupa developed relationships with laser measurement suppliers such as Research Technologies of Edmonds, Wash., Leica Inc. of Norcross, Ga., and SMX Corp. of Kennett Square, Pa. The companies would eventually design specialized laser systems and then continue to market those machines for other purposes.
Research Technologies' laser measurement system uses a planar scanning laser with a rotating head in conjunction with specially designed laser targets. The RT-1000 keeps the laser's hot spot within the beam stable while tracking objects anywhere within a 360° arc. The laser operates in the red at 670 nm and delivers 3 mW of eye-safe power to measure from distances of up to 100 ft. When connected to a computer, the RT-1000 can closely track an object by moving the laser head in increments as small as 0.1 µm.
In addition to decreasing the position variances among parts, Research Technologies estimates that its system reduces from hours to minutes the time needed to make individual measurements. Also, data from computerized laser measurements is automatically recorded for the airplane manufacturer.
From 2-D to 3-D
While the planar system worked fine for 2-D horizontal, vertical and slope measurements, Advanced Integration's contract to assemble fighter planes for British Aerospace requires the positioning of many parts in three-dimensional space.
SMX is developing the latest of these 3-D measuring systems. The SMX Tracker4500 uses two beams: one from a HeNe laser and one from an infrared laser at 1550 nm. The infrared laser produces a 0.7-mW beam with a diameter of 7 mm and divergence of 0.29 mrad and is capable of locating an object in 3-D space to within 1.1 µm/m at up to 34 m. A PC or hand remote controls the positioning of the infrared beam for "instant" absolute distance measurement.
The HeNe laser tracks objects across any geometric surface. Between the two beams, company representatives say, the system can reacquire a target without having to stop and take a baseline measurement.