In addition to being the largest commercial aircraft in the world, the recently unveiled double-deck A380 from Airbus (Toulouse, France) is incorporating a number of innovative assembly technologies.

Among these technologies is the use of huge wing assembly E4380 robots manufactured by Electroimpact (Mukilteo, WA). These massive four-story-high, 80-ton yoke-shaped machines fully straddle the wings in order to drill, tap and rivet stringers to the skin panels along the wings' entire span.

Each E4380 has a head that drills thousands of holes. The E4380 then applies all rivets and bolts as it traverses the stringer-skin combinations, which are held in place by a series of support columns. The heads must remain perpendicular to the skin surface, which means constantly adjusting for camber, airfoil contour, dihedral, taper and sweepback anywhere along the wing.

The wings themselves are over 100 feet long and assembled in a 900,000-square-foot Airbus facility in Broughton, UK. Despite their enormous size, the machines provide a 40 percent reduction in space and save enormous amounts of time and labor.

To ensure positional accuracy, each E4380 and its components depends on a number of RG4 linear encoders from Renishaw Inc. (Hoffman Estates, IL). An open, noncontact optical linear encoder, the RG4 offers resolutions from 10 to 0.1 micrometers and speeds up to 15 meters per second. The RGS40 scale used with each E4380 is made from thin, flexible steel, gold plated for high reflectivity and corrosion resistance. A lacquer coating provides handling and contamination resistance, and allows easy cleaning. It is available in precut lengths or continuous rolls, with self-adhesive backing.

Each of the four E4380s at the Broughton plant incorporates more than a kilometer of 40-micrometer tape to determine the positions of the different tools and the basic position of each of the machines relative to the wing under construction.

The precision achieved with the encoders is "absolutely amazing-it gives us a highly repeatable process," says Electroimpact founder and president Peter Zieve.

Because the RGS40 scale is mounted directly to the machine, it matches the thermal expansion of the base material. Differential movement between the scale and substrate is close to zero, even over significant temperature changes. The read head is equipped with an integral setup LED indicator that provides a green signal when the system is in optimum working mode. The head maintains a 0.8-millimeter gap from the tape, which eliminates any problems with wear, friction and hysteresis.

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