Accommodating up to 840 passengers and with a wingspan in excess of 90 meters, the new Airbus A380 Superjumbo, unveiled on Jan. 18, is the largest commercial aircraft in the world. So building the giant double-decker calls for some highly innovative assembly techniques.
One such technique is the use of several huge wing assembly robots from Electroimpact, Inc (Mukilteo, WA) that depend upon Renishaw RG4 linear encoder systems for positioning accuracy. The four machines incorporate over 1 km of Renishaw 40 µm metal scale tape to determine the precise position of traveling "yokes." These massive four-story-high, 80 ton structures straddle the wings in order to drill, tap, and rivet stringers to the skin panels along the entire span.
Designated low-voltage electromagnetic riveters (LVERs), the huge twin-towered yokes run on beds capable of supporting the entire wingspan. Each head must drill thousands of holes and apply all the rivets and bolts as it traverses the stringer/skin combinations, with their support columns. The heads must always be perpendicular to the skin surface and so have to adjust to match geometry changes for camber, airfoil contour, dihedral, taper, and sweepback, anywhere along the wing.
Fundamental to the process is location of the complex CNC riveting/drilling head, which in turn depends upon the linear accuracy, of the whole yoke structure as it picks up signals from the Renishaw RG4 linear encoder system.
"The positioning precision achieved with the Renishaw encoders is absolutely amazing," says Peter Zieve, Electroimpact president and founder. "It gives us a highly repeatable process."
Electroimpact has played a significant role in providing Europe''s Airbus Industrie with groundbreaking equipment for wing assemblies, ranging from the early Airbus A320 family to the four-engine A340, and now the huge A380 wings. The Airbus automated fastening cells represent a vast improvement on earlier riveting systems, stressed Zieve. They offer 40% space reduction and save enormous amounts of time and labor by eliminating the need to first manually tack components, then split them for deburring, before retacking.
Measuring more than 45 meters along the lead edge, the A380 wings are built in Broughton, North Wales, UK, in a specially constructed, 900,000 sq ft facility. Wing panels are machined from aluminum billets or castings up to 35 meters long, with up to 70% metal removal. The four Electroimpact lines in the initial "Stage Zero" wing-build stations each have one LVER already installed, with second units on each machine in the course of construction, bringing the total number up to eight.
Precision With Tape Simplicity
Electroimpact sourced Renishaw''s encoder systems for use with its original A320 equipment and has been happy to stay with Renishaw at each succeeding stage of growth, said Zieve: "We are now designing all our machines with Renishaw linear encoder systems in mind."
Key factors in that commitment, he said, have been Renishaw''s proven global support and the application ease of the metal tape scale for the RG4 linear encoder system, which is available in continuous roll form. Supplied on a reel, the self-adhesive, flexible, 40-pitch scale was simply cut to the length required and fitted in-situ along the full traversing distance of the 160 m long wing assembly machine.
An open, non-contact, optical linear encoder, the RG4 system has a range of compact readheads offering resolutions from 10.0 µm to 0.1 µm and finer, speeds up to 15 meters/second, and industry standard output.
The RGS40 scale is made from thin, flexible steel strip, gold plated for high reflectivity and corrosion resistance. A tough lacquer coating provides handling and contamination resistance and allows easy cleaning. Offered in precut lengths or on continuous rolls, the scale has a self-adhesive backing for mounting to most engineering materials including metals, ceramics, and composites.
Scale installation is quick and easy at any stage of machine build without the need for drilling. By mounting directly to the machine, the scale 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 Electroimpact system also uses Renishaw''s patented integral setup LED indicator, unique to the RG range. This simplifies installation with a green "go" signal when optimum installation conditions are met. The tri-color LED -- green, orange, and red -- gives continuous indication of signal strength, eliminating need for specialized setup or a test and service kit. Tri-state error indication on the incremental output channels warns of low signal amplitude during operation, eliminating the danger of encoder count loss.
For demanding manufacturing applications, such as the wing robots, Renishaw offers the industrial-strength RGH41 readhead. Ultra-compact design -- 1.7 x 1.06 x .67 in. (44 x 27 x 17 mm) -- and shop-hardened, full metal jacket construction allow great application flexibility and plug-and-play convenience. Applications range from miniaturized electronics and board production to scientific stages, metrology and testing, robots, laser cutting, linear-motor drives, and automated assembly.
The non-contact optical encoder runs on the 40 µm pitch scale with 0.8 mm ride height. Proven in industrial applications on a wide range of Renishaw linear encoders, the non-contact readhead design eliminates wear, friction, and hysteresis as reliability problems, while EMI/RFI shielding avoids "noise" effects. Patented filtering optics average reflections from multiple scale facets, ensuring excellent signal stability and accuracy even with contamination or minor damage to the scale.
First commercial flight of the A380 -- in 550-seat, 3-class configuration -- is scheduled for 2006. A range of up to 8,000 nautical miles allows nonstop intercontinental flights between most of the world''s major cities. More than 120 aircraft have been ordered to date. A three-deck, long-range freighter version of the aircraft, able to carry up to 335,000 tons of cargo on standard pallets over distances up to 5,600 natural miles, will enter service in 2008.