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Rotary positioning for high places.

Rotary positioning for high places

General Electric's Astro Space Div has applied a rotary-positioning table engineered by Eimeldingen Corp as part of NASA's Upper Atmosphere Research Satellite (UARS) program. Located at GE's Windsor, NJ, facility, the precision rotary table supports and positions a 30-ton turnover fixture plus an assembled UARS spacecraft.

The spacecraft, scheduled for launch in late 1991, is 35 ft long x 16 ft across, and it will weigh about 8 tons. GE uses the 13-ft-dia rotary table for positioning, assembly, and instrument alignment.

"Key table specifications called for positioning accuracy within 1 arc sec, repeatability within 0.5 arc sec, and capability of horizontal and vertical positioning in a clean-room environment," says William V De Genova, senior design engineer, GE Astro Space, "and Eimeldingen showed us a most innovative approach."

De Genova, who studied air-bearing approaches for the installation, designed the large turnover fixture, which mounts on the rotary table. Mounting hardware includes large bolts, T-slots, and shear pins.

"Working closely with our engineering staff, Eimeldingen solved the problem of oil-mist released from typical table lubricants," says De Genova. "Also, they integrated a special worm drive to make the table effectively free of backlash." He says the table has registered no discernible error over nearly two years of use and more than 100 hours of operating time.

Hans Geppert, general manager of Eimeldingen, called on a number of company design technologies to write specifications for the project. He notes, "Our major challenge was to make the tabletop stiff enough to support the combined 38-ton mass of the turnover fixture and satellite. To add stability, we

"The tabletop consists of highgrade ductile cast iron, and we stiffened the base weldment with acrylic concrete. On-site hand lapping achieved flatness within 0.001"."

To meet the requirement for oil-free air at GE's Class Ten Thousand clean room (many times cleaner than a hospital operating room), engineers apply dry nitrogen to the system instead of filtered air. Furthermore, they developed an airtight seal to prevent outgasing from lubricants. Finally, plastic-coated bearings and radial bearing surfaces made of bronze prevent oxidizing.

Fully assembled, the table weighs about 26 metric tons, can support more than 60 tons, and rotates in either direction at a rate of 0.00058 to 0.85 rpm. Delivery--from design to finished product--took about one year and included two weeks of installation.
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Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Publication:Tooling & Production
Date:Mar 1, 1990
Words:393
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