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Precision motion expands image recorder's capabilities
Continuous film transport system designed by Michael Ostrelich facilitates fast, large-format, digital-image recording
By John Lewis, Northeast Technical Editor -- Design News, March 3, 1997
Shelton, CT--Space Imaging Corp. of Thornton, CO, plans to launch commercial satellites that orbit the earth every 98 minutes, collect up to two 10,000 sq-km areas of imagery in a single 10-minute pass, and revisit sites every 1.5 to 3 days.
News, utility, and other organizations demand accurate, time-critical, space-based information products and services, resulting in development of larger, more efficient formats for data collection, storage, and conversion. Michael Ostrelich, senior staff at Image Graphics Inc. (IGI), has addressed the latter. He designed a larger format electron beam recorder (EBR) that employs a continuous media transport in place of the previous design's fixed-frame format. "Larger formats provide more detailed information," says Ostrelich.
The new EBR produces a high-resolution image 26 inches long that is available for analysis in about 5 minutes. "Moving from the fixed-frame format to a continuous-motion format was the best way to stay ahead of new sensor capabilities," says Ostrelich.
The continuous transport's components--including capstan, supply and take-up drives, tensioning arms, and guide rollers--all mount to a single base plate to simplify service and maintenance. Ceramic bearings from Barden Corp., Danbury, CT, support the capstan.
Three Inland frameless-dc brush motors (T-2988D), with 0.85 lb-ft of torque and individual drives, rotate the capstan module, as well as the supply and take-up drives. All incorporate double-layer shielding from Philadelphia, PA-based Amuneal Mfg. Corp. to prevent electromagnetic interference on the recording beam.
A carrier-band sine/cosine system, the capstan drive servo operates at two speeds to drive both 5-inch and 9.5-inch media. Even with a 36,000-count encoder from Heidenhain, Schaumburg, IL, mounted directly to the motor's shaft, the capstan's low rotational speed, 1/3 rpm, made responsive control challenging. Engineers met the challenge by using a frequency multiplier to boost the capstan's sampling frequency to 50 kHz. Accuracies of less than 1 arc-second are maintained over a 30:1 speed range.
Heidenhain encoders in the supply reel, take-up reel, and tensioning arms produce 4,096 counts per revolution. Delta Tau Data Systems' PMAC uses feedback from tension arm encoders that are actuated by 1-lb constant-force negator springs from Ametek Inc. (Wallingford, CT) to control motor speeds at the supply and take-up reels. Engineers at IGI used MATLAB software to model control system disturbances such as motor ripple torque, film flutter, bearing vibrations, and high-frequency noise.
Additional details…Contact Michael Ostrelich, Image Graphics Inc., 917 Bridgeport Ave., Shelton, CT 06484, (203) 926-0100.
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