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News Release from: Reliance Precision Mechatronics | Subject: Angular measuring rack system
Edited by the Engineeringtalk Editorial
Team on 04 October 2001
Angular measuring rack system for Hubble
telescope
After success at Jodrell bank, Reliance gear has been involved with the Hubble Tracking Telescope in America where a similar angular measuring rack package has been fitted
Twenty years ago, engineers in charge of the Lovell telescope at Jodrell Bank were having measurement problems The original azimuth measuring system on the telescope, installed in 1958, was a chain and sprocket drive around Magslips, and could only achieve a repeatability of 5 arc mins
This article was originally published on Engineeringtalk on 10 Oct 2000 at 8.00am (UK)
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When the astronomers needed higher accuracy for their observations, the telescope engineers contacted Reliance Gear Co of Huddersfield, well known then, as now, for their instrumentation and measurement expertise.
Reliance was marketing its Angular Measuring Rack product at this time.
This was a rack measuring system designed for machine tool rotary tables, where the measuring device cannot be mounted on the central axis.
As the Lovell telescope rotates on a central shaft diameter of 1.5 metres, Reliance Engineers felt that mounting the measuring device on axis was not an option, and that supplying a modified version of their Angular Measuring Rack would be the ideal solution for improved repeatability on the telescope.
Reliance Engineers tackled the problem in the following way.
They manufactured a split ring with a known, machined rack seating diameter, to fit around the telescope's central shaft.
Racks were clamped to the ring to conform exactly to the seating diameter.
The racks in the rack circle were positioned with their midpoints at exact angular locations to prevent accumulated errors from rack to rack, and a flex plate assembly ensured complete backlash elimination.
The new solution provided repeatability within 2.5 arc sec., much to the delight of Jodrell Bank astronomers.
Because of this success, on a much more recent project, Reliance has been involved with the Hubble Tracking Telescope in America where a similar angular measuring rack package has been fitted.
However with modern high resolution counting electronics the repeatability has now been improved to 0.33 arc sec.
Twenty years on, Reliance is involved in a further refurbishment of the Lovell telescope.
The original angular measuring rack will remain in place and will be enhanced with a new suite of geared measuring transducers.
The expectations are that the fully refurbished Lovell Telescope will match the 0.33 arc sec.
resolution achieved by its American counterpart - a performance which the pioneers of the Lovell Telescope could only have dreamed of when it was constructed almost 50 years ago.
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