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12 September 2011 Maintaining hexapod range while co-pointing the Large Binocular Telescope
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The Large Binocular Telescope on Mt Graham in Arizona consists of two 8.4 m telescopes mounted on a common gimbal. Each independent telescope has hexapods controlling the position of individual optical elements. These can be used to drive each telescope to point to a common target (or known offsets to these) as is required for many of the observational modes of the telescope. The hexapods have a limited range of travel, particularly the primary mirror hexapods. This paper discusses the approach that has been taken to achieve optical co-pointing while maintaining the maximum possible range of travel in the hexapods. The approach described here is, starting with collimated but not co-pointed telescopes, to first calculate a coma-free rotation of the optical elements that will equalize the percentage consumption of range on pairs of hexapod elements that affect {X,Y} pointing; i.e. {X, Ry} and {Y, Rx} respectively. On a collimated telescope this results in a state which maximizes the available range of travel of the hexapods for a given set of initial hexapod values. Next a further calculation step is taken which achieves optical co-pointing. This step takes into account what range of travel is available for each hexapod for the given "range-balanced" starting point, then allocates a percentage of the required optical copointing to each telescope so as to maximize the available range of hexapod travel on each side. This technique has been applied successfully to both the prime-focus and "bent-Gregorian" modes of the telescope.
© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A. Rakich, D. Thompson, and O. P. Kuhn "Maintaining hexapod range while co-pointing the Large Binocular Telescope", Proc. SPIE 8131, Optical System Alignment, Tolerancing, and Verification V, 81310H (12 September 2011);


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