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13 May 2013 Alignment of a large outdoor antenna surface using a laser tracker
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The Large Millimeter Telescope (LMT) currently employs a 32.5m diameter primary reflector composed of 84 surface segments. Global alignment of the surface is carried out using the best-fit parabola. Surface alignment follows an iterative procedure that consists of measuring the surface with a laser tracker to determine the deviations from the theoretical surface, followed by surface adjustments at the segment level. Global alignment of the primary surface presents many unusual problems related to the measurement of a large object in a non-metrology environment. The LMT antenna is located at high altitude (4700m, 15000ft) in a rural setting, where mean temperatures oscillate around zero degrees centigrade, thus presenting a challenge for traditional sensitive metrology equipment such as the laser tracker. Measurement of the antenna surface with the laser tracker requires the use of fiducial points that can be used to tie the measurement of each segment position to a common reference. Several approaches to the allocation of fiducial markers on and around the antenna are discussed in this paper. In-house data analysis provides a surface error and detailed output for the iterative adjustment of individual segments in order to reduce the global surface error. In this paper we discuss many aspects of the global alignment process with particular emphasis on making optimum use of laser tracker metrology.
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Andrea Leon-Huerta, Maribel Lucero Alvarez, Emilio Hernandez Rios, Carlos Tzile Torres, Lizeth Cabrera Cuevas, David Castro Santos, Josefina Hernandez Lázaro, David M. Gale, Grant Wilson, and Gopal Narayanan "Alignment of a large outdoor antenna surface using a laser tracker", Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 878839 (13 May 2013);

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