13 May 2013 Iterative alignment of reflector segments using a laser tracker
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Abstract
The Large Millimeter Telescope (LMT) is a 50m diameter millimetre-wave radio telescope situated on the summit of Sierra Negra, Puebla, at an altitude of 4600 meters. The reflector surface of the LMT currently employs84 segments arranged in three annular rings. Each segment is comprised of 8 precision composite subpanels located on five threaded adjusters. During the current primary surface refurbishment, individual segments are aligned in the telescope basement using a laser tracker. This allows increased spatial resolution in shorter timescales, resulting in the opportunity for improved logistics and increased alignment precision. To perform segment alignment an iterative process is carried out whereby the surface is measured and subpanel deformations are corrected with the goal of 40 microns RMS. In practice we have been able to achieve RMS errors of almost 20 microns, with 35 microns typical. The number of iterations varies from around ten to over 20, depending mainly on the behaviour of the mechanical adjusters that support the individual subpanels. Cross marks scribed on the reflector surface are used as fiducials, because their positions on the paraboloid are well known. Measurement data is processed using a robust curve fitting algorithm which provides a map of the surface showing the subpanel deviations. From this map the required subpanel adjuster movements are calculated allowing surface improvement in a stepwise manner.
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Lizeth Cabrera Cuevas, Lizeth Cabrera Cuevas, Maribel Lucero Alvarez, Maribel Lucero Alvarez, Andrea Leon-Huerta, Andrea Leon-Huerta, Emilio Hernandez Rios, Emilio Hernandez Rios, Josefina Hernandez Lázaro, Josefina Hernandez Lázaro, Carlos Tzile Torres, Carlos Tzile Torres, David Castro Santos, David Castro Santos, David M. Gale, David M. Gale, Grant Wilson, Grant Wilson, Gopal Narayanan, Gopal Narayanan, David R. Smith, David R. Smith, } "Iterative alignment of reflector segments using a laser tracker", Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 87882Y (13 May 2013); doi: 10.1117/12.2020947; https://doi.org/10.1117/12.2020947
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