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28 July 2014 Metrology and surface adjustment of primary reflector panels on the LMT
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The primary reflector of the Large Millimeter Telescope (LMT) Alfonso Serrano is presently composed of 84 surface panels arranged in three concentric rings, providing a 32.5 meter collecting area. Each panel comprises 8 precision composite subpanels having electro-formed nickel skins bonded to an aluminum honeycomb core. Differential thread adjusters beneath each subpanel allow for the manual removal of tip/tilt and piston errors, in addition to facilitating some fine tuning of the surface shape. An assembled panel provides a surface area of approximately 8-12 square meters.

Preparation of surface panels in 2012 and 2013 for Early Science observations made use of a Leica laser tracker. Measurement and adjustment of panels was carried out off the antenna, achieving a mean panel RMS surface error of 29.5μm for the 67 panels processed to date, with a spread of 23-37μm. A panel stability check consisting of surface walk-on tests and repeat metrology resulted in an increase in the mean surface error to 31.0μm. Following installation, in situ tracker measurements of 19 panels showed a final mean error of 45.3μm. Panels are adjusted by hand using an iterative process. In-house data processing uses fiducial marks scribed onto the subpanel molds and replicated during manufacture, to achieve accurate registration of the surface point cloud during data fitting. The number of iterations varies, depending mainly on the behavior of the differential adjusters. A well-behaved panel may be set within around 7 hours. In this paper we describe the iterative panel surface adjustment process used to date. We focus on metrology technique and data processing using the laser tracker, and present comparisons with trial photogrammetry measurements.

© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Maribel Lucero Alvarez, Carlos Tzile Torres, Emilio Hernandez Rios, David Castro Santos, Lizeth Cabrera Cuevas, Andrea Leon-Huerta, Josefina Lázaro Hernandez, David M. Gale, Grant Wilson, Gopal Narayanan, and David R. Smith "Metrology and surface adjustment of primary reflector panels on the LMT", Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91513S (28 July 2014);

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