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Proceedings Paper

Evaluation of large conic concave surfaces using a coordinate measurement machine and genetic algorithms
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Paper Abstract

The design and construction of next-generation telescopes involves the development of new technologies capable of fabricating and testing large dimension mirrors with small f-numbers in order to get rapid surfaces. Secondary mirrors in Cassegrain-type telescopes are convex and hyperbolic. When the dimensions are increased and its f-number is reduced, the difficulty in testing the surface increases exponentially and traditional optical testing is no longer feasible. The present study offers a technique developed to test a mould to be used in fabricating the secondary mirror of the Large Millimeter Telescope (LTM). The mould is a hyperboloid surface with a conic constant of -1.1474, a paraxial curvature radius of 1764.94 mm and a diameter of 1600 mm. Since the telescope will work within wavelengths ranging from 1 to 3 mm, surface errors must be less than 15 μm in rms. The mould was evaluated by measuring the coordinates of 53,824 points on its surface using an advanced coordinates measurement machine (CMM) at the National Institute of Astrophysics, Optics and Electronics (INAOE) in Mexico. From this we obtained the shape of the conic surface that better fits this distribution of points, using a Genetic Algorithms (GA) program developed for this purpose. Finally, the results obtained are shown.

Paper Details

Date Published: 29 August 2008
PDF: 10 pages
Proc. SPIE 7066, Two- and Three-Dimensional Methods for Inspection and Metrology VI, 70660R (29 August 2008); doi: 10.1117/12.795725
Show Author Affiliations
A. Santiago-Alvarado, Univ. Tecnológica de la Mixteca (Mexico)
S. Vázquez-Montiel, Instituto Nacional de Astrofísca, Óptica y Electrónica (Mexico)
J. González-García, Univ. Tecnológica de la Mixteca (Mexico)
A. López-López, Univ. Tecnológica de la Mixteca (Mexico)

Published in SPIE Proceedings Vol. 7066:
Two- and Three-Dimensional Methods for Inspection and Metrology VI
Peisen S. Huang; Toru Yoshizawa; Kevin G. Harding, Editor(s)

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