20 July 2010 Prototyping and testing of mechanical components for the GRAVITY spectrometers
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Abstract
GRAVITY is a 2nd generation VLTI Instrument which operates on 6 interferometric baselines by using all 4 UTs. It will offer narrow angle astrometry in the infrared K-band with an accuracy of 10 ìas. The University of Cologne is part of the international GRAVITY consortium and responsible for the design and manufacturing of the two spectrometers. One is optimized for observing the science object, providing three different spectral resolutions and optional polarimetry, the other is optimized for a fast fringe tracking at a spectral resolution of R=22 with optional polarimetry. In order to achieve the necessary image quality, the current mechanical design foresees 5 motorized functions, 2 linear motions and 3 filter wheels. Additionally the latest optical design proposal includes 20 degrees of freedom for manual adjustments distributed over the different optical elements. Both spectrometers require precise linear and rotational movements on micrometer or arcsecond scales. These movements will be realized using custom linear stages based on compliant joints. These stages will be driven by actuators based on a Phytron/Harmonic Drive combination. For dimensioning and in order to qualify the reliability of these mechanisms, it is necessary to evaluate the mechanisms on the base of several prototypes. Due to the cryogenic environment the wheel mechanisms will be driven by Phytron stepper motors, too. A ratchet mechanism, which is currently in the beginning of his design phase, will deliver the required precision to the filter wheels. This contribution will give a first impression how the next mechanical prototypes will look like. Besides, advantages of purchasing and integrating a distance sensor and a resolver are reported. Both are supposed to work under cryogenic conditions and should achieve high resolutions for the measuring of movements inside the test cryostat.
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Michael Wiest, Sebastian Fischer, Markus Thiel, Marcus Haug, Ralf-Rainer Rohloff, Christian Straubmeier, Constanza Araujo-Hauck, Senol Yazici, Frank Eisenhauer, Guy Perrin, Wolfgang Brandner, Karine Perraut, Antonio Amorim, Markus Schöller, Andreas Eckart, "Prototyping and testing of mechanical components for the GRAVITY spectrometers", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 77393Q (20 July 2010); doi: 10.1117/12.856123; https://doi.org/10.1117/12.856123
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