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Proceedings Paper

Communication architecture system for fiber positioning of DESI spectrograph
Author(s): Karim Kaci; Guillermo Glez-de-Rivera; Fernando Lopez-Colino; M. Sofia Martinez-Garcia; Jose L. Masa; Javier Garrido; Justo Sanchez; Francisco Prada
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Paper Abstract

This paper presents a design proposal for controlling the five thousand fiber positioners within the focal plate of the DESI instrument. Each of these positioners is a robot which allows positioning its optic fiber with a resolution within the range of few microns. The high number and density of these robots poses a challenge for handling the communication from a central control device to each of these five thousand. Furthermore, an additional restriction applies as the required time to communicate to every robot of its position must be smaller than a second. Additionally. a low energy consumption profile is also desired.

Both wireless and wired communication protocols have been evaluated, proposing single-technology-based architectures and hybrid ones (a combination of them). Among the wireless solutions, ZigBee and CyFi have been considered. Using simulation tools these wireless protocols have been discarded as they do not allow an efficient communication. The studied wired protocols comprise I2C, CAN and Ethernet.

The best solution found is a hybrid multilayer architecture combining both Ethernet and I2C. A 100 Mbps Ethernet based network is used to communicate the central control unit with ten management boards. Each of these boards is a low-cost, low-power embedded device that manages a thirty six degrees sector of the sensing plate. Each of these boards receives the positioning data for five hundred robots and communicate with each one through a fast mode plus I2C bus. This proposal allows to communicate the positioning information for all five thousand robots in 350 ms total.

Paper Details

Date Published: 22 July 2016
PDF: 11 pages
Proc. SPIE 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 99121V (22 July 2016); doi: 10.1117/12.2232877
Show Author Affiliations
Karim Kaci, Univ. Autónoma de Madrid (Spain)
Guillermo Glez-de-Rivera, Univ. Autónoma de Madrid (Spain)
Fernando Lopez-Colino, Univ. Autónoma de Madrid (Spain)
M. Sofia Martinez-Garcia, Univ. Autónoma de Madrid (Spain)
Jose L. Masa, Univ. Autónoma de Madrid (Spain)
Javier Garrido, Univ. Autónoma de Madrid (Spain)
Justo Sanchez, Instituto de Astrofísica de Andalucía (Spain)
Francisco Prada, Instituto de Astrofísica de Andalucía (Spain)
Univ. Autónoma de Madrid (Spain)

Published in SPIE Proceedings Vol. 9912:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II
Ramón Navarro; James H. Burge, Editor(s)

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