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Proceedings Paper

Design of a prototype position actuator for the primary mirror segments of the European Extremely Large Telescope
Author(s): A. Jiménez; E. Morante; T. Viera; M. Núñez; M. Reyes
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Paper Abstract

European Extremely Large Telescope (E-ELT) based in 984 primary mirror segments achieving required optical performance; they must position relatively to adjacent segments with relative nanometer accuracy. CESA designed M1 Position Actuators (PACT) to comply with demanding performance requirements of EELT. Three PACT are located under each segment controlling three out of the plane degrees of freedom (tip, tilt, piston). To achieve a high linear accuracy in long operational displacements, PACT uses two stages in series. First stage based on Voice Coil Actuator (VCA) to achieve high accuracies in very short travel ranges, while second stage based on Brushless DC Motor (BLDC) provides large stroke ranges and allows positioning the first stage closer to the demanded position. A BLDC motor is used achieving a continuous smoothly movement compared to sudden jumps of a stepper. A gear box attached to the motor allows a high reduction of power consumption and provides a great challenge for sizing. PACT space envelope was reduced by means of two flat springs fixed to VCA. Its main characteristic is a low linear axial stiffness. To achieve best performance for PACT, sensors have been included in both stages. A rotary encoder is included in BLDC stage to close position/velocity control loop. An incremental optical encoder measures PACT travel range with relative nanometer accuracy and used to close the position loop of the whole actuator movement. For this purpose, four different optical sensors with different gratings will be evaluated. Control strategy show different internal closed loops that work together to achieve required performance.

Paper Details

Date Published: 5 August 2010
PDF: 14 pages
Proc. SPIE 7733, Ground-based and Airborne Telescopes III, 773354 (5 August 2010); doi: 10.1117/12.857158
Show Author Affiliations
A. Jiménez, Compañia Española de Sistemas Aeronauticos S.A. (Spain)
E. Morante, Compañia Española de Sistemas Aeronauticos S.A. (Spain)
T. Viera, Instituto de Astrofísica de Canarias (Spain)
M. Núñez, Instituto de Astrofísica de Canarias (Spain)
M. Reyes, Instituto de Astrofísica de Canarias (Spain)

Published in SPIE Proceedings Vol. 7733:
Ground-based and Airborne Telescopes III
Larry M. Stepp; Roberto Gilmozzi; Helen J. Hall, Editor(s)

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