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Voice-coil technology for the E-ELT M4 Adaptive Unit

Abstract 175

Submitted by Daniele GALLIENI


D. Gallieni (1), M. Tintori (1), M. Mantegazza (1), E. Anaclerio (1), L. Crimella (1), M. Acerboni (1), R. Biasi (2), G. Angerer (2), M. Andrigettoni (2), A. Merler (2), D. Veronese (2), J.-L. Carel (3), G. Marque (3), E. Molinari (4), D. Tresoldi (4), G. Toso (4), P. Spanò (4), M. Riva (4), A. Riccardi (5), E. Vernet (6), N. Hubin (6), L. Jochum (6), P. Madec (6), M. Dimmler (6), F. Koch (6)


(1) A.D.S. International S.r.l., via Roma 87, 23868 Valmadrera, Italy; (2) Microgate, via Stradivari 4, 39100 Bolzano, Italy; (3) SAGEM Defense Securite, Avenue de la Tour Maury, 91280 Saint-Pierre du Perray, France; (4) INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy; (5) INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy; (6) ESO – Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany;


We present our design of the E-ELT M4 Adaptive Unit based on voice-coil driven deformable mirror technology. This technology was developed by INAF-Arcetri, Microgate and ADS team in the past 15 years and it has been adopted by a number of large ground based telescopes as the MMT, LBT, Magellan and lastly the VLT in the frame of the Adaptive Telescope Facility project. Our design is based on contactless force actuators made by permanent magnets glued on the back of the deformable mirror and coils mounted on a stiff reference structure. We use capacitive sensors to close a position loop co-located to each actuator. A dedicated high performance parallel computer is used to implement the local de-centralized control at actuator level plus a centralized feed-forward computation of all the actuators forces. This allowed achieving in our previous systems dynamic performances well in line with the requirements of the M4AU case. The actuator density of our design is in the order of 30-mm spacing for a figure of about 6000 actuators on the M4AU and it allows fulfilling the fitting error and corrections requirements of the E-ELT high order DM. Moreover, our contact-less technology makes the DM tolerant to up 10% actuators failures without spoiling system capability to reach its specified performances, besides allowing large mechanical tolerances between the reference structure and the deformable mirror. Finally, we present the Demonstration Prototype we are building in the frame of the M4AU Phase B study to measure the optical dynamical performances predicted by our design. Such a prototype will be fully representative of the M4AU features, in particular it will address the controllability of two adjacent segments of the 2-mm thick mirror and implement the actuators “brick” concept that has been adopted to dramatically improve the maintainability of the final unit.

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