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SPIE Symposium on SPIE Astronomical Telescopes and Instrumentation: Optical and Infrared Interferometry II, San Diego : États-Unis (2010)
A New Control Architecture For Multi-Beam Fringe Tracker
Lionel Vincent1, Mazen Alamir1, Jean-Baptiste Le Bouquin2, Karine Perraut3, Pierre Kern3, Laurent Jocou3, Jean Philippe Berger3

Fringe-tracking has long been recognized as a critical system for modern astronomical ground interferometry to stabilise observations. The incoming generation of trackers is intended to co-phase a large number of telescopes simultaneously, bringing new questions related to control and redundancy. In this paper, we propose a new control architecture for the 4/6-telescope Second Generation Fringe Tracker, currently under study for the Very Large Telespoes Interferometer (VLTI). The main feature of the proposed solution lies in the explicit handling of coupling and redundancy. This enables in particular to tune the different baselines control-related weighting coefficients according to the presence of noise and or potential loss of flux. Moreover, the unavoidable delays are explicitly taken into account in the control design while an observer is used to reconstruct the dynamic of the atmospheric OPD. The control design is based on a multi-variable state space representation making possible the use of standard Linear Quadratic design. The resulting controller can still be expressed in a transfer function form. The efficiency of the proposed solution is illustrated through dedicated simulations involving realistic data.
1:  GIPSA-lab - Grenoble Images Parole Signal Automatique
2:  ESO - European Southern Observatory - Chile
3:  LAOG - Laboratoire d'Astrophysique de Grenoble