21 July 2010 A new control architecture for multi-beam fringe tracker
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Fringe-tracking is a critical issue for modern astronomical ground interferometry. The incoming generation of fringe trackers is intended to simultaneously co-phase a large number of telescopes, bringing new questions related to control and redundancy. In this paper, a new control architecture is proposed for the 4/6-telescope Second Generation Fringe Tracker. Such a system is currently under study for the Very Large Telescope Interferometer (VLTI). The main features of the proposed solution lie in the explicit handling of many aspects that is rarely taken into account altogether. These are: delay in the transmission of set-points, coupling between the different delay lines and redundancy in the measurement. The proposed solution is based on Linear Quadratic Regulator design together with an extended dynamic observer that recovers the first moments of the disturbance dynamics (atmospheric pistons). The resulting multi-variable solution enables in particular to tune the different baselines control-related weighting coefficients according to the quality of the related measurements. While state-space framework underlines the proposed control design methodology, the resulting controller can still be expressed in a transfer function form to fit classical implementation scheme generally adopted in the targeted application community. The efficiency of the proposed solution is illustrated through dedicated simulations involving realistic data.
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L. Vincent, L. Vincent, M. Alamir, M. Alamir, J. B. Le Bouquin, J. B. Le Bouquin, L. Jocou, L. Jocou, K. Rousselet-Perraut, K. Rousselet-Perraut, P. Kern, P. Kern, J. P. Berger, J. P. Berger, } "A new control architecture for multi-beam fringe tracker", Proc. SPIE 7734, Optical and Infrared Interferometry II, 773447 (21 July 2010); doi: 10.1117/12.856822; https://doi.org/10.1117/12.856822

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