Large scale structured control for segmented mirrors

Large scale structured control for segmented mirrors

Dominicus, S.

Verhaegen, M. (mentor)
Doelman, R. (mentor)

Mechanical, Maritime and Materials Engineering

Delft Center for Systems and Control

2016-11-23

The next generation of ground-based telescopes have a segmented primary mirror consisting of up to 800 segments which are mounted on a support truss. These segments are actively controlled to correct for external disturbances of which wind loading is the primary source. As mirror size and number of segments grows ever larger, dynamic coupling between the mirror segments has increased impact on the system. The controller design methods currently proposed in literature either omit the dynamics of the support truss, are too computationally complex for large-scale implementation or lack an optimal control point-of-view in the controller design. We start by applying necessary transformations to the finite element model, which improve the numeric conditioning of the model. In contrast to the original model, the transformed model can be used for simulation and controller design. In order to reject the wind loading and other disturbances, H2 optimal distributed dynamic output feedback controllers with low on-line computational complexity are designed. Furthermore, a differentiable sparsity-promoting term can be added to the objective function, so that the controller design procedure finds a (locally) optimal sparsity pattern in the controller matrices, which we can interpret as a distributed controller. Current control strategies for the new generation of segmented mirrors reduce the effect of the disturbances to a level which can be corrected by the adaptive optics system. In simulation, the closed-loop Root-mean-square (RMS) wavefront errors are in the order of 2 nm, far below the diffraction limit of 28nm RMS wavefront error. Since the influence of the wind disturbance in this work is reduced to below the diffraction limit no correction by the adaptive optics is required, the adaptive optics system of the telescope can be fully employed to reduce atmospheric turbulence.

large-scale
control
telescopes
segmented mirrors
structured control
distributed control
sparse
active optics

http://resolver.tudelft.nl/uuid:4c0218d6-5fef-4108-9b3e-4f2a5389c095

2019-11-23

Student theses

master thesis

(c) 2016 Dominicus, S.