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Control for Large Scale
Adaptive Optical Systems
Hong Song, Karel Hinnen, Rogier Ellenbroek,
Rufus Fraanje, Gleb Vdovin and Michel Verhaegen
Delft University of Technology
Delft Center for Systems and Control
Mekelweg 2 , 2628 CD Delft
The Netherlands
Tel: +31 15 2783748, Fax: +31 15 2786679
Email: [email protected]
Introduction
Adaptive optics (AO) is a technique to actively sense,
estimate and correct the wavefront distortions introduced in
a light beam as it propagates through a turbulent medium
(see Fig. 1). One important application is to compensate for
the effects of atmospheric turbulence in ground-based
telescopes, which may result in considerable resolution
improvements (see Fig. 2). Other applications include laser
beam focusing, correction of human eyes aberration [1],
etc.
Approach
Nonlinear Control
Pre-linearization, feedback linearization, sliding control and
adaptive control are possible solutions to the problem of
nonlinearity. Meanwhile, the speed, cost and stability of
the system should also be accounted for.
Nonlinearity !!
Figure 1. Schematic of AO system
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•
•
•
Pre-linearization
Feedback linearization
Sliding control
Adaptive control
II) Extension to Adaptive Algorithms
It is well known that the turbulence statistics change with
time. To ensure an optimal performance during
observation, the AO system has to be able to respond to
these changes. This may be achieved by developing an
adaptive control strategy.
III) Electronics & Distributed control
For future telescopes adaptive mirrors will be needed that
have many thousands of actuators. The electronics and
control design of such a large-scale mirror is far from
trivial and solutions are sought in the field of distributed
control and multiplexing control [2].
Figure 2. Image of the nuclear region of a nearby galaxy as seen without
(left) and with (right) adaptive optics.
Objective
AO gives rise to challenging control problems:
1. Nonlinearity of the actuators in the AO system will
degrade the system performance badly if it is not taken
into account in the control unit. Therefore the first
objective is to investigate new control strategies to
compensate for the nonlinearity of the system.
2. The current generation of AO systems do not account
for the dynamic behaviour of turbulence. The second
objectives is to develop innovative control strategies
that are able to take advantage of the dynamics.
3. Another important issue is the scalability of the system.
To enable future AO systems, with extremely large
numbers of sensors and actuators, distributed control
strategies have to be developed.
Delft Centre for Mechatronics and Microsystems
Acknowledgement
This project is part of the Delft Centre for Mechatronics and
Microsystems and is supported by IOP Precision Engineering.
The project is part of a co-operation with OKO Technology
and TNO.
References
[1] Gleb Vdovin, M. Loktev, A. Simonov, Song Hong,
[2]
Subjective adaptive correction of the aberrations of the
human eye, Proc. SPIE Vol. 5823, p. 154-163, 2005.
Hong
Song,
Aleksey
N.
Simonov,
Gleb
Vdovin,
Multiplexing control of a multi-channel piezoelectric
deformable mirror, Proc. SPIE Vol. 6018, 60181F
(2005)
Delft University of Technology