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Research Papers

Laser Beam Jitter Control Using Recursive-Least-Squares Adaptive Filters

[+] Author and Article Information
Hyungjoo Yoon1

Satellite Control System Department, Korea Aerospace Research Institute, Daejeon 305-333, Koreadrake.yoon@gmail.com

Brett E. Bateman2

Department of Physics, U.S. Naval Postgraduate School, Monterey, CA 93943batemans2001@att.net

Brij N. Agrawal

Distinguished Professor of Department of Mechanical and Astronautical Engineering, Director of Space Research and Design Center, U.S. Naval Postgraduate School, Monterey, CA 93943agrawal@nps.edu

The “reference signal” in this paper must not be confused with the “reference input” in the control theory context, which generally means a desired output value.

Note that the standard state-space model with additive white Gaussian system and measurement noises is used in the design, so the designed LQG controller may be suboptimal against the real disturbance in this application.

1

Corresponding author.

2

Present address: U.S. Navy.

J. Dyn. Sys., Meas., Control 133(4), 041001 (Apr 06, 2011) (8 pages) doi:10.1115/1.4003372 History: Received April 07, 2009; Revised October 14, 2010; Published April 06, 2011; Online April 06, 2011

The primary focus of this research is to develop and implement control schemes for combined broadband and narrowband disturbances to optical beams. The laser beam jitter control testbed developed at the Naval Postgraduate School is used for development of advanced jitter control techniques. First, we propose a least quadratic Gaussian feedback controller with integrator for cases when only the error signal (the difference between the desired and the actual beam positions) is available. An anti-notch filter is also utilized to attenuate a vibrational disturbance with a known frequency. Next, we develop feedforward adaptive filter methods for cases when a reference signal, which is highly correlated with the jitter disturbance, is available. A filtered-X recursive least-squares algorithm with an integrated bias estimator is proposed to deal with a constant bias disturbance. Finally, experimental results are provided to validate and compare the performance of the developed control techniques. The designed adaptive filter has a simple structure but shows good jitter rejection performance, thanks to the use of a reference signal.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Laser beam jitter control testbed. (a) Schematic; (b) photograph.

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Figure 2

Input and output signals for system identification (axis-1, magnified)

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Figure 3

Bode plot of the identified systems

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Figure 4

Block diagram for LQG feedback controller with error integral

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Figure 5

Block diagram for simple feedback control loop

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Figure 6

Magnitude plot of anti-notchlike filter (ωd=50 Hz)

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Figure 7

Block diagram for simplified RLS implementation

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Figure 8

Block diagram for FXRLS implementation

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Figure 9

Equivalent diagram of FXRLS implementation when Ŝ(z)=S(z)

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Figure 10

Comparison of beam position errors

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Figure 11

Comparison of controllers for broadband noises

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Figure 12

Comparison of controllers for narrowband disturbance

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Figure 13

Comparison of controllers for broadband/narrowband disturbance

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