In many Industrial servo-control implementations, the radial and focus loops are considered as decoupled, e.g. DVD drives. The impact of such phenomena on the robustness of the servo is evaluated by using experimental data. A controller is designed to reduce the coupling effect by using a suitable disturbance model into problem formulation.

2. In many Industrial servo-control
implementations, the radial and focus loops are
considered as decoupled, e.g. DVD drives.
The impact of such phenomena on the
robustness of the servo is evaluated by using
experimental data.
A controller is designed to reduce the coupling
effect by using a suitable disturbance model
into problem formulation.

3. A Blu-ray Disc can store up to 50 GB on a dual
layer.
All DVD drives use a linear actuator to
minimize the optical cross coupling.
Several causes of cross coupling are
Mechanical, electro-magnetic and/or optical
cross-coupling.

4. Track Disturbances
Specifications: maximum tracking errors
The reference servo

6. The vertical deviations (i.e. the vertical
movement of the optical pickup unit when the
disc rotates) are generally produced by disc
tilt/ or warping
The radial deviations are produced by the disc
eccentricity which corresponds to the distance
variation between the geometrical center of the
data track and the center hole of the disc.

9. The design of a given disc drive controller is
done through a translation of time-domain
specifications into frequency ones, based on a
theoretical disturbance model.
These specifications are represented with the
dashed line in Figure 2.

10. Radial sensitivity function and disturbances.
Focus sensitivity function and disturbances.

13. Simulation results using experimental data
Uncertainty modeling and robustness analysis
Robust stability and performance analysis

17. The controlled system can be analyzed using μ-
analysis.
Robust performance analysis, a measure of how big
perturbation to a system can be to assure the
desired closed loop performance.
The coupling effect should be bounded by an unit
gain, which is an admissible value for “playability”.
Thus, the proposed controllers are quite robust
with respect to the obtained ones from the
reference servos and those obtained from the
current industrial controllers.

18. A disturbance model for Blu-ray Disc
servomechanisms has been validated under
experimental data and suitable robust
controller has been designed.
The control design process takes into account
the disturbance model for the purpose of
reducing the coupling effect.
The model designed is enough accurate to
describe the coupling behavior, and it could be
useful for high-bandwidth controller design.

19. http://www.elsevier.com/wps/find/journald
escription.cws_home/933/description
http://www.howstuffworks.com/
http://www.wikipedia.org/