Enrique Sanchez Vidal

Linear quadratic controller with fault detection in compact disk players

The design of the positioning controllers in optical disk drives are today subjected to a trade off between an acceptable suppression of external disturbances and an acceptable immunity against surfaces defects. In this paper an algorithm is suggested to detect defects of the disk surface combined with an observer and a linear quadratic regulator. As a result, the mentioned trade off is minimized and the playability of the tested compact disk player is considerably enhanced.

A study on the surface defects of a compact disk

Optical disk drives are widely used today. However, even though the technology has been available to the consumer during 20 years, there are still performance issues to be improved. This study reveals a way of dealing with the photo diode signals in the optical pick-up to improve the performance of the optical disk drives.

Open and closed loop parametric system identification in compact disk players

By measuring the current through the coil of the actuators in the optical pick-up in a compact disk player, open loop parametric system identification can be performed. The parameters are identified by minimizing the least-squares loss function of the ARX model. The only parameter which cannot be identified in open loop is the optical gain. This is therefore estimated in closed loop. Practical results are analyzed and show very accurate estimates of the real parameters.

Model predictive control of a wave energy converter

In this paper reactive control and Model Predictive Control (MPC) for a Wave Energy Converter (WEC) are compared. The analysis is based on a WEC from Wave Star A/S designed as a point absorber. The model predictive controller uses wave models based on the dominating sea states combined with a model connecting undisturbed wave sequences to sequences of torque. Losses in the conversion from mechanical to electrical power are taken into account in two ways. Conventional reactive controllers are tuned for each sea state with the assumption that the converter has the same efficiency back and forth. MPCs are designed for each sea state using a model assuming a linear loss torque. The mean power results from two controllers are compared using both loss models. Simulation results show that MPC can outperform a reactive controller if a good model of the conversion losses is available.

Parametric uncertainty with perturbations restricted to be real on 12 CD mechanisms

12 actual CD mechanisms that differ by having worst-case behaviors with respect to various properties are considered. An uncertainty model is based on a parametric description of plants where the perturbations are restricted to be real and /spl mu/-theory is applied to design a controller meeting the worst case focus deviations. Satisfactory results were achieved in the 12 CD mechanisms with the synthesized controller after a controller order reduction.

Adaptive Feature Based Control of Compact Disk Players

Many have experienced the problem that their Compact Disc players have difficulties playing Compact Discs with surface faults like scratches and fingerprints. The cause of this is due to the two servo control loops used to keep the Optical Pick-up Unit focused and radially on the information track of the Compact Disc. The problem is to design servo controllers which are well suited for handling surface faults which disturb the position measurement and still react sufficiently against normal disturbances like mechanical shocks. In previous work of the same authors a feature based control scheme for CD-players playing CDs with surface fault is derived and described. This feature based control scheme uses precomputed base to remove the surface fault influence from the position measurements. In this paper an adaptive version of the feature based control scheme is proposed and described. This adaptive scheme can in contrast with the other scheme adapt to the given fault. The adaptive scheme recomputes the feature extraction bases which is used to remove fault components from the measurements, at each encounter of the given fault. The improvements of this adaptive scheme are illustrated by simulations, with the clear result that the adaptive scheme clearly adapts better to the given faults compared with the non-adaptive version of the feature based control scheme.

Deterministic method for obtaining nominal and uncertainty models of CD drives

In this paper a deterministic method for obtaining the nominal and uncertainty models of the focus loop in a CD-player is presented based on parameter identification and measurements in the focus loop of 12 actual CD drives that differ by having worst-case behaviors with respect to various properties. The method provides a systematic way to derive a nominal average model as well as a structured multiplicative input uncertainty model, and it is demonstrated how to apply /spl mu/-theory to design a controller based on the models obtained that meets certain robust performance criteria.

Current feedback for shock disturbance attenuation in a compact disc player

Control of compact disc mechanisms is highly challenging not least due to the many conflicting control objectives arising from a large number of disturbances of rather different physical natures. A method is proposed which enables the control system to distinguish between some of the disturbance classes. A significant robustness problem is solved by a simple adaptive scheme which takes real-time constraints into consideration. The results show a significant attenuation of mechanical shocks for the compact disc mechanism.

Accommodation of Repetitive Sensor Faults— Applied to Surface Faults on Compact Discs

Surface defects such as scratches and fingerprints on compact discs (CDs) can cause CD players to lose focus and tracking on the discs. A scheme for handling these defects has previously been proposed. In this brief, adaptive and predictive versions of this scheme are developed. The adaptive scheme can be used to adapt the accommodation to specific surface defects on specific discs, while the predictive scheme can be used to jump between tracks with surface defects on the disc. Sufficient and necessary stability conditions for the proposed accommodation schemes are derived as well. Performance of the accommodation scheme is discussed. Both proposed methods show their potentials through simulations with a CD player playing a CD with a surface defect (scratch).

Stability of Closed Loop Controlled Repetitive Periodic System applied to control of CD-Players

In this paper a criterion for stability of specific control scheme for handling linear dynamic control systems with repetitive periodic sensor faults is derived. The given system and control scheme are described and defined. By combining these with the lifting technique a necessary and sufficient stability criterion is derived. This criterion is following applied to an example on a feature based control scheme for handling CD-players playing CDs with surface faults. This feature based control scheme is handling repetitive periodic sensor faults. The feature based control scheme approximates the repetitive sensor faults (surface faults). The fault approximations are subsequently subtracted from the measurements, and the influence from these repetitive sensor faults are thereby removed from the computed control signals.