H.F. Mikkelsen

Detection of surface defects and servo signal restoration for a compact disc player

Compact disc (CD) players have been on the market for more than two decades, and the involved technologies, including control are very mature. Some problems, however, still remain with respect to playing CDs having to surface defects like scratches and fingerprints. Two servo control loops are used to keep the optical pick-up unit (OPU) focused and radially locked to the information track of the CD. The problem is to design servo controllers which are well suited for both handling surface defects and disturbances like mechanical shocks. The handling of surface defects requires a low-controller bandwidth which is in conflict with the requirement for the handling of disturbances. This control problem can be solved by the use of a fault tolerant control strategy, where the fault detection is very important. The OPU feeds the controllers with detector signals. Based on these, focus and radial distances can be estimated and a pair of residuals can be computed. This paper introduces a model-based method to estimate focus and radial distances as well as residuals, which have the potential to improve the control of a CD player in case of a surface defect. The methods are applied to experimental data of a scratch. The results of this experimental work show the potential of the method.

Modelling of the optical detector system in a compact disc player servo system

The cross-couplings between focus and radial tracking servos in compact disc players are important, but the optical cross couplings are not well described in the literature. In this paper and optical model of a compact disc player based on the three beam single foucault detector principle is found. The general principle of the three beam focus and radial detector system is first described, followed by a non-linear static model of the relationship between the detector signals as outputs and focus and radial errors as inputs. The parameters in these models are found by using actual data from a compact disc player, and the model is validated by comparing the simulated model response to the measured system response to a given set of inputs. This validation shows that the derived model gives a good and usable description of the optical three beam single foucault detector system in a compact disc player, which includes the cross couplings between focus and radial loops.

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.

A simulation model of focus and radial servos in compact disc players with disc surface defects

Compact disc players have been on the market in more than two decades. As a consequence most of the control servo problems have been solved. One large remaining problem to solve is the handling of compact discs with severe surface defects like scratches and fingerprints. This paper introduces a method for making the design of controllers handling surface defects easier. A simulation model of compact disc players playing discs with surface defects is presented. The main novel element in the model is a model of the surface defects. That model is based on data from discs with surface defects. This model is used to compare a high bandwidth with a low bandwidth controllers performance of handling surface defects.

Estimating focus and radial distances, and fault residuals from CD player sensor signals by use of a Kalman estimator

Optical cross coupling between focus and radial loops in compact disc players is a problem both in nominal operations, but also in detection of defects such as scratches and finger prints. Using a Kalman estimator with an internal reference, the actual focus and radial distances are estimated. The sensor inputs to the Kalman estimator are computed focus and radial distances and are found by solving the inverse problem of an optical model of the compact disc player. Two pairs of decoupled fault features are found based on the optical model, estimated and calculated focus and radial errors.

Using digital signal processing techniques in light controllers

In some European countries, the electric power stations sends out controlling codes modulated onto the net frequency in order to synchronize all the public timers. These features are detected as modulated noise by the light controllers in the house. A digital filtering technique that does not require a dedicated digital signal processor is presented. A small, low-cost, 8-b processor is used to handle the remote-control commands and at the same time digitally process the signals fed to the triac-component in order to remove blinking effects and direct-current displacements. The noise cancelling method is described, and general results and some suggestions for improvements of the method are given. >

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.

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.