Feature-based handling of surface faults in compact disc players

Abstract

Compact Disc players have been on the market in more than two decades, and a majority of the involved control problems have been solved. However, there are still problems with playing Compact Discs related to surface faults like scratches and fingerprints. Two servo control loops are used to keep the Optical Pickup 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 disturbs the position measurement and still react sufficiently against normal disturbances like mechanical shocks. In this paper a novel method called feature based control is presented. The method is based on a fault tolerant control scheme, which uses extracted features of the surface faults to remove those from the detector signals used for control during the occurrence of surface faults. The extracted features are Karhunen-Loève approximations of the surface faults. The performance of the feature based control scheme controlling Compact Disc Players playing Compact Discs with surface faults have been validated by experimental work with positive conclusive results.

Adaptive Feature Based Control of Compact Disk Players

“…An important observation which is made in [5] and [12], states that a surface fault does not vary much from one encounter to the next encounter.…”

“…A stability criterion for this feature based control scheme is derived in [5] and [11]. The criterion is given by Lemma 1.…”

“…The use of the fault handling method proposed in [5] and [12] introduces a potential problem. The approximating basis is precomputed being the best approximation basis of the entire fault class.…”

“…The estimations of the fault components are performed by the use of Karhunen-Loève bases, see [14], computed based onē[n] containing measured surface faults. Denote the matrices with focus and radialē[n] measurements as column vectors: D f and D r respectively, see [5]. The approximating bases can subsequently be computed as the Karhunen-Loève basis of these matrices.…”

“…In the PhD work by the first author of this paper, see [5], a scheme based on fault tolerant control and signal processing was presented. This scheme is called feature based control, since features are extracted from the detected surface faults and subsequently used to remove the influence from surface faults on the distance signals.…”