Discrimination between different kind of surface defects on Compac Discs

Compact Disc players have problems playing discs with surface defects such as scratches and finger prints. The problem is that handling normal disturbances such as mechanical shocks etc, require a high bandwidth of the controllers which keep the Optical Pick-Up focused and radial tracked on the information track on the disc. In order for the controllers to handle the surface defects it is required that they are non-sensitive to the frequency contents of the defect, since a defect can be viewed as a disturbance on the measurements. A simple solution to this problem is to decrease the controller bandwidth during the defect. However, due to the variation of defects a more adaptive control strategy would be preferable. In this paper the defects are categorised into three groups. A discriminator is designed, based on the local most discriminating basis vectors of the Karhunen-Loève and Haar bases as well as the mean of defect groups vectors. In these bases the discrimination rule is simple. The defect in question is a member of the group it is closest too. The Karhunen-Loève basis gives a correct classification rate of more than 85.7% with 3 basis vectors and the Haar basis of more than 94.6% with 5 basis vectors.