Method and Apparatus for Detecting Cracks in an Optical Record Carrier

Method of reading data from and detecting a crack in an optical record carrier (10) comprising the steps of:

• reading data from said record carrier by use of an irradiation beam, and generating a data signal (RF),
• tracking a data track along which said data are recorded on the optical record carrier and generating a tracking error signal (TE) and a focus error signal (FE),
• controlling the axial and the radial position of a read-out spot of said radiation beam on said optical record carrier by use of a focus control signal (FA) and a radial control signal (RA), and
• determining whether there is a crack in said optical record carrier by checking
• a) whether said focus error signal (FE) and/or said tracking error signal (TE) show a significant peak, and
• b) whether said focus control signal (FA) and/or said radial control signal (RA) show a significant step change.

Computer program comprising program code means for performing the following steps when said computer program is executed by an apparatus comprising a reading unit for reading data from an optical record carrier (10) by use of a radiation beam and for generating a data signal (RF):

• tracking a data track along which data are recorded on the optical record carrier and generating a tracking error signal (TE) and a focus error signal (FE),
• controlling the axial and the radial position of a read-out spot of said radiation beam on said optical record carrier by use of a focus control signal (FA) and a radial control signal (RA), and
• determining whether there is a crack in said optical record carrier by checking
• a) whether said focus error signal (FE) and/or said tracking error signal (TE) show a significant peak, and
• b) whether said focus control signal (FA) and/or said radial control signal (RA) show a significant step change.

A crack detection unit for use in an apparatus for reading data from an optical record carrier operative for

• receiving a focus error signal (FE) and/or tracking error signal (TE) and a focus control signal (FA) and/or a radial control signal (RA), and for
• determining if there is a crack in said optical record carrier by checking
• a) if the focus error signal (FE) and/or the tracking error signal (TE) shows a significant peak, and
• b) if the focus control signal (FA) and/or the radial control signal (RA) shows a significant step change.