Patent ID: 7394050

Claim:
A detection method to detect, while an optical disc is spinning in an optical disc player, whether vertical deviation of the optical disc occurs, the optical disc player comprising: a pickup head predeterminedly positioned at a focal distance from the optical disc for generating a focus error signal having a plurality of S-curves therein; and a focus actuator configured to actuate the pickup head based on direction from an input control signal, so that the pickup head is kept substantially at the focal distance from the optical disc; the vertical deviation disc detection method comprising the following steps: before the optical disc player successfully focuses on the disc, designing a waveform of the input control signal to enable the actuator to actuate the pickup head back and forth repeatedly within a predetermined range, and consequently to enable the pickup head to generate the focus error signal having plural S-curves; identifying at least one zero crossing point of the S-curves in the focus error signal and at least one intersecting point where the input control signal intersects the S-curves; obtaining from the input control signal at least one input control value corresponding to the intersecting point and the zero crossing point; calculating the variation of a plurality of obtained input control values; and determining whether vertical deviation of the optical disc occurs based on the calculated variation of the input control values.