Patent ID: 8416662

Claim:
An optical disc drive comprising: a disc holder to hold a disc; a pickup head comprising a light source, a photo sensor, and an objective lens, the light source to emit light to pass through the objective lens and project on the disc, the photo sensor to detect reflected light reflected by the disc; a focus servo comprising a focus error signal (FES) generating unit, a focus driver, and a focus controller, the FES generating unit to generate a focus error signal according to a signal from the photo sensor, the focus driver to drive the objective lens to move with respect to the disc between an uppermost position and a lowermost position, the focus controller to control the focus driver to drive the objective lens; an S-curve identifying unit to determine whether one or more S curves appear in a waveform of the focus error signal when the lens moves from the lowermost position to the uppermost position; a counter to count the number of the one or more S curves; a judging unit to determine whether the disc exhibits vertical deviation based on a comparison result of the number of the one or more S curves with a first preset value; and a disc identifying unit to determine the type of the disc; wherein when the number of the one or more S curves is no more than the first preset value, the focus controller controls the focus driver to drive the lens to move from the uppermost position to the lowermost position, the counter counts the number of S curves appearing when the lens moves from the uppermost position to the lowermost position, and the judging unit is configured to determine whether the disc exhibits vertical deviation based on a comparison result of the number of the S curves appearing when the lens moves from the uppermost position to the lowermost position with a second preset value; and the judging unit is configured to determine the first preset value and the second preset value based on the type of the disc.