Patent ID: 8531925
Filing Date: 2013-09-10
Classification: G11B

Abstract:
1. An optical disc device which reproduces information data recorded in an optical disc with a plurality of recording layers using a laser beam, comprising: an optical pickup that includes a laser light source for generating the laser beam, an objective lens for irradiating the recording layers of the optical disc with the laser beam, a focus actuator for finely adjusting a vertical position of the objective lens with respect to a recording track of the recording layer of the optical disc, a tracking actuator for finely adjusting a radial position of the objective lens with respect to the recording track of the recording layer of the optical disc, and an optical detector that detects the laser beam reflecting from the optical disc, and reads and converts the information data written in the recording track of the recording layer of the optical disc into an electric signal so as to be output; a servo control unit which generates a first drive signal used for finely adjusting the vertical position of the objective lens with respect to the recording track of the recording layer of the optical disc so that the signal is supplied to the focus actuator, a second drive signal used for finely adjusting the radial position of the objective lens with respect to the recording track of the recording layer of the optical disc so that the signal is supplied to the tracking actuator, and a third drive signal used for finely adjusting power of the laser beam generated by the laser light source so that the signal is supplied to the optical pickup; and a signal processing unit which processes the electric signal output from the optical pickup, and generates a focus error signal indicating an error of the vertical position of the objective lens with respect to the recording track of the recording layer of the optical disc, and a tracking error signal indicating an error of the radial position of the objective lens with respect to the recording track of the recording layer of the optical disc, both of which are supplied to the servo control unit for generation of the first and the second drive signals, wherein the servo control unit generates a servo-control-off signal, which indicates an occurrence of a servo-control-off relative to the position of the objective lens with respect to the recording track, based on the focus error signal and/or the tracking error signal; and wherein when the servo-control-off signal is detected during reproduction at each laser beam power value upon reading from the optical disc, the servo control unit generates the third drive signal that is supplied to the optical pickup so that the laser beam power is set to a specified power value corresponding to a reading power value of the recording layer which is a lowest power value among those power values required for reading the plurality of recording layers.