Patent ID: 7463560
Filing Date: 2008-12-09
Classification: G11B

Abstract:
1. An optical disc device which performs either or both of data recording to or data reproduction from a reflection layer of an optical disc on which data is recorded and which is covered with a light-transmitting cover layer, comprising: an objective lens for condensing laser light emitted from a laser light source onto the reflection layer through the light-transmitting cover layer; a light receiving element for receiving reflection light from the reflection layer of the optical disc in order to convert the reflection light to an electrical signal; and detection means for detecting a thickness of the cover layer on the basis of a time difference between a focus error signal corresponding to a surface of the optical disc and a focus error signal corresponding to the reflection layer, both of which are obtained through the light receiving element when a relative distance between the objective lens and the optical disc is linearly changed in a focus search of the optical disc, wherein the detection means includes means for judging a movement speed of the objective lens on the basis of a drive voltage for an actuator which linearly changes the relative distance between the objective lens and the optical disc, and the thickness of the cover layer is calculated by multiplying the time difference by the judged movement speed of the objective lens.