Patent ID: 7894313
Filing Date: 2011-02-22
Classification: G11B

Abstract:
1. An optical disc recording and reproducing apparatus comprising: an optical pickup that has a photo detector of which a light reception area is divided into four areas including a first quadrant, a second quadrant, a third quadrant and a fourth quadrant by an X-axis and a Y-axis in a case where a radial direction of an optical disc is set to the X-axis and a track direction of the optical disc is set to the Y-axis, and that is configured to project a laser beam emitted from a laser diode onto the optical disc through an objective lens, receive the laser beam reflected from the optical disc by the photo detector, and output first, second, third and fourth detection signals from the first, second, third and fourth quadrants of the light areas; a focus servo section that is configured to shift the objective lens in a direction perpendicular to a recording surface of the optical disc; a system controller that is interconnected between the optical pickup and the focus servo section and is operable to control the optical pickup; a first memory that is configured to store levels of the first, second, third and fourth detection signals which are detected by the photo detector as A, B, C and D when the focus servo section lifts the objective lens up in a state that the laser diode is turned on; a tracking servo section that is configured to shift the objective lens in the radial direction of the optical disc; and a second memory that stores a correction table which represents a relationship between a ratio of ((A+D)/(B+C)) in the X-axis and a correction amount of lens shift in a stepped manner within a movable range of the objective lens; wherein the system controller calculates the ratio of ((A+D)/(B+C)) based on the levels A, B, C and D which are stored in the first memory after the focus servo section performs a focus-on operation; wherein the system controller controls the tracking servo section to perform a tracking operation so as to shift the objective lens in the direction of the X-axis by the correction amount with respect to the calculated ratio ((A+D)/(B+C)) based on the correction table.