Patent ID: 6266301
Filing Date: 2001-07-24
Classification: G11B

Abstract:
An optical storage device for at least reading information from an optical storage medium by an optical head, comprising:an optical head including an objective lens for irradiating said optical storage medium with a laser beam, a track actuator for driving said objective lens for scanning said laser beam at a slant across tracks on said optical storage medium, and a divided-by-4 light receiving unit for receiving the laser beam from said optical storage medium;moving means for moving at least said objective lens and said track actuator of said optical head;a first signal processing unit for calculating a track error signal on the basis of outputs of said divided-by-4 light receiving unit;a second signal processing unit for calculating a shift signal for indicating a shift quantity of said objective lens on the basis of the output of said divided-by-4 light receiving unit; anda control unit for controlling one of said track actuator and said moving means by the track error signal, and controlling another one of said track actuator and said moving means so that the laser beam passing through said objective lens is located at the center of said objective lens according to said shift signal,wherein said first signal processing unit comprises a differential circuit for calculating an X-directional change in a reflected light distribution of said divided-by-4 light receiving unit; andsaid second signal processing unit comprises a differential circuit for calculating a Y-directional change in said reflected light distribution of said divided-by-4 light receiving unit, said X and Y direction being in an orthogonal relationship.