Patent attributes
An optical disc drive according to the present invention can read data from any of multiple types of optical discs, of which the information storage layers are located at mutually different depths under their surface. When this drive is loaded with an optical disc, the servo controller of the drive changes a first type of drive signal to adjust a focus position by changing distances from the lens to the disc and/or a second type of drive signal to adjust tilt of the lens by changing the angles defined by the lens with respect to the disc a number of times, thereby changing settings to be determined by a combination of the focus position and the tilt. A signal quality rater measures multiple index values to rate the quality of a reflected light signal as the settings are changed. Then, the optical disc drive recognizes the type of the given optical disc based on those index values and reads data from the optical disc recognized.
