Patent ID: 8411542

Claim:
A method for controlling layer changes for an optical disk drive, wherein a focus of a laserbeam emitted by a pickup head of the optical disk drive is moved from a current data layer of a disk to a target data layer of the disk, the method comprising: performing a spherical aberration correction process with respect to the target data layer; lowering an objective lens of the pickup head to a low position to move the focus of the laserbeam off the surface of the disk; raising the objective lens towards the disk; generating a focusing error signal while the objective lens is being raised; starting to detect whether a S-curve corresponding to the target data layer are present in the focusing error signal; generating a series of angle indexes corresponding to a plurality of revolution angles of the disk; and recording a focus servo output (FOO) signal during one revolution of the disk to obtain a series of FOO values with respect to the angle indexes.