An important part of operating optical disk drives is the precision needed in its servo positioning system. A tracking error signal derived from the relationship of an objective lens to a set of tracks on an optical disk is the independent input to servo positioners. This indication of relative position of the light beam (objective lens) relative to the tracks on the disk can be in error because of misadjustment of optical detectors or other elements resulting in TES amplitude and off-set errors. Such errors detract from the precision of the operation of the servo positioning system. Optical characteristics as well as variations in track geometries on some optical disk also contribute to such errors. It is desired to provide a means for compensating or accommodating such variations in optical disk drives for ensuring the maintenance of servo positioning precision.
Another error aspect for servo position precision is a dynamic change in the relationship of the beam to the optical axis of the objective lens. During certain motions seeking and track following, the center of the beam is off axis from the optical axis of the objective lens. This causes a refraction resulting in a position indicating error. It is also desired to compensate for such dynamic changes in the beam position with respect to the optical axis of the objective lens.