Abstract: An adaptive feed forward controller inserts signals into control loops of an optical disc player and/or recorder at a frequency of the rotation of the disc and one or more harmonics thereof, while at the same time maintaining the stability of the control loops. This makes the control loops more responsive to harmonic components of eccentric and/or tilt motion of a track being followed, a characteristic of poor quality optical discs. The quality of playback or recording such discs is thereby improved. Signal processing forming the control loops including the adaptive feed forward controller is carried out by a software controlled processor on an integrated circuit chip within the optical disc instrument. A signal representing the frequency of rotation of the disc, which is used in the signal processing, can be derived from the control loop rather than by directly measuring rotation with a transducer in the rotating system.

Abstract: An optical disc machine initially identifies a disc positioned in it by moving the focal point of its optical pick-up unit between an outer surface and an interior reflective data carrying surface. The time required for the focal point to travel between the two reflective layers, proportional to the distance between the layers, is compared with one or more thresholds to identify the type of disc present. Example types are CDs and DVDs that can be distinguished from each other because of different distances between their two layers. Variations in the velocity of a motive source that drive the focal point to traverse the disc are compensated in order to avoid erroneous measurements of the distance between reflective layers, and thus to avoid misidentifying the disc types. Different types of DVDs or CDs may also be identified by measurement of reflected light intensity with respect to a threshold that is updateable.