HIGH-PRECISION TRACKING CONTROL-SYSTEM FOR DIGITAL VIDEO DISK PLAYERS

The advent of digital video disks (DVD) has lead to narrower tracks along with a demand for higher density in the field of optical disks. This general and recent trend requires the improvement of follow-up capability within limits which are not detrimental to stability and speed of response. We have developed a new adaptive repetition control system that can improve followup capability by applying repetition control theory to tracking control, and which can change the learning capacity according to such nonperiodic components as insufficient stability margin (one of the problems in repetition control), disk drive vibration and disk defects, in response to the degree of track correlation. Furthermore, the division of the learning portion into two stages, namely long-term and short-term storage memories, compensates for the short-term memory being degraded by insufficient correlation and enhance the learning capability when disturbance occurs. As a result we were able to reduce the track error by disk eccentricity down to 0.02 mu m or less in a DVD disk with an eccentricity similar to compact disks (CD), and can confirm that the disk functions in a stable fashion even with interference from irregular disturbances.