Fast Access Method Of Optical Disk Memory

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Abstract
A fast access control method of optical disk memory was developed. When this method is used, an optical spot can directly reach any destination track by driving a linear motor which carries the optical head in radial direction of a pregrooved disk, even though its track pitch is as narrow as only 1.6 μm. To realize this method, in the first, distorted track crossing signal by recorded pits, which was detected by a split-type photo detector in an optical head, was compensated by an appropriate signal processing method. Therefore, the total number of crossing tracks can be counted correctly and the traveling velocity of the head can be controlled accurately by utilizing the compensated crossing sensor signal. In the next, a state observer based on the advanced control theory was applied to make the velocity controlling performance improve high enough. As a result, the track crossing velocity of the optical spot has been able to be controlled accurately while seeking. Since it hardly needs to make reseeks and any track jump motion, the average access time of optical disk memory has been shortened no more than 70 msec including average rotational latency.

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