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Optical Disk Drive Lens Centering

IP.com Disclosure Number: IPCOM000039726D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Conly, DJ: AUTHOR [+2]

Abstract

In an optical disk drive, a lens carriage positions the lens such that the lens is ideally always exactly perpendicular to the disk's data track being accessed. However, if the carriage positioning system is limited to discrete positions (for example, the carriage is driven by a stepper motor), and the disk's data track is eccentric, the best carriage position that can be achieved is a position such that the lens' radial excursions from this ideal perpendicular state are minimized. Since a centered state is frequently disrupted (on lens movement seeks across the disk), the method to reachieve the centered state must be fast in order to minimize the impact on the rated access time of the disk drive. Immediately after acquiring a state where the head is tracking, control logic begins sampling the lens position.

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Optical Disk Drive Lens Centering

In an optical disk drive, a lens carriage positions the lens such that the lens is ideally always exactly perpendicular to the disk's data track being accessed. However, if the carriage positioning system is limited to discrete positions (for example, the carriage is driven by a stepper motor), and the disk's data track is eccentric, the best carriage position that can be achieved is a position such that the lens' radial excursions from this ideal perpendicular state are minimized. Since a centered state is frequently disrupted (on lens movement seeks across the disk), the method to reachieve the centered state must be fast in order to minimize the impact on the rated access time of the disk drive. Immediately after acquiring a state where the head is tracking, control logic begins sampling the lens position. A fixed number of samples, equally-spaced in time, are taken over the period of a single disk revolution and saved in an electronic memory as a function of disk position. When the revolution is completed, the average of the highest and lowest position deviation samples is computed and compared to a desired nominal value. Based on this comparison, the lens carriage is driven one step in the direction which will move the sampled average toward the desired nominal value. The difference between sampled average and desired nominal is also subtracted from each recorded position sample to yield a desired profile recorded in memory. The sampling revolution is repeated, but this time only the highest and lowest samples are recorded. At the end of this second sampling revolution, the average of the highest and l...