Teac Corporation

Shin Fujimoto

Yukihiko Okada

CD-ROMS of more or less poor quality, such as those having eccentric center holes or uneven weight distributions circumferentially, tend to overload tracking and focusing servos and hence to invite read errors and retries. Each disk on being loaded into the disk drive is therefore checked as to its eccentricity and wobbling preparatory to reading. The disk is set into rotation at a predetermined speed of, typically, eight times the standard audio CD speed. Disk eccentricity is checked by counting the pulses produced by the transducer as the spot of the read beam crosses the track turns, the tracking servo being cut off for this check. The greater the number of pulse generated during a complete disk revolution, the more eccentric is the disk. Wobble check is done by measuring the maximum amplitude of a focusing servo signal being applied to a focusing actuator coil. The disk is read at eight times the standard audio CD speed if it clears both checks, and at four times the standard audio CD speed if it fails to clear either check.

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Iruma, Japan

Shin Fujimoto