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Browse Prior Art Database

Feed Forward Track Following

IP.com Disclosure Number: IPCOM000034831D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 4 page(s) / 90K

Publishing Venue

IBM

Related People

Baca, FA: AUTHOR [+4]

Abstract

Track following in optical disk having extremely high track densities is enhanced by profiling the radial run out and compensating the track following servo with information concerning the profiled run out. The profile is time averaged for minimizing the influence of nonrepeatable disturbances, such as noise which occur in the measured profile samples. The greater the noise level, the more significant the time averaging becomes to highly faithful track following. The second aspect is (Image Omitted) to advance the profile in time to compensate for time delays in the servo circuitry. The reason for this time advance is that the analog control signal has a significant high frequency energy as a result of media optical noise and electronic noise, all of which is accentuated by zero compensation circuits.

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Feed Forward Track Following

Track following in optical disk having extremely high track densities is enhanced by profiling the radial run out and compensating the track following servo with information concerning the profiled run out. The profile is time averaged for minimizing the influence of nonrepeatable disturbances, such as noise which occur in the measured profile samples. The greater the noise level, the more significant the time averaging becomes to highly faithful track following. The second aspect is

(Image Omitted)

to advance the profile in time to compensate for time delays in the servo circuitry. The reason for this time advance is that the analog control signal has a significant high frequency energy as a result of media optical noise and electronic noise, all of which is accentuated by zero compensation circuits. A Bessel low- pass filter having the electronic characteristic of a constant time delay over frequency bands is used in the signal sampling. The filter delay along with the circuit delays of other circuitry can adversely affect the feed forward compensation. As shown in the figures, optical disk has an extremely large number of concentric data tracks and is rotated in the direction of the arrow on the shaft mounted on frame. The track access positioning system includes a coarse positioner which is relatively movable radially of the disk on the frame. A second fine positioner is radially movably mounted on the coarse positioner and carries the objective lens for sending and receiving a laser light beam to and from the optical disk. Other optics in the optical disk recorder player are not shown for purposes of brevity, it being understood that such optics can be either mounted on a frame or on the coarse positioner for reducing the inertial effects on the fine positioner actions. The preferred form of the coarse positioner follows the actions of the fine positioner; to this end, a position sensor is mounted on the coarse positioner for sensing the relative position between the fine positioner and the coarse positioner. The output of the position sensor is applied directly to a coarse position servo. The fine positioner is controlled by a fine position actuator driven by the illustrated fine position servo circuits, which include feed forward circuits of the present disclosure. A track reference signal is compared with the sense position of the fine positioner with respect to the optical disk in a sum circuit 1. The output of sum circuit 1 is applied to electronic compensation circuits of usual design. The output of the compensation circuit is applied to the second sum circuit 2 which receives a feed forward profile from the feed forward circuit. The output signal of sum circuit 2 is applied to the power amplifier A to the fine position actuator. The radial profile used for feed forward track following compensation varies as a function of the track radial position on the disk. A most accurate profile is deri...