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Browse Prior Art Database

Track Monitor for Optical Disks

IP.com Disclosure Number: IPCOM000059943D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

In an optical disk storage, representing digital information by pits, arranged along tracks on a reflecting surface, a track sensor scans a plurality of pits, surrounding the pit being read or written, to obtain an accurate track position signal. In Fig. 1, images of pits 2 are shown projected on sensor 1 consisting of longitudinal light receptor fields (stripes) 3, whose width is about equal to half the pit width. If adjusted correctly, two adjacent stripes 3 are covered by the pit images. Every stripe is electrically connected to its third lateral neighbor by lines 6 to 8; electrical output signals then represent an average of all the pit images received by one of the three groups of photodetector stripes. The total number of pits covered should be of the order of several hundred.

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Track Monitor for Optical Disks

In an optical disk storage, representing digital information by pits, arranged along tracks on a reflecting surface, a track sensor scans a plurality of pits, surrounding the pit being read or written, to obtain an accurate track position signal. In Fig. 1, images of pits 2 are shown projected on sensor 1 consisting of longitudinal light receptor fields (stripes) 3, whose width is about equal to half the pit width. If adjusted correctly, two adjacent stripes 3 are covered by the pit images. Every stripe is electrically connected to its third lateral neighbor by lines 6 to 8; electrical output signals then represent an average of all the pit images received by one of the three groups of photodetector stripes. The total number of pits covered should be of the order of several hundred. In the center of the track sensor, a four-quadrant photodetector 4 is located to receive the image of the read/write light spot 5 and to provide automatic focussing. The track signal is obtained by subtracting the averaged electrical signals on lines 6 to 8; it is then fed to an appropriate track positioning control loop. In place of the symmetrical photoreceptor stripes of Fig. 1, asymmetrical configurations can be used to allow monitoring multiple track crossings. In addition, the contribution of track signals can be weighted (electrically or optically by appropriate illumination) according to their distance from the read/write track. Imaging errors may be...