Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Patent
1988-10-11
1992-06-09
Envall, Jr., Roy N.
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
369 4428, 369 4429, 369 54, G11B 7085
Patent
active
051213702
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of track accessing in an optical recording apparatus and, in particular, to a novel technique for a beam spot to quickly cross the plural tracks while the number of tracks the beam spot has crossed is accurately checked.
2. Description of Related Art
An optical recording disk system is hereinafter described as an example of prior art optical recording systems. In an optical recording disk system, as shown in FIG. 1A, data is written onto a recording track on a recording medium, a disk 1, by a beam spot focused thereon and the data is read out from a reflected light therefrom. The system employed in FIG. 1A is constituted as follows. The optical recording disk 1 is rotating around its axle driven by a motor 1a. An optical head 2 coarsely travels along a radial direction of the disk which is driven by a motor. The motor which is not shown is controlled by a carriage controller 5. The optical head 2 is constituted so that a light emitted from a semiconductor laser 24, as a light source, is introduced via a lens 25 and a polaroid beam splitter 23 into an object lens 20. The light is focused by the object lens 20 as a beam spot BS so as to project onto the optical disk 1, and a light reflected from the optical disk 1 is input via the object lens 20 by the polaroid beam splitter 23 into a 4-division light receiver 26. The optical head 2 may be referred to as a carriage 2.
In such an optical recording disk, tracks are formed with a pitch of several micrometers, typically 1.6 .mu.m, in great numbers along a radial direction of the optical disk 1. Accordingly, even a little eccentricity, typically 100 .mu.m peak to peak, may cause a large track-displacement for a narrow single track, and an undulation of the optical disk 1 causes a displacement of a focusing point of the beam spot as well. Therefore, it is necessary for the beam spot to be less than 1 .mu.m to follow these displaced and/or undulated tracks.
For these purposes, there are provided a focus-actuator (focus coil) 22 for moving the object lens 20 on the optical head 2 along the axial direction of the lens so as to change the location of the focusing point, and a trackactuator (tracking coil) 21 for moving the object lens 20 (i.e. along left and right directions in the figure) so as to change the location of the beam spot along the orthogonal (i.e. radial) direction of the tracks. There are also provided a focus servo controller 4 for generating a focusing error signal FES from the light signal of the light receiver 26 to drive the focus actuator 22, and a fine tracking servo controller 3 for generating a tracking error signal TES from the light signal of the light receiver 26 to drive the track actuator 21.
The principle of fine tracking control depends, as shown in FIG. 1B and 1C, on the utilization of a diffraction phenomena of the beam spot BS caused by a coaxial or spiral guide groove (track) 10 provided in advance on the optical disk 1. In other words, the fact that distribution of the amount of the reflected light into the light receiver 26 is varied by the light diffraction at the track 10 depending on the relative position of the beam spot BS to the track 10, is utilized in order to acquire the beam spot's position error from the track 10. For example, when a push-pull method having a four-division light receiver which consists of four photo diodes 26a, 26b, 26c and 26d is employed as it is conventionally used, the reflected light distributions at the light receiver 26 are such that: for the case where the location of the beam spot P.sub.1 is deviating toward left hand side of the track 10 as shown in FIG. 1C, the distribution is as shown in FIG. ID; for the case where the beam spot P.sub.1 is not deviating from the track 10 (i.e. on track), the distribution is as shown in FIG. 1E; and for the case where the location of the beam spot P.sub.2 is deviating toward right hand side of the figure from the track 10, the distribution is as shown in FIG. 1F. Therefor
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Envall Jr. Roy N.
Fujitsu Limited
Young W. R.
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