Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1991-01-17
1993-05-11
Psitos, Aristotelis
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369 4423, 369 4428, 369 4435, 369 4441, 369112, G11B 713
Patent
active
052107302
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a tracking error detecting apparatus for use in a multi-beam optical disk device in which signals are recorded or reproduced by using a plurality of beam spots.
In an optical disk device, a record track on an optical disk is traced with the aid of a light beam spot by moving an optical head in a radial direction of the disk while the optical disk is rotated. In order to trace the record track correctly by the light beam, the tracking control and focusing control are effected.
The tracking control has been carried out by various methods, and a typical push-pull method (sometimes called far field method) will be explained. As shown in FIG. 1a, FIG. 1b and FIG. 1c, in a surface of an optical disk 1 there are formed grooves 2, and a light beam spot is projected on the disk surface by means of an objective lens 3. A distribution of the intensity of light reflected by the disk 1 is shown by P. FIG. 2 illustrates the construction of a tracking error detecting circuit in which output signals from two-divided photodiode 4 having two elements 4a and 4b are supplied to a differential amplifier 5 which then produces a tracking error signal T.
Upon the two elements 4a and 4b of the two-divided photodiode 4 is made incident a light spot S of the light beam reflected from the disk. FIG. 1b shows the case in which the tracking is correctly attained, and intensity of light spot S formed on each of the elements 4a and 4b is equal to each other. Therefore, the tracking error signal T generated by the differential amplifier 5 is zero.
FIG. 1a and FIG. 1c depict the cases in which the tracking is not correctly attained, and the center of the light beam spot is deviated from the center of the groove 2. In this case the intensities of the light spot S reflected from the optical disk 1 and impinging upon the elements 4a and 4b are not identical with each other. Therefore, the differential amplifier 5 generates the tracking error signal T having positive or negative polarity and the tracking error signal T thus obtained is used to perform the tracking control.
The focusing control has been effected in various methods. In FIG. 3, the light reflected by the optical disk 1 is made incident upon a photo detector 8 by means of the objective lens 3 and cylindrical lens 7. The photo detector 8 is divided into four light receiving elements 8a, 8b, 8c and 8d as illustrated in FIG. 4. Output signals Ia, Ib, Ic and Id generated from the elements 8a, 8b, 8c and 8d, respectively are added by adders and then are supplied to a differential amplifier 9 to derive a focusing error signal F=(Ia+Ib)-(Ic+Id).
When the optical disk 1 is in the in-focus position, the light beam reflected by the optical disk 1 forms a circular light beam spot S on the light receiving element 8 as shown in FIG. 5b, so that the focusing error signal F becomes zero. However, when the optical disk 1 is in the out-of-focus position, the reflected light beam spot S having a shape shown in FIG. 5a or FIG. 5c is formed on the light receiving element 8, and thus the focusing error signal F having positive or negative polarity is generated. The objective lens 3 is moved by the automatic focusing control mechanism to attain the correct focus condition.
FIG. 6 is a view showing a whole construction of the above mentioned tracking control and focusing control. In the focusing control system, the focusing error signal F generated by the differential amplifier 9 is amplified by an amplifier 10a and then is supplied to a lens driving mechanism 11f which moves the objective lens 3. In the tracking control system, the tracking error signal produced by the differential amplifier 5 is supplied via an amplifier 10b to a lens driving mechanism 11t to move the objective lens 3. J1 denotes a slider signal for accessing a desired track, and when the optical head is moved in the radial direction to access a desired track, the slider signal is supplied via a driving amplifier 10c to a slider 12. To this end the optical head is placed on
REFERENCES:
patent: 4010317 (1977-03-01), Bouwhuis
patent: 4507766 (1985-03-01), Saimi et al.
patent: 4969137 (1990-11-01), Sugiyama et al.
patent: 5027337 (1991-06-01), Takahashi et al.
patent: 5081614 (1992-01-01), Takahashi et al.
Hayashi Akio
Nakagawa Shozo
Okabe Koichi
ASACA Corporation
Edun Muhammad
Psitos Aristotelis
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