Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1996-12-02
1998-11-24
Hindi, Nabil
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369112, 369119, 369 4437, G11B 700
Patent
active
058417451
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process and arrangements for the tracking and for the elimination of scanning disturbances of optical information carriers such as, for example, CD, magneto-optical, phase change or write once disks.
The so-called multi-beam or three-beam principle is known for the scanning and especially for the guidance of a scanning beam on an optical information carrier, cf. KRIEG, Bernhard: Praxis der digitalen Franzis Workbook!, Franzis Verlag GmbH, 1989, pp. 45 et seq. An auxiliary light spot for tracking is provided in each instance ahead of and behind a main light spot for information reproduction or information recording, in the tangential direction. The auxiliary light spots are aligned in each instance to the extent of one half on the track, in the radial direction (cf. attached FIG. 2) and serve to generate a radial error signal. To this end, the light reflected by the information carrier is in each instance then obtained by difference formation from the intensities of the reflected light beams of the two auxiliary light spots or auxiliary beams respectively; in this case, the first auxiliary signal is time-delayed by an amount which is obtained from the spacing of the auxiliary light spots and the scanning speed, cf. player DA-100 from the Hitachi company. It is disadvantageous that detected disturbance signals which are caused by faults of the information carrier such as, for example, scratches, dropouts, black dots or even by the information content of the synchronization signals cannot be entirely eliminated by difference formation, since in the case of a time delay the signals are falsified in dependence upon the signal character with respect to the steepness of their signal flanks. Furthermore, in the event of differing scanning speeds or alterations of the spacing of the auxiliary light spots from the main-eight spot, a constant signal delay leads to a lesser extinction of disturbance signals, so that in the radial servo circuit forces are generated which may lead to a disturbance of the scanning or to loss of the track.
The auxiliary light spots and the main light spot on the optical disk are generated using a laser beam by splitting by means of a grating into 0-order and +/- first-order beams and focusing by means of an objective and the +/- first order beams the auxiliary light spots. With typical dimensioning, the directions of propagation of the light beams or respectively laser beams differ by less than one degree and the focal points are generated, by an objective lens, approximately in the information plane of the information carrier. An adequate spatial separation of the light spots on the optical disk in accordance with the arrangement in FIG. 2 is necessary, in order to be able to detect the auxiliary light spots individually and to use them for tracking. In in differing size, for reasons of better distinction from the main light spot H, although the light spots are, as a rule, of equal size.
The object of the invention is to avoid the disadvantages of the tracking and of the elimination of disturbances by time-delaying of an auxiliary light spot signal and subsequent difference formation, with low expenditure.
This object is achieved by the invention specified in claims 1 and 4. Advantageous further developments are specified in the subclaims.
The invention is based on the principle that in the case of a scanning device operating in accordance with the multibeam principle, scanning beams are provided in such a manner that the auxiliary beams for tracking impinge on the information carrier to be scanned in the form of two auxiliary beams lying side by side on the track radius. In this case, these auxiliary beams can be provided jointly, impinging on the information carrier either ahead of or behind the main light spot, and serve not only for the known tracking, but also at the same time for the advantageous elimination of scanning disturbances. A time-delaying of an auxiliary light spot signal, which time delaying leads to disadvantageous signal alterations, is no l
REFERENCES:
patent: 4160269 (1979-07-01), Kramer et al.
patent: 5434834 (1995-07-01), Shinoda et al.
patent: 5694385 (1997-12-01), Takahashi et al.
Kuhn Hans-Robert
Richter Hartmut
Deutsche Thomson-Brandt GmbH
Hindi Nabil
Tripoli Joseph S.
Wein Frederick A.
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