Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1988-10-11
1991-07-23
McElheny, Jr., Donald
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369 4425, 369 4434, G11B 700
Patent
active
050349392
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns equipment for playing back and optionally also recording data that are read by an optical pick-up system by means of guiding a beam of light along the data-storage tracks of a rotating disk-shaped recorded medium and that are then decoded in a decoder that emits a pulse from its error output terminal for every bit error.
SUMMARY OF THE INVENTION
Equipment of this type, compact-disk players, optico-magnetic equipment for playback and recording, DRAW-disk recorders and players, and videodisk players for example, are equipped with an optical pick-up system consisting of a laser diode, several lenses, a prism beam divider, and a photodetector. The design and function of an optical pick-up are described on pages 209 to 215 of Electronic Components and Applications, Vol. 6, No. 4, (1984).
BRIEF DESCRIPTION OF THE DRAWINGS
The lenses focus the beam of light emitted by the laser diode onto the compact disk, whence it is reflected onto the photodetector. The data stored on the compact disk are obtained along with actual values for the focusing circuit and for the tracking circuit from the output signal from the photodetector. The actual value for the focusing circuit is called the "focusing error" and the actual value for the tracking circuit the "radial tracking error" in the aforesaid reference.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The component that controls the focusing circuit is a coil, which generates a magnetic field that displaces an objective lens along the optical axis. The focusing circuit, in displacing the lens, keeps the beam of light emitted by the laser diode constantly focused on the compact disk. The tracking circuit, which is also often called the "radial drive mechanism," displaces the optical pick-up system radially in relation to the compact disk, keeping the beam of light positioned on the spiral data-storage tracks on the disk.
The radial drive mechanism in some equipment comprises a "coarse drive mechanism" and a "fine drive mechanism." The coarse drive mechanism can for example be a spindle that radially displaces the overall optical pick-up system, consisting of the laser diode, the lenses, the prism beam divider, and the photodetector. The fine drive mechanism tilts the beam of light radially at a small prescribed angle, allowing it to travel a short distance along the radius of the compact disk as the result of the tilting motion alone. In other words, the fine drive mechanism varies the radial vector component of the beam of light in relation to the compact disk. The tangential angle at which the beam strikes the disk, on the other hand, is always 90.degree. C. The vector component of the beam of light tangential to the compact disk is accordingly zero.
The data signals emitted by the photodetector are, as already mentioned herein, decoded in a decoder that emits a pulse at its error output terminal, the C1F1 output terminal, at every bit error.
The number of bit errors depends, among other factors, on the angle at which the beam of light strikes the compact disk at an angle thereto. Since a compact disk, however, is not perfectly flat and circular but is subject to deviations in tolerance, the right angle at which the beam of light tangentially strikes the compact disk cannot be optimally established for all scanning points when the compact-disk player is manufactured. This situation increases the number of bit errors.
The object of the invention, accordingly, is to decrease the number of bit errors in equipment for playing back data.
This object is attained in accordance with the invention in that a signal for controlling an adjustment stage is obtained from the bit-error rate and is employed to vary the vector component of the beam of light that is tangential to the recorded medium.
In the drawings,
FIG. 1 illustrates one embodiment of the invention and
FIG. 2 illustrates another embodiment of the invention.
The embodiment illustrated in FIG. 1 will now be specified and its function explained.
What is called the error
REFERENCES:
patent: Re31166 (1983-03-01), Korda
patent: 4755980 (1988-07-01), Yoshimaru et al.
Kurz Arthur
Uhde Dietmar
Deutsche Thomson-Brandt GmbH
Fogiel Max
McElheny Jr. Donald
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