Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-10-16
2001-04-17
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S053130
Reexamination Certificate
active
06219317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for recording and/or reproducing information signals for an optical disc. More particularly, it relates to an optical disc recording and/or reproducing method and apparatus for recording or reproducing information signals for an optical disc as a servo control operation s performed.
2. Description of the Related Art
Up to now, a disc-shaped recording medium for recording information signals, such as optical disc, is in widespread use. The optical disc recording and/or reproducing apparatus is configured for illuminating laser light on an optical disc from an optical pickup to record or reproduce information signals on or from the signal recording surface of the recording medium.
Recently, there is an increasing demand for a high recording density optical disc having a large data storage capacity. This high density recording is possible by reducing the diameter of a light spot of a laser light beam illuminated from an optical pickup on the signal recording surface.
The light spot diameter is changed by e.g., the wavelength of the laser light beam and by the numerical aperture NA of an objective lens. It is noted that the diameter of the light spot focussed on the signal recording surface is proportionate to the wavelength of the laser light and inversely proportionate to the numerical aperture NA of the objective lens.
Thus, high density recording on an optical disc becomes possible by shortening the wavelength of the laser light or by increasing the numerical aperture NA of the objective lens.
On the other hand, the depth of focus of the light spot is proportionate to its wavelength and inversely proportionate to the square of the numerical aperture NA of the objective lens. Since the depth of focus is reduced in case of using means for enabling high recording density, it is necessary to reduce the focussing error for assuring recording/reproduction.
Moreover, since the track pitch is narrowed by increasing the recording density, it is also necessary to reduce the tracking error for assuring recording/reproduction.
Thus, for realization of high recording density, suitable measures need to be used to reduce the follow-up errors of focussing servo and tracking servo that are mainly responsible for occurrences of focussing and tracking errors.
It is noted that, if a shock is applied from outside to a device, there are produced transient errors which need to be suppressed. Although it is possible to increase the servo followup performance by broadening the servo band and increasing the gain, steady-state servo stability is impaired by increasing the gain thus producing negative effects.
Specifically, should the servo band and the gain be increased to improve servo followup characteristics, there is raised a problem that the servo followup error is increased against expectations, such as by excess reaction to noise components of a higher frequency band.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and apparatus for recording and/or reproducing an optical disc in which servo with high followup performance can be applied as servo errors are suppressed without obstructing steady-state stability.
The present invention provides an optical disc recording and/or reproducing apparatus for performing a servo control operation based on focussing error signals and tracking error signals from an optical pickup including impact detection means for detecting an impact applied from outside, and servo means for performing a servo control operation based on the focussing error signals and tracking error signals. The servo control operation is such an operation that is switched between a first state having a usual servo followup performance and a second state higher in a servo followup performance higher than the first state. The optical disc recording and/or reproducing apparatus also includes control means for checking the strength of an impact detected by the impact detection means for switching the servo control operation of the servo means to the second state when the strength of the impact exceeds a pre-set value.
Thus, with the present optical disc recording and/or reproducing apparatus, the control means sets servo means to the second state having a higher servo followup performance if the impact strength sensed by the impact detection means exceeds a pre-set strength.
Also, with the present optical disc recording and/or reproducing method, the impact strength applied from outside is discriminated and, if the impact strength exceeds a pre-set strength, the servo means is switched from the first state of the usual servo followup performance to the second state of the servo followup performance higher than that of the first state.
With the optical disc recording and/or reproducing apparatus of the present invention, the servo means can be set to the second state of higher servo followup performance, under control by the control means, to perform the servo operation, if the impact strength sensed by the impact detection means exceeds a pre-set strength.
That is, with the present optical disc recording and/or reproducing apparatus, the servo of high followup performance can be applied, without impairing steady-state stability, under suppressing occurrence of servo errors.
With the optical disc recording and/or reproducing method of the present invention, the impact strength applied from outside is discriminated and, if the impact strength exceeds a pre-set strength, the servo operation is performed as the first state of the usual servo followup performance is switched to the second state of the higher servo followup performance. That is, the servo of high followup performance can be applied, without impairing steady-state stability, under suppressing occurrence of servo errors.
REFERENCES:
patent: 4722079 (1988-01-01), Matsumoto
patent: 5286965 (1994-02-01), Okada
patent: 5825729 (1998-10-01), Ogasawara et al.
patent: 05144029 (1993-06-01), None
Edun Muhammad
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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