Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Patent
1989-04-21
1991-12-03
Envall, Jr., Roy N.
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
369 4435, 369 4442, 369 4429, 2502015, G11B 700
Patent
active
050704915
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an error signal generating circuit applicable to the reading of the optical recording medium which effects control of a servo mechanism utilizing a focus or tracking error signal.
BACKGROUND ART
An optical recording medium, such as a card type optical memory, which has a high density data recording capability and is capable of being carriable, has recently attracted the attention of many people.
In the optical recording medium such as a card type optical memory, recording is done by forming optically (or magnetooptically) changed states according to data to be recorded at discrete spots on the surface thereof, and then a light beam, such as a laser beam, is projected thereonto to read the changed states.
Specifically, fine unevenness or light and dark patterns are provided on a surface of the optical memory card onto which a light beam is projected to recognize the recorded data according to the difference of reflectivity, refractive index, or transmissivity of the medium to the projected light beam. Alternatively, the recording medium may be photothermo-magnetically recorded and the recorded data may be read depending upon the change of polarization of the projected light due to the magnetooptical effect.
The optical memory card has a clock track for enabling synchronization with data reading/writing and a tracking guide line functioning as a reference for a light beam from a reading optical system to accurately trace a track. The track and line are provided for each of the data track in the conventional optical memory card and juxtaposed each other.
In the tracking adjustment for light irradiated onto the optical recording medium, a tracking error signal is generated, based on the output from the photodetector for tracking error detection and a tracking servo mechanism is controlled, based on the tracking error signal to automatically keep the optimum tracking conditions.
In the focus adjustment for light irradiated onto the optical recording medium, a focus error signal is generated, based on the output from the photodetector for focus error detection and a focus servo mechanism is controlled according to the focus error signal to keep the optimum focus conditions.
However, if there is a dust or scar on the optical recording medium, it may possibly occur that light is not incident upon the photodetector for the error detection. In this case, a false error signal is generated and normal reading (or writing) is not attained.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide an error signal generating circuit which is capable of carrying out the reading of data without any substantial trouble otherwise normal focus or tracking control would not effected due to dust or scar on an optical recording medium.
The present invention features, as illustrated in FIG. 1, an error signal generating circuit which generates an error signal based on a read signal from an optical recording medium, which circuit comprises:
an error detection means responsive to the read signal to output the error signal;
a disorder detection means responsive to the read signal to detect disorder;
a signal hold means holding an output from the error detection means just before the disorderly state has occurred, during a period when the output from the disorder detection means represents the disorderly state; and
a switching means responsive to the output from the error detection means and the output from the signal hold means to selectively supply the output from the hold means when the output from the disorder detection means represents the disorderly state and selectively supply the output from the error detection means when the output from the disorder detection means does not represent the disorderly state.
In one embodiment of the present invention, the error signal is a signal for controlling the focus of light irradiated onto the optical recording medium.
In another embodiment of the present invention, the error signal is a signal for controlling the trac
REFERENCES:
patent: 4517666 (1985-05-01), Ando
patent: 4821251 (1989-04-01), Hosoya
Electronic Component and Application 6(1984), 4, pp. 209-14.
Envall Jr. Roy N.
Kabushiki Kaisha CSK
Tran Thang V.
LandOfFree
Error signal generating circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Error signal generating circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Error signal generating circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1700872