Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal processing for controlling recording light...
Reexamination Certificate
1999-10-29
2002-04-30
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal processing for controlling recording light...
C369S053190
Reexamination Certificate
active
06381206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording apparatus for recording a video signal, an audio signal and the like onto an optical recording disk, and relates, more particularly to, a technique for reducing an influence of a tilt of a disk in a circumferential direction applied to a recording and reproduction of information, in a recording apparatus for carrying out a recording and reproduction of information by transmitting a laser beam onto a transparent substrate of the disk.
2. Description of the Related Art
A recording and reproduction of information onto and from an optical disk is carried out by irradiating laser beams onto the optical disk. The laser beams irradiated onto the optical disk are collected on the optical disk.
In order to increase the recording density of information recorded on the optical disk, the numerical aperture of an objective lens is made larger and the diameter of a light spot formed on the optical disk is made smaller. With this arrangement, it is possible to record the information on the optical disk as a smaller mark. As a result, it is possible to increase a spatial frequency in the circumferential direction of a recording signal and to narrow a track pitch. This method has been widely known in general as a method of increasing the recording density of information.
However, the increasing the numerical aperture of an objective lens has a problem of making larger an influence of a tilt of the disk applied to a recording and reproduction of information. More specifically, when a tilt is generated on the disk, the quantity of aberration generated at a light spot becomes large, and when the diameter of the light spot becomes larger, the distribution of the light spot does not become symmetrical. As a result, it becomes difficult to accurately carry out a recording and reproducing processing of information.
Regarding a tilt of a disk in a radial direction of the disk, it is possible to correct the tilt by adjusting the angle of a pickup or the disk whenever necessary, so that it is possible to reduce an influence of this tilt. On the other hand, regarding a tilt of the disk in a circumferential direction of the disk, it is difficult to correct this tilt by a mechanical adjustment as the speed of variation of the tilt is fast.
When information is recorded on an optical disk in the status where the disk is tilted in a circumferential direction, there is a case where a mark to be recorded on the disk by an irradiation of laser beams is deviated from a position at which the mark should be originally recorded. Such a deviation in the recording spot appears as a jitter of information at the time of reproducing the information, and this jitter degrades the quality of a reproduced signal. A problem like this also occurs when an optical disk has not a flat surface but has a variation in the thickness of the disk, not only when the disk is tilted.
Further, the quantity of aberration generated by the tilt of the optical disk is proportional to the thickness of a transparent substrate constituting the optical disk. Therefore, it is possible to make smaller the quantity of the aberration by reducing the thickness of the transparent substrate. However, when the thickness of the transparent substrate is made smaller, there arises a problem that the performance of the optical disk is lowered due to a hurt or a stain on the disk surface.
Further, the quantity of aberration may be made smaller by reducing the total thickness of the optical disk. However, when the total thickness of the disk is reduced, there arises a problem that the disk as a whole or the disk substrate is easily distorted.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical recording apparatus capable of correctly recording information onto a recording disk even when there is generated a tilt in the recording disk in a circumferential direction of the disk.
An optical recording apparatus in accordance with the present invention includes: a tilt detecting device for detecting a circumferential direction component of a tilt of a recording medium with respect to a laser beam light axis; a recording pulse signal generating device for generating a recording pulse signal by coding an information signal to be recorded and outputting the generated recording pulse; a modulating device for receiving the recording pulse from the recording pulse signal generating device, and modulating an intensity of a laser beam based on the received recording pulse signal; a laser beam irradiating device for applying the modulated laser beam onto the recording medium; and a recording pulse signal control device for controlling a sending timing at which the recording pulse signal is sent from the recording pulse signal generating device to the modulating device, based on the circumferential direction component detected by the tilt detecting device.
In this optical recording apparatus, the recording pulse signal generating device carries out an encoding of an information signal to be recorded, and generates a recording pulse signal. The modulating device modulates the intensity of a laser beam based on this recording pulse signal. The laser beam irradiating device irradiates the laser beam whose intensity has been modulated, to the recording medium. As a result, the information signal is recorded.
The recording of an information signal onto a recording medium is carried out by first heating the recording medium by a laser beam to change optical characteristics of the material of the recording medium, thereby to form marks onto the recording medium. Thus, the information signal is recorded onto the recording medium. Accordingly, when the irradiated surface of the recording medium has a tilt in the circumferential direction of the disk, the center of the spot light quantity of the laser beam is deviated from a proper position due to a generation of aberration.
In the above aspect of the optical recording apparatus according to the present invention, the deviation of the center of the light quantity of the light spot is overcome in the following manner. When the tilt detecting device has detected a circumferential direction component of a tilt of the optical disk with respect to the laser beam light axis, the recording pulse signal control device controls the sending timing of the recording pulse signal to the modulating device, based on a detection output of the circumferential direction component of the tilt. For example, when the center of the light quantity of the light spot has deviated in a direction to gain time, the recording pulse signal control device delays the sending timing of the recording pulse signal from the reference timing. On the other hand, when the center of the light quantity has deviated in a direction to lose time, the recording pulse signal control device advances the sending timing of the recording pulse signal from the reference timing.
As a result, a temperature gradient on the recording medium changes in a similar manner to that of the case where there is no tilt, so that an edge position of a mark to be recorded becomes at a proper position. Accordingly, it is possible to prevent an occurrence of a jitter at the time of a reproduction and to prevent an increase in the error rate. Further, it is possible to carry out a stable recording and reproduction of an information signal even when a disk having a large deformation quantity is used. Furthermore, it is possible to compensate the disk for a warp, so that it is possible to carry out a recording and reproduction of an information signal onto and from a thin disk.
The aforementioned optical recording apparatus in accordance with the present invention, the circumferential direction component may include a component indicating a tilt angle of a recording surface of the recording medium. Furthermore, when the recording surface at a front side of a laser beam in a relatively proceeding direction of the laser beam is tilted in a direction to leave away from the la
Morgan & Lewis & Bockius, LLP
Pioneer Corporation
LandOfFree
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