Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2000-03-31
2002-10-22
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S013050, C369S013270
Reexamination Certificate
active
06469960
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to information storage apparatuses, and more particularly to an information storage apparatus which stores information by emitting a laser beam on a recording medium while a magnetic field is being applied.
Recently, optical discs have become a subject of attention as multimedia is being developed rapidly. It is desired for the optical discs to have an increasingly larger amount of storage. For example, a 3.5-inch MO has increased to a maximum of 1.3 GB. In order to achieve the large amount of storage, it is required to minimize a laser beam spot, to improve the accuracy of a focus servo, and to control the laser power accurately.
2. Description of the Related Art
In general, in a storage apparatus for use with a replaceable recording medium, the replaceable recording medium is mechanically displaced to a spindle motor when the replaceable recording medium is inserted and a medium supporting part has a mechanical tolerance. Moreover, the disk surface of the recording medium is physically uneven and distorted.
Thus, the recording medium is tilted at an angle to an optical head. Disadvantages known as tilt and skew occur.
FIG. 1
is a diagram showing a state of reading from a recording medium.
FIG. 2
is a graph showing one distance between an optical head and the recording medium and another distance between an electromagnet and the recording medium, in correspondence with a rotation degree of the recording medium.
In
FIG. 1
, the surface of the recording medium
102
is not perpendicular but is tilted with respect to a spindle shaft
101
of a spindle motor
100
.
In this state, when the recording medium
102
is rotated by the spindle motor
100
and a beam spot
105
from the optical head
103
scans on a track
104
, a distance between the optical head
103
and the surface of the recording medium
102
is depicted by a sine curve with solid line shown in
FIG. 2
in correspondence with the rotation degree.
On the other hand, the electromagnet
106
and the optical head
103
face each other and the recording medium
102
is provided between the electromagnet
106
and the optical head
103
. Thus, a distance between the electromagnet
106
and the surface of the recording medium
102
is depicted by a cosine curve with dotted line in correspondence with the rotation degree.
Further,
FIG. 3
is a diagram showing another state of reading from a recording medium.
FIG. 4
is a graph showing a characteristic of a tilt of the recording medium with respect to the optical head in the state shown in FIG.
3
.
FIG. 5
is a graph showing a distance between the recording medium and the electromagnet in the state shown in FIG.
3
.
FIG. 3
shows a state in which a recording medium
110
is a distorted plate. In this state, when the optical head
103
moves in an arrow A
2
direction, that is, from the inner side to the outer side, a vertical distance between the optical head
103
and the surface of the recording medium decreases as shown in FIG.
4
. Also, as shown in
FIG. 5
, the vertical distance between the electromagnet
106
and the surface of the recording medium
110
is greater on the outer side and less on the inner side.
Accordingly, in the state in
FIG. 1
or
FIG. 3
, an incident beam emitted from the optical head can not be perpendicular with respect to the recording medium. Thus, the shape of the laser spot is distorted. Consequently, an expected laser power for reading or writing can not be achieved. In addition, an external magnetic field applied to the recording medium
110
is changed by a distance between the recording medium
110
and the electromagnet
106
. Thus, an expected magnetic field strength can not be achieved.
In a case in which the expected laser power is not achieved, an unexpected laser power does not affect the quality of reading or writing when a recording density such as a track per inch (TPI) or a bit per inch (BPI) is low. However, when the recording density is high, an error rate is increased and can not be ignored.
Also, in a case in which the expected external magnetic field strength is not achieved, an unexpected magnetic field strength does not affect the quality of reading or writing when the recording density is low. However, when the recording density is high, the error rate is increased and can not be ignored.
Therefore, a method is provided to correct the tilt and skew of the recording medium
102
or
110
by adjusting a tilt of the spindle motor
100
.
In the method in which the tilt and skew of the recording medium
102
or
110
is corrected by adjusting the spindle motor
100
, it is required to provide a mechanism for controlling the inclination of the spindle motor
100
and a sufficient space for the mechanism. Disadvantageously, when the spindle motor
100
is mechanically adjusted, it is difficult to carry out the adjustment at a high rotation speed.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an information storage apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an information storage apparatus in which a proper external magnetic field strength is obtained by controlling the external magnetic field strength, instead of adjusting a tilt of a recording medium,
The above objects of the present invention are achieved by an information storage apparatus for emitting a light beam to a recording medium and recording information on the recording medium by applying an external magnetic field to a position illuminated by the light beam, including: an external magnetic field control part controlling an external magnetic field strength based on the illuminated position on the recording medium.
According to the present invention, the external magnetic field strength is controlled based on the illuminated position on the recording medium. Therefore, it is possible to properly read or write data from or to the recording medium even if the recording medium is distorted or tilted.
Also, the above objects of the present invention are achieved by a method for emitting a light beam to a recording medium and recording information on the recording medium by applying an external magnetic field to a position illuminated by the light beam, including the step of: controlling an external magnetic field strength based on the illuminated position on the recording medium.
According to the present invention, the method can be provided to properly read or write data from or to the recording medium even if the recording medium is distorted or tilted.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.
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Dinh Tan
Fujitsu Limited
Greer Burns & Crain Ltd.
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