Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1999-10-19
2004-04-27
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S118000
Reexamination Certificate
active
06728192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to information recording media which comprise a high density information recording means such as an optical information recording medium including an optical disk or a magnetic information recording medium including a fixed magnetic disk or a floppy disk, a tracking error signal detection apparatus for the information recording media, and an information recording apparatus which can precisely record, reproduce and erase information on the information recording media using the tracking error signal detection apparatus, and also relates to methods of adjusting an information recording apparatus.
2. Disclosure of the Prior Art
A track pitch of a conventional magnetic recording media on which information is recorded, such as a floppy disk. Therefore, the track pitch is much wider than that of an optical disk, which is about 1.6 &mgr;m. Accordingly, a rough track location using a mechanical method such as a stepping motor has been sufficient. However, in order to realize a magnetic recording medium having a larger capacity, a track pitch from several &mgr;m to several tens &mgr;m m is required. In this case, a precise track location becomes necessary.
FIG. 1
shows a configuration of a conventional magnetic recording apparatus which detects a tracking error signal by using light. In
FIG. 1
, a linearly polarized divergent beam
70
radiated from a semiconductor laser light source
10
is converted to a parallel beam by a collimator
20
and the parallel. beam enters a polarizing beam splitter
30
. All the parallel beam
70
entering the polarizing beam splitter
30
passes through the polarizing beam splitter
30
and enters a ¼ wavelength plate
31
. The parallel beam
70
is converted to a circularly polarized beam by passing through the ¼ wavelength plate
31
and is focused on a magnetic recording medium
40
by an object lens
21
.
FIG. 2
shows the relationship between the magnetic recording medium
40
and the focused light beam
70
. The magnetic recording medium
40
has tracks Tn−1, Tn, Tn+1 . . . , which include the area on which information is recorded or reproduced by a magnetic head
99
with a certain pitch pt (approximately 20 &mgr;m). Further, discrete guiding grooves Gn−1, Gn, Gn+1 . . . , which enable the optical detection of a signal synchronizing A tracking error signal and which enables rotations of the magnetic recording medium
40
, are formed in the middle of adjacent tracks.
The beam
70
reflected and diffracted by the magnetic. recording medium
40
passes through the object lens
21
again, and enters the ¼ wavelength plate
31
. By passing through the ¼ wavelength plate
31
again, the beam
70
is converted to a linearly polarized beam having a 90° phase change of the light source
10
. All the beam passing through the ¼ wavelength plate
31
is reflected by the polarizing beam splitter
30
and enters a photodetector
50
. The incident light beam is converted into an electric signal by the photodetector
50
and inputted to a signal processing portion
80
.
As illustrated in
FIG. 1
, the photodetector
50
has two light sensing portions
501
,
502
. Signals outputted from the light sensing portions
501
,
502
are converted to voltage signals by current-voltage (I-V) converting portions
851
,
852
respectively, and inputted to a differential operation part
871
. The differential operation part
871
subtracts the two voltage signals outputted from the I-V converting portions
851
,
852
.
When a beam
70
from the optical system has a displacement x from the center of a guiding groove such as Gn on a magnetic recording medium
40
, voltage signals v
21
, v
22
outputted from the I-V converting portions
851
,
852
become sine waves having opposite phases which can be approximately represented by the below mentioned formulae (1) and (2). The signals v
21
, v
22
can be illustrated as FIG.
3
(
a
) and (
b
).
v21
=
-
A
·
sin
(
2
π
x
/
pt
)
+
B
(
1
)
v22
=
A
·
sin
(
2
π
x
/
pt
)
+
B
(
2
)
In the formulae (1) and (2), A is an amplitude and B is a DC component.
A signal v
23
outputted from the I-V converting portion
871
can be represented by the below mentioned formula (3) and outputted from a terminal
801
as the tracking error signal.
v
23
=2
·A
·sin(2
&pgr;x/pt
) (3)
The signal v
23
can be illustrated as FIG.
3
(
c
). The tracking error signal v
23
outputted from the terminal
801
is inputted to a driving portion
90
to adjust relative positions of a magnetic recording medium
40
and a base
95
including a tracking error signal detection optical system
100
and a magnetic head
99
for recording and reproducing information so as to form a desired track on the magnetic recording medium
40
. The tracking error signal detection method is known as the push pull method.
(First Problem)
In a conventional magnetic recording apparatus using a magnetic head
99
for recording and reproducing information, and an optical system
100
for the detection of a tracking error signal, a distance d between a point S
1
at which the magnetic head
99
contacts a magnetic recording medium
40
and a focal point S
2
of a beam
70
from the optical system needs to be at least several hundred &mgr;m to several mm. That is, the point S
1
at which the magnetic head
99
contacts the magnetic recording medium
40
and the focal point S
2
of the beam
70
scan different tracks on the magnetic recording medium
40
.
In assembling a magnetic recording apparatus, the distance d is adjusted so as to have the working point of the tracking servo at the midpoint S
3
of the signal amplitude of the tracking error signal v
23
as illustrated in FIG.
3
(
c
) when the point S
1
is on a track of the magnetic recording medium
40
. However, temperature or humidity change causes expansion or contraction of the magnetic recording medium
40
and the track pitch pt changes accordingly. Therefore, in the tracking operation at the point S
3
using the tracking error signal v
23
obtained from the optical system
100
, the point S
1
becomes off track and thereby drastically deteriorates the information reproduction characteristics.
In this case, for example, if a point S
4
is the working point on the tracking error signal when the point S
1
is on the track, a tracking servo can be enabled by applying an offset voltage to the tracking servo. However, the dynamic range of the orientation illustrated by the arrow D
1
lowers and thereby deteriorate the followability in the case disturbance generates. Further, as the point S
4
moves farther from the point S
3
, the servo gain of the tracking operation lowers. When the point S
4
eventually reaches the point S
5
, a new problem occurs that the servo gain of the tracking becomes 0 thereby completely losing the tracking servo.
On the other hand, in an optical disk apparatus where the beam used to detect tracking error signals and the beam used to record information on the information recording medium are identical, a configuration forming a track on or between the guiding grooves so as to record and reproduce information with a further high density is proposed. However, in this configuration, when the relationship pt>&lgr;/NA is satisfied where &lgr; is a wavelength of the beam radiated from the light source, NA is an numerical aperture of the object lens at the information recording medium side, and pt is a cycle of marks or guiding grooves formed on the information recording medium to enable the detection of the tracking error signals, a problem similar to the above mentioned problem occurs when the predetermined angle between the beam focused by the object lens and the information recording medium can not be sustained.
Specific examples include the case having a wavelength &lgr; of 650 nm, a numerical aperture NA of 0.6, a cycle pt of
Kadowaki Shin-ichi
Nishino Seiji
Nishiwaki Seiji
Sano Kousei
Tanaka Shin-ichi
Huber Paul W.
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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