Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-12-14
2004-05-25
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C369S013010
Reexamination Certificate
active
06741416
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a tracking signal generating device for obtaining a tracking error signal for positioning an optical head or a magnetic head in recording and/or reproducing information with respect to an information recording medium such as a high-density floppy disk, optical disk, or the like and to a magnetic recording/reproducing system carrying out tracking control using the tracking signal generating device.
2. Related Background Art
The intervals between tracks where a series of information is recorded are reduced with the increase in recording density with which information is recorded on a magnetic disk such as a floppy disk. This makes it difficult to position a magnetic head or the like in a direction perpendicular to the tracks with a mechanical precision. Consequently, an optical positioning technique has been required.
For instance, in a high-density floppy disk, tracks formed of tracking pit rows are arranged at an interval of about 20 &mgr;m so that a magnetic head can track information tracks arranged at an interval of about 10 &mgr;m. In this case, using an optical system with an numerical aperture NA of about 0.04 on a disk side with a wavelength of a light source of 780 nm, a tracking error signal can be obtained. The tracks to be tracked are formed of pit rows whose lengths are 40 to 70 &mgr;m. The lengths of the pit rows are determined depending on the radial position so that signals from the tracks obtained at a revolution rate of 720 per minute have a frequency of 20 kHz. A conventional example used for obtaining a tracking signal from such a disk is described with reference to
FIG. 15
as follows.
Light emitted from a semiconductor laser
101
as a light source is incident on a diffraction grating
162
provided at a first plane of a diffraction element
160
to generate ±1st-order diffracted lights (not shown in the figure). In this case, zero-order light is referred to as a main beam (M) and ±1st-order diffracted lights as sub-beams (S
1
and S
2
).
The main beam and the sub-beams pass through a diffraction grating
161
provided at a second plane of the diffraction element
160
and are converged by a lens
104
as a converging means. The main beam and the sub-beams that have become converged lights are focused on a disk
107
as an information recording medium with an aperture being limited so that a desirable numerical aperture (NA) is obtained through an aperture
105
.
With reference to
FIG. 16
, the relationship between the beams and a pit row on the disk is described. There are tracks
204
formed of rows of pits
205
on the disk
107
. On the disk
107
, a beam row formed of a main beam (M)
201
and two sub-beams (S
1
and S
2
)
202
and
203
is positioned so as to have a predetermined angle &thgr;
0
with respect to a track
204
of the disk
107
.
In the figure, l denotes an interval between M and S
1
or S
2
on the disk
107
, Tp indicates an interval between two adjacent tracks
204
, and Tpp denotes a radial distance from M to S
1
or S
2
. A tangential direction is a circumferential direction in the disk
107
and a radial direction is a direction of the radius of disk
107
.
Returning to
FIG. 15
, the main beam and the sub-beams reflected from the disk
107
pass through the aperture
105
and the lens
104
again and are diffracted by the diffraction grating
161
, and then enter a photodetector
108
R or
108
L.
The photodetectors
108
R and
108
L include a plurality of detection regions to receive the main beam and the sub-beams separately, and output signals corresponding to the quantity of received beams. The three beams irradiate locations different in a direction perpendicular to the tracks on the disk
107
. Therefore, signals obtained from the three detection regions are different in modulation degree from one another. Through calculation of these signals by a tracking error signal generating device shown in
FIG. 17
, the relative positional relationship between the track and the beam irradiation locations can be detected.
Next, the following description is directed to the tracking error signal generating device shown in FIG.
17
. One sub-beam S
1
of the two sub-beams is received by a detection region
301
of the photodetector
108
L and a detection region
304
of the photodetector
108
R and the respective photodetectors
108
L and
108
R output currents corresponding to the quantity of the received beams. The currents are converted to a voltage signal by an I-V amplifier
401
, which then is output. Similarly, the main beam M is received by a detection region
302
of the photodetector
108
L and a detection region
305
of the photodetector
108
R, and current signals corresponding to the quantity of the received beams are converted to a voltage signal by an I-V amplifier
402
, which then is output. Furthermore, another sub-beam S
2
also is received by a detection region
303
of the photodetector
108
L and a detection region
306
of the photodetector
108
R, and current signals corresponding to the quantity of the received beams are converted to a voltage signal by an I-V amplifier
403
, which then is output.
In this case, generally, the three beams M, S
1
, and S
2
generated by the diffraction grating
161
are affected by diffraction efficiency and their quantities received by the photodetectors
108
L and
108
R are different from one another. Therefore, the I-V amplifiers
401
,
402
, and
403
have a gain ratio canceling the influence of the diffraction efficiency.
Next, the signals output from the I-V amplifiers
401
,
402
, and
403
are input into bandpass filters
404
,
405
, and
406
, respectively, and are subjected to bandpass with signals of 20 kHz as a frequency used for the reproduction of a pit row being centered. The signals output from the bandpass filters
404
,
405
, and
406
are input into detection circuits
407
,
408
, and
409
, respectively. From the signals of 20 kHz, their envelope signals are extracted. The amplitudes of the envelope signals reflect the positional relationships between the track and the beams on the disk
107
and vary accordingly.
The signal output from the detection circuit
407
is indicated as Ss
1
, the signal output from the detection circuit
408
as Sm, and the signal output from the detection circuit
409
as Ss
2
.
Further, an amplitude level of the signal Sm (½ of the difference between a maximum value and a minimum value of the signal Sm when an optical beam moves for a distance equal to or more than the interval Tp in the radial direction on the disk
107
) is indicated as Lm, amplitude levels of the signals Ss
1
and Ss
2
as L
1
and L
2
, respectively, a phase of the signal Ss
1
with respect to the signal Sm as &phgr;
1
, and a phase of the signal Ss
2
with respect to the signal Sm as &phgr;
2
. In this case, the signals Sm, Ss
1
, Ss
2
and the phases &phgr;
1
and &phgr;
2
are expressed by
Sm=Lm
×sin &thgr;, Eq. 1
Ss
1
=
L
1
×sin(&thgr;−&phgr;
1
), Eq. 2
Ss
2
=
L
2
×sin(&thgr;+&phgr;
2
), and Eq. 3
&phgr;
1
=&phgr;
2
=2
&pgr;×Tpp/Tp,
Eq. 4
wherein &thgr; can be obtained by &thgr;=2&pgr;×Lj/Tp, where Lj denotes a radial distance between the track
204
and the main beam M.
Next, a differential operational circuit
410
receives the signals Ss
1
and Sm and outputs a difference signal Sa thereof. In addition, a differential operational circuit
411
receives the signals Sm and Ss
2
and outputs a difference signal Sb thereof. These difference signals Sa and Sb are expressed by
Sa=Sm−Ss
1
=
La
×sin(&thgr;+&phgr;
a
) and Eq. 5
Sb=Ss
2
−
Sm=Lb
×sin(&thgr;+&phgr;
b
), Eq. 6
wherein the amplitude levels La and Lb of the signals Sa and Sb and the phase differences &phgr;a and &phgr;b are expressed by
tan
φ
Hatada Hajime
Kadowaki Shin-ichi
Ohmura Ikuo
Sano Kousei
Hudspeth David
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Wong K.
LandOfFree
Tracking signal generating device and method, and magnetic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tracking signal generating device and method, and magnetic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tracking signal generating device and method, and magnetic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3250507