Magnetic disk unit and method of manufacture thereof

Details Magnetic disk unit and method of manufacture thereof Magnetic disk unit and method of manufacture thereof

1999-05-19

2003-01-07

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S077030, C360S073030, C360S078010, C369S112020, C369S118000

Reexamination Certificate

active

06504667

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic disk unit which radiates laser beams onto a recording medium and positions a magnetic head, and a method of the manufacture thereof. Specifically, the present invention relates to a magnetic disk unit for improving the quality of optical sensor signals for positioning a magnetic head, thereby improving positioning accuracy, and a method of the manufacture thereof.
2. Description of Related Art
The present mainstream of recording media attachable to and detachable from magnetic disk units is 3.5-inch disks. The track density of such recording media has reached about 2100 to 2500 TPI (tracks per inch) with the recording capacity of 100 to 120 megabytes. In order to enable recording, erasing, or playing back information of high recording densities, accurate positioning of a magnetic head to a recording medium is essential. Therefore, a recording medium is provided with a servo stitch for detecting the position of an optical tracking servo, and on the positioning of a magnetic head to magnetic tracks, closed-loop optical servo control is performed using the servo stitch for position detecting.
FIG. 7
is a diagram illustrating a conventional magnetic disk unit.
FIG. 8
is a diagram illustrating the optical system of the magnetic disk unit shown in FIG.
7
. In
FIGS. 7 and 8
, the numeral
20
indicates a disk recording medium;
20
a
indicates lands of specific lengths formed concentrically on the bottom surface of the recording medium
20
;
20
b
indicates position detecting servo stitches comprising grooves provided intermittently having a reflection factor different from the reflection factor of the lands
20
a
;
21
indicates a laser source (hereafter referred to as LD);
22
indicates a laser beam emitted from the LD
21
;
23
indicates a 3-beam diffraction grating which splits the laser beam
22
into three beams;
24
indicates an aperture;
25
indicates an objective lens for converging the laser beam
22
from a hologram element
29
, and guiding reflected light beams from the recording medium
20
to the hologram element
29
;
26
indicates a mirror for guiding the laser beam
22
to the recording medium
20
, and guiding light beams reflected from the recording medium
20
to the objective lens
25
;
27
indicates a beam splitter;
28
indicates a photodiode (hereafter referred to as PD), which has three light receiving parts
28
a
-
28
c
;
29
indicates a hologram element comprising the aperture
24
and the beam splitter
27
; and
30
indicates a laser source-photodiode unit (hereafter referred to as LD-PD unit) comprising the LD
21
, the PD
28
, and the hologram element
29
.
Also,
31
a
-
31
c
indicate amplifiers; each of RSM, RS
1
, and RS
2
indicates a feedback resistance;
32
indicates an arithmetic circuit;
32
a
indicates a driving amplifier; and
33
indicates a voice coil motor for moving a carriage
37
.
Furthermore,
34
indicates a magnetic head for recording information on
2
the recording medium
20
or playing back information recorded on the recording medium
20
;
34
a
indicates a light path for passing the laser beam and reflected light beams;
35
indicates a magnetic gap of the magnetic head
34
;
36
indicates a head support plate for supporting the magnetic head
34
; and
37
indicates a carriage for fixing the head support plate
36
, and movably supporting the structure comprising components
21
-
30
together with the magnetic head
34
.
The operation of this unit will be described below referring to
FIGS. 7 and 8
. The recording medium
20
is rotated by a medium driving motor (not shown) at a constant speed. The magnetic head
34
is supported by the head support plate
36
, and the magnetic gap
35
slides on the bottom surface of the recording medium
20
.
FIG. 8
is a conceptual diagram illustrating sensing the tracking information of the magnetic disk unit and illustrating a closed-loop optical servo control. The laser beam
22
emitted from the LD
21
passes through the
3
-beam diffraction grating
23
, and split into three laser beams
22
a
,
22
b
, and
22
c
, which pass through the aperture
24
and enter in the objective lens
25
. Laser beams
22
a
,
22
b
, and
22
c
, which have passed through the objective lens
25
, are reflected from mirror
26
and radiated onto the bottom surface of the recording medium
20
perpendicularly, and form three corresponding beam spots M, S
1
, and S
2
on the surface of the recording medium
20
. At this time, the optic axis of the laser beam
22
emitted from the LD
21
is in parallel to the recording medium
20
.
Here, if the laser beam
22
parallel to the recording medium
20
emitted from the LD
21
is radiated onto the recording medium
20
perpendicularly using a mirror
26
, the adjustment of the optic axis is difficult because this principle acts with light beams reflected by the mirror
26
. Therefore, corresponding the fluctuation of the angle of the mirror
26
and the angle of the laser beam
22
radiated onto the bottom surface of the recording medium
20
, the adjustment for optimizing the quantity of laser beams that return to light receivers
28
a
to
28
c
by aligning the LD-PD unit
30
shown in
FIG. 7
in X and Y directions.
Since the light path of the laser beam
22
can be set long by using mirror
26
regardless of the limitation of the thickness of the magnetic disk unit, the effective diameter of the objective lens
25
for achieving the beam-spot diameters &phgr;M, &phgr;S
1
, and &phgr;S
2
can be expanded, and the quantity of light into light receivers
28
a
to
28
c
can be increased.
As
FIG. 8
shows, servo stitches
20
b
, which represent information, are formed on the bottom surface of the recording medium
20
. The magnetic disk unit senses the location from difference in the quantity of reflected light from beam spots M, S
1
, and S
2
in terms of reflection factors between the land
20
a
on the bottom surface of the recording medium
20
where no locating servo stitches
20
b
are present and the locating servo stitches
20
b
. Three reflected light beams from the recording medium
20
(shown by dotted line in
FIG. 8
) enter into the objective lens
25
. Since the optical system is a non-telecentric system, the three reflected light beams after passing through the objective lens
25
do not necessarily pass through the center of the aperture
24
, and are guided by the beam splitter
28
to light receivers
28
a
to
28
c.
Although the three reflected light beams are received by the light receivers
28
a
to
28
c
respectively, they not always pass through the center of the aperture
24
. Therefore, the light-beam receiving ratios of the light receivers
28
a
to
28
c
vary according to the angle of the mirror
26
and the angle of the laser beam
22
radiated to the bottom surface of the recording medium
20
. In order to optimize the quantity of the laser beams returning to the light receivers
28
a
to
28
c
, the quantity of light beams are adjusted so that the quantity of light beams received by the light receiver
28
a
corresponding to the beam spot M is maximized, and the quantities of light beams received by the light receivers
28
b
and
28
c
corresponding to the beam spots S
1
and S
2
are equalized.
FIG. 9
shows the relationship between the servo stitch
20
b
, Beam spots M, S
1
, and S
2
, and the output of PD
28
. As
FIG. 9
shows, tracking information, that is the position data in the radial direction of the recording medium
20
, is determined by the quadrature phase method through the use of the output values of the light receivers
28
a
to
28
c
when the beam spots M, S
1
, and S
2
traverse the servo stitch
20
b
in the radial direction. The output waveform of PD
28
at this time must be sinusoidal waves, and for this reason each of the beam spot diameters &phgr;M, &phgr;S
1
, and &phgr;S
2
is optimized according to the pitch P of the servo stitch
20
b
. This optimization depends on the diameter of th

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