Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-09-05
2003-09-09
Dorvil, Richemond (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C369S013110, C369S013120, C356S453000
Reexamination Certificate
active
06618218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a displacement detecting apparatus capable of detecting a positional fluctuation of an object in a non-contact manner, where the positional displacement is minute displacement in the order of nanometers, and an information recording apparatus using such a displacement detecting apparatus.
2. Related Background Art
FIG. 1A
of the accompanying drawings shows a perspective view of an information recording reproducing apparatus according to the prior art. The apparatus is comprised of a hard disc drive
1
for writing a servo track signal from a signal generator (SG)
48
into a hard disc, and a rotary positioner system
2
for effecting highly accurate rotary positioning. The hard disc drive
1
comprises a disc-shaped hard disc
3
, a slider
4
having a magnetic head at its tip end, a magnetic head arm
5
, a voice coil motor
6
, a voice coil motor driver
7
, a spindle
8
, etc. Also, the rotary positioner system
2
comprises a push rod
9
, a push rod arm
10
, a positioning control motor
11
, a rotary encoder
12
for detecting the amount of rotation of the rotary shaft of the control motor
11
, a signal processor
13
for analyzing the detection output from the rotary encoder
12
and sending a positioning command signal to the servo track signal writing position of the magnetic head, a control motor driver
14
for driving the control motor
11
by the command signal of the signal processor
13
, etc.
With such a construction, the writing and reading of magnetic information are effected on any track on the surface of the hard disc
3
being rotated at a high speed, by the arcuately operating magnetic head arm
5
through the magnetic head. At this time, in order to effect highly accurate positioning, the cylindrical surface of the push rod
9
is pushed against the side of the magnetic head arm
5
, and the push rod arm
10
is rotated by the control motor
11
while feedback control is effected by the system of the rotary encoder
12
, the signal processor
13
and the control motor driver
14
, and positioning is effected while the magnetic head arm
5
is sequentially finely fed through the intermediary of the push rod
9
. At this time, in order to effect contact reliably, usually some electric current is supplied to the voice coil motor
6
and pushing is also effected against the push rod
9
from the magnetic head arm
5
side.
FIG. 1B
of the accompanying drawings shows a perspective view of another highly accurate positioning apparatus. This detecting apparatus is comprised of a laser source
15
, mirrors
16
,
17
, a beam splitter
18
, a retro-reflector
19
, like a corner cube provided on a magnetic head arm
5
, and a light receiving element
20
. Movement of the magnetic head is measured with high accuracy not by the magnetic head arm
5
being mechanically pushed, but by optical means.
In this apparatus, by the utilization of a Michelson-type interferometer comprising the laser source
15
, the mirrors
16
,
17
, the beam splitter
18
and the retro-reflector
19
, the interference light of two light beams passed from the retro-reflector
19
via the mirror
16
and the mirror
17
is detected by the light receiving element
20
, thereby to obtain positional information of the magnetic head arm
5
. On the basis of the obtained detection signal, a signal processor
13
issues a command, and an electric current to be supplied to a voice coil motor
6
is controlled by a voice coil motor driver
7
, thereby to directly move the magnetic head arm
5
and effect appropriate control.
FIG. 1C
of the accompanying drawings shows a perspective view of the optical system of an optical-type sensor unit
20
according to the prior art, and in the optical-type sensor unit
20
, there are successively arranged a multimode laser diode light source
21
, a collimator lens
22
, a non-polarizing beam splitter
23
, and a probe-shaped polarizing prism
24
having a polarizing beam splitter surface
24
a
and a reference reflecting mirror surface
24
b
on which reflecting evaporated film is formed. In the reflecting direction of the non-polarizing beam splitter
23
, there are arranged a quarter wavelength plate
25
, a beam diameter limiting opening plate
26
, a beam amplitude dividing diffraction grating
27
having staggered grating structure, polarizing plate analyzers
28
a
to
28
d
disposed with their polarization azimuths deviated by 45° from one another, and light receiving elements
29
a
to
29
d.
With such a construction, divergent light from the multimode laser diode light source
21
is made into a loosely condensed light beam L by the collimator lens
22
, and is transmitted through the non-polarizing beam splitter
23
and then passes through the probe-shaped polarizing prism
24
, and is divided into polarized components in the polarizing beam splitter surface
24
a
. An S-polarized light beam reflected by the polarizing surface
24
a
emerges from the end surface of the probe-shaped polarizing prism
24
and is condensed near the beam waist of the measuring surface
5
a
of the magnetic head arm
5
, and the reflected light thereof becomes a divergent spherical wave and passes along the original optical path and returns to the probe-shaped polarizing prism
24
. On the other hand, a P-polarized light beam transmitted through the polarizing surface
24
a
is condensed at a position deviating from the beam waist on the reference reflecting mirror surface
24
b
in the end portion, and the reflected light thereof passes along the original path and likewise returns to the probe-shaped polarizing prism
24
.
These two light beams are re-combined on the polarizing surface
24
a
of the probe-shaped polarizing prism
24
and become linearly polarized light beams orthogonal to each other, and do not directly interfere with each other and become bright and dark signals, but yet when these two light beams are reflected in the non-polarizing beam splitter
23
and transmitted through the quarter wavelength plate
25
, the linearly polarized light beams orthogonal to each other are converted into oppositely circularly polarized light beams, and these two light beams have their vibration surfaces vector-combined and are re-converted into a linearly polarized light beam rotated by the fluctuation of the phase difference therebetween.
This rotated linearly polarized light beam is amplitude-divided into four light beams by the phase diffraction grating
27
, and these four divisional light beams are transmitted through the polarizing plate analyzers
28
a
to
28
d
, whereby they are converted into interference light beams in which the timing of light and darkness shifts by 90° each in terms of phase, and are received by the respective light receiving elements
29
a
to
29
d
. On the basis of the light reception signals of these light receiving elements
29
a
to
29
d
, a minute fluctuation of the position of the measuring surface
5
a
of the magnetic head arm
5
is detected with high accuracy of 1 nm or less.
In the above-described rotary positioner system
2
of
FIG. 1A
, however, vibration due to rotation or the like of the hard disc
3
is transmitted to the magnetic head arm
5
, and is further transmitted to the control motor
11
through the cylindrical surface of the push rod
9
. Therefore, highly accurate positioning is hindered and the capability of writing information such as a high-density servo track signal is reduced. For this reason, as a method of detecting minute displacement, there is known an electrostatic capacity sensor or the like utilizing impedance, e.g. electrostatic capacity, between the measuring surface
5
a
of the magnetic head arm
5
and the push rod
9
of the measuring probe. However, in this case there is a problem in that, if the area of the measuring surface
5
a
is small, the measuring resolving power will be reduced and the output will drift.
Also, in the above-described optical positioning apparatus of
FIG. 1B
, it is necessary t
Horyu Sakae
Ishizuka Ko
Kadoshima Takayuki
Kadowaki Hidejiro
Kaneda Yasushi
Canon Kabushiki Kaisha
Dorvil Richemond
Fitzpatrick ,Cella, Harper & Scinto
Olson Jason
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