Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-12-02
2001-04-24
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240, C324S252000, C338S03200R
Reexamination Certificate
active
06222361
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magneto-resistive effect sensor having its magnetically sensitive area formed of a material exhibiting the magneto-resistive effect and to a position detection device employing this magneto-resistive effect sensor.
2. Description of the Related Art
There has so far been known a magnetic position detection device for detecting the rotational position of an rotating object or the position of an object performing a linear movement.
FIG. 1
shows an example of this type of the magnetic position detection device.
A position detection device
100
has an elongated magnetic scale
110
, and a magneto-resistive effect sensor (MR sensor)
120
, having its magnetically sensitive portion formed by a thin film. One of the magnetic scale
110
or the MR sensor
120
is mounted on a moving object, with the other being mounted on a reference unit.
On the magnetic scale
110
, alternate N and S poles are formed along its length as periodic position signals at a recording pitch &lgr;.
The MR sensor
120
is held on, for example, a holding mechanism, not shown, and is arranged facing a magnetized surface of the magnetic scale
110
carrying the position signals of the magnetic scale
110
. This MR sensor
120
is moved in translation along the position signals of the magnetic scale
110
as it is kept at a pre-set gap distance from the magnetized surface of the magnetic scale
110
. The MR sensor
120
, thus translated, detects the position signals to convert the detected position signals into electrical signals which are outputted to outside over a flexible cable
130
etc.
With the above-described position detection device
100
, the relative position between the magnetic scale
110
and the MR sensor
120
can be detected at an interval P equal to one-half the recording pitch &lgr; to enable detection of the moving position of an object.
Meanwhile, a permanent magnet can be mounted along with an MR sensor for scale signals and an MR sensor for a point-of-origin signals on a head holder in order to apply biasing magnetization across the MR sensor for scale signals and the MR sensor for a point-of-origin signals.
The MR sensor
120
will be explained in further detail.
The MR sensor
120
is comprised of a substrate
121
of a non-magnetic material, such as glass, and a strip-shaped magnetically sensitive portion
122
formed thereon by depositing a ferromagnetic material, such as Fe—Ni or Ni—Co, as shown in FIG.
2
. This magnetically sensitive portion
122
demonstrates a magneto-resistive effect in which, when the dc current flows therethrough longitudinally, its resistance becomes maximum and minimum for the minimum strength of the signal magnetic field impressed in a direction perpendicular to the current flowing through the magnetically sensitive portion
122
and which is parallel to the film surface and for the maximum strength of the signal magnetic field impressed in a direction perpendicular to the current flowing through the magnetically sensitive portion
122
and which is parallel to the film surface, respectively.
On this MR sensor
120
, there are formed first to fourth magnetically sensitive portions
122
a
to
122
d
in a direction parallel to its longitudinal direction as the magnetically sensitive portion
122
. The first and second magnetically sensitive portions
122
a
,
122
b
are arranged at an interval therebetween equal to a detection pitch P for the position signals of the magnetic scale
110
. Similarly, the third and fourth magnetically sensitive portions
122
c
,
122
d
are also arranged at an interval therebetween equal to the detection pitch P for the position signals of the magnetic scale
110
. The interval between the second and third magnetically sensitive portions
122
b
and
122
c
is set to P/2.
The magnetically sensitive portions
122
a
,
122
b
are electrically connected in series with each other by an electrode
123
a
, while the magnetically sensitive portions
122
c
,
122
d
are electrically connected in series with each other by an electrode
123
b
. The end of the magnetically sensitive portion
122
b
not connected to the electrode
123
a
is connected by an electrode
124
in series with the end of the magnetically sensitive portion
122
c
not connected to the electrode
123
b
. The end of the magnetically sensitive portion
122
a
not connected to the electrode
123
a
is grounded via electrode
125
a
, while the end of the magnetically sensitive portion
122
d
not connected to the electrode
123
b
is connected via an electrode
125
b
to a constant voltage source. By interconnecting the magnetically sensitive portions
122
a
to
122
d
in this manner, an equivalent circuit as shown in
FIG. 3
is constituted in the MR sensor
120
to permit a sensor output to be detected at the electrode
124
.
The operation of the MR sensor
120
is hereinafter explained.
The above-described MR sensor
120
is moved relative to the position signals on the magnetic scale
110
responsive to the object movement. If, for example, the magnetically sensitive portions
122
a
,
122
b
of the MR sensor
120
are moved to over the N and S poles of the position signals, as shown in
FIG. 4
, the magnetically sensitive portions
122
a
,
122
b
exhibit a maximum resistance value because the strength of the magnetic field of stray magnetic flux component in the plane of the magnetically sensitive surface is zero. At this time, the magnetically sensitive portions
122
c
,
122
d
exhibit the minimum resistance value because the maximum magnetic field of stray magnetic flux component in the plane of the magnetically sensitive surface is applied. The result is that a maximum potential is produced at the electrode
124
.
If conversely the magnetically sensitive portions
122
c
,
122
d
of the MR sensor
120
are moved over the N and S poles of the position signals, as shown in
FIG. 5
, the magnetically sensitive portions
122
c
,
122
d
exhibit a maximum resistance value because the strength of the magnetic field of stray magnetic flux component in the plane of the magnetically sensitive surface is zero. At this time, the magnetically sensitive portions
122
a
,
122
b
exhibit the minimum resistance value because the maximum magnetic field of the component in the plane of the magnetically sensitive surface is applied. The result is that minimum potential is produced at the electrode
124
.
It is thus possible with the MR sensor
120
to output at the electrode
124
a signal generated in conformity to a period equal to one-half the recording pitch &lgr; of the position signals, by movement of the MR sensor
120
on the magnetic scale
110
, to detect the position of movement of an object.
In the magnetic position detection device
100
, the MR sensor
120
and the magnetic scale
110
are adapted to perform relative movement with a pre-set spatial gap therebetween because in general the MR sensor
120
and the magnetic scale
110
cannot be brought in use into contact with each other. The gap length between the MR sensor
120
or the magnetic scale
110
affects the output sensitivity of the MR sensor
120
, in much the same way as the recording pitch &lgr; of the position signals of the magnetic scale
110
or the strength of the magnetic field applied from the position signal to the MR sensor
120
.
FIGS. 6C
shows output characteristics of the MR sensor
120
with respect to changes in the gap length x between the MR sensor
120
and the magnetic scale
110
. It is noted that these output characteristics are derived from resistance changes in the MR sensor
120
.
The output characteristics shown here are those for a case in which the MR sensor
120
is provided facing a surface of a flat-plate-shaped magnetic scale
110
having position signals recorded thereon, as shown in
FIG. 6A
, and in which the width L of the recording signals of the magnetic scale
110
is sufficiently longer than the length l along the longitudinal direction of the magnetically sensitive portion
122
Kusumi Masaaki
Shimano Tadahiko
Maioli Jay H.
Sony Precision Technology Inc.
Strecker Gerard R.
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