Azimuth meter

Details Azimuth meter Azimuth meter

2003-10-06

2004-12-07

Gutierrez, Diego (Department: 2859)

Geometrical instruments

Indicator of direction of force traversing natural media

Magnetic field responsive

C324S252000

Reexamination Certificate

active

06826842

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a flat azimuth meter or bearing sensor having a plane coil laminated with thin film magneto resistive elements (hereinafter referred to as “magneto resistive elements”) and to a small and light azimuth meter suitable for mobile devices.
BACKGROUND ART
When a current is applied to a magneto resistive element in a direction of an easy axis of magnetization, and at the same time, a magnetic field is applied in a direction perpendicular thereto, an electric resistance in the current direction has a magneto-resistance effect, that is, it is reduced depending on a magnetic field strength. A relationship between the electric resistance (hereinafter referred to as “resistance”) and the applied magnetic field strength can substantially be shown as in FIG.
20
.
Assuming Hk denotes a saturation magnetic field, when a biasing magnetic field on the order of ½·Hk is applied to a magneto resistive element, there is a substantially linear relationship between an external magnetic field H and the resistance R. An external magnetic field can be measured by using the linear relationship between the external magnetic field H and the resistance R when a certain biasing magnetic field is applied. Then, when each of two components orthogonal to each other of the earth magnetism is detected by two groups of magneto resistive elements that an appropriate bias is applied to, bearings can be measured at a measuring point.
There is used an azimuth meter or a bearing sensor comprising an MR bridge constituted by four magneto resistive elements
91
,
92
,
93
, and
94
that are orthogonal to each other as shown in
FIG. 21
, and two bias coils
101
and
102
that are wound around a holder mounted outside of the magneto resistive elements so that two orthogonal biasing magnetic fields can be applied both at an angle of 45 degrees with respect to the current directions of the magneto resistive elements.
FIG. 22
is a schematic cross-sectional view thereof, and
FIG. 23
is a perspective view thereof.
In measurement of bearings, a +x-direction bias is applied by one bias coil
101
(referred to as an x-direction coil) to the four magneto resistive elements
91
,
92
,
93
, and
94
constituting the MR bridge to measure an intermediate potential difference among the magneto resistive elements, and then, a −x-direction bias is applied by the same bias coil
101
to the magneto resistive elements to measure the intermediate potential difference among the magneto resistive elements. A difference between the intermediate potential differences measured when the +x-direction bias is applied and when the −x-direction bias is applied is proportional to sin &thgr;, the angle &thgr; being an angle between the horizontal component of the earth magnetism and the x-axis.
Next, a +y-direction bias is applied by the other bias coil
102
(referred to as a y-direction coil) to the four magneto resistive elements
91
,
92
,
93
, and
94
constituting the MR bridge to measure an intermediate potential difference among the magneto resistive elements, and then, a −y-direction bias is applied by the same bias coil
102
to the magneto resistive elements to measure the intermediate potential difference among the magneto resistive elements. A difference between the intermediate potential differences measured when the +y-direction bias is applied and when the −y-direction bias is applied is proportional to sin(&pgr;/2−&thgr;), that is, cos &thgr;.
From the y-directional output Vy and the x-directional output Vx, the bearings can be measured as the direction &thgr; of the horizontal component of the earth magnetism as follows:
&thgr;=tan
−1
(
Vx/Vy
).
However, the relationship between the magnetic field applied to the magneto resistive element and the resistance practically involves a hysteresis as shown in
FIG. 24
, rather than FIG.
20
. When the applied magnetic field strength H is increased, it reaches a level of saturation via the upper curve in
FIG. 24
, and when it is decreased from the level, it traces the lower curve.
Therefore, when measuring bearings, the saturation magnetic field is applied before the application of the biasing magnetic field in consideration of the hysteresis.
For example, as disclosed in Japanese Patent Laid-Open No. 5-157565, when measuring bearings using the azimuth meter composed of the magneto resistive elements and two orthogonal bias coils as described above, the saturation magnetic field Hk is applied in +x direction, and then the intermediate potential difference between the magneto resistive elements is measured while applying the +x-direction biasing magnetic field Hb. Then, the saturation magnetic field −Hk is applied in −x direction by the same bias coil, and then the intermediate potential difference between the magneto resistive elements is measured while applying the −x-direction biasing magnetic field −Hb. The difference between the intermediate potential differences at the time of applications of the +x-direction bias and the −x-direction bias thus obtained is defined as an x-direction output Vx.
Then, the saturation magnetic field is applied in the +y direction by the other bias coil, and then the intermediate potential difference between the magneto resistive elements is measured while applying the +y-direction biasing magnetic field. Then, the saturation magnetic field is applied in the −y direction by the same bias coil, and then the intermediate potential difference between the magneto resistive elements is measured while applying the −y-direction biasing magnetic field. The difference between the intermediate potential differences at the time of applications of the +y-direction bias and the −y-direction bias thus obtained is defined as an y-direction output Vy. Based on the Vx and Vy, bearings are measured in the manner as described above.
The orthogonal four magneto resistive elements assembled into the MR bridge described above may be formed as zigzag magneto resistive elements formed by etching a Ni-based alloy film deposited on a ceramic substrate. Thus, the magneto resistive elements can be quite small and thin. However, since the two bias coil wound around them in x direction and y direction are provided outside the magneto resistive element bridge, the azimuth meter has, at the smallest, a thickness of the order of 3 mm and an area of the order of 10 mm×10 mm.
In the procedure of measuring bearings explained in the above description, it is required to carry out measuring four times because the bias is applied in +x direction and −x direction by the x-direction coil, the bias is applied in +y direction and −y direction by the y-direction coil, and then calculation is carried out.
Furthermore, in order to eliminate the effect of the hysteresis, before the biasing magnetic field is applied, the saturation magnetic field of the same direction as that of the biasing magnetic field is applied. After the application of the saturation magnetic field, application of the biasing magnetic field of the same direction tends to make the gradient of the curve for the resistance of the magneto resistive element, and the magnetic field be decreased, so that the output to be measured becomes low.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an azimuth meter or a bearing sensor of a significantly reduced thickness and area.
Furthermore, another object of the present invention is to provide an azimuth meter or a bearing sensor in which the number of applications of a current to a coil and the number of measurements are less than before.
For example, an azimuth meter according to the invention comprises: a plane coil wound into a rectangular shape; and at least two groups of thin film magneto resistive elements disposed substantially parallel to the plane of the plane coil, in which each of said groups of magneto resistive elements

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