Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-09-30
2001-02-27
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C324S207120
Reexamination Certificate
active
06194893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic detector for detecting changes in a magnetic field caused by movement of a moving member of magnetic material, and more particularly to a magnetic detector with a function of detecting alternately projected and recessed portions of a moving member of magnetic material in a power-on condition (referred to as a power-on function hereinafter).
2. Description of the Related Art
There is a known technique for detecting changes in a magnetic field wherein electrodes are formed at both ends of a magnetic field sensitive surface of magnetic field sensing devices (magnetoresistive devices are used in the description here) to construct a bridge; a constant-voltage and constant-current power supply is connected between the two opposing electrodes of the bridge to convert changes in the resistance value of the magnetic field sensing device into voltage changes, and changes in the magnetic field acting on the magnetic field sensing devices are detected on the basis of the voltage changes.
FIG. 9
is a circuit diagram showing an arrangement of a processing circuit in such a sensor using ordinary magnetic field sensing devices.
In
FIG. 9
, a Wheatstone bridge circuit
1
is made up of magnetic field sensing devices or resistances RA, RB, RC and RD given including at least one or more magnetic field sensing devices. Input terminals of a differential amplification circuit
2
are connected to a middle junction
4
between RA, RB and a middle junction
5
between RC, RD. A middle junction between RA, RD is connected to a power source terminal vcc, and a middle junction between RB, RC is connected to a ground GND. A differential amplification output
8
from the differential amplification circuit
2
is supplied to a comparison circuit
3
in a next stage.
In the above circuit, resistance values of the magnetic field sensing devices are changed upon changes in the magnetic field applied to resistances RA, RB, and a voltage at the middle junction
4
between RA, RB is changed corresponding to such changes in the applied magnetic field. The voltage across the middle junctions
4
and
5
is amplified by the differential amplification circuit
2
, and a final output
9
having a level of “0” or “1” is obtained from the comparison circuit
3
.
FIG. 10
is a schematic view showing a construction of a conventional magnetic detector.
In
FIG. 10
, the conventional magnetic detector comprises a rotary member of magnetic material
10
having a shape capable of changing a magnetic field, a magnetic field sensing device
11
, magnetic field sensing elements
11
a
,
11
b
, a magnet
13
, and a rotary shaft
12
. When the rotary shaft
12
rotates, the rotary member of magnetic material
10
is also rotated in synchronous relation therewith.
The pitch center of the magnetic field sensing elements (resistances)
11
a
,
11
b
of the magnetic field sensing device
11
is arranged to be offset from the center of the magnet
13
by a predetermined amount.
In the above magnetic detector, upon rotation of the rotary member of magnetic material
10
, the magnetic field applied to the resistances
11
a
,
11
b
of the magnetic field sensing device
11
is changed, and as shown in by way of example
FIG. 11
, the differential amplification output
8
is changed corresponding to the shape of the rotary member of magnetic material
10
. As a result, a signal representing the final output
9
corresponding to the shape of the rotary member of magnetic material
10
can be obtained with the circuit shown in FIG.
9
.
However, the magnetic circuit arrangement used in the conventional detector has had the following problems.
When the bridge is made up of magnetic field sensing devices and fixed resistances, a difference between their temperature coefficients. Also, when the bridge is made up of magnetic field sensing devices with a plurality of elements, a difference in the temperature coefficients occurs due to a difference in the magnetic field applied to the elements. Since there is such a difference in temperature coefficients, as shown in
FIG. 12
, the differential amplification output
8
(ROOM) at room temperature and the differential amplification output
8
(HOT) at high temperature exhibit temperature characteristics depending on changes in the applied magnetic field. This gives rise to a large deviation in the edge detecting accuracy of the alternately projected and recessed portions of the rotary member of magnetic material.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic detector with a power-on function which can essentially eliminate the temperature characteristics of a magnetic field sensing device and improve the temperature characteristics of the edge detecting accuracy of alternately projected and recessed portions of a moving member of magnetic material.
A magnetic detector according to a first aspect of the present invention comprises a magnetic field generating means for generating a magnetic field, a moving member of magnetic material disposed with a predetermined gap remaining relative to the magnetic field generating means and having alternately projected and recessed portions to change the magnetic field generated by the magnetic field generating means, a magnetic field sensing device comprising a plurality of magnetic field sensing elements that detects changes in the magnetic field by movement of the moving member of magnetic material, and means for adjusting changes in the magnetic field caused by the alternately projected and recessed portions of the moving member of magnetic material.
In a magnetic detector according to a second aspect of the present invention, in addition to the features of the first aspect, the magnetic flux crosses the plurality of magnetic field sensing elements at a first predetermined angle when the recessed portion of the moving member of magnetic material is opposed to the magnetic field sensing device, the magnetic flux crosses the plurality of magnetic field sensing elements at a second predetermined angle when the projected portion of the moving member of magnetic material is opposed to the magnetic field sensing device, and the magnetic field generating means is adjusted so that the first and second predetermined angles are symmetrical with respect to the direction vertical to a plane in which the plurality of magnetic field sensing elements are arranged.
In a magnetic detector according to a third aspect of the present invention, in addition to the features of the first aspect, the magnetic flux crosses the plurality of magnetic field sensing elements at a first predetermined angle when the recessed portion of the moving member of magnetic material is opposed to the magnetic field sensing device, the magnetic flux crosses the plurality of magnetic field sensing elements at a second predetermined angle when the projected portion of the moving member of magnetic material is opposed to the magnetic field sensing device, and the magnetic field sensing device is adjusted so that the first and second predetermined angles are symmetrical with respect to the direction vertical to a plane in which the plurality of magnetic field sensing elements are arranged.
In a magnetic detector according to a fourth aspect of the present invention, in addition to the features of the first aspect, the magnetic flux crosses the plurality of magnetic field sensing elements at a first predetermined angle when the recessed portion of the moving member of magnetic material is opposed to the magnetic field sensing device, the magnetic flux crosses the plurality of magnetic field sensing elements at a second predetermined angle when the projected portion of the moving member of magnetic material is opposed to the magnetic field sensing device, and a magnetic guide is provided and adjusted so that the first and second predetermined angles are symmetrical with respect to the direction vertical to a plane in which the plurality of magnetic field sensing eleme
Hatazawa Yasuyoshi
Nada Takuji
Shinjo Izuru
Yokotani Masahiro
Mitsubishi Denki & Kabushiki Kaisha
Patidar Jay
Sughrue Mion Zinn Macpeak & Seas, PLLC
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