Magnetic detector

Details Magnetic detector Magnetic detector

2003-04-25

2004-11-16

LeDynh, Bot (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207220

Reexamination Certificate

active

06819101

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic detector for applying a bias magnetic field to the magnetic resistance element in detecting a multipole-magnetized moving body with a magnetic resistance element (MR element).
2. Description of the Related Art
For example, there is the system wherein electrodes are respectively formed in ends of each of magnetic resistance segments constituting a magnetic resistance element to construct a bridge circuit, and a power source with constant voltage and current is connected between the two opposite electrodes of the bridge circuit to convert a change in resistance value of the magnetic resistance segment into a change in voltage, thereby detecting a change in magnetic field acting on the magnetic resistance element.
A conventional magnetic detector will now be described with reference to the associated ones of the accompanying drawings.
FIGS. 4A and 4B
are respectively a perspective view and a plan view each showing a construction of the conventional magnetic detector.
In
FIGS. 4A and 4B
, reference numeral
1
designates a disc-like magnetic moving body having projections in its periphery and having a shape for changing a magnetic field; reference numeral
2
designates a processing circuit portion in which a circuit is printed on the surface of a board; reference numerals
2
a
and
2
d
designate respectively magnetic resistance segments; reference numerals
2
b
and
2
c
designate respectively magnetic resistance segments; reference numeral
3
designates a magnet; and reference numeral
4
designates a rotational axis of the magnetic moving body
1
. The rotational axis
4
is rotated so that the magnetic moving body
1
is also rotated synchronously therewith. Incidentally, for example, the magnetic resistance segments
2
a
and
2
d
are illustrated by one black block because the individual segments are so compacted that one segment can not be illustrated independently.
FIG. 5
is a circuit diagram showing a construction of the processing circuit portion of the conventional magnetic detector employing a magnetic resistance element.
In
FIG. 5
, the magnetic resistance element is constituted by the magnetic resistance segments
2
a
to
2
d.
Also, in the figure, reference numeral
12
designates a differential amplification circuit, reference numeral
13
designates an A. C. coupling circuit, reference numeral
14
designates a comparison circuit, reference numeral
15
designates an output circuit, reference symbol
15
T designates a transistor, and reference symbol
15
Z designates an output terminal.
In
FIG. 5
, a constant voltage VCC is applied to the bridge circuit constituted by the magnetic resistance segments
2
a
to
2
d
or fixed resistors to convert the changes in resistance values of the magnetic resistance segments
2
a
to
2
d
due to the change in magnetic field into a voltage change. The signal which has been obtained by the conversion into the voltage change is amplified by the amplification circuit
12
to be inputted to the comparison circuit
14
through the A. C. coupling circuit
13
. The signal a level of which has been compared with a predetermined voltage by the comparison circuit
14
is converted into a final output signal having a level of “0” or “1” (=VCC) by the transistor
15
T in the output circuit
15
to be outputted from the output terminal
15
Z.
Next, the operation of the conventional magnetic detector will be described with reference to
FIGS. 6A
to
6
E.
FIGS. 6A
to
6
E are timing charts showing the operation of the conventional magnetic detector. In
FIGS. 6A
to
6
E,
FIG. 6A
shows the magnetic moving body
1
,
FIG. 6B
shows magnetic fields applied to the magnetic resistance segments
2
a,
2
b,
2
c
and
2
d,
respectively,
FIG. 6C
shows resistance values of the magnetic resistance segments
2
a
to
2
d,
FIG. 6D
shows an output signal of the differential amplification circuit
12
, and
FIG. 6E
shows a final output signal.
The magnetic moving body
1
shown in
FIGS. 4A and 4B
is rotated about the rotational axis
4
to change the magnetic fields applied to the magnetic resistance segments
2
a,
2
b,
2
c
and
2
d.
Thus, as shown in
FIGS. 6A and 6B
, the magnetic fields applied to the magnetic resistance segments
2
a
to
2
d
are changed according to the shape of the magnetic moving body
1
.
Furthermore, as shown in
FIGS. 6C and 6D
, the resistance values of the magnetic resistance segments
2
a
to
2
d
are changed due to the change in magnetic field, thereby obtaining the output signal of the differential amplification circuit
12
. Then, as shown in
FIG. 6E
, the waveform of the output signal of the differential amplification circuit
12
is shaped by the comparison circuit
14
, thereby being capable of obtaining the final output signal having the level “1” or “0” corresponding to the shape of the magnetic moving body
1
.
In recent years, there has been made the demand for high resolution for realizing high performance even in magnetic detectors. However, the restrictions on the irregularity pitch for minimum detection, and the shape and processing of the magnetic moving body
1
in magnetic detectors place limitation on realizing the high resolution with the increase of the number of irregularities of the magnetic moving body
1
.
Then, as an effective method for realizing the high resolution, there is a method of detecting a multipole-magnetized moving body as shown in
FIGS. 7A and 7B
.
FIGS. 7A and 7B
are respectively a perspective view and a plan view each showing a construction of another conventional magnetic detector.
In
FIGS. 7A and 7B
, reference numeral
10
designates a multipole-magnetized moving body; reference numeral
2
designates a processing circuit portion in which a circuit is printed on a board; reference numerals
2
a
and
2
d
designate respectively magnetic resistance segments; reference numerals
2
b
and
2
c
designate respectively magnetic resistance segments; reference numeral
3
designates a magnet; and reference numeral
4
designates a rotational axis of the moving body
10
. The rotational axis
4
is rotated so that the moving body
10
is also rotated synchronously therewith. Incidentally, for example, the magnetic resistance segments
2
a
and
2
d
are illustrated by one black block because the individual segments are so compacted that one segment can not be illustrated independently.
FIGS. 9A
to
9
E are timing charts showing the operation of another conventional magnetic detector shown in
FIGS. 7A and 7B
. In
FIGS. 9A
to
9
E,
FIG. 9A
shows the moving body
10
,
FIG. 9B
shows the magnetic fields applied to the magnetic resistance segments
2
a,
2
b,
2
c
and
2
d,
respectively,
FIG. 9C
shows the resistance values of the magnetic resistance segments
2
a
to
2
d,
FIG. 9D
shows an output signal of the differential amplification circuit
12
, and
FIG. 9E
shows a final output signal.
Now, the operating magnetic field range of the magnetic resistance element (constituted by the magnetic resistance segments
2
a
to
2
d
) becomes a problem.
FIG. 8
is a graphical representation showing the operating magnetic field (MR loop characteristics) of the magnetic resistance element. In
FIG. 8
, the axis of abscissa represents the applied magnetic field (A/m), and the axis of ordinate represents the resistance change rate (%).
As shown in
FIG. 8
, since the resistance value (resistance change rate) of the magnetic resistance element becomes maximum with no magnetic field (applied magnetic field being zero) is applied thereto (when the magnitude of the applied magnetic field is zero), and decreases by application of the magnetic field irrespective of the direction, it is necessary to set the operating magnetic field range without crossing no magnetic field (zero magnetic field).
In the case of the conventional magnetic detector firstly described, the magnetic fields applied to the magnetic resistance element (constituted by the magnetic resist

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