Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-07-12
2003-06-10
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207120, C324S207250, C324S174000
Reexamination Certificate
active
06577122
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic detection apparatus for detecting the strength of a magnetic field to find the position of a magnetic moving object.
2. Description of the Related Art
A typical example of such a magnetic detection apparatus has been known which is constructed as follows, for instance; magnetoelectric conversion elements in the form of magnetoresistance elements having electrodes formed at their respective ends are coupled with one another to provide a bridge circuit with a power supply of a constant voltage and a constant current connected with two opposed electrodes of the bridge circuit, so that a change in the resistance value of each magnetoresistance element is converted into a corresponding voltage change, which is then detected as a change in the magnetic field acting on each magnetoresistance element to thereby find the position of a magnetic moving object.
FIG. 16
is an electric circuit diagram of such a magnetic detection apparatus.
In this magnetic detection apparatus, a constant voltage is applied to a bridge circuit formed of a magnetoresistance element
1
and a fixed resistor
2
, so that a change in the resistance of the magnetoresistance element
1
caused by a change in a magnetic field applied thereto is converted into a corresponding voltage change which is then amplified by an amplification circuit
3
and input to a comparison circuit
4
. The signal input to the comparison circuit
4
is compared with a prescribed voltage so that it is converted into a final output signal of “0” or “1” by means of an output circuit
5
. This final signal is output from an output terminal
6
.
FIGS. 17A and 17B
illustrate the arrangement of a known magnetic detection apparatus.
FIG. 17A
is a perspective view thereof, and
FIG. 17B
is a partial plan view of FIG.
17
A.
This magnetic detection apparatus is arranged in opposition to one of detected portions in the form of teeth
12
a
and grooves
12
b
of a magnetic moving object in the form of a rotating member
11
.
The known magnetic detection apparatus includes a magnetoelectric conversion element in the form of a magnetoresistance element
15
having a magnetic resistance value which varies with a change in a magnetic field applied thereto, a magnet
14
with the direction of magnetization thereof oriented to the rotating member
11
, the amplification circuit
3
for amplifying a signal in the form of a voltage change converted from a change in the resistance value of the magnetoresistance element
15
, and a processing circuit
16
incorporating therein the comparison circuit
4
and the output circuit
5
.
With the magnetic detection apparatus as constructed above, the rotating member
11
is caused to rotate in synchronization with the rotation of a rotation shaft
10
, so that a magnetic field applied to the magnetoresistance element
15
from the magnet
14
is accordingly varied. As a result, the resistance value of the magnetoresistance element
15
changes between the time when a tooth
12
a
of the rotating member
11
comes to face the magnetoresistance element
15
and the time when a groove
12
b
of the rotating member
11
comes to face the magnetoresistance element
15
, as illustrated in FIG.
18
. Thus, the output of the amplification circuit
3
also changes accordingly. Then, the output of the amplification circuit
3
is waveform shaped by means of the processing circuit
16
, so that the output terminal
6
of the processing circuit
16
generates a final output signal of “1” or “0” corresponding to a tooth
12
a
or a groove
12
b
of the rotating member
11
.
FIGS. 19A through 19C
illustrate a change in a bias magnetic field applied to the magnetoresistance element
15
by the magnet
14
when the magnetoresistance element
15
is shifted or displaced from a predetermined position with respect to an opposed tooth
12
a
or an opposed groove
12
b
of the rotating member
11
in a radial direction thereof (i.e., in a rotating member facing direction, as indicated at arrow B, in which the magnetoresistance element
15
faces the rotating member
11
), and when the magnetoresistance element
15
is shifted or displaced from the predetermined position with respect to an opposed tooth
12
a
and an opposed groove
12
b
of the rotating member
11
in a circumferential direction thereof (i.e., in a direction as indicated at arrow A). From
FIG. 19C
, it can be seen that the bias magnetic field changes more greatly when the magnetoresistance element
15
is displaced in the direction of arrow B, i.e., in a radial direction of the rotating member
11
, than when the magnetoresistance element
15
is displaced in the direction of arrow A, i.e., in a circumferential direction of the rotating member
11
.
FIG. 20
illustrates the respective operation waveforms of the resistance value of the magnetoresistance element
15
, the output of the amplification circuit
3
and the final output of the output terminal
6
when the magnetoresistance element
15
is displaced in the direction of arrow B with respect to the detected portions in the form of the teeth
12
a
and the grooves
12
b
of the rotating member
11
. In this figure, solid lines represent the operation waveforms when the magnetoresistance element
15
is in a normal position; dotted lines represent the operation waveforms when the magnetoresistance element
15
is out of the normal position; and alternate long and two short dashes lines represent comparison voltages.
As can be seen from this figure, the timing of position detection of a tooth
12
a
or a groove
12
b
of the rotating member
11
shifts by a period of time T
1
when the magnetoresistance element
15
is displaced from its normal position. As a result, there arises a problem that the position of a tooth
12
a
or a groove
12
b
is not able to be detected accurately by a positional shift or displacement of the magnetoresistance element
15
.
SUMMARY OF THE INVENTION
The present invention is intended to obviate the problem as referred to above, and has for its object to provide a magnetic detection apparatus which is capable of ensuring good-performance in detecting the position of a detected portion even if there is a shift or displacement in the position of a magnetoelectric conversion element.
Bearing the above object in mind, according to the present invention, there is provided a magnetic detection apparatus comprising: at least one magnetoelectric conversion element disposed to face a detected portion of a magnetic moving object; a magnet with a direction of magnetization thereof oriented in a direction perpendicular to a radial direction of the magnetic moving object in which the magnet faces the magnetic moving object; and a magnetic guide having at least two pole projections formed in a spaced apart relation with respect to each other in a radial direction of the magnetic moving object in which the magnetic guide faces the detected portion of the magnetic moving object. The at least one magnetoelectric conversion element is disposed between the pole projections when viewed from a direction perpendicular to the radial direction of the magnetic moving object in which the magnetic guide faces the detected portion of the magnetic moving object.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the invention taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4612502 (1986-09-01), Spies
patent: 4935698 (1990-06-01), Kawaji et al.
patent: 6064198 (2000-05-01), Wolf et al.
patent: 6111403 (2000-08-01), Yokotani et al.
patent: 2745880 (1978-04-01), None
patent: 4025837 (1992-02-01), None
patent: 19850677 (1999-11-01), None
Fukami Tatsuya
Nada Takuji
Shinjo Izuru
Yokotani Masahiro
Mitsubishi Denki & Kabushiki Kaisha
Strecker Gerard R.
Sughrue & Mion, PLLC
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