Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-03-09
2002-12-17
Ramirez, Nestor (Department: 2834)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250, C310S06800R, C310S152000, C310S154010, C310S154060, C310S154240
Reexamination Certificate
active
06496002
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rotation detector, and more specifically, to a rotation detector including a rotor having magnetic sensing elements.
FIG. 10
illustrates how an absolute position detection type detector detects rotational position. The rotation detector includes a rotor
30
, which is fixed to a rotating shaft and integrally rotates with the shaft. N pole zones
32
and S pole zones
33
are alternately formed at sixty degree intervals on the rotor
30
in a circumferential direction. At positions facing the rotor
30
, first to third magnetic resistance elements
31
are arranged around the axis O of the rotor
30
at forty-degree intervals. Each of the first to third resistance elements
31
detects the N pole zone
32
and the S pole zone
33
, which alternately pass by the resistance elements
31
at sixty-degree intervals during the rotation of the rotor
30
.
When the N pole zone
32
is detected, the first to third resistance elements
31
respectively output H-level signals SG
1
, SG
2
, SG
3
. When the S pole zone
33
is detected, the resistance elements
31
respectively output L-level signals SG
1
, SG
2
, SG
3
. When each resistance element
31
detects a change from the N pole zone
32
to the S pole zone
33
, each of the signals SG
1
, SG
2
, SG
3
changes from the H level to the L level. Contrarily, when each resistance element
31
detects a change from the S pole zone
33
to the N pole zone
32
, each of the signals SG
1
, SG
2
, SG
3
changes from the L level to the H level.
As shown in
FIG. 10
, the signals SG
1
, SG
2
, SG
3
of the resistance elements
31
change gradually between the L and H levels. The reason for this is that the direction of magnetic flux changes gradually when the detected zone changes from the N pole zone
32
to the S pole zone
33
. Three comparators (not shown) respectively receive the signals SG
1
, SG
2
, SG
3
and adjust the waveforms of the signals SG
1
, SG
2
, SG
3
, thus generating detection signals S
1
, S
2
, S
3
that change sharply between the L and H levels.
More specifically, each comparator compares an output signal with a reference value, which is a middle level between the H level and the L level. When the output signal is greater than the reference value, the comparator generates an H level detection signal S
1
, S
2
, S
3
. When the output signal is lower than the reference value, the comparator generates an L level detection signal S
1
, S
2
, S
3
. The reference value is the level of the signals SG
1
, SG
2
, SG
3
output when the border between the N pole zone
32
and the S pole zone
33
passes by each of the first to third resistance elements
31
. When any one of the detection signals S
1
, S
2
, S
3
changes from the L level to the H level or from the H level to the L level, the rotational position of the rotor
30
(or rotation shaft) is determined based on the state of the other detection signals. In the case of
FIG. 10
, the rotational position (absolute position) is detected in the range of zero to hundred twenty degrees at intervals of twenty degrees.
However, it is difficult to precisely form the N pole zone
32
and the S pole zone
33
alternately at sixty-degree intervals on the rotor
30
in the circumferential direction. Accordingly, the rotational position is not detected at twenty-degree intervals with precision at the point when the detection signals S
1
, S
2
, S
3
change from the L level to the H level or from the H level to the L level.
The objective of the present invention is to provide a rotation detector that detects rotational position with high precision.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a rotation detector is provided. The rotation detector includes a rotor having a shaft, magnets and magnetism detection elements. Axial projections are located at predetermined intervals about the rotor. The magnets are located between the projections and the shaft. Each magnetism detection element detects magnetism of corresponding one of the magnets and includes a plurality of magnetic resistors. A movement of the projections changes the flux of the magnets. Each resistor is switched between a first state, in which its resistance is great, and a second state, in which its resistance is small. The resistors are divided into two groups. The groups are substantially symmetrical relative to a group centerline such that, when the direction of the flux changes, the resistors in one group are in the opposite state from that of the resistors in the other group. The centerline of changes in the direction of the flux caused by movements of the projections matches the group centerline.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
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Kogiso Katsuya
Nishibe Yasushi
Taniguchi Masahiro
Usui Shinji
Gonzalez Julio C.
Kabushiki Kaisha Tokai Rika Denki Seisakusho
Sawyer Law Group LLP
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