Angle sensor

Details Angle sensor Angle sensor

2002-04-19

2004-06-22

Le, N. (Department: 2862)

Electricity: measuring and testing

Magnetic

Displacement

C324S207200, C324S207210

Reexamination Certificate

active

06753681

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to an angle sensor. For more detail, the invention relates to an angle sensor using a magnetoelectric conversion element.
PRIOR ART
Up to now, a rotational angle displacement sensor which uses a Hall effect as a detecting element is known as an angle sensor for detecting a rotational angle (for example, Japanese Patent Application Laid-Open Publications No. 61-75213 and No. 62-291502). The rotational angle displacement sensor of this kind excels in that a rotational angle can be detected in non-contact condition.
FIGS. 21 and 22
show a plan view and a cross sectional view of a prior rotational angle displacement sensor for detecting a rotational angle displacement of a rotational axis. In
FIG. 22
, a rotational angle displacement sensor
51
includes a rotational axis portion
52
as a rotational member, a yoke
53
and a permanent magnet
54
. The rotational axis portion
52
is connected to a detected rotational axis (not shown) in a body and rotates around an axial center (Z axis) with the detected rotational axis.
The yoke
53
is a cylindrical member with a bottom portion which is formed on a top end of the rotational axis portion
52
. A central axial line of a cylindrical portion
53
a
is coincided with the axial center (Z axis) of the rotational axis portion
52
. The cylindrical portion
53
a
rotates around the central axial line (Z axis) in a body with the rotation of the rotational axis portion
52
.
The cylindrical permanent magnet
54
is fixed to an inner side surface of the cylindrical portion
53
a
. A central axial line of the permanent magnet
54
is coincided with the axial center (Z axis) of the rotational axis portion
52
. Accordingly, the permanent magnet
54
rotates around the central axial line (Z axis) in a body with the rotation of the rotational axis portion
52
.
The cylindrical permanent magnet
54
is magnetized in such a manner that the front side (lower side in
FIG. 21
) is a N pole and that the rear side (upper side in
FIG. 21
) is S pole. A magnetic field which forms a magnetic flux heading from the N pole to the S pole is generated in the cylindrical portion of the magnet
54
as shown by broken line arrow. A characteristic curve shown by X mark in
FIG. 4
is a diagram which shows the magnetic flux density distribution on a X axis line (right and left direction) in the cylindrical portion of the permanent magnet
54
under the condition shown in
FIG. 21. A
characteristic curve shown by X mark in
FIG. 5
is a diagram which shows the magnetic flux density distribution on a Y axis line (front and rear direction) in the cylindrical portion of the permanent magnet
54
under the condition shown in FIG.
21
.
In a space of the cylindrical portion of the permanent magnet
54
, a Hall element
55
as a magnetoelectric conversion element is disposed. A center of the Hall element
55
is coincided with the central axial line (Z axis) of the permanent magnet
54
and the Hall element
55
is arranged along the Y axis direction (front and rear direction) under the condition shown in FIG.
21
. The direction of magnetism which the Hall element
55
detects is in parallel with the X axis direction in FIG.
21
. When the permanent magnet
54
rotates around the central axial line (Z axis), the relative position between the permanent magnet
54
(N, S poles) and the Hall element
55
changes. The Hall element
55
detects this change of the relative position. The Hall element
55
outputs a detect signal corresponding to the variation of the relative position, namely the rotational angle.
PROBLEM THAT THE INVENTION IS TO SOLVE
Meanwhile, in the rotational angle displacement sensor
51
, the variation of the relative position between the Hall element
55
and the permanent magnet
54
, so called, an axis deviation generates structurally easily by the measuring error of the rotational axis portion
52
and so on, the mounting error of the Hall element
55
and so on or the temperature change or the wear. This axis deviation makes the detection by the Hall element
55
generate an error and the detecting accuracy deteriorates.
Namely, under the condition shown in
FIG. 21
, the variation of the magnetic flux density distribution in the cylindrical portion of the permanent magnet
54
increases as the distance relative to the magnetic poles of the permanent magnet
54
decreases on the basis of the central axis (Z axis). Especially, the variation of the magnetic flux density distribution in the Y axis direction shown in
FIG. 5
is larger than the variation of the magnetic flux density distribution in the X axis direction shown in FIG.
4
. For example, in
FIG. 5
, when the disposed position of the Hall element
55
is shifted from the center, the variation of the magnetic flux density becomes extremely large amount.
Accordingly, when the relative position between the Hall element
55
and the permanent magnet
54
is changed, the variation of the magnetic flux density becomes large and the large variation appears as a detection error. Therefore, it is desired to reduce the variation of the magnetic flux density in the X axis and the Y axis directions as much as possible. Namely, it is desired to equalize the magnetic flux density. Because, in case of that the magnetic flux density is equalized, even if the axis deviation generates, the variation of the magnetic flux density is small and the detection error can be reduced.
Further, in the cylindrical permanent magnet
54
, the variation of the magnetic flux density in the Z axis direction is also large. Accordingly, in case of that the relative position in the Z axis direction also changes, similar problems occur. Therefore, it is desirable that the magnetic flux density distribution is also equalized in the Z axis direction. Then, a permanent magnet which equalizes the magnetic flux density distribution is suggested (for example, Japanese Patent Application Laid-Open Publication No. 10-132506).
FIGS. 18 and 19
shows a cross-sectional view of permanent magnets
56
,
57
which equalize the magnetic flux density distribution in the Z axis direction. In the permanent magnet
56
, a circular groove
56
b
which constitutes a magnetic flux density distribution correction portion is formed on an inner circumferential surface
56
a
. Further, in the permanent magnet
57
, circular projecting portions
57
b
which constitute a magnetic flux density distribution correction portion are formed at both end portions of an inner circumferential surface
57
a
.
FIG. 20
shows characteristic curves of the magnetic flux density distribution on the Z axis. The characteristic curve shown by X mark is a characteristic curve of the permanent magnet
54
which none is given on the inner circumferential surface and the characteristic curve shown by &Circlesolid; mark is a characteristic curve of the permanent magnets
56
,
57
which the magnetic flux density distribution correction portion is formed on the inner circumferential surface. Namely, the variation of the magnetic flux density distribution on the Z axis of the permanent magnets
56
,
57
which the magnetic flux density distribution correction portion is formed is smaller than that of the permanent magnet
54
which the magnetic flux density distribution correction portion is not formed.
In case of the permanent magnets
56
,
57
which equalize the magnetic flux density distribution on the Z axis by the correction of the form, however, since the form of the magnets is specific, high technique is required for manufacturing the magnets and therefore the manufacturing cost is increased. Namely, in case of that the permanent magnets
56
,
57
are made of sintered magnet, a pressing die is required for pressing the magnet powder and it is difficult to die-cut. Further, it is very difficult to accurize the measure of the magnet after sintering. Further, in case of that the permanent magnets are made of plastic magnet, the forming die is also required and it is also difficult to die-cut. Therefore, it is necessa

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