Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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[67190/973217]
Device for Contactless Sensing of the Position of an Object
and Related Use
Field of the Invention
The present invention relates to a device for contactless sensing of the
position
of an object with respect to a predetermined starting position, as well as to
a use of the
device as a potentiometer.
Related Technoloev
An angular position sensing device and use thereof are disclosed in PCT
Patent Application WO 94/17426.
In layers of ferromagnetic transition metals such as Ni, Fe or Co and their
alloys, electric resistance may depend on the size and direction of a magnetic
field
permeating the material. The effect occurring with such layers is called
"anisotropic
magnetoresistance (AMR)" or "anisotropic magnetoresistive effect." It is based
physically on different scattering cross sections of electrons with different
spins and
spin polarities of the D band. The electrons are referred to as majority and
minority
1 ~ electrons. For corresponding magnetoresistive sensors, a thin layer of
such a
magnetoresistive material with a magnetization in the plane of the layer is
usually
provided. The change in resistance with rotation of the magnetization with
regard to
the direction of a current passed over the sensor may then amount to a few
percent of
the normal isotropic (= ohmic) resistance.
Furthermore, it has long been known that mufti-layer magnetoresistive
systems containing several ferromagnetic layers can be arranged in a stack
with the
layers separated by metallic interlayers and with their respective
magnetizations lying
in the plane of the layer. The thicknesses of the individual layers are
selected to be
much smaller than the mean free path length of the conduction electrons. In
addition
to the above-mentioned anisotropic magnetoresistive effect (AMR), a giant-
magnetoresistive effect or giant magnetoresistancc (GMR) can occur in such
multi-
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layer systems (see, for example. European Patent EP-A 483 373). Such a GMR
effect
is based on the difference in scattering of minority and majority conduction
electrons
at the interfaces between the ferromagnetic layers and the adjacent layers, as
well as
on scattering effects within these layers. in particular when using alloys.
The GMR
effect is an isotropic effect. It may be much greater than the anisotropic
effect, AMR.
In such mufti-layer systems having a GMR effect, adjacent metallic layers are
at first
inversely magnetized, with a bias layer or a bias layer part that is
magnetically harder
than the measurement layer. Under the influence of an external magnetic field,
i.e., a
component of this field impressed in the plane of the layer, the initial
antiparallel
orientation of magnetizations can then be converted to a parallel orientation.
This fact
is utilized with corresponding magnetic field sensors.
A sensor of this type is disclosed in the aforementioned PCT Patent
Application WO 94/17426. It is part of a device for contactless sensing of the
angular
position of an object. For this purpose, the object is rigidly connected to a
permanent
magnet which is arranged in a plane parallel to the plane of the measurement
layer so
that it can rotate over the measurement layer in such a way that its axis of
rotation
coincides with the central normal to the surface of the measurement layer. In
the
measurement layer, the magnet generates a magnetic field component which can
thus
rotate with respect to a preferential magnetic axis of a bias part of the
sensor and
therefore leads to a similar rotation of the magnetization in the magnetically
softer
measurement layer. The electric resistance of the sensor thus depends on the
angle
between the magnetization of the measurement layer and the preferential
magnetic
direction of the bias part. This dependence is generally anisotropic owing to
the
predetermined shape (geometry) of the layer structure of the sensor. However,
a
corresponding device for sensing angular position. which may form a
contactless
potentiometer in particular, is limited to a common axis of symmetry of the
magnet
and the sensor about which either the magnet or the sensor itself is arranged
to rotate.
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~ummarv of the Invention
An object of the present invention is to provide a device in which the above
described restriction is eliminated.
The present device comprises a magnetic field generating device and a sensor
device having at least one current-carrying sensor with an enhanced
magnetoresistive
effect and a layer system with at least one magnetically soft measurement
layer with a
magnetization that can be rotated in the plane of the layer and at least one
magnetically harder bias part with a magnetization that is at least mostly
unchanged.
The object to be sensed is rigidly connected to this sensor device or to the
magnetic
field generating device.
In particular, the present invention provides a device (2, 20, 25, 30, 35, 40)
for
contactless sensing of the position of an object with respect to a
predetermined
starting position
- having a magnetic field generating device (3, 31, 41) which forms a magnetic
pole (42a) on an imaginary reference line (L,, L,) or several magnetic poles
(4~, 4,~ arranged in a row along the line and generating alternating magnetic
field directions,
having a sensor device (5, 21, 28, 35) containing at least one current-
carrying
sensor (6, 22, 23, 26, 27, 36-38) with an enhanced magnetoresistive effect,
having a layer system (8) with at least one magnetically soft measurement
layer (9) with a magnetization (Mm) that can rotate in the plane of its layer
and
at least one magnetically harder bias part ( I 1 ) with a magnetization (Mb,
Mbi,
Mb,, Mb;) that is at least mostly unchanged, and
2~ - having a rigid connection of the object to the sensor device or the
magnetic
field generating device,
the magnetic field generating device:
a) being arranged with respect to the sensor device so that the at least one
sensor is laterally offset with respect to the ima~:inary reference line of
the at least one
magnetic pole. and a central normal (Z~) to the pole face (F~, F~, 42a) of the
at least
-,
J
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one magnetic pole lies at least approximately in the plane (E,) of the
measurement
layer (9) of the at least one sensor or in a plane parallel to it, and
b) being movable relative to the sensor device so that the magnetic field (h,
h')
of the at least one magnetic pole is sensed by the measurement layer of the at
least one
sensor, and multiple runs through all or part of the sensor characteristic
curve are
effected, corresponding to the number (n) of magnetic poles detected, whereby
essentially only a directional dependence of the magnetoresistive effect of
the at least
one sensor is utilized.
The central normal to the pole face of the at least one magnetic pole should
lie
at least approximately in the plane of the measurement layer of the layer
system of the
at least one sensor or in a plane parallel to it. In other words, with the
device
according to the present invention, minor deviations in the claimed
orientation of the
central normal by even a few degrees should be included.
The advantages associated with this embodiment of the position sensing
device of the present invention can be seen in particular in that, first,
contactless
sensing of angular positions of objects in the entire angle range of
3fi0° or of linear
positions can be achieved and, second, demands regarding the required accuracy
of
the assembly positions of the magnetic field generating device and the sensor
device
are reduced. By using at least one sensor for the sensor device having a layer
system
with an enhanced magnetoresistive effect, essentially only the dependence of
the
sensor measurement signal on the direction of the external magnetic field is
utilized
here but the dependence on its field strength is not used, with the at least
one magnetic
pole being moved past by the side of the sensor device at the reference line.
With the device according to the present invention, both a linear and a
rotational position of any object can be detected without contact. The device
has two
main units. namely a device for generating a magnetic field component and a
device
for sensing this magnetic field component to generate an output signal which
depends
essentially only on the direction of the magnetic field. One of these two
devices is
rigidly connected to the object. so that its position is to be detected with
respect to a
predetermined starting position or relative to the position of the other
device. The
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magnetic field generating device has one or more magnetic poles that are to be
passed
one or more times by the sensor or detection device and face the latter,
preferably with
a lateral distance being maintained between the sensor device and the at least
one
magnetic pole. If only one magnetic pole is provided, it can be regarded as
lying on
an imaginary reference line. When several magnetic poles are used, they should
be
arranged in a row along a similar imaginary reference line, with the magnetic
fields
generated by the magnetic poles having variable, preferably alternating or
periodic
magnetic field directions with respect to the sensor device along this line.
This
reference line may be a straight line or a curved line. In the case of a
straight line, it is
possible to detect a linear position of an object in particular. With a curved
line, a
circumferential line of a circle such as that formed by a magnet wheel, for
example,
may be formed. Thus, preferably angular positions between 0° and
360° can be
detected. This device, which can be regarded as a sensor device and is
sensitive to the
orientation of the magnetic field, comprises at least one current-carrying
sensor. A
plurality of similar sensors may be electrically connected to form the sensor
device
and may form a Wheatstone bridge, for example. Each sensor has a multi-layer
system with an enhanced magnetoresistive effect, in particular a GMR effect.
The
layer system contains at least one magnetically softer measurement layer with
a
magnetization that is rotatable in the plane of the layer. Parallel to it
there is arranged
a bias part with a bias layer or a bias layer system, where the bias part is
magnetically
harder and has an at least largely unchanged magnetization under the influence
of the
magnetic field of the at least one magnetic pole. Similar mufti-layer systems
with a
GMR effect are known, for example, from European Patent A 483 373, German
Patents DE-A 42 32 244, DE-A 42 43 357 or DE-A 42 43 358.
Due to the high sensitivity of GMR sensors, no differential arrangement such
as that required, for example, with Hall sensors (see, for example, Magnetic
.Sensors,
the data book by Siemens A(i, 1989, page ~7) is necessary with the position
sensing
device according to the present invention; this permits smaller spacings
between
adjacent magnetic poles, and thus a correspondingly greater resolution and/or
a
corresponding miniaturization can be achieved.
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With a position sensing device having these features, its magnetic field
generating device should be arranged in a predetermined manner with regard to
the
sensor device according to the present invention.
For this purpose, the plane of the measurement layer of the mufti-layer system
of the at least one sensor and the pole face of the at least one magnetic pole
of the
magnetic field generating device are considered as being on the imaginary
reference
line. The at least one magnetic pole should not be above the area of the
surface of the
measurement layer in the column-like volume which is perpendicular to the
surface,
as in the related art according to the above-mentioned PCT Patent Application
WO
94/17426; instead, the at least one magnetic pole and thus the imaginary
reference line
should be outside this area or just adjacent to this area. Such an arrangement
of the
sensor is regarded as a ''laterally offset'' arrangement. In particular, a
distance which
is to be regarded as a lateral distance is maintained between the measurement
layer or
the sensor and the magnetic pole. At the same time, the magnetic field
generating
device should be oriented in such a way that a central normal to the center of
the pole
face runs either at least approximately in the plane of the measurement layer
or in a
plane parallel to it (allowing minor deviations in this alignment of the
normal). Such
an arrangement is based on the fact that with the mufti-layer system having an
enhanced magnetoresistive effect, used for the at least one sensor, a
dependence on
field strength plays practically no role within a conventional measurement
range or
measurement window, but instead only the dependence on the magnetic field
orientation with respect to the initial magnetization in the measurement layer
is
utilized.
Furthermore. the magnetic field generating device and the sensor device
should be movable relative to one another so that the magnetic field of the at
least one
magnetic pole of the magnetic field generating device is detected by the
measurement
layer of the mufti-layer system of the at least one sensor, and passage of the
at least
one magnetic pole through the detection range of the sensor device causes
multiple
runs through all or part of the sensor characteristic curve, corresponding to
the number
of magnetic poles present or detected. Resistance values which can be assumed
by the
6
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sensor device in passage of the at least one magnetic pole past its at least
one
measurement layer and which can be represented in a diagram are regarded as
the
sensor characteristic curve.
It is of course also possible for the magnetic poles of the magnetic field
generating device to be passed repeatedly through the detection range of the
sensor
device (or vice versa). Then the sensor characteristic curve or a portion
thereof is run
through in accordance with the total number of magnetic poles detected in
succession
by the sensor device.
A position sensing device according to the present invention makes it possible
in an especially advantageous manner to create a contactless potentiometer.
Further advantageous embodiments of the position sensing device according to
the present invention include:
a) that the at least one sensor (6, 22, 23, 26, 27, 36-38) is arranged so that
it is
laterally offset by a predetermined distance (ao, a;, as) from the imaginary
reference
line (L,, L,) of the at least one magnetic pole (4~, 4k, 42a);
b) that the reference line (L,) is at least approximately a straight line;
c) that the reference line (L,) is at least approximately the circumferential
line
of a magnet wheel (3, 41 );
d) that the sensor device (21, 28, 35) comprises several electrically
interconnected sensors (22, 23; 26, 27; 36-38);
e) that two sensors (21, 22) are provided, with their bias parts of their
layer
systems having magnetization directions (Mb,, Mb~) forming approximately a
right
angle to one another:
f) that three sensors l36-38) are provided, with the bias parts of their layer
systems having magnetization directions (Mh;) forming an angle (x) of at least
approximately 120° to one another;
g) that the sensors (22. 23; 36-38) are in a common plane (E,); and
h) that the sensors (26, 27) are in parallel planes (E,, E~).
Moreover, the present invention also provides a use of the device by providing
a contactless potentiometer, at least a portion of which is comprised of the
present
7
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device for contactless sensing described above.
According to a broad aspect of the invention,
there is provided a device for contactless sensing of a
position of an abject with respect to a predetermined
starting position comprising: a magnetic field generating
device having at least one magnetic pole at an imaginary
reference line, the at least one magnetic pole having a
magnetic field and a pole face with a central normal; and a
sensor device including at least one current-carrying sensor
having an enhanced magnetoresistive effect, the at least one
sensor having a layer system including at least one
magnetically soft measurement layer having a measurement
layer magnetization capable of rotation in a plane of the
measurement layer and at least one magnetically harder bias
part having a substantially unchangeable bias part
magnetization; one of the sensor device and the magnetic
field generating device being in a fixed relation to the
object; the magnetic field generating device being arranged
with respect to the sensor device so that the at least one
sensor is laterally offset with respect to the imaginary
reference line of the at least one magnet pole so that the
at least one magnet pole is arranged outside of a columnar
volume perpendicular to a surface of the measurement layer
of the sensor and so that the central normal of the magnet
pole lies substantially in one of the plane of the
measurement layer and a plane parallel to the plane of the
measurement layer; and the magnetic field generating device
being movable relative to the sensor device so that the
magnetic field of the at least one magnetic pole may be
sensed by the measurement layer and so that at least a part
of a characteristic curve of the at least one sensor is
passed through at a number of times corresponding to the
number n of the at least one magnetic pole detected, whereby
8
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only a directional dependence of the enhanced
magnetoresistive effect of the at least one sensor is
substantially utilized.
According to another broad aspect of the
invention, there is provided a contactless potentiometer
comprising: a magnetic field generating device having at
least one magnetic pole at an imaginary reference line, the
at least one magnetic pole having a magnetic field and a
pole face with a central normal; and a sensor device
including at least one current-carrying sensor having an
enhanced magnetoresistive effect, the at least one sensor
having a layer system including at least one magnetically
soft measurement layer having a measurement layer
magnetization capable of rotation in a plane of the
measurement layer and at least one magnetically harder bias
part having a substantially unchangeable bias part
magnetization; one of the sensor device and the magnetic
field generating device being in a fixed relation to an
object; the magnetic field generating device being arranged
with respect to the sensor device so that the at least one
sensor is laterally offset with respect to the imaginary
reference line of the at least one magnet pole so that the
at least one magnet pole is arranged outside of a columnar
volume perpendicular to a surface of the measurement layer
of the sensor and so that the central normal of the pole
face lies substantially in one of the plane of the
measurement layer and a plane parallel to the plane of the
measurement layer; and the magnetic field generating device
being movable relative to the sensor device so that the
magnetic field of the at least one magnetic pole may be
sensed by the measurement layer and so that at least a part
of a characteristic curve of the at least one sensor is
passed through at a number of times corresponding to the
8a
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number n of the at least one magnetic pole detected, whereby
only a directional dependence of the enhanced
magnetoresistive effect of the at least one sensor is
substantially utilized.
Brief Description of the Drawings
To further illustrate the present invention,
reference is made to the drawing below, in which in the farm
of diagrams:
Figures 1 and 2 show top and side views of a first
embodiment of a rotational position sensing device with one
magnet wheel;
Figure 3 shows a sectional view of a sensor of
this rotational position sensing device;
Figures 4 and 5 show side views of a second and
third embodiment of a similar device;
Figure 6 shows a side view of one embodiment of a
linear position sensing device with a linear pole
arrangement;
Figure 7 shows a top view of a fourth embodiment
of a rotational position sensing device with a magnet wheel;
and
Figure 8 shows a top view of a fifth embodiment of
a rotational position sensing device according to this
invention with another magnet wheel.
In the figures, corresponding parts are labeled with
the same notation. Parts not shown in detail are of common
knowledge, so they are not described below.
8b
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Detailed Description
According to the embodiment of a device 2
indicated in Figures 1 and 2 for sensing a rotational
position, its magnetic field generating device is designed
as a magnet wheel 3. The magnet wheel is mounted so that it
can rotate about a reference axis G1 and is mounted on the
shaft of an electric motor, for example. It has magnetic
poles 4~ with alternating polarities arranged in a row in the
circumferential direction on a reference line L1 running
along its outer circumference. Of n magnetic poles
(where 1 <_ j _< n), only four are shown in the figure, two
with an N polarity (= north pole) and two with an S polarity
(= south pole). The magnetic field between adjacent poles
of different polarities is indicated by a field line h.
8c
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Magnet wheel 3 is arranged at a distance afl of its reference line L, from the
side of a sensor 6 of a sensor device 5. The sensor, which is not drawn to
scale here in
comparison with the magnet wheel in the figures, has current I flowing through
it and
has a known GMR mufti-layer system. Figure 3 shows one possible embodiment of
a
suitable mufti-layer system. The mufti-layer system in Figure 3 is based on an
embodiment known from PCT Patent Application WO 94/15223, for example.
Mufti-layer system 8 comprises a
magnetically soft measurement layer 9 with a magnetization Mm which can be
rotated
in the plane of the layer. This measurement layer is magnetically decoupled
from a
fixed-magnetization layer part 11 via a decoupling layer 10. This layer part
11, which
is also known as the bias part, is magnetically harder by comparison.
According to
the embodiment illustrated here, it contains a bias layer 12 with a
magnetization Mb.
This layer 12 is antiferromagnetically coupled to another magnetic layer i4
with a
magnetization Ma f opposite to that of magnetization Mb. Therefore, it can be
regarded
as an artificial antiferromagnet. Such an embodiment of the mufti-layer system
has
the advantage in particular that the orientation of magnetization M~, of
measurement
layer 9 is practically unaffected by magnetizations Mb and Maf of bias part
11.
Since the concrete embodiment of the bias part with sensors having an
enhanced magnetoresistive effect, which can be used for the position sensing
devices
according to the present invention, is not critical, the bias part may be, for
example, a
natural antiferromagnet such as that used in spin valve systems. Of course, a
bias part
formed by a single magnetic layer is also suitable.
As also shown in Figure l and in particular in Figure 2, sensor 6 should be
arranged with regard to magnet wheel 3 in such a way that a reference axis G,
(= axis
2~ of rotation) of the magnet wheel is at least approximately parallel to a
normal to the
sensor plane E, (indicated by hatching). Then a central normal Z" lies on pole
face F~
of the at least one magnetic pole 4~ in plane E, of the sensor or the plane of
the surface
of measurement layer 9 or in a plane parallel to it. A reference a.~cis A, of
sensor b in
plane E, need not necessarily intersect the axis of rotation G,. In other
words, it is
possible to have an arrans~ement of sensor 6 with its axis shifted in parallel
to axis A,
9
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shown here. Reference axis A, in particular is perpendicular to magnetization
Mm of
measurement layer 9 without an external magnetic field and it passes through
the
center of the measurement layer surface.
When magnet wheel 3 is rotated about reference axis G,, magnetic poles 4~
with their pole faces F~ are facing sensor 6 directly one after the other.
With such a
rotation, the resistance characteristic cun~e of GMR sensor 6 is run through n
times.
Since the direction of magnetization Mm of magnetically soft measurement layer
9 in
GMR sensor 6 follows the acting magnetic field over a wide range of the field,
and
since the change in resistance of the multi-layer stack depends only on the
relative
angle of magnetizations M~" in the measurement layer with respect to
magnetization
Mb in the bias part, the signal delivered by the sensor representing the angle
position
of magnet wheel 3 is advantageously independent of the distance ao between the
magnet wheel and the sensor in a wide range.
Furthermore, as Figure 2 shows, normal Z~ need not necessarily lie in plane E,
of sensor 6, but instead it may also be shifted by a distance a, with respect
to this
plane.
With the rotational position sensing device 2 shown in Figures 1 and 2, a
partition or casing wall can be inserted into the space characterized by a
distance ao
between magnet wheel 3 and sensor 6. This wall must be made of a non-
ferromagnetic material. Such a design can be provided in particular when the
magnet
wheel or the sensor, for example, is to be built into a casing or arranged in
different
ambient media which are to be separated by a partition.
The embodiment of a device 20 shown in Figure 4 for sensing the rotational
position of a magnet wheel 3 (according to Figure 1 ) with n magnetic poles 4~
has a
sensor device 21 with a pair of magnetoresistive sensors 22 and 23. In the
figure, the
sensors have not been drawn to scale (they have been enlarged for reasons of
clarity)
in comparison with the magnet wheel. They are connected electrically, and
current I
flows through them. Their multi-layer systems are in a common plane E,.
Central
normal Z~ of each magnetic pole 4~ is oriented parallel to this plane. The
magnetic
field component emanating from pole face F~ at this point is also pointed in
the
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direction of this normal; this field component is represented by the character
~ in a
known way. As also shown in this figure, the mufti-layer systems of sensors 22
and
23 are oriented relative to one another so that the directions of
magnetization Mb, and
Mb, of their bias parts preferably form a right angle to one another. A
reference axis
A, common to the sensors, pointing in the direction of a normal to the plane
of the
sensors and running centrally between the sensors spaced a distance apart,
forms a 90°
angle with a plane of the axis of rotation G, of magnet wheel 3. In comparison
with
this axis of rotation, reference axis A, may be shifted laterally by a
distance a2.
Reference axis A, need not lie in the same plane as axis of rotation G,. When
magnet
wheel 3 rotates about its axis G,, the resistance characteristic curve of the
GMR
sensors is run through n times (per revolution of the magnet wheel), and the
two
sensors each supply a 90° phase-shifted periodic signal. This leads,
for example, to
better sampling of the fundamental resolution, which is determined by the
number of
poles of the magnet wheel, than could be achieved with two Hall sensors
arranged
side by side with a predetermined distance between them. The two GMR sensors
22
and 23 may be arranged advantageously in direct proximity side by side, e.g.,
on the
same chip. Furthermore, the embodiment shown here advantageously permits
detection of the direction of rotation.
In deviation from position sensing device 20 according to Figure 4, with the
embodiment of a rotational position sensing device 25 shown in Figure 5, GMR
sensors 26 and 27 of sensor device 28 are not arranged in a common plane but
instead
are in parallel planes E, and E~. The mufti-layer systems of the sensors may
be
produced either by hybrid techniques or by suitable coating and structuring of
a wafer
29 either on its opposite flat sides or on one side. The sensors have a common
reference axis A; in the direction of the normals to their faces. Reference
axis A3
which runs in the area of the centers of the sensors. for example, is again
parallel to
the axis of rotation G, of magnet wheel 3 or is in the extension of the axis
of rotation
G,. Reference axis A; may lie in a different plane tcom axis of rotation G,.
Owing to
the allowed tolerances in spacing, the sensors of device 25 deliver a signal
that is
phase-shitted by 90° but has at least approximately the same amplitude.
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According to Figures 1 through ~. it was assumed that a reference line L, of
the magnetic poles of a magnetic field generating device describes a
circumferential
line of a magnet wheel 3. Likewise, however, the reference line may also form
a
straight line. Such an embodiment is obtained more or less when a magnet wheel
with an infinitely large radius is selected. One embodiment of a linear
position
sensing device is shown in Figure 6. This device 30 contains as the magnetic
field
generating device a magnetic strip 31 extending along a straight reference
line L, with
n successive magnetic poles 4~ (where 1 <_ k <_ n) of alternating polarity.
Reference
line L, runs in a direction perpendicular to the normal or reference axis A~
to GMR
sensor 6 (e.g., according to Figure 1 ). The magnetic strip should be oriented
with
respect to axis A, so that axis A, runs in the plane of pole faces Fk of the
strip or in a
plane parallel to it. Then the central normal Z~ of each pole face Fk in turn
lies in a
plane parallel to plane E, of the mufti-layer system of sensor 6. A lateral
distance a3
may be maintained between the mufti-layer system of the sensor and magnetic
strip
31. In other words. in this embodiment of a position sensing device, sensor 6
may
also be at the side above pole faces F~. The resistance characteristic curve
of GMR
sensor 6 is run through n times as sensor 6 moves along a line parallel to and
a
distance a3 away from reference line L~ or as the magnetic strip moves along
reference
line L,. The direction of magnetization Mm of magnetically soft measurement
layer 9
of sensor 6 follows the acting magnetic field of magnetic strip 31 in a wide
range of
the field, and the change in resistance of the mufti-layer system depends only
on the
angle of magnetizations Mm in its measurement layer and Mb in its bias part or
bias
layer 12, so therefore the signal delivered by the sensor device indicating
the position
of magnetic strip 31 is advantageously independent of distance a3 between
magnetic
strip 31 and sensor 6 in a wide range.
The embodiments of position sensing devices according to the present
invention as illustrated in Figures 1 through 6 provide for the sensors to be
oriented so
that magnetizations Mm of the magnetically soft measurement layer of their
respective
mufti-layer systems. with said magnetizations not yet influenced by the
magnetic field
generating element (magnet wheel 3 or magnetic strip 31 ), are parallel to
reference
12
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line L, or L, and are optionally perpendicular to axis of rotation G,, where
magnetizations Mb of the respective bias parts are oriented parallel or
perpendicular to
Mm. However, a position sensing device according to the present invention is
not
limited to such orientations of magnetizations Mm and Mb. Thus it is also
possible to
arrange their sensors so that magnetizations Mb of their bias parts are at an
angle to the
respective reference line. Figure 7 shows an example.
With position sensing device 34 shown in Figure 7, instead of the arrangement
of a sensor device shown in Figures 4 and 5 with two sensors, such a device 35
with
more than two sensors, e.g., three sensors 36 to 38 arranged in one plane is
used.
These sensors, which are spaced an average distance a4 from magnet wheel 3,
are
preferably arranged at an angle x = 120° of their face axes in the
sensor plane or the
directions of magnetizations Mb; of their bias parts (where 1 <_ i <_ 3) to
one another.
Therefore, for 360° detection, only two linear ranges of 60°
each are needed of each
sensor instead of 90° each according to the embodiment in Figures 4 and
5. Again in
this embodiment, the extensive field strength independence of GMR sensors is
utilized, because the three sensors 36 through 38 are arranged at different
distances
from magnet wheel 3.
Figure 8 shows one embodiment of a rotational position sensing device 40
with a magnet wheel 41 as a magnetic field generating device having only a
single
magnetic double pole 42. The double pole formed by a bar magnet, for example,
is
arranged so that it extends radially with regard to axis of rotation G, of
magnet wheel
41. In other words. only one magnetic pole 42a of this rod magnet is facing
GMR
sensor 6 (e.g., according to Figure 1) of a sensor device while maintaining a
distance
as. The magnetic field generated by the bar magnet is indicated by field lines
h'.
Device 40 shown here can be used to generate trigger pulses or counting pulses
in
particular.
13
