CA2232916C - Device for contactless sensing of the position of an object and related use - Google Patents
Device for contactless sensing of the position of an object and related use Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
- G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
- G01D5/142—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices
- G01D5/145—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices influenced by the relative movement between the Hall device and magnetic fields
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/30—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring angles or tapers; for testing the alignment of axes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/06—Measuring direction or magnitude of magnetic fields or magnetic flux using galvano-magnetic devices
- G01R33/09—Magnetoresistive devices
- G01R33/093—Magnetoresistive devices using multilayer structures, e.g. giant magnetoresistance sensors
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- Transmission And Conversion Of Sensor Element Output (AREA)
- Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
Abstract
A position sensing device (2) contains a magnetic field generating device (3) having at least one magnetic pole (4j) and a sensor device (5) with at least one sensor (6) with an enhanced magnetoresistive effect. The magnetic field generating device (3) should be arranged with respect to the sensor device (5) in such a way that the sensor (6) is laterally offset with respect to the magnetic pole (4j), and a central normal (Z n) to the pole face (F l) of the magnetic pole is at least approximately in the plane (E l) of a measurement layer (9) of the sensor (6) or in a plane parallel to it. In addition, the magnetic field generating device (3) should be movable so that the magnetic field (h) of the magnetic pole (4j) is detected by the measurement layer (9) of the sensor (6), and a run through all or part of the sensor characteristic curve is induced, with essentially only dependence on the direction of the magnetoresistive effect of the sensor being utilized.
Description
[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-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.
~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
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 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.
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 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 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 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 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 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 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, 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 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 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.
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 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.
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-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.
~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
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 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.
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 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 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 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 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 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 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, 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 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 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.
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 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.
Claims (38)
1. A device for contactless sensing of a position of an object 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 14a 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 only a directional dependence of the enhanced magnetoresistive effect of the at least one sensor is substantially utilized.
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 14a 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 only a directional dependence of the enhanced magnetoresistive effect of the at least one sensor is substantially utilized.
2. The device as recited in claim 1 wherein the at least one sensor is laterally offset by a predetermined distance from the imaginary reference line of the at least one magnetic pole.
3. The device as recited in claim 1 wherein the imaginary reference line approximates a straight line.
4. The device as recited in claim 2 wherein the imaginary reference line approximates a straight line.
5. The device as recited in claim 1 wherein the imaginary reference line approximates a circumferential line of a magnetic pole wheel.
6. The device as recited in claim 2 wherein the imaginary reference line approximates a circumferential line of a magnetic pole wheel.
7. The device as recited in claim 1 wherein the at least one sensor device includes a plurality of electrically inter-connected sensors.
8. The device as recited in claim 2 wherein the at least one sensor device includes a plurality of electrically inter-connected sensors.
9. The device as recited in claim 3 wherein the at least one sensor device includes a plurality of electrically inter-connected sensors.
10. The device as recited in claim 5 wherein the at least one sensor device includes a plurality of electrically inter-connected sensors.
11. The device as recited in claim 7 wherein the plurality of electrically interconnected sensors is a first sensor having a first layer system having a first bias part with a first magnetization direction and a second sensor having a second layer system having a second bias part with a second magnetiza-tion direction, the first magnetization direction forming approximately a right angle to the second magnetization direction.
12. The device as recited in claim 7 wherein the plurality of electrically interconnected sensors are three sensors having layer system bias parts having bias part magnetization directions forming an angle of approximately 120° to one another.
13. The device as recited in claim 7 wherein the plurality of electrically interconnected sensors are in a common plane.
14. The device as recited in claim 11 wherein the plurality of electrically interconnected sensors are in a common plane.
15. The device as recited in claim 12 wherein the plurality of electrically interconnected sensors are in a common plane.
16. The device as recited in claim 7 wherein the plurality of electrically interconnected sensors are in parallel planes.
17. The device as recited in claim 11 wherein the plurality of electrically interconnected sensors are in parallel planes.
18. The device as recited in claim 12 wherein the plurality of electrically interconnected sensors are in parallel planes.
19. The device as recited in claim 1 wherein the at least one magnetic pole includes a plurality of magnetic poles arranged in a row along the imaginary reference line for generating alternating magnetic field directions.
20. 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 measure-ment 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 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.
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 measure-ment 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 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.
21. The contactless potentiometer as recited in claim 20 wherein the at least one sensor is laterally offset by a predetermined distance from the imaginary reference line of the at least one magnetic pole.
22. The contactless potentiometer as recited in claim 20 wherein the imaginary reference line approximates a straight line.
23. The contactless potentiometer as recited in claim 21 wherein the imaginary reference line approximates a straight line.
24. The contactless potentiometer as recited in claim 20 wherein the imaginary reference line approximates a circumfer-ential line of a magnetic pole wheel.
25. The contactless potentiometer as recited in claim 21 wherein the imaginary reference line approximates a circumfer-ential line of a magnetic pole wheel.
26. The contactless potentiometer as recited in claim 20 wherein the at least one sensor device includes a plurality of electrically interconnected sensors.
27. The contactless potentiometer as recited in claim 21 wherein the at least one sensor device includes a plurality of electrically interconnected sensors.
28. The contactless potentiometer as recited in claim 22 wherein the at least one sensor device includes a plurality of electrically interconnected sensors.
29. The contactless potentiometer as recited in claim 24 wherein the at least one sensor device includes a plurality of electrically interconnected sensors.
30. The contactless potentiometer as recited in claim 26 wherein the plurality of electrically interconnected sensors is a first sensor having a first layer system having a first bias part with a first magnetization direction and a second sensor having a second layer system having a second bias part with a second magnetization direction, the first magnetization direction forming approximately a right angle to the second magnetization direction.
31. The contactless potentiometer as recited in claim 26 wherein the plurality of electrically interconnected sensors are three sensors having layer system bias parts having bias part magnetization directions forming an angle of approximately 120° to one another.
32. The contactless potentiometer as recited in claim 26 wherein the plurality of electrically interconnected sensors are in a common plane.
33. The contactless potentiometer as recited in claim 30 wherein the plurality of electrically interconnected sensors are in a common plane.
34. The contactless potentiometer as recited in claim 31 wherein the plurality of electrically interconnected sensors are in a common plane.
35. The contactless potentiometer as recited in claim 26 wherein the plurality of electrically interconnected sensors are in parallel planes.
36. The contactless potentiometer as recited in claim 30 wherein the plurality of electrically interconnected sensors are in parallel planes.
37. The contactless potentiometer as recited in claim 31 wherein the plurality of electrically interconnected sensors are in parallel planes.
38. The contactless potentiometer as recited in claim 20 wherein the at least one magnetic pole includes a plurality of magnetic poles arranged in a row along the imaginary reference line for generating alternating magnetic field directions.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19712833.5 | 1997-03-26 | ||
| DE1997112833 DE19712833C2 (en) | 1997-03-26 | 1997-03-26 | Device for contactless position detection of an object and use of the device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2232916A1 CA2232916A1 (en) | 1998-09-26 |
| CA2232916C true CA2232916C (en) | 2006-05-02 |
Family
ID=7824757
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2232916 Expired - Fee Related CA2232916C (en) | 1997-03-26 | 1998-03-24 | Device for contactless sensing of the position of an object and related use |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0867692B1 (en) |
| KR (1) | KR100532795B1 (en) |
| CA (1) | CA2232916C (en) |
| DE (2) | DE19712833C2 (en) |
| TW (1) | TW366413B (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6534971B1 (en) | 1999-04-21 | 2003-03-18 | Robert Bosch Gmbh | Measurement device for the non-contact detection of an angle of rotation |
| DE19937206C2 (en) * | 1999-06-11 | 2003-05-08 | Siemens Ag | Position determination device and use of a position determination device and method for producing a scale for such a device |
| DE10044839B4 (en) * | 1999-09-27 | 2004-04-15 | Siemens Ag | Inductive position sensor |
| DE19960190A1 (en) * | 1999-12-14 | 2001-07-05 | Bosch Gmbh Robert | Control valve |
| US6828780B2 (en) | 2001-05-01 | 2004-12-07 | Balluff Gmbh | Position measuring system having an inductive element arranged on a flexible support |
| DE10140710A1 (en) * | 2001-05-21 | 2003-01-02 | Ruf Electronics Gmbh | Angle sensor with magneto-resistive sensor elements |
| DE10233080A1 (en) * | 2002-07-19 | 2004-02-12 | Fernsteuergeräte Kurt Oelsch GmbH | sensor device |
| DE102007021320A1 (en) | 2007-05-07 | 2008-11-20 | Infineon Technologies Ag | Sensor for detecting a magnetic field direction, magnetic field direction detection, method for producing magnetic field sensors and write-in device for the production of magnetic field sensors |
| US8797024B2 (en) | 2011-02-01 | 2014-08-05 | Infineon Technologies Ag | Sensor |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0719923B2 (en) * | 1984-12-14 | 1995-03-06 | 日本電装株式会社 | Position detector |
| JP3088478B2 (en) * | 1990-05-21 | 2000-09-18 | 財団法人生産開発科学研究所 | Magnetoresistive element |
| DE4232244C2 (en) * | 1992-09-25 | 1998-05-14 | Siemens Ag | Magnetic resistance sensor |
| DE4243357A1 (en) * | 1992-12-21 | 1994-06-23 | Siemens Ag | Magnetoresistance sensor with shortened measuring layers |
| DE4243358A1 (en) * | 1992-12-21 | 1994-06-23 | Siemens Ag | Magnetic resistance sensor with artificial antiferromagnet and method for its production |
| DE4301704A1 (en) * | 1993-01-22 | 1994-07-28 | Siemens Ag | Device for detecting an angular position of an object |
| JP3189464B2 (en) * | 1993-02-19 | 2001-07-16 | 株式会社デンソー | Rotational position detector |
| JP3395402B2 (en) * | 1994-10-14 | 2003-04-14 | 住友電気工業株式会社 | Travel detector |
| DE19536433C2 (en) * | 1995-09-29 | 1999-04-08 | Siemens Ag | Device for contactless position detection of an object and use of the device |
-
1997
- 1997-03-26 DE DE1997112833 patent/DE19712833C2/en not_active Expired - Fee Related
-
1998
- 1998-02-11 TW TW087101834A patent/TW366413B/en not_active IP Right Cessation
- 1998-03-13 EP EP19980104627 patent/EP0867692B1/en not_active Expired - Lifetime
- 1998-03-13 DE DE59813986T patent/DE59813986D1/en not_active Expired - Fee Related
- 1998-03-24 CA CA 2232916 patent/CA2232916C/en not_active Expired - Fee Related
- 1998-03-26 KR KR1019980010418A patent/KR100532795B1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0867692A1 (en) | 1998-09-30 |
| KR100532795B1 (en) | 2006-02-13 |
| EP0867692B1 (en) | 2007-05-02 |
| KR19980080674A (en) | 1998-11-25 |
| DE19712833C2 (en) | 1999-10-14 |
| DE19712833A1 (en) | 1998-10-01 |
| TW366413B (en) | 1999-08-11 |
| CA2232916A1 (en) | 1998-09-26 |
| DE59813986D1 (en) | 2007-06-14 |
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| EEER | Examination request | ||
| MKLA | Lapsed |
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