Patent Description:
Magnetic sensor systems, in particular angular position sensor systems are known in the art. They offer the advantage of being able to measure an angular position without making physical contact, thus avoiding problems of mechanical wear, scratches, friction, etc..

Many variants of position sensor systems exist, addressing one or more of the following requirements: using a simple or cheap magnetic structure, using a simple or cheap sensor device, being able to measure over a relatively large range, being able to measure with great accuracy, requiring only simple arithmetic, being able to measure at high speed, being highly robust against positioning errors, being highly robust against an external disturbance field, providing redundancy, being able to detect an error, being able to detect and correct an error, having a good signal-to-noise ratio (SNR), etc..

Often two or more of these requirements conflict with each other, hence a trade-off needs to be made.

It is an object of embodiments of the present invention to provide a position sensor system, a position sensor device, and a method of determining a position of a sensor device relative to a magnetic source having a plurality of magnetic poles.

It is an object of embodiments of the present invention to provide such a system and device and method, which provide an improved accuracy.

It is an object of embodiments of the present invention to provide such a system and device and method, which are suitable for use in an industrial and/or automotive environment.

It is an object of embodiments of the present invention to provide such a position sensor system, wherein the cost of the position sensor device is reduced (e.g. smaller chip area).

It is an object of embodiments of the present invention to provide such a position sensor system, wherein the semiconductor substrate of the position sensor device has a reduced footprint.

It is an object of embodiments of the present invention to provide such a position sensor system, wherein the mounting requirements of the sensor device are relaxed.

It is an object of embodiments of the present invention to provide such a position sensor system, that is more robust against ageing effects, (e.g. related to misalignment, mechanical wear).

It is an object of embodiments of the present invention to provide such a position sensor system, requiring a less powerful processor, and/or requiring less processing power.

It is an object of embodiments of the present invention to provide such a position sensor system, requiring less storage space (e.g. to store a lower number of coefficients).

It is an object of embodiments of the present invention to provide such a position sensor system, which is substantially insensitive to an external disturbance field.

These and other objectives are accomplished by embodiments of the present invention.

In a first aspect, the present invention provides a position sensor system according to claim <NUM>.

It is a major advantage of this system that the dimensions of the sensor device, in particular the distance between the sensor elements can be chosen independent from the distance between the tracks of the magnetic source. This makes it possible (inter alia) to optimise the magnetic sensor device and the magnetic source independent from each other.

It is a major advantage of the system that the distance between the sensor elements is smaller than the distance between the tracks of the magnetic source, because this allows the size and the costs of the semiconductor substrate of the sensor device to be reduced.

It is an advantage of this system wherein the magnetic source comprises a first track with the first periodicity and a second track with the second periodicity, instead of only a single track with multiple periodicities, because the latter is more difficult (and thus more expensive) to produce.

The magnetic source may be or may comprise one or more permanent magnets, or may be formed as a monolithic piece of magnetic material, or may be composed of two monolithic pieces of magnetic material, such as for example two linear strips, or two magnetic rings mounted together.

In an embodiment, a ratio of the first number of pole pairs (N1) and the second number of pole pairs (N2) is (N-<NUM>)/N, where N is an integer number in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, for example N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or. , or N1=<NUM> and N2=<NUM>.

In an embodiment, a ratio of the first number of pole pairs (N1) and the second number of pole pairs (N2) is (N-<NUM>)/N, where N is an odd integer number in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, for example N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N1=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>, or N1=<NUM> and N2=<NUM>.

In an embodiment, the magnetic source comprises two rings of magnetic material, spaced from each other by a layer or a zone of a non-magnetic material, such as e.g. plastic or ceramic or a non-magnetic metal or alloy, e.g. aluminum or copper. The non-magnetic material may have a thickness of at least <NUM>, or a thickness in the range from about <NUM> to <NUM>. In case the two rings are concentric rings arranged as shown in <FIG>, they may each have a width (in the radial direction) of about <NUM> to about <NUM>. In case the two rings having the same radius, and are arranged as shown in <FIG>, they may each have a width (in the axial direction) of about <NUM> to about <NUM>.

In an embodiment, the magnetic source comprises two substantially linear strips of magnetic material, spaced from each other by a layer or a zone of a non-magnetic material. The non-magnetic material may have a thickness of at least <NUM>, or a thickness in the range from about <NUM> to <NUM>. Alternatively, the two strips are separated from each other by means of groove.

In an embodiment, the predefined sensor distance is <NUM>% to <NUM>% of the predefined track distance. Or in other words, a ratio of the sensor distance "ds" over the track distance "dt" is a value in the range from <NUM>% to <NUM>%.

In an embodiment, the predefined sensor distance (ds) is a value in the range from <NUM> to <NUM>, or in the range from <NUM> to <NUM>, and the predefined track distance (dt) is at least <NUM>% or at least <NUM>% or at least <NUM>% or at least <NUM>% or at least <NUM>% or at least <NUM>% or at least <NUM>% or at least <NUM>% larger than the predefined sensor distance.

In an embodiment, the predefined sensor distance (ds) is at most <NUM>% of the predefined track distance (dt), or at most <NUM>%, or at most <NUM>%, or at most <NUM>%.

In an embodiment, the ratio (ds/dt) is at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%, or at most <NUM>%.

In an embodiment, the predefined sensor distance (ds) is at least <NUM>% of the predefined track distance (dt), or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%.

In an embodiment, the ratio (ds/dt) is at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%, or at least <NUM>%.

In an embodiment, the position sensor system is an angular position sensor system.

In an embodiment, the measurement range is <NUM>°.

In an embodiment, the magnetic source is rotatable about a rotation axis; and the first track and the second track are concentric circular tracks located in a single plane perpendicular to the rotation axis.

In this embodiment, the first track T1 has a first, circular centerline with a first radius, and the second track T2 has a second, circular centerline with a second radius, and the difference between the first and the second radius is equal to the predefined track distance "dt".

In this embodiment, preferably, the first sensor position P1 and to second sensor position P2 are located on a virtual line passing through the rotation axis, this virtual line is preferably parallel to the plane containing the first track and the second track, for example as illustrated in <FIG>.

In an embodiment, the magnetic source is rotatable about a rotation axis; and the first track and the second track are cylindrical tracks about said rotation axis, and spaced apart along said rotation axis; and the first track (T1) has a first outer radius (R1), and the second track (T2) has a second outer radius (R2) equal to the first outer radius.

In this embodiment, preferably, the first sensor position and to second sensor position are located on a virtual line parallel to the rotation axis, for example as illustrated in FIG.

In an embodiment, the first number (N1) of pole pairs is a value in the range from <NUM> to <NUM>; and the second number (N2) of pole pairs is a value in the range from <NUM> to <NUM>.

In an embodiment, the first number (N1) of pole pairs is a value in the range from <NUM> to <NUM>, and the second number (N2) of pole pairs is a value in the range from <NUM> to <NUM>.

In an embodiment, the position sensor system is a linear position sensor system; and the first track is the first linear segment, and the second track is a second linear segment parallel to the first linear segment.

In this embodiment, preferably the first sensor position and to second sensor position are located on a virtual line perpendicular to the first and second linear segments, for example as illustrated in <FIG>.

In an embodiment, the processing unit is configured for: b) estimating a transverse position of the sensor device relative to the magnetic tracks, based on at least some of the measured magnetic field components; and c) for determining the position of the sensor device based on at least some of the measured magnetic field components and based on the estimate transverse position.

The "transverse position" is a radial position in the example of <FIG>, and is a lateral position in the example of <FIG>. Such a method is illustrated e.g. in <FIG>.

In an embodiment, the processing unit is configured for: b) calculating a first set of quadrature components and a second set of quadrature components based on at least some of the measured components using a predefined set of coefficients; and c) for determining the position of the sensor device based on the first and second set of quadrature components.

Step b) may comprise calculating each of said quadrature components as a weighted sum of only two of the measured magnetic field components, for example as illustrated in <FIG>. Thus, in this embodiment, only two weighting factors are required for each quadrature component, i.e. a total of only eight coefficients.

It is an advantage of this embodiment that the set of coefficients is predetermined, for example stored in non-volatile memory before actual use of the sensor device.

In an embodiment, the sensor device comprises a non-volatile memory, and the set of coefficients are stored in said non-volatile memory.

The coefficients may be determined by performing a calibration test after mounting of the sensor device relative to the magnet, and determining an optimal set of coefficients based on the measurements performed during the calibration test. This may considerably relax the mounting tolerances, and/or improve the accuracy of the position sensor system.

In an embodiment, the number of coefficients is at most eight.

In an embodiment, the processing unit is configured for: b) estimating a transverse position of the sensor device relative to the magnetic tracks, based on at least some of the measured components, and for determining a set of coefficients based on the estimated transverse position; and c) for calculating a first set of quadrature components and a second set of quadrature components based on at least some of the measured components, using the set of coefficients determined in step b); d) determining the position of the sensor device based on the first and second set of quadrature components.

It is an advantage of this embodiment that the set of coefficients is dynamically determined or dynamically adjusted as a function of the transverse position, e.g. caused by mechanical mounting tolerances or by mechanical drift or wear. In this way, the accuracy of the absolute position can be improved. This dynamic recalibration may be performed by the sensor device itself, for example periodically, and/or may be initiated for example by an external processor.

In an embodiment, the transverse position of the sensor device is determined based on a ratio of one or more of |Bx1|/|Bz1| or |Bx1|/|By1| or |By1|/|Bz1| or |Bx2|/|Bz2| or |Bx2|/|By2| or |By2|/|Bz2| at one or more predefined positions (e.g. estimated using an initial set of coefficients), or may be based on a maximum ratio of of one or more of |Bx1|/|Bz1| or |Bx1|/|By1| or |By1|/|Bz1| or |Bx2|/|Bz2| or |Bx2|/|By2| or |By2|/|Bz2| at a random position over a full rotation, or may be based on the value of the gradient |dBx/dx| at one or more angular positions (e.g. as illustrated in <FIG>) or in an angular subrange, or may be based on the maximum value of the gradient |dBx/dx| over the measurement range.

It is also described, although not being part of the present invention, a method of determining a position of a sensor device movable along a predefined path relative to a magnetic source or vice versa, the magnetic source comprising a first plurality of magnetic pole pairs arranged along a first track having a first periodicity, and comprising a second plurality of magnetic pole pairs arranged along a second track having a second periodicity different from the first periodicity, wherein centrelines of the tracks are spaced apart by a predefined track distance, the method comprising the steps of: a) measuring at least two orthogonal magnetic field components (e.g. By1, Bz1) at a first sensor location, and measuring at least two orthogonal magnetic field components (e.g. By2, Bz2) at a second sensor location, spaced from the first sensor location by a predefined sensor distance smaller than the predefined track distance in a direction transverse to the tracks (e.g. substantially perpendicular to the tracks); b) determining the position of the sensor device based on at least some of the measured magnetic field components.

One of the measured magnetic field components is tangential to the direction of relative movement (typically indicated as "By" in this application).

Step a) comprises: measuring at least two (e.g. By1, Bz1) or at least three (e.g. Bx1, By1, Bz1) orthogonal magnetic field components at a first sensor location, and measuring at least two (e.g. By2, Bz2) or at least three (e.g. Bx2, By2, Bz2) orthogonal magnetic field components at a second sensor location, spaced from the first sensor location by a predefined sensor distance smaller than the predefined track distance in a direction transverse to the tracks (e.g. substantially perpendicular to the tracks); and wherein step b) comprises: i) estimating a transverse position (e.g. offset) of the sensor device relative to the tracks based on at least some of the measured magnetic field components; ii) determining the position of the sensor device based on at least some of the measured magnetic field components and based on the estimated transverse position.

Step b) comprises: i) calculating a first set of quadrature components and a second set of quadrature components based on at least some of the measured magnetic field components using a set of equations with a predefined set of coefficients; ii) determining the position of the sensor device based on the first and second set of quadrature components.

The set of equations can comprise or consist of four equations, or four polynomial equations, or four linear equations, or four equations each with only two terms and two coefficients (or weighting factors).

According to another aspect, the present invention is also directed to a position sensor device, configured for performing any of the methods of <FIG> or <FIG> or <FIG>, or variants thereof using magnetic field gradients, as described in the detailed description.

Particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims.

The term "track" as part of a magnetic source, as used herein, typically refers to a ring-shaped or annular shaped or cylindrical shaped object when talking about an angular position sensor system for example as illustrated in <FIG>, and typically refers to a beam-shaped object when talking about a linear position sensor system, for example as illustrated in <FIG>.

The tracks of the magnetic source of <FIG> and FIG. (c) have a "width" extending in the radial direction R, the axial direction A, and the transverse direction T, respectively.

The term "centreline of a track" as used herein refers to a virtual line or curve, situated at the surface of the track, in the middle of the width. For example, in <FIG> the centreline is a circle having a radius equal to the average of the inner radius and the outer radius of the respective track; in <FIG> the centreline is a circle having a radius equal to the outer radius of the track, and situated halfway the width (in the axial direction); in <FIG> the centreline is line in the middle of the track (halfway the transverse direction).

The expression "the tracks are spaced apart by a distance dt" as used herein means that centrelines of the tracks are spaced by the distance "dt", for example as illustrated in <FIG>.

The expression "the sensors or sensor structures are spaced apart by a distance ds" as used herein means that centres (or a reference point) of the sensors or sensor structures are spaced apart by the distance "ds", for example as illustrated in <FIG>.

The present invention relates to linear and angular position sensor systems, linear and angular position sensor devices, and methods of determining a linear or an angular position relative to a magnetic source, and in particular to position sensor systems with high accuracy.

The present invention provides a position sensor system comprising a magnetic source, and a sensor device which is movable along a predefined path relative to the magnetic source. The magnetic source comprises a first plurality (N1) of magnetic pole pairs arranged along a first track having a first periodicity, and comprises a second plurality (N2) of magnetic pole pairs arranged along a second track having a second periodicity different from the first periodicity. A centreline (or central line or central curve) of the first track is spaced from a centreline (or central line or central curve) of the second track by a predefined track distance "dt". The sensor device comprises at least four magnetic sensitive elements configured for measuring at least two first orthogonal magnetic field components (typically referred to herein as: By1, Bz1) at a first sensor location (P1), and at least two second orthogonal magnetic field components (typically referred to herein as: By2, Bz2) at a second sensor location (P2). The first sensor location (P1) is spaced from the second sensor location (P2) by a predefined sensor distance "ds". The sensor device further comprises a processing unit configured for determining said linear or angular position based on at least a subset of the measured signals (e.g. based on, or based solely on By1, Bz1, By2, Bz2).

According to an important aspect of the present invention, the predefined sensor distance "ds" is smaller than the predefined track distance "dt", measured in a direction transverse to the tracks.

It is a major advantage of this system that the dimensions of the sensor device, in particular the distance between the sensor elements can be chosen independent of the distance between the tracks of the magnetic source. This makes it possible (inter alia) to optimise the magnetic sensor device and the magnetic source independent from each other, and also allows a single sensor device to be used in combination with various magnetic sources.

It is a major advantage of the system that the distance "ds" between the sensor elements is smaller (e.g. at least <NUM>% smaller) than the distance "dt" between centrelines of the tracks of the magnetic source, because this allows the size and the costs of the semiconductor substrate of the sensor device to be reduced. This is especially important in a highly competitive market.

It is an advantage of this system wherein the magnetic source comprises a first track with the first periodicity and a second track with the second periodicity, instead of only a single track with multiple periodicities, because the former magnetic source is easier to produce. For example, if the first and second tracks are linear tracks (e.g. as illustrated in <FIG>), the magnetic source may be composed of two magnetic strips, each of which may be produced separately, and then arranged side by side in the plane (e.g. as illustrated in <FIG>. As another example, if the first and second tracks are circular tracks having a same radius but a different number of poles (e.g. as illustrated in <FIG>, the magnetic source may be composed of two magnetic rings which may be produced separately, and then arranged side-by-side axially. As another example, if the first and second tracks are circular tracks having a different radius and a different number of poles (e.g. as illustrated in <FIG>, the magnetic source can be composed of two magnetic rings which may be produced separately, and then arranged concentrically, in a plane.

Examples of such position sensor systems are shown in <FIG>.

More specifically, <FIG> shows an angular position sensor system 1500a comprising a magnetic source 1510a comprising two concentric tracks T1, T2 located in a single plane, and a sensor device 1520a arranged above or below that plane.

<FIG> shows an angular position sensor system 1500b comprising a magnetic source 1510b comprising two circular tracks T1, T2 arranged on a cylindrical surface, and a sensor device 1520b arranged as a satellite around that cylindrical surface.

<FIG> shows a linear position sensor system 1500c comprising a magnetic source 1510c comprising two linear parallel tracks T1, T2 located in a single plane, and a sensor device 1520c arranged above that plane.

As mentioned above, the number of magnetic pole pairs N1 of the first track T1 is different from the number of magnetic pole pairs of the second track. In certain embodiments, the ratio of the first number of pole pairs (N1) and the second number of pole pairs (N2) is (N-<NUM>)/N, where N is an integer number in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, for example N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), etc..

In an embodiment, a ratio of the first number of pole pairs (N1) and the second number of pole pairs (N2) is (N-<NUM>)/N, where N is an odd integer number in the range from <NUM> to <NUM>, preferably in the range from <NUM> to <NUM>, for example N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N1=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>), or N1=<NUM> and N2=<NUM> (ratio=<NUM>/<NUM>).

As will be explained in more detail further, by measuring two orthogonal magnetic field components at the first and at the second sensor location P1, P2, it is possible to determine a unique position relative to the magnetic source, with high accuracy.

The invention will mainly be explained referring to the angular position sensor system shown in <FIG> for simplifying the description, but the present invention is not limited thereto, and the same principles also apply to other variants, mutatis mutandis.

<FIG> show a conceptual view of an angular position sensor system <NUM> corresponding to that of <FIG>. In the specific example shown, the magnetic source <NUM> comprises two magnetic rings: an inner ring having N1=<NUM> pole pairs, and an outer ring having N2=<NUM> pole pairs, but the present invention is not limited thereto and the rings may comprise another number of magnetic pole pairs. The rings may be axially magnetised. The example also shows a sensor device <NUM> capable of measuring two or three orthogonal magnetic field components in each of two sensor locations P1, P2, for example an axial field component in a direction A which is parallel to the rotation axis, a radial field component oriented in the radial direction R, and a tangential field component oriented in a circumferential direction T, tangential to a virtual circle.

<FIG> shows an enlarged view of a portion of <FIG>, and shows that the first magnetic track T1 is a ring with a first inner and outer radius, and the second magnetic track T2 is a ring with a second inner and outer radius. The first track T1 has a first width W1, and the second track T2 as a second width W2. In the example shown, the first width W1 and the second width W2 are equal, but that is not absolutely required for the invention to work, and the invention will also work if the width W1 of the first track T1 is larger or smaller than the second width W2 of the second track T2.

<FIG> is a perspective view illustrating the relative position of the sensor device <NUM> having two sensor positions P1, P2 relative to the magnetic tracks T1, T2. As shown, a projection of the first and the second sensor position P1, P2 on a plane containing the first and the second centreline <NUM>, <NUM> are preferably located on a line segment which is oriented radially.

Contrary to what developers would normally choose, the inventors decided not to locate the first and second sensor position above the centrelines <NUM>, <NUM>, i.e. above the middle of the tracks T1 and T2, but they decided to move the sensor locations closer together. Indeed, as can be seen, the distance "ds" between the projections of the first and second sensor position P1, P2 is smaller than the distance "dt" between the centrelines <NUM>, <NUM> of the tracks. It could not be predicted beforehand whether this solution would work at all, let alone how well the solution would work.

While not shown <FIG>, there may be a code-free region between the first track T1 and the second track T2. This region may for example be formed by a groove. This groove may be left open, or may be filled with a non-magnetic material, e.g. a plastic, a ceramic, a non-magnetic metal or alloy (e.g. to avoid accumulation of dust or particles). Even if a code-free region is present, the two sensor positions P1, P2 are preferably located "above" the magnetic material, i.e. above the magnetized zones, e.g. as illustrated in more detail in <FIG>.

While the representation of <FIG> seems to suggest that the sensor device contains a substrate and that the two sensor positions have to be located at the top of that substrate, this is not absolutely required, and the sensor locations P1, P2 may also be located underneath the substrate, as may be obtained by turning the sensor device upside-down. In this way, the sensor elements can be closer to the tracks, the measured signals can be larger, the signal-to-noise ratio (SNR) may be increased and/or crosstalk may be reduced, and the overall accuracy may be improved.

<FIG> shows a mathematical model of a variant of the magnetic source <NUM> of <FIG>, comprising an inner ring comprising or consisting of a magnetic material and an outer ring comprising or consisting of magnetic material, spaced apart from each other by a non-magnetic material (e.g. by air).

In the specific example shown in <FIG>, the inner ring <NUM> is made of or comprises a magnetic material having an inner radius of <NUM> and an outer radius of <NUM>, hence has a width W1 of <NUM>. The outer ring <NUM> is made of or comprises a magnetic material having an inner radius of <NUM> and an outer radius of <NUM>, and a width W2 of <NUM>. In the example, both rings have a height (in the axial direction) of <NUM>. But of course this is only an example, and embodiments of the present invention are not limited to these specific dimensions.

<FIG> also shows the relative position and orientation of the sensor device <NUM> with respect to the magnetic source <NUM>. This figure also shows a first coordinate system relative to the magnetic source comprising the axes A (axial direction), R (radial direction), T (tangential direction), and a second coordinate system connected to the sensor device <NUM>, having an X-axis corresponding to the radial direction R, a Y-axis corresponding to the direction of relative movement, in this example the circumferential direction T, and a Z-axis, parallel to the rotation axis A. The sensor device <NUM> preferably comprises a semiconductor substrate, and the X and Y axis are parallel to the semiconductor substrate, and the Z-axis is orthogonal to the semiconductor substrate.

This model was used in a computer simulation, the results of which are described further.

<FIG> is a top view showing orthogonal projections of the relative locations of the first sensor positions P1 on the inner ring <NUM> of the magnetic source, and <FIG> is a top view showing orthogonal projections of the relative locations of the second sensor positions P2 on the outer ring <NUM> of the magnetic source. As can be seen, these positions are not located on the centrelines (in the middle) of the rings, but are deliberately off-center. In the particular example shown, the two sensor positions are spaced apart by ds=<NUM>, and the first sensor positions P1 are located at a radius of <NUM> - <NUM> =<NUM>, and the second sensor positions P2 are located at the radius of <NUM> + <NUM> = <NUM>, but of course the present invention is not limited to this example, and other sensor positions may also be used. In fact, it is not required that the distance between P1 and the first centreline is substantially equal to the distance between P2 and the second centreline, but in preferred embodiments that is the case.

<FIG> shows an enlarged cross-sectional view in a plane perpendicular to the plane in which the magnetic rings are located, and passing through the first and the second sensor location P1, P2. As shown, the first sensor position P1 is preferably located "vertically above" the inner ring <NUM>, and the second sensor position P2 is preferably located "vertically above" the outer ring <NUM>, although this is not absolutely required, and the invention may still work if one or both of the sensor positions P1, P2 is located "vertically above" the non-coded region, an example of which will be discussed in relation to <FIG>. As can also be seen, projections of the first and second sensor location P1, P2 (at <NUM> and <NUM>) are located between the centreline <NUM> of the inner ring (at <NUM>) and the centreline <NUM> of the outer ring (at <NUM>). It is noted that the sensor locations of this embodiment are in fact offset quite far from the centrelines (<NUM> / <NUM> = <NUM>%).

The sensor device of <FIG> may comprise at each sensor location two or four horizontal Hall elements and a magnetic flux concentrator (IMC), for example as shown in more detail in <FIG>, but other sensor structures may also be used. Such an IMC disk may have a diameter of about <NUM> to about <NUM>. The sensor device may be arranged at a small axial distance from the magnetic rings, e.g. at a distance "g" in the range from <NUM> to <NUM>, or in the range from <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>.

<FIG> is a graph obtained by a computer-simulation, showing the amplitude of the magnetic field component Bz (=Baxial) as would be measured by the sensor device <NUM> of <FIG>, located about <NUM> above the rings. The component Bz is oriented in the axial direction of the magnetic source having ten pole pairs on its outer ring <NUM>, and having eight pole pairs on its inner ring <NUM>, which are clearly visible. The centreline <NUM> of the inner ring (or magnetic track) <NUM>, and the centreline <NUM> of the outer ring (or magnetic track) <NUM> are indicated as white dotted circles. The projected positions of the first and second sensor elements P1, P2 are indicated by means of black circles situated between the dotted centrelines. As was to be expected, the signal Bz is largest above the respective centrelines <NUM>, <NUM>, but degrades fast with increasing distance from these centrelines.

<FIG> is a graph obtained by computer-simulation, showing the amplitude of the magnetic field component By (=Btang) tangential to the direction of relative movement, i.e. oriented in the circumferential direction. As can be seen, there is considerable overlap (or cross-talk) between the magnetic field generated by the inner ring and the outer ring.

<FIG> is a graph obtained by computer-simulation, showing the amplitude of the magnetic field component Bx (=Bradial) oriented in a radial direction of the magnetic source, perpendicular to the direction of relative movement. Again, there is large overlap or cross-talk between the magnetic field created by the inner ring and the magnetic field created by the outer ring.

The reader will agree that it is impossible to predict whether a position sensor system where the sensor elements are located offset from the centrelines, will still work, let alone to predict or even estimate how good or how bad the performance will be. The zones indicated by <NUM> and <NUM> will be described further.

Anyway, while not the only solution, the inventors came to the idea of using a linear transformation to convert the measured signals (in particular By and Bz measured at the two sensor locations P1, P2) into two sets of quadrature signals.

<FIG> shows a set of linear equations that can be used in embodiments of the present invention to convert at least some of the measured signals of the magnetic field components, in particular Bz (=Baxial) and By (=Btang) into two sets of quadrature components, one set being represented by (Bsin1, Bcos1) and the other set being represented by (Bsin2, Bcos2). From these sets, two angles can then be calculated, for example in accordance with the following formulas: α1=arctan(Bsin1/Bcos1) and α2=arctan(Bsin2/Bcos2).

The first angle α1 is indicative of an angular position of the inner ring (in the example having a periodicity of <NUM>°/<NUM>=<NUM>°, hence having an ambiguity of integer multiples of <NUM>°), and the second angle α2 is indicative of an angular position of the outer ring (in the example having a periodicity of <NUM>°/<NUM>=<NUM>°, thus having an ambiguity of integer multiples of <NUM>°). The combination of the two angles (α1, α2), however, corresponds to a unique angular position of the sensor device relative to the magnetic source.

The set of equations of <FIG> contain eight coefficients. Suitable or optimal coefficients values a1, a2, b1, b2, c1, c2, d1, d2 can be found by simulations, or by measurement, and by using known techniques, such as curve-fitting techniques and/or least mean square error techniques. It is also possible to optimize the coefficients values for each particular assembly, e.g. by performing measurements of a particular system during a calibration test after assembly, and by optimizing the parameters for that assembly, but of course that is more difficult and more expensive. It would be more desirable if one could work with a single set of predefined coefficients. The sensor device may comprise a non-volatile memory <NUM> (see <FIG>), and the coefficients values may be stored in the non-volatile memory as parameters.

Experiments were performed to find out how good or how bad the resulting position would be, in terms of accuracy.

<FIG> shows a graph with waveforms of two orthogonal magnetic field components Bz1, By1, as can be measured at first sensor locations P1, in the vicinity of the first track T1, more in particular "vertically above" the inner track T1, e.g. as shown in <FIG>. The amplitude (vertical axis) is shown in arbitrary units as a function of the mechanical position (horizontal axis) of the sensor device. As can be seen, the signals Bz1, By1 have a periodicity of <NUM>°/<NUM>=<NUM>°, and the amplitude of Bz1 seems to be fairly constant, but the amplitude of By1 is not constant.

<FIG> shows a graph with two quadrature waveforms (Bsin1, Bcos1) as can be obtained by a linear transformation using the set of equations shown in <FIG> and suitable coefficients. It is very surprising that the curves of <FIG> look like a perfect sine and a cosine, especially when considering the amount of cross-talk shown in <FIG>, and considering that the translation is only a simple set of linear equations. In fact, it is also possible to use higher-order polynomials, e.g. second order or third-order polynomials.

<FIG> shows a graph illustrating a typical error (in degrees) between the calculated angle α1 based on the sets of quadrature signals (Bsin1, Bcos1) shown in <FIG>, and the actual position. The amplitude is shown in degrees as a function of the angular position of the sensor device. It is simply amazing that the angular position "α1" of the inner ring <NUM> can be determined with an inaccuracy smaller than ±<NUM>°, despite the amount of cross-talk.

Similar simulations and calculations were performed for the signals measured at the second sensor location P2, situated near the outer track T2, more in particular "vertically above" the outer track T2, e.g. as shown in <FIG>.

<FIG> shows a graph with waveforms of two orthogonal magnetic field components Bz2, By2, as can be measured at the second sensor location P2. The amplitude (vertical axis) is shown in arbitrary units as a function of the angular position (horizontal axis) of the sensor device <NUM> relative to the magnet <NUM>. As can be seen, these measured signals have a periodicity of <NUM>°/<NUM>=<NUM>°.

<FIG> shows a graph with two quadrature waveforms (Bsin2, Bcos2) as can be derived from the measured signals (By2, Bz2), e.g. by means of a linear transformation using the set of equations shown in <FIG>.

<FIG> shows a graph illustrating a typical error (in degrees) between the calculated angle α2 based on the sets of quadrature signals (Bsin2, Bcos2) shown in <FIG>, and the actual angular position of the sensor device <NUM>. The error amplitude (vertical axis) is shown in degrees as a function of the angular position (vertical axis) of the sensor device. Again, it is simply amazing that the angular position "α2" of the outer ring <NUM> can be determined with an inaccuracy smaller than ±<NUM>°, despite the considerable amount of cross-talk.

From the simulations of <FIG> it can be understood that, since the angular position α1 of the sensor device <NUM> with respect to the inner ring <NUM> can be determined with an accuracy better than ±<NUM>° (but with an ambiguity of multiples of <NUM>°), and since the angular position α2 of the sensor device <NUM> with respect to the outer ring <NUM> can be determined with an accuracy better than ±<NUM>° (but with an ambiguity of multiples of <NUM>°), that the overall angular position of the sensor device <NUM> relative to the magnetic source containing both rings can be determined with an overall accuracy better than ±<NUM>° (and without ambiguity). Indeed, the overall angular position can be found e.g. by finding a set of integer values "k1" and "k2" for which (α1 + k1*<NUM>°) = (α2 + k2*<NUM>°), which is equal to the overall angular position, where k1 is an integer value smaller smaller than N1, and k2 is an integer value smaller than N2. Of course, other formulas to calculate the overall position may also be used.

The inventors wanted to know what would happen if the sensor device <NUM> was built or programmed with the set of coefficients optimized for the envisioned position described above, i.e. for a radial position of P1 at <NUM> and a radial position of P2 at <NUM>, in case of a mechanical mispositioning of <NUM>.

<FIG> shows a waveform similar to the waveform of <FIG>, indicative for the angular error of the sensor device <NUM> relative to the inner ring <NUM>, as would be obtained when applying the linear transformation mentioned above, using the same coefficients mentioned above (e.g. being hardcoded, or retrieved from the non-volatile memory), in case of a mechanical mispositioning of <NUM>. As can be seen, the angle α1 has a worst-case error of about ±<NUM>°.

<FIG> shows a waveform similar to the waveform of <FIG>, indicative for the angular error of the sensor device <NUM> relative to the outer ring <NUM>, as would be obtained when applying the linear transformation mentioned above, using the same coefficients mentioned above (e.g. being hardcoded, or retrieved from the non-volatile memory), in case of a mechanical mispositioning of <NUM>. As can be seen, the angle α2 has a worst-case error of about ±<NUM>°.

Since the angular position α1 only needs to be known for solving the ambiguity of the outer ring, the inaccuracy of the outer ring <NUM> is dominant in this case, since it has the larger number of pole pairs. It can thus be understood that the overall error of the overall angular position sensor system <NUM> using a fixed, predefined set of coefficients would be about ±<NUM>° in case of a mispositioning of <NUM>, which is acceptable for some application, but too large for some applications.

One solution to reduce this inaccuracy is to increase the number of pole pairs, which will typically increase the cost of the magnetic source <NUM>. Another solution to address this problem of mispositioning, already suggested above, is to determine the optimum coefficients in a calibration test, after assembling the position sensor system, and storing the coefficients in a non-volatile memory of the device. This works if the mispositioning is static, but does not work if the mispositioning drifts over time. Yet another solution which also works if the mispositioning drifts over time will be described further, when discussing <FIG> and <FIG>.

<FIG> show examples of sensor devices with various sensor structures as may be used in embodiments of the present invention.

<FIG> shows a schematic representation of a sensor device 820a with two magnetic sensors structures spaced apart over a predefined distance Δx along the X-axis, as can be used in embodiments of the present invention. Each sensor structure of this device comprises four horizontal Hall elements H1-H4 arranged near the periphery of an integrated magnetic flux concentrator IMC. Each sensor structure is capable of measuring three orthogonal magnetic field components, Bx, By, Bz, as described in more detail in patent publication <CIT>) and in patent application <CIT> mentioned above. In order to understand the present invention, it suffices to know that the component Bx1 is proportional to (H1-H3), and that the component By1 is proportional to (H2-H4), and that the component Bz is proportional to (H1+H2) or to (H2+H4) or to (H1+H2+H3+H4). Thus, the sensor device 820a has eight magnetic sensor elements, and is capable of measuring two sets of three orthogonal magnetic field components, namely (Bx1, By1, Bz1) at a first sensor position P1, and (Bx2, By2, Bz2) at a second sensor position P2. But the present invention is not limited to this particular sensor device, and devices with other sensor structures may also be used.

<FIG> shows another sensor device comprising two magnetic sensors structures spaced apart over a predefined distance Δx, each sensor structure comprising one horizontal Hall element (for measuring Bz) and two vertical Hall elements, one for measuring Bx, and one for measuring By. The magnetic sensor device 820b is thus also capable of measuring three orthogonal magnetic field components, namely (Bx1, By1, Bz1) at the first sensor position P1, and (Bx2, By2, Bz2) at the second sensor position P2.

<FIG> shows another sensor device comprising two magnetic sensors structures spaced apart over a predefined distance Δx, each sensor structure comprising only two horizontal Hall elements arranged on opposite sides of an IMC disk, and located on a virtual line perpendicular to the X-axis. Each sensor structure is capable of measuring two orthogonal components By, Bz at each of the sensor locations P1, P2. It is an advantage of this sensor device that it requires only four horizontal Hall elements instead of eight.

<FIG> shows another sensor device comprising two magnetic sensors structures spaced apart over a predefined distance Δx, each sensor structure comprising one horizontal Hall element and one vertical Hall element. Each sensor structure is capable of measuring two orthogonal components By, Bz. It is an advantage of this sensor device that it does not require integrated magnetic flux concentrators, hence may be easier to produce.

<FIG> shows a variant of <FIG>, and <FIG> shows a variant of <FIG>. The sensor devices of <FIG> and of <FIG> each comprise four sensor structures spaced apart in the X and in the Y-direction, instead of only two sensor structures. These devices are capable not only of measuring (Bx1, By1, Bz1) at P1, and (Bx2, By2, Bz2) at P2, but are also capable of determining spatial gradients of Bx, By and Bz at the two sensor locations P1, P2 along the circumferential direction, i.e. (dBx/dy, dBy/dy, dBz/dy).

The gradient signals dBy/dy and dBz/dy at P1 and P2 can then be transformed into two sets of quadrature signals in a similar manner as described above, e.g. using a set of linear or polynomial equations with a relatively small number of coefficients, e.g. predefined coefficients, which may be determined by simulation, or by measurement, or after assembly. The coefficients may be stored in non-volatile memory. A first angle α1 relative to the inner ring, and a second angle α2 relative to the second ring can then be calculated based on an arctangent function of the quadrature signals. It is an advantage that the gradient signals are highly insensitive to an external disturbance field, and thus also the overall angular position will be highly insensitive to an external disturbance field.

According to principles of the present invention, the distance Δx between the sensor positions P1 and P2, and between the sensor positions P3 and P4 are smaller than the distance "dt" between two centrelines, e.g. at least <NUM>% smaller. The distance Δy does not need to be matched to the pole distances, but is used to determine gradient signals along the Y-direction. The value of Δy may be substantially equal to Δx, but that is not absolutely required, and it is also possible that Δy is larger or smaller than Δx. The distance Δy is preferably not too small, because otherwise the SNR of the difference signal may become too small. The distance Δy is preferably not too large, because otherwise the difference signal will deviate more from a spatial derivative, which may decrease the accuracy, and also because the cost of the sensor device increases as the area of the semiconductor substrate increases. The skilled person having the benefit of the present disclosure can find a reasonable compromise.

In preferred embodiments, each of the distances Δx and Δy are smaller than the track distance "dt", e.g. at least <NUM>% smaller.

<FIG> shows a variant of <FIG> further capable of measuring magnetic field gradient signals dBy/dy and dBz/dy. But <FIG> can also be considered to be a variant of <FIG>, not capable of determining Bx or dBx/dy, which are not used in all embodiments of the present invention.

Functionally the sensor device of <FIG> the same capabilities, the sensor device of <FIG> have the same capabilities, the sensor device of <FIG> have the same capabilities, and the sensor device of <FIG> have the same capabilities.

<FIG> show various examples of sensor devices which can be used in embodiments of the present invention, but the present invention is not limited thereto, and other sensor structures may also be used, for example sensor structures comprising magneto-resistive elements.

The predefined distance Δx may be a value in the range from about <NUM> to about <NUM>, e.g. from about <NUM> to about <NUM>, e.g. equal to about <NUM>. The predefined distance Δy may be a value in the range from about <NUM> to about <NUM>. As mentioned above, Δy (to be oriented in the circumferential direction of the magnetic source) may be larger or smaller than Δx (to be oriented in the radial direction of the magnetic source).

<FIG> shows a high-level block-diagram of a sensor device <NUM> as can be used in embodiments of the present invention. In fact, the hardware may be similar or identical to the hardware of the devices described in patent publication <CIT>) and in patent application <CIT>, but the algorithm performed by the controller <NUM> is different, as will be described in <FIG>. A brief description of the hardware is provided here for completeness.

The position sensor device <NUM> of comprises a plurality of magnetic sensor elements (in the example: SE1 to SE8), arranged in a particular manner on a semiconductor substrate, e.g. as shown in <FIG>.

The position sensor device <NUM> further comprises a processing circuit <NUM>, for example a programmable processing unit adapted for determining, e.g. calculating a set of values (By1, Bz1, By2, Bz2) or a set of values (Bx1, By1, Bz1, Bx2, By2, Bz2) based on the signals obtained from the sensor elements, e.g. by summation or subtraction, and/or amplification, and/or digitization, etc..

The processing unit <NUM> is further adapted for determining a linear or an angular position according to one of the algorithms as will be described further in <FIG>. This position may be provided at an output of the device, e.g. in a digital or analog manner.

While not explicitly shown, the sensor device <NUM> typically also comprises biasing circuitry, readout circuitry, one or more amplifiers, analog-to-digital convertors (ADC), etc. Such circuits are well known in the art, and are not the main focus of the present invention.

Devices used in the present invention comprise at least four sensor elements, but they may comprise more than four sensor elements, e.g. eight sensor elements or twelve sensor elements, or sixteen sensor elements. The sensor elements may be chosen from the group consisting of: horizontal Hall elements, vertical Hall elements, magneto-resistive elements, e.g. XMR or GMR elements, etc..

<FIG> shows a flow-chart of a method <NUM> of determining a position (e.g. a liner or angular position) of a sensor device movable along a predefined path (e.g. linear or circular path) relative to a magnetic source, wherein the magnetic source comprises a first plurality N1 of magnetic pole pairs arranged along a first track T1 having a first periodicity, and comprises a second plurality N2 of magnetic pole pairs arranged along a second track T2 having a second periodicity different from the first periodicity, and wherein centrelines <NUM>, <NUM> of the tracks T1, T2 are spaced apart by a predefined track distance "dt". The method <NUM> comprises the following steps:.

Preferably one of the magnetic field components (indicated as By in this application) is tangential to the direction of relative movement, and preferably the other magnetic field component (indicated as Bz in this application) is orthogonal to the direction of relative movement. The latter is preferably also orthogonal to the semiconductor substrate, although that is not absolutely required.

The method may also comprise the step of: providing <NUM> a magnetic source comprising a first plurality (N1) of magnetic pole pairs arranged along a first track T1 having a first periodicity, and comprising a second plurality (N2) of magnetic pole pairs arranged along a second track T2 having a second periodicity different from the first periodicity, wherein centrelines <NUM>, <NUM> of the tracks T1, T2 are spaced apart by a predefined track distance "dt". This step is indicated as optional (dotted lines), because it is not really part of the algorithm performed by the processor of the sensor device, but rather a precondition or prerequisite.

The position of the sensor device relative to the magnetic source can be determined in several ways, a few of which are described next:
In an embodiment, "determining said position based on at least a subset of the measured signals" comprises: i) calculating two sets of quadrature components as a linear combination of only two magnetic field components, for example as depicted in <FIG>, and then ii) calculating or determining a first angle α1 by using an arctangent function of the first set of quadrature components (Bsin1, Bcos1), and calculating or determining a second angle α2 by using an arctangent function of the second set of quadrature components (Bsin2, Bcos2), and iii) by finding the overall linear or angular position based on said first and said second angle α1, α2 (e.g. by solving the ambiguity).

In a variant of this embodiment, a non-linear transformation is used to convert the measured signals into quadrature signals, e.g. using a set of non-linear equations, e.g. second order or third order equations.

In another embodiment, "determining said position based on at least a subset of the measured signals" comprises: i) calculating or determining a first angle α1 by using an arctangent function of the first set of measured components By1, Bz1, and calculating or determining a second angle α2 by using an arctangent function of the second set of measured components By2, Bz2, then ii) correcting the first angle α1 according to a first predefined, non-linear function (e.g. stored in a non-volatile memory of the sensor device as a first piece-wise-linear approximation), and correcting the second angle α2 according to a second predefined, non-linear function (e.g. stored in the non-volatile memory as a second piecewise linear approximation), and iii) by finding the overall linear or angular position based on said first and said second corrected angles (e.g. by solving the ambiguity).

In yet another embodiment, "determining said position based on at least a subset of the measured signals" comprises: i) calculating or determining a first angle α1 by using a first "modified arctangent function" of the first set of measured components (By1, Bz1), and calculating or determining a second angle α1 by using a second "modified arctangent function" of the second set of measured components (By2, Bz2); and ii) by finding the linear or angular position based on said first and said second angle α1, α2.

The first angle α1 may be calculated (in step i) in accordance with the following formula:<MAT> , where By1 and Bz1 are two magnetic field components measured at the first sensor location P1, and K1 and K2 are predefined constants; and the second angle α2 may be calculated (in step i) in accordance with the following formula: α2 = arctan(K3+K4*(Bz2/By2)), where By2 and Bz2 are two magnetic field components measured at the second sensor location P3, and K3 and K4 are predefined constants. The predefined coefficients and/or the predefined constants may be determined by design, by simulation, or by a calibration, and may be stored in a non-volatile memory of the sensor device.

There are but three possible ways to determine the position, but the present invention is not limited hereto, and other ways may also be used.

In addition to the advantages mentioned above, this method offers the further advantage of being highly insensitive to an external strayfield.

<FIG> shows a flow-chart of a method <NUM> of determining a position (e.g. a linear or angular position) of a sensor device movable along a predefined path (e.g. linear or circular path) relative to a magnetic source, wherein the magnetic source comprises a first plurality N1 of magnetic pole pairs arranged along a first track T1 having a first periodicity, and comprises a second plurality N2 of magnetic pole pairs arranged along a second track T2 having a second periodicity different from the first periodicity, and wherein centrelines <NUM>, <NUM> of the tracks T1, T2 are spaced apart by a predefined track distance "dt". This method can be seen as a special case of the method of <FIG>. The method <NUM> comprises the following steps:.

In the system of <FIG> the transverse position is a radial offset, e.g. an (unintended) offset from its nominal (intended) mounting position for which the coefficients of the equations of <FIG> were optimized. In the system of <FIG>, the transverse position is a lateral offset.

In an embodiment, the transverse position of the sensor device is estimated or determined based on one or more of the following ratios: |Bx1|/|Bz1| or |Bx1|/|By1| or |By1|/|Bz1| or |Bx2|/|Bz2| or |Bx2|/|By2| or |By2|/|Bz2| at one or more predefined positions. The predefined position may be estimated using an initial or predefined set of coefficients. In a variant, the transverse position of the sensor device is estimated or calculated based on a maximum value of one or more of said ratios, considered over substantially the entire measurement range (e.g. over a full rotation or over the full stroke), or may be based on the value of the gradient |dBx/dx| at one or more angular positions or in an angular subrange, or may be based on the maximum value of the gradient |dBx/dx| over the measurement range. The gradient |dBx/dx| may be calculated as |Bx1-Bx2| or proportional thereto, where Bx1 is measured at the first sensor location P1, and Bx2 is measured at the second sensor location P2. Looking back at the simulations of <FIG>, the inventors came to the insight that, even though the signal Bx (oriented in the radial direction) seems to be completely useless to determine the angular position, it can be very advantageously used to determine radial offset, which in turn allows to dynamically adjust the coefficients, which allows to improve the accuracy despite said radial offset.

In other words, it is an advantage of the method of <FIG> that it allows the effect of position offset (as was discussed in <FIG> to be mitigated. In this way, the accuracy of the position sensor system can be improved, and the mounting requirements can be relaxed, and the size of sensor device can be reduced (because ds<dt).

In a variant of the method of <FIG>, step a) comprises measuring magnetic field components at four different locations P1 to P4 (e.g. as shown in <FIG>), and determining magnetic field gradients, and determining the position based on these gradients (e.g. similar as described in the variant of <FIG>). This method not only offers the advantage of being highly insensitive to position offset, but also offers the advantage of being highly insensitive to an external strayfield.

<FIG> shows a flow-chart of a method <NUM> of determining a position (e.g. a linear or angular position) of a sensor device movable along a predefined path (e.g. linear or circular path) relative to a magnetic source, wherein the magnetic source comprises a first plurality N1 of magnetic pole pair arranged along a first track T1 having a first periodicity, and comprises a second plurality N2 of magnetic pole pairs arranged along a second track T2 having a second periodicity different from the first periodicity, and wherein centrelines <NUM>, <NUM> of the tracks T1, T2 are spaced apart by a predefined track distance "dt". This method can be seen as a special case of the method of <FIG>. The method <NUM> comprises the following steps:.

In an embodiment, step c) comprises calculating a first angle α1 and a second angle α2 using an arctangent function, and finding an overall angle α by resolving the ambiguity related to the first periodicity and the second periodicity.

In a variant of the method of <FIG>, step a) comprises measuring two orthogonal magnetic field components in at least four different sensor locations P1-P4, and determining magnetic field gradients; and step b) comprises: calculating a first and second set of quadrature signals based on these gradients. This method would be highly robust against an external disturbance field.

<FIG> shows a flow-chart of a method <NUM> of determining a position (e.g. a linear or angular position) of a sensor device movable along a predefined path (e.g. a linear or circular path) relative to a magnetic source, wherein the magnetic source comprises a first plurality N1 of magnetic pole pairs arranged along a first track T1 having a first periodicity, and comprises a second plurality N2 of magnetic pole pairs arranged along a second track T2 having a second periodicity different from the first periodicity, and wherein centrelines <NUM>, <NUM> of the tracks T1, T2 are spaced apart by a predefined track distance "dt". This method can be seen as a special case and/or as a variant or combination of the methods of <FIG>, <FIG> and <FIG>. The method <NUM> comprises the following steps:.

It is an advantage of this method that the set of coefficients is not fixed, but is dynamically adjusted, depending on the estimated transverse position. This offers the advantage of mitigating the effect of lateral offset (e.g. due to mechanical tolerances), and thus may the position error (e.g. as discussed in <FIG>).

It is noted that the transverse position need not be measured in each and every particular position, but is a long-term effect. It is therefore possible to determine the estimated transverse position "between" two actual position measurements, e.g. during an in-situ self-calibration-procedure or the like, optionally taking into account historical data, such as maximum signal values over the entire measurement range, or one or more of the above mentioned ratios (e.g. |Bx|/|Bz|, etc.). In other words, step b) and step c) need not necessarily be performed between step a) and step e), and step b) and step c) need not be performed every executing of the method of <FIG>, but may be skipped. Of course, if historical data is stored in the non-volatile memory, extra memory space needs to be allocated.

<FIG> shows a flow-chart of a method <NUM> of determining a position (e.g. a linear or angular position) of a sensor device movable along a predefined path (e.g. linear or circular path) relative to a magnetic source, wherein the magnetic source comprises a first plurality N1 of magnetic pole pairs arranged along a first track T1 having a first periodicity, and comprises a second plurality N2 of magnetic pole pairs arranged along a second track T2 having a second periodicity different from the first periodicity, and wherein centrelines <NUM>, <NUM> of the tracks T1, T2 are spaced apart by a predefined track distance "dt". This method can be seen as a special case of <FIG>, and/or as a variant or combination of the methods of <FIG>. The method <NUM> comprises the following steps:.

As mentioned above, it is not required to perform steps d) and e) each and every execution. It suffices for example to perform steps d) and e) only now and then (e.g. once every second, or once every minute, or even once every hour, depending on the application), because lateral offset is related to mispositioning, which is typically a long-term effect. Furthermore, it is not required that steps d) and e) are performed for each and every (linear or angular) position, but in some embodiments of the present invention, they are only executed within certain angular ranges, or at certain angular positions (with some tolerance margin).

Reference is made to <FIG> which is a duplicate of <FIG>, with information added. Indeed, when trying to find a solution to detect the radial offset, the inventors discovered that the simulation of <FIG> surprisingly also shows "unexpected regions" which seem to appear especially between the two circles defined by the first and second sensor location P1, P2. This was not at all expected. In fact, ten interesting angular locations are indicated by letters A to K, which may be particularly interesting for determining not only the presence but also the amount of radial offset based on the signal |Bx1-Bx2| or (Bx1-Bx2)/(Bx1+Bx2). Indeed, in locations A, B, C, D, the radial gradient should be approximately equal to zero, if the sensor device is not radially shifted (with respect its original position). If the sensor device is radially shifted inwards, the signal at the second (outer) sensor location P2 will be larger (in absolute value) than the signal at the inner sensor location P1. Likewise, if the sensor is shifted radially outwards, the signal at P2 will be smaller in absolute value than the signal at P1. Thus, at the angular locations A, B, C or D, the radial gradient dBx/dx is an excellent indicator for the radial shift of the sensor device. More in particular: (i) comparing this magnitude with a predefined threshold can be used to detect radial shift, (ii) the sign of dBx/dx is an indicator for the direction of the radial shift of the sensor device (inwardly or outwards), (iii) and the amplitude of dBx/dx, or the relative amplitude (Bx1-Bx2)/(Bx1+Bx2) is an indicator for the amount of radial shift. But the locations A, B, C, D may not be the only interesting locations, since also at the angular locations F, G, H, I the amplitude of the radial gradient will strongly vary in case of radial shift. Thus in these locations, the radial gradient dBx/dx or the relative gradient may also be used to determine the amount of radial shift of the sensor device. The angular locations E and K may also be used, but seem less useful than the the other angular positions. It is of course also possible to combine the information obtained from various angular locations in order to determine the radial offset. Referring back to <FIG>, it can now be better understood that in a particular embodiment of this method, step d) comprises making use of the radial signal Bx, or of the spatial gradient of that signal dBx/dx or of the ratiometric signal (Bx1-Bx2)/(Bx1+Bx2).

For completeness it is repeated that the signal dBx/dx is not the only possible way to determine radial offset of the sensor device, and there may be other ways to determine radial offset, as already stated above, e.g. based on on the ratio, or the maximum ratio of the signals By, Bz.

<FIG> shows an angular position sensor system 1500a comprising a magnetic source 1510a comprising two concentric tracks located in a single plane, and a sensor device 1520a arranged above or below that plane. In the example, the first track T1 is formed by an inner ring having eight pole pairs, and the second track T2 is formed by an outer ring having ten pole pairs. These rings are preferably axially magnetized. The sensor device "sees" eight poles when moving over the inner ring, and "sees" ten poles when moving over the outer ring (or when the sensor device is stationary and the magnetic source is rotated). The centrelines <NUM>, <NUM> of these tracks are two concentric circles having a different radius. The centrelines <NUM>, <NUM> are spaced apart by a track distance "dt" in the radial direction. The distance between the sensor locations P1 and P2 of the sensor device is "ds", which is smaller than the track distance "dt", preferably at least <NUM>% smaller. The first and second sensor location P1, P2 are preferably located on a virtual line X which is radially oriented with respect to the magnetic source. There may be an uncoded region, e.g. in the form of a circular groove situated between the tracks T1, T2, optionally filled with a non-magnetic material.

<FIG> shows an angular position sensor system 1500b comprising a magnetic source 1510b comprising two cylindrical tracks having a same radius, and a sensor device 1520b arranged as a satellite movable around these cylindrical tracks (or vice versa). The centrelines <NUM>, <NUM> of the first and second track T1, T2 is a first circle and a second circle, a portion of which is shown in <FIG>. These centrelines <NUM>, <NUM> are spaced apart by a track distance "dt" in the axial direction A. There may be an uncoded region, e.g. in the form of a circular groove situated between the tracks T1, T2, optionally filled with a non-magnetic material.

<FIG> shows a linear position sensor system 1500c comprising a magnetic source 1510c comprising two parallel, linear tracks T1, T2 located in a single plane, and a sensor device 1520c arranged above or below that plane. Also shown is an orthogonal coordinate system connected to the magnetic source, comprising a height direction H, a longitudinal direction L, and a transverse direction T. In the example shown, the first track T1 is formed by a first multi-pole magnet having eight pole pairs, and the second track T2 is formed by a second multi-pole magnet having ten pole pairs. These magnets are preferably magnetized in the height direction H. The sensor device 1520c "sees" eight poles (four North poles and four south poles) of the first track T1, and ten poles of the second track T2, when moving over the magnetic structure in the longitudinal direction L (or vice versa). The centrelines <NUM>, <NUM> of these tracks are two parallel lines, spaced apart by a track distance "dt" in the transverse direction T. There may be an uncoded region, e.g. in the form of a circular groove situated between the tracks T1, T2, optionally filled with a non-magnetic material.

The position sensor systems of <FIG> are of course only examples, and the present invention is not limited thereto, but only by the claims. For example, the number of pole pairs of each track may be different from those illustrated in the examples, and the sensor device may have other sensor structures, e.g. as illustrated in <FIG>, or other suitable sensor structures.

Claim 1:
A position sensor system (1500a; 1500b; 1500c) for determining a position of a sensor device (1520a; 1520b; 1520c) movable along a predefined path relative to a magnetic source (1510a; 1510b; 1510c) or vice versa, the position sensor system comprising:
- said magnetic source (1510a; 1510b; 1510c) comprising a first plurality (N1) of magnetic pole pairs arranged along a first track (T1) having a first periodicity or pole distance, and comprising a second plurality (N2) of magnetic pole pairs arranged along a second track having a second periodicity different from the first periodicity, wherein a centreline (<NUM>) of the first track (T1) is spaced from a centreline (<NUM>) of the second track (T2) by a predefined track distance (dt), and wherein the first magnetic track (T1) is spaced from the second magnetic track (T2) by a non-coded region;
- said sensor device (1520a; 1520b; 1520c) being configured for measuring a first set of at least two orthogonal magnetic field components (By1, Bz1; By1, Bx1, Bz1) at a first sensor location (P1), and for measuring a second set of at least two orthogonal magnetic field components (By2, Bz2; By2, Bx2, Bz2) at a second sensor location (P2), wherein the first sensor location (P1) is spaced from the second sensor location (P2) by a predefined sensor distance (ds) smaller than the predefined track distance (dt), in a direction transverse to the tracks (T1, T2);
and wherein a projection of one or both of the first and second sensor position (P1, P2) is located vertically above said non-coded region;
and wherein the sensor device (1520a; 1520b; 1520c) further comprises a processing unit (<NUM>) configured for determining said position based on at least some of the measured signals (By1, Bz1, By2, Bz2).