阅读说明：本技术 多极磁体、制造多极磁体的方法和包含其的传感器系统 (Multi-pole magnet, method of manufacturing multi-pole magnet, and sensor system including the same ) 是由 Y·比多 于 2019-06-11 设计创作，主要内容包括：一种多极磁体形式的永磁体(101),包括具有中心轴(A)的各向同性磁性材料,其被磁化使得在虚拟圆(c)上考虑的磁场基本上位于与圆相切的虚拟平面(ε)中,并且根据圆上的位置在该虚拟平面内旋转。一种制造磁体的方法(1300),包括：a)提供包含各向同性磁性材料的成形体；b)提供至少四个电导体段；c)同时使电流在每个导体段中流动。以这种方式制造的磁体。使用此类磁体以用于角位置感测。一种角位置传感器系统(100),包括此类磁体。(A permanent magnet (101) in the form of a multipole magnet, comprising an isotropic magnetic material having a central axis (a), which is magnetized such that a magnetic field considered on a virtual circle (c) lies substantially in a virtual plane (epsilon) tangential to the circle and rotates in this virtual plane depending on the position on the circle. A method (1300) of manufacturing a magnet, comprising: a) providing a shaped body comprising an isotropic magnetic material; b) providing at least four electrical conductor segments; c) while allowing current to flow in each conductor segment. A magnet manufactured in this manner. Such magnets are used for angular position sensing. An angular position sensor system (100) comprising such a magnet.)

1. Permanent magnet in the form of a multipole magnet (101)

It is characterized in that the preparation method is characterized in that,

-the magnet comprises an isotropic magnetic material;

-the magnet has an axis (a);

the magnet is magnetized such that it creates a residual magnetic field (B) located, for each point (p) of an imaginary circle (c) lying in a plane (λ) perpendicular to the axis (A) and having a center (m) substantially on the axis (A), substantially in a virtual plane (ε) tangent to the imaginary circle in the point (p) and parallel to the axis (A), the magnetic field (B) further defining an angle (β) with respect to the plane (λ) containing the circle (c), the angle (β) rotating as a function of the position (θ) of the point (p) on the imaginary circle (c).

2. The permanent magnet according to claim 1, wherein,

wherein the magnet has an opening or cut-out with a tubular shape;

and wherein said imaginary circle (c) is defined as a cross-section of said plane (λ) perpendicular to said axis (A), and said tubular shape.

3. The permanent magnet according to claim 2, wherein,

wherein the tubular opening or the tubular cut is a cylindrical through hole or a conical through hole or a cylindrical cut or a conical cut.

4. The permanent magnet according to claim 1, wherein,

wherein said angle (β) rotates monotonically as a function of said position (θ) of said point (p) on said imaginary circle (c); or

Wherein said angle (β) is substantially linearly rotated as a function of said position (θ) of said point (p) on said imaginary circle (c).

5. The permanent magnet according to claim 1, wherein,

wherein the remanent magnetic field (B) has a magnetic field component (Br)_x，Br_y，Br_z) The magnetic field component at a point located on the circular cross-section may be represented or approximated by the following set of equations or an equivalent set of equations:

wherein N is an integer value of at least 4, Br_x、Br_yAnd Br_zRespectively the x-component, y-component and z-component, Br, of the remanent magnetic field_{All the same property}Is the magnitude of the remanent magnetic field, and θ is the angle around the axis.

6. The permanent magnet according to claim 1, wherein,

wherein the outer surface of the permanent magnet has a circular or regular polygonal cross-section with the plane (λ) containing the virtual circle (c), such as a square or a hexagon or an octagon.

7. A method of manufacturing a permanent magnet in the form of a multi-pole magnet having an axis (a), the multi-pole magnet having a plurality (N) of at least four poles as seen from a point on the axis (a);

the method comprises the following steps:

a) providing a shaped body comprising or consisting of an isotropic magnetic material, the shaped body having an axis (a) and a center (c);

b) providing a number (N) of at least four electrical conductor segments (c1, c2, c3, c4) arranged in a plane (δ) perpendicular to said axis (a), said conductor segments being radially oriented with respect to said axis (a) and angularly spaced by 360 ° divided by said number (N) of angles;

c) simultaneously applying or inducing or otherwise causing a current to flow through each of the plurality of conductor segments, the current in even conductor segments flowing toward the axis (A), the current in odd conductor segments flowing out of the axis (A).

8. The method of claim 7, wherein the first and second light sources are selected from the group consisting of,

wherein the shaped body provided in step a) further comprises a plurality of radially oriented grooves for receiving the electrical conductor segments;

and wherein step b) further comprises: inserting the plurality of electrical conductor segments at least partially into the recess.

9. A sensor system (100) comprising:

a permanent magnet according to claim 1;

a sensor device (102) arranged at an axial distance (dz) from the magnet and at a radial offset (dr) from the axis (A) and adapted to determine at least one magnetic quantity (Bx, By, Bz) or at least one derived quantity (dBx/dx, dBx/dy, dBy/dx, dBy/dy, dBz/dx, dBz/dy) or at least one magnetic field gradient created By the magnet.

10. The sensor system (100) of claim 9,

-wherein the sensor device (102) comprises at least three magnetic sensor elements (804) lying in a plane perpendicular to the axis (a) of the magnet, the at least three magnetic sensor elements being non-collinear.

11. The sensor system (100) of claim 9,

-wherein the sensor system (1) is an angular position sensor system.

12. The sensor system of claim 11, wherein the sensor system,

-wherein the sensor device (102) is adapted to determine one or more field gradients (dBx/dx, dBx/dy, dBy/dx, dBy/dy, dBz/dx, dBz/dy) of the magnetic field created by the magnet in a plane perpendicular to the axis (a) and to determine an angular position (θ) of the sensor device (102) relative to the permanent magnet based on the field gradients.

13. The sensor system of claim 11, wherein the sensor system,

wherein the angular position is calculated based on the following equation or an equivalent equation:

wherein N is an even integer of at least 4, θ_mIs a calculated angular position of the sensor device (102) relative to the magnet (101), and wherein dBx/dy, dBy/dx, dBx/dx and dBy/dy are in-plane field gradients.

14. The sensor system of claim 11, wherein the sensor system,

wherein the permanent magnet (101) further comprises two perpendicularly magnetized dipoles arranged on opposite sides of the isotropic magnet for allowing determination of an angular position within a range of 360 °.

Technical Field

The present invention relates generally to the field of multi-pole permanent magnets, methods of making them, and sensor systems, particularly angular position sensor systems, incorporating them.

Background

Sensor systems, in particular linear or angular position sensor systems, are known in the art. In such systems, a non-uniform magnetic field is typically generated (e.g., by a static current, or by a permanent magnet) and measured by a sensor device that includes one or more sensor elements and readout circuitry and a processor that calculates a linear or angular position based on the measurements.

Various sensor arrangements and various techniques for determining angular position are known in the art, each having its advantages and disadvantages, e.g., in terms of cost, compactness, angular range, accuracy, signal sensitivity, robustness to unwanted external fields, robustness to position errors (e.g., axial distance and/or radial offset), processing complexity, etc.

For example, US2002021124a1 describes a sensor for detecting the direction of a magnetic field using a magnetic field concentrator and a horizontal Hall effect (Hall-effect) element.

WO9854547a1 describes a magnetic rotation sensor with four sensor elements arranged in the vicinity of a two-pole magnet. The angular position is calculated as an arctangent (arctan) function of the ratio of the differential signals. This arrangement is said to be robust to offset and sensitivity variations and to constant external magnetic fields.

WO2014029885a1 describes a sensor arrangement for measuring absolute angular position using a multi-pole magnet. Some embodiments described herein are highly robust to position errors, and/or to constant external magnetic fields, and/or to constant external field gradients, for example by using more complex algorithms, and/or by using more complex magnets and/or by using a larger number of sensor elements.

There is always room for improvement or replacement.

Disclosure of Invention

It is an object of embodiments of the present invention to provide a permanent magnet suitable for use in an angular position sensor system, as well as a method of manufacturing such a magnet, as well as a magnet manufactured according to such a method, and a position sensor system comprising such a magnet.

It is a particular object of embodiments of the present invention to provide a sensor system (e.g. an angular position sensor system) that is highly robust or more robust to position errors (e.g. axial distance and/or radial off-axis position deviations relative to the magnet) and/or to position error drift over time.

It is also an aim of embodiments of the present invention to provide a sensor system that is more accurate (for a given axial distance and/or radial offset) over the lifetime of the sensor system (compared to prior systems), despite mechanical drift (change in position), and/or the presence of vibrations.

It is an aim of particular embodiments of the present invention to provide an angular position sensor system comprising a multi-pole ring magnet and a sensor device in which position errors (e.g. axial displacement and/or radial offset) of the sensor device and the ring magnet due to mechanical drift and/or mechanical wear and/or mechanical vibrations are reduced.

These objects are achieved by a multi-pole permanent magnet, and a method of manufacturing such a magnet, and a magnet manufactured by such a method, and by a sensor system comprising such a magnet according to embodiments of the present invention.

According to a first aspect, the present invention provides a permanent magnet in the form of a multi-pole magnet, wherein the magnet comprises an isotropic magnetic material; the magnet has a shaft; the magnet is magnetized such that the magnet creates a remanent magnetic field that, for each point of an imaginary circle lying in a plane perpendicular to said axis and having a center lying substantially on said axis, lies substantially in a virtual plane tangent to said virtual circle in said point and parallel to said axis, the magnetic field further defining an angle relative to a plane containing the circle, the angle rotating as a function of the position of the point on the imaginary circle.

Preferably, the multipole magnet is at least a quadrupole as seen from a point on said axis, at a distance (e.g. about 1.5mm) from the magnet.

The axis is preferably the central axis of the magnet.

Although ideally the magnetic field vector lies exactly in a virtual plane tangential to the virtual circle, in practice there will always be some deviation. Wherein "substantially in a virtual plane tangential to said virtual circle" means that the orientation of the actual magnetic field vector makes an angle with the tangential plane of less than 30 °, or less than 25 °, or less than 20 °, or less than 15 °, or less than 10 °, or less than 5 °.

The magnet has the advantage of generating a more uniform or more ideal signal, allowing a sensor system comprising the magnet to be more robust to position errors of the sensor device relative to the magnet, and to aging effects (such as mechanical wear) and to vibrations.

More specifically, such a magnet is advantageous in that it provides a magnetic field having a substantially constant in-plane field gradient (at least in a cylindrical space at a relatively small distance from the magnet and close to the axis). Such magnets are ideally suited for use in linear sensors or angle sensor systems, having reduced sensitivity to axial distance changes ("air gaps") and/or radial offsets ("off-axis").

Wherein "the magnetic field is in a plane" means that the "magnetic field vector" is in the plane.

In an embodiment, the magnet is made of an isotropic magnetic material, or is made entirely of an isotropic magnetic material. Magnets made from a single material are easier to manufacture. The material may be, for example, neodymium or ferrite, but other isotropic magnetic materials may also be used.

In an embodiment, the magnetic field is rotationally symmetric around an axis, wherein the period is 360 °/2-180 °, or wherein the period is 360 °/3-120 °, or wherein the period is 360 °/4-90 °, or typically a period of 360 °/N, wherein N is an integer value equal to 2 or 3 or 4 or 5 or 6. For example, a so-called "quadrupole ring magnet" or "quadrupole disk magnet" has a rotational symmetry of 180 °/2, since the magnetic field (as seen by a sensor device located near the axis) will look the same if the ring magnet is rotated 180 ° around its axis. For a six-pole magnet, the period would be 120 °, and so on.

In an embodiment, the magnet has an opening or cut-out having a tubular shape; and an imaginary circle is defined as a cross-section of the plane perpendicular to the axis, and the tubular shape. Wherein "cut-out" means, for example, a blind hole. Wherein "opening" refers to a through hole.

In an embodiment, the tubular opening or cut-out is a surface of revolution about the axis.

In an embodiment, the tubular opening or the tubular cut is a cylindrical through hole or a conical through hole or a cylindrical cut or a conical cut. The use of cylindrical or conical cut-outs or through-holes is advantageous, since such openings or cut-outs can be easily manufactured, for example, by drilling or milling.

In an embodiment, the angle is monotonically rotated as a function of the position of the point on the imaginary circle.

In an embodiment, the angle is substantially linearly rotated as a function of the position of the point on the imaginary circle. An advantage of the magnet is that the angle β rotates substantially linearly as a function of the angular position θ, since this is easier to calculate, for example using a "linear interpolation" of the table data rather than using a goniometric function. This generally means that with a given code size or a given table size a higher accuracy can be achieved.

In an embodiment, the remanent magnetic field has a magnetic field component that at a point located on said circular cross-section may be represented by the following set of equations or an equivalent set of equations:

wherein N is an even integer of at least 4 (e.g. N-4, or N-6, or N-8), Br_x、Br_yAnd Br_zRespectively the x-component, y-component and z-component, Br, of the remanent magnetic field_{All the same property}Is the magnitude of the remanent magnetic field and theta is the angle around the axis.

In an embodiment, N is equal to 4, in which case the magnetization can be represented by the following formula:

note that, in this case, the speed of change of the angle β between the magnetic field vector B and the plane λ is twice the angular position θ of the point p on the imaginary circle c.

In an embodiment, the outer surface of the permanent magnet has a circular or regular polygonal cross-section with a plane containing a virtual circle, such as a square or a hexagon or an octagon. The outer surface may be a cylindrical surface, or a conical surface, or a pyramidal surface.

According to a second aspect, the present invention provides a method of manufacturing a permanent magnet in the form of a multi-pole magnet having an axis, the multi-pole magnet having a plurality of at least four poles, as seen from a point on the axis; the method comprises the following steps: a) providing a shaped body comprising or consisting of an isotropic magnetic material, the shaped body having an axis and a center; b) providing a number of at least four electrical conductor segments arranged in a plane perpendicular to the axis, the conductor segments being radially oriented with respect to the axis and angularly spaced 360 ° apart by the number of angles; c) simultaneously applying or inducing or otherwise causing a current to flow through each of the plurality of conductor segments, the current in even conductor segments flowing to the axis, the current in odd conductor segments flowing out of the axis.

Preferably, the currents have substantially equal amplitudes, for example at least 1kA, or at least 2kA, or at least 5kA, or at least 10kA, or at least 20kA, or at least 30kA, or at least 40kA, or at least 50kA, or at least 60 kA.

The plane is preferably located at a distance of at most 5.0mm, preferably at most 4.0mm, or at most 3.0mm, or at most 2.0mm from the surface of the shaped object.

To produce a quadrupole magnet (N ═ 4), four conductor sections at 90 ° intervals can be used.

To produce a six-pole magnet (N ═ 6), six conductor segments spaced 60 ° apart may be used, and so on.

In an embodiment, the shaped body provided in step a) further comprises a plurality of radially oriented grooves for receiving said electrical conductor segments; and step b) further comprises: inserting a plurality of electrical conductor segments at least partially into the recess.

According to a third aspect, the invention also provides a permanent magnet manufactured or manufacturable by the method according to the second aspect.

In an embodiment, the magnet is a multi-pole ring magnet that creates a magnetic field that is oriented in the positive Z-axis direction in two angular positions; and the magnetic field is oriented in the negative Z-axis direction in two angular positions; and the magnetic field is oriented in a positive X-axis direction in an angular position; and the magnetic field is oriented in a negative X-axis direction in an angular position; and the magnetic field is oriented in a positive Y-axis direction in an angular position; and the magnetic field is oriented in a negative Y-axis direction in an angular position, wherein X, Y and the Z-axis are orthogonal axes of a cartesian coordinate system, the Z-axis coinciding with the magnet axis at a central position of the cartesian coordinate system.

According to a fourth aspect, the invention also provides a sensor system comprising: the permanent magnet according to the first or third aspect; a sensor device arranged at an axial distance from the magnet and radially offset from the axis and adapted to determine at least one magnetic quantity or at least one derived quantity created by the magnet.

The use of a permanent magnet is advantageous because it allows the magnetic field to be created in a passive manner, i.e. without consuming power.

The advantage is that the sensor system is more robust to mechanical drift than a sensor system with "perpendicularly magnetized anisotropic permanent magnets".

An advantage is that for a given radial offset and/or axial distance, the error is reduced compared to a sensor system with a "perpendicularly magnetized anisotropic permanent magnet".

The magnetic quantity may be, for example, a magnetic field component Bx or By or Bz (in an orthogonal axis system) or Br (radial component) or Bt (tangential component, perpendicular to the radial component). The derived magnetic value may for example be a magnetic field gradient, more specifically a spatial field gradient measured in a plane perpendicular to the axis. The "at least one derived quantity" may for example be one or more or all of the following spatial field gradients: dBx/dx, dBx/dy, dBy/dx and dBy/dy. The sensor system may be, for example, a linear position sensor system or an angular position sensor system. Preferably, the sensor device is an Integrated Chip (IC) containing a semiconductor device (e.g. a CMOS device).

In an embodiment, the sensor device comprises at least three magnetic sensor elements located in a plane perpendicular to the axis of the magnet, the at least three magnetic sensor elements being non-collinear.

In an embodiment the sensor device comprises at least four sensor elements located on a circle, for example as described in WO2014029885a1, but the invention is not limited to such sensor devices and other sensor devices capable of measuring in-plane field gradients and deriving angular positions therefrom may also be used.

In an embodiment, the sensor device comprises at least two sets of at least three magnetic sensor elements, the at least three magnetic sensor elements of each set being non-collinear. An advantage of this embodiment is that the sensor device provides redundancy allowing fault detection or even fault correction.

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

In an embodiment, the sensor device is adapted to determine one or more field gradients of the magnetic field generated by the magnet in a plane perpendicular to the axis, and to determine the angular position of the sensor device relative to the permanent magnet based on said field gradients.

In an embodiment, the angular position is calculated based on the following equation or an equivalent equation:

where N is an even integer of at least 4 (e.g. N-4, or N-6, or N-8), θ_mIs a calculated angular position of the sensor device (102) relative to the magnet (101), and wherein dBx/dy, dBy/dx, dBx/dx and dBy/dy are in-plane field gradients.

In an embodiment, N is equal to 4, in which case the angular position may be calculated by the following equation or an equivalent:

in an embodiment, the permanent magnet further comprises two perpendicularly magnetized dipoles arranged on opposite sides of the isotropic magnet for allowing determination of an angular position within a 360 ° range. This embodiment combines the advantages of the present invention with the "angular range extension principle" described in EP3321638(a1), overcoming the inherent 180 ° range limitation of a quadrupole or the inherent 120 ° range limitation of a hexapole magnet.

According to a fifth aspect, the invention also relates to the use of a magnet as described above for angular position sensing.

Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and features of other dependent claims as appropriate and not merely as explicitly set out in the claims.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiment(s) described hereinafter.

Drawings

Fig. 1 shows a multi-pole ring magnet according to an embodiment of the invention, and shows a sensor system according to an embodiment of the invention, comprising the magnet and a sensor device.

Fig. 1(a) partially shows a top view of a ring magnet having a shaft and four poles, as seen from a point on the shaft. The magnetization of this magnet is better shown in part (c) of fig. 6.

Fig. 1(b) partially shows a side view of the quadrupole ring magnet of part 1(a) arranged relative to a sensor device located at an axial distance dz from the ring magnet and at a radial offset dr from the central axis of the ring magnet.

Fig. 2(a) partially shows a classic ring magnet made of anisotropic magnetic material, which is axially magnetized (also referred to herein as "perpendicular magnetization").

Part (b) of fig. 2 is a computer plot showing the magnitude of the Z component of the remanent magnetic field of the magnet of part (a) of fig. 2.

Fig. 2(c) section shows mathematical formulas describing X, Y and the magnetic field components in the Z direction of the axially magnetized anisotropic magnet shown in fig. 2(a) section.

Fig. 3 shows a simulated plot of the magnetic field values Bx, By, Bz of the magnetic field generated By the axially magnetized anisotropic magnet shown in part (a) of fig. 2, as may be measured in a plane located at 1.5mm from the magnet, and also shows the spatial field gradients dBx/dx, dBx/dy, dBy/dx, dBz/dy, dBz/dx derived therefrom.

Fig. 4(a) partially shows the arrangement (in top view) of a jig comprising a ring magnet made of isotropic magnetic material, thereby illustrating a method of manufacturing a magnet according to an embodiment of the present invention.

Fig. 4(b) partially shows the arrangement of fig. 4(a) in a side view.

Fig. 4(c) section shows mathematical formulas describing X, Y and remaining magnetic field components in the Z direction of the isotropic magnet shown in fig. 4(a) section and fig. 4(b) section.

Fig. 4(d) partially shows a mathematical formula that can be used to calculate the angular position of the sensor device relative to the magnet based on the in-plane field gradient.

Fig. 5 shows a simulated plot of the magnetic field values Bx, By, Bz for an isotropic magnet magnetized according to the method shown in part (a) of fig. 4 and part (b) of fig. 4.

Fig. 6 shows a 3D representation of the magnetic field generated by a ring magnet magnetized as shown in part (a) of fig. 4, corresponding to the 2D representation shown in fig. 5.

Fig. 6(a) and 6(b) show a ring magnet having a central axis a, and a virtual circle having its center on the axis, and a point on the circle, and a plane parallel to the axis a and tangential to the virtual circle containing the point, and a magnetic field vector lying in the tangential plane.

Part (c) of fig. 6 shows several points on a virtual circle and shows how the magnetic field vector "rotates" in the tangential plane as the points move along the circle, or for different points on the circle.

Part (d) of fig. 6 shows the magnetic field vectors in eight specific locations spaced 45 ° apart on the ring magnet of part (a) of fig. 6.

Part (e) of fig. 6 is a 2D representation showing how the magnetic field vector of the magnet of part (a) of fig. 6 "rotates" in the tangential plane as a function of angular position.

Part (f) of fig. 6 is a 2D representation similar to part (e) of fig. 6, but for comparison with the perpendicular magnetization anisotropic magnet of fig. 2.

Fig. 7 shows a simulated plot of the magnetic field values Bx, By, Bz of the isotropic magnet proposed By the present invention, magnetized as shown in fig. 4, and having the same dimensions as the magnet in fig. 3, as can be measured in a plane located at 1.5mm from the magnet, and also showing the spatial field gradients dBx/dx, dBx/dy, dBy/dx, dBz/dy, dBz/dx derived therefrom.

Part (a) of fig. 8 is a grayscale version of an enlarged view of plot dBx/dy of fig. 7, a so-called "isotropic magnet with rotating magnetic field", according to an embodiment of the invention. The four white dots represent sensor elements of the sensor device, which may be arranged with respect to the magnets in the central circular area, but with a certain radial offset.

Part (b) of fig. 8 is a schematic representation of the relative positions of a magnet and a sensor apparatus comprising a two or three sensor arrangement, as may be used in some embodiments of the present invention.

Part (a) of fig. 9 shows the magnet part of part (b) of fig. 6 arranged relative to the sensor device. (only a portion is shown for illustrative purposes).

Part 9(B) and part 9(d) show computer simulations of the magnitude | B | of the magnetic field of the "anisotropic quadrupole ring magnet with perpendicular magnetization" of fig. 2 in color and grey scale, respectively. As can be seen, the field is equally strong at the bottom and at the top.

Part 9(c) and part 9(e) show computer simulations of the magnitude | B | of the magnetic field of an "isotropic quadrupole ring magnet with rotating magnetic field" as in fig. 4 to 8 in color and grey scale, respectively. As can be seen, the field is stronger at the bottom than at the top.

Fig. 9(f) shows a comparison of the field By along the X-axis for the anisotropic magnet of fig. 9(b) and 9(d) and the isotropic magnet of fig. 9(c) and 9 (e).

Fig. 10 shows a simulation of the maximum position error (over an angular range) for the sensor system of fig. 1 when using an exemplary "anisotropic quadrupole ring magnet with perpendicular magnetization" (curve with squares) with an outer diameter of 14mm compared to using an "isotropic ring magnet with rotating magnetization" (curve with triangles) as proposed by the present invention for a radial offset of 1.4mm and various axial positions (air gaps) ranging from 1.5mm to 4.5 mm.

Fig. 11 shows the maximum position error (over a range of angles) for the sensor system of fig. 1 when using the exemplary "anisotropic quadrupole ring magnet with perpendicular magnetization" (curve with squares) with an outer diameter of 14mm compared to using the "isotropic quadrupole ring magnet with rotating magnetization" (curve with triangles) as proposed by the present invention for an axial distance of 1.5mm and various radial offsets ranging from 0.2mm to 2.0 mm.

Fig. 12 shows several alternative shapes of "isotropic magnets with rotating magnetic field" that may be used in embodiments of the present invention. Only a portion of the magnets are shown for illustrative purposes. In part (a) of fig. 12, the magnet is a ring-shaped magnet having a cylindrical through hole and a cylindrical outer wall. In part (b) of fig. 12, the magnet is a ring-shaped magnet having a conical through-hole and a cylindrical outer wall. In part (c) of fig. 12, the magnet has a cylindrical through-hole in a beam-shaped (beam-shaped) object having an outer surface with a square section. In part (d) of fig. 12, the magnet has a conical through-hole in a beam-shaped object having an outer surface of a square section. In part (e) of fig. 12, the magnet is a disk-shaped magnet having a central cutout in the form of a cylinder. In part (f) of fig. 12, the magnet has a cylindrical through hole with a first diameter and has a concentric cut with a second diameter. In part (g) of fig. 12, the magnet is a disk-shaped magnet without a central opening or cutout.

The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Any reference signs in the claims shall not be construed as limiting the scope. The same reference numbers in different drawings identify the same or similar elements.

Detailed Description

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and relative dimensions do not correspond to actual reductions to practice of the invention.

Moreover, the terms first, second, and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence temporally, spatially, in ranking, or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Furthermore, the terms top, bottom and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term 'comprising', used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Accordingly, the terms are to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but do not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "an apparatus comprising means a and B" should not be limited to an apparatus consisting of only components a and B. This means that for the present invention, the only relevant components of the device are a and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as will be apparent to one of ordinary skill in the art from this disclosure.

Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, although some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are intended to fall within the scope of the invention and form different embodiments as would be understood by those of skill in the art. For example, in the appended claims, any of the claimed embodiments may be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

In this context, the expression "perpendicularly magnetized ring magnet" means the same as "axially magnetized ring magnet", as shown for example in part (a) of fig. 2.

The present invention relates to a permanent multipole magnet for a sensor system, for example for an angular position sensor system 100, and to a method of manufacturing such a magnet, and to a magnet manufactured using such a magnet, and to a sensor system comprising such a permanent multipole magnet and a sensor device arranged at a distance from the magnet.

The sensor system 100 may be a linear position or angular position sensor system comprising a multi-pole ring-shaped or disc-shaped magnet 101 and comprising a sensor device 102, for example in the form of an integrated circuit, comprising at least three or at least four sensor elements 804 for measuring one or more values of a magnetic field generated by a permanent magnet and/or for measuring or calculating values derived therefrom (e.g. the field gradient may be measured by a differential circuit or may be calculated by adding or subtracting several values (analog or digital)). The sensor device 102 also typically includes a processor for calculating a linear or angular position based on those measurements and/or calculations, although such processing is not the primary focus of the present invention.

As alluded to in the background section, it is highly desirable to construct a sensor system 100 that enables the sensor system 100 to measure values (e.g., linear or angular position values) with high accuracy in the following manner: is highly robust to positional shifts, e.g. of the sensor device 102 relative to the magnet 101, and to sensitivity variations, e.g. absolute magnetic field strength, and to disturbing fields, in particular constant external magnetic fields, i.e. having constant amplitude and orientation, and preferably also constant field gradients. There are many sensor systems in the prior art that address some of these requirements.

As the size of the assemblies continues to decrease (e.g., for ring magnets having outer diameters of less than 30mm, or less than 25mm, or less than 20mm, or less than 15 mm), the difficulty of properly positioning the assemblies that are movable relative to each assembly in an economical manner is increasing, particularly in a manufacturing environment. It is a major challenge to envisage or develop sensor systems or sensor arrangements that are highly insensitive to position errors (e.g. the axial distance between the magnet and the sensor device, herein also referred to as "axial distance" or "air gap", and/or highly insensitive to the radial distance with respect to variations in the magnet axis, herein also referred to as "radial offset" or "off-axis"). However, such a sensor system will be easier to install, since tolerances can be relaxed.

Creating a sensor system that is robust to mechanical drift over the lifetime of the sensor system is even more challenging. Although initial installation errors due to misalignment of the sensor device and the magnet can be handled by calibration tests during manufacture, where values (related to a particular offset) are measured and stored in the sensor device for later use and angular correction in application, this solution does not work anymore if one or both of the axial distance "dz" and/or the radial offset "dr" drift over time (e.g. due to mechanical drift or wear, or due to vibrations). The known solutions using calibration cannot be used anymore because the offset position is unknown.

The inventors of the present invention faced the problem of designing a sensor system (and its components) that is more robust to positioning errors, preferably without significantly reducing the accuracy of the sensor system and/or preferably without significantly reducing the robustness to (unwanted) constant external fields and/or preferably without reducing the robustness to (unwanted) external field gradients.

The inventors have conceived to provide a sensor system 100 (see fig. 1), which sensor system 100 comprises a sensor device 102 and a multipole magnet 101, which multipole magnet 101 comprises or consists of an isotropic magnetic material, which is magnetized in a very specific manner. The sensor device 102 is arranged at a distance (e.g. from about 0.5mm to 5.0mm, for example at about 1.5mm) from the multi-pole magnet 101 and is adapted to measure or determine at least one quantity of the magnetic field and/or to measure or determine a value derived therefrom, such as an in-plane magnetic field component Bx, By, or an out-of-plane field component Bz, or an in-plane field gradient dBx/dy, dBy/dx, dBx/dx, dBy/dy, dBz/dx, dBz/dy or an out-of-plane gradient dBz/dz, dBx/dz, dBy/dz or combinations thereof.

More specifically, as will be explained in more detail in fig. 6, the magnet has a central axis a and is magnetized such that, for each point p of an imaginary circle c lying in a plane λ perpendicular to said axis a and having a center m substantially on said axis a, a magnetic field vector B lies in a virtual plane epsilon tangent to said virtual circle c in the point p and parallel to said axis a, the magnetic field vector B further defining an angle β with respect to the plane λ containing the circle, the angle β rotating as a function of the position θ of the point p on the imaginary circle c. This is visualized in fig. 6(c) and 6 (d).

Simulations have shown that, surprisingly, the magnetic field causes at least some of the above-mentioned magnetic quantities to be significantly more uniform or more constant in a limited space in the vicinity of the magnet, more specifically, the cylindrical region has a radius of less than 15mm, or less than 10mm, or less than 5.0mm, or less than 4.0mm, or less than 3.0mm, or less than 2.0mm, or less than 1.5mm, or less than 1.0mm, within a cylindrical space located at a distance dz in the range of from about 0.5mm to about 8.0mm, or in the range of about 1.0mm to about 5.0mm from the magnet. As shown in fig. 7 (bottom left), the results were actually surprising. Apart from the fact that it is even possible to produce a magnetic field with a "rotation vector" as described above (fig. 6b), the fact that the resulting in-field gradients dBx/dy and dBy/dx are very constant (see fig. 7 bottom left and fig. 8) is unexpected. Furthermore, as will be described in more detail in section (e) of fig. 9, it is another surprise that the "rotating magnetic field" also provides an amplifying effect at the bottom side of the magnet. This is also unexpected.

It is expressly noted that the principles of the present invention do not require a specific sensor device, but will work with any sensor device 102 capable of measuring and/or processing in-plane field gradients to determine linear or angular position.

By way of example only, and without the invention being limited thereto, a sensor device 102 as may be used in embodiments of the present invention may comprise a plurality of vertical hall elements arranged around a circle and oriented for measuring a radial field component Br, or a plurality of vertical hall elements arranged around a circle and oriented for measuring a tangential field component Bt, or a plurality of horizontal hall elements with IMC for measuring a radial or tangential field component Br, Bt or another in-plane field component Bx, By, or other suitable sensor elements, for example as described in WO2014029885a1, the entire content of which is incorporated herein By reference; and includes circuitry or a processor for calculating a linear or angular position based on the measured values, for example using an arctan or arctan2 function (also known as an arctangent function), or using a fourier or inverse fourier transform, or using any other suitable mathematical function or algorithm.

For completeness, when it is mentioned herein that the magnetic field has N poles, it is in fact meant that when the sensor device 102 is arranged on or at a (relatively small) radial distance "dr" from the axis "a" and at an axial distance "dz" from the magnet (as shown in fig. 1), N poles can be "seen" or measured or experienced. Thus, for example, the so-called "axially magnetized anisotropic ring magnet" in fig. 2, also referred to herein as a "perpendicularly magnetized anisotropic ring magnet", is quadrupole in that (as shown in fig. 2 b) the magnetic field component Bz has two north poles and two south poles. Such ring magnets are commonly referred to as "quadrupole ring magnets". Likewise, the "isotropic ring magnet with rotating magnetization" of fig. 5(c) also has four poles, and is therefore also quadrupole. The fact that the Bx and By field components have only two poles (one north and one south) is irrelevant.

For ease of description, the invention will be described with respect to an example of a quadrupole ring magnet, but the principles of the invention are not limited to quadrupole magnets (quadrupoles) but may also be applied to hexapole or octopole magnets or even higher order magnets, and the magnets need not be ring magnets with a cylindrical central opening, but will also work with other shapes, such as for example disc magnets with cylindrical cutouts (see fig. 12 e).

In the examples described herein, the dimensions of the ring magnet are as follows (see fig. 1): the thickness h1 is 3.5mm, the inner diameter d1 is 5.0mm, and the outer diameter d2 is 14.0mm, but of course the invention is not limited thereto and other dimensions may be used.

Reference is made to the accompanying drawings.

Fig. 1(a) shows, in part, a top view of an exemplary quadrupole ring magnet 101 and fig. 1(b) shows, in part, a side view of an exemplary quadrupole ring magnet 101, which quadrupole ring magnet 101 comprises or is made of an isotropic magnetic material (e.g. neodymium or ferrite) that is magnetized in a particular manner that will be further described (in fig. 4a and 4 b) to produce a magnetic field having very interesting and totally unexpected characteristics, which can be used very advantageously in the sensor system shown in fig. 1 (b).

Fig. 1(b) partially shows a side view of the quadrupole ring magnet of fig. 1(a) and also shows a sensor device 102, in the example of fig. 1(b) partially an integrated semiconductor device 102, which integrated semiconductor device 102 is located at an axial distance "dz" (also referred to as "air gap") from the surface 107 of the ring magnet 101. Sensor device 102 (or indeed the center point of the sensor device defined by sensor element 804 inside the sensor device) is positioned with a radial offset "dr" (also referred to as "off-axis") from the central axis a of ring magnet 101. Ideally, the sensor device 102 would be mounted at a predetermined distance dz from the surface 107, for example dz 1.50mm, and with zero radial offset from the central axis a, meaning dr 0.00mm, but in practice the axial and radial distances dz, dr would vary slightly from this ideal mounting position. As already mentioned above, the constant offsets dz and dr can be easily handled by calibration tests during the manufacturing process, where certain values are measured and stored, and then retrieved and used during normal operation, but offset drift over time is currently not accounted for.

The inventors have conceived of solving the problems related to incorrect positioning (axial distance and/or radial offset from the intended position) and mechanical drift, not in the sensor device 102 but mainly in a multipole magnet, which is not uncommon considering that integrated circuits can implement very complex algorithms, whereas magnets cannot.

Furthermore, it is well known that the residual magnetic field strength of isotropic ferrite materials is typically limited to a maximum of about 120mT in X, Y, Z directions, while anisotropic ferrite materials typically have a residual magnetization of about 230mT along a preferred axis (e.g., the Z-axis of the "perpendicular magnetization" ring magnet of fig. 2). It is also well known that a weaker magnetic field generally means: weaker electrical signals, greater amplification required, greater error, greater sensitivity to external interference, etc. The problem of providing a permanent magnet for a sensor system that needs to be more accurate and/or less sensitive to mechanical drift and/or less sensitive to external magnetic fields and preferably all of these are not logical choices is thus solved using a magnet with an isotropic magnetic material, which is however the present invention proposes.

Fig. 2(a) partially shows the magnetic field generated by a ring magnet made of anisotropic magnetic material with its preferred direction in the Z-axis, and is "axially magnetized", also referred to herein as "perpendicular magnetization". As is known in the art, the magnetic field of such magnets abruptly changes direction at the transition between the north and south poles.

Part (b) of fig. 2 is a computer plot showing the magnitude of the Z component of the magnetic field of the magnet of part (a) of fig. 2 for a point of the magnet.

Fig. 2(c) shows in part a mathematical formula describing the X, Y and Z direction magnetic field components of the axially magnetized anisotropic magnet shown in part 2(a) at a point "p" on the magnet, where "Br" represents the "remanent magnetic field". As can be seen, the Bx and By components are zero, and the Bz component is constant, but changes sign every 90 °. The magnitude of the magnetic field measured at these points is typically about 230 mT.

Fig. 3 (top row) shows a simulated plot of the magnetic field components Bx, By, Bz of the magnetic field created By an exemplary anisotropic and axially magnetized ring magnet having the same dimensions as the exemplary ring magnet shown in part (a) of fig. 1, namely thickness h 1-3.5 mm, inner diameter d 1-5.0 mm, and outer diameter d 2-14.0 mm, as may be measured in a plane located at a distance dz of 1.5 mm.

FIG. 3 (second row and bottom row) also shows spatial field gradients dBx/dx, dBx/dy, dBy/dx, dBz/dy, dBz/dx that may be derived therefrom.

As can be seen, even though the Bx and By values of the magnetic field are zero in a point on the magnet itself (see fig. 2c), the plane at a small distance from the magnet (e.g. about 1.5mm) isThe values Bx and By at each point in (b) are not zero. They are particularly large at the transition between the two poles.

However, the primary purpose of FIG. 3 is to show that the magnetic field gradients dBx/dy and dBy/dx (represented by the dashed rectangular areas) are substantially constant within a central region having a diamond shape. This is consistent with fig. 14 and 15 of WO2014029885a1, showing that the "amplitude" of the in-plane field components br (r) and bt (r) varies more or less linearly as a function of radius in the "linear region". The actual values of the measured gradients dBx/dy and dBy/dx vary like the sine and cosine functions of θ, so by measuring these orthogonal gradients, the angular position can be determined, for example, by using an arctangent function.

Part 4(a) and part 4(b) are schematic representations (in top view and in side view, respectively) of a jig comprising a shaped body comprising or made of an isotropic magnetic material to illustrate a method of manufacturing a "magnet with rotating magnetization" as described herein.

As illustrated by the flowchart of fig. 13, the method comprises the steps of:

a) providing 1301 a shaped body comprising or consisting of an isotropic magnetic material; the compact has a central axis a and a center c.

b) A number 1302 (N) of at least four electrical conductor segments c1, c2, c3, c4 arranged in a plane δ perpendicular to said axis a are provided, oriented radially with respect to said axis a and angularly spaced by an angle of 360 ° divided by said number N. In the example shown, N is equal to 4, so there are four conductor segments angularly spaced by 90 °. It should be noted that the electrical conductor segments may be interconnected. They may for example be part of a single electrical conductor, or part of two electrical conductors, or part of three electrical conductors. The distance between the magnet surface and the plane delta is preferably as small as possible.

c) While applying a current (preferably of equal magnitude) through each of said number N of conductor segments c1, c2, c3, c4, the current in the even conductor segments flowing towards axis a and the current in the odd conductor segments flowing out of said axis a, provided that the conductors are consecutively numbered such that the even and odd conductor segments are interleaved.

The current used may be at least 1kA, preferably at least 2kA, preferably at least 5kA, or at least 10kA, or at least 20kA, or at least 30kA, or at least 40kA, or at least 50kA, for example about 60 kA.

The ring magnet may optionally have radial recesses (not shown) for receiving the conductor segments. These grooves provide the further advantage that they allow easy identification of the weak and strong sides of the magnet, as will become clear when discussing fig. 9, thereby helping to avoid misalignment.

Fig. 4(c) section shows mathematical formulas describing X, Y and the magnetic field components in the Z direction for the isotropic quadrupole magnets shown in fig. 4(a) and 4(b) sections for points of the magnets themselves. As can be understood from these equations, the magnetic field is independent of the radial position on the magnet (see also fig. 5). The formula in section (c) of fig. 4 is valid for a quadrupole magnet, but can be generalized to a multipole magnet as follows:

where N is the number of poles visible from a point on the shaft at a distance from the magnet, which is also equal to the number of conductive segments of the clamp as in part (a) of fig. 4.

FIG. 4(d) partially shows a diagram that can be used forMathematical formulas for calculating the angular position of the sensor device 102 relative to a quadrupole magnet if the sensor device is located in a planeAnd has a plurality of at least three sensor elements 804 that are not collinear, i.e., sensor elements 804 that are not located on a single straight line, as shown, for example, in fig. 1. However, in practice it is preferred to measure the field gradient by at least four sensor elements which lie on two perpendicular lines, preferably on a circle, for example as shown in fig. 8, for example as described in more detail in WO2014029885a 1. The formula in section (d) of fig. 4 is valid for a quadrupole magnet, but can be generalized to a multipole magnet as follows:

where N is the number of poles visible from a point on the shaft at a distance from the magnet, which is also equal to the number of conductive segments of the clamp as in part (a) of fig. 4.

Fig. 5 shows a simulated plot of the magnetic field values Bx, By, Bz for an isotropic magnet magnetized according to the method shown in fig. 4(a) and 4(b) for a point of the magnet itself (not for a point within the central opening).

As can be understood from fig. 5, the ring magnet has a period of rotational symmetry of 180 ° (meaning that the magnetization of the magnet appears the same when the ring magnet is rotated 180 ° about the central axis a). For a hexapole magnet, the period of rotational symmetry would be 360/3-120, for an octapole magnet, 360/4-90, and so on.

Fig. 6 is a 3D representation of the magnetic field of a ring magnet magnetized as shown in part 4(a) and part 4(b), which is consistent with the 2D representation shown in fig. 5.

Part 6(a) and part 6(B) show a ring magnet having an axis "a" and show a virtual circle "c" having a centre "m" substantially located on the axis a (which may in practice be slightly offset) and showing a point "p" located on the virtual circle "c", and showing a plane "epsilon" parallel to the axis a and tangential to the virtual circle "c" and containing the point "p", and showing that the magnetic field vector B lies in the tangential plane epsilon.

Part of fig. 6(c) shows several points "p" on a virtual circle "c" and shows for each of these points how the magnetic field vector B "rotates" in the tangential plane epsilon "as the point" p "moves along the circle. Or in other words how the angle β between the plane λ perpendicular to the axis a and the magnetic field vector B varies as a function of the angular position θ of the point p on the virtual circle c. A magnet thus magnetized is referred to herein as an "isotropic magnet with a rotating magnetic field" or an "isotropic magnet with a rotating magnetization".

Part (d) of fig. 6 shows magnetic field vectors B in eight specific points on the ring magnet of part (a) of fig. 6. As can be seen, the magnetic field B

-oriented in the direction of the positive Z-axis in two angular positions (θ 3, θ 7); and

-oriented in the direction of the negative Z-axis in two angular positions (θ 1, θ 5); and

-oriented in the direction of the positive X-axis in one angular position (θ 0); and

-oriented in the direction of the negative X-axis in one angular position (θ 4); and

-oriented in the direction of the positive Y-axis in one angular position (θ 6); and

-oriented in the direction of the negative Y-axis in one angular position (theta 2),

wherein X, Y and the Z-axis are orthogonal axes of a cartesian coordinate system located in the center c, and wherein the Z-axis coincides with the central axis a of the magnet.

Part 6(e) is a 2D representation showing how the magnetic field vector of the magnet of part 6(a) "rotates" in the tangential plane epsilon as a function of angle theta, which defines the angular position of point "p" on circle "c". In a preferred embodiment, the angle β varies substantially linearly as a function of θ.

Part (f) of fig. 6 is a 2D representation similar to part (e) of fig. 6, but for comparison with the perpendicular magnetization anisotropic magnet of fig. 2.

Fig. 7 (top row) shows a simulated plot of the magnetic field values Bx, By, Bz for an isotropic magnet having the same dimensions as the above-described exemplary magnet (h 1-3.5 mm, d 1-5.0 mm, d 2-14.0 mm) but magnetized using the method of fig. 13 (e.g., By using the jig shown in part (a) of fig. 4).

FIG. 7 (second and third rows) shows the spatial field gradients dBx/dx, dBx/dy, dBy/dx, dBz/dy, dBz/dx derived therefrom. It was completely unexpected, and in fact very surprising, that the diamond shape of fig. 3 was transformed into an almost perfect circle.

Fig. 8 is a grayscale version of an enlarged view of the plot dBx/dy of fig. 7 (bottom left) with the addition of four white dots, representing four sensor elements 804 of the sensor device 102, which may be arranged in a central circular region relative to the magnet, at a distance from the magnet.

As can be appreciated from fig. 7 and 8, the in-plane field gradients (particularly dBx/dy and dBy/dx) of the "isotropic ring magnet with rotating magnetic field" as described herein are more uniform and in a larger area than the field gradients of the "anisotropic perpendicularly magnetized ring magnet" shown in fig. 2 and 3. One reason for this is that the circle of fig. 8 is convex, while the diamond shape of fig. 3 is concave.

The fact that the amplitude of the gradient is substantially constant within the circle means that the amplitude of the field gradient measured anywhere within the circular area is substantially independent of the offset position, but depends only on the angle θ between the sensor device and the ring magnet, wherein the amplitude varies slightly, and thus the value of the field gradient depends not only on said angle θ, but (to a greater extent) also on the offset position, as compared to the magnet of fig. 3.

The circular shape also provides another advantage, shown schematically in part (b) of fig. 8, that is, it allows two or three sensor structures to be placed within a circle instead of just one without significantly reducing accuracy.

In an embodiment, the sensor device 102 includes two semiconductor dies embedded in a single package. This embodiment provides redundancy that allows defects to be detected, which is very important in some applications, for example in automotive applications. Furthermore, it is beneficial that both sensor structures, e.g. semiconductor dies, are located at substantially the same distance from the magnet and will therefore measure substantially the same signal.

In a particular embodiment, the sensor device 102 includes three sensor structures, e.g., three semiconductor dies, all of which may be located within a circular area. Such a sensor device allows not only to detect errors but also to correct potential defects, for example by discarding one of the three values that deviate most from the others.

Although the advantages of redundancy are known per se in the art, the circular shape associated with the "isotropic magnet with rotating magnetization" makes it possible to use redundancy for smaller magnet sizes than is possible for a diamond shape, or in other words, this allows the size of the redundant angle sensor system to be reduced.

The inventors have encountered another surprise, as will be explained with reference to fig. 9. The rotating magnetization also causes an asymmetric magnetic field, resulting in an effective magnetic gain on one side of the magnet.

Part (a) of fig. 9 shows the magnet part of part (b) of fig. 6 arranged relative to the sensor device. The purpose of this figure is to make the meaning of the rectangular cross-section of the portion of fig. 9(b) to the portion of fig. 9(e) clearer.

Part 9(B) and part 9(d) show computer simulations of the magnitude | B | of the magnetic field of the "anisotropic quadrupole ring magnet with perpendicular magnetization" with the above exemplary dimensions (h 1-3.5 mm, d 1-5.0 mm, d 2-14.0 mm) in color and grayscale, respectively. In a color picture, white line segments are shown to indicate typical positions of the sensor device, and black line segments are shown in a grayscale picture. As can be seen, the magnitude of the magnetic field is substantially the same on either side (above or below) of the magnet, without magnification, but the magnetic field strength of the anisotropic magnet is already relatively large.

Part (c) of fig. 9 and part (e) of fig. 9 show computer simulations of the magnitude | B | of the magnetic field of the "isotropic quadrupole ring magnet with rotating magnetization" as described above with the same exemplary dimensions (h 1-3.5 mm, d 1-5.0 mm, d 2-14.0 mm) described above in color and grayscale, respectively. In a color picture, white line segments are shown to indicate typical positions of the sensor device 102, and black line segments are shown in a grayscale picture. As can be seen, the magnetic field amplitude is stronger at the bottom side of the magnet than at the top side of the magnet. The sensor device 102 is preferably located on the side of the magnet where the magnetic field is stronger.

Surprisingly, the passive amplification makes the magnetic field of the isotropic magnet (with a typical maximum remanent magnetic field strength of 120mT) almost the same strength as the magnetic field of the anisotropic magnet (with a typical maximum remanent magnetic field strength of 230 mT). This is better shown in fig. 9 (f).

Part (f) of fig. 9 shows the field By along the X-axis. Due to the magnetic gain of the rotating magnetization, "perpendicularly magnetized anisotropic ferrites" and "isotropic ferrites with rotating magnetization" obtain equivalent magnetic field strengths, although the remanent magnetization of isotropic ferrites is much weaker compared to anisotropic ferrites.

Fig. 10 and 11 explain how this translates into reduced sensitivity to axial and/or radial position errors.

Fig. 10 shows the maximum position error (within the angular range) of the sensor system 100 of fig. 1, for a position sensor 102 located at a radial offset dr-1.4 mm and for various axial positions (air gaps) varying from 1.5mm to 4.5mm, using an "anisotropic ring magnet with perpendicular magnetization" (with a square curve) and using an "isotropic ring magnet with rotating magnetic field" as proposed in this document, the magnets having the exemplary dimensions as mentioned above.

As can be appreciated, for a sensor system having an "isotropic magnet with rotating magnetic field", the maximum error is much lower, so the magnet may significantly improve robustness to axial and/or radial displacement of the magnet 101 relative to the sensor device 102, or in other words, an "isotropic magnet with rotating magnetic field" as described herein may significantly improve accuracy and may significantly reduce the effect of mechanical offset drift over the lifetime of the sensor system 100.

The (worst case) angle error (at some air gap and off-axis) is calculated as the measured angle θ during the entire rotation_mAnd the maximum difference between the actual angle θ, using the following equation: delta theta_max＝max|θ-θ_mL, where θ_mIs calculated using the formula mentioned in section (d) of fig. 4.

Fig. 11 shows the maximum position error (within the angular range) of the sensor system 100 of fig. 1 for various radial offset values (dr) ranging from 0.2mm to 2.0mm for a position sensor located at an axial distance (or air gap dz) of 1.5mm, when using an "anisotropic ring magnet with perpendicular magnetization" (curve with square shape) and when using an "isotropic ring magnet with rotating magnetic field" (curve with triangle shape) as proposed by the present invention, the magnets having the exemplary dimensions as mentioned above.

As can be seen from the curves with triangles, the error is about 2.2 ° (about 2.0mm for off-axis) by using an anisotropic ring magnet, while the error is less than about 0.7 ° using an isotropic ring magnet. This is a 3-fold improvement.

The present invention has been described so far using a ring magnet as an example, but the present invention is not limited thereto, and other shapes may be used.

Fig. 12 shows several other shapes of "isotropic magnets with rotating magnetic field" that may be used in embodiments of the present invention. Only a portion of the magnets are shown for illustrative purposes. In part (a) of fig. 12, the magnet is a ring-shaped magnet having a cylindrical through hole and a cylindrical outer wall. In part (b) of fig. 12, the magnet is a ring-shaped magnet having a conical through-hole and a cylindrical outer wall. In part (c) of fig. 12, the magnet has a cylindrical through-hole in a beam-shaped object having an outer surface of a square section. In part (d) of fig. 12, the magnet has a conical through-hole in a beam-shaped object having an outer surface of a square section. In part (e) of fig. 12, the magnet is a disk-shaped magnet having a cylindrical cutout.

The invention is applicable to magnets having cylindrical or conical openings (through holes or slits), but is also applicable to other surfaces of revolution, such as parabolic or elliptical openings or slits, and even to shapes without openings or slits, such as the disk-shaped magnet shown without a central opening or slit in fig. 12(g) section.

Although a circular or disc shape is preferred, the invention will work with other external geometries as well, such as a square, a hexagon or an octagon, or another polygonal shape.

Part (f) of fig. 12 shows a variation of the magnet of part (a) of fig. 12, with two central openings, a first opening (e.g., at the top) having a first inner diameter, and a second concentric opening (e.g., at the bottom) having a second inner diameter different from the first diameter. Other variations are also possible.

As already mentioned above, each of these shapes may further have radial grooves for accommodating conductor segment(s) for magnetizing the magnet.

Although not explicitly shown, the principles of the present invention may also be combined with the principles described in EP3321638(a1), the entire content of which is incorporated herein by reference, in particular fig. 15 (adding two identical cylindrical dipoles arranged on opposite sides of a ring magnet or a disc magnet) and fig. 32 and fig. 33 (adding two perpendicularly magnetized partial ring magnets arranged on opposite sides of a ring magnet or a disc magnet), and the algorithm of fig. 17 for determining angular positions within an angular range of 360 °. In this way, the advantages of the present invention can be combined with the "angular range expansion principle" described in EP3321638(a 1).

While various features of the invention are illustrated in different drawings and in different embodiments, it is contemplated that the features of the different embodiments may be combined as will be apparent to one of skill in the art upon reading this document.

Finally, although the invention has been described for an "ideal case" in which the magnetic field in the magnet can be expressed by the equations of part (c) of fig. 4, the skilled person will understand that in practice the residual magnetic field of an actual magnet will not exactly equal these equations, but only approximately equally. However, it is important to realize that the advantageous effect of "being highly robust to radial and axial drift" provided by the present invention does not depend directly on how close the formula is to the part of fig. 4(c), but on the homogeneity of the magnetic field induced outside the magnet material, more specifically in the small cylindrical space at a small distance from the magnet. It is further noted that although the formula of part (d) of fig. 4 expresses an ideal case, in practice a correction to the formula may be included and is typically included in the sensor device in a manner known per se in the art, for example using look-up tables and linear interpolation.