WO2016174506A1

WO2016174506A1 - Rotational angle magnetic sensor

Info

Publication number: WO2016174506A1
Application number: PCT/IB2015/054668
Authority: WO
Inventors: Luis Alexandre Machado Da Rocha; Daniel AGOSTINHO LEITE RIBEIRO DIAS; João Manuel GONÇALVES DOS SANTOS; José João CUNHAL FONTAÍNHAS; Diógenes José VEIGA DE ARAÚJO; Jorge Miguel NUNES DOS SANTOS CABRAL
Original assignee: Bosch Car Multimedia Portugal, S.A.; Universidade Do Minho
Priority date: 2015-04-30
Filing date: 2015-06-22
Publication date: 2016-11-03

Abstract

Rotational angle sensor comprising a two coil assembly, wherein the two coils are arranged coaxially and separately with respect to their shared coil axis by an axial interspacing; a 2-axis magnetic sensor within said interspacing; and an electronic circuit arranged such that, when in operation, a magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils; wherein the two coil assembly and the magnetic sensor are rotatably arranged in respect of each other, in particular the electronic circuit comprises a differentiator of the magnetic sensor signals received between alternating time periods of opposite field directions, in particular the alternating time periods being consecutive alternating time periods. Method of operation thereof comprising applying a magnetic field with alternating time periods of opposite field directions and same magnetic magnitude and differentiating the magnetic sensor signal received between alternating time periods.

Description

D E S C R I P T I O N

ROTATIONAL ANGLE MAGNETIC SENSOR

Technical field

[0001] The present disclosure relates to rotational sensors. More specifically to magnetic position sensors that measure angular displacements that can reach 360^ and that is not sensitive to external fields.

Background Art

[0002] Measurement of angular position is required in several fields like automotive, aeronautic and industrial processes. Typical applications are, but not limited to, motor shafts position sensing, steering wheel position sensing, pedal position sensing, torque sensing and valve position sensing.

[0003] In prior art several ways of obtaining the angular position of a device using the orientation of a magnetic field are presented. One of the most common arrangement is described in Patent EP1083406 that combines a rotary permanent magnet and two magneto-sensitive elements (Hall effect for example) to measure the radial component of the magnetic field in two different points, which result in two quadrature sinusoidal signals that after processing allows obtaining the angular orientation between 0 and 360^ degrees.

[0004] Another common solution is presented by Melexis (MLX90316), in which two components of the magnetic field, Bx and By for example, are measured in the same plane for one IC. While a magnet diametrically magnetized rotates, two signals in quadrature (sine and cosine) are provided, and by calculating the arctangent of the ratio of these two signals the angular orientation is obtained.

[0005] The drawback of these two solutions is its sensitivity to parasitic external magnetic fields.

[0006] In order to reduce the interference of the external magnetic fields, patent US8587294B2 describes an angular position sensor with very low sensitivity to external magnetic fields. The described arrangement uses two ICs orthogonally placed to measure two components of the magnetic field (normal and tangential, for example) generated by a rotary diametrically magnetized magnet. The subtraction of the both normal components and the subtraction of both tangential components make it possible to cancel the external interference. The disadvantage of this solution is the use of two ICs, which can lead to measurement errors due to the incorrect placement of one IC relative to the other. Another disadvantage is the cost of the sensor that will increase with the use of two ICs.

[0007] Also known in prior art is the solution presented by Austria Microsystems (AS5163), which describes a differential principle to measure the vertical component (Bz) of the magnetic field to calculate the absolute angle value. The arrangement involves the use of four Hall Effect elements, equally spaced inside of one IC, placed under a diametrical magnetised rotating magnet, to generate four sinusoidal wave forms shifted by 90° from its neighbour. The differential principle is implemented by subtracting the signals of the opposing sets of sensors, such that the signal from an external interference field is subtracted and will be minimized in the angle signal. The angle is obtained by calculating the arctangent of the ratio between the two resulting signals.

[0008] Inductive rotational angle sensors are also presented in prior art, for example, patent US20100277162A1. The arrangement consists of using two separate coils, which are placed coaxially with respect to a coil axis. The space between the coils enable an influencing element that will interact with these coils and produces a chance in the magnetic flux density (generated by the coils) that induces a variation on the inductance of the coils as a function of its position. The influencing element can be rotated about a shaft, which is parallel to the coils, to transmit the rotational movement to be sensed. This approach enables measuring a rotational angle in a range less than or equal to 360^. Once again the problem of this solution is the external magnetic fields that can interact with the magnetic fields created by the coils and will introduce errors on the measurement of the angular position.

[0009] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.

General Description

[0010] The present invention aims at solving the perturbation from non-homogenous stray magnetic fields present on the vehicle during the operation of the angular position sensor, whose operational principle is magnetic, by using a differential measurement of an inductive generated magnetic field.

[0011] The present invention consists in a new system and method for improving the operation of the angular position sensor in a vehicle, through the elimination of the parasitic magnetic field. The presented approach uses inductive magnetic field generation, similar to the setup described in US20100277162A1, but here the induced magnetic field is alternated in two directions (by changing the current direction). This arrangement enables a differential measurement that eliminates any constant external field present during the measurement, greatly improving the accuracy of the sensor.

[0012] The present invention consists in an angular position sensor, immune to stray magnetic fields, for sensing 360 degrees of absolute rotation. With this new sensor, a method to cancel the effect of the stray magnetic fields presents on the vehicle is provided by using a differential measurement of a created magnetic field. [0013] The sensor comprises:

- two identical circular coils, placed symmetrically along a common axis in the same horizontal plane and separated by a distance similar to radius R, are used to produce a uniform magnetic field on the centre, through induction of a current. The intensity of the magnetic field is adjustable, for example, by changing the coils current.

- a 2-axis magnetic sensor, with digital or analogue output, on the same horizontal plane, is placed between the coils equidistant to the coils, to measure the components Bx and By of the magnetic field.

[0014] The rotation of the structure that contains the coils (in the case the sensor is fixed), or the structure that contains the magnetic sensor (in the case the coils are fixed) will result in the variation of the magnitude Bx and By. The differential measurement is implemented by creating two magnetic fields with opposite directions and same magnitude by reversing the direction of the current induced in the coils at a constant period, T_s. The direction of the current is reversed by using a H-bridge.

[0015] Since stray fields will interact with the fields created (add or subtract), the subtraction of the magnetic fields, measured for the two currents (forward and reverse), will cancel the effect of the external field.

[0016] With this new system, it is possible to place the sensor in multiple locations inside the vehicle, i.e., the sensor can be placed in locations where high stray magnetic fields are present (close to batteries and power cables for instance). Furthermore, the proposed solution does not use a permanent magnet to obtain the magnetic field and since it can compensate stray magnetic fields, the magnitude of the magnetic field required to the angular position sensor operation can be made smaller in comparison with the known solutions (that use permanent magnets), without compromising the resolution of the sensor. Also, a single 2-axis magnetic sensor is required to obtain the rotation angle for external magnetic field compensation, reducing the number of required sensors. [0017] It is disclosed a rotational angle sensor comprising:

two coil assembly, wherein the two coils are arranged coaxially and separately with respect to their shared coil axis by an axial interspacing;

a 2-axis magnetic sensor;

an electronic circuit arranged such that, when in operation, a magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils;

wherein the two coil assembly and the magnetic sensor are rotatably arranged in respect of each other.

[0018] In an embodiment, the electronic circuit comprises a differentiator of the magnetic sensor signals received between alternating time periods of opposite field directions.

[0019] In an embodiment, the alternating time periods are consecutive alternating time periods.

[0020] An embodiment comprises a data processor for generating the alternating time periods of opposite field directions and for differentiating the magnetic sensor signals received between alternating time periods of opposite field directions.

[0021] In an embodiment, the two coils are identical circular coils.

[0022] In an embodiment, the magnetic sensor is arranged between the coils equidistant to the coils.

[0023] In an embodiment, the electronic circuit comprises a H-bridge for reversing the direction of the electronic current flowing through the coils such that the magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils.

[0024] In an embodiment, the magnetic sensor is fixed and the two coil assembly is rotatably arranged in respect of the magnetic sensor.

[0025] In an embodiment, the two coil assembly is fixed and the magnetic sensor is rotatably arranged in respect of the two coil assembly. [0026] In an embodiment, the magnetic sensor is a Hall-effect sensor or magnetoresistive sensor.

[0027] In an embodiment, the two coils are connected in series.

[0028] In an embodiment, the magnetic sensor or the two coil assembly are arranged to rotate about a shaft which is perpendicular to the coil co-axis.

[0029] In an embodiment, one or both of the coils comprises a coil core of a ferromagnetic material or plastic material.

[0030] In an embodiment, the rotational angle sensor further comprises:

a shaft for rotating the magnetic sensor and the two coil assembly in respect of each other;

a support assembly for supporting said shaft and the two coil assembly and the magnetic sensor.

[0031] It is also disclosed a method of operating a rotational angle magnetic sensor, said sensor comprising:

a 2-axis magnetic sensor;

wherein the two coil assembly and the magnetic sensor are rotatably arranged in respect of each other,

said method comprising applying an electric current to the two coils such that a magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils;

differentiating the magnetic sensor signals received between alternating time periods of opposite field directions for obtaining a sensor measurement of the rotational angle.

[0032] An embodiment comprises applying the electric current and differentiating the magnetic sensor signals by an electronic circuit which comprises a differentiator for the magnetic sensor signals received between alternating time periods of opposite field directions. [0033] In an embodiment, the alternating time periods are consecutive alternating time periods.

[0034] An embodiment comprises using a data processor for generating the alternating time periods of opposite field directions and for differentiating the magnetic sensor signals received between alternating time periods of opposite field directions.

[0035] An embodiment comprises reversing the direction of the electronic current flowing through the coils the electronic circuit comprises reversing a H-bridge of said electronic circuit such that the magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils.

Brief Description of the Drawings

[0036] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of invention.

[0037] Figure 1 shows a block diagram of the sensor where the following elements are present:

Microcontroller (1);

H-Bridge (2);

Coils (3) and;

2 axis magnetic sensor (4);

[0038] Figure 2 depicts the sensor (4) and coils (3) with configuration for the case where the sensor is rotating.

[0039] Figure 3 depicts the sensor (4) and coils (3) with configuration for the case where the coils are rotating.

[0040] Figure 4 depicts a flow chart with the sequence for a full cycle measurement. For each cycle, a value of the rotation, with stray magnetic field compensation, is obtained. Detailed Description

[0041] The present application describes the method of operation of an angular position sensor immune to stray magnetic fields. The invention includes 4 mains blocks, as depicted in Fig. 1. The microcontroller (1) is responsible for controlling the magnetic field generation in the coils (3) through a H-bridge (2), along with the acquisition of the magnetic sensor (4) readings and calculation of the rotation. As depicted in Fig. 2 and Fig. 3, the 2-axes magnetic sensor (4) is placed between the coils (3), equidistant, and in the same horizontal plane as the coils (3) center. Based on the chosen configuration, either the sensor (4) can rotate (Fig. 2) or both coils (3) rotate (Fig. 3). The rotation angle to be measured and depending on the configuration used (Fig. 2 or Fig. 3), is applied or to the sensor (Fig. 2) or to the coils (Fig. 3).

[0042] Operation of the sensor is schematically shown in FIG.l while Fig. 4 presents a flow chart with the required sequence for a single measurement. The microcontroller (1) generates a square wave, at a frequency F_s, which controls the current direction at the H-bridge (2). The H-bridge (2) is responsible for changing the current direction on the coils (3) and therefore two magnetic fields, with same amplitude and opposite direction, are applied to the sensor (4) within one period, T_s. For each half-period, the microcontroller reads the magnetic sensor (4) and after one period, the values are used by the microcontroller (1) to calculate the difference between the two consecutive measurements in each axis (in order to eliminate any existing stray magnetic field). The resulting values are then used to calculate the rotation angle (the angle between the sensor (4) measurement axes - x, y in Fig. 2 and Fig. 3 - and the induced magnetic field at the coils (3)).

[0043] The mechanism to cancel the stray magnetic field is explained in detail next. In the absence of any stray magnetic field along axis x and y (Sx and Sy) and applying the differential measurement (Bxi and Byi during positive current and Bx₂ and By₂ during negative current), we have:

Signal_x = Bxi - Bx₂ Signal_y = Byi - By₂

[0044] As the magnetic fields have the same magnitude and opposite directions (Bx₂ = -Bxi, By₂ = -Byi) we obtain:

Signal_x = Bxi - (-Bxi) = 2*Bxi

Signal_y = Byi - (-Byi) = 2*Byi

[0045] Thereby, calculation of the inverse tangent (arctangent) of the ratio of these two components will give the angular orientation (a): a = arctan((Signal_x)/(Signal_y))

[0046] Now, if we consider the existence of stray magnetic field (Sx and Sy), we have:

Signal_x = (Bxi+Px) - (Bx₂+Px)

Signal_y = (Byi+Py) - (By₂+Py)

[0047] Considering the perturbation constant along a period T_s, and since the generated magnetic fields have the same magnitude and opposite directions, we obtain:

Signal_x = (Bxi+Px) - (-Bxi+Px) = 2*Bxi

Signal_y = (Byi+Py) - (-Byi+Py) = 2*Byi

[0048] As demonstrated, by using a differential measurement of the magnetic field, the Signal_x and Signal_y, used to calculate the angular orientation, have the same value for the two cases: with or without the presence of a stray magnetic field. Thus, stray magnetic fields are eliminated in the calculation of the angular orientation.

[0049] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. [0050] Flow diagrams of particular embodiments of the presently disclosed methods are depicted in figures. The flow diagrams do not depict any particular means, rather the flow diagrams illustrate the functional information one of ordinary skill in the art requires to perform said methods required in accordance with the present disclosure.

[0051] It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of steps described is illustrative only and can be varied without departing from the disclosure. Thus, unless otherwise stated the steps described are so unordered meaning that, when possible, the steps can be performed in any convenient or desirable order.

[0052] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0053] The above described embodiments are combinable.

[0054] The following claims further set out particular embodiments of the disclosure.

Claims

C L A I M S

Rotational angle sensor comprising:

a 2-axis magnetic sensor;

Rotational angle sensor according to the previous claim wherein the electronic circuit comprises a differentiator of the magnetic sensor signals received between alternating time periods of opposite field directions.

Rotational angle magnetic sensor according to the previous claim wherein the alternating time periods are consecutive alternating time periods.

Rotational angle sensor according to any of the previous claims comprising a data processor for generating the alternating time periods of opposite field directions and for differentiating the magnetic sensor signals received between alternating time periods of opposite field directions.

Rotational angle sensor according to any of the previous claims wherein the two coils are identical circular coils.

Rotational angle sensor according to any of the previous claims wherein the magnetic sensor is arranged between the coils equidistant to the coils.

7. Rotational angle sensor according to any of the previous claims wherein the electronic circuit comprises a H-bridge for reversing the direction of the electronic current flowing through the coils such that the magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils.

8. Rotational angle sensor according to any of the previous claims wherein the magnetic sensor is fixed and the two coil assembly is rotatably arranged in respect of the magnetic sensor.

9. Rotational angle sensor according to any of the previous claims wherein the two coil assembly is fixed and the magnetic sensor is rotatably arranged in respect of the two coil assembly.

10. Rotational angle sensor according to any of the previous claims wherein the magnetic sensor is a Hall-effect sensor or magnetoresistive sensor.

11. Rotational angle sensor according to any of the previous claims wherein the two coils are connected in series.

12. Rotational angle sensor according to any of the previous claims wherein the magnetic sensor or the two coil assembly are arranged to rotate about a shaft which is perpendicular to the coil co-axis.

13. Rotational angle sensor according to any of the previous claims wherein one or both of the coils comprises a coil core of a ferromagnetic material or plastic material.

14. Rotational angle sensor according to any of the previous claims comprising:

15. Method of operating a rotational angle magnetic sensor, said sensor comprising: two coil assembly, wherein the two coils are arranged coaxially and separately with respect to their shared coil axis by an axial interspacing;

a 2-axis magnetic sensor;

16. Method according to the previous claim wherein the method comprises applying the electric current and differentiating the magnetic sensor signals by an electronic circuit which comprises a differentiator for the magnetic sensor signals received between alternating time periods of opposite field directions.

17. Method according to any of the claims 15 - 16 wherein the alternating time periods are consecutive alternating time periods.

18. Method according to any of the claims 15 - 17 comprising using a data processor for generating the alternating time periods of opposite field directions and for differentiating the magnetic sensor signals received between alternating time periods of opposite field directions.

19. Method according to any of the claims 15 - 18 wherein the two coils are identical circular coils.

20. Method according to any of the claims 15 - 19 wherein the magnetic sensor is arranged between the coils equidistant to the coils.

21. Method according to any of the claims 15 - 20 wherein reversing the direction of the electronic current flowing through the coils the electronic circuit comprises reversing a H-bridge of said electronic circuit such that the magnetic field with alternating time periods of opposite field directions and same magnetic magnitude is generated between the two coils.

22. Method according to any of the claims 15 - 21 wherein the magnetic sensor is fixed and the two coil assembly is rotatably arranged in respect of the magnetic sensor.

23. Method according to any of the claims 15 - 22 wherein the two coil assembly is fixed and the magnetic sensor is rotatably arranged in respect of the two coil assembly.

24. Method according to any of the claims 15 - 23 wherein the magnetic sensor is a Hall-effect sensor.

25. Method according to any of the claims 15 - 23 wherein the magnetic sensor is a magnetoresistive sensor.

26. Method according to any of the claims 15 - 25 wherein the two coils are connected in series.

27. Method according to any of the claims 15 - 26 wherein the magnetic sensor or the two coil assembly are arranged to rotate about a shaft which is perpendicular to the coil co-axis.

28. Method according to any of the claims 15 - 27 wherein one or both of the coils comprises a coil core of a ferromagnetic material or plastic material.

29. Method according to any of the claims 15 - 28 wherein the rotational angle sensor further comprises: