Angle Sensor

Abstract

To suppress noise involved with amplification of output of a sensor circuit and accurately measure an angle.SOLUTION: An angle sensor includes: a bridge circuit 1a as a sensor circuit including a magnetic resistance effect element; magnets 3 and 4 for generating a magnetic field which rotates around the axis X of rotation; a voltage detector 11 for detecting an output voltage of the bridge circuit 1a; and a rotation angle calculation unit 12 for calculating the rotation angle of the magnetic field on the basis of the detected voltage. The bridge circuit 1a, the rotary body 2, and the magnets 3, 4 are arranged so that a rotary surface 7 of a magnetic field intersects with a sensor surface 6a with a thin film resistance pattern of the magnetic resistance effect element formed. A reference position where the output voltage of the bridge circuit 1a becomes zero is not on the line of intersection between the rotary surface 7 and the sensor surface 6a of the magnetic field, and the angle β formed by the reference position and the line of intersection on the sensor surface 6a is in the range of -90°≤β<-45°or 45°<β≤90°.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an angle sensor using a magnetoresistive element. [Background technology]

[0002] Torque tube level gauges are a type of level gauge that measures the liquid level in a tank. Torque tube level gauges fix one end of a torque tube, attach an arm to the other end of the torque tube to hang a float, and use an angle sensor to detect the twisting of the torque tube in response to the buoyancy that the float receives from the liquid surface, thereby measuring the liquid level.

[0003] FIG. 10 is a diagram showing the configuration of an angle sensor 100. The angle sensor 100 measures the rotation angle of a magnetic field generated by magnets 3 and 4 attached to a rotating body 2. A sensor circuit 1 using a magnetoresistive element, a Hall element, or the like is used to measure the angle (see Patent Document 1). In FIG. 10, reference numeral 5 indicates the direction of the magnetic field generated by the magnets 3 and 4, and reference numeral 6 indicates the measurement surface of the sensor circuit 1. Generally, the sensor circuit 1 is installed so that the measurement surface and the rotation plane of the magnetic field are parallel, as shown in FIG. 10.

[0004] The angle sensor used in the torque tube type liquid level gauge described above uses an anisotropic magnetoresistive effect (AMR) element as the detection element, and a bridge circuit made up of AMR elements is placed parallel to the plane of rotation of the magnetic field, and the angle is measured by utilizing the change in the midpoint potential difference of the bridge circuit depending on the rotation angle of the magnetic field.

[0005] The output of this angle sensor goes through two cycles per rotation of the magnetic field, and the unique correspondence between the rotation angle of the magnetic field and the output of the angle sensor is at most half that cycle. For this reason, the angle sensor cannot measure angles greater than 90°. Also, although it depends on the specifications of the level gauge, the torsion angle of the torque tube being measured is only a few degrees, so the change in the output of the angle sensor is small. For this reason, the signal needs to be electrically amplified, but increasing the gain poses the problem of risking noise contamination. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-104454 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide an angle sensor that can suppress noise associated with amplification of the output of a sensor circuit and can measure angles with high accuracy. [Means for solving the problem]

[0008] The angle sensor of the present invention comprises a sensor circuit including a magnetoresistive element, a magnetic field generating unit configured to generate a magnetic field that rotates around a rotation axis, an output electrical signal detecting unit configured to detect an output electrical signal of the sensor circuit, and a rotation angle calculating unit configured to calculate the rotation angle of the magnetic field based on the output electrical signal detected by the output electrical signal detecting unit, wherein the sensor circuit and the magnetic field generating unit are arranged so that the plane of rotation of the magnetic field intersects a sensor surface on which a thin film resistor pattern of the magnetoresistive element is formed, the reference position at which the output voltage of the sensor circuit is zero is not on the intersection line between the plane of rotation of the magnetic field and the sensor surface, and the angle β between the reference position on the sensor surface and the intersection line is in the range of -90°≦β<-45° or 45°<β≦90°.

[0009] In one configuration example of the angle sensor of the present invention, the rotation angle calculation unit calculates a rotation angle θ of the magnetic field on the sensor surface based on the output electrical signal detected by the output electrical signal detection unit, and calculates φ=tan θ based on the rotation angle θ, an inclination angle α of the rotation plane of the magnetic field with respect to the sensor surface, and an angle β between the reference position on the sensor surface and the intersection line. -1 {tan(θ-β) / cosα}+tan -1 The rotation angle φ of the magnetic field on the plane of rotation is calculated by (tan β / cos α). In addition, in one configuration example of the angle sensor of the present invention, the rotation angle calculation unit calculates the rotation angle θ from the output electrical signal detected by the output electrical signal detection unit using an approximation function that indicates the relationship between the output electrical signal of the sensor circuit and the rotation angle θ. Moreover, one configuration example of the angle sensor of the present invention is characterized in that the magnetic field is saturated with respect to the magnetoresistive effect element of the sensor circuit regardless of the rotation angle. [Effects of the Invention]

[0010] According to the present invention, the sensor circuit and magnetic field generating unit are arranged so that the plane of rotation of the magnetic field intersects with the sensor surface on which the thin film resistor pattern of the magnetoresistive element is formed, and the angle β between the reference position where the output electrical signal of the sensor circuit is zero and the intersection line between the plane of rotation of the magnetic field and the sensor surface is set in the range of -90°≦β<-45° or 45°<β≦90°.This makes it possible to expand the angular range narrower than 90 degrees on the plane of rotation of the magnetic field to a range of 90 degrees on the sensor surface, thereby suppressing noise associated with amplification of the output of the sensor circuit and enabling accurate angle measurement. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the configuration of a conventional liquid level gauge. [Figure 2] FIG. 2 is a circuit diagram of a bridge circuit configured with AMR elements. [Figure 3] FIG. 3 is a diagram showing the configuration of a level gauge according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the configuration of an angle sensor according to an embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing an example of the trajectory of the magnet accompanying the rotation of the rotor in the angle sensor. [Figure 6] FIG. 6 is a diagram showing the trajectory of the magnet accompanying the rotation of the rotor in the angle sensor according to the embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing the relationship between the tilt angle of the rotation plane of the magnetic field relative to the sensor surface, the angle of the reference position on the sensor surface relative to the intersection line between the rotation plane of the magnetic field and the sensor surface, and the range of measurable rotation angles. [Figure 8] FIG. 8 is a diagram showing the relationship between the tilt angle of the rotation plane of the magnetic field relative to the sensor surface, the angle of the reference position on the sensor surface relative to the intersection line between the rotation plane of the magnetic field and the sensor surface, and the range of measurable rotation angles. [Figure 9] FIG. 9 is a block diagram showing an example of the configuration of a computer that realizes an angle sensor according to an embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing the configuration of a conventional angle sensor. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Conventional example] Before describing the embodiments of the present invention, a conventional level gauge and angle sensor will be described in detail. The configuration of a conventional level gauge is shown in Fig. 1. The level gauge comprises an angle sensor 100, a torque tube 101, a float 102 that floats on the surface of a liquid 106 to be measured, a torque arm 103, and a torque rod 104.

[0013] The end of torque tube 101 on the angle sensor 100 side is fixed by a torque tube housing (not shown). A torque arm 103 supported by a knife-edge fulcrum 105 is attached to the other end of torque tube 101. A float 102 is suspended from the tip of torque arm 103. When installed, torque tube 101 is used in a twisted state due to the weight of float 102.

[0014] Buoyancy, which is generated in proportion to the liquid level of liquid 106, is transmitted via torque arm 103 from which float 102 is suspended, generating torsional stress. Torque rod 104 is connected to torque arm 103 and rotates until the bending moment caused by buoyancy balances out with the spring force caused by the rigidity of torque tube 101. Rotating body 2 of angle sensor 100 is fixed to the tip of torque rod 104, and the liquid level can be measured by measuring the rotation angle of the magnetic field generated by magnets 3 and 4 attached to rotating body 2 with angle sensor 100.

[0015] Figure 2 shows a bridge circuit 1a, a sensor circuit made up of AMR elements whose electrical resistance changes with a magnetic field. Bridge circuit 1a is made up of a first series circuit 10-5 in which a first AMR element 10-1 and a second AMR element 10-2 are connected in series, and a second series circuit 10-6 in which a third AMR element 10-3 and a fourth AMR element 10-4 are connected in series, connected in parallel.

[0016] As shown by the double-headed arrows in Figure 2, the magnetic sensing direction (the direction of the magnetic field in which the resistance value is minimum) of the facing AMR elements 10-1 and 10-4 is the same, and the magnetic sensing direction of the facing AMR elements 10-2 and 10-3 is the same. In addition, the magnetic sensing directions of adjacent AMR elements are perpendicular to each other.

[0017] When the plane of rotation of the magnetic field generated by the angle sensor's magnet is parallel to the sensor surface on which the thin-film resistance patterns of the four AMR elements 10-1 to 10-4 are formed (a surface parallel to the magnetic sensing direction of the AMR elements 10-1 to 10-4 and parallel to the plane of the paper in Figure 2), if a constant current I is passed through the bridge circuit 1a from a power supply not shown, the midpoint potential difference V(θ), which is the output electrical signal, (the potential difference between the midpoint of the first series circuit 10-5 and the midpoint of the second series circuit 10-6) is expressed by equation (1) depending on the rotation angle θ of the magnetic field.

[0018]

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[0019] From equation (1), the midpoint potential difference V(θ) is a periodic function with an amplitude of V0 and two periods per rotation of the magnetic field. The rotation angle θ of the magnetic field can be calculated from the midpoint potential difference V(θ) using equation (2).

[0020]

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[0021] Once the half cycle is exceeded, the rotation angle θ cannot be uniquely determined for the midpoint potential difference V(θ), so the angle measurement range of conventional angle sensors is limited to 90 degrees.

[0022] [Example] FIG. 3 shows the configuration of a liquid level gauge according to an embodiment of the present invention, and FIG. 4 shows the configuration of an angle sensor according to an embodiment of the present invention. The same components as those in FIGS. 1 and 10 are designated by the same reference numerals. In this embodiment, as shown in FIGS. 3 and 4, the bridge circuit 1a (sensor circuit), rotor 2, and magnets 3 and 4 (magnetic field generator) of angle sensor 100a are arranged so that the plane of rotation 7 of the magnetic field intersects with sensor surface 6a on which the thin-film resistor patterns of AMR elements 10-1 to 10-4 are formed, within the tilt angle range of greater than 0 degrees and less than 90 degrees. Magnets 3 and 4 are attached to rotor 2, which is fixed to the tip of torque rod 104, and rotate about rotation axis A as rotor 2 rotates. An extension of rotation axis A passes through the center of diamond-shaped (square) bridge circuit 1a shown in FIG. 2.

[0023] In a magnetically saturated state, the output of AMR elements 10-1 to 10-4 is constant regardless of the distance from magnets 3 and 4, and depends only on the angle of the magnetic field. Therefore, when magnetic field rotation plane 7 is inclined with respect to sensor surface 6a as shown in Figure 4, it is not necessary to consider changes in distance due to the rotation orbit of magnets 3 and 4, as long as the magnetic field strength is strong enough to cause AMR elements 10-1 to 10-4 to be magnetically saturated, even at the position within the measurement range where magnets 3 and 4 are furthest from AMR elements 10-1 to 10-4.

[0024] As the rotor 2 rotates, the magnets 3 and 4 describe a perfect circular trajectory within the plane of rotation 7 of the magnetic field. Here, if the rotation angle of the magnetic field is φ, the angle between the plane of rotation 7 of the magnetic field and the sensor surface 6a is α (0<α<90 degrees), and the rotation angle of the magnetic field on the sensor surface 6a is θ, then, as mentioned above, there is no need to consider the distance from the magnets 3 and 4, and so the rotation of the magnets 3 and 4 can be thought of as an elliptical trajectory rather than a perfect circle. Specifically, if the radius of rotation of the magnets 3 and 4 is R, then the trajectory of the magnets 3 and 4 can be thought of as the trajectory of an ellipse 8 in Figure 5, with the minor axis R and the major axis R / cosα.

[0025] From FIG. 5, formulas (3) to (6) are obtained. cosφ=cosθ (3) sinφ=sinθ / cosα (4) tanφ=sinφ / cosφ=(sinθ / cosα) / cosθ = tanθ / cosα (5) φ=tan -1 (tanθ / cosα) (6)

[0026] Here, equation (8) is obtained from equation (7).

[0027]

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[0028]

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[0029] Also, since sin2θ=V(θ) / V0, if we set V(θ) / V0=x, we obtain equation (9).

[0030]

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[0031] Therefore, the rotation angle φ of the magnetic field can be obtained from the output electrical signal of the bridge circuit 1a. Now, let us consider how the range of the rotation angle φ of the magnetic field, which corresponds to the 90° range of -45°≦θ≦45°, changes depending on the inclination angle α of the rotation plane 7 of the magnetic field relative to the sensor surface 6a. Within this range of θ, -1≦sin2θ≦1, and the rotation angle φ of the magnetic field reaches its maximum value φ when θ is 45°. max When θ is -45°, the minimum value φ min Take.

[0032]

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[0033]

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[0034] Maximum value φ maxand the minimum value φ min The difference between these, i.e., the range Δφ of the measurable rotation angle φ of the magnetic field, is given by equation (12).

[0035]

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[0036] When the tilt angle α = 0°, φ = θ, so the measurable range of the magnetic field rotation angle φ is Δφ = 90°. When the tilt angle α = ±90°, the magnetic field rotation angle φ does not depend on the value of θ, so it cannot be measured.

[0037] In the example of Figure 5, bridge circuit 1a, rotor 2, and magnets 3 and 4 are arranged so that the direction (reference position) in which midpoint potential difference V(θ), which is the output electrical signal of bridge circuit 1a, becomes zero coincides with the intersection (L in Figure 5) of the magnetic field rotation plane 7 (plane of orbit 8 in Figure 5) and sensor plane 6a. In Figures 2 and 5, the reference position is indicated by θ0. In the example of Figure 2, reference position θ0 is a direction parallel to the magnetic sensing direction of AMR elements 10-2 and 10-3 and perpendicular to the magnetic sensing direction of AMR elements 10-1 and 10-4.

[0038] In contrast, this embodiment describes a case where the plane of rotation 7 of the magnetic field is not parallel to the sensor surface 6a and the reference position θ0 of the bridge circuit 1a is not on the intersection line L between the plane of rotation 7 of the magnetic field and the sensor surface 6a. As in the case above, an extension of the rotation axis A passes through the center of the bridge circuit 1a, but here we consider a case where the reference position θ0 of the bridge circuit 1a is shifted by an angle β from the intersection line L on the sensor surface 6a and by an angle ψ from the intersection line L on the plane of rotation of the magnetic field, as shown in Figure 6.

[0039] By substituting φ → φ-ψ and θ → θ-β in equation (6), equation (13) is obtained.

[0040]

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[0041] Furthermore, the relationship shown in equation (14) also holds between the angles ψ and β.

[0042]

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[0043] By substituting equation (14) into equation (13), the rotation angle φ of the magnetic field is given by equation (15).

[0044]

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[0045] If we rearrange the right-hand side of equation (15) and express it using x, we get equation (16).

[0046]

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[0047] The range Δφ of the rotation angle φ of the magnetic field that can be measured in the range of -45°≦θ≦45° varies depending on the inclination angle α of the rotation plane 7 of the magnetic field relative to the sensor surface 6a and the angle β of the reference position θ0 on the sensor surface 6a relative to the intersection line L between the rotation plane of the magnetic field and the sensor surface 6a. The maximum value of the rotation angle φ when the rotation angle θ changes by 90 degrees from -45° to 45° when the angles α and β are within the ranges of -90°≦α≦90° and -90°≦β≦90°, respectively, is defined as φ. max , the minimum value is φ min The range Δφ of the measurable rotation angle φ is defined as φ max -φ min FIG. 7 is a diagram showing the relationship between angles α and β and the range Δφ of the measurable rotation angle φ. However, in FIG. 7, the ranges of α<0 and β<45 are omitted. Also, 700 in FIG. 7 indicates the range of conditions where measurement is not possible.

[0048] According to Figure 7, when the tilt angle α of the rotation plane 7 of the magnetic field relative to the sensor surface 6a is 0°, the measurable range of rotation angles φ is Δφ = 90°, regardless of the angle β. In the range of β < -45° and β > 45°, Δφ < 90°, which is narrower than the range of rotation angles θ. For example, when β = 90° and α = 86°, the measurable range of rotation angles φ is Δφ = 7.98°. This range of rotation angles φ Δφ corresponds to the range of -45° ≦ θ ≦ 45° on the sensor surface 6a, so it can be said that the angle range is expanded by approximately 11.3 times.

[0049] That is, even if the change in the rotation angle φ of the magnetic field is small, the change in the rotation angle θ on the sensor surface 6a is large, so it is possible to increase the change in the midpoint potential difference V(θ) of the bridge circuit 1a relative to the change in the rotation angle φ. As a result, in this embodiment, it is not necessary to greatly amplify the midpoint potential difference V(θ) of the bridge circuit 1a, so it is possible to suppress noise associated with the amplification of the midpoint potential difference V(θ), and it becomes possible to accurately measure the rotation angle φ of the magnetic field.

[0050] FIG. 8 shows an enlarged view of FIG. 7 for -90°≦β≦90°. However, detailed description of the ranges of -90°≦β<-45° and 45°<β≦90° is omitted in FIG. 8. From equation (16), FIG. 8 is symmetrical with respect to the tilt angle α=0. On the other hand, since sin2β is present in equation (16), φ max、 φ min differs depending on whether the angle β is positive or negative, but Δφ=φ max -φ min FIG. 8, which shows the relationship between the β and β, is symmetric with respect to β=0.

[0051] In addition, when the tilt angle α is approximately 65° or more (or -65° or less) within the range of -45°≦β≦45°, the rotation angle φ becomes discontinuous depending on the value of the angle β. Discontinuity means that the rotation angle φ shifts by 180° midway. In Figure 8, 800 indicates the range including the discontinuous point. In this embodiment, the discontinuity does not cause any problems since the angle is used in the range of -90°≦β<-45° or 45°<β≦90°.

[0052] In this embodiment shown in FIG. 4, a power supply 13 supplies a constant current I to the bridge circuit 1a. A voltage detection unit 11 detects a midpoint potential difference V(θ) of the bridge circuit 1a. The voltage detection unit (output electrical signal detection unit) 11 includes an amplifier (not shown) that amplifies the detected midpoint potential difference V(θ). In this embodiment, the change in the midpoint potential difference V(θ) relative to a change in the rotation angle φ can be made large, so the gain of the amplifier can be made smaller than in angle sensors used in conventional liquid level gauges.

[0053] The rotation angle calculation unit 12 of this embodiment calculates the rotation angle θ of the magnetic field on the sensor surface 6a based on the midpoint potential difference V(θ) detected by the voltage detection unit 11, and calculates the rotation angle φ of the magnetic field (the rotation angle of the rotor 2 and torque rod 104) using equation (15) based on the rotation angle θ and the known angles α and β. In this case, the rotation angle calculation unit 12 calculates the rotation angle θ of the magnetic field from the midpoint potential difference V(θ) using a pre-registered approximation function that indicates the relationship between the midpoint potential difference V(θ) and the rotation angle θ of the magnetic field.

[0054] In the above embodiment, the rotation angle θ of the magnetic field on the sensor surface 6a is calculated based on the midpoint potential difference V(θ) of the bridge circuit 1a. Alternatively, a constant voltage may be applied to the bridge circuit 1a, and the rotation angle θ of the magnetic field on the sensor surface 6a may be calculated based on the current value A(θ) flowing through the bridge circuit 1a. Furthermore, although a liquid level gauge is used as an example in the explanation of FIG. 3, it goes without saying that the angle sensor 100a of this embodiment can be applied to devices other than a liquid level gauge.

[0055] The rotation angle calculation unit 12 described in this embodiment can be realized by a computer including a CPU (Central Processing Unit), a storage device, and an interface with the outside, and a program that controls these hardware resources. An example configuration of this computer is shown in FIG. 9. The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The I / F 202 is connected to the hardware of the voltage detection unit 11, etc. The CPU 200 executes the processing described in this embodiment in accordance with the program stored in the storage device 201. [Industrial Applicability]

[0056] The present invention can be applied to a technique for measuring a rotation angle. [Explanation of symbols]

[0057] 1a...bridge circuit, 2...rotating body, 3, 4...magnet, 10-1 to 10-4...AMR element, 11...voltage detection unit (output electrical signal detection unit), 12...rotation angle calculation unit, 13...power supply, 100a...angle sensor, 101...torque tube, 102...float, 103...torque arm, 104...torque rod, 105...knife edge fulcrum.

Claims

1. a sensor circuit including a magnetoresistive element; a magnetic field generating unit configured to generate a magnetic field that rotates around a rotation axis; an output electrical signal detection unit configured to detect an output electrical signal of the sensor circuit; a rotation angle calculation unit configured to calculate a rotation angle of the magnetic field based on the output electrical signal detected by the output electrical signal detection unit, the sensor circuit and the magnetic field generating unit are arranged so that a plane of rotation of the magnetic field intersects with a sensor surface on which a thin film resistance pattern of the magnetoresistive effect element is formed, An angle sensor characterized in that the reference position where the output voltage of the sensor circuit is zero is not on the intersection line between the rotation plane of the magnetic field and the sensor surface, and the angle β between the reference position on the sensor surface and the intersection line is in the range of -90°≦β<-45° or 45°<β≦90°.

2. 2. The angle sensor according to claim 1, The rotation angle calculation unit calculates a rotation angle θ of the magnetic field on the sensor surface based on the output electrical signal detected by the output electrical signal detection unit, and calculates φ=tan θ based on the rotation angle θ, an inclination angle α of the rotation plane of the magnetic field with respect to the sensor surface, and an angle β between the reference position on the sensor surface and the intersection line. -1 {tan(θ-β) / cosα}+tan -1 An angle sensor characterized by calculating a rotation angle φ of the magnetic field on the plane of rotation by (tan β / cos α).

3. 3. The angle sensor according to claim 2, The rotation angle calculation unit calculates the rotation angle θ from the output electrical signal detected by the output electrical signal detection unit using an approximation function that indicates the relationship between the output electrical signal of the sensor circuit and the rotation angle θ.

4. 4. The angle sensor according to claim 1, An angle sensor characterized in that the magnetic field is saturated with respect to the magnetoresistive effect element of the sensor circuit regardless of the rotation angle.

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