Position Sensor

Abstract

To detect a position of a movable part with a resolution finer than before.SOLUTION: A position sensor includes: a bridge circuit 1 that is a sensor circuit including a magneto resistance effect element; a magnet 11 that linearly moves on a plane 9 crossing a sensor plane 6 on which a thin film resistor pattern of the magneto resistance effect element is formed; a sensor output detection unit 21 that detects output of the bridge circuit 1; an angle calculation unit 22 that calculates an angle of a magnetic field generated by the magnet 11 on the basis of the output of the bridge circuit 1; and a position calculation unit 23 that calculates coordinates of the magnet 11 on the basis of the angle of the magnetic field.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a position sensor that detects the position of a movable part that moves linearly. [Background technology]

[0002] Conventionally, linear encoders and the like have been common position sensors that detect position non-contact with high precision (see Patent Document 1). Linear encoders are classified into magnetic and optical types. As shown in FIG. 15, an optical linear encoder comprises a scale 200 with slits formed therein and a detector 201 that detects position information, and detects position by having the detector 201 detect light that has passed through or been reflected by the scale 200. A magnetic linear encoder detects position by using a magnetic sensor to detect changes in the magnetic field distribution created by a magnetic scale in which south and north poles are finely arranged alternately.

[0003] In conventional techniques, both magnetic and optical linear encoders use a scale, which has the problem that it is not possible to detect a position with a resolution finer than the interval between graduations on the scale. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-121277 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide a position sensor that can detect the position of a movable part with a finer resolution than conventional ones. [Means for solving the problem]

[0006] The position sensor of the present invention is characterized by comprising a sensor circuit including a magnetoresistive element, a magnet configured to move linearly on a plane intersecting a sensor surface on which the thin film resistance pattern of the magnetoresistive element is formed, a sensor output detection unit configured to detect the output of the sensor circuit, an angle calculation unit configured to calculate the angle of a magnetic field generated by the magnet based on the output of the sensor circuit, and a position calculation unit configured to calculate the coordinates of the magnet based on the angle of the magnetic field.

[0007] Furthermore, one configuration example of the position sensor of the present invention is characterized in that the reference position where the output voltage of the sensor circuit becomes zero coincides with the intersection line between the plane and the sensor surface, the magnet moves linearly on the plane in the direction of the intersection line, and the position calculation unit calculates the coordinate of the magnet in the direction of the intersection line based on the angle of the magnetic field. Furthermore, one configuration example of the position sensor of the present invention is characterized in that the reference position where the output voltage of the sensor circuit is zero is not on the intersection line between the plane and the sensor surface, the magnet moves linearly on the plane in the direction of the intersection line, and the position calculation unit calculates the coordinate of the magnet in the direction of the intersection line based on the angle of the magnetic field and the angle between the reference position on the sensor surface and the intersection line.

[0008] The position sensor of the present invention is characterized by comprising: a sensor circuit including a magnetoresistive element; a first magnet configured to move linearly along a trajectory on a plane parallel to a sensor surface on which a thin film resistance pattern of the magnetoresistive element is formed; a second magnet arranged at a fixed position on the plane so as to face the first magnet with the sensor circuit therebetween; a sensor output detection unit configured to detect the output of the sensor circuit; an angle calculation unit configured to calculate the angle of a magnetic field generated by the first and second magnets based on the output of the sensor circuit; and a position calculation unit configured to calculate the coordinates of the first magnet based on the angle of the magnetic field.

[0009] In addition, in one configuration example of the position sensor of the present invention, the first magnet moves linearly in the direction of the trajectory that intersects with the direction of the reference position where the output voltage of the sensor circuit is zero, and the position calculation unit calculates the coordinates of the first magnet on the trajectory based on the distance from the sensor circuit to the intersection between the direction of the reference position and the trajectory, the distance from the sensor circuit to the second magnet, and the angle of the magnetic field. In addition, in one configuration example of the position sensor of the present invention, the first and second magnets of the cylindrical body are magnetized so that their magnetic poles face each other in the radial direction, and are housed inside the housing tube in a state where free rotation around the axis is allowed, and are arranged so that their axial direction is perpendicular to the direction of the orbit of the first magnet. In addition, in one configuration example of the position sensor of the present invention, the sensor circuit is a bridge circuit in which four of the magnetoresistive effect elements are connected, and the output of the sensor circuit detected by the sensor output detection unit is the midpoint potential difference of the bridge circuit. [Effects of the Invention]

[0010] According to the present invention, by providing a sensor circuit including a magnetoresistive element, a magnet that moves linearly on a plane that intersects with the sensor surface on which the thin film resistance pattern of the magnetoresistive element is formed, a sensor output detection unit that detects the output of the sensor circuit, an angle calculation unit that calculates the angle of the magnetic field generated by the magnet based on the output of the sensor circuit, and a position calculation unit that calculates the coordinates of the magnet based on the angle of the magnetic field, it is possible to detect the position of the magnet, which is a moving part, with finer resolution than conventionally possible.

[0011] In addition, the present invention provides a sensor circuit including a magnetoresistive element, a first magnet that moves linearly on a trajectory on a plane parallel to the sensor surface on which the thin film resistance pattern of the magnetoresistive element is formed, a second magnet that is arranged at a fixed position on the plane so as to face the first magnet with the sensor circuit in between, a sensor output detection unit that detects the output of the sensor circuit, an angle calculation unit that calculates the angle of the magnetic field generated by the first and second magnets based on the output of the sensor circuit, and a position calculation unit that calculates the coordinates of the first magnet based on the angle of the magnetic field, thereby making it possible to detect the position of the first magnet, which is a movable part, with finer resolution than conventional devices. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of a conventional angle sensor. [Figure 2] FIG. 2 is a circuit diagram of a bridge circuit configured with AMR elements. [Figure 3] FIG. 3 is a diagram illustrating the principle of the angle sensor used in the present invention. [Figure 4] FIG. 4 is a diagram showing the orbit of the magnet accompanying the rotation of the rotor in the angle sensor of FIG. [Figure 5] FIG. 5 is a diagram showing the trajectory of the magnet accompanying the rotation of the rotor in the angle sensor of FIG. [Figure 6] FIG. 6 is a diagram showing the configuration of a position sensor according to a first embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing the trajectory of a magnet projected onto the sensor surface according to the first embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing the configuration of a position sensor according to a second embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing the trajectory of a magnet projected onto the sensor surface according to the second embodiment of the present invention. [Figure 10] FIG. 10 is a diagram illustrating the effect of the position sensor according to the second embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing the configuration of a position sensor according to a third embodiment of the present invention. [Figure 12] FIG. 12 is a diagram showing the trajectory of the first magnet projected onto the sensor surface according to the third embodiment of the present invention. [Figure 13] FIG. 13 is a cross-sectional view of the first and second magnets according to the third embodiment of the present invention. [Figure 14] FIG. 14 is a block diagram showing an example of the configuration of a computer that realizes the position sensors according to the first to third embodiments of the present invention. [Figure 15] FIG. 15 is a diagram showing the configuration of a conventional linear encoder. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Principle of the Invention] In this invention, position is detected using an angle sensor that uses an anisotropic magnetoresistive effect (AMR) element. With an angle sensor that uses an AMR element, if the trajectory of the magnet that generates the magnetic field is known, the position of the magnet can be measured from the angle of the magnetic field even if the magnet moves linearly rather than rotationally.

[0014] In angle sensors using AMR elements or Hall elements, the angle of the magnetic field is generally measured by rotating a magnet around the periphery of the sensor circuit. However, as in the present invention, by moving the magnet across the surface of the sensor circuit rather than around the periphery of the sensor circuit, the angle of the magnetic field can be detected, making it possible to measure position with higher accuracy and finer resolution than conventional methods.

[0015] [Conventional example] First, before describing the embodiments of the present invention, a conventional angle sensor will be described in detail. FIG. 1 is a diagram showing the configuration of an angle sensor. The angle sensor measures the rotation angle of a magnetic field generated by magnets 3 and 4 attached to a rotating body 2. A bridge circuit 1, which is a sensor circuit using AMR elements, is used to measure the angle. In FIG. 1, 5 indicates the direction of the magnetic field generated by magnets 3 and 4, and 6 indicates the sensor surface of bridge circuit 1. In a conventional angle sensor, as shown in FIG. 1, the sensor surface 6 is installed so that it is parallel to the rotation plane of the magnetic field.

[0016] Figure 2 shows a bridge circuit 1 made up of AMR elements whose electrical resistance changes with a magnetic field. Bridge circuit 1 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.

[0017] 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.

[0018] When the plane of rotation of the magnetic field generated by the magnets 3 and 4 of the angle sensor is parallel to the sensor surface 6 (a plane 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) on which the thin-film resistance patterns of the four AMR elements 10-1 to 10-4 are formed, if a constant current I is passed through the bridge circuit 1 from a power supply not shown, the midpoint potential difference V(θ) (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.

[0019]

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[0020] 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).

[0021]

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[0022] 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.

[0023] [I. When the magnetic field rotation plane and the sensor surface are not parallel] Next, in the first and second embodiments of the present invention, the magnet that generates the magnetic field travels on a trajectory on a plane that intersects with the sensor surface of the angle sensor at an angle α. Therefore, before explaining this configuration in detail, we will explain the operation of the angle sensor when the plane of rotation intersects with the sensor surface.

[0024] Figure 3 is a diagram explaining the principle of the angle sensor used in the present invention. In the configuration of Figure 3, bridge circuit 1, rotor 2, and magnets 3 and 4 are arranged so that the rotation plane 7 of the magnetic field intersects with sensor plane 6. Magnets 3 and 4 are attached to rotor 2 and rotate around rotation axis A as rotor 2 rotates. An extension of rotation axis A passes through the center of diamond-shaped (square) bridge circuit 1 shown in Figure 2.

[0025] 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 6 as shown in Figure 3, 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.

[0026] 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 6 is α, and the rotation angle of the magnetic field on the sensor surface 6 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 4, with the minor axis R and the major axis R / cosα.

[0027] From FIG. 4, 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)

[0028] Here, equation (8) is obtained from equation (7).

[0029]

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[0030]

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[0031] Also, since sin2θ=V(θ) / V0, if we set V(θ) / V0=v, we obtain equation (9).

[0032]

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[0033] Therefore, the rotation angle φ of the magnetic field can be calculated from the output of the bridge circuit 1. Now, 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 6. 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.

[0034]

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[0035]

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[0036] Maximum value φ max and 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).

[0037]

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[0038] When the tilt angle α = 0°, φ = θ, so the measurable range of the magnetic field rotation angle φ is Δφ = 90°. On the other hand, when the tilt angle α = ±90°, the rotation angle φ does not depend on the value of θ, so it cannot be measured.

[0039] [II. When the magnetic field rotation plane and the sensor surface are not parallel and there is no reference position on the intersection of the plane] In the example of Figure 4, the bridge circuit 1, rotor 2, and magnets 3 and 4 are arranged so that the direction (reference position) in which the midpoint potential difference V(θ) of bridge circuit 1 is zero coincides with the intersection (L in Figure 4) of the plane of rotation of the magnetic field (the plane of orbit 8 in Figure 4) and sensor plane 6. In Figures 2 and 4, the reference position is indicated by θ0. In the example of Figure 2, the reference position θ0 is 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.

[0040] In contrast, the example in Fig. 5 will be described for the case where the plane of rotation of the magnetic field (the plane of trajectory 8 in Fig. 5) is not parallel to the sensor surface 6 and the reference position θ0 of the bridge circuit 1 is not on the intersection L between the plane of rotation of the magnetic field and the sensor surface 6. Here, as shown in Fig. 5, we consider the case where the reference position θ0 of the bridge circuit 1 is shifted by an angle β from the intersection L on the sensor surface 6 and by an angle ψ from the intersection L on the plane of rotation of the magnetic field.

[0041] By substituting φ → φ-ψ and θ → θ-β in equation (6), equation (13) is obtained.

[0042]

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[0043] Furthermore, the relationship shown in equation (14) also holds between the angles ψ and β.

[0044]

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[0045] By substituting equation (14) into equation (13), the rotation angle φ of the magnetic field is given by equation (15).

[0046]

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[0047] If we rearrange the right-hand side of equation (15) and express it using v, we get equation (16).

[0048]

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[0049] 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 of the magnetic field relative to the sensor surface 6 and the angle β of the reference position θ0 on the sensor surface 6 relative to the intersection line L between the rotation plane of the magnetic field and the sensor surface 6. In the present invention, the position of the magnet is detected by utilizing the operating principle of the angle sensor explained in FIGS.

[0050] [First Example] 6 is a diagram showing the configuration of a position sensor according to a first embodiment of the present invention. The position sensor of this embodiment is composed of a bridge circuit 1 (sensor circuit), a magnet 11 which is a movable part that moves linearly on a plane 9 intersecting with a sensor surface 6 on which a thin-film resistance pattern of an AMR element is formed, a power supply 20 which supplies current to the bridge circuit 1, a sensor output detection unit 21 which detects the output of the bridge circuit 1, an angle calculation unit 22 which calculates the angle of the magnetic field generated by the magnet 11 based on the output of the bridge circuit 1, and a position calculation unit 23 which calculates the coordinates of the magnet 11 based on the angle of the magnetic field.

[0051] In this embodiment, the magnet 11, which is the movable part, moves linearly on a plane 9 that intersects with the sensor surface 6 of the bridge circuit 1 at an angle α, as shown by the trajectory p in Figure 6. The intersection between the plane 9 and the sensor surface 6 passes through the center of the bridge circuit 1. However, the trajectory p does not pass through the center of the bridge circuit 1.

[0052] Magnet 11 is mounted, for example, on the carriage of a linear guide mechanism (not shown), and the carriage moves along the rails of the linear guide mechanism, allowing it to move linearly on plane 9. When using a linear guide mechanism, it is desirable that the carriage and rails be made of a non-magnetic material that is not attracted to magnet 11 and is magnetically permeable so that the magnetic lines of force of magnet 11 can pass through them.

[0053] The direction of the intersection line between plane 9 and sensor surface 6 is defined as x, the direction perpendicular to the x direction on sensor surface 6 as y, the normal direction to sensor surface 6 as z, the direction of the reference position of bridge circuit 1 on sensor surface 6 as θ0, and the angle of the magnetic field from the reference position θ0 on sensor surface 6 as θ. This embodiment is an example in which the reference position θ0 coincides with the x direction. Figure 7 is a diagram in which the trajectory p of magnet 11 in Figure 6 is projected onto sensor surface 6.

[0054] In this embodiment, v is defined as shown in equation (17) based on the midpoint potential difference V(θ)=V0·sin2θ of the bridge circuit 1, which is the output of the angle sensor. v=V(θ) / V0=sin2θ (17)

[0055] If the coordinates of magnet 11 are f(θ) = (x, y, z) and the length of the line projected onto sensor surface 6 from the center of bridge circuit 1 to magnet 11 as shown in Figures 6 and 7 is L(θ), then the x-coordinate, y-coordinate, and z-coordinate of the magnet are given by equations (18) to (20), respectively. x = L(θ) cos(θ) (18) y = L(θ) sin(θ) (19) z=y・tanα=L(θ)・sin(θ)・tanα (20)

[0056] For example, if the magnet 11 is predetermined to move linearly in the x direction, the position of the magnet 11 can be expressed by equation (21). y=c (21)

[0057] In equation (21), c is a constant. Therefore, the length L(θ) is determined as shown in equation (22). L(θ)=c / sin(θ) (22)

[0058] From equations (17) to (22), the x coordinate and z coordinate of magnet 11 can be calculated as equations (23) and (24), respectively.

[0059]

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[0060] z=c tan α (24) In this case, z does not appear in the x term, so fluctuations in z do not affect the measurement of x.

[0061] 6 supplies a constant current I to the bridge circuit 1. A sensor output detection unit 21 detects the midpoint potential difference V(θ) of the bridge circuit 1 as the sensor output.

[0062] Based on the midpoint potential difference V(θ), the angle calculation unit 22 calculates the angle θ of the magnetic field on the sensor surface 6. In this case, the angle calculation unit 22 may calculate the 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 angle θ of the magnetic field.

[0063] The position calculation unit 23 calculates the x coordinate of the magnet 11 using equation (23) based on the angle θ of the magnetic field and the known constant c. In this way, in this embodiment, the position of the magnet 11 can be calculated.

[0064] In this embodiment, the magnetic field angle θ is detected using the principle of an angle sensor that uses a bridge circuit 1 configured with AMR elements 10-1 to 10-4. Because the angle sensor can continuously detect the magnetic field angle θ, there is no resolution restriction like in conventional linear encoders. Therefore, in this embodiment, the position of the magnet 11 can be detected with a higher resolution than conventional ones.

[0065] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 8 is a diagram showing the configuration of a position sensor according to the second embodiment of the present invention. In the first embodiment, the plane 9 through which the magnet 11 passes is not parallel to the sensor surface 6, and the plane 9 is defined so that the reference position θ0, which is the direction in which the midpoint potential difference V(θ) of the bridge circuit 1 becomes zero, coincides with the intersection of the plane 9 and the sensor surface 6.

[0066] In contrast, this embodiment describes a case where the plane 9 is not parallel to the sensor surface 6 and the reference position θ0 of the bridge circuit 1 is not on the intersection line between the plane 9 and the sensor surface 6. As in the first embodiment, the intersection line between the plane 9 and the sensor surface 6 passes through the center of the bridge circuit 1.

[0067] The direction of the intersection line between plane 9 and sensor surface 6 is defined as x, the direction perpendicular to the x direction on sensor surface 6 is defined as y, the normal direction to sensor surface 6 is defined as z, the direction of the reference position of bridge circuit 1 on sensor surface 6 is defined as θ0, the angle of the magnetic field from reference position θ0 on sensor surface 6 is defined as θ, and the angle between reference position θ0 on sensor surface 6 and the intersection line (x-axis) is defined as β. Figure 9 is a diagram showing the trajectory p of magnet 11 in Figure 8 projected onto sensor surface 6.

[0068] As in the first embodiment, if the coordinates of magnet 11 are f(θ) = (x, y, z) and the length of the line projected onto sensor surface 6 from the center of bridge circuit 1 to magnet 11 as shown in Figures 8 and 9 is L(θ), then the x-coordinate, y-coordinate, and z-coordinate of the magnet are given by equations (25) to (27), respectively. x=L(θ)·cos(θ-β) ···(25) y=L(θ)·sin(θ-β) ···(26) z=y tanα=L(θ) sin(θ-β) tanα (27)

[0069] As in the first embodiment, when magnet 11 is predetermined to move linearly in the x direction, the position of magnet 11 can be expressed by equation (21). Therefore, length L(θ) is determined by equation (28). L(θ)=c / sin(θ-β) (28)

[0070] From equations (17) and (25) to (28), the x coordinate and z coordinate of magnet 11 can be calculated as equations (29) and (24), respectively.

[0071]

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[0072] In addition, equation (29) was transformed into equation (30) by changing tan θ.

[0073]

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[0074] As with the first embodiment, fluctuations in z do not affect the measurement of x. Since angle sensors have a track record of measuring with a resolution of 1 / 100° or less, when c = 1 mm, it is theoretically possible to detect the x coordinate of magnet 11 with a resolution of about 10 μm in the vicinity of v = 0.

[0075] The closer c is to 0 (the closer the orbit of magnet 11 is to the center of bridge circuit 1), the more accurately it is possible to detect short-distance movements of magnet 11. The relationship between v and x / c is shown in Figure 10. Figure 10 shows that the slope becomes gentler near x / c = 0, and the output change v becomes larger for small movements of magnet 11.

[0076] The operations of the power supply 20, the sensor output detector 21, and the angle calculator 22 are the same as those described in the first embodiment. The position calculation unit 23a of this embodiment calculates the x coordinate of the magnet 11 using equation (29) based on the magnetic field angle θ calculated by the angle calculation unit 22, the known constant c, and the known angle β.

[0077] [Third Example] In the first and second embodiments, only one magnet was used. To align the magnetic field, it is desirable to use two magnets. When using two magnets, it is difficult to move the pair of magnets so that they are symmetrical about the center of the bridge circuit. Therefore, in this embodiment, the position of the second magnet is fixed relative to the first magnet, which is the movable part. It is desirable for the magnetic field generated by the first and second magnets to pass through the center of the bridge circuit, but since it is difficult to place a magnet in the center of the bridge circuit, the second magnet is placed outside the bridge circuit.

[0078] 11 is a diagram showing the configuration of a position sensor according to this embodiment. The position sensor according to this embodiment includes a bridge circuit 1, a first magnet 11-1 which is a movable part that moves linearly along a path on a plane parallel to the sensor surface 6 of the bridge circuit 1, a second magnet 11-2 which is disposed at a fixed position on the plane so as to face the first magnet 11-1 with the bridge circuit 1 therebetween, a power supply 20 which supplies current to the bridge circuit 1, a sensor output detection unit 21b which detects the output of the bridge circuit 1, an angle calculation unit 22b which calculates the angle of the magnetic field generated by the first and second magnets 11-1 and 11-2 based on the output of the bridge circuit 1, and a position calculation unit 23b which calculates the coordinates of the first magnet 11-1 based on the angle of the magnetic field.

[0079] Reference numeral 12 in FIG. 11 indicates the direction of the magnetic field generated by magnets 11-1 and 11-2. In this embodiment, the plane on which magnets 11-1 and 11-2 are arranged is parallel to the sensor surface of bridge circuit 1. As in the first and second embodiments, magnet 11-1 is mounted on, for example, a carriage of a linear guide mechanism (not shown), and as the carriage moves along the rails of the linear guide mechanism, it moves linearly in a direction perpendicular to the reference position θ0 of bridge circuit 1. In this embodiment, the direction perpendicular to this reference position θ0 is defined as x.

[0080] 12 is a diagram in which the trajectory p of the magnet 11-1 in FIG. 11 is projected onto the sensor surface 6. As shown in FIG. 12, the distance from the center of the bridge circuit 1 to the intersection point between the reference position θ0 of the bridge circuit 1 and the trajectory p of the magnet 11-1 is defined as L A , the distance from the center of bridge circuit 1 to magnet 11-2 is L B The angle of the magnetic field from the reference position θ0 of the bridge circuit 1 on the sensor surface 6 is defined as ω, and the angle between the center of the bridge circuit 1 and the magnet 11-1 is defined as λ. From the midpoint potential difference V(ω) = V0 sin2ω of the bridge circuit 1, v is defined as shown in equation (31). v=V(ω) / V0=sin2ω (31)

[0081] distance L A ,L B The relationship between the angle λ and the angle ω is as shown in equations (32) and (33). L A tanλ=(L A +L B )·tanω ···(32)

[0082]

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[0083] Therefore, the x coordinate of the magnet 11-1 is given by equation (34).

[0084]

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[0085] The power supply 20 of this embodiment supplies a constant current I to the bridge circuit 1. The sensor output detection unit 21b detects the midpoint potential difference V(ω) of the bridge circuit 1 as the sensor output.

[0086] Based on the midpoint potential difference V(ω), the angle calculation unit 22b calculates the angle ω of the magnetic field on the sensor surface 6. In this case, the angle calculation unit 22b may calculate the angle ω of the magnetic field from the midpoint potential difference V(ω) using a pre-registered approximation function that indicates the relationship between the midpoint potential difference V(ω) and the angle ω of the magnetic field.

[0087] The position calculation unit 23b calculates v by equation (31) based on the angle ω of the magnetic field, and compares the calculated v with the known distance L A ,L B Based on this, the x coordinate of the magnet 11-1 is calculated using equation (34).

[0088] Magnets 11-1 and 11-2 need to attract each other, but because the position of magnet 11-2 is fixed while the position of magnet 11-1 changes, it is possible that magnets 11-1 and 11-2 will repel each other. Therefore, even if the position of magnet 11-1 changes, the positions of the magnetic poles are automatically changed so that magnets 11-1 and 11-2 will attract each other.

[0089] Cross sections of magnets 11-1 and 11-2 are shown in Figure 13. Magnets 11-1 and 11-2 are each formed in a cylindrical shape, and are magnetized with two poles, an N pole and an S pole, facing each other in the radial direction of the cylinder. The housing cylinders 13-1 and 13-2 are made of a non-magnetic material (e.g., synthetic resin) that is not attracted to the magnets 11-1 and 11-2 but is magnetically permeable so that the magnetic lines of force of the magnets 11-1 and 11-2 can pass through, and are formed into a cylindrical shape with both ends closed. The magnets 11-1 and 11-2 are housed in the cylindrical internal spaces of the housing cylinders 13-1 and 13-2, respectively.

[0090] The inner diameter of the housing cylinders 13-1 and 13-2 is slightly larger than the outer diameter of the magnets 11-1 and 11-2. The length of the internal space of the housing cylinders 13-1 and 13-2 is slightly longer than the length of the magnets 11-1 and 11-2. This structure allows the magnets 11-1 and 11-2 to rotate freely around their axes inside the housing cylinders 13-1 and 13-2. The inner wall surfaces of the housing cylinders 13-1 and 13-2 may be surface-treated to ensure smoothness between them and the magnets 11-1 and 11-2.

[0091] The magnets 11-1 and 11-2 and the housing cylinders 13-1 and 13-2 as described above are arranged so that the axial direction of the magnets 11-1 and 11-2 is perpendicular to the direction of the orbit p of the magnet 11-1 (parallel to the direction of the reference position θ0).

[0092] Even if magnets 11-1 and 11-2 were to repel each other when magnet 11-1 moved linearly, magnets 11-1 and 11-2 would rotate around their axes inside housing tubes 13-1 and 13-2, respectively, causing the opposite poles of magnets 11-1 and 11-2 to attract each other. In other words, the positions of the magnetic poles of magnets 11-1 and 11-2 are automatically changed. Therefore, even if the position of magnet 11-1 changes, magnets 11-1 and 11-2 will not repel each other. The structure of magnets 11-1 and 11-2 described above is disclosed in Japanese Patent No. 3822062. Note that magnets 11-1 and 11-2 do not need to have the same shape.

[0093] The angle calculation units 22, 22b and the position calculation units 23, 23a, 23b described in the first to third embodiments 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 of the configuration of this computer is shown in FIG. 14. The computer includes a CPU 300, a storage device 301, and an interface device (I / F) 302. The hardware of the sensor output detection units 21, 21b and the like are connected to the I / F 302. The CPU 300 executes the processes described in the first to third embodiments in accordance with the program stored in the storage device 301. [Industrial Applicability]

[0094] The present invention can be applied to a technique for detecting the position of a movable part that moves linearly. [Explanation of symbols]

[0095] 1...bridge circuit, 10-1 to 10-4...AMR elements, 11, 11-1, 11-2...magnets, 13-1, 13-2...accommodating cylinders, 20...power supply, 21, 21b...sensor output detection units, 22, 22b...angle calculation units, 23, 23a, 23b...position calculation units.

Claims

1. a sensor circuit including a magnetoresistive element; a magnet configured to move linearly on a plane intersecting a sensor surface on which the thin film resistance pattern of the magnetoresistive element is formed; a sensor output detection unit configured to detect an output of the sensor circuit; an angle calculation unit configured to calculate an angle of a magnetic field generated by the magnet based on an output of the sensor circuit; a position calculation unit configured to calculate coordinates of the magnet based on the angle of the magnetic field, a reference position where the output voltage of the sensor circuit becomes zero is not on the intersection line between the plane and the sensor surface; the magnet moves linearly on the plane in the direction of the line of intersection, The position sensor is characterized in that the position calculation unit calculates the coordinate of the magnet in the direction of the intersection line based on the angle of the magnetic field and the angle between the reference position on the sensor surface and the intersection line.

2. a sensor circuit including a magnetoresistive element; a first magnet configured to move linearly along a path on a plane parallel to a sensor surface on which a thin film resistance pattern of the magnetoresistive element is formed; a second magnet disposed at a fixed position on the plane so as to face the first magnet with the sensor circuit interposed therebetween; a sensor output detection unit configured to detect an output of the sensor circuit; an angle calculation unit configured to calculate an angle of a magnetic field generated by the first and second magnets based on an output of the sensor circuit; and a position calculation unit configured to calculate coordinates of the first magnet based on the angle of the magnetic field.

3. 3. The position sensor according to claim 2, the first magnet moves linearly in a direction of the trajectory that intersects with a direction of a reference position where an output voltage of the sensor circuit is zero; a position calculation unit that calculates the coordinates of the first magnet on the trajectory based on the distance from the sensor circuit to the intersection of the direction of the reference position and the trajectory, the distance from the sensor circuit to the second magnet, and the angle of the magnetic field.

4. 4. The position sensor according to claim 2, The first and second magnets are cylindrical, with their magnetic poles magnetized so that they face each other in the radial direction, and are housed inside a housing cylinder in a state that allows free rotation around the axis, with their axial direction perpendicular to the direction of the orbit of the first magnet.

5. 5. The position sensor according to claim 1, the sensor circuit is a bridge circuit in which four of the magnetoresistive effect elements are connected, A position sensor, wherein the output of the sensor circuit detected by the sensor output detection unit is a midpoint potential difference of the bridge circuit.

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