Magnetic detection system and magnetic sensor

Abstract

To improve the accuracy of detecting changes in the position of magnets. [Solution] The magnetic detection system 200 comprises a magnetic sensor 100 and a processing circuit 201. The magnetic sensor 100 has a first magnetoresistive element and a second magnetoresistive element, which are giant magnetoresistive elements, and a bias magnet 5. The bias magnet 5 applies a first bias magnetic field to the first magnetoresistive element along a first direction. The bias magnet 5 applies a second bias magnetic field to the second magnetoresistive element along the first direction, which is equal in strength to the first bias magnetic field and is in the opposite direction to the first bias magnetic field. When the strength of the external magnetic field along the first direction is within a predetermined range, the magnetic sensor 100 outputs an output signal to the processing circuit 201 that is proportional to the strength of the external magnetic field along the first direction. Based on the output signal, the processing circuit 201 detects the change in position of the magnet that moves relative to the coil due to magnetic interaction with the coil through which current flows.

Description

Technical Field

[0001] The present disclosure relates to a magnetic detection system and a magnetic sensor, and more particularly, to a magnetic detection system and a magnetic sensor including a bias magnet.

Background Art

[0002] The drive device described in Patent Document 1 includes an actuator that changes the relative position between a lens unit and an imaging element, a magnetic field detection unit that detects magnetic field information corresponding to the relative position between the lens unit and the imaging element, a storage unit that stores reference information based on the output of the magnetic field detection unit when the lens unit or the imaging element is located at a reference position, and a control unit that controls the driving amount of the actuator based on the magnetic field information and the reference information.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a magnetic field detection unit (magnetic detection system and magnetic sensor) included in a drive device as described in Patent Document 1, it is desired to improve the detection accuracy of the relative position of the detection target (position change of the magnet).

[0005] In view of the above reasons, the present disclosure is made, and an object thereof is to provide a magnetic detection system and a magnetic sensor capable of improving the detection accuracy of the position change of a magnet.

Means for Solving the Problems

[0006] A magnetic detection system according to one aspect of the present disclosure comprises a magnetic sensor having a first magnetoresistive element and a second magnetoresistive element, which are giant magnetoresistive elements, and a bias magnet, and a processing circuit connected to the magnetic sensor. The bias magnet applies a first bias magnetic field to the first magnetoresistive element along a first direction, and applies a second bias magnetic field to the second magnetoresistive element along the first direction, with equal strength to the first bias magnetic field and in the opposite direction to the first bias magnetic field. The first magnetoresistive element has first and second ends, which are both ends in a second direction perpendicular to the first direction. The second magnetoresistive element has third and fourth ends, which are both ends in the second direction. A control voltage is applied to the first end from a power supply. The second end is connected to the third end. The fourth end is connected to ground. The processing circuit is connected to the connection point between the second and third ends. The magnetic sensor outputs an output signal proportional to the intensity when an external magnetic field is applied to the first magnetoresistive element and the second magnetoresistive element, and the intensity of the external magnetic field along the first direction is within a predetermined range. Based on the output signal, the processing circuit detects a change in the position of a magnet that moves relative to a coil due to magnetic interaction with the coil through which current flows.

[0007] A magnetic sensor according to one aspect of the present disclosure is a magnetic sensor used in the magnetic detection system. The magnetic sensor comprises a first magnetoresistance element and a second magnetoresistance element, which are giant magnetoresistance elements, and a bias magnet. [Effects of the Invention]

[0008] According to this disclosure, the accuracy of detecting changes in the position of a magnet can be improved. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic plan view of a magnetic detection system according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a block diagram of the magnetic detection system described above. [Figure 3] Figure 3 is a cross-sectional view of a motor on which the magnetic detection system described above is installed. [Figure 4] Figure 4 is a schematic diagram showing the usage status of the magnetic detection system described above. [Figure 5] Figure 5 is a schematic diagram showing the usage status of the magnetic detection system described above. [Figure 6] Figure 6 is a cross-sectional view of the magnetic sensor included in the magnetic detection system described above. [Figure 7] Figure 7 is a circuit diagram of the first full-bridge circuit included in the magnetic detection system described above. [Figure 8] Figure 8 is a circuit diagram of the second full-bridge circuit included in the magnetic detection system described above. [Figure 9] Figure 9 is a graph showing the relationship between the intensity of the output signal from the magnetic detection system described above and the external magnetic field. [Figure 10] Figure 10 is a graph showing the relationship between the intensity of the differential signal output by the magnetic detection system described above and the angle of the external magnetic field. [Figure 11] Figure 11 is a graph showing the relationship between the intensity of the output signal from the magnetic detection system and the position of the magnetic detection system. [Modes for carrying out the invention]

[0010] Preferred embodiments of this disclosure will be described in detail below with reference to the drawings. Common elements in the embodiments described below are denoted by the same reference numerals, and redundant descriptions of common elements may be omitted. The embodiments and modifications described below are only a part of the various embodiments of this disclosure. Furthermore, the embodiments and modifications described below can be modified in various ways depending on the design, etc., as long as the objectives of this disclosure are achieved. It is also possible to combine the configurations of the modifications as appropriate.

[0011] Each figure described in the present disclosure is a schematic diagram, and the respective ratios of the sizes and thicknesses of each component in each figure do not necessarily reflect the actual dimensional ratios. Note that the arrows indicating each direction in the drawings are for example only and are not intended to define the direction during the use of the magnetic detection system 200 (magnetic sensor 100). Also, the arrows indicating each direction in the drawings are merely for explanation and do not involve any entity.

[0012] Note that the "orthogonal (perpendicular)" as referred to in the present disclosure means not only the state where the angle between the two is exactly 90°, but also includes the state where the two intersect within a certain range of difference. That is, the angle between the two that are orthogonal falls within a certain range of difference (for example, 10° or less) with respect to 90°. That is, the "orthogonal" as referred to in the present disclosure includes the case where the angle formed by the two is 80° or more and 100° or less. Similarly, for the "parallel" as referred to in the present disclosure, it means not only the state where the two do not strictly intersect, but also includes the state where the two are arranged within a certain range of difference. For example, the "parallel" as referred to in the present disclosure includes the case where the inclination of the other with respect to one is 10° or less. That is, the "parallel" as referred to in the present disclosure includes the case where the angle formed by one and the other is -10° or more and 10° or less.

[0013] (1) Overview First, the overview of the magnetic detection system 200 according to the embodiment will be described with reference to FIGS. 1 and 2.

[0014] The magnetic detection system 200 includes a magnetic sensor 100 and a processing circuit 201.

[0015] The magnetic sensor 100 has a first magnetoresistive element and a second magnetoresistive element that are giant magnetoresistive effect elements, and a bias magnet 5.

[0016] The processing circuit 201 is connected to the magnetic sensor 100.

[0017] The bias magnet 5 applies a first bias magnetic field along a first direction to the first magnetoresistive element.

[0018] The bias magnet 5 applies a second bias magnetic field to the second magnetoresistive element along the first direction, with equal strength to the first bias magnetic field and in the opposite direction to the first bias magnetic field.

[0019] The first magnetoresistive element has a first end and a second end, which are the two ends in a second direction perpendicular to the first direction.

[0020] The second magnetoresistive element has a third end and a fourth end, which are the two ends in the second direction.

[0021] The first terminal receives a control voltage Vcc from the power supply.

[0022] The second end is connected to the third end.

[0023] The fourth end is connected to ground.

[0024] The processing circuit 201 is connected to the connection point between the second terminal and the third terminal.

[0025] When an external magnetic field is applied to the first magnetoresistive element and the second magnetoresistive element, and the strength of the external magnetic field along the first direction is within a predetermined range, the magnetic sensor 100 outputs an output signal to the processing circuit 201 that is proportional to the strength of the external magnetic field along the first direction.

[0026] Based on the output signal, the processing circuit 201 detects the change in position of the magnet 81, which moves relative to the coil 61 due to magnetic interaction with the coil 61 through which current flows.

[0027] The coil 61 and magnet 81 are, for example, part of the motor M1.

[0028] Here, "proportional to the intensity along the first direction of the external magnetic field" includes not only cases where it is exactly proportional to the intensity along the first direction of the external magnetic field, but also cases where it is approximately proportional.

[0029] Furthermore, in this embodiment, the output signal output by the magnetic sensor 100 is a voltage signal. In other words, the signal strength of the output signal corresponds to the voltage value of the output signal.

[0030] In the magnetic detection system 200 configured as described above, the magnetic sensor 100 is sensitive only to the component of the externally applied magnetic field (external magnetic field) in the direction along the first direction. Therefore, in the magnetic detection system 200, the influence of the disturbing magnetic field F1 can be easily removed from the output signal output by the magnetic sensor 100 by determining the strength of the disturbing magnetic field F1 in the first direction, which is generated when current flows through the coil 61. This improves the detection accuracy of the position change of the magnet 81.

[0031] (2) Composition In this embodiment, we will describe a case in which the magnetic detection system 200 is used to determine the rotation angle of the rotor 8 of the motor M1 (see Figures 3 and 4). In other words, in this embodiment, the magnetic detection system 200 determines the rotation angle of the rotor 8, which has multiple magnets 81, by detecting changes in the positions of the multiple magnets 81. In this embodiment, the magnetic detection system 200 is configured as, for example, a single module.

[0032] The components of the motor M1 and the magnetic detection system 200 are described below. In the following description, the X, Y, and Z axes are defined as mutually orthogonal axes. Note that the X, Y, and Z axes are virtual axes and do not represent a physical configuration.

[0033] (2.1) Motor As shown in Figure 3, the motor M1 comprises a stator 6, a rotor 8, a rotating shaft 9, and a housing 15.

[0034] (2.1.1) Stator As shown in Figure 3, the stator 6 has a stator core 60, a plurality of teeth 62, and a plurality of coils 61.

[0035] The stator core 60 is, for example, annular in a plan view from the axial direction D1. The axial direction D1 is parallel to the rotation axis 9, which will be described later. The stator core 60 is formed from a magnetic material, such as silicon steel sheet. More specifically, the stator core 60 is formed by laminating multiple silicon steel sheets in the thickness direction. Therefore, the cross-section of the stator core 60 along the circumferential direction is rectangular.

[0036] Each of the multiple teeth 62 protrudes from the inner circumferential surface of the stator core 60 toward the center of the stator core 60. The multiple teeth 62 are arranged at equal intervals along the circumferential direction of the stator core 60. Each of the multiple teeth 62, like the stator core 60, is formed by laminating multiple silicon steel sheets in the thickness direction. The multiple teeth 62 may be formed integrally with the stator core 60 or may be formed separately.

[0037] Multiple coils 61 correspond one-to-one with multiple teeth 62. Each of the multiple coils 61 is formed by winding a conductor around the outer surface of the corresponding tooth 62. The winding axis direction of each of the multiple coils 61 is aligned with the protruding direction of the corresponding tooth 62.

[0038] (2.1.2) Rotor The rotor 8 rotates relative to the stator 6 described above. By rotating relative to the stator 6, the rotor 8 rotates the rotating shaft 9, which will be described later. In other words, power (rotational torque) is transmitted to the rotating shaft 9 by the rotor 8 rotating relative to the stator 6.

[0039] As shown in Figure 3, the rotor 8 has a rotor core 82 and a plurality (for example, 8) of magnets (permanent magnets) 81.

[0040] The rotor core 82 is, for example, cylindrical and positioned so that the direction of its central axis is parallel to the axial direction D1. The rotor core 82 is formed of a magnetic material, such as silicon steel sheet. More specifically, the rotor core 82 is formed by laminating multiple silicon steel sheets in the direction of their thickness.

[0041] The rotor core 82 has a shaft hole. The shaft hole is located in the center of the rotor core 82 and penetrates the rotor core 82 in the thickness direction (axial direction D1). The inner diameter (diameter) of the shaft hole is approximately the same as the outer diameter (diameter) of the rotating shaft 9.

[0042] Each of the multiple permanent magnets 81 is, for example, a neodymium magnet. Each of the multiple permanent magnets 81 is, for example, arc-shaped in a plan view from the axial direction D1. The multiple magnets 81 are arranged along the outer circumferential surface of the rotor core 82 and are arranged in a ring shape in a plan view from the axial direction D1. As a result, multiple magnetic poles 80 (south poles and north poles) are alternately arranged along the circumferential direction of the rotor core 82.

[0043] More specifically, as shown in Figure 4, the multiple magnetic poles 80 are arranged in the direction of rotation of the rotor 8 such that north poles and south poles alternate. In Figure 4, the multiple magnetic poles 80 are arranged such that north poles and south poles alternate every 45° along the direction of rotation of the rotor 8. Note that in Figure 4, each magnetic pole 80 is labeled with the letter "N" to represent the north pole or "S" to represent the south pole, but these are letters added for explanatory purposes and are not actually attached. The same applies to the "N" and "S" attached to the bias magnet 5.

[0044] As described above, the rotor 8 rotates due to the magnetic interaction between the magnetic field generated by the multiple permanent magnets 81 and the magnetic field generated by the current flowing through the multiple coils 61 of the stator 6, and transmits the resulting torque (rotational torque) to the rotating shaft 9. In other words, each permanent magnet 81 moves (rotates) relative to the multiple coils 61 due to the magnetic interaction with the multiple coils 61 through which the current flows.

[0045] (2.1.3) Rotation axis As shown in Figure 3, the rotating shaft 9 is, for example, a round bar extending along the axial direction D1. The rotating shaft 9 is attached to the rotor core 82 by being inserted through the axial hole of the rotor core 82. The rotating shaft 9 then rotates in conjunction with the rotation of the rotor 8. In other words, the rotating shaft 9 is connected to the rotor 8 and rotates in conjunction with the rotation of the rotor 8.

[0046] (2.1.4) Enclosure The housing 15 is, for example, a molded product made from die-cast aluminum. The housing 15 is, for example, a hollow cylindrical shape.

[0047] As shown in Figure 3, the housing 15 has a case 151 and a cover 152. The case 151 and the cover 152 are molded products made from die-cast aluminum.

[0048] Case 151 is cylindrical with one side (the top side in Figure 3) open. As shown in Figure 3, Case 151 has a shaft hole 1511. The shaft hole 1511 penetrates the bottom plate 1512 of Case 151 at its center, along the thickness direction (axial direction D1) of the bottom plate 1512. The shaft hole 1511 is circular in plan view from the axial direction D1. The inner diameter (diameter) of the shaft hole 1511 is larger than the outer diameter (diameter) of the rotating shaft 9.

[0049] The cover 152 is, for example, disc-shaped. As shown in Figure 3, the cover 152 has an axial hole 1521 and a through hole 1522. The axial hole 1521 penetrates the cover 152 in the center of the cover 152 along the thickness direction (axial direction D1) of the cover 152. The axial hole 1521 is circular in plan view from the axial direction D1 and is the same size as the axial hole 1511.

[0050] The through-hole 1522 is located opposite the rotor core 82 of the rotor 8 in the axial direction D1. The through-hole 1522 penetrates the cover 152 along the thickness direction (axial direction D1). The through-hole 1522 is rectangular in shape, for example, when viewed from the axial direction D1. The through-hole 1522 is sized to allow the magnetic detection system 200 to pass through.

[0051] The enclosure 15 is assembled as a single unit by attaching the cover 152 to the case 151 so as to cover the top opening of the case 151.

[0052] The case 151 and cover 152, i.e., the housing 15, which are assembled as a single unit, house at least the stator 6 and rotor 8. More specifically, as shown in Figure 3, the housing 15 houses the stator 6, rotor 8, part of the rotating shaft 9, and part of the magnetic sensing system 200.

[0053] The housing 15 rotatably holds the rotating shaft 9, which is partially exposed through the shaft hole 1511 of the case 151 and the shaft hole 1521 of the cover 152, via a plurality of bearings (not shown).

[0054] (2.2) Motor control device As shown in Figure 2, the motor control device 3 that controls the motor M1 includes a communication unit 31, a motor control unit 32, and a current control unit 33.

[0055] The communication unit 31 includes a communication interface for communicating with the magnetic detection system 200. A suitable communication method, such as wireless or wired communication, is used for communication between the communication unit 31 and the magnetic detection system 200.

[0056] The motor control unit 32 generates command values ​​(current command values) for the current to be supplied to the multiple coils 61 in order to control the motor M1.

[0057] The current control unit 33 includes, for example, an inverter. The current control unit 33 supplies current to multiple coils 61 of the motor M1 according to the current command value output from the motor control unit 32.

[0058] (2.3) Magnetic detection system As shown in Figures 1 to 3, the magnetic detection system 200 comprises a substrate 202, a magnetic sensor 100 mounted on the substrate 202, and a processing circuit 201.

[0059] The substrate 202 is, for example, a printed circuit board. The magnetic sensor 100 and the processing circuit 201 are mounted on the mounting surface 2021 of the substrate 202.

[0060] As shown in Figure 3, the magnetic detection system 200 is attached to the housing 15 by inserting a portion of the substrate 202 into a through-hole 1522 in the housing of the motor M1, and fixing the substrate 202 to the housing 15 with the magnetic sensor 100 located inside the housing 15.

[0061] In the magnetic detection system 200, the magnetic sensor 100 and the rotor 8 are positioned opposite each other in the axial direction D1, and the Z-axis of the magnetic sensor 100 is fixed to the housing 15 such that it is aligned with the radial direction of the rotor 8.

[0062] (2.3.1) Magnetic Sensors As shown in Figures 1 and 6, the magnetic sensor 100 comprises a bias magnet 5, a first protective film 71, a GMR film 72, a thermal oxide film 73, a substrate 74, and a second protective film 75. Note that in Figure 1, only the GMR film 72 and the bias magnet 5 are shown, while the first protective film 71, thermal oxide film 73, substrate 74, and second protective film 75 are omitted from the illustration.

[0063] The bias magnet 5 has a rectangular parallelepiped shape, as shown in Figures 1 and 6. The bias magnet 5 is a single component. The bias magnet 5 can be, for example, a permanent magnet or an electromagnet. In this embodiment, the bias magnet 5 is a permanent magnet as an example. The bias magnet 5 is, for example, a ferrite magnet or a neodymium magnet.

[0064] The bias magnet 5 has multiple (eight in this embodiment) magnetic poles 50. More specifically, the bias magnet 5 is provided with a pair of sets of four magnetic poles 50, and the pair of sets is aligned in the Z-axis direction. In each set, the four magnetic poles 50 are located on the same plane.

[0065] The eight magnetic poles 50 are arranged such that adjacent magnetic poles 50 are opposite poles in the X-axis direction, and adjacent magnetic poles 50 are opposite poles in the Y-axis direction. Furthermore, the eight magnetic poles 50 are arranged such that adjacent magnetic poles 50 are opposite poles in the Z-axis direction.

[0066] As shown in Figures 7 and 8, the bias magnet 5 generates a bias magnetic field B1 along the positive direction of the X-axis, a bias magnetic field B2 along the negative direction of the X-axis, a bias magnetic field B3 along the positive direction of the Y-axis, and a bias magnetic field B4 along the negative direction of the Y-axis.

[0067] As shown in Figure 6, the substrate 74 is in the shape of a plate. The substrate 74 is, for example, a silicon substrate. However, the substrate 74 is not limited to a silicon substrate; for example, it may be an alumina substrate.

[0068] The GMR film 72 is formed on the surface of the substrate 74. More specifically, the GMR film 72 is indirectly formed on the surface of the substrate 74 via the thermal oxide film 73. As a result, the substrate 74 holds the GMR film 72.

[0069] The GMR film 72 comprises multiple layers, which are electrically connected to each other via through-holes.

[0070] The GMR film 72 includes a first full-bridge circuit 1 (see Figure 7) and a second full-bridge circuit 2 (see Figure 8).

[0071] As shown in Figure 7, the first full-bridge circuit 1 includes a first series circuit 11 and a second series circuit 12.

[0072] The first series circuit 11 and the second series circuit 12 are connected in parallel to each other. The first series circuit 11 includes a first magnetoresistive element 111 and a second magnetoresistive element 112. The first magnetoresistive element 111 and the second magnetoresistive element 112 are electrically connected in series to each other.

[0073] The second series circuit 12 includes a third magnetoresistance element 121 and a fourth magnetoresistance element 122. The third magnetoresistance element 121 and the fourth magnetoresistance element 122 are electrically connected in series with respect to each other.

[0074] The first magnetoresistance element 111 and the third magnetoresistance element 121 are adjacent to each other in the X-axis direction. Similarly, the second magnetoresistance element 112 and the fourth magnetoresistance element 122 are adjacent to each other in the X-axis direction. A bias magnetic field B1 from the bias magnet 5, aligned with the positive X-axis direction, is applied to the first magnetoresistance element 111 and the third magnetoresistance element 121. A bias magnetic field B2 from the bias magnet 5, aligned with the negative X-axis direction, is applied to the second magnetoresistance element 112 and the fourth magnetoresistance element 122.

[0075] As shown in Figure 8, the second full-bridge circuit 2 includes a third series circuit 21 and a fourth series circuit 22. The third series circuit 21 and the fourth series circuit 22 are connected in parallel with each other. The third series circuit 21 includes a fifth magnetoresistance element 211 and a sixth magnetoresistance element 212. The fifth magnetoresistance element 211 and the sixth magnetoresistance element 212 are electrically connected in series with each other. The fourth series circuit 22 includes a seventh magnetoresistance element 221 and an eighth magnetoresistance element 222. The seventh magnetoresistance element 221 and the eighth magnetoresistance element 222 are electrically connected in series with each other.

[0076] The fifth magnetoresistance element 211 and the seventh magnetoresistance element 221 are adjacent to each other in the Y-axis direction. Similarly, the sixth magnetoresistance element 212 and the eighth magnetoresistance element 222 are adjacent to each other in the Y-axis direction. A bias magnetic field B3 from the bias magnet 5, aligned with the positive direction of the Y-axis, is applied to the fifth magnetoresistance element 211 and the seventh magnetoresistance element 221. A bias magnetic field B4 from the bias magnet 5, aligned with the negative direction of the Y-axis, is applied to the sixth magnetoresistance element 212 and the eighth magnetoresistance element 222.

[0077] As shown in Figures 1, 7, and 8, the magnetic sensor 100 further includes a first output terminal 1T, a second output terminal 2T, a third output terminal 3T, and a fourth output terminal 4T. The first output terminal 1T outputs a first output signal from the first connection point J1 between the first magnetoresistive element 111 and the second magnetoresistive element 112. In other words, the first series circuit 11 outputs a first output signal. The second output terminal 2T outputs a second output signal from the second connection point J2 between the third magnetoresistive element 121 and the fourth magnetoresistive element 122. In other words, the second series circuit 12 outputs a second output signal. The third output terminal 3T outputs a third output signal from the third connection point J3 between the fifth magnetoresistive element 211 and the sixth magnetoresistive element 212. In other words, the third series circuit 21 outputs a third output signal. The fourth output terminal 4T outputs the fourth output signal from the fourth connection point J4 between the seventh magnetoresistive element 221 and the eighth magnetoresistive element 222. In other words, the fourth series circuit 22 outputs the fourth output signal.

[0078] In this embodiment, the first output signal is a -cos signal, the second output signal is a +cos signal, the third output signal is a +sin signal, and the fourth output signal is a -sin signal. In other words, the first and second output signals are in opposite phase, and the third and fourth output signals are in opposite phase.

[0079] Hereinafter, the first magnetoresistance element 111, the second magnetoresistance element 112, the third magnetoresistance element 121, the fourth magnetoresistance element 122, the fifth magnetoresistance element 211, the sixth magnetoresistance element 212, the seventh magnetoresistance element 221, and the eighth magnetoresistance element 222 may each be referred to as magnetoresistance element 300. In other words, the magnetic sensor 100 is equipped with a plurality (eight) of magnetoresistance elements 300.

[0080] As shown in Figure 1, the GMR film 72 further includes power terminals H10 and H20, and reference terminals L10 and L20. The power terminals H10 and H20 are high-potential terminals electrically connected to the high-potential side circuit of the power supply. The reference terminals L10 and L20 are low-potential terminals electrically connected to the low-potential side circuit (reference potential circuit) of the power supply. In this embodiment, the reference terminals L10 and L20 are grounding terminals electrically connected to the ground circuit.

[0081] The first terminal E11 of the first magnetoresistive element 111 is electrically connected to the power supply terminal H10, which is connected to the power supply. As a result, a control voltage Vcc is applied to the first terminal E11 from the power supply. The second terminal E12 of the first magnetoresistive element 111 is electrically connected to the first terminal E21 of the second magnetoresistive element 112. The second terminal E22 of the second magnetoresistive element 112 is electrically connected to the reference terminal L20, which is ground. The first output terminal 1T is electrically connected to the first connection point J1 between the first magnetoresistive element 111 and the second magnetoresistive element 112.

[0082] The first terminal E31 of the third magnetoresistive element 121 is electrically connected to the reference terminal L10, which is ground. The second terminal E32 of the third magnetoresistive element 121 is electrically connected to the first terminal E41 of the fourth magnetoresistive element 122. The second terminal E42 of the fourth magnetoresistive element 122 is electrically connected to the power supply terminal H20. As a result, a control voltage Vcc is applied to the second terminal E42 from the power supply. The second output terminal 2T is electrically connected to the second connection point J2 between the third magnetoresistive element 121 and the fourth magnetoresistive element 122.

[0083] The first terminal E51 of the fifth magnetoresistive element 211 is electrically connected to the reference terminal L10, which is ground. The second terminal E52 of the fifth magnetoresistive element 211 is electrically connected to the first terminal E61 of the sixth magnetoresistive element 212. The second terminal E62 of the sixth magnetoresistive element 212 is electrically connected to the power supply terminal H10. As a result, a control voltage Vcc is applied to the second terminal E62 from the power supply. The third output terminal 3T is electrically connected to the third connection point J3 between the fifth magnetoresistive element 211 and the sixth magnetoresistive element 212.

[0084] The first terminal E71 of the seventh magnetoresistive element 221 is electrically connected to the power supply terminal H20. As a result, a control voltage Vcc is applied to the first terminal E71 from the power supply. The second terminal E72 of the seventh magnetoresistive element 221 is electrically connected to the first terminal E81 of the eighth magnetoresistive element 222. The second terminal E82 of the eighth magnetoresistive element 222 is electrically connected to the reference terminal L20, which is ground. The fourth output terminal 4T is electrically connected to the fourth connection point J4 between the seventh magnetoresistive element 221 and the eighth magnetoresistive element 222.

[0085] The first output terminal 1T, the second output terminal 2T, the third output terminal 3T, and the fourth output terminal 4T are electrically connected to the processing circuit 201. Note that in Figure 1, for simplification, only the first output terminal 1T is shown as being connected to the processing circuit 201.

[0086] In Figures 1, 7, and 8, the magnetoresistive element 300 is depicted as a rectangle when viewed from the Z-axis direction. However, this shape is a schematic representation used to show the orientation of the magnetoresistive element 300 and does not necessarily correspond to the actual shape of the magnetoresistive element 300.

[0087] The electrical resistance of the magnetoresistive element 300 changes according to the strength of the applied magnetic field. The magnetic sensor 100 outputs the change in the electrical resistance of the magnetoresistive element 300 as a voltage signal.

[0088] Viewed from the Z-axis direction, the magnetoresistive elements 300 are arranged as follows, with respect to the center of the magnetic sensor 100: The first magnetoresistive element 111 and the third magnetoresistive element 121 are located on the negative side of the Y-axis from the center. The second magnetoresistive element 112 and the fourth magnetoresistive element 122 are located on the positive side of the Y-axis from the center. The fifth magnetoresistive element 211 and the seventh magnetoresistive element 221 are located on the negative side of the X-axis from the center. The sixth magnetoresistive element 212 and the eighth magnetoresistive element 222 are located on the positive side of the X-axis from the center.

[0089] The magnetoresistive element 300 is, for example, a giant magnetoresistive (GMR) element. The magnetoresistive element 300 is not sensitive in a predetermined direction (for example, the Z-axis direction) but is isotropically sensitive in directions intersecting the predetermined direction (for example, the X-axis direction and the Y-axis direction).

[0090] Here, the inventors confirmed, through the verification described below, that the second full-bridge circuit 2 (third series circuit 21 and fourth series circuit 22) in the magnetic sensor 100 of this embodiment is sensitive only to the component of the external magnetic field in the direction along the Y axis.

[0091] The graph in Figure 9 shows the change in the intensity of the fourth output signal from the fourth output terminal 4T in the fourth series circuit 22 when the intensity of the external magnetic field is changed for each case where the angle θ1 of the magnetic field applied to the magnetic sensor 100 from the outside with respect to the X axis is 0°, 30°, 45°, 60°, and 90°. Here, the angle θ1 is defined as positive in the clockwise direction with respect to the plane of the paper in Figure 8, with the X axis as the reference (0°). In other words, when the angle θ1 is 0°, the external magnetic field is in the positive direction of the X axis, and when the angle θ1 is 90°, the external magnetic field is in the positive direction of the Y axis.

[0092] As shown in Figure 9, when the angle θ1 is 30°, 45°, 60°, and 90°, the strength of the external magnetic field is proportional to the strength of the fourth output signal when the strength of the external magnetic field is within a predetermined range. Note that the strength of the external magnetic field is considered positive when the component of the external magnetic field along the Y axis is oriented in the positive direction of the Y axis, when the direction of the external magnetic field is decomposed into the direction along the X axis and the direction along the Y axis.

[0093] Here, the third output signal from the third output terminal 3T in the third series circuit 21 is also represented by a graph as shown in Figure 9. In this case, the strength of the external magnetic field is considered positive when the component of the external magnetic field along the Y axis is oriented in the negative direction of the Y axis, when the direction of the external magnetic field is decomposed into the direction along the X axis and the direction along the Y axis.

[0094] In other words, in Figure 9, when a positive external magnetic field is applied to the third series circuit 21, a negative external magnetic field of equal absolute value is applied to the fourth series circuit 22. For example, in Figure 9, when an external magnetic field of 100mT is applied to the third series circuit 21, an external magnetic field of -100mT is applied to the fourth series circuit 22. At this time, the third output signal will have the intensity of the signal when an external magnetic field of 100mT is applied. The fourth output signal will have the intensity of the signal when an external magnetic field of -100mT is applied. Here, the processing circuit 201 generates a differential signal between the third output signal and the fourth output signal. That is, the intensity of the differential signal is the difference between the intensity of the third output signal when an external magnetic field of 100mT is applied and the intensity of the fourth output signal when an external magnetic field of -100mT is applied. As mentioned above, when the angle θ1 is 30°, 45°, 60°, and 90°, the strength of the external magnetic field and the strength of the third output signal are proportional. Therefore, the strength of the third output signal when an external magnetic field of 100mT is applied will be different from the strength of the fourth output signal when an external magnetic field of -100mT is applied. In other words, the strength of the differential signal will not be zero.

[0095] On the other hand, when the angle θ1 is 0°, that is, when the direction of the external magnetic field is perpendicular to the Y-axis, the strength of the external magnetic field and the strength of the third output signal are not proportional, and the relationship between the strength of the external magnetic field and the strength of the third output signal is symmetrical with respect to the vertical axis. In other words, the strength of the third output signal when an external magnetic field of 100mT is applied is the same as the strength of the fourth output signal when an external magnetic field of -100mT is applied. In other words, the strength of the differential signal is 0.

[0096] Next, Figure 10 will be explained. Figure 10 is a graph comparing the measured value S1 and the calculated value S2 of the differential signal between the third output signal and the fourth output signal when the angle θ1 is changed, in the case where an external magnetic field of 100mT is applied to the third series circuit 21 (that is, when an external magnetic field of -100mT is applied to the fourth series circuit 22).

[0097] Here, the calculated values ​​S2 for angles θ1 of 0°, 30°, 45°, and 60° are obtained by multiplying the measured value S1 when angle θ1 is 90° by sin0°, sin30°, sin45°, and sin60°, respectively. In other words, the calculated value S2 is the intensity of the differential signal assuming that the second full-bridge circuit 2 detected only the component of the applied external magnetic field in the direction along the Y axis. As shown in Figure 10, the measured value S1 and the calculated value S2 are in close agreement. That is, it was confirmed that the second full-bridge circuit 2 is sensitive only to the component of the external magnetic field in the direction along the Y axis.

[0098] Furthermore, the inventors performed the same verification described above on the first full-bridge circuit 1 (first series circuit 11 and second series circuit 12) and confirmed that the first full-bridge circuit 1 in the magnetic sensor 100 of this embodiment is sensitive only to the component of the external magnetic field in the direction along the X-axis. The verification for the first full-bridge circuit 1 was performed by swapping the X-axis and Y-axis as in the verification for the second full-bridge circuit 2.

[0099] The thermal oxide film 73 covers the surface of the substrate 74. The thermal oxide film 73 is formed on the surface of the substrate 74 by heat treatment of the substrate 74. In this embodiment, the substrate 74 is a silicon substrate, and the thermal oxide film 73 is a silicon oxide film.

[0100] As shown in Figure 6, the first protective film 71 covers the GMR film 72. The first protective film 71 is formed from, for example, a resin, or a metal oxide such as Al2O3 (alumina), or a metal nitride.

[0101] As shown in Figure 6, the second protective film 75 covers the bias magnet 5 mounted on the back surface of the substrate 74 (the surface opposite to the surface on which the GMR film 72 is located). The second protective film 75 is formed from, for example, a resin.

[0102] (2.3.2) Processing Circuit The processing circuit 201 determines the rotation angle of the rotor 8 based on the first output signal, second output signal, third output signal, and fourth output signal. In other words, the processing circuit 201 detects the positions of the multiple permanent magnets 81 of the rotor 8 relative to the multiple coils 61 based on the first output signal, second output signal, third output signal, and fourth output signal.

[0103] As shown in Figure 2, the processing circuit 201 includes a processing unit 41, a storage unit 42, and a communication unit 43.

[0104] The processing unit 41 can be implemented, for example, by a computer system including one or more processors (microprocessors) and one or more memories. The processing unit 41 functions by one or more processors executing one or more programs stored in one or more memories. In this case, the programs are pre-recorded in the memory of the processing unit 41, but they may also be provided via telecommunication lines such as the Internet, or recorded on non-temporary recording media such as memory cards.

[0105] The processing unit 41 includes a first acquisition unit 411, a second acquisition unit 412, an angle calculation unit 413, and a disturbance removal unit 414. Note that the first acquisition unit 411, the second acquisition unit 412, the angle calculation unit 413, and the disturbance removal unit 414 do not necessarily represent actual physical configurations, but rather represent functions realized by the processing unit 41.

[0106] The functions of the first acquisition unit 411, the second acquisition unit 412, the angle calculation unit 413, and the disturbance removal unit 414 will be explained in detail in "(3) Operation Examples".

[0107] The memory unit 42 stores various types of information. The memory unit 42 is a semiconductor memory such as ROM (Read Only Memory), RAM (Random Access Memory), or EEPROM (Electrically Erasable Programmable Read Only Memory). The memory unit 42 may also be implemented by the memory of the processing unit 41.

[0108] The communication unit 43 includes a communication interface for communicating with the motor control device 3. A suitable communication method, such as wireless or wired communication, is used for communication between the communication unit 43 and the motor control device 3.

[0109] (3) Example of operation Next, we will describe an example of the operation of the magnetic detection system 200.

[0110] The magnetic detection system 200 is fixed to the housing 15 such that the magnetic sensor 100 and the rotor 8 face each other in the axial direction D1, and the Z-axis set on the magnetic sensor 100 is aligned with the radial direction of the rotor 8. Multiple magnetic poles 80 formed by multiple magnets 81 on the rotor 8 form a magnetic field. As the rotor 8 rotates, the direction of the magnetic field applied to the magnetic sensor 100 changes. The processing circuit 201 determines the positional changes of the multiple magnets 81 based on the output signal of the magnetic sensor 100. In other words, the processing circuit 201 determines the rotation angle of the rotor 8.

[0111] (3.1) Disturbance removal operation The external magnetic field applied to the magnetic sensor 100 is the sum of a first external magnetic field (disturbing magnetic field) F1 (see Figure 3) generated from multiple coils 61 through which current flows, and a second external magnetic field (signal magnetic field) F2 (see Figure 5) generated from multiple magnetic poles 80. In other words, the output signal from the magnetic sensor 100 is the sum of the signal caused by the disturbing magnetic field F1 and the signal caused by the signal magnetic field F2. Therefore, by removing the signal caused by the disturbing magnetic field F1 from the output signal from the magnetic sensor 100, the detection accuracy of the negative position change of the multiple magnets 81 (rotation angle of the rotor 8) by the magnetic detection system 200 can be improved.

[0112] The following describes the disturbance removal operation that removes the influence of the disturbing magnetic field F1 from the output signal of the magnetic field sensor 100.

[0113] First, we will explain the operation of removing the disturbance signal F1 from the output signal of the magnetic sensor 100 in the second full-bridge circuit 2.

[0114] As described above, the fourth series circuit 22 is sensitive only to the component of the external magnetic field along the Y-axis. Therefore, when the intensity of the external magnetic field along the Y-axis is within a predetermined range, the fourth series circuit 22 outputs a fourth output signal to the processing circuit 201 that is proportional to the intensity of the external magnetic field along the Y-axis, based on the relationship between the external magnetic field and the fourth output signal when the angle θ1 in Figure 9 is 90°. Here, the proportionality coefficient between the intensity of the external magnetic field along the Y-axis and the fourth output signal (first intensity proportionality coefficient), that is, the first intensity proportionality coefficient between the external magnetic field and the fourth output signal when the angle θ1 is 90°, is determined by, for example, actual measurement and stored in the memory unit 42 in advance. The predetermined range of the intensity of the external magnetic field along the Y-axis is, as an example, the range in which the absolute value is 2.5 times or less the absolute value of the bias magnetic fields B3 and B4. Note that the predetermined range may be a range other than the above range, as long as the intensity of the external magnetic field along the Y-axis and the fourth output signal are proportional.

[0115] More specifically, when a disturbance magnetic field F1 and a signal magnetic field F2 are applied to the fourth series circuit 22, the fourth series circuit 22 outputs a fourth output signal V43 to the processing circuit 201. Here, the fourth output signal V43 is a signal obtained by adding a fourth output signal V41, which is proportional to the intensity of the disturbance magnetic field F1 along the Y axis (first intensity), and a fourth output signal V42, which is proportional to the intensity of the signal magnetic field F2 along the Y axis (second intensity). The fourth output signal V43 is output to the processing circuit 201 when the third intensity, which is the sum of the first and second intensities, is within a predetermined range. Therefore, the fourth output signal V42 can be calculated by removing the fourth output signal V41 from the fourth output signal V43. In the fourth series circuit 22, the first intensity is defined as positive when the component of the disturbance magnetic field F1 along the Y axis is oriented in the positive direction of the Y axis, and the second intensity is defined as positive when the component of the signal magnetic field F2 along the Y axis is oriented in the positive direction of the Y axis.

[0116] The removal of the fourth output signal V41 from the fourth output signal V43 is performed by the processing circuit 201. The removal of the fourth output signal V41 from the fourth output signal V43 by the processing circuit 201 is described below.

[0117] First, the first acquisition unit 411 of the processing circuit 201 acquires the value of the fourth output signal V43 from the magnetic field sensor 100 (fourth series circuit 22).

[0118] Next, the second acquisition unit 412 of the processing circuit 201 acquires the current command value from the motor control unit 32.

[0119] The disturbance removal unit 414 of the processing circuit 201 calculates a first intensity along the Y-axis of the disturbance magnetic field F1 applied to the magnetic sensor 100 based on the current command value. In other words, the disturbance removal unit 414 calculates the first intensity based on the value of the current flowing through the multiple coils 61 (current value). More specifically, the disturbance removal unit 414 calculates the first intensity based on the current value and a function (first intensity function) that represents the relationship between the current value and the first intensity. That is, the disturbance removal unit 414 calculates the first intensity by substituting the current value indicated by the current command value into the first intensity function.

[0120] The first intensity function is stored in the memory unit 42 beforehand, for example. The first intensity function is obtained by changing the current values ​​of the currents flowing through the multiple coils 61 in an analysis model that reproduces the positional relationship between the multiple coils 61 and the magnetic sensor 100, for example, using electromagnetic field simulation. Alternatively, the first intensity function may be obtained by actual measurement.

[0121] The disturbance removal unit 414 calculates the fourth output signal V41 based on the calculated first intensity and the first intensity proportionality coefficient described above. In other words, the disturbance removal unit 414 calculates the fourth output signal V41 by multiplying the calculated first intensity by the first intensity proportionality coefficient.

[0122] The disturbance removal unit 414 calculates the fourth output signal V42 by removing the fourth output signal V41 from the fourth output signal V43. In other words, V42 = V43 - V41.

[0123] Furthermore, the third series circuit 21 is sensitive only to the component of the external magnetic field along the Y-axis. Therefore, when the intensity of the external magnetic field along the Y-axis is within a predetermined range, the third series circuit 21 outputs a third output signal to the processing circuit 201 that is proportional to the intensity of the external magnetic field along the Y-axis, based on the relationship between the external magnetic field and the third output signal when the angle θ1 in Figure 9 is 90°. Here, the first intensity proportionality coefficient between the intensity of the external magnetic field along the Y-axis and the third output signal, that is, the first intensity proportionality coefficient between the external magnetic field and the third output signal when the angle θ1 is 90°, is determined by measurement and stored in the storage unit 42 in advance.

[0124] When a disturbance magnetic field F1 and a signal magnetic field F2 are applied to the third series circuit 21, the third series circuit 21 outputs a third output signal V33 to the processing circuit 201. Here, the third output signal V33 is a signal obtained by adding a third output signal V31, which is proportional to the first intensity of the disturbance magnetic field F1 along the Y axis, and a third output signal V32, which is proportional to the second intensity of the signal magnetic field F2 along the Y axis. The third output signal V33 is output to the processing circuit 201 when the third intensity, which is the sum of the first and second intensities, is within a predetermined range. Therefore, the third output signal V32 can be calculated by removing the third output signal V31 from the third output signal V33. In the third series circuit 21, the first intensity is defined as positive when the component of the disturbance magnetic field F1 along the Y axis is in the negative direction of the Y axis, and the second intensity is defined as positive when the component of the signal magnetic field F2 along the Y axis is in the negative direction of the Y axis.

[0125] The removal of the third output signal V31 from the third output signal V33 is performed by the processing circuit 201. The removal of the third output signal V31 from the third output signal V33 by the processing circuit 201 is described below.

[0126] First, the first acquisition unit 411 of the processing circuit 201 acquires the value of the third output signal V33 from the magnetic field sensor 100 (third series circuit 21).

[0127] Next, the second acquisition unit 412 of the processing circuit 201 acquires the current command value from the motor control unit 32.

[0128] The disturbance removal unit 414 of the processing circuit 201 calculates a first intensity along the Y-axis of the disturbance magnetic field F1 applied to the magnetic sensor 100 based on the current command value. In other words, the disturbance removal unit 414 calculates the first intensity based on the value of the current flowing through the multiple coils 61 (current value).

[0129] More specifically, the disturbance removal unit 414 calculates the first intensity based on the current value and a function (first intensity function) that represents the relationship between the current value and the first intensity. In other words, the disturbance removal unit 414 calculates the first intensity by substituting the current value indicated by the current command value into the first intensity function.

[0130] The disturbance removal unit 414 calculates the third output signal V31 based on the calculated first intensity and the first intensity proportionality coefficient described above. In other words, the disturbance removal unit 414 calculates the third output signal V31 by multiplying the calculated first intensity by the first intensity proportionality coefficient.

[0131] The disturbance removal unit 414 calculates the third output signal V32 by removing the third output signal V31 from the third output signal V33. In other words, V32 = V33 - V31.

[0132] Next, we will explain the operation of removing the first external signal from the output signal from the magnetic sensor 100 in the first full-bridge circuit 1.

[0133] As described above, the first series circuit 11 is sensitive only to the component of the external magnetic field along the X-axis. Therefore, when the intensity of the external magnetic field along the X-axis is within a predetermined range, the first series circuit 11 outputs a first output signal to the processing circuit 201 that is proportional to the intensity of the external magnetic field along the X-axis. Here, the second intensity proportionality coefficient between the intensity of the external magnetic field along the X-axis and the first output signal is determined by measurement, similar to the first intensity proportionality coefficient, and is stored in the storage unit 42 in advance. The predetermined range of the intensity of the external magnetic field along the X-axis is, for example, a range in which the absolute value is 2.5 times or less the absolute value of the bias magnetic fields B1 and B2.

[0134] When a disturbance magnetic field F1 and a signal magnetic field F2 are applied to the first series circuit 11, the first series circuit 11 outputs a first output signal V13 to the processing circuit 201. Here, the first output signal V13 is a signal obtained by adding together the first output signal V11, which is proportional to the intensity of the disturbance magnetic field F1 along the X axis (fourth intensity), and the first output signal V12, which is proportional to the intensity of the signal magnetic field F2 along the X axis (fifth intensity). The first output signal V13 is output to the processing circuit 201 when the sixth intensity, which is the sum of the fourth intensity and the fourth intensity, is within a predetermined range. Therefore, the first output signal V12 can be calculated by removing the first output signal V11 from the first output signal V13. In the first series circuit 11, the fourth intensity is defined as positive when the component of the disturbance magnetic field F1 along the X-axis is oriented in the positive direction of the X-axis, and the fifth intensity is defined as positive when the component of the signal magnetic field F2 along the X-axis is oriented in the positive direction of the X-axis.

[0135] The removal of the first output signal V11 from the first output signal V13 is performed by the processing circuit 201. The removal of the first output signal V11 from the first output signal V13 by the processing circuit 201 is described below.

[0136] First, the first acquisition unit 411 of the processing circuit 201 acquires the value of the first output signal V13 from the magnetic field sensor 100 (first series circuit 11).

[0137] Next, the second acquisition unit 412 of the processing circuit 201 acquires the current command value from the motor control unit 32.

[0138] The disturbance removal unit 414 of the processing circuit 201 calculates a fourth intensity along the X-axis of the disturbance magnetic field F1 applied to the magnetic sensor 100 based on the current command value. In other words, the disturbance removal unit 414 calculates the fourth intensity based on the value of the current flowing through the multiple coils 61 (current value).

[0139] More specifically, the disturbance removal unit 414 calculates the fourth intensity based on the current value and a function (second intensity function) that represents the relationship between the current value and the fourth intensity. In other words, the disturbance removal unit 414 calculates the fourth intensity by substituting the current value indicated by the current command value into the second intensity function.

[0140] The second intensity function is stored in the memory unit 42 beforehand, for example. The second intensity function is obtained by changing the current values ​​of the currents flowing through the multiple coils 61 in an analysis model that reproduces the positional relationship between the multiple coils 61 and the magnetic sensor 100, for example, using electromagnetic field simulation. Alternatively, the second intensity function may be obtained by actual measurement.

[0141] The disturbance removal unit 414 calculates the first output signal V11 based on the calculated fourth intensity and the second intensity proportionality coefficient described above. In other words, the disturbance removal unit 414 calculates the first output signal V11 by multiplying the calculated fourth intensity by the second intensity proportionality coefficient.

[0142] The disturbance removal unit 414 calculates the first output signal V12 by removing the first output signal V11 from the first output signal V13. In other words, V12 = V13 - V11.

[0143] Furthermore, the second series circuit 12 is sensitive only to the component of the external magnetic field along the X-axis. Therefore, when the intensity of the external magnetic field along the X-axis is within a predetermined range, the second series circuit 12 outputs a second output signal to the processing circuit 201 that is proportional to the intensity of the external magnetic field along the X-axis. Here, the second intensity proportionality coefficient between the intensity of the external magnetic field along the X-axis and the second output signal is determined by measurement and stored in the storage unit 42 beforehand.

[0144] When a disturbance magnetic field F1 and a signal magnetic field F2 are applied to the second series circuit 12, the second series circuit 12 outputs a second output signal V23 to the processing circuit 201. Here, the second output signal V23 is a signal obtained by adding a second output signal V21, which is proportional to the fourth intensity of the disturbance magnetic field F1 along the X-axis, and a second output signal V22, which is proportional to the fifth intensity of the signal magnetic field F2 along the X-axis. The second output signal V23 is output to the processing circuit 201 when the sixth intensity, which is the sum of the fourth and fifth intensities, is within a predetermined range. Therefore, the second output signal V22 can be calculated by removing the second output signal V21 from the second output signal V23. In the second series circuit 12, the fourth intensity is defined as positive when the component of the disturbance magnetic field F1 along the X-axis is directed in the negative direction of the X-axis, and the fifth intensity is defined as positive when the component of the signal magnetic field F2 along the X-axis is directed in the negative direction of the X-axis.

[0145] The removal of the second output signal V21 from the second output signal V23 is performed by the processing circuit 201. The removal of the second output signal V21 from the second output signal V23 by the processing circuit 201 is described below.

[0146] First, the first acquisition unit 411 of the processing circuit 201 acquires the value of the second output signal V23 from the magnetic field sensor 100 (second series circuit 12).

[0147] Next, the second acquisition unit 412 of the processing circuit 201 acquires the current command value from the motor control unit 32.

[0148] The disturbance removal unit 414 of the processing circuit 201 calculates a fourth intensity along the X-axis of the disturbance magnetic field F1 applied to the magnetic sensor 100 based on the current command value. In other words, the disturbance removal unit 414 calculates the fourth intensity based on the value of the current flowing through the multiple coils 61 (current value).

[0149] More specifically, the disturbance removal unit 414 calculates the fourth intensity based on the current value and a function (second intensity function) that represents the relationship between the current value and the fourth intensity. In other words, the disturbance removal unit 414 calculates the fourth intensity by substituting the current value indicated by the current command value into the second intensity function.

[0150] The disturbance removal unit 414 calculates the second output signal V21 based on the calculated fourth intensity and the second intensity proportionality coefficient described above. In other words, the disturbance removal unit 414 calculates the second output signal V21 by multiplying the calculated fourth intensity by the second intensity proportionality coefficient.

[0151] The disturbance removal unit 414 calculates the second output signal V22 by removing the second output signal V21 from the second output signal V23. In other words, V22 = V23 - V21.

[0152] Since the position of the magnetic sensor 100 is fixed relative to the multiple coils 61, the first output signal V11, the second output signal V21, the third output signal V31, and the fourth output signal V41 do not depend on the rotation angle of the rotor 8.

[0153] (3.2) Detection operation Next, we will explain how the magnetic detection system 200 determines the rotation angle of the rotor 8.

[0154] In the following explanation, the rotation angle detection operation of the rotor 8 is described by assuming that the position of the rotor 8 is virtually fixed and that the position of the magnetic sensor 100 changes relative to the rotor 8. Specifically, the position of the magnetic sensor 100 is described as changing in the order of positions L1, L2, L3, and L4 relative to the rotor 8, as shown in Figures 4 and 5. The X and Y axes also rotate as the magnetic sensor 100 moves. At positions L1, L2, L3, and L4, the magnetic sensor 100 is positioned opposite the rotor 8 in the axial direction D1. At positions L1, L2, L3, and L4, the Z axis set for the magnetic sensor 100 is aligned with the radial direction of the rotor 8.

[0155] The magnetic detection system 200 determines the positional changes of the multiple permanent magnets 81, i.e., the rotation angle of the rotor 8, based on the first output signal V12, second output signal V22, third output signal V32, and fourth output signal V42, which are output signals from which the influence of the disturbing magnetic field F1 has been removed.

[0156] As the position of the magnetic sensor 100 changes in the order of positions L1, L2, L3, and L4 (actually, as the rotor 8 rotates), the first output signal V12, the second output signal V22, the third output signal V32, and the fourth output signal V42 change in a sinusoidal or cosine wave pattern, respectively. Figure 11 shows the waveforms of the second output signal V22 and the third output signal V32. Note that the first output signal V12 is the inverse phase signal of the second output signal V22, and the fourth output signal V42 is the inverse phase signal of the third output signal V32, so the figures for the first output signal V12 and the fourth output signal V42 are omitted.

[0157] When the magnetic sensor 100 is at position L2, opposite the center of the magnetic pole 80 of the rotor 8's north pole, a signal magnetic field F2 aligned with the positive X-axis is applied to the magnetic sensor 100. In this case, the first full-bridge circuit 1 (first magnetoresistive element 111, second magnetoresistive element 112, third magnetoresistive element 121, and fourth magnetoresistive element 122), which is sensitive only to the X-axis component of the external magnetic field, senses the signal magnetic field F2, while the second full-bridge circuit 2 (fifth magnetoresistive element 211, sixth magnetoresistive element 212, seventh magnetoresistive element 221, and eighth magnetoresistive element 222), which is sensitive only to the Y-axis component of the external magnetic field, does not sense the signal magnetic field F2. Therefore, when the magnetic sensor 100 is at position L2, the second output signal V22 is minimized and the first output signal V12 is maximized (see Figure 11).

[0158] When the magnetic sensor 100 is at position L4, opposite the center of the south pole magnetic pole 80 of the rotor 8, the direction of the signal magnetic field F2 of the rotor 8 is reversed compared to position L2, so the second output signal V22 is maximized and the first output signal V12 is minimized (see Figure 11).

[0159] When the magnetic sensor 100 is at position L1, facing the boundary between the north and south magnetic poles 80 of the rotor 8, a signal magnetic field F2 aligned with the negative direction of the Y-axis is applied to the magnetic sensor 100. In this case, the second full-bridge circuit 2, which is sensitive only to the component of the external magnetic field aligned with the Y-axis, detects the signal magnetic field F2, while the first full-bridge circuit 1, which is sensitive only to the component of the external magnetic field aligned with the X-axis, does not detect the signal magnetic field F2. Therefore, when the magnetic sensor 100 is at position L1, the third output signal V32 is at its maximum and the fourth output signal V42 is at its minimum (see Figure 11).

[0160] When the magnetic sensor 100 is located at position L3, opposite the boundary between the north and south magnetic poles 80 of the rotor 8, the direction of the signal magnetic field F2 of the rotor 8 is reversed compared to position L1. As a result, the third output signal V32 is minimized and the fourth output signal V42 is maximized (see Figure 11).

[0161] As shown in Figures 4 and 11, the second output signal V22 and the third output signal V32 repeat the same waveform each time the relative rotation angle between the magnetic sensor 100 and the rotor 8 changes by 90°, which corresponds to twice the width of the magnetic pole 80. In other words, a rotation angle of 90° corresponds to one period of the second output signal V22 and the third output signal V32.

[0162] Here, the phase difference between the second output signal V22 and the third output signal V32 corresponds to a rotation angle that is half the width of the magnetic pole 80. In other words, the phase difference between the second output signal V22 and the third output signal V32 is one-quarter of a period. Therefore, assuming the third output signal V32 is a sine wave, the second output signal V22 corresponds to a cosine wave relative to the third output signal V32.

[0163] The angle calculation unit 413 of the processing circuit 201 determines the rotation angle of the magnetic sensor 100 (actually the rotor 8) based on the first output signal V12, the second output signal V22, the third output signal V32, and the fourth output signal V42. Specifically, the processing circuit 201 generates a first differential signal, which is the differential signal of the first output signal V12 and the second output signal V22. The waveform of the first differential signal is a cosine wave with the amplitude doubled in the first output signal. The processing circuit 201 also generates a second differential signal, which is the differential signal of the third output signal V32 and the fourth output signal V42. The waveform of the second differential signal is a sine wave with the amplitude doubled in the third output signal V32.

[0164] The angle calculation unit 413 determines the phase at which the first differential signal and the second differential signal intersect (have the same value) based on the first differential signal, which is a cosine wave, and the second differential signal, which is a sine wave. The angle calculation unit 413 determines that the magnetic sensor 100 (actually the rotor 8) has rotated 45°, which is the rotation angle corresponding to the width of the magnetic pole 80, between the time the first differential signal and the second differential signal intersect and the time they intersect again. As a result, the magnetic detection system 200 can determine the rotation angle of the rotor 8.

[0165] (4) Variations The embodiments described above are merely one of many embodiments of this disclosure. The embodiments described above can be modified in various ways depending on the design, etc., as long as the objectives of this disclosure are achieved. The following lists some modifications of the embodiments described above. The modifications described below can be combined and applied as appropriate.

[0166] The magnetic detection system 200 is not limited to detecting the rotation angle of the object to be detected (the rotor 8 in the above embodiment). The magnetic detection system 200 may also be used to detect the linear movement of the object to be detected.

[0167] The magnetic detection system 200 does not have to be configured as a single module; the magnetic sensor 100 and the processing circuit 201 may each be configured as separate modules.

[0168] The power supply terminal H10 electrically connected to the first magnetoresistive element 111 and the power supply terminal H10 electrically connected to the sixth magnetoresistive element 212 may be separate terminals. Similarly, the power supply terminal H20 and the reference terminals L10 and L20 may be individually provided for each magnetoresistive element 300.

[0169] (5) Summary As described above, the magnetic detection system (200) according to the first embodiment comprises a magnetic sensor (100) and a processing circuit (201). The magnetic sensor (100) has a first magnetoresistive element and a second magnetoresistive element, which are giant magnetoresistive elements, and a bias magnet (5). The processing circuit (201) is connected to the magnetic sensor (100). The bias magnet (5) applies a first bias magnetic field to the first magnetoresistive element along a first direction. The bias magnet (5) applies a second bias magnetic field to the second magnetoresistive element along the first direction, which is equal in strength to the first bias magnetic field and in the opposite direction to the first bias magnetic field. The first magnetoresistive element has a first end and a second end, which are its ends in a second direction perpendicular to the first direction. The second magnetoresistive element has a third end and a fourth end, which are its ends in the second direction. A control voltage (Vcc) is applied to the first end from a power supply. The second end is connected to the third end. The fourth end is connected to ground. The processing circuit (201) is connected to the connection point between the second end and the third end. When an external magnetic field is applied to the first magnetoresistive element and the second magnetoresistive element, and the strength of the external magnetic field along the first direction is within a predetermined range, the magnetic sensor (100) outputs an output signal to the processing circuit (201) that is proportional to the strength of the external magnetic field along the first direction. Based on the output signal, the processing circuit (201) detects the change in position of the magnet (81) that moves relative to the coil (61) due to magnetic interaction with the coil (61) through which current flows.

[0170] According to this embodiment, by determining the strength of the first external magnetic field (F1) generated by the flow of current through the coil (61) along a first direction, the influence of the first external magnetic field (F1) can be easily removed from the output signal output by the magnetic sensor (100). This improves the detection accuracy of the change in the position of the magnet (81).

[0171] In the magnetic detection system (200) according to the second embodiment, in the first embodiment, the magnetic sensor (100) applies a first external magnetic field (F1), which is an external magnetic field generated from a coil (61), and a second external magnetic field (F2), which is an external magnetic field generated from a magnet (81), to a first magnetoresistive element and a second magnetoresistive element. When the third intensity, which is the sum of a first intensity along the first direction of the first external magnetic field (F1) and a second intensity along the first direction of the second external magnetic field (F2), is within a predetermined range, the magnetic sensor (100) outputs a third output signal, which is the sum of a first output signal proportional to the first intensity and a second output signal proportional to the second intensity, to a processing circuit (201). The processing circuit (201) calculates a first output signal based on the first intensity and the proportionality coefficient between the intensity along the first direction of the external magnetic field and the output signal, calculates a second output signal by removing the first output signal from the third output signal, and detects a change in the position of the magnet (81) based on the second output signal.

[0172] According to this embodiment, the influence of the first external magnetic field (F1) can be easily removed from the output signal output by the magnetic sensor (100). This improves the detection accuracy of the change in position of the magnet (81).

[0173] In the magnetic detection system (200) according to the third embodiment, the processing circuit (201) has a storage unit (42) in which a first intensity and a proportionality coefficient between the intensity of the external magnetic field along a first direction and the output signal are stored in advance.

[0174] According to this embodiment, the influence of the first external magnetic field (F1) can be easily removed from the output signal output by the magnetic sensor (100). This improves the detection accuracy of the change in position of the magnet (81).

[0175] In the magnetic detection system (200) according to the fourth embodiment, in the second or third embodiment, the processing circuit (201) calculates a first intensity based on the value of the current flowing through the coil (61).

[0176] According to this embodiment, the influence of the first external magnetic field (F1) can be more reliably removed from the output signal output by the magnetic sensor (100).

[0177] In the magnetic detection system (200) according to the fifth embodiment, in the fourth embodiment, the processing circuit (201) calculates a first intensity based on the value of the current flowing through the coil (61) and a function that represents the relationship between the value of the current flowing through the coil (61) and the first intensity.

[0178] According to this embodiment, the influence of the first external magnetic field (F1) can be more reliably removed from the output signal output by the magnetic sensor (100).

[0179] In the magnetic detection system (200) according to the sixth embodiment, in any of the first to fifth embodiments, the coil (61) and the magnet (81) are part of the motor (M1).

[0180] According to this embodiment, the accuracy of detecting the rotation angle of the rotor (8) of the motor (M1) can be improved.

[0181] The magnetic sensor (100) according to the seventh embodiment is used in a magnetic detection system (200) according to any of the first to sixth embodiments. The magnetic sensor (100) comprises a first magnetoresistance effect element and a second magnetoresistance effect element, which are giant magnetoresistance effect elements, and a bias magnet (5).

[0182] According to this embodiment, by determining the strength of the first external magnetic field (F1) generated by the flow of current through the coil (61) along a first direction, the influence of the first external magnetic field (F1) can be easily removed from the output signal output by the magnetic sensor (100). This improves the detection accuracy of the change in the position of the magnet (81). [Explanation of symbols]

[0183] 5 Bias Magnets 8 rotors 42 Storage section 61 coils 81 Magnets (Permanent Magnets) 100 Magnetic Sensors 200 Magnetic Detection Systems 201 Processing Circuit F1 First external magnetic field F2 Second external magnetic field M1 Motor Vcc control voltage

Claims

1. A magnetic sensor comprising a first magnetoresistance element and a second magnetoresistance element, which are giant magnetoresistance elements, and a bias magnet, The system comprises a processing circuit connected to the magnetic sensor, The bias magnet is A first bias magnetic field is applied to the first magnetoresistive element along the first direction. A second bias magnetic field is applied to the second magnetoresistive element along the first direction, having the same strength as the first bias magnetic field and being in the opposite direction to the first bias magnetic field. The first magnetoresistive element has a first end and a second end, which are the two ends in a second direction perpendicular to the first direction, The second magnetoresistive element has a third end and a fourth end, which are the two ends in the second direction. The first end has a control voltage applied to it from the power supply. The second end is connected to the third end, The aforementioned fourth end is connected to ground. The processing circuit is connected to the connection point between the second end and the third end, The magnetic sensor outputs an output signal proportional to the strength of the external magnetic field when an external magnetic field is applied to the first magnetoresistive element and the second magnetoresistive element, and the strength of the external magnetic field along the first direction is within a predetermined range, to the processing circuit. The processing circuit detects, based on the output signal, the change in the position of the magnet that moves relative to the coil due to magnetic interaction with the coil through which current flows. Magnetic detection system.

2. The magnetic sensor applies a first external magnetic field, which is the external magnetic field generated from the coil, and a second external magnetic field, which is the external magnetic field generated from the magnet, to the first magnetoresistive element and the second magnetoresistive element, and when the third intensity, which is the sum of the first intensity of the first external magnetic field along the first direction and the second intensity of the second external magnetic field along the first direction, is within the predetermined range, the magnetic sensor outputs a third output signal, which is the sum of the first output signal, which is the output signal proportional to the first intensity, and the second output signal, which is the output signal proportional to the second intensity, to the processing circuit. The processing circuit calculates a first output signal based on the first intensity and the proportionality coefficient between the intensity of the external magnetic field along the first direction and the output signal, calculates a second output signal by removing the first output signal from the third output signal, and detects the change in the position of the magnet based on the second output signal. The magnetic detection system according to claim 1.

3. The processing circuit has a storage unit in which the proportionality constant is stored in advance. The magnetic detection system according to claim 2.

4. The processing circuit calculates the first intensity based on the value of the current flowing through the coil. The magnetic detection system according to claim 2 or 3.

5. The processing circuit calculates the first intensity based on the value of the current and a function representing the relationship between the value of the current and the first intensity. The magnetic detection system according to claim 4.

6. The coil and the magnet are part of the motor. A magnetic detection system according to any one of claims 1 to 3.

7. A magnetic sensor used in the magnetic detection system according to any one of claims 1 to 3, The system comprises a first magnetoresistance element and a second magnetoresistance element, which are giant magnetoresistance elements, and a bias magnet. Magnetic sensor.

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