Foreign object detection device

Abstract

To provide a foreign object detection device detecting a foreign object on the basis of a signal outputted from a magnetic sensor, with increased intensity of signals outputted.SOLUTION: The foreign object detection device comprises: a first magnetic sensor including a first sensitive element that has uniaxial magnetic anisotropy in a first direction, to which a bias magnetic field is applied toward a second direction intersecting the first direction, and which due to magnetic impedance effect senses a magnetic field; and a second magnetic sensor including a second sensitive element that is arrayed in a direction intersecting the first direction with respect to the first magnetic sensor, to which a bias magnetic field is applied toward the second direction same as first magnetic sensor, and which due to the magnetic impedance effect senses a magnetic field. On the basis of signals outputted from the first magnetic sensor and the second magnetic sensor, a foreign object included in a target moving in a direction where the first magnetic sensor and the second magnetic sensor are arrayed is detected.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a foreign object detection device. [Background technology]

[0002] As a conventional technique, Patent Document 1 discloses a metallic foreign matter detection device that uses a magnetic sensor to detect magnetic fluctuations in an AC magnetic field resulting from metallic foreign matter present on the surface or inside of a substrate. This metallic foreign matter detection device uses a cancellation coil to generate a predetermined magnetic field in response to the AC magnetic field, thereby canceling out noise components other than the magnetic fluctuations resulting from metallic foreign matter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-102513 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a foreign object detection device that detects foreign objects based on a signal output from a magnetic sensor, it is preferable to increase the signal strength of the output signal in order to improve the detection accuracy of minute foreign objects. SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to increase the strength of a signal output from a magnetic sensor in a foreign object detection device that detects foreign objects based on a signal output from the magnetic sensor. [Means for solving the problem]

[0005] According to the present invention, the following inventions (1) to (5) are provided. (1) A first magnetic sensor (first magnetic sensor 40A) including a first sensing element (sensing element 50) having uniaxial magnetic anisotropy in a first direction, to which a bias magnetic field is applied in a second direction intersecting the first direction, and sensing the magnetic field by a magneto-impedance effect; a second magnetic sensor (second magnetic sensor 40B) including a second sensing element (sensing element 50) that is arranged next to the first magnetic sensor in a direction intersecting the first direction, is applied with a bias magnetic field in the same direction as the first magnetic sensor that faces the second direction, and senses a magnetic field by a magnetic impedance effect; A foreign object detection device that detects a foreign object (foreign object 91) contained in an object (object 9) moving in the direction in which the first magnetic sensor and the second magnetic sensor are aligned based on the difference between the signals output from the first magnetic sensor and the second magnetic sensor. (2) the first magnetic sensor and the second magnetic sensor are arranged side by side at a predetermined distance (distance D); The foreign object detection device according to (1) detects a minute foreign object having an outer diameter that is one-tenth or less of the distance based on the difference between the signals output from the first magnetic sensor and the second magnetic sensor. (3) The foreign object detection device according to (2), wherein the distance between the first magnetic sensor and the second magnetic sensor is in the range of 1 mm or more and 20 mm or less. (4) The first magnetic sensor further includes a first focusing member (focusing member 41) facing the first sensing element and focusing external magnetic field lines on the first sensing element, and a bias magnetic field is applied to the first sensing element via the first focusing member; The second magnetic sensor further includes a second focusing member (focusing member 41) facing the second sensing element and focusing magnetic lines from the outside to the second sensing element, and a bias magnetic field is applied to the second sensing element via the second focusing member.A foreign object detection device as described in (1) to (3). (5) The first magnetic sensor further includes a first diverging member (diverging member 42) facing the first sensing element and diverging magnetic field lines that have passed through the first sensing element to the outside, and a bias magnetic field is applied to the first sensing element via the first focusing member and the first diverging member, The second magnetic sensor further includes a second diverging member (diverging member 42) facing the second sensing element and diverging magnetic lines that have passed through the second sensing element to the outside, and a bias magnetic field is applied to the second sensing element via the second focusing member and the second diverging member, as described in the foreign object detection device of (4). Effect of the Invention

[0006] According to the present invention, in a foreign object detection device that detects a foreign object made of a magnetic material based on a signal output from a magnetic sensor, it is possible to increase the strength of the output signal. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic diagram illustrating a foreign object detection device to which the present embodiment is applied; [Diagram 2] 2 is a schematic diagram for explaining the configuration of a magnetic sensor unit, and is an enlarged view of the magnetic sensor unit in the detection unit shown in FIG. 1. FIG. [Diagram 3] 3(a) and 3(b) are views of the first magnetic sensor and the second magnetic sensor in the magnetic sensor unit shown in FIG. 2, respectively, viewed from direction III. [Figure 4] 1(a) and 1(b) are diagrams illustrating an example of a sensing element to which the present embodiment is applied. [Diagram 5] 13(a) and 13(b) are diagrams showing the state of magnetic field lines generated by the first magnet to the fourth magnet in the first magnetic sensor and the second magnetic sensor. [Figure 6] 1 is a diagram showing the relationship between a magnetic field applied in the longitudinal direction of a sensing portion in a sensing element of a first magnetic sensor and a second magnetic sensor and an impedance Z of the sensing element. [Figure 7] FIG. 2 is a diagram showing an example of a circuit configuration of a magnetic sensor unit according to the embodiment. [Figure 8] 4 is a graph showing an example of a change over time in an output signal Vab output from a bridge circuit portion of a magnetic sensor unit to which the present embodiment is applied. [Figure 9]13(a) and 13(b) are diagrams illustrating an example of the positional relationship between a first magnetic sensor and a second magnetic sensor, and a foreign object included in an object moved by a moving mechanism. [Figure 10] 11 is a graph showing an example of a change over time in an output signal Vab output from a bridge circuit portion of a magnetic sensor portion when bias magnetic fields in opposite directions are applied to a sensing element of a first magnetic sensor and a sensing element of a second magnetic sensor. [Figure 11] 6(a) and 6(b) are diagrams illustrating the magnitude of noise in the output signal Vab. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. (Configuration of foreign object detection device 1) 1 is a schematic diagram illustrating a foreign object detection device 1 to which this embodiment is applied. The foreign object detection device 1 of this embodiment detects a foreign object 91 made of a magnetic material and contained in an object 9 moving along a predetermined moving direction. Note that hereinafter, the foreign object 91 made of a magnetic material and contained in the object 9 may be simply referred to as a foreign object 91. The foreign object detection device 1 includes a moving mechanism 10 that moves the object 9 along a predetermined moving direction, a magnetizing unit 20 that magnetizes foreign object 91 included in the object 9, and a detection unit 30 that detects the foreign object 91 magnetized by the magnetizing unit 20. In the foreign object detection device 1 of this embodiment, the magnetizing unit 20 and the detection unit 30 are arranged side by side in the direction in which the object 9 is moved by the moving mechanism 10.

[0009] The moving mechanism 10 is configured by a so-called belt conveyor. The moving mechanism 10 includes a pair of rollers 11, 12, and a belt 15 wound around the rollers 11, 12. In the moving mechanism 10, one of the rollers 11 is driven to rotate at a predetermined rotation speed by a driving means (not shown). This causes the belt 15 to circulate in the direction of the arrow A shown in FIG. 1. The moving mechanism 10 moves the object 9 placed on the belt 15 from the left side to the right side in Fig. 1 at a predetermined moving speed by the belt 15 which moves in a circular manner. As a result, the object 9 is guided to the magnetizing unit 20 and the detection unit 30 in this order.

[0010] The moving speed of the object 9 by the moving mechanism 10 (i.e., the moving speed of the foreign object 91 contained in the object 9) varies depending on the configuration of the magnetic sensor unit 31 of the detection unit 30 described later, but can be, for example, in the range of 30 mm / sec or more and 500 mm / sec or less.

[0011] The magnetizing unit 20 magnetizes the foreign matter 91 contained in the target object 9 moved by the moving mechanism 10 . The magnetization unit 20 includes a pair of permanent magnets 21, 22 arranged opposite to each other across the belt 15 of the movement mechanism 10. When the object 9 moved by the movement mechanism 10 passes between the pair of permanent magnets 21, 22, the magnetization unit 20 magnetizes a foreign matter 91 included in the object 9. 1, a pair of permanent magnets 21, 22 are arranged such that the N pole (e.g., the N pole of permanent magnet 21) and the S pole (e.g., the S pole of permanent magnet 22) face each other across the belt 15 of the movement mechanism 10. In the magnetization unit 20, magnetic field lines that cross the belt 15 in the thickness direction are generated between the permanent magnets 21 and 22. As a result, in the magnetization unit 20, foreign matter 91 included in the target object 9 that is placed on the belt 15 and moved is magnetized by the magnetic field lines. In addition, the arrangement of the permanent magnets 21 and 22 in the magnetizing unit 20 is not limited to that shown in Fig. 1 as long as the magnetizing unit 20 generates magnetic lines of force for magnetizing the foreign matter 91 included in the target object 9. Moreover, electromagnets may be used instead of the permanent magnets 21 and 22.

[0012] The detection unit 30 detects a foreign object 91 contained in the target object 9 moved by the moving mechanism 10 and magnetized by the magnetizing unit 20 . The size of the foreign object 91 that can be detected by the detection unit 30 of this embodiment varies depending on the configuration of the magnetic sensor unit 31 (described later) and the material of the foreign object 91, but is in the range of 10 μm or more.

[0013] The detection unit 30 of this embodiment includes a magnetic sensor unit 31 that outputs an electric signal corresponding to a foreign object 91 contained in the target object 9 using a plurality of magnetic sensors (a first magnetic sensor 40A and a second magnetic sensor 40B described below). The detection unit 30 also includes a shielding unit 33 that covers the magnetic sensor unit 31 and a portion of the belt 15 that faces the magnetic sensor unit 31 and shields it from the outside. The detection unit 30 also includes a control unit 35 that controls the magnetic sensor unit 31.

[0014] The shielding unit 33 has a box-like shape and houses therein the magnetic sensor unit 31 and a part of the belt 15. In addition, the shielding unit 33 is provided with openings 331, 332 on the upstream side and downstream side in the moving direction of the belt 15 facing the magnetic sensor unit 31, through which the belt 15 and the object 9 placed on the belt 15 pass. The shielding portion 33 is made of a magnetic shielding material such as iron, stainless steel, etc. The shielding portion 33 shields the internal space of the shielding portion 33 and the magnetic sensor portion 31 and the like housed in the shielding portion 33 from an external magnetic field.

[0015] The control unit 35 determines whether or not a foreign object 91 is present on the target 9 based on the electrical signals output from the first magnetic sensor 40A and the second magnetic sensor 40B of the magnetic sensor unit 31. Although details will be described later, the control unit 35 in this embodiment determines whether or not a foreign object 91 is present on the target 9 based on the difference between the electrical signals output from the first magnetic sensor 40A and the second magnetic sensor 40B (output signal Vab of the bridge circuit unit 70 described later).

[0016] The control unit 35 has, for example, a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) (not shown), a RAM (Random Access Memory) (not shown), etc. The ROM stores a basic program (operation system) executed by the CPU, various settings, etc. The CPU uses the RAM as a working area and executes application programs read from the ROM or a storage unit (not shown) such as a semiconductor memory or a HDD (Hard Disk Drive).

[0017] (Configuration of magnetic sensor unit 31) Next, the configuration of the magnetic sensor unit 31 included in the detection unit 30 will be described. Fig. 2 is a schematic diagram for explaining the configuration of the magnetic sensor unit 31, and is an enlarged view of the magnetic sensor unit 31 in the detection unit 30 shown in Fig. 1. In Fig. 2, the depth direction of the paper (direction from the back to the front) is indicated as the x-direction, the up-down direction of the paper (direction from the bottom to the top) is indicated as the y-direction, and the lateral direction of the paper (direction from the left to the right) is indicated as the z-direction.

[0018] 3(a)-(b) are views of the first magnetic sensor 40A and the second magnetic sensor 40B in the magnetic sensor unit 31 shown in FIG. 2, respectively, as viewed from the III direction. In addition, FIG. 3(a)-(b) correspond to views of the first magnetic sensor 40A and the second magnetic sensor 40B in the magnetic sensor unit 31 as viewed from the upstream side of the moving direction of the target object 9 by the moving mechanism 10. In FIG. 3, the first magnetic sensor 40A and the second magnetic sensor 40B are shown such that the vertical direction (from bottom to top) of the paper is the x direction, the horizontal direction (from right to left) of the paper is the y direction, and the depth direction (from front to back) of the paper is the z direction. In addition, in FIG. 3(a)-(b), magnetic field lines generated by the first magnet 61 to the fourth magnet 64 described later are indicated by arrows. In the magnetic sensor unit 31 of this embodiment, the x direction is an example of a first direction, and the second direction is an example of a y direction.

[0019] The magnetic sensor unit 31 includes a first magnetic sensor 40A and a second magnetic sensor 40B. The first magnetic sensor 40A and the second magnetic sensor 40B are arranged side by side in the z direction. In addition, the first magnetic sensor 40A and the second magnetic sensor 40B are arranged side by side in the movement direction of the target object 9 (see FIG. 1) by the movement mechanism 10 (see FIG. 1). In this embodiment, the z direction is an example of the direction in which the first magnetic sensor 40A and the second magnetic sensor 40B are arranged side by side. In the magnetic sensor unit 31 of this embodiment, the first magnetic sensor 40A and the second magnetic sensor 40B have the same structure. In the following, the same reference numerals will be used to describe components that the first magnetic sensor 40A and the second magnetic sensor 40B have in common.

[0020] Although not shown, in the case where the object 9 moved by the moving mechanism 10 has a shape elongated in the x direction or where multiple objects 9 are lined up in the x direction, the detection unit 30 may have multiple magnetic sensor units 31 including the first magnetic sensor 40A and the second magnetic sensor 40B arranged in the x direction. By adopting such a configuration, the detection unit 30 can detect a foreign object 91 included in the object 9 having a shape elongated in the x direction or a foreign object 91 included in multiple objects 9 lined up in the x direction by the multiple magnetic sensor units 31.

[0021] The first magnetic sensor 40A and the second magnetic sensor 40B each include a sensing element 50, a focusing member 41 that focuses magnetic lines of force from the external space onto the sensing element 50, and a dissipating member 42 that dissipates the magnetic lines of force that have passed through the sensing element 50. In the first magnetic sensor 40A and the second magnetic sensor 40B, the focusing member 41, the sensing element 50, and the dissipating member 42 are arranged in this order. In this example, the focusing member 41, the sensing element 50, and the dissipating member 42 are arranged side by side in the y direction. Furthermore, the first magnetic sensor 40A and the second magnetic sensor 40B each have four magnets (a first magnet 61, a second magnet 62, a third magnet 63, and a fourth magnet 64) that apply a predetermined bias magnetic field Hb to the sensing element 50. Here, the first magnetic sensor 40A refers to the area surrounded by a dashed line shown in Figure 3(a), the second magnetic sensor 40B refers to the area surrounded by a dashed line shown in Figure 3(b), and the other areas may be referred to as the external space or the outside.

[0022] In the magnetic sensor section 31, the sensing element 50 of the first magnetic sensor 40A is an example of a first sensing element, the focusing member 41 of the first magnetic sensor 40A is an example of a first focusing member, and the diverging member 42 of the first magnetic sensor 40A is an example of a first diverging member. Furthermore, in the magnetic sensor section 31, the sensing element 50 of the second magnetic sensor 40B is an example of a second sensing element, the focusing member 41 of the second magnetic sensor 40B is an example of a second focusing member, and the diverging member 42 of the second magnetic sensor 40B is an example of a second diverging member.

[0023] The sensing element 50 senses a magnetic field or a change in a magnetic field in the y-direction due to the magneto-impedance effect. The configuration of the sensing element 50 will be described in detail later.

[0024] The focusing member 41 has a facing portion 411 facing the sensing element 50, and a wide portion 412 that is wider in the x direction than the facing portion 411. That is, the focusing member 41 has a T-shape in plan view with the facing portion 411 as a vertical bar and the wide portion 412 as a horizontal bar. The focusing member 41 has a predetermined constant thickness in the z direction. The thickness of the focusing member 41 in the z direction can be in the range of 1 mm to 5 mm.

[0025] In the focusing member 41, the width in the x direction of the portion of the facing portion 411 facing the sensing element 50 can be approximately the same as the width in the x direction of the sensing element 50, for example, 4.2 mm. In addition, in the focusing member 41, the length in the y direction of the facing portion 411 is, for example, 4.5 mm. Furthermore, in the focusing member 41, the width of the wide portion 412 in the x direction is, for example, 13 mm, and the length in the y direction is, for example, 2 mm. Note that these values ​​are merely examples and other values ​​may be used.

[0026] The diverging member 42 has a facing portion 421 facing the sensing element 50, and a wide portion 422 that is wider in the x direction than the facing portion 421. That is, the diverging member 42 has a T-shaped planar shape, similar to the focusing member 41. The diverting member 42 has a predetermined constant thickness in the z direction. The thickness of the diverting member 42 in the z direction may be in the range of 1 mm to 5 mm.

[0027] In the diverging member 42, the width in the x direction of the portion of the facing portion 421 facing the sensing element 50 can be approximately the same as the width in the x direction of the sensing element 50, for example, 4.2 mm. In addition, in the diverging member 42, the length in the y direction of the facing portion 421 is, for example, 4.5 mm. Furthermore, in the diverging member 42, the width of the wide portion 422 in the x direction is, for example, 13 mm, and the length in the y direction is, for example, 2 mm. Note that these values ​​are merely examples and other values ​​may be used.

[0028] In other words, in the first magnetic sensor 40A and the second magnetic sensor 40B, the wide portion 412, the facing portion 411, the sensing element 50, the facing portion 421, and the wide portion 422 of the focusing member 41 are arranged in this order in the y direction. The focusing member 41 and the diverging member 42 have the same T-shape in plan view and are arranged symmetrically in the y direction with the sensing element 50 in between.

[0029] 3, the facing portion 411 is provided at the center of the wide portion 412 in the x direction. However, the facing portion 411 does not have to be provided at the center of the wide portion 412, and may be provided at one end or the other end of the wide portion 412 in the y direction. That is, the focusing member 41 may have an L-shaped planar shape. The same applies to the diverging member 42.

[0030] The focusing member 41 and the dissipation member 42 are made of a soft magnetic material. A soft magnetic material is a material that is easily magnetized by a magnetic field, but quickly returns to a state where there is no magnetization or where the magnetization is small when the magnetic field is removed, and has a so-called small coercive force. Here, the focusing member 41 and the dissipation member 42 are made of ferrite, as an example. An example of such a ferrite is MnZn, with an initial magnetic permeability of 2500±25% and a saturation magnetic flux density Bs of 420 mT. Moreover, the facing portion 411 and the wide portion 412 of the focusing member 41 are integrally formed, and the facing portion 421 and the wide portion 422 of the diverging member 42 are integrally formed.

[0031] As shown in FIG. 3, the magnetic field lines from the external space enter the wide portion 412 of the focusing member 41 from the right side (-y direction side) in FIG. 3, are focused as they proceed from the wide portion 412 to the facing portion 411, and exit from the facing portion 411. The magnetic field lines that have passed through the sensing element 50 enter the facing portion 421 of the diverging member 42. The magnetic field lines diverge as they proceed from the facing portion 421 to the wide portion 422, and exit from the wide portion 422 to the external space. That is, in the first magnetic sensor 40A and the second magnetic sensor 40B, the magnetic field lines from the external space are focused by the focusing member 41, and the magnetic flux density, which is the density of the magnetic field lines, increases so that they pass through the sensing element 50. In FIG. 3, the magnetic field in the external space (hereinafter referred to as the external magnetic field) is indicated by the symbol H.

[0032] The diverting member 42 has the same planar shape as the focusing member 41, and is disposed symmetrically in the y direction with respect to the sensing element 50. The diverting member 42 is provided so that the magnetic field lines focused by the focusing member 41 pass through the sensing element 50 in a focused state. That is, in the first magnetic sensor 40A and the second magnetic sensor 40B, the provision of the diverting member 42 makes it easier for the magnetic field lines to pass through the sensing element 50 in parallel. If the magnetic sensor unit 31 has a required sensitivity, the first magnetic sensor 40A and the second magnetic sensor 40B do not need to include the dissipation member .

[0033] In the magnetic sensor unit 31 of this embodiment, the first magnetic sensor 40A and the second magnetic sensor 40B mainly sense the magnetic field in the area where the wide portion 412 of the focusing member 41 faces in the space between the magnetic sensor unit 31 and the belt 15 of the moving mechanism 10. In addition, in the magnetic sensor unit 31 of this embodiment, the first magnetic sensor 40A mainly senses the magnetic field in the region facing the wide portion 412 of the focusing member 41 of the first magnetic sensor 40A, while it hardly senses the magnetic field in the region facing the wide portion 412 of the focusing member 41 of the second magnetic sensor 40B. Similarly, the second magnetic sensor 40B mainly senses the magnetic field in the region facing the wide portion 412 of the focusing member 41 of the second magnetic sensor 40B, while it hardly senses the magnetic field in the region facing the wide portion 412 of the focusing member 41 of the first magnetic sensor 40A. In the following, the area of ​​the space between the magnetic sensor unit 31 and the belt 15 of the moving mechanism 10 where the first magnetic sensor 40A mainly senses the magnetic field may be referred to as the sensing area S1 by the first magnetic sensor 40A, and the area where the second magnetic sensor 40B mainly senses the magnetic field may be referred to as the sensing area S2 by the second magnetic sensor 40B.

[0034] In the magnetic sensor unit 31 of this embodiment, the distance from the first magnetic sensor 40A and the second magnetic sensor 40B to the belt 15 is preferably 1 mm or more and 10 mm or less. If the distance from the first magnetic sensor 40A and the second magnetic sensor 40B to the belt 15 is excessively long, the first magnetic sensor 40A and the second magnetic sensor 40B may have difficulty sensing a change in the magnetic field caused by a foreign object 91 contained in the object 9 moving on the belt 15. Furthermore, if the distance from the first magnetic sensor 40A and the second magnetic sensor 40B to the belt 15 is excessively short, the size of the object 9 that can detect the foreign object 91 is likely to be limited. In this embodiment, the distance from the first magnetic sensor 40A and the second magnetic sensor 40B to the belt 15 is the distance along the y direction from the wide portion 412 of the focusing member 41 of the first magnetic sensor 40A and the second magnetic sensor 40B to the surface of the belt 15.

[0035] (Relationship between the first magnetic sensor 40A and the second magnetic sensor 40B) Returning to FIG. 2, the relationship between the first magnetic sensor 40A and the second magnetic sensor 40B will be described. In the magnetic sensor unit 31 of this embodiment, it is preferable that the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B (hereinafter simply referred to as the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B) along the z direction (i.e., the direction of movement of the object 9 by the moving mechanism 10) is sufficiently large compared to the outer diameter of the foreign object 91 that is expected to be detected by the detection unit 30.

[0036] More specifically, the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B is preferably 10 times or more the outer diameter of the foreign object 91 that is expected to be detected by the detection unit 30, and more preferably 30 times or more. This makes it difficult for foreign object 91 contained in object 9 moved by movement mechanism 10 to exist across sensing area S1 of first magnetic sensor 40A and sensing area S2 of second magnetic sensor 40B. In addition, in detection unit 30, the change in the magnetic field caused by foreign object 91 contained in object 9 moved by movement mechanism 10 is difficult to be simultaneously sensed by first magnetic sensor 40A and second magnetic sensor 40B. In this case, the foreign object detection device 1 is capable of detecting a minute foreign object 91 having an outer diameter that is less than one-tenth, and more preferably less than one-thirtieth, of the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B.

[0037] Furthermore, the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B is preferably 400 times or less, more preferably 200 times or less, and even more preferably 100 times or less, the outer diameter of the foreign object 91 expected to be detected by the detection unit 30. If the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B is excessively large, the magnetic sensor unit 31 tends to become large in size.

[0038] For example, when it is assumed that the detection unit 30 is to detect a foreign object 91 having an outer diameter of approximately 30 μm, the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B is preferably 1 mm or more and 20 mm or less, and more preferably 5 mm or more and 15 mm or less.

[0039] In this embodiment, the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B means the distance (interval) along the z direction between the focusing member 41 of the first magnetic sensor 40A and the focusing member 41 of the second magnetic sensor 40B, as shown in Fig. 2. In other words, the distance D between the first magnetic sensor 40A and the second magnetic sensor 40B means the distance (interval) along the movement direction of the target object 9 by the movement mechanism 10.

[0040] (Sensing element 50) Next, the sensing element 50 provided in the first magnetic sensor 40A and the second magnetic sensor 40B of the magnetic sensor unit 31 will be described. Figures 4(a)-(b) are diagrams illustrating an example of the sensing element 50 to which this embodiment is applied. Figure 4(a) is a plan view of the sensing element 50, and Figure 4(b) is a cross-sectional view taken along line IVB-IVB in Figure 4(a). In Figure 4(a), the vertical direction (bottom to top) of the paper is the x-direction, the horizontal direction (right to left) of the paper is the y-direction, and the depth direction (front to back) of the paper is the z-direction.

[0041] 4(b), the sensor element 50 has a structure in which a sensor circuit 500 made of a soft magnetic material (soft magnetic layer) is laminated on a non-magnetic substrate 505. In the sensor element 50 of this embodiment, the substrate 505 and the sensor circuit 500 are laminated in the z direction. In addition, the z direction is the thickness direction of the sensor element 50. The substrate 505 may be, for example, an oxide substrate such as glass or sapphire, a semiconductor substrate such as silicon, or a metal substrate such as aluminum, stainless steel, or a metal plated with nickel phosphorus. In addition, for example, when a material having a lower electrical resistance than the sensory circuit 500, such as a metal substrate, is used as the substrate 505, it is preferable to provide an insulating layer on the surface of the substrate 505 on which the sensory circuit 500 is provided, to insulate the substrate 505 from the sensory circuit 500.

[0042] The sensing circuit 500 includes a plurality of sensing parts 51, a connection part 52 that connects adjacent sensing parts 51 in a zigzag manner in series, and terminal parts 53 provided at one end and the other end of the series-connected sensing parts 51.

[0043] The sensing part 51 has a rectangular planar shape having a long side direction and a short side direction. As shown in Fig. 4(a), the sensing part 51 has a long side direction in the y direction and a short side direction in the x direction. In this example, six sensing parts 51 are arranged in parallel in the x direction. Each of the sensitive parts 51 has a length in the longitudinal direction of 1 mm to 2 mm and a width in the lateral direction of 50 μm to 150 μm. The interval between adjacent sensitive parts 51 is 50 μm to 150 μm. The above-mentioned values ​​of the length and width of the sensing portion 51, the number of sensing portions arranged in parallel, etc. are merely examples, and may be changed depending on the value of the magnetic field to be sensed, the soft magnetic material to be used, etc.

[0044] Each sensing part 51 is provided with uniaxial magnetic anisotropy in a direction intersecting the longitudinal direction, for example, in a short-side direction perpendicular to the longitudinal direction. The direction intersecting the longitudinal direction may have an angle of more than 45° with respect to the longitudinal direction. This allows the sensing part 51 to exhibit a magneto-impedance effect. In other words, the sensing part 51 is a magneto-impedance effect element. Further, although details will be described later, a bias magnetic field Hb of a predetermined magnitude is applied to each of the sensing parts 51 by the first magnet 61 to the fourth magnet 64.

[0045] The connection parts 52 are provided between the ends of adjacent sensing parts 51, and connect the adjacent sensing parts 51 in series in a zigzag manner. In the sensing circuit 500 shown in FIG. 4(a), six sensing parts 51 are arranged in parallel, so there are five connection parts 52. The number of connection parts 52 varies depending on the number of sensing parts 51. For example, if there are three sensing parts 51, there are two connection parts 52.

[0046] The terminal portion 53 is provided at each end of the sensing portion 51 that is not connected by the connection portion 52. The terminal portion 53 may be of any size as long as it is large enough to connect an electric wire or the like. Since the sensing circuit 500 of this embodiment has six sensing portions 51, the two terminal portions 53 are both provided on the left side in FIG. 4(a). If the number of sensing portions 51 is odd, the two terminal portions 53 may be provided separately on the left and right.

[0047] As the soft magnetic material constituting the sensing part 51, the connection part 52 and the terminal part 53 of the sensing circuit 500, it is preferable to use an amorphous alloy (hereinafter, referred to as the Co alloy constituting the sensing circuit 500) in which high melting point metals such as Nb, Ta and W are added to an alloy mainly composed of Co. Examples of the Co alloy constituting the sensing circuit 500 include CoNbZr, CoFeTa and CoWZr. The Co alloy constituting such a sensing circuit 500 can be formed by, for example, a sputtering method.

[0048] The sensing part 51, the connection part 52 and the terminal part 53 of the sensing circuit 500 are integrally formed from a single layer of soft magnetic material. Since the soft magnetic material is conductive, it is possible to pass a current from one terminal part 53 to the other terminal part 53. One or both of the connection portion 52 and the terminal portion 53 may be made of a conductor. Examples of the conductor that constitutes the connection portion 52 and the terminal portion 53 include Ag, Cu, Au, and Al. Also, the connection portion 52 and the terminal portion 53 may be made of different conductors.

[0049] (First magnet 61 to fourth magnet 64) Returning to FIGS. 3(a) and 3(b), the first magnet 61 to the fourth magnet 64 provided in the first magnetic sensor 40A and the second magnetic sensor 40B of the magnetic sensor unit 31 will be described. The first magnet 61 to the fourth magnet 64 are made of permanent magnets such as neodymium magnets, ferrite magnets, etc. Here, a permanent magnet is a material that generates magnetization without receiving a magnetic field or current from the outside. The magnetic flux density of the permanent magnets constituting the first magnet 61 to the fourth magnet 64 varies depending on the magnitude of the bias magnetic field Hb applied to the sensing element 50, and can be, for example, about 20 mT to 500 mT.

[0050] The first magnet 61 to the fourth magnet 64 are provided at both ends in the x direction of the wide portion 412 of the focusing member 41 and at both ends in the x direction of the wide portion 422 of the diverging member . Specifically, the first magnet 61 is provided at an end of the wide portion 412 of the focusing member 41 in the x direction so as to be in contact with the sensing element 50. The first magnet 61 is also arranged so that its N pole is in contact with the wide portion 412 of the focusing member 41. The second magnet 62 is provided at the end of the wide portion 412 of the focusing member 41 in the -x direction so as to be in contact with the sensing element 50. The second magnet 62 is also arranged so that its N pole is in contact with the wide portion 412 of the focusing member 41.

[0051] The third magnet 63 is provided at the end of the wide portion 422 of the diverging member 42 in the x direction so as to be in contact with the sensing element 50. The third magnet 63 is also arranged so that its S pole is in contact with the wide portion 422 of the diverging member 42. The fourth magnet 64 is provided at the end of the wide portion 422 of the diverging member 42 in the -x direction so as to be in contact with the sensing element 50. The fourth magnet 64 is also arranged so that its S pole is in contact with the wide portion 422 of the diverging member 42.

[0052] Additionally, in the first magnetic sensor 40A and the second magnetic sensor 40B, the south pole of the first magnet 61 and the north pole of the third magnet 63 face each other in the y direction through a gap between the wide portion 412 of the focusing member 41 and the wide portion 422 of the diverging member 42. Similarly, in the first magnetic sensor 40A and the second magnetic sensor 40B, the south pole of the second magnet 62 and the north pole of the fourth magnet 64 face each other in the y direction through a gap between the wide portion 412 of the focusing member 41 and the wide portion 422 of the diverging member 42.

[0053] Here, in the magnetic sensor section 31 of this embodiment, the positions at which the first magnet 61 to the fourth magnet 64 are provided and the directions in which the magnetic poles (south pole, north pole) of the first magnet 61 to the fourth magnet 64 face are the same in the first magnetic sensor 40A and the second magnetic sensor 40B.

[0054] In the first magnetic sensor 40A and the second magnetic sensor 40B, magnetic field lines are generated that are directed from the N poles to the S poles of the first magnet 61 to the fourth magnet 64. As a result, a predetermined bias magnetic field Hb is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. 5(a) and 5(b) are diagrams showing the state of magnetic field lines generated by the first magnet 61 to the fourth magnet 64 in the first magnetic sensor 40A and the second magnetic sensor 40B.

[0055] 5(a)-(b), in the first magnetic sensor 40A and the second magnetic sensor 40B, magnetic field lines emanating from the N pole of the first magnet 61 pass through the wide portion 412 and the facing portion 411 of the focusing member 41, and penetrate the sensing element 50. Similarly, magnetic field lines emanating from the N pole of the second magnet 62 pass through the wide portion 412 and the facing portion 411 of the focusing member 41, and penetrate the sensing element 50. Then, the magnetic field lines that have passed through the sensing element 50 pass from the facing portion 421 of the dissipation member 42 through the wide portion 422 and reach the south poles of the third magnet 63 and the fourth magnet 64 . Also, the magnetic field lines emanating from the N pole of the third magnet 63 reach the S pole of the first magnet 61 through the gap between the wide portion 422 of the diverting member 42 and the wide portion 412 of the focusing member 41. Similarly, the magnetic field lines emanating from the N pole of the fourth magnet 64 reach the S pole of the second magnet 62 through the gap between the wide portion 422 of the diverting member 42 and the wide portion 412 of the focusing member 41.

[0056] As a result, in the first magnetic sensor 40A and the second magnetic sensor 40B, magnetic field lines from the first magnets 61-64 pass through the sensing element 50 via the converging member 41 and the diverging member 42. More specifically, in the first magnetic sensor 40A and the second magnetic sensor 40B, magnetic field lines directed in the y direction pass through the respective sensing parts 51 of the sensing element 50. As a result, in the first magnetic sensor 40A and the second magnetic sensor 40B, a bias magnetic field Hb of a predetermined magnitude is applied to each sensing portion 51 of the sensing element 50. In addition, in the magnetic sensor unit 31 of this embodiment, the bias magnetic field Hb of the same direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. In this example, as shown in Figs. 5(a)-(b), the bias magnetic field Hb directed in the y direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B.

[0057] (Functions of the First Magnetic Sensor 40A and the Second Magnetic Sensor 40B) Next, a description will be given of the operation of the first magnetic sensor 40A and the second magnetic sensor 40B. As described above, the first magnetic sensor 40A and the second magnetic sensor 40B have the same configuration, and therefore the first magnetic sensor 40A and the second magnetic sensor 40B have the same operation. 6 is a diagram showing the relationship between the magnetic field applied in the longitudinal direction (y direction) of the sensing portion 51 of the sensing element 50 of the first magnetic sensor 40A and the second magnetic sensor 40B and the impedance Z of the sensing element 50. In Fig. 6, the horizontal axis represents the magnetic field H, and the vertical axis represents the impedance Z. The impedance Z of the sensing element 50 is measured by passing a high-frequency current between the two terminal portions 53.

[0058] 6, the impedance Z of the sensing element 50 increases or decreases as the absolute value of the magnetic field H increases in the positive or negative direction, with the magnetic field H being 0 (H=0) as the boundary. Also, the amount of change in impedance Z with respect to the change in the magnetic field H (i.e., the slope of the graph) differs depending on the magnitude of the magnetic field H. Therefore, by using the portion where the change ΔZ in impedance Z is steep relative to the change ΔH in the applied magnetic field H (i.e., the portion where ΔZ / ΔH is large), it is possible to extract a weak change in the magnetic field H as the change ΔZ in impedance Z. In Fig. 6, the magnetic field H where the change ΔZ in impedance (ΔZ / ΔH) relative to the change ΔH in the magnetic field H is the largest in the region where the magnetic field H is positive is shown as magnetic field Hb.

[0059] In this way, the first magnetic sensor 40A and the second magnetic sensor 40B can measure the amount of change ΔH of the magnetic field H in the vicinity of the magnetic field Hb with high accuracy. Therefore, in the first magnetic sensor 40A and the second magnetic sensor 40B of this embodiment, the first magnet 61 to the fourth magnet 64 are used to apply a magnetic field Hb (sometimes referred to as a bias magnetic field Hb) to the sensing portion 51 of the sensing element 50 as a bias magnetic field.

[0060] (Circuit configuration of magnetic sensor unit 31) FIG. 7 is a diagram showing an example of a circuit configuration of the magnetic sensor unit 31 of the present embodiment. As shown in FIG. 7, the magnetic sensor section 31 has a bridge circuit section 70 including a first magnetic sensor 40A and a second magnetic sensor 40B. In addition to the first magnetic sensor 40A and the second magnetic sensor 40B, the bridge circuit section 70 includes a first capacitor 71 connected in series to the first magnetic sensor 40A and a second capacitor 72 connected in series to the second magnetic sensor 40B. Specifically, the bridge circuit section 70 includes a first series circuit section 81 in which the first magnetic sensor 40A and the first capacitor 71 are connected in series via a first connection point 73. The bridge circuit section 70 also includes a second series circuit section 82 in which the second magnetic sensor 40B and the second capacitor 72 are connected in series via a second connection point 74.

[0061] Furthermore, in the bridge circuit section 70, an end of the first series circuit section 81 on the first magnetic sensor 40A side and an end of the second series circuit section 82 on the second magnetic sensor 40B side are connected via a third connection point 75. Furthermore, in the bridge circuit section 70, an end of the first series circuit section 81 on the first capacitor 71 side and an end of the second series circuit section 82 on the second capacitor 72 side are connected via a fourth connection point 76. As a result, in the bridge circuit section 70, the first series circuit section 81 and the second series circuit section 82 are connected in parallel, and a bridge circuit is formed by the first magnetic sensor 40A, the second magnetic sensor 40B, the first capacitor 71 and the second capacitor 72.

[0062] Further, in the bridge circuit section 70, a voltage application section 83 is connected between the third connection point 75 and the fourth connection point 76. A high-frequency voltage having a predetermined frequency is applied to the bridge circuit section 70 by the voltage application section 83 via the third connection point 75 and the fourth connection point 76. Specifically, the voltage application unit 83 applies a high-frequency voltage having a predetermined amplitude and frequency to the bridge circuit unit 70. The magnitude (amplitude) of the high-frequency voltage applied by the voltage application unit 83 can be in the range of 0.1 V to 10 V, for example. Note that the conditions of the high-frequency voltage applied by the voltage application unit 83 to the bridge circuit unit 70 can be set according to, for example, the circuit configuration of the bridge circuit unit 70 and the size and material of the expected foreign object 91, and are not limited to the above ranges.

[0063] Further, in the bridge circuit section 70, a voltage measurement section 85 is connected to the first connection point 73 and the second connection point 74. The voltage measurement section 85 in this embodiment measures the voltage Va of the first connection point 73 and the voltage Vb of the second connection point 74, and outputs the difference (Va-Vb) between the voltage Va of the first connection point 73 and the voltage Vb of the second connection point 74. Hereinafter, the difference between the voltage Va of the first connection point 73 and the voltage Vb of the second connection point 74 output by the voltage measurement section 85 may be referred to as an output signal Vab. Although details will be described later, in the magnetic sensor unit 31 of this embodiment, the control unit 35 (see FIG. 1) detects a foreign object 91 in the target object 9 (see FIG. 1) based on the output signal Vab output from the voltage measurement unit 85.

[0064] (Regarding the output signal Vab in the magnetic sensor unit 31) Next, the output signal Vab output by the voltage measuring unit 85 in the bridge circuit unit 70 of the magnetic sensor unit 31 will be described. In the following, the impedance of the first magnetic sensor 40A is represented as Z1, the impedance of the second magnetic sensor 40B as Z2, the impedance of the first capacitor 71 as Z3, and the impedance of the second capacitor 72 as Z4. In this embodiment, the impedance Z3 of the first capacitor 71 and the impedance Z4 of the second capacitor 72 are equal (Z3=Z4). In the bridge circuit section 70 of the magnetic sensor unit 31 to which this embodiment is applied, when the high-frequency voltage applied by the voltage application section 83 is Vin, the output signal Vab, which is the difference between the voltage Va at the first connection point 73 and the voltage Vb at the second connection point 74, is expressed by the following equation (1). Vab={(Z1*Z4-Z2*Z3) / (Z1+Z2)*(Z3+Z4)}Vin…(1)

[0065] In addition, the bridge circuit section 70 satisfies the equilibrium condition when the magnetic field sensed by the first magnetic sensor 40A and the second magnetic sensor 40B is a predetermined reference value (for example, when the magnetic field sensed by the first magnetic sensor 40A and the second magnetic sensor 40B is 0H). Specifically, when the first magnetic sensor 40A and the second magnetic sensor 40B are at predetermined reference values, the product of the impedance Z1 of the first magnetic sensor 40A and the impedance Z4 of the second capacitor 72 is equal to the product of the impedance Z2 of the second magnetic sensor 20B and the impedance Z3 of the first capacitor 71 (Z1*Z4=Z2*Z3).

[0066] Therefore, in the bridge circuit portion 70 of the magnetic sensor unit 31, when the magnetic field sensed by the first magnetic sensor 40A and the second magnetic sensor 40B is a predetermined reference value (for example, 0H), the output signal Vab becomes 0. In other words, in the foreign object detection device 1 of this embodiment, when the foreign object 91 of the target 9 is not present in the sensitive area S1 of the first magnetic sensor 40A and the sensitive area S2 of the second magnetic sensor 40B, the output signal Vab of the bridge circuit section 70 becomes 0.

[0067] In the bridge circuit 70 of the magnetic sensor unit 31, when the magnetic field sensed by the first magnetic sensor 40A changes from the reference value, the impedance Z1 of the first magnetic sensor 40A changes. In addition, when a foreign object 91 of the target 9 is present in the sensing area S1 of the first magnetic sensor 40A, the magnetic field in the sensing area S1 changes from the reference value, and the impedance Z1 of the first magnetic sensor 40A changes. Similarly, when the magnetic field sensed by the second magnetic sensor 40B changes from the reference value, the impedance Z2 of the second magnetic sensor 40B changes. In addition, when a foreign object 91 of the target 9 is present in the sensing area S2 sensed by the second magnetic sensor 40B, the magnetic field in the sensing area S2 changes from the reference value, and the impedance Z2 of the second magnetic sensor 40B changes. As described above, the first magnetic sensor 40A and the second magnetic sensor 40B have the same configuration. The same bias magnetic field Hb is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. Therefore, in the magnetic sensor unit 31 of this embodiment, the change in impedance Z with respect to the change in the sensed magnetic field H is equal between the first magnetic sensor 40A and the second magnetic sensor 40B.

[0068] On the other hand, in the bridge circuit portion 70, the impedance Z3 of the first capacitor 71 and the impedance Z4 of the second capacitor 72 do not change with the change in the magnetic field. As a result, in the magnetic sensor unit 31 of this embodiment, the output signal Vab of the bridge circuit unit 70 changes in response to a change in the impedance Z1 of the first magnetic sensor 40A or a change in the impedance Z2 of the second magnetic sensor 40B. That is, the magnitude of the output signal Vab of the bridge circuit unit 70 corresponds to the difference (Z1-Z2) between the impedance Z1 of the first magnetic sensor 40A and the impedance Z2 of the second magnetic sensor 40B.

[0069] Fig. 8 is a graph showing an example of a change over time in the output signal Vab output from the bridge circuit unit 70 of the magnetic sensor unit 31 to which this embodiment is applied. In Fig. 8, the horizontal axis represents the passage of time, and the vertical axis represents the magnitude of the output signal Vab. Fig. 8 also shows the change over time in the output signal Vab when a high-frequency voltage with a frequency of 50 MHz and an amplitude of 1 V is applied to the bridge circuit unit 70 by the voltage application unit 83. 9(a) and 9(b) are diagrams illustrating an example of the positional relationship between the first magnetic sensor 40A and the second magnetic sensor 40B and a foreign object 91 contained in the target object 9 moved by the movement mechanism 10. FIG.

[0070] 9(a), when a foreign object 91 contained in the object 9 reaches a sensing area S1 of the first magnetic sensor 40A as the object 9 is moved by the moving mechanism 10, the magnetic field in the sensing area S1 increases due to the foreign object 91. As a result, the impedance Z1 of the first magnetic sensor 40A increases. On the other hand, since the foreign object 91 is not present in the sensing area S2 of the second magnetic sensor 40B, the magnetic field in the sensing area S2 does not change, and the impedance Z2 of the second magnetic sensor 40B does not change. In this case, the impedance Z1 of the first magnetic sensor 40A becomes larger than the impedance Z2 of the second magnetic sensor 40B (Z1>Z2), and the output signal Vab becomes a positive value. In FIG. 8, the time indicated by T1 corresponds to the time when the foreign object 91 contained in the object 9 exists in the sensing region S1 by the first magnetic sensor 40A. As shown in FIG. 8, when the foreign object 91 exists in the sensing region S1, the output signal Vab has a waveform including a peak protruding in the positive direction (hereinafter, referred to as the first peak P1).

[0071] As shown in FIG. 9(b), as the object 9 moves by the moving mechanism 10 and the foreign object 91 contained in the object 9 moves from the sensing region S1 by the first magnetic sensor 40A to the sensing region S2 by the second magnetic sensor 40B, the influence of the foreign object 91 disappears, and the magnetic field in the sensing region S1 returns to a predetermined reference value (for example, 0H). Accordingly, the impedance Z1 of the first magnetic sensor 40A decreases to the original value. Also, the magnetic field in the sensing region S2 increases due to the foreign object 91 that has moved to the sensing region S2 by the second magnetic sensor 40B. As a result, the impedance Z2 of the second magnetic sensor 40B increases. In this case, the impedance Z2 of the second magnetic sensor 40B becomes larger than the impedance Z1 of the first magnetic sensor 40A (Z1 < Z2), and the output signal Vab becomes a negative value. In FIG. 8, the time indicated by T2 corresponds to the time when the foreign object 91 contained in the object 9 exists in the sensing region S2 by the second magnetic sensor 40B. As shown in FIG. 8, when the foreign object 91 exists in the sensing region S2, the output signal Vab has a waveform including a peak protruding in the negative direction (hereinafter, referred to as the second peak P2).

[0072] Thus, in the magnetic sensor unit 31 of the present embodiment, when a foreign object 91 exists in the object 9 moved by the moving mechanism 10, as the object 9 moves from the sensing region S1 to the sensing region S2, the output signal Vab successively shows the first peak P1 due to the change in the impedance Z1 of the first magnetic sensor 40A and the second peak P2 due to the change in the impedance Z2 of the second magnetic sensor 40B.

[0073] In the detection unit 30, the control unit 35 detects the presence of a foreign object 91 in the object 9 by comparing the peak signal value in the output signal Vab with a predetermined threshold value. That is, the control unit 35 can determine that a foreign object 91 is present in the object 9 when the absolute value of the peak signal value in the output signal Vab exceeds the absolute value of the threshold value. For example, the control unit 35 of the present embodiment compares the signal value of the first peak P1 in the output signal Vab with a predetermined first threshold V1, thereby making it possible to detect the presence of a foreign object 91 on the object 9 at the timing when the object 9 passes through the sensing area S1 of the first magnetic sensor 40A. Similarly, the control unit 35 compares the signal value of the second peak P2 in the output signal Vab with a predetermined second threshold V2, thereby making it possible to detect the presence of a foreign object 91 on the object 9 at the timing when the object 9 passes through the sensing area S2 of the second magnetic sensor 40B.

[0074] As described above, in the detection section 30 of this embodiment, in the magnetic sensor section 31, the bias magnetic field Hb is applied in the same direction to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. In the detection unit 30 of this embodiment, the bridge circuit unit 70 outputs as an output signal Vab the difference between the voltage Va at the first connection point 73 to which the first magnetic sensor 40A is connected and the voltage Vb at the second connection point 74 to which the second magnetic sensor 40B is connected. As a result, when a foreign object 91 is present in the target 9, a first peak P1 projecting in the positive direction and a second peak P2 projecting in the negative direction appear successively in the output signal Vab.

[0075] Here, consider a case where, unlike this embodiment, bias magnetic fields in opposite directions are applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B in the magnetic sensor unit 31. For example, consider a case where a bias magnetic field Hb in the y direction is applied to the sensing element 50 of the first magnetic sensor 40A as shown in Fig. 5(a), and a bias magnetic field (magnetic field Hb' shown in Fig. 6) in the -y direction is applied to the sensing element 50 of the second magnetic sensor 40B, opposite to the example shown in Fig. 5(b). Fig. 10 is a graph showing an example of a change over time in the output signal Vab output from the bridge circuit section 70 of the magnetic sensor unit 31 when bias magnetic fields in opposite directions are applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. Like Fig. 8, Fig. 10 shows a change over time in the output signal Vab when a high-frequency voltage with a frequency of 50 MHz and an amplitude of 1 V is applied to the bridge circuit section 70 by the voltage application section 83.

[0076] 9(a), when a foreign object 91 included in the target 9 reaches a sensing area S1 of the first magnetic sensor 40A, the magnetic field in the sensing area S1 is increased by the foreign object 91. In this case, as in the above example, the impedance Z1 of the first magnetic sensor 40A increases, while the impedance Z2 of the second magnetic sensor 40B does not change. As a result, the impedance Z1 of the first magnetic sensor 40A becomes larger than the impedance Z2 of the second magnetic sensor 40B (Z1>Z2), and the output signal Vab becomes a positive value. 10, the time indicated by T1 corresponds to the time when the foreign object 91 included in the target 9 is present in the sensing area S1 of the first magnetic sensor 40A. As shown in Fig. 10, while the foreign object 91 is present in the sensing area S1, the output signal Vab has a waveform including a peak (hereinafter referred to as a first peak P1') that protrudes in the positive direction.

[0077] 9(b), when the foreign object 91 included in the target 9 moves to the sensing area S2 of the second magnetic sensor 40B, the magnetic field in the sensing area S1 returns to a reference value (e.g., 0H), and the impedance Z1 of the first magnetic sensor 40A drops to its original value. In addition, the magnetic field in the sensing area S2 increases due to the foreign object 91 that has moved to the sensing area S2 of the second magnetic sensor 40B. Here, a bias magnetic field Hb' in the opposite direction to that of the sensing element 50 of the first magnetic sensor 40A is applied to the sensing element 50 of the second magnetic sensor 40B. Therefore, the magnetic field in the sensing area S2 increases, and the impedance Z2 of the second magnetic sensor 40B drops. In this case, the impedance Z2 of the second magnetic sensor 40B becomes smaller than the impedance Z1 of the first magnetic sensor 40A (Z1>Z2), and the output signal Vab has a positive value. 10, the time indicated by T2 corresponds to the time when the foreign object 91 included in the target 9 is present in the sensing area S2 of the second magnetic sensor 40B. As shown in Fig. 10, while the foreign object 91 is present in the sensing area S2, the output signal Vab has a waveform including a peak (hereinafter referred to as a second peak P2') that protrudes in the positive direction.

[0078] In this way, when bias magnetic fields of opposite directions are applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B, as the object 9 moves from the sensing area S1 to the sensing area S2, a first peak P1' protruding in the positive direction and a second peak P2' protruding in the positive direction appear in succession in the output signal Vab. In this case, the control unit 35 detects the presence of the foreign matter 91 in the target 9 by comparing the signal values ​​of the first peak P1' and the second peak P2' in the output signal Vab with a predetermined threshold value.

[0079] Here, in terms of improving the accuracy of detecting the foreign matter 91, it is preferable that the absolute value of the peak signal value in the output signal Vab (hereinafter, referred to as signal intensity) is large in the detecting section 30. In this embodiment, by applying a bias magnetic field Hb in the same direction to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B, the signal strength of the peak in the output signal Vab becomes larger than when a bias magnetic field in an opposite direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. In addition, in the detection unit 30 of this embodiment, the signal strength of the first peak P1 and the second peak P2 in the output signal Vab becomes larger than the signal strength of the first peak P1' and the second peak P2' in the output signal Vab when a bias magnetic field in an opposite direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. As a result, the foreign object detector 1 of this embodiment can improve the detection accuracy of the foreign object 91 by the detector 30. In addition, the foreign object detector 1 of this embodiment can easily detect the foreign object 91 even when the target object 9 contains a very small foreign object 91 having an outer diameter of about several tens of μm.

[0080] In addition, in order to improve the accuracy of detecting the foreign object 91, it is preferable that the detection unit 30 has a large S / N ratio, which is the ratio of the peak signal value (Signal) to the noise (Noise) in the output signal Vab. In this embodiment, by applying a bias magnetic field Hb in the same direction to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B, noise in the output signal Vab can be reduced compared to the case where bias magnetic fields in opposite directions are applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B.

[0081] 11(a)-(b) are diagrams for explaining the magnitude of noise in the output signal Vab, and are examples of FFT data obtained by performing a fast Fourier transform (FFT) on the time change of the output signal Vab when the magnetic field sensed by the first magnetic sensor 40A and the second magnetic sensor 40B is a predetermined reference value (e.g., 0H). In FIG. 11(a)-(b), the horizontal axis is frequency (Hz) and the vertical axis is FFT data (mV / √Hz). Fig. 11(a) shows FFT data of the output signal Vab by the magnetic sensor unit 31 of this embodiment when a bias magnetic field Hb of the same direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. Fig. 11(b) shows FFT data of the output signal Vab when a bias magnetic field of an opposite direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B.

[0082] Here, noise originating from an external magnetic field rather than from foreign object 91 on object 9 is normally sensed simultaneously by first magnetic sensor 40A and second magnetic sensor 40B regardless of the position of foreign object 91 on object 9. In this embodiment, since the bias magnetic field Hb in the same direction is applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B, the amount of change in impedance Z1 of the first magnetic sensor 40A and the amount of change in impedance Z2 of the second magnetic sensor 40B due to sensing noise are equal to each other. As a result, the noise sensed by the first magnetic sensor 40A and the noise sensed by the second magnetic sensor 40B cancel each other out in the output signal Vab, which is the difference between the voltage Va at the first connection point 73 and the voltage Vb at the second connection point 74. This makes it possible to reduce the noise in the output signal Vab.

[0083] For example, in the output signal Vab shown in FIG. 11(a), noise near frequencies of 50 Hz and 150 Hz is reduced compared to the output signal Vab in FIG. 11(b) in which bias magnetic fields in opposite directions are applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B. In this manner, in this embodiment, by applying the bias magnetic field Hb in the same direction to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B, it is possible to reduce noise in the output signal Vab and increase the S / N ratio, which is the ratio of the peak signal value (Signal) to the noise (Noise) in the output signal Vab. This makes it possible to improve the detection accuracy of the foreign object 91 by the detection unit 30 in the foreign object detection device 1 of this embodiment.

[0084] Although the embodiment and examples of the present invention have been described above, the present invention is not limited to the embodiment. Various modifications and combinations may be made as long as they do not go against the spirit of the present invention.

[0085] For example, in the magnetic sensor unit 31 of the present embodiment, the first magnetic sensor 40A and the second magnetic sensor 40B are arranged so that the thickness direction of the sensing element 50 coincides with the z direction, which is the movement direction of the object 9 by the movement mechanism 10, but this is not limited to this. In the magnetic sensor unit 31, as long as the first magnetic sensor 40A and the second magnetic sensor 40B are aligned in the z direction, which is the movement direction of the object 9 by the movement mechanism 10, the first magnetic sensor 40A and the second magnetic sensor 40B may be arranged so that the thickness direction of the sensing element 50 coincides with the x direction, for example.

[0086] In the first magnetic sensor 40A and the second magnetic sensor 40B in the magnetic sensor unit 31 of the present embodiment, the bias magnetic field Hb is applied to the sensing element 50 using four permanent magnets, the first magnet 61 to the fourth magnet 64, but this is not limited to the above. In the magnetic sensor unit 31, a single or multiple permanent magnets other than four may be used as long as a bias magnetic field Hb facing in the same direction can be applied to the sensing element 50 of the first magnetic sensor 40A and the sensing element 50 of the second magnetic sensor 40B, and an electromagnet may be used instead of the first magnet 61 to the fourth magnet 64. [Explanation of symbols]

[0087] Reference Signs List 1...foreign object detection device, 10...moving mechanism, 20...magnetizing section, 30...detecting section, 31...magnetic sensor section, 35...control section, 40A...first magnetic sensor, 40B...second magnetic sensor, 41...focusing member, 42...diverging member, 50...sensing element, 61...first magnet, 62...second magnet, 63...third magnet, 64...fourth magnet, 70...bridge circuit section

Claims

1. a first magnetic sensor including a first sensing element having uniaxial magnetic anisotropy in a first direction, to which a bias magnetic field is applied in a second direction intersecting the first direction, and sensing a magnetic field by a magneto-impedance effect; a second magnetic sensor including a second sensing element that is arranged next to the first magnetic sensor in a direction intersecting the first direction, is applied with a bias magnetic field in the same direction as the first magnetic sensor that faces the second direction, and senses a magnetic field by a magnetic impedance effect; A foreign object detection device that detects a foreign object contained in an object moving in a direction in which the first magnetic sensor and the second magnetic sensor are aligned based on the difference between the signals output from the first magnetic sensor and the second magnetic sensor.

2. the first magnetic sensor and the second magnetic sensor are arranged side by side at a predetermined distance, 2. The foreign object detection device according to claim 1, wherein a minute foreign object having an outer diameter that is one-tenth or less of the distance is detected based on a difference between signals output from the first magnetic sensor and the second magnetic sensor.

3. 3. The foreign object detecting device according to claim 2, wherein the distance between the first magnetic sensor and the second magnetic sensor is in the range of 1 mm to 20 mm.

4. the first magnetic sensor further includes a first focusing member facing the first sensing element and focusing magnetic lines from an outside on the first sensing element, and a bias magnetic field is applied to the first sensing element via the first focusing member; The foreign object detection device described in claim 1, wherein the second magnetic sensor further includes a second focusing member facing the second sensing element and focusing magnetic lines from the outside to the second sensing element, and a bias magnetic field is applied to the second sensing element via the second focusing member.

5. the first magnetic sensor further includes a first diverging member facing the first sensing element and diverging magnetic field lines that have passed through the first sensing element to the outside, and a bias magnetic field is applied to the first sensing element via the first focusing member and the first diverging member; The foreign object detection device described in claim 4, wherein the second magnetic sensor further includes a second diverging member facing the second sensing element and diverging magnetic lines of force that have passed through the second sensing element to the outside, and a bias magnetic field is applied to the second sensing element via the second focusing member and the second diverging member.

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