Inspection equipment

Abstract

To miniaturize the inspection device, the external magnetic field applied to the magnetic detector is reduced without increasing the total width in the detection width direction of the magnetic detector. [Solution] The system includes a transport means 12 for transporting the object to be inspected 26, a magnetization means 11 for magnetizing the object to be inspected 26, a magnetic detector 13 positioned downstream of the magnetization means 11 in the transport direction by the transport means 12 for detecting a magnetic field due to the residual magnetism of magnetic foreign matter 27 contained in the object to be inspected 26, and an external magnetic field canceling coil 22 positioned adjacent to the magnetic detector 13 in the transport direction by the transport means 12 for generating a magnetic field in the opposite direction to the external magnetic field applied to the magnetic detector 13.

Description

Technical Field

[0001] The present invention relates to an inspection apparatus for detecting magnetic foreign matter contained in an object to be inspected conveyed on a conveyance path.

Background Art

[0002] For powdery or granular materials, molded parts, and various packaged commodities, there is a risk of foreign matter contamination caused by falling fixtures such as screws during the manufacturing process or chipping of blades in the cutting process. When a large number of objects to be inspected are conveyed continuously, high-performance sensors are required to remove faint mixed-in foreign matter.

[0003] Conventionally, there are inspection methods such as optical inspection and X-ray fluoroscopy, but there are packaging and conveyance forms to which these methods cannot be applied, so methods for detecting foreign matter based on other principles are required.

[0004] As one method for detecting foreign matter, there is a method of detecting residual magnetism possessed by magnetic foreign matter moving along a conveyance path with a magnetic sensor. However, it is known that detection becomes difficult when the size of magnetic foreign matter becomes very small, since the residual magnetism value becomes extremely small.

[0005] In the case of an inspection apparatus as described above, it is common to have a configuration in which a magnetizer for magnetizing the object to be inspected is provided upstream of the conveyance path, and a magnetic sensor for detecting a weak magnetic field is installed downstream of the magnetizer.

[0006] Amid the demands for higher sensitivity in detecting weak magnetic fields and miniaturization of the entire apparatus, the following problems exist.

[0007] When inspection equipment is miniaturized, the distance between the magnetic sensor and the magnetizer decreases, causing the magnetizer's magnetic field to be applied to the sensor. If a magnetic field other than the magnetic field of the object being inspected is applied from the outside, including the magnetizer's magnetic field, depending on the strength of the external magnetic field, the magnetic field of the magnetic detector or the circuit may become saturated, potentially rendering the magnetic detector inoperable. This possibility is particularly high when using a highly sensitive magnetic detector. To solve this problem, the external magnetic field, namely the magnetizer's magnetic field, must be canceled out or blocked. Patent documents 1 and 2 describe methods such as placing the sensor inside an external magnetic field canceling coil or detection coil to cancel out the surrounding magnetic field, and Patent document 3 describes a method of blocking the magnetic field using a magnetic shield, thereby reducing the influence of the external magnetic field. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-100322 [Patent Document 2] Japanese Patent Publication No. 2019-78714 [Patent Document 3] Japanese Patent Publication No. 2020-30155 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] In Patent Documents 1 and 2, in the case of multi-channel line sensors, depending on the diameter of the coil used for cancellation, a space may be created between adjacent magnetic detectors, potentially resulting in a dead zone. Furthermore, if the coil diameter is reduced to eliminate the dead zone, the cancellation magnetic field applied to the magnetic detector will not be uniform at the edges of the magnetic detector, potentially reducing sensitivity as the magnetization magnetic field cannot be partially canceled out. While it is conceivable to use a sufficiently large coil to enclose all magnetic detectors, this would create a dead zone when using multiple magnetic sensors in a row, as described later. In Patent Document 3, depending on the structure, a dead zone may be created similar to 1 and 2, and since the magnetic sensing surface cannot be shielded, it may not be a problem in the case of weak magnetic fields. However, if the distance to the magnetizer is close and the magnetic field is strong, or if the diameter of the transport path is large, the magnetic field of the magnetizer may be applied to the magnetic detector, potentially causing magnetic saturation of the magnetic detector or circuit saturation. [Means for solving the problem]

[0010] To solve the above problems, the inspection apparatus according to the present invention is A transport means for transporting the object to be inspected, A magnetization means for magnetizing the object to be inspected, A magnetic detector is positioned downstream of the magnetization means in the transport direction by the transport means, and detects a magnetic field due to the residual magnetism of magnetic foreign matter contained in the object to be inspected. An external magnetic field canceling coil is positioned adjacent to the magnetic detector in the transport direction by the transport means and generates a magnetic field in the opposite direction to the external magnetic field applied to the magnetic detector. It is characterized by having the following features. [Effects of the Invention]

[0011] According to the present invention, the magnetic field of the magnetizer applied to each magnetic detector can be reduced with a low current without increasing the detection width of the device. [Brief explanation of the drawing]

[0012] [Figure 1]It is a schematic diagram showing a configuration example of an inspection apparatus according to an embodiment of the present invention. [Figure 2] It is a schematic diagram for explaining the magnetic field of a magnetization means according to an embodiment of the present invention. [Figure 3] It is a schematic diagram for explaining the structure of a magnetic detector according to an embodiment of the present invention. [Figure 4] It is a schematic diagram for explaining the arrangement of an external magnetic field canceling coil according to an embodiment of the present invention. [Figure 5] It is a diagram for explaining the magnetic field of an external magnetic field canceling coil according to an embodiment of the present invention. [Figure 6] It is a schematic diagram for explaining the arrangement of an external magnetic field canceling coil according to a modified example of the embodiment of the present invention. [Figure 7] It is a schematic diagram for explaining the structure and arrangement of an external magnetic field canceling coil according to a modified example of the embodiment of the present invention. [Figure 8] It is a block diagram for explaining the configuration of a processing apparatus according to an embodiment of the present invention. [Figure 9] It is a block diagram for explaining the functions of a signal processing unit and an arithmetic processing unit according to an embodiment of the present invention. [Figure 10] It is a flow diagram for explaining the operation of an inspection apparatus according to an embodiment of the present invention. [Figure 11] It is a block diagram for explaining the hardware of an arithmetic processing unit according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention (hereinafter, the present embodiment) will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same function may be denoted by the same reference numeral to omit repeated description.

[0014] [1. Configuration of Inspection Apparatus] An example configuration of the inspection apparatus according to the present embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram illustrating an example configuration of the inspection apparatus according to the present embodiment. The inspection apparatus 10 shown in FIG. 1 is an example of the inspection apparatus according to the present embodiment.

[0015] As shown in FIG. 1, the inspection apparatus 10 includes a magnetizing means 11, a conveying means 12, magnetic detectors 13, 14, 16, 17, magnetic shielding means 15, 18, a processing apparatus 19, and fixing members 20, 21.

[0016] It should be noted that the configuration of the inspection apparatus 10 illustrated in FIG. 1 is merely an example, and may be appropriately modified depending on the embodiment. For example, it is possible to omit the magnetizing means 11, omit the pair of magnetic detectors 13, 14 located on the upper side of the conveyance path or the pair of magnetic detectors 16, 17 located on the lower side of the conveyance path among the magnetic detectors 13, 14, 16, 17, and omit the magnetic shielding means 15, 18. Furthermore, as will be described later, the number and arrangement of the magnetic detectors may be changed. Such modifications naturally also fall within the technical scope of the present embodiment. Even when the magnetizing means 11 is omitted in the inspection apparatus 10, magnetization is still performed on the upstream side of the magnetic detector in the conveyance direction by other means, and the above-described problem remains the same.

[0017] Furthermore, a modification in which the conveying means 12 is omitted is also possible. In the example of FIG. 1, the object to be inspected 26 is moved to the inspection area of the magnetic detector by the conveying means 12, but for example, if a mechanism is adopted in which a unit configured of the magnetic detector moves toward the object to be inspected 26, the conveying means 12 can be omitted. In other words, any configuration is acceptable as long as the object to be inspected 26 moves relative to the magnetic detectors 13, 14. Furthermore, in the example of FIG. 1, the processing apparatus 19 is included in the inspection apparatus 10, but a modification is also possible in which the processing apparatus 19 is separated, the conveying means 12 is omitted, and the inspection apparatus 10 is defined as a magnetic detector unit that does not include the conveying means 12 and the processing apparatus 19. Such modifications naturally also fall within the technical scope of the present embodiment.

[0018] In the following explanation, for simplicity, the transport direction of the object under inspection 26 will be referred to as the Y direction (rightward direction in Figure 1), the direction perpendicular and upward to the transport path as the Z direction (upward direction in Figure 1), and the direction perpendicular to the YZ plane as the X direction (forward direction in the paper). In addition, depending on the position of a certain element, the upstream position on the transport path may be referred to as the "previous stage," and the downstream position on the transport path as the "later stage." Although only one object under inspection is shown in the figure, in reality, multiple objects under inspection may be transported continuously along the transport path.

[0019] (Regarding the magnetization method) First, the magnetization means 11 will be described. The magnetization means 11 is a magnetic field generating mechanism composed of, for example, magnets and coils. The magnetization means 11 is positioned in front of the magnetic detectors 13, 14, 16, and 17, and is installed so that the object to be inspected 26 passes between the upper part 11a and the lower part 11b. In the example in Figure 2, the magnetization means 11 is installed so that the direction of application of the magnetic field is in the Z direction, and a static magnetic field in the Z direction is applied to the magnetic foreign matter 27 of the object to be inspected 26 passing between the upper part 11a and the lower part 11b to magnetize it.

[0020] It is preferable that the direction in which the static magnetic field is applied is set to the same direction as the magnetic field detection direction of the magnetic detectors 13, 14, 16, and 17. In this case, the direction in which the magnetic foreign object 27 is magnetized coincides with the magnetic field detection direction of the magnetic detectors 13, 14, 16, and 17, so that the detection sensitivity of the magnetic detectors 13, 14, 16, and 17 is increased and the detection accuracy is improved. Note that magnetization by the magnetization means 11 is not limited to a static magnetic field.

[0021] Furthermore, as mentioned above, if the magnetization means 11 is close to the magnetic detectors 13, 14, 16, and 17, the magnetic field applied from the magnetization means 11 will be applied to the magnetic detectors 13, 14, 16, and 17. This could lead to magnetic saturation and circuit saturation in the magnetic detectors 13, 14, 16, and 17, so it is preferable that no external magnetic field, including the magnetization magnetic field from the magnetization means 11, is applied. In this embodiment, by providing external magnetic field canceling coils 22 to 25, which will be described later, a magnetic field is generated in the opposite direction to the external magnetic field applied to the magnetic detectors 13, 14, 16, and 17, thereby canceling out the external magnetic field. The strength of the magnetic field applied from the magnetization means 11 varies depending on the strength of the magnetization means 11 and the distance between the magnetization means 11 and the magnetic detectors 13, 14, 16, and 17, so the strength of the magnetic field applied to magnetic detector 13 or 16 and magnetic detector 14 or 17 will be different. If the axis of symmetry in the Z direction of the magnetizing magnetic field formed by the magnetizing means 11 is different from the center in the Z direction of the magnetic detectors 13, 16 or 14, 17, the strength of the magnetic field applied to each of the magnetic detectors 13, 14, 16, and 17 will be different.

[0022] (Regarding the means of transport) Next, the conveying means 12 will be described. The conveying means 12 is a conveying mechanism for conveying the object to be inspected 26. The conveying means 12 includes, for example, the conveying belt 12a shown in Figure 1, conveying rollers 12b, 12c, 12d, 12e, and a driving means (not shown) such as a motor. The configuration of the conveying means 12 (belt conveyor) shown in Figure 1 is just one example of a conveying path, and alternatively, a conveying means with a different configuration (for example, a means that uses gravity to convey the object to be inspected 26) may be applied.

[0023] In the example shown in Figure 1, the object to be inspected 26 is placed on the conveyor belt 12a in front of the magnetization means 11. The conveyor belt 12a is moved by conveyor rollers 12b, 12c, 12d, and 12e, which rotate at a constant speed by the power of the drive means, and the object to be inspected 26 loaded on the conveyor surface of the conveyor belt 12a is conveyed. The conveyor belt 12a is positioned to pass between the upper part 11a and the lower part 11b of the magnetization means 11, below the magnetic detectors 13 and 14, and above the magnetic detectors 16 and 17. The object to be inspected 26 is conveyed by the conveyor belt 12a, passing through the magnetization region where the object to be inspected 26 is magnetized by the magnetization means 11, to the inspection region where the magnetic detectors 13, 14, 16, and 17 are located.

[0024] (Regarding magnetic detectors) Next, the magnetic detectors 13, 14, 16, and 17 will be described. The magnetic detectors 13, 14, 16, and 17 are magnetic sensors, such as orthogonal fluxgate type sensors or magnetic impedance sensors. The magnetic detectors 13 and 14 are fixed in place by the fixing members 20. Similarly, the magnetic detectors 16 and 17 are fixed in place by the fixing members 21. The fixing members 20 and 21 are made of, for example, sheet metal or resin. Note that the shape of the fixing members 20 and 21 is not limited to the example in Figure 1 and can be changed as desired. The magnetic detectors 13, 14, 16, and 17 have the same structure and are configured to have the same characteristics. Therefore, in the following, the magnetic detector 13 will be described in detail, and detailed descriptions of the magnetic detectors 14, 16, and 17 may be omitted.

[0025] Now, let's refer to Figure 3. Figure 3 is a schematic diagram illustrating an example of the structure of a magnetic detector according to this embodiment. As shown in Figure 3, the magnetic detector 13 includes a non-magnetic substrate 131, a plurality of magnetic materials 132 (magnetic materials M1 to M6) as magnetometers, and a coil 133. In the example in Figure 3, the number of magnetic materials placed on the non-magnetic substrate 131 is 6, but the number of magnetic materials may be 2 to 5, or 7 or more.

[0026] The non-magnetic substrate 131 is formed from a material such as ceramic or glass. The magnetic materials M1 to M6 may be magnetic thin films and are arranged on one plane of the non-magnetic substrate 131. For example, the magnetic materials M1 to M6 can be created by depositing magnetic thin films on one plane of the non-magnetic substrate 131 by sputtering or vapor deposition, and then shaping the magnetic thin films into a desired form. This method allows for the easy formation of a large number of magnetic materials at once.

[0027] The shape of the magnetic materials M1 to M6 may be linear with its longitudinal direction in the Z direction (the same direction as the magnetic field applied by the magnetization means 11), as shown in the example in Figure 3, or it may be a rod with its longitudinal direction in the Z direction and a cross-section parallel to the XY plane (conveyor surface) that is circular or rectangular. The magnetic materials M1 to M6 are arranged at predetermined intervals so as to be parallel to each other. During the operation of the magnetic detector 13, a high-frequency current is applied to the magnetic materials M1 to M6.

[0028] The magnetic materials M1 to M6 may be electrically connected in series or parallel by a wiring pattern not shown, and a high-frequency current may be applied to them collectively, or individual high-frequency currents may be applied to each of the magnetic materials M1 to M6. In this case, the currents applied to each of the magnetic materials M1 to M6 may be supplied from the same drive source, or the same value of current may be supplied from different drive sources.

[0029] The coil 133 is a wire or thin film made of a conductive material and is wound around the magnetic materials M1 to M6. If the magnetic detector 13 is a magnetic impedance sensor, the coil 133 functions as a bias coil for applying a bias magnetic field. If the magnetic detector 13 is an orthogonal fluxgate type sensor, the coil 133 functions as a detection coil for detecting the magnetic field around the magnetic materials M1 to M6. The magnetic detector 13 obtains the total magnetic field amount by summing the strength of the external magnetic field applied to each of the magnetic materials M1 to M6, converts the total magnetic field amount into a voltage, and outputs it as a detection signal to the processing unit 19.

[0030] As described above, since the longitudinal directions of the magnetic materials M1 to M6 are aligned in the Z direction, the magnetic field detection direction by the magnetic detector 13 is in the Z direction. When the direction in which the magnetic field is applied by the magnetization means 11 is set to the Z direction, the direction in which the magnetic foreign matter 27 is magnetized coincides with the magnetic field detection direction of the magnetic detector 13, thus increasing the detection sensitivity of the magnetic detector 13 and improving detection accuracy.

[0031] Next, Figure 4 will be described. Figure 4 is a schematic diagram illustrating the arrangement of the magnetic detectors according to this embodiment. As described above, the magnetic detectors 13, 14, 16, and 17 have the same structure and characteristics. The pair of magnetic detectors 13 and 14 have their magnetic sensing surfaces (hereinafter referred to as magnetic sensing surfaces) arranged in parallel. Similarly, the pair of magnetic detectors 16 and 17 are also arranged so that their magnetic sensing surfaces are parallel to each other.

[0032] Incidentally, the pair of magnetic detectors 13 and 14 are arranged with their respective magnetic sensing surfaces spaced at a predetermined distance L in the Y direction. In the following description, when describing the position of the magnetic detectors, the diagrams show the center of the magnetic detector in the Y direction as the reference point, but in reality, the magnetic sensing surface of the magnetic detector is the reference point. For example, in Figure 4, both magnetic detectors 13 and 14 are arranged so that their magnetic sensing surfaces are located at the bottom of the diagram, but the distance L and length shown in Figure 4 remain unchanged. The distance L is defined by the fixing member 20. Furthermore, it is preferable to set the distance L to a distance at which the phases of the detection signal of magnetic detector 13 and the detection signal of magnetic detector 14 are separated (a phase-separable distance). With this setting, the magnetic field due to the residual magnetism of magnetic foreign matter transported in the Y direction is detected with a phase shift by the distance L, making it easy to separate from background magnetic field noise detected as an in-phase signal. As a result, magnetic field noise generated by surrounding motors and electronic equipment can be effectively removed. Similarly, the distance between magnetic detectors 16 and 17 in the Y direction can be fixed at a phase-separable distance by the fixing member 21.

[0033] (Regarding the external magnetic field cancellation coil) Next, the external magnetic field canceling coils 22, 23, 24, and 25 will be described again with reference to Figure 1. In this embodiment, the external magnetic field canceling coils 22, 23, 24, and 25 are constructed with the same shape, so the explanation will basically use the external magnetic field canceling coil 22 as an example, and this explanation is also applicable to the other external magnetic field canceling coils. The external magnetic field canceling coil 22 is a wire or thin film made of a conductive material, and is wound around a magnetic or non-magnetic material. When wound around a magnetic material, the external magnetic field can be canceled with a lower current compared to when it is wound around a non-magnetic material. The external magnetic field canceling coils 22 and 23 are fixed in place by the fixing member 20.

[0034] Here, referring to Figures 4 and 5, we will further explain why the external magnetic field can be reduced with a low current by the arrangement configuration of the external magnetic field canceling coil 22.

[0035] The coils 22, 23, 24, and 25 for canceling out external magnetic fields are positioned adjacent to the magnetic detectors when viewed from the Z direction (direction perpendicular to the XY plane), without placing the magnetic detectors inside them. In particular, the coil wires 22a are positioned parallel to the direction in which the magnetic detectors are positioned (see arrow A in Figure 4). At this time, it does not matter whether it is on the upstream or downstream side of the transport path, but it is preferable to position them within the space L provided between the magnetic detectors 13 and 14 as described above. Furthermore, it is preferable that the coil width in the direction of magnetic detector placement be equal to the total width of the multiple magnetic detectors arranged in that direction, in which case the magnetic detectors 13, 14, 16, and 17 are not enlarged in the direction of placement. From the perspective of a uniform magnetic field, it would be better to separate each side of the external magnetic field cancellation coil 22 into individual wires, making the distance between wire 22a and the magnetic detector 13 as close to 0 as possible, and the width in the direction of wires 22b and 22d also close to 0. However, as described later, this would increase the current and make assembly difficult. Therefore, it is easier to handle if the width of wires 22a and 22c is the same as the total width of the magnetic detector, the distance between wire 22a and the magnetic detector 13 is as close as possible, about 2-5 mm, and the width in the direction of wires 22b and 22d is about 3-5 mm. In the case of multiple magnetic detectors 13, 14, 16, and 17, one coil is sufficient for each line in which the multiple magnetic detectors 13, 14, 16, and 17 are arranged. This allows for lower currents because each line can be handled individually, rather than using a single coil that is individually adjusted for each magnetic detector 13, 14, 16, and 17.

[0036] Furthermore, when the external magnetic field canceling coil is positioned so that the magnetic detector is placed inside, as shown in Figure 5(1), a magnetic field that deviates significantly from the desired magnetic field strength is applied near the edges of the magnetic detector, and the width of the external magnetic field canceling coil in the positioning direction becomes larger than that of the magnetic detector. On the other hand, by not placing the magnetic detector inside the external magnetic field canceling coil but arranging it adjacent to it, as shown in Figure 5(2), the deviation of the magnetic field applied near the edges of the magnetic detector from the desired magnetic field strength can be reduced, and the width of the external magnetic field canceling coil in the positioning direction can be kept to the same level as that of the magnetic detector.

[0037] One reason why the magnetic field is not uniform in the linear direction in which the magnetic detectors 13, 14, 16, and 17 are arranged is that when the external magnetic field cancellation coil 22 is disassembled into individual wires and examined, wires 22b and 22d are found to be the main cause. In the case of a coil in which magnetic detectors 13, 14, 16, and 17 are placed inside and the width in the linear direction in which the magnetic detectors 13, 14, 16, and 17 are arranged is narrowed as much as possible, the magnetic detectors 13, 14, 16, and 17 at the ends will be in close contact with wires 22b and 22d, and a very strong magnetic field in the same direction as wires 22a and 22c, generated by wires 22b and 22d, will be applied to the ends of the magnetic detectors. As a result, the effect on the ends of the coil becomes very strong. In contrast, in this embodiment, the magnetic detectors at the ends will not be in close contact with wires 22b and 22d, and only the magnetic field generated by wires 22a and 22c will be applied to the magnetic detectors. Thus, the influence at the ends can be reduced compared to when the magnetic detectors 13, 14, 16, and 17 are placed internally. The shorter the distance between wire 22a and the magnetic detector, the wider the uniform magnetic field region in the center of the arrangement direction becomes, but the abrupt changes at the ends increase, and as wire 22a moves away from the magnetic detector, the region where the magnetic field collapses at the ends widens. Also, narrowing wires 22b and 22d can reduce the influence at the ends, but since the magnetic field of wire 22a is canceled out by wire 22c, problems arise such as having to increase the number of turns of the coil or the current to generate the necessary magnetic field. For this reason, the dimensions should be changed to optimal values ​​as needed.

[0038] As described above regarding the magnetization means, since the magnetic field strength applied to each of the magnetic detectors 13, 14, 16, and 17 is different, it is preferable that the current flowing through each of the external magnetic field cancellation coils 22, 23, 24, and 25 is different for each. If there is sufficient margin in the magnetic saturation of the magnetic detectors 13, 14, 16, and 17, the current may be the same for each.

[0039] If there is sufficient margin in the magnetic saturation of the magnetic detectors 13, 14, 16, and 17, or if good assembly accuracy can be maintained, and depending on the spacing L, it is also possible to arrange two magnetic detectors, including magnetic detector 14 which is spaced apart from magnetic detector 13 in the Y direction as shown in Figure 6, in correspondence with one external magnetic field canceling coil 22. In that case, since the magnetic field strength applied from the magnetization means changes with distance, the magnetic field applied to magnetic detector 13 is stronger than the magnetic field applied to magnetic detector 14, so it is preferable to set the distance L2 between wire 22a and magnetic detector 13 and the distance L3 between wire 22c and magnetic detector 14 to L2 ≤ L3. Furthermore, the external magnetic field canceling coils 22, 23, 24, and 25 can also be changed to cancellation magnetic field patterns wired on a substrate, etc., as shown in Figure 7. In Figure 7, only an excerpt of patterns arranged so that the excitation current flows parallel to multiple patterns parallel to the X direction is shown. With such a cancellation magnetic field pattern, a magnetic field can be formed on the magnetic detector 13 parallel to the Z direction. In this case, the effect is equivalent to that of wires 22b, 22c, and 22d, with only the influence of wire 22a as described above. Therefore, it is preferable that the distance between the cancellation magnetic field pattern wired on the substrate and the magnetic detector 13 is as close to zero as possible, and the wire width is equal to the total width of the sensor.

[0040] However, it is not possible to use a single external magnetic field canceling coil to handle both the magnetic detector 13 and the magnetic detector 14, which are spaced apart in the Y direction, because the direction of the magnetic field generated would be opposite at the positions of the magnetic detector 13 and the magnetic detector 14 in the pattern wired on this substrate.

[0041] Regarding the current flowing through the external magnetic field cancellation coils 22, 23, 24, and 25, it is preferable to control it using a feedback output (feedback current) or a DA (Digital to Analog) converter according to the sensor output, but it is also acceptable to flow an arbitrary fixed current suitable for a particular environment.

[0042] (Regarding magnetic shielding means) Next, referring again to Figure 1, the magnetic shielding means 15 and 18 will be described. In the example in Figure 1, the magnetic detectors 13 and 14 are surrounded by the magnetic shielding means 15. Similarly, the magnetic detectors 16 and 17 are surrounded by the magnetic shielding means 18. The magnetic shielding means 15 and 18 are made of high-permeability materials such as permalloy or silicon steel sheets, and prevent the intrusion of magnetic fields from the outside, thereby shielding them from the influence of external magnetism.

[0043] However, the magnetic shielding means 15 has an opening on the transport path side to expose the magnetic detectors 13 and 14 to the object 26 being inspected that passes below (on the transport path side) the magnetic detectors 13 and 14, and a magnetic field from a magnetic foreign object can reach the magnetic detectors 13 and 14 through this opening. Similarly, the magnetic shielding means 18 has an opening on the transport path side to expose the magnetic detectors 16 and 17 to the object 26 being inspected that passes above (on the transport path side) the magnetic detectors 16 and 17, and a magnetic field from a magnetic foreign object can reach the magnetic detectors 16 and 17 through this opening.

[0044] By providing magnetic shielding means 15 and 18, background magnetic field noise reaching the magnetic detectors 13, 14, 16, and 17 can be blocked, further improving detection accuracy. In the example shown in Figure 1, one magnetic shielding means covers a pair of magnetic detectors, but one magnetic shielding means may cover one magnetic detector and a corresponding external magnetic field cancellation coil, or all magnetic detectors may be covered by one magnetic shielding means with an appropriately provided opening.

[0045] (Regarding the processing unit) Next, the processing unit 19 will be described with reference to Figures 8 and 9. Figure 8 is a block diagram illustrating the configuration of the processing unit according to this embodiment. Figure 9 is a block diagram illustrating the functions of the signal processing unit and arithmetic processing unit according to this embodiment.

[0046] As shown in Figure 8, the processing unit 19 includes a signal processing unit 191, an arithmetic processing unit 192, and a display unit 193.

[0047] The signal processing unit 191 controls the drive of the magnetic detectors 13, 14, 16, and 17, and processes the detection signals from the magnetic detectors 13, 14, 16, and 17. For example, as shown in Figure 9, the signal processing unit 191 includes a signal detection unit 191a, an amplification unit 191b, and an AD (Analog to Digital) conversion unit 191c.

[0048] The signal detection unit 191a receives detection signals corresponding to the total magnetic field amount H detected from each of the magnetic detectors 13, 14, 16, and 17. The signal detection unit 191a may also display the waveform of the detection signal on the display unit 193. The amplification unit 191b amplifies the detection signal received by the signal detection unit 191a. The AD conversion unit 191c converts the analog detection signal amplified by the amplification unit 191b into a digital signal. The digital signal output from the AD conversion unit 191c is output to the arithmetic processing unit 192. The detection signal may also be processed as an analog signal, in which case the AD conversion unit 191c may be omitted.

[0049] The arithmetic processing unit 192 determines the presence or absence of magnetic foreign matter based on the digital signal output from the signal processing unit 191. If the arithmetic processing unit 192 is configured with an analog circuit such as an OP (Operational) amplifier, the presence or absence of magnetic foreign matter is determined based on the detection signal amplified by the signal processing unit 191. For example, as shown in Figure 9, the arithmetic processing unit 192 includes a noise reduction unit 192a and a determination unit 192b.

[0050] The noise reduction unit 192a removes background magnetic field noise components (noise signals) by performing noise reduction processing on sets of digital signals corresponding to detection signals from magnetic detectors 13 and 14, and on sets of digital signals corresponding to detection signals from magnetic detectors 16 and 17. For example, differential processing and averaging processing can be applied as noise reduction processing.

[0051] When detection signals from a pair of magnetic detectors are differentially processed, the detection signal caused by the magnetic field from the magnetic foreign object will have a waveform with peaks at the top and bottom. On the other hand, background magnetic field noise is removed by differential processing. Because background magnetic field noise is removed with a high rejection rate by differential processing, even minute magnetic foreign objects can be detected.

[0052] However, in the case of conventional technology where the magnetic field detection directions of a pair of magnetic detectors are not the same, the background magnetic field noise components in the detection signal are not in phase, and the background magnetic field noise cannot be removed by differential processing. In this case, the detection accuracy is reduced due to the strong influence of the background magnetic field noise. On the other hand, in this embodiment, since the magnetic field detection directions of the magnetic detectors 13, 14, 16, and 17 are the same, the influence of the background magnetic field noise can be removed by differential processing, and high detection accuracy can be achieved.

[0053] The determination unit 192b acquires a signal from which the influence of background magnetic field noise has been removed by the noise reduction unit 192a, and determines the presence or absence of magnetic foreign matter based on the acquired signal. For example, the determination unit 192b determines that magnetic foreign matter is present if the signal strength exceeds a predetermined threshold. The determination unit 192b then displays the determination result on the display unit 193.

[0054] If the inspection device 10 is equipped with removal means (not shown) for removing the object 26 containing magnetic foreign matter from the transport path, the determination unit 192b may control the removal means to remove the object 26 containing the magnetic foreign matter when it determines that magnetic foreign matter is present.

[0055] (Regarding the operation of the inspection equipment) Next, the operation of the inspection device 10 will be described with reference to Figure 10. Figure 10 is a flowchart illustrating the foreign object detection operation of the inspection device according to this embodiment.

[0056] (S101) The object to be inspected 26 is placed on the conveyor belt 12a in front of the magnetization means 11, and is conveyed in the Y direction along the conveyor path, passing through the magnetization region where the magnetization means 11 is located, to the inspection region where the magnetic detectors 13, 14, 16, and 17 are located. In the magnetization region, magnetic foreign matter in the object to be inspected 26 is magnetized by the magnetic field (e.g., static magnetic field) generated by the magnetization means 11. The direction of the static magnetic field applied by the magnetization means 11 is the Z direction, which is the same as the magnetic field detection direction of the magnetic detectors 13, 14, 16, and 17. Therefore, the magnetic foreign matter is magnetized in the Z direction.

[0057] (S102) When the object to be inspected 26 is transported to the inspection area, each of the magnetic detectors 13, 14, 16, and 17 detects a magnetic field caused by the residual magnetism of a magnetic foreign object in the object to be inspected 26. Since the magnetic field detection direction of all magnetic detectors 13, 14, 16, and 17 is the Z direction, the magnetic detectors 13, 14, 16, and 17 detect the Z component of the magnetic field from the magnetic foreign object and output the detection signal to the processing device 19.

[0058] As shown in Figure 4, the pair of magnetic detectors 13 and 14, which are positioned side by side in the Y direction, are adjacent to each other, so that at least one of the magnetic detectors can detect the magnetic field from the magnetic foreign object. Similarly, for the pair of magnetic detectors 16 and 17, at least one of the magnetic detectors can detect the magnetic field from the magnetic foreign object. Therefore, if a magnetic foreign object is present, a detection signal is sent from at least one magnetic detector to the processing unit 19.

[0059] (S103) The signal processing unit 191 of the processing unit 19 receives detection signals from the magnetic detectors 13, 14, 16, and 17, and amplifies the received detection signals. The signal processing unit 191 also performs AD conversion on the analog detection signals to generate digital detection signals. However, if the process of determining the presence or absence of magnetic foreign matter is performed using an analog circuit, AD conversion may be omitted. The detection signals processed by the signal processing unit 191 are output to the arithmetic processing unit 192.

[0060] (S104) The arithmetic processing unit 192 acquires the detection signal output from the signal processing unit 191 and applies noise reduction processing to the acquired detection signal. For example, as noise reduction processing, the arithmetic processing unit 192 performs differential processing or averaging processing on two detection signals corresponding to a pair of magnetic detectors 13 and 14. The arithmetic processing unit 192 also performs differential processing or averaging processing on two detection signals corresponding to a pair of magnetic detectors 16 and 17. These noise reduction processing processes can reduce the influence of background magnetic field noise. In the processing performed by the arithmetic processing unit 192, the two detection signals corresponding to magnetic detectors 13 and 14 are shifted in phase based on the distance L between magnetic detectors 13 and 14 and the transport speed of the transport belt 12a before processing is performed.

[0061] Furthermore, the arithmetic processing unit 192 performs a determination process to determine the presence or absence of magnetic foreign matter based on the noise-removed detection signal. For example, the arithmetic processing unit 192 determines that magnetic foreign matter is present if the signal intensity of at least one or both of the noise-removed detection signals corresponding to the pair of magnetic detectors 13 and 14, and the noise-removed detection signals corresponding to the pair of magnetic detectors 16 and 17 exceeds a predetermined threshold.

[0062] (S105) The arithmetic processing unit 192 displays the determination result regarding the presence or absence of magnetic foreign matter on the display unit 193. The arithmetic processing unit 192 may also display the signal waveform of the detection signal on the display unit 193. Furthermore, if there is a removal means (not shown) for removing the object to be inspected 26 containing magnetic foreign matter from the transport path, the arithmetic processing unit 192 may control the removal means to remove the object to be inspected 26 containing magnetic foreign matter.

[0063] Once process S105 is complete, the series of processes shown in Figure 10 is finished. However, while the inspection device 10 is in operation, objects to be inspected are placed one after another on the conveyor belt 12a and inspections are performed continuously, so the foreign object detection operation shown in Figure 10 is performed for each object to be inspected. Alternatively, the foreign object detection operation is performed continuously without distinction between objects to be inspected.

[0064] (Hardware) Next, with reference to Figure 11, the hardware configuration of the computer 30 capable of realizing the functions of the arithmetic processing unit 192 will be described. Figure 11 is a block diagram illustrating the hardware of the arithmetic processing unit according to this embodiment. Note that the configuration of the computer 30 is an example, and some elements may be omitted or new elements may be added.

[0065] As shown in Figure 11, the computer 30 includes a processor 31, memory 32, a display interface 33, a communication interface 34, and a connection interface 35.

[0066] The processor 31 can be a CPU (Central Processing Unit), DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit), FPGA (Field Programmable Gate Array), GPU (Graphic Processing Unit), etc. The memory 32 can be, for example, ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), flash memory, etc. The functions of the noise reduction unit 192a and the determination unit 192b described above can be realized using the processor 31 and memory 32.

[0067] The display interface 33 is an interface for connecting display devices such as LCDs (Liquid Crystal Displays) and ELDs (Electro-Luminescence Displays). These display devices are examples of the display unit 193 described above. The communication interface 34 is an interface for connecting to wired and / or wireless networks. The communication interface 34 can be connected to, for example, a wired LAN (Local Area Network), a wireless LAN, an optical communication network, a mobile phone network, etc.

[0068] The connection interface 35 is an interface for connecting external devices. Examples of connection interfaces 35 include USB (Universal Serial Bus) ports, IEEE 1394 ports, and SCSI (Small Computer System Interface). Input interfaces such as keyboards, mice, touch panels, and touchpads can be connected to the connection interface 35.

[0069] Furthermore, a computer-readable storage medium 36 may be connected to the connection interface 35. The computer-readable storage medium 36 may be, for example, a magnetic storage medium, an optical disk, a magneto-optical disk, or a semiconductor memory. For example, the processor 31 may read a program stored in the computer-readable storage medium 36 and store it in the memory 32, and then control the operation of the computer 30 according to the program read from the memory 32. The program may be stored in the memory 32 in advance, or it may be downloaded from a network via the communication interface 34.

[0070] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these also naturally fall within the technical scope of the present invention. [Explanation of symbols]

[0071] 10, 10a Inspection device 11, 11a, 11b Magnetizing means 12 Conveying means 13, 13a, 13b, 14, 14a, 14b, 16, 17 Magnetic detectors 15, 18 Magnetic shielding means 19 Processing Unit 20, 21 Fixing members 22, 23, 24, 25 External magnetic field cancellation coil 26. Items to be inspected 27 Magnetic foreign matter 132, M1, M2, M3, M4, M5, M6 magnetic material 133 coils 191 Signal Processing Unit 191a Signal detection unit 191b Amplifier 191c AD conversion unit 192 Arithmetic Processing Unit 192a Noise reduction section 192b Judgment part 193 Display section

Claims

1. A transport means for transporting the object to be inspected, A magnetization means for magnetizing the object to be inspected, A magnetic detector is positioned downstream of the magnetization means in the transport direction by the transport means, and detects a magnetic field due to the residual magnetism of magnetic foreign matter contained in the object to be inspected. An external magnetic field canceling coil is positioned adjacent to the magnetic detector in the transport direction by the transport means and generates a magnetic field in the opposite direction to the external magnetic field applied to the magnetic detector. An inspection device characterized by being equipped with

2. The inspection apparatus according to claim 1, characterized in that the magnetic field generated by the external magnetic field cancellation coil is controlled using a feedback current based on the signal detected by the magnetic detector.

3. The magnetic detector comprises a pair of magnetic detectors arranged at a first interval in the transport direction. Multiple linear magnetic materials are arranged on a first plane, which is one plane of one of the pair of magnetic detectors, and multiple linear magnetic materials are arranged on a second plane, which is one plane of the other of the pair of magnetic detectors. The inspection apparatus according to claim 1, characterized in that the pair of magnetic detectors have parallel magnetic field detection directions.

4. The inspection apparatus according to claim 3, characterized in that the pair of magnetic detectors are arranged such that the magnetic field detection direction of each magnetic detector is perpendicular to the transport direction.

5. The set includes a fixing member for arranging the pair of magnetic detectors, The inspection apparatus according to claim 3 or 4, characterized in that the first interval is set such that the phase of the noise signal detected by each of the pair of magnetic detectors is shifted.

6. The inspection apparatus according to claim 4, characterized in that the direction in which the magnetic field is applied by the magnetization means is parallel to the direction in which the magnetic field is detected.

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