Defect Detection Equipment

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The defect detection device addresses the issue of device size increase by employing a magnetic body with scanned permeability peaks to measure defects using AC magnetic fields and eddy currents, allowing precise defect detection without enlarging the device.

JP7789235B2Active Publication Date: 2025-12-19MITSUBISHI ELECTRIC CORP

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Patent Information

Application Number: JP2024571565
Authority / Receiving Office: JP · JP
Patent Type: Patents
Current Assignee / Owner
Filing Date: 2023-01-20
Publication Date: 2025-12-19
Estimated Expiration: 2043-01-20

AI Technical Summary

Technical Problem

Conventional defect detection devices for pipes become larger due to the need for multiple processing circuits corresponding to the number of magnetic sensors arranged in a grid pattern, leading to an increase in device size.

Method used

A defect detection device that uses a magnetic body to generate multiple magnetic fields with a peak permeability distribution, which is scanned to detect defects using AC magnetic fields and eddy currents, with a control circuit to measure defect position and size without increasing device size.

Benefits of technology

Enables accurate measurement of defect position and size while maintaining a compact device size by utilizing a single inspection coil and control circuit to analyze induced magnetic field changes.

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Abstract

A defect detection device (1) comprises: a magnetic material (10); a magnetic field generation circuit (100) that forms a first magnetic permeability distribution (μ) having a peak within a magnetic body (10) by generating a plurality of first magnetic fields (41, 42) within the magnetic body (10), and moves the peak position (Xp) of a first magnetic permeability distribution (μ) in a predetermined first scanning direction (X) by changing the plurality of first magnetic fields (41, 42); an inspection circuit (200) that outputs a detected voltage at each position in the first scanning direction by applying an alternating magnetic field to an inspection target (50) to generate eddy currents in inspection areas (X1-X2) and detecting changes in the induced magnetic field caused by changes in the eddy currents, when the magnetic field generation circuit (100) moves the peak position of the first magnetic permeability distribution (μ) in the first scanning direction; and a control circuit (30) that detects the position and size of the defect of the inspection target in the first scanning direction on the basis of the detected voltage.

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Description

[Technical Field]

[0001] The present disclosure relates to a defect detection device that detects defects in an inspection object. [Background technology]

[0002] In pipes (e.g., metal pipes such as copper pipes) used for water supply, drainage, cooling water, etc., corrosion inside the pipes can cause water leaks. In order to address defects before such events occur, it is necessary to measure and predict the progression of corrosion. For example, Patent Document 1 proposes a non-destructive inspection device that includes a sheet substrate covering an object to be inspected, an excitation coil arranged on the sheet substrate, an excitation power supply, multiple magnetic sensors (e.g., multiple Hall elements) arranged in a grid pattern on the sheet substrate, a magnetic sensor circuit, and a computer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-114533 (see, for example, FIGS. 1, 2, 5, 6, and paragraphs 0025 to 0034) Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional device measures defects in the inspection object at the positions of multiple magnetic sensors arranged in a grid pattern, which requires the preparation of a number of processing circuits equal to the number of magnetic sensors, resulting in the problem of the device becoming larger.

[0005] An object of the present disclosure is to provide a defect detection device that can measure the position and size of a defect that occurs in an inspection object while suppressing an increase in the size of the device. [Means for solving the problem]

[0006] The defect detection device disclosed herein is characterized by comprising: a magnetic body arranged to overlap an inspection area of an inspection object; a magnetic field generating circuit that generates a plurality of first magnetic fields within the magnetic body to form a first permeability distribution having a peak within the magnetic body and changes the plurality of first magnetic fields to move the position of the peak of the first permeability distribution in a predetermined first scanning direction; an inspection circuit that, when the magnetic field generating circuit moves the position of the peak of the first permeability distribution in the first scanning direction, applies an AC magnetic field to the inspection object to generate eddy currents in the inspection area while detecting changes in the induced magnetic field generated due to changes in the eddy currents, thereby outputting a detection voltage at each position in the first scanning direction; and a control circuit that controls the operation of the magnetic field generating circuit and the inspection circuit and detects the position and size of a defect in the inspection object in the first scanning direction based on the detection voltage. [Effects of the Invention]

[0007] According to the defect detection device of the present disclosure, it is possible to measure the position and size of a defect that has occurred in an inspection object while suppressing an increase in the size of the device. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1A is a diagram illustrating a schematic configuration of a defect detection device according to a first embodiment, and FIG. 1B is a diagram illustrating a hardware configuration of a control circuit. [Figure 2] 10A to 10C are waveform diagrams illustrating the operating principle of the defect detection device. [Figure 3] 1 is a schematic perspective view showing an inspection coil, a magnetic body, and a coil of a defect detection device according to a first embodiment (before being attached to an inspection object). [Figure 4] 1 is a schematic perspective view showing an inspection coil (after being attached to an inspection object) of the defect detection device according to the first embodiment, and a magnetic body and coil (before being attached to an inspection object). FIG. [Figure 5] 1 is a schematic perspective view showing an inspection coil, a magnetic body, and a coil of the defect detection device according to the first embodiment (after being attached to an inspection object). FIG. [Figure 6] FIG. 10 is a diagram schematically illustrating the configuration of a defect detection device according to a second embodiment. [Figure 7] FIG. 10 is a schematic perspective view showing the inspection coils (excitation coil and detection coil) of the defect detection device according to the second embodiment. [Figure 8] FIG. 10 is a schematic perspective view showing an inspection coil (excitation coil and detection coil) of a defect detection device according to a modified example of the second embodiment. [Figure 9] 10(A) and 10(B) are a schematic perspective view and a schematic cross-sectional view showing a magnetic body and a coil (before being attached to an inspection object) of a defect detection device according to a third embodiment. [Figure 10] FIG. 10 is a diagram schematically illustrating a configuration of a defect detection device according to a fourth embodiment. [Figure 11] 10(A) is a schematic perspective view showing a magnetic body and a coil of a defect detection device according to a fourth embodiment (before being attached to an inspection object), and FIG. 10(B) is a schematic plan view of the magnetic body. [Figure 12] FIG. 11 is a schematic perspective view showing the configuration of a magnetic body, a coil, and a magnet of a defect detection device according to a fifth embodiment (before being attached to an inspection object). [Figure 13] 10(A) is a schematic perspective view showing a magnetic body and a coil of a defect detection device according to a sixth embodiment (before being attached to an inspection object), and FIG. 10(B) is a schematic plan view of the magnetic body. [Figure 14] 10(A) is a schematic perspective view showing a magnetic body and a coil of a defect detection device according to a seventh embodiment (before being attached to an inspection object), and FIG. 10(B) is a schematic plan view of the magnetic body. [Figure 15] FIG. 13 is a schematic perspective view showing a magnetic body, a coil, and a magnet (before being attached to an inspection object) of a defect detection device according to an eighth embodiment. [Figure 16] FIG. 13 is a diagram schematically illustrating the configuration of a defect detection device according to a ninth embodiment. [Figure 17] FIG. 13 is a schematic perspective view showing an exciting coil and a Hall element as a magnetic sensor of a defect detection device according to a ninth embodiment (before being attached to an inspection object). DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a defect detection device according to an embodiment will be described with reference to the drawings. The following embodiments are merely examples, and the embodiments can be appropriately combined and modified.

[0010] First Embodiment FIG. 1A is a diagram schematically illustrating the configuration of a defect detection device 1 according to the first embodiment, and FIG. 1B is a diagram illustrating the hardware configuration of a control circuit 30. As shown in FIG.

[0011] The defect detection device 1 is a magnetic body 10 that is arranged so as to overlap (i.e., face) the inspection areas X1 to X2 of the inspection object 50, and generates a plurality of (two in FIG. 1(A)) first magnetic fields 41 and 42 in the magnetic body 10, thereby forming a magnetic permeability distribution (first magnetic permeability distribution) μ(X) having a peak in the magnetic body 10, and by changing the first magnetic fields 41 and 42, the position X of the peak of the magnetic permeability distribution μ(X) is p and a magnetic field generating circuit 100 that moves the magnetic field generating circuit 100 in a predetermined first scanning direction (X direction). The inspection object 50 is a non-magnetic metal, such as copper, SUS, or aluminum. The inspection object 50 is a pipe or a plate material. The magnetic body 10 is preferably a soft magnetic body. The magnetic body 10 may also be a bendable sheet-like member.

[0012] The defect detection device 1 also includes an inspection circuit 200 that, when the magnetic field generating circuit 100 moves the position of the peak of the magnetic permeability distribution μ(X) in the first scanning direction, applies an AC magnetic field to the inspection object 50 to generate eddy currents in the inspection area X1-X2, and detects changes in the induced magnetic field caused by changes in the eddy currents, thereby outputting a detection voltage at each position in the first scanning direction, and a control circuit 30 that controls the operation of the magnetic field generating circuit 100 and the inspection circuit 200, and detects the position and size of the defect in the inspection object in the first scanning direction based on the detection voltage.

[0013] The magnetic field generating circuit 100 includes a coil (first coil) 11 and a coil (second coil) 12, which are respectively arranged on both sides of the inspection region X1-X2 of the magnetic body 10 in the first scanning direction, a first power supply 13 that supplies a first direct current I1 to the coil 11, and a second power supply 14 that supplies a second direct current I2 to the coil 12. Each of the coil 11 and the coil 12 is formed of a conductor wound around the magnetic body 10 (more specifically, around the vicinity of the end). The coil 11 and the coil 12 are wound so that the direction of the first magnetic field 41 and the direction of the first magnetic field 42 are opposite to each other.

[0014] The inspection circuit 200 includes an inspection coil 20 arranged to overlap the inspection regions X1-X2, an oscillation circuit 21 that applies an AC current to the inspection coil 20 to generate an AC magnetic field, and a detection circuit 22 that detects the induced current flowing in the inspection coil 20 due to changes in the induced magnetic field generated by changes in eddy currents flowing in the inspection object 50 and outputs a detection voltage corresponding to the induced current. The inspection coil 20 functions as an excitation coil that applies an eddy current to the inspection object 50 using the AC magnetic field, and as a detection coil that detects the induced magnetic field generated by the eddy current. The frequency of the AC current output from the oscillation circuit 21 can be set within a range from 100 Hz to several hundred kHz, but is generally set within a range from 1 kHz to 100 kHz.

[0015] As shown in FIG. 1B, the control circuit 30 includes a processor 31 such as a CPU (Central Processing Unit), a memory 32 as a storage device, and an interface 33. The control circuit 30 is configured, for example, by a processing circuit. The processing circuit may be dedicated hardware, or may include a CPU that executes a program stored in the memory 32. The memory 32 is, for example, a semiconductor memory such as a RAM (Random Access Memory). The memory 32 may also include a non-volatile storage device such as an HDD (Hard Disk Drive). The control circuit 30 may also include a mixture of components including a processing circuit and components including a processor.

[0016] Figures 2(A) to (C) are waveform diagrams showing the operating principle of the defect detection device 1. Figure 2(A) shows the magnetic field distribution B(X) in the magnetic body 10 in the first scanning direction when the first direct current I1 flowing through the coil 11 and the second direct current I2 flowing through the coil 12 are equal, and the magnetic permeability distribution μ(X) in the magnetic body 10 at that time. When I1 = I2, at the intermediate position between the position X = X1 and the position X = X2, the magnetic field distribution B(X) = 0, and the position X of the peak of the magnetic permeability distribution μ(X) p is at the position X = 0.

[0017] Figure 2(B) shows the magnetic field distribution B(X) in the magnetic body 10 in the first scanning direction when the first direct current I1 flowing through the coil 11 is greater than the second direct current I2 flowing through the coil 12, and the magnetic permeability distribution μ(X) in the magnetic body 10 at that time. When I1 > I2, at a position closer to X1 than the intermediate position between the position X = X1 and the position X = X2, the magnetic field distribution B(X) = 0, and the position X of the peak of the magnetic permeability distribution μ(X) p is obtained. When I1 < I2, at a position closer to X2 than the intermediate position between the position X = X1 and the position X = X2, the magnetic field distribution B(X) = 0, and the position X of the peak of the magnetic permeability distribution μ(X) p is obtained.

[0018] Figure 2(C) is a diagram showing the waveform of the change in the first direct current I1 flowing through the coil 11 and the second direct current I2 flowing through the coil 12, and the position X where the magnetic permeability μ in the magnetic body becomes maximum p2(C) is a diagram showing an example of a waveform of a change in an induced voltage detected by the inspection coil when the inspection coil is swept from position X1 to X2. As shown in the upper part of FIG. 2(C), by changing the first DC current I1 and the second DC current I2, the peak position of the magnetic permeability distribution can be changed within the range from X1 to X2. For example, by setting I1 = I' and I2 = I", the peak position of the magnetic permeability distribution can be set to the position X = X'. As shown in the upper part of Figure 2(C), by scanning the peak position of the magnetic permeability distribution from X1 to X2, an example of the detection voltage detected by the detection circuit 22 becomes, for example, as shown in the lower part of Figure 2(C). In Figure 2(C), the fluctuation part at position Xa of the detection voltage with a relatively small amplitude corresponds to the relatively small defect 51 in Figure 1(A), and the fluctuation part at position Xb of the detection voltage with a relatively large amplitude corresponds to the relatively large defect 52 in Figure 1(A). In this way, the amplitude of the fluctuation of the detection voltage is proportional to the volume of the defect in the inspection object 50.

[0019] position p When the magnetic permeability distribution μ(X) in the magnetic body 10 is maximized (i.e., X=X p When the voltage V(X p ) is expressed by the following equation (1).

[0020]

number

[0021] 3 is a schematic perspective view showing the inspection coil 20, magnetic body 10, and coils 11 and 12 of the defect detection device 1 according to embodiment 1 (before being attached to the pipe that is the inspection target 50). The number of turns of the coils 11 and 12 can be any number, but it is desirable that the number of turns of the coils 11 and 12 be the same.

[0022] Figure 4 is a schematic oblique view showing the inspection coil 20 of the defect detection device 1 of embodiment 1 (after being spirally attached to the piping that is the inspection object 50), the magnetic body 10, and the coils 11 and 12 (before being attached to the inspection object).

[0023] 5 is a schematic perspective view showing the inspection coil 20, magnetic body 10, and coils 11 and 12 of the defect detection device 1 according to embodiment 1 (after being spirally attached to a pipe that is an inspection object 50). In this way, by forming the inspection coil 20 on a flexible substrate and making the magnetic body 10 a sheet-like member (for example, a thin film, a resin, a rubber sheet containing magnetic powder, etc.), the inspection coil 20, magnetic body 10, and coils 11 and 12 can be attached along the inspection object 50.

[0024] As described above, the defect detection device 1 according to the first embodiment can measure the position (position in the X direction) and size of a defect in the inspection object 50 using one inspection coil 20, one oscillation circuit 21, and one detection circuit 22. In other words, the defect detection device 1 can measure the position and size of a defect that has occurred in the inspection object 50 while preventing the device from becoming too large.

[0025] Second Embodiment Fig. 6 is a diagram schematically showing the configuration of a defect detection device 2 according to embodiment 2. In Fig. 6, components that are the same as or correspond to those shown in Fig. 1(A) are assigned the same reference numerals as those shown in Fig. 1(A). The defect detection device 2 according to embodiment 2 differs from the defect detection device 1 according to embodiment 1 in that it has, as inspection coils for the inspection circuit 200a, an excitation coil 20a connected to an oscillation circuit 21 and a detection coil 20b connected to a detection circuit 22.

[0026] 7 is a schematic perspective view showing the inspection coils (excitation coil 20a and detection coil 20b) of the defect detection device 2 according to embodiment 2 (before being attached to the pipe that is the inspection target 50). In this case, the excitation coil 20a and the detection coil 20b are provided separately so that the excitation coil 20a surrounds the detection coil 20b, and therefore it is possible to prevent the excitation magnetic field generated by the excitation coil 20a from affecting the detection coil 20b.

[0027] 8 is a schematic perspective view showing the inspection coils (excitation coil 20a and detection coil 20b) of a defect detection device 2a (before being attached to a pipe that is an inspection target 50) according to a modified example of embodiment 2. In this case, the excitation coil 20a and the detection coil 20b are separately provided so that they are aligned, and therefore it is possible to prevent the excitation magnetic field generated by the excitation coil 20a from affecting the detection coil 20b.

[0028] According to the defect detection device 2 or 2a, by configuring the excitation coil 20a and the detection coil 20b to be separated, the detection coil 20b detects only the induced magnetic field, thereby improving the accuracy of defect detection.

[0029] Other than the above, the second embodiment is the same as the first embodiment.

[0030] Third Embodiment 9(A) and 9(B) are a schematic perspective view and a schematic cross-sectional view showing the magnetic body 10 and coils 11a and 12a (before being attached to the inspection object 50) of the defect detection device 3 according to the third embodiment. FIG. 9(B) shows a cross section taken along line IX-IX in FIG. 9(A). In the defect detection device 3 according to the third embodiment, the coils 11a and 12a are each composed of a coil pattern arranged on the end of the magnetic body 10. The coil patterns are formed by a wiring pattern formed on a substrate.

[0031] According to the defect detection device 3, the excitation coil can be made thin and flexible, so that the excitation coil portion can also be wound around the pipe as the inspection target 50. This allows the defect detection device 3 to be made smaller.

[0032] In all other respects, the third embodiment is the same as the first or second embodiment.

[0033] Fourth Embodiment Fig. 10 is a diagram schematically illustrating the configuration of a defect detection device 4 according to embodiment 4. In Fig. 10, components that are the same as or correspond to those shown in Fig. 1(A) are assigned the same reference numerals as those shown in Fig. 1(A). The defect detection device 4 according to the fourth embodiment differs from the defect detection device 1 according to the first embodiment in that the magnetic field generating circuit 100a generates a plurality of (e.g., two) second magnetic fields within the magnetic body 10a to form a second permeability distribution having a peak within the magnetic body 10a, and changes the plurality of second magnetic fields to move the position of the peak of the second permeability distribution in a predetermined second scanning direction (Y direction) different from the first scanning direction (X direction); the inspection circuit 200 applies an AC magnetic field to the inspection object 50 when the magnetic field generating circuit 100a moves the position of the peak of the second permeability distribution in the second scanning direction, thereby generating eddy currents in the inspection area, and detects changes in the induced magnetic field generated due to changes in the eddy currents, thereby outputting detection voltages at each position in the second scanning direction; and the control circuit 30 controls the operation of the magnetic field generating circuit 100a and the inspection circuit 200, and further has the function of detecting the position and size of defects in the inspection object in the second scanning direction (Y direction) based on the detection voltages.

[0034] Specifically, the magnetic field generating circuit 100a has a coil (third coil) 11c and a coil (fourth coil) 12c arranged on either side of the inspection area of the magnetic body 10 in the second scanning direction, a third power supply 13c that passes a third direct current I3 through the coil 11c, and a fourth power supply 14c that passes a fourth direct current I4 through the coil 12c.

[0035] 11(A) is a schematic perspective view showing the magnetic body 10a and coils 11, 12, 11c, and 12c of the defect detection device 4 according to the fourth embodiment (before being attached to the inspection target 50), and FIG. 11(B) is a schematic plan view of the magnetic body 10a. In the defect detection device 4, the first DC current I1 and the second DC current I2 passed through the coils 11 and 12 are changed as shown in FIG. 2(C), thereby enabling the detection of the position and size of a defect in the X direction (here, the longitudinal direction of the magnetic body 10a) of the inspection target 50 in FIG. 11(A). In addition, the defect detection device 4 is able to detect the position and size of a defect in the Y direction (here, the width direction of the magnetic body 10a) of the inspection target 50 in FIG. 11(A) by changing the third DC current I3 and the fourth DC current I4 passed through the coils 11c and 12c as shown in FIG. 2(C).

[0036] As described above, according to the fourth embodiment, by providing four excitation coils, the position of a defect can be detected two-dimensionally.

[0037] Furthermore, according to embodiment 4, by using four excitation coils, the region of the magnetic permeability peak in the magnetic body 10a can be made into a point-like region, and therefore detection can be performed with higher position resolution than in embodiment 1, in which the region of the magnetic permeability peak in the magnetic body 10a is a linear region.

[0038] In the fourth embodiment, an example in which the number of excitation coils is four has been described, but if the number of excitation coils is three or more, it is possible to detect the position of a defect two-dimensionally.

[0039] In other respects than those mentioned above, the fourth embodiment is the same as any of the first to third embodiments.

[0040] Fifth Embodiment FIG. 12 is a schematic perspective view showing the configuration of the magnetic body 10a, coils 11 and 12, and permanent magnets 15 and 16 of the defect detection device 5 according to the fifth embodiment (before being attached to the inspection target 50). In FIG. 12, components identical to or corresponding to those in FIG. 11(A) are denoted by the same reference numerals as those in FIG. 11(A). The permanent magnets 15 and 16 are arranged on the magnetic body 10a with a gap therebetween in a predetermined second scanning direction (Y direction) different from the first scanning direction (X direction). The polarity of the permanent magnets 15 and 16 on the magnetic body 10a side is the same (north pole in the figure). If the strengths of the permanent magnets 15 and 16 are the same, the center position in the Y direction of the magnetic body 10a in FIG. 12 corresponds to the peak position of the magnetic permeability distribution in the Y direction.

[0041] According to the defect detection device 5 of embodiment 5, by using two excitation coils and two permanent magnets 15, 16, the region of the magnetic permeability peak in the magnetic body 10a can be made into a point-like region, so that defects can be detected with higher positional resolution than in embodiment 1, in which the region of the magnetic permeability peak in the magnetic body 10a is a linear region.

[0042] Although the fifth embodiment has been described with reference to an example in which the number of permanent magnets is two, the number of permanent magnets may be at least two, and may be three or more.

[0043] In other respects than those mentioned above, the fifth embodiment is the same as any of the first to fourth embodiments.

[0044] Sixth Embodiment FIG. 13(A) is a schematic perspective view showing the magnetic body 10b and coils 11 and 12 of the defect detection device 6 according to the sixth embodiment (before being attached to the inspection object 50), and FIG. 13(B) is a schematic plan view of the magnetic body 10b. In the defect detection device 6 according to the sixth embodiment, the shape of the magnetic body 10b includes two annular shapes that form a closed magnetic circuit. While the magnetic body 10 according to the first embodiment forms an open magnetic circuit with terminals, the magnetic body 10b according to the sixth embodiment forms a closed magnetic circuit without terminals. This significantly reduces the demagnetizing field generated at the terminals, allowing the coils 11 and 12 to be driven at a low voltage. Furthermore, the reduction in external leakage magnetic field reduces the occurrence of malfunctions of external devices.

[0045] In all other respects, the sixth embodiment is the same as any of the first to fourth embodiments.

[0046] Seventh Embodiment FIG. 14(A) is a schematic perspective view showing the magnetic body 10c and coils 11, 12, 11c, and 12c of the defect detection device 7 according to the seventh embodiment (before being attached to the inspection target 50), and FIG. 14(B) is a schematic plan view of the magnetic body 10c. In FIGS. 14(A) and 14(B), components identical to or corresponding to those in FIGS. 11(A) and 11(B) are denoted by the same reference numerals as those in FIGS. 11(A) and 11(B). In the defect detection device 7 according to the seventh embodiment (FIGS. 11(A) and 11(B)), the magnetic body 10c has a shape including four annular shapes forming a closed magnetic circuit. While the magnetic body 10a in the fourth embodiment forms an open magnetic circuit with terminals, the magnetic body 10c in the seventh embodiment forms a closed magnetic circuit without terminals. This significantly reduces the demagnetizing field generated at the terminals, allowing the coils 11 and 12 to be driven at a low voltage. Furthermore, the reduction in external leakage magnetic field reduces the occurrence of malfunctions of external devices. In addition, the annular structure minimizes the demagnetizing field and reduces the magnetic resistance (inductance of the excitation coil), making it possible to drive the excitation coil with less voltage.

[0047] In all other respects, the seventh embodiment is the same as any of the first to fourth embodiments.

[0048] Eighth Embodiment FIG. 15 is a schematic perspective view showing the magnetic body 10c, coils 11 and 12, and permanent magnets 15 and 16 of the defect detection device 8 according to the eighth embodiment (before being attached to the inspection target 50). In FIG. 15, components identical to or corresponding to those in FIG. 12 are designated by the same reference numerals as those in FIG. 12. In the defect detection device 8 according to the eighth embodiment, the shape of the magnetic body 10c includes four annular shapes that form a closed magnetic circuit. While the magnetic body 10a in the fifth embodiment (FIG. 12) forms an open magnetic circuit with terminals, the magnetic body 10c in the eighth embodiment forms a closed magnetic circuit without terminals. This significantly reduces the demagnetizing field generated at the terminals, allowing the coils 11 and 12 to be driven at a low voltage. Furthermore, the reduction in external leakage magnetic field reduces the occurrence of malfunctions of external devices.

[0049] According to the defect detection device 8 of embodiment 8, by using two coils 11, 12 and two permanent magnets 15, 16, the region of the magnetic permeability peak in the magnetic body 10c can be made into a point-like region, so that defects can be detected with higher positional resolution than in embodiment 1, in which the region of the magnetic permeability peak in the magnetic body 10c is a linear region.

[0050] In the eighth embodiment, an example in which the number of permanent magnets 15, 16 is two has been described, but the number of permanent magnets may be at least two, and may be three or more.

[0051] In other respects than those mentioned above, the eighth embodiment is the same as any of the first to seventh embodiments.

[0052] Ninth Embodiment FIG. 16 is a diagram schematically showing the configuration of a defect detection device 9 according to a ninth embodiment. In FIG. 16, components that are the same as or correspond to those shown in FIG. 1(A) are assigned the same reference numerals as those shown in FIG. 6. The defect detection device 9 according to the ninth embodiment differs from the defect detection device 2 according to the second embodiment in that a magnetic sensor 23 having a plurality of Hall elements (magnetic detection elements) 23a is used as a magnetic field detection sensor of an inspection circuit 200b. The Hall elements 23a have the function of detecting an induced magnetic field generated by an eddy current.

[0053] 17 is a schematic perspective view showing an excitation coil 20a serving as an inspection coil and a plurality of Hall elements 23a arranged in the X direction as magnetic sensors of a defect detection device 9 (before being attached to an inspection object 50) according to a ninth embodiment. FIG. 17 shows an example in which a plurality of Hall elements 23a are arranged in an array. The outputs of the plurality of Hall elements 23a are connected in parallel, for example, and a detection circuit 22 detects a sum signal of the plurality of signals output from the plurality of Hall elements 23a. The sum signal detected by the detection circuit 22 is transmitted to the control circuit 30 as a single integrated detection signal.

[0054] In the ninth embodiment, the magnetic field sensitivity of the Hall element (magnetic resistance element) is a constant value regardless of the frequency of the excitation or induced magnetic field, so there is an advantage that the sensitivity does not decrease when the oscillation circuit is excited by switching between multiple frequencies. Incidentally, the magnetic field sensitivity of the detection coil is proportional to the frequency, so the lower the frequency, the more the sensitivity decreases.

[0055] In all other respects, the ninth embodiment is the same as any of the first to eighth embodiments. [Explanation of symbols]

[0056] 1 to 9, 2a defect detection device, 10, 10a, 10b, 10c magnetic material, 11, 11a first coil, 12, 12a second coil, 11c third coil, 12c fourth coil, 13 first power supply, 14 second power supply, 13c third power supply, 14c fourth power supply, 15, 16 permanent magnet, 20 inspection coil, 20a excitation coil, 20b detection coil, 21 oscillation circuit, 22 detection circuit, 23a Hall element (magnetic detection element), 30 control circuit, 50 inspection object, 51, 52 defect, 100, 100a magnetic field generation circuit, 200, 200a, 200b inspection circuit, X position in first scanning direction, I1 first DC current, I2 second DC current, I3 is the third DC current, I4 is the fourth DC current.

Claims

1. a magnetic body arranged to overlap an inspection area of an inspection object; a magnetic field generating circuit that generates a plurality of first magnetic fields in the magnetic material to form a first magnetic permeability distribution having a peak in the magnetic material, and that changes the plurality of first magnetic fields to move the position of the peak of the first magnetic permeability distribution in a predetermined first scanning direction; an inspection circuit that, when the magnetic field generating circuit moves the position of the peak of the first magnetic permeability distribution in the first scanning direction, applies an AC magnetic field to the inspection object to generate an eddy current in the inspection area, and detects a change in an induced magnetic field generated due to the change in the eddy current, thereby outputting a detection voltage at each position in the first scanning direction; a control circuit that controls the operations of the magnetic field generating circuit and the inspection circuit and detects the position and size of the defect in the inspection target in the first scanning direction based on the detection voltage; A defect detection device comprising:

2. The magnetic field generating circuit includes: a first coil and a second coil respectively disposed on both sides of the inspection area of the magnetic body in the first scanning direction; a first power supply that supplies a first direct current to the first coil; a second power supply that supplies a second direct current to the second coil; 2. The defect detection device according to claim 1, further comprising:

3. Each of the first coil and the second coil is formed of a conductive wire wound around the magnetic body.

3. The defect detection device according to claim 2.

4. Each of the first coil and the second coil is configured with a coil pattern disposed on an end of the magnetic body.

3. The defect detection device according to claim 2.

5. the magnetic field generating circuit generates a plurality of second magnetic fields in the magnetic body to form a second magnetic permeability distribution having a peak in the magnetic body, and changes the plurality of second magnetic fields to move the position of the peak of the second magnetic permeability distribution in a predetermined second scanning direction different from the first scanning direction; the inspection circuit applies an AC magnetic field to the inspection object to generate an eddy current in the inspection area while detecting a change in an induced magnetic field caused by the change in the eddy current when the magnetic field generation circuit moves the position of the peak of the second magnetic permeability distribution in the second scanning direction, thereby outputting a detection voltage at each position in the second scanning direction; The control circuit controls the operations of the magnetic field generating circuit and the inspection circuit, and detects the position and size of the defect in the inspection target in the second scanning direction based on the detection voltage.