WO2004094939A1

WO2004094939A1 - Magnetic probe

Info

Publication number: WO2004094939A1
Application number: PCT/JP2003/005132
Authority: WO
Inventors: Kazuhiro Yamakawa; Kazuaki Tabata
Original assignee: Azuma Systems Co., Ltd
Priority date: 2003-04-22
Filing date: 2003-04-22
Publication date: 2004-11-04
Also published as: AU2003235389A1; JPWO2004094939A1

Abstract

A magnetic probe comprising a detection coil the shape of which is changeable freely depending on a test object or a required sensing accuracy precisely detects a change in the magnetic flux along the surface of the test object. A magnetic probe (1), which detects a change in the magnetic flux in the vicinity of the surface of an object (2) while generating an AC magnetic field inside the object (2) containing a metal component and/or in the space on the surface of the object (2), comprises a ferromagnetic core (3) having object proximity sections (3a), forming a looped magnetic circuit through the inside of the object (2) and/or the space on the surface of the object (2), an excitation coil (4) AC-exciting the core (3) and generating an AC magnetic field along the surface of the object inside the object (2) and/or in the space on the surface of the object (2), and a detection coil (5) the coil center line of which extends along the surface of the object (2), the coil outer face of which locally faces the surface of the object (2), and which detects a change in the magnetic flux in the vicinity of the surface of the object (2).

Description

Description Magnetic probe Technical field

The present invention belongs to the technical field of magnetic probes used for surface inspection, flaw detection inspection, residual stress inspection, material inspection, etc. of an object containing a metal component, and in particular, freely forms according to the inspection object and required detection accuracy. The present invention relates to a magnetic probe capable of performing high-precision inspection while using a detection coil that can be changed. Background art

2. Description of the Related Art Magnetic probes that use magnetism, particularly an alternating magnetic field, to perform various tests on a subject containing a metal component are known. This type of magnetic probe has already been used for surface inspection, flaw detection inspection, residual stress inspection, material inspection, etc. of specimens containing metal components, but it is necessary to improve the detection accuracy in order to expand the range of use Is strongly desired. Therefore, a U-shaped core that forms a loop-shaped magnetic circuit in the interior of the subject and the surface space of the subject exists, and this core is AC-excited to produce the inside of the subject and the surface of the subject. A magnetic probe has been proposed that includes an excitation coil that generates an AC magnetic field in space and a detection coil that locally detects a change in magnetic flux near the surface of the subject (for example, Japanese Patent Application Laid-Open No. 60-173). See No. 51.)

Since the magnetic probe configured as described above forms a magnetic circuit with the subject, it can generate a local strong magnetic field at a desired position on the subject, and the exciting unit and the detecting unit However, the independent magnetic probe has an advantage that the detection coil can be miniaturized.However, the above-described conventional magnetic probe has a disadvantage in that the detection coil is arranged such that the coil center line is directed perpendicular to the surface of the subject. Since the change in magnetic flux is detected using a general-purpose magnetic detection element such as a Hall element, there has been a problem that the detection accuracy is limited and the application of the magnetic probe is limited.

That is, the AC magnetic field generated by the excitation coil is substantially parallel to the surface of the subject. There is a magnetic change due to the surface shape or scratches of the subject, mainly a force that appears as a change in magnetic flux along the surface of the subject.A detection coil arranged perpendicular to the surface of the subject is a magnetic flux. Since only the vertical component of the change is detected, there is a drawback that it is not possible to detect even a minute change in the magnetic flux density along the surface of the subject.

In the case of a magnetic probe, the shape of the detection unit must be changed as appropriate according to the inspection target and the required detection accuracy.However, the size of a magnetic detection element such as a Hall element is specified in advance, and the shape can be freely changed. Due to the low degree of accuracy, there are drawbacks in that the applications of the magnetic probe are limited and the required accuracy cannot be secured.

An object of the present invention is to form a loop-shaped magnetic circuit by an excitation coil and a core, and to detect a change in magnetic flux locally near the surface of a subject without using a general-purpose magnetic detection element. To provide a magnetic probe that can detect a change in magnetic flux in the direction along the surface of the subject with extremely high accuracy, while using a detection coil whose shape can be freely changed according to the required detection accuracy. It is in. Disclosure of the invention

It was created in view of the above-mentioned circumstances to solve these problems, and is to generate an AC magnetic field inside the specimen containing a metal component and / or in the surface space of the specimen, A magnetic probe that detects a change in magnetic flux near the surface of a subject, has a plurality of subjects close to each other, and forms a loop-shaped magnetic circuit in the interior of the subject and in the space of the subject or the surface of the subject. A ferromagnetic core, an exciting coil that generates an alternating magnetic field along the surface of the subject in the subject and / or in a surface space of the subject by exciting the core with an alternating current; And a detection coil that is arranged so that the outer peripheral surface of the coil locally faces the surface of the subject and detects a change in magnetic flux near the surface of the subject.

With this configuration of the magnetic probe, a magnetic detection element such as a Hall element can be used to detect a local magnetic flux change near the surface of the subject while forming a loop-shaped magnetic circuit with the excitation coil and the core. A detection coil that can be freely changed in shape, etc. according to the inspection object and required detection accuracy without using However, by arranging the detection coil so that the coil center line is along the surface of the object and the coil outer peripheral surface is locally opposed to the surface of the object, the magnetic flux changes in the direction along the surface of the object. Can be detected with extremely high accuracy. In addition, since the detection coil arranged in this manner can be easily miniaturized in the direction along the surface of the subject, it is necessary to scan the magnetic probe (or move the subject) while inspecting the surface of the subject. The resolution can be easily improved.

Further, the detection coil is a differential coil capable of detecting a differential voltage, and a pair of coils constituting the differential coil are arranged along the surface of the subject. In this case, the detection accuracy can be further improved by canceling the inherent error and the temperature error of the coil.

Further, the detection coil is characterized in that it is formed using a spiral coil having a small thickness in a coil center line direction. In this case, the resolution of the magnetic probe can be improved by performing the inspection while scanning the magnetic probe or the subject in the direction of the coil center line of the detection coil.

The detection coil is formed as a thin-film circuit pattern on a base material made of an insulator. In this case, the thickness of the detection coil in the direction of the center line of the coil is remarkably reduced, and the resolution of the magnetic probe can be further increased.

Further, the detection coil is a differential coil capable of detecting a differential voltage, and a pair of coils constituting the differential coil is formed in a laminated shape with the base material interposed therebetween. . In this case, not only can the resolution of the magnetic probe be drastically improved, but also the inherent error and temperature error of the coil can be offset to obtain highly reliable inspection data. Further, if a base material for a thin film substrate is used, an extremely thin detection coil can be formed by the existing thin film substrate manufacturing technology.

Further, a plurality of the detection coils are provided so as to be arranged along the surface of the subject. In this case, two-dimensional detection data can be obtained by scanning the magnetic probe or the subject in a direction orthogonal to the arrangement direction of the detection coils. If arranged in a magnetic probe Two-dimensional detection data can be obtained without scanning the subject. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a side view showing a basic configuration of a magnetic probe.

FIG. 2 is a perspective view showing a basic form of a detection coil.

FIG. 3 is a block diagram showing a detection circuit.

4 (A) to 4 (F) are explanatory views showing various embodiments of the core.

5 (A) to 5 (C) are explanatory views showing various embodiments of the exciting coil. FIGS. 6A to 6C are explanatory views showing various embodiments of the detection coil.

() Is a side view of the detection coil, (B) is a plan view of the detection coil, and (C) is a side sectional view of the detection coil.

7 (A) to 7 (C) are explanatory views showing various embodiments of the detection coil, (A) is a front view and a side view of the detection coil, (B) is a front view of the detection coil, (C) 3 is a plan view of a detection coil.

8 (A) to 8 (E) are explanatory diagrams showing examples of arrangement of a core and a detection coil. BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described with reference to the drawings.

[Magnetic probe]

First, the basic configuration of the magnetic probe according to the present invention will be described. FIG. 1 is a side view showing a basic configuration of a magnetic probe. The magnetic probe 1 shown in this figure generates at least a core 3 and an excitation coil 3 in order to detect a magnetic flux change near the surface of the subject 2 while generating an alternating magnetic field inside the subject 2 and a surface space containing a metal component. It comprises a coil 4 and a detection coil 5.

The core 3 has a plurality of specimen proximity portions 3a, and is formed using a ferromagnetic material so as to form a loop-shaped magnetic circuit, with the inside of the specimen 2 and a surface space. ing.

The exciting coil 4 is wound around the core 3, and an AC voltage having a predetermined frequency is applied. When an AC voltage is applied to the excitation coil 4, the core 3 is AC-excited, and the inside of the subject 2 and the

4-1 Replacement Form (Rule 26) An alternating magnetic field along the surface of the subject 2 is generated in the surface space. The magnetic flux of this AC magnetic field is determined by the material of the subject 2 (flux change factors: magnetic permeability, conductivity, etc.), the surface state (flux change factors: magnetic permeability, conductivity, eddy current, detection gap, leakage magnetic flux, etc.), internal It changes according to the state (magnetic flux change factors: permeability, conductivity, eddy current, leakage flux, etc.).

4-2 Replacement Form (Rule 26) This change in magnetic flux includes a component parallel to the surface of the subject 2 and a component perpendicular to the surface of the subject 2. In the case of a relatively large change in magnetic flux, a large change also occurs in the vertical component. In the case of a small change in magnetic flux, the vertical component hardly changes, and the change mainly appears in the parallel component.

The detection coil 5 is arranged so that the coil center line is along the surface of the subject 2 and the outer peripheral surface of the coil is locally opposed to the surface of the subject 2, and changes the magnetic flux near the surface of the subject 2. To detect. That is, the magnetic probe 1 of the present invention, when forming a loop-shaped magnetic circuit by the exciting coil 4 and the core 3 and detecting a local magnetic flux change near the surface of the subject 2, includes the detecting coil 5 The coil center line is arranged along the surface of the subject 2 without being arranged perpendicular to the surface of the subject 2. This makes it possible to accurately detect even a small change in magnetic flux in which the vertical component hardly changes and the parallel component mainly changes.

[Detection circuit]

FIG. 2 is a perspective view showing a basic form of a detection coil, and FIG. 3 is a block diagram showing a detection circuit. The detection coil 5 shown in FIG. 2 is a differential coil capable of detecting a differential voltage. The pair of coils L1, L2 constituting the differential coil are connected in series so as to be arranged along the surface of the subject 2, and in addition to the terminals T1, T2 drawn from both ends thereof, It has a center tap terminal T 3 that is drawn out between the coils L l and L 2.

As shown in FIG. 3, the coils L 1 and L 2 form a bridge circuit 6 with a pair of resistors R 1 and R 2 (or a variable resistor). Are output. In the bridge circuit 6, when there is no subject 2, the resistance values of the resistors R1 and R2 are initially adjusted so that the differential output has a predetermined value. As a result, it is possible to not only obtain a detection signal in which the intrinsic errors and temperature errors of the coils L 1 and L 2 have been offset, but also increase the resolution in the coil center line direction.

The differential output of the bridge circuit 6 is amplified by the differential amplifier circuit 7 and then input to the synchronous detection circuit 8. The synchronous detection circuit 8 inputs a synchronization signal from the AC excitation circuit section 10 of the excitation coil 4 via the 90 ° phase shifter 9 and, at the same time, outputs the differential signal at the cycle.

Five The output is detected and a magnetic flux change signal is obtained. Since the magnetic flux change signal is a differential signal (differential signal) of the coils L 1 and L 2, the detection circuit shown in FIG. 3 includes an integration circuit that performs an integration process using the scanning distance of the magnetic probe 1 as a parameter. Next, each part of the magnetic probe 1 will be described in detail.

[Core]

FIG. 4 is an explanatory diagram showing various embodiments of the core. Each of the cores 3 shown in this figure is a ferromagnetic material capable of forming a magnetic circuit, and is formed using, for example, ferrite. As shown in FIG. 4 (A), the shape of the core 3 (side view) is a U-shape, a U-shape as shown in FIG. 4 (B), and a U-shape as shown in FIG. 4 (C). A V-shape or a C-shape as shown in FIG. 4 (D) can be adopted. The dimensions of the core 3 are set according to the excitation range (inspection range). For example, as shown in FIG. 4 (E), if the width of the core 3 is increased in the winding direction of the excitation coil 4, By arranging a large number of detection coils 5 one-dimensionally on the inner periphery, the inspection area can be expanded. Also, as shown in FIG. 4 (F), even if a plurality of cores 3 are arranged in parallel, the same effect can be obtained.

[Excitation coil]

FIG. 5 is an explanatory view showing various embodiments of the exciting coil. Each of the excitation coils 4 shown in this figure is made of a conductive wire coated with an insulating material, and is wound around the core 3. The winding position of the exciting coil 4 with respect to the core 3 is not limited to the upper part of the core 3 as shown in FIG. 5 (A), but may be the left and right legs of the core 3 as shown in FIG. 5 (B). Well. Further, as shown in FIG. 5 (C), the excitation coil 4 may be wound around the upper part of the core 3 and the left and right legs. The frequency of the AC voltage applied to the exciting coil 4 is set in consideration of the skin effect of the subject 2 due to the AC magnetic field. For example, when inspecting the surface of the subject 2, it is preferable to increase the frequency of the AC voltage, and when inspecting the inside or back surface of the subject 2, it is preferable to decrease the frequency of the AC voltage.

[Detection coil]

6 and 7 are explanatory diagrams showing various embodiments of the detection coil. The detection coils 5 shown in these figures are all air-core coils. For example, Figure 6 (

6 The detection coil 5 (equivalent to that shown in FIG. 2) of A) has coils L 1 and L 2 formed by winding a non-magnetic core material 5 a with an insulated conductor. 6 (B) is a biaxial type in which a pair of detection coils 5 are integrated in a cross shape, and both detection coils 5 are arranged along the surface of the subject 2. . According to the two-axis type configured in this manner, even if one of the detection coils 5 is parallel to a linear defect (a crack or the like) of the subject 2, the other detection coil 5 does not respond to the linear defect. Since they intersect, linear defects can be reliably detected without overlooking them.

FIG. 6 (C) shows the detection coil 5 formed so that the thickness in the coil center line direction is as small as possible. A coil winding groove having a predetermined width (for example, 50 μm) is provided at a predetermined interval (for example, 50 μππ) at an outer peripheral portion of a winding frame (bobbin) 5 b used for the detection coil 5. The detection coil 5 is formed by winding a multi-layered conductive wire in each coil winding groove. The detection coil 5 thus configured has a small thickness in the coil center line direction and a small interval between the coils L 1 and L 2, so that the resolution in the coil center line direction can be significantly improved.

The detection coil 5 shown in FIG. 7 is formed as a thin-film circuit pattern (spiral coil) on a base material 5c made of an insulator. Such a detection coil 5 can be formed by, for example, an existing thin-film substrate manufacturing technology. However, if a semiconductor manufacturing technology or a micromachining technology is used, a finer and thinner detection coil can be formed.

The detection coil 5 shown in FIG. 7 uses a base material 5c (for example, a ceramic substrate) for a thin film substrate, and forms a conductor layer (for example, a copper foil) formed on the front and back thereof based on a circuit pattern. The thin-film coils Ll and L2 are formed by vapor deposition. In other words, a pair of coils L 1 and L 2 constituting the differential coil are formed in a laminated shape with the extremely thin base material 5 c interposed therebetween, so that the resolution in the coil center line direction can be drastically improved. become.

Further, in the detection coil 5 formed as described above, as shown in FIG. 7 (B), it is easy to arrange a plurality of coils Ll and L2 one-dimensionally. By arranging a plurality of coils Ll and L2 in one dimension in this way, the magnetic probe 1 or the subject 2

7 By scanning in the direction orthogonal to the arrangement direction of the coils LI and L2, two-dimensional detection data can be obtained. Further, as shown in FIG. 7 (C), the detection coil 5 in which a plurality of coils Ll and L2 are one-dimensionally arranged may be juxtaposed in the scanning direction of the magnetic probe 1. In this case, by disposing the coils L 1 and L 2 formed on the front and rear detection coils 5 at a half pitch from each other, it is possible to eliminate a gap in the one-dimensional array direction and prevent detection leakage. . Note that a plurality of detection coils 5 may be arranged in two dimensions. In this case, two-dimensional detection data can be obtained without scanning the magnetic probe 1 or the subject 2.

[Arrangement of core and detection coil]

FIG. 8 is an explanatory diagram showing an example of arrangement of a core and a detection coil. As shown in this figure, in the magnetic probe 1, the arrangement relationship between the core 3 and the detection coil 5 can be arbitrarily set according to the form of the subject 2, the inspection location, and the purpose of the inspection. FIG. 8 (A) shows a basic arrangement relationship, wherein the detection coil 5 is arranged between the core 3 and the vicinity 3a of the subject. FIG. 8 (B) shows an example of an arrangement in which a C-shaped core 3 is used, and is suitable for an end face inspection of the subject 2 and the like. FIG. 8 (C) shows an arrangement suitable for inspecting the outer peripheral surface of a round bar or a pipe, and the detection coil 5 is arranged so as to sandwich the subject 2. FIG. 8D shows an example in which the core 3 and the detection coil 5 are arranged with the subject 2 interposed therebetween. Further, FIG. 8 (E) shows an arrangement suitable for inspection of an end face of a round bar or the like.

The magnetic probe 1 configured as described above detects a local magnetic flux change near the surface of the subject 2 while forming a loop-shaped magnetic circuit by the excitation coil 4 and the core 3, such as a Hall element. Although the detection coil 5 whose shape can be freely changed according to the inspection target and the required detection accuracy is used without using the magnetic detection element, the detection coil 5 and the coil center line are By arranging the coil along the surface and with the coil outer peripheral surface being locally opposed to the surface of the subject 2, it is possible to detect a magnetic flux change in the direction along the surface of the subject 2 with extremely high accuracy. .

In addition, since the detection coil 5 arranged in this manner can be easily miniaturized in the direction along the surface of the subject 2, it is possible to scan the magnetic probe 1 (or move the subject).

8 When the surface of the subject 2 is inspected, the resolution can be easily improved. The detection coil 5 is a differential coil capable of detecting a differential voltage, and a pair of coils L constituting the differential coil In the case where 1, 1 and L 2 are arranged along the surface of the subject 2, the inherent errors and temperature errors of the coils L 1 and L 2 are canceled out, so that the detection accuracy can be further improved.

When the detection coil 5 is formed using a spiral coil having a small thickness in the direction of the coil center line, the magnetic probe 1 or the subject 2 is inspected while scanning in the direction of the coil center line of the detection coil 5. By doing so, the resolution of the magnetic probe 1 can be increased.

When the detection coil 5 is formed as a thin-film circuit pattern on the base material 5c made of an insulator, the thickness of the detection coil 5 in the direction of the coil center line is dramatically reduced, and the magnetic probe 1 The resolution can be further increased. In addition, since the pair of coils Ll and L2 can be formed in a laminated shape with the base member 5c interposed therebetween, the differential output type detection coil 5 can be dramatically thinned. If the base material 5c for a thin film substrate is used, the detection coil 5 can be easily formed using the existing thin film substrate manufacturing technology.

When a plurality of detection coils 5 are arranged along the surface of the subject 2, the magnetic probe 1 or the subject 2 is scanned in a direction orthogonal to the arrangement direction of the detection coils 5. In this way, two-dimensional detection data can be obtained, and by arranging the plurality of detection coils 5 two-dimensionally, two-dimensional detection data can be obtained without scanning the magnetic probe 1 or the subject 2. be able to. Industrial applicability

The present invention relates to a magnetic probe used for surface inspection, flaw detection inspection, residual stress inspection, material inspection, and the like of an object containing a metal component, and in particular, freely adjusts a shape and the like according to an inspection object and a required detection accuracy. This is useful for performing high-precision inspections using a changeable detection coil.

Claims

Range of request

1. A magnetic probe that detects a change in magnetic flux near the surface of an object while generating an AC magnetic field inside the object containing metal components and in the surface space of the object. A ferromagnetic core that forms a loop-shaped magnetic circuit in the interior of the subject and / or the surface space of the subject,

The core is AC-excited, and the specimen is placed inside the specimen and in the surface space of the specimen.

冃

An exciting coil for generating an alternating magnetic field along the surface of the

A detection coil that is arranged so that the coil center line is along the surface of the subject and the outer peripheral surface of the coil is locally opposed to the surface of the subject, and detects a change in magnetic flux near the surface of the subject;

A magnetic probe comprising:

2. The magnet according to claim 1, wherein the detection coil is a differential coil capable of detecting a differential voltage, and a pair of coils constituting the differential coil are arranged along the surface of the subject. probe.

3. The magnetic probe according to claim 1, wherein the detection coil is configured using a spiral coil having a small thickness in a coil center line direction.

4. The magnetic probe according to claim 3, wherein the detection coil is formed as a thin-film circuit pattern on a base material made of an insulator.

5. The detection coil is a differential coil capable of detecting a differential voltage, and a pair of coils constituting the differential coil is formed in a laminated shape with the base material interposed therebetween. Item 4. The magnetic probe according to Item 4.

6. The magnetic probe according to any one of claims 1 to 5, wherein a plurality of the detection coils are provided so as to be arranged along a surface of the subject.

Ten