Eddy current testing device

Abstract

To downsize an eddy current inspection device without deteriorating the detection capability of the eddy current inspection device.SOLUTION: An eddy current inspection device 10 applies a magnetic field to an inspection object 1, generates an eddy current in the inspection object 1 by an electromagnetic induction phenomenon caused by the magnetic field, and detects a change in magnetic flux caused by the eddy current. The eddy current inspection device 10 includes an excitation coil 11 for applying a magnetic field to the inspection object 1, and a detection coil 12 for detecting a change in magnetic flux. The excitation coil 11 and the detection coil 12 are coupled to each other so that the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12 are orthogonal to each other. When viewed in the axial direction R of the detection coil 12, the detection coil 12 overlaps the excitation coil 11. The exciting coil 11 is formed in a circular shape when viewed from the axial direction T.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present invention relates to an eddy current inspection device that applies a magnetic field to an inspection object formed of a conductive material and inspects the inspection object based on eddy currents generated in the inspection object thereby.

Background Art

[0002] An eddy current inspection device includes an excitation coil and a detection coil. When current is supplied to the excitation coil, a magnetic field is applied to the inspection object. Eddy currents are generated in the inspection object due to the electromagnetic induction phenomenon caused by this magnetic field. If there are defects such as scratches near the surface of the inspection object, the distribution of the eddy currents changes, and the voltage induced in the detection coil changes. Based on this change, the presence or absence of defects in the inspection object can be detected.

[0003] Note that eddy current inspection devices that generate uniform eddy currents near the surface of an inspection object for the above-described inspection are disclosed in, for example, Patent Documents 1 and 2. When generating such uniform eddy currents, an electromotive force is generated in the detection coil only when there is a defect near the surface of the inspection object, and the presence or absence of the defect can be detected based on the presence or absence of this electromotive force.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is desirable to miniaturize an eddy current inspection device without degrading the detection ability of the eddy current inspection device. In addition, it is desirable to be able to perform the above-described inspection based on eddy currents on a wide range of an inspection object at once.

[0006] Therefore, the object of the present invention is to provide a technology that can achieve at least one of the following (1) and (2). (1) To enable miniaturization of the eddy current testing device without reducing its detection capability. (2) To enable eddy current-based testing to be performed on a wide area of ​​the object being inspected in a single test. [Means for solving the problem]

[0007] Regarding (1) above, it is assumed that the axial direction of the excitation coil and the axial direction of the detection coil are orthogonal to each other, and that the detection coil overlaps with the excitation coil when viewed in the axial direction of the detection coil. Under this assumption, conventionally, in order to generate a uniform eddy current in the object to be inspected, an excitation coil with a rectangular shape when viewed in the axial direction has been used (for example, Patent Document 1). In Patent Document 2, however, the excitation coil has a circular shape when viewed in the axial direction of the detection coil, but when viewed in the axial direction of the detection coil, the detection coil and the excitation coil do not overlap and are offset from each other. Therefore, Patent Document 2 has a configuration different from the above assumption.

[0008] In contrast, the inventors of this invention have discovered that, under the above premise, by making the shape of the excitation coil, as viewed from the axial direction, circular, the eddy current inspection device can be miniaturized without reducing the detection capability compared to the conventional case using a rectangular excitation coil.

[0009] In other words, in order to achieve (1) above, the eddy current inspection device according to the first aspect of the present invention is a device that applies a magnetic field to an object to be inspected, generates eddy currents in the object to be inspected by electromagnetic induction caused by the magnetic field, and detects the change in magnetic flux caused by the eddy currents, An excitation coil for applying the magnetic field to the object to be inspected, The system includes a detection coil for detecting the change in magnetic flux, The excitation coil and the detection coil are coupled to each other such that their axial directions are perpendicular to each other. When viewed in the axial direction of the detection coil, the detection coil overlaps with the excitation coil. The excitation coil is formed in a circular shape when viewed from the axial direction of the excitation coil.

[0010] To achieve (2) above, the eddy current testing apparatus according to the second aspect of the present invention is: Multiple inspection units that apply a magnetic field to an object to be inspected, generate eddy currents in the object through electromagnetic induction caused by the magnetic field, and detect changes in magnetic flux caused by the eddy currents, A holder for holding the plurality of inspection units, Each inspection unit comprises an excitation coil for applying the magnetic field to the object to be inspected, and a detection coil for detecting changes in the magnetic flux. Taking the direction from the rear end to the front end of the holder as the reference direction, In each of the inspection units, the central axis of the excitation coil is perpendicular to the reference direction, the central axis of the detection coil is parallel to the reference direction, and the excitation coil and the detection coil overlap in the reference direction. Each of the aforementioned inspection units is offset from the others when viewed from the aforementioned reference direction. [Effects of the Invention]

[0011] According to the first aspect of the present invention, since an excitation coil with a circular shape when viewed from the axial direction is used, when the outer diameter of the excitation coil is on the order of millimeters, it becomes easier to wind the excitation coil to a smaller size compared to an excitation coil with a rectangular shape when viewed from the axial direction. As a result, it becomes easier to miniaturize the eddy current testing device compared to conventional devices. Furthermore, it was confirmed that this device can be miniaturized without reducing its ability to detect defects in the object being inspected, compared to an eddy current inspection device using an excitation coil with a rectangular shape when viewed from the axial direction.

[0012] According to a second aspect of the present invention, a plurality of inspection units held by a holder are each shifted from one another when viewed from a reference direction. Accordingly, the plurality of inspection units can each be simultaneously opposed to a plurality of local regions on an inspection surface of an inspection object. Thereby, it becomes possible to simultaneously inspect the presence or absence of defects in these local regions. Thus, inspection of a wide range of an inspection object can be performed at once.

Brief Description of Drawings

[0013] [Figure 1A] Shows the configuration of an eddy current inspection apparatus according to a first embodiment of the present invention. [Figure 1B] It is a cross-sectional view taken along line 1B-1B of FIG. 1A. [Figure 2A] Shows eddy currents generated near an inspection surface of an inspection object. [Figure 2B] It is a diagram showing dimensions of each part in FIG. 1B. [Figure 3A] Shows an eddy current inspection apparatus provided with a holder in the first embodiment. [Figure 3B] It is a view taken along arrow 3B-3B of FIG. 3A. [Figure 4] It is an explanatory diagram of an example using an eddy current inspection apparatus according to the first embodiment. [Figure 5A] Shows a Lissajous waveform obtained by an example. [Figure 5B] Shows a Lissajous waveform obtained by a reference example. [Figure 6] Shows an eddy current inspection apparatus of a reference example having a rectangular excitation coil. [Figure 7A] Shows the configuration of an eddy current inspection apparatus according to a second embodiment of the present invention. [Figure 7B] It is a view taken along arrow 7B-7B of FIG. 7A. [Figure 8A] It is an explanatory diagram of an eddy current inspection method using an eddy current inspection apparatus according to the second embodiment. [Figure 8B] It is an explanatory diagram of another eddy current inspection method using an eddy current inspection apparatus according to the second embodiment. [Figure 9A]The configuration of an eddy current testing device according to a third embodiment of the present invention is shown. [Figure 9B] This is a view from the arrow 9B-9B in Figure 9A. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described based on the drawings. Common parts in each figure are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] [First Embodiment] Figure 1A shows the configuration of the eddy current testing device 10 according to the first embodiment of the present invention. Figure 1B is a cross-sectional view taken along line 1B-1B in Figure 1A. Figure 1A is a view taken along the line 1A-1A in Figure 1B.

[0016] (Main components of an eddy current testing device) The eddy current inspection device 10 according to the first embodiment generates eddy currents in an object to be inspected 1 made of a conductive material, and inspects for defects such as scratches based on these eddy currents. The eddy current inspection device 10 comprises an excitation coil 11 and a detection coil 12.

[0017] The excitation coil 11 generates eddy currents in the object under inspection 1 through electromagnetic induction by applying a magnetic field to the object under inspection 1. In other words, the excitation coil 11 generates a magnetic field when current is supplied to it and applies this magnetic field to the object under inspection 1. The current flowing through the excitation coil 11 may be an alternating current.

[0018] The object 1 that generates eddy currents in this way may be the bottom plate of an oil tank (for example, the bottom plate having welded parts such as welded joints), but is not limited to this, and may be other objects (for example, piping). Furthermore, the object 1 may be a base material formed of a conductive material with a coating film formed on its surface. In this case, the excitation coil 11 may generate the eddy currents described above on the base material.

[0019] According to the first embodiment, the excitation coil 11 is formed in a circular shape when viewed from the axial direction of the excitation coil 11. In this case, the excitation coil 11 may be formed in a cylindrical shape. The excitation coil 11 is made by winding a wire covered with an insulating film around its central axis Ce. In each figure, the axial direction of the excitation coil 11 is the direction of the arrow indicated by the symbol T.

[0020] The detection coil 12 detects the change in magnetic flux caused by the eddy currents in the object being inspected 1. That is, the change in magnetic flux passing through the detection coil 12 generates an electromotive force in the detection coil 12. This change in magnetic flux is caused by defects such as scratches in the object being inspected 1. For example, as shown in Figure 1B, the eddy current inspection device 10 is placed facing the inspection surface 1a of the object being inspected 1, and the eddy current inspection device 10 is moved along the inspection surface 1a while a magnetic field is applied to the object being inspected 1 by the excitation coil 11. When the detection coil 12 passes directly over a defective area in the object being inspected 1, the magnetic flux passing through the detection coil 12 changes. This generates an electromotive force in the detection coil 12. Based on the electromotive force generated in the detection coil 12 in this way, the presence or absence of defects such as scratches in the object being inspected 1 can be detected.

[0021] The detection coil 12 may be formed in a circular shape when viewed from the axial direction R of the detection coil 12, as shown in Figure 1A. In this case, the detection coil 12 may be formed in a cylindrical shape. The detection coil 12 is made by winding a wire covered with an insulating film around a central axis Cd. In each figure, the axial direction of the detection coil 12 is the direction of the arrow indicated by the symbol R, and the direction perpendicular to both direction T and direction R is indicated by the symbol S.

[0022] The detection coil 12 may be positioned radially outward from the excitation coil 11, as shown in Figure 1B. In this case, the end face of the detection coil 12 with an axial radius R may be in contact with the outer circumferential surface of the excitation coil 11.

[0023] The excitation coil 11 and the detection coil 12 are coupled to each other such that the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12 are perpendicular to each other. This coupling may be achieved by coupling the excitation coil 11 and the detection coil 12 to a holder 15 described later, or by other means (e.g., adhesive).

[0024] As shown in Figure 1A, when viewed in the axial direction R of the detection coil 12, the detection coil 12 is located in the center of the excitation coil 11. In this case, when viewed in the axial direction R of the detection coil 12, the central axis Cd of the detection coil 12 may be located at the center of the excitation coil 11 in the axial direction T of the excitation coil 11 (left-right direction in Figure 1A), and at the center of the excitation coil 11 in the direction S perpendicular to the axial direction T of the excitation coil 11.

[0025] Figure 2A is a view of the excitation coil 11 and detection coil 12 as seen through the lens in Figure 1A, and shows the eddy current Ie generated near the inspection surface 1a of the object to be inspected 1. That is, Figure 2A shows the eddy current Ie as viewed in the axial direction R of the detection coil 12. The eddy current Ie generated in the object to be inspected 1 by the excitation coil 11 may occur near the inspection surface 1a in a direction perpendicular to the central axis Ce of the excitation coil 11 and along the inspection surface 1a, as shown in Figure 2A. If the material of the object to be inspected 1 is uniform and there are no scratches or other damages, this eddy current Ie may occur uniformly in the region where the detection coil 12 faces the axial direction R.

[0026] The eddy current testing device 10 may further include a core 13 provided inside the excitation coil 11 and a core 14 provided inside the detection coil 12, as shown in Figure 1B. The cores 13 and 14 are made of a material with higher magnetic permeability than air. This material may be, for example, ferrite, but is not limited to this. When the cores 13 and 14 are used, the aforementioned conductors constituting the excitation coil 1 and the detection coil 12 may be wound around the cores 13 and 14. However, one or both of the cores 13 and 14 may be omitted.

[0027] (Relationship between the dimensions of each part) Figure 2B is a diagram showing the dimensions of each part in Figure 1B. The external dimension D1 of the detection coil 12 in the direction S (left-right direction in Figure 2B) perpendicular to both the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12 is greater than or equal to the inner diameter De1 of the excitation coil 11, and may be less than or equal to the outer diameter De2 of the excitation coil 11.

[0028] Here, if the detection coil 12 is formed in a circular shape when viewed from its axial direction R as shown in Figure 1A, the external dimension D1 of the detection coil 12 is the outer diameter of the detection coil 12 (the same applies hereafter).

[0029] The dimensions of the detection coil 12 in direction S may be expressed as follows: That is, the outer dimensions D1 of the detection coil 12 in direction S, which is perpendicular to both the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12, may be 2 / 3 or more, 3 / 4 or more, or 4 / 5 or more of the outer diameter De2 of the excitation coil 11.

[0030] On the other hand, the external dimensions of the detection coil 12 in the axial direction T (left-right direction in Figure 2A) of the excitation coil 11 may be less than or equal to the dimensions De3 of the excitation coil 11 in the axial direction T. For example, the external dimensions of the detection coil 12 in the axial direction T of the excitation coil 11 may be substantially the same as the dimensions of the excitation coil 11 in the axial direction T.

[0031] Furthermore, as shown in Figure 1A, the excitation coil 11 and the detection coil 12 may be arranged such that the detection coil 12 (for example, the entire detection coil 12) overlaps with the excitation coil 11 when viewed from the axial direction R of the detection coil 12. Also, as shown in Figure 1A, the excitation coil 11 and the detection coil 12 may be arranged such that the extension of the central axis Cd of the detection coil 12 is perpendicular to the central axis Ce of the excitation coil 11.

[0032] (Holder) The eddy current testing device 10 described above may include a holder 15 that holds the excitation coil 11 and the detection coil 12. Figure 3A shows the eddy current testing device 10 with the holder 15. Figure 3B is a view along the line 3B-3B in Figure 3A. The excitation coil 11 and the detection coil 12 are coupled to the holder 15, so the excitation coil 11 and the detection coil 12 may be coupled to each other.

[0033] The holder 15 may be made of a material (non-magnetic material) that does not interfere with the function of the excitation coil 11 and the detection coil 12. The excitation coil 11 and the detection coil 12 may be embedded in the rubber or resin holder 15. If cores 13 and 14 are provided, the cores 13 and 14 may also be embedded in the rubber or resin holder 15.

[0034] When the excitation coil 11 and the detection coil 12 are provided inside the holder 15, the end face of the detection coil 12 opposite to the excitation coil 11 in its axial direction R may be exposed to the outside of the holder 15.

[0035] The holder 15 may be connected to wiring for supplying current to the excitation coil 11 and wiring for detecting the electromotive force generated in the detection coil 12. For example, a cable 16 bundling these wires together is connected to the holder 15, and these wires are electrically connected to the excitation coil 11 and the detection coil 12, respectively, within the holder 15.

[0036] A person can hold the holder 15 by hand and move the tip surface 15a of the holder 15 along the inspection surface 1a of the object to be inspected 1, thereby inspecting for defects in the object to be inspected 1 within the range of movement.

[0037] (Effects of the first embodiment)

[0038] Since the excitation coil 11 has a circular shape when viewed from the axial direction T, when the outer diameter of the excitation coil 11 is on the order of millimeters (for example, 10 mm or less or 5 mm or less), it becomes easier to wind the excitation coil 11 to be smaller compared to an excitation coil with a rectangular shape when viewed from the axial direction. As a result, it becomes easier to miniaturize the eddy current testing device 10 compared to conventional devices.

[0039] Furthermore, in the eddy current inspection device 10 according to the first embodiment, it was confirmed in the embodiments described later that it is possible to miniaturize it without reducing its ability to detect defects in the object to be inspected 1, compared to an eddy current inspection device using an excitation coil with a rectangular shape when viewed from the axial direction.

[0040] The external dimensions of the detection coil 12 in a direction T perpendicular to both the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12 may be greater than or equal to the inner diameter of the excitation coil 11 and less than or equal to the outer diameter of the excitation coil 11. By making the dimensions of the detection coil 12 approximately equal to the dimensions of the excitation coil 11 in this way, the defect detection capability based on eddy currents generated in the object under inspection 1 can be improved.

[0041] Furthermore, the external dimensions of the detection coil 12 in a direction S perpendicular to both the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12 may be 2 / 3 or more of the outer diameter of the excitation coil 11. By bringing the dimensions of the detection coil 12 in direction S closer to the dimensions of the excitation coil 11 in axial direction T, the defect detection capability based on eddy currents generated in the object under inspection 1 can be improved.

[0042] (Examples) The inspection surface 1a of the object to be inspected 1 shown in Figure 4 was inspected using the eddy current inspection device 10 according to the first embodiment. Figure 4 is a view from a direction perpendicular to the inspection surface 1a. Although the eddy current inspection device 10 is shown in Figure 4, its cable 16 is not shown. A defect (discharge notch 1b) was formed on the inspection surface 1a by discharge. This discharge notch 1b has a length (horizontal dimension in Figure 4) of 4 mm, a width (vertical dimension in Figure 4) of 0.3 mm, and a depth of 2 mm.

[0043] With the tip surface 15a of the holder 15 in contact with the inspection surface 1a, and with alternating current supplied to the excitation coil 11, the holder 15 was moved along the inspection surface 1a in the direction of arrow A in Figure 4. When the tip surface 15a of the holder 15 (i.e., the detection coil 12) passed over the discharge notch 1b, the electromotive force (output voltage) data output from the detection coil 12 is shown as a Lissajous waveform in Figure 5A.

[0044] Figure 5A shows the waveforms of the X and Y signals of the output voltage of the detection coil 12, represented as the X-axis and Y-axis components, respectively. The X signal is obtained by synchronously detecting the output voltage of the detection coil 12 with a reference signal, and the Y signal is obtained by synchronously detecting the output voltage of the detection coil 12 with a signal whose phase is delayed by 90 degrees from the reference signal. The reference signal is the AC current flowing through the excitation coil 11.

[0045] (Reference example) Using the eddy current testing apparatus 20 shown in Figure 6 as a reference example, experiments were conducted on the discharge notch 1b of the inspection surface 1a shown in Figure 4, under the same conditions as the above-described embodiment, except as described below.

[0046] The eddy current testing device 20 consists of a rectangular excitation coil 21 and a cylindrical detection coil 22, both arranged inside a holder 25. In Figure 6, reference numeral 26 indicates a cable having the same function as the cable 16 described above. In the excitation coil 21, the dimensions in three mutually orthogonal directions, including its axial direction, are several millimeters larger than the dimensions in directions R, S, and T of the corresponding excitation coil 11. The outer diameter of the detection coil 22 is about 1 mm smaller than the outer diameter of the detection coil 12.

[0047] Using such an eddy current testing device 20, the holder 25 was moved along the inspection surface 1a with the tip surface 25a of the holder 25 facing the inspection surface 1a, and an alternating current was supplied to the excitation coil 11, similar to the embodiment. When the tip surface 25a of the holder 25 passed over the discharge notch 1b, the electromotive force (output voltage) data output from the detection coil 12 is shown as a Lissajous waveform in Figure 5B.

[0048] (Comparison of Examples and Reference Examples) As can be seen from Figures 5A and 5B, the eddy current testing device 10 of the embodiment is smaller than the eddy current testing device 20 of the reference example, yet it is able to obtain a Lissajous waveform larger than that of the reference example. Thus, it has been confirmed that the eddy current testing device 10 according to the first embodiment can be miniaturized without reducing its detection capability.

[0049] [Second Embodiment] Figure 7A shows an eddy current testing device 100 according to a second embodiment of the present invention. Figure 7B is a view along the line 7B-7B in Figure 7A. The eddy current testing device 100 according to the second embodiment comprises a plurality of testing units 10. Each testing unit 10 may have the same configuration as the eddy current testing device 10 of the first embodiment, except for points not described below. The eddy current testing device 100 according to the second embodiment comprises a holder 35 (hereinafter referred to as the main holder) that holds the plurality of testing units 10.

[0050] Each inspection unit 10 includes the excitation coil 11 and detection coil 12 as described in the first embodiment. In each inspection unit 10, the axial direction T of the excitation coil 11 and the axial direction R of the detection coil 12 are orthogonal to each other, and when viewed in the axial direction R of the detection coil 12, the detection coil 12 (for example, the entire detection coil 12) overlaps with the excitation coil 11. Each inspection unit 10 may further have the holder 15 (hereinafter referred to as sub-holder) described above. Multiple inspection units 10 may have the same configuration as each other.

[0051] When inspecting the object to be inspected 1 with the eddy current inspection device 100, the side of the main holder 35 facing the inspection surface 1a of the object to be inspected 1 is designated as the tip side (lower side in Figure 7A). The direction from the rear end of the holder 35 toward the tip side is designated as the reference direction. In the second embodiment, the reference direction coincides with the axial direction R of each detection coil 12, as will be described later, so in the following description and corresponding drawings, the reference direction is indicated by the symbol R. Furthermore, the direction perpendicular to the reference direction R is designated as the first direction, and the direction perpendicular to both the reference direction R and the first direction is designated as the second direction. In the second embodiment, the first direction and the second direction coincide with the directions S and T in the first embodiment, respectively, so in the following description and corresponding drawings, the first direction and the second direction are indicated by the symbols S and T, respectively.

[0052] In the second embodiment, the multiple inspection units 10 may be offset from each other in the first direction S when viewed from the second direction T. For example, the multiple inspection units 10 may be offset from each other in the first direction S such that the central axes Cd of each detection coil 12 are (for example) the same distance apart when viewed from the second direction T. In one example, as shown in Figure 7B, the multiple inspection units 10 may be arranged in the first direction S. That is, the multiple inspection units 10 may overlap when viewed from the first direction S. For example, the central axes Cd of each detection coil 12 of the multiple inspection units 10 may be oriented in the reference direction R and may overlap when viewed from the first direction S.

[0053] In each inspection unit 10 held in the main holder 35, the orientation of the central axis Cd of the detection coil 12 coincides with the reference direction R in this embodiment, as shown in Figure 7A. In this case, the orientation of the central axis Ce of the excitation coil 11 in each inspection unit 10 held in the main holder 35 coincides with the second direction T in this embodiment, but it may also coincide with the first direction S.

[0054] In the second embodiment, the main holder 35 holds each inspection unit 10 (i.e., its sub-holder 15) so that it can move in the reference direction R within a predetermined range in the reference direction R. When each inspection unit 10 is at the limit position on the tip side within the predetermined range, the tip of the inspection unit 10 protrudes from the tip surface 35a of the main holder 35 in the reference direction R (tip side), as shown in Figure 7A.

[0055] Multiple housing holes 35b may be formed inside the main holder 35. Multiple inspection units 10 are placed in each of these housing holes 35b. Each inspection unit 10, while positioned in its corresponding housing hole 35b, is movable in the reference direction R within the predetermined range as described above. In other words, the housing holes 35b guide the movement of the inspection units 10.

[0056] Each housing hole 35b has an opening 35b1 on the tip surface 35a of the main holder 35, as shown in Figure 7B. Through this opening 35b1, the tip of the inspection unit 10 protrudes from the tip surface 35a of the main holder 35 in the reference direction R (tip side) as described above. The main holder 35 may have a lid member 35c that closes the rear end opening of the housing hole 35b. The lid member 35c is detachably attached to the rear end surface of the main holder 35 body, which forms the housing hole 35b, by appropriate means (e.g., screws), as shown in Figure 7A. This closes the rear end opening of the housing hole 35b. With the lid member 35c removed from the main body, the inspection unit 10 can be housed in the housing hole 35b through the rear end opening of the housing hole 35b and removed from the housing hole 35b.

[0057] Each housing hole 35b may have a shape that prevents the corresponding inspection unit 10 from moving further toward the tip when it is in the limit position described above. For example, in this state, the inspection unit 10 may engage with the inner surface of each housing hole 35b in the reference direction R.

[0058] In the example shown in Figure 7A, each housing hole 35b has a tapered shape at its tip. This tapered shape may be such that the cross-section of a virtual plane perpendicular to the reference direction R gradually decreases as it moves towards the tip. Each inspection unit 10 (for example, its sub-holder 15) has a tapered shape that matches the tapered shape of the housing hole 35b in the range from the tip opening 35b1 of the corresponding housing hole 35b to a predetermined position at the rear end when in the limit position described above. This prevents each inspection unit 10 from moving further towards the tip.

[0059] Each housing hole 35b may have a shape that prevents the corresponding inspection unit 10 from rotating around its axis (the axis facing the reference direction R). For example, each housing hole 35b and the corresponding inspection unit 10 may be rectangles whose cross-sectional shapes, defined by a virtual plane perpendicular to the reference direction R, are aligned within a predetermined range in the reference direction R (for example, the portion having the tapered shape described above). This prevents the inspection unit 10 from rotating around its axis.

[0060] In the second embodiment, the eddy current testing device 100 includes a force-applying part 31. The force-applying part 31 is provided for each testing unit 10 and pushes the testing unit 10 toward the front end so that the testing unit 10 is positioned at the limit position. The force-applying part 31 may be, for example, a spring (a coil spring in the example of Figure 7A), but other means may also be used. In the example of Figure 7A, each coil spring 31 is held between the rear end face of the sub-holder 15 and the cover member 35c of the main holder 35.

[0061] With this configuration, the inspection unit 10 is held in the limit position by the force application part 31 when no external force is acting on it. On the other hand, when the front end surface of the inspection unit 10 (i.e., the front end surface 15a of the sub-holder 15) is pushed toward the rear end (in the direction opposite to the reference direction R), it can move toward the rear end against the force of the force application part 31.

[0062] (Effects of the second embodiment) The multiple inspection units 10 held in the main holder 35 are each offset from one another in the first direction S when viewed from the reference direction R. Therefore, the multiple inspection units 10 can each simultaneously face multiple local areas (for example, multiple adjacent local areas) on the inspection surface 1a of the object to be inspected 1. This makes it possible to simultaneously inspect for defects in these local areas. Thus, a wide area of ​​the object to be inspected 1 can be inspected at once.

[0063] Figure 8A is an explanatory diagram of an eddy current testing method when multiple inspection units 10 (i.e., each detection coil 12) are arranged in a first direction S perpendicular to the reference direction R. Figure 8A is a view from the reference direction R and shows only the detection coils 12 and inspection surfaces 1a of the multiple inspection units 10.

[0064] With the tip surfaces of multiple inspection units 10 (the tip surfaces 15a of the sub-holders 15) facing the inspection surface 1a of the object to be inspected 1 in the reference direction R, a magnetic field is applied to the object to be inspected 1 by the excitation coils 11 of each inspection unit 10, and as shown in Figure 8A, the multiple detection coils 12 (i.e., holders 35) are moved along the inspection surface 1a in the second direction T. During this movement, the tip surfaces of each inspection unit 10 (the tip surfaces 15a of the sub-holders 15) may be in contact with the inspection surface 1a, or they may be separated from the inspection surface 1a with a gap between them. This eddy current testing method allows the eddy current testing device 100 described above to perform testing over a wide area of ​​the object to be tested 1 in a single operation.

[0065] In this type of eddy current testing method, even if there is a region (region i enclosed by a dashed line in Figure 8A) that the detection coil 12 does not pass through between the movement trajectories of the detection coils 12 of adjacent testing units 10 when viewed in the reference direction R, the eddy current testing device 100 can still detect whether a defect exists in the object under inspection 1 in that region i (hereinafter referred to as the gap region i) and the interior directly below it. This is because the electromotive force of the detection coil 12 adjacent to the gap region i changes due to the defect.

[0066] On the other hand, depending on the inspection conditions (for example, the material of the object to be inspected 1, the width W of the spacing region i, and the detection sensitivity of the eddy current inspection device 100), it may not be possible to detect whether a defect exists directly below the spacing region i in the object to be inspected 1 using the eddy current inspection method described above. In this case, the following eddy current inspection method can be performed using the eddy current inspection device 100 described above.

[0067] With the tip surfaces of multiple inspection units 10 (the tip surfaces 15a of each sub-holder 15) facing the inspection surface 1a of the object to be inspected 1 in the reference direction R, a magnetic field is applied to the object to be inspected 1 by the excitation coil 11 in each inspection unit 10, and the main holder 35 is moved along the inspection surface 1a in a direction oblique to the second direction T (hereinafter referred to as the direction of movement), as shown in Figure 8B. During this movement, the tip surfaces of each inspection unit 10 (the tip surfaces 15a of the sub-holder 15) may be in contact with the inspection surface 1a, or they may be separated from the inspection surface 1a with a gap between them. As a result, in the case of Figure 8B, the width W of the spacing region i in the direction perpendicular to the direction of movement becomes smaller than or disappears compared to the case of Figure 8A (width W in Figure 8A), so it is possible to detect whether a defect exists in the spacing region i and the interior directly below it.

[0068] The main holder 35 holds each inspection unit 10 so that it can move in the reference direction R within a predetermined range in the reference direction R, and the inspection unit 10 is pushed toward the tip by the force application part 31 so that its tip portion is positioned at the limit position where it protrudes from the tip surface 35a of the main holder 35. In this configuration, when the main holder 35 is slid along the inspection surface 1a while the tip surfaces of multiple inspection units 10 (i.e., the tip surfaces 15a of each sub-holder 15) are in contact with the inspection surface 1a during inspection, each inspection unit 10 can be displaced relative to the main holder 35 to follow the unevenness of the inspection surface 1a as it passes over it. Therefore, a wide area of ​​the inspection surface 1a can be easily inspected while the tip surfaces of multiple inspection units 10 are in contact with the inspection surface 1a.

[0069] [Third Embodiment] Figure 9A shows an eddy current testing device 100 according to a third embodiment of the present invention. Figure 9B is a view along the line 9B-9B in Figure 9A. In the third embodiment, it is the same as in the second embodiment, except for the points described below.

[0070] In the second embodiment, multiple inspection units 10 arranged in the first direction S are considered as one group G, and in the third embodiment, as shown in Figure 9B, multiple groups G are provided offset from each other in the second direction T which is orthogonal to both the reference direction R and the first direction S. In the example in Figure 9B, three groups G1 to G3 are provided. Note that in Figure 9A, only the lowermost group G1 of these groups G1 to G3 is shown. Note that the number of groups G is not limited to three as in Figure 9B, but may be two or four or more.

[0071] In one group G, the central axis Cd of a detection coil 12 from another group is located in the region between adjacent detection coils 12, when viewed from a second direction T.

[0072] Furthermore, in one group G, in the region between adjacent detection coils 12, the central axes Cd of two or more other detection coils 12 in the other two or more groups G may be offset from each other in the first direction S when viewed from the second direction T.

[0073] In this case, in each group G, the region between each adjacent pair of detection coils 12 may, when viewed from the second direction T, have the central axes Cd of two or more (for example, all of the other) detection coils 12 in the group G offset from each other in the first direction S. Here, in each group G, the region between each adjacent pair of detection coils 12 may, when viewed from the second direction T, have only the central axis Cd of any one of the multiple detection coils 12 in each of the other two or more groups.

[0074] The main holder 35 holds multiple inspection units 10 of each of the multiple groups G arranged as described above.

[0075] (Effects of the third embodiment) In one group G, the central axis Cd of the detection coils 12 of other groups is located in the region between adjacent detection coils 12 when viewed from the second direction T. Therefore, even if a defect cannot be detected in the part of the object under inspection 1 facing that region in the reference direction R during inspection using one group G, it can be detected by the excitation coils 11 and detection coils 12 of other groups G.

[0076] In one group G, in the region between adjacent detection coils 12, the central axes Cd of two or more detection coils 12 in other groups G may be offset from each other in the first direction S when viewed from the second direction T. In this way, when viewed from the second direction T, it becomes possible to arrange multiple detection coils 12 closely in the first direction S.

[0077] The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical idea of ​​the present invention. For example, the eddy current testing apparatus 10,100 according to the first, second, and third embodiments described above do not have to have all of the above-described features, and may have only some of the above-described features.

[0078] Furthermore, you may adopt any of the following modification examples 1-3 individually, or you may adopt any combination of two or more of modification examples 1-3. In this case, the points not mentioned below are the same as those described above.

[0079] (Example of change 1) In the second or third embodiment described above, the excitation coil 11 does not have to be circular when viewed from its axial direction T.

[0080] (Example of change 2) In the second and third embodiments, each inspection unit 10 may be fixed to the main holder 35. In this case, the force application part 31 may be omitted. In this case, the sub-holder 15 of each inspection unit 10 may be integrated with the main holder 35 or may be part of the main holder 35.

[0081] (Example of change 3) In the first, second, or third embodiment described above, the detection coil 12 may have a circular shape when viewed from its axial direction R, or it may have another shape (for example, a rectangle). Furthermore, in the second or third embodiment, the excitation coil 11 may have a rectangular or other shape when viewed from its axial direction T. The rectangle may have a pair of sides parallel to the first direction S described above and a pair of sides parallel to the reference direction R described above. [Explanation of Symbols]

[0082] 1 Object to be inspected, 1a Inspection surface, 1b Discharge notch, 10 Eddy current testing device (inspection unit), 11 Excitation coil, 12 Detection coil, 13 Core, 14 Core, 15 Holder (sub-holder), 15a Tip surface (tip surface of inspection unit), 16 Cable, 20 Eddy current testing device as an example, 21 Excitation coil, 22 Detection coil, 25 Holder, 25a Tip surface of holder, 26 Cable, 31 Force acting part (coil spring), 35 Holder (main holder), 35a Tip surface, 35b Housing hole, 35b1 Opening on the tip side, 35c Cover member, 100 Eddy current testing device, Ce Central axis of the excitation coil, Cd Central axis of the detection coil, R Axial direction of the detection coil (reference direction), S Direction perpendicular to both the axial direction of the detection coil and the axial direction of the excitation coil, T Axial direction of the excitation coil (second direction)

Claims

[Claim 1] An eddy current testing device that applies a magnetic field to an object to be inspected, generates eddy currents in the object through electromagnetic induction caused by the magnetic field, and detects the change in magnetic flux caused by the eddy currents, An excitation coil for applying the magnetic field to the object to be inspected, The system includes a detection coil for detecting the change in magnetic flux, The excitation coil and the detection coil are coupled to each other such that their axial directions are perpendicular to each other. When viewed in the axial direction of the detection coil, the detection coil overlaps with the excitation coil. The excitation coil is formed in a circular shape when viewed from the axial direction of the excitation coil. The external dimensions of the detection coil in a direction perpendicular to both the axial direction of the excitation coil and the axial direction of the detection coil are greater than or equal to the inner diameter of the excitation coil and less than or equal to the outer diameter of the excitation coil. The external dimensions of the detection coil in the axial direction of the excitation coil are the same as the axial dimensions of the excitation coil. The detection coil is positioned radially outward of the excitation coil. An eddy current testing device wherein the end face of the detection coil in the axial direction of the detection coil is in contact with the outer circumferential surface of the excitation coil.

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