Eddy current inspection device and eddy current inspection method

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 and an eddy current inspection method for applying a magnetic field to an inspection object made of a conductive material and inspecting the inspection object based on eddy currents generated in the inspection object. [Background technology]

[0002] An eddy current inspection device is equipped with an excitation coil and a detection coil. When a current is supplied to the excitation coil, it applies a magnetic field to the object being inspected. This magnetic field causes electromagnetic induction, which generates eddy currents in the object being inspected. If there is a defect, such as a scratch, near the surface of the object being inspected, the distribution of the eddy currents changes, causing a change in the voltage induced in the detection coil. Based on this change, it is possible to detect the presence or absence of defects in the object being inspected.

[0003] Eddy current inspection devices that generate uniform eddy currents near the surface of an object to be inspected for the above-mentioned inspection are disclosed, for example, in Patent Documents 1 and 2. When a uniform eddy current is generated in this way, an electromotive force is generated in the detection coil only when there is a defect near the surface of the object to be inspected, 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] JP 2006-322860 A [Patent Document 2] JP 2007-108032 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is desirable to reduce the size of an eddy current inspection device without reducing the detection capability of the device, and it is also desirable to be able to perform the above-mentioned eddy current-based inspection on a wide area of ​​an object to be inspected at once.

[0006] Therefore, an object of the present invention is to provide a technique that can achieve at least one of the following (1) and (2). (1) To make it possible to reduce the size of an eddy current inspection device without reducing the detection capability of the device. (2) It makes it possible to perform eddy current-based inspection on a wide area of ​​an object to be inspected at once. [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 mutually orthogonal, and that the detection coil overlaps the excitation coil when viewed in the axial direction of the detection coil. On this assumption, in the past, an excitation coil that is rectangular when viewed in the axial direction was used to generate a uniform eddy current in the object to be inspected (for example, Patent Document 1). In Patent Document 2, the excitation coil is circular when viewed in the axial direction, but the detection coil and the excitation coil are shifted from each other without overlapping each other when viewed in the axial direction of the detection coil. Therefore, Patent Document 2 has a configuration different from the above assumption.

[0008] In response to this, the inventors of the present application have discovered that, under the above premise, by making the shape of the excitation coil circular when viewed from the axial direction, it is possible to reduce the size of the eddy current inspection device without reducing the detection capability, compared to the conventional case in which a rectangular excitation coil is used.

[0009] That is, in order to achieve the above (1), an eddy current inspection device according to a first aspect of the present invention is a device that applies a magnetic field to an inspection object, generates an eddy current in the inspection object by an electromagnetic induction phenomenon caused by the magnetic field, and detects a change in magnetic flux caused by the eddy current, an excitation coil for applying the magnetic field to the inspection object; a detection coil for detecting a change in the magnetic flux; the excitation coil and the detection coil are coupled to each other such that an axial direction of the excitation coil and an axial direction of the detection coil 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 in the axial direction of the excitation coil.

[0010] In order to achieve the above (2), an eddy current inspection apparatus according to a second aspect of the present invention comprises: a plurality of inspection units that apply a magnetic field to an object to be inspected, generate eddy currents in the object to be inspected by an electromagnetic induction phenomenon 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 of the inspection units includes an excitation coil that applies the magnetic field to the inspection object, and a detection coil that detects a change in the magnetic flux, A direction from the rear end side to the front end side of the holder is set as a reference direction, In each of the inspection units, a central axis of the excitation coil is perpendicular to the reference direction, a 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; The plurality of inspection units are offset from one another when viewed from the reference direction. Effect of the Invention

[0011] According to the first aspect of the present invention, since an excitation coil having a circular shape as viewed from the axial direction is used, when the outer diameter of the excitation coil is on the order of millimeters, it is easier to wind the excitation coil small compared to an excitation coil having a rectangular shape as viewed from the axial direction, which makes it easier to reduce the size of the eddy current inspection device than before. It was also confirmed that compared to an eddy current inspection device that uses an excitation coil that is rectangular in shape when viewed from the axial direction, it is possible to reduce the size of the device without reducing the ability to detect defects in the object being inspected.

[0012] According to the second aspect of the present invention, the multiple inspection units held by the holder are offset from each other when viewed from the reference direction. Therefore, the multiple inspection units can be simultaneously faced to multiple local areas on the inspection surface of the inspection object. This makes it possible to simultaneously inspect the presence or absence of defects in these local areas. Therefore, inspection of a wide range of the inspection object can be performed at once. [Brief description of the drawings]

[0013] [Figure 1A] 1 shows the configuration of an eddy current inspection device according to a first embodiment of the present invention. [Figure 1B] 1B is a cross-sectional view of FIG. 1A along line 1B-1B. [Figure 2A] 1 shows eddy currents occurring near the inspection surface of an inspection object. [Figure 2B] FIG. 2 is a diagram showing dimensions of each part in FIG. 1B. [Figure 3A] 1 shows an eddy current inspection device including a holder in a first embodiment. [Figure 3B] FIG. 3B is a view taken along the line 3B-3B of FIG. 3A. [Figure 4] FIG. 2 is an explanatory diagram of an example using the eddy current inspection device according to the first embodiment. [Figure 5A] 1 shows a Lissajous waveform obtained according to an embodiment. [Figure 5B] 13 shows a Lissajous waveform obtained in accordance with a reference example. [Figure 6] 1 shows an eddy current inspection device of a reference example having a rectangular excitation coil. [Figure 7A] 4 shows the configuration of an eddy current inspection device according to a second embodiment of the present invention. [Figure 7B] 7B-7B in FIG. 7A. [Figure 8A] 10 is an explanatory diagram of an eddy current inspection method using an eddy current inspection device according to the second embodiment. FIG. [Figure 8B] 10 is an explanatory diagram of another eddy current inspection method using the eddy current inspection device according to the second embodiment. FIG. [Figure 9A]1 shows the configuration of an eddy current inspection device according to a third embodiment of the present invention. [Figure 9B] 9B-9B in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are used to designate the same parts, and duplicated explanations will be omitted.

[0015] [First embodiment] Fig. 1A is a diagram showing the configuration of an eddy current inspection device 10 according to a first embodiment of the present invention. Fig. 1B is a cross-sectional view taken along line 1B-1B of Fig. 1A. Fig. 1A is a view taken along line 1A-1A of Fig. 1B.

[0016] (Main components of eddy current inspection equipment) The eddy current inspection device 10 according to the first embodiment is for generating an eddy current in an inspection object 1 made of a conductive material, and for inspecting the presence or absence of defects such as scratches based on the eddy current. The eddy current inspection device 10 includes an excitation coil 11 and a detection coil 12.

[0017] The excitation coil 11 applies a magnetic field to the inspection object 1, thereby generating eddy currents in the inspection object 1 through an electromagnetic induction phenomenon caused by the magnetic field. That is, the excitation coil 11 generates a magnetic field when a current is supplied to it, and applies the magnetic field to the inspection object 1. The current passed through the excitation coil 11 may be an alternating current.

[0018] The inspection object 1 in which such eddy currents are generated may be a bottom plate of an oil tank (for example, the bottom plate having a welded portion such as a welded joint portion), but is not limited thereto and may be other objects (for example, piping). Furthermore, the inspection object 1 may be an object in which a coating film is formed on the surface of a base material portion formed of a conductive material as the base material. In this case, the excitation coil 11 may generate the above-mentioned eddy currents in the base material portion.

[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 formed by winding a conductor covered with an insulating film around its central axis Ce. In each drawing, 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 a change in magnetic flux caused by the above-mentioned eddy current in the inspection object 1. That is, an electromotive force is generated in the detection coil 12 due to the change in the magnetic flux passing through the detection coil 12. The change in magnetic flux is caused by a defect such as a scratch in the inspection object 1. For example, as shown in FIG. 1B, the eddy current inspection device 10 is placed opposite the inspection surface 1a of the inspection object 1, and the eddy current inspection device 10 is moved along the inspection surface 1a while a magnetic field is applied to the inspection object 1 by the excitation coil 11. When the detection coil 12 passes directly above the defective portion in the inspection object 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 a defect such as a scratch in the inspection object 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 Fig. 1A. In this case, the detection coil 12 may be formed in a cylindrical shape. The detection coil 12 is formed by winding a conductor covered with an insulating film around a central axis Cd. In each drawing, 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 the direction T and the direction R is indicated by the symbol S.

[0022] 1B, the detection coil 12 may be disposed radially outside the excitation coil 11. In this case, the end face of the detection coil 12 in the axial direction 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 so 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 below, or by other means (for example, an adhesive).

[0024] 1A , when viewed in the axial direction R of the detection coil 12, the detection coil 12 is located at 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 is located at the center of the excitation coil 11 in the axial direction T of the excitation coil 11 (the left-right direction in FIG. 1A ), and may be located at the center of the excitation coil 11 in a direction S perpendicular to the axial direction T of the excitation coil 11.

[0025] 2A is a perspective view of the excitation coil 11 and the detection coil 12 in FIG. 1A, and shows the above-mentioned eddy current Ie generated near the inspection surface 1a of the inspection object 1. That is, FIG. 2A shows the eddy current Ie when viewed in the axial direction R of the detection coil 12. The eddy current Ie generated in the inspection object 1 by the excitation coil 11 may be generated in the vicinity of 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 FIG. 2A. If the material of the inspection object 1 is uniform and there are no damaged parts such as scratches, this eddy current Ie may be generated uniformly in the area facing the detection coil 12 in the axial direction R.

[0026] The eddy current inspection 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 FIG. 1B. The cores 13 and 14 are formed of a material having a higher magnetic permeability than air. The material may be, for example, ferrite, but is not limited to this. When the cores 13 and 14 are used, the above-mentioned 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 dimensions of each part) 2B is a diagram showing the dimensions of each part in FIG. 1B. The outer dimension D1 of the detector coil 12 in a direction S (the left-right direction in FIG. 2B) perpendicular to both the axial direction T of the excitation coil 11 and the axial direction R of the detector coil 12 may be equal to or larger than the inner diameter De1 of the excitation coil 11 and equal to or smaller than the outer diameter De2 of the excitation coil 11.

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

[0029] The dimension of the detection coil 12 in the direction S may be expressed as follows: That is, the outer dimension D1 of the detection coil 12 in the 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, 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 outer dimension of the detection coil 12 in the axial direction T (left and right direction in FIG. 2A) of the excitation coil 11 may be equal to or smaller than the dimension De3 of the excitation coil 11 in the axial direction T. For example, the outer dimension of the detection coil 12 in the axial direction T of the excitation coil 11 may be substantially the same as the dimension of the excitation coil 11 in the axial direction T.

[0031] 1A, the excitation coil 11 and the detection coil 12 may be arranged so that the detection coil 12 (e.g., 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 in FIG. 1A, the excitation coil 11 and the detection coil 12 may be arranged so that an extension line 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 above-mentioned eddy current inspection device 10 may include a holder 15 that holds the excitation coil 11 and the detection coil 12. Fig. 3A shows the eddy current inspection device 10 that includes the holder 15. Fig. 3B is a view taken along the line 3B-3B in Fig. 3A. By connecting the excitation coil 11 and the detection coil 12 to the holder 15, the excitation coil 11 and the detection coil 12 may be connected to each other.

[0033] The holder 15 may be formed of a material (non-magnetic material) that does not impede the functions 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. When the 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 exciting coil 11 and the detecting coil 12 are provided inside the holder 15 , the end face of the detecting coil 12 opposite to the exciting coil 11 in the axial direction R may be exposed to the outside of the holder 15 .

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

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

[0037] (Effects of the first embodiment)

[0038] Since the excitation coil 11 has a circular shape as 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 is easier to wind the excitation coil 11 in a smaller size than when an excitation coil has a rectangular shape as viewed from the axial direction. This makes it easier to miniaturize the eddy current inspection device 10 than before.

[0039] Moreover, in the case of the eddy current inspection device 10 according to the first embodiment, it has been confirmed in the examples described below that it is possible to reduce the size of the device without reducing the ability to detect defects in the object to be inspected 1, compared to an eddy current inspection device using an excitation coil that is rectangular in shape when viewed from the axial direction.

[0040] The outer dimension of the detection coil 12 in the 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 equal to or larger than the inner diameter of the excitation coil 11 and equal to or smaller than the outer diameter of the excitation coil 11. By making the dimension of the detection coil 12 as large as the dimension of the excitation coil 11 in this manner, the defect detection capability based on the eddy current induced in the inspection object 1 can be improved.

[0041] Furthermore, the outer dimension of the detector 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 detector coil 12 may be 2 / 3 or more of the outer diameter of the excitation coil 11. By bringing the dimension of the detector coil 12 in the direction S closer to the dimension of the excitation coil 11 in the axial direction T in this manner, the defect detection capability based on the eddy current induced in the inspection object 1 can be improved.

[0042] (Example) The inspection surface 1a of the inspection object 1 shown in Fig. 4 was inspected using the eddy current inspection device 10 according to the first embodiment. Fig. 4 is a view seen from a direction perpendicular to the inspection surface 1a. Note that Fig. 4 shows the eddy current inspection device 10, but the cable 16 is not shown. A scratch (discharge notch 1b) was formed on the inspection surface 1a by discharge. This discharge notch 1b has a length (dimension in the left-right direction in Fig. 4) of 4 mm, a width (dimension in the up-down direction in Fig. 4) of 0.3 mm, and a depth of 2 mm.

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

[0044] 5A shows waveforms in which the X signal and Y signal of the output voltage of the detection coil 12 are represented as 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 an AC current passed through the excitation coil 11.

[0045] (Reference example) Using the eddy current inspection device 20 of the reference example shown in FIG. 6, an experiment was carried out on the discharge notch 1b of the inspection surface 1a shown in FIG. 4 under the same conditions as in the above-mentioned embodiment except for those described below.

[0046] The eddy current inspection device 20 has an excitation coil 21, which is rectangular when viewed from the axial direction, and a cylindrical detection coil 22, disposed inside a holder 25. In Fig. 6, reference numeral 26 denotes a cable having the same function as the above-mentioned cable 16. In the excitation coil 21, the dimensions in three mutually orthogonal directions including the axial direction are each several millimeters larger than the dimensions in the directions R, S, and T of the corresponding excitation coil 11. The outer diameter of the detection coil 22 is smaller than that of the detection coil 12 by about 1 mm.

[0047] Using such an eddy current inspection device 20, similarly to the embodiment, 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 AC current being supplied to the excitation coil 11. When the tip surface 25a of the holder 25 passed a position above the discharge notch 1b, data on the electromotive force (output voltage) output from the detection coil 12 is shown as a Lissajous waveform in FIG. 5B.

[0048] (Comparison between Examples and Reference Examples) 5A and 5B, the eddy current inspection device 10 of the example is smaller than the eddy current inspection device 20 of the reference example, but obtains a Lissajous waveform larger than or equal to that of the reference example. In this way, it was confirmed that the eddy current inspection device 10 according to the first embodiment can be made smaller without deteriorating the detection capability.

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

[0050] Each inspection unit 10 includes the excitation coil 11 and detection coil 12 in the first embodiment described above. 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 perpendicular to each other, and when viewed in the axial direction R of the detection coil 12, the detection coil 12 (e.g., the entire detection coil 12) overlaps the excitation coil 11. Each inspection unit 10 may further include the holder 15 described above (hereinafter, a sub-holder). The multiple inspection units 10 may have the same configuration as each other.

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

[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 such that the central axes Cd of the respective detection coils 12 are spaced apart (for example, at the same interval) from each other in the first direction S when viewed from the second direction T. In one example, as shown in FIG. 7B , the multiple inspection units 10 may be arranged in the first direction S. That is, the multiple inspection units 10 may overlap each other when viewed from the first direction S. For example, the central axes Cd of the respective detection coils 12 of the multiple inspection units 10 may face the reference direction R and overlap each other when viewed from the first direction S.

[0053] In each inspection unit 10 held by 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 Fig. 7A. In this case, in each inspection unit 10 held by the main holder 35, the orientation of the central axis Ce of the excitation coil 11 coincides with the second direction T in this embodiment, but may 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) in a predetermined range of the reference direction R so as to be movable in the reference direction R. When each inspection unit 10 is at the limit position on the tip side of the predetermined range, the tip of the inspection unit 10 protrudes in the reference direction R (tip side) from the tip surface 35a of the main holder 35 as shown in FIG.

[0055] A plurality of accommodating holes 35b may be formed inside the main holder 35. A plurality of inspection units 10 are disposed in each of these accommodating holes 35b. Each of the inspection units 10 is movable in the reference direction R within the above-mentioned predetermined range while being disposed in the corresponding accommodating hole 35b, as described above. That is, the accommodating hole 35b guides the movement of the inspection unit 10.

[0056] Each accommodation hole 35b has an opening 35b1 in the tip surface 35a of the main holder 35 as shown in FIG. 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 cover member 35c that closes the opening on the rear end side of the accommodation hole 35b. The cover member 35c is removably attached to the rear end surface of the main body of the main holder 35 forming the accommodation hole 35b as shown in FIG. 7A by appropriate means (e.g., screws). This may close the opening on the rear end side of the accommodation hole 35b. With the cover member 35c removed from the main body, the inspection unit 10 may be accommodated in the accommodation hole 35b and may be removable from the accommodation hole 35b through the opening on the rear end side of the accommodation hole 35b.

[0057] Each accommodation hole 35b may have a shape that prevents the corresponding inspection unit 10 from moving further toward the tip side from the state in which the corresponding inspection unit 10 is in the limit position. For example, in this state, the inspection unit 10 may be adapted to engage with the inner surface of each accommodation hole 35b in the reference direction R.

[0058] In the example of Fig. 7A, each of the accommodation holes 35b has a tapered shape at its tip side. This tapered shape may be a shape in which the cross section in a virtual plane perpendicular to the reference direction R becomes gradually smaller as it moves toward the tip side. When each of the inspection units 10 (e.g., its sub-holder 15) is in the limit position, it has a tapered shape that matches the tapered shape of the corresponding accommodation hole 35b in the range from the tip side opening 35b1 of the corresponding accommodation hole 35b to a predetermined position on the rear end side. This prevents each of the inspection units 10 from moving further toward the tip side.

[0059] Each accommodation 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 accommodation hole 35b and the corresponding inspection unit 10 may be rectangular in shape such that their cross-sectional shapes in a virtual plane perpendicular to the reference direction R match each other 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 inspection device 100 includes a force application unit 31. The force application unit 31 is provided for each inspection unit 10, and pushes the inspection unit 10 toward the tip side so that the inspection unit 10 is located at the limit position. The force application unit 31 may be, for example, a spring (a coil spring in the example of FIG. 7A), but may be other means. In the example of FIG. 7A, each coil spring 31 is held between the rear end surface of the sub-holder 15 and the cover member 35c of the main holder 35.

[0061] With this configuration, when no external force is applied, the inspection unit 10 is held in the limit position by the force application part 31. On the other hand, when the tip surface of the inspection unit 10 (i.e., the tip surface 15a of the sub-holder 15) is pressed toward the rear end (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 by the main holder 35 are offset from each other in the first direction S when viewed from the reference direction R. Therefore, the multiple inspection units 10 can be made to face multiple local areas (e.g., multiple local areas adjacent to each other) on the inspection surface 1a of the inspection object 1 at the same time. This makes it possible to simultaneously inspect the presence or absence of defects in these local areas. Therefore, inspection of a wide range of the inspection object 1 can be performed at once.

[0063] 8A is an explanatory diagram of an eddy current inspection method in which a plurality of inspection units 10 (i.e., each detection coil 12) are arranged in a first direction S perpendicular to a reference direction R. Fig. 8A is a diagram viewed from the reference direction R, and only illustrates the detection coils 12 and the inspection surface 1a of the plurality of inspection units 10.

[0064] With the tip surfaces of the multiple inspection units 10 (tip surface 15a of the sub-holder 15) facing the inspection surface 1a of the inspection object 1 in the reference direction R, the multiple detection coils 12 (i.e., holder 35) are moved along the inspection surface 1a in the second direction T as shown in Fig. 8A while a magnetic field is applied to the inspection object 1 by the excitation coil 11 of each inspection unit 10. During this movement, the tip surface of each inspection unit 10 (tip surface 15a of the sub-holder 15) may be in contact with the inspection surface 1a or may be separated from the inspection surface 1a with a gap therebetween. According to such an eddy current inspection method, the above-mentioned eddy current inspection device 100 can be used to inspect a wide range of the inspection object 1 at once.

[0065] In such an eddy current inspection method, even if there is an area (area i surrounded by a dashed line in FIG. 8A) through which the detection coils 12 do not pass between the movement trajectories of the detection coils 12 of adjacent inspection units 10 when viewed in the reference direction R, it is possible for the eddy current inspection device 100 to detect whether a defect exists in the area i (hereinafter referred to as the interval area i) and the area directly below it in the inspection object 1. This is because the electromotive force of the detection coil 12 adjacent to the interval area i changes due to the defect.

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

[0067] With the tip faces of the multiple inspection units 10 (tip face 15a of each sub-holder 15) facing the inspection surface 1a of the inspection object 1 in the reference direction R, a magnetic field is applied to the inspection object 1 by the excitation coil 11 in each inspection unit 10, while 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 moving direction) as shown in Fig. 8B. During this movement, the tip face of each inspection unit 10 (tip face 15a of the sub-holder 15) may be in contact with the inspection surface 1a or may be separated from the inspection surface 1a with a gap therebetween. As a result, in the case of FIG. 8B, the width W of the interval region i in the direction perpendicular to the movement direction becomes smaller than in the case of FIG. 8A (width W of FIG. 8A) or disappears, making it possible to detect whether a defect exists within the interval region i and the area 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 of the reference direction R, and the inspection units 10 are pushed toward the tip side by the force application portion 31 so that their tip portions are positioned at the limit position where they protrude from the tip surface 35a of the main holder 35. With this configuration, when the main holder 35 is slid along the inspection surface 1a while the tip faces of the multiple inspection units 10 (i.e., the tip faces 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 so as to follow the uneven portions of the inspection surface 1a when passing over the uneven portions. Therefore, a wide range of the inspection surface 1a can be easily inspected while the tip faces of the multiple inspection units 10 are in contact with the inspection surface 1a.

[0069] [Third embodiment] Fig. 9A shows an eddy current inspection device 100 according to a third embodiment of the present invention. Fig. 9B is a view taken along the line 9B-9B in Fig. 9A. The third embodiment is the same as the second embodiment except for the points described below.

[0070] In the second embodiment, a plurality of inspection units 10 arranged in the first direction S are regarded as one group G, whereas in the third embodiment, as shown in FIG. 9B, a plurality of groups G are arranged shifted from one another in a second direction T perpendicular to both the reference direction R and the first direction S. In the example of FIG. 9B, three groups G1 to G3 are provided. Note that, of these groups G1 to G3, only the group G1 at the bottom of FIG. 9B is illustrated in FIG. 9A. Note that the number of groups G is not limited to three as in the case of FIG. 9B, and may be two or four or more.

[0071] When viewed from the second direction T, in a region between adjacent detection coils 12 in one group G, the central axes Cd of the detection coils 12 in the other group are located.

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

[0073] In this case, in the region between each pair of adjacent detector coils 12 in each group G, the central axes Cd of the detector coils 12 of the other two or more (e.g., all other) groups G may be positioned so as to be shifted from each other in the first direction S when viewed from the second direction T. Here, in the region between each pair of adjacent detector coils 12 in each group G, only the central axis Cd of any one of the multiple detector coils 12 in each of the other two or more groups may be positioned so as to be shifted from each other in the first direction S when viewed from the second direction T.

[0074] The main holder 35 holds a plurality of test units 10 for each of the plurality of groups G arranged as described above.

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

[0076] In a region between adjacent detector coils 12 in one group G, the central axes Cd of the detector coils 12 of two or more other groups G may be positioned so as to be shifted from each other in the first direction S when viewed from the second direction T. In this way, it is possible to arrange the multiple detector coils 12 densely in the first direction S when viewed from the second direction T.

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

[0078] In addition, any one of the following modified examples 1 to 3 may be adopted alone, or any combination of two or more of modified examples 1 to 3 may be adopted. In this case, the points not described below are the same as those described above.

[0079] (Change example 1) In the second or third embodiment described above, the exciting coil 11 does not have to be circular when viewed in the axial direction T thereof.

[0080] (Change example 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 portion 31 may be omitted. In this case, the sub-holder 15 of each inspection unit 10 may be integrated with the main holder 35 and may be a part of the main holder 35.

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

[0082] 1 inspection object, 1a inspection surface, 1b discharge notch, 10 eddy current inspection 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 inspection device of reference example, 21 excitation coil, 22 detection coil, 25 holder, 25a tip surface of holder, 26 cable, 31 force application part (coil spring), 35 holder (main holder), 35a tip surface, 35b accommodation hole, 35b1 opening on tip side, 35c cover member, 100 eddy current inspection device, Ce central axis of excitation coil, Cd central axis of detection coil, R axial direction of 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

1. An eddy current inspection device that applies a magnetic field to an object to be inspected, generates an eddy current in the object to be inspected by an electromagnetic induction phenomenon caused by the magnetic field, and detects a change in magnetic flux caused by the eddy current, an excitation coil for applying the magnetic field to the inspection object; a detection coil for detecting a change in the magnetic flux; the excitation coil and the detection coil are coupled to each other such that an axial direction of the excitation coil and an axial direction of the detection coil are perpendicular to each other; When viewed in the axial direction of the detection coil, the detection coil overlaps with the excitation coil, An eddy current inspection device, wherein the excitation coil is formed into a circular shape when viewed in the axial direction of the excitation coil.

2. 2. The eddy current inspection device according to claim 1, wherein an outer dimension 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 is equal to or larger than an inner diameter of the excitation coil and is equal to or smaller than an outer diameter of the excitation coil.

3. 3. The eddy current inspection device according to claim 1, wherein an outer dimension 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 is 2 / 3 or more of an inner diameter of the excitation coil.

4. 3. The eddy current inspection device according to claim 1, wherein an outer dimension of the detection coil in the axial direction of the excitation coil is the same as an axial dimension of the excitation coil.

5. a plurality of inspection units that apply a magnetic field to an object to be inspected, generate eddy currents in the object to be inspected by an electromagnetic induction phenomenon 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 of the inspection units includes an excitation coil that applies the magnetic field to the inspection object, and a detection coil that detects a change in the magnetic flux, A direction from the rear end side to the front end side of the holder is set as a reference direction, In each of the inspection units, a central axis of the excitation coil is perpendicular to the reference direction, a 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; An eddy current inspection device, wherein the plurality of inspection units are offset from one another when viewed from the reference direction.

6. The eddy current inspection device according to claim 5 , wherein the plurality of inspection units are arranged in a first direction perpendicular to the reference direction.

7. A plurality of the inspection units arranged in the first direction are regarded as one group, and the plurality of groups are provided so as to be shifted from one another in a second direction perpendicular to both the reference direction and the first direction, 7. The eddy current inspection device according to claim 6, wherein when viewed from the second direction, a central axis of the detection coil of another group is located in a region between adjacent inspection units in one group.

8. 8. The eddy current inspection device according to claim 7, wherein in a region between adjacent inspection units in one of the groups, when viewed from the second direction, the central axes of the detection coils of two or more other of the groups are positioned so as to be shifted from each other in the first direction.

9. the holder holds each of the inspection units so as to be movable in the reference direction within a predetermined range of the reference direction; When each of the inspection units is at a tip end limit position within the predetermined range, a tip end of the inspection unit protrudes from a tip end surface of the holder toward the tip end, 9. The eddy current inspection device according to claim 5, further comprising a force application section provided for each of the inspection units, the force application section pushing the inspection unit toward a tip side so that the inspection unit is positioned at the limit position.

10. An eddy current inspection method using the eddy current inspection device according to claim 6, An eddy current inspection method, comprising: a state in which the tip ends of the plurality of inspection units are faced to an inspection surface of an object to be inspected in the reference direction; and while a magnetic field is applied to the object to be inspected by the excitation coil in each of the inspection units, the holder is moved along the inspection surface in a direction oblique to a second direction perpendicular to both the reference direction and the first direction.

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