JP2009287981A - Eddy-current flaw detector and eddy-current flaw detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the phases of flaw signals constant, with respect to flaws in all of directions in an eddy-current flaw detecting probe constituted so that two exciting coils are arranged so as to allow the coil axes of them to cross each other at a right angle and separate exciting power supplies are respectively connected to the exciting coils. <P>SOLUTION: The exciting power supplies EV1 and EV2 which differ in frequencies are connected to the exciting coils 11 and 12 and are arranged so that the coil axes of them may cross each other at right angles, and the frequency of the exciting power supply EV1 is set to f1, while the frequency of the exciting power supply EV2 is set to f2. The detection output of a detection coil separately performs synchronous detection by a reference current, having the same frequency as the exciting power supplies EV1 and EV2 to separately take out flaw signals. The maximum amplitude characteristics of both flaw signals after synchronous detection are indicated by graphs b1 and b2. The phases of both flaw signals after synchronous detection are not changed by the angles of the flaws. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an eddy current flaw detector and an eddy current flaw detection method.

Conventionally, a rotating eddy current flaw detection probe that detects flaws in all directions using a rotating magnetic field (rotating eddy current) has been proposed (see, for example, Patent Document 1).
A conventional eddy current flaw detection probe using a rotating magnetic field will be described with reference to FIGS.
6A and 6B are diagrams showing the arrangement of the excitation coil and the detection coil. FIG. 6A is a plan view, FIG. 6B is a cross-sectional view of the X1 portion in FIG. (C) is sectional drawing of the arrow direction of X2 part of Fig.6 (a).

The eddy current flaw detection probe includes an excitation coil unit 1 and a detection coil 2, and the excitation coil unit 1 includes two (a pair) square excitation coils 11 and 12. The excitation coils 11 and 12 have the other excitation coil 12 disposed (inserted) inside the one excitation coil 11 so that the coil axes (coil central axes) of both excitation coils are orthogonal (coil surfaces are also orthogonal). It is arranged. In addition, the detection coil 2 has a coil axis orthogonal to the coil axes of the excitation coils 11 and 12 (the coil surface is orthogonal to the coil surfaces of both excitation coils), and is substantially at the center of the outer peripheral surface (outside) of the excitation coil 11. It is arranged. The excitation coils 11 and 12 are placed on the inspection surface M1 of the object M to be inspected so that the coil axis is parallel to the inspection surface M1 (the coil surface is orthogonal to the inspection surface M1). Between the exciting coil 11 and the inspection surface M1, it is installed so that the coil axis is orthogonal to the inspection surface M1 (the coil surface is parallel to the inspection surface M1). The coil surface is a surface orthogonal to the coil axis surrounded by the windings.
In the eddy current flaw detection probe shown in FIG. 6, the exciting coils 11 and 12 are formed by being wound around one bobbin, and therefore, the other exciting coil 12 is disposed (inserted) inside one exciting coil 11. It is not always necessary to insert the other inside one, and the two exciting coils may be disposed so that the coil axes are orthogonal to each other.

FIG. 7 is a diagram for explaining an excitation method for generating a rotating magnetic field by the excitation coils 11 and 12 of FIG.
FIG. 7A shows a state in which an excitation power source is connected to the excitation coil, and FIG. 7B is a diagram for explaining the relationship between a scratch direction (angle) and a scratch signal, and a scratch signal pattern (vector waveform). ). In FIG. 7B, the horizontal axis represents the amplitude of the zero-phase component of the scratch signal, and the vertical axis represents the amplitude of the 90-degree phase advance component of the scratch signal.
Excitation power sources EV1 and EV2 having the same frequency and a phase difference of 90 degrees are connected to the excitation coils 11 and 12, respectively. When an excitation current is supplied from the excitation power sources EV1 and EV to the excitation coils 11 and 12, a rotating magnetic field is generated, and a rotating eddy current is generated (inducted) on the inspection surface M1 of the inspection object M.
If there is a scratch on the inspection surface M1, a detection output (a high-frequency scratch signal) is generated (inducted) in the detection coil 2 due to the rotating eddy current. The detection output of the detection coil 2 is synchronously detected with a reference current (carrier wave) having the same frequency as the excitation current, and a scratch signal is extracted.

The phase of the scratch signal changes depending on the direction (angle) of the scratch. When the scratch direction is, for example, 0 °, 45 °, or 135 °, the scratch signal pattern (vector waveform) is the same as that shown in FIG. , Like ro, ha. That is, the phase of the scratch signal changes depending on the direction of the scratch. However, the amplitude does not change.
The direction of the flaw is expressed as an angle with respect to the scanning direction, where the angle of a flaw (a flaw long in the scanning direction) in the scanning direction of the eddy current flaw detection probe (for example, the direction orthogonal to the coil axis of the exciting coil 11) is 0 degree. .
FIG.7 (c) shows the test result performed using the eddy current flaw detection probe of Fig.7 (a), and the angle of a crack is 0 degree | times, 30 degree | times, 60 degree | times, 90 degree | times, 120 degree | times, 150 degree | times, It is the figure which piled up the pattern of the crack signal at the time of 180 degree | times. Also from this figure, it can be seen that the phase of the scratch signal changes depending on the direction of the scratch. In FIG. 7C, the horizontal axis represents the amplitude of the zero-phase component of the scratch signal, and the vertical axis represents the amplitude of the 90-degree advanced phase component.
In the test shown in FIG. 7C, an aluminum inspected object (test object) obtained by electric discharge machining of a scratch having a length of 20 mm, a depth of 2 mm, and a width of 0.2 mm was used, and an excitation current of 128 kHz was used.

JP 2002-131285 A

When excitation currents having the same frequency and a phase different by 90 degrees are supplied to the excitation coils 11 and 12 of the rotating eddy current flaw detection probe shown in FIG. 7A, the phase of the scratch signal changes depending on the direction (angle) of the scratch. The direction of the scratch can be known based on the phase of the scratch signal. However, in addition to the scratch signal, noise may be detected in the detection coil 2, and in that case, it may be difficult to determine whether the scratch signal is noise.
Even if noise is mixed in the scratch signal, for example, when flaws in the welded portion are detected, noise due to the unevenness of the welded portion is also detected, but the direction of the scratch in the welded portion can be predicted to some extent in advance. The phase of the scratch signal generated by the scratch can also be predicted in advance. Therefore, in that case, it can be determined relatively easily from the phase of the signal detected by the detection coil 2 whether it is a scratch signal or noise. On the other hand, in the case of an inspected object in which the direction of the scratch cannot be predicted, the scratch signal and the noise may be detected with the same phase.
In the case of an inspected object in which the direction of the scratch cannot be predicted, it may not be possible to determine the direction of the scratch, so it may be desired to detect the presence or absence of a scratch in all directions.
In view of this point, the present invention has an object to provide an eddy current flaw detector in which the phase of a flaw signal does not change depending on the flaw direction, using the eddy current flaw probe shown in FIGS.

In order to achieve the object of the present invention, the eddy current flaw detector according to claim 1 includes two excitation coils and one detection coil whose coil axes are orthogonal to each other, and the detection coil has two coil axes. It is arranged on the outer peripheral surface of the exciting coil so as to be orthogonal to the coil axis of the exciting coil, the coil axes of the two exciting coils are parallel to the inspection surface of the object to be inspected, and the coil axis of the detecting coil is the inspection surface An eddy current flaw detection probe that is installed so as to be orthogonal to the excitation power supply that supplies excitation currents of different frequencies to the two excitation coils, and the detection output of the detection coil uses a reference current of the same frequency as the excitation current It is characterized by having two synchronous detectors that detect the above.
The eddy current flaw detector according to claim 2 is the eddy current flaw detector according to claim 1, wherein the two excitation coils are composed of two parts, and the outer peripheral surface is between the two parts. It is characterized by being.
The eddy current flaw detection method according to claim 3 includes two excitation coils and one detection coil whose coil axes are orthogonal to each other, and the detection coil has a coil axis orthogonal to the coil axes of the two excitation coils. Arranged on the outer peripheral surface of the exciting coil, the two exciting coils are used with the coil axis parallel to the inspection surface, and the detection coil installed so that the coil axis is perpendicular to the inspection surface of the object to be inspected. A current flaw detection probe is used, excitation currents of different frequencies are supplied to two excitation coils, and the detection output of the detection coil is detected by two synchronous detectors using a reference current having the same frequency as the excitation current. And
The eddy current flaw detection method according to a fourth aspect of the present invention is the eddy current flaw detection method according to the third aspect, wherein the two exciting coils are composed of two parts, and the outer peripheral surface is between the two parts. It is characterized by being.

Since the phase of the scratch signal detected according to the present invention does not change depending on the direction (angle) of the scratch, whether the scratch signal or noise is detected even if noise is detected outside the scratch signal due to the state of the object to be inspected, etc. It can be determined relatively easily, and the present invention can detect scratches in all directions. In addition, since the present invention supplies excitation currents having different frequencies to two (a pair) excitation coils, scratch signals generated by both excitation coils can be taken out separately. Can be performed separately or added together.
In addition, the eddy current flaw detection probe of the present invention can simplify the configuration of the eddy current flaw detection probe because only one detection coil is required although the flaw signals generated by the two exciting coils are separately taken out.
Since the two exciting coils of the eddy current flaw detection probe of the present invention are each divided into two parts, the positioning of the detection coil is simplified when manufacturing the eddy current flaw detection probe.

  An eddy current flaw detection probe and an eddy current flaw detection device according to an embodiment of the present invention will be described with reference to FIGS.

Before describing the embodiment, the eddy current flaw detection probe of FIG. 1 will be described.
The configuration and arrangement of the excitation coil unit 1 and the detection coil 2 of the eddy current flaw detection probe shown in FIG. 1A are the same as those shown in FIG. 6 and FIG.

The inventor of the present application has studied various excitation methods in which the phase of the scratch signal does not change depending on the direction (angle) of the scratch with respect to the eddy current flaw detection probe of FIG. 1A. As a result, the excitation power supply having the same frequency (f) and the same phase. Using EV1 and EV2, excitation current is simultaneously supplied from both excitation power supplies to the excitation coils 11 and 12, and the detection output of the detection coil 2 is synchronously detected with a reference current having the same frequency (f) as the excitation current to extract a scratch signal. In this case, it was found that the phase of the scratch signal does not change depending on the direction of the scratch.
For example, when a 128 kHz exciting current having the same phase is supplied to the exciting coils 11 and 12, the scratch signal pattern (vector waveform) is shown in FIG. 2A when the scratch direction is 45 degrees, 0 degrees, and 135 degrees. It can be seen that the phase of the scratch signal does not change depending on the direction of the scratch. The amplitude of the scratch signal varies depending on the direction of the scratch.

FIG.2 (b) shows the test result done using the eddy current flaw detection probe of Fig.1 (a). In FIG. 2B, the horizontal axis indicates the amplitude of the zero-phase component of the scratch signal, and the vertical axis indicates the amplitude of the 90-degree advanced phase component. Here, the direction (angle) of the scratch is expressed as an angle with respect to the scanning direction, where the angle of the scratch long in the scanning direction of the eddy current flaw detection probe (for example, the direction orthogonal to the coil axis of the exciting coil 11) is 0 degree. (B) is a diagram in which scratch signal patterns are superimposed when the scratch angle is 0 degree, 10 degrees, 20 degrees,..., 170 degrees, and 180 degrees. It can be seen that the phase does not change depending on the direction of the scratch. This test result is the same for the excitation current having a frequency other than 128 kHz.
In the test of FIG. 2 (b), an aluminum inspected object having a 20 mm length, a depth of 2 mm, and a width of 0.2 mm was subjected to electric discharge machining, and an excitation current of 128 kHz was used.

Next, excitation currents of the same frequency (128 kHz) and the same phase are supplied to the excitation coils 11 and 12 of the eddy current flaw detection probe in FIG. 1A, and the maximum of the scratch signals extracted by synchronous detection with a reference signal of 128 kHz. Amplitude characteristics (peak
FIG. 1B illustrates the maximum amplitude of a scratch signal when the scratch angle is 0 degree, 10 degrees, 20 degrees,..., 170 degrees, and 180 degrees. The maximum amplitude of the scratch signal at each angle of the scratch is as shown in the graph a, and is maximum near the scratch angle 45 (that is, the flaw detection sensitivity is maximum), and minimum near 135 degrees (that is, the flaw detection sensitivity is minimum). .
When exciting currents having the same frequency and the same phase are supplied to the exciting coils 11 and 12, the phase of the scratch signal does not change depending on the scratch angle as described above. However, as shown in FIG. 1B, the amplitude of the scratch signal varies greatly depending on the angle of the scratch, and particularly becomes small near 135 degrees, so that the flaw detection sensitivity is low. Therefore, it is insufficient for flaw detection in all directions. is there.

An eddy current flaw detection probe according to an embodiment of the present invention in which this point is improved will be described with reference to FIGS.
First, FIG. 3 will be described.
The configuration and arrangement of the excitation coil unit 1 and the detection coil 2 of the eddy current flaw detection probe shown in FIG. 3A are the same as those shown in FIGS. 6 and 7A. The excitation power supplies EV1 and EV2 have different frequencies and are set to f1 (133 kHz) and f2 (128 kHz), respectively.
The excitation coils 11 and 12 are simultaneously supplied with excitation currents of frequencies f1 and f2 from excitation power sources EV1 and EV2, and the detection output (high-frequency scratch signal) of the detection coil 2 is used as a reference current (carrier wave) of frequencies f1 and f2. And synchronous detection separately to extract the scratch signal separately.
The maximum amplitude characteristics (peak to peak characteristics) of the scratch signal when the scratch angle is 0 degree, 10 degrees, 20 degrees,..., 170 degrees, 180 degrees are shown in the graphs b1 and b2 in FIG. It becomes like this. Graph b1 shows the maximum amplitude characteristic of a scratch signal obtained by synchronous detection with a reference current of frequency f1 (128 kHz), and graph b2 shows the scratch signal obtained by synchronous detection with a reference current of frequency f2 (133 kHz). Maximum amplitude characteristics.

In the graph b1, the maximum amplitude is maximum near the scratch angle of 0 degrees and 180 degrees, and is minimum near 90 degrees. That is, the flaw detection sensitivity is maximized when the scratch angle is around 0 ° and 180 °, and is minimized near 90 °. On the other hand, in the graph b2, the maximum amplitude is minimum near the scratch angle of 0 degrees and 180 degrees, and is maximum near 90 degrees. That is, the flaw detection sensitivity is minimum when the scratch angle is near 0 ° and 180 °, and is maximum near 90 °.
Accordingly, the graphs b1 and b2 are in a complementary relationship with each other, and the combined maximum amplitude characteristics are substantially constant. Therefore, if the scratch signals in both graphs are used, scratches in all directions can be detected. In that case, the flaw signals of both graphs may be used separately, or both flaw signals may be added and used. In the case of addition, the maximum amplitude of the scratch signal is substantially constant even if the scratch angle changes, so that it is easy to determine the presence or absence of the scratch signal.
The frequencies f1 and f2 are not limited to 128 kHz and 133 kHz, but may be other frequencies. If both frequencies are too far apart, the frequency characteristics at the time of flaw detection may change. Set.

  Since the eddy current flaw detection probe shown in FIG. 3A supplies excitation currents having different frequencies to the excitation coils 11 and 12, scratch signals generated by both excitation coils can be taken out separately. Therefore, scratch signals taken out separately can be used separately or added. Since the phase of the scratch signal does not change depending on the angle of the scratch, it is easy to determine whether it is a scratch signal or noise. The eddy current flaw detection probe shown in FIG. 3 (a) has only one detection coil 2 although the flaw signals generated by the two exciting coils are separately taken out, so that the configuration of the eddy current flaw detection probe can be simplified. Become.

Next, with reference to FIG. 4, the phase characteristic of the scratch signal when the exciting currents having the frequencies f1 and f2 are supplied to the eddy current flaw detection probe shown in FIG.
4A corresponds to the scratch signal pattern (vector waveform) of the graph b1 in FIG. 3B, and FIG. 4B shows the test result of the pattern.
4A shows the scratch signal pattern when the scratch angle is 0 degrees, 45 degrees, and 90 degrees. Even if the scratch angle changes, the phase of the scratch signal changes. I understand that there is no.
FIG. 4B is a diagram in which scratch signal patterns are superimposed when the scratch angle is 0 degree, 10 degrees, 20 degrees,..., 170 degrees, and 180 degrees. It can be seen that the phase of the scratch signal does not change even if the angle of is changed.

FIG. 5 shows an example in which an eddy current flaw detector using the eddy current flaw probe shown in FIG.
First, the eddy current flaw detector shown in FIG.
Excitation currents having different frequencies are supplied to the excitation coils 11 and 12 from the excitation power sources EV1 and EV2. The synchronous detectors 31 and 32 are supplied with the detection output (high-frequency scratch signal) of the detection coil 2, and the synchronous detector 31 is supplied with a reference current having the same frequency as that of the excitation power supply EV1 from the reference power supply RV1. The synchronous detector 32 is supplied with a reference current having the same frequency as that of the excitation power supply EV2 from the reference power supply RV2. The synchronous detectors 31 and 32 synchronously detect a flaw signal of the detection coil 2 with each reference current and supply a detection output to the signal processing circuit 33. The signal processing circuit 33 determines the presence or absence of a flaw by using the detection outputs of the synchronous detectors 31 and 32 separately or added. The determination may be made by an observer visually or may be displayed on a display device or the like.

Next, the exciting coil in FIG. 5B will be described. FIG. 5B shows the exciting coils 11 and 12 separately by disassembling the eddy current flaw detection probe.
The exciting coil 11 is divided into parts 111 and 112, and both parts are connected in series. That is, the exciting coil 11 forms one exciting coil by the portions 111 and 112. Similarly, the exciting coil 12 is divided into parts 121 and 122, and both parts are connected in series. That is, the exciting coil 12 forms one exciting coil by the portions 121 and 122.
When the excitation coil is divided as shown in FIG. 2B, the detection coil 2 may be disposed between the portions 111 and 112 of the excitation coil 11, so that when the eddy current flaw detection probe is manufactured, the detection coil 2 is positioned. It will be easy.

An eddy current flaw detection probe in which the phase of the scratch signal does not change depending on the direction of the scratch is shown. The pattern of the crack signal of the eddy current flaw detection probe of FIG. 1 is shown. 1 shows an eddy current flaw detection probe according to an embodiment of the present invention. The pattern of the crack signal of the eddy current flaw detection probe of FIG. 3 is shown. The example which divided | segmented the eddy current flaw detector and excitation coil which concern on the Example of this invention is shown. The structure of the conventional rotating eddy current flaw detection probe is shown. A conventional rotating eddy current flaw detection probe and a scratch signal pattern are shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Excitation coil part 11,12 Excitation coil 111,112,121,122 Part 2 of excitation coil 11,12 Detection coil 31,32 Synchronous detector 33 Signal processing circuit EV1, EV2 Excitation power supply RV1, RV2 Reference power supply M Metal covered Inspection object

Claims (4)

  The coil axis is composed of two excitation coils and one detection coil, and the detection coil is arranged on the outer peripheral surface of the excitation coil so that the coil axis is orthogonal to the coil axes of the two excitation coils. Each excitation coil has an eddy current flaw probe that is installed and used so that the coil axis is parallel to the inspection surface of the object to be inspected and the coil axis is orthogonal to the inspection surface. An eddy current flaw detector comprising: an excitation power source for supplying excitation currents of different frequencies; and two synchronous detectors for detecting the detection output of the detection coil using a reference current having the same frequency as the excitation current.   2. The eddy current flaw detector according to claim 1, wherein the two exciting coils are composed of two parts, and the outer peripheral surface is between the two parts.   The coil axis is composed of two excitation coils and one detection coil, and the detection coil is arranged on the outer peripheral surface of the excitation coil so that the coil axis is orthogonal to the coil axes of the two excitation coils. Each excitation coil uses an eddy current flaw detection probe that is installed so that the coil axis is parallel to the inspection surface of the object to be inspected and the coil axis is orthogonal to the inspection surface. An eddy current flaw detection method characterized in that excitation currents of different frequencies are supplied, and detection output of a detection coil is detected by two synchronous detectors using a reference current having the same frequency as the excitation current.   4. The eddy current flaw detection method according to claim 3, wherein the two exciting coils are composed of two parts, and the outer peripheral surface is between the two parts.

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