JP2010276431A - Eddy current flaw detector and eddy current flaw detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eddy current flaw detector and an eddy current flaw detection method allowing to quantitatively determine a set frequency of a bandpass filter, capable of obtaining an optimum S/N ratio, without depending on experience of operators, even if a test piece to be detected for flaws has a complex shape. <P>SOLUTION: In the eddy current flaw detector 10, an eddy current sensor 23 detects eddy current generated at each rotating normal test piece Ta and defective test piece Tb, a signal processing device 12 generates a healthy shape signal and a defective shape signal, based on the change of the eddy current detected by the eddy current sensor 23, an analyzer 13 computes a noise-generating frequency, by FFT-analysis and comparing the normal shape signal and the defective shape signal generated by the signal processing device 12, and a set device 22 sets the frequency computed by the analyzer 13 as a set frequency of the bandpass filter 21. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an eddy current flaw detection apparatus and an eddy current flaw detection method, and more specifically to a technique for detecting a defect in a test piece by eddy current measurement.

  Conventionally, an eddy current flaw detector has been used as a technique for detecting defects such as cracks that occur during induction hardening and cutting cracks that occur during cutting, mainly for long shaft members such as shaft members (for example, , See Patent Document 1 and Patent Document 2).

  In the conventional eddy current flaw detector, an eddy current sensor having an AC coil is brought close to a test piece to generate eddy current by electromagnetic induction, and the eddy current generated in the test piece is detected by the eddy current sensor. Based on the change in the eddy current detected by the eddy current sensor, the signal processing device generates a shape signal that is a signal indicating the change in the eddy current, and a setting frequency that is a frequency for attenuating the signal is input in advance. By inputting the shape signal to the bandpass filter, it is determined whether there is a defect in the test piece.

  In the conventional eddy current flaw detector, the eddy current signal detected by the eddy current sensor is separated into an X-axis component and a Y-axis component that are 90 degrees different from each other, and noise (generated by the shape and material of the test piece is generated in the X-axis component). The signal is adjusted so that a defect signal is obtained for the Y-axis component. In addition, a normal test piece with no defect and a defective test piece with a defect are measured several times alternately, and the operator adjusts the frequency of the bandpass filter each time it is measured, so that the shape of the XY waveform of the oscilloscope is obtained. The defect signal is identified based on this, and the set frequency of the bandpass filter in the eddy current flaw detector is determined.

JP-A-8-313493 JP 2004-212141 A

  However, when the test piece that is the object of flaw detection has a complicated shape, noise generated by the shape of a spline or the like is similar to a defect signal. In other words, according to the prior art, since the operator specifies a defect signal based on the shape of the XY waveform on the oscilloscope for a test piece having a complicated shape, the frequency to be set in the bandpass filter It was difficult to grasp quantitatively. In other words, it has been difficult to obtain a set frequency of a bandpass filter that can obtain an optimum SN ratio (defect signal to noise ratio).

Further, since the determination of the shape of the XY waveform in the oscilloscope depends on the operator's experience, there is a problem that the set frequency of the bandpass filter differs depending on the operator. That is, there is a difference in the flaw detection accuracy in the eddy current flaw detection apparatus, and there is a possibility that a detection error such as overdetection or miss of a defect may occur due to a flaw detection accuracy defect.
Furthermore, since it is necessary for the operator to work repeatedly, it takes a long time to obtain the set frequency, which leads to an increase in working time in eddy current flaw detection.

  Therefore, in the present invention, in view of the above situation, even if the test piece to be flawed has a complicated shape, the set frequency of the bandpass filter that can obtain the optimum SN ratio (defect signal to noise ratio), An eddy current flaw detection apparatus and a eddy current flaw detection method that can be quantitatively grasped without depending on the experience of an operator are provided.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  That is, in claim 1, an eddy current sensor having an AC coil is brought close to a rotated test piece to generate eddy current by electromagnetic induction, and the eddy current generated in the test piece is detected by the eddy current sensor. Based on the change in the eddy current detected by the eddy current sensor, a shape signal that is a signal indicating the change in the eddy current is generated by the signal processing device, and a set frequency that is a frequency for attenuating the signal is preset. An eddy current flaw detector comprising: an eddy current measuring unit that determines whether there is a defect in the test piece by inputting the shape signal to a band pass filter; and a setting unit that sets a set frequency of the band pass filter. A frequency analysis unit that performs FFT analysis on the shape signal generated by the eddy current measurement unit; For each of the healthy test piece that has been rotated without rotation and the defective test piece that has been rotated with a defect, the eddy current sensor is brought close to generate an eddy current by electromagnetic induction, and the healthy test piece and the defective test piece The eddy current generated in each is detected by the eddy current sensor, and based on the change in the eddy current detected by the eddy current sensor, the signal processing device is a signal indicating the change in the eddy current in the healthy test piece. A shape signal and a defect shape signal that is a signal indicating a change in the eddy current in the defect test piece are generated, and the normal shape signal and the defect shape signal generated by the eddy current measurement unit are FFT-processed by the frequency analysis unit. By analyzing and comparing, the frequency at which noise is generated is calculated, and in the setting unit, the frequency analyzing unit Frequencies issued, is set as the said setting frequency in the band-pass filter.

  In claim 2, an eddy current is generated by electromagnetic induction for each of the healthy test piece rotated without defects and the defective test piece rotated with a defect, and the healthy test piece and the defective test piece Detecting the eddy current generated in each, and based on the change in the eddy current, a healthy shape signal that is a signal indicating the change in the eddy current in the healthy test piece, and the change in the eddy current in the defective test piece A noise is generated by performing FFT analysis and comparing the normal shape signal and the defect shape signal generated in the shape signal generation step and the shape signal generation step that generates a defect shape signal that is a signal indicating The frequency analysis step for calculating the frequency of the current and the frequency calculated in the frequency analysis step An eddy current caused by electromagnetic induction generated in the rotated test piece is detected based on a setting step that is set as a set frequency that is a frequency at which the signal is attenuated, and the eddy current is detected based on the detected change in the eddy current of the test piece. An eddy current flaw detection is performed by generating a shape signal that is a signal indicating a change in current and inputting the shape signal to a bandpass filter in which the set frequency is set in the setting step, thereby determining the presence or absence of a defect in the test piece. And a process.

  As effects of the present invention, the following effects can be obtained.

  According to the present invention, in the eddy current flaw detection apparatus and the eddy current flaw detection method, even if the test piece that is the object of flaw detection has a complicated shape, it is possible to obtain an optimum SN ratio (defect signal to noise ratio). Can be quantitatively grasped without depending on the operator's experience.

The figure which showed the outline | summary of the eddy current testing apparatus which concerns on one Embodiment of this invention. The figure which showed the operation | movement procedure of the eddy current test method which concerns on one Embodiment of this invention. (A) is the figure which showed the FFT analysis result of the healthy test piece, (b) is the figure which similarly showed the FFT analysis result of the defect test piece.

Next, embodiments of the invention will be described.
It should be noted that the technical scope of the present invention is not limited to the following examples, but broadly covers the entire scope of the technical idea that the present invention truly intends, as will be apparent from the matters described in the present specification and drawings. It extends.

[Eddy current flaw detector 10]
First, an outline of an eddy current flaw detector 10 according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the eddy current flaw detector 10 includes an eddy current measuring unit including a signal processing device 12, a band pass filter 21, and an eddy current sensor 23.

  Specifically, the eddy current measuring unit includes an eddy current sensor 23 including an alternating current coil including an excitation coil and a detection coil, a signal processing device 12 electrically connected to the eddy current sensor 23, and the signal processing device 12. An electrically connected band pass filter 21 is provided as a main component.

  The eddy current sensor 23 applies eddy current to the alternating current coil, thereby causing eddy current to flow into the test piece T by electromagnetic induction generated between the alternating current coil and a test piece T (healthy test piece Ta) as a conductor. At the same time as generating an electric current, an eddy current generated in the test piece T can be detected.

  The signal processing device 12 is configured to supply a current to the eddy current sensor 23 and to generate a shape signal based on a change in eddy current detected by the eddy current sensor 23. Here, the shape signal is a signal indicating a change in the eddy current in the test piece T, and an analysis result (FFT waveform) is obtained by performing a fast Fourier transform analysis (hereinafter, FFT analysis) on the shape signal. In addition, as will be described later, the presence or absence of a defect in the test piece T can be determined based on the shape signal.

The bandpass filter 21 is a filter circuit in which a set frequency is set in advance, and is configured to attenuate a signal having a frequency set by the set frequency. That is, by setting the frequency excluding the frequency component indicating the defect signal in the bandpass filter 21 as the set frequency, only the frequency component indicating the defect signal is passed through the shape signal input to the bandpass filter 21. . That is, with this configuration, the signal processing device 12 can determine whether or not there is a defect in the test piece T by inputting the shape signal generated by the signal processing device 12 to the bandpass filter 21.
In addition, the defect in this specification means the crack which generate | occur | produces in induction hardening, the cutting crack which generate | occur | produces at the time of cutting, etc.

Further, the eddy current flaw detector 10 includes a setting unit including a setting device 22.
The setting device 22 is electrically connected to the bandpass filter 21 and is configured to be able to set the set frequency of the bandpass filter 21.

  In the eddy current flaw detector 10 configured as described above, as shown in FIG. 1, a test piece T is attached to a rotating device 80 formed of a lathe or the like and rotated as indicated by an arrow α in FIG. Then, the eddy current sensor 23 in a state where an alternating current is supplied to the alternating current coil is brought close to the test piece T and is scanned in the axial direction of the test piece T (direction of arrow A in FIG. 1). Thereby, an eddy current is generated in the test piece T due to the electromagnetic induction effect generated between the test piece T and the AC coil, and the eddy current sensor 23 detects the eddy current generated in the test piece T. is there.

  Based on the change in the eddy current detected by the eddy current sensor 23, the signal processing device 12 generates a shape signal. Thereafter, by inputting the shape signal to the band-pass filter 21 in which the setting frequency is set in advance by the setting device 22, the signal processing device 12 determines the presence or absence of a defect in the test piece T.

Further, the eddy current flaw detection apparatus 10 further includes a frequency analysis unit including the analysis apparatus 13.
The analysis device 13 is electrically connected to the signal processing device 12 and is configured to perform FFT analysis on the shape signal generated by the signal processing device 12. Specifically, since the defect signal to be detected by the eddy current flaw detector 10 is only the Y component, phase adjustment is performed using a healthy test piece Ta as described later, and the healthy test piece Ta and the defect test piece Tb are Only the Y component is subjected to frequency analysis by the analysis device 13, and the frequency component of the defect signal is specified.
As shown in FIG. 1, the healthy test piece Ta in the present specification is a normal test piece having no defect, and the defective test piece Tb is a minimum that needs to be detected, for example, with respect to a normal test piece. It is a test piece having a defect in which a defect of size is made by electric discharge machining or the like.

[Eddy current flaw detection method]
Next, an eddy current flaw detection method performed by the eddy current flaw detector 10 configured as described above will be described with reference to FIGS.
As shown in FIG. 2, the eddy current flaw detection method according to an embodiment of the present invention generates an eddy current by electromagnetic induction for each of the rotated healthy test piece Ta and the defective test piece Tb, and the healthy test piece Ta and Detecting an eddy current generated in each of the defect test pieces Tb, and based on the change in the eddy current, a healthy shape signal that is a signal indicating the change in the eddy current in the healthy test piece Ta, and the defect test piece A shape signal generation step (steps S1 and S3) for generating a defect shape signal which is a signal indicating a change in the eddy current in Tb, and the normal shape signal and the defect shape signal generated in the shape signal generation step are FFT By analyzing and comparing, the frequency at which the noise signal related to the shape and material of the test piece T is generated is calculated. A frequency analysis step (steps S2 and S4 to S6), a setting step (step S7) for setting the frequency calculated in the frequency analysis step as a set frequency of the band-pass filter 21, and an electromagnetic wave on the rotated test piece T A shape signal is generated based on a change in the eddy current of the test piece T detected while generating an eddy current by induction, and the shape signal is input to the bandpass filter 21 in which the set frequency is set in the setting step. The eddy current flaw detection step (step S8) for determining whether or not there is a defect in the test piece T.

Each step will be described in detail.
First, in the shape signal generation step (step S1), in the eddy current measuring unit, the eddy current sensor 23 is brought close to the AC coil while the AC current is applied to the healthy test piece Ta rotated on the rotating device 80. An eddy current is generated by electromagnetic induction, and an eddy current generated in the healthy test piece Ta is detected by the eddy current sensor 23. Then, based on the change in the eddy current detected by the eddy current sensor 23, the signal processing device 12 generates a healthy shape signal. Here, the healthy shape signal is a signal indicating a change in the eddy current in the healthy test piece Ta.

  Next, in the frequency analysis step (step S2), the analysis apparatus 13 performs an FFT analysis on the healthy shape signal generated by the signal processing apparatus 12, and an FFT analysis result (FFT waveform) is obtained as shown in FIG. obtain.

  Next, in the shape signal generation step (step S3), the eddy current measurement unit similarly applies the alternating current to the alternating current coil through the eddy current sensor 23 for the defect test piece Tb rotated on the rotating device 80. To generate an eddy current due to electromagnetic induction, and the eddy current sensor 23 detects the eddy current generated in the defect test piece Tb. Then, based on the change in the eddy current detected by the eddy current sensor 23, the signal processing device 12 generates a defect shape signal. Here, the defect shape signal is a signal indicating a change in the eddy current in the defect test piece Tb.

Next, in the frequency analysis step (step S4), the analysis device 13 performs FFT analysis on the defect shape signal generated by the signal processing device 12, and the FFT analysis result (FFT waveform) is obtained as shown in FIG. obtain.
Note that the order of steps S1 and S2 and steps S3 and S4 can be switched. That is, it is possible to generate the defect shape signal for the defect test piece Tb and perform the FFT analysis, and then generate the healthy shape signal for the healthy test piece Ta and perform the FFT analysis.

  Next, in the frequency analysis step (step S5), the analysis device 13 compares the FFT waveform of the normal shape signal with the FFT waveform of the defect shape signal, and specifies the frequency component indicating the defect signal.

  A method for specifying a frequency component indicating a defect signal will be specifically described with reference to FIG. FIG. 3A is a diagram showing an FFT waveform of a healthy shape signal generated from the healthy test piece Ta, and FIG. 3B is a diagram showing an FFT waveform of a defect shape signal similarly generated from the defect test piece Tb. .

  When the FFT waveform of the normal shape signal shown in FIG. 3A and the FFT waveform of the defect shape signal shown in FIG. 3B are overlaid and compared, the voltage peak differs depending on the frequency. Specifically, in FIG. 3A, the voltage has a peak at a frequency near the center value, whereas in FIG. 3B, the voltage has a peak at a frequency smaller than the center value. Thereby, it can be specified that the frequency component at which the voltage peaks in FIG. 3B is the frequency component indicating the defect signal. In other words, a frequency component having a difference in the FFT waveform obtained from the healthy test piece Ta and the defect test piece Tb can be specified as indicating a defect signal.

  Next, in the frequency analysis step (step S6), the analysis device 13 calculates a frequency at which a noise signal component related to the shape and material of the test piece T is generated. Specifically, as shown in FIG. 3, since the frequency component indicating the defect signal is specified in the frequency analysis step (step S5), the frequency component other than the frequency component indicating the defect signal is a frequency component in which noise is generated. Is calculated as That is, the frequency other than the frequency component indicating the defect signal at which the voltage peaks in FIG. 3B is calculated as the frequency component (see FIG. 3A) in which noise is generated.

  Next, in the setting step (step S7), the setting device 22 sets the frequency at which the noise component calculated by the analysis device 13 is generated as the set frequency of the bandpass filter 21.

In the eddy current flaw detection step (step S8), the test piece T that is the object of flaw detection is attached to the rotating device 80 constituted by a lathe or the like, and the eddy current sensor 23 is brought close to the AC coil in a state where the AC current is supplied. Then, an eddy current due to an electromagnetic induction effect is generated in the test piece T, and the eddy current generated in the test piece T is detected by the eddy current sensor 23.
Based on the change in the eddy current detected by the eddy current sensor 23, the signal processing device 12 generates a shape signal. Thereafter, in the setting step (step S7), the setting device 22 inputs the shape signal to the bandpass filter 21 in which the setting frequency is set. Then, the band-pass filter 21 attenuates the signal having the frequency of the noise component set at the set frequency and passes only the frequency component indicating the defect signal, whereby the presence or absence of the defect in the test piece T in the signal processing device 12. Is judged.

  That is, in the eddy current flaw detector 10 according to an embodiment of the present invention, the eddy current measuring unit is configured to bring the eddy current sensor 23 closer to each of the rotated normal test piece Ta and the defective test piece Tb to cause eddy current by electromagnetic induction. And eddy currents generated in the healthy test piece Ta and the defective test piece Tb are detected by the eddy current sensor 23. Then, based on the change in the eddy current detected by the eddy current sensor 23, a healthy shape signal and a defect shape signal are generated by the signal processing device 12, and the healthy shape generated by the signal processing device 12 by the analysis device 13. The frequency at which noise is generated is calculated by comparing the signal and the defect shape signal by performing FFT analysis, and the setting device 22 sets the frequency calculated by the analysis device 13 as the set frequency of the bandpass filter 21. It is configured as follows.

  By configuring as described above, the set frequency of the band-pass filter 21 that can obtain the optimum SN ratio (defect signal to noise ratio) even when the test piece T that is the object of flaw detection has a complicated shape is set. It is possible to grasp quantitatively without depending on the experience of the operator.

  Specifically, the shape signal is obtained for both the healthy test piece Ta and the defect test piece Tb, and the FFT analysis result (FFT waveform) is compared to generate the shape signal and the shape of the test piece T. It is possible to separate the noise that is a signal and the defect signal. As a result, the frequency component of the defect signal can be grasped quantitatively and with high accuracy without depending on the shape and material of the test piece T, so that the band-pass filter 21 capable of obtaining an optimum S / N ratio can be obtained. The set frequency can be obtained.

  Moreover, since it becomes possible to obtain | require the setting frequency of the band pass filter 21 without being based on an operator's experience by comprising as mentioned above, it prevents that the setting frequency of the band pass filter 21 changes with operators. be able to. That is, the flaw detection accuracy in the eddy current flaw detector 10 can be made uniform, and the flaw detection accuracy can be improved, thereby preventing detection errors such as overdetection and missed defects.

  Further, by configuring as described above, the set frequency of the bandpass filter 21 that has been obtained by the operator's repeated work can be quantitatively obtained by several processes, so that the working time in eddy current flaw detection is achieved. Can be greatly shortened.

DESCRIPTION OF SYMBOLS 10 Eddy current flaw detector 12 Signal processing device 13 Analysis device 21 Band pass filter 22 Setting device 23 Eddy current sensor 80 Rotating device Ta Healthy test piece Tb Defect test piece

Claims (2)

An eddy current sensor having an AC coil is brought close to the rotated test piece to generate eddy current due to electromagnetic induction, and the eddy current generated in the test piece is detected by the eddy current sensor, and the eddy current sensor detects the eddy current. Based on the change in eddy current, a signal processing device generates a shape signal that is a signal indicating the change in eddy current, and the shape signal is applied to a bandpass filter in which a set frequency that is a frequency to attenuate the signal is set in advance. An eddy current measuring unit that determines the presence or absence of defects in the test piece by inputting;
An eddy current flaw detector comprising a setting unit for setting a set frequency of the band pass filter,
A frequency analysis unit for performing FFT analysis on the shape signal generated by the eddy current measurement unit;
In the eddy current measuring unit, for each of the healthy test piece rotated without a defect and the defective test piece rotated with a defect, the eddy current sensor is brought close to generate an eddy current due to electromagnetic induction, and The eddy current generated in each of the healthy test piece and the defective test piece is detected by the eddy current sensor, and the eddy current in the healthy test piece is detected by the signal processing device based on the change in the eddy current detected by the eddy current sensor. A normal shape signal that is a signal indicating the change of the defect, and a defect shape signal that is a signal indicating the change in the eddy current in the defect test piece,
In the frequency analysis unit, the normal shape signal and the defect shape signal generated by the eddy current measurement unit are FFT-analyzed and compared to calculate a frequency at which noise is generated,
In the setting unit, the frequency calculated by the frequency analysis unit is set as the setting frequency in the bandpass filter.
An eddy current flaw detector characterized by the above. An eddy current generated by electromagnetic induction is generated for each of the healthy test piece rotated without a defect and the defective test piece rotated with a defect, and the eddy current generated in each of the healthy test piece and the defective test piece. , And based on the change in the eddy current, a normal shape signal that is a signal indicating the change in the eddy current in the healthy test piece, and a defect that is a signal that indicates the change in the eddy current in the defect test piece A shape signal generating step for generating a shape signal;
A frequency analysis step of calculating a frequency at which noise is generated by performing FFT analysis and comparing the healthy shape signal and the defect shape signal generated in the shape signal generation step;
Setting the frequency calculated in the frequency analysis step as a set frequency that is a frequency for attenuating a signal in a bandpass filter; and
Eddy current due to electromagnetic induction generated in the rotated test piece is detected, and based on the detected change in eddy current of the test piece, a shape signal that is a signal indicating the change in eddy current is generated, and the setting step An eddy current flaw detection step for determining the presence or absence of defects in the test piece by inputting the shape signal to a bandpass filter in which the set frequency is set in
An eddy current flaw detection method characterized by the above.

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