JP2001056317A - Eddy cufrrent flaw detection method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a flaw even if the spaced-apart distance between a flaw detection coil and a material to be inspected changes. SOLUTION: A plurality of the flaw detection coils 16 formed on a printed circuit board 22 in a required pattern are arranged to the surface opposed to a material to be inspected of a probe 14 and successively changed over to scan the surface of the material to be inspected to detect a flaw over a required region. A plurality of distance sensors 28 are arranged on the printed circuit board 22 corresponding to the flaw detection coils 16 to measure the actual spaced-apart distances from the surface of the material to be inspected to the flaw detection coils 16. After the flaw detection signals from the flaw detection coils 16 are corrected on the basis of the distance signals from the distance sensors 28, a flaw is judged on the basis of the correction signals thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detection method and apparatus, and more particularly, to a method for detecting a material to be inspected by sequentially switching a plurality of flaw detection coils disposed opposite to the surface of the material to be inspected. The present invention relates to an eddy current flaw detection method and apparatus for scanning a surface to detect a surface defect.

[0002]

2. Description of the Related Art An electronic scanning type eddy current flaw detector is known as a means for detecting defects such as flaws and cracks existing on the surface of a long inspection material such as a flat plate manufactured by cold rolling. I have. In this eddy current flaw detection device, a plurality of flaw detection coils configured by laminating an excitation coil and a detection coil are arranged in a required pattern on a surface of the probe facing the surface of the material to be inspected. Each of the flaw detection coils is configured to generate an eddy current on the surface of the material to be inspected by a magnetic field generated through the excitation coil, and to generate an induced current in the detection coil by the eddy current. If there is a defect on the surface of the material to be inspected, the eddy current changes according to the depth and size of the defect, and the defect is detected by outputting a flaw detection signal using the induced current that fluctuates accordingly. It is configured to During the flaw detection by the eddy current flaw detection device having the above-described configuration, the surface of the material to be inspected is scanned to detect the presence of a defect in a required area by sequentially switching the plurality of flaw detection coils and performing flaw detection of each corresponding portion. It is supposed to.

[0003]

In the eddy current flaw detection apparatus, a constant threshold value is applied to a flaw detection signal output from each flaw detection coil in a state where the separation distance between the material to be inspected and the probe is kept constant. Is set, and when a high flaw detection signal exceeding the threshold value is output, it is determined that there is a defect. However, when the material to be inspected has a warp, distortion, or the like, the distance from each of the flaw detection coils to the surface of the material to be inspected changes, and accordingly, the level of the flaw detection signal also changes. There is a problem that the accuracy of detecting a defect at a certain threshold value is reduced. That is, if the separation distance between the flaw detection coil and the material to be inspected increases, the detection sensitivity of the detection coil decreases, so that even if a defect exists, the level of the flaw detection signal is lower than the threshold value. And the defect may be overlooked.

If the threshold value is set low, it is possible to detect the presence of a defect even if the separation distance is large. In this case, however, in a portion where the separation distance is short,
A minute flaw, noise, or the like that need not be detected is detected, which causes a problem of excessive detection.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems inherent in the prior art, and has been proposed in order to preferably solve the problem. It is an object of the present invention to provide an eddy current flaw detection method and apparatus capable of detecting a defect with high accuracy even when the value changes.

[0006]

[MEANS FOR SOLVING THE PROBLEMS]
In order to appropriately achieve the intended purpose, the eddy current flaw detection method according to the present invention includes a plurality of flaw detection coils facing the surface of the material to be inspected, and sequentially switches and scans the plurality of flaw detection coils. In an eddy current flaw detection device for flaw detection existing on the surface of the material to be inspected, a separation distance from the coil for flaw detection to the surface of the material to be inspected is measured by a distance sensor corresponding to the coil. The defect detection is performed after correcting the flaw detection signal output from the coil based on the distance signal output from the corresponding distance sensor.

In order to suitably achieve the above-mentioned desired object, an eddy current flaw detection apparatus according to another invention of the present application includes a plurality of flaw detection coils facing a surface of a material to be inspected. In the eddy current flaw detection device that flaw-detects a defect present on the surface of the material to be inspected by sequentially switching and scanning, the switching is performed in synchronization with the switching of the plurality of flaw detection coils. A plurality of distance sensors that measure the distance from the corresponding flaw detection coil to the surface of the material to be inspected, and the flaw detection signal output from each of the flaw detection coils is converted into a distance signal output from the corresponding distance sensor. And a determination means for performing a defect determination after the correction based on the correction based on the correction.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an eddy current flaw detection method and apparatus according to the present invention will be described below with reference to the accompanying drawings by way of preferred embodiments.

FIG. 1 and FIG. 2 show a schematic configuration of an eddy current flaw detector according to an embodiment.
Reference numeral 0 denotes a probe provided in the vicinity of the pass line of the long flat plate-shaped inspection object 12 and facing the surface 12a of the inspection object 12. The material to be inspected 12 in the probe 14
A plurality of flaw detection coils 16 are arranged in a pattern shown in the figure on the surface facing the. Then, the surface 1 of the inspected material 12
The inspection target material 12 is subjected to flaw detection while the surface facing the probe 14 with respect to 2a is maintained at a preset separation distance M.

The flaw detection coil 16 is an excitation coil 18 (see FIG. 3) that magnetizes the material 12 to be inspected and generates an eddy current.
And a detection coil 20 for generating an induced current by the eddy current are printed on a printed circuit board 22 in a stacked state. Incidentally, the detection coil 20 is wound in a figure eight shape (differential winding), and the excitation coil 18 is wound in a square shape.

Each of the flaw detection coils 16 is connected to a flaw detection electronic switch 24 shown in FIG.
Is configured to scan the surface 12a of the device and detect a flaw over a required area. In the flaw detection coil 16, as described above,
An eddy current is generated on the surface 12a of the material 12 to be inspected by a magnetic field generated through the exciting coil 18 by energization, and an induced current is generated in the detection coil 20 by the eddy current. And the flaw detection signal according to the induced current
(See FIG. 4A) is output, and the determination means 26 shown in FIG.
To be entered.

In the embodiment, as shown in FIG. 1, there are ten flaw detection lines 12 in the feeding direction of the material to be inspected 12 and two rows in the width direction intersecting with the inspection material 12 in total. The coil 16 is arranged in alignment with the printed circuit board 22. Therefore, for convenience of explanation, in the case where the flaw detection coil 16 is pointed out, in FIG.
.., Ch19, ch1, ch2, ch3... Ch19. Then, the plurality of flaw detection coils 16 are moved to ch0 by the flaw detection electronic switch 24.
Is set to be sequentially switched from to ch19.

The printed board 22 is provided with a plurality of distance sensors 28 at predetermined intervals in the width direction. Each of the distance sensors 28 is a coil printed on the printed circuit board 22, and energizes the coil to excite the inspection target material 12. It is configured to measure an actual separation distance N of up to 16. Then, a measurement signal output from each distance sensor 28 is input to the determination means 26. In the embodiment, ten distance sensors 28 are provided in correspondence with each column in which the two flaw detection coils 16 and 16 are arranged along the feeding direction of the inspection target material 12, and for convenience of explanation, , No. 0, No. 1, No. 2, No. 3,... No. 9 attached from the right side in FIG.

All the distance sensors 28 are connected to a distance electronic switch 30 shown in FIG.
8 is configured to be sequentially switched by the switch 30 in synchronization with the switching of the flaw detection coils 16 in each column. That is, the ch0 and ch1
When the flaw detection is performed by the flaw detection coils 16, 16, ch2 and ch3, and the flaw detection coils 16, 16 of ch18 and ch19, the No. 0 The distance sensor 28 of No. 1, the distance sensor 28 of No. 1... The distance sensor 28 of No. 9 measures the actual separation distance N from the corresponding coil 16 for flaw detection to the surface 12 a of the inspection object 12. Is set.

The flaw detection coil 16 and the distance sensor 2
The determination means 26 to which the output signal from the detector 8 is input corrects the actual flaw detection signal obtained from the flaw detection coil 16 based on the distance signal obtained from the distance sensor 28. That is, the correction signal obtained by correcting the flaw detection signal based on the distance signal is obtained by increasing or decreasing the flaw detection signal in accordance with the difference between the set separation distance M and the actual separation distance N. All of the flaw detection coils 16 can be regarded as flaw-detected at the same set separation distance M with respect to the surface 12a. Then, the obtained correction signal is compared with a preset threshold value K for determining the defect F with respect to the level of the flaw detection signal, and when the correction signal exceeds the threshold value K, the presence of the defect F is determined. (See FIG. 4 (c)).

[0016]

Next, the operation of the eddy current flaw detector according to the above-described embodiment will be described in relation to the eddy current flaw detection method.
As described above, at the time of flaw detection of the inspection material 12, the opposing surface of the probe 14 on which the flaw detection coil 16 is disposed is opposed to the surface 12a of the inspection material 12 by a predetermined separation distance. . Further, a threshold value K for determining the defect F is set for the level of the flaw detection signal based on the set separation distance M. It is assumed that the inspection target material 12 has a warp in the width direction, and the defect F exists on the substantially central surface 12a in the width direction which is the most distant from the opposing surface of the probe 14 (see FIG. 2).

In this state, when the inspection material 12 fed along the pass line passes through the position where the probe 14 is provided, each of the flaw detection coils 16 is moved from the ch0 to the ch1.
9 are sequentially switched to perform flaw detection of a corresponding portion. That is, in the portion of the inspection material 12 corresponding to each of the flaw detection coils 16, a magnetic field generated from the excitation coil 18 is generated on the surface 12 a of the inspection material 12, and is induced to the detection coil 20 by an eddy current caused by the magnetic field. An electric current is generated. Then, each of the flaw detection coils 16 outputs a flaw detection signal corresponding to the induced current, and this is input to the determination means 26 shown in FIG.

An actual flaw detection signal detected by each flaw detection coil 16 appears as shown in FIG. 4A, for example. In this case, the defect F
Exists, the flaw detection coil 1 corresponding to the site
The level of the flaw detection signal output from 6 is higher than other flaw detection signals. However, as described above, since the inspection material 12 has a warp in which the portion where the defect F exists is separated from the flaw detection coil 16, the flaw detection signal is based on the preset set separation distance M. In this state, it is determined that the defect F does not exist.

Accordingly, in the embodiment, the flaw detection coil 16 is used.
The distance sensors 28 corresponding to the respective columns
Are switched in synchronization with the switching of the corresponding flaw detection coils 16, 16, and the actual separation distance between the surface 12 a of the inspection object 12 to be flawed by the flaw detection coils 16, 16 and the coils 16, 16. Measure N. Then, a distance signal (see FIG. 4B) output from each distance sensor 28 is input to the determination means 26.

The determining means 26 corrects the flaw detection signal from each of the flaw detecting coils 16 based on the distance signal from the distance sensor 28, and makes a defect determination based on the obtained correction signal. That is, the signal is increased or decreased according to the difference between the set separation distance M and the actual separation distance N. As a result, as shown in FIG. The level exceeds K, and the defect F can be detected. As described above, by correcting the actual flaw detection signal in accordance with the distance variation, the material to be inspected 12
However, even if the object has warpage or distortion, the detection accuracy of the surface defect F can be improved, and the quality accuracy of the inspection target material 12 can be improved. Moreover, since it is not necessary to set the threshold value K excessively low, there is no possibility of detecting minute flaws, noises, and the like that need not be detected.

In the embodiment, the case where the type of detecting the magnetic fluctuation is adopted as the distance sensor has been described. However, the type of the sensor is not limited to this, and an optical sensor using a laser or the like is used. Can be used. Further, the arrangement pattern and the number of arrangements of the flaw detection coil and the distance sensor are not limited to those of the embodiment, and can be appropriately changed according to the specifications of the inspection target material to be flaw-detected. Further, in the embodiment, one distance sensor is arranged corresponding to two flaw detection coils. However, one distance sensor is arranged corresponding to one flaw detection coil, or three or more flaw detection coils are supported. Then, a configuration in which one distance sensor is disposed can be adopted.

Although the embodiment has been described with respect to the case where the flaw detection is performed on the upper surface side of the plate-like inspection material,
There may be distortion or deformation in (edge) etc.
Defect detection using a distance sensor can also be employed for flaw detection on this side surface.

[0023]

As described above, according to the eddy current flaw detection method and apparatus according to the present invention, the flaw detection signal actually detected by the flaw detection coil is changed according to the change in the separation distance between the coil and the material to be inspected. By performing the correction, highly accurate flaw detection is always achieved. In other words, even if the material to be inspected has warpage or distortion, the surface defect can be accurately detected,
Quality accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a main part of an eddy current flaw detector according to a preferred embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a relationship between a probe and a material to be inspected in the eddy current flaw detector according to the embodiment.

FIG. 3 is a control block diagram of the eddy current testing device according to the embodiment.

FIG. 4 is a graph showing a flaw detection signal from a flaw detection coil, a distance signal from a distance sensor, and a correction signal obtained by correcting a flaw detection signal according to the embodiment with a distance signal.

[Explanation of symbols]

 12 Inspection material 12a Surface 16 Flaw detection coil 26 Judgment means 28 Distance sensor

Claims (2)

[Claims] 1. A flaw detection coil (16) facing a surface (12a) of a material to be inspected (12).
By sequentially switching and scanning (16), the material to be inspected (12)
In the eddy current flaw detection device for detecting a defect existing on the surface (12a) of the test object, the separation distance from the flaw detection coil (16) to the surface (12a) of the inspection object (12) corresponds to the coil (16). Distance sensor (2
8), the flaw detection signal output from each of the flaw detection coils (16) is corrected based on the distance signal output from the corresponding distance sensor (28), and then defect determination is performed. Eddy current flaw detection method. 2. A plurality of flaw detection coils (16) facing a surface (12a) of a material to be inspected (12), wherein the plurality of flaw detection coils are provided.
By sequentially switching and scanning (16), the material to be inspected (12)
In the eddy current flaw detector for detecting a defect existing on the surface (12a) of the flaw detection coil (16), it is disposed in correspondence with the flaw detection coil (16), and is switched in synchronization with the switching of the plurality of flaw detection coils (16). A plurality of distance sensors (28) for measuring the distance from the flaw detection coil (16) to the surface (12a) of the material to be inspected (12), and a flaw detection signal output from each of the flaw detection coils (16), An eddy current flaw detection device comprising: a determination unit (26) for performing a defect determination after correcting based on a distance signal output from a corresponding distance sensor (28).