JPS59217158A - Defect detector - Google Patents

Abstract

PURPOSE:To automatize a defect detector by providing a moving magnetic generator for feeding a moving magnetic field to an object to be inspected to perform an image processing of a magnetic flux leaking from a defective part of the object being inspected using a magnetic detector comprising a plurality of magnetosensitive elements. CONSTITUTION:A moving magnetic field generator 13 comprises an electromagnet 13a, which is made up of cores 14 and 15 arranged almost at the right angle to each other in a U-shape and excitation coils 16 and 17 wound thereon. A magnetic detector 18 is formed by arranging magnetosensitive elements comprising Hall elements in matrix and a support/movement mechanism 19 moves the electromagnet 13a and the detector 18 to the surface of a sample 5 keeping a fixed distance therebetween. An image processor 20 is composed of an AC power source 21 for feeding currents different in the phase to the coils 16 and 17, a preprocessor 22 for amplifying and selecting output of the detector 18, an image processor 23 and a controller 24. With such an arrangement, defects of the sample 5 are detected by detecting vertical component of a leakage magnetic flux and the result can be automatically displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a defect detection device that magnetically detects defects such as cracks in oil tanks, gas tanks, etc.

Conventionally, there is a device shown in FIG. 1 as a device for detecting crack defects in oil tanks, gas tanks, etc.

In the figure, reference numeral 1 denotes an excitation coil for generating a magnetic field, which is wound approximately at the center of a U-shaped iron core 2, and forms an electromagnet 3 together with the iron core 2. 4 is a power supply, and the electromagnet 3
The excitation coil 1 is connected to supply an excitation current to the excitation coil 1 . Reference numeral 5 designates a sample as an object to be inspected, which has a welded portion 6. Magnetic flux lines 7 are generated by the electromagnet 3 and distributed inside the sample 5 and near the surface. 8 is the sample 5
This is a crack-like defect that occurred in the welded part 6 of the figure.

Further, FIG. 2 is a diagram showing the pattern of magnetic particles attracted to the defective part 8 of the sample 5, where 9 indicates the leakage magnetic flux lines in the longitudinal direction of the defective part 8, and 10 shows the defective part 8 of the sample 5. The leakage magnetic flux lines perpendicular to the longitudinal direction of are shown. Reference numeral 11 indicates a magnetic particle attraction pattern generated by the leakage magnetic flux lines 10, and the magnetic particles are scattered on the surface of the sample 5 facing the electromagnet 3.

Reference numeral 12 denotes a magnetic particle attraction pattern generated by the leakage magnetic flux lines 9 in the longitudinal direction of the defective portion 8, which are distributed at both ends of the defective portion 8 of the sample 5.

With such a configuration, upon inspection, first, the power supply 4 is turned on and an excitation current is caused to flow through the excitation coil 1 of the electromagnet 3. Then, the iron core 2 of the electromagnet 3 is magnetized, and a magnetic flux is generated in a magnetic path formed by the sample 5 and the iron core 2. At this time, the magnetic flux passing through the defective part 8 of the welded part 6 of the sample 5 leaks 16 flux because the magnetic resistance of the defective part 8 is very large, and the magnetic field around the defective part 8 becomes large. It becomes. Next, when the magnetic powder is completely scattered on the surface of sample 5,
The magnetic particles are attracted intensively by the action of the magnetic field near the defective part 8, so the magnetic particle pattern 11 (or 12
) is formed. Then, the operator determines the length l of the magnetic particle pattern.
The defective portion 8 is detected.

However, in such conventional defect detection equipment,
The size 2 and distribution of the magnetic particle pattern 11, 12 differ depending on whether the magnetic flux passing through the defective part 8 passes perpendicularly or parallel to the defective part 8, and in particular, the magnetic flux passes perpendicularly to the defective part 8. Then, the generation of leakage magnetic flux 10 becomes extremely sharp, while when passing in parallel, the generation of leakage magnetic flux 9 is small.
In order to accurately identify the defective part 8, it is necessary to rotate the electromagnet 3 and scatter the magnetic particles while changing the direction of the magnetic flux passing through the defective part 8, which poses the problem of very low work efficiency. there were.

In addition, since magnetic particles are used to detect the defective part 8, the magnetic particles are attracted in a chain over a wide range in proportion to the magnitude of the magnetic flux generated in the defective part 8, and the defective part 8 can be accurately detected. I couldn't do much. Furthermore, under high temperature and high humidity,
Alternatively, the work of detecting defects in tanks at high places is difficult, and combined with the fatigue of the workers, the defect detection varies greatly, making it almost impossible to expect reliable detection.

In addition, the only way to record on the magnetic particle patterns 11 and 12' that cover all of the songs in the tank is with adhesive tape or photographs, which results in an enormous amount of data, which poses problems such as the need for space and time when storing and retrieving data. Ta.

This invention was made by focusing on the above-mentioned problems.
A moving magnetic field generator supplies a moving magnetic field to the object to be inspected, a magnetic flux leaking from a defective part of the object is detected by a magnetic detector consisting of a plurality of magnetic sensing elements, and the output signal of the magnetic detector is detected. It is an object of the present invention to provide a defect detection device capable of detecting all defective parts of the object to be inspected through image processing using an image processing device, thereby solving the problems of the conventional art.

An embodiment of the present invention will be described below with reference to FIGS. 3 to 10.

Note that the same reference numerals are given to the same or corresponding parts as in the conventional example.

In Fig. 3, reference numeral 2 denotes a moving magnetic field generator, which is made up of a pair of electromagnets 13a, and the electromagnets 13a have a U-shape and are arranged at right angles to each other, as shown in Fig. 5. 1st
．． The second core 14.15 and its first core 14.15. Second core 14.1
5, respectively, and generate a magnetic field. It consists of a second excitation coil 16 and 17. Reference numeral 18 denotes a magnetic sensor as a magnetic detector, which is formed by arranging magnetic sensing elements A1 to A m n f in a matrix of Hall elements shown in FIG. 4, and is disposed on the electromagnet 13a. Reference numeral 19 denotes a support and movement mechanism, which is configured to move the electromagnet 13a and the magnetic detector 18 while maintaining a constant distance from the surface of the sample 5. 20 is an image processing device, and the first. an AC power supply 21 that supplies currents with different phases to the second excitation coils 16 and 17; a preprocessor 22 that amplifies and selects the output signal output from the magnetic detector 18; and an output of the preprocessor 22. and a controller 24 that controls each part in accordance with the movement of the support moving mechanism 19 and the phase of the AC power supply 21.

The preprocessor 23 is a magnetic sensing element A of the magnetic detector 18.
, 1 to Amn, and a multiplexer 25 that sequentially selects the outputs of the plurality of amplifiers 811 to BmH according to a control signal from the controller 24 to obtain an output. Become. The image processor 23 also includes an A/D converter 2 that converts an analog output signal obtained from the multiplexer 25 of the preprocessor 22 into a digital signal according to a control signal from the controller 24.
6, the digital output signal (hereinafter referred to as data) of the A/D converter 26 is stored in correspondence with the arrangement of the magnetically sensitive elements Al, -Amn of the magnetic detector 18 according to the control signal of the controller 24. a memory 27; a signal processor 28 that converts the data stored in the memory 27 into an image and quantifies the shape of the defective portion 8; and the signal processor 28.
The monitor 29 outputs the processed results, and the data recorder 30 records the output data of the monitor 29.

In addition, in FIG. 6, 31 is the magnetic flux passing through the first iron core 14 and the sample 5, and 32 is the leakage leaked to the outside of the sample 5 (into the air here) due to the magnetic saturation of the defective part 8 of the sample 5. The magnetic flux consists of a component Fv perpendicular to the surface of the sample 5 and a component Fh perpendicular to the surface of the sample 5, and the perpendicular component Fv is detected by each of the magnetic sensing elements A11 to Amn of the magnetic detector 18. .

FIG. 7 shows the first output of the electromagnet 13 from the AC power supply 21 shown in FIG. This is a diagram showing the waveforms of excitation currents I, I2 supplied to the second excitation coils 16, 17, respectively. Excitation current 2 is delayed in phase by 90P with respect to excitation current I. tA,
tB and tc indicate timing (time).

FIG. 8 shows the excitation current I shown in FIG. 7 for the electromagnet 13a.
FIG. 3 is an explanatory diagram showing a rotating magnetic field generated inside the sample 5 when excited by I2. Figure (5), (Bl.

tC) are timings tA and tB in FIG. 7, respectively.
, tc, the direction in which the rotating magnetic field is generated in the sample 5 is shown. Further, FA, FB, and Fc are composite magnetic fields, and the first . Magnetic fields FA, ~FA4, F generated in the magnetic circuit formed by the second iron core 14.15 and the sample 5
B, -LFB4, Fc, ~Fc.

The timings tA and tB are obtained by synthesizing all of them, respectively.
, tc, respectively.

FIG. 9 shows leakage magnetic flux 32 generated in a linear defect 33.
(5) is an explanatory diagram showing the magnitude of the vertical component Fv of
is perpendicular S9o and parallel S to the longitudinal direction of the linear defect 33. and a 45° slope S4. This shows the case where a magnetic circuit is formed. The same figure (B) shows the vertical component F of the leakage magnetic flux 32 generated in the linear defect portion 33 by the rotating magnetic field shown in FIG.
W is detected by the magnetically sensitive elements AIl to Amn of the magnetic detector 18, the detected value is binarized, and the detected value is binarized.
This is an image obtained by plotting (black circles in the figure) in correspondence with the arrangement of ~Amn. &, l indicates the length of the linear defect portion 33.

FIG. 10 is an explanatory diagram showing the distribution of leakage magnetic flux 32 and its perpendicular component FV when a rotating magnetic field is applied to a defective part 34 having an elliptical defect shape. (A) , (corresponds to uniform).

Next, the effect will be explained. The electromagnet 13a is arranged almost perpendicularly to the sample 5 as shown in FIG. An excitation current L+I2 shown in FIG. 7 is applied to the second excitation coils 16 and 17, respectively, and the Second
When the iron cores 14 and 15 are excited, composite magnetic fields FA, FB, and Fc are sequentially generated in the counterclockwise direction at timings tA, tB, and tc as shown in FIG. 8, and a rotating magnetic field is formed. Ru.

At this time, if a defect 8 exists in the surface layer of the sample 5 as shown in FIG. 6, the rotating magnetic field (same as the magnetic flux 31 in FIG. 6) is perpendicular to the cross section of the defect 8. When passing, leakage magnetic flux 32 is generated on the surface of the sample 5. At this time, as shown in FIG. 3, the vertical component Fv of the leakage magnetic flux 32 is divided into multi-IJ square shapes and detected by the magnetic sensing elements A1 to Amn of the magnetic detector 18 present on the surface of the sample 5. be done. The magnitude of the vertical component FV of the leakage magnetic flux 32 detected by the magnetic detector 18 and its distribution on the surface of the sample 5 vary depending on the direction of the rotating magnetic flux 31 and the shape of the defective part 8. In FIG. 9 (5), the elliptical defect portion 34 is caused by the rotational magnetic flux 3 as shown in FIG. 10 (5).
1 corresponds to the angles bO, S45, and SQO.

In this way, the magnetically sensitive elements A, 1 of the magnetic detector 18
The output detected by ~Amn is input to the preprocessor 22 of the image processing device 20, and the amplifier 81 of the preprocessor 22
The signal is amplified by 1 to smn and input to the multiplexer 25 at the subsequent stage. At this time, the controller 24 controls the rotating magnetic field 31 (combined magnetic fields FA, FB,
Fc) and transmits a synchronizing signal to drive the multiplexer 25 to control the magnetic sensing elements A11 to Am.
The outputs of n are sequentially selected and input to the A/D converter 26. Then, the data converted into a digital signal by the A/D converter 26 is transmitted to the magnetic sensing element A of the magnetic detector 18.
, ~Amn are stored at storage addresses in the memory 27 corresponding to the arrangement. Then, the signal processor 28
Based on the data stored in 7, the image is processed as shown in FIG. 9+131 or FIG.
The image is recorded on the data recorder 30. At this time,
The maximum length of the image showing the defect shape by the signal processor 28/! Find the maximum length l and use the specified format (JIS G
0565), the extent of the crack defect portions 33 and 34 is detected and displayed on the monitor 29.

In this manner, when the series of detection operations is completed, the electromagnet 13a and the magnetic detector 18 are moved to the next inspection area by the support movement mechanism 19.

Through the above operations, the defective parts 33 and 31 knees are automatically detected.
Can be displayed and recorded.

In the above embodiment, as shown in FIG. 7, the electromagnet 13a is excited using sinusoidal excitation currents I, I2 to generate a rotating magnetic field, but when the excitation current 1. , I2 may be a rectangular wave, a trapezoidal wave, a triangular wave, etc. In addition, the electromagnet 13
The rotating magnetic field generated by a does not necessarily have to rotate one revolution, but it is possible to use a DC excitation current to generate the rotating magnetic field in Figure 8 (5), (C
) as shown in the figure (B), only the two directions of the magnetic fields FA and Fc, or in addition to the two directions of the magnetic fields FA and Fc, the direction of the magnetic field FB shown in the same figure (B) and the direction perpendicular to the magnetic field FB, that is, four directions. Needless to say, defects can be detected using magnetic field scanning alone. In addition, although the magnetic sensing elements A to Amn are used as the magnetic detector 18, a magnetoresistive element, a winged wire element, a pickup coil, etc. may be used instead.

As explained above, according to the present invention, the configuration is
a moving magnetic field generator that supplies a moving magnetic field to an object to be inspected; a magnetic detector that is made up of a plurality of magnetically sensitive elements and detects magnetic flux leaking from a defective portion of the object to be inspected; Since the device is equipped with an image processing device that displays the defective parts of the object to be inspected by image processing the output signal, the defective parts can be visually observed by exciting an electromagnet and scattering magnetic particles as in the conventional method. Compared to the case of detection, there is no need to scatter magnetic particles or physically rotate the electromagnet, so the defect detection work can be easily learned by oneself, and the detection accuracy can be improved. It has a lot of action and effect.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a defect detection device using a conventional magnetic particle detection method, FIG. 2 is a diagram of a magnetic particle pattern obtained by the defect detection device shown in FIG. 1, and FIG. 3 is a block diagram of a defect detection device according to the present invention. , Fig. 4 is a detailed view of the magnetic detector and preprocessor shown in Fig. 3, Fig. 5 is a three-dimensional layout showing the electromagnet and sample shown in Fig. 3, and Fig. 6 is the generation of leakage magnetic flux at the defective part. 7 is a waveform diagram showing the excitation current waveform that excites the electromagnet shown in FIG. 3. FIG. 8 is an explanatory diagram showing the rotating magnetic field generated by the electromagnet shown in FIG. 3. The 9th section and (B) are the distribution diagram of the leakage magnetic flux generated by the linear defect, the defect shape diagram detected by the magnetic detector and obtained by image processing, and the 10th section and (B) are respectively due to the elliptical defect. It is a leakage magnetic flux distribution diagram and a defect shape diagram obtained by image processing. 5... Sample 8, 33, 34... Defect part 13... Rotating magnetic field generation Container 13a...Electromagnet 14...First iron core 15...Second iron core 16...First excitation coil 17...Second excitation coil 18. ... Magnetic detector 19 ... Supporting and moving mechanism 20 ... Image processing device 21 ... AC power supply 22 ... Preprocessor 23. ... Image processor 24 ... Controller 2G ... AID converter 27 ... Memory 28 ... Signal processor 29 ... ...Monitor 30...Data recorder 31...Passing magnetic flux 32...Leakage magnetic flux C2.~Amn...Magnetic sensing element B o -B
m n...Amplifier FA, FB, Fc...
...Rotating magnetic surface, the same reference numerals in the figures indicate the same or corresponding parts. Agent Masuo Oiwa Figure 10

Claims (5)

[Claims] (1) A moving magnetic field generator that supplies a moving magnetic field to the object to be inspected; a magnetic detector that is made up of a plurality of magnetically sensitive elements and detects magnetic flux leaking from a defective part of the object to be inspected; and the magnetic detection device. and an image processing device that displays a defective portion of the object to be inspected by performing image processing on an output signal of the device. (2) The defect detection device according to claim 1, wherein the moving magnetic field generator is comprised of a plurality of electromagnets driven by rotating magnetic fields generated by alternating current power supplies having mutually different phases. (3) The defect detection device according to claim 1 or 2, wherein the magnetic detector is composed of magnetically sensitive elements arranged in a matrix. (4) The image processing device includes a plurality of amplifiers that correspond to the plurality of magnetically sensitive elements and amplify the outputs of the plurality of magnetically sensitive elements, and a multiplexer that sequentially selects and outputs the plurality of amplifier outputs. 3. The preprocessor comprises a preprocessor, an image processor that converts the output signal of the preprocessor into an image, and a signal processing controller that issues control signals to each part. The defect detection device described in . (5) The image processing device constituting the image processing device includes an A/D converter, a memory that stores output data of the A/D converter at an address corresponding to the matrix array of the magnetically sensitive elements, and the A/D converter. A signal processor that converts the output of the /D converter into an image to quantify and detect defects in the inspected object, a monitor that outputs the processing results of the signal processor, and a record of all the detection results of the imaged defective parts. 5. The defect detection device according to claim 4, further comprising a data recorder for detecting defects.