JPH0682425A - Flaw detection method and flaw detection device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a flaw detection method and a flaw detection device for extracting a defect signal by improving S / N and improving detectability of the defect signal. [Structure] Linearly polarized light is continuously irradiated in the width direction from one end to the other end of a steel plate H via an optical scanner 4. If the period during which the optical scanner 4 scans from one end of the steel plate H to the other end is one cycle,
The nth cycle scanning, the (n + 1) th cycle scanning, etc. are performed respectively. The light sequentially condensed by the light guide rod 2 for each cycle is converted into an electric signal and sequentially input to the differential amplifier 8 to become a detection signal. The designated signal among these is input to the signal storage unit 7, stored and held for a predetermined period, and becomes a reference signal. The differential amplifier 8 obtains the difference between the reference signal and the detection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic flux leakage flaw detection method for detecting surface flaws and internal flaws generated in a steel sheet and an apparatus used for the flaw flaw detection method.

[0002]

2. Description of the Related Art A leakage magnetic flux flaw detection method is known as a flaw detection method for a flaw generated in a steel sheet. Usually, the device used for the leakage magnetic flux flaw detection method is a magnetizer for magnetizing the material to be inspected,
It is composed of a magnetic field detector for detecting the defect leakage magnetic flux leaking from the defect, and a signal processing device for amplifying the output of the magnetic field detector and processing the signal.

When the material to be inspected is, for example, a steel sheet, the traveling steel sheet is magnetized, a magnetic field detector is arranged on the magnetized sheet, and a defect signal in the output of the magnetic field detector is detected. Since the magnetic flux leakage flaw detection on a steel sheet is performed at high speed, it cannot be detected by scanning the magnetic field detector, and a plurality of magnetic field detectors such as coils or Hall elements are arranged in the width direction of the steel sheet, that is, in the direction intersecting the traveling direction. Set up. The detected defect signal is due to a flaw in the steel plate, and a signal due to noise is mixed therein.
Noise varies depending on the steel type or rolling conditions,
When the same amount of noise is generated in the adjacent magnetic field detectors, the noise is removed to detect flaws in the steel sheet by obtaining the difference between the output values of these magnetic field detectors (Japanese Patent Laid-Open No. HEI 3). No. 134557), the noise of the steel sheet can be removed by this, the S / N of the defect signal can be improved, and the minute flaw can be detected.

However, since the width dimension of the steel sheet is long, a large number of magnetic field detectors and a large number of amplifiers connected to each of them must be arranged in the apparatus, so that such a leakage magnetic flux flaw detector has a large number of elements. Equipment costs, maintenance labor, and costs were required. Further, the method disclosed in the above publication is intended for noise difference processing between magnetic field detectors arranged in the width direction of the steel sheet, and is not an effective method for noise continuously generated in the steel sheet traveling direction.

[0005]

The applicant of the present invention has proposed a magneto-optical flaw detector which uses a magneto-optical element as a magnetic field detector and irradiates it with linearly polarized light to detect flaws on a steel sheet. Kaihei 3-245052). This device uses a magneto-optical element array in which a plurality of magneto-optical elements are arranged in series as a magnetic field detector,
This is provided in the length from one end to the other end of the traveling steel plate in the width direction. The steel sheet is magnetized in the width direction intersecting the traveling direction. Then, linearly polarized light is made incident on an optical scanner composed of a rotating mirror arranged above the magnetic field detector, and scanning is performed so that the reflected light from this optical scanner sequentially irradiates from one end to the other end of the magneto-optical element array. To be done. At this time, the linearly polarized light is reflected by the surface of the magneto-optical element array that faces the steel plate, and the reflected light is sequentially collected by the light guide bar arranged above the magnetic field detector. This light is converted into an electric signal by a photoelectric converter and amplified by an amplifier to output a signal representing the leakage magnetic field distribution in the width direction of the steel sheet. Then, by repeating this irradiation, the flaw detection of the entire surface of the steel sheet is performed.

In this magneto-optical flaw detector, the magnetic flux is changed by the leakage magnetic flux from the defect existing in the steel sheet, the magneto-optical element causes Faraday rotation, and the plane of polarization of the incident linearly polarized light is rotated. The amount of light emitted changes in proportion to the leakage magnetic flux from the defect. Since the change can be detected by detecting the change by sequentially collecting and electrically converting this light amount by one light guide rod, it is sufficient to connect one amplifier, and it is not necessary to dispose a plurality of amplifiers.

However, the magnetic field detector of this device is
Since a plurality of magneto-optical elements are connected in series, when the reflected light from the linearly polarized magnetic field detector irradiated in the width direction is sequentially detected, noise due to the joint of the magneto-optical elements occurs. Further, there is a problem that noise caused by flapping when the steel sheet travels is generated, and the S / N is reduced by these noises.

The present invention was made by paying attention to the fact that these noises are generated in the same amount in the traveling direction of the steel sheet, and the leakage magnetic field detected in the width direction at a predetermined position in the traveling direction of the inspected material. A flaw detection method and a flaw detection device that improve the S / N of a defect signal by extracting the leakage magnetic field signal detected in the width direction at positions separated by a predetermined distance from the signal and improve the detectability of the defect signal. The purpose is to provide.

[0009]

A flaw detection method according to a first aspect of the present invention magnetizes a traveling inspected material in a direction intersecting the traveling direction, and obtains a leakage magnetic field distribution in a direction intersecting the traveling direction of the inspected material. In the flaw detection method for detecting a defect of the material to be inspected by obtaining the leakage magnetic field signal represented in time series,
The first leakage magnetic field signal at a predetermined position in the traveling direction of the inspection material is stored, and the first leakage magnetic field signal and the second leakage magnetic field signal at a position separated from the predetermined position by a predetermined distance. It is characterized by obtaining the difference between and.

A flaw detector according to a second aspect of the present invention magnetizes a traveling inspected material in a direction intersecting the traveling direction, and outputs a leakage magnetic field signal representing a leakage magnetic field distribution in a direction intersecting the traveling direction of the inspected material. In the flaw detection device for detecting defects in the material to be inspected by calculating in series, a magnetic field detector arranged in a direction intersecting the traveling direction of the material to be inspected, and the magnetic field detector output from the magnetic field detector. A signal storage unit for storing a leak magnetic field signal, and a differential amplifier for obtaining a difference between the stored leak magnetic field signal and the leak magnetic field signal output at a position separated by a predetermined distance in the traveling direction, To do.

[0011]

In the flaw detection method and flaw detection apparatus of the present invention, the leakage magnetic field distribution in the direction intersecting the traveling direction of the material to be inspected is detected in time series at positions separated by a predetermined distance in the traveling direction. The first leakage magnetic field signal at a predetermined position of the inspection material is stored in the signal storage unit, and the first leakage magnetic field signal and the second leakage magnetic field signal at a position separated from the detected position by a predetermined distance in the traveling direction. By obtaining the difference with the leakage magnetic field signal with a differential amplifier,
It is possible to remove the noise generated in the same amount in the traveling direction, such as the noise caused by the joint of the magnetic field detector and the noise caused by the traveling state of the material to be inspected.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a block diagram showing the configuration of a magneto-optical flaw detector according to the present invention. The steel sheet H, which is the material to be inspected, runs and is magnetized in the width direction of the steel sheet H by a magnetizer (not shown) arranged in the width direction of the steel sheet H, that is, in the direction intersecting the running direction. A magneto-optical element array 1 which is a magnetic field detector is arranged above the traveling area in a length from one end to the other end in the width direction of the steel plate H. Magneto-optical element array 1
Is formed by connecting a plurality of magneto-optical elements in a straight line, and a reflective film is vapor-deposited on the surface facing the steel plate H. A laser light source 3 and a polarizer (not shown), and an optical scanner 4 including a rotating mirror for making linearly polarized light emitted from the laser light source 3 through the polarizer enter the magneto-optical element array 1 at a predetermined incident angle. It is arranged. An optical rod 2 as a light concentrator is arranged above the magneto-optical element array 1 in parallel with the magneto-optical element array 1 at a predetermined interval and is reflected by a reflection film of the magneto-optical element array 1. It collects the light that is emitted.

The light collected by the light guide rod 2 is photoelectric converter 5
Is converted into an electric signal and this output signal is input to the amplifier 6. The output signal amplified by the amplifier 6 is analog /
The signal is digitally converted by a digital converter (not shown) and input to and stored in the signal storage unit 7 which stores and holds for a predetermined period. The signal read from the signal storage unit 7 is analog-converted by a digital / analog converter (not shown) and input to the differential amplifier 8 which detects the difference between the two signals. The output signal from the amplifier 6 is also input to the differential amplifier 8, and the differential amplifier 8 obtains the difference between these signals and outputs the signal.

On the other hand, the differential start signal detector 9 is arranged in the scanning area of the optical scanner 4 and at a position deviated from the arrangement position of the magneto-optical element array 1. The difference start signal detector 9 receives the irradiation light from the optical scanner 4, inputs a timing signal for starting scanning in the width direction of the steel plate H of the optical scanner 4 to the signal storage unit 7, and adjusts to this timing. The signal stored in the signal storage unit 7 is output.

When the steel plate H is to be flaw-detected by the magneto-optical flaw detector having such a structure, the laser light source 3 irradiates the magneto-optical element array 1 with linearly polarized light through the optical scanner 4. The optical scanner 4 continuously irradiates linearly polarized light from one end to the other end of the magnetized steel plate H traveling at a constant speed in the width direction by its rotating mirror. FIG. 2 is an explanatory diagram showing how linearly polarized light is emitted through the optical scanner 4. If the period during which the optical scanner 4 scans from one end to the other end of the steel plate H is one cycle, as shown in FIG. 2, at the positions separated by a predetermined distance in the traveling direction, the nth cycle scanning, the n + 1th cycle scanning, ... n + a cycle scan, n +
The scanning of the (a + 1) th cycle, ... Is performed. The linearly polarized light thus radiated is reflected by the reflective film of the magneto-optical element array 1, and the reflected light is sequentially condensed by the optical rod 2 in each cycle and converted into an electric signal by the photoelectric converter 5. The amplifier 6
Is input to.

From the signal amplified by the amplifier 6, FIG.
A signal waveform as shown in FIG. 3 is obtained, which shows the leakage magnetic field distribution in the width direction of the steel plate H. FIG. 3 (a) shows the signal waveform of the nth cycle scanning, and FIG. 3 (b) shows the signal waveform of the (n + 1) th cycle scanning. The defect signal z is included in the signal waveform of the (n + 1) th cycle scanning. Signals other than the defect leakage magnetic flux signal are generated in these signal waveforms, such as a seam signal x resulting from the seam of the magneto-optical element array and a flapping signal y resulting from the position variation of the magneto-optical element due to flapping of the steel plate. .

The signal of the n-th scanning scan represents the first leakage magnetic field distribution, is input to the signal storage unit 7 and is stored and held for a predetermined period. This is used as a reference signal. 1 of optical scanner 4
The output signal of the differential start signal detector 9 for detecting the scanning start timing for each cycle is input to the signal storage unit 7, and the signal waveform of the leakage magnetic field distribution of the reference signal is output to the differential amplifier 8 at the timing. To be done.

On the other hand, the second leakage magnetic field distribution n +
The signals of the first scan, the n + 2th scan, ... Are sequentially input from the amplifier 6 to the differential amplifier 8. This is the detection signal. First, in the differential amplifier 8, the signal storage unit 7
The signal of the nth period scanning which is the reference signal input from
The detection signal of the (n + 1) th cycle scanning, which is the detection signal, is input, the difference between them is obtained, and the signal is output.

In this manner, by subtracting the reference signal of the nth cycle scanning from the detection signal of the (n + 1) th cycle scanning, the seam signal x that appears in each scanning and the flap signal y that appears consecutively in several cycles. Can be removed and the defect signal z remains. As a result, it is possible to improve the S / N and obtain the defects existing in the portion of the steel plate H that has been scanned in the (n + 1) th cycle. Subsequently, the detection signals of the n + 2th cycle scanning, the n + 3th cycle scanning, ... Are input to the differential amplifier 8 and the differences from the reference signal are obtained.

A computer (not shown) is connected to the signal storage unit 7, and the reference signal stored in the signal storage unit is updated every predetermined period according to an instruction from the computer. That is, when the predetermined period for storing the reference signal is set to the a cycle, the signal of the (n + a) th scanning is input from the amplifier 6 to the signal storage unit 7, and is stored in place of the reference signal of the nth scanning. Then, the n + a cycle scanning signal and the n + a + 1 cycle scanning signal, ... Are sequentially input to the differential amplifier 8 to obtain the difference, and the signals obtained by removing the joint signal x and the flap signal y are output respectively.

As described above, by obtaining the difference between the detection signal and the reference signal for each period in the width direction of the material to be inspected, noises such as the seam signal x and the flap signal y can be removed. It is possible to improve / N and obtain a defect signal.

The predetermined period for storing the reference signal is set by the number of cycles in which the respective signals such as the seam signal x, the flap signal y, and the defect signal appear continuously.
The number of cycles is sufficiently shorter than the number of cycles in which the seam signal x and the flap signal y continuously appear, and is longer or the same as the number of cycles in which defective signals continuously appear.

When the reference signal contains sudden noise such as electric noise, a plurality of reference signals are stored in the signal storage unit 7 according to the above-mentioned instruction of the computer, and these are averaged. Turn into. As a result, a sudden reference noise is averaged to obtain a reduced reference signal. Then, the difference between the reference signal and the detection signal is obtained, and the S / N can be improved to detect the defect signal without being affected by sudden noise.

In such a device, the signal storage interval is a =
When the steel plate H is inspected for 4 cycles and the number of times of averaging the reference signal is 4, S / N = 1 in the waveform of the detection signal, and S / N in the waveform in which the difference between the detection signal and the reference signal is obtained. / N = 10. From this, it can be seen that the defect detectability is improved.

In this embodiment, the photoelectric converter 5
Although the output from is input to the signal storage unit after being amplified, the output is not limited to this, and may be input to the signal storage unit after performing appropriate waveform processing, for example, differentiation processing.

[0026]

As described above, in the flaw detection method and flaw detection device of the present invention, noise existing in the traveling direction can be removed, so that flaw detection with high S / N and improved defect detection capability can be performed. It can be carried out, and the present invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a magneto-optical flaw detector according to the present invention.

FIG. 2 is an explanatory diagram showing how linearly polarized light is emitted.

FIG. 3 is a signal waveform diagram of a detection signal.

[Explanation of symbols]

 1 Magneto-Optical Element Array 2 Optical Rod 3 Laser Light Source 4 Optical Scanner 5 Photoelectric Converter 6 Amplifier 7 Signal Storage 8 Differential Amplifier 9 Difference Start Signal Detector H Steel Plate

Claims (2)

[Claims] 1. A traveling magnetic material to be inspected is magnetized in a direction intersecting the traveling direction, and a leakage magnetic field signal representing a leakage magnetic field distribution in a direction intersecting the traveling direction of the inspection material is obtained in time series, In the flaw detection method for detecting a defect of the inspection material, the first leakage magnetic field signal at a predetermined position in the traveling direction of the inspection material is stored, and the first leakage magnetic field signal and the predetermined leakage magnetic field signal from the predetermined position are stored. A flaw detection method characterized by obtaining a difference from the second leakage magnetic field signal at positions separated from each other. 2. A traveling magnetic material to be inspected is magnetized in a direction intersecting the traveling direction, and a leakage magnetic field signal representing a leakage magnetic field distribution in a direction intersecting the traveling direction of the inspection material is obtained in time series, In a flaw detector for detecting defects in the material to be inspected, a magnetic field detector arranged in a direction intersecting a traveling direction of the material to be inspected, and a signal for storing the leakage magnetic field signal output from the magnetic field detector. A flaw detection apparatus comprising: a storage unit; and a differential amplifier that obtains a difference between the stored leakage magnetic field signal and the leakage magnetic field signal output at a position separated by a predetermined distance in the traveling direction.