JPH10267688A - Signal processing method, method for detecting defect of steel board, and their device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal processing method wherein a desired signal component is detected with high sensitivity out of the output signal of a detection element. SOLUTION: The output signals of detection elements 21-1 to 21-n are amplified and filtered, so that such signal component of desired frequency band as noise component is attenuated is obtained. Here, amplification and filtering processes are split into 2 stages, and the low-frequency component of the noise component is attenuated is obtained by the first-stage amplification and filtering processes 22-1 to 22-n, 23-1 to 23-n, and then, the signal component of the desired frequency band where noise component is attenuated by the second-stage amplification and filtering processes 29-1 to 29-n, 30-1 to 30-n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention amplifies and filters a minute output signal from a detection element,
The present invention relates to a signal processing method and apparatus for obtaining a signal component of a desired frequency band in which a noise component has been attenuated, and a method and an apparatus for detecting a defect of a steel sheet using the signal processing method and apparatus.

[0002]

2. Description of the Related Art Conventionally, in order to enhance detection sensitivity of a detection element, differential processing of an output signal from the detection element is generally performed. In this case, a high-pass filter is often used for differentiation, but in order to avoid malfunction due to noise at a frequency higher than the desired frequency band, a low-pass filter may be further combined or a band-pass filter may be used instead. It has also been used. When a frequency filter is used as described above, generally, in order to sufficiently exhibit the performance of the filter,
The output signal of the detection element is once amplified by an amplifier and then supplied to a filter.

Such a signal processing method is described in, for example, "Handbook for Nondestructive Inspection" (edited by the Japan Nondestructive Inspection Association, published by Nikkan Kogyo Shimbun), pages 517 to 534. This is effective when the output signal of a magnetic sensor that detects a leakage magnetic flux generated from a steel plate serving as a detection element as in a defect detection device is particularly weak. As an example of application to such a defect detection device, for example,
Japanese Patent Application Publication No. 30450 discloses a configuration shown in FIG.

In the defect detection apparatus shown in FIG. 7, a number of magnetic sensors 1-1,..., 1-n are arranged in the width direction of the steel sheet (not shown), which is magnetized and moves. , The magnetic flux leakage of the steel sheet is detected by each of the magnetic sensors, and the output of each magnetic sensor is output to the corresponding amplifier 2-1.
., 2-n, then multiply circuits 3-1,.
3-n is supplied to one input terminal. In addition, an amplitude correction value corresponding to the actual traveling speed of the steel sheet is supplied to the other input terminal of each multiplication circuit, thereby correcting a change in the amplitude of the output signal of each magnetic sensor due to a change in the traveling speed of the steel sheet. I am trying to do it.

For this reason, in FIG. 7, a pulse generator (PG) 4 for generating a pulse having a frequency proportional to the actual running speed of the steel sheet is provided, and an amplitude correction value corresponding to each running speed of the steel sheet is converted into a digital signal. Memory (M
EM) 5 and the output of PG 4 is converted to the frequency voltage (F /
V) After being converted into a voltage by the conversion circuit 6, the voltage output is converted to A
A / D conversion circuit 7 converts the signal into a digital signal to generate an address signal of MEM 5, thereby reads out a corresponding amplitude correction value, and converts the amplitude correction value into an analog signal by D / A conversion circuit 8 to convert each signal into an analog signal. The signal is supplied to the other input terminal of the multiplication circuit.

The outputs of the multiplying circuits 3-1,..., 3-n are output from corresponding bandpass filters (BPF) 9-1,.
, 9-n to remove noise components other than the frequency band of the defective signal. Where each BP
For F, a variable center frequency is used, and the center frequency is determined by changing the output of the F / V conversion circuit 6 to the voltage frequency (V /
F) The control is performed based on the signal whose frequency has been converted by the conversion circuit 10, that is, according to the traveling speed of the steel sheet. The outputs of these BPFs 9-1,..., 9-n pass through corresponding squaring circuits 11-1,.
Is compared with the reference value from the reference value setting unit 13 by the comparator 14, and a defect detection signal is output when the output of the analog aggregation circuit 12 exceeds the reference value.

[0007]

However, in the signal processing as shown in FIG. 7, since there is a problem due to the low-frequency component of noise as described below, a sufficient amount of amplification and noise are actually provided. Removal may not be obtained. That is, in general, the signal output from the detection element has a larger amplitude in the low-frequency component than in the high-frequency component. Therefore, if an attempt is made to sufficiently amplify a desired detection signal (a defect signal in FIG. 7), As shown in FIG. 8, a noise component having a lower frequency than the detection signal is saturated in the power supply voltage of the amplifier. Since this saturated portion contains apparently a large amount of harmonic distortion, even if an attempt is made to remove such low-frequency components by passing such a signal through a BPF or a high-pass filter (HPF), as shown in FIG. Since these harmonic distortions not present in the noise frequency remain as noise, the high-frequency distortion may be erroneously recognized as a detection signal. Such a problem is particularly serious in online measurement in which low-frequency noise occurs due to elongation of a steel sheet, such as the above-described apparatus for detecting a defect of a steel sheet by the magnetic flux leakage inspection method.

On the other hand, if the amplification factor of the amplifier is suppressed to avoid erroneous recognition of the detection signal due to the saturation of the low frequency component as described above, the performance of the filter cannot be sufficiently exhibited as described above, and Cannot be removed effectively.

As described above, since the operation of amplifying the detection signal by the amplifier for increasing the detection sensitivity is opposite to the operation of removing the noise by the frequency filter, the amplification amount of the detection signal is conventionally determined by trial and error. . For this reason, there is a problem that the amplification amount becomes an intermediate value, and a sufficiently satisfactory detection sensitivity cannot be obtained.

The present invention has been made in view of such a conventional problem, and a first object of the present invention is to provide a signal capable of detecting a signal component in a desired frequency band with high sensitivity from an output signal of a detection element. It is intended to provide a processing method.

Further, a second object of the present invention is to provide a signal processing device appropriately configured so that the above-described signal processing method can be implemented with a simple configuration.

Further, a third object of the present invention is to provide a method for detecting a defect in a steel sheet which can detect a defect in a running steel sheet with high sensitivity by a magnetic flux leakage inspection method.

A fourth object of the present invention is to provide an apparatus for detecting a defect in a steel sheet which is appropriately configured so that the above-described defect detection method can be implemented with a simple configuration.

[0014]

In order to achieve the first object, the present invention amplifies and filters an output signal of a detection element to obtain a signal component of a desired frequency band in which a noise component is attenuated. On the other hand, the amplification and filtering processes were divided into two stages, the low-frequency components of the noise components were attenuated in the first stage amplification and filtering processes, and then the noise components were attenuated in the second stage amplification and filtering processes. It is characterized in that a signal component of a desired frequency band is obtained.

The amount of amplification in the first stage is 5 to 5 times the total amount of amplification.
The value of 0% is preferable in that a signal component in a desired frequency band is detected with high sensitivity without saturating a low frequency component of the noise component.

According to another aspect of the present invention, there is provided a signal processing apparatus for amplifying and filtering an output signal of a detection element to obtain a signal component in a desired frequency band in which a noise component is attenuated. , A first amplifying unit, a first noise attenuating unit, a second amplifying unit, and a second noise attenuating unit, which are sequentially connected in series, and at least the first noise attenuating unit has a noise component. The low frequency component is configured to be attenuated.

It is preferable that the second noise attenuating means has a high-pass filter and a low-pass filter coupled in series, since only the signal component in a desired frequency band is detected with high sensitivity.

The amplification factor in the first amplification means is set to 5 to 50% of the total amplification factor, so that a signal component in a desired frequency band can be highly sensitive without saturating a low frequency component among noise components. It is preferable in that the detection is performed.

Further, in order to achieve the third object,
According to the present invention, when detecting a defect of a running steel sheet by a leakage magnetic flux detection method, an output signal of a magnetic sensor for detecting a leakage magnetic flux generated from the steel sheet is processed by the signal processing method according to claim 1 or 2. It is characterized by the following.

In the above-described defect detection method, the filter constant in at least one of the first-stage and second-stage filtering processes is changed in accordance with the traveling speed of the steel sheet, in that the defect detection sensitivity is further increased. preferable.

Further, in order to achieve the fourth object,
The present invention provides a steel sheet defect detection device that detects a defect of a running steel sheet by a magnetic flux leakage detection method, wherein an output signal of a magnetic sensor that detects a leakage magnetic flux generated from the steel sheet is provided.
According to another aspect of the present invention, the signal processing apparatus is configured to supply the signal to the signal processing apparatus according to the third, fourth or fifth aspect of the present invention.

In the above-described defect detection device,
At least one threshold value of the second noise attenuating means is configured to be changed according to the traveling speed of the steel sheet,
This is preferable in that the detection sensitivity of defects is further increased.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an example of a steel plate defect detection device embodying the present invention. This embodiment shows a defect detecting apparatus for a steel sheet which detects a defect of a running steel sheet by a magnetic flux leakage inspection method, and is opposed to a steel sheet (not shown) which is magnetized and moves and has a large number in a width direction thereof. Magnetic sensors 21-1, as detecting elements for detecting the leakage magnetic flux of the disposed steel sheet,
, 21-n. The output of each of these magnetic sensors is
A first amplifier 22-constituting a corresponding first amplifier means;
, 22-n, and then a high-pass filter (HPF) 23-1, 23-1 constituting a first noise attenuating means.
.., 23-n to be filtered to attenuate unwanted low frequency component noise.

Each of the HPFs 23-1,..., 23-n
In order to correspond to the frequency component of the output signal of each magnetic sensor changing according to the running speed of the steel sheet, its filter constant (cutoff frequency), that is, the threshold value of the attenuating low frequency component is set to the actual value of the steel sheet. It is configured to change according to the traveling speed. Therefore, a pulse generator (PG) 24 for generating a pulse having a frequency proportional to the actual traveling speed of the steel sheet is provided, and a control value of a filter constant corresponding to each traveling speed of the steel sheet is stored in a memory (MEM) 25 in advance.
And the output of the PG 24 is counted by the counter 26 to obtain M
An address signal of the EM 25 is generated, a control value of a filter constant corresponding to the actual traveling speed is read, and the control value is passed through the proportional converter 27 to each of the HPFs 23-1,.
23-n to set respective filter constants.

The outputs of the HPFs 23-1,..., 23-n are output from the corresponding gain adjusters 28-1,.
Through the second amplifier (AM) constituting the second amplifying means.
P) 29-1,..., 29-n, and amplifies the respective amplified outputs.
,..., And 30-n to be filtered to attenuate unwanted noise components. In this embodiment, a high-pass filter (HPF) and a low-pass filter (LP
F), and the filter constant of each HPF is set to the HPF 23-1,
, 23-n, the output of the proportional converter 27 is set in proportion to the actual running speed of the steel sheet. In FIG. 1, HPFs constituting each second noise attenuating means are denoted by reference numerals 31-1,.
The PF is indicated by reference numerals 32-1,..., 32-n.

The second noise attenuating means 30-1,.
The outputs of 30-n are the corresponding full-wave rectifiers 33-1,.
., 33-n to convert the signal into a DC signal and convert the analog signal to analog signal 3
4, the output of the analog aggregation circuit 34 is compared with the reference value from the reference value setting unit 35 by the comparator 36, and when the output of the analog aggregation circuit 34 exceeds the reference value, a defect detection signal is output. To do it.

In the configuration shown in FIG. 1, each of the magnetic sensors 21-1,..., 21-n generally has a lower amplitude due to elongation of a steel plate which becomes a noise than an amplitude of a high frequency component which becomes a defect signal. A signal having a larger amplitude of the frequency component is output. Therefore, in this embodiment, the first amplifier 22
,..., 22-n are set to such an extent that the input signal can be sufficiently amplified within a range where the low-frequency signal component in the output signal does not exceed the power supply voltage of the amplifier. Specifically, the type of magnetic sensor, the type of noise,
Although it depends on the frequency band of the target signal and the like, in this embodiment, the target gain, that is, the total gain determined by both the corresponding gains of the first and second amplifiers, is generally Assuming that the gain is almost the same as that of the conventional defect detection device shown in FIG.
Range, more preferably about 10 to 20%,
,..., 22-n are set.

According to this structure, the output signal of each magnetic sensor has its low-frequency signal component, which becomes noise, saturated by the corresponding first amplifier to the power supply voltage of the amplifier as shown in FIG. 2, for example. And the frequency spectrum is as shown in FIG. 3, for example. Therefore, the outputs of the first amplifiers 22-1,..., 22-n are connected to HPs constituting the corresponding first noise attenuating means.
, 23-n, the low-frequency signal component is effectively removed, and the frequency spectrum of the output signal is, for example, as shown in FIG. The value can be made substantially equal to the peak value of the high-frequency signal component as a defect signal.

Thereafter, each of these HPFs 23-1,.
, 23-n are connected to the corresponding second amplifier 29-
, 29-n so that the total gain becomes the target gain, and outputs the amplified outputs to the corresponding second noise attenuating means 30-1,. 30-n, the amplitude and frequency spectrum of the output signal of each of the HPFs 31-1,..., 31-n are as shown in, for example, FIGS. 5 and 6, respectively. The signal component is effectively attenuated, and an output signal is obtained in which the high-frequency signal component, which is the target defect signal, is effectively amplified. Moreover, in this embodiment, the HPFs 23-1,.
, 23-n and each second noise attenuating means 30-1,.
.., HPFs 31-1,..., 3 constituting 30-n
1-n are similarly configured to attenuate the low-frequency signal component, which is a noise component, in two stages, so that a double attenuation effect can be obtained. Also, each second noise attenuating means 30-1,.
F, and the filter constant of the HPF, that is, the lower limit of the pass band (low frequency side) is made variable according to the traveling speed of the steel sheet, and the filter constant of the LPF, that is, the upper limit of the pass band (high frequency side) is fixed. Therefore, unwanted noise components can be stably removed.

Therefore, the outputs of the second noise attenuating means 30-1,..., 30-n are rectified by the corresponding full-wave rectifiers 33-1,. The output of the analog aggregation circuit 34 and the reference value from the reference value setting unit 35 are compared by a comparator 36.
As a result, it is possible to detect a defect of a running steel plate with high sensitivity without causing a detection error.

It should be noted that the present invention is not limited to only the above-described embodiment, and various modifications or changes can be made. For example, the second amplifiers 29-1,..., 2
9-n preceding stage gain adjusters 28-1,..., 28-
n can also be omitted. In the above-described embodiment, the HPF 23-
,..., 23-n and each second noise attenuating means 30
-1,..., 30-n, HPFs 31-1,.
, 31-n are configured such that the filter constant is variable according to the traveling speed of the steel sheet. At least one of the filter constants of the HPFs 31-1,. 23-n may be fixed according to the traveling speed, and the filter constants of the preceding HPFs 23-1,..., 23-n may be fixed. In both cases, the filter constant can be fixed.

Further, each second noise attenuating means 30-1,
,..., 30-n can also be constituted by bandpass filters. Further, in the above-described embodiment, the purpose is determined by the first amplifiers 22-1,..., 22-n and the corresponding second amplifiers 29-1,. Although the total amplification amount has been described as being substantially the same as that of the conventional defect detection device, in the case of the above embodiment,
The signals input to the second amplifiers 29-1,..., 29-n are, as shown in FIG. 4, for example, as shown in FIG. Since the peak value and the peak value of the high-frequency signal component, which is a defect signal, can be made substantially equal, the amplification factor of these second amplifiers can be increased, and the target amplification factor can be made larger than in the conventional defect detection device. . This makes it possible to detect defects with higher sensitivity.

Further, the present invention provides a signal processing method for amplifying and filtering an output signal of a detecting element to obtain a signal component of a desired frequency band in which a noise component is attenuated, in addition to the above-described apparatus for detecting a defect of a steel plate. And can be widely applied to equipment.

[0034]

As described above, according to the signal processing method of the present invention, when the output signal of the detection element is amplified and filtered to obtain a signal component of a desired frequency band in which a noise component is attenuated, The amplification and filtering processes are divided into two stages, and the first-stage amplification and filtering processes attenuate the low-frequency components of the noise components, and then the second-stage amplification and filtering processes attenuate the noise components. , A signal component in a desired frequency band can be detected with high sensitivity.

Further, according to the signal processing apparatus of the present invention, the first amplifying means, the first noise attenuating means, the second amplifying means, and the second noise attenuating means are sequentially connected in series. At least the first noise attenuating means obtains a signal component in a desired frequency band in which the noise component has been attenuated from the output signal of the detection element with a simple configuration in which the low frequency component of the noise component is attenuated. Can be.

Further, according to the method for detecting a defect of a steel sheet by the magnetic flux leakage inspection method according to the present invention, the output signal of the magnetic sensor for detecting the leakage magnetic flux generated from the running steel sheet is used as the signal processing method according to the present invention. Therefore, the defect of the steel plate can be detected with high sensitivity.

Further, according to the apparatus for detecting a defect of a steel sheet by the magnetic flux leakage inspection method according to the present invention, the output signal of the magnetic sensor for detecting the leakage magnetic flux generated from the running steel sheet is used as the signal processing apparatus according to the present invention. It is possible to detect defects in a steel sheet with high sensitivity by using a simple structure for supplying the steel sheet to the processing.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an example of a steel sheet defect detection device embodying the present invention.

FIG. 2 is a diagram illustrating an example of a waveform of an output signal of a first amplifier illustrated in FIG. 1;

FIG. 3 is a diagram showing an example of a frequency spectrum.

FIG. 4 is a diagram illustrating an example of a frequency spectrum of an output signal of a high-pass filter included in the first noise attenuator illustrated in FIG. 1;

FIG. 5 is a diagram showing an example of a waveform of an output signal of a high-pass filter constituting the second noise attenuating means shown in FIG.

FIG. 6 is a diagram showing an example of a frequency spectrum.

FIG. 7 is a block diagram showing a configuration of a conventional steel plate defect detection device.

8 is a diagram showing a waveform of an output signal of the amplifier shown in FIG.

9 is a diagram showing a waveform of an output signal of the bandpass filter shown in FIG.

[Explanation of symbols]

21-1 to 21-n Magnetic sensor 22-1 to 22-n First amplifier 23-1 to 23-n High-pass filter (first noise attenuation means) 24 pulse generator 25 memory 26 counter 27 proportional converter 28- 1-28-n gain adjuster 29-1 to 29-n second amplifier 30-1 to 30-n second noise attenuation means 31-1 to 31-n high-pass filter 32-1 to 32-n low-pass filter 33-1 to 33-n Full-wave rectifier 34 Analog collective circuit 35 Reference value setting device 36 Comparator

Claims (9)

[Claims] 1. Amplifying and filtering an output signal of a detection element to obtain a signal component in a desired frequency band in which a noise component has been attenuated, dividing the amplification and filtering into two stages. A signal processing method comprising: attenuating a low-frequency component of noise components in a filtering process; and obtaining a signal component in a desired frequency band in which the noise component has been attenuated in a second-stage amplification and filtering process. 2. The signal processing method according to claim 1, wherein the first-stage amplification amount is set to 5 to 50% of a total amplification amount. 3. A signal processing apparatus for amplifying and filtering an output signal of a detection element to obtain a signal component of a desired frequency band in which a noise component is attenuated, wherein the first amplifying means is sequentially coupled in series. , A first noise attenuating means, a second amplifying means and a second noise attenuating means, wherein at least the first noise attenuating means is configured to attenuate a low frequency component of the noise component. A signal processing device characterized by the above-mentioned. 4. The signal processing device according to claim 3, wherein said second noise attenuating means has a high-pass filter and a low-pass filter coupled in series. 5. The signal processing device according to claim 3, wherein an amplification factor of the first amplifying unit is set to 5 to a total amplification factor.
A signal processing device characterized in that the ratio is 50%. 6. An output signal of a magnetic sensor for detecting a leakage magnetic flux generated from the steel sheet when detecting a defect of the running steel sheet by a leakage magnetic flux flaw detection method, according to claim 1 or 2. A method for detecting a defect in a steel sheet, comprising: 7. The method for detecting a defect of a steel sheet according to claim 6, wherein a filter constant in at least one of the first-stage and second-stage filtering processes is changed according to a traveling speed of the steel plate. Steel sheet defect detection method. 8. A steel sheet defect detecting apparatus for detecting a defect of a running steel sheet by a magnetic flux leakage inspection method, wherein an output signal of a magnetic sensor for detecting a leakage magnetic flux generated from the steel sheet is output. A defect detection device for a steel plate, wherein the defect detection device is configured to supply the signal to the signal processing device of (1). 9. The apparatus for detecting a defect of a steel sheet according to claim 8, wherein at least one of the threshold values of the first and second noise attenuating means is changed according to a traveling speed of the steel sheet. A steel sheet defect detection device.