JP2018009866A - Signal processing device and signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To favorably extract a component associated with change of a magnetic field coming from a magnetic leakage flux from a signal detected by a magnetic sensor in a magnetic leakage flux flaw detection method using an AC magnetic field.SOLUTION: A signal processing device 4 included in a magnetic leakage flux flaw detection system 1 comprises a signal acquisition unit 11 that acquires a magnetic signal associated with secular change of a magnetic field detected in a magnetic sensor 3 by the magnetic sensor 3 scanning on a flaw detection surface E of an object O applied with an AC magnetic field, a processing unit 12 that subtracts a mean value for a latest predetermined interval respectively for each point included in the magnetic signal acquired in the signal acquisition unit, and an output unit 14 that outputs the magnetic signal after processing in the processing unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a signal processing apparatus and a signal processing method.

  As a nondestructive inspection method using a magnetic sensor for detecting a flaw (JIS Z 2300: 2009) on the surface layer of an object, a magnetic flux leakage method (Magnetic Flux Leakage: MFL) is known. The leakage magnetic flux flaw detection method is a method in which a magnetic sensor is used to measure a change in a magnetic field due to a magnetic flux leaking from a flaw by magnetizing a flaw detection surface of an object. In the leakage magnetic flux flaw detection method, either a DC magnetic field or an AC magnetic field is applied as a method of magnetizing the flaw detection surface of the object. For example, Patent Document 1 discloses a configuration for detecting a leakage magnetic flux after applying an alternating magnetic field to an object.

JP-A-1-248050

  The method of detecting the magnetic field due to the magnetic flux that leaks because the AC magnetic field cannot be applied to the flaw detection surface is known to have excellent surface flaw detectability because the magnetic flux concentrates on the surface side of the material due to the skin effect. It has been. On the other hand, when an alternating magnetic field is applied, the magnetic flux in the object always changes, so the magnetic sensor also detects this change in magnetic flux. In addition, noise associated with application of an alternating magnetic field is also mixed. Therefore, it may be difficult to detect the magnetic field derived from the leakage magnetic flux.

  The present invention has been made in view of the above, and it is possible to suitably extract a component related to a change in a magnetic field derived from a leakage magnetic flux from a signal detected by a magnetic sensor in a leakage magnetic flux flaw detection method using an alternating magnetic field. It is an object to provide a simple signal processing apparatus and signal processing method.

  In order to achieve the above object, a signal processing apparatus according to an aspect of the present invention is configured to cause a magnetic sensor to scan a flaw detection surface of an object to which an AC magnetic field is applied, so that the time of the magnetic field detected by the magnetic sensor is increased. A signal acquisition unit that acquires a magnetic signal related to a local change, a processing unit that subtracts the average of the nearest predetermined intervals for each point included in the magnetic signal acquired by the signal acquisition unit, and a process performed by the processing unit And an output unit for outputting the magnetic signal after being processed.

  In addition, the signal processing method according to an aspect of the present invention includes a magnetic sensor that scans a flaw detection surface of an object to which an alternating magnetic field is applied, thereby detecting a magnetic field related to a temporal change in the magnetic field detected by the magnetic sensor. A signal acquisition step of acquiring a signal, a processing step of subtracting the average of the most recent predetermined section for each point included in the magnetic signal acquired in the signal acquisition step, and a magnetic field after being processed in the processing step And an output step for outputting a signal.

  According to the signal processing apparatus and the signal processing method, the process of subtracting the average of the latest predetermined section is performed on the magnetic signal acquired by the signal acquisition unit. By subtracting the average, it becomes possible to remove the noise component derived from the measurement by the magnetic sensor with an alternating magnetic field applied, and the magnetic signal after processing changes the magnetic field derived from the leakage magnetic flux. It becomes possible to extract the component which concerns on suitably.

  Here, the said process part can be set as the aspect which further performs a frequency filter process about the said magnetic signal after deducting the average of the said predetermined area.

  As described above, the component associated with the application of the AC magnetic field can be canceled by further performing frequency filtering on the magnetic signal after the average of the most recent predetermined interval is subtracted. Therefore, in the magnetic signal after processing, a component related to the change in the magnetic field derived from the leakage magnetic flux is more preferably extracted.

  The predetermined section may be an integer multiple of the frequency of the alternating magnetic field applied to the object.

  As described above, when the predetermined section when subtracting the average is made to correspond to the frequency of the AC magnetic field, it is possible to remove the noise component in a state where the component that fluctuates due to the application of the AC magnetic field is canceled. Thus, it is possible to suitably extract a component relating to a change in the magnetic field derived from the leakage magnetic flux.

  ADVANTAGE OF THE INVENTION According to this invention, the signal processing apparatus and signal processing which can extract suitably the component which concerns on the change of the magnetic field derived from the leakage magnetic flux from the signal detected by the magnetic sensor in the leakage magnetic flux flaw detection method using an alternating current magnetic field A method is provided.

1 is a diagram showing a schematic configuration of a leakage magnetic flux flaw detection system including a signal processing device according to an embodiment of the present invention. It is a figure explaining the leakage magnetic flux flaw detection method. It is a figure explaining the signal processing method by a signal processor. It is a figure which shows the example of the magnetic signal detected by a magnetic sensor. It is a figure which shows the result of having calculated the moving average from the magnetic signal. It is a figure which shows the result of having deducted the moving average from the signal of FIG. It is a figure which shows the result of having performed the frequency filter process with respect to FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram showing a schematic configuration of a leakage magnetic flux flaw detection system 1 including a signal processing device according to an embodiment of the present invention. A leakage magnetic flux flaw detection system 1 shown in FIG. 1 is a system that performs inspection by a magnetic flux flux detection method (Magnetic Flux Leakage: MFL), which is a kind of nondestructive inspection using magnetic field measurement.

  As shown in FIG. 2 (A), the leakage magnetic flux flaw detection method is an inspection method that uses a magnetic sensor T to search for a flaw X that may exist on the surface or surface of an object O made of a ferromagnetic material. . As shown in FIG. 2B, in the leakage magnetic flux flaw detection method, a magnetic flux F in a predetermined direction is generated on the object O by magnetizing the object O by various methods. When there is a flaw X that blocks the magnetic flux F, a leakage magnetic flux Fa is generated due to the flaw X. By causing the magnetic sensor T to scan in the scanning direction D on the flaw detection surface E of the object O, the leakage magnetic flux Fa is detected. The leakage magnetic flux flaw detection method using a signal from the magnetic sensor T has an advantage that the flaw detection automation and the digitization of the result are easier than the magnetic particle flaw detection method conventionally employed.

  Returning to FIG. 1, the leakage magnetic flux flaw detection system 1 will be described. The leakage magnetic flux inspection system 1 includes an AC magnetizer 2 that applies an AC magnetic field to a test surface E of a ferromagnetic object O, and a magnetic sensor that detects a magnetic field in the vicinity of the test surface E to which an AC magnetic field is applied. 3 and a signal processing device 4 for processing a signal related to the magnetic field detected by the magnetic sensor 3.

  The AC magnetizer 2 is an AC interpole magnetizer, and an AC magnetic field is applied to the substantially U-shaped magnetizer 21 whose both ends are in contact with the flaw detection surface of the object O. By forming, an alternating magnetic field is applied to the object O between both ends of the magnetizer 21. In this state, the magnetic sensor 3 is scanned along the flaw detection surface E of the object O to which an AC magnetic field is applied, thereby measuring the magnetic field in the vicinity of the flaw detection surface E. The magnetic sensor 3 outputs an electrical signal corresponding to the detected magnitude of the magnetic field to the signal processing device 4.

  The magnetic sensor 3 is a sensor capable of measuring the magnitude of the magnetic field in the vicinity of the flaw detection surface E. Specifically, the magnetic sensor 3 includes an MI (Magneto-Impedance) sensor, a GMR (Giant Magneto Resistive effect) sensor, a TMR (Tunnel Magneto-Resistance) sensor, an AMR (Anisotropic Magneto-Resistance) sensor, and an FG (Flux-Flux- Gate) sensors, Hall elements, SQUID (Superconducting Quantum Interference Device) sensors, coils, and the like can be used. As shown in FIG. 1, the magnetic sensor 3 is disposed at a position facing the flaw detection surface E of the object O. The magnetic sensor 3 and the flaw detection surface E may be in contact with each other, or the magnetic sensor 3 and the flaw detection surface E may be separated from each other. Further, when the magnetic sensor 3 and the flaw detection surface E are separated from each other, it is preferable to keep the distance between the magnetic sensor 3 and the flaw detection surface E constant. An electrical signal corresponding to the magnitude of the magnetic field detected by the magnetic sensor 3 in the vicinity of the flaw detection surface E is output from the magnetic sensor 3 to the signal processing device 4.

  The signal processing device 4 has a function of acquiring a magnetic signal that is an electrical signal from the magnetic sensor 3 and extracting a change in a signal derived from a flaw from the magnetic signal. The magnetic signal from the magnetic sensor 3 is a signal related to the change over time of the magnetic field detected by the magnetic sensor. As described above, an alternating magnetic field is applied to the object O when measuring the leakage magnetic flux. Therefore, the magnetic sensor 3 detects not only the leakage magnetic flux but also the change of the magnetic flux in the object O derived from the application of the alternating magnetic field. The signal processing device 4 removes a component that changes due to application of an alternating magnetic field from a signal that indicates a change in the magnetic field detected by the magnetic sensor 3 and extracts only a component that originates from the leakage magnetic flux.

  The signal processing device 4 includes a CPU (Central Processing Unit), a RAM (Random Access Memory) and a ROM (Read Only Memory) that are main storage devices, a communication module that performs communication with other devices, and an auxiliary device such as a hard disk. The computer is configured with hardware such as a storage device. And the function as the control part 5 is exhibited when these components operate | move.

  As shown in FIG. 1, the signal processing device 4 includes a signal acquisition unit 11, a processing unit 12, a processing condition storage unit 13, and an output unit 14.

  The signal acquisition unit 11 has a function of acquiring an electrical signal related to the magnitude of the magnetic field measured by the magnetic sensor 3. The electrical signal acquired by the signal acquisition unit 11 is sent to the processing unit 12.

  The processing unit 12 removes a component related to a magnetic field that changes due to application of an alternating magnetic field from the electric signal (magnetic signal) from the magnetic sensor 3 acquired by the signal acquisition unit 11, and generates a magnetic field derived from leakage magnetic flux. The process which extracts only the component which concerns on is performed. Although specific processing will be described later, the processing unit 12 performs processing for calculating an average (moving average in this embodiment) and subtracting the calculation result from the magnetic signal, and frequency filtering processing.

  The processing condition storage unit 13 has a function of storing processing conditions when the processing unit 12 performs processing related to extraction of components derived from leakage magnetic flux. The processing conditions may include conditions set according to the AC magnetizer 2. Further, the processing conditions may be set in advance by the user of the leakage magnetic flux flaw detection system 1. As described above, when the condition for processing the electrical signal from the magnetic sensor 3 in the processing unit 12 is determined in advance, the condition is stored in the processing condition storage unit 13. And when the process which concerns on an electrical signal in the process part 12 is implemented, a process is performed with reference to the information stored in the process condition storage part 13. FIG.

  The output unit 14 has a function of outputting an electrical signal after being processed by the processing unit 12. Although the output method is not particularly limited, for example, a method of displaying on a monitor or the like, a method of transmitting the image data to another apparatus, or the like can be used. In the signal processing device 4, when the position information of the magnetic sensor 3 is also acquired, the signal processing device 4 may be configured to output in correspondence with the position information of the magnetic sensor 3.

  Next, a signal processing method in the signal processing device 4 of the leakage magnetic flux flaw detection system 1 will be described with reference to FIGS. FIG. 3 is a flowchart for explaining the signal processing method. 4 to 7 are diagrams illustrating the results of various processes performed by the processing unit 12.

  First, in the magnetic flux leakage flaw detection system 1, while an AC magnetic field is applied to the flaw detection surface of the object O and its periphery by the AC magnetizer 2, a region where the AC magnetic field is applied by the magnetic sensor 3 is scanned. Thereby, the magnetic sensor 3 detects a magnetic field on the flaw detection surface of the object O, and outputs an electric signal (magnetic signal) corresponding to the magnitude of the magnetic field to the signal processing device 4. The signal acquisition unit 11 of the signal processing device 4 acquires an electrical signal (magnetic signal) corresponding to the change in the magnetic field detected by the magnetic sensor 3 (S01: signal acquisition step).

  FIG. 4 shows an example of a magnetic signal output from the magnetic sensor 3. In the example shown in FIG. 4, the magnetic field detected by the magnetic sensor 3 when the magnetic sensor 3 is reciprocated on the flaw detection surface of the object O on which the scratch is provided after the operation of the AC magnetizer 2 is started. Is detected as the output amplitude. In FIG. 4, the magnetic signal from the magnetic sensor 3 is plotted with the number of data points from the start of acquisition of the magnetic signal as the horizontal axis and the output amplitude of the magnetic signal as the vertical axis. FIG. 4 also shows an operation start T1 and an operation end T2 of the AC magnetizer 2. FIG. 4 shows the results of measurement with the AC frequency by the AC magnetizer 2 being 50 Hz and the sampling frequency of the magnetic sensor 3 being 5000 Hz. As shown in FIG. 4, when an alternating magnetic field is applied near the flaw detection surface of the object O by the alternating current magnetizer 2, fluctuations in alternating magnetic flux in the object O resulting from the application of the alternating magnetic field and the alternating current magnetizer 2. The magnetic flux in the vicinity of the flaw detection surface changes under the influence of mechanical noise or electrical noise derived from the above operation or movement of the magnetic sensor 3. Thus, the measurement by the magnetic sensor 3 is performed in a state where it is difficult to detect only the change in magnetic flux derived from the leakage magnetic flux derived from the flaw of the object O that is the original detection target as a magnetic field. .

  Therefore, the processing unit 12 performs two processes on the magnetic signal from the magnetic sensor 3. As the first process, a process related to subtraction of the moving average is performed. Specifically, a moving average is calculated for the magnetic signal from the magnetic sensor 3 (S02: processing step). Then, the calculated moving average is subtracted (subtracted) from the output amplitude of each point of the magnetic signal from the magnetic sensor 3 (S03: processing step). For example, the processing condition relating to the calculation of the moving average may be stored in the processing condition storage unit 13 or may be directly designated by the user.

  FIG. 5 is a diagram showing a result of calculating a simple moving average as a moving average for the magnetic signal shown in FIG. Here, the average of every 100 most recent data points is calculated as the moving average. The 100 points are data points corresponding to one cycle of the alternating magnetic field. As described above, when the moving average is calculated using the data points corresponding to one cycle of the alternating magnetic field, the component related to the magnetic field that varies due to the alternating magnetic field can be canceled. When data in a section corresponding to an integral multiple of the period of the AC magnetic field is used for the moving average, the component related to the magnetic field that varies due to the AC magnetic field can be canceled as described above. Even when the section that does not correspond to the period of the alternating magnetic field is selected as the section of the data used for the moving average, the component related to the magnetic field that varies due to the alternating magnetic field is averaged. Therefore, the data section used for the moving average can be changed as appropriate.

  As shown in FIG. 5, when the moving average is calculated, irregularities whose period is not constant are seen in the vicinity of the data points 4000 to 14000. These components are components mainly derived from mechanical noise or electrical noise. In this way, when the moving average is calculated, a component derived from noise can be extracted.

  FIG. 6 shows a result of subtracting the calculation result of the simple moving average shown in FIG. 5 from each point of the magnetic signal shown in FIG. Comparing FIG. 4 and FIG. 6, it can be seen that the concavo-convex component existing in the vicinity of the data points 4000 to 14000 is small. That is, a component derived from noise can be removed.

  In FIG. 6, there are components whose output amplitude changes finely as in FIG. 4. This is a component derived from an alternating magnetic field. Therefore, frequency filter processing is performed as second processing (S04: processing step). For example, the processing conditions related to the frequency filter processing may be stored in the processing condition storage unit 13 or may be directly designated by the user.

  FIG. 7 is a diagram illustrating a result after the frequency filter process is performed on the waveform illustrated in FIG. 6. In FIG. 7, the components in the region corresponding to the frequency of the alternating magnetic field are cut. Specifically, the high frequency cutoff frequency is set to 70 Hz, the low frequency cutoff frequency is set to 30 Hz, and processing for preferentially transmitting an electric signal having an AC magnetic field frequency of 50 Hz is performed. As a result, as shown in FIG. 7, the periodic magnetic field change component due to the AC magnetic field is canceled, the data between the operation start T1 and the operation end T2 of the AC magnetizer 2 is flattened, and the magnetic sensor Only the peak S of the electric signal derived from the leakage magnetic flux detected when 3 passes over the scratch (in FIG. 7, 10 peaks appear) is extracted. As described above, in the signal processing device 4, only the component derived from the leakage magnetic flux can be extracted by performing the subtraction of the moving average component and the frequency filter processing on the magnetic signal from the magnetic sensor 3. .

  Then, the information regarding the magnetic signal after this process is output as an output result from the output part 14 (S05: output step). Thus, a series of processes related to signal processing by the signal processing device 4 is completed.

  As described above, according to the signal processing device 4 and the signal processing method according to the present embodiment, with respect to the magnetic signal acquired from the magnetic sensor, first, by performing the process of subtracting the moving average, Can remove different components, that is, components derived from noise or the like. Furthermore, by performing the frequency filter processing, it is possible to remove a component of a periodic magnetic flux change caused by applying an alternating magnetic field. As a result, the component derived from the leakage magnetic flux that is the original detection target can be suitably extracted from the magnetic signal from the magnetic sensor 3.

  Further, the processing related to the extraction of the component derived from the leakage magnetic flux in the signal processing device 4 does not need to be performed in conjunction with the AC magnetic field applied to the object O by the AC magnetizer 2. It is a simple process. In order to specify a magnetic field change or noise component accompanying application of an alternating magnetic field, it is common to first specify a component derived from an alternating magnetic field applied to the object O. Therefore, for example, it is necessary to perform processing in conjunction with the AC magnetizer 2 and the signal processing device 4 such as receiving a signal from the AC magnetizer 2 that applies an AC magnetic field to the object O on the signal processing device 4 side. there were. On the other hand, according to the method described in the present embodiment, even if the information related to the AC magnetic field applied by the AC magnetizer 2 is not held by the signal processing device 4, the detection target is detected from the magnetic signal from the magnetic sensor 3. The component originating in the leakage magnetic flux which is can be extracted suitably. Therefore, the signal processing device 4 according to the present embodiment can be used in combination with AC magnetizers that apply AC magnetic fields at different frequencies.

  The processing unit 12 may be configured not to perform frequency filter processing. When at least a component derived from noise or the like is removed using a moving average, a component that periodically changes due to application of an alternating magnetic field and a component that originates from leakage magnetic flux remain in the processed signal. Since the component accompanying the application of the alternating magnetic field is a periodic change, it can be easily distinguished from the non-periodic component derived from the leakage magnetic flux. Therefore, if a component derived from noise or the like is removed using at least a moving average, a component derived from leakage magnetic flux can be suitably extracted. However, as described in the above embodiment, when the frequency filter process is performed, the portion related to the periodic change can also be canceled, so that the component derived from the leakage magnetic flux becomes significant as shown in FIG. Magnetic signals can be obtained.

  Moreover, in the said embodiment, the predetermined area at the time of subtracting a moving average is made to respond | correspond to the frequency of an alternating current magnetic field. In this case, it is possible to remove the noise component in a state where the component that fluctuates due to the application of the alternating magnetic field is canceled, so that it is possible to suitably extract the component related to the change in the magnetic field derived from the leakage magnetic flux. Become.

  As described above, the leakage magnetic flux flaw detection system 1 including the signal processing device 4 and the signal processing method according to the embodiment of the present invention have been described, but the present invention is not necessarily limited to the above-described embodiment, and does not depart from the gist thereof. Various changes can be made in the range.

  For example, although the case where the signal processing device 4 is realized by one device has been described in the above embodiment, the signal processing device 4 may be configured by a plurality of devices.

  The means for applying an AC magnetic field to the object O is not limited to the AC magnetizer 2 described in the above embodiment, and a known method can be used.

  In the above-described embodiment, after the signal processing device 4 acquires a set of magnetic signals related to the temporal change of the magnetic field detected by the magnetic sensor 3, a series of processing related to extraction of components derived from leakage magnetic flux is performed. Explained the case. However, a series of processes related to extraction of components derived from leakage magnetic flux can be performed simultaneously with the measurement of the magnetic field by the magnetic sensor 3. That is, the signal processing device 4 may be configured to acquire the magnetic signal sent from the magnetic sensor 3 and perform the processing related to the subtraction of the moving average and the frequency filter processing while outputting the magnetic signal, and output the processed magnetic signal. . With such a configuration, the magnetic signal from the magnetic sensor 3 can be processed and output in real time by the signal processing device 4.

  Further, in the above embodiment, the case where the simple moving average is used among the moving averages as the average for the magnetic signal has been described. However, the moving average obtained by changing the weighting for each data such as the weighted moving average and the exponential moving average is used. It may be used. An average different from the moving average may be used. Examples of the average different from the moving average include, for example, the average of several points selected from the average of all data included in a predetermined section. Thus, the average calculation method for removing the component derived from noise can be changed as appropriate.

DESCRIPTION OF SYMBOLS 1 Leakage magnetic flux inspection system 2 AC magnetizer 3 Magnetic sensor 4 Signal processing device 11 Signal acquisition part 12 Processing part 13 Processing condition storage part 14 Output part 21 Magnetizer 22 AC power supply E Test surface O Object

Claims (4)

A signal acquisition unit that acquires a magnetic signal related to a temporal change of the magnetic field detected by the magnetic sensor by scanning the flaw detection surface of the object to which the alternating magnetic field is applied;
For each point included in the magnetic signal acquired in the signal acquisition unit, a processing unit for subtracting the average of the most recent predetermined section,
An output unit for outputting a magnetic signal after being processed in the processing unit;
A signal processing apparatus.   The signal processing apparatus according to claim 1, wherein the processing unit further performs frequency filter processing on the magnetic signal after subtracting an average of the predetermined section.   The signal processing apparatus according to claim 1, wherein the predetermined section is an integer multiple of a frequency of an alternating magnetic field applied to the object. A signal acquisition step of acquiring a magnetic signal related to a change over time of the magnetic field detected by the magnetic sensor by scanning the flaw detection surface of the object to which the alternating magnetic field is applied;
For each point included in the magnetic signal acquired in the signal acquisition step, a processing step of subtracting the average of the nearest predetermined section, respectively,
An output step of outputting a magnetic signal after being processed in the processing step;
A signal processing method.

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