KR102083599B1 - Apparatus and method for measuring thickness of construction - Google Patents

Abstract

Structure thickness measuring apparatus according to the present invention, the IDT (Interdigital transducers) sensor for generating a predetermined wave so that the surface wave propagates along the structure, a scanning unit for scanning the vibration generated in the structure, the scanning from the scanning unit And a signal processor configured to calculate a thickness of the structure based on a signal collector configured to measure a vibration signal of the structure and the vibration signal measured by the signal collector. In particular, the frequency and wavelength of the surface wave generated by the IDT sensor is characterized in that it is calculated based on the wave sensitivity and mode separation degree determined according to the material and thickness of the structure.

Description

Structure thickness measuring apparatus and method {APPARATUS AND METHOD FOR MEASURING THICKNESS OF CONSTRUCTION}

The present invention relates to an apparatus, a method and a system for measuring the thickness of a structure and the occurrence of wall thinning by using an interdigital transducer (IDT) sensor.

As structures installed in plants, including nuclear power plants, age, the thinning of the structures occurs. The thinned structure may fail to withstand the design internal pressure and cause damage. Therefore, in order to prevent this, a device for measuring the thickness and defects of the structure in advance is called a structure thickness measuring device.

In general, the structure thickness measurement apparatus measures the thickness of the structure using a technique using ultrasonic waves, vibration signals and pulses. Specifically, the structure thickness measuring device is configured to transmit the ultrasonic wave, vibration signal or pulse signal of the structure to the structure, and receive the signal reflected back from the portion of the thin or defective structure to inspect the state of the structure.

Regarding the structure thickness measurement apparatus, Korean Patent No. 10-1764706 (Date of Registration, July 28, 2017) discloses a structure thickness measurement system and its measuring method using a local spatial wave number filtering technique. .

The system for measuring the thickness of a structure disclosed in Korean Patent No. 10-1764706 includes a piezoelectric element (PZT) bonded to a structure to be inspected and a mirror for implementing scanning to generate image information related to the thickness of the structure. And a laser Doppler Vibrometer (LDV) for collecting signals related to thickness, and a signal processor for processing the collected signals.

However, this configuration alone can be confirmed only when the thickness of the structure to be inspected is reduced by about 25% or more compared to the normal thickness, so that detailed monitoring is difficult. In order to ensure the safety of the structure, it is necessary to detect the change in thickness more than 25% in the actual field, and the need to represent the thickness change as image information.

That is, since the excitation part disclosed in Korean Patent No. 10-1764706 is composed only of a contact piezoelectric element or a non-contact vibration sensor, it is limited to perform more detailed monitoring.

Recently, IDT sensors, which are sensors for structural health monitoring, have been developed and researched. Interdigital transducers (IDT) sensors generate surface waves {SAW (Surface Acoustic Wave) or Rayleigh wave} by applying a voltage to electrodes arranged in a comb pattern on the piezoelectric material. Refers to a method of evaluating the integrity of a structure (eg, measuring the skin's thickness) using generated surface waves. Here, the IDT sensor refers to an apparatus for constructing an electrode using a cutting technique on flat piezoelectric substrates and for generating or receiving a surface wave by applying a voltage to the electrode.

An object of the present invention is to provide a structure thickness measuring apparatus and method that can visualize the thickness of the structure, the initial thickness change of the structure.

It is also an object of the present invention to provide a structure thickness measuring apparatus and method that can detect the thickness or thinning of a structure using surface waves, and further image the thickness change of the structure.

As a means for solving the above problems, the structure thickness measuring apparatus according to the present invention, the IDT (Interdigital transducers) sensor for generating a predetermined wave, so that the surface wave propagates along the structure, to scan the vibration generated in the structure It includes a scanning unit, a signal collecting unit for measuring the vibration signal of the structure scanned from the scanning unit, and a signal processing unit for calculating the thickness of the structure based on the vibration signal measured by the signal collection unit. In particular, the frequency and wavelength of the surface wave generated by the IDT sensor is characterized in that it is calculated based on the wave sensitivity and mode separation degree determined according to the material and thickness of the structure.

By the above means, the structure thickness measuring apparatus according to the present invention can monitor the thickness of the structure in detail.

Specifically, the structure thickness measuring apparatus according to the present invention, the effect that can detect a thickness change of about 5% is derived.

1 is a conceptual diagram showing a conventional structure thickness measuring apparatus.
FIG. 2 is a graph related to the operation of the structure thickness measuring apparatus shown in FIG. 1. FIG.
3 is a graph related to the operation of the structure thickness measuring apparatus shown in FIG.
Figure 4a is a conceptual diagram showing an IDT sensor included in the structure thickness measuring apparatus according to the present invention.
Figure 4b is a conceptual diagram showing an IDT sensor included in the structure thickness measuring apparatus according to the present invention.
5 is a flowchart illustrating a structure monitoring method according to the present invention.
6 is a conceptual view showing the inspection target of the structure thickness measuring apparatus according to the present invention.
7a to 7c are graphs relating to the operation of the structure thickness measurement apparatus according to the present invention.
8a to 8c are graphs related to the operation of the structure thickness measurement apparatus according to the present invention.
9 is a conceptual diagram showing an image generated by the structure thickness measuring apparatus according to the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, the structure thickness measuring apparatus and system which concern on this invention are demonstrated in detail with reference to drawings.

Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the following description of the embodiments disclosed herein, if it is determined that the detailed description of the related known technology may obscure the gist of the embodiments disclosed herein, the detailed description thereof will be omitted.

In the present specification, the same or similar reference numerals are used to designate the same or similar components in different embodiments and modifications, and duplicate description thereof will be omitted.

The accompanying drawings are only for easily understanding the embodiments disclosed in the present specification, and the technical idea disclosed in the present specification is not limited by the accompanying drawings, and all changes and equivalents included in the spirit and scope of the present invention are provided. It should be understood to include water or substitutes.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

1 shows an embodiment of a conventional structure thickness measuring apparatus.

As shown in FIG. 1, the structure thickness measuring apparatus includes a PZT excitation part 20 bonded to the structure to be inspected 31.

In addition, the structure thickness measuring apparatus may include a scanning unit, a signal collecting unit 33 and a signal processing unit 34 formed of a plurality of mirrors (Horizontal mirror, Vertical mirror).

 As shown in FIG. 1, the PZT excitation unit 20, the scanning unit 200, the signal collection unit 33, and the signal processing unit 34 may be connected by wire or wirelessly to transmit and receive signals and data. It is preferably carried out according to the instructions of the administrator (worker).

In addition, the defect information including the final thickness of the structure calculated by the signal processor 34 is preferably transmitted to a separate monitoring means (not shown) so that the manager (worker) can easily check.

To learn more about each configuration, the PZT excitation unit 20 may transmit a continuous wave excitation to the structure to be measured. In detail, the PZT excitation unit 20 may include a contact piezoelectric element or a non-contact vibration sensor, and may transmit an excitation of several kHz to several MHz according to a manager's instruction.

The PZT excitation unit 20 further includes power amplification means 31 and waveform generation means 32 for setting a frequency band of continuous wave excitation transmitted to the structure to be measured and amplifying the power according to the set frequency band. It is preferable to be configured.

The power amplifying means 31 and the waveform generating means 32 may control the PZT excitation unit 20 to set the frequency band of the continuous wave excitation transmitted to the structure to be measured under the control of the manager.

The scanning unit 200 may scan the vibration generated in the structure by the continuous wave excitation of the PZT excitation unit 20. As shown in FIG. 1, the scanning unit 200 may scan vibration generated in a structure to be scanned, means for irradiating a laser to the vibrating structure, and scan the structure in a predetermined direction and reflect the same. It is preferably configured to include means for scanning a laser.

The signal collection unit 33 may measure the vibration signal of the structure scanned from the scanning unit 200 and transmit it to the signal processing unit 34.

The signal collecting unit 33 is composed of a laser doppler vibrometer (LDV).

The signal processor 34 may measure the thickness of the structure by analyzing the vibration signal measured by the signal collector 33 using a local spatial wave number filtering technique.

In detail, the signal processor 34 may perform bandpass filtering to extract a single frequency component of the vibration signal measured by the signal collector 33 and the vibration signal in the form of a three-dimensional matrix. In order to transform a into a 2D matrix, Fast Fourier Transform (FFT) may be performed to obtain a Steady State Response signal.

Using the steady state response signal, a predetermined mode is separated and a local wavenumber filter technique is used to calculate a scattering diagram for each thickness of the structure, and then the correlation between the wave number and the thickness of the structure is calculated. To calculate the final thickness of the structure using this.

In addition, through the thickness of the structure, it is possible to effectively predict the position of the defect, the depth, the size of the defect included in the structure.

Here, since the wave number is inversely proportional to the wavelength, the thinner the wave number, the larger the wave number and the thinner the wave number. By using this, a correlation between the wave number and the thickness of the structure may be calculated to finally calculate the thickness of the structure.

In other words, in the signal processor 34, the vibration signal measured from the LDV of the signal collector 33 through the scanning unit 200 may be represented as V [x, y, t] in the form of a three-dimensional matrix. The bandpass filtering may be performed to extract a single frequency component included in the vibration signal.

In addition, in order to convert the 3D matrix form into the 2D matrix form, the FFT may be performed to obtain a steady state response signal having only a frequency component f0.

By performing 2D FFT on the acquired steady-state response signal, V [kx, ky, f0] can be calculated, and after removing the preset mode (eg, S0 mode), removing the S0 mode. It is preferable to multiply by Wh [kx, ky, f0].

By multiplying the mode-separated V [kx, ky] by W [kx, ky, kc], and then performing a 2D FFT, we can calculate kc where | z [k, y, kc] | is the maximum value. In this case, it is preferable to perform the local spatial wave number filtering technique by dividing the calculated region by and smoothing. That is, the local spatial wave number filtering technique is to smooth the minimized occurrence of errors and actual wave numbers without distorting the original signal.

After that, by calculating the dispersion diagram of the structure for each thickness, a correlation representing the correlation between the wave number and the thickness of the structure can be derived, and the thickness of the structure can be calculated using the derived correlation.

That is, the wave sensitivity and mode separation according to frequency can be calculated using the calculated dispersion line for each thickness of the structure, and the thickness of the structure can be finally calculated using the calculated wave sensitivity and mode separation.

In more detail, as shown in the following table, it can be represented.

2 and 3 show graphs related to the operation of the structure thickness measurement apparatus of FIG. 1 described above.

According to the graphs shown in FIGS. 2 and 3, the structure thickness measuring apparatus of FIG. 1 has a problem that the thickness change of the structure to be inspected can be detected only when the thickness of the structure to be inspected is reduced to about 70% or less of the initial thickness.

This problem is due to the fact that the structure thickness measuring apparatus described with reference to FIG. 1 uses an inspection technique using a difference in wavenumber for each thickness of a test object. That is, the structure thickness measuring apparatus of FIG. 1 cannot be inspected unless there is a difference in the number of waves according to the thickness, and thus the inspection is mainly performed using a low frequency (0 to 250 kHz).

2 and 3, when the 250 kHz or more, the sensitivity of the thickness change monitoring is drastically reduced.

In order to solve this problem, the structure thickness measuring apparatus proposed by the present invention, by replacing the PZT excitation unit 32 with an IDT sensor in the structure thickness measuring apparatus shown in Figure 1, the effect that can detect a more detailed thickness change Is derived.

Two measures are considered to increase the sensitivity of structure monitoring.

In the structure monitoring method using an IDT sensor, a mode having a high wavenumber sensitivity or a mode having a high degree of separation between modes is selected.

First, FIG. 4 illustrates an IDT sensor 400 included in a structure thickness measuring apparatus proposed by the present invention.

The IDT sensor 400 is manufactured by laser precision processing of piezoelectric material, and is inexpensive compared to general sensors, and can be manufactured according to the size, shape, and frequency desired by the user, and can easily generate a wave wave. have. In addition, there is an advantage that can be applied to a variety of materials, such as steel structure composite, plastic, concrete.

4A and 4B illustrate one embodiment of an IDT sensor 400.

The IDT sensor 400 shown in FIG. 4A generates surface waves having a predetermined wavelength [lambda]. IDT sensor 400 provided in the structure thickness measuring apparatus according to the present invention, the PZT consisting of the upper electrode, the lower electrode on the PZT substrate is designed and manufactured by processing the upper electrode into a shape desired by the user with a laser.

Referring to FIG. 4B, the standard of the electrode formed by the IDT sensor 400 is illustrated, and the wavelength of the surface wave can be changed by adjusting the distance λ between the branch electrodes of one electrode.

In addition, the intensity of the surface wave can be changed by adjusting the length of one branch electrode L, the width We of the branch electrodes, and the distance Ws between the different electrodes.

5 illustrates a structure monitoring method according to the present invention.

First, the sensitivity and mode separation degree can be calculated based on the material and thickness of the structure to be inspected (S501).

The frequency and wavelength applied to the IDT sensor may be calculated using the calculated wave sensitivity and mode separation (S502).

Structure thickness measuring apparatus according to the present invention, by using the IDT sensor produced according to the calculated frequency and wavelength, it is possible to detect the weight information of the structure to be inspected (S503).

In addition, the structure thickness measuring apparatus may generate image information related to the thickness of the structure based on the detected weight information (S504).

In the conventional method performed by the structure thickness measuring apparatus of FIG. 1, PZT is used to excite a bending mode. In the present technology, an IDT sensor for having a desired mode is used to excite a structure. The wave sensitivity is defined by Equation 1 below and is expressed as a derivative of the wave number by thickness.

는 파수변화율,

는 두께변화율, f는 주파수이다.In Equation 1

Is the wave change rate,

Is the thickness change rate, and f is the frequency.

가 클수록 두께변화에 민감한 파수이며,

는 주파수에 따라 변화하므로, 재질과 두께가 결정되면 주파수에 따른

를 계산해야 한다.

The larger is the frequency sensitive to the change in thickness.

Changes with frequency, so if the material and thickness are determined,

Must be calculated.

In addition, for clear imaging, each mode must be completely separated, which is referred to as “mode separation”, and is represented by Equation 2 below.

와

는 서로 다른 두 모드의 파수이다.In Equation 2

Wow

Is the frequency of the two different modes.

이 클수록 인접 모드간 분리가 잘되며,

이 작으면 인접 모드간 분리가 어려워 영상으로 두께 변화를 구분하기 어렵다.

The larger the better separation between adjacent modes,

If the size is small, it is difficult to separate the adjacent modes, and thus it is difficult to distinguish the thickness change by the image.

성분만을 가지는 Steady state response (정상파 응답)를 획득한다. Steady state response를 2D FFT를 수행하여

를 계산하고, 모드를 분리하기 위하여 특정모드를 제거하기 위한

을 곱한다. 모드 분리된

에

을 곱한 후, 2D IFFT를 수행하여

가 최대가 되는

를 계산하고, 영역을 나누어 국소공간 웨이브넘버 필터링을 하여 스무딩한다. 마지막으로, 두께 별 구조물의 분산선도를 계산한 후, 웨이브넘버와 두께의 상관식을 도출하고 이 식을 이용하여 구조물의 두께를 나타낸다.The thickness imaging method of the structure is the same as the conventional method. The signal measured from the LDV through scanning is a three-dimensional matrix of v [x, y, t] as shown in Figure 7, and bandpass filtering is performed to extract a single frequency component. In order to transform a 3D matrix into a 2D matrix, FFT (Fast Fourier Transform) is performed.

Obtain a steady state response with only components. Steady state response by 2D FFT

To remove a particular mode in order to calculate

Multiply by Mode-separated

on

After multiplying by 2D IFFT

Is the maximum

Calculate and smooth the local space wave number filtering. Finally, after calculating the scatter diagram of the structure by thickness, the correlation between wave number and thickness is derived and the thickness of the structure is represented using this equation.

6 is an example of an inspection target of the structure thickness measuring apparatus according to the present invention.

The test subjects were 300 mm in width, 300 mm in length, and 6 mm in thickness, and thinner defects were prepared in 40 mm, 40 mm in length, 0.3 mm, 0.6 mm, 0.9 mm, and 1.2 mm in thickness. Thinning defect thickness ratio is formed 5%, 10%, 15%, 20% with the goal of detecting defects below 25% of new materials.

7A to 7C show the frequency sensitivity according to the thickness for each frequency, and FIG. 8A to 8C show the mode separation according to the thickness for each frequency.

Referring to FIGS. 7A to 7C and 8A to 8C, it can be seen that the A0 mode has low wave sensitivity in a thick material, which is not suitable for the thinning test.

In the S0 mode, the frequency sensitivity per thickness increases as the frequency increases. Since the thickness of the specimen to be detected is currently within 4.8 mm to 6 mm, the effect of the S0 mode is maximized when excited at 0.422 MHz. Although the sensitivity of the A1 mode is higher than the S0 mode in the thickness range of 4.8 mm to 6 mm, the signal separation is difficult due to the low mode separation of the A1 mode, which is not suitable for use. Accordingly, in this example, an IDT sensor of 0.40 MHz S0 mode is used.

9 is image information generated by using a signal detected from an inspection object.

As shown in FIG. 9, it is confirmed that 20% thinning portion, 15% thinning portion, 10% thinning portion, and 5% thinning portion are all distinguished from the surroundings.

Claims (6)

Interdigital transducers (IDT) sensors for generating predetermined waves so that surface waves propagate along the structure;
A scanning unit scanning the vibration generated in the structure;
A signal collector which measures the vibration signal of the structure scanned from the scanning unit; And
And a signal processor configured to calculate a thickness of the structure based on the vibration signal measured by the signal collector.
The frequency and wavelength of the surface wave generated by the IDT sensor,
Characterized in that it is calculated based on the sensitivity and mode separation degree determined according to the material and thickness of the structure,
The mode separation degree is defined by the following equation,

Wow

Structure thickness measuring apparatus, characterized in that the waveguide of two different modes. The method of claim 1,
The frequency sensitivity is defined by the following equation,

In the above equation

Is the wave change rate,

The thickness change rate, f is the structure thickness measuring apparatus, characterized in that the frequency. delete The method of claim 1,
The signal processing unit,
Bandpass filtering is performed to extract a single frequency component of the vibration signal measured by the signal collector,
In order to convert the vibration signal in the form of a three-dimensional matrix into a two-dimensional matrix, FFT (Fast Fourier Transform) is performed to obtain a steady state response signal, and after separating a predetermined mode, a local spatial wave And performing a number filtering technique and calculating a dispersion diagram for each thickness of the structure, and calculating the thickness of the structure by calculating a correlation between the wave number and the thickness. The method of claim 4, wherein
The signal processor
Structure thickness measurement device, characterized in that for calculating the frequency sensitivity and the mode sensitivity using the calculated dispersion line for each thickness of the structure. Detecting information related to the material and the thickness of the structure;
Calculating a sensitivity and mode separation degree corresponding to the structure using the detected material and thickness;
Sensing the thinning information associated with the structure using an IDT sensor designed according to the calculated wave sensitivity and mode separation; And
Generating image information related to the thickness of the structure based on the detected thinning information;
The mode separation degree is defined by the following equation,

Wow

The method of monitoring the structure, characterized in that the waveguide of two different modes.

Images