JP7131438B2 - Anomaly detection device, anomaly detection system, and anomaly detection method - Google Patents

Description

The present invention relates to an abnormality detection device, an abnormality detection system, and an abnormality detection method that detect an abnormality in an object using terahertz waves.

Conventionally, in steel structures such as bridges, a non-metallic layer made of a non-metallic material such as resin typified by paint is provided as an anticorrosion layer on the surface of a metal layer made of a metallic material. The simplest method for detecting an abnormality such as a corrosion thinning portion on the surface of the metal layer existing under the non-metal layer is to remove the non-metal layer and visually confirm the abnormality. However, since it is necessary to check a wide range in a bridge or the like, the work of removing the non-metallic layer requires a great deal of time and effort. Therefore, there is a demand for a method of detecting anomalies on the surface of a metal layer without removing the non-metal layer.

In recent years, terahertz wave imaging, for which research and development is progressing, has attracted attention and is expected to be applied to non-destructive inspection and sensing. The terahertz wave has the property that most of the terahertz waves are transmitted through non-metallic materials such as resins, while most of the terahertz waves are reflected when irradiated onto metallic materials. Techniques for detecting abnormalities on the surface of a metal layer existing under a non-metal layer made of resin or the like by utilizing such properties of terahertz waves are being studied.

For example, Non-Patent Document 1 discloses an imaging apparatus based on an electronic device system of a reflective optical system using a resonant tunneling diode (RTD), which is capable of two-dimensional imaging using the properties of terahertz waves. It is According to the technique described in Non-Patent Document 1, properties such as unevenness of the lower metal layer can be measured and imaged without removing the non-metal layer provided on the upper layer of the metal layer. Since an abnormal portion such as a corrosion thinned portion of a metal layer is not smooth and has random unevenness, the abnormal portion can be detected by measuring the unevenness of the surface of the metal layer using terahertz waves.

In the above-mentioned technology, in order to measure the unevenness of the surface of a metal material, that is, the distance to the surface using terahertz waves, it is necessary to use a pulse wave with a small time width in order to obtain the necessary measurement resolution. . However, a complicated mechanism is required to use the pulse wave of the terahertz wave. Therefore, a method using a so-called terahertz continuous wave, in which a terahertz wave is emitted continuously, has been studied. Unlike the pulse wave of the terahertz wave, the terahertz continuous wave does not require a complicated mechanism.

Jun Yamaguchi, "Development of Terahertz Imaging System", PIONEER R&D (2014)

On the other hand, in an abnormal portion such as a corrosion thinning portion, it is conceivable that the intensity of the reflected wave decreases due to the scattering of the irradiated terahertz continuous wave by the unevenness of the corrosion thinning portion. Therefore, a method of evaluating the unevenness of the surface of the object by measuring the intensity of the reflected wave of the terahertz continuous wave has also been studied. However, when a terahertz continuous wave is irradiated from the side of the non-metallic layer to an object in which a non-metallic layer is provided on a substrate made of a metallic material (hereinafter referred to as a metallic substrate), the reflected wave on the surface of the metallic substrate and the non-metallic Because of interference with reflected waves on the surface of the metal layer, it has been extremely difficult to extract only information about the uneven shape of the corrosion thinning portion produced on the surface of the metal substrate. Therefore, there has been a demand for a technique capable of extracting information on the uneven shape of the surface of the metal substrate and detecting abnormal portions such as corrosion thinning portions occurring on the surface of the metal substrate.

The present invention has been made in view of the above, and an object of the present invention is to provide an object having a non-metallic layer on the upper layer of a metal substrate, and to remove the non-metallic layer on the surface of the underlying metal substrate without removing the non-metallic layer. An object of the present invention is to provide an abnormality detection device, an abnormality detection system, and an abnormality detection method capable of detecting an abnormality that has occurred.

(1) In order to solve the above-described problems and achieve the object, an abnormality detection device according to one aspect of the present invention provides a terahertz signal at a predetermined position on the surface of an object having a non-metallic layer provided on the upper layer of a metal substrate. A terahertz wave transmitting means configured to be able to irradiate a wave and capable of scanning the surface of the object; radiating terahertz waves of at least two different frequencies from the terahertz wave detecting means capable of scanning the surface of the object while associating the coordinates with the coordinates, and the terahertz wave transmitting means at a predetermined position of the object; When the terahertz wave detection means detects the intensity of each of the reflected waves of the at least two frequencies reflected by the object, the terahertz waves of the two frequencies detected by the terahertz wave detection means analysis means for calculating an intensity difference from the intensity of each reflected wave, and extracting a coordinate at which the absolute value of the calculated intensity difference is equal to or less than a predetermined value as an abnormal portion of the surface of the metal substrate; It is characterized by having

(2) In the abnormality detection device according to one aspect of the present invention, in the invention of (1) above, the at least two types of frequencies include a first frequency and a second frequency that are different frequencies, and the first frequency is A frequency at which the intensity of the first reflected wave of the terahertz wave becomes maximum when the terahertz wave transmitting means irradiates the terahertz wave to a healthy portion of the surface of the metal substrate that is not the abnormal portion of the object. and the second frequency is such that when the terahertz wave transmitting means irradiates the sound portion of the metal substrate with the terahertz wave to the object, the intensity of the second reflected wave of the terahertz wave is minimal. It is characterized by being a frequency that becomes

(3) In the abnormality detection device according to one aspect of the present invention, in the invention of (1) or (2), the predetermined value is calculated by the analysis means for each coordinate associated by the terahertz wave detection means. In the intensity difference absolute value distribution generated from the absolute value of the discrete intensity difference calculated and the number of coordinates of each of the calculated absolute values of the discrete intensity difference, the number of coordinates is minimized and a value that minimizes the absolute value of the intensity difference.

(4) An anomaly detection system according to an aspect of the present invention is configured to be able to irradiate a terahertz wave to a predetermined position on the surface of an object having a non-metallic layer provided on a metal substrate, and and a terahertz wave transmitting means capable of scanning the surface of the object, and capable of detecting the intensity of the terahertz wave reflected at the predetermined position of the object, and capable of scanning the surface of the object while associating it with coordinates. a terahertz wave measuring means comprising a terahertz wave detecting means; and terahertz waves of at least two different frequencies from the terahertz wave transmitting means, respectively, to predetermined positions of the object, wherein the terahertz wave detecting means When the intensities of the reflected waves of the terahertz waves of at least two frequencies reflected by the object are detected, the reflected waves of the terahertz waves of the two frequencies detected by the terahertz wave detecting means and an analysis means for extracting coordinates at which the absolute value of the calculated intensity difference is equal to or less than a predetermined value as an abnormal portion on the surface of the metal substrate, the intensity data can be transmitted and received.

(5) An abnormality detection method according to an aspect of the present invention is configured to be able to irradiate a terahertz wave to a predetermined position on a surface of an object having a nonmetallic layer provided on a metal base, and a first irradiation step of irradiating the object with a terahertz wave of a first frequency by means of a terahertz wave transmitting means capable of scanning the surface of the object; a terahertz wave detection unit configured to detect the intensity of the reflected wave of the terahertz wave of the first frequency reflected by the object by means of terahertz wave detection means capable of scanning the surface of the object while associating the surface with the coordinates; a second irradiation step of irradiating the surface of the object with a terahertz wave having a second frequency different from the first frequency by the terahertz wave transmitting means; a second detection step of detecting the intensity of the reflected wave of the reflected terahertz wave of the second frequency; the intensity of the reflected wave of the terahertz wave at the predetermined position detected in the first detection step; and the second detection. An intensity difference from the intensity of the reflected wave of the terahertz wave at the predetermined position detected in the step is calculated. and an analysis step of extracting as a part.

According to the abnormality detection device, the abnormality detection system, and the abnormality detection method according to the present invention, the terahertz wave is irradiated from the side of the nonmetallic layer to the object having the nonmetallic layer on the metal substrate. When measuring the intensity of the reflected wave, it becomes possible to detect an abnormality occurring on the surface of the underlying metal substrate without removing the non-metallic layer.

FIG. 1 is a diagram showing the overall configuration of an abnormality detection device according to one embodiment of the present invention. FIG. 2 is a block diagram schematically showing the configuration of the abnormality detection device 1 for explaining the problems of the prior art. FIG. 3 is a block diagram schematically showing the configuration of the abnormality detection device 1 for explaining the problems of the prior art. FIG. 4 is a diagram showing the intensity I ₁ (x, y) at the measurement position of the reflected wave L ₂₁ of the terahertz wave and the intensity I ₂ (x, y) at the measurement position of the reflected wave L ₂₂ of the terahertz wave. FIG. 5 shows (a) an example of an image of the intensity I ₁ (x, y) of the reflected wave L ₂₁ , (b) an example of an image of the intensity I ₂ (x, y) of the reflected wave L ₂₁ , and ( c) A diagram showing an example of an image of the intensity difference ΔI. FIG. 6 shows (a) the intensity I ₁ (x, y) value of the reflected wave L ₂₁ , (b) the intensity I ₂ (x, y) value of the reflected wave L ₂₂ , and (c ) is a chart showing an example of the absolute value of the intensity difference ΔI. FIG. 7 is a graph of the intensity difference absolute value distribution of the number of coordinates for each absolute value of the _intensity difference corresponding to FIG.

An embodiment of the present invention will be described below with reference to the drawings. In addition, in all the drawings of the following one embodiment, the same reference numerals are given to the same or corresponding parts. Moreover, the present invention is not limited to the one embodiment described below.

(Abnormality detection device)
First, an abnormality detection device according to an embodiment of the present invention will be described. FIG. 1 is a block diagram showing the configuration of an abnormality detection device 1 according to one embodiment. As shown in FIG. 1 , an abnormality detection device 1 according to one embodiment includes a terahertz wave transmitter 10 , a terahertz wave detector 20 , and an analysis controller 30 . In one embodiment, an object 80 to be inspected is provided with a coating layer 82 made of various resins as a non-metal layer on a steel material 81 as a metal substrate. The coating layer 82 preferably functions as an anti-corrosion layer for the underlying steel surface 81a, which is the surface of the metal substrate, but may be an adhesive or the like. As the object 80, for example, in addition to a steel structure having a paint coating, a predetermined surface of a base made of a metal material such as aluminum (Al) or stainless steel (SUS) is used as a base, and an uncoated layer is formed on the base. Various objects on which a metal layer is formed can be used.

The abnormality detection device ₁ according to _one embodiment is configured to be able to irradiate the surface of the object 80 with the terahertz wave as the incident wave L1, and to detect the reflected wave L2 of the terahertz wave reflected from the object 80. It is composed of a reflection type terahertz wave measurement device. That is, the abnormality detection device 1 has both terahertz wave transmission means and terahertz wave detection means. Here, the terahertz wave is an electromagnetic wave belonging to the so-called terahertz region, which is a frequency region of the order of about 1 terahertz (1 THz=10 ¹² Hz), specifically 100 GHz to 10 THz (10 ¹¹ to 10 ¹³ Hz). The terahertz region is a frequency region that has both rectilinearity of light and transparency of electromagnetic waves. In the present embodiment, the wavelength of the terahertz wave can be selected according to the expected surface roughness of the portion where the steel surface 81a, which is the base, has corrosion thinning, that is, the abnormal portion. For example, if the expected surface roughness of the abnormal portion is about 10 μm to several hundred μm, it is preferable to select a wavelength that scatters at a surface roughness of about 10 μm to several hundred μm. In this case, the frequency of the terahertz wave is, for example, 3 THz or more and 30 THz or less, but is not necessarily limited to this range. Note that the wavelength of the terahertz wave may be defined by the wavelength in the coating layer 82 as necessary.

A terahertz wave transmitter 10 as terahertz wave transmitting means includes a terahertz wave generating element 11 including, for example, a resonant tunneling diode (RTD), a hemispherical lens 12, a collimating lens 13, and an objective lens 14. have. A photo conductive antenna (PCA) may be used instead of the resonant tunneling diode. Although the terahertz wave transmitter 10 constitutes an optical system arranged linearly, it is not necessarily limited to being arranged linearly. It may be an optical system that further includes such as to bend the terahertz wave. The transmission optical system including the terahertz wave transmitter 10 is configured to be able to irradiate the surface of the object 80 with the terahertz wave at a predetermined angle θ ₀ and scan the surface of the object 80 . Here, the predetermined angle θ ₀ is 0 degrees or more and less than 90 degrees (0°≦θ ₀ <90°). When the predetermined angle θ ₀ is 0°, the terahertz wave enters the surface of the object 80 perpendicularly.

The terahertz wave detector 20 includes, for example, a terahertz wave detection element 21 such as an RTD, a hemispherical lens 22 and a condenser lens 23 . The terahertz wave detector 20 is provided in the abnormality detection device 1 in a state in which the terahertz wave detection element 21 can receive the reflected terahertz wave L ₂ . Although the terahertz wave detector ₂₀ constitutes an optical system arranged linearly, it is not necessarily limited to being arranged linearly. may be an optical system that bends the . The reflection position of the object 80 in the reflected wave L ₂ detected by the terahertz wave detector 20 is output to the analysis control unit 30, which will be described later, as information on coordinates (x, y) set on the steel surface 81a. Also, the intensity I(x, y) of the reflected wave L ₂ detected by the terahertz wave detector 20 is associated with the coordinates and output to the analysis control unit 30 .

The analysis control section 30 as analysis means includes a signal amplification section 31 , a bias generation section 32 , a lock-in detection section 33 , an analysis processing section 34 and a storage section 35 . The analysis control unit 30 performs various controls on the terahertz wave transmitter 10 . The analysis control unit 30 also performs various processes on the terahertz wave signal detected by the terahertz wave detector 20 . The signal amplifier 31 amplifies the signal detected by the terahertz wave detector 20 and outputs it to the lock-in detector 33 as terahertz wave reception data. The bias generator 32 generates a bias voltage to bias the terahertz wave generation element 11 and the terahertz wave detection element 21, thereby changing the transmitted terahertz wave or the detected terahertz wave according to the bias voltage. The terahertz waves emitted or detected by the terahertz wave generating element 11 and the terahertz wave detecting element 21 may be weak. In this case, lock-in detection is used to detect terahertz waves. During lock-in detection, the terahertz wave transmitter 10 uses the modulated reference signal as the bias voltage of the terahertz wave generation element 11, thereby removing the noise component of the terahertz wave detection signal. The storage unit 35 stores the detected terahertz wave reception data, particularly data of the intensity I(x, y) of the reflected wave L ₂ of the terahertz wave. The analysis processing unit 34 performs various analysis processes on the received terahertz wave data stored in the storage unit 35 .

(Abnormality detection method)
Next, an abnormality detection method by the abnormality detection device 1 configured as described above will be described. First, the problems of the prior art will be described in detail. 2 and 3 are block diagrams schematically showing the configuration of the abnormality detection device 1 for explaining the problems of the prior art.

As shown in FIG. 2, when the steel surface 81a of the steel material 81, which is the metal base, is not corroded, the portion where the corrosion is not occurring (hereinafter referred to as the sound portion) is smooth, so the reflection of the terahertz wave in the sound portion Waves travel in the direction of specular reflection. Therefore, if the terahertz wave detector ₂₀ is provided in the direction of specular reflection with respect to the incident wave L1 of the terahertz wave, the reflected wave L2 of the terahertz wave in the sound portion is detected as a strong signal by the terahertz wave detector ₂₀ . Probability is high.

On the other hand, as shown in FIG. 3, when corrosion thinning occurs on the steel surface 81a of the steel material 81 and a corroded portion 81ab exists as an abnormal portion, the reflection of the terahertz wave to the incident wave L ₁ to the corroded portion 81ab Since the wave _L2 is scattered, the reflection direction is not constant. _When detecting the reflected wave L2 of the terahertz wave, the terahertz wave detector 20 is arranged at a position assuming specular reflection. Therefore, the reflected wave L ₂ with respect to the incident wave L ₁ to the corroded portion 81ab is more likely to be detected as a weak signal by the terahertz wave detector 20 .

Furthermore, when measuring the steel surface 81a of the steel material 81 by irradiating the continuous wave of the terahertz wave from the coating layer 82 side of the object 80, the reflected wave on the surface 82a of the coating layer 82 and the steel surface 81a of the steel material 81 Interference occurs due to reflected waves at Here, since the thickness of the coating layer 82 is not uniform, the intensity of the detected reflected wave L2 changes depending _on the measurement position even in a healthy portion due to the interference phenomenon of the terahertz wave. Further, even at a position where the corroded portion 81ab exists in the lower layer of the coating layer 82, since the reflected wave L2 exists in the corroded portion _81ab , an interference phenomenon of terahertz waves occurs.

Thus, when measuring the steel surface 81a underlying the coating layer 82 using continuous terahertz waves, the strength of the detected terahertz waves varies regardless of the presence or absence of the corroded portion 81ab. Therefore, when the terahertz wave transmitter 10 and the terahertz wave detector 20 of the abnormality detection device ₁ described above are scanned integrally and the intensity distribution of the detected terahertz wave reflected wave L2 is measured, the magnitude of the intensity is mixed up. distribution. Here, if the intensity of the detected reflected wave L2 is increased, the brightness is increased, and if the intensity is _decreased , the intensity is _decreased . . Therefore, it is extremely difficult to determine the presence or absence of the corroded portion 81ab and to extract the location of the corroded portion 81ab simply by imaging the result of measurement of the object 80 by the abnormality detection device 1 .

As a result of intensive studies by the present inventors, the present inventor has come up with a method of independently irradiating at least two types of terahertz waves of different frequencies at the same measurement position on the object 80 . Specifically, the reflected wave _L21 as the first reflected wave is detected for the incident wave _L11 of the first frequency, which is one of the two types of frequencies. A reflected wave _L22 is detected as a second reflected wave from the incident wave _L12 of the second frequency. Conventionally, when the object 80 is irradiated with terahertz waves from the side of the coating layer 82 and the intensity of the reflected waves L ₂₁ and L ₂₂ is measured, even if the measurement position is the healthy portion 81aa of the steel material 81, the corroded portion 81ab can be measured. Also, the reflected waves L ₂₁ and L ₂₂ have different intensities, making it difficult to distinguish and extract the corroded portion 81ab.

The inventor of the present invention has further conducted intensive studies, and has devised a method of independently measuring at least two types of reflected waves and using the difference in intensity of the reflected waves. That is, the inventors conducted various studies on the principle of generation of the magnitude of the intensity of the reflected waves L ₂₁ and L ₂₂ , and found that the principle of generation of the magnitude of the intensity of the reflected waves L ₂₁ and L ₂₂ in the healthy portion 81aa and the corroded portion 81ab is as follows. I noticed something different. Specifically, when the steel surface 81a of the steel material 81 at the measurement position is the healthy portion 81aa, interference occurs between the reflected wave from the surface 82a of the coating layer 82 and the reflected wave from the steel surface 81a of the steel material 81, and the coating layer 82 The strength changes according to the thickness of the On the other hand, when the steel surface 81a of the steel material 81 at the measurement position is the corroded portion 81ab, the reflected wave is scattered by the unevenness of the surface, so that the intensity changes to decrease.

Based on the principle described above, the change in intensity of the reflected wave in the healthy portion 81aa depends on the frequency of the terahertz wave used for measurement. In other words, the change in the intensity of the reflected wave reflected by the healthy portion 81aa is determined by the path difference and the wavelength, ie, the frequency, of the terahertz waves causing interference. Therefore, when the wavelength of the terahertz wave irradiated to the healthy portion 81aa is changed, the intensity of the reflected terahertz wave changes depending on the wavelength due to interference. On the other hand, the change in intensity of the reflected wave reflected by the corroded portion 81ab does not depend on the frequency of the terahertz wave used for measurement. In other words, even if the wavelength of the terahertz wave irradiated to the corroded portion 81ab, that is, the frequency is changed, the intensity of the reflected wave hardly changes. Therefore, in the corroded portion 81ab, there is a high possibility that the intensity of the reflected waves L ₂₁ and L ₂₂ will be small regardless of the frequencies of the incident waves L ₁₁ and L ₁₂ . Therefore, it can be determined that there is a high possibility that the corroded portion 81ab exists at the measurement position where the absolute value of the difference in intensity between the reflected waves L ₂₁ and L ₂₂ having different wavelengths is less than a predetermined value, preferably approximately 0. .

Specifically, first, the terahertz wave transmitter 10 and the terahertz wave detector 20 are scanned integrally with respect to the surface 82a of the object 80 . This scanning is performed at least twice by changing the frequency of the terahertz wave. As a result, at least two intensities of reflected waves L ₂ (L ₂₁ , L ₂₂ ) are detected.

Thereafter, the analysis control unit 30 forms an image of the intensity distribution of the reflected wave L2 of the terahertz wave detected for _each measurement position. Alternatively, the analysis control unit 30 applies the intensity of the reflected wave L ₂ of the terahertz wave detected at each measurement position to the pixels of the image to form an image of intensity distribution. In imaging, for example, the higher the intensity of the reflected wave L2, the brighter the image, and the _lower the intensity, the darker the image. In this case, the higher the brightness of the pixel, the higher the intensity of the reflected wave L2, and the _lower the brightness, the _lower the intensity of the reflected wave L2. The imaging process described above is performed for at least two reflected waves L ₂ (L ₂₁ , L ₂₂ ).

Here, the at least two frequencies with which the object 80 is irradiated are frequencies different from each other, and frequencies f ₁ (k) and f ₂ (l) shown in the following equations (1) and (2), respectively, are Select is preferred.

θ₀：入射角、ｋ：任意の整数、ｃ：真空での光速度、ｄ：被覆層８２の厚さ、ｎ：被覆層８２の絶対屈折率
テラヘルツ波の反射波の干渉によって強度が小さくなる条件（強度の極小条件）

θ₀：入射角、ｌ：任意の整数、ｃ：真空での光速度、ｄ：被覆層８２の厚さ、ｎ：被覆層８２の絶対屈折率 Conditions where intensity increases due to interference of reflected waves of terahertz waves (maximum intensity condition)

θ ₀ : incident angle, k: arbitrary integer, c: speed of light in vacuum, d: thickness of coating layer 82, n: absolute refractive index of coating layer 82 Intensity decreases due to interference of reflected waves of terahertz waves Condition (minimum strength condition)

θ ₀ : incident angle l: arbitrary integer c: speed of light in vacuum d: thickness of coating layer 82 n: absolute refractive index of coating layer 82

In equations (1) and (2), the propagation velocity v of the terahertz wave when the terahertz wave passes through the coating layer 82 may be used instead of the light velocity c in a vacuum. The propagation velocity v can be derived by calculating from the refractive index n of the coating layer 82 or by measuring the terahertz wave passing through the coating layer 82 . The thickness d of the coating layer 82 can be derived by calculating the average of the thicknesses actually measured at a plurality of measurement points or by setting the thickness to a design specification.

Next, a specific method of detecting an abnormality will be described. FIG. 4 shows ₍ a) the intensity at the measurement position of the reflected wave _L21 with respect to the incident wave L11 and ₍ b) the measurement of the reflected wave _L22 with respect to the incident wave L12 when the object 80 is irradiated with the terahertz wave. FIG. 10 is a diagram showing intensity at position; In this embodiment, as shown in FIG. 4A, the terahertz wave transmitter 10 of the abnormality detection device 1 is used to determine the coordinates (x, y) of the predetermined measurement position of the object 80 as the first irradiation step. is irradiated with a terahertz wave of frequency f ₁ (k) as the first frequency. Along with this, the incident wave L ₁₁ of the terahertz wave of frequency f ₁ (k) is reflected as the reflected wave L ₂₁ . ₂₁ intensities I ₁ (x,y) are measured. Similarly, as shown in FIG. 4(b), the terahertz wave transmitter 10 of the abnormality detection device 1 is used to set the coordinates (x, y) of the predetermined measurement position of the object 80 as the second irradiation step. A terahertz wave of frequency f ₂ (l) as two frequencies is irradiated. Along with this, the incident wave L ₁₂ of the terahertz wave of frequency f ₂ (l) is reflected as the reflected wave L ₂₂ . ₂₂ intensities I ₂ (x,y) are measured.

The analysis processing unit 34 creates an image based on the intensity I ₁ (x, y) of the input reflected wave L ₂₁ . In this case, it is preferable to convert the image to the brightness of the pixel at the position corresponding to the measurement coordinates of the intensity I ₁ (x, y). FIG. 5(a) shows an example of an image created by the analysis processing unit 34. As shown in FIG. In the image 210 shown in FIG. 5(a), the normal portion 81aa has a small change in luminance, and there is a luminance difference portion 211 in which the pixel luminance is largely different from the others. Further, in the image image 210, even if the corroded portion 81ab exists, there exists a portion 212 in which the brightness of the pixels does not differ greatly from the others. The reflected wave L ₂₁ is a reflected wave whose intensity I ₁ (x, y) increases in the sound portion 81aa.

Similarly, the analysis processing unit 34 creates an image based on the intensity I ₂ (x, y) of the input reflected wave L ₂₂ . Also in this case, it is preferable to convert the intensity I ₂ (x, y) of the reflected wave L ₂₂ into the brightness of the pixel at the position corresponding to the measurement coordinates. FIG. 5(b) shows an example of the image created by the analysis processing unit 34. As shown in FIG. In the image 220 shown in FIG. 5B, the change in luminance is small in the normal portion 81aa, and there is a luminance difference portion 221 where the pixel luminance is largely different from the others. Further, in the image image 220, even if the corroded portion 81ab is present, there is also a portion 222 where the brightness of the pixels does not differ greatly from the others. Note that the reflected wave L ₂₂ is a reflected wave whose intensity I ₂ (x, y) is reduced in the sound portion 81aa.

Next, intensity distributions related to the luminance distributions shown in FIGS. 5(a) and 5(b) will be described. FIGS. 6(a) and 6(b) are tables showing the intensity of reflected waves corresponding to the luminance distributions shown in FIGS. 5(a) and 5(b), respectively. In FIGS. 6(a) and 6(b), for simplicity of explanation, five coordinates are set in each of the X-axis direction and the Y-axis direction, the number of measurement positions is 25, and the intensity is An example of integers with a minimum value of 0 and a maximum value of 7 is shown. Note that the number of measurement positions can be varied. In addition, the interval between adjacent measurement positions can be set to various intervals such as several millimeters to several tens of centimeters. Regarding the intensity of the reflected wave, after setting the minimum value and the maximum value, it is possible to set various values for the intervals between the steps of the intensity. The table shown in FIG. 6(a) is an example in which the maximum value of intensity is 7, the minimum value is 0, and the interval between intensity levels is 1, which is an integer. In the example shown in FIG. 6A, for example, the intensity I ₁ (x2, y3) of the reflected wave L ₂₁ at the coordinates (x2, y3) is "7". Similarly, in the example shown in FIG. 6B, for example, the intensity of the reflected wave L22 at the coordinates ₍ x2, y3) is "1".

Next, as an analysis step, the analysis processing unit 34 of the analysis control unit 30 generates the terahertz waves of two frequencies f ₁ (k) and f ₂ (l) at the same coordinates as shown in the following equation (3). (x, y), respectively, and the difference (intensity difference ΔI) between the intensities (I ₁ (x, y), I ₂ (x, y)) of the reflected waves L ₂₁ and L ₂₂ obtained Calculate the absolute value.
ΔI=|I ₁ (x, y)−I ₂ (x, y)| (3)

Here, FIG. 6(c) shows a table of results of calculating the absolute value ΔI of the intensity difference from the tables of the intensity I(x, y) shown in FIGS. 6(a) and 6(b). As shown in FIG. 6(c), the absolute value ΔI of the intensity difference is derived for each coordinate (x, y). The analysis processing unit 34 determines that the corroded portion 81ab exists at the coordinates (x, y) where the absolute value ΔI of the intensity difference is equal to or less than the predetermined threshold value _αth .

Here, an example of a method of setting the predetermined threshold value α _th for judging the healthy portion 81aa and the corroded portion 81ab will be described. FIG. 7 is a graph of the intensity difference absolute value distribution of the number of coordinates corresponding to the intensity difference absolute value _ΔI in FIG. The horizontal axis of the graph shown in FIG. 7 is the absolute value ΔI of the discrete intensity difference, and the vertical axis is the number of the coordinates (x, y) of the measurement position appearing at each absolute value ΔI of the discrete intensity difference ( hereinafter, coordinate numbers). That is, in FIG. 7, the number of coordinates at which the absolute value ΔI of the intensity difference is 0 is 5, and the number of coordinates at which the absolute value ΔI of the intensity difference is 1 is 1 in the table of FIG. 6(c). , the data are plotted. In place of the absolute value .DELTA.I of the intensity difference, the brightness of each pixel forming the image may be used. In this case, the number of pixels is used instead of the number of coordinates.

The analysis processing unit 34 performs least-squares approximation using, for example, spline interpolation or an n-th order polynomial on the points plotted with the data of the coordinate numbers and the absolute values ΔI of the intensity differences shown in FIG. is smoothed. After that, the analysis processing unit 34 extracts the minimum point of the number of coordinates in the graph obtained by smoothing (the curve in FIG. 7), and calculates the absolute value ΔI of the intensity difference at the minimum point closest to the origin 0 as a predetermined value. Set the threshold α _th . That is, the threshold value α _th is set to a value that minimizes the number of coordinates and minimizes the absolute value of the intensity difference. In the graph shown in FIG. 7, the threshold α _th is about 1.5. In the example shown in FIG. 6C, the analysis processing unit 34 determines that the corroded portion 81ab exists at the position of the coordinates (x, y) where the absolute value ΔI of the intensity difference is 1.5 or less of the threshold value _αth . judge. In the example shown in FIG. 6C, coordinates (x1, y4), coordinates (x3, y3), coordinates (x3, y4), and coordinates (x4, y3) where the absolute value ΔI of the intensity difference is "0" , and the coordinates (x4, y4) and the coordinates (x1, y5) where the intensity difference ΔI is "1", it is determined that the corroded portion 81ab exists. It should be noted that the threshold value α _th can be set arbitrarily. In this case, the threshold value α _th is preferably approximately zero.

FIG. 5(c) is an image of the absolute value ΔI of the intensity difference obtained from FIGS. 5(a) and 5(b). FIG. 5(c) is a binarized image corresponding to FIG. 6(c) where the absolute value ΔI of the intensity difference is equal to or less than the threshold value α _th and the portion is greater than the threshold value α _th . The analysis processing unit 34 derives the image 230 shown in FIG. 5(c) by calculating the difference between the luminance in FIG. 5(a) and the luminance in FIG. is equal to or smaller than the threshold value α _th , it is determined that the corroded portion 81ab exists.

According to the embodiment described above, the step of irradiating a terahertz wave to a predetermined position of the object 80 and measuring the intensity of the reflected wave of the reflected terahertz wave is performed using at least two types of terahertz waves of different wavelengths (frequencies). is extracted as the corroded portion 81ab, where the absolute value of the difference between the intensities of these two types of reflected waves is equal to or less than the threshold value _αth . Even if the layer 82 is provided, the corroded portion 81ab of the steel material 81 can be detected without removing the coating layer 82 .

Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and various modifications are possible based on the technical idea of the present invention. For example, the configuration of the abnormality detection device mentioned in the above-described embodiment is merely an example, and a device with a different configuration may be used as necessary. Moreover, the present invention is not limited by the description and drawings forming part of the disclosure of the present invention according to the above-described embodiments.

In the above-described embodiment, the same coordinates (x, y) of the object 80 are irradiated with terahertz waves of two different frequencies, and the intensities of the reflected waves L ₂₁ and L ₂₂ are measured. . In this regard, the frequencies of the terahertz waves irradiated to the object 80 are not limited to the two frequencies f ₁ (k) and f ₂ (l), and the above-mentioned equations (1) and (2) A frequency f ₃ (m) (m: any integer) other than f 3 (m) may be used. Also, the terahertz wave transmitter 10 and the terahertz wave detector 20 are scanned three times, and three frequencies f ₁ (k), f ₂ (l), and f ₃ (m) are selected for each scan. may be used. When using three frequencies f ₁ (k), f ₂ (l), and f ₃ (m), the frequency f ₃ (m) is the frequency f ₃ (m) shown in the following equation (4). is preferred.
f3(m)= _{ f1 ₍ m)+f2(m)}/ ₂ (4)

That is, first, the same coordinates (x, y) of the object 80 are irradiated with terahertz waves of three frequencies, respectively, and the intensities of the three reflected waves I ₁ (x, y) and I ₂ (x, y) ), I ₃ (x, y). Next, the intensities of the two reflected waves are sequentially selected from the three measured intensities of the reflected waves, and the absolute values of the three intensity differences are obtained according to the following equations (5-1) to (5-3). ΔI ₁ , ΔI ₂ and ΔI ₃ are calculated. Using the calculated absolute values ΔI ₁ , ΔI ₂ , and ΔI ₃ of the three intensity differences, the above-described abnormality detection methods are executed in three ways, so that the corroded portion 81ab can be detected with higher accuracy. Become.
ΔI ₁ =|I ₁ (x, y)−I ₂ (x, y)| (5-1)
ΔI ₂ =|I ₂ (x, y)−I ₃ (x, y)| (5-2)
ΔI ₃ =|I ₃ (x, y)−I ₁ (x, y)| (5-3)

It is also possible to use four or more frequencies. Even when four or more terahertz wave frequencies are used, it is preferable to include the above frequencies f ₁ (k) and f ₂ (l). At the frequencies f ₁ (k) and f ₂ (l) described above, the difference between the maximum constructive intensity and the maximum destructive intensity is maximized due to the interference of the reflected waves of the terahertz waves. This is because the difference in intensity of the reflected wave _L2 can be increased.

For example, in one embodiment described above, the abnormality detection device 1 has been described, but the configuration is not necessarily limited to a configuration including all of them. That is, the terahertz wave transmitter 10 and the terahertz wave detector 20 can be integrated into a terahertz wave measuring instrument. In this case, the analysis control unit 30 may be composed of a personal computer or the like. When the terahertz wave measuring instrument and the analysis control section 30 are configured separately, data can be transmitted and received between the terahertz wave measuring instrument and the analysis control section 30 via LAN communication or various networks such as the Internet. It is configurable. That is, the terahertz wave measuring instrument may be configured to measure the intensity of the terahertz wave reflected from the surface of the object 80 and supply intensity data to the separate analysis control unit 30 via the network. good. In this case, the terahertz wave measuring device as the terahertz wave measuring means and the analysis control unit 30 constitute an abnormality detection system.

1 Abnormality detection device 10 Terahertz wave transmitter 11 Terahertz wave generation element 20 Terahertz wave detector 21 Terahertz wave detection element 30 Analysis control unit 34 Analysis processing unit 35 Storage unit 80 Target object 81 Steel material 81a Steel surface 81aa Healthy portion 81ab Corroded portion 82 Coating layer 82a Surfaces ₂₁₀ , ₂₂₀ , 230 Image images ₂₁₁ , 221 Brightness difference portions L1, L11, L12 Incident waves L2, _L21 , L22 Reflected waves _{ΔI , ΔI1} , _ΔI2 , _ΔI3 Intensity differences absolute value α _th threshold

Claims (4)

a terahertz wave transmitting means configured to be able to irradiate a terahertz wave to a predetermined position on the surface of an object having a non-metallic layer provided on a metal substrate and capable of scanning the surface of the object;
a terahertz wave detection means configured to be able to detect the intensity of the terahertz wave reflected at the predetermined position of the object and capable of scanning the surface of the object while associating it with coordinates;
The terahertz wave transmitting means emits terahertz waves of at least two different frequencies to predetermined positions of the object, and the terahertz wave detection means detects the terahertz waves of the at least two frequencies reflected by the object. When the intensity of each reflected wave is detected, an intensity difference is calculated from the intensity of each reflected wave of the terahertz waves of the two types detected by the terahertz wave detection means, and the calculated intensity difference an analysis means for extracting the coordinates at which the absolute value of is equal to or less than a predetermined value as an abnormal portion of the surface of the metal base ,
wherein the at least two frequencies include a first frequency and a second frequency that are different from each other;
The first frequency is the frequency of the first reflected wave of the terahertz wave when the terahertz wave transmitting means irradiates the terahertz wave to a normal portion of the surface of the metal substrate that is not the abnormal portion of the object. is the frequency at which the intensity is maximum,
The second frequency is a frequency at which the intensity of the second reflected wave of the terahertz wave is minimized when the terahertz wave transmitting means irradiates the sound portion of the metal substrate with the terahertz wave to the object. An abnormality detection device characterized by: The predetermined value is the absolute value of the discrete intensity difference calculated by the analysis means for each coordinate associated by the terahertz wave detection means, and the coordinate of each of the calculated absolute values of the discrete intensity difference. 2. The anomaly according to claim 1 , wherein the absolute value distribution of the intensity difference generated from the number of the coordinates is the minimum and the absolute value of the intensity difference is the minimum detection device. a terahertz wave transmitting means configured to be able to irradiate a terahertz wave to a predetermined position on the surface of an object having a non-metallic layer provided on a metal substrate and capable of scanning the surface of the object; a terahertz wave measuring means configured to detect the intensity of the terahertz wave reflected at the predetermined position of and capable of scanning the surface of the object while associating the coordinates with the terahertz wave detection means;
The terahertz wave transmission means emits terahertz waves of at least two different frequencies to predetermined positions of the object, and the terahertz wave detection means reflects the terahertz waves of the at least two frequencies by the object. When the intensity of each reflected wave is detected, an intensity difference is calculated from the intensity of each reflected wave of the terahertz waves of the two types detected by the terahertz wave detection means, and the calculated intensity difference an analysis means for extracting, as an abnormal portion of the surface of the metal substrate, the coordinates at which the absolute value of is equal to or less than a predetermined value,
configured to be able to transmit and receive data of the intensity via a network ,
wherein the at least two frequencies include a first frequency and a second frequency that are different from each other;
The first frequency is the frequency of the first reflected wave of the terahertz wave when the terahertz wave transmitting means irradiates the terahertz wave to a normal portion of the surface of the metal substrate that is not the abnormal portion of the object. is the frequency at which the intensity is maximum,
The second frequency is a frequency at which the intensity of the second reflected wave of the terahertz wave is minimized when the terahertz wave transmitting means irradiates the sound portion of the metal substrate with the terahertz wave to the object. An anomaly detection system characterized by: A terahertz wave transmitting means capable of scanning the surface of an object, which is configured to be able to irradiate a terahertz wave at a predetermined position on the surface of the object having a non-metallic layer provided on the upper layer of the metal base, and to scan the surface of the object A first irradiation step of irradiating a terahertz wave of a first frequency on the
The intensity of the terahertz wave reflected at the predetermined position of the object can be detected, and the terahertz wave detection means capable of scanning the surface of the object while associating it with the coordinates reflects the terahertz wave reflected by the object. a first detection step of detecting the intensity of the reflected wave of the terahertz wave of the first frequency;
a second irradiation step of irradiating the surface of the object with a terahertz wave having a second frequency different from the first frequency by the terahertz wave transmitting means;
a second detection step of detecting, by the terahertz wave detection means, the intensity of the reflected wave of the terahertz wave of the second frequency reflected by the object;
calculating an intensity difference between the intensity of the reflected terahertz wave at the predetermined position detected in the first detection step and the intensity of the reflected terahertz wave at the predetermined position detected in the second detection step; and an analysis step of extracting the coordinates at which the calculated absolute value of the intensity difference is equal to or less than a predetermined value as an abnormal portion of the surface of the metal substrate ,
wherein the at least two frequencies include a first frequency and a second frequency that are different from each other;
The first frequency is the frequency of the first reflected wave of the terahertz wave when the terahertz wave transmitting means irradiates the terahertz wave to a healthy portion of the surface of the metal substrate that is not the abnormal portion of the object. is the frequency at which the intensity is maximum,
The second frequency is a frequency at which the intensity of the second reflected wave of the terahertz wave is minimized when the terahertz wave transmitting means irradiates the sound portion of the metal substrate with the terahertz wave to the object. is
An anomaly detection method characterized by:

Images