JP2007212364A - Method and device for determining surface abnormality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve surface abnormality determination at higher sensitivity or higher accuracy than a conventional method. <P>SOLUTION: This surface abnormality determination method comprises light emitting stages (S35-S37) of emitting light having a specific wavelength zone to a surface, detecting stages (S35 and S37) of detecting the reflected light of the light as image data of the surface, and an abnormality determining stage (S38) of calculating the intensity of the reflected light in the specific wavelength zone with respect to the image data of the surface and determining the abnormal state (rust state) on the surface based on this intensity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a surface abnormality determination method and a surface abnormality determination device for determining occurrence of abnormality such as rust and deterioration on various surfaces such as an inner wall surface of a steel pipe and a surface of a clay pipe used for steel tower materials.

  Steel pipes used for power transmission towers are usually galvanized to prevent corrosion, but after long-term use, they are galvanized due to the effects of rainwater and wind that enter the steel pipe. Deteriorates and rust is generated on the inner wall surface of the steel pipe. The rust of steel pipes used for steel tower materials significantly deteriorates the strength of the steel tower and impairs its safety and durability. It is necessary to apply.

Conventionally, an internal corrosion detection method for efficiently determining the occurrence of rust on the inner wall surface of a steel pipe by image analysis processing has been proposed (Patent Document 1). In this internal corrosion detection method, an inner wall surface of a steel pipe is imaged, and in this captured image, rust is applied to an image area in which the three attributes (tristimulus values) of lightness, saturation, and hue satisfy predetermined conditions. It is determined that the area has occurred.
JP 9-229869 (published September 5, 1997)

  However, the internal corrosion detection method of Patent Document 1 has the following problems.

  That is, as described above, the internal corrosion detection method of Patent Document 1 images the inner wall surface of a steel pipe, and in this captured image, the brightness, saturation, and hue (tristimulus values) that are the three attributes of the image color are predetermined. An image area that satisfies the conditions is determined to be an area where rust has occurred. However, in such rust determination based on the color information of the image, the detection sensitivity of rust cannot be improved beyond a predetermined level.

  Because the color information of the image is defined based on human visual characteristics, the amount of information of the continuous spectrum of the reflected light is converted into three attribute values (tristimulus values) by integration using a color matching function. Are summarized in Therefore, the amount of information of the color information of the image is remarkably smaller than that of the spectral distribution of the image light. Therefore, when the rust is determined based on the image color information as in the internal corrosion detection method of Patent Document 1, the image of the rusted area and the image of the rustless area are the same color due to human visual characteristics. This is because the difference between the two images cannot be identified even if the reflected light spectra of the two images are different. In other words, the internal corrosion detection method disclosed in Patent Document 1 cannot accurately detect the occurrence of rust based on the original information amount of the spectral reflection characteristics on the inner wall surface of the steel pipe.

  Moreover, in the internal corrosion detection method of Patent Document 1, as a premise for determining the occurrence of rust, the luminance value (pixel value) of an image obtained by imaging the inner wall of the steel pipe satisfies a predetermined condition. It is necessary to adjust the lighting conditions for illuminating the inner wall of the steel pipe. Such adjustment of illumination conditions necessitates adjustment of the position and angle of the light source or detector (inspection head) inside a narrow and long steel tube, or the necessity of providing a complicated light emission intensity adjustment mechanism in the light source. Therefore, it is extremely complicated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an abnormality determination method that realizes rust determination with higher sensitivity or higher accuracy than conventional methods and does not require complicated illumination adjustment. It is to provide.

In order to solve the above problems, the abnormality determination method according to the present invention includes a light irradiation stage for irradiating a surface with light having a specific wavelength range, and detection for detecting reflected light of the light as image data of the surface. And an abnormality determination step of calculating an intensity of reflected light in the specific wavelength region in the surface image data and determining an abnormal state on the surface based on the intensity.

  In addition, in order to solve the above-described problem, the abnormality determination device according to the present invention detects a light irradiation unit that irradiates a surface with light having a specific wavelength range, and detects reflected light of the light as image data of the surface. And an abnormality determination unit that calculates an intensity of reflected light in the specific wavelength region in the image data of the surface and determines an abnormal state on the surface based on the intensity. .

  In the above configuration, the light having a specific wavelength range refers to various types of light whose intensity of a predetermined wavelength range component is not substantially zero, and the form thereof is not particularly limited. For example, the light having a specific wavelength range includes various types of laser light and lamp light.

  According to said structure, the reflected light of the light irradiated to the surface of the determination target object is detected as the image data of the said surface by various light detection means, such as CCD and C-MOS. Then, in the detected image data, the intensity of the reflected light in the specific wavelength range is calculated, and the presence or state of the abnormality on the surface is determined based on this intensity.

According to the present invention, it is possible to accurately detect even a surface abnormality that cannot be identified by the human eye based on surface spectral information.
In addition, as a method of judging the abnormal state on the surface based on the intensity of the reflected light in a specific wavelength range, a method of comparing the intensity of the reflected light with a predetermined threshold, or comparing the intensity distribution of the reflected light in different wavelength ranges It is possible to adopt a technique to do so. For example, the ratio of the intensity of the reflected light to the intensity of the incident light or the difference between the intensity of the incident light and the intensity of the reflected light may be calculated, and the abnormal state on the surface may be determined based on these values. In particular, when determining an abnormal state on the surface based on the ratio of the intensity of the reflected light to the intensity of the incident light, the distance between the inspection head equipped with the light source and the light detection means and the surface of the determination target is fixed to a predetermined value. Even if it is not performed, since the fluctuation of the ratio value is small, it is possible to realize stable abnormality determination without requiring complicated adjustment of illumination conditions and the like.

  In order to solve the above-described problem, the abnormality determination method according to the present invention has a plurality of different wavelength ranges in the light irradiation stage in the above-described configuration, and in the abnormality determination stage, An abnormal state on the surface is determined based on the intensity of reflected light calculated in each wavelength region.

  In the above-described configuration, the plurality of different wavelength ranges include not only wavelength ranges in which the spectrum distributions do not overlap at all, but also wavelength ranges in which the main portions (periphery of the peak portion) of the spectrum distributions do not overlap. . That is, in the plurality of wavelength regions, these spectral distributions may partially overlap in the base portion.

  As a means for emitting a plurality of lights whose wavelength ranges do not overlap, an LED having a relatively narrow emission band can be suitably used.

  According to said structure, the reflected light of the several light which has the different wavelength range irradiated on the surface of the determination target object is detected as image data of the said surface by various light detection means, such as CCD and C-MOS. . Then, the intensity of the reflected light in each wavelength region is calculated in the detected image data, and the presence or state of the abnormality on the surface is determined based on these intensities.

  In addition, as a method for determining an abnormal state on the surface based on the intensity of reflected light in the specific wavelength region, a method of comparing the intensity distribution of reflected light in each wavelength region with each other, A method of deriving a parameter value by calculating the intensity and comparing the parameter value with a threshold can be employed.

  According to the present invention, abnormality determination based on multispectral analysis using reflected light information of a plurality of different wavelength regions is performed instead of abnormality determination based on color information of a reflected light image. Even surface abnormalities that cannot be identified can be accurately detected. This is because multi-spectral analysis obtains information about incident light on the imaging system as information on continuous spectral distribution of light, so that the values of three attributes (tristimulus values) after integration operation by a color matching function are performed. This is because the amount of information or the characteristic amount of incident light obtained is significantly greater than the color information analysis obtained as (1). That is, according to the abnormality determination method according to the present invention, it is possible to realize accurate abnormality determination without being affected by the establishment of the color matching function, in addition to the above-described effects.

In the abnormality determination method according to the present invention, in the above configuration, in the light irradiation stage, it is also preferable to perform irradiation while sequentially switching light having different wavelength ranges.
According to said structure, when irradiating the light (1st light, 2nd light, ...) which has a mutually different wavelength range on the surface of a determination target object, and detecting the reflected light, it is 1st. After the reflected light is detected while irradiating the light, the reflected light is detected while irradiating the second light, and so on. Thereby, since the reflected light detected in the detection stage can be completely separated in time, an optical member for separating the reflected light (various wavelength band filters, color filters, prisms, etc.) is not necessary. . Therefore, it becomes easy to adopt a monochrome video camera having generally high sensitivity as the light detection means in the detection stage.

  On the other hand, when the surface of the determination target is irradiated with a plurality of lights (first light, second light,...) At the same time and the reflected light is detected at the same time, irradiation of the plurality of lights or these Detection of reflected light can be performed in parallel. Therefore, since the time required for these processes can be shortened, it is possible to realize abnormality determination at high speed. In this case, a color video camera provided with a color filter can be used as the light detection means in the detection stage.

  In the abnormality determination method according to the present invention, in the above configuration, it is preferable to select a plurality of wavelength regions in the light irradiation stage so that image data having a plurality of colors is obtained as the image data of the surface.

  In the above configuration, the image data composed of a plurality of colors is data of images of a plurality of colors that allow a human to visually confirm whether there is an abnormality on the surface of the determination target or the state thereof. Considering the abundance of information, this image data is ideally a full-color display of all natural colors. However, when the image data is displayed on a display or the like, it is normal on the surface of the judgment object. Any multi-color display that can visualize the state of the abnormal part and the distinction between the part and the abnormal part may be used.

  Such a selection of a plurality of wavelength ranges includes combinations of the three primary colors of red (R), green (G), and blue (B), as well as combinations of ultraviolet (UV), green (G), and red (R), and ultraviolet. A combination of (UV) + white (W) is conceivable. Note that white (W) can be regarded as combined light having the three primary wavelengths of red (R), green (G), and blue (B).

  According to the above configuration, since the detected image data and the determination result can be displayed as a color image on a display or the like, the determination result, that is, the presence or absence of a surface abnormality and its state can be easily confirmed with the naked eye. Become. That is, such a color image is easy to understand and confirm, and is effective in reducing the human monitoring burden.

  In the abnormality determination method according to the present invention, in the above-described configuration, in the abnormality determination stage, an area value of an abnormal region in the surface image data is calculated, and an abnormal level of an abnormal state on the surface is calculated based on the area value. Is preferably determined.

  According to the above configuration, when the abnormal area gradually increases as the occurrence of abnormalities on the surface progresses, the area value of the abnormal area in the surface image data is calculated, and based on this area value, that is, The abnormal level of the abnormal state on the surface is determined according to the level of the area value. Thereby, it is possible to accurately determine not only the presence / absence of abnormality on the surface but also the occurrence or progress level of abnormality according to the area.

  In the abnormality determination method according to the present invention, it is also preferable that the surface is a steel surface, and in the abnormality determination stage, a rust state on the steel surface is determined.

  In particular, in the above-described configuration, the specific wavelength range in the light irradiation stage includes a plurality of different wavelength ranges, including a first wavelength range of 500 nm or less and a second wavelength range of greater than 500 nm. preferable.

  According to said structure, the light which has a 1st wavelength range which has a wavelength of 500 nm or less and the light which has a 2nd wavelength range larger than 500 nm are irradiated to a steel surface simultaneously or at a different timing. At this time, if rust is generated on the steel surface, the reflectance of light in the first wavelength range is due to the reflection / absorption characteristics of rust and the surface characteristics of rust. Decrease significantly than rate. This phenomenon is because the reflection and absorption characteristics of iron oxide itself, which is the main component of rust, change greatly with the boundary of about 500 nm, and the steel surface becomes rough due to rust formation or erosion. This is because the reflected light becomes diffusive particularly in the short wavelength region.

  Therefore, according to the above configuration, the reflected light intensity of the light in the first wavelength region and the reflected light intensity of the light in the second wavelength region irradiated on the surface of the determination target are calculated, and these intensities are calculated. Based on this, the presence or state of rust on the steel surface is determined.

  Thereby, the more accurate abnormality determination which determined the rust reflection / absorption characteristic and surface characteristic in the steel surface is realizable.

  In the above-described configuration, the abnormality determination method according to the present invention is preferably such that the second wavelength region is 600 nm or more.

  This is because, particularly in the wavelength region of 600 nm or more, the difference in reflected light intensity between the region where rust is generated on the steel surface and the region where rust is not generated is almost the minimum level, and the wavelength dependency is also reduced. Therefore, when the second wavelength range is 600 nm or more and compared with the reflected light intensity of the first wavelength range, the accuracy of rust detection or rust determination is improved and stable rust is secured while ensuring a wide dynamic range. Detection or rust determination can be realized.

  In the above configuration, the abnormality determination method according to the present invention is preferably the inner wall surface of the steel pipe tower for power transmission.

  According to the present invention, it is possible to easily and appropriately perform abnormality determination even on the inner wall surface of a steel pipe that is difficult to inspect due to its shape and light shielding properties. In addition, the inner wall surface of the steel pipe tower for power transmission may be galvanized.

  According to the abnormality determination method according to the present invention, the abnormality determination is performed based on the spectrum information of the surface of the determination target. Therefore, even if the abnormality cannot be identified by human eyes, it is possible to accurately detect the abnormality. Can do.

(Embodiment 1)
[1. System configuration〕
An embodiment of the present invention is described below with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a steel pipe rust inspection system 1 that executes rust determination on the inner wall steel surface of a steel pipe tower for power transmission.

  As shown in FIG. 1, the steel pipe rust inspection system 1 includes an inspection head 11, a transmission unit 12, a reception unit 13, a personal computer (PC) 14, and a power supply unit 15. In the drawing, a steel pipe 10 that constitutes a power transmission tower and surrounds an inspection head that enters the inside of the tower and whose inner wall is subjected to rust inspection is indicated by a broken line.

  The inspection head 11 is a configuration for capturing an image of the inner wall of the steel pipe at an arbitrary position while moving the inside of the steel pipe by an external force or an installed driving force, and acquiring the image data. And a camera that detects the reflected light as image data.

  The transmission unit 12 and the reception unit 13 are transmission / reception interfaces that are connected so as to be able to perform data communication via an optical fiber, wireless communication, or the like. The communication line connecting the transmission unit 12 and the reception unit 13 is preferably an optical fiber digital communication line in order to suppress transmission deterioration due to a strong electric field generated from the transmission line.

  The personal computer (PC) 14 centrally controls the operation or control of the steel pipe rust inspection system 1 as a whole. For example, the PC 14 transmits a control signal to a camera, which will be described later, and controls camera image capture, electronic shutter operation, gain adjustment, exposure adjustment, white balance adjustment, format specification of captured image data, and the like. The power supply unit 15 supplies driving power to the inspection head 11, the transmission unit 12, the reception unit 13, and the PC 14.

  FIG. 2 is an explanatory diagram illustrating a configuration example of the inspection head 11.

  The inspection head 11 shown in FIG. 2 includes a light source 21 a and a light source 21 b at both ends of a cylindrical transparent cover 20. The light source 21a is an LED that mainly emits light in the ultraviolet region (light in the first wavelength region) having a wavelength of 500 nm or less, and the light source 21b is visible light (second wavelength) having a wavelength of 600 nm or more. This is an LED that emits light of a region. Here, the wavelength range of the light source 21a is the light receiving sensitivity of the light receiving element of the camera that receives light, the damage or tolerance of the light receiving element due to light reception, the availability of the light source, and the acquisition of the light receiving elements corresponding to the wavelength region and other wavelength regions. Considering ease of handling, etc., it is more preferably 300 to 470 nm, and further preferably 400 to 410 nm.

  The light emitted from the light source 21a and the light source 21b is irradiated in the direction of the arrow in FIG. 2, and when reflected by the inner wall of the steel pipe, it passes through the transparent cover 20, and a part thereof is an omnidirectional mirror 22 (for example, V stone Incident 30mm diameter omnidirectional mirror). The light reflected by the omnidirectional mirror 22 is collected by the lens 23 in the traveling direction. The image light incident on the lens 23 is imaged by a camera 24 (monochrome video camera such as FLEA manufactured by Point Gray Research) equipped with the lens 23. The image data captured and acquired by the camera 24 is transmitted to the transmission unit 12 through a transmission cable 25 of a predetermined data transmission standard (for example, IEEE1394 standard). In this way, the inspection head 11 can simultaneously image the inside of the steel pipe in the entire circumferential direction and realize efficient rust determination.

  An illumination control cable 26 is connected between the light source 21a and the light source 21b and the camera 24 so that the PC 14 controls the illumination operation of these light sources. Further, when the inspection head 11 is moved inside the steel pipe, the support portion 27 is used for smoothly moving the inspection head 11 inside the steel pipe while keeping the position of the inspection head 11 in the steel pipe radial direction near the center of the steel pipe axis. It is an auxiliary elastic member.

  The image data of the inner wall of the steel pipe captured and acquired by the inspection head 11 in this way is converted into a predetermined data format by the function of the transmission unit 12 and then transmitted to the reception unit 13. The image data received by the receiving unit 13 is taken into the PC 14 and data processing or data recording is performed by the calculation function of the PC 14. Note that the image data of the steel surface in this specification may be still image data or moving image data. If moving image data is employed, real-time rust determination can be made, compared with still image data, but the burden of calculation processing increases.

[2. Operation flow of steel pipe rust inspection system)
Next, the operation in which the steel pipe rust inspection system 1 executes the abnormality determination method of the present invention will be described. FIG. 3 is a flowchart showing an operation flow example of the steel pipe rust inspection system 1. This flow is composed of nine stages of processing consisting of S31 (abbreviation for step 31; the same applies hereinafter) to S39.

  S31 to S34 are processes for adjusting in advance the exposure amount when the camera 24 of the inspection head 11 images the inner wall of the steel pipe. That is, the reference light source is used to irradiate the inner wall of the steel pipe with light that serves as a reference for adjusting the exposure amount (S31), and the steel surface image formed by the reflected light is imaged in all directions by the camera 24 (S32). Then, the captured image data is taken into the PC 14, and an area in which the rust occurrence state is to be determined is specified in the captured steel surface range in accordance with an instruction from the computing device of the PC 14 or a user of the PC 14 ( S33). In response to this area designation, the PC 14 analyzes the image state of the designated area designated in S33, and sends a control instruction signal to the camera 24 so that the exposure amount in the designated area is appropriate. Then, the exposure adjustment is executed (S34).

  In addition, since the inspection head 11 of the steel pipe rust inspection system 1 includes a plurality of light sources 21a and 21b for irradiating a plurality of lights having different wavelength ranges as described above, any of the light source lights is irradiated. Even so, the processes of S31 to S34 are repeated while sequentially switching and using these light sources as the reference light source of S31 so that the exposure state of the designated area designated in S33 is good. In a dark imaging environment such as inside a steel pipe, the depth of field becomes shallow, and the out-of-focus state tends to expand from the center of imaging, so the lens aperture can be opened slightly or the camera shutter speed can be slowed down. Therefore, it is preferable that the imaging state be as bright as possible.

  Next, S35 to S39 are each process from imaging of the inner wall of the steel pipe to be actually subjected to rust determination until executing rust determination processing and recording data. As described above, the inspection head 11 of the steel pipe rust inspection system 1 includes two light sources 21a and 21b for irradiating a plurality of lights having different wavelength ranges. That is, an image is captured by the camera 24 while illuminating the steel surface including the designated area with a certain light source (for example, the light source 21a) (S35). When the imaging process is completed, another light source (for example, the light source 21b) is switched to another light source (S36), and the camera 24 shoots an image while illuminating the steel surface (S37). The imaging process of S35 to S37 is executed while switching the light sources 21a and 21b.

  All the image data obtained by the imaging processing of S35 to S37 is taken into the PC 14, and rust determination processing is performed by the calculation processing of the PC 14 (S38), and the determination result is a recording medium provided (for example, a hard disk) as necessary. (S39). Details of the rust determination process in S38 will be described later.

  In the above description, the imaging processing of S35 to S37 is executed while switching between the two light sources 21a and 21b. Furthermore, the inspection head 11 of the steel pipe rust inspection system 1 uses image data consisting of a plurality of colors as imaging data. It is preferable to combine a large number of light sources 21a, 21b,. Here, the image data composed of a plurality of colors is image data expressed in a plurality of colors so that a human can visually confirm the rust state on the surface of the steel pipe. Specifically, if the image data is displayed on a display or the like, it is a multi-color display that can distinguish between a normal part and an abnormal part and visualize the state of the abnormal part on the surface of the determination target Good.

  Such a selection of a plurality of wavelength ranges includes combinations of the three primary colors of red (R), green (G), and blue (B), as well as combinations of ultraviolet (UV), green (G), and red (R), and ultraviolet. A combination of (UV) + white (W) is conceivable. Note that white (W) can be regarded as combined light having the three primary wavelengths of red (R), green (G), and blue (B).

  When combining such a large number of light sources, as shown in FIG. 4 (S41 to S49 correspond to S31 to S39, respectively), the processing of S46 to S47 is performed as many times as the number of light sources used for irradiation of the steel surface. Will be repeated.

  Note that the image data captured by the camera 24 of the inspection head 11 by the above operation flow causes a predetermined image distortion due to the optical characteristics of the omnidirectional mirror 22. It is preferable to correct the distortion of the image plane (input image plane) of the image data and convert the data into image plane (virtual screen) data as observed when the inner wall of the steel pipe is observed from the vertical direction of the wall surface (see FIG. 5).

[3. (Use a monochrome or color camera)
In the description so far, the system configuration or operation flow of the steel pipe rust inspection system 1 has been described on the assumption that a monochrome video camera is adopted as the camera 24 of the steel pipe rust inspection system 1. A color camera can also be used as the camera 24. This section describes the advantages of using a monochrome camera and the advantages of using a color camera.

  In this section, monochrome video cameras and monochrome still cameras are simply referred to as “monochrome cameras”, and color video cameras and color still cameras are simply referred to as “color cameras”. Collectively.

  Since a monochrome camera generally has sensitivity to a wide range of wavelengths, it is used for multispectral analysis by utilizing the narrow emission wavelength range of the LEDs constituting the light source 21a and the light source 21b as they are. be able to.

  FIG. 6 shows how the light-receiving sensitivity of a monochrome camera with three types of LEDs having different emission wavelength ranges (left side in the figure) captured by a monochrome camera having a wide range of spectral sensitivity characteristics (center in the figure). It is a graph which shows whether it becomes (right side in a figure). In all the graphs in the figure, the vertical axis indicates the light intensity, and the horizontal axis indicates the wavelength. As shown in the figure, the light emission of LEDs with different wavelength peaks and non-overlapping wavelength distributions has different wavelength regions in which the monochrome camera has light receiving sensitivity.

  When a monochrome camera is employed as the camera 24 of the steel pipe rust inspection system 1, the light emission wavelength ranges of these LED light sources are independent so as not to overlap each other so that each light emission of the light source 21a and the light source 21b can be identified during imaging. Thus, the light emission timing of each light source may be shifted as in the light source switching process of S36.

  Many of the currently marketed monochrome cameras have high sensitivity characteristics in a wide wavelength range, and can detect light emitted from LEDs having any of red / green / blue / near ultraviolet wavelengths. In particular, by combining red / green / blue / near-ultraviolet LEDs and performing imaging processing while switching these lighting, it is possible to create a color image by synthesizing the imaging data when each color LED is lit. it can. In order to synthesize a natural color image, it is preferable to combine the respective color LEDs that are switched and lit so that the light emission of the LED group becomes a white or pseudo white light source as a whole. Moreover, a more appropriate color image can be obtained by performing known white balance processing and adjusting the brightness of the captured image data when each color LED is turned on.

On the other hand, the color camera has a built-in color filter composed of a plurality of colors, and the detection wavelength range is limited by the color filter. That is, the spectral sensitivity characteristic of the color camera is in a state of being divided for each wavelength region corresponding to each color of the color filter. Therefore, a color camera is not suitable for spectral analysis of a light source having a wide emission band, but if a LED light source having a narrow emission wavelength range that falls within each wavelength range corresponding to each color of the color filter is selected and used, a multi-spectrum It can be used for analysis (see FIG. 7).
When a monochrome camera is adopted as the camera 24 of the steel pipe rust inspection system 1, it is necessary to irradiate and image the inner wall of the steel pipe while switching a plurality of narrow band light sources (see FIG. 8). When a color camera is employed as the camera 24 of the inspection system 1, it is possible to take an image while simultaneously irradiating the steel pipe surface with a plurality of narrow-band light sources (see FIG. 9).

  Monochrome cameras do not have color filters, so they have the advantage of high detection sensitivity and low noise, while color cameras do not require light source switching, so they can be imaged or inspected in a short time. . That is, when a color camera is employed, irradiation of a plurality of lights (first light, second light,...) Or detection of these reflected lights can be performed in parallel. Compared with the case where the processes are sequentially performed, the time required for the process can be shortened. In addition, when imaging with a color camera, it is also preferable to perform known gamma correction processing on the captured image data.

[4. (Determination of rust area)
Next, the principle or procedure in which the steel pipe rust inspection system 1 performs rust determination based on the reflected light image data of the steel surface will be described (see S38 in FIG. 3).

(4-1. Reflectance of rust area)
When the rust is generated on the steel surface, the present inventors greatly reduce the reflectance particularly when the wavelength is irradiated with light having a wavelength of 500 nm or less, that is, perform rust spectrum analysis. For this purpose, the inventors have found that 500 nm is a characteristic wavelength.

  FIG. 10 is a graph showing the results of an experiment on how the wavelength dependence of reflectance changes when rust occurs on an actual steel surface. In the graph of the figure, the vertical axis indicates the intensity of the reflectance, and the horizontal axis indicates the wavelength (nm) of the irradiation light. In this graph, due to the standardization of the intensity of reflected light, the wavelength dependence of the reflectance of the steel surface on which rust has not occurred is apparently lost. According to the graph of FIG. 10, the reflectance of the steel surface on which rust has occurred is lower than that on the steel surface on which rust has not occurred in the entire wavelength region of the irradiated light. And the difference between the reflectivity of the steel surface where rust is generated and the reflectivity of the steel surface where rust is not generated, that is, the amount of decrease in reflectivity due to the generation of rust increases as the wavelength decreases in the wavelength region of 600 nm or less. Thus, the maximum level is obtained in the wavelength region of 500 nm or less. That is, when rust is generated on the steel surface, the reflectance in a wavelength region of 600 nm or less, particularly 500 nm or less, is significantly reduced due to changes in rust reflection / absorption characteristics and rust surface characteristics. This phenomenon is caused by the fact that the reflection / absorption characteristics of iron oxide, the main component of rust, change greatly around 500 nm, and the steel surface becomes rough due to rust formation or erosion. This is because the reflected light becomes diffusive.

  In addition, in order to measure the reflectance of a steel surface in the wide wavelength range of FIG. 10, two types of light sources having different wavelengths were used. Specifically, an ultraviolet LED having an emission spectrum shown in FIG. 11 is used as the light source on the short wavelength side, and a tungsten halogen lamp having an emission spectrum shown in FIG. 12 is used as the light source on the long wavelength side. The reflectance was measured.

(4-2. Details of rust determination processing)
The steel pipe rust inspection system 1 detects the rust on the inner wall of the steel pipe with high sensitivity by utilizing the property that the steel surface reflectance in the short wavelength region greatly decreases depending on the presence or absence of rust on the steel surface as described above. It is. Specifically, when the inspection head 11 is inserted into the steel pipe and moved to an arbitrary position, illumination light (first light) having a wavelength of 500 nm or less is first emitted by the light source 21a in the designated region to be inspected inside the steel pipe. The image is captured by the camera 24 while applying light, and then the image is captured by the camera 24 while applying illumination light (second light) having a wavelength greater than 500 nm by the light source 21b. It should be noted that the maximum brightness of image data when imaged while irradiating the light from the light source 21a onto the complete diffusion surface and the maximum brightness of image data when imaged while irradiating the light from the light source 21b onto the complete diffusion surface in advance. It is preferable to calculate a ratio and use this ratio for correction processing of pixel value calculation described later.

  Then, the PC 14 uses the light source 21a to illuminate the steel surface with illumination light having a wavelength of 500 nm or less, and illuminates light (second light having a wavelength greater than 500 nm by the light source 21b with each pixel of image data captured by the camera 24. The ratio of the pixel value of each corresponding pixel is calculated with respect to each pixel of the image data when imaged by the camera 24 while illuminating the steel surface with light. Since the pixel values of these image data reflect the luminance of the image, the above calculation processing is the ratio between the reflected light intensity when the light source 21a is turned on and the reflected light intensity when the light source 21b is turned on. Is equivalent to calculating.

  The PC 14 compares the calculated pixel value ratio (intensity of reflected light) with a predetermined threshold value, and thereby distinguishes between a region where rust is generated and a region where rust is not generated on the imaged steel surface. . The appropriate value that should be set as the above threshold value depends on the spectral characteristics of the light source used. To determine this threshold value, an appropriate rust area judgment result is obtained while imaging a steel surface sample that can be visually checked for rust. The threshold may be adjusted so that Further, not only one threshold value but two or more threshold values may be provided. By setting appropriate two or more thresholds, not only whether or not rust has occurred, but also identifying the type of rust that has occurred (eg, white rust, red rust, etc.) It is possible. For example, TH1 and TH2 are set as the above threshold values (TH1 <TH2), and when the pixel value ratio R is R <TH1, it is determined that “red rust has occurred”, and the pixel value ratio R is TH1 <= R. When <TH2, it is determined that “rust does not occur”, and when the pixel value ratio R is TH2 <= R, it can be determined that “white rust occurs”.

  According to the above configuration, a plurality of lights having different wavelength ranges irradiated on the same steel surface in the light irradiation stage are detected as image data of the steel surface in the detection stage, and the image is detected in the rust determination stage. In the data, the intensity of each reflected light is calculated, and rust on the steel surface is determined by comparing this intensity with a predetermined threshold.

  That is, in the abnormality determination method according to the present invention, rust determination based on multispectral analysis using reflected light information of a plurality of different wavelength regions is performed instead of rust determination based on color information of the reflected light image. Even rust that cannot be identified by human eyes can be accurately detected. That is, in the multispectral analysis, information about the incident light to the imaging system is obtained as information on the continuous spectral distribution of light, so that the values of the three attributes (tristimulus) after the integration operation by the color matching function is performed. As compared with color information analysis obtained as a value), the amount of information or characteristic amount of incident light obtained is significantly increased. Thereby, according to the abnormality determination method according to the present invention, it is possible to realize accurate rust determination without being affected by the establishment of the color matching function.

  The abnormality determination method included in the present invention is broadly summarized into two aspects in principle.

FIG. 13 conceptually shows the first method in determining the surface abnormality. In the graph of the figure, the horizontal axis indicates the wavelength, and the vertical axis indicates the light intensity. As shown in the figure, in the first method, incident light having an intensity I _i (400) having a wavelength region near 400 nm is irradiated onto the steel surface, and this reflected light is detected as image data. Then, in the image data, calculates the intensity of the reflected light in the wavelength range of 400nm near _I so as (400) and _I Mo (400), and the difference between _I Mo (400) The intensity _I so (400) Based on this, a rust portion (SO) and a non-rust portion (MO) on the surface are determined.

FIG. 14 conceptually shows the second method in determining the surface abnormality. In the graph of the figure, the horizontal axis indicates the wavelength, and the vertical axis indicates the light intensity. As shown in the figure, the steel surface is irradiated with incident light having an intensity I _i (400) having a wavelength region near 400 nm and incident light having an intensity I _i (600) having a wavelength region near 600 nm. The reflected light is detected as image data. In this image data, the intensities I _so (400), I _Mo (400), I _so (600), and I _Mo (600) of the reflected light calculated in each wavelength range are calculated, and based on these intensity values. Thus, for example, based on the difference between I _so (600) / I _so (400) and I _Mo (600) / I _Mo (400), the rust portion (SO) and the non-rust portion (MO) on the surface are determined. To do. As described above, in order to accurately perform the rust determination region based on the difference in the intensity of the emitted light between the respective wavelength ranges, the incident light intensity I _i (400) and the incident light intensity I _i ( It is necessary to calibrate the intensity of the incident light so as to balance with (600).
When determining the abnormal state on the surface based on the ratio of the intensity of the reflected light to the intensity of the incident light, the distance between the inspection head equipped with the light source and the light detection means and the surface of the determination target is fixed to a predetermined value. Even if it is not performed, since the fluctuation of the ratio value is small, it is possible to realize stable abnormality determination without requiring complicated adjustment of illumination conditions or the like.

  In fact, when the present inventors made a prototype experiment of the steel pipe rust inspection system 1, even if the distance between the inspection head 11 and the inner wall of the steel pipe and the light intensity of the light source 21a and the light source 21b are changed, the determination result of the rust region is greatly affected. Did not occur. For reference, FIG. 15 shows a photographic image of a steel pipe sample containing rust on the surface used in the prototype experiment, and FIG. 16 shows a light source 21a turned on in the steel pipe sample shown in FIG. The result of actually calculating the ratio between the reflected light intensity of the light source and the reflected light intensity when the light source 21b is turned on is displayed in a multi-value image. Since the image of FIG. 16 is before the projective transformation process, a predetermined image distortion occurs due to the optical characteristics of the omnidirectional mirror 22 described above.

  Furthermore, the steel pipe rust inspection system 1 calculates the area value of the rust region in the image data of the steel surface in the rust determination stage, and determines the generation level of rust on the steel surface based on the area value. Is preferred.

  According to the above configuration, the area value of the rust region in the image data of the steel surface (or the area of the rust region is the total image area) corresponding to the situation that the rust region gradually expands as rust generation on the steel surface proceeds. The ratio of rust generation on the steel surface is determined by a method such as comparing the area value with a predetermined threshold value. Thereby, not only the presence or absence of rust on the steel surface, but also the generation or progress level of rust according to the area can be accurately determined.

  That is, the steel pipe rust inspection system 1 determines that as the area value of the specified rust region or the area ratio occupied in the image is larger, the more severe rust where corrosion is progressing is generated. For the determination of the rust generation level, in addition to the area value of the specified rust region or the area ratio occupied in the image, the above-described rust type information may be used in combination as appropriate. For example, when a large area of red rust is generated, it is determined that the rust is extremely severe, whereas when a small area of white rust is generated, it is determined that the rust is extremely mild. .

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

  The abnormality determination method according to the present invention can be widely applied to the determination of rust and deterioration on various surfaces such as a steel surface and the surface of a clay pipe. Particularly, it is suitable for automatic determination of rust generation on a wide area surface such as an inner wall surface of a steel pipe used for steel tower materials.

It is a block diagram which shows schematic structure of the steel pipe rust inspection system which performs one Embodiment of the abnormality determination method which concerns on this invention. It is explanatory drawing which shows the structural example of a test | inspection head. It is a flowchart which shows the example of an operation | movement flow of a steel pipe rust inspection system. It is a flowchart which shows the other operation | movement flow example of a steel pipe rust inspection system. It is a conceptual diagram which shows the outline | summary of a projective transformation process. It is a graph which shows what the light reception sensitivity of the monochrome camera will be when the light emission of three types of LED which has a different light emission wavelength range is imaged with the monochrome camera which has a wide spectral sensitivity characteristic. It is a graph which shows how the light reception sensitivity of the monochrome camera will be, when the light emission of three types of LED which has a different light emission wavelength range is imaged with the color camera provided with a color filter. It is a figure which shows a mode that a steel pipe surface is irradiated while switching a some narrow-band light source, and it images with a monochrome camera. It is a figure which shows a mode that it images with a color camera, irradiating a steel pipe surface simultaneously with a some narrow band light source. It is a graph which shows how the wavelength dependence of a reflectance will change when rust arises on an actual steel surface. It is a graph which shows the emission spectrum of ultraviolet LED. It is a graph which shows the emission spectrum of a tungsten halogen lamp. It is a graph which shows notionally the 1st method in surface abnormality judging. It is a graph which shows notionally the 2nd method in surface abnormality judging. It is a photographic image of the steel pipe sample which contains rust on the surface. It is a multi-value image which shows the result of having irradiated the said steel pipe sample with the some light which has a different wavelength range, and calculating the intensity | strength of each reflected light.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel pipe rust inspection system 10 Steel pipe 11 Inspection head 12 Transmission part 13 Reception part 14 Personal computer (PC)
DESCRIPTION OF SYMBOLS 15 Power supply unit 20 Transparent cover 21a Light source 21b Light source 22 Omnidirectional mirror 23 Lens 24 Camera 25 Transmission cable 26 Illumination control cable 27 Support part

Claims (10)

A light irradiation step of irradiating the surface with light having a specific wavelength range;
Detecting the reflected light of the light as image data of the surface;
A surface abnormality determination method, comprising: calculating an intensity of reflected light in the specific wavelength region in the image data of the surface, and determining an abnormality state on the surface based on the intensity. The specific wavelength range in the light irradiation step is a plurality of different wavelength ranges,
The surface abnormality determination method according to claim 1, wherein in the abnormality determination step, an abnormal state on the surface is determined based on the intensity of reflected light calculated in each wavelength region.   The surface abnormality determination method according to claim 2, wherein in the light irradiation step, light having different wavelength ranges is irradiated while being sequentially switched.   4. The surface abnormality determination method according to claim 2, wherein a plurality of wavelength regions in the light irradiation stage are selected so that image data of a plurality of colors is obtained as the surface image data.   5. The abnormality determination step of calculating an area value of an abnormal region in the image data of the surface and determining an abnormal level of an abnormal state on the surface based on the area value. The surface abnormality determination method according to any one of claims. The surface is a steel surface;
The surface abnormality determination method according to any one of claims 1 to 5, wherein, in the abnormality determination step, the rust state on the steel surface is determined as an abnormal state. The specific wavelength range in the light irradiation step is a plurality of different wavelength ranges,
The surface abnormality determination method according to claim 6, comprising a first wavelength range of 500 nm or less and a second wavelength range of greater than 500 nm.   The surface abnormality determination method according to claim 7, wherein the second wavelength region is 600 nm or more.   9. The surface abnormality determination method according to claim 6, wherein the steel surface is an inner wall surface of a steel pipe tower for power transmission. A light irradiation unit for irradiating the surface with light having a specific wavelength range;
A detection unit for detecting reflected light of the light as image data of the surface;
A surface abnormality determination device comprising: an abnormality determination unit that calculates an intensity of reflected light in the specific wavelength region in the image data of the surface and determines an abnormality in the surface based on the intensity.

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