JPH04296645A - Defect detecting method - Google Patents

Abstract

PURPOSE:To detect faraway defect with high accuracy and high S/N by a light spot irradiating an object to be inspected, taking a thermal image at the irradiated position by an infrared image device, and giving differentiating treatment to the obtained thermal image signal or, after differentiating treatment, giving differential treatment to the differentiated reference thermal image signal. CONSTITUTION:A light spot (infrared ray) is radiated onto the surface of an object to be inspected. A thermal image at radiated position is taken by an infrared image device (infrared camera), and a differentiating treatment is given to the image focused. The differentiated image is displayed on a CRT. On the CRT screen, contours of defects and light spots are clearly displayed, and the form and size of light spots, heating area, presence of defect in the heating area, and form and size of defects can be detected visually. Also reference thermal image free from defect is pre-taken, the differentiating image of the thermal image signal is memorized. Then the differential image between the memorized image and the differentiated image is displayed on the CRT and a defect is judged by comparing the difference between the displayed image and the obtained differentiated image, to detect the defect securely.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a defect detection method, and particularly to a method for detecting defects for the purpose of maintaining large structures such as buildings and bridges, outdoor electrical equipment, and plant equipment. The inspection object can be heated from a distance, and defects can be detected with high precision by measuring the surface temperature of the inspection object from a long distance using an infrared imaging device.

0002

[Prior Art] Figure 3 shows, for example, the literature (1988 NATO
ASI Series, Vol. FIG. 44 is a configuration diagram of a device used in a conventional defect detection method published in 2003. FIG. 4 shows calculation results of the surface temperature of the model shown in FIG. 3. In the figure, 1 is an infrared imaging device, 2 is a heater, and 3 is a laminated material, including aluminum 31 and epoxy 32.
, and foam material 33. 4 is a defect inside the laminated material.

Next, the operation will be explained. From FIG. 3, the laminated material 3 moves from the right side of the page to the left side at a constant speed. The surface of the laminated material 3 is heated by the heater 2,
The surface temperature of the laminated material 3 is measured by the infrared imaging device 1 . By arranging the heater 2 and the infrared imaging device 1 as shown in FIG. 3, defects 4 inside the laminated material 3 can be detected as a thermal image. FIG. 4 shows the difference in surface temperature between the case where there is an internal defect (curve B) and the case where there is no internal defect (curve A), determined by computer simulation. It is clear that the surface temperature of the defective portion has increased, and from this it is possible to determine the presence of a defect. In order to detect a defective image with a high S/N ratio, differential image processing that takes the difference between a normal image and a defective image is usually performed. In order to further clarify the defect image, binarization processing is performed.

0004

The conventional defect detection method is performed as described above, and image processing, that is, signal processing method is an important technique for obtaining high precision and high S/N. However, in the above-mentioned difference processing, since the temperature increase position and the defect position do not correspond accurately as shown in FIG. 4, there is a drawback that the defect part is determined to be larger. Furthermore, the thermal images of the normal and defective areas are not images of the same location in the laminate. Therefore, there was a problem that was disadvantageous in terms of S/N. In addition, in the non-destructive internal inspection method disclosed in Japanese Patent Application Laid-Open No. 60-213854, a method for accurately detecting defects from one image without performing differential processing is described, but the content is based on the method of detecting defects using isothermal curves. Since it is basic to draw and analyze the image, the drawback of judging the defective part as being larger is unavoidable. Furthermore, since it is not a heating method, high S/N cannot be expected. As described above, conventional defect detection methods using infrared imaging devices have drawbacks such as not being able to accurately measure the size of defects, requiring two images to perform differential processing, and worsening the S/N ratio. Ta. Furthermore, since the inspection is performed using infrared rays, the inspection area cannot be seen with the naked eye, resulting in the problem of uncertainty in the inspection area.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a defect detection method with higher accuracy and higher S/N than conventional methods.

[0006]

[Means for Solving the Problems] A defect detection method according to the present invention irradiates an object to be inspected with a light spot, captures a thermal image of the irradiated position with an infrared imaging device, and differentiates the obtained thermal image signal. After processing or differential processing, the reference thermal image signal is subjected to differential processing and differential processing is performed to determine defects.

[0007]

[Operation] Since the signal processing method according to the present invention uses differential processing, the dimensions of the light spot shape, that is, the heated area can be specified, and the inspection area can be clearly defined. Furthermore, the size of defects can be detected with high precision. In addition, defects can be detected with high accuracy from a single image, and since it uses a heating method, the S/N is high.
becomes.

[0008]Furthermore, if the reference thermal image signal is subjected to differential processing after differential processing and then differential processing is performed, defects can be clearly determined, although there is a disadvantage due to the use of two images.

[0009]

[Example] Example 1. Examples of the present invention will be described below. FIG. 1 is an explanatory diagram for explaining the defect detection method of the present invention, showing a surface temperature pattern that would be obtained by an infrared imaging device (not shown) and a temperature pattern after signal processing. This temperature pattern was obtained by computer simulation. In the figure, 5 is the object to be inspected, 6 is the light spot, 71 and 72 are the surface temperature patterns of the object to be inspected with and without defect 4, respectively.
3 is a differential temperature pattern obtained by subtracting pattern 72 from surface temperature pattern 71, and 74 and 75 are differential temperature patterns of surface temperature patterns 71 and 72, respectively. The surface of the object to be inspected 5 is heated by the irradiation of the light spot 6. The heat diffuses into the interior of the object to be inspected 5 by thermal conduction. The diffusion state differs depending on whether there is a defect 4 inside or not. As a result, the surface temperature of the object to be inspected 5 differs. By the way, even if the temperature pattern measured by the infrared imaging device is pattern 71, it is doubtful whether the presence of a defect can be determined. Since there are high and low temperature patterns in the temperature pattern 71, it is recognized that there is an abnormality, but it is difficult to determine the existence of a defect, and the size of the defect cannot be determined. Further, although the presence of a defect can be determined from the differential temperature pattern 73, it is extremely difficult to determine the size of the defect. However, it is clear that the differential temperature pattern 74 shows a peak at the edge of the defect and the light spot, and the difference in the defect area from the differential temperature pattern 75 when there is no defect is obvious. In this way, by performing differential processing on the measured thermal image, the heated region can be identified, and the presence or absence of a defect within the heated region and the shape and size of the defect can be determined.

FIG. 2 is a flowchart showing a defect detection method according to an embodiment of the present invention. In step S1, an inspection surface N is determined, and in step S2, a light spot (infrared rays) is irradiated onto this inspection surface N. In step S3, a thermal image of the inspection surface N is taken with an infrared imaging device (infrared camera),
In step S4, differential processing is performed on this captured image. This differential image is displayed on the CRT in step S5,
Defects are visually determined from the screen (step S6). That is, the circle of the defect and the light spot is clearly displayed on the screen, and the shape and size of the light spot, the heated area, the presence or absence of a defect existing in the heated area, the shape and size of the defect, etc. can be detected. In step S7, the light spot position is moved using N+1 as a new inspection surface, and the same operation is repeated until the inspection surface becomes N=M (M: inspection end surface) (step S8).

Example 2. Note that step S in the above embodiment
In Step 6, a reference thermal image without defects is captured in advance, a differential image of this thermal image signal is stored, and a difference image between this reference differential image and the differential image obtained in step S4 is displayed on a CRT. , the defect may be determined based on the difference from the differential image displayed in step S5, and the defect is displayed more clearly.

0012

As described above, according to the present invention, an object to be inspected is irradiated with a light spot, a thermal image of the irradiated position is taken by an infrared imaging device, and the obtained thermal image signal is subjected to differential processing or After the differential processing, the differential processing of the reference thermal image signal is performed to perform differential processing to determine a defect, so that a defect image with high accuracy and high S/N can be obtained. In addition, since the heating area can be determined, the inspection location can be specified and the inspection time can be shortened.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram illustrating a defect detection method of the present invention.

FIG. 2 is a flowchart showing a defect detection method according to an embodiment of the present invention.

FIG. 3 is a configuration diagram showing an apparatus used in a conventional defect detection method.

FIG. 4 is a characteristic diagram showing the surface temperature of an object to be inspected in a conventional defect detection method.

[Explanation of symbols]

1 Infrared rays 4 Defects 5 Object to be inspected 6. Light spot

Claims (1)

[Claims] Claim 1: A step of irradiating a light spot onto an object to be inspected, a step of capturing a thermal image of the irradiation position with an infrared imaging device, and differential processing of the thermal image signal obtained by the infrared imaging device, or after differential processing. A defect detection method that performs differential processing using a differentially processed reference thermal image signal to determine defects.