JPH03205540A - Defect detection method - Google Patents

Abstract

PURPOSE:To accurate detect a defect without being affected by variation in lighting state by varying a threshold value so that the area rate in an area wider than a defect detection area is within a specific range. CONSTITUTION:A moving base 3 is moved and stopped so that the visual field of a CCD camera 4 is positioned on the internal surface of the entrance part of a tube body 1 and an image of the entrance part internal surface irradiated by an irradiation device 5 is picked up by the camera 4 to send its video signal to an image processor 6. The window of the processor 6 is widened to the entire visual field of the camera and the threshold value is compared with a brightness value of each picture element to convert the picked-up image in the window into binary data. Then a control arithmetic unit 7 measures the area of a black display part and judges whether or not the area measured value is within the specific range; and the threshold value is increased or decreased until the specific range is entered, and when the measured value enters the specific range, a defect part is displayed with proper size.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a defect detection method for detecting defects in an object to be inspected by image processing.

2. Description of the Related Art In recent years, image processing has been put into practical use in inspection departments of production lines to detect defects in objects to be inspected, such as tubes. An example of a method for detecting defects on the inner surface of a tube is to output an image captured by a CCD camera to an image processing device while illuminating the inner surface of the tube, and then output the image taken by a CCD camera to an image processing device, which then calculates the brightness value of each pixel. is compared with a threshold value fixed to a predetermined value and binarized, and a portion whose brightness value is smaller than the threshold value, that is, a shadow portion caused by the defective portion, is detected as a defective portion. Then, the area of the defective portion within the defect detection area (window) of the image processing device is measured, and the quality of the tubular body is determined based on this area value.

Problems to be Solved by the Invention However, the conventional defect detection method described above has a problem in that the binarized images of the same defect differ due to changes in ambient brightness or changes in illumination over time. In other words, for example, when the lighting condition worsens (darkens), the shadow area becomes larger even for the same defect, so when binarized, the area of the defect increases, making it difficult to judge whether the tube is good or bad. , there was a risk of making the wrong decision.

The present invention solves the above problems, and provides a defect detection method that does not incorrectly judge the quality of an object to be inspected, such as a pipe, even if there are changes in ambient brightness or changes in lighting over time. The purpose is to

Means for Solving the Problems In order to solve the above problems, the present invention calculates each area ratio of the binarized portion in an area wider than the defect detection area before performing defect detection, and sets each area ratio within a predetermined range. The threshold value is set by changing the threshold value so that the value falls within the range of 0.1 to 1.0, and the defect detection area is binarized using this threshold value to perform defect detection.

Effect In the above configuration, by calculating each area ratio of the binarized part in an area wider than the defect detection area and changing the threshold value so that each area ratio falls within a predetermined range, it is possible to The threshold value is set high, and when it is dark, the threshold value is set low, so that the area of the defective part in the binarized image is properly detected without being affected by surrounding brightness or secular changes in illumination. This prevents erroneously determining whether the object to be inspected is good or bad.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

First, equipment for detecting defects will be explained with reference to FIG. Reference numeral 1 designates a tube body as an object to be inspected. This tube body 1 is held rotatably around the tube axis by a plurality of pairs of rotating rollers 2, and is rotated by a motor 3 attached to a predetermined rotating roller 2. . These rotating rollers 2 are supported by a movable table 3 that is movable in the direction along the tube axis, and the tube body 1 is moved in the tube axis direction together with the movable table 3 by a drive device (not shown). 4 and 5 are the tube body 1 due to the movement of the tube body 1.
A COD camera and an illumination device that can be freely inserted into the COD camera are arranged so that the irradiation area of the illumination device 5 is in the field of view of the COD camera 4. An image processing device 6 is connected to the CCD camera 4, and a video signal from the CCD camera 4 is output to the image processing device 6. The image processing device 6 is connected to a control/arithmetic device 7, such as a personal computer, via a communication line or the like, and data is exchanged therewith.

Next, the defect detection method will be explained according to the flowchart shown in FIG.

First, in step S1, the field of view of the CCD camera 4 is
The movable table 3 is moved and stopped so as to be positioned on the inner surface of the entrance portion of the tube body 1, and the CCD camera 4 images the inner surface of the entrance portion of the tube body 1 illuminated by the illumination device 5. The image captured by the CCD camera 4 is input to the image processing device 6 as a video signal. Next, in step S2, the window (display area) of the image processing device 6 is expanded to cover the entire camera field of view X, and in this state,
As shown in step S3, a certain initially set threshold value is compared with the brightness value of each pixel, and the captured image in the window is binarized (pixels whose brightness value is smaller than the threshold value are displayed in black, and the brightness value is Pixels larger than the threshold are displayed in white). At this time, if the surroundings of tube body 1 are bright, as shown in Fig. 3 (
As shown in a), the defect part a is displayed smaller and the boundary part b between the illuminated part and the non-illuminated part is located close to the outer frame of the camera field of view X, so that the black display part is The percentage is displayed small. In addition, even when the same location is imaged, if the surrounding area is dark or the lighting has deteriorated over time, the defect area a may appear thicker, as shown in Figure 3(b). At the same time, the boundary portion b is located away from the outer peripheral frame of the camera field of view X and closer to the center, so that a large proportion of the black display portion is displayed. In step S4, the area of the black display portion is measured by the control calculation device 7. In step S5, it is determined whether the area measurement value is within a preset value range. In this case, if the measured value is smaller than the set range as shown in FIG. 3(a), steps S6 to S7
Step S3 is performed again after increasing the threshold value by a predetermined value.
If the measured value is larger than the set value range as shown in FIG. 3(b), step S6 to step S
Proceed to Step 8, decrease the threshold by a predetermined value, and repeat Step S.
Return to 3. The threshold value is then increased or decreased repeatedly until the measured value falls within the set range. As a result, when the measured value falls within the set range, the boundary part b in the binarized image will be at the position shown in Figure 3 (C), and the defect part a will be at an appropriate size without being affected by the illumination condition. is displayed. Thereafter, in step S, the window is reduced to the defect detection area y so that no non-illuminated portion is within the window. Then, in step SIO, defect detection work is performed. In other words, tube body 1
While rotating and moving appropriately in the direction of the tube axis, C
The CD camera 4 sequentially images the inner surface of the tubular body 1, and the image processing device 6 performs binarization processing using the threshold set above.
The area of the defective portion a is measured to determine whether the tubular body 1 is good or bad.

This allows defect detection work to be performed accurately without being affected by lighting conditions.

Note that the CCD camera imaging position for setting the threshold value described above is not limited to the population area, but is located at a predetermined distance from the entrance area of the tube body 1.
It may be inserted inside. Further, although the case of the tube body 1 is shown as the object to be inspected, the present invention can also be applied to a plate material or the like.

Effects of the Invention As described above, according to the present invention, before performing defect detection, each area ratio of the binarized portion is determined in an area wider than the defect detection area, and a threshold value is set so that each area ratio falls within a predetermined range. By changing , defects can be detected accurately without being affected by changes in illumination conditions, and the reliability of defect inspection is improved.

[Brief explanation of drawings]

The drawings relate to one embodiment of the present invention; FIG. 1 is a schematic perspective view of defect detection equipment, FIG. 2 is a flowchart of a defect detection method, and FIGS. 3(a) to (C) each show captured images. FIG. DESCRIPTION OF SYMBOLS 1... Tube body (object to be inspected), 4... CCD camera (imaging device), 5... Illumination device, 6... Image processing device, 7... Control calculation device, X... Camera field of view, y...
・Defect detection area.

Claims (1)

[Claims] 1. Illuminating the surface of the object to be inspected, outputting the image captured by the imaging device to an image processing device, which compares the brightness value of each pixel with a threshold value and binarizes it,
This is a defect detection method for detecting a location where the luminance value is smaller than the above threshold value as a defective part, and before performing defect detection, the area ratio of each binarized part is calculated in an area wider than the defect detection area,
A defect detection method in which a threshold value is set by changing the threshold value so that each area ratio falls within a predetermined range, and the defect detection area is binarized using the threshold value to perform defect detection.