JPH06241740A - Electro-resistance welded tube weld beam defective cutting and defect detecting method - Google Patents

Abstract

PURPOSE:To automatically detect the defective cutting at a welded steel tube cut section on the on-line basis by fine line processing a cross section-shaped image, extracting the cut section via intensity, and comparing an approximate curve with the cut cross sectional shape. CONSTITUTION:A steel pipe 5 is arranged so that the step shape of a cut face immediately after being cut by a cutting tool 6 can be recognized as an image. A slit light projector 1 is installed at the prescribed angle against the steel pipe 5, and a television camera 2 is installed at a position perpendicular to the steel pipe 5. The slit light 3 from the projector 1 is radiated to the outer cut face of the steel pipe 5, and the obtained outer cut cross sectional image is photographed by the television camera 2. The outer cut cross sectional image is inputted to an image processing device 7, the image is fine line processed, and a cut section is extracted by the cross sectional shape intensity distribution difference. The cut section cross sectional shape wave-form is secondarily approximated, the obtained approximate curve is compared with the cut section cross sectional shape wave-form, and the local irregular defect in the cut section is detected. When the defect is detected, it is reported by a warning device 8 and a marking device 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting defects such as bite wear and tooth chipping due to defective bead cutting of electric resistance welded pipe.

[0002]

2. Description of the Related Art As a method for detecting defective cutting / defects of ERW pipe welding beads, a shape detector using a laser beam cutting method is known from Japanese Patent Laid-Open No. 57-108705. The light cutting method is a shape measuring method in which the slit light 3 is projected onto the surface to be measured 4 at a light cutting angle θ ₁ as shown in FIG. 3 and its cross-sectional shape can be equivalently measured when viewed from an angle θ ₂ different from this. Is. In JP-A-57-108705, it is not possible to quantify the light-section image until recording. That is, the evaluation of the weld bead cutting shape depends on the human visual judgment and does not reach the automatic defect detection.

As an automatic cutting shape measuring method, Japanese Patent Laid-Open No.
There is 7-137027, but rather than directly calculating the cutting shape, it is judged from the difference between the profile obtained by the optical cutting angle and the reference formula calculated from the inner diameter of the pipe in advance, so the measurement error is large. It is difficult to detect cutting defects based on defects.

As a method for quantifying the cutting shape by signal processing the light-cutting image, the cutting part and the non-cutting base material of Japanese Patent Application No. 3-273449 filed by the present applicant are used. Although there is step measurement of the butt shape, it is not possible to detect the step change between the cutting part and the non-cutting part, and it is impossible to detect the shape change in the cutting part, that is, the local shape change due to chipping of the bite, wear, etc. .

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In No. 37027, it is impossible to detect with high accuracy because it is greatly affected by the molding state at the time of pipe making. Therefore, cutting defects / defects after welding bead cutting are generally judged by visual judgment and / or touch, and it is currently difficult to detect defects during online pipe making. The present invention advantageously solves this problem, and it is an object of the present invention to provide a method for automatically detecting a cutting defect in a welded steel pipe cutting portion online.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to capture an image of a steel pipe bead cutting portion by a slit light and an optical cutting method by a television camera when measuring the shape of the electric resistance welded pipe after welding bead cutting. In the method of detecting bead cutting defects / defects, the cross-sectional shape image is thinned to calculate the cross-sectional shape, the cut portion and the non-cut base material are distinguished by the brightness of the cross-sectional shape, and the distinct cutting is performed. Detecting defective cutting / defects by electric welded pipe welding, characterized by accurately detecting a defective cutting / defect due to bead cutting by calculating an approximate curve in the part and calculating the difference between the approximate curve and the cutting cross-sectional shape Is the way.

That is, according to the present invention, a bead shape immediately after cutting is obtained by irradiating a slit light with a television camera by a light cutting method, and the cutting portion is judged from the brightness difference between the cutting portion and the non-cutting base material. , Not only the step shape difference between the base material and the cutting portion is obtained, but an approximate curve is calculated in the cutting portion and the difference between the approximate curve and the cross-sectional shape in the cutting portion is obtained, which occurs during cutting in the cutting portion. The defect can be accurately detected.

[0008]

The present invention will be described with reference to FIGS. FIG. 1A is obtained by plotting the maximum luminance in the y-axis direction in FIG. 3 along the x-axis from the light section image. In this state, it is not clear where the cutting part is.

Therefore, the luminance state on the waveform of FIG. 1A is plotted along the x-axis as in FIG. 1A.
It is (b). The slit light is mainly specularly reflected on the cutting surface immediately after cutting, and the slit light is mainly diffusely reflected on the non-cutting portion because the background of the steel pipe is unchanged. Therefore, in the image of the television camera that captures the diffused reflection light, the luminance in the cut portion is lower than the luminance distribution in the non-cut portion. Therefore, if the range in which the brightness is lowered in FIG. 1B is calculated, it becomes a cutting portion.

As a method thereof, for example, if the waveform of FIG. 1B is differentiated in the x-axis direction as shown in FIG.
(A). The area between the maximum value and the minimum value in FIG. 2A is the cutting portion, and if this result is used, it is possible to easily detect the shape defect in the cutting portion. That is,
The approximate shape waveform as shown in FIG. 2B can be obtained by accurately extracting the cut portion from the shape waveform of FIG. 1A and performing curve fitting (waveform approximation) such as the least-squares approximation method.

By calculating the difference between FIG. 1 (a) and FIG. 2 (b), the local change of the cutting portion shown in FIG. 2 (c), that is, the local change due to bite chipping, abrasion, etc. It is possible to detect a specific shape change.

[0012]

EXAMPLE An example in which the present invention is applied to the external shape inspection of a steel pipe will be described with reference to FIG. Wall thickness 2.1 mm External shape 2
As shown in FIG. 4, a steel pipe 5 of 5.6 mm has an optical arrangement such that the step shape can be visually recognized on the cut surface immediately after cutting the bite 6, that is, the slit light projector 1 is installed at 19 ° to the steel pipe,
Similarly, the television camera 2 was installed at a position perpendicular to the steel pipe.

The slit light 3 from the slit light projector 1 was applied to the outer surface of the steel pipe, and the resulting cut surface image was photographed by the television camera 2. The cut-out cross-section video signal is input to the image processing device 7, the image is thinned, the cut portion is extracted by the cross-sectional shape luminance distribution difference, the cut-section cross-sectional waveform is quadratic-approximated, and the obtained approximate curve and the By comparing with the waveform of the cross-sectional shape of the cut portion, it was possible to detect a local unevenness defect in the cut portion.

The result of the measurement by the image processing is a convex flaw having a height of 0.81 mm continuing in the longitudinal direction of the pipe, and the measured result after sampling the sample after pipe making is 0.78 mm. It was As described above, according to the electric resistance welded pipe welding bead cutting defect / defect detection method of the present invention, an actual cutting defect can be measured with an accuracy of 0.1 mm or less.

Further, in most cases, cutting defects and defects in the cutting portion due to defective bits continue in the longitudinal direction of the steel pipe, so it is clear that the defect signal should be added to improve the detection accuracy. . Further, at the time of detection, the alarm device 8, the marking device 9, and the like are used to notify the user, so that mass production of defective products can be prevented.

[0016]

As described above, the method of the present invention makes it possible to guarantee the quality of all pieces online by accurately determining the cutting defects and defects in the bead cutting portion.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a procedure of an operation of the present invention.

FIG. 2 is also an explanatory diagram of a procedure of the operation of the present invention.

FIG. 3 is a diagram illustrating the principle of a light cutting method.

FIG. 4 is an example in which the present invention is stressed for measuring the internal cutting bead cutting shape of a steel pipe.

[Explanation of symbols]

 1 Slit Light Projector 2 TV Camera 3 Slit Light 4 Surface to be Measured 5 Steel Pipe 6 Cutting Bit 7 Image Place Ideal 8 Alarm Device 9 Marking Device

Claims (1)

[Claims] 1. A method for detecting a weld bead cutting defect / defect by capturing an image of a steel pipe bead cutting portion by a slit light and a light cutting method by a television camera when measuring the shape of a welded pipe after welding bead cutting, The cross-sectional shape image is thinned to calculate the cross-sectional shape, and the brightness of the cross-sectional shape is used to distinguish between the base material which is the non-cutting part and the cutting part, and the approximated curve is calculated in the distinguished cutting part. An electric resistance welded pipe welding bead cutting defect / defect detection method, which accurately detects a cutting defect / defect due to bead cutting by calculating a difference between a curve and a cutting cross-sectional shape.