JPH06229744A - Flaw inspection method for steel plate - Google Patents

Abstract

PURPOSE:To allow the detection of slight and serious flaws and determination of the longitudinal pitch of flaw by connecting a serious flaw detecting circuit having a texture treating function in parallel with a slight flaw detecting circuit and a pitch determining circuit. CONSTITUTION:Surface of a steel plate 2 is scanned with a laser light in the lateral direction and a reflected light is received 3 and sent to a slight flaw detecting circuit A. Signals outputted after gray level conversion are processed by one filter selected by performing differentiation in X, Y and XY directions. The number of pixels in an outputted signal higher than a threshold value is then calculated and a signal representative of slight flaw is outputted when the number of pixels exceeds a predetermined value. On the other hand, a pitch determining circuit analyzes the longitudinal pitch of flaw and detects slight flaw and continuous flaw. A serious flaw detecting circuit B erases a texture signal and following signals on the screen of an image monitor and outputs a signal representative of serious flaw when the number of amplified signals higher than a threshold value exceeds a predetermined value. This method prevents the overdetection of slight flaw and missing of serious flaw at the time of preventing overdetection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a surface flaw of a steel sheet by receiving reflected light.

[0002]

2. Description of the Related Art Conventionally, in a steel manufacturing line, a surface inspection apparatus for irradiating a surface of a steel sheet with light and subjecting an electric signal corresponding to the reflected light to predetermined signal processing to inspect whether or not there is a flaw on the surface of the steel sheet. Is used. The electric signal corresponding to the reflected light includes defect information as a change in voltage, and the electric signal is discriminated by a predetermined threshold to extract and display the defect information. That is, FIG. 3 is an explanatory diagram of a conventional density conversion function for extracting defect information. As shown in FIG. 3, two parameters, a defect signal and a formation signal, can be set on the screen of the image monitor as an electric signal corresponding to the reflected light. That is, the formation signal is erased by a, the signal is amplified by b, the signal of the defective portion is emphasized, and the defect information is extracted and displayed.

Further, in order to extract a slight defect signal, a differential filter and mask processing are used. With regard to this filter processing function, one of three filters of differential processing in the X direction, Y direction, and XY direction is selected and processed with respect to the signal output after density conversion, and the defective portion is extracted. . For signals above the threshold value output by this filter processing, the number of signals that similarly exceed the threshold value in the surrounding pixels is calculated, and if the number exceeds a certain value, it is output as a defect. Has been taken.

[0004]

In the inspection of steel plate surface flaws as described above, the level of the formation signal a or lower is erased by the formation process, so that the defect signal of the level a or higher is emphasized. However, since a signal below the a level is erased, a heavy defect can be detected, but a light defect cannot be detected. Further, when the detection accuracy is increased because a slight defect signal is extracted by the filter processing, there is a problem that a noise signal due to formation is over-detected.

In view of the above problems of the conventional technique,
It is an object of the present invention to provide a steel plate flaw inspection method capable of taking out light defects, heavy defects, and pitch determination in the longitudinal direction of flaws at the same time by one signal.

[0006]

The gist of the present invention for achieving such an object is to optically scan the surface of a steel sheet during line running in the width direction and receive the reflected light to receive the steel sheet. A surface inspection method for inspecting surface defects, characterized by having a light defect detection discriminating circuit and a pitch discriminating circuit, and being connected in parallel with a heavy defect detecting discriminating circuit having a formation processing function etc. There is a steel plate flaw inspection method.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings which are embodiments. FIG. 1 is an explanatory view showing an embodiment according to the present invention. The laser projector 1 irradiates the surface of the steel plate 2 with a laser spot in the width direction. The light receiver 3 receives the steel plate surface reflection of the laser light by a photomultiplier tube or the like and converts it into a voltage intensity signal. The signal processing device 4 detects the presence or absence of a flaw on the surface of the steel plate that has processed the voltage intensity signal, determines the extent of the flaw, the flaw in the steel sheet width direction, and creates a grayscale image of the flaw. The tracking device 5 calculates the number of rotations of the bridle roll 6 that conveys the steel sheet 2 by the pulse transmitter 7, and thereby calculates the conveyance amount of the steel sheet 2 that is conveyed in the direction of the arrow A.

When the signal processing device 4 detects a flaw on the surface of the steel sheet, the alarm device 9 detects the flaw and detects the flaw position and the inspection table 1
When it reaches 0, when the tracking device 5 determines it, a buzzer sound or the like having a different volume or timbre is generated depending on the degree of the flaw. When the flaw of the steel plate surface is detected by the signal processing device 4, the flaw position display device 11 turns on the lamp corresponding to the position of the flaw in the steel plate width direction determined by the signal processing device 4. The image monitor 8 displays a grayscale image of a defect obtained by processing the voltage intensity signal by the signal processing device 4 on the CRT.

FIG. 2 is an explanatory view of a steel plate flaw inspection method according to the present invention. From the laser projector 1 toward the surface of the steel plate 2,
For example, a He-Ne laser is optically scanned in the width direction, the reflected light is received, and the reflected light sent to the discrimination circuit for light defect detection A is subjected to a differential filter, a mask process, etc. for extracting a light defect signal. For the signal output after tone conversion using
1 from 3 types of differential processing in X direction, Y direction and XY direction
When two filters are selected, the number of signals that exceed the threshold value in the surrounding pixels is calculated for signals above the threshold value output by the filter processing, and the number exceeds a certain value. Output as a defect.

On the other hand, in order to analyze the pitch in the longitudinal direction of flaws, a pitch determination circuit for determining continuous flaws can be installed to detect light defects and continuous flaws. By connecting a discrimination circuit for heavy defect detection having a formation processing function in parallel with these, the formation signal is erased by a on the screen of the image monitor, the signal is amplified by b, and the signal of the defective portion is amplified. Emphasize. For signals above the threshold value output by this filter processing, the number of signals that exceeded the threshold value was calculated for peripheral pixels as in the case of light defect detection, and the number exceeded a certain value. If it is output as a defect.

As a result, according to the present invention, as described above, the formation processing function is combined with the conventional threshold value based on the differential intensity, and the formation signal a for the unevenness of the pickling edge portion, for example.
If the value of is set to a high value, over-detection of the formation of the edge part will be eliminated, and it will be applied to full-width detection, and it will be possible to detect continuous flaws by flaw pitch analysis, and linear flaws such as balding and sliver It becomes possible to detect two kinds of things at once by one signal such as a surface flaw such as a mountain shape or yellowing, and other flaws such as a flaw and a jump flaw.

[0012]

As described above, according to the present invention, it is possible to simultaneously solve the problem of overdetection when detecting a light defect and the overlooking of a serious defect when preventing the overdetection, and Only continuous defects can be detected,
It is possible to improve the detection rate and reduce over-detection.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment according to the present invention,

FIG. 2 is an explanatory view of a steel plate flaw inspection method according to the present invention,

FIG. 3 is an explanatory diagram of a conventional density conversion function for extracting defect information.

[Explanation of symbols]

 1 Laser Projector 2 Steel Plate 3 Light Receiver 4 Signal Processing Device 5 Tracking Device 6 Bridle Roll 7 Pulse Transmitter 8 Image Monitor 8 9 Alarm Device 10 Inspection Stand 11 Defect Position Display Device

Claims (1)

[Claims] 1. A surface inspection method for optically scanning the surface of a steel sheet during line running in the width direction and receiving the reflected light to inspect for defects on the surface of the steel sheet. A steel sheet flaw inspection method comprising a discrimination circuit for heavy defect detection having a formation processing function and the like connected in parallel therewith.