JPH06102195A - Inspection method and device for surface flaw - Google Patents

Abstract

PURPOSE:To obtain an inspection method and device for surface flaw in which inspection of surface is done to detect flaw with high sensitivity even if the surface temperature of the inspected matter is high. CONSTITUTION:Before the scattered light from a hot roll steel plate 22 goes into a CCD line sensor camera 28, an optical filter 32 provided on the CCD line sensor camera 28 eliminates the intensity of wave length over 550nm. As the result, the noize due to radiation energy of electro-magnetic wave of wave length over 550nm is eliminated and thus, the inspection of the surface is done with high sensitivity and flaw can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection apparatus for inspecting the surface of a material to be inspected and inspecting the surface of the material to be inspected. For example, it is suitable for inspecting the surface of a hot rolled steel sheet. The present invention relates to a surface defect inspection device.

[0002]

2. Description of the Related Art A typical conventional surface defect inspection apparatus will be described with reference to FIG. FIG. 12 is an explanatory diagram showing a schematic configuration of a conventional surface defect inspection apparatus. In this conventional surface defect inspection apparatus, the surface 10a of the strip-shaped inspected material 10 continuously conveyed in the direction of arrow A is illuminated by the light source 12 arranged above the inspected material 10. This surface 10
The line sensor camera 1 in which the image of a uses a one-dimensional CCD or the like
4, the video signal from the line sensor camera 14 is processed by an image processing device (not shown), so that the surface 10a of the inspected material 10 is inspected and defects are extracted.

[0003]

However, when detecting defects in high-temperature inspected materials such as hot-rolled steel sheets using the above-mentioned conventional surface defect inspection apparatus, the sensitivity of the line sensor camera changes from the visible light range to the infrared range. The electromagnetic waves emitted from the object to be inspected are also detected by this line sensor camera because they extend to the area. As a result, there is a problem that the S / N of the detection signal is significantly reduced. Further, depending on the surface temperature of the object to be inspected, the S / N is not improved enough to detect a signal indicating a surface defect even if an infrared cut filter is used. If the output of the light source is increased in order to increase the S / N forcibly, the scattered light due to the surface defects will be stronger and the S / N will be improved, but the light source will be burdened and the life of the light source will be shortened. .

In view of the above circumstances, the present invention provides a surface defect inspection method and apparatus for inspecting a surface by inspecting the surface with high sensitivity even if the surface temperature of the material to be inspected is high. To aim.

[0005]

The present inventor has conducted various experiments and researches in order to achieve the above object, and as a result, the radiant energy of electromagnetic waves radiated from a high temperature surface has a wavelength of 500 nm or less. The inventors have found that it does not affect the region and have completed the present invention. Specifically, the surface defect inspection method of the present invention is a surface for irradiating the surface of a material to be inspected with light and detecting a surface light defect of the material to be inspected by detecting reflected light of the light reflected by this surface. In the defect inspection method,
When detecting the reflected light, the electromagnetic waves emitted from the surface are removed. The shortest wavelength of the electromagnetic wave to be removed is preferably in the range of 500 nm to 700 nm.

Further, the surface defect inspection apparatus of the present invention detects the surface defect of the material to be inspected based on the image pickup signal output from the image pickup device which detects the reflected light of the light irradiated on the surface of the material to be inspected. In the surface defect inspection device that
It is characterized by being provided with an optical filter for blocking electromagnetic waves emitted from the surface.

In this image pickup device, the shortest wavelength of the electromagnetic wave to be shielded is 500 n according to the change of the surface temperature of the object to be inspected.
It is preferable to include a selection unit that selects the optical filter in the range of m to 700 nm. Further, it is preferable that the image pickup device includes an optical amplifier on the downstream side of the optical path of the optical filter.

Experiments on which the present invention is based will be described. The present inventor designed and manufactured a high-temperature steel plate surface observation furnace equipped with a window for surface observation, which can lower the internal pressure to 10 ^-2 Torr and can heat the sample temperature to 900 ° C. The radiant energy emitted was measured. Among electromagnetic waves radiated from a black body in radiative equilibrium at the absolute temperature T, if the radiant energy density between wavelengths λ and λ + dλ is pλdλ, the logical expression of pλdλ follows Planck's radiation law,

[0009]

[Equation 1]

Is given by the equation (1) (the vertical axis represents the radiant energy density and the horizontal axis represents the wavelength. The same applies to FIGS. 2 and 3). Where h is Planck's constant,
c is the speed of light and k _B is the Boltzmann constant. On the other hand, the radiant energy from the surface of the high temperature steel sheet without the oxide scale was as shown in the graph of FIG. 2 and was close to the theoretical formula. As a result, it was found that the radiant energy from the surface at 700 ° C. had no effect on 500 nm or less.

Since the actual high temperature surface has an oxide scale, the radiant energy was also measured on the surface having an oxide scale. This radiant energy is
As shown in the graph below, the radiant energy from the surface at 700 ° C is 50 even for the surface with oxide scale.
It was found that it did not affect the thickness below 0 nm. As a result of the above experiment, when the surface defect is detected by irradiating the surface of the high-temperature steel plate with light and detecting the reflected light from this surface with an imaging device, noise due to the radiant energy of electromagnetic waves emitted from the surface of the high-temperature steel plate To lower the ingredients,
Higher by selecting the shortest wavelength in the wavelength range that is appropriately cut according to the surface temperature (hereinafter, this wavelength is referred to as the "cut wavelength"), and blocking all electromagnetic waves longer than this cut wavelength with an optical filter. It was found that the S / N can detect defects on the surface of the high temperature steel plate.

Based on this viewpoint, an experiment was conducted in which the surface defects of the hot rolled steel sheet having a surface temperature of 700 ° C. were imaged by a one-dimensional imager. The results of this experiment will be described with reference to FIGS. The vertical axis in each of FIGS. 4 to 6 indicates the intensity of the image pickup signal of the one-dimensional image pickup device, and the horizontal axis indicates the width direction of the hot-rolled steel sheet. FIG. 4 is a graph when an image is taken without a filter, FIG. 5 is a graph when only an infrared cut filter is installed in the image pickup device, and FIG. 6 is a case where an optical filter for cutting a wavelength region of 500 nm or more is installed in the image pickup device. The graph of is shown.

From these graphs, it was found that a high S / N can be obtained when an optical filter for cutting a wavelength region of 500 nm or more is installed in the image pickup device.

[0014]

According to the present invention, since the image pickup device is provided with the optical filter for blocking the electromagnetic wave radiated from the surface of the object to be inspected,
When the surface of the material to be inspected has a high temperature, it is possible to almost completely prevent the electromagnetic wave radiated from the high temperature surface from being detected by the image pickup device, and the S / N of the image pickup signal can be improved.

The shortest wavelength of the electromagnetic wave to be removed is 500 nm to 7 depending on the change in the surface temperature of the object to be inspected.
When the optical filter can be selected in the range of 00 nm, it is possible to prevent the light amount from being decreased more than necessary, so that the detection sensitivity can be improved. Furthermore, when the image pickup device is provided with an optical amplifier, it is possible to efficiently compensate for the shortage of the amount of light due to being blocked by the optical filter.

[0016]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 7 is a block diagram showing a schematic configuration of a surface defect inspection apparatus according to an embodiment of the present invention, showing a state in which the surface of a hot rolled steel sheet is inspected. A portion 22a of the hot rolled steel plate 22 moving in the direction of arrow A is the white light 26 from the rod-shaped light source 24.
Is continuously irradiated with, and a part of this is scattered by 22a. A part of the scattered light is incident on the CCD line sensor camera 28, and the surface of the hot-rolled steel sheet 22 is imaged. A metal halide lamp is used as the rod-shaped light source 24. This metal halide lamp is, as shown in FIG. 9, compared with the conventional halogen lamp shown in FIG.
It has a relatively high intensity at short wavelengths. In addition, the power source 30 for the light source
Supplies power to the rod-shaped light source 24.

The CCD line sensor camera 28 is provided with an optical filter 32, and this optical filter 32 is provided.
Is 55 when the scattered light scattered by the part 22a of the hot rolled steel plate 22 is incident on the CCD line sensor camera 28.
The intensity at wavelengths longer than the cut wavelength of 0 nm is removed. The wavelength of the electromagnetic wave emitted from the hot surface of the hot-rolled steel sheet 22 is 5
Even if it exceeds 50 nm, CCD line sensor camera 2
Since the optical filter 32 blocks the incidence of the electromagnetic wave on the laser beam 8, the noise due to the radiation energy of the electromagnetic wave having a wavelength of more than 550 nm is removed by the optical filter 32.

When there is a defect on the surface of the hot-rolled steel plate 22, the intensity of the detection signal obtained by the CCD line sensor camera 28 changes greatly. This detection signal is CC
It is transmitted from the D line sensor camera 28 to the A / D conversion device 34, and is A / D converted by the A / D conversion device 34. The A / D-converted detection signal is signal-processed by the defect extraction signal processing device 36 to extract the defect.

The detected signal representing the extracted defect is transmitted to the defect discriminating image processing device 38, and the defect discriminating image processing device 38 performs image processing to discriminate the defect type and grade. The result of this image processing is displayed on the display device 40 for the operator. This optical filter 32
The CCD line sensor camera 28 equipped with can also be inspected for surface defects by being connected to a known image processing device.

Next, with reference to FIG. 10, a CCD line sensor camera in which the optical filter used can be changed according to the change in the surface temperature of the hot rolled steel sheet will be described. FIG. 10A is a side view showing a schematic configuration of this CCD line sensor camera, and FIG. 10B is a front view showing an optical filter. The optical filter 50 provided in the CCD line sensor camera 28 is a hot rolled steel plate 22 (see FIG. 7).
Light scattered from the surface of the camera passes through the camera lens 52 and the CCD
500 nm when entering the line sensor camera 28
The intensity in the wavelength region longer than the cut wavelength between ˜700 nm is cut. This optical filter 50 is equipped with three types of filters 50a, 50b, 50c,
Information from a temperature sensor (not shown) enters the filter driver 54 so that the appropriate filter can be selected. A well-known motor or the like is used as the filter driving device 54, and the optical filter 50 is rotated based on the information from the temperature sensor so that the optimum filter matches the camera lens 52. Therefore, the cut wavelength can be appropriately selected according to the surface temperature of the hot-rolled steel sheet 22.

Each of the filters 50a, 50b and 50c is used when the surface temperature of the hot-rolled steel sheet 22 is 600 ° C. or lower and cuts 700 nm in wavelength, 600 ° C. to 700 ° C.
Used at the time of cutting wavelength 600nm, 700 ℃
It is used in the above case and the cut wavelength is set to 500 nm. 70 when using CCD line sensor camera
Since there is a sensitivity peak near 0 nm and the sensitivity disappears around 1200 nm, the wavelength range to be cut by the filter is 1200 nm when the cut wavelength is 500 nm to 700 nm.
Up to m is enough.

Next, a CCD line sensor camera equipped with an image intensifier will be described with reference to FIG. FIG. 11 is a side view showing a schematic configuration of this CCD line sensor camera. Optical filter 50 (Fig. 1
Scattered light incident through the optical filter 5
Since the wavelength region longer than the cut wavelength at 0 is removed, the amount of light for detection may be insufficient, and the image intensifier 55 compensates for the insufficient amount of light by amplifying the intensity of scattered light.

The scattered light incident through the camera lens 52 is imaged and amplified on the light receiving surface of the image intensifier 55, and is imaged again on the CCD line sensor camera 28 through the relay lens 56. As described above, in the surface defect inspection apparatus of the present embodiment, since the optical filter removes the intensity in the wavelength region longer than 500 nm to 700 nm, the noise component of the imaging signal due to the radiant energy from the surface of the hot rolled steel sheet disappears. As a result, the defect detection of the hot-rolled steel sheet can be performed in the same state as the defect detection of the steel sheet surface at room temperature.

Further, the surface defect inspection apparatus of the present embodiment is not limited to the hot-rolled steel sheet, but also when the external light is forcibly incident on the material to be inspected having a high temperature surface such as a slab to detect defects, It can be applied by changing the wavelength range removed by the optical filter.

[0025]

As described above, according to the present invention, the electromagnetic wave radiated from the surface of the material to be inspected is removed by the optical filter before being detected by the imaging device.
Noise due to radiant energy from the surface of the material to be inspected is eliminated. Therefore, even if the surface temperature of the material to be inspected is high,
This surface can be inspected with high sensitivity to detect defects. Moreover, in order to obtain a high S / N, it is not necessary to raise the output of the light source more than necessary, the load on the light source can be reduced, and the life of the light source can be extended.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the radiation energy density and the wavelength of electromagnetic waves emitted from a black body in radiation balance.

FIG. 2 is a graph showing the relationship between the radiant energy density of electromagnetic waves radiated from the surface of a high temperature steel plate and the wavelength in the absence of oxide scale.

FIG. 3 is a graph showing the relationship between the radiant energy density of electromagnetic waves radiated from the surface of a high temperature steel sheet on which oxide scale is formed and the wavelength.

FIG. 4 is a graph showing the intensity of an image pickup signal of a one-dimensional image pickup device when an image is picked up without a filter.

FIG. 5 is a graph showing the intensity of an image pickup signal when only an infrared cut filter is installed in a one-dimensional image pickup device.

FIG. 6 is a graph showing the intensity of an image pickup signal when an optical filter that cuts a wavelength region of 500 nm or more is installed in a one-dimensional image pickup device.

FIG. 7 is a block diagram showing a schematic configuration of a surface defect inspection apparatus according to an embodiment of the present invention, showing a state of inspecting the surface of a hot rolled steel sheet.

FIG. 8 is a graph showing the spectral intensity of a halogen lamp.

FIG. 9 is a graph showing the spectral intensity of a metal halide lamp.

10A is a side view showing a schematic configuration of a CCD line sensor camera, and FIG. 10B is a front view showing an optical filter.

FIG. 11: CCD with image intensifier
It is a side view which shows schematic structure of a line sensor camera.

FIG. 12 is an explanatory diagram showing a schematic configuration of a conventional surface defect inspection apparatus.

[Explanation of symbols]

 22 hot rolled steel plate 28 CCD line sensor camera 32, 50 optical filter 55 image intensifier

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakazu Yokoo 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Satoshi Maruyama 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Susumu Moriya 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Headquarters

Claims (5)

[Claims] 1. A surface defect inspection method for detecting a surface defect of the material to be inspected by irradiating the surface of the material to be inspected with light and detecting reflected light of the light reflected by the surface, A method for inspecting a surface defect, which comprises removing an electromagnetic wave emitted from the surface when detecting light. 2. The surface defect inspection method according to claim 1, wherein the shortest wavelength of the electromagnetic wave to be removed is in the range of 500 nm to 700 nm. 3. A surface defect inspection apparatus for detecting a surface defect of the material to be inspected based on an image pickup signal output from an image pickup apparatus for detecting reflected light of light irradiated on the surface of the material to be inspected, The surface defect inspection apparatus, wherein the image pickup apparatus includes an optical filter that blocks an electromagnetic wave emitted from the surface. 4. The shortest wavelength of the electromagnetic wave blocked by the imaging device is 5 in accordance with a change in the surface temperature of the inspection object.
The surface defect inspection apparatus according to claim 3, further comprising a selection unit that selects an optical filter in a range of 00 nm to 700 nm. 5. The surface defect inspection apparatus according to claim 3, wherein the image pickup apparatus includes an optical amplifier on the downstream side of the optical path of the optical filter.