JPS60125546A - Detector for surface flaw of red heat object - Google Patents

Abstract

PURPOSE:To improve the precision by constituting a device with a focusing optical system which projects a red heat object, an optical element for obtaining image surfaces of two systems, a visible band filter, a shorter wavelength filter, image pickup elements of two systems, and a signal processing part which binarizes photoelectric signals of them. CONSTITUTION:The device is provided with an illuminating device 2 which illuminates a red heat slab 1 and has spectral radiation in the visible range, a focusing optical system 4 which projects the slab 1, and an optical element which obtains image surfaces of two systems from this optical system 4. On the optical path branched into two, a filter 6 through which visible range radiation passes, a shorter wavelength filter 8, image pickup elements 7 and 9, and a signal processing part 10 are constituted. The spontaneous light of the red heat object 1 is detected in a shorter wavelength range of visible radiation, and the shadow light of flaws is grasped in a longer wavelength rage, and two photoelectric signals are inputted from a gain adjusting circuit to a dividing circuit, and the output is binarized. Thus, accurate and flexible flaw discrimination is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for detecting surface defects on a material to be tested, and
This invention relates to a method for non-contact detection of surface flaws on slabs.

Conventional Structure and Problems Two methods have been proposed for detecting surface flaws on a red-hot object: a contact method and a non-contact method. However, in the contact type, since the target object is at a high temperature, heat resistance of the contact part is required, and flatness of the target object becomes a problem, and sufficient detection accuracy cannot be expected.

Therefore, a non-contact detection method is generally used to detect surface flaws on a red-hot object.

Optical methods are generally used to detect surface flaws in a non-contact manner, and the following two methods have been proposed so far.

One method is to irradiate a red-hot object with light in the visible or ultraviolet range, capture a shadow image of the surface of the red-hot object, and detect defects from this image signal.

The other method is detection based on the self-luminescence of a red-hot object. This is a method that uses the temperature difference between the surface of a red-hot object and the inside of the red-hot object exposed by a flaw to take an image in the infrared region, and detects a flaw from this video signal.

However, with the above two methods, the former may lead to a erroneous judgment that if there are irregularities other than flaws on the surface of the red-hot object, they are also considered flaws, and the latter may cause surface irregularities depending on the surface condition of the red-hot object. Since temperature non-uniformity occurs, this method alone has the disadvantage that a sufficient signal-to-noise ratio cannot be obtained.

Furthermore, Japanese Patent Laid-Open No. 131192/1983 proposes a method in which the above two methods are implemented in one optical system and each flaw is detected using a separate system depending on the type of flaw. However, this method still includes the drawbacks of the two optical detection methods described above and is not a substantial improvement. For example, when the surface of a red-hot object has irregularities that are not flaws, irradiation with light in the visible or ultraviolet region produces shadows from the irregularities.
This method identifies this as a flaw. Furthermore, the SN ratio of the video signal is not improved by self-emission.

Also, JP-A-52-139482 and JP-A-55
-160837 also obtains binary signals of flaws from each of the two detection methods described above, and ANDs these signals, so it still contains the drawbacks of the two methods described above, and is not an essential improvement. is not.

OBJECT OF THE INVENTION The present invention aims to solve the problems of the optical detection method described above, and is an optical detection means, which enables surface flaws on a red-hot object to be detected with high precision. 0 Constitution of the Invention which Provides a Detection Device The device according to the present invention projects an image of the surface of a red-hot object by one imaging optical system, separates this projected image into two optical paths, and selects one of the passing wavelengths. A signal processing unit that divides one of the photoelectric signals of the image pickup devices located on both projection planes by the other, with the wavelength range set in the near-infrared range or the visible range and the other wavelength range set as the wavelength range shorter than the visible range. This is a device for detecting surface flaws on red-hot objects. Furthermore, this device has two illumination devices that emit spectral radiation in the near-infrared region or the visible region, which is one of the above-mentioned passing wavelength regions.

With the above configuration, the long wavelength side of the near-infrared region or visible region is used to detect the shadow image of a flaw on a red-hot object by illumination, and the short wavelength side of the visible region with a good S/N ratio is used for detection of the self-emission of the red-hot object. Do it on your side.

Also, among the photoelectric outputs of both obtained in this way,
By performing binarization processing on the quotient obtained by dividing one by the other, more flexible flaw discrimination can be realized than when each is binarized alone.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an example of the surface flaw detection device of the present invention.
Hot steel billets in steel plants, especially continuous casting facilities (
This device is used as a surface flaw detection device for slabs. In this case, the surface temperature of the slab is approximately 800-900℃,
The internal temperature is 1000°C. As shown in Fig. 1, this device includes an illumination device 2, which has spectral radiation mainly in the near-infrared region or visible region, which illuminates a red-hot object, that is, a hot slab 1, and a slab surface illuminated by this illumination device. Consisting of an imaging device 3 that captures images, and a signal processing unit 10 that processes signals from this imaging device, this illumination device 2 uses a sharp cut light source and a light source that has spectral radiation also in the infrared region, such as an incandescent light bulb, for example. It is composed of a combination of filters, etc.

In the imaging device 3, 4 is a projection optical system for projecting the surface of the hot slab 1. 6 is a half mirror provided on the image field side, which divides the optical path into two and forms two imaging surfaces. Reference numerals 7 and 9 are image pickup elements arranged on the two imaging planes.

A sharp cut filter 8 is arranged in the optical path of the image sensor 9 so as to have sensitivity in the near-infrared region and the visible region, and a sharp cut filter 8 is arranged in the optical path of the image sensor 7 so as to have sensitivity mainly in the short wavelength side of the visible region. , an infrared cut filter 6 is arranged.

FIG. 2 shows a block diagram of the signal processing unit 1o, in which 7 and 9 are image sensors, 33 and 34 are gain adjustment circuits for adjusting the gain and linear characteristics of the photoelectric signal of the image sensor, and 36 is a gain adjustment circuit. A division circuit for dividing one of the photoelectric outputs from the circuits 33 and 34 by the other and calculating the quotient; 37 is a division circuit for comparing the output of the division circuit with the reference voltage generating section 36 and converting it into a binary value; A digitizing circuit 38 represents a flaw determination signal from the binarizing circuit 374C.

The operation of the flaw inspection device of this embodiment configured as described above will be described below.

The image sensor 8 captures a shadow image of the hot slab 1 caused by the illumination light from the illumination device 2 . That is, hot slab 1
The concave portion on the surface of the photoelectric sensor becomes a shadow, and the photoelectric signal corresponding to one line of scanning of the image sensor takes the form as shown in FIG. 3, 17. Further, the image sensor 7 images the self-luminous pattern of the hot slab 1.

That is, in FIG. 3, there is a flaw 11 on the surface blood of the hot slab 10.
If there is, the high-temperature portion of the slab interior 14 is exposed, and a flaw signal 22 as shown in C can be obtained.

In general, all objects can be said to radiate thermal energy determined by their own temperature and emissivity.

In the case of a black body (emissivity is 1), this amount of radiant energy is
It is expressed by the following formula.

Meλ=C1λ5/(@!p,!-' 1) [WC
m-2/J-'] (1) where Meλ is the spectral radiation emittance, T is the absolute temperature of the perfect radiator, λ is the wavelength, and C1 and C2 can be expressed as constants.

In Fig. 3, the temperature inside the hot slab 14 is 1000.
When formula (1) is illustrated assuming that the temperature of the slab surface 13 is 850° C., a spectral radiation distribution as shown in FIG. 4 is obtained.

In Fig. 1, if a solid-state image sensor made of silicon is used as the image sensor, the sensitivity wavelength range of this element is 0.4.
μm to 1.2 μm. Therefore, the sensitivity wavelength range of the image sensor 7 is 0, taking into consideration the characteristics of the infrared cut filter 6.
．． 4 μm to 0.7 μm.

In other words, as can be seen from Fig. 4, among the self-luminous radiation of slab defects, it is possible to utilize radiation in the short wavelength side, for example, in the visible range of 0.7 μm or less, compared to the near-infrared region. A photoelectric signal with a sufficient SN ratio can be obtained.

Also, a sharp cut filter 8 (for example, 0.73
μ. The sensitivity wavelength range of the solid-state image sensor 9 is 0.73 μm considering the characteristics of the R-73 filter that passes the above light.
~1.2μ. On the other hand, by using the above-mentioned R-73 filter as the sharp cut filter of the illumination device, the shadow image due to the wavelength band of the illumination light can be directly transmitted to the image sensor 9.
If you can catch it, it will be K. In this case, 0.73 μm ~
Since the self-luminous radiation of 1.2 μm will also be detected at the same time, the output of the optical radiation from the illumination light should be sufficiently large and the level ratio with the self-luminous radiation should be about 10 = 1 to 20:1. The influence of self-luminous radiation can be removed.

Further, by using an incandescent light bulb such as a halogen light bulb in the lighting device, stable illumination light can be obtained regardless of the scanning frequency of the detector, and efficient illumination light can be obtained in the near-infrared region. Furthermore, there is no fluctuation in illumination light due to the movement of the bright spot inside the arc tube like in a discharge lamp.

As shown in the above embodiment, the detection of the self-luminous component of the slab flaw is carried out at 0.4 μm to 0.7 μm, and the detection of the shadow image of the slab flaw by the illumination device is performed at 0.7 μm to 1.2 μm.
By using the wavelength range of , the SN of both wavelength ranges is
A flaw signal with a good ratio can be obtained.

Note that the wavelength setting of the sharp cut filter used in the illumination device 2 and the imaging device 3 can be moved to the short wavelength side and the long wavelength side, centering on the wavelength setting tio-73μ, especially when supplementing the light amount in the short wavelength range. is 0.73μ. By using a sharp cut filter on the longer wavelength side, it is possible to balance both photoelectric signals.

Further, by using a red reflective dichroic mirror instead of the half mirror 60, it is possible to reduce crosstalk between light incident on both light receivers and obtain a flaw signal with a good S/N ratio.

Next, the operation of the signal processing section will be explained based on FIG. As described above, the photoelectric signal obtained when the hot slab 1 having the cross section shown in FIG. 3a is imaged becomes the signal shown in FIG. 2c. In addition to the flaw signal 17 caused by the flaw 11 on the hot slab 1, the photoelectric signal 16 of the image sensor 9 that captures a shadow image includes a signal 16 caused by a recess on the surface of the hot slab, and a signal 16 caused by a concave portion on the surface of the hot slab. There are signals 18.19 caused by high reflectors and low reflectors. In addition, the photoelectric signal 21 of the image sensor 7 that images the self-luminous pattern includes the hot slab 1
In addition to the flaw signal 22 due to the flaw 11 above, there is a signal 23 caused by the irregular temperature distribution on the slab surface.

If the above two signals are individually binarized, the photoelectric signal 15 becomes 16, 17.19, and the photoelectric signal 21
In this case, 22 and 23 are each taken as a flaw signal, and even if you take the logical sum or logical product of these two signals, signals other than flaws, such as false signals caused by 19 and 23, are easily detected as flaws. box office.

In this signal processing, as shown in FIG. 6, the level of the photoelectric signals obtained by the image sensors 7 and 9 is adjusted in the gain adjustment circuits 33 and 34 based on the average signal voltage of the portion without flaws.

The signals of the gain adjustment circuits 33 and 34 are transmitted to the divider circuit 35.
Divide one signal by the other at .

The signal output 25 shown in FIG.
is emphasized from the two photoelectric signals, but the other photoelectric signal waveforms 16, 1B, 19, and 23 are all canceled out.

The principle of the above determination method will be explained based on FIG. 6.

FIG. 5a illustrates the flaw discrimination method shown in the conventional example. When the shadow light decreases below Q or the self-emission exceeds P, it is determined that there is a flaw. In other words, II other than ■ other areas
, N, and IV are determined to be defects.

On the other hand, in Figure 5, the area above the curve connected by P/Q/, that is, the area marked ■, is not determined to be a flaw, and this P
It is shown that a defect is determined in the region (2) below /Q/, that is, when the output of the division circuit that divides the photoelectric output due to self-emission by the deflection of shadow light exceeds a certain value.

A comparison of a and b in FIG. 5 shows that in the present invention, 39.40 areas in the IQ area are determined to be free of defects, and 41 areas are determined to be defective.

Applying the measurement example in FIG. 4 to FIG. 5, it can be seen that 16 and 19 of the photoelectric signals of shadow light belong to region 39, and 23 of the photoelectric signals of self-emission belong to region 40. This shows that the flaw determination method is more flexible than conventional methods.

That is, the gain of the photoelectric signals of self-emission and shadow light is determined by the gain adjustment circuit 33. .about.34, a determination curve p/Q/ having arbitrary linear characteristics within a certain limit can be set according to actual measurement data, and a flexible algorithm can be formed for defect determination.

In the above embodiment, the output of the division circuit for both optical signals is binarized using one threshold, but a multi-value circuit system is arranged in place of the binarization circuit 37. hand,
The area (■) may be divided depending on the type of flaw.In addition, in order to prevent the judgment level shown in Figure 6 from changing due to a reduction in photoelectric output due to dirt on the projection optical system, etc., a gain adjustment circuit is used. By appropriately storing the output signals of 33 and 34 and providing a function of automatically shifting the reference voltage of the reference voltage generating section 36 based on this information, stable determination operation can be maintained over a long period of time.

Effects of the Invention The device for detecting surface flaws on a red-hot object according to the present invention detects self-luminescence of a red-hot object in the short wavelength range of visible radiation, and detects shadow light due to flaws in the wavelength range from the long wavelength range of visible radiation to the near-infrared range. By capturing these two photoelectric signals and inputting them to a division circuit through their respective gain adjustment circuits, and binarizing the output of this division circuit, it is possible to set a flaw judgment standard according to the actually measured flaw judgment data. As a result, an accurate and flexible flaw determination method can be provided, and its practical value can be said to be extremely large.

[Brief explanation of drawings]

FIG. 1 shows a lighting device among the configurations according to the present invention. 2 is a diagram illustrating the principle of an imaging device and a signal processing section. Figure 2 is a block diagram of the signal processing section, Figure 3 is a block diagram of the signal processing section.
Figure a is the shape of the hot slab surface, Figure 3 b-d are photoelectric signals obtained corresponding to the above a, Figure 3 e is the flaw inspection ratio signal, and Figure 4 is calculated based on formula (1). Fig. 6a shows the conventional example of the flaw signal detection principle.
Each figure shows a diagram of the flaw detection principle according to the present invention. 1...Hot slab, 2...Lighting device,
3... Imaging device, 4... Projection optical system,
Half mirror 17 for 5. Image sensor, 8.
-Sharp cut filter, 9...imaging device, 1o...signal processing unit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 4 Figure 5 Kyo - & (μ river)

Claims (1)

[Claims] An illumination device that mainly emits spectral radiation in the near-infrared or visible region, an imaging optical system for projecting the red-hot object illuminated by this illumination device, and two systems of imaging planes from this imaging optical system. an optical element for obtaining a signal, a filter that passes radiation in the near-infrared region or visible region, and a filter that passes visible radiation on the short wavelength side of the visible region, which is provided separately on each of the two divided optical paths; surface flaws on a red-hot object, which is composed of image pickup devices located on the imaging planes of the above two systems, and a signal processing unit that divides one of the photoelectric signals from the image pickup device by the other and binarizes it. Detection device.