JPH0610658B2 - Surface defect detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface defect detection apparatus for detecting defects such as flaws on the surface of an inspection object such as a metal plate.

(Prior art and its problems) As a surface defect detection device of this type, the surface of the object to be inspected is irradiated with a laser beam and optically scanned, and the surface defect is caused by the difference in the reflection characteristics between the normal part and the defective part. The one that is designed to detect is widely used. In addition, such a device is required to have a function of detecting only a defect by distinguishing it from dirt that is originally harmless.

An example of a conventional device having such a function (Japanese Patent Laid-Open No. 58-58
26252) is shown in FIG. 4, and the output waveform of the apparatus is shown in FIG. In this apparatus, a laser beam 2 emitted from a laser light source 1 is reflected by a rotating mirror 4 through a collimator 3, and the reflected light causes the surface of a metal plate 5 as an object to be inspected to be optically scanned in the width direction thereof. Is configured to. The specularly reflected light of the reflected light reflected on the surface of the metal plate 5 by the optical scanning is received by one light receiver 6, and the diffusely reflected light of the reflected light is received by another light receiver 7. Next, the photoelectric conversion outputs a and b obtained from the respective light receivers 6 and 7 according to the respective amounts of received light are
After being amplified by the amplifiers 8 and 9, respectively, the analog arithmetic circuit 10 performs the arithmetic processing described later, thereby eliminating the output component due to the surface stain. Further, the operation output thus obtained is sent to the differential processing circuit 11 in the next stage.

In the above device, when the dirt 12 having a light absorbing property is present on the surface of the metal plate 5 as shown in FIG.
As shown in FIG. 6B, a low level signal a ₁ corresponding to the dirt 12 is generated at the output a of the specular reflection light receiver 6. On the other hand, as shown in FIG. 5C, the low level signal b ₁ corresponding to the stain 12 is also generated at the output b of the irregular reflection light receiver 7. Therefore, the calculation output c obtained by taking the difference between the two in the analog calculation circuit 10 of FIG.
As shown in FIG. 5D, these signals a ₁ and b ₁ are canceled and erased.

On the other hand, the surface of the metal plate 5 has a flaw 1 as shown in FIG.
When 3 exists, the specular reflection light decreases and the diffuse reflection light increases in that portion, so that the low level signal a ₂ corresponding to the flaw 13 is generated in the output a of the specular reflection light receiver 6, whereas
At the output b of the irregular reflection light receiver 7, a high level signal b ₂ is generated corresponding to the flaw 13. Therefore, these signals a ₂ ,
In the calculation output c obtained by subtracting b ₂ from each other,
An enhanced low level signal c ₁ will result.

The signal c is differentiated by the differential processing circuit 11 of FIG. 4 to be the differential processing output d shown in FIG. 5 (E), and the signal c ₁ corresponding to the flaw 13 is indicated by the symbol d ₁ in this differential output d. It becomes a differential waveform and is detected as a defect signal by being compared with a threshold value e of a predetermined level. Through the above processing, only the original flaw 13 is detected as a defect without misidentifying the stain 12 as a defect.

By the way, as for the stains present on the surface of a general metal plate, not only those in which specular reflection light and diffuse reflection light are reduced equally as described above, but there are many stains in which the reduction rate of specular reflection light differs depending on the type of stain. is there. Therefore, the output corresponding to these stains is not erased but is mistakenly recognized as a defect by simply subtracting the receiver outputs of specularly reflected light and irregularly reflected light as in the conventional example. For example, in the case of dirt in which specular reflection light decreases but irregular reflection light does not change, it is detected as a defect. Further, in the case of dust that does not need to be a defect or an extremely fine flaw, since the specular reflection light does not change much and only the diffuse reflection light increases, it is also detected as a defect. Further, in the case of the above-mentioned conventional example, the differential processing output d shown in FIG.
In addition, a part of the end surface signals d ₂ and d ₃ (signals corresponding to the end edges of the object to be inspected) in the optical scanning are also output in the same manner as the original defect signal d ₁ , which may be mistaken for a defect. Have.

(Object of the Invention) The present invention is intended to overcome the above-mentioned problems in the prior art, and to eliminate defects on the surface of the object to be inspected, such as various stains having different reflection characteristics, dust, and fine defects. An object of the present invention is to provide a surface defect detection device that can be clearly identified and detected as something that is not considered to be.

(Means for Achieving the Object) In order to achieve the above object, in the surface defect detecting apparatus of the present invention, the case where the surface of the object to be inspected is normal is used as a reference.
Differentiated signals obtained by differentiating the received light signals of the specularly reflected light and the diffusely reflected light are discriminated by the respective threshold values, and a logical operation is performed on the discriminated signals to obtain a value of the received light amount. A light reception signal increase / decrease detection unit that generates a detection output when one increases and the other decreases is provided, and the surface defect is detected based on the detection output of the light reception signal increase / decrease detection unit.

(Embodiment) FIG. 1 shows a schematic view of a surface defect detecting apparatus according to an embodiment of the present invention, FIG. 2 shows an output waveform of a discrimination process for surface flaws and stains in the apparatus, and FIG. 3 is black. The output waveforms of the discrimination processing for dirt and very fine flaws are shown respectively.

In FIG. 1, an optical scanning means 15 for optically scanning the surface of a metal plate 14 as an object to be inspected comprises a laser light source 16, a collimator 17, and a rotating mirror 18, and a laser beam 19 extracted from the laser light source 16 is a collimator. After passing through 17, the light is reflected by the rotating mirror 18, and the surface of the metal plate 14 is scanned by the reflected light. On one side of the metal plate 14 on which optical scanning is performed, a light receiver 20 that receives specularly reflected light of the reflected light reflected from the surface of the metal plate 14 by light irradiation, and irregularly reflected light of the reflected light. And a light receiver 21 for receiving the light. These light receivers 20 and 21 are composed of photoelectric conversion elements such as photomultipliers and photocells, and outputs p and s corresponding to the respective received light amounts are obtained. A differential circuit 23 and a comparator 24 are connected to the next stage of the specular reflection light receiver 20 via an amplifier 22, and a differential circuit 26 and a comparator circuit 26 are similarly connected to the next stage of the irregular reflection light receiver 21 via an amplifier 25. The comparator 27 is connected. The specular reflection light comparator 24 has a negative value from the O level of the output q of the differentiating circuit 23 (the O level of which corresponds to the output level of the light receiver 20 when the surface of the metal plate 14 is a normal surface). A first threshold value (shown by symbol f in FIG. 2 (B) and FIG. 3 (B)) which is biased to the polarity side by a predetermined level is set. On the other hand, in the diffused light comparator 27,
The output t of the differentiating circuit 26 (its O level corresponds to the output level of the light receiver 21 when the surface of the metal plate 14 is a normal surface) is biased by a predetermined level to the positive polarity side from the O level. Second threshold value (Fig. 2 (E), Fig. 3 (E)
Is set). The binarized outputs r and u obtained from the comparators 24 and 27 are sent to the AND circuit 28 at the next stage, and are configured to take a logical product here. The light reception signal increase / decrease detection means 30 is configured by these.

Next, the operation of this apparatus will be described below separately for the case where the surface of the metal plate 14 has surface flaws and normal stains and the case where there are black stains and extremely fine flaws.

When Surface Defects and Ordinary Contamination are Present When surface scanning defects on the surface of the metal plate 14 irradiated with the laser beam 19 have surface defects, the specular reflection light decreases while the irregular reflection light increases. Therefore, a low-level signal p ₁ corresponding to the surface flaw is generated at the output p (Fig. 2A) of the specular reflection light receiver 20. Therefore, the amplifier 22
The partial processing output q (FIG. 2 (B)) from the differentiating circuit 23 which receives the output p amplified by
Differential waveform _{q 1} corresponding to ₁ is generated.

This differential processing output q is compared and discriminated with the first threshold value f in the comparator 24, and as the binarized output r shown in FIG. 2 (C), the High signal r ₁ corresponding to the differential waveform q ₁ is obtained. Is output.

On the other hand, a high level signal s ₁ corresponding to the surface flaw is generated at the output s (FIG. 2 (D)) of the diffused reflected light receiver 21 that receives the increased diffused reflected light. Therefore, the differential processing output t (FIG. 2 (E)) from the differential circuit 26 that receives the output s amplified by the amplifier 25 has a differential waveform t ₁ corresponding to the high level signal s ₁ . This differential processing output t is compared and discriminated with the second threshold value g in the comparator 27, and as the binarized signal u shown in FIG. 2 (F), the High signal u ₁ corresponding to the differential waveform t ₁ is obtained. Is output. In the AND circuit 28 at the next stage, the comparators 24 and 27
As shown in FIG. 2 (G), the output signal r and u of the high signal v ₁ corresponding to the surface flaw are taken as the output v.
Is obtained.

On the other hand, if the optical scanning portion on the surface of the metal plate 14 has normal dirt, the specular reflection light decreases, while the diffuse reflection light hardly changes. Therefore, at the output p of the specular reflection light receiver 20, a low-level signal p ₂ corresponding to the stain is generated. Therefore, the differential processing output q of the specular reflection light differentiating circuit 23 has a differential waveform q ₂ corresponding to the low-level signal p ₂ . This differential processing output q is
A comparison-discrimination with the threshold value f, the as shown in FIG. 2 (C) as a binarized output r of the comparator 24 the differential waveform q ₂
A High signal r ₂ corresponding to is output.

On the other hand, in the output s of the light receiver 21 which receives the diffused reflected light that does not increase or decrease, the signal change corresponding to the stain does not occur. Therefore, the differential processing output q of the diffused reflection light differentiating circuit 26 does not generate the differential waveform corresponding to the stain and the High signal corresponding to the stain does not occur as the binarized output u of the comparator 27. Therefore, only the High signal from one comparator 24 is input to the AND circuit 28, and the AND circuit 2
The output v of 8 becomes a Low signal. That is, the stain is not detected as a defect.

Further, the outputs p and s of the respective light receivers 20 and 21 exhibit steep rises and falls at the start end and the end of one scanning section of the optical scanning, so the end face waveform q ₃ corresponding to these outputs q and t is obtained. , Q ₄ , t ₃ , t ₄ occur, but in the specular reflection light comparator 24, only the end face waveform q ₄ on the terminal side crosses the first threshold value f, while the diffuse reflection light comparator 24. In FIG. 27, only the end face waveform t ₃ on the starting end side has the second threshold value g.
Since it only crosses the two comparators 24, 27
Therefore, the High signals r ₃ and u ₃ corresponding to the end surface signals are not obtained at the same time, and the signals corresponding to the start end and the end of the optical scanning are not mistakenly recognized as a defect.

When Black Stain and Very Fine Scratches If there is black stain on the optical scanning portion of the metal plate 14, both the reflected light and the diffused reflected light are reduced. Therefore, low-level signals p ₂ ′ and s ₂ ′ corresponding to the black stains are generated at the outputs p and s of the photodetectors 20 and 21, respectively, as shown in FIGS. 3 (A) and 3 (D). , These signals p ₂ ′, s ₂ ′
Are respectively passed through differentiating circuits 23 and 26, and are shown in FIG.
As shown in FIG. 3 (E), almost the same differential waveforms q ₂ ′, t
₂ '.

Meanwhile, in order to compare and discriminate the regular reflection comparator 24 the differential processing output q with negative polarity threshold f, dropper of FIG. 3 (B) to the differential waveform q ₂ as shown _'(first half Part)
Crosses the threshold value f, whereas the diffuse reflection light comparator 27 compares and discriminates the differential processing output t with the positive polarity threshold value g, so that as shown in FIG. The rising part (second half) of the differential waveform t ₂ ′ crosses the threshold value g.
Therefore, the High signals r ₂ ′ and u ₂ ′ corresponding to the black stains output from the comparators 24 and 27 do not occur at the same position on the time axis, and the AND circuit 28 corresponds to the black stains. High signal cannot be obtained. That is,
Black stains are not detected as defects.

On the other hand, if the light scanning portion on the surface of the metal plate 14 has an extremely fine flaw (similarly in the case of dust), the specular reflection light does not change and only the diffuse reflection light increases. Therefore only the output s of the diffuse reflection light-receiving unit 21, a high level signal s _{1 'occurs,} only the high level signal s ₁ to the differential processing output t of the differentiating circuit _26' corresponding to the flaw differential waveform t corresponding to ₁ 'occurs. The differential waveform t ₁ ′ is compared and discriminated by the comparator 27 with the second threshold value g and is output as a High signal u ₁ ′. On the other hand, from the specular reflection light comparator 24, the
Since no signal is output, the AND circuit 28 does not output a High signal corresponding to the minute defect. Therefore, extremely fine flaws are not detected as defects. That is, it is clearly distinguished from the above-mentioned normal surface flaw.

Incidentally, the dirt usually has a larger spread than the surface flaw. Therefore, in reality, there are many cases where surface flaws are present in a dirty portion. Even in such a case, it is clear that according to the present embodiment in which the differential processing is performed, only the surface scratch can be detected from the dirt portion having a large spread.

In the above embodiments, the specular reflection light decreases and the diffuse reflection light increases. An example is shown in which normal surface flaws that exhibit reflection characteristics are detected by distinguishing them from other stains or microscopic flaws that are insufficient to be regarded as defects, but specular reflection light increases and irregular reflection occurs in display defects. There is also a glossy defect having a reflection characteristic so that the light is reduced. Therefore, in order to detect such a defect, in the above-described embodiment, the positive and negative polarities of the threshold values f and g are compared with each other by the comparator 24. , 27 can be reversed to detect in the same manner.

Further, as the processing for picking up the signal component corresponding to the dirt and the flaws from the outputs of the light receivers 20 and 21, the differential processing is performed in the above embodiment, but the present invention is not limited to this and other means may be used. You may make it emphasize the signal component of dirt and a flaw. Further, when only one of the outputs of the two light receivers 20 and 21 is inverted and then differentiated, the same polarity is used as the above first and second threshold values. Therefore, it is not essential that the first and second threshold values have different polarities. When the type that outputs a High signal when the input signal is smaller than the threshold value is used as the comparators 24 and 27, N is used instead of the AND circuit 28.
An OR circuit may be used.

As described above, the present invention can be achieved by various discriminations and logical operations.

(Effects of the Invention) As described above, according to the surface defect detection device of the present invention,
Defects on the surface of the object to be inspected should be clearly identified and detected from ultra-small flaws that cannot be regarded as various stains or defects with different reflection characteristics and edge signals generated at the beginning and end of the optical scanning section. It is possible to obtain the effect that the surface inspection accuracy is significantly improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a surface defect detecting apparatus according to an embodiment of the present invention, FIG. 2 is an output waveform diagram of a surface flaw and normal stain discrimination processing in the embodiment, and FIG. 3 is a black stain in the embodiment. And FIG. 4 is an output waveform diagram of the ultra-fine flaw discrimination process, FIG. 4 is a schematic diagram of a conventional surface defect detecting device, and FIG. 5 is an output waveform diagram of signal processing of the conventional device. 15 ... Optical scanning means, 20 ... Regular reflection light receiver, 21
...... Diffuse reflection light receiver, 23 ...... Regular reflection light differentiation circuit, 24 ...... Regular reflection light comparator, 26 ...... Diffuse reflection light differentiation circuit, 27 ...... Diffuse reflection light comparator, 28 …… AND Circuit 30 ... Light receiving signal increase / decrease detection means

Claims (1)

[Claims] 1. An object to be inspected is irradiated with light from a light source, and specularly reflected light and irregularly reflected light from the object to be inspected are respectively received by a light receiving means, and based on respective light receiving amounts in the light receiving means. In a surface defect detecting device for detecting a surface defect existing on the surface of the object to be inspected, with respect to the case where the surface of the object to be inspected is a normal surface, the received light signals of the specular reflection light and the irregular reflection light are differentiated. The differentiated signal obtained by the above is discriminated by each threshold value, and by performing a logical operation on the discriminated signal, a detection output is obtained when one of the received light amounts increases and the other decreases. A surface defect detecting apparatus, comprising: a light-reception signal increase / decrease detection unit that generates the light-reception signal; and detecting the surface defect based on a detection output of the light-reception signal increase / decrease detection unit.