JPH0458901B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is useful for detecting surface defects (eaves,
The present invention relates to a device for detecting irregularities (irregularities, rust, etc.), and more specifically, to a device that irradiates the surface of a material to be inspected with a light beam such as a laser and detects defects based on the state of the reflected light.

[Prior art]

BACKGROUND OF THE INVENTION Various devices have been developed and put into practical use to accurately inspect defects on the surface of a material to be inspected, such as a steel plate, in a short period of time.

For example, Japanese Patent Application Laid-open No. 10793/1986 includes a light receiver that receives only specularly reflected light from the surface of the material to be inspected and a light receiver that receives only diffusely reflected light, and by comparing the light reception results of both, An apparatus for detecting defects on the surface of a material to be inspected has been proposed.

In addition, in Japanese Patent Publication No. 59-33855, the distribution state of the reflected and scattered light from the surface of the material to be inspected is detected by detecting the reflected and scattered light from the surface of the material to be inspected using multiple photodetectors, and from this result, the distribution state of the reflected and scattered light from the surface of the material to be inspected is detected. A method for detecting defects has been proposed.

Furthermore, JP-A No. 51-31281 discloses a method in which reflected light from the surface of a material to be inspected is received by a plurality of photodetectors, and the output of each photodetector is detected via a separate variable gain circuit. The gain of each variable gain circuit is set so that the light reflected from the normal material surface is blocked.In other words, an electric filter is configured with multiple variable gain circuits, and thereby A device has been proposed that detects only reflected light caused by defects.

Furthermore, Japanese Patent Application Laid-Open No. 58-77642 discloses that by providing a light receiver that receives reflected light so that the amount of reflected light from a specific defect matches the amount of reflected light from a normal part, reflections caused by defects other than the specific defect can be reduced. A method of detecting light has been proposed.

[Problem that the invention seeks to solve]

As described above, various inventions have been proposed for the purpose of detecting defects on the surface of a material to be inspected. Since the light receiver and the light receiver that receives diffusely reflected light are each fixed, it is possible to deal with changes in the quality of the inspected material or changes in its condition that are not defects, such as changes in surface roughness due to differences in processing and finishing methods. It is necessary to replace each receiver or change the installation position. Therefore, although it is effective when detecting defects based on a certain normal state, it is not possible to quickly respond when the defect detection criteria is changed.

In the second invention of Japanese Patent Publication No. 59-33855, there is a possibility that a change in normal reflected light due to a change in the inspected material or a difference in processing/finishing method may be detected as reflected light due to a defect. To deal with this situation, the quality of the material to be inspected, processing and
It is necessary to know in advance the distribution state of reflected and scattered light depending on the finishing method, etc., and adjust the positions of the plurality of light receivers each time.

In the third invention of JP-A No. 51-31281, by appropriately changing and setting the gain of each gain circuit,
Although it is possible to respond to changes in material, etc., it is still necessary to check in advance the gain that should be set in each gain circuit according to the material, etc. of the material to be inspected, and readjust it each time. When detecting defects based on a normal state other than the normal state that has been investigated in advance, it is necessary to interrupt the inspection process and perform readjustment each time.

In the fourth invention of JP-A-58-77642, the "specific defect" here refers to a certain state that is not substantially a defect, in other words, a specific state change within a range that can be considered as a normal state. However, a "specific defect" that is not a substantial defect will be detected as a defect, and a "specific defect" that is not a substantial defect will be detected as a defect. When changing to a "specific defect" that is not a defect, it is necessary to check in advance the mounting angle position of the light receiver, etc., and reset it each time.

In this way, with devices and methods for detecting defects on the surface of inspected materials that have already been proposed, when a specific processing or finishing is applied to a specific material, in other words, the standard normal state is fixed. It is considered to be effective in cases such as those described above. However, it is either impossible to follow and respond to changes in conditions within a range that can be considered normal due to changes in materials, processing/finishing methods, etc., or even if it is possible to respond to changes in the condition of the inspected material in advance. It is necessary to investigate various conditions within the range that can be considered normal for the various materials and processing/finishing methods for each, and if these are reset each time, work efficiency will decrease. There is a problem with doing so. Furthermore, in devices and methods that use a large number of photodetectors, signal processing circuits, etc., the burden of accurate adjustment and maintenance becomes large, and it must be said that there are many problems in terms of economic efficiency and workability. I don't get it.

The present invention has been made in view of the above circumstances, and is applicable not only to inspected materials that have undergone specific processing and finishing to specific materials, but also when the material of the inspected material changes or when processed. In the case of a change in the finishing method, for example, in the case of a rolled material, the condition of the surface of the rolled material changes over time due to wear of the rolling rolls, or if the surface of the material to be inspected has been adhered to. It is possible to respond to changes in oil film thickness over time without interrupting inspection work.
Another object of the present invention is to provide an apparatus for detecting defects on the surface of a material to be inspected, which can accurately detect defects by two-dimensionally detecting reflected light from the surface of the material to be inspected.

[Means for solving problems]

In the present invention, reflected light from the surface of the material to be inspected is received as a two-dimensional image by a two-dimensional light receiver, and the average pattern of the reflected light during a period in which no large defects are detected is sent to a variable optical filter as the filter pattern. A configuration is adopted in which defects on the surface of the inspected material are detected by projecting the reflected light from the surface of the inspected material onto this filter and allowing only the reflected light caused by the defect to pass through the variable optical filter.

The present invention provides an apparatus for detecting defects on the surface of a material to be inspected by comparing the state of reflected light of an irradiated light beam from the surface of the material to be inspected and the state of the reflected light from a normal material surface. a light splitter that splits the reflected light from the surface of the inspected material of the light beam into two; a two-dimensional light receiver that receives one of the reflected lights split by the light splitter as a two-dimensional image; an averaging device that adds the light reception results of the light receiver in time series and obtains an average value; a filter pattern creator that creates a two-dimensional filter pattern corresponding to the average value obtained by the averaging device; a variable optical filter on which the filter pattern created by the filter pattern creator is set and on which the other reflected light split by the light splitter is projected; and a light that detects the light that has passed through the variable optical filter. a detector; a defect determiner that determines defects on the surface of the inspected material based on the detection results of the photodetector; The present invention is characterized by comprising a timing circuit that causes the filter pattern generator to read an average value of light reception results of the two-dimensional light receiver as a normal filter pattern.

[Effect]

In the present invention, reflected light caused by a defect is detected based on the average value of a two-dimensional image pattern of reflected light from the surface of a material to be inspected that changes within a range that can be considered normal over a predetermined period in the past. Therefore, even if the condition of the surface of the material to be inspected gradually changes due to changes in the surface of the rolled material due to wear of the rolling rolls or changes in the state of the oil film on the surface of the material to be inspected, it is not necessary to change the setting of the conditions or rework the material. The pattern of normal reflected light, which is the standard for detecting defects, changes automatically without the need for adjustments, improving processing speed, inspection efficiency, and improving economic efficiency and workability.
Inspection accuracy will also be improved. In addition, even if there is a change in the quality of the material to be inspected or a change in the processing/finishing method, the conditions can be reset using the pattern of the two-dimensional image of the light reflected from the normal surface of the inspected material as a reference. It is possible to respond quickly without any problems.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

FIG. 1 is a block diagram of a signal processing system shown together with a schematic diagram of an optical system showing the configuration of a surface defect detection apparatus according to the present invention.

In the figure, reference numeral 1 denotes an oscillator for a laser beam B as a light beam, and the laser beam B emitted by this oscillator is given to a scanning optical system 2.

In this embodiment, the scanning optical system 2 is composed of a polygonal mirror 20, a reflecting mirror 21, etc.
The irradiation direction of the laser beam B is moved in a direction (main scanning direction) perpendicular to the moving direction (sub scanning direction) indicated by the white arrow. Therefore, laser beam B
is scanned in the main scanning direction by the scanning optical system 2, and is scanned in the sub-scanning direction by moving the inspected material 3 in the sub-scanning direction. In addition to the above-described configuration, the scanning optical system 2 may have a configuration using a vibrating mirror or the like.

In the figure, reference numeral 3 denotes a material to be inspected, such as a rolled steel plate, and the reflected light R of the laser beam B reflected on the surface of the material to be inspected 3 is incident on a light receiving optical system 4.

The light receiving optical system 4 includes a condenser lens 40 that condenses the reflected light R of the laser beam B from the surface of the inspected material 3, and a condensing lens 40 that condenses the reflected light R of the laser beam B from the surface of the inspected material 3.
The received reflected light R is further divided into two directions using a half mirror or the like, and one of them is focused on the light receiving surface of the two-dimensional light receiver 5, and the other is focused on the filter surface of the variable optical filter 8. Imager light splitter 41
It is composed of etc.

Specifically, the two-dimensional light receiver 5 has a structure in which photoelectric conversion elements such as two-dimensional image sensors are arranged in a matrix, so that the reflected light R of the laser beam B can be It receives a two-dimensional image and converts the pattern into an electrical signal. The electric signal of the two-dimensional image as a result of the light reception is given to an averaging unit 6.

The averaging unit 6 receives a timing signal as shown in FIG. 3a from a timing circuit 12, which will be described later, to determine the electrical signal value of the pattern of the two-dimensional image of the reflected light R of the laser beam B received by the two-dimensional light receiver 5. The average value is calculated and output to the filter pattern generator 7 when the input of the timing signal is stopped.

The filter pattern generator 7 outputs the average value of the pattern of the reflected light R given from the averaging unit 6, that is, the electric signal of the two-dimensional image of the reflected light R from the surface of the inspected material 3 received by the two-dimensional light receiver 5. A two-dimensional filter pattern as shown in FIG. 2e, for example, is created based on the average value of the values. This created filter pattern is given to the variable optical filter 8 and set as its filter pattern. However, from the timing circuit 12 to the filter pattern generator 7
When a cancel signal as shown in FIG. 3c is applied to the filter, the filter pattern is not set to the variable optical filter 8.

As described above, the other of the reflected lights R of the light beam B split by the light splitter 41 is imaged on the variable optical filter 8 on its filter surface. This variable optical filter 8 is constructed by disposing a large number of liquid crystals or BSO (Bi ₁₂ SiOC ₂₀ crystals) having an electro-photoelectric (Pockels) effect, and controlling each of them electrically and optically through transparent electrodes. This optical filter is configured such that a non-(semi-)transparent pattern of a desired shape, that is, a filter pattern, can be arbitrarily set on a surface. The filter pattern to be set on this variable optical filter 8 is given from the filter pattern creator 7 as described above.

The condensing optical system 9 condenses the reflected light R after passing through the variable optical filter 8 and forms an image on the detection surface of the photodetector 10 .

The photodetector 10 detects the optical intensity of an optical image formed on its detection surface and converts it into an electrical signal. Therefore, the optical intensity converted into an electrical signal by this photodetector 10 is the reflected light R from the surface of the inspected material 3.
This is the optical intensity obtained by subtracting the optical intensity of the portion corresponding to the filter pattern set in the variable optical filter 8 from the optical intensity of .

The defect determiner 11 determines the presence or absence of a defect based on whether or not the electric signal given from the photodetector 10 described above, in other words, the intensity of the light that has passed through the variable optical filter 8, is greater than or equal to a predetermined value. If it is determined that there is a defect detection signal as shown in FIG.

The timing circuit 12 determines the timing of filter pattern creation by the filter pattern creator 7. Specifically, the timing circuit 12:
As shown in FIG. 3a, a timing signal of a predetermined length is repeatedly output to the averaging device 6 at predetermined time intervals, and the averaging device 6 outputs a timing signal of a predetermined length to the two-dimensional photoreceiver 5 during one timing signal period. The average value of the light reception results is outputted to the filter pattern generator 7.
The filter pattern creator 7 creates a filter pattern based on this, outputs the created filter pattern to the variable optical filter 8, and sets it as the filter pattern. However, if the defect detection signal is output from the defect determiner 11 to the timing circuit 12 during the timing signal output period, the timing circuit 12 sends a cancel signal to the filter pattern generator 7 as shown in FIG. 3c. , the filter pattern generator 7 is prohibited from outputting a filter pattern to the variable optical filter 8.

Therefore, the filter pattern of the variable optical filter 8 is such that only when no defect is detected over a predetermined period set as one output period of a timing signal to the timing circuit 12, the reflected light R during that period is is updated to the average pattern. That is, for example, in a case where the oil film thickness on the surface of the inspected material 3 gradually changes and the state of the reflected light R of the laser beam B gradually changes due to this, the filter set in the variable optical filter 8 Since the pattern also changes gradually as the oil film thickness on the surface of the inspected material 3 changes, it will not be determined as a defect. In addition, if the material of the inspected material 3 is changed and the pattern of the normal reflected light R changes greatly, for example, the two-dimensional pattern of the reflected light R of the inspected material 3 that is considered normal by visual inspection etc. If the light reception pattern by the light receiver 5 is set as a normal pattern in the variable optical filter 8, then this filter pattern will change to the normal pattern every time a predetermined period set as one cycle of the timing signal passes in the timing circuit 12. Since the pattern of the reflected light R is automatically reset, there is no need to interrupt the inspection work each time to reset various conditions such as resetting the filter pattern, changing the position of the member, etc.

Next, the operation of the apparatus of the present invention configured as described above will be described below according to the pattern of the reflected light R of the laser beam B shown in FIG. 2, a schematic diagram of the filter pattern, etc., and the timing chart shown in FIG. 3. explain.

The laser beam B oscillated and irradiated by the laser oscillator 1 is reflected by the mirror surface of the rotating polygonal mirror 20, further reflected by the reflecting mirror 21, and projected onto the surface of the inspected material 3. At this time, as the rotating polygonal mirror 20 rotates, the projection direction of the laser beam B moves in the main scanning direction perpendicular to the traveling direction of the inspected material 3, and as the non-inspected material 3 moves, the laser beam B moves in the sub-scanning direction. move in the direction.

Now, the reflected light R of the laser beam B from the surface of the inspected material 3 is condensed by the condenser lens 40, enters the light splitter 41, and is split into two.

One of the two-split reflected light R is formed as a two-dimensional image on the light-receiving surface of the two-dimensional light receiver 5, and the pattern thereof is converted into an electric signal and given to the averaging unit 6. By the way, when the surface of the inspected material 3 is normal with no defects and there is no oil film, the projected laser beam B is regularly reflected, so the reception pattern of the reflected light R received by the two-dimensional light receiver 5 is as follows. Second
Figure a shows a circular pattern with a clear outline. This circular light-receiving pattern is converted into an electrical signal and provided to the averaging unit 6.

The averaging unit 6 calculates the electric signal of the light receiving pattern given from the two-dimensional light receiver 5 in synchronization with the rise of the timing signal TS as shown in FIG. Addition is started, the average value is determined in synchronization with the rise of the timing signal TS, and the result is output to the filter pattern generator 7.

When the filter pattern creator 7 receives the average value output from the averaging device 6, it creates a filter pattern corresponding to the average value output. Specifically, Figure 2a
For the normal light reception pattern shown in Figure 2e,
Create a filter pattern as shown below. That is,
It blocks (or attenuates) the light rays in the portion where the amount of light received in the light receiving pattern of the light receiver 9 is more than a predetermined amount, and allows the light rays in the portion where the amount of light received in the light receiving pattern of the light receiver 9 is less than the predetermined amount to pass through. The filter pattern creator 7 creates a filter pattern,
This is output to the variable optical filter 8.

On the other hand, each time a new filter pattern as shown in FIG. 2e is provided to the variable optical filter 8 from the filter pattern generator 7 as described above, this new filter pattern is set.
Therefore, a pattern of reflected light R after passing through the variable optical filter 8, which is similar to the light receiving pattern imaged on the two-dimensional light receiver 5, enters the condensing optical system 9, and this pattern is detected by the photodetector. The image is formed on 10 detection planes.

The photodetector 10 receives light from the condensing optical system 9 and converts the amount of light received from an optical image formed on its detection surface into an electrical signal and outputs it to the defect determiner 11 .

The defect determiner 11 compares the level of the electrical signal given from the photodetector 10 with a predetermined level, and if it is higher than the predetermined level, determines that a defect exists, and performs defect detection as shown in FIG. 3c. The signal ES is output to a display device or a storage device (not shown), and is also output to the timing circuit 12.

A case in which this defect detection signal ES is output will be specifically explained below. First, when the reflected light R without defects is incident on the variable optical filter 8, the variable optical filter 8 is set with a filter pattern corresponding to the normal reflected light R as shown in FIG. 2e. The amount of light passing through the variable optical filter 8 is very small or zero. Therefore, the defect determiner 11 does not output the defect detection signal ES. However, the reflected light R from a portion of the surface of the inspected material 3 where there is a defect, such as an eave,
The pattern is normal reflected light R, as shown in Figure 2b.
This shows a pattern in which components diffusely reflected by the eaves are added to the pattern. Therefore, when the pattern of the reflected light R from this eaves part is projected onto the variable optical filter 8, which has a filter pattern corresponding to the normal reflected light R as shown in FIG. 2a,
As shown in FIG. 2f, the variable pattern optical filter 8 has a large amount of light only in the diffusely reflected portion caused by the eaves.
is projected on. However, in such a case, the defect determiner 11 detects a high-level defect, as shown in FIG. Outputs signal ES.

On the other hand, when the timing circuit 12 receives the defect detection signal ES from the defect determiner 11, the third
As shown in FIG. c, a cancel signal CS is output to the filter pattern generator 7.

When this cancel signal CS is given,
The filter pattern generator 7 does not output a new filter pattern to the variable optical filter 8, and therefore the variable optical filter 8 receives the previous filter pattern, that is, the previous timing signal.
The filter pattern created during the TS period continues to be set. As a result, a new filter pattern created including the pattern of the reflected light R caused by the defect will not be set on the variable optical filter 8.
This means that a normal pattern of reflected light R is always set.

By the way, when the surface condition of the inspected material 3 gradually changes, for example when the inspected material 3 is a rolled steel plate, the inspected material 3 changes as the rolling rolls wear out.
A situation occurs in which the surface condition of a rolled steel sheet changes gradually. Alternatively, there may be a situation where the surface of the material to be inspected 3 itself is normal, but the thickness of the oil film covering the surface varies greatly. For example, Figure 2c shows the pattern of the reflected light R when the thickness of the oil film on the surface of the inspected material 3 is relatively thick, but in such a case, the pattern of the reflected light R that should originally be circular. The outline of the image becomes slightly blurred.
Therefore, when this pattern of reflected light R is projected onto the variable optical filter 8 having the filter pattern shown in FIG. Although this is detected by the photodetector 10, the defect determiner 11 does not output the defect detection signal ES at this level of light intensity.

On the other hand, in the above case, the two-dimensional light receiver 5 receives a pattern of reflected light R with a slightly blurred outline as shown in FIG. Therefore, the averager 6
The average value outputted to the filter pattern generator 7 becomes a pattern having a slightly larger outline than the pattern of the reflected light R shown in FIG. 2a. However, at this time, since the defect detection signal ES is not output from the defect determiner 11, the cancel signal CS is not output from the timing circuit 12.
Therefore, a new filter pattern having a slightly larger outline than that shown in FIG. 2a is set on the variable optical filter 8. For this reason, the filter pattern set in the variable optical filter 8 changes to follow the pattern of the reflected light R, which is in a normal surface state but gradually changes due to changes in the oil film thickness. 3. It is not determined that a surface defect exists.

FIG. 2d shows a pattern of reflected light R from the surface of the inspected material 3, which has directionality on the surface. In such a material to be inspected 3, the pattern of the reflected light R takes on an elliptical shape according to the directionality of the surface of the material to be inspected 3. If the material etc. of the inspected material 3 is changed and the pattern of the reflected light R from the normal, that is, defect-free surface of the inspected material 3 changes significantly, the inspected material 3 At the first time when the material is changed, the reflected light R from the normal surface of the inspected material 3
The pattern is read by the two-dimensional light receiver 5, and is used as a new filter pattern by the variable optical filter 8.
You can set it to . This makes it possible to immediately perform inspection work without having to perform troublesome resetting and adjustment of various conditions including scanning such as resetting the filter pattern of the variable optical filter 8, or changing the position of each member. .

〔effect〕

As described above, in the present invention, the pattern of the reflected light of the laser beam, which is the standard for determining the presence or absence of defects, changes according to changes in the surface of the inspected material within a range that can be considered normal. There is no need to reset or adjust various conditions of the equipment in response to changes in the oil film on the material surface or changes in the surface condition of the material to be inspected due to wear of rolling rolls in the case of rolled steel plates. Alternatively, even if the processing/finishing method has been changed, it can be easily and quickly implemented by simply setting the pattern of reflected light from the normal surface of the inspected material as the filter pattern of the variable optical filter. It is possible.
Therefore, according to the present invention, defects on the surface of a material to be inspected such as a rolled steel plate can be detected efficiently and economically with a relatively simple device configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the signal processing system shown together with a schematic diagram of the optical system of the device of the present invention, Fig. 2 is a schematic diagram of the reflected laser beam and filter pattern, and Fig. 3 is a schematic diagram of the reflected light of the laser beam and the filter pattern.
The figure is a timing chart of the signal processing system. B... Laser beam, R... Reflected light, 1... Laser beam oscillation device, 2... Scanning optical system, 3...
Material to be inspected, 4... Light receiving optical system, 5... Two-dimensional light receiver, 6... Averager, 7... Filter pattern creator, 8... Variable optical filter, 9... Condensing optical system, 10 ...Photodetector, 11...Defect determiner,
12...Timing circuit.

Claims (1)

[Claims] 1. Defects on the surface of the material to be inspected are detected by comparing the state of the reflected light of the irradiated light beam from the surface of the material to be inspected and the state of the reflected light from the normal surface of the material. The apparatus includes: a light splitter that splits the reflected light from the surface of the inspected material of the light beam into two; a two-dimensional light receiver that receives one of the reflected lights split by the light splitter as a two-dimensional image; An averaging device that adds the light reception results of the two-dimensional light receiver in time series and obtains an average value; and a filter pattern creation device that creates a two-dimensional filter pattern corresponding to the average value obtained by the averaging device. a variable optical filter on which the filter pattern created by the filter pattern generator is set, and onto which the other reflected light split by the light splitter is projected; a photodetector for detecting; a defect determiner for determining defects on the surface of the inspected material based on the detection results of the photodetector; A surface defect detection device comprising: a timing circuit that causes the filter pattern generator to read an average value of the summed light reception results of the two-dimensional light receiver.