JP7543345B2 - Surface inspection device and detection processing method using the same - Google Patents

Description

The present invention relates to a surface inspection device for metal workpieces and a detection processing method using the same, and more specifically, to a surface inspection device for detecting defects in a metal workpiece while the metal workpiece is being transported on a conveyor, and a detection processing method using the same.

In the field of metal processing, inspection equipment is widely used to detect defects in industrial products during the manufacturing process using optical means.

For example, a surface defect inspection method for steel plate is known in which light is projected onto the surface of a steel plate to be inspected, the reflected light is collected, photoelectric conversion and two-dimensional Fourier transformation are performed, and the characteristics of the defect are extracted as parameters for identifying the type of surface defect based on the power spectrum distribution in frequency space, the type of defect is identified based on this, and a threshold level for the defect signal is set in accordance with the identified type of defect to determine the harmfulness of the defect (see, for example, Patent Document 1).
In addition, a metal surface defect inspection device is known that includes a light-projecting means that emits linear light, a reflecting means that reflects the linear light and irradiates it onto the surface of a metal material, and an imaging means that images the portion of the metal material surface that is irradiated with the linear light (see, for example, Patent Document 2).
Also known is a defect inspection device that has a first illumination that irradiates an object to be inspected with a first light at an illumination angle θ, a second illumination that irradiates a position irradiated with the first light at an illumination angle α different from the illumination angle θ, a line-type color sensor that receives reflected light of the first light and reflected light of the second light, and a defect detection unit that adjusts the brightness of the first light or the second light (see, for example, Patent Document 3).

Special Publication No. 61-42221 JP 2018-17629 A Patent No. 6901806

However, the metal surface defect inspection device described in Patent Document 1, the metal surface defect inspection device described in Patent Document 2, and the defect inspection device described in Patent Document 3 all use reflected light from a certain direction, so there is a problem that, for example, if the defect is a linear flaw (hereinafter referred to as a "linear flaw"), it can be difficult to detect depending on the direction of the linear flaw.

The present invention was made in consideration of the above circumstances, and aims to provide a surface inspection device and a detection processing method using the same that can detect even linear flaws, regardless of their orientation.

The inventors conducted extensive research to find a solution to the above-mentioned problems, and discovered that the above-mentioned problems could be solved by placing the camera at the center of the inspection unit when viewed from above through the housing, and arranging the light source unit so as to surround the camera, which led to the completion of the present invention.

The present invention is a surface inspection device for detecting defects in metal workpieces while the workpieces are being transported on a conveyor, the surface inspection device comprising a support frame provided above the conveyor, an inspection unit attached to the support frame, and a control unit connected to the inspection unit, the inspection unit having a housing portion having no bottom wall portion, a camera attached to the top wall portion of the housing portion, and a light source portion attached to the inner surface side of the side wall portion of the housing portion, the camera being disposed at the center when viewed from above through the housing portion, and the light source portion being disposed so as to surround the camera, the control unit receiving image data of the metal workpiece photographed by the camera, and detecting defects in the metal workpiece based on the image data.

In the present invention, it is preferable that at least a first inspection unit group and a second inspection unit group are formed in which a plurality of inspection units are linearly arranged in the width direction of the metal workpiece.
In this case, in the present invention, it is preferable that the inspection units of the first inspection unit group and the second inspection unit group are arranged in a staggered pattern when viewed from above, and that a specific portion of the metal workpiece in the width direction passes through the photographable range of at least one of the inspection units of the first inspection unit group and the inspection unit of the second inspection unit group.

In the present invention, it is preferable that the angle of view of the camera in the conveying direction of the metal workpiece is 28 to 53 degrees, the angle of view in the width direction of the metal workpiece is 45 to 61 degrees, the shortest vertical distance between the light source unit and the camera is 300 mm or less, and the shortest vertical distance between the metal workpiece and the camera is 350 mm or less.

The present invention also relates to a detection processing method using a surface inspection device, in which a control unit carries out a receiving step of receiving image data of still images taken by each camera, an integration step of combining the multiple image data into integrated data, a processing step of applying image processing to the integrated data, and a detection step of comparing the integrated data after image processing with integrated data after image processing in a case in which there is no defect in the metal workpiece, and detecting areas where there are differences in values as defects.
In this case, the image processing is preferably a binarization process.

In the surface inspection device of the present invention, the transported metal workpiece is photographed by a camera, and the control unit analyzes the image data, thereby making it possible to detect defects in the metal workpiece.
In this case, in the inspection unit, when viewed from above through the housing part, the camera is positioned at the center and the light source part is positioned to surround the camera, so that the light irradiated to the metal workpiece has no directionality.
This makes it possible to detect defects such as line scratches, regardless of their orientation.

In the surface inspection device of the present invention, since the inspection unit is attached to the support frame, it can be installed later on an existing conveyor or the like.
Furthermore, the position of the inspection unit can be easily adjusted.

In the surface inspection apparatus of the present invention, since the first inspection unit group and the second inspection unit group are formed, the accuracy of defect detection can be further improved.
In this case, the inspection units of the first inspection unit group and the second inspection unit group are arranged in a staggered pattern when viewed from above, and a specific portion of the metal workpiece in the width direction passes through the photographable range of at least one of the inspection units of the first inspection unit group and the inspection unit of the second inspection unit group, thereby preventing missed detections.
In some cases, it may be possible to detect defects in metal workpieces between the inspection units of one inspection unit group using the inspection units of the other inspection unit group.
In other words, since it is possible to capture images of the entire metal workpiece in parts near the center of the imageable range of each camera, distortion near the edges of the imageable range can be ignored, resulting in improved accuracy in detecting defects.

In the surface inspection device of the present invention, by adopting a camera whose angle of view in the transport direction of the metal workpiece is within the above-mentioned range, it is possible to maintain a constant transport speed for the metal workpiece without reducing the accuracy of defect detection.
In addition, by setting the shortest vertical distance between the light source unit and the camera within the above range, and setting the shortest vertical distance between the metal workpiece and the camera within the above range, sufficient illuminance can be maintained within the camera's shooting range, and the accuracy of defect detection can be further improved.

The detection processing method of the present invention uses the above-mentioned surface inspection device, and the control unit carries out a receiving step, an integration step, a processing step, and a detection step, making it possible to detect even linear flaws regardless of their orientation.
At this time, if the image processing is a binarization process, the accuracy of defect detection can be further improved, and the defect detection speed can also be improved.

FIG. 1 is a perspective view that shows a schematic diagram of a surface inspection apparatus according to the present embodiment. FIG. 2 is a perspective view that shows a schematic diagram of an inspection unit of the surface inspection apparatus according to the present embodiment. 3A and 3B are explanatory diagrams for explaining the positional relationship between the camera and light source unit and the metal workpiece in the surface inspection device according to this embodiment. FIG. 4 is a flowchart of the detection processing method according to this embodiment. FIG. 5 is a top view that shows a schematic diagram of a surface inspection apparatus according to another embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary.
In the drawings, the same elements are given the same reference numerals and duplicated explanations are omitted.
In addition, unless otherwise specified, the positional relationships such as up, down, left, right, etc. are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

FIG. 1 is a perspective view that shows a schematic diagram of a surface inspection apparatus according to the present embodiment.
As shown in FIG. 1, a surface inspection device 100 according to this embodiment is a device for detecting defects in a metal workpiece W while the metal workpiece W is being transported by a conveyor C.
Here, the metal workpiece is a flat metal workpiece, and it does not matter whether it is magnetic or not.
Specific examples of materials that can be used include iron, copper, aluminum, titanium, and steel (including high tensile materials and ultra-high tensile materials).
Furthermore, the "defects" of the metal workpiece W that can be detected by the surface inspection device 100 include linear defects, indentations, adhesion of contaminants, scratches, and the like.

In the surface inspection apparatus 100, the conveyor C may be a general one having a belt C1 and a roll C2 on which the belt C1 is stretched.
In addition, an encoder C3 for calculating the transport distance of the metal workpiece W is attached to the roll C2.
In addition, the transport speed of the metal workpiece W by the conveyor C is preferably 60 to 90 m/min, from the viewpoint of enabling the surface inspection device 100 to accurately detect defects and not impairing productivity.

The surface inspection device 100 includes a support frame F provided above a conveyor C, a plurality of inspection units 10 attached to the support frame F, and a control unit 20 connected to the inspection units 10 .
In the surface inspection device 100, when a metal workpiece W transported by a conveyor C passes directly below the inspection unit 10, it is photographed by the camera 2 of the inspection unit 10. Then, as described below, the control unit 20 detects defects in the metal workpiece W by analyzing the photographed image data.

The support frame F is provided above the conveyor C and is supported on both sides by support tables FD.
Therefore, the support frame F and the support table FD have an inverted U-shape when viewed from the front, and are disposed so as to straddle the conveyor C. This makes it possible to install the surface inspection device 100 on an existing conveyor or the like as a retrofit.
In addition, a plurality of inspection units 10 are directly attached to the support frame F.
That is, a plurality of inspection units 10 are suspended from a support frame.
Moreover, the position of the inspection unit 10 can be adjusted vertically and horizontally.

FIG. 2 is a perspective view that shows a schematic diagram of an inspection unit of the surface inspection apparatus according to the present embodiment.
In FIG. 2, the housing of the inspection unit is shown in a see-through manner.
As shown in FIG. 2, the inspection unit 10 has a housing part 1 , and a camera 2 and a light source part 3 attached to the housing part 1 .

The housing 1 is made up of a plate-like upper wall 1a and side walls 1b extending downward from the four sides of the upper wall 1a.
That is, the housing 1 is in the shape of a rectangular prism having an open bottom (having no bottom wall) and surrounded on all four sides by side walls 1b, and is hollow inside.

In the housing 1, a camera 2 is attached substantially at the center of the upper wall 1a so that the shooting direction faces vertically downward.
The camera 2 is not particularly limited, but may be a so-called line sensor camera, a USB camera, a WEB camera, a CMOS camera, or the like.
Furthermore, the camera 2 may be one that shoots moving images or one that shoots still images, but it is preferable that the camera 2 has a function of saving image data of continuous still images.
In this case, it is preferable that the resolution of the image data of the still image captured by the camera 2 is 640×480 pixels or more.
The image data of the still image captured by the camera 2 is transmitted to a control unit 20, which will be described later.

In the housing 1, a strip-shaped light source unit 3 extending horizontally is attached to the lower end of each of the inner faces of the four side walls 1b.
That is, the light source unit 3 is attached to each of the four side wall portions 1b.
The light source unit 3 is not particularly limited, but may be an incandescent lamp, a fluorescent lamp, a discharge lamp, an LED, or the like.

For these reasons, in the inspection unit 10 , when viewed from above through the housing part 1 , the camera 2 is disposed at the center, and the light source part 3 is disposed so as to surround the camera 2 .
As a result, the light irradiated onto the metal workpiece W directly below the camera 2 does not exhibit directionality.
As a result, defects such as line scratches can be easily detected regardless of their orientation.

3A and 3B are explanatory diagrams for explaining the positional relationship between the camera and light source unit and the metal workpiece in the surface inspection device according to this embodiment.
As shown in FIG. 3, it is preferable that the camera 2 has a viewing angle θ1 in the conveying direction X of the metal workpiece W of 28 to 53 degrees.
If the angle of view θ1 of the camera 2 in the conveying direction X of the metal workpiece W is less than 28 degrees, the conveying speed of the metal workpiece W needs to be slower than when the angle of view θ1 is within the above range, which has the disadvantage of reducing productivity.
On the other hand, if the angle of view θ1 of the camera 2 in the transport direction X of the metal workpiece W exceeds 53 degrees, the detection accuracy may be insufficient depending on the location of the defect, compared to when the angle of view θ1 is within the above range.

Similarly, it is preferable that the angle of view θ2 of the camera 2 in the width direction Y of the metal workpiece W is 45 to 61 degrees.
If the angle of view θ2 of the camera 2 in the width direction Y of the metal workpiece W is less than 45 degrees, it will be necessary to install a large number of cameras, which will result in higher costs compared to when the angle of view θ2 is within the above range.
On the other hand, if the angle of view θ2 of the camera 2 in the width direction Y of the metal workpiece W exceeds 61 degrees, the detection accuracy may be insufficient depending on the location of the defect, compared to when the angle of view θ2 is within the above range.

It is preferable that the shortest distance D1 in the vertical direction between the light source unit 3 and the camera 2 is 300 mm or less, and the shortest distance D2 in the vertical direction between the metal workpiece W and the camera 2 is 350 mm or less.
In this case, sufficient illuminance can be maintained while the camera 2 is positioned as close as possible to the metal workpiece W, thereby further improving the accuracy of defect detection.

Returning to FIG. 1, in the surface inspection device 100, a plurality of inspection units 10 are linearly arranged in the width direction Y of the metal workpiece W to form an inspection unit group 10a.
In addition, a plurality of inspection unit groups 10a are arranged in the transport direction X of the metal workpiece W.
Specifically, it has a downstream inspection unit group (hereinafter referred to as the "first inspection unit group") 10a1 in which seven inspection units 10 are arranged in a line along the width direction Y of the metal workpiece W, and an upstream inspection unit group (hereinafter referred to as the "second inspection unit group") 10a2 in which six inspection units 10 are arranged in a line along the width direction Y of the metal workpiece W, and the first inspection unit group 10a1 and the second inspection unit group 10a2 are arranged side by side along the transport direction X of the metal workpiece W.
At this time, the row of the inspection units 10 in the first inspection unit group 10a1 and the row of the inspection units 10 in the second inspection unit group 10a2 are parallel to each other.
This makes it possible to repeatedly inspect specific areas of the metal workpiece W, thereby further improving the accuracy of detecting defects.

In the surface inspection apparatus 100, the inspection units 10 of the first inspection unit group 10a1 and the inspection units 10 of the second inspection unit group 10a2 are arranged in a staggered pattern when viewed from above, so that the inspection units 10 of the second inspection unit group 10a2 are located upstream between the inspection units 10 of the first inspection unit group 10a1.
As a result, a specific portion in the width direction of the metal workpiece W passes through the photographable range of at least one of the inspection units 10 of the first inspection unit group 10a1 and the inspection units 10 of the second inspection unit group 10a2. The photographable range R is a range in which photographing is possible, specifically, a region included in the angle of view of the camera 2 that is not obstructed by the housing and is between the camera 2 and the metal workpiece W (see FIG. 3).

As a result, specific areas across the entire width of the metal workpiece W are inspected at least by the inspection unit 10 of the first inspection unit group 10a1 or the inspection unit 10 of the second inspection unit group 10a2, thereby preventing detection misses.
Furthermore, when inspection is performed using the inspection units 10 of the first inspection unit group 10a1 and the inspection units 10 of the second inspection unit group 10a2, for example, even if the inspection units 10 of the first inspection unit group 10a1 photograph near the end of the photographable range R, the inspection units 10 of the second inspection unit group 10a2 can photograph near the center of the photographable range R, so distortion near the end of the photographable range R can be ignored.
As a result, the accuracy of detecting defects in the metal workpiece W can be further improved.

The control unit 20 is connected to the camera 2 of the inspection unit 10 via a wired or wireless connection, and is capable of receiving image data of the metal workpiece 2 captured by the camera 2 .
Then, in the control unit 20, the received image data is subjected to image processing, such as binarization, and then defects in the metal workpiece 2 are detected.
This makes it possible to improve the accuracy of defect detection in the surface inspection device 100 and also to improve the defect detection speed.
The control unit 20 is a general-purpose computer equipped with a general central processing unit (CPU), an arithmetic processing unit, a recording unit, an image processing unit, an input/output unit (keyboard, display), and the like.

Next, a detection processing method using the surface inspection apparatus 100 according to this embodiment will be described.
FIG. 4 is a flowchart of the detection processing method according to this embodiment.
As shown in FIG. 4, in the detection processing method according to this embodiment, the control unit 20 of the surface inspection apparatus 100 executes at least a receiving step S1, a integrating step S3, a processing step S4, and a detecting step S5.
This makes it possible to detect even linear flaws, regardless of their orientation.

First, in a receiving step S1, image data of successive still images captured by each camera 2 is received.
Here, the image data of successive still images is obtained by successively photographing the metal workpiece W being transported by the same camera 2, and the way the light hits a specific portion varies.
The control unit 20 receives this image data for each camera 2. The control unit 20 then records the received image data in the recording unit.
Next, in the control unit 20, a first binarization process is performed on the plurality of image data in a pre-processing step S2, whereby the data volume of the image data can be reduced and the subsequent processing can be performed at a higher speed.

Next, in the control unit 20, in an integration step S3, a so-called image synthesis is performed in which the multiple binarized image data are combined to generate integrated data.
This image synthesis is performed by identifying the part of the metal work W photographed by camera 2 based on the transport speed of the metal work W, the transport position of the metal work W calculated by encoder C3, and the camera's shooting speed, and then overlaying image data of the same part.
This makes it possible to ignore distortion near the edges of the image data.
In addition, by overlaying images with different lighting conditions, defects that could not be captured by a camera with a certain lighting condition can be seen, improving detection accuracy.

Next, in the control unit 20, in processing step S4, a second binarization process is performed on the integrated data in which the image data has been integrated.
Next, in a detection step S5, the binarized integrated data is again compared with the binarized data of a defect-free metal workpiece W, and a detection process is performed in which areas with differences in value are detected as defects.
This allows even line flaws to be detected regardless of their orientation.
If necessary, a detected defect is displayed on a display or the like along with the position where the defect is detected.

Although the above describes a preferred embodiment of the present invention, the present invention is not limited to the above embodiment.

In the surface inspection device 100 according to this embodiment, the housing 1 of the inspection unit 10 is in the shape of a rectangular prism with an open bottom surface, but as long as the bottom surface is open and the interior is hollow, the shape is not limited to a rectangular prism, and may be a polygonal prism other than a rectangular prism, a polygonal truncated pyramid, a cylinder, a truncated cone, etc.

The surface inspection apparatus 100 of this embodiment has a downstream side 1 in which five inspection units 10 are arranged in a line along the width direction Y of the metal workpiece W, and a second inspection unit group 10a2 in which four inspection units 10 are arranged in a line along the width direction Y of the metal workpiece W, but the number of inspection units 10 is not particularly limited.
Furthermore, the first inspection unit group 10a1 and the second inspection unit group 10a2 are arranged side by side along the transport direction X of the metal workpiece W, but another inspection unit group 10a may also be arranged.

FIG. 5 is a top view that shows a schematic diagram of a surface inspection apparatus according to another embodiment.
As shown in FIG. 5, in a surface inspection apparatus 101 according to another embodiment, four rows of inspection unit groups 10a are arranged side by side along the transport direction X of the metal workpiece W.
The inspection units 10 are arranged in a staggered manner when viewed from above.
Such a surface inspection device 101 is divided into two rows of inspection unit groups 10a on the upstream side and two rows of inspection unit groups 10a on the downstream side, with the two rows of inspection unit groups 10a on the upstream side being mainly designed to detect linear flaws, and the two rows of inspection unit groups 10a on the downstream side being mainly designed to detect indentation defects.
This makes it possible to further improve the detection accuracy.
It is also possible to improve the transport speed of the metal workpiece W.

In the detection processing method according to this embodiment, the control unit executes a receiving step S1, a pre-processing step S2, an integrating step S3, a processing step S4, and a detection step S5, but the pre-processing step S2 is not essential.
Furthermore, although binarization is performed as the image processing, the present invention is not limited to this, and image superposition and creation of a weight map may also be performed.

In the detection processing method according to this embodiment, the control unit may perform image correction to correct image distortion before performing the first binarization process on the image data.

INDUSTRIAL APPLICABILITY The surface inspection apparatus and the detection processing method using the same of the present invention can be used in the field of metal processing as an apparatus for detecting defects in a metal workpiece while the metal workpiece is being transported on a conveyor.
According to the surface inspection device and the detection processing method using the same of the present invention, even linear flaws can be detected regardless of their orientation, and detection can be performed with high accuracy for the entire metal workpiece.

Reference Signs List 1: Housing 1a: Upper wall 1b: Side wall 10: Inspection unit 10a: Inspection unit group 10a1: First inspection unit group 10a2: Second inspection unit group 100, 101: Surface inspection device 2: Camera 20: Control unit 3: Light source unit C: Conveyor C1: Belt C2: Roll C3: Encoder R: Photographable range W: Metal workpiece

Claims (6)

A surface inspection device for detecting defects in a flat metal workpiece while the metal workpiece is being transported by a conveyor, comprising:
A support frame provided above the conveyor;
an inspection unit attached to the support frame;
A control unit connected to the inspection unit;
Equipped with
At least a first inspection unit group and a second inspection unit group are formed in which a plurality of the inspection units are linearly arranged in the width direction of the metal workpiece,
the inspection units of the first inspection unit group and the second inspection unit group are arranged in a staggered manner in a top view,
A specific portion of the metal workpiece in the width direction passes through a photographable range of at least one of the inspection units of the first inspection unit group and the inspection unit of the second inspection unit group,
the inspection unit includes a housing portion having no bottom wall portion, a camera attached to an upper wall portion of the housing portion, and a light source portion attached to an inner surface side of a side wall portion of the housing portion,
When viewed from above through the housing, the camera is disposed at the center, and the light source unit is disposed so as to surround the camera,
The shortest distance between the light source unit and the camera in the vertical direction is 300 mm or less,
The shortest distance between the metal workpiece and the camera in the vertical direction is 350 mm or less,
A surface inspection device in which the control unit receives image data of continuous still images of the metal workpiece taken by the camera, and detects defects in the metal workpiece based on the image data. A surface inspection device as described in claim 1, wherein, when photographing a specific portion of the metal workpiece, one of the inspection units of the first inspection unit group and the inspection unit of the second inspection unit group photographs near the edge of the photographable range, the other photographs near the center of the photographable range . The support frame is provided above the conveyor and is supported on both sides by support bases.
The support frame and the support base are in an inverted U-shape when viewed from the front and are arranged to straddle the conveyor,
A plurality of the inspection units are suspended from the support frame,
2. The surface inspection apparatus according to claim 1 , wherein the inspection unit is adjustable in position up, down, left and right . The defect is a line defect, an indentation, an adhesion of a contaminant, or a scratch,
The conveying speed of the metal workpiece is 60 to 90 m/min.
2. A surface inspection device according to claim 1 , wherein the camera has an angle of view of 28 to 53 degrees in the conveying direction of the metal workpiece, and an angle of view of 45 to 61 degrees in the width direction of the metal workpiece. In order to detect defects in metal workpieces while the workpieces are being transported on a conveyor,
A support frame provided above the conveyor, an inspection unit attached to the support frame, and a control unit connected to the inspection unit,
the inspection unit includes a housing portion having no bottom wall portion, a camera attached to an upper wall portion of the housing portion, and a light source portion attached to an inner surface side of a side wall portion of the housing portion,
When viewed from above through the housing, the camera is disposed at the center, and the light source unit is disposed so as to surround the camera,
A detection processing method using a surface inspection device, in which the control unit receives image data of the metal workpiece photographed by the camera and detects defects in the metal workpiece based on the image data,
The control unit:
A receiving step of receiving image data of successive still images captured by each of the cameras;
An integration step of combining a plurality of image data into integrated data;
a processing step of performing image processing on the integrated data;
a detection step of comparing the integrated data after the image processing with integrated data after the image processing when the metal workpiece has no defects, and detecting areas where there is a difference in value as defects;
A detection processing method for carrying out the above. The detection processing method according to claim 5, wherein the image processing is a binarization process.

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