JP2017146302A - Surface defect inspection device and surface defect inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface defect inspection device and a surface defect inspection method that make a precise inspection of surface defects with a simple structure when an inspecting target is a cylindrical or columnar material.SOLUTION: A surface defect inspection device 1 includes: an imaging device 30 for imaging a cylindrical or columnar inspection target material; an image processor 40 for detecting a surface defect of the inspection target material on the basis of changes in the luminance of the image taken by the imaging device 30; a conveying device 10 arranged on a manufacturing line for conveying the inspection target material while rolling the material along a predetermined slope; and an indirect illumination device 20 disposed between the conveying device 10 and the imaging device 30 for illuminating the inspection material, the imaging device 30 imaging the inspection target material conveyed by the conveying device 10 and illuminated by the indirect illumination device 20.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface defect inspection apparatus and method for a cylindrical or columnar inspection object, and more particularly to a surface defect inspection apparatus and method for optically inspecting surface defects such as steel pipes and round bars.

  In the manufacturing process of steel pipes, defects such as oysters, cracks, adhesion of foreign substances, and dirt may occur on the surface of the steel pipe. For the purpose of quality assurance, these surface defects are automatically inspected over the entire length. Or very important in quality control. For example, if there is a plating adhesion failure on a steel pipe whose surface is plated, the exposed portion rusts and pitting, and there is a concern that troubles such as leakage of the transport fluid may occur.

  For this reason, the conventional defect inspection of the surface of a steel pipe has been performed by visual inspection or optical inspection using a camera or the like in addition to inspection by various non-destructive inspection (NDI) techniques. And as a surface defect inspection method of such a steel pipe, as shown in patent documents 1 to 3, for example, a steel pipe surface is photographed with a camera to obtain an image, and a luminance change portion in the obtained image is extracted as a defect portion. Thus, development of an apparatus for detecting surface defects has been performed.

  For example, Patent Document 1 includes a bright field illumination that illuminates the front surface of a steel pipe, and a pair of dark field illuminations that illuminate both sides of the steel pipe from a lateral direction perpendicular to the bright field illumination. A technique is described in which a surface is photographed to obtain an image, and a luminance change portion of the image is extracted as a defective portion. In the technique in this Patent Document 1, particularly in the case of a steel pipe or steel bar having a small diameter of φ300 mm or less, the bright area on the surface of the steel pipe is narrowed only by the bright field illumination. Therefore, the bright area is obtained by using the dark field illumination from both sides together. It is possible to illuminate almost the entire upper half of the steel pipe surface.

  Moreover, in patent document 2, the upper part and side edge of the surface of a steel pipe are irradiated by irradiating a steel pipe side edge part from the diagonally upper side of both sides of a steel pipe with a pair of long condensing illuminations extended long along the axial center direction of a steel pipe. A technique is described in which the brightness of the part is made substantially equal, the surface of the steel pipe is photographed with a television camera from the center position of both illuminations to obtain an image, and the brightness change part of the image is extracted as a defective part. The technique in Patent Document 2 inspects a steel pipe while rotating about its axis, and can inspect defects such as surface scratches, dirt, and shape defects.

  In Patent Document 3, a two-dimensional camera, a one-dimensional camera, and a plurality of halogen lamps are arranged along the axial direction on the upper part of the conveyance path of the steel pipe conveyed in the axial direction, and measurement is performed with the two-dimensional camera. A technique for inspecting steel pipe surface inspection data with a one-dimensional camera by correcting the brightness using the amount of light reflected from the surface of the steel pipe is described. In the technique in Patent Document 3, the entire length of the steel pipe can be inspected by conveying the steel pipe while rotating it.

  In addition to the above-mentioned Patent Documents 1 to 3, as disclosed in Patent Document 4, the inventors have an imaging unit having an imaging region that covers the entire circumference of a steel pipe that is an object to be inspected, and a plurality of linear light sources. Has proposed a surface defect inspection apparatus that uses a line sensor camera that identifies the position of a steel pipe in the field of view.

  Patent Document 5 discloses a dome member that has a dome shape that expands toward the object to be inspected (wire material), a camera that is disposed at the opening of the dome member, and a lower dome member. Disclosed is a wire surface flaw detector provided with a light source that is provided inside the side opening end at equal intervals and irradiates light toward the camera side to uniformly irradiate the surface of the wire with light reflected by the reflecting surface. ing.

JP 2006-292580 A Japanese Patent No. 2962125 Japanese Patent No. 4023295 JP2015-64301A JP 2011-163955 A

  However, in the method of Patent Document 1, in order to inspect the entire surface of the steel pipe, it is necessary to rotate the steel pipe in the circumferential direction without moving in the axial direction. It is necessary to provide a steel pipe rotating mechanism and the like, which increases the cost. In addition, there is a problem that the inspection process lowers the conveyance efficiency, and consequently the productivity of the line is lowered, and there is a concern that disturbance such as the distance between the camera and the surface of the steel pipe fluctuates due to the bending or flattening of the steel pipe. The same applies to the method of Patent Document 2.

  Further, Patent Document 3 is a method for inspecting a steel pipe while being spirally conveyed, and is widely used in ultrasonic inspection and the like. However, since only one place in the circumferential direction is essentially measured, If the adjustment of the rotation speed and conveyance speed is not strictly controlled, inspection omission (uninspected area) will occur, and as in Patent Documents 1 and 2, the bending and flattening of the steel pipe will now affect the accuracy of the helical conveyance. As a result, there is a problem that the inspection is affected.

  Further, in the method of Patent Document 4, the surface gloss of the steel pipe has a great influence on the inspection result. For example, when inspecting a steel pipe having a strong specularity, the light from the light source is reflected on the steel pipe and halation occurs. There was a problem of affecting.

  Furthermore, in the method of Patent Document 4, in order to reduce the influence of surface gloss, it is necessary to make the intensity distribution of the reflected light from the steel pipe closer to the circumferential direction. There was a problem that the specific sensitivity of the steel pipe position by the characteristic line sensor camera was lowered.

  Further, the method of Patent Document 5 assumes an inspection in which an object to be inspected is conveyed (vertically fed) in the axial direction, and a portion that becomes a blind spot of a camera arranged in the opening of the dome member cannot be inspected. There was a problem. In addition, when the dome illumination composed of the dome member and the light source disclosed in Patent Document 5 is installed in a conveying device that conveys the steel pipe in a direction perpendicular to the axial direction of the steel pipe, for example, the steel pipe is inspected. Since the irradiation length in the axial direction of the steel pipe changes depending on the position, there is a problem that the outer surface of the entire steel pipe cannot be inspected.

  The present invention has been made in view of the above, and when inspecting a surface defect of a cylindrical or columnar object to be inspected, the surface defect inspection can be performed with a simple configuration and high accuracy. An object is to provide an apparatus and a surface defect inspection method.

  In order to solve the above-described problems and achieve the object, a surface defect inspection apparatus according to the present invention includes an imaging apparatus that images a cylindrical or columnar object to be inspected, and luminance of an image captured by the imaging apparatus. An image processing apparatus comprising: an image processing device that detects a surface defect of the object to be inspected based on a change, and is provided on a production line and transported while rolling the object to be inspected along a predetermined inclination And an indirect illumination device that is disposed between the transport device and the imaging device and illuminates the object to be inspected, the imaging device being transported by the transport device, and the The inspected object illuminated by the indirect illumination device is imaged.

  Further, the surface defect inspection apparatus according to the present invention is the above-described invention, wherein the indirect illumination device includes a semi-cylindrical reflecting material whose concave surface is a light reflecting surface, and a light source disposed on the reflecting surface side of the reflecting material. And illuminating the object to be inspected being transported by the transport device by reflecting light from the light source by a reflecting surface of the reflecting material.

  In the surface defect inspection apparatus according to the present invention as set forth in the invention described above, the reflecting material is disposed such that its axial direction is parallel to the axial direction of the object to be inspected, and is orthogonal to the axial direction of the reflecting material. The width in the direction to perform is larger than the circumference of the object to be inspected.

  In the surface defect inspection apparatus according to the present invention as set forth in the invention described above, the light source is provided linearly in the axial direction of the reflector.

  In the surface defect inspection apparatus according to the present invention as set forth in the invention described above, the imaging apparatus is an area sensor camera arranged at the center in the axial direction and the width direction of the reflecting material.

  The surface defect inspection apparatus according to the present invention is the surface defect inspection apparatus according to the present invention, wherein the surface defect inspection apparatus is disposed on a side opposite to the imaging apparatus with respect to the inspection object within the field of view of the imaging apparatus, and the inspection object rolls. An auxiliary illumination device provided in parallel with the direction is further provided, and the imaging device images the object to be inspected illuminated from the side opposite to the imaging device by the auxiliary illumination device.

  In order to solve the above-described problems and achieve the object, a surface defect inspection method according to the present invention is an imaging step of imaging a cylindrical or columnar object to be inspected by an imaging device, and an image is captured in the imaging step. An image processing step of detecting a surface defect of the object to be inspected based on a change in luminance of an image, wherein the imaging step is performed at a predetermined inclination by a conveying device provided on a production line. The object to be inspected is conveyed while being rolled along and is illuminated by an indirect illumination device.

  In the surface defect inspection method according to the present invention as set forth in the invention described above, the imaging step is disposed on a side opposite to the imaging device with respect to the object to be inspected in a field of view of the imaging device, and The object to be inspected is illuminated from the side opposite to the imaging device by an auxiliary illumination device provided in parallel with the rolling direction of the inspection object, and the image processing step is illuminated by the auxiliary illumination device. The position of the inspection object is detected based on the image of the inspection object.

  According to the present invention, it is possible to inspect a surface defect without being affected by the surface gloss of the inspection object by capturing an image while illuminating the inspection object by the indirect illumination device. In addition, since the inspection object can be inspected over the entire length and the entire circumference by inspecting the surface defect while rolling the inspection object by a conveying device provided on the production line, for example, an inspection object rotation mechanism dedicated to inspection Etc., and there is no need to add an installation space or a transport path of the inspection object separately, so that the inspection object can be inspected with low-cost equipment investment. Therefore, according to the present invention, when inspecting a surface defect of an object to be inspected formed in a cylindrical shape or a columnar shape, a surface defect inspection can be performed with high accuracy with a simple configuration.

FIG. 1 is a diagram schematically showing a configuration of a surface defect inspection apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing the configuration of the indirect illumination device of the surface defect inspection apparatus according to the embodiment of the present invention. FIG. 3 is a diagram illustrating an operation principle of the indirect illumination device of the surface defect inspection device according to the embodiment of the present invention. FIG. 4 is an explanatory diagram for explaining the reflected light and the uniform irradiation width on the surface of an object to be inspected (steel pipe) when a conventional light source (direct illumination) is used. FIG. 5 is an explanatory diagram for explaining the reflected light and the uniform irradiation width on the surface of the object to be inspected (steel pipe) when the indirect illumination device of the surface defect inspection device according to the embodiment of the present invention is used. FIG. 6 is a diagram illustrating an example of a captured image group of an object to be inspected (steel pipe) by the surface defect inspection apparatus according to the embodiment of the present invention. FIG. 7 is a diagram in which the captured image group of the object to be inspected (steel pipe) shown in FIG. 6 is synthesized into a development view for one round of the object to be inspected. FIG. 8 is a flowchart showing a processing procedure of the surface defect inspection apparatus according to the embodiment of the present invention. FIG. 9 is a perspective view schematically showing a configuration of Modification 1 of the surface defect inspection apparatus according to the embodiment of the present invention, which includes a plurality of imaging devices and a plurality of indirect illumination devices. FIG. 10 is a perspective view schematically showing a configuration of Modification Example 2 of the surface defect inspection apparatus according to the embodiment of the present invention, which includes a plurality of imaging devices, a plurality of indirect illumination devices, and a plurality of auxiliary illumination devices. FIG. 11 is an image of a steel pipe imaged by a conventional method. FIG. 12 is a graph showing the luminance distribution along the line A-A ′ of FIG. 11. FIG. 13 is an image of a steel pipe imaged by the surface defect inspection apparatus according to the embodiment of the present invention. FIG. 14 is a graph showing the luminance distribution along the line B-B ′ in FIG. 13.

  Hereinafter, embodiments of a surface defect inspection apparatus and a surface defect inspection method according to the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

[Surface defect inspection equipment]
The surface defect inspection apparatus is for inspecting a surface defect of a cylindrical or columnar inspection object. As shown in FIG. 1, the surface defect inspection apparatus 1 includes a transport device 10, an indirect illumination device 20, an imaging device 30, an image processing device 40, and a display device 50. In addition, as a to-be-inspected object of the surface defect inspection apparatus 1, although a steel pipe, a round bar, etc. are mentioned, below, the example using the steel pipe P as shown in FIG. 1 is demonstrated.

  The conveying apparatus 10 conveys the steel pipe P. The conveying apparatus 10 is provided on the production line of the steel pipe P, and specifically is a conveying slope provided with a predetermined inclination as shown in FIG. The conveying device 10 conveys the steel pipe P while rolling it along the inclination.

  Here, in the production line of cylindrical or columnar products including the steel pipe P, when these are conveyed in a direction perpendicular to the axial direction, a conveying device (as shown in FIG. 1) is provided. It is generally performed to use the conveyance slope 10. Therefore, it is not necessary to newly provide a steel pipe rotating mechanism, an inspection table, or the like dedicated to inspection by inspecting surface defects on such a transport device 10. In addition, the surface of the conveyance apparatus 10 which contacts the steel pipe P at the time of conveyance is different in color tone from the surface of the steel pipe P and suppresses reflection in order to facilitate identification from the steel pipe P during image processing to be described later. It is desirable to apply a material such as matte white or black, or lay a black rubber plate.

  The indirect lighting device 20 indirectly illuminates the steel pipe P conveyed by the conveying device 10 with reflected light. As illustrated in FIG. 1, the indirect illumination device 20 is disposed above the transport device 10 and between the transport device 10 and the imaging device 30. The indirect lighting device 20 includes a reflective material 21 and a light source 22 as shown in FIGS. 2 and 3.

  As shown in FIG. 2, the reflecting material 21 has a semicylindrical cross section. Any material can be used as the material of the reflecting material 21 as long as it is a material that can be formed in a semi-cylindrical shape, such as metal, wood, resin, etc., but a material that has good diffuse reflectance with respect to visible light is used. It is desirable.

  A through hole 21 a in which the imaging device 30 is disposed is formed in the upper part of the reflective material 21. The through-hole 21a is formed in the minimum size to the extent that the field of view of the imaging device 30 can be secured at the center in the axial direction and the width direction of the reflective material 21. Further, as shown in FIG. 3, the reflective material 21 has a concave surface side as a reflection surface 21b of light from the light source 22, and the reflection surface 21b reflects light from the light source 22 toward the steel pipe P side.

  The reflecting material 21 is arranged so that its axial direction is parallel to the axial direction of the steel pipe P. Further, the width of the reflecting material 21, that is, the width in the direction orthogonal to the axial direction of the reflecting material 21 is formed larger than the circumferential length of the steel pipe P.

  As shown in FIG. 2, the light source 22 is a linear light source (bar light source) provided linearly in the axial direction of the reflector 21. As shown in FIG. 3, a total of two light sources 22 are disposed on the reflective surface 21b side of the reflective material 21, and a pair of left and right light sources 22 irradiate light toward the reflective surface 21b. As a result, the reflected light and the multiple reflected light are diffused, and the steel pipe P is irradiated with light from various directions as indicated by solid line arrows in FIG.

  As the light source 22, a fluorescent light, a light guide, or a linear light source in which LED elements that have been improved in recent years are arranged can be used. The arrangement of the light sources 22 is not limited to that shown in FIG. 1, and the number of the light sources 22 may be two or more. However, the optical axes (refer to the solid line arrows in FIG. It is desirable to set the arrangement and number of light sources 22 so that

  As shown in FIG. 1, the indirect lighting device 20 is configured to reflect the light from the light source 22 by the reflecting surface 21 b of the reflecting material 21 and be transported by the transport device 10 as shown in FIG. 1. Indirect lighting.

  The imaging device 30 images the steel pipe P that is transported by the transport device 10 and that is illuminated by the indirect illumination device 20. As shown in FIG. 2, the imaging device 30 is disposed at a position of a through hole 21 a formed at the center in the axial direction and the width direction of the reflective material 21, and is transported by the transport device 10 below the reflective material 21. The steel pipe P to be imaged is imaged at a predetermined imaging cycle. Then, the imaging device 30 outputs a plurality of captured images to the image processing device 40.

  As the imaging device 30, an area sensor camera such as a CCD or a CMOS can be used. Here, the number of pixels and the angle of view of the imaging device 30 include the size of the surface defect that needs to be detected and the inspection field of view, or a plurality of imaging devices 30 arranged to cover the field of view (see FIG. 9 described later), etc. To be determined.

  In general, the number of pixels of the imaging device 30 (specifically, area sensor camera) is larger in the horizontal pixel (Nx) than in the vertical pixel (Ny), and is about “Nx: Ny = 4: 3”. For this reason, it is desirable that the horizontal direction of the visual field coincide with the axial direction of the steel pipe P, and the vertical direction of the visual field coincide with the conveying direction (rolling direction) of the steel pipe P. The vertical direction of the visual field needs to cover a range slightly longer than the outer diameter of the steel pipe P, while the visual field per pixel is about half to ５ of the size of the surface defect that needs to be detected. It is desirable to make it finer.

  For example, when a steel pipe P having an outer diameter of 100 mm is inspected and a surface defect (for example, wrinkles) of φ2 mm is to be detected, the field of view in the transport direction of the steel pipe P needs to be “π × 100 = 314 mm”, and the resolution per pixel Is “2 × (1/5) = 0.4 mm”. Accordingly, it is sufficient that the vertical field of view of the imaging device 30 is about 320 mm and the number of pixels in the vertical direction is about “320 ÷ 0.4 = 800 pixels”.

  On the other hand, when the visual field in the vertical direction of the imaging device 30 is set to 320 mm, the horizontal visual field (the visual field in the axial direction of the steel pipe P) of the imaging device 30 is “from the relationship of“ Nx: Ny = 4: 3 ”. 320 ÷ 3 × 4 = 430 mm ”. Therefore, for example, when the steel pipe P is a long body extending over several meters, a large number of imaging devices 30 are required. In such a case, the setting of the number of pixels and the field of view described above may be corrected so that the number of the imaging devices 30 can be kept within a few while maintaining the resolution.

  For example, when inspecting a steel pipe P having an axial length of 5000 mm (5 m) with four imaging devices 30, the horizontal field of view of the imaging device 30 is “5000/4 = 1250 mm” and the resolution per pixel is Assume that the number of pixels in the horizontal direction of the imaging device 30 is 3200 pixels. In this case, the number of pixels in the vertical direction of the imaging device 30 is “3200 × (3/4) = 2400 pixels”. Such an imaging apparatus 30 of 3200 pixels × 2400 pixels can be realized by using a commercially available area sensor camera.

  Here, in FIG. 1, among the three dash-dot lines extending from the imaging device 30, the middle one-dot chain line is the central axis of the lens of the imaging device 30, and the two dash-dot lines on both sides are the field of view of the imaging device 30 ( Vertical field of view). As shown in the figure, the imaging device 30 continuously performs imaging while the steel pipe P that rolls within the field of view moves by the circumference. Then, a surface defect is detected from the plurality of images by an image processing device 40 described later. In addition, what is necessary is just to determine the imaging cycle which the imaging device 30 images the steel pipe P within a visual field, for example considering the conveyance speed (rolling speed) of the steel pipe P, the uniform irradiation width | variety of a conveyance direction, etc.

  The above-described “uniform irradiation width” indicates a width at which the illuminance of the image of the surface of the steel pipe P illuminated by the indirect illumination device 20 is considered to be uniform. In the above-described Patent Document 4, the uniform irradiation width is determined and used from the curvature of the steel pipe, the arrangement interval of the illumination, and the like. However, in the surface defect inspection apparatus 1 according to the present embodiment, this uniform is obtained by using the indirect illumination. The irradiation width is considerably widened.

  For example, FIG. 4 is a diagram illustrating an example of a uniform irradiation width of the steel pipe P when direct illumination is used as in Patent Document 4, and FIG. 5 is a diagram of the steel pipe P when indirect illumination is used as in this embodiment. It is a figure which shows an example of uniform irradiation width. 4 and 5, W represents the uniform irradiation width, and D represents the diameter of the steel pipe P.

  When direct illumination was used as in Patent Document 4, if the diameter D of the steel pipe P was 100 mm (peripheral length was 320 mm), the uniform irradiation width W was about 15 mm. Therefore, the imaging device 30 needs to take an image every time the steel pipe P rolls 15 mm within the field of view, and the number of times of imaging is “320 ÷ 15 = 21.3 → 22 times”.

  On the other hand, when using indirect illumination as in this embodiment, assuming that the diameter D of the steel pipe P is 100 mm (peripheral length is 320 mm), the uniform irradiation width W is about 35 mm. Therefore, the imaging device 30 only needs to take an image every time the steel pipe P rolls 35 mm within the field of view, and the number of times of imaging is “320 ÷ 35 = 9.14 → 10 times”. As described above, by using indirect illumination as in the present embodiment, the number of times of imaging by the imaging device 30 is significantly reduced as compared with the case of using direct illumination.

  Here, when detecting the movement of the steel pipe P for each uniform irradiation width W from an imaged image, it is possible to detect, for example, by calculating the center of gravity of a bright portion of a horizontal line in the image. On the other hand, in order to avoid the complexity of data processing, as shown in FIG. 1, when a proximity sensor 61 and a trigger circuit 62 are separately provided and the steel pipe P entering the field of view of the imaging device 30 is detected by the proximity sensor 61. Alternatively, the trigger signal from the trigger circuit 62 may be output to the imaging device 30 to image the steel pipe P.

  Alternatively, the above-described trigger circuit 62 and a laser distance meter for measuring the transport distance of the steel pipe P may be provided separately, and a trigger signal from the trigger circuit 62 may be output to the imaging device 30 for every fixed transport distance to capture an image. Good. Further, when the rolling of the steel pipe P can be regarded as a constant speed because the inclination of the conveying device (conveying slope) 10 is gentle, the proximity sensor 61 detects only the timing at which the steel pipe P enters the field of view of the imaging device 30. Thereafter, images may be taken a predetermined number of times at preset time intervals.

  By continuously capturing images while the steel pipe P is rolling in the field of view of the imaging device 30 as described above, a plurality of images of the surface of the steel pipe P are acquired as shown in FIG. The figure is an image group in which a steel pipe P being transported by the transport device 10 and illuminated by the indirect illumination device 20 is captured by the image capturing device 30, and (1) to (25) indicate the order of image capturing. Show. Further, a circular mark is marked on the steel pipe P shown in FIG.

  Here, in the example of FIG. 6, since the imaging cycle is shorter than the movement due to the rotation of the steel pipe P, the same position of the steel pipe P is captured in a plurality of images. Under such imaging conditions, if the steel pipe P has a defect, the same defect is imaged a plurality of times. Therefore, in order to avoid duplication detection, it is necessary to perform duplication check that performs matching between images and cuts duplication portions. However, if the imaging cycle is too long, defects may be missed, so it is desirable to set the imaging cycle as short as possible.

  The image processing device 40 performs image processing on the image of the steel pipe P picked up by the image pickup device 30, and detects a surface defect of the steel pipe P based on a luminance change of the image. The image processing device 40 performs well-known defect detection processing such as shading correction and binarization processing on each image input from the imaging device 30 to detect a luminance change portion in the image as a surface defect.

  The image processing apparatus 40 also calculates the type and occurrence position of the detected surface defect. For example, the image processing device 40 calculates the type of surface defect based on the defect feature amount. Further, the image processing device 40 calculates the axial generation position of the surface defect based on the horizontal position of the surface defect in the image. Further, the image processing device 40 detects the surface defect based on the information on which image the surface defect was detected in the n images captured continuously and the vertical position of the surface defect in the image. The axial direction generation position is calculated. Then, the image processing device 40 outputs the calculated surface defect type and occurrence position to the display device 50.

  The display device 50 displays the type and occurrence position of surface defects in the steel pipe P by, for example, numerical values or charts. As shown in FIG. 7, the display device 50 displays, for example, an image obtained by combining images of the entire circumference of the steel pipe P as a development view from an image group (see FIG. 6) that has undergone duplication check in the image processing device 40.

  According to the surface defect inspection apparatus 1 having the above-described configuration, the surface defect is inspected without being affected by the surface gloss of the steel pipe P by capturing an image while illuminating the steel pipe P with the indirect illumination device 20. It becomes possible. In other words, by using indirect illumination, it is possible to prevent reflection of a light source that is a problem in direct illumination and to enlarge a region with uniform illuminance (uniform irradiation width W), so that high-precision inspection can be performed. It becomes feasible.

  In addition, since the steel pipe P can be inspected over the entire length and the entire circumference by inspecting the surface defect while rolling the steel pipe P by the conveying device 10 provided on the production line, for example, a steel pipe rotation mechanism dedicated for inspection is provided. It is not necessary to add an additional installation space or a transport route for the steel pipe P, and the steel pipe P can be inspected with an inexpensive equipment investment. Therefore, according to the surface defect inspection apparatus 1, when inspecting the surface defect of the steel pipe P formed in the cylindrical shape or the columnar shape, the surface defect inspection can be performed with high accuracy with a simple configuration.

[Surface defect inspection method]
A surface defect inspection method using the surface defect inspection apparatus 1 described above will be described with reference to FIG. The surface defect inspection method includes a detection step, an imaging step, an image processing step, and a display step.

  First, in the detection step, the proximity sensor 61 detects the presence or absence of the steel pipe P that has entered the field of view of the imaging device 30 (step S1). And when the steel pipe P is not detected (No in step S1), the proximity sensor 61 repeats the process of step S1. On the other hand, when the steel pipe P is detected (Yes in step S1), the trigger circuit 62 outputs a trigger signal to the imaging device 30 (step S2).

  Subsequently, in the imaging step, the imaging device 30 images the steel pipe P that is being conveyed by the conveying device 10 and illuminated by the indirect illumination device 20 based on the trigger signal at a predetermined imaging period (step S3). ). Subsequently, in the image processing step, the image processing device 40 detects a surface defect of the steel pipe P based on the luminance change of the image captured by the imaging device 30 (step S4). Finally, in the display step, the display device 50 displays the detection result (type of surface defect and occurrence position) of the surface defect in the steel pipe P (step S5).

[Modification 1 of surface defect inspection apparatus]
Here, as described above, when the length of the steel pipe P is larger than the horizontal field of view of the imaging device 30 (the field of view of the steel pipe P in the axial direction), for example, as in the surface defect inspection apparatus 1A shown in FIG. A plurality of imaging devices 30 may be arranged along the axial direction of the steel pipe P, and a plurality of sets of indirect illumination devices 20 may be arranged correspondingly. Further, when a plurality of sets of indirect illumination devices 20 are arranged as shown in the figure, the adjacent imaging devices 30 are horizontally arranged so that no inspection leakage or light quantity imbalance occurs at the boundary portion between the adjacent reflecting materials 21. It is desirable to design the directional field of view to overlap.

  Moreover, about the reflective material 21 of the indirect illumination device 20, instead of arranging a plurality as shown in FIG. 9, for example, a light source 22 designed according to the length of the steel pipe P and mounted inside the reflective material 21, A plurality of pipes may be added along the axial direction of the steel pipe P.

[Modification 2 of the surface defect inspection apparatus]
As shown in FIG. 10, the surface defect inspection apparatus 1B according to Modification 2 has a plurality of auxiliary illumination devices 70 added to the configuration of the surface defect inspection apparatus 1A described above.

  The auxiliary illumination device 70 is disposed in the field of view of the imaging device 30, and one auxiliary illumination device 70 is disposed in the field of view for each imaging device 30. The auxiliary illumination device 70 is disposed on the opposite side of the steel pipe P from the imaging device 30, that is, on the lower side of the steel pipe P, and irradiates the steel pipe P from the lower side. The auxiliary lighting device 70 is linearly provided in a direction parallel to the rolling direction of the steel pipe P. As the auxiliary lighting device 70, as with the light source 22, a fluorescent light, a light guide, or a linear light source in which LED elements are arranged can be used.

  In the surface defect inspection apparatus 1B, the imaging device 30 images the steel pipe P illuminated from the side opposite to the imaging device 30 by the auxiliary illumination device 70. Then, the image processing device 40 detects the position of the steel pipe P (in the case of the second modification, the edge position) based on the image of the steel pipe P illuminated by the auxiliary lighting device 70.

  Here, FIG. 11 is an image of the steel pipe P imaged by the surface defect inspection apparatus that does not include the auxiliary illumination device 70, and FIG. 12 is a graph showing the luminance distribution along the line AA ′ in FIG. . As shown in FIGS. 11 and 12, the portion where the steel pipe P is present in the image has higher luminance than the background portion around the steel pipe P. On the other hand, as can be seen from both figures, the luminance in the portions C and D corresponding to the edge positions E1 and E2 of the steel pipe P to be originally detected is substantially the same as the luminance of the pixel corresponding to the surrounding background portion. Depending on the environment in which the surface defect inspection apparatus according to the present invention is placed, in particular, brightness, only an image as shown in FIG. 11 may be obtained. In this case, detection by setting a threshold or the like is difficult, and instability such as the influence of the luminance of an object reflected in the background tends to occur.

  On the other hand, FIG. 13 is an image of the steel pipe P imaged by the surface defect inspection apparatus 1B shown in FIG. 10, and FIG. 14 is a graph showing the luminance distribution along the line B-B ′ of FIG. As shown in FIGS. 13 and 14, the brightness of the portion where the steel pipe P is present in the image is lower than that of the background portion around the steel pipe P. That is, in the surface defect inspection apparatus 1B, a part of the light from the auxiliary illumination device 70 is blocked by the steel pipe P in the field of view of the imaging device 30 by irradiating light from the auxiliary illumination device 70 toward the steel pipe P. . Thereby, the difference between the luminance at the portions E and F corresponding to the edge positions E3 and E4 of the steel pipe P and the luminance of the pixels corresponding to the surrounding background portion can be further increased.

  Therefore, according to the surface defect inspection apparatus 1B, the image picked up by the image pickup apparatus 30 is subjected to image processing by the image processing apparatus 40, whereby the position of the steel pipe P within the field of view of the image pickup apparatus 30 is determined. Detection can be performed more easily regardless of the environment in which the apparatus is placed. Furthermore, it becomes easier to synthesize images for the entire circumference of the steel pipe P.

  Moreover, according to the surface defect inspection apparatus 1B, since it is possible to detect the exact position of the steel pipe P when the steel pipe P blocks the light from the auxiliary illumination device 70, as shown in FIG. Further, the proximity sensor 61 and the trigger circuit 62 that detect the position of the steel pipe P are also unnecessary. Therefore, according to the surface defect inspection apparatus 1B, when inspecting the surface defect of the steel pipe P formed in a cylindrical shape or a columnar shape, it becomes possible to perform the surface defect inspection with high accuracy with a simpler configuration.

  Hereinafter, the present invention will be described more specifically with reference to examples. In the present embodiment, as shown in FIG. 9 described above, a surface defect inspection apparatus (Modification 1) corresponding to a long steel pipe was used. Specifically, in a steel pipe production line with a diameter of 100 mm and a length of 5 m, an imaging device and an indirect illumination device are installed on the existing conveyance slope (conveyance device) to inspect the surface defects (specifically, flaws) of the steel pipe. did.

  As the imaging device, a CMOS area sensor camera of 3200 pixels × 2400 pixels was used, the resolution was 0.4 mm, the visual field size was 1280 mm in the horizontal direction, and 400 mm in the vertical direction. The light source of the indirect illumination device was arranged at intervals of 200 mm so as to sandwich the imaging device from both sides as shown in FIG. 9 and parallel to the axial direction of the steel pipe. Furthermore, in order to inspect over the entire length of the steel pipe, four imaging devices and light sources were installed side by side in the axial direction of the steel pipe.

  As a proximity sensor, an LED transmitted light type cold metal detector is used, and image input / output and image processing function in a digital input / output (DIO) input function installed in a personal computer, an image capture board, and a personal computer. Made by software etc.

  With the above apparatus configuration, 28 times of imaging were performed while the steel pipe was rotated once. The duplication of the obtained images was checked, and 10 images were selected. These selected images were joined together to inspect surface defects around the steel pipe. As a result, it was confirmed that harmful surface defects that could only be detected by visual inspection over a long period of time can be detected 100% by the above apparatus configuration without using extra time and work for inspection. It was.

  Further, by using the surface defect inspection apparatus (Modification 2) shown in FIG. 10 described above, imaging is performed 28 times during one rotation of the steel pipe, and duplication of the obtained images is checked to obtain 10 sheets. Images were selected, and these selected images were joined together to inspect surface defects around the steel pipe. Also in this case, it was confirmed that 100% of surface defects could be detected.

  The surface defect inspection apparatus and the surface defect inspection method according to the present invention have been specifically described above with reference to embodiments and examples for carrying out the invention. However, the gist of the present invention is not limited to these descriptions. Should be construed broadly based on the claims. Needless to say, various changes and modifications based on these descriptions are also included in the spirit of the present invention.

1,1A, 1B Surface defect inspection device 10 Conveyance device (conveyance slope)
DESCRIPTION OF SYMBOLS 20 Indirect illumination apparatus 21 Reflector 21a Through-hole 21b Reflecting surface 22 Light source 30 Imaging device (area sensor camera)
40 Image processing device 50 Display device 61 Proximity sensor 62 Trigger circuit 70 Auxiliary lighting device P Steel pipe (inspected object)

Claims (8)

An imaging device for imaging a cylindrical or columnar inspection object;
An image processing apparatus for detecting a surface defect of the object to be inspected based on a change in luminance of an image captured by the imaging apparatus;
In a surface defect inspection apparatus comprising:
A conveying device that is provided on a production line and conveys the object to be inspected while rolling along a predetermined inclination;
An indirect illumination device that is disposed between the transfer device and the imaging device and illuminates the object to be inspected;
With
The surface defect inspection apparatus characterized in that the imaging apparatus images the object to be inspected that is transported by the transport apparatus and is illuminated by the indirect illumination device. The indirect lighting device is:
A semi-cylindrical reflector whose concave surface is a light reflecting surface;
A light source disposed on the reflective surface side of the reflective material;
With
The surface defect inspection apparatus according to claim 1, wherein the object to be inspected being transported by the transport apparatus is illuminated by reflecting light from the light source on a reflection surface of the reflective material. The reflective material is arranged so that its axial direction is parallel to the axial direction of the object to be inspected,
The surface defect inspection apparatus according to claim 2, wherein a width of the reflecting material in a direction orthogonal to the axial direction is larger than a circumferential length of the object to be inspected.   The surface defect inspection apparatus according to claim 2, wherein the light source is linearly provided in an axial direction of the reflecting material.   5. The surface defect inspection apparatus according to claim 2, wherein the imaging device is an area sensor camera disposed at a center in an axial direction and a width direction of the reflecting material. In the field of view of the imaging device, further comprising an auxiliary illumination device disposed on the opposite side of the imaging device with respect to the object to be inspected and provided in parallel with the rolling direction of the object to be inspected,
The said imaging device images the said to-be-inspected object illuminated from the opposite side to the said imaging device with the said auxiliary illumination device, The Claim 1 characterized by the above-mentioned. Surface defect inspection device. An imaging step of imaging a cylindrical or columnar object to be inspected by an imaging device;
An image processing step of detecting a surface defect of the object to be inspected based on a change in luminance of the image captured in the imaging step;
In the surface defect inspection method including
In the imaging step, the object to be inspected is conveyed while being rolled along a predetermined inclination by a conveyance device provided on a production line and illuminated by an indirect illumination device. Surface defect inspection method. In the field of view of the imaging device, the imaging step is performed by an auxiliary illumination device disposed on the opposite side of the imaging device from the imaging device and parallel to the rolling direction of the testing device. , To image the inspected object illuminated from the opposite side of the imaging device,
The surface defect inspection method according to claim 7, wherein the image processing step detects a position of the inspection object based on an image of the inspection object illuminated by the auxiliary illumination device.