CN112986258B - Surface defect detection device and method for judging surface where surface defect is located - Google Patents
Surface defect detection device and method for judging surface where surface defect is located Download PDFInfo
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Abstract
The invention discloses a surface defect detection device and a method for judging the surface where the surface defect is located, wherein the device is used for detecting the surface defect on a transparent object to be detected which moves along a first direction relative to the surface defect detection device, and comprises two light sources and two cameras; the two light sources are symmetrical about the normal plane of the surface of the object to be measured and obliquely shoot the surface of the object to be measured to form a coincident irradiation area on the surface of the object to be measured; the two cameras are line scanning cameras and are all positioned in dark fields of the two light sources, the optical axes of the two cameras respectively have a perpendicular intersection and inclined intersection relationship with the surface of the object to be measured, and the two cameras intersect at the same intersection point in the irradiation area and jointly define a plane perpendicular to the normal plane; the method is based on the device and judges the surface where the surface defect is located according to the corresponding relation of defect images which are displayed in the composite images of the two cameras by the same surface defect, and is particularly suitable for the surface defect with a certain scale along the first direction.
Description
Technical Field
The invention relates to the field of surface defect detection, in particular to a surface defect detection device and a method for judging the surface where a surface defect is located.
Background
In the prior art, when a machine vision technology is used to detect surface defects of an object to be detected, the detection device generally cannot determine the surface of the object to be detected where the surface defects are located, and only all the detected defects can be regarded as being located on the surface (hereinafter referred to as the upper surface) of the object to be detected, which is close to the detection device. However, when the object to be measured has a transparent property (e.g., the object to be measured is glass), even if a defect is located on a surface (hereinafter referred to as a lower surface) of the object to be measured far away from the detecting device, the defect is detected by the detecting device because the transparent property of the object to be measured can be photographed by the imaging device, and at this time, if the defect actually located on the lower surface is also regarded as being located on the upper surface, the detection passing rate of the object to be measured may be greatly affected. For example, when the object to be measured is a mobile phone glass cover plate, the surface defect of the bonding surface does not affect the use experience of the user, so that the product still should be regarded as qualified only when the bonding surface has the surface defect.
In order to solve the above-mentioned problems, chinese patent application publication CN107764834a proposes a device and a method for automatically detecting surface defects of transparent parts, wherein a top view camera and a side view camera are disposed above a part to be detected, and the device is configured to take a photograph of the part to be detected traveling along a first direction in a dark field environment of a light source; based on the device, two specific methods for distinguishing the surface where the surface defect is located are proposed: when the surface defects are respectively positioned on the upper surface and the lower surface of the part to be tested, the imaging result of the side view camera can generate defect images with the same pattern but different numbers, and the surfaces where the surface defects are positioned are distinguished according to the different numbers of the defect images; the other method is that after the imaging result of the side view camera is inverted according to the cosine projection rule, the inverted imaging result is compared with the distance from the defect image to the reference point in the imaging result of the top view camera to distinguish the surface where the surface defect is located.
However, in practical detection, although the above-mentioned technical solution has a better differentiating effect on the spot defect, it cannot effectively differentiate the surface where the surface defect having a certain scale along the first direction (such as a crack and a scratch extending along the first direction) is located.
Disclosure of Invention
The invention aims to overcome at least one defect or problem in the background art, and provides a surface defect detection device and a method for judging the surface where the surface defect is located, which are suitable for detecting and judging the surface defect of a transparent object to be detected moving along a specific direction and the surface where the surface defect is located, and are particularly suitable for the surface defect with a certain scale along the specific direction.
To achieve the above object, a first aspect of the present invention provides a first aspect of the present invention, which relates to a surface defect detecting device for detecting surface defects on a first surface and a second surface parallel to each other of a transparent object to be detected, the second surface being farther from the surface defect detecting device than the first surface, the object to be detected moving relative to the surface defect detecting device in a first direction parallel to the first surface; comprising the following steps: a first light source obliquely irradiating the first surface and forming an irradiation region on the first surface; a second light source symmetrically arranged with the first light source about a normal plane perpendicular to the first direction, obliquely projecting the first surface and forming an overlapping irradiation area on the first surface with the first light source; a first camera which is a line scanning camera with a line scanning direction perpendicular to the first direction and is configured such that a field of view is located in a dark field of the first light source and the second light source and continuously photographs an object to be measured; the optical axis of the lens is perpendicular to the first surface and intersects with the first surface at a first intersection point positioned in the irradiation area; the second camera is a line scanning camera with the line scanning direction perpendicular to the first direction and is configured to have a field of view positioned in dark fields of the first light source and the second light source and continuously shoot an object to be detected; the optical axis of the lens is inclined to the first surface and is intersected with the first surface and the optical axis of the first camera at the first intersection point; a plane defined by the optical axis of the second camera and the optical axis of the first camera is perpendicular to the normal plane; the first light source and the second light source emit collimated light or converged light, and when the first light source and the second light source emit converged light, a converged focus of the converged light forms the irradiation area.
Based on the first technical scheme, the invention also has the second technical scheme: the first intersection point is located in the normal plane.
Based on the first technical scheme, the invention also has the third technical scheme: the first light source and the second light source are parallel light sources or converging light sources.
Based on the first technical scheme, the second technical scheme or the third technical scheme, the invention also has the fourth technical scheme, and the surface defect detection device further comprises: an image analysis device that synthesizes images continuously captured by the first camera and the second camera into a first synthesized image and a second synthesized image, respectively; the method further comprises the steps of identifying closed areas with each gray value exceeding a first threshold value in the first composite image and marking each identified closed area as a corresponding first defect image; inverting the second composite image into a third composite image according to a perspective imaging principle, identifying a closed area of each gray value exceeding a first threshold value in the third composite image, and marking each identified closed area as a corresponding second defect image; the method also uses each first defect image in the first composite image as a reference, and searches all second defect images corresponding to the first defect images in the third composite image; if two second defect images corresponding to the first defect images are found according to the first corresponding relation, judging that the surface defects corresponding to the first defect images are positioned on the first surface; if only one second defect image corresponding to the first defect image is found according to the first corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the second surface; if a second defect image corresponding to the first defect image is found according to the second corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the first surface; the first corresponding relation is that the overall shapes of the two defect images are similar, and the absolute value of the area difference of the two defect images is smaller than a second threshold; the second corresponding relation is that the shapes of the head and the tail of the two defect images along the first direction are similar, the shapes of the middle parts of the two defect images are dissimilar, and the absolute value of the area difference of the two defect images is larger than a second threshold value.
In order to achieve the above object, a fifth aspect of the present invention provides a method for determining a surface on which a surface defect is located, and is based on the surface defect detecting device according to the first or second or third aspect; the method comprises the following steps: synthesizing images continuously shot by the first camera and the second camera into a first synthesized image and a second synthesized image respectively; identifying closed areas with each gray value exceeding a first threshold value in the first composite image and marking each identified closed area as a corresponding first defect image; inverting the second composite image into a third composite image according to a perspective imaging principle, identifying a closed area of each gray value exceeding a first threshold value in the third composite image, and marking each identified closed area as a corresponding second defect image; searching all second defect images corresponding to the first defect images in the third composite image by taking each first defect image in the first composite image as a reference; if two second defect images corresponding to the first defect images are found according to the first corresponding relation, judging that the surface defects corresponding to the first defect images are positioned on the first surface; if only one second defect image corresponding to the first defect image is found according to the first corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the second surface; if a second defect image corresponding to the first defect image is found according to the second corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the first surface; the first corresponding relation is that the overall shapes of the two defect images are similar, and the absolute value of the area difference of the two defect images is smaller than a second threshold; the second corresponding relation is that the shapes of the head and the tail of the two defect images along the first direction are similar, the shapes of the middle parts of the two defect images are dissimilar, and the absolute value of the area difference of the two defect images is larger than a second threshold value.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) The applicant has found that in the prior art solutions cited above, when the upper surface of the object to be measured has a surface defect of a certain dimension along the first direction of travel, for the first judging method, the real image and the virtual image of the surface defect partially coincide in the imaging result of the side view camera, so that for this surface defect, judging errors occur because it is impossible to find two defect images appearing in pairs and in the same form in the imaging result of the side view camera, that is, it is impossible to judge the surface on which the surface defect of the above type is located by the imaging result of the side view camera only. In the second judging method, since the defect images of the surface defects in the two-phase imaging result are not dots, a marked comparison point cannot be defined in the two defect images and the corresponding judgment can be performed by comparing the distances between the comparison points of the two defect images and the reference point.
Based on the above findings, the applicant considered comparing and making further decisions on the imaging results of the top and side cameras by corresponding ways of shape similarity, but this way was highly dependent on the shape similarity of the real images of the same surface defect in the imaging results of the two cameras.
Further, the applicant has found that: since most surface imperfections are not actually planar in configuration, they may appear as bumps, pits, or other more complex solid configurations. When only one oblique light source is adopted for dark field illumination, the imaging result of the top view camera can reflect the complete outline of the surface defect more than the imaging result of the side view camera, and as the surface defect has a more complex three-dimensional structure, the imaging gap of the two phases for the real image of the same surface defect is correspondingly increased, and no specific rule exists for carrying out inversion correction on the imaging deviation of the imaging result of the side view camera. In this way, since the imaging gap between the two cameras for the real image of the same surface defect is too large, it is not practical to use the imaging result of the two cameras to determine the surface on which the surface defect of the type is located on the basis of the prior art scheme cited above.
In the surface defect detection device of the first aspect of the present invention, since two light sources are adopted and are configured to be symmetrically disposed about a normal plane perpendicular to the first direction and form the same irradiation area on the object to be detected, when the object to be detected travels along the first direction, the two light sources irradiate the object to be detected in directions facing and facing away from the first direction, respectively, so that the surface defect travels along the first direction to the irradiation area and is irradiated in two opposite directions respectively by the two light sources, the possibility that diffuse reflection light generated by the surface defect can enter the field of view of the second camera is greatly increased, so that the imaging result of the second camera can reflect a more complete outline of the surface defect, the difference of the imaging of the two cameras on the real image of the same surface defect is greatly reduced, and the shape similarity of the defect image of the same surface defect in the imaging result of the two cameras is improved, thereby being beneficial to shape correspondence of the defect image of the same surface defect in the imaging result of the two cameras on the basis, and especially the surface defect along the first direction has a certain surface dimension.
In addition, two light sources are adopted to jointly illuminate an object to be detected, and illumination brightness is improved, so that contrast of a defect image and a non-defect image in imaging results of each camera in a dark field environment is improved, gray values of cracks and scratches are improved, and identification of a defect image corresponding to a surface defect in the imaging results is facilitated.
Furthermore, the optical axes of the two cameras intersect at the same intersection point in the irradiation area and the plane defined by the intersection points is perpendicular to the normal plane, so that the optical axes of the two cameras are ensured to be positioned at the same plane parallel to the first direction, and therefore, the imaging result of the second camera is only inverted according to the perspective imaging principle, the imaging result of the second camera is prevented from being compared with the imaging result of the first camera after being subjected to unnecessary inversion, and the judgment efficiency is improved. And the two cameras continuously shoot by adopting a line scanning camera with the line scanning direction perpendicular to the advancing direction of the object to be detected, compared with the surface scanning camera, the field depth is larger, and the gray level change can be captured more accurately, so that the detection precision is higher.
(2) According to the surface defect detection device in the second technical scheme, the intersection point of the optical axes of the two cameras is limited to be located on the normal plane, namely, the intersection point is located in the middle of the irradiation area along the first direction, the light is stronger and more stable, the light which is diffusely reflected to the two cameras through the surface defects is more, and the shape similarity of defect images of the same surface defect in the imaging results of the two cameras is further improved.
(3) The fifth technical solution is to provide a method for determining a surface where a surface defect is located and a device for detecting a surface defect according to the fourth technical solution, which are based on the device for detecting a surface defect according to the foregoing technical solution, and provide a method for determining a surface where a surface defect is located and a corresponding device respectively.
The method includes the steps that after an imaging result of a first camera is synthesized into a first synthesized image, and an imaging result of a second camera is synthesized and inverted correspondingly to form a third synthesized image, all closed areas with gray values exceeding a first threshold value are identified and correspondingly marked as a first defect image and a second defect image. And finally, judging the surface of the surface defect corresponding to each first defect image according to the searching result.
In particular, depending on the type of surface defect and the surface on which it is located, its development in two composite images has three cases:
(1) if the surface defect is positioned on the first surface and does not have a certain scale along the first direction, the first defect image corresponding to the surface defect in the first composite image is one, the second defect image corresponding to the surface defect in the third composite image is two, and the three defect images are similar in overall shape and smaller in area difference; (2) if the surface defect is positioned on the first surface and has a certain scale along the first direction, the first defect image corresponding to the surface defect in the first composite image is one, the second defect image corresponding to the surface defect in the third composite image is one, the head and tail shapes of the second defect image and the first defect image along the first direction are similar, the middle shapes of the second defect image and the first defect image are dissimilar, and the area difference of the second defect image and the first defect image is larger; (3) if the surface defect is located on the second surface, the defect image corresponding to the surface defect in the first composite image and the third composite image is one no matter whether the surface defect has a certain scale along the first direction, and the two defect images are similar in overall shape and small in area difference.
Thus, according to the three specific cases, the first correspondence relationship of the two correspondence relationships is that the overall shapes of the two defect images are similar and the absolute value of the area difference of the two defect images is smaller than the second threshold, and the second correspondence relationship is that the shapes of the head and the tail of the two defect images along the first direction are similar, the shapes of the middle parts of the two defect images are dissimilar and the absolute value of the area difference of the two defect images is larger than the second threshold. Based on the difference of the corresponding second defect images searched for by different corresponding relations, the surface where the corresponding surface defects are located can be reversely pushed according to different searching results.
After the surface defects corresponding to all the first defect images in the first composite image are judged, whether the object to be detected is qualified or not can be judged according to the distribution condition of the surface defects on the first surface and the second surface, and if all the surface defects only exist on a specific surface with higher defect tolerance (such as the joint surface of a mobile phone glass cover plate), the object to be detected is judged to be qualified, and unnecessary reduction of detection passing rate caused by excessive detection is avoided.
In addition, it can be seen that, because the method is based on the detection device, the shape similarity of the defect images corresponding to the same surface defect in the two composite images is higher, so that the accuracy can be higher when the corresponding reference with similar shape is applied to the defect images corresponding to the same surface defect in the two composite images, and the surface where the surface defect is located is further judged, and the method is particularly suitable for the surface defect with a certain scale along the first direction.
(4) In summary, the technical contribution of the present invention to the prior art is as follows: the invention firstly provides a corresponding relation based on shape similarity to correspond the defect image of the same surface defect in the imaging result of the two phases, and judges the surface where the surface defect is located according to the corresponding result. On the basis, the invention further provides a symmetrical double-light source illumination scheme to reduce the imaging gap of two phases relative to the real image of the same surface defect and improve the shape similarity of the defect image of the same surface defect in the imaging result of the two phases, thereby ensuring the accuracy of the judging process on the basis.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the description of the embodiments below are briefly introduced, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a surface defect detecting device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram showing a state of a surface defect detecting device according to an embodiment of the present invention when the surface defect detecting device detects a surface defect, wherein the surface defect is located on a first surface of an object to be detected and the object to be detected moves to a first position;
FIG. 3 is a schematic diagram showing a state of a surface defect detecting device according to an embodiment of the present invention when the surface defect detecting device detects a surface defect, wherein the surface defect is located on a first surface of an object to be detected and the object to be detected moves to a second position;
FIG. 4 is a schematic diagram showing a state of a surface defect detecting device according to an embodiment of the present invention when the surface defect is detected, wherein the surface defect is located on a second surface of an object to be detected and the object to be detected moves to a third position;
FIG. 5 is a schematic diagram showing a state of a surface defect detecting device according to an embodiment of the present invention when the surface defect is detected, wherein the surface defect is located on a second surface of an object to be detected and the object to be detected moves to a fourth position;
FIGS. 6a and 6b are schematic diagrams of a first composite image and a third composite image, respectively, when a surface defect is located on a first surface and does not have a certain dimension along a first direction;
FIGS. 7a and 7b are schematic diagrams of a first composite image and a third composite image, respectively, when a surface defect is located on a first surface and has a certain dimension along a first direction;
FIGS. 8a and 8b are schematic diagrams of a first composite image and a third composite image, respectively, when a surface defect is located on a second surface and does not have a scale in a first direction;
fig. 9a and 9b are schematic diagrams of a first composite image and a third composite image, respectively, when a surface defect is located on a second surface and has a certain dimension along a first direction.
The main reference numerals illustrate: the conveying mechanism 1, the object 2 to be measured, the first surface 21, the second surface 22, the first light source 31, the second light source 32, the irradiation region 33, the first camera 41, the first optical axis 411, the second camera 42, and the second optical axis 421.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It is to be understood that the described embodiments are preferred embodiments of the invention and should not be taken as excluding other embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without creative efforts, are within the protection scope of the present invention.
In the claims, specification and drawings hereof, unless explicitly defined otherwise, the terms "first," "second," or "third," etc. are used for distinguishing between different objects and not for describing a particular sequential order.
In the claims, specification and drawings of the present invention, unless explicitly defined otherwise, references to orientation words such as "center", "lateral", "longitudinal", "horizontal", "vertical", "top", "bottom", "inner", "outer", "upper", "lower", "front", "rear", "left", "right", "clockwise", "counterclockwise", "high", "low", etc. are based on the orientation and positional relationship shown in the drawings and are merely for convenience of description and to simplify the description, and do not indicate or imply that the apparatus or element referred to must have a particular orientation or be constructed and operated in a particular orientation, nor should it be construed as limiting the specific scope of the invention.
In the claims, specification and drawings of the present invention, the terms "comprising," having, "and variations thereof as used herein, are intended to be" including but not limited to.
The technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings.
Referring to fig. 1, there is shown a surface defect detecting apparatus for detecting a surface defect of an object 2 to be measured according to an embodiment of the present invention.
The object 2 to be measured has a first surface 21 and a second surface 22 parallel to each other, the first surface 21 and the second surface 22 being substantially flat to enable specular reflection of light at areas of the first surface 21 and the second surface 22 that do not have surface defects. The object 2 to be measured should furthermore be transparent in order to enable light to transmit through the object 2 to be measured and to enable surface defects on the first surface 21 or the second surface 22 to be observed on the other surface after being irradiated with light and reflected and refracted. In the present embodiment, the object to be measured 2 is exemplarily shown as a flat glass, but the object to be measured may be another object having the above-described characteristics.
Furthermore, the object 2 to be measured is also moved relative to the surface defect detecting device in a first direction parallel to the first surface 21. The above-described relative movement relationship can be achieved by holding the surface defect detecting device stationary and moving the object 2 to be measured, for example, in the present embodiment, the object 2 to be measured is placed on a conveying mechanism 1 constituted by a plurality of conveying rollers, and the conveying mechanism 1 moves in the first direction relative to the surface defect detecting device. It goes without saying, however, that the above-described relative movement relationship can also be achieved by holding the object 2 to be measured stationary and moving the surface defect detecting device.
Further, in this embodiment, the surface of the object 2 to be measured, which is close to the surface defect detecting device, is defined as a first surface 21, and the surface of the object, which is far from the surface defect detecting device, is defined as a second surface 22. Thus, according to the illustrated direction, the first surface 21 is the upper surface of the object 2 to be measured, and the second surface 22 is the lower surface of the object 2 to be measured. It should be understood that this is for convenience of description only, and that the first surface 21 and the second surface 22 do not refer to a particular functional surface of the object 2 to be measured, and thus should not be interpreted in a limiting manner.
Returning to the surface defect detection means, it comprises a first light source 31, a second light source 32, a first camera 41, a second camera 42 and image analysis means (not shown in the figure).
The first light source 31 and the second light source 32 both emit collimated light or converging light and obliquely irradiate the first surface 21, and the second light source 32 and the first light source 31 are symmetrically arranged about a normal plane perpendicular to the first direction and form an overlapping irradiation area 33 on the first surface 21. In other words, the specular reflection light paths formed on the first surface 21 by the light rays emitted by the first light source 31 and the second light source 32 are completely reversed, and the two light sources (31, 32) irradiate the object 2 to be measured in the directions facing toward and away from the first direction, respectively. It should be noted that, the oblique incidence indicates that the included angle formed by the emergent direction of each light beam and the surface to be irradiated is an acute angle. The collimated light includes two cases, one is a light beam with a basically parallel emergent direction after being collimated, and the other is a parallel light beam. In a preferred structure of this embodiment, the first light source 31 and the second light source 32 are parallel light sources, and compared with a common collimated light source, the outgoing directions of the light beams have no deviation, so that the imaging of surface defects in each camera is not affected. Further, when the first light source 31 and the second light source 32 are both converging light sources and emit converging light, a converging focal point of the converging light forms the irradiation region 33.
The first camera 41 and the second camera 42 are both line scan cameras, the line scan direction is perpendicular to the first direction, and the fields of view of the two cameras (41, 42) are both located in the dark fields of the first light source 31 and the second light source 32 and continuously shoot the object 2 to be measured. Wherein the first optical axis 411 of the first camera 41 is perpendicular to the first direction and intersects the first surface 21 at a first intersection point located in the irradiation area 33, and the second optical axis 421 of the second camera 42 is inclined to the first surface 21 and intersects the first surface 21 at the first intersection point, and the first intersection point is located in the normal plane. In addition, since the first optical axis 411 and the second optical axis 421 intersect, they together define a plane and both optical axes (411, 421) are located in the plane. In this embodiment, the plane defined by the first optical axis 411 and the second optical axis 421 is perpendicular to the normal plane. Further, regarding the dark field, it is actually a configuration for limiting the camera under a specific light source and a specific reflecting surface, that is, neither the light directly emitted from the light source nor the light specularly reflected by the reflecting surface enters the field of view of the camera, only the light diffusely reflected by the reflecting surface may enter the field of view of the camera, so that the non-defective area is visualized as black and the defective area is visualized as white in the imaging result of the camera.
It goes without saying that the illumination area 33 formed by the first light source 31 and the second light source 32 together covers the first surface 21 in a second direction perpendicular to the first direction and parallel to the first surface, and that the fields of view of the first camera 41 and the second camera 42 also cover the first surface 21 in the second direction, so that the object 2 to be measured can be entirely scanned and illuminated by the two light sources (31, 32) and entirely photographed by the two cameras (41, 42) after moving in the first direction.
The image analysis means synthesizes images continuously photographed by the first camera 41 and the second camera 42 into a first synthesized image and a second synthesized image, respectively. Further, the image analysis apparatus performs the following processing on the first composite image and the second composite image: for the first composite image, the image analysis device identifies closed areas with each gray value exceeding a first threshold value in the first composite image and marks each identified closed area as a corresponding first defect image; for the second composite image, the image analysis device inverts the second composite image into a third composite image according to a perspective imaging principle, identifies a closed area of each gray value exceeding a first threshold value in the third composite image, and marks each identified closed area as a corresponding second defect image. After that, the image analysis device further executes a determination method for determining a surface of the first composite image where the surface defect corresponding to each of the first defect images is located, and a specific procedure of the determination method will be described in detail below. In this embodiment, the image analysis device is a computer having image processing and analysis capabilities.
Next, referring to fig. 2 to 5, a case when the surface defect detecting device is applied to detect the object 2 to be detected will be described. For a more visual representation, the surface defects in fig. 2-4 are each illustratively shown as a speckled defect, but should not be so limited.
In fig. 2 and 3, the surface defect a of the object 2 to be measured is located on the first surface 21 and the object 2 to be measured is moved to the first position and the second position, respectively. It can be seen that when the object 2 to be measured is in the first position, the surface defect a cannot be captured by the first camera 41, but it forms a virtual image a' symmetrical with respect to the second surface 22, which can be captured by the second camera 42; when the object 2 to be measured is located at the second position, the surface defect a can be captured by the first camera 41 and the second camera 42. In fig. 4 and 5, the surface defect B of the object 2 to be measured is located on the first surface 21 and the object 2 to be measured is moved to the third position and the fourth position, respectively. It can be seen that when the object 2 to be measured is located at the third position, the surface defect B can be photographed by the second camera 42, but cannot be photographed by the first camera 41; while when the object 2 to be measured is located at the fourth position, the surface defect B may be photographed by the first camera 41 but not by the second camera 42.
Based on the description of fig. 2-5 above, referring again to fig. 6a-9b, when a surface defect is located on a different surface of the object 2 to be measured and when the surface defect has or does not have a certain dimension in the first direction, the defect image that the surface defect exhibits in the first and third composite images will also be different. It should be noted that fig. 6a-9b are all reverse-colored for aesthetic reasons and to avoid large areas of black in the drawings. In other words, the black areas in fig. 6a-9b represent surface defects, while the white areas represent non-surface defects.
Fig. 6a and 6b show schematic diagrams of the first and third composite images with surface defects on the first surface 21 and without a certain scale in the first direction. In fig. 6a and 6b, the surface defect is a spot defect, the number of corresponding first defect images in the first composite image is one, the number of corresponding second defect images in the third composite image is two, and the three defect images have similar overall shapes and smaller absolute values of area differences.
Fig. 7a and 7b show schematic diagrams of the first and third composite images with surface defects on the first surface 21 and having a certain scale in the first direction. In fig. 7a and 7b, the surface defect is a long-strip defect, the corresponding first defect image in the first composite image is one, the corresponding second defect image in the third composite image is also one, the shapes of the head and tail of the second defect image and the first defect image along the first direction are similar, the shapes of the middle parts of the second defect image and the first defect image are dissimilar, and the absolute value of the area difference of the two is larger.
Fig. 8 a-9b show schematic diagrams of the first and third composite images with the surface defects on the second surface 22, wherein the surface defects of fig. 8a and 8b are both speckled defects and the surface defects of fig. 9a and 9b are both elongated defects. It can be seen that, whether the surface defect has a certain scale along the first direction or not, the defect image corresponding to the surface defect in the first composite image and the third composite image is one, and the two defect images have similar overall shapes and smaller absolute values of area differences.
Based on the above surface defect detection device, an embodiment of the present invention provides a method for determining a surface where a surface defect is located, which includes the steps of image synthesis, inversion, and identification of a corresponding defect image performed by the above described image analysis device, as well as the following steps:
and searching all second defect images corresponding to the first defect images in the third composite image by taking each first defect image in the first composite image as a reference. If two second defect images corresponding to the first defect image are found according to the first correspondence, it is determined that the surface defect corresponding to the first defect image is located on the first surface 21. If only one second defect image corresponding to the first defect image is found according to the first correspondence, it is determined that the surface defect corresponding to the first defect image is located on the second surface 22. If a second defect image corresponding to the first defect image is found according to the second correspondence, it is determined that the surface defect corresponding to the first defect image is located on the first surface 21. The first corresponding relation is that the overall shapes of the two defect images are similar, and the absolute value of the area difference of the two defect images is smaller than a second threshold; the second corresponding relation is that the shapes of the head and the tail of the two defect images along the first direction are similar, the shapes of the middle parts of the two defect images are dissimilar, and the absolute value of the area difference of the two defect images is larger than a second threshold value.
It should be noted that, the correspondence of two images with similar shapes as a reference and the comparison of the areas of the two images are already mature prior art in the field of image processing, and the specific algorithm is more and is not the focus of the present invention, so the present invention will not be repeated. Further, the above-described specific process of inverting the second composite image according to the perspective imaging principle can be referred to patent document CN108198214 a.
As can be seen from the above description, the surface defect detecting device of the present embodiment, after adopting the two light sources with the above configuration, greatly reduces the imaging gap of the two cameras (41, 42) for the real images of the same surface defect, improves the shape similarity of the corresponding defect images of the same surface defect in the two-camera imaging results, and has practical significance by comparing the two-camera imaging results to obtain further information on the basis, thereby being beneficial to shape correspondence of the defect images of the same surface defect in the two-camera imaging results on the basis, and judging the surface where the surface defect (especially the surface defect with a certain dimension along the first direction) is located according to the corresponding results.
The method for determining the surface on which the surface defect is located according to the embodiment has higher accuracy when the corresponding reference of the shape similarity is applied to correspond to the corresponding defect image of the same surface defect in the two composite images, and further determine the surface on which the surface defect is located, and is particularly suitable for the surface defect having a certain scale along the first direction.
After the above-mentioned determination is performed on the surface defects corresponding to all the first defect images in the first composite image, whether the object to be detected is qualified or not can be determined according to the distribution condition of the surface defects on the first surface 21 and the second surface 22. If all the surface defects are only present on a specific surface with high defect tolerance (such as a bonding surface of a mobile phone glass cover plate), it can be determined that the object 2 to be detected is still qualified, and unnecessary reduction of detection passing rate caused by excessive detection is avoided.
The foregoing description of the embodiments and description is presented to illustrate the scope of the invention, but is not to be construed as limiting the scope of the invention. Modifications, equivalents, and other improvements to the embodiments of the invention or portions of the features disclosed herein, as may occur to persons skilled in the art upon use of the invention or the teachings of the embodiments, are intended to be included within the scope of the invention, as may be desired by persons skilled in the art from a logical analysis, reasoning, or limited testing, in combination with the common general knowledge and/or knowledge of the prior art.
Claims (3)
1. A surface defect detection device for detecting surface defects on a first surface and a second surface of a transparent object to be detected, which are parallel to each other, the second surface being further away from the surface defect detection device than the first surface, the object to be detected moving relative to the surface defect detection device in a first direction parallel to the first surface;
characterized by comprising the following steps:
a first light source obliquely irradiating the first surface and forming an irradiation region on the first surface;
a second light source symmetrically arranged with the first light source about a normal plane perpendicular to the first direction, obliquely projecting the first surface and forming an overlapping irradiation area on the first surface with the first light source;
a first camera which is a line scanning camera with a line scanning direction perpendicular to the first direction and is configured such that a field of view is located in a dark field of the first light source and the second light source and continuously photographs an object to be measured; the optical axis of the lens is perpendicular to the first surface and intersects with the first surface at a first intersection point positioned in the irradiation area; the first intersection point is positioned on the normal plane;
the second camera is a line scanning camera with the line scanning direction perpendicular to the first direction and is configured to have a field of view positioned in dark fields of the first light source and the second light source and continuously shoot an object to be detected; the optical axis of the lens is inclined to the first surface and is intersected with the first surface and the optical axis of the first camera at the first intersection point; a plane defined by the optical axis of the second camera and the optical axis of the first camera is perpendicular to the normal plane;
the first light source and the second light source emit collimated light or converged light, and when the first light source and the second light source emit converged light, a converged focus of the converged light forms the irradiation area;
an image analysis device that synthesizes images continuously captured by the first camera and the second camera into a first synthesized image and a second synthesized image, respectively; the method further comprises the steps of identifying closed areas with each gray value exceeding a first threshold value in the first composite image and marking each identified closed area as a corresponding first defect image; inverting the second composite image into a third composite image according to a perspective imaging principle, identifying a closed area of each gray value exceeding a first threshold value in the third composite image, and marking each identified closed area as a corresponding second defect image; the method also uses each first defect image in the first composite image as a reference, and searches all second defect images corresponding to the first defect images in the third composite image; if two second defect images corresponding to the first defect images are found according to the first corresponding relation, judging that the surface defects corresponding to the first defect images are positioned on the first surface; if only one second defect image corresponding to the first defect image is found according to the first corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the second surface; if a second defect image corresponding to the first defect image is found according to the second corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the first surface; the first corresponding relation is that the overall shapes of the two defect images are similar, and the absolute value of the area difference of the two defect images is smaller than a second threshold; the second corresponding relation is that the shapes of the head and the tail of the two defect images along the first direction are similar, the shapes of the middle parts of the two defect images are dissimilar, and the absolute value of the area difference of the two defect images is larger than a second threshold value.
2. A surface defect inspection apparatus as claimed in claim 1 wherein: the first light source and the second light source are parallel light sources or converging light sources.
3. A method for determining a surface on which a surface defect is located, comprising: the method is based on a surface defect detection apparatus as claimed in claim 1 or 2, and comprises:
synthesizing images continuously shot by the first camera and the second camera into a first synthesized image and a second synthesized image respectively;
identifying closed areas with each gray value exceeding a first threshold value in the first composite image and marking each identified closed area as a corresponding first defect image;
inverting the second composite image into a third composite image according to a perspective imaging principle, identifying a closed area of each gray value exceeding a first threshold value in the third composite image, and marking each identified closed area as a corresponding second defect image;
searching all second defect images corresponding to the first defect images in the third composite image by taking each first defect image in the first composite image as a reference; if two second defect images corresponding to the first defect images are found according to the first corresponding relation, judging that the surface defects corresponding to the first defect images are positioned on the first surface; if only one second defect image corresponding to the first defect image is found according to the first corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the second surface; if a second defect image corresponding to the first defect image is found according to the second corresponding relation, judging that the surface defect corresponding to the first defect image is positioned on the first surface; the first corresponding relation is that the overall shapes of the two defect images are similar, and the absolute value of the area difference of the two defect images is smaller than a second threshold; the second corresponding relation is that the shapes of the head and the tail of the two defect images along the first direction are similar, the shapes of the middle parts of the two defect images are dissimilar, and the absolute value of the area difference of the two defect images is larger than a second threshold value.
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