Device and method for detecting dark crack imaging after brittle sheet material cutting

Abstract

The invention discloses a dark crack imaging detection device and method after cutting of a brittle sheet material, and the device comprises a camera which is used for obtaining an imaging image of the surface of a to-be-detected workpiece; and the coaxial eccentric illumination light source is arranged on the side of the camera, guides illumination light into the direction coaxial with the imaging optical axis of the camera through the optical reflection and lens assembly, and is used for providing multidirectional eccentric illumination for the surface of the workpiece to be detected, so that cracks on the surface of the workpiece present different optical reflection brightness in different illumination directions. Distinguishable brightness difference signals can be stably generated in different illumination directions, so that the dark crack imaging contrast ratio is remarkably enhanced, and misjudgment is reduced; and through programmed multi-directional illumination and a camera acquisition process, automatic judgment of cracks in different directions is completed.

Description

Technical Field

[0001] This invention belongs to the field of crack detection technology, and relates to an imaging detection device and method for dark cracks after cutting brittle thin plate materials. Background Technology

[0002] With the widespread application of brittle materials such as semiconductor chips, display panels, and small electronic glass substrates in precision manufacturing, surface integrity testing after material cutting has become a crucial factor affecting product reliability. During the cutting process, due to factors such as stress concentration, micro-vibration, and tool wear, extremely fine initial cracks often form on or near the surface of the material, commonly referred to as "hidden cracks." These cracks can reach lengths of hundreds of micrometers, while their width is often less than 1 micrometer, making them difficult to detect with the naked eye and conventional microscopic inspection.

[0003] Currently, the industry generally adopts two types of detection methods: (1) Infrared or transmission imaging method: using infrared light or visible light transmission to detect internal defects, but for surface defects...

[0004] (2) Artificial microscopic examination: Under a microscope, the reflection characteristics are observed by changing the incident angle to detect cracks.

[0005] However, this method heavily relies on the operator's experience, resulting in low efficiency, poor repeatability, and the inability to automate the process.

[0006] Prenatal testing.

[0007] Because the reflection signal of dark cracks is extremely weak in the early stages of formation, they are often misjudged as qualified products during factory inspection. After entering the subsequent assembly process, they are prone to propagation under thermal cycling or mechanical stress, leading to electrical failure of the device or fracture of the overall structure. Therefore, how to perform high-contrast, automated optical inspection of dark cracks on the surface of brittle thin sheet materials after cutting, without manual intervention, has become a long-standing and unresolved key technical problem in the industry. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing an imaging detection device and method for dark cracks after cutting brittle thin sheet materials. By constructing a coaxial optical system with multi-directional eccentric illumination characteristics, the cracks on the material surface produce distinguishable brightness responses under different illumination orientations. Then, based on the brightness changes, high-precision imaging detection of dark cracks is achieved.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] An imaging detection device for hidden cracks after cutting brittle thin sheet materials, comprising:

[0011] A camera is used to acquire an image of the surface of a workpiece to be tested.

[0012] A coaxial eccentric illumination source is positioned to the side of the camera and, through an optical reflection and lens assembly, guides the illumination light in a direction coaxial with the imaging optical axis of the camera. This source is used to provide multi-directional eccentric illumination to the surface of the workpiece under test, so that the cracks on the workpiece surface exhibit different optical reflection brightness under different illumination directions.

[0013] The coaxial eccentric lighting source includes a lamp panel and a light-diffusing component;

[0014] The lamp panel is provided with two or more independent light sources, which are symmetrically distributed along the center of the lamp panel. Each group of light sources can be lit sequentially or alternately to produce eccentric lighting light from different directions.

[0015] The light homogenizing component is located in front of the light-emitting end of the lamp board and is used to spatially homogenize and directionally shape the light emitted by each light source so that the brightness distribution is uniform and the irradiation angle is consistent when the shaped light shines on the workpiece being tested.

[0016] Furthermore, the lamp panel is provided with left and right light source groups and upper and lower light source groups, and the four light sources are centrally symmetrically distributed around the center point of the lamp panel.

[0017] Furthermore, the light homogenizing component includes integrating bars, which are located in front of the light source of the lamp panel to perform spatial mixing and homogenization of the light emitted by the corresponding light source.

[0018] Furthermore, the light-diffusing component includes a light-diffusing plate located in front of the integrating bar to further smooth the light intensity distribution and eliminate local bright spots.

[0019] Furthermore, the light homogenizing component includes two collimating lenses, which are sequentially arranged in front of the light homogenizing plate to collimate the homogenized light into approximately parallel light, so as to illuminate the surface of the workpiece under test along the imaging optical axis of the camera.

[0020] Furthermore, it also includes an optical path combining module, which includes a semi-transparent mirror disposed below the camera, used to refract the illumination light into the optical axis of the camera, and allow the light reflected from the workpiece under test to be transmitted into the camera to achieve coaxial combining of the illumination optical path and the imaging optical path.

[0021] A method for detecting hidden cracks in brittle thin sheet materials after cutting, applied to the aforementioned detection device, characterized by comprising the following steps:

[0022] After the workpiece to be tested is fixed on the testing platform, the imaging optical axis of the camera is controlled to be vertically aligned with the surface of the workpiece to be tested.

[0023] Each light source group in the coaxial eccentric illumination source is lit sequentially, and the corresponding surface reflection image is captured by the camera when only a single light source group is lit at a time.

[0024] By comparing the brightness or performing grayscale difference operations on two frames of images obtained from opposite lighting directions, a brightness difference distribution map is obtained.

[0025] The judgment is based on the brightness changes in each region of the brightness difference distribution map;

[0026] Based on the judgment result, crack distribution information or alarm signals are output to realize automatic detection of the cut workpiece.

[0027] Furthermore, the step of performing brightness comparison or grayscale difference operation on two frames of images obtained from opposite lighting directions to obtain a brightness difference distribution map includes the following steps:

[0028] Brightness comparison is performed on images acquired under left and right illumination to detect cracks along the vertical direction; brightness comparison is performed on images acquired under top and bottom illumination to detect cracks along the horizontal direction.

[0029] Furthermore, the judgment based on the brightness changes of each region in the brightness difference distribution map includes the following steps: When the brightness of the same location shows a significant reversal or difference under opposite lighting directions, the region is determined to be a dark crack; When the brightness of the same location remains basically consistent under different lighting directions, the region is determined to be a cutting channel.

[0030] By applying the technical solution of this invention, distinguishable brightness difference signals can be stably generated under different lighting orientations, thereby significantly enhancing the imaging contrast of dark cracks and reducing misjudgments. Through a programmed multi-directional lighting and camera acquisition process, automatic judgment of cracks with different orientations can be completed, reducing manual angle adjustment and subjective intervention, and improving the consistency and repeatability of results. The device and method are easy to interface with existing vision platforms / transportation cycles, enabling online detection at continuous workstations. The detection cycle and coverage area expand linearly with the acquisition and motion parameters, comprehensively achieving high detection rate, high stability, and high efficiency in industrial applications.

[0031] Other features and advantages of the invention will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0032] The present invention will now be described in detail with reference to the accompanying drawings, so that the above-mentioned advantages of the present invention will become more apparent.

[0033] Figure 1 This is a schematic diagram showing a dark crack appearing as a bright line;

[0034] Figure 2 This is a schematic diagram of a dark crack appearing as a dark line;

[0035] Figure 3 This is a schematic diagram of a device for imaging and detecting dark cracks after cutting brittle thin sheet materials according to the present invention;

[0036] Figure 4 This is a schematic diagram illustrating the use of the imaging detection device for dark cracks after cutting brittle thin sheet materials according to the present invention.

[0037] Figure 5 This is a schematic diagram of the lamp plate of the imaging detection device for dark cracks after cutting brittle thin sheet material according to the present invention;

[0038] Figure 6 This is a schematic diagram of the integrating rod assembly of an imaging detection device for dark cracks after cutting brittle thin sheet materials according to the present invention.

[0039] Figure 7 This is a schematic diagram of the coaxial eccentric illumination source assembly of a device for imaging and detecting dark cracks after cutting brittle thin sheet materials according to the present invention.

[0040] Figure 8 This is a schematic diagram of a coaxial eccentric illumination source for an imaging detection device for dark cracks after cutting brittle thin sheet materials according to the present invention.

[0041] Figure 9 This is a schematic projection of the use of the imaging detection device for dark cracks after cutting brittle thin sheet material according to the present invention;

[0042] Figure 10 This is a flowchart of a method for detecting dark cracks after cutting brittle thin sheet materials according to the present invention. Detailed Implementation

[0043] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0044] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0046] In the embodiments of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] Reference Appendix Figure 1-5 As shown, this embodiment provides an imaging detection device for dark cracks after cutting brittle thin sheet materials, including a camera 100 and a coaxial eccentric illumination source 200. The camera 100 is used to acquire an image of the surface of the workpiece to be tested; the coaxial eccentric illumination source 200 is disposed to the side of the camera 100, and guides the illumination light in a direction coaxial with the imaging optical axis of the camera 100 through optical reflection and lens assembly, so as to provide multi-directional eccentric illumination to the workpiece surface within the field of view of the camera 100, so that the cracks on the workpiece surface produce different optical reflection brightness under different illumination directions. The lighting source 220 includes a lamp panel 210 and a light-diffusing component 300. The lamp panel 210 is provided with two or more sets of independent light sources 220. Each light source 220 is symmetrically distributed along the center of the lamp panel 210 and can be lit sequentially or alternately to produce eccentric lighting light in different directions. The light-diffusing component 300 is located in front of the light-emitting end of the lamp panel 210 and is used to spatially homogenize and directionally shape the light emitted by the light source 220, so that when the shaped light shines on the workpiece being measured, the brightness distribution is uniform and the illumination angle is consistent, thereby ensuring the consistency of lighting conditions in all directions.

[0048] During operation, the control module sequentially illuminates each group of light sources 220. After integration, diffusion, and collimation by the light homogenizing component 300, the light forms a uniformly bright, off-center illumination beam, which is then guided through a reflector to the optical axis of the camera 100, maintaining coaxiality with the imaging channel. Due to the slight tilt angle difference in the crack cross-section, its reflection direction changes with the incident direction. Under different illumination orientations, the same crack area will exhibit a significant brightness reversal phenomenon. The brightness difference in the image acquired by the camera 100 constitutes the basis for subsequent crack identification.

[0049] This design is based on the principle of the reflection dependence of the crack surface of brittle materials on the incident angle. Traditional coaxial illumination is perpendicular to the incident angle, resulting in weak crack reflection signals that are easily drowned out by background light. This embodiment introduces independently controllable eccentric light sources 220 into the coaxial illumination structure, causing a slight offset angle between the illumination direction and the imaging optical axis. This maintains the coaxial consistency between illumination and imaging while stimulating differences in crack cross-section reflection under multi-directional illumination. After homogenization by the homogenizing component 300, the imaging brightness remains stable when switching between different light sources 220, providing balanced optical conditions for brightness difference analysis.

[0050] The device in this embodiment can significantly enhance the brightness contrast between dark cracks and the background under multi-directional illumination. The combination of the lamp board 210 and the light-uniforming component 300 ensures uniform and consistent illumination, reducing the impact of uneven light spots on detection accuracy. The light source 220 can be lit sequentially to achieve multi-directional acquisition without changing the workpiece posture or the position of the optical system, improving the automation level and overall efficiency of the inspection. At the same time, the lighting and imaging channels are arranged coaxially, effectively avoiding the shadow and geometric distortion problems of traditional oblique illumination systems, making crack imaging clearer and more stable. The device has a compact structure and a reasonable optical path, and can be directly integrated into an industrial vision inspection system to achieve rapid, high-contrast automatic detection of dark cracks after cutting brittle thin sheet materials.

[0051] In this embodiment, the lamp panel 210 is provided with four sets of light sources: left and right (220 groups) and top and bottom (220 groups). These four light sources are centrally symmetrically distributed around the center point of the lamp panel 210. Each set of light sources 220 consists of two groups of light sources located horizontally and vertically. The illumination centers of all four sets of light sources 220 point towards the central area of ​​the lamp panel 210, ensuring that the irradiated light, after entering the uniform light distribution component 300, forms a spatially uniform and directionally controllable illumination field. This centrally symmetrical arrangement ensures that the illumination angle is symmetrically distributed near the center point of the lamp panel 210, facilitating control of the illumination direction and maintaining overall illumination balance when switching between different sets of light sources 220.

[0052] During the detection process, the system can illuminate either the left and right light sources (220 groups) or the top and bottom light sources (220 groups). When illuminated by the left and right light sources (220 groups), the incident light mainly forms eccentric illumination along the horizontal direction, which enhances the brightness difference of the reflected light from the vertical cracks. When illuminated by the top and bottom light sources (220 groups), the incident light forms eccentric illumination along the vertical direction, which enhances the brightness difference of the reflected light from the horizontal cracks. Since the four light sources (220 groups) are centrally symmetrical in space, the illumination conditions between each group are highly consistent in terms of intensity, distance, and incident angle. Therefore, the images obtained from illumination from different directions are comparable in brightness distribution, providing a reliable basis for subsequent differential analysis based on brightness changes.

[0053] The design concept of this symmetrical arrangement structure is to achieve directional consistency and brightness symmetry of the illumination field through the geometric balance of the light source 220. Traditional single-sided or offset light source 220 illumination often results in brightness shifts in the detection results due to light intensity attenuation and uneven angle. However, the four-point centrally symmetrical arrangement in this embodiment can ensure that illumination from opposite directions has the same luminous flux and incident conditions, thereby producing a symmetrical complementary bright and dark response in crack reflection imaging.

[0054] Therefore, this embodiment achieves illuminance balance during multi-directional illumination switching, making the brightness changes of cracks under different illumination directions more significant and quantifiable, improving the system's detection contrast and judgment accuracy, while avoiding shadows, overexposure of reflections and image deviations caused by unilateral illumination, further improving the overall detection stability and repeatability.

[0055] Reference Appendix Figure 6-9 As shown in this embodiment, the light homogenizing component 300 includes integrating rods 310, which are respectively located in front of each light source 220 of the lamp panel 210, and are used to perform spatial mixing and homogenization processing on the light emitted by the corresponding light source 220. Each integrating rod 310 is an independent optical channel, with its light-incident end facing the light-emitting surface of the corresponding light source 220, and its light-emitting end arranged towards the center of the lamp panel 210. The interior of the integrating rod 310 is a high-reflectivity light guide channel structure, and the light is fully mixed after multiple reflections inside, so that the light from different positions and different incident angles forms a uniform distribution of surface light source 220 at the light-emitting end.

[0056] This structure eliminates the illumination instability caused by uneven brightness and differences in the shape of the emitting surfaces among the light source chips 220 through optical mixing. Compared to direct illumination by the LED array, the multiple reflections of the integrating rod 310 can diffuse local bright spots into a uniform light field, significantly improving illumination uniformity. When the system switches between different groups of light sources 220, the output brightness and angular distribution of each integrating rod 310 remain consistent, thereby ensuring a consistent imaging brightness benchmark under multi-directional illumination and avoiding error signals caused by uneven illumination in the differential image.

[0057] The design concept of this embodiment is to utilize the optical mixing characteristics of the integrating rod 310 to transform the point light source 220 or small surface light source 220 into a uniform quasi-surface light source 220, thereby achieving spatial consistency of the illumination field. The setting of the integrating rod 310 ensures that the eccentric light source group 220 can still obtain the same illuminance distribution and light emission angle when independently illuminated, providing stable optical conditions for subsequent brightness difference detection.

[0058] By adopting the above structure, this embodiment significantly improves the uniformity and stability of the light field of the illumination system, avoiding image noise and misjudgment caused by uneven light intensity; at the same time, it realizes the independent controllability of the light source 220 module, so that the detection device does not need additional compensation or calibration when switching illumination in multiple directions, thereby improving the detection reliability and operating efficiency of the system.

[0059] In this embodiment, the light homogenizing component 300 includes a light homogenizer 320, which is located in front of the integrating rod 310 to further smooth the illumination distribution and eliminate local bright spots. The light homogenizer 320 is an optical diffusion element with high transmittance, and its installation position corresponds to the light-emitting end of the integrating rod 310, arranged close to or at a certain distance, to perform secondary homogenization processing on the light field output by the integrating rod 310.

[0060] Even after the multiple reflected rays inside the integrating rod 310 converge at the light-emitting end, slight brightness fluctuations or localized light spots may still exist. The light homogenizer 320, through microstructural scattering, diffuses the emitted light within a small angle range, creating a smoother brightness transition region in space. The light treated by the light homogenizer 320 has uniform brightness and no obvious light spots, thus further ensuring the stability of light received by the workpiece surface.

[0061] The design concept of this structure is to achieve deep optimization of the illumination field through a combined homogenization method. The integrating rod 310 is mainly responsible for the macroscopic mixing of light and the equalization of energy distribution, while the homogenizer 320 compensates for subtle brightness fluctuations, forming a composite homogenization system that combines uniformity and directional consistency. The synergistic effect of the two ensures that each of the 220 sets of eccentric light sources can provide a light field condition with uniform brightness and consistent illuminance during switching.

[0062] Through the above design, this embodiment effectively eliminates the interference of local light spots on the brightness of the imaging area, making the brightness comparison analysis under multi-directional illumination more reliable; at the same time, it reduces the background noise caused by non-uniform illumination, improves the overall contrast and detection stability of dark crack imaging, and provides more accurate optical input conditions for subsequent brightness difference judgment.

[0063] In this embodiment, the light homogenizing component 300 includes two collimating lenses 330, which are sequentially disposed in front of the light homogenizing plate 320. These lenses collimate the homogenized light rays into approximately parallel light, illuminating the surface of the workpiece along the imaging optical axis of the camera 100. The two collimating lenses 330 are arranged at intervals; the first lens converges the light and corrects its direction, while the second lens re-collimates and fine-tunes the angle of the outgoing light, minimizing the divergence angle of the transmitted light and forming a uniform, approximately parallel light field.

[0064] In this embodiment, the light brightness distribution after processing by the integrating bar 310 and the homogenizing plate 320 is relatively uniform, but there is still a problem of inconsistent divergence angles in some light rays. Setting two collimating lenses 330 can effectively suppress the scattering and spread of light, converting the light rays that originally had small-angle divergence into quasi-parallel light, ensuring that their illumination direction is strictly consistent with the imaging optical axis of the camera 100. When illuminating the surface of the workpiece being measured, the incident light rays in all directions are approximately parallel, and the illumination angle is stable and consistent, thereby ensuring that the difference in reflected brightness in the crack area is caused only by micro-geometric changes in the surface, rather than by deviations in the illumination angle.

[0065] The design concept of this embodiment is to achieve high-precision light collimation using a dual-lens structure. Compared with a single lens, a dual-lens structure can optimize the optical path to reduce aberrations and increase parallelism, while also achieving a larger effective illumination area within a limited structural size. This design ensures that the off-center illumination light rays coincide with the imaging optical axis when entering the coaxial optical path, thereby eliminating the influence of optical path offset on the imaging center.

[0066] By adopting the above structure, this embodiment enables the light output by the uniform light component 300 to have good directional consistency and optical stability, ensuring that the incident angle and illuminance distribution remain the same when switching between different light sources (220 groups) from multiple directions, thereby improving the imaging contrast and detection accuracy of dark cracks. This dual-lens collimation structure also reduces light diffraction and energy loss, enhancing the system's light efficiency and signal stability, and providing balanced and highly consistent illumination conditions for subsequent image acquisition.

[0067] This embodiment also includes an optical path combining module, which includes a semi-transparent mirror disposed below the camera 100. This mirror refracts the illumination light into the optical axis of the camera 100 and allows reflected light from the workpiece to be transmitted into the camera 100, thereby achieving coaxial combining of the illumination and imaging optical paths. The semi-transparent mirror preferably employs a partially reflective, partially transmissive optical beam splitter. Its reflecting surface is arranged at a 45° angle to the imaging optical axis of the camera 100, with one side receiving incident light from the off-center illumination source 220 and the other side facing the surface of the workpiece.

[0068] During system operation, the homogenized light emitted from the eccentric illumination source 220 is first collimated by a double lens to form an approximately parallel light field, which then strikes a semi-transparent mirror. This mirror reflects the incident light, causing it to propagate along the imaging optical axis of the camera 100 and illuminate the surface of the workpiece under test, achieving coaxial incidence of the illumination light. The light signal reflected back from the surface of the workpiece is then transmitted through the semi-transparent mirror into the imaging channel of the camera 100, forming a complete coaxial optical path structure. Through this optical path design combining refraction and transmission, the system achieves a high degree of overlap between the illumination and imaging optical paths while maintaining a compact structure.

[0069] The design concept of this structure is to utilize the beam-splitting characteristics of a semi-transparent mirror to synthesize the optical paths of illumination and imaging, allowing the off-center illumination light to act on the detection area in a coaxial direction without interfering with the camera 100's acquisition of reflected signals. Compared to traditional external illumination schemes, the optical path synthesis module in this embodiment eliminates the need for an additional illumination angle adjustment mechanism, maintaining consistency between the illumination direction and the imaging direction, and avoiding shadows, reflection blind spots, and uneven brightness caused by the misalignment of the light source 220 and the lens axis.

[0070] By adopting the above structure, this embodiment enables the detection system to achieve a collinear optical axis design for illumination and imaging within a compact space, significantly improving illumination utilization and imaging signal-to-noise ratio; the uniform distribution of illumination light along the optical axis helps to clearly reveal the reflection characteristics of dark cracks; at the same time, it reduces the impact of optical path differences on focal position and imaging quality, improves the optical stability and detection repeatability of the device, and provides a stable and quantifiable optical input basis for subsequent automatic detection algorithms.

[0071] Reference Appendix Figure 1-10 As shown, this embodiment provides a method for detecting dark cracks in brittle thin sheet materials after cutting, applied to the aforementioned device. First, the workpiece to be tested is fixed on the testing platform, and the imaging optical axis of the camera 100 is controlled to be vertically aligned with the workpiece surface, ensuring the detection area is located at the center of the camera 100's field of view, thus guaranteeing spatial consistency between incident illumination and reflected imaging. Subsequently, each of the 220 groups of coaxial eccentric illumination sources 200 is sequentially illuminated. With only one group of light sources 220 illuminated at a time, the camera 100 acquires a surface reflection image under the corresponding azimuth illumination. Through programmed control, automatic switching of multi-azimuth illumination can be achieved without manual adjustment of the workpiece posture or the angle of the light source 220, thereby ensuring consistent acquisition conditions for each frame of image.

[0072] After acquiring images under illumination from various directions, the system compares the brightness or performs grayscale difference calculations on two frames obtained from opposite illumination directions to calculate the brightness difference at the same location under different illumination orientations, thus obtaining a brightness difference distribution map. Cracked areas, due to their slightly tilted surfaces, exhibit significant changes in reflected light intensity with different incident directions, resulting in brightness reversals or obvious differences. In contrast, cut surfaces or intact areas have smooth surfaces, and the reflected light shows minimal variation under illumination from all directions, with essentially consistent brightness. Based on this brightness response characteristic, the system judges each region in the brightness difference distribution map. When the brightness at the same location shows a significant contrast under opposite illumination directions, the region is identified as a dark crack; when the brightness variation is small and consistent, it is identified as a cut surface or a defect-free area.

[0073] Finally, based on the judgment results, crack distribution information or alarm signals are output. The output results can display the location and extent of cracks on the workpiece surface through image overlay, or the judgment signal can be directly sent to the host computer or production control system to achieve automatic identification and screening of defect areas.

[0074] The design concept of this embodiment is to utilize the reflection dependence of dark cracks on the incident angle under eccentric illumination, so that the crack area produces a brightness reversal effect under illumination from the opposite direction, thereby determining the presence of cracks through brightness differences. Unlike traditional single-direction illumination or manual angle adjustment observation methods, this method can complete multi-directional illumination imaging on the same detection platform, and the brightness difference judgment is objective and reliable, eliminating the uncertainty caused by differences in operator experience.

[0075] By employing the above steps, this embodiment achieves automated detection of hidden cracks after cutting brittle thin sheet materials, possessing technical advantages such as high-contrast imaging, high recognition accuracy, and high detection efficiency. Firstly, the eccentric illumination method significantly enhances the brightness difference of the crack reflection signal, improving the ability to reveal hidden cracks. Secondly, multi-directional automatic illumination and grayscale difference analysis standardize and quantify the judgment process, ensuring detection consistency. Thirdly, the system can complete full-field detection without mechanical adjustment, making it suitable for online rapid detection applications on continuous production lines.

[0076] In this embodiment, the process of comparing the brightness or performing grayscale difference calculations on two frames of images obtained from opposite illumination directions to obtain a brightness difference distribution map includes the following steps: First, the brightness of images acquired under left-right illumination is compared to detect cracks extending in the vertical direction; second, the brightness of images acquired under up-down illumination is compared to detect cracks extending in the horizontal direction. By distinguishing the correspondence between the illumination direction and the crack orientation, the brightness variation characteristics of cracks in different directions can be extracted respectively.

[0077] During the detection process, the system first illuminates the left light source group 220 and acquires an image, then illuminates the right light source group 220 and acquires a second frame image. Since the vertical cracks exhibit bright and dim reflection responses under the left and right illuminations respectively, the brightness difference in this area between the two frames is significantly higher than that of the background area. Therefore, the brightness distribution of the vertical cracks can be obtained through grayscale difference between the two frames. Similarly, when the system sequentially illuminates the upper and lower light source groups 220, the horizontal cracks exhibit opposite brightness changes under the upper and lower illuminations. The brightness difference features of the horizontal cracks can be extracted by the difference between the corresponding two frames.

[0078] The design of this detection step utilizes the difference in reflection from the incident direction due to the micro-tilt angle of the crack surface, allowing cracks with different orientations to produce maximum brightness contrast under corresponding directional illumination. By dividing the calculation path according to the illumination direction, the directional identification of cracks in both horizontal and vertical directions can be achieved simultaneously, while maintaining the simplicity and efficiency of the judgment logic.

[0079] The configuration of this embodiment enables the system to extract crack feature signals from different directions based on multi-directional illumination acquisition. This improves the targeting of brightness difference calculation and avoids mutual interference between crack signals from different directions in a single differential operation, thereby enhancing the resolution and reliability of the detection results. Through this direction-corresponding brightness difference calculation, the device can more accurately identify the types of cracks generated by different cutting directions, providing a clear directional basis for subsequent brightness distribution fusion and comprehensive judgment.

[0080] In this embodiment, the judgment based on the brightness changes of each region in the brightness difference distribution map includes the following steps: when the brightness of the same location shows a significant reversal or difference under opposite lighting directions, the region is determined to be a dark crack; when the brightness of the same location remains basically consistent under different lighting directions, the region is determined to be a cutting channel.

[0081] During the detection process, the system first performs grayscale difference analysis on two frames of images obtained under left-right or top-bottom illumination to generate a brightness difference distribution map. Then, it compares the brightness changes under different illumination directions for each pixel or region. If a pixel is bright under one illumination direction but dim under the opposite direction, it indicates that the surface at that location has a strong reflection direction dependence on the incident direction, a typical characteristic of dark crack reflection. Conversely, if the brightness at that location remains approximately constant under multi-directional illumination, it indicates that the surface of that area is smooth and the reflection is stable, typically a cut or normal surface.

[0082] This judgment process is based on the optical reflection mechanism of cracks in brittle materials. Dark cracks form in areas of concentrated cutting stress, and their cross-sections exhibit slight tilt angles or differences in opening morphology, resulting in significant variations in the reflection intensity of incident light from different directions, thus manifesting as a reversal in brightness distribution. In contrast, cutting tracks are smooth grooves formed during processing, and their reflective surface remains consistently aligned with the incident direction, without significant brightness fluctuations. Utilizing this physical principle, cracks and cutting tracks can be accurately distinguished by the magnitude and directional characteristics of brightness variations.

[0083] The design concept of this embodiment is to use changes in optical brightness as the criterion for crack identification, rather than relying on image morphology or geometric features, thereby achieving a direct physical determination of the existence of cracks. This method has the advantages of objective judgment criteria, simple algorithm implementation, and strong robustness, and is suitable for detection needs under different workpiece materials and different cutting methods.

[0084] By adopting the above steps, this embodiment effectively avoids misjudgment caused by similar morphology and realizes highly reliable crack identification based on the brightness reversal law; the system can stably obtain brightness difference signals under multi-directional illumination switching conditions, thereby improving detection accuracy and repeatability, and providing quantifiable judgment basis and standardized process for dark crack imaging detection.

[0085] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for imaging and detecting hidden cracks after cutting brittle thin sheet materials, characterized in that, include: A camera (100) is used to acquire an image of the surface of the workpiece to be tested; A coaxial eccentric illumination source (200) is set to the side of the camera (100) and guides the illumination light into a direction coaxial with the imaging optical axis of the camera (100) through an optical reflection and lens assembly. It is used to provide multi-directional eccentric illumination to the surface of the workpiece to be tested, so that the cracks on the surface of the workpiece exhibit different optical reflection brightness under different illumination directions. The coaxial eccentric lighting source (200) includes a lamp panel (210) and a light-diffusing component (300). The lamp panel (210) is provided with two or more independent light sources (220). The light sources (220) are symmetrically distributed along the center of the lamp panel (210). Each group of light sources (220) can be lit sequentially or alternately to produce eccentric lighting light in different directions. The light homogenizing component (300) is disposed in front of the light-emitting end of the lamp plate (210) and is used to spatially homogenize and directionally shape the light emitted by each light source (220) so that the brightness distribution is uniform and the irradiation angle is consistent when the shaped light shines on the workpiece under test.

2. The imaging detection device for dark cracks after cutting brittle thin plate materials according to claim 1, characterized in that, The lamp panel (210) is provided with left and right light source (220) groups and upper and lower light source (220) groups, and the four light sources (220) are centrally symmetrically distributed around the center point of the lamp panel (210).

3. The imaging detection device for dark cracks after cutting brittle thin plate materials according to claim 1, characterized in that, The light homogenizing component (300) includes an integrating bar (310), which is located in front of the light source (220) of the lamp panel (210) and is used to perform spatial mixing and homogenization of the light emitted by the corresponding light source (220).

4. The imaging detection device for dark cracks after cutting brittle thin plate materials according to claim 3, characterized in that, The light-diffusing component (300) includes a light-diffusing plate (220) located in front of the integrating bar (310) for further smoothing the light intensity distribution and eliminating local bright spots.

5. The imaging detection device for dark cracks after cutting brittle thin plate materials according to claim 4, characterized in that, The light homogenizing component (300) includes two collimating lenses (330). The two collimating lenses (330) are arranged in front of the light homogenizing plate (220) to collimate the homogenized light into approximately parallel light so as to illuminate the surface of the workpiece under test along the imaging optical axis of the camera (100).

6. The imaging detection device for dark cracks after cutting brittle thin plate materials according to any one of claims 1, characterized in that, It also includes an optical path synthesis module, which includes a semi-transparent mirror disposed below the camera (100) for refracting the illumination light into the optical axis direction of the camera (100) and allowing the reflected light from the workpiece under test to be transmitted into the camera (100) to achieve coaxial synthesis of the illumination optical path and the imaging optical path.

7. A method for detecting dark cracks after cutting brittle thin sheet materials, applied to the detection device described in any one of claims 1-6, characterized in that, Includes the following steps: After the workpiece to be tested is fixed on the testing platform, the imaging optical axis of the camera (100) is vertically aligned with the surface of the workpiece to be tested. Each light source (220) group in the coaxial eccentric illumination source (200) is lit sequentially, and the corresponding surface reflection image is captured by the camera (100) when only a single light source (220) group is lit at a time; By comparing the brightness or performing grayscale difference operations on two frames of images obtained from opposite lighting directions, a brightness difference distribution map is obtained. The judgment is based on the brightness changes in each region of the brightness difference distribution map; Based on the judgment result, crack distribution information or alarm signals are output to realize automatic detection of the cut workpiece.

8. The detection method according to claim 7, characterized in that, The step of comparing the brightness or performing grayscale difference operations on two frames of images obtained from opposite lighting directions to obtain a brightness difference distribution map includes the following steps: Brightness comparison is performed on images acquired under left and right illumination to detect cracks along the vertical direction; brightness comparison is performed on images acquired under top and bottom illumination to detect cracks along the horizontal direction.

9. The detection method according to claim 8, characterized in that, The determination based on the brightness variation of each region in the brightness difference distribution map includes the following steps: When the brightness of the same location shows a significant reversal or difference under opposite lighting directions, the region is determined to be a dark crack; When the brightness of the same location remains basically consistent under different lighting directions, the region is determined to be a cutting channel.

Images