Foreign body inspection equipment

Abstract

To improve the accuracy of detecting foreign matter that is included in a test object having a planar light source.SOLUTION: An imaging device 10 generates a first measurement image which is composed of the luminance value of light emitted from a planar light source 52 which is a test object 1. A wavelength selection filter 21 is located between the planar light source 52 and the imaging device 10 in the imaging direction of the imaging device 10. A control device 11 detects foreign matter of the test object 1 using a measurement image. In a specific wavelength region, the intensity of spectral characteristic of the planar light source 52 is larger than the intensity of spectral characteristic of foreign matter. The wavelength selection filter 21 does not allow light of a specific wavelength region to pass through and allows light not included in the specific wavelength region to pass through.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a foreign matter inspection device that inspects an object to be inspected, having a surface light source, for the presence or absence of foreign matter. [Background technology]

[0002] Conventionally, foreign matter inspection devices that inspect an object having a surface light source for the presence of foreign matter have been known. For example, Japanese Patent Application Laid-Open No. 2008-170325 (Patent Document 1) discloses a stain defect detection device that detects display defects in liquid crystal panels. In an image of a liquid crystal panel captured by a CCD camera, the stain defect detection device compares the difference and ratio between the average brightness value of a given pixel and the brightness value of the given pixel, the difference and ratio being located at point symmetric positions about the given pixel and a predetermined distance apart, with predetermined thresholds, to comprehensively determine whether the liquid crystal panel has a stain defect based on the size and contrast of the given pixel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-170325 Summary of the Invention [Problem to be solved by the invention]

[0004] The average luminance value of two point-symmetric pixels calculated by the stain defect detection device disclosed in Patent Document 1 is likely to vary depending on the predetermined value of the distance between the two pixels, and therefore, the accuracy of stain defect detection may decrease depending on the distance between the two pixels.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to improve the detection accuracy of foreign matter contained in an inspection object having a planar light source. [Means for solving the problem]

[0006] A foreign matter inspection device according to the present disclosure inspects an inspection object having a surface light source for the presence of foreign matter. The foreign matter inspection device includes a first imaging device, a first wavelength-selective filter, and a control device. The first imaging device generates a first measurement image composed of luminance values ​​of light emitted from the surface light source. The first wavelength-selective filter is disposed between the surface light source and the first imaging device in a first imaging direction of the first imaging device. The control device controls the first imaging device and the inspection object and detects foreign matter using the first measurement image. In a specific wavelength range, the intensity of the spectral characteristics of the surface light source is greater than the intensity of the spectral characteristics of the foreign matter. The first wavelength-selective filter does not pass light in the specific wavelength range but passes light not included in the specific wavelength range. [Effects of the Invention]

[0007] According to the foreign matter inspection device according to the present disclosure, the first wavelength-selective filter can improve the detection accuracy of foreign matters contained in an inspection object having a planar light source. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing the configuration of a foreign matter inspection device according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of the lighting fixture of FIG. [Figure 3] 2 is a diagram showing an example of the spectral characteristics of the secondary surface light source of FIG. 1 and an example of the spectral transmission characteristics of the wavelength selection filter of FIG. [Figure 4] FIG. 2 is a block diagram showing the functional configuration of the control device of FIG. 1. [Figure 5] 2 is a diagram showing an example of a measurement image input from a camera 10 to the control device of FIG. 1. [Figure 6] FIG. 6 is a diagram showing the luminance distribution between the two pixels in FIG. 5. [Figure 7] 5 is an example of a reference image generated by the reference image generating unit of FIG. 4. [Figure 8] FIG. 8 is a diagram showing the luminance distribution between the two pixels in FIG. 7. [Figure 9] 8 is a diagram showing an example of a difference image between the measurement image in FIG. 5 and the reference image in FIG. 7. FIG. [Figure 10] 10 is a diagram showing an example of a distribution of gray level differences between two pixels in the difference image of FIG. 9. FIG. [Figure 11] FIG. 10 is a diagram showing an example of a binarized image of the difference image of FIG. 9. [Figure 12] 12 is a diagram showing an example of a detection distribution between two pixels in the binarized image of FIG. 11. FIG. [Figure 13] FIG. 10 is a diagram showing an example of the correlation between the visual size and the camera-detected size under optimal conditions. [Figure 14] FIG. 2 is a hardware configuration diagram of the control device of FIG. [Figure 15] FIG. 10 is a diagram showing the configuration of a foreign matter inspection device according to a second embodiment. [Figure 16] FIG. 16 is a block diagram showing the functional configuration of the control device of FIG. 15. [Figure 17] FIG. 16 is a diagram showing an example of a measurement image input from a camera to the control device of FIG. 15. [Figure 18] FIG. 18 is a diagram showing the luminance distribution between the two pixels in FIG. 17. [Figure 19] 16 is a diagram showing an example of a measurement image input from a camera to the control device of FIG. 15. FIG. [Figure 20] FIG. 20 is a diagram showing the luminance distribution between the two pixels in FIG. 19. [Figure 21] 16 is a diagram showing an example of a measurement image input from a camera to the control device of FIG. 15. FIG. [Figure 22] FIG. 22 is a diagram showing the luminance distribution between the two pixels in FIG. 21. [Figure 23] 20 is a diagram showing a converted image generated from the measurement image of FIG. 19 by an image shape conversion unit. FIG. [Figure 24] 22 is a diagram showing a converted image generated by an image shape conversion unit from the measurement image of FIG. 21. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and their description will not be repeated in principle.

[0010] Embodiment 1 Fig. 1 is a diagram showing the configuration of a foreign substance inspection device 100 according to embodiment 1. In Fig. 1, the X-axis, Y-axis, and Z-axis are perpendicular to one another. The same applies to Figs. 2, 5, 7, 9, 11, 15, 17, 19, 21, 23, and 24, which will be described later.

[0011] As shown in FIG. 1, the foreign matter inspection device 100 includes a housing 101, a camera 10 (first image capture device), a wavelength-selective filter 21 (first wavelength-selective filter), and a control device 11. The foreign matter inspection device 100 inspects whether or not a foreign matter is present in a lighting fixture 1 (inspection target) having primary light sources 2a and 2b. The housing 101 accommodates the camera 10, the wavelength-selective filter 21, and a secondary surface light source 52 (surface light source) of the lighting fixture 1. The lighting fixture 1 is disposed at a predetermined position in the housing 101. The lighting fixture 1 includes, for example, a display device having a liquid crystal panel. The housing 101 blocks external light other than that from the lighting fixture 1 from entering the interior of the housing 101. The inner walls of the housing 101 are blackened to prevent stray light due to reflection within the housing 101.

[0012] First, we will explain the configuration of lighting fixture 1. Figure 2 is a diagram showing the configuration of lighting fixture 1 in Figure 1. As shown in Figure 2, lighting fixture 1 includes primary light sources 2a and 2b, a scattering plate 3, a reflecting plate 4, frames 5a and 5b, and a lighting driver 6.

[0013] The scattering plate 3 extends in the X-axis direction and has a front surface 3a and a back surface 3b that face each other in the Z-axis direction. The scattering plate 3 guides light. The scattering plate 3 is formed from a transparent resin plate and contains minute scattering particles 3d. The scattering plate 3 includes a transparent member (for example, a transparent resin plate) that transmits visible light. The transparent member contains minute scattering particles 3d on the nano-order whose particle diameter is smaller than the wavelength of visible light. The scattering particles 3d are, for example, inorganic oxides such as ZnO, TiO2, ZrO2, SiO2, or Al2O3.

[0014] The primary light sources 2a and 2b are arranged at both ends of the scattering plate 3, facing each other in the X-axis direction. Each of the primary light sources 2a and 2b emits visible light 51 toward the scattering plate 3. Examples of the primary light sources 2a and 2b include LEDs (Light Emitting Diodes).

[0015] The reflector 4 reflects the light that has passed through the rear surface 3b of the scattering plate 3 and returns the light to the scattering plate 3. An example of the reflector 4 is a white reflective sheet. The frames 5a and 5b connect the primary light sources 2a and 2b, the scattering plate 3, and the reflector 4 to one another so that they are held in predetermined positions. The illumination driver 6 controls each of the primary light sources 2a and 2b to control the amount of light emitted from the primary light sources.

[0016] Visible light 51 is emitted from each of the primary light sources 2a and 2b toward the scattering plate 3. When the visible light 51 hits scattering particles 3d while passing through the scattering plate 3, Rayleigh scattering occurs. As a result, the scattered light of the visible light 51 is diffused in all directions.

[0017] When scattered visible light 51 strikes the rear surface 3b of the scattering plate 3, the component of the scattered light whose angle of incidence on the rear surface 3b is smaller than the critical angle with respect to air passes through the rear surface 3b of the scattering plate 3. The light that has passed through the rear surface 3b of the scattering plate 3 is returned to the interior of the scattering plate 3 by the reflector 4, thereby preventing light loss due to scattering. The critical angle is the smallest angle of incidence at which total reflection occurs at the boundary between two media when light travels from a medium with a high refractive index to a medium with a low refractive index.

[0018] When scattered light hits the surface 3a of the scattering plate 3, the component of the scattered light whose angle of incidence on the surface 3a is smaller than the critical angle with respect to air passes through the surface 3a and forms a planar secondary surface light source 52 outside the lighting fixture 1.

[0019] Referring again to FIG. 1, the foreign matter inspection device 100 judges whether the lighting device 1 is good or bad depending on the number of foreign matters present in the secondary surface light source 52 of the lighting device 1. The camera 10 is disposed to face the secondary surface light source 52 in the Z-axis direction. That is, the imaging direction Dr1 of the camera 10 is parallel to the Z-axis and perpendicular to the secondary surface light source 52 at point 3c (specific point) on the secondary surface light source 52. Point 3c is, for example, the center point of the secondary surface light source 52. The camera 10 generates a measurement image (first measurement image) composed of luminance values ​​of light emitted from the secondary surface light source 52. The imaging range Ir1 of the camera 10 includes the secondary surface light source 52. The camera 10 includes a monochrome image sensor 20. The image sensor 20 may be, for example, a monochrome CCD (Charge Coupled Device).

[0020] The wavelength-selective filter 21 is disposed between the camera 10 and the secondary surface light source 52 in the imaging direction Dr1, and includes the imaging range Ir1 of the camera 10. Light from the secondary surface light source 52 is incident on the camera 10 via the wavelength-selective filter 21. The camera 10 captures an image of the luminance distribution (measurement image) of the secondary surface light source 52 via the wavelength-selective filter 21. The camera 10 outputs a signal corresponding to the captured measurement image to the control device 11.

[0021] Regarding the image sensor 20, a CCD that includes RGB (Red-Green-Blue) color filters, such as a Bayer type, has the disadvantage that the resolution decreases due to the interpolation process between pixels, while a three-chip CCD that separates light into RGB, such as a prism type, maintains the resolution but is expensive.

[0022] Monochrome CCDs are known as CCDs that maintain resolution while being relatively low cost. Since the input information to a monochrome CCD is a luminance distribution, it is possible to extract luminance differences from images captured by a monochrome CCD. However, it is not possible to extract color differences from the image.

[0023] If a foreign object with a relatively low contrast exists within the secondary surface light source 52 and has a different color from the entire surface-shaped secondary surface light source 52, the foreign object can be visually identified because the color of the foreign object differs from the color of the surrounding area. On the other hand, foreign object inspection of an image captured by a monochrome CCD uses the luminance difference between each of multiple pixels contained in the image. Therefore, it is often difficult to achieve the same accuracy in foreign object inspection of an image captured by a monochrome image sensor 20 as in visual foreign object inspection, which can also focus on the color difference between the foreign object and its surrounding area.

[0024] Therefore, in the foreign matter inspection device 100, a wavelength-selective filter 21 that blocks light in a specific wavelength range is disposed between the secondary surface light source 52 and the camera 10 in the imaging direction of the camera 10. In the specific wavelength range, the intensity of the spectral characteristics of the secondary surface light source 52 is greater than the intensity of the spectral characteristics of the foreign matter. Conversely, in wavelength ranges other than the specific wavelength range, the intensity of the spectral characteristics of the secondary surface light source 52 is less than the intensity of the spectral characteristics of the foreign matter. By blocking light in the specific wavelength range from entering the camera 10 using the wavelength-selective filter 21, the difference in luminance between pixels corresponding to foreign matters and pixels not corresponding to foreign matters increases in the image captured by the image sensor 20. In other words, the color difference between the foreign matter and its surroundings is reflected in the luminance difference between pixels corresponding to the foreign matter and pixels not corresponding to the foreign matter, so that pixels corresponding to the foreign matter are emphasized more than pixels not corresponding to the foreign matter in the image captured by the image sensor 20. As a result, the accuracy of foreign matter detection using the image can be improved.

[0025] Fig. 3 is a diagram showing an example of the spectral characteristics (relationship between the wavelength and spectral intensity of light emitted from the secondary surface light source 52) of the secondary surface light source 52 in Fig. 1, as well as an example of the spectral transmission characteristics (relationship between the wavelength and transmittance of light received by the wavelength selection filter 21) of the wavelength selection filter 21 in Fig. 1. In the spectral characteristics of the secondary surface light source 52, the solid line represents the average spectral characteristics of the entire secondary surface light source 52, and the dotted line represents the spectral characteristics of foreign matter of different hues present in the secondary surface light source 52.

[0026] As shown in FIG. 3, in the spectral characteristics of the secondary surface light source 52, the spectral intensity of the foreign matter (dotted line) is relatively lower than the spectral intensity of the secondary surface light source 52 (solid line) in the blue wavelength range Rng1 (specific wavelength range). The specific wavelength range is, for example, a blue wavelength range of 430 nm to 490 nm. Conversely, in wavelength ranges longer than the wavelength range Rng1 (green and red wavelength ranges), the spectral intensity of the foreign matter is relatively higher than the spectral intensity of the secondary surface light source 52. In the spectral transmission characteristics of the wavelength-selective filter 21, the transmittance in the wavelength range Rng1 is 0. That is, the wavelength-selective filter 21 blocks light in the wavelength range Rng1 and transmits light with wavelengths longer than the wavelength range Rng1. In the light that has passed through the wavelength-selective filter 21, the degree of reduction in luminance in areas other than the area corresponding to the foreign matter is greater than the degree of reduction in luminance in the area corresponding to the foreign matter. In the camera 10, a luminance distribution in which color difference is added to luminance difference is input to the image sensor 20. As a result, in the image captured by the imaging element 20, pixels corresponding to foreign matter are emphasized more than pixels not corresponding to foreign matter.

[0027] FIG. 4 is a block diagram showing the functional configuration of the control device 11 in FIG. 1. The control device 11 may be, for example, a personal computer that reads and executes a predetermined program (e.g., a foreign substance inspection program). As shown in FIG. 4, the control device 11 includes an imaging control unit 12, an illumination control unit 13, an image processing unit 14, and a parameter setting unit 19. The imaging control unit 12 controls the camera 10 in the foreign substance inspection device 100. The illumination control unit 13 controls the lighting fixture 1. The image processing unit 14 processes the measurement image (input image) input to the control device 11 from the camera 10. The parameter setting unit 19 stores, for example, standard values ​​for foreign substances and desired brightness level information for the input image.

[0028] The image processing unit 14 includes an image storage unit 15, a reference image generation unit 16, a foreign matter detection unit 17, and a foreign matter determination unit 18. The image storage unit 15 temporarily stores image data such as measurement images. The reference image generation unit 16 estimates an ideal image (reference image) when no foreign matter is present from the input image and generates it. The foreign matter detection unit 17 compares the input image with the reference image to detect foreign matter in the input image. The foreign matter determination unit 18 determines the pass / fail of the inspection object based on the foreign matter detected by the foreign matter detection unit 17.

[0029] The measurement image captured by the imaging control unit 12 is input to the image processing unit 14. The image processing unit 14 stores the input measurement image in the image storage unit 15. The image processing unit 14 compares the brightness of the lighting device 1 (the central or average gradation data of the measurement image) with the desired gradation range recorded in the parameter setting unit 19. If the brightness of the lighting device 1 is not within the desired gradation range, the lighting control unit 13 adjusts the brightness of the lighting device 1 so that the brightness of the lighting device 1 falls within the desired gradation range by sending a signal to the lighting driving unit 6 of the lighting device 1 to control the brightness.

[0030] Next, the operation of the reference image generation unit 16 will be described using FIGS. 5 to 8. FIG. 5 is a diagram showing an example of a measurement image input from the camera 10 to the control device 11 in FIG. 1. In FIG. 5, the coordinates of pixels A, A1, and A2 are (X3, Y2), (X1, Y2), and (X5, Y2), respectively. Also, the coordinates of pixels B, C, D, and E are (X2, Y3), (X4, Y3), (X4, Y1), and (X2, Y1), respectively (X1 < X2 < X3 < X4 < X5, Y1 < Y2 < Y3). The quadrilateral BCDE is a square centered on pixel A. FIG. 6 is a diagram showing the luminance distribution between pixels A1 and A2 in FIG. 5.

[0031] Referring to FIGS. 5 and 6, in FIG. 6, the luminance of pixel A (position X3) peaks (is convex) between positions X1 and X5. Pixel A tends to be brighter than its surroundings, so there is a possibility of a foreign object. However, if there is luminance unevenness between positions X1 and X5, the accuracy of determining how much brighter pixel A is than its surroundings (how many gray levels brighter) may decrease. Therefore, in the foreign object inspection device 100, the reference image generation unit 16 calculates the average value of the brightness (luminance) of the pixels included in the positive direction BCDE (surrounding area) centered on pixel A, which includes a part of the area between pixels A1 and A2. This average value is presumed to be the ideal brightness that pixel A should originally have (the brightness when there is no foreign object). The reference image generation unit 16 performs the average value calculation process for all pixels of the measurement image, thereby presuming and generating a reference image when there is no foreign object in the measurement image, and saving it in the image storage unit 15.

[0032] FIG. 7 is an example of a reference image generated by the reference image generation unit 16 in FIG. 4. In FIG. 8, the coordinates of pixels Ar, Ar1, and Ar2 are (X3, Y2), (X1, Y2), and (X5, Y2), respectively. FIG. 8 is a diagram showing the luminance distribution between pixels Ar1 and Ar2 in FIG. 7. Referring to FIGS. 6 to 8, the luminance distribution in FIG. 8 has fewer irregularities than the luminance distribution in FIG. 6.

[0033] The larger the area size of the surrounding area for generating the reference image, the smoother the luminance distribution of the reference image becomes, and the less unevenness there is in the luminance distribution. The area size of the surrounding area is preferably the upper limit size of the foreign matter detection standard. For example, if the foreign matter detection standard is "0.2 mm 2 If the standard is that a product is deemed defective if there is even one of the above foreign objects, the area size of the surrounding area is 0.2 mm 2 It is desirable to set the value to about 10 to 20 times the number of pixels corresponding to the pixel. The shape of the surrounding area of ​​any pixel used to calculate the original brightness of the pixel is not limited to a square, and may be, for example, a circle with the pixel at its center.

[0034] Next, the operation of foreign object detection unit 17 will be described with reference to FIGS. 9 to 12. FIG. 9 is a diagram showing an example of a difference image between the measurement image of FIG. 5 and the reference image of FIG. 7. In FIG. 9, the coordinates of pixels A10, A11, and A12 are (X3, Y2), (X1, Y2), and (X5, Y2), respectively. Foreign object detection unit 17 calculates the absolute value of the difference (tone difference) between the luminance value of each pixel in the measurement image of FIG. 5 and the luminance value of the corresponding pixel in the reference image of FIG. 7, generates the difference image of FIG. 9 in which each pixel has this absolute value, and stores it in image storage unit 15.

[0035] FIG. 10 is a diagram showing an example of the distribution of gradation differences between pixels A11 and A12 in the difference image of FIG. 9. Pixels located at positions with larger gradation differences correspond to foreign objects with higher contrast. As shown in FIG. 10, foreign object detection unit 17 compares the gradation difference of each pixel in the difference image with a predetermined threshold value T. Foreign object detection unit 17 sets pixels whose gradation difference is equal to or greater than threshold value T to 1, and pixels whose gradation difference is less than threshold value T to 0, thereby generating a binarized image and storing it in image storage unit 15.

[0036] FIG. 11 is a diagram showing an example of a binarized image of the differential image in FIG. 9. In FIG. 11, the coordinates of pixels A20, A21, and A22 are (X3, Y2), (X1, Y2), and (X5, Y2), respectively. FIG. 12 is a diagram showing an example of a detection distribution between pixels A21 and A22 in the binarized image of FIG. 11. As shown in FIG. 12, 1 is continuous in the range of positions X3a to X3b (X3a < X3 < X3b) including position X3. The foreign object detection unit 17 detects a group of pixels in which 1 is continuous (a plurality of pixels in the range of positions X31 to X32 between pixels A11 and A12 in FIG. 12) as a candidate for a foreign object.

[0037] The threshold value T is determined from the correlation between the size of a foreign object detected from each of a plurality of samples having foreign objects by visual inspection (visual detection size) and the number of pixels detected as foreign object pixels (camera detection size) by applying the threshold value T to the binarized image derived from the measurement image of the sample. Specifically, by changing the threshold value T as a parameter and comparing the size of the group of pixels detected by the foreign object detection unit 17 for each threshold value T with the size of the pixels detected by visual inspection, the optimal condition that maximizes the correlation is determined, and the threshold value T is selected to satisfy the optimal condition. FIG. 13 is a diagram showing an example of the correlation between the visual size and the camera detection size under the optimal condition. As shown in FIG. 13, the correlation between the camera detection size and the visual size is approximated as a straight line C1. In addition, in the selection of the threshold value T, the need for correlation accuracy of foreign objects smaller than the lower limit size of the foreign object determination standard and foreign objects larger than the upper limit size is low. Therefore, it is desirable that the optimal condition is a condition with a high correlation for foreign objects within the range of not less than the lower limit size and not more than the upper limit size.

[0038] Next, the operation of the foreign matter determination unit 18 will be described. Pass / fail determination data conforming to foreign matter specifications set for each foreign matter size is read from the parameter setting unit 19. Table 1 below shows an example of a foreign matter specification table including pass / fail determination data. The pass / fail determination data records the pass quantity for each foreign matter size range. The foreign matter determination unit 18 classifies foreign matters detected by the foreign matter detection unit 17 in accordance with the pass / fail determination data. For each classified foreign matter size range, the foreign matter determination unit 18 compares the number of detected foreign matters (detected quantity) with the pass quantity. If the detected quantity of foreign matters is equal to or less than the pass quantity in all classifications, the foreign matter determination unit 18 determines the inspection object as a non-defective product, and if the detected quantity is greater than the pass quantity in even one classification, the foreign matter determination unit 18 determines the inspection object as a defective product.

[0039] [Table 1]

[0040] With the above-described configuration, the foreign matter inspection device 100 detects at least one foreign matter present in the secondary surface light source 52 of the lighting fixture 1. The foreign matter inspection device 100 determines the pass / fail of the inspection object by counting the number of foreign matters included in each foreign matter classification. In the first embodiment, a case where one type of wavelength-selective filter is used has been described. If multiple types of color tones are expected for foreign matters included in the inspection object, multiple wavelength-selective filters having spectral characteristics corresponding to the multiple types may be used. Specifically, the wavelength-selective filters that transmit light may be switched in order by a switching device (not shown), and the visible light from the secondary surface light source 52 may be measured, and the pass / fail of the inspection object may be determined for each wavelength-selective filter.

[0041] FIG. 14 is a hardware configuration diagram of the control device 11 in FIG. 1. As shown in FIG. 14, the control device 11 includes a processing circuit 31, a memory 32, an input / output unit 33, and a display unit 34. The processing circuit 31 may include dedicated hardware or a central processing unit (CPU) that executes programs stored in the memory 32. When the processing circuit 31 includes dedicated hardware, the processing circuit 31 may be, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. When the processing circuit 31 includes a CPU, the functions of the control device 11 are realized by software, firmware, or a combination of software and firmware. The CPU is also called a central processing unit, processing device, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor).

[0042] The software or firmware is written as a program and stored in memory 32. Memory 32 stores, for example, software programs for controlling camera 10, controlling lighting fixture 1, and inspecting for foreign objects. Processing circuit 31 executes the programs stored in memory 32. Memory 32 includes non-volatile or volatile semiconductor memory (e.g., random access memory (RAM), read-only memory (ROM), flash memory, erasable programmable read-only memory (EPROM), or electrically erasable programmable read-only memory (EEPROM)), as well as magnetic disks, flexible disks, optical disks, compact disks, minidiscs, or digital versatile disks (DVDs).

[0043] As described above, the foreign matter inspection device according to the first embodiment can improve the detection accuracy of foreign matters contained in an inspection object having a planar light source.

[0044] Embodiment 2 In the first embodiment, a foreign substance inspection apparatus including one imaging device has been described, whereas in the second embodiment, a foreign substance inspection apparatus including multiple imaging devices will be described.

[0045] 15 is a diagram showing the configuration of foreign matter inspection device 200 according to embodiment 2. In the configuration of foreign matter inspection device 200, housing 101 and control device 11 of FIG. 1 are replaced with housing 201 and control device 11a, respectively, and camera 10a (second image capturing device), camera 10b (third image capturing device), wavelength selecting filter 21a (second wavelength selecting filter), and wavelength selecting filter 21b (third wavelength selecting filter) are added. Other than this, the configuration of foreign matter inspection device 200 is the same as the configuration of foreign matter inspection device 100, and therefore description of the similar configuration will not be repeated.

[0046] As shown in Fig. 15, housing 201 houses cameras 10, 10a, and 10b, wavelength-selective filters 21, 21a, and 21b, and secondary surface light source 52 of lighting fixture 1. Lighting fixture 1 is placed at a predetermined position in housing 201. Housing 201 blocks external light other than that from lighting fixture 1 from entering the interior of housing 201. The inner walls of housing 201 are blackened to prevent stray light due to reflection within housing 201.

[0047] The imaging direction Dr2 of the camera 10a is tilted from the imaging direction Dr1 of the camera 10 and intersects with the imaging direction Dr1 at point 3c of the secondary surface light source 52. The imaging range Ir2 of the camera 10a includes the secondary surface light source 52. The camera 10a includes a monochrome imaging element 20a. The imaging element 20a may be, for example, a monochrome CCD.

[0048] The wavelength-selective filter 21a is disposed between the camera 10a and the secondary surface light source 52 in the imaging direction Dr2 and includes the imaging range Ir2 of the camera 10a. Light from the secondary surface light source 52 enters the camera 10a via the wavelength-selective filter 21a. The camera 10a captures an image of the luminance distribution of the secondary surface light source 52 via the wavelength-selective filter 21a. The camera 10a outputs a signal corresponding to the captured measurement image (second measurement image) to the control device 11a.

[0049] The imaging direction Dr3 of camera 10b is tilted from the imaging direction Dr1 of camera 10 and intersects with the imaging direction Dr1 at point 3c of secondary surface light source 52. The imaging range Ir3 of camera 10b includes secondary surface light source 52. Camera 10b includes a monochrome imaging element 20b. The imaging element 20b may be, for example, a monochrome CCD.

[0050] The wavelength-selective filter 21b is disposed between the camera 10b and the secondary surface light source 52 in the imaging direction Dr3 and includes the imaging range Ir3 of the camera 10b. Light from the secondary surface light source 52 enters the camera 10b via the wavelength-selective filter 21b. The camera 10b captures an image of the luminance distribution of the secondary surface light source 52 via the wavelength-selective filter 21b. The camera 10b outputs a signal corresponding to the captured measurement image to the control device 11a.

[0051] The cameras 10a and 10b are arranged to be line-symmetric with respect to the imaging direction Dr1. The spectral transmission characteristics of each of the wavelength selection filters 21a and 21b are the same as the spectral transmission characteristics of the wavelength selection filter 21.

[0052] Fig. 16 is a block diagram showing the functional configuration of the control device 11a of Fig. 15. The functional configuration of the control device 11a is a configuration in which the imaging control unit 12, image processing unit 14, and foreign matter determination unit 18 of Fig. 4 are replaced with an imaging control unit 12a, an image processing unit 14a, and a foreign matter determination unit 18a, respectively. Other than this, the functional configuration of the control device 11a is the same as the functional configuration of the control device 11, and therefore description of the similar functional configuration will not be repeated.

[0053] As shown in FIG. 16, the imaging control unit 12a further includes an exposure time adjustment unit 22. The exposure time adjustment unit 22 adjusts the exposure time of each of the cameras 10a and 10b (the time during which light hits each of the imaging elements 20a and 20b). The image processing unit 14a further includes an image shape conversion unit 23. The image shape conversion unit 23 converts the measurement images captured by each of the cameras 10a and 10b so as to conform to the measurement image captured by the camera 10.

[0054] First, the operation of the exposure time adjustment unit 22 will be described. FIG. 17 is a diagram showing an example of a measurement image input from the camera 10 to the control device 11a in FIG. 15. In FIG. 17, the coordinates of pixels A31 and A32 are (X11, Y10) and (X12, Y10), respectively (X11 < X12). FIG. 18 is a diagram showing the luminance distribution between pixels A31 and A32 in FIG. 17. FIG. 19 is a diagram showing an example of a measurement image input from the camera 10a to the control device 11a in FIG. 15. In FIG. 19, the coordinates of pixels A41 and A42 are (X13, Y10) and (X14, Y10), respectively (X13 < X14). FIG. 20 is a diagram showing the luminance distribution between pixels A41 and A42 in FIG. 19. FIG. 21 is a diagram showing an example of a measurement image input from the camera 10b to the control device 11a in FIG. 15. In FIG. 21, the coordinates of pixels A51 and A52 are (X15, Y10) and (X16, Y10), respectively (X15 < X16). FIG. 22 is a diagram showing the luminance distribution between pixels A51 and A52 in FIG. 21.

[0055] As shown in FIGS. 19 to 22, due to the influence of the light distribution characteristics of the lighting fixture 1, the luminance distribution from the front direction (imaging direction Dr1) differs from the luminance distribution in the oblique direction (imaging direction Dr2 or Dr3). Furthermore, the portion of the secondary surface light source 52 relatively farther from each of the cameras 10a and 10b (the rear side) tends to be brighter than the portion of the secondary surface light source 52 relatively closer to the camera (the front side) due to the influence of light (direct light from the primary light sources 2a and 2b) that passes through the surface 3a of the scattering plate 3 without multiple reflections within the scattering plate 3. For example, in FIG. 20, the luminance at position X14 (pixel A42) on the rear side of the secondary surface light source 52 is higher than the luminance at position X13 (pixel A41) on the front side of the secondary surface light source 52. Furthermore, in FIG. 22, the luminance at position X15 (pixel A51) on the rear side of the secondary surface light source 52 is higher than the luminance at position X16 (pixel A52) on the front side of the secondary surface light source 52.

[0056] 19 and 21, in the measurement images of the secondary surface light source 52 captured by each of the cameras 10a and 10b, the front portion of the secondary surface light source 52 is larger than the rear portion of the secondary surface light source 52. In order to fit the entire secondary surface light source 52 in the measurement image, in FIG. 15, the cameras 10a and 10b are arranged so that the distance L2 from point 3c to the camera 10a and the distance L3 from the camera 10b are each longer than the distance L1 from the point 3c to the camera 10. Note that, in order to fit the entire secondary surface light source 52 in the measurement image, the focal lengths of the lenses mounted on each of the cameras 10a and 10b may be made shorter than the focal length of the lens mounted on the camera 10, thereby making each of the distances L2 and L3 equal to the distance L1.

[0057] With respect to the placement of each of the cameras 10a and 10b, the brightness of the portion behind the secondary surface light source 52 is higher than the brightness of the portion in front of it. If the brightness of the measurement image captured by each of the cameras 10a and 10b is set to the same brightness as the measurement image captured by the camera 10, the brightness of the portion behind the secondary surface light source 52 may exceed the upper limit of the gradation range, resulting in over-gradation, and the portion behind the secondary surface light source 52 may not be captured. Therefore, the desired gradation range for each of the cameras 10a and 10b recorded in the parameter setting unit 19 must be set lower than the desired gradation range for the camera 10. In the foreign substance inspection device 200, the exposure time adjustment unit 22 adjusts the exposure times of the image capturing elements 20a and 20b of the cameras 10a and 10b to be shorter than the exposure time of the image capturing element 20. This adjustment prevents over-gradation in each of the cameras 10a and 10b.

[0058] Other methods for preventing over-gradation include narrowing the aperture of each of cameras 10a and 10b, and increasing the gain of the cameras. The former method results in differences in the depth of field between camera 10 and each of cameras 10a and 10b, resulting in differences in focus performance. The latter method also increases noise components, which can be added to the difference image generated by foreign object detection unit 17, potentially resulting in erroneous detection of foreign objects. Therefore, adjusting the exposure time as described above is a desirable method for preventing over-gradation.

[0059] Next, the operation of the image shape conversion unit 23 will be described. As shown in each of FIGS. 19 and 21, the cameras 10a and 10b are arranged so that the imaging direction of each of the cameras 10a and 10b is oblique to the imaging direction Dr1 of the camera 10. Therefore, the shape of the secondary surface light source 52 captured by the cameras 10a and 10b is a different shape (e.g., a trapezoid) from the shape of the secondary surface light source 52 in the measurement image of the camera 10 (e.g., a square or rectangle). Furthermore, because the distance from each of the cameras 10a and 10b to the front side and the back side of the secondary surface light source 52 differs, the size per pixel of the measurement image differs depending on the position of the secondary surface light source 52. Therefore, it is not possible to directly measure the size of a foreign object from the measurement images of the cameras 10a and 10b. Therefore, in the foreign substance inspection apparatus 200, the image shape conversion unit 23 converts the measurement images captured by each of the cameras 10a and 10b to generate converted images in which the shape of the secondary surface light source 52 in the measurement images is adapted to the shape of the secondary surface light source 52 in the measurement images captured by the camera 10. That is, the image shape conversion unit 23 converts the secondary surface light source 52 in each of the measurement images captured by the cameras 10a and 10b so that it has the same shape and size as the secondary surface light source 52 in the measurement image captured by the camera 10. By converting the trapezoidal shape in the measurement image by the image shape conversion unit 23 into a square or rectangular shape, the size per pixel in the converted measurement image becomes uniform. FIG. 23 is a diagram showing a converted image generated by the image shape conversion unit 23 from the measurement image of FIG. 19. FIG. 24 is a diagram showing a converted image generated by the image shape conversion unit 23 from the measurement image of FIG. 21.

[0060] One method for converting a trapezoidal measurement image into a rectangular or square shape is to detect the four sides of the measurement image. In this method, the intersections of the sides of the trapezoidal shape included in the measurement image to be converted (e.g., the measurement images from cameras 10a and 10b) are considered to be the four corner vertices. In this method, the luminance distribution in the measurement image to be converted is interpolated so that the coordinates of the four corner vertices match the coordinates of the four corner vertices of a rectangle or square included in the target measurement image (e.g., the measurement image from camera 10).

[0061] Camera 10 captures a measurement image and outputs a signal corresponding to the measurement image to control device 11a. Each of cameras 10a and 10b captures a measurement image with the exposure time adjusted by exposure time adjustment unit 22 and outputs a signal corresponding to the measurement image to control device 11a. Control device 11a stores the measurement images received from each of cameras 10, 10a, and 10b in image storage unit 15.

[0062] The image shape conversion unit 23 compares the measurement image of camera 10 stored in the image storage unit 15 with the measurement images of cameras 10a and 10b. The image shape conversion unit 23 converts the shape of each of the measurement images of cameras 10a and 10b so that the vertices of the four corners of surface 3a in each of the measurement images of cameras 10a and 10b match the vertices of the four corners of surface 3a in the measurement image of camera 10. The image shape conversion unit 23 stores the converted measurement images (converted images) of cameras 10a and 10b in the image storage unit 15.

[0063] The measurement image from camera 10 and the converted images from cameras 10a and 10b stored in image storage unit 15 are processed by reference image generator 16 and foreign matter detector 17. As a primary judgment, foreign matter determiner 18a judges whether the inspection object is pass / fail for the measurement image from camera 10 and the converted images from cameras 10a and 10b. As a comprehensive judgment, foreign matter determiner 18a judges the inspection object as a defective product if it judges it as a defective product for at least one measurement image, and judges it as a pass / fail product if it judges it as a non-defective product for all measurement images.

[0064] As described above, the foreign matter inspection device 200 detects foreign matter present in the secondary surface light source 52 of the lighting device 1 from multiple imaging directions and counts the quantity of each classification of foreign matter according to its size for each imaging direction, thereby comprehensively determining the quality of the lighting device 1. Since the foreign matter inspection device 200 detects foreign matter from multiple measurement images captured from multiple imaging directions, it is possible to further improve the foreign matter detection accuracy compared to the foreign matter inspection device of embodiment 1.

[0065] The exposure time may be adjusted for the camera 10 arranged in front of the surface 3a, in addition to the cameras 10a and 10b arranged obliquely with respect to the secondary surface light source 52. By adjusting the exposure time for the camera 10 as well, it becomes possible to capture an image of the secondary surface light source 52 without being affected by the brightness of the lighting device 1.

[0066] As described above, the foreign matter inspection device according to the second embodiment can further improve the detection accuracy of foreign matters contained in an inspection object having a planar light source compared to the first embodiment.

[0067] The embodiments disclosed herein are intended to be combined as appropriate within the scope of compatibility. The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0068] 1 lighting fixture, 2a, 2b primary light source, 3 scattering plate, 3a surface, 3b back surface, 3c point, 3d scattering particle, 4 reflector, 5a, 5b frame, 6 lighting drive unit, 10, 10a, 10b camera, 11, 11a control device, 12, 12a imaging control unit, 13 lighting control unit, 14, 14a image processing unit, 15 image memory unit, 16 reference image generation unit, 17 foreign object detection unit, 18, 18a foreign object determination unit, 19 parameter setting unit, 20, 20a, 20b imaging element, 21, 21a, 21b wavelength selection filter, 22 exposure time adjustment unit, 23 image shape conversion unit, 31 processing circuit, 32 memory, 33 input / output unit, 34 display unit, 51 visible light, 52 secondary surface light source, 100, 200 Foreign substance inspection device, 101, 201 housing, A, A1, A2, A10 to A12, A20 to A22, A31, A32, A41, A42, A51, A52, Ar, Ar1, Ar2, B to E pixels, C1 line, Dr1 to Dr3 imaging direction, Ir1 to Ir3 imaging range, L1 to L3 distance, Rng1 wavelength range, T threshold, X1, X3b, X3, X3a, X5, X13 to X16, X31, X32 position.

Claims

1. A foreign matter inspection device that inspects whether or not a foreign matter is present in an inspection object having a surface light source, a first imaging device that generates a first measurement image composed of luminance values ​​of light emitted from the planar light source; a first wavelength selection filter disposed between the surface light source and the first imaging device in a first imaging direction of the first imaging device; an image processing unit that detects the foreign matter using the first measurement image, In a first wavelength range, the intensity of the spectral characteristic of the surface light source is greater than the intensity of the spectral characteristic of the foreign matter; In a second wavelength range not included in the first wavelength range, the intensity of the spectral characteristic of the surface light source is smaller than the intensity of the spectral characteristic of the foreign matter; The first wavelength selection filter blocks light in the first wavelength range and passes light in the second wavelength range.

2. 2. The foreign matter inspection device according to claim 1, wherein the image processing unit calculates, for each of a plurality of pixels included in the first measurement image, an average value of a plurality of luminance values ​​included in a predetermined region including the pixel, generates a difference image having an absolute value of a difference between the luminance value of the pixel and the average value as a difference value for the position of the pixel, and detects the foreign matter using the difference image.

3. a housing that houses the first imaging device, the first wavelength selection filter, and the surface light source; 3. The foreign matter inspection device according to claim 1, wherein an inner wall of the housing is subjected to a blackening treatment.

4. a second imaging device that generates a second measurement image composed of luminance values ​​of light emitted from the planar light source; a second wavelength selection filter disposed between the surface light source and the second imaging device in a second imaging direction of the second imaging device, the image processing unit detects the foreign matter using the first measurement image and the second measurement image; 4. The foreign matter inspection device according to claim 1, wherein the second wavelength selection filter does not pass light in the first wavelength range but passes light in the second wavelength range.

5. the first imaging direction is perpendicular to the surface light source; The foreign matter inspection device according to claim 4 , wherein the second imaging direction is inclined from the first imaging direction.

6. each of the first imaging device and the second imaging device includes an imaging element; 6. The foreign matter inspection apparatus according to claim 5, further comprising an imaging control unit that sets an exposure time of the imaging element of the second imaging device to be shorter than an exposure time of the imaging element of the first imaging device.

7. 7. The foreign matter inspection device according to claim 5, wherein the image processing unit converts the second measurement image to generate a converted image in which a shape of the surface light source in the second measurement image is adapted to a shape of the surface light source in the first measurement image, and detects the foreign matter using the first measurement image and the converted image.

8. a third imaging device that generates a third measurement image composed of luminance values ​​of light emitted from the planar light source; a third wavelength selection filter disposed between the surface light source and the third imaging device in a third imaging direction of the third imaging device, the image processing unit detects the foreign matter using the first measurement image, the second measurement image, and the third measurement image; the third wavelength selective filter does not pass light in the first wavelength range but passes light in the second wavelength range; the second imaging device and the third imaging device are arranged line-symmetrically with respect to the first imaging direction, 8. The foreign matter inspection device according to claim 5, wherein the first imaging direction, the second imaging direction, and the third imaging direction intersect at a specific point on the surface light source.

Images