Inspection device and inspection method

Abstract

To reduce the effect of hot spots on the inspection of an inspection object.SOLUTION: An inspection device includes an illumination device, an imaging device, and an image processing device having a processor. The image processing device acquires a reference image showing an image of a reference member coaxially illuminated by the illumination device and imaged by the imaging device, acquires an inspection image showing an image of an inspection object coaxially illuminated by the illumination device and imaged by the imaging device, and generates a corrected image by subtracting, for each of a plurality of pixels in the inspection image, the luminance value of a pixel in the reference image that corresponds to the position of the pixel in the inspection image from the luminance value of the pixel in the inspection image.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an inspection device and an inspection method. [Background technology]

[0002] As disclosed in Patent Document 1, an appearance inspection of an industrial product is carried out in the manufacturing process of the industrial product. In the appearance inspection, an inspection target illuminated by an illumination device is imaged by an imaging device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 150607 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a possibility that a hot spot phenomenon will occur, in which an image of the light source of the lighting device is projected onto the surface of the inspection object. If a hot spot phenomenon occurs and a part of the surface of the inspection object becomes bright as a spot, there is a possibility that the inspection object will fail.

[0005] The technology disclosed in this specification aims to reduce the influence of the hot spot phenomenon when inspecting an object to be inspected. [Means for solving the problem]

[0006] This specification discloses an inspection apparatus including an illumination device, an imaging device, and an image processing device having a processor. The image processing device acquires a reference image showing an image of a reference member coaxially illuminated by the illumination device and captured by the imaging device, acquires an inspection image showing an image of an object to be inspected coaxially illuminated by the illumination device and captured by the imaging device, and generates a corrected image by subtracting, for each of a plurality of pixels in the inspection image, the luminance value of a pixel in the reference image corresponding to the position of the pixel in the inspection image from the luminance value of the pixel in the inspection image. [Effects of the Invention]

[0007] According to the technology disclosed in this specification, the influence of the hot spot phenomenon is reduced when inspecting an object to be inspected. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram schematically illustrating an inspection device according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing an inspection device according to an embodiment. [Figure 3] FIG. 3 is a flowchart illustrating a detection method according to an embodiment. [Figure 4] FIG. 4 is a diagram illustrating a method for acquiring a reference image according to the embodiment. [Figure 5] FIG. 5 is a diagram illustrating a method for acquiring an inspection image according to the embodiment. [Figure 6] FIG. 6 is a diagram illustrating a method for generating a corrected image according to the embodiment. [Figure 7] FIG. 7 is a diagram schematically illustrating an image processing apparatus according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment will be described with reference to the drawings. In the embodiment, a local coordinate system, which is an XYZ Cartesian coordinate system, is defined for the inspection device 1, and the positional relationship of each part will be described with reference to the local coordinate system. The direction parallel to the X axis in a horizontal plane is defined as the X axis direction. The direction parallel to the Y axis in the horizontal plane, which is perpendicular to the X axis, is defined as the Y axis direction. The direction parallel to the Z axis, which is perpendicular to the horizontal plane, is defined as the Z axis direction. A plane including the X axis and the Y axis will be referred to as the XY plane as appropriate. The XY plane is parallel to the horizontal plane. The Z axis is parallel to a vertical line. The Z axis direction is the up-down direction. The +Z direction is the upward direction, and the -Z direction is the downward direction.

[0010] [Inspection equipment] 1 is a diagram schematically illustrating an inspection device 1 according to an embodiment. The inspection device 1 is an appearance inspection device that inspects the appearance of an inspection object W. As shown in FIG. 1, the inspection device 1 includes a table 2, an imaging device 3, and an illumination device 4.

[0011] The table 2 supports an inspection object W. The inspection object W includes an industrial product. The industrial product includes a metal product. The industrial product may be a part, a work in progress, or a finished product. An example of an industrial product is an engine cylinder block.

[0012] The imaging device 3 images the inspection object W supported on the table 2. The imaging device 3 images the inspection object W from above. The imaging device 3 has an imaging optical system 5 and an image sensor 6. The imaging optical system 5 has an optical element. The optical axis AX of the imaging optical system 5 is parallel to the Z axis. The image sensor 6 acquires an image of the inspection object W via the imaging optical system 5. Examples of the image sensor 6 include a CCD (Couple Charged Device) image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0013] The lighting device 4 illuminates the inspection object W supported on the table 2 with illumination light. The imaging device 3 captures an image of the inspection object W while the inspection object W is illuminated by the lighting device 4.

[0014] In the embodiment, the illumination device 4 has a coaxial illumination unit 7 and a side oblique illumination unit 8. The coaxial illumination unit 7 coaxially illuminates the inspection object W. Coaxial illumination refers to an illumination method in which illumination light is irradiated onto the inspection object W from a direction parallel to the optical axis AX. The side oblique illumination unit 8 illuminates the inspection object W from a side oblique direction. Side oblique illumination refers to an illumination method in which illumination light is irradiated onto the inspection object W from outside the optical axis AX.

[0015] The coaxial illumination unit 7 has a light source 9 and a half mirror 10. The light source 9 emits illumination light. An example of the light source 9 is a light emitting diode (LED). The light source 9 emits white light as the illumination light. At least a portion of the half mirror 10 is arranged on the optical axis AX. In the embodiment, the half mirror 10 is arranged inside the imaging optical system 5. The illumination light emitted from the light source 9 is reflected by the half mirror 10 and irradiated onto the inspection object W. The illumination light reflected by the inspection object W passes through the imaging optical system 5 and the half mirror 10, and then enters the image sensor 6.

[0016] The side oblique illumination unit 8 includes a light source 11 and a support member 12. The light source 11 emits illumination light. An example of the light source 11 is a light emitting diode (LED). The light source 11 emits white light as illumination light. The light source 11 is ring-shaped and arranged to surround the optical axis AX. In the embodiment, the side oblique illumination unit 8 performs ring illumination, which is a type of side oblique illumination. Ring illumination refers to an illumination method in which illumination light is irradiated onto the inspection object W from the ring-shaped light source 11 arranged to surround the optical axis AX. The optical axis AX of the imaging optical system 5 is arranged inside the annular light source 11. The support member 12 supports the light source 11. The support member 12 is arranged around the light source 11. The upper end of the support member 12 is fixed to the imaging device 3. The lower end of the support member 12 is arranged below the light source 11.

[0017] The side oblique illumination unit 8 has a plurality of light sources 11. The light sources 11 include a first light source 11A having a first inner diameter, a second light source 11B having a second inner diameter larger than the first inner diameter, and a third light source 11C having a third inner diameter larger than the second inner diameter. Of the plurality of light sources 11, the first light source 11A is disposed at a position farthest from the table 2, the second light source 11B is disposed at a position next farthest from the table 2 after the first light source 11A, and the third light source 11C is disposed at a position closest to the table 2.

[0018] When illumination light is emitted from the light source 9 of the coaxial illumination unit 7, illumination light is not emitted from each of the first light source 11A, the second light source 11B, and the third light source 11C. When illumination light is emitted from the first light source 11A, illumination light is not emitted from each of the second light source 11B, the third light source 11C, and the light source 9. When illumination light is emitted from the second light source 11B, illumination light is not emitted from each of the third light source 11C, the light source 9, and the first light source 11A. When illumination light is emitted from the third light source 11C, illumination light is not emitted from each of the light source 9, the first light source 11A, and the second light source 11B.

[0019] [Image processing device] 2 is a block diagram showing the inspection device 1 according to the embodiment. As shown in FIG. 2, the inspection device 1 includes an image processing device 13 and an imaging device 3.

[0020] The image processing device 13 includes a computer, and has a processor 14, a main memory 15, a storage 16, an input / output interface 17, and a communication interface 18.

[0021] The processor 14 includes a CPU (Central Processing Unit). The processor 14 may also include a GPU (Graphics Processing Unit).

[0022] The main memory 15 includes a non-volatile memory such as a read only memory (ROM) and a volatile memory such as a random access memory (RAM).

[0023] The storage 16 is a recording medium that records computer programs and data in a manner that can be read by the processor 14. Examples of the storage 16 include a hard disk or a semiconductor memory. In this embodiment, the storage 16 records an image processing program 19 and an operating system 20 as computer programs.

[0024] The processor 14 reads the image processing program 19 from the storage 16, loads it into the main memory 15, and executes processing in accordance with the image processing program 19. The image processing device 13 performs its functions according to the image processing program 19.

[0025] The input / output interface 17 includes an input / output circuit. The imaging device 3 is connected to the input / output interface 17. The image processing device 13 acquires an image from the imaging device 3 via the input / output interface 17.

[0026] The communication interface 18 communicates via a communication network. An example of the communication interface 18 is a local area network (LAN) module. The image processing device 13 transmits data to an external computer via the communication interface 18 and the communication network. The image processing device 13 receives data from an external computer via the communication network and the communication interface 18. A computer program may be distributed to the image processing device 13 via the communication network.

[0027] [Hot spot phenomenon] When the inspection object W is coaxially illuminated by the coaxial illumination unit 7 of the illumination device 4, a hot spot phenomenon may occur. The hot spot phenomenon is a phenomenon in which an image of the light source 9 of the coaxial illumination unit 7 is projected onto the surface of the inspection object W. The hot spot phenomenon is a phenomenon in which a portion of the surface of the inspection object W becomes locally bright in a spot shape due to the light source 9 when the inspection object W is coaxially illuminated. If a hot spot phenomenon occurs, it may be difficult for the inspection device 1 to properly inspect the inspection object W.

[0028] In the following description, a locally bright spot-like portion generated by the occurrence of a hot spot phenomenon will be referred to as a hot spot portion Hs.

[0029] In the embodiment, even if a hot spot phenomenon occurs when the imaging device 3 captures an image of the inspection object W, the image processing device 13 performs image processing so as to reduce the influence of the hot spot phenomenon.

[0030] [Inspection method] 3 is a flowchart showing a detection method according to an embodiment. As shown in FIG. 3, the image processing device 13 performs the following steps: a process of acquiring a reference image Ma (step S1), a process of acquiring an inspection image Mb (step S2), and a process of calculating the difference between the luminance values ​​of pixels in the reference image Ma and the luminance values ​​of pixels in the inspection image Mb that correspond to each other as an inter-pixel operation between the reference image Ma and the inspection image Mb, thereby generating a corrected image Mc (step S3).

[0031] <Acquisition of reference image Ma> FIG. 4 is a diagram illustrating a method for acquiring a reference image Ma according to an embodiment. In the embodiment, the reference image Ma refers to an image of a reference member that is coaxially illuminated by the coaxial lighting unit 7 of the lighting device 4 and captured by the imaging device 3. The optical reflectance of the surface of the reference member is lower than the optical reflectance of the surface of the inspection object W. The surface of the reference member is a flat surface. In the embodiment, the reference member is a table 2. As shown in FIG. 4, when acquiring the reference image Ma, the inspection object W is not supported on the table 2. The imaging optical system 5 and the surface of the table 2 face each other. The surface of the table 2 is a flat surface. The surface of the table 2 and the optical axis AX are perpendicular to each other.

[0032] With no inspection object W supported on the table 2, illumination light is emitted from the light source 9 of the coaxial illumination unit 7. The table 2 is coaxially illuminated with illumination light of a first intensity. The imaging device 3 captures an image of the surface of the table 2 coaxially illuminated with illumination light of the first intensity. The image processing device 13 acquires a reference image Ma that shows an image of the table 2 coaxially illuminated by the coaxial illumination unit 7 and captured by the imaging device 3.

[0033] As shown in FIG. 4, the occurrence of the hot spot phenomenon may result in the generation of a hot spot Hs in the reference image Ma.

[0034] <Acquisition of inspection image Mb> 5 is a diagram illustrating a method for acquiring an inspection image Mb according to an embodiment. In the embodiment, the inspection image Mb refers to an image of the inspection object W that is coaxially illuminated by the coaxial illumination unit 7 of the illumination device 4 and imaged by the imaging device 3. As shown in FIG. 5, when acquiring the inspection image Mb, the inspection object W is supported on the table 2. The imaging optical system 5 and the surface of the inspection object W supported on the table 2 face each other.

[0035] With the inspection object W supported on the table 2, illumination light is emitted from the light source 9 of the coaxial illumination unit 7. The inspection object W is coaxially illuminated with illumination light of a first intensity. The imaging device 3 images the surface of the inspection object W coaxially illuminated with illumination light of the first intensity. The image processing device 13 acquires an inspection image Mb that shows the image of the inspection object W coaxially illuminated by the coaxial illumination unit 7 and imaged by the imaging device 3.

[0036] As shown in FIG. 5, the occurrence of the hot spot phenomenon may result in the generation of a hot spot Hs in the inspection image Mb.

[0037] <Generation of corrected image Mc> 6 is a diagram illustrating a method for generating a corrected image Mc according to an embodiment. In the embodiment, the corrected image Mc refers to an image obtained by subtracting, for each of a plurality of pixels in the inspection image Mb, the brightness value of a pixel in the reference image Ma corresponding to the position of the pixel in the inspection image Mb from the brightness value of the pixel in the inspection image Mb.

[0038] In the local coordinate system defined in the inspection device 1 (imaging device 3), the position of the reference image Ma and the position of the inspection image Mb are the same. Also, in the local coordinate system, the size and shape of the reference image Ma and the size and shape of the inspection image Mb are the same. The imaging conditions when acquiring the reference image Ma and the imaging conditions when acquiring the inspection image Mb are the same.

[0039] The number of pixels in reference image Ma is the same as the number of pixels in inspection image Mb, and there is a one-to-one correspondence between each of the multiple pixels in reference image Ma and each of the multiple pixels in inspection image Mb.

[0040] When generating the corrected image Mc, the image processing device 13 subtracts the luminance value va of the pixel of the reference image Ma corresponding to the position of the pixel in the inspection image Mb from the luminance value vb of the pixel in the inspection image Mb for each of the multiple pixels in the inspection image Mb to generate the corrected image Mc. That is, the image processing device 13 performs a difference calculation between the luminance value va of the pixel in the reference image Ma and the luminance value vb of the pixel in the inspection image Mb whose pixel values ​​(positions) correspond to each other as an inter-pixel calculation between the reference image Ma and the inspection image Mb to generate the corrected image Mc.

[0041] That is, the image processing device 13 subtracts the luminance value va of the pixel present at the pixel value (x[m], y[n]) of the reference image Ma from the luminance value vb of the pixel present at the pixel value (x[m], y[n]) of the inspection image Mb. Note that x[m] indicates the position of the pixel in the X-axis direction in the local coordinate system, and y[n] indicates the position of the pixel in the Y-axis direction in the local coordinate system. m and n are natural numbers.

[0042] In the graph shown in FIG. 6, the horizontal axis represents pixel values ​​(pixel positions in the image), and the vertical axis represents pixel brightness values. Line La represents the brightness distribution of reference image Ma. Line Lb represents the brightness distribution of inspection image Mb. Line Lc represents the brightness distribution of corrected image Mc. As indicated by lines La and Lb, hotspots Hs, which are areas of locally high brightness, are generated in both reference image Ma and inspection image Mb due to the occurrence of hotspots. By performing a difference calculation, the locally high brightness areas are alleviated in corrected image Mc, as indicated by line Lc. In other words, the effects of the hotspots are reduced in corrected image Mc. By evaluating the appearance of inspection object W based on corrected image Mc in which the effects of the hotspots are reduced, the occurrence of inspection defects for inspection object W is suppressed.

[0043] [Lighting Condition] In the embodiment, the imaging conditions when the imaging device 3 images the table 2 to acquire the reference image Ma are the same as the imaging conditions when the imaging device 3 images the inspection object W to acquire the inspection image Mb. Furthermore, the illumination conditions when the coaxial illumination unit 7 illuminates the table 2 are the same as the illumination conditions when the coaxial illumination unit 7 illuminates the inspection object W. When the table 2 is illuminated with illumination light of a first intensity, the inspection object W is also illuminated with illumination light of the first intensity. When the table 2 is illuminated with illumination light of a second intensity, the inspection object W is also illuminated with illumination light of the second intensity. When the image processing device 13 acquires the reference image Ma of the table 2 coaxially illuminated with illumination light of the first intensity, it acquires the inspection image Mb of the inspection object W coaxially illuminated with illumination light of the first intensity. When the image processing device 13 acquires the reference image Ma of the table 2 coaxially illuminated with illumination light of a second intensity, it acquires the inspection image Mb of the inspection object W coaxially illuminated with illumination light of the second intensity.

[0044] When the intensity of the illumination light emitted from the light source 9 is determined by the current value supplied to the light source 9, the current value supplied to the light source 9 when illuminating the table 2 with the coaxial illumination unit 7 is the same as the current value supplied to the light source 9 when illuminating the inspection object W with the coaxial illumination unit 7.

[0045] FIG. 7 is a diagram schematically illustrating an image processing device 13 according to an embodiment. As shown in FIG. 7, reference images Ma (Ma1, Ma2, Ma3) representing images of the table 2 illuminated with a plurality of illumination lights having different intensities may be stored in advance in the image processing device 13. In the example shown in FIG. 7, the image processing device 13 pre-stores a first reference image Ma1 representing an image of the table 2 illuminated with illumination light of a first intensity, a second reference image Ma2 representing an image of the table 2 illuminated with illumination light of a second intensity, and a third reference image Ma3 representing an image of the table 2 illuminated with illumination light of a third intensity. Note that the number of reference images Ma having different illumination light intensities stored in the image processing device 13 is not limited to three, and may be any number, such as nine.

[0046] When the inspection image Mb is a first inspection image Mb1 captured with illumination light of a first intensity, the image processing device 13 performs a difference calculation between the first reference image Ma1 and the first inspection image Mb1 to generate a corrected image Mc. When the inspection image Mb is a second inspection image Mb2 captured with illumination light of a second intensity, the image processing device 13 performs a difference calculation between the second reference image Ma2 and the second inspection image Mb2 to generate a corrected image Mc. When the inspection image Mb is a third inspection image Mb3 captured with illumination light of a third intensity, the image processing device 13 performs a difference calculation between the third reference image Ma3 and the third inspection image Mb3 to generate a corrected image Mc.

[0047] [effect] As described above, according to the embodiment, the image processing device 13 acquires a reference image Ma showing an image of the table 2, which is a reference member, coaxially illuminated by the lighting device 4 and imaged by the imaging device 3, acquires an inspection image Mb showing an image of the inspection object W, which is coaxially illuminated by the lighting device 4 and imaged by the imaging device 3, and for each of the multiple pixels in the inspection image Mb, subtracts the brightness value of the pixel in the reference image Ma corresponding to the position of the pixel in the inspection image Mb from the brightness value of the pixel in the inspection image Mb to generate a corrected image Mc.

[0048] According to the embodiment, a corrected image Mc is generated by subtracting the luminance value of a pixel in the reference image Ma that corresponds to the position of the pixel in the inspection image Mb from the luminance value of the pixel in the inspection image Mb, thereby reducing the influence of hot spots in the corrected image Mc. By evaluating the appearance of the inspection object W based on the corrected image Mc in which the influence of hot spots has been reduced, the occurrence of inspection defects for the inspection object W is reduced.

[0049] In the embodiment, the table 2 is used as the reference member. As a result, the table 2 does not support the inspection object W, and the image processing device 13 can smoothly acquire the reference image Ma.

[0050] In the embodiment, the optical reflectance of the surface of the table 2, which is the reference member, is lower than the optical reflectance of the surface of the inspection object W. If the optical reflectance of the surface of the table 2 is high, the brightness value of the hot spot Hs generated when the table 2 is coaxially illuminated may saturate, and halation may occur in the reference image Ma. If halation occurs in the reference image Ma, it may be difficult to generate an appropriate corrected image Mc in which the effects of the hot spot phenomenon are reduced. According to the embodiment, halation in the reference image Ma is suppressed, so an appropriate corrected image Mc is generated.

[0051] In the embodiment, when the image processing device 13 acquires a reference image Ma of a reference member coaxially illuminated with illumination light of a first intensity, it acquires an inspection image Mb of an inspection object W coaxially illuminated with illumination light of the first intensity. When the image processing device 13 acquires a reference image Ma of a reference member coaxially illuminated with illumination light of a second intensity, it acquires an inspection image Mb of the inspection object W coaxially illuminated with illumination light of the second intensity. In other words, the corrected image Mc is generated by pixel-to-pixel calculation of the reference image Ma and the inspection image Mb, which are coaxially illuminated with illumination light of the same intensity. This generates an appropriate corrected image Mc in which the effects of the hot spot phenomenon are reduced. [Explanation of symbols]

[0052] 1...inspection device, 2...table, 3...imaging device, 4...illumination device, 5...imaging optical system, 6...image sensor, 7...coaxial illumination unit, 8...side oblique illumination unit, 9...light source, 10...half mirror, 11...light source, 11A...first light source, 11B...second light source, 11C...third light source, 12...support member, 13...image processing device, 14...processor, 15...main memory, 16...storage, 17...input / output interface, 18...communication interface, 19...image processing program, 20...operating system, AX...optical axis, Hs...hot spot portion, La...line, Lb...line, Lc...line, Ma...reference image, Ma1...first reference image, Ma2...second reference image, Ma3...third reference image, Mb...inspection image, Mb1...first inspection image, Mb2...second inspection image, Mb3...third inspection image, Mc...corrected image, W...inspection object

Claims

1. A lighting device; An imaging device; an image processing device having a processor, The image processing device includes: acquiring a reference image showing an image of a reference member coaxially illuminated by the illumination device and captured by the imaging device; acquiring an inspection image showing an image of the inspection object that is coaxially illuminated by the illumination device and captured by the imaging device; generating a corrected image by subtracting, for each of a plurality of pixels of the inspection image, a luminance value of a pixel of the reference image corresponding to the position of the pixel of the inspection image from a luminance value of the pixel of the inspection image; Inspection equipment.

2. a table for supporting the test object; the imaging device images the inspection object supported on the table; the reference member includes the table; The inspection device according to claim 1 .

3. the optical reflectance of the surface of the reference member is lower than the optical reflectance of the surface of the inspection object; The inspection device according to claim 1 .

4. The image processing device includes: When a reference image of a reference member coaxially illuminated with illumination light of a first intensity is acquired, acquiring an inspection image of the inspection object coaxially illuminated with illumination light of the first intensity; The inspection device according to claim 1 .

5. an image processing device having a processor, acquiring a reference image showing an image of the reference member that is coaxially illuminated by the illumination device and captured by the imaging device; acquiring an inspection image showing an image of the inspection object that is coaxially illuminated by the illumination device and captured by the imaging device; generating a corrected image by subtracting, for each of a plurality of pixels of the inspection image, a luminance value of a pixel of the reference image corresponding to the position of the pixel of the inspection image from a luminance value of the pixel of the inspection image; Testing method.

Images