JP2005291844A - Surface defect inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface defect inspection apparatus capable of suppressing the false detection of a defect to the utmost even when using an illumination part constituted by combining a plurality of layout patterns wherein light emitting elements are continuously arranged so as to leave dark surfaces of predetermined shapes inside. <P>SOLUTION: The surface defect inspection apparatus is equipped with a defect evaluation means 6 for detecting the defect on the surface to be inspected, which is illuminated with irrediation light due to the illumination part wherein light emitting elements are continuously arranged so as to leave dark surfaces of predetermined shapes inside, by evaluating an imaging screen. The defect evaluation means 6 has an insolated point extraction part 63 for judging the isolated protruded brightness region in the light and shade image of the surface to be inspected as a defect candidate and a defect candidate sorting part 64 for removing the defect candidate contained in the region showing the light emitting image of the light emitting elements in a light and shade image from the defect candidate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an illuminating unit configured by combining a plurality of layout patterns in which light emitting elements are continuously arranged so as to leave a dark surface of a predetermined shape inside, and a surface to be inspected illuminated by light irradiated by the illuminating unit The present invention relates to a surface defect inspection apparatus including an image pickup camera for picking up images and defect evaluation means for evaluating an output signal of the image pickup camera and detecting defects on the surface to be inspected.

  A typical example of this type of inspection apparatus is a technique used for inspecting the painted surface of an automobile body. In such a surface inspection, unevenness, scratches, etc. existing on the painted surface as the surface to be inspected are the inspection objects. As an inspection technique using pattern-shaped inspection light, so-called stripes, that is, illuminating illumination light that creates the light and darkness of vertical stripes on the painted surface, and the painted surface in the irradiated state is imaged with an imaging camera, There is a technique for performing a surface inspection using the obtained captured image. (Technology disclosed in Patent Document 1 and Patent Document 2).

  For example, when the painted surface is moved in a predetermined direction (for example, the X direction), an image portion of a defect such as an uneven surface on the painted surface has coordinates in a direction orthogonal to the moving direction (for example, the Y direction). There is one that detects defects by using the image while changing the direction coordinate (X coordinate) without changing, and in the captured image of the defect area, the light stripe portion is dark and dark stripes. Since the defect is identified using the fact that it is brightly imaged at the part, the defect is captured as an intermediate gradation image of a bright part and a dark part of the stripe (see Patent Document 1).

In order to detect a defect called "Yuzu skin" that is a periodic unevenness of the surface, it tries to find a group of coating thickness by fluctuation on the captured image of the boundary line of light and dark stripes as inspection light There is a thing (refer patent document 2). In this inspection method, it is not necessary to move the surface to be inspected, but in general, there is a paint surface on which a disturbance that causes displacement in the boundary image of the stripe occurs over a relatively wide range of the paint surface. It becomes a detection target.
JP-A-8-145906 (FIGS. 5, 9, and 15) JP-A-9-126744 (FIG. 13)

  In the above-described conventional surface inspection methods such as Patent Documents 1 and 2, the illumination unit that illuminates the surface to be inspected irradiates the painted surface with a stripe-shaped light / dark pattern. In order to cause the irradiation light to wrap around from many directions when there is a defect on the surface to be inspected, the illumination unit is It is preferable to compose a plurality of layout patterns in which light emitting elements are continuously arranged so as to leave a dark surface of a predetermined shape inside, but a large amount of light is emitted in the image of the surface to be inspected obtained through the imaging camera. The light emission image of the element exists, and the light emission image of the light emitting element arranged continuously is intermittent depending on the shape of the surface to be inspected, etc. There is a problem that properly made.

  In view of the above situation, the problem of the present invention is that even when using an illumination unit configured by combining a plurality of layout patterns in which light emitting elements are continuously arranged so as to leave a dark surface of a predetermined shape on the inner side, the defect The object is to provide a surface inspection apparatus in which erroneous detection is suppressed as much as possible.

  In order to solve the above problems, a surface inspection apparatus according to the present invention includes an illumination unit configured by combining a plurality of layout patterns in which light emitting elements are continuously arranged so as to leave a dark surface of a predetermined shape on the inside, and the illumination An imaging camera that images a surface to be inspected illuminated by irradiation light from the unit, and a defect evaluation unit that evaluates an output signal of the imaging camera and detects a defect in the surface to be inspected. An isolated point extraction unit that determines an isolated protruding luminance region in the bright and dark image of the surface to be inspected generated from the output signal as a defect candidate, and a region that indicates a light emission image of the continuously arranged light emitting elements in the bright and dark image A defect candidate selection unit that excludes the defect candidates included in the defect candidates from the defect candidates.

  In this configuration, with respect to a defect existing inside the irradiation point of the light emitting element group continuously arranged in a ring shape, that is, on the surface to be inspected opposite to the dark surface, the irradiation light is irradiated from the entire circumferential direction of the defect. A part of it will be hit, and the defect image will be brightly floated in the dark dark surface image, making it possible to detect defect candidates as isolated protruding luminance areas in the light and dark image and arranging them continuously. In contrast to the fact that the light emission image of the light emitting element is detected as an isolated protruding luminance region (also referred to as an isolated point), the isolated point existing on the extended line of the continuous light emission image in a predetermined pattern is detected. By excluding from defect candidates, false detection errors are reduced. By moving the surface to be inspected relative to the imaging camera or illumination unit, the defect always comes off the irradiation point of the light emitting element group and comes to the position facing the dark surface. The area of the continuous light emission image as the area may be excluded from the defect determination target area.

  Since an illumination unit with many light emitting elements arranged continuously is used, the reflected light from the surface to be inspected of the light emitted from the light emitting elements is captured by the imaging camera, and the emitted image is displayed in the image output from the imaging camera. However, the luminance value of the light emission image varies depending on the inspection conditions, particularly the condition of the surface to be inspected. In the present invention, the luminance value of the light emission image is an important reference for defect determination. Therefore, in order to compensate for such fluctuations, the normal value that is a reference when generating the bright and dark image from the output signal from the imaging camera is used. A pre-processing unit that performs image processing so that the luminance level of the continuous light-emitting image region at the time of actual inspection substantially matches the luminance level of the light-emitting image of the continuously arranged light-emitting elements obtained from the surface to be inspected. Conveniently. Applying luminance adjustment to the acquired captured image in advance so as to match the luminance level of the light emission image obtained with respect to the reference inspection surface leads to improvement in accuracy of subsequent defect determination.

When the surface to be inspected is smaller than the field of view of the imaging camera, subjects other than the surface to be inspected (background, etc.) will enter the acquired image, but the position information of such unnecessary image areas can be predicted in advance. In the present invention, an unnecessary image area such as a background is added to the peripheral area including the protruding luminance area excluded from the defect candidates described above. It has also been proposed to mask the income image with the integrated region as a non-defect determination target region.
Other features and advantages of the present invention will become apparent from the following description of embodiments using the drawings.

  As an example of the surface defect inspection apparatus according to the present invention, FIG. 1 shows a schematic configuration diagram of an apparatus for inspecting a painted surface of an automobile body 1 after completion of a painting process conveyed to the left side of a sheet by a conveyor 2. ing. The surface defect inspection apparatus includes an illumination unit 3 that irradiates a painted surface of an automobile body 1 that is an inspection surface with illumination light as inspection light, and an imaging camera 4 that images the inspection surface illuminated by the illumination unit 3. A controller 5 that evaluates the presence of defects on the surface to be inspected using an output signal from the imaging camera 4 and outputs the evaluation defects, and a monitor as an output device connected to the output unit 10 of the controller 5 12 and the printer 13. The controller 5 includes an illumination / imaging control unit 9 that controls the illumination unit 3, and an image input unit 7 that takes in an output signal from the imaging camera 4 and develops it in the memory 8 as digital image data (hereinafter simply referred to as an input image). Defect evaluation means 6 for performing defect evaluation using the input image is provided. Further, the controller 5 is connected to the host computer 14 as a host controller of the surface defect inspection apparatus via the communication unit 11 so as to be able to transmit data. The host computer 14 stores information on the automobile body 1 to be inspected and operation information on the conveyor 2 that are downloaded to the controller 5 as necessary. Further, defect information on the painted surface generated by the controller 5 is also stored. Is also uploaded from the controller 5 to the host computer 14 and stored therein. Further, a projector 15 or a printer controlled by a terminal connected to the host computer 14 via a network is provided in the inspection / verification station, and is based on defect information sent from the controller 5 of the surface defect inspection apparatus via the host computer 14. The defect position is instructed to the inspector.

  The light emitting surface 3a of the illuminating unit 3 and the lens surface 4a of the imaging camera 4 are arranged so as to face the surface to be inspected of the automobile body 1 conveyed by the conveyor 2, or the light emitting surface 3a and Following control is performed with respect to the surface to be inspected so that the vertical line of the lens surface 4a and the vertical line of the surface to be inspected are as coincident or parallel as possible.

  The illuminating unit 3 has a large number of light emitting elements (in this embodiment, LED elements are used and hence referred to as LED elements hereinafter. Of course, the light emitting elements of the present invention are not limited to LED elements, but other light emitting elements). 30 may be a net-like (ring-shaped) layout pattern that leaves a hexagonal space, and the hexagonal layout pattern is repeated continuously (between adjacent LED elements 30). It has a configuration arranged). The space left by the LED elements 30 arranged in a hexagonal mesh shape is referred to herein as a dark surface 31 and is a black or dark plate surface.

  Although many dark surfaces 31 appear by the LED elements 30 arranged in a net shape, the imaging camera 4 illuminates so that the lens surface 4a of the imaging camera 4 is positioned on the dark surface 31 that is located at the most center among them. Part 3 is incorporated. The number of imaging cameras 4 is appropriately determined depending on the size of the light emitting surface 3a of the illumination unit 3.

  The controller 5 uses a CPU as a core member and constructs a functional unit for performing various operations of the surface defect inspection apparatus by hardware and / or software, as shown in FIG. As a functional unit particularly related to the present invention, a preprocessing unit 60A for converting the input image developed in the memory 8 into a form suitable for defect detection, and a defect on the surface to be inspected using the preprocessed input image Can be divided into the defect determination unit 60B.

  The preprocessing unit 60A includes a luminance adjustment unit 61 that performs luminance adjustment on an input image and a binarization processing unit 62 that performs binarization processing on the input image that has undergone luminance adjustment. The luminance adjustment unit 61 of this embodiment is not only for gamma adjustment but also for LED elements obtained from a normal inspection surface in which the luminance level of the luminescent image included in the input image is a reference for each paint color or paint surface. It is configured to perform luminance adjustment in units of pixel areas so as to reach the luminance level of the luminescent image. The binarization processing unit 62 applies a smoothing filter to the input image for binarization threshold value determination unit 62a for determining the binarization threshold value from the density histogram of the input image by a statistical method or noise elimination. And an image feature extraction unit 62b that applies an edge enhancement filter such as a Sobel filter to enhance the outline of the light emission image or defect image, and uses the binarization threshold value determined by the binarization threshold value determination unit 62a. The input image emphasized by the extraction unit 62b is converted into a binarized image.

  An example of the input image binarized by the binarization processing unit 62 is shown in FIG. In this binarized bright and dark image, areas with high luminance are displayed in white, but LED element groups, which are light-emitting images continuously arranged in a hexagonal layout pattern, are continuously connected in a hexagonal shape. Displayed as a white outline, the painted surface area facing the dark surface 31 is displayed as a dark region, and in some cases, an existing coating defect is displayed as a white independent region that floats in the dark region due to diffuse reflection from the surrounding light. Is done. For this reason, in the defect detection, it is only necessary to find an area where luminance is protruding (a white area in this embodiment) and is not continuous in a predetermined pattern, that is, an isolated point in the binarized image. Become. A well-known image processing algorithm for searching for a continuous pixel or an isolated area while having a luminance value (density value) of a predetermined level can be used.

  However, due to the variation of the reflection characteristics with respect to the irradiation light due to the shape of the surface to be inspected here, as shown in an enlarged view in FIG. 5, the light emission image of the LED element 30 that originally appears as a continuous line is interrupted. May occur, and the interrupted portion may be erroneously detected as a defect. The defect determination unit 60B is substantially constituted by a program so as to appropriately avoid such erroneous detection. In other words, the defect determining unit 60B includes a defect candidate extracting unit 63 that detects a discontinuous independent pixel region composed of a predetermined number of pixels as an isolated point to be a defect candidate, and LED elements that are continuously arranged. The defect candidate selection unit 64 that excludes defect candidates included in the region showing the 30 light emission images from the defect candidates, and the unnecessary image regions such as isolated point regions and backgrounds excluded from the defect candidates by the defect candidate selection unit 64 are integrated. Then, an image mask generation unit 65 that performs mask processing as a non-defect determination target region, and a labeling process that assigns different labels (numbers) to different defect candidate regions in order to identify a plurality of defect candidate regions located outside the image mask. Based on the area information from the area calculation unit 67, the label setting unit 66 to be performed, the area calculation unit 67 for calculating the area of each labeled defect candidate area, And a defect determination unit 68 for writing the defect map to determine the candidate true defect. The defect candidate selection unit 64 checks whether or not a defect candidate has been extracted a predetermined number of times from images sequentially sent from the imaging camera 4 in order to select the defect candidate extracted by the defect candidate extraction unit 63. A defect candidate time-series determination unit 64a that prevents a suddenly occurring bright region from being recognized as a defect candidate, and a light emission image in which defect candidates (isolated points) extracted as shown in FIG. 5 are continuous. A light emission image discontinuous portion searching unit 64b is provided that prevents the discontinuity portion of the light emission image from being recognized as a defect candidate by checking whether or not it is located on the extension line. This search for the non-continuous portion of the luminescent image can be performed using a shape feature extraction algorithm or the like that extracts a dark region located in the extended line region of the discontinuity while tracing the continuous luminescent image pixels, An isolated point existing in this discontinuous region is excluded from defect candidates.

The procedure for defect evaluation of the painted surface by the defect evaluation means 6 configured as described above will be described below with reference to the flowchart of FIG.
First, the frame images sequentially sent from the imaging camera 4 via the image input unit 7 are taken into the memory 8 (# 01). The captured input image is adjusted in luminance (density value) by the luminance adjustment unit 61 (# 02). In this case, the feature amount of the input image is required. It is preferable that the feature amount is obtained by dividing the input image by a predetermined number of partitions and using the maximum value of the density average value calculated for each partition as the feature amount. This feature amount can be used for the adjustment of the lens aperture of the imaging camera 4 for the determination of the next binarization threshold. The binarization threshold value is determined by the binarization threshold value determination unit 62a (# 03), and the image feature extraction unit 62b performs image smoothing and edge enhancement (# 04). To a binary image (# 05).

  From the binarized input image, the fall candidate extraction unit 63 extracts an isolated bright pixel region having a number of pixels within a predetermined number (predetermined from image resolution or the like) as a defect candidate (# 06). . Of the extracted defect candidates, defect candidates belonging to isolated points that are instantaneously and locally generated by disturbance light or the like are excluded from the defect candidates by the defect candidate time-series determination unit 64a (# 07), and further extracted defect candidates. Among these, defect candidates belonging to isolated points located in the discontinuous region of the light emission image are excluded from the defect candidates by the light emission image discontinuous portion searching unit 64b (# 08).

  The peripheral region including the discontinuous region of the light emission image found by the light emission image discontinuous portion searching unit 64b is the shape information of the vehicle body 1 as the inspection object transmitted from the host computer 14 and the conveyance position information by the conveyor 2 The image mask generation unit 65 performs mask processing as an unnecessary pixel area together with the background area other than the painted surface as the surface to be inspected determined based on (# 09). In this embodiment, since the transport position information obtained from the host computer 14 may be different from the actual position, the positional deviation of the automobile body 1 is checked in real time using a laser sensor or the like, and the image is displayed. The position of the mask is corrected (# 10).

  After selecting defect candidates and removing the background image in this way, the remaining defect candidates (isolated points) are labeled (# 11), and the area of the isolated points to which each label is assigned is calculated ( # 12) Only isolated points satisfying a preset area condition (whether or not having an area equal to or greater than the threshold) are determined as true defects (# 13), and their coordinate positions and sizes are stored in the defect map. Write (# 14).

  The procedure of the defect evaluation of the painted surface by the defect evaluation means 6 is completed as described above. When the inspection of the painted surface is completed through this procedure, the controller 5 of the surface defect inspection apparatus via the host computer 14 at the painted surface inspection / collation station. Among the defect maps sent from, the defect matching is performed using the defect map assigned with the ID that matches the ID of the automobile body carried into the painted surface inspection matching station. At this time, it is advantageous to operate the projector 15 so as to point out the defect location based on the corresponding defect map in order to facilitate the collation work by the inspector. Of course, the defect information based on such a defect map may be output to paper by the printer 13 connected to the output unit of the surface defect inspection apparatus, and the output paper may be directly attached to the automobile body 1.

  In the embodiment described above, the illuminating unit 3 is configured by the LED element group continuously arranged in a hexagonal mesh shape. Other than these may be adopted. Further, instead of arranging the imaging camera 4 in the dark surface surrounded by the LED element group, the imaging camera 4 may be arranged outside the illumination unit 3. In this case, the imaging angle of the imaging camera 4 with respect to the surface to be inspected It is convenient to artificially convert the input image into an image that accurately faces the irradiation surface 3a of the illuminating unit 3 by correcting the input image based on the above.

  In the embodiment described above, the input image is converted into a binarized image for defect detection. However, the present invention is not limited to the binarization of the input image. It is also within the scope of the present invention to perform defect detection using a multi-valued image.

Configuration diagram schematically showing a surface defect inspection apparatus according to the present invention Schematic diagram showing the illumination unit and imaging camera Functional block diagram showing the configuration of the defect evaluation means mounted on the surface defect inspection apparatus Explanatory drawing explaining the binarized input image Explanatory drawing explaining the isolated point which exists in the discontinuous part of a light emission image Flow chart showing the procedure for defect evaluation of the surface to be inspected by the defect evaluation means

Explanation of symbols

3: Illumination unit 4: Imaging camera 5: Controller 6: Defect evaluation means 30: Light emitting element (LED element)
31: Dark surface 60A: Pre-processing unit 60B: Defect determination unit 61: Brightness adjustment unit 62: Binarization processing unit 63: Defect candidate (isolated point) extraction unit 64: Defect candidate selection unit 65: Image mask generation unit 66: Label setting unit 67: Area calculation unit 68: Defect determination unit

Claims (3)

An imaging unit configured to combine a plurality of layout patterns in which light emitting elements are continuously arranged so as to leave a dark surface of a predetermined shape inside, and an imaging for imaging a surface to be inspected illuminated by light emitted from the illumination unit It is composed of a camera and defect evaluation means for evaluating an output signal of the imaging camera and detecting a defect on the surface to be inspected,
The defect evaluation means includes an isolated point extraction unit that determines an isolated protruding luminance region in the bright and dark image of the surface to be inspected generated from the output signal as a defect candidate, and the continuously disposed light emitting elements in the bright and dark image A surface defect inspection apparatus comprising: a defect candidate selection unit that excludes the defect candidates included in a region showing a light emission image from defect candidates.   The brightness level of the continuous light emitting image area at the time of actual inspection is set to the brightness level of the light emitting image of the continuously arranged light emitting elements obtained from the normal inspection surface that is a reference when generating the light and dark image from the output signal. The surface defect inspection apparatus according to claim 1, further comprising a preprocessing unit that performs image processing so that the levels coincide with each other.   3. The surface defect inspection according to claim 2, wherein the peripheral area including the protruding luminance area excluded from the defect candidates and the unnecessary image area such as a background are integrated and masked as a non-defect determination target area. apparatus.

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