WO2015022271A1

WO2015022271A1 - Method and device for detecting defects of a flat surface

Info

Publication number: WO2015022271A1
Application number: PCT/EP2014/067093
Authority: WO
Inventors: Achim RAULF; Sascha Lang; Horst Janssen
Original assignee: Thyssenkrupp Steel Europe Ag
Priority date: 2013-08-12
Filing date: 2014-08-08
Publication date: 2015-02-19
Also published as: DE102013108722A1; DE102013108722B4

Abstract

The invention relates to a method for detecting defects (2) of a flat surface (3) of a product (4), particularly a metal product. In order to be able to reliably detect and classify small and extremely small defects on flat surfaces, a method is proposed, wherein a surface section (8) to be examined is illuminated by an illuminating unit (6), at least two recordings of the surface section (8) to be examined are produced with different exposure by means of a camera unit (5) while the surface section (8) to be examined is illuminated by the illuminating unit (6), at least the recordings of the surface section (8) to be examined produced with different exposure are transferred to an image-processing unit, and an image for detecting defects (2) is produced by the image-processing unit by superimposing at least the recordings of the surface section (8) to be examined produced with different exposure.

Description

Method and device for detecting defects of a flat surface

The invention relates to a method for detecting defects of a plane

Surface of a product, in particular a metal product. Furthermore, the invention relates to an apparatus for carrying out such a method.

In the quality control of flat surfaces scratches, craters, elevations and other surface defects (defects / anomalies) are sought, which are to be reliably detected. This applies in particular to the assessment of surfaces of metal products, such as steel or steel

Lightweight flat products whose quality is very demanding. In this case, "flat products" are usually understood to mean all rolled products present in the hot or cold-rolled state as strip, sheet metal, blank or blank. For the non-destructive testing of surfaces optical methods are recommended. However, surface defects can often be difficult to detect with optical methods without prior preparation of the surface to be examined. Therefore, the surface portions to be examined each of

If necessary, metal products are sampled in sections with one

Dimensionally stable abrasive (grindstone) slightly ground. This sanding of each surface section to be assessed is usually done manually today. In this case, the test piece to be examined stands still, while the inspector loops over the respective section by moving the generally cuboid, block-like grindstone with its flat grinding surface under slight pressure over the respective surface section to be assessed. By suitable

Sanding the surface highlights fine local bumps, while fine bumps appear as dark spots on an otherwise glossy surface. When detecting defects of flat surfaces by means of optical methods is regularly taken by a camera a recording of the examined

Surface section generated and generated from it an image. In order to be able to produce an image with a high contrast, the surface section to be examined is illuminated, for which purpose the camera can be assigned a lighting arrangement, such as a luminaire. The image is displayed on a display, so that the

Checker can decide if the quality specifications to the surface of the

Products are observed by the examined surface section.

In order to detect surface defects with known methods and devices, however, the defects must have a certain minimum size. The minimum size of defects depends on the resolution or pixel size used. Often, depending on the product already defects with a corresponding

Minimum size have a significant impact on the quality of the product. The effect of the defects on the product depends on the nature of the defect. In order to determine the type of defect, the defect must be more than just visible. Rather, other properties of the defect must be recognizable. There is thus a need for improvement in the known devices and methods with regard to the reliable detection of small and smallest defects on flat surfaces.

The present invention is therefore based on the object, the method and the device respectively of the aforementioned type and previously described in such a way and further develop that the reliable detection of small and smallest defects of planar surfaces can be further improved, so that different Defektausbildungen distinguished and can be classified. This object is achieved according to claim 1, by a method of the type mentioned, in which a surface to be examined of a lighting unit is illuminated, in which of the surface to be examined by means of a camera unit at least two shots with different exposure are generated while the to be examined

Surface section is illuminated by the lighting unit, in which

at least the images produced with different exposure are transferred from the surface section to be examined to an image processing unit and by the image processing unit by superposition

at least one of the images to be examined of the surface section to be examined is used to produce an image for detecting defects.

Furthermore, this object is achieved by a device according to the preamble of

Claim 10, characterized in that a lighting unit for illuminating a surface section to be examined is provided, that a camera unit for generating at least two shots of the examined

Surface section with different exposure during the illumination of the surface to be examined portion is provided with the illumination unit and that an image processing unit for generating an image by

Overlay at least of the two images produced with different exposure of the surface to be examined is provided.

The invention has recognized that even small and smallest defects of even

Product surfaces, such as metal products, such as in the form of tapes, blanks, blanks, sheets or semi-finished can be reliably detected when produced by the surface to be examined successively several differently exposed images and these recordings are fed to an evaluation. As a result of a corresponding evaluation, an image with very high contrast can be generated by superposition of the images, on which

Surface defects are very clear and prominent. Surface defects can be detected even if they are very small. This allows, if necessary, not only to recognize the defects as such, but also the defects according to to classify predetermined categories. The prerequisite is, of course, that the resolution of the images is large enough or the pixel size of the images is small enough. In addition, it is preferable if the recordings are digital recordings, since they can be easily processed in the image processing unit.

The recordings can be at least partially overlaid. A superimposition of the images leads to an increase in the contrast, whereby, for example, a pixel-based overlay or an object-based overlay can take place. In a pixel-based overlay, the pixels of the images are at least in the

Essentially completely superimposed. An object-based overlay overlays only those pixels that can be assigned to specific objects. These objects may be surface defects or objects that are, with a certain probability, a surface defect. Whether this is actually the case can be determined, for example, as a result of the higher contrast after the overlay. An object-based overlay may have the advantage that only recognized as relevant areas of the images must be superimposed, which can reduce the computational effort. However, it must first be determined which areas can be relevant, which in turn means an additional effort.

The overlay image is a new image in which the subject can match the images used to create the image. However, the picture as such does not correspond to any of the recordings, but is only produced from these recordings. In this case, the image produced can in principle have a higher contrast, the more images of different exposure of the overlay are used. The exposures may be chosen such that at least one shot is overexposed and at least one shot is underexposed. Alternatively or additionally, of course, a shot can be generated at an optimal exposure. Then high contrasts can be calculated by superimposing

Image to be obtained. The recordings can be necessary as to their Distinguish clearly already exposure, so that it can be calculated from a new image with high contrast.

It may be preferred, in particular, for a recording to be overexposed if the surface section to be examined remains uniform, a photograph underexposed, and a photograph to be exposed substantially correctly or optimally. From these images, a very high-contrast image is then generated in the image processing unit by overlaying. In the case of those to be classified and, if necessary, classified according to their nature

Surface defects can basically be any local anomaly of the surface. Corresponding defects can be, for example, elevations, depressions, structural deviations and / or deviations of the composition. In this case, the elevations may be formed by the material of the product and / or a foreign material adhering to the product. In addition, the elevations such as the depressions may be formed, for example point or elongated. Wells can therefore be roughly in the shape of craters or

Have scratches that can be elongated or curved. As an alternative or in addition to an elevation or depression, the surface defect may also be characterized by a local deviation with regard to the structure and / or the composition of the product, as long as it is optically detectable. By a structure, for example, a crystal structure, a microstructure, an (an) isotropy or the like can be understood. Hereinafter, further preferred embodiments of the method and the device will be described, wherein not in each case explicitly between the

Further development of the method and the development of the device is distinguished. The preferred features with regard to the method and the device will become apparent to the person skilled in the art on the basis of the context. In a first preferred embodiment of the method is characterized by the

Overlay several shots produces an image that at least partially has a higher contrast than each shot of the multiple

Recordings. The image processing thus leads to an increase in contrast to the individual images, which are the basis of the overlay. In this case, the contrast can also only be increased locally, for example if it has previously been determined that these sections of the image are relevant for the detection and / or classification of surface defects. The image processing unit can thus use an object-based overlay.

Depending on the type of surface defect, the quality of the image may depend on the direction of the surface to be examined

Lighting unit is illuminated. So that the surface defects in the

Consequently, for some surface defects, the surface section to be examined can offer itself from one direction in the image

Substantially perpendicular to the surface section to illuminate. Other

On the other hand, surface defects may be better detected in the images if the surface section to be examined is illuminated from a direction which encloses a very acute angle with the surface section to be examined. Therefore, the surface section to be examined is preferably illuminated successively from different directions, and when the surface section to be examined is illuminated from each individual direction, at least one image of the surface section to be examined is produced. These recordings can then be fed to the image processing unit as described. Preferably, when illuminated from a constant direction at least two, preferably at least three, images are produced with different exposure. However, it is further preferred if, when the surface section to be examined is illuminated from a plurality of directions, in particular each individual direction, in each case a plurality of exposures with different exposure are generated. Preferably, two images are generated, one of which

Image overexposed and a shot underexposed. Further preferred may add a third shot, which is essentially correctly or optimally exposed. If necessary, further overexposed and / or underexposed images may be added. It can be done so that only the shots of the

Image processing unit are superimposed to a new image that were taken in the same lighting situation. Then it can then be determined on the basis of the superimposition for each illumination situation determined separate images, which image for the detection and classification of

Surface defects is particularly well suited. However, it is also possible to superimpose images of different lighting situations, for example if the contrast of the image can be further increased as a result.

In order to be able to illuminate the surface section to be examined simply and quickly one after the other from different directions, the

Lighting unit include multiple lights. As a result of the different lights for different illumination of the surface to be examined, neither the lighting unit or the lamp nor the camera must be moved or swung. In this way the method and the device are considerably simplified. In addition, the life and reliability of the device, in particular the lighting unit and the camera unit are increased. Although it would be structurally easier to pivot the camera, but it requires an additional drive and an additional control. In addition, according to the invention exactly predetermined ratios of lighting unit and camera on the one hand to each other and on the other hand to be examined

Surface section set and secured. The life of the camera is always very accommodating if it does not have to be constantly swiveled. A different lighting means at least that of the

examining surface section of several lights in succession is illuminated differently. The luminaires are aligned in such a way that the luminaires sequentially exclude the surface section to be examined

to light different directions. The illumination can thus be carried out successively from different sides of the surface section to be examined. Alternatively or additionally, the surface section to be examined can be illuminated from different angles relative to the surface section to be examined. Depending on the nature of the defect, it can be better recognized if the surface is illuminated from a direction that includes a very small angle with the surface. Other defects can be better recognized if the illumination direction and the surface are at a significantly greater angle

lock in. It will usually offer that each of the

different lighting conditions is caused by a single lamp, while the other lights emit no light. But it can also be provided that at least partially a plurality of lights for a

Illumination state is used, wherein one or more at least partially different lights are used to provide a different lighting state.

For a better recognizability and / or classification of surface defects in the images to be created from superposing images, it may be expedient to illuminate the surface section to be examined from different directions with light of different color. It can also be varied when lighting from one direction, the color for two consecutive shots. However, this is preferred only in exceptional cases. So the light can be for

different recordings have a different wavelength distribution. If necessary, these can each be monochromatic light. Particularly useful can be used as different colors, such as the easier evaluation half, the primary colors blue, red and / or yellow. When exposures are taken from different directions and different colors when exposed, and then overlaid by the image processing unit to obtain a new image, the corresponding image subsequently analyzed for color components. For example, it can be determined at which illumination angle a defect or a class of defects can be detected particularly well. The essential parts of the defect are then represented, for example, only in a certain color. The determination of the color components of the defect can also be the

Classification of the defects serve, for example because it is known that individual classes are particularly well recognizable at certain lighting angles. It is understood that even with lighting with different colored light from different directions, the images for multiple directions need not be superimposed. An analysis can also be made if several different images are generated for each lighting situation and the images are compared with one another.

In order to fundamentally improve the quality of the recordings taken for the detection of surface defects, it makes sense if the one to be examined

Surface section is sanded before generating the recordings. Only then can even the smallest defects be made visible. A grinding of the surface section to be examined is particularly useful when the surface of a metal product to be examined for defects. The grinding of the surface can lead, in particular in this case, to the smallest elevations of the surface in relation to the immediate one

Surroundings appear shiny, while the finest depressions appear on an otherwise shiny surface as dark spots. For this reason, the defects of the surface may be picked up after sharpening with a higher contrast, so that the image processing unit may possibly provide a better suitable image for the detection of surface defects. Finally, the surface defects due to grinding can be classified much more accurately with regard to their type of defect.

Defects of flat surfaces can be detected in a particularly simple and accurate manner if the grinding takes place by means of, for example, a robot arm and / or

Linear system, comprising at least one linear drive, guided Grinding device takes place. In this way, reproducible grinding results are obtained, so that a reproducible defect detection and

Defect classification is possible. Alternatively or additionally, the

Camera unit and / or the lighting unit are held by a robot arm and / or linear system and, if necessary, are guided relative to the surface, so that the respectively predetermined and to be examined surface portion can be checked for surface defects. In this case, it is especially appropriate for the camera unit and / or the illumination unit to be held on the same robot arm and / or the same linear system as the grinding device. Thus, the camera unit and / or the lighting unit can be forcibly tracked to the grinding device. Thus, the grinding device can be moved further along the surface, and that during a to be examined

Surface section recordings are generated, the camera unit and / or the exposure unit may also be held on a different robot arm and / or linear system as the grinding device. Overall, the reproducibility of the classification of surface defects according to the respective type of defect can be correspondingly refined.

To increase the quality of the recordings and / or of the

Image processing unit provided image, it may be expedient if several successive surface sections to be examined in succession are examined.

Alternatively or additionally, the camera unit and / or the illumination unit can be arranged substantially stationary relative to the surface section to be examined, namely while the desired images of the surface section to be examined are generated. For example, it can be ensured that recordings of exactly matching

Surface sections are obtained so as to be able to provide by means of the image processing unit a suitable image for the detection of surface defects. The illumination unit and / or the camera unit can in principle be positioned in a stationary manner relative to the surface section to be examined until the images of the surface section to be examined have been generated. The

The camera unit and / or the lighting unit can then be moved further relative to the surface and used to test the next one to be examined

Surface section are positioned. It is particularly simple in terms of the method and the device when both the surface and the camera unit and / or the lighting unit are absolutely silent and the

Camera unit and / or the lighting unit is not only positioned relative to the surface to be examined stationary while it moves in absolute terms.

In order to be able to base the detection and / or classification of the surface defects on a high contrast image, the image processing unit may, by means of suitable software, select from the several exposures of a surface section to be examined with respect to the direction of illumination, the color of the light during illumination and / or the exposure can create an image. In this image then information from several shots flow, which are then summarized in the new image. In this case, the suitable recordings for generating a corresponding image can first be selected from the available recordings. It is particularly preferred in this case if the surface section to be examined by the

In the image processing unit, an image is generated and provided in the form of a high dynamic range image (HDRI), since corresponding images can comprise very high contrasts. It is particularly useful when photographs are available that differ in terms of their exposure. The software required to create a high dynamic range image is called HDR software and is available on the market. In order to be able to easily and reliably recognize the surface defects on the basis of the image generated or provided by the image processing unit, the image provided by the image processing unit for detecting defects can be displayed on a display. However, the detection of the surface defects can also be automated as needed, for which purpose the image can alternatively or additionally be further processed by a software for detecting defects.

To make a plurality of lights simple and reliable relative to that

To be able to position the investigating surface section, a plurality of luminaires, preferably all luminaires of the lighting unit, can be held stationary or directly on a support unit. This can preferably be done so that the surface to be examined depending on the activation of the lights from different angles relative to the examined

Surface section can be illuminated. It is constructive and particularly preferred in terms of high reproducibility, if a number of lights, if necessary, all lights, on the same side of the

examining surface section are provided. This leads in particular to a simpler design of the device, but can also lead to positive effects in terms of the method.

In order to be able to position the illumination unit and the camera unit exactly and in a predetermined manner relative to the surface section to be examined, namely during the production of images of the object to be examined

Surface section at different lighting conditions, a control device may be provided which controls this positioning. The

Control means may alternatively or additionally also control the sequence of the method, that is to say in particular the different illumination of the surface section to be examined and / or the production of images of the surface section to be examined as a function of the different ones

Lighting conditions. Alternatively or additionally, a positioning device can be provided for the predetermined positioning of the camera unit and / or the illumination unit relative to the surface section to be examined. This makes it possible, if necessary, the camera unit and / or the lighting unit substantially exactly in a predetermined manner relative to the examined

Position surface section. Also, the lighting unit and the camera unit relative to each other by the positioning device in

be positioned in a predetermined manner.

The invention will be explained in more detail with reference to a drawing showing only one embodiment. In the drawing shows

Fig. 1 shows a device according to the invention in a schematic representation and

Fig. 2 shows the device of Fig. 1 in the implementation of the

inventive method. 1 shows a device 1 for detecting defects 2 or anomalies on flat surfaces 3 of a product 4, wherein the product 4 in the device 1 shown and so far preferred is a metal product, preferably as part of a metal strip , The device 1 comprises a camera unit 5 and a lighting unit 6, wherein the lighting unit 6 has four separate lamps 7, 7 '. In this context, separate luminaires 7, 7 'are understood to mean that the luminaires 7, 7' are arranged spatially separated from one another in order to illuminate the surface section 8 of the product to be examined from different directions. Separately, however, also means that the luminaires 7, 7 'can be activated differently, so that different illumination states with respect to the surface section 8 to be examined can be generated. In the case of the device 1 which is preferred and preferred so far, a luminaire 7 'is designed as a ring light through the center of which a camera 9 of the camera unit 5 can take a picture of the surface sections 8 to be examined. The light 7 'in the form of a ring light and the camera 9 of the camera unit 5 are aligned substantially perpendicular to the surface portion 8 to be examined. In addition, three more lights 7 are provided, which are connected to a

Carrying unit 10 are mounted and aligned in a fixed orientation. The

Alignment of the lights TT on the support unit 10 is such that the four lights 7,7 'to be examined surface portion 8 from different angles relative to the surface to be examined section 8 and

Camera unit 5 and the camera 9 can illuminate. In the dargstellten and so far preferred device 1, the angles may be, for example, 5 °, 30 °, 60 ° and 90 °, either based on the examined

Surface portion 8 or the viewing angle of the camera unit 5 and the camera. 9

Furthermore, the camera unit 5 which is shown and in this respect is preferred

Cost reasons, only a camera 9 on. However, other cameras would be conceivable. If necessary, the surface section to be examined simultaneously could be enlarged by a plurality of cameras. Thus, for example, each camera takes a picture of another surface section, the surface sections preferably overlapping slightly. The single ones

Surface sections are alternatively or additionally preferably provided so as to form a contiguous common surface section.

Regardless of the number of cameras, this is in each case a digital camera for automatic further processing of the images.

The illustrated and so far preferred device 1 is fixed with a

Grinding device 11 is connected for grinding the surface portion 8 to be examined. The illustrated and so far preferred grinding device 11 comprises an abrasive 12 and a force sensor 13 for preferably automated Grinding of the surface section 8 to be examined and can be moved back and forth in two directions of grinding, which are perpendicular to each other and parallel to the surface portion to be examined, as shown by the arrows shown in Figs. 1 and 2. Due to the firm connection between the device 1 for detecting surface effects and the

Grinding device 11, the apparatus 1 for detecting surface defects of the grinding device 11 can be tracked to already ground

To investigate surface sections. But this can also be waived. Then, for example, the grinding device 11 and the device 1 for detecting surface defects on different robot arms or

Be held linear systems and be positioned by these.

With reference to FIG. 2, in particular, the method for the detection of

Surface defects described in more detail. This method is used to a portion of a product 4 in the form of a metal strip in the sense of

Quality assurance offline from the production of the metal strip to investigate defects or surface anomalies. For this purpose, a grinding region 14 of the metal strip is ground by means of the grinding device 11. In this

Anschleifbereich 14 different surface sections are checked to see whether small and smallest defects 2 are present. In the presently described and so far preferred method, first of all the grinding area 14 is ground. Which way the grinding device 11 takes along the product 4, is shown by the dashed arrow. Subsequently, several surface sections of this grinding area 14 are then examined for defects 2. Nevertheless, the grinder 11 and the defect detecting apparatus 1 are fixed in common to a robot arm, not shown, to save another robot arm including a controller for positioning the defect detecting apparatus 1. By means of the positioning and control devices, not shown, the device 1 for detecting surface defects at a specific location of the Grinding area 14 moves and positioned there to carry out the investigation. In this case, the surface section 8 to be examined is successively illuminated individually by each of the luminaires 7, 7 'in order to produce different ones

To generate lighting conditions. Each lamp can be 7,7 'to

illuminate surface of investigation 8 multiple times, each with light of a different color or wavelength distribution. But it can too

be provided that each light emits 7,7 'only light of a color, but the colors of the light from light 7,7' to light 7 ', 7 may be different. In any case, lighting conditions of the examined

Surface section 8 is generated, which differ in terms of the illumination angle and / or the color of the light used for the illumination. In each illumination state, at least one image is also generated by the camera unit 5 from the surface section 8 to be examined. In the method described here, however, it is preferable for at least three exposures per illumination state to be exposed to different intensities in order to obtain at least one underexposed and at least one overexposed exposure. In addition, it is provided in the described and so far preferred method that the third exposure corresponds approximately to an optimal, correct or correct exposure for displaying a defect 2 in the one shot.

The various images generated by a surface section 8 to be examined by the camera unit 5 are referred to a not shown

Transfer image processing unit, which may be integrated into the camera unit 5 and preferably calculated by means of HDR software, taking into account the images, a high-contrast image of the surface to be examined section. This image is transferred from the image processing unit to a display, not shown, or to an evaluation device, not shown, for the automatic detection of defects.

Claims

P a n t a n s p r e c h e

1. A method for detecting defects (2) of a flat surface (3) of a product (4), in particular metal product,

in which a surface section (8) to be examined by a

Lighting unit (6) is illuminated,

wherein at least two images with different exposure are generated by the surface section (8) to be examined by means of a camera unit [5] while the surface section (8) to be examined is illuminated by the illumination unit (6),

in which at least the recordings produced with different exposure from the surface section (8) to be examined to a

Image processing unit to be transferred and

in the case of that of the image processing unit by superimposing at least the images produced with different exposure of the

surface (8) an image for detecting defects (2) is generated.

2. The method according to claim 1,

in which an image is generated by superimposing a plurality of images that at least in sections has a higher contrast than each individual image of the plurality of images.

3. The method according to claim 1 or 2,

in which the surface section (8) to be examined differs from the

Illuminating unit (6), preferably with a plurality of lights [7,7 '), successively illuminated from different directions and in which of the surface to be examined section (8) by means of the camera unit [5) when illuminated from each direction at least one Aufnah preferably at least two images are generated with different exposure.

4. The method according to any one of claims 1 to 3,

in which the surface section [8] to be examined is illuminated from at least one first direction with light of a first color and from at least one second direction with light from a second color deviating from the first, and at which of the surface section (8) to be examined by means of the camera unit (5) when lighting from the first direction and the second direction in each case at least one recording is generated, preferably at least two images are generated with different exposure.

5. The method according to any one of claims 1 to 4,

in which the surface section [8] to be examined is ground before generating the recordings.

6. The method according to claim 5,

in which the grinding is carried out by a grinding device (11) guided by a robot arm and / or a linear system and in which the camera unit (5) and / or the illumination unit (6) are operated by the same robot arm, the same linear system, another robot arm or another Linear system of the grinding device (11) is tracked.

7. The method according to any one of claims 1 to 6,

in which successively several surface sections (8) to be examined are examined step by step.

8. The method according to any one of claims 1 to 7,

in which the camera unit (5) and / or the illumination unit (6) consists of several during illumination of the surface section (8) to be examined Directions substantially stationary relative to the one to be examined

Surface section [8] is arranged.

Method according to one of claims 1 to 8,

in which the image processing unit by means of suitable software, in particular a so-called High Dynamic Range Software (HDR software), preferably from several different recordings from

surface section (8) generates and provides an image in the form of a high dynamic range image (HDRI).

Method according to one of claims 1 to 9,

wherein the image provided by the image processing unit for detecting defects is displayed on a display and / or from a display

Software for the detection of defects is further processed.

Device (1) for detecting defects (2) of a flat surface [3] of a product (4), in particular a metal product, preferably for carrying out the method according to one of claims 1 to 10,

d a d u r c h g e k e n e, a lighting unit (6) for illuminating a subject to be examined

Surface section (8) is provided, that a camera unit (5) for generating at least two images of the examined

Surface section (8) with different exposure during the illumination of the surface to be examined section (8) with the

Lighting unit is provided and that an image processing unit for generating an image by superimposing at least the two with

different exposure generated recordings of the surface to be examined section [8] is provided.

12. Device according to claim 11,

For example, the illumination unit (6, 6 ') comprises a plurality of luminaires [7, 7') for illuminating the surface section (8) to be examined successively from different directions and, preferably, at least partially with light

Color, has.

Device according to claim 11 or 12,

The device (1) is held by a robot arm and / or linear system and is movable relative to the surface (3).

Device according to one of claims 11 to 13,

a plurality of lights (7, 7 ') are held stationary on a support unit (10) in such a way that the surface section (8) to be examined can be illuminated successively from different angles, preferably from the same side.

Device according to one of claims 11 to 14,

d a d u r c h g e k e n e z e i c h e n d a s s, a control device for controlling the lighting unit (6) and / or the

Camera unit (5) for generating images of the examined

Surface section (8) is provided with different lighting.

Device according to one of claims 11 to 15,

d a d u r c h g e k e n e c i n e s d a s s, a positioning device for the predetermined positioning of the

Camera unit (5) and / or the lighting unit (6) is provided relative to the surface to be examined portion (8).