Test setup and method for fluorescence-based inspection

Description

[0001] The present invention relates to a test arrangement and a method for fluorescence-based inspection of a product containing at least one fluorophore.

[0002] In many areas of the manufacturing industry, optical inspection devices and corresponding inspection methods are used to examine manufactured products for errors and defects. This process usually involves processing and evaluating images of the products being inspected. The results of the respective evaluation are more reliable the more clearly the errors and defects in the images can be visually distinguished from the flawless areas of the products.

[0003] In some applications, special optical or spectral properties are exploited to better highlight errors and defects in the images. For example, fluorescence-based inspection devices and methods are used for products containing fluorophores, fluorochromes, or other types of fluorescent carriers. In particular, fluorescence-based inspection evaluates images of the products that have been excited to fluoresce, based on the primary illumination effects produced. However, under certain circumstances, fluorescence can highlight not only the errors and defects but also other areas of the products that are irrelevant to the inspection. This can lead to errors and defects not being detected, or to perfect areas of the products being incorrectly classified as defective.This inevitably leads to a loss of quality, productivity and / or efficiency.

[0004] The publication DE 20 301 286 U1 shows a control system for the automatic optical inspection of colored surfaces, e.g., floor coverings coated with an at least partially transparent protective layer. The system features a shortwave light source used to illuminate the covering and the protective layer. Sensors are provided to detect reflected and backscattered light. Local defects in the protective layer cause a local increase in the backscattered light, allowing defects to be localized.

[0005] Consequently, the object of the present invention is to provide means that allow fluorescence-based inspections to be carried out with increased detection accuracy.

[0006] This object is achieved according to the invention by a test arrangement according to claim 1.

[0007] The present invention is advantageous because irradiating the inspection area with the first electromagnetic radiation containing the excitation spectrum can excite the at least one fluorophore to fluoresce. Thus, the optical properties of the at least one fluorophore can be imaged in the at least one fluorescence image and accordingly utilized for fluorescence-based inspection.

[0008] Unwanted secondary illumination effects caused by the at least one fluorophore in the emission spectrum, which are also depicted in the at least one fluorescence image and highlight areas of the product irrelevant for the inspection, can be imitated by irradiating the inspection area with the second electromagnetic radiation containing the emission spectrum and thus specifically reproduced in the at least one reference image. This advantageously makes it possible to eliminate the secondary illumination effects when generating the correction image, so that they are no longer visible in the correction image or at least only visible to a reduced extent. Thus, the fluorescence-based inspection can be carried out using the correction image with increased detection accuracy.

[0009] The object underlying the invention can further be achieved by a method according to claim 10.

[0010] The method according to the invention also benefits from the advantages already mentioned. In particular, the method according to the invention allows secondary illumination effects caused by the at least one fluorophore, which are depicted in the at least one fluorescence image, to be specifically reproduced in the at least one reference image and can thus be eliminated when generating the correction image. This will be explained in more detail below.

[0011] The excitation spectrum and the emission spectrum of the at least one fluorophore are known or predefined depending on the application. The excitation spectrum can represent a continuous excitation wavelength range or a discrete excitation wavelength. The emission spectrum, in turn, can represent a continuous emission wavelength range or a discrete emission wavelength.

[0012] The solution according to the invention can be further improved by various embodiments, each of which is advantageous in itself and can be combined with one another as desired. These embodiments and the advantages associated with them are discussed below. The features described below can, even if this is not explicitly stated, be used both for the method according to the invention and for the test arrangement according to the invention. Thus, a method feature that is explicitly described only in the context of the method can also represent a device feature. Conversely, a device feature that is only described in the context of the device can also represent a method feature. A device, a facility, a module, a block, or a unit can correspond to a method step or a function of a method step.Analogously, aspects described within the scope of a method step also represent a description of a corresponding block, module, device, apparatus or property thereof. The advantages described with reference to the apparatus also apply to the method according to the invention and vice versa.

[0013] According to the test arrangement according to the invention, the image data processing device is configured to generate the correction image by calculating the difference between the at least one fluorescence image and the at least one reference image. Accordingly, in the method according to the invention, the correction image is generated by calculating the difference between the at least one fluorescence image and the at least one reference image. This represents a simple way of generating the correction image. In particular, the image data processing device can have a subtraction module for performing the subtraction. The subtraction module can be configured to subtract the color values ​​or brightness values ​​from the image data of the at least one fluorescence image and the at least one reference image pixel by pixel and to output the respective result value as the color value or brightness value of the associated pixel of the correction image.

[0014] To increase accuracy, a geometry adjustment and / or a contrast adjustment can be performed between the at least one fluorescence image and the at least one reference image before the difference is formed. For this purpose, the image data processing device can accordingly have a geometry adjustment module and / or a contrast adjustment module. The geometry adjustment module can be configured to align the at least one fluorescence image and the at least one reference image so that they are mutually congruent or at least approximately congruent. The contrast adjustment module can, in turn, be configured to mutually adjust or at least approximately adjust the contrast ratios of the at least one fluorescence image and the at least one reference image.

[0015] To automate the fluorescence-based inspection, the image data processing device can be configured to perform a preferably automatic shape recognition in the correction image. For this purpose, the image data processing device can have a shape recognition module. The shape recognition module can be configured to compare the pixels of the correction image with a predefined threshold based on their color values ​​or brightness values ​​and to categorize them depending on whether the threshold value is exceeded or not met. Furthermore, the shape recognition module can be configured to group neighboring pixels of the same category into pixel groups. Furthermore, the shape recognition module can be configured to identify pixel groups of a specific minimum size and recognize them as a shape.

[0016] In addition to the so-called threshold method just described purely as an example, other methods or algorithms known from the state of the art can of course also be used for shape recognition.

[0017] The image data processing device and its components, i.e., the subtraction module, the geometry adjustment module, the contrast adjustment module, and / or the shape recognition module, can be implemented independently of one another by hardware and / or software, in particular by computer-implemented methods. The image data processing device is, for example, an image data processor.

[0018] According to a further possible embodiment, the first wavelength range can lie outside the emission spectrum of the at least one fluorophore. In other words, the first wavelength range does not overlap with the emission spectrum of the at least one fluorophore. This ensures that the first electromagnetic radiation does not contribute to the occurrence of the aforementioned secondary illumination effects. Consequently, the secondary illumination effects are as weak as possible in the at least one fluorescence image.

[0019] To ensure that the fluorescence of the at least one fluorophore is depicted as little as possible in the at least one reference image, the second wavelength range preferably lies outside the excitation spectrum of the at least one fluorophore. This means that the second wavelength range does not overlap with the excitation spectrum of the at least one fluorophore.

[0020] The test arrangement can be configured to irradiate the inspection area with the first electromagnetic radiation and the second electromagnetic radiation by means of the radiation source device. The respective irradiation preferably takes place with a time delay. For example, the radiation source device can have two different emitters or light sources for this purpose, of which the first emitter is configured to generate the first electromagnetic radiation and the second emitter is configured to generate the second electromagnetic radiation.

[0021] According to the invention, the first emitter is configured as a UV lamp, UV light, black light lamp, or black light illuminator. According to the invention, the first electromagnetic radiation is UV-A radiation. Thus, a wide variety of fluorophores can be excited. Of course, the present invention is not limited to UV-A radiation and can also utilize other types of radiation depending on the application.

[0022] The second emitter can be configured as a polychrome LED, a color LED, or in particular as a blue light LED. The second emitter is preferably a narrowband lamp or light fixture, in particular a monochromatic lamp or light fixture, that generates light with the wavelength of the emission spectrum. Thus, illumination conditions comparable to the illumination conditions of the at least one fluorescence image can be created in the at least one reference image.

[0023] The first spotlight and / or the second spotlight can each be configured as a flashing light. Alternatively, the first spotlight and / or the second spotlight can be configured to continuously radiate light toward the inspection area. Accordingly, the inspection arrangement is configured to dim the first spotlight and / or the second spotlight as needed.

[0024] According to a space-saving embodiment, the radiation source device can also have a single controllable radiator, such as a controllable LED, which is designed to generate the first electromagnetic radiation and the second electromagnetic radiation.

[0025] According to a further embodiment, the beam source device can also comprise several individual emitters and / or adjustable emitters. These can advantageously illuminate the inspection area from two directions. This would have the advantage of achieving homogeneous illumination.

[0026] According to a further possible embodiment, the first wavelength range is not contained in the at least one fluorescence image. The at least one fluorophore is thus more clearly visible in the at least one fluorescence image since there is no overlap with the first electromagnetic radiation. For this purpose, the inspection arrangement can, for example, have a filter device between the inspection area and the recording device, which is designed to block the first wavelength range and / or to only allow the second wavelength range, preferably the emission spectrum, to pass through. In particular, the filter device can have corresponding optical filters, i.e. band-stop filters and / or band-pass filters. Alternatively or additionally, a sensitivity of the recording device can be limited to the second wavelength range.This sensitivity limitation can be implemented in the recording device on the hardware and / or software side.

[0027] To prevent interference with ambient light, the at least one fluorescence image and / or the at least one reference image can be generated while completely or partially shielding from ambient light. For this purpose, the inspection setup can optionally include a light shielding device for darkening or at least darkening the inspection area. Alternatively, the inspection setup can also include a darkroom.

[0028] The recording device can, for example, have a single camera, in particular a fluorescence camera, for generating the images. Of course, the recording device can also have two different cameras.

[0029] Advantageously, the recording device is designed to repeatedly generate the images. Accordingly, the image processing device is also capable of repeatedly processing the images. This allows multiple products to be inspected consecutively and / or piecewise, even if their spatial extent exceeds the inspection area.

[0030] Particularly suitable for the inspection of multiple and / or elongated products is a design of the inspection system that includes a conveyor device, such as a conveyor belt, for moving the product through the inspection area. In particular, this enables continuous relative movement between the product and the receiving device. The images can be taken during this continuous relative movement. This allows high inspection speeds to be achieved. In other words, thanks to the continuous relative movement, multiple products and / or multiple sub-areas of a product can be inspected in a shorter time while in motion.

[0031] Additionally or alternatively, the recording device can be configured as a line scan camera. This enables continuous recording of the product, allowing products of any length to be inspected. For this purpose, the line scan camera is continuously moved relative to the product. This relative movement can be achieved by means of the conveyor and / or by moving the line scan camera itself. The recording device can be configured to capture the images during this relative movement.

[0032] According to another possible embodiment, the inspection system is configured to record the at least one fluorescence image and the at least one reference image pixel-synchronously. In other words, for each pixel in the at least one fluorescence image, there is a corresponding pixel in the at least one reference image that depicts the same location in the inspection area, and vice versa. This increases the accuracy of the inspection system and the method according to the invention, particularly with regard to generating the correction image.

[0033] To achieve pixel synchronicity during continuous relative movement, the recording device can have two line scan cameras arranged spaced apart from one another or adjacent to one another. The inspection area is alternately irradiated with the first electromagnetic radiation and the second electromagnetic radiation, and images are recorded alternately with the two line scan cameras. The recording frequency of the two line scan cameras is set such that the time interval between two consecutive images corresponds to the quotient of the spatial distance between the two line scan cameras and the feed speed of the conveyor.

[0034] Pixel synchronicity can also be achieved if, instead of two line scan cameras spaced apart from each other, a multi-line line scan camera or a matrix camera is controlled line by line or in multiple lines, whereby the distance between the controlled lines of the matrix camera is taken into account in the above-mentioned quotient instead of the distance between the two line scan cameras.

[0035] Preferably, the conveyor device can have a rotary encoder that specifies a clock frequency to which the recording frequency of one or two cameras can be adapted.

[0036] In order to avoid motion blur in the at least one fluorescence image and the at least one reference image, the product can remain stationary within the scope of the method according to the invention, at least during each recording. This also makes it easy to achieve pixel synchronicity between the at least one fluorescence image and the at least one reference image. Preferably, the recording device in this embodiment is designed as a matrix camera. When inspecting several products, these can be moved discontinuously into the inspection area, e.g. using the conveyor device, and each remain static in the inspection area for a certain dwell time. The respective image recordings are generated within this dwell time.

[0037] In order to prevent the first electromagnetic radiation from overlapping with the second electromagnetic radiation in the image recordings, the recording of the at least one fluorescence image and the at least one reference image in the method according to the invention can be carried out with a time delay and / or a location delay.

[0038] The test arrangement according to the invention is suitable for a product composed of multiple layers or plies, wherein one layer contains the at least one fluorophore. The product can be, for example, an industrial product, in particular a multi-layer, multi-layered and / or laminated composite material or a product made of such a composite material, e.g., but not exclusively, one or more flooring laminates.

[0039] For the sake of clarity, the layer containing the at least one fluorophore is hereinafter referred to as the "fluorophore layer", although this layer does not have to consist entirely of the at least one fluorophore and may contain other components in addition to the at least one fluorophore.

[0040] The test setup according to the invention makes it possible to reliably detect defects (such as holes, cracks, detachments, and / or folds) in the fluorophore layer while minimizing the disruptive influence of secondary illumination effects. Thus, the quality of the product, particularly with regard to the fluorophore layer, can be reliably tested without secondary illumination effects distorting or influencing the results.

[0041] The secondary illumination effects can specifically be images of patterns, decorations, logos, inscriptions and / or other markings that are located, for example, on a layer of the product that is directly or indirectly adjacent to the fluorophore layer, are illuminated by the fluorophore layer when fluorescing, and therefore appear together with the defects in the at least one fluorescence image. Detecting the defects from the at least one fluorescence image alone, and in particular distinguishing them from the patterns, decorations, logos, inscriptions and / or other markings, is correspondingly difficult. Therefore, according to the invention, the patterns, decorations, logos, inscriptions and / or other markings are also specifically made visible in the at least one reference image. The defects, however, are only depicted in the at least one fluorescence image.Thus, the patterns, decorations, logos, inscriptions and / or other markings can be eliminated when generating the correction image, while the defects are transferred into the correction image.

[0042] The test arrangement according to the invention and also the method according to the invention are thus suitable, among other things, for the quality testing of flooring laminates, as long as a laminate layer contains the at least one fluorophore. The method according to the invention can therefore be used, in particular, as a quality testing method for such flooring laminates.

[0043] To ensure irradiation of the fluorophore layer, the fluorophore layer can be a topmost and / or outermost layer of the product. Alternatively, any number of layers transparent to the first electromagnetic radiation and the second electromagnetic radiation can be located between the fluorophore layer and the beam source device. The fluorophore layer is preferably located between the beam source device and a layer of the product that reflects the first electromagnetic radiation and the second electromagnetic radiation.

[0044] The invention is explained in more detail below by way of example with reference to the drawings. The combination of features illustrated by way of example in the embodiments shown can, in accordance with the above explanations, be supplemented by further features in accordance with the properties of the test arrangement according to the invention and / or the method according to the invention required for a specific application. Individual features can also be omitted from the described embodiments, also in accordance with the above explanations, if the effect of this feature is not important in a specific application. In the drawings, the same reference numerals are always used for elements with the same function and / or the same structure.

[0045] They show: Fig. 1: a schematic representation of a test arrangement with a test arrangement according to a first exemplary embodiment; Fig. 2: a schematic representation of a test arrangement with a test arrangement according to a second exemplary embodiment; Fig. 3: a schematic representation of a test arrangement with a test arrangement according to a third exemplary embodiment; Fig. 4: a schematic representation of a test arrangement with a test arrangement according to a fourth exemplary embodiment; and Fig. 5: a schematic representation of a fluorescence image, a reference image, and a correction image.

[0046] The structure and function of a test arrangement 2 according to the invention are described below with reference to Fig. 1 bis 5 described by way of example. Although some aspects of the invention are described only in the context of the test arrangement 2, it is of course possible for these aspects to also represent a description of the corresponding method, wherein, for example, a block, a module, a unit, a device, or a property of the test arrangement 2 corresponds to a method step or a function of a method step. Analogously, aspects that are described in the context of a method step also correspondingly represent a description of a block, a module, a unit, a device, or a property of the test arrangement.

[0047] In Fig. 1 A simplified, schematic representation of an exemplary embodiment of the test arrangement 2 is shown. The test arrangement 2 is intended for a fluorescence-based inspection of a product 6 containing at least one fluorophore 4. Depending on the application, the at least one fluorophore 4 has a known or predefined excitation spectrum and a known or predefined emission spectrum. The excitation spectrum can represent a continuous excitation wavelength range or a discrete excitation wavelength. The emission spectrum, in turn, can represent a continuous emission wavelength range or a discrete emission wavelength.

[0048] As in Fig. 1 As shown, the test arrangement 2 comprises, among other things, a beam source device 14, a recording device 16 and an image data processing device 18.

[0049] The recording device 16 serves to generate image recordings 24 of an inspection area 20 in which the product 6 can be arranged and / or is arranged.

[0050] The beam source device 14 serves to generate a first electromagnetic radiation 21 and a second electromagnetic radiation 22. The first electromagnetic radiation 21 has a first wavelength range that contains the excitation spectrum of the at least one fluorophore 4. The second electromagnetic radiation 22 has a second wavelength range that contains the emission spectrum of the at least one fluorophore 4. The first wavelength range preferably lies outside the emission spectrum and thus does not overlap with it. The second wavelength range preferably lies outside the excitation spectrum, so that they do not overlap.

[0051] As further stated in Fig. 1 As shown, the radiation source device 14 may comprise a single controllable radiator 55, such as a controllable LED, which is designed to generate the first electromagnetic radiation 21 and the second electromagnetic radiation 22, respectively.

[0052] In Fig. 2 An alternative embodiment is shown in which the radiation source device 14 has a first emitter 51 and a separate second emitter 52, wherein the first emitter 51 is configured to generate the first electromagnetic radiation 21 and the second emitter 52 is configured to generate the second electromagnetic radiation 22. For example, the first emitter 51 can be configured as a UV lamp 56. Accordingly, the first electromagnetic radiation 21 can be UV-A radiation 58.

[0053] The second radiator 52 can be designed as a polychrome lamp or a narrow-band lamp 60, in particular a monochromatic lamp 62, more precisely a color lamp 64, for example a blue light lamp, which generates light with the wavelength of the emission spectrum.

[0054] The first radiator 51 and the second radiator 52 are in the embodiment shown the Fig. 2 each designed as a flash light 66. Alternatively, the first spotlight 51 and / or the second spotlight 52 can shine continuously in the direction of the inspection area 20 and be dimmed alternately.

[0055] In another in Fig. 3 In the embodiment shown, the first radiator 51 and the second radiator 52 are arranged at a distance from one another and illuminate the inspection area 20 from two sides. Both the first radiator 51 and the second radiator 52 provide both electromagnetic radiations 21 and 22. In an alternative arrangement (not shown), only the first electromagnetic radiation 21 can be provided in the radiator 51 and only the second electromagnetic radiation 22 in the radiator 52. In a further Fig. 4 In the embodiment shown, two further radiators 53 and 54 are provided in addition to the first radiator 51 and the second radiator 52. Radiator 51 and the radiator 52 provide the first electromagnetic radiation 21, whereas radiator 53 and the radiator 54 provide the second electromagnetic radiation 22.

[0056] The test arrangement 2 is designed accordingly to irradiate the inspection area 20 with the first electromagnetic radiation 21 and to record with the recording device 16 at least one fluorescence image 26 of the inspection area 20 irradiated with the first electromagnetic radiation 21 (see Fig. 5 ). Furthermore, the test arrangement 2 is designed to irradiate the inspection area 20 with the second electromagnetic radiation 22 and to record with the recording device 16 at least one reference image 28 of the inspection area 20 irradiated with the second electromagnetic radiation 22 (see Fig. 5 ).

[0057] Although in Fig. 1 and 2Both the first electromagnetic radiation 21 and the second electromagnetic radiation 22 are shown, the respective irradiation with the first electromagnetic radiation 21 and the second electromagnetic radiation 22 preferably takes place with a time offset. Accordingly, the recording of the at least one fluorescence image 26 and the at least one reference image 28 also takes place with a time offset from one another.

[0058] The recording device 16 can, for example, have a single camera 68, in particular a fluorescence camera 70, or even several cameras. The cameras 68 of the embodiments shown in Fig. 1 and 2are each configured as line scan cameras 72, 72a, 72b. In these embodiments, the inspection arrangement 2 also includes a conveyor 74, in particular a conveyor belt 76, for moving the product 6 through the inspection area 20. This enables a continuous relative movement 78 between the product 6 and the receiving device 16. Alternatively or additionally, the receiving device 16 can also be moved relative to the product 6.

[0059] As in Fig. 1 As shown, the recording device 16 can have two line scan cameras 72a, 72b. The two line scan cameras 72a, 72b can be arranged next to one another or at a distance from one another. Thus, the inspection area 20 can be alternately irradiated with the first electromagnetic radiation 21 and the second electromagnetic radiation 22 and can be recorded alternately with the two line scan cameras 72a, 72b. Preferably, the recording frequency of the two line scan cameras 72a, 72b is set such that a time interval between two consecutive recordings corresponds to the quotient of the spatial distance 80 between the two line scan cameras 72a, 72b and the feed speed of the conveyor 74. In this way, pixel synchronism between the at least one fluorescence image 26 and the at least one reference image 28 can be achieved. Optionally, the conveyor 74 may have a rotary encoder 82 that provides a timing for this purpose.

[0060] The sensitivity of the recording device 16 can be limited to the second wavelength range by hardware and / or software. Thus, with the illustrated embodiment, the first wavelength range is not imaged in the at least one fluorescence image 26.

[0061] Optionally, the test arrangement 2 can comprise a filter device (not shown) between the inspection area 20 and the recording device 16. The filter device can be configured to block the first wavelength range and / or to pass only the second wavelength range, preferably the emission spectrum. In particular, the filter device can comprise corresponding optical filters, ie, band-stop filters and / or bandwidth filters.

[0062] Furthermore, the test arrangement 2 can optionally comprise a light shielding device (not shown) for darkening or at least darkening the inspection area 20. Alternatively, the test arrangement 2 can also comprise a darkroom.

[0063] The image data processing device 18 serves for image processing of the image recordings 24, 26, 28. In particular, the image data processing device 18 is designed to generate a correction image 30 based on the at least one fluorescence image 26 and the at least one reference image 28 (see Fig. 5 ).

[0064] The correction image 30 can be generated, for example, by subtracting the at least one fluorescence image 26 and the at least one reference image 28. For this purpose, the image data processing device 18 can have a subtraction module 34 for performing the subtraction. The subtraction module 34 can be configured to subtract the color values ​​or brightness values ​​from the image data of the at least one fluorescence image 26 and the at least one reference image 28 pixel by pixel and to output the respective resulting value as the color value or brightness value of an associated pixel in the correction image 30.

[0065] Optionally, the image data processing device 18 can further comprise a geometry adjustment module 36 for performing a geometry adjustment and a contrast adjustment module 40 for performing a contrast adjustment. The geometry adjustment module 36 can be configured to align the at least one fluorescence image 26 congruently or at least approximately congruently with the at least one reference image 28. The contrast adjustment module 40 can, in turn, be configured to mutually adjust or at least approximately adjust the contrast ratios of the at least one fluorescence image 26 and the at least one reference image 28.

[0066] In addition, the image data processing device 18 can have a shape recognition module 44 for performing a, preferably automatic, shape recognition in the correction image 30. The shape recognition module 44 can be configured to perform the shape recognition using a threshold method or another method or algorithm known from the prior art.

[0067] The image data processing device 18 and its components, i.e., the subtraction module 34, the geometry adjustment module 36, the contrast adjustment module 40, and / or the shape recognition module 44, can be implemented independently of one another using hardware and / or software, in particular using computer-implemented methods. The image data processing device 18 is configured, for example, as an image data processor 50.

[0068] The functioning of the test arrangement 2 according to the invention is explained below using a concrete application example.

[0069] The product 6 may, for example, be an industrial product composed of several layers or plies, in particular a multi-layer, multi-layer and / or laminated composite material or a product made of such a composite material, for example, but not exclusively, a flooring laminate 8.

[0070] A layer 10 of the product 6 contains the at least one fluorophore 4. For better comprehensibility of the text, the layer 10 with the at least one fluorophore 4 is referred to below as fluorophore layer 12, although this layer 10 does not have to consist entirely of the at least one fluorophore 4 and can have further components in addition to the at least one fluorophore 4.

[0071] In the example shown the Fig. 1 The fluorophore layer 12 is shown as the uppermost and outermost layer of the product 6. However, the present invention can also be used for products in which further layers transparent to the first electromagnetic radiation 21 and the second electromagnetic radiation 22 are located on the fluorophore layer 12.

[0072] The fluorophore layer 12 is located in the example shown in the Fig. 1 on a layer 86 of the product 6 which reflects the first electromagnetic radiation 21 and the second electromagnetic radiation 22, in particular the emission spectrum. The fluorophore layer 12 is preferably arranged such that it is located between the beam source device 14 and the reflective layer 86 and between the receiving device 16 and the reflective layer 86.

[0073] The reflective layer 86 may have markings such as patterns, decorations, logos or inscriptions, which represent a perfect characteristic of the product 6. In Fig. 1 A marking 88 is indicated purely as an example.

[0074] The fluorophore layer 12 may have unwanted defects 90, 92, which are not visible to the naked eye or with conventional optical inspection measures due to the transparency and / or the small layer thickness of the fluorophore layer 12. Such defects 90, 92 include, for example, holes 94 in the fluorophore layer 12 or detachments 96 and folds 98 of the fluorophore layer 12. This is shown in the magnification 100 in Fig. 1 Here, the fluorophore layer 12 is shown partially rolled up for purposes of differentiation from the reflective layer 86.

[0075] As in Fig. 5 As shown on the left, the defects 90, 92 can be made visible in the at least one fluorescence image 26, especially since defects 90 at which the fluorophore layer 12 is interrupted do not fluoresce and defects 92 at which the fluorophore layer 12 is doubled fluoresce differently than the rest of the fluorophore layer 12. In particular, the defects 90, 92 differ significantly in their optical properties from the rest of the fluorophore layer 12.

[0076] At the same time, however, the marking 88 also becomes visible in the at least one fluorescence image 26, since the fluorophore layer 12, when fluorescing, produces secondary illumination effects which make the marking 88 appear in the at least one fluorescence image 26.

[0077] Under certain circumstances, the difference between defects 90, 92 and marking 88 may not be clear enough to make a reliable distinction, for example in the context of shape recognition.

[0078] According to the invention, the aforementioned secondary illumination effects are therefore specifically recreated in the at least one reference image 28. This is achieved in particular because the second wavelength range of the second electromagnetic radiation 22 contains the emission spectrum of the at least one fluorophore 4, and thus the illumination conditions that existed at the time the secondary illumination effects occurred can be simulated. Consequently, the marking 88 is also imaged in the at least one reference image 28.

[0079] As in Fig. 5 shown centrally, the defects 90, 92 are not visible in the at least one reference image 28, since the second wavelength range preferably does not overlap with the excitation spectrum of the at least one fluorophore 4. In particular, when recording the at least one reference image 28, no or at least only very little fluorescence of the at least one fluorophore 4 is triggered, so that the defects 90, 92 do not appear or at least not as clearly as in the at least one fluorescence image 26.

[0080] Consequently, when generating the correction image 30, the visibility of the marking 88 can be completely eliminated or at least reduced, while the visibility of the defects 90, 92 remains unchanged or at least decreases only slightly. This is Fig. 5 shown on the right.

[0081] With the aid of the test arrangement 2 according to the invention and with the aid of the method according to the invention, the correction image 30 can thus be generated in such a way that a more reliable detection of the defects 90, 92 is possible by eliminating the disturbing influence of the marking 88.

Claims

1. Test arrangement (1, 2) for the fluorescence-based inspection of a laminate product composed of a plurality of layers (10, 12, 86), wherein one layer (10, 12) contains at least one fluorophore (4) with an excitation spectrum and an emission spectrum, wherein the test arrangement (2) comprises - a beam source device (14) for generating first electromagnetic radiation (21) in a first wavelength range containing the excitation spectrum of the at least one fluorophore (4), wherein the first beam source device (14) is in the form of a UV lamp, UV light fitting, black-light lamp or black-light light fitting and thus the first electromagnetic radiation (21) is UV-A radiation, and second electromagnetic radiation (22) in a second wavelength range containing the emission spectrum of the at least one fluorophore (4), - a capturing device (16) for generating images (24) of an inspection region (20) in which the product (6) can be arranged, and - an image data processing device (18) for processing the images (24), and is configured to capture, by means of the capturing device (16), at least one fluorescence image (26) of the inspection region (20) irradiated with the first electromagnetic radiation (21) and to capture, by means of the capturing device (16), at least one reference image (28) of the inspection region (20) irradiated with the second electromagnetic radiation (22), and wherein the image data processing device (18) is configured to generate a correction image (30) by differencing the at least one fluorescence image (26) and the at least one reference image (28).

2. Test arrangement (1, 2) according to claim 1, wherein the image data processing device (18) has a subtraction module (34) for carrying out the differencing.

3. Test arrangement (1, 2) according to claim 2, wherein the subtraction module (34) is configured to subtract, pixel by pixel, the color values or brightness values from the image data of the at least one fluorescence image (26) and of the at least one reference image (28) and to output the relevant result value as a color value or brightness value of the corresponding pixel of the correction image (30).

4. Test arrangement (1, 2) according to any of claims 1 to 3, wherein the image data processing device (18) is configured to perform shape recognition in the correction image (30).

5. Test arrangement (1, 2) according to any of claims 1 to 4, wherein the first wavelength range lies outside the emission spectrum of the at least one fluorophore (4).

6. Test arrangement (1, 2) according to any of claims 1 to 5, wherein the second wavelength range lies outside the excitation spectrum of the at least one fluorophore (4).

7. Test arrangement (1, 2) according to any of claims 1 to 6, wherein the second electromagnetic radiation (22) can be generated by a blue-light lamp.

8. Test arrangement (1, 2) according to any of claims 1 to 7, wherein the test arrangement (1, 2) has a conveyor apparatus (74) for moving the product (6) through the inspection region (20), and wherein the capturing device (16) is in the form of a line scan camera (72) or a multi-line line scan camera, or a matrix camera in line mode or multi-line mode.

9. Test arrangement (1, 2) according to any of claims 1 to 8, wherein the test arrangement (1, 2) is configured to capture the at least one fluorescence image (26) and the at least one reference image (28) pixel-synchronously.

10. Method for the fluorescence-based inspection of a laminate product composed of a plurality of layers (10, 12, 86), wherein one layer (10, 12) contains at least one fluorophore (4) with an excitation spectrum and an emission spectrum, comprising the following steps: - positioning the laminate product in an inspection region (20), - capturing at least one fluorescence image (26) of the inspection region (20) irradiated with first electromagnetic radiation (21) containing the excitation spectrum of the at least one fluorophore (4), - capturing at least one reference image (28) of the inspection region (20) irradiated with second electromagnetic radiation (22) containing the emission spectrum of the at least one fluorophore (4), and - generating a correction image (30) by differencing the at least one fluorescence image (26) and the at least one reference image (28).

11. Method for the fluorescence-based inspection of a laminate product, wherein color values or brightness values are subtracted, pixel by pixel, from the image data of the at least one fluorescence image (26) and of the at least one reference image (28), and the respective result values are output as a color value or brightness value of the associated pixel of the correction image (30).