SENSOR AND METHOD FOR INSPECTING VALUE DOCUMENTS, SENSOR SYSTEM AND VALUE DOCUMENT PROCESSING DEVICE

Description

[0001] The invention relates to a sensor and a method for checking valuable documents, in particular banknotes, a sensor system and a valuable document processing device.

[0002] To prevent counterfeiting, valuable documents, especially banknotes, are equipped with so-called security or authentication features. Depending on the type and design, the features present on a valuable document can differ significantly in their optical properties. For example, a valuable document might have a printed window with high electromagnetic permeability and simultaneously a micro-perforation with significantly lower electromagnetic permeability.During the automated verification of such valuable documents, it can therefore occur that the electromagnetic radiation striking different features of a valuable document is reflected, transmitted, and / or absorbed to significantly different degrees, or that the features exhibit significantly different luminescence. As a result, depending on the feature, too little or too much radiation may reach a detector designed to detect the radiation emitted by the valuable document. This can lead to the corresponding detector signal being too weak and lost in the noise, or the detector being overloaded. In such cases, a reliable verification of the features cannot be guaranteed.

[0003] US Patent 2010 / 0128964 discloses a method for examining securities, whereby the security is illuminated with light of multiple wavelengths and an image is captured at the corresponding wavelengths using a line scan camera. The patent also discloses the examination of multiple security features in different areas of the security, whereby the areas can be illuminated with different light intensities and wavelengths.

[0004] US 2020 / 0111277 A1 also discloses the examination of securities, whereby an RGB image and optionally an image under UV illumination are captured.

[0005] It is an object of the invention to provide a sensor, a method, a sensor system and a document processing device for the most reliable possible testing of documents with different features.

[0006] This task is solved by a sensor and a method according to the independent claims and a sensor system and a document processing device with such a sensor or sensor system.

[0007] A sensor for checking valuable documents, in particular banknotes, according to a first aspect of the present disclosure, comprises: at least one radiation source configured to subject a valuable document to electromagnetic radiation, and a detector configured to detect electromagnetic radiation emanating from the valuable document (e.g., transmitted, remitted, or emitted) in at least two different spectral ranges (so-called color channels) with spatial resolution (pixel by pixel), and thereby generating a (spatially resolved) detector signal for each of the spectral ranges (color channels) corresponding to the intensity of the detected electromagnetic radiation in the respective spectral range, in particular recording an image or partial image of the valuable document for each of the spectral ranges (color channels), e.g., a transmission image or partial image, a remission image or partial image, or a luminescence image or partial image.The at least two different spectral ranges include a first and a second spectral range that is different from the first, and possibly one or more further spectral ranges that are different from the first.

[0008] Aspects of the present disclosure are based on the approach of establishing or implementing a color channel-specific attenuation in the first spectral range relative to the second spectral range in the sensor. The color channel-specific attenuation can, for example, a color channel-specific attenuation of the electromagnetic radiation of the first spectral range irradiated onto the security document relative to the electromagnetic radiation of the second spectral range irradiated onto the security document and / or a color channel-specific attenuation of the electromagnetic radiation of the first spectral range to be detected by the detector relative to the electromagnetic radiation of the second spectral range to be detected by the detector and / or a color channel-specific attenuation for the (spatially resolved) detector signals of the first spectral range relative to the (spatially resolved) detector signals of the second spectral range.

[0009] Preferably, when examining the respective security document, the color channel-specific attenuation within the respective security document, i.e., during the detection of the electromagnetic radiation emanating from the respective security document, is constant over time. Therefore, no dynamic attenuation of the first spectral range relative to the second spectral range is required during the detection of the electromagnetic radiation emanating from the security document (reduced measurement effort).

[0010] Preferably, the color channel-specific attenuation of the intensity in the first spectral range or of the detector signals of the first spectral range relative to that of the intensity in the second spectral range or relative to the detector signals of the second spectral range is at least a factor of 5, particularly preferably at least a factor of 10.

[0011] Color channel-specific attenuation can be achieved on the detector side and / or on the illumination side. In particular, color channel-specific attenuation (on the detector side) can be implemented using a color channel-specific filter and / or a color channel-specific (color channel-selective) amplifier. Alternatively or additionally, color channel-specific attenuation (on the illumination side) can be implemented using a color channel-specific filter and / or color channel-specific (spectral-selective) attenuation of the radiation source(s).

[0012] The sensor has an evaluation device which is designed to check a first feature provided on or in the valuable document, in particular an authenticity or security feature, (only) on the basis of the detector signals generated for the at least one first spectral range, and to check a second feature provided on or in the valuable document (different from the first feature), in particular an authenticity or security feature, taking into account the detector signals generated for the at least one second spectral range.

[0013] In particular, the evaluation system can be configured to check the first feature (only) based on the detector signals generated for the at least one first spectral range, without considering the detector signals generated for the at least one second spectral range. The evaluation system can also be configured to check the second feature (only) based on the detector signals generated for the at least one second spectral range, without considering the detector signals generated for the at least one first spectral range, or taking into account the detector signals generated for both the at least one first and the at least one second spectral range (e.g., to obtain higher detection signals for the second feature). The first and second features are spatially offset from each other, and in particular, do not overlap, and are arranged on or within the respective security document.

[0014] For color channel-specific attenuation, the sensor can have at least one color channel-specific filter, which is / are arranged between the detector and the valuable document and / or between the radiation source and the valuable document, and which is / are configured to attenuate the electromagnetic radiation emanating from or impinging on the valuable document in the first spectral range relative to the second spectral range, preferably by a factor of at least 5, particularly preferably by a factor of at least 10. The color channel-specific filter has the advantage that the color channel-specific attenuation is then achieved without a (complex) color channel-specific correction or amplification of the detector signals.

[0015] Alternatively or additionally, the sensor for color channel-specific attenuation can have at least one amplifier configured to amplify the detector signals generated for the different spectral ranges, wherein the amplification of the (spatially resolved) detector signals generated for the first spectral range is smaller than the amplification of the (spatially resolved) detector signals generated for the second spectral range, preferably by a factor of at least 5, and particularly preferably by a factor of at least 10.

[0016] The sensor's radiation source(s) can be suitable for illuminating the valuable document (especially simultaneously) with electromagnetic radiation of the first and second spectral ranges and, if necessary, further spectral ranges (e.g., with white light containing the first and second spectral ranges). This is the case, for example, when the sensor performs a remission or transmission test of the first and second features. For example, an LED array arranged perpendicular to the transport direction of the valuable document is used as the radiation source. This array includes LEDs for both the first and second spectral ranges, distributed along its length.

[0017] Preferably, the first and second spectral ranges lie within the visible spectrum. This has the advantage that the spectral range in which the sensor inspects the first and second features is precisely where a human observer would inspect them—namely, within the visually visible spectrum. Especially for first and second features designed for visual inspection, the result of the automated sensor inspection is then more comparable to the result of visual inspection.

[0018] For color channel-specific attenuation, the radiation source(s) can be attenuated in such a way that their emission intensity in the at least one first spectral range is lower, preferably by a factor of at least 5, and particularly preferably by a factor of at least 10, than in the at least one second spectral range. Color channel-specific attenuation of the radiation source(s) also has the advantage that it is achieved without (complex) color channel-specific correction or amplification of the detector signals. The radiation sources are, for example, several spectrally distinct LEDs for the first and second spectral ranges, which are typically operated such that their emission intensity is comparably high, i.e., differs by at most a factor of 2.For example, red, blue and green LEDs are operated simultaneously to produce white light.

[0019] A sensor system according to a second aspect of the present disclosure comprises a sensor according to the first aspect and a security document, in particular a banknote, which has: at least a first feature, in particular a authentication or security feature, which is configured to emit electromagnetic radiation, in particular to transmit, remit and / or emit, and at least a second feature, in particular an authentication or security feature, which is configured to emit electromagnetic radiation, in particular to transmit, remit and / or emit, wherein the first feature has a higher remission or transmission and / or lower absorption for the electromagnetic radiation with which the security document is exposed than the second feature.wherein the difference in remission / transmission / absorption for the electromagnetic radiation of the first and second spectral ranges is in particular at least a factor of 5, e.g. at least a factor of 10. According to the invention, the first authentication or security feature is a (essentially transparent) window integrated into the valuable document, which is covered with a film. The film can be unstructured or uniformly transparent in the area of ​​the window, or it can have one or more motifs, symbols, or alphanumeric characters there. In particular, the second authentication or security feature is a microperforation of the valuable document, which has a multitude of small holes and / or transparent areas in the valuable document, in particular each with a diameter of less than 1 mm, which together form, for example, one or more motifs, symbols, or alphanumeric characters.

[0020] A document processing device according to a third aspect of the present disclosure comprises: a sensor according to the first aspect or a sensor system according to the second aspect and a transport device which is configured to transport documents of value, in particular relative to the sensor.

[0021] In a method for checking valuable documents, in particular banknotes, according to a fourth aspect of the present disclosure, electromagnetic radiation is generated by at least one radiation source, with which a valuable document is exposed, and electromagnetic radiation emanating from the valuable document is detected by a detector having a plurality of detector elements arranged at different locations in at least two different spectral ranges / color channels, spatially resolved (pixel), and thereby generates a (spatially resolved) detector signal for each of the spectral ranges corresponding to the intensity of the detected electromagnetic radiation in the respective spectral range, in particular recording an image or partial image of the valuable document for each of the spectral ranges.The first (authenticity or security) feature provided on or in the security document (mentioned above) is checked (only) using the detector signals generated for at least one first spectral range (of the spectral ranges mentioned above). The second (authenticity or security) feature provided on or in the security document (mentioned above) is checked taking into account the detector signals generated for at least one second spectral range (of the spectral ranges mentioned above).

[0022] A color channel-specific attenuation is / will be established in the first spectral range relative to the second spectral range, in particular a color channel-specific attenuation of the electromagnetic radiation of the first spectral range radiated onto the security document relative to the electromagnetic radiation of the second spectral range radiated onto the security document and / or a color channel-specific attenuation of the electromagnetic radiation of the first spectral range to be detected by the detector relative to the electromagnetic radiation of the second spectral range to be detected by the detector and / or a color channel-specific attenuation for the detector signals of the first spectral range relative to the detector signals of the second spectral range.

[0023] In particular, the electromagnetic radiation emanating from the security document orwith which the valuable document is exposed, are attenuated in the first spectral range relative to the second spectral range by means of at least one filter arranged between the detector and the valuable document and / or between the radiation source and the valuable document, or the (spatially resolved) detector signals generated for the different spectral ranges are amplified by means of an amplifier, wherein the amplification of the detector signals generated for the first spectral range is less than the amplification of the detector signals generated for the second spectral range, or a color channel-specific attenuation of the radiation source(s) suitable for emission in the first and second spectral ranges takes place, wherein the radiation source(s) are operated in particular such that their intensity in the at least one first spectral range is lower, preferably by a factor of at least 5, than in the at least one second spectral range.

[0024] Unless otherwise stated, the terms "spectral range", "spectral channel" and "color channel" are used synonymously in connection with the present disclosure.

[0025] Color channel-specific attenuation can be achieved on the detector side by using at least one filter arranged on or in front of the detector, for example, a so-called RGB detector with color channels in the red, green, and blue spectral ranges. This filter attenuates the electromagnetic radiation emanating from the security document in at least one first color channel compared to at least one second color channel, in particular by a factor of at least 5, preferably by a factor of at least 10. The filter can be designed as a so-called spectral filter, which attenuates, in particular absorbs, the electromagnetic radiation more strongly in at least one first color channel or spectral range than in at least one second color channel or spectral range. Alternatively or additionally, the filter can also be designed as a so-called neutral density filter, in which spectrally non-selective or non-selective filters are placed in front of detector pixels that are assigned to at least one first color channel.Spectrally homogeneous filter elements are arranged, by which the electromagnetic radiation incident on the detector pixels of at least one first color channel is attenuated compared to other detector pixels assigned to at least one second color channel. Alternatively or additionally, it can be provided that the detector signals obtained for the different color channels are amplified to different degrees, wherein the amplification of the detector signals obtained for at least one first color channel is, in particular by at least a factor of 5, preferably by at least a factor of 10, smaller than the amplification of the detector signals obtained for at least one second color channel.

[0026] The color channel-specific attenuation can also be achieved on the illumination side, by having the radiation source for illuminating the valuable document generate electromagnetic radiation whose intensity in at least one first color channel is lower than in at least one second color channel, in particular by a factor of at least 5, preferably by a factor of at least 10. For example, the radiation source can have two or more light sources, for example in the form of LEDs, each emitting light in the different color channels or spectral ranges, wherein the light emitted in at least one first color channel or spectral range has an intensity, in particular by a factor of at least 5, preferably by a factor of at least 10, lower than the light emitted in at least one second color channel or spectral range. Alternatively or additionally, the radiation source (which, for example,emits white light) and the security document is provided with a filter, in particular a spectral filter, which attenuates the electromagnetic radiation generated by the radiation source in at least a first color channel compared to at least a second color channel, in particular by at least a factor of 5, preferably by at least a factor of 10.

[0027] The color channel-specific attenuation described above (detector-side or illumination-side) ensures that the electromagnetic radiation to be detected or detected by the detector has a lower intensity in the at least one first color channel than in the at least one second color channel. The detector thus generally provides usable detector signals for the at least one first color channel, particularly without overloading, even when the intensity of the electromagnetic radiation emanating from the valuable document is relatively high, for example, in the case of a transmission measurement under bright-field illumination of a printed window provided in the valuable document. In contrast, the electromagnetic radiation to be detected or detected by the detector...The detected electromagnetic radiation in the at least one second color channel has a higher intensity than in the at least one first color channel, so that the detector for the at least one second color channel generally delivers usable detector signals of sufficient amplitude or above a certain signal-to-noise ratio even when the intensity of the electromagnetic radiation emanating from the document is relatively low, for example, in the case of a transmission measurement under bright-field illumination of a so-called microperforation with very small diameters of, for example, 100 µm provided in the document. Based on the detector signals obtained for the at least one first and second color channel respectively, the different features (window or microperforation in the above example) can then be examined.Without the color channel-specific attenuation, the difference between the detector signals of the first feature and the detector signals of the second feature would be so large that it would exceed the dynamic range of the detector.

[0028] The color channel-specific attenuation makes it possible to examine the first and second features of the respective document based on a single measurement / image capture by the detector, i.e., different features on the same document whose optical properties / absorption differ significantly from each other.

[0029] Overall, the invention thus enables a reliable examination of securities with different features. In particular, the measurement effort required to measure these features is reduced.

[0030] Preferably, the first feature has a higher reflectance (in the case of detection in reflection geometry) or higher transmittance (in the case of detection in transmission geometry) and / or a lower absorption (in the case of detection in transmission geometry) for the electromagnetic radiation applied to the security document than the second feature. In the case of luminescent, and in particular fluorescent, features, the electromagnetic radiation emitted by the first feature has a higher intensity than the electromagnetic radiation emitted by the second feature. Due to the detector- and / or illumination-side color channel-specific attenuation described above, it is possible to detect both the first and the second feature in a single measurement process and to use the resulting detector signals for their verification, even if the transmittance or reflectance is higher than the second feature.The luminescence intensity of the first feature is significantly higher (especially by at least a factor of 10) than that of the second feature.

[0031] The detector comprises a multitude of detector elements (pixels) arranged at different locations, which spatially resolve the electromagnetic radiation emanating from the valuable document. The detector is, in particular, an image sensor (with detector pixels arranged in a line or two dimensions) that captures an image or partial image of the valuable document for both the first and second spectral ranges. The detector is preferably a CCD or CMOS camera with detector elements arranged along a line or over a two-dimensional surface, which are equipped with an absorbing color mask, so-called Bayer filter or Bayer matrix, wherein a color filter (in one of the three primary colors red (R), green (G), or blue (B)) is provided in front of each individual detector element. Alternatively, the detector could also be, for example, a...This involves a CMOS or CCD sensor in which – instead of several adjacent detector elements (pixels) – three superimposed sensor elements, each sensitive to different color channels, are used to record color information with each pixel. This achieves spatially resolved and spectrally resolved detection of the electromagnetic radiation emitted by the valuable document, according to spectral ranges or color channels.

[0032] To perform a transmission or remission test of the first and second features, the radiation source is set up to subject the security document to electromagnetic radiation in the first and second spectral ranges.

[0033] Preferably, the radiation source is configured to expose the first and second features of the respective security document to electromagnetic radiation in the first and second spectral ranges, particularly to the same electromagnetic radiation (of the same intensity and with the same spectral profile) during the inspection. For example, the security document to be inspected is continuously exposed to the same electromagnetic radiation (as it passes the sensor) – either continuously or by means of multiplex illumination. Therefore, it is unnecessary to dynamically adjust the intensity of the electromagnetic radiation (or other measurement parameters) to the feature during the inspection of different features of the same security document.

[0034] Alternatively, the radiation source can be configured to illuminate the first feature only with electromagnetic radiation from the first spectral range (not the second spectral range) and the second feature only with electromagnetic radiation from the second spectral range (not the first spectral range). This can be done dynamically as the document passes by. Or, if the first and second features are positioned on / in the document at a distance perpendicular to the transport direction, the color channel-specific attenuation can remain constant (i.e., be non-dynamic) during transport and be limited to the corresponding spatial area (defined perpendicular to the transport direction) in which the first feature is located on the document.Even then, it is unnecessary to dynamically adjust the intensity of electromagnetic radiation during the examination of different features of the same security document.

[0035] For example, the color-channel-specific filter can be spatially arranged so that it attenuates only the electromagnetic radiation of the (e.g., upper / lower) section of the security document containing the first feature, but not the electromagnetic radiation of the (e.g., lower / upper) section containing the second feature. Alternatively, the detector signals of the first spectral range can be amplified less only in the security document section containing the first feature, but not in the security document section containing the second feature. Or, in the spatial area of ​​the radiation source corresponding to the first feature (e.g.,In the case of LED radiation sources (in the form of an LED array oriented perpendicular to the transport direction, with spectrally distinct LEDs), only those radiation sources that illuminate the first feature with electromagnetic radiation from the second spectral range are switched on (but not those from the second spectral range). Within the spatial area of ​​the radiation source corresponding to the second feature, only the radiation sources of the second spectral range are switched on. However, both radiation sources can also be switched on in the latter area to illuminate the second feature with electromagnetic radiation from both the first and second spectral ranges (higher intensity is achievable).

[0036] Preferably, the filter is configured to attenuate the electromagnetic radiation in the at least one first spectral range relative to the at least one second spectral range to the same extent for essentially all detector elements (pixels). The color channel-specific attenuation is thus performed identically for all detector elements (pixels), allowing the use of a simple spectral filter. This enables the testing of features with significantly different optical properties in a particularly simple and robust manner.

[0037] Preferably, the at least one filter is configured to attenuate the electromagnetic radiation emanating from or impinging upon the valuable document such that the intensity of the electromagnetic radiation detected by the detector in the at least one first and second spectral ranges is greater than a lower intensity threshold (noise) of the detector and less than an upper intensity threshold (overload, saturation) of the detector. Alternatively or additionally, the at least one radiation source may be configured to impart electromagnetic radiation to the valuable document in such a way that the intensity of the electromagnetic radiation detected by the detector in the at least one first and second spectral ranges is greater than a lower intensity threshold (noise) of the detector and less than an upper intensity threshold (overload, saturation) of the detector.The second spectral range is greater than a lower intensity threshold (noise) of the detector and less than an upper intensity threshold (overdrive, saturation) of the detector. In both of the aforementioned designs, it is particularly ensured that in a single measurement process (irradiation of the valuable document and detection of the electromagnetic radiation emanating from the valuable document), both the electromagnetic radiation emanating from a more strongly reflecting, transmitting, or luminescent first feature in the at least one first color channel and the electromagnetic radiation emanating from a significantly less strongly reflecting, transmitting, or luminescent second feature in the at least one second color channel can be reliably detected and converted into corresponding detector signals without them being too low or due to detector overdrive in the first or second color channel.The second color channel is unusable.

[0038] Preferably, the first feature exhibits better detectability or higher contrast in the at least one first spectral range than in the at least one second spectral range. Alternatively or additionally, the second feature exhibits better detectability or higher contrast in the at least one second spectral range than in the at least one first spectral range. This preferred embodiment is based on the approach of selecting or using the color channel(s) for testing a feature in which the feature in question can be detected particularly well, for example, because the spatial structure of the respective feature is particularly recognizable and / or has particularly high contrast in this color channel, and / or any influences from electromagnetic radiation emanating from other features or areas of the security document are particularly low.This ensures a particularly reliable examination of different features on the security document.

[0039] Further advantages, features and applications of the present invention will become apparent from the following description in conjunction with the figures. The figures show: Fig. 1 is an example of a security document processing device; Fig. 2 is an example of a banknote with two different features; Fig. 3 is an example of a sensor for checking security documents; and Fig. 4a) to f) is a schematic representation to illustrate the detection or verification of two different features by means of color channel-specific attenuation of the electromagnetic radiation detected by the detector.

[0040] Figure 1Figure 1 shows a schematic representation of a document processing device. In a receiving unit 2, also referred to as an input tray, documents 1, in particular banknotes, are provided, preferably in the form of a stack. By means of a singulation device (not shown), the documents 1 are individually removed from the stack and transferred to a transport unit 3, by which they are conveyed through the document processing device.

[0041] The valuable documents are examined for their optical properties using a sensor 10. For this purpose, the sensor 10 has a radiation source 11 that generates electromagnetic radiation, which is used to irradiate the valuable document 1 being examined. The electromagnetic radiation emanating from the valuable document 1, e.g., remitted, reflected, transmitted, and / or emitted due to luminescence, is spatially resolved by a detector 12 in at least two different spectral ranges, corresponding to different color channels (e.g., red, green, and blue) of the detector 12.

[0042] In the present example, radiation source 11 and detector 12 are arranged in a transmission geometry, in which the detector 12 detects the electromagnetic radiation transmitted by the valuable document 1. Depending on the arrangement of the radiation source 11 relative to the detector 12, this results in either bright-field illumination (essentially perpendicular angle of incidence of the radiation on the valuable document 1) or dark-field illumination (oblique angle of incidence of the radiation on the valuable document 1).

[0043] Alternatively or in addition to the transmission geometry, radiation source 11 and detector 12 can also be arranged in reflection geometry above one side of the value document 1 in order to detect the electromagnetic radiation reflected, remitted and / or emitted by the value document 1.

[0044] In addition to such an optical sensor 10, further sensors (not shown) may also be provided for recording or checking further properties of the valuable documents 1.

[0045] Depending on the result of the inspection, controlled switches 4 and 5 transfer the individual valuable documents 1 to a first or second output tray 6 or 7. For example, valuable documents 1 of good quality are placed in the first output tray 6, and valuable documents 1 of poor quality are placed in the second output tray 7. Depending on the application, the valuable documents 1 can be placed in the different output trays 6 and 7 alternatively or additionally based on their denomination or the presence of a suspicion of forgery. Further switches and output trays (not shown) or additional processing facilities, such as a shredder for destroying valuable documents 1 with specific properties, may also be provided, as indicated by an arrow at the end of the transport path.

[0046] Figure 2Figure 1 shows an example of a security document 1 in the form of a banknote with two different features. In the present example according to the invention, a first feature M1 is designed as a transparent window in the form of a film integrated into the security document 1, which is printed with motifs, symbols and / or alphanumeric characters. In a second feature M2, the number "200" is incorporated into the security document 1 in the form of a so-called microperforation. Such a microperforation consists of a multitude of small holes and / or transparent areas in the security document 1, each typically having a diameter between 100 and 300 µm, which together form a pattern, in this case the number "200".

[0047] Due to their properties, the first feature M1 and the second feature M2 have significantly different transmittances for electromagnetic radiation. Thus, detecting and testing the microperforation of feature M2 in transmission requires bright-field illumination with a relatively high intensity. In contrast, detecting and testing the printed window of feature M1 in transmission requires a considerably lower illumination intensity. The differences in the required intensity can be so large that they affect the dynamics of detector 12 (see Fig. 1 ) exceed. Then either the second feature M2 (microperforation) would be too dark, i.e., not detectable, or the first feature M1 (window) would be overexposed and therefore also not detectable.

[0048] To enable reliable detection and testing of such features with strongly different optical properties, a color channel-specific attenuation of the electromagnetic radiation to be detected or detected by the detector is carried out on the detector and / or illumination side, which is described in more detail below.

[0049] Figure 3 Figure 10 shows an example of a sensor 10 for checking valuable documents 1. A radiation source 11 generates electromagnetic radiation 8, which is applied to the valuable document 1 to be checked. The electromagnetic radiation 8 can be, for example, visible (VIS), infrared (IR) and / or ultraviolet (UV) radiation.

[0050] In the case of the bright-field illumination shown here, the electromagnetic radiation 8 strikes the document 1 essentially perpendicularly. Alternatively, dark-field illumination can also be provided, in which the electromagnetic radiation 8 strikes the document obliquely, as indicated by the two dashed arrows.

[0051] To generate the electromagnetic radiation 8, the radiation source 11 can, for example, be designed as a white light source or have two or more light sources 16 that generate electromagnetic radiation in different spectral ranges. For example, the light sources 16 can be light-emitting diodes (LEDs) that emit electromagnetic radiation in the red, green, or blue spectral range.

[0052] By mixing the electromagnetic radiation emitted by the light-emitting diodes, white or at least essentially white light can also be obtained.

[0053] The electromagnetic radiation 9 transmitted by the security document 1 is detected by a detector 12, which in the example shown is designed as a camera having a plurality of detector elements 17 arranged along a line or area on a CCD or CMOS basis, which are also called pixels.

[0054] An absorbing color mask 18, for example in the form of a so-called Bayer filter, is provided in front of the detector elements 17, so that a color filter is located in front of each detector element 17, which is transparent in the red (R), green (G) or blue (B) spectral range (see the enlarged top view of a section of the color mask 18). The detector 12 can thus detect the electromagnetic radiation 9 emanating from the security document 1 not only with spatial resolution, but also with spectral resolution in three color channels (RGB).

[0055] In the present example, a color channel-specific attenuation of the electromagnetic radiation to be detected by the detector 12 is carried out on the detector side by providing a spectral filter 13 in front of the detector 12 - in addition to the color mask 18 - which attenuates the electromagnetic radiation 9 emanating from the value document 1 more strongly in at least one of the color channels (R, G, B), e.g. red and blue, than in at least one of the other color channels, e.g. green.

[0056] The spatially resolved detector signals obtained in the present example for the red and blue color channels are then used in an evaluation unit 19 to check a first feature located on the security document 1 (see e.g. feature M1 in Fig. 2 ) which has a higher transmittance for electromagnetic radiation 8 than a second feature located on the security document 1 (see e.g. feature M2 in Fig. 2In contrast, the detector signals obtained for the green color channel are used in the evaluation unit 19 to test the second feature, which has a lower transmittance for electromagnetic radiation 8. Thus, to test the features, which differ significantly in their optical properties (transmittance in this example), the detector signals obtained for the spectrally different intensity color channels (red and blue vs. green) are used.

[0057] Preferably, the intensity of the electromagnetic radiation 8, with which preferably the entire security document 1 and / or at least both features are exposed, is selected such that the second feature mentioned in the present example can be detected well with lower transmittance, in particular by ensuring that the detector signals obtained for the green color channel are sufficiently high and, in particular, have a good signal-to-noise ratio.

[0058] Preferably, the spectral filter 13 is selected with respect to its filter properties such that the detector 12 is not overloaded or reaches saturation, at least in the red and / or blue color channels, when detecting the electromagnetic radiation 9 transmitted by the security document 1. In the present example, the spectral filter 13 must therefore absorb significantly more strongly in the red and blue spectral ranges than in the green spectral range. The spectral filter 13 can essentially extend over all detector elements 17 of the detector 12 and, in particular, does not need to cover only specific pixels, in this case, the detector elements 17 intended for the detection of red and blue light, which allows for a particularly simple implementation of the color channel-specific attenuation.

[0059] The intensity of the electromagnetic radiation 8, with which the document 1 is exposed, can be kept constant spatially and / or temporally. This eliminates, for example, the need for dynamic adjustment of the illumination intensity to the feature currently being captured on the document 1 as it passes the sensor 10, or for multiplex illumination of the document 1 to capture two transmission images with different illumination intensities.

[0060] Alternatively, a different spectral range (e.g., red or blue instead of green) can be used to represent the less transparent second feature (e.g., the microperforation of feature M2 in Fig. 2 ), which requires high intensity, to detect. The detection of the first feature (e.g., the printed window of feature M1 in Fig. 2), which requires a lower intensity, can then be determined using the detector signals obtained for the other two spectral channels.

[0061] Preferably, for the testing of the first or second feature, the color channels in which the feature in question can be detected particularly well are specifically selected, for example because it has a high contrast in these spectral ranges.

[0062] In the case of the printed window of the first feature, detection can be further adapted to the feature spectrally by mixing the two color channels, thus enabling even better recognition. The neighboring (monochrome) pixels are combined into a single color pixel (e.g., 2*G+R+B). By adjusting the color mixtures (R+G+B), specific color filters can be created, meaning that spectrally specific information can be read out (e.g., G-0*R-0*B = Green). This can be used to increase the contrast of a printed color.

[0063] The evaluation unit 19 can easily distinguish which feature (M1 or M2) is present and which spectral channels are used for detecting or testing the feature by analyzing the detector signals. For the second feature (see M2: low-transmittance microperforation), only one usable, sufficiently strong detector signal is present, e.g., in the green (G) color channel. In the case of the first feature (see M1: high-transmittance window), usable signals are present in the red (R) and blue (B) color channels, whereas the detector 12 is overloaded in the green color channel, or the signals are at least very strong and therefore cannot be used for testing.

[0064] Alternatively or additionally to the spectral filter 13, a color-channel-specific attenuation of the electromagnetic radiation detected by the detector 12 can be performed on the detector side by adjusting the gain of the received detector signals for the different color channels or color pixels (e.g., green with a higher gain than red and blue). This can be achieved by an amplifier 15, which is integrated into the detector 12 or provided separately from the detector 12.

[0065] This also achieves the effects and advantages described above in connection with the use of spectral filter 13.

[0066] Even though in the present example sensor 10 is designed as a transmission sensor, the above explanations and advantages also apply accordingly to the detection of the electromagnetic radiation reflected, remitted and / or emitted by the security document 1 due to luminescence.

[0067] Advantageously, none of the variants described above require dynamic adjustment of the illumination intensity during document transport. Instead, the selection of channels, filters, and gain is already performed during the adaptation of sensor 10 to the respective documents and their characteristics, and remains constant throughout document processing. This eliminates the need for feedback regarding the precise position of the document relative to sensor 10, and also avoids the need for fast-acting components. This simplifies implementation and reduces the potential for errors. Furthermore, in this case, even features with significantly different absorption or transmittance that are closely adjacent or located at the same position relative to the document's transport direction can be detected.

[0068] Figure 4a to 4fFigure 1 shows a schematic representation illustrating the detection or testing of the two differently permeable features M1 (printed window) and M2 (microperforation) by means of color channel-specific attenuation of the electromagnetic radiation detected by detector 12.

[0069] Figure 4a shows an example of a spectral composition (intensity versus wavelength) of the electromagnetic radiation 8 produced by the radiation source 11 (see Figure 3 ) from the blue to the green to the red spectral range.

[0070] As from the in Figure 4b As can be seen in the example shown for the transmission spectra (transmittance versus wavelength) of features M1 and M2, the first feature M1 has a significantly higher transmittance for electromagnetic radiation than the second feature M2. The different levels of transmittance or intensity in Fig. 4a-fIt can only be determined schematically, i.e., not quantitatively. It typically differs by one or more orders of magnitude.

[0071] Figure 4c shows an example of the transmission spectrum of the spectral filter 13, which attenuates the electromagnetic radiation more strongly in the blue and red spectral range (B and R respectively) than in the green spectral range (G).

[0072] Figure 4d Figure 1 shows an example of the spectral composition of the electromagnetic radiation detected by detector 12 after the electromagnetic radiation 8 emitted by radiation source 11 has been transmitted by the first feature M1 or second feature M2 of the security document 1 and filtered by the spectral filter 13 according to the diagram. Figure 4c The transmission spectrum shown was filtered.

[0073] How Figure 4eTo clarify, the detection or verification of the second feature M2 is primarily based on the electromagnetic radiation detected in the green (G) color channel, since the electromagnetic radiation detected in the blue (B) and red (R) color channels does not provide sufficiently high and therefore usable detector signals. Preferably, however, the sum intensity of all color channels (R+G+B) will be used for the detection or verification of the second feature M2 in order to verify the second feature with even greater intensity.

[0074] How Figure 4f As can be seen, in contrast, only the electromagnetic radiation detected in the blue (B) and / or the red (R) color channel is used for the detection or testing of the first feature M1, whereas the electromagnetic radiation detected in the green (G) leads to a saturation or overload of the detector, so that its detector signals are not taken into account when testing the first feature.

[0075] At the in Figure 3 In the example shown for sensor 10, in addition to or as an alternative to the detector-side color channel-specific attenuation by means of spectral filter 13 or amplifier 15, a corresponding color channel-specific attenuation can also be provided on the side of the radiation source 11 by selectively attenuating the illumination intensity spectrally.

[0076] This can preferably be achieved by using spectrally separated light sources with different intensities 16, e.g., LEDs for red, green, and blue, which together can produce white light. By attenuating the intensity of the electromagnetic radiation emitted in the individual color channels in a color-channel-specific manner, these light sources can be adapted to the different absorption behavior or transmittances of the various characteristics.

[0077] For example, a light source 16 (e.g., a green LED) can be provided to emit green light of higher intensity, which is used to detect or verify the second feature M2 (microperforation), which has a higher absorption rate. The first feature M1 (window), which has a lower absorption rate, is detected or verified using light from less intense light sources 16 in the red and / or blue spectral illumination channels.

[0078] As an alternative to using spectrally different emitting light sources 16, the radiation source 11 can be designed as a white light source and provided with a corresponding spectral filter 14 (dashed line) which only attenuates the spectral range of the illumination in which the low-absorbing first feature M1 (window) is detected, but not the remaining spectral range.

[0079] The different intensities of the light emitted by the spectrally separated light sources 16, or the white light source with the spectral filter 14, thus replace the spectral filter 13 described above in front of the detector 12 or the amplifier 15. The above explanations, in particular regarding the technical effects and advantages in connection with the use of the spectral filter 13 or amplifier 15, therefore also apply accordingly to the color channel-specific attenuation of the illumination intensity.

[0080] The color channel-specific attenuation of the illumination intensity can preferably be static, i.e., a constant intensity ratio of the light sources 16 is used, independent of the position of the document 1 being inspected. For example, the light sources 16 of different intensities are operated simultaneously, i.e., the respective document is illuminated at the same time by the light of the different light sources 16, which is a particularly simple implementation since no dynamic switching on and off of the light sources 16 is required during the inspection of the respective document.

[0081] Alternatively, it is also possible to dynamically design a color channel-specific attenuation of the illumination intensity by making the color channel-specific attenuation of the intensity for a wavelength or a color channel dependent on the position of the feature M1, M2 on the value document 1 relative to the detector 12, whereby usually a single switching of the intensity and / or switching on certain LEDs (e.g. green) and switching off other LEDs (e.g. red and blue) during the detection of the electromagnetic radiation emanating from the respective value document 1 is sufficient.

[0082] Instead of the one in Figure 3In addition to the spectral filter 13 used in the sensor 10 shown, which attenuates the electromagnetic radiation striking all detector elements 17 or color pixels of the detector 12 in the same way (e.g., a red- and blue-absorbing color filter), a "checkerboard" so-called neutral density filter can be used. This filter causes strong attenuation only in front of the detector elements 17 or pixels of a specific color channel (e.g., red and blue) (pixels for detecting the first feature M1 or window) and no or only slight attenuation in front of other pixels (pixels for detecting the second feature M2 or microperforation). The preceding explanations, particularly regarding the technical effects and advantages, in connection with the use of the spectral filter 13 or amplifier 15, therefore also apply accordingly to the use of a neutral density filter.

Claims

1. A sensor (10) for verifying security documents (1), in particular banknotes, comprising - at least one radiation source (10) configured to irradiate a security document (1) with electromagnetic radiation (8), and - a detector (12) comprising a plurality of detector elements (17) arranged at different locations, which is configured to detect electromagnetic radiation (9) emitted by the security document (1) in at least two different spectral ranges (R, G, B) and, in doing so, to generate for each of the spectral ranges (R, G, B) a detector signal corresponding to the intensity of the detected electromagnetic radiation in the respective spectral range (R, G, B), - an evaluation device (19) which is configured - to verify a first authenticity or security feature (M1) provided on or in the security document (1) on the basis of the detector signals generated for at least a first spectral range (R, B), - to verify a second feature (M2), in particular an authenticity or security feature, provided on or in the security document, taking into account the detector signals generated for at least a second spectral range (G), characterised in that - the sensor is configured to have a colour-channel-specific attenuation in the first spectral range relative to the second spectral range, in particular a colour-channel-specific attenuation of the electromagnetic radiation incident on the security document, or a colour- -channel-specific attenuation of the electromagnetic radiation to be detected by the detector, or a colour-channel-specific attenuation of the detector signals of the detector, and - the first authenticity or security feature (M1), which is verified on the basis of the detector signals generated for the at least one first spectral range (R, B), is a window integrated into the security document which is covered by a film, and - the evaluation device is configured to check the window integrated into the security document and covered by a film on the basis of the detector signals generated for the at least one first spectral range (R, B), in which the colour-channel-specific attenuation relative to the second spectral range is established at the sensor .

2. Sensor (10) according to claim 1, wherein the sensor comprises, for the colour-channel-specific attenuation, at least one colour-channel-specific filter (13 or 14) which is arranged between the detector (12) and the security document (1) and / or between the radiation source (11) and the security document (1) and which is configured to attenuate the electromagnetic radiation (9 or 8) emitted by the security document (1) or to which the security document (1) is exposed, in the at least one first spectral range (R, B) relative to the at least one second spectral range (G), preferably by a factor of at least 5.

3. Sensor (10) according to one of the preceding claims, wherein the sensor comprises, for the colour-channel-specific attenuation, at least one colour-channel-specific amplifier which is configured to amplify the detector signals generated for the different spectral ranges (R, G, B), wherein the amplification of the detector signals generated for the at least one first spectral range (R, B) , preferably by a factor of at least 5, is lower than the amplification of the detector signals generated for the at least one second spectral range (G).

4. A sensor (10) according to one of the preceding claims, wherein the radiation source(s) (11) is / are suitable for irradiate the security document (1) with electromagnetic radiation (8) of the first and second spectral ranges, and for the colour-channel-specific attenuation, a colour-channel-specific attenuation of the radiation source(s) takes place, in which the radiation source(s) are operated such that their emission intensity in the at least one first spectral range (R, B) is lower, preferably by a factor of at least 5, than in the at least one second spectral range (G).

5. A sensor (10) according to any one of the preceding claims, wherein the first authenticity or security feature (M1) exhibits higher reflectance or transmittance and / or lower absorption for the electromagnetic radiation (8) to which the security document (1) is exposed than the second feature (M2).

6. Sensor (10) according to claim 2, wherein the filter (13, 14) is configured to attenuate the electromagnetic radiation in the at least one first spectral range (R, B) relative to the at least one second spectral range (G) to the same extent for substantially all detector elements (17).

7. A sensor (10) according to claim 2 or 6, wherein the at least one filter (13, 14) is configured to attenuate the electromagnetic radiation (8, 9) emitted by the security document (1) or with which the security document (1) is exposed ( ) such that the intensity of the electromagnetic radiation detected by the detector (12) in the at least one first or second spectral range (R, B or G) is in each case greater than a lower intensity threshold of the detector (12) and less than an upper intensity threshold of the detector (12).

8. A sensor (10) according to one of the preceding claims, wherein the at least one radiation source (11) is configured to irradiate the security document (1) with the electromagnetic radiation (8) in such a way that the intensity of the electromagnetic radiation detected by the detector (12) in the at least one first or second spectral range (R, B and G respectively) is in each case greater than a lower intensity threshold of the detector (12) and less than an upper intensity threshold of the detector (12).

9. A sensor system (1, 10) comprising a sensor (10) according to one of the preceding claims and a security document (1), in particular a banknote, which comprises: - at least one first authenticity or security feature (M1) which is designed to emit electromagnetic radiation (9), in particular to transmit, reflect and / or emit it, and - the at least one second feature (M2), in particular an authenticity or security feature, which is configured to emit electromagnetic radiation (9), in particular to transmit, reflect and / or emit, wherein the first authenticity or security feature (M1) exhibits a higher re mission or transmission and / or lower absorption for the electromagnetic radiation (8) to which the security document (1) is exposed than the second feature (M2).

10. Sensor system (1, 10) according to claim 9, wherein - the first authenticity or security feature (M1) exhibits better detectability / higher contrast in the at least one first spectral range (R, B) than in the at least one second spectral range (G) and / or - the second feature (M2) exhibits better detectability / higher contrast in the at least one second spectral range (G) than in the at least one first spectral range (R, B).

11. A security document processing device comprising a sensor (10) according to any one of claims 1 to 8 or a sensor system (1, 10) according to claim 9 or 10, and a transport device (3) which is adapted to convey security documents (1), in particular relative to the sensor (10).

12. A method for verifying security documents (1), in particular banknotes, in which - at least one radiation source (11) generates electromagnetic radiation (8) which is directed at a security document (1), and - a detector (12), comprising a plurality of detector elements (17) arranged at different locations, detects electromagnetic radiation (9) emitted by the security document (1) in at least two different spectral ranges (R, G, B) and, in doing so, generates for each of the spectral ranges (R, G, B) a detector signal corresponding to the intensity of the detected electromagnetic radiation in the respective spectral range (R, G, B) , - a first feature (M1) provided on or in the security document (1), in particular an authenticity or security feature, is checked on the basis of the detector signals generated for the at least one first spectral range (R, B), and - a second feature (M2) provided on or in the security document, in particular an authenticity or security feature, is checked taking into account the detector signals generated for the at least one second spectral range (G), characterised in that - the first authenticity or security feature (M1), which is checked on the basis of the detector signals generated for the at least one first spectral range (R, B), is a window integrated into the security document which is covered by a film, and - a colour-channel-specific attenuation is provided in the first spectral range relative to the second spectral range, in particular a colour-channel-specific attenuation of the electromagnetic radiation incident on the security document, or a colour-channel-specific attenuation of the electromagnetic radiation to be detected by the detector, or a colour-channel-specific attenuation of the detector signals of the detector, and - the window integrated into the security document and covered with a film is examined on the basis of the detector signals generated for the at least one first spectral range (R, B) in which the colour-channel-specific attenuation relative to the second spectral range is configured in the sensor.

13. The method according to claim 12, wherein the colour-channel-specific attenuation is effected by at least one colour-channel-specific filter (13, or 14), which is arranged between the detector (12) and the security document (1) and / or between the radiation source (11) and the security document (1), and which attenuates the electromagnetic radiation (9 or 8), which emanates from the security document (1) or to which the security document (1) is exposed, in the at least one first spectral range (R, B) relative to the at least one second spectral range (G), preferably by a factor of at least 5.

14. A method according to claim 12 or 13, wherein the colour-channel-specific attenuation is effected by at least one colour-channel-selective amplifier (15) which amplifies the detector signals generated for the different spectral ranges (R, G, B), wherein the amplification of the detector signals generated for the at least one first spectral range (R, B) is, preferably by a factor of at least 5, lower than the amplification of the detector signals generated for the at least one second spectral range (G).

15. A method according to any one of claims 12 to 14, wherein the radiation source(s) (11) is / are adapted to irradiate the security document (1) with electromagnetic radiation (8) of the first and second spectral ranges, and the colour-channel-specific attenuation is achieved by colour-channel-specific attenuation of the radiation source(s), wherein the radiation source(s) is / are operated such that its / their intensity in the at least one first spectral range (R, B) is lower, preferably by at least a factor of 5, than in the at least one second spectral range (G).