EP3811343B1 - Method and sensor for testing documents - Google Patents

Method and sensor for testing documents Download PDF

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Publication number
EP3811343B1
EP3811343B1 EP19733663.9A EP19733663A EP3811343B1 EP 3811343 B1 EP3811343 B1 EP 3811343B1 EP 19733663 A EP19733663 A EP 19733663A EP 3811343 B1 EP3811343 B1 EP 3811343B1
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EP
European Patent Office
Prior art keywords
spectral
document
detector
excitation light
luminescence
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EP19733663.9A
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German (de)
French (fr)
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EP3811343A1 (en
Inventor
Wolfgang Deckenbach
Julia DANHOF
Ulf EHRHARDT
Martin Clara
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Giesecke and Devrient Currency Technology GmbH
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Giesecke and Devrient Currency Technology GmbH
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    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
    • G07D7/12—Visible light, infrared or ultraviolet radiation
    • G07D7/1205—Testing spectral properties
    • G—PHYSICS
    • G07—CHECKING-DEVICES
    • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
    • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
    • G07D7/06—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using wave or particle radiation
    • G07D7/12—Visible light, infrared or ultraviolet radiation
    • G07D7/121—Apparatus characterised by sensor details

Definitions

  • the invention relates to a method and a sensor for checking documents, e.g. documents of value, in particular for checking the authenticity of documents, e.g. documents of value.
  • the luminescence of an examined value document is checked, for example, to distinguish genuine value documents from counterfeits.
  • the counterfeit documents of value to be recognized can be composed counterfeits, which are assembled from parts of different documents of value.
  • the composed forgeries can be composed of parts of genuine and forged documents of value. There are many suggestions for detecting composed forgeries, each of which will detect some composed forgeries but not others.
  • One way of detecting composed forgeries is if the substrate of the genuine value document is provided with a luminescent substance over its entire surface, but the forged section of the composed forgery was made from a non-luminescent substrate.
  • a composed forgery can be recognized by the fact that the luminescence is not fully present, but is missing in some places of the composed forgery (in the forged section of the composed forgery).
  • reflectance and luminescence measurement can be carried out at almost the same value document position. This is possible both statically, ie without relative movement between the document of value and the detector, but also in the case when the document of value and the detector are transported relative to one another. In the latter case, the measurement times for the remission and luminescence measurement should follow each other accordingly. Since only exactly one detector is used to detect the reflectance measurement value and the luminescence measurement value, an additional detector for reflectance measurement can be dispensed with.
  • the measured reflectance value can be falsified by luminescence occurring at the same time as the reflectance (in the case of fast-growing luminescence, for example organic luminescent substances).
  • a superimposition of remission and luminescence is detected during illumination with excitation light.
  • the reflectance measured value detected during illumination with excitation light then contains a proportion of the reflectance intensity and a proportion of the luminescence intensity.
  • One Quantitative evaluation of the measured remission value is made more difficult due to the falsification caused by the luminescence occurring at the same time as the illumination.
  • the invention is based on the idea of reducing the falsification of the reflectance measured value due to the luminescence (occurring at the same time as the reflectance) in that the excitation light in the detection beam path is not blocked as much as is otherwise usual, but part of the excitation light is targeted up to is passed to the detector. This ensures that the part of the excitation intensity that hits the detector far exceeds the luminescence intensity that occurs at the same time as the excitation. Because with the same illumination intensity or excitation intensity of the value document, a significantly increased remission intensity is then detected, while the detected luminescence intensity remains the same (since the excitation intensity impinging on the value document remains unchanged).
  • the relative proportion of the remitted excitation intensity in the reflectance measured value detected during the illumination thus increases sharply in comparison to the relative proportion of the luminescence.
  • the reflectance measured value detected during the illumination is therefore no longer or only slightly falsified by the luminescence emitted during the illumination with excitation light.
  • the same detector is used to record both measured values, ie the remission measured value and the luminescence measured value. If the detector comprises a plurality of sections that can be read out separately from one another, the same detector sections are illuminated and read out when the two measured values are recorded.
  • the luminescence of the security feature to be detected can be a phosphorescence and the respective Luminescence measurement value can be a phosphorescence measurement value of the document of value.
  • the spectral detection filter located in the detection beam path has a transmission of at least 0.5% in the spectral range of the excitation light.
  • the maximum of the transmission spectrum in the spectral range of the excitation light is at least 0.5%. This increased transmission of the spectral detection filter ensures that the excitation intensity hitting the detector far exceeds the luminescence intensity occurring at the same time as the excitation.
  • the spectral detection filter preferably has a transmission in the range from 0.5% to 20%, preferably in the range from 1% to 10%, in the spectral range of the excitation light.
  • a blocking filter is usually installed in the detection beam path between the document of value and the detector, which only lets the luminescence light through and blocks as far as possible all spectral ranges that are not to be detected, i.e. the excitation light is also almost completely blocked.
  • a blocking filter is used for this purpose, which specifically reduces the spectral range of the excitation light by a factor of 10 4 to 10 6 in order to ensure that as far as possible only the luminescence is measured.
  • the invention can be used for any type of value document check in which both remission measured values and luminescence measured values of a value document are evaluated.
  • the invention enables improved detection of remission measurement values and luminescence measurement values at almost the same value document position in order to compare these measurement values with one another.
  • This can be used as part of an authenticity check that seeks to detect composed forgeries aims, but also for other authenticity checks in which the luminescence of the value document is checked.
  • the luminescent substance to be checked can be present over the entire surface of the document of value or in the substrate of the document of value or only in one or more partial areas.
  • the spectral detection filter only transmits a portion of the excitation light remitted by the document of value.
  • the excitation light remitted by the document of value is partially absorbed or reflected by the spectral detection filter.
  • the spectral detection filter transmits at least a 0.5% portion of the excitation light incident on the spectral detection filter that was remitted by the document of value, but preferably at most a portion of 20% of the excitation light incident on the spectral detection filter that was remitted by the document of value.
  • the luminescence light of the document of value is preferably transmitted almost completely through the spectral detection filter.
  • the spectral detection filter preferably has a transmission of at least 80%.
  • the maximum of the transmission spectrum in the spectral range of the luminescent light is at least 80%.
  • the maximum transmission that the spectral detection filter has in the spectral range of the luminescence light is preferably greater by at least a factor of four than the maximum transmission that it has in the spectral range of the excitation light.
  • the spectral detection filter differs from common neutral density filters in that its transmission depends on the wavelength of the light incident on the spectral detection filter (i.e. its transmission spectrum is not uniform over all wavelengths).
  • the spectral detection filter is a bandpass filter with at least two transmission bands, in particular an interference filter.
  • the spectral detection filter has a transmission spectrum that has a (spectral) luminescence transmission band in the spectral range of the luminescence light of the document of value and one or more additional (spectral) transmission bands in the spectral range of the excitation light.
  • the luminescence transmission band overlaps spectrally with the luminescence light of the document of value.
  • the luminescence transmission band can partially overlap spectrally with the luminescent light of the document of value or can completely enclose it spectrally.
  • the at least one additional transmission band overlaps spectrally with the excitation light.
  • the transmission spectrum of the spectral detection filter can, for example, have an additional transmission band that spectrally completely encloses the excitation light.
  • the additional transmission band(s) can partially overlap spectrally with the excitation light.
  • the luminescence transmission band and the at least one additional transmission band are, for example, spectrally separated from one another (in particular not spectrally overlapping).
  • the transmission spectrum of the spectral detection filter--with appropriate modulation of the transmittance--can also extend continuously from the spectral range of the luminescence light to the spectral range of the excitation light.
  • the spectral detection filter preferably has a greater transmission in its luminescence transmission band than in its additional one(s). transmission band/s.
  • the maximum transmission in its luminescence transmission band is at least a factor of 4 greater than the maximum transmission in the at least one additional transmission band.
  • the detection filter has a uniform spectral transmission laterally (in the plane of the detection filter). Each lateral section of the spectral detection filter therefore has the same spectral transmission. Both the luminescence light of the document of value impinging on the spectral detection filter and at least 0.5% of the excitation light impinging on the spectral detection filter (remitted by the document of value) are transmitted through the spectral detection filter—in each case at the same lateral position of the detection filter.
  • the spectral detection filter thus transmits the luminescence light impinging on it and the excitation light impinging on it independently of the lateral position along the spectral detection filter.
  • the spectral detection filter has the luminescence transmission band and the at least one additional transmission band each at the same lateral position along the spectral detection filter.
  • the at least one additional transmission band is preferably at a spectral distance of at least 10 nm, preferably at least 20 nm, from the at least one luminescence transmission band. at which the transmission of the respective transmission band has dropped to 50% of the maximum value of the respective transmission band.
  • the spectrum of the excitation light can have a spectral excitation band that has an upper spectral edge (long-wavelength side of the spectrum) and a lower spectral edge (short-wavelength side of the spectrum).
  • the spectral detection filter has a first additional spectral transmission band that is spectrally in the lower spectral edge of the excitation band and a second additional spectral transmission band that is spectrally in the upper spectral edge of the excitation band.
  • a temperature drift of the excitation band has little or no influence on the level of the spectral detection filter transmitted excitation intensity.
  • the same advantage is achieved if the additional spectral transmission band of the spectral detection filter spectrally completely encloses the excitation band of the excitation light.
  • the document of value With some sensors, it is common for the document of value to be transported relative to the detector during detection, for example to be transported past it. This can be done at a relatively low speed of 0.1-1 m/s, but preferably at a high speed of 1-15 m/s.
  • the respective remission measured value is then detected in a first detection area of the document of value and the respective luminescence measured value, which is detected immediately after the reflectance measured value, in a second detection area of the document of value.
  • the reflectance measured value is detected at a point in time at which the respective first detection area is illuminated with an excitation light pulse of the excitation light.
  • the respective luminescence measurement value is detected at a point in time at which the second Detection area is no longer illuminated with an excitation light pulse of the excitation light.
  • the time interval between the detection of the remission measured value and the detection of the luminescence measured value is preferably chosen such that the respective first and second detection area, the first and second measured value of which are detected immediately one after the other, in terms of area (measured by their area on the document of value) overlap at least 50%, preferably at least 80%.
  • the relatively high transmission of the spectral detection filter in the spectral range of the excitation light means that the detector detects an increased intensity during illumination with excitation light, which usually far exceeds the luminescence intensity.
  • the transmission of the detection filter in the spectral range of the excitation light is not as great as in the case of a large falsification.
  • conventional photodetectors, amplifier circuits and A/D converters are suitable for determining both the low intensity of the luminescent light when the illumination is switched off and the intensity of the excitation light during illumination.
  • the detector detects the respective remission measured value and the respective luminescence measured value with the same sensitivity.
  • the dynamic range of the measurement is then large enough that both the remission measured value and the luminescence measured value can be detected without overdriving.
  • the transmission of the spectral detection filter is selected in particular in such a way that it is somewhat lower in the spectral range of the excitation light than the transmission from which the intensity of the excitation light transmitted through the detection filter increases detection is overridden.
  • one or more photodiodes of the material systems Si, Ge, InAs or InGaAs are preferably used as a detector.
  • the photocurrents thus detected can be processed with a transimpedance converter of suitable amplification and subsequent digitization with a sufficiently large dynamic range. This is preferably done linearly over the dynamic range.
  • the luminescent substance of the bank note to be detected occurs quickly (i.e. the measured remission value is strongly falsified), a relatively high transmission of the detection filter in the spectral range of the excitation light is required in order to keep the falsification low. However, this leads to a relatively high intensity for the measured remission value during illumination with excitation light.
  • the dynamic range during detection in particular the dynamic range of the amplifier circuit and/or the A/D converter, is not sufficient (so that the measured value saturates when the remission measured value is detected)
  • the measurement signals are recorded with carried out with different sensitivities.
  • the sensitivity of the detector is reduced for reflectance measurement during illumination with excitation light.
  • the measured reflectance value detected by the detector and the measured luminescence value detected by the detector can be measured with different sensitivities, the measured reflectance value being measured with a lower sensitivity than the measured luminescence value.
  • the control device can be set up to switch over the detector or an electronic circuit connected to it (for example an amplifier circuit) in such a way that the remission measured value has a lower sensitivity is measured as the luminescence reading. For example, in the period between the detection of the respective remission measured value and the respective luminescence measured value, a sensitivity setting of the detector or of an amplifier connected to the detector or of a current-voltage converter connected to the detector can be switched so that the remission -measured value is measured with lower sensitivity than the luminescence measured value.
  • the bias voltage of the detector or the gain of the electronic amplifier which amplifies the output signal of the detector, or the transimpedance of a current-to-voltage converter connected to the detector be switched over in such a way that the remission measured value is detected with less sensitivity than the luminescence measured value.
  • the sensitivity can be switched over by a switching signal from the control device, which is generated synchronously with the excitation light pulses, for example.
  • the sensitivity setting of the detector is preferably switched over immediately before the start of the excitation light pulse in such a way that the remission measured value is detected with lower sensitivity than the luminescence measured value, and switched back again immediately after the end of the excitation light pulse for the detection of the reflectance measured value.
  • the sensitivity can be switched with a switching time of 50 ⁇ s to 1 ms, preferably with a switching time of 70 ⁇ s to 300 ⁇ s.
  • the controller may be a processor programmed with appropriate software to control the illuminator and detector.
  • the processor can also be configured to generate a control signal that switches the sensitivity of the detector.
  • the evaluation device can also be a processor with the appropriate Software for evaluating the reflectance and luminescence measurements is programmed.
  • the processor is set up, for example, to analyze the measurement signals and to assess the authenticity, and it outputs the result of the authenticity assessment or forwards it for further processing.
  • the control device and the evaluation device can be different devices or can be formed by the same device, which is set up both to control the illumination device and the detector and to check the document of value based on the at least one remission measured value detected by the detector and based on the at least one luminescence measurement value detected by the detector.
  • the same processor can be used for both.
  • the detector is in particular a semiconductor-based detector, e.g. a photodiode, preferably with a charge carrier lifetime of at most 20 ⁇ s. Despite intensive irradiation with excitation light, the detector is then able to detect low intensities again after a short time. This allows a faster measurement or a short time interval between the two measurements and thus a large spatial overlap of the detection areas, especially in the case of high transport speeds of the document of value.
  • a detection beam path formed between the document of value and the detector contains a spectral detection filter whose spectral transmission is selected such that the luminescence light of the document of value impinging on the spectral detection filter and at least 0.5% of the excitation light impinging on the spectral detection filter, which was remitted by the document of value, is transmitted.
  • the evaluation can be based on a single discrete remission or luminescence measurement value or on the basis of several of the respective measurement values that are offset against each other (eg averaged).
  • the measured values can be detected at discrete points in time or by temporal integration over a period of time within the respective excitation pulse (for the reflectance measured value) or after the end of the respective excitation pulse (for the luminescence measured value). Between each two excitation light pulses there can also be two or more Luminescence measurement values are detected with different time intervals from the respective excitation light pulse and these luminescence measurement values are used to check the document of value, for example offset against one another.
  • the document of value and the detector can be moved relative to each other and the lighting along the document of value can be switched on and off alternately. Alternatively, the illumination and detection can also take place without relative movement.
  • the documents whose authenticity is checked using the method according to the invention and the sensor are, in particular, documents of value, for example banknotes, tickets, cheques, coupons, vouchers, etc.
  • documents of value for example banknotes, tickets, cheques, coupons, vouchers, etc.
  • other documents e.g. ID documents, can also be checked using the method according to the invention and the sensor .
  • a device for checking documents for example documents of value
  • the device can be used which has the above-mentioned sensor for checking (and optionally further sensors).
  • the device can be designed for processing documents of value, for example for checking the authenticity and/or for sorting.
  • the device can have a transport device which is set up to transport the document, eg document of value, and the detector or the sensor which has the detector relative to one another during detection, eg the document of value past the sensor or detector to transport.
  • the control device of the sensor can be set up to control the detector in such a way that the respective remission measured value and the respective luminescence measured value are detected with such a short time interval from one another that the detection ranges overlap by at least 50%, preferably by at least 80%, on the document, eg document of value, from which the respective remission measured value and the respective luminescence measured value are detected.
  • the invention is explained below using the example of the authenticity check of a banknote 3 in whose substrate a luminescent substance is introduced over the entire surface, the luminescence of which is evaluated for the authenticity check.
  • the banknote considered in this example Figure 2a has--in addition to the luminescent substance--an imprint of fluorescent printing ink 11. Furthermore, the denomination 13 of the bank note is printed and an area is provided with non-fluorescent ink 12 .
  • FIG. 1 shows a sensor 10 which is used both for detecting remission measured values and luminescence measured values of a document of value, such as banknote 3 Figure 2a , is set up.
  • the bank note 3 is transported in one direction (e.g. in 1 from right to left) past the sensor 10 so that the detector 6 can successively detect several measured values as a function of the position x along the banknote 3.
  • the same detector 6 is used to measure the remission and luminescence of the bank note.
  • the senor 10 has an illumination device with two light-emitting diodes 1a and 1b, which illuminate the banknote 3 from an oblique direction.
  • the spectral range of the lighting device is selected in such a way that the light emitted by the lighting device is designed to optically excite the luminescent substance present over the entire surface of the bank note.
  • the lighting device is switched on and off periodically in order to excite the banknote 3 to luminescence at a large number of positions x along the banknote with excitation light pulses.
  • the detection beam path 8 of the sensor 10 the light emanating from the bank note 3 passes through a front glass 2, then a lens 4, a spectral detection filter 5 and a further lens 4, which directs the light onto the detector 6.
  • the spectral detection filter 5 is used to attenuate the excitation light A.
  • the sensor 10 also has a control device 7, which provides for the periodic switching on and off of the lighting device, at specific times the detection of the remission and luminescence measurement values and forwards the reflectance and luminescence measurement values detected by the detector to the evaluation device 9, which carries out an authenticity check using the reflectance and luminescence measurement values.
  • the excitation light A of the illumination device is used both to excite the luminescence of the luminescence substance present over the entire surface and as illumination light for the remission measurement.
  • the detector 6 detects a measured remission value. After the end of the respective excitation light pulse, the detector 6 detects a measured luminescence value.
  • the remission measured value and the luminescence measured value are detected with the shortest possible time interval from one another. In this way, remission and luminescence measurement can be carried out at almost the same value document position x.
  • the detection area of the reflectance measurement (first detection area D1) and the detection area of the luminescence measurement (second detection area D2) preferably overlap by at least 80% in terms of area, cf. figure 5 .
  • the measured reflectance value can be falsified by luminescence occurring at the same time as the reflectance. So it comes from a fast onset of luminescence, as seen in Figure 3b shown results in an erroneous increase in reflectance reading.
  • a superimposition of remission and luminescence is detected, cf. 3c .
  • the measured remission value detected during illumination with excitation light in such a case does not result from the remission intensity alone, but also contains a proportion of luminescence intensity.
  • the measured remission value used for the authenticity check can therefore be falsified by luminescence occurring at the same time as the illumination.
  • the remission measured value can also be falsified by the fact that a fast-sounding additional fluorescence, such as that of the fluorescent printing ink 11, is detected, which the bank note emits in response to the excitation light pulse of the excitation light A only in the area of the fluorescent printing ink 11, cf .
  • Figures 2a and 2b the remission intensity R emanating from the bank note 3 along a line S is sketched as a function of the position x along the bank note.
  • the remission intensity of the bank note is also suppressed.
  • the fluorescence F of the fluorescent printing ink 11 emanates from the bank note 3 in this area--in addition to remission--which significantly increases the measured value detected in this area. Therefore, at the x-position of the fluorescent printing ink 11, there is also an erroneous increase in the reflectance measured value detected during the illumination with excitation light.
  • the reflectance measured values MR detected during the illumination with excitation light can therefore be falsified both in the case of a fast-sounding luminescent substance applied over the entire surface and by additional fluorescence F of other locally applied colors or fluorescent substances.
  • the measured luminescence values of a luminescent substance that is introduced over the entire surface of the substrate are examined and compared with the measured remission values of the banknote. If the falsified reflectance measured values are now used for this comparison, this can lead to an incorrect assessment of the authenticity of the respective bank note.
  • a portion of the excitation light A usually still penetrates to the detector.
  • the detector - despite the blocking filter - penetrating excitation light can have an intensity comparable to the luminescence to be detected, as is the case in the 3c is shown.
  • a blocking filter in the detection beam path 8 for the excitation light A, but using a larger proportion of the excitation light A up to the detector 6 is allowed through.
  • the low attenuation of the excitation light A in the detection beam path 8 means that the proportion of the detected excitation intensity is significantly increased, while (for falsification leading) contribution of the luminescence - due to unchanged excitation intensity of the bank note - remains the same (the excitation intensity hitting the bank note is not influenced by the changed attenuation in the detection beam path). Since the excitation intensity let through to the detector - due to the lower attenuation - is then much greater than the (falsifying) contribution that the luminescence intensity contributes to the remission measured value, the luminescence then only leads to a negligible falsification of the remission measured value.
  • the reflectance measured value MR detected at time t1 remains almost uncorrupted by the luminescence L.
  • the measured luminescence value ML is detected at time t2.
  • the falling branch of the luminescence curve 3d corresponds to that 3c , but the larger y-scaling in 3d results in the falling branch of the luminescence curve and thus also the measured luminescence value ML being further down the y-axis.
  • the reflectance measured value MR detected at time t1 is off compared to the case 3c is greatly increased.
  • the transmission of the spectral detection filter for the excitation light does not have to be increased so much. Then both the increased reflectance measured value MR and the significantly lower luminescence measured value ML can be detected with the same detector 6 with sufficient accuracy. If necessary, a special detector 6 can be used, which has a particularly large dynamic range.
  • a dynamic sensitivity switch can be carried out during the measurement.
  • a current-voltage converter with switchable gain is used for this purpose, cf 6 electronic circuit shown.
  • the control device 7 of the sensor 10 ensures that the amplification of the current-voltage converter is switched over with the aid of a semiconductor switch S1, which is optionally brought into the open or closed state via a control signal Us from the control device 7 .
  • the control device 7 opens the semiconductor switch S1 with the aid of the control signal Us so that the current-voltage converter—for the detection of the low luminescence measured value ML—has a high gain.
  • the timing of the Control signal Us preferably placed so that the semiconductor switch S1 is closed before the start of the excitation light pulse and is only opened again after the end of the excitation light pulse.
  • a semiconductor detector with a highly doped substrate is preferably used as detector 6, for example a silicon photodiode with a highly doped Si substrate.
  • a semiconductor detector is used whose substrate has a charge carrier lifetime that is significantly shorter than the time interval between the excitation light pulse and the detection of the luminescence measured value ML.
  • the charge carrier lifetime in the substrate of the semiconductor detector is preferably at most 20 ⁇ s, particularly preferably at most 10 ⁇ s. This means that the measured luminescence value ML can be detected at a very short time interval after the end of the excitation light pulse, for example as early as 50 ⁇ s-200 ⁇ s after the end of the excitation light pulse.
  • first detection area D1 the detection area of the luminescence measurement
  • second detection area D2 the detection area of the luminescence measurement
  • FIG 4a an example of the spectral profile of the excitation light A used to excite the banknote and of the luminescent light L emitted by the banknote is shown.
  • a transmission spectrum T of a spectral detection filter 5, which is located in the detection beam path 8 of the sensor 10, is shown as an example.
  • the transmission spectrum T in Figure 4a has a spectral luminescence transmission band BL in the spectral range of the luminescence light L and an additional spectral transmission band BA in the spectral range of the excitation light A, which spectrally completely encloses the spectral excitation band of the excitation light A.
  • the transmission band BL can likewise completely enclose the luminescence light, but alternatively only allow a spectral component of the luminescence light L to pass through.
  • the spectral detection filter 5 lets through, for example, 20% of the excitation light in the additional spectral transmission band BA and 95% in the spectral luminescence transmission band BL.
  • the spectral distance ⁇ F between the two transmission bands BA and BL, measured at the half-value points of the respective transmission band BA or BL, is preferably at least 10 nm, cf. Figure 4a .
  • an interference filter is used as the spectral detection filter 5, in which the transmission bands BL and BA are selected according to the spectral position of the luminescence light L and the excitation light A.
  • the transmission spectrum T of the spectral detection filter 5 can have different forms.
  • the additional spectral Transmission band BA can be positioned symmetrically or asymmetrically around the spectral curve of the excitation light A.
  • Fig. 4b-e four examples of the additional spectral transmission band BA are shown, which only partially overlap with the spectral excitation band of the excitation light A.
  • the additional spectral transmission band BA can, for example, lie in the upper spectral edge of the excitation light A (cf. Figure 4b ) or in the lower spectral edge of the excitation light A (cf. Figure 4c ).
  • the spectral shape of the additional spectral transmission bands Figures 4d and 4e is chosen so that the spectral detection filter 5 has an additional spectral transmission band in each of the two spectral flanks of the excitation light A, specifically a first additional transmission band BA u that lies spectrally in the lower spectral flank of the excitation light A, and a second additional transmission band BA o , which lies spectrally in the upper spectral edge of the excitation light A.
  • a spectral shift of the spectral excitation band to longer wavelengths would lead to an increased intensity in the transmission band BA o of the long-wave edge and to a reduced intensity in the transmission band BA u of the short-wave edge.
  • both changes run counter to each other and at least partially balance each other out.
  • a single additional transmission band in only one of the two flanks would be less favorable since no such compensation would take place.
  • a third additional transmission band BA m can also be present in the spectral center of the excitation light.

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  • General Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
  • Inspection Of Paper Currency And Valuable Securities (AREA)

Description

Die Erfindung betrifft ein Verfahren und einen Sensor zur Prüfung von Dokumenten, z.B. von Wertdokumenten, insbesondere zur Echtheitsprüfung von Dokumenten, z.B. von Wertdokumenten.The invention relates to a method and a sensor for checking documents, e.g. documents of value, in particular for checking the authenticity of documents, e.g. documents of value.

Aus dem Stand der Technik sind verschiedene Verfahren zur Erkennung gefälschter Wertdokumente bekannt. Zur Echtheitsprüfung von Wertdokumenten, insbesondere von Banknoten, können diese auf ihre Lumineszenzeigenschaften geprüft werden. Zur Lumineszenz können Fluoreszenz und/oder Phosphoreszenz beitragen. Zur Detektion der Fluoreszenz- und/oder Phosphoreszenz werden Messwerte nach Ende eines Anregungslichtpulses detektiert, z.B. in der Dunkelphase zwischen zwei Anregungslichtpulsen.Various methods for detecting counterfeit documents of value are known from the prior art. To check the authenticity of documents of value, in particular banknotes, these can be checked for their luminescence properties. Fluorescence and/or phosphorescence can contribute to the luminescence. To detect fluorescence and/or phosphorescence, measured values are detected after the end of an excitation light pulse, e.g. in the dark phase between two excitation light pulses.

Zur Unterscheidung echter Wertdokumente von Fälschungen wird z.B. die Lumineszenz eines untersuchten Wertdokuments geprüft. Bei den zu erkennenden gefälschten Wertdokumenten kann es sich um composed-Fälschungen handeln, die aus Teilen unterschiedlicher Wertdokumente zusammengesetzt sind. Die composed-Fälschungen können aus Teilen echter und gefälschter Wertdokumente zusammengesetzt sein. Zur Erkennung von composed-Fälschungen gibt es viele Vorschläge, mit denen jeweils manche composed-Fälschungen erkennbar sind, andere jedoch nicht.The luminescence of an examined value document is checked, for example, to distinguish genuine value documents from counterfeits. The counterfeit documents of value to be recognized can be composed counterfeits, which are assembled from parts of different documents of value. The composed forgeries can be composed of parts of genuine and forged documents of value. There are many suggestions for detecting composed forgeries, each of which will detect some composed forgeries but not others.

Eine Möglichkeit zur Erkennung von composed-Fälschungen gibt es, falls das Substrat des echten Wertdokuments vollflächig mit einem lumineszierenden Stoff versehen ist, der gefälschte Abschnitt der composed-Fälschung aber aus einem nichtlumineszierenden Substrat hergestellt wurde. Eine solche composed-Fälschung kann daran erkannt werden, dass die Lumineszenz nicht vollflächig vorhanden ist, sondern an manchen Stellen der composed-Fälschung (im gefälschten Abschnitt der composed-Fälschung) fehlt.One way of detecting composed forgeries is if the substrate of the genuine value document is provided with a luminescent substance over its entire surface, but the forged section of the composed forgery was made from a non-luminescent substrate. Such a composed forgery can be recognized by the fact that the luminescence is not fully present, but is missing in some places of the composed forgery (in the forged section of the composed forgery).

Für die Beurteilung der Lumineszenz-Messwerte werden diese beispielsweise im Vergleich zu Remissions-Messwerten des Wertdokuments betrachtet. Dafür ist es wünschenswert, an möglichst jeweils derselben Position des Wertdokuments die Intensität der Lumineszenz mit der Intensität der Remission des Wertdokuments zu vergleichen. Bisher wird für die Remissionsmessung eines Wertdokuments ein zusätzlicher Detektor benötigt, der zusätzlich zu dem Lumineszenz-Detektor bereit gestellt werden muss. Mit einem zusätzlichen Detektor ist die Messung von Remission und Lumineszenz an derselben Position des Wertdokuments jedoch schwierig, gerade dann wenn das Wertdokument - wie meist üblich - zu dessen Prüfung nacheinander durch die Erfassungsbereiche der beiden verwendeten Detektoren transportiert wird. Relevanter Stand der Technik kann in der US2016125682 A1 und in der DE102008044883 A1 gefunden werden, die sich mit der Lumineszenzmessung von Wertdokumenten bzw. von Halbleiterwafern befassen.For the assessment of the luminescence measurement values, these are considered in comparison to the remission measurement values of the document of value, for example. For this it is desirable to compare the intensity of the luminescence with the intensity of the remission of the document of value at the same position of the document of value. To date, an additional detector has been required for measuring the remission of a document of value, which has to be provided in addition to the luminescence detector. With an additional detector, however, it is difficult to measure remission and luminescence at the same position on the document of value, especially when the document of value—as is usually the case—is transported through the detection areas of the two detectors used one after the other for its examination. Relevant prior art can be found in US2016125682 A1 and in the DE102008044883 A1 be found that deal with the luminescence measurement of documents of value or semiconductor wafers.

Es ist daher eine Aufgabe der Erfindung, die Detektion der Lumineszenz und der Remission von demselben Dokument zu verbessern.It is therefore an object of the invention to improve the detection of luminescence and reflectance from the same document.

Diese Aufgabe wird durch die Merkmale der unabhängigen Ansprüche gelöst. In davon abhängigen Ansprüchen sind vorteilhafte Ausgestaltungen und Weiterbildungen der Erfindung angegeben.This object is solved by the features of the independent claims. Advantageous refinements and developments of the invention are specified in dependent claims.

Die Erfindung wird nachfolgend am Beispiel von Wertdokumenten erläutert, ist aber nicht auf Wertdokumente beschränkt, sondern auch für andere Dokumente geeignet.The invention is explained below using the example of documents of value, but is not limited to documents of value, but is also suitable for other documents.

Um die Messung von Remission und Lumineszenz von demselben Wertdokument zu verbessern, wird vorgeschlagen, denselben Detektor für die Remissionsmessung und die Lumineszenz-Messung des Wertdokuments zu verwenden, wobei dieser Detektor den Remissions-Messwert während der Beleuchtung des Wertdokuments mit einem für die Lumineszenz-Anregung verwendeten Anregungslicht detektiert und dieser Detektor den Lumineszenz-Messwert nach Ausschalten der Beleuchtung detektiert. Zur Remissionsmessung des Wertdokuments wird dabei die Remission des für die Lumineszenz-Messung eingestrahlten Anregungslichts detektiert. Das Anregungslicht wird also sowohl zur Anregung der Lumineszenz als auch als Beleuchtungslicht für die Remissionsmessung verwendet. Da zur Detektion des Remissions-Messwerts und des Lumineszenz-Messwerts ein und derselbe Detektor verwendet wird, können Remissions- und Lumineszenz-Messung an nahezu derselben Wertdokumentposition durchgeführt werden. Dies ist sowohl statisch möglich, d.h. ohne Relativbewegung zwischen Wertdokument und Detektor, aber auch in dem Fall, wenn das Wertdokument und der Detektor relativ zueinander transportiert werden. In letzterem Fall sollten dazu die Messzeitpunkte für die Remissions- und die Lumineszenz-Messung entsprechend kurz aufeinander folgen. Da zur Detektion des Remissions-Messwerts und des Lumineszenz-Messwerts nur genau ein Detektor verwendet wird, kann auf einen zusätzlichen Detektor zur Remissionsmessung verzichtet werden.In order to improve the measurement of remission and luminescence from the same document of value, it is proposed to use the same detector for the remission measurement and to use the luminescence measurement of the document of value, this detector detecting the measured reflectance value during the illumination of the document of value with an excitation light used for the luminescence excitation and this detector detecting the measured luminescence value after switching off the illumination. In order to measure the remission of the value document, the remission of the excitation light irradiated for the luminescence measurement is detected. The excitation light is thus used both to excite the luminescence and as illumination light for reflectance measurement. Since one and the same detector is used to detect the reflectance measured value and the luminescence measured value, reflectance and luminescence measurement can be carried out at almost the same value document position. This is possible both statically, ie without relative movement between the document of value and the detector, but also in the case when the document of value and the detector are transported relative to one another. In the latter case, the measurement times for the remission and luminescence measurement should follow each other accordingly. Since only exactly one detector is used to detect the reflectance measurement value and the luminescence measurement value, an additional detector for reflectance measurement can be dispensed with.

Bei einer solchen Remissionsmessung während des Beleuchtens mit Anregungslicht kann der Remissions-Messwert jedoch durch eine gleichzeitig mit der Remission auftretende Lumineszenz (bei schnell anklingender Lumineszenz z.B. organischer Lumineszenz-Stoffe) verfälscht sein. Während der Beleuchtung mit Anregungslicht wird in solchen Fällen eine Überlagerung von Remission und Lumineszenz detektiert. Der während der Beleuchtung mit Anregungslicht detektierte Remissions-Messwert enthält dann einen Anteil der Remissions-Intensität und einen Anteil der Lumineszenz-Intensität. Eine quantitative Auswertung des Remissions-Messwerts wird aufgrund der Verfälschung durch die gleichzeitig mit der Beleuchtung auftretende Lumineszenz erschwert. Um aus dem verfälschten Remissions-Messwert den tatsächlichen Anteil der Remission zu bestimmen (ohne der überlagert detektierten Lumineszenz), könnte ein nachträgliches Herausrechnen in Betracht gezogen werden (z.B. den Lumineszenz-Anteil von dem Messwert zu subtrahieren). Dies erweist sich aber als schwierig, wenn die Höhe und der zeitliche Verlauf der Lumineszenz nicht bekannt sind.With such a reflectance measurement during illumination with excitation light, however, the measured reflectance value can be falsified by luminescence occurring at the same time as the reflectance (in the case of fast-growing luminescence, for example organic luminescent substances). In such cases, a superimposition of remission and luminescence is detected during illumination with excitation light. The reflectance measured value detected during illumination with excitation light then contains a proportion of the reflectance intensity and a proportion of the luminescence intensity. One Quantitative evaluation of the measured remission value is made more difficult due to the falsification caused by the luminescence occurring at the same time as the illumination. In order to determine the actual portion of the remission from the falsified remission measured value (without the superimposed detected luminescence), a subsequent calculation could be considered (eg subtracting the luminescence portion from the measured value). However, this proves to be difficult if the level and the time course of the luminescence are not known.

Die Erfindung basiert auf dem Gedanken, die Verfälschung des Remissions-Messwerts aufgrund der (gleichzeitig mit der Remission auftretenden) Lumineszenz dadurch zu verringern, dass das Anregungslicht im Detektionsstrahlengang nicht- wie sonst üblich - möglichst stark blockiert wird, sondern ein Teil des Anregungslicht gezielt bis zum Detektor durchgelassen wird. Damit wird erreicht, dass der auf den Detektor treffende Anteil der Anregungsintensität die gleichzeitig mit der Anregung auftretende Lumineszenz-Intensität weit übertrifft. Denn bei gleicher Beleuchtungsintensität bzw. Anregungsintensität des Wertdokuments wird dann eine deutlich erhöhte Remissions-Intensität detektiert, während die detektierte Lumineszenz-Intensität gleich bleibt (da die auf das Wertdokument treffende Anregungsintensität unverändert bleibt). Der relative Anteil der remittierten Anregungsintensität an dem während der Beleuchtung detektierten Remissions-Messwert nimmt dadurch im Vergleich zum relativen Anteil der Lumineszenz stark zu. Der während der Beleuchtung detektierte Remissions-Messwert ist daher nicht mehr oder nur mehr geringfügig durch die während der Beleuchtung mit Anregungslicht emittierte Lumineszenz verfälscht.The invention is based on the idea of reducing the falsification of the reflectance measured value due to the luminescence (occurring at the same time as the reflectance) in that the excitation light in the detection beam path is not blocked as much as is otherwise usual, but part of the excitation light is targeted up to is passed to the detector. This ensures that the part of the excitation intensity that hits the detector far exceeds the luminescence intensity that occurs at the same time as the excitation. Because with the same illumination intensity or excitation intensity of the value document, a significantly increased remission intensity is then detected, while the detected luminescence intensity remains the same (since the excitation intensity impinging on the value document remains unchanged). The relative proportion of the remitted excitation intensity in the reflectance measured value detected during the illumination thus increases sharply in comparison to the relative proportion of the luminescence. The reflectance measured value detected during the illumination is therefore no longer or only slightly falsified by the luminescence emitted during the illumination with excitation light.

Der verwendete Sensor zur Prüfung von Dokumenten, z.B. von Wertdokumenten, umfasst:

  • eine Beleuchtungseinrichtung zum Beleuchten eines Dokuments, z.B. eines Wertdokuments, mit einem oder mehreren Anregungslichtpulsen eines Anregungslichts, das dazu geeignet ist, das Dokument, z.B. Wertdokument, zur Emission von Lumineszenzlicht anzuregen, und
  • einen Detektor zum Detektieren mindestens eines Remissions-Messwerts des Dokuments, z.B. Wertdokuments, zu mindestens einem Zeitpunkt, zu dem das Dokument, z.B. Wertdokument, mit einem Anregungslichtpuls des Anregungslichts beleuchtet wird, und zum Detektieren mindestens eines Lumineszenz-Messwerts des Dokuments, z.B. Wertdokuments, zu mindestens einem Zeitpunkt nach Ende des jeweiligen Anregungslichtpulses, und
  • einen Detektionsfilter, der sich in einem zwischen dem Dokument, z.B. Wertdokument, und dem Detektor gebildeten Detektionsstrahlengang befindet, und
  • eine Steuereinrichtung zur Steuerung der Beleuchtungseinrichtung und des Detektors und
  • eine Auswerteeinrichtung zum Prüfen des Dokuments, z.B. Wertdokuments, anhand des von dem Detektor detektierten mindestens einen Remissions- Messwerts und anhand des von dem Detektor detektierten mindestens einen Lumineszenz- Messwerts, insbesondere zur Echtheitsprüfung des Dokuments, z.B. Wertdokuments.
The sensor used to check documents, e.g. documents of value, includes:
  • an illumination device for illuminating a document, eg a document of value, with one or more excitation light pulses of an excitation light which is suitable for stimulating the document, eg document of value, to emit luminescent light, and
  • a detector for detecting at least one measured remission value of the document, e.g. document of value, at at least one point in time at which the document, e.g. document of value, is illuminated with an excitation light pulse of the excitation light, and for detecting at least one luminescence measured value of the document, e.g. document of value, at least at one point in time after the end of the respective excitation light pulse, and
  • a detection filter which is located in a detection beam path formed between the document, eg a document of value, and the detector, and
  • a control device for controlling the illumination device and the detector and
  • an evaluation device for checking the document, eg document of value, using the at least one remission measured value detected by the detector and using the at least one measured luminescence value detected by the detector, in particular for checking the authenticity of the document, eg document of value.

Bei dem Sensor wird derselbe Detektor für die Erfassung beider Messwerte, d.h. des Remissions- Messwerts und des Lumineszenz- Messwerts, verwendet. Falls der Detektor mehrere getrennt voneinander auslesbare Abschnitte umfasst, werden bei der Erfassung beider Messwerte jeweils dieselben Detektor-Abschnitte beleuchtet und ausgelesen. Die Lumineszenz des zu detektierenden Sicherheitsmerkmals kann eine Phosphoreszenz sein und der jeweilige Lumineszenz-Messwert ein Phosphoreszenz-Messwert des Wertdokuments sein.With the sensor, the same detector is used to record both measured values, ie the remission measured value and the luminescence measured value. If the detector comprises a plurality of sections that can be read out separately from one another, the same detector sections are illuminated and read out when the two measured values are recorded. The luminescence of the security feature to be detected can be a phosphorescence and the respective Luminescence measurement value can be a phosphorescence measurement value of the document of value.

Der im Detektionsstrahlengang befindliche spektrale Detektionsfilter hat im Spektralbereich des Anregungslichts eine Transmission von mindestens 0,5%. Das Maximum des Transmissionsspektrums im Spektralbereich des Anregungslichts beträgt mindestens 0,5%. Durch diese erhöhte Transmission des spektralen Detektionsfilters wird erreicht, dass die auf den Detektor treffende Anregungsintensität die gleichzeitig mit der Anregung auftretende Lumineszenz-Intensität weit übertrifft. Vorzugsweise weist der spektrale Detektionsfilter im Spektralbereich des Anregungslichts eine Transmission im Bereich von 0,5% bis 20%, bevorzugt im Bereich von 1% bis 10%, auf.The spectral detection filter located in the detection beam path has a transmission of at least 0.5% in the spectral range of the excitation light. The maximum of the transmission spectrum in the spectral range of the excitation light is at least 0.5%. This increased transmission of the spectral detection filter ensures that the excitation intensity hitting the detector far exceeds the luminescence intensity occurring at the same time as the excitation. The spectral detection filter preferably has a transmission in the range from 0.5% to 20%, preferably in the range from 1% to 10%, in the spectral range of the excitation light.

Im Gegensatz dazu wird bei den bisherigen Lumineszenzsensoren üblicherweise ein Sperrfilter im Detektionsstrahlengang zwischen Wertdokument und dem Detektor eingebaut, der nur das Lumineszenzlicht durchlässt und alle Spektralbereiche so weit wie möglich blockiert, die nicht detektiert werden sollen, d.h. auch das Anregungslicht nahezu vollständig blockiert. Beispielsweise wird dazu ein Sperrfilter verwendet, der gezielt den Spektralbereich des Anregungslichts um einen Faktor 104 bis 106 reduziert, um zu erreichen, dass möglichst nur die Lumineszenz gemessen wird.In contrast, with previous luminescence sensors, a blocking filter is usually installed in the detection beam path between the document of value and the detector, which only lets the luminescence light through and blocks as far as possible all spectral ranges that are not to be detected, i.e. the excitation light is also almost completely blocked. For example, a blocking filter is used for this purpose, which specifically reduces the spectral range of the excitation light by a factor of 10 4 to 10 6 in order to ensure that as far as possible only the luminescence is measured.

Die Erfindung ist für jede Art der Wertdokumentprüfung einsetzbar, bei der sowohl Remissions-Messwerte als auch Lumineszenz-Messwerte eines Wertdokuments ausgewertet werden. Besonders vorteilhaft ermöglicht die Erfindung eine verbesserte Detektion von Remissions-Messwerten und Lumineszenz-Messwerten an nahezu derselben Wertdokumentposition, um diese Messwerte miteinander zu vergleichen. Dies kann im Rahmen einer Echtheitsprüfung eingesetzt werden, die das Auffinden von composed-Fälschungen zum Ziel hat, aber auch für andere Echtheitsprüfungen, bei denen die Lumineszenz des Wertdokuments geprüft wird. Der zu prüfende Lumineszenzstoff kann vollflächig auf dem Wertdokument oder im Substrat des Wertdokuments vorhanden sein oder auch nur in einem oder mehreren Teilbereichen.The invention can be used for any type of value document check in which both remission measured values and luminescence measured values of a value document are evaluated. In a particularly advantageous manner, the invention enables improved detection of remission measurement values and luminescence measurement values at almost the same value document position in order to compare these measurement values with one another. This can be used as part of an authenticity check that seeks to detect composed forgeries aims, but also for other authenticity checks in which the luminescence of the value document is checked. The luminescent substance to be checked can be present over the entire surface of the document of value or in the substrate of the document of value or only in one or more partial areas.

Der spektrale Detektionsfilter transmittiert nur einen Anteil des von dem Wertdokument remittierten Anregungslichts. Das von dem Wertdokument remittierte Anregungslicht wird durch den spektralen Detektionsfilter teilweise absorbiert oder reflektiert. Der spektrale Detektionsfilter transmittiert mindestens einen Anteil von 0,5% des auf den spektralen Detektionsfilter auftreffenden Anregungslichts, das von dem Wertdokument remittiert wurde, doch vorzugsweise höchstens einen Anteil von 20% des auf den spektralen Detektionsfilter auftreffenden Anregungslichts, das von dem Wertdokument remittiert wurde.The spectral detection filter only transmits a portion of the excitation light remitted by the document of value. The excitation light remitted by the document of value is partially absorbed or reflected by the spectral detection filter. The spectral detection filter transmits at least a 0.5% portion of the excitation light incident on the spectral detection filter that was remitted by the document of value, but preferably at most a portion of 20% of the excitation light incident on the spectral detection filter that was remitted by the document of value.

Das Lumineszenzlicht des Wertdokuments wird aber bevorzugt nahezu vollständig durch den spektralen Detektionsfilter transmittiert. Im Spektralbereich des Lumineszenzlichts des Wertdokuments weist der spektrale Detektionsfilter vorzugsweise eine Transmission von mindestens 80% auf. Das Maximum des Transmissionsspektrums im Spektralbereich des Luminesenzlichts beträgt mindestens 80%. Vorzugsweise ist die maximale Transmission, die der spektrale Detektionsfilter im Spektralbereich des Lumineszenzlichts aufweist, um mindestens einen Faktor vier größer ist als die maximale Transmission, die er im Spektralbereich des Anregungslichts aufweist.However, the luminescence light of the document of value is preferably transmitted almost completely through the spectral detection filter. In the spectral range of the luminescence light of the document of value, the spectral detection filter preferably has a transmission of at least 80%. The maximum of the transmission spectrum in the spectral range of the luminescent light is at least 80%. The maximum transmission that the spectral detection filter has in the spectral range of the luminescence light is preferably greater by at least a factor of four than the maximum transmission that it has in the spectral range of the excitation light.

Der spektrale Detektionsfilter unterscheidet sich von üblichen Neutraldichtefiltern dadurch, dass seine Transmission von der Wellenlänge des auf den spektralen Detektionsfilter auftreffenden Lichts abhängt (d.h. sein Transmissionsspektrum ist nicht über alle Wellenlängen gleichmäßig). Beispielsweise ist der spektrale Detektionsfilter ein Bandpassfilter mit mindestens zwei Transmissionsbanden, insbesondere ein Interferenzfilter.The spectral detection filter differs from common neutral density filters in that its transmission depends on the wavelength of the light incident on the spectral detection filter (i.e. its transmission spectrum is not uniform over all wavelengths). For example, the spectral detection filter is a bandpass filter with at least two transmission bands, in particular an interference filter.

In manchen Ausführungsbeispielen weist der spektrale Detektionsfilter ein Transmissionsspektrum auf, das eine (spektrale) Lumineszenz-Transmissionsbande im Spektralbereich des Lumineszenzlichts des Wertdokuments aufweist und eine oder mehrere zusätzliche (spektrale) Transmissionsbanden im Spektralbereich des Anregungslichts. Die Lumineszenz-Transmissionsbande überlappt spektral mit dem Lumineszenzlicht des Wertdokuments. Die Lumineszenz-Transmissionsbande kann mit dem Lumineszenzlicht des Wertdokuments spektral teilweise überlappen oder dieses spektral vollständig einschließen. Die mindestens eine zusätzliche Transmissionsbande überlappt spektral mit dem Anregungslicht. Das Transmissionsspektrum des spektralen Detektionsfilters kann z.B. eine zusätzliche Transmissionsbande aufweisen, die das Anregungslicht spektral vollständig einschließt. Alternativ kann/können die zusätzliche/n Transmissionsbande/n mit dem Anregungslicht spektral teilweise überlappen.In some exemplary embodiments, the spectral detection filter has a transmission spectrum that has a (spectral) luminescence transmission band in the spectral range of the luminescence light of the document of value and one or more additional (spectral) transmission bands in the spectral range of the excitation light. The luminescence transmission band overlaps spectrally with the luminescence light of the document of value. The luminescence transmission band can partially overlap spectrally with the luminescent light of the document of value or can completely enclose it spectrally. The at least one additional transmission band overlaps spectrally with the excitation light. The transmission spectrum of the spectral detection filter can, for example, have an additional transmission band that spectrally completely encloses the excitation light. Alternatively, the additional transmission band(s) can partially overlap spectrally with the excitation light.

Die Lumineszenz-Transmissionsbande und die mindestens eine zusätzliche Transmissionsbande sind beispielsweise spektral voneinander getrennt (insbesondere spektral nicht überlappend). Alternativ zu spektral voneinander getrennten Transmissionsbanden kann sich das Transmissionsspektrum des spektralen Detektionsfilters - bei entsprechender Modulation des Transmissionsgrades - auch durchgehend vom Spektralbereich des Lumineszenzlichts bis zum Spektralbereich des Anregungslichts erstrecken.The luminescence transmission band and the at least one additional transmission band are, for example, spectrally separated from one another (in particular not spectrally overlapping). As an alternative to spectrally separate transmission bands, the transmission spectrum of the spectral detection filter--with appropriate modulation of the transmittance--can also extend continuously from the spectral range of the luminescence light to the spectral range of the excitation light.

In seiner Lumineszenz-Transmissionsbande weist der spektrale Detektionsfilter vorzugsweise eine größere Transmission auf als in seiner/ n zusätzlichen Transmissionsbande/n. Beispielsweise ist die maximale Transmission in seiner Lumineszenz-Transmissionsbande um mindestens einen Faktor 4 größer ist als die maximale Transmission in der mindestens einen zusätzlichen Transmissionsbande.The spectral detection filter preferably has a greater transmission in its luminescence transmission band than in its additional one(s). transmission band/s. For example, the maximum transmission in its luminescence transmission band is at least a factor of 4 greater than the maximum transmission in the at least one additional transmission band.

Der Detektionsfilter weist lateral (in der Ebene des Detektionsfilters) insbesondere eine gleichmäßige spektrale Transmission auf. Jeder laterale Abschnitt des spektralen Detektionsfilters hat also dieselbe spektrale Transmission. Durch den spektralen Detektionsfilter wird - jeweils an derselben lateralen Position des Detektionsfilters - sowohl das auf den spektralen Detektionsfilter treffende Lumineszenzlicht des Wertdokuments als auch mindestens 0,5% des auf den spektralen Detektionsfilter treffenden (von dem Wertdokument remittierten) Anregungslichts transmittiert. Der spektrale Detektionsfilter transmittiert das auf ihn treffende Lumineszenzlicht und das auf ihn treffende Anregungslicht also unabhängig von der lateralen Position entlang des spektralen Detektionsfilters. Zum Beispiel weist der spektrale Detektionsfilter die Lumineszenz-Transmissionsbande und die mindestens eine zusätzliche Transmissionsbande jeweils an derselben lateralen Position entlang des spektralen Detektionsfilters auf.In particular, the detection filter has a uniform spectral transmission laterally (in the plane of the detection filter). Each lateral section of the spectral detection filter therefore has the same spectral transmission. Both the luminescence light of the document of value impinging on the spectral detection filter and at least 0.5% of the excitation light impinging on the spectral detection filter (remitted by the document of value) are transmitted through the spectral detection filter—in each case at the same lateral position of the detection filter. The spectral detection filter thus transmits the luminescence light impinging on it and the excitation light impinging on it independently of the lateral position along the spectral detection filter. For example, the spectral detection filter has the luminescence transmission band and the at least one additional transmission band each at the same lateral position along the spectral detection filter.

Vorzugsweise hat die mindestens eine zusätzliche Transmissionsbande von der mindestens einen Lumineszenz-Transmissionsbande spektral einen Abstand von mindestens 10 nm, bevorzugt von mindestens 20 nm. Als spektraler Abstand der Transmissionsbanden wird dabei der spektrale Abstand der beiden einander spektral am nächsten liegenden Halbwertspunkte des Transmissionsspektrums bezeichnet, an denen die Transmission der jeweilige Transmissionsbande auf 50% des Maximalwerts der jeweiligen Transmissionsbande abgefallen ist.The at least one additional transmission band is preferably at a spectral distance of at least 10 nm, preferably at least 20 nm, from the at least one luminescence transmission band. at which the transmission of the respective transmission band has dropped to 50% of the maximum value of the respective transmission band.

Beispielsweise kann das Spektrum des Anregungslicht eine spektrale Anregungsbande aufweisen, die eine obere spektrale Flanke (langwellige Seite des Spektrums) und eine untere spektrale Flanke (kurzwellige Seite des Spektrums) aufweist. In einigen Ausführungsbeispielen weist der spektrale Detektionsfilter eine erste zusätzliche spektrale Transmissionsbande auf, die spektral in der unteren spektralen Flanke der Anregungsbande liegt, und eine zweite zusätzliche spektrale Transmissionsbande, die spektral in der oberen spektralen Flanke der Anregungsbande liegt. Der Vorteil von zusätzlichen spektralen Transmissionsbanden in beiden spektralen Flanken der Anregungsbande ist es, dass dadurch ein spektrales Schieben des Anregungslichts während der Messung (z.B. temperaturbedingt) ausgeglichen wird, d.h. eine Temperaturdrift der Anregungsbande hat keinen oder kaum Einfluss auf die Höhe der durch den spektrale Detektionsfilter transmittierten Anregungsintensität. Derselbe Vorteil wird erreicht, wenn die zusätzliche spektrale Transmissionsbande des spektralen Detektionsfilters die Anregungsbande des Anregungslichts spektral vollständig einschließt.For example, the spectrum of the excitation light can have a spectral excitation band that has an upper spectral edge (long-wavelength side of the spectrum) and a lower spectral edge (short-wavelength side of the spectrum). In some embodiments, the spectral detection filter has a first additional spectral transmission band that is spectrally in the lower spectral edge of the excitation band and a second additional spectral transmission band that is spectrally in the upper spectral edge of the excitation band. The advantage of additional spectral transmission bands in both spectral flanks of the excitation band is that a spectral shift of the excitation light during the measurement (e.g. due to temperature) is compensated for, i.e. a temperature drift of the excitation band has little or no influence on the level of the spectral detection filter transmitted excitation intensity. The same advantage is achieved if the additional spectral transmission band of the spectral detection filter spectrally completely encloses the excitation band of the excitation light.

Bei manchen Sensoren ist es üblich, dass das Wertdokument während des Detektierens relativ zum Detektor transportiert wird, z.B. an diesem vorbei transportiert wird. Dies kann mit relativ geringer Geschwindigkeit von 0,1 -1 m/s erfolgen, bevorzugt aber mit hoher Geschwindigkeit von 1-15 m/ s. Während des Transportierens des Wertdokuments wird der jeweilige Remissions-Messwert dann in einem ersten Detektionsbereich des Wertdokuments detektiert und der jeweilige Lumineszenz-Messwert, der unmittelbar nach dem Remissions-Messwert detektiert wird, in einem zweiten Detektionsbereich des Wertdokuments. Der Remissions-Messwert wird zu einem Zeitpunkt detektiert, zu dem der jeweilige erste Detektionsbereich mit einem Anregungslichtpuls des Anregungslichts beleuchtet wird. Der jeweilige Lumineszenz-Messwert wird zu einem Zeitpunkt detektiert, zu dem der zweite Detektionsbereich nicht mehr mit einem Anregungslichtpuls des Anregungslichts beleuchtet wird.With some sensors, it is common for the document of value to be transported relative to the detector during detection, for example to be transported past it. This can be done at a relatively low speed of 0.1-1 m/s, but preferably at a high speed of 1-15 m/s. During the transport of the document of value, the respective remission measured value is then detected in a first detection area of the document of value and the respective luminescence measured value, which is detected immediately after the reflectance measured value, in a second detection area of the document of value. The reflectance measured value is detected at a point in time at which the respective first detection area is illuminated with an excitation light pulse of the excitation light. The respective luminescence measurement value is detected at a point in time at which the second Detection area is no longer illuminated with an excitation light pulse of the excitation light.

Der zeitliche Abstand zwischen dem Detektieren des Remissions-Messwerts und dem Detektieren des Lumineszenz-Messwerts wird vorzugsweise so gewählt, dass der jeweilige erste und zweite Detektionsbereich, deren erster und zweiter Messwert unmittelbar nacheinander detektiert werden, flächenmäßig (gemessen an ihrer Fläche auf dem Wertdokument) zu mindestens 50% überlappen, bevorzugt zu mindestens 80%.The time interval between the detection of the remission measured value and the detection of the luminescence measured value is preferably chosen such that the respective first and second detection area, the first and second measured value of which are detected immediately one after the other, in terms of area (measured by their area on the document of value) overlap at least 50%, preferably at least 80%.

Die relativ große Transmission des spektralen Detektionsfilters im Spektralbereich des Anregungslichts führt dazu, dass der Detektor während der Beleuchtung mit Anregungslicht eine erhöhte Intensität detektiert, die die Lumineszenz-Intensität üblicherweise weit übertrifft. Bei langsam anklingenden Lumineszenzstoffen (bzw. geringer Verfälschung des Remissions-Messwerts) und geringen Transportgeschwindigkeiten wird keine so große Transmission des Detektionsfilters im Spektralbereich des Anregungslichts benötigt als im Fall einer großen Verfälschung. In diesen Fällen sind übliche Photodetektoren, Verstärkerschaltungen und A/D-Wandler dazu geeignet, sowohl die geringe Intensität des Lumineszenzlichts bei ausgeschalteter Beleuchtung zu bestimmen als auch die Intensität des Anregungslichts während der Beleuchtung. Der Detektor detektiert den jeweiligen Remissions-Messwert und den jeweiligen Lumineszenz-Messwert dabei mit derselben Empfindlichkeit. Der Dynamikbereich der Messung ist dann groß genug, dass sowohl den Remissions-Messwert als auch den Lumineszenz-Messwert ohne Übersteuerung detektiert werden kann. Die Transmission des spektralen Detektionsfilters wird insbesondere so gewählt, dass diese im Spektralbereich des Anregungslichts etwas geringer ist als eine diejenige Transmission, ab der die Intensität des durch den Detektionsfilter transmittierten Anregungslicht die Detektion übersteuert. Um bei der Messung der beiden Messwerte einen möglichst großen Dynamikbereich zur Verfügung zu haben, wird als Detektor bevorzugt eine oder mehrere Photodioden der Materialsysteme Si, Ge, InAs oder InGaAs verwendet. Die damit detektierten Fotoströme können mit einem Transimpedanzwandler geeigneter Verstärkung sowie anschließender Digitalisierung mit hinreichend großem Dynamikbereich verarbeitet werden. Bevorzugt erfolgt dies linear über den Dynamikbereich.The relatively high transmission of the spectral detection filter in the spectral range of the excitation light means that the detector detects an increased intensity during illumination with excitation light, which usually far exceeds the luminescence intensity. In the case of slow-sounding luminescent substances (or slight falsification of the remission measured value) and low transport speeds, the transmission of the detection filter in the spectral range of the excitation light is not as great as in the case of a large falsification. In these cases, conventional photodetectors, amplifier circuits and A/D converters are suitable for determining both the low intensity of the luminescent light when the illumination is switched off and the intensity of the excitation light during illumination. The detector detects the respective remission measured value and the respective luminescence measured value with the same sensitivity. The dynamic range of the measurement is then large enough that both the remission measured value and the luminescence measured value can be detected without overdriving. The transmission of the spectral detection filter is selected in particular in such a way that it is somewhat lower in the spectral range of the excitation light than the transmission from which the intensity of the excitation light transmitted through the detection filter increases detection is overridden. In order to have the largest possible dynamic range available when measuring the two measured values, one or more photodiodes of the material systems Si, Ge, InAs or InGaAs are preferably used as a detector. The photocurrents thus detected can be processed with a transimpedance converter of suitable amplification and subsequent digitization with a sufficiently large dynamic range. This is preferably done linearly over the dynamic range.

Falls der zu detektierende Lumineszenzstoff der Banknote zeitlich schnell anklingt (d.h. den Remissions-Messwert stark verfälscht), wird eine relativ große Transmission des Detektionsfilters im Spektralbereich des Anregungslichts benötigt, um die Verfälschung gering zu halten. Dies führt jedoch zu einer relativ hohen Intensität für den Remissions-Messwert während der Beleuchtung mit Anregungslicht. Falls in einem solchen Fall der Dynamikbereich bei der Detektion, insbesondere der Dynamikbereich der Verstärkerschaltung und/oder des A/D-Wandlers, nicht ausreicht (so dass der Messwert bei der Detektion des Remissions-Messwerts in Sättigung geht) wird eine Erfassung der Messsignale mit unterschiedlicher Empfindlichkeit durchgeführt. Für die Remissionsmessung während der Beleuchtung mit Anregungslicht wird die Empfindlichkeit des Detektors dabei reduziert. Der von dem Detektor detektierte Remissions-Messwert und von dem Detektor detektierte Lumineszenz-Messwert können mit unterschiedlicher Empfindlichkeit gemessen werden, wobei der Remissions-Messwert mit geringerer Empfindlichkeit gemessen wird als der Lumineszenz-Messwert.If the luminescent substance of the bank note to be detected occurs quickly (i.e. the measured remission value is strongly falsified), a relatively high transmission of the detection filter in the spectral range of the excitation light is required in order to keep the falsification low. However, this leads to a relatively high intensity for the measured remission value during illumination with excitation light. If, in such a case, the dynamic range during detection, in particular the dynamic range of the amplifier circuit and/or the A/D converter, is not sufficient (so that the measured value saturates when the remission measured value is detected), the measurement signals are recorded with carried out with different sensitivities. The sensitivity of the detector is reduced for reflectance measurement during illumination with excitation light. The measured reflectance value detected by the detector and the measured luminescence value detected by the detector can be measured with different sensitivities, the measured reflectance value being measured with a lower sensitivity than the measured luminescence value.

Die Steuereinrichtung kann dazu eingerichtet sein, den Detektor oder eine mit diesem verbundene elektronische Schaltung (z.B. Verstärkerschaltung) so umzuschalten, dass der Remissions-Messwert mit geringerer Empfindlichkeit gemessen wird als der Lumineszenz-Messwert. Beispielsweise kann in dem Zeitraum zwischen der Detektion des jeweiligen Remissions-Messwerts und des jeweiligen Lumineszenz-Messwerts eine Empfindlichkeits-Einstellung des Detektors oder eines mit dem Detektor verbundenen Verstärkers oder eines mit dem Detektor verbundenen Strom-Spannungs-Wandlers so umgeschaltet werden, dass der Remissions-Messwert mit geringerer Empfindlichkeit gemessen wird als der Lumineszenz-Messwert. Insbesondere kann in dem Zeitraum zwischen der Detektion des jeweiligen Remissions-Messwerts und des jeweiligen Lumineszenz-Messwerts die Vorspannung des Detektors oder die Verstärkung des elektronischen Verstärkers, der das Ausgangssignal des Detektors verstärkt, oder die Transimpedanz eines mit dem Detektor verbundenen Strom-Spannungs-Wandlers so umgeschaltet werden, dass der Remissions-Messwert mit geringerer Empfindlichkeit detektiert wird als der Lumineszenz-Messwert. Die Empfindlichkeit kann durch ein Schaltsignal der Steuereinrichtung umgeschaltet werden, das z.B. synchron mit den Anregungslichtpulsen erzeugt wird. Vorzugsweise wird die Empfindlichkeits-Einstellung des Detektors unmittelbar vor Beginn des Anregungslichtpulses so umgeschaltet, dass der Remissions-Messwert mit geringerer Empfindlichkeit detektiert wird als der Lumineszenz-Messwert, und unmittelbar nach Ende des Anregungslichtpulses für die Detektion des Remissions-Messwerts wieder zurück geschaltet. Die Empfindlichkeit kann mit einer Umschaltzeit von 50 µs bis 1 ms umgeschaltet werden, vorzugsweise mit einer Umschaltzeit von 70 µs bis 300 µs.The control device can be set up to switch over the detector or an electronic circuit connected to it (for example an amplifier circuit) in such a way that the remission measured value has a lower sensitivity is measured as the luminescence reading. For example, in the period between the detection of the respective remission measured value and the respective luminescence measured value, a sensitivity setting of the detector or of an amplifier connected to the detector or of a current-voltage converter connected to the detector can be switched so that the remission -measured value is measured with lower sensitivity than the luminescence measured value. In particular, in the period between the detection of the respective reflectance measured value and the respective luminescence measured value, the bias voltage of the detector or the gain of the electronic amplifier which amplifies the output signal of the detector, or the transimpedance of a current-to-voltage converter connected to the detector be switched over in such a way that the remission measured value is detected with less sensitivity than the luminescence measured value. The sensitivity can be switched over by a switching signal from the control device, which is generated synchronously with the excitation light pulses, for example. The sensitivity setting of the detector is preferably switched over immediately before the start of the excitation light pulse in such a way that the remission measured value is detected with lower sensitivity than the luminescence measured value, and switched back again immediately after the end of the excitation light pulse for the detection of the reflectance measured value. The sensitivity can be switched with a switching time of 50 µs to 1 ms, preferably with a switching time of 70 µs to 300 µs.

Die Steuereinrichtung kann ein Prozessor sein, der mit entsprechender Software zur Steuerung der Beleuchtungseinrichtung und des Detektors programmiert ist. Der Prozessor kann auch dazu ausgebildet sein, ein Steuersignal zu erzeugen, das die Empfindlichkeit des Detektors umschaltet. Die Auswerteeinrichtung kann auch Prozessor sein, der mit entsprechender Software zur Auswertung der Remissions- und Lumineszenz-Messwerte programmiert ist. Der Prozessor ist z.B. zur Analyse der Messsignale und zur Echtheitsbewertung eingerichtet und gibt das Ergebnis der Echtheitsbewertung aus oder zur Weiterverarbeitung weiter. Die Steuereinrichtung und die Auswerteeinrichtung können unterschiedliche Einrichtungen sein oder können durch dieselbe Einrichtung gebildet werden, die sowohl zur Steuerung der Beleuchtungseinrichtung und des Detektors eingerichtet ist, als auch zum Prüfen des Wertdokuments anhand des von dem Detektor detektierten mindestens einen Remissions- Messwerts und anhand des von dem Detektor detektierten mindestens einen Lumineszenz-Messwerts. Beispielsweise kann derselbe Prozessor für beides verwendet werden.The controller may be a processor programmed with appropriate software to control the illuminator and detector. The processor can also be configured to generate a control signal that switches the sensitivity of the detector. The evaluation device can also be a processor with the appropriate Software for evaluating the reflectance and luminescence measurements is programmed. The processor is set up, for example, to analyze the measurement signals and to assess the authenticity, and it outputs the result of the authenticity assessment or forwards it for further processing. The control device and the evaluation device can be different devices or can be formed by the same device, which is set up both to control the illumination device and the detector and to check the document of value based on the at least one remission measured value detected by the detector and based on the at least one luminescence measurement value detected by the detector. For example, the same processor can be used for both.

Der Detektor ist insbesondere ein halbleiterbasierter Detektor, z.B. eine Photodiode, bevorzugt mit einer Ladungsträgerlebensdauer von höchstens 20 µs. Trotz intensiver Bestrahlung mit Anregungslicht ist der Detektor dann nach kurzer Zeit wieder zur Detektion von geringen Intensitäten fähig. Dies erlaubt eine schnellere Messung bzw. einen geringen zeitlichen Abstand der beiden Messungen und damit großen räumlichen Überlapp der Detektionsbereiche, gerade auch im Fall großer Transportgeschwindigkeiten des Wertdokuments.The detector is in particular a semiconductor-based detector, e.g. a photodiode, preferably with a charge carrier lifetime of at most 20 µs. Despite intensive irradiation with excitation light, the detector is then able to detect low intensities again after a short time. This allows a faster measurement or a short time interval between the two measurements and thus a large spatial overlap of the detection areas, especially in the case of high transport speeds of the document of value.

Die Erfindung betrifft auch ein Verfahren zur Prüfung von Dokumenten, z.B. Wertdokumenten, insbesondere zur Echtheitsprüfung der Dokumente bzw. Wertdokumente, mit den Schritten:

  • Beleuchten eines Dokuments, z.B. Wertdokuments, mit einem oder mehreren Anregungslichtpulsen eines Anregungslichts, das dazu geeignet ist, das Dokument, z.B. Wertdokument, zur Emission von Lumineszenzlicht anzuregen,
  • Detektieren mindestens eines Remissions-Messwerts des Dokuments, z.B. Wertdokuments ,zu mindestens einem Zeitpunkt, zu dem das Dokument, z.B. Wertdokument, mit einem Anregungslichtpuls des Anregungslichts beleuchtet wird, mittels eines Detektors,
  • Detektieren mindestens eines Lumineszenz-Messwerts des Dokuments, z.B. Wertdokuments ,zu mindestens einem Zeitpunkt nach Ende des jeweiligen Anregungslichtpulses mittels des Detektors,
  • Prüfen des Dokuments, z.B. Wertdokuments, anhand des von dem Detektor detektierten mindestens einen Remissions- Messwerts und anhand des von dem Detektor detektierten mindestens einen Lumineszenz- Messwerts.
The invention also relates to a method for checking documents, for example documents of value, in particular for checking the authenticity of the documents or documents of value, with the steps:
  • illuminating a document, e.g. a document of value, with one or more excitation light pulses of an excitation light which is suitable for stimulating the document, e.g. a document of value, to emit luminescent light,
  • Detecting at least one remission measured value of the document, e.g. document of value, at least at a point in time at which the document, e.g. document of value, is illuminated with an excitation light pulse of the excitation light, by means of a detector,
  • detecting at least one measured luminescence value of the document, e.g. a document of value, at least at a point in time after the end of the respective excitation light pulse by means of the detector,
  • Checking the document, for example a document of value, based on the at least one remission measured value detected by the detector and based on the at least one luminescence measured value detected by the detector.

Beim Detektieren des Remissions-Messwerts und des Lumineszenz-Messwerts befindet sich in einem zwischen dem Wertdokument und dem Detektor gebildeten Detektionsstrahlengang ein spektraler Detektionsfilter, dessen spektrale Transmission so gewählt ist, dass durch den Detektionsfilter sowohl das auf den spektralen Detektionsfilter auftreffende Lumineszenzlicht des Wertdokuments als auch mindestens 0,5% des auf den spektralen Detektionsfilter auftreffenden Anregungslichts transmittiert wird, das von dem Wertdokument remittiert wurde.When detecting the measured remission value and the measured luminescence value, a detection beam path formed between the document of value and the detector contains a spectral detection filter whose spectral transmission is selected such that the luminescence light of the document of value impinging on the spectral detection filter and at least 0.5% of the excitation light impinging on the spectral detection filter, which was remitted by the document of value, is transmitted.

Die Auswertung kann auf Basis eines einzigen diskreten Remissions- bzw. Lumineszenz-Messwerts oder auf Basis mehrerer der jeweiligen Messwerte erfolgen, die miteinander verrechnet (z.B. gemittelt) werden. Die Messwerte können zu diskreten Zeitpunkten detektiert werden oder durch zeitliches Aufintegrieren über einen Zeitabschnitt innerhalb des jeweiligen Anregungspulses (beim Remissions-Messwert) bzw. nach Ende des jeweiligen Anregungspulses (beim Lumineszenz-Messwert) detektiert werden. Zwischen jeweils zwei Anregungslichtpulsen können auch zwei oder mehrere Lumineszenz-Messwerte mit jeweils unterschiedlichem Zeitabstand zum jeweiligen Anregungslichtpuls detektiert werden und diese Lumineszenz-Messwerte zur Prüfung des Wertdokuments verwendet werden, z.B. miteinander verrechnet werden.The evaluation can be based on a single discrete remission or luminescence measurement value or on the basis of several of the respective measurement values that are offset against each other (eg averaged). The measured values can be detected at discrete points in time or by temporal integration over a period of time within the respective excitation pulse (for the reflectance measured value) or after the end of the respective excitation pulse (for the luminescence measured value). Between each two excitation light pulses there can also be two or more Luminescence measurement values are detected with different time intervals from the respective excitation light pulse and these luminescence measurement values are used to check the document of value, for example offset against one another.

Das Wertdokument und der Detektor können relativ zueinander bewegt werden und die Beleuchtung entlang des Wertdokuments abwechselnd ein- und ausgeschaltet werden. Alternativ kann die Beleuchtung und Detektion auch ohne Relativbewegung erfolgen.The document of value and the detector can be moved relative to each other and the lighting along the document of value can be switched on and off alternately. Alternatively, the illumination and detection can also take place without relative movement.

Die Dokumente, deren Echtheit mit dem erfindungsgemäßen Verfahren und dem Sensor geprüft wird, sind insbesondere Wertdokumente, beispielsweise Banknoten, Tickets, Schecks, Coupons, Gutscheine, etc. Mit dem erfindungsgemäßen Verfahren und dem Sensor können aber auch andere Dokumente, z.B. Ausweisdokumente, geprüft werden.The documents whose authenticity is checked using the method according to the invention and the sensor are, in particular, documents of value, for example banknotes, tickets, cheques, coupons, vouchers, etc. However, other documents, e.g. ID documents, can also be checked using the method according to the invention and the sensor .

Zur Durchführung des erfindungsgemäßen Verfahrens kann eine Vorrichtung zur Prüfung von Dokumenten, z.B. Wertdokumenten, verwendet werden, die den oben genannten Sensor zur Prüfung (und ggf. weitere Sensoren) aufweist. Die Vorrichtung kann zur Bearbeitung, z.B. zur Echtheitsprüfung und/oder zur Sortierung, von Wertdokumenten ausgebildet sein. Insbesondere kann die Vorrichtung eine Transporteinrichtung aufweisen, die dazu eingerichtet ist, das Dokument, z.B. Wertdokument, und den Detektor bzw. den Sensor, der den Detektor aufweist, während des Detektierens relativ zueinander zu transportieren, z.B. das Wertdokument an dem Sensor bzw. Detektor vorbei zu transportieren. Die Steuereinrichtung des Sensors kann dazu eingerichtet sein, den Detektor so anzusteuern, dass der jeweilige Remissions-Messwert und der jeweilige Lumineszenz-Messwert mit derart geringem zeitlichem Abstand voneinander detektiert werden, dass die Detektionsbereiche auf dem Dokument, z.B. Wertdokument, von denen der jeweilige Remissions-Messwert und der jeweilige Lumineszenz-Messwert detektiert werden, zu mindestens 50%, bevorzugt zu mindestens 80%, überlappen.To carry out the method according to the invention, a device for checking documents, for example documents of value, can be used which has the above-mentioned sensor for checking (and optionally further sensors). The device can be designed for processing documents of value, for example for checking the authenticity and/or for sorting. In particular, the device can have a transport device which is set up to transport the document, eg document of value, and the detector or the sensor which has the detector relative to one another during detection, eg the document of value past the sensor or detector to transport. The control device of the sensor can be set up to control the detector in such a way that the respective remission measured value and the respective luminescence measured value are detected with such a short time interval from one another that the detection ranges overlap by at least 50%, preferably by at least 80%, on the document, eg document of value, from which the respective remission measured value and the respective luminescence measured value are detected.

Nachfolgend wird die Erfindung anhand der begleitenden Zeichnungen beispielhaft beschrieben. Es zeigen:

Fig. 1
Schematischer Aufbau eines erfindungsgemäßen Sensors,
Fig. 2a
Beispiel für eine Banknote mit fluoreszenzierender Druckfarbe,
Fig. 2b
Verlauf der von der Banknote aus Fig. 2a ausgehenden Remissionsintensität R und Fluoreszenzintensität F als Funktion der Position x entlang der Banknote,
Fig. 3a-d
zeitlicher Verlauf der Anregungsintensität (Fig. 3a), der Lumineszenz-Intensität der Banknote (Fig. 3b), der Überlagerung aus Lumineszenz-Intensität und der (bei starker Unterdrückung) detektierten Anregungsintensität (Fig. 3c), der Überlagerung aus Lumineszenz-Intensität und der (bei geringer Unterdrückung) detektierten Anregungsintensität (Fig. 3d,)
Fig. 4a-e
fünf Beispiele für Transmissionsspektren des spektralen Detektionsfilters im Vergleich zur spektralen Lage des Anregungslichts und des Lumineszenzlichts,
Fig. 5
zweidimensionale Lage des ersten und zweiten Detektionsbereichs auf der Banknote,
Fig. 6
elektrische Schaltung zur Umschaltung der Empfindlichkeit bei der Detektion.
The invention is described below by way of example with reference to the accompanying drawings. Show it:
1
Schematic structure of a sensor according to the invention,
Figure 2a
Example of a banknote with fluorescent ink,
Figure 2b
History of the banknote Figure 2a outgoing remission intensity R and fluorescence intensity F as a function of the position x along the banknote,
Fig. 3a-d
Time course of the excitation intensity ( Figure 3a ), the luminescence intensity of the banknote ( Figure 3b ), the superimposition of the luminescence intensity and the (in the case of strong suppression) detected excitation intensity ( 3c ), the superimposition of the luminescence intensity and the (with low suppression) detected excitation intensity ( 3d ,)
Fig. 4a-e
five examples of transmission spectra of the spectral detection filter compared to the spectral position of the excitation light and the luminescence light,
figure 5
two-dimensional position of the first and second detection area on the bank note,
6
electrical circuit for switching the sensitivity during detection.

Die Erfindung wird im Folgenden am Beispiel der Echtheitsprüfung einer Banknote 3 erläutert, in deren Substrat vollflächig ein Lumineszenzstoff eingebracht ist, dessen Lumineszenz zur Echtheitsprüfung ausgewertet wird.The invention is explained below using the example of the authenticity check of a banknote 3 in whose substrate a luminescent substance is introduced over the entire surface, the luminescence of which is evaluated for the authenticity check.

Die in diesem Beispiel betrachtete Banknote aus Fig. 2a weist- zusätzlich zu dem Lumineszenzstoff - einen Aufdruck aus fluoreszierender Druckfarbe 11 auf. Desweiteren ist der Nennwert 13 der Banknote aufgedruckt und ein Bereich mit nichtfluoreszierender Druckfarbe 12 versehen.The banknote considered in this example Figure 2a has--in addition to the luminescent substance--an imprint of fluorescent printing ink 11. Furthermore, the denomination 13 of the bank note is printed and an area is provided with non-fluorescent ink 12 .

Fig. 1 zeigt einen Sensor 10, der sowohl zur Erfassung von Remissions-Messwerten als auch von Lumineszenz-Messwerten eines Wertdokuments, wie z.B. der Banknote 3 aus Fig. 2a, eingerichtet ist. Die Banknote 3 wird mit Hilfe einer Transporteinrichtung entlang einer Richtung (z.B. in Fig. 1 von rechts nach links) an dem Sensor 10 vorbeitransportiert, so dass der Detektor 6 nacheinander mehrere Messwerte als Funktion der Position x entlang der Banknote 3 detektieren kann. Für die Messung von Remission und Lumineszenz der Banknote wird derselbe Detektor 6 verwendet. 1 FIG. 1 shows a sensor 10 which is used both for detecting remission measured values and luminescence measured values of a document of value, such as banknote 3 Figure 2a , is set up. The bank note 3 is transported in one direction (e.g. in 1 from right to left) past the sensor 10 so that the detector 6 can successively detect several measured values as a function of the position x along the banknote 3. The same detector 6 is used to measure the remission and luminescence of the bank note.

Der Sensor 10 weist in einer Ausführungsform eine Beleuchtungseinrichtung mit zwei Leuchtdioden 1a und 1b auf, die die Banknote 3 aus schräger Richtung beleuchten. Der Spektralbereich der Beleuchtungseinrichtung ist so gewählt, dass das von der Beleuchtungseinrichtung ausgestrahlte Licht zur optischen Anregung des auf der Banknote vollflächig vorhandenen Lumineszenzstoffs ausgebildet ist. Die Beleuchtungseinrichtung wird periodisch ein- und ausgeschaltet, um die Banknote 3 an einer Vielzahl von Positionen x entlang der Banknote mit Anregungslichtpulsen zur Lumineszenz anzuregen. Im Detektionsstrahlengang 8 des Sensors 10 durchläuft das von der Banknote 3 ausgehende Licht ein Frontglas 2, anschließend eine Linse 4, einen spektralen Detektionsfilter 5 und eine weitere Linse 4, die das Licht auf den Detektor 6 richtet. Der spektrale Detektionsfilter 5 wird zur Dämpfung des Anregungslichts A verwendet. Der Sensor 10 weist ferner eine Steuereinrichtung 7 auf, die für das periodische Ein- und Ausschalten der Beleuchtungseinrichtung sorgt, zu bestimmten Zeitpunkten die Detektion der Remissions- und Lumineszenz-Messwerte auslöst und die von dem Detektor detektierten Remissions- und Lumineszenz-Messwerte an die Auswerteeinrichtung 9 weiterleitet, die eine Echtheitsprüfung anhand der Remissions- und Lumineszenz-Messwerte durchführt.In one embodiment, the sensor 10 has an illumination device with two light-emitting diodes 1a and 1b, which illuminate the banknote 3 from an oblique direction. The spectral range of the lighting device is selected in such a way that the light emitted by the lighting device is designed to optically excite the luminescent substance present over the entire surface of the bank note. The lighting device is switched on and off periodically in order to excite the banknote 3 to luminescence at a large number of positions x along the banknote with excitation light pulses. In the detection beam path 8 of the sensor 10, the light emanating from the bank note 3 passes through a front glass 2, then a lens 4, a spectral detection filter 5 and a further lens 4, which directs the light onto the detector 6. The spectral detection filter 5 is used to attenuate the excitation light A. The sensor 10 also has a control device 7, which provides for the periodic switching on and off of the lighting device, at specific times the detection of the remission and luminescence measurement values and forwards the reflectance and luminescence measurement values detected by the detector to the evaluation device 9, which carries out an authenticity check using the reflectance and luminescence measurement values.

Das Anregungslicht A der Beleuchtungseinrichtung wird sowohl zur Anregung der Lumineszenz des vollflächig vorhandenen Lumineszenzstoffs als auch als Beleuchtungslicht für die Remissionsmessung verwendet. Während der Beleuchtung mit einem für die Lumineszenzanregung verwendeten Anregungslichtpuls, vgl. Fig. 3a, detektiert der Detektor 6 einen Remissions-Messwert. Nach Ende des jeweiligen Anregungslichtpulses detektiert der Detektor 6 einen Lumineszenz-Messwert. Um eine Messung von Remission und Lumineszenz der Banknote an möglichst derselben Wertdokumentposition zu erreichen, werden der Remissions-Messwert und der Lumineszenz-Messwert mit möglichst geringem zeitlichem Abstand voneinander detektiert. Auf diese Weise können Remissions- und Lumineszenz-Messung an nahezu derselben Wertdokumentposition x durchgeführt werden. Bevorzugt überlappen der Detektionsbereich der Remissionsmessung (erster Detektionsbereich D1) und der Detektionsbereich der Lumineszenz-Messung (zweiter Detektionsbereich D2) flächenmäßig zu mindestens 80%, vgl. Fig. 5.The excitation light A of the illumination device is used both to excite the luminescence of the luminescence substance present over the entire surface and as illumination light for the remission measurement. During the illumination with an excitation light pulse used for the luminescence excitation, cf. Figure 3a , the detector 6 detects a measured remission value. After the end of the respective excitation light pulse, the detector 6 detects a measured luminescence value. In order to measure the remission and luminescence of the bank note at the same value document position, the remission measured value and the luminescence measured value are detected with the shortest possible time interval from one another. In this way, remission and luminescence measurement can be carried out at almost the same value document position x. The detection area of the reflectance measurement (first detection area D1) and the detection area of the luminescence measurement (second detection area D2) preferably overlap by at least 80% in terms of area, cf. figure 5 .

Da die Remissionsmessung während des Beleuchtens mit dem Anregungslicht A durchgeführt wird, kann der Remissions-Messwert jedoch durch eine gleichzeitig mit der Remission auftretende Lumineszenz verfälscht sein. So kommt es durch eine schnell anklingende Lumineszenz, wie sie in Fig. 3b gezeigt ist, zu einer fehlerhaften Erhöhung des Remissions-Messwerts. Während der Beleuchtung mit Anregungslicht wird in solchem Fällen eine Überlagerung von Remission und Lumineszenz detektiert, vgl. Fig. 3c. Der während der Beleuchtung mit Anregungslicht detektierte Remissions-Messwert ergibt sich in einem solchen Fall nicht aus der Remissions-Intensität allein, sondern enthält auch Anteil an Lumineszenz-Intensität. Der zur Echtheitsprüfung verwendete Remissions-Messwert kann daher durch eine gleichzeitig mit der Beleuchtung auftretende Lumineszenz verfälscht sein.However, since the reflectance measurement is carried out during the illumination with the excitation light A, the measured reflectance value can be falsified by luminescence occurring at the same time as the reflectance. So it comes from a fast onset of luminescence, as seen in Figure 3b shown results in an erroneous increase in reflectance reading. In such cases, during illumination with excitation light, a superimposition of remission and luminescence is detected, cf. 3c . The measured remission value detected during illumination with excitation light in such a case does not result from the remission intensity alone, but also contains a proportion of luminescence intensity. The measured remission value used for the authenticity check can therefore be falsified by luminescence occurring at the same time as the illumination.

Darüber hinaus kann der Remissions-Messwert auch dadurch verfälscht sein, dass eine schnell anklingende zusätzliche Fluoreszenz, wie die der fluoreszierenden Druckfarbe 11, detektiert wird, die die Banknote als Reaktion auf den Anregungslichtpuls des Anregungslichts A nur im Bereich der fluoreszierenden Druckfarbe 11 emittiert, vgl. Fig. 2a und 2b. In Fig. 2b ist die entlang einer Linie S von der Banknote 3 ausgehende Remissions-Intensität R als Funktion der Position x entlang der Banknote skizziert. Im Bereich des Nennwerts 13 und der nichtfluoreszierender Druckfarbe 12 ergibt sich eine geringere Remissions-Intensität als außerhalb der bedruckten Bereiche. Im Bereich der fluoreszierenden Druckfarbe 11 ist die Remission der Banknote ebenfalls unterdrückt. Allerdings geht von der Banknote 3 in diesem Bereich - zusätzlich zur Remission - die Fluoreszenz F der fluoreszierenden Druckfarbe 11 aus, die den in diesem Bereich detektierten Messwert deutlich erhöht. An den x-Position der fluoreszierenden Druckfarbe 11 kommt es daher zusätzlich zu einer fehlerhaften Erhöhung des während der Beleuchtung mit Anregungslicht detektierten Remissions-Messwerts.In addition, the remission measured value can also be falsified by the fact that a fast-sounding additional fluorescence, such as that of the fluorescent printing ink 11, is detected, which the bank note emits in response to the excitation light pulse of the excitation light A only in the area of the fluorescent printing ink 11, cf . Figures 2a and 2b . In Figure 2b the remission intensity R emanating from the bank note 3 along a line S is sketched as a function of the position x along the bank note. In the area of the nominal value 13 and the non-fluorescent printing ink 12, there is a lower remission intensity than outside the printed areas. In the area of the fluorescent printing ink 11, the remission of the bank note is also suppressed. However, the fluorescence F of the fluorescent printing ink 11 emanates from the bank note 3 in this area--in addition to remission--which significantly increases the measured value detected in this area. Therefore, at the x-position of the fluorescent printing ink 11, there is also an erroneous increase in the reflectance measured value detected during the illumination with excitation light.

Die während der Beleuchtung mit Anregungslicht detektierten Remissions-Messwerte MR können daher sowohl im Fall eines schnell anklingenden vollflächig aufgebrachten Lumineszenzstoffs als auch durch eine zusätzliche Fluoreszenz F anderer, lokal aufgebrachter Farben oder Fluoreszenzstoffe verfälscht sein.The reflectance measured values MR detected during the illumination with excitation light can therefore be falsified both in the case of a fast-sounding luminescent substance applied over the entire surface and by additional fluorescence F of other locally applied colors or fluorescent substances.

Zur Echtheitsprüfung der Banknote 3 werden beispielsweise die Lumineszenz-Messwerte eines vollflächig ins Substrat eingebrachten Lumineszenzstoffs untersucht und dabei mit den Remissions-Messwerten der Banknote verglichen. Werden nun für diesen Vergleich die verfälschten Remissions-Messwerte verwendet, so kann dies zu einer fehlerhaften Echtheitsbeurteilung der jeweiligen Banknote führen.To check the authenticity of the banknote 3, for example, the measured luminescence values of a luminescent substance that is introduced over the entire surface of the substrate are examined and compared with the measured remission values of the banknote. If the falsified reflectance measured values are now used for this comparison, this can lead to an incorrect assessment of the authenticity of the respective bank note.

Bei einem Lumineszenzsensor wird üblicherweise im Detektionsstrahlengang des Detektors ein Sperrfilter eingebaut, der das Anregungslicht möglichst stark unterdrückt, z.B. auf einen Faktor von T*=10-5 dämpft, damit möglichst wenig Anregungslicht zum Detektor gelangt. Da jedoch trotz des Sperrfilters eine vollständige Unterdrückung des Anregungslichts nicht gelingt, für das Anregungslicht aber einer erhebliche Intensität verwendet wird, dringt üblicherweise dennoch ein Teil des Anregungslichts A zum Detektor vor. Das zum Detektor - trotz des Sperrfilters - vordringende Anregungslicht kann eine mit der zu detektierenden Lumineszenz vergleichbare Intensität aufweisen, wie es im Fall der Fig. 3c gezeigt ist.In a luminescence sensor, a blocking filter is usually installed in the detection beam path of the detector, which suppresses the excitation light as much as possible, eg by a factor of T*=10 -5 , so that as little excitation light as possible reaches the detector. However, since complete suppression of the excitation light is not possible despite the blocking filter, but a considerable intensity is used for the excitation light, a portion of the excitation light A usually still penetrates to the detector. The detector - despite the blocking filter - penetrating excitation light can have an intensity comparable to the luminescence to be detected, as is the case in the 3c is shown.

Es wurde herausgefunden, dass das Problem der Verfälschung der Remissions-Messwerte MR (durch die gleichzeitig auftretende Lumineszenz) dadurch gelöst werden kann, dass im Detektionsstrahlengang 8 für das Anregungslicht A kein Sperrfilter verwendet wird, sondern ein größerer Anteil des Anregungslichts A bis zum Detektor 6 durchgelassen wird. Im Detektionsstrahlengang 8 des Sensors 10 wird - an Stelle des Sperrfilters - ein spektraler Detektionsfilter 5 eingebaut, welcher das Anregungslicht nur teilweise unterdrückt, z.B. nur auf einen Faktor von T=10-2, und nicht - wie sonst üblich - möglichst stark unterdrückt. Die geringer Dämpfung des Anregungslichts A im Detektionsstrahlengang 8 führt dazu, dass der Anteil der detektierten Anregungsintensität deutlich erhöht wird, während der (zur Verfälschung führende) Beitrag der Lumineszenz - aufgrund unveränderter Anregungsintensität der Banknote - gleich bleibt (die auf die Banknote treffende Anregungsintensität wird durch die veränderte Dämpfung im Detektionsstrahlengang nicht beeinflusst). Da die zum Detektor durchgelassene Anregungsintensität - aufgrund der geringeren Dämpfung - dann viel größer ist als der (verfälschende) Beitrag, den die Lumineszenz-Intensität zum Remissions-Messwert beisteuert, führt die Lumineszenz dann nur mehr zu einer vernachlässigbaren Verfälschung des Remissions-Messwerts.It was found that the problem of the falsification of the reflectance measured values MR (due to the luminescence occurring at the same time) can be solved by not using a blocking filter in the detection beam path 8 for the excitation light A, but using a larger proportion of the excitation light A up to the detector 6 is allowed through. Instead of the blocking filter, a spectral detection filter 5 is installed in the detection beam path 8 of the sensor 10, which only partially suppresses the excitation light, eg only by a factor of T=10 -2 , and not - as is otherwise usual - suppressed as much as possible. The low attenuation of the excitation light A in the detection beam path 8 means that the proportion of the detected excitation intensity is significantly increased, while (for falsification leading) contribution of the luminescence - due to unchanged excitation intensity of the bank note - remains the same (the excitation intensity hitting the bank note is not influenced by the changed attenuation in the detection beam path). Since the excitation intensity let through to the detector - due to the lower attenuation - is then much greater than the (falsifying) contribution that the luminescence intensity contributes to the remission measured value, the luminescence then only leads to a negligible falsification of the remission measured value.

In Fig. 3c ist der zeitliche Verlauf der auf den Detektor 6 auftreffenden Intensität im bisher üblich Fall einer möglichst starken Dämpfung des Anregungslichts gezeigt (Transmission des spektralen Detektionsfilters 5 von T*=10-5). Und in Fig. 3d ist der zeitliche Verlauf der auf den Detektor 6 auftreffenden Intensität im Fall einer geringeren Dämpfung des Anregungslichts gezeigt (Transmission des spektralen Detektionsfilters 5 von T=10-2). Beim Vergleich der Fig. 3c und 3d ist zu erkennen, dass im Fall der starken Dämpfung der zum Zeitpunkt t1 detektierte Remissions-Messwert MR deutlich durch die Lumineszenz L verfälscht ist. Im Fall der geringeren Dämpfung bleibt der zum Zeitpunkt t1 detektierte Remissions-Messwert MR dagegen von der Lumineszenz L nahezu unverfälscht. Zum Zeitpunkt t2 wird der Lumineszenz-Messwert ML detektiert. Der abfallende Ast der Lumineszenzkurve aus Fig. 3d entspricht dem aus Fig. 3c, doch die größere y-Skalierung in Fig. 3d führt dazu, dass der abfallende Ast der Lumineszenzkurve und damit auch Lumineszenz-Messwert ML auf der y-Achse weiter unten liegen. An der größeren y-Skalierung in Fig. 3d ist zudem erkennbar, dass der zum Zeitpunkt t1 detektierte Remissions-Messwert MR im Vergleich zum Fall aus Fig. 3c stark erhöht ist.In 3c shows the time profile of the intensity incident on the detector 6 in the hitherto customary case of the strongest possible attenuation of the excitation light (transmission of the spectral detection filter 5 of T*=10 -5 ). And in 3d shows the time profile of the intensity incident on the detector 6 in the case of a lower attenuation of the excitation light (transmission of the spectral detection filter 5 of T=10 -2 ). When comparing the Figures 3c and 3d it can be seen that in the case of strong attenuation, the reflectance measured value MR detected at time t1 is clearly corrupted by the luminescence L. In the case of lower attenuation, on the other hand, the reflectance measured value MR detected at time t1 remains almost uncorrupted by the luminescence L. The measured luminescence value ML is detected at time t2. The falling branch of the luminescence curve 3d corresponds to that 3c , but the larger y-scaling in 3d results in the falling branch of the luminescence curve and thus also the measured luminescence value ML being further down the y-axis. At the larger y scale in 3d it can also be seen that the reflectance measured value MR detected at time t1 is off compared to the case 3c is greatly increased.

Falls der zu detektierende Lumineszenzstoff der Banknote zeitlich langsam anklingt (d.h. den Remissions-Messwert nicht übermäßig verfälscht) braucht die Transmission des spektralen Detektionsfilters für das Anregungslicht nicht so stark erhöht zu werden. Dann können sowohl der erhöhte Remissions-Messwert MR als auch der deutlich geringere Lumineszenz-Messwert ML mit demselben Detektor 6 mit ausreichender Genauigkeit detektiert werden. Gegebenenfalls kann ein spezieller Detektor 6 verwendet werden, der einen besonders großen Dynamikbereich hat.If the luminescent substance to be detected in the banknote sounds slowly over time (i.e. does not excessively falsify the remission measured value), the transmission of the spectral detection filter for the excitation light does not have to be increased so much. Then both the increased reflectance measured value MR and the significantly lower luminescence measured value ML can be detected with the same detector 6 with sufficient accuracy. If necessary, a special detector 6 can be used, which has a particularly large dynamic range.

Falls der zu detektierende Lumineszenzstoff der Banknote zeitlich schnell anklingt (d.h. den Remissions-Messwert stark verfälscht), ist eine deutlich erhöhte Transmission des spektralen Detektionsfilters für das Anregungslicht notwendig. Um in diesem Fall eine Übersteuerung des der Messung zu vermeiden, kann bei der Messung eine dynamische Empfindlichkeitsumschaltung durchgeführt werden. Beispielsweise wird dazu ein in der Verstärkung umschaltbarer Strom-Spannungs-Wandler verwendet, vgl. die in Fig. 6 gezeigte elektronische Schaltung. Die Steuereinrichtung 7 des Sensors 10 sorgt für eine Umschaltung der Verstärkung des Strom-Spannungs-Wandlers mit Hilfe eines Halbleiterschalters S1, der über ein Steuersignal Us der Steuereinrichtung 7 wahlweise in den geöffneten oder den geschlossenen Zustand gebracht wird. Während der Beleuchtung mit einem Anregungslichtpuls ist S1 geschlossen, so dass der niederohmige Widerstand R2 dem hochohmigen Wiederstand R1 parallel geschaltet ist. Für die Detektion des großen Remissions-Messwerts MR hat der Strom-Spannungs-Wandler dann eine niedrige Verstärkung. Nach Detektion des Remissions-Messwerts MR öffnet die Steuereinrichtung 7 den Halbleiterschalter S1 mit Hilfe des Steuersignals Us, damit der Strom-Spannungs-Wandler - für die Detektion des niedrigen Lumineszenz-Messwerts ML - eine große Verstärkung hat. Zur Vermeidung von Übersteuerungszuständen wird der zeitliche Ablauf des Steuersignals Us vorzugsweise so gelegt, dass der Halbleiterschalter S1 bereits vor Beginn des Anregungslichtpulses geschlossen wird und erst nach Ende des Anregungslichtpulses wieder geöffnet wird.If the luminescent substance of the banknote to be detected occurs quickly (ie greatly falsifies the reflectance measured value), a significantly increased transmission of the spectral detection filter for the excitation light is necessary. In order to avoid overdriving the measurement in this case, a dynamic sensitivity switch can be carried out during the measurement. For example, a current-voltage converter with switchable gain is used for this purpose, cf 6 electronic circuit shown. The control device 7 of the sensor 10 ensures that the amplification of the current-voltage converter is switched over with the aid of a semiconductor switch S1, which is optionally brought into the open or closed state via a control signal Us from the control device 7 . During the illumination with an excitation light pulse, S1 is closed, so that the low-impedance resistor R2 is connected in parallel with the high-impedance resistor R1. The current-voltage converter then has a low amplification for the detection of the large reflectance measured value MR. After the remission measured value MR has been detected, the control device 7 opens the semiconductor switch S1 with the aid of the control signal Us so that the current-voltage converter—for the detection of the low luminescence measured value ML—has a high gain. To avoid overload conditions, the timing of the Control signal Us preferably placed so that the semiconductor switch S1 is closed before the start of the excitation light pulse and is only opened again after the end of the excitation light pulse.

Für eine erhöhte Stabilität der elektronischen Schaltung können Kondensatoren verwendet werden, die zu den Widerständen parallel geschaltet sind. Durch eine entsprechende Wahl der Kondensatoren kann zudem die Verstärkungsbandbreite eingestellt werden. Die Kapazitätswerte C1 und C2 der Kondensatoren können beispielsweise entsprechend nachfolgender Formel gewählt werden: C x = 1 4 πR x f c 1 + 1 + 8 πR x f c C i

Figure imgb0001

  • mit Rx=R1 bzw. R2 und Cx= C1 bzw. C2
  • fc = Verstärkungs-Bandbreite-Produkt des Operationsverstärkers OP
  • Ci = Summe von Photodiodenkapazität und OP-Eingangskapazität.
For increased stability of the electronic circuit, capacitors can be used, which are connected in parallel with the resistors. The amplification bandwidth can also be set by appropriately selecting the capacitors. The capacitance values C1 and C2 of the capacitors can be selected according to the following formula, for example: C x = 1 4 πR x f c 1 + 1 + 8th πR x f c C i
Figure imgb0001
  • with R x =R1 or R2 and C x = C1 or C2
  • fc = gain-bandwidth product of operational amplifier OP
  • Ci = sum of photodiode capacitance and OP input capacitance.

Um einen geringen Lumineszenz-Messwert bereits sehr kurz nach der Beleuchtung mit dem intensivem Anregungslichtpuls zu detektieren, wird als Detektor 6 vorzugsweise ein Halbleiterdetektor mit hochdotiertem Substrat verwendet, beispielsweise eine Silizium-Photodiode mit hochdotiertem Si-Substrat. Insbesondere wird ein Halbleiterdetektor verwendet, dessen Substrat eine Ladungsträgerlebensdauer aufweist, die deutlich geringer ist als der zeitliche Abstand zwischen dem Anregungslichtpuls und dem Detektieren des Lumineszenz-Messwerts ML. Bevorzugt beträgt die Ladungsträgerlebensdauer im Substrat des Halbleiterdetektors höchstens 20 µs, besonders bevorzugt höchstens 10 µs. Damit wird erreicht, dass der Lumineszenz-Messwert ML in sehr geringem zeitlichen Abstand nach Ende des Anregungslichtpulses detektiert werden kann, z.B. bereits 50µs- 200µs nach Ende des Anregungslichtpulses. Dies ermöglicht auch bei großer Transportgeschwindigkeit der Banknoten, dass der Detektionsbereich der Remissionsmessung (erster Detektionsbereich D1) und der Detektionsbereich der Lumineszenz-Messung (zweiter Detektionsbereich D2) flächenmäßig stark überlappen, z.B. zu mindestens 80%, vgl. Fig. 5.In order to detect a low measured luminescence value very shortly after illumination with the intense excitation light pulse, a semiconductor detector with a highly doped substrate is preferably used as detector 6, for example a silicon photodiode with a highly doped Si substrate. In particular, a semiconductor detector is used whose substrate has a charge carrier lifetime that is significantly shorter than the time interval between the excitation light pulse and the detection of the luminescence measured value ML. The charge carrier lifetime in the substrate of the semiconductor detector is preferably at most 20 μs, particularly preferably at most 10 μs. This means that the measured luminescence value ML can be detected at a very short time interval after the end of the excitation light pulse, for example as early as 50 μs-200 μs after the end of the excitation light pulse. This enables the detection range of the reflectance measurement to be extended even if the banknotes are transported at high speeds (first detection area D1) and the detection area of the luminescence measurement (second detection area D2) overlap greatly in terms of area, for example by at least 80%, cf. figure 5 .

In Fig. 4a ist ein Beispiel für den spektralen Verlauf des zur Anregung der Banknote verwendeten Anregungslichts A und des von der Banknote emittierten Lumineszenzlichts L gezeigt. Außerdem ist in Fig. 4a beispielhaft ein Transmissionsspektrum T eines spektralen Detektionsfilters 5 gezeigt, der sich im Detektionsstrahlengang 8 des Sensors 10 befindet. Das Transmissionsspektrum T in Fig. 4a weist eine spektrale Lumineszenz-Transmissionsbande BL im Spektralbereich des Lumineszenzlichts L auf und eine zusätzliche spektrale Transmissionsbande BA im Spektralbereich des Anregungslichts A, die die spektrale Anregungsbande des Anregungslichts A spektral vollständig einschließt. Die Transmissionsbande BL kann das Lumineszenzlicht ebenfalls vollständig einschließen, aber alternativ auch nur einen spektralen Anteil des Lumineszenzlichts L durchlassen.In Figure 4a an example of the spectral profile of the excitation light A used to excite the banknote and of the luminescent light L emitted by the banknote is shown. In addition, Figure 4a a transmission spectrum T of a spectral detection filter 5, which is located in the detection beam path 8 of the sensor 10, is shown as an example. The transmission spectrum T in Figure 4a has a spectral luminescence transmission band BL in the spectral range of the luminescence light L and an additional spectral transmission band BA in the spectral range of the excitation light A, which spectrally completely encloses the spectral excitation band of the excitation light A. The transmission band BL can likewise completely enclose the luminescence light, but alternatively only allow a spectral component of the luminescence light L to pass through.

Der spektrale Detektionsfilter 5 lässt in der zusätzlichen spektralen Transmissionsbande BA beispielsweise 20% des Anregungslichts durch und in der spektralen Lumineszenz-Transmissionsbande BL 95%. Der spektrale Abstand ΔλF der beiden Transmissionsbanden BA und BL, gemessen an den Halbwertspunkten der jeweiligen Transmissionsbande BA bzw. BL, liegt bevorzugt bei mindestens 10 nm, vgl. Fig. 4a. Beispielsweise wird als spektraler Detektionsfilter 5 ein Interferenzfilter verwendet, bei dem die Transmissionsbanden BL und BA entsprechend der spektralen Lage des Lumineszenzlichts L und des Anregungslichts A gewählt werden.The spectral detection filter 5 lets through, for example, 20% of the excitation light in the additional spectral transmission band BA and 95% in the spectral luminescence transmission band BL. The spectral distance Δλ F between the two transmission bands BA and BL, measured at the half-value points of the respective transmission band BA or BL, is preferably at least 10 nm, cf. Figure 4a . For example, an interference filter is used as the spectral detection filter 5, in which the transmission bands BL and BA are selected according to the spectral position of the luminescence light L and the excitation light A.

Das Transmissionsspektrum T des spektralen Detektionsfilters 5 kann verschiedene Formen haben. Beispielsweise kann die zusätzliche spektrale Transmissionsbande BA symmetrisch oder asymmetrisch um die Spektralkurve des Anregungslichts A positioniert sein. In Fig. 4b-e sind vier Beispiele für die zusätzliche spektrale Transmissionsbande BA gezeigt, die nur teilweise mit der spektralen Anregungsbande des Anregungslichts A überlappen. Die zusätzliche spektrale Transmissionsbande BA kann z.B. in der oberen spektralen Flanke des Anregungslichts A liegen (vgl. Fig. 4b) oder in der unteren spektralen Flanke des Anregungslichts A (vgl. Fig. 4c).The transmission spectrum T of the spectral detection filter 5 can have different forms. For example, the additional spectral Transmission band BA can be positioned symmetrically or asymmetrically around the spectral curve of the excitation light A. In Fig. 4b-e four examples of the additional spectral transmission band BA are shown, which only partially overlap with the spectral excitation band of the excitation light A. The additional spectral transmission band BA can, for example, lie in the upper spectral edge of the excitation light A (cf. Figure 4b ) or in the lower spectral edge of the excitation light A (cf. Figure 4c ).

Die spektrale Form der zusätzliche spektrale Transmissionsbanden aus Fig. 4d und 4e ist so gewählt, dass der spektrale Detektionsfilter 5 in beiden spektralen Flanken des Anregungslichts A jeweils eine zusätzliche spektrale Transmissionsbande hat, und zwar eine erste zusätzliche Transmissionsbande BAu, die spektral in der unteren spektralen Flanke des Anregungslichts A liegt, und eine zweite zusätzliche Transmissionsbande BAo, die spektral in der oberen spektralen Flanke des Anregungslichts A liegt. Damit wird erreicht, dass die durch den spektralen Filter 5 transmittierte Intensität des Anregungslichts A selbst bei einer etwaigen spektrale Drift des Anregungslichts A (die z.B. aufgrund einer Temperaturänderung auftreten kann) nicht verändert wird. Denn beispielsweise würde eine spektrale Verschiebung der spektralen Anregungsbande zu größeren Wellenlängen zu einer erhöhten Intensität in der Transmissionsbande BAo der langwelligen Flanke führen und in der Transmissionsbande BAu der kurzwelligen Flanke zu einer reduzierten Intensität. Das heißt, beide Änderungen sind gegenläufig zueinander und gleichen sich zumindest teilweise aus. Im Gegensatz dazu wäre eine einzige zusätzliche Transmissionsbande in nur einer der beiden Flanken ungünstiger, da keine derartige Kompensation erfolgen würde. Optional kann auch einen dritte zusätzliche Transmissionsbande BAm in der spektralen Mitte des Anregungslichts vorhanden sein.The spectral shape of the additional spectral transmission bands Figures 4d and 4e is chosen so that the spectral detection filter 5 has an additional spectral transmission band in each of the two spectral flanks of the excitation light A, specifically a first additional transmission band BA u that lies spectrally in the lower spectral flank of the excitation light A, and a second additional transmission band BA o , which lies spectrally in the upper spectral edge of the excitation light A. What is thereby achieved is that the intensity of the excitation light A transmitted through the spectral filter 5 is not changed even if there is any spectral drift in the excitation light A (which can occur, for example, due to a temperature change). For example, a spectral shift of the spectral excitation band to longer wavelengths would lead to an increased intensity in the transmission band BA o of the long-wave edge and to a reduced intensity in the transmission band BA u of the short-wave edge. This means that both changes run counter to each other and at least partially balance each other out. In contrast to this, a single additional transmission band in only one of the two flanks would be less favorable since no such compensation would take place. Optionally, a third additional transmission band BA m can also be present in the spectral center of the excitation light.

Claims (15)

  1. A sensor for checking documents, in particular value documents, e.g. for checking the authenticity of the documents, comprising:
    - an illumination device (1a, 1b) for illuminating a document (3) with one or several excitation light pulses of an excitation light (A) which is suitable to excite the document to emit luminescent light (L), and
    - a detector (6) for detecting at least one remission measurement value (MR) of the document and at least one luminescence measurement value (ML) of the document, and
    - a detection filter (5) which is located in a detection ray path (8) formed between the document (3) and the detector (6), and
    - a control device (7) for controlling the illumination device (1a, 1b) and the detector (6), wherein the control device (7) is arranged to drive the detector (6) such that the detector (6) detects at least one remission measurement value (MR) of the document at at least one point in time at which the document is illuminated with an excitation light pulse of the excitation light (A), and detects at least one luminescence measurement value (ML) of the document at at least one point in time after the end of the respective excitation light pulse,
    - an evaluation device (9) for checking the document on the basis of the at least one remission measurement value (MR) detected by the detector and on the basis of the at least one luminescence measurement value (ML) detected by the detector, characterized in that the detection filter (5) is a spectral detection filter whose spectral transmission is selected such that both the luminescent light of the document impinging on the spectral detection filter and at least 0.5% of the excitation light (A) impinging on the spectral detection filter (5) are transmitted through the spectral detection filter (5).
  2. The sensor according to claim 1, characterized in that the spectral transmission of the spectral detection filter (5) is selected such that at least 80% of the luminescent light of the document impinging on the spectral detection filter is transmitted through the spectral detection filter (5).
  3. The sensor according to any of the preceding claims, characterized in that a maximum transmission which the spectral detection filter (5) has in the spectral region of the luminescent light (L) is greater by at least a factor of 4 than a maximum transmission which the spectral detection filter (5) has in the spectral region of the excitation light (A).
  4. The sensor according to any of the preceding claims, characterized in that the spectral detection filter (5) has a transmission spectrum which has a spectral luminescence transmission band (BL) in the spectral region of the luminescent light (L) of the document and at least one additional spectral transmission band (BA) in the spectral region of the excitation light (A).
  5. The sensor according to claim 4, characterized in that the at least one additional transmission band (BA) spectrally overlaps, in particular partially spectrally overlaps, with the excitation light (A) or spectrally completely encloses the excitation light (A).
  6. The sensor according to claim 4 or 5, characterized in that the spectral detection filter (5) has a greater transmission in its luminescence transmission band (BL) than in its at least one additional transmission band (BA).
  7. The sensor according to any of claims 4 to 6, characterized in that the additional transmission band (BA) has a spectral distance from the luminescence transmission band (BL) of at least 10 nm, preferably of at least 20 nm.
  8. The sensor according to any of claims 4 to 7, characterized in that the excitation light (A) has a spectral excitation band with an upper spectral flank and a lower spectral flank, and the spectral detection filter (5) has a first additional spectral transmission band (BAu), which lies spectrally in the lower spectral flank of the excitation band (A), and has a second additional spectral transmission band (BAo) which lies spectrally in the upper spectral flank of the excitation band (A).
  9. The sensor according to any of the preceding claims, characterized in that the control device (7) is arranged to drive the detector (6) or an electronic circuit connected therewith such that the respective remission measurement value (MR) is measured with lower sensitivity than the respective luminescence measurement value (ML).
  10. The sensor according to claim 9, characterized in that the control device (7) is arranged to switch over a sensitivity setting of the detector (6) or of an amplifier connected with the detector (6) or of a current-voltage converter connected with the detector in the time period between the detection of the respective remission measurement value (MR) and the respective luminescence measurement value (ML) such that the remission measurement value (MR) is measured with lower sensitivity than the luminescence measurement value (ML).
  11. The sensor according to any of the preceding claims, characterized in that the detector (6) is a semiconductor-based detector with a charge carrier lifetime of at most 20 µs.
  12. A method for checking documents, in particular for checking the authenticity of the documents, comprising the steps of:
    - illuminating a document (3) with one or several excitation light pulses of an excitation light (A) which is suitable to excite the document to emit luminescent light (L),
    - detecting at least one remission measurement value (MR) of the document at at least one point in time at which the document is illuminated with an excitation light pulse of the excitation light (A), by means of a detector (6),
    - detecting at least one luminescence measurement value (ML) of the document at at least one point in time after the end of the respective excitation light pulse by means of the detector (6),
    - checking the document (3) on the basis of the at least one remission measurement value (MR) detected by the detector (6) and on the basis of the at least one luminescence measurement value (ML) detected by the detector,
    wherein in a detection ray path (8) formed between the document (3) and the detector (6) there is located a spectral detection filter (5) whose spectral transmission (T) is selected such that both the luminescent light (L) of the document impinging on the spectral detection filter (5) and at least 0.5% of the excitation light (A) impinging on the spectral detection filter (5), which has been remitted by the document, is transmitted through the spectral detection filter (5).
  13. The method according to claim 12, characterized in that the document (3) and detector (6) are transported relative to each other during detection and that the remission measurement value and the luminescence measurement value are detected with such a small time interval between each other that the detection regions (D1, D2) on the document, from which the respective remission measurement value and the respective luminescence measurement value are detected, overlap by at least 50%, preferably by at least 80%.
  14. An apparatus for checking a document with a sensor according to any of claims 1 to 11.
  15. The apparatus according to claim 14 having a transport device which is arranged to transport the document (3) and the detector (6) relative to each other during the detection of the remission and luminescence measurement value, characterized in that the control device (7) of the sensor (10) is arranged to drive the detector (6) such that the respective remission measurement value (MR) and the respective luminescence measurement value (ML) are detected with such a short time interval between each other that the detection regions (D1, D2) on the document, from which the respective remission measurement value and the respective luminescence measurement value are detected, overlap by at least 50%, preferably by at least 80%.
EP19733663.9A 2018-06-20 2019-06-17 Method and sensor for testing documents Active EP3811343B1 (en)

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DE102018004884.6A DE102018004884A1 (en) 2018-06-20 2018-06-20 Method and sensor for checking documents
PCT/EP2019/000189 WO2019242879A1 (en) 2018-06-20 2019-06-17 Method and sensor for testing documents

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DE102016000012A1 (en) * 2016-01-05 2017-07-06 Giesecke & Devrient Gmbh Authenticity check of value documents
DE102021006158A1 (en) 2021-12-14 2023-06-15 Giesecke+Devrient Currency Technology Gmbh Sensor and method for checking value documents, sensor system and value document processing device

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DE102008044883A1 (en) 2008-08-29 2010-03-04 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Luminescent radiation measuring method for sawn coarse silicon wafer used to manufacture silicon solar cell, involves determining corrected intensity value so that measured reflection intensities are scaled with location-independent factor
DE102009058805A1 (en) * 2009-12-18 2011-06-22 Giesecke & Devrient GmbH, 81677 Spectral sensor for checking value documents
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US10650630B2 (en) * 2014-10-31 2020-05-12 Honeywell International Inc. Authentication systems, authentication devices, and methods for authenticating a value article
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DE102018004884A1 (en) 2019-12-24
EP3811343A1 (en) 2021-04-28
US11756362B2 (en) 2023-09-12

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