EP3400583B1 - Checking the authenticity of value documents - Google Patents

Description

The present invention relates to a method as well as a testing sensor and a testing device for checking a document of value for authenticity.

When checking the authenticity of valuable documents, such as banknotes, identification documents, securities or the like, it is particularly important to also check their integrity or completeness in order to rule out so-called "snippet forgeries" or compound forgeries. In these cases, the document of value is composed of several, possibly forged, partial documents or certain sections of the document of value have been replaced by forged sections. Such authenticity tests, which are often based on the evaluation of emission radiation from a luminescence feature that is present in or on the document of value, are implemented by combined test methods or test sensors which, in addition to the actual luminescence measurement, also carry out a remission or reflection measurement.

Such a test sensor, in which a spectrally resolving luminescence sensor includes a spectral detector with a diffraction grating, is described, for example, in DE 10 2004 035 494 A1 . A separate detector is used to measure reflectance, which means that the test sensor requires a lot of space and its production requires a lot of design effort.

Next is over DE 10 2008 028 689 A1 and the DE 10 2008 028 690 A1 a spectrally resolving luminescence sensor is known for calibration purposes In addition, a reference radiation source and a light scanner are used to determine the position of a document of value to be checked. The reference radiation is designed in such a way that it lies within the spectral range of the luminescence sensor, so that no separate detector is required as a light sensor. In order to be able to determine the spectral properties of a document of value to be checked without interference, the reference radiation is switched off as soon as an edge of the document of value is detected. However, this has the disadvantage that either no reflectance measurement can be carried out within the document of value or, given the usual transport speeds of the documents of value to be checked, only a low spatial resolution of the luminescence measurement is achieved.

Furthermore, from the US 2010/0128964 A1 a system for mapping valuable documents is known. The document of value is illuminated sequentially with light sources that emit light of different wavelengths. An image is taken of each light source. The captured images are superimposed, creating an overall picture. The partial images or the entire image are checked with an entry in a comparison table.

From the US 2015/0310689 A1 a method for checking a banknote for adhesive strips is known. The banknote is illuminated by several light sources, each of which emits light of different wavelengths. One image line is recorded per wavelength, with the images of each wavelength being combined per image line.

Furthermore shows document JP 4058246 B2 a method for detecting an adhesive strip on a banknote. A banknote is exposed to light of a first wavelength, which is absorbed by the adhesive strip illuminated with light of a second wavelength, which is not absorbed by the adhesive strip.

EP 3 142 080 A1 shows an image reading device comprising a sensor, a light source and an image capture controller.

In this respect, it is the object of the present invention to propose a method for checking documents of value which, on the one hand, enables the use of a test sensor with little space and design effort and, on the other hand, offers a sufficiently high spatial resolution.

This task is solved by a method and a test sensor and a test device with the features of the independent claims. Advantageous refinements and developments of the invention are specified in the claims dependent thereon.

To check a document of value, in particular for its integrity or completeness, the document of value is guided past the test sensor according to the invention in a transport direction. The document of value to be checked has a security area which extends over the entire extent of the document of value to be checked in the transport direction, and in or on which a substantially homogeneously distributed luminescence feature is present. The luminescent feature is introduced into the volume of the document of value in the security area as homogeneously or evenly distributed as possible, or it is applied in the security area as a coating or varnish on the document of value, for example in the form of a luminescent paint or varnish. The security area preferably extends over the entire document of value, so that the luminescent feature is essentially evenly distributed in or on the entire document of value. The luminescence feature present in or on the security area can be excited to luminescence, i.e. to phosphorescence and/or fluorescence, by means of an excitation radiation.

According to the invention, the document of value is checked by a scanning sequence that is repeated several times as the document of value is transported past the test sensor, in the context of which the document of value is irradiated and scanned. The scanning sequence repeated several times is then preferably followed by the actual test for integrity and/or authenticity, in which the previously scanned spectral values are appropriately evaluated.

The scanning sequence, which is repeated several times, includes a first irradiation phase and a subsequent second irradiation phase. In the first irradiation phase, the security area of the valuable document is irradiated with test radiation and excitation radiation in a detection or test area of the test sensor. The test radiation is designed in such a way that the portion of the test radiation remitted by the safety area lies at least partially in a detection spectral range of the test sensor. Accordingly, the excitation radiation is designed to cause emission radiation of the luminescent feature, which also emits at least partially in the detection spectral range of the test sensor.

During the first irradiation phase, in which the safety area is irradiated simultaneously with the test radiation and the excitation radiation, preferably towards the end of the first irradiation phase, a Location-dependent remission spectral value is sampled in a spectrally resolved manner, which includes, on the one hand, portions of the remitted test radiation and, on the other hand, portions of the emission radiation of the luminescence feature emitted due to the excitation radiation. After the first irradiation phase, the safety area is irradiated only with the excitation radiation in a second irradiation phase in the test area of the test sensor and, preferably at the end of the second irradiation phase, at least one location-dependent emission spectral value is sampled with spectral resolution.

The document of value is checked for authenticity. A classification as genuine or fake is carried out on the basis of at least one spatially-resolved remission spectral value that has been sampled several times in a spatially resolved manner, in particular at different locations, and at least one location-dependent emission spectral value that has been sampled several times in a spatially resolved manner, in particular at different locations.

It should be noted here that an intensity of the remission spectral value includes, on the one hand, intensity components of the remitted test radiation and, on the other hand, also intensity components of an emission radiation of the luminescent feature excited by the excitation radiation, since the safety area is irradiated with both the test radiation and the excitation radiation during the first irradiation phase.

In one embodiment, in order to check in particular the authenticity of the document of value, a spatially resolved reflectance curve is formed from the location-dependent reflectance spectral values recorded in the course of the several scanning sequences, which reflects the reflectance spectral values scanned along the security area in the transport direction. Accordingly, a spatially resolved emission curve is formed from the location-dependent emission spectral values recorded in the course of the several scanning sequences, which reproduces the emission spectral values scanned along the safety area in the transport direction. Each remission/emission spectral value of the remission/emission curve thus reflects the remitted/emitted radiation intensity at a specific position of the security area of the document of value, which is caused by the first or second irradiation phase.

The remission curve reflects the extent of the valuable document in the transport direction, while the emission curve reflects that area of the valuable document in the transport direction in which the luminescence feature could be detected.

In one embodiment, the document of value is finally classified as complete and/or genuine after it has been passed completely past the test sensor if the remission curve and the emission curve have a qualitatively comparable curve, because this means that the luminescence feature is present along the entire extent of the document of value is present in the transport direction. If the two curves have curves that are not qualitatively comparable, a counterfeit can be assumed since the luminescent feature is not present in a counterfeit area of the value document that results from the emission curve.

To carry out the method according to the invention, a corresponding test sensor according to the invention is used. This includes a test radiation source which generates test radiation which is at least partially remitted by the document of value in the detection spectral range of the test sensor, and an excitation radiation source which generates an excitation radiation which excites the luminescence feature to produce emission radiation which is also at least partially in the detection spectral range of the test sensor emitted. Furthermore, the test sensor comprises a scanning unit which scans test radiation remitted by the document of value and emission radiation emitted by the luminescence feature as location-dependent remission spectral values and location-dependent emission spectral values in the detection spectral range. The detection of the emission spectral values and the remission spectral values is carried out in a spectrally resolved manner with preferably more than two spectral channels, in particular more than eight spectral channels and particularly preferably with more than sixteen spectral channels. A control unit of the test sensor coordinates the radiation sources and the scanning unit in such a way that the scanning sequence is continuously repeated while the document of value is guided past the test sensor. An evaluation unit of the test sensor finally forms the remission curve and the emission curve in the manner described above and compares their curve profiles qualitatively.

On the one hand, the invention offers the advantage that no additional scanning or detection channel is required for detecting the remission spectral values, since both the emission spectral values and the remission spectral values are at least partially in the same detection spectral range of the test sensor. This enables a comparatively compact test sensor with reduced design manufacturing effort.

Furthermore, the invention enables maximum spatial resolution and intensity of the emission curve, since the luminescent feature is already excited to emit during the irradiation of the document of value with the test radiation in the first irradiation phase, and not only after the test radiation has been switched off with the onset of the second irradiation phase. The spatial/temporal distance between successive emission spectral values is thereby reduced by the length of the first irradiation phase compared to conventional solutions. Since, according to the invention, the first irradiation phase is also used to excite the luminescence feature, the intensities or amplitudes of the emission spectral values are also clearer, since the luminescence feature can be optically inflated over the maximum time available.

During the evaluation, the emission and remission curves are checked for qualitative comparability. This means in particular that no quantitative comparison or a signal-theoretical correlation of the curves is made, but that the two curves are only compared with regard to their local/temporal widths, which in the case of a genuine document of value essentially correspond to its extent along the direction of transport or the duration of the Transport past the test sensor. For example, the two curves can, if necessary after suitable noise correction or local/temporal low-pass filtering, be subjected to edge detection, for example using edge or high-pass filters. Beforehand, the two curves can be processed using suitable intensity threshold values in order to obtain significant or above-threshold reflectance/emission spectral values of noise-dependent ones or interference-related spectral values that cannot be attributed to a remission of the test radiation or an emission of the luminescence feature.

The evaluation unit preferably determines the number of significant or above-threshold reflectance/emission spectral values or the corresponding pixels under the preferably smoothed reflectance/emission curve. The emission curve and the remission curve are considered to be qualitatively comparable if the emission curve essentially has significant intensities at those location/time positions or pixels at which the remission curve also forms significant intensities.

Here, the quotient can be formed from the pixels with significant intensities in the remission curve and in the emission curve, so that it can be assumed that the two curves are qualitatively comparable if this quotient is approximately one. In order to compensate for noise or detection-related measurement errors, a suitable interval can be selected for the quotient depending on the spatial resolution of the two curves, for example an interval between 0.9 and 1.1 or, preferably, an interval between 0.95 and 1.05 .

Alternatively, the evaluation unit determines the number of pixels in which the remission curve has significant intensities but the emission curve has subthreshold values. Here the document of value is classified as inauthentic if this number of pixels suspected of being counterfeit exceeds a certain threshold value of, for example, 0, 1, 2, etc.

The duration of the first irradiation phase is preferably set between 0.5 µs and 500 µs, particularly preferably between 1 µs and 50 µs. The ratio between the duration of the first irradiation phase and the duration of the entire scanning sequence is preferably between 1:1000 and 1:4, particularly preferably between 1:100 and 1:5. This means that the proportion of the first irradiation phase, in which the document of value is irradiated with both the test radiation and the excitation radiation, in the total duration of the scanning sequence, i.e. the total duration of the irradiation with the excitation radiation, is between approximately 0.1% and 25 % and is preferably between about 1% and 20%. The transport speed at which a document of value to be checked is guided past the test sensor is between 1 m/s and 13 m/s, preferably in the range of 4-12 m/s.

According to the invention, the scanning sequence is designed such that the excitation irradiation can take place without interruption, in that the first irradiation phase of a scanning sequence immediately follows the second irradiation phase of the previous scanning sequence. The irradiation with the test radiation then takes place in pulses during the first irradiation phase, each interrupted by the second irradiation phase.

The at least one remission spectral value is sampled towards the end of the first irradiation phase, preferably with the end of the first irradiation phase, while the at least one emission spectral value is sampled towards the end of the second irradiation phase, preferably with the end of the second irradiation phase. Through this design of the scanning sequence, on the one hand, maximum spatial resolution of the emission curve can be ensured and, on the other hand, maximum intensity of the emission spectral values can be achieved.

In an alternative embodiment of the scanning sequence according to the invention, the second irradiation phase is immediately followed by a rest phase in which there is neither irradiation by the test radiation nor by the excitation radiation. In this embodiment, the irradiation by the excitation radiation also takes place in pulses, each during the first and second irradiation phases and interrupted by the rest phase. The first irradiation phase of a scanning sequence then immediately follows the rest phase of the previous scanning sequence. In this case, emission spectral values are also recorded during the rest phase, preferably towards the end of the rest phase, so that a maximum intensity of the emission spectral values can be ensured if the luminescence marker is still emitting after the excitation radiation has been switched off.

The pulsed irradiation with the excitation radiation allows the multiple sampling of emission spectral values within a scanning sequence during and/or after the excitation radiation pulse, so that the temporal onset/decay behavior of the luminescence feature can also be determined depending on the location by comparing the emission spectral values sampled within a scanning sequence. This location-dependent onset/decay behavior can then be taken into account during the authenticity test, since the temporal progression of the emission spectral values within a scanning sequence provides information about the emission properties and the exact type of luminescence feature being tested. The emission spectral values sampled several times can be compared, for example, with corresponding location-dependent reference spectral values that were determined in advance for the document of value in question.

Preferably, the document of value is irradiated with a spectrally narrow-band test radiation so that it is only detected in one or a few spectral channels of the detector. The test radiation is preferably not suitable for significantly stimulating luminescence in the valuable document.

Furthermore, the document of value is irradiated with a preferably narrow-band excitation radiation, the excitation radiation taking place in the ultraviolet (UV), in the visible (VIS) and/or in the infrared spectral range (IR). This can also include several different wavelength ranges. This ensures that the test radiation causes no or only a small amount of emission radiation of the luminescence feature in the detection spectral range, so that the sampled emission spectral values can be traced back as far as possible exclusively to the excitation radiation and as little as possible to the test irradiation.

Preferably, the test radiation source comprises an LED or semiconductor laser radiation source, for example an edge emitter laser diode. The test radiation source particularly preferably comprises a narrow-band VCSEL or surface emitter radiation source. Accordingly, the excitation radiation source preferably comprises an LED or semiconductor laser radiation source, particularly preferably a narrow-band VCSEL or surface emitter radiation source.

In order to allow the best possible evaluation of the reflectance and emission values, the reflectance spectral values and/or emission spectral values are preferably corrected with regard to noise and interference influences. Scattered radiation components or electronic or electromagnetic interference radiation components can be eliminated from the remission spectral values and/or emission spectral values by an offset correction are, whereby the corresponding correction parameters are determined either in advance by scanning a reference substrate with the test sensor or, preferably, by scanning during the authenticity test at times when no document of value is passed by the test sensor (dark measurement), for example before the start of the authenticity test or between two consecutive documents of value to be checked.

The reflectance spectral values are preferably further corrected in such a way that only those sampled spectral components which are actually attributable to the test irradiation and their remission by the document of value are included in them. Accordingly, those sampled spectral components and/or intensity components or intensities that are attributable to emission radiation of the luminescence feature as a result of the excitation irradiation are filtered out or eliminated from the sampled remission spectral values. For efficient differentiation between the respective spectral components of the remitted remission radiation and the emission radiation emitted by the luminescence feature, a narrow-band test radiation is particularly suitable, so that the remission/emission spectral values sampled with spectral resolution can be effectively filtered.

Instead of spectral components, intensity components or intensities of the remitted radiation can also be determined.

Alternatively, the contribution expected at the earlier time of sampling of the remission spectral value can be interpolated from the emission spectral values measured at the later time and their time course and can thus be deducted to a good approximation.

At higher transport speeds, a non-negligible local or temporal offset can develop between the remission curve and the emission curve, since the document of value to be checked is moved further between the scanning of the remission spectral values and the scanning of the emission spectral values. This offset can be compensated for as part of the authenticity test by shifting the emission curve relative to the remission curve by exactly the time interval that lies between the sampling of the remission spectral values and the sampling of the emission spectral values.

The test sensor according to the invention, together with the transport device, which guides the document of value past the test sensor during the authenticity check in such a way that the test area of the test sensor moves continuously over the security area of the document of value, forms a test device according to the invention. Here, the transport speed of the document of value and the duration of a scanning sequence are preferably coordinated with one another in such a way that the resulting spatial resolution of the reflectance curve and/or emission curve is sufficiently high to enable a reliable authenticity check. A sufficient spatial resolution exists, for example, if the boundaries of the document of value or the security area can be precisely detected or if the spatial resolution is sufficient to depict an important detail of the appearance or an imprint of the document of value.

Figur 1

die Schritte des Verfahrensablaufs des erfindungsgemäßen Prüfverfahrens;

Figur 2

eine Illustration eines echten Wertdokuments (Fig. 2a) sowie eines gefälschten Wertdokuments (Fig. 2b);

Figur 3

zwei Ausgestaltungen einer Abtastsequenz mit kontinuierlicher Anregungsstrahlung (Fig. 3a) und gepulster Anregungsstrahlung (Fig. 3b);

Figur 4

quantitative Darstellungen der Emissions- und Remissionskurve für das echte Wertdokument gemäß Figur 2a (Fig. 4a) und das gefälschte Wertdokument gemäß Figur 2b (Fig. 4b); und

Figur 5

zwei bevorzugte Ausführungsformen des erfindungsgemäßen Prüfsensors mit getrennten Bestrahlungswegen (Fig. 5a) und einem gemeinsamen Bestrahlungsweg (Fig. 5b).

Further features and advantages of the invention result from the present description of exemplary embodiments of the invention as well as further alternative embodiments in connection with the following drawings, which show:

Figure 1

the steps of the procedure of the test method according to the invention;

Figure 2

an illustration of a real document of value ( Fig. 2a ) and a forged document of value ( Fig. 2b );

Figure 3

two embodiments of a scanning sequence with continuous excitation radiation ( Fig. 3a ) and pulsed excitation radiation ( Fig. 3b );

Figure 4

quantitative representations of the emission and remission curve for the real document of value Figure 2a ( Fig. 4a ) and the forged document of value according to Figure 2b ( Fig. 4b ); and

Figure 5

two preferred embodiments of the test sensor according to the invention with separate irradiation paths ( Fig. 5a ) and a common radiation path ( Fig. 5b ).

Figure 1 shows the steps of a method for checking the authenticity of a document of value 1 with one of the in Figure 5 shown test sensors 10, comprising a scanning sequence A repeating steps S1 to S4 several times and a final evaluation step S5. The sampling sequence A is in Figure 3 illustrated while Figure 4 the evaluation illustrates. A value document 1 that can be verified using this method shows the Figure 2 .

Figure 2a illustrates a genuine document of value 1 with a security area 2, in or on which one or more luminescent features 3 are present, which are caused by a suitable excitation radiation L to produce fluorescence or be stimulated to phosphorescence. In particular, the luminescence feature 3 can be excited with longer wavelengths (Stokes luminescence) or shorter wavelengths (anti-Stokes luminescence or upconverter) and emit in a specific emission spectral range. The luminescent feature 3 is introduced as homogeneously or evenly distributed as possible over preferably the widest possible areas of the volume of the document of value 1, which can consist of paper or plastic (polymer), or, alternatively, is printed or painted over the entire surface of the security area 2.

The security area 2 is preferably equipped with the luminescence feature 3 along the complete extent of the document of value 1 in a transport direction T. Deviating from Figure 2a The security area 2 can also extend over the entire surface of the document of value 1 or can take on almost any coherent geometric shape. These preferably extend over the entire extent of the document of value 1 in the transport direction.

Figure 2b In contrast, illustrates a counterfeit value document 1, in which a so-called "snippet forgery" is present in a forgery area F, which protects the security area 2 compared to that of the Figure 2a impaired in such a way that the luminescent feature 3 can no longer be detected over the entire extent of the document of value 1 in the transport direction T.

The method according to the invention according to Figure 1 is based, on the one hand, on the consideration that a remission caused by a test radiation P on the document of value 1 is available for detection or scanning and can be evaluated much more quickly than one caused by the excitation radiation L caused luminescence emission of the luminescence feature 3. On the other hand, the method according to the invention is based on the knowledge that irradiation of the document of value 1 by the test radiation P can also be realized in parallel and without interference with the irradiation of the document of value 1 by the excitation irradiation L in order to clear the luminescence feature 3 more effectively optically pumping up and stimulating luminescence emission than with sequential irradiation with the test radiation P and the excitation radiation L. The optical pumping of the luminescence feature 3 already while the document of value 1 is irradiated with the test radiation P is particularly useful for phosphorescence features, since their excitation or .Onset or decay times can range from a few microseconds to a few milliseconds.

While the document of value 1 is guided past the test sensor 10 along the transport direction T and over a time axis t, steps S1 to S4 of the scanning sequence A are repeated several times. In a first step S1, the document of value 1 is first irradiated with both the test radiation P and the excitation radiation L as part of a first irradiation phase A1. A correspondingly set up scanning unit 14 of the test sensor 10 then scans in step S2 spectral components of both the remitted test radiation P and the emission radiation emitted by the luminescence feature 3, which result from the first irradiation phase A1. Instead of spectral components, spectrally superimposed intensity components can be sampled by the scanning unit 14.

This situation is also in Figure 3 shown, which illustrates two different variants of a scanning sequence A according to the invention in the dashed area. It is shown there that the document of value 1 during the first irradiation phase A1 is irradiated with both the test radiation P and the excitation radiation L, while at the end of the first irradiation phase A1 the sampling of remission spectral values R takes place according to step S2, which includes both remitted intensity components of the test radiation P and emitted intensity components of the emission radiation of the luminescence feature 3 include. The test radiation P is remitted directly from the document of value 1, so that in addition to the pure light transit time, no waiting or integration times are necessary, but the sampling of the remission spectral values R in step S2 can take place directly against or at the end of the first irradiation phase A1.

The reflectance spectral values R are preferably sampled synchronously and very quickly, so that the intensities attributable to the individual spectral channels of the scanning unit 14 can be evaluated in parallel. The rapid scanning prevents the relevant spectral channels from smearing while the document of value 1 moves in the transport direction T. The sampling step S2 can be carried out using photodiodes and suitable sample-and-hold circuits or using CCD or CMOS detectors with charge accumulation and a suitable array architecture with synchronous shifting of the charges of an entire spectral line into a darkened storage area of the test sensor 10.

At the transition between the first irradiation phase A1 and the second irradiation phase A2, i.e. immediately after the scanning step S2, the test radiation P is switched off, while the irradiation with the excitation radiation L continues and lasts throughout the entire second irradiation phase A2 (step S3). Finally, in step S4, the scanning unit 14 is read out again in order to obtain emission spectral values E determine which, due to the optical pumping of the luminescence feature 3, already have sufficiently strong emission intensities during the first irradiation phase A1. The separate sampling of the emission spectral values E without superimposed spectral components of the remitted test radiation P in step S4 allows a particularly precise and reliable test of the luminescence feature 3, since otherwise incorrect or deviating emission radiation, which is caused, for example, by fake luminescence features, may not be reliably detected, if the emission spectral values E are not sampled with sufficient intensity or are covered by the test radiation P.

As in Figure 3a shown, the scanning sequence A is repeated continuously and continuously at least until the document of value 1 has been completely guided past the test sensor 10, so that for the authenticity check in step S5, remission spectral values R and emission spectral values E along the entire extent of the document of value 1 in the transport direction T in a spatial resolution, which depends on the one hand on the total duration of the scanning sequence A and on the other hand on the transport speed of the document of value 1.

Figure 3a also illustrates that the first irradiation phase A1 is of significantly shorter duration than the second irradiation phase A2. The test radiation P is directed at the valuable document 1 with very short pulse lengths so that the emission spectral values E, which are crucial for the authenticity test, are disturbed as little as possible by remitted test radiation P and the highest possible spatial resolution is also achieved. The temporal proportion of the first illumination phase A1 in the entire scanning sequence A is therefore between 0.1% and 25%, and preferably between 1% and 20%. Here, the duration of the entire scanning sequence A is preferably formed by the sum of the durations of the first lighting phase A1 and the second lighting phase A2. The absolute duration of the first irradiation phase A1, i.e. the pulse length of the test irradiation P, is in the range from 0.5 µs to 500 µs, preferably in the range from 1 µs to 50 µs.

With such short pulse lengths of the test radiation P, depending on the specific design of the scanning unit 14 and an evaluation unit 17 of the test sensor 10, it may be necessary to scan the remission spectral values R (step S2) only after the end of the first irradiation phase A1 in order to determine the time constant of either parasitic or deliberately installed low-pass filtering of the scanning unit 14 must be taken into account, because a certain time must then be waited until the remission spectral values R caused by the short pulse length of the test radiation P have also formed electronically and can be effectively scanned.

After the test radiation P has been switched off, the document of value 1 is continuously further irradiated with the excitation radiation L in the second irradiation phase A2 (step S3) in order to further optically pump up the luminescence feature 3. Towards or with the end of this phase of optical pumping, i.e. at the end of the second irradiation phase A2, emission spectral values E can then be sampled (step S4), which are essentially exclusively due to the emission radiation of the optically pumped or maximally excited luminescence feature 3.

Immediately following the scanning of the emission spectral values E in step S4, the scanning sequence A begins again with the first irradiation phase A1, by further pulsed irradiation with the test radiation P (step S1), as in Figure 3a is shown.

Although Figure 3a If only one sampling of emission spectral values E is provided per sampling sequence (step 4), several emission spectral values E can also be sampled with a time offset in the course of the second irradiation phase A2 (step S4 '), in order to thereby also map the on/off behavior of the luminescence feature 3 and for one to make location-dependent authenticity testing usable. This shows, for example, the alternative embodiment of the scanning sequence A according to Figure 3b , in which the second irradiation phase A2 is followed by a rest phase A3 before a further scanning sequence A begins again with the first irradiation phase A1.

With the scanning sequence A according to Figure 3b Not only is the test radiation P pulsed, but also the excitation radiation L, albeit with a significantly longer pulse length. The irradiation with pulsed excitation radiation L allows a single (step S4) or multiple (steps S4', S4) sampling of emission spectral values E during and/or after the pulsed irradiation with the excitation radiation L, that is within the second irradiation phase A2 and/or the Rest phase A3, for example once within and once at the end of the second irradiation phase A2 (step S4 ') and finally towards or at the end of the rest phase (step S4), shortly before the first irradiation phase A1 of the next scanning sequence A begins. Here too, a location-dependent evaluation of the on/off behavior of the luminescent feature 3 can be carried out and thus lead to an improved authenticity check, which not only takes into account the mere presence of a luminescent feature 3 over the entire extent of the document of value along the transport direction T, but also the time behavior depending on the location the emission of the luminescence feature 3. In a preferred embodiment, a sampling of emission spectral values E takes place relatively shortly after the end of the first irradiation phase A1 or the sampling of the remission spectral values R, so that the luminescence contribution to the remission spectral values R can be estimated more precisely.

The temporal proportion of the first illumination phase A1 in the entire scanning sequence A is therefore between 0.1% and 25%, and preferably between 1% and 20%. The absolute duration of the first irradiation phase A1, i.e. the pulse length of the test irradiation P, is in the range from 0.5 µs to 500 µs, preferably in the range from 1 µs to 50 µs. The duration of the entire scanning sequence A is preferably determined by the sum of the durations of the phases A1+A2+A3 and is dominated by the duration of the second lighting phase A2, i.e. the duration of the rest phase A3 is also relatively short. The absolute duration of the rest phase A3 is preferably in the range from 0.1 µs to 500 µs, in particular in the range from 10 µs to 100 µs. This enables particularly good inflation of even relatively slow luminescence features 3 while at the same time having good spatial resolution.

Deviating from Figure 3b the sampling of the reflectance spectral values R, as already in connection with Figure 3a described, only take place after the end of the irradiation by the test radiation P, i.e. only within the irradiation phase A2, in order to compensate for any electronic running times of the scanning unit 14.

To evaluate the measured reflectance R and emission spectral values E in step S5, correction and compensation methods are first used. For this purpose, the two spectral values R, E are subjected to an offset or background correction, in which any effects caused by scattered radiation or electronic/electromagnetic radiation Spectral components are eliminated. The correction parameters used can either be predefined in the evaluation unit 17, or can only be determined in the course of the test method according to the invention, for example by dark measurements without test irradiation P and excitation irradiation L at times when no document of value 1 is present. Alternatively or additionally, it is also possible to normalize the sampled reflectance/emission spectral values R, E to predetermined or currently detected intensities or to reference spectral values measured using a calibration substrate.

In the case of the remission spectral values R, with narrow-band test irradiation P, only one spectral channel of the scanning unit 14 is preferably read out and in the case of a broader spectrum of the remitted test irradiation P, several spectral channels are read out at the same time. Only those spectral channels of the scanning unit 14 that correspond to the spectrum of the remitted test irradiation P are evaluated by eliminating spectral components from the remission spectral values R that result from the emission radiation excited during the first irradiation phase A1. The relevant parameters of this spectral filtering can in turn either be predefined in the evaluation unit 17 or can be determined in the course of the test procedure. Likewise, in the case of spectral overlap between the emission radiation and the test radiation, the intensity contribution of the emission radiation can be corrected on the corresponding spectral channels of the remission spectral values R. In this case, estimated values for the time course of the intensity of the emission radiation are determined on the basis of a linear or exponential model, which model the temporal emission behavior of the luminescence feature 3. In this way, interference components resulting from on/off are eliminated from the sampled remission spectral values R. Decay effects of the emission radiation during the first irradiation phase A1 result.

If a luminescence feature 3 is tested with a short on/off time compared to the duration of the first irradiation period A1, those spectral components that can be attributed to emission radiation from the luminescence feature 3 during the first irradiation phase A1 can be at least approximately eliminated directly, i.e without temporal modeling of the on/off behavior of the luminescent feature 3.

The reflectance spectral values R corrected in this way are then stored in a memory of the test sensor 10 for evaluation by the evaluation unit 17 together with the associated measurement positions in the value document 1. The corrected emission spectral values E are also saved together with the associated measurement positions. The location-dependent, possibly corrected, remission spectral values R or emission spectral values E are then combined into a spatially resolved remission curve RC or emission curve EC over the time axis t.

One or both curves RC, EC are then smoothed, for example by calculating a moving average, a moving median or a moving percentile from several adjacent spectral values R, E of the respective curve RC, EC. If necessary, the curves RC, EC can also be normalized to a suitable intensity value, for example to the respective intensity maximum or the respective intensity median, but in particular in the case of the emission curve EC, an additional check is carried out with regard to whether a Absolute lower intensity threshold makes sense in order to be able to reliably identify any counterfeits with feature intensity that is too low.

Depending on the local resolution of the scanning sensor 19 and the transport speed of the valuable document 1 along the transport direction T, additional movement compensation can be carried out. For this purpose, the two curves EC, RC are shifted relative to one another within the scope of the time interval between the sampling of the remission spectral values R (step S2) and the sampling of the emission spectral values E (step S4). Particularly with a high spatial resolution, a local/temporal offset between the remission spectral values R recorded somewhat earlier in time and the emission spectral values E recorded somewhat later in time can be corrected with regard to the qualitative comparison of the curves RC, EC.

The actual local dimension of the document of value 1 along the transport direction T is then determined by edge detection of the reflectance curve RC, for example by digital edge or high-pass filtering. In the simplest case, those extreme positions of the reflectance curve RC can be determined at which the reflectance spectral values R rise above the intensity median or fall below the intensity median again. However, it is less susceptible to noise to linearly interpolate between a suitable intensity quantile (e.g. 75%, corresponds to almost white) and a minimum of the reflectance curve RC or an intensity quantile of approximately 5% and to determine from this those (two) positions of the reflectance curve RC at which the reflectance curve RC intersects the intensity quantiles of 50% (or alternatively the mean of 5% and 75% quantiles). The difference between the two positions then results in the extent of the document of value 1 along the transport direction T. The intensity quantiles are determined depending on the respective appearance or the expected remitted intensity distribution of the value document 1 to be checked.

The authenticity of the checked document of value 1 or its integrity or completeness is ultimately determined to rule out snippet forgery when the width of the corrected reflectance curve RC is qualitatively comparable to the width of the corrected emission curve EC. A measure of the completeness of the value document 1 is the quotient of the number of curve points (or pixels) with significant or above-threshold emission spectral values E and the number of curve points (or pixels) with significant or above-threshold remission spectral values R, which are essentially correspond to the extent of the valuable document 1 along the transport path T. The significant emission spectral values E are then those whose intensity lies between specified lower and upper threshold values or those determined during the test.

Based on the curves of the Figure 4 This results in a ratio (quotient) of approximately 1 for the real banknote Figure 2a (see. Fig. 4a ) and a measure (quotient) of approximately 0.82 for the counterfeit document of value Figure 2b (see. Fig. 4b ).

The method according to the invention according to Figure 1 is realized by using a test sensor 10 according to the invention. The Figures 5a and 5b show two preferred embodiments of such a test sensor 10, the scanning unit 14 of which is designed with the scanning sensor 19, the test area 4, under which the document of value 1 to be checked is preferred in the transport direction T with a transport speed between 1 m / s and 13 m / s between 4m/s and 11 m/s, is passed to scan spectrally resolved.

The scanning unit 14 detects emission radiation emitted by the luminescence feature 3 in a specific detection spectral range of the scanning sensor 19 and supplies emission spectral values E that reflect spectral properties of the scanned emission radiation. To excite the luminescence feature 3, an excitation radiation source 13 irradiates the test area 4 with the excitation radiation L. The excitation radiation L is matched to the luminescence feature 3 in such a way that emission radiation is caused in the optical range, for example in the ultraviolet (UV), visible (VIS) or infrared Spectral range (IR). The excitation radiation L is preferably spectrally narrow-band, but can also be broad-band or comprise a superposition of different narrow-band and/or broad-band radiation components.

The test area 4 is also irradiated with the test radiation P by an irradiation source 12 in order to determine the presence of a document of value 1 in the test area 4 at the time of scanning based on the remitted remission spectral values R or to determine its extent in the transport direction T by evaluating the resulting remission curve RC.

The test radiation source 12 generates a test radiation P with a spectral distribution that partially or, if possible, completely overlaps the detection spectral range of the scanning unit 14 or the scanning sensor 19. The test radiation P is particularly preferably spectrally narrow-band and can only be detected in one or a few spectral channels of the scanning sensor 19. The test radiation P generated is preferably spectral in this way designed so that it does not stimulate the luminescent feature 3 to produce any significant emission radiation. Preferably, the proportion of emission radiation caused by the luminescence feature 3 in the intensity of the sampled remission spectral values R is less than 10%.

The test radiation source 12 generates the test radiation P with a suitable light source, for example a light-emitting diode or laser diode, particularly preferably with an edge emitter or a VCSEL or a VCSEL array. If necessary, additional optical units, filters or phosphor converters are introduced into the beam path of the test sensor 10 in order to ensure a desired, possibly narrow-band spectrum of the test radiation P with a corresponding spectral overlap with the spectrum of the emission radiation emanating from the luminescence feature 3 in the detection spectral range of the scanning sensor 19. Here, the optics of the test sensor 10 are designed such that the test radiation P is coupled into a beam path to the scanning unit 14 by remission or scattering on the surface of a document of value 1 as soon as the document of value 1 moves into the test area 4.

Furthermore, the test sensor 10 includes a control/evaluation unit 17, which controls the test radiation source 12 and the excitation radiation source 13 in such a way that a scanning sequence A according to Figure 3a or 3b is realized. The control/evaluation unit 17 also checks the value document 1 for authenticity or completeness based on the determined remission curve RC and emission curve EC.

The test sensor 10 according to Figure 5a directs the test radiation P directly onto the test area 4, and thus onto the valuable document 1, whereby apertures or lighting optics can also be used. By Test area 4 locally overlapping with the test radiation P, the excitation radiation L is coupled in from the excitation radiation source 13 via a dichroic radiation splitter 16 and directed with the optics 15 onto the document of value 1 being transported past. The excitation radiation source 13 includes, for example, a light-emitting diode or a semiconductor laser, in particular a VCSEL or VCSEL array. Both the test radiation P remitted by the document of value 1 and the emission radiation emitted by the luminescent feature 3 are coupled into the scanning unit 14 via the optics 15 and detected there in a spectrally resolved manner by the scanning sensor 19. For this purpose, the scanning unit 14 includes a spectrographic device 18 and the scanning sensor 19, which records the spectral components and spectral components in spectral resolution that are generated by the spectrographic unit 18.

With the test sensor 10 after Figure 5b The document of value 1 can alternatively be irradiated by means of a combined irradiation unit 11, which includes suitable irradiation sources 12, 13 for generating the test radiation P and the excitation radiation L. In this embodiment of the test sensor 10, both radiations are coupled together via the dichroic radiation splitter 16 into the beam path of the test sensor 10 in the direction of the test area 4.

The typical polarization dependence in the spectral edge region of dielectric interference filters on dichroic mirrors can be exploited, for example by deflecting linearly polarized radiation (in particular test radiation) on a dichroic mirror with high reflectivity (preferably greater than 80%), while the document of value diffuses 1 remitted radiation also spectral components of the includes perpendicular polarization components, which are therefore transmitted sufficiently well, for example in a range of greater than 40%.

Claims (19)

1. Method for checking a document of value (1) guided past a checking sensor (10) in a transport direction (T), wherein a luminescence feature (3) is present distributed substantially homogeneously in or on a security region (2) extending in the transport direction (T) over the document of value (1) and has a sampling sequence (A) repeating multiple times as the document of value (1) is guided past the checking sensor (10), the method comprising the steps of:

   - irradiating (S1) a checking region (4) of the checking sensor (10) which at least partially overlaps the security region (2) with excitation radiation (L) and checking radiation (P) in a first irradiation phase (A1), wherein the checking radiation (P) is designed to be at least partially remitted by the document of value (1) in a detection spectral range of the checking sensor (10), and the excitation radiation (L) is designed to bring about emission radiation of the luminescence feature (3) in the detection spectral range;

   - sampling (S2) at least one spatially dependent remission spectral value (R) in the checking region (4) in the first irradiation phase (A1);

   - irradiating (S3) the checking region (4) only with the excitation radiation (L) in a second irradiation phase (A2);

   - sampling (S4) at least one spatially dependent emission spectral value (E) in the checking region (4) after the first irradiation phase (A1); and

   - performing an authenticity check (S5) according to which the document of value (1) is classified as being genuine or not genuine on the basis of the at least one spatially dependent remission spectral value (R), which has been sampled multiple times in a spatially resolved manner, and of the at least one spatially dependent emission spectral value (E), which has been sampled multiple times in a spatially resolved manner, wherein the sampling (S2) of the at least one remission spectral value (R) takes place towards the end of the first irradiation phase (A1), wherein the second irradiation phase (A2) immediately follows the first irradiation phase (A1), and the sampling (S4) of the at least one emission spectral value (E) takes place towards the end of the second irradiation phase (A2), wherein the sampling sequence (A) begins again after the end of the second irradiation phase (A2) or the sampling sequence (A) comprises a rest phase (A3) which follows the second irradiation phase (A2) and in which the document of value (1) is not irradiated by the checking sensor (10), wherein the sampling sequence (A) begins again after the end of the rest phase (A3) and the sampling (S4) of the at least one spatially dependent emission spectral value (E) takes place in the rest phase (A3), preferably towards the end of the rest phase (A3).
2. Method according to Claim 1, characterized in that the dimension of the document of value (1) in the transport direction (T) is ascertained from the number of significant remission spectral values (R), wherein an emission spectral value (E) and/or a remission spectral value (R) is considered to be significant if it lies above a lower threshold value and optionally below an upper threshold value.
3. Method according to either of Claims 1 and 2, characterized in that for the authenticity check (55), the number of significant remission spectral values (R) in relation to the number of significant emission spectral values (E) is checked.
4. Method according to any of Claims 1 to 3, characterized in that the document of value (1) is classified as being genuine if a spatially resolved remission curve (RC), formed from the multiply sampled, at least one spatially dependent remission spectral value (R), and a spatially resolved emission curve (EC), formed from the multiply sampled, at least one spatially dependent emission spectral value (E), have a qualitatively comparable curve profile.
5. Method according to Claim 4, characterized in that the dimension of the document of value (1) in the transport direction (T) is ascertained from the number of significant remission spectral values (R) under the preferably smoothed remission curve (RC), and the remission curve (RC) and the emission curve (EC) are considered (S5) to be qualitatively comparable if the emission curve (EC) has emission spectral values (E) which are significant substantially at locations at which the remission curve (RC) also has significant remission spectral values (R).
6. Method according to any of Claims 1 to 5, characterized in that the time duration of the first irradiation phase (A1) lies between 0.5 µs and 500 µs, preferably between 1 µs and 50 µs, and the ratio between the time duration of the first irradiation phase (A1) and the time duration of the sampling sequence (A) lies between 1:1000 and 1:4, preferably between 1:100 and 1:5, wherein the transport speed at which the document of value (1) is guided past the checking sensor (10) is between 1 m/s and 13 m/s, preferably between 4 and 11 m/s.
7. Method according to any of Claims 1 to 6, characterized by sampling (S4', S4) multiple times at least one spatially dependent emission spectral value (E) within the sampling sequence (A), wherein a growth/decay behaviour of the luminescence feature (3) is ascertained on the basis of the plurality of sampled, at least one emission spectral value(s) (E), which behaviour is taken into account (S5) during the check.
8. Method according to any of Claims 1 to 7, characterized in that, based on at least one emission spectral value (E) sampled (S4; S4') within an individual sampling sequence (A), a spatially dependent authenticity check is carried out by comparing the sampled (S4), at least one emission spectral value (E) with reference spectral values and/or by ascertaining, on the basis of a plurality of sampled (S4, S4'), at least one emission spectral value(s) (E), a growth/decay behaviour of the luminescence feature (3), which is compared with a reference growth/decay behaviour.
9. Method according to any of Claims 1 to 8, characterized in that the document of value (1) is irradiated (S1) with narrowband checking radiation (P), which is designed to bring about no, or only little, emission radiation of the luminescence feature (3) in the detection spectral range, and is irradiated (S3) with preferably narrowband excitation radiation (L) in the ultraviolet, visible and/or infrared spectral range.
10. Method according to any of Claims 1 to 9, characterized in that the checking radiation (P) is generated by a checking-radiation source (12) which comprises an LED or semiconductor laser radiation source, preferably a narrowband VCSEL radiation source, and in that the excitation radiation (L) is generated by an excitation-radiation source (13) which comprises an LED or semiconductor laser radiation source, preferably a narrowband VCSEL radiation source.
11. Method according to any of Claims 1 to 10, characterized in that the sampled remission spectral values (R) and/or emission spectral values (E) are corrected, in particular before the remission curve (RC) and/or emission curve (EC), if provided, are formed (S5), by substantially eliminating stray radiation components or electronic stray radiation components from the remission spectral values (R) and/or the emission spectral values (E) by way of an offset correction, wherein correction parameters of the offset correction are ascertained by sampling a reference substrate by way of the checking sensor (10) or by sampling by way of the checking sensor (10) before a first sampling sequence (A) or between two documents of value (1) guided past the checking sensor (10).
12. Method according to any of Claims 1 to 11, characterized in that the sampled remission spectral values (R) are corrected, in particular before the remission curve (RC), if provided, is formed (S5), by extracting those spectral components of the remission spectral values (R) which result from remitted radiation components of the checking irradiation (P) and/or eliminating those spectral components from the remission spectral values (R) which result from the emission radiation of the luminescence feature (3).
13. Method according to Claim 4 or 5, characterized in that an offset, resulting from the document of value (1) being guided past the checking sensor (10), between the remission curve (RC) and the emission curve (EC) is compensated by shifting the emission curve (EC) in relation to the remission curve (RC) by the time duration between the sampling (S2) of the at least one remission spectral value (R) and the sampling (S4) of the at least one emission spectral value (E).
14. Method according to Claim 4 or 5, characterized in that the transport speed at which the document of value (1) is guided past the checking sensor (10) and the time duration of the sampling sequence (A) are matched to one another such that the remission curve (RC) and/or the emission curve (EC) has a spatial resolution that is sufficient for a reliable authenticity check (S5).
15. Checking sensor (10) for checking a document of value (1) for authenticity, comprising

    a checking-radiation source (12), which is configured to generate checking radiation (P) which is at least partially remitted by the document of value (1) in a detection spectral range of the checking sensor (10);

    an excitation-radiation source (13), which is configured to generate excitation radiation (L) which causes a luminescence feature (3) present in or on the document of value (1) to emit emission radiation in the detection spectral range;

    a sampling unit (14), which is configured to sample checking radiation (P) remitted by the document of value (1) and emitted emission radiation in the detection spectral range;

    wherein the checking sensor (10) is configured to repeat multiple times while the document of value (1) is guided past the checking sensor (10) a sampling sequence (A) in connection with which the document of value (1) is irradiated in a first irradiation phase (A1) by the checking-radiation source (12) and the excitation-radiation source (13) and is irradiated in a second irradiation phase (A2) only by the excitation-radiation source (13), wherein the sampling unit (14) samples at least one spatially dependent remission spectral value (R) in the first irradiation phase (A1) and samples at least one spatially dependent emission spectral value (E) after the first irradiation phase (A1),

    wherein the checking sensor (10) is furthermore configured such that the sampling (S2) of the at least one remission spectral value (R) takes place towards the end of the first irradiation phase (A1), wherein the second irradiation phase (A2) immediately follows the first irradiation phase (A1), and that the sampling (S4) of the at least one emission spectral value (E) takes place towards the end of the second irradiation phase (A2), wherein the sampling sequence (A) begins again after the second irradiation phase (A2) has ended, and

    wherein the checking sensor furthermore comprises an evaluation unit (17), which is configured to classify the document of value (1) as being genuine or not genuine on the basis of the at least one spatially dependent remission spectral value (R), which has been sampled multiple times in a spatially resolved manner, and of the at least one spatially dependent emission spectral value (E), which has been sampled multiple times in a spatially resolved manner, wherein the emission spectral values and the remission spectral values are detected in a spectrally resolved manner with more than two spectral channels.
16. Checking sensor (10) according to Claim 15, characterized in that the evaluation unit (17) classifies the document of value (1) as being genuine if a spatially resolved remission curve (RC), formed from the multiply sampled, at least one spatially dependent remission spectral value (R), and an emission curve (EC), formed from the multiply sampled, at least one spatially dependent emission spectral value (E), have a qualitatively comparable curve profile.
17. Checking sensor (10) according to Claim 15 or 16, characterized in that the checking sensor (10) is designed and configured to check a document of value (1) guided past the checking sensor (10) for authenticity and/or completeness in accordance with a method according to any of Claims 1 to 15.
18. Checking device, comprising a checking sensor (10) according to any of Claims 15 to 17, and a transport device (20), which is configured to guide a document of value (1) in the transport direction (T) past the checking sensor (10) in a manner such that the document of value (1) can be checked for authenticity and/or completeness in accordance with a method according to any of Claims 1 to 14.
19. Use of a checking sensor (10) according to Claim 15 to 17 for checking a document of value (1) for authenticity and/or completeness in accordance with a method according to any of Claims 1 to 14.

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