SENSOR AND METHOD FOR CHECKING VALUE DOCUMENTS, IN PARTICULAR BANK NOTES, AND VALUE DOCUMENT PROCESSING APPARATUS

Abstract

A sensor and a method for checking value documents are provided, each having a luminescent sheet-like substrate and a luminescent feature applied to a partial surface of the substrate, and to a value document processing apparatus. From the spectral vectors obtained for a plurality of measurement points and characterizing the intensity of the luminescent radiation of the value document detected in at least two spectral ranges, substrate intensity values and feature intensity values are determined, based on which a pure substrate mask is determined, which contains only those measurement points which reliably lie outside the feature. From the spectral vectors of the measurement points contained in the pure substrate mask, a mean substrate vector is determined, based on which corrected substrate intensity values and corrected feature intensity values and/or a spectral signature of the substrate and/or of the feature are or is, respectively, determined from the spectral vectors.

Claims

1-15. (canceled)

16. A sensor for checking value documents, in particular banknotes, each having a luminescent sheet-like substrate and a luminescent feature applied to a partial surface of the substrate, comprising: a detection device which is configured to detect luminescence radiation emitted by a value document to be checked in at least two different spectral ranges in a spatially resolved manner, wherein a plurality of measurement points is obtained, to each of which a spectral vector is assigned which contains at least two intensity values which characterize the intensity of the luminescence radiation detected at the respective measurement point in the at least two spectral ranges, and an evaluation device which is configured a) to determine, for each of a plurality of measurement points, a substrate intensity value and a feature intensity value from the spectral vectors using a predetermined substrate basis vector and a predetermined feature basis vector, the substrate basis vector and the feature basis vector each having at least two intensity values, which characterize the expected intensity of the luminescence radiation emitted by the substrate or feature, respectively, in the at least two spectral regions, b) to determine, on the basis of the substrate intensity values and feature intensity values, a pure substrate mask which contains those measurement points which correspond to locations on the value document which lie outside the feature, and c1) to determine, from the spectral vectors of the measurement points contained in the pure substrate mask, a mean substrate vector which contains at least two intensity values which are obtained in each case by combining, in particular by averaging or quantile formation, the intensity values contained in the spectral vectors for each of the at least two spectral ranges, and i) to determine, for each of a plurality of measurement points, a corrected feature intensity value and/or a corrected substrate intensity value from the spectral vectors using the mean substrate vector, and/or ii) to determine a spectral signature of the substrate and/or a spectral signature of the feature, by which a spectral composition of the luminescence radiation emitted by the substrate or the feature, respectively, is characterized, using the mean substrate vector, and/or c2) to determine a temporal behavior of the luminescence radiation emitted by the substrate and/or the feature using measurement points contained in the pure substrate mask, and d) to check, in particular with regard to authenticity, the value document on the basis of the corrected feature intensity values and/or on the basis of the corrected substrate intensity values and/or on the basis of the spectral signature of the substrate and/or of the feature and/or on the basis of the temporal behavior of the luminescence radiation emitted by the substrate and/or by the feature.

17. The sensor according to claim 16, wherein the evaluation device is configured to correct the predetermined substrate basis vector using the mean substrate vector or to replace the predetermined substrate basis vector with the mean substrate vector, wherein a corrected substrate basis vector is obtained.

18. The sensor according to claim 16, wherein the evaluation device is configured to compare the mean substrate vector with the predetermined substrate basis vector using a predetermined comparison criterion, and, if the comparison criterion is met, to correct the substrate basis vector using the mean substrate vector or to replace the substrate basis vector with the mean substrate vector, and/or if the comparison criterion is not met, to classify the value document as a value document to be rejected.

19. The sensor according to claim 16, wherein the evaluation device is configured to, to determine, on the basis of the feature intensity values, a feature mask which contains those measurement points which correspond to locations lying on the feature, subtract the mean substrate vector from each of the spectral vectors of the measurement points contained in the feature mask, wherein background-corrected spectral vectors of the measurement points contained in the feature mask are obtained, and determine, from the background-corrected spectral vectors of the measurement points contained in the feature mask, a mean feature vector which contains at least two intensity values each of which being obtained by combining, in particular by averaging, the intensity values contained in the background-corrected spectral vectors for each of the at least two spectral ranges.

20. The sensor according to claim 19, wherein the evaluation device is configured to correct the predetermined feature basis vector using the mean feature vector or to replace the predetermined feature basis vector with the mean feature vector, wherein a corrected feature basis vector is obtained.

21. The sensor according to claim 17, wherein the evaluation device is configured to determine the corrected substrate intensity values and corrected feature intensity values using the corrected substrate basis vector and the, in particular corrected, feature basis vector from the spectral vectors.

22. The sensor according to claim 16, wherein the evaluation device is configured, for checking the value document, in particular with regard to authenticity, to compare the corrected substrate intensity values of one or more measurement points or the intensity values of the mean substrate vector with one or more predetermined substrate intensity values, and/or to compare the corrected feature intensity values of one or more measurement points or the intensity values of the mean feature vector with one or more predetermined feature intensity values.

23. The sensor according to claim 16, wherein the evaluation device is configured: to determine, when determining the spectral signature of the substrate, a, in particular scalar, signature value of the substrate from the at least two intensity values of the mean substrate vector, and/or to determine, when determining the spectral signature of the feature, a, in particular scalar, signature value of the feature from the at least two intensity values of the mean feature vector, wherein the evaluation device is in particular configured, for checking the value document, in particular with regard to authenticity, on the basis of the spectral signature of the substrate and/or on the basis of the spectral signature of the feature, to compare the signature value of the substrate and/or the signature value of the feature in each case with one or more predetermined comparison value(s) of the substrate or with one or more predetermined comparison value(s) of the feature, respectively.

24. The sensor of claim 23, wherein, during checking, the check result “authentic” is assigned to the value document if the at least two intensity values of the mean substrate vector are above a threshold and the at least two intensity values of the mean feature vector are above the same or above another threshold, and the signature value of the feature and the signature value of the substrate are different from each other.

25. The sensor according to claim 16, wherein the detection device is configured to detect the luminescence radiation emitted by the value document to be checked for a plurality of measurement points at two or more points in time, wherein to each of the measurement points two or more intensity values are assigned which characterize the intensity of the luminescence radiation detected at the respective measurement point at the two or more points in time.

26. The sensor according to claim 25, wherein the evaluation device is configured to determine, on the basis of the intensity values, obtained for each one of the points in time, of the measurement points contained in the pure substrate mask, a background value, in particular by quantile formation, wherein for each of two or more points in time a background value is obtained, and to determine, on the basis of the feature intensity values, a feature mask which contains those measurement points which correspond to locations lying on the feature, and to subtract, from the intensity values, obtained for each one of the points in time, of the measurement points contained in the feature mask, the background value respectively obtained for this point in time, wherein a corrected feature value of the measurement points contained in the feature mask is obtained for each of two or more points in time, and to combine the corrected feature values, obtained for each one of the points in time, of the measurement points contained in the feature mask to form a mean corrected feature value, in particular by averaging, wherein a mean corrected feature value is obtained for each of two or more points in time, and to check the value document, in particular with regard to authenticity, using the mean corrected feature values of two or more of the points in time.

27. The sensor according to claim 25, wherein the evaluation device is configured, to determine, for determining the temporal behavior of the luminescence radiation emitted by the substrate, a mean substrate value for each of two or more of the points in time or each of the points in time, wherein the respective mean substrate value of the respective point in time is obtained by combining, in particular by averaging, the intensity values of the measurement points contained in the pure substrate mask, and to check the value document, in particular with regard to authenticity, using the mean substrate values of two or more of the points in time.

28. The sensor according to claim 27, wherein the evaluation device is configured, to determine, on the basis of the feature intensity values, a feature mask containing those measurement points which correspond to locations lying on the feature, and to combine the intensity values of the measurement points contained in the feature mask respectively obtained for one of the points in time to form a mean substrate feature value, in particular by averaging, wherein one mean substrate feature value is obtained for each of several of the points in time, and to subtract the mean substrate values obtained for the points in time from the mean substrate feature values obtained for the points in time, wherein one mean feature value is obtained for each of several points in time, and to check the value document, in particular with regard to authenticity, on the basis of the mean feature values of two or more of the points in time.

29. A value document processing apparatus for processing, in particular checking and/or counting and/or sorting and/or destroying, value documents, in particular banknotes, comprising a sensor according to claim 16 and a transport device which is configured to convey a value document towards the sensor and/or past the sensor and/or away from the sensor.

30. A method for checking value documents, in particular banknotes, each having a luminescent sheet-like substrate and a luminescent feature applied to a partial surface of the substrate, wherein luminescence radiation emitted by a value document to be checked is detected in at least two different spectral ranges in a spatially resolved manner, wherein a plurality of measurement points are obtained, to each of which a spectral vector is assigned which contains at least two intensity values which characterize the intensity of the luminescence radiation detected at the respective measurement point in the at least two spectral ranges, and wherein a) for each of a plurality of measurement points, a substrate intensity value and a feature intensity value are determined from the spectral vectors using a predetermined substrate basis vector and a predetermined feature basis vector, the substrate basis vector and the feature basis vector each having at least two intensity values, which characterize the expected intensity of the luminescence radiation emitted by the substrate or feature, respectively, in the at least two spectral regions, b) on the basis of the substrate intensity values and feature intensity values, a pure substrate mask is determined which contains those measurement points which correspond to locations on the value document lying outside the feature, and c1) from the spectral vectors of the measurement points contained in the pure substrate mask, a mean substrate vector is determined which contains at least two intensity values which are obtained in each case by combining, in particular by averaging or quantile formation, the intensity values contained in the spectral vectors for each of the at least two spectral ranges, and i) for each of a plurality of measurement points, a corrected feature intensity value and optionally a corrected substrate intensity value is determined from the spectral vectors using the mean substrate vector, and/or ii) a spectral signature of the substrate and/or of the feature, by which a spectral composition of the luminescence radiation emitted by the substrate or the feature, respectively, is characterized, is determined using the mean substrate vector, and/or c2) using measurement points contained in the pure substrate mask, a temporal behavior of the luminescence radiation emitted by the substrate and/or by the feature is determined, and d) the value document is checked, in particular with regard to authenticity, on the basis of the corrected feature intensity values and/or on the basis of the corrected substrate intensity values and/or on the basis of the spectral signature of the substrate and/or of the feature and/or on the basis of the temporal behavior of the luminescence radiation emitted by the substrate and/or by the feature.

Description

[0085] Further advantages, features and possible applications of the present invention will be apparent from the following description in connection with the figures showing:

[0086] FIG. 1 an example of a value document processing apparatus with a sensor for checking value documents;

[0087] FIG. 2 an example of intensity values of a luminescence radiation detected in two spectral channels K0 (top) and K1 (bottom) in a spatially resolved manner;

[0088] FIG. 3 an example of paper intensities (bottom) and print intensities (top) determined from the intensity values shown in FIG. 2;

[0089] FIG. 4 an example of a paper mask (top) and a print mask (bottom);

[0090] FIG. 5 an example of an extended print mask (top) and a pure paper mask (bottom);

[0091] FIG. 6 an example of paper intensities (bottom) and print intensities (top) determined using readapted basis vectors from the intensity values shown in FIG. 2;

[0092] FIG. 7 a first example of a scatter plot illustrating intensity values of luminescence radiation detected in two spectral channels K0 and K1;

[0093] FIG. 8 a second example of a scatter plot illustrating the determination of the spectral signature of the print feature; and

[0094] FIG. 9 examples of decay curves.

[0095] FIG. 1 shows a schematic representation of an example of a value document processing apparatus 1 with an input device 9, for example a so-called input tray, for receiving a stack 10 of value documents 2, in particular banknotes, which are individually removed from the stack 10 by means of a separating device not shown and conveyed along a transport path 6 by means of a transport device 4. In the present example, the transport device 4 has transport belts, which are guided over a plurality of transport rollers 4a-4c, shown only schematically, and switches 5a-c.

[0096] Furthermore, a sensor is provided for checking the value documents 2, which has at least one detection device 3 which is configured to detect electromagnetic radiation emitted by a value document 2 to be checked in at least two different spectral channels or spectral ranges in a spatially resolved manner.

[0097] In the example shown, the value documents 2 each have a sheet-shaped substrate, which is usually formed by paper, a film or a so-called hybrid paper and which is provided, for example, over its entire surface with a luminescent feature, so that it can be excited to emit luminescent radiation, for example by irradiation with an electromagnetic excitation radiation. In addition, a further luminescence feature is locally applied to, in particular printed on, a partial surface of the substrate, which is also referred to as a “print feature” or “feature” and can also be excited to emit luminescence radiation.

[0098] Furthermore, an irradiation device 8 is provided, e.g. an IR light source, which is configured to irradiate the value document 2 to be checked with electromagnetic excitation radiation so that the substrate and the feature applied or printed thereon can be excited to emit luminescence radiation.

[0099] The luminescence radiation detected by the detection device 3 in a spatially resolved manner thus provides signals for each measurement point in the at least two different spectral channels, which represent a measure of the spectral intensities of the detected luminescence radiation. For the area of the substrate without an applied or printed feature, different spectral intensity ratios are usually obtained than for the area of the applied or printed feature.

[0100] The detection device 3 may be any type of sensor system for spatially resolved detection of the luminescence radiation emitted by the value document 2 in the visible and/or non-visible (e.g. ultraviolet and/or infrared) spectral range, such as a camera or a single-track or multi-track sensor. Optionally, further sensors (not shown), such as ultrasonic, magnetic and/or capacitive sensors, may be provided in the value document processing apparatus 1 for detecting further properties of the value documents 2.

[0101] On the basis of the luminescence radiation detected in at least two spectral ranges by means of the detection device 3 and/or properties detected by means of any further sensors, the value document 2 is checked in an evaluation device 7, for example with regard to authenticity, soiling and/or condition, and output to one of several output compartments 11a-d depending on the result of the check. For this purpose, the switches 5a-c are controlled or actuated accordingly by the evaluation device 7 and/or a control device. Preferably, the evaluation device 7 is designed as a computer and/or the evaluation device 7 has a processor for data processing and a memory for storing data.

[0102] The processing or evaluation of the luminescence radiation, which is detected in the at least two spectral ranges in a spatially resolved manner, in the evaluation device 7 is explained in more detail below by means of examples.

Intensities

[0103] FIG. 2 shows an example of intensity distributions of the luminescence radiation emitted by a banknote in two different spectral channels K0 (top) and K1 (bottom). The numbers indicate the measured intensities I0, I1 or at least a measure for the intensities I0, I1 at the respective measurement point in the respective spectral channel.

[0104] In the example, stripes of zero measurements are visible at the left and right edges, respectively, which correspond to measurements outside the banknote, whereas luminescence intensities were measured in both spectral channels at all measurement points inside the banknote.

[0105] In the present example, the measured intensities I0 and I1 of the luminescence radiation detected for each of the measurement points in the spectral channels K0 and K1 result from the intensities I.sub.P and I.sub.D of the luminescence radiation emitted by the paper (substrate) and print feature, respectively, as follows: [0106] I0 = b.sub.0,P I.sub.P + b.sub.0,D I.sub.D and [0107] I1 = b.sub.1,P I.sub.P + b.sub.1,D I.sub.D,where the coefficients b.sub.0,P and b.sub.1,P form a reference basis vector (b.sub.0,P, b.sub.1,P) for the paper feature and the coefficients b.sub.0,D and b.sub.1,D form a reference basis vector (b.sub.0,D, b.sub.1,D) for the print feature. Accordingly, the intensities I0 and I1 obtained for each of the measurement points each form a vector (I0,I1), which is also referred to as a spectral vector in the context of the present disclosure.

[0108] The mentioned coefficients or the corresponding reference basis vectors can be stored in the evaluation device 7. They were determined during previous measurements, for example, and can be readapted using machine learning if necessary.

[0109] With the reference basis vectors presupposed as known or predetermined, or the corresponding coefficients, the two equations given above for I0 and I1 represent a 2×2 system of equations that can easily be resolved for the intensities I.sub.P and I.sub.D for the paper (substrate) or print feature. This applies accordingly to more than two spectral channels and/or more than two different luminescence features, preferably with the number of spectral channels matching the number of different luminescence features. This enables an unique solution of the system of equations. In the present example, as described above, the paper and print intensities for each measurement point are calculated from the measured intensities I0 and I1 using stored reference basis vectors (0.9397, 0.3420) for the paper feature and (0.4848, 0.8746) for the print feature.

[0110] FIG. 3 illustrates the obtained distributions of the paper intensity (bottom) and the print intensity (top) as 2D distributions. In particular, in the case of the print intensity distorted negative values occur, which is attributed to the fact that the spectral signatures, i.e. the spectral composition of the luminescence radiation emitted in each case, of the feature substances actually present deviate from the reference basis vectors used, so that the calculation of the intensities is subject to errors. Therefore, the intensity distributions from FIG. 3 are only used to determine a paper mask and a print mask.

[0111] Using the paper intensities shown in FIG. 3 (bottom), the paper mask is now calculated, for example, as follows: All measurement points with a paper intensity ≥10 are set to “1” in the paper mask, the remaining measurement points to “0”. In the resulting paper mask shown in FIG. 4 (top), the edge areas outside the banknote are clearly visible.

[0112] Analogously, using the print intensities shown in FIG. 3 (top), the print mask is calculated, for example, as follows: All measurement points with a print intensity ≥10 are set to “1” in the print mask, the remaining measurement points to “0”. The resulting print mask is shown in FIG. 4 (bottom). In an extended print mask, those measurement points receive the value “1”, in whose 3×3 environment at least one measurement point in the print mask has the value “1”. This closes holes in the print mask and avoids edge measurement points with a small but measurable contribution of the print feature. The resulting extended print mask is shown in FIG. 5 (top). A pure paper mask corresponds to the paper mask minus the extended print mask and is shown in FIG. 5 (bottom).

[0113] By averaging the spectral vectors (I0, I1) of the measurement points contained in the pure paper region, a mean measured paper vector (65.44, 21.26) is obtained. The normalized mean measured paper vector (0.9511, 0.3090) serves as readapted basis vector for the paper feature. By means of the readapted basis vector for the paper feature, the paper and print intensity can now be calculated again for each measurement point. FIG. 6 shows the resulting paper intensities (bottom) and print intensities (top). As can be seen, there are no more distorted, negative values –as in FIG. 3. This shows that the (renewed) calculation of the paper and print intensities using the readapted basis vectors enables a higher accuracy of the intensity determination.

Spectral Signature

[0114] FIG. 7 shows an example of the recorded luminescence intensities of a banknote in two spectral channels K0 and K1 as a scatter plot. Each point and each circle corresponds to a measurement point, the ordinate shows the intensity in channel K1 and the abscissa the intensity in channel K0. The spectral vectors represented as points correspond to the pure paper feature. They all fall on a line through the origin and differ only in their magnitude, for example due to absorbing overprintings.

[0115] Many of these spectral vectors are also very similar in magnitude and nearly coincide at approximately (80, 170). These spectral vectors correspond to the undisturbed paper feature. In addition, there are spectral vectors represented as circles, which do not lie on the mentioned origin line. They correspond to measurement points in the feature-print area, i.e. where the paper and the print feature contribute to the detected intensity of the luminescence radiation. Typically, these measurement points lie on a second straight line that intersects the first straight line at the point of the undisturbed paper feature. This illustrates that the luminescence in the feature print area is composed of the (undisturbed) luminescence of the paper feature and the luminescence of the print feature. The intensity of the print feature can vary due to the print design (ink distribution and thickness).

[0116] For the background subtraction, the mean measured paper vector is calculated as described above, which corresponds to the cluster of measurement points of the undisturbed paper feature. The mean measured paper vector is then subtracted from all spectral vectors from the feature print area, which is illustrated by the arrows in FIG. 7.

[0117] The background-corrected measured values then lie on an origin line, as shown in FIG. 8. This origin line corresponds to the spectral signature of the print feature, in this example about (230, 50).

Time Behavior

[0118] To evaluate the time behavior of the print feature, the pure paper area and the feature print area are first determined as described above. For each measurement point, at least one decay curve is available in the form of two or more time-shifted intensity measurements. Optionally, more than one decay curve may also be available for each measurement point, e.g. decay curves for several spectral channels. The decay curves of all measurement points in the pure paper area are calculated with each other (e.g. by averaging) to obtain a mean paper decay curve. For example, each spectral channel is treated separately. Likewise, the decay curves of all measurement points in the feature print area are calculated with each other (e.g. by averaging) to obtain a mean combined decay curve per spectral channel.

[0119] FIG. 9 shows an intensity-time diagram (in arbitrary units) with the mean paper decay curve of a spectral channel (“paper”, squares) and the mean combined decay curve (“paper + print”, circles) of the same spectral channel for an exemplary banknote. By subtracting the two curves, the mean decay curve of the spectral channel for the pure print feature (“print”, checks) is obtained, which can be further evaluated and/or used in the checking of the banknote.