METHOD AND DEVICE FOR TESTING A SUBSTRATE WITH A LUMINESCENT SUBSTANCE

Abstract

A method is provided for checking a substrate with a specified luminescent substance incorporated and/or applied areally. A substrate luminescent characteristic value for the substrate is ascertained, for which purpose a number N of luminescence intensity values are captured at respectively different locations on the value document, and the substrate luminescence characteristic value is ascertained in dependence on a rank order of the luminescence intensity values. It can be checked whether the substrate luminescence characteristic value meets a specified criterion.

Claims

1-16. (canceled)

17. A method for checking a substrate, including a substrate for a value document or a substrate of a value document, with a specified luminescent substance incorporated and/or applied areally, in which a substrate luminescence characteristic value for the substrate is ascertained, for which purpose a number N of luminescence intensity values are provided at respectively different locations on the value document, and the substrate luminescence characteristic value is ascertained in dependence on a rank order of the luminescence intensity values, and it is checked whether the substrate luminescence characteristic value meets a specified criterion.

18. The method according to claim 17, wherein for ascertaining the substrate luminescence characteristic value, a positive number p is specified with 0.4<p<1, and a value is ascertained below which or equal to which there lies at least a portion p of the luminescence intensity values and equal to which or above which there lies at least the remainder of the luminescence intensity values, and the substrate luminescence characteristic value is determined in dependence on the ascertained value.

19. The method according to claim 17, wherein for determining the substrate luminescence characteristic value, non-negative numbers p and q<1-p are specified with 0.4<p<1, and those of the luminescence intensity values are used which are greater than or equal to the p*N smallest ones of the luminescence intensity values and smaller than or equal to the q*N greatest ones of the luminescence intensity values, or those of the luminescence intensity values are used which are greater than the p*N smallest ones of the luminescence intensity values and smaller than or equal to the q*N greatest ones of the measurement values.

20. The method according to claim 19, wherein for ascertaining the substrate luminescence characteristic value, the luminescence intensity values are used or summed for forming an average value.

21. The method according to claim 17, wherein p> 0.5 is greater than 0.6.

22. The method according to claim 17, wherein the substrate luminescence characteristic value is at least approximately related to specified standard conditions.

23. The method according to claim 17, wherein it is checked whether the ascertained substrate luminescence characteristic value meets a specified authenticity criterion for the presence of a substrate to be regarded as authentic, and, depending on the result of the check, an authenticity signal is generated which represents an indication of the presence of an authentic substrate or a forged substrate.

24. The method according to claim 17, wherein the substrate is a substrate for producing value documents, and wherein it is checked whether the ascertained substrate luminescence characteristic value meets a specified quality criterion and depending on the result of the check a quality signal is generated which represents an indication of the presence of a substrate having a sufficient concentration of the luminescent substance.

25. A method for ascertaining substrate luminescence characteristic values for a plurality of value document substrates, wherein the method according to claim 17 is carried out for each of the value document substrates, wherein for providing the luminescence intensity values the value document substrates are respectively transported past a luminescence sensor, and the respective ascertaining of the substrate luminescence characteristic value is effected independently of the position and orientation of the value document.

26. The method according to claim 17, wherein the rank order represents an order according to the magnitude of the individual luminescence intensity values provided or wherein a rank order is given on the basis of ascendingly adjacent intervals each of which has associated therewith a rank or rank index, and the luminescence intensity values have each associated therewith the rank which corresponds to that one of the intervals in which they respectively lie.

27. An apparatus for checking a substrate, including a substrate for a value document or a substrate of a value document, with a specified luminescent substance incorporated and/or applied areally, comprising: a luminescence sensor for capturing a luminescence intensity for the specified luminescent substance and forming a corresponding luminescence intensity value for different locations on the substrate, and an evaluation device which is connected to the luminescence sensor via a data link for transmitting the luminescence intensity values and is configured to execute a method according to claim 17, wherein as luminescence intensity values there are used luminescence intensity values for the substrate which are captured with the luminescence sensor.

28. The apparatus according to claim 27, wherein the luminescence sensor and the evaluation device are configured to capture the luminescence intensity values for the substrate while the same is transported past the luminescence sensor at a specified transport speed.

29. The apparatus according to claim 28, which further has a transport apparatus for transporting the substrate along a transport path at the specified transport speed, the luminescence sensor being disposed at the transport path.

30. The apparatus according to claim 27, which further has an output device with at least two output units, whose transport device is configured to feed a substrate transported past the luminescence sensor to a first or a second one of the output units in dependence on a sorting signal of the evaluation device, and in which the evaluation device is arranged to emit a sorting signal to the transport device in dependence on the result of checking the criterion.

31. A computer program with program code upon whose execution by a processor a method according to claim 17 is executed.

32. A computer-readable storage medium on which a computer program according to claim 31 is stored.

Description

[0037] The invention will hereinafter be explained further by way of example with reference to the drawings.

[0038] FIG. 1 shows a schematic view of a value document processing apparatus in the form of a bank note sorting apparatus,

[0039] FIG. 2 shows a schematic representation of a luminescence sensor of the value document processing apparatus in FIG. 1 in a direction transverse to a transport direction,

[0040] FIG. 3 shows a schematic representation of a value document and of locations on the value document for which luminescence intensity values were captured,

[0041] FIG. 4 shows a schematic representation of luminescence intensity values for the value document in FIG. 3 as a function of the capture location in the longitudinal direction of the value document,

[0042] FIG. 5 shows a simplified flowchart of a first embodiment example of a method for checking a substrate for a value document or a value document having a specified luminescent substance,

[0043] FIG. 6 shows a simplified flowchart of a second embodiment example of a method for checking a substrate for a value document or a value document having a specified luminescent substance.

[0044] A value document processing apparatus 10 in FIG. 1, in the example an apparatus for processing value documents 12 in the form of bank notes, is configured for sorting value documents in dependence on the recognition of the authenticity of processed value documents. In this embodiment example, authentic value documents contain a luminescent substance that has characteristic luminescence properties. The components of the apparatus described in the following are disposed in a housing (not shown) of the apparatus or are held thereon, unless they are referred to as external.

[0045] The apparatus has a feeding device 14 for feeding value documents, an output device 16 for receiving processed, i.e. sorted value, documents, and a transport device 18 for transporting singled value documents from the feeding device 14 to the output device 16.

[0046] The feeding device 14 comprises, in the example, an input pocket 20 for a value document stack and a singler 22 for singling value documents from the value document stack in the input pocket 20 and for feeding the singled value documents to the transport device 18.

[0047] The output device 16 has, in the example, two output sections 24 and 26 into which processed value documents can be outputted sorted according to the result of the processing. In the example, each of the sections comprises a stack pocket and a stacking wheel (not shown) by means of which fed value documents can be deposited in the stack pocket. In other embodiment examples, one of the output sections may be replaced by a device for destroying bank notes.

[0048] The transport device 18 has at least two branches 28 and 30 at the ends of which one of the output sections 24 or 26 is respectively disposed, and, at the branching point, a gate 32 controllable by actuating signals, by means of which value documents are feedable to the branches 28 and 30 and thus to the output sections 24 and 26 in dependence on actuating signals.

[0049] On a transport path 36, defined by the transport device 18, between the feeding device 14, in the example more precisely the singler 22, and the first gate 32 after the singler 22 in the transport direction there is disposed a sensor device 38 which measures physical properties of the value documents when the value documents are transported past in the transport direction T and forms sensor signals rendering the measurement results. In this example, the sensor device 38 has two sensors, namely an optical transmission sensor 40 which captures a transmission color image and a transmission IR image of the value document, and a luminescence sensor 42 which captures luminescence properties of the value document in a locally resolved manner. The sensor signals formed by the sensors correspond to measurement data or raw data of the sensors, which, depending on the sensor, could already have been subjected to a correction, for example in dependence on calibrating data and/or noise properties.

[0050] For capturing and displaying operating data, the value document processing apparatus 10 has an input/output device 46. The input/output device 46 is realized in this example by a touch-sensitive display device (“touch screen”). In other embodiment examples, it may comprise, for example, a keyboard and a display device, for example an LCD display.

[0051] A control and evaluation device 48 is connected via signal connections to the sensor device 38, the input/output device 46 and the transport device 18, in particular the gate 32.

[0052] The control and evaluation device 48 forms a data processing device and has, besides corresponding data interfaces (not shown in the Figures) for the sensor device 38 or the sensors thereof, a processor 50 and a memory 52 connected to the processor 50 in which at least one computer program with program code is stored. Upon the execution of the computer program, the control and evaluation device 48 or the processor 50 evaluates the signals or measurement values of the sensor device 38 and controls the apparatus in accordance with the properties of the value documents. Thus, in its function as an evaluation device, it may evaluate the sensor signals, in particular for ascertaining an authenticity class of a processed value document, and in its function as a control device, it may drive the transport device 18 in accordance with the evaluation and optionally store the measurement data. In other embodiment examples there may also be provided an evaluation device separate from the control device, which is connected via interfaces to the sensors of the sensor device 38, on the one hand, and the control device, on the other hand. In still other embodiment examples, the luminescence sensor 42 may have its own sensor evaluation device which may be connected to a second sensor evaluation device for evaluating the signals of the other sensors of the sensor device 38 and via the latter to the control device or directly to the control device. The sensor evaluation device and the second sensor evaluation device then form an evaluation device. The evaluation device is configured for evaluating the sensor signals and delivers the respective result to the control device which drives the transport device. The evaluation operations described in the following may then be carried out by the evaluation device alone.

[0053] Further, the control and evaluation device 48 drives the input/output device 46 such, among other things, that it displays operating data, and captures via this input/output device operating data which correspond to inputs of an operator.

[0054] During operation, value documents are singled out of the feeding device 14 and transported past the sensor device 38 or therethrough. The sensor device 38 captures or measures physical properties of the value document respectively transported past or through it and forms sensor signals or measurement data which describe the measurement values for the physical properties. The control and evaluation device 48 classifies the value document, in dependence on the sensor signals of the sensor device 38 for a value document and on classification parameters stored in the evaluation device, into one of at least two specified authenticity classes, and by emitting actuating signals drives the transport device 18, here more precisely the gate 32, such that the value document is output, corresponding to its class ascertained upon the classification, into an output section of the output device 16, which output section is associated with the class. The association with one of the specified authenticity classes or the classification is effected here in dependence on at least one specified authenticity criterion.

[0055] For the check of value documents hereinafter described in more detail, for each of the value documents luminescence intensity measurement values are used as luminescence intensity values, which are captured by means of the luminescence sensor 40 using excitation radiation of a specified intensity, while the value document is transported past the luminescence sensor 40.

[0056] The luminescence sensor 40 and the control and evaluation device 48 are configured to capture the luminescence intensity values for the substrate while the same is transported past the luminescence sensor at a specified, for example constant, transport speed. More specifically, the luminescence sensor 40 shown schematically in FIG. 2 has an excitation radiation source 44 that generates optical radiation in a specified wavelength region, a deflection device 45 that directs the excitation radiation to a region of the transport path, and a measuring device 47 that is arranged to detect luminescence radiation emanating from the value document 12 that was generated by the excitation radiation. Optionally, still further optical elements, for example focusing elements such as lenses or filtering elements, can be provided in the beam path from the excitation source to the transport path or from the transport path to the measuring device 47. These are not shown in FIG. 2.

[0057] The luminescence sensor 40 is designed such that it is suitable for measuring luminescence radiation which is characteristic of the luminescent substance in the value document. This means that the wavelength region of the excitation radiation is chosen such that the excitation radiation is suitable for exciting the specific luminescent substance in the respective value document to emit luminescence radiation. The excitation radiation source 44 is configured accordingly.

[0058] For example, as a deflection device 45 a semitransparent mirror can be used which reflects the excitation radiation in the direction of the transport path, but allows luminescence radiation to be detected to pass through.

[0059] The measuring device 47 is arranged to measure the intensity of luminescence radiation which emanates from the value document and has been produced by illuminating the value document with excitation radiation from the excitation radiation source 44. For this purpose, the measuring device 47 can have elements by means of which radiation in the specified wavelength region characteristic of the luminescent substance can be separated from any other radiation components that may be present, for example filters or dispersing devices such as optical gratings. In other embodiment examples, however, separation via temporal properties of the luminescence radiation would also be conceivable. Furthermore, the measuring device can have corresponding photodetection elements. In the present example, the luminescence sensor is configured to capture luminescence intensity measurement values for four tracks extending side by side in the transport direction on the value document. The local resolution in the transport direction results from the fact that luminescence measurements are carried out at specified intervals, so that during transport at a specified, substantially constant transport speed, measurement values are captured at constant local intervals on the value document. Furthermore, the excitation radiation source 44, the deflection device 45 and the measuring device 47 are arranged such that measurement data for several, in the example four, locations of the transport path or capture locations on a value document in the transport path are captured for one point in time. Thus, for one value document, four tracks of luminescence intensity measurement values are obtained, which are used as luminescence intensity measurement values in this embodiment example.

[0060] FIGS. 3 and 4 represent exemplary results of a luminescence intensity measurement for a value document 12 into whose substrate 100 a luminescent substance with at least approximately locally constant concentration is incorporated. FIG. 3 illustrates the place of the measuring points or capture locations on the represented value document. Since the value document was transported with the longitudinal direction parallel to the transport direction, they lie in four tracks; the luminescence intensity values for capture locations of the tracks are marked with different symbols. FIG. 3 also shows axes of a coordinate system for locations on the value document in freely chosen but then fixed units (“arbitrary units”).

[0061] The method described below for checking a substrate of a value document with a specified luminescent substance incorporated and/or applied areally is particularly suitable for checking value documents which have at least one luminescent substance at least approximately uniformly distributed in the substrate, but which have further features which lead to the fact that when luminescent radiation of the luminescent substance is excited, luminescence intensity values are measured which are not characteristic of the substrate itself, i.e. the substrate in the region without such features. Examples of this are shown schematically in FIG. 3. The value document 12 comprises the substrate 100 into which the luminescent substance is uniformly incorporated. Elements are located in or on the substrate that influence the strength of the excited luminescence radiation compared to regions without such elements. A watermark 102 is formed in the substrate 100, in the region of which too high intensities are measured, which are caused by the changed thickness of the substrate. Further, printed regions 104 are located on the substrate 100 that attenuate or almost completely absorb the excitation radiation entering the substrate and/or the luminescence radiation exiting the substrate 100. In addition, an application element 106 with an optical security feature may be applied to the substrate 100, which extends across the value document and likewise attenuates the excitation and/or luminescence radiation. In the example, it is a foil strip.

[0062] In FIG. 4, the luminescence intensity values for the value document in FIG. 3 are plotted as a function of the capture location in the transport direction. While the abscissa indicates the coordinates in the direction of transport, in the example the longitudinal direction of the value document, in the units in FIG. 3, the ordinate corresponds to the measured intensities, likewise in freely chosen but then fixed units (arbitrary units).

[0063] It can be seen in FIG. 3 and FIG. 4 that the luminescence intensities or luminescence intensity values vary greatly with the capture location, although the luminescent substance is distributed at least approximately homogeneously, i.e. with at least approximately the same concentration in the substrate. As can be further seen in FIGS. 3 and 4, the presence of the elements 104 and 106 causes the luminescence sensor to measure a lower luminescence intensity for these regions than would be expected due to the concentration of luminescent substance in the substrate 100 and the thickness of the substrate 100. If one would use these measured intensities just like that to check the authenticity, the check, for example by comparison with a reference value, would too often result in an indication of a forgery, although such a forgery is not present. Alternatively, the authenticity criterion could be chosen relatively broadly in order to reliably recognize all authentic bank notes as such. This would make the authenticity check rather inaccurate, as even a forged luminescent substance would only have to meet these broad authenticity criteria.

[0064] A similar effect would be the result in the case of local soilings, i.e. soilings that do not extend over the entire substrate, on the value document.

[0065] The method described below for checking a substrate of a value document with a specified luminescent substance incorporated and/or applied areally does not use the location dependence of the luminescence intensity measurement values or luminescence intensity values, but a rank order of the luminescence intensity values for the entire value document, a division or separation, for example according to tracks, not taking place. A first embodiment example is illustrated in FIG. 5.

[0066] For carrying out the method there is stored in the memory 52 a computer program with program code upon whose execution by means of the processor 50 the hereinafter described method is executed. The control and evaluation device 48 hence represents in particular also an evaluation device within the meaning of the present invention.

[0067] For checking a value document, luminescence intensity measurement values are first captured at various locations on the value document by means of the sensor device 38, more precisely the luminescence sensor 40, in step S10 and provided as luminescence intensity measurement values. In the example, measurement values are captured along four tracks, in each case 27 at different capture locations along a track. The total number N of luminescence intensity measurement values and thus luminescence intensity values is therefore 108.

[0068] A substrate luminescence characteristic value or luminescence characteristic value is then ascertained in steps S12 and S14 in dependence on a rank order of the luminescence intensity values.

[0069] In this embodiment example, the rank order is given by the magnitude of the luminescence intensity values. In step S12, a rank order of the captured luminescence intensity values is defined. For this, the captured luminescence intensity values are sorted according to their magnitude, for example in ascending order, and thus ordered. This order is independent of the capture location. In the example, the mentioned luminescence intensity values x.sub.i for the capture locations i are ordered according to their magnitude independently of the capture location; the integer index i being greater than or equal to 1 and smaller than or equal to 108. This results in a rank order of the values x.sub.i: If the integer J with 1<= J <= 108 denotes a rank index, the result is a rank order x.sup.(J) (x.sup.(1))<=x.sup.(2) <= ... <= x.sup.(108)), which, however, generally deviates from the series of luminescence intensity values x.sub.i, i = 1 to 108, defined by the capture locations.

[0070] In step S14, for a specified number p, which is between 0.4 and 1, a value is then ascertained below which or equal to which there lies at least a portion p of the luminescence intensity values and equal to which or above which there lies at least the remainder of the luminescence intensity values. In the example, the p-quantile is ascertained, in the example thus a number which is greater than or equal to at least the portion p of the captured luminescence intensity values, i.e. of the smallest p*N luminescence intensity values, and which is smaller than or equal to at least the remainder, i.e. the greatest, (1-p)*N luminescence intensity values. This value is used as the substrate luminescence characteristic value or luminescence characteristic value. The portion p can be chosen depending on the area and arrangement of the absorbing regions, i.e. here the of the print and the strip-shaped element. For typical bank notes or bank notes with large regions that absorb luminescent radiation and/or excitation radiation, a value p of 0.7 gives good results, one of 0.8 gives better results. This is due to the fact that luminescence intensity values for capture locations with absorbing regions, which therefore tend to be too small, are not taken into account. In the example, p=0.8 is chosen for p, for example. Thus, for determining the substrate luminescence characteristic value, a value is ascertained below which or equal to which there lies at least a portion 0.8 of the luminescence intensity values. Here it is p.Math.N = 0.8.Math.108 = 86.4 luminescence intensity values. Round up to the nearest integer so that at least 87 luminescence intensity values are smaller than or equal to the value to be ascertained. At the same time, at least (1-p).Math.N = 0.2.Math.108 = 21.6 luminescence intensity values should be greater than or equal to the value to be ascertained. Again, round up to the nearest integer so that at least 22 luminescence intensity values are greater than or equal to the value to be ascertained. The value to be ascertained is therefore x.sup.(J) for J=87 (the values x.sup.(1) to x.sup.(87) are smaller than or equal to, x.sup.(87) to x.sup.(108) are greater than or equal to x.sup.(87)).

[0071] In step S16, it is checked whether the substrate luminescence characteristic value thus ascertained meets a specified criterion, and depending on the result of the check, a signal representing the result of the check is generated and emitted. More precisely, in this embodiment example, it is checked whether the ascertained substrate luminescence characteristic value meets a specified authenticity criterion for the presence of a substrate to be regarded as authentic. Depending on the result of the check, an authenticity signal is emitted, which represents an indication of the presence of an authentic substrate or a forged substrate. In this embodiment example, the criterion is a threshold value criterion, i.e. it is checked whether the ascertained substrate luminescence characteristic value exceeds a threshold value. Exceeding the threshold value is considered an indication of authenticity, undershooting it an indication of the presence of a forgery. In other embodiment examples, as an authenticity criterion, there may also be checked whether the ascertained substrate luminescence characteristic value lies within an interval which is specified for authentic value documents of the checked type. The threshold value or the interval can be obtained, for example, by examining reference value documents or substrates, such as unused authentic value documents. The authenticity signal can be used to form a sorting signal. In other embodiment examples, results of a check of measurement values from other sensors may also be used.

[0072] Since the local place of the capture locations for which luminescence intensity values have been captured or provided is irrelevant, the method can produce the same results to a very good approximation independently of the position of the value document, in the example number upright or upside down, and the orientation of the value document, in the example number left or right. The same applies in the case where value documents of different types with the same substrate are used, for example value documents of different denominations but of the same currency, if the substrate material is the same.

[0073] A second embodiment example illustrated in FIG. 6 differs from the first embodiment only in that the substrate luminescence characteristic value is ascertained in a different manner in dependence on a rank order of the luminescence intensity values.

[0074] All process steps except for steps S14 and S16 are therefore unchanged, steps S14 and S16 are replaced by steps S14′ and S16′. The same applies to the apparatus.

[0075] In step S14′, for ascertaining the substrate luminescence characteristic value, non-negative numbers p<1 and q<1-p representing portions of the N luminescence intensity values are specified. For ascertaining the luminescence characteristic value or substrate luminescence characteristic value, those of the luminescence intensity values are used which are greater than the p*N smallest ones of the measurement values and smaller than the q*N greatest ones of the measurement values, where p>0.4. In the example, p=0.745 and q=0.15.

[0076] In the example, the used ones of the luminescence intensity values ordered in step S12 have ranks or rank indices J greater than or equal to p.Math.N = 0.745.Math.108 = 80.46. It is rounded to the nearest integer, so here it is rounded down to 80. At the same time, the luminescence intensity values used have rank indices or ranks J smaller than or equal to (1-q).Math.N = 0.85.Math.108 = 91.8. It is rounded down to the nearest integer, i.e. 91. The ranks or rank indices J of the luminescence intensity values used are therefore greater than or equal to 80 and smaller than or equal to 91: Therefore, for ascertaining the luminescence characteristic value or substrate luminescence characteristic value, the luminescence intensity values x.sup.(80) to x.sup.(91) are used.

[0077] This means that, again independently of the local arrangement, the lowest p*N luminescence intensity values, which are influenced for example by the imprint or the foil element, and the q*N highest luminescence intensity values, which are increased due to for example the watermark, are not taken into account in the further ascertainment. From the remaining luminescence intensity values taken into account, an average value is now formed, in the example a simple arithmetic average value, which is used as the substrate luminescence characteristic value. The luminescence intensity values taken into account or used, which are distinguished by their rank order but not their capture location, belong to different capture locations on the substrate or value document. This is illustrated in FIG. 3, in which the symbols of those luminescence intensity values that were used in the averaging are represented as black-filled symbols, while those of the other, unused luminescence intensity values are represented as symbols with no filling, only with a frame.

[0078] The luminescence intensity values x.sup.(80) to x.sup.(91) used result, in the example, in an average value of 101, which is represented in FIG. 4 by a corresponding horizontal line.

[0079] In step S16′, which is changed in accordance with the different ascertainment of the substrate luminescence characteristic value in step S14′, an authenticity criterion is again used as a criterion. In the example, step S16′ differs from step S16 in that as an authenticity criterion it is checked whether the ascertained substrate luminescence characteristic value lies within an interval that is specified for the type of substrate or, in this case, value document. The interval limits can be ascertained analogously to the first embodiment example.

[0080] A further embodiment example differs from the embodiment example last described only in that step S14′ is replaced by a step S14″. The latter is somewhat modified compared to step S14′. For ascertaining the substrate luminescence characteristic value, now those of the luminescence intensity values are used which are greater than or equal to the at least p*N smallest ones of the luminescence intensity values and smaller than or equal to the at least q*N greatest ones of the luminescence intensity values are used, where again p>0.4. In the example, again, p=0.745 and q=0.15. Otherwise, step S14″ is unchanged compared to step S14′.

[0081] In the example, the used ones of the luminescence intensity values ordered in step S12 are greater than or equal to the at least p.Math.N = 0.745.Math.108 = 80.46 smallest luminescence intensity values. It is rounded up to the next integer, so here to 81. At the same time, the luminescence intensity values used are smaller than or equal to the (1-q).Math.N = 0.15.Math.108 = 16.2 greatest luminescence intensity values. It is rounded up to the nearest integer, i.e. 17. The greatest 17 luminescence intensity values have the ranks or rank indices 92 to 108. The ranks or rank indices J of the luminescence intensity values used are therefore greater than or equal to 81 and smaller than or equal to 92: Thus, for ascertaining the substrate luminescence characteristic value, the luminescence intensity values x.sup.(81) to x.sup.(92) are used.

[0082] As before, this means that, again independently of the local arrangement, the lowest p*N luminescence intensity values, which are influenced for example by the imprint or the foil element, and the q*N highest luminescence intensity values, which are increased due to for example the watermark, are not taken into account in the further ascertainment.

[0083] Further embodiment examples differ from the first two embodiment examples in that not an authenticity criterion is used, but a quality criterion. As a quality criterion, it is checked in each case whether the ascertained substrate luminescence characteristic value lies within an interval that defines the range of substrates to be considered suitable. As a signal, there is then formed a signal that represents an indication that the substrates are suitable for use.

[0084] Further embodiment examples differ from the described embodiment examples in that the ascertained luminescence characteristic value is at least approximately related, in the example normalized, to specified standard conditions. In the example, it is specified as standard conditions that a normalization to the intensity of the excitation radiation used in the capturing of the luminescence intensity values takes place. To a good approximation, this then has no influence on the magnitude of the luminescence intensity values or the substrate luminescence characteristic value. In a first alternative, the luminescence intensity values are normalized by the excitation intensity of the excitation radiation, i.e. for example divided by it or multiplied by the reciprocal. The luminescence intensity values are then a monotonic function of the measurement values or luminescence intensity measurement values. However, the application of a division or multiplication by a constant has no influence on the formation of the rank order and the determination of the substrate luminescence characteristic value based on the rank order. However, the magnitude of the substrate luminescence characteristic value is changed as a consequence of the division or multiplication. In a second alternative, the ascertained substrate luminescence characteristic value can be divided by the excitation intensity of the excitation radiation. The parameters of the criterion, for example the threshold value or the interval limits, for both alternatives can be chosen independently of the intensity of the excitation radiation.

[0085] In the embodiment examples, the check of the paper web and the check of a value document produced from the paper web with imprints that absorb excitation radiation and/or luminescence radiation will result in at least approximately equal substrate luminescence characteristic values, in particular if these are normalized. The quantity known as the luminescence characteristic value can therefore be used very well as a characteristic value for the substrate, even if it has been further processed.

[0086] In still other embodiment examples, the substrate may be a paper web that is transported past the luminescence sensor. Luminescence intensity values are ascertained for at least one section of specified length of the web. In particular, for this section, a quality check in accordance with the previously described embodiment examples can be carried out. The result of the check then indicates whether or not the substrate is suitable for further processing into a value document.

[0087] Still other embodiment examples differ from the second embodiment example and variations thereof in that only a sum is formed instead of the average value.

[0088] Further embodiment examples differ from the preceding embodiment examples in the formation of the rank order. There is given a rank order on the basis of intervals that are adjacent to each other in ascending order and therefore do not overlap, each of which interval has a rank or rank index associated therewith, and the luminescence intensity values are each associated with the rank that corresponds to that of the intervals in which they respectively lie. In particular, for forming the rank order, a number of more than 10, in the example equally sized, successive intervals or classes is formed which together cover the range of luminescence intensity values, and an ascending rank index is associated with each of these. The rank order of the luminescence intensity values is ascertained based on in which of the intervals or which of the classes a respective one of the luminescence intensity values lies. This rank order is then used in the following method steps.

[0089] In one specific example, the captured N, N=108, luminescence intensity measurement values are the same as in the first embodiment example. Instead of the value p=0.8, the value p=0.75 is used. The measuring range of the luminescence sensor is mapped to the range from 0 to 256 by scaling (multiplication) with a suitable factor S. S can be, for example, the reciprocal of the magnitude of the measuring range starting at 0.

[0090] Then the luminescence intensity measurement values are scaled in the same way with the factor S so that the resulting luminescence intensity values are in the range between 0 and 256.

[0091] The luminescence intensity values formed in this way are now classified according to their magnitude into 256 adjacent intervals, the length of which is 1 and the lower limit of which is in each case another integer between 0 and 255. These successive intervals form classes which are denoted with the lower limit of the interval and form a rank index. For classification into the classes, it is sufficient to delete the decimal places in the luminescence intensity values, i.e. to replace the luminescence intensity values by their integer part. With this method, the luminescence intensity values are brought into a rank order. The rank index or rank order index of the luminescence intensity values is then given in each case by the rank index or the lower limit of the interval in which they were classified. Therefore, the case can occur that two slightly different luminescence intensity measurement values fall into the same class, i.e. receive the same rank index, i.e. in individual intervals or classes there can be present several luminescence intensity values.

[0092] For the classes present, there thus arises a frequency distribution of the luminescence intensity values among the classes. Luminescence intensity values in one class have the same rank index.

[0093] From the frequency distribution, there can now be ascertained, by successively adding up the frequencies in the classes starting from 0 in ascending order, the class in which the value of p*N, in the example with p=0.75 and N=108 of p*N=81, is exceeded for the first time. The luminescence characteristic value is then given precisely by the lower limit of the ascertained interval or the designation of the corresponding class. Optionally, the ascertained value can be scaled with 1/S.

[0094] In another variant of the example, only 128 classes could be formed instead of 256, allowing the method to be carried out faster, but the resulting luminescence characteristic value would be somewhat less accurate.

[0095] These embodiment examples offer the advantage that they require little computing time and are therefore executable in real time even on fast-running bank note processing apparatuses.

[0096] Alternatively, it would also be possible to rank the individual resulting luminescence intensity values in ascending order of magnitude and ascertain the eighty-first luminescence intensity value.

[0097] For still other variants, a different scaling factor can also be used, which depends, for example, on the magnitude of the greatest luminescence intensity value. For example, the scaling factor can be determined such that the luminescence intensity values are between 0 and 1, for which S would be chosen as the reciprocal of the greatest luminescence intensity value occurring.

[0098] Then, for example, the number of intervals of equal length and thus classes can be specified so that the length of the intervals results from the reciprocal of the number of classes.

[0099] Further embodiment examples may differ from the previously described embodiment examples in that the luminescence sensor is designed such that the captured and passed-on luminescence intensity measurement values can only take a specified number of discrete values, for example, analogous to optical sensors, integer numbers in the region of 0 to 255.

[0100] Other embodiment examples may differ from the previously described embodiment examples in that other designs of luminescence sensors known in the art are used. In particular, excitation radiation and luminescence radiation can be separated even without a deflection device 45 according to their spatial and/or spectral properties. For example, the excitation radiation can be irradiated at a first angle onto a value document located in the transport path, while the measuring device 47 detects the luminescence radiation only at a second angle different from the angle of the remitted excitation light.