EP1567991B1 - Method and device for verifying valuable documents - Google Patents

Abstract

A method and apparatus for checking value documents having an authenticity feature in the form of at least one luminescent substance, includes forming a measuring vector from the measuring values corresponding to different frequencies and/or frequency domains of the luminescence radiation, and performing an allocation of the measuring vector to one of a plurality of given reference vectors corresponding to different authenticity features by allocating at least one object allocation area to each reference vector and checking which object allocation area the measuring vector is located in.

Description

The invention relates to a method and a device for checking documents of value having an authenticity feature in the form of at least one luminescent substance, wherein the document of value is irradiated with light and the luminescence radiation emanating from the document of value is detected in a spectrally resolved manner in order to determine whether the authenticity feature in the checked document of value actually exists is available.

For the purposes of the present invention, a luminescent, e.g. a fluorescent or phosphorescent authenticity feature a single substance or a mixture of several substances understood that show a luminescence.

There are a number of known systems for checking the authenticity of such value documents. A system is known for example from DE 23 66 274 C2 of the applicant. In this system, to check the authenticity of a banknote, i. H. in particular, the examination of whether a fluorescent authenticity feature is actually present in a banknote to be tested, this irradiated and recorded the remitted fluorescence radiation spectrally resolved. The evaluation is carried out by comparing the signals from different photocells of the spectrometer.

Although this method works very reliably in most cases, it can, especially when there are several possible authenticity features that have a very similar spectral behavior, give rise to difficulties in distinguishing and thus deciding which of these authenticity features actually exists in the tested value document is.

US 5 678 677 A discloses a classification scheme for recognizing and classifying banknotes, based on the classification of n-dimensional measurement vectors in the scanning of spectral regions.

On this basis, it is the object of the present invention to provide a method and a device for checking value documents, which allow a distinction between authenticity features with a similar spectral profile in a simple and reliable manner.

This object is solved by the independent claims.

The present invention is thus based on the finding that a simple and reliable distinction between different authenticity features can best be obtained if a measurement vector is formed from the measured values which correspond to different frequencies and / or frequency ranges of the luminescence radiation, and a class assignment of Measuring vector to one of a plurality of predetermined reference vectors that correspond to different authenticity characteristics, characterized in that the reference vectors each at least one class assignment area is assigned and checked, in which class assignment area is the measurement vector. The measuring vector can consist of the measured values per se and / or variables derived therefrom.

The determination of the class assignment regions and thus the class assignment from the measuring vector to one of the reference vectors can preferably be carried out by a comparison of the measuring vector with a plurality of reference vectors or with at least one variable, which depends on at least two reference vectors.

A particularly preferred example of the former variant may be that the authenticity feature whose reference vector has the smallest difference, such as the smallest distance to the measuring vector, is determined or determinable as being present in the value document to be tested. This approach has especially with authenticity features a very similar spectral course proved to be much more suitable than a procedure in which it is checked whether the intensity and / or the course of a measured luminescence radiation differs only by a maximum of a predetermined value of the intensity or the course of a reference radiation.

The second-mentioned variant, in which no comparison of the measuring vector with each individual reference vector itself, but with at least one derived from at least two reference vectors size is performed significantly reduces the computational effort and is therefore particularly advantageous when it comes to high test speeds. A particularly preferred example of this is that the size, which depends on at least two reference vectors, serves as a separation surface between the two reference vectors, e.g. a (n-1) dimensional hyperplane is formed between the two n-dimensional reference vectors, the separation surface separating the class assignment regions of the two reference vectors. In this case, e.g. determines the position of the measuring vector with respect to the separating surface.

The test system according to the invention can preferably be extended to include a further step, in which it is checked whether the magnitude of the measurement vector is greater than a predetermined reference value or not. This step is particularly preferably performed prior to the step of assigning the class assignment areas and / or the step of checking in which of these areas the measurement vector is located. As a result, a significant time savings in the evaluation can be achieved because the subsequent time-consuming evaluation steps of the examination of the class allocation areas are no longer necessary if the simple amount check already delivers a negative result.

This procedure proves to be particularly useful in the examination of authenticity features whose luminescent radiation to a significant extent in the non-visible, such. ultraviolet or especially in the infrared spectral range. By this magnitude comparison, e.g. already recognized a number of mismatched features in forged value documents that emit only in the visible spectral range. Among other things, for the aforementioned reasons, the measuring vector is thus preferably formed from measured values of the infrared spectral range.

Preferably, it may alternatively or additionally be provided that the measuring vector and the reference vectors are normalized in a similar manner. For n-dimensional measurement and reference vectors, this can be done, for example, by normalizing to an n-1 dimensional unit sphere, so that the magnitude of all normalized vectors is the same, i.e., the same. in particular has the value 1.

Such standardization has the advantage that a simple comparison of the measuring vector with the reference vectors is made possible, which is largely independent of the quantity or concentration in which the authenticity feature is actually introduced in the banknote or how high the total intensity of the measured radiation actually is. In contrast to known methods of color space analysis, for example, in which the absolute values of the individual color components are essential for a correct color determination, this is not absolutely necessary in the luminescence test according to the invention, since in this case essentially only the shape of the spectral curves acquired, but not on their absolute intensity values arrive.

In particular, in the aforementioned case of normalization, it may prove to be a disadvantage that the measurements have a background signal, which does not originate from the luminescence radiation and superimposes the luminescence radiation. This background signal interferes with the evaluation, since the ratios of the measuring vectors to the reference vectors change significantly as a function of the height of the background signals due to the normalization and can thus lead to less accurate results of the evaluation.

Preferably, therefore, a background signal is taken into account in the evaluation of the measured values, which does not originate from the Lunünzenzstrahlung. In particular, an amount may be deducted from the measured values to form the measuring vector, which amount depends on the size of the background signal. The amount may vary from measured value to measured value of the measuring vector, i. it is also possible to use a background vector generated by the background signal. The amount will be particularly preferably dependent on the size of a minimum and / or maximum of the measured values and / or a ratio of a plurality of measured values to one another. If the emission spectrum of the background signal is known, by measuring the background signal at a single or e.g. a few frequencies of the background vector are calculated. If the background vector is known, it can e.g. stored in the sensor stored and be deducted without measurement of the measured values.

Further advantages of the present invention will become apparent from the appended dependent claims and the following description of preferred embodiments. It shows the
Figure 1 is a schematic view of a test apparatus according to a first embodiment; the
FIG. 2 shows a two-dimensional representation for illustrating the method according to the invention; the
FIG. 3 shows a two-dimensional representation to illustrate the class assignment method according to the invention and FIG
FIG. 4 shows a schematic view of a spectral curve L1 measured by a banknote and of a portion L2 of the spectral curve L1 that is due only to the luminescence radiation.

The test system according to the invention can be used in all devices which check luminescent authenticity features. Although not limited thereto, the following describes the particularly preferred variant of checking banknotes in banknote processing devices, which can serve, for example, for counting, sorting, depositing and / or paying out banknotes.

FIG. 1 illustrates in particular a device 1 which, in addition to components already known per se, which are not shown, also has, among other things, a transport device 2 by means of which banknotes 3 are occasionally transported past a checking device 4. The checking device 4 can be designed to check the authenticity, the state or the nominal value of the banknotes 3. In particular, the test device 4 has a light source 5, a spectral sensor 6 and an evaluation device 7, which is connected via a signal line 8 at least with the spectral sensor 6. The light source 5 serves to irradiate the banknote 3 with light beams 9 at an oblique angle to the banknote surface and the spectral sensor 6 for detecting and spectral decomposition of the remitted from the banknote surface radiation 10. Preferably, the spectral sensor 6 detects by means of a spectrometer 6 luminescence 10 in the infrared Spectral range. The signals detected by the spectral sensor 6 are transmitted via the signal line 8 to the computer-based evaluation device 7, which checks on the basis of the measured signals whether a specific authenticity feature is present in the banknote 3.

The device 1 is distinguished, in particular, by the type of evaluation of the measurement signals in the evaluation device 7. This can be done, for example, according to an embodiment of the method according to the invention in the following manner:

All or at least a subset of the measured values of the spectral sensor 6, which respectively correspond to different frequencies or frequency ranges, are represented as measuring vector X. Let the measuring vector X = (x ₁ ,..., X _n ) be, for example, a measure of the spectral curve of the recorded luminescent radiation 10 of the banknote 3, where x ₁ to x _n are values which, on the basis of the measuring signals of n different photocells of the Spectral sensors 6 are formed. The spectral values x ₁ to x _n can preferably correspond to the measured luminescence intensity at different frequencies or frequency ranges in an invisible to the eye, such as ultraviolet or particularly preferably infrared spectral range. The measuring vector X thus represents, at least in the case n> 1, preferably n≥5 or n≥10; a measure of the shape, ie the course of the measured spectral curve.

A comparison of this measuring vector X with k predetermined reference vectors A ₁ ,..., A _k is now carried out in the manner described below by way of example. For better clarity, a simple case design is described with reference to Figures 2 and 3, in which the measuring vector X has only two measured values x ₁ and x ₂ , ie the vector dimension n is equal to 2. In this case, the measuring vector X becomes a point X represented in the two-dimensional diagram of Figure 2 and Figure 3, wherein each axis of the diagram corresponds to another coordinate of the measuring vector X.

The vectors A = (a ₁ ,..., A _n ) and B = (b ₁ ,..., B _n ) are in an exemplary manner two predetermined reference vectors A ₁ = A, A ₂ = B corresponding to the spectral curves of two possible authenticity features, one of which may possibly be present in the checked banknote 3.

In order to decide whether at all one of the two allowed authenticity features is present in or on the banknote, it can first be checked whether the magnitude of the measurement vector X, i. | X | exceeds a predetermined threshold. If this is not the case, the banknote can already be rejected here as unreal. The threshold can be 0, but is preferably chosen so that counterfeits without authenticity feature are already distinguishable here certainly. In the exemplary case of FIGS. 2 and 3, this reference value R has, for example, an amount | R | from 0.4. With this test, counterfeits can be sorted out, in which the authenticity features are present in themselves, but in too low a concentration. This is particularly preferred because in the variant described in the infrared spectral range is measured and counterfeits usually have intensities in this spectral range, which are either negligible or at least substantially lower than the intensities of the authenticity features A, B in real banknotes 3.

As mentioned, this criterion is that the amount | X | of the measuring vector X must correspond to at least one reference value R, particularly preferably used for the preliminary evaluation of the measured values. This may mean, for example, that this minimum value comparison of the amount | X | the measuring vector X is performed before the class assignment of the reference vector A, B is performed with the smallest difference to the measuring vector X. This variant of the upstream amount check can significantly increase the speed of the banknote check.

If the amount of the measuring vector X is above the predetermined threshold, it must be decided which of the authenticity features A, B is actually present in the banknote 3.

(i=1,...,l) eingeteilt, wobei diese den Referenzvektoren (A₁,..., A_k) zugeordnet sind. Im einfachsten Fall gibt es für jeden Referenzvektor genau ein Klassenzuordnungsgebiet, im allgemeinen Fall kann es mehrere Klassenzuordnungsgebiete pro Referenzvektor geben. Um zu entscheiden, welches Echtheitsmerkmal in oder auf der Banknote 3 vorhanden ist, wird festgestellt, in welchem Klassenzuordnungsgebiet G _m der Meßvektor X liegt, d.h. es wird der Index m gesucht mit X ∈ G _m . Im dargestellten zweidimensionalen Beispiel sind diese Gebiete Halbebenen G_A, G_B, wie in Figur 3 veranschaulicht ist. Im allgemeinen Fall sind die Klassenzuordnungsgebiete Durchschnitte von endlich vielen Halbebenen.For this purpose, the following procedure can be implemented: The affine space IR ⁿ , in which the measurement and reference vectors (X, A ₁ ,..., A _k ) are located, becomes class assignment areas G _i ⊆

( i = 1, ..., l ), these being assigned to the reference vectors (A ₁ , ..., A _k ). In the simplest case there is exactly one class assignment area for each reference vector, in the general case there can be several class assignment areas per reference vector. In order to decide which authenticity feature is present in or on the banknote 3, it is determined in which class assignment area G _m the measurement vector X lies, ie the index m is searched with X ∈ G _m . In the illustrated two-dimensional example, these regions are half-planes G _A , G _B , as illustrated in FIG. In the general case, the class allocation areas are averages of finitely many half-levels.

The class assignment regions can now be defined either via the reference vectors A, B (in the general case A ₁ ,..., A _k ) or via a description of the hyperplanes delimiting them.

In the former case, for example, the one reference vector A, B is determined which has the smallest difference to the measuring vector X. For this purpose, the distance of the measuring vector X to all possible authenticity features, ie in the case specifically described, can be calculated for the two reference vectors A, B. The distance can be considered Euclidean distance between the relevant vectors, in the example so d (X, A) and d (X, B) are calculated. Instead of the Euclidean distance, every function d (X, A) can be used with the following property: For any measurement vectors X and reference vectors A, B, then d (X, A) ≥ d (X, B) if | XA | ≥ | XB | applies.

Alternatively, this procedure can be implemented in another way, which leads exactly to the same result: The class allocation areas are defined in the second case by a separation area T, which contains the two reference vectors A, B (in the general case A ₁ ,..., A _k ) limited. This variant has the advantage, in particular in real-time environments, that the computational effort is reduced.

|u ₁ y ₁+...+u _n y _n -u ₀=0} beschreiben wobei (u ₁, ..., u _n ) ein Normalenvektor der Hyperebene T ist. Das Vorzeichen von u ₁ x ₁ + ... + u _n x _n - u ₀ gibt nun an, auf welcher Seite der Hyperebene T die Messung X liegt.In order to test whether a measurement vector X lies in a class assignment domain G _i (ie X ∈ G _i ), one must check for all G _i bounding interfaces T whether X lies on the "right" side. As a separating surface, it is preferable to have n-1-dimensional hyperplanes T, for example as points {{ y ₁ , ..., y _n ) ∈

| u ₁ y ₁ + ... + a _n y _n - u ₀ = 0} describe where (u _1, ..., u _n) is a normal vector of the hyperplane T. The sign of u ₁ x ₁ + ... + u _n x _n - u ₀ now indicates on which side of the hyperplane T the measurement X lies.

In order to increase the reliability of detection, it may be required in a preferred embodiment of the method that an assignment of the measuring vector X to one of the reference vectors A, B takes place only if their mutual distance d (X, A) or d (X, B ) does not exceed a predetermined threshold.

It can be determined in this sense that the class allocation areas G _A , G _B are limited so that the class allocation areas do not touch anymore. In this way arises between the class allocation areas G _A , G _B "no man's land", ie areas that are not assigned to any class and thus no reference vector A ₁ , ..., A _k . Banknotes 3, the measuring vector lying in these areas, for example, provided with a warning after the test in the test device 4 can be controlled or transferred to a special filing.

In a possible extension of the method, it is taken into account in the definition of the class allocation areas that the probability that a measurement vector X corresponds to one of at least two reference vectors A, B is not uniformly distributed, but is e.g. has a correlation.

In the methods described so far, however, it should be noted that the distance of the measuring vector X from the reference vectors A, B increases with its intensity and the intensity of the individual reference curves A, B. As a result, when one of the two possible authenticity features is introduced into the checked banknote 3 in a significantly higher amount and concentration, the distance of its reference vector A or B to the measurement vector X can also be correspondingly larger.

In order to find a distance measure of the authenticity features A, B, which is independent of the measured total intensity or the amount and concentration of the individual authenticity features in the banknote 3, in a particularly advantageous embodiment of the invention, both the reference vectors A, B, as well as the Measurement vector X normalized. In the case of the two-dimensional representation according to FIG. 2, for example, normalization to the unit circle E is carried out. This means that the normalized vectors A / | A | (ie A by amount of A), B / | B | and X / | X | are formed, which all have a normalized amount of 1. In the general n-dimensional case of k reference vectors A ₁ , ..., A _k , each n components have the projection on the n-dimensional unit sphere E.

With this standardization, all measuring vectors X, which differ only in length, are identified. As shown in FIG. 2, they lie on lines of origin through the measuring vector X. This procedure corresponds to the transition from the affine space IR ⁿ to a projective space IP ^n-1 , whose elements in the associated affine space are lines of origin, which are also described below the associated vectors X, A, B ... are described. The transition to a projective space has proved to be very advantageous, especially in the examination of authenticity features, which have a similar spectral behavior.

In order to make the assignment of the measurement vector X to one of the reference vectors A, B shown in the example, in the simplest case, the distance d (X, A) and d (X, B) of the normalized measurement vector X / (X) is normalized to all Reference vectors A / | A | or B / | B | calculated. The classification is in turn carried out for the authenticity feature whose reference vector A, B has the smallest distance d (X, A) d (X, B) to the measurement vector X, in the illustrated case thus the authenticity feature A.

An Stelle des euklidischen Abstands kann jede Funktion d(X,A) verwendet werden mit folgender Eigenschaft: Für beliebige Messvektoren X und Referenzvektoren A, B gilt d(X,A) ≥ d(X,B) genau dann wenn $\left|\frac{X}{\left|X\right|}-\frac{A}{\left|A\right|}\right|\ge \left|\frac{X}{\left|X\right|}-\frac{B}{\left|B\right|}\right|\hspace{0.17em}\mathrm{gilt}.$

As distance d (X, A) of two vectors, in this and in the aforementioned case, for example, the Euclidean distance of the normalized vectors X, A can be used: $d\left(X.A\right)=\left|\frac{X}{\left|X\right|}-\frac{A}{\left|A\right|}\right|,$

Instead of the Euclidean distance, every function d (X, A) can be used with the following property: For any measurement vectors X and reference vectors A, B, d (X, A) ≥ d (X, B) if and only if $\left|\frac{X}{\left|X\right|}-\frac{A}{\left|A\right|}\right|\ge \left|\frac{X}{\left|X\right|}-\frac{B}{\left|B\right|}\right|\mathrm{applies},$

In a first example, as the distance d (X, A) of the vectors X and A, the angle between the lines of origin defined by them can be used.

Der Abstand d(X,A) entspricht hier der Länge des Lots von X auf die durch A definierte Ursprungsgerade.In a second example, the following expression can be used as the distance d (X, A) of the vectors X and A: $d\left(X.A\right)=\left|X-<X.A>\cdot A/{\left|A\right|}^2\right|,$

The distance d (X, A) here corresponds to the length of the lot from X to the origin straight line defined by A.

Dieser Ausdruck ist besonders dann bevorzugt, wenn der Abstand zeitkritisch berechnet werden muß, da man sich hier die aufwendige Berechnung der Wurzel im zweiten Beispiel erspart.In another example, as the distance d (X, A) of the vectors X and A, the following expression can be used: $d\left(X.A\right)={\left|X-<X.A>\cdot A/{\left|A\right|}^2\right|}^2,$

This expression is particularly preferred when the distance must be calculated time-critical, since this saves the time-consuming calculation of the root in the second example.

verwendet werden, wobei g eine beliebige streng monotone Funktion ist.In another example, as the distance d (X, A) of the vectors X and A, the expression $d\left(X.A\right)=G\left(\left|\frac{X}{\left|X\right|}-\frac{A}{\left|A\right|}\right|\right)$

where g is any strictly monotone function.

Numerous developments and alternatives are conceivable for the exemplary embodiment described above in detail.

For example, although the case of only two possible authentication features has been described and illustrated in the figures, it will be understood that a generalization to more than two authenticity features is possible. Likewise, of course, a generalization to measurement and reference vectors X, A ₁ , ..., A _k , possible, the more than n = 2 components, ie more than two spectral measurements per banknote 3 have.

Furthermore, it can also be provided that the luminescence radiation 10 of a banknote 3 is measured at different times and this is taken into account in the evaluation. On the one hand, it can be determined here whether the measured radiation 10 of the checked banknote 3 actually has the time behavior to be expected for the respective type of luminescence. In this case, the banknotes 3 are preferably irradiated intermittently in time by the light source 5, in order to obtain e.g. to be able to measure the decay behavior of the luminescence radiation 10 in a time-resolved manner. In this case, a time-dependent representation of the measuring vectors X and / or the reference vectors A, B can also be chosen with particular preference, and the distance formation can be carried out in a time-dependent manner.

A further idea of the present invention is that the measurement of the luminescence radiation takes place only at predetermined subregions of the banknote surface, which are chosen to be nominal value-specific in a particularly preferred manner. This can be done, for example, by illuminating the light source 5 only one or more specific subregions of the banknote 3 during transport to a test device 3, or by taking into account information about the position of the respectively illuminated subregions of the banknote 3 during evaluation in the evaluation device 7. This location-dependent measurement of the luminescence radiation 10 can be used, for example, to be able to also distinguish spatially coded authenticity marks which are not homogeneously introduced in the banknote paper.

Furthermore, the luminescence radiation 10 also does not necessarily have to be measured in reflection, but alternatively or additionally, it can also be measured and evaluated in transmission.

As has been mentioned, it can be disturbing in the evaluation if the measurement signals have a background signal which does not originate from the luminescence radiation and which superimposes the luminescence radiation 10. This disturbing background signal falsify the ratios of the individual measuring vectors to the reference vectors during normalization.

To illustrate the problem is shown in Figure 4 in a schematic manner with the solid line L1 drawn by the spectral sensor 6 measured spectral course of the measured signals of an illuminated bill 3, i. the dependence of the measured signal intensity I (f) of the measuring signal frequency f shown. However, the portion of the measuring curve L1 actually derived only from the luminescence radiation 10, corresponding to the dashed line L2, is lower in magnitude and superimposed by an interfering background signal which does not originate from the luminescence radiation 10.

In order to calculate this background signal, on the one hand, a reference measurement in a banknote gap can be carried out. In this case, measured values are recorded by means of the spectral sensor 6 when no banknote 3 is located in the detection range of the spectral sensor 6. The signals thus obtained then represent a measure of the strength of the background signal and can be taken into account in the subsequent formation or evaluation of the measuring vectors, e.g. be subtracted from the measured values in the measurement of the subsequent banknote 3.

However, there are spectral sensors 6, in which the measurement conditions in the measurement with banknote 3 are so clearly distinguished in comparison to the measurement without banknote 3 that the background signals measured in the case without a banknote are not representative of the background signals measured with banknote.

Alternatively, for example, the size of a relative, preferably the absolute minimum and / or maximum of the measurement signals can be determined in a spectral range used for further evaluation. This may be, for example, a point in the spectrum at which the luminescent substances to be tested do not usually emit. In the spectrum of FIG. 4, this minimum is exemplarily at the frequency f _Min1 and has an intensity I _Min1 . By subtracting at least from the portion of the spectrum to be further evaluated, this minimum intensity _value I _Min1 , ie, the difference I (f) - I _{Min1 is} formed for the spectral range _under consideration, an effective measurement signal is obtained, which essentially only affects the luminescence radiation 10 , decreases according to the curve L2 and in which the background signals are substantially subtracted.

A further variant is the following: Since the luminescent substances to be detected have a previously known spectral curve, the ratio of the intensity of the luminescence radiation at two different frequencies has a constant, known value. The two frequencies may preferably be selected to correspond to a maximum and a minimum of the spectral curve. In the case of FIG. 4, for example, let the intensity _ratio I (f _max ) / I (f _{Min 2} ) of the luminescence _radiation 10, corresponding to curve _{L 2} , be equal to a constant value ko. However, the actual measured in the examination of the banknote 3 measurement curve L1 has an intensity ratio I (f _max ) / I (f _Min2 ) = I _Max / I _Min2 , which is less than this value ko. This difference is caused precisely by the background signals which overlay the luminescence spectrum L2.

It is now calculated by which measure I ₀ the intensity of the entire spectrum I (f) must be lowered, so that the intensity ratio I (f _max ) / I (f _Min2 ) again corresponds to the value k ₀ typical for the expected luminescence _radiation 10. By subtracting this value I ₀ from the entire spectral range of the curve L2 considered, one obtains again an effective measuring signal, which essentially only goes back to the luminescent radiation 10, corresponding to the curve L2, and in which the background signals are essentially subtracted.

It should be emphasized that, instead of a linear offset, that is to say a deduction of a constant value I _Min1 or I ₀ from the measurement intensity I (f) of the measurement curve L2, another nonlinear offset can also be subtracted, in which the subtracted value coincides with the reference value Frequency f varies. That is, the amount may be different from measured value to measured value of the measuring vector, ie a background vector generated by the background signal may also be used. This makes sense, even if the background signals have a non-linear course, ie an amount that is not constant over all frequencies f. If the emission spectrum of the background signal is known, the background vector can be calculated by measuring the background signal at a single or multiple frequencies. If the background vector is known, it can for example be stored in the sensor and also be subtracted from the measured values without measurement.

In addition, the said methods for compensating the background signals can also be used advantageously in other luminescence evaluation methods, independently of the subject matter of the main claims.

The procedure according to the invention thus makes possible a simple and reliable testing and differentiation of authenticity features, in particular with a very similar spectral profile, which can be contained in value documents.

Claims (15)

1. A method for checking value documents (3) having an authenticity feature in the form of at least one luminescent substance, the value document (3) being irradiated with light (9) and the luminescence radiation (10) emanating from the value document (3) detected with spectral resolution to determine whether the authenticity feature is present in the value document (3),
   characterized in that
   a measuring vector (X) is formed from the measuring values corresponding to different frequencies and/or frequency domains of the luminescence radiation (10), and an object allocation of the measuring vector (X) to one of a plurality of given reference vectors (A ₁, ..., A _k ) corresponding to different authenticity features is done by allocating at least one object allocation area (G ₁, ..., G _l ) to each reference vector (A ₁, ..., A _k ), and checking which object allocation area (G ₁, ..., G _l ) the measuring vector (X) is located in.
2. A method according to claim 1, characterized in that the checking method has a further step for checking whether the amount (|X|) of the measuring vector (X) is greater than a given reference value (R).
3. A method according to claim 2, characterized in that the step of checking whether the amount (|X|) of the measuring vector (X) is greater than a given reference value (R) is carried out before the step of allocating the measuring vector (X) to one of a plurality of given reference vectors (A ₁, ..., A _k ).
4. A method according to at least one of the previous claims, characterized in that the measuring vector (X) and the reference vectors (A ₁ , ..., A _k ) are normalized.
5. A method according to at least one of the previous claims, characterized in that the object allocation of the measuring vector (X) to one of the reference vectors (A _m ) is done by comparing the measuring vector (X) with a plurality of reference vectors (A₁, ..., A _k ) and/or with at least one quantity (T) which depends on at least two reference vectors (A ₁, ..., A _k ).
6. A method according to at least one of the previous claims, characterized in that the object allocation of the measuring vector (X) to one of the reference vectors (A _m ) is done by determining the smallest difference, e.g. the smallest distance (d(X,A _m )) from the measuring vector (X) to the reference vectors (A ₁ , ..., A _k ).
7. A method according to at least one of the previous claims, characterized in that the quantity (7) which depends on at least two reference vectors (A, B) is formed as a separation plane (T) between the two reference vectors (A, B), such as an (n-1) dimensional hyperplane (T) between the two n-dimensional reference vectors (A, B), the separation plane (T) separating the object allocation areas (G _A , G _B ) of the two reference vectors (A, B) from each other.
8. A method according to at least one of the previous claims, characterized in that the object allocation of the measuring vector (X) to one of the reference vectors (A _m ) is determined by determining the position of the measuring vector (X) relative to the separation plane (7).
9. A method according to at least one of the previous claims, characterized in that the luminescence radiation (10) is measured with time resolution on a value document (3) to be checked, whereby the comparison of measuring vector (X) and reference vectors (A, B) can be done time-dependently.
10. A method according to at least one of the previous claims, characterized in that the measurement of the luminescence radiation (10) is done only on one or more predetermined partial areas of the value document surface which can be predetermined denomination-specifically.
11. A method according to at least one of the previous claims, characterized in that the measuring vector (X) comprises measuring values of the infrared or ultraviolet, i.e. an invisible, spectral range.
12. A method according to at least one of the previous claims, characterized in that the evaluation of the measuring values takes account of a background signal (L2-L1) which does not come from the luminescence radiation (10).
13. A method according to claim 13, characterized in that, for forming the measuring vector, an amount depending on the magnitude of the background signal (L2-L1) is subtracted from the measuring values.
14. A method according to claim 14, characterized in that the amount is dependent on the magnitude of a minimum and/or maximum of the measuring values and/or a ratio of two measuring values.
15. An apparatus (1) for checking value documents (3) having an authenticity feature in the form of at least one luminescent substance, having a light source (5) for irradiating the value document (3) and a spectral sensor (6) for detecting with spectral resolution the luminescence radiation (10) emanating from the value document (3), and having an evaluation device (7) connected to the spectral sensor (6) for determining whether the authenticity feature is present in the value document (3),
    characterized in that
    the evaluation device (7) is designed so that a measuring vector (X) is formed from the measuring values corresponding to different frequencies and/or frequency domains of the luminescence radiation (10), and an object allocation of the measuring vector (X) to one of a plurality of given reference vectors (A ₁, ..., A _k ) corresponding to different authenticity features is done by allocating at least one object allocation area (G ₁, ..., G _l ) to each reference vector (A ₁, ..., A _k) and checking which object allocation area the measuring vector (X) is located in.

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