METHOD AND SENSOR FOR TESTING VALUE DOCUMENTS

Abstract

AMENDMENT TO THE ABSTRACT Please replace the Abstract in the application with the following Abstract, insert the following after the claims:

ABSTRACT A method for checking value documents, in particular with regard to their authenticity and/or with regard to their value-document type, involves the following steps: detecting a first plurality of intensity courses on a value document, combining the first plurality of intensity courses or a second plurality of intensity courses selected from the first plurality into a combined intensity course, determining a time constant τ of the combined intensity course, checking the value document based on the time constant τ of the combined intensity course. A corresponding sensor is provided for checking value documents, and an apparatus enables value-document processing with the aforementioned sensor.

Claims

1-15. (canceled)

16. A method for checking value documents which are transported for their checking past a sensor in a transport direction, and which have a security feature with a luminescent substance which, as a reaction to a luminescence excitation by an excitation source, emits a luminescence which has as a function of time t an intensity course with a characteristic time constant τ0, having the following steps: detecting a first plurality of intensity courses on a value document, combining the first plurality of intensity courses or a second plurality of intensity courses selected from the first plurality into a combined intensity course, determining a time constant τ of the combined intensity course, checking the value document, with regard to its authenticity and/or with regard to its value-document type, on the basis of the time constant τ of the combined intensity course.

17. The method according to claim 16, wherein precisely one type of luminescence is detected and/or the luminescent substance emits precisely one type of luminescence and/or the value document has precisely one luminescent substance and/or the intensity course of the luminescence is mono-exponential.

18. The method according to claim 16, wherein the excitation source gives off an excitation pulse, a light pulse, for luminescence excitation, and in that the detected intensity courses are respectively composed of a sequence of several, precisely two or three, discrete intensity values which are detected at respectively predetermined measurement times relative to the excitation pulse, respectively up to a predetermined end time point of measurement.

19. The method according to claim 16, wherein the further step of: selecting the second plurality of intensity courses from the first plurality on the basis of a selection criterion, wherein the selection criterion is met when an intensity value at a predetermined time point of measurement, or a value derived therefrom, reaches or exceeds a predetermined threshold value, wherein the predetermined time point of measurement is the first time point of measurement after the end of the respective luminescence excitation, including the first time point of measurement after the end of the respective excitation pulse.

20. The method according to claim 16, wherein the value documents are transported past the sensor at a transport speed in the range of 1 to 12 m/s.

21. The method according to claim 16, wherein the characteristic time constant τ0 of the luminescence of the value document lies in the range of 10 .Math.s to 5 ms.

22. The method according to claim 16, wherein the combining of the first or second plurality of intensity courses is effected component-by-component, wherein the component-by-component combining is effected by addition, averaging, quantile or median determination of the first or second plurality of intensity courses.

23. The method according to claim 16, wherein the determination of the time constant τ of the combined intensity course is carried out via a non-linear least-square fit, a linear least-square fit to the logarithmized intensity course, the decay quotient, the derivative function or the antiderivative function.

24. The method according to claim 16, wherein the value documents are transported past the sensor at a predetermined, constant transport speed, for example with the help of a transport device, and/or that the excitation source excites the value document over the full area or excites the value document at least in a partial region which contains a capture region which is swept over by a detection region of a photodetector of the sensor during the detecting of the respective intensity course.

25. The method according to claim 16, wherein the first plurality is 2, 3, 4, 6, 8, 10, 12, 16, 20, 25, 30, 40, 50, 70, 100 or more.

26. The method according to claim 16, wherein the first plurality is at least 4.

27. The method according to claim 16, wherein the first plurality of intensity courses is detected, sequentially, from different locations on the value document, wherein the first plurality of intensity courses is detected in the transport direction one after another, side by side and one after another or exclusively one after another.

28. A sensor for checking value documents, comprising: at least or precisely one excitation source for exciting a luminescence of a value document, and one or more photodetectors for detecting an intensity course of the luminescence which the value document, excited by the excitation source, sends out in a detection region, a control device which is designed for driving the photodetector(s) such that the photodetector(s) detect(s) a first plurality of intensity courses on the value document, an evaluation device which is designed for combining the first plurality of intensity courses or a second plurality of intensity courses selected from the first plurality into a combined intensity course, determining a time constant τ of the combined intensity course, checking the value document on the basis of the time constant τ of the combined intensity course, with regard to its authenticity and/or with regard to its value-document type.

29. The sensor according to claim 28, wherein the sensor, including the control device and/or the evaluation device, is designed for carrying out the method according to a method for checking value documents which are transported for their checking past a sensor in a transport direction, and which have a security feature with a luminescent substance which, as a reaction to a luminescence excitation by an excitation source, emits a luminescence which has as a function of time t an intensity course with a characteristic time constant τ0, having the following steps: detecting a first plurality of intensity courses on a value document, combining the first plurality of intensity courses or a second plurality of intensity courses selected from the first plurality into a combined intensity course, determining a time constant τ of the combined intensity course, checking the value document, with regard to its authenticity and/or with regard to its value-document type, on the basis of the time constant τ of the combined intensity course.

30. An apparatus for processing value documents, having a sensor according to claim 28 and having a transport device for transporting the value documents past the sensor, wherein the control device of the sensor is devised to drive the excitation source such that the excitation source excites the luminescence precisely or at least one capture region on the value document which is swept over by the detection region during the detecting of the respective intensity course.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Further advantages of the invention will be described hereinafter on the basis of the embodiment example explained in the accompanying figures. The exemplary embodiment represents a preferred embodiment which in no way limits the invention. The figures shown are schematic representations which do not necessarily reflect the real proportions, but rather serve for improved clarity of the embodiment example. Specifically, the figures show:

[0048] FIG. 1 a schematic view of an embodiment example with a value document and a stationary sensor in an apparatus for processing value documents;

[0049] FIG. 2 a plan view of a value document; and

[0050] FIG. 3 a diagram with intensity courses.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0051] FIG. 1 schematically shows a detail of an apparatus 1 for processing value documents 2 which can be designed for checking and optionally sorting the value documents. In it a value document 2, in the present case a bank note, is transported past a sensor 3 along a transport direction at a constant speed of, for example, 10 m/s with the help of a transport device (transport belt 11 or transport rollers) of the apparatus 1. In the present case, the sensor 3 consists of an excitation source 4 in the form of a pulsed light source which, with the aid of the excitation pulses or light flashes having a duration of for example 10 .Math.s, respectively excites at least one partial region of the value document 2. The sensor 3 further comprises a photodetector 5, in the present case in the form of a photodiode, on whose light-sensitive region a surface of the value document 2 is imaged, for example as schematically represented in FIG. 1 with the aid of two lenses. An optical filter, for example for shielding the excitation light and/or for selecting the spectral component of the luminescence to be detected, can furthermore be provided between the lenses. In the present embodiment example, a circular detection region 5a with a diameter of 5 mm results from the area of the light-sensitive region of the photodetector due to the enlargement of the optical imaging in the plane of the value document 2. Furthermore, the stationary sensor 3 comprises an evaluation device 8 which reads out the detected intensity values of the photodetector 5 and carries out the checking of the value document. The control device 9 initiates the sending out of the excitation pulses of the excitation source 4 and the detecting of the measurement values with the photodetector 5.

[0052] In FIG. 2, the value document 2 transported in transport direction T is shown in plan view. Here, the luminescent substance is uniformly distributed in value document 2, wherein the value document 2 is provided in a partial region with an intensity-reducing overprinting 6 which reduces the existing intensity of the detectable luminescent radiation to 10% of the remaining, not-covered region of the value document 2.

[0053] Furthermore, FIG. 2 shows the capture regions 7a - 7d of four intensity measurements a - d which are respectively swept over by the detection region 5a of the photodetector 5 during the detection of the intensity courses. The detection region 5a shown in dashed lines in FIG. 2 corresponds to the detection region of the photodetector 5 at the beginning of the first measurement a, that is to say at its time point of measurement zero, at or immediately after the end of the excitation pulse associated with this measurement. During the four measurements a to d outlined by way of example in FIG. 2, the intensity courses a to d schematically illustrated in FIG. 3 are detected. In the process, the respectively associated excitation pulse excites at least the respective capture region 7a to 7d. Shown are respectively measurements with a duration of 2 ms, in which the value document 2 moves by 20 mm at a transport speed of 10 m/s. As can be seen from FIG. 2, the first measurement a takes place in the capture region 7a, which is located exclusively in the not-covered region of the value document 2. Correspondingly, an intensity course not falsified by the spatial structures of the value document 2 is detected here (intensity course a in FIG. 3). The intensity course a detected in measurement a therefore decreases mono-exponentially with a decay constant of 500 .Math.s in the present case.

[0054] During the subsequent measurement b, the capture region 7b lies both in the not-covered region of the value document 2 and in the overprinted region 6 and sweeps over a leading edge of the overprinted region 6. At the beginning of the measurement, after giving off the relevant excitation pulse, the detection region 5a lies still completely in the not-covered region. After 500 .Math.s, the detection region 5a begins to enter the overprinting 6 and at 1000 .Math.s lies completely in the overprinted region. Therefore, the intensity course b detected in the measurement b begins to drop at a time of measurement of 500 .Math.s (in addition to the exponential drop) and reaches an intensity value of 10% of the undistorted intensity value at a time of measurement of 1000 .Math.s and then further drops off exponentially.

[0055] The third measurement c takes place exclusively in the overprinted region. Correspondingly, an exclusively mono-exponential drop results here (intensity course c in FIG. 3) which, however, amounts to only 10% of the intensity of intensity course a at each time point of measurement.

[0056] During the fourth measurement d, the capture region 7d again sweeps over an edge, here the trailing edge of the overprinting 6, so that the measurement first begins in the overprinted region. At a time point of measurement of 700 .Math.s, the detection region 5a begins to emerge from the overprinting 6, so that here (see intensity course d in FIG. 3) an increase of the intensity results, so that as of a time point of measurement of 1200 .Math.s the intensity measured in measurement d corresponds to the intensity of the intensity course a.

[0057] Furthermore, FIG. 3 illustrates the intensity course combined component-by-component, which results from component-by-component averaging of the four intensity courses a to d. The time constant τ is then determined on the basis of the combined intensity course e. In the present case this is done on the basis of the decay quotient according to above Formula 1, wherein for this purpose the intensity values at the time points of measurement 10 .Math.s and 1000 .Math.s are employed. For comparison, the decay time τ determined according to the derivative function (Formula 2) is also shown, with T = 1000 .Math.s and Δ = 10 .Math.s, wherein for this purpose the intensity values at the time points of measurement of 990 .Math.s, 1000 .Math.s and 1010 .Math.s are employed (which are not explicitly listed in the table, however).

[0058] The table below shows the various detected intensity values and the decay times obtained therefrom.

TABLE-US-00001 Intensity values Time constant τ avg. 10 .Math.s 1000 .Math.s (Formula 1) (Formula 2) Intensity course a 0.9802 0.1353 500 .Math.s 500 .Math.s Intensity course b 0.9802 0.0257 273 .Math.s 87 .Math.s Intensity course c 0.0980 0.0135 500 .Math.s 500 .Math.s Intensity course d 0.0980 0.0744 3387 .Math.s -785 .Math.s Average of the time constant (prior art) 1165 .Math.s 75 μs Intensity values or time constant of the combined intensity course (invention) 0.53911 0.0622 459 .Math.s 500 .Math.s Actual time constant of the luminescence: 500 .Math.s

[0059] It can be seen from the measurements a and c, in which no edge of the overprinting 6 is swept over during the detecting of the intensity course (capture regions 7a and 7c), the correct, actual decay time or time constant τ.sub.0 von 500 .Math.s results with both calculation methods according to Formula 1 as well as Formula 2. However, as soon as the spatial structures, in the present case the edges of the overprinting 6, of the value document 2 are swept over during the detecting of an intensity course (measurements b and d; capture regions 7b and 7d), completely incorrect decay times (negative decay time of -785 .Math.s) result in both calculation methods. The shown time-constant averaging, which is characterized as prior art and based on the time constants τ determined in the four measurements (intensity courses a to d), also results respectively in averaged time constants τ of 1165 .Math.s or 75 .Math.s, which deviate markedly from the actual value of 500 .Math.s.

[0060] If, on the other hand, as described in the present case, the intensity values of the four individual courses a to d are first combined component-by-component, that is to say respectively at the same time points of measurements, into a common intensity course (combined intensity course e) and the time constant τ is only determined therefrom in accordance with the Formulae 1 and/or 2, then time constants τ result with both calculation methods which do not deviate or deviate only slightly, from the actual value of τ.sub.0 = 500 .Math.s.

[0061] In the embodiment example illustrated above, on the basis of the four measurements a to d, the intensity courses typically occurring during a determination of the luminescence drop, of which a subset is falsified due to the spatial structures of the value document 2, are illustrated merely by way of example. However, the greater the number of detected intensity courses, which are initially combined to form a common intensity course, the closer statistically the combined intensity course will lie to the undistorted decay curve of the luminescent substance (scaled by a factor which reflects the average coverage/shielding yet does not matter in the calculation of the time constant τ) and accordingly the closer the time constant τ determined on the combined intensity course will lie to the actual value τ.sub.0.

[0062] Thus, the present invention provides an approach for determining a time constant τ which reliably deviates only slightly from the (expected) characteristic time constant τ.sub.0 of the luminescent substance employed, and which in the process is largely independent of the spatial structures specifically present on the value document 2 and thus requires no knowledge of the actual local distribution of the luminescent substance or of any shielding on the value document 2. Thus, the present invention can be applied to many value documents designed differently in terms of the distribution of the luminescent substance or any shielding, without requiring knowledge of the position of the corresponding spatial structures.