SENSOR FOR VERIFYING VALUE DOCUMENTS

Abstract

A sensor for verifying value documents and designed to determine the luminescence time constant of a value document that is moved past the sensor for verification purposes, and the provision of a velocity correction of the luminescence time constant of the value document in the sensor. The relative movement between the value document and the sensor causes movement effects, resulting in a distortion of the intensity curve from which the luminescence time constant is derived. The luminescence time constant is corrected using a sensor-specific corrective factor ascertained for the velocity of the movement of the value document during the verification process. For this purpose, different sensor-specific corrective factors are used for different examples of sensors that are nominally identical in design and are part of the same sensor production series.

Claims

1.-26. (canceled)

27. A method for providing a velocity correction of a luminescence time constant of a value document in a sensor which is configured for measuring a change over time in a luminescence of the value document while the respective value document is transported past the sensor, and which is configured for determining the luminescence time constant of the respective value document on the basis of the measured change over time in the luminescence and for verifying the luminescence of the respective value document, comprising the following steps: a) determining at least one sensor-specific parameter on the basis of a measurement at the sensor or on the basis of a measurement with the aid of the sensor, b) storing the at least one sensor-specific parameter in the sensor, c) providing a velocity correction, which, during the verification of the luminescence of a value document transported past the sensor at a verification transport velocity, is usable for correcting a luminescence time constant determined for the respective value document, in a correction device of the sensor, wherein the correction device, for the velocity correction of the luminescence time constant of the respective value document, is configured: on the basis of the at least one sensor-specific parameter stored in the sensor and by means of information made available in the sensor regarding the verification transport velocity of the value document, to determine a sensor-specific correction factor which is applicable to the verification transport velocity of the value document to be verified in each case, and to correct the luminescence time constant determined for the value document with the aid of the sensor-specific correction factor applicable to the verification transport velocity of the value document in order to determine a corrected luminescence time constant for the value document, wherein the sensor is designed to verify the luminescence of the respective value document on the basis of the corrected luminescence time constant.

28. The method according to claim 27, wherein a velocity dependence of a sensor-generally applicable correction factor is stored in the sensor, which velocity dependence assigns in each case a sensor-generally applicable correction factor to different possible transport velocities of a value document to be verified, and the sensor-generally applicable correction factor applicable to the verification transport velocity of the respective value document is used for the velocity correction of the luminescence time constant determined for the respective value document.

29. The method according to claim 27, wherein at least one correction assignment, in particular offset value assignment or correction table or correction formula, is stored in the sensor, which correction assignment, for different possible sensor-specific offset values of the sensor, assigns in each case an offset-dictated correction factor to in each case different possible transport velocities of a value document to be verified, and in that during the velocity correction it is provided that on the basis of the correction assignment, in particular on the basis of the offset value assignment or correction table or correction formula, with the aid of the sensor-specific parameter stored in the sensor, the sensor-specific correction factor is determined which is applicable to the sensor-specific parameter of the sensor stored in the sensor and to the verification transport velocity of the value document, and the luminescence time constant of the value document is corrected with the aid of the sensor-specific correction factor determined on the basis of the correction assignment and applicable to the verification transport velocity.

30. The method according to claim 27, wherein the correction device is configured to determine the sensor-specific correction factor applicable to the verification transport velocity depending on information made available to the sensor regarding the transport direction of the value document to be verified relative to the sensor and/or wherein the correction device is configured to determine the sensor-specific correction factor applicable to the verification transport velocity depending on information made available to the sensor regarding a target value of the luminescence time constant of the value document to be verified.

31. The method according to claim 27, wherein the sensor-specific parameter stored in the sensor is a sensor-specific offset value of the sensor, which is characteristic of a sensor-specific offset along the transport direction of the value document between an illumination region and a detection region of the sensor, in particular a sensor-specific offset length of the sensor, which indicates the distance along the transport direction of the value document between the illumination region and the detection region.

32. The method according to claim 27, wherein in step a) when determining the sensor-specific parameter, the following steps are carried out: a1) transporting a reference medium provided with a reference luminescent material past the sensor at a reference transport velocity along a transport direction, wherein the reference luminescent material has a specified luminescence time constant, and a2) measuring the change over time in the luminescence of the reference luminescent material by means of the sensor at the reference transport velocity while the reference medium is transported past, and a3) determining a reference medium time constant of the reference luminescent material for the reference transport velocity on the basis of the change over time in the luminescence of the reference luminescent material measured at the reference transport velocity, and a4) determining a specific sensor-specific correction factor applicable to the reference transport velocity on the basis of the determined reference medium time constant of the reference luminescent material and on the basis of the specified luminescence time constant of the reference luminescent material, and wherein in step b) when storing the sensor-specific parameter in the sensor, the following steps are carried out: b1) storing the specific sensor-specific correction factor applicable to the reference transport velocity as a sensor-specific parameter in the sensor or b2) storing a sensor-specific offset parameter, which was determined on the basis of the specific sensor-specific correction factor and the value of the reference transport velocity, as a sensor-specific parameter, and wherein in step c) when providing the velocity correction, the correction device, for the velocity correction of the luminescence time constant of the respective value document, is configured to determine, in particular to calculate, the sensor-specific correction factor which is applicable to the verification transport velocity of the value document to be verified in each case by means of information made available to the sensor regarding the verification transport velocity of the value document and on the basis of the specific sensor-specific correction factor stored in the sensor and optionally the value of the reference transport velocity stored in the sensor or on the basis of the sensor-specific offset parameter of the sensor stored in the sensor, if the verification transport velocity does not correspond to the reference transport velocity.

33. The method according to claim 32, wherein the specific sensor-specific correction factor applicable to the reference transport velocity and the value of the reference transport velocity have been/are stored in the sensor, and for the velocity correction it is provided that on the basis of the specific sensor-specific correction factor and the value of the reference transport velocity and the sensor-generally applicable correction factor applicable to the reference transport velocity the sensor-specific offset parameter of the sensor is ascertained, and the sensor-specific correction factor which is applicable to the verification transport velocity of the value document is determined on the basis of the ascertained sensor-specific offset parameter of the sensor, wherein the sensor-specific offset parameter of the sensor is calculated on the basis of the specific sensor-specific correction factor and the value of the reference transport velocity and the ideal correction factor applicable to the reference transport velocity, in particular with the aid of the following calculation formula:
a=(K(v0)?K0(v0))/(K0(v0).Math.arctan(v0/3)).

34. The method according to claim 32, wherein a correction table has been/is stored in the sensor, which correction table indicates for a plurality of possible offset parameters in each case the offset-dictated correction factor applicable to the respective offset parameter as a function of the transport velocity of the value document, and in that during the velocity correction it is provided that in order to ascertain the sensor-specific correction factor applicable to the verification transport velocity the sensor-specific correction factor which is applicable to the verification transport velocity of the value document and the respective sensor is determined on the basis of the correction table, and the luminescence time constant of the value document is corrected with the aid of the sensor-specific correction factor determined on the basis of the correction table.

35. The method according to claim 32, wherein in the sensor the velocity dependence of the sensor-generally applicable correction factor has been/is stored, and the sensor-specific offset parameter has been/is stored or, for the velocity correction, is determined from the specific sensor-specific correction factor, and a correction formula has been/is stored, which is designed for calculating the sensor-specific correction factor on the basis of the sensor-specific offset parameter and also on the basis of the verification transport velocity of the value document and on the basis of the sensor-generally applicable correction factor applicable to the verification transport velocity of the value document, and in that during the velocity correction it is provided that the sensor-generally applicable correction factor applicable to the verification transport velocity of the value document is determined on the basis of the velocity dependence of the sensor-generally applicable correction factor, and by means of the correction formula, the sensor-specific correction factor of the sensor applicable to the verification transport velocity is calculated on the basis of the sensor-generally applicable correction factor applicable to the verification transport velocity of the value document, and the sensor-specific offset parameter of the sensor and the value of the verification transport velocity of the value document, for example by means of the correction formula
K(vP)=(K0(vP).Math.(1+a.Math.arctan(vP/3)).

36. The method according to claim 27, wherein the method is carried out for a plurality of sensor specimens of the same sensor type series, wherein the sensor-specific parameter, in particular the specific sensor-specific correction factor or the sensor-specific offset value, is determined in a manner specific to each sensor specimen and is stored in the respective sensor specimen.

37. The method according to claim 27, wherein a velocity dependence of the sensor-specific correction factor is stored in the sensor, which velocity dependence assigns in each case a sensor-specific correction factor applicable to the respective transport velocity to different possible transport velocities of the value document, and in that in step c) when providing the velocity correction, the correction device for the velocity correction of the luminescence time constant of the respective value document is configured, on the basis of the velocity dependence of the sensor-specific correction factor stored in the sensor and by means of information made available to the sensor regarding the verification transport velocity of the value document, to determine the sensor-specific correction factor which is applicable to the verification transport velocity of the value document.

38. The method according to claim 32, wherein determining the sensor-specific parameter in accordance with steps a1) to a4) is carried out at the sensor successively for a plurality of different reference transport velocities of the reference medium, wherein for each of the reference transport velocities in each case a specific sensor-specific correction factor is determined for the respective reference transport velocity on the basis of a respectively determined reference medium time constant of the reference luminescent material and on the basis of the specified luminescence time constant of the reference luminescent material, the velocity dependence of the sensor-specific correction factor is determined from the specific sensor-specific correction factors of the different reference transport velocity, and the velocity dependence of the sensor-specific correction factor applicable to the respective sensor is stored in the sensor.

39. A sensor for verifying value documents which, for their verification, are transported past the sensor along a transport direction at a verification transport velocity, wherein the sensor comprises at least one excitation light source for exciting a luminescence of the value document, and comprises at least one photodetector for detecting the luminescence of the value document excited by the excitation light source, is configured for measuring the change over time in the luminescence of the value document while the value document is transported past the sensor, by means of the at least one photodetector, and comprises an evaluation device configured to determine a luminescence time constant of the value document at the verification transport velocity on the basis of the measured change over time in the luminescence of the value document, and comprises a correction device, in which is provided a velocity correction for correcting the luminescence time constant determined for the respective value document, and wherein at least one sensor-specific parameter is stored in the sensor, and wherein the correction device, for correcting the luminescence time constant of the value document transported past the sensor at a verification transport velocity, is configured, on the basis of the at least one sensor-specific parameter stored in the sensor and by means of information made available to the sensor regarding the verification transport velocity, to determine a sensor-specific correction factor which is applicable to the verification transport velocity of the value document, and wherein the sensor, in particular the correction device or the evaluation device of the sensor, is configured to correct the luminescence time constant determined for the value document with the aid of the at least one sensor-specific correction factor applicable to the verification transport velocity of the value document, in order to determine a corrected luminescence time constant for the value document, and wherein the sensor, in particular the evaluation device of the sensor, is configured to verify the luminescence of the respective value document on the basis of the corrected luminescence time constant.

40. The sensor according to claim 39, wherein the method was carried out at the sensor, wherein the sensor, in particular the correction device of the sensor, contains the velocity correction.

41. The sensor according to claim 39, wherein the sensor-specific parameter stored in the sensor is a sensor-specific offset value of the sensor, which is characteristic of the sensor-specific offset along the transport direction of the value document between an illumination region and a detection region of the sensor, in particular a sensor-specific offset length of the sensor, which indicates the distance along the transport direction of the value document between the illumination region and the detection region, and/or wherein the sensor-specific parameter stored in the sensor is a specific sensor-specific correction factor which is applicable specifically to the respective sensor and to a reference transport velocity of the value document.

42. The sensor according to claim 39, wherein at least one correction assignment, in particular offset value assignment or correction table or correction formula, is stored in the sensor, which correction assignment, for different possible sensor-specific offset values of the sensor, assigns in each case an offset-dictated correction factor to in each case different possible transport velocities of the value document to be verified, and in that during the velocity correction it is provided that on the basis of the correction assignment, in particular offset value assignment or correction table or correction formula, with the aid of the sensor-specific parameter stored in the sensor, the sensor-specific correction factor is determined which is applicable to the sensor-specific parameter of the sensor stored in the sensor and to the verification transport velocity of the value document, and the luminescence time constant is corrected with the aid of the sensor-specific correction factor determined on the basis of the correction assignment and applicable to the verification transport velocity.

43. The sensor according to claim 39, wherein at least one velocity dependence, of the sensor-specific correction factor is stored in the sensor, which velocity dependence assigns in each case a sensor-specific correction factor to different transport velocities, and the correction device for correcting the luminescence time constant of the value document transported past the sensor at the verification transport velocity is configured, by means of the information made available to the sensor regarding the verification transport velocity, on the basis of the velocity dependence of the sensor-specific correction factor stored in the sensor, to determine the sensor-specific correction factor which is applicable to the verification transport velocity of the value document.

44. The sensor according to claim 39, wherein the correction device is configured to determine the sensor-specific correction factor applicable to the verification transport velocity depending on information made available to the sensor regarding the verification transport direction of the value document to be verified relative to the sensor.

45. The sensor according to claim 39, wherein the correction device is configured to determine the sensor-specific correction factor applicable to the verification transport velocity depending on information made available to the sensor regarding a target value of the luminescence time constant of the value document to be verified.

46. An apparatus for processing value documents comprising a sensor according to claim 39, and a transport device for transporting the value document to be verified in each case past the sensor along a transport direction at a verification transport velocity.

47. A method for verifying value documents by means of the sensor according to claim 39, wherein the following steps are carried out: A) transporting a value document to be verified past the sensor along a transport direction at a verification transport velocity and measuring the change over time in the luminescence of the value document by means of the sensor while said value document is transported past, B) making available information regarding the verification transport velocity of the value document in the sensor, C) determining a sensor-specific correction factor which is applicable to the verification transport velocity of the value document on the basis of the sensor-specific parameter stored in the sensor and by means of the information made available to the sensor regarding the verification transport velocity, D) determining a luminescence time constant of the value document at the verification transport velocity on the basis of the measured change over time in the luminescence of the value document, E) correcting the luminescence time constant of the value document with the aid of the sensor-specific correction factor applicable to the verification transport velocity of the value document in order to determine a corrected luminescence time constant for the value document, F) verifying the value document on the basis of the corrected luminescence time constant.

Description

[0103] The invention is explained below by way of example with reference to the following figures, in which:

[0104] FIG. 1 shows a schematic set-up of a value document processing apparatus comprising the sensor;

[0105] FIG. 2a shows an excitation pulse of the luminescence excitation,

[0106] FIG. 2b shows a temporal profile of the luminescence intensity emitted by a value document in the case of a static verification (v=0),

[0107] FIGS. 2c-d show a temporal profile of the luminescence intensity of the value document at a transport velocity v=vP for a first sensor specimen (FIG. 2c) and for a second sensor specimen (FIG. 2d), different therefrom, of the same sensor type series,

[0108] FIG. 2e shows a velocity dependence K(v) of the sensor-specific correction factor for the first and second sensor specimens and as a mathematical function G(v) for two opposite transport directions for a third sensor specimen, [0109] FIG. 3 shows a schematic plan view of the measurement plane of the sensor with various offset lengths d.

[0110] The decay time of the luminescence is used hereinafter as an example of the luminescence time constant. However, the invention equally relates to other luminescence time constants, such as e.g. the luminescence build-up time or others.

[0111] FIG. 1 shows by way of example the schematic set-up of a value document processing apparatus 1 comprising an introduction compartment 2, in which a stack of value documents 3 to be processed is provided, and a separator 8, which successively detects in each case one (e.g. the respective bottommost or topmost) value document of the introduced stack and transfers it to amerely schematically represented in the illustration chosentransport device 10 (transport belts and/or transport rollers), which transports the value documents past a sensor 25 in the transport direction x.

[0112] In the example illustrated, the sensor 25 comprises a photodetector 20 comprising at least one photosensitive element which converts the luminescence intensities emitted by the value document transported past into corresponding sensor signals. The photodetector 20 can also comprise a plurality of such photosensitive elements, e.g. for different spectral components of the luminescence light. The sensor 25 can also be designed for verifying the value documents 3 in one or more measurement tracks on the respective value document, wherein a respective photodetector 20 having one or more photosensitive elements is present for each of the measurement tracks. The optical excitation of the value documents is effected e.g. by means of excitation light sources 23, 24 arranged on both sides of the photodetector 20, which illuminate the value document with excitation light in an illumination region 6, cf. FIG. 3. The sensor 25 is arranged on the left-hand side of the transport pathas viewed in the transport direction x of the value documents. Another sensor 29 can be arranged opposite the sensor 25, on the right-hand side of the transport path. The photodetector 20 is designed for the temporally resolved measurement of the luminescence of the value documents during or after the end of the optical excitation. For this purpose, the photodetector 20 is controlled by a control device of the sensor (not shown) in such a way that it detects the luminescence of the detection region 9 (cf. FIG. 3) at a plurality of detection times t, (i=1, . . . , n).

[0113] The sensor signals detected from the measurement location to be verified of the value documents are forwarded to an evaluation device 22 of the sensor by the photodetector. The evaluation device 22 can be contained in the housing of the sensor 25 or outside that, e.g. in a central evaluation device of the value document processing apparatus 1. The evaluation device 22 determines the luminescence time constant t(vP) on the basis of the sensor signals detected at the different detection times. One or more sensor-specific parameter(s)depending on the exemplary embodiment either the sensor-specific correction factor K(v0) or the offset parameter a or the offset length d or the velocity dependence of the sensor-specific correction factor K(v)are stored in a memory area 26 of the evaluation device 22. A correction device 21 of the evaluation device 22 can access the information stored in the memory area 26 in order to use it for the velocity correction of the luminescence time constant.

[0114] Further information can be stored in the memory area 26, such as e.g. information regarding the verification transport velocity vP of the value documents, which can be different depending on the type or setting of the value document processing apparatus 1. Moreover, one or more tables and/or one or more mathematical functions can also be stored in the memory area 26, which are used during the velocity correction of the luminescence time constant, cf. the following exemplary embodiments.

[0115] From the intensity values of the value documents measured by the photodetector 20 at the detection times t, (i=1, . . . , n), the evaluation device determines the luminescence time constant t(vP) of a security feature of the value documents and transfers it to the correction device 21, which carries out the velocity correction according to the invention on the basis of the sensor-specific parameter(s) stored in the memory area 26 and by means of the information regarding the verification transport velocity vP of the value documents. The luminescence time constant t*(vP) corrected by the correction device 21 is then used by the evaluation device 22 as a verification criterion for the value documents, in particular for assessing the authenticity of the value documents.

[0116] Depending on the authenticity of the respective value document ascertained by the evaluation device 22, the diverters 11 and 12 along the transport path are controlled by the control device 50 in such a way that the value document is transported into one of the dispensing compartments 30, 31 of the value document processing apparatus 1. By way of example, value documents which were recognized as authentic are placed in a first dispensing compartment 30, while value documents categorized as inauthentic or suspected counterfeit are placed in a second dispensing compartment 31. At the end of the illustrated transport path (reference numeral 13), further dispensing compartments and/or other devices can be provided, for example for storing or for destroying value documents, such as e.g. cassettes for protected storage of the value documents or a shredder. If a value document was not able to be recognized, for example, then for such a value document a special dispensing compartment can be provided, into which value documents of this type are placed and provided for a separate treatment, for example by an operator.

[0117] In the example illustrated, the value document processing apparatus 1 furthermore comprises an input/output device 40 for the input of data and/or control commands by an operator, for example by means of a keyboard or a touchscreen, and for the output or display of data and/or information concerning the processing process, in particular concerning the value documents processed in each case.

[0118] FIGS. 2a-c show the temporal behavior of the luminescence of a value document that is emitted by a luminescent security feature of the value document. FIG. 2a shows the intensity profile of the optical excitation pulse A, which is directed at the value document for luminescence excitation and ends at the time t=0. FIG. 2b illustrates the intensity profile I0(t) detected during a static measurement as a function of the time after the end (t=0) of the excitation pulse A, i.e. when the value document is not moved relative to the detector (v=0). Such a static measurement is carried out e.g. during a manual verification of individual value documents. In the example considered, the luminescence is detected at three detection times t1, t2, t3, cf. FIG. 2b. During the static measurement, the detected luminescence intensity of the security feature decays with the specified luminescence time constant t0 of the security feature, e.g. where t0=250 ?s. During the static measurement, different sensor specimens 25a, 25b of the same sensor type series yield the same measurement result of the luminescence time constant.

[0119] If, during the mechanical verification in a value document processing apparatus, the same value document is transported at a transport velocity of e.g. vP=8 m/s past a first sensor specimen 25a of a particular sensor type series, the photodetector 20 of said sensor specimen detects the intensity profile Ia(t)illustrated in FIG. 2cas a function of the time after the end (t=0) of the excitation pulse A emitted by the excitation light sources 23, 24. For comparison purposes, the intensity profile I0(t) detected in the static case with the decay time t0 is also illustrated in a dashed manner in FIG. 2c. The decay time ta resulting from the intensity profile Ia(t) is ta=147 ?s and is thus distinctly shorter than the decay time t0=250 ?s of the static measurement.

[0120] The relative movement of the value document relative to the sensor 25 has the effect that a shorter decay time ta is determined than in the static case. This results from the fact that during the detection the value documents continue to be moved by a certain length which is comparable with the size of the detection region and illumination region. The position of the illumination region on the value document thus changes during the measurement, and the measured intensity profile at the detector corresponds to a convolution from the temporal behavior of the luminescent material and the movement-dictated change in the overlap between the illumination region and the detection region on the value document.

[0121] FIG. 2d illustrates the corresponding intensity profile Ib(t) of the same value document when the latter, during the mechanical verification of the value documents in the value document processing apparatus 1, is transported at the same verification transport velocity of e.g. vP=8 m/s past a second sensor specimen 25b, which belongs to the same sensor type series as the sensor specimen 25a, i.e. is nominally structurally identical thereto. The decay time tb resulting from the intensity profile Ib(t) of the second sensor specimen 25b is tb=179 ?s and thus lies between the decay time ta of the sensor specimen 25a of 147 ?s and the decay time t0=250 ?s of the static measurement. Despite the sensor specimens 25a and 25b being nominally structurally identical, very different decay times ta, tb are thus determined from the same value document at a verification velocity vP?0.

[0122] It is assumed that these differences in the decay times ta, tb, or generally of the luminescence time constants, crucially result from geometric inaccuracies of the position and/or the angle of the optical excitation and of the photodetector, and also the installation position of the sensor in the value document processing apparatus. Since these inaccuracies vary from one sensor specimen to another, a sensor-specific correction of the measured luminescence time constant is carried out according to the invention.

[0123] In order to take account of the sensor-specific differences, one or more sensor-specific parameter(s) applicable specifically to the respective sensor specimen are used for the velocity correction of the luminescence time constant. The determination of the sensor-specific parameter(s) is carried out e.g. before the delivery of the sensor by the sensor manufacturer or after delivery of the sensor to the customer during a sensor calibration which is occasionally carried out and in which the sensor can be installed in the value document processing apparatus or else in a sensor measuring station provided specially for this purpose. During calibration, the respective sensor can e.g. also be adjusted with regard to the detected intensity.

1st Exemplary Embodiment

[0124] In the first exemplary embodiment, a single, specific sensor-specific correction factor K(v0) ascertained by means of a reference medium transported past the sensor is used as a sensor-specific parameter. The reference medium is provided with a reference luminescent material and is in sheet form, for example. The ascertainment of the specific sensor-specific correction factor K(v0) is carried out by the sensor manufacturer orafter the delivery of the sensorduring the calibration of the sensor installed in the value document processing apparatus.

[0125] As an example, a reference medium is considered whose reference luminescent material has a specified luminescence time constant, in particular decay time, of tR0=250 appropriately matching the value document to be verified. In order to determine the sensor-specific correction factor K(v0), the reference medium is transported past the respective sensor specimen once at a reference transport velocity v0. For this reference transport velocity v0, a temporally resolved measurement of the luminescence emitted by the reference luminescent material is detected by the photodetector 20 of the sensor. The measured change over time in the luminescence of the reference medium is used to determine a reference medium time constant tR(v0) of the reference luminescent material for the reference transport velocity v0. On the basis of the determined reference medium time constant tR(v0) and on the basis of the specified luminescence time constant tR0 of the reference luminescent material, a specific sensor-specific correction factor K(v0) for the reference transport velocity v0 is determined. By way of example, this is done by forming the relationship K(v0)=tR0/tR(v0) between the reference medium time constant tR(v0) determined for the reference transport velocity v0 and the specified luminescence time constant of the reference luminescent material tR0. The specific sensor-specific correction factor K(v0) which was determined in a manner specific to the respective sensor is stored in the memory area 26 of the evaluation device 22 and assigned there to the reference transport velocity v0, the value of which is likewise stored in the memory area 26.

[0126] For the sensor specimen 25a, a decay time tR(v0)=147 ?s was determined with this reference medium at the reference transport velocity v0=8 m/s. A value of K(v0)=1.70 thus results as a specific sensor-specific correction factor K(v0), which value is stored in a manner linked with the reference transport velocity v0=8 m/s in the memory area 26 of the sensor specimen 25a.

[0127] For the sensor specimen 25b, by contrast, a decay time tR(v0)=179 ?s was determined with the same reference medium at the reference transport velocity v0=8 m/s. A value of K(v0)=1.40 thus results as a specific sensor-specific correction factor K(v0), which value is stored in a manner linked with the reference transport velocity v0=8 m/s in the memory area 26 of the sensor specimen 25b.

[0128] In addition to the specific sensor-specific correction factor K(v0), a sensor-generally applicable correction assignment, e.g. a correction table T or a correction formula F, is stored in the memory area 26 of the respective sensor.

1st Exemplary EmbodimentFirst Variant

[0129] In a first variant of the first exemplary embodimentbefore delivery of the sensorsa correction table T usable for all the sensor specimens of this sensor type series is created for the velocity correction of the luminescence time constants, which correction table is then stored in the memory area 26 of the respective sensor 25 together with the specific sensor-specific correction factor K(v0).

[0130] In order to determine the values contained in the correction table T, an ideal reference sensor 25R4 is used, for example, which is known to have no offset between its illumination region and its detection region. The reference medium mentioned above is transported past the reference sensor 25R4 at different transport velocities v and a temporally resolved measurement of the luminescence emitted by the reference luminescent material is detected by the photodetector 20 of the reference sensor. The measured change over time in the luminescence of the reference medium is used to determine in each case the reference medium time constant tR(v) of the reference luminescent material for the respective transport velocity v. On the basis of the reference medium time constant tR(v) of the reference luminescent material and on the basis of the specified luminescence time constant tR0=250 ?s of the reference luminescent material, the relationship tR0/tR(v) is formed in each case. This yields the velocity dependence of an ideal correction factor K0(v) as indicated in table 1. The correction factors indicated therein are applicable to a sensor of this sensor type series which has no spatial offset between its illumination region and its detection region.

TABLE-US-00001 TABLE 1 Correction factors for the ideal reference sensor 25R4 Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 Decay time 250 225 212 200 185 172 160 149 138 128 tR(v) [?s] Correction factor 1 1.11 1.18 1.25 1.35 1.45 1.56 1.68 1.81 1.96 K0(v)

[0131] In the case of a sensor type series which has a predefined offset between the illumination region and the detection region of the sensors owing to the dictates of design, a reference sensor is used in which the offset corresponds exactly to the predefined offset, and a correction table is thus created whose correction factors are applicable to a sensor (which is ideal for the sensor type series) whose offset between illumination region and detection region corresponds exactly to the predefined offset.

[0132] In order to determine the correction table T mentioned above, before delivery of the sensor, a corresponding velocity dependence of the correction factor K(v)=t0/tR(v) can additionally be ascertained for different further reference sensors 25R1, 25R2, . . . of the sensor type series of the sensor 25, which actually have an offset (or an offset deviating from the predefined offset) between illumination region and detection region, said offset being of different magnitudes. Table 2 shows the correction table T ascertained in this way, which indicates the offset-dictated correction factors K1(v0), K1(v1), K2(v0), K2(v1), . . . for seven different reference sensors. The correction table T thus ascertained by the sensor manufacturer is applicable to all sensor specimens of the sensor type series of the sensor 25 and is stored in the memory area of the individual sensor specimens 25a, 25b.

TABLE-US-00002 TABLE 2 Correction table T with offset-dictated correction factors K1(v), . . . , K7(v) for sensors of the sensor type series of the sensor 25 with different offsets Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 Reference sensor 1.00 1.01 1.04 1.08 1.14 1.21 1.29 1.37 1.47 1.58 25R1 (a =? 0.15) Reference sensor 1.00 1.04 1.09 1.13 1.21 1.29 1.38 1.48 1.58 1.71 25R2 (a =? 0.1) Reference sensor 1.00 1.08 1.13 1.19 1.28 1.37 1.47 1.58 1.70 1.83 25R3 (a = ?0.05) Reference sensor 1.00 1.11 1.18 1.25 1.35 1.45 1.56 1.68 1.81 1.96 25R4 (a = 0, ideal) Reference sensor 1.00 1.14 1.23 1.31 1.42 1.53 1.65 1.78 1.92 2.09 25R5 (a = 0.05) Reference sensor 1.00 1.18 1.27 1.37 1.49 1.61 1.74 1.88 2.04 2.21 25R6 (a = 0.1) Reference sensor 1.00 1.21 1.32 1.42 1.56 1.69 1.83 1.99 2.15 2.34 25R7 (a = 0.15)

[0133] As an alternative to the measurement of the luminescence time constant tR(v) of a reference medium by means of different reference sensors at different transport velocities v of the reference medium, the correction table T can also be determined by means of a mathematical simulation of the detection process of the sensor, in which the temporal profile of the luminescence intensity of the luminescent material is taken as a basis and from that the movement-dictated change over time in the overlap between the illumination region and the detection region on the value document is calculated.

[0134] As an alternative to the correction factors Ki(v), however, the correction table can also contain just the purely offset-dictated portion Bi(v) of these correction factors, from which the ideal correction factors K0(v) (applicable to an offset-free sensor) are worked out. The purely offset-dictated correction factors Bi(v) result from the correction factors Ki(v) contained in table 2 in each case by way of division: Bi(v)=Ki(v)/K0(v). In the sensor, a correction table with the purely offset-dictated correction factors Bi(v) for different reference sensors is then stored, and additionally the velocity dependence of the ideal correction factor K0(v), cf. table 1.

[0135] The sensor specimens 25a, 25b with the specific sensor-specific correction factor K(v0) respectively stored therein and the correction table T stored therein are then delivered to the customer by the sensor manufacturer, and the customer uses the respective sensor e.g. in a value document processing apparatus.

[0136] During the verification of the value documents by the respective sensor specimen 25a, 25b, in which the respective specific sensor-specific correction factor K(v0) is stored, the sensor-specific correction factor K(vP) applicable to the verification transport velocity vP is determined on the basis of the correction table T stored in the sensor specimen 25a, 25b. For this purpose, firstly the specific sensor-specific correction factor K(v0) (in the case of sensor specimen 25a: K(v0)=1.70; in the case of sensor specimen 25b: K(v0)=1.40) is compared with those correction factors which are contained in the correction table T and which are applicable to the reference transport velocity (v0=8 m/s). From these, that reference sensor is selected whose correction factor for the reference transport velocity v0 corresponds to, or deviates the least from, the specific sensor-specific correction factor K(v0) of the respective sensor specimen. From this it transpires that the sensor specimen 25a approximately corresponds to the reference sensor 25R4 (K0(v0)=K4(v0)=1.68) and the sensor specimen 25b approximately corresponds to the reference sensor 25R1 (K1(v0)=1.37). On the basis of the correction table T, that sensor-specific correction factor Ki(vP) of the respectively corresponding reference sensor which is applicable to the verification transport velocity (vP, e.g. 10 m/s) is then selected, i.e. K4(vP)=1.96 in the case of the sensor specimen 25a and K1(vP)=1.58 in the case of the sensor specimen 25b. These correction factors can be used as a sensor-specific correction factor K(vP) of the respective sensor specimen in the case of vP=10 m/s.

[0137] Ifas herethe specific sensor-specific correction factor K(v0) does not exactly match one of the correction factors of a reference sensor that are applicable to the reference transport velocity in the correction table T, alternatively during the determination of the sensor-specific correction factor K(vP) it is also possible to use the correction factors from the two reference sensors whose correction factors Ki(v0), Kj(v0) for the reference transport velocity v0 deviate the least from the specific sensor-specific correction factor K(v0). These are for example the reference sensors 25R4 and 25R5 in the case of sensor specimen 25a, and the reference sensors 25R1 and 25R2 in the case of sensor specimen 25b. During the determination of the sensor-specific correction factor for the verification transport velocity vP, the two correction factors of these two reference sensors that are associated with the transport velocity vP are interpolated in order to determine the sensor-specific correction factor K(vP) more accurately. For the sensor specimen 25a, the correction factors of the reference sensors 25R4 and 25R5 for vP=10 m/s are interpolated, which yields K(vP)=1.99. For the sensor specimen 25b, the correction factors of the reference sensors 25R1 and 25R2 for vP=10 m/s are interpolated, which yields K(vP)=1.61.

[0138] If the verification transport velocity vP does not exactly match one of the transport velocities v contained in the correction table, it is possible to interpolate the corresponding correction factors of the two transport velocities v closest to the verification transport velocity vP from the correction table T.

[0139] With the aid of the sensor-specific correction factor K(vP) which was determined on the basis of the correction table T, the respective sensor specimen 25a, 25b can carry out the velocity correction of the luminescence time constant t(vP) measured at the value document to be verified. The corrected luminescence time constant t*(vP) arises e.g. by way of multiplication t*(vP)=t(vP).Math.K(vP).

[0140] The luminescence time constant of the value document measured at the verification transport velocity vP=10 m/s in the sensor 25a is approximately ta(vP)=128 Multiplication by the sensor-specific correction factor K(vP)=1.99 of the sensor specimen 25a yields from this a corrected luminescence time constant of ta*(vP)=255 ?s for the verified value document. In the case of the second sensor specimen 25b, with the luminescence time constant tb=158 measured at vP=10 m/s, multiplication by the sensor-specific correction factor K(vP)=1.61 of the sensor specimen 25b yields a corrected luminescence time constant of tb*(vP)=254 ?s for the same verified value document. Both corrected luminescence time constants thus approximately match the decay time of the value document t0=250 ?s determined during the static measurement. In order to verify the value document, this corrected luminescence time constant ta* and tb*, respectively, is compared e.g. with a target value (here t0=250 ?s) and, in the case of a deviation from the target value which is greater than an acceptance range, the value document is segregated as suspected counterfeit by the value document processing apparatus 1.

[0141] In contrast to the sensor-specific correction according to the invention, in the case of a sensor-independent correction of the measured time constant only with the sensor-generally applicable correction factor K0(vP)=1.96 (see table 1), a distinctly different luminescence time constant would possibly be obtained, thus e.g. a corrected time constant tb*=tb(vP)K0(vP)=310 ?s in the case of the sensor 25b. In order for the value document here still to be recognized as authentic, a significantly larger acceptance range around the specified 250 ?s would have to be chosen, thereby making it distinctly easier to counterfeit the security feature.

1st Exemplary EmbodimentSecond Variant

[0142] In a second variant of the first exemplary embodiment, in the individual sensors 25a, 25b of the sensor type series, in addition to the specific sensor-specific correction factor K(v0)instead of the correction table Ta mathematical correction formula F is stored, specifying a set of possible velocity dependences of the correction factor K(vP) for different offset parameters a. The correction formula F can be determined by the sensor manufacturer e.g. on the basis of the correction table T (for instance by fitting a fit function to the table values) or by means of mathematical simulation. For the sensor type series of the sensor 25, this yields e.g. the correction formula

K(vP)=(K0(vP).Math.(1+a.Math.arctan(vP/3))(F),

specifying the velocity dependence of the correction factor K(vP) depending on the offset parameter a and depending on the verification transport velocity vP of the value document. The offset parameters a applicable to the reference sensors 25R1-25R7 are concomitantly indicated in the first column of table 2. Other correction formulas generally arise for other sensor type series.

[0143] Moreover, the velocity dependence of the correction factors K0(v) applicable to the ideal, offset-free reference sensor 25R4 is stored in the sensor (cf. table 1). From the velocity dependence of the ideal correction factor K0(v), that ideal correction factor (K0(v0)=1.68) is selected which is applicable to the reference transport velocity (v0=8 m/s). On the basis of the specific sensor-specific correction factor K(v0) stored in the sensor and the reference transport velocity v0 linked therewith and by means of the ideal correction factor K0(v0) for the reference transport velocity v0, the sensor can calculate the sensor-specific offset parameter a of the sensor with the aid of the following formula derived from (F):

a=(K(v0)?K0(v0))/(K0(v0)arctan(v0/3))(F*)

[0144] With formula F* this yields a sensor-specific offset parameter of approximately a=+0.01 for the sensor specimen 25a and a sensor-specific offset parameter of approximately a=?0.14 for the sensor specimen 25b. The calculation of a by means of formula F* can be effected by the sensor manufacturer or after delivery of the sensor. Preferablyin addition to K(v0)the sensor-specific offset parameter a is also stored in the memory area 26 of the respective sensor specimen 25a, 25b in order to have it available possibly for later velocity corrections with other verification transport velocities vP.

[0145] After delivery of the sensor, before the value document verification in a value document processing apparatus, the sensor-specific correction factor K(vP) applicable to the verification transport velocity is calculated on the basis of the correction formula F. For this purpose, from the velocity dependence of the ideal correction factor K0(v), the ideal correction factor (K0(vP)=1.96) applicable to the verification transport velocity (e.g. vP=10 m/s) of the value document is selected. From that, with the aid of the correction formula F, the sensor-specific correction factor K(vP) of the sensor is calculated which is applicable to the ascertained sensor-specific offset parameter a of the sensor and the verification transport velocity vP of the value document. In this way, K(vP)=1.99 is obtained in the case of the sensor specimen 25a, and K(vP)=1.61 in the case of the sensor specimen 25b. With the aid of the sensor-specific correction factor K(vP) determined on the basis of the correction formula F, the respective sensor specimen 25a, 25b can carry out the velocity correction of the luminescence time constant t(vP) measured at the value document to be verified: t*(vP)=t(vP).Math.K(vP).

2nd Exemplary Embodiment

[0146] In the second exemplary embodimentinstead of the specific sensor-specific correction factor K(v0)the abovementioned sensor-specific offset parameter a is used as a sensor-specific parameter and, before delivery of the sensor, is stored in the memory area 26 of the sensor 25, together with a sensor-generally applicable correction assignment, e.g. the correction table T or the correction formula F.

[0147] The sensor-specific offset parameter a of the sensor can be calculatedas described in the first exemplary embodimentwith the aid of the formula F* from the specific sensor-specific correction factor K(v0) whichas in the first exemplary embodimentis determined by measurement of the luminescence time constant of the reference medium transported past the sensor at the reference transport velocity v0. As a sensor-specific offset parameter, the value a=+0.01 is stored in the sensor specimen 25a, and the value a=?0.14 in the sensor specimen 25b.

[0148] In addition to the sensor-specific offset parameter a, either the correction table T described in the first exemplary embodiment is also stored in the sensor specimens 25a,b, which correction table indicates the offset-dictated correction factors Ki(v) for sensors of the sensor type series of the sensor 25 depending on the offset parameter a and depending on the transport velocity v of the value document. As an alternative to the correction table T, the correction formula F can also be storedin addition to the sensor-specific offset parameter ain the sensor specimens 25a,b, which correction formula indicates the velocity dependence of the correction factor K(v) depending on the sensor-specific offset parameter a and depending on the transport velocity v of the value document for sensors of this sensor type series. The sensor with the sensor-specific offset parameter a stored therein and the correction table T or correction formula F stored therein is then delivered to the customer by the sensor manufacturer, and the customer uses this sensor to carry out the value document verification using a value document processing apparatus.

[0149] The verification transport velocity vP of the value document is required for ascertaining the sensor-specific correction factor K(vP) applicable to the verification transport velocity vP. This verification transport velocity can be communicated to the sensor by the value document processing apparatus, and can optionally be stored in the sensor. The verification of the value documents by means of the sensor then proceeds as follows:

[0150] If the correction table T is stored in the sensor 25, the correction device 21 of the sensor, on the basis of the sensor-specific offset parameter a of the sensor and on the basis of the correction table T, then determines the sensor-specific correction factor K(vP) which is applicable to the verification transport velocity vP of the value document and the sensor-specific offset parameter a of the sensor. If the sensor-specific offset parameter a of the respective sensor does not exactly match one of the possible offset parameters of the correction table T, it is possible to interpolate the two correction factors of the possible offset parameters deviating the least from the sensor-specific offset parameter a from the correction table T. Moreover if the verification transport velocity vP does not exactly match one of the transport velocities v contained in the correction table, it is possible to interpolate the corresponding correction factors of the two transport velocities v closest to the verification transport velocity vP from the correction table T. In this regard, the sensor-specific correction factor K(vP) applicable to the sensor-specific offset parameter a of the sensor and to the verification transport velocity vP of the value document can be calculated accurately.

[0151] If the correction formula F is stored in the sensor 25, the velocity dependence of the correction factors K0(v) applicable to the ideal reference sensor 25R4 is preferably also stored in the sensor (cf. table 1). From this velocity dependence, that ideal correction factor K0(vP) which is applicable to the verification transport velocity vP of the value document is selected. From that, the correction device 21 of the sensor, with the aid of the correction formula F, on the basis of the sensor-specific offset parameter a of the sensor, calculates the sensor-specific correction factor K(vP) which is applicable to the verification transport velocity vP of the value document and the sensor-specific offset parameter a of the sensor.

[0152] Correcting the measured luminescence time constant t(vP) with the aid of the sensor-specific correction factor K(vP) is effected by calculating t*(vP)=t(vP).Math.K(vP), as in the first exemplary embodiment.

3rd Exemplary Embodiment

[0153] In the third exemplary embodiment, the sensor-specific offset length d of the sensor is used as a sensor-specific parameter and, before delivery of the sensor, is stored in the memory area 26 of the sensor 25, together with a sensor-generally applicable offset value assignment. The sensor 25 with the offset length d stored therein and the offset value assignment is then delivered to the customer, and the customer uses this sensor to carry out the value document verification in a value document processing apparatus 1.

[0154] The sensor-specific offset length d is the distance measured along the transport direction of the value document in the measurement plane between the illumination region, in which the value document to be verified by the sensor is excited to luminescence, and the detection region, in which the sensor detects the luminescence of the value document to be verified. By way of example, the distance between the center point or centroid of the illumination region and the center point or centroid of the detection region is used as an offset length d. For elucidating the offset length d, FIG. 3 shows four possible combinations of illumination region 6 and detection region 9 and their center points or centroids 7 and 4, respectively.

[0155] In order to measure the sensor-specific offset length d of the sensor 25, on the part of the sensor manufacturer, it is possible to position a planar projection surface (screen) in the measurement plane of the sensor, which is parallel to the sensor surface and is situated at that distance from the sensor surface at which the value documents are transported past the sensor during the verification of the value documents (measurement plane). That is followed by switching on the excitation light sources of the sensor and marking the illumination region thereby illuminated on the planar projection surface. Afterward, the detection region is determined by successively illuminating only individual sections of the illumination region and taking the detected signal into consideration in each case: if a minimum signal from there is detected, the respectively illuminated section belongs to the detection region, otherwise it does not. Finally, the center point or centroid 7 of the illumination region 6 and the center point or centroid 4 of the detection region 9 are determined and marked and the distance between them along the transport direction x is measured, this distance being used as a sensor-specific offset length d.

[0156] With the aid of a plurality of reference sensors of the same type series for which different offset lengths d were determined, it is possibleanalogously to the correction table T of the first exemplary embodimentto create as an offset value assignment e.g. an offset value table D, indicating for a plurality of offset lengths d=d1, d2, . . . in each case the offset-dictated correction factor Ki(v) applicable to the respective offset length as a function of the transport velocity v of the value document, cf. table 3. Alternatively, the offset value table D can also be determined by means of mathematical simulation. The offset value table D is stored in the sensor.

TABLE-US-00003 TABLE 3 Offset value table D with correction factors Ki(v) for sensors of the sensor type series of the sensor 25 with different offset lengths d Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 d = ?1 mm 1.00 1.01 1.04 1.08 1.14 1.21 1.29 1.37 1.47 1.58 d = ?0.5 mm 1.00 1.06 1.11 1.16 1.25 1.33 1.43 1.53 1.64 1.77 d = 0 mm 1.00 1.11 1.18 1.25 1.35 1.45 1.56 1.68 1.81 1.96 d = +0.5 mm 1.00 1.16 1.25 1.34 1.45 1.57 1.69 1.83 1.98 2.15 d = +1 mm 1.00 1.21 1.32 1.42 1.56 1.69 1.83 1.99 2.15 2.34

[0157] After the delivery of the sensor, during the value document verification on the basis of the offset value table D and on the basis of the information made available to the sensor regarding the verification transport velocity vP and on the basis of the offset length d of the sensor, the sensor-specific correction factor K(vP) is determined which is applicable to the verification transport velocity vP of the value document. Depending on the offset length d of the sensor and the verification transport velocity vP, the sensor-specific correction factor K(vP) can be taken directly from the offset value table D or can be calculated by interpolation of the table values. Correcting the luminescence time constant t(vP) with the aid of the correction factor K(vP) determined on the basis of the offset value table D is effected by calculating t*(vP)=t(vP).Math.K(vP), as in the first exemplary embodiment.

[0158] As an alternative to the offset value table D, a corresponding mathematical correction formula for a set of curves K(v,d) can also be produced (for instance by fitting the table values) and stored in the sensor and used for calculating K(vP) on the basis of the offset length d and the verification transport velocity vP.

[0159] The correction factors Ki(v) of the offset value table D shown in table 3 allow a complete movement-dictated correction of the luminescence time constant. As an alternative thereto, however, the offset value table D can also contain just the purely offset-dictated portion Bi(v) of these correction factors, from which the ideal correction factors K0(v) (applicable to an offset-free sensor) are worked out, cf. table 4. The purely offset-dictated correction factors Bi(v) result from the correction factors Ki(v) contained in table 3 in each case by way of division: Bi(v)=Ki(v)/K0(v). In the sensor, an offset value table D with the purely offset-dictated correction factors Bi(v) for different offset lengths d1, d2, . . . is then stored, and additionally the velocity dependence of the ideal correction factor K0(v), cf. table 1.

[0160] During the value document verification, by means of the offset length d stored in the relevant sensor, on the basis of this offset value table D, the purely offset-dictated sensor-specific correction factor B(vP) of the relevant sensor which is applicable to the verification transport velocity vP of the value document can then be selected (or calculated by interpolation).

TABLE-US-00004 TABLE 4 Offset value table D with purely offset-dictated correction factors Bi(v) for sensors of the sensor type series of the sensor 25 with different offset lengths d for opposite transport directions of the value document. Offset [mm] Velocity [m/s] ?12 ?8 ?4 0 4 8 12 ?0.5 Correction factor 1.09 1.08 1.06 1.00 0.94 0.92 0.91 0.0 Correction factor 1.00 1.00 1.00 1.00 1.00 1.00 1.00 0.5 Correction factor 0.91 0.92 0.94 1.00 1.06 1.08 1.09 1.0 Correction factor 0.82 0.83 0.87 1.00 1.13 1.17 1.18 1.5 Correction factor 0.73 0.75 0.81 1.00 1.19 1.25 1.27

[0161] From the velocity dependence of the ideal correction factor K0(v), the ideal correction factor K0(vP) which is applicable to the verification transport velocity vP of the value document is correspondingly selected. In order to correct the value document time constant t(vP) with the aid of the offset-dictated correction factor B(vP) selected from the table, the two correction factors are multiplied: t*(vP)=t(vP).Math.B(vP).Math.K0(vP).

4th Exemplary Embodiment

[0162] In the fourth exemplary embodiment, a plurality of sensor-specific parameters are determined in the form of a velocity dependence of the sensor-specific correction factor K(v) and are stored in the sensor. The sensor with the velocity dependence of the sensor-specific correction factor K(v) stored therein is then used for the value document verification by means of a value document processing apparatus.

[0163] In the fourth exemplary embodiment, the velocity dependence of the sensor-specific correction factor K(v) is determined by measurement of the luminescence time constant of a reference medium at different transport velocities v with the aid of the relevant sensor specimen, in which the velocity dependence of the sensor-specific correction factor is then stored.

[0164] In order to determine the velocity dependence of the sensor-specific correction factor, each sensor specimen is calibrated in a specific manner with the aid of a reference medium which is transported past the respective sensor specimen at different transport velocities v0, v1, . . . . This can be carried out before delivery of the sensor on the part of the sensor manufacturer, e.g. at a sensor measuring station suitable for this purpose, or only upon or after the start-up of the sensor in the respective value document processing apparatus. In this case, the specified luminescence time constant tR0 of the reference medium preferably corresponds to the target value of the luminescence time constant t0 of the value documents to be verified.

[0165] For each transport velocity v at which the reference medium is transported past the respective sensor 25, a temporally resolved measurement of the luminescence emitted by the reference luminescent material is detected by the photodetector 20 of the sensor. From the measured change over time in the luminescence of the reference medium, a reference medium time constant tR(v) of the reference luminescent material is in each case determined for the respective transport velocity v. On the basis of the respectively determined reference medium time constant tR(v) of the reference luminescent material and on the basis of the specified luminescence time constant tR0 of the reference luminescent material, a sensor-specific correction factor K(v) is in each case determined for the respective transport velocity v1, v2, e.g. the relationship K(v0)=tR0/tR(v0), K(v1)=tR0/tR(v1), . . . . The respective sensor-specific correction factor K(v) is assigned to the respective transport velocity v0, v1, . . . , as is shown e.g. in table 5. In this example, the sensor specimen 25a was used to determine the luminescence time constant of a reference medium which is provided with a reference luminescent material having a time constant of tR0=250 ?s and is transported past the sensor specimen 25a at the velocities v=0 m/s to v=10 m/s.

TABLE-US-00005 TABLE 5 Velocity dependence of the sensor-specific correction factor for the sensor specimen 25a Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 Correction factor 1 1.12 1.19 1.27 1.37 1.47 1.58 1.70 1.83 1.99 K(v)

[0166] The discrete assignment from table 5 for different transport velocities v0, v1, . . . forms a velocity dependence K(v) of the sensor-specific correction factor K. This velocity dependence K(v) of the sensor-specific correction factor is stored in the sensor specimen 25a before the value document verification, e.g. in the memory area 26.

[0167] For the sensor specimen 25b, using the same reference medium, correspondingly different decay times tR(v) were determined for the respective transport velocities. Correspondingly different sensor-specific correction factors result therefrom, cf. table 6. The velocity dependence K(v) indicated in table 6 is stored in the sensor specimen 25b.

TABLE-US-00006 TABLE 6 Velocity dependence of the sensor-specific correction factor for the sensor specimen 25b Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 Correction factor 1 1.02 1.06 1.11 1.17 1.24 1.32 1.40 1.50 1.61 K(v)

[0168] As an alternative to the discrete values in table 5 and in table 6, respectively, a mathematical function can also be stored as a velocity dependence K(v) of the sensor-specific correction factor in the respective sensor, which mathematical function specifies values for the correction factor K(v) continuously in a velocity range (e.g. from 0 m/s to 12 m/s), e.g. for a third sensor specimen 25c a fit function G(v) that is fitted to the measured discrete values K(v0), K(v1), . . . (cf. FIG. 2e). The correction factor K(vP) for the verification transport velocity vP then arises simply by inserting the respective verification transport velocity vP into the fit function G(v) by way of K(vP)=G(vP).

[0169] The correction device 21 of the respective sensor contains a velocity correction which, during the verification of the luminescence of the value documents, is used for correcting the luminescence time constant t determined for the respective value document. The velocity correction has recourse to the velocity dependence K(v) of the sensor-specific correction factor stored in the respective sensor, i.e. to table 5 in the case of the sensor specimen 25a, to table 6 in the case of the sensor specimen 25b, and to the fit function G(v) in the case of the sensor specimen 25c. For the velocity correction of the luminescence time constant, the correction device 21 uses information regarding the verification transport velocity vP of the value documents to be verified, e.g. vP=8 m/s. This information is communicated to the sensor 25 from the control device 50 of the value document processing apparatus 1 to the sensor 25.

[0170] After the delivery of the sensor by the sensor manufacturer, value documents are verified by the sensor in a value document processing apparatus 1. For verifying the value documents, the latter are transported past the sensor specimen 25a at a verification transport velocity vP, for example at vP=8 m/s. It is assumed that the sensor specimen 25a detects a decay time of t=147 ?s from a value document to be verified. With the aid of the sensor-specific correction factor K(8 m/s)=1.70 applicable to the verification transport velocity vP=8 m/s and the sensor specimen 25a, for the purpose of the velocity correction, the detected decay time of t=147 ?s is multiplied by the sensor-specific correction factor K=1.70. This results in a corrected luminescence time constant t*(8 m/s)=t K(8 m/s)=147 ?s 1.40=250 ?s.

[0171] It is also possible to verify whether the verification transport velocity vP of the value documents matches one of the discrete transport velocities v0, v1, . . . in table 5 or 6, respectively, as was stored in the sensor. If a correction factor K(vP) has not been explicitly stored in the sensor for the verification transport velocity vP of the respective value document processing apparatus 1, it is possible e.g. to select which of the stored transport velocities deviates the least from the verification transport velocity vP of the value documents. The sensor-specific correction factor K(vP) assigned to this transport velocity is then used for correcting the decay time. This can be done with the reservation that the velocity deviation lies below a specific threshold, e.g. <10%. If the value documents are transported past the sensor specimen 25a e.g. at a verification transport velocity vP=3.25 m/s during the verification in a value document processing apparatus, then the sensor-specific correction factor K=1.19 stored for v=3 m/s is selected from table 1 and used for the correction of the detected decay time.

[0172] However, if the verification transport velocity vP of the value documents deviates more than acceptably from all the transport velocities v0, v1, . . . stored in the sensor, at least two transport velocities v1, v2 are selected from the transport velocities stored in the sensor, e.g. those deviating the least from the verification transport velocity vP, and the two sensor-specific correction factors K(v1), K(v2) assigned thereto. The sensor-specific correction factor K(vP) applicable to the verification transport velocity vP is determined from the at least two selected sensor-specific correction factors K(v1), K(v2) e.g. by interpolation.

5th Exemplary Embodiment

[0173] In the fifth exemplary embodiment, too, a plurality of sensor-specific parameters in the form of a velocity dependence of the sensor-specific correction factor K(v) are determined and are stored in the memory area 26 of the sensor 25. The sensor with the velocity dependence of the sensor-specific correction factor K(v) stored therein is then used for value document verification in a value document processing apparatus.

[0174] In the fifth exemplary embodiment, however, the velocity dependence of the sensor-specific correction factor K(v) is determined on the basis of a measurement of the luminescence time constant tR(v0) of a reference medium at only exactly one reference transport velocity v0 with the aid of this very sensor in which the velocity dependence of the sensor-specific correction factor is stored. On the basis of the specific sensor-specific correction factor K(v0)=tR(v0)/tR0 calculated therefrom, from the correction table T mentioned above, that row (that reference sensor) is selected in which, in the column for v0, the correction factor assumes the value K(v0) determined for the specific sensor. This row selected from the correction table T corresponds to the velocity dependence of the sensor-specific correction factor K(v) and is stored in the sensor. If there is not an exact match between K(v0) and a value of the correction table T in the column for v0, a row interpolated from the two closest rows can be determined and stored as a velocity dependence of the sensor-specific correction factor K(v) in the respective sensor. This can be carried out by the sensor manufacturer or after delivery of the sensor, for instance during the calibration of the sensor in the value document processing apparatus.

[0175] As an alternative to the correction table T, the velocity dependence of the sensor-specific correction factor K(v) can also be determined by way of the sensor-specific offset parameter a which is calculated by means of the formula F* on the basis of the specific sensor-specific correction factor K(v0)=tR(v0)/tR0 and the reference transport velocity v0 and the ideal correction factor K0(v0). By means of this sensor-specific offset parameter a and also on the basis of the velocity dependence of the ideal correction factor K0(v), the velocity dependence of the sensor-specific correction factor K(v) can then be calculated by means of formula F and be stored in the sensor. The sensor with the velocity dependence of the sensor-specific correction factor K(v) stored therein is then used for value document verification in a value document processing apparatus.

[0176] If e.g. the offset parameter a=?0.05 is ascertained for a specific sensor specimen, then the following velocity dependence of the sensor-specific correction factor K(v) results from the correction table T, cf. table 2, which velocity dependence is then stored in the sensor:

TABLE-US-00007 TABLE 7 Velocity dependence of the sensor-specific correction factor K(v) for a sensor of the sensor type series of the sensor 25 with offset parameter a = ?0.05. Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 K(v) for a = ?0.05 1.00 1.08 1.13 1.19 1.28 1.37 1.47 1.58 1.70 1.83

[0177] The correction assignment T or F respectively indicated above was ascertained for a reference medium having a luminescence time constant tR0=250 ?s and is used for ascertaining the sensor-specific correction factor for the velocity correction of the luminescence time constant of value documents whose target value of the luminescence time constant lies in the range of 100 ?s to 5 ms.

[0178] In additionanalogously to the correction assignment T, Fat least one further correction assignment T, F which is applicable to value documents having a different target value of the luminescence time constant can be ascertained by means of a different reference medium having a different luminescence time constant. On the basis thereofin addition to the velocity dependence of the sensor-specific correction factor K(v) indicated aboveone or more further velocity dependences K(v), K(v) of the sensor-specific correction factor, each of which is applicable to a different value range of the luminescence time constant of the value documents to be verified, can also be ascertained and be stored in the sensor. By way of example, the further velocity dependence K(v), which was ascertained for a different reference medium having a luminescence time constant tR0=110 ?s, can be stored in the sensor, and is used for value documents having a target value of the luminescence time constant in the range of 60 ?s to 160 ?s for the purpose of ascertaining the sensor-specific correction factor for the velocity correction of the luminescence time constant of the value documents. As an alternative to using a further correction assignment T, F, the further velocity dependences K(v), K(v) of the sensor-specific correction factor stored in the sensor can also be ascertained by (sensor-specific) measurement of the luminescence time constant of the different reference medium (having the luminescence time constant tR0=110 ?s), by means of the respective sensor, by means of the different reference medium being transported past the respective sensor at different transport velocities analogously to the 4th exemplary embodiment.

6th Exemplary Embodiment

[0179] In the sixth exemplary embodiment, too, a plurality of sensor-specific parameters in the form of a velocity dependence of the sensor-specific correction factor K(v) are determined and stored in the sensor, preferably before delivery of the sensor. The sensor with the velocity dependence of the sensor-specific correction factor K(v) stored therein is then delivered to the customer, and the customer uses this sensor to carry out the value document verification in a value document processing apparatus.

[0180] In the sixth exemplary embodiment, however, the velocity dependence of the sensor-specific correction factor K(v) is determined by measurement of the offset length d of this very sensor (i.e. sensor specimen) in which the velocity dependence of the sensor-specific correction factor is stored. On the basis of the offset length d, the velocity dependence of the sensor-specific correction factor K(v) is determined on the basis of the offset value table D (or a corresponding correction formula), by selection of the table row associated with the offset length d in the offset value table D, cf. table 3 or 4, or by interpolation of the two rows whose offset lengths are closest to the offset length d. The velocity dependence of the sensor-specific correction factor K(v) determined in this way is then stored in the memory area 26 of the sensor 25. The sensor with the velocity dependence of the sensor-specific correction factor K(v) stored therein is then delivered to the customer, and the customer carries out the value document verification.

[0181] If e.g. the offset length d=1 mm is ascertained for a specific sensor specimen, then the following velocity dependence of the sensor-specific correction factor K(v) results from the offset value table D, cf. table 3, and is then stored in the sensor:

TABLE-US-00008 TABLE 8 Velocity dependence of the sensor-specific correction factor K(v) for a sensor of the sensor type series of the sensor 25 with offset length d = +1 mm Velocity v [m/s] 0 2 3 4 5 6 7 8 9 10 K(v) for d = +1 mm 1.00 1.21 1.32 1.42 1.56 1.69 1.83 1.99 2.15 2.34

[0182] If the sensor is one which, transversely with respect to the transport direction, comprises more than one measurement track in the region of the security feature to be verified, then the offset length of each individual measurement track is measured. If the correction device 21 uses measurement values of the value document from a plurality of tracks for determining the luminescence time constants of the value document, then the measured luminescence time constants can first be corrected in a measurement track-dependent manner and then be combined to form a resultant luminescence time constant t(vP). Alternatively, an effective offset length can be calculated from the individual offset lengths of the different measurement tracks. For this purpose, the offset lengths of the different measurement tracks are weighted in the way that the correction device 21 weights the luminescence time constants of the individual measurement tracks for the determination of the resultant time constants. For determining the velocity dependence of the sensor-specific correction factor K(v), this effective offset length is then used as the offset length d of the sensor.

7th Exemplary Embodiment

[0183] In the seventh exemplary embodiment, too, a plurality of sensor-specific parameters in the form of a velocity dependence of the sensor-specific correction factor K(v) are determined and stored in the sensor. The sensor with the velocity dependence of the sensor-specific correction factor K(v) stored therein is then used for the verification of value documents.

[0184] In the seventh exemplary embodiment, however, in each case a separate velocity dependence of the sensor-specific correction factor for both opposite transport directions of the value documents relative to the sensor is stored in the memory area 26 of the sensor 25. By way of example, for the transport direction in which the sensoras viewed along the transport direction of the value documentslies on the left-hand side of the transport path, a first velocity dependence K1(v) of the sensor-specific correction factor is stored in the sensor (negative velocity values). Moreover for the transport direction in which the sensoras viewed along the transport direction of the value documentslies on the right-hand side of the transport path, a second velocity dependence Kr(v) of the sensor-specific correction factor is stored in the sensor (positive velocity values). The first velocity dependence K1(v) of the sensor-specific correction factor is applicable to the installation position of the sensor 25 in the value document processing apparatus 1 as shown in FIG. 1. The second velocity dependence Kr(v) of the sensor-specific correction factor is applicable to a different installation position, in which the sensor 25 is installed in the value document processing apparatus 1 at the opposite side, instead of the sensor 29, cf. FIG. 1.

[0185] The following tables 9, 10 present the two velocity dependences K1(v) and Kr(v) of the sensor-specific correction factor for the third sensor specimen 25c of the sensor type series mentioned above.

TABLE-US-00009 TABLE 9 Velocity dependence Kl(v) of the sensor-specific correction factor for sensor specimen 25c in the left installation position Velocity v [m/s] ?12 ?8 ?4 0 Decay time tR [?s] 135 178 229 250 Correction factor Kl(v) 1.85 1.40 1.09 1.00

TABLE-US-00010 TABLE 10 Velocity dependence Kr(v) of the sensor-specific correction factor for sensor specimen 25c in the right installation position Velocity v [m/s] 0 4 8 12 Decay time tR [?s] 250 177 128 93 Correction factor Kr(v) 1.00 1.41 1.95 2.69

[0186] FIG. 2e shows a mathematical function G(v), which was determined on the basis of the two velocity dependences K1(v) and Kr(v) for the third sensor specimen 25c. For comparison, the sensor-specific correction factors for the sensor specimens 25a and 25b are also depicted in FIG. 2e.

[0187] In order to determine the velocity dependence of the sensor-specific correction factor K(v), the procedure as in the fourth, fifth or sixth exemplary embodiment can be adopted, but for both mutually opposite transport directions of the value document relative to the sensor. For example, analogously to the fourth exemplary embodiment, in order to determine K1(v) and Kr(v) for the respective sensor specimen, the reference medium (having a known specified luminescence time constant tR0) can be correspondingly transported past the sensor along both opposite transport directions at different transport velocities v0, v1, . . . and the decay time tR1(v0), tR1(v1), tRr(v0), tRr(v1), . . . can in each case be determined. The respective measured decay times are then used to determine the sensor-specific correction factors K1(v0), K1(v1), Kr(v0), Kr(v1), . . . for a plurality of transport velocities v0, v1, . . . along the first transport direction and along the second transport direction. The sensor-specific correction factors correspondingly arise by means of forming the relationship: K1(v0)=tR0/tR1(v0), K1(v1)=tR0/tR1(v1), . . . , Kr(v0)=tR0/tRr(v0), Kr(v1)=tR0/tRr(v1), . . . .

[0188] In order to select the correct one of the two velocity dependences K1(v) or Kr(v) during the verification of the value documents, the correction device 21 acquires information regarding the verification transport direction of the value documents relative to the sensor, e.g. from the control device 50, which also communicates the information regarding the verification transport velocity vP. The information regarding the verification transport direction can be communicated by the control device explicitly or else simply by way of the sign of the transport direction, e.g. negative velocity values for the transport direction shown in FIG. 1 (or when the sensor 25 is in the left installation position), and positive velocity values for the opposite transport direction (or when the sensor is in the right installation position). The correction device 21 then selects either the first velocity dependence of the correction factor K1(v) or the second velocity dependence of the correction factor Kr(v) depending on the information made available to the sensor 25 regarding the verification transport direction. On the basis of the selected first or respectively second velocity dependence of the sensor-specific correction factor K1(v), Kr(v) and by means of the information made available to the sensor regarding the verification transport velocity vP, the correction device 21 determines the sensor-specific correction factor K1(vP) or Kr(vP) which is applicable to the verification transport velocity vP and the verification transport direction of the value documents. The luminescence time constant t(vP) of the value documents that is detected by the sensor 25 is then corrected with the aid of the sensor-specific correction factor K1(vP) or respectively Kr(vP) applicable to the verification transport velocity vP and to the verification transport direction of the value documents, e.g. t*(vP)=t(vP).Math.K1(vP) in the case of the left installation position from FIG. 1 or respectively t*(vP)=t(vP).Math.Kr(vP) in the case of a right installation position.