HK1178301B

HK1178301B - Sensor for verifying value documents

Info

Publication number: HK1178301B
Application number: HK13105222.4A
Authority: HK
Inventors: Wolfgang Deckenbach; Martin Clara; Wolfgang Rauscher
Original assignee: Giesecke+Devrient Currency Technology Gmbh
Priority date: 2010-04-14
Filing date: 2011-04-12
Publication date: 2017-11-03

Description

Sensor for checking valuable documents

Technical Field

The invention relates to a sensor and a method for checking value documents and to a device having such a sensor.

Background

Sensors are generally used to check the value documents, with the aid of which the type of the value documents is determined, and/or with the aid of which the authenticity of the value documents and/or their state is checked. Such sensors are used, for example, to check bank notes, checks, documents, credit cards, check cards, tickets, coupons, etc. The value documents are examined in a value document processing device, which contains one or more different sensors depending on the properties of the value documents to be examined. In order to check documents of value, they are usually moved relative to the sensor, with the documents of value either being transported past the sensor or vice versa.

The document of value to be examined can have one or more fluorescent substances, for example, in which the decay time and/or the spectral properties of the fluorescence are examined. The fluorescent substance of the document of value may be present on a part or the entire area of the document of value. In order to check the decay time of the fluorescence, it is known to illuminate the value document with light pulses and, in the dark phase between the light pulses, to detect the fluorescence intensity of the value document at different times after the end of the illumination pulse. A disadvantage here is that the value document is checked intermittently due to the pulsed illumination and the relative movement between the sensor and the value document. Since the dark phase leads to a periodic interruption of the optical excitation of the value document, no fluorescent check is carried out at regular intervals along the value document.

It is also known to illuminate a document of value to be examined at a point in its transport path with excitation light and to detect fluorescence of the document of value by means of a detector which is arranged at a distance from the illumination device at a point downstream of the transport path. If a two-dimensional image sensor is used as a detector, the decay time of the value document fluorescence can be determined from the spatial decay of the fluorescence in the direction of the value document movement. The disadvantage here is that only a limited range of decay time values can be determined with this method in the case of low speed of movement of the document of value.

Disclosure of Invention

The invention aims to solve the technical problem of providing a sensor for checking valuable documents, which can check the decay time of fluorescence of valuable documents in a larger decay time numerical range when the moving speed is lower.

This technical problem is solved by the subject matter of the independent claims. Advantageous further developments and designs of the invention are specified in the dependent claims.

The sensor according to the invention is designed for checking value documents present in the sensor measuring plane. In order to check the value document, the value document and the sensor are moved relative to one another, the value document being moved relative to the sensor in the direction of movement. In this case, the value document is generally conveyed along or past the stationary sensor in the direction of movement. Alternatively, however, the sensor can also be transported relative to a stationary value document, or both. The sensor is provided for checking the fluorescence decay time of the value document. Here, the decay time is checked on the basis of the fluorescence signal of the sensor detector. The sensor can be used only for checking documents of value transported past the sensor one by one, but it is also possible to check a sheet comprising a plurality of documents of value or a continuous web having a plurality of documents of value in the direction of movement. For example, the sensor is also suitable for checking a material web composed of a value document that has not yet been produced, in order to check it already during the production of the value document.

The sensor has an illumination device for illuminating a section of the measuring plane of the sensor, so that the document of value is illuminated in said section of the measuring plane by the excitation light when it is moved relative to the sensor. Furthermore, the sensor has a plurality of detectors for detecting fluorescence light, which is emitted by the value document illuminated with excitation light in different detection regions of the measuring plane when it is moved relative to the sensor. The detection regions of the detectors of the sensor are arranged offset to one another in the direction of movement of the value document. The illuminated section and the detection area of the detector are each fixed in position in the measurement plane of the sensor. The excitation light of the illumination device is designed to excite fluorescence of the value document to be examined in such a way that the value document emits fluorescence that can be detected by the detector.

The first detector of the sensor is arranged to generate a first fluorescence signal of a first detection region, which overlaps the illuminated segment in the measurement plane. The first fluorescent signal corresponds to fluorescent light detected in the first detection zone. The second detector of the sensor is arranged to generate a second fluorescence signal of a preceding detection zone, which is situated in front of the first detection zone in the measuring plane, viewed in the direction of movement of the value document. The second fluorescence signal corresponds to the fluorescence detected in the preceding detection zone. The length of the illuminated segment, viewed in the direction of movement, is preferably greater than or equal to the length of the first detection zone.

The sensor preferably also has a third detector, which is provided for generating a third fluorescence signal of the subsequent detection region. This subsequent detection zone is situated behind the first detection zone, viewed in the direction of movement, in the measurement plane. The third fluorescence signal corresponds to the fluorescence detected in the subsequent detection zone. The third detector allows the sensor to more accurately determine the long decay time. The sensor may be designed without a third detector. In one embodiment, the subsequent detection region, viewed in the direction of movement, is situated so far behind the first detector that it does not overlap the illumination section of the measuring plane.

In order to check the value document, the measuring plane illumination section is illuminated continuously and the fluorescence of the value document is detected continuously by the detector while the illumination is taking place. In contrast to the examination with pulsed illumination and detection for this purpose with a time offset, the value document can thus be examined without interruption. A spectral filter is usually provided in front of the detector, which blocks the excitation light of the illumination device, so that the excitation light scattered on the value document is not detected together.

The sensor may furthermore have one or more further detectors, which are each provided for generating a further fluorescence signal of a further detection region. The one or more further detection zones are located behind the preceding detection zone and in front of the first detection zone in the measurement plane, as seen in the direction of motion of the value document. Optionally, the fluorescence signal of the further detector can also be used to check the decay time. For this purpose, for example, a proportional relationship of the fluorescence signal of one of the further detectors to the first fluorescence signal can be established in each case. It is advantageous to use the fluorescence signal of one of the further detectors for checking the decay time, since the decay time can thus be checked or determined more accurately. The first, second and, if appropriate, further detectors and, if appropriate, the third detector can be formed, for example, by a one-dimensional or two-dimensional photodetector array.

The sensor is configured to check the decay time of the fluorescence of the value document under certain conditions using the second fluorescence signal and the fluorescence signal of the at least one further detector of the sensor. The other fluorescence signal is used together with the second fluorescence signal in a detector, for example one of the other detectors mentioned above of the first detector or the sensor. The conditions under which the second fluorescence signal and the fluorescence signals of the other detectors are used for checking the decay time can be specified.

The sensor may be arranged to adjust these conditions after the sensor has been put into operation. The conditions for checking the decay time using the second fluorescence signal and the fluorescence signal of the further detector may comprise measuring conditions for checking the value document and/or properties of the value document itself to be checked, for example the type of the value document. For example, for such a document of value whose decay time of the fluorescence is expected to be shorter than the specified decay time, the decay time can be checked using the second fluorescence signal and the fluorescence signal of at least one of the other detectors of the sensor, in particular the second and the first fluorescence signal, or the fluorescence signal of at least one of the second and the further detector. The selection of the fluorescence signal on which the decay time of the test is based can be carried out to a certain extent online, for example by means of information which is only known in the context of the value document test.

Preferably, the sensor is configured to check the decay time of the fluorescence of the value document on the basis of the first and second fluorescence signals. The sensor can furthermore be configured to check said decay time on the basis of the first and second fluorescence signal, or alternatively on the basis of the first and third fluorescence signal. The selection of the first and second or the selection of the first and third fluorescence signal can be carried out depending on the measurement conditions and/or depending on the properties of the value document to be examined. The sensor can furthermore be configured to check the decay time of the fluorescence of the value document, optionally on the basis of the first and second fluorescence signals, or on the basis of the first and third fluorescence signals, or on the basis of the first and second and third fluorescence signals.

The sensor may be provided with information about the speed of movement of the value document relative to the sensor. For example, the speed of movement of the value document can be adjusted within the sensor. Information about the speed of movement used in the checking of value documents can also be entered externally, for example by means of a device in which the sensor is installed. This can be done before the value document is checked. The sensor can also acquire the actual movement speed to some extent online, or the movement period of the value document to be checked can be acquired, for example, by a device which also controls the movement of the value document. The speed of movement of the value document can be determined from the movement of the value document by means of one or more diaphragms. The diaphragm can be arranged in the device before and/or after the sensor along the transport path of the value document. The speed of movement can be determined from the time span of the signals of two diaphragms arranged at a distance along the transport path, for example by means of the time span of the value document edge or other configurations of the signals. The speed of movement can also be determined mechanically, for example, by means of a wheel which is moved by the transport system, by the value document, by the paper or by a web.

The sensor according to the invention can also be designed to determine the speed of movement of the document of value itself. For example, one or more diaphragms may be integrated into the sensor for this purpose. For example, the sensor has for this purpose an aperture along the transport path in front of the detection region of the detector, which uses the fluorescence signal of the detection region for checking the decay time, and an aperture is arranged downstream of this. The movement speed can therefore be determined from the time interval of the value document edge or from other configurations of the diaphragm signal, given a known diaphragm distance. If the length of the document of value is known or the length of a structure of the document of value is known, the movement speed can also be determined from the signal of the single sensor diaphragm.

The speed of movement of the value document can also be determined from the fluorescence signal detected by the sensor. For example, the speed of movement may be determined by comparing the fluorescence signals detected by at least two of the detectors as a function of time, for example by comparing the fluorescence signals of the first and second detectors. This comparison provides the time span of the fluorescence signal, at which the fluorescence signal is detected due to the offset in position of the detector in the direction of movement. Here, for example, the time span of certain structures of the fluorescence signal or an increase or an attenuation of the fluorescence signal detected at the leading edge or the trailing edge of the value document can be used. The speed of movement of the individual value documents can be determined from the measured time intervals and the known spatial offset of the detector in the transport direction. The movement speed can also be determined from the fluorescence signal of the detector unique to the sensor if the length of the value document or the length of a structure of the value document is known.

The sensor is in particular configured such that the fluorescence signal for checking the fluorescence decay time is selected as a function of the speed of movement of the value document and the sensor relative to one another during checking of the value document. For example, the sensor is set up to check the decay time of the fluorescence on the basis of the first and second fluorescence signals if a first speed threshold value for the speed of movement is undershot. Furthermore, the decay time of the fluorescence is checked on the basis of the first and third fluorescence signals if a second speed threshold value, which is greater than or equal to the first speed threshold value, is higher than the movement speed. Furthermore, the decay time of the fluorescence can be checked on the basis of the first, second and third fluorescence signals, if it is between the first and second speed threshold. In order to check the decay time of the fluorescence, the sensor establishes, for example, a second and/or third proportional relationship with the first fluorescence signal. The respective proportional relationship may, for example, be compared with one or more threshold values in order to check whether the decay time is shorter or longer than a specified time or within a specified time window.

In one embodiment, the first detector has a spectral sensitivity that is different from the spectral sensitivity of the second detector and different from the spectral sensitivity of the third detector. The spectral sensitivity of the first detector differs from the spectral sensitivity of the second and third detectors in that the emission of the value document to be examined in a spectral region differing from the fluorescence detected by the sensor with respect to its decay time can be detected either by the first detector or by both the second and third detector. The additional emitted light may be in a spectral region of longer or shorter wavelength than the fluorescence whose decay time is examined. For example, the additional emitted light can only be detected with the first detector, whereas the additional emitted light cannot be detected by the second and third detector, respectively. Alternatively, the additional emitted light can only be detected by the second and third detector, respectively, whereas the additional emitted light cannot be detected by the first detector. To obtain different spectral sensitivities of the detectors, different types of detectors may be used, but the first detector may also use a different spectral filter than that used for the second and third detectors. The additional emitted light can likewise be a fluorescence of the document of value.

The additional emission light, for which the sensor is provided for the examination, can be an emission light emitted by the same value document whose fluorescence decay time is examined. In this case, for example, an area of the document of value is examined for additional emitted light, which is outside the area of the document of value which emits the above-mentioned fluorescence. The two value document regions of the value document may be separate value document regions from each other or partially overlap. In the latter case, however, it is preferred to examine the decay time of the fluorescence outside the overlap region. The additional emitted light may also be emitted by other value documents than the one whose decay time of the fluorescence is examined.

In the measuring plane, the front detection zone preferably overlaps the illuminated portion in such a way that, when checking a document of value, only a partial region of the front detection zone, which is located at the end of the front detection zone viewed in the direction of movement, is illuminated with excitation light. The partial region illuminated in the front detection region extends, viewed in the direction of movement, from the center of the front detection region or from a position behind the center of the front detection region up to the end of the front detection region. In the direction of movement, from the beginning of the preceding detection zone up to the center, there is no overlap in the measurement plane between the preceding detection zone and the illuminated segment. Preferably, the illuminated partial area of the front detection zone is comprised between 20% and 50% by area of the front detection zone.

In one embodiment, the first detection region overlaps the illuminated section in the measurement plane in such a way that, during the examination of the value document, only a partial region of the first detection region is illuminated with the excitation light, which partial region, viewed in the direction of movement, is located at the beginning of the first detection region. Viewed in the direction of movement, the center of the illumination section is located, for example, in front of the first detection zone. The illuminated partial region of the first detection region, viewed in the direction of movement, preferably extends from the beginning of the first detection region up to the center of the first detection region. In this case, in the direction of movement, no overlap with the illumination area occurs in the measuring plane from the center of the first detection area to the end of the first detection area. In this embodiment, of all detection regions, the first detection region overlaps the illuminated segment most in the measurement plane. Preferably, the illuminated partial region of the first detection region comprises at least 30% of the first detection region by area. In particular, the first detection regions overlap the illuminated portion such that substantially half of the first detection regions are illuminated by the excitation light during the examination of the value document.

The invention further relates to a device which is designed for the use of a sensor according to the invention for checking value documents. The device can be a value document checking device for checking the authenticity of value documents, a value document deposit device or processing machine which can check and optionally sort the value documents.

The invention also relates to a method for checking valuable documents, comprising the following steps: the value document and the sensor provided for checking the value document are moved relative to one another for checking the value document, wherein the value document is moved in the direction of movement relative to the sensor and relative to the illuminated section. A section of the measuring plane of the sensor is illuminated by the illumination device, so that the value document is illuminated with excitation light in the illuminated section when the value document is moved relative to the sensor and relative to the illuminated section. The sensor has a plurality of detectors for detecting fluorescent light, which is emitted by the value document illuminated with excitation light in different detection regions of the measuring plane. The decay time of the fluorescence of the document of value is then checked on the basis of the fluorescence signal of the detector. The detection regions of the detector are arranged offset to one another in the direction of movement of the value document. In the detection step, the first detector generates a first fluorescence signal of a first detection region which overlaps the illuminated segment in the measurement plane, and the second detector generates a second fluorescence signal of a preceding detection region which, viewed in the direction of movement, is situated in front of the first detection region in the measurement plane.

Furthermore, in the detection step, the third detector may generate a third fluorescence signal of a subsequent detection zone, which detection zone is situated behind the first detection zone in the measurement plane, viewed in the direction of movement. Other sensors, similar to the sensors, can carry out corresponding method steps in the method according to the invention for their design features.

The relative movement between the sensor and the value document to be examined can be implemented by means of the above-described device. The remaining method steps can be carried out by the above-described sensor. The illumination device may be an integral part of the sensor. The decay time can be verified by the sensor itself. Alternatively, however, the decay time can also be checked outside the sensor.

Drawings

The invention is illustrated below with the aid of the accompanying drawings. In the drawings:

FIGS. 1a-c schematically show the structure of the sensor with the illumination light path and illumination section B (FIGS. 1a, 1c) and with the detection light path and detection zones D1, D2, D3 (FIGS. 1B, 1 c);

FIGS. 2a-b show the relative arrangement of illumination zones and detection zones in two embodiments in a top view of the measuring plane of the sensor;

3a-d show graphs of the variation of the fluorescence intensity as a function of the position x in the direction of movement of the value document for two different speeds of movement and two different decay times;

FIGS. 4a-c show the fluorescence signals S1, S2 and S3 of detectors D1, D2 and D3 as a function of decay time for two different speeds of motion;

FIGS. 5a-b show the proportional relation S3/S1 of the third and first fluorescence signal as a function of decay time (FIG. 5a) and the proportional relation S2/S1 of the second and first fluorescence signal as a function of decay time (FIG. 5 b).

Detailed Description

Fig. 1a-c schematically show the structure (x-z plane) of a sensor 100 for checking value documents. The value document W moves in the direction of movement T relative to the sensor 100 and at the same time passes through the measuring plane E of the sensor 100. The value document plane here lies substantially in the measuring plane E of the sensor 100. For checking value documents, it is moved through an illumination section B of the measuring plane E, in which the excitation light of the illumination device 8 of the sensor 100 impinges on the measuring plane, see fig. 1 a. The light path of the excitation light is directed from the illumination device 8 via a lens 9 to the beam splitter 6, which diverts a portion of the excitation light and directs the excitation light from the beam splitter 6 via a further lens 7 to the measurement plane E. The excitation light of the illumination device 8 causes fluorescence of the document of value W to be optically excited and can, for example, be in the spectral region of ultraviolet, visible or infrared light. As illumination means, for example, lamps, one or more light-emitting diodes or one or more lasers can be used.

The sensor also comprises a plurality of detectors 1, 2, 3, which can be mounted, for example, on a common carrier 4. As detector, for example, a single photodiode or a single phototransistor can be used, but for this purpose also a photodetector array or a two-dimensional photodetector array can be used, the individual elements of which form the detector. Each detector is designed for detecting fluorescence of the value document, which can be in the ultraviolet, visible or infrared spectral region. The detector may be provided with a spectral filter (not shown) which suppresses the spectral range of the illumination light and/or which transmits only the fluorescence to be detected. The detectors detect fluorescence light emitted by respective detection regions of the respective detectors lying in the measurement plane E. The first detector 1 thus detects the fluorescence light emitted by the first detection zone D1, the second detector 2 detects the fluorescence light emitted by the preceding detection zone D2, the preceding detection zone D2 being situated in front of the first detection zone D1 in the direction of movement T of the value document, and the third detector 3 detects the fluorescence light emitted by the subsequent detection zone D3, the subsequent detection zone D3 being situated behind the first detection zone D1 in the direction of movement T of the value document W, see fig. 1 b. The fluorescence of each detection zone D1-D3 is collected by lens 7, passed through beam splitter 6 and through lens 5, and focused onto each detector 1-3.

By moving the value document W in the direction of movement T, not only the value document region which is located precisely within the illumination section B, but also the value document region connected thereto in the direction of movement T, is made to fluoresce. The first detection zone D1 and the preceding detection zone D2 are positioned such that they partially overlap the illumination zone B. Subsequent detection zone D3 is in this example outside illumination zone B, see fig. 1 c. During the movement of the document of value W relative to the sensor 100, the fluorescence of the document of value W is continuously detected by the detectors 1, 2, 3, for example over the entire document of value W.

Fig. 2a shows a top view (x-y plane) of the measuring plane E of the sensor 100, from which the relative arrangement of the illumination zone B and the detection zones D1, D2, D3 can be seen. The shape of the illumination section B and the detection zones D1, D2, D3 may be arbitrary. The shape of the illumination zone B is rectangular in this example, while the shape of the detection zones D1, D2, D3 is circular. The illumination section B overlaps the first detection zone D1 in the illuminated partial region D10 of the first detection zone D1 and overlaps the preceding detection zone D2 in the illuminated partial region D20 of the preceding detection zone D2. The value document W is moved in the direction of movement T (x-direction) through the section of the measuring plane E indicated in fig. 2 a.

During the movement of the value document W through the measuring plane E of the sensor 100 in the direction of movement T, the detectors 1, 2, 3 continuously detect the intensity of the fluorescence emitted by the value document W. The continuously detected fluorescence intensity L is plotted in fig. 3a-d, respectively, as a function of the position coordinate x parallel to the direction of movement T of the document of value W. Here, the fluorescence intensity is normalized or scaled to the maximum intensity value at that time. Ideally, the fluorescence intensities plotted in fig. 3a-D detected by the detectors 1, 2, 3 remain the same as long as the region of the value document that emits fluorescence uniformly moves through the detection regions D1, D2, D3.

In addition, detection zones D1-D3 and illumination zone B are depicted above FIGS. 3a-D, respectively, at corresponding x positions. FIGS. 3a and 3c show the speed v of movement of a document of value W_gFluorescence intensity at lower conditions, FIGS. 3b and 3d show high movement velocity v_hThe fluorescence intensity in the case. In FIGS. 3a and 3d, respectively, the fluorescence intensity L of a "slow" fluorescent substance whose fluorescence intensity has a longer decay time τ is plotted_lIn FIGS. 3b and 3c, the fluorescence intensity L of a "fast" fluorescent substance is plotted, respectively, with a shorter decay time τ_k. In all four cases, the highest fluorescence intensity was detected in the first detection zone D1. Whether or not and how much fluorescence intensity can be detected in the preceding and subsequent detection zones D2 and D3 depends on the decay time of the fluorescence and the speed of movement of the value document W.

In fig. 4a-c for two different movement velocities v_gAnd v_hThe fluorescence signal S1 of the first detector 1, the fluorescence signal S2 of the second detector 2, and the fluorescence signal S3 of the third detector 3 are expressed in relation to the fluorescence decay time τ, respectively. At a decay time of τ_lOf "slow" fluorescence and low speed of motion v_gIn the case of (fig. 3 a), the first detector 1 (first detection zone D1) and the third detector 3 (subsequent detection zone D3) detect a strong fluorescence signal S1 or S3, see fig. 4a and 4 b. In contrast, the fluorescence signal S2 of the second detector 2 (preceding detection zone D2) is small, see FIG. 4 c. In this case, in order to check the decay time of fluorescence, the fluorescence signals S1 and S3 of the first and third detectors 1, 3 are used. For this purpose, for example, a ratio S3/S1 can be established, on the basis of which the decay time of the fluorescence can be checked and, if necessary, unambiguously determined, see FIG. 5 a.

At a decay time of τ_lOf "slow" fluorescence and high speed of motion v_hIn the case of (as shown in fig. 3 d) and in the case of having a decay time τ_kOf (2) fast fluorescence and high speed of movement v_hIn the case of (fig. 3 b), the first detector 1 (first detection zone D1) and the third detector 3 (subsequent detection zone D3) detect a strong fluorescence signal S1 or S3, see fig. 4a and 4 b. In contrast, the fluorescence signal S2 of the second detector 2 (preceding detection zone D2) is small, see FIG. 4 c. In order to check the decay time of the fluorescence, the fluorescence signals S1 and S3 of the first and third detectors 1, 3 are also used in this case. For this purpose, a proportional relationship S3/S1 can be established, for example, on the basis of which the decay time of the fluorescence can be checked and, if necessary, unambiguously determined, see FIG. 5 a.

At a decay time of τ_kOf "fast" fluorescence and low speed of motion v_gIn the case of (fig. 3 c), the first detector 1 (first detection zone D1) detects a strong fluorescence signal S1, see fig. 4 a. In this case, however, the fluorescence signal S3 of the third detector 3 (subsequent detection zone D3) is negligibly small, see fig. 4 b. In contrast, the fluorescence signal S2 of the second detector 2 (preceding detection zone D2) is strong in this case, see fig. 4 c. To is coming toThe decay time of the fluorescence is examined, in this case using the fluorescence signals S1 and S2 of the first and second detectors 1, 2. For this purpose, a proportional relationship S2/S1 can be established, for example, on the basis of which the decay time of the fluorescence can be checked and, if necessary, unambiguously determined, see FIG. 5 b.

At a lower or at two speeds of movement v_gAnd v_hIn the case of intermediate movement speeds, the decay time of the fluorescence can also be checked with all three fluorescence signals S1, S2 and S3. In this case, for example, the decay time τ is substantially equal to_kAnd τ_lThe decay time τ of the mean value leads to a distinct fluorescence signal S1, S2, S3 in all three detectors 1, 2 and 3. For example, in a certain medium speed range, the decay time τ can be checked by means of all three fluorescence signals S1, S2 and S3, for example by establishing two proportionality relationships S3/S1 and S2/S1, while at lower speeds it can be checked by means of the first and second fluorescence signals S1, S2.

Detectors 1, 2 and 3 may have similar or identical spectral sensitivities. However, in the following exemplary embodiments, the first detector 1 has a different spectral sensitivity than the second detector 2 and the third detector 3, the spectral sensitivity of the second detector 2 and the third detector 3 being at least approximately the same. The change in their spectral sensitivity profiles is preferably at least approximately the same within a common spectral region covering all three detectors 1, 2, 3. By virtue of the different spectral sensitivities of the first detector 1, the sensor 100 is able to detect, in addition to the checking of the decay time τ, additional emission of the value document W, for example fluorescence caused by another fluorescent substance than the fluorescence whose decay time τ is checked. In this case, the additional emitted light is preferably detected in regions of the document of value in which no fluorescence whose decay time τ is detected occurs.

In a first variant of this embodiment, a first detector 1 is used whose spectral sensitivity covers an additional spectral region, which is not covered by both the second detector 2 and the third detector 3. For example, the spectral sensitivity of the first detector 1 extends up to a spectral region of longer wavelength than the spectral sensitive regions of the second detector 2 and the third detector 3. In this first variant, the first detector 1 detects a distinct fluorescence signal, which corresponds to an additional fluorescence intensity in the additional spectral region. Neither the second detector 2 nor the third detector 3 detects a fluorescence signal from fluorescence in this additional spectral region. The emission of additional emitted light can be clearly demonstrated, since this case is clearly distinguishable from all the cases shown in fig. 3, 4 and 5. Since there is always also a significant fluorescence signal detected by the second detector 2 or the third detector 3.

In a second variant of this embodiment, a second detector 2 and a third detector 3 are used, whose spectral sensitivities cover additional spectral regions, respectively, which are not covered by the first detector 1. For example the spectral sensitivity of the second detector 2 and the third detector 3, respectively, extends up to a spectral region longer than the wavelength of the first detector 1. In this second variant, the second detector 2 and the third detector 3 each detect a distinct fluorescence signal, which corresponds to an additional fluorescence intensity in the additional spectral region. The first detector 1 does not detect a fluorescence signal from fluorescence in this additional spectral region, but only the second or third detector. In this variant, the emission of additional emitted light can also be clearly demonstrated and can be clearly distinguished from all the cases of fig. 3, 4 and 5. Since in any of these latter cases the first detector 1 detects a significant fluorescence signal.

Fig. 2b shows a further embodiment in which the sensor 100 has further detectors n which detect fluorescence of the illuminated value document W, which emits fluorescence in further detection regions Dn of the measuring plane E when the value document is moved relative to the sensor 100. The further detection zones Dn are situated in the direction of movement T after the preceding detection zone D2 but before the first detection zone D1. The first, second, third and further detectors 1, 2, 3, n can be formed by a one-dimensional photodetector array, wherein the detectors are designed on the same substrate, for example. Similar to the first, second and third detectors, further detectors n generate further fluorescence signals Sn of further detection regions Dn. Similar to the third fluorescence signal, it may be advantageous for certain measurement conditions to also use the fluorescence signal Sn for checking the decay time, for which purpose, for example, a proportional relation Sn/S1 is established. Furthermore, the sensor 100 can have further detectors m which detect the fluorescence of the illuminated value document W in further detection regions Dm of the measuring plane E. These detection areas Dm are behind the first detection area D1 in the direction of motion T. The fluorescence signal Sm can also be used to check the decay time of the fluorescence.

Claims

1. A sensor (100) for checking a value document (W) present in a sensor measuring plane (E), wherein, for checking the value document (W), the value document (W) and the sensor (100) are moved relative to one another in such a way that the value document (W) is moved relative to the sensor (100) in a movement direction (T), comprising:

-an illumination device (8) for illuminating a section (B) of the sensor measuring plane (E) in order to illuminate the value document (W) with excitation light within said section (B) when the value document (W) moves relative to the sensor (100), and

-a plurality of detectors (1, 2, 3, n) for detecting fluorescence light which is emitted by a value document (W) illuminated with excitation light in different detection regions (D1, D2, D3, Dn) of a measurement plane (E) when the value document (W) is moved relative to the sensor (100), wherein the detection regions (D1, D2, D3, Dn) of the detectors (1, 2, 3, n) are arranged offset from one another in the direction of movement (T) of the value document (W),

and wherein the sensor (100) is provided for checking the decay time of the fluorescence of the value document (W) on the basis of the fluorescence signal of the detector (1, 2, 3, n), characterized in that:

-the first detector (1) is arranged for generating a first fluorescence signal (S1) of a first detection region (D1), the first detection region (D1) overlapping the illuminated segment (B) in the measurement plane (E), and

-the second detector (2) is arranged for generating a second fluorescence signal (S2) at a preceding detection zone (D2) which, viewed in the direction of motion (T), precedes the first detection zone (D1) in the measurement plane (E).

2. A sensor according to claim 1, characterized in that the third detector (3) of the sensor is arranged for generating a third fluorescence signal (S3) of a subsequent detection zone (D3), which subsequent detection zone (D3) is situated behind the first detection zone (D1) in the measurement plane (E) viewed in the direction of movement (T).

3. A sensor according to claim 2, characterized in that the first detector (1) has a spectral sensitivity which differs from the spectral sensitivity of the second detector (2) and from the spectral sensitivity of the third detector (3) such that additional emission light of the value document (W) to be examined in a spectral region differing from fluorescence can be detected either by the first detector (1) or by the second detector (2) and the third detector (3), respectively.

4. A sensor according to one of claims 1 to 3, characterized in that the sensor has one or more further detectors (n) each arranged for generating a further fluorescence signal (Sn) of a further detection zone (Dn), wherein the further detection zone or zones (Dn) are located behind the preceding detection zone (D2) and in front of the first detection zone (D1) in the measurement plane (E) as seen in the direction of movement (T).

5. A sensor according to one of claims 1 to 3, characterized in that the sensor is provided for checking the decay time of the fluorescence of the value document (W) under predetermined conditions using the second fluorescence signal (S2) and the fluorescence signal (S1, Sn) of at least one other detector (1, 2, 3, n, m) of the sensor (100).

6. A sensor according to one of claims 1 to 3, characterized in that the sensor is arranged to check the decay time using the second fluorescence signal (S2) and the fluorescence signal (S1, S3, Sn, Sm) of at least one other detector (1, 2, 3, n, m) of the sensor (100) when the decay time of the fluorescence thereof is expected to be shorter than a defined decay time for the value document (W) to be checked.

7. A sensor according to one of claims 1 to 3, characterized in that the sensor is arranged to select the fluorescence signal (S1, S2, S3) for checking the fluorescence decay time on the basis of the speed of movement of the value document (W) and the sensor (100) relative to one another when checking the value document.

8. A sensor according to one of claims 1 to 3, characterized in that the sensor is arranged to check the decay time of the fluorescence of the value document (W) on the basis of the first fluorescence signal (S1) and the second fluorescence signal (S2).

9. A sensor according to one of claims 1 to 3, characterized in that the sensor is arranged to check the decay time of the fluorescence of the value document (W) selectively on the basis of the first fluorescence signal (S1) and the second fluorescence signal (S2) or on the basis of the first fluorescence signal (S1) and the third fluorescence signal (S3).

10. A sensor according to one of claims 1 to 3, characterized in that the preceding detection zone (D2) overlaps the illuminated section (B) in such a way that, during the examination of the value document (W), only a partial region (D20) of the preceding detection zone (D2) is illuminated with excitation light, which partial region (D20) is at the end of the preceding detection zone (D2) viewed in the direction of movement.

11. A sensor according to claim 10, characterized in that the illuminated part-area (D20) of the front detection zone (D2), viewed in the direction of movement, extends from the center of the front detection zone (D2) or from a position behind the center of the front detection zone (D2) up to the end of the front detection zone (D2).

12. A sensor according to one of claims 1 to 3, characterized in that the first detection zone (D1) overlaps the illuminated section (B) in such a way that, during the examination of the value document (W), only a subregion (D10) of the first detection zone (D1) is illuminated with excitation light, the subregion (D10) of the first detection zone (D1), viewed in the direction of movement, being at the beginning of the first detection zone (D1).

13. A sensor as claimed in claim 12, characterized in that the illuminated part-area (D10) of the first detection zone (D1) extends, viewed in the direction of movement, at least from the beginning of the first detection zone (D1) up to the center of the first detection zone (D1).

14. A device for checking documents of value (W), characterized in that it has a sensor according to one of the preceding claims.

15. A method for checking a value document (W) by means of a sensor according to one of claims 1 to 13, comprising the following steps:

-the value document (W) to be examined is moved in a movement direction (T) relative to a sensor provided for examining the value document (W), wherein the value document (W) is moved in the movement direction (T) relative to the sensor,

-illuminating a section (B) of the sensor measuring plane (E) by means of an illumination device (8), so that the value document (W) is illuminated in the illuminated section (B) by the excitation light when it is moved relative to the sensor (100),

-detecting fluorescent light by means of a plurality of detectors, which fluorescent light is emitted by value documents (W) illuminated with excitation light in different detection regions (D1, D2, D3) of a measurement plane (E) when said value documents (W) are moved relative to the sensor (100), wherein the detection regions (D1, D2, D3) of the detectors are arranged offset from one another in the direction of movement (T) of the value documents (W), and wherein a first detector (1) generates a first fluorescent signal (S1) of a first detection region (D1), the first detection region (D1) overlaps the illuminated section (B) in the measurement plane, and a second detector (2) generates a second fluorescent signal (S2) of a preceding detection region (D2), which preceding detection region (D2) is situated in front of the first detection region (D1) in the measurement plane, viewed in the direction of movement (T),

-checking the decay time of the fluorescence of the value document (W) on the basis of the fluorescence signal of the detector.