EP1265198A2 - Device and method for investigating documents - Google Patents

Abstract

The arrangement has at least one stimulation device for stimulating luminescent light (16) in or on the document (10) under investigation and at least two detector units (1,2) for detecting at least some of the luminescent light emitted by the document. The detector units are arranged one behind the other in relation to the luminescent light emitted by the document. AN Independent claim is also included for the following: a method of investigating documents.

Description

The invention relates to a device for examining documents, in particular value, ID or security documents, with at least an excitation device for excitation of luminescent light in or on a document to be examined and at least two detector units to capture at least part of what is emitted by the document Luminescence light. The invention also relates to a corresponding one Method.

To increase the security against counterfeiting, ID, security or Documents of value, such as Banknotes, provided with features or with suitable ones Printed security inks, which luminescent substances contain. These are substances that e.g. by light, electric fields, Radiation or sound can be excited to emit light. at The authenticity check usually includes the documents to be checked Illuminated light of a certain spectral range and that of the luminescent Substances of the document emitted luminescent light are detected. Based on the intensity and / or spectral characteristics of the emitted Luminescent light can then be determined if the document is genuine or is fake.

The reliability of statements about the authenticity of the checked documents is particularly dependent on the accuracy with which is the spectral characteristic, i.e. the color of the luminescent light is analyzed. Such an analysis can be done, for example, by spectrometers take place, which, however, a relatively high technical effort as well require high manufacturing costs. Therefore provide a simpler solution individual detector units, e.g. Photodiodes or photomultipliers, with different spectral sensitivity. Depending on the spectral characteristic of the luminescent light, the detector units deliver different Detector signals, which are then used for the spectral analysis of the luminescent light can be used.

However, devices of this type have the disadvantage that this is by the individual Detector units each detected luminescent light due to Parallax errors are generally not from exactly the same spatial Part of the document comes from. This will make a reliable assessment the color properties of a portion of the document outgoing luminescent light impossible. This is especially true of Disadvantage if partial areas with small dimensions on their luminescent properties should be examined, since there are already minor ones Parallax errors to particularly large inaccuracies in the spectral Analysis of the luminescent light can lead.

It is an object of the invention, a device and a corresponding Specify procedures, which with a simple structure, a higher reliability when examining the luminescence properties of documents, especially allow documents of value, ID or security.

This object is achieved by the device according to claim 1 and the Method according to claim 18 solved.

The invention is based on the idea that the detector units are related on the direction of that emitted by the document and on the detector units striking luminescent light are arranged one behind the other. As a result, the luminescent light strikes one after the other arranged detector units and is detected by them.

The arrangement of the detector units according to the invention ensures that that all detector units arranged directly one behind the other emitted from a common spatial portion of the document Can capture luminescent light. Any parallax errors that occur with a laterally offset arrangement of detector units would occur, are arranged one behind the other by the arrangement of the detector units according to the invention greatly reduced. From those of the individual detector units Spectral components of the luminescent light recorded can then make statements about the luminescent properties of the document with high reliability be derived.

In a preferred embodiment of the invention it is provided that at least one first detector unit for that spectral subrange of the luminescent light is permeable, which with at least one behind the second detector unit arranged in the first detector unit shall be. The first detector unit then becomes a first spectral one Part of the luminescent light is captured, while a second spectral Part of the luminescent light pass through the first detector unit can and detected by the second detector unit arranged behind it becomes. The first detector unit acts like an optical filter in front of the second detector unit behind. For certain applications it is therefore usually possible to dispense with additional optical filters.

The detector units are preferably photodiodes, which are arranged in layers on top of each other and a so-called Form a sandwich diode. This creates a very compact arrangement of the Detector units reached.

In principle, the detector units can also be elements which light using other physical detection principles, e.g. using the avalanche effect.

In a further preferred embodiment of the invention, that the individual detector units on a common component, in particular semiconductor component, which is at least comprises two photosensitive layers, in particular p-n junctions, where each layer, in particular each p-n junction, has one Corresponds to the detector unit. Due to the small distance between the detector units is a particularly strong reduction in this embodiment of parallax errors.

The photodiodes or p-n junctions preferably have different ones Absorptionskanten, wherein the absorption edge at least a first Photodiode or a first p-n junction at smaller wavelengths is at least one behind the first photodiode as the absorption edge arranged second photodiode or one behind the first p-n junction arranged second p-n junction.

A particularly simple and reliable derivation of statements about the spectral properties of the detected luminescent light from those of the Detector signals generated on the basis of individual detector units can a division of two detector signals and / or the difference of two logarithmic detector signals.

Fig. 1

einen bevorzugten Aufbau der erfindungsgemäßen Vorrichtung;

Fig. 2

eine erste Ausführungsform der erfindungsgemäß angeordneten Detektoreinheiten;

Fig. 3

a) und b) jeweils eine zweite Ausführungsform der erfindungsgemäß angeordneten Detektoreinheiten;

Fig. 4

Beispiele für spektrale Empfindlichkeiten der in Fig. 2 bzw. Fig. 3 dargestellten Detektoreinheiten; und

Fig. 5

ein Schaltbild der in Fig. 3 dargestellten zweiten Ausführungsform der erfindungsgemäß angeordneten Detektoreinheiten.

The invention is explained in more detail below on the basis of exemplary embodiments illustrated in the figures. Show it:

Fig. 1

a preferred structure of the device according to the invention;

Fig. 2

a first embodiment of the detector units arranged according to the invention;

Fig. 3

a) and b) each have a second embodiment of the detector units arranged according to the invention;

Fig. 4

Examples of spectral sensitivities of the detector units shown in FIGS. 2 and 3; and

Fig. 5

a circuit diagram of the second embodiment of the detector units arranged according to the invention shown in FIG. 3.

Fig. 1 shows a preferred structure of the device according to the invention. A document to be examined, in the example shown a bank note 10, is indicated by means of transport rollers 40 and transport belts 41 Transport device transported past the sensor system 7. Here, the bank note 10 with the excitation light 15 of the light sources 12 irradiated. The light sources 12 are, for example, fluorescent tubes, Incandescent lamps, lasers or LEDs, which each emit light, that is suitable for the excitation of luminescent light in or on the bank note 10 is. The excitation light 15 is preferably ultraviolet (UV light. For the elimination of spectral components at higher Wavelengths, i.e. for example in the visible or infrared spectral range, can appropriate filters (not shown) in front of the light sources 12th to be ordered.

In the example shown, luminescent light 16 in is excited or on the document by the light 15 of the light sources 12. A corresponding one Luminescence is therefore referred to as photoluminescence. Alternatively or additionally, it can also be by electromagnetic or electric fields, radiation or sound other types of luminescence phenomena, such as. Electro-, radio- or sonoluminescence, in or be excited on the document. The suggestion is made by appropriate Excitation devices, e.g. electrical contacts or field plates, Radiation sources for cathode, ion or x-rays, Ultrasound sources or antennas.

In an alternative embodiment of the invention it is provided that the excitation light 15 emitted by the respective light sources 12 at different Wavelengths or wavelength ranges. That with different Wavelengths or wavelength ranges of excited luminescent light 16 leaves even more precise statements about the luminescent properties the banknote 10 too. It can in particular be provided that the Light sources 12 illuminate the banknote 10 either individually or in combination and this with individually or combined illuminated banknote 10 detected luminescent light 16 is evaluated. Will be in the example shown 1 first illuminated with only one light source 12, then detect the two detector units 1 and 2 a first pair of intensity values. Subsequent illumination with the other light source 12 generates a second pair of intensity values. With simultaneous lighting with Finally, a third pair of intensity values is obtained for both light sources 12. By comparing and / or arithmetically linking the here received, i.a. different, intensity values will be a particularly accurate Examination of the luminescent properties of the examined banknote 10 reached.

Depending on the temporal decay behavior, there can be between Phosphorescent or fluorescent light can be distinguished. The invention The device or the method is suitable for examination of phosphorescent and fluorescent light alike.

The luminescent light 16 excited in or on the bank note 10 is emitted by the banknote 10 emits and strikes two detector units 1 and 2, which according to the invention are arranged one behind the other that the the bank note 10 outgoing luminescent light 16 successively on the individual Detector units 1 and 2 meet and are detected by them can. The two detector units 1 and 2 each have different ones spectral sensitivities so that each has a different spectral component of the luminescent light 16 is detected. Accordingly differ the detector signals S generated by the detector units 1 and 2, which can be fed to an evaluation device 9 for evaluation and analysis.

Between the bank note 10 and the detector devices 1 and 2 is in an optical device 13 is provided in the example shown, which the luminescent light 16 emitted by the bank note 10 onto the detector units 1 and 2 steers, especially focused. It is preferably This is an imaging optic which covers a partial area 11 of the Banknote 10 maps to the detector units 1 and 2. Preferably be self-focusing lenses, so-called Selfoc lenses, are used for this purpose. at self-focusing lenses are cylindrical optical Elements made of a material which is one of the optical axis of the Cylinder has a refractive index decreasing towards its cladding. By using Selfoc lenses, the distance between the Banknote 10 and the detector units 1 and 2 independent and adjustment-free 1: 1 image of the portion 11 of the bank note 10 to be examined reached on the detector units 1 and 2.

In this example, a filter 14 is arranged in front of the detector units 1 and 2, which for those spectral subregions of the luminescent light 16 is permeable, which detects with the detection units 1 and 2 should be.

2 shows a first embodiment of the arrangement according to the invention Detector units shown. The individual detector units are as photodiodes 1 and 2 formed and related to the direction of the Document emitted luminescent light 16 arranged one behind the other. The individual photodiodes 1 and 2 each have a p-n junction 3/4 or 5/6 between a p-doped 3 or 5 and an n-doped 4 or 6 semiconductor layer. The doping profile is greatly simplified shown and generally gives not the actual proportions of the Layer thicknesses again. There are spacers between the photodiodes 1 and 2 8 provided to avoid electrical short circuits. To any To keep parallax errors as low as possible, the height of the spacers should 8 should not be chosen too large and in the order of magnitude Height of the photodiodes 1 and 2 are. Optionally, also with appropriate Spacers 8 spaced apart, a filter 14 in front of the photodiode 1 be arranged. In addition, it is also possible to have a corresponding Provide filters (not shown) between the individual photodiodes 1 and 2. With the electrical connections 17 voltages between tapped the differently doped semiconductor layers 3/4 or 5/6 and forwarded as detector signals S to an evaluation unit (not shown).

FIGS. 3a and 3b each show a second embodiment of the invention Arrangement shown. FIG. 3a shows a component 20 which the detector units 1 and 2 are integrated together, wherein component 20 has two p-n junctions 22/21 and 23/21, respectively each correspond to a detector unit 1 or 2. The n-doped semiconductor layer 21 here forms the substrate on which the two p-n junctions 22/21 or 23/21 are applied in layers. The doping profile is here also shown in a very simplified form and generally gives not the actual Ratios of the layer thicknesses again. Analogous to that in figure 2 example shown here are voltages with suitable connections 17 tapped and as detector signals S to an evaluation unit (not shown).

Figure 3b shows a variant of the second embodiment of the invention Arrangement. The component 30 shown comprises two layers trained p-n junctions 32/33 and 34/33, which on a common Substrate 31 are applied. The substrate 31 itself can be a Semiconductor or ceramic substrate. In terms of how this works The explanations for FIG. 3a apply analogously to the embodiment.

The detector units 1 and 2 shown in FIGS. 2, 3a and 3b are chosen so that the first detector unit 1 for that spectral sub-range of the luminescent light 16 is transparent, which with the behind the first detector unit 1 arranged second detector unit 2 can be detected should. Those designed in particular as photodiodes or p-n junctions Detector units 1 and 2 have different absorption edges on, wherein the absorption edge of the first photodiode 1 and first p-n transition 3/4, 32/33 or 22/21 at smaller wavelengths lies as the second absorption edge behind the first photodiode 1 or the first p-n transition 3/4, 32/33 or 22/21 arranged second Photodiode 2 or second p-n junction 5 / 6.34 / 33 or 23/21.

In the sandwich-like arrangement of the individual shown in Figure 2 Detector units 1 and 2 one above the other become the respective p-n junctions 3/4 or 5/6 preferably on different semiconductor materials realized. For example, for the first detector unit 1 Photodiode based on silicon (Si) and for the second detector unit 2 a photodiode based on germanium (Ge) is used. wavelength below about a micron can then be from the photodiode 1 can be detected on the basis of silicon during wavelengths penetrate this photodiode 1 above about a micrometer and from the photodiode 2 arranged behind it on the basis of Germanium can be detected. Analogously, photodiodes can be used based on silicon and indium gallium arsenide (InGaAs) or silicon and lead sulfide (PbS) can be combined to make the luminescent light 16 to be detected in two different spectral subregions. In addition, of course, is the combination of several corresponding photodiodes possible, e.g. B. from silicon, indium gallium arsenide and lead sulfide.

In the embodiments of the invention shown in FIGS. 3a and 3b Arrangement is the different permeability or sensitivity of the detector units 1 and 2 by selecting suitable ones Semiconductor materials and / or a corresponding doping of the respective material reached. A corresponding component 20 or 30 leaves can be realized, for example, on the basis of silicon, the first p-n junction 22/21 or 32/33 due to a lower penetration depth for short-wave Light is particularly sensitive. However, long-wave light can penetrate deeper into the layer system and of the stronger in the long-wave Spectral range sensitive second p-n transition 23/21 and 34/33 detected become.

In principle, it is also possible to use individual components 20 or 30 accordingly to arrange the embodiment shown in Fig. 2 in a row. With a suitable selection of the semiconductor materials used can be the luminescent light 16 hereby in more than two spectral subregions easily capture.

FIG. 4 shows an example for different spectral sensitivities E. of the detector units 1 and 2 shown in FIGS. 2 and 3 can be seen from the diagram, the spectral sensitivity E1 is the first detector unit 1 in the region of short wavelengths λ, while the spectral sensitivity E2 behind the first detector unit 1 arranged second detector unit 2 at higher wavelengths λ their Maximum reached. The respective behavior is complementary to this spectral permeability of the detector units 1 and 2. The spectral The transmittance of the detector unit 1 is accordingly at higher wavelengths λ greatest, so that the luminescent light in this partial area of the Spectrum can penetrate the detector unit 1 and finally by the Detector unit 2 can be detected.

Figure 5 shows a circuit diagram of the second shown in Figures 3a and 3b Embodiments. Detector units 1 and 2, i.e. the corresponding p-n junctions 22/21 and 23/21 or 32/33 and 34/33, of the component 20 and 30 are oppositely connected in series photodiodes shown, the cathodes of a common potential 18th lie. Via the anode outputs 19 of the photodiodes, the signals S1 and S2 fed to an evaluation device 9. In the evaluation device 9, the signals S1 and S2 are each in a logarithmic amplifier 28 logarithmically amplified and then to a differential amplifier 29 laid. Since the difference between two logarithmic values is the logarithm of the quotient of both values is the output voltage Ua of the differential amplifier 29 proportional to the logarithm of the quotient of the two detector signals S2 / S1 and thus independent of the absolute Intensity of the luminescent light 16. From the output voltage Ua can then make statements about the spectral properties, in particular about the color of the detected luminescent light 16 with particularly high reliability be derived.

The spectral properties of the lunimescent light 16, in particular the Wavelength, e.g. the central wavelength, and / or the wavelength range and / or the color can not only be visible according to the invention Spectral range, but also in invisible spectral ranges, such as e.g. in the infrared or ultraviolet, can be detected and analyzed.

It is an alternative or in addition to the analog evaluation described also possible to digitize the detector signals S1 and S2 first and then in a digital, especially computer-based, evaluation derive statements about the luminescent light from the digitized signals.

Claims (24)

Device for examining documents, in particular documents of value, identification or security, with at least one excitation device for excitation of luminescent light (16) in or on a document (10) to be examined and at least two detector units (1, 2) for detecting at least part of the luminescent light (16) emitted by the document (10), characterized in that
the detector units (1, 2) are arranged one behind the other based on the luminescent light (16) emitted by the document (10). Apparatus according to claim 1, characterized in that the excitation device comprises at least one light source (12) for illuminating the document (10) with excitation light (15) which is suitable for exciting luminescent light (16) in or on the document (10) , Device according to one of claims 1 to 2, characterized in that the detector units (1, 2) have different spectral sensitivities (E1, E2). Device according to one of claims 1 to 3, characterized in that at least one first detector unit (1) is transparent to at least one spectral sub-region of the luminescent light (16), which has at least one second detector unit (2) arranged behind the first detector unit (1). can be detected. Device according to one of claims 1 to 4, characterized in that the detector units (1, 2) are designed as photodiodes. Apparatus according to claim 5, characterized in that at least one optical filter is arranged at least between two photodiodes. Device according to one of claims 1 to 6, characterized in that the detector units (1, 2) are integrated on a common component (20, 30). Device according to Claim 7, characterized in that the component (20, 30) comprises at least two photosensitive layers, in particular pn junctions (22/21, 23/21, 32/33, 34/33), each photosensitive layer, In particular, each pn junction (22/21, 23/21, 32/33, 34/33) corresponds to one detector unit (1, 2). Device according to claim 8, characterized in that the photosensitive layers, in particular pn junctions (22/21, 23/21, 32/33, 34/33), are formed in layers and on a common substrate (21, 31), in particular one Semiconductor or ceramic substrate are applied. Device according to Claim 9, characterized in that the photosensitive layers, in particular pn junctions (22/21, 23/21, 32/33, 34/33), in layers with respect to the luminescent light (16) emitted by the document (10) are arranged one above the other. Device according to one of claims 5 to 10, characterized in that the photodiodes or pn junctions (22/21, 23/21, 32/33, 34/33) have different absorption edges and the first absorption edge of at least one first photodiode or at least one first pn junction (22/21, 32/33) at smaller wavelengths (λ) than the second absorption edge of at least one second photodiode arranged behind the first photodiode or at least one behind the first pn junction (22/21, 32/33) arranged second pn junction (23/21, 34/33). Device according to one of claims 1 to 11, characterized in that an optical device (13) is provided for directing the luminescent light (16) emanating from the document (10) onto the detector units (1, 2). Apparatus according to claim 12, characterized in that the optical device (13) comprises at least one lens, in particular a self-focusing lens, for focusing the luminescent light (16) emanating from the document (10) onto the detector units (1, 2). Device according to one of claims 1 to 13, characterized in that an evaluation device (9) is provided for deriving statements about the spectral properties, in particular about the wavelength, such as the central wavelength, and / or the wavelength range and / or the Color, of the detected luminescent light (16) from detector signals (S, S1, S2) generated by the detector units (1, 2). Apparatus according to claim 14, characterized in that the evaluation device (9) comprises a logarithmic amplifier (28) for logarithmizing individual detector signals (S, S1, S2). Device according to one of claims 14 to 15, characterized in that the evaluation device (9) comprises a differential amplifier (29) for forming the difference between two detector signals (S, S1, S2) or between two logarithmic detector signals (S, S1, S2) , Device according to one of claims 14 to 16, characterized in that the evaluation device (9) for deriving statements about the spectral properties, in particular about the wavelength, such as the central wavelength, and / or the wavelength range and / or the color of the detected Luminescent light (16) on the base the division of two detector signals (S, S1, S2) and / or the difference between two logarithmic detector signals (S, S1, S2) is formed. Method for examining documents, in particular value, identification or security documents, in which a document (10) to be examined is excited to emit luminescent light (16) and at least part of the luminescent light (16) emitted by the document (10) is detected by at least two detector units (1, 2), characterized in that
the luminescent light (16) successively strikes the detector units (1, 2) arranged one behind the other and is thereby detected by them. Method according to claim 18, characterized in that the document (10) is illuminated with excitation light (15) which is suitable for excitation of luminescent light (16) in or on the document (10). Method according to one of claims 18 to 19, characterized in that the luminescent light (16) is detected by detector units (1, 2) with different spectral sensitivities (E1, E2). Method according to one of claims 18 to 20, characterized in that at least one spectral sub-region of the luminescent light (16) passes through at least one first detector unit (1) and is detected by at least one second detector unit (2) arranged behind the first detector unit (1). Method according to one of claims 18 to 21, characterized in that the detector units (1, 2) generate detector signals (S, S1, S2) and statements on the spectral properties, in particular on the wavelength, from the detector signals (S, S1, S2) , such as the central wavelength, and / or the wavelength range and / or the color, of the detected luminescent light (16) can be derived. Method according to Claim 22, characterized in that the derivation of statements about the spectral properties, in particular about the wavelength, such as the central wavelength, and / or the wavelength range and / or the color, of the detected luminescent light (16) on the basis the division of two detector signals (S, S1, S2) and / or the difference between two logarithmic detector signals (S, S1, S2). Device according to Claim 2, characterized in that at least two light sources (12) are provided, the excitation light (15) of the respective light sources (12) being at different wavelengths or in different wavelength ranges.

Images