EP1602083A1

EP1602083A1 - Method and testing device for testing valuable documents

Info

Publication number: EP1602083A1
Application number: EP03750545A
Authority: EP
Inventors: Norbert Holl
Original assignee: Giesecke and Devrient GmbH
Current assignee: Giesecke and Devrient GmbH
Priority date: 2002-09-17
Filing date: 2003-09-15
Publication date: 2005-12-07
Also published as: DE10243051A1; US20060140468A1; CN100440260C; WO2004027718A1; AU2003270195A1; CN1682250A; US8107712B2

Abstract

The invention relates to a method and a corresponding testing device for testing a valuable document (1). According to the invention, the valuable document (1) is illuminated at least in a partial region by an intensity (IB), and the intensity (IT) of the light transmitted through the partial region of the valuable document (1) and the intensity (IR) of the light reflected by the partial region of the valuable document (1) is detected at different measuring points (2). In order to eliminate the influence of the thickness variations in the valuable document by simple testing, the intensities (IT, IR) of the transmitted and reflected light are separately detected, the sum (IT + IR) of the intensities (IT, IR) of the transmitted and reflected light is calculated for the various measuring points (2), and the sum (IT + IR) is then compared with a pre-determined norm value (IS).

Description

Method and test facility for checking documents of value

The invention relates to a method for checking documents of value, in particular banknotes, and a corresponding checking device according to the preamble of claims 1 and 13, respectively.

Generic methods and test devices are used, among other things, to check banknotes for their condition, in particular with regard to soiling and stains. The amount of light transmitted by a bank note to be checked and / or the light reflected by the bank note is used to determine the degree of contamination of the bank note to be checked. Since the reflection and transmission behavior varies greatly with the thickness of the banknote paper, changes in the thickness of the banknote, for example due to batch-related thickness fluctuations and / or in the area of watermarks, stains or other soiling, can no longer be detected with sufficient reliability.

In DE 100 05 514 AI it is proposed to provide compensation illumination to compensate for thickness fluctuations, with which the document of value to be checked is illuminated from both sides in a measuring range with an intensity that is constant over the entire measuring range. At the same time, a detector detects the intensity of the light radiated from the one side onto the value document and reflected from the value document and from the other side onto the value document and transmitted through the value document. Here, the intensity detected by the detector remains constant even with a change in the thickness of the value document over the measuring range for a clean value document. Deviations in the intensity he ate from a predetermined standard value, on the other hand, indicate changes, in particular stains and soiling, in the banknote. A problem with this method, however, is that uniform illumination is required from both sides of the security over the entire measuring range, ie the illumination profile of both light sources must be identical on both sides in order to achieve ideal compensation. Otherwise, over- or under-compensation means that thickness fluctuations are not completely compensated for and can influence the measurement result. As experience shows, manufacturing tolerances in the previously common lighting principles lead to deviations of approximately +/- 15% in the intensity of the lighting profile. Incorrect compensation of the lighting by 15% with a typical nominal thickness of the value document of 80 μm can already lead to deviations of the detected intensity by 3% from the standard value. However, deviations of this magnitude are too high for reliable detection of dirt and stains.

It is therefore an object of the present invention to provide an alternative to the known prior art, which enables reliable checking of value documents without great technical effort and in a cost-effective manner, depending on fluctuations in the thickness of the value document.

This object is achieved by the method and the test device with the features of claims 1 and 13, respectively. Advantageous refinements and developments of the invention are specified in dependent claims.

The inventive method is characterized in that the intensities of the transmitted and reflected light are recorded separately for the different measuring locations each form the sum of the intensities of the transmitted and reflected light and the sum is compared with a predetermined standard value.

The test device according to the invention further develops the known devices in that the lighting system and the detector system are designed for separate detection of the intensity of the transmitted and the reflected light, an evaluation unit for forming the sum of the intensities of the transmitted and reflected light for the different measuring locations and is provided for comparing the sum with a predetermined standard value.

The detected reflected light is in particular diffusely reflected, i.e. remitted, light.

The invention is based on the idea of designing the lighting system and the detector system in such a way that on the one hand the intensity of the transmitted light and on the other hand the intensity of the reflected light can be detected separately. The intensities of the transmitted and reflected light are added up in an evaluation unit for each individual measurement location, so that exactly one sum intensity value is obtained for each measurement location. The individual total intensity values are then compared in each case with a predetermined standard value in order to infer the presence of contamination from any deviations.

In a preferred development of the invention, it is provided that the intensity values recorded at the different measuring locations are corrected before the formation of the sum to compensate for locally different measuring conditions. A corresponding correction unit can be used as well as one for the Addition of the corrected intensity values trained addition unit can be realized in the form of hardware. However, it is also possible to implement these units in the form of software on a microprocessor or the like, which is used, for example, to control the test device. Likewise, these can also be software implementations on a conventional computer to which the Raw data are transmitted from the detector system for correction.

The correction takes into account, in particular, local fluctuations in the intensity of the lighting given during the measurement. The fluctuations in measured values caused by fluctuations in the illumination profile can be greatly reduced in this way, which further increases the reliability of the method. A special effort in the construction of the lighting system is not necessary.

With this method, a correction to compensate for locally different detector specifications, such as, for example, different sensitivities of the individual detector elements and different dark currents, can also take place at the same time.

In order to carry out these corrections, each measured intensity value is preferably reduced by a dark current measured value determined for the relevant measurement location before the sum is formed. In addition, each intensity value is additionally multiplied by a correction factor determined for the respective measurement location. For this purpose, the test device preferably has a memory in which dark current measurement values and correction factors are stored for the various measurement locations. These data are e.g. B. during assembly or commissioning of the test facility as well as NEN later determined in special adjustment measurements and then stored in the non-volatile memory.

The dark current measurement values are determined by intensity measurements with the lighting switched off. These dark currents are deviations of the individual detector elements of the detector system from zero. It is therefore sufficient if such a dark current value is measured for each individual detector element, which then applies to all measuring locations that were measured with this detector element.

The correction factors serve on the one hand to compensate for the different lighting intensities and on the other hand to compensate for the sensitivities of the individual detector elements with which the measurements are carried out at the individual measuring locations. Different, location-dependent correction factors are required for the transmission measurement and the reflection measurement. Since each detector element observes exactly one point within the illumination profile, it is also sufficient here if a correction factor for the transmission and for the reflection is determined for each detector element and these correction factors are then used for all measurement locations measured with this detector element. The correction factors are obtained on the basis of intensity values, which are measured under ideal conditions when comparing measurements on standardized sample documents, for example on homogeneous white foils.

If the value documents to be checked also show light absorption in addition to light scattering, the transmission intensities which have already been corrected can also be weighted with a weighting factor which takes the absorption into account before addition. A particularly effective test device, which is able to check documents of value over a large area with a high throughput, has a transport device in which the documents of value are guided past the lighting system and a detector system suitably positioned for measurement in a transport direction.

The lighting system generates a lighting profile that extends transversely to the transport direction. This can be achieved with an illumination device consisting of a row of light-emitting diodes or also by means of a field with a plurality of rows of light-emitting diodes extending transversely to the transport direction.

Accordingly, the detector system preferably has one or more detector devices which comprise a plurality of detector elements which are positioned in a row transversely to the direction of transport in a manner suitable for the illumination profile. This can e.g. are a row of photodiodes or a plurality of rows of photodiodes arranged one behind the other.

The invention allows simple and inexpensive checking of banknotes and other documents of value for signs of wear. Another advantage of this method is that the separately measured reflection and transmission intensities can be evaluated to derive statements regarding further properties of the value documents. For example, the measured reflection intensities can be used for authenticity testing. The transmission intensity values can be used to detect holes and cracks. The invention is explained in more detail below with reference to the accompanying figures using exemplary embodiments. Show it:

FIG. 1 shows a schematic illustration of the arrangement of a lighting system and a detector system for a test device according to a first exemplary embodiment;

FIG. 2 shows a schematic illustration of the arrangement of an illumination system and a detector system for a test device according to a second exemplary embodiment;

FIG. 3 shows an example of the thickness curve in the area of a watermark on a banknote; and

FIG. 4 shows a typical course of the reflection and transmission intensities along a measurement track in the case of a non-soiled banknote without absorption.

In the first exemplary embodiment of a testing device according to the invention shown in FIG. 1, the lighting system consists only of one lighting device which illuminates the document of value, here a bank note 1, from one side 13 in the area around a specific measuring location 2. The bank notes 1 are drawn past the lighting device 7 for measurement in a transport direction R.

The lighting device 7 is a light-emitting diode line which extends across the entire width of the bank note 1 transversely to the transport direction R and which thus produces a wide illumination profile running transversely to the transport direction R. The light is slanted in Direction of transport R is emitted onto bank note 1 and is focused as homogeneously as possible over the entire lighting profile onto a narrow area around measuring point 2 f. This can be achieved, for example, with the aid of suitable, in particular cylindrical, lenses. Instead of a single row of light-emitting diodes, the lighting device 7 can also have a plurality of rows of light-emitting diodes arranged parallel to one another, ie an entire array of light-emitting diodes.

At a short distance behind the lighting system 3 there is a detector system 4 in the transport direction R. This detector system 4 here consists of two detector devices 8 and 9. The first detector device 8 is arranged on the same side of the bank note 1 as the lighting device 7 and detects the intensity IR of the reflected, in particular remitted, light component. The second detector device 9 is located directly in the beam direction of the light emitted by the illuminating device 7 on the opposite side 14 of the bank note 1. This detector device 9 detects the intensity Ir of the light component transmitted by the bank note 1.

The two detector devices 8 and 9 each have a plurality of detector elements which are arranged next to one another in a row transverse to the transport direction. For example, this is a row of photodiodes. Alternatively, several rows of such detector elements can also be arranged in parallel next to one another, i.e. it can be a whole field of detector elements.

By using a row of detector elements arranged transversely to the transport direction R, measurements are consequently measured along a plurality of measurement tracks running parallel to one another in the transport direction R. During the transport of the banknote 1 in the transport direction R, the intensity is measured in a regular cycle by the detector device 8, so that ultimately, after a banknote has been transported through the testing device, a full-surface “transmission image” and a full-surface “reflection image” of the banknote 1 be preserved.

The distance between the individual detector elements determines the local resolution in the direction of the banknote width running transversely to the transport direction R. Such a detector device can usually have between 200 and 600 sensor elements in a row, so that accordingly between 200 and 600 measurement tracks are measured side by side on a bank note 1. The resolution in the transport direction R, however, is given by the transport speed and the measuring rate. Typically, the spatial resolution in the transport direction R is between 0.1 and 1 mm, although experience has shown that the spatial resolution is 7/16 mm

0.4375 mm a good detection of small dirt stains is already achieved with sufficient elimination of the influence of the banknote cloud.

The intensities detected by the two detector devices 8 and 9

IR (X) and Iτ (x) along the measurement tracks, i.e. for each individual measurement location along a measurement track, are processed as follows; where x is the position of a pixel, i.e. the location coordinate in the transport direction R:

There is first a correction (“Fiat Field Correction”) of the measured intensities IR (X) and Iτ (x) according to the formulas

I _RK (x) = a (x) (l _R (x) - I _RD (x)) (1) and I _τκ (x) = b (x). (l _τ (x) -I _ro (x)) (2)

IRK (x) and Iτκ (x) are the corrected intensity values. The values a (x) and b (x) are location-dependent correction factors for the reflection or the transmission to compensate for fluctuations in the illumination profile generated by the illumination device 7 and to compensate for the sensitivities of the individual detector elements at the different locations x. The values IRD (X) and ITD (X) are dark current intensities. These are measured intensity components which are caused by dark currents from the respective detector elements at the individual locations x. According to formulas (1) and (2), the dark current intensities are first subtracted from the measured intensities IR (X) and Iτ (x) before a correction with the correction factors takes place.

The dark current intensities and the correction factors are determined in separate adjustment measurements during the manufacture of the test device and / or at later times. First, the intensities IRD (X) and ITD (X) due to the dark currents at the individual locations x are determined by a measurement with the light source switched off. Measurements are then carried out on a standard sample, for example a homogeneous white film, to determine the correction factors. For this purpose, the intensity IR _S (X) of the reflected portion of the light and the intensity Iτs (x) of the transmitted portion of the light are measured with the light source switched on, ie exactly as in the measuring mode. Then the correction factors a (x) and b (x) according to the formulas

and

1 b ( _X ): (4) (I _τs (x) - I _TD (x))

calculated.

After the correction, the corrected intensity values are added for each position x

^I Rκ ( ^x ) + I _Η ( ^x ) = I _s (x), (5)

where I _s (x) is worth the sum intensity. The total intensity value I _s (x) of a clean banknote is equal to 1 at all positions x (with appropriate normalization) or another constant standard value. In the case of soiled banknotes, this value deviates from the normal value in the areas of soiling.

If the banknote to be checked shows light absorption in addition to light scattering, as can be the case, for example, with different production batches of banknotes, an addition according to the formula can be weighted with a weighting factor c (x)

I _RK (x) + c (x) - I _τκ (x) = I _s () (6)

respectively.

Figure 2 shows a second embodiment of a test device according to the invention. Here, the lighting system 5 has two lighting devices 10 and 11. The lighting device 10 is here how the lighting device 7 is constructed in the first exemplary embodiment and also aligned accordingly. The lighting device 11 arranged on the other side 14 of the bank note 1 is also constructed in the same way as the first lighting device 10. In contrast to the exemplary embodiment according to FIG 10 and illuminated by the second lighting device 11, which is realized via a corresponding control of the two lighting devices 10 and 11.

The detector system 6 now has only one detector device 12, which is constructed and positioned identically to the first detector device 8 in the exemplary embodiment according to FIG. 1. This detector device 12 now measures the radiation emitted by the first lighting device 10 onto the bank note 1 and light reflected by the banknote 1 and times the light emitted by the second lighting device 11 on the opposite side 14 onto the banknote 1 and transmitted by the banknote 1. The lighting cycle is preferably selected so fast relative to the measuring cycle that both an intensity signal IR for the reflection and an intensity signal Iτ for the transmission are measured at each measurement location along a measurement track. That there are again full-area images of the intensity values IR and Iτ with respect to the reflection and the transmission for each individual banknote. This data is processed in exactly the same way as in the first-mentioned exemplary embodiment.

For dirt detection, essentially certain areas in the white field, ie in unprinted areas, of the bank note 1 are preferably selected in order to use the intensity values measured there to determine the amount of dirt to determine degree of efficiency. Typical dimensions of such areas are between 10 and 40 mm. Frequently, however, it is precisely these areas of the banknotes in which there are watermarks and large fluctuations in thickness occur.

This is illustrated by FIG. 3, which shows a course of the thickness of a banknote. Here, the thickness d is plotted over the location x on the bank note 1 along the transport direction R. The paper of the banknote has a nominal thickness ds of 80 μm, which is shown by the dashed line. In fact, the average thickness dM of the banknote is around 50 μm. It is only in the area w of a bar watermark that there are markedly large fluctuations in thickness, in which in some areas the thickness d comes close to the target thickness d _s of 80 μm.

In the measurement method according to the invention, the effects of such thickness fluctuations on the measurement results are almost completely eliminated, so that it is easily possible to measure the degree of contamination of banknotes even in these white fields provided with watermarks.

FIG. 4 shows the detected intensities Iτ and IR for the transmitted or reflected portion of the light above the location x on the bank note 1 with bar watermarks described in connection with FIG. 3. The intensities I _R and Iτ are plotted in the form of proportions of the total radiation normalized to 1. Accordingly, the total intensity value Is, ■ consisting of the sum of the transmitted and reflected intensity, is exactly 1. This is shown in FIG. 4 by the dashed line. As can clearly be seen, the sum Is, in particular in the area w of the bar watermark, is 1, which indicates very good compensation of the Influence of the thickness variations is due. As already explained in more detail above, particularly good compensation can be achieved by corresponding corrections of the detected intensity values IR or Iτ, in particular on the basis of dark current measurement values and / or correction factors.

In the event of contamination by stains, etc., the sum signal in the region of the contamination lies on a value which deviates from 1, usually a lower value, so that this can be recognized by a simple comparison of the sum signal with the expected standard value.

Claims

P atentan speech

1. Method for checking a value document (1), in which the value document (1) is illuminated with an intensity (IB) at least in a partial area and the intensity (Iτ) of the through the partial area at one or more measuring locations (2) of the value document (1) transmitted light and the intensity (IR) of the light reflected from the partial area of the value document (1), in particular remitted, is detected, characterized in that the intensities (Iτ, IR) of the transmitted and reflected light are recorded separately , the sum (Iτ + IR) of the intensities (Iτ, IR) of the transmitted and reflected light is formed for the measuring location or the individual measuring locations (2) and. the sum (Iτ + IR) is compared with a predetermined standard value (Is).

2. The method according to claim 1, characterized in that the intensity values (Iτ, I _R ) detected at the measuring location or the individual measuring locations (2) are corrected prior to the summation to compensate for locally different measuring conditions.

3. The method according to claim 2, characterized in that the correction to compensate for local fluctuations in intensity of the lighting given in the measurement is carried out.

4. The method according to claim 2 or 3, characterized in that the correction is carried out to compensate for locally different detector specifications.

5. The method according to claim 4, characterized in that each detected intensity value (Iτ, IR) is reduced before the sum formation by a dark current measurement value (ITD, IRD) determined for the measurement location in question (2).

6. The method according to claim 5, characterized in that to determine the dark current measured values (ITD, IRD) intensity measurements are carried out with the lighting switched off.

7. The method according to any one of claims 1 to 6, characterized in that each detected, possibly by a dark current measured value (ITD,

IRD) reduced intensity value (Iτ, IR) is multiplied by a correction factor (a, b) determined for the measuring location (2) of the respective intensity value (Iτ, IR).

8. The method according to claim 7, characterized in that the correction factors (a, b) are obtained on the basis of intensity values which are determined in intensity measurements on comparison documents.

9. The method according to any one of claims 1 to 8, characterized in that the document of value (1) in a transport direction (R) past an illumination system (3, 5) and a detector system (4, 6) positioned thereon and with the illumination system (3, 5) at least on one side (13, 14) of the value document (1) a cross illumination profile extending to the transport direction (R) is generated.

10. The method according to claim 9, characterized in that with a plurality of detector elements, which are positioned transversely to the transport direction (R) in a row, detects the intensity values (Iτ, IR) along a plurality of measurement tracks running parallel to the transport direction (R) become.

11. The method according to any one of claims 1 to 10, characterized in that the document of value (1) is illuminated from one side (13) and that with a in the area of the same page (13) of the document of value (1) positioned first detector means (8) the intensity (IR) of the reflected portion of the light and the intensity (Iτ) of the transmitted portion of the light can be detected with a second detector device (9) positioned in the region of the opposite side (14) of the value document (1).

12. The method according to any one of claims 1 to 10, characterized in that the document of value (1) is alternately illuminated by a first and an opposite second page (13, 14) and with one in the area of the first page (13) of the document of value ( 1) positioned detector device (12) alternately in accordance with the intensity (Iτ) of the light transmitted from the second side (14) through the value document (1) and the intensity (IR) of the reflected portion of that from the first

Side (13) forth on the value document (1) falling light is detected.

13.Test facility for checking value documents (1), comprehensive

a lighting system (3, 5) for illuminating a document of value (1) with an intensity (IB) at least in a partial area,

- A detector system (4, 6) in order to detect at one or more measuring locations (2) light transmitted by the document of value (1) and light reflected, in particular remitted, from the document of value, characterized in that the lighting system (3, 5) and the detector system (4, 6) is designed for separate detection of the intensity (Iτ, IR) of the transmitted and the reflected light and an evaluation unit for forming the sum (Iτ + IR) of the intensities (Iτ, IR) of the transmitted and reflected light for the measuring site or the individual measuring sites (2) and for comparing the sum (Iτ + IR) with a predetermined standard value (Is) is provided.

14. Test device according to claim 13, characterized in that the evaluation unit has a correction unit for correcting the detected intensity values (Iτ, IR) of the transmitted light and the reflected light for the measurement location or the individual measurement locations (2) to compensate for locally different measurement conditions and an addition unit for adding the corrected intensity values for the measuring location or the relevant measuring locations (2).

15. Test device according to claim 14, characterized in that the correction unit has means to compensate for local fluctuations in intensity of the illumination generated during the measurement by the illumination system (3, 4).

16. Test device according to claim 14 or 15, characterized in that the correction unit has means to compensate for locally different specifications of the detector system (4, 6).

17. Test device according to one of claims 13 to 16, characterized by a memory with dark current measurement values (ITD, IRD) stored for different measurement locations (2), which correspond to the transmission or reflection intensity values detected when the lighting is switched off, and / or with for Different measurement locations (2) store correction factors (a, b) for the transmission or reflection intensity values determined during a measurement.

18. Test device according to one of claims 13 to 17, characterized by a transport device for the value document (1) for a measurement in a transport direction (R) on the lighting system (3,

5) and the detector system (4, 6) positioned for this purpose.

19. Testing device according to claim 18, characterized in that the lighting system (3, 5) generates a lighting profile extending transversely to the transport direction (R).

20. Test device according to claim 19, characterized in that the detector system (4, 6) has a detector device (8, 9, 12) which comprises a plurality of detector elements positioned transversely to the transport direction (R).

21. Test device according to one of claims 13 to 20, characterized in that the lighting system (3) has a lighting device (7) which the document of value (1) from a first side te (13) from illuminated, and that the detector system (4) has a first detector device (8) which is assigned to the lighting device (7), is positioned on the same side (13) of the value document (1) and - the intensity (IR ) of the reflected portion of the light, and has a second detector device (9) which is assigned to the lighting device (7), is positioned on the opposite side (14) of the value document (1) and - the intensity (Iτ) "of the transmitted Proportion of light detected.

22. Testing device according to one of claims 13 to 20, characterized in that the lighting system (5) comprises a first lighting device (10) which illuminates the document of value (1) at least in a partial area from a first side (13), a second lighting device (11), which illuminates the document of value (1) in the partial area from a second side (14), and - has a control device which controls the lighting devices (10, 11) in such a way that the first or the second lighting device (10 , 11) illuminates the document of value (1), and that the detector system (6) has a detector device (12) arranged on the first side (13) and assigned to the two lighting devices (10, 11) in order to alternate the intensity (Iτ) of the light transmitted from the second side (14) through the value document (1) or the intensity ( _IR ) of the reflected portion of the value document from the first side (13) (1) to detect falling light.