EP0466119B1 - Apparatus and method for checking documents - Google Patents

Abstract

In an apparatus for testing documents, the optical illuminating unit comprises at least one light guide provided with fluorescent substance for directing at least two light fractions of different wavelengths onto a common area of the document. The light fractions are switched on and off by the time-division multiplex method. Special switching regulators are provided for regulating not only the switch-on and switch-off operation of the illumination sources but also the brightness thereof.

Description

The invention relates to a device or a Procedure for checking documents with a control unit and a scanner for recording the from Document remitted and / or by the document transmitted light.

In central locations such as commercial and state banks banknotes are counted, checked and sorted almost only with fully automatic sorting and testing machines. These machines recognize or check the banknotes based on various criteria. Preferred test criteria are the size, the thickness and the printed image of the Grades. Most of the measurements on the printed image take place Cases by means of electro-optical processes, this is the banknote over the entire surface or in predetermined surface areas scanned with electro-optical sensors. The so obtained measurement signals are either directly or after signal processing with predefined acceptance ranges compared. The comparison result is mostly along with the results of further measurements for assessment the banknote used.

The manufacturing tolerances, pollution, wear and tear of the Banknotes and other effects even lead to consistently valid grades for a wide range of measurements and consequently to wide acceptance areas. Wide acceptance areas however, the likelihood of misjudgments increases. On the other hand, the sorting and Automatic testers are particularly high in the securities sector Showing reliability, especially what that Detect denominations and sort out invalid ones and useless banknotes. For this The reason for this is that more and more sophisticated measuring methods are used in the machines for use.

CH-PS 476 356 describes a device which in As part of the optical check, banknotes also on your checks characteristic color shades. For testing the banknote in a limited area Light from a broadband light source is illuminated. The reflected light is here in an optical Cutting system, such as a glass prism, in different wavelength ranges separated. The in the Color brightness present in the respective wavelength ranges comes with several, assigned photoelectric Detectors recorded. The measurement signals are in Threshold levels evaluated so that if they match a correct signal of the measured values with the tolerance ranges is delivered.

However, the proposed arrangement is for banknote sorting and automatic testers only with large ones, currently not more tolerable restrictions can be used. Modern Sorting and testing machines are characterized by a high Processing capacity and transport the banknotes at speeds of several meters each Second. This results in short dwell times for the Banknotes in the sensor area; the luminous efficacy that in this time is usually without color testing near the lower tolerance range. Through the spectral splitting of the light into several wavelength ranges there is very little on the individual sensor Light intensity available, the resulting high Signal noise sets the achievable reliability rate sometimes so far that the advantages of a Check for color nuances to be completely canceled.

DE-OS 38 15 375 describes a device for testing the authenticity of documents based on color. The The device is composed of several similar modules. Each module consists of a lighting system consisting of light guides and a photo sensor. Specific Optical components such as color filters ensure that each module only in a selected spectral range is sensitive. The document is sent to the Guided past modules; the photo sensors of the Modules line the document in different predetermined lines Spectral ranges and forward the measured values to Evaluation device further.

As a separate module is provided for each spectral range the modules with all the necessary components to provide multiple times what besides the big one Construction volume for a noticeable increase in the price of the machines leads, especially if - as suggested in the DE-OS - expensive fiber bundles used as light guides will. The use of filters for spectral separation the light component not only increases the cost of the testing device, but also worsens efficiency between that available on the measuring surface Light output to the irradiated light output.

The invention has for its object a device and a corresponding method for optical Examination of documents in at least two spectral ones Propose areas, the above disadvantages be avoided.

This object is achieved by the features of Claims 1 and 11 solved.

An essential feature of the solution according to the invention is in that to illuminate the document with light different spectral ranges one with fluorescent material provided light guide is used, the at the same time as a light guide for other radiation sources is being used. With fluorescent material Light guides, for example so-called fluorescent plates, have been known for a long time. they consist of a transparent plastic in which fluorescent Dye molecules are stored. Acting on the plate Light is absorbed by the molecules and generally emitted again as longer-wave light. The light emitted in the plate in all spatial directions becomes to a large extent in the plate via total reflections collected and occurs at the plate edges as High intensity fluorescent light. With the help of Fluorescent plates can be a document on very simple Way with light of a first spectral range with large Illuminated intensity and very homogeneous distribution will. For the light of a wider spectral range According to the invention, the fluorescent plate only serves as Light guide. The light from this second spectral source will coupled over one of the edges or narrow sides of the plate and occurs over total reflections in the plate on another edge. For that particular light Spectral range are preferably light emitting diodes used. Due to their design, LEDs emit light their light in a limited solid angle range, whereby effective coupling of light into the light guide can be achieved. The light from the second spectral source can also from a second fluorescent plate are generated that to the one generating the first light Plate is optically coupled.

With the solution according to the invention it is comparatively low design effort, d. H. especially without the use of filter elements, possible light different spectral ranges with great intensity and homogeneous distribution to a common measuring point of the document and evaluate it with just one detector. Because of the use of an optical fiber the lighting geometry varies in a variety of ways will. When using a plate-shaped light guide is a homogeneous column-shaped illumination of the security possible. That from the edge of the plate in the form of a Lobe emerging light can be used directly to illuminate the Object to be used. But it is also possible by appropriate shaping of the trailing edge, by Imaging of the trailing edge on the test object or by the superimposition of several light lobes of several exit surfaces one or more fluorescent plates set the desired lighting geometry.

Illuminate an area of the document with Light of different spectral ranges requires if filter arrangements are to be dispensed with, one different kind of separation of the light components to a selective To enable analysis in the spectral ranges used.

According to a development of the invention, it is therefore proposed the different spectral sources whose Light components directly or indirectly via a common one Optical fibers are guided to the measuring point in such a way modulate that the measuring range only in one Spectral range is illuminated. The spectral sources are therefore time-alternating in time-division multiplexing switched on and off, the switching frequency is chosen so high that during the run a sufficient number of measured values are recorded in a document can be.

The basic prerequisites for fast clocking are accordingly short rise and decay times of the radiation sources itself. Therefore, on the one hand, there are light-emitting diodes used, their light directly through the light guide reaches the measuring point and on the other hand fluorescent lamps, their light to stimulate fluorescence emission is used. Fluorescent lamps demonstrate low heat emission and have a high luminous efficiency for this reason, preferably suitable for generating the Fluorescent light.

Both for the light emitting diodes and for the Fluorescent tubes are special according to the invention Switching regulator provided in addition to a fast clocking the radiation sources are low loss automatic Enable brightness control.

Further advantages and developments of the invention result itself from the subclaims and from the following Description of the exemplary embodiments with reference to the Characters.

Fig. 1, 2

eine Prinzipdarstellung eines Sensors auf der Basis einer Fluoreszenzplatte,

Fig. 2

eine Anordnung mit zwei gekrümmten Fluoreszenzplatten,

Fig. 3

eine Anordnung zur Messung in drei Spektralbereichen,

Fig. 4, 5

spezielle Ausführungsformen der Austrittskante,

Fig. 6

Optik zur Fokussierung der Austrittskeule auf die Meßfläche,

Fig. 7

eine Schaltungsprinzip für den getakteten Betrieb von Leuchtstoffröhren,

Fig. 8

ein Ablaufschema der getakteten Ansteuerung der Leuchtstoffröhren,

Fig. 9

ein Prinzipschaltbild für den getakteten Betrieb von Leuchtdioden.

Show it

1, 2

a schematic representation of a sensor based on a fluorescent plate,

Fig. 2

an arrangement with two curved fluorescent plates,

Fig. 3

an arrangement for measurement in three spectral ranges,

4, 5

special embodiments of the trailing edge,

Fig. 6

Optics for focusing the exit lobe on the measuring surface,

Fig. 7

a circuit principle for the clocked operation of fluorescent tubes,

Fig. 8

a flow diagram of the clocked activation of the fluorescent tubes,

Fig. 9

a basic circuit diagram for the clocked operation of LEDs.

1 shows a first embodiment highly schematic arrangement of the device according to the invention for checking securities, for example Banknotes, using two spectral sources and one Fluorescent plate.

A banknote 1 in is transported by means of a transport system 6 Direction of arrow 2 guided past the sensor arrangement. Of the Illumination part of the sensor consists of a fluorescent plate 3, two fluorescent tubes 4 and another Illumination device 5, for example light emitting diodes. The plate 3 consists of a plastic in which a fluorescent dye is homogeneously distributed. Such Plates are commercially available. The immediately Fluorescent tubes 4 arranged next to the plate illuminate the surface of the plate with light of a short Wavelength. The light penetrates the plate and is absorbed by the dye; a lot of the absorbed Energy is used as fluorescent light for a longer period Wavelength as the absorbed again emitted. The spectrum of the fluorescent light is typical a band approximately 100 nanometers wide, depending on the dye the wavelength center of gravity is currently available Panels in a range from blue to that far red. Due to total reflection within the The fluorescent light mainly occurs on the plate Narrow sides or edges of the plate. About the loss of light to keep small, the edges of the plate that not required as entry or exit edges for the light are mirrored. For good efficiency the fluorescent lamps and the fluorescent plate are in to coordinate their spectra. Fluorescent lamps with an emission in the blue spectral range are suitable for green to red emitting fluorescent plates, while for blue emitting plates one in the ultraviolet Lamp area is preferable.

According to the invention, the fluorescent plate 3 serves simultaneously as a light guide for the second lighting device 5. For an effective light coupling this directly above the leading edge 7 of the plate, optionally arranged via optical coupling media. The light of the light emitting diodes used here, for example penetrates the plate and is due to total reflection on the base and top surface to the trailing edge guided. The wavelength of the diodes is to avoid of losses to choose so that they are not in an absorption band the fluorescent plate falls.

The light from both spectral sources leaves the plate the trailing edge 9 and causes according to the Geometry of the exit surface the homogeneous illumination a strip-shaped surface with high luminance.

The one that is remitted or let through from the banknote Light can be detected by several detectors 13, 14, 15 will. Line detectors are preferred for this purpose used such as a CCD array. The signals the detectors can be used alone or combined accordingly be evaluated. When arranging the components It is generally important to ensure that at suitable points Shields 11 are to be attached to the impact of Avoid stray light or extraneous light on the detectors. Should separate color separations be evaluated, the two lighting sources 4 and 5 in time-multiplexing operated, that is, they are alternating switched light and dark. Reading the Detectors are in phase with the alternating cycle; the The resulting measurement signal is therefore given alternately Follow the two color separations that are saved separately and / or have it processed.

2 shows an embodiment of the invention Facility used to achieve homogeneous illumination the measuring surface two symmetrically arranged Has fluorescent plates 20, 21. To a compact To get the sensor, the two plates 20, 21 around the Lighting device 4 arranged arched. As long as the bending radius is significantly larger than the plate thickness, are the light losses due to light emission on the surfaces the plate is negligible. The light of the Lighting devices are coupled in analogy to FIG. 1. The light emitting diodes 24, 25 are on the narrow sides 22, 23 of the plate arranged; the phosphor source 4 illuminates the surfaces of the fluorescent plates 20, 21. The inside of the support structures 38 and 39 are mirrored; this means that it is broadcast in all directions in space Light from the fluorescent source 4 onto the fluorescent plates thrown back. In the embodiment shown can preferably be a U-shaped fluorescent lamp be used, the observation through the gap the lamp is possible. A suitable lamp for this is for example the so-called Dulux-S lamp from Osram.

The two trailing edges are for coupling out the light of the fluorescent plates 20, 21 beveled and possibly mirrored. The slopes couple the rays of light from the plates at a certain angle and lead them to the desired area of the banknote 1. The angles of the slopes can be chosen that the two exit lobes 32 and 33 of the fluorescent plates more or less strong on the banknote overlap.

The detector 13 is in a shaft 68 between the arranged in both lighting parts and so against stray light well protected. With one arranged in the shaft Imaging system 12 can be the desired illuminated one Area of banknote 1 mapped onto detector 13 will. To protect against dirt and damage is between the transport path of the banknotes and the Sensor arrangement a cover 40 with a window 42 assembled. To separate the color components, as in Fig. 1 already described, the spectral sources and Detector controlled in time-division multiplex mode.

In principle, the arrangement shown can also be used for measurement can be used in three or four spectral ranges. For example, if you swap one of the two rows of LEDs 24 or 25 against one in another Wavelength-emitting type, so stand at the measuring point three spectral colors are available. A fourth Color can be emitted by using different emitters Fluorescence molecules in the two plates 20 and Add 21.

3 shows an alternative arrangement for generation of three or more spectral colors at the measuring point. In In this case there are two with different fluorescent substances provided fluorescent plates 45 and 46 over their Narrow sides or edges 49 connected to one another. The Surfaces of the edges and their connection are like this procure that the light can pass freely. The two plates 45 and 46 are from the two fluorescent lamps 50 and 52 illuminated. To increase efficiency are the two lamps with suitably shaped Surround reflectors 53. The fluorescent materials of the plates and the respective excitation light are chosen so that the emission light of a plate which is directed towards the Banknotes following plate happens with as little loss as possible. As in previous embodiments described, the plates 45, 46 also serve as Light guide for a further lighting device 48.

As the previous exemplary embodiments show, there is another advantage of the invention in the variety of Possibilities to combine the individual components and the spectral ranges and lighting geometries too vary. The sensor can thus be optimally metrological Adjust requirements. For transmission measurements it is usually sufficient to use the trailing edge of the Fluorescence plate, as shown in Fig. 1, directly as To use light source. It should be noted that the Brightness drops monotonically with the distance of the measuring surface. A maximum brightness at a predetermined distance from Sensor can, however, by overlaying several exit lobes or by optically imaging the exit surface can be achieved. 2 already has a first example shown for the overlay principle where the zone highest brightness at some distance from the trailing edges of the fluorescent plates. In the overlay area have changes in distance between the measurement object and lighting source have less impact on changes in brightness.

4 shows a further embodiment for the Overlay principle. The trailing edge of the fluorescent plate 3 is in this case over its entire length in Middle part has been provided with a mirror 56. This measure shifts the intensity maximum away from the exit surface. The diminution the absolute brightness in the measuring surface 62 due to the partial mirroring can be achieved by taking measures at the Catch the leading edge. By mirroring 57 the Leading edge has the light reflected back so Another possibility to one of the two exit windows 59 or 60 to arrive. When mirroring the leading edge However, the permeability for the Light from a light source 5 are respected, for example through a wavelength selective mirroring for the fluorescent light or through a corresponding window 61 can be taken into account.

5 shows a further embodiment for the Overlay principle. It is in a predetermined Distance creates an area 62 of optimal brightness and scattered light in the detector is largely avoided at the same time. The two fluorescent plates 64 and 65 are in this Case arranged at 45 ° to the measuring surface, the exit surfaces 55 on both plates thus point to one common area. Between the two plates is the detector shaft 68, in which in the known imaging optical system 12 and a linear detector 13 are arranged. A partial mirroring 66 of the trailing edges in connection with the symmetrical The arrangement moves zone 62 of maximum brightness away from the sensor into an area that is different from document 1 is happening. The lighting devices here in the Detail, not shown, can, for example shown in Fig. 2 can be selected.

Get high quality brightness levels one with the help of optical images of the trailing edge. It should first be noted that in principle with the help any spherical or cylindrical imaging optics an image of the trailing edge can be generated in the measuring surface can. Because of the limited space in one Sensor module and the special lighting and observation requirements are particularly compact optics preferred, which simultaneously has several optical functions meet, such as the simultaneous redirection and focusing light rays.

6 shows a section through a symmetrical structure Sensor module, the light of the fluorescent plates 3 with imaging deflecting optics on the measuring surface is projected. The color components of the light are generated in the manner already described and to the Leaving edges of the fluorescent plates 3 passed. After leaving the plate, the light hits the image Deflection optics 71. The deflection and imaging takes place by reflecting the light rays on the two mirrored Surfaces 73 and 74. The ray path for the marginal rays the exit lobe is dotted Lines shown. The light first penetrates the Glass body 71 and is on the mirrored surface 73rd reflected; surface 73 is a section of a Parabolic surface that is shaped so that the light as Parallel beam to surface 74 is reflected. The Surface 74, which is also the shape of a parabolic surface has, the light focuses on the measuring surface 63. Zum Protection of the vitreous against damage and dirt is a protective layer 76 with a window in the beam path inserted. The focus point is due to the position of the Parabolic surfaces laterally shifted with respect to the vitreous and lies exactly under the detector shaft 68. Symmetrical to the detector shaft is a mirror image second deflecting optics 72 arranged, it ensures in the measuring surface for a homogeneous and largely distance-independent Illumination. Scanning the passing Banknote 1 in the measurement area is made using a Imaging optics 12 and a line detector 13. The walls 79 of the detector shaft are opaque and protect the sensor from stray light.

The entire optical structure of the sensor module can be extremely compact design, advantageous for assembly is the uncritical positioning of the optical components. As a positive feature of the sensor structure comes added that the components - because adjustment devices are not necessary - practically during the lifetime the spectral sources are completely adjustment-free; what a good reproducibility of the measurement results guaranteed.

Just like the optics, the spectral sources also have to ensure constant measuring conditions for long periods, this means, among other things, that in their Brightness should be stabilized over time. As another There is also a requirement that the spectral sources alternate must be switched on and off so that you can go through Time-division multiplexing, for example, separate color separations who can receive banknotes. To meet these demands meet, according to a development of the invention special switching regulators for controlling the spectral sources suggested. These switching regulators control the Performance practically only by briefly switching on and off the power supply. But since there is one Have switch-off operations carried out practically without loss, these switching regulators set the electrical power optimally in light output. Capacitive and inductive Components in the circuit of the spectral sources ensure a largely continuous power and light flow during the switch-on phase.

Fig. 7 shows an embodiment of a switching regulator for the brightness-controlled operation of a Fluorescent lamp. The lamp 80 is in series with one Inductance 81 on the secondary side of a transformer 82. In series with the directly heated electrodes a capacitor 84 is connected. The two components 81 and 84 form a series resonance circuit. The Gas discharge from the lamp runs parallel to the capacity. Another resonant circuit is through the primary winding of the transformer 82 with the capacitance 85 is formed. A control circuit 87 controls the current flow on the Primary side via a switching transistor 89 with a such frequency and pulse shape that with minimal power consumption a given brightness is kept constant becomes. The current brightness is from a photoelectric Detector 88 detects and the controller 87 as Control signal passed on. By varying the frequency the control pulse SP can control the brightness of the fluorescent lamp be managed. With the help of another one signal I / O acting on the controller becomes the control pulse sequences and thus also the lamp on or off. It has been shown that the circuit too then still works properly when the control pulses supplied in synchronism with the I / O signal in so-called "bursts" become, which ultimately only the multiplex operation with other radiation sources is possible.

8 shows the temporal interaction of the I / O signal with the control pulses SP of the control circuit and the intensity I of the fluorescent lamp. The I / O signal determines the on and off phases of the fluorescent lamp. In each case with a positive I / O signal there will be a consequence generated by switching pulses SP. Depending on the signal the frequency of the switching pulses becomes a brightness sensor regulated in such a way that, for example, at a Decrease the brightness by increasing the frequency Power supply to the lamp is increased. The inductive and capacitive components of the circuit smooth the power flow to the lamp and ensure the duty cycle a largely constant brightness. In banknote machines that use the banknotes Transport speeds of several meters per second, the frequency of the I / O signal is in the Size of about 10 kilohertz. To regulate the To achieve brightness, the frequency of the control pulses preferably chosen to be a factor of 10 higher.

The light emitting diodes must also be in phase opposition to the fluorescent lamp be switched on and off periodically, brightness control is also necessary.

A block diagram for a switching regulator that is based on the The characteristic curve of the light-emitting diodes is matched in FIG. 9 reproduced. The light emitting diodes 90 are connected in series and are therefore operated with a power supply will. Because the light emission from light emitting diodes it increases approximately linearly with the through current regulated by pulse width modulation of the current will. For this is in series with the LEDs Switching transistor 95 is provided, which is from a pulse width modulator 99 is controlled. A sensor 96 that the brightness of the diodes takes up, its signal leads to the Pulse width modulator too. Depending on the signal level of this sensor becomes the pulse width of the switching pulses in the way changed that its constant brightness ensures is. To the current and voltage peaks during smoothing the on period of the control pulses is the Inductor 91 connected in series with the LEDs. This limits the current rise when switched on of switching transistor 95. The one stored in the coil Energy becomes available after the switching transistor is switched off fed to the diodes 90 via the freewheeling diode 93, whereby the current flow even during the switch-off breaks Transistor is held upright. The same purpose also has the capacity parallel to the LEDs 98. To maintain a control range is here too the switching frequency is necessary Increase the machine cycle by at least a factor of 10.

In addition to the lossless brightness control of the spectral sources have those shown in Figs. 7 and 9 Circuits have the further advantage that the supply voltage can fluctuate within wide limits without the Reproducibility of the measurement signals is impaired.

Claims (16)

1. An apparatus for testing documents having an optical means (4, 5, 24, 25) for illuminating the document (1) in at least one spectral range and a means (13, 14, 15) for taking up the light diffusely reflected by the document and/or transmitted through the document, characterized in that the illuminating means comprises at least one light guide (3, 20, 21, 45, 46, 64, 65) provided with fluorescent substance for directing at least two light fractions of different wavelengths onto a common area (62, 63) of the document (1).
2. The apparatus of claim 1, characterized in that the light guide (3, 20, 21, 45, 46, 64, 65) is a plastic body having several flat or curved surfaces (73, 74) and several narrow sides or edges (7, 9, 22, 23, 47, 48, 59, 60, 61, 55), and the first light fraction is the fluorescent light which arises by excitation of radiation from a light source (4) directed onto at least one of the surfaces and which exits at an edge facing the document (1).
3. The apparatus of claim 2, characterized in that the second light fraction comes from a light source (5) whose light enters via one of the edges and exits via the edge facing the document (1).
4. The apparatus of claim 2, characterized in that the second light fraction is the fluorescent light of a further light guide (3) which is coupled optically to the first light guide.
5. The apparatus of claim 1, characterized in that the light guide is a plate (3), the first light source comprises one or more fluorescent lamps (4) whose light is coupled in via a surface of the plate (3), and the second light source comprises one or more light-emitting diodes (5, 24, 25) whose light is coupled into the plate via a narrow side (7, 22, 23).
6. The apparatus of claim 1, characterized in that two light guides (64, 65) are provided which are oriented with each other at an angle of about 45° based on the normal of the document (1), and positioned relative to the document such that the document is located in the superposed area (62) of the emitted lobes.
7. The apparatus of claim 1 or 6, characterized in that the exit edge of the light guide is provided with certain optically reflective areas (56, 66) to influence the form of the exit light lobe.
8. The apparatus of claim 1 or 6, characterized in that an optical unit (71) is provided between the exit edge of the light guide (3) and the document (1) for imaging the exit edge of the light guide on the document (1).
9. The apparatus of claim 1, characterized in that the light sources (80, 90) are connected with switching regulators (81 - 89, 91 - 99) that regulate both the switch-on and switch-off phases of the light sources and the brightness thereof.
10. The apparatus of claim 1, characterized in that the illuminating means comprises two light guides (3) provided with fluorescent substance, and an optical element (71) is provided for deflecting the light fractions of the light guides and focusing them onto a common surface (63) of the document (1).
11. A method for testing documents (1) which are illuminated with light of different spectral ranges and scanned to take up the light diffusely reflected and/or transmitted by the document (1), characterized in that the light fractions of different wavelengths are directed onto a common area of the document (1) via one light guide (3, 20, 21, 45, 46, 64, 65) provided with a fluorescent substance in each case, the light fractions of different wavelengths being switched on and off by the time-division multiplex method.
12. The method of claim 11, characterized in that the light fraction of a first wavelength is produced by irradiating the surface of the light guide with the excitation light of the fluorescent substance.
13. The method of claim 12, characterized in that the excitation light is produced using fluorescent lamps, the lamps being connected with a switching regulator (81 - 89, 91 - 99) which produces control pulse sequences (bursts) dependent on the brightness of the lamp in synchronism with the switch-on and switch-off operation of said lamp.
14. The method of claim 11, characterized in that the light of a second wavelength is directed onto the document (1) by light guiding technology via the light guide (3, 20, 21, 45, 46, 64, 65) provided with fluorescent substance.
15. The method of claim 14, characterized in that the light is produced using light-emitting diodes (5, 24, 25, 90) connected with a switching regulator (91 - 99) which produces pulse width modulated control signals in synchronism with the switch-on and switch-off operation of the light-emitting diodes.
16. The method of claim 11, characterized in that at least two light fractions of different wavelengths are directed onto the common area of the document (1) via at least one light guide (3, 20, 21, 45, 46, 64, 65) provided with fluorescent substance, the light fractions being switched on and off by the time-division multiplex method.

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