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(11) | EP 0 780 811 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and device for the characterization and discrimination of banknotes and legal tender documents |
| (57) Method and device for the characterization and discrimination of banknotes and legal
tender documents, which method incorporates the conveyance of the document to be effected
along a path on which such document is lit using wide spectrum and/or infrared light
sources. The acquisition of images using a linear sensor and the analysis of the coloring
of these images. The wide spectrum light source works intermittently during the document
analysis stage and continuously during the stand by stage. The wide spectrum lighting means (13) incorporate a concentric reflector (15) and a transparent tube (16) inside which the lamp is encapsulated. The device does further include a linear light sensor (12). |
[0001] This invention refers to a method for the characterization and discrimination of legal tender documents, particularly banknotes, through the analysis of the color of the images obtained from these banknotes or documents. The invention does furthermore include the device used to perform the above method.
[0002] More specifically, the method object of this invention is of the type that includes the conveyance of the document to be analyzed along a path where it is lit up using wide spectrum and/or infrared light sources, the acquisition of document images using a linear sensor and the analysis of the color of said images, where the wide spectrum light source preferentially consists of a fluorescent tube.
[0003] The use of specific and linear sensors is already known for the acquisition of images of banknotes and documents so as to enable their identification.
[0004] Within the second previously mentioned group, to which this invention belongs, is already known the use of a sequential lighting monochrome linear sensor in different colors of the visible spectrum and infrared, as described in E-0537513A1. Also known are systems that use linear color (RGB components) and wide spectrum and infrared lighting sensors, as described in the Spanish patent applications number 9302692 and 9402631, duly lodged by the authors of this application.
[0005] The invention belongs to the second group, which has the advantage, in respect of the first group, of analyzing all of the visible spectrum, whereas those using a monochrome sensor do only analyze the response of the document to certain colors, present in monochrome light sources (narrow light spectrum), typically made up using light sensitive diodes of different colors, such as green, yellow, red and infrared. The end result of all of this is to improve the quality of banknote discrimination based on color metering analysis.
[0006] Also known are zone document analysis procedures, which use different lighting and signal treatment criteria, depending upon the areas of interest. This procedure has de disadvantage that, even though a full document analysis is obtained, it is not fully effected for all the colors of the available lighting sources (wide spectrum plus infrared).
[0007] As already mentioned, the method of the invention is of the type that uses wide spectrum linear lighting and color sensors, being that light source preferably of the fluorescent type, so as to achieve a lighting mode that covers all of the visible spectrum with a good level of response in shorter wave lengths (blue). This feature is advantageous in comparison with other wide spectrum light sources such as, for instance, incandescent lights, which present an optimal response to red and near by infrared wave lengths but which performance decrease substantially in respect of shorter wave lengths. Another advantage of fluorescent light sources, and particularly of the cold cathode ones, is the low level of inertia that they feature whenever they are made to work in on-off cycles, thus allowing the alternation of the wide spectrum lighting with other available light sources, without appreciably penalizing analysis times.
[0008] Notwithstanding the foregoing, the previously described light sources show two major disadvantages: one of them is the large degree of dependence of the level of lighting to the temperature of the light source; the second one is their drop in respect of working life as the level of power supplied to the light source is increased.
[0009] The object of this invention is to avoid the previously described disadvantages by using a system that makes it possible to optimize the level of luminosity of the source and to keep it at the same temperature and, therefore, at the same level of performance, during the document analysis and stand by stages, thus obtaining RGB images of all of the types of light used during a single passage of the document through the document analysis device.
[0010] In the traditional banknote characterization and discrimination procedures there is the possibility of voiding the acceptance of a document or else modifying the tolerance levels so as to consider it as acceptable. Traditionally, these functions have been carried out through the activation of switches already prepared for that purpose, or else changing the operating program. All of the above systems feature the dual disadvantage of occupying a substantial space and offering very few tolerance selection possibilities.
[0011] The method subject of this invention has also the object of allowing the simple and independent adjustment of security levels for each of the face values of the admissible documents. This adjustment is effected, in accordance with the invention, in a graphical and proportional manner, which is to say, that there is a direct relation between the previously programmed security range (acceptance/rejection) and the correction of tolerances that is automatically performed by the document discrimination device.
[0012] In accordance with the method of the invention, in order to maintain the temperature of the wide spectrum light source at a constant level, that light source has to be subjected to a different mode of operation during its document analysis and stand by stages. During the document analysis stage, the fluorescent lamp, which constitutes the wide spectrum light source, operates intermittently, featuring a 100% lighting level during its operating periods. During this document analysis stage the infrared light source does also work intermittently, alternating its operation with that of the wide spectrum light source. During the stand by stage the fluorescent lamp works continuously, at a lighting level equivalent to its total average lighting level during the document analysis stage.
[0013] With this operating system, the wide spectrum light source permanently remains at the same operating temperature, independently of whether the device currently is in document analysis or stand by mode. According to another characteristic of the invention, to optimize the level of luminosity of the wide spectrum light source there is a reflector that surrounds that light source, as well as a transparent cover, made of glass or plastic, that encloses the light source, so that the reflector may be internally or externally located in respect of the cover. The reflector is fitted with a lengthwise window type opening aimed towards the document examination line. The reflector makes it possible to optimize the level of luminosity of the lighting source and the transparent capsule or cover makes it possible to insulate the light source from the surrounding environmental conditions so as to maintain an optimum operating temperature, with a lesser energy consumption, all of which will bring about a longer lamp working life.
[0014] In accordance with the method of the invention, the variation of the values of the acceptance parameters and tolerances for the various face values are effected through the examination of a sample document that includes a number of well defined areas, each of which is capable of being related to one of the face values of the admissible documents and which may be programmed in respect of its variable amplitude and/or coloring shading. The amplitude of the variation achieved will be a function of the shaded surface and/or the color used in the corresponding area. The sample document will consist of a programming card combining color marks on its upper surface, transparent to infrared radiation, with infrared opaque inks on its lower surface, allowing a large number of different functions or alternatively supplying an amount of data which will be sufficient to reprogram the document discrimination device to accept new face values.
[0015] Upon performing the method object of this invention, the RGB images corresponding to each one of the lighting sources are acquired during the document analysis stage throughout the length of the banknote being analyzed. In accordance with this invention, all of the acquired images originate from the same line of the document being analyzed, allowing the obtainment of parameters representing each one of the areas subjected to each one of the different lighting methods as well as the generation of new parameters of the same area, corresponding to the different lighting methods used. The arithmetical mean, normal deviation, upper range, lower range and points above the mean may be used as representative parameters at a given area for a given lighting. The relations between the previously mentioned parameters, such as differences and quotients, will be preferably used as relative parameters in a single area under different lighting conditions.
[0016] Each step of the trip of the banknote through the device may take place after the acquisition of the various lines by the linear light sensing device, each of them under one of the different lighting methods, alternatively used. The acquisition of each line may also be effected by lighting the document alternatively with each one of the available light sources, whilst at the same time the document is displaced a distance shorter than the resolution of the optical system.
[0017] The features and advantages of this invention may be far more easily understood by reading the description below, prepared with reference to the attached drawings, in which:
[0018] Figure number 1 is a schematic lengthwise cross sectional view of a device used to perform the method object of this invention.
[0019] Figure number 2 is a time diagram representing the operation of the infrared and wide spectrum fluorescent light sources.
[0020] Figure number 3 is a block schematic diagram of the electronic control and signal treatment system of the device.
[0022] The banknote identification device shown in figure 1 incorporates a banknote or other document conveyance and guidance system, an image acquisition system and an electronic device control and signal treatment system, as described below.
[0023] The conveyance and guiding system is made up of an actuation motor 1, driving 2 and freely rotating 3 conveyance pulleys, and two parallel plates 4 and 5, out of which the upper plate 4 will be transparent and be located in the document reading area, whereas the lower one 5 is to be white and translucent.
[0025] At the ends of the guiding plates 4 and 5 will be located couples of light detectors 7 and 8, which purpose is to detect the introduction of the banknote at one end and its acceptance at the opposite end.
[0026] The image acquisition system is made up of an optical system and a lighting system. The optical system includes a lens 9, a diaphragm 10 and a mirror 11, to be focused upon a line 6 of the document being subjected to analysis upon a linear sensor 12. The lighting system includes a wide spectrum light source 13 and an infrared light source 14. The wide spectrum light source 13 will preferably be of the fluorescent type, so as to achieve a degree of lighting that covers all of the visible spectrum with a good level of response in shorter wave lengths (blue). This feature is advantageous when compared with other wide spectrum light sources, such as for instance the incandescent light sources, which present an optimal level of response to red and near by infrared, but which performance decrease substantially at shorter wave lengths. Another advantage of the fluorescent light sources, and particularly of the cold cathode ones, is the low level of inertia that they show when they are operated in on-off cycles, thus allowing the alternation of wide spectrum lighting with other available light sources without appreciably penalizing the amount of time required for document analysis.
[0027] Notwithstanding the foregoing, the fluorescent type light sources feature two major disadvantages: the first one is the high degree of dependence of the lighting level to the temperature of the light source, and the second disadvantage is the operating life drop experienced as the level of power supplied to the light source is increased.
[0028] To avoid these disadvantages, in accordance with the invention, appropriate means are duly arranged to optimize the level of luminosity of the light source and, on the other hand, the light source is further subjected to a specific mode of operation designed to permanently maintain it at the same operating temperature, independently of whether the device is in the document analysis or stand-by mode.
[0029] The means used to optimize the level of luminosity of the light source consist of a reflector 15 that surrounds the fluorescent tube 13 and with which it is possible to beam the light towards the document examination line 6. There is furthermore a transparent capsule 6 that surrounds the tube 13, insulating that tube from the surrounding environmental conditions and allowing it to maintain its optimal operating temperature with a lower level of energy consumption, thus achieving a light source operating life increase.
[0030] The reflector 15 will include a window type lengthwise opening in the direction of the light, being that opening capable of incorporating a variable cross section between its central and end areas. Furthermore, this reflector may also feature a central reflection area that could be different to its end reflection areas.
[0031] Regarding the wide spectrum light source operating system in the document analysis and stand by stages, that light source is subjected to an intermittent operating mode during the document analysis stage, featuring a 100% level of lighting during the unit operation periods, which then becomes continuos during the stand by stage, with a lighting level equivalent to the total average lighting level during the document analysis stage.
[0032] The infrared light source shall also operate intermittently during the document analysis stage, alternating its operation with that of the wide spectrum light source.
[0033] The time diagrams included in figure 2 respectively represent in diagrams A and B the operation of the wide spectrum fluorescent and infrared light sources in their document analysis and stand by stages, being it possible to appreciate the intermittent operation of the light sources during the document analysis stage and during their alternation, reaching the wide spectrum light source a 100% lighting level during its operating periods, whereas during the stand by stage the wide spectrum light source reaches a lighting level equivalent to the total mean lighting level of this source during the document analysis stage, corresponding therefore to 50% of the above level.
[0034] The RGB images corresponding to each one of the lighting sources are acquired during the document analysis stage are acquired throughout the whole length of the banknote,, with the added particularity that all of the images originate at the same line 6 of the banknote being analyzed. From these images are then obtained the parameters representing each one of the areas for each one of the light levels and the new parameters of a single area, corresponding to different lighting levels, are also generated. The arithmetical mean, normal deviation, upper range, lower range and points above the mean may be used as representative parameters at a given area for a given lighting. The relations between the previously mentioned parameters, such as differences and quotients, will be preferably used as relative parameters in a single area under different lighting conditions.
[0035] Each step of the travel of the banknote through the device shown in figure 1 takes place after the acquisition of the various lines by the linear light sensing device 12, each of them under one of the different lighting methods, alternatively used.
[0036] In a different manner, the acquisition of each line is effected by lighting the document alternatively with each one of the available light sources 13 and 14, whilst at the same time the document is displaced a distance shorter than the resolution of the optical system.
[0037] The operation described may be obtained using an electronic device control and signal treatment system, of which figure 3 represents a block diagram. This diagram represents, using the same item reference numbers already used in figure 1, the linear sensor 12, the wide spectrum light source 15 and the infrared light source 14. The linear sensor 12 receives light from light source 15 reflected upon the lower diffuser plate 5, figure 1, in the absence of a banknote. The values read are conditioned in the amplifier 17 and, after being digitized in the analogue to digital converter 18, are then compared by the microprocessor 19 against reference values contained in an external memory device that may be of the EPROM or FLASII type, both in respect of the stand by and document analysis values. Depending upon the result of the comparison, the microprocessor 19 shall act upon the digital to analogue converter 21 to increase or decrease the light source 15 power level, which will correspond to the required lighting levels. Thus, the operation is cyclically repeated during the period of inactivity (document stand by mode). It is thus achieved that the device be insensible to major heat level changes, together with a significant increase in respect of the working life of the fluorescent light source.
[0038] Item number 22 of the schematic diagram shown in figure 3 represents a volatile memory device, of the RAM type.
[0039] A typical document analysis and identification sequence is explained below. As previously explained, the wide spectrum light source will be stabilized at the stand by level. The infrared light source 14 will also be calibrated according to already known systems, as explained in the Spanish application 9402631. The available lighting sources and sensing elements are calibrated whenever the presence of a incoming document is detected by the inlet detectors 7, figure 1, for instance as explained in the previously mentioned document. Once the conveyance system has driven the document forward up to the analysis area 6, successive lines of the document are then acquired, alternating the application of the 13 and 14 lighting sources, so that at the end of the banknote analysis procedure there will then be a full image of the banknote stored in the RAM memory 22 of the device for each one of the available lighting levels. This may be achieved in two different ways: the first one would be to acquire the same line of the banknote using the various lighting levels available, without moving the document, and the second one would involve causing a forward movement of the document between the successive acquisitions for the different lighting levels, as long as the forward progression of the document be shorter than the resolution of the optical system. Once the document has been fully acquired it will then be identified, being this a procedure that may be performed in a manner similar to that described in the Spanish application 9402631, proceeding to classify the width and length of the document followed by a study of the areas of interest, which will give rise to document identifying parameters of the type described in the Spanish applications 9302692 and 9402631, which will then allow the final classification of the document.
[0040] Figure 4 represents a sample document, shaped as a programming card, through which may be effected the variation of the values of the acceptance parameters and tolerances of the various admissible face values. The card shown in figure 4 includes a number of blank boxes 22 that are associated to each one of the face values of the admissible documents. These boxes are shaded using a variable amplitude and/or color, being the amplitude of the variation achieved a function of the shaded surface and/or the color used in the corresponding area.
[0041] Each one of the blank boxes is associated to each one of the face values of the admissible documents. We may, for instance, program it so that, whenever the device detects this card type, it shall then analyze each one of the boxes in order to determine the extent of the shaded area and the color in which it has been shaded. If, for example, the first box has been shaded using green ink up to 50% of its length, we shall then interpret that the acceptance tolerance is to be increased by 50% in respect of that already allowed. On the other hand, should the shading be found to be of a red color, it will then interpret that the acceptance tolerance is to be reduced by 50% in respect of that already allowed. We may therefore establish tolerance increase and reduction criteria as a function of both the amplitude of the shaded area and the shading color used. A specific case would that of black colored shading, which we may associate, for instance, with an assignment of absolute tolerances between 0% and 100%. Another specific case may be that of a blank box, which could be interpreted as a desire to inhibit the corresponding document face value. An additional security feature would be the inclusion of an internal switch, non accessible from the outside, to prevent unforeseen handling.
[0042] The programming card may be printed so that it contains different types of visible and infrared inks, allowing it to contain a volume of information sufficient to allow even the reprogramming of the discriminating device to enable it to accept new face values. For example, colored marks on its upper surface, transparent to infrared radiation, may be combined with infrared opaque inks on its lower surface, permitting a very large number of different functions.
1. Method for the characterization and discrimination of banknotes and legal tender documents,
including the conveyance of the document to be analyzed along a path in which such
document is lit using wide spectrum and/or infrared light sources, the acquisition
of images of the document through the use of a lineal sensor and the analysis of the
coloring of those images, in which the wide spectrum light source preferentially consists
of a fluorescent tube, characterized because the wide spectrum light source is subjected
to a different operating mode during its document analysis and stand by stages, featuring
intermittent operation during the document analysis stage, using a 100% lighting level
during the turned on periods, and being continuously lit during the stand by stage,
with a lighting level equivalent to the average total lighting level during the document
analysis stage; and because the values of the acceptance parameters and tolerances
of the various admissible face values are modified through the examination of a sample
document that includes a number of well defined areas, each of which is capable of
being related to one of the face values of the admissible documents and which may
further be programmed through their variable amplitude and/or coloring shading effected
as a function of the shaded surface and/or color used in the corresponding area.
2. Method according to claim number 1, characterized in that the level of luminosity
of the fluorescent lamps is optimized using a reflector that concentrically surrounds
the wide spectrum light source and through the use of a transparent cover, glass or
plastic based, that encloses the light source, being such reflector fitted with a
lengthwise window type opening aimed in the document lighting direction.
3. Method according to claim number 1, in which the RGB images for each of the lighting
sources are acquired throughout the length of the banknote during the document analysis
stage, characterized in that all of the images acquired originate from the same line
of the document analyzed, for the obtainment of parameters representing each one of
the areas with each one of the light types and the generation of new parameters of
a single area, corresponding to different light levels, from which relations such
as differences and quotients, capable of being used as relative parameters, will then
be obtained.
4. Method according to claims 1 and 3, characterized in that each step in the forward
travel of the banknote takes place after the acquisition of the different lines by
the linear sensor, each one of them under one of the different light types, alternatively
used.
5. Method according to claims 1 and 3, characterized in that the acquisition of each
line is effected by lighting the document alternatively with each of the available
light sources, at the same time that the document is displaced a distance that is
shorter than the resolution of the optical system.
6. Method according to claim 1, characterized in that the modification of parameters
and tolerances includes the identification of the sample document, the measurement
of the amplitude and analysis of the coloring of the shaded surface in each of the
areas of the document, which correspond to each one of the admissible face values,
and the assignment of new tolerances; featuring the new value a relation established
in accordance with a previously established function related to the extent and color
of the designated areas.
7. Method according to claims 1 and 6, characterized in that the sample document consist
of a programming card combining color marks on its upper surface, transparent to infrared
radiation, and infrared opaque inks on its lower surface, allowing a large number
of different functions or else supplying an amount of information sufficient to program
the document discrimination device to accept new face values.
8. Device for the characterization and discrimination of banknotes and legal tender documents,
incorporating conveyance (1-2) and guidance (4-5) means, wide spectrum lighting means
of the fluorescent type (13) and infrared light emitters (14), and linear light sensor
(12) and electronic signal treatment means, characterized because the fluorescent
tube (13) incorporates a concentric reflector (15) with a lengthwise window type opening
aimed in the direction of the light, being the lamp encapsulated within a transparent
tube (16) made of glass or plastic material.
9. Device according to claim 8, characterized in that the reflector features a reflection
area that is variable from its central area towards its end areas.
10. Device according to claim 9, characterized in that the lengthwise opening of the reflectors
has a variable cross section between its central and end areas.