Apparatus for authenticating documents

Abstract: In apparatus for authenticating documents (12) such as banknotes, light reflected from, or transmitted through, a document (12), is formed by a lens system (20) to a beam (32) which is directed to a series of wavelength selective beam splitters (34) each of which transmits light of greater than a characteristic wavelength and reflects light of lesser wavelength. The characteristic wavelengths of the beam splitters (34) increase or decrease along the series. The resulting output beams (36) are sensed by photosensors (40) to produce electrical signals which are digitized. The resulting data is analyzed, for example, by comparison with corresponding data derived from a genuine document, to provide an output signal on a line (48) indicative of the authenticity of the document (12).

Description: This invention relates to apparatus for authenticating documents. Automatic machines which accept banknotes and other valuable documents such as cheques are becoming more widely used. It is important for such machines to authenticate the documents, that is, to distinguish between genuine and counterfeit documents. U.K. Patent Application No. GB-A-2 192 275 discloses a system for authenticating banknotes by detecting colours thereof by reflected or transmitted light. Optical fibre bundles direct light from a light source onto the banknote, and the reflected or transmitted light is incident on three colour filters which pass the light they transmit to respective further optical fibres which transmit the light to respective photosensors. The output signals from the photosensors are analyzed to determine the authenticity of the banknote. US-A-4526466 discloses an apparatus for authenticating sheet materials in which a particular diffraction grating structure operates as a diffractive subtractive colour filter responsive to the angle of incidence of continuous spectrum polychromatic light. The authenticity of a sample sheet material is determined by comparing the colour filtering characteristics of the sample with those of a genuine reference sample. It is an object of the present invention to provide apparatus for authenticating documents which operates in an efficient manner. Therefore, according to the present invention, there is provided apparatus for authenticating documents, including light source means adapted to direct light towards a document to be authenticated, comprising beam producing means adapted to produce a light beam derived from said document, beam splitting means disposed in the path of said light beam, photosensing means adapted to sense light output derived from said beam splitting means, and processing means adapted to process output signals from said photosensory means to determine the authenticity of said document characterised in that the beam splitting means includes a plurality of serially-arranged wavelength selective beam splitters each adapted to transmit and reflect respective waveband portions of the light incident thereon. It will be appreciated that apparatus according to the invention is efficient since substantially all the light energy reflected from or transmitted by the document is utilized in the authentication analysis, whereas in the known system, referred to hereinabove, only a fraction of the light (one-third) from the document incident on each colour filter is used in the authentication procedure. Also, the design and fabrication of wavelength selective beam splitters having the desired transmission/reflection characteristics is relatively straightforward. One embodiment of the present invention will now be described by way of example, with reference to the accompanying drawing, in which Fig. 1 is a simplified diagram illustrating apparatus according to the invention for authenticating documents. Referring to Fig. 1 there is shown a simplified diagram of a document authentication system 10 according to the present invention. A document 12 to be authenticated is fed by transport means, shown schematically as roller pairs 14 and 16, in the direction of arrow 18 along a feed path 20. Typically, the document 12 is a banknote, but may be a cheque or other valuable document, according to the application. The document 12 is fed through a sensing station 22 where broadband (white) light sources 24 and 26 direct narrow, collimated beams of light to illuminate a small circular area on the document 12. Typically the illuminated area may have a diameter of around 5mm, but the diameter could be less, e.g. around 2mm, or could be greater than 5mm. Light reflected from this area is directed to a beam splitting device 28. The light passes through a lens system 30, contained in the device 28, the lens system providing a substantially collimated output light beam 32. In a modification, instead of two light sources 24 and 26, only a single light source (e.g. 24) may be provided. The light beam 32 is directed to a sequence of wavelength selective beam splitters 34, referenced individually as 34-1 to 34-4, respectively. The beam splitters 34 are disposed at an angle of 45 degrees to the path of the light beam 32. Each beam splitter 34 transmits light having a wavelength longer than a characteristic wavelength and reflects light having a lesser wavelength. The beam splitters 34-1 to 34-4 are arranged to have progressively larger characteristic wavelengths. It will readily be appreciated that, with this arrangement the light beam 32 is split into a number of reflected parallel beams 36, referenced individually as 36-1 to 36-4, and an in-line output beam 36-5. Thus, the beam 36-1 contains light having a wavelength shorter than the characteristic wavelength of the beam splitter 34-1; the beam 36-2 contains light having a wavelength between the characteristic wavelengths of the beam splitters 34-1 and 34-2, etc., with the output beam 34-5 containing light with a wavelength greater than the characteristic wavelength of the beam splitter 34-4. Thus, it will be appreciated that the beam 32 has been split into five beams 36-1 to 36-5 which are effectively of different colours. The beams 36-1 to 36-5 are directed to narrow band-pass filters 38-1 to 38-5 respectively, which provide narrow band output beams which are applied to respective photosensors 40, referenced individually as photosensors 40-1 to 40-5. It should be understood that the narrow band-pass filters 38 are optional, and in an alternative arrangement may be omitted, although this may reduce the accuracy of document authentication. The outputs of the photosensors 40 are connected to respective amplifiers 42, referenced individually as amplifiers 42-1 to 42-5, which have outputs connected to respective analog-to-digital converters 44, referenced individually as analog-to-digital converters 44-1 to 44-5. The outputs of the analog-to-digital converters 44-1 to 44-5 are connected via a digital multiplexor 45 to a processor system 46 which provides an output on a line 48 indicative of the authenticity of the document 12 being tested. The processor system 46 also provides control signals for control of the light sources 24 and 26 and the document transport means. However such functions are not pertinent to the present invention, and therefore will not be described in detail herein. In a modification, instead of the digital multiplexor 45, an analog multiplexor could be used at an earlier stage so that only a single, multiplexed analog-to-digital converter would be needed instead of the five converters 44 shown in Fig. 1. The operation of the document authentication system 10 will now be described. The document 12 to be authenticated is fed at constant speed along the feed path 20 in the direction of the arrow 18. As the document 12 moves, the light reflected from the small circular illuminated area of the document forms the beam 32, which is split into five components in the manner described hereinabove. As the document 12 moves along the feed path 20, the photosensors 40 detect colour components, in dependence on the characteristics of the beam splitters 34 and filters 38. The output signals from the photosensors 40 are amplified in the amplifiers 42 and digitized in the analog-to-digital converter 44. Typically, such digitizing takes place with a sampling rate of 500Hz. A suitable sampling rate is chosen, dependent on the resolution of the image data on the document 12 and the transported speed of the document 12. The sampling rate may be selected in the range from about 50Hz to about 5KHz, for example. The digitized output is converted to parallel form in the converter 45, the resulting data consisting of a repeated series of words, representing the changing five colour component values sensed as the document 12 moves through the station 22. This data may be stored in a memory (not shown) in the processor system 46, and compared with corresponding reference data derived from a genuine document, to determine the authenticity of the document 12. Such procedures are known, and will not be further described herein. The output signal on the line 48, indicative of the authenticity of the document 12 and, optionally of other determined characteristics of the document 12, such as denomination for a banknote, for example, can be used in various ways depending on the application. For example, a document determined as non-authentic can be returned to an entry slot, or diverted to a reject bin. If the signal on the line 48 is indicative of the document 12 being genuine, a transaction can be performed, for example if the document is a banknote, a financial transaction may be initiated. It should be understood that the apparatus shown in Fig. 1 may provide for a calibration operation to be carried out. For example, a calibration document may be transported through the sensing station 22, or a calibration strip may be built into the transport system in the sensing station. As is known, a calibration operation compensates for variations which may occur in the relative responses of the photosensors resulting, for example, from variations in the electronics and spectra of the light sources. Modifications of the described embodiment are possible. For example, instead of analyzing reflected light characteristics, the light sources 24 and 26 could be replaced by a single light source 52, disposed on the opposite side of the document 12 to the beam splitter unit 24. With this arrangement transmittance characteristics are sensed and analyzed. Also, with this modified arrangement, calibration may be effected by sampling the light source 52 directly, although it may be desirable to introduce a neutral density filter into the light path to avoid saturating the photosensors. In another modification, instead of utilizing a small circular area for colour analysis, a narrow strip across the width of the document could be illuminated and light reflected therefrom or transmitted therethrough could be analyzed. This would require suitably shaped lens systems, and would produce larger amounts of data for use in the authentication analysis. In still another modification, light could be guided by optical fibres for direction onto the document 12. Also, the light reflected from (or transmitted through) the document 12 could be directed towards the beam splitting device 28 by optical fibres also. In yet another modification, the beam splitters 34 could be arranged in order of decreasing characteristic wavelength, instead of increasing characteristic wavelength. In summary, there has been described a document authentication system which provides a versatile means of obtaining spectral bands, since the beam splitters 34 can be readily removed, replaced or added to. Furthermore, such wavelength selective beam splitters are easy to manufacture. A further advantage is that the cost and complexity of a prismatic spectrometer is avoided. Also, wavelength selective beam splitters have stable characteristics, enabling a stable spectral response, and minimizing calibration requirements. Thus the system is particularly suitable for use in self-service environments.

Claims: Apparatus for authenticating documents, including light source means (24,26, 52) adapted to direct light towards a document (12) to be authenticated, comprising beam producing means (30) adapted to produce a light beam (32) derived from said document (12), beam splitting means (28) disposed in the path of said light beam (32), photosensing means (40) adapted to sense light output derived from said beam splitting means (28), and processing means (42, 44, 45, 46) adapted to process output signals from said photosensory means (40) to determine the authenticity of said document (12), characterised in that the beam splitting means (28) includes a plurality of serially-arranged wavelength selective beam splitters (34), each adapted to transmit and reflect respective waveband portions of the light incident thereon. Apparatus according to claim 1, characterized in that said serially-arranged beam splitters (34) each transmit light having a wavelength greater than a respective characteristic wavelength, and reflect light having a lesser wavelength. Apparatus according to claim 2, characterized in that said serially-arranged beam splitters (34) have characteristic wavelengths which increase in value along the series. Apparatus according to any one the preceding claims, characterized in that respective band-pass filter means (38) are disposed between said beam splitters (34) and said photosensing means (40). Apparatus according to any one of the preceding claims, characterized in that said processing means includes analog-to-digital converter means (44, 45) coupled to a processor system (46). Apparatus according to claim 5, characterized in that said processor system (46) is adapted to compare digital data provided by said analog-to-digital converter means (44, 45) with reference data derived from a genuine document. Apparatus according to any one of the preceding claims, characterized in that said light source means (24, 26) and said light beam producing means (30) are located on the same side of said document (12) being authenticated, whereby light reflected from said document (12) is utilized to provide said light beam (32). Apparatus according to any one of claims 1 to 6, characterized in that said light source means (52) and said light beam producing means (30) are located on opposite sides of said document (12) being authenticated, whereby light transmitted through said document (12) is utilized to provide said light beam (32). Apparatus according to any one of the preceding claims, characterized in that transport means (14, 16) are provided adapted to feed said document (12) past said light beam producing means (30). Apparatus according to claim 9, characterized in that said document (12) is fed at a constant speed. Apparatus according to any one of the preceding claims, characterized in that said light source means (24, 26, 52) includes a broadband light source. Apparatus according to any one of the preceding claims, characterized in that said light beam producing means (30) includes a lens system. Apparatus according to any one of claims 1 to 10, characterized in that said light beam producing means includes optical fibres.

Inventors: ECCLES JOHN, ECCLES, JOHN
Applicants: NCR INT INC, NCR INTERNATIONAL, INC.
Application year: 1996
Main classification: G07D7
IPC codes: G07D7