IE70663B1

IE70663B1 - Method for analysing a fiduciary or security document exhibiting printed graphics and two superimposed security marks and device for implementation of the method

Info

Publication number: IE70663B1
Application number: IE921299A
Authority: IE
Inventors: Olivier Puyplat; Jean-Claude Fremy
Original assignee: Banque De France
Priority date: 1991-04-18
Filing date: 1992-04-22
Publication date: 1996-12-11
Also published as: FR2675607A1; DE69206867T2; EP0509917A1; IE921299A1; EP0509917B1; FR2675607B1; RU2089938C1; DE69206867D1; OA09540A

Abstract

The invention relates to a method and a device for analysing a document comprising two superposed grids (100, 200), of which one is a periodic watermarked grid and one is a coding by dividing up the printed graphics into parallel bands. According to the invention, sensors are available (300), arranged perpendicularly to the direction of movement of the document, with an interdistance (d) equal to the width (e) of the parallel bands, then the coding of the second grid (200) is checked by adding the responses from each band and from its conjugate, and the first grid (100) is analysed by subtraction of the responses of each non-coded band and of its conjugate. Application to the authentication of a document, especially bank notes.

Description

The invention relates to fiduciary or security documents of the type comprising printed graphics and security marks, the said documents possibly being, in particular, banknotes, and, more particularly, to the analysis of documents comprising two superimposed security marks.

Numerous security marks have already been used for authentication of documents, but these marks are generally of a single type, and their means of analysis is then adapted to the particular type of security mark in question.

Thus, documents have long existed whose security marks are produced by using a magnetic wire totally or alternately embedded in the paper of the document, this wire also possibly being coded: these documents are attractive, as they are well suited to mechanised use, the corresponding processing machines being equipped in order to detect the presence of the magnetic wire in the document which is moving past, and possibly to recognise the coding of this wire, so as to authenticate the said document. Such a technique, in reality, exhibits limits in terms of the effectiveness of the authentication of the documents, which makes it necessary to provide complicated codings.

There also exist documents whose security marks rest on the principle of a variation in density of the fibres (volume or surface mass) with a particular coding. Thus, a repetitive dry stamping has been proposed, along a band parallel to one edge of the document, the said stamping provided on manufacture of the paper thus making it possible to cause the density to vary along the said band, with this band being crushed when the document is printed. As a variant, a succession of stages of embossing and of counter-embossing has been used for the forming web, which makes it possible to obtain a succession of dark and light areas for the document, according to a particular watermark of the watermarked grid type, the said grid being repetitive or otherwise.

These techniques, however, exhibit limitations, since, most o£ the time, they impose constraints with regard to the orientation (long edge or short edge parallel to the direction of movement), to the presentation (recto-verso) of the document, and to the « direction of its movement (right-left) in a processing machine.

For analysis of such documents, then, capacitive sensors are used (the variations in the surface mass inducing variations in the signal originating from the sensor used), or microwave sensors, or even infrared sensors of the emitter-receiver type operating with wavelengths of the order of three micrometers (start of the thermal infrared region).

Such sensors are relatively simple in structure, but they do not permit authentication of documents comprising only a watermark with variations of surface mass: in the particular case of banknotes, these sensors in particular do not make it possible to detect the face value of the said notes.

Moreover, in the case of known sensors operating in infrared, the wavelengths used are much too long to reveal the ink of printed graphics.

In any event, the calculation processing remains relatively complicated in every case.

It has finally been proposed to code documents with successions of bars some of which absorb and others of which reflect infrared radiation, in order to authenticate the said documents. For analysis of such documents, then, sensors of the bar code type are used, similar to those which are used in the field of labelling. Such sensors are, however, restricted to reading this one type of coding. > Generally, these different security marks have been used alone or juxtaposed, with, in the latter case, » the necessity of using different types of sensors for successive detection of the said marks.

It appears necessary nowadays to improve these techniques of authentication in order to combat ever more sophisticated techniques used to attempt to forge the documents.

In the particular case of banknotes, the additional problem of mechanised detection of the face value must also be resolved.

The person skilled in the art, however, encounters great difficulties in seeking to combine different security marks, as, on the one hand, analysis techniques rapidly become inextricable, and necessitate the use of different sensors, which are often bulky and/or difficult to make mutually compatible, and, on the other hand, to the extent that solutions are arrived at which most often impose a constraint with regard to the presentation and the orientation of the document.

Moreover, the machines used for sorting, counting and/or distribution are being developed in order to have ever higher performance in terms of working time per document.

This explains, no doubt, why specialists have generally confined themselves to the use of security marks of a single type, as a function of the eventual goal (especially authentication or detection of the face value in the case of banknotes).

It appears extremely attractive to succeed in analysing a document by simultaneously reading two superimposed grids, with, in particular, a first grid which is repetitively watermarked, and with a second grid result30 Ing from a chopping of the printed graphics into parallel bands, these bands extending parallel to the direction of movement of the document and being coded perpendicularly to this direction of movement symmetrically on either side of the axis of the document which is parallel to the said direction of movement.

The parallel bands of the second grid are provided so as to have the same width in order to facilitate analysis of the document: in the case where the wave of the first grid extends in a common direction which is essentially not perpendicular and not parallel to the direction of movement of the document, this same band width (e) is given by the formula T e = 2 sin β (where T is the wavelength of the first grid and β the acute angle which the two abovementioned directions make), and in the case where these two directions are essentially parallel, this same band width (e) is substantially equal to T/2 (half-wavelength of the first grid).

The problem that the invention proposes to resolve is to succeed in analysing a document of the abovementioned type with two superimposed grids using a single analysis and processing system.

The subject of the invention is thus a method for analysing such a document, as well as a device for implementation of the method, making it possible to resolve the abovementioned problem simply and reliably.

The objective of the invention is also to design a method and a device for analysis permitting, in the particular case of banknotes, both improved assistance with authentication and easy mechanised detection of the face value of the note.

Finally, the objective of the invention is to produce a method and a device for analysis which are compatible with the high-speed processing machines used for sorting, counting and/or distribution.

What is involved more particularly is a method for analysing a fiduciary or security document moving in a defined direction, by simultaneously reading two superimposed grids, with a first grid which is repetitively watermarked, and whose wave extends in a common direction essentially not perpendicular and not parallel to the direction of movement, and with a second grid organised into bands according to a binary coding, the said bands extending parallel to the direction of movement, and being coded perpendicular to the said direction of movement, symmetrically on either side of the axis of the document which is parallel to the said direction of movement, and the said bands exhibiting the same band width e given by the formula: T e = 2 sin β where T is the wavelength of the first grid and β the angle between the said common direction and the said direction of movement, characterised in that it comprises the following steps: • means of detection are arranged on the basis of at least one per band of the second grid, these means being organised along a general direction perpendicular to the direction of movement, with a separation equal to the width of the parallel bands of the said second grid; • the coding of the second grid is verified by adding the response of each band and of its symmetrical figure which is its conjugate, so as to eliminate the influence of the first grid, and by comparing the results obtained with the theoretical coding values; • the first grid is analysed by subtraction of the responses of each band without coding and of its symmetrical figure.

Preferably, the means of detection are situated on the median axis of the associated bands of the second grid: this is attractive, as it avoids any risk of impairing the analysis in the case of a misaligned document (loss of signal due to increasing noise).

As a variant, the invention relates to a method for analysing a fiduciary or security document moving in a defined direction, by simultaneously reading two superimposed grids, with a first grid which is repetitively watermarked, and whose wave extends in a common direction essentially parallel to the direction of movement, and with a second grid which is organised into .15 - 6 bands according to a binary coding, the said bands extending parallel to the direction of movement, and being coded perpendicular to the said direction of movement, symmetrically on either side of the axis of the document which is parallel to the said direction of , movement, and the said bands exhibiting the same band width substantially equal to the half-wavelength of the first grid, characterised in that it comprises the following steps: > means of detection are arranged on the basis of at least one per band of the second grid, these means being organised along a general direction perpendicular to the direction of movement and situated on the median axis of the associated bands, with, on one side of the said axis of the document, first means of detection mutually aligned, and, on the other side of the said axis, second means of detection also mutually aligned but offset with respect to the first means of detection by a distance substantially equal to the half-wavelength of the first grid; « the coding of the second grid is verified by adding the response of each band and of its symmetrical figure which is its conjugate, so as to eliminate the influence of the first grid, and by comparing the results obtained with the theoretical coding values; • the first grid is analysed by subtraction of the responses of each band without coding and of its symmetrical figure.

The invention also relates to a device for the implementation of the method, characterised in that it comprises: » « means of detection grouped together on a read bar arranged perpendicular to the direction of movement, * the said means being constituted by sensors equal in number to the number of parallel bands of the second grid of the document to be analysed; • means for processing the signals originating from the various sensors, the said means of processing comprising, on the one hand, in succession, summing means making it possible to add the response of each band and of its symmetric band which is its conjugate, integrator means making it possible to integrate the output signals from the said summing means over the whole length of the document, and comparator means making it possible to compare the results obtained with the theoretical coding values of the second grid of the document to be analysed, so as to verify the said coding of the said second grid and to validate the document analysed when the said second grid is a match,, and, on the other hand, in succession, differentiator means making it possible to subtract the responses of each band and of its conjugate band, selector means associated with the said differentiator means so as to keep only the responses relating to the bands without coding, filtering means making it possible to filter signals at the fundamental frequency of the first grid of the document to be analysed, and means for recognition and for validation, so as to analyse the said first grid and to validate the document analysed when the said first grid is a match.

Preferably, means of switching are provided upstream and downstream of the integrator means, the said means of switching being controlled by the passage of an edge of the document to be analysed in front of a fixed member such as a photodiode (integrated or separate) in order to detect the start and the end of the passage of the document in front of the means of detection, in such a way that the said integrator means operate only for the length of the said document.

Advantageously also, the comparator means are equipped with an alarm operating when a difference between results is outside a predetermined bracket. As a variant, the comparator means are equipped with an alarm operating when a ratio between results is outside a predetermined bracket.

It is equally attractive that means of decoding are provided downstream of the comparator means, so as to identify the document, and in particular, when the said . document is a banknote, to detect the face value of the said banknote.

Moreover, supplementary summing means are provided between the selector means and the means of filtering, so as to obtain a single signal representing the sum of the in-phase signals originating from the said selector means.

Preferably also, amplifier means are provided between the sensors and the associated summing or differentiating means.

According to a particular embodiment, the read bar exhibits equidistant, substantially circular apertures associated with each sensor.

As a variant, the read bar exhibits slot-shaped apertures associated with each sensor, each slot being inclined so as to be substantially perpendicular to the direction of propagation of the wave from the first grid of the document; according to yet another variant, the read bar exhibits cruciform apertures associated with each sensor, the two branches of each aperture being inclined in such a way as to be substantially parallel and perpendicular to the direction of propagation of the wave from the first grid of the document.

It may prove advantageous that at least one of the sensors is multiple.

In particular, the multiple sensor is constituted by two adjacent identical sensors arranged on either side of the median axis of each band of the second grid * of the document. As a variant, the multiple sensor is constituted by four identical sensors arranged in a * square, the edges of the square being parallel and perpendicular to the direction of movement.

Advantageously, the single or multiple sensors are photodiodes, or phototransistors, or photo-resistor cells, each of the said sensors being associated with optical filters in order to be matched to the desired wavelength.

Preferably also, the sensors of the bar are organised in order to exhibit the same gain and the same origin offset, in such a way as to ensure balancing of the various paths.

Moreover, according to a particular example, it is attractive that the read bar comprises a single row of sensors arranged perpendicular to the direction of movement, the said sensors being equidistant from each other by a distance substantially equal to the width of the parallel bands of the second grid of the document to be analysed.

In a variant, the read bar comprises two parallel rows of sensors arranged perpendicular to the direction of movement, with one row per half-bar, the said rows being offset with respect to each other by a predetermined distance substantially equal to the halfwavelength of the first grid of the document to be analysed, and the sensors of any one row being equidistant from each other by a distance substantially equal to the width of the parallel bands of the second grid of the said document.

Other characteristics and advantages of the invention will become clearer in the light of the description which will follow and of the attached drawings, concerning a particular embodiment, with reference to the figures in which: Figure 1 illustrates a rectangular document intended to be analysed by a method and a device in accordance with the invention, a document whose first and second security marks have been represented in dotted lines, these marks being superimposed; Figure 2 is a plan view illustrating the first security mark of the abovementioned document, which is produced in the form of a watermarked repetitive grid, here organised in a square, so that it can be seen against the light, with alternating light and · dark areas corresponding to the variations in the surface mass in this watermarked area; Figure 3 illustrates, in plan view, the contoured face of a matrix making it possible to emboss the forming web during manufacture of the document, in order to obtain a watermarked repetitive grid similar to that of Figure 2, the undulations, here sinusoidal, of this contoured face making it possible to produce the desired variations of the surface mass in this watermarked area, the edges of this matrix being moreover chamfered in order to soften the contrasts at the edges of the said area; Figures 4 to 8 are sections, respectively through IV-IV, V-V, VI-VI, VII-VII and VIII-VIII of Figure 3, permitting better understanding of the organisation of the contoured face of the matrix, and in particular of its chamfered edges, with respect to the mean plane of the said face; Figures 4a to 8a are curves illustrating the variations in the surface mass of the watermarked area obtained with the abovementioned matrix, these curves corresponding respectively to the sections of Figures 4 to 8 (the curves of variations of the surface mass in the paper are, in effect, direct transforms from the corresponding curves of the variations of the relief of the face of the embossing matrix); Figures 9 and 10 illustrate the document of Figure 1, with two different codings of the parallel bands of the second grid, as this document appears, for example, when it is examined under infrared (for printed graphics with a pair of inks one of which reflects infrared and the other of which does not), with, here, eight parallel bands, coded respectively 1 011 1101 and 0 110 0110; Figure 11 is a view against the light of the watermarked repetitive grid obtained with the matrix illustrated above, with a square contour with chamfered edges, and with a particular phase shifting with respect to the axes of the square (which are preferably coincident with the two axes of symmetry of the rectangular document); Figure 12 is a view on a larger scale showing an area of the document where the two security marks are superimposed (here there are six parallel bands of the second grid, which cross the watermarked area with the first repetitive grid), this view making it possible to understand how the two superimposed grids are arranged for an interleaving which is compatible with analysis by a single member in front of which the document moves, in accordance with the invention; Figure 13 supplements the preceding view by showing a bar of sensors in accordance with the invention, permitting analysis of the abovementioned document, with a sensor for each parallel band of the second grid, the said bar being arranged perpendicular to the direction of movement of the document; Figure 14 illustrates a variant of the invention in which the direction (DC) of propagation of the wave of the watermarked grid is not, as before, inclined at 45 with respect to the direction of movement (DD), but is parallel to the said direction of movement, the bar of sensors in accordance with the invention being, in this case, arranged differently, with two rows of sensors offset as can be seen on the figure; Figures 15a to 15d are partial views illustrating different variants of arrangement of the sensors of the bar of Figure 13, with, respectively, apertures as inclined slots, cruciform apertures, multiple sensors with two adjacent sensors, and multiple sensors with four sensors arranged in a square; Figure 16 is a diagram of a device for analysis in accordance with the invention, associated here with the bar of sensors of Figure 13, showing the means * which can be used for processing the signals originating from the different sensors, so as, on the one hand, to verify the coding of the second grid and to validate the document analysed when the second grid is a match, and, on the other hand, to analyse the first grid and to validate the document analysed when the first grid is a match.

Figure 1 illustrates a document 1, here of rectangular shape, whose long edge is denoted 2 and whose short edge is denoted 3..

This document exhibits on one face (recto or verso), printed graphics G, here illustrating a hangglider. Graphics can naturally also be . provided on the other face of the document 1.

In accordance with the invention, the document 1 comprises two superimposed security marks 100, 200,. here represented in dotted lines.

The first security mark 100 exhibits the form of a repetitive watermarked grid, delimited by a closed contour C which is inside the edges 2, 3 of the document 1. This first security mark is thus clearly visible against the light, and then exhibits a succession of bands 101, 102 which are alternately darker and lighter.

The appearance of these bands 101, 102 results from the variations in the surface mass in this watermarked area.

The second security mark 200 is also produced in the form of a grid, but this second mark results from chopping of the printed graphics G into, parallel bands 201, 202 which are coded.

The bands 201, 202 are first of all arranged symmetrically with respect to an axis of symmetry of the document 1, in this example the axis X'X, which is * parallel to the long edge 2 of the said document. Thus there is an even number of bands, arranged on either side of the axis X'X. The other axis of the document is denoted Y'Y in Figure 1.

The direction of the bands 201, 202 is denoted DD, and it will be seen that this direction coincides with the direction of movement of the document when the said document is being analysed.

It is not indispensable for the bands 201, 202 to occupy the whole of the document 1: thus in Figure 1 can be seen two areas ZL which are not occupied by the coding. In the particular case of a banknote, these two areas ZL could serve for the numbering.

These bands 201, 202 are, moreover, coded according to a binary coding (0 or 1), and symmetrically with respect to the axis of symmetry X'X of the document 1. The coding of the bands 201, 202 is thus organised along the axis Y'Y.

It is then attractive that the graphics G of the document are printed with a pair of inks of the same shade, one of which reacts and the other of which does not react to a predetermined excitation, in such a way as to define the chopping of the said graphics into parallel bands.

Although it is possible to use different types of excitation (magnetic pigments, microwaves, UV radiation, radioactive source), it is attractive to choose infrared radiation. The wavelength of the infrared is then chosen in such a way as to obtain the best rendering of the pair constituted by the two security marks 100, 200 so that the response curves concerned during analysis of the document coincide, at least in part.

For preference a wavelength will be chosen which is slightly less than a micrometre, and in particular lies between 0.8 and one micrometre (thus the low infrared region is involved, which is very far from the thermal infrared sometimes used for analysis of docu35 ments, where the wavelengths are at least equal to three micrometres).

When the graphics of the document are printed with a pair of inks one of which reflects infrared and the other of which does not, examination of the said document under infrared corresponds to an image of the type of those illustrated in Figures 9 and 10.

In Figure 9 are thus to be found in succession a band 202 coded 1 (absorbs infrared, and thus allows the relevant part of the graphics to be seen, as well the relevant area of the first watermarked grid 100), a band 201 coded 0 (reflects infrared, and thus masks the graphics, allowing only the relevant area of the first watermarked grid 100 to appear), then two bands 202, coded 1. The symmetry of the coding with respect to the axis X'X then implies the successive presence of two bands .202, of a band 201, and finally of a band 202.

The binary coding illustrated in Figure 9 is thus 10111101.

Figure 10 illustrates another coding with the same number of parallel bands: the coding, is then 01100110 (the symmetry of the coding with respect to the axis X'X is naturally always adhered to).

In Figures 9 and 10 eight parallel bands are provided, such that in fact 2*, i.e. 16, different codings are available.

More generally, with 2n bands coded 0 or 1, 2“ different codings are available.

Coding by chopping of the printed graphics can be carried out on the recto, the verso or both. In the latter case, reading of the document will be facilitated if the same coding is used on the recto and on the verso, the corresponding bands thus being directly superimposed; this possibility can prove to be attractive to the extent that it makes it possible to improve resistance to ageing.

In practice, a number of bands at least equal to the number of documents to be detected will be chosen (this will be the case, for example, for banknotes, when the second mark is used for mechanised detection of the face value of the note analysed), the number of bands moreover remaining limited by the technological possibilities of the means of analysis working over very fine bands.

It will, moreover, be possible to print the graphics (on the recto and/or oh the verso) with other inks which do not react to the excitation corresponding to the coding in parallel bands (for example to an infrared radiation).

This possibility can be used for banknotes, offset printing, in particular rotogravure, permitting easy juxtaposition of colours, thanks to the cutout rollers (there are no register problems with the colours, as the same imprinting plate is always used).

Figure 2 makes it easier to distinguish the watermarked area corresponding to the first security mark 100, as it appears when seen against the light.

The watermarked grid 100 is thus repetitive (regular alternation of dark and light areas), and the period is denoted T. Moreover, as will be explained in detail later, this watermarked grid comprises waves which preferably have a sinusoidal surface mass profile.

Figure 2 also shows that the wave of the watermarked grid 100 extends in a common direction DC which is essentially not perpendicular to the direction DD of the chopping bands of the second grid 200.

In the case in point, the abovementioned directions DC and DD form between them an angle β which here is 45°, which permits reading of the document in two perpendicular directions (parallel to the long edge, which is generally the case for processing machines, especially for banknotes, or even parallel to the short edge).

As a variant, other values can be chosen for the angle β between the two abovementioned directions, but to the detriment of the corresponding advantage. Figure 14 illustrates a particular case where the directions DC and DD are essentially parallel, this case resulting in a particular layout of the detection sensors, as will be described later with reference to this figure.

It is also appropriate to note, in Figure 2, the presence of a particular phase shift for the waves of the first grid 100 with respect to the centre of the square which here is at the intersection of the axes X'X and Y'Y of the document. The choice of such a phase shift, for example, as is the case here, bringing the edge of a band to the centre 0 of the square, will be a function of the mode of analysis used and the corresponding means of processing. It will be seen, in fact, that this permits a sensor situated at any distance from the axes X'X or Y'Y to always receive the same signal (to within π or 2 k).

The arrangement illustrated in Figure 1 remains, in any event, the most attractive, as the arrangement of the two superimposed grids, namely the watermarked repetitive grid 100 and the coded grid 200 in parallel bands of chopping of the printed graphics, permits completely indiscriminate reading of the document (independent of the presentation, orientation and direction of passage of the document).

Figure 3 illustrates the contoured face of a matrix 110 permitting embossing of the forming web during manufacture of the document, in order to obtain a watermarked repetitive grid similar to that of Figure 2. This contoured face exhibits undulations, here sinusoidal, which propagate in a common direction DC inclined at 45°.

The contoured face of the matrix 110 thus exhibits a succession of troughs 111 and of peaks 112 (which may be seen better in the transverse section of Figure 4), which make it possible to produce the alternately light 102 and dark 101 areas for the watermarked grid 100 of the document.

The associated curve IV of Figure 4a, showing the variations in the surface mass in the watermarked area of the document (along direction DC), is here in direct relationship with the curve of the variations in the relief of the matrix 110 illustrated in Figure 4. - 17 It is interesting to note in Figure 4a that the amplitude variations of the sinusoidal waves of the watermarked grid occur around the mean plane denoted PM of the document (which makes it possible to have independence in reading with respect to the presentation of the document).

The period T will preferably be chosen to be large with respect to the dimensions of the document, for example of the order of 10 mm for a banknote, so that the security mark 100 is as discreet as possible. The same applies for the side of the square, which for example will be of the order of 60 mm.

The cross-sections of Figures 5 to 8 moreover make it easier to distinguish the particular chamfering of the edges 113 of the matrix 110. This chamfering is, in fact, organised either towards the bottom (chamfered edges 113'), or towards the top (chamfered edges 113) with respect to the mean plane of the contoured face of the matrix 110.

This translates into chamfered edges for the watermarked area, as emerges from the curves V to VIII giving the corresponding variations of the surface mass, this occurring on either, side of the mean plane PM of the document. Thus a watermarked square is produced, whose edges are lacy, which avoids sudden contrast transitions around the watermarked area, and makes the security mark more discreet.

Figure 11 illustrates (seen against the light) the watermarked repetitive grid 100 obtained with a forming web which has been previously embossed with the abovementioned matrix 110: the chamfered edges 103 of the square will be particularly noted. The dark 101 and light 102 areas for their part correspond to those described above with reference to Figure 2.

Figure 12 shows, on a larger scale, the area of the document 1 where the two security marks 100 and 200 are superimposed.

The areas in bands 101 and 102 o£ the watermarked repetitive grid 100, alternately dark and light, exhibit the same width which is equal to the half-period T/2 of the sinusoidal wave of the said grid.

The inclination of these bands 101 and 102 is denoted by the angle β between the directions DC and DD (the angle β here equals 45°).

Figure 12 also makes it possible to distinguish the parallel coded bands 201, 202 of the second security mark 200 corresponding to the chopping of the printed graphics.

The coded bands exhibit the same width e which is determined, .in the .majority of cases, as a function of the watermarked grid, that is to say more precisely of the period T and of the angle β.

Figure 12 shows a right angled triangle ABC corresponding to a particularly advantageous arrangement for reading the document, a triangle whose hypotenuse AB corresponds to the width e of each of the bands 201 or 202, and one side of which corresponds to the half-period T/2: this gives the relation T e = 2 sin β.

In the particular case illustrated here, β - 45°, thus T 72, which corresponds, for example, to a band width of 10 mm (with six bands), for a period of 14.14 mm.

The abovementioned relationship can, however, only be used within certain limits, that is to say when the angle β is greater than a reference angle β0 corresponding to a band width e0 covering half of the width (1) of the document: this limit case would correspond, in effect, to the presence of two bands symmetrical with respect to the axis X'X.

For example, with a banknote whose width is of the order of 80 no, the reference angle βα would be of the order of 10°.

When the angle β becomes less than this reference angle β0, the width e of the bands 201, 202 of the chopping of the printed graphics is essentially chosen as a function of the coding required.

The particular case of a nil angle is illustrated in Figure 14: the bands 101, 102 of the first grid 100 are then orthogonal to the bands 201, 202 of the second grid 200, and a width e can then be chosen advantageously equal to the half-period T/2 (the representation would then correspond to a perfect squaring-off of the square into six orthogonal bands).

In practice, the number of chopping bands will be chosen from the start as a function of the number of documents to be coded, of the manufacturing techniques making it possible to produce these coded bands, and also of symmetry constraints. This choice will also be guided by the precision of the reading machine used for analysis of the document. Next the possible angles β will be determined, it being understood that an angle of 45” offers the most advantages, as has been explained above.

The document thus comprising two superimposed security marks 100, 200 of the abovementioned type is very beneficial in so far as the super imposition of these two marks has the effect of affecting the individual reading of the said marks.

This leads to a considerable improvement in the effectiveness of authentication.

When the document is a banknote, the first security mark 100 and the second security mark 200 serve for authentication of the note, and the second security mark 200 serves for mechanised detection of the face value of the said note.

This will emerge more clearly from the method of analysis And from the associated device, which will now be described by reference to Figures 13 to 16.

Figure 13 illustrates, in effect, the area of the document 1 where the two security marks 100 and 200 are superimposed (as for Figure 12), with, moreover, a read The means of detection appear here in the form of sensors 300, with at least one sensor per coded band 201 or 202 of the second grid 200 (here, one per band). These means are organised along a general direction D which is perpendicular to the direction DD which is that of the movement of the document in the reading machine (direction DD is also that of the coded bands 201, 202), and with a spacing d equal to the width e of the said coded bands 201 or 202.

It is moreover, advantageous that the means of detection 300 are situated on the median axis (a) of the associated bands 201 or 202 of the second grid 200: thus any risk of impairment of the analysis in the event of misalignment of the document with respect to the sensors of the read bar is avoided (there would be a loss of signal due to an increase in noise).

A single read bar may be involved, whose sensors comprise emitter and receiver means, and under which the document to be analysed passes. As a variant, two superimposed read bars may be involved, one of which comprises emitter means and the other receiver means, and between which the document to be analysed passes. Figure 13 then shows schematically either this single bar, or one of the two superimposed bars (the other being below the latter).

Figure 13 also makes it possible to understand that, when a sensor 300 associated with a coded band 201 or 202 reads a surface mass minimum (sensor at the.centre of an inclined band 102, on the axis of the said band), the sensor 300 associated with the symmetric band 201 or 202 (conjugate band) reads a surface mass maximum (sensor at the centre of an inclined band 101, on the axis of the said band): this results from the fact that the arrange- * ment of the watermarked grid with sinusoidal wave profile is such that there is phase opposition in the waves on either side of the axis X'X of the document, at the same distance from the said axis.

More generally, at every moment an interrelation is found between the response of a coded band 201 or 202 and the response of the symmetric coded band (conjugate band), when the document passes under the read bar 301.

This therefore leads to formulating the characteristics of the method of analysis of the document, according to which: . means of detection 300 are arranged on the basis of at least one per band 201, 202 of the second grid 200, these means being organised along a general direction D perpendicular to the direction of movement DD, with a spacing d equal to the width e of the parallel bands 201, 202 of the said second grid; . the coding of the second grid 200 is verified by adding the response of each band coded 0 or 1 and of its symmetric figure which is its conjugate, so as to eliminate the influence of the first grid 100, and by comparing the results obtained with the theoretical coding values; . the first grid 100 is analysed by subtraction of the responses of each band without coding coded. 0 and of its symmetric figure.

According to this method, by adding the response of each coded band and that of its conjugate band, the result is both to eliminate the signal resulting from the first watermarked grid, and to improve the response to the coding of the bands, for example the response to infrared: preferably, decoding by synchronous integration is used for each pair of coded bands (a pair being constituted by a coded band and its symmetric or conjugate figure), then a mutual comparison of the results obtained with the theoretical coding values.

By subtracting the responses of the pairs of bands without coding (coded 0), in particular the levels of absorption of the infrared radiation, the first watermarked grid can be all the more easily analysed as the signal to noise ratio of this grid is greatly improved (in effect, a signal is available whose amplitude is double by virtue of the phase opposition of the watermarked grid between the conjugate coded bands of a single channel).

In the case of Figure 14, in which the directions DC and DD are substantially parallel (the two superimposed grids then forming a squaring-off of the watermarked area), it is necessary to modify the read bar 301.

In place of a single row of sensors 300 arranged perpendicular to the direction of movement DD, the read bar 301 then comprises two parallel rows of sensors 300', 300 arranged perpendicular to the direction of movement DD, with one row per half-bar: these two rows of sensors (each here comprising three sensors 300' or 300) are then offset with respect to each other by a predetermined distance dx which is preferably substantially equal to the half-wavelength T/2 of the first grid, in such a way as to return to the previous phase opposition between corresponding sensors.

The sensors 300' or 300 of a single row are, moreover, situated on the median axis (a) of the associated coded bands 201, 202 of the second grid, and are equidistant from each other by a distance d substantially equal to the width e of the said coded bands.

This therefore leads to formulating the characteristics of such a variant of the method of analysis, according to which: means of detection 300', 300” are arranged on the basis of at least one per band 201, 202 of the second grid 200, these means being organised along a general direction D perpendicular to the direction of movement DD and situated on the median axis a of the associated bands 201, 202, with, on one side of the said axis X'X of the document 1, first means of detection 300' mutually aligned, and, on the other side of the said axis X'X, second means of detection 300 also mutually aligned but offset with respect to the first means of detection 300' by a distance dx substantially equal to the half-wavelength T/2 of the first grid 100; the coding of the second grid 200 is verified by adding the response of each band coded 0 or 1 and of its symmetric figure which is its conjugate, so as to eliminate the influence of the first grid 100, and by comparing the results obtained with the theoretical coding values; . the first grid 100 is analysed by Subtraction of the responses of each band without coding coded 0 and of its symmetric figure.

Thus, here again the same process of analysis is found, with addition of the responses of the conjugate coded bands, and subtraction of the absorption levels of the pairs of bands for the channel or channels which are not used for coding (bands coded 0).

Such an analysis process is thus very attractive, as it permits double analysis of the two superimposed security marks with one single bar of sensors, and this notwithstanding the fact that the superposition of these two marks has the effect of affecting the individual reading of each of them.

This analysis process will be discussed in detail below with reference to Figure 16, which diagrammatically illustrates a complete analysis device for the signals originating from the various sensors, so as on the one hand to verify the coding of the second grid and to validate the document analysed when the grid read is a match, and on the other hand to analyse the first grid and to validate the document analysed when the grid read is also a match.

There naturally exist many ways of producing the read bar, as will emerge from the variants described below by way of example.

The read bar 301 can exhibit substantially circular equidistant apertures 302 associated with each sensor 300, as is illustrated in Figure 13.

As a variant, slot-shaped apertures 303 may be provided (Figure 15a): each slot is then inclined in such a way as to be substantially perpendicular to the direction of propagation of the wave of the first grid (each slot is thus inclined through the same angle β with respect to the direction of movement DD).

According to another variant, cruciform apertures 304 are provided (Figure 15b), whose two branches are respectively parallel and perpendicular to the direction of propagation of the wave of the first grid. This makes it possible to further increase the integration surface for the first grid and to have a higher mean value for the measured signal, as in this case an integrated sampling process is used.

According to yet another variant illustrated in Figures 15c and 15d, at least one of the sensors is multiple (here the six sensors are multiple). In Figure 15c, each multiple sensor 300 is constituted by two adjacent identical sensors 300x arranged on either side of the median axis (a) of each coded band 201 or 202. The response of the sensor 300 is then the sum of the responses of the two sensors 300x. In Figure 15d, each multiple sensor 300 is constituted by four identical sensors 3002 arranged in a square, the square being centred on the median axis (a) of each coded band 201 or 202, and the edges of the square being parallel and perpendicular to the direction of movement DD.

It goes without saying that the variants of Figures 15a to 15d can be adapted to the case of the bar with two offset rows illustrated in Figure 14, then with two offset rows of inclined or cruciform slots, or two offset rows of multiple sensors.

Generally, the sensors 300 or 300', 300** of the read bar 301 will preferably be organised to exhibit the same gain and the same origin offset, in such a way as to ensure balancing of the different paths.

The single or multiple sensors can be photodiodes, or phototransistors, or even photo-resistor cells, each of these sensors being preferably associated with optical filters in order to be perfectly matched to the desired wavelength.

There will now be described a complete analysis device for the signals originating from the various sensors of the read bar, referring to Figure 16.

The read bar 301 is again present, with, here, six sensors 300 for one document with six coded bands parallel to the direction of movement, including three sensors producing a respective signal denoted SA, SB, SC, and three other sensors producing a respective signal SA', SB', SC' corresponding to the conjugate coded bands.

The device for analysis comprises means 400 for processing the signals originating from the sensors 300.

These means of processing comprise two units, each of which is associated with a grid 100 or 200 of the document.

The first unit permits verification of the coding of the second grid of the document passing by the bar of sensors, and validation of the document analysed when this grid is a match.

This first unit comprises, first of all, summing means 401 associated with each pair of coded bands. The signals obtained thus correspond to signals SA + SA', SB + SB' and SC + SC' (these additions include, each time, the sum of a signal and of this same signal phase shifted by »), with, preferably, prior amplification by means of interposed amplifiers 413. These signals are sent to associated integrator means 402 permitting integration over all of the length of the analysed document.

Thus are obtained signals IA, IB, IC associated with each pair of coded bands. These signals are sent to comparator means 403 for comparison of the results obtained with the theoretical coding values of the second grid of the document to be analysed.

Preferably, means of switching 408, 409 are provided upstream and downstream of the integrator means, these means of switching (shown here diagrammatically by switches) being respectively controlled by the passage of the front edge and of the rear edge of the document before a fixed member, such as a photodiode, (one at least of the sensors of the read bar may, as a variant, itself carry out a supplementary function of detection of the passage of the note, which avoids having to provide a separate photodiode): the control of the means 408, 409 is shown diagrammatically here by a central directing unit 415.

By virtue of this fixed detection member (integrated or separate photodiode), integration can reliably be carried out over the whole length of the document. This is particularly beneficial in the case of banknotes of the same width and of different lengths.

The comparator means 403 first of all make it possible to verify that each value IA, IB, IC indeed lies within a predetermined bracket whose limits are defined as a function of the inks, of the opacity of the paper, and of other parameters relating to the document in question.

The comparator means 403 are equipped with a contrast alarm 410 operating when a difference between results is outside a predetermined bracket. In this case, all of the differences Ij.-Ij are compared to the limits of the bracket, and the alarm 410 operates if there is no ink reacting to the known excitation (infrared radiation for example), or if the ink does not react correctly to this excitation.

As a variant, the contrast alarm 410 operates when a ratio between results is outside a predetermined bracket. The comparator means 403 then comprise logarithmic ratio amplifiers and a window comparator (positive or negative). In this case, all the values Log (^) are compared to the limits of the bracket. This variant is attractive for the symmetry of the results if the responses are inverted, for its high sensitivity for a given scale within small contrast deviations, and for the fact that it gives a maximum response for black and minimum for white.

Preferably, the first unit finally comprises means of decoding 411 downstream from the comparator means 403, so as to identify the document and in particular, when the document is a banknote, so as to detect the face value of the note. These means of decoding 411 have the inequalities I1j in memory for each document, which permits easier identification of the document analysed.

The second unit comprises, first of all, differentiating means 404 associated with each pair of coded bands. The signals obtained thus correspond to signals |SA-SA' I, |SB-SB'| and |SC-SC'|, with, here again, preferably, prior amplification by interposed amplifiers 413. Each difference corresponds, due to the phase opposition for the watermarked grid, to twice the original signal freed of the perturbations due to dirt on the document and to the look-through of the paper. .

Selector means 405 are also provided, downstream of each of the differentiating means 404, in order to retain only the responses relating to the bands without coding (coded 0). These means are shown diagrammatically here by switches directed by the central unit 415, the switch associated with bands SC and SC' (coded 0) here being closed.

It is beneficial to send the signals obtained to supplementary summing means 412 (the signals being in phase, in effect n times the signal is obtained, with n = 1, 2 or 3 here).

Next are found means of filtering 406 permitting filtering of the signals at the fundamental frequency of the first grid, which permits the useful signal to be isolated. This signal is finally sent to means 407 of recognition and of validation, so as to analyse the first grid of the document, and to validate the document when the watermarked grid is a match, or failing that to cause an associated alarm 414 to operate. These means 407 could comprise a window comparator on the amplitude and/or a threshold detection of the harmonic distortion, or even a detection of the number of periods.

It goes without saying that the amplifier 413, summing 401 and integrating 402 means of the first unit, and the amplifier 413 and differentiating 404 means of the second unit could be grouped together in one operating unit.

The method and the device for analysis which have just been described in detail considerably improve assistance with authentication.

If the document is falsified, this can result from a failure to comply with the coding in parallel bands (second grid), but then the decoding circuit will not validate the document and moreover reading of the watermarked grid on the channel in question will not be possible by reason of the ink being sensitive to infrared. This can also result from falsification of the watermarked repetitive grid (first grid), but then, if the amplitude is too high, detection is easy; if the phase is not complied with, the signal coming from the difference of the paths is then very much attenuated, and if the profile is not sinusoidal, measurement of harmonic distortion permits detection.

The invention is not limited to the embodiments which have just been described, but encompasses on the contrary all the variants taking up, with equivalent means, the essential characteristics set out above.

Claims

1. Method for analysing a fiduciary or security document (1) moving in a defined direction (DD), by simultaneously reading two superimposed grids (100, 200), 5 with a first grid (100) which is repetitively watermarked, and whose wave extends in a common direction (DC) essentially not perpendicular and not parallel to the direction of movement (DD), and with a second grid (200) organised into bands (201, 202) according to a binary 10 coding (0 or 1), the said bands extending parallel to the direction of movement (DD), and being coded perpendicular to the said direction of movement, symmetrically on either side of the axis (X'X) of the document (1) which is parallel to the said direction of movement (DD), and 15 the said bands exhibiting the same band width (e) given by the formula T e = 2 sin β 20 where T is the wavelength of the first grid (100) and β the angle between the said common direction (DC) and the said direction of movement (DD), characterised in that it comprises the following steps: means of detection (300) are arranged on the basis 25 of at least one per band (201, 202) of the second grid (200), these means being organised along a general direction (D) perpendicular to the direction of movement (DD), with a separation (d) equal to the width (e) of the parallel bands (201, 202) of the 30 said second grid; • the coding of the second grid (200) is verified by adding the response of each band (coded 0 or 1) and of its symmetrical figure which is its conjugate, so as to eliminate the influence of the first grid 35 (100), and by comparing the results obtained with the theoretical coding values; • the first grid is analysed (100) by subtraction of the responses of each band without coding (coded 0) and of its symmetrical figure.

2. Method according to Claim 1, characterised in that the means of detection (300) are situated on the median axis (a) of the associated bands (201, 202) of the second grid (200).

3. Method for analysing a fiduciary or security document (1) moving in a defined direction (DD), by simultaneously reading two superimposed grids (100, 200), with a first grid (100) which is repetitively watermarked, and whose wave extends in a common direction (DC) essentially parallel to the direction of movement (DD) , and with a second grid (200) which is organised into bands (201, 202) according to a binary coding (0 or 1), the. said bands extending parallel to the direction of movement (DD), and being coded perpendicular to the said direction of movement, symmetrically on either side of the axis (X'X) of the document (1) which is parallel to the said direction of movement (DD), and the said bands exhibiting the same band width (e) substantially equal to the half-wave length (T/2) of the first grid (100), characterised in that it comprises the following steps: • means of detection (300', 300) are arranged on the basis of at least one per band (201, 202) of the second grid (200), these means, being organised along a general direction (D) perpendicular to the direction of movement (DD) and situated on the median axis (a) of the associated bands (201, 202), with, on one side of the said axis (X'X) of the document (1), first means of detection (300') mutually aligned, and, on the other side of the said axis (X'X), second means of detection (300**) also mutually aligned but offset with respect to the first means of detection (300') by a distance (d x ) substantially equal to the half-wavelength (T/2) of the first grid (100); • the coding of the second grid (200) is verified by adding the response of each band (coded 0 or 1) and of its symmetrical figure which is its conjugate, so as to eliminate the influence of the first grid 31 10 (100), and by comparing the results obtained with the theoretical coding values; . the first grid (100) is analysed by subtraction of the responses of each band without coding (coded 0) and of its symmetrical figure.

4. Device for the implementation of the method according to one of Claims 1 to 3, characterised in that it comprises: • means of detection (300; 300', 300) grouped together on a read bar (301) arranged perpendicular to the direction of movement (DD), the said means being constituted by sensors equal in number to the number of parallel bands of the second grid of the document to be analysed; . means (400) for processing the signals originating from the various sensors (300; 300', 300), the said means of processing comprising, on the one hand, in succession, summing means (401) making it possible to add the response of each band (coded 0 or 1) and of its symmetric band which is its conjugate, integrator means (402) making it possible to integrate the output signals from the said summing means over the whole, length of the document, and comparator means (403) making it possible to compare the results obtained with the theoretical coding values of the second grid of the document to be analysed, so as to verify the said coding of the said second grid and to validate the document analysed when the said second grid is a match, and, on the other hand, in succession, differentiator means (404) making it possible to subtract the responses of each band (coded 0 or 1) and of its conjugate band, selector means (405) associated with the said differentiator means so as to keep only the responses relating to the bands without coding (coded 0), filtering means (406) making it possible to filter signals at the fundamental frequency of the first grid of the document to be analysed, and means (407) fox recognition and for validation, so as to analyse the said first grid and to validate the document analysed when the said first grid is a match.

5. Device according to Claim 4, characterised in that means of switching (408, 409) are provided upstream and downstream of the integrator means (402), the said means of switching being controlled by the passage of an edge (3) of the document to be analysed in front of a fixed member such as a photodiode in order to detect the start and the end of the passage of the document in front of the means of detection (300; 300', 300), in such a way that the said integrator means operate only for the length of the said document.

6. Device according to Claim 4 or 5, characterised in that the comparator means (403) are equipped with an alarm (410) operating when a difference between results is outside a predetermined bracket.

7. Device according to Claim 4 or 5, characterised in that the comparator means (403) are equipped with an alarm (410) operating when a ratio between results is outside a predetermined bracket.

8. Device according to one of Claims 4 to 7, characterised in that means of decoding (411) are provided downstream of the comparator means (403), so as to identify the document, and in particular, when the said document is a banknote, to detect the face value of the said banknote.

9. Device according to Claim 4, characterised in that supplementary summing means (412) are provided between the selector means (405) and the means of filtering (406), so as to obtain a single signal representing the sum of the in-phase signals originating from the said selector means.

10. Device according to one of Claims 4 to 9, characterised in that amplifier means (413) are provided between the sensors (300; 300', 300) and the associated summing (401) or differentiating (404) means.

11. Device according to one of Claims 4 to 10, characterised in that the read bar (301) exhibits equidistant, substantially circular apertures (302) associated with each sensor (300; 300', 300).

12. Device according to one of Claims 4 to 10, characterised in that the read bar (301) exhibits slotshaped apertures (303) associated with each sensor (300; 300', 300), each slot (303) being inclined so as to be substantially perpendicular to the direction of propagation of the wave from the first grid of the document.

13. Device according to one of Claims 4 to 10, characterised in that the read bar (301) exhibits cruciform apertures (304) associated with each sensor (300; 300', 300), the two branches of each aperture (304) being inclined in such a way as to be substantially parallel and perpendicular to the direction of propagation of the wave from the first grid of the document.

14. Device according to one of Claims 4 to 13, characterised in that at least one of the sensors (300; 300', 300) is multiple.

15. Device according to Claim 14, characterised in that the multiple sensor is constituted by two adjacent identical sensors (300 x ) arranged on either side of the median axis (a) of each band of the second grid of the document.

16. Device according to Claim 14, characterised in that the multiple sensor is constituted by four identical sensors (300 z ) arranged in a square, the edges of the square being parallel and perpendicular to the direction of movement (DD).

17. Device according to one of Claims 4 to 16, characterised in that the single or multiple sensors (300; 300', 300: 300 x , 300 2 ) are photodiodes, or phototransistors, or photo-resistor cells, each of the said sensors being associated with optical filters in order to be matched to the desired wavelength.

18. Device according to one of Claims 4 to 17, characterised in that the sensors (300; 300', 300”) of - 34 the bar (301) are organised in order to exhibit the same gain and the same origin offset, in such a way as to ensure balancing of the various paths.

19. Device according to one of Claims 4 to 18, 5 characterised in that the read bar (301) comprises a single row of sensors (300) arranged perpendicular to the direction of movement (DD), the said sensors being equidistant from each other by a distance (d) substantially equal to the width of the parallel bands of the 10 second grid of the document to be analysed.

20. Device according to one of Claims 4 to 19, characterised in that the read bar (301) comprises two parallel rows of sensors (300', 300) arranged perpendicular to the direction of movement, with one row per 15 half-bar, the said rows being offset with respect to each other by a predetermined distance (d x ) substantially equal to the half-wavelength of the first grid of the document to be analysed, and the sensors (300' or 300”) of any one row being equidistant from each other by a distance (d) 20 substantially equal to the width of the parallel bands of the second grid of the said document.

21. A method according to claim 1 or 3 for analysing a fiduciary or security document, substantially as hereinbefore described.

22. A device according to claim 4, substantially as hereinbefore described with reference to the accompanying drawings.