IE74178B1

IE74178B1 - Fiduciary or security document exhibiting printed graphics and security marks

Info

Publication number: IE74178B1
Application number: IE921298A
Authority: IE
Inventors: Oliver Puyplat
Original assignee: Banque De France
Priority date: 1991-04-18
Filing date: 1992-04-22
Publication date: 1997-07-16
Also published as: DE69205875T2; EP0509916B1; OA09539A; EP0509916A1; DE69205875D1; FR2675428A1; IE921298A1; RU2069626C1; FR2675428B1

Abstract

The invention relates to a fiduciary or security document with a printed design and security markings. According to the invention, the document (1) comprises two superposed security markings (100, 200), of which one is a periodic watermark grid and one is a coding by the cutting of the printed image (G) into parallel strips, the effect of the superposition of these two security markings thus being to affect the individual reading of said markings. The invention is used on fiduciary or security documents, for example on banknotes.

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.

Documents of this type 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 of 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 - 2 its movement (right-left) in a processing machine.

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.

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).

The object of the invention is to produce a fiduciary or security document whose security marks achieve both improved assistance with authentication and easy detection.

The object of the invention is also to design a document whose security marks are arranged in such a way as to be independent of the presentation and the orientation of the said document, and of its spacial arrangement with respect to the direction of movement.

The object of the invention is also to design a document whose security marks are as discreet as possible when examined with the naked eye, so as not to draw attention.

Finally the object of the invention is to produce a document capable of being analysed by means of analysis carrying out calculation processing which are both uncomplicated and very reliable.

What is involved is more particularly a fiduciary or security document exhibiting printed graphics and security marks, characterised in that it comprises two superimposed security marks each produced in the form of a grid, namely a first security mark which is exhibited in the form of a repetitive watermarked grid, and a second security mark which results from a chopping of the printed graphics into parallel bands arranged and coded according to a binary coding, symmetrically with respect to an axis of symmetry of the document, the wave of the said watermarked grid extending in a common direction essentially not perpendicular to the direction of the said bands of chopping of the printed graphics, the superimposition of these two security marks thus having the effect of affecting the individual reading of the said marks.

Preferably, the watermarked grid forming the first security mark comprises waves with a sinusoidal surface mass profile. This, in fact, avoids the presence of sharp contrasts in the regions of the edges of the wave (a wave of square or rectangular shape would in fact be sharper and less discreet). In particular, the variations in amplitude of the waves of the watermarked grid take place around the mean plane of the said document which permits independence of the presentation of the document.

Advantageously also, the wave of the watermarked grid extends substantially in a common direction making an angle of 45’ with respect to the direction of the bands of chopping of the printed graphics. Thus the possibility is arrived at of reading the document not only independently of the presentation and of the orientation of the said document, but also regardless of its spacial position with respect to the direction of movement.

According to another advantageous characteristic, the watermarked grid defines a surface whose closed contour is inside the edges of the said document, the said surface being entirely crossed by bands of chopping . of the printed graphics.

Preferably also, the watermarked grid is organised in a square, the dimensions of this square being preferably chosen to be relatively large in order to preserve good flatness of the document (the problem is particularly acute if bundles or piles comprising a large number of documents are used), and so as to further enhance the discreetness of this security mark. Advantageously also, the edges of the square are chamfered: thus any insert phenomenon in the region of the edges, resulting from a higher contrast, is avoided, so that the discreetness of this security mark is further improved.

According to a particular embodiment, the bands of chopping of the printed graphics exhibit the same predetermined width which is a function of the angle β between the common direction of propagation of the wave of the watermarked grid and the direction of the bands of chopping, when the said angle is greater than a reference angle corresponding to a band width reaching half of the width of the said document; in particular, the width e of the bands of chopping is given by the formula Τ e = -, χ sin^ where T is the wavelength of the watermarked grid. The identical nature of the widths of the bands of chopping and the symmetry of their arrangement makes it possible to facilitate analysis of the document, while allowing several possible codings: this is particularly attractive in the case where the document is a banknote, coding then permitting detection of the face value.

As a variant, the bands of chopping of the printed graphics exhibit the same width depending only on the coding sought and not on the angle between the common direction of propagation of the wave of the watermarked grid and the direction of the bands of chopping, when the said angle β is less than a reference angle corresponding to a band width reaching half of the width of the said document. This will be the case, for example, with a direction of propagation parallel to the direction of the bands of chopping, but the analysis technique will then have to be adapted as a consequence.

For preference also, the graphics of the said 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. The excitation may be of various types (inks reacting or not reacting to infrared, to microwaves, to ultraviolet, to magnetic pigments, or even to a radioactive source).

In particular then, the graphics are also printed with other inks which do not react to the said predetermined excitation, for example which do not absorb infrared, and similarly for graphics possibly also provided on the verso of the said document.

In the case of a document comprising printed graphics on its two faces, it is attractive that the bands of chopping of the graphics can be coded on the recto, or on the verso, or on the recto and on the verso of the said document.

In particular, the graphics of the said document are printed with a pair of inks one of which reflects infrared and the other of which does not.

Finally, in the case where the document is a bank note, it is then attractive that a note is involved whose first and second security marks serve for authentication of the note, and whose second security mark serves for mechanical detection of the face value of the said note.

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 in accordance with the invention, 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; Figure 13 supplements the preceding view by showing a bar of sensors 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 according to 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 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 associated 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 documents, 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, 2n 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 on 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 π) .

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.

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 of 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 45s).

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 βα 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 mm, the reference angle β0 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 superimposition 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 bar 301 equipped with means of detection.

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 super17 imposed 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 arrangement 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 egual 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 π), 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 Ii-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 (ij) 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 Ii 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'|, |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 guestion 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. Fiduciary or security document exhibiting printed graphics and security marks, characterised in that it comprises two superimposed security marks (100, 200) each produced in the form of a grid, namely a first security mark (100) which is exhibited in the form of a repetitive watermarked grid, and a second security mark (200) which results from a chopping of the printed graphics (G) into parallel bands (201, 202) arranged and coded according to a binary coding (0 or 1), symmetrically with respect to an axis of symmetry (X'X) of the document (1), the wave of the said watermarked grid extending in a common direction (DC) essentially not perpendicular to the . direction (DD) of the said bands of chopping of the printed graphics, the superimposition of these two security marks (100, 200) thus having the effect of affecting the individual reading of the said marks.

2. Document according to Claim 1, characterised in that the watermarked grid forming the first security mark (100) comprises waves with a sinusoidal surface mass profile.

3. Document according to Claim 2, characterised in that the variations in amplitude of the waves of the watermarked grid (100) take place around the mean plane of the said document (1).

4. Document according to one of Claims 1 to 3, characterised in that the wave of the watermarked grid (100) extends substantially in a common direction (DC) making an angle of 45° with respect to the direction (DD) of the bands (201, 202) of chopping of the printed graphics.

5. Document according to one of Claims 1 to 4, characterised in that the watermarked grid (100) defines a surface whose closed contour (C) is inside the edges (2, 3) of the said document (1), the said surface being entirely crossed by bands (201, 202) of chopping of the printed graphics.

6. Document according to Claim 5, characterised in that the watermarked grid (100) is organised in a square.

7. Document according to Claim 6, characterised in that the edges (103) of the square are chamfered.

8. Document according to one of Claims 1 to 7, characterised in that the bands (201, 202) of chopping of the printed graphics exhibit the same predetermined width (e) which is a function of the angle (β) between the common direction (DC) of propagation of the wave of the watermarked grid (100) and the direction (DD) of the bands of chopping (201, 202), when the said angle (β) is greater than a reference angle (β 0 ) corresponding to a band width (e 0 ) reaching half of the width (1) of the said document (1) .

9. Document according to Claim 8, characterised in that the width (e) of the bands of chopping (201, 202) is given by the formula T e = -, 2 x 3ϊηβ where T is the wavelength of the watermarked grid (100).

10. Document according to one of Claims 1 to 7, characterised in that the bands (201, 202) of chopping of the printed graphics exhibit the same width (e) depending only on the coding sought and not on the angle (β) between the common direction (DC) of propagation of the wave of the watermarked grid (100) and the direction (DD) of the bands of chopping (201, 202), when the said angle (β) is less than a reference angle (β„) corresponding to a band width (e 0 ) reaching half of the width (1) of the said document (1).

11. Document according to one of Claims 1 to 10, characterised in that the graphics (G) of the said document (1) 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 (201, 202).

12. Document according to Claim 11, characterised in that the graphics (G) are also printed with other inks which do not react to the said predetermined excitation, for example which do not absorb infrared, and similarly for graphics possibly also provided on the verso of the 5 said document.

13. Document according to Claim 1 and Claim 11 or 12, comprising printed graphics (G) on its two faces, characterised in that the bands (201, 202) of chopping of the said graphics are coded on the recto, or on the verso, or 10 on the recto and on the verso of the said document (1).

14. Document according to one of Claims 11 to 13, characterised in that the graphics (G) of the said document (1) are printed with a pair of inks one of which reflects infrared and the other of which does not.

15. 15. Document according to one of Claims 1 to 14, characterised in that the said document is a banknote, whose first and second security marks (100, 200) serve for authentication of the note, and whose second security mark (200) serves for mechanical detection of the face 20 value of the said note.

16. A fiduciary or security document according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings.