Security devices

A sheet element, such as a banknote, having an authenticating device in the form of a strip extending across the sheet and having at least one edge provided with a non-rectilinear portion or portions providing difficulty in copying for the forger and preferably shaped to provide coded information relating to the sheet element. In the case of a banknote, one or both edges of the strip may have wavy-shaped portion or portions, of which characteristics such as amplitude and periodicity can be employed to encode such information as the issuing authority, currency, denomination and serial number. Other aspects of the invention concern a method of verification comprising providing a sheet element as above and sensing the non-rectilinear edge or edges to derive the coded information, and a method of slitting a sheet comprising operating a slitting assembly to slit the sheet along a number of slitting lines into a plurality of strips as aforesaid.

FIELD OF THE INVENTION 
This invention relates to security devices to prevent forgery and more 
particularly to devices for authenticating various items of sheet 
material, such as banknotes, credit cards and other valuable documents, 
security personnel passes and the like. 
BACKGROUND OF THE INVENTION 
Present techniques intended to prevent successful counterfeiting of, say, 
banknotes include the use of intricate designs, watermarks and inlaid 
linear metallized plastic strips, the intention being that the application 
of these devices to banknote paper is sufficiently difficult to make it 
likely that forged notes will be readily recognisable by their poor 
quality. However, the effectiveness of such preventive measures is 
continuously being eroded as the techniques and apparatus available to the 
forger become more advanced and easier to operate, thus making it 
potentially easier to simulate the present form of banknotes. 
It is therefore desirable that the production of the security device, 
and/or its application to the document concerned should involve the use of 
devices or resources which, by reason of their nature, complexity, cost or 
other factors would not normally be available to the forger and would be 
difficult to imitate successfully. Further it should preferably be readily 
possible to test the document to establish its authenticity. 
SUMMARY OF THE INVENTION 
According to one aspect of the invention, there is provided a sheet element 
having an authenticating device comprising a film having at least one edge 
which is provided with a non-rectilinear portion or portions. The said 
portion or portions may be shaped to provide coded information relating to 
the sheet element. 
Preferably the film comprises a narrow strip running through the material 
of the sheet, for instance as a security thread in a banknote, of which 
all or part of one or both edges may be contoured and provide said coded 
information. The contouring of the two sides may be different, and the 
information may be related to any function of the combination of the two, 
such as the difference in amplitude, shape or pitch of the contours. 
Alternatively, the shape of the contour may be provided in order to be 
difficult to copy or obviously false when copied, to prevent easy 
withdrawal of the thread or for any other desirable purpose. 
The sheet element may be a banknote, the information carried by the edge 
contour or contours relating, for example, to the denomination or issuing 
authority of the note. The edge contour or contours may carry further 
information relating, for example, to a legible number carried by the 
sheet element to distinguish it from other similar elements, such as the 
serial number, or part thereof, on a banknote. This or other information 
may also be carried on the strip in the form of apertures extending 
therethrough and arranged in a predetermined pattern. 
The information carried by the edge contour or contours can be sensed, read 
and processed, for instance optically magnetically or by any other 
suitable means to verify the authenticity of the sheet element and to 
identify the characteristics of the element to which this information 
relates. 
According to a further aspect of the invention, a method of verification 
comprises providing a sheet element as hereinbefore defined in which the 
non-rectilinear portion or portions is or are shaped to provide coded 
information relating to the sheet element and sensing said at least one 
edge of the authenticating device to derive said coded information. 
According to another aspect of the invention there is provided a method of 
slitting a sheet comprising operating slitting means to slit the sheet 
along one or more slitting lines and separating the sheet along said 
slitting line or lines into a plurality of films, each having at least one 
edge the shape of which is defined by the shape of a said slitting line, 
and is provided with a non-rectilinear portion or portions. 
A particular method, according to this aspect of the invention, of slitting 
a sheet to produce a plurality of strips comprises directing a plurality 
of beams of electromagnetic or corpuscular radiation at the sheet, 
advancing the sheet relative to the beams, said beams defining a plurality 
of impingement points mutually spaced laterally of the direction of 
relative advancement of the sheet, and separating the sheet along the 
paths followed by said impingement points. 
In a preferred embodiment a plurality of substantially parallel laser 
slitting beams, derived from a single main beam, are directed toward the 
sheet to penetrate and cut the said sheet, the slitting beams being 
controlled in any required manner to displace the said impingement points 
laterally of said direction of advancement to produce strips having coded 
edge contours. 
Alternatively, the strips may be provided with a suitabe contour or 
contours by producing suitably shaped slitting lines by means of rotary 
mechanical cutters, dies, heated wires or high pressure fluid jets; a 
combination of such slitting means and one or more slitting beams may 
alternatively be employed. For example a set of spaced alternately 
arranged rotary cutters and laser beams may be so controlled that the 
cutters produce straight edges and the beams produce predetermined 
contoured edges of adjacent strips.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference first to FIGS. 1 and 2, a technique of slitting a sheet 1 of 
suitable material into a multiplicity of similar security films, in the 
form of strips, or threads 2, is diagrammatically illustrated. A laser 
beam 3 from a source 4 is divided by a system of partially reflecting 
pivotable mirrors 5 into a number of slitting beams 6 directed towards the 
sheet 1 to impinge substantially normally thereon. This sheet may, for 
instance, be made of a similar metallic coated material to that currently 
used for making security threads for banknotes, or of magnetic or other 
coated or uncoated material including the thin film coated substrate 
material disclosed in our copending Application Ser. No. 836,136 filed 
Sept. 23, 1977 now U.S. Pat. No. 4,186,943. The advantages in employing 
this latter material will be discussed later. 
The sheet 1 is advanced relative to the slitting beams 6 in a direction, in 
its own plane, normal to the plane of FIG. 2, and the mirrors are 
controllably pivoted in accord with a predetermined program about pivot 
axes also normal to the plane of FIG. 2 to cause the impingement points of 
the slitting beams 6 on the sheet 1 to follow predetermined meandering 
paths 7. The beams 6 are of sufficient power to cut through the sheet 
material, and these paths 7 accordingly define the edges of the strips, or 
threads 2 into which the sheet 1 is subsequently divided. Each pair of 
adjacent slitting beams defines the two lateral edges of a respective 
thread 2. The mirrors 5 may for instance be pivoted synchronously and 
cyclically so that the paths 7 are at all points parallel to each other, 
to form threads, such as those illustrated in FIGS. 1c and 1d, of 
substantially constant width measured transverse the direction of relative 
advancement. Alternatively, the cyclic control of the mirrors may be such 
that each is pivoted in antiphase to its immediate neighbors to form 
threads such as those illustrated in FIGS. 1a and 1b, of cyclically 
varying width. 
In another method, adjacent mirrors may be pivoted so as to produce 
contours of different pitch and amplitude as in FIG. 7, or with at least 
one straight edge as in 1e or intermittently as in FIG. 8. 
The threads 2, after separation, may be cut into suitable lengths which are 
then inserted into or affixed to the surface of the sheet material of the 
documents concerned. In this particular instance the lengths of thread are 
worked into the paper of banknotes in place of the straight edged thread 
currently employed. The various dimensional parameters of the edge 
variations of the thread, such as basic shape, pitch or period of 
repetition, width ratios where the width of the thread changes, or the 
differences between any such properties of the two edges can be chosen to 
relate to particular features of the banknote, such as the issuing 
authority, denomination, note cypher. FIGS. 3a to 3g illustrate seven 
threads of different shapes, of which the first four, FIGS. 3a to 3d, are 
of constant width but of a serpentine configuration, with different 
pitches and amplitudes for four different denominations of banknote, for 
example 1, 5, 10 or 20 units of currency. FIGS. 3e, 3f are of sinusoidally 
varying width, with different patterns of width variation for two 
different issuing authorities, and FIG. 3 g has one recilinear edge 
contour. The non-rectilinear edges of the strips of FIGS. 1 and 3 are all 
of a wavy shape. 
The form of security thread described above facilitates interrogation to 
check the authenticity of the banknote or other document incorporating the 
thread by means of a relatively simple device such as that illustrated in 
FIG. 4 of the drawings. The interrogation device illustrated includes a 
photo-diode array 9, an optical assembly 10 positioned and arranged to 
illuminate the array 9 with a collimated light beam, and means (not shown) 
defining a travel path for a banknote 11, such that the banknote will pass 
through the gap between the optical assembly 10 and the photo-diode array 
9 with the security thread 2 interrupting the light path therebetween. The 
banknote is constrained to travel, relative to the array 9 and assembly 10 
in a direction indicated by arrow A, substantially parallel to the thread 
2 so that in a period whose duration depends upon the length of the thread 
and the speed of travel of the banknote the entire length of the thread 
will pass in front of and partially mask the array 9 which will 
accordingly generate a specific recognizable signal whose waveform depends 
upon the shape and proportions of the thread 2. It may not be necessary to 
scan the entire length of the thread, but to choose an adequate sample or 
samples of the strip length to enable the dominant pattern to be decoded, 
thus eliminating the random effect of overprinting and soiling. The 
derived signal could be checked against a replaceable programmable device 
defining the predetermined waveform of a particular thread type. The 
signal could be employed for instance in a note-sorting machine to verify 
and sort the notes according to denomination, origin or batch, or in a 
vending machine to activate a mechanism for supplying the goods or 
material concerned, and for determining and rendering the appropriate 
change. Other interrogation systems may be employed such as one which 
responds to the difference between the magnetic properties such as 
permeability of the thread material and that of the surrounding paper to 
produce specific signal waveforms in accordance with the edge contours of 
the thread within the note. 
It is also envisaged to use a verification system on which the banknote or 
other document is moved at right angles to the direction of the thread or 
in which the document is held stationary whilst it is scanned in any 
appropriate direction. 
The above described techniques accordingly provide means of encoding 
information which might be printed, or otherwise legibly provided on a 
document, by forming a security thread incorporated in or on the document 
with a predetermined edge contour. 
Further information concerning the document can readily be encoded on the 
security thread, as illustrated in FIGS. 5 and 6. FIG. 5 illustrates a 
banknote 11 of which the security thread 2 has two wavy edges providing an 
overall coded width variation, with a relatively greater periodicality 
coded contour 12 on all or part of the thread edges. The further 
information carried in the contour 12 may also be legibly provided on the 
document, such as the serial number, or part thereof, on a banknote, or 
alternatively may be non-evident data such as the date of manufacture of 
the paper, or of printing of the banknote. A somewhat more advanced 
interrogation device than that illustrated in FIG. 4 will clearly be 
required to decode the two superimposed edge contours of the thread shown 
in FIG. 5. 
It is also envisaged that by introducing a common relationship between an 
attribute of the contoured edge or edges, such as the number of peaks per 
unit of thread length, and the value of the document or banknote, a basis 
would be consituted for use in a machine capable of dispensing notes to a 
total value to be keyed into the machine as a total number of peaks or 
accepting and accounting for a number of mixed notes by totalling the 
number of peaks. 
A further development comprises the incorporation in the thread 2 of a 
pattern of fine holes 15 (see FIG. 6) produced by a laser or other means, 
and representing a code which may be independent, or may be related to any 
information found elsewhere on the thread or in the printing on the 
banknote. This pattern could be produced mechanically or by a laser 
assembly before the thread is incorporated in the paper or incorporated in 
the printing machine which prints the banknotes, and could therefore 
encode information related to printed references, once again serial 
numbers or parts thereof on the banknote. 
In FIG. 7, primary and secondary information is encoded on opposite edges 
of the strip 2 in the form of wavy, or oscillatory contouring of which the 
periodicity and/or amplitude independently determines the information 
concerned. 
In FIG. 8, information is encoded on a contoured edge of the strip, the 
contour consisting of groups 16 of wavy, or oscillatory variations. The 
lengths and/or spacing of the groups may be the variable characteristics 
employed to encode the information. 
Many types of material can be used for the sheet from which the threads are 
cut, so that the threads may be plain, colored, printed, coded, coated 
with a thin film, metallic, magnetic, partially magnetic or any other 
preferred type of thread material in a chosen pattern with very little 
restriction. 
The codes applied to the edge contour of the strip or thread could be 
internationally agreed, so that a single encoding system could encompass 
banknotes of many different currencies, and a banknote of any of the 
currencies could be verified in a common verification device suitably 
programmed. 
An advantageous feature of the above-described note verification system, as 
discussed at the outset, is the increased difficulty of forging a banknote 
containing it to a deceptive visual standard as compared with the uniform 
thread currently used in banknotes. Forgeries could accordingly be more 
easily detected by the public. Forgery to a standard of accuracy required 
to defeat a verification device, especially one adapted to the form of 
thread illustrated in FIGS. 5 and 6, would be more difficult to achieve. 
Where the material of the thread is coated to produce the optical 
characteristics described in our afore-mentioned co-pending patent 
application, the difficulty in producing a deceptive forgery is increased 
even further. 
Where the laser or other method of slitting by heat is employed, a raised 
bead 17 is formed along the edge as shown in cross-section in FIG. 9. When 
the thread is worked into the paper 18 of the banknote this forms a 
corresponding raised pattern in the paper which is visually recognizable, 
adding to the difficulty of making a deceptive forgery. It may also assist 
the Blind by providing a tactile method of authenticating notes and 
discriminating between denominations. 
The formation of the threads in the manner illustrated in FIGS. 1 and 2 
minimizes wastage of the sheet material. This can be an important 
advantage when the quantity and cost of such material employed in the 
production of banknotes is considered. 
The form of security thread described herein could readily be incorporated 
in present banknotes with little or no change to the note design, though 
some development of the current techniques employed for working the thread 
into the banknote paper might be required due to the non-uniform shape, 
thus fulfilling or enhancing the afore-mentioned desired object of making 
forgery more difficult.