Documents coded by means of machine-readable optical markings

There is described a method of producing a document coded with machine-readable information, said document having an information carrier with a multiplicity of storage positions, wherein selected storage positions are occupied by respective machine-readable optical markings, which markings cause a predetermined modification of incident light; the geometrical position of the markings on the information carrier represents coded information. In the method disclosed, such an optical marking is introduced into each storage position, and subsequently, selected optical markings are cancelled or altered. Also described are documents coded by means of the disclosed method, as well as a device for cancelling or altering the optical markings.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION 
This invention relates to documents, and more particularly, but not 
exclusively to methods of producing documents which have an information 
carrier with a multiplicity of storage positions, wherein selected storage 
positions are provided with machine-readable information. 
Documents such as identity cards, credit cards, securities, cheques, travel 
tickets, entrance cards and the like, with machine-readable information 
thereon, are known in various forms. Most of the documents which are 
usually employed nowadays, which have coded information in the form of 
magnetic or optical markings, can be forged at relatively small cost. 
A very high degree of security from forging is achieved in a known 
machine-readable document which contains a hologram, which has the 
holographic image of a reference number which is binary coded by a given 
pattern of light spots which are delimited from each other. Such a 
hologram which includes a coded reference number and information 
concerning genuineness can be relatively easily read and tested for 
genuineness, by a machine. On the other hand, maufacture of such a 
hologram requires thorough technical knowledge and expensive technical 
aids, which are not readily accessible, so that forgeries which are likely 
to be successful can only be achieved at very high cost. In a document 
with such a hologram, the reference number is incorporated at the stage of 
the holographic recording of the pattern of light spots, that is to say, 
at an early stage in the production method. This means that a separate 
hologram must be produced for each document with which an individual 
reference number is to be associated, and the individual numbers of a 
series of documents must be known to the producer of the hologram. 
According to the present invention there is provided a method of producing 
a document which has an information carrier with a multiplicity of storage 
positions, wherein selected storage positions are occupied by respective 
machine-readable optical markings, which markings cause a predetermined 
modification of incident light and whose geometrical position on the 
information carrier represents coded information, in which method a said 
optical marking is introduced into each storage position, and, 
subsequently, selected said optical markings are cancelled or altered.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1, reference numeral 2 denotes a document, which can be an identity 
card, a credit card, a security, a cheque, a travel ticket, an entrance 
card, and so on. The document 2 has an information carrier 3 with a 
multiplicity of discrete storage positions 4 which are denoted in the 
drawings by squares shown in dotted or solid lines. In production of the 
document 2, an optical marking 5 is introduced into each of the storage 
positions 4 which in the example in FIG. 1 are arranged in two lines 6 and 
7. The optical marking 5 causes a characteristic modification of incident 
light, and represents information concerning genuineness of the document, 
which is difficult to forge. 
The optical markings 5 can be read by a machine. In a reading device which 
is described in greater detail hereinafter, each of these markings 5 cause 
a predetermined characteristic modification of the ray path of an incident 
light beam, by refraction or diffraction of the reflected or transmitted 
beam. A particularly high degree of security against forging is achieved 
if the optical markings 5 provided at the storage positions 4 have a 
structure which causes a characteristic diffraction of incident light. The 
markings 5 are preferably holograms which can be produced by interference 
of coherent light or synthetically, that is to say, with the aid of 
computers. Such holograms are preferably introduced into the storage 
positions of the information carrier 3 by an embossing process, and in 
this case the information carrier 3 comprises a thermoplastic material and 
can be a film or a thin layer applied to the document 2. 
As shown in FIG. 2, in which the same components as in FIG. 1 are denoted 
by the same reference numerals, coded information is introduced into the 
document 2 by selected markings 5' being cancelled again, or altered in 
such a way that they no longer cause the same characteristic modification 
of incident light, as the unaltered markings 5. In the document 2 which is 
coded in this manner, the coded information resides in the geometrical 
position of the remaining markings 5. Each remaining marking 5 represents 
on the one hand a binary information unit and on the other hand, a piece 
of information concerning genuineness of the document 2. 
In the embodiment of FIG. 2, the second and fifth markings in line 6, and 
the third marking in line 7, have been cancelled. If a binary "1" is 
associated with the remaining markings 5, and a binary "0" is associated 
with the cancelled markings 5', as shown in the drawing, line 6 contains 
the word 101101, and line 7 contains the word 110111. 
For the purpose of reading the coded information stored in the 
above-described manner, and the information concerning genuineness of the 
document 2, each storage position 4 is scanned optically in the reading 
device. Reading can be effected in a serial or parallel mode of operation. 
In the case of serial reading, all the storage positions 4 are 
interrogated in succession with a single optical scanning device, while in 
the case of parallel reading all the storage positions 4 are scanned 
simultaneously. It is also possible to perform a mixed mode of operation, 
in which case for example all the storage positions 4 of one column are 
scanned simultaneously, and the different columns are scanned in 
succession. 
If the optical markings are simple diffraction gratings of predetermined 
grating frequency and orientation, the optical scanning device can 
comprise a light source and a single light sensor. The detection of 
markings 5 in the form of complex light-diffracting structures can be 
effected with a plurality of light sensors which interrogate the reading 
light beam which has been modified by a marking 5, from characteristic 
angles of view. In the case of serial reading, the respective region of 
the document 2 which is to be interrogated, is limited to a single marking 
with a shield or the like. 
It is readily apparent that the optical markings 5 can also be provided 
outside the storage positions 4, without disadvantageous results. 
Accordingly, an information carrier, whose entire surface carries a 
light-modifying marking, in particular a diffraction grating or hologram, 
can subsequently be coded by selected regions of the marking 5 being 
cancelled or altered. FIG. 3 shows an information carrier 8 which is coded 
in this way. The storage positions of this information carrier 8, which 
are once again denoted by reference numeral 4, are first determined by the 
local cancellation or alteration of the marking 5. This permits a much 
greater degree of freedom of coding the document 2. In the reading device, 
it can be ensured by using a shield or the like that only regions which 
lie within the storage positions 4 of the information carrier 8 are 
interrogated. 
FIG. 4 shows an information carrier 9 which has been coded. The information 
carrier 9 includes an information track 10 with the optical markings 5 and 
a timing track 11 which is parallel to the track 10, and which has optical 
markings 12. The markings 12 of the track 11 are preferably of the same 
configuration as the markings 5 so that they can be scanned with identical 
means in the reading device. A light beam which is modified by the 
markings 12 energizes a light sensor in the reading device, which produces 
an electrical scanning signal for decoding the stored coded information, 
in accordance with known processes. 
FIGS. 5 and 6 show that coded information can also be recorded in such a 
way that the reading signal which is produced in serial scanning from the 
optical markings 5 of a single information track includes both the 
information and also a timing signal with which a decoding circuit can be 
cycled. FIG. 5 shows an information carrier 13 whose information track 14 
includes the storage positions 4 with optical markings 5; in this case the 
storage positions 4 abut in rows without gaps. When coding (see FIG. 6), 
only selected markings 5' of even-numbered storage positions 4 are 
cancelled, whereas the markings 5 of uneven-numbered storage positions are 
not altered. A binary "0" is represented by cancelling two successive 
even-numbered markings, while in the case of a binary "1", the first 
even-numbered marking is not cancelled. A document coded in this way can 
be read with a reading device whose stop aperture is equal to or smaller 
than the length of a cancelled optical marking 5'. The electrical signal 
produced in the reading device by scanning the remaining markings 5 is 
pulse length-coded, and can be decoded in accordance with known processes. 
The advantages of the above-described production method are now readily 
apparent. As the actual coding of the document 2 is effected by cancelling 
or altering selected optical markings 5', the information which is to be 
stored in a given example of an issued series of documents 2 only needs to 
be known in the last phase of the production method. The producer of the 
optical markings 5 does not therefore need to know the information to be 
stored and, in large equipment and therefore at low cost and with a small 
amount of work can produce documents 2 which are all identical and which 
are only subsequently individualized by the cancellation or alteration of 
selected markings 5'. The operation of cancelling or altering of selected 
markings 5, as the last operation in the production method, can be 
effected in a decentralized fashion directly before issue of a document 2, 
for which purpose expensive technical aids are not required. The 
individual information contained in a finished document 2 therefore has to 
be known only to the person who is entrusted with issuing the document 2, 
so that the level of security is substantially increased. However, the 
degree of security from forgeries, which is high in itself, in respect of 
documents 2 on which information is stored in the form of optical markings 
5 such as halograms, diffraction gratings and the like, is not impaired. 
Obviously, when coding a document care must be taken that the stored 
information cannot be altered in a meaningful manner by the unauthorized 
cancellation or alteration of markings of the coded document. A meaningful 
alteration of the information on the document would be possible for 
example in a document which had been coded using the know 4-bit-BCD-code; 
in this case it would be possible for example for a numerical reference 
"3" represented by the code 0011 to be converted into one of the numerical 
references "0", "1" or "2" by the cancellation of markings. 
In order to prevent meaningful alteration of information, the optical 
markings 5' which are cancelled when coding the document are 
advantageously selected in accordance with an error recognition code. A 
particularly suitable error recognition code of this kind is one in which 
faults cannot result in one sign becoming another sign which satisfies the 
laws of the code and which therefore cannot be recognized as being in 
error. The laws of the error recognition code can be applied both to the 
relationship between the individual bits of each reference incorporated in 
the document, and also the relationship between the individual references. 
For example, a decimal number can be coded in accordance with the 
2-out-of-5 code, that is to say, each decimal number is represented by two 
remaining and three cancelled markings so that no meaningful alteration in 
the stored information can be effected by cancelling markings, in the 
event of an attempted fraud. Alpha-numerical information can be coded for 
example in a 3-out-of-7 code. Finally, testing or parity bits can be 
stored on the document, which bits make it possible for a parity check of 
the read information to be carried in the reading device. 
Coding of the document is advantageously effected in an automatically 
operating coding device which selects given optical markings on the basis 
of the information to be stored and the code used, and cancels such 
selected markings with a cancellation device or alters their 
characteristic light-modifying properties. In the case of markings in the 
form of diffraction gratings or holograms which are embossed in 
thermoplastic material, cancellation or alteration of the markings is 
preferably effected by a thermal action, the thermoplastic material being 
locally melted or softened. This can be effected with an electrically 
heated melting element, by high-frequency or ultrasonic heating, by an 
electrical arc and the like. The markings can also be cancelled or altered 
by perforating, scraping off, grinding off, or by a chemical process. 
Cancellation or alteration of the markings can be effected in a parallel 
or a serial mode of operation. 
Before coding of the document 2, its information carrier 3, 8, 9 or 13 is 
advantageously covered with a covering layer which is opaque to visible 
light and which has a higher melting point than the information carrier. 
When coding such a document 2, the markings 5' can be cancelled or altered 
by local melting or softening of the information carrier through the 
covering layer, without damaging it, so that the information remains 
concealed in visible light. 
If the stored information is to be interrogated by transmission, both the 
cover layer and the information carrier, and possibly the carrier member 
of the document, which lies below the information carrier, must be 
transparent to the reading light beam. For example, the individual layers 
of the document can comprise a material which transmits infra-red 
radiation, so that the information which is hidden when using visible 
light can be read with the reading light beam produced by a 
gallium-arsenide light-emitting diode. In the case of a document which is 
intended for reflection interrogation, either the cover layer or the 
information carrier, or a document carrier member which is disposed below 
the information carrier, must transmit the reading light beam, depending 
on the side from which the information is to be available for reading; the 
other layers of the document can be opaque both for visible light and for 
the reading light beam. 
FIG. 7 shows an advantageous embodiment of a coding device. This device 
comprises an introducing means 15, a converter 16 and a cancelling means 
17 which operates in parallel. The introducing means 15 has a scanning 
field 18 with which numerical or alpha-numerical symbols can be 
introduced. The converter 16 which is connected between the means 15 and 
the means 17 converts the symbols introduced, into binary symbols, and by 
way of leads 19 and 20, on the basis of the information to be stored and 
the code used, delivers short current pulses to selected heating elements 
of a multiplicity of heating elements 21 which are arranged on a carrier 
22 of the cancellation means 17 in the same geometrical position as the 
storage positions 4 (FIGS. 1 to 6) on the document to be coded. When this 
is done, the selected markings 5' of the document (not shown in FIG. 7) 
which lies in close contact on the heating elements 21 are destroyed or 
altered by the thermal effect. 
Each heating element 21 is preferably formed by a thin layer of electrical 
resistance material which is applied to the carrier 22 that comprises 
insulating material. Electrodes 23 and 24 which electrically connect the 
leads 19 and 20 to the heating elements 21 advantageously comprise a thin 
layer of electrically conductive material. The heating elements 21 and the 
electrodes 23 and 24 can be made by photo-lithographic methods or by 
etching methods. 
As can be seen from FIG. 8, which shows a greatly enlarged view in 
cross-section of the cancellation means 17, a thin insulating layer 25 is 
advantageously applied to the free regions of the heating elements 21 and 
to the electrodes 23 and 14, thereby providing a smooth surface for the 
cancellation means, and providing protection for the parts which lie below 
the insulating layer 25. 
FIG. 9 shows parts of a reading device for reading a document 26 which has 
been produced in accordance with the above-described method and whose 
information carrier 27 has a single information track 28 with optical 
markings 5 in the form of embossed reflection holograms. Cancelled 
markings are again denoted by reference 5'. A light source 31, light 
sensors 32 to 34, a shield 35 and a lens 36 are secured to a carriage 30 
which is movable in a manner which is not shown in detail, in the 
direction of a double-headed arrow 29, parallel to the information track 
28. 
For the purposes of reading the document 26 which is inserted into a holder 
(not shown), the carriage 30 is moved along the information track 28 at a 
constant or known speed. When this is done, a reading light beam 37 from 
the light source 31 passes in succession through the lens 36 and the 
shield 35, to impinge on the individual storage positions 4. If the 
particular storage position upon which the light beam impinges is occupied 
by a genuine unaltered marking 5, the light beam 37 is modified in the 
predetermined characteristic manner. In the embodiment illustrated, three 
light beams 38 to 40 are reflected by the markings 5, and these light 
beams represent the holographic image of a light spot pattern which is 
holographically stored in the form of a marking, and fall onto the light 
sensors 32 to 34 which are arranged in appropriate characteristic angles 
of view. An electronic switching logic means (not shown) evaluates the 
signals produced by the light sensors 32 to 34, and responds. 
If on the other hand the reading light beam 37 impinges on a storage 
position 4 with a cancelled or altered marking 5' the ray path of the 
reading device is not modified in the characteristic manner, the light 
sensors 32 to 34 are not energized, or are not energized with the correct 
intensity, and the electronic switching logic means does not respond. The 
reading device therefore checks the genuineness of the document 26, and at 
the same time reads the stored information. The output signal of the 
switching logic means can be decoded with means known in the data storage 
art. 
The above-described reading device can be modified in many ways. It is 
possible for the document 26 to be transported when reading the 
information, instead of the carriage 30. For the purposes of reading a 
document with a plurality of information tracks, such tracks can be 
scanned in succession; however, separate light sensors can also be 
arranged on the carriage 30, for each information track. Finally, all the 
storage positions 4 can be simultaneously scanned with a multiplicity of 
light sensors and one or more light sources.