Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Structure of Security Elements Effective by Optical Diffraction
and Apparatus for Examining Such Elements
The invention relates to the structure of security elements effective by
optical diffraction and to an apparatus for examining such elements.
Hitherto, documents with security elements effective by optical
diffraction, in particular holograms, are controlled by complex optical
testing
technology. In such a process the test object must be positioned with great
precision. The entire examination process takes so much time that such
examination methods cannot be applied in fast-moving processing machines.
It is not possible to examine documents provided, for instance, with so-called
optically variable devices (OVD) within a document processing machine
because it is operating at high speed. In U.S. patent 4,255,652 there is
described an apparatus for detecting identification indicia in documents
provided with electrically conductive areas. An electric charge is transmitted
to one of the electrically conductive areas by means of a first capacitive
element extending across and arranged over with width of the document. As
the document to be examined is moved further, the charged electrically
conductive moves under a second capacitive element extending across the
with of the document to be examined, by means of which the charge is
withdrawn. An evaluation and decoding circuit will then generate a typical
signal function.
This apparatus and its applied functional principle are based upon
relatively large electrically conductive areas extending across the width of
the
document to be examined as the size of the transported charge strongly
diminishes with smaller surfaces. A simultaneous examination of several
conductive areas is as impossible as it is to define their geometric shape and
size. This is particularly true of designs with delicate members.
Furthermore, European patent 0,097,570 proposes a device for
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examining the dielectric properties of sheet-like materials, in which the
material to be examined is guided between contact pairs of a series of
capacitors of a certain configuration. A change in the dielectric properties
leads to a change in the voltage at the receiving electrodes. The signals are
individually amplified and evaluated.
In this device which relates to the examination of the dielectric
properties of the sheet material, in particular of water marks, the oscillator
frequency is simultaneously fed to all capacitors which may result in coupling
between adjacent channels. Increasing the spacing between the capacitors
to prevent this deficiency reduces the attainable geometric resolution. Hence,
only coarse structures can be recognized. For controlling problems of
transient oscillations at the receiving contacts of the capacitors, only a
relatively low switching frequency is permissible which leads to low limits as
to
the speed of examination. For structural reasons, such a device can also not
be used in quickly-running processing machines. In European patent
0,338,378 there is described a combined process for printing and forming a
holograms with the reflection material being applied either to the hologram
only or also to the surrounding material. The material outside of the hologram
is either removed by etching or, to prevent damage to the support layer, it is
left on the support layer.
German patent DE 27 47 156 describes a method and a testing
apparatus for examining the genuineness of holographically secured identity
cards. The OVD is reproduced and a visual control is executed. This
process is unsuited for an examination which is quick and,efficient and which
can be performed independently of personal intervention. European patent
EP 0,042,946 describes an apparatus for the generation of scanning patterns
which are examined by laser, mirror and lens systems as well as a photo-
detector. In this case, too, the economic complexity is very high. It
increases
even more where the material to be examined is to be tested in an unsorted
state. To prevent pre-sorting, a multiple arrangement of the authenticity
testing system would be necessary. Demetallizations in security elements
effective by optical diffraction have also become known for achieving optical
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effects which have hitherto been examined only by optical methods. As is
known from U.S. patents 5,248,544 and 5,388,862 optically variable security
elements such as holograms mentioned previously and security threads are
provided with of metal layers. In holograms, the metal layers serve for
reflection, and the security threads appear opaque in penetrating light.
Phase-shifted patterns of lightness will be recognized in penetrating light of
metallized and demetallized areas in a beam or meandering pattern.
It is the task of the invention to eliminate the disadvantages of the state
of the art and to propose a structure of security elements effective by
optical
diffraction, particularly OVD's, holograms or kinegrams, which may be
examined quickly, without human intervention and with insignificant effort.
Furthermore, it is a task of the invention to propose an apparatus for
examining documents containing such security elements. The apparatus is to
be used in document processing machines as well as is manual testing
apparatus for examining document provided with security elements effective
by optical diffraction.
These tasks are accomplished by the invention hereinafter described.
The use of holograms and other security elements effective by optical
diffraction for making certificates and other securities as well as banknotes
secure against counterfeiting are currently ever more prevalent. Such
documents are, for instance, the 1997 series of German marks which in
addition to electrically conductive security strips possess a security element
effective by optical diffraction formed by a kinegram. The capability of quick
examination represents a further security stage in the evaluation of the
elements effective by optical diffraction as a mark of genuineness. Elements
which are effective by optical diffraction are made up of a metallized layer,
among other things. This metallization layer is electrically conductive. The
electrical conductivity changes in accordance with the layer thickness. In
accordance with the invention, the element effective by optical diffraction is
provided with a discontinuous metallization layer and/or partially metallized
layers and/or zone of metallized layers in different planes which represent a
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target-oriented electrical encoding of data. The shape of the encoding
resembles geometric figures, more particularly lines, grid-lines, bows and/or
circles arranged orderly as well as at random. A partially metallized layer
arranged above the support layer contains several demetallized segments. A
discontinuous metallization layer contains segments of different electrical
conductivity.
The apparatus is provided with a capacitively operating scanner. This
scanner consists of a plurality of transmitting electrodes in a side by side
arrangement and receiving electrodes disposed in parallel thereto. The
scanner is disposed within a document processing machine such that the
optical and mechanical sensors present in conventional document processing
machines will activate the examining device in accordance with the invention.
A sensor support is preferably used for reducing detection and measurement
errors. This sensor support receives all examination sensors. In this manner,
the spacings between the sensors are minimized and the sensors are always
arranged in a defined position. Energizing of the individual transmitting
electrodes by electric energy takes place in timed intervals by means of an
energizing electronic having a switching frequency in the kHz-range. Aside
from the current supply the energizing electronic circuit contains as main
components a multiplexes, an oscillator for providing energy for the
transmitting electrodes and an oscillator for energizing the multiplexes.
When there is electrical conductivity, the energy of any energized
electrode is capacitively coupled between the transmitting electrode and a
receiving electrode. If no electrically conductive material is present, there
will
be no transfer of energy between the energized transmitting electrode and the
receiving electrode. The signal pattern at the receiving electrode is
converted
into a corresponding signal image. The signal image is dependent upon the
structure of the metallized layer of the optically effective diffraction
element. If
the optically effective diffraction elements are provided with a discontinuous
metallization layer, several segments of the metallization layer will be of
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differing electrical conductivities. An electronic evaluation circuit at the
output
of the receiving electrode compares the signal image of the test object
against appropriate reference signals. The electronic evaluation in essence
consists of a current source, an amplifier, a demodulator, a comparator, a
micro-processor having a memory as well as filters for suppressing
extraneous and interference signals.
Aside from the software for the micro-processor there are stored in the
memory reference signal images which are compared against the signal
image of the document being examined. Since the scanner extends across
the entire width of the document every electrically conductive characteristic
will be detected by the apparatus in accordance with the invention. The
comparison against the reference signal image generates a classifying signal
for further processing. Accordingly, a document detected as a forgery, for
instance, could be removed by stopping the examining apparatus. The
reduce interference the sensor support is connected to a platen for supporting
the electronic energizing and evaluating circuits.
The entire test apparatus is provided within a document processing
machine so that the need for space may be kept relatively small. The
transmitting and receiving electrodes are arranged above and below the
documents in the document processing machine such that scanning is
positively ensured. This may be accomplished, for instance, by means of
belts or within range of deflecting devices so that during transport the
document is pressed against the transmitting and receiving electrodes.
In an alternate electrode arrangement it is within the ambit of the
invention to position an elongate transmitting electrode in parallel to a
linear
array of a plurality of receiving electrodes arranged in a side by side
relationship. In this case, received signals are processed by means of
multiplexers. The remaining electronic evaluation circuit corresponds to the
one already described. A further embodiment of the transmitting and
receiving electrodes is characterized by a plurality of transmitting and
receiving electrodes arranged in side by side relationship and/or in a row.
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Energization as well as reception of the signals are processed by multiplexing
and demultiplexing methods, as the case may be.
When used in manual apparatus, they are analogously equipped with
means for transporting the document or the scanner the function of which is
similar to the feeding devices of copying machines, optical image insertion
scanners or facsimile machines.
In an alternative embodiment, there is provided a device which defines
the position of the capacitively operating scanner of a test apparatus in
accordance with the invention relative to the document by means of abutment
elements. In this case the document is examined only in the area of the
transmitting and receiving electrodes.
The characteristics of the invention are apparent not only from the
claims but also from the specification and the drawings, whereby individual
characteristics may define advantageous patentable embodiments either by
themselves or with others as sub-combinations, for which protection is
applied for here. Embodiments of the invention are depicted in the drawings
and will be described in greater detail hereinafter.
In the drawings:
Fig. 1 is a schematic presentation of a document with an OVD and
meandering demetallized layers;
Fig. 2 is a schematic presentation of a document with an OVD and
strip-shaped demetallized layers;
Fig. 3 is a schematic presentation of a document with an OVD and
strip-
shaped demetallized layers;
Fig. 4 is a schematic presentation of a document with an OVD and
grid-
shaped demetallized layers;
Fig. 5 is a schematic presentation of a document with an OVD and
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several security elements;
Fig. 6 is a block circuit diagram of a testing apparatus;
Fig. 7 is a schematic presentation of the scanner with a plurality of
transmitting and receiving electrodes;
Fig. 8 is a schematic presentation of the scanner with one transmitting
electrode and a plurality of receiving electrodes;
Fig. 9 is a schematic presentation of the scanner with a plurality of
transmitting and receiving electrodes;
Fig. 10 is a schematic presentation in side elevation of the scanner and
a document to be examined;
Fig. 11 is a schematic section of an OVD with demetallized segments;
Fig. 12 is a voltage - time diagram of the evaluation signal;
Fig. 13 is a schematic section of an OVD with a discontinuous
metallization layer;
Fig. 14 is a voltage - time diagram of the evaluation signal.
The examples of Figs. 1 - 5 depict documents provided with security
elements in accordance with the invention, all of which contain target-
oriented
electrical encoding. The encoding is not carried out as an encryption of any
kind of data but rather electrically conductive examination indicia are set up
in
a target-oriented manner by an arrangement of electrically conductive
structures relative to each separated by non-conductive structures, the
electrical encoding of which will generate a predetermined signal pattern by
means of the test apparatus in accordance with the invention, the signal
pattern being compared to an established stored reference signal pattern.
This results in the intended high test speed. The capacitively operating
scanner of the apparatus in accordance with the invention has also been
schematically shown.
Fig. 1 presents the schematic structure of an OVD 1 provided with a
metallization layer 2. The metallization layer 2 has a demetallized zone 3.
When seen in top elevation view, the demetallized zone 3 is of meandering
configuration. The width of the meander-shaped demetallized zone is greater
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than the smallest distance between two electrodes. The capacitively
operating scanner consists of a plurality of transmitting electrodes 5
arranged
in side by side relationship and a receiving electrode 6 disposed in parallel
to
this linear array.
Fig. 2 depicts the schematic structure of an OVD in which alternating
metallized and demetallized strip-shaped zone 7 are disposed in parallel to
each other. The zones 7,8 which in top elevation are of strip-like
configuration may extend parallel to or normal to the document feed direction.
The latter arrangement is depicted in Fig. 3. The distance between two zones
of the same electrical conductivity is between .2 and 1.0 mm. The widths of
the zones of the same electrical conductivity are varying.
The combination of the characteristics of the examples 2 and 3 is
depicted in Fig. 4. Alternating metallized strip-like zones 7 and demetallized
strip-like zones are disposed parallel to the document feed direction. The
metallized zones 7 are interrupted by a strip-like demetallized zone 9
extending vertically thereto.
Fig. 5 depicts a document provided with several OVD. The deliberate
combination of optically effective diffraction elements results in further
encoding. The accuracy of the examinations is increased thereby.
Figs. 6 - 9 depict the block circuit diagram as well as different
embodiments of the capacitively operating scanner 4.
Fig. 6 depicts the block circuit diagram of a test apparatus in
accordance with the invention, consisting of an electronic energizing circuit,
a
capacitively operating scanner 4 and an electronic evaluation circuit. Aside
from the current source, the electronic energizing circuit essentially
consists
of a demultiplexer 10, an oscillator 11 for providing energy for the
transmitting
electrodes and an oscillator 12 for energizing the demultiplexer.
The electronic evaluation circuit essentially consists of a current
source, an amplifier 13, a demodulator 14, a comparator 15, a micro-
processor 16 provided with a memory and filters for the suppression of
extraneous and interference signals.
Cast into a sensor support are the transmitting and receiving
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electrodes. These form a capacitively operating scanner 4 extending across
the entire document feed width. The strip-shaped receiving electrode extends
transversely of the document feed direction. The transmitting electrodes are
arranged in parallel to the receiving electrode. The distance of a
transmitting
electrode to the receiving electrode is conditioned upon electrically
conductive
examination characteristics typical of the document. Placing several
transmitting electrodes in a linear array makes it possible in the
longitudinal
axis of the capacitively operating scanner 4 to detect several electrically
conductive characteristics at the same time. The resolution attainable by this
arrangement depends upon the number of the applied transmitting
electrodes. In the present embodiment the resolution at one scannable point
per mm extends in both the longitudinal and transverse directions.
The minimum spacing between neighboring transmitting electrodes is
limited by the interfering capacitive coupling among the electrodes. To
prevent it and to reduce interference of neighboring electrodes, the
transmitting electrodes are sequentially energized by a multiplexer 10. The
documents are being examined independent of their disposition as a result of
the transmitting electrodes being arranged across the entire width of the
document fee direction. Accordingly, pre-sorting of several documents in a
document processing machine may be dispensed with.
Fig. 7 is a schematic rendition of the scanner 4 provided with a plurality
of transmitting electrodes 5 and one receiving antenna 6. Energization and
evaluation are performed by circuit of the block diagram of Fig. 6.
Fig. 8 is a schematic presentation of an embodiment of the capacitively
operating scanner provided with one transmitting electrode 17 and a plurality
of receiving electrodes 18. In a manner different from the block circuit
diagram of Fig. 6, the transmitting electrode 17 is energized by an
oscillator.
The signals of the receiving electrodes 18 are processed by a multiplexer.
The additional electronic evaluation circuit consisting of a current supply,
an
amplifier, a demodulator, a comparator, a micro-processor provided with a
memory as well as filters for the suppression of extraneous and interference
signals is the same as in Fig. 6.
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Fig. 9 is a schematic presentation of a further embodiment of the
capacitively operating scanner provided with a plurality of transmitting
electrodes 19 and a plurality of receiving electrodes 20. There alternatingly
arranged in a linear array. Accordingly, the energizing signals of the
transmitting electrodes 19 as well as the evaluation signals of the receiving
electrodes 20 are processed by multiplexing and demultiplexing processes.
Fig. 10 is a schematic presentation in side elevation of the capacitively
operating scanner 4 and a document to be examined. The OVD consists of
partial metallizations 21 as well as of an electrically insulating support
foil 22.
Fig. 11 depicts a schematic sectional view of an OVD consisting of a
support layer 23 and a partially metallized layer 24. The partially metallized
layer 24 consists of several demetallized segments 25. Fig. 12 presents the
associated evaluation signal in a voltage - time diagram.
Fig. 13 is a schematic sectional view of an OVD consisting of a support
foil 26 and a discontinuous metallization layer 27. The discontinuous
metallization layer 27 is provided with segments 28, 29, 30, 31, 32 of
different
electrical conductivity. Fig. 14 shows the associated evaluation signal in a
voltage - time diagram.
In the context of the present invention, the structure of optically
effective diffraction elements and an apparatus for examining such elements
have been described on the basis of concrete embodiments. It is to be noted,
however, that the present invention is not limited by the details of the
description of the embodiments as changes and variances are being claimed
within the scope of the claims. Accordingly, in addition to optically
effective
diffraction elements other electrically conductive characteristics may also be
detected. The deliberate combination of optically effective diffraction
elements with other electrically conductive characteristics results in further
encoding. At the same time, further electrically conductive test
characteristics
such as, for example, an electrically conductive security strip or encodings
made of electrically conductive dye may be classified by the examining
apparatus according to the invention.
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