[0001] The present invention relates to a security thread reader and a method of detecting
a security thread within a document. More particularly, this invention relates to
a security thread reader and a method for detecting the presence of a security thread
in a document in which the security thread has one or more regions of magnetic material
and one or more optically visible markings.
[0002] Counterfeiting of documents, most notably of currency, is a problem experienced throughout
the world. Governments worldwide have invested heavily in the development of increasingly
advanced methods of protecting their national currencies, and numerous protection
mechanisms applicable equally to currency and other types of documents have resulted
from these developments. For example, the Euro banknote includes several security
features, which taken in combination form a significant impediment to a counterfeiter
in producing an identical copy of an authentic banknote. For instance, the Euro banknotes
are printed on a pure cotton paper, giving them a unique feel when handled. Some areas
on the face of the banknotes are printed in relief so that they can be identified
by touch. Other security features are discernible by sight, in some cases by viewing
light transmitted through the banknote, and in other cases specifically when the banknote
is viewed at a particular orientation to a light source. In particular, the Euro banknote
provides a watermark, the watermark more particularly including a picture and characters
indicative of the value of the banknote, which is visible when the banknote is held
between the viewer and a light source. The Euro banknote also includes a security
thread, which is visible, again visible when the banknote is held between the viewer
and a light source, as a dark line running between opposite edges of the banknote.
Certain denominations of Euro currency also provide a foil hologram patch which shows
a particular motif and the value of the banknote when the banknote is tilted, and
a colour-shifting ink which causes the value numerals printed on the banknote to change
colour when the banknote is tilted.
[0003] Security threads may be incorporated into a paper substrate of the banknotes during
the manufacturing process. For instance, in the Euro banknotes a security thread is
manufactured by forming a metal layer of aluminium on a polyester substrate, and then
stripping off or by demetallising some parts of the aluminium to form recessed characters
or negative transparent scripts. These scripts are readable by visually inspecting
the banknotes when held in front of a backlight. An alternative format of security
thread may be provided using an insulator-metal transition (IMT) process by which
a combination of magnetic and metallic materials can be deposited on a discontinuous
basis.
[0004] A challenge arises in providing automated systems which are able to detect and verify
these sophisticated security features. Measures which improve security are highly
advantageous.
[0005] One aspect of the invention provides a security thread reader for detecting the presence
of a security thread in a document, the security thread having one or more regions
of magnetic material and one or more optically visible markings, the security thread
reader comprising:
a magnetic field detector operable to detect the magnetic material within the security
thread and to determine, based on this detection, one or more areas within the document
at which the security thread is present;
a controller operable to set a specified target area of the document to include at
least a portion of the one or more areas within the document at which it has been
determined that the security thread is present;
an optical scanner operable to generate an image of the specified target area; and
an image processor operable to process an area of the scanned image corresponding
to the specified target area of the document to identify the optically visible markings
within the security thread.
[0006] In a document, the security thread itself may be relatively narrow compared to the
dimensions of the document itself. Accordingly, the markings or script provided on
the security thread may also be relatively small, which in turn requires the optical
resolution of an optical reader arranged to discern the markings or script present
on the security thread to be relatively high. The invention recognises that a high
resolution image generated for the entire document, which will generally be required
where optical techniques are being used to detect the presence of a security thread
within a banknote, may comprise a disadvantageously large quantity of data. The need
to handle this large quantity of image data would be likely to result in higher data
storage and image processing demands and/or slower operation. For instance, a larger
image data buffer may be required to store the image data while image processing takes
place, and the image processor may require increased processing power to perform the
necessary image processing on the large volume of data.
[0007] Additionally, the invention further recognises that there may be other markings present
on the non security thread portions of the document which may confuse the image processor,
resulting in inaccurate or spurious results. Accordingly, it is desirable to constrain
the operation of the processor to the area of the security thread to improve reliability.
[0008] The reduction in size of the area to be scanned also enables the use of smaller,
lighter, simpler and potentially cheaper scan heads of the optical scanner.
[0009] Although the type of document to which the present invention is applicable may be
any document having a security thread, the present invention is particularly advantageous
when applied to banknotes having a security thread. For instance, the methods described
herein could be applied to currency counting machines, vending machines, ticket machines
or paying-in cashpoints.
[0010] While it may be possible to provide a magnetic field detector capable of magnetically
scanning a document for a magnetic thread in which the magnetic field detector remains
static relative to the document, preferably either or both of the magnetic field detector
and the document are moved relative to the other during the magnetic scanning operation.
This enables one or more smaller, lighter, simpler and potentially cheaper sensors
to be provided and positioned close to the document enabling weaker magnetic activity
to be observed.
[0011] Similarly, while it may be possible to provide an optical scanner capable of optically
scanning a document in which the optical scanner remains static relative to the document,
such as a large scale Charge Couple Device (CCD) arrangement, preferably either or
both of the optical scanner and the document are moved relative to the other during
the optical scanning operation. This enables a smaller optical scanner to be located
closer to the document to provide a high resolution image of a designated portion
of the document.
[0012] To alleviate problems of stringing, an anti-stringing mechanism can be provided in
which if the relative motion between either of the magnetic field detector or the
optical scanner and the document is reversed then a transaction associated with the
document is cancelled. The reversal in relative motion may cause, and be detected
as a result of, a second detection of the security thread by the magnetic field detector.
Alternatively, because the reversal in relative motion will cause an inversion of
the scanned image of the optically visible markings if the optical scanning process
in operation at the time when the document is being retracted, the image processor
can detect the reversal of relative motion by detecting the inversion of the optically
visible markings. Whichever method is used to detect the reversal of relative motion,
a user will be unable to retract a document from the security thread reader without
invalidating the transaction.
[0013] In assessing the presence, position and authenticity of a document, quantities such
as the length, thickness and magnetic strength of the security thread can be measured
by the magnetic field detector. For instance, a magnetic thickness value indicative
of the cross sectional dimensional characteristics of the security thread can be ascertained,
the magnetic thickness value being determined as a function of the signal amplitude
of the magnetic field detector. While it can be appreciated that various types of
magnetic field detector may be suitable for use with the present invention, preferably
the magnetic field detector comprises one or more Hall-effect sensors. Hall-effect
sensors are particularly suitable due to their small size, low cost and high sensitivity.
[0014] The one or more regions of magnetic material may include one or more of several different
types of magnetic material, including ferromagnetic material.
[0015] Security threads in banknotes or other documents may not be visible using light reflected
from the document if the security thread is embedded below the surface of the document.
The security threads in such documents can only be viewed when the document is held
in front of a light source such as a backlight. Accordingly, for such documents the
optical scanner should include a light emitting element for emitting light and a light
receiving element for receiving light, the light emitted from the light emitting element
being transmitted through the document before being received by the light receiving
element. To obtain a very high resolution image and to accordingly improve the likelihood
of the image processor correctly identifying the optically visible markings within
the security thread, the light emitting element should preferably provide substantially
coherent light, for instance laser light. Whilst this laser light feature is preferred,
it is not essential.
[0016] A number of image processing operations may be suitable for identifying the optically
visible markings. For instance the image processor may comprise an optical character
recognition (OCR) function for this purpose. Alternatively, the image processor may
comprise a pattern matching function.
[0017] Another aspect of the invention provides a method of detecting the presence of a
security thread in a document, the security thread having one or more regions of magnetic
material and one or more optically visible markings, the method comprising the steps
of:
detecting the magnetic material within the security thread;
determining, based on the result of the detection step, one or more areas within the
document at which the security thread is present;
setting a specified target area of the document to include at least a portion of the
one or more areas within the document at which it has been determined that the security
thread is present;
generating an image of the specified target area; and
processing an area of the scanned image corresponding to the specified target area
of the document to identify the optically visible markings within the security thread.
[0018] Embodiments of the invention will now be described, by way of example only, with
reference to the accompanying drawings in which:
Figure 1 schematically illustrates an example banknote comprising a security thread;
Figure 2 is a schematic block diagram of a security thread reader according to an
embodiment of the present invention;
Figure 3 schematically illustrates the operation of a magnetic field detector and
an expected output of the magnetic field detector in accordance with an embodiment
of the invention;
Figures 4A and 4B are schematic flow diagrams illustrating the operation of a security
thread reader according to an embodiment of the present invention;
Figure 5 is a schematic flow diagram illustrating the operation of a security thread
reader according to an embodiment of the invention in which an anti-stringing mechanism
is provided.
[0019] Referring to Figure 1, a banknote suitable for use with an embodiment of the present
invention is illustrated. The banknote 10 is provided with a security thread 20 which
crosses from an edge 30 of the banknote 10 to an opposite edge 40 of the banknote
10. In the present case, as is the case with existing currency, the security thread
20 crosses the shortest dimension of the banknote 10, although the embodiments of
the invention described hereinafter may be adapted to operate on banknotes having
an alternative security thread position, such as a thread running from an edge 50
to an edge 60. The security thread 20 may be fixed to a surface of the banknote 10,
or more preferably may be either wholly or partially embedded within the banknote
10. The security thread 20 may be constructed in a number of ways and consist of a
number of different materials, including at least some magnetic material. The magnetic
material may exhibit any type of magnetism that either generates a sufficiently strong
magnetic field to be detected (either without an external influence, or with an external
influence such as an electric field or another magnetic field) or which perturbs an
external magnetic field sufficiently for the perturbation of the external magnetic
field to be detected.
[0020] Figure 1 further illustrates an expanded view of the security thread 20. The example
security thread 20 shown is exemplary of that which is visible on a 20 Euro note.
It can be seen that the security thread 20 is provided with the markings "EURO 20".
A left-to-right mirror image of this marking is also provided such that the marking
"EURO 20" can be recognised when the banknote 10 is held up in front of a light source
irrespective of the face of the banknote 10 being viewed. The security thread 20 illustrated
is relatively difficult to counterfeit at least partly due to the level of detail
provided in the markings on the security thread 20.
[0021] The functional arrangement of a security thread reader 100 according to an embodiment
of the present invention is schematically illustrated in the block diagram of Figure
2. The security thread reader 100 comprises a magnetic field detector 110 and an optical
scanner 140. The magnetic field detector 110 performs the function of locating the
security thread 20 within a banknote 10. The magnetic field detector 110 will produce
a characteristic analog output signal in the presence of the magnetic material present
within the security thread 20. An analog-to-digital converter 120 is provided to convert
the analog output signal generated by the magnetic field detector 110 into a corresponding
digital signal. This corresponding digital signal will be passed to a processor 170
via an input/output device 130. The processor 170 includes decision logic 180, which
may be either hardware or software based and which uses the digitised output signal
from the magnetic field detector to determine whether a security thread is present
within the banknote 10, and if it is so present then to determine its location on
the banknote 10. The decision logic 180 will use this determined position to control
optical scanning and image processing functions of the security thread reader 100.
The decision logic 180 may comprise a database of characteristic signals which can
be compared to the detected magnetic signals to determine whether the detected magnetic
signal meets matches one or more stored magnetic signals. The result of this comparison
can be used to assist in determining the presence of the security thread 20 and potentially
to determine the nature, for instance type or denomination, of the banknote 10.
[0022] The optical scanner 140 performs the function of optically scanning the banknote
10, and in particular the security thread 20 within the banknote 10, to generate a
digital image. If the optical scanner provided were to provide an analog rather than
a digital output, an analog-to-digital converter would be provided to digitise the
analog output. The digital output data is then passed to an image buffer 160 via an
input/output device 150. The image buffer 160 will store image data corresponding
to at least a portion of the banknote 10. The image data within the image buffer 160
is available to the processor 170. In order to detect optically visible markings which
include character data, such as text, the processor 170 also includes an optical character
recognition (OCR) module 190 which can identify the presence of the character data
within the image data stored in the image buffer 160. In an alternative embodiment
which may be more suitable where abstract or picture based markings are provided on
the magnetic strip rather than character-based markings, a pattern recognition module
may be provided instead of the OCR module to determine the presence of predetermined
markings within the image data stored in the image buffer 160. In either case the
markings can be compared against a database of markings and/or criteria in order to
identify the authenticity and characteristics such as the type or denomination of
the banknote 10.
[0023] The optical scanner 140 may be a single head or multi-head scanner and may for instance
comprise a CMOS array, and may user either non-coherent or coherent light, such as
laser light. The use of laser light in an optical scanner is particularly advantageous
where a high-resolution image is required.
[0024] The processor 170 acts as a controller to control the operation of the optical scanner
140 and the image processing functions of the processor 170. Specifically, the processor
170 will ensure that an image area to be processed includes the security thread 20.
Preferably, areas of the banknote 10 remote from the security thread 20 will not be
processed, resulting in a reduction in the data handling requirements of the security
thread reader 100. Four main arrangements of the security thread reader 100 are envisaged,
although alternative arrangements are also envisaged.
A) The magnetic field detector 110 initially locates the position of the security
thread 20, and the optical scanner 140 subsequently scans only the portion of the
document identified by the magnetic field detector 110 as having the security thread
20 embedded therein.
B) The magnetic field detector 110 passes across the banknote 10 with the optical
scanner 140 following behind it at a predetermined distance. When the magnetic field
detector 110 locates the security thread 20, the optical scanner commences scanning
a predetermined time later, when the optical scanner 140 has reached the position
at which the security thread 20 has been located.
C) The optical scanner 140 scans the banknote 10 and the image buffer 160 buffers
the most recently acquired data. The magnetic field detector 110 follows behind the
optical scanner 140 at a predetermined distance. When the magnetic field detector
110 locates the security thread 20, the optical scanner 140 ceases scanning the banknote
10 and a portion of the image buffer 160 corresponding to the detected position of
the security thread is processed by the processor 170.
D) The optical scanner 140 scans the entire banknote 10 (either independently from
or in synchronisation with the magnetic field detector), but the processor 170 only
processes image data designated by the decision logic 180 as corresponding to the
position of the security thread 20.
[0025] Figure 3 schematically illustrates the relative motion of a magnetic field detector
210 across the banknote 10 of Figure 1. As with Figure 1, the four edges of the banknote
10 are labelled as edges 30, 40, 50 and 60. In the present embodiment the magnetic
field detector 210 passes across the face of the banknote 10 from the edge 50 towards
the edge 60 in the direction of the arrows. Clearly it would be equally valid for
the magnetic field detector 210 to pass across the banknote 10 from the edge 60 to
the edge 50. It will be appreciated that the motion of the magnetic field detected
210 is relative motion with respect to the banknote 10. Embodiments in which the banknote
10 is stationary and the magnetic field detector 210 is in motion and alternative
embodiments in which the magnetic field detector 210 is stationary and the banknote
10 is in motion are equally valid, and each have their own advantages depending on
the particular application to which the apparatus is being applied. Additionally,
other embodiments in which both the banknote 10 and the magnetic field detector 210
move can also be envisaged.
[0026] Although it will be appreciated that the magnetic field detector 210 could consist
of only a single magnetic field detecting element, in the present embodiment an array
of magnetic field detecting elements 210a, 210b, 210c and 210d make up the magnetic
field detector 210. By providing an array of magnetic field detecting elements, a
larger portion of the banknote 10 can be investigated without providing a single element
with a longer and more complex scan path across the surface of the banknote 10. The
magnetic field detecting elements 210a, 210b, 210c and 210d may be either independent
from each other, or could be connected in series or parallel. The magnetic field detecting
elements 210a, 210b, 210c and 210d may be used, in addition to detecting the presence
of the security thread, to determine the length of the security thread, this length
being compared with a database to identify the type and denomination of the banknote
10.
[0027] The particular method used to detect the presence of the magnetic material within
the security thread 20 will depend at least in part on the nature of the magnetic
material. For strongly magnetic materials, the magnetic field generated by the magnetic
material may be observed directly using a magnetic sensor. For a less strongly magnetic
material it may be necessary or advantageous to induce the magnetic material to generate
a magnetic field, for instance by the application of an electric field or an external
magnetic field to the security thread 20. Alternatively, the magnetic field detector
could also be provided with a magnetic field generator, with the generated magnetic
field being continuously monitored for perturbations. In this way, the presence or
movement of the magnetic material within the generated magnetic field would perturb
the generated magnetic field in a characteristic way which would be recognised by
the magnetic field detector. In the Figure 3 embodiment, the security thread 20 comprises
magnetic material which provides a strong enough magnetic field for direct sensing
of the magnetic field to be possible.
[0028] A number of different kinds of magnetic field based sensors exist which could be
applied to the present invention. For instance, the presence of magnetic material
in a security thread could be detected using resonant inductive circuits or capacitative
circuits similar to those used in the reading heads of a tape recorder.
[0029] Preferably, the magnetic material within the security thread 20 is detected using
one or more Hall effect sensors. Hall effect sensors comprise one or more semiconductor
platelets in which an electric current is passed through from one edge to an opposite
edge. A Hall voltage is generated across the plate in a direction transverse to the
current flow when an external magnetic field acts perpendicularly to the direction
of the current through the semiconductor platelet. The Hall voltage generated is dependent
on the magnetic flux density perpendicular to the plane of the Hall plate. The Hall
plate and associated evaluation circuitry can be integrated onto a single silicon
chip, for instance using CMOS technology to form a robust and compact sensor unit.
[0030] Referring to Figure 3, the magnetic field detector 210 comprises four magnetic field
detecting elements 210a, 210b, 210c and 210d arranged during a magnetic scan operation
in a line across the width of the banknote 10 from the edge 30 to the edge 40. Each
of the magnetic field detecting elements 210a, 210b, 210c and 210d comprises a hall
effect sensor as described above. As the magnetic field detecting elements 210a, 210b,
210c and 210d traverse the banknote 10 from the edge 50 to the edge 60, the Hall voltage
output V
HALL from each of the elements 210a, 210b, 210c and 210d is monitored. In the absence
of a magnetic field, the magnetic field detecting elements 210a, 210b, 210c and 210d
will generate a small residual voltage V
0 known as an offset voltage which is due to influences such as the structural properties
and the temperature of the material. The decision logic 180 described above with reference
to Figure 2 is configured to consider the security thread 20 to be present only if
the Hall voltage V
HALL exceeds a predetermined threshold voltage V
THRESH. The decision voltage may also require the Hall voltage V
HALL to exceed the threshold voltage V
THRESH for at least a predetermined minimum distance of the banknote 10 to reduce the likelihood
of false detection of the security thread 20 as a result of background electrical
or magnetic fluctuations. The lower portion of Figure 3 graphically illustrates the
V
HALL output signal as a function of the position of one of the magnetic field detecting
elements 210a with respect to the banknote 10. The V
HALL output signal may differ from one element to another element as a result of, for
example a discontinuity in the security thread 20 or demagnetisation of part of the
magnetic material within the security thread 20.
[0031] It can be seen from Figure 3 that when the magnetic field detecting element 210a
moves close to the security thread 20, an increase in magnetic activity associated
with the presence of the security thread 20 results in an increase in the Hall output
voltage V
HALL of the magnetic field detecting element 210a. The Hall output voltage V
HALL will reach a maximum value when the magnetic field detecting element 210a is at its
closest to the security thread 20, and will then fall back to its original level as
the element moves away from the security thread 20. Therefore, if a security thread
20 is present in the banknote 10, the Hall output voltage V
HALL should exceed the threshold voltage V
THRESH while the magnetic field detecting element 210a is proximate the security thread
20.
[0032] The steps involved in the operation of the security reader 100 in an example embodiment
of the invention will now be described with reference to Figures 4A and 4B. Referring
to Figure 4A, at a step S1 the security thread reader 100 is initialised by specifying
in advance a threshold voltage V
THRESH and a minimum time period τ for which the Hall voltage V
HALL must exceed the threshold voltage V
THRESH for the security thread 20 to be considered as present within the banknote 10. The
Current Position, CP along the scanning track of the magnetic field detecting elements
210a, 210b, 210c and 210d and a counter, t are both initialised to zero.
[0033] At a step S2, magnetic scanning of the banknote 10 commences and relative motion
between the magnetic field detecting elements 210a, 210b, 210c and 210d begins, with
the Current Position, CP of the magnetic field detecting elements 210a, 210b, 210c
and 210d being incremented in accordance with the relative motion.
[0034] At a step S3, the measured Hall voltage V
HALL of the magnetic field detecting elements 210a, 210b, 210c and 210d is compared to
the threshold voltage V
THRESH. If the Hall voltage V
HALL is below the threshold voltage V
THRESH then the scanning step S2 continues and no further action is taken. If the Hall voltage
V
HALL is above the threshold voltage V
THRESH then it is considered that the security thread 20 may have been encountered and the
process moves on to a step S4.
[0035] At the step S4 a counter is started and a counter value, t begins incrementing. Also
at the step S4, a variable STStart, corresponding to a possible start position of
the security thread 20, is set to the current position CP of the magnetic field detecting
elements 210a, 210b, 210c and 210d.
[0036] At a step S5 the magnetic scan process continues and at a step S6 the Hall voltage
V
HALL is again compared to the threshold voltage V
THRESH. At the step S6, if the Hall voltage V
HALL is above the threshold voltage V
THRESH then the magnetic scan process continues and no further action is taken. If the Hall
voltage V
HALL is below the threshold voltage V
THRESH then the process moves on to a step S7.
[0037] At the step S7 the counter which was started at the step S4 is stopped and the counter
value, t is thus frozen. Also at the step S7, a variable STEnd, corresponding to a
possible end position of the security thread 20, is set to the current position CP
of the magnetic field detecting elements 210a, 210b, 210c and 210d.
[0038] At a step S8, the frozen value of the counter value t is compared to the minimum
time period τ which was set earlier in the step S 1. If the counter value t is less
than the minimum time period τ then it is considered that the magnetic thread has
not been detected and the process moves on to a step S9, where the counter value t
is reset to zero. Following the step S9, the process returns back to the step S2 where
the security thread reader continues to magnetically scan the banknote 10 for the
security thread 20. However, if at the step S8 it is determined that the counter value
t is greater than or equal to the minimum time period τ then it is considered that
the security thread 20 has been detected and that its location within the banknote
10 is now known. The process then moves on to a step S10, which is illustrated in
Figure 4B.
[0039] Although in the present embodiment a time counter is used, it will be appreciated
that because the time is simply a function of the distance moved by the magnetic field
detecting elements 210a, 210b, 210c and 210d across the banknote 10, and because the
relative motion is being tracked to identify the current position of elements 210a,
210b, 210c and 210d and thus the position of the security thread, this information
could be used instead of the time counter.
[0040] At the step S10, an optical scan area is designated. In this embodiment, the optical
scan area is set as a strip of the banknote 10 bounded by the edges 30 and 40 of the
banknote and by the positions STStart and STEnd designated by the magnetic thread
detection process in steps S1 to S9. This optical scan area should correspond to the
position of the security thread 20 within the banknote 10.
[0041] At a step S11, the area designated in the step S10 is optically scanned to generate
image data corresponding to the security thread 20 of the banknote 10. The image data
generated is stored to an image buffer in a step S12.
[0042] At a step S 13, the buffered image data is processed using a technique such as optical
character recognition (OCR) or pattern matching to identify the markings present on
the security thread 20.
[0043] The method described above with reference to Figures 4A and 4B can be applied to
a banknote reader such as a vending machine or ticket machine. With banknote readers
within this field of technology it is highly desirable to provide anti-stringing safeguards.
"Stringing" is the term applied to the practice of withdrawing a banknote from a banknote
reader after validation of the transaction has taken place but before the banknote
has been fully and irretrievably stored into the machine. This results in the user
both retaining the banknote and also obtaining the result of the transaction. Methods
of anti-stringing include attaching string or an adhesive tape to the banknote prior
to its insertion into the banknote reader and then pulling back on the string or tape
between the time of validation of the transaction and the storage of the banknote.
[0044] Figure 5 schematically illustrates an embodiment of the invention in which an anti-stringing
mechanism is provided. In this embodiment of the invention, the steps S1 to S13 as
described above with reference to Figures 4A and 4B are carried out to obtain an identification
of the markings present on a security thread 20 within a banknote 10. In a step S14
this identification is used to determine the authenticity (and denomination) of the
banknote 10. If the banknote 10 is determined not to be authentic, then the process
moves on to step S 15 where the transaction is terminated. At this time the banknote
10 could either be returned to the user or confiscated. Additionally the banknote
reader comprising the security thread reader could conduct a predetermined course
of action such as alerting the proprietor of the banknote reader that a potentially
counterfeit banknote has been detected.
[0045] If the banknote 10 is determined to be authentic then the process moves on substantially
simultaneously to steps S16, S17 and S18. At the step S16 the transaction is validated.
At the step S 17 the banknote reader initiates storage of the banknote 10. At the
step S 18 the magnetic field detecting elements 210a, 210b, 210c and 210d measure
the magnetic flux from a portion of the banknote 10 at which they are currently located.
Specifically, the magnetic field detecting elements 210a, 210b, 210c and 210d will
be positioned such that the security thread 20 would need to pass by them in the event
that the banknote were to be retracted from the banknote reader. Note that the magnetic
scanning in the step S18 does not include system driven relative motion between the
banknote and the magnetic field detecting elements 210a, 210b, 210c and 210d as was
the case with steps S2 and S5 in Figure 4A. Relative motion between the banknote 10
and the magnetic field detecting elements 210a, 210b, 210c and 210d in step S 18 will
result only from a user retracting the banknote or from the banknote finally being
stored into the banknote reader. In the latter case the security thread will not pass
by the magnetic field detecting elements 210a, 210b, 210c and 210d because it will
be travelling into rather than out of the banknote reader.
[0046] At a step S19 the measured Hall voltage V
HALL of the magnetic field detecting elements 210a, 210b, 210c and 210d is compared to
the threshold voltage V
THRESH. If the Hall voltage V
HALL is below the threshold voltage V
THRESH then the scanning step S 19 continues and no further action is taken. If the Hall
voltage V
HALL is above the threshold voltage V
THRESH then it is considered that the security thread 20 may have been encountered and the
process moves on to a step S20. At the step S20 the magnetic scan process continues
and at a step S21 the Hall voltage V
HALL is again compared to the threshold voltage V
THRESH. At the step S21, if the Hall voltage V
HALL is above the threshold voltage V
THRESH then the magnetic scan process continues and no further action is taken. If the Hall
voltage V
HALL is below the threshold voltage V
THRESH then it is considered that the security thread has been encountered and that stringing
is therefore taking place. In this event the process will move on to the step S15
and the transaction will be terminated.
[0047] The steps S18 to S21 will continue until either the security thread 20 is detected
and the transaction therefore invalidated or until the banknote has been finally stored
after the step S 17. As such, it is not possible to retract the banknote without termination
of the transaction occurring. In this way, the stringing problem identified above
is addressed.
[0048] Although illustrative embodiments of the invention have been described in detail
herein with reference to the accompanying drawings, it is to be understood that the
invention is not limited to those precise embodiments, and that various changes and
modifications can be effected therein by one skilled in the art without departing
from the scope of the invention as defined by the appended claims.
1. A security thread reader for detecting the presence of a security thread in a document,
the security thread having one or more regions of magnetic material and one or more
optically visible markings, the security thread reader comprising:
a magnetic field detector operable to detect the magnetic material within the security
thread and to determine, based on this detection, one or more areas within the document
at which the security thread is present;
a controller operable to set a specified target area of the document to include at
least a portion of the one or more areas within the document at which it has been
determined that the security thread is present;
an optical scanner operable to generate an image of the specified target area; and
an image processor operable to process an area of the scanned image corresponding
to the specified target area of the document to identify the optically visible markings
within the security thread.
2. A security thread reader according to claim 1, wherein the document is a banknote.
3. A security thread reader according to claim 1 or claim 2, wherein either or both of
the magnetic field detector and the document are moved relative to the other.
4. A security thread reader according to any preceding claim, wherein either or both
of the optical scanner and the document are moved relative to the other.
5. A security thread reader according to claim 3 or claim 4, wherein if the relative
motion between either of the magnetic field detector or the optical scanner and the
document is reversed then a transaction associated with the document is cancelled.
6. A security thread reader according to claim 5, wherein the reversal in relative motion
results in, and is detected as a result of, a second detection of the security thread
by the magnetic field detector.
7. A security thread reader according to claim 5, wherein reversal in relative motion
results in an inversion of the scanned image of the optically visible markings, the
image processor detecting the reversal of relative motion by detecting the inversion
of the optically visible markings.
8. A security thread reader according to any preceding claim, wherein the magnetic field
detector determines the length of the security thread.
9. A security thread reader according to any preceding claim, wherein the magnetic field
detector determines a magnetic thickness value indicative of the dimensional characteristics
of the security thread, the magnetic thickness value being determined as a function
of the signal amplitude of the magnetic field detector.
10. A security thread reader according to any preceding claim, wherein the magnetic field
detector comprises one or more Hall-effect sensors.
11. A security thread reader according to any preceding claim, wherein the one or more
regions of magnetic material comprise a ferromagnetic material.
12. A security thread reader according to any preceding claim, wherein the optical scanner
includes a light emitting element for emitting light and a light receiving element
for receiving light, the light emitted from the light emitting element being transmitted
through the document before being received by the light receiving element.
13. A security thread reader according to claim 12, wherein the light emitted from the
light emitting element is substantially coherent.
14. A security thread reader according to any preceding claim, wherein the image processor
comprises an optical character recognition (OCR) function for identifying the optically
visible markings.
15. A method of detecting the presence of a security thread in a document, the security
thread having one or more regions of magnetic material and one or more optically visible
markings, the method comprising the steps of:
detecting the magnetic material within the security thread;
determining, based on the result of the detection step, one or more areas within the
document at which the security thread is present;
setting a specified target area of the document to include at least a portion of the
one or more areas within the document at which it has been determined that the security
thread is present;
generating an image of the specified target area; and
processing an area of the scanned image corresponding to the specified target area
of the document to identify the optically visible markings within the security thread.