JP2001521230A - Bill validator for bank notes with conductive strips - Google Patents

Abstract

A device for validating the authenticity of a document uses changes in capacitance due to the presence of an electrically conductive security thread extending across the document or the presence of a watermark. The device uses a drive arrangement (14) for moving of a document such as a bank note, past a sensing arrangement (16, 24) which senses changes in capacitance due to movement of a security thread or watermark therapist. A frequency generator produces a high frequency time varying oscillator signal and provides this signal to an elongate oscillator electrode extending across the path of movement. A lead elongate measuring electrode is electrically conductive and positioned in front of the oscillator electrode and extends across said path and a trailing elongate measuring electrode is positioned behind the oscillator electrode and extends across the path. The signals from the measuring and the oscillator electrode are provided to a signal processing arrangement. The signal processing arrangement processes the signals relative to detect changes in amplitude and phase shift between the signals caused by a conductive security thread or the watermark passing by the electrodes. Chosen separation distances and using of two sensors placed on opposite sides of bank note reduces the signal intensity variations, caused by the wobbling of the bank note and changes in separation distance of the bank note from the sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION

The present application relates to sensors used in verifiers to detect conductive security threads provided on currency and other documents.

[0002]

BACKGROUND OF THE INVENTION

It is well known to provide a conductive security thread in a currency, such as the US currency. These security threads can be detected using sensors that operate based on changes in capacitance due to the presence of the security threads. The conductivity of the security thread may be continuous or it may be segmented.

[0003] US Patent No. 5,419,424 discloses an apparatus for sensing security threads in documents. This patent has a number of sensors and has a horizontal arrangement to distinguish between security threads having discrete segments along the length and conductive lines such as pencil lines on the document. Disclosed is a structure that uses horizontal and vertical electrodes in combination with the configured feed electrode.

[0004] As can be appreciated, security thread sensing is used in combination with other sensing and evaluation techniques to collectively determine whether a particular document is authentic. Typically, the document is moved along a predetermined path and is moved past a fixed sensor. These sensors provide inputs that are evaluated as the bill passes to provide a prediction of whether the document is genuine. This evaluation and prediction occurs quickly, usually when the customer is waiting for its consequences, such as approval for the purchase.

[0005] In currency sensing, the state of the currency varies widely, from relatively fresh hand-cut bills to those that are fairly frayed and may have a series of folds or folds. there's a possibility that. As it passes along its path, the banknote is usually controlled in a guide device, but there is some movement of the currency from the centerline in the guide, and therefore the banknote is swayed in its guide there's a possibility that. This wobble can have a dramatic effect on the capacitance sensor, which is relatively sensitive to changes in the separation distance between the note and the sensor. Most capacitance sensors require that the sensor be in close contact with the bill, and this can cause the currency to become stuck in the verifier. Thus, when the separation interval is small, the quality of the signal from the capacitance sensor is improved, but there are significant service and reliability issues caused by the jamming of the bill in the verifier. In addition, as the currency passes the verifier, the sway of the banknote can cause the separation distance to change quickly, and the signal from its capacitance sensor can also change rapidly. The signal from the capacitance sensor is expected to increase and decrease, but whether those changes were caused by a wobble or a change in the position of the security sled as it passed by the sensor. It is difficult to know.

[0006] Prior art devices have tended to reduce the separation distance between the sensor and the bill to improve signal strength, but this has not been entirely satisfactory.

[0007] The present invention overcomes some of these problems. It has also been found that changes in capacitance due to watermarking can be recognized and used as part of the verification process.

[0008]

Summary of the Invention

Apparatus for verifying the authenticity of a document, comprising, in accordance with the invention, a conductive security thread extending across the document and extending longitudinally along a predetermined path of the apparatus. A drive device for moving the generator, a generator providing a high-frequency time-varying oscillator signal, and a conductive, connected to the generator, applying a time-varying oscillating signal to the electrodes, An elongate oscillator electrode, where the electrodes are arranged to extend across the path, and an elongate measurement electrode, which makes the elongate measurement electrode conductive and is located in front of the vibrating electrode, and extends the elongate measurement electrode. And an elongate measuring electrode at the rear end that is conductive and is located behind the oscillator electrode and extends across its path. The device is connected to a measurement electrode, receives an output signal from the electrode,
The apparatus further includes a signal processing device that generates the measurement signal. The signal processing device receives a time-varying oscillating signal as a reference signal. The signal processing device processes the measurement signal relative to the reference signal and detects changes in electrical properties caused by the passage of the conductive security sled through the electrodes.

With the above arrangement, the security thread generates a first change in capacitance for the leading measuring electrode when the security thread is between the leading electrode and the oscillator electrode. As the document moves further, a security thread will be placed between the oscillator electrode and the trailing elongate electrode. These changes in capacitance result in changes in the amplitude and phase shift of the measurement signal relative to the reference signal, which can be easily detected. By placing the leading electrode on one side of the oscillator electrode and the trailing elongate measuring electrode on the opposite side of the oscillator electrode, the signal caused by the security thread is changed by the change in separation distance. Can be separated from

Also, according to the present invention, the positioning of the electrode relative to its path is 1-1.
It can be quite large, on the order of 2 mm, and the space between the leading and oscillator electrodes is also about 1 mm, which has been found to be the same separation distance between the oscillator and trailing electrodes. However, this relatively large separation distance reduces the strength of the measurement signal and also greatly reduces the effect of the motion of the banknote on the measurement signal amplitude as it passes along its path. This result is related to the non-linear dependence of the measured signal versus the separation distance. Larger distances reduce the likelihood of document jams compared to conventional practices of reducing or minimizing separation distance.

According to one aspect of the invention, the signal generator generates a vibration signal having a frequency in a range of 50 to 150 MHz. This frequency range is useful for larger separation distances and separation distances between the electrodes.

In one preferred embodiment, two sensing devices are provided on opposite sides of the currency path in opposite relation. Different frequencies are used to reduce interference. With this device, the movement of currency off-center increases the signal at one sensing device and decreases the signal at the opposite sensing device. The signal is processed and an evaluation is made based on the signals from both sensing devices.

An apparatus for verifying the authenticity of a document having a watermark on the surface of the document includes a drive device for moving the document longitudinally along a predetermined path of the apparatus; A generator for generating a high-frequency time-varying oscillator signal, an elongated oscillator electrode, a leading elongated measuring electrode, and a trailing elongated measuring electrode, wherein the oscillator electrode is electrically conductive, Connected to the generator to be applied, the elongated oscillator electrode is generally positioned to extend across the path. A leading elongate measuring electrode is conductive and is placed in front of the oscillator electrode and extends across the path. A trailing elongate measuring electrode is conductive, is located behind the oscillator electrode, and extends across the path. A signal processing device is connected to the measurement electrode, receives an output thereof, and generates a measurement signal. Further, the signal processing device receives a time-varying oscillator signal as a reference signal. The signal processor processes the measurement signal relative to the reference signal for changes in amplitude and phase shift caused by the watermark passing through the electrodes.

The present invention relates to an improvement in an apparatus for verifying the authenticity of a document, wherein the document has a plurality of security-related features, the features are sensed and compared to a reference signal, and the document is identified. Can be evaluated, and one of the security-related features is a watermark. The device includes an optical sensor and a capacitance sensor, and a drive device for moving the document longitudinally along the predetermined path of the device past the sensor. A processing unit is provided for processing the signal from the sensor, comparing a reference signal to the received signal, and providing an authenticity evaluation of the document. A capacitance sensor is placed to scan the watermark and can identify it in response to the presence of the watermark.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The currency verifier 2 has a processing section 4 that guides the verified document into the security box 6 and cooperates. The processing section 4 is provided with an inlet 10 so that the user can first insert the document into the verifier, after which the drive device 14 moves the document along a predetermined path, indicated as 12. Control movement. As the document moves along this predetermined path, it is evaluated by sensors 16 and 24,
It is determined whether it is genuine. If so, the note is then passed into security box 16. If rejected,
The drive 14 normally reverses the document and discharges it through the intake 10.

There are several different ways to assess the validity of a document, and usually a verifier such as that shown in FIG. 2 provides several different ways to determine whether a bill is genuine. Use sensing and evaluation techniques. For example, it may include a light emitting device, a magnetic sensor, and / or a capacitance sensor for determining a reflected pattern.

The capacitance sensor of FIG. 2 includes an oscillator electrode 32 with a connection 33. A leading measuring electrode 34 is placed in front of the oscillator electrode 32 relative to the direction of moving the document through the verifier. A trailing measuring electrode 36 is provided on the opposite side of the oscillator electrode, with the leading and trailing measuring electrodes separated by a similar distance shown as 31 from the oscillator electrode. This device also has a connection 33
, 35 and 37 are also included. Arrows 9 indicate the direction of movement of the document past the electrodes, and it can be seen that each electrode is positioned across the width of the document and transverse to the direction of movement shown as 9. Document 7 is shown generally and is fed past electrodes 32, 34 and 36. As shown in FIG. 2a, the document 7 has a security thread 21 extending across the width of the document. The security thread is a conductive thread and may be either continuous or discrete conductive segments. First, it is described because successive security threads generate stronger signals.

As the security thread 21 passes through the leading electrode 30, it enters the gap between the leading electrode 34 and the oscillator electrode 32. This effectively couples the two electrodes, causing the signal from electrode 34 to suddenly increase in intensity and change the phase shift. As the document moves continuously along a given path, capacitive coupling between the leading electrode and the oscillator electrode is reduced. As the security thread 21 passes over the oscillator electrode, it then begins to couple with the trailing electrode 36.

FIG. 3 shows an outline of the signal processing device. A high frequency signal generator 38 supplies a signal to the oscillator electrode 32. This high frequency signal is also provided to the synchronization detector 46. Therefore, a reference signal 44, which is basically a high frequency signal supplied to the oscillator electrode 32, is provided to the synchronization detector 46. The synchronization detector 46 receives a signal 47 from the leading measuring electrode and a signal 45 from the trailing electrode. The difference between these signals is determined, and in turn a measurement signal 49 is generated. Synchronization detector 46 uses measurement signal 49 and reference signal 44 to form an output signal that varies with changes in the amplitude and phase of the input signal with respect to the reference signal. In particular, the polarity of the output signal of the sync detector, which indicates that the security sled passes through the leading and trailing electrodes, is opposite.

Further, the signal processing device can operate normally even in a situation where only the phase shift is registered. This situation occurs when the amplitude of the high frequency signal at each input of the synchronous detector is sufficiently large and saturated. In the sensor according to the invention, this is achieved either by lengthening the electrodes or by increasing the amplitude of the generator signal.

Returning to FIG. 2, it can be seen that the three electrodes are parallel strips of a conductor supported by a dielectric film 51. The oscillator electrode is in the center of the active area of the sensor. The measuring electrode is parallel to and symmetrical with respect to the oscillator electrode, forming an equal capacitance therebetween. The size of the spacing between the oscillator electrode and the measurement electrode is selected based on considerations as more fully described below. The connection between the measuring electrode and the oscillator electrode is extended to provide a connection to a corresponding terminal of the sensing unit. Between these connection parts are shielding conductors, which are connected to ground terminals.

As shown in FIG. 3, the output from the synchronization detector 46 is supplied to an AC amplifier 48. This allows the signal to be conveniently processed and converted into a digital signal for evaluation.

The electrodes are placed on the path in the verifier and the document is pulled lengthwise through the device. In this device, the security sled is parallel to the longitudinal axis of the electrode. As the document is pulled under the sensor, certain portions of the banknotes sequentially pass under the sensor. Since the dielectric properties of the dyes used in banknote paper and printing processes are fairly uniform, the phase and amplitude of the signal from the measuring electrode in relation to the phase and amplitude of the signal on the oscillator electrode are generally the same. Has been left. In addition, although there is some variation in the separation between the document and the sensor, which occurs for both measurement electrodes, changes to the separation are essentially offset.

FIG. 5 shows a circuit diagram of an equivalent capacitance bridge circuit generated by the arrangement of the electrodes 32, 34, 36 and 50 in the sensor. The bridge circuit 51 registers the change in capacitance and phase as the banknote security strip passes over it. This circuit diagram represents a sensor powered by a high frequency oscillator 38 provided on an electrode 44 and shows no banknotes around the sensor. Output signals 47 and 45 are provided to a synchronization detector.

As shown in FIG. 5, the bridge circuit 51 includes two sections. The first section is associated with the leading electrode and the second section is associated with the trailing electrode. In the first section, capacitance 52 is created by the electric field between tip electrode 34 and oscillator electrode 32. The capacitance 54 is formed by the tip electrode 36, the ground shield electrode 50, and the input capacitance of the synchronous detector 2. In the second section, the capacitance 56
Is formed by the rear end electrode 36, the ground shield electrode 32, and the input capacitance of the synchronous detector 2. Synchronous detector 2 for capacitances 53 and 54
Ohm resistors at the inputs are also coupled. The values of these resistors are of the same order of magnitude as the impedance of the bridge capacitance at the operating frequency. Due to their presence, any change in the capacitance of the arms of the bridge will result in a change in the phase shift of the signal at the corresponding input of the synchronous detector 2 with respect to the reference signal.

FIG. 6 shows the capacitance present in the bridge circuit 51 as the security strip 21 passes through, the capacitance being formed between the strip and each electrode, whereby the total capacitance in the bridge circuit 51 Increase. These are shown as capacitances 60, 62, 64 and 66.

The size of the capacitance 66 between the security strip 21 and the ground 50 depends on the type of the security strip 21. A continuous strip of metal produces a relatively high capacitance value for capacitance 66. The series of discrete metal sections in the security strip 21 produce a small capacitance, which can be distinguished from the signal in the absence of a security breach.

As the security strip passes between the tip electrode and the oscillator electrode, the impedance associated with the security strip capacitance in the first section of the bridge circuit increases significantly. Then, as the security strip passes between the trailing electrode and the oscillator electrode, the impedance of the corresponding capacitance in the second section of the bridge circuit increases significantly.

These changes in impedance cause the bridge circuit to become unbalanced, which in turn changes the phase and amplitude of the high frequency signal provided to the input of the synchronous detector. In particular, the signals associated with the strip passing through the leading and trailing electrodes are out of phase with respect to each other.

Thus, as a result of the security strip passing close to the sensor at the output of the sync detector 46, the voltage initially increases in one polarity,
It then increases at the opposite polarity. This voltage, after being amplified by the AC amplifier, is large enough for further processing of the signal. By using an AC amplifier, the need to balance the bridge and the sync detector is reduced, thus eliminating the need for manual adjustment for balance. Basically, there is sufficient tolerance in this system, and the signal is still easy to detect, even if the bridge is slightly unbalanced. This simplifies the circuit and reduces cost.

As a bank note passes along a path in the verifier, the distance between the bank note and the sensor can change. Such fluctuations occur for certain bank notes. That is, the bank note may be wavy or bent, or its position in the guide may fluctuate. This change in separation distance causes additional noise, which can contribute to the imbalance of the bridge at the passage of banknotes, and, on the other hand, the signal formed by the conductive security strip A change in the amplitude of Increasing the spacing of the sensor from the centerline of a given path reduces the effect on signal amplitude of fluctuations in the distance between the sensor and the banknote. These folds and the like are known to cause upsets as bank notes pass through the verifier, and this upset is usually zero.
. It is in the range of 2 to 0.3 mm. The sensors are preferably located 3 to 5 times this sway distance from the center line, and preferably about 1 to 1.2 mm apart. In this configuration, the shaking can be allowed. Eliminating wobble is not practical because it can cause jamming.

It is known that this arrangement can also be used for conductive security threads, which are continuous or discrete segments. Basically, changes in the output signal of the sensor are opposite between a continuous security thread and a discrete security thread due to the capacitance effect of the security thread for the case. In either case, the detection of this sensor works normally for both types of security threads and can recognize each type due to variations in the shape of the output signal.

It can be appreciated that the present invention may involve the use of one or two sensors. In the one-sensor embodiment, a single bridge circuit provides all signals to the synchronous detector.

In a two sensor embodiment, two sensors are placed in the verification device,
They are arranged so that they oppose each other and that the document to be verified passes between them. FIG. 1 shows a verifier with two sensors 16 and 24. This two-sensor configuration allows for a capacitance signal to be generated that accumulates as the security strip passes between the sensors. This two-sensor arrangement is provided on the opposite side of the guide, where changes in position increase the signal at one sensing device and decrease the signal at the other sensing device. Combining these signals contributes to reducing the effects of sway.

FIG. 4 shows a block diagram of the arrangement of the two sensors. Essentially, the two-sensor arrangement comprises two functionally identical but separate signal processors. Each signal processing device operates like the arrangement described in FIG.

FIG. 4 shows an arrangement configuration of each sensor which is distinguished from each other by a subscript notation of A and B. Thus, the two signal processors are synchronization detectors 46A and 46A.
B, high frequency generators 38A and 38B, amplifiers 48A and 48B, electrode signals 45A, 45B, 47A and 47B, and reference signals 44A and 44B. The outputs from the amplifiers 48A and 48B are provided to a signal summation device 49, which generates an output signal 70, which can be converted to a digital signal for processing.

When a banknote shakes when the banknote passes through the sensor, the distance of the banknote from the sensor fluctuates. The two sensors allow the verification system to compensate for the sway distance of the document from the single sensor. As the document passes through two sensors, it becomes closer to one of the sensors. Thus, the cumulative output signal from the two sensors reduces fluctuations in the signal caused by the wobble. 1
To minimize crosstalk between the signal of one sensor and the signal of another sensor, high frequency generators 38A and 38B each generate a frequency that is different from each other and is not harmonically related to each other. . The difference between the generators must be outside the bandwidth of the sensor's AC amplifier. For example, the difference between the frequencies of the generators is preferably 10% to 20% within the operating range of 50 to 150 MHz.

A US $ 50 bill generally shown as 100 in FIG. 7 has a number of immobilized security features applied to the bill at the time of its manufacture. A security thread 102 is embedded in the paper of the document and can be sensed by a capacitance sensor. There are various printing functions, such as 106, which are specifically designed to make the reproduction of this image difficult. In addition to these features, the paper may also include a watermark 104. Watermarking and printing features are usually considered to be visual features of the document,
On the other hand, the security thread 102 is what is sensed. The positions of these various security functions are set for each bill of each denomination. Thus, the note can be scanned, the particular denomination identified, and the reference signal and the scanned result checked to determine if the note is genuine.

In the case of the capacitance sensor described in the previous figures, it is possible to recognize these security features in the scanning of the bill. For example, in the capacitance scan shown in FIG. 8, the security thread 102 responds 11 generally corresponding to the location of the security thread.
2 occurs. In addition, it is possible to see how the watermark 104, a visual security feature, causes a change in the capacitance detected by the capacitance sensor. The change in capacitance due to the watermark signal is shown generally as 114.

FIG. 9 shows the response taken through the central location of the banknote, and
It can know how the thread 102 generated the response 122 and also know how the watermark 104 generated the response 124. The watermark 104 can be sensed using a capacitance sensor,
It has been found that additional information can be provided that is used to provide a prediction of whether the bill is genuine. The method of applying the watermark and the ink associated with the watermark establishes a specific capacitance that can be sensed and recognized. This signal is generally consistent for a particular banknote value.

While various preferred embodiments of the present invention have been described in detail herein, it should be understood that various changes can be made without departing from the spirit of the invention or the scope of the appended claims. , Those skilled in the art will understand.

[Brief description of the drawings]

 Preferred embodiments of the present invention are shown in the following drawings.

FIG. 1 is a partial cross-sectional view of a currency verifier.

FIG. 2 is a partial plan view showing the electrode sensing device, and FIG. 2A is a plan view of a document including a security thread.

FIG. 3 shows a general signal processing device.

FIG. 4 illustrates an alternative embodiment of the present invention.

FIG. 5 shows an equivalent circuit diagram of the electrode sensing device.

FIG. 6 shows an equivalent circuit of the electrode sensing device when a bill containing a security thread is detected.

FIG. 7 illustrates a US $ 50 bill with various security features.

8 is a representation of the capacitance reading of the US $ 50 bill of FIG. 7;

FIG. 9 shows the signal response from a capacitance sensor through the central section of a US $ 50 bill.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM, HR, HU, ID, IL, IS, JP, KE, KG, KP , KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, UZ, VN, YU, ZW [Continued from Summary] By using two sensors located on the opposite side, the bank Reduces signal strength fluctuations caused by fluctuations in banknotes and fluctuations in the separation distance of banknotes from sensors.

Claims (11)

[Claims] 1. An apparatus for verifying the authenticity of a document, said document having a conductive security thread extending across said document, said apparatus comprising: A drive for moving the document in a longitudinal direction along a path; a generator for providing a high-frequency time-varying oscillator signal; a conductive and connected to the generator; An elongate oscillator electrode, which is positioned to extend generally across said path; and an electrically conductive, positioned in front of said oscillator electrode, extending across said path. An elongate measuring electrode at the distal end, an elongate measuring electrode at the rear end that is electrically conductive and is positioned behind the oscillator electrode and extends across the path. A signal processing device connected to the measurement electrode for receiving the output thereof and generating a measurement signal, the signal processing device also receiving the time-varying oscillator signal as a reference signal, A processing device processes the measurement signal relative to the reference to detect amplitude variations and changes in phase shift caused by a conductive security thread passing through the electrodes. apparatus. 2. An apparatus for verifying the authenticity of a document according to claim 1, wherein said elongated measuring electrodes are each separated from said oscillator electrode by about 1 mm. 3. Apparatus for verifying the authenticity of a document according to claim 2, wherein the electrode is on average about 1 mm from the document as the document moves past the electrode. . 4. Apparatus for verifying the authenticity of a document according to claim 3, wherein the signal generator generates an oscillator signal having a frequency in the range of 50 to 150 MHz. 5. Apparatus for verifying the authenticity of a document according to claim 4, wherein said apparatus is designed for validating US banknotes. 6. The apparatus for verifying the authenticity of a document according to claim 1, wherein said processing unit compares a differential signal obtained from said measuring electrode with said reference signal, An apparatus comprising a synchronization detector for detecting said change in amplitude. 7. The apparatus for verifying the authenticity of a document according to claim 6, wherein the processing unit further comprises an AC amplifier for amplifying an output signal of the synchronization detector. 8. The apparatus for verifying the authenticity of a document according to claim 7, further comprising a shield electrode associated with each electrode lead, wherein said measurement is caused by a change in capacitance detected by said lead. A device adapted to reduce undesired contributions to the signal from the working electrode or the oscillator electrode. 9. The apparatus for verifying the authenticity of a document according to claim 1, wherein the path includes a document guide for maintaining the document at a distance of at least 0.5 mm from the electrode. 10. The apparatus for verifying the authenticity of a document according to claim 9, wherein the document guide is about ± 0.3 m from the center of the guide.
An apparatus adapted to allow movement of the document about the electrode by m. 11. An apparatus for verifying the authenticity of a document, comprising a plurality of security functions that can be sensed and compared to a reference signal for evaluating the authenticity of the document. One of which is a watermark, wherein the device comprises a light sensor and a capacitance sensor, a drive device for moving the document longitudinally along a predetermined path through which the device passes, and a signal from the sensor. And a processing unit for comparing the reference signal to a received signal and providing a true or false evaluation of the document, wherein the capacitance sensor is arranged to scan the watermark. And the capacitance sensor is responsive to the presence of the watermark to enable its identification. Equipment.