WO2017222365A1

WO2017222365A1 - Method for testing banknote quality and device for testing banknote quality

Info

Publication number: WO2017222365A1
Application number: PCT/NL2016/050440
Authority: WO
Inventors: Thomas Buitelaar
Original assignee: Thomas Buitelaar
Priority date: 2016-06-22
Filing date: 2016-06-22
Publication date: 2017-12-28

Abstract

The invention relates to a method for testing banknote quality, comprising the steps of: – providing a banknote; 5 – in a first analysis step, projecting light with a light source under an angle of incidence onto one of the faces of the banknote and capturing at an angle of detection with a detector the light projected, different from the angle of incidence; 10 – after the first analysis step, changing at least one of the angle of incidence and the angle of detection; – in a second analysis step, projecting, after having changed at least one of the angle of incidence and the angle of detection, light from the angle of incidence onto the 15 one face of the banknote and capturing the light projected at the angle of detection which is different from the angle of incidence in the second projection step with a detector; and – comparing the detected projected light from the first analysis step and the second analysis step in order to 20 detect creases and plain surfaces in the banknote. The invention further relates to a device for testing banknote quality.

Description

Method for testing banknote quality and device for testing banknote quality

The invention relates to a method for testing banknote quality.

After production and commissioning of banknotes, they are subjected to wear, either when they are stored in for instance a wallet or a pocket, or when they are used or transferred, in which case the banknote will get in touch with human hands. It is important to assess the quality of a banknote from time to time in order to determine if the banknote still complies with the required standards, in which case it should be recirculated, or if it should be rejected, in which case it may be destroyed. These processes are

currently carried out in sorting devices, preferably

concurrently with the step of validation of the authenticity of the banknote. In these devices, throughputs of up to approximately 100,000 banknotes per hour are not an exception.

Historically, banknotes have a paper substrate. On a paper substrate, contaminations are easily detected by various methods, such as measurement of the reflection of the banknote and the color of the light reflected. On a paper banknote, contamination will result in a decrease of reflection and, since blue light will be absorbed to a higher extent compared to red or yellow light, the reflected light will be more reddish or yellowish. Although the performance of these techniques is reasonable, it is still observed that high numbers of banknotes are inadvertently rejected, resulting in high costs for the production of replacement banknotes.

In addition, since the 1990s, more and more countries shift from paper-based banknotes towards polymer banknotes (such as banknotes made of biaxially oriented polypropylene) . Currently available techniques for testing have an even lower reliability on polymer banknotes due to various reasons. For instance, contaminations show a lower adhesion to polymer banknotes compared to paper-based

banknotes. In addition, the ink used for printing polymer banknotes has a much higher tendency to set off from the substrate over time compared to paper-based banknotes, which may lead to an increase of reflection after use, instead of a decrease of reflection as seen in paper-based banknotes.

It is now an object of the invention to reduce or even obviate the above-mentioned drawbacks.

This object is achieved according to the invention with a method for testing banknote quality, comprising the steps of :

- providing a banknote;

- in a first analysis step, projecting light with a light source under an angle of incidence onto one of the faces of the banknote and capturing at an angle of detection with a detector the light projected, different from the angle of incidence ;

- after the first analysis step, changing at least one of the angle of incidence and the angle of detection;

- in a second analysis step, projecting, after having changed at least one of the angle of incidence and the angle of detection, light from the angle of incidence onto the one face of the banknote and capturing the light projected at the angle of detection which is different from the angle of incidence in the second projection step with a detector; and

- comparing the detected projected light from the first analysis step and the second analysis step in order to detect creases and plain surfaces in the banknote.

In the method according to the invention, the light reflecting from is a banknote is captured at least twice with a difference in at least one of angle of incidence or angle of detection. With just one capture, a two-dimensional image would be obtained from the banknote. With two captures wherein the position of at least the angle of incidence of the light source or the angle of detection (the configuration of light) is changed in the second capture, it is possible to obtain a simulation of a three-dimensional capture. Creases will result in shadows in the image, which will change in orientation and size based on the angle of incidence and angle of detection.

It is observed that the amount of creases in a banknote are a good indicator for the quality of the banknote. Especially in polymer banknotes, creases will be more

difficult to remove from polymer banknotes than in paper-based banknotes, and the ink will most likely set off near or in the creases .

LEDs are an example of suitable light sources, since they can be switched on and off very rapidly.

In a preferred embodiment of the method according to the invention, the angles of incidence and the angles of detection are within the same plane, which plane is

perpendicular to the one face of the banknote, and preferably parallel to the longitudinal direction of the banknote.

In each of the two configurations of light, the pattern of the shadows resulting from the creases will be different. It is easier to correlate two captures when the angles of incidence and the angles of detection are within the same plane which is perpendicular to the one face of the banknote, and more preferably parallel to the longitudinal direction of the banknote.

In another preferred embodiment of the method according to the invention, the detector comprises a camera, directed towards the one side of the banknote, which camera is at a fixed position during the first and second analysis step, wherein the angle of incidence is smaller than 90 degrees in the first analysis step and larger than 90 degrees in the second analysis step.

Two images are made in which the light originates from an angle or incidence is smaller and larger than 90 degrees (i.e. opposing sides of the camera), preferably at the same angle of incidence with reference to the normal to the banknote. By making two images, the shadows resulting from the creases in the banknote will be in different directions, which makes it possible to assess the quality of the banknote based on the two-dimensional images of the creases.

In yet another preferred embodiment of the method according to the invention, the light source comprises a light source of green light, such as light with a wave length of approximately 525 nm, or a light source of infrared light, for instance light with a wavelength between 800 - 1000 nm, and preferably approximately 850 nm. The upper value of 1000 nm is preferred in order to reduce the chance of difficulties in detection with the camera.

It has been found that green light and infrared light are suitable wavelengths for lighting in order to show creases in polymer banknotes.

In even another preferred embodiment of the method according to the invention, the step of comparing comprises the step of subtracting the captured detected light made in the first and the second analysis step to obtain a subtracted photo with creases and plain surfaces.

When the two captures are subtracted, the result will be an image of the creases in the banknote, whereas the printing on the banknote, which will be the same in both captures, will disappear. This makes it easy to make a true assessment of the quality of the banknote.

In again another preferred embodiment of the method according to the invention, the comparing step comprises the step of quantifying the number or surface area of the plain surfaces of the banknote from the subtracted photo.

The subtracted image is easy to analyse due to the absence of print patterns on the image. Algorithms may be used in order to analyse the subtracted photo, e.g. by counting maxima and minima, which may take the form of, possibly coupled, pixel elements. Using pattern recognition techniques, it is possible to quantify number and/or surface area of the creases .

It is especially found that a good indication of the quality of a banknote may be obtained by quantifying areas with a low variability. Banknotes which show a low variability (in number, in size or a combination of number and size) will typically have a good quality and may be recirculated, whereas banknotes with a high variability should be rejected.

In another preferred embodiment of the method according to the invention, the projected light is detected by at least one phototransistor , arranged at different angles of detection relative to the one face of the banknote in the first and second analysis step, wherein the comparison step comprises the steps of:

- calculating the differences between values

detected in the at least one phototransistor;

- correlating the calculating the differences to obtain a crease factor.

In this embodiment, the banknote will be exposed to light (preferably white light) at an angle of incidence, preferably between 20 and 90 degrees with respect to the banknote face, and the light reflected will be measured using phototransistors at an angle of detection, at the opposing side of the normal to the face of the banknote, preferably also at angles between 20 and 90 degrees. As an alternative for phototransistors, photodiodes with amplifiers may also be used .

It is for instance possible to use light sources at intervals of approximately 10 degrees, which will result in both light sources and phototransistors at angles of 20, 30, 40, 50, 60, 70, 80 and near 90 degrees (since exactly 90 degrees would mean that the light source and the

phototransistor overlap) . In this case, a preferred method of measurement involves the use of light at one of the angles of incidence, during which the reflection is detected at all angles of detection. When repeating this method for all angles of incidence, a total of 8 x 8 = 64 measurements will be obtained .

It is observed that particular combinations of angles of incidence and angles of detection show good results. These angles are (with respect to the banknote face) :

Since it is possible to switch the light sources and detectors in this method very rapidly, this the preferred option when the method is performed in a device in which the banknotes are moved continuously.

Each of the phototransistors will output a value

(typically between 0 and 1023) . By making comparisons, it is possible to assess the quality of the banknote.

In yet another preferred embodiment of the method according to the invention, the method comprises the steps of:

- carrying out the method on a reference banknote in order to obtain a reference crease factor;

- carrying out the method on a banknote to be tested; and - comparing the crease factor from the reference banknote with the crease factor from the banknote to be tested .

In order to reliably assess the quality of banknotes, it is preferred to compare the crease factor of banknotes to be tested with a crease factor from a reference banknote which does meet the standards. In other words, the reference banknote serves as a calibration. The degree of deviation between this reference banknote and banknotes tested will provide an indication for the quality of the banknote.

Again, algorithms may be used in order to determine the crease factor, e.g. by multiple regression analysis.

In again another preferred embodiment of the method according to the invention the method comprises, after the first and second analysis steps, the steps of:

- moving the banknote over a predetermined distance in the longitudinal direction of the banknote; and

- after moving the banknote, repeating the first and second analysis steps.

The method is preferably carried out in a device in which the banknotes are moved or carried through the device, for instance by rollers, such as known in currently used devices for checking the authenticity of banknotes. This makes it possible to make the captures of only a small segment of the banknote. After moving the complete banknote along the detector, the captures of all segments under the same

recording conditions are merged to a complete image.

When moving the banknotes through the device, it is preferred to move the banknote continuously, for instance at a speed of approximately 10 meters per second. This improves the throughput through the device. In this case, the embodiment using phototransistors may be preferred over the embodiment using a camera, since the latter embodiment requires very rapid switching. For this reason, it is, especially in the latter embodiment, also possible to move the banknote stepwise over predetermined intervals, wherein the at least two

captures are taken on the same segment of the banknote, in order to increase the accuracy.

In a highly preferred embodiment of the method according to the invention, the banknote is a polymer

banknote .

It has been found that the method according to the invention, and the preferred embodiments thereof, are highly suitable for testing the quality of polymer banknotes.

The invention further relates to a device for testing banknote quality, comprising:

- a carrier, for carrying a banknote;

- at least one light source, which light source is directed towards the carrier at an angle of incidence;

- at least one detector, which detector is directed towards the carrier at an angle of detection, different from the angle of incidence, for capturing light received from the light source via a banknote carried by the carrier.

The device according to the invention is an example of a device suitable for carrying out the method according to the invention. In the carrier, a banknote is arranged such that it will be exposed the light from the light source when the light source is turned on, and such that the detector will be able to detect the light reflecting from the banknote.

In a preferred embodiment of the device according to the invention, wherein the detector comprises a camera, which camera is at a fixed position, wherein the light sources comprise a first light source arranged at an angle of

incidence smaller than 90 degrees and a second light source arranged at an angle of incidence larger than 90 degrees.

In this embodiment, a camera (preferably a monochrome camera) is arranged at a distance from the carrier, such that it can detect the light from the light source. On opposing sides of the camera, a light source is arranged to light the banknote arranged in the carrier. Preferably, two light sources are arranged, each at the same position with respect to the camera, but on opposing sides. The lights are preferably arranged in a light frame.

Preferably, the wavelength of the light is green or infrared, since it has been found that green light and

infrared light are suitable wavelengths for lighting in order to show creases in polymer banknotes.

Other light sources may also be arranged in the device, such as for instance light sources used for verifying the authenticity of the banknote. These light sources may be arranged adjacent to the light sources used for the invention, but also behind the carrier, where applicable.

In another preferred embodiment of the device according to the invention, the device comprises a frame with a semicircle-shape and a radius, with a row of light sources arranged along the first half of the semicircle-shape, and wherein the at least one detector comprises a row of

phototransistors , arranged along the opposing second half of the semicircle-shape, wherein the centre of the semicircle- shape is arranged at or near the carrier.

In this embodiment, the banknote will be exposed in the device to light (preferably white light) at an angle of incidence, preferably between 20 and 90 degrees with respect to the banknote face, and the light reflected will be measured using phototransistors at an angle of detection, at the opposing side of the normal to the face of the banknote, preferably also at angles between 20 and 90 degrees.

The row may be two-dimensional but is preferably three-dimensional, in order to be able to capture a wide area. In yet another preferred embodiment of the device according to the invention, the device comprises feeding means, for feeding banknotes towards and from the carrier.

In this embodiment, the carrier is connected to feeding means, such as rollers, which may feed the banknotes into and out from the carrier. In this way a high throughput of banknotes is possible.

These and other features of the invention are further elucidated with reference to the accompanying

drawings .

Figure 1 shows a top view of a device according to a first embodiment of the invention.

Figures 2A, 2B and 2C show the image obtained with the device according to figure 1, when using respectively the first light source, the second light source, and when

subtracting the images from figures 2A and 2B.

Figure 3 shows a device according to a second embodiment of the invention.

Figure 1 shows a first embodiment of a device 1 according to the invention. The device 1 comprises a carrier 2 with a banknote 3 on top of it. A monochromic camera 4 is arranged directed towards the banknote 3 at a 90 degrees angle to the face of the banknote 3. At respective angles a and ', light sources 5, 6 are arranged. Light emitted from these light sources 5, 6 may be captured by camera 4. The banknote 3 may be moved in direction 14.

Figure 2A shows a banknote 3 with creases 7, 8, 9, 10, 11, 12. In figure 2A, light source 6 was turned on and light source 5 was turned off, resulting in shadows 7a, 8a, 9a, 10a, 11a and 12a to the right. In figure 2B, light source 5 was turned on and light source 6 was turned off, resulting in shadows 7b, 8b, 9b, 10b, lib, 12b to the left. When

subtracting both images, as shown in figure 2C, the creases 7, 8, 9, 10, 11, 12 may be assessed purely, without the image printed on the banknote 3. The capture may for instance be distributed in segments 13a-i for further assessment.

Figure 3 shows another device 20 according to the invention. The device 20 comprises a carrier 21, with a semicircle shaped shell 22 facing the banknote 23 arranged in the carrier 21. The shell 22 has a first half (A) with light sources (LEDs transmitting white light) 24, 25, 26, 27, 28, 29, 30, 31, arranged at β-angles of 20, 30, 40, 50, 60, 70, 80 and approximately 90 degrees respectively. The shell also has a second half (B) with phototransistors 32, 33, 34, 35, 36, 37, 38, 39, arranged at γ-angles of 20, 30, 40, 50, 60, 70, 80 and approximately 90 degrees respectively. The banknote 23 may be moved in direction 40.

Claims

1. Method for testing banknote quality, comprising the steps of :

- providing a banknote;

- in a first analysis step, projecting light with a light source under an angle of incidence onto one of the faces of the banknote and capturing at an angle of detection with a detector the light projected, different from the angle of incidence;

2. Method according to claim 1, wherein the angles of incidence and the angles of detection are within the same plane, which plane is perpendicular to the one face of the banknote, and preferably parallel to the longitudinal

direction of the banknote.

3. Method according to claim 1 or 2, wherein the detector comprises a camera, directed towards the one side of the banknote, which camera is at a fixed position during the first and second analysis step, wherein the angle of incidence is smaller than 90 degrees in the first analysis step and larger than 90 degrees in the second analysis step.

4. Method according to claim 3, wherein the light source comprises a light source of green light, such as light with a wave length of approximately 525 nm, or a light source of infrared light.

5. Method according to claim 3 or 4, wherein the step of comparing comprises the step of subtracting the captured detected light made in the first and the second analysis step to obtain a subtracted photo with creases and plain surfaces.

6. Method according to claim 5, wherein the comparing step comprises the step of quantifying the number or surface area of the plain surfaces of the banknote from the subtracted photo.

7. Method according to claim 1 or 2, wherein the projected light is detected by at least one phototransistor , arranged at different angles of detection relative to the one face of the banknote in the first and second analysis step, wherein the comparison step comprises the steps of:

- calculating the differences between values detected in the at least one phototransistor;

- correlating the calculating the differences to obtain a crease factor.

8. Method according to claim 7, wherein the method comprises the steps of:

- carrying out the method on a banknote to be tested; and

- comparing the crease factor from the reference banknote with the crease factor from the banknote to be tested.

9. Method according to any of the preceding claims, comprising, after the first and second analysis steps, the steps of : - moving the banknote over a predetermined distance in the longitudinal direction of the banknote; and

- after moving the banknote, repeating the first and second analysis steps.

10. Method according to any of the preceding claims, wherein the banknote is a polymer banknote.

11. Device for testing banknote quality, comprising:

- a carrier, for carrying a banknote;

12. Device according to claim 11, wherein the detector comprises a camera, directed towards the carrier, which camera at a fixed position, wherein the light sources comprise a first light source arranged at an angle of

13. Device according to claim 11, wherein the device comprises a frame with a semicircle-shape and a radius, with a row of light sources arranged along the first half of the semicircle-shape, and wherein the at least one detector comprises a row of phototransistors , arranged along the opposing second half of the semicircle-shape, wherein the centre of the semicircle-shape is arranged at or near the carrier .

14. Device according to any of the claims 11 to 13, wherein the device comprises feeding means, for feeding banknotes towards and from the carrier.