EP3614349B1 - Method for inspecting the surface of coins - Google Patents

Description

The invention relates to a method for checking the surface of coins for contamination, in particular due to chemical processes according to patent claim 1.

Coin processing and coin counting machines are known from the prior art which are technically capable of detecting forgeries. For this purpose, geometric and physical, eg electromagnetic, properties of the coins are determined so that counterfeit coins can be detected based on deviations from specified geometric or physical parameters. Due to the EU regulation no. 1210/2010 of the European Parliament of December 15, 2010 EU member states are free to refuse reimbursement for unfit euro coins that have been altered either willfully or by a process which could reasonably be expected to alter the design of the coin. Such non-refundable coins, which are clearly recognizable by their visual appearance, are however accepted by the coin processing machines known from the prior art. The DE 102 22 771 A1 and DE 10 2009 020497 A1 disclose methods of inspecting coins in which profiles of reflected light are recorded and their properties used to inspect the coins.

The object of the invention is therefore to provide a remedy in this regard and to provide a method that automatically detects optically altered or soiled coins.

• eine zu untersuchende Münze relativ zu einem optischen Aufnahmegerät derart bewegt wird, dass sich Bereiche der Oberfläche des Münzbilds im Aufnahmebereich des Aufnahmegeräts befinden,
• während der Bewegung der zu untersuchenden Münze mit dem optischen Aufnahmegerät entlang zumindest eines Oberflächenbereichs und während dieser Zeit Oberflächenpunkte des Münzbilds in zumindest zwei optischen Wellenlängenbereichen aufgenommen werden, wobei derart für jeden der Wellenlängenbereiche jeweils ein Profil erstellt wird, das die Reflexion in dem betreffenden Wellenlängenbereich für eine Anzahl von zeitlich aufeinander folgenden Aufnahmen darstellt, die vom Münzbild der zu untersuchenden Münze während ihrer Bewegung erstellt wurden,
• vorab zumindest ein Referenzprofil einer Referenzmünze aufgenommen und zur Verfügung gehalten wird, das derart zentriert ist, dass die Mitte des im Aufnahmebereich des Aufnahmegeräts erfassten Münzbilds der Mitte des erstellten Referenzprofils entspricht, und das derart gestreckt oder gestaucht ist, dass die Breite des erfassten Münzbilds im erstellten Referenzprofil einer vorgegebenen Standardbreite entspricht,
• das erstellte Profil der zu untersuchenden Münze derart verschoben und gestreckt oder gestaucht wird, dass die Mitte des erfassten Münzbilds der zu untersuchenden Münze in der Mitte des erstellten Profils liegt und dass die Breite des erfassten Münzbilds im erstellten Profil der vorgegebenen Standardbreite entspricht,
• das erstellte Profil der zu untersuchenden Münze mit dem zumindest einen Referenzprofil der Referenzmünze verglichen und ein diesbezüglicher Übereinstimmungsmaßwert ermittelt wird, und
• eine Verschmutzung festgestellt wird, wenn der ermittelte Übereinstimmungsmaßwert eine einen vorgegebenen Schwellenwert unterschreitende Übereinstimmung indiziert.

The invention solves this problem with a method for checking the surface of coins for contamination, in particular due to chemical processes, with the features of patent claim 1. According to the invention it is provided that

• a coin to be examined is moved relative to an optical recording device in such a way that areas of the surface of the coin image are in the recording area of the recording device,
• during the movement of the coin to be examined with the optical recording device along at least one surface area and during this time surface points of the coin image are recorded in at least two optical wavelength ranges, with a profile being created for each of the wavelength ranges that reflects the reflection in the relevant wavelength range for represents a number of chronologically consecutive recordings that were made of the coin image of the coin to be examined during its movement,
• at least one reference profile of a reference coin is recorded and made available in advance, which is centered in such a way that the center of the coin image recorded in the recording area of the recording device corresponds to the center of the reference profile created, and which is stretched or compressed in such a way that the width of the recorded coin image created reference profile corresponds to a specified standard width,
• the created profile of the coin to be examined is shifted and stretched or compressed in such a way that the center of the recorded coin image of the coin to be examined lies in the center of the created profile and that the width of the recorded coin image in the created profile corresponds to the specified standard width,
• the created profile of the coin to be examined is compared with the at least one reference profile of the reference coin and a corresponding measure of conformity is determined, and
• contamination is detected when the ascertained degree of conformity indicates a conformity that falls below a predetermined threshold value.

Such a check of coins for contamination using reflection profiles recorded in different optical wavelength ranges offers the advantage compared to checking using image processing algorithms that less computing effort is required and the hardware costs for the implementation of such a comparison method are significantly lower. A further advantage of the method according to the invention is that, in contrast to an image processing method using a coin image comparison, different motifs of coins of the same denomination do not have to be taken into account.

A particularly reliable detection of dirty coins can be ensured if surface points of the coin image are recorded along a predetermined number of surface areas of the coin to be examined in at least two optical wavelength ranges, with a profile being created for each of the wavelength ranges for each of the surface areas. In this way it is possible to record measurement profiles from a number of surface areas or tracks for each coin and to compare them with the reference profile, so that soiled coins are reliably detected.

In order to reliably detect soiling of the coin image in different colors, it can be provided that each profile created for a coin to be examined comprises a plurality of individual color profiles, with each of the individual color profiles being recordings of the Includes surface points of the same surface area of each coin to be examined. In this way, for example, individual color profiles are created in the red, green or blue spectral range for each surface area or each track, which can be compared with the reference profile so that colored soiling can also be detected easily and reliably.

A particularly low level of processing effort when checking the coin to be examined is ensured if an uncontaminated coin is specified as the reference coin and contamination is detected in the coin to be examined if the match value determined for the created profile of the coin to be examined indicates a deviation from the reference profile that exceeds the specified threshold.

• eine Anzahl von Referenzprofilen für mehrere unterschiedliche Arten von Referenzmünzen vorgegeben wird, wobei die Referenzmünzen insbesondere eine oder mehrere unverschmutzte und eine oder mehrere auf unterschiedliche Weise verschmutzte Referenzmünzen umfassen,
• das für die zu untersuchende Münze erstellte Profil mit jedem der Referenzprofile verglichen wird und derart jeweils ein Übereinstimmungsmaßwert für jedes der Referenzprofile erhalten wird, und
• die zu untersuchende Münze als unverschmutzt oder verschmutzt erkannt wird, wenn aufgrund des jeweiligen Übereinstimmungsmaßwerts eine Übereinstimmung mit einem der Referenzprofile der Referenzmünzen ermittelt wird.

A particularly reliable detection of coins soiled in different ways can be ensured if

• a number of reference profiles is specified for several different types of reference coins, the reference coins in particular comprising one or more uncontaminated and one or more reference coins contaminated in different ways,
• the profile established for the coin to be examined is compared with each of the reference profiles and in this way a corresponding score is obtained for each of the reference profiles, and
• the coin to be examined is recognized as clean or dirty if a match with one of the reference profiles of the reference coins is determined on the basis of the respective match measure value.

By comparing the profile created for the coin to be examined with reference profiles of different types of reference coins, it is ensured that soiling of the most varied types is detected on the coin to be examined.

A further improvement in the detection of soiled coins can be achieved if a reference profile is used for each type of reference coin, which includes a number of coin type reference profiles created for such reference coins, with the coin type reference profiles each being individually centered and stretched or compressed, and when the profile created for the coin to be examined is compared with each individual coin type reference profile and a corresponding match measure value is determined for each of the coin type reference profiles.

This ensures that for each type of reference coin or for each type of soiling, several coin type reference profiles are available, in which, for example, different degrees of soiling for the same type of soiling of the coin image are covered, so that soiling of the coin to be examined is reliable is recognized.

For reliable detection of different types of contamination in a coin to be examined, it can also be provided that each reference profile comprises a plurality of individual reference color profiles, with each of the individual reference color profiles comprising recordings of the surface points of the same surface area of the respective reference coin taken in different wavelength ranges. In this way it is possible to compare individual color profiles determined for a coin to be examined with the corresponding individual reference color profiles of the respective spectral range and thus to reliably detect contamination.

In order to ensure a mathematically simple comparison of the profile determined for the coin to be examined with the reference profile, it can be provided that, in order to determine the measure of conformity value when comparing the at least one profile created for the coin to be examined with the at least one reference profile, a measure of similarity, in particular the cross-correlation or the sum of the squared deviations or the sum of the absolute deviations, is calculated and/or a comparison based on a feature extraction is carried out.

In order to prevent coins that are soiled in any way from being found to be free of defects with the greatest possible certainty, it can be provided that, if profiles are available for a number of surface areas of the coin to be examined, when comparing the for the coin to be examined created profile with the at least one reference profile, contamination is already detected in the coin to be examined if the degree of conformity determined for the profile of a single surface area indicates contamination.

In order not to have to compare the profile created for the coin to be examined with all available reference profiles, it can be provided that the denomination of the coin to be examined is determined and the at least one reference profile is selected on the basis of the denomination determined. It is like that possible to limit the comparison to reference profiles available for the identified denomination, thereby minimizing the computational effort associated with the comparison.

In order to prevent profiles from being created although no area of the coin image of the coin to be examined is in the recording area of the recording device during the movement of the coin to be examined, it can be provided that the recording of predetermined surface areas with the optical recording device is deactivated if the detected denomination indicates that surface areas of the coin to be examined are outside the recording area of the recording device.

This avoids creating profiles that only include background readings that are captured without having areas of a coin's coin image in the capture area.

• für jede Münzseite der zu untersuchenden Münze für zumindest einen Oberflächenbereich Oberflächenpunkte des Münzbilds in zumindest zwei optischen Wellenlängenbereichen aufgenommen werden, wobei derart für jeden der Wellenlängenbereiche jeweils ein Profil erstellt wird,
• das für die zweite Münzseite erstellte Profil zentriert und gestreckt oder gestaucht wird, sodass die Mitte des erfassten Münzbilds in der Mitte des erstellten Profils liegt und dass die Breite des erfassten Münzbilds im erstellten Profil der vorgegebenen Standardbreite entspricht, und
• das zumindest eine für die zweite Münzseite erstellte Profil mit zumindest einem Referenzprofil verglichen wird und ein diesbezüglicher Übereinstimmungsmaßwert ermittelt wird.

For the particularly reliable detection of soiling in a coin to be examined, it can also be provided that

• for each coin side of the coin to be examined, surface points of the coin image are recorded in at least two optical wavelength ranges for at least one surface area, with a profile being created for each of the wavelength ranges in this way,
• the profile generated for the second face of the coin is centered and stretched or squashed so that the center of the captured coin image is at the center of the generated profile and the width of the captured coin image in the generated profile is the specified standard width, and
• the at least one profile created for the second side of the coin is compared with at least one reference profile and a corresponding degree of conformity is determined.

This ensures that contamination that is only on one side of the coin to be examined is reliably detected, since both sides of the coin to be examined are recorded.

In order to minimize the computing effort when processing the created profiles when both coin sides of a coin to be examined are checked, it can be provided that the at least one profile created for the second coin side is compared to the same reference profile as the profile created for the first side of the coin and/or that the at least one profile created for the second side of the coin to be examined according to the centering and/or stretching or compression that for the corresponding profile created for the first side of the coin were determined, is centered and/or stretched or compressed.

In this way, the centering or stretching or compression that was determined for the corresponding profile of the first side of the coin can be adopted for the profile created for the second side of the coin.

In order to correct, for example, changing lighting conditions or measured value inaccuracies caused by the recording device when creating the profiles, it can be provided that the device drift of the optical recording device is carried out using the brightness value that is determined without the coin to be examined and the device drift determined in this way for correction of the profile created for the coin to be examined.

In order to be able to use the method according to the invention, for example, with existing coin processing devices, it can be provided that the movement of the coin to be examined is effected relative to the optical recording device by the coin to be examined rolling along an inclined plane or, in particular, on a conveyor belt or belt , is promoted or transported along a free-flight route past the optical recording device.

Since the method according to the invention is insensitive to the type of transport that leads to the movement of the coin to be examined relative to the recording device, the method according to the invention can be implemented easily in a large number of known coin processing devices.

In order to only start recording surface points of the coin image when a coin to be examined is actually located in the recording area of the recording device, it can be provided that the point in time is determined, in particular by a trigger unit arranged directly in front of the recording area of the recording device, at which the coin to be examined enters the recording area and the comparison of the at least one profile created for the coin to be examined with the at least one reference profile is carried out a predetermined time interval after the detection of entry into the recording area. In this way it is avoided that the profiles created contain a large number of background readings, which do not contain information about the reflections of the coin design.

Further advantages and refinements of the invention result from the description and the accompanying drawings.

In the following, the invention is shown schematically in the drawings using particularly advantageous, but non-limiting, exemplary embodiments and is described by way of example with reference to the drawings.

• Fig. 1 eine Anordnung zur Durchführung eines erfindungsgemäßen Verfahrens mit einem Aufnahmegerät 20 mit einem Detektor 2,
• Fig. 2 eine alternative Anordnung zur Durchführung eines erfindungsgemäßen Verfahrens mit einem Aufnahmegerät mit drei Detektoren zu Aufnahme von drei Spuren bzw. Oberflächenbereichen,
• Fig. 3a zeigt die während des Abrollens einer 2-Euro-Münze aufgenommenen Oberflächenpunkte des Münzbilds eines Oberflächenbereichs,
• Fig. 3b die die während einer linearen Bewegung aufgenommenen Oberflächenpunkte des Münzbilds eines Oberflächenbereichs einer 2-Euro-Münze,
• Fig. 4a den Verlauf dreier Oberflächenbereiche, entlang denen Oberflächenpunkte des Münzbilds aufgenommen wurden, während einer rollenden Bewegung,
• Fig. 4b den Verlauf dreier Oberflächenbereiche, die während einer linearen Bewegung der Münze aufgenommen wurden,
• Fig. 5 beispielhaft ein Referenzprofil und ein ermitteltes Profil mit jeweils drei Einzelreferenzfarbprofilen bzw. Einzelfarbprofilen,
• Fig. 6 beispielhaft für drei Oberflächenbereiche einer zu untersuchenden Münze ermittelte Profile und zwei Referenzprofile,
• Fig. 7 beispielhaft drei Münzart-Referenzprofile und drei ermittelte Profile,
• Fig. 8 ein Beispiel für die Ermittlung des Übereinstimmungsmaßwerts mit Hilfe einer Merkmalsextraktion.

Show below:

• 1 an arrangement for carrying out a method according to the invention with a recording device 20 with a detector 2,
• 2 an alternative arrangement for carrying out a method according to the invention with a recording device with three detectors for recording three tracks or surface areas,
• Figure 3a shows the surface points of the coin image of a surface area recorded during the rolling of a 2 euro coin,
• Figure 3b the surface points of the coin image recorded during a linear movement of a surface area of a 2-euro coin,
• Figure 4a the course of three surface areas along which surface points of the coin image were recorded during a rolling movement,
• Figure 4b the course of three surface areas that were recorded during a linear movement of the coin,
• figure 5 as an example a reference profile and a determined profile, each with three individual reference color profiles or individual color profiles,
• 6 profiles determined as an example for three surface areas of a coin to be examined and two reference profiles,
• 7 exemplarily three coin type reference profiles and three determined profiles,
• 8 an example for the determination of the measure of conformity with the help of a feature extraction.

1 shows a first example of an arrangement for carrying out a method according to the invention for checking the surface of coins for soiling. Such an arrangement can be integrated, for example, in a coin counting or coin sorting machine known from the prior art or subsequently in a Such a coin counting machine can be installed. The arrangement comprises an optical image recording device 20, which in the exemplary embodiment shown has a color sensor 2, a processing unit 4, a trigger unit 5, for example a light barrier, and four lighting elements 3, which in the exemplary embodiment are each monochrome, for example white, light-emitting diodes. includes. The lighting elements 3 are selected in such a way that the most diffuse illumination possible is ensured, since the metallic surface of clean coins reflects strongly, while the reflectivity of the surface of dirty coins is correspondingly reduced. The arrangement also includes an optional ejection unit 6, which is controlled by the processing unit 4 and ejects coins that have been recognized as non-refundable or soiled.

With the method described below, soiled coins can advantageously be recognized in a wide variety of ways. The soiling of the coins can be, for example, complete or partial discoloration of the coin image. Another known type of contamination is, for example, that the design of the coins is at least partially covered by patterns or images or has been changed or partially removed by chemical processes, mechanical action or heat treatment.

As a first step of the method according to the invention, in the exemplary embodiment in 1 During the movement of the coin 1 to be examined past the optical recording device 20, surface points of the coin image 10 are recorded with the recording device 20 along a surface region O of the coin 1 to be examined in at least two optical wavelength ranges.

In the exemplary embodiment shown, the coin 1 to be examined rolls or slides, driven by gravity, along an inclined plane, in the exemplary embodiment a rail, and in the process passes the recording area of the optical recording device 20. The at least partially rolling movement that causes the Coin 1 is carried out, surface points of the coin image 10 or the surface color of the coin image 10 are recorded by the recording device 20 between the times t ₀ and t _e , which are located along a curve on the surface of the coin 1 to be examined, as is shown in Figure 3a is shown. In this case, a surface area O of the coin 1 to be examined is detected along the lying S-shaped curve, which extends along the entire coin image 10 . This means that at Bimetallic coins both surface points located on the ring and on the pill are included.

Alternatively, the movement of the coin 1 to be examined relative to the optical recording device can also be effected, for example, by linearly conveying the coin 1 to be examined on a conveyor belt or belt or by transporting it past the optical recording device 20 along a free flight path. An example of the surface area O recorded between the times t ₀ and t _e of a coin 1 to be examined that is transported linearly past the recording device 20 is shown in FIG Figure 3b shown.

In order to start the recording of the surface points in a targeted manner when the coin 1 to be examined enters the recording area of the recording device 20, and to start further processing of the determined data at a predetermined time interval, a light barrier is provided in the exemplary embodiment shown, which is located immediately before the Recording area of the recording device 20 is arranged and detects the point in time at which the coin to be examined 1 enters the recording area of the recording device 20 . In this case, the light barrier provides a signal that starts the recording of surface points of the coin 1 to be examined and triggers further processing of the recorded data at a predetermined time interval after detection.

However, such a light barrier is by no means absolutely necessary for carrying out a method according to the invention. As an alternative to this, the recording device 20 can also create continuous recordings, with the aid of signal processing algorithms then being used to determine those recordings which contain the reflections from surface points of the coin image 10 of a coin 1 to be examined.

In the exemplary embodiment shown, the color sensor 2 of the recording device 20 is 1 around a photodiode field, each of which is equipped with a red, green or blue filter. As an alternative to this, the arrangement for carrying out a method according to the invention can also comprise an unfiltered photodiode as the color sensor 2, for example. When recording with such a recording device 20, a signal is obtained as the measurement result, the signal value of which is proportional to the brightness at the respective color wavelength. The lighting fixtures 3 are in the exemplary embodiment shown, there are four white light-emitting diodes, which ensure the most diffuse possible illumination of the recording area.

From the surface points of the coin image 10 recorded in at least two optical wavelength ranges, as described above, a profile P is created for each of the wavelength ranges, which represents the reflection that the recorded surface points have in the relevant wavelength range for a number of successive recordings .

When creating the profile P, the device drift of the optical recording device 20 can also be taken into account by using the brightness value, which is determined without coin 1 to be examined, for a correction of the profile P.

For example, a single profile P for a surface area O of the coin 1 to be examined can be created if the color sensor 2 of the recording device 20 registers the reflections of the recorded surface points of the coin image 10 unfiltered. Alternatively, the recording device 20 can also include a color sensor 2 with photodetector groups for the red, green or blue spectral range, so that while the coin 1 to be examined is transported through the recording area of the recording device 20, surface points of the coin image 10 are recorded in several different wavelength ranges , so that for each recorded surface area O of the coin image 10 individual color profiles PF _r , PF _g , PF _b can be created, for example for the red, green and blue spectral range. Optionally, a brightness measurement can be carried out if the recording device 20 includes an unfiltered detector group.

_{In _ _} figure 5 shown. In order to subsequently determine whether the coin 1 to be examined has soiling, the created profile P or possibly the three individual color profiles PF _r , PF ₉ , PF _b of the profile P are compared with at least one reference profile R of a reference coin.

For this comparison, at least one reference profile R of a reference coin is recorded in advance and stored and made available in the processing unit 4, for example. For example, an uncontaminated coin can be specified as a reference coin, in which the coin image is neither discolored nor, for example, changed by the influence of heat or chemical substances. Examples of the profiles created for a clean or unpolluted 2 euro coin are given in the Figures 5, 6 and 7 shown.

In the Figures 5, 6 and 7 the x-axis shows the resolution in mm scaled with the measurement resolution r [mm/r] and the y-axis shows the degree of reflection [RG] in the respective spectral range. The temporal resolution (horizontal axis) of the Figures 5, 6 and 7 The profile P or reference profile R shown results from the minimum achievable time for the read or write processes of the processing unit used. The vertical axis is the frequency measured, ie indirectly proportional to the color value. If, for example, a complete RGB measurement is possible every t=0.2 ms, a coin speed of approx. v=1.4 m/s results in a resolution r on the coin of r = v t = 1.4 · 0.2 ≈ 0.3 mm.

For good comparability of the at least one reference profile R with the at least one profile P created for the coin 1 to be examined, the reference profile R is centered in such a way that the center of the coin image of the reference coin captured in the recording area of recording device 20 corresponds to the center of the reference profile R created. Furthermore, the reference profile R is stretched or compressed in such a way that the width of the recorded coin image in the created reference profile R corresponds to a specified standard width. Finally, the reference profile R recorded and processed in this way is kept available for the method according to the invention.

The created profile P of the coin 1 to be examined is also shifted and stretched or compressed in such a way that the center of the detected coin image 10 of the coin 1 to be examined lies in the center of the profile P created. Furthermore, the width of the detected coin image 10 is stretched or compressed in such a way that it corresponds to the specified standard width in the profile P created. This centering or stretching or compression of the profiles P has the advantageous effect that the different widths of the profiles P caused by the different rolling or sliding speeds of the coins 1 to be examined are unified or the center of the profile P created is aligned with the center of the measuring points on the coin 1 to be examined is brought into agreement.

, c=1,...,N, wobei N die Länge des gesamten Profils ist.In order to bring the reference profile R or the determined profile P to the specified standard width, a linear interpolation is carried out between the reflections recorded for the individual surface points. Centering the determined Profile P or the reference profile R takes place by forming the cumulative sum and shifting the relevant profile P or reference profile R from the center position H of the shifted profile to the central profile center position at N /2. The position H of the shifted profile is given by the position of half the total sum of the individual measured values in a profile and is calculated by $H={\mathrm{argmin}}_c\left({\displaystyle {\sum }_{i=1}^{c}x>{\displaystyle {\sum }_{i=1}^{N}x/2}}\right)$

, c=1,...,N, where N is the length of the entire profile.

wobei T die Anzahl Trainingsprofile w₁, ...w_T, d.h. der Referenzprofile R, ist. Die Weite w eines Profils P berechnet sich aus w = b - a, a = argmin _i (x(i) > B), b = argmax _i (x(i) > B), i=1,...N, wobei B ein Schwellwert ist.The stretching or compression is determined for a training set, for example for the previously examined reference coins. In this case, for example, the denomination is determined for each reference coin using the known examination methods for determining the denomination on the basis of geometric or physical parameters, and an average width is determined for each denomination examined w determined and the stretching or compression on the width w adjusted. The average width is given by $\bar{w}={\displaystyle {\sum }_{i=1}^T{w}_i/\mathrm{T}}$

where T is the number of training profiles w ₁ , . . . w _T , ie the reference profiles R. The width w of a profile P is calculated from w = b - a , a = argmin _i ( x ( i ) > B ), b = argmax _i ( x ( i ) > B ), i=1,...N, where B is a threshold.

The width w of the coin profile can be estimated, for example, by measuring the speed, for which purpose, for example, a second trigger unit 5 or a light barrier that is installed in front of the recording device 20 can be used. From the time difference between passing the first and the second light barrier, the speed of the coin 1 to be examined can be calculated and the stretching or compression to be used can be deduced. The stretching or compression by the factor w / w is then carried out, for example, by interpolation between the individual points of the profile P created Width or coin width can be determined.

If the profile P created for the coin 1 to be examined is now preprocessed in this way, the profile created is compared with the at least one reference profile R of the reference coin that is kept available, and a relevant correspondence measure value is determined. If this determined measure of conformity value If a match with the reference coin that falls below a predetermined threshold value is indicated, contamination is detected in the coin 1 to be examined.

If, for example, the profile P created for a soiled coin 1 to be examined is compared with the reference profile R created for an unpolluted or clean reference coin and a corresponding measure of conformity is determined, contamination is found in the coin 1 to be examined if, for example, the profile created for the P determined degree of conformity value indicates a deviation from the reference profile R that exceeds the predetermined threshold value. This means that the correspondence transmitted for a soiled coin 1 to be examined is so low that the determined degree of conformity falls below the predetermined threshold value.

If this is the case, the processing unit 4 can determine, for example, that the coin 1 to be examined is too dirty. The result is a signal that is either sent to the existing machine control or, for example, controls a lifting magnet for coin ejection. The coin is rejected and ejected again, for example via a mechanical ejection unit 6 which is controlled by the processing unit 4 . Furthermore, other measured values, e.g. color measured values, can optionally be transmitted to the machine control.

As already described above for the profile P determined for the coin 1 to be examined, such a reference profile R created for a reference coin can also include several individual color reference profiles RF _r , RF _g , RF _b , for example in the red, green and blue spectral range. Such a reference profile R with three individual color reference profiles RF _r , RF _g , RF _b is in figure 5 shown schematically. The individual reference color profiles RF _r , RF _g , RF _b of the reference profile R include the recordings of the same surface points of the coin image or the same surface area of the coin image of the reference coin taken in different frequency and/or wavelength ranges. If individual color profiles PF _r , PF _g , PF _b are available for the profile P determined for the coin 1 to be examined, these are compared with the individual reference color profiles RF _r , RF _g , RF _b corresponding to the respective spectral range and a corresponding measure of correspondence value is determined for each spectral range .

As in 2 is shown, instead of a recording device 20 with a color sensor 2, an arrangement for carrying out a method according to the invention can also be a recording device 20 with a plurality of color sensors 2a, 2b, 2c, which are designed, for example, as photodiodes with a red, green or blue filter or unfiltered are, include. As in 2 As can be seen, the structure of the arrangement for carrying out the method according to the invention is otherwise the same as in 1 with four lighting bodies 3, a processing unit 4 and a trigger unit 5, which is a light barrier. At the in 2 shown arrangement, the recording area of the recording device 20 is larger than in FIG 1 illustrated recording device 20 with a single color sensor 2, so that a larger area of the coin image 10 of the coin to be examined 1 can be detected while it rolls past the recording device 20 or is moved past.

If a coin 1 to be examined is moved past a recording device 20 constructed in this way, surface points of the coin image are recorded in at least two optical wavelength ranges along three surface areas O ₁ , O ₂ , O ₃ . _{In _ _} Figure 4a shown. Figure 4b shows three such surface areas O ₁ , O ₂ , O ₃ , which were recorded during a linear movement of the 2-euro coin 1a past the recording device 20 .

A profile P ₁ , P ₂ , _{P 3 is} created for each of the wavelength ranges for each of the surface areas O ₁ , O ₂ , O 3 . An example of three such profiles P ₁ , P ₂ , P ₃ , which are used for the in Figure 4a surface areas shown were determined on the 2 euro coin 1a is in 6 shown. At the in 6 The profiles P ₁ , P ₂ , P ₃ shown are the reflections of the surface areas O ₁ , O ₂ , O ₃ in the green color range. As previously mentioned, such profiles P ₁ , P ₂ , P ₃ can each also include a plurality of individual color profiles PF _r , PF ₉ , PF _b , which each reflect the reflections of the surface points of the respective surface areas O ₁ , O ₂ , O ₃ in different frequency and/or include wavelength ranges. The individual reference profiles RF are each individually centered and stretched or compressed.

In addition or as an alternative to this, surface points along one or more surface areas O ₁ , O ₂ , O ₃ can also be recorded for each coin side of a coin 1 to be examined and profiles P can be created. The centering and / or Stretching or compression determined for the profile P corresponding to the same surface area O ₁ , O ₂ , O ₃ on the first side of the coin can advantageously be adopted.

In the case of a recording device 20 with a plurality of color sensors 2a, 2b, 2c, for example when coins with a small diameter, such as the one in 2 1 cent coin 1b shown, are examined, it may be the case that one of the color sensors 2a, 2b, 2c would only record background values if the coin 1b to be examined moves past it, since no area of the coin image 10b is in its recording area located. Therefore, the recording of predetermined surface areas O ₁ , O ₂ , O ₃ with the optical recording device 20 can optionally be deactivated.

In a known coin counting device, for example, this can be linked to the previously performed determination of the denomination, so that the available denomination of the coin to be examined is accessed and, if the determined denomination indicates that surface areas of the coin to be examined are outside the recording area of the recording device 20 are located, this surface area is inactivated.

If a profile P ₁ , P ₂ , P ₃ is created for a plurality of surface areas O ₁ , O ₂ , O ₃ comprising two or more individual color profiles PF _r , PF _g , PF _b in this way, this is, as described above, with the at least a reference profile R, which was created for a reference coin and is kept available, for example, in the processing unit 4, and a corresponding measure of correspondence value is determined. When selecting the reference profile R to be used for the comparison, the determined denomination can advantageously also be used in order to select the at least one reference profile R based on the determined denomination and thus to avoid a more extensive, more complex comparison.

As an alternative or in addition to the individual reference color profiles RF _r , RF _g , RF _b described above, each reference profile R can also include several individual reference profiles R ₁ , R ₂ created for different surface areas of the respective reference coin, which record the surface points of different surface areas O ₁ , O ₂ , O ₃ of the respective reference coin, as stated in 6 is shown. The reference profiles R ₁ , R ₂ are each individually centered and stretched or compressed.

In a method according to the invention, a number of reference profiles R can also be specified for a number of different types of reference coins. The reference coins include, for example, one or more unpolluted reference coins and one or more reference coins soiled in different ways. This advantageously ensures that a wide variety of types of soiled coins are stored in order to compare them with the coin 1 to be examined. The types of soiling can be, for example, complete discoloration or discoloration affecting only certain areas of the coin design. Coins can also be used as reference coins, for example, in which the coin image is at least partially covered, for example by patterns or images, or has been modified or partially removed by chemical processes, mechanical deformation or heat treatment.

The profile P created for the coin to be examined is compared with each of these coin type reference profiles RM ₁ , RM ₂ , RM ₃ (see 7 ) are compared and in this way a measure of conformity is determined for each of the reference profiles RM ₁ , RM ₂ , RM ₃ . Each of these coin type reference profiles RM _1; As previously described, RM ₂ , RM ₃ can also include individual reference profiles for different surface areas O ₁ , O ₂ , O ₃ of the same reference coin or individual color reference profiles of the same surface area O ₁ , O ₂ , O ₃ for different spectral areas.

Each coin type reference profile RM _1; RM ₂ , RM ₃ each also comprise a number of reference profiles made for different reference coins soiled in the same way, each individually centered and stretched or compressed. Thus, for each type of soiling, there are advantageously several coin type reference profiles RM _1; RM ₂ , RM ₃ are available, so that the coin 1 to be examined can be compared not only with different types of reference coins, but also with a number of coin type reference profiles RM, each of which represents the same type of soiling.

If the profile P created for a soiled coin 1 to be examined is compared with the coin type reference profiles RM ₁ , RM ₂ , RM ₃ created for reference coins soiled in different ways, a relevant correspondence measure value for each of the coin type reference profiles RM _1; RM ₂ , RM ₃ determined, if necessary also for several surface areas O ₁ , O ₂ , O ₃ or spectral areas of the same coin 1 to be examined. It is sufficient for the determination of contamination if the profile P ₁ , P ₂ , P ₃ of a single of the surface areas O ₁ , O ₂ , O ₃ indicates contamination, as is shown in 7 is shown. In 7 only the profile P ₁ of the surface area O ₁ indicates a match with the coin type reference profile RM ₃ of a soiled reference coin, while the other two profiles P ₂ , P ₃ of the surface areas O ₂ , O ₃ indicate no soiling.

, mit k = 0,..N - 1, wobei N die Profillänge bezeichnet.The comparison of the profile P created for the coin 1 to be examined with the at least one reference profile R can be carried out, for example, by means of a calculated cross-correlation C of the measured profiles P with a set of reference profiles {R} of clean and dirty coins in the three color channels f = { r , g ,b } where RF is a reference profile from the set of all reference profiles. The cross-correlation for a displacement of k measurement points of a profile in the color channel f, where f = { r,g,b }, is given by $C_f\left(k\right)={\displaystyle {\sum }_{n=1}^N{x}_f\left(n\right)\cdot y_f\left(\left(n+k\right)\mathrm{model}N\right)}$

, with k = 0,.. N - 1, where N denotes the profile length.

The shift between the profile P created for the coin 1 to be examined and the reference profile R results from s = argmax _k C _g ( k ), k=0,...,N-1.

Messpunkte, wobei D _2€ der Durchmesser der größten zu untersuchenden Münze 1, beispielsweise der 2-Euro-Münze, ist. Der Parameter r bezeichnet die Auflösung, z.B. r=0.3mm, und der Faktor 2 in der Formel gewährleistet, dass die Münze vollständig im Aufnahmebereich bzw. im Profil enthalten ist.The profile length N is typically given by

Measuring points, where D _2€ is the diameter of the largest coin 1 to be examined, for example the 2 euro coin. The parameter r denotes the resolution, eg r=0.3mm, and the factor 2 in the formula ensures that the coin is completely contained in the receiving area or profile.

The total cross-correlation CC is then CC = _Cr ( s ) + _Cg ( s ) + _Cb ( s ).

The cross-correlation is thus determined between the profile P created for the coin 1 to be examined and the set of reference profiles R which, for example, reference profiles R are stored in the processing unit 4 . If the measure of conformity between the profile P created for the coin 1 to be examined and the set of reference profiles R has been determined, the class clean or dirty is assigned to the coin 1 to be examined in a classification step, for example, if the determined measure of conformity exceeds a predetermined threshold value, Correspondence, for example, with coin type reference profiles RM shows that indicate a complete recoloring of the coin image. Instead of the cross-correlation CC, for example, a quadratic or absolute deviation can also be calculated as a measure of similarity when determining the measure of conformity. Possible classifiers that are trained using reference profiles for clean and/or dirty coins are, for example, decision trees, neural networks, k-nearest neighbors, the k-means, - or a linear discriminant analysis.

. wobei die zentralen Mittelwerte, d.h. die mittleren Reflektionswerte in unterschiedlichen Wellenlängen im Bereich der Münze, aus zentrierten Profilen ermittelt werden. Die Länge der Mittelwertfilter ist 2m+1, wobei m entsprechend der Auflösung r und der Münzgröße zu wählen ist.As an alternative to this, a feature extraction can be carried out to determine the measure of conformity value. The profiles are centered and stretched or compressed and a feature vector is determined and compared with reference feature vectors. One possible feature vector is a triple of single color profile averages $f=\left(\begin{array}{ccc}{\displaystyle {\sum }_{n=N/2-m}^{N/2+m}{x}_{\mathrm{right}}\left(n\right)}& {\displaystyle {\sum }_{n=N/2-m}^{N/2+m}{x}_G\left(n\right)}& {\displaystyle {\sum }_{n=N/2-m}^{N/2+m}{x}_b\left(n\right)}\end{array}\right)$

. the central mean values, ie the mean reflection values in different wavelengths in the area of the coin, being determined from centered profiles. The length of the averaging filter is 2m+1, where m is to be chosen according to the resolution r and the coin size.

This feature vector is calculated for the reference profiles R and the profiles P established for the coins 1 to be examined and a classifier is applied. 8 shows examples of such feature vectors, represented in a feature space. The degrees of reflection RG for the green, red and blue spectral range are given on the x, y and z axes. Coins soiled in different ways are shown with a + as a symbol, while unpolluted coins are marked with an o as a symbol.

Alternatively, a classification can be performed, e.g. using decision trees, neural networks, k-nearest neighbors, k-means, or linear discriminant analysis, in which a differentiation function is determined that indicates whether a profile created for a coin 1 to be examined P, for example, matches the stored reference profile R of a clean or dirty reference coin.

Claims (16)

1. Method for inspecting the surface of coins (1) for contamination, particularly caused by chemical processes, wherein

   - a coin (1; 1a, 1b) is moved relative to an optical capturing device (20) such that regions of the surface of the coin design are located in the recording region of the capturing device (20),

   - during the movement of the coin (1; 1a, 1b) to be inspected with the optical capturing device (20) along at least one surface region (O; O₁, O₂, O₃) and during this time surface points of the coin design (10; 10a, 10b) are captured in at least two optical wavelength ranges, wherein in each case a profile (P; P₁, P₂, P₃) is set in such a manner for each of the wavelength ranges which represents the reflection in the wavelength range concerned for a number of images following one another temporally, which were made of the coin design (10; 10a, 10b) of the coin (1; 1a, 1b) to be inspected during its movement,

   - in advance at least one reference profile (R; R₁, R₂, R₃) of a reference coin is captured and kept available, which is centred such that the middle of the coin design captured in the capture region of the capturing device (20) corresponds to the middle of the created reference profile (R, R₁ R₂, R₃), and which is stretched or compressed such that the width of the captured coin image in the created reference profile (R, R₁ R₂, R₃, R4) corresponds to a predetermined standard width,

   - the created profile (P; P₁ P₂, P₃) of the coin (1; 1a, 1b) to be inspected is displaced and stretched or compressed such that the middle of the detected coin design (10; 10a, 10b) of the coin (1; 1a, 1b) to be inspected is situated in the middle of the created profile (P; P₁, P₂, P₃) and that the width of the captured coin image (10; 10a, 10b) in the created profile (P; P₁, P₂, P₃) corresponds to the predetermined standard width,

   - the created profile (P; P₁, P₂, P₃) of the coin (1; 1a, 1b) to be inspected is compared with the at least one reference profile (R; R₁, R₂, R₃, R4) of the reference coin and a consistency value in this respect is determined, and

   - a contamination is ascertained when the determined consistency value indicates a consistency which undershoots a predetermined threshold value.
2. Method according to claim 1, characterised in that from the coin to be inspected (1; 1a, 1b), respective surface points of the coin design (10; 10a, 10b) along a predetermined number of surface regions (O; O₁, O₂, O₃) are captured in at least two optical wavelength ranges, wherein thus in each case a profile (P; P₁, P₂, P₃) for each of the surface regions (O; O₁, O₂, O₃) is created for each of the wavelength ranges.
3. Method according to claim 1 or 2, characterised in that each created profile (P; P₁, P₂, P₃) of a coin (1; 1a, 1b) to be inspected comprises in each case several individual colour profiles (PF_r, PF_g, PF_b), wherein each of the individual colour profiles (PF_r, PF_g, PF_b) includes images of the surface points of the same surface region (O; O₁, O₂, O₃) of the respective coin (1; 1a, 1b) to be inspected which have been captured in respectively other wavelength ranges.
4. Method according to any of the preceding claims, characterised in that an uncontaminated coin is prespecified as a reference coin and a contamination is determined for the coin (1; 1a, 1b) to be inspected when the consistency value determined for the created profile P₁, P₂, P₃) of the coin (1; 1a, 1b) to be inspected indicates a deviation from the reference profile (R; R₁, R₂, R₃) which overshoots the predetermined threshold value.
5. Method according to any of the preceding claims, characterised in that

   - a number of reference profiles (R; R₁, R₂, R₃) is predetermined for several different types of reference coins, wherein the reference coins comprise in particular one or several reference coins which are uncontaminated and one or several reference coins which are contaminated in different ways,

   - the profile (P; P₁ P₂, P₃) created for the coin (1; 1a, 1b) to be inspected is compared with each of the reference profiles R; R₁, R₂, R₃) and thus in each case a consistency value is obtained for each of the reference profiles (R; R₁, R₂, R₃), and

   - the coin (1; 1a, 1b) to be inspected is recognised as uncontaminated or contaminated when on the basis of the respective consistency value a consistency with one of the reference profiles (R; R₁, R₂, R₃) of the reference coins is determined.
6. Method according to any of the preceding claims, characterised in that for each type of reference coin in each case one reference profile (R; R₁, R₂, R₃) is used which comprises a number of coin type reference profiles (RM) for reference coins of this sort, wherein the coin type reference profiles (RM) are in each case individually centred and stretched or compressed, and
   that the profile (P; P₁ P₂, P₃) created for the coin to be inspected is compared with each single coin type reference profile (RM) and a consistency value in this regard is determined for each of the coin type reference profiles (RM).
7. Method according to any of the preceding claims, characterised in that each reference profile (R; R₁, R₂, R₃)comprises in each case several individual reference colour profiles (RF_r, RF_g, RF_b), wherein each of the individual reference colour profiles (RF_r, RF_g, RF_b) includes images of the surface points of the same surface region of the respective reference coin captured in respectively different wavelength ranges.
8. Method according to any of the preceding claims, characterised in that for determining the consistency value when comparing the at least one profile (P; P₁ P₂, P₃) created for the coin (1; 1a, 1b) to be inspected with the at least one reference profile (R; R₁, R₂, R₃)a similarity value, in particular the cross-correlation or the sum of the quadratic deviations for the sum of the absolute deviations is calculated and/or a comparison is carried out based on a characteristic extraction.
9. Method according to any of the preceding claims, characterised in that if profiles (P; P₁ P₂, P₃) for a number of surface regions of the coin (1; 1a, 1b) to be inspected are available, when comparing the profile (P; P₁, P₂, P₃) created for the coin (1; 1a, 1b) to be inspected with the at least one reference profile (R; R₁ R₂, R₃) a contamination is determined in the case of the coin (1; 1a, 1b) to be inspected if the consistency value determined for the profile (P; P₁ P₂, P₃) of one single one of the surface regions indicates a contamination.
10. Method according to any of the preceding claims, characterised in that the denomination of the coin (1; 1a, 1b) to be inspected is determined and the at least one reference profile (R; R₁, R₂, R₃) is selected on the basis of the determined denomination.
11. Method according to claim 10, characterised in that the capture of predetermined surface regions with the optical capturing device (20) is deactivated when the determined denomination indicates that surface regions (O; O₁, O₂, O₃)of the coin (1; 1a, 1b) to be inspected are located outside capturing region of the capturing device (20).
12. Method according to any of the preceding claims, characterised in that for each coin side of the coin (1; 1a, 1b) to be inspected, for at least one surface region (O; O₁, O₂, O₃), surface points of the coin design (10; 10a, 10b) are captured in at least two optical wavelength ranges, wherein thus respectively one profile (P; P₁ P₂, P₃) is created for each of the wavelength ranges,

    - the profile (P; P₁ P₂, P₃) created for the second coin side is centred and stretched or compressed, such that the middle of the captured coin design is situated in the middle of the created profile (P') and that the width of the captured coin design in the created profile (P; P₁, P₂, P₃) corresponds to the predetermined standard width, and

    - the at least one profile (P; P₁, P₂, P₃) created for the second coin side is compared with at least one reference profile (R; R₁, R₂, R₃) and a consistency value is determined in this regard.
13. Method according to claim 12, characterised in that the at least one profile (P; P₁, P₂, P₃)created for the second coin side is compared with the same reference profile (R; R₁, R₂, R₃) as the profile (P; P₁, P₂, P₃) created for the first coin side and/or
    that the at least one profile (P: P₁, P₂, P₃) created for the second coin side of the coin to be inspected is centred and/or stretched or compressed according to the centring and/or stretching or compressing which were determined for the corresponding profile (P; P₁ P₂, P₃) created for the first coin side.
14. Method according to any of the preceding claims, characterised in that the equipment drift of the optical capturing device (20) takes place on the basis of the brightness value which is determined without the coin (1; 1a, 1b) to be inspected and the equipment drift determined in this manner is used for correcting the profile (P; P₁, P₂, P₃) created for the coin (1; 1a, 1b) to be inspected.
15. Method according to any of the preceding claims, characterised in that the movement of the coin (1; 1a, 1b) to be inspected is effected relative to the optical capturing device, in that the coin (1; 1a, 1b) to be inspected rolls along an inclined plane or is conveyed, in particular on a conveyor belt or belt, or is transported along a free flight path past the optical capturing device (20).
16. Method according to any of the preceding claims, characterised in that the point in time is specified, particularly by means of a trigger unit (5) arranged directly prior to the capturing region of the capturing device (20), at which the coin (1; 1a, 1b) to be inspected enters into the capturing region and at a predetermined time interval after the detection of the entrance into the capturing region the comparison of the at least one profile (P; P₁ P₂, P₃) created for the coin (1; 1a, 1b) to be inspected with the at least one reference profile (R; R₁ R₂, R₃) is carried out.

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