EP3590103B1 - Magnetic testing of valuable documents - Google Patents

Description

The invention relates to a method and a magnetic sensor for the magnetic testing of valuable documents.

Valuable documents generally have various security features to make them more difficult to forge or which are specific to the respective type of valuable document. The authenticity of a document of value or the type of document of value is checked using special testing devices which include a detector arrangement and a transport device which guides the document of value past the detector arrangement. The detector arrangement determines measured values at many measuring points on the surface of the valuable document that represent certain properties of its security features. The measured values determined are then used to check the authenticity of the document and compared, for example, with reference values.

However, the measured values can be distorted because the distance between the document of value and the detector fluctuates. This connection is usually such that the measurement signal decreases as the distance between the detector and the measuring point increases. This distance can not only change from one document of value to the next, but can also change within a document of value, so that measuring points of the same document of value that are checked one after the other occupy different distances from the detector. This varying distance is caused, for example, by bends and corrugations of the document, especially in used banknotes, or by the fluttering of the valuable documents when they are passed quickly through the testing device.

In order to avoid incorrect tests, when testing magnetic properties, it is desirable to make the measurement results as dependent as possible on the distance between the document of value and the detector minimize. However, the distance dependence of the magnetic measurement signal is particularly noticeable when the document of value is at a small distance from the detector.

In the DE 102 56 235 A1 It was therefore proposed to stabilize a valuable document during transport through the testing device, for example by roller-belt systems or pressure and suction systems or the like, in order to minimize the variation in the distance. However, there are obvious disadvantages due to high levels of wear and the system components, which are extremely complex and therefore prone to repairs.

From the EP2304699 B1 a guide element is known, with which mechanical stabilization of the document of value is also achieved in order to reduce fluctuations in the distance of the document of value from the magnetic sensor.

Plus it's from the DE102005000698 A1 known to measure the distance with the help of an additional sensor and to correct the measurement signals based on the measured distance. However, this additional sensor is complex and requires a lot of space.

The WO2004/055739 A1 discloses two individual inductive sensor elements that are arranged on opposite sides of the transport path of a document of value, so that the documents of value are transported between the two inductive sensor elements.

Accordingly, it is the object of the present invention to propose a simpler solution in order to achieve results when testing the magnetic properties of valuable documents that are not distorted by the varying distance to the detector.

This object is achieved according to the invention by a method and a magnetic sensor with the features of the independent claims. Into it Dependent claims indicate advantageous refinements and developments of the invention.

To test the magnetic properties of the document of value, in particular a security element of a document of value, the document of value is transported past a magnetic sensor along a transport direction. The magnetic sensor has, transverse to the transport direction of the valuable document, i.e. perpendicular or oblique to the transport direction of the valuable document, a measuring sensor line with a plurality of magnetosensitive measuring sensor elements, which are arranged at a target distance from a transport plane of the valuable document. Furthermore, the magnetic sensor has at least one further magnetosensitive sensor element, preferably at least two further magnetosensitive sensor elements, which, viewed from the document of value being transported past, is/are arranged behind the measuring sensor line along a line parallel to the measuring sensor elements and a larger one Distance from the transport plane of the document of value has/s than the measuring sensor elements. The magnetosensitive measuring sensor elements and the magnetosensitive further sensor element(s) are referred to below simply as measuring sensor elements and further sensor elements.

The measuring sensor elements detect measurement signals of the document of value at several measuring points of the document of value, which are arranged on the document of value along a measuring line transverse to the transport direction. The further sensor element(s) detect(s) a correction signal(s) at a respective correction measuring point of the value document, which lies on the same measuring line(s) as the measuring points. In order to calculate the distance dependence of the measurement signals, the measurement signals detected at the measuring points are measured using the at the Correction measuring point/s detected correction signal/s corrected. The measurement signals from the measuring points corrected in this way are used to check the magnetic properties of the document of value. The correction signals of the correction measuring points are preferably detected simultaneously with the measuring signals of the measuring points in order to be able to carry out the distance correction as accurately as possible.

To correct the measurement signals detected at the measuring points, the respective measurement signal is compared with the respective correction signal. Due to the greater distance of the at least one further sensor element from the document of value compared to the measuring sensor elements, the correction signal is lower than the measuring signal of the respective measuring point. The respective measurement signal of the respective measuring point is corrected based on the signal drop that the correction signal determined for this measuring point has in comparison to the measurement signal of the respective measuring point.

From the detected correction signal(s) that is/are detected at the respective correction measuring point, a correction signal can be determined for the respective measuring point of the measuring line at which the measuring sensor elements have detected the respective measuring signal. The expression "correction signal determined for the measuring point" includes the case that the correction measuring point and the measuring point on the value document are identical, but also includes the case that the correction measuring points are not identical to the measuring points, but rather the measuring signal of a measuring point using the /the correction signal(s) of one/several correction measuring point(s) adjacent to the respective measuring point, for example the closest one on the document of value, is corrected. The correction signal from another sensor element is used, for example, to correct the measurement signals from several measuring points that are in the vicinity of the correction measuring point of this further sensor element.

To correct the measurement signals detected at the measurement points of the document of value, the respective measurement signal of a measurement point is compared with the correction signal determined for this measurement point, for example by calculating the ratio of the correction signal and the measurement signal. Based on the signal drop that the correction signal determined for this measuring point has in comparison to the measuring signal of the respective measuring point (e.g. based on the ratio between the measuring signal of the respective measuring point and the correction signal determined for this measuring point), the (local) distance of the respective measuring point is then determined Value document is calculated by the respective measuring sensor element. With the help of the determined (local) distance of the value document from the measurement sensor element, the respective measurement signal that the respective measurement sensor element has detected at the respective measurement point is corrected, in particular with the aid of a known distance dependence of the measurement signal. The corrected measurement signal of the respective measuring point is determined, for example, by inserting the distance determined for the respective measuring point into the distance dependence of the measurement signal determined in advance of the value document inspection.

The correction is carried out qualitatively in such a way that the measurement signal of the measuring sensor elements is corrected upwards if the determined distance exceeds the target distance that the transport plane of the document of value has to the measuring sensor elements, and is corrected downwards if the determined distance is Target distance falls below. The size of this correction depends on the ratio of the respective measurement signal of a measuring point to the correction signal determined for this measuring point. The corrected measurement signal corresponds, for example, to the measurement signal that comes from the measurement sensor elements would be detected at the target distance of the value document from the measuring sensor elements.

The distance dependence mentioned can, for example, be known from a data sheet of the measuring sensor elements or have been determined based on its data. However, it can also have been simulated or determined empirically in advance of the value document check for the measuring sensor elements. For example, in advance of the value document check, a distance dependency is determined for the measurement sensor elements of the magnetic sensor, which reflects the course of the measurement signal of the measurement sensor elements as a function of the distance between the value document and the measurement sensor elements. In the same way, a (further) distance dependence is determined for the at least one further sensor element, which reflects the course of the correction signal as a function of the distance between the document of value and the measuring sensor elements. For example, the dependence of the distance on the relationship between the correction signal and the measurement signal is determined from the course of the measurement signal and the course of the correction signal as a function of the distance.

The determined distance is a local distance in that it is only valid individually for the respective measuring point, with the distances determined for different measuring points normally differing from one another. To correct the respective measurement signal, the individual distance determined for the respective measuring point can be inserted into the known distance dependence of the measurement signal in order to determine a correction factor that applies individually to the respective measuring point, which is offset against the measurement signal of the respective measuring point. Accordingly, the correction factor for the respective measuring point is individual, with the correction factors being different for the different measuring points usually differentiate from each other.

The corrected measurement signal of the respective measuring point can be determined by inserting the distance of the measuring point determined for the respective measuring point into the known distance dependence of the measurement signal of the measuring sensor elements, for example determined in advance of the value document check, in order to obtain a distance dependence that applies individually to the respective measuring point Determine correction factor. The respective measurement signal of the respective measuring point can then be multiplied by the correction factor determined for the respective measuring point in order to obtain the corrected measurement signal.

To compare the respective correction signal with the respective measurement signal, the ratio between the respective correction signal and the respective measurement signal is preferably formed. From the relationship between the respective correction signal and the respective measurement signal, the distance of the respective measuring point of the document of value from the respective measuring sensor element is determined with the aid of the known distance dependence of the ratio. From this distance, which was determined individually for the respective measuring point of the document of value, a local correction factor is determined for the respective measuring point of the document of value. To correct the measurement signal, the measurement signal of the respective measuring point is offset (e.g. multiplied or divided) with the respective local correction factor that was determined for the respective measuring point. However, the correction of the detected measurement signal is preferably only carried out for those measurement signals of the security element to be tested that reach or exceed a predetermined threshold. This avoids an otherwise incorrect correction. This means that cases in which very low measurement signals are detected are ignored in relation to the correction e.g. are distorted by noise or interference, would be calculated into nonsensical values by (even smaller and also distorted) correction signals. Those measurement signals that fall below the specified threshold are not corrected and are not used to test the magnetic properties of the security element.

In the case of the magnetic sensor, the number of further sensor elements is preferably smaller than the number of measuring sensor elements, in particular smaller by at least a factor of 2. For example, the measuring sensor elements can be arranged regularly at 2mm intervals from one another and the other sensor elements at 10mm intervals from one another. It was recognized that the distance of the valuable document from the magnetic sensor usually only changes significantly over a length of several mm (viewed perpendicular to the transport direction). Due to the smaller number of correction sensor elements compared to the measuring sensor elements, distance correction is possible with less effort. The measurement signal of those measurement sensor elements that lie along the measurement line between two of the further sensor elements can be corrected using the correction signals of the further sensor elements that are closest to these measuring elements.

In particular, the density of the further sensor elements of the magnetic sensor in the direction perpendicular to the transport direction of the valuable document is selected such that the magnetic sensor has at least one further sensor element for each 20 mm section of the valuable document perpendicular to the transport direction of the valuable document. The number of additional sensor elements is thus adapted to the characteristic length perpendicular to the transport direction, to which the distance of the document of value from the magnetic sensor changes.

The measurement signal of the measurement points of such measurement sensor elements, behind which no further sensor element is arranged, is preferably corrected with the help of the correction signals from at least two correction measurement points. To correct the measurement signal of these measurement sensor elements, the correction signals of the other sensor elements or values derived from these correction signals (e.g. the distance) can be interpolated (interpolation in the y direction). For example, the correction signal itself is interpolated and then used to correct the measurement signals of the measurement sensor elements in between. A fit of the correction signals of these measuring points (in the case of more than two correction measuring points, in particular a polynomial fit) can be carried out along the measuring line. A correction signal can thus be generated for those measuring sensor elements behind which no further sensor element is arranged. Alternatively, the local distance of the correction measuring points of the value document from the measuring sensor elements can first be determined from the correction signal and then, by interpolating the distance values, the local distance can also be determined for the measuring sensor elements in between (behind which no further sensor element is arranged). of the document of value can be determined.

Furthermore, in the case of a security element extended in the transport direction, such as a motif or image printed with magnetic ink, interpolation of the correction signals or the values derived therefrom (e.g. distance values) in the transport direction (x-direction) is also preferred. With such a security element, while the document of value is being transported past, the measurement signals are detected from measuring points of a two-dimensional section (ROI) of the document of value, which extends both vertically and along the transport direction. The measurement signals of the Measuring points of this two-dimensional section (ROI) are preferably compared with a minimum value. The minimum value is, for example, higher than the threshold mentioned above (below which the measurement signal is ignored). The measurement signal of such a measurement point, whose measurement signal reaches or exceeds the minimum value, is corrected by the correction signal detected at the respective measurement point or at the nearest adjacent correction measurement point. However, the measurement signal of such a measurement point, whose measurement signal falls below the minimum value (but exceeds the above-mentioned threshold), is corrected with the help of the correction signals from at least two, preferably at least three, correction measurement points of this two-dimensional section (ROI). Their correction signals are interpolated to determine an interpolated correction signal for the respective measuring point.

In particular, the correction signals of at least two correction measuring points of this two-dimensional section are interpolated, which are offset along the transport direction to the respective measuring point. For example, one of the correction measuring points - viewed in the transport direction of the valuable document - is selected at the beginning of the ROI and another correction measuring point at the end of the ROI. The interpolation of several correction signals in the case of low measurement signals has the advantage that even small measurement values are taken into account for testing the two-dimensional security element, but their (incorrect) correction with a single, very small correction measurement value that is detected for this measurement point is avoided. In addition, one or more further correction measuring points of this two-dimensional section (ROI), which are offset perpendicularly or obliquely to the transport direction to the respective measuring point, can also be used for the interpolation.

From the correction signals from two or more than two correction measuring points, an average distance of the two-dimensional section (ROI) from the measuring sensor elements can be determined, which is valid for the two-dimensional section (ROI) as a whole. Then the measurement signals of all measurement points of this two-dimensional section (ROI) can be corrected using this average distance of the two-dimensional section (ROI).

The invention also relates to a magnetic sensor for checking the magnetic properties of the document of value. The magnetic sensor contains the above-mentioned measuring sensor line, which has a plurality of magnetosensitive measuring sensor elements arranged at a target distance from the transport plane of the document of value, and the further magnetosensitive sensor element(s) in relation to the document of value being transported past , is/are arranged behind the measuring sensor line along a line parallel to the measuring sensor elements and is/are at a greater distance from the transport plane of the document of value than the measuring sensor elements.

For example, the measuring sensor elements and the at least one further sensor element are arranged on the opposite sides of the same carrier. Since their distance from each other is determined particularly precisely, the distance correction is also more precise.

The measuring sensor elements and the at least one further sensor element preferably use the same measuring principle. Since they use the same measuring principle, all magnetic influences, such as magnetic field disturbances, which influence the measuring signal of the measuring sensor elements, have a similar effect on the measuring signal of the other sensor element(s). There If magnetic interference affects both in the same way, a particularly precise distance correction can be achieved with the additional sensor element(s) that use the same measuring principle. The measuring sensor elements and the further sensor element(s) are preferably identical in construction. The measurement signals of the measurement sensor elements and the other sensor element(s) are then only different due to the different distance from the document of value. This enables a particularly precise correction of the distance dependence.

Furthermore, the magnetic sensor contains a control device which is set up to control the measuring sensor line in such a way that the measuring sensor elements detect measurement signals of the valuable document at several measuring points on the valuable document, which are arranged along a measuring line transverse to the transport direction on the valuable document, and that / to control the other sensor element(s) so that they detect a correction signal at the respective correction measuring point of the document of value, which lies on the same measuring line. The control device controls the measuring sensor line and the further sensor element(s) according to the method described above and has corresponding software to carry out the method described above.

Furthermore, the magnetic sensor has an evaluation device which is set up to correct the measurement signals detected at the measuring points of the document of value with the aid of the correction signal(s) detected at the correction measuring point(s) of the document of value, in order to thereby reduce the distance dependence of the measurement signals to calculate it out and to check the value document on the basis of the corrected measurement signals from several of the measurement points. The evaluation device can be housed in the housing of the magnetic sensor, but it can also be arranged outside of it be. The evaluation device and the control device can be combined in one device.

The evaluation device is set up to evaluate the detected measurement signals and correction signals according to the method described above and has corresponding software for this purpose. The evaluation software carries out the distance correction described and checks the magnetic properties of the valuable document.

The invention also relates to a device for testing the magnetic properties of a document of value. This can be a valuable document processing device, in particular a checking device or a sorting device for valuable documents, or an input or Payout device for documents of value. The device has the magnetic sensor described above, as well as possibly also other sensors, and a transport device for transporting the document of value in the transport plane along a transport direction, which transports the documents of value to be checked past the magnetic sensor one after the other.

Fig. 1a

ein erstes Beispiel einer Mess-Sensorzeile und weiterer magnetosensitiver Elemente eines Magnetsensors im Querschnitt,

Fig. 1b

ein zweites Beispiel einer Mess-Sensorzeile und weiterer magnetosensitiver Sensorelemente eines Magnetsensors im Querschnitt,

Fig. 2

Prüfung eines Wertdokuments mit Hilfe eines Magnetsensors, der zwei Mess-Sensorzeilen aufweist,

Fig. 3

ein Wertdokument in ungleichmäßigem Abstand zum Magnetsensor,

Fig. 4a

im Vorfeld der Wertdokumentprüfung ermittelter Verlauf der Sensorsignale der Mess-Sensorelemente (M) und der weiteren Sensorelemente (K) als Funktion des Wertdokumentabstands,

Fig. 4b

Verhältnis der Sensorsignale der Mess-Sensorelemente (M) und der weiteren Sensorelemente (K) als Funktion des Wertdokumentabstands,

Fig. 5a

den Verlauf des von dem Wertdokument detektierten Messsignals der Mess-Sensorelemente,

Fig. 5b

den Verlauf des von dem Wertdokument detektierten Korrektursignals der weiteren Sensorelemente,

Fig. 5c

das mit Hilfe des Korrektursignals korrigierte Messsignal des Wertdokuments,

Fig. 6a

Verhältnis des Korrektursignals zu dem Messsignal an bestimmten y-Positionen,

Fig. 6b

Verlauf des für das Wertdokument ermittelten Abstands von der Mess-Sensorzeile,

Fig. 6c

aus dem Abstand aus Fig. 6b und dem Signalverlauf aus Fig. 4a ermittelte Korrekturfaktor als Funktion der Position y.

Further advantages, features and possible applications of the present invention result from the following description in connection with the figures. Show it:

Fig. 1a

a first example of a measuring sensor line and further magnetosensitive elements of a magnetic sensor in cross section,

Fig. 1b

a second example of a measuring sensor line and further magnetosensitive sensor elements of a magnetic sensor in cross section,

Fig. 2

Checking a document of value using a magnetic sensor that has two measuring sensor lines,

Fig. 3

a document of value at an uneven distance from the magnetic sensor,

Fig. 4a

Course of the sensor signals of the measuring sensor elements (M) and the other sensor elements (K) determined in advance of the valuable document check as a function of the value document distance,

Fig. 4b

Ratio of the sensor signals of the measuring sensor elements (M) and the other sensor elements (K) as a function of the value document distance,

Fig. 5a

the course of the measurement signal of the measurement sensor elements detected by the valuable document,

Fig. 5b

the course of the correction signal of the other sensor elements detected by the valuable document,

Fig. 5c

the measurement signal of the document of value corrected with the help of the correction signal,

Fig. 6a

Ratio of the correction signal to the measurement signal at certain y positions,

Fig. 6b

Course of the distance determined for the valuable document from the measuring sensor line,

Fig. 6c

from a distance Fig. 6b and the signal curve Fig. 4a determined correction factor as a function of the position y.

In Figure 1a a measuring sensor line of a magnetic sensor 10 with magnetosensitive measuring sensor elements 7 is shown. For each of the measuring sensor elements 7, the magnetic sensor also has a further magnetosensitive sensor element 8, which is arranged behind the magnetosensitive sensor elements 7 with respect to the document of value BN. The sensor elements 7 and 8 are arranged on the same substrate 9, for example a circuit board that also provides the electrical connections to the sensor elements.

Figure 1b shows a second example of a measuring sensor line of a magnetic sensor with magnetosensitive measuring sensor elements 7 and further magnetosensitive sensor elements 8 on the same substrate 9. In this example, however, there are fewer further magnetosensitive sensor elements 8 than measuring sensor elements 7. In this case, if there is not actually a further sensor element 8 for each measuring point, ie the number of further sensor elements is less than the number of measuring sensor elements, one and the same further sensor element 8 can be used to correct the measurement signal of several measuring sensor elements 7, ie several measuring points on the value document can be used. The correction signal of the respective further sensor element 8 is assigned to the measurement signals of those measuring sensor elements 7 which are arranged closest to the respective further sensor element along the y-direction.

Figure 2 shows schematically a magnetic sensor 10 of a device for processing valuable documents, into which the valuable documents 1 are entered individually or in batches, then checked, sorted and stored in the device for processing valuable documents or output again. A document of value 1 is transported along a transport path first past a magnetization device, which provides a magnetic field A, and then past a magnetic sensor 10 with two sensor lines 12, 14. Depending on the requirements of the magnetic sensor, it can alternatively have only one of the two sensor lines 12, 14. The magnetic field A magnetizes high and low coercive magnetic areas of the document of value 1. For example, the magnetic field A in Transport direction T of the valuable document 1. The magnetic field A can also include several sections with different magnetic field directions. The magnetic field A can be provided, for example, by two magnets lying opposite one another, between which the document of value 1 is transported and whose magnetic north poles N point towards one another, so that a magnetic field A parallel to the transport direction T results between them. For magnetization, another pair of magnets can also be used, in which the two magnetic south poles point towards each other, for example to achieve anti-parallel magnetization of low-coercivity magnetic areas. Alternatively, only a magnet arranged on one side of the transport path can be used for magnetization, as long as a sufficiently large magnetic field strength is achieved to magnetize the document of value. Alternatively, the first magnetic field A can also be provided by just a single bar magnet or by a horseshoe magnet analogous to magnet 18.

The document of value 1 has a security element 2 with magnetic coding. In this example, the security element 2 is designed as a security thread which has a magnetic coding of magnetic areas 2 along its longitudinal direction, between which there is non-magnetic material. These magnetic areas 2 can include high-coercivity magnetic areas and/or low-coercivity magnetic areas and optionally also combined magnetic areas that contain both high-coercivity and low-coercivity magnetic material. If necessary, the document of value also has a soft magnetic magnetic area 11 outside the security thread.

After magnetization in the magnetic field A, the document of value 1 is transported past the magnetic sensor 10, which is spatially separated from it Magnetic field A is installed in the device for processing valuable documents. The magnetic sensor 10 contains two sensor rows 12, 14, each of which has a large number of similar magnetosensitive measuring sensor elements 7 which are arranged in a row. Each of these measuring sensor elements 7 supplies a magnetic signal, so that in this example a large number of first magnetic signals are detected using the measuring sensor elements 7 of the sensor line 12 and a large number of second magnetic signals are detected using the further magnetosensitive elements 8 of the sensor line 14, which have the same section of the security element 2 being transported past.

While detecting the first magnetic signals, the security element 2 is not exposed to a magnetic field. The magnetosensitive elements 7 of the second sensor line 14 detect the second magnetic signals of the security element 2 under the influence of a second magnetic field B, which acts on the security element 2 before and during the detection of the second magnetic signals. The second magnetic field B is provided by a magnet 18 arranged on one side of the transport path and is extended in such a way that it already magnetizes the security element 2 before it comes into the detection range of the second sensor line 14. The poles N, S of the magnet 18 are aligned so that a magnetic field B results in the transport plane anti-parallel to the transport direction T of the document of value. The magnetic field strength of the magnetic field A is, for example, at least twice the magnetic field strength of the magnetic field B. Detecting the second magnetic signals under the influence of the second magnetic field B has the advantage that the second sensor line 14 can be used not only for detecting the different magnetic areas of the security element 2, but that it can also detect magnetic signals from soft magnetic magnetic areas 11 of the security element 2, which can be present on the document of value outside the security element 2.

The measuring sensor elements 7 of each of the sensor lines 12, 14 are each arranged on a common circuit board (wiring of the circuit boards not shown) and connected to a control and evaluation device 19, which uses the measuring sensor elements 7 and the further sensor elements 8 to detect the Controls magnetic signals and evaluates their magnetic signals. The circuit board of the sensor line 14 and the magnet 18 are mechanically fixed to one another by casting so that they form a structural unit. The control and evaluation device 19 receives magnetic signals from the two sensor lines 12, 14 and processes and analyzes them. The control and evaluation device 19 can be arranged together with the sensor lines 12, 14 in the same housing. Data can be sent from the control and evaluation device 19 to the outside via an interface, for example to a device that further processes the data or to a display device that provides information about the result of the value document check.

On the underside of the circuit board 9 of the sensor line 12, several of the further sensor elements 8 are arranged, with the help of whose measurement signal the distance correction according to the invention of the measurement signal of the measurement sensor elements 7 is carried out. In this example, fewer sensor elements 8 are used than measuring sensor elements 7, as in Fig. 1b is shown. Alternatively, a corresponding further sensor element 8 can also be present for each measuring sensor element 7 on the back of the circuit board 9, as shown in Fig. 1a is shown. The second sensor line 14 on the underside of the circuit board 9 is preferably also equipped with further sensor elements 8 in order to be able to carry out a distance correction for the measurement signal from the measurement sensor elements 7 of the second sensor line 14. Amplifier chips for amplifying the detected measurement signal and correction signal can be arranged on the underside of the circuit boards 9.

In Fig. 3 For example, a valuable document 1 is shown in a side view (viewing in the transport direction), which has an uneven distance from the surface of the measuring sensor elements 7, which is at z=0. In the right area, the value document is almost twice as far away from the sensor surface as in the left area.

In order to enable correction of the distance fluctuations of the document of value, the course of the signals of the measuring sensor elements and the other sensor elements is determined as a function of the distance of the document of value a before the value document is checked. For this purpose, for example, a document of value is placed one after the other at different distances from an arrangement of one or more measuring sensor elements and one or more further sensor elements, which corresponds to the arrangement of the measuring sensor elements 7 and further sensor elements 8 in the magnetic sensor later used for checking the value document. For each distance a, a measurement signal from the respective measurement sensor element and a correction signal from the respective further sensor element are detected. Both signals show distance dependence, which decreases as the distance a of the value document increases, cf. Fig. 4a , where M denotes the measurement signals of the measuring sensor elements and K denotes the correction signals of the other sensor elements. Due to the larger distance a of the further sensor elements 8 from the document of value, the correction signals of the further sensor elements 8 are always below the measurement signals of the measurement sensor elements 7. The measurement signals Fig. 4a were standardized to a nominal target distance d of the value document from the measuring sensor elements of 1 mm.

The ratio of the in is then determined for the different value document distances a Figure 4a signals shown (quotient M/K) are formed.

This results in the in Fig. 4b shown dependence of the value document distance a on the ratio K/M of the measurement signals M of the measurement sensor elements 7 to the correction signals K of the further sensor elements 8. The in Figure 4b Dependency shown can be stored in the control and evaluation device 19 of the magnetic sensor as a function or as a lookup table.

The distance correction will be explained below using the example of the measurement signals that the first sensor line 12 detects from the security thread of the document of value 1, with which the magnetization of the document of value 1 is detected without an external magnetic field, but also applies in the same way to a distance correction of the measurement signals of the sensor line 14, which detects the magnetization of the document of value 1 in the magnetic field. The distance correction described below is also suitable for other types of magnetic security elements of valuable documents, e.g. for a motif or partial motif made of magnetic printing ink.

In Fig. 5a The measurement signal from the sensor line 12 is shown as an example, which is detected by a magnetic security element which has several magnetic areas b1, b2, b3 and b4 along a direction designated y. The arrangement of the magnetic areas along the security element (along the y-direction) is shown above the diagram in Fig. 5a sketched. This in Fig. 5a The measurement signal shown was detected by a large number of measurement sensor elements 7, which are arranged along the y-direction. For example, these are the measurement signals of the measurement sensor elements 7 detected at a certain point in time while the document of value equipped with this security element is transported past the magnetic sensor. In this example, each magnetic area b1-b4 supplies a measurement signal as a function of the location coordinate y in the form of a double peak. Fig. 5b shows the corresponding correction signal that the additional sensor elements 8 arranged behind the measuring sensor elements 7 detect at the same measurement time from the magnetic areas b1-b4 of this security element. The double peaks of the correction signals are smaller than those of the measurement signals of the measurement sensor elements 7, corresponding to the greater distance of the further sensor elements 8 from the document of value. To quantify the measurement signals and the correction signals, for example, the maximum of the double peak is determined and this maximum value is used as a measurement signal for further evaluation M or correction signal K is used. Alternatively, the peak-to-peak amplitude of the double peaks or the height of only one of the peaks or the area under one or both peaks of the double peak can also be used.

To determine a correction function F(y) for the measurement signal M Fig. 5a For the measuring points along the y-direction, the respective correction signal K is compared with the respective measuring signal M of the measuring point, for example by forming the ratio. Fig. 6a shows the ratio of these signals as a function of the location coordinate y for those measuring points at which both a measurement signal M and a correction signal K were detected. Since the number of additional sensor elements 8 is less than the number of measuring sensor elements 7, and therefore both signals are only present for a few measuring points, the ratio formation is limited to those measuring points along the y-direction for which a correction signal is actually detected became.

However, the ratio is preferably only formed for those measuring points or sensor elements that deliver a clear measurement signal, for example whose measurement signal is above a certain threshold S. For example, the in 5a and 5b indicated threshold of S=1 is used.

Measuring points at which the measuring signal of the respective measuring sensor element 7 or the correction signal of the respective further sensor element 8 lie below the threshold S=1 are ignored for the ratio formation and the subsequent distance correction, for example the measuring points in the range y=40, in which according to Figure 5a There is also no magnetic area. This avoids any incorrect distance correction, which can lead to severely distorted values.

From the in Fig. 6a Depending on the conditions shown, the distance of the document of value from the measuring sensor elements 7 at the respective y-position is determined for each of the y-positions selected in this way. For this purpose, the ratio at the respective y-position - using the in Fig. 4b shown relationship between ratio and distance, which was determined in advance of the value document examination - converted into a distance. Fig. 6b shows the course of the local distance determined in this way of the respective measuring point of a value document from the measuring sensor elements 7 for the selected y-positions. In addition, a fit function adapted to this is shown, which has a continuous course and is used to determine the value document distance for each of the measuring sensor elements 7 (including those whose y position was not selected).

By inserting the in Fig. 6b shown actual distance values of the document of value into the distance dependence of the expected measurement signal determined in advance of the value document inspection Fig. 4a For each y-position there is a certain factor by which the measurement signal of the respective measuring sensor element is falsified due to the actually determined distance. For example, in the range y=55, where an actual value document distance of approximately 1.9 mm was determined, this results from the distance dependence of the value document determined in advance of the value document inspection measurement signal Fig. 4a , a measurement signal reduced by a factor of around 2.3 compared to the distance y=1 (corresponding to a share of around 43%, cf. Fig. 4a ). For a distance correction, the measurement signal at y=55 must therefore be multiplied by a correction factor of 2.3. In this way the in Fig. 6c The correction function F(y) shown is determined, which indicates this correction factor F for each individual y-position.

The measurement signal M(y) is used to correct the distance Fig. 5a , which the measuring sensor elements 7 have detected from the magnetic areas b1-b4, is multiplied by the correction function F (y). The result of this correction is in Fig. 5c shown. Due to the predetermined standard distance of a=1 mm, this correction results in the measurement signal that would be expected from the document of value if it were transported past all y-positions at the ideal standard distance of 1 mm. In comparison to the actually detected measurement signal Fig. 5a , in which the left double peak of the magnetic area b1 is significantly larger than the right three double peaks, the distance correction carried out leads to, firstly, the double peaks of the two long magnetic areas b1 and b3 being aligned with one another and secondly also the double peaks of the two short magnetic areas b2 and b4 be aligned with each other. The corrected measurement signal is then used to check the value document. In particular, a magnetic coding of a security element of the document of value can be checked or the magnetic imprint of a document of value can be checked. To check the document of value, the corrected measurement signal is compared, for example, with a measurement signal expected for the security element. The result can be used, for example, as part of a quality check or an authenticity check of the document of value or to determine the identity of the document of value.

Claims (15)

1. Method for checking magnetic properties of a value document (1), the method comprising the following steps:

   - transporting a value document (1) past a magnetic sensor (10) in a transport direction (x), wherein the magnetic sensor, transversely to the transport direction of the value document, comprises a measurement sensor line having a plurality of magnetosensitive measurement sensor elements (7) which are arranged at a target distance (d) from a transport plane of the value document, and wherein the magnetic sensor has at least one further magnetosensitive sensor element (8), which is arranged behind the measurement sensor line, when viewed from the value document which is transported past, and has a greater distance from the transport plane of the value document than the measurement sensor elements,

   - detecting measurement signals (M) of the value document by the measurement sensor elements (7) at a plurality of measurement points (y) of the value document, which measurement points are arranged on the value document along a measurement line transversely to the transport direction (x),

   - detecting a correction signal (K) by at least one of the further sensor elements at at least one correction measurement point of the value document,

   - determining corrected measurement signals (M') of the measurement points by correcting the measurement signals detected at the measurement points (y) using the correction signal detected at the at least one correction measurement point,

   - checking magnetic properties of the value document on the basis of the corrected measurement signals (M') of a plurality of measurement points (y).
2. Method according to claim 1, characterized in that for correcting the measurement signals detected at the measurement points (y) of the value document, the following steps are carried out:

   - comparing the relevant measurement signal (M) of a measurement point (y) with a correction signal (K) determined for this measurement point, and

   - determining a distance of the relevant measurement point (y) of the value document by the relevant measurement sensor element (7) on the basis of a signal drop that the correction signal (K) determined for this measurement point (y) has in comparison with the measurement signal of the relevant measurement point,

   - correcting the relevant measurement signal (M), which the relevant measurement sensor element (7) has detected at the relevant measurement point, using the determined distance of the value document from the measurement sensor element (7) with the aid of a known distance dependence of the measurement signal of the measurement sensor elements (7).
3. Method according to claim 2, characterized in that the measurement signal (M) of the measurement sensor elements (7) is corrected upward if the determined distance (a) exceeds the target distance (d) and is corrected downward if the determined distance (a) does not meet the target distance, and the magnitude of this correction depends on the ratio of the relevant measurement signal (M) of a measurement point (y) to the correction signal (K) determined for this measurement point (y).
4. Method according to claim 2 or 3, characterized in that, for correcting the relevant measurement signal, the distance (a) determined for the relevant measurement point (y) is used in a known distance dependence of the measurement signal of the measurement sensor elements (7), in order to determine a correction factor that applies to the relevant measurement point (y), which correction factor is calculated using the measurement signal of the relevant measurement point.
5. Method according to any of the preceding claims, characterized in that the correction signals of the correction measurement points are detected simultaneously with the measurement signals of the measurement points.
6. Method according to any of the preceding claims, characterized in that the number of the further sensor elements (8) is at least two and is less than the number of measurement sensor elements (7), and the measurement signal of the measurement points of those measurement sensor elements behind which no further sensor element (8) is arranged is corrected using the correction signals of at least two correction measurement points, in particular using the two adjacent correction measurement points closest to the measurement point.
7. Method according to claim 6, characterized in that, for correcting the measurement signal of the measurement sensor elements (7) behind which no further sensor element (8) is arranged, the correction signals of the further sensor elements or values derived from these correction signals are interpolated.
8. Method according to any of the preceding claims, characterized in that the correction of the detected measurement signals is carried out only for those measurement signals of the measurement sensor elements which reach or exceed a predetermined threshold (S).
9. Method according to any of claims 1 to 7, characterized in that, while the value document is being transported past the magnetic sensor, the measurement signals of measurement points of a two-dimensional portion (11) of the value document are detected, which portion extends both transversely to the transport direction and in the transport direction, and in that the measurement signals (M) of the measurement points of this two-dimensional portion (11) are compared with a predetermined threshold, and in that for those measurement points of which the measurement signal does not meet the predetermined threshold, this measurement signal is corrected using the correction signals of at least two, preferably at least three, correction measurement points of this two-dimensional portion (11) which are offset from these measurement points in the transport direction, and is optionally also corrected using the correction signal of one or more correction measurement points of this two-dimensional portion (11) which are offset from these measurement points transversely to the transport direction.
10. Method according to claim 9, characterized in that overall a mean distance is determined from the correction signals of two or more than two correction measurement points for the two-dimensional portion (11), which mean distance the two-dimensional portion has from the measurement sensor elements, and the measurement signals of all measurement points of this two-dimensional portion (11) are corrected using this average distance of the two-dimensional portion (ROI).
11. Magnetic sensor for checking magnetic properties of a value document (1), which is transported past the magnetic sensor in a transport plane in a transport direction, comprising

    - a measurement sensor line (12, 14) having a plurality of magnetosensitive measurement sensor elements (7) arranged on one side of a carrier (9), and

    - at least one further magnetosensitive sensor element (8) arranged on the opposite side of the carrier along a line parallel to the measurement sensor elements, so that the measurement sensor line can be arranged transversely to a transport direction of a value document and at a target distance (d) from the transport plane of the value document such that the at least one further magnetosensitive sensor element (8) is arranged behind the measurement sensor line, with respect to the document of value which is transported past, and has a greater distance from the transport plane of the value document than the measurement sensor elements,

    characterized by

    - a control device (19), which is designed to control the measurement sensor line in such a way that the measurement sensor elements detect measurement signals of the value document at a plurality of measurement points of the value document, which measurement points are arranged on the value document along a measurement line transversely to the transport direction, and to control the at least one further sensor element such that it detects at least one correction signal at at least one correction measurement point of the value document,

    - an evaluation device (19), which is designed to correct the measurement signals detected at the measurement points of the value document using the correction signal detected at the at least one correction measurement point of the value document, in order thereby to calculate therefrom the distance dependence of the measurement signals, and to check the magnetic properties of the value document on the basis of the corrected measurement signals of a plurality of the measurement points.
12. Magnetic sensor according to claim 11, characterized in that the magnetic sensor has a plurality of further sensor elements (8) which are arranged along the line parallel to the measurement sensor elements (7).
13. Device (1) for checking magnetic properties of a value document (1), comprising:

    - a transport device for transporting the value document (1) in a transport plane in a transport direction (x),

    - a magnetic sensor for checking magnetic properties of the value document (3), which value document can be transported past the magnetic sensor in the transport plane in the transport direction by means of the transport device, comprising

    - a measurement sensor line (12, 14),arranged transversely to the transport direction of the value document, which measurement sensor line comprises a plurality of magnetosensitive measurement sensor elements (7) which are arranged at a target distance (d) from the transport plane of the value document, characterized by

    - at least one further magnetosensitive sensor element (8) which is arranged behind the measurement sensor line, with respect to the value document which is transported past, and is arranged along a line parallel to the measurement sensor elements and has a greater distance from the transport plane of the value document than the measurement sensor elements,

    - a control device (19), which is designed to control the measurement sensor line in such a way that the measurement sensor elements detect measurement signals of the value document at a plurality of measurement points of the value document, which measurement points are arranged on the value document along a measurement line transversely to the transport direction, and to control the at least one further sensor element such that it detects at least one correction signal at at least one correction measurement point of the value document,

    - an evaluation device (19), which is designed to correct the measurement signals detected at the measurement points of the value document using the correction signal detected at the at least one correction measurement point of the value document, in order thereby to calculate therefrom the distance dependence of the measurement signals, and to check the magnetic properties of the value document on the basis of the corrected measurement signals of a plurality of the measurement points.
14. Device according to claim 13, characterized in that the measurement sensor elements (7) and the at least one further sensor element (8) are arranged on the opposite sides of the same carrier.
15. Device according to claim 13 or 14, characterized in that the magnetic sensor comprises a plurality of further sensor elements (8) which are arranged along a line perpendicularly to the transport direction of the value document.

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