MAGNETIC TESTING OF VALUABLE DOCUMENTS

Abstract

A method for checking of magnetic properties of value documents with the aid of a magnetic sensor comprises a measuring sensor row having a plurality of magneto-sensitive measuring sensor elements, as well as at least one further magneto-sensitive sensor element which is arranged behind the measuring sensor elements and has a greater distance from the transport plane of the value document than the measuring sensor elements. By means of the further sensor elements, correction signals are detected at correction measuring points of the value document, which are disposed on the same measuring line as the measuring points. In order to eliminate the distance dependence of the measuring signals, the respective measuring signal of each measuring point is corrected on the basis of the signal drop which the correction signal ascertained for this measuring point has in comparison to the measuring signal of the respective measuring point.

Claims

1.-15. (canceled)

16. A method for checking the magnetic properties of a value document, having the following steps of: transporting a value document past a magnetic sensor along a transport direction, wherein the magnetic sensor has, transverse to the transport direction of the value document, a measuring sensor row with a plurality of magneto-sensitive measuring sensor elements, which are arranged at a target distance to a transport plane of the value document, and wherein the magnetic sensor has at least one further magneto-sensitive sensor element, which, viewed from the value document transported past, is arranged behind the measuring sensor row and has a greater distance from the transport plane of the value document than the measuring sensor elements, detecting measuring signals of the value document by the measuring sensor elements at a plurality of measuring points of the value document, which is arranged on the value document along a measuring line transversely to the transport direction, detecting a correction signal by at least one of the further sensor elements at at least one correction measuring point of the value document, ascertaining corrected measuring signals of the measuring points by correcting the measuring signals detected at the measuring points with the aid of the correction signal detected at at least one correction measuring point, checking magnetic properties of the value document on the basis of the corrected measuring signals of a plurality of measuring points.

17. The method according to claim 16, wherein the following steps are carried out for correcting the measuring signals detected at the measuring points of the value document: comparing the respective measuring signal of a measuring point with a correction signal ascertained for this measuring point and ascertaining a distance of the respective measuring point of the value document from the respective measuring sensor element on the basis of a signal drop which the correction signal ascertained for this measuring point has in comparison to the measuring signal of the respective measuring point, correcting the respective measuring signal detected by the respective measuring sensor element at the respective measuring point with the aid of the ascertained distance of the value document from the measuring sensor element making use of a known distance dependence of the measuring signal of the measuring sensor elements.

18. The method according to claim 17, wherein the measuring signal of the measuring sensor elements is corrected upward, if the ascertained distance exceeds the target distance, and is corrected downward, if the ascertained distance undershoots the target distance, and the dimension of this correction depends on the ratio of the respective measuring signal of a measuring point to the correction signal ascertained for this measuring point.

19. The method according to claim 17, wherein for correcting the respective measuring signal, the distance ascertained for the respective measuring point is inserted into a known distance dependence of the measuring signal of the measuring sensor elements, in order to ascertain a correction factor that is applicable to the respective measuring point and that is offset against the measuring signal of the respective measuring point.

20. The method according to claim 16, wherein the correction signals of the correction measuring points are detected simultaneously with the measuring signals of the measuring points.

21. The method according to claim 16, wherein the number of further sensor elements is at least two, but in particular is smaller than the number of measuring sensor elements, and the measuring signal of the measuring points of such measuring sensor elements, behind which no further sensor element is arranged, is corrected with the aid of the correction signals of at least two correction measuring points, in particular with the aid of the two correction measuring points most closely adjacent to the measuring point.

22. The method according to claim 21, wherein, for correcting the measuring signal of the measuring sensor elements, behind which no further sensor element is arranged, the correction signals of the further sensor elements or values derived from these correction signals are interpolated.

23. The method according to claim 16, wherein the correction of the detected measuring signals is carried out only for such measuring signals of the measuring sensor elements which reach or exceed a predetermined threshold.

24. The method according to claim 16, wherein during the transport of the value document past the magnetic sensor, the measuring signals of measuring points of a two-dimensional section of the value document are detected, said section extending both transversely to the transport direction and along the transport direction, and that the measuring signals of the measuring points of this two-dimensional section are compared with a predetermined threshold and that for such measuring points whose measuring signal undershoots the predetermined threshold, this measuring signal is corrected with the aid of the correction signals of at least two, preferably at least three, correction measuring points of this two-dimensional section, which correction measuring points are shifted along the transport direction with respect to these measuring points, and optionally additionally corrected with the aid of the correction signal of one or a plurality of correction measuring points of this two-dimensional section, which are shifted transversely to the transport direction with respect to these measuring points.

25. The method according to claim 24, wherein from the correction signals of two or more than two correction measuring points for the two-dimensional section overall an average distance is ascertained which the two-dimensional section has from the measuring sensor elements, and the measuring signals of all measuring points of this two-dimensional section are corrected with the aid of this average distance of the two-dimensional section.

26. The method according to claim 25, wherein one of the correction measuring points employed for ascertaining the average distanceviewed in the transport direction of the value documentis disposed at the beginning of the two-dimensional section and a further correction measuring point is disposed at the end of the two-dimensional section.

27. A magnetic sensor for checking magnetic properties of a value document, which is transported past the magnetic sensor in a transport plane along a transport direction, comprising a measuring sensor row arranged transversely to the transport direction of the value document, which has a plurality of magneto-sensitive measuring sensor elements arranged at a target distance to the transport plane of the value document, at least one further magneto-sensitive sensor element which, with reference to the value document transported past, is arranged behind the measuring sensor row and is arranged along a line parallel to the measuring sensor elements and has a greater distance from the transport plane of the value document than the measuring sensor elements, wherein a control device adapted to so control the measuring sensor row that the measuring sensor elements detect measuring signals of the value document at a plurality of measuring points of the value document, said measuring points being arranged on the value document along a measuring line transversely to the transport direction, and to so control the at least one further sensor element that it detects at least one correction signal at at least one correction measuring point of the value document, an evaluation device adapted to correct the measuring signals detected at the measuring points of the value document with the aid of the correction signal detected at the at least one correction measuring point of the value document, thereby to eliminate the distance dependence of the measuring signals and to check the magnetic properties of the value document on the basis of the corrected measuring signals of a plurality of the measuring points.

28. The magnetic sensor according to claim 27, wherein the measuring sensor elements and the at least one further sensor element are arranged on the mutually opposing sides of the same carrier.

29. The magnetic sensor according to claim 27, wherein the magnetic sensor has a plurality of further sensor elements, which are arranged along a line perpendicular to the transport direction of the value document, wherein the density of the further sensor elements of the magnetic sensor perpendicular to the transport direction of the value document is chosen in particular such that the magnetic sensor has at least one further sensor element for each 20 mm section of the value document perpendicular to the transport direction of the value document.

30. An apparatus for checking magnetic properties of a value document, comprising: a transport device for transporting the value document in a transport plane along a transport direction, a magnetic sensor according to claim 28.

Description

[0034] Further advantages, features and application possibilities of the present invention will result from the following description in connection with the figures. There are shown:

[0035] FIG. 1a a first example of a measuring sensor row and further magneto-sensitive elements of a magnetic sensor in cross section,

[0036] FIG. 1b a second example of a measuring sensor row and further magneto-sensitive sensor elements of a magnetic sensor in cross section,

[0037] FIG. 2 check of a value document with the aid of a magnetic sensor having two measuring sensor rows,

[0038] FIG. 3 a value document at an irregular distance to the magnetic sensor,

[0039] FIG. 4a progression of the sensor signals of the measuring sensor elements (M) and of the further sensor elements (K) ascertained before the value document check, as a function of the value document distance,

[0040] FIG. 4b ratio of the sensor signals of the measuring sensor elements (M) and the further sensor elements (K) as a function of the value document distance,

[0041] FIG. 5a the progression of the measuring signal of the measuring sensor elements detected from the value document,

[0042] FIG. 5b the progression of the correction signal of the further sensor elements detected from the value document;

[0043] FIG. 5c the measuring signal of the value document corrected with the aid of the correction signal,

[0044] FIG. 6a the ratio of the correction signal to the measuring signal at specific y-positions,

[0045] FIG. 6b progression of the distance from the measuring sensor row ascertained for the value document,

[0046] FIG. 6c correction factor ascertained from the distance of FIG. 6b and the signal progression of FIG. 4a as a function of the position y.

[0047] In FIG. 1a a measuring sensor row of a magnetic sensor 10 with magneto-sensitive measuring sensor elements 7 is shown. For each of the measuring sensor elements 7, the magnetic sensor also has in each case a further magneto-sensitive sensor element 8, which is arranged behind the magneto-sensitive sensor elements 7 with reference to the value document BN. The sensor elements 7 and 8 are arranged on the same substrate 9, for example on a circuit board, which also makes available the electrical connections to the sensor elements.

[0048] FIG. 1b shows a second example of a measuring sensor row of a magnetic sensor with magneto-sensitive measuring sensor elements 7 and further magneto-sensitive sensor elements 8 on the same substrate 9. In this example, however, there are fewer further magneto-sensitive sensor elements 8 than measuring sensor elements 7. For this case, if there is not actually a further sensor element 8 present for each measuring point, i. e. if the number of further sensor elements is smaller than the number of measuring sensor elements, one and the same further sensor element 8 can be employed to correct the measuring signal of a plurality of measuring sensor elements 7, i. e. a plurality of measuring points on the value document. In this case, the correction signal of the respective further sensor element 8 is assigned to the measuring signals of those measuring sensor elements 7 which are arranged most closely adjacent to the respective further sensor element along the y-direction.

[0049] FIG. 2 shows schematically a magnetic sensor 10 of an apparatus for processing value documents, to which the value documents 1 are fed individually or in stacks, subsequently checked, sorted and stored in the apparatus for processing value documents or dispensed again. A value document 1 is transported along a transport path first past a magnetization device which makes available a magnetic field A, and thereafter past a magnetic sensor 10 with two sensor rows 12, 14. Depending on the requirements posed to the magnetic sensor, it can alternatively also have only one of the two sensor rows 12, 14. By the magnetic field A highly coercive and lowly coercive magnetic regions of the value document 1 are magnetized. For example, the magnetic field A points in the transport direction T of the value document 1. However, the magnetic field A can also comprise several sections of different magnetic field direction. The magnetic field A can be, for example, made available by two mutually opposing magnets, between which the value document 1 is transported through and whose north magnetic poles N face each other, so that there results between these a magnetic field A parallel to the transport direction T. For magnetizing, in addition, also a further pair of magnets can be employed, in which the two magnetic south poles face each other, for example to achieve an anti-parallel magnetization of lowly coercive magnetic regions. Alternatively, it is also possible to employ for magnetizing only one magnet arranged on one side of the transport path, as long as a sufficiently large magnetic field strength for magnetizing the value document is obtained thereby. Alternatively, the first magnetic field A can also be made available by a single bar magnet or by a horseshoe magnet analogous to the magnet 18.

[0050] The value document 1 has a security element 2 with a magnetic coding. The security element 2 is formed in this example as a security thread having along its longitudinal direction a magnetic coding of magnetic regions 2, between which non-magnetic material is located. These magnetic regions 2 can comprise highly coercive magnetic regions and/or lowly coercive magnetic regions and optionally also combined magnetic regions which contain both highly and lowly coercive magnetic material. Optionally, the value document also has a magnetically soft magnetic region 11 outside the security thread.

[0051] After magnetization in the magnetic field A, the value document 1 is transported past the magnetic sensor 10 which is installed in the apparatus for processing value documents so as to be spatially separate from the magnetic field A. The magnetic sensor 10 contains two sensor rows 12, 14 which respectively have a multiplicity of magneto-sensitive measuring sensor elements 7 of the same kind, which are arranged in a row. Each of these measuring sensor elements 7 supplies a magnetic signal, so that in this example a multiplicity of first magnetic signals are detected with the aid of the measuring sensor elements 7 of the sensor row 12 and a multiplicity of second magnetic signals are detected with the aid of the further magneto-sensitive elements 8 of the sensor row 14, which relate to the same section of the security element 2 transported past.

[0052] During the detecting of the first magnetic signals, the security element 2 is not subjected to any magnetic field. The magneto-sensitive elements 7 of the second sensor row 14 detect the second magnetic signals of the security element 2 under the action of a second magnetic field B, which acts on the security element 2 before and during the detecting of the second magnetic signals. The second magnetic field B is made available by a permanent magnet 18 arranged on one side of the transport path and has an extension such that it already magnetizes the security element 2 before the latter comes into the capture region of the second sensor row 14. The poles N, S of the magnet 18 are so aligned that there arises in the transport plane a magnetic field B anti-parallel to the transport direction T of the value document. The magnetic field strength of the magnetic field A amounts to, for example, at least twice the magnetic field strength of the magnetic field B. The detecting of the second magnetic signals under the action of the second magnetic field B has the advantage that the second sensor row 14 can be employed not only for detecting the different magnetic regions of the security element 2, but that it can also detect magnetic signals of magnetically soft magnetic regions of the security element 2, which can be present on the value document outside the security element 2.

[0053] The measuring sensor elements 7 of each of the sensor rows 12, 14 are each arranged on a common printed circuit board (wiring of the printed circuit boards not shown), and connected to a control and evaluation device 19, which drives the measuring sensor elements 7 and the further sensor elements 8 to detect the magnetic signals and evaluates their magnetic signals. The printed circuit board of the sensor row 14 and the magnet 18 are fixed mechanically to each other by potting so as to form one constructional unit. The control and evaluation device 19 receives magnetic signals from the two sensor rows 12, 14 and processes and analyzes them. The control and evaluation device 9 can be arranged together with the sensor rows 12, 14 in the same housing. Via an interface, data can be sent from the control and evaluation device 19 outside, for example to a device that processes the data further or to a display device that informs about the result of the value document check.

[0054] On the lower side of the printed circuit board 9 of the sensor row 12, a plurality of the further sensor elements 8 are arranged in each case, with the aid of whose measuring signal the distance correction according to the invention of the measuring signal of the measuring sensor elements 7 is carried out. In this example, fewer sensor elements 8 than measuring sensor elements 7 are employed, as shown in FIG 1b. Alternatively, however, a corresponding further sensor element 8 can also be present for each measuring sensor element 7 on the back side of the circuit board 9, as shown in FIG 1a. The second sensor row 14 on the lower side 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 also for the measuring signal of the measuring sensor elements 7 of the second sensor row 14. Amplifier chips for amplifying the detected measuring signal and correction signal can be arranged on the lower side of the printed circuit boards 9.

[0055] In FIG. 3, by way of example, a value document 1 is shown in a side view (viewing direction in the transport direction), which has an irregular distance to the surface of the measuring sensor elements 7, which is at z=0. In the right region, the value document has a distance to the sensor surface that is almost twice as large as in the left region.

[0056] In order to make possible a correction of the distance fluctuations of the value document, the progression of the signals of the measuring sensor elements and of the further sensor elements is ascertained as a function of the value document distance a before the value document check. For this purpose, for example, a value document is successively placed at different distances to an arrangement of one or a plurality of measuring sensor elements and one or a plurality of further sensor elements, said arrangement corresponding to the arrangement of the measuring sensor elements 7 and further sensor elements 8 in the magnetic sensor employed later for the value document check. For each distance a, a measuring signal of the respective measuring sensor element and a correction signal of the respective further sensor element are detected. Both signals show distance dependence, which decreases with increasing distance a of the value document, cf FIG. 4a, wherein M designates the measuring signals of the measuring sensor elements and K designates the correction signals of the further sensor elements. Due to the greater distance a of the further sensor elements 8 from the value document, the correction signals of the further sensor elements 8 are always below the measuring signals of the measuring sensor elements 7. The measuring signals of FIG. 4a were normalized to a nominal target distance d of the value document from the measuring sensor elements of 1 mm.

[0057] Subsequently, the ratio of the signals shown in FIG. 4a (quotient M/K) is formed for the various value document distances a. This results in the dependence of the value document distance a shown in FIG. 4b from the ratio K/M of the measuring signals M of the measuring sensor elements 7 to the correction signals K of the further sensor elements 8. The dependence shown in FIG. 4b can be stored in the control and evaluation device 19 of the magnetic sensor as a function or as a look-up table.

[0058] The distance correction will be explained in the following using the example of the measuring signals detected by the first sensor row 12 from the security thread of the value document 1, with which the magnetization of the value document 1 without external magnetic field is detected, but is equally applicable to a distance correction of the measuring signals of the sensor row 14, which detects the magnetization of the value document 1 in the magnetic field. However, the distance correction described in the following is also suitable for other types of magnetic security elements of value documents, for example for a motif or partial motif of magnetic printing ink.

[0059] FIG. 5 a shows, by way of example, the measuring signal of the sensor row 12, detected by the same from a magnetic security element which has a plurality of magnetic regions b1, b2, b3 and b4 along a direction designated by y. The arrangement of the magnetic regions along the security element (along the y-direction) is sketched above the diagram in FIG. 5a. The measuring signal represented in FIG. 5a was detected by a multiplicity of measuring sensor elements 7 which are arranged along the y-direction. For example, these are the measuring signals of the measuring sensor elements 7 detected at a specific point in time, while the value document equipped with this security element is transported past the magnetic sensor. As a function of the position coordinate y, in this example each magnetic region b1-b4 supplies a measuring signal in the form of a double peak. FIG. 5b shows the corresponding correction signal detected by the further sensor elements 8 arranged behind the measuring sensor elements 7 from the magnetic regions b1-b4 of this security element at the same measuring time. The double peaks of the correction signals are lower than those of the measuring signals of the measuring sensor elements 7, corresponding to the greater distance of the further sensor elements 8 from the value document. To quantify the measuring signals and the correction signals, for example, the maximum of the double peak is determined, and this maximum value is employed for the further evaluation as a measuring signal M or correction signal K. Alternatively, however, it is also possible to employ respectively 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.

[0060] In order to determine a correction function F(y) for the measuring signal M of FIG. 5a, the respective correction signal K is compared with the respective measuring signal M of the measuring point for the measuring points along the y-direction, for example by forming the ratio. FIG. 6a shows the ratio of these signals as a function of the position coordinate y for those measuring points at which both a measuring signal M and a correction signal K were detected. Since the number of further sensor elements 8 is smaller than the number of measuring sensor elements 7, and thus both signals are present only for a few measuring points, the ratio formation is limited to those measuring points along the y-direction for which a correction signal was actually detected as well.

[0061] However, the ratio is preferably formed only for such measuring points or sensor elements which supply a clear measuring signal, for example whose measuring signal is above a certain threshold S. For example, the threshold of S=1 drawn in FIGS. 5a and 5b is employed for this purpose. 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 are below the threshold S=1 are ignored for the ratio formation and the subsequent distance correction, for example the measuring points in the region y=40, in which according to FIG. 5a, no magnetic region is present. This avoids a possibly erroneous distance correction, which can lead to strongly falsified values.

[0062] From the ratios shown in FIG. 6a, the distance of the value document from the measuring sensor elements 7 at the respective y-position is determined for each of the y-positions chosen in this way. For this purpose, the ratio at the respective y-position is converted into a distance on the basis of the relationship between ratio and distance ascertained before the value document check, as shown in FIG. 4b. FIG. 6b shows the progression ascertained in this manner of the local distance of the respective measuring point of a value document from the measuring sensor elements 7 for the chosen y-positions. In addition, a fit function adjusted thereto is drawn in, which has a continuous progression, and is employed to determine the value document distance for each of the measuring sensor elements 7 (thus also including those whose y-position was not chosen).

[0063] By integrating the actual distance values of the value document shown in FIG. 6b into the distance dependence of the expected measuring signal of FIG. 4a ascertained before the value document check, a specific factor results for each y position by which the measuring signal of the respective measuring sensor element is falsified due to the actually ascertained distance. For example, in the region y=55, where an actual value document distance of approximately 1.9 mm was ascertained, there results, on the basis of the distance dependence of the measuring signal of FIG. 4a ascertained before the value document check, a measuring signal that is reduced by a factor of approximately 2.3 in comparison to the distance y=1 (corresponding to a proportion of about 43%, cf FIG. 4a). For a distance correction, the measuring signal at y=55 is therefore to be multiplied by a correction factor of 2.3. In this manner, the correction function F(y) shown in FIG. 6c is ascertained, which indicates this correction factor F for each individual y-position.

[0064] For distance correction, the measuring signal M(y) of FIG. 5a detected from the magnetic regions b1-b4 by the measuring sensor elements 7 is multiplied with the correction function F(y). The result of this correction is represented in FIG. 5c. Due to the standard spacing of a=1 mm defined before, through this correction the measuring signal is obtained which would be expected from the value document if it were transported past all y-positions at the ideal standard distance of 1 mm. In comparison to the actually detected measuring signal of FIG. 5a, in which the left double peak of the magnetic region b1 is significantly higher than the right three double peaks, the distance correction carried out leads firstly to the double peaks of the two long magnetic regions b1 and b3 being matched to one another and secondly to the double peaks of the two short magnetic regions b2 and b4 also being matched to one another. The corrected measuring signal is subsequently employed to check the value document. In particular, a magnetic coding of a security element of the value document can thus be checked or the magnetic imprint of a value document can be checked. To check the value document, the corrected measuring signal is compared, for example, with a measuring signal expected for the security element. The result can be employed, for example, in the context of a quality check or an authenticity check of the value document or to determine the identity of the value document.