WO2000068899A1

WO2000068899A1 - Device for detecting a magnetic characteristic of a test object

Info

Publication number: WO2000068899A1
Application number: PCT/CH2000/000206
Authority: WO
Inventors: Martin Paping; Markus Jungen
Original assignee: De La Rue International Limited
Priority date: 1999-05-06
Filing date: 2000-04-10
Publication date: 2000-11-16
Also published as: AU3548300A; EP1050855A1; TW446920B; EP1181672A1

Abstract

A device for detecting a test object (3) fitted with a magnetic characteristic (12) and guided on a transport track (2) characterized in that as many magnetic field sensors (5.1, ..., 5.N; 6.1, ..., 6.N) as possible are mounted in a constructional unit (1) along the entire width of the transport track. Magnetizing means also extend along the entire width of the transport track. The magnetic field sensors are Hall sensors in the shape of a chip, which are placed at regular distances on at least one, preferably two straight lines (7, 8) crosswise in relation to the direction of transport. The device is particularly suitable for banknote detection automatic machines.

Description

Device for detecting a magnetic identifier of a test object

Technical field

The invention relates to a device for detecting a test object provided with a magnetic identifier and guided on a transport path with a plurality of magnetic field sensors and at least one magnetization means. Furthermore, the invention relates to a bank note checking machine with such a device. State of the art

From EP 0 640 841 A1 a device for checking the magnetic property of an American banknote is known. Four magnetic heads are used, which are connected in series in the transport direction of the banknote. The first head applies a saturation field. If the banknote moves away from the area of influence of this head, a magnetic saturation remanence remains, which is read by the second head, which can be combined with the first to form a structural unit. The third head applies a non-saturating field of opposite polarity and the fourth head reads the magnetic remanence field. If the banknote is genuine, the remanence field signals read by the second and fourth head are opposite in opposite directions, that is to say they are out of phase by 180 °. Counterfeits with high coercivity show a different behavior and can thus be recognized.

The method known from EP 0 640 841 A1 thus measures the magnetic behavior (hysteresis curve) of a magnetizable layer of low particle density.

Sensor arrangements are also known with which the different strip spacings of a US banknote can be detected. WO 94/12952 is cited as an example. For each magnetic stripe pattern to be recognized, two or more sensors are placed next to one another, at a distance corresponding to the period of the respective stripe pattern. So e.g. To differentiate between three different stripe patterns, three different sensor arrangements with typically three magnetoresistive sensors arranged next to each other are required.

The known devices are specifically geared to the identification features present in US banknotes and cannot readily be used for other currencies.

Presentation of the invention The object of the invention is to provide a device of the type mentioned at the outset, which is suitable for checking a multiplicity of different magnetic identification features without the need for a structural change.

The solution to the problem is defined by the features of claim 1. Accordingly, a test device for banknotes (test object) comprises the largest possible number of magnetic field sensors and at least one magnetizing means for magnetizing a test area. The magnetic field sensors and the magnetization means each extend over the entire width of the transport path of the banknote, the magnetic field sensors being accommodated in a structural unit which extends over an entire width of the transport path.

The invention makes it possible to equip automatic test machines for different currencies with a standardized test device for checking the magnetic identification of whatever type. The differentiation related to the test object can be achieved purely in software. In other words, the hardware is the same for all applications, only a different (specific) software is loaded.

Depending on the embodiment of the invention, for example depending on the size of the magnetization means or the magnetic field strengths to be generated, the magnetization means are advantageously housed outside or together with the magnetic field sensors within the assembly.

The magnetizing means preferably comprise a permanent magnet which extends over the entire width. In order to bring this magnetic field into the surface of the test object, two pole shoes, which also extend over the entire width of the transport path, can be provided with a gap in between.

The field for premagnetizing or saturating the layer can also be generated with electromagnetic means. The magnetic field sensors used are preferably the Hall element sensors of the type described in EP 0 772 046 A2 (Sentron AG). These can be integrated in a chip and take up little space. They can detect low field strengths parallel to the chip surface and are relatively insensitive to external interference fields (for example also to stray fields from the magnetization means).

A magnetic field sensor of the type described has two flux concentrators with an air gap between them and at least one Hall element outside the air gap. At least some of the magnetic field lines leading from the first flux concentrator to the second flux concentrator flow through the Hall element. The sensors mentioned can be integrated on a chip using the known techniques of microelectronics. Such a so-called cylindrical Hall element is sensitive to the magnetic field that is parallel to the surface in which the magnetic flux concentrators are integrated. Overall, such an element is particularly well adapted to the direction of magnetization of the banknote.

To improve the geometric resolution, the sensors can be constructed in two rows arranged offset from one another. The sensors in the rear row are therefore in the spaces between those in the front row. The two rows are arranged as close together as possible. The distance between the rows is e.g. in the order of the distance between the sensors within a row. If the banknotes are transported transversely to their longitudinal direction, several dozen sensors are typically provided per row according to the invention. In this way, a geometric resolution in the range of a few millimeters can be achieved.

The magnetic field sensors are advantageously arranged on a plate-shaped carrier element, which is attached on the end face and essentially perpendicular to a circuit board for signal processing. The carrier element (with all Hall sensors) is considerably smaller than the circuit board mentioned (which can be equipped on both sides). The result is a compact T-shaped construction. If a magnetic shield (partition) is provided between the magnetizing means and the carrier element or the sensors, the dimensions of the structural unit in the direction of the note transport direction can be minimized.

To protect against dust and damage, the magnetic field sensors can be arranged behind a cover (e.g. an epoxy resin plate coated with copper). This is in accordance with the basic idea of the invention to create a self-contained unit which can be inserted as a finished module in a holder of an automatic test machine and connected in terms of data via a standardized interface.

As already mentioned, the test device according to the invention is specifically for banknote recognition, in combination e.g. suitable with optical test units. According to the same principle, other test objects with a geometric magnetic marking can also be examined.

From the following detailed description and the entirety of the claims, further advantageous embodiments and combinations of features of the invention result.

Brief description of the drawings

The drawings used to explain the exemplary embodiment show:

Fig. 1 is a schematic representation of a module according to the invention in the

Top view;

Fig. 2 is a schematic representation of the module in cross section.

In principle, the same parts are provided with the same reference symbols in the figures.

Ways of Carrying Out the Invention 1 shows a top view of a module 1 according to the invention. It is arranged on a transport path 2, which runs here in the plane of the drawing and is symbolized by two lines. Its width is greater than the width B of the transport track 2.

Banknotes 3 are conveyed unreferenced on the transport path 2 at a relatively high speed in the transport direction 4. Unreferenced means that the lateral position with respect to the web boundaries is not fixed. A first banknote can therefore be located more on the left and a subsequent second one more on the transport path 2. It is even possible for bank note 3 to arrive with a slight inclination. In the example according to FIG. 1, the bank note 3 is conveyed in the transverse direction, i. H. the long side of the bank note 3 is perpendicular to the transport direction 4.

According to the invention, module 1 has a large number of Hall sensors 5.1, ..., 5.N, 6.1, ..., 6.N. They are preferably arranged in two rows 7, 8 (transverse to the transport direction 4). On each row 7, 8 there are e.g. N = 40 to N = 50 Hall sensors with the smallest possible mutual distance. The Hall sensors 6, 1. ..., 6, N of the second row 8 are placed in the spaces between the Hall sensors 5.1, ... 5.N of the first row 7. The resolution (viewed transversely to the direction of transport 4) can thus be brought to several lines per centimeter.

The sensor arrangement described is preceded by a small magnetizing gap 9 which extends over the entire width of the module 1. It is formed between the two pole pieces 10, 1 1. It brings a saturating magnetic field into the transport path (and thus into the test object).

When the bank note 3 with its magnetic identifier 12 is guided past the module 1, the magnetizing gap first pre-magnetizes the identifier 12 (which is, for example, a number printed with magnetic ink). If the identifier 12 then passes the Hall sensors, these are activated. This means that the Hall sensors in the affected area signal a magnetic field. Through a clocked activation of the sensors, the bank note 3 can additionally generate a resolution in the transport direction and thus a magnetic pixel image. In principle, this can processed digitally like an optical image. For referencing the magnetic pixel image, the result of an optical position determination (derived with a module upstream in the transport direction) can be used if necessary.

It should be noted that the magnetic identifier, wherever it is on the test object and what dimensions it has, can be detected with the device according to the invention.

In order to achieve a good signal-to-noise ratio, the bandwidth of the amplifier should be adapted to the speed of the banknote and the desired spatial resolution. (With a banknote speed of e.g. v = 800 mm / s and a desired resolution of Lmin = 2 mm, Lmax = 10 mm, the required frequency band lies between Fmin = v / Lmax = 80 Hz and Fmax = v / Lmin = 400 Hz.)

2 shows an example of the cross section of a specific embodiment. A rod-shaped permanent magnet 14 is attached to the front of a carrier 13 (which can, for example, be an integral part of the module housing). (The longitudinal axis of the permanent magnet 14 is perpendicular to the plane of the drawing.) To the side of the permanent magnet 14 are the (magnetically conductive) pole pieces 10 and 11, which form a magnetizing gap 9 where they adjoin the transport path 2.

A shield 15 is provided laterally next to the pole shoe 11 in the carrier 13. For example, it is a partition made of a suitable material. It is perpendicular to the transport path 2 (front of the module) and is intended to keep the stray field of the magnetizing means mentioned away from the sensor part of the module 1. Depending on the strength of the stray field, the shield 15 can also be omitted.

The strength of the stray field acting on the sensor part can be influenced by varying the distance of the magnetizing gap 9 from the sensor part. An enlargement of this distance and thus a reduction in the stray field is achieved by a carrier 13 extended in the direction of the pole piece 10 or by attaching the permanent magnet 14 outside the carrier 13, for example in a separate module. The sensor part is closed toward the transport path 2 by an epoxy resin plate 16, for example with a copper coating 17 (spring bronze) as a cover. The coated side of the epoxy resin plate 16 and that in front of the side of the pole shoes 10, 11 form a continuous smooth plane, on which the bank note (driven by suitably arranged rollers) can slide. A ceramic circuit board 19 is attached to the back of the epoxy resin plate 16. It carries the Hall sensors 5.1, 6.1 designed as chip elements.

So that the distance between the Hall sensors 5.1, 6.1 from the transport path 2 (and thus from the banknote) can be kept as small as possible, the epoxy resin plate 16 is provided in the corresponding area with a recess 18 (e.g. milling).

The ceramic circuit board 19 is attached to the front of a circuit board 22 for the sensor electronics via two angle pin strips 20, 21. The latter is thus perpendicular to the front of module 1. The sensor electronics carries out the processing (amplification, multiplexing) of the sensor signals so that they can be passed on to an evaluation unit (not shown) via a uniform interface.

The linear arrangement of the Hall sensors generates an analog voltage proportional to the magnetic field for each pixel.

The module 1 has a housing made of aluminum and is preferably provided with mounting elements or mechanical couplings, so that it can be installed in a banknote recognition machine with just a few hand movements.

The invention is not limited to the described embodiments. Basically, one or two rows of sensors are preferred, but in special circumstances more (e.g. three) rows can also be provided. The sensor elements of the different rows should be placed offset to one another in order to achieve the greatest possible resolution.

Instead of Hall sensors, other components can also be used. In any case, however, the distance between the sensors does not imply a periodicity of a agreed magnetic structure of the test object, but is aimed at the desired image resolution. Usually the sensors are placed as close to each other as possible. The electronics can also be at least partially integrated on the magnetic field sensor chip.

The structural design according to FIG. 2 allows a compact design, but its type is not essential for the objective of the invention. In particular, there are also other options for designing the front end or for accommodating the sensor electronics.

In summary, it can be stated that the invention has created a versatile structural unit which is advantageous in terms of production technology in order to detect and test magnetic patterns.

Claims

claims

1. Device for detecting a test object (3) provided with a magnetic identifier (12) and guided on a transport path (2) with several magnetic field sensors and at least one magnetizing means, characterized in that the magnetic field sensors and the magnetizing means are located over the whole

Extend the width of the transport path and that the largest possible number of magnetic field sensors (5.1, ..., 5.N; 6.1, ..., 6.N) are accommodated in a structural unit (1) which extends over an entire width of the transport path.

2. Device according to claim 1, characterized in that the magnetizing means are also accommodated in the structural unit.

3. Device according to claim 1 or 2, characterized in that the magnetizing means comprise a rod-shaped permanent magnet (14).

4. Device according to one of claims 1 to 3, characterized in that the magnetic field sensors are cylindrical Hall elements with a sensitivity to a field parallel to a surface of the test object and that they are in regular

Distances are arranged on at least one straight line (7, 8).

5. Device according to one of claims 1 to 4, characterized in that the magnetic field sensors are arranged offset on two straight lines (7, 8) lying directly one behind the other.

6. Device according to one of claims 1 to 5, characterized in that the magnetic field sensors (5.1, ..., 5.N; 6.1, ..., 6.N) on a ceramic carrier plate (19) on the front side and essentially are mounted perpendicular to a printed circuit board (22) equipped with signal conditioning electronics.

7. Device according to one of claims 1 to 6, characterized in that a magnetic shield is provided between the magnetizing means and the magnetic field sensors (5.1, ..., 5.N; 6.1, ..., 6.N).

8. Device according to one of claims 1 to 7, characterized in that the magnetic field sensors (5.1, .... 5.N; 6.1, .... 6.N) to the transport path (2) through a metal-coated epoxy resin plate (16 ) are covered.

9. Device according to one of claims 1 to 8, characterized in that more than 20 magnetic field sensors (5.1, ..., 5.N; 6.1, ..., 6.N) are provided in order to detect a banknote identifier .

10. banknote checking machine with at least one device according to claim 1.

1 1. Banknote checking machine according to claim 10, characterized in that optical detectors for determining the position and location of the supported banknote are also provided.