HK1111215B - Position detector and method for detecting a position of a packaging material with magnetic marking - Google Patents

Description

Position detector and method for detecting the position of a packaging material with magnetic markings

Technical Field

The present invention relates to a position detector arrangement for determining the position of a packaging material with magnetic markings, and to a method for determining the position of a packaging material with magnetic markings.

Background

It is known that magnetic sensors or detector elements can be used to establish and record the occurrence of a magnetic field, and it is also known that magnetic labels can be provided on a carrier readable by a magnetic sensor. Difficulties will frequently occur if magnetic sensors of the known type are used to detect magnetic marks which have been applied, for example, to a sheet of packaging material (web) to control the forwarding of the sheet or to control other working operations, because of the presence of strong magnetic interference fields. For example, in packaging machines, sealing is frequently performed by means of induction coils which are energized with a high current to induce a strong magnetic field. Similarly, in modern machines, there are electrical machines (e.g., motors and transformers) that can generate significant magnetic fields. In european patent No.317879, a method and apparatus are described for suppressing the influence of magnetic interference fields when detecting magnetic marks or marks applied on a carrier. However, there is still a need for improved position detection for determining the position of the packaging material.

Disclosure of Invention

In view of the above, it is an object of the present invention to solve or at least reduce the problems discussed above. In particular, it is an object to provide an efficient position determination of the packaging material.

The invention is based on the understanding that the sum of the output signals from a plurality of magnetic sensors means the suppression of magnetic interference.

According to a first aspect of the present invention, there is provided a position detector arrangement for detecting the position of a packaging material carrying a magnetic marking, comprising a sensor assembly comprising a plurality of magnetic sensor units, each unit comprising an output providing an output signal, wherein the magnetic sensor units are arranged in at least two pairs of sensor units, the sensor units of each pair being arranged with opposite sensitivity directions, and the sensor units being arranged to sense the magnetic marking of the packaging material; a signal processing component connected to the output of the magnetic sensor, comprising a combiner arranged to aggregate the output signals of the sensor into an aggregate signal; and a detector arranged to determine the position of the packaging material from the aggregate signal.

One benefit of this aspect is to allow for efficient position determination when magnetic disturbances are coming from e.g. electrical machines, and when dust is coming from e.g. the packaging material. In addition, one advantage is that the sensor does not need to be in direct contact with the packaging material. Again, one benefit is that signal processing is simple.

Each sensor unit pair may comprise one magnetic sensor unit arranged in operation closer to the packaging material than the other magnetic sensor of the pair.

The sensor unit may be a Wheatstone bridge (Wheatstone bridges) comprising magneto-resistive sensors.

The detector may be arranged to determine the position by detecting a zero crossing of the aggregate signal.

The detector may comprise means for detecting a predetermined level of the aggregate signal before the zero crossing occurs. The detector may comprise means for detecting a predetermined change in the level of the aggregated signal prior to the zero crossing.

These features provide a correct look-up for the zero crossing by observing the level or slope of the signal, or both. These features also enable fast detection, i.e. providing a detection output signal with little or no latency.

The apparatus may further include a first magnetic compensation sensor unit disposed with its sensitivity direction perpendicular to the sensitivity directions of the plurality of magnetic sensor units, and a second magnetic compensation sensor unit disposed with its sensitivity direction perpendicular to the sensitivity directions of the plurality of magnetic sensor units and the sensitivity direction of the first magnetic compensation sensor unit.

The signal processing assembly may be connected to the first and second magnetically compensated sensor cells and arranged to suppress signal components from the plurality of magnetic sensor cells perpendicular to a sensitivity direction of the plurality of magnetic sensor cells.

The position detector means may comprise adjusting means for said output signal of said magnetic sensor unit.

The sensitivity direction of the magnetic sensor unit and the magnetic direction of the magnetic labels may be parallel or anti-parallel, respectively. Alternatively, the sensitivity direction of the magnetic sensor unit may be perpendicular to the magnetic direction of the magnetic labels.

The quotient between the spacing between the two sensors facing the marking and the size of the marking in the position detection direction is between 0.6 and 3, preferably between 0.7 and 1.8, preferably between 0.85 and 1.4, and preferably approximately 1.

According to a second aspect of the present invention, there is provided a method for determining the position of a packaging material carrying magnetic markings, comprising the steps of: generating a plurality of sensor signals responsive to the magnetic force of the magnetic marker using a plurality of magnetic sensor pairs, each magnetic sensor pair comprising magnetic sensor cells arranged in anti-parallel; aggregating the sensor signals into an aggregate signal; and determining a location from the aggregate signal.

The benefits of this aspect are substantially the same as the first aspect of the invention.

The step of determining the position may comprise the steps of: detecting a zero crossing of the aggregated signal; and determining the position from the zero crossing.

The method may further comprise the steps of: generating a first compensation signal dependent on a first magnetic force component in the direction perpendicular to the sensitivity direction of the magnetic sensor pair; generating a second compensation signal dependent on a second magnetic force component in a direction perpendicular to the direction of sensitivity of the magnetic sensor to the component and the first magnetic force component; and compensating the sensor signal field of the magnetic sensor pair for a magnetic force component perpendicular to the sensitivity direction of the magnetic sensor pair by means of the first and second compensation signals.

The method may further comprise the step of adjusting the output of said magnetic sensor.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the art unless otherwise specifically defined herein. All references to "a/an/the (element, device, component, means, step, etc.) are to be interpreted openly as referring to at least one of said element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

The term "magnetic force" should be interpreted as any amount of magnetism. The term "magnetic sensor" should be interpreted as any device that can detect or measure magnetic force. The term "sensitivity direction" means the direction in which a positive magnetic quantity results in a positive electrical output signal. The term "pair of sensor units" should be understood as functional and not referring to the number of physical devices.

Other objects, features and advantages of the present invention will become apparent from the following more detailed disclosure, from the appended dependent claims and from the accompanying drawings.

Drawings

The foregoing and other objects, features and advantages of the invention will be better understood from the following non-limiting detailed description of a preferred embodiment of the invention with reference to the drawings, in which like reference numerals are used for like elements, and in which:

FIG. 1 is a block diagram schematically illustrating a position detection apparatus according to an embodiment of the present invention;

FIG. 2 is a block diagram schematically illustrating a position detection apparatus according to an embodiment of the present invention;

FIG. 3 is a schematic diagram showing the location of two pairs of sensor units according to one embodiment of the present invention;

4a-4e are signal diagrams schematically showing the timing of signals when a magnet or magnetized portion of the packaging material passes a sensor unit arranged according to the display of FIG. 3;

FIG. 5 is a schematic diagram showing the location of two pairs of sensor units according to one embodiment of the present invention;

6a-6e are signal diagrams showing the timing of signals as the magnet or magnetized portion of the packaging material passes over the sensor unit according to the configuration shown in FIG. 5;

FIG. 7 is a schematic diagram showing the location of two pairs of sensor units and a compensation sensor according to one embodiment of the present invention;

FIG. 8 is a schematic diagram showing the location of two pairs of sensor units with conventional sensors according to one embodiment of the present invention;

FIG. 9 is a schematic wiring diagram of a position determining device according to the embodiment of the present invention depicted in FIG. 8;

fig. 10 is an electrical wiring diagram of a magnetic sensor unit according to an embodiment of the present invention;

FIG. 11 is an electrical wiring diagram of an adder circuit according to one embodiment of the invention;

FIG. 12 schematically illustrates a combined connection of two sensor units and an adder according to an embodiment of the invention;

FIG. 13 is a schematic wiring diagram of an adder circuit according to an embodiment of the invention;

FIG. 14 is a flow chart of a method for determining the position of a packaging material with magnetic markings according to one embodiment of the present invention; and

FIG. 15 is a flow chart of a method for determining the position of a packaging material with magnetic markings according to one embodiment of the present invention.

Detailed Description

Fig. 1 is a block diagram schematically illustrating a position determining apparatus 100 configured to determine the position of a packaging material (not shown) by determining time when a magnetic marker is disposed in, on, or beside the packaging material. The apparatus 100 includes a plurality of sensors 102 that provide output signals responsive to the magnetic force of the magnet or magnetized material. The output signals are aggregated in a signal processing device 104 to produce an aggregated signal, which is provided to a detector 106. The detector 106 determines the position of the magnetic marker from the aggregate signal.

Fig. 2 is a block diagram schematically illustrating a position determining apparatus 200 arranged to determine the position of the packaging material (not shown) by determining the time during which magnetic marks arranged in, on or beside the material, or in, on or beside a magnetized portion of the material, pass the apparatus 200. The position determining apparatus 200 includes a power source 202 for providing power to the electronic components of the apparatus 200. The apparatus 200 comprises a plurality of magnetic sensor units 204, 205, 206, 207 arranged in pairs 208, 209. In each pair 208, 209, one magnetic sensor cell 204, 206 is arranged with its sensitivity direction in one direction and the other magnetic sensor cell 205, 207 is arranged with its sensitivity direction in the opposite direction, i.e. the magnetic sensors 204, 205, 206, 207 of a pair are arranged anti-parallel. By sensitivity direction is meant the relationship between the output signal polarity and the direction of the magnetic force (i.e. magnetic field or magnetic current). The outputs of the magnetic sensor units 204, 205, 206, 207 are aggregated in one or more adder circuits 210, 211, 212 to produce an aggregate signal of the sensor output signals. The aggregate signal is analyzed in a detector 214, which detector 214 is arranged to determine a certain well-defined point of the aggregate signal. The well-defined point of the aggregate signal may be a center zero crossing of the aggregate signal.

FIG. 3 is a schematic diagram showing the location of two sensor unit pairs 301, 302, each comprising two sensor units 304, 305, according to one embodiment of the present invention; 306. 307, with antiparallel sensitivity directions 308, 309; 310. 311, and a portion of wrapping material 312, where the wrapping material is moving from right to left as indicated by arrow 313, and within which is disposed a magnet 314. In order to obtain an output signal from the sensors 304-307, which signal is aggregated to provide an aggregate signal from which easily detectable and well-defined zero crossings can be determined, the spacing a between the sensors of the sensor pair in the device, measured in the direction of exposure of the magnetic marker to the sensor, i.e. in the position determining direction, is substantially equal to the size b of the magnetic marker. Here, the distance a is the distance between the center of the sensor device and the center of the outer sensor unit 304, since it is empirically found that this is a practically effective spacing. When the magnetic marker approaches the sensor, a concurrent output (current output) of the sensor will be provided. The quotient a/b between the spacing a between a pair of sensors and the dimension b of the magnetic marker is preferably between 0.6 and 3, more preferably between 0.7 and 1.8, even more preferably between 0.85 and 1.4, and most preferably about 1.

Fig. 4a-4e are signal diagrams showing the timing of signals when a magnet or magnetized portion of the packaging material passes the sensor unit according to the configuration shown in fig. 3. Fig. 4a shows the output signal of the first sensor unit pair when the magnet passes. Since the magnetic field is in the same direction as the sensitivity of the sensor cell, the output signal has a positive polarity and increases as the magnet approaches. The output signal decreases as the magnetic field component decreases in the sensitivity direction as the magnet passes by, to change polarity when the magnetic field component becomes negative in the sensitivity direction. As the magnet continues to pass, the output signal gradually increases to zero. Fig. 4b shows the output signal of the second sensor unit of the first sensor unit pair when the magnet passes. The output signal has an opposite polarity due to the anti-parallel arrangement compared to the output signal of the first sensor unit of the pair shown in fig. 4a, and the output signal varies temporally in time due to the arrangement of the second sensor unit beside the first sensor unit. Interference from more distant magnetic sources (e.g. motors, power lines, etc.) than from the magnetic markers will result in zero when the output signals from the sensor units of the pair are aggregated, since they have opposite sensitivity directions and are arranged in close proximity to each other, i.e. experience the same interference. Thereby, interference is suppressed. For reasons of simplicity, any disturbances are not shown in the signal diagram, since they may obscure the aggregation principle of the output signal.

Similar to fig. 4a and 4b, which describe the first pair of sensor units, fig. 4c and 4d show the output signals of the second pair of sensor units depicted in fig. 3. Fig. 4c shows the output signal of the first sensor unit of the second pair, which is only slightly changed in time because its sensitivity direction has a similar shape and polarity as the output of the second sensor of the first pair, and because the position (where the sensor unit is arranged) is close to the second sensor of the first pair, which is depicted as zero time change in fig. 4 c. The output signal of the second sensor unit of the second pair as depicted in fig. 4d is similar in shape, but further varies with time and, because of its parallel sensitivity direction, has a similar polarity as the first sensor output of the first pair. Fig. 4e depicts the aggregate signal, including the aggregate output signal of the sensor unit. The position is determined from the aggregated signal by determining a zero crossing 400, as will be described below.

FIG. 5 is a schematic diagram showing the location of two sensor unit pairs 501, 502, each sensor unit pair comprising two sensor units 504, 505, according to one embodiment of the present invention; 506. 507 and having antiparallel sensitivity directions 508, 509; 510. 511 and shows a portion of the wrapping material 512 where the wrapping material is moving from right to left as indicated by arrow 513 and a magnet 514 is disposed within the material. In order to obtain the output signal from the sensors 504-507, which signals are aggregated to provide an aggregate signal from which easily detectable and well-defined zero crossings can be determined, the spacing a between the sensors of the sensor pair in the device, measured in the direction in which the magnetic mark is exposed to the sensor, is substantially equal to the size b of the magnetic mark. When the magnetic marker is in proximity to the sensor, a concurrent output of the sensor will be provided. The quotient a/b between the spacing a between a pair of sensors and the dimension b of the magnetic marker is preferably between 0.6 and 3, more preferably between 0.7 and 1.8, even more preferably between 0.85 and 1.4, and most preferably about 1. Fig. 6a-6e are signal diagrams showing the timing of signals when a magnet or magnetized portion of the packaging material passes the sensor unit according to the configuration shown in fig. 5. Fig. 6a shows the output signal of the first sensor unit pair when the magnet passes. The output signal is negative because the magnetic field is opposite to the sensitivity direction of the sensor unit, and decreases when the magnet is close. When the magnet coincides with the sensor unit, the output signal increases, because the magnetic field component in the sensitivity direction is approximately along the magnetic field lines of the magnet. The output signal gradually decreases to zero as the magnet continues to pass, then becomes negative when the magnet has passed the sensor unit, and finally drops to zero when the magnet is farther away. Fig. 6b shows the output signal of the second sensor unit of the first sensor unit pair when the magnet passes. The output signal has the opposite polarity due to the anti-parallel arrangement compared to the output signal of the first sensor unit of the pair shown in fig. 6a and has a smaller absolute value because the second sensor unit is arranged further away from the mark than the first sensor unit. Interference from more distant magnetic sources (e.g. motors, power lines, etc.) than from the magnetic markers will result in zero when the output signals from the sensor units of the pair are aggregated, since they have opposite sensitivity directions and are arranged in close proximity to each other, i.e. experience the same interference. Thereby, interference is suppressed. For reasons of simplicity, any disturbances are not shown in the signal diagram, since they may obscure the aggregation principle of the output signal.

Similar to fig. 6a and 6b, which depict the first pair of sensor cells, fig. 6c and 6d show the output signals of the second pair of sensor cells depicted in fig. 5. Fig. 6c shows the output signal of the first sensor unit of the second pair, which has a similar shape, but, due to its direction of sensitivity, has an opposite polarity to the first sensor output of the first pair, and, due to the position where the sensor unit is arranged, the output signal varies with time. As depicted in fig. 6d, the output signal of the second sensor unit of the second pair is similar in shape, but further opposite in polarity and has a smaller absolute value similar to the output of the second sensor of the first pair due to its distance from the mark. Fig. 6e depicts the aggregate signal, which comprises the aggregate output signal of the sensor units. The position is determined from the aggregated signal by determining the mid-zero crossing 600.

FIG. 7 is a schematic diagram showing the location of two pairs of sensor units 701, 702, each pair comprising two sensor units 704, 705 according to one embodiment of the present invention; 706. 707 and having antiparallel sensitivity directions 708, 709; 710. 711 and a portion of packaging material 712 is shown where the packaging material is moving from right to left as indicated by arrow 713 and where a magnet 714 is disposed within the material. In fig. 7, one of the sensor units 705 is depicted as being slightly tilted by an angle α, i.e. not being exactly parallel to the other sensor 704 of the sensor unit pair 702. This will result in the sensor unit 705 providing a signal with less interference rejection, according to the sensor pair principle. To compensate for this signal, a first magnetically compensated sensor unit 716 is arranged with its sensitivity direction 717 perpendicular to the main direction of the sensor units 704, 705, 706, 707 of the sensor unit pairs 701, 702, and a second magnetically compensated sensor unit 718 is arranged with its sensitivity direction 719 perpendicular to the main direction of the sensor units 704, 705, 706, 707 of the sensor unit pairs 701, 702 and the magnetically compensated sensor unit 716. By increasing or decreasing the values received by the compensation sensors 716, 718, any angular deviation of the sensor units 704, 705, 706, 707 of the sensor unit pairs 701, 702 can be compensated.

FIG. 8 is a schematic diagram showing the location of two pairs of sensor units 801, 802 having a common sensor unit 805, and thus each comprising "two" sensor units 804, 805, according to an embodiment of the present invention; 805. 807 and having antiparallel sensitivity directions 808, 809; 809. 811 and shows a portion of the packaging material 812 where the packaging material is moving from right to left as indicated by arrow 813 and where a magnet 814 is disposed within the material. In order to obtain an output signal from the sensors 804 and 807, which signal is aggregated to provide an aggregate signal from which easily detectable and well-defined zero crossings can be determined, the spacing a between the sensors of a sensor pair in the device, measured in the direction of exposure of the magnetic marks to the sensors, is substantially equal to the size b of the magnetic marks. When the magnetic marker is in proximity to the sensor, a concurrent output of the sensor will be provided. The quotient a/b between the spacing a between a pair of sensors and the dimension b of the magnetic marker is preferably between 0.6 and 3, more preferably between 0.7 and 1.8, even more preferably between 0.85 and 1.4, and most preferably about 1.

Fig. 9 schematically shows a wiring diagram of an assembly 900 according to the embodiment of the invention depicted in fig. 8. The assembly comprises a first sensor pair 902 comprising sensors 906, 907 and a second sensor pair 904 comprising sensors 907, 908, i.e. the sensor pairs 902, 904 have a common sensor 907. The signals from the first sensor pair 902, i.e. the signals from the sensors 906,907, are aggregated in a first aggregation means 910. The signals from the second sensor pair 904, i.e. the signals from the sensors 907, 908, are aggregated in the second aggregation means 912. The aggregate signals from the first and second aggregation means 910, 912 are aggregated in the third aggregation means 914 to provide an aggregate signal from which the detector 916 can determine the position of the magnetic marker.

Fig. 10 is an electrical wiring diagram of a magnetic sensor unit 1000 according to an embodiment of the present invention. The sensor unit 1000 includes four magnetic sensors 1002, 1003, 1004, 1005 connected to form a wheatstone bridge 1006. The bridge 1006 is energized at input terminals 1008, 1009 by a drive voltage or drive current (depending on the type of the magnetic sensors 1002, 1003, 1004, 1005). The magnetic sensors 1002, 1003, 1004, 1005 may be magneto-resistive, Hall (Hall) sensors, or inductive sensors. The output of the sensor unit 1000 is provided at the output terminals 1010, 1011.

According to an embodiment of the present invention, one sensor unit may include a single magnetic sensor. The magnetic sensor may be a magneto-resistive, hall sensor, or inductive sensor.

FIG. 11 is an electrical wiring diagram of an adder circuit 1100 configured to aggregate output signals from two sensor units, according to one embodiment of the invention. The output signal from the first sensor unit is provided to the input terminals 1102, 1104 of the adder circuit 1100. And the output signal from the second sensor unit is provided to the input terminals 1106, 1108 of the adder circuit 1100. The potentiometer 1110 may be used as a variable voltage divider and is connected between input terminals 1102 and 1106, each of which is connected to a sensor unit. The potentiometer 1110 is used to balance the input signals of the two sensors. The slider (wiper) terminal of the potentiometer 1110 is connected to the input of an amplifier 1112 (e.g., an operational amplifier). The other input of the amplifier 1112 is connected to input terminals 1104, 1108, each of which is connected to a sensor unit. Preferably, the amplifier stage has a feedback resistor 1114 to control the gain. At output terminal 1116, an aggregate of the sensor unit output signals is provided.

Fig. 12 schematically shows the combined wiring of two sensor units 1201, 1202 and one adder 1203.

Fig. 13 is a schematic wiring diagram of an adder circuit 1300 comprising a first adder 1301 and a second adder 1302, each connected to two sensor units (not shown), and a third adder 1303 connected to said first and second adders 1301, 1302. A potentiometer 1304, which may be used as a variable voltage divider, is connected between the outputs of the first and second adders 1301, 1302. The potentiometer 1304 serves to balance the signals from the first and second adders 1301, 1302. The wiper terminal 1306 of the potentiometer 1304 is coupled to an input of the third summer 1303. The other input 1308 of the adder is connected to an active zero generator (not shown), or to ground. At the output terminal 1310, an aggregate signal of the sensor unit output signals is provided.

FIG. 14 is a flow chart of a method for determining the position of a packaging material with magnetic markings according to one embodiment of the present invention. In a sensor signal generating step 1420, a plurality of sensor signals are responsive to a magnetic force (e.g., a magnetic field or a magnetic flow) from the magnetic label of the packaging material. The sensor signal is generated by a plurality of magnetic sensor units, each including a pair of magnetic sensors disposed in anti-parallel proximity to each other. In a magnetic interference suppression step 1422, magnetic interference from magnetic sources that are further away than the marker is suppressed by aggregating the sensor signals of each sensor of the sensor pair. Thus, by this anti-parallel arrangement, interference from remote magnetic sources is suppressed. All sensor signals from the sensor pair are aggregated to form an aggregate signal, at a sensor signal aggregation step 1424. The location is determined from the aggregate signal, at a location determining step 1428.

FIG. 15 is a flow chart of a method for determining the position of a packaging material with magnetic markings according to one embodiment of the present invention. At a sensor signal generating step 1500, a plurality of sensor signals are generated in response to a magnetic force (e.g., a magnetic field or a magnetic flow) from the magnetic label of the packaging material. The sensor signal is generated by a plurality of magnetic sensor units, each including a pair of magnetic sensors disposed in anti-parallel proximity to each other. In a sensor signal adjustment step 1501, the signals of the plurality of sensor units are adjusted to an equilibrium state, i.e. the levels of the signals are equal for a certain level of magnetic force exposure. In a magnetic interference suppression step 1502, the sensor signal of each sensor of the sensor pair is suppressed by aggregating magnetic interference from magnetic sources that are further away from the mark. Thus, by this anti-parallel arrangement, interference from remote magnetic sources is suppressed. In a compensation step 1503, the sensor signal is adjusted in case of misalignment (aligned) of the sensitivity direction of any sensor unit. This situation can arise when any sensor is not exactly in line with the other sensors. The compensation step 1503 may be performed by determining magnetic forces in a first vertical direction (i.e., perpendicular to the direction of intended sensitivity of the sensors of the sensor pair) and in a second vertical direction (i.e., perpendicular to the direction of intended sensitivity of the sensors of the sensor pair and the first vertical direction). The sensor signal may then be compensated for magnetic forces in the first and second perpendicular directions. At a sensor signal aggregation step 1504, all sensor signals from the sensor pair are aggregated to form an aggregate signal. At a zero crossing determination step 1506, a zero crossing of the aggregate signal is determined. "zero" means a certain predetermined level, which may be ground or an active zero level generated by a zero level generator. The position is determined by the time the zero crossing is determined, at a position determination step 1508.

Thus, position detection of the packaging material may be provided in the production of the packaging material, e.g. in a packaging machine, for proper printing in the production of packages of packaging material, e.g. for proper obtaining of printed text and images, openings, etc., and in the processing of the formed packages, e.g. for applying opening and closing devices, stickers, etc. The invention allows such operations to be accurately synchronized. In addition, any of the features of the above-described embodiments may be used in combination.

The invention has been described primarily in conjunction with the foregoing embodiments. However, one of ordinary skill in the art will readily appreciate that other embodiments than the above described are equally possible within the scope of the invention, as defined by the appended claims.

Claims (14)

1. A position detector device (100, 200, 900) for detecting a position of a packaging material (312, 512, 712, 812) with a magnetic marker (314, 514, 714, 814), comprising:

a sensor assembly comprising a plurality of magnetic sensor units (102, 204, 205, 206, 207, 304, 305, 306, 307, 504, 505, 506, 507, 704, 705, 706, 707, 804, 805, 807, 906, 907, 908, 1000, 1201, 1202), each magnetic sensor unit comprising an output providing an output signal, wherein the plurality of magnetic sensor units are arranged in at least two sensor unit pairs (208, 209, 301, 302, 501, 502, 701, 702), the sensor units of each pair being arranged with opposite sensitivity directions (308, 309, 310, 311, 508, 509, 510, 511, 708, 709, 710, 711, 808, 809, 811), and the sensor units being arranged to sense magnetic indicia of the packaging material;

a signal processing component (104) connected to the output of the magnetic sensor unit, comprising a combiner (210, 211, 212, 910, 912, 914, 1100, 1203, 1301, 1302, 1303) arranged to aggregate the output signals of the magnetic sensor unit into an aggregate signal;

a detector (106, 214, 916) arranged to determine the position of the packaging material from the aggregate signal; and

a first magnetically compensated sensor cell (716) arranged with its sensitivity direction (717) perpendicular to the sensitivity direction of the plurality of magnetic sensor cells; and a second magnetic compensation sensor unit (718) arranged with its sensitivity direction (719) perpendicular to the sensitivity directions of the plurality of magnetic sensor units and the first magnetic compensation sensor unit.

2. The apparatus of claim 1, wherein each sensor unit pair comprises: one magnetic sensor unit being arranged closer to the packaging material than the other magnetic sensor unit of the pair.

3. The device according to claim 2, wherein the magnetic sensor unit is a wheatstone bridge (1006) comprising magneto-resistive sensors (1002, 1003, 1004, 1005).

4. The apparatus of claim 3, wherein the detector is arranged to determine the position by detecting a zero crossing of the aggregate signal.

5. The apparatus of claim 4, wherein the detector comprises means for detecting a predetermined level of the aggregate signal before the zero crossing occurs.

6. The apparatus of claim 5, wherein the detector comprises means for detecting a predetermined change in level before the zero crossing occurs.

7. The apparatus of claim 1, wherein the signal processing component is coupled to the first and second magnetically compensated sensor cells and is configured to suppress signal components from the plurality of magnetic sensor cells that are perpendicular to the sensitivity direction of the plurality of magnetic sensor cells.

8. The device according to claim 7, comprising adjusting means (1110) for the output signal of the magnetic sensor unit.

9. The apparatus according to claim 8, wherein the sensitivity direction of the magnetic sensor unit and the magnetic direction of the magnetic marker are parallel and anti-parallel, respectively.

10. The device according to claim 8, wherein the sensitivity direction of the magnetic sensor unit is perpendicular to the magnetic direction of the magnetic labels.

11. The apparatus of claim 10, wherein a quotient between a spacing between two magnetic sensor cells facing the magnetic marker and a size of the magnetic marker in a position detection direction is between 0.6 and 3.

12. A method for detecting the position of a packaging material carrying magnetic markings, comprising the steps of:

generating a plurality of sensor signals by a plurality of magnetic sensor pairs in response to magnetic forces of the magnetic labels, wherein each magnetic sensor pair comprises magnetic sensor cells arranged in anti-parallel;

aggregating the sensor signals into an aggregate signal;

determining a location from the aggregate signal;

generating a first compensation signal dependent on a first magnetic force component in a direction perpendicular to the sensitivity direction of the pair of magnetic sensors;

generating a second compensation signal dependent on a second magnetic force component in a direction perpendicular to the sensitivity direction of the magnetic sensor pair and the first magnetic force component; and

compensating the sensor signal field of the magnetic sensor pair for a magnetic force component perpendicular to the sensitivity direction of the magnetic sensor pair by means of the first and second compensation signals.

13. The method of claim 12, wherein the step of determining a location comprises the steps of:

detecting a zero crossing of the aggregated signal; and

determining the location from the zero crossing.

14. The method of claim 12, further comprising the step of adjusting the output of the magnetic sensor.