FR2956240A1 - Magnetic readhead for use in data reading device in e.g. electronic payment terminal in shop, has magnetic circuits including gaps located at distances from front face respectively, where one of distance is higher than other distance - Google Patents

Abstract

The head (31) has a magnetic circuit (40) including a gap (43) located at a distance (d1) from a front face (35) of the head. Another magnetic circuit (50) includes another gap (53) located at another distance (d2) from the front face of the head, where the other distance is higher than the former distance. The magnetic circuits comprise magnetic rings (41, 51) opened by the gaps respectively. The magnetic circuits respectively comprise current conductor windings (45, 55) placed around the rings. An independent claim is also included for a magnetic card reading device comprising a combination element providing a signal representing flux variation associated with the passage of a magnetic track.

Description

B10135 1 MAGNETIC READ HEAD

Field of the Invention The present invention relates to a device for reading a magnetic track. It is more particularly a magnetic reading head of an electronic payment terminal or a check reader. BACKGROUND OF THE PRIOR ART Certain electronic payment terminals are adapted to read cards provided with magnetic tracks, or magnetic cards. In this case, there is provided a magnetic card reader, having for example the form of a slot, open at its ends, in which a user can scroll a magnetic card. A magnetic reading head, connected to a printed circuit of the terminal, is flush with an inner wall of the slot. The read head is used to read data stored on a magnetic strip of the user's card, when scrolling the card in the slot. Figure 1 is a front view schematically showing a magnetic read head 1 such as can be found in the current electronic payment terminals.

Figure 2 is a sectional view of the read head 1 of Figure 1 along the plane 2-2.

B10135

2 The read head 1 comprises a housing 3 of approximately parallelepipedal general shape, containing in particular one or more electromagnetic reading circuits. The housing 3, generally metallic, comprises a front face 5, intended to be flush with an inner wall of the slot of the reader. The front face 5 is slightly curved, so that a magnetic card 7 (Figure 2) can scroll against this face without the risk of hanging the housing 3. The front face 5 comprises one or more slots 8, horizontal (in the orientation of Figure 1), defining read channels, three channels 9a to 9c (Figure 1) in this example, positioned at different heights so as to read on magnetic tracks positioned at different heights of the card. This allows the reader to be compatible with different categories of magnetic cards. All the reading channels are similar, for example, at the level of the channel 9b, the box 3 contains a magnetic reading circuit comprising a ring-shaped magnetic core 11b (FIG. 2) disposed in a plane parallel to the lower faces. and upper case (in the orientation of Figure 1). The ring 11b is not closed but is interrupted by a nonmagnetic air gap 13b, generally consisting of air or a solid non-magnetic material such as brass or a resin. The gap 13b is in contact or at a very short distance from the portion of the pathway 9b in contact with which is intended to slide the magnetic card, and is generally covered with a protective varnish. A conductive winding 15b is formed around the region of the ring opposite the gap 13b. In practice, the height of the air gap 13b is slightly greater than the height of the magnetic tracks that can be read. The width of the gap is related to the write resolution of the data on the magnetic track. In the field of magnetic payment cards, the width of the gap is generally between 5 and 50 pm.

B10135

Magnetic readout circuits are also associated with the readout channels 9a and 9c. FIG. 1 shows the air gaps 13a and 13c of the magnetic circuits associated with the channels 9a and 9c. To improve the mechanical strength of the head, and / or for security reasons, the inside of the casing 3 is generally embedded in a resin (not shown) during a final manufacturing step. The scrolling of a magnetic strip of the card 7 in front of the air gap 13 of the reading channel 9 involved causes a variation of magnetic flux in the corresponding core 11. This results in the appearance of an induced current and therefore a variation of the voltage VOUT across the winding 15. The payment terminals generally comprise a processing module, not shown, for extracting from the signal VOUT the information stored on the magnetic track. A disadvantage of read heads of this type is that they are very sensitive to external electromagnetic disturbances. The signal VOUT is therefore noisy. If the read head is used in a highly disturbed environment, it may become impossible to extract the information stored on the magnetic card from the VOUT signal. This can occur in particular in an electronic payment terminal located in a store, near a security door anti-theft. In the case of a motorized magnetic drive of checks, the drive motors of the apparatus are also a source of disturbance of the read head. In addition, the various wireless telecommunications devices are as many possible sources of disturbance for the read heads. Some payment terminals include a software module and / or noise filtering hardware. However, in addition to the additional cost involved in the prediction of such a module, this solution does not completely overcome the external disturbances, especially when the disturbances are of high amplitude and / or generate parasitic signals in the same band. frequency as the useful signal.

B10135

Terminals comprising, in addition to the usual magnetic read head, an additional magnetic noise measuring head and a signal processing module for reconstructing, from the signals supplied by the read head and the head of the terminal, have also been proposed. noise measurement, an estimate of the useful non-noisy signal. An embodiment of such a terminal, adapted to the magnetic reading of checks, is described in document FR-A-2898726. Such a solution has the disadvantage of resulting in a significant additional cost and bulk, related to the presence of the additional measuring head and the signal processing module. SUMMARY Thus, an object of an embodiment of the present invention is to provide a magnetic read head at least partially overcoming some of the disadvantages of the solutions of the prior art. Another object of an embodiment of the present invention is to provide such a read head providing a signal independent of any parasitic disturbances.

Another object of an embodiment of the present invention is to provide such a read head easy to achieve. Another object of an embodiment of the present invention is to provide such a head requiring no signal processing module. Another object of an embodiment of the present invention is to provide such a reading head compatible with the usual payment terminals. Thus, an embodiment of the present invention provides a magnetic read head in front of a front face of which is intended to scroll a magnetic track, comprising: at least a first magnetic circuit adapted to provide a first signal representative of a variation magnetic flux related to the running of the track and to external disturbances; and at least one second magnetic circuit adapted to B10135

provide a second signal representative of a magnetic flux variation related to external disturbances. Another embodiment of the present invention provides a magnetic read head comprising: at least a first magnetic circuit comprising a first air gap located at a first distance from a front face of the head; and at least one second magnetic circuit comprising a second gap located at a second distance from the front face, the second distance being greater than the first distance.

According to one embodiment of the present invention, the first magnetic circuit comprises a first magnetic ring open by the first air gap, and a first conductive winding around the first ring; and the second magnetic circuit comprises a second magnetic ring open by the second air gap, and a second conductive winding around the second ring. According to an embodiment of the present invention, the second distance is 0.3 to 3 mm greater at the first distance.

According to one embodiment of the present invention, the first and second rings are arranged in parallel first and second planes. According to an embodiment of the present invention, the first and second planes are merged.

According to an embodiment of the present invention, the first and second windings are arranged in first and second parallel directions. According to one embodiment of the present invention, the first and second windings are connected in series in phase opposition. According to an embodiment of the present invention, the first and second windings are connected in parallel in phase opposition. According to an embodiment of the present invention, the head further comprises a combination element for providing B10135

6 a signal representative of the difference between the magnetic flux variation seen by the first magnetic circuit and the magnetic flux variation seen by the second magnetic circuit.

Another embodiment of the present invention provides a magnetic card reading device comprising a reading head of the aforementioned type, in front of which the front face of which is intended to scroll a magnetic strip, in which: the first magnetic circuit is adapted to providing a first signal representative of a magnetic flux variation related to the passage of the magnetic track and to external disturbances; and the second magnetic circuit is adapted to provide a second signal representative of a magnetic flux variation related to external disturbances, the reading device further comprising a combination element to provide a third signal representative of the flow variation related to the passage of the magnetic track. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features, and advantages will be set forth in detail in the following description of particular embodiments in a non-limiting manner with reference to the accompanying drawings, in which: FIG. , schematically represents the front face of a magnetic read head; Figure 2, previously described, is a sectional view of the read head in the plane 2-2 of Figure 1; Fig. 3 is a sectional view schematically showing an embodiment of a magnetic stripe reading device adapted to provide a signal independent of environmental disturbances; FIG. 4 is a sectional view schematically showing an embodiment of a read head adapted to provide a signal independent of the disturbances of the environment; B10135

Fig. 5 is a sectional view schematically showing an alternative embodiment of the read head of Fig. 4; and FIGS. 6 to 8 are electrical diagrams illustrating various alternative embodiments of the magnetic reading heads described with reference to FIGS. 4 and 5. Detailed description For the sake of clarity, the same elements have been designated with the same references in the various figures and, moreover, the various figures are not drawn to scale. In addition, only the elements useful for understanding the invention have been shown and described. In the present description, the terms "orientation" and "forward", "backward", "lower", "upper", "height", "width", "horizontal", "vertical", "center" Referring arbitrarily to a read head in the orientation of Fig. 1. The present invention will be described in connection with an exemplary device adapted for reading magnetic charge cards, but more generally applies to any magnetic reading, for example in the fields of magnetic reading checks, transport tickets, audio media, computer disks, etc. Figure 3 is a sectional view in the same plane as Figure 2 schematically representing an exemplary embodiment of a device 30 for reading magnetic tracks, adapted to provide a signal independent of the electromagnetic disturbances of the environment The device 1 comprises a magnetic reading head 31 of general shape substantially identical to that of the read head 1 of Figures 1 and 2. The head 31 comprises a housing 33, for example metallic, containing in particular one or more electromagnetic reading circuits. The housing 33 comprises a front face 35 of slightly convex cross-section (in the plane of the figure), including slots 38 B10135

8 horizontal and parallel to each other, defining read channels (a single read channel 39 is visible in Figure 3). The housing 33 contains at least a first magnetic circuit 40, comprising a ring-shaped magnetic core 41 defining the path 39, and arranged in a plane substantially parallel to the lower and upper faces of the housing. The ring 41 is opened by a nonmagnetic gap 43, for example air, vacuum, or a non-magnetic solid material such as brass, a resin, or any other suitable material. The air gap 43 is located in contact with or at a very short distance from the portion of track 39 in front of which is intended to slide a magnetic card 37. In other words, the gap 43 is located at a distance dl very small, by example less than 0.5 mm, the portion of the front face in contact with which the card 37 is intended to scroll. In this example, the gap 43 is positioned substantially in the center of the slot 38 defining the reading path 39. A conductive winding 45 is formed around the ring 41, for example around the region of the ring 41 opposite to 43. In contrast to the read head 1 of Figure 2, the magnetic core 41 of the magnetic circuit 40 does not occupy the entire width of the read head. At the reading channel 39, in the same plane as the magnetic circuit 40, the housing 33 further contains a second magnetic circuit 50. The circuit 50 comprises a magnetic core 51 in the form of a ring, opened by a non-magnetic air gap 53. The gap 53 is located on the side of the slot 38, relatively close to the gap 43. However, the air gap 53 is located at a distance d2, greater than the distance d1, of the front face of the head of the reading. More generally, the read head 31 is such that during the scrolling of a magnetic card in front of the reading path 39, the air gap 53 is further away from the magnetic track read than the air gap 43. By way of example , the distance between the air gap 53 and the card 37 may be greater than 0.3 to B10135

9 3 mm at the distance between the gap 43 and the card 37. A conductive winding 55 is formed around the region of the ring 51 opposite the gap 53. The scrolling of a magnetic strip of the card 37 in front of the gap 43 causes a variation of magnetic flux in the core 41 of the magnetic circuit 40. This results in the appearance of a current induced in the conductive winding 45 and therefore a variation of the voltage VOUT across the winding 45. As in the case of the read head described with reference to FIG. 2, the VOUT signal is noisy. It is in fact the sum of a useful signal VUTIL, representative of the variations of magnetic flux induced by the scrolling of the magnetic track in front of the gap, and of a noise signal VB, representative of the magnetic flux variations induced by external disturbances. The distance between the air gap 53 of the second magnetic circuit 50 and the magnetic card is such that the movement of the magnetic strip in front of the channel 39 does not cause any significant variation in the magnetic flux in the core 51. Thus, the voltage at the terminals of the winding 55 represents only the variations of magnetic flux induced by the disturbances of the environment. This voltage corresponds substantially to the component VB of the signal VOUT. In practice, if the distance between the magnetic track and the air gap 53 is greater than 1 mm, the movement of the magnetic track in front of the gap does not cause any significant variation in the magnetic flux in the core 51. In the example of 3, the track 39 of the read head 31 provides two output signals, the noisy signal VOUT, read across the winding 45, and the signal VB, representative of the noise of the environment, read across the terminals. the winding 55. The reading device 30 further comprises a signal processing module 57, receiving the signals VOUT and VB, and providing a signal VUTIL representative of the magnetic flux variations induced by the running of the track B10135

10 magnetic, regardless of external disturbances. The module 57 may be an operational amplifier subtractor (VUTIL = VOUT - VB) and is particularly simple to implement. If necessary, the module 57 takes into account a ratio related to windings 45 and 55 different from each other. Alternatively, the module 57 may be placed inside the read head, provided that it has a power supply. According to a preferred embodiment, the magnetic circuits 40 and 50 have similar characteristics. In particular, the impedances, the dimensions of the air gaps, and the number of turns of the windings, are approximately identical. In addition, the windings 45 and 55 are preferably arranged in parallel or combined directions. In addition, the air gap 53 is preferably disposed near the gap 43, so as to measure a noise signal VB as close as possible to the noise affecting the useful signal. An advantage of such a magnetic strip reading device is that it provides a signal substantially independent of environmental disturbances, and whatever the intensity and the frequency band disturbances. Such a device is furthermore easy to implement and easy to integrate into an existing payment terminal. Indeed, such a device does not require the provision of a complex filter module of the output signal of the read head. In addition, the general shape of the read head and the dimensions of the read head are substantially identical to those of conventional read heads. FIG. 4 is a sectional view in the same plane as FIG. 3 schematically showing another embodiment of a reading path of a magnetic read head adapted to directly supply a signal independent of the electromagnetic disturbances of the 'environment. The B10135 head

11 of reading 61 is structurally identical to the head 31 described in connection with Figure 3. However, the windings 45 and 55 are connected in phase opposition. An opposite phase connection designates the fact that the voltages induced across the windings by the same magnetic flux variation are in phase opposition. In practice, this means that the induced currents traverse the windings in opposite directions of rotation (symbolized by the positions of the phase points). In this example, the windings 45 and 55 are connected in series, and arranged in the same direction, but have opposite winding directions. As a result, the currents induced in the windings 45 and 55 by the disturbances of the environment cancel each other out. Thus, during the running of a magnetic track in front of the track 39, the dipole formed by putting the windings 45 and 55 in series directly provides a VUTIL signal at its terminals, representative of the variations in magnetic flux related to the scrolling of the magnetic card in front of the gap 43, independently of any external disturbance. In this example, the magnetic cores 41 and 51 are in contact with each other, however, the invention is not limited to this particular case. Such a read head has the advantage over the reading device of FIG. 3 of not requiring any signal processing module and therefore of being directly compatible with the existing payment terminals. FIG. 5 is a sectional view in the same plane as FIG. 4 schematically showing an embodiment variant 61 'of the reading head 61 described with reference to FIG. 4. A difference between the head 61' and the head 61 lies in the geometrical arrangement of ring magnetic cores. In the head 61 ', the magnetic rings are formed from two identical magnetic pieces 63g and 63d, substantially U-shaped. The U-shaped pieces 63g and 63d are placed on either side of a central rectilinear magnetic rod. 65, so that the piece 65 closes the two formed U B10135

12 by 63g and 63d. On the side of the slot 38, the end of each U is separated from the part 65 by an air gap. In the magnetic noise measuring circuit 50 (left side of the figure), the U-shaped piece 63g is slightly further away from the front face of the head than in the magnetic circuit 40 for reading the signal. Thus, the air gap 53 'of the circuit 50 is farther from the region of passage of the magnetic card than the gap 43' of the circuit 40. One advantage of such a read head is that its series production is facilitated by the fact that the cores of the magnetic circuits for reading the useful signal and for measuring the noise are made from identical parts. FIG. 6 is an equivalent electrical diagram of another embodiment of a reading head 61 "structurally identical to the head 61 of FIG. 4. In the head 61", the windings 45 and 55 are connected in parallel in FIG. phase opposition. The signal VUTIL output of the head 61 ", representative of the magnetic flux variations related to the scrolling of the magnetic strip independently of the external disturbances, is read across the dipole formed by the paralleling of the windings. Equivalent electrical diagram of an embodiment variant of a read head 71. The head 71 comprises three reading channels 39a, 39b, 39c, Each channel is associated with a magnetic circuit for reading the noisy signal and a magnetic measurement circuit. For each channel, the windings of the useful signal reading and noise measurement circuits are connected in series and in phase opposition, The head 71 supplies signals VaUTIL, VbUTIL, VcUTIL respectively representative of the magnetic flux variations. related to the running of magnetic tracks in front of the tracks 39a, 39b, 39c Each signal VaUTIL, VbUTIL, VcUTIL is read at the terminals of the dipole formed by the setting in ser ie windings associated with the corresponding channel.

B10135

FIG. 8 is an equivalent electrical diagram of an alternative embodiment 81 of the read head of FIG. 7. The head 81 comprises three read channels 89a, 89b, 89c. Each channel is associated with a magnetic circuit for reading the noisy signal of the type described in relation to FIG. 2. The head 81 further comprises a magnetic noise measuring circuit 85, for example a magnetic circuit of the type described in connection with FIG. 2, but whose air gap is slightly set back from the front face of the read head, so that the scrolling of a magnetic strip in front of the front face of the read head does not cause any variation in magnetic flux in the circuit 85. The winding of the noise measuring circuit 85 is connected in series and in phase opposition to each of the windings of the signal reading circuits associated with the read zones 89a, 89b, 89c. The head 81 provides output signals VaUTIL, VbUTIL, VcUTIL, respectively representative of magnetic flux variations related to the scrolling of magnetic tracks in front of the channels 89a, 89b, 89c. Each signal VaUTIL, VbUTIL, VcUTIL is read across the dipole formed by putting in series the corresponding windings. The common magnetic noise measuring circuit 85 may be placed either at a fourth virtual read channel, in a plane distinct from the read zones 89a to 89c, or at one of the reading zones 89a to 89c. according to an arrangement of the type described with reference to FIGS. 3 to 5. According to an alternative embodiment, if the circuit 85 is placed in a plane distinct from the reading zones 89a to 89c, its air gap will not necessarily be set back from the front face. Indeed, in this case a height shift may be sufficient to make the circuit 85 insensitive to magnetic flux variations related to the scrolling of the magnetic card in front of the front panel. Particular embodiments of the present invention have been described. Various variations and modifications will be apparent to those skilled in the art.

B10135

In particular, it will be noted that for each of the embodiments described with reference to FIGS. 6 to 8, variants may be provided in which the signal reading windings (VOUT) and the noise measurement (VB) windings are not directly connected to each other, but are connected to a simple signal processing module of the type described in connection with Figure 3, this module can be disposed in or outside the read head. Note that in the case where the windings are directly connected to each other, the electrical connections in phase opposition can be made inside or outside the read head. In addition, those skilled in the art will implement the desired operation regardless of the number of reading zones.

Moreover, although the above description relates only to read heads, those skilled in the art will be able to implement the desired operation in magnetic writing heads.

Claims (10)

REVENDICATIONS1. Magnetic read head (31; 61; 71; 81) comprising: at least one first magnetic circuit (40) comprising a first gap (43) located at a first distance (d1) from a front face (35) of the head; and at least one second magnetic circuit (50) including a second gap (53) located at a second distance (d2) from the front face, the second distance being greater than the first distance. 10 The head of claim 1, wherein: the first magnetic circuit (40) comprises a first magnetic ring (41) open by the first air gap, and a first conductive winding (45) around the first ring; and the second magnetic circuit (50) comprises a second magnetic ring (51) open by the second air gap, and a second conductive winding (55) around the second ring. The head of claim 1 or 2, wherein the second distance (d2) is 0.3 to 3 mm greater than the first distance (d1). 4. Head according to claim 2 or 3, wherein the first and second rings are arranged in first and second parallel planes. The head of claim 4, wherein the first and second planes are merged. 6. Head according to any one of claims 2 to 5, wherein the first and second windings are arranged in first and second parallel directions. 7. Head according to any one of claims 2 to 6, wherein the first and second windings are connected in series in phase opposition. 8. Head (61 ") according to any one of claims 2 to 6, wherein the first and second windings are connected in parallel in phase opposition.B10135 16 9. Head according to any one of claims 1 to 6, further comprising a combination element for providing a signal representative of the difference between the magnetic flux variation seen by the first magnetic circuit and the magnetic flux variation seen by the second magnetic circuit. 10. Device (30) for reading a magnetic card comprising a read head (31) according to any one of claims 1 to 6, in front of the front of which is intended to scroll a magnetic track, wherein: the first circuit magnetic device (40) is adapted to provide a first signal (VOUT) representative of a variation of magnetic flux related to the passage of the magnetic track and to external disturbances; and the second magnetic circuit (50) is adapted to provide a second signal (VB) representative of a magnetic flux variation related to external disturbances, the reading device further comprising a combining element (57) for providing a third signal (VUTIL) representative of the flux variation related to the passage of the magnetic track.