EP0231549A1 - Protected enclosure with electrical switch and its application - Google Patents

Abstract

A protected enclosure L comprises at least one wall element E provided with an electrical switch C1, C2 itself protected by a thin and flexible probe S, B which on the one hand transmits the external mechanical control P and on the other hand allows the detection of an intrusion at this weak point of the protected enclosure.

Application: Security enclosure with keypad for entering the access code, in particular for electronic payment system.

Description

The subject of the present invention is a protected enclosure containing electronic means for processing binary data, at least one wall element of which comprises at least one switch to be activated by a movement causing the contact of two isolated conductors in the rest state, the switch (s) being arranged to transmit binary signals from the outside to the inside of the enclosure.

The present invention also relates to the application of such a protected enclosure to a box containing secret information, in particular for electronic payment system.

Such a box is known from the international PCT application published under the number WO 85/04742 in which a credit card payment application is described; payment can only be made after verification of a personal authentication code, the code is transmitted in the protected enclosure using a keyboard.

Other applications such as electronic door entry systems, or ticket machines, now well known to the public, also include a protected enclosure and a keyboard for providing an access code.

Such a keyboard consists of a set of switches and it constitutes a weak point in the wall of the protected enclosure.

The object of the present invention is to remedy this drawback.

To this end, according to the present invention, a protected enclosure is particularly remarkable in that at least said wall element is provided with a detection probe in the form of a relatively conductive track for detecting any unauthorized penetration attempt inside the enclosure, said detection probe having at least one thin and flexible part which covers the switch by constituting an electric barrier through which the control movement of the switch (s) is mechanically transmitted.

Thus the presence of a thin and flexible probe covering the switch, on the one hand allows the mechanical transmission of the control of the switch from the outside to the inside of the protected enclosure, on the other hand prohibits unauthorized entry inside the protected enclosure by detecting any attempted intrusion.

According to the present invention, when said relatively conductive track of all or part of the probe extending mainly parallel to a direction X a protected enclosure is particularly remarkable in that in superposition on said probe, it is provided with a probe additional whose relatively conductive track extends mainly parallel to a direction Y substantially perpendicular to the direction X.

Thus an intrusion attempt which succeeds in slipping between two tracks of a probe would have no chance of slipping again between two tracks of the other probe.

A probe consisting of narrow relatively conductive lines obtained by screen printing of a conductive ink on a flexible insulating support, it is remarkable according to the present invention that the relatively conductive track has a high electrical resistance to reduce the consumption of electrical energy.

Indeed, in some applications, for example that described in the application already cited, it is expected that the housing is portable and, to do this, it is provided with a battery or a battery whose life will be d '' even longer if the probe consumes a minimum of electrical energy.

According to the present invention, a protected enclosure is also particularly remarkable in that a probe consists of at least:
- an opaque aluminum layer
- an insulating polyester layer
- a layer of discontinuous thickness of relatively conductive track screen-printed with lamellar silver ink
- a layer of a polymerized insulating varnish remaining flexible after polymerization
- Each constituent being intimately connected to the next, in the above order, by means of a flexible solvent adhesive so that the probe is flexible and opaque.

The flexible and thin polyester being transparent, it is advantageous, to make the task of a possible intruder as difficult as possible, to add an opaque layer and also to intimately bind the different layers so that an intruder cannot proceed or by sliding a tool between the tracks he could have seen, or by "peeling" the different layers of the probe.

In a preferred embodiment in which the detection probe (s) being connected to a Wheatstone bridge provided with a differential amplifier to amplify any imbalance of the bridge and, in this case, to emit the signal detection, a protected enclosure is particularly remarkable in that the relatively conductive track is split to form two tracks arranged to be continuously parallel to each other and which are connected to the Wheatstone bridge so that the two currents which , respectively, run through them in opposite directions.

This arrangement is particularly advantageous because on the one hand the probe becomes insensitive to certain similar and simultaneous disturbances in the duplicated tracks which avoids false alerts, and on the other hand it becomes very risky to try to short-circuit two adjacent tracks hoping to be below the sensitivity threshold of the Wheatstone bridge.

In general, the object of the invention is to strengthen the security of the weak point of a protected enclosure, not by preventing intrusion but rather by detecting it, this detection then being used to trigger an alarm or take any suitable provision.

• La figure 1 représente, en coupe, un interrup­teur selon l'invention.
• La figure 2 représente, en coupe, une sonde sé­rigraphiée.
• La figure 3 représente, en coupe, un interrup­teur protégé avec deux sondes superposées.
• La figure 4 représente un mode de connexion des pistes dédoublées avec une seule sonde.
• La figure 5 représente un mode de connexion avec deux sondes.

The present invention has other advantages due in particular to certain peculiarities of technical implementation; it will be better understood with the aid of a nonlimiting example of an embodiment described with the aid of the following appended drawings:

• Figure 1 shows, in section, a switch according to the invention.
• FIG. 2 represents, in section, a screen-printed probe.
• Figure 3 shows, in section, a protected switch with two superimposed probes.
• FIG. 4 represents a mode of connection of the split tracks with a single probe.
• FIG. 5 represents a mode of connection with two probes.

Figure 1 shows the section of a switch located in a location D formed in a wall element E of the enclosure L, it comprises two conductors generally perpendicular to each other C1 and C2 separated by an insulator I in which is formed a recess T; as shown, the two conductors, at rest, do not touch; when an action P is exerted in the direction of the arrow, the conductor C2 is pushed back until it comes into contact with the conductor C1; when the action ceases, a return system, or the inherent elasticity of the assembly, brings the assembly back to the rest position shown, and there is no longer any contact between the two conductors C1 and C2. The P action can be exercised directly, or indirectly with a command button.

The L enclosure would it be protected by all kinds of shielding, concrete walls, ... the switch is nonetheless a weak point.

According to the invention, the action P is transmitted through a thin and flexible probe constituted by an electrical barrier B fixed on an insulating support S; the electrical barrier B is represented in the form of dashes because it consists of a relatively conductive track which winds on the insulating support S.

FIG. 4 presents an implementation mode; an E3 probe is shown with its connection to a Wheatstone bridge; replacing a single track B (FIG. 1) two tracks J1 and J2 are now provided, the respective paths of which, substantially parallel to the direction X, are continuously parallel to each other; track J1 is connected to the CD branch of the Wheatstone bridge, its resistance has a value of R1; track J2 is connected to branch AB of the Wheatstone bridge, its resistance has a value R2 which is not necessarily identical to the value R1 if only because of manufacturing dispersions. Initially the Wheatstone bridge is balanced in a known manner with adjustment means; if now, during operation, a local mechanical stress, for example the action P or other, appears in the hatched zone Z the values R1 and R2 will change; the tracks are, as described below, narrow enough for the zone Z to necessarily cover several tracks. Taking into account the connection mode of the tracks, the local mechanical stress does not unbalance the Wheatstone Bridge because the change in R1 and R2 which results therefrom is similar in value and simultaneous over time; if there had been only one runway, it is clear that a local constraint could have unbalanced the Wheatstone bridge and that an unnecessary alert would have been reported.

The symmetry of connection of tracks J1 and J2 in two branches of the Wheatstone bridge also provides immunity to any electrical noise, such as due to induced parasites for example, and also to a deviation of temperature which can be global as well, summer / winter for example, as local, sunbeam on zone Z for example; this arrangement of the split tracks thus ensures that the Wheatstone bridge is unbalanced only in the useful cases namely the cases of attempted intrusion.

A balanced Wheatstone bridge is well known as a measuring instrument but it is less well known as an intrusion detection instrument and it is remarkable, according to the invention, that the connections of tracks J1 and J2 to terminals A, B and C , D of the bridge are "head to tail" so that the currents i1 in J1, and i2 in J2, are in opposite directions; more precisely, if the connection C M P D was made from where the current i1, the second connection must be B O N A from where the current i2, and not B N O A; this feature allows in particular a more reliable detection of a short circuit caused, for example by a micro-drill, between adjacent tracks.

In FIG. 5 is shown, in addition to the probe E3, an additional probe E4 similar to E3; the only significant difference between E3 and E4 concerns the general direction of the slopes; in E3 it is the direction X whereas in E4 it is the direction Y which is, preferably, but this is not an obligation, perpendicular to X; to keep the same advantages as with E3, the tracks of E4 are similarly connected between H and G on the one hand, and between E and F on the other hand; other connection modes (not shown) are possible without departing from the scope of the invention, for example it is possible to connect between A and B an E3 track in series with an E4 track, the other two tracks being connected in series between C and D; the terminals H, G, E, F then being available.

For clarity, the known means of the initial balancing of the bridge have not been shown in FIG. 5; probes E3 and E4 are shown as two separate elements but it is also possible to produce them by adequate folding from a single screen-printed element; moreover, one and the same flat element, in the form of a hopscotch game, after folding, can constitute a probe for the six sides of a safety box.

The detection device, Di in FIG. 4, is, for example, a differential amplifier capable of detecting an imbalance of 10 mV; taking this value into account, it can be seen that the devices described above provide comfort for "non-detection" of electrical noise since these can commonly induce values greater than 10 mV such as 50 mV which therefore should not be detected as intrusion attempts.

It is also advantageous to make the probe so that the consumption of electrical energy is very low; this goal is achieved with tracks with high electrical resistance, for example between 2 K ohm and 50 K ohm. So when the power comes from a battery, or a battery, the detection device has a long service life; if the detection device is used for a protected case, the use of a battery, or battery, even provides the advantage that the assembly is then small, and transportable with its secret data which, if necessary, are destroyed in the event of intrusion.

To combine these qualities, the probe is produced by screen printing of a conductive liquid on an insulating support; advantageously the insulating support is a thin and flexible polyester layer, and the conductive liquid is composed of resin, a solvent and silver powder with a lamellar structure; for a protected case of dimensions 150 x 110 x 20 mm, the electrical resistance of a track J1 produced is then of the order of 15 K ohm for a track width of 0.3 mm each track being axially distant from 0, 6 mm from its neighbor; in the case of a connection conforming to that of FIG. 5, the equivalent resistance of the bridge is 15 K ohm, hence an intensity i of 500 μA at 7V, thus achieving autonomy of the order of 2 months with supply means of a reasonable weight and size; of course the numerical values indicated are not limiting.

It is also advantageous to cover the tracks with a layer of varnish to protect them against oxidation and insulate them electrically.

The polyester layer, the resin of the conductive ink, and the varnish are chosen such that after drying, or evaporation, the probe remains flexible.

In a preferred embodiment, the detection probe is provided with an additional opaque layer so that a possible fraudster does not see the location of the tracks through the polyester and / or the varnish which are generally transparent.

The opaque layer is advantageously obtained with a thin sheet of aluminum.

A preferred embodiment is shown in FIG. 2 which represents in section a probe terminated with a layer (POLY2) of polyester, a layer (ALU) of aluminum, a layer (POLY1) of polyester, the screen-printed conductive circuit ( INK) and the protective varnish layer (VER), each constituent being intimately connected to the next by means of a flexible solvent adhesive so that the probe is flexible and opaque.

With such a probe, a preferred embodiment of a switch is shown in FIG. 3. Two protection probes (E3X) and (E4Y) are superimposed by presenting the polyester layer on the side of the control, respectively POL11 and POL21, not screen printed; thus a fraudster will not be able to see the drivers here identified INK1 and INK2 respectively; it is advantageous to connect the aluminum layers ALU1 and ALU2 either to ground or to a determined potential; it is also advantageous to bond (COL), with a polyurethane adhesive which remains flexible after polymerization, the two protective elements E3X and E4Y on their opposite faces, namely the varnish VER1 and the polyester POL21; the POL11 and POL21 layers may appear superfluous but it turns out that the varnish (VER1) sticks better to polyester (POL21) than to aluminum (ALU2) which justifies the presence of the polyester layer (POL21), or (POLY2) in FIG. 2, as well as the presence, for the sake of standardization of manufacture and supply, of the polyester layer (POL11); it is clear that these are improvements which are not essential for the production of a switch according to the invention; for a good understanding of the system, in FIG. 3 is shown the electrical part of the switch with the conductors C1, C2 insulated by an insulator I, preferably a double-sided sticker, comprising recesses (T); the conductors to be connected C1, C2, are generally produced on a foldable support (POCLA) to obtain a keyboard, but there are other embodiments such as, for example, that described in FIG. 6 of the PCT document already cited.

For information,
an opaque layer of aluminum has a thickness of between 7 μm and 20 μm, preferably 12 μm,
- an insulating polyester layer has a thickness of between 15 µm and 30 µm, preferably 23 µm
- the thickness of a screen-printed strip is between 4 µm and 15 µm
- the thickness of the varnish is between 10 µm and 40 µm, preferably 20 µm
the thickness of each layer of adhesive is practically negligible and in any case less than 10 μm so that it follows that the total thickness of the two detection elements E3X and E4Y shown in FIG. 3 is of the order of 180 µm of materials with the flexibility and flexibility necessary to transmit the control movement (P) to the conductor (C1) to be connected to the conductor (C2).

Claims (8)

1. Protected enclosure containing electronic means for processing binary data, at least one wall element of which comprises at least one switch to be activated by a movement causing the contact of two isolated conductors in the resting state, the switch (es) (s) being arranged to transmit binary signals from the outside to the inside of the enclosure, characterized in that at least the said wall element is provided with a detection probe in the form of a relatively conductive track to detect any unauthorized penetration attempt inside the enclosure, said detection probe having at least one thin and flexible part which covers the switch constituting an electrical barrier through which the movement of the switch (s) control. 2. Protected enclosure according to claim 1, said relatively conductive track of all or part of the probe extending mainly parallel to a direction X, characterized in that in superposition with said probe, it is provided with an additional probe, the relatively conductive track extends mainly parallel to a direction Y substantially perpendicular to the direction X. 3. Protected enclosure according to claim 1 or 2, a probe consisting of narrow relatively conductive lines obtained by screen printing of a conductive ink on a flexible insulating support, characterized in that, the relatively conductive track has a high electrical resistance for reduce electrical energy consumption. 4. Protected enclosure according to claim 3 characterized in that a probe has an electrical resistance between 2 K ohm and 50 K ohm. 5. Protected enclosure according to any one of the preceding claims, characterized in that a probe consists of at least:
- an opaque aluminum layer
- an insulating polyester layer
- a layer of discontinuous thickness of relatively conductive track screen-printed with lamellar silver ink
- a layer of a polymerized insulating varnish remaining flexible after polymerization,
- Each constituent being intimately connected to the next, in the above order, by means of a flexible solvent adhesive so that the probe is flexible and opaque. 6. Protected enclosure according to claim 5 characterized in that
- the opaque aluminum layer has a thickness of between 7 μm and 20 μm,
- the polyester insulating layer has a thickness of between 15 μm and 30 μm,
- the thickness of a relatively conductive track is between 4 μm and 15 μm,
- the thickness of the varnish being between 10 µm and 40 µm
the thickness of each layer of adhesive being practically negligible and in any case less than 10 μm so that the total thickness of a flexible probe is between 40 μm and 150 μm. 7. Protected enclosure according to any one of the preceding claims, the detection probe (s) being connected to a Wheatstone bridge provided with a differential amplifier to amplify any imbalance of the bridge and, in this case, emit the detection signal, characterized in that the relatively conductive track is split to form two tracks arranged to be continuously parallel to each other and which are connected to the Wheatstone bridge so that the two currents which, respectively , run through them in opposite directions. 8. Application of a protected enclosure according to any one of the preceding claims to a security box containing secret information, the said signal detection issued in the event of an intrusion, in particular for controlling the destruction of secret information.

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