EP3007198B1 - Actuator - Google Patents

Description

1. Domain

The proposed technique relates to an actuator. The technique relates more particularly to an actuator for electrical contact. Such actuators are used in electronic devices to establish or break an electrical contact at a printed circuit board at a location where the printed circuit track is deliberately interrupted to precisely detect this electrical contact. Such actuators are for example used to generate electrical contacts on a card when keys on a keyboard are pressed or to detect a break in a previously established electrical contact.

2. Prior art

The documents DE102010048805 And EP1014408 disclose actuators of the prior art.

Actuators are very practical and used in a wide variety of electronic devices. Actuators are mainly of two types: the switch and the puck. These terms are immediately recognized by those skilled in the art and do not have French translations which represent their functions in electronics.

The switch is a component to be soldered or glued to a printed circuit board at the location where electrical contact must be established. The switch , however, has the disadvantage of requiring soldering or bonding, which is not necessarily always possible or desirable.

A puck generally comes in the form of a pebble. The base of the roller can be round or in the shape of a metal indentation on which it is supposed to make contact. The puck includes, at one of its ends, a conductive surface. This conductive surface is generally made using a conductive ink or any other relatively inexpensive conductive material. Indeed, with a view to reducing costs, pucks are not essential elements of the electronic device, inexpensive materials are used. The puck is also actuated by a rod (located opposite the conductive part). The rod must be firm enough to provide pressure on the electrical contact. The upper, when elastic, can more easily accept dimensional variations. This rod, elastic or not, is often directly integrated into another element which is located on the surface of an electronic device and which is accessible by the user. The puck can then be operated via this rod.

In another example, the puck can also be directly integrated into the keyboard keys: for example, the silicone keyboards of calculators, remote controls, certain payment terminals, etc.

One of the problems with the puck is that it does not necessarily age very well: repeated action on a keyboard key can over time damage the conductive surface of the puck and render the key inoperable. In fact, the puck does not guarantee quality electrical contact when the conductivity material used is inexpensive. This is why we frequently encounter large pucks with equally large metal footprints. However, such configurations are not always possible. Additionally, the puck is not necessarily “coupled” with another element. Therefore, during assembly, difficulties may arise to ensure a correct position of a puck which is, so to speak, floating: there may be problems as to the final position of the puck. Finally, very often, the deformable material of the puck is used as a return means (as a spring) to ensure that the puck returns to its initial position after being stressed: this contributes to the rapid deterioration of the puck.

Therefore, there is a need for an actuator which can have both the advantages of the puck while avoiding the disadvantages.

3. Summary

The proposed technique does not have these drawbacks of the prior art. More particularly, the proposed technique relates to an actuator (A) for creating an electrical contact between two tracks of a printed circuit board.

• une pièce en polymère (PSM), formant un bras comprenant une extrémité de contact (E1) et une extrémité de mise en mouvement ;
• une partie métallique (PM), solidarisée avec l'extrémité de contact (E1), ayant globalement une forme de calotte ; ladite extrémité (E1) de l'actuateur supportant ladite partie métallique (PM), étant entourée par une enceinte (EP) se prolongeant jusqu'à une base de contact (BPM) de la partie métallique (BPM), ladite enceinte comprenant une base destinée à entrer en contact avec ladite carte de circuit imprimé et recouverte d'une encre conductrice.

Such an actuator includes:

• a polymer part (PSM), forming an arm comprising a contact end (E1) and a moving end;
• a metal part (PM), secured to the contact end (E1), generally having the shape of a cap; said end (E1) of the actuator supporting said metal part (PM), being surrounded by an enclosure (EP) extending to a contact base (BPM) of the metal part (BPM), said enclosure comprising a base intended to come into contact with said printed circuit board and covered with a conductive ink.

Thus, such an actuator allows both to offer significant flexibility of implementation while guaranteeing high electrical conductivity.

According to a particular characteristic, the metal part (PM) has the shape of a spherical cap.

Thus, when it receives pressure, this spherical cap is able to deform at its center to allow contact to be established with the tracks of the circuit. printed and when the pressure stops, returns to its initial shape. This spherical cap shape contributes to the longevity of the actuator.

According to a particular embodiment, the polymer part (PSM) is made of silicone with a hardness of 60 shores A.

Thus, electrical contact can be made as long as the actuator exerts sufficient force on the actuator. This part is thus slightly deformable but it is sufficiently rigid for the metal part to be pressed.

According to a particular embodiment, the metal part (PM), secured to the contact end (E1) using an adhesive whose tearing force is substantially equal to 100 grams.

Thus, the actuator withstands a significant number of requests and offers significant resistance to sabotage attempts, for example when it comes to “hacking” a terminal comprising sensitive data, such as a payment terminal. In this case, the actuator is used to make a normally closed contact throughout the duration of use of the terminal, except in the case of disassembly (where the electrical circuit is open) for example by a user who tries to open the terminal fraudulently to place a spy device there.

According to a particular characteristic, the metal part (PM) is composed of a gold-plated spring steel sheet.

Thus the conductivity of the electrical contact is high and its reaction (its deformation) is immediate in the event of disassembly, even after a very long period of time in the activated position.

According to the invention, the end (E1) of the actuator supporting the metal part (PM) is surrounded by an enclosure (EP) extending to a contact base (BPM) of the metal part (BPM).

Thus, a protective barrier is formed around the metal part, particularly against dust.

According to a particular embodiment, the enclosure (EP) generally has the shape of a cone whose apex is a point on the line passing through the central axis of the polymer part (PSM).

4. Figures

• la figure 1 illustre le principe général de la technique proposée pour un actuateur objet de la technique décrite, sous la forme d'une coupe ;
• la figure 2 illustre une empreinte métallique sur laquelle l'actuateur prend place ;
• la figure 3 illustre une empreinte métallique comprenant des anneaux de garde ;
• la figure 4 illustre un mode de réalisation de l'actuateur.

Other characteristics and advantages of the proposed technique will appear more clearly on reading the following description of a preferred embodiment, given by way of a simple illustrative and non-limiting example, and the appended drawings, among which:

• there figure 1 illustrates the general principle of the technique proposed for an actuator subject to the technique described, in the form of a section;
• there figure 2 illustrates a metal impression on which the actuator takes place;
• there Figure 3 illustrates a metal impression including guard rings;
• there Figure 4 illustrates an embodiment of the actuator.

5. Description 5.1. Reminder of the principle

The general principle of the technique is presented in relation to the figure 1 . The principle of the technique, as explained previously, consists of providing the actuator (A) with a metal part (PM). This metal part is used to make contact on a corresponding metal footprint (EMp) of a printed circuit board (CCI).

More particularly, this metallic part (PM) is not of any shape. This metal part has the general shape of a cap, a cap which can be spherical or elliptical or rectangular, as shown in figure 1 . The base (BPM) of this metal part, which corresponds to the portion which comes into contact with the corresponding metal footprint of the printed circuit board, is of a shape more or less similar to that of the metal footprint. For example, when the metal imprint forms a circle with a diameter equal to half a centimeter, the base of the metal part of the actuator also forms a circle with a diameter substantially equal to half a centimeter.

The function of the metal part is twofold: the metal part is used to provide good electrical conductivity, which makes it possible to differentiate the actuator of the present technique from the traditional puck. The geometry (i.e. the geometric shape) of this metal part is also adapted to reproduce an operation close to that of the switch, namely that the force exerted on the metal part to establish electrical contact on the metal impression is restored at least partially by the metal part itself (and not by a molded silicone part), in order to extend the life of the actuator. Thus, the force used to make electrical contact deforms the part metallic: this therefore “seeks” to return to its initial form by restoring the energy initially supplied.

Indeed, the actuator (A) also comprises a polymer part (PSM), possibly molded, for example in the form of a cylinder or a rectangular parallelepiped. This polymer part (PSM) forming an arm comprising a contact end (E1) and a moving end (it is through this end that the pressure is exerted - for example from a key on a keyboard -). The size of this polymer part is adapted, case by case, depending on the situation. This polymer part (PSM) gives the actuator sufficient elasticity to accept position differences due to manufacturing errors of the parts, and deformations that may occur during the life of the product (shocks, falls, aging, variations in temperature).

A contact end (E1) of this cylinder is fixed to the metal part (PM) of the actuator (A). This fixing can be carried out by any necessary means such as glue. This end (E1) may have a diameter different from that of the cylinder. More particularly, the diameter of this bonding end can be adapted to the shape of the cap.

In addition, the end (E1) of the actuator supporting the metal part (PM) is surrounded by an enclosure (EP) which serves as protection during assembly manipulations. This enclosure (EP) is sufficiently flexible not to disrupt the operation of the actuator and more particularly the establishment of electrical contact by the metal part. This enclosure (EP) also makes it possible to create a sealing barrier between the metal part (PM) and the external environment. The enclosure creates a chamber within which the metal part takes place. According to the invention, the base of this enclosure, which comes into contact with the printed circuit, can itself be covered with a conductive ink. Indeed, a known hacking technique for this type of device consists of using a conductive ink to create a short circuit between two rings (for example D2 at A1). The ink maintains contact even when the actuator is removed. The guard ring is then used to detect a short circuit between the EMP ring and itself. If necessary, a terminal protection countermeasure is then triggered. The presence of the guard ring therefore establishes a normally open electrical contact which is used to detect hacking by adding a conductive ink (or any other electrically conductive liquid). A protective countermeasure can then be triggered.

Thus, unlike the pucks and switches of the prior art, the actuator as proposed integrates excellent conductivity (which provides a real advantage for the establishment of electrical contact). This conductivity is ensured by the metal part of the actuator. In addition, the proposed actuator is simple to implement and does not require any bonding or welding operation, unlike the switch. In a way, the proposed actuator combines both the advantages of the switch and the puck without having the disadvantages.

In the following, we present an embodiment of the actuator in which the metal part takes the form of a spherical cap (CS). The use of such an actuator is of course not limited to printed circuits. It can also be used in any other situation where it is of interest.

5.2. Description of an embodiment

As explained previously, the actuator of the technique described is intended to come into contact with a metal imprint, deposited for example on an electronic card.

Such a metallic imprint (E0), described in relation to the figure 2 , generally takes a circular shape. More particularly, the metal impression comprises at least one external ring (A1) and an internal disc (D2). Of course, other shapes can also be used depending on requirements. This type of metal imprint is generally used to transmit an electrical signal for activating a key, such as a key located on the surface of a case. This technique is often used for example in electronic control devices such as controllers, joysticks, control keyboards, terminals (payment terminals). For example, for a classic keyboard with twelve keys, twelve such fingerprints are screen-printed or printed on a printed circuit board (or on a motherboard).

The key activation signal is initiated by bringing into contact for example the external ring (A1) and an internal disk (D2). When contact is made, a microprocessor or other electronic component arrangement receives an electrical pulse and interprets this pulse based on the functionality implemented in the device in question.

Many variations of the metal impression exist. For example, a metal impression may include one or two guard rings (AG), internal external or both, as described in Figure 3 . Guard rings are used to prevent fraudulent introductions. The guard rings are then connected for example to the ground of the electronic circuit, so that when a fraudulent introduction of a device is made, an electrical contact is immediately established between the guard ring and another of the rings of the metal imprint. Therefore, security measures for the electronic device in question can be automatically implemented. This type of security measure is generally reserved for terminals comprising sensitive data, such as for example payment terminals or devices controlling access to sensitive data.

In any case, as indicated previously, it is necessary to have an actuator to establish contact between the disk and the ring. To do this, previous techniques are generally content to use a switch glued or soldered on the electronic circuit board or even a puck (when a switch is used, this replaces the imprint on the card as well as the actuator). The actuator is used to establish electrical contact between the outer ring (A1) and the inner disk (D2).

The actuator of the present technique operates according to the same principle. THE figures 4 And 5 present an embodiment of this actuator. In Figure 4 , the actuator is represented in three dimensions, in an exploded manner. The actuator (A) comprises a polymer part (PSM), in the form of a cylinder. This one piece of polymer (PSM) comprises an end (E1) called the bonding end. This polymer part (PSM) is a molded silicone part. The diameter of this bonding end is less than the diameter of the cylinder. More specifically, the diameter of this bonding end is substantially equal to the diameter of the internal disk (D2). The metal part (PM) of the actuator (A) is in the form of a spherical cap (CS) whose radius, at the base, is substantially equal to the radius of the external ring (A1), namely four millimeters in this embodiment. The height of the spherical cap (CS) is proportional to the radius and the force to be exerted on the cap to make contact. The spherical cap (SC) is glued to the end (E1) with glue (Gl).

In addition, the end (E1) of the actuator supporting the metal part (PM) is surrounded by an enclosure (EP) which serves as protection during manipulations during assembly. In this embodiment, the enclosure is integrated into the polymer part, thus forming a single part, as presented in Figure 4 . This enclosure generally has the shape of a cone whose apex is a point on the line passing through the central axis of the molded silicone cylinder (apex of the cone shown in dotted lines). The radius of this cone is greater than the radius of the spherical cap (CS), that is to say greater than four millimeters. The base of this cone also ensures the stability of the actuator when it is placed on the printed circuit board.

In Figure 5 , a section of the actuator is shown when the actuator is activated: in this figure, the spherical cap (CS) is pressed in its center. From then on, an electrical contact is established between the external ring (A1) and the internal disc (D2). In this embodiment, the polymer part (PSM) is made of silicone with a hardness of 60 shores A, just like the EP enclosure (shown in dotted lines). In this embodiment, the metal part (PM) is secured to the contact end (E1) using an adhesive whose tearing force is substantially equal to 100 grams (+/- 20 grams) . Furthermore, the metal part (PM) is made of gold-plated spring steel sheet.

Other embodiments are obviously possible. For example, it is entirely possible that the polymer part (PSM) is in the form of a rectangular parallelepiped instead of a cylinder and that the enclosure (EP) could then have a pyramidal shape. In addition, it is also possible to change the shape of the metal part according to the needs. Although the spherical cap is advantageous in certain situations, it is also possible that the shape of this cap is modified (hyperbolic cap, etc.). Thus, any metal part, deformable or not, can be used according to needs.

• un contact électrique de qualité grâce au contact or/or entre la calotte sphérique métallique et la carte électronique. Le courant de détection est très faible (50µA).
• une garantie d'actionner la calotte sphérique métallique en son centre par le fait que la concentricité de la calotte sphérique et de l'actuateur est donnée par la précision de réalisation de ce composant, et non par le résultat de l'assemblage de plusieurs pièces.
• une pièce unique évite la nécessité de maintenir la calotte sphérique métallique par un autre moyen coûteux (adhésif, circuit souple adhésivé, soudure, ...)
• une sécurité de fonctionnement grâce à un écrasement maîtrisé de l'actuateur. La longueur de l'actuateur étant importante, la force appliquée à la calotte sphérique métallique peut être maîtrisée car une variation de cote de hauteur reste faible par rapport à la hauteur.
• une résistance aux manipulations et aux décollements intempestifs lors du montage et des opérations d'entretien.
• une étanchéité de la calotte sphérique par rapport à l'environnement extérieur.

The proposed technique thus presents numerous advantages, in all its embodiments, including:

• quality electrical contact thanks to the gold/gold contact between the spherical metal cap and the electronic card. The detection current is very low (50µA).
• a guarantee of actuating the spherical metal cap at its center by the fact that the concentricity of the spherical cap and the actuator is given by the precision of production of this component, and not by the result of the assembly of several parts .
• a single piece avoids the need to maintain the spherical metal cap by another expensive means (adhesive, adhesive flexible circuit, welding, etc.)
• operational safety thanks to controlled crushing of the actuator. The length of the actuator being large, the force applied to the spherical metal cap can be controlled because a variation in height dimension remains small compared to the height.
• resistance to handling and untimely detachment during assembly and maintenance operations.
• sealing of the spherical cap in relation to the external environment.

Claims (6)

1. Actuator (A) for creating an electrical contact between two tracks of a printed circuit board, comprising:

   - a polymer part (PSM), forming an arm comprising a contact end (E1) and a moving end;

   - a metal part (PM), secured to said contact end (E1), having the general shape of a cap,

   - said end (E1) of the actuator supporting said metal part (PM), being surrounded by an enclosure (EP) extending up to a contact base (BPM) of the metal part (BPM), characterised by:
   said enclosure comprising a base intended to come into contact with said printed circuit board and covered with a conductive ink.
2. Actuator according to claim 1, characterised in that said metal part (PM) has the shape of a spherical cap.
3. Actuator according to claim 1, characterised in that said polymer part (PSM) is made of silicone having a hardness of 60 Shore A.
4. Actuator according to claim 1, characterised in that said metal part (PM) is secured to said contact end (E1) using an adhesive whose tearing force is substantially equal to 100 grams.
5. Actuator according to claim 1, characterised in that said metal part (PM) is composed of a gold-plated spring steel sheet.
6. Actuator according to claim 1, characterised in that said enclosure (EP) has the general shape of a cone whose apex is a point of the straight line passing through the central axis of the polymer part (PSM).

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