The present invention relates to a user interface, e.g. a control console or a control board comprising one or more keys, comprising at least one resistive force sensor for determining the force being applied by a user. In particular, the present invention relates to a user interface, e.g. a control console or a control board, comprising at least one innovative resistive force sensor.

Keys, control consoles and/or control boards are known which comprise: a contact surface, which is adapted to be pressed by a user, and a device adapted to detect the force being applied by the user onto said contact surface.

Force detection may occur in different ways, e.g. by means of an infrared sensor or a capacitive sensor capable of measuring the variation in the position of said contact surface or an element connected thereto, the movement of which is countered by a coil spring. The infrared solution is particularly costly and difficult to implement on a control board. Capacitive solutions, though less expensive, are not reliable whenever there may be some components of the force to be measured that are not perpendicular to the contact surface.

Some solutions for determining the force applied onto a surface are also known which utilize a resistive system, e.g. strain gauge sensors or structures whereon ink with carbon nanotubes is deposited. Such solutions have an inherent limitation which is essentially due to the force range that they can detect; in fact, such sensor types can only be used for applications wherein the applied forces exceed 20N.Moreover, they may require very large application surfaces, so that they cannot be miniaturized and/or do not allow any travel of the surface onto which said force is applied.

It must be pointed out that control consoles or control boards, as well as keys, must be able to react by moving, thereby activating the associated function, when forces are applied thereto which however do not exceed 5N.

Furthermore, in the automotive field there is an increasing demand for innovative solutions capable of reducing the manufacturing costs while ensuring high measurement accuracy, and in particular for force sensors capable of sensing forces of less than 5N and of providing accurate readings with low uncertainty, wherein the readings must not be adversely affected by any forces that are transversal to those being perpendicularly applied onto the contact surface.

The solutions currently known in the art do not permit reducing the manufacturing costs, nor miniaturizing such technology for application to control boards or keys, even small ones, while still ensuring high accuracy.

Moreover, none of the currently known solutions can correctly sense the applied force when the key has to cover a travel, particularly when the travel of the key is 1mm the most.

The present invention aims at solving these and other technical problems by providing an innovative solution for making a user interface, e.g. a control console, which comprises at least one innovative resistive force sensor.

One aspect of the present invention relates to a user interface, e.g. a control console or a control board, having the features set out in the appended claim 1. The features and advantages of the user interface according to the present invention will become apparent in the light of the following description of some preferred embodiments and of the annexed drawings, wherein:

Figure 1 shows a perspective view of a user interface, in the form of a control console, according to the present invention;

Figure 2 shows a sectional view relative to a vertical plane of the user interface of Figure 1, illustrating one possible location of a preferred embodiment of the resistive force sensor according to the present invention;

Figures 3A and 3B show a portion of one possible embodiment of the resistive force sensor according to the present invention in two different operating configurations of the user interface; in particular, Figure 3A shows a portion of the force sensor, in particular a metallic leaf, in an idle configuration of the user interface, in which no force is being applied onto the contact surface; Figure 3B shows the same portion of the force sensor of Figure 3A in an active configuration of the user interface, in which a force is being applied onto the contact surface;

Figures 4A and 4B show different views of the assembly including the resistive force sensor and a printed circuit board; in particular, Figure 4A shows a perspective view of a printed circuit board with three resistive force sensors associated therewith; Figure 4B shows another perspective view of the printed circuit board of Figure 4A, wherein one resistive force sensor is visible in more detail;

Figure 5 is a Cartesian graph showing the trend of the variation occurring in the resistance of the resistive force sensor as a function of the travel of the contact surface of the user interface, as well as the variation occurring in the force being applied onto the contact surface of the user interface as a function of the travel of the contact surface;

Figure 6 shows the force measurement system, which includes a plurality of resistive force sensors connected to a processing unit.

With reference to the above-mentioned figures, reference numeral 1 designates as a whole a user interface, e.g. a control console or a control board.

User interface 1 according to the present invention is particularly suitable for use in vehicles, e.g. in cabins of motorcars, thus becoming an interface for the user. Said user interface 1 is, for example, a control console or a control board.

User interface 1 according to the present invention comprises: at least one contact surface 2, whereon a user exerts a force in order to selectively activate or deactivate one or more functions; and at least one printed circuit board or PCB 4, whereon at least one electronic circuit 40 is realized for suitably controlling at least one function, wherein such at least one function can be activated by the user by acting upon said at least one contact surface 2.

User interface 1 according to the present invention further comprises at least one actuating device 3. Said actuating device 3 is adapted to suitably transmit a movement imparted to said at least one contact surface 2 towards said printed circuit board or PCB 4.

User interface 1 according to the present invention further comprises at least one force sensor 6 adapted to sense a force exerted on said at least one contact surface

2.

Preferably, said force sensor 6 is a resistive sensor, and said at least one force sensor 6 is located between said at least one actuating device 3 and said at least one printed circuit board or PCB 4.

Being resistive, said force sensor 6 is inexpensive, can be easily miniaturized, and is applicable to different types of user interfaces, such as consoles or dashboards, even small ones, like those employed in the automotive industry.

For the purposes of the present description, the term function or functions refers to a functionality or a service, preferably comprised in vehicles, e.g. in cabins of motorcars, which can be controlled and/or adjusted by means of user interface 1 according to the present invention, which is provided in the form of a control console, e.g. for opening a car roof, activating and controlling the heating and/or air conditioning system, using voice interfaces, activating and controlling music reproduction devices, etc. Each function or service is suitably controlled and managed by means of a respective electronic circuit, e.g. an electronic circuit 40 at least partly realized on the printed circuit board or PCB 4.

The preferred embodiment of user interface 1, wherein said at least one force sensor 6 is located between said at least one actuating device 3 and said at least one printed circuit board or PCB 4, makes it possible to at least suitably space apart contact surface 2 from printed circuit board or PCB 4, thus allowing a desired movement and/or travel of said contact surface 2, and ensuring that the force applied by a user will be appropriately transferred to force sensor 6, in particular via said actuating device 3. Preferably, the present embodiment ensures that force sensor 6 will only perceive the component along an axis "Z" of the force being applied onto said contact surface 2, wherein said axis "Z" is the normal to said contact surface 2.

Describing now in detail one preferred, but non limiting, possible embodiment of resistive force sensor 6 of user interface 1 according to the present invention, said force sensor 6 comprises: an electric circuit section 42 and a metallic leaf 62.

In an alternative embodiment (not shown), said force sensor 6 comprises: pads and a tip.

In the preferred embodiment of resistive force sensor 6, said electric circuit section 42 has a predefined length. Said electric circuit section 42 is made from a resistive compound, e.g. a resistive paste, having a known resistivity value.

Said electric circuit section 42, having predefined and known length, width ad thickness, and being made of resistive material having a known resistivity value, permits creating a resistive impedance, in particular a resistance, of a known value.

Said electric circuit section 42 is connected, at a first end thereof, to an electronic circuit 40 provided on said printed circuit board or PCB 4.

In one possible embodiment, said electric circuit section 42 is a portion or section of an electronic circuit 40 comprised in said printed circuit board or PCB 4. Preferably, said electric circuit section 42 is connected in series with said electronic circuit 40, and therefore the second end of electric circuit section 42 is connected to said electronic circuit 40. Alternatively, the second end of electric circuit section 42 is left floating.

Preferably, said electric circuit section 42 is a thin film of resistive paste having known thickness, width and length, deposited on said printed circuit board or PCB 4.

Said metallic leaf 62 is a conductive metallic leaf made of electrically conductive metallic material such as, for example, copper, or coated with an electrically conductive layer.

Said metallic leaf 62 is adapted to change its interaction with said electric circuit section 42 along said electric circuit section 42; for example, said metallic leaf 62 is adapted to move, preferably slide, on said electric circuit section 42 along said electric circuit section 42, or said metallic leaf 62 is adapted to change the overlapping area in contact with said electric circuit section 42, e.g. by bending.

Said metallic leaf 62 is adapted to change its shape, e.g. by becoming deformed, thus changing its interaction with said electric circuit section 42 along the length of said electric circuit section 42.

Preferably, said metallic leaf 62 is electrically connected, at a first end thereof, to an electronic circuit 40 provided on said printed circuit board or PCB 4; while said metallic leaf 62 is electrically connected, at the opposite or second end thereof, to said electric circuit section 42. Preferably, said electronic circuit 40 to which the first end of metallic leaf 62 is connected is the same electronic circuit 40 to which the first end of said electric circuit section 42 is connected. Preferably, said force sensor 6 is connected in series with an electronic circuit 40.

More in general, the change occurring in the interaction between said metallic leaf 62 and said electric circuit section 42 causes a variation in the resistance that is present, and therefore measurable, between said first end of metallic leaf 62 and the first end of electric circuit section 42.

In a preferred embodiment, force sensor 6 according to the present invention is designed in a manner such that, as the force being applied onto said contact surface 2 increases, the resistance between said first end of metallic leaf 62 and the first end of electric circuit section 42 decreases. In an alternative embodiment, an increase in the applied force results in increased resistance.

In the preferred embodiment, said actuating device 3 is adapted to act upon said metallic leaf 62, preferably in a direct manner, thereby producing a variation in the interaction between said metallic leaf 62 and said electric circuit section 42 according to the force being applied onto said contact surface 2, e.g. by moving, e.g. sliding, or overlapping said metallic leaf 62 along said electric circuit section 42.

The present embodiment provides correspondence between the variation occurring in the force being applied onto said contact surface 2 and the resistance value that is present, and therefore measurable, across said resistive force sensor

6.

In a preferred, but merely illustrative and non limiting, embodiment, said metallic leaf 62 is designed in a manner such as to transform a movement along a first axis, e.g. the axis "Z", imparted thereto through actuating device 3, into a movement of at least the second end of the same metallic leaf 62 along an axis perpendicular to said first axis, e.g. perpendicular to said axis "Z", e.g. along the axis of extension of said electric circuit section 42.

More in general, said metallic leaf 62 is designed to have a known elastic constant, e.g. in the range of 5N/m to lON/m.

Said metallic leaf 62 may be implemented in different forms, each one having a different shape, structure and/or material, all equally suitable for producing a change in the interaction with said electric circuit section 42, thereby changing the resistance, which is present and hence measurable, depending on the force being applied onto said contact surface 2.

More in general, said user interface 1 can take at least two different operating configurations, in particular an idle configuration and an active configuration. For the purposes of the present description, the term "idle configuration" refers to that configuration of user interface 1 in which no force is being applied onto contact surface 2. For the purposes of the present description, the term "active configuration" refers to that configuration of user interface 1 in which a force is being applied onto contact surface 2. Preferably, when a force is applied onto contact surface 2, the same contact surface 2 will translate downwards, covering a travel of, preferably, less than 1mm or, even more preferably, less than 0.5m, e.g. approximately 0.4mm.

The resistive force sensor 6 is designed in a manner such that, when user interface 1 is in the idle configuration, there is a first resistance of a known value between said first end of metallic leaf 62 and the first end of electric circuit section 42, whereas when user interface 1 is in the active configuration there is a second electric resistance, preferably lower than said first electric resistance, wherein the second electric resistance may vary from 1.5 to 100 times said first electric resistance.

In a preferred, but merely illustrative and non limiting, embodiment of user interface 1 according to the present invention, said metallic leaf 62 has two arms (621, 622). Said arms (621, 622) being constrained and electrically connected to each other. In such illustrative and non limiting embodiment, said actuating device 3 acts upon said metallic leaf 62 at the point of mutual connection between said two arms (621, 622) of metallic leaf 62. Said two arms (621, 622) of metallic leaf 62 being disposed along mutually incident directions, and said arms (621, 622) being mutually incident at the point of mutual constraint.

In the present embodiment, depending on the force being applied onto said metallic leaf 62 through said actuating device 3, the distance between the ends of the two arms (621, 622) will change. Therefore, such metallic leaf 62 will change its own shape.

Describing now more in detail a preferred, but merely illustrative and non-limiting, embodiment of user interface 1 according to the present invention, a first arm 621 of metallic leaf 62 is fixed, at a first end thereof, to said printed circuit board or PCB 4, and in particular to an electronic circuit 40, while at its other end, or second end, said first arm 621 is fixed to a first end of a second arm 622. At its other end, or second end, said second arm 622 is adapted to move, preferably slide, on said electric circuit section 42.

The variation occurring in the position of the second end of the second arm 622 along said electric circuit section 42 will cause a change in the resistance that is present, and therefore measurable, between said first end of metallic leaf 62 and the first end of electric circuit section 42, which will be dependent on the force being applied on said metallic leaf 62 through said actuating device 3.

Going more into details of the preferred embodiment, the greater the force applied onto said metallic leaf 62, the closer the second end of metallic leaf 62, in particular the second end of the second arm 622, will get, by sliding, to the first end of electric circuit section 42, thereby reducing the portion of resistive compound of said electric circuit section 42 through which current can flow, and hence reducing the resistance between said first end of metallic leaf 62 and the first end of electric circuit section 42. In the present embodiment, the distance between said first arm 621, which is constrained, whether directly or indirectly, to printed circuit board or PCB 4, and said second arm 622 will change as a function of the force being applied onto said metallic leaf 62 through said actuating device 3, said second arm 622 being able to move, preferably slide, along said electric circuit section 42.

In one possible embodiment, arms (621, 622) of the metallic leaf are capable of changing their mutual distance, thereby allowing said actuating device 3 to cover a substantially linear travel of 0.2mm to 0.4mm. Such a variation in the shape of metallic leaf 62 can be obtained with a force of approximately 0.5N to 4.5N. More in general, the movement, preferably the sliding movement, of the second end of metallic leaf 62, in particular of the second end of second arm 622, on said electric circuit section 42 is such as to allow an electric or electronic current to flow, without solution of continuity, even during the application and/or variation of the force on said contact surface 2.

In a preferred embodiment of user interface 1 according to the present invention, said metallic leaf 62 is made as one piece and suitably bent. In alternative embodiments (not shown), said metallic leaf is made up of two portions mechanically constrained, e.g. hinged, and electrically connected to each other.

In the preferred embodiment of metallic leaf 62 made as one piece, it is bent to define said first arm 621 and said second arm 622. Preferably, the first arm 621 and the second arm 622 have, in their respective central portion, a substantially similar shape, e.g. similar thickness, width and length. Such a solution makes it possible to increase the rigidity of metallic leaf 62 to avoid flexing of one or both of arms (621, 622). In an alternative embodiment, the structure of said second arm 622 is different from that of said first arm 621, in particular said second arm 622 being thinner.

More in general, the shape of arms (621, 622) of the metallic leaf can be defined according to specific requirements, e.g. the range of forces to be perceived, the travel to be covered, the total number of sensors in user interface 1, the material of said metallic leaf 62, etc.

Figures 3A and 3B show a portion of one possible embodiment of resistive force sensor 6 according to the present invention in two different operating configurations. In the present embodiment, metallic leaf 62 is made as one piece. The first end of metallic leaf 62 is mechanically constrained and electrically connected to said printed circuit board or PCB 4; whereas the second end of metallic leaf 62 is in electric contact with electric circuit section 42, which in turn is connected to an electronic circuit 40. Said metallic leaf 62 is acted upon by said actuating device 3, a portion of which is shown in the drawing.

In particular, Figure 3A shows a portion of force sensor 6, in particular a metallic leaf 62, in an idle configuration of user interface 1, in which no force is being applied onto contact surface 2. The distance between the ends of metallic leaf 62 is known, and is represented in the drawing as a double-headed arrow. Figure 3B shows the same portion of force sensor 6 of Figure 3A in an active configuration of user interface 1, in which a force is being applied onto contact surface 2. Such force is transferred from actuating device 3 to force sensor 6, causing the second end of metallic leaf 62 to slide along said electric circuit section 42. By comparing Figure 3B and Figure 3A, one can see that the distance between the ends of metallic leaf 62, represented in the drawings as a double-headed arrow, has increased.

In the configuration of Figure 3A, between said first end of metallic leaf 62 and the first end of electric circuit section 42 there is a first electric resistance, the value of which is indicatively known, e.g. lower than 40kQ, e.g. approximately 36kQ. Whereas, in the configuration of Figure 3B, between said first end of metallic leaf 62 and the first end of electric circuit section 42 there is a second electric resistance, preferably lower than said first electric resistance, e.g. lower by 1.5 to 10 times, e.g. lower than 20 kQ, e.g. approximately 18kQ.

More in general, resistive force sensor 6 according to the present invention is designed to be able to detect forces applied onto said contact surface 2 not exceeding approximately 5N. Preferably, said resistive force sensor 6 is designed to undergo a variation in its electric resistance comprised between a minimum value and a maximum value, wherein the maximum value is 1.5 to 10 times, preferably 2 to 5 times, greater than the minimum value. By way of non limiting example, said force sensor 6 is designed to undergo a variation in its electric resistance of 10 kQ to 40 kQ, in particular for applied forces in the range of 0.5N to 4.5N.

Figure 5 shows, by way of non-limiting example, a Cartesian graph indicating the trend of the variation occurring in the resistance of resistive force sensor 6 depending on the travel of contact surface 2 of user interface 1, as well as the variation occurring in the force applied onto contact surface 2 of user interface 1 depending on the travel covered by contact surface 2. Observing the graph, the axis of abscissas indicates the travel, expressed in millimeters, of contact surface 2, the left-hand axis of ordinates indicates the force applied onto contact surface 2, expressed in Newtons; while the right-hand axis of ordinates indicates the resistance, expressed in kOhm, which can be measured across resistive force sensor 6.

Analysing such graph, it is clear that force sensor 6 is so designed that, for a travel of contact surface 2 of approximately 0.4 mm, a resistance variation will be obtained, in particular starting from 38kQ and reaching 20kQ, which will correspond to a force applied onto said contact surface 2 of approximately 4.5N. The graph shown herein represents an experimental test carried out on one possible embodiment of the user interface 1, e.g. like the one shown in Figure 1, with a single force sensor 6. In this graph, one can see that the force increases linearly with the travel of contact surface 2. Moreover, the implementation solution of resistive force sensor 6 with a metallic leaf 62 shows a substantially linear trend in the travel range of 0 to 0.4mm of contact surface 2.

A preferred embodiment of user interface 1 according to the present invention comprises a processing unit 7. Said processing unit 7 is adapted to determine the force being applied onto said at least one contact surface 2 as a function of the force being sensed by said at least one resistive force sensor 6. In the present embodiment, said processing unit 7 can determine the force being applied onto said contact surface 2 by monitoring the resistance variations measurable across resistive force sensor 6, e.g. between said first end of metallic leaf 62 and the first end of electric circuit section 42, or across a pair of pads.

By way of non-limiting example, by having a constant current flow through an electronic circuit 40, in particular the electric circuit to which both said electric circuit section 42 and said metallic leaf 62 of force sensor 6 are connected, it will be possible to determine the voltage variation between said first end of metallic leaf 62 and the first end of electric circuit section 42, or vice versa.

More in general, the resistance variation caused by the changed interaction between said metallic leaf 62 and said electric circuit section 42 can be detected by said processing unit 7, which, more in general, is adapted to take measurements of electric quantities such as, for example, voltage, current, resistance, impedance, etc.

In one possible embodiment of said user interface 1, said actuating device 3 is adapted to suitably convert the movement exerted by the user onto said contact surface 2 by applying a force thereto into a movement that will ensure a change of state as regards the function associated with said contact surface 2 or at least a portion thereof. Said movement may cause a mechanical switching of electric contacts or may be detected by a motion sensor and/or a touch sensor, which will generate an electric signal upon reaching a particular point along the travel of said actuating device 3.

More in general, said actuating device 3 is at least adapted to transmit the force applied onto said contact surface 2 towards said printed circuit board or PCB 4, and in particular towards said at least one resistive force sensor 6.

Many different embodiments and implementations, even from a functional viewpoint, of said actuating device 3 may be conceived, which will be dictated also by the design specifications of the user interface 1, such as, for example, the necessary travel and the tactile feeling to be perceived by the user while acting upon said contact surface 2. For this reason, actuating device 3 will not be described herein in its construction details, but solely from a functional viewpoint; nevertheless, a person skilled in the art will still be able to understand the essential mechanical aspects necessary for its correct implementation and operation. Said at least one electronic circuit 40, comprised in the printed circuit board or PCB 4, may be a plurality of tracks defining the path of the electronic signals adapted to at least control one or more functions or functionalities and/or necessary for the operation of said at least one resistive force sensor 6. Preferably, at least one electronic circuit 40 is adapted to electronically connect said force sensor 6 to said processing unit 7, which may be either comprised in the printed circuit board or PCB 4 included in user interface 1 or be situated in a remote position from said user interface 1 and/or said printed circuit board or PCB 4. In a preferred, but merely illustrative and non limiting, embodiment of user interface 1, said resistive force sensor 6, and in particular said electric circuit section 42 and said metallic leaf 62 of resistive force sensor 6, is connected in series with an electronic circuit 40 provided on said printed circuit board or PCB 4, which electronic circuit 40 is adapted to electronically connect the corresponding force sensor 6 to processing unit 7, said electric circuit section 42 being preferably connected in series with electronic circuit 40.

One exemplary, but non-limiting, possible embodiment of user interface 1 according to the present invention is shown in Figure 1. Figure 1 shows, in fact, a perspective view of one possible embodiment of user interface 1 according to the present invention. In Figure 1 contact surface 2 is visible, which lies on top of an external structure 12 of user interface 1. Said external structure 12 defines an inner volume, in which the elements and devices comprised in user interface 1 according to the present invention are suitably housed, without however being visible in said Figure 1. In the illustrated embodiment, said contact surface 2 is represented as a single surface. In alternative embodiments (not shown), more than one contact surface 2 may be provided, even having different shapes, which may be identifiable as keys.

More in general, said contact surface 2 is visible to the user once user interface 1 has been assembled in its final location, which may be the interior of a vehicle, e.g. a dashboard or a console; whereas said external structure 12 is not normally visible to the user.

More in general, on said at least one contact surface 2 the user can exert a force, preferably having a component along an axis "Z", e.g. along an axis perpendicular to the surface defined by contact surface 2 itself.

Said at least one resistive force sensor 6 comprised in user interface 1 is advantageously electronically connected to said processing unit 7 in such a way that the latter can determine the force being applied onto said at least one contact surface 2 as a function of the force being sensed by said at least one force sensor 6, said force sensor 6 being preferably adapted to sense the force being applied onto said contact surface 2 in the component thereof that is parallel to said axis "Z".

More in general, one or more resistive force sensors 6 may be connected to said processing unit 7. When more than one force sensor 6 associated with the same contact surface 2 are electronically connected to said processing unit 7, said processing unit 7 may be suitably programmed for determining a place, spot or sub-region of contact surface 2 whereon the user is exerting a force. Such an embodiment defines a force measurement system. In this embodiment, several functions or services can be associated with one contact surface 2, since a different function or service can be associated with each place, spot or sub-region definable on said contact surface 2.

Figure 6 shows one possible embodiment of a force measurement system. The illustrated embodiment shows a plurality of force sensors 6, preferably all of the resistive type, which are electronically connected to a processing unit 7. As can be easily understood from the figure, the number of force sensors 6 comprised, for example, in the force measurement system may vary from the four sensors shown in Figure 6. Moreover, as aforementioned, by increasing the number of force sensor 6 and conveniently designing their arrangement, e.g. their distribution, relative to contact surface 2, said processing unit 7 can be programmed for determining which place, spot or sub-region of contact surface 2 the user is exerting a force on.

A preferred, but merely illustrative and non-limiting, embodiment of user interface 1 according to the present invention includes at least three resistive force sensors 6 arranged on the plane defined by said printed circuit board or PCB 4. The presence of at least three force sensors 6 permits a triangulation of the place, spot or sub-region of application of the force onto said contact surface 2 by a user. An even more preferable embodiment, like the one shown by way of example in Figure 4A, comprises only three force sensors 6 suitably arranged to permit, via said processing unit 7, a triangulation of the place, spot or sub-region of application of the force onto said contact surface 2 by a user. In this respect, if the force being applied onto said contact surface 2 is asymmetric relative to the surface defined by contact surface 2, e.g. relative to an axis of symmetry "X", it will be possible to determine which zone of one contact surface 2 a force is being exerted on.

A preferred embodiment of user interface 1 according to the present invention comprises only one actuating device 3 even when it includes a plurality of contact surfaces 2.

An alternative, but merely illustrative and non limiting, embodiment of user interface 1 according to the present invention includes a second embodiment of resistive force sensor 6. In such exemplary embodiment (not shown), said resistive force sensor 6 comprises at least one tip and at least one pair of pads. Said at least one tip is made of viscoelastic polymeric materials having conductive properties, e.g. conductive elastomers such as conductive rubber, conductive silicone, or elastomers with a conductive coating, etc., and therefore suitable for conducting an electric current. By way of non-limiting example, said conductive coating comprises copper or graphite pigments. Said pair of pads are arranged proximal to each other, e.g. side by side, but are not electrically connected to each other. Said pair of pads are realized on said printed circuit board or PCB 4. In one possible embodiment, said pair of pads are comprised in an electronic circuit 40 which is electronically connected to said processing unit 7. Said at least one tip is adapted to act upon said pair of pads to connect them electrically to each other with some electric resistance. Such electric resistance is variable, preferably such variability being inversely proportional to the variation of the area of said tip in contact with said pair of pads. In general, the electric resistance that can be measured between said pair of pads will change with the area of said tip in contact with said pair of pads. The larger the area of said tip in contact with said pair of pads, the lower the resistance that will be measured across said pads. Conversely, the smaller the area of said tip in contact with said pair of pads, the higher the resistance that will be measured across said pads. Preferably, said tips are conveniently housed in suitable housings formed in the structure of actuating device 3, for the purpose of holding said tips in position. This alternative embodiment of resistive force sensor 6 may be used in user interface 1 as a redundant force sensor complementing the previously described preferred embodiment of resistive force sensor 6, which comprises metallic leaf 62.

Going now into the construction details of one possible embodiment of user interface 1, Figure 2 shows one possible embodiment of user interface 1, in particular the embodiment illustrated in Figure 1. Said Figure 2 shows one possible location of a preferred embodiment of resistive force sensor 6 according to the present invention. As can be seen, actuating device 3 is constrained to said contact surface 2 and moves integrally therewith, preferably such that at least the component along said axis "Z" of the force applied onto said contact surface 2 by the user will be transferred to actuating device 3. Preferably, a first end of said actuating device 3 is constrained to contact surface 2, while the opposite end of actuating device 3 faces towards said printed circuit board or PCB 4. Between said printed circuit board or PCB 4 and said actuating device 3 there is, as shown, a force sensor 6. Said actuating device 3 is adapted to act directly upon said force sensor 6, and in particular upon said metallic leaf 62. In the illustrated embodiment, said at least one contact surface 2 is mechanically connected to said at least one actuating device 3, so that they will move integrally. Said at least one actuating device 3 is preferably connected to said external structure 12 of user interface 1 through suitable damping means. Said damping means are, for example, adapted to absorb and attenuate any transverse forces, with respect to said axis "Z", that might affect said contact surface 2, and hence said actuating device 3.

In Figure 2 one can also see further construction details of external structure 12 and of printed circuit board or PCB 4. Such details can be easily understood by a person skilled in the art, and will not therefore be described any further.

Lastly, user interface 1 illustrated in Figure 2 is in an idle configuration.

Figures 4A and 4B show, in different views, the assembly including resistive force sensor 6 and a printed circuit board or PCB 4.

In particular, Figure 4A shows a perspective view of a printed circuit board or PCB 4 with three resistive force sensors 6 associated therewith. In the illustrated embodiment, which is merely exemplary and non-limiting, the three force sensors 6 are so arranged as to form the vertices of an isosceles or equilateral triangle.

More in general, said force sensors 6, preferably three force sensors 6, are suitably disposed on the plane defined by said printed circuit board or PCB 4, thus permitting a triangulation of the place of application of the force onto said contact surface 2, e.g. via said processing unit 7.

Figure 4A shows some different possible embodiments of metallic leaves 62 comprised in force sensor 6. In particular, two metallic leaves 62 are visible which have two different shapes; in particular one metallic leaf 62 has arms with substantially similar central portions, whereas another force sensor 6 comprises a metallic leaf 62 wherein the two arms of metallic leaf 62 are different from each other. The figure also shows various electric circuit sections 42 comprised in respective force sensors 6. The change occurring in the interaction between metallic leaf 62 and the respective electric circuit section 42 will make it possible to determine the force being applied onto said contact surface 2 based on the resulting resistance variation measurable across such force sensor 6.

Figure 4B shows, in another perspective view, the printed circuit board of Figure 4A and only one resistive force sensor 6. From this figure it is possible to understand further construction details of the preferred embodiment of resistive force sensor 6.

The figure shows metallic leaf 62 made as one body or piece. In this figure one can see the first arm 621 of metallic leaf 62, which is fixed, at a first end thereof, to said printed circuit board or PCB 4, and in particular to an electronic circuit 40. The connection of the first arm 621 to printed circuit board or PCB 4 is both electrical and mechanical. In particular, said first arm 621 cannot change the point of mechanical and electrical connection with said electronic circuit 40. At the other end, or second end, said first arm 621 continues with a curved portion, which is acted upon by said actuating device 3, and becomes the first end of the second arm 622. The other end, or second end, of said second arm 622 is adapted to move, in particular slide, on said electric circuit section 42, in particular on the portion thereof which is made of resistive paste.

From Figure 4B one can understand how said actuating device 3 acts upon said metallic leaf, causing it to move as indicated by the double-headed arrow. Depending on the action exerted by actuating device 3 on such metallic leaf 62, the latter will become deformed and will cause the second end of its second arm 622 to slide as indicated by the arrow.

From the same Figure 4B one can also infer the longitudinal and transversal dimensions of electric circuit section 42, which is electrically connected to an electronic circuit 40.

This figure also shows an embodiment of the metallic leaf wherein the central portions of the two arms (621, 622) are substantially similar. In fact, the central portions of both arms (621, 622) have a planar shape with a trapezoidal outline.

More in general, the use of a resistive force sensor 6 capable of changing its own electric resistance between a minimum value and a maximum value, wherein the maximum value is 1.5 to 10 times greater, preferably 2 to 5 times greater, than the minimum value, e.g. lOkQ to 40kQ, makes it possible to easily interface such force signal 6 with electronic signals, e.g. digital electronic signals.

Preferably, user interface 1 comprises one or more devices, such as transducers and/or actuators, capable of providing feedback to the user following the application of a force onto said contact surface 2 and the resulting activation or deactivation of one or more associated functions, in particular following a change of state of at least one electronic circuit 40 comprised in the printed circuit board or PCB 4. Said one or more devices may also provide visual, audible and/or tactile feedback to the user exerting a force on such contact surface 2. The types of feedback that may be provided to a user interacting with user interface 1 are per se known and may be obtained in several possible ways, depending on the type of visual, audible and/or tactile feedback that needs to be provided to the user.

In a preferred possible embodiment of user interface 1, described herein by way of non-limiting example, a haptic feedback actuator is comprised. Said haptic feedback actuator is adapted to act upon said contact surface 2 to provide haptic feedback to the user when the force applied onto said contact surface 2, and sensed by said at least one force sensor 6, exceeds a predefined threshold. More in general, said haptic feedback actuator may be able to provide haptic feedback to the user whenever an electronic circuit 40, comprised in printed circuit board or PCB 4, changes its state, in particular after the user has touched said contact surface 2. In a preferred embodiment of user interface 1 according to the present invention, said haptic feedback actuator is of the magnetic type. In one possible embodiment, said magnetic haptic feedback actuator comprises at least one permanent magnet and at least one electromagnet. Said electromagnet can be suitably activated to appropriately displace, by attracting and/or repulsing it, said permanent magnet. Said haptic feedback actuator is advantageously mounted on a mobile support capable of moving, preferably along a vertical axis "Z", in order to suitably act upon said contact surface 2. In general, said haptic feedback actuator can impart at least one impulse or vibration to said contact surface 2.

More in general, said user interface 1 may comprise one or more keys (not shown), which may even not be conveniently connected to said at least one force sensor 6.

Preferably, the field of application of user interface 1 according to the present invention regards control consoles or boards, through which the user can transmit a command by appropriately acting upon said contact surface 2, obtaining feedback, e.g. haptic feedback, following the action exerted on such contact surface 2.

User interface 1 according to the present invention makes it possible to recognize, and preferably determine, the actuation force being exerted by a user on a contact surface 2, which is visible to a user.

User interface 1 according to the present invention can, by means of resistive force sensors 6, detect the force, or at least the vertical component thereof, which is being exerted on said contact surface 2 and transmitted through actuating device 3.

The preferred embodiment of said force sensor 6 is particularly inexpensive, strong and reliable, since it is not affected by transverse movements, thus being quite insensitive to transverse force components, in addition to being small and particularly easy to manufacture and assemble.

Moreover, the preferred embodiment of user interface 1 is designed in a manner such that the geometry and arrangement of the sensor will maximize the resistance variation within the force range normally employed for interacting with control boards, in particular for forces comprised between IN and 4N.

Furthermore, the preferred embodiment makes it possible to obtain a reliable and durable sensor, since the latter is not affected by drifts and/or malfunctions.

Any alternative embodiments which have not been illustrated and/or described herein, but which can be inferred by a person skilled in the art in light of the present description and the annexed drawings, shall be considered to fall within the protection scope of the present invention .

REFERENCE NUMERALS User interface 1 External structure 12 Contact surface 2 Actuating device 3 Printed circuit board 4 Electronic circuits 40 Electric circuit section 42 Force sensor 6 Metallic leaf 62 First arm 621 Second arm 622 Processing unit 7 Axis

Axis of symmetry "X"