WO2015181763A2

WO2015181763A2 - Force gauge

Info

Publication number: WO2015181763A2
Application number: PCT/IB2015/054005
Authority: WO
Inventors: Renato Andreola; Daniele BUCCI; Gilberto ROMBOLI
Original assignee: Nanolever S.R.L.
Priority date: 2014-05-30
Filing date: 2015-05-28
Publication date: 2015-12-03
Also published as: WO2015181763A3

Abstract

Described is a force gauge (1) comprising a proximity sensor (2) formed by a first flat component (3) lying in a first plane P1 and a conductor plate (4) lying in a second plane P2 parallel to the first plane P1; the first flat component (3) and the conductor plate (4) are movable relative to each other between a spaced-apart position and a close-together position along a main axis (D) and are connected to each other by a constraining system at least in part elastically deformable along the main axis (D) in such a way as to allow the relative movement of the conductor plate (4) and the first flat component (3) in particular when a force F is applied to the conductor plate (4) from the opposite side relative to the first flat component (3); the gauge (1) comprises a computerised command and control unit (5) in communication with the first flat component (3) and configured for detecting from the first flat component (3) a measurement signal representing a variation of an electrical quantity determined by a movement (ΔS) of the conductor plate (4) relative to the first flat component (3), calculating a value of the movement (ΔS) measured along the main axis (D) starting from the measurement signal and correlating the value of the movement to a value of the force F as a function of the mechanical characteristics of the hollow element (7).

Description

DESCRIPTION

FORCE GAUGE.

Technical field

This invention relates to a force gauge and in particular a weight force gauge, to which explicit reference will be made without limiting the scope of the invention, based on a movement transducer of the inductive or capacitive type.

Background art

A type of weight force gauge commonly used in various technical sectors are the so-called "load cells".

In general, a load cell is a transducer which is used for converting a force into an electric signal; the conversion is indirect and is based on the deformation of a system of extensometers by the force to be measured; the system of extensometers converts the deformation into an electric signal, for example based on the variation of resistance in a respective conductor.

More specifically, a load cell comprises a main metallic body to which are applied, in predetermined zones, one or more extensometers which read the mechanical deformation of the material (the compression or traction) of the metallic body itself by means of the variation in electrical resistance which that deformation causes on their electric circuit. In order to amplify the extent of the signal a very common choice is to use four extensometers connected to each other in a Wheatstone bridge configuration; more simple configurations are also known which require the use of one or two extensometers.

The load cells of known type have some drawbacks.

The load cells require a correction of the non-linearity, a frequent calibration and a compensation of the variations of measurement due to temperature variations. A detachment of the extensometers from the body may occur during use or a deterioration of the electrical connections, which are relatively rigid, of the extensometers themselves.

The load cells of known type are thus very expensive and delicate in relation to the expected performance.

Disclosure of the invention

In this context, the main aim of this invention is to overcome the above- mentioned drawbacks.

The aim of this invention is to provide a force gauge, in particular a weight force gauge but also in general a gauge of other forces commonly involved in the operation of machines and industrial plants, which is precise and reliable and with costs lower than those of the load cells of known type.

The technical purpose indicated and the aims specified are substantially achieved by a force gauge according to claim 1.

Brief description of drawings

Further features and advantages of this invention are more apparent in the detailed description below, with reference to a preferred, non-restricting, embodiment of a force gauge as illustrated in the accompanying drawings, in which:

Figure 1 is schematic perspective view in cross section and partly in blocks of a force gauge according to this invention;

Figure 2 is a schematic top plan view of the force gauge of Figure 1 ;

Figure 3 is a schematic view in cross section, with some parts cut away for greater clarity, of the force gauge of Figure 1 ;

Figure 4 is schematic side view partly in blocks of a second embodiment of a force gauge according to this invention;

Figure 5 is a schematic perspective view in cross section, with some parts cut away for greater clarity, of the gauge of Figure 4; Figure 6 is a schematic top plan view of the gauge of Figure 4;

Figure 7 is a schematic cross section view of the gauge of Figure 4 through the plane VII-VII of Figure 6;

Figure 8 is a basic schematic perspective view of a gauge according to this invention in a first open operating configuration;

Figure 9 illustrates the guage of Figure 8 in a second operating configuration;

Figure 10 is schematic side view of a third embodiment of a force gauge according to this invention;

Figure 1 1 is schematic side view of a third embodiment of a force gauge according to this invention.

Detailed description of preferred embodiments of the invention

With particular reference to Figures 1 , 4, 7, 8 and 9, the numeral 1 denotes a force gauge according to this invention.

The gauge 1 is structured to provide as output the value of a force F applied to it, in particular and preferably a weight force or, more simply, a weight.

The gauge 1 comprises a mechanical conversion part A and an electronic conversion and processing part B.

In practice, as described in more detail below, the part A of the gauge 1 associates to the force F applied to the gauge 1 a movement AS whilst the part B of the gauge converts the movement AS into a measurement signal which is processed in such a way as to obtain again the movement AS the value of which is correlated to the value of the force F as a function of the characteristics of the part A.

The gauge 1 , in particular the part B of it comprises a proximity sensor, illustrated schematically and labelled 1 , of substantially known type and described only insofar as necessary for understanding this invention.

The sensor 2 comprises a first flat component 3 lying in a first plane P1 and a flat conductor plate 4, for example made of metal, for example in the form of a metal disc, lying in a second plane P2 parallel to the first plane PL

In other words, the first flat component 3 defines or identifies the first plane P1 and the conductor plate 4 defines or identifies the second plane P1. The first flat component 3, as explained in more detail below, is an electronic component which comprises a first and a second main direction of extension whilst a third dimension is negligible compared to those measured along the first and the second direction of extension.

The first flat component 3 and the conductor plate 4 face along a main axis D at a right angle to the first and to the second plane P1 , P2.

The component 3 and the plate 4 are movable relative to each other between a spaced-apart position, for example shown in Figures 3, 7 and 8, and a close-together position, shown in Figure 9, and they are movable along the main axis D.

The component 3 and the plate 4 are movable between the close-together position and the spaced-apart position in such a way that the respective planes P1 , P2 remain parallel to each other, that is, the component 3 and the plate 4 are movable between the close-together position and the spaced-apart position remaining substantially parallel to each other.

The gauge 1 , in particular the electronic conversion and processing part B of it, comprises a computerised command and control unit, schematically illustrated with a block 5, in communication with the component 3.

More specifically, the component 3 has a pair of terminals, not illustrated, and the unit 5 is in communication with both the terminals; for simplicity and as an example only a single connection of the unit 5 with the component 3 is shown.

Preferably, the component 3 is made integrated in a type PCB printed circuit 6 substantially of known type.

In a first embodiment, the sensor 2 is of the inductive type and the first component 3 is defined by a flat conductor coil of substantially known type; the coil 3 defines in practice an inductor having inductance L extending in the plane P1 parallel to the plane P2.

In an embodiment not illustrated, the gauge comprises, if the sensor 2 is of the inductive type and the first component is defined by a conductor coil, at least a second flat conductor coil lying on the first plane P1 or on a plane parallel thereto, and connected in series or in parallel to the first conductor coil, on the basis of the performance expected from the proximity sensor 2.

If the sensor 2 is of the inductive type and the first component is defined by a conductor coil the part B of the gauge 1 also comprises a capacitor C, not illustrated, connected in series or in parallel to the coil 3.

The operation of the electronic conversion and processing part B is in part of substantially known type.

Very briefly, once the coil 3 is energised, a movement of the plate 4 relative to the coil 3 causes a variation of the magnetic field linked with the plate 4 and consequently a variation of the inductance and the resistance of the coil 3.

The variation of the electrical parameters of the coil 3 determines a variation of the resonance frequency of the coil 3 as a function of the movement of the plate 4 relative to the coil 3.

A measurement of the variation of the impedance with the resonance frequency following the movement of the plate 4 makes it possible to determine the value of the movement AS, in particular if a relationship between the resonance frequency and AS is know.

A preferred proximity sensor 2 of the inductive type adopted in the gauge 1 is the LDC1000 sensor of Texas Instruments® and reference should be made to the relative manual for a more thorough understanding of the operation.

The computerised unit 5 is in practice designed to power the conductor coil 3 in such a way as to generate an electromagnetic field linked with the plate 4 and detect from the conductor coil 3 a measurement signal S1 which represents, in this embodiment, a variation of the electromagnetic field generated from the conductor coil.

This variation is determined, as already indicated, by a variation of the electrical parameters of the coil 3 caused by the movement As of the conductor plate 4 relative to the conductor coil 3.

In a second embodiment, the proximity sensor 2 is of the capacitive type and the first component 3 is defined by a capacitive sensor of substantially known type, for example in the form of a metal disc.

Schematically, the capacitive sensors are based on the principle of detecting an electrical capacitance of a capacitor.

In a preferred embodiment, a first active portion, the first component 3 in the example illustrated, constitutes the actual capacitive sensor and defines a winding of a capacitor.

The conductor plate 4, in particular connected to earth, forms a second winding of the same capacitor.

Also in this embodiment, the electronic conversion and processing part B is in part of substantially known type.

Very briefly, once the capacitive sensor is energised, a movement of the plate 4 relative to the sensor 3 determines a variation of the electrical capacitance of the capacitor formed by the sensor 3 and by the plate 4. A measurement of the variation of the electrical capacitance of the above- mentioned capacitor following the movement of the plate 4 allows the value of the movement AS to be determined.

A preferred proximity sensor 2 of the capacitive type adopted in the gauge 1 is controlled by the FDC 1004 of Texas Instruments® and reference should be made to the relative manual for a more thorough understanding of the operation.

The computerised unit 5 is in practice designed to power the sensor 3 in such a way as to generate an electric field linked with the plate 4 and detect from the sensor 3 the measurement signal S1 which in this embodiment represents a variation in the electrical capacitance. This variation is determined, as already indicated, by a variation of the electrical capacitance measured by means of the sensor 3 caused by the movement AS of the conductor plate 4 relative to the sensor 3.

In general, the unit 5 is also configured for calculating the value of the movement AS measured along the main axis D starting from the measurement signal S1 .

The gauge 1 , in particular the mechanical conversion part A of the gauge, comprises constraining means operating between the plate 4 and the first component 3 for constraining the plate 4 to the component 3 allowing their relative movement between the above-mentioned close-together and spaced-apart positions.

In particular, the constraining means are at least partly elastically deformable along the main axis D in such a way as to allow the movement of the plate 4 and of the first component 3 between the close-together and spaced-apart positions keeping the first and the second plane P1 , P2 parallel with each other, in particular when the force F is applied to the conductor plate 4 from the opposite side relative to the component 3.

More specifically, the computerised unit 5 is configured for correlating the value of the movement AS, as previously predetermined, to the value of the force F as a function of the constraining means, in particular as a function of their mechanical characteristics, such as, for example, Newton's constant K.

Looking in more detail at the constraining means, with particular reference to Figures 1 to 9, it may be noted that, preferably, they comprise a hollow element 7 for connecting the conductor plate 4 with the first flat component 3.

The hollow element 7 is dimensioned for deforming in such a way as to allow the movement of the plate 4 and the first component 3 between the close-together and spaced-apart positions keeping the first and the second plane P1 and P2 parallel, that is, between the plate 4 and the component 3. The hollow element 7 has a face or portion 8 for applying the force F that is, a face or portion 8 designed for the application of the force F.

In one embodiment, shown for example in Figures 1 to 7, the plate 4 is made in a single body with the hollow element 7.

In the schematic embodiment of Figures 8 and 9 the plate 4 itself defines the application portion 8.

The hollow element 7 is, preferably, in the form of a tube having axis coinciding with the main axis D.

The conductor plate 4 and the component 3 are respectively associated with a first end 7a and a second end 7b of the hollow element 7.

The hollow element 7 comprises a side wall 9 which is deformable according to the main axis D of the gauge 1.

The gauge illustrated in Figures 1 to 3, 8 and 9 comprises the substantially cylindrical hollow element 7 and the side wall 9 is substantially cylindrical. In one embodiment, the conductor plate 4 and the component 3 define, respectively, a first base and a second base of the hollow element 7 and the gauge 1.

Generally speaking, the constraining means or the hollow element 7 comprise a side wall 9 for joining the conductor plate 4 and the component 3. The side wall 9 has a thickness s such that, having fixed the construction material of the hollow element, the movement of the plate 4 relative to the component 3 between the close-together and spaced-apart positions occurs keeping them parallel to each other.

It should be noted that, having fixed the component 3, both in the case of the conductor coil and the capacitive sensor, in practice the optimum working distance "d" between the plate 4 and the component 3 is also established, that is, the working distance "d" is determined, between a maximum value and a minimum value, measured along the axis D, at which the sensor 2 operates correctly.

Preferred materials which can be used for making the hollow element 7 are, for example, titanium alloys, for example Ti6AINb or Ti6AI4V, stainless steels, for example 15-5PH or 316L or H13 or 1 ,2709, aluminium alloys, for example AISM2 or AISilOMg or AISi7Mg, chromium and cobalt alloys, for example CoCr ASTM F75, Inconel® HX either 625 or 718.

The dimensioning of the constraining means, in particular of the hollow element 7 and of the side wall 9, is such that the component 3 and the plate 4, in the movement between the close-together and spaced-apart positions, are always in at a distance compatible with the working distance "d".

In particular with reference to Figures 1 , 3, 5 and 7, it may be noted that the constraining means comprise a rigid arm 10 for supporting the conductor plate 4.

The arm 10 extends inside the hollow element 7, preferably along the main axis D, and has a relative end 10a integral with the hollow element 7 at the first end 7a.

A second end 10b of the arm 10 supports the plate 4 facing the flat component 3 at the working distance "d".

A deformation of the side wall 9 caused by the application of the force F determines a movement of the plate 4 towards the coil 3, in particular by means of the arm 10.

The cylindrical structure of the hollow element allows the gauge 1 to be given a high stiffness for a preferred use with high loads, that is to say, high values of the force F, for example in the order of 10 kN with element made of Ti6AINb, due to low deformations of the side wall 9.

As illustrated in Figures 4, 5, and 7 the hollow element 7 has the side wall 9 with a corrugated profile 11 in such a way as to obtain lower rigidities compared with those of the solution with cylindrical wall to obtain high deformations, compatible with the working distance "d", also with relatively low loads, for example in the order of 1 kN with the element made of Ti6AINb. In other words, the wall 9 has on a relative outer face and on a relative inner face a succession of humps 12 and depressions 3 which give them a concertina structure.

In other words, the wall 9 has a succession of depressions and humps, transversal to the main axis D, which define the undulating or corrugated profile of the wall 9.

In order to limit the lines of the electromagnetic field, the hollow element 7 is made preferably of metallic material, for example steel.

The hollow element 7 allows in practice to transfer the movement determined by the force F applied to the surface 8 to the plate 4; the plate

4 is in practice subject to indirect application of the force F.

The gauge 1 preferably comprises a metallic screen 14 positioned parallel to the flat component 3, that is, parallel to the plane P1 of the component

3, and positioned on the opposite side of the conductor plate 4 relative to the component 3.

The screen 14 is preferably associated with the element 7 and defines the above-mentioned base at the component 3.

Preferably, given the relative small and complex geometries, the element 7 of the gauge 1 is preferably made with laser prototype production from metal powders.

As mentioned, the control unit 5 is configured to correlate the value of the movement AS, obtained in a substantially known manner, to the value of the force F as a function of or on the basis of the structural parameters, such as, for example, material, geometry of the hollow element 7.

In practice, the mechanical part A of the gauge 1 makes it possible to correlate the force F applied to the gauge 1 to the movement AS and vice versa, that is, it allows the force F starting from the movement AS to be determined.

The part B of the gauge 1 allows determination of the movement AS by the electrical parameters of the component 3 and determination of the force F from the value of the movement AS and the physical and geometrical characteristics of the constraining means.

More specifically, the part B of the gauge 1 allows determination of the movement AS by the electrical parameters of the conductor coil or the capacitive sensor and determination of the force F from the value of the movement AS and the physical and geometrical characteristics of the constraining means.

In alternative embodiments not illustrated, the constraining means comprise further systems for fixing relative to the plate 4 and the component 3, so as to guarantee the relative movements described with particular reference to the hollow element 7 as well as allowing the correlation of the movements measured with the force F applied to the constraining means.

With reference to Figures 10 and 11 , it may be noted that the constraining means, that is, the system which defines the mechanical conversion part A, comprise an elastically deformable platform 15 on a lower face of which, with reference to the drawings, is fixed the conductor plate 4.

The constraining means comprise a frame 16 supporting the platform 15 and anchoring the first flat component 3 facing the conductor plate 4 at the working distance "d".

In these embodiments, the force F determines an elastic deformation of the platform 15 to which corresponds a movement of the plate 4 towards the component 3 in the manner described above.

A preferred application or embodiment of the gauge 1 is integrated in a cooking top of substantially known type.

In practice, according to one aspect of the invention, the platform 15 is a glass-ceramic platform of a cooking top of known type to which one or more conductor plates 4 are applied.

The platform 15 is suitably supported by the frame 16 which allows a deformation under the action of the weight force F. A plurality of first flat components 3 are each positioned at a corresponding plate 4 in the manner described above and connected to the computerised unit 5.

The weight of the saucepans, and of the ingredients inside them, positioned on the platform 15 is measured in the manner described.

One or more portions 8 for applying the force F, that is, in the example, for positioning the saucepans, are provided in the platform 15 on the side opposite the corresponding conductor plates 4.

In one embodiment, illustrated for example in Figure 10, the constraining means comprise, as mentioned, the platform 15, for example parallelepiped.

The platform 15 is made for example of ceramic glass and has a first dimension of 900 mm, a second dimension of 600 mm and thickness of 5 mm.

The platform 15 is preferably supported by the entire perimeter by a frame 16.

A force F of 10 Newtons applied in the centre of the platform 15 along the main axis D determines a lowering by 0.04 mm of the centre of the platform 15.

A force F of 200 Newtons applied in the centre of the platform 15 along the main axis D at right angles to the platform 15 determines a lowering of the centre by 0.8 mm.

At the centre of the platform there is the conductor plate 4, for example in the form of metal film.

Facing the conductor plate 4, along the main axis D there is the component 3, the conductor coil or the capacitive sensor, for example supported by an arm 17 or by another similar supporting system not illustrated.

The movement of the plate 4 towards the component 3 is determined by the bending of the platform 15; given the extent of the movement and the dimensions of the plate 4 relative to the platform 15, the movement AS is considered to occur along the axis D.

In an embodiment illustrated in Figure 11 the frame 16 supports the platform 15 by means of a central zone of it and the conductor plate 4 is positioned in a more perimeter zone of the platform 15.

A process for making a movement measuring device as described above, in the case of a proximity sensor of the inductive type, comprises a first step of calculating the conductor coil 3, in particular calculation of the number of turns of the coil 3.

The number of turns, in substantially known manner, is determined by the expected precision and by any geometrical constraints imposed by the use of the gauge 1.

On the basis, in particular, of the number of turns obtained, the working distance "d" is determined within which the conductor plate 4 and the coil 3 must move between the close-together and spaced-apart positions.

The constraining means are, in general, regardless of the proximity sensor adopted, dimensioned as a function of the maximum force F which can be measured in such a way that the movement AS is uniquely correlated with the corresponding force and remains inside the optimum working distance "d" for the proximity sensor used.

In other words, the dimensioning of the part A of the gauge 1 , in particular of the hollow element 7, occurs in such a way that a predetermined force applied to the surface 8, that is, directly or indirectly to the plate 4, corresponds to a predetermined movement of the plate 4 relative to the component 3.

Advantageously, the working distance "d" is set along the main axis D of the hollow element 7.

The size of the base in which the component 3 is located is in practice preferably determined by the shape and by the size of the component 3, whilst the opposite base, from which, for example, the arm 10 extends, is preferably equal to that at the component 3. The dimensioning of the hollow element 7 concerns in particular the dimensioning of the side wall 9 and more specifically the thickness "s" of the wall on the basis of the material adopted.

In the case of the solution of Figure 10 or Figure 11 , the relative positioning of plate 4 and component 3, that is to say, in particular the positioning of the arm 17 relative to the platform 15, is calculated on the basis of the deformability of the platform 15.

With reference by way of example to Figures 8 and 9, the application, in use, of the force F to the face 8 of the gauge 1 determines a deformation of the side wall 9 of the hollow element 7 which corresponds to the movement of the plate 4 towards the component 3.

In the case of the platform 15, the application of the force F determines a bending of the platform 5 with consequent moving of the plate 4 towards the component 3.

The component 3 is powered by the unit 5 and the movement of the plate 4 causes, in short, a modification of an electrical quantity correlated with the component 3, for example a modification of the electrical parameters of the conductor coil or the capacitive sensor from which the unit 5 derives the value of the movement AS.

The unit 5 re-processes the value of the movement AS calculated in this way and correlates it, for example using a series of unique correspondences tabulated and stored in the unit 5, to the value of the force F.

Advantageously, the control unit 5 comprises, in a relative memory of known type, a series of values of the movement AS each associated with a corresponding value of force F, for example determined experimentally on the basis of the mechanical properties of the constraining means.

In other words, the unit 5 stores a mathematical model which allows the movement AS to be combined with a corresponding value of the force F applied to the face 8 of the gauge 1. The preferred presence of the arm 10 means that the conductor plate 4 is relatively far from the face 8 for applying the force F so that the measurement is not influenced, for example, by the temperature of object of which weight is to be determined, as already mentioned preferred example of force F to be measured with the gauge 1.

The invention described brings important advantages.

The measurement of the force is linked to a mechanical deformation of the element 7 whilst the electronic components, in particular the component 3, keep the relative mechanical characteristics unchanged without the risk of damage.

The cost of the gauge 1 as described is relatively low as the electronic conversion and reprocessing part B is relatively simple and reliable.

The arm 10 makes the gauge 1 substantially insensitive to the temperature, thus optimising the performance.

The gauge 1 may be advantageously applied for the measurement of the forces commonly involved in the operation of machines and industrial plants.

Claims

1. A force gauge comprising at least one proximity sensor (2) comprising a first component (3) defining a first plane P1 ;

a flat conductor plate (4) defining a second plane P2,

the first flat component (3) and the conductor plate (4) facing each other along a main axis (D) and being movable relative to each other along the main axis (D) between a spaced-apart position and a close-together position, the gauge being characterised in that it comprises

constraining means (7, 8, 10) operating between the conductor plate (4) and the first flat component (3) in order to constrain the conductor plate (4) to the first flat component (3), the constraining means (7, 8, 10) being at least partly elastically deformable along the main axis (D) so as to allow the conductor plate (4) and the first flat component (3) to move between the spaced-apart and close-together positions when a force F is applied to the conductor plate (4) on the side opposite the first flat component (3), the gauge comprising a computerised control and drive unit (5) in communication with the first flat component (3) and configured to:

power the first flat component (3) in such a way as to generate an electromagnetic field linked with the conductor plate (4);

detect from the first flat component (3) at least one measurement signal representing a variation of an electrical quantity determined by a movement (AS) of the conductor plate (4) relative to the first flat component (3);

calculate from the measurement signal a value of the movement (AS) measured along the main axis (D);

correlate the value of the movement (AS) with a value of the force F as a function of the constraining means.

2. The force gauge according to claim 1 , wherein the first flat component (3) comprises at least one flat conductor coil lying in the first plane P1 , the measurement signal representing a variation of the electromagnetic field generated by the conductor coil, the electromagnetic field defining the electrical quantity.

3. The gauge according to claim 2, wherein the gauge comprises at least a second flat conductor coil lying in the first plane P1 or in a plane parallel thereto and connected in series or in parallel to the first flat component (3) defined by the conductor coil.

4. The force gauge according to any one of the preceding claims, wherein the first flat component (3) comprises at least one capacitive sensor lying in the first plane P1 , the measurement signal representing a variation of an electrical capacitance between the capacitive sensor and the conductor plate (4), the variation of an electrical capacitance being determined by the movement (AS) of the conductor plate (4) relative to the capacitive sensor, the capacitance defining the electrical quantity.

5. The gauge according to any one of the preceding claims, wherein the first plane P1 and the second plane P2 are parallel to each other, the main axis (D) being at right angles to the first and second planes P1 , P2, the constraining means being structured to allow the conductor plate (4) and the first flat component (3) to move between the spaced-apart position and close-together positions while keeping the first and second planes P1 , P2 parallel to each other, the first flat component (3) and the conductor plate (4) remaining parallel.

6. The gauge according to any one of the preceding claims, wherein the constraining means (7, 8, 10) comprise a hollow constraining element (7) by which the conductor plate (4) is constrained to the first flat component (3) and which is dimensioned to be deformed in such a way as to allow the conductor plate (4) and the first flat component (3) to move between the spaced-apart position and close-together positions while keeping the first and second planes P1 , P2 parallel to each other.

7. The gauge according to claim 6, wherein the hollow element (7) comprises the conductor plate (4), the conductor plate (4) being made as a single part with the hollow element (7) and constituting a portion thereof.

8. The gauge according to claim 6 or 7, wherein the hollow element (7) is in the form of a tube whose axis coincides with the main axis (D), the conductor plate (4) and the first flat component (3) being associated with a first end (7a) and a second end (7b) of the tube, respectively, the tube defining a side wall (9) which is deformable along the main axis (D) of the gauge.

9. The gauge according to claim 8, wherein the side wall (9) is cylindrical.

10. The gauge according to any one of claims 6 to 9, wherein the conductor plate (4) and the first flat component (3) respectively define a first base and a second base of the hollow element (7) and of the gauge parallel to each other.

11. The gauge according to claim 10, wherein the hollow element (7) comprises a side wall (9) joining the conductor plate (4) and the first flat component (3), the side wall (9) having at least one thickness "s" such that displacement between the first and the second base occurs while keeping the first and the second base parallel to each other, the conductor plate and the first flat component also being parallel to each other.

12. The gauge according to any one of claims 6 to 14, wherein the constraining means (7, 8, 10) comprise a rigid arm (10) for supporting the conductor plate (4), the rigid arm (10) extending inside the hollow element (7) along the main axis (D) and having a first end (10a) which is integral with the hollow element (7) at a first end (7a) of the hollow element and a second end (10b) which supports the conductor plate (4).

13. The gauge according to any one of the preceding claims, wherein the constraining means (7, 8, 10) comprise an application portion (8) for applying the force F.

14. The gauge according to any one of the preceding claims, wherein the first flat component (3) is integrated in a printed circuit.

15. The gauge according to any one of the preceding claims, wherein the constraining means (7, 8, 10) comprise a metallic screen (14) parallel to the first flat component (3) and located on the side of the conductor plate (4) opposite the first flat component (3).

16. The gauge according to any one of the preceding claims, wherein the constraining means (7, 8, 10) comprise a hollow constraining element (7) by which the conductor plate (4) is constrained to the first flat component (3) and which is dimensioned to be deformed in such a way as to allow the conductor plate (4) and the first flat component (3) to move between the spaced-apart position and close-together position while keeping the first and second planes P1 , P2 parallel to each other, the hollow element (7) comprising a side wall (9) which is deformable along the main axis (D) and which joins the conductor plate and the first flat component (3), the side wall (9) having at least one thickness "s" and a shape such as to allow movement of the conductor plate (4) and the first flat element (3), the side wall (9) comprising a sequence of depressions (13) and humps (12) transversal to the main axis (D) and defining an at least partly undulated profile of the side wall (9).

17. The gauge according to any one of the preceding claims, wherein the constraining means comprise a platform (15) supporting the conductor plate (4) and a frame (16) supporting the platform (15) and the first flat component (3) facing the conductor plate (4), the force F causing a deformation of the platform (15) which corresponds to the movement (AS) of the conductor plate (4) relative to the first flat component (3).

18. The gauge according to claim 17, wherein the frame (16) supports the platform (15) by a perimeter of it, the conductor plate (4) being located in a central zone of the platform (15).

19. The gauge according to claim 17, wherein the frame (16) supports the platform (15) by a central zone of it, the conductor plate (4) being located in a perimeter zone of the platform (15).

20. A cooking top comprising a platform (15) made of glass-ceramic and a frame (16) supporting the glass-ceramic platform (15) characterised in that it comprises a force gauge (1) according to any one of claims 1 to 19 wherein the constraining means comprise the glass-ceramic platform (15) and the frame (16), the first component being supported by the frame (16) and the conductor plate (4) being integral with the glass-ceramic platform (15).

21. A process for making a force gauge (1) according to any one of claims 1 to 19, the process being characterised in that it comprises:

a step of calculating the constraining means (7, 8, 10) as a function of a distance "d" between the conductor plate and the first flat component to allow the relative movement of the conductor plate (4) and the first flat component between the spaced-apart and the close-together positions, the step of calculating the constraining means (7, 8, 10) comprising a step of dimensioning the constraining means (7, 8, 10) to correlate a movement (AS) of the conductor plate (4) towards the first flat component with the force F applied to the conductor plate (4).

22. The process according to claim 21 , wherein the step of calculating the constraining means (7, 8, 10) is based on the maximum value of the force F applicable to the force gauge (1 ), the maximum value of the force F causing the conductor plate to move towards the first flat component by a predetermined amount.

23. The process according to claim 21 , wherein the step of dimensioning the constraining means to correlate a movement of the conductor plate towards the conductor coil with the force F applied to the conductor plate comprises a step of dimensioning the cylindrical side wall of the hollow element as a function of the dimensions of the first and second base.

24. The process according to any one of claims 21 to 23 comprising a step of calculating a number of turns of the conductor coil (3) as a function of the geometrical constraints determined by the positioning of the gauge in use, the;

a step of calculating the working distance "d" between the conductor coil (3) and the conductor plate (4) measured along the main axis (D) as a function of the number of turns of the conductor coil.