EP4507971A1

EP4507971A1 - Apparatus for detecting the level of a liquid product in a packaging machine

Info

Publication number: EP4507971A1
Application number: EP23719897.3A
Authority: EP
Inventors: Maurizio Bonarelli; Andrea CASAGRANDE; Lorenzo FABI; Stefano SINIGARDI; Enrico VERSARI
Original assignee: GD SpA
Current assignee: GD SpA
Priority date: 2022-04-12
Filing date: 2023-04-03
Publication date: 2025-02-19
Also published as: IT202200007211A1; WO2023199161A1

Abstract

Described herein is an apparatus (40) for detecting the level of a liquid product (202) within a tube (200) of packaging material in a packaging machine (10), which comprises a floating device (42) mobile along a main axis (I) and a detection unit (48) for detecting the position of the floating device (42) along the main axis (I). The floating device (42) comprises a hollow body (43) and a plurality of magnets (45) arranged within said hollow body (43), substantially in one and the same plane orthogonal to the main axis (I), distributed about the latter, and set apart from one another. Each magnet (45) has a magnetic north pole and a magnetic south pole aligned along a magnetic axis (M) parallel to the main axis (I).

Description

"Apparatus for detecting the level of a liquid product in a packaging machine"

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TEXT OF THE DESCRIPTION

The present invention relates to an apparatus for detecting the level of a product within a vertical tube of packaging material in a packaging machine.

In particular, the solution described herein has been devised for a packaging machine for the formation of containers filled with a liquid product and sealed, starting from a web of packaging material.

In a machine of the aforesaid type, the web of packaging material is fed along a work path parallel to the longitudinal direction of the web and, at a forming and sealing unit of the machine, is curled about a vertical axis to form a tube that is filled with the liquid product to be packaged. A duct for supplying the liquid product extends at least in its terminal part along said vertical axis and is designed to deliver the liquid product into the tube, in particular up to a pre-set level.

Provided in succession on the vertical tube thus formed and partially filled with liquid product are transverse sealing bands that define on the tube single semi-finished containers, sealed and filled, which are then separated from the tube via cutting.

For proper operation of the process referred to above it is important to keep the liquid product within a certain range around the pre-set level in the vertical tube obtained from the web of packaging material.

For this purpose, systems are used for measuring the level of the liquid product, for example comprising a floating device positioned within the tube, for instance mounted on the terminal part of the supply duct and mobile with respect thereto along the vertical axis, in particular as a function of the level of the liquid product in the tube, and an external detection unit for determining the position of the floating device along said vertical axis.

The floating device houses magnetic means capable of generating a magnetic flux that can be detected outside the tube, whilst the detection unit is configured for detecting the aforesaid magnetic flux and determining the position of the floating device along the vertical axis as a function of the magnetic flux detected. The present applicant has noted that the floating device represents a component that is relatively costly to be used on a machine, above all considering the fact that it is a consumable component and hence frequently replaced on account of the wear to which it is subject as a result both of rubbing on the supply duct and of degradation due to interaction with the liquid product in which it is partially immersed.

The present applicant has noted, in particular, that the magnetic means, in order to generate the aforesaid magnetic flux that can be properly detected outside the tube and guarantee reliability of the measuring system, have a considerable weight and/or are made of special metal alloys. These specifications contribute in a non-negligible way to the costs of the floating device and, in the second place, lead to an increase in the overall weight of the floating device itself.

The present applicant has, in fact, also noted that the weight of the magnetic means present in the floating device is such that the latter, to be able to vary its own position along the vertical axis as a function of the level of the liquid product in the tube, i.e., to be able to float in the liquid product, must have a relatively large volume.

Moreover, the floating device must be built so that the liquid product in which it is partially immersed does not come into contact with the magnetic means, altering the physical properties thereof and having an adverse effect upon the reliability of the final measurement.

As a consequence of the foregoing, i.e., of the materials used and of the structural features required for guaranteeing reliability of the system for measuring the level of the liquid product, the present applicant has found that the costs of the materials and the costs of production of the floating device described are considerable.

The present applicant has hence felt the need to modify the design of the floating device in order to reduce the corresponding costs, without, however, reducing the reliability of the system for measuring the level of the liquid product.

The present applicant has above all noted that re-sizing and discretizing the magnetic means, for example using a plurality of magnets of small size, in particular distributed about the vertical axis, i.e., about the axis of movement of the floating device, enables reduction of the overall weight of the magnetic means used and consequently the production costs, but adversely affects the performance and hence the reliability of the system for measuring the level of the liquid product.

The present applicant has, in fact, found that the magnetic flux detected by the external detection unit is variable as a function of the angular position assumed about the aforesaid vertical axis by the floating device, within which the small magnets are located. Consequently, in operation, the external detection unit detects intensities of the magnetic flux that differ according to the orientation assumed by the floating device about its vertical axis of movement.

More in particular, the present applicant has realized that the magnetic flux detected outside the tube by the external detection unit varies according to the size, orientation, and distribution of the small magnets within the floating device.

The present applicant has hence found that it is possible to orient and distribute appropriately a plurality of magnets of suitable dimensions within the floating device so as to reduce the overall weight of the latter and contain the production costs thereof, without reducing the reliability and performance of the system for measuring the level of the liquid product and in some cases even improving them.

In the present description, as likewise in the claims associated thereto, some terms and expressions are to be considered, except where otherwise explicitly indicated, as having the meaning given in the ensuing definitions.

The term “parallel” is meant to refer to a substantial parallelism between two elements, comprising both the ideal case, where these elements are arranged with respect to one another so as to form a zero angle, and more frequent cases, where the two elements are arranged with respect to one another so as to form a nonzero but in any case negligible angle or an angle that is not important for the purposes of operation of the present invention, for example 10°.

By the term “constant” used herein in relation to the magnetic flux generated by the magnets carried by the floating device is meant an invariability of the magnetic flux or in any case a variability thereof within a predefined tolerance range. A product is referred to as being “liquid” when it is made up entirely or at least for 50% of a fluid substance having a well-defined volume that is practically invariable as the pressure varies, but without a shape of its own. For the purposes of the present disclosure, considered as liquid products are also foodstuff products, such as beverages added with carbon dioxide, fruit and/or vegetable juices, fruit and/or vegetable shakes, fruit and/or vegetable smoothies, soups containing at least 50% water, and cosmetic products for personal treatment, such as lotions, perfumes, shampoos, shower gels, etc.

According to a first aspect, the present invention regards an apparatus for detecting the level of a liquid product within a tube, preferably vertical, preferably of packaging material, preferably in a packaging machine.

Preferably, the apparatus comprises a floating device, which is preferably mobile along a main axis. Preferably, the apparatus comprises a detection unit, in particular for determining the position of said floating device along said main axis.

Preferably, said floating device comprises a hollow body. Preferably, said floating device comprises a plurality of magnets, preferably arranged within said hollow body. Preferably, said magnets are substantially in one and the same plane orthogonal to said main axis, preferably distributed about said main axis, preferably set apart from one another. Preferably, each magnet of said plurality has a magnetic north pole and a magnetic south pole, respectively, which are aligned along a respective magnetic axis, preferably parallel to said main axis.

Thanks to the aforesaid characteristics, the floating device is able to subject the external detection unit to a magnetic flux of constant intensity, whatever the orientation of the floating device about the main axis, so that the detections of the intensity of the magnetic flux made by the detection unit will be affected only by the position of the floating device along the main axis and not also by its angular position about the axis itself.

According to a second aspect, the present invention concerns a packaging machine for the production of containers filled with a liquid product and sealed, starting from a web of packaging material, comprising a detection apparatus according to the first aspect.

Thanks to the aforesaid characteristics, the packaging machine is able to operate always in an optimal condition in which the liquid product that fills the tube of packaging material is at a pre-set level.

According to a third aspect, the present invention concerns a method for detecting the level of a liquid product along a main axis within a tube, preferably vertical, preferably of packaging material, preferably in a packaging machine.

Preferably, the method comprises providing a floating device, preferably comprising a hollow body, preferably a plurality of magnets, the latter preferably being arranged within said hollow body.

Preferably, the method comprises providing said floating device within said tube, in particular so that said magnets will be arranged substantially in one and the same plane orthogonal to said main axis, preferably distributed about said main axis and preferably set apart from one another. Preferably, each magnet of said plurality has a magnetic north pole and a magnetic south pole, which are aligned along a respective magnetic axis, preferably parallel to said main axis. Preferably, said floating device is mobile along said main axis, in particular as a result of a variation of level of said liquid product in said tube of packaging material.

Preferably, the method comprises generating, in particular via said magnets of said floating device, a magnetic flux substantially constant along a circular trajectory about said main axis.

Preferably, the method comprises detecting, in particular via a detection unit, the position of said floating device along said main axis.

Preferably, the method comprises processing said detected magnetic flux, in particular for determining a position of said floating device along said main axis.

According to one or more of the aforesaid aspects, the present invention may comprise one or more of the characteristics described in what follows. In one or more embodiments, said magnets are arranged at one and the same distance from said main axis.

In one or more embodiments, said magnets set apart from one another are set at equal angular distances apart about said main axis.

In one or more embodiments, said hollow body comprises two ends, in particular opposite to one another along said main axis. Preferably, said orthogonal plane is in a central position between said two ends of said hollow body along said main axis. In other words, preferably said orthogonal plane is at an equal distance from said two ends along said main axis.

Thanks to the aforesaid characteristics, the floating device may be mounted on the duct for supplying the liquid product according to either of the two possible orientations along the main axis, without proper operation of the measuring system being jeopardized. There are thus eliminated possible errors of installation of the floating device owing to the orientation of the latter along the main axis, which would lead to altered operation of the machine, with consequent production of defective containers that have to be rejected and corresponding waste of product and materials.

In one or more embodiments, said magnets are permanent magnets.

In one or more embodiments, said magnets have each the shape of a cylinder, with the axis of the cylinder preferably parallel to said main axis.

In one or more embodiments, said cylindrical magnets have a constant radius. Preferably, the geometrical axis of each cylinder is set apart from the geometrical axis of the next cylinder by a distance comprised between 2.2 times and 5 times said radius.

Thanks to the aforesaid characteristics, it is possible to reduce to the minimum the amount of magnetic material used for obtaining as whole a substantially uniform magnetic flux along a circular trajectory about the main axis.

In one or more embodiments, said hollow body is cylindrical in shape. Preferably, said cylindrical hollow body has an outer cylindrical wall. Preferably, said cylindrical hollow body has an inner cylindrical wall. Preferably, said cylindrical hollow body has two end walls that define a tubular cylindrical cavity.

In one or more embodiments, said cylindrical hollow body is constituted by two coaxial half-portions. In one or more embodiments, said two coaxial half-portions are connected together via fast-coupling means. Alternatively, said two coaxial half-portions are welded together.

In one or more embodiments, said floating device comprises a housing ring, preferably set within said hollow body, preferably provided with seats, in particular housed within which are said magnets.

In one or more embodiments, said housing ring is set at an equal distance from said two end walls of said cylindrical hollow body.

Thanks to the aforesaid characteristics, the floating device has a structure that is simple, inexpensive, and easy to assemble.

In one or more embodiments, said detection unit is a Hall-effect sensor.

In one or more embodiments, said machine comprises a duct for supplying the liquid product, which preferably extends along said main axis at least in its terminal part and is preferably configured to deliver said liquid product into said tube. Preferably, said floating device is mounted on said terminal part of said duct, in particular slidably mobile with respect thereto along said main axis.

In one or more embodiments, said machine comprises a forming and sealing unit. Preferably, said forming and sealing unit is designed to curl the web about said main axis to obtain a tube. Preferably, said forming and sealing unit is designed to seal along said main axis the web curled to form a tube. Preferably, said forming and sealing unit is designed to fill the tube with a liquid product. Preferably, said forming and sealing unit is designed to provide on the tube, in succession, sealing bands transverse to the main axis that define on the tube single semi-finished containers, sealed and filled with the liquid product.

In one or more embodiments, said orthogonal plane is in a central position between two ends of said hollow body along said main axis, preferably at an equal distance from said two ends of said hollow body along said main axis. Preferably, providing said floating device within said tube includes positioning said hollow body so that said two ends will be located along said main axis, preferably irrespective of the orientation of said two ends along said axis.

Thanks to the aforesaid characteristics, the floating device may be mounted on the duct for supplying the liquid product according to either of the two possible orientations along the main axis.

It is pointed out that some steps of the method described above may be independent of the order of execution referred to, except where there is expressly indicated as necessary a sequentiality or simultaneity between two or more steps. Moreover, some steps may be optional. Moreover, some steps may be carried out in a repetitive way, or else may be carried out in series or in parallel with other steps of the method.

Further characteristics and advantages of the present invention will emerge clearly from the ensuing description with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:

- Figure 1 is a schematic illustration of an example of the apparatus described herein;

- Figure 2 is a partially sectioned perspective view of the floating device used in the apparatus described herein;

- Figure 3 is a cross-sectional view of the floating device of Figure 2, according to the plane III-III of Figure 2;

- Figure 4 is a cross-sectional view of the floating device of Figure 2, according to the plane IV-IV of Figure 2;

- Figure 5 is a schematic illustration of an example of packaging machine comprising the apparatus described herein.

In the ensuing description, various specific details are illustrated aimed at enabling an in-depth understanding of the embodiments. The embodiments may be provided without one or more of the specific details, or with other methods, components, or materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that various aspects of the embodiment will not be obscured.

The references provided herein are used merely for convenience and hence do not define the sphere of protection or the scope of the embodiments.

With reference to Figure 5, illustrated therein is a packaging machine 10 for forming containers filled with a liquid product 202 and sealed starting from a web 100 of packaging material.

In the packaging machine 10, the web 100, preferably wound off a reel 12, is fed along a work path K. The web 100 can pass through a series of stations for treating the web itself along the work path K (for example, for application of a heat-sealable band along a longitudinal edge of the web, sterilization of the inner side of the web, application on the web of a closing device or element, etc.).

The packaging machine 10 comprises a forming and sealing unit 15, where the work path K extends along a main axis I, in particular vertical, of the forming and sealing unit 15, and the web 100 of packaging material is curled about said main axis so as to form a tube 200 that is closed longitudinally via a longitudinal sealing band 204, via which the opposite longitudinal edges 100A, 100B of the web 100 are fixed together.

The packaging machine 10 further comprises a duct 20 for supply of the liquid product 202, which has a terminal part 22 that extends along the main axis I until it is inserted into the tube 200.

The duct 20 supplies the liquid product 202 into the tube 200 so as to fill it and keep the level of the liquid product 202 around a predefined mean value during operation of the machine.

In the forming and sealing unit 15, on the bottom region of the tube 200 sealing bands 208 are provided in succession, transverse to the main axis I, which define on the bottom region of the tube 200, one at a time, single semi-finished containers 300, sealed and filled with the liquid product 202.

Via cutting, each semi-finished container 300 is separated from the tube 200.

The semi-finished containers 300 may possibly be subjected to further folding operations to impart thereon a given final configuration.

With reference now to Figure 1, this is a schematic cross-sectional view of the forming and sealing unit 15 at the top region of the tube 200 formed within the unit itself.

According to the solution described herein, the packaging machine 10 comprises an apparatus 40 for detecting the level of the liquid product 202 within the vertical tube 200, comprising a floating device 42 mobile along the main axis I and a detection unit 48 for determining the position of the floating device 42 along the main axis I.

The floating device 42 comprises a hollow body 43, which is mounted on the terminal part 22 of the duct 20 and is slidably mobile with respect thereto along the main axis I, with the possibility of sliding freely along the latter.

In the embodiment illustrated, the hollow body 43 comprises a through central opening 44, of a diameter greater than the external diameter of the terminal part 22 of the duct 20, which is engaged by the terminal part 22 itself

In one or more preferred embodiments, like the one illustrated, the hollow body 43 has an outer shape with circular symmetry, preferably substantially cylindrical. Further possible shapes may, for example, be toroidal, spherical, frustoconical, etc.

The floating device 42 further comprises a plurality of magnets 45 arranged within said hollow body 43, substantially in one and the same plane orthogonal to said main axis I, distributed about the main axis I.

In the embodiment illustrated, the magnets 45 are arranged in series, preferably equidistant, along a circular trajectory about the main axis I.

According to an important characteristic of the solution described herein, the magnets 45 are oriented so as to have their respective magnetic north pole and their respective magnetic south pole aligned along a respective magnetic axis M parallel to the main axis I. In particular, the magnetic north poles of all the magnets 45 face in one and the same direction (for example, upwards), and the magnetic south poles of all the magnets 45 face in the opposite direction (for example, downwards).

The above arrangement of the magnets enables generation of a substantially constant magnetic flux along a generic circular trajectory about the main axis I.

Thanks to the aforesaid characteristic, the floating device 42 is able to subject the external detection unit 48 to a magnetic flux of constant intensity, whatever the orientation of the floating device 42 about the main axis I, so that the detections of the intensity of the magnetic flux made by the detection unit 48 will be affected only by the position of the floating device along the main axis I and not also by its angular position about the axis itself.

In the embodiment illustrated, each magnet 45 has the shape of a cylinder, with the geometrical axis of the cylinder parallel to the main axis I.

Preferably, the magnets 45 have identical dimensions. In other words, in the case of cylindrical magnets, these magnets have a constant radius R. The number of magnets 45 evidently depends upon the requirements and the needs of the specific applications. In general, the number of magnets is selected so that the overall magnetic flux determined by the ensemble of the magnets is substantially constant along a generic circular trajectory about the main axis I.

In this connection, the present applicant has found that it is possible to meet the aforesaid condition of uniformity of the magnetic flux when the magnets have the shape of a cylinder, establishing that the geometrical axis of each cylinder be set apart from the geometrical axis of the next cylinder by a distance comprised between 2.2 times and 5 times the aforesaid radius R, in particular 3.8 times this radius R.

In this way, there are appropriately designed both the weight of the magnets 45, in order to reduce to a minimum the overall weight of the floating device 42 and consequently contain the production costs thereof, and the orientation and distribution of the magnets 45 themselves within the floating device 42 so that the overall magnetic flux will be substantially constant along a generic circular trajectory about the main axis I, in order not to degrade the reliability and performance of the apparatus 40.

Preferably, the magnets 45 are permanent magnets.

In one or more preferred embodiments, like the one illustrated, the floating device 42 comprises a housing ring 46, which is set within the hollow body 43 and is provided with a plurality of seats 46A, each for housing a respective magnet.

The hollow body 43 of cylindrical shape comprises an outer cylindrical wall 43 A, an inner cylindrical wall 43B, and two ends opposite to one another along the main axis I, in particular end walls 43 C, 43C’. The outer cylindrical wall 43 A, the inner cylindrical wall 43B, and the two end walls 43C, 43C’ define a tubular cylindrical cavity 43D. The housing ring 46 is set at an equal distance from the two end walls 43 C, 43 C’ of the cylindrical hollow body 43 so that the tubular cylindrical cavity 43D is divided into two by the housing ring 46.

In one or more preferred embodiments, like the one illustrated, the cylindrical hollow body 43 is constituted by two coaxial half-portions 431, 4311, connected together via fast-coupling means or else welded together. Set between the two coaxial half-portions 431, 4311 of the cylindrical hollow body 43 is the housing ring 46.

The detection unit 48 is, for example, a Hall-effect sensor.

It is to be noted that the arrangement of the magnets 45 in a central plane of the hollow body 43 with respect to the extension of the latter along the main axis I enables installation of the floating device 42 on the terminal part 22 of the duct 20 according to either of the two possible orientations along the main axis I (i.e., with a first end wall 43C set at the top and a second end wall 43 C’ set at the bottom, or vice versa), without this altering operation of the apparatus 40. In fact, the magnetic flux generated by the magnets develops along the main axis I in a way symmetrical with respect to the aforesaid central plane of the hollow body 43 and hence does not change configuration within the apparatus 40, in particular, in a position corresponding to the detection unit 48, whether the orientation of the floating device 42 along the main axis I is in one direction or in the opposite direction.

When the packaging machine 10 is operating, the web 100 of packaging material is fed along the work path K towards the forming and sealing unit 15. Here the web 100 is curled about the main axis I to obtain the tube 200, where the two opposite longitudinal edges 100 A of the tube 200 are set on top of one another and sealed along the aforesaid main axis I. On the tube 200 the transverse sealing bands 208 are provided in succession so as to obtain that the sealed bottom ends of the tube 200 follow one another in succession. The tube 200 may then be filled with the liquid product 202 to be packaged.

The floating device 42 is prearranged within the tube 200 as illustrated above and, by virtue of its specific weight, moves along the main axis I as a result of the variations of level of liquid product 202 in the tube 200.

The magnets 45 of the floating device 42 generate the constant magnetic flux about the main axis I that is detected by the detection unit 48. The magnetic flux detected may then be processed to determine the position of the floating device 42 along the main axis I, which is strictly correlated to the level of liquid product 202 along the main axis I itself.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary, even significantly, with respect to what has been illustrated herein purely by way of non-limiting example, without thereby departing from the scope of the invention, as defined in the annexed claims.

Claims

1. An apparatus (40) for detecting the level of a liquid product (202) within a vertical tube (200) of packaging material in a packaging machine (10), said apparatus (40) comprising a floating device (42) mobile along a main axis (I) and a detection unit (48) for determining the position of said floating device (42) along said main axis (I), wherein said floating device (42) comprises a hollow body (43) and a plurality of magnets (45) arranged within said hollow body (43), substantially in one and the same plane orthogonal to said main axis (I), distributed about said main axis (I), and set apart from one another, each magnet (45) of said plurality having a respective magnetic north pole and a respective magnetic south pole aligned along a respective magnetic axis (M) parallel to said main axis (I).

2. The apparatus according to claim 1, wherein said magnets (45) are arranged substantially at one and the same distance from said main axis (I).

3. The apparatus according to claim 1 or claim 2, wherein said magnets (45) set apart from one another are set at equal angular distances apart about said main axis (I).

4. The apparatus according to any one of the preceding claims, wherein said hollow body (43) comprises two ends (43C, 43C’) opposite to one another along said main axis (I), said orthogonal plane being at an equal distance from said two ends (43 C, 43 C’) along said main axis (I).

5. The apparatus according to any one of the preceding claims, wherein said magnets (45) are permanent magnets.

6. The apparatus according to any one of the preceding claims, wherein said magnets (45) are each cylindrical in shape, with the geometrical axis of said cylinder parallel to said main axis (I).

7. The apparatus according to claim 6, wherein said magnets (45) having the shape of a cylinder have a constant radius (R), the geometrical axis of each cylinder being set apart from the geometrical axis of the next cylinder by a distance comprised between 2.2 times and 5 times said radius (R).

8. The apparatus according to any one of the preceding claims, wherein said hollow body (43) is cylindrical in shape.

9. The apparatus according to claim 8, wherein said cylindrical hollow body (43) has an outer cylindrical wall (43A), an inner cylindrical wall (43 B), and two end walls (43 C, 43 C’) that define a tubular cylindrical cavity (43 D).

10. The apparatus according to claim 8 or claim 9, wherein said cylindrical hollow body (43) is constituted by two coaxial half-portions (431, 4311).

11. The apparatus according to claim 10, wherein said two coaxial half-portions (431, 4311) are connected together via fast-coupling means, or else welded together.

12. The apparatus according to any one of the preceding claims, wherein said floating device (42) comprises a housing ring (46) set within said hollow body (43) and provided with seats (46A) housed within which are said magnets (45).

13. The apparatus according to claim 12, when depending upon any one of claims 9 to 11, wherein said housing ring (46) is set at an equal distance from said two end walls (43 C, 43 C’) of said cylindrical hollow body (43).

14. The apparatus according to any one of the preceding claims, wherein said detection unit (48) is a Hall-effect sensor.

15. A packaging machine (10) for making containers filled with a liquid product (202) and sealed, starting from a web (100) of packaging material, comprising a detection apparatus (40) according to any one of the preceding claims.

16. The machine according to claim 15, comprising a duct (20) for supplying the liquid product (202), which extends along said main axis at least in its terminal part (22) and is configured to deliver said liquid product (202) into said tube (200), wherein said floating device (42) is mounted on said terminal part (22) of said duct (20) and is slidably mobile with respect thereto along said main axis (I).

17. A method for detecting the level of a liquid product (202) along a main axis (I) within a vertical tube (200) of packaging material in a packaging machine (10), comprising:

- providing a floating device (42) comprising a hollow body (43) and a plurality of magnets (45) arranged within said hollow body (43);

- providing said floating device (42) within said tube (200) so that said magnets (45) will be arranged substantially in one and the same plane orthogonal to said main axis (I), distributed about said main axis (I), and set apart from one another, each magnet (45) of said plurality having a respective magnetic north pole and a respective magnetic south pole aligned along a respective magnetic axis (M) parallel to said main axis (I), said floating device (42) being mobile along said main axis (I) as a result of a variation of level of said liquid product (202) in said tube (200) of packaging material;

- via said magnets (45) of said floating device (42) generating a magnetic flux substantially constant along a circular trajectory about said main axis (I);

- via a detection unit (48), detecting said magnetic flux of said floating device (42); and

- processing said detected magnetic flux to determine a position of said floating device (42) along said main axis (I).

18. The method according to claim 17, wherein said orthogonal plane is set at an equal distance from two ends (43C, 43C’) of said hollow body (43) along said main axis (I), and wherein providing said floating device (42) within said tube (200) includes positioning said hollow body (43) so that said two ends (43 C, 43 C’) will be located along said main axis (I) irrespective of the orientation of said two ends (43 C, 43 C’) along said axis (I).