WO2015033308A1

WO2015033308A1 - A machine for forming filter-bags for infusion products with knots

Info

Publication number: WO2015033308A1
Application number: PCT/IB2014/064293
Authority: WO
Inventors: Roberto Conti
Original assignee: I.M.A. Industria Macchine Automatiche S.P.A.
Priority date: 2013-09-09
Filing date: 2014-09-05
Publication date: 2015-03-12
Also published as: ITBO20130478A1; EP3044099B1; EP3044099A1

Abstract

Described is a machine (100) for forming filter-bags (1) for infusion products, comprising a station (15) for forming and joining a first portion of string (16) to a tag (17), and for positioning and joining a second portion of the string (16) to top edges (12) of a length (10) of filter material; the forming and joining station (15) comprising a unit (22) provided with two separate needles (23, 24); movement means (27) configured to move the needles (23, 24) to pierce the tag (17) in at least two points and, respectively, the top edges (12) and a fold (14) of the length (10) of filter material; a carousel (28) at least for moving and positioning at least the second portion of string (16) from a first joining zone (18) to a second joining zone (21 ); a first unit (29) having first gripping means (30) configured for forming, in phase coordination with the first needle (23), at least a first knot (19) with a portion of a first auxiliary string (25) and joining the tag (17) to the first portion of string (16); a second unit (31) having second gripping means (32) configured for forming, in phase coordination with the second needle (24), a second knot (20) with a portion of a second auxiliary string (26) for joining the length (10) of filter material to the second portion of string (16).

Description

DESCRIPTION

A MACHINE FOR FORMING FILTER-BAGS FOR INFUSION PRODUCTS WITH KNOTS Technical field

This invention relates to a machine for forming filter-bags for infusion products, in particular tea, coffee, camomile, etc.

Attention is focused in this specification on a machine for forming filter- bags provided with string associated, at a first end, to the bag itself and, at a second end, to a tag for gripping and manipulating the filter-bag.

Background art

More specifically, but without limiting the invention, the machine according to this invention forms bags of the two lobe type (that is to say, with two chambers placed side by side for containing the infusion product) equipped with the string and the tag.

The first end of the string is associated with the filter-bag at the top ends of the two lobes of the filter-bag.

The top ends of the two lobes of the filter-bag are folded together to form a fold for closing the lobes, the fold being held by suitable gripping elements which, at the same time, also fix the first end of the string.

The tag, in the shape of an inverted "V shape, is inserted across the top end of the filter-bag formed. The string is collected beneath the tag, between the bag and the tag.

Currently, one of the prior art machines for forming this type of filter-bag comprises a line for forming the filter-bag along which there are a series of stations for forming the filter-bag:

- a station for unwinding a continuous strip of filter material, for example filter paper, along the formation line;

- a station for dosing infusion product on the strip of filter paper; - a station for folding the strip to form a continuous tube;

- a station for longitudinally sealing the continuous tube to form chambers or lobes in continuous succession;

- a station for cutting the strip to form lengths of filter paper with individual filter-bags (in this case with two lobes joined together on a bottom);

- a station for folding and erecting the bag in such a way as to move into mutual contact the free top open edges of the two lobes;

- a station for folding the free top edges to form at least one fold for closing the edges;

- a first station for joining, with a first gripping element, a string to a tag, both coming from corresponding feed units (reels);

- a station for transporting a predetermined quantity of string with tag to

- a second station for joining the string to the filter-bag with a second gripping element and closing the end of the filter-bag.

In the proximity of the latter station the string is also collected close to the filter-bag and the tag inserted on the top of the filter-bag.

The first and second joining station, which are particularly relevant to this specification, each consist of a punch movable in both directions along a horizontal plane to move towards and away from, respectively, the tag with string and the top of the filter-bag with string.

Each punch has a head shaped to house a portion of metal wire, or staple, suitably cut from a corresponding continuous feed wire.

The metal staple is formed in the shape of a "U" by the head of the punch in such a way as to allow the penetration of the two ends of the staple on the tag and, respectively, on the top end of the filter-bag.

The two metal staples are deformed after their penetration into the tag and filter-bag by the combined effect of the pushing of the punches and the presence of corresponding contact elements located on the side opposite the operating zone of the punches: in this way, the tag is anchored to the wire and the wire is anchored to the filter-bag.

It should be noted that the two punches operate in the proximity of the conveyor station consisting of a carousel, rotating about a vertical axis, and configured for carrying wire and tags from a joining point where the wire is joined to the tag at a zone where the wire is joined to top end of the filter-bag.

In this latter zone there is also the collection of the wire and the subsequent insertion of the tag across of the top end of the filter-bag.

The closing of these types of filter-bags with metal staples has always been used for filter-bags made from natural fibres which are not reclosable with other prior art systems (for example heat sealing).

However, the metal staple has some drawbacks, due in particular to a lower quality of the filter-bag, which have, in effect, had an adverse affect on its widespread commercial use. In other words, the metal points are considered to be potentially harmful from an environmental point of view and potentially pollutant during infusion of the filter-bag in water.

Replacement of the metal staples in the filter-bags with knots formed with string made of natural fibres, for example cotton, is also known.

The prior art machines are inadequate for making these knots.

Disclosure of the invention

The aim of this invention is to provide a machine for forming filter-bags for infusion products (in particular tea, coffee, camomile) suitable for the current methods of forming the filter-bag required, whilst maintaining a high level of reliability and productivity which is typical of the prior art machines.

These aims are fully achieved by the machine for forming filter-bags for infusion products according to this invention as characterised in the appended claims.

More specifically, the machine for forming filter-bags for infusion products comprises a station for unwinding a continuous strip of filter material; a station for dosing infusion product on the strip of filter material; a station for folding the strip of filter material to form a continuous tube; a station for longitudinal joining of the tube to form closed chambers or lobes, containing individual doses of product, in continuous succession; a station for cutting the strip to form lengths of filter paper with two lobes; a station for rotating the length in such a way as to move into mutual contact top edges of the two lobes; a station for folding the top edges of the length to form at least one fold for closing the free edges; a station for forming and joining a first portion of the string to a tag, in a first zone of the station and with a first gripping element, and for positioning and joining a second portion of the string to the top edges of the length of filter material, with a second gripping element, with simultaneously top closing of the length of filter paper itself in a second zone of the station different from the first zone.

According to the invention, the forming and joining station comprises a unit provided with two separate piercing elements or needles, each positioned close to one of the first and second joining zones of the station and each having a first and a second continuous auxiliary string.

Also according to the invention, the machine 100 comprises means for moving the needles along a horizontal plane, in both directions, and at least along a direction inclined with respect to the horizontal plane to pierce in at least two points the tag and, respectively, the top edges and the closing fold of the length of filter material and insert the first or the second auxiliary string.

Again according to the invention, the forming and joining station has a carousel for moving and positioning at least the second portion of string from the first zone for joining the first portion of string with the tag to the second joining zone.

Also according to the invention, the forming and joining station has a first unit for manipulating the first auxiliary string having first means for gripping the first auxiliary string, positioned in proximity to the first joining zone and on the side opposite the tag relative to the corresponding first needle. The first gripping means are configured to form, in phase coordination with the movement of the first needle, at least one first knot for joining between the tag and the first portion of string with a portion of the first auxiliary string. Also according to the invention, the forming and joining station has a second unit for manipulating the second auxiliary string having second means for gripping the second auxiliary string, positioned in proximity to the second joining zone and on the side opposite the top edges and the closure fold of the length of filter paper relative to the corresponding second needle. These second gripping means are configured to form, in phase coordination with the movement of the second needle, a second knot for joining between the length of filter paper and the second portion of string with a portion of the second auxiliary string.

The station structured in this way allows a simultaneous formation of the first and the second knot, making this operation extremely quick and secure.

The second joining zone is engaged by the folded top edges and by the fold of the length of filter paper arranged on a side and supported by a gripper forming part of the carousel rotating about a horizontal axis and defining a part of the folding station.

The positioning of the length of filter paper on a side allows the second unit to be positioned on one side and the second needle on the other at the top edges of the length and to form the second knot precisely and securely on the same length.

The first and second joining zones (defined by two needles and by two units) are located on opposite sides of the positioning carousel, that is, at diametrically opposite points of the carousel, to correctly unwind the string necessary for the length and allow the movement of the string with the tag, already joined to each other, along a semi-arc defined by the movement of the carousel.

Preferably, the first gripping means of the first unit comprise a first pair of crochet hooks placed side by side along a vertical plane to be operative at different heights corresponding to the passage of the first needle in such a way as to intercept the first auxiliary string connected to the first needle and to retain it to form a loop on the side of them. The pair of crochet hooks is connected to corresponding movement means synchronised and in phase with the means for moving the first needle for a correct gripping coordination of the first string during the entrance and/or exit of the first needle.

The second gripping means of the second unit comprise a second pair of crochet hooks placed side by side along a vertical plane to be also operative at different heights corresponding to the passage of the second needle in such a way as to intercept the second auxiliary string connected to the second needle and to retain it to form a loop on the side of them. The pair of crochet hooks is connected to corresponding movement means synchronised and in phase with the means for moving the second needle for a correct gripping coordination of the second string during the entrance and/or exit of the second needle.

The structure of the two gripping units allows a fast and precise formation of the loops designed to generate the joining knot and also their positioning on a vertical plane considerably reduces the dimensions of the unit.

Preferably, the means for moving the first and the second needle are connected to a single control shaft and configured to move the needles in a synchronised way and in phase coordination.

The presence of a single control shaft allows the reduction of the dimensions of the unit and a phase synchronization in the forming of the first and second knot.

In effect, the piercing unit comprises the movement means subdivided in a first group of cam means connected to the single control shaft to enable the synchronized movement of the needles, along the horizontal plane, and a second group of cam means connected again to the single control shaft to obtain the movement along the inclined plane, in both directions, of both the needles, in such a way as to obtain a double piercing by each needle in different points, that is, at different heights with respect to the horizontal plane on which the needles move.

The first needle also comprises a head for pushing a portion of the tag positioned in the first joining zone. The pushing head defines an element for retaining the continuous string inside the folded tag and for performing contact functions during the piercing movement of the first needle. Moreover, the pushing head is configured for forming, in cooperation with a rear abutting element of the joining zone, a central fold on the tag for defining two wings: this folded configuration facilitates the piercing of the first needle along both the wings of the tag so defined.

The first and second unit comprise a corresponding first and second cutting unit operatively positionable in proximity of the corresponding first and second joining zone and configured to cut the relative portion of the first and second auxiliary string, wound and knotted, from the remaining first and second continuous auxiliary string arranged on the first and second needle.

Each unit is therefore configured to cut the string in a zone very close to the corresponding knot generated in such a way as to reduce to a minimum the quantity of string protruding from the knot, thus avoiding waste of material and maintaining a good appearance of the knot on the formed filter-bag.

Each first and second unit is also provided with corresponding suction means, each operatively positionable in the proximity of the relative first and second needle to retain the corresponding first and second auxiliary string inside a through seat made on each of the needles.

The suction units allow the auxiliary string to be kept on the needles after cutting of the corresponding auxiliary string without separating the string from the needle during the backward movement of the needle.

Preferably, the first unit comprises a first shaft for supporting an operating head comprising the first gripping means and the first cutting unit. The first shaft is positioned vertically, that is, parallel to the vertical axis of rotation of the carousel for moving and positioning the continuous string and the tag.

Preferably, the second unit comprises a second shaft for supporting an operating head comprising the second gripping means and the second cutting unit. The second shaft extends vertically, that is, transversely to the vertical axis of rotation of the carousel for moving and positioning the continuous string and the tag.

Preferably, the first unit has the first shaft connected by a kinematic mechanism with the first gripping means for allowing a transmission of motion on the first gripping means to define the synchronised movement with the first needle.

In light of this, the first shaft is connected in two relative different zones along its longitudinal axis with first and second cam means.

The first cam means control the movement, in phase, of the first pair of crochet hooks, that is, their rotation about a corresponding horizontal axis, for retaining and releasing the first auxiliary string, in such a way as to intercept the same first auxiliary string during the piercing of the first needle to form a plurality of loops.

The second cam means control the movement in height in both directions, that is, along the vertical axis, of the entire operating head so as to move the first pair of crochet hooks and the first cutting unit away from/towards the first joining zone.

Preferably, the first unit has an auxiliary shaft, parallel to the first shaft, and associated at its bottom end with the first cutting unit positioned on the operating head.

The auxiliary shaft is connected to third cam means for moving the first cutting unit, in phase with the first needle and the pair of crochet hooks, for separating the knotted portion of the first auxiliary string from the rest of the first auxiliary string.

The second unit has means for rotating it about a horizontal axis in such a way as to move the second unit towards/away from the second joining zone in phase synchronisation with the movement of the second needle and with that of the carousel.

The second unit has the second shaft connected by a kinematic mechanism with its operating head and with the second pair of crochet hooks to allow a transmission of motion on the same operating head and on the second pair of crochet hooks.

In light of this, the second shaft is connected in three relative different zones along its longitudinal axis with fourth, fifth and sixth cam means. The fourth cam means control the movement in height in both directions, that is, along a vertical plane, of the operating head to actuate, with the second cutting units, the separation of the knotted portion of the second auxiliary string from the rest of the second auxiliary string and, simultaneously, movement of the second gripping means away from/towards the second joining zone.

The fifth cam means control the movement, in phase, of the second pair of crochet hooks, that is, their rotation about a corresponding horizontal axis, for retaining and releasing the second auxiliary string, during the piercing of the second needle so as to form a plurality of loops.

The sixth cam control the rotation of the operating head about a horizontal axis for moving the operating head towards/away from the second joining zone, in phase synchronisation with the movement of the second needle. This structural combination of the two units is extremely rational and has reduced overall dimensions, but it allows the series of basic movements of its components to obtain a correct knotting and separation of the auxiliary strings and the moving of the operating head towards or away from the joining zones.

The moving away of each head is essential for freeing the operating zones for passage of the string and tag on one side and the positioning and releasing of the length of filter paper with relative string and tag on the other.

This invention also provides a method for forming a filter-bag for infusion products comprising the steps of:

- preparing a continuous strip of filter paper;

- depositing a succession of doses of infusion product on the continuous strip;

- folding longitudinal sides of the continuous strip on to each other to form a continuous tube within which the doses of infusion product are arranged;

- closing longitudinally the tubular strip;

- separating pieces of filter paper, each comprising at least one pair of lobes, from the continuous tubular strip;

- folding the pair of lobes towards each other in such a way as to move into mutual contact the corresponding upper, or top, free edges;

- folding the top edges of the pair of lobes on to each other to form a closing fold in contact with a front surface of one of the two lobes;

- providing a gripping tag provided with a central fold to configure two wings;

- providing a continuous string with a first portion positioned along the central fold of the tag and a second portion, spaced from the first portion, positioned alongside the top edges of the lobes;

According to the invention, the method also comprises the following steps: - providing a first, continuous, auxiliary string;

- providing a second, continuous, auxiliary string;

- making a first knot with a portion of the first auxiliary string to block the first portion of continuous string to the tag by piercing the tag in at least two points, in a first joining zone of a forming and joining station;

- making a second knot with a portion of the second auxiliary string to block the second portion of continuous string to the top free edges and to the fold of the lobes by piercing the top free edges and the fold in at least two points and to firmly close the filter-bag so formed in a second joining zone of the forming and joining station, different from the first joining zone; - moving and positioning at least the second portion of string from the first joining zone of the first portion of string with the tag to the second joining zone.

Brief description of the drawings

These and other features of the invention will become more apparent from the following detailed description of a preferred, non-limiting embodiment of it, with reference to the accompanying drawings, in which:

- Figure 1 is a schematic front view, with some parts cut away to better illustrate others, of a machine for forming filter-bags for infusion products according to this invention;

- Figure 2 is a top plan view, with some parts cut away to better illustrate others, of a station for forming and joining knots with auxiliary string of the machine Figure 1 ;

- Figure 3 illustrates an enlarged detail A relating to a first joining zone of the station of Figure 2;

- Figure 4 illustrates an enlarged detail B relating to a second joining zone of the station of Figure 2;

- Figure 5 illustrates a part of the station of Figure 2, in particular the first joining zone in a side view with some parts cut away and others in cross section;

- Figure 6 illustrates a part of the station of Figure 2, in particular the second joining zone in a side view with some parts cut away and others in cross section;

- Figure 7 illustrates an enlarged detail C of the first joining zone of Figure

5;

- Figure 8 illustrates an enlarged detail C of the second joining zone of

Figure 6;

- Figure 9 illustrates a part of the first joining zone, in particular of the cam means for moving a first means, in a partial side view, with some parts cut away to better illustrate others;

- Figure 10 illustrates a cam means for moving gripping means which are positioned on a second means positioned in the second joining point in a view from E relative to the Figure 6 and with some parts cut away to better illustrate others;

- Figure 1 1 illustrates an operating head connected to the cam means of Figure 10 in a schematic side view, with some parts cut away;

- Figures 12 and 13 illustrate another cam means for moving an operating head of the second unit positioned in the second joining point in a view from E relative to the Figure 6, the figures illustrating the operating heads in lowered and raised positions, respectively;

- Figure 14 illustrates a further cam means for rotating the operating head of the second unit positioned in the second joining point in a view from E relative to the Figure 6 and with some parts cut away to better illustrate others;

- Figures 15 to 22 illustrate a corresponding sequence of operating positions of a second needle and of second gripping means to form a knot for joining between a length of filter paper and a continuous string for connection with a tag; all the figures are schematic side views with some parts cut away to better illustrate others;

- Figures 23 to 29 illustrate a corresponding sequence of steps for forming a filter-bag made with the machine illustrated in the previous figures: the figures are schematic perspective views from Figure 23 to 28, and a side view in Figure 29.

Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, and in particular with reference to Figure 1 and Figures 23 to 29, the machine according to this invention, denoted in its entirety by the numeral 100, makes and packages filter-bags 1 for infusion products.

More specifically, but without limiting the invention, the filter-bags 1 contain infusion products such as tea, coffee, camomile, etc.

This text describes the forming of a filter-bag of the so-called two-lobed type, that is to say, with two chambers placed side by side each containing a dose of infusion product. The filter-bag 1 also comprises a string 16 for joining the filter-bag 1 with a gripping tag 17. The gripping tag 17 comprises a fold which makes two wings, the griping tag 17 being positioned across a fold 14 of the filter-bag 1 , and the string 16 being positioned and housed between one top edge 12 of the filter-bag 1 and a respective wing of the gripping tag 17.

It should be noted that the machine 100 according to this invention is described and illustrated only with regard to the stations of relevance to this invention, whilst other stations regarding, for example, over-wrapping of the filter-bag 1 or packaging of the filter-bags 1 are not present, as they are not of specific and direct relevance in this invention.

The machine 100 defines a production line for forming the filter-bag 1 along which a series of stations for forming the filter-bag 1 are positioned. In light of this, the machine 100 comprises a station 2 for unwinding a continuous strip 3 of filter material, for example filter paper.

More specifically, the unwinding station 2 comprises a continuous reel of filter paper unwound along a flat path (Figures 1 and 23).

The machine 100 comprises a station 4 for dosing infusion product on the strip 3 of filter paper fed on the flat path.

In light of this, the dosing station 4 comprises a vertical hopper with dosing means synchronized with the feeding speed of the continuous strip 3 for placing doses 5 of products at preset distances on the continuous strip 3 of filter paper (Figures 1 and 23).

The machine 100 comprises a station 6 for folding the strip of filter material 3 to form a continuous tube of filter paper wrapped around the doses 5 of product and with the two free longitudinal flaps thus obtained superposed on one another (Figure 24).

The machine 100 then comprises a station 7 for longitudinally joining the tube to form chambers or lobes 8 with individual doses 5 of product in continuous succession (Figure 24).

In light of this, the longitudinal joining is carried out by means, for example, of folding and subsequent knurling, or hot sealing performed continuously. The machine 100 also comprises a station 9 for cutting the continuous tube to form lengths 10 of filter paper provided with two lobes 8 with corresponding doses 5 of infusion product (Figure 25).

The separation into lengths 10 of filter paper is carried out by cutting and forming the two opposite open ends of the length 10.

The machine 100 also comprises a station 1 1 for rotating the length 10 of filter paper in such a way as to move into contact the free top open edges 12 of the two lobes 8 (Figure 26).

The machine 100 also comprises a station 13 for folding the free top open edges 12 of the length of filter paper to form at least one fold 14 for closing the free edges 12 (Figures 1 and 27).

In light of this, the station 13 for folding the free top open edges 12 comprises a carousel 34 rotating about a horizontal axis and provided with a plurality of radial arms having, at their ends, a corresponding gripper 33 for retaining the length 10 of filter paper for moving it along an arc-shaped path designed to intercept a unit 57 for folding the free top open edges 12 to form the closing fold 14 (Figure 1 ).

The machine 100 also comprises a station 15 for forming and joining a first portion of continuous string 16 to the gripping tag 17, in a first zone 18 of the station 15 and by means of a first gripping element 19 (Figures 1 , 2 and 28).

The station 15 also performs the positioning and joining of a second portion of the string 16 to the top edges 10 of the length 12 of filter paper, with a second gripping element 20, with simultaneous closing of the top of the length 10 of filter paper in a second zone 21 of the station 15 different from the above-mentioned first zone 18 (Figures 1 , 2 and 28).

It should be noted that the continuous string 16 is fed by a relative station 58 comprising a corresponding spool 59 (Figure 1 ) of continuous string 16. In light of this, the tag 17 is fed continuously from a reel 105 of paper for tags 17 to be then separated into single tags 17 (operation not illustrated). According to the invention (see Figures 2, 3 and 4), the forming and joining station 15 comprises a piercing unit 22 provided with two separate piercing elements or needles 23 and 24, each positioned close to one of the first and second joining zones 18 and 21 of the station 15.

Also according to the invention, each first and second needle 23 and 24 has a first 25 and a second 26 continuous auxiliary string.

Again according to the invention, the station 15 has means 27 for moving the needles 23 and 24 along a horizontal plane, in both directions, and at least along a direction inclined with respect to the horizontal plane to pierce in at least two points the tag 17 and, respectively, the top edges 12 and the closing fold 14 of the length 10 of filter paper so as to insert the first 25 or the second 26 auxiliary string (Figures 2 to 8 and 15 to 22).

Again according to the invention, the station 15 has a carousel 28 for moving and positioning at least the second portion of string 16 from the first zone 18 for joining the first portion of string 16 with the tag 17 to the second joining zone 21 (Figure 2).

Also according to the invention, the station 15 comprises a first unit 29 for manipulating the first auxiliary thread 25 (Figure 7).

The first unit 29 has first means 30 for gripping the first auxiliary string 25, positioned in proximity to the first joining zone 18 and on the side opposite the tag 17 relative to the corresponding first needle 23.

The first gripping means 30 are configured to form, in phase coordination with the movement of the first needle 23, a first knot 19 for joining (thus defining the first gripping element) between the tag 17 and the first portion of string 16 with a portion of the first auxiliary string 25 (Figures 2, 3, 5, 7,

9).

Again according to the invention, the station 15 comprises a second unit

31 for manipulating the second auxiliary string 26 having second means

32 for gripping the second auxiliary string 26 (Figure 8).

The second gripping means 32 are positioned in the proximity of the second zone joining 21 and on the side opposite the top edges 12 and the closing fold 14 of the length 10 of filter paper relative to the corresponding second needle 24.

These second gripping means 32 are configured to form, in phase coordination with the movement of the second needle 24, a second knot 20 for joining (thus defining the second gripping element) between the length 10 of filter paper and the second portion of string 16 with a portion of the second auxiliary string 26 (Figures 2, 4, 6, 8 and 10 to 14).

It should be noted that the second joining zone 21 is engaged by the folded top edges 12 and by the fold 14 of the length 10 of filter paper arranged on a side and supported by a gripper 33 forming part of the carousel 34 rotating about the folding station 6.

In light of this, therefore, the arc-shaped path of the carousel 34 is used to position the top edges 12 of the length 10 of filter paper in the second joining zone 21.

It should be noted that the first and second joining zone 18 and 21 are located on opposite sides of the positioning carousel 28.

Basically, the first and second joining zone 18 and 21 are positioned at diametrically opposite points of the carousel 28 to allow a movement of the string 16 with the tag 17 along a semi-arc defined by the movement of the carousel 28.

This architecture allows the operations for knotting the first and second auxiliary string 25 and 26 to be performed simultaneously on the string 16 with the tag 17 and, on the other side of the carousel 28, between the string 16 and the top edges 12 with fold 14 of the length 10 of filter paper. It should be noted that the components forming the piercing unit 22, having the first and second needle 23 and 24, are supported by an arm 53 having one end hinged, in 53Z, to a supporting case 54 of the machine 100.

The piercing unit 22 can rotate about a vertical axis to move the two needles 23 and 24 towards or away from the first and second joining zone

18 and 21 (Figure 2) during any maintenance operations. Preferably, the means 27 for moving the first and the second needle 23 and 24 are connected to a single control shaft 37 and configured to move the needles 23 and 24 in a synchronised way and in phase coordination (Figure 2, 5 and 6).

In light of this, the piercing unit 22 comprises the movement means 27 subdivided in a first group of cam means 27a connected to the single control shaft 37 to enable the synchronized movement of the needles 23 and 24, along the horizontal plane, and a second group of cam means 27b connected again to the single control shaft 37 to obtain the movement along the inclined plane, in both directions, of both the needles 23 and 24, in such a way as to obtain a double piercing by each needle 23 and 24 in different points, that is, at different heights with respect to the horizontal plane on which the needles 23 and 24 move.

More specifically, the piercing unit 22 comprises a shaft 37 with a horizontal axes on which a plurality of annular cam-shaped profiles 27a and 27b are connected, distributed along its length.

These profiles 27a and 27b are structurally similar for both the needles 23 and 24 and, therefore, the reference numerals are the same for both the piercing units.

A first group of profiles 27a is connected to a first fork 60 provided with a pair of cam follower rollers in contact with the profile 27a for transmitting the drive to a first lever 61 extending vertically (that is, perpendicularly to the shaft 37) and articulated, at its lower end, to the rear end of a carriage 62 for supporting the corresponding needle 23 or 24: this lever 61 is configured for moving the corresponding needle 23 or 24 along the horizontal plane and in both directions (arrows F60).

The second group of profiles 27b is connected to a second fork 63 provided with a pair of cam follower rollers in contact with the profile 27b for transmitting the drive to a second lever 64 vertically articulated, at its lower end, to the front end, that is, closest to the needle 23 or 24, of the carriage 62 for supporting the corresponding needle 23 or 24. This second lever 64 is configured for moving the corresponding needle 23 or 24, when required, along a plane inclined relative to the horizontal plane and in both directions (arrows F63), raising the front end of the carriage 62, in phase with the other lever 61 , at least during the piercing movement performed by the needle 23 or 24.

The raising of the needle 23 or 24 is performed alternately at a piercing stroke of the needle 23 or 24 along the horizontal plane.

It should be noted that the first needle 23 also comprises a pushing head 38 (Figure 3) positioned in the first joining zone 18 and forming an element for:

- retaining the continuous string 16 inside the folded tag 17 and

- performing contact functions during the piercing movement of the first needle 23.

The pushing head 38 is configured for forming, in cooperation with a rear abutting element 39 (forming part of the first joining zone 18), a central fold on the tag 17 for defining two wings in such a way as to allow a piercing of the first needle 23 along both the wings of the tag 17 so defined (see Figure 3).

In light of this, the control shaft 37 has a third group of cam-shaped profiles 27c (Figure 5) which do not coincide with the first two 27a and 27b.

This third group of a cam-shaped profiles 27c is connected to a third fork 65 positioned radially opposite on the shaft 27 relative to the other two groups of profiles 27a and 27b.

The third fork 65 is provided with a pair of cam follower rollers in contact with the profile 27c for transmitting the drive to a third lever 66 extending vertically (that is, perpendicularly to the shaft 37) and articulated, at its lower end, to the rear end of an auxiliary carriage 67 supporting the pushing head 38 and positioned at the top and parallel to the carriage 62 of the first needle 23.

The third lever 66 and the cam profiles 27c are configured for moving the head 38 along the horizontal plane and in both directions (arrows F60), with a stroke towards the first joining point 18, maintaining this position until the complete making of the first knot 19 (three strokes of the first needle 23) and away from the first joining point 18.

It should be noted that the machine 100 comprises two separate spools 55 and 56 with corresponding first and second auxiliary string 25 and 26 each feeding the corresponding first and second needle 23 and 24 (Figure 1 ). Preferably, the first gripping means 30 of the first unit 29 comprise a first pair of crochet needles 30a and 30b arranged side by side along a vertical plane and connected to corresponding first movement means synchronised and in phase with the movement means 27 of the first needle 23 (Figures 5 and 7).

Also preferably, the second gripping means 32 of the second unit 31 comprise a second pair of crochet needles 32a and 32b arranged side by side along a vertical plane and connected to corresponding second movement means synchronised and in phase with the movement means 27 of the second needle 24 (Figures 6 and 8).

The two pairs of crochet hooks 30a, 30b and 32a and 32b are structurally similar and each comprise:

- a hook 30a, 30b, 32a, 32b gripping the auxiliary string 25 or 26;

- a head 73 supporting the hook 30a, 30b, 32a, 32b keyed onto a shaft 74 for passage of the horizontal axis motion;

- a wheel 75 partly toothed keyed to the shaft 74, positioned on a plane parallel to the head 73, for controlling the drive to the hook 30a, 30b, 32a, 32b.

Each pair of crochet hooks 30a, 30b, 32a, 32b has the hooks facing each other for performing the movements of gripping and releasing the string 25 or 26 with directions of rotation opposite to each other (the reason is described in more detail below).

Preferably, each first and second unit 29 and 31 comprises a corresponding first and second cutting unit 40 and 41 operatively positionable in proximity of the corresponding first and second joining zone 18 and 21 and configured to separate the relative portion of the first and second auxiliary string 25 and 26, wound and knotted to form the knots 19 and 20, from the remaining first and second continuous auxiliary string 25 and 26 arranged on the first and second needle 23 and 24.

It should also be noted that the machine 100 also comprises means 42 and 43 for retaining the two auxiliary strings 25 and 26 (Figures 7 and 8). In light of this, the means 42 and 43 are each operatively positionable in the proximity of the relative first and second needle 23 and 24 and configured to retain the corresponding first and second auxiliary string 25 and 26 inside a through seat 23a, 24a made on each of the needles 23 and 24 (Figures 3 and 4).

It should be noted that the first unit 29 has an extension of its relative operating components along a vertical axis, that is, parallel to the axis of rotation of the carousel 28 (Figures 5 and 9).

In light of this, the first unit 29 comprises a first shaft 35 for supporting a first operating head 44 comprising the first gripping means 30 and the first cutting unit 40.

The first shaft 35 is connected by a kinematic mechanism with the first gripping means 30 for allowing a transmission of motion on the first gripping means 30.

It should be noted that the first shaft 35 is positioned parallel to the vertical axis of rotation of the carousel 28 for moving and positioning the continuous string 16 and the tag 17.

Also in light of this, the above-mentioned first operating head 44 is a box- shaped supporting element for the two crochet hooks 30a, 30b.

Similarly, the first operating head 44 is associated with the first cutting unit 40 comprising a plate 68 positioned in front of the needle 23 (Figure 3). The plate 68 has a through opening provided with two surfaces 69 opposite each other and with teeth for cutting the first auxiliary string 25.

In light of this, the means 42 for retaining the first auxiliary string 25 are housed in the above-mentioned pushing head 38.

The retaining means 42 comprise an elastic element 70 shaped and provided with a flexible rod for retaining the first auxiliary string 25 against a vertical plate 71 of the pushing head 38.

Preferably, the first unit 29 comprises the first shaft 35 (vertical) connected in two relative different zones along its longitudinal axis with first and second cam means 45 and 46 (Figure 5).

The first cam means 45 configure control of the movement, in phase, of the first gripping means 30, that is, their rotation about a corresponding horizontal axis, for retaining and releasing the first auxiliary string 25 in such a way as to intercept the same first auxiliary string 25, during the piercing of the first needle 23, designed to form a plurality of loops.

The second cam means 46 configure the movement in height in both directions, that is, along the vertical axis, at least of the first operating head 44 so as to move the first gripping means 30 and the first cutting unit 40 away from/towards the first joining zone 18.

In light of this, the first shaft 35 is slidable inside a sleeve 72 rigidly supporting the first operating head 44.

The first shaft 35 has its bottom end housed in the first operating head 44 and forming a rack 76 meshing in the wheels 75, partially with teeth, for moving the crochet hooks 30a, 30b and 32a and 32b in phase with the movement of the needles 23 and 24.

The first and second cam means 45, 46 comprise a control shaft 77 with a horizontal axis positioned above the shaft 35 and provided with cam profiles configured for obtaining the synchronised movements of the components present in the first operating head 44.

The first cam means 45 comprise a fork 78, provided with cam follower rollers in contact with the cam profiles of the control shaft 77 and an arm articulated to the first shaft 35 to allow vertical movement in both directions of the first shaft 35 in such a way as to obtain the predetermined sequence of semi-circular movements of the crochet hooks 30a, 30b. The second cam means 46 comprise a further fork 79 positioned parallel to the other fork 78, provided with cam follower rollers in contact with the respective profile on the control shaft 77.

The fork 79 is connected to an arm in turn associated with the sleeve 72 to control the raising or lowering of the first operating head 44 and also of the first shaft 35 relative to the first joining zone 18.

It should be noted that this movement of the first operating head 44 is necessary to allow the free movement for evacuating the continuous string 16 and tag 17 and for positioning a new tag 17 on the continuous string 16 in the first joining zone 18.

Moreover, the first means 30 comprise an auxiliary shaft 47, positioned parallel to the first shaft 35, and associated at its bottom end with the first cutting unit 40 positioned on the first operating head 44.

The auxiliary shaft 47 is connected to third cam means 48 for moving the first cutting unit 40, in phase with the first needle 23 and the first gripping means 30, for separating the knotted portion of the first auxiliary string 25 from the rest of the first auxiliary string 25 (Figure 9).

In light of this, the third cam means 48 comprise a further fork 80 positioned parallel to the other two forks 78 and 79, provided with cam follower rollers in contact with a respective profile on the control shaft 77. The fork 80 is connected to an arm 81 which is in turn articulated to the auxiliary shaft 47 to move the auxiliary shaft 47 vertically in both directions and thus perform the cutting of the first auxiliary string 25 thanks to interception of the string 25 by the toothed surface 69 of the cutting plate 68.

The auxiliary shaft 47 is connected with the first shaft 35 and it moves in height together with the entire first operating head 44 (during the movement of the head away from and towards the first joining zone 18) due to its connection to the first cutting unit 40.

It should be noted that the second unit 31 has an extension of its relative operating components along a horizontal axis, that is, transversely to the axis of rotation of the carousel 28 (Figures 2 and 6).

Moreover, the second unit 31 has means for rotating it about a horizontal axis in such a way as to move the second unit 31 towards/away from the second joining zone 21 in phase synchronisation with the movement of the second needle 24 (Figure 14).

In light of this, the second unit 31 comprises a second shaft 36 for supporting a second operating head 49 comprising the second gripping means 32 and the second cutting unit 41 (Figure 10).

The second shaft 36 is connected by a kinematic mechanism with the second operating head 49 and with at least the second gripping means 32 for allowing a transmission of motion on the second operating head 49 and on the second gripping means 32.

As already mentioned, the second shaft 36 is positioned transversely to the vertical axis of rotation of the carousel 28 for moving and positioning the continuous string 16 and the tag 17.

As in the previous unit, the second operating head 49 is the box-shaped supporting element for the second pair of crochet hooks 32a, 32b.

The second operating head 49 is associated with the second cutting unit 41 comprising a plate 82 positioned in front of the second needle 24 (Figures 4, 12, 13).

The plate 82 has a through opening provided with two surfaces 83 opposite each other and with teeth for cutting the second auxiliary string 26 (as described in more detail below).

In this second unit 31 , the second operating head 49 also supports the means 43 for retaining the second auxiliary string 26.

In light of this, the means 43 for retaining the second auxiliary string 26 comprise a suction unit 84 configured for positioning, in use, the respective suction nozzle 85 close to the second needle 24 in such a way as to retain the second auxiliary string 26 inside the seat 24a of the second needle 24 (Figure 1 1 ).

The second unit 31 comprises the second shaft 36 connected in three relative different zones along its longitudinal axis with fourth 50, fifth 51 and sixth 52 cam means (Figure 6).

The fourth cam means 50 configure control of the movement in height in both directions, that is, along a vertical plane, of the second operating head 49 to enable the second cutting unit 41 to separate the knotted portion of the second auxiliary string 26 from the rest of the second auxiliary string 26 and to move the second gripping means 32 away from/towards the second joining zone 21 (Figure 12).

The fifth cam means 51 configure control of the synchronised movement of the second gripping means 32, that is, for their rotation about a corresponding horizontal axis, for retaining and releasing the second auxiliary string 26 in such a way as to intercept the same second auxiliary string 26, during the piercing of the second needle 24, for forming a plurality of loops (Figures 10 and 1 1 ).

The sixth cam means 52 configure the above-mentioned rotation of the second operating head 49 about a horizontal axis for moving the second operating head 49 towards/away from the second joining zone 21 , in phase synchronisation with the movement of the second needle 24.

It should be noted that the second shaft 36 consists of three different components (Figure 6):

- an internal shaft 36a;

- a first cylindrical sleeve 86 which houses coaxially free to rotate the internal shaft 36;

- a second cylindrical sleeve 104 which, in turn, houses coaxially the first cylindrical sleeve 86; this second sleeve 104 supports the second operating head 49 in its entirety.

In light of this, this set of three cam means 50, 51 , 52 comprise a joint control shaft 87 positioned parallel to the second shaft 36 and provided with a set of cam profiles for moving the second operating head 49 and the second pair of crochet hooks 32a, 32b.

A first fork 94 (which is part of the fourth cam means 50), provided with cam follower rollers, is in contact with the cam profiles of the control shaft 87.

This fork 94 has a radial arm 95 provided with a free toothed end 96 engaged on a toothed wheel 97 keyed to the internal shaft in 36a (Figures 12 and 13).

The internal shaft 36a is provided, at the top, with a pin 98 projecting inside the second operating head 49 and connected to the cutting plate 82.

The rotation imparted to the inner shaft 36a by the kinematic combination between the toothed wheel 97 and the arm 95 generates the rotation of the head pin 98 in such a way as to allow the raising or lowering of the cutting plate 82 in such a way as to separate, during the raising movement, the second auxiliary string 25 from the knot 20 formed by cutting/tearing with the toothed surface 83 (Figures 12 and 13).

A second fork 88 (which is part of the fifth cam means 51 ), provided with cam follower rollers, is in contact with the cam profiles of the control shaft 87. The fork 88 has a radial arm 89 provided with a free toothed end 90 engaged on a toothed wheel 91 keyed on the first sleeve 86 (Figures 10 and 1 1 ).

The first sleeve 86 is provided, at the top, with a further pin 92 (positioned so as not to interfere with the pin 98) projecting inside the second operating head 49 and articulated to a rack 93 engaging in the toothed wheels 75 of the crochet hooks 32a, 32b.

The rotation imparted to the first sleeve 86 by the kinematic combination between the toothed wheel 91 and the arm 89 generates the rotation of the head pin 92 in such a way as to allow vertical movement in both directions of the rack 93 so as to obtain the predetermined sequence of semi-circular movements of the crochet hooks 32a, 32b.

It should be noted that the pin 92 engages with a slot present on the second operating head 49, which guides the stroke of the pin 92 and enables the lower and upper stroke limit stop. A third fork 99 (which is part of the sixth cam means 52), provided with cam follower rollers, is in contact with the cam profiles of the control shaft 87.

The third fork 99 has a radial arm 101 provided with a free toothed end 102 engaged on a toothed wheel 103 keyed directly on the second shaft 104 (Figure 14).

The second sleeve 104 is associated directly, at the top, to the second operating head 49 and, therefore, the rotation imparted to the second sleeve 104 by the kinematic combination between the toothed wheel 102 and the radial arm 101 generates the complete rotation of the entire second operating head 49.

The first sleeve 86 and the inner shaft 36a, having the respective pins 92 and 98 connected to the second operating head 49, follow the rotation of the latter in this specific movement.

The complete rotation of the entire second operating head 49 makes it possible to free the second joining zone 21 to facilitate extraction of the length 10 of filter paper and the perform, on the one hand, the steps for completing the length just closed and, on the other, positioning a new length 10 to be closed.

The structure described above thus makes it possible to form two knots 19 and 20 simultaneously in two different joining zones 18 and 21.

The composition the knots is shown in Figures 15 and 22 which illustrate the operation performed in the second joining zone 21 by the second needle 24, but the same procedure is identical in the first joining zone 18. The second needle 24 is positioned in front of the top edges 12 and the fold 14 of the length 10 and the second portion of the continuous string 16 is next to the top edges 12 on the side of the crochet hooks 32a, 32b which, together with the rest of the second operating head 49, are lowered and in standby position (Figure 15)

The second needle 24 performs the first horizontal piercing stroke (lower) forming a first hole on the top edges 12 and 14, and passes beyond the crochet hooks 32a and 32b in a central corridor between the two, carrying on the opposite side of the top edges 12 the second auxiliary string 26. The upper crochet hook 32a rotates downwards and intercepts the second auxiliary string 26 on the side of the second needle 24. (Figure 16).

The second needle 24 performs the exit stroke, in the opposite direction to the entry stroke, allowing the generation of a first loop C1 around the hook 32a in such a way as to keep a portion of the second auxiliary string 26 on the side of the hooks 32a and 32b (Figure 17).

At this point, the second needle 24 performs the second piercing stroke with a direction inclined upwards to form a second transit hole on the top edges 12 and the fold 14 at a height different from the previous hole and carry the second string 26 on the side of the auxiliary hooks 32a and 32b. It should be noted that the second portion of continuous string 16 is positioned on the side of the top edges 12 in an intermediate zone between the two holes formed by the second needle 24 in such a way as to be locked by the loops being formed.

During the second stroke of the second needle 24, the upper hook 32a releases the first loop C1 which moves towards the top edges 12 and in such a way as to leave the space for raising the lower hook 32b which intercepts, in turn, the second auxiliary string 26 when the second needle 24 is at the maximum entry stroke. (Figure 18)

The second needle 24 then performs a second exit stroke to allow the formation of a second loop C2 around the lower hook 32b.

During the exit of the second needle 24 from the top edges 12, the lower hook 32b rotates downwards, and releases the second loop C2 to the upper hook 32a (which simultaneously rotates downwards) to allow the superposing of the two loops C1 , C2. (Figure 19)

At this point, the second needle 24 performs a third horizontal piercing stroke along the first hole formed previously, whilst the upper hook 32a, rotating upwards, releases the second loop C2 which tightens on the first loop C1 and on the second portion of continuous string 16. During the third stroke of the second needle 24, the upper hook 32a rotates again downwards and intercepts the second auxiliary 26 string. (Figure 20)

At this point, the second needle 24 performs the last return stroke to obtain the third loop C3 which is subsequently released by the upper hook 32a. (Figure 21 )

The withdrawal of the second needle 24 and the presence of the three loops C1 , C2, C3 of the portion of the second auxiliary string 26 determine the knotting between the top edges 12 and the closing fold 14 and the second end of the continuous string 16.

With the second needle 24 located in the withdrawn position, the second cutting unit 41 is moved (upwards) to separate the knotted portion from the remaining second auxiliary string 26.

Simultaneously, the retaining means 43 prevent, by suction, the second auxiliary string 26 from escaping from the seat 24a of the second needle 24 due the release of tension of the second string 26 by cutting. (Figure 22)

As already mentioned, the steps described are exactly the same also for the first needle 23 and the units related to the formation of the first knot 19. In this case, the first needle 23 penetrates the tag 17 in the proximity of the central fold in such a way that both the wings of the tag 17 pass beyond the first auxiliary string 25.

Inside the central fold of the tag 17 there is the first portion of continuous string 16 which is affected by the first auxiliary string 25 thanks to the bilateral piercings of the first needle 23.

The first auxiliary string 25, in this case, is retained by the above- mentioned elastic retaining means 42 during formation of the loops and during separation of the first auxiliary string 25 from the knot 19.

This invention also provides a method for forming a filter-bag 1 for infusion products comprising the steps of:

- preparing a continuous strip 3 of filter paper (Figure 23); - depositing a succession of doses 5 of infusion product on the continuous strip 3 (Figure 23);

- folding longitudinal sides of the continuous strip 3 on to each other to form a continuous tube within which the doses 5 of infusion product are arranged (Figure 24);

- closing longitudinally the tubular strip 3 (Figure 24);

- separating from the continuous tube 3 lengths 10 of filter paper, each comprising at least a pair of doses 5 of infusion product (Figure 25);

- folding the length 10 of filter paper on itself in such a way as to bring corresponding free top open edges 12 into mutual contact and to form a pair of lobes 8 with the corresponding doses 5 of product (Figure 26);

- folding the top edges 12 of the pair of lobes 8 on to each other to form a closing fold 14 in contact with a front surface of one of the two lobes 8 (Figure 27);

- providing a gripping tag (17) provided with a central fold to configure two wings (Figure 28);

- providing a continuous string 16 with a first portion positioned along the central fold of the tag 17 and a second portion, spaced from the first portion, positioned alongside the top free edges 12 of the lobes 8.

According to the invention, the method also comprises the following steps:

- providing a first, continuous, auxiliary string 25;

- providing a second, continuous, auxiliary string 26;

- making a first knot 19 with a portion of the first auxiliary string 25 to block the first portion of continuous string 16 to the tag 17 by piercing the tag 17 in at least two points, in the first joining zone 18 of the forming and joining station 15;

- making a second knot 20 with a portion of the second auxiliary string 26 to block the second portion of continuous string 16 to the top free edges 12 and to the fold 8 of the lobes 8 by piercing the top free edges 12 and the fold 14 in at least two points and to firmly close the filter-bag 1 so formed in the second joining zone 21 of the forming and joining station 15, different from the first joining zone 18 (Figure 28);

- moving and positioning at least the second portion of string 16 from the first joining zone 18 of the first portion of string 16 with the tag 17 to the second joining zone 21.

Preferably, the method comprises a step of cutting the first auxiliary string 25 from its knotted portion between the tag 17 and the continuous string

16 after the step of making the second knot 19.

Preferably, the method comprises a step of cutting the second auxiliary string 26 from its knotted portion between the top edges 12 and the continuous string 16 after the step of making the second knot 20.

It should be noted that the method also comprises a step for collecting the portion of continuous string 16 between its two lengths knotted to the tag

17 and, respectively, to the top edges 12 at a front surface of one of the lobes 8 (Figure 29).

In light of this, the step of collecting the portion of string 16 is performed during the step of moving and positioning the second portion of string 16 from the first joining zone 18 to the second joining zone 21 .

Preferably, the method comprises a step of inserting the tag 17 folded in a "V" shape across the closed top edges 12 of the two lobes 8 with covering and retaining of the portion of string 16 collected between the front of one of the lobes 8 and a wing of the tag 17.

This invention also provides a filter-bag 1 for infusion products.

The filter-bag 1 comprises a length 10 of filter paper formed by two chambers or lobes 8 containing a respective dose 5 of infusion product. Each lobe 8 is closed and joined to the other lobe 8 to a corresponding end forming the bottom of the filter-bag 1.

The two lobes 8 are joined and in contact, at the opposite end to the base, with the top edges 12 folded to form a closing fold 14 on the front of one of the lobes 8.

The filter-bag 1 also comprises a string 16 for connecting the length 10 of filter paper to a gripping tag 17. The string 16 is locked, at its first end, to the tag 17 by a first knot 19 made with a portion of a first auxiliary string 25.

The string 16 is locked, at its second end, to the folded top edges 12 of the lobes 8 by a second knot 20 made with a portion of a second auxiliary string 26.

The gripping tag 17 is folded to form two wings and located astride the fold 14, the string 16 being positioned and housed between a top edge 12 and a relative wing of the gripping tag 17.

Claims

1 . A machine for forming filter-bags (1 ) for infusion products, including:

- a station (2) for unwinding a continuous strip (3) of filter material;

- a station (4) for dosing doses (5) of infusion product on the strip (3) of filter material;

- a station (6) for folding the strip (3) of filter material to form a continuous tube;

- a station (7) for longitudinally joining the continuous tube to form chambers, or lobes, (8), with single doses (5) of product in continuous succession;

- a station (9) for cutting the continuous tube to form lengths (10) of filter material with two lobes (8);

- a station (1 1 ) for rotating the length (10) so as to bring top edges (12) of the length (10) of filter material into mutual contact;

- a station (13) for folding the top edges (12) of the length (10) to form at least one fold (14) for closing the top edges (12);

- a station (15) for forming and joining a first portion of string (16) to a gripping tag (17), in a first joining zone (18) of the forming and joining station (15) and by means of a first knot (19), and for positioning and joining a second portion of the string (16) to the top edges (12) of the length (10) of filter material, by means of a second knot (20), simultaneously closing the length (10) of filter material on top in a second joining zone (21 ) of the forming and joining station (15), different from the first joining zone (18);

characterized in that the forming and joining station (15) comprises:

- a piercing unit (22) provided with two distinct piercing elements, or needles, (23, 24), respectively arranged in the proximity of the first (18) and second (21 ) joining zone of the forming and joining station (15) and having a first (25) and a second (26) continuous auxiliary string, respectively; means (27) for moving the needles (23, 24) along a horizontal plane, in both directions, and along a direction inclined with respect to the horizontal plane to pierce in at least two points the tag (17), and the top edges (12) and the closing fold (14), respectively, and for inserting the first (25) and the second (26) auxiliary string, respectively;

- a carousel (28) for moving and positioning at least the second portion of string (16) from the first zone (18) for joining the first portion of string (16) with the tag (17) to the second joining zone (21 );

- a first unit (29) for manipulating the first auxiliary string (25) having first means (30) for gripping the first auxiliary string (25); the first gripping means (30) being arranged in proximity of the first joining zone (18), opposite the corresponding first needle (23), and configured for forming, in phase coordination with the first needle (23), the first knot (19) for joining the tag (17) and the first portion of string (16) with a portion of the first auxiliary string (25);

- a second unit (31 ) for manipulating the second auxiliary string (26) having second means (32) for gripping the second auxiliary string (26); the second gripping means (26) being arranged in proximity of the second joining zone (21 ), opposite the corresponding second needle (24), and configured for forming, in phase coordination with the second needle (24), the second knot (20) for joining the length (10) of filter material and the second portion of the string (16) with a portion of the second auxiliary string (26).

2. The machine according to claim 1 , wherein the second joining zone (21 ) is engaged by the top edges (12) and the closing fold (14) of the length (10) of filter material arranged on a side and supported by a gripper

(33) of a carousel (34) rotating about a horizontal axis of the station (13) for folding the top edges (12) of the length (10).

3. The machine according to any one of the preceding claims, wherein the first (18) and second (21 ) joining zones are arranged diametrically opposite to each other on the moving and positioning carousel (28).

4. The machine according to any one of the preceding claims, wherein the first gripping means (30) of the first unit (29) comprise a first pair of crochet needles (30a, 30b) arranged side by side on a vertical plane and connected to corresponding first movement means synchronized and in phase with the movement means (27) of the first needle (23).

5. The machine according to any one of the preceding claims, wherein the second gripping means (32) of the second unit (31 ) comprise a second pair of crochet needles (32a, 32b) arranged side by side on a vertical plane and connected to corresponding second movement means synchronized and in phase with the movement means (27) of the second needle (24).

6. The machine according to any one of the preceding claims, wherein the movement means (27) of the first needle (23) and of the second needle (24) are connected to a single control shaft (37) and configured to move the needles (23, 24) in a synchronised way and in phase coordination.

7. The machine according to any one of the preceding claims, wherein the first needle (23) comprises a head (38) for pushing a piece of the tag (17), arranged in the first joining zone (18), and designed to retain the string (16) inside the folded tag (17), and acting as abutment during piercing movements of the first needle (23); the pushing head (38) being configured for forming, in cooperation with a rear abutting element (39), a central fold in the tag (17) defining two wings and for enabling the first needle (23) to pierce both wings of the tag (17) so defined.

8. The machine according to any one of the preceding claims, wherein the first (29) and second (31 ) units comprise, respectively, a corresponding first (40) and second (41 ) cutting units operatively positioned in proximity of the corresponding first (18) and second (21 ) joining zone and configured to separate the relative portion of the first (25) and second (26) auxiliary string, wound and knotted, from the remaining first (25) and second (26) continuous auxiliary string, respectively, arranged on the first (23) and second (24) needle, respectively.

9. The machine according to any one of the preceding claims, comprising means (42, 43) for retaining, respectively, the first (25) and second (26) auxiliary string, operatively arranged in proximity of the first (23) and second (24) needle, respectively, and configured for retaining the corresponding first (25) and second (26) auxiliary string within a through seat (23a, 24a) formed on the first (23) and the second (24) needle, respectively.

10. The machine according to any one of the preceding claims, wherein the first unit (29) comprises a first shaft (35) for supporting a first operating head (44) comprising the first gripping means (30) and the first cutting unit (40); the first shaft (35) being connected by a kinematic mechanism to the gripping means (30) to move the first gripping means (30); the first shaft (35) being arranged parallel to the vertical axis of rotation of the moving and positioning carousel (28).

1 1 . The machine according to any one of the preceding claims, wherein the first shaft (35) has a longitudinal axis and is connected in two different zones along the longitudinal axis to:

- first cam means (45) for controlling, in phase, the first gripping means (30) in rotation about a corresponding horizontal axis, for retaining and releasing the first auxiliary string (25) in such a way as to intercept the same first auxiliary string (25), during piercing movements of the first needle (23), and to form a plurality of loops; - second cam means (46) for moving the first operating head (44) along a vertical axis in both directions so as to move the first gripping means (30) and the first cutting unit (40) away from/towards the first joining zone (18).

12. The machine according to any one of the preceding claims, wherein the first means (30) comprise an auxiliary shaft (47), arranged parallel to the first shaft (35) and associated with the first cutting unit (40) arranged on the first operating head (44); the auxiliary shaft (47) being connected to third cam means (48) for moving the first cutting unit (40), in phase with the first needle (23) and the first gripping means (30), to separate a knotted portion of the first auxiliary string (25) from the rest of the first auxiliary string (25).

13. The machine according to any one of the preceding claims, wherein the second unit (31 ) has means for rotating about a horizontal axis in such a way as to move the second unit (31 ) towards/away from the second joining zone (21 ) in phase with the second needle (24).

14. The machine according to any one of the preceding claims, wherein the second unit (31 ) comprises a second shaft (36) supporting a second operating head (49) comprising the second gripping means (32) and the second cutting unit (41 ); the second shaft (36) being connected by a kinematic mechanism to the second operating head (49) and to the second gripping means (32) to move the second operating head (49) and the second gripping means (32); the second shaft (36) being arranged transversally with respect to the vertical axis of rotation of the moving and positioning carousel (28).

15. The machine according to any one of the preceding claims, wherein the second shaft (36) has a longitudinal axis and is connected in three different zones along the longitudinal axis to: - fourth cam means (50) for moving along a vertical plane in both directions the second operating head (49) and enabling the second cutting unit (41 ) to separate a knotted portion of the second auxiliary string (26) from the rest of the second auxiliary string (26) and to move the second gripping means (32) away from/towards the second joining zone (21 );

- fifth cam means (51 ) for moving in phase the second gripping means (32), in particular for rotating the second gripping means (32) about a corresponding horizontal axis, and for retaining and releasing the second auxiliary string (26), in such a way as to intercept the second auxiliary string (26) whilst the second needle (24) pierces the fold (14), to form a plurality of loops;

- sixth cam means (52) for rotating the second operating head (49) about a horizontal axis and moving the second operating head (49) towards/away from the second joining zone (21 ), in phase with the second needle (24).

16. The machine according to any one of the preceding claims, wherein the piercing unit (22) comprises the movement means (27) subdivided in a first group of cam means (27a) connected to the single control shaft (37) to enable a synchronized movement of the first and second needles (23, 24) along a horizontal plane and a second group of cam means (27b) connected to the single control shaft (37) to obtain a movement along an inclined plane, in both directions, of both the needles (23, 24), in such a way as to obtain a double piercing by each needle (23, 24) in different points, at different heights with respect to the horizontal plane on which the needles (23, 24) move.

17. The machine according to any one of the preceding claims, wherein the piercing unit (22) is supported by an arm (53) having an end hinged to a support case (54) of the machine (100) and being rotatable about a vertical axis to move the first (23) and the second (24) needle towards/away from the first (18) and the second (21 ) joining zone, respectively.

18. The machine according to any one of the preceding claims, including two distinct spools (55, 56) for the first (25) and the second (26) auxiliary string, respectively, feeding the first (23) and second (24) needle, respectively.

19. A method for forming a filter-bag (1 ) for infusion products comprising the steps of:

- providing a continuous strip (3) of filter material;

- depositing a succession of doses (5) of infusion product on the continuous strip (3);

- folding longitudinal sides of the continuous strip (3) on to each other to form a continuous tube within which the doses (5) of infusion product are arranged;

- longitudinally closing the continuous tube;

- separating from the continuous tube lengths (10) of filter material, each comprising at least a pair of doses (5) of infusion product;

- folding the length (10) of filter material in such a way as to bring corresponding top edges (12) of the length (10) into mutual contact and to form a pair of lobes (8) with corresponding doses (5) of infusion product;

- folding the top edges (12) to form a closing fold (14) in contact with a front surface of one of the two lobes (8);

- providing a gripping tag (17) provided with a central fold to configure two wings;

- providing a continuous string (16) with a first portion positioned along the central fold of the tag (17) and a second portion, spaced from the first portion, positioned alongside the top edges (12);

characterised in that it further comprises the steps of:

- providing a first, continuous, auxiliary string (25);

- providing a second, continuous, auxiliary string (26); - making a first knot (19) with a portion of the first auxiliary string (25) to block the first portion of continuous string (16) to the tag (17) by piercing the tag (17) in at least two points, in a first joining zone (18) of a forming and joining station (15);

- making a second knot (20) with a portion of the second auxiliary string (26) to block the second portion of continuous string (16) to the top edges (12) and to the closing fold (14) by piercing the top edges (12) and the closing fold (14) in at least two points and to firmly close the filter-bag (1 ) so formed in a second joining zone (21 ) of the forming and joining station (15), different from the first joining zone (18);

- moving and positioning at least the second portion of string (16) from the first joining zone (18) of the first portion of string (16) with the tag (17) to the second joining zone (21 ).

20. The method according to claim 19, comprising a step of cutting the first auxiliary string (25) from a knotted portion between the tag (17) and the continuous string (16) after the step of making the second knot (19).

21 . The method according to claim 19 or 20, comprising a step of cutting the second auxiliary string (26) from a knotted portion between the top edges (12) and the continuous string (16) after the step of making the second knot (20).

22. The method according to any one of claims 19 to 21 , comprising a step of collecting the portion of continuous string (16) between the first and second portion, blocked to the tag (17) and, respectively, to the top edges (12) during the moving and positioning step.

23. The method according to claim 22, comprising a step of inserting the tag (17) folded in the shape of a "V" across the closing fold (14), the continuous string (16) being collected and retained between a lobe (8) and a respective wing of the tag (17).