TECHNICAL FIELD The present invention relates to a forming method for producing sealed packages of pourable food products from a tube of sheet packaging material, and to a forming unit implementing said method.

BACKGROUND ART Many pourable food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature-treated) milk, <BR> <BR> wine, tomato sauce, etc. , are sold in packages made of sterilized packaging material.

A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing a web of laminated packaging material.

The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal plastic material, e. g. polyethylene, and, in the case of aseptic packages for long-storage products, such as UHT milk, also comprises a layer of oxygen-barrier material, defined, for example, by aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material eventually

defining the inner face of the package contacting the food product.

As is known, such packages are produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material. More specifically, the web of packaging material is unwound off a reel and fed through an aseptic chamber of the packaging machine, where it is sterilized, e. g. by applying a sterilizing agent, such as a hydrogen peroxide, which is later removed by heating, and/or by subjecting the packaging material to radiation of appropriate wavelength and intensity; and the web so sterilized is kept in a closed, sterile environment, and is folded into a cylinder and sealed longitudinally to form a continuous tube in known manner.

The tube of packaging material, which thus forms an extension of the aseptic chamber, is fed continuously in a vertical direction, is filled with the sterilized or sterile-processed food product, and is fed through a forming unit for producing individual packages. That is, inside the forming unit, the tube is sealed along equally spaced transverse sections to form a continuous strip of pillow packs connected to one another by respective transverse sealing bands, i. e. extending crosswise to the travelling direction of the tube; and the pillow packs are separated by cutting the relative transverse sealing bands, and are then fed to a folding station where they are folded mechanically to form respective finished

parallelepiped-shaped packages.

As described, for example, in European Patent EP-B- 0887265, forming units are known comprising two chain conveyors defining respective endless paths and supporting respective numbers of jaws. The two paths have respective branches substantially facing and parallel to each other, and between which the tube of packaging material fed, so that the jaws on one conveyor cooperate with corresponding jaws on the other conveyor along said branches of the respective paths to grip the tube at a number of successive cross sections and seal and cut the packages.

That is, each jaw on one conveyor defines, with the corresponding jaw on the other conveyor, a respective sealing assembly which interacts cyclically with the tube of packaging material.

The portion of the tube gripped between each pair of jaws is typically sealed by heating means carried on one of the jaws and for locally melting the layers of heat- seal plastic material gripped between the jaws.

Forming units are also known which only comprise two pairs of jaws, which act alternately on the tube of packaging material to grip and seal, e. g. heat seal, it along a number of equally spaced cross sections.

Once sealing is completed, a cutting member, carried by one of the jaws and interacting with the tube of packaging material, is activated to cut the tube along the centreline of the sealed cross section and so detach

a pillow pack from the bottom end of the tube of packaging material. Since the bottom end is sealed transversely, the relative jaws, on reaching the bottom dead-centre position, can be opened to avoid interfering with the upper portion of the tube ; and, at the same time, the other pair of jaws, operating in the same way, moves down from a top dead-centre position to repeat the gripping/forming, sealing and cutting operations as described above.

One problem posed by known forming units has to do with the so-called"decoration correction"system.

That is, the web of packaging material normally has a series of equally spaced printed images or decorations on the portions eventually defining the outer surfaces of the packages, so that the web must be fed to the forming unit in such a manner as to"register"the package forming, sealing and cutting operations with respect to the sequence of decorations. Though the printed decorations are equally spaced, the position of each with respect to the position of the forming unit jaws may vary, firstly on account of varying deformation of the packaging material by the mechanical pressures exerted on it by the jaws, and secondly due to the pulsating pressure of the pourable food product inside the tube of packaging material. A system for correcting the decoration position is therefore required, in that, on high-speed packaging machines, even minute deviations from the theoretical register position of the

decorations, if not corrected immediately, may escalate and eventually result in the production of unacceptable packages which must be rejected.

On modern packaging machines, such a system comprises an optical sensor for detecting the position of a marker, such as a bar code, a pour hole, or a fold line, repeated at regular intervals on the web of packaging material eventually forming the fill tube; and a control unit for comparing the detected position of the marker with a theoretical position.

On some commercial machines, each two interacting jaws are combined with two traction members, which exert adjustable pull on opposite sides of the tube of packaging material to correct its vertical feed. The traction members are activated after the relative jaws grip the tube of packaging material, and before the next two jaws act on the upstream cross section of the tube.

The traction members are normally fitted movably to one of the jaws in each pair, and are movable by varying amounts between two limit positions.

On detecting a decoration position error, the control unit adjusts the speed of the web feed motor. If this is not enough, the traction members are activated to adjust their travel so as to slightly increase or reduce pull on the packaging material. In other solutions, the control unit acts directly on the traction members, with no possibility of adjusting the speed of the web feed motor; and the operation is repeated until the decoration

and theoretical positions match.

In addition to correcting feed of the tube of packaging material, the traction members also simultaneously fold the packaging material towards the cross section gripped between the relative jaws, so as to form triangular tabs at the top and bottom end corners of the pillow packs.

To correct the decoration position with respect to the position of the two jaws interacting with the tube of packaging material, the traction members are moved by varying amounts between the two limit positions, and only perform a complete movement in particular conditions.

As a result, the traction members fail to ensure optimum folding and forming of the packaging material towards the section gripped between the relative pair of jaws, i. e. at the ends of the pillow packs, which in fact can only be achieved by always moving the traction members as close as possible to the underlying sealing portion of the tube.

DISCLOSURE OF INVENTION It is an object of the present invention to provide a forming method for producing sealed packages of pourable food products from a tube of sheet packaging material, designed to control and correct vertical feed of the tube, and also to ensure optimum folding and forming of the ends of the pillow packs.

According to the present invention, there is provided a forming method for producing sealed packages

of pourable food products from a tube of sheet packaging material, as claimed in Claim 1.

The present invention also relates to a forming unit implementing said method, and as claimed in Claim 4.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a view in perspective, with parts removed for clarity, of a forming unit in accordance with the teachings of the present invention; Figure 2 shows a partial schematic elevation of the Figure 1 unit; Figures 3 and 4 show views in perspective, from opposite sides, of a jaw of the Figure 1 unit; Figure 5 shows a schematic front view of a jaw cooperating with the packaging material, of a packaging material decoration register control device ; Figures 6,7 and 8 show partial schematic elevations, with parts removed for clarity, of a jaw and a cam assembly forming part of the Figure 5 control device, in three different operating conditions; Figure 9 shows a larger-scale view in perspective of the cam assembly in Figures 6,7 and 8.

BEST MODE FOR CARRYING OUT THE INVENTION Number 1 in Figures 1 and 2 indicates as a whole a forming unit for continuously producing sealed packages 2 of a pourable food product, such as pasteurized or UHT

milk, fruit juice, wine, etc. , from a tube 3 of packaging material.

Tube 3 is formed in known manner upstream from unit 1 by longitudinally folding and sealing a web of heat- seal sheet material, and is filled with the sterilized or sterile-processed food product for packaging.

The packaging material of tube 3 is printed beforehand with a succession of identical, equally spaced decorations 4 (Figure 5) on the portions of the material eventually forming the outer surfaces of packages 2; and each decoration 4 comprises a bar code 5 (Figure 2).

Unit 1 comprises a frame 6 (Figure 1) defined by two sides 7a, 7b, and by two parallel transverse walls 8a, 8b fixed rigidly between sides 7a, 7b and defining, with sides 7a, 7b, a gap 9; and two chain conveyors 10,11 supported by frame 6 and having respective jaws 12, 13 (only one pair shown in Figure 1) which cooperate with each other and interact with the tube 3 of packaging material fed along a vertical path A through gap 9.

Conveyors 10, 11 define respective endless paths P, Q, along which jaws 12,13 travel, and which extend about respective walls 8a, 8b of frame 6.

Conveyor 10 comprises an articulated chain 15 extending along path P ; and two drive wheels 16 meshing with both sides of chain 15 at the bottom end of path P.

Jaws 12 are an integral part, and form alternate links, of chain 15, and are connected to one another in articulated manner by pairs of rods 17.

More specifically (Figures 3 and 4), each jaw 12 comprises a main body 20, which is elongated perpendicularly to path A, is parallel to wall 8b, and has respective end enlargements 21,22, each having a projecting first and second pin 23,24 with respective axes B, C spaced apart and parallel to the major dimension of body 20. Rods 17 articulate on pins 23,24 of jaws 12, so as to connect pins 23 of one jaw 12 to pins 24 of the adjacent jaw 12.

Similarly, conveyor 11 comprises an articulated chain 25 extending along path Q; and two drive wheels 26 meshing with chain 25 at the bottom end of path Q. Chain 25 is defined by a number of jaws 13 connected to one another in articulated manner and only described in detail as regards features differing from those of jaws 12. Parts of jaws 13 identical or corresponding to those of jaws 12 are indicated using the same reference numbers. Briefly, each jaw 13 comprises a main body 20 having pairs of end pins 23,24, on which articulate rods 17 connecting adjacent pairs of jaws 13.

Each jaw 12 (Figure 3) comprises an induction heating member 29 fitted to main body 20, crosswise to path A of tube 3. Heating member 29 comprises two straight parallel active surfaces 30, and is powered electrically by two contact brushes 31 which, in use, cooperate in sliding manner with a power bar (not shown) fitted to frame 6 and extending along the portion of path P inside gap 9.

Instead of heating member 29, each jaw 13 comprises a pressure bar 32, which cooperates with heating member 29 of corresponding jaw 12 to grip a cross section of tube 3 (Figure 2). On a front surface facing corresponding jaw 12 in use (Figure 1), bar 32 is fitted in known manner with two strips of relatively flexible elastomeric material, which cooperate with the packaging material in opposition to active surfaces 30 of heating member 29.

In other words, each jaw 12 on conveyor 10 defines with the corresponding jaw 13 on conveyor 11 a jaw assembly which interacts cyclically with tube 3 of packaging material.

Jaws 12 and 13 (Figures 1,3, 4) also comprise respective devices 33 for controlling the volume of packages 2 as they are formed. Each device 33-known, for example, from EP-B-0887265, and therefore not described in detail-substantially comprises a half- shell 34 hinged to main body 20 about an axis D parallel to axes B and C by means of two supporting brackets 35 integral with half-shell 34.

As shown in Figure 1, each half-shell 34 cooperates at the front with a complementary half-shell 34 to form a substantially parallelepiped-shaped cavity for housing a package 2 being formed; and each device 33 comprises a cam follower roller 36 fitted idly to a supporting bracket 37 fitted integrally to the back of relative half-shell 34.

Cam followers 36 of jaws 12 and 13 cooperate with respective cams 38 fitted to walls 8a and 8b of frame 6, and of which only the one relative to conveyor 11 is shown in Figure 1.

The movement of jaws 12 and 13 is controlled by respective pairs of cams 40,41 fitted to walls 8a, 8b of frame 6 and cooperating with respective pairs of cam follower rollers 42,43 fitted to end enlargements 21,22 of jaws 12 and 13. The rollers 42,43 in each pair are coaxial with respective pins 24,23, and are offset axially with respect to each other so as to cooperate with respective cams 40,41.

More specifically, wall 8a (Figure 1) is fitted with two pairs of cams 40, 41 which cooperate with respective pairs of rollers 42,43 of jaws 12; and, similarly, wall 8b is fitted with two pairs of cams 40,41 which cooperate with respective pairs of rollers 42,43 of jaws 13.

Cams 40,41 have respective substantially U-shaped portions 40a, 41a extending about top edges of respective walls 8a, 8b to define return portions for respective chains 15,25 of conveyors 10,11 opposite respective drive wheels 16,26 ; and respective portions 40b, 41b extending along respective walls 8a, 8b inside gap 9.

Portions 40a, 41a define portions Pl, Q1 along which jaws 12 and 13 approach and contact tube 3 of packaging material; and portions 40b, 41b define facing, substantially parallel portions P2, Q2 of paths P, Q,

along which jaws 12 and 13 are maintained contacting under pressure to form the seals defining packages 2 at respective substantially flat transverse sealing bands 44, thus forming a continuous strip defined by a number of parallelepiped-shaped container portions 45 connected to one another by sealing bands 44, which are cut along path P or downstream from unit 1 to form packages 2.

Cams 40,41 release relative chains 15,25 at respective portions P3, Q3 of paths P, Q, downstream from respective drive wheels 16,26.

Along portions P3, Q3, chains 15,25 cooperate with respective pairs of tensioners 46 for maintaining chains 15,25 taut enough to ensure contact between rollers 42, 43 of jaws 12, 13 and relative cams 40,41.

Each jaw 12 also comprises a pair of movable traction members 50, which interact with tube 3 of packaging material to feed it correctly along path A, and which are located over heating member 29 with reference to portion P2 of path P.

Traction members 50 (Figures 3,5, 6,7, 8) comprise respective traction tabs 51 located on opposite sides of path A of tube 3 and symmetrical with and adjacent to tube 3. Tabs 51 are integral with respective pins 52 having axes E perpendicular to path A and to the major dimension of heating member 29, extend substantially radially with respect to pins 52, and have respective lateral edges 54 substantially parallel to axes E of pins 52 and which cooperate with tube 3.

Pins 52 are fitted to rotate freely through main body 20 of jaw 12 (Figures 6,7, 8), and have respective end portions 55 projecting from the rear of main body 20.

Pins 52 are counter-rotated, i. e. by equal angles in opposite directions so as to move tabs 51 symmetrically with respect to path A, by an articulated mechanism 60 (Figures 4,6, 7,8) at the back of main body 20.

More specifically, traction members 50 are movable by varying amounts between a first and second, respectively vertical and horizontal, limit position.

In the first limit position (Figure 3) traction members 50 are positioned with tabs 51 substantially vertical, i. e. parallel to the feed direction of tube 3 along path A, and do not interact with tube 3. In the second limit position (Figure 8), traction members 50 are positioned with tabs 51 substantially horizontal and close to heating member 29.

As they are moved, traction members 50 exert pull on tube 3 and, at the same time, fold the packaging material by varying amounts towards band 44 sealed by jaws 12 and 13 associated with traction members 50.

With reference to Figures 4,6, 7,8, mechanism 60 comprises a first-class control lever 61 fitted to end 55 of one of pins 52, which defines the fulcrum of lever 61 and is located, in use, on the side 7b side of frame 6.

Lever 61 comprises a first arm 62 fitted on the end with a cam follower roller 63 having an axis parallel to axes E of pins 52; and a second arm 64 hinged to one end

65a of a rod 65. Rod 65 extends crosswise to main body 20, intersects a plane containing axes E of pins 52, and is hinged, close to its opposite end 65b, to a rod 66 fitted to end portion 55 of the other pin 52.

A spring 67, fitted to main body 20, acts on the free end 65b of rod 65 to keep mechanism 60 normally in a rest configuration (Figure 4), in which lever 61 is almost horizontal, and cam follower roller 63 projects laterally outwards of jaw 12, i. e. on the opposite side of pin 52 of lever 61 to path A of tube 3.

Cam follower roller 63 cooperates with a partly variable profile cam assembly 68 (Figures 6 to 9) fitted to wall 8a, adjacent to a cam 40.

Cam assembly 68 is associated with a control assembly 69-shown only partly and schematically in Figures 5 and 9 and described in detail in the Applicant's Patent Application EP-B-0887265-which, together with cam assembly 68, forms part of a control device 70 for controlling the movement of traction members 50.

Cam assembly 68 substantially comprises a fixed top cam 71 and a fixed bottom cam 72 (Figure 9), which are substantially U-shaped and fitted about respective top and bottom edges of wall 8a to control the position of cam follower roller 63, and therefore of mechanism 60, at the opposite ends of path P of jaws 12. Cam assembly 68 also comprises a movable cam 73 and a fixed cam 74, which are located along wall 8a, inside gap 9, to control the

position of cam follower roller 63 substantially along portion P2 of path P of jaws 12.

More specifically, fixed cam 71 is fitted to the top edge of wall 8a, laterally contacting a cam 40, and comprises, on the opposite side to cam 40, a rolling track 75, for cam follower roller 63, lying substantially in a vertical plane along its whole length except for a lead-in ramp portion 90 (Figure 9) located at the end of cam 71 outside wall 8a.

Movable cam 73 is fitted close to wall 8a, in an intermediate position between fixed top cam 71 and fixed cam 74, so as to slide in a plane parallel to wall 8a, and defines a substantially trapezoidal rolling track 77 defined by an up-ramp portion 78 adjacent to fixed cam 71, by a constant-lift intermediate portion 79, and by a down-ramp portion 80 adjacent to fixed cam 74.

Portions 78 and 80 are formed on respective end portions 81,82 of movable cam 73 fitted respectively in sliding manner to fixed cam 71 and fixed cam 74 to maintain continuity between the cams.

Cam 73 is movable substantially parallel to wall 8a so as to adjust both the maximum lift of cam 73 defined by intermediate portion 79 of rolling track 77, and the points connecting cam 73 to fixed cams 71 and 74.

The position of movable cam 73 and, therefore, the amount by which traction members 50 are moved between the first and second limit position, are controlled in known manner, as stated, by control assembly 69.

According to an important aspect of the present invention, fixed cam 74 is shaped to produce, following the sealing operation performed by each pair of jaws 12 and 13, an additional, substantially complete movement of the respective pair of traction members 50 from the first to the second limit position, so as to fold the packaging material of tube 3 substantially completely towards the newly sealed band 44 of tube 3.

More specifically, as shown in Figures 6 to 9, fixed cam 74, connected rigidly to wall 8a, defines a rolling track 83 having, in succession, a substantially flat, vertical first portion 84 located closer to path A by a predetermined amount with respect to the plane of track 75 of fixed cam 71; an up-ramp second portion 85, along which traction members 50 are moved into the second limit position; and a down-ramp third portion 86 terminating substantially in the same plane as the start of lead-in portion 90 of cam 71.

Fixed bottom cam 72 is substantially a safety cam, and cooperates with cam follower roller 63 on the opposite side with respect to cams 71,73 and 74, to ensure mechanism 60 is restored to the rest position shown in Figure 4. For which purpose, fixed cam 72 defines a rolling track 87 having, in succession with reference to path A, a first portion 88 substantially parallel to portion 86 of rolling track 83 of fixed cam 74; and a constant-lift portion 89 for maintaining cam follower roller 63 in position to engage lead-in portion

90 of cam 71.

Control assembly 69 is connected to a central control unit 91 for governing operation of unit 1, and which receives a signal S generated by an optical sensor 92 facing tube 3, upstream from where tube 3 interacts with jaws 12 and 13, and for detecting the presence of bar codes 5 of decorations 4.

Central control unit 91 compares the instant a bar code 5 is detected by optical sensor 92 with a time window defined by an internal"clock"of central control unit 91.

Unit 1 operates as follows.

The two conveyors 10, 11 are run in opposite directions, as indicated by the arrows in Figure 2, so that respective jaws 12, 13 cooperate with tube 3 of packaging material from the end of portions PI, Q1 of respective paths P, Q and along respective portions P2, Q2 with a law of motion defined by the profiles of cams 40, 41.

The work cycle will now be described in more detail with reference to one jaw 12 of conveyor 10 and the corresponding jaw 13 of conveyor 11, all the other jaws 12 and 13 obviously performing the same cycle at time intervals depending on the output rate.

Along portions Pi and Q1, jaws 12 and 13 are brought together to gradually deform and"flatten"tube 3 at a transverse band 44.

At the end of portions Pl, Q1, devices 33 for

controlling the volume of packages 2 are activated; and half-shells 34 of jaws 12 and 13 are brought together frontwards to define a parallelepiped-shaped cavity defining the volume of container portion 45 of the package 2 being formed.

Container portion 45 is connected to each sealing band 44 by two substantially trapezoidal connecting walls 95 (Figures 2 and 5) formed as tube 3 is gradually compressed by jaws 12 and 13 along portions P1, Q1 of respective paths P, Q; and walls 95 have respective sloping lateral edges 96, with which traction members 50 cooperate as of the end of portions Pl, Q1, i. e. before the maximum gripping pressure is applied.

Along portions P2, Q2 of respective paths P, Q, jaws 12 and 13 are gripped firmly against tube 3; and heating member 29 is powered to seal the two superimposed portions of packaging material defining band 44.

The following is a detailed description of the way in which traction members 50 are controlled by cam assembly 68 and relative control assembly 69.

As jaw 12 travels along portion P1 of path P, cam follower roller 63 cooperates with fixed top cam 71, which first moves it from the rest position by means of portion 90, and then maintains it in an intermediate position by means of portion 75. The rotation of lever 61 caused by the movement of roller 63 rotates pin 52 of lever 61, and produces an equal opposite rotation of the other pin 52, to which motion is transmitted by the

articulated inverted parallelogram system defined by arm 64, rod 65 and rod 66.

The rotation of pins 52 moves tabs 51 of traction members 50 towards tube 3.

When cam follower roller 63 reaches the up-ramp portion 78 of movable cam 73, lever 61 is gradually rotated further, so that, as stated above, tabs 51 of traction members 50 are moved further towards tube 3, and at this stage interact with edges 96 of walls 95 to "pull"tube 3 downwards. This takes place after sealing the band 44 of tube 3 gripped between heating member 29 and pressure bar 32 of jaws 12 and 13.

The extent of the action performed by tabs 51 depends on the position of movable cam 73, which is controlled by control device 69 governed by central control unit 91.

Central control unit 91 determines whether signal S from optical sensor 92-indicating the presence of a bar code 5-is generated within a predetermined time window, depending on an internal clock of central control unit 91.

If it is-meaning decorations 4 on the packaging material are positioned correctly-the configuration of cam 73 remains unchanged.

Conversely, if the instant in which bar code 5 is detected lags or leads with respect to the theoretic time window, central control unit 91 moves movable cam 73 towards or, respectively, away from tube 3, thus

increasing or reducing the travel of tabs 51, and the pull and folding action exerted by tabs 51 on tube 3.

Once the action of tabs 51 is completed, the following jaws 12 and 13 seal the upstream band 44 of tube 3, thus completing the formation of a container portion 45 with the aid of volume control devices 33.

On leaving movable cam 73, cam follower roller 63 travels along the profile of fixed cam 74, portion 84 of which restores roller 63 to the intermediate position (Figure 7) and rotates traction members 50 into the first limit position, thus moving tabs 51 away from tube 3.

At this stage, half-shells 34 of jaws 12 and 13 begin opening, and, when cam follower roller 63 reaches up-ramp portion 85, traction members 50 are again rotated into the second limit position.

This rotation of traction members 50 folds the packaging material of tube 3 substantially completely towards the bottom sealing band 44 of the newly formed package 2, and flattens relative walls 95 substantially completely.

Along portion 86 of fixed cam 74, cam follower roller 63 is restored to a position corresponding to the rest configuration of mechanism 60, thus moving tabs 51 away from tube 3.

The profile of fixed bottom cam 72 ensures cam follower roller 63 is maintained in this position until jaw 12 finishes interacting with the packaging material.

Though control is described with reference to one

jaw 12, jaws 12 of conveyor 10 obviously all interact successively with cam assembly 68, so that each is controlled to exert more or less pull on tube 3, and the position of cam 73 is adjusted with time, and by closed- loop control, to ensure decorations 4 are centred correctly on packages 2.

The advantages of the forming unit 1 and method according to the teachings of the present invention will be clear from the foregoing description.

In particular, by performing an additional substantially complete movement of relative traction members 50 after each package 2 is sealed, in addition to the movement performed to correct feed of tube 3 along path A, walls 95 of packages 2 coming off unit 1 can be folded perfectly, while at the same time still using traction members 50 to register the position of decorations 4 on respective packages 2.

The additional movement of traction members 50 provides for weakening the packaging material in the fold area of top walls 95 of packages 2.

The above additional operation only affects the package 2 with which traction members 50 are currently interacting, and not the next package 2, which is completely enclosed by the upstream jaws 12, 13 and relative half-shells 34.

Clearly, changes may be made to unit 1 as described herein without, however, departing from the scope of the accompanying Claims.

In particular, unit 1 may be of the type featuring two pairs of jaws acting cyclically and alternately on tube 3.