BACKGROUND ART As is known, many pourable food products, such as fruit juice, 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 fibrous material, e. g. paper, 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; the web of packaging material is sterilized on the packaging machine itself, e. g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed, e. g. vapourized by heating, from the surfaces of the packaging material; and the web of packaging material so sterilized is kept in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.

The tube is filled with the sterilized or sterile- processed food product, and is sealed and cut along equally spaced transverse sections to form pillow packs, which are then folded mechanically to form the finished, e. g. substantially parallelepiped-shaped, packages.

Alternatively, the packaging material may be cut into blanks, which are folded on forming spindles into packages, which are then filled with the food product and sealed. One example of the this type of package is the so-called"gable-top"package known by the trade name Tetra Rex (registered trademark).

Once formed, packages of the above type may undergo further operations, such as application of a closable opening device.

The most commonly marketed opening devices comprise a frame defining an opening and fitted about a rupturable or removable portion on the top wall of the package; and a cap hinged or screwed to the frame, and which is removable to open the package. Alternatively, other, e. g. slidable, opening devices are also known to be used.

The rupturable portion of the package may be defined, for example, by a so-called"prelaminated"hole, i. e. a hole formed in the fibrous layer of the packaging material before it is covered with the barrier layer, which thus remains whole and closes the hole to ensure airtight, aseptic sealing, while at the same time being pierced easily.

The opening devices described are normally heat sealed or glued directly to the packages by applicator units, which also perform a number of preliminary steps, such as localized heating or application of adhesive.

EP-A-1 228 967, for example, describes an applicator unit substantially comprising a continuously-rotating carousel conveyor for conveying the packages from a loading station to an unloading station via a number of work stations and paths comprising, in particular, a feed station for feeding the opening the opening devices onto the carousel conveyor, and where the opening devices are picked up by respective grippers fitted to the carousel conveyor itself; a number of processing stations for heating the opening devices ; and an application station for applying the opening devices to respective packages.

In known applicator units of the type briefly described above, an opening device may fail to be supplied to the feed station or to be picked up by the relative gripper. So, to prevent overheating of the empty gripper exposed directly to the heaters in the absence of the opening device, known units are provided with a sensor for detecting the presence of the opening devices ; and deflecting devices for intercepting the heat produced by the heaters in response to a sensor-generated signal indicating a missing opening'device.

A major drawback resulting from failure to apply the opening device to a package lies in the package, filled with the product and of considerable value by being at the end of the production cycle, having to be rejected.

DISCLOSURE OF INVENTION It is an object of the present invention to provide a unit for applying opening devices to packages of pourable food products, designed to eliminate the aforementioned drawbacks.

According to the present invention, there is provided an applicator unit as claimed in Claim 1.

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 schematic plan view of a unit, in accordance with the present invention, for applying opening devices to packages of pourable food products ;

Figure 2 shows a section along line 11-II of a valve of the Figure 1 unit ; Figure 3 shows a section along line III-III in Figure 2 of the valve in the open position ; Figure 4 shows a section along line III-III in Figure 2 of the valve in the closed position; Figure 5 shows a larger-scale schematic plan view of a detail of the Figure 1 unit.

BEST MODE FOR CARRYING OUT THE INVENTION Number 1 in Figure l indicates as a whole a unit for applying. opening devices. 2 to packages 3 of pourable food products.

Packages 3 are produced on a packaging unit (not shown) from a web of sheet packaging material comprising a layer of paper material covered on both sides with layers of heat-seal plastic material, e. g. polyethylene; and a layer of barrier material, such as aluminium, located inwards with respect to the layer of paper material, and in turn covered internally by another layer of plastic material.

Each package 3, which is parallelepiped-shaped in the example shown, has, on a top wall 4, a rupturable portion 5 conveniently defined by a so-called "prelaminated"hole, i. e. a hole formed in the fibrous layer of the packaging material before the fibrous layer is covered with the barrier layer, which closes the hole to ensure airtight, aseptic sealing, while at the same time being easily rupturable.

Opening devices 2 are made of thermoplastic material, and each comprise in known manner a frame 6, which is heat sealed about rupturable portion 5 on wall 4 of a respective package 3, and defines a pour opening (not shown); and a cap 7 or cover screwed or hinged to the frame to close said opening. Opening devices 2 conveniently comprise known means, not shown, for piercing or removing rupturable portion 5 of package 3 to unseal the package.

Unit 1. comprises a : first conveying device defined by a linear step conveyor 8*for feeding a succession of packages 3 along a preferably straight path PI ; a second linear step conveyor 9 for feeding a succession of opening devices 2 along a straight path Pr parallel to and in the opposite direction to path PI in the example shown; and a step-operated carousel conveyor 10, which rotates about a vertical axis A, has a number of grippers 11 for gripping opening devices 2, and feeds opening devices 2 from a pickup station 12 coincident with one of the stop stations of second conveyor 9, to an application station 13 for applying opening devices 2 to respective packages 3, and which is coincident with one of the stop stations of first conveyor 8.

More specifically, carousel conveyor 10 feeds opening devices 2 along a circular path Pc through a number of intermediate processing stations 14,15, 16, where opening devices 2 are stopped and heated to partly melt the material. More specifically, stations 14 and 15

have respective hot-air heating devices 17,18 for generating and directing respective hot-air jets underneath opening devices 2 at respective stations 14, 15; and station 16 has a hydrogen burner 19, which generates a microflame for locally melting the thermoplastic material of opening device 2. Two electrodes 20 are also provided close to station 16 to ignite the microflame.

Second conveyor 9 and carousel conveyor 10 together define a ; second conveying device 21 for feeding opening devicesg2 to applicationtstation 13 along a mixed second path P2 defined by paths Pr and Pc.

First conveyor 8 comprises a conveyor belt 22 defining a continuously-moving supporting surface for packages 3 ; and lateral belt feed devices 23 cooperating with respective opposite sides of packages 3. More specifically, the two feed devices 23 are step-operated, are symmetrical with respect to a vertical plane M containing path PI, and are fitted with respective numbers of vertical feed bars 24 equally spaced by a distance d defining the spacing of packages 3 on first conveyor 8.

Conveyor 8 also comprises a known input synchronizing device 25 comprising two lateral brake belts 26 located on opposite sides of conveyor belt 22 and symmetrical with respect to plane M. Belts 26 are controlled by a motor 27, and interact with the incoming packages 3 fed randomly along conveyor belt 22 to arrest

them when motor 27 is off, and to release them one by one along path PI when motor 27 is turned on.

Conveyor 8 also comprises a clamping device 2S defined by two step-operated belts 29 synchronized with feed devices 23 and cooperating frictionally with respective sides of packages 3 as of a station 30 of conveyor 8 downstream from a pickup station 31 where the packages are picked up by feed devices 23, as described in detail later on.

Heating devices 17, 18 each comprise an electric . heater. 32 generating. hot air at a. given temperature, e. g.

650°, in known manner; a nozzle 33 facing respective processing station 14, 15 of carousel conveyor 10 ; and a two-position, three-way rotary valve 34 interposed between heater 32 and nozzle 33 to connect heater 32 selectively to the nozzle and an exhaust.

Each rotary valve 34 (Figures 2 to 4) comprises a casing 35 defining a cylindrical inner chamber 36; a rotary slide 37 defined by a rod 38 and by a head 39 rotating in airtight manner inside chamber 36; and a rotary pneumatic actuator 40 for activating slide 37.

Casing 35 has two coaxial radial openings 41,42 connected to heater 32 and nozzle 33 respectively; and an axial exhaust opening 43 opposite pneumatic actuator 40 and communicating with the outside.

Head 39 of slide 37 comprises a diametrical through hole 44 alignable with openings 41,42 in casing 35, and a lateral milled portion 45 facing in a direction

perpendicular to the axis of hole 44, and is movable by pneumatic actuator 40 between an open position wherein hole 44 is coaxial with openings 41,42 and so connects heater 32 to nozzle 33, and an exhaust position wherein milled portion 45 connects opening 41 to exhaust opening 43, and opening 42 is closed hermetically by head 39.

Pneumatic actuator 40 is conveniently detached from casing 35 of valve 34 by a number of spacers 46 and a finned body 47 in series with spacers 46, to minimize heat.. transmission from chamber 36 to pneumatic actuator 40.... For the same reason, rod 38 of rotary slide 37 is connected to an output member 48 of pneumatic actuator 40 by a prismatic joint 49 preventing direct contact between output member 48 and rod 38.

Burner 19 (Figure 5) is fitted to a support 50 hinged to a fixed structure of unit 1 about a vertical axis B, and which is movable, under control of a pneumatic cylinder 51, between a first position wherein burner 19 is located beneath gripper 11 at station 16, and a second position wherein burner 19 is far enough away for the microflame to have no harmful effect on gripper 11, and wherein the two electrodes 20 are operated when necessary to ignite the microflame.

Finally, unit 1 is equipped with a control system 52 comprising a sensor 53 for determining the presence of an opening device 2 at a given station along conveyor 9 ; a sensor 54 at pickup station 12, to determine opening devices 2 are actually picked up by respective grippers

11 ; and a number of solenoid valves 55, 56, 57 connected to a compressed-air source 58, and which respectively control pneumatic actuators 40 at stations 14 and 15 and pneumatic cylinder 51, to control the position of rotary valves 34 and burner 19. Control system 52 also comprises a control unit 59, which receives signals from sensors 53,54, and generates control signals for controlling solenoid valves 55, 56, 57 and motor 27.

Sensor 53 determines the presence of an opening device 2 at a station 60, of second conveying device 21 of conveyor 9,, located upstream from application station 13 by a number N2 of steps, measured along path P2 of opening devices 2, at least equal to, and preferably greater than, the number N1 of steps, measured along path PI of packages 3, between the output of synchronizing device 25 and application station 13.

Two technical requirements determine the number N1 of steps.

Firstly, a definite position of packages 3 with respect to feed devices 23 must be ensured, in which each package contacts and is fed forward by two bars 24, and is clamped in this position by belts 29. This position calls for at least the two stations 30,31.

Secondly, the top wall 4 of each package 3 must be preheated by a heater 61 located over at least two stations 62, 63 downstream from station 30 and upstream from application station 13.

In the example shown, in which N1 equals four,

station 60 is conveniently located along conveyor 9 one step upstream from pickup station 12, i. e. a total of five steps (N2 =5) upstream from application station 13 along path P2.

Operation of unit 1 will be described with reference to the processing cycle of one package 3 and relative opening device 2, the operations described obviously being repeated cyclically at each step.

Opening device 2 is fed in steps along path P2 defined partly by path Pr or conveyor 9, and partly by .-path Pc on carousel'conveyor 10'.

At station 60, sensor 53 performs the presence detecting function at a cycle step conveniently indicated "step 0".

If present, the opening device 2 is located at step 1 at the next station along conveyor 9 defining pickup station 12, is picked up by a gripper 11, and sensor 54 determines the actual presence of opening device 2 on relative gripper 11.

At the same time, control unit 59 starts motor 27 of synchronizing device 25 to release and feed the package 3 corresponding to the detected opening device 2 along belt 22 to feed devices 23. The package is released within a time window calculated so that, given the travelling speed of belt 22, the package is positioned between two successive pairs of bars 24 at station 31.

At step 2, opening device 2 is fed by carousel conveyor 10 to processing station 14, where pneumatic

actuator 40 keeps valve 34 in the open position, so that nozzle 33 is supplied with hot air generated by heater 32.

At the same time, feed devices 23 move forward one step. The difference between the travelling speed of feed devices 23 and that of belt 22 must be such as to ensure an incoming pair of bars 24 contacts and pushes package 3 to station 30, where belts 29 clamp the package with respect to feed devices 23 to maintain the definite position defined by contact with bars 24.

At step 3, opening {device 2 is fed to processing station 15, where pneumatic actuator 40 keeps valve 34 in the open position, so that nozzle 33 is supplied with hot air generated by heater 32; and, at the same time, package 3 is fed to station 62 beneath heater 61.

At step 4, opening device 2 is fed to processing station 16, where pneumatic cylinder 51 keeps support 50 in the first position with burner 19 beneath opening device 2 carried by gripper 11 ; and, at the same time, package 3 is fed to station 63 beneath heater 61.

At step 5, opening device 2 and package 3 are both fed to application station 13, where opening device 2 is applied to package 3.

Package 3 then continues along conveyor 8 to an output (not shown) of unit 1.

The cycle described above applies to the normal operating condition in which opening device 2 is supplied and picked up correctly.

Conversely, in the event no opening device 2 is detected by sensor 53 at step 0, control unit 59 diables motor 27 at step 1, so that package 3 is not fed along conveyor 8, and, at step 5, gripper 11 is empty and there is no corresponding package 3.

In the event no opening device 2 is detected by sensor 54 at step 1-that is, the opening device 2 is missing on conveyor 9 or has not been picked up by gripper 11-control unit 59 performs the following operations : at step, 2, solenoid valve 55''is switched, so that valve 34 at first processing station 14 switches to exhaust to prevent hot air from being directed onto the empty gripper 11; at step 3, solenoid valve 56 is switched, so that valve 34 at second processing station 15 switches to exhaust to prevent hot air from being directed onto the empty gripper 11 ; at step 4, solenoid valve 57 is switched, so that pneumatic cylinder 51 at processing station 16 moves support 50 into the second position to prevent exposure of the empty gripper 11 to the microflame produced by burner 19.

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

First and foremost is the economic advantage of no longer rejecting packages 3 in the event of failure by conveyor 9 to supply respective opening devices 2.

Secondly, by detecting the presence of opening devices at station 12, grippers 11 are protected against heaters 32 and burner 19, thus increasing their working life and so reducing the maintenance cost of unit 1.

Clearly, changes may be made to unit 1 as described and illustrated herein without, however, departing from the scope of the present invention as defined in the accompanying Claims.

In particular, path P2 may be of any shape, e. g. totally linear or totally circular ; and second conveying device 21 may ! be of any type'. In particular, conveyor 9 or carousel conveyor 10 or both may be replaced by continuous conveyors or even robotized arms.

Similarly, path PI and conveyor 8 may also be other than as described.

Intermediate processing stations 14,15, 16 may differ in number and function, e. g. may be replaced by a gluing station, in the event opening devices 2 are applied to packages 3 using adhesive.

Sensor 53 may be located anywhere upstream from application station 13, provided the opening device detecting function is performed sufficiently in advance to prevent package 3 from being fed to application station 13.

Sensor 54 may also be eliminated, if there is no need to determine pickup by grippers 11 ; in which case, control unit 59 may also use the sensor 53 signal to control solenoid valves 55, 56, 57.