Machine for packaging pourable food products

Abstract: A machine (1) for packaging pourable food products in packages formed from a continuous tube (2) of packaging material (4) having crease lines (13) for assisting folding of the packaging material, and wherein a control device (60) for controlling feed of the tube (2) has an optical sensor (62) for detecting the position of prelaminated holes (5) formed on the material (4) and in register with the crease lines (13), and a control unit (63) for controlling actuators (7, 56, 25) for correcting the longitudinal and angular position of the tube (2) in response to respective longitudinal and transverse position errors (E 1 , E 2 ) of the holes (5) detected by the optical sensor (62).

Description: The present invention relates to a machine for packaging pourable food products. Machines for packaging pourable food products, such as fruit juice, wine, tomato sauce, pasteurized or long-storage (UHT) milk, etc., are known in which the packages are formed from a continuous tube of packaging material defined by a longitudinally sealed web. 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 barrier material defined, for example, by an aluminium film, which is superimposed on a layer of heat-seal plastic material and in turn covered with another layer of heat-seal plastic material eventually defining the inner face of the package contacting the food product. To produce aseptic packages, the web of packaging material is unwound off a reel and fed through an aseptic chamber in which it is sterilized, e.g. by applying a sterilizing agent such as hydrogen peroxide, which is later vaporized by heating and/or by subjecting the packaging material to radiation of appropriate wavelength and intensity. The sterilized web is then folded into a cylinder and sealed longitudinally to form, in known manner, a continuous, vertical, longitudinally sealed tube. The tube of packaging material, in other words, forms an extension of the aseptic chamber, and is filled continuously with the pourable food product and then fed to a forming and (transverse) sealing unit for forming the individual packages and on which pairs of jaws grip and seal the tube transversely into pillow packs. The pillow packs are then separated by cutting the sealing portion between the packs, and are fed to a final folding station where they are folded mechanically into the shape of the finished packages. The forming process involves folding the packaging material along crease lines formed beforehand as part of the material manufacturing process. The material manufacturing process typically comprises laminating steps to produce the various layers of which the material is formed; a number of printing steps to print graphics or designs periodically recurring along the material with a pitch equal to the length of material used to produce each package; and the above-mentioned creasing step performed either on the finished material or only on a subset of material layers comprising at least the paper layer. Holes are also known to be formed in the paper layer before it is covered with a continuous layer of barrier material to form so-called "prelaminated" holes closed by the barrier material which ensures hermetic, aseptic sealing while at the same time being easily pierced. The holes in the paper layer may conveniently be formed using the same tool as for the crease lines, in which case, the barrier material is laminated afterwards. Packaging materials with prelaminated holes are used for aseptic packages with straws or opening devices, e.g. of the type comprising a hinged lid or screw cap. The various operations in the packaging material manufacturing process are performed using, as a register mark, an optical register code printed on the material in the course of the first printing step. The same code is normally also used on the forming machine to control feed of the material through the various work stations. More specifically, as is known, a so-called "design correction" device acts on the packages being formed to variably "draw" the material in the feed direction and ensure that the mechanical forming operations are performed in register with the design on the packages (see e.g. EP 25 235). Material manufacturing tolerances, however, may result in position errors of the optical register code with respect to the crease lines, so that frequent manual adjustment of the design correction device (based on the optical register code) is required to prevent the forming members from interacting with the material incorrectly with respect to the crease lines. On known packaging machines, the angular position of the tube of packaging material may vary, in use, with respect to the desired angular position, on account of the lateral edges of the web not being perfectly straight, and the effect produced by the pairs of jaws successively striking the tube. As this may have negative effects on the quality of the longitudinal and transverse seals, and on the accuracy with which the packages are formed, known machines are provided with devices for manually adjusting the angular position of the tube (see e.g. EP 903 292). Such devices, however, are relatively time-consuming, and may involve shutting down the machine with consequent loss of production. Systems have also been proposed for automatically adjusting the angular position of the tube of packaging material, but call for the use of a dedicated sensor to determine the position of the longitudinal seal. It is an object of the present invention to provide a machine for packaging pourable food products, designed to solve the aforementioned problems typically associated with known machines. According to the present invention, there is provided a machine for packaging pourable food products in packages formed from a continuous web of packaging material, said machine comprising a longitudinal folding unit for longitudinally folding said web to form a continuous tube; a forming unit having at least two pairs of jaws interacting cyclically with said tube to seal the tube along equally spaced transverse bands; and a control device for controlling the feed of said tube, and in turn comprising means for correcting the longitudinal position of said tube, and means for correcting the angular position of said tube; said packaging material comprising a design, and a series of crease lines to assist folding of the packaging material on said forming unit; characterized in that said control device for controlling the feed of said tube comprises detecting means for detecting the position of optically detectable elements formed on said material and in register with said crease lines; and means for controlling said means for correcting the longitudinal position of said tube and said means for correcting the angular position of said tube in response to respective longitudinal and transverse position errors of said optically detectable elements detected by said detecting means. Controlling the position of the tube of packaging material on the basis of a position reference in register with the crease lines prevents any manufacturing tolerances, which might result in the crease lines not being perfectly in register with the design, from impairing sealing quality and the forming process. Successive operations on the package employing the edges of the package as a reference, as when applying opening devices over the holes, are also performed correctly, by formation of the package being controlled on the basis of a position reference in register with the crease lines. The present invention therefore provides for improving finished package quality and reducing manual adjustment of the machine. In a preferred embodiment of the present invention, the position of the prelaminated holes in the material is used as an element for detecting the position of the tube of packaging material; the position of the holes is compared with a memorized reference position; and any longitudinal and transverse errors are used to correct the feed of the material and the angular position of the tube respectively. Using the prelaminated holes as position detecting elements enables both the longitudinal and angular position of the tube to be controlled using one sensor. 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 front view of a packaging machine featuring a packaging material feed adjusting device in accordance with the present invention; Figure 2 shows a view in perspective of a station for supplying and folding the packaging material; Figure 3 shows a schematic side view of a forming station on the Figure 1 machine; Figure 4 shows a diagram of the packaging material feed adjusting device according to the invention; Figure 5 shows a portion of packaging material. With reference to Figures 1 to 3, number 1 indicates as a whole a packaging machine for producing packages of a pourable food product, such as pasteurized or UHT milk, fruit juice, wine, etc. In particular, machine 1 provides for producing aseptic sealed packages of a pourable food product from a tube 2 of heat-seal packaging material 4, in turn formed by longitudinally folding and sealing a web 3 of packaging material. Material 4 (Figure 5) conveniently comprises a layer 4a of paper material; and a layer 4b of barrier material defined, for example, by a sheet of aluminium. Layers 4a and 4b are fixed to each other by an intermediate layer of thermoplastic material (not shown), e.g. polyethylene, and are covered on opposite faces with further layers of polyethylene (not shown). Layer 4a of paper material comprises a succession of holes 5 formed prior to laminating layer 4b; and a series of crease lines 13 (Figure 4) for assisting folding of the material when forming the packages, and which periodically recur with a pitch P equal to the distance between the holes and to the length of the portion of web 3 required to produce each package. Holes 5 and lines 13 are conveniently formed on the same fixture so that they are perfectly in register with each other. Layer 4b is whole at holes 5 to ensure hermetic, aseptic sealing of the package until it is opened; and pull-off or other types of opening devices (not shown) are later fitted over holes 5. Material 4 also comprises a design 14 defined by a succession of graphics periodically recurring with pitch P and each comprising an optical register code 15. Design 14 conveniently also comprises a white area 15a surrounding each hole 5 (Figure 5). Web 3 of packaging material 4 is unwound off a reel (not shown) and fed by known guide roller devices (not shown) through a known sterilizing unit (not shown) to a top aseptic chamber 6 of machine 1, which communicates with the sterilizing unit and through which web 3 is fed along a horizontal path P1. Web 3 is then diverted downwards by a roller 7 - forming part of a system of rollers, one of which is powered - and is fed downwards along a vertical path P2 extending inside a vertical chamber or tower 8. Inside tower 8, web 3 is folded longitudinally into a cylinder to form tube 2, which has a longitudinal axis A parallel to path P2 and is sealed longitudinally by a sealing device 10 and by means of a known heat-seal strip not described in detail. Tube 2 is filled continuously with the food product by means of a known filling device 11 (not described in detail), and is fed to a known forming unit 12 described below only as regards the parts pertinent to the present invention. More specifically, machine 1 comprises a folding unit 9 for longitudinally folding web 3 to form tube 2, and which is defined by a number of known folding assemblies 16, 17, 18 located along path P2 inside tower 8 and interacting with web 3 to fold it gradually into a cylinder and overlap the opposite lateral portions of web 3 (Figures 1 and 2) to form the tube of packaging material. Assemblies 16, 17, 18 comprise respective numbers of substantially cylindrical folding rollers 21, 22, 23 having respective axes perpendicular to axis A, and defining polygons surrounding axis A so that the respective lateral surfaces define successive compulsory passages for web 3 of packaging material being folded. As it is fed through the passages, the web passes from an open C shape defined by folding rollers 21 of folding assembly 16, to a substantially circular shape defined by folding rollers 23 of folding assembly 18. The axes of rollers 21, 23 of folding assemblies 16, 18 are fixed, whereas folding rollers 22 of assembly 17 are fitted to a C-shaped supporting plate 24 connected to the structure of machine 1 so as to be angularly adjustable about axis A to adjust the angular position of tube 2 being formed with respect to axis A. The rotation of plate 24 is controlled by an actuator 25 via a transmission, e.g. a screw-nut screw, mechanism 26. The speed at which web 3 is fed through folding assemblies 16, 17, 18 is determined by the movement of assemblies 35, 35', and is influenced by an electric motor 27 powering folding roller 7. Once sealed longitudinally, tube 2 is fed to forming unit 12. Unit 12 comprises a supporting structure 33 defining two vertical guides 44 arranged symmetrically with respect to a longitudinal vertical mid-plane α of the unit through axis A, and the respective axes of which lie in a transverse vertical mid-plane τ of unit 12. Axis A therefore defines the intersection of planes α and τ. Unit 12 comprises, in known manner, two forming assemblies 35, 35' movable vertically along respective guides 44 and interacting alternately with tube 2 of packaging material to grip and heat seal cross sections of the tube. Since assemblies 35, 35' are symmetrical with respect to plane α, only one (assembly 35) is shown in detail in Figure 3 and described below. In the accompanying drawings, the corresponding parts of assemblies 35, 35' are indicated using the same reference numbers. With reference to Figures 1 and 3, assembly 35 substantially comprises a slide 36 movable along respective guide 44; and two jaws 37 hinged at the bottom to slide 36, about respective horizontal axes 38 parallel to and symmetrical with respect to plane τ, so as to open and close substantially "bookfashion". More specifically, each jaw 37 comprises a main control body 39, which is substantially in the form of an appropriately ribbed quadrangular plate (Figures 1 and 3), extends along a work plane β of jaw 37 containing respective axis 38, is hinged close to its bottom side to slide 36, and comprises a respective control arm 40 projecting from a face of body 39 facing away from plane β. Jaws 37 also comprise respective supporting arms 41, which are fitted to the top ends of respective bodies 39 of respective jaws 37, and project towards and beyond plane α, in a direction parallel to respective axes 38 and substantially along respective work planes β, so as to be located on opposite sides of tube 2. The projecting portions of arms 41 are fitted with respective bar-shaped sealing elements 42, 43 (Figure 3) which interact with tube 2, and which may be defined, for example, by an inductor for generating current in the aluminium layer of the packaging material and melting the thermoplastic layer as a consequence of the Joule effect, and by a mating pad against which to grip tube 2 to the required pressure. The reciprocating movement of slides 36 and the opening/closing movement of jaws 37 are controlled in known manner (not described) by pairs of vertical rods (not shown) in turn controlled by rotary cams or servomotors. Jaws 37 are movable between a closed position in which respective sealing elements 42, 43 grip tube 2, and a fully-open position. At the transverse sealing step, tube 2 is heat sealed along equally spaced transverse bands 45 (Figure 4). Over respective sealing elements 42, 43, arms 41 of jaws 37 support respective package volume control tabs 46 having a C-shaped cross section open at the front, and which cooperate with each other, after the transverse sealing operation performed by elements 42, 43, to define a cavity of predetermined shape and volume enclosing and forming tube 2 into a rectangular-section shape. The above forming step (Figure 4) produces "pillow" packs 47, each comprising a main portion 48 of the same shape and volume as the finished package; and transition portions 49 connecting main portion 48 to respective adjacent sealing bands 45, and defined laterally by substantially triangular faces 50. One of jaws 37 comprises, in known manner, two folding tabs 54 for controlling, together with folding roller 7, the longitudinal feed of tube 2 through forming unit 12. Folding tabs 54 (Figures 3 and 4) are located on either side of tube 2, are symmetrical with respect to axis A and adjacent to tube 2, rotate about respective axes perpendicular to plane β, and are rotated in opposite directions by a known design correction device 51 - active at the forming step - so as to act on lateral faces 50 of transition portions 49 of the pillow packs and exert variable pull on tube 2. Device 51 comprises, for example, a variable-geometry or variable-position cam 52, shown purely schematically in Figure 4, which interacts with a cam follower 53 carried by jaw 37 and connected to tabs 54 by a transmission mechanism 55 also shown purely schematically. Examples of such a control device are illustrated in Italian Patent Application n. MI97A-002473 and in European Patent Application n. 99830715.1 filed by the present Applicant. The travel of tabs 54, and therefore the amount of pull exerted on tube 2, is adjustable, as described in detail later on, by means of an actuator 56 acting, for example, on the position of cam 52. Actuator 25 controlling tube folding assembly 17, electric motor 27 powering folding roller 7, and actuators 56 of design correction devices 51 of respective assemblies 35, 35' form part of a device 60 for controlling the feed of tube 2 of packaging material. In addition, device 60 also comprises a conventional first optical sensor 61 for reading the optical register code 15 printed on material 4; a second optical sensor 62 for detecting the position of holes 5; and a control unit 63 connected at the input to sensors 61, 62, and at the output to actuators 25, 56 and to motor 27. The second optical sensor 62 is conveniently defined by a video camera, e.g. a CCD type, which "reads" a portion of material 4 at holes 5. To avoid acquiring and processing an excessive amount of data, first sensor 61 is used to generate an enabling signal I 1 , which changes state in response to detection of a code 15 and is supplied to control unit 63 to read-enable the second optical sensor. Sensor 62 is thus only read-enabled at each hole 5 or at one of every N number of holes 5, and supplies control unit 63 with signals I 2 indicating the position of holes 5 and relative, for example, to a conventionally coded pixel matrix. Control unit 63 compares the position of the detected hole 5 with a memorized reference position (Figure 5) and calculates a longitudinal position error E 1 of tube 2, and a transverse position error E 2 of hole 5, obviously correlated to the twist angle of tube 2. Control unit 63 generates a signal O 1 for controlling electric motor 27; signals 02 (identical) for controlling actuators 56; and a signal O 3 for controlling actuator 25. Signals O 1 and O 2 are correlated in conventional manner with value E 1 , and signal O 3 with value E 2 . In actual use, the speed at which material 4 is supplied to folding assemblies 16, 17, 18 and to forming unit 12 is determined by motor 27 controlled by control unit 63. Being known and partly deducible from the above description, operation of assemblies 16, 17, 18 and forming unit 12 is not described in detail. If the longitudinal position of tube 2 is correct, i.e. if the absolute value of E 1 is below a predetermined threshold value, the control unit maintains a constant speed of motor 27. Conversely, in the presence of an error E 1 , the supply speed of material 4 is corrected by control unit 63 appropriately modulating signal O 1 . If the resulting correction is not sufficient, in addition to motor 27, control unit 63 also acts on design correction device 51 by appropriately adjusting, by means of signal O 2 , the amount of pull exerted by folding tabs 54. According to the present invention, the above controls, in themselves known, are performed on the basis of position errors of holes 5 - which, as stated, are in register with crease lines 13 - and not on the basis of optical code 15 in register with and forming part of design 14. In a preferred embodiment of the present invention, signal I 1 of first sensor 61 is only used to generate a "read window" in which second sensor 62 actually reads the position of material 4 based on the position of a hole 5 at a given instant, and supplies control unit 63 with a signal I 2 indicating the matrix of pixels detected. The white area 15a surrounding each hole 5 simplifies the reading. Another important characteristic of the present invention is that signal I 2 is also used to calculate the transverse position error of the hole, and so correct twisting of tube 2 by means of folding assembly 17. More specifically, in response to a transverse position error E 2 , control unit 63 commands actuator 25, by means of signal O 3 , to rotate folding assembly 17 in one direction or the other depending on the error sign. This control is also performed on the basis of the position of holes 5 as opposed to optical code 15. Clearly, changes may be made to machine 1 as described herein without, however, departing from the scope of the invention. In particular, second sensor 62 may be replaced by any type of sensor, e.g. defined by a linear succession of photosensitive elements extending crosswise to the feed direction of tube 2, to reconstruct the position of holes 5 by scanning the area of the hole as the material is fed forward, as opposed to picking up an instantaneous image. Moreover, different position references may be used, providing they are in register with crease lines 13.

Claims: A machine (1) for packaging pourable food products in packages formed from a continuous web (3) of packaging material (4), said machine (1) comprising a longitudinal folding unit (9) for longitudinally folding said web (3) to form a continuous tube (2); a forming unit (12) having at least two pairs of jaws (37) interacting cyclically with said tube (2) to seal the tube along equally spaced transverse bands (45); and a control device (60) for controlling the feed of said tube (2), and in turn comprising means (7,27; 51) for correcting the longitudinal position of said tube (2), and means (17, 25) for correcting the angular position of said tube (2); said packaging material (4) comprising a design (14), and a series of crease lines (13) to assist folding of the packaging material on said forming unit (12); characterized in that said control device (60) for controlling the feed of said tube comprises detecting means (62) for detecting the position of optically detectable elements (5) formed on said material (4) and in register with said crease lines (13); and means (63) for controlling said means (7,27; 51) for correcting the longitudinal position of said tube and said means (17, 25) for correcting the angular position of said tube (2) in response to respective longitudinal and transverse position errors (E 1 , E 2 ) of said optically detectable elements (5) detected by said detecting means (62). A machine as claimed in Claim 1, characterized in that said optically detectable elements are prelaminated holes (5) in said material (4). A machine as claimed in Claim 1 or 2, characterized in that said means for correcting the longitudinal position of said tube comprise a powered roller (7) located upstream from said longitudinal folding unit (9). A machine as claimed in one of the foregoing Claims, characterized in that said means (51) for correcting the longitudinal position of said tube comprise two folding tabs (54) carried by one jaw (37) in each pair of jaws (37) and which interact with and subject said material (4) to a variable amount of pull. A machine as claimed in any one of the foregoing Claims, characterized in that said means for correcting the angular position of said tube (2) comprise at least one folding assembly (17) forming part of said longitudinal folding unit (9) and which rotates about a longitudinal feed axis (A) of said tube (2); and an actuator (25) controlled by said control device (60) to adjust the position of said folding assembly (17) about said axis (A). A machine as claimed in any one of the foregoing Claims, characterized by comprising a sensor (61) for detecting an optical register code (15) formed on said material (4) and in register with said design (14); said sensor (61) being connected to said control device (60) and generating a signal (I 1 ) for read-enabling said detecting means (62). A machine as claimed in any one of the foregoing Claims, characterized in that said detecting means comprise a video camera (62).

Inventors: BASSISSI FABIO, GALAVOTTI GIORGIO, PALTRINIERI ROBERTO, BASSISSI, FABIO, GALAVOTTI, GIORGIO, PALTRINIERI, ROBERTO
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 2000
Main classification: B65B41
IPC codes: B65B41, B65B9, G01B11, B65B57