Device for adjusting the transverse position of a strip of packaging material

Abstract: A device (1) for adjusting the transverse position of a strip (2) of packaging material on a packaging machine for producing packages containing a pourable food product, the device having a slide (12) movable crosswise with respect to the strip (2) and carrying a gripping member (14) for moving the strip transversely; and a system (3, 7, 8) for automatically adjusting the position of the slide (12) in response to signals generated by optical sensors (41, 42) for detecting respective limit positions of the strip (2).

Description: The present invention relates to a device for adjusting the transverse position of a strip of packaging material on 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 strip. The packaging material has a multilayer structure comprising a layer of paper material covered on both sides with layers of heat-seal 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 is 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 strip of packaging material is unwound off a reel and fed through an aseptic chamber, in which it is sterilized, for example, by applying a sterilizing agent, such as hydrogen peroxide, which is later evaporated by heating, and/or by subjecting the packaging material to radiation of an appropriate wavelength and intensity, and the sterilized strip is folded into a cylinder and sealed longitudinally to form, in known manner, a continuous vertical longitudinally sealed tube. In other words, the tube of packaging material forms an extension of the aseptic chamber, and is filled continuously with the pourable food product and then sent to a forming and (transverse) sealing unit for forming the individual packages and in which the tube is gripped between pairs of jaws to seal the tube transversely and form pillow packs, which are then separated by cutting the sealed portions between the packs. The pillow packs are then fed to a final folding station where they are folded mechanically into the finished shape. On known packaging machines of the type briefly described above, the strip of packaging material, before being folded into a tube, is fed along a path defined by pairs of cylindrical, powered or idle rollers extending across the full width of the strip, but which do not guide the strip transversely. The transverse position of the strip is defined by manually adjusted guide devices comprising a pair of rollers cooperating on opposite sides with a longitudinal portion, close to the edge, of the strip, and carried by a slide movable along a guide in a direction parallel to the strip feed plane and perpendicular to the strip feed direction. Any error in the transverse position of the strip - which may occur, for example, after splicing two reels or in the event the strip deviates laterally as opposed to being perfectly straight - may result in faulty packages. When a fault is detected, e.g. by inspecting the packages coming off the machine, the error is correctable by manually adjusting the guide device. The time taken, however, to stop the machine, make the manual adjustment and restart the machine results in a considerable loss in production, both in terms of downtime and the packages rejected. EP-A-0 307 125 discloses a device for adjusting the transverse position of a web of packaging material in a packaging machine having the features of the preamble of claim 1. In particular, the device includes a pair of laterally offset optical sensors detecting the position of one edge of the web and a control circuit for actuating a member controlling the lateral position of the web so as to maintain the edge of the web between the pair of sensors. Sensing the edge of the web may not be feasible or advisable in any situations, or may constitute a technical limitation. Therefore, there is a need in the field to provide an improved device which is free from this limitation. A further object of the present invention is to provide an improved device for adjusting the transverse position of a web of packaging material which is provided with holes adapted to receive opening devices, and particularly multilayered web packaging material for producing aseptic packages. These objects are achieved by a device according to claim 1. 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 device for adjusting the transverse position of a strip of packaging material in accordance with the present invention; Figures 2 and 3 show a front view and a view in perspective respectively of a detail in Figure 1; Figure 4 shows, schematically, a control system of the Figure 1 device; Figure 5 shows an operating block diagram of a control unit of the Figure 4 system. Number 1 in Figures 1 to 3 indicates as a whole a device for adjusting the transverse position of a strip of packaging material on a packaging machine (not shown) for producing packages containing a pourable food product, such as pasteurized or UHT milk, fruit juice, wine, etc. More specifically, the machine is designed to produce aseptic sealed packages, containing a pourable food product, from a tube of packaging material formed by longitudinally folding and sealing a strip 2 of heat-seal sheet packaging material. The material conveniently comprises a layer 4a of paper material, and a layer 4b of barrier material defined, for example, by a sheet of aluminium; and the above two layers are fixed to each other by an intermediate layer (not shown) of thermoplastic material, e.g. polyethylene, and are covered on opposite faces with further layers of polyethylene (not shown). Layer 4a of paper material conveniently comprises a succession of holes 5 formed prior to lamination, and at which layer 4b is whole, to enable subsequent application of pull-off or other types of opening devices (not shown), while at the same time ensuring the package remains whole and aseptic until opened. Holes 5 are located close to a longitudinal edge 6a of strip 2, and are equally spaced with a spacing p equal to the length of the portion of strip 2 required to produce each package. Strip 2 is unwound off a reel (not shown) and is fed through the machine along a path defined by numbers of pairs of drive or transmission rollers (not shown). Device 1 is assigned to a vertical portion of the feed path of strip 2; in Figure 1, π indicates the feed plane of strip 2, and A the (vertical) feed direction of the strip; and, in the example shown, strip 2 travels downwards in steps, with stops of, for example, 120 ms between successive steps. Device 1 substantially comprises a regulating and guide assembly 3 located close to a longitudinal edge 6b, opposite edge 6a, of strip 2; an assembly 7 for detecting the transverse position of the strip; and a control unit 8. More specifically, assembly 3 (Figures 2 and 3) comprises a supporting structure 10 fixed to the frame (not shown) of the machine; an electric step motor 11 fixed to structure 10; and a slide 12 controlled by motor 11 via a transmission mechanism 13, and which slides in a direction B lying in plane π and perpendicular to direction A. The slide carries a gripping member 14 - described in detail later on - for gripping in sliding manner and moving strip 2 in direction B. More specifically, motor 11 has an output shaft 15 having an axis parallel to direction B; and transmission mechanism 13 substantially comprises a screw 16 coaxial with and connected prismatically to the shaft, i.e. so as to be rotated by, but to slide axially and freely with respect to, shaft 15. Screw 16 and shaft 15 are connected, for example, by a radial pin 17 carried by a nonthreaded end 18 of the screw housed in sliding manner inside an axial cavity (not shown) of shaft 15; and the ends of pin 17 engage in sliding manner respective diametrically-opposite longitudinal slots 20 (only one shown in Figure 2) on shaft 15. Screw 16 is fitted through a guide member 22 fixed to structure 10, and is screwed through a nut screw 23 fixed to guide member 22, so that rotation of shaft 15, and hence of screw 16, results in axial displacement of the screw. The end 24 of screw 16 opposite end 18 is connected in angularly-free, axially-fixed manner to slide 12, e.g. by means of a thrust bearing 25, so that axial displacement of screw 16 is transmitted to slide 12 and by slide 12 to strip 2 via gripping member 14. Slide 12 is connected prismatically to guide member 22 by two lateral plates 26 fixed to the slide and sliding along opposite lateral faces of guide member 22. Gripping member 14 substantially comprises a supporting plate 27 hinged, close to its own bottom end, to slide 12 about an axis C perpendicular to directions A and B. The opposite end of the plate is fitted with an arm 28 supporting on the free end a fork-shaped guide shoe 29 having a substantially V-shaped section and cooperating, in use, with edge 6b of strip 2. Gripping member 14 is subjected to the elastic action of a low-stiffness spring 30 stretched between a fastening member 31 to structure 10, and an auxiliary arm 32 projecting transversely from plate 27. The elastic force exerted by spring 30 is low, and serves solely to hold shoe 29 in contact with strip 2 and so prevent in-service oscillation of member 14. Plate 27 supports two shafts 33 having axes parallel to each other, perpendicular to plate 27 and incident with respect to axis C, and which are fitted with respective idle rollers 34 rolling on opposite sides of strip 2. The distance between the axes of shafts 33 is conveniently adjustable to vary the contact pressure between rollers 34 and the material defining strip 2. In actual use, gripping member 14 is tilted forwards, as shown in Figure 2, in a position defined by a balance between the action of spring 30, the reaction of strip 2 on shoe 29, and the frictional force between the moving strip 2 and rollers 34. As said frictional force increases alongside an increase in the contact pressure between rollers 34 and strip 2, the inclination of gripping member 14 also increases accordingly. With reference to Figure 1, assembly 7 for detecting the transverse position of the strip comprises a supporting structure 40 fixed to the machine frame and fitted with two optical, e.g. optical-fiber, sensors 41, 42 (see enlarged detail), which are positioned facing the portion of strip 2 with holes 5, and are located at the point at which the holes are arrested as strip 2 is fed forward in steps. More specifically, sensors 41, 42 are separated, crosswise with respect to strip 2, by a distance d slightly less than the transverse dimension of holes 5, so as to "read" the holes close to respective opposite ends. Sensors 41, 42 generate respective signals s1, s2, which, appropriately amplified by respective amplifiers not shown, are supplied to control unit 8 (Figure 4). Signals s1, s2 assume different states, depending on whether the respective sensor 41, 42 is positioned facing the inner portion of the hole (i.e. layer 4b of aluminium material) or an outer edge of the hole (i.e. layer 4a of paper material), so that sensors 41, 42 are able to determine two transverse limit positions of strip 2, each defined by the switching of signal s1 or s2 when respective sensor 41 or 42 is positioned facing a respective margin of hole 5. Control unit 8 also receives input signals s3, s4 from a main machine control unit 43, e.g. a PLC type. More specifically, s3 relates to the operating state of the machine (e.g. s3=1 if the machine is operative, s3 = 0 if the machine is not operative); and s4 is a device 1 enabling signal generated by unit 43 in time with the other operations governed by unit 43, and conveniently varies impulsively from a low-value (s4=0) to a high-value (s4=1) whenever strip 2 is stopped with a hole 5 facing sensors 41, 42. Control unit 8 generates an output signal s5 for controlling electric motor 11. Figure 5 shows a block diagram of the program performed by control unit 8. From a start block 44, a first block 45 initializes a counter K, and is followed by an acquisition block 46, which reads the state of signals s3 and s4. Block 46 then goes on to a block 47, which determines whether the state of both signals s3, s4 indicates an enabling condition (e.g. s3=1 and s4=1). In the event of a negative response, block 47 goes back to block 46. In the event of a positive response, the program goes on to a block 48, which increases counter K, and from block 48 to a comparing block 49, which compares the counter value with a predetermined threshold value K 0 , e.g. 10. If K is other than K 0 , comparing block 49 goes back to acquisition block 46; conversely, if K equals K 0 , block 49 goes on to an acquisition block 50 to acquire signals s1 and s2 of sensors 41, 42. The next block 51 detects the state of signal s1. If it is high (sensor 41 inside hole 5), block 51 goes on to a block 52, which determines the state of signal s2. If this is also high (sensor 42 inside hole 5) - thus indicating the strip is positioned between the limit positions - block 52 goes on to an end-of-cycle block 53. Conversely, if block 51 detects a low-level signal s1 (sensor 41 outside hole 5, thus indicating the first limit position detected by sensor 41 has been exceeded), block 51 goes on to a control block 54, which operates electric motor 11 in such a direction (e.g. clockwise) as to move strip 2 towards the second limit position (rightwards in Figure 1). Similarly, if block 52 determines a low-level signal s2 (sensor 42 outside hole 5, thus indicating the second limit position detected by sensor 42 has been exceeded), block 52 goes on to a control block 55, which operates electric motor 11 in such a direction (e.g. anticlockwise) as to move strip 2 towards the first limit position (leftwards in Figure 1). Operation of device 1, which is already partly obvious from the foregoing description, is as follows. At each stop of strip 2, the main machine control unit 43 supplies a device 1 enabling signal s4. To avoid adjustment oscillation problems, as opposed to all of holes 5, device 1 reads and possibly corrects the position of the holes with a predetermined sampling frequency 1/K 0 (e.g. one hole every ten). If either limit position is found to be exceeded, the strip is moved in direction B towards the opposite limit position by operating motor 11 in the "screwing" or "unscrewing" direction of screw 16 inside nut screw 23; and the resulting displacement of slide 12 is transmitted to strip 2 substantially by shoe 29 in the "push" direction (rightwards in the drawings), and by rollers 34 in the "pull" direction (leftwards in the drawings). The advantages of device 1 according to the present invention will be clear from the foregoing description. In particular, the device provides for automatically adjusting the transverse position of the strip, thus avoiding machine stoppages, production losses or rejects. Moreover, device 1 is cheap and easy to produce, and involves no major alterations of known machines featuring manual adjustment devices. Clearly, changes may be made to device 1 without, however, departing from the scope of the accompanying Claims. For example, transmission mechanism 13 may be formed in any other way. In particular, as opposed to rotating screw 16, electric motor 11 may rotate nut screw 23, e.g. by means of a toothed-belt transmission. In which case, screw 16 may be connected rigidly to slide 12 and locked angularly so as to move in response to rotation of nut screw 23. Moreover, sensors 41, 42 may be separated by a distance slightly greater, as opposed to smaller, than the dimension of the holes, so as to "read" strip 2 outside the holes and so generate, for the same operating conditions, signals of opposite states to those described.

Claims: A device (1) for adjusting the transverse position of a strip (2) of packaging material on a packaging machine for producing packages containing a pourable food product, the device (1) comprising: a slide (12) movable in a first direction (B) parallel to a feed plane (n) of said strip (2) and substantially perpendicular to a feed direction (A) of said strip (2) in said plane (π); gripping means (14) carried by said slide (12) and for gripping in sliding manner an edge (6b) of said strip (2); and adjusting means (3, 7, 8) for adjusting the position of said slide (12) in said first direction; said adjusting means (3, 7, 8) comprising an actuator (11) for controlling said slide (12); a first sensor (41) for detecting a first limit position of said strip (2) and generating a first signal (s1); a second sensor (42) for detecting a second limit position of said strip and generating a second signal (s2) ; and a control unit (8) connected to said first and said second sensor (41, 42), and which controls said actuator (11) to move said slide (12) towards said second limit position of said strip (2) in response to a value of said first signal (s1) indicating said first limit position of said strip (2) has been exceeded, and towards said first limit position of said strip (2) in response to a value of said second signal (s2) indicating said second limit position of said strip (2) has been exceeded; said first and said second sensor (41, 42) are optical sensors for detecting optical references (5) of said strip; characterized in that said strip (2) is defined by a number of layers (4a, 4b), and comprises a succession of holes (5) formed in at least one (4a) of said layers (4a, 4b) and defining said optical references; said first and said second sensor (41, 42) being located facing a portion of said strip having said holes (5); and said limit positions of said strip being defined by the detection of transversely opposite margins of said holes (5) by said first and said second sensor (41, 42). A device as claimed in claim 1, characterized in that said control unit (8) comprises enabling means (49) for enabling detection of said holes (5) with a predetermined sampling frequency (1/K 0 ). A device as claimed in any one of the foregoing Claims, characterized in that said actuator is an electric motor (11); transmission means (13) being interposed between an output member (15) of said motor (11) and said slide (12). A device as claimed in Claim 3, characterized in that said transmission means (13) comprise a screw-nut screw mechanism (16, 23).

Inventors: BOSCHI ALESSANDRO, BOSCHI, ALESSANDRO
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 2000
Main classification: B65B41
IPC codes: B65B41, B65B9