Patent Publication Number: US-6655251-B2

Title: Method and device for cutting film-like materials, for instance for automatic packaging installations

Description:
The present invention relates to the cutting of film-like materials. 
     The solution according to the invention has been developed with particular attention paid to the possible application in automatic packaging systems, for example, for packaging foodstuffs. In particular, the present invention has been developed for possible use in machines for applying tear bands. 
     The corresponding prior art is extremely extensive, as is demonstrated, for instance, by documents such as IT-B-1 041 468 (to which there corresponds GB-A-1 558 998) and U.S. Pat. No. 3,298,891. 
     Devices of this basic, common type essentially comprise, with some variations, a ribbon of film-like wrapping material with tear bands applied to the ribbon and oriented transversely with respect to the direction of extension (and of advance) of the ribbon. 
     The tear bands are obtained starting from a further ribbon of film-like material that is made to advance by steps through a cutting unit. The cutting unit acts in a direction transverse to the direction of feed of the further ribbon of film-like material so as to cut from that ribbon, strips of reduced width, usually selectively variable according to the requirements of use. 
     The strips of material thus obtained, which are to constitute the tear bands, are then taken up by a transferring device which carries out application of the strips to the wrapping material. This application of the tear bands takes place at given distances corresponding to the dimensions of the products to be wrapped. 
     The main problem regarding the making of devices of the type described above is linked to the fact that the operation of cutting the tear bands is intrinsically discontinuous since it has to be performed by steps, whereas usually it is desirable that the wrapping material on which the tear bands are applied should be kept continually advancing at a practically constant speed. 
     The need to reconcile the intermittent operation of the cutting unit that forms the tear bands with the continuous movement of the wrapping material on which the tear bands are applied is more often than not met by adjustments to (according to various modalities) the transferring device. Usually, the transferring device will pick up the tear bands as soon as they have been formed, slowing down or stopping altogether in a position corresponding to the cutting unit, and will then follow a movement of rotation with an acceleration such that, when the tear band, carried by the transferring device, reaches the position in which it is to be transferred onto the wrapping material, it will be advancing at a speed practically corresponding to the speed that the wrapping material is advancing, which is kept continuous and constant. 
     Consideration of such an arrangement has become increasingly important among the critical factors considered since, according to the by now constant trend in the sector, the speed of operation of the ensemble described (expressed in general in terms of number of tear bands applied per unit time) increases as the rates of operation of the packaging plants increases. 
     The above-mentioned critical factors also involve the cutting unit, which is frequently built with the use of rotating blades, which may possibly cooperate with counterblades (anvils) carried by the transferring device. A solution of this type is described, for instance, in the Italian patent application for industrial invention TO96A000806. 
     The above cutting solutions of a dynamic type present, however, the drawback of being difficult to implement, in particular as regards the need to adjust the cutting device exactly and to regulate its operation so that it may be adapted to possible variations in the dimensions of the tear bands and/or in the thickness and nature of the film-like material from which the tear bands are cut. 
     In various applications that make use of film-like material that is to be cut at pre-set distances, there is already known the solution of resorting to automatic cutting devices which are able to carry out an operation of shearing. These are cutting devices that comprise a blade and a counterblade hinged together like the blades of a pair of scissors or shears. 
     A solution of the above kind, which is able to ensure good precision in performing the cutting operation, is, however, not applicable, except in very particular cases, to the cutting of tear bands. Usually, the tear bands are made up of very narrow strips which are cut from ribbons of film-like material, and the width of the film-like material defines the length of the tear bands. Since the cutting area ends up being somewhat long, it is necessary to use blades of corresponding extension. Precisely on account of the hinging of the blades in a position corresponding to respective proximal ends, the distal ends of the blades themselves must carry out a somewhat extensive travel, which proves far from compatible with the need to operate at ever-increasing speeds. 
     The purpose of the present invention is to provide a solution that is able to overcome the drawbacks of the known solutions just described. 
     According to the present invention, the above purpose is achieved by a cutting process having the characteristics specifically recalled in the ensuing claims. The invention also relates to the corresponding device. 
    
    
     The invention will now be described, purely by way of non-limiting example, with reference to the attached drawings, in which: 
     FIG. 1 illustrates, in a general side elevation, part of a device for applying tear bands, made according to the invention; 
     FIG. 2 is a fragmentary, cross-sectional view taken along line II—II of FIG. 1; and 
     FIGS. 3 to  5  are schematic representations of successive steps of operation of a device according to the invention. 
    
    
     In the view of FIG. 1, the reference number  10  designates, as a whole, a device for cutting and applying tear bands, designed to be used, for example, in the context of a system for automatic packaging of products, such as foodstuffs. 
     According to a configuration in itself known, the device  10  is designed to be traversed by a film-like wrapping material F (which is usually made to advance at a constant speed), on which there are to be applied, at selectively identified regular distances apart, tear bands B having a width selectively identified according to the specific requirements of an application. 
     The tear bands B are obtained starting from a further film-like material C fed off a roll or roller (not illustrated) toward a cutting unit  12 , where the film-like material C undergoes cutting in the transverse direction so as to give rise to the bands B. The bands thus formed are taken up by an applying device  14 , usually consisting of a rotating structure comprising a plurality of gripping units  16  (normally operating by suction), which are designed to pick up the tear bands B from the cutting device  12  to transfer them onto the film-like material F. The foregoing corresponds to criteria of implementation and use which are altogether known in the prior art (also in different possible variant embodiments) and which, as such, do not require a detailed description herein. 
     From the side elevation of FIG. 1 it may be noted that the transferring device  14  rotates about a main respective axis X 14  and carries, associated to it, a fixed contrast element  18 . The latter element, which performs the function of counterblade, has a cutting edge  18   a , which is usually located at a short distance from the ideal cylindrical surface along which the movement of rotation (or, to be more precise, orbital movement) of the gripping units  16  about the axis X 14  takes place. In particular, the cutting edge  18   a  is approximately co-extensive with one of the generatrices of the aforesaid ideal cylindrical surface. 
     The reference number  20  designates a blade provided with a respective cutting edge  20   a  designed to cooperate with the cutting edge  18   a  so as to carry out cutting of the film-like material from which the tear bands B are made. 
     In the view of FIG. 1, the reference number  22  designates a motor-driven roller which has the function of an unwinding roller and is designed to control advance of the film-like material C by successive steps the length of which is selectively determined (in a known way) so as to correspond to the width of the tear bands that are to be made. 
     The reference number  24  designates a piece of supporting equipment (mounted in a fixed position with respect to the framework of the device  10 ) designed to define a passage or gap  26  through which the film arriving from the unwinding roller  22  can be fed regularly toward the cutting area where the cutting edges  18   a  and  20   a  act. 
     The blade  20  is carried by a respective piece of actuating equipment  28  (see also FIG.  2 ), which is basically made up of a pair of side brackets that support the blade  20  in a condition of sliding support—in a plane XT defining in practice the cutting plane (see FIG.  1 )—against the equipment  24 . In particular, the brackets in question support the blade  20  at points corresponding to its ends, designated by  30  and  32 , respectively. 
     The supporting action (and, as will be more clearly seen from what follows, the controlling action) of the blade  20  takes place by means of two articulated-joint elements, such as ball-and-socket joints,  34  and  36 , each of which acts between a respective end  30 ,  32  of the blade  20  and a corresponding bracket  301 ,  321  of the actuating device  28  subjected to the action of a cam assembly  38 ,  40 . 
     Both of the cam assemblies  38 ,  40  rotate about a common axis X 42  which is parallel both to the line along which the cutting edge  18   a  of the counterblade  18  extends and to the axis X 14  about which the transferring device  14  rotates. 
     Usually, the two cam assemblies  38 ,  40  are mounted in phase with each other in the sense that the imaginary straight lines that connect the geometrical center of the eccentric pivot of each assembly to the common axis of rotation X 42  lie in the same plane where the axis X 42  lies. The distances that separate the geometrical centers of the two cam assemblies  38 ,  40  from the axis X 42 —i.e., in practice, the degrees of eccentricity of the two assemblies  38  and  40 —are, however, different from one another. 
     For instance, in the example of embodiment illustrated herein, the degree of eccentricity of the assembly  38  is greater than the degree of eccentricity of the assembly  40  (of course, this relationship could be reversed). 
     In this way, the set of parts just described may be mounted in such a way that the cutting edge  20   a  of the blade  20  usually presents a skewed orientation with respect to the line of extension of the cutting edge  18   a  of the counterblade  18 . 
     In a preferred way, the position of assembly of the elements described is chosen in such a way that the cutting edge  20   a  (and the blade  20  as a whole) lies on a generatrix of the orbital path described by the gripping elements  16  about the axis X 14  only when the cam assemblies  38  and  40  are in the position of rotation such that the geometrical centers of the respective eccentric pivots are in the position of maximum approach to the transferring device  14 . In other words, only in this condition (i.e., the one to which, as will appear more clearly in what follows, FIG. 5 refers), the cutting edge  20   a  extends along a straight line substantially parallel to the axis of rotation X 14  of the transferring device  14 . 
     As a result of being mounted on the cam assemblies  38 ,  40  and of the different degree of eccentricity of these assemblies, when the blade  20  is in the position where it is furthest away from the transferring device  14  (i.e., when the cam assemblies  38  and  40  are in an angularly opposed position—i.e., translated by 180° in their angular movement of rotation—with respect to the position described previously), the end of the blade  20  carried by the cam assembly with the greater degree of eccentricity (in the example illustrated here, it is the end  30  carried by the cam assembly  38 ) is, with respect to the ideal cylindrical surface on which the gripping members  16  orbit in the transferring device  14 , at a distance greater than the opposite end (in the example here illustrated, the end  32 ) carried by the cam assembly  40 . This situation is clearly recognizable in FIG.  3 . 
     Furthermore, the dimensions of the parts involved and the degree of eccentricity of the two cam assemblies  38 ,  40  are chosen in such a way that, in the position just described (blade  20  in the position where it is furthest away from the transferring device  14 ), the end  32  of the blade  20  that is closer to the device  14 , and hence to the counterblade  18 , is in any case at a distance from the counterblade  18  itself sufficient to create a space that is enough to enable the film C coming from the gap  26  to advance in the space between the cutting edge  20   a  of the blade  20  and the cutting edge  18   a  and of the counterblade  18 . 
     Control in rotation of the cam assemblies  38  and  40  about the axis X 42 , driven by a shaft  44  operated by a motor (not shown, but of a known type) enables forward and backward movement of the blade  20  between the two end positions described previously (i.e., a position where the blade is furthest away from the transferring device  14 , see FIG. 3, and a position where the blade is closest to the transferring device  14 , see FIG.  5 ). 
     The rotational movement of the shaft  44  is coordinated with the movement of the feed roller  22  in such a way that, when the blade  20  is furthest away from the transferring device  14 , as described previously, the feed roller  22  causes the film C to advance in the area between the cutting edges  18   a  and  20   a  by a distance of advance corresponding to the width of the tear bands that are to be cut. Movement of the film C is not hindered by the blade  20  and by the counterblade  18 , which at this point are in any case separated from one another. 
     Once the condition described has been reached, as a result of the rotation of the cam assemblies  38  and  40  driven by the shaft  44 , the blade  20  starts advancing again toward the transferring device  14 . 
     The above movement may be controlled both continuously and intermittently by causing the shaft  44  to rotate accordingly. In any case, the movement in question causes the blade  20  and the counterblade  18  to interact, carrying out the cutting of a tear band starting from the film-like material C (see FIG.  4 ). 
     Precisely on account of the different degree of eccentricity of the two assemblies  38  and  40 , the closing movement of the cutting edges  20   a  and  18   a  on the film-like material C is obtained (as represented schematically in FIG. 4) starting from the ends of the cutting edges  18   a  and  20   a  located in positions corresponding to the assembly  40  having smaller eccentricity, toward the opposite ends located in a position corresponding to the assembly  38  having greater eccentricity. 
     This fact is immediately understandable if it is borne in mind that, when the blade  20  is in the position where it is furthest away from the transferring assembly  14 , the end  32  carried by the assembly  40  is, with respect to the transferring device  14 , at a smaller distance as compared to the end  30  carried by the assembly  38  (see again FIG.  3 ). 
     Instead, when the blade  20  has reached the position where it is closest to the assembly  14 , it is with its cutting edge  20   a  set practically parallel to the axis X 14  in a condition where the edge is substantially tangent to the ideal cylindrical surface along which the orbital movement of the gripping elements  16  takes place (FIG.  5 ). 
     The movement of cutting the film C thus takes place according to a typical shearing action, but without hinging of the blades  20  and  18  on a common axis. 
     The result described (it will be appreciated that the representation of FIGS. 3 to  5  has been deliberately emphasized for reasons of clarity of illustration) is in fact achievable by imparting on the ends  30  and  32  of the blade  20  substantially linear and parallel travel paths: in particular, it is possible to impart on the end  30  carried by the cam assembly  38  a travel (measured in the cutting plane XT—see FIG. 1) only slightly greater than the amplitude of the corresponding travel imparted on the opposite end  32 . 
     In this way, a drawback that is intrinsic in the solutions based upon the use of cutting blades which are hinged together according to a general scissors configuration is overcome. 
     The gripping units  16  of the transferring device  14  may pick up the part of film-like material C that has just undergone cutting (see, once again, FIG. 5) with an orientation that is substantially parallel to the direction of extension of the cutting edge  18   a  of the counterblade  18 , hence precisely in a position corresponding to the ideal cylindrical surface on which the orbital movement of the aforesaid elements  16  takes place. 
     At the end of the cutting operation, the cutting edge  20   a  of the blade  20  is in fact oriented in a direction that is substantially parallel to the aforesaid direction of picking-up. 
     The movement of the blade  20  described previously can be controlled in a highly precise way both with respect to the rate (which can be regulated by adjusting the speed of rotation, which may possibly be modulated as has already been said, of the assemblies  38  and  40  about the axis X 42 ) and the amount of travel imparted on the two ends of the blade (an amount that may be determined a priori by defining the degrees of eccentricity of the assemblies  38  and  40 ), and also with respect to the possible adjustment of any pre-loading imparted on the blade  20  in view of its cooperation with the counterblade  18 . 
     In this connection, it has proved preferable to resort to solutions which, with respect to the relative spatial location of the axis X 42  and the region of cooperation of the cutting edges  18   a ,  20   a  (hence, of the cutting plane XT), will avoid any stresses that might result in jamming of the two cutting edges. 
     Recourse to solutions that tend to locate the axis X 42  so that it coincides or substantially coincides with the plane XT in which the relative movement of the cutting edges  18   a ,  20   a  is performed has proved particularly advantageous. A solution that has proved preferential is the one in which the axis X 42  is displaced at least slightly with respect to the plane XT on the side where the counterblade  18  is found. In this way, the action of controlling the blade  20  by means of the cam assemblies  38  and  40  is obtained in such a way as to counter any tendency toward jamming of the blade  20  against the counterblade  18 . The pre-loading deemed necessary in order to ensure a proper cutting action (also accounting for the specific characteristics of the film C) can thus be adjusted with precision. This may be obtained by means of a pressure element  46 —preferably acting under the action of a load spring  48  with a selectively adjustable pre-loading by means of a screw-type adjustment member  50 —which acts on the blade  20  or on the elements carrying the blade  20 . 
     Of course, without prejudice to the principle of the invention, the details of implementation and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the annexed claims. This applies in particular to the possibility of imparting on the ends of a blade, such as a blade  20 , a movement of the type described previously, by resorting, instead of to cam assemblies, to linear actuators subjected to a control function—operated, for example, by means of a digital control device—chosen, for instance, in such a way as to impart on the ends a movement that substantially resembles a harmonic motion.