Abstract:
Tobacco products are wrapped by a unit equipped with a rotating drum carrying a set of holder mechanisms around the periphery, each rotatable about an axis parallel to the axis of the drum, by which single products are supported and carried through an assembly station together with leaves of wrapping material received from a vacuum roller turning on an axis parallel to the axis of the drum; the vacuum roller revolves tangentially to the drum at the assembly station and comprises a system by which each leaf is transferred to a gripper associated with the support mechanism. The transfer system is timed to operate in a situation of substantially zero relative peripheral velocity between the support mechanism and the vacuum roller.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a unit, and to a relative method, for wrapping tobacco products. 
     Wrapping units of the type referred to herein can be utilized in packer machines by which groups of cigarettes, each enveloped previously in an inner wrapper of metal foil paper, are enfolded in packets of soft type. 
     Another application for such units, for example, is that of machines by which packets of cigarettes are overwrapped, also known as cellophaners. 
     The wrapping material used by a cigarette packer consists in leaves of a pliable paper, whereas the material used by a cellophaner consists in leaves of a transparent thermoplastic film. 
     The tobacco products, whether groups of cigarettes or completed packets, will generally present the appearance of a rectangular prism delimited axially by two end faces, and transversely by two larger lateral faces and two smaller lateral faces, or flank faces, extending parallel to a longitudinal axis. 
     The products are wrapped by a unit of the type in question while advancing along a predetermined feed direction. 
     To obtain a correctly formed wrap, given the high output speeds at which modern packaging machines are designed to operate, it is indispensable that the leaves of wrapping material be kept continuously and fully under control when fed to the unit and during the wrapping steps, to ensure that they do not become incorrectly positioned and mis-timed relative to the products, as this would result in the finished packet wrapper or overwrap presenting unsightly creases or blemishes. 
     Wrapping units of conventional type comprise a transfer system by which the aforementioned tobacco products are directed along a predetermined path and through an assembly station where each one is paired with a leaf of wrapping material, consisting of paper in the case of a cigarette packer, and polypropylene in the case of an overwrapper. 
     The leaf is separated from a continuous strip of wrapping material by a cutting step and fed to the assembly station through the agency of a conveyor that comprises a vacuum roller, set in continuous rotation. 
     The product transfer system comprises a wrapping wheel set in rotation continuously about an axis parallel to the axis of the vacuum roller, and revolving tangentially to the selfsame roller at the assembly station. 
     The wrapping wheel is furnished peripherally with a plurality of mechanisms rotatable about corresponding pivots parallel to the axis of the wrapping wheel, each supporting a respective product. 
     Each of the support mechanisms incorporates a gripper by which one end of a respective leaf of wrapping material, advancing on the vacuum roller, is intercepted at the assembly station. 
     The transfer of the leaf of material to the mechanism holding a relative product occurs with the jaws of the gripper spread apart in readiness to receive, and is favored by a higher tangential velocity of the vacuum roller. 
     At the moment when the end or leading edge of the leaf registers in contact with the bottom of the slot afforded by the open gripper, the jaws close and the support mechanism begins to turn on the respective pivot, whereupon the leaf of material will be bent, with the aid also of fixed folding means, and formed gradually into a tubular wrap around the product. 
     While effective, this conventional wrapping method has been found nonetheless to occasion certain drawbacks, particularly when operating at the high output speeds of modern packaging machines. 
     It happens frequently that the jaws of the gripper do not close exactly at the moment when the leaf makes contact. 
     The closing movement of the gripper jaws may be retarded or advanced, but in either case the position assumed by the leaf of wrapping material in relation to the corresponding product will be incorrect, and the wrap consequently defective. Where the closing movement is retarded, moreover, the leaf will be deformed on striking the gripper, and pinched against the bottom of the slot between the jaws. 
     The object of the present invention is to provide a unit for wrapping tobacco products such as will be able to meet the operating requirements implicit in the foregoing outline, with regard to the high output speeds of modern cigarette packers and cellophaners. 
     A further object of the invention is to provide a method of wrapping tobacco products such as will be able to meet the operating requirements implicit in the foregoing outline, with regard likewise to the high output speeds of modern machines. 
     SUMMARY OF THE INVENTION 
     The stated object is duly realized in a unit for wrapping tobacco products according to the present invention, comprising a rotating drum furnished peripherally with a plurality of mechanisms rotatable about axes parallel to the axis of the drum, by which products are supported and carried through an assembly station together with leaves of wrapping material, a conveyor supplying such leaves, rotatable about an axis parallel to the axis of the drum and revolving substantially tangential to the selfsame drum at the assembly station, and means associated with the rotating conveyor, by which single leaves of material are transferred to each mechanism of the rotating drum. 
     Advantageously, the tangential velocity of the support mechanisms when passing through the assembly station is substantially the same as the tangential velocity of the rotating conveyor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: 
         FIGS. 1 and 2  show a portion of an overwrapping machine, viewed schematically in a front elevation with certain parts omitted and comprising a wrapping unit according to the present invention, illustrated in two successive operating steps; 
         FIG. 3  shows a packet of cigarettes, viewed in perspective, such as would be overwrapped by the unit of  FIG. 1 ; 
         FIG. 4  shows an enlarged detail of  FIG. 2 , in a front elevation view; 
         FIG. 5  is a detail of  FIG. 4 , illustrated schematically and in perspective; 
         FIGS. 6 and 7  show an alternative embodiment of the detail in  FIG. 4 , viewed schematically in a front elevation view and illustrated in two successive operating steps. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , numeral  1  denotes a portion of an overwrapping machine, or cellophaner, comprising a unit  2  for wrapping packets  3  of rectangular parallelepiped geometry, as illustrated in  FIG. 3 , aligned on a longitudinal axis A and presenting two larger longitudinal walls denoted  4  and  5 , also two smaller longitudinal walls or flanks denoted  6  and  7 , and two end walls or end faces disposed transversely to the longitudinal axis A, denoted  8  and  9 . 
     The unit  2  comprises transfer means  10  by which the packets  3  are directed along a feed path P and through an assembly station  11  where a leaf  12  of wrapping material (generally polypropylene) is paired with each packet  3 . 
     The aforementioned leaves  12  of material are fed to the assembly station  11  by a conveyor  13  such as will cause a continuous strip  14  of material to decoil from a roll (not illustrated) and advance toward a cutting device, shown schematically as a blade  15 , by which the selfsame material is divided into single leaves  12  and carried thus by the conveyor  13  along the feed path P toward the assembly station  11 . 
     The conveyor  13  comprises a hollow vacuum roller  16  set in rotation continuously about a relative axis  17  in a direction indicated by the arrow denoted F 1 . 
     The tubular wall  18  of the roller  16  presents a plurality of through holes  19  connected to a source of negative pressure (not illustrated). 
     Accordingly, both the free end of the strip  14 , and the leaves  12  cut from the strip, are retained by suction on the cylindrical surface presented by the tubular wall  18  of the roller  16 . In addition, the leaves  12  separated by the cutting device  15  will also be spaced apart at a predetermined distance one from the next. 
     The aforementioned transfer means  10  comprise a wrapping wheel, consisting in a drum  20  positioned substantially tangential to the roller  16  and set in rotation continuously about an axis  21  parallel to the axis  17  of the selfsame roller, in a direction indicated by the arrow denoted F 2 . 
     The drum  20  is furnished peripherally with a plurality of mechanisms  22  equispaced angularly and mounted freely to respective pivots  23  of which the axes  24  lie parallel to the axis  21  of the drum. 
     Each mechanism  22  comprises a hollow cylindrical body  25 , aligned concentrically on the respective pivot  23  and affording an axial lateral opening  26 . 
     The cylindrical body  25  of each mechanism  22  houses gripping means  27 , appearing as two substantially radial jaws  28 , mounted freely on pivots disposed parallel to the aforementioned axis  24  and creating a slot  29  within the axial lateral opening  26  such as will accommodate a packet  3  disposed with its longitudinal axis A lying parallel to the axis  24  of the mechanism, and with the larger side walls  4  and  5  offered in contact to the two jaws  28 . 
     With the drum  20  set in rotation, each mechanism  22  is made to pivot on its axis  24  through the agency of conventional actuator means (not illustrated), in a manner shortly to be described. 
     The block denoted  30  represents a feed unit by which packets  3  are directed into the slot  29  of each mechanism  22  at an infeed position  31  lying upstream of the assembly station  11 , considered relative to the direction of rotation F 2  of the drum  20 . 
     Located downstream of the assembly station  11 , likewise relative to the direction of rotation F 2  of the drum  20 , are fixed folding means  32  comprising a plate or mantle  33  that combines with the drum  20  to create a channel  34  centered on the axis  21  of the selfsame drum and extending as far as a station (not illustrated) where the packets  3  are released. 
     The cylindrical surface  35  of the mantle  33  directed toward the drum  20  presents a plurality of suction holes  36 , uniformly distributed over the selfsame surface. 
     As illustrated to advantage in  FIG. 4 , the vacuum roller  16  carries two diametrically opposed pivots  37  located internally of the tubular wall  18 , with axes parallel to the axis  17  of the roller, each providing a fulcrum point for one end of an L-shaped arm  38  of which the free end  39  rides in close proximity to a plurality of openings  40  presented by the tubular wall  18 , as will be made clear in due course. 
     The arms  38  and the relative pivots  37  provide means by which to transfer the leaves  12  of wrapping material. With the vacuum roller  16  set in rotation, each arm  38  in turn is caused by actuator means (not shown) to pivot between a first position retracted entirely within the tubular wall  18  ( FIG. 1 ), and a second position, assumed at the assembly station  11  ( FIGS. 2 and 4 ), in which the relative free ends  39  project through the aforementioned openings  40 , externally of the tubular wall  18 . 
     Immediately upstream of the slot  29 , considered relative to a first direction of rotation indicated by the arrow denoted F 3 , each mechanism  22  is equipped externally with means  41 , consisting in gripper means  42 , by which to restrain one end of a leaf  12  of material. 
     Such gripper means  42  comprise a jaw  43  of curved profile anchored rigidly to the cylindrical body  25 , and a movable jaw  44  mounted freely to a pivot  44   a  disposed parallel to the axis  24  of the mechanism, which is caused by actuator means (not shown) to alternate between an open position, and a closed position of contact with the rigidly anchored jaw  43  ( FIG. 4 ); this same fixed jaw  43  functions also as a locating element for the aforementioned free end  39  of the arm  38  when in the second position. 
     As illustrated in  FIG. 5 , the profile presented by the free end  39  of the arm  38  and the profile presented by the free end of the movable jaw  44  are matched to that of the jaw  43  associated rigidly with the body  25 . More exactly, these same free ends are identifiable as pluralities of teeth, denoted  45  and  46  respectively, arrayed parallel with the axis  24  of the cylindrical body  25  and offset one from another in such a way that the arm  38  and the jaw  44  are able to close on the fixed jaw  43 , sequentially or simultaneously, without mutual interference. 
     In operation, with the drum  20  set in rotation, each support mechanism  22  is brought in turn to the infeed position  31 . 
     When occupying this position  31 , the mechanism  22  is set angularly on the relative axis  24  in such a way that the axial lateral opening  26  will be directed toward the feed unit  30  with the gripper jaws  28  spread apart to accommodate an advancing packet  3 , which is insertable to the point where a leading flank face  6  engages in contact with the back wall of the slot  29 . 
     The jaws  28  then close, securing the packet  3  firmly on the rotating drum  20 . 
     Along the segment of the feed path P corresponding substantially to a rotation of the drum  20  through 90° between the infeed position  31  and the assembly station  11 , the mechanism  22  in question pivots on its axis  24  in a direction, denoted F 3 , opposite to the direction of rotation F 2  of the drum  20 , so as bring the packet  3  into a position of minimum radial encumbrance, that is to say with the larger side walls  4  and  5  disposed approximately parallel to the plane of tangency between the drum  20  and the vacuum roller  16 . 
     This position of minimum encumbrance is maintained as the mechanism  22  passes through the assembly station  11 , where the end of the leaf  12  of wrapping material will be transferred from the roller  16  to the drum  20 . 
     During the course of this transfer step, the tangential velocity of the cylindrical body  25 , and therefore of the associated gripper means  42 , is controlled in such a way as substantially to match the tangential velocity of the vacuum roller  16 . 
     The vacuum roller  16  is timed relative to the wrapping drum  20  in such a way that the openings  40  occupied by the projecting teeth  45  of each arm  38  will reach the assembly station  11  simultaneously with the gripper means  42 , and accompanied by the leading edge of a leaf  12  positioned on the surface of the roller  16 . 
     At this point, the arm  38  rocks anticlockwise on its pivot  37 , as viewed in  FIG. 4 , with the result that the leading edge of the leaf  12  will be bent perpendicularly to the feed direction F 1  and pinned against the fixed jaw  43 . 
     During a momentary pause in the relative movement of the vacuum roller  16  and the drum  20 , with the leading edge of the leaf  12  held fast, that is to say before the arm  38  returns to its retracted position, the movable jaw  44  will close on the fixed jaw. 
     The finger-like ends of the arm  38  and of the movable jaw  44  are embodied in such a way that both can interact simultaneously with the leading edge presented by the leaf  12  of wrapping material, and thus keep it permanently under control. 
     As discernible from the foregoing, the arm  38  constitutes means by which to divert and immobilize the leading edge of the leaf  12  and, once the movable jaw  44  has closed, will pivot back to its retracted position entirely within the tubular wall  18  of the roller  16 . 
     Meanwhile, having progressed beyond the assembly station  11 , the mechanism  22  advances toward the fixed folding means  32 , pivoting anticlockwise as viewed in  FIG. 1  (arrow F 4 ), and reaches the entry to the channel  34 , where the packet  3  reassumes a position of maximum radial encumbrance relative to the drum  20 . 
     During this step in which the drum  20  and the mechanism  22  in question rotate simultaneously, the leaf  12  of wrapping material separates by degrees from the surface of the vacuum roller  16  and is retained immediately, by the force of suction, on the surface  35  of the mantle  33 . 
     At the same time, as a result of the mechanism  22  and the packet  3  rotating in the direction of the arrow denoted F 4 , the leaf  12 , which continues to be tensioned by the aspirating action of the vacuum roller  16 , is caused progressively to cling to a radially outermost flank face  6  or  7  of the packet  3  at a position denoted  47 , located internally of the channel  34  and diametrally opposite to the infeed position  31 . 
     The steps by which the leaf  12  is formed into a tubular wrap will be completed in familiar fashion, neither described nor illustrated herein, downstream of the aforementioned position  47 . 
     Whilst the foregoing description relates to a cellophaner or overwrapper, it would be applicable equally in the case of a cigarette packer; in this instance, self-evidently, the wrapping drum  20  will be supplied by the feed unit  30  not with packets of cigarettes, but with groups of cigarettes enveloped previously in wrappers of metal foil paper, and the leaves  12  of wrapping material will consist of paper rather than clear plastic. 
     It will be seen that the step of transferring the leaf  12  from the roller  16  to the rotating drum  20  occurs, in accordance with the present invention, at a moment of zero relative velocity between these same two components and with the leaf  12  of material continuously under control, its leading edge pinned between the arm  38  and the fixed gripper jaw  43 , and thereafter, in unbroken sequence, between the movable jaw  44  and the fixed jaw  43  of the gripper means  42 . 
     Moreover, and as illustrated in  FIGS. 6 and 7 , the arms  38  might be replaced by pneumatic means  48  comprising a plurality of nozzles  49  arrayed parallel with the axis  17  of the roller  16  and oriented in such a manner as to divert the leading edge of the leaf  12  toward the fixed jaw  43 . 
     Finally, as illustrated in  FIG. 7 , the restraint means aforementioned might comprise suction holes  50 , coinciding with the fixed gripper jaw  43 , connected to a source of negative pressure (not illustrated) and configured in such a way as to retain the leading edge of the leaf  12  diverted by the nozzles  49  or by the arm  38 . 
     The present invention relates also to a method of wrapping tobacco products, of which the steps are readily discernible from the content of the foregoing specification.