Abstract:
Packets of prismatic geometry referable to a longitudinal axis, presenting two larger side faces, two smaller flank faces and two end faces, are overwrapped by a method including a step in which each packet, enveloped initially by a tubular wrap projecting beyond the two end faces, is inserted into a holder of a transfer wheel in such a way that two appendages of the tubular wrap projecting at either end from a first flank face of the packet are flattened over the end faces; the appendages are pinned immediately along two lines coinciding substantially with the corner edges of the end face as the packet enters the relative holder, and held stably in position during a subsequent step of transferring the single packets from a feed station to an outfeed conveyor.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a method and to a relative unit for overwrapping products generally and packets in particular. 
   The invention finds application to advantage in the tobacco industry, for end-of-line operations in which leaves or sheets cut from a strip of transparent material are used to overwrap packets containing tobacco products, and in particular packets of cigarettes, to which reference is made explicitly in the present specification albeit implying no limitation in scope. 
   More particularly, the present invention relates to a method for overwrapping packets substantially of rectangular prismatic shape delimited axially by two end faces, and laterally by two larger faces and two smaller or flank faces extending parallel to the longitudinal axis of the rectangular prism. 
   A typical overwrapping unit comprises conveyor means by which the packets are taken up together with relative sheets of material, whereupon each sheet is formed into a tubular wrap about the respective packet, coaxial with the longitudinal axis of the selfsame packet and clinging thus to the two larger faces and the two flank faces. 
   The two meeting edges of the sheet overlap along one flank of the packet and are sealed together so as to anchor the tubular wrap, which projects at each end beyond the end faces. 
   Conventionally, the overwrapping is completed by making a succession of end folds against each end face, first folding and flattening an appendage of the sheet projecting from one flank face, then the appendage projecting from the other flank face, and finally the appendages projecting from the larger faces, which are flattened one over the other. 
   Adopting a different overwrapping method, as disclosed for example in Europe patent n o  1260442, the first appendage projecting from a first flank face of the packet can be folded against the end face before the tubular wrap is sealed. 
   Given the characteristics of the overwrapping materials widely employed, typically polypropylene or other heat-sealable plastics, which are highly elastic and unable to retain a fold unassisted, the conveyor means must be equipped with mechanisms capable of holding the appendages of the wrap in place after the end folds have been made. 
   The function of such mechanisms will cease the moment that the end folds are fastened one to another by a final heat-sealing step that completes the overwrapping operation. 
   The method in question nonetheless imposes definite limitations on overwrapping machines used in the industry, and while suitable for those of reciprocating design, it is not applicable to more modern machines typified by continuous motion and high output speeds. 
   The object of the present invention is to provide a method of overwrapping packets such as will meet the practical requirements indicated above while operating at the high output speeds of which modern cigarette makers and packers are capable. 
   SUMMARY OF THE INVENTION 
   The stated object is realized according to the present invention in a method for overwrapping packets of substantially rectangular prismatic shape presenting two larger side faces parallel one with another and with a longitudinal axis, two smaller or flank faces disposed parallel to the longitudinal axis and at right angles to the larger faces, and two end faces lying transverse to the longitudinal axis. 
   The method disclosed envisages the steps of inserting single packets into holders carried by a transfer wheel, each disposed with the longitudinal axis parallel to the axis of the wheel and enveloped by a tubular wrap projecting beyond the two end faces, directing each packet into the relative holder in such a way that appendages of the tubular wrap projecting from one flank face of the packet are folded against the respective end faces, and finally stabilizing the appendages during the step of inserting the packet into the relative holder and/or during a step of transferring the single packets from a feed station to an outfeed conveyor. 
   The stated object is realized similarly in a unit for overwrapping packets typically of rectangular prismatic shape, presenting two larger side faces parallel one with another and with a longitudinal axis, two smaller or flank faces disposed parallel to the longitudinal axis and at right angles to the larger faces, and two end faces lying transverse to the longitudinal axis. 
   Such a unit comprises a feed conveyor by which packets enveloped each in a tubular wrap projecting beyond the two end faces are advanced singly toward a feed station, and a transfer wheel equipped with a plurality of gripper assemblies, each affording a holder able to admit a packet disposed with its longitudinal axis parallel to the axis of the wheel, by which the packets are transferred from the feed station to a release station serving the outfeed conveyor. 
   Each holder is composed of pinching means able to restrain the packet, and two side walls by which appendages of the tubular wrap projecting from one flank face of the packet are folded against the respective end faces, the pinching means and the fold-making side walls together constituting means by which to stabilize the folded appendages. 

   
     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: 
       FIG. 1  shows a portion of an overwrapping unit according to the present invention, viewed schematically in elevation with certain parts cut away, and illustrated in a preferred embodiment; 
       FIG. 2  shows a detail of the unit in  FIG. 1 , viewed schematically in a section on II-II; 
       FIG. 3  shows a detail of  FIG. 1 , viewed schematically and in perspective; 
       FIG. 4  is an enlarged detail of  FIG. 3 ; 
       FIGS. 5 to 9  are perspective views illustrating a sequence of five overwrapping steps performed on a packet of cigarettes by the unit of  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1  of the drawings,  1  denotes an outfeed portion, in its entirety, of a unit  2  for overwrapping packets of cigarettes  3  in leaves or sheets  4  of transparent material, for example polypropylene. 
   Such packets  3  are rectangular and prismatic in shape, referable to a longitudinal axis denoted  5 , presenting two larger side faces  6  parallel one with another and with the longitudinal axis  5 , two smaller or flank faces  7  disposed parallel to the longitudinal axis  5  and at right angles to the larger faces  6 , and two end faces  8  disposed transversely to the longitudinal axis  5 . 
   The outfeed portion  1  of the unit  2  includes a feed conveyor  9  (part of which visible in  FIG. 1 ) set in rotation clockwise, as viewed in  FIG. 1 , about an axis denoted  10 , by which successive packets  3  are advanced with their axes  5  disposed parallel to the axis  10  of the conveyor, each enveloped in part by a sheet  4  of transparent material, toward a feed station  11 . 
   Also forming part of the outfeed portion  1  is a transfer wheel  12  set in rotation anticlockwise, as viewed in  FIG. 1 , about an axis  13  parallel to the axis  10  of the conveyor  9 , interposed between the feed station  11  and a release station  14  serving a substantially horizontal outfeed conveyor belt  15  of which one end is looped about a return pulley coinciding with the transfer wheel  12 . 
   The sheets  4  are wrapped around the respective packets  3  by the conveyor  9  in conventional manner, not illustrated, so that each is formed into a tubular wrap  4 ′ (see  FIG. 5 ) centered on an axis coinciding with the longitudinal axis  5 , that is, a wrap  4 ′ clinging to the four side faces  6 - 6  and  7 - 7  of the packet  3  and secured along one flank face  7  by a sealed seam  16  uniting two overlapped edges of the sheet  4 . 
   The feed conveyor  9  is equipped peripherally with a plurality of assemblies  17 , equispaced one from another and pivotable about axes  18  disposed parallel to the axis  10  of rotation, each affording a holder  19  proportioned to accommodate a single packet  3  wrapped in a relative sheet  4 . 
   The holder  19  is delimited by a back wall  20  designed to make contact with one flank  7  of the packet  3 , and two side walls  21  and  22  designed to engage the two larger side faces  6  of the packet. The front part of the holder  19 , opposite the back wall  20 , remains open. 
   As discernible from  FIG. 3 , and for reasons that will become clear in due course, the holder  19  is proportioned in such a way that the two ends of the packet  3  project one on either hand, together with the two ends of the tubular wrap  4 ′. 
   With reference to  FIG. 5 , each end of the tubular wrap  4 ′ comprises two appendages denoted  23  and  24  projecting from the two larger side faces  6 , an appendage  25  projecting from the flank face  7  offered to the back wall  20 , and an appendage  26  projecting from the flank face  7  along which the sealed seam  16  is applied. 
   One portion  27  of the side wall denoted  21  (which advances forwardmost in the direction of rotation of the conveyor  9 ) is mounted pivotably to a hinge pin  28  parallel with the axis  10  of the conveyor, coupled to actuator means (not illustrated), and capable thus of combining with the opposite side wall  22  to function as gripping means by which the packet  3  is retained internally of the holder  19 . 
   As illustrated in  FIGS. 1 and 2 , the transfer wheel  12  comprises a drum  29  mounted to a shaft  30  of which the axis coincides with the axis  13  of the wheel. 
   The drum  29  is equipped at the right hand end, as viewed in  FIG. 2 , with a cylindrical flange  29   a  centered on the axis  13  and carrying a number of shafts  31  centered on respective axes  31 ′ and extending toward the opposite end of the drum  29 . 
   The shafts  31  are equispaced angularly around and parallel to the axis  13  of the wheel, and serve to carry respective gripper assemblies  32  each affording a holder  33  such as will accommodate a packet  3  disposed with its axis  5  parallel to the aforementioned axis  13 . 
   Each assembly  32  comprises two mutually parallel arms  34  anchored at respective ends to the opposite ends of a single shaft  31 . 
   The free end presented by each arm  34  of the gripper assembly  32  serves to carry a respective shaft  35  of which the axis  35   a  is disposed parallel to the axis  13  of the wheel  12 . The two shafts  35  are axially aligned one with another and carry the holder  33  between their respective ends. 
   Both sets of shafts  31  and  35  are coupled to actuator means (not illustrated) such as will cause the arms  34  to pivot on the respective axes  31   a  relative to the drum  29 , and the holders  33  to rotate about the respective axes  35   a  relative to the arms  34 , during the rotation of the transfer wheel  12  about its axis  13 . 
   In the example illustrated, the single holder  33  comprises two L-shaped elements denoted  36 , each mounted to the end of a respective shaft  35 . 
   The elements  36  in question present two first portions  36   a  lying in a common plane, parallel to the axis  13  of the wheel and combining to establish a back wall  37  of the holder  33  such as will engage the flank face  7  of the packet  3  occupying the open front of the holder  19  afforded by each assembly  19  of the conveyor  9 . 
   The elements  36  also present two portions  36   b  normal to the first portions  36   a , disposed mutually parallel and separated by a distance substantially equal to the longitudinal dimension of a single packet  3 , of which the free ends are fashioned with a rounded profile. 
   The two parallel portions  36   b  establish two further walls of the holder  33 , and more exactly two side walls  38  by which the two corresponding appendages  26  of the tubular wrap  4 ′ are folded at the moment when the packet  3  is directed into the holder  33 . 
   As illustrated in  FIG. 6 , the step of folding each appendage  26  has the effect of forming two triangular folds  26 ′, doubled against the innermost surfaces of the adjoining appendages  23  and  24 . 
   Each shaft  35  of the gripper assembly  32  is ensheathed by a tubular element or sleeve  39  that carries gripping means  40   a  comprising two jaws  40  and  41  of width substantially matching the width of the packet  3 , pivotable about respective axes  42  and  43  extending mutually parallel and transverse to the shaft axis  35   a . The gripping means  40   a  in question constitute means  44  by which to pinch the packet  3  across the opposite endmost edges of the larger side faces  6 , and are capable of movement induced by actuator means (not illustrated) between an open position, illustrated in  FIG. 1 , and a closed position illustrated in  FIGS. 1 ,  2  and  3 . 
   The jaws denoted  40 , uppermost as illustrated in  FIG. 3 , present a free gripping end of width substantially identical to that of the packet  3  and are equipped on the side farthest from the back wall  37  with a drag tooth  45  designed to engage one of the flank faces  7  of the packet  3  when released from the conveyor  9  to the transfer wheel  12 . 
   As illustrated in  FIG. 4 , it will be seen that with the pinching means  44  in the closed position, the two fold-making longitudinal corner edges  46  of each side wall  38  engage substantially in contact with a gripping face  47  of the corresponding jaw  40  and  41 . 
   Consequently, as illustrated in  FIGS. 6 ,  7  and  8 , each edge  26   a  of a relative folded appendage  26 , coinciding with one side of the relative triangular fold  26 ′ and overlapping part of the corresponding corner edge of a respective end face  8 , will be pinned between the corner edge  46  of the wall  38  and the face  47  of the jaw together with a part  48  of the edge of the appendage  23  or  24  projecting from the respective larger side face  6  of the packet  3 . 
   As illustrated in  FIGS. 1 and 4 , the unit  2  further comprises heating means denoted  49 , located along the two opposite longitudinal corner edges  46  of each fold-making side wall  38  and consisting, for example, in electrical resistance elements. 
   Similarly, the unit  2  comprises heating means  50  located on an area  47 ′ of the gripping face  47  presented by each jaw  40  and  41 , positioned to coincide with the aforementioned corner edges  46 . 
   The outfeed conveyor belt  15 , which advances in the direction denoted F 1 , is equipped with slats  51  delimiting pockets  52  each designed to accommodate a relative packet  3 . 
     53  denotes a horizontal guide element positioned above the top branch of the belt  15  at a distance substantially equal to the depth of one packet  3 . 
     54  denotes one of two second fold-making side walls (one only being visible in  FIG. 1 ) by which the two appendages  25  of the tubular wrap  4 ′ opposite to the appendages denoted  26  are flattened against the end faces  8  (see  FIG. 8 ). 
     55  and  56  denote two helical fold-making elements by which the remaining appendages  23  and  24  of the tubular wrap  4 ′ extending on either side from the two larger faces  6  of the packet  3  are flattened against the end faces  8 , overlapping one another (see  FIGS. 8 and 9 ). 
     57  denotes one of two heat-seal devices, one only being visible in  FIG. 1 , by which the two appendages  23  and  24  are bonded one to another over a substantially central area of the end face  8 , excluding the aforementioned edges  26   a  and  48 , to complete the ends  8 ′ of the overwrapping. 
   In operation, each holder  19  of the conveyor  9  containing a single packet  3  approaches the entry to the feed station  11 , which extends through an arc of predetermined length, and draws alongside a holder  33  of the transfer wheel  12 , the two holders being substantially aligned at this juncture on an axis transverse to the longitudinal axis  5  of the packet  3 . 
   During this step, the packet  3  will be actively restrained by the aforementioned gripping means  22  and  27  of the one holder  19 , whilst the gripping means  40   a  of the other holder  33  are spread, thus allowing interpenetration of the two holders to the point at which the flank face  7  of the packet  3  presenting the sealed seam  16  registers against the back wall  37 , and the ends projecting from the first gripping means  22  and  27  are caused to locate between the jaws  40  and  41  of the second gripping means  40   a.    
   At this point, the jaws  40  and  41  are caused by respective actuator means to close and the gripping means  22  and  27  are spread, allowing the teeth  45  to draw the packet  3  from the holder  19  at the exit end of the feed station  11 . 
   Restrained between the jaws  40  and  41 , with the transfer wheel  12 , the arms  34  and the holders  33  rotating anticlockwise (as viewed in  FIG. 1 ), the packet  3  arrives at the release station  14  turned through an angle of some 180° from the position in which it had left the holder  19  of the conveyor  9 . 
   On entering the release station  14 , accordingly, the packet  3  will assume a position in which the larger side face  6  engaging the bottom jaw  40  lies substantially in the same plane as that occupied by the top branch of the conveyor belt  15 . 
   At this stage, the gripping means  40   a  are spread, and the flank face  7  opposite to that presenting the sealed seam  16  on the tubular wrap  4 ′ is engaged by a slat  51  passing between the two pairs of jaws  40  and  41 , through the gap that separates the aforementioned portions  36   a  of the two L-shaped elements denoted  36 . 
   As the packet  3  advances along the belt  15 , the two projecting appendages  25  are flattened by the second fold-making side walls  54  against the respective end faces  8 , whereupon the remaining appendages  23  and  24  are flattened by the helical fold-making elements  55  and  56  likewise against the end faces  8 , one overlapping the other. 
   Finally, the two appendages  23  and  24  are secured one to another by the heat-seal devices  57  to complete the closure of the overwrapping  4 . 
   It will be seen that the step of transferring the packet  3  from the feed conveyor  9  to the transfer wheel  12 , during which the respective holders  19  and  33  are caused to interlock, comprises the step of stabilizing the appendages denoted  26 . 
   This stabilizing action, applied along respective lines denoted  58  in the drawings, is generated by the combined action of the aforementioned edges  26   a  and  48  of stabilizing means afforded by the longitudinal corner edges  46  of each side wall  38  and the contact areas  47 ′ of the gripping faces  47 . 
   The stabilizing means  46  and  47 ′ in question might operate applying compression alone, or with the aid of the aforementioned heating means  49  and  50 . Either solution will ensure that the folded appendage  26  remains stably in place during the remainder of the transfer steps described above. 
   To advantage, moreover, and as discernible from  FIG. 9 , the heat-seal  57 ′ applied to each pair of appendages  23  and  24  by the heat-seal devices  57  is located in an area of the relative end  8 ′ not occupied by the stabilization lines  58 . 
   It will be seen from the foregoing that there is no need to equip the unit  2  with mechanisms serving specifically to retain the first appendages  26  in the position assumed following the folding steps. 
   In effect, such mechanisms are replaced by the aforementioned stabilizing means  46  and  47 ′, which are one and the same as the means serving to fold the appendages  26  and remain active during the relative folding step and/or during the step of transferring the packets  3  from the feed station  11  to the release station  14 .