Abstract:
A unit for packing products, wherein a feed line, for supplying a strip of packing material, feeds the strip with a given movement to a cutting device for cutting the strip into a succession of sheets of packing material, and then to a feed station for feeding each sheet to a packing wheel moving with a further movement through the feed station; and wherein a compensating roller, having a compensating store, is interposed between the cutting device and the feed station.

Description:
BACKGROUND OF THE INVENTION 
   More specifically, the present invention relates to a unit for packing groups of products, the unit comprising a packing wheel operating with a first movement; a feed station for feeding packing material in sheets to said packing wheel; a feed line operating with a second movement to feed packing material in the form of a continuous strip; a cutting device located along said feed line to cut the continuous strip into said sheets; and feed means for feeding said sheets successively to said feed station; said packing wheel comprising a number of seats, each for receiving a respective said product, and a number of gripping means, each associated with a respective said seat and travelling through said feed station with said first movement to receive a respective said sheet. 
   In known packing units, particularly packing units normally used in the tobacco industry for packing groups of packets of cigarettes, the continuous strip is normally fed continuously, the packing wheel is normally rotated in steps, and the feed means comprise an intermediate suction roller located immediately downstream from the cutting device, and which first receives the end of the continuous strip before it is cut, and then feeds a sheet, as soon as it is cut off, to the packing wheel. 
   Operation of the intermediate roller is therefore conditioned by both the feed movement of the continuous strip, and the rotation movement of the packing wheel, and should, theoretically, be controlled to rotate with a surface speed at least equal, at the continuous strip receiving point and instant by instant, to the travelling speed of the continuous strip, and at most equal, at the transfer point to the packing wheel and instant by instant, to the travelling speed of the packing wheel. 
   When, as is normally the case, for example, in packing units for packing groups of packets of cigarettes, the continuous strip and the packing wheel travel at different speeds, and the intermediate roller receives the continuous strip as it is transferring a sheet to the packing wheel, control of the intermediate roller, which is normally driven by a main motor of the packing unit and speed-controlled by cam systems, is obviously extremely difficult and not always satisfactory. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a unit for packing groups of products, designed to satisfactorily transfer sheets of packing material from a cutting station, for cutting a continuous strip, to a packing wheel. 
   According to the present invention, there is provided a unit for packing products, the unit comprising a packing wheel operating with a first movement; a feed station for feeding packing material in sheets to said packing wheel; a feed line operating with a second movement to feed packing material in the form of a continuous strip; a cutting device located along said feed line to cut the continuous strip into said sheets; and feed means for feeding said sheets successively to said feed station; said packing wheel comprising a number of seats, each for receiving a respective said product, and a number of gripping means, each associated with a respective said seat and travelling through said feed station with said first movement to receive a respective said sheet; the unit being characterized in that said feed means comprise a movable compensating assembly in turn comprising a movable compensating store for said packing material. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
       FIG. 1  shows a partial, schematic side view of a preferred embodiment of the packing unit according to the present invention; 
       FIG. 2  shows a larger-scale, partly sectioned view of a detail of the  FIG. 1  packing unit; 
       FIG. 3  shows a section along line III—III in  FIG. 2 ; 
       FIG. 4  shows a view in perspective of a detail in  FIG. 2 ; 
       FIGS. 5 to 9  show the  FIG. 2  detail in respective different operating positions. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Number  1  in  FIG. 1  indicates as a whole a packing unit of a cartoning machine  2 , unit  1  receiving, at an input  3 , a succession of groups  4  of packets  5  of cigarettes together with respective blanks  6  of packing material; folding blanks  6  about respective groups  4  to form a succession of packed groups  7 ; and successively feeding a second packing wheel (not shown) with packed groups  7  together with respective sheets  8  of overwrapping material, which are folded successively about respective packed groups  7  to form a succession of overwrapped groups (not shown). 
   In the example shown, each group  4  comprises ten packets  5  arranged in two superimposed rows, and is in the form of a rectangular parallelepiped, which is positioned with its longitudinal axis perpendicular to the  FIG. 1  plane, and is fed to unit  1  by a pusher  9  located at a loading station  11  and acting in a substantially horizontal direction  10  parallel to the  FIG. 1  plane. 
   Packing unit  1  comprises a packing wheel  12  tangent to loading station  11  and rotating anticlockwise in steps about an axis  13  perpendicular to the  FIG. 1  plane. Packing wheel  12  comprises a number of seats  14 , each paired with a respective gripper  15  located downstream from seat  14 , in the rotation direction of packing wheel  12 , and comprising a jaw  16 , which faces rearwards in the rotation direction of packing wheel  12 , projects outwards with respect to a cylindrical outer surface  17  of packing wheel  12 , and is rotated, by a known cam device (not shown) and about a respective axis substantially coincident with a respective generating line of cylindrical surface  17 , between a closed work position contacting cylindrical surface  17 , and a normal open position. 
   When a seat  14  is arrested at loading station  11 , the adjacent seat  14 , downstream in the rotation direction of packing wheel  12 , is arrested at a packing station  18  where packing wheel  12  is connected to a known folding device  19 , which oscillates, about an axis  20 , between a raised rest position and a lowered work position in which folding device  19  performs a sequence of operations to fold each blank  6  completely about respective group  4  and form a respective packed group  7 . 
   Packing unit  1  also comprises a feed line  21  for feeding sheets  8  of overwrapping material to packing wheel  12  at a feed station  22  located downstream from packing station  18  and upstream from a transfer station (not shown) to the second wheel (not shown). Feed line  21  comprises a number of guide pulleys  23  for guiding a continuous strip  24  of overwrapping material unwound off a reel (not shown) in a direction  25  by a feed unit  26  pulling strip  24  via a known pneumatic tensioning device  27  with a take-up well. 
   In the example shown, feed unit  26  comprises, successively in direction  25 , two pairs of opposite, counter-rotating traction rollers  28  for strip  24 ; a pneumatic traction assembly  29  immediately downstream from rollers  28 ; a cutting assembly  30  for cutting strip  24  transversely into a succession of sheets  8  of overwrapping material; and a feed assembly  31  for feeding a sheet  8  of overwrapping material, just cut off strip  24 , to feed station  22 . 
   Cutting assembly  30  comprises a blade  32  oscillating about an axis parallel to axis  13 ; and a fixed cutting block  33  facing blade  32  and on the opposite side of strip  24  to blade  32 . 
   As shown in  FIGS. 3 and 4 , feed assembly  31  comprises a tubular body  34  fitted through a fixed annular supporting plate  35  and having an axis  36  parallel to axis  13 . Tubular body  34  houses an electric motor  37 , a stator  38  of which is integral with tubular body  34 , and a rotor  39  of which is fitted to a shaft  40  coaxial with axis  36 . Shaft  40  comprises a portion outside tubular body  34  and fitted inside an end portion of a tubular casing  41  of a compensating roller  42 , which is coaxial with axis  36  and has an outer surface  43  tangent to cylindrical surface  17  of packing wheel  12  at feed station  22 , and having a number of central grooves  44  enabling passage of grippers  15 , in the open position, through feed station  22 . 
   As shown in  FIG. 3 , casing  41  is closed at one end by shaft  40  and at the other end by a plug  45 , which combines with shaft  40  to define the ends of a chamber  46  inside casing  41  and communicating with the outside through an axial slot  47  ( FIG. 2 ) with rounded lateral walls. The length of chamber  46  is adjustable by means of an adjusting device  48  comprising two walls  49 , which are mounted inside chamber  46 , crosswise to axis  36 , to slide, parallel to axis  36 , along chamber  46 , and have respective radial appendixes  50  engaging and sliding along slot  47 . Adjusting device  48  also comprises two screws  51 , each of which extends through plug  45 , parallel to axis  36 , is axially fixed with respect to shaft  40 , and comprises two oppositely threaded end portions  52  connected to respective walls  49  by respective screw-nut screw couplings to move walls  49  in opposite directions when screws  51  are activated. 
   Feed assembly  31  also comprises two suction circuits  53  and  54  extending along shaft  40  and both communicating with an external suction pump (not shown); circuit  53  comes out at outer surface  43  of casing  41  through a number of holes  55  immediately downstream from slot  47  in the rotation direction of the compensating roller; and circuit  54  comes out inside chamber  46  through a central hole  56  diametrically opposite slot  47 . 
   In actual use, when a seat  14 , housing a respective group  4  and a respective partly folded blank  6 , is arrested at packing station  18  ( FIG. 1 ), the relative gripper  15  is arrested at feed station  22 , and folding device  19 , formerly in the raised rest position, is moved into the lowered work position to finish folding blank  6  and obtain a packed group  7  in known manner. 
   At the same time, as shown in  FIG. 5 , strip  24 , formerly stationary at cutting assembly  30 , begins moving forward, and its leading end, on reaching the periphery of compensating roller  42 , whose walls  49  have already been adjusted to obtain a chamber  46  of a length approximately equal to but no less than the width of strip  24 , is sucked by holes  55  onto outer surface  43 . During this operation, packing wheel  12  remains stationary, while compensating roller  42  rotates (clockwise in  FIG. 5 ) about axis  36  at a surface speed at least equal to the travelling speed imparted to strip  24  by feed unit  26 . 
   Since sheets  8  of overwrapping material are to be released to packing wheel  12  at a speed substantially equal to the surface speed of packing wheel  12  at the time the sheets are released, and since packing wheel  12  is currently stationary, electric motor  37  is speed-controlled to begin slowing down as soon as slot  47  ( FIG. 6 ) moves past cutting assembly  30 , and a portion of strip  24  begins to become tensioned across slot  47 . 
   As a consequence of the electric motor slowing down, the portion of strip  24  not taken up by compensating roller  42  is sucked inside chamber  46  through slot  47  by the vacuum generated inside chamber  46  by suction circuit  54  through hole  56 , and forms inside chamber  46  a bend  57  of a length proportional to the difference between the travelling speed of strip  24  and the surface speed of compensating roller  42 . 
   In other words, chamber  46  acts as a compensating store for strip  24 , and makes the surface speed of compensating roller  42  independent of feed line  21  and the travelling speed of strip  24 . 
   When the total portion of strip  24  released to compensating roller  42  reaches a length equal to the length of a sheet  8  of overwrapping material ( FIG. 7 ), supply of strip  24  is arrested temporarily, so that part of strip  24  is absorbed by tensioning device  27  to allow cutting assembly  30  to cut strip  24  crosswise and detach a sheet  8  of overwrapping material from strip  24 . 
   During this operation, compensating roller  42  continues rotating and slowing down, and is eventually positioned with holes  55  close to the periphery of packing wheel  12 . At this point, packing wheel  12  begins rotating once more about axis  13  ( FIG. 8 ) to move the gripper  15 , previously located immediately upstream from compensating roller  42 , at gradually increasing surface speed through feed station  22 . During this movement, electric motor  37  is also accelerated, and is controlled so that holes  55  travel through feed station  22  at the same speed as and in time with gripper  15 , which is opened and then closed to grip the leading end of sheet  8  of overwrapping material and gradually remove sheet  8  of overwrapping material from compensating roller  42  ( FIG. 9 ). 
   At this point, compensating roller  42  is again slowed down to prevent sheet  8  of overwrapping material from being released faster than it is taken up by packing wheel  12 , and to allow packing wheel  12  to eliminate bend  57  before slot  47  gets past feed station  22 . 
   In other words, chamber  46  also acts as a compensating store for sheet  8  of overwrapping material, and makes the surface speed of compensating roller  42  independent of packing wheel  12  once gripper  15  grips the leading end of sheet  8  of overwrapping material. 
   Once sheet  8  of overwrapping material is released, compensating roller  42  is restored to the  FIG. 5  start position to feed another sheet  8  of overwrapping material to packing wheel  12 .