Abstract:
A unit for forming a continuous mat of tobacco with denser portions, wherein the mat of tobacco is formed on a suction conveyor belt looped about a return pulley and extending through two successive shredded tobacco feed stations; and wherein the return pulley, located at one of the two feed stations, has a number of radial suction seats, each for retaining a localized quantity of tobacco on the conveyor belt.

Description:
[0001]     The present invention relates to a unit for forming a continuous mat of tobacco.  
       BACKGROUND OF THE INVENTION  
       [0002]     More specifically, the present invention relates to a unit of the type comprising a conveyor belt extending along a given path; feed means located along said path to feed a continuous mat of shredded tobacco onto said conveyor belt; and suction means located on the opposite side of said conveyor belt to said feed means, and cooperating with said feed means to retain said continuous mat of shredded tobacco on said conveyor belt.  
         [0003]     In cigarette manufacturing, the continuous mat is fed onto a continuous strip of paper, which is folded transversely about the mat to form a continuous cigarette rod, which is then cut into cigarette portions, which in turn are subsequently cut and rolled to form a succession of normally filter-tipped cigarettes.  
         [0004]     When cutting and rolling the cigarette portions, the tobacco particles inside tend to separate and spill from the ends of the cigarette portions. To eliminate this drawback, the continuous cigarette rod is so formed that, when cut into cigarette portions, the density of the tobacco at the ends of the cigarette portions is greater than that of the tobacco in the intermediate portions of the cigarette portions.  
         [0005]     This is normally achieved, in units for forming a continuous mat of tobacco of the type described above, using pressure devices located downstream from the feed means to compact given portions of the continuous mat of tobacco, or using shaving disks, also located downstream from the feed means and having peripheral cavities arranged so that the mat of tobacco is shaved less or not at all at given areas spaced along the mat of tobacco with a spacing equal to the length of the cigarette portions to be produced.  
         [0006]     Though widely used, the above methods do not always succeed in achieving the desired result, owing to the mat of tobacco simply comprising a totally heterogeneous bed of shredded dry leaves, whose response to external processing differs from one point to another.  
         [0007]     To eliminate this drawback, as opposed to variously processing the mat of tobacco, it has been proposed to obtain denser portions along the mat by adding to the mat a succession of localized masses of tobacco. In U.S. Pat. No. 3,795,249 and U.S. Pat. No. 4,693,262, for example, denser portions are achieved by depositing on the conveyor belt, upstream from the feed means, extra amounts of tobacco, which are fed beforehand by further feed means to respective suction radial seats on a wheel external to the conveyor belt and positioned with a lateral surface tangent to the conveyor belt. By virtue of said suction means, the extra quantities of tobacco are deposited on the conveyor belt at the point of tangency between the wheel and the conveyor belt.  
         [0008]     This solution obviously has major drawbacks, owing to the wheel being located outside the tobacco feed means. That is, transferring the masses of tobacco formed on the wheel to the conveyor belt seriously complicates the structure of the unit, and involves repeated handling of the shredded tobacco, thus reducing the quality of the finished cigarettes.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide a unit for forming a continuous mat of tobacco with denser portions, designed to eliminate the aforementioned drawbacks.  
         [0010]     According to the present invention, there is provided a unit for forming a continuous mat of tobacco with denser portions, the unit comprising a conveyor belt extending along a given path; first feed means located along said path and for feeding a first continuous stream of shredded tobacco onto said conveyor belt; and first suction means located on the opposite side of said conveyor belt to said first feed means, and cooperating with said first feed means to retain a continuous mat of shredded tobacco on said conveyor belt; and being characterized by comprising second feed means for feeding a second continuous stream of shredded tobacco onto said conveyor belt; and second suction means located on the opposite side of said conveyor belt to said second feed means, and cooperating with said second feed means to retain on said conveyor belt a succession of localized quantities of shredded tobacco spaced along said conveyor belt with the same spacing as said denser portions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]     The present invention will be described with reference to the accompanying drawing, which shows a partial section, with parts removed for clarity, of a preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     Number  1  in the accompanying drawing indicates as a whole a cigarette manufacturing machine comprising a unit  2  for forming a continuous mat  3  of tobacco; and a unit  4  for receiving mat  3  from unit  2  and forming a continuous cigarette rod (not shown).  
         [0013]     Unit  2  comprises a conveyor  5  defined by a belt  6  permeable to air and looped about a number of pulleys—at least one of which is a drive pulley  7  powered by a motor  8 —for guiding belt  6  along an endless path P. For the sake of simplicity, in addition to pulley  7 , the accompanying drawing shows only a guide pulley  9  and a return pulley  10 , which are fitted to a frame  11  to rotate about respective parallel, horizontal axes  12  and  13 . More specifically, return pulley  10  defines, along belt  6 , the start of a substantially horizontal, straight bottom conveying branch  14 , and the end of a top return branch  15 .  
         [0014]     Unit  2  also comprises a suction box  16  connected to a suction circuit  17 , and having a perforated wall  18  which extends, in contact with a top surface of conveying branch  14 , substantially from a point of tangency  19  between conveying branch  14  and the periphery of return pulley  10 , and past a feed device  20  located beneath conveying branch  14  and comprising an upflow channel  21  for feeding onto the bottom surface of conveying branch  14  a continuous stream  22  of shredded tobacco, which, in use, is retained by suction on the bottom surface of conveying branch  14  to form mat  3  (only partly, as explained later on).  
         [0015]     Return pulley  10  comprises an internal pneumatic distributor  23 , in turn comprising a fixed annular plate  24  coaxial with axis  13  and having a curved suction cavity  25 , which extends, anticlockwise in the drawing, about axis  13  along an arc of about 180° from point of tangency  19 , communicates on one side with a suction circuit  26 , and on the other side is positioned facing and tangent to an end surface of a wheel  27  forming part of pneumatic distributor  23  and having a hub  28  coaxial with axis  13  and fitted to the output shaft of a motor  29 . Wheel  27  comprises an outer annular body  30  connected to hub  28  by spokes  31  defining a number of cavities  32 , each of which moves past and communicates with suction cavity  25 , and communicates with a respective radial passage  33  formed through annular body  30 . Return pulley  10  also comprises a perforated annular jacket  34  coaxial with axis  13 , fitted idly to annular body  30 , and engaged externally by belt  6 .  
         [0016]     Unit  2  also comprises a further feed device  35 , in turn comprising a downflow channel  36  for a stream  37  of shredded tobacco, which, in use, flows onto the portion of belt  6  extending along at least part of suction cavity  25 .  
         [0017]     In actual use, belt  6  is operated so that conveying branch  14  travels in a given direction  38  past the outlet of upflow channel  21 , and so as to rotate jacket  34  about axis  13  at a given angular speed. At the same time, motor  29  is activated to rotate wheel  27  about axis  13  at an angular speed which is maintained substantially equal to the angular speed of jacket  34  by a known negative feedback control. As return pulley  10  rotates, the vacuum in suction cavity  25  is therefore transmitted, through jacket  34 , to portions  39  of belt  6  aligned with radial passages  33 , and more specifically with the radial passages  33  whose respective cavities  32  communicate instant by instant with suction cavity  25 .  
         [0018]     The particles in stream  37  of shredded tobacco fed along downflow channel  36  are therefore retained by portions  39  of belt  6 , as portions  39  travel along suction cavity  25 , so as to form, on belt  6  and at portions  39 , a succession of tobacco quantities  40  equally spaced along belt  6  with a spacing equal to the length of the cigarette portions (not shown) being produced.  
         [0019]     As return pulley  10  rotates, tobacco quantities  40  reach point of tangency  19  where suction through suction cavity  25 , cavities  32 , and radial passages  33  is replaced by suction through perforated wall  18  of suction box  16 . As a result, quantities  40  travel past point of tangency  19  and together with conveying branch  14  in direction  38  past upflow channel  21 , where quantities  40  are covered by the particles in stream  22  retained by suction on the underside of conveying branch  14 . In other words, downstream from feed device  20 , conveying branch  14  supports a continuous mat  3  of shredded tobacco having thicker portions  41  equally spaced with a spacing equal to the length of the cigarette portions (not shown), which are formed by a known cutting head (not shown) cutting a continuous cigarette rod (not shown) formed by feeding mat  3  onto a strip  42  of paper supplied by a conveyor  43  along unit  4 , and by folding strip  42  of paper transversely (in known manner not shown) about mat  3 .  
         [0020]     In connection with the above, it should be pointed out that, to simply rotate wheel  27  synchronously with jacket  34 , jacket  34  and wheel  27  need simply be made integral with each other, thus eliminating motor  29 . Motor  29  and wheel  27 , as shown, are provided, however, by constituting an adjusting device  44 , which, by simply adjusting motor  29 , provides for keeping quantities  40  spaced along belt  6  in time with the known cutting head (not shown), despite any stretch of belt  6  or slack of pulleys  7 ,  9  and  10 .