Abstract:
Tipping papers are cut from a continuous strip of material advancing along a set feed path by a unit comprising a suction roller and a roller equipped with blades, which combine to separate the single papers from the strip at a prescribed frequency; the tension of the advancing strip is varied cyclically by diverter elements associated with the suction roller and capable of movement at intervals coinciding with the frequency of the cutting stroke between two limit positions, one located externally and the other internally of the outer surface presented by the suction roller.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a unit for preparing leaves of paper material. 
   The invention finds application to advantage in cigarette making machines, and in particular filter tip attachments by which single tipping papers are cut from a continuous strip decoiled from a roll; reference is made explicitly to this art field in the following specification, albeit implying no limitation in general scope. 
   Filter tipped cigarettes are assembled generally by interposing a double length filter plug between two axially aligned cigarette sticks, then joining the filter to the sticks on either side by affixing a previously gummed tipping paper, and ultimately cutting the double assembly in half to create two single filter cigarettes. 
   Employing prior art methods, tipping papers are obtained from a continuous strip of paper material caused to advance along a predetermined feed path, first through a gumming device by which adhesive is applied to one face of the strip, and thereafter to a cutting device by which the strip is divided up into single leaves of predetermined length. 
   The cutting device operates downstream of the gumming device, relative to the direction followed by the advancing strip, and comprises two rollers contrarotating tangentially to one another about parallel axes, one with an aspirating surface by which the strip is drawn forward; each roller is equipped with respective blades arranged angularly at uniform pitch around its peripheral surface. 
   Each blade presented by one of the two rollers will interact typically with a corresponding blade of the other roller in such a way as to sever the strip along transverse lines, executing a so-called scissor cut. Accordingly, each blade of one roller combines with a blade of the other roller to create a scissor device which, when the rollers are driven in rotation, is designed to separate successive tipping papers by shearing point-to-point across the strip. 
   After the cut, the tipping papers are held on the surface of one of the two rollers, and more exactly the suction roller, before being transferred in succession to a station where each is offered to an aforementioned assembly composed of a double length filter plug and two cigarette sticks. 
   For the operation of joining the assemblies to be performed correctly, the tipping papers cut from the strip must be suitably distanced one from the next; this is accomplished by causing the suction roller to rotate at a peripheral speed greater than the linear speed of the advancing strip. 
   Because the scissor cut is generated by degrees, signifying that the separation of the single paper does not occur instantaneously but only after a given interval of time, the difference between the peripheral speed of the suction roller and the linear speed of the advancing strip prevents the papers being detached cleanly from the strip. As a result of the traction force exerted by the suction roller, in effect, the advancing strip is subjected to a pulling action which the narrowing portion of material gradually becomes unable to withstand as the final stage of the scissor cut is reached and tension in the uncut portion of the strip becomes excessive, so that the tipping paper separates by tearing, before a clean cut can be completed. The papers detached in this manner cannot therefore be utilized as they are marred by irregularities along the line of the cut at the point where the final separation occurs. 
   To overcome such drawbacks, prior art methods include the expedient of inserting a cyclically activated diverter between the gumming device and the cutting device, by which the tension of the strip is varied at intervals matching the stroke frequency of the cutting device. More exactly, the diverter serves to relax the tension of the strip during the cutting stroke 
   With higher and higher strip feed speeds being adopted to accommodate increasingly fast production tempos, it can happen, due to the inherent elastic properties of the strip of paper material and the vibration generated by the diverter in the length of strip extending between the selfsame diverter and the cutting device, that the steps of relaxing the tension and making the cut will slip out of phase, and there is a risk of the material tearing along the final part of the cutting line. 
   The object of the invention is to provide a unit for preparing leaves of paper material such as will be unaffected by the aforementioned drawback. 
   SUMMARY OF THE INVENTION 
   The stated object is realized according to the present invention in a unit for preparing leaves of paper material from a continuous strip advancing along a predetermined feed path, equipped with cutting means such as will separate the leaves in succession from the strip at a selected cutting frequency utilizing a first aspirating roller and a second blade roller contrarotating substantially tangential one to another, also means associated with the first conveyor, by which the tension of the advancing strip can be varied cyclically and synchronously with the action of the cutting means. Such tension varying means incorporate diverter elements capable of cyclical movement generated synchronously with the cutting frequency between two limit positions, relative to the peripheral surface of the first 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: 
       FIG. 1  illustrates a portion of a filter tip attachment equipped with a unit for preparing leaves of paper material embodied in accordance with the present invention, viewed schematically in a front elevation; 
       FIG. 2  illustrates an enlarged detail of the unit shown in  FIG. 1 , viewed in perspective; 
       FIGS. 3 to 6  illustrate a detail of the unit of  FIG. 1  in a sequence of operating steps. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 and 2  of the accompanying drawings,  1  denotes a portion, in its entirety, of a cigarette maker, and in particular a filter tip attachment, comprising a unit  2  by means of which to prepare leaves  3  of paper material, or tipping papers, obtained from a continuous strip  4  caused to decoil from a relative bulk roll (not indicated) and advance along a predetermined feed path P in a direction denoted D, at a predetermined tension and linear speed. 
   As illustrated in  FIG. 1 , the unit  2  comprises cutting means  5  which in turn are composed of a first conveyor  6  consisting in a suction roller  7 , and a second conveyor  8  consisting in a second roller  9  turning substantially tangential to the first at a station  10  where the strip  4  is divided into single leaves  3 . 
   The rollers  7  and  9  are mounted to respective horizontal and mutually parallel shafts  11  and  12  carried in a frame  13  presented by the portion  1  of the cigarette maker and rotatable thus in opposite directions, turning clockwise and counterclockwise respectively as viewed in  FIG. 1 . 
   The second roller  9  carries a plurality of substantially radial blades  14  equispaced around and projecting from its peripheral surface  15 , whilst the suction roller  7  comprises a disc  16  keyed onto the relative shaft  11  and furnished at the periphery  17  with a plurality of cantilevered aspirating sectors  18  equispaced angularly around the circumference and extending parallel to the axis of rotation of the roller  7 , in such a way that the respective outer surfaces  19  of these same sectors  18  combine to create an outer cylindrical surface  20  that is set in rotation at a peripheral speed greater than the linear speed of the strip  9  advancing along the feed path P. 
   The outer surface  19  of each sector  18  presents a plurality of holes  21  connected in conventional manner by way of ducts  22 , extending parallel with the shaft  11 , to a source of negative pressure not illustrated in the drawings. The positioning of the sectors  18  around the periphery  17  of the disc  16 , moreover, is such that each remains distanced from the next, with the result that the outer surface  20  of the roller  7  presents a plurality of gaps  23 . 
   The outer surface  19  of each sector  18  presents a longitudinal corner edge  24  extending parallel to the axis of the first roller  7  and trailing in the direction of rotation, such as will combine with a corresponding blade  14  of the second roller  9  as it penetrates the relative gap  23  during the rotation of the rollers  7  and  9  and, when passing through the cutting station  10 , establish a scissor device by which the continuous strip  4  is sheared across to generate a single leaf  3 . 
   Still in  FIG. 1 , the filter tip attachment also comprises a roller  25  mounted to a shaft  26  lying parallel to the shafts  11  and  12  aforementioned, rotatable clockwise and furnished peripherally with grooves  27  each serving to accommodate a respective assembly  28  of two cigarette sticks separated by a double length filter plug, which is retained by suction in conventional manner; the assemblies  28  are caused to advance on the roller  25  transversely to their own axes through a transfer station  29  at which a tipping paper  3  is released by the suction roller  7  onto the outer surface of each successive assembly  28 , whereupon the filters and cigarette sticks are joined together. 
   In the example of the accompanying drawings, the unit  1  further comprises means  30 , associated with the suction roller  7 , by which to vary the tension of the continuous strip  4 . Such means  30  comprise diverter elements consisting in three cylindrical rods  31  extending parallel to the shaft  11  of the roller  7 . Each rod  31  is supported at one end by one corresponding arm  32  of a flange  33  presenting three such arms  32  equispaced angularly at 120°. 
   The flange  33  is mounted to the projecting end of a shaft  34 , rotatable about a relative axis  35  of which the position is fixed, extending parallel to the two roller shafts  11  and  12  and carried by a bulkhead  36  facing the frame  13  in such a way that the rods  31  extend from the flange  33  on the side of the roller  7  opposite to that occupied by the disc  16  supporting the aspirating sectors  18 . 
   In other words, the aspirating sectors  18  and the cylindrical rods  31  are cantilevered from their supporting elements, namely the disc  16  and the flange  33 , respectively, which occupy positions of mutual opposition on either side of the feed path P followed by the advancing strip  4 . 
   The cylindrical rods  31  extend toward the disc  16  through a distance such that their free ends lie in close proximity to the disc and are able to revolve thus around the axis  35 , which occupies a fixed position between the axis of the shaft  11  carrying the suction roller  7 , and the outer surface  20  of this same roller  7 . As discernible from  FIG. 1 , in particular, the shaft denoted  34  is coupled to the shaft  11  of the suction roller  7  by way of an interposed train of gears  37 ,  38  and  39  functioning also as means by which to adjust the timing between the rotation of the suction roller  7  and that of the tension varying means  30  in such a way that the three cylindrical rods  31  can be made to alternate cyclically and at the same frequency as the cutting means  5  between a first limit position radially behind the surface  20  of the suction roller  7  and a second limit position radially beyond the selfsame surface  20 , by passing through the aforementioned gaps  23 . 
   In operation, the continuous strip  4  advances at a predetermined linear speed along the feed path P through a gumming station  40  and a guide roller  41 , ultimately reaching the outer surface  20  of the suction roller  7  which, in order to distance the leaves  3  separated at the cutting station  10 , is caused to rotate at a peripheral speed greater than the linear speed of the advancing strip  4 . This difference in speed causes the strip  4  positioned upstream of the cutting station  10  to slip on the outer surfaces  19  of the sectors  18 , against which it is held by suction. 
   It will be seen from  FIGS. 1 and 3  that after a leaf  3  has been cut, and as the strip  4  advances a distance corresponding to the length of a further leaf  3 , one of the rods  31  of the tension varying means  30 , orbiting around the fixed axis  35  as the relative shaft  34  rotates synchronously with the suction roller  7 , will pass through a gap  23  and assume the second limit position radially beyond the surface  20  of the suction roller  7  as indicated in  FIG. 3 . In this configuration, the strip  4  is engaged by the rod  31  and diverted from the feed path P, with the result that the length of the path is effectively increased and loop of strip  4  is formed around the rod  31 . 
   With the suction roller  7  continuing to rotate on its shaft  11  and the rod  31  continuing to revolve about the axis  35 , as illustrated in the sequence of  FIGS. 4 to 6 , the rod  31  will be returned from the second limit position beyond the surface  20  of the roller  7  to the first limit position behind the selfsame surface. During this step, the slipping movement of the strip  4  against the surfaces  19  of the aspirating sectors  18  is practically eliminated as the loop formed initially over the rod  31  is gradually taken up, and the operation of preparing a further leaf  3 , in which a blade  14  combines with the edge  24  of a corresponding sector  18  to make a scissor cut across the strip, is completed without tearing the paper material. 
   Thereafter, the next cylindrical rod  31  will pass through the next corresponding gap  23  to begin a new cycle, diverting the strip  4  in readiness for a further leaf  3  to be cut.