Abstract:
A shingling apparatus for sheets of paper or paperboard includes a pair of independently operable vacuum plenums in a gap between an in-feed conveyor and a reduced speed shingling conveyor. One of the vacuum plenums decelerates an incoming sheet to shingling conveyor speed while the second vacuum plenum captures and pulls down the tail of the sheet to allow the faster moving following sheet to override the tail. This dual vacuum action enhances sheet control, requires very little vertical displacement of the sheets at the vacuum plenums, and enhances the squareness of the shingle that is formed. The system may also include a downstream shingle separator including a translating connection that assists in pulling the necessary gap between downstream shingle portion being directed into a stacker and an upstream shingle portion that is accumulated until the downstream shingle portion is stacked and discharged.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention pertains to a system for compressing a conveyed line of paper or paperboard sheets into a shingle and, more particularly, to such a system utilizing a dual plenum vacuum shingling device. The system may also include a shingle separation subsystem.  
         [0002]     Vacuum shingling is well known and well developed in the art of handling sheets of paper and paperboard. When sheets of paper or paperboard are cut to length for further downstream conversion, they are usually delivered from a knife or other cutoff device as a high speed line of closely spaced sheets, often moving at a speed of 1,000 feet per second (about 300 meters per second) or more. In order to compress the line of sheets to facilitate handling, as for example for forming stacks of sheets, the line of sheets is formed into a shingle which continues to advance at a much reduced speed. In order to form a shingle, the sheets must be slowed considerably and handled in a manner such that the lead edge of each following sheet is made to overrun the tail edge of the sheet immediately preceding it. This may require the sheets to be slowed on a shingling conveyor to a speed that is only 20% of incoming line speed or less.  
         [0003]     Because of wide variations in line speed at which the sheets are fed, the percent shingle (overlap) required, sheet length and basis weight of the paper or paperboard sheets, many different ways have been developed for shingling and for controlling sheets in the shingling process. Another complication is introduced when sheets are preprinted or finished on the exposed top sides such that contact of the sheets with overhead snubber wheels, brushes or the like is undesirable or impossible. In such cases, vacuum shingling by which the sheets are captured and slowed from line speed by applying a vacuum to the undersides of the sheets is a common practice.  
         [0004]     Nevertheless, it would be desirable to have a vacuum shingling system that would be adaptable to handle a wider range of sheet sizes and basis weights, over a wide range of delivery line speeds and shingle overlap and, in particular, with a system that would not include devices that rub and could scuff finished upper sheet surfaces.  
       SUMMARY OF THE INVENTION  
       [0005]     In accordance with the present invention, an apparatus is provided for shingling a line of sheets having sensitive surface quality that prevents the use of potentially scuffing surface engaging devices and for forming a shingle from sheets delivered at high in-feed speeds.  
         [0006]     In a preferred embodiment, the apparatus includes an in-feed conveyor that carries a line of closely spaced sheets on a generally planar sheet conveying surface at a first speed; a shingling section that receives the line of sheets from the downstream end of the in-feed conveyor, including a shingling conveyor having a shingle forming surface operable at a second speed less than the first speed; a vacuum station that separates the in-feed conveyor and the shingling conveyor, the vacuum station including an upstream vacuum chamber having a first vacuum surface defining a first vacuum opening and an adjacent downstream vacuum chamber having a second vacuum surface defining a second vacuum opening; the first vacuum surface positioned to slope upward from an upstream edge positioned below the downstream end of the sheet conveying surface to a downstream edge adjacent the second vacuum surface, the second vacuum surface positioned to lie generally parallel to and at or below the plane of the sheet conveying surface of the in-feed conveyor; and a vacuum control operable to apply vacuum independently to the upstream chamber to drop the tail end of each sheet leaving the in-feed conveyor onto the first vacuum surface and to the downstream chamber to decelerate each sheet to the second speed.  
         [0007]     Preferably, the upstream edge of the first vacuum surface is adjustably positioned in a range of bout 0.5-0.75 inch (about 13-19 mm) below the sheet conveying surface. The second vacuum surface is preferably adjustably positioned in a range of about 0-0.25 inch (about 0-6 mm) below the sheet conveying surface of the in-feed conveyor. In one embodiment, the first vacuum surface is upwardly convex and joins the upstream of the second vacuum surface at a generally horizontal tangent. The vacuum control is preferably operable to apply vacuum to the upstream and downstream chambers independently of one another.  
         [0008]     In a presently preferred embodiment, an air nip is positioned over the shingling conveyor and includes a narrow slot that extends across the width of the sheets and is positioned to direct a thin stream of air against the lead edge of a sheet on the shingling conveyor to nip the sheet on the shingling conveyor during application of vacuum to the downstream vacuum chamber. The air nip may be adjustably positionable in the direction of sheet movement. Alternately, the apparatus may include a snubber wheel assembly that is positioned over the shingling conveyor and is operative to engage the lead edge of a sheet and to nip the sheet on the shingling conveyor during application of vacuum to the downstream vacuum chamber. The snubber wheel assembly may be adjustably positionable horizontally in the direction of sheet movement. In another embodiment, a vacuum conveyor belt is positioned to operate over the vacuum surfaces at the second speed. A cam roll may also be positioned between the vacuum surfaces, the cam roll having an inoperative surface portion below the vacuum surfaces and an operative position rotatable into sheet engaging position above the vacuum surfaces in response to said vacuum control.  
         [0009]     In a further embodiment of the invention, a shingle separating apparatus is operatively connected to the downstream end of the shingling conveyor. The shingle separating apparatus preferably comprises a shingle separating conveyor; a vacuum plenum providing an operative connection between the shingling conveyor and the shingle separating conveyor, the vacuum plenum having a vacuum opening exposed to a shingle traveling thereover; a second vacuum control operable to apply vacuum from the vacuum opening to the tail end of a first sheet defining an upstream shingle portion to be separated from a downstream shingle portion; and, a shingle separating conveyor drive operative in response to the vacuum control to accelerate the shingle separating conveyor and the downstream shingle portion to a third speed greater than the second speed. The apparatus may include a nip roller device positioned over the shingle separating conveyor and operative in response to the second vacuum control to engage the last sheet of the downstream shingle portion. In a presently preferred embodiment, the shingle separating apparatus includes a shingle holding conveyor providing with the vacuum plenum the operative connection, and the shingle holding conveyor and the shingle separating conveyor comprise belt conveyors, each operating around respective pairs of head and tail pulleys; a first translating connection includes the vacuum plenum interconnecting the shingle holding conveyor head pulley and the shingle separating conveyor tail pulley; a second translating connection interconnecting the stub conveyor tail pulley and the shingle separating conveyor head pulley; and, a translation device that is operable to move the first translating connection downstream at a fourth speed to separate the downstream shingle portion from the upstream shingle portion. Preferably, the fourth speed is equal to the third speed.  
         [0010]     The present invention also includes a method for shingling a line of sheets that are delivered in closely spaced relation from the downstream end of a generally horizontal in-feed conveyor, the method comprising the steps of: (1) positioning a first vacuum surface to slope upwardly from an upstream edge below the downstream end of the in-feed conveyor to a downstream edge; (2) positioning a second vacuum surface to extend generally horizontally downstream from adjacent the downstream edge of the first vacuum surface generally coplanar with or slightly below the plane of said in-feed conveyor to a downstream edge; (3) positioning a generally horizontal shingling conveyor to extend downstream from the downstream end of said second vacuum surface; (4) operating the in-feed conveyor at a first speed and operating said shingling conveyor at a second speed less than said first speed; (5) applying a vacuum to the second vacuum surface to decelerate each sheet to approach said second speed; (6) applying a vacuum to said first vacuum surface to drop the tail of each sheet leaving the in-feed conveyor onto the first vacuum surface; and (7) controlling the application of vacuum to said first and second vacuum surfaces in response to movement of the tail end of the sheet past each respective surface.  
         [0011]     Preferably, the method also includes the step of adjustably positioning the upstream edge of the first vacuum surface in a range of about 0.5-0.75 inch (about 13-19 mm) below the in-feed conveyor. A method also preferably includes the step of adjustably positioning the second vacuum surface in a range of about 0-0.25 inch (about 0-6 mm) below the in-feed conveyor.  
         [0012]     The method may also include the additional steps of (1) positioning a shingle separating conveyor downstream of the shingling conveyor; (2) connecting the upstream end of the shingle separating conveyor to a translating device including a vacuum plenum; and (3) operating the translating device to move the shingle separating conveyor and vacuum plenum downstream at a selected speed to separate a downstream shingle portion carried thereon from an upstream shingle portion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a generally schematic side elevation of a sheeter system incorporating the apparatus and performing the method of the subject invention.  
         [0014]      FIG. 2  is a schematic side elevation view of the dual modulated vacuum shingler of the present invention.  
         [0015]      FIG. 3  is an enlarged detail of a portion of  FIG. 2 .  
         [0016]      FIG. 4  is a generally schematic side elevation of the shingle separating conveyor of the present invention showing thereon a line of shingled sheets.  
         [0017]      FIG. 5  is a side elevation view similar to  FIG. 4  showing the downstream translation of the shingle separating conveyor.  
         [0018]      FIG. 6  is an alternate embodiment of the vacuum section shown in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Referring initially to  FIG. 1 , a sheeter  10  converts a paper or paperboard web  11  wound from a roll  12  mounted on a roll stand  13  to one or more streams of sheets  20  that are eventually accumulated in a vertical stack in a downstream stacker  15 . The stacks are carried on pallets  16  for discharge from the stacker  15 . In the sheeter system shown, the web  11  from one of the rolls  12  passes initially through a tension decurler  19  where the curl in the web resulting from winding on the roll is removed. The web then passes through a tension isolator and a web aligner  29  from which it is directed into a slitter  17  which slits the web  11  longitudinally into two or more parallel web portions. The slitter  17  may also include scoring tools that provide longitudinal score lines in the running web portions to, for example, facilitate subsequent folding of the converted sheets. The longitudinal web portions continue through a rotary cutoff knife  18  which severs each web portion laterally into a continuous stream of rectangular sheets  20  (see  FIG. 3 ). The knife outfeed includes a sheet conveyor  21  that also comprises an in-feed conveyor to the vacuum shingler of the present invention. The sheet conveyor or in-feed conveyor  21  operates at a slight overspeed with respect to the speed of the web entering the cutoff knife  18  such that a small gap is pulled between the trailing edge of each cut sheet and the leading edge of the web that follows. Thus, the in-feed conveyor  21  carries a line of closely spaced sheets  20  into the dual modulated vacuum shingler  22  of the present invention.  
         [0020]     In the shingler  22 , the line of sheets  20  is compressed by shingling them one atop another by successively slowing each lead sheet in a manner permitting its lead edge to overlap the tail edge of the preceding sheet. The shingler includes a shingling conveyor  24  on which the shingle is formed operating at a substantially lower speed than the in-feed conveyor  21 . Immediately downstream from the shingling conveyor  24 , a shingle separator  25  separates and accelerates a downstream shingle portion which is conveyed into the stacker  15  to form a stack  14 , while the gap between the downstream and upstream shingle portions created at the shingle separator  25  permits the stack  14  to be unloaded from the stacker which is then readied to receive and stack the following shingle portion.  
         [0021]     It is critically important to form a shingle that is straight and square in order to achieve high stack quality in the stacker  15 . In the industry, there are a number of methods used to reliably form a high quality shingle at high speeds. Most methods utilize a vacuum plenum between the in-feed conveyor and the shingling conveyor to help decelerate the sheets to the shingling conveyor speed. In addition, shinglers typically also utilize snubber wheels or rollers positioned above the upstream end of the shingling conveyor to form a decelerating nip with the shingling conveyor. The snubber wheels or rollers help decelerate the high speed sheets by nipping the lead edge of each sheet onto the trailing edge of the preceding sheet on the shingling conveyor  24  which, as indicated, is operating at a substantially lower speed than the in-feed conveyor  21 . It is common, for example, to decelerate the sheets to 20% of the in-feed conveyor speed (creating an 80% overlap in the shingle). This rapid deceleration presents a significant challenge to maintaining squareness in the shingle and the difficulty increases as line speeds increase.  
         [0022]     Webs  11  that are preprinted with graphics or provided with sensitive coatings often cannot tolerate scuff marks on the upper surface as a result of decelerating contact with snubber wheels or rollers. In accordance with one aspect of the present invention, the vacuum shingler  22  of the present invention provides reliable high speed shingling without the need for physically contacting the upper surfaces of the sheets in a manner that permits line speed as high as 1,500 fpm (about 8 mps).  
         [0023]     Referring now particularly to  FIGS. 2 and 3 , the in-feed conveyor  21 , comprising upper and lower tape belts  26  and  27 , captures the lead edge  28  of the web  11  just as the rotary cutoff knife  18  severs the web to form a sheet  20 . The slight overspeed of the belts  26  and  27  with respect to web speed into the knife  18 , creates a small gap between the trailing edge  30  of the cut sheet and the lead edge of the web moving into and through the knife, all in a manner well known in the art. The in-feed conveyor  21  carries the closely spaced sheets into the vacuum shingler  22  of the present invention where the sheets are serially captured in a vacuum section  31  and decelerated to the lower speed of the shingling conveyor  24 . The vacuum section  31  includes an upstream first vacuum surface  32  that includes an upwardly sloping surface to which a vacuum is applied through a first vacuum slot  33 . In the presently preferred embodiment, the first vacuum surface  32  is joined at its downstream edge with the upstream edge of a second vacuum surface  34  that is generally horizontally disposed and to which vacuum is applied via a second vacuum slot  35 . Each of the vacuum surfaces  32  and  34  has its own vacuum plenum  36  and  37 , respectively, so that vacuum may be applied to each separately. Vacuum through the respective slots  33  and  35  is selectively applied by a conventional sliding shuttle valve  38  which may also be controlled to modulate the vacuum force. It has been found that the use of dual vacuum plenums  36  and  37  greatly enhances sheet control and shingle quality. Furthermore, the timing of the application of vacuum to the sheets, as well as the modulation thereof, may be adjusted and controlled to provide optimum shingling for sheets of varying size and basis weight and for different in-feed conveyor speeds. The vertical positioning of the vacuum plenums may also be adjusted within a relatively small range, again based on sheet parameters and line speed. In particular, the use of two independently controlled vacuum plenums permits shingling to be effectively accomplished with a very small vertical displacement of the sheets from the plane of the in-feed conveyor, thereby minimizing the opportunity for sheet misalignment. Finally, effective shingling may be accomplished without the use of snubber wheels over the shingling conveyor but, if the sheet and operating parameters require some additional nipping force, the system of the present invention includes an air nip to provide a supplemental downward nipping force on the sheet being shingled.  
         [0024]     In  FIG. 3 , an intermediate sheet  40  is shown under the control of the vacuum section  31  with the leading edge  43  of the intermediate sheet  40  overlapping (shingled on) the trailing edge  44  of a lead sheet  41  on the shingling conveyor  42 . Using the system vacuum control (not shown, but of a conventional construction), vacuum is applied to the second (downstream) vacuum surface  34  as soon as the leading edge  43  of intermediate sheet  40  reaches the vacuum slot  35 . The vacuum force captures the sheet  40  and decelerates it to the lower speed of the shingle conveyor  24  or to an even lower speed. However, as is well known in the art, the leading edge  45  of the next trailing sheet  42  (which is traveling at the much higher in-feed speed) will quickly overtake the intermediate sheet  40  and, if some means of dropping trailing edge of the intermediate sheet is not provided, edge butt will occur between the intermediate sheet  40  and the trailing sheet  42 , resulting in disruption of the shingle. Thus, as the trailing edge  46  of the intermediate sheet  40  leaves the downstream end of the in-feed conveyor  21 , vacuum is applied by the controller to the first vacuum plenum  36  and the trailing end of the intermediate shingle  40  is sucked down onto the first vacuum surface  32  by the vacuum applied through the slot  33 . This clears the trailing edge  46  of sheet  40  so the leading edge  45  of the next sheet  42  can begin to override it without disruptive contact.  
         [0025]     The upstream edge  47  of the first vacuum surface  32  may be vertically positioned below the plane of the in-feed conveyor  21  by a small distance, preferably variable within a range of about 0.5-0.75 inch (about 13-19 mm). The first vacuum surface slopes upwardly from its upstream edge such that it joins the upstream edge  48  of the second vacuum surface  34  at a generally horizontal tangent line. The first vacuum surface  32  may be curved and upwardly convex to provide smooth transition of the sheets. The second vacuum surface  34  is preferably disposed horizontally and is vertically adjustable within a small range of coplanar with the in-feed conveyor  21  (sometimes referred to as board pass height) to a position about 0.25 inch (about 6 mm) below the plane of the in-feed conveyor. Adjustments of the vertical position of the first and second vacuum surfaces  32  and  34 , again, depends on many variables including sheet length, sheet basis weight, in-feed line speed and shingling conveyor speed.  
         [0026]     In order to operate at higher line speeds and correspondingly higher shingling speeds, it may be necessary to provide a supplemental nipping force to assist the sheet stopping force applied by the second vacuum plenum  37 . This supplemental nipping force is applied downwardly to nip the sheet on the shingling conveyor  24  just as the trailing edge of the sheet leaves the in-feed conveyor and the vacuum controller applies a vacuum to the second vacuum surface  34  to decelerate the sheet. However, because rotary snubber wheels can damage sensitive pre-printed or coated sheet surfaces, an air nip  50 , positioned over the shingling conveyor  24 , is used to provide this supplemental nipping force. The air nip  50  comprises a thin slit  51  that extends the full width of the sheets through which compressed air is blown to create a uniform air curtain directed downwardly against the sheet. The air nip nozzle  52  may be adjustable vertically as well as rotationally around a horizontal axis so that the air curtain may be directed either slightly in an upstream direction or a downstream direction, depending on sheet and operating parameters. The air controller may also be operated to modulate the air flow and thus the force of the air nip. In addition, the air nip  50  may be adjustably positioned longitudinally over the shingling conveyor to accommodate varying sheet lengths. Of course, if sheet surface quality is not an issue, conventional snubber wheels  59 , shown in phantom in  FIG. 2 , may be used instead. A supplemental nipping force may also be applied by alternate means, including tape belts that are located above the shingle. The belts are adjustable vertically to move down to nip the shingle against the shingling conveyor  24 . Such nipping belts may also be positioned to provide a downward nip force on the vacuum section  31 , including a modified section utilizing  FIG. 6  cam roller.  
         [0027]      FIG. 6  shows a modification of the vacuum section  31  previously described and shown in  FIG. 3 . In  FIG. 6 , the first and second vacuum plenums  36  and  37  have been separated and a cam roller  53 , rotatable on a horizontal axis, is positioned between the plenums. Instead of a roller, a series of axially spaced cam wheels could be substituted. The cam roller  53  has a cylindrical surface  54  that makes tangent contact with the underside of a sheet (such as intermediate sheet  40 ) moving over the modified vacuum section  49 . The cam roller  53  also has a flat surface  55  which, when the roller  53  is rotated 180° from the position shown in  FIG. 6 , places the flat surface out of contact with a sheet traveling through the vacuum section  49 . Rotation of the cam roller  53  is timed to coincide with release of the vacuum from the vacuum plenums  36  and  37  so that the roller is rotated through the arc of its cylindrical surface  54  (in the direction shown by the arrow) to contact the sheet and assist in moving it onto the shingling conveyor. The cam roller  53  may be used as a substitute for the air nip  50  or the snubber wheels  59 , or in addition to either.  
         [0028]     As an alternate to the cam roller  53 , a porous vacuum belt (not shown) could be mounted to operate over the vacuum surfaces  32  and  34  at shingling conveyor speed to assist in moving the sheets. Operation of the porous vacuum belt may be timed to coincide with the application of vacuum to vacuum plenums or the belt could be operated continuously.  
         [0029]      FIGS. 4 and 5  show details of the shingle separator  25  which is positioned immediately downstream of the shingling conveyor  24 . The shingle separator includes two independently operable conveyors comprising an upstream shingle holding conveyor  56  and a downstream shingle separating conveyor  57  which are interconnected with a first translating connection  58  that includes a vacuum plenum  60 . The respective opposite ends of the conveyors  56  and  57  are interconnected with a second translating connection  61 . The holding conveyor  56  and the separating conveyor  57  may comprise any type of suitable belt conveyor, such as tape belt conveyors. The shingle holding conveyor  56  includes a head pulley  62  and a tail pulley  63 . Similarly, the shingle separating conveyor includes a head pulley  64  and a tail pulley  65 . The first translating connection  58  (including the vacuum plenum  60 ) interconnects the holding conveyor head pulley  64  and the separating conveyor tail pulley  65 . Correspondingly, the second translating connection  61  interconnects the holding conveyor tail pulley  63  and the separating conveyor head pulley  64 .  
         [0030]     In operation, the holding conveyor  56  and the separating conveyor  57  are positioned as shown in  FIG. 4  and operated together at the same speed as the upstream shingling conveyor  24 . When it is desired to separate a downstream shingle portion  66  from an upstream shingle portion  67  to create a gap therebetween to facilitate operation of the stacker  15 , the separating conveyor  57  is accelerated and vacuum is applied to the vacuum plenum  60  to capture the lead edge of first sheet  68  of the upstream shingle portion  67 . Acceleration of the shingle separating conveyor  57  pulls the downstream shingle portion  68  away from the upstream shingle portion  67 . A nip roll  69  in contact with the last sheet  70  of the downstream shingle portion may be used to help assure that the last sheet  70  is pulled free of the singled first sheet  68  of the upstream shingle portion. Simultaneously, the first translating connection  58  is operated to move downstream at the same speed as the accelerated separating conveyor  57  carrying the downstream shingle portion  66 . This movement provides a gap between the shingle portions  66  and  67  which permits the upstream shingle portion  67  to be accumulated while the downstream shingle portion  66  is cleared from the separating conveyor  57  for stacking. It should be noted that the second translating connection  61  moves with the first translating connection  58  at the same speed but in the opposite direction, as shown in phantom in  FIG. 5 . After the downstream shingle portion  66  is cleared from the separating conveyor  57 , the separating conveyor is slowed to the speed of the holding conveyor  56  and the shingling conveyor  24 . The vacuum to vacuum plenum  60  is shut off, releasing the first sheet  68  of the upstream shingle portion  67  and the first translating connection  58  is reversed and moved back to the  FIG. 4  starting position.