Patent Publication Number: US-10329114-B2

Title: Stacker hopper with feed interrupt

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 62/256,421, filed Nov. 17, 2015, the entire contents of which is hereby incorporated by reference. 
    
    
     TECHNOLOGICAL FIELD 
     The present disclosure is directed to an accumulator for a hopper of a sheet stacking system, and to a method of operating the accumulator, and, more specifically, to a sheet stacking system having a hopper with an accumulator configured to interrupt a cascading flow of sheets exiting a conveyor and to support a partial stack of sheets while a main stack of previously deposited sheets is removed from beneath the accumulator. 
     BACKGROUND 
     A conventional stacking apparatus  10  is illustrated in  FIG. 1 . The stacking apparatus  10  is configured for use adjacent to a rotary die cut machine  12  which cuts blanks (not illustrated) from sheets of material, for example, corrugated paperboard. The stacking apparatus  10  includes a receiving or “layboy” section  14  that receives the blanks from the die cut machine  12  and discharges them onto a transfer conveyor  16 . The transfer conveyor  16  carries the blanks to an inclined main conveyor  18 , and the blanks travel along the main conveyor  18  to its downstream end  20  where they are discharged into a hopper  22 . 
     After the blanks are discharged from the downstream end  20  of the main conveyor  18 , they impact against a backstop  24  and fall either a) directly onto a discharge conveyor  28  or b) onto elevating fingers  26  which controllably lower stacks of the blanks onto the discharge conveyor  28 . As the stack  30  on the elevating fingers  26  grows, the elevating fingers  26  drop, either continuously or periodically, so that the sheets leaving the main conveyor  18  are always falling approximately the same distance from the downstream end  20  onto the elevating fingers  26  or onto the partial stack  30  on the discharge conveyor  28 . In other embodiments, the sheets may fall on a fixed height platform or conveyor, and the downstream end  20  of the main conveyor  18  may rise to stay a relatively fixed distance above the top of the growing stack  30 . 
     When the stack  30  has reached a desired height, the elevating fingers  26  lower the stack  30  to a level even with the discharge conveyor  28 , if elevating fingers  26  are used, and the discharge conveyor  28  moves the finished stack  30  away from the stacking apparatus  10 . When the stack  30  has been transferred from the elevating fingers (or when the stack has moved away from the location beneath the hopper  22  if the stack was formed directly on the discharge conveyor  28 ), the elevating fingers  26  rise toward the hopper  22  for receiving additional sheets from the downstream end  20  of the main conveyor  18 . 
     The rotary die cut machine  12  operates substantially continuously, and sheets of material therefore continue to traverse the stacking apparatus  10  and reach the hopper  22  even when a finished stack is being removed from the discharge conveyor  28  and/or when the elevating fingers  26  are lowering the stack  30  toward the discharge conveyor  28 . During the time that the stack  30  is being removed from beneath the hopper  22 , accumulator shelves  32  are extended to receive sheets as they leave the downstream end  20  of the main conveyor  18 . When a finished stack has been removed from beneath the hopper  22  and the elevating fingers  26  are back in position for receiving additional sheets, the accumulator shelves  32  retract and drop the sheets that have accumulated thereon onto the elevating fingers  26  or onto the discharge conveyor  28 . Additional sheets exiting the downstream end  20  of the stacking apparatus  10  fall onto the stack, and the process repeats until the stack on the elevating fingers  26  or the discharge conveyor  28  reaches a desired height. 
     It is common to include a tamping device in the hopper  22 . Such a tamping device repeatedly presses in against the stack on the accumulator shelves  32 —either from one or both sides or from the front and/or back, to align or square the small stack on the accumulator shelves  32 . It is often desirable to finish squaring or tamping the stack on the accumulator shelves  32  before withdrawing the accumulator shelves  32  and dropping the small stack onto the elevating fingers  26  or the discharge conveyor  28 . 
     Modern rotary die cut machines and stackers operate at increasingly high speeds, and the number of sheets transported per minute is thus increasing. To maintain a high throughput, it is desirable to keep the rotary die cut machine and the stacker operating continuously. However, with present stacker designs, it is difficult or impossible to finish tamping a small stack of sheets on the accumulator shelves and drop that small stack from the accumulator before the next sheets start to fall from the end of the main conveyor. This is particularly true when the stackers employ a blowing device to cause the sheets exiting the discharge end of the main conveyor to fall faster than they would under the force of gravity alone, particularly in the case of large sheets that tend to float on a cushion of air as they drop. In such devices, it is difficult or impossible to consistently time accumulator operation so that a laterally extendable accumulator shelf can be inserted into a falling stack of sheets without either damaging the edges of the sheets or possibly causing a jam. 
     SUMMARY 
     These problems and others are addressed by embodiments of the present disclosure, a first aspect of which comprises a sheet stacking system including a conveyor configured to carry sheets from a conveyor intake end to a conveyor discharge end and having a hopper at the discharge end configured to receive the sheets ejected from the discharge end of the conveyor and guide the sheets as they fall in a cascade path onto a platform associated with the hopper. The falling sheets form a main stack on the platform. The hopper has a backstop facing the discharge end of the conveyor such that the sheets ejected from the discharge end impact against the backstop before forming the main stack. The system also includes a first accumulator comprising at least one first support extending through the backstop which support is shiftable from a retracted position to an extended position. The at least one first support is movable vertically relative to the backstop in the extended position from a raised location outside the cascade path to a lowered location in the cascade path. 
     Another aspect of the disclosure comprises a method of operating the above sheet stacking system that includes placing the at least one support in the extended position at the raised location, discharging sheets from the conveyor such that they impact the backstop below the at least one support and fall onto the platform or onto sheets supported by the platform to form the main stack, moving the at least one first support in the extended position from the raised location to the lowered location while the sheets fall along the cascade path, shifting the at least one second support from the retracted position to the extended position, and forming a first partial stack on the at least one first support and on the at least one second support above the main stack. 
     Yet another aspect of the disclosure comprises a sheet stacking system that includes a conveyor configured to carry sheets from a conveyor intake end to a conveyor discharge end and a hopper at the discharge end configured to receive the sheets ejected from the discharge end of the conveyor and guide the sheets as they fall in a cascade path onto a platform associated with the hopper. The falling sheets form a main stack on the platform. The hopper has a backstop facing the discharge end of the conveyor such that the sheets ejected from the discharge end impact against the backstop before forming the main stack. The system also includes an accumulator comprising at least one support extending through the backstop, the at least one support having a substantially horizontal upper support surface having a free end and a bottom surface extending away from the free end at an acute angle to the upper support surface and forming a triangle when viewed from a side of the hopper. The at least one support is shiftable from a retracted position to an extended position relative to the backstop, and the at least one support is movable vertically relative to the backstop in the extended position from a raised location to a lowered location 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic elevational view of a conventional rotary die cut machine and a conventional stacking system. 
         FIG. 2  is a schematic elevational view of a rotary die cut machine and a stacking system according to an embodiment of the present disclosure. 
         FIG. 3  is a detail view of the discharge end of the stacking system of  FIG. 2 . 
         FIGS. 4-6  illustrate the formation of a stack at the discharge end of the stacking system of  FIG. 2 . 
         FIG. 7  is a schematic side elevation view of the interrupt fingers of the stacking system of  FIG. 2  shown in extended and retracted positions. 
         FIG. 8  is a top plan view of the discharge end of the stacking system of  FIG. 2 . 
         FIG. 9  is an end elevational view of the stacking system of  FIG. 2  with the backstop removed for illustration purposes 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, wherein the showings are for purposes of illustrating embodiments of the disclosure only and not for the purpose of limiting same,  FIG. 2  shows a main conveyor  100  having an intake end  102  and a discharge end  104  which is configured to carry sheets  106  in a sheet travel direction (sometimes referred to as a “downstream” direction) from the intake end  102  toward the discharge end  104 . As the sheets  106  reach the discharge end  104 , they are ejected into a hopper  108  which hopper  108  comprises, among other elements discussed hereinafter and best illustrated in  FIG. 8 , a backstop  110 , a front wall  112 , a fixed side guide  114 , a movable side guide  116 , and a bottom opening  108 . The movable side guide  116  and an actuator  117  form a tamper for tamping or squaring stacks of sheets in the hopper  108 . 
     The forward edges of the sheets  106  leaving the discharge end  104  of the main conveyor  100  begin to drop under the force of gravity and, optionally, the force of a downward flow of air produced by a blower  120 . The downstream motion of each sheet  106  is arrested when the sheet  106  impacts against the backstop  110 . This occurs at approximately the same time a trailing edge of the sheet  106  passes the discharge end  104  of the main conveyor  100 , and each sheet  106  thus falls under the force of gravity, and optionally the force of the air flow produced by the blower  120 , toward a receiving device which may comprise, for example, a conventional discharge conveyor  122  or elevating fingers  124 . The present embodiment includes elevating fingers  124 ; however, persons of ordinary skill in the art will understand that the elevating fingers  124  could be omitted, for example, if the discharge end  104  of the main conveyor  100  can be raised during conveyor operation. The function of the hopper  108  remains substantially the same whether or not the elevating fingers  124  are used. 
     The sheets  106  are ejected substantially continuously from the discharge end  104  of the main conveyor  100  and form a cascade of sheets that travel along what is referred to herein as a “cascade path”  126 . This cascade path  126  comprises the volume through which the sheets  106  pass between the discharge end  104  of the main conveyor  100  and the elevating fingers  124  or other receiving device. Much of the cascade path  126  is defined by the elements of the hopper  108 , namely, the backstop  110 , the front wall  112 , the fixed side guide  114  and the movable side guide  116 . Because the leading edges of the sheets  106  begin to drop toward the elevating fingers  124  before the trailing edge of the sheets  106  pass the discharge end  104 , the upper edge  128  of the cascade path  126 , shown by a dashed line in  FIGS. 3 and 5 , curves and meets the backstop  110  at a location that is lower than the discharge end  104  of the main conveyor  100 . 
     If nothing obstructs the cascade path  126 , the sheets leaving the discharge end  104  of the main conveyor  100  will land on the elevating fingers  124 , or on sheets  106  that were previously deposited on the elevating fingers  124 , and form a stack. The elevating fingers  124  are configured to lower stacks of the sheets  106  onto the discharge conveyor  122  so that the discharge conveyor  122  can move the finished stacks transverse to the downstream direction and away from the bottom opening  118  of the hopper for further processing. However, the flow of sheets  106  leaving the discharge end  104  of the main conveyor  100  does not stop while the elevating fingers  124  and the discharge conveyor  122  are removing finished stacks of the sheets  106 . It is therefore necessary to provide at least one accumulator for catching and retaining falling sheets  106  until the elevating fingers  124  are back in position to receive the sheets  106  falling from the bottom opening  118  of the hopper  108 . 
     The hopper  108  includes an accumulator shelf  132  that is shiftable between retracted and extended positions relative to the front wall  112  of the hopper  108  and accumulator pins  134  that are shiftable between retracted and extended positions relative to the backstop  110  of the hopper  108 . It is known from the prior art to use an accumulator shelf to catch falling sheets while a finished stack is removed from below a hopper. However, as the speeds at which the rotary die cut machine and the main conveyor  100  increase, and especially when the blower  120  is used to make the sheets  106  fall through the hopper  108  faster than they would under the force of gravity alone, it becomes increasingly difficult to time the operation of an accumulator shelf so that it extends into a space between two falling sheets  106  rather than impacting the edge of a falling sheet and causing a jam. 
     To address this problem, the disclosed stacking system includes a novel accumulator  136  that may be used alone or together with another accumulator  138 . The novel accumulator may be referred to hereinafter as the “first” accumulator and other accumulator as a “second” accumulator even though it is not always necessary to provide the second accumulator  138 . 
     The first accumulator  136  comprises a plurality of first supports  140  that are configured to be selectably and controllably extended and retracted relative to the backstop  110 . To this end, the backstop  110  may be formed from a unitary sheet of material having a plurality of parallel slits (not illustrated) or, alternately, formed as a plurality of closely spaced strips of material separated by elongated gaps through which the first supports  140  can project. 
     Each of the first supports  140  has a generally horizontal top surface  142  (see  FIG. 7 ) and an angled lower surface  144  that meets the top surface  142  at an acute angle at a tip  146 . Each of the first supports  140  is slidably mounted in a housing  148  located on the opposite side of the backstop  110  from the main conveyor  100 , which housing  148  also supports a horizontal actuator  150 , which may comprise a pneumatic cylinder, for example. The horizontal actuator  150  is configured to extend in order to slide the first support  140  through the backstop  110  to an extended position and to retract to pull the first support  140  back into the housing  148  into a retracted position.  FIG. 7  illustrates the first support  140  in the extended position and the retracted position; two configurations of the first support  140  are shown in two housings  148  on a single vertical shaft  152  for illustration purposes. Only one housing  148  is provided on each vertical shaft  152  in actual embodiments. 
     The housing  148  is also mounted for vertical sliding movement on the vertical shaft  152  under the control of a vertical actuator  154 , another pneumatic cylinder, for example, for sliding movement between a raised location, illustrated in  FIGS. 4 and 5 , and a lowered location illustrated in  FIGS. 2 and 3 . The horizontal actuator  150  and the vertical actuator  154  are independently controllable by a suitable controller, which may comprise, for example, a microprocessor or a PLC, preferably the controller that controls other operations of the overall stacking system. 
     The first accumulator  136  also includes a plurality of second supports  158 , in this case, a plurality of pins  158 , that are configured to move between an extend position and a retracted position relative to the front wall  112  of the hoper  108 . The pins  158  are vertically fixed and are located at the approximate level of the lowered location of the first supports  140 . That is, when the first supports  140  are in the extended position at the lowered location and the pins  158  are in the extended position, the top surfaces  142  of the first supports  140  and the pins  158  support sheets  106  in the hopper  108  in a substantially horizontal orientation. 
     When the second supports  158  are in the retracted position, they are located outside the cascade path  126 , and when the second supports  158  are in the extended position they extend into the cascade path  126 . When the first supports  140  are in the retracted position, they are located outside the cascade path  126 . When the first supports  140  are in the extended position, they are located outside the cascade path  126  when they are at the raised location and they are located in the cascade path  126  when they are at the lowered location. 
     The operation of the disclosed stacking system will now be described with reference to  FIGS. 4-6 . 
     In  FIG. 4 , the elevating fingers  124  are raised to a location near the bottom opening  118  of the hopper  108  and in position to receive sheets  106  from the hopper  108 . The sheets  106  are supported by the accumulator shelf  132  and the pins  134  of the second accumulator  138 , and additional sheets  106  are falling onto the partial stack on the second accumulator  138 . The partial stack is also being tamped at this time by the action of the actuator  117  repeatedly pressing the movable side guide  116  against sheets  106  on the partial stack to square them against the fixed side guide  114 . Because the elevating fingers  124  are in position to receive additional sheets  106 , having just deposited a previous stack of sheets  106  on the discharge conveyor  122 , for example, the controller causes the accumulator shelf  132  and the pins  134  to retract and drop the partial stack of sheets  106  onto the elevating fingers  124 . 
       FIG. 5  shows the partial stack of sheets  106  supported on the elevating fingers  124  after being dropped from the second accumulator  138 . The main conveyor  100  continues to eject sheets  106  from the discharge end  104  into the hopper  108 , and the blower  120  moves the sheets  106  along the cascade path  126  to the top of the growing partial stack of sheets  106  on the elevating fingers  124 . At this time, the elevating fingers  124  are lowered such that each of the sheets  106  falling from the discharge end  104  of the main conveyor  100  falls approximately the same distance onto the top of the growing partial stack. 
     When the partial stack has reached a desired size, the elevating fingers  124  must be lowered to place the now-finished stack on the discharge conveyor  122 . However, because of the rapid rate at which the sheets  106  traverse the cascade path  126  and the small spacing between adjacent ones of the sheets  106 , it is not practical to extend the accumulator shelf  132  and pins  134  of the second accumulator  138  into the cascade path  126 . This is because it is likely that either the accumulator shelf  132  or the pins  134  will impact a side of one of the sheets  106  and misalign the sheets  106  in a manner that interferes with efficient stack formation and/or causes a jam that requires the rotary die cut machine and the main conveyor  100  to be stopped while the jam is cleared. 
     To avoid such a problem, the first accumulator  136  is actuated as follows. During the process of forming a partial stack on the second accumulator  138  and later on the elevating fingers  124 , the first supports  140  of the first accumulator  136  have been in the raised location and the extended position (See  FIGS. 4 and 5 ), and the pins  158  of the first accumulator  136  have been in the retracted position. The tips  146  of the first supports  140  are located outside the cascade path  126  as shown in  FIGS. 4 and 5  because the leading edges of the sheets  106  drop under the forces of gravity and the airflow from the blower  120 . The pins  158  are also retracted and located outside the cascade path  126  such that they do not interfere with the flow of sheets  106  along the cascade path  126  and through the hopper  108 . 
     In order to interrupt the flow of the cascading sheets  106 , the vertical actuator  154  is fired to rapidly drive the housing  148  downwardly and this moves the first support  140  downwardly into the lowered position illustrated in  FIG. 6 . This lowering takes place very quickly, on the order of a tenth of a second, and such that is appears substantially instantaneous to an observer. As the first support  140  travels in the downward direction, its angled lower surface  144  crosses the upper edge  128  of the cascade path  126  and enters into the cascade path  126 . Because the sheets  106  at the location where the first support  140  enters the cascade path  126  tend to be oriented with their leading edges tipping downwardly, it is likely that an incoming sheet  106  will come into contact the first support  140  in one of two ways, neither of which will lead to a jam. 
     First, if the vertical actuator  154  fires when a sheet  106  is in the location illustrated in  FIG. 5 , with the leading edge of the sheet  106  below the angled lower surface  144  of the first support  140 , the downward movement of the first support  140  will drive the angled lower surface  144  of the first support  140  into contact with the top of the sheet  106  and press the sheet  106  downwardly toward the stack forming on the elevating fingers  124 . Alternately, if the vertical actuator  154  fires before the leading edge of the sheet  106  has reached a position beneath the angled lower surface  144 , the first support  140  will reach the lowered location of  FIG. 6  before the most recently ejected sheet  106  and it will be in position to receive the incoming sheet  106  on the horizontal top surface  142  thereof. 
     Because the angle of the angled lower surface  144  and the orientation of the sheets  106  exiting the discharge end  104  of the main conveyor  100 , and the speed at which the first support  140  is moved from the raised location to the lowered location by the vertical actuator  154 , it is nearly impossible to create a jam between an incoming sheet  106  and the tip  146  of the first support  140 . 
     The pins  158  of the first accumulator  136  are shifted to the extended position at approximately the same time the first support  140  reaches the lowered location. Because of the manner in which the sheets  106  fall from the discharge end  104  of the main conveyor, larger gaps exist between the trailing edges of the falling sheets along the hopper front wall  112 . It is therefore generally easier to time the movement of the pins  158  so that they do not impact against an edge of a falling sheet  106 . 
     The first accumulator  136  then accumulates several sheets  106  while a final tamping is performed on the stack of sheets  106  on the elevating fingers  124 , and the elevating fingers  124  drop from the position illustrated in  FIG. 6  to place the finished stack of sheets  106  onto the discharge conveyor  122 . Once the top of the stack of sheets  106  on the elevating fingers  124  has cleared the bottom opening  118  of the hopper  108 , the accumulator shelf  132  and the pins  134  of the second accumulator  138  are shifted from their retracted positions to their extended positions. Because the incoming sheets are at this time still being caught by the first accumulator  136 , there is no danger of driving the edge of the accumulator shelf  132  into the edge of a falling sheet  106  and there is no need to precisely time the shifting of the second accumulator to the extended position. 
     With the second accumulator  138  in position, the pins  158  of the first accumulator  136  are retracted and the first supports  140  of the first accumulator  136  are retracted by the horizontal actuator  150 . With the first supports  140  including their tips  146  completely out of the cascade path  126 , the vertical actuator  154  shifts the housing  148  back to the raised location and the horizontal actuator  150  shifts the first supports  140  into the extended position of  FIG. 4  at which point the cycle repeats. 
     The present invention has been described herein in terms of a preferred embodiment. However, modifications and additions to this disclosure will become apparent to those of ordinary skill in the art upon a reading of the foregoing detailed description. For example, while the stacking system of the disclosed embodiment includes first and second accumulators, it is possible to use the disclosed first accumulator as the only accumulator in a stacking system. It is intended that all such additions and modifications form a part of the present invention to the extent they fall within the scope of the several claims appended hereto.