Patent Publication Number: US-7717419-B2

Title: Accumulator having rotary drive

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of U.S. Provisional Patent Application No. 60/908,585, filed Mar. 28, 2007, the entire contents of which is hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention is directed to an apparatus for stacking sheets of material that includes an accumulator and to a method for using the apparatus. More specifically, the present invention is directed to an apparatus for stacking sheets of material that includes an accumulator system with a rotary drive and to a method of using the apparatus. 
   2. Description of Related Art 
   Devices for stacking sheets of material, such as sheets of corrugated material, are well known. One example of a commercially available device is the AGS2000 Rotary Die Cut Stacker made by the assignee of the present invention, A.G. Stacker, Inc., Weyers Cave, Va. Further examples of such devices are disclosed in U.S. Pat. Nos. 3,321,202 to Martin and 3,419,266 to Martin, each of which is expressly incorporated by reference in its entirety. 
     FIGS. 1-4  illustrate a conventional apparatus for stacking corrugated blanks. As illustrated therein, a stacking machine  100  typically comprises a layboy section  102  which receives corrugated blanks, such as those produced by a rotary die cut machine  101 , and discharges the corrugated blanks onto a transfer conveyor  104 . The transfer conveyor  104  receives the blanks and transports them to a main conveyor  106 . The main conveyor  106  has an intake end  108  and a discharge end  110 . At its intake end  108 , the main conveyor  106  is mounted to a base  112  at a pivot point  114  so that the conveyor may be pivoted to raise the discharge end  110  of the conveyor  106 . At the discharge end  110  of the conveyor  106 , an accumulator section  116  is controllable to selectively receive discharged blanks or to allow the discharged blanks to fall to the ground or another conveyor to form a stack. 
   In operation, the main conveyor  106  is pivoted about the pivot point  114  to lower the discharge end  110  of the conveyor to an initial position (the position illustrated in  FIG. 2 ). Sheets of material (not illustrated) exit the die cutter  101  and are fed onto the main conveyor  106  at intake end  108 , transported along the length of the main conveyor  106  to discharge end  110 , and discharged from the main conveyor  106 . As they are discharged, the sheets often strike a backstop  118  in the accumulator section  116  that stops the forward momentum of the sheets. The sheets settle down, typically onto a discharge conveyor (not illustrated), to form a stack of sheets (not illustrated). As additional sheets drop onto the top of the stack, the stack grows in height, and main conveyor  106  is pivoted to raise the discharge end  110  to a position higher than the top of the growing stack.  FIG. 3  illustrates main conveyor  106  in the raised position. 
   Once a stack of sheets has reached a desired height, it is removed, and the process of forming an additional stack begins. However, to permit time to remove a finished stack without stopping main conveyor  106 , accumulator section  116  is employed. Accumulator section  116  catches or accumulates a small stack of sheets as main conveyor  106  continues to operate so that the completed stack on the discharge conveyor can be removed. When the completed stack is removed, the main conveyor is returned to the lowered position illustrated in  FIG. 2 , the small stack on the accumulator is dropped onto the transfer conveyor, and additional sheets are added to the top of this new stack. 
   The accumulator section  116  includes a plurality of catcher elements  120 . Catcher elements  120  include a first catching member  122  and a plurality of extending members  124 . When the catcher elements  120  are activated, the first catching member  122  is rotated into the position shown in  FIG. 2 . The extending members  124  are moved from the retracted position shown in  FIG. 2  into an extended position where they extend at least partially across the bottom of the accumulator section  116  to catch sheets exiting the main conveyor  106 . After the stack below the accumulator section  116  has been removed, the extending members  124  are retracted to drop the partial stack being formed thereon onto a discharge conveyor. 
   Existing accumulator designs are complex and generally require considerable manufacturing labor. As illustrated in  FIG. 4 , a conventional accumulator includes an air cylinder  132  having a projecting rod  134  extending perpendicularly to the direction of travel of the main conveyor  106 , which rod drives a bar  136 . The bar  136  is connected to a gear rack  138  extending transversely across the width of the main conveyor  106 . The gear rack  138  engages a plurality of horizontally disposed large pinion gears  140  on pinion shafts  142  which pinion shafts  142  also each support a small pinion gear  144  (the pinions and pinion shafts are enclosed in housings that are not shown). The small pinion gears  144 , in turn, engage rack teeth  146  on the sides of the extending members  124  and cause the extending members to extend and retract when the small pinion gears  144  rotate. 
   The gear ratio between the diameter of the large pinion gears  140  and small pinion gears  144  is selected to allow the eight inch travel of a typical air cylinder rod  134  to move the extending members a distance of about 20 inches. With this arrangement, linear motion must be converted to rotary motion, the rotary motion must be amplified with a selected gear ratio, and the rotary motion must be reconverted to linear motion to operate the accumulator. This arrangement is not only relatively expensive to manufacture, but in addition, the air cylinder may limit the accuracy with which the extending members  124  can be positioned. 
   There have been other attempts to address the problem of sufficient velocity control and position control in conventional systems. For example, U.S. Pat. No. 6,042,108 to Morgan discloses a flexible curtain which is extended into the stream of sheets. The disclosed flexible curtain system is complex with many moving parts and increases both material and manufacturing costs. Accordingly, it would be desirable to provide an improved accumulator system for a sheet stacking device. 
   SUMMARY OF THE INVENTION 
   These and other problems are addressed by embodiments of the present invention, a first aspect of which comprises a sheet stacking device that includes a support frame and a conveyor pivotably connected to the support frame that has an intake end and a discharge end. The conveyor carries sheets of material from an upstream location near the intake end to a downstream location near the discharge end. An accumulator is provided at the discharge end and includes a plurality of elongate fingers; at least one of the plurality of elongate fingers includes a rack having teeth along a first side. A rotatable drive shaft extends in the width direction of the conveyor, and a gear having teeth is mounted on the drive shaft with at least one of the gear teeth projecting into a space between adjacent ones of the rack teeth. A rotary actuator is operably connected to the drive shaft, the rotary actuator rotating the drive shaft in a first direction to move the outer end of the at least one of the plurality of elongate fingers away from the conveyor discharge end and in a second direction to move the outer end of the at least one of the plurality of elongate fingers toward the discharge end. 
   Another aspect of the invention comprises a sheet stacking device that includes a support frame and a conveyor having an intake end pivotably connected to the support frame and a discharge end. The conveyor is configured to carry sheets of material in a direction of travel from an upstream location near the intake end to a downstream position near the discharge end, and an accumulator is mounted at the discharge end. The accumulator includes a plurality of housings, each of the housings having an interior and a channel having a channel bottom, at least some of the channel bottoms including an opening. A plurality of elongate fingers extend through and are slidably supported by the channels. A first set of the plurality of elongate fingers has a first surface having a gear rack bounded by first and second planar surface portions. A rotatable drive shaft extends through the plurality of housings in the width direction of the conveyor, and a plurality of gears are mounted on the drive shaft. Each of the plurality of gears extends through an opening in one of the channel bottoms and has teeth engaging the rack teeth of one of the elongate fingers. The sheet stacking apparatus also includes a rotary actuator operably connected to the drive shaft, the rotary actuator rotating the drive shaft in a first direction to move the outer ends of the elongate fingers away from the conveyor discharge end and in a second direction to move the outer ends of the elongate fingers toward the discharge end. 
   An additional aspect of the invention comprises a method that is practiced with a sheet stacking device comprising a support frame, a conveyor having an intake end pivotably connected to the support frame and a discharge end. The sheet stacking device also includes an accumulator mounted at the discharge end, the accumulator comprising a plurality of elongate fingers and having rack teeth along a first side thereof. A rotatable drive shaft extends under the plurality of elongate fingers and has drive gears engaging the rack teeth and rotary actuator is operably connected to the drive shaft. The method includes steps of operating the conveyor to transport sheets of material along the conveyor in a direction from said intake end toward said discharge end and dropping the sheets to form a primary stack adjacent the discharge end, and raising the discharge end to maintain the discharge end at an elevation greater than a height of the primary stack. The method further includes controlling the rotary actuator to turn the drive shaft and the gears mounted on the drive shaft to extend the outer ends of the plurality of fingers away from the discharge end of the conveyor and into the path of sheets of material exiting the discharge end of the conveyor, forming a secondary stack on the plurality of fingers, moving the primary stack away from the sheet stacking device, and controlling the rotary actuator to turn the drive shaft and gears mounted on the drive shaft to move the outer ends of the plurality of fingers toward the discharge end of the conveyor to drop the secondary stack. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects of embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a top plan view of a conventional sheet stacking device having a main conveyor and an accumulator section; 
       FIG. 2  is a side elevational view of the sheet stacking device of  FIG. 1  with the main conveyer section in a lowered position; 
       FIG. 3  is a side elevational view of the sheet stacking device of  FIG. 1  with the main conveyor in a raised position; 
       FIG. 4  is a front elevational view of a portion of the accumulator section of the sheet stacking device of  FIG. 1 ; 
       FIG. 5  is a top plan view of a sheet stacking device according to an embodiment of the present invention having a main conveyor and an accumulator; 
       FIG. 6  is a top plan view of a portion of the accumulator of the device of  FIG. 5  isolated from the stacking device for illustration purposes; 
       FIG. 7  is a side elevational view, partly in section, of the accumulator of  FIG. 5 ; 
       FIG. 8  is a front elevational view of a portion of the accumulator of  FIG. 5 ; and 
       FIG. 9  is a perspective view of a portion of the accumulator of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings, wherein the showings are provided for purposes of illustrating a presently preferred embodiment of the invention only, and not for the purpose of limiting same,  FIG. 5  illustrates the discharge end  110  of stacking apparatus  100  equipped with a novel accumulator  200 . With reference to  FIG. 8 , accumulator  200  comprises first and second angled brackets  202  (only one of which is illustrated) depending from a support plate  203  mounted near the discharge end  110  of main conveyor  106  below the end of the conveyor  106 . The angled brackets  202  support a drive shaft  204  having a plurality of pinion gears  206  mounted at intervals therealong and keyed to drive shaft  204  so as to rotate therewith. A rotary actuator such as electric motor  208 , which may comprise, for example, an electric stepper motor, is mounted to one of the angled brackets  202 , and a rotor shaft  210  of the motor  208  is coupled to drive shaft  204  with a coupling assembly  212 . A controller  213  is operatively connected to, electric motor  208  to cause motor  208  to rotate in first and second direction to turn drive shaft  204  in first and second directions for reasons discussed further hereinbelow. 
   A plurality of drive housings  214  and idler housings  216  are secured to the underside of support plate  204  between angled brackets  202  each of which housings  214 ,  216  includes transversely spaced openings  218  for receiving the drive shaft  204  and a longitudinal opening  220  (with respect to the operating direction of main conveyor  106 ) for receiving a finger member as discussed below. Drive housings  214  include an interior  222  to accommodate the pinion gears  206 . Longitudinal openings  220  may be referred to as channels and include a channel bottom wall  224  and opposed channel side walls  226 . The longitudinal openings  220  of drive housings  214  also include an opening  228  (illustrated in  FIG. 7 ) in channel bottom wall  224 . 
   The drive housings  214  and idler housings  216  may be formed in two or more pieces to facilitate assembly and may be formed from a material having good wear resistance and machinablility. Suitable materials include DELRIN, sold by E.I. DuPont de Nemours &amp; Company, and ACETRON and NYLATRON, both available from Quadrant Engineering Plastic Products. NYLATRON is presently preferred for this application. Polymer bearings  230  may be included in the housing interior  222  to provide additional wear resistance between the pinion gears  206  and drive housing  214 . Suitable polymer bearings  230  are available from Igus Inc. of East Providence, R.I. 
   Referring now to  FIGS. 5-8 , first finger members  232  comprise elongated and generally rectangular rods having a gear rack  234  including a plurality of teeth  236  formed along one side  238  thereof. The gear rack  234  is bounded by first and second planar edge portions  240  in which no teeth are present. The teeth  236  do not project beyond the planar edge portions  240 . First finger members  236  are slidably mounted in longitudinal openings  220  of drive housings  214  with first side  238  slidably supported by channel bottom wall  224  and the opposite sides of drive finger member  232  guided by channel side walls  226 . A pinion gear  206  extends from interior  222  through opening  238  and into longitudinal opening  220  and engages gear rack  234 . 
   Accumulator  200  also includes a plurality of second finger members  242  which are generally similar in size and shape to first finger members  232  but second finger members  242  do not include a gear rack. Second finger member  242  are slidably received in idler housings  216  wherein they are retained transversely but slide freely in a longitudinal direction. A tie rod  244  connects the second finger members  242  to the first finger members  232  so that movement of the first finger members also causes the second finger members to move. The relative number of first and second finger members can vary. An accumulator may comprise no second finger members, for example, in which case all first finger members would be directly driven by a pinion gear or an accumulator may include only one first finger member that drives all second finger members via a tie rod. In practice, it is generally preferable to make every second or third finger member a first finger member so that a driving force is applied evenly along the width of the accumulator. The disclosed embodiment includes four driven, first finger members and six second or non directly driven finger members. 
   In operation, when the stack being formed by conveyor  106  has reached a predetermined height, the controller  213  actuates electric motor  208  to rotate drive shaft  204  in a first direction. Pinion gears  206  keyed to the drive shaft  204  rotate with the drive shaft and engage teeth  236  of gear racks  234  of each first finger member  232  to drive first finger members  232  along longitudinal channels  220  and extend first finger members and any second finger members  242  into the path of descending sheets of material falling off the end of the main conveyor  106 . Sheets are accumulated on the extended first and second finger members  232 ,  242  until a primary stack of sheets (not illustrated) has been removed from the region beneath the discharge end  110  of the main conveyor  106 . The discharge end of main conveyor  106  is then lowered and the electric motor  208  is driven to rotate the drive shaft  204  in a second direction to retract first and second fingers  232 ,  242  and drop the secondary stack of sheets that has accumulated thereon. 
   As known to those skilled in the relevant art, a stepper motor system is an electro-mechanical rotary actuator that converts electrical pulses into unique shaft rotations. This rotation is directly related to the number of pulses. This provides highly accurate and repeatable velocity and position control. Since the stepper motor converts electrical energy into discrete motions or steps, it can move the accumulator rack and/or extending members to a specified length with enhanced velocity and position control. Once energized, pulses are sent from a drive amplifier to the stepper motor so that the stepper motor is then enabled for precise positioning. The drive or control processor (not shown) controls position, velocity and torque. Suitable drive amplifiers for stepper motors are available from Anaheim Automation Inc. of Anaheim, Calif. The utilization of a rotary actuator, such as a stepper motor or a servo motor, provides accurate position and velocity control. 
   While the invention has been shown and described with reference to a certain exemplary embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, while the present invention has been described with respect to an upstacking style sheet device, it should be understood that it is also applicable to other sheet stacking devices that use accumulators. A proximity sensor may also be provided to sense when the rack is at a certain position, such as a home position and provide a self-correcting component to the system by maintaining the rack location. It is intended that all such changes comprise a part of the present invention to the extent they come within the scope of the several claims appended hereto.