Patent Publication Number: US-7905481-B2

Title: Method for feeding a shingled stack of sheet material

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/149,446, filed Feb. 3, 2009, the specification of which is hereby incorporated by reference. This application also relates to commonly-owned, Utility patent application Ser. No. 12/488,968 entitled “MAILPIECE INSERTER ADAPTED FOR ONE-SIDED OPERATION (OSO) AND INPUT CONVEYOR MODULE THEREFOR”. 
     TECHNICAL FIELD 
     This invention relates to a method for feeding sheet material and, more particularly, to a method for feeding a shingled stack of sheet material which eliminates discontinuities in the shingled stack to enable a continuous flow of sheet material to a downstream processing station. The method also facilitates feeding of sheet material from a single side of the processing device, e.g., a mailpiece inserter. 
     BACKGROUND ART 
     Mailpiece creation systems such as mailpiece inserters are typically used by organizations such as banks, insurance companies, and utility companies to periodically produce a large volume of mailpieces, e.g., monthly billing or shareholders income/dividend statements. In many respects, mailpiece inserters are analogous to automated assembly equipment inasmuch as sheets, inserts and envelopes are conveyed along a feed path and assembled in or at various modules of the mailpiece inserter. That is, the various modules work cooperatively to process the sheets until a finished mailpiece is produced. 
     A mailpiece inserter includes a variety of apparatus/modules for conveying and processing sheet material along the feed path. Depending upon the speed and capabilities of the inserter, such apparatus typically include various/modules for (i) feeding and singulating printed content material in a “feeder module”, (ii) accumulating the content material to form a multi-sheet collation in an “accumulator”, (iii) folding the content material to produce a variety of fold configurations such as a C-fold, Z-fold, bi-fold and gate fold, in a “folder”, (iv) feeding mailpiece inserts such as coupons, brochures, and pamphlets, in combination with the content material, in a “chassis module” (v) inserting the folded/unfolded and/or nested content material into an envelope in an “envelope inserter”, (vi) sealing the filled envelope in “sealing module” (vii) printing recipient/return addresses and/or postage indicia on the face of the mailpiece envelope at a “print station” and (viii) controlling the flow and speed of the content material at various locations along the feed path of the mailpiece inserter by a series of “buffer stations”. In addition to these commonly employed apparatus/modules, mailpiece inserter may also include other modules for (i) binding the module to close and seal filled mailpiece envelopes and a (ii) a printing module for addressing and/or printing postage indicia. 
     These modules are typically arranged in series or parallel to maximize the available floor space and minimize the total “footprint” of the inserter. Depending upon the arrangement of the various modules, it is oftentimes necessary for operators to feed the inserters, i.e., with envelopes, inserts and other sheet material, from two or more locations about the periphery of the inserter. Furthermore, depending upon the “rate of fill/feed”, some stations are more workload intensive than other stations. For example, an insert station of a chassis module may demand seventy-five percent (75%) of an operator&#39;s time while an envelope feed station may require twenty-five percent (25%) of another operator. 
     While a cursory examination of the workload requirements may lead to the conclusion that greater efficiencies are achievable, i.e., by employing a single operator to perform both functions, the configuration of many mailpiece inserters oftentimes does not facilitate the combination of these operations. For example, attending to the chassis module, i.e., adding inserts/sheet material to each of the overhead feeders, is performed from one side of the inserter while attending to the envelope feed station is performed from another side of the inserter. As such, it is difficult for a single operator to move between stations to maintain i.e., feeding sheet material to, both stations. 
     In addition to the distance and inconvenience associated with maintaining each station, it is important to ensure that the envelope feed station is properly “primed” and continuously fed. That is, the first six (6) to ten (10) envelopes must be fed into the ingestion area of the feed station at a prescribed angle and, thereafter, by a continuous stream of shingled envelopes. Should a gap, break/interruption, or discontinuity develop in a shingled stack, it will be necessary to “re-prime” the feed station. As such, re-priming requires that the feed station be temporarily stopped/halted such that the next six (6) to ten (10) envelopes, i.e., those immediately following the gap/break in the stack, be fed into the ingestion area of the station. It will be appreciated that the requirement to re-prime the station results in inefficient operation of the station. 
     A need, therefore, exists for a method for feeding sheet material as a continuous shingled stack to a downstream processing station a continuous stream sheet material conveyor system which facilitates one-sided operation of a sheet handling apparatus, such as a mailpiece inserter, to maintain efficient operation thereof, e.g., a continuous stack of shingled sheet material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate presently preferred embodiments of the invention and, together with the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
         FIG. 1  is a perspective view of a mailpiece inserter including a One-Sided-Operation (OSO) input module according to the present invention including Right-Angle Turn (RAT) input and extensible conveyors for receiving and delivering mailpiece envelopes to a feed conveyor which, in turn, delivers the envelopes to an insert module. 
         FIG. 2  is a schematic top view of the mailpiece inserter and OSO input module shown in  FIG. 1 . 
         FIG. 3  is a schematic sectional view from the perspective of line  3 - 3  of  FIG. 2  wherein the extensible conveyor is in a retracted position. 
         FIG. 4  is a schematic sectional view from the perspective of line  4 - 4  of  FIG. 2  wherein the extensible conveyor is in an extended position. 
         FIG. 5  is top view of the extensible conveyor of the OSO input module. 
         FIGS. 6   a  through  6   g  depict the movement of a shingled stack of envelopes on the feed and extensible conveyors, and the drive system to dispense the mailpiece envelopes on the extensible conveyor into shingled engagement with the mailpiece envelopes on the feed conveyor. 
         FIG. 7  is a flow diagram of the method steps employed to feed the shingled stack of sheet material and control the motion of aligned conveyors to deliver mailpiece envelopes to a downstream processing device. 
         FIG. 8  is a schematic sectional view of an alternate embodiment of the extensible conveyor, i.e., from an identical perspective and position as that portrayed in  FIG. 3  above, wherein the recurved segment is produced by wrapping the continuous belt around a spring biased rolling element capable of displacing vertically by an amount equal to the horizontal displacement of the extensible segment. 
         FIG. 9  is a schematic sectional view of the alternate embodiment shown in  FIG. 8 , wherein the extensible conveyor is in a fully extended position. 
     
    
    
     SUMMARY OF THE INVENTION 
     A method is provided for feeding a shingled stack of sheet material to a downstream processing device. The method includes the step of identifying a discontinuity in the shingled stack of sheet material wherein the discontinuity has a length dimension from an aft end of a downstream portion of the shingled sheet material to a forward end of an upstream portion of the shingled sheet material. In a next step, the motion of first and second serially arranged conveyors are controlled such that the length dimension of the discontinuity is substantially equal to a prescribed gap of known length dimension. The first serially arranged conveyor supports the upstream portion of the shingled sheet material and the second serially arranged conveyor supports the downstream portion of the shingled sheet material. The deck of the first conveyor is advanced over the deck of the second conveyor toward the aft end of the downstream portion by the length dimension of the prescribed gap. The upstream portion is then dispensed into shingled engagement with the downstream portion to produce a continuous stack of shingled sheet material. 
     DETAILED DESCRIPTION 
     A One-Sided Operation (OSO) input module  10  is described and depicted for use in combination with a conventional mailpiece inserter having a plurality of stations/modules for processing sheet material and producing a mailpiece. In the context used herein “sheet material” is any substantially planar substrate such as sheets of paper, cardboard, mailpiece envelopes, postcards, laminate etc, While the invention is described in the context of a mailpiece inserter, the OSO input module  10  is applicable to the dispensation of any sheet material which requires that the material remain shingled and continuously feed to a processing station. Furthermore, while the mailpiece inserter disclosed and illustrated herein depicts the stations/modules which are most relevant to the inventive system/method, it should be borne in mind that a typical mailpiece inserter may include additional, or alternative, stations/modules other than those depicted in the illustrated embodiment. 
       FIGS. 1 and 2  depict perspective and top views of a mailpiece inserter  8  having an OSO input module  10  to facilitate loading/feeding of mailpiece envelopes  12  from one side of the mailpiece inserter  8 . Furthermore, the OSO input module  10  provides a continuous stream/flow of mailpiece envelopes  12  to optimize throughput by minimizing/eliminating downtime of the inserter  8 . Before discussing the details and integration of the OSO input module  10  with the other modules of the inserter  8 , it will be useful to provide a brief operational overview of the various stations/modules of mailpiece inserter  8 . 
     The mailpiece inserter  8  includes a chassis module  14  having a plurality of overhead feeders  14   a - 14   f  for building a collation of content material on the deck  16  of the chassis module  14 . More specifically, the chassis module deck  16  includes a plurality of transport fingers  20  for engaging sheet material  22  laid on the deck  16  by an upstream feeder (not shown) or added to the sheet material  22  by the overhead feeders  14   a - 14   f . The transport fingers  20  move the sheet material  22  beneath each of the overhead feeders  14   a - 14   f  such that additional inserts may be combined with the sheets  22 , i.e., as the sheets pass under the feeders  14   a - 14   f , to form a multi-sheet collation  24 . These collations  24  are conveyed along the deck  16  to an insert module  30  which prepares the mailpiece envelopes  12  for receiving the collations  24 . While the chassis module  14  is defined herein as including overhead feeders  14   a - 14   f  and transport fingers  20  for building and transporting sheet material/collations  22 ,  24 , it should be appreciated that the chassis module  14  may be any device/system for preparing and conveying content material for insertion into a mailpiece envelope. 
     As sheet material collations  24  are produced and conveyed along the deck  16  of the chassis module  14 , mailpiece envelopes  12  are, simultaneously, conveyed on the deck  38  of a feed conveyor  40  to an upstream end  30 U of the insert module  30 . More specifically, a first portion SS 1  of the shingled stack SS of mailpiece envelopes  12  is prepared on the transport deck  38  and conveyed along a feed path FPE which is substantially parallel to the feed path FPC of the sheet material collations  24 . In the context used herein, a “shingled stack” means mailpiece envelopes which are stacked in a shingled arrangement along the feed path FPE of the OSO input module  10  and/or feed conveyor  40 , including portions SS 1 , SS 2 , SS 3  thereof which define a discontinuity in the shingled stack. Furthermore, while the shingled stack SS refers to any shingled envelopes conveyed along the feed path FPE, the specification may refer to first and second portions SS 1 , SS 2  or, alternatively, downstream and upstream portions (i.e., the downstream portion is that portion closest to the insert module and the upstream portion which follows the downstream portion as the stack is conveyed along the feed path FPE) to define where a discontinuity begins and ends. 
     A forward end SS 1 F of a first portion SS 1  of the stack is primed for ingestion by the insert module  30  to facilitate the feed of subsequent envelopes  12  from the stack. The envelopes  12  are singulated upon ingestion and conveyed from the upstream to the downstream ends,  30 U and  30 D, respectively, of the insert module  30 . As the envelopes  12  travel downstream, the flap  12 F of each envelope  12  is lifted to open the envelope  12  for receipt of the content material  24  produced by the chassis module  14 . Once filled, the flap  12 F is moistened and sealed against the body of the envelope to produce a finished mailpiece  12 M. Thereafter, the finished mailpieces  12 M are stacked on a large conveyor tray (not shown) to await further processing, e.g., address printing or postage metering. Mailpiece inserters of the type described are fabricated and supplied under the trade name FLOWMASTER RS by Sure-Feed Engineering located in Clearwater, Fla., a wholly-owned subsidiary of Pitney Bowes Inc. located in Stamford, Conn. 
     The throughput of the mailpiece inserter  8  determines the rate of sheet material consumption and the need to replenish the supply of sheet material/inserts  22 ,  24  and mailpiece envelopes  12 . As the throughput increases, greater demands are placed on an operator to fill each of the overhead feeders  14   a - 14   f  while maintaining a continuous supply of mailpiece envelopes  12  to the insert module  30 . The OSO input module  10  of the present invention facilitates these operations by permitting an operator to replenish the supply of sheet material/inserts  22  and envelopes  12  from a single workstation/area WS. That is, the OSO input module  10  enables an operator to feed mailpiece envelopes/sheet material  12 ,  22  from one side of the inserter  8 , i.e., without ignoring one operation to attend to another. Furthermore, the OSO input module  10  accommodates short feed interruptions, i.e., a discontinuity D in the shingled stack SS, by introducing a “prescribed gap” in the shingled stack SS and employing an extensible conveyor  50  to fill the prescribed gap PG. These features will be more clearly understood by the following description and illustrations. 
     In  FIGS. 2-5 , the OSO input module  10  includes an extensible conveyor  50  and a Right Angle Turn input module  100  upstream of the extensible conveyor  50 . The extensible conveyor  50  is aligned with the deck  38  of the feed conveyor  40  and comprises a (i) continuous belt  52  defining a deck  50 D for supporting and conveying mailpiece envelopes  12 , (ii) an extensible support structure  60  adapted to support and accommodate motion of the continuous belt  52 , and (iii) a drive system  80  operative to extend and retract the continuous belt  52  along the feed path FPE of the feed conveyor  40 , and drive the belt  52  to dispense additional mailpiece envelopes  12 , i.e., a second portion SS 2  of the shingled stack SS onto the aft end SS 1 A of the first portion SS 1  of the shingled stack SS. In the context used herein, the extensible and/or RAT conveyors  50 ,  100  of the OSO input module  10  may be viewed as upstream conveyors which are disposed over, and aligned with, the feed conveyor  40  which may be viewed as downstream conveyor relative to the upstream extensible and RAT conveyors  50 ,  100 . 
     The belt  52  of the extensible conveyor  50  has a width dimension which is slightly larger than the width of the envelopes to be conveyed, is fabricated from a low elongation material, and includes a plurality of cogs (not shown) molded/machined into each side of its lateral edges. With respect to the latter, the cogs engage gear teeth of the support structure  60  to precisely control the motion/displacement of the continuous belt  52 . The significance of cogs in the belt  52  will be more thoroughly understood when discussing the operation and control of the extensible conveyor  50 . 
     The extensible support structure  60  includes an extensible segment  62  operative to extend and retract relative to a fixed segment  64 . Each of the extensible and fixed segments  62 ,  64  includes a plurality of rolling elements  66 E,  66 F which function to support and accommodate motion of the continuous belt  52 . While the rolling elements  66 E,  66 F are illustrated as cylindrical rollers, it will be appreciated that other any structure which supports the belt and rotates about an axis to facilitate motion thereof may be employed. Each rolling element  66 E,  66 F is mounted for rotation between sidewall structures  68 E,  68 F of the respective extensible and fixed segments  62 ,  64 . More specifically, the rolling elements  66 E are mounted for rotation between the sidewall structures  68 E of the extensible segment  62 , and the rolling elements  66 F are mounted for rotation between the sidewall structures  68 F of the fixed segment  64 . 
     The rolling elements  66 E,  66 F and continuous belt  52  are arranged such that the deck  50 D of the belt  52  is advanced forward and aft (i.e., extended and retracted) by the relative movement of the extensible segment  62 . This may be achieved by uniquely arranging of the rolling elements  66 E,  66 F such that the deck  50 D translates fore and aft while the belt  52  may also be driven around the rolling elements  66 E,  66 F. More specifically, this may be achieved by causing a coupled pair of rolling elements  66 E associated with the extensible segment  62  to move relative to a rolling element  66 F associated with the fixed segment  64 , or enabling at least one of the rolling elements  66 E,  66 F associated with either of the segments  62 ,  64  to move independent of the other rolling elements  66 E,  66 F, e.g., within a track or other guided mount. 
     In one embodiment of the invention, shown in  FIGS. 3 and 4 , the means for extending/retracting the belt is effected by arranging the rolling elements  66 E,  66 F such that the belt  52  follows a serpentine path and defines a recurved segment RS 1  (i.e., an S-shape). In the context used herein, the term “recurved segment” is a segment of the continuous belt  52  which (i) extends between a rolling element  66 E associated with the extensible segment  62  and a rolling element  66 F associated with the fixed segment  64 , and (ii) wraps around each of the rolling elements  66 E,  66 F on opposite sides, e.g., a first end of the segment RS 1  engages the rolling element  66 E on a side corresponding to the upper surface of the belt  52 , i.e., the deck  50 D for transporting envelopes  12 , and a second end of the segment RS 1  engages the rolling element  66 F on a side corresponding to the underside surface of the belt  52 . As the extensible segment  62  translates forward and aft, therefore, the recurved segment RS 1  of the belt  52  shortens and lengthens to extend and retract the belt  52 . 
     In another embodiment of the invention, shown in  FIGS. 8 and 9 , the means for extending/retracting the belt is effected by a recurved segment RS 2  produced by mounting one of the rolling elements  66 M in a guide track which facilitates independent motion of the rolling element  66 M. In this embodiment, the rolling element  66 M translates vertically, upwardly and downwardly, as the extensible segment  62  translates forward and aft. More specifically, the rolling element  66 M moves upwardly in response to extension of the extensible segment  62 , i.e., due to the forward movement of the segment  62  and forward advancement of the belt  52 . Retraction of the extensible segment  62  causes the rolling element  66 M to move downwardly under the influence of a tension spring  67 . That is, as the deck  50 D of the belt  52  shifts aft to reduce its length, an equal length of belt is moved downwardly with the rolling element  66 M. Once again, as the extensible segment  62  translates forward and aft, the recurved segment RS 2  of the belt  52  shortens and lengthens to extend and retract the belt  52 . These relationships will be better understood when describing the interaction of the extensible and fixed segments  62 ,  64  and the operation of the extensible conveyor  50 . 
     In the embodiment illustrated in  FIGS. 3 and 4 , the extensible segment  62  translates relative to the fixed segment  64 , i.e., in the direction of the feed path FPE, by means of a track or guide (not shown) interposing the sidewall structures  68 E,  68 F of the segments  62 ,  64 . The track or guide may be similar in construction to the rails of a conventional desk or cabinet draw or, alternatively, a series of rollers may rotationally mounted to one of the segments  62 ,  64  for engaging a elongate slot of the other of the segments  62 ,  64 . 
     In  FIG. 5 , the drive system  80  includes a linear actuator  82  operative to extend and retract the extensible segment  62  relative to the fixed segment  64 , and a belt drive mechanism  90  operative to drive the continuous belt  52  about the rolling elements  66 E,  66 F. More specifically, the linear actuator  82  includes an elongate shaft  84  and a moveable element  86  slideably mounted over or within the elongate shaft  84 . The elongate shaft  84  is mounted at one end to a sidewall  68 F of the fixed segment  64  while the moveable element is mounted to a sidewall  68 E of the extensible element  62 . The moveable element  86  may be driven along the shaft  84  electrically i.e., by an induction coil, or pneumatically by a pressure chamber disposed internally of the shaft  84 . The moveable element  86  may comprise a coupled pair of ferromagnetic elements wherein a ferromagnetic piston/plug  88 I (shown in phantom) slides internally of the shaft  84  by the application of pressure to one side of the ferromagnetic piston/plug while venting the opposing side to atmospheric pressure. A ferromagnetic outer sleeve/ring  88 E, disposed externally of the shaft  84 , is magnetically coupled to the ferromagnetic piston/plug  88 I to follow its motion. That is, the internal ferromagnetic piston/plug  88 I translates linearly within the shaft  84  (in response to pneumatic pressure) while the ferromagnetic outer sleeve/ring  88 E follows the internal piston/plug  88 I to extend and retract the extensible segment  62 . 
     The belt drive mechanism  90  includes a motor  92  for driving the continuous belt  52  by means of an overrunning clutch  94 . More specifically, the motor  92  drives the overrunning clutch  94  which drives the belt  52  around the rolling elements  66 E,  66 F to advance the belt  52  along the feed path FPE. The clutch  94  drives the belt  52  in one direction and “overruns” in the opposite direction. The overrunning feature is necessary to prevent the extensible conveyor  50  from back-driving the clutch  94  when the extensible segment  62  moves forwardly from is retracted or home position. In the described embodiment, the overrunning clutch  94  is a sprag clutch, though the clutch may be any of a variety of clutch types. 
     The extensible conveyor  50  is shown in the home or retracted position in  FIG. 3  and in the extended position in  FIG. 4 . By examination of the figures, it will be apparent that the continuous belt  52  follows a serpentine path around the rolling elements  66 E,  66 F, and that the extension length of the module  50  is directly proportional to the belt length within the recurved segment. As alluded to earlier, when the extensible conveyor  50  is retracted, i.e., in its home position (as seen in  FIG. 3 ), the length of the recurved segment is at a maximum, and when the extensible conveyor  50  is fully extended (as seen in  FIG. 4 ), the length of the recurved segment is a minimum. The extensible support structure  60 , which includes the rolling elements and sidewall structures  66 E,  66 F,  68 E,  68 F, also includes a plurality of runners/rails  76  (shown in phantom in  FIG. 5 ) operative to support, and slideably engage, an underside surface  52 L of the belt  52 . The rails  76  are disposed between pairs of rolling elements  66 E,  66 F and support an upper portion of the belt  52  to maintain a substantially planar deck  50 D. That is, since the continuous belt  52  is not under tension, the rails  76  function to prevent the deck  50 D from drooping/sagging under the force of gravity. 
     The deck  50 D of the belt  52  includes a horizontal deck  50 H and an inclined deck  50 IN disposed downstream of the horizontal deck  50 H. Hence, mailpiece envelopes  12  transition from the horizontal deck  50 H to the inclined deck  50 IN and move downwardly toward the deck  38  of the feed conveyor  40 , i.e., as mailpiece envelopes  12  are conveyed along the inclined deck  50 IN. The slope of the inclined deck  50 IN is a function of the height dimension of the extensible conveyor  50 , however, to prevent the second portion SS 2  of the shingled envelope stack SS from cascading/sliding downwardly under the force of gravity, it will be appreciated that the slope angle θ of the inclined deck  50 IN is preferably shallow. The slope angle θ of the inclined deck  50 IN becomes increasingly sensitive depending upon the type and/or surface characteristics of the mailpiece envelopes  12 . For example, envelopes  12  having a smooth satin surface (i.e., low friction surface) will require that the inclined deck  50 IN define a low slope angle θ while envelopes  12  having a fibrous, heavy weight, surface (i.e., a high friction surface) may provide greater flexibility of design by enabling a higher slope angle θ. In the described embodiment, the slope angle θ is preferably less than about forty degrees (40°) to about ten degrees (10°) and, more preferably, about thirty degrees (30°) to about fifteen degrees (15°). 
     In  FIGS. 1 through 5 , the Right Angle Turn (RAT) input conveyor  100  bridges, i.e., is disposed over, an upstream end of the chassis module  14  and curves into alignment with the input end  50 I (see  FIGS. 1 and 2 ) of the extensible conveyor  50 . More specifically, the RAT input conveyor  100  is disposed upstream of the extensible conveyor  50  and includes: (i) an input end  100 I adapted to receive the second, third and/or additional portions SS 2 , SS 3  . . . SSN of the shingled stack SS, (ii) an output end  100 E aligned with, and adapted to supply, the input end  50 I of the extensible conveyor  50 , and (iii) an arcuate transport deck  100 D extending from the operator workstation WS of the chassis module  14  to the input end  50 I of the extensible conveyor  50 . The deck  100 D may be fabricated from a compliant woven fabric to facilitate redirection in the plane of the fabric, i.e., forming an arc over a span of about six to ten feet (6′ to 10′). Alternatively, the deck  104  may comprise a series of interlocking molded plastic elements which may be variably spaced along the length of each plastic element. That is, the elements may be closely spaced along one edge and separated along the opposite edge to produce a “fanning” effect. The combined fanning of the elements causes the deck to turn as a function of its geometry, i.e., the angular increments which are achievable between each of the elements. This type of conveyor deck, also known as a “turn curve belt”, is available from Ashworth Bros. Inc. located in Winchester, Va. under the trade name Advantage 120 and Advantage 200. 
     A plurality of Envelope Position Detectors (EPDs)  110 ,  116 ,  118  and  120  are operative to sense a discontinuity in the shingled stack SS of mailpiece envelopes  12  and issue position signals PS 1 -PS 4  indicative of the discontinuity. Furthermore, first and second Conveyor Position Detectors (CPDs)  112 ,  114  are operative to sense the position of the extensible conveyor  50  and issue position signals CPS 1 , CPS 2  indicative of the extended/retracted positions EX, HM of the extensible conveyor segments  62  relative to the fixed conveyor segment  64 . Upon sensing a discontinuity in the shingled envelope stack SS, a processor  130 , responsive to the position signals CPS 1 -CPS 2 , drives/throttles the speed of the input conveyors  40 ,  50 ,  100  and the drive system  80  for extending and retracting the extensible conveyor  50 . 
     To understand the operation of the OSO input module  10  and its integration with the mailpiece inserter  8 , it is best to examine a hypothetical involving an operator feeding the OSO and chassis modules  10 ,  14  from a single side, i.e., from the workstation/area WS, adjacent the overhead feeders  14   a - 14   f  of the chassis module  14 . Upon initial set-up of the mailpiece inserter  8 , a first portion SS 1  of the shingled envelope stack SS is disposed along the deck  38  of the feed conveyor  40 . Set-up also includes the step of priming the forward end SS 1 F of the first portion SS 1  of the shingled stack SS for ingestion by the insert module  30 . A second portion SS 2  of the shingled stack SS is also laid on the extensible and arcuate conveyor decks  50 D,  100 D of the OSO module  10 . In this embodiment, it is assumed that the second portion SS 2  of the shingled envelope stack SS extends the length of the OSO input module  10 , i.e., from the input end  100 I of the RAT input conveyor  100  to the output end  50 E of the extensible conveyor  50 . The second portion SS 2 , therefore, functions to replenish the supply of mailpiece envelopes  12 , i.e., associated with the first portion SS 1  of the shingled envelope stack SS, being are ingested by the insert module  30 . 
     While  FIGS. 3 and 4  depict the spatial relationship between the feed and extensible conveyors  40 ,  50 , i.e., in the extended and retracted positions EX, HM, respectively,  FIGS. 6   a - 6   f  depict the sequence for conveying, dispensing, and producing the prescribed gap PG in the mailpiece envelopes  12 . In  FIGS. 2 ,  6   a - 6   c , the feed conveyor  40  incrementally conveys the first portion SS 1  of the shingled envelope stack SS along the feed path FPE as the envelopes  12  are consumed by the insert module  30  (see  FIG. 2 ). During this operation, the controller  130  drives the motor M 2  of the feed conveyor  40  in response to a measured rate of envelope consumption by the insert module  30 . That is, the motor M 2  is essentially driven by an envelope consumption signal derived from the insert module  30 . 
     As the mailpiece envelopes  12  are conveyed along the deck  38  of the feed conveyor  40  ( FIGS. 6   b  and  6   c ), the aft end SS 1 A of the first portion SS 1  of shingled envelopes  12  moves downstream, in the direction of arrow CA, away from the extensible conveyor  50 , and away from the second portion SS 2  of shingled envelopes  12 . This operation produces a prescribed gap GP of known dimension (i.e., along the feed path FPE) in the shingled envelope stack SS, which gap GP which may be closed, i.e., made continuous, by the extensible conveyor  50  of the OSO input module  10 . The first Envelope Position Detector (EPD)  110 , disposed downstream of the extensible conveyor  50 , senses the aft end SS 1 A of the first portion SS 1  of shingled envelopes  12  at a first location L 1  along the feed path FPE. The first EPD  110  issues a first position signal PS 1 , indicative of the discontinuity, to the processor  130  which controls the drive system  80  of the extensible conveyor  50 , i.e., the extension/retraction of the extensible segment  62  and the motion of the envelope conveyors  40 ,  50 ,  100 . In response to the first position signal PS 1 , the processor  130  activates the linear actuator  82  to extend the extensible conveyor  50  (see  FIG. 6   d ) and advance the deck  50 D, i.e., in the direction of arrow FA, toward the aft end SS 1 A of the shingled stack SS. 
     Forward motion of the extensible segment  62  is terminated when the first Conveyor Position Detector (CPD)  112  senses the fully extended position EX (see  FIG. 4 ) of the extensible segment  62 . More specifically, the first CPD  112  is disposed in combination with the sidewalls  68 E,  68 F of the extensible and fixed segments  62 ,  64  (see  FIG. 5 ) and issues a fully extended position signal CPS 1  when the extensible segment  62  reaches a threshold position, i.e., the fully extended position EX, relative to the fixed segment  64 . In response to the fully-extended position signal CPS 1 , the processor  130  activates the drive system  80  such that the motor M 1  drives the continuous belt  52  to dispense envelopes into shingled engagement with the aft end SS 1 A of the shingled stack SS 1 .  FIG. 6   d  shows the envelopes being gravity fed from the inclined deck  50 IN of the belt  52 , in the direction of arrow GF to the deck  38  of the feed conveyor  40 . 
     After a short time delay, i.e., sufficient to allow the additional envelopes  12  to engage the first portion SS 1  of the shingled envelope stack SS 1 , the processor  130  activates the linear actuator  82  to reverse direction while continuing to drive the belt  52 . As a result, shingled envelopes  12  are dispensed while the extensible segment  62  retracts to a home position HM. Rearward motion of the extensible segment  62  is terminated when a second CPD  114  senses the home position HM. More specifically, the second CPD  114  is disposed in combination with the sidewalls  68 E,  68 F of the extensible and fixed segments  62 ,  64  and issues a fully retracted position signal CPS 2  when the sidewall  68 E associated with the extensible segment  62  reaches a threshold position, i.e., the fully retracted or home position HM, relative to the fixed segment  64 . In response to the fully retracted position signal CPS 2 , the processor  130 , deactivates the linear actuator  82  while continuing to drive the motors M 1 , M 2 , M 3  of the feed and OSO input module conveyors  40 ,  50 ,  100 . Control of these motors M 1 , M 2 , M 3  to feed the shingled stack SS to the insert module  30  are discussed in greater detail below. 
     A second EPD  116  senses whether a discontinuity is present in the shingled stack SS at a second location L 2 , upstream of the first location L 1 , and corresponding to the home position HM of the extensible conveyor  50 . If no discontinuity is sensed by the second EPD  116 , the processor  130  synchronously drives the motors M 1 , M 2 , M 3 , to convey a steady stream of mailpiece envelopes  12  from the OSO input module conveyors  50 ,  100  to the feed conveyor  40 , and, finally to the insert module  30 . The processor  130 , therefore, drives the motors M 1 , M 3  of the OSO input module  10  synchronously with the motor M 2  of the feed conveyor  40 . It will be recalled that the motor M 2  of the feed conveyor  40  is being driven in response to signals derived from the insert module  30 . 
     If the second EPD  116  senses a discontinuity in the shingled stack SS at the second location L 2 , i.e., sensing an aft end SS 1 A of the first portion SS 1  of the shingled envelope stack SS, a second position signal PS 2  is issued by the second EPD  116 . In response to the second position signal PS 2 , the processor  130 , drives the motors M 1 , M 3  of the OSO input module conveyors  50 ,  100  to “run-up” a second portion SS 2  of the shingled envelope stack SS to a third location L 3 . More specifically, upon receipt of the second position signal PS 2 , the processor  130 , drives the conveyor decks  50 D,  100 D at increased speed relative to the deck  38  of the feed conveyor  40  to rapidly convey the forward end SS 2 F of the second portion SS 2  to a “ready position” at location L 3  along the feed path FPE. This also has the effect of minimizing the length of the discontinuity as will be discussed in greater detail below. 
     A third EPD  118  senses when a forward end SS 2 F of the second portion SS 2  of the shingled envelope stack SS reaches the ready position and issues a third position signal PS 3  indicative thereof to the processor  130 . The processor  130 , then, stops driving the motors M 1 , M 3  of the OSO input module conveyors  50 ,  100 , but continues driving the motor M 2  of the feed conveyor  40 . As such, the second portion SS 2  of the shingled envelope stack SS is advanced forward to the ready position at location L 3 , while the first portion SS 1  downstream of the second portion SS 2  continues toward the insert module  30 . Hence, the motors M 1 , M 3  of the OSO input module conveyors  50 ,  100  are no longer synchronized with the motor M 2  of the feed conveyor  40 . Although, the motor M 2  of the feed conveyor  40  remains responsive, though the processor  130 , to signals from the insert module  30 . As the first portion SS 1  of the shingled envelope stack SS progresses downstream of the extensible conveyor  50 , the prescribed gap PG is once again produced and the cycle of extension, dispensation, retraction, run-up and envelope conveyance continues once again. 
     In the described embodiment, the second and third locations L 2 , L 3  are essentially concurrent, i.e., lie at the same point along the feed path FPE, however, the second and third EDPs  116 ,  118  may lie in different planes to obtain a different perspective on the leading and trailing edges of the mailpiece envelopes  12 . That is, by projecting a beam of light energy from an alternate perspective, the ability of a detector to sense the presence/absence of an envelope/stack of envelopes can be improved. 
     In another embodiment of the invention, the method for controlling the inserter  8  obviates run-out of mailpiece envelopes  12  to the insert module  30 , and the requirement to re-prime the module  30  for ingestion of envelopes  12 , i.e., a laborious task requiring the attention of a skilled operator. More specifically, should the OSO input module  10  lack a supply of envelopes to replenish the shingled stack SS, i.e., the processor  130 , issues a shut-down signal to stop the motor M 2  of the feed conveyor  40 . In this embodiment, two criteria must be satisfied to execute an extension/retraction cycle of the OSO input module  10 . More specifically, when the first EPD  110  detects a discontinuity at the first location L 1 , i.e., the location where the first and second portions SS 1 , SS 2  of the shingled envelope stack SS are joined to produce a continuous stack SS, the third EPD  116  must also detect that the mailpiece envelopes  12  are queued, i.e., at the ready position at location L 3 , to initiate an extension/retraction cycle of the OSO input module  10 . If no mailpiece envelopes  12  are detected at location L 3 , i.e., in the absence of a ready position signal PS 3 , the processor  130  shuts down the feed conveyor  40  and issues a cue to the operator to replenish a supply of mailpiece envelopes  12  on the OSO input module conveyors  50 ,  100 . Consequently, the first or downstream portion of the shingled stack SS, i.e., extending from location L 1  to the insert module  30 , remains on the feed conveyor  40  to await the issuance of a “start-up” signal from the processor  130 . 
     The operator replenishes the supply of mailpiece envelopes  12  by sequentially stacking envelopes  12 , e.g., one box of envelopes at a time, at the input end of the OSO input module  10 , i.e., the input end  100 I of the RAT input conveyor  100 . Inasmuch as the RAT input conveyor  100  bridges an upstream end of the chassis module  14  and curves into alignment with the input end  50 I of the extensible conveyor  50 , the operator may input mailpiece envelopes  12  from the workstation WS. It will be appreciated that the location of this workstation WS also accommodates input to the overhead feeders  14   a - 14   f  of the chassis module  14 . 
     In another embodiment, it may be desirable to employ a fourth EPD  120 , upstream of the second and third EPDs  116 ,  118 , to sense a discontinuity in the shingled envelope stack SS, e.g., between a second and third portion SS 2 , SS 3  thereof, at an upstream location L 4 . With this information, i.e., that a discontinuity has been sensed, a “flag” can be set such that the third EPD  118 , or any of the other downstream EPDs  110 ,  116 , can anticipate that a discontinuity, or gap in the shingled stack, will occur, when it will occur, and/or the length/duration of the gap/discontinuity in the shingled stack SS. 
     From the foregoing, it will be appreciated that the OSO input module  10  facilitates one-sided operation, i.e., from a single workstation WS or area, by permitting interruptions, or a discontinuity, in the shingled stack of envelopes. That is, the OSO input module  10  allows an operator to attend to the overhead feeders  14   a - 14   f  of the chassis module  14  while one or more gaps/discontinuities develop in the shingled stack SS along the feed path of the input module  10 . In  FIG. 7 , a flow diagram of the method for controlling a mailpiece inserter  8  having an OSO input module  10  is summarized. More specifically, in the described embodiment, the method for controlling the mailpiece inserter  8  includes the steps of: (A) identifying a discontinuity in a shingled stack, (B) minimizing the length of the discontinuity (i.e., the dimension from the aft end of a downstream portion of shingled envelopes to a forward end of an upstream portion of shingled envelopes) when the length dimension is less than a prescribed gap PG of known length dimension, (C) controlling the motion of first and second serially arranged conveyors, i.e., the OSO input module and feed conveyors  40 ,  50 ,  100 , to produce the prescribed gap PG, (D) eliminating the discontinuity by advancing the conveyor deck  50 D of the extensible conveyor  50 , and the shingled envelopes disposed thereon, by the length of the prescribed gap, and (E) dispensing the upstream portion into shingled engagement with the downstream portion. 
     In step B, the length of the discontinuity may be minimized by increasing the speed of the OSO input module conveyors  50 ,  100  relative to the speed of the feed conveyor  40  when the discontinuity passes from the OSO input module  10  to the feed conveyor  40 . This discontinuity is sensed by the second EPD  116  which monitors when the aft end SS 1 A of the first/downstream portion SS 1  of the shingled envelope stack SS has been dropped, gravity fed, from the inclined deck  50 DIN of the extensible conveyor  50  to the feed conveyor  40 . 
     In step C, the second or upstream portion SS 2  of the shingled envelope stack SS is retained on the conveyor decks  50 D,  100 D of the OSO input module  10  while the first or downstream portion SS 1  of the shingled envelope stack SS is conveyed forward, along the deck  38  of the feed conveyor  40  toward the insert module  30 . Conveyance of the first portion SS 1  continues until the discontinuity is sensed by the first EPD  110 . Additionally, the motion of the second portion SS 2  is retained in response to a signal issued by the third EPD  118 . 
     In step D, the discontinuity is eliminated by cycling the OSO input module  10  and advancing the deck  50 D of the extensible conveyor  50 . In one embodiment shown in  FIGS. 3 ,  4  and  5 , the deck  50 D is advanced by wrapping a continuous belt  52  around a plurality of rolling elements  66 E,  66 F in a serpentine pattern. The serpentine pattern defines a recurved segment RS which shortens as the conveyor  50  extends and lengthens as the conveyor retracts. In another embodiment shown in  FIGS. 8 and 9 , the continuous belt  52  wraps around a plurality of rolling elements  66 E,  66 F in an path having a recurved segment RS 2  which projects downwardly from the horizontal deck  52 H. Furthermore, the recurved segment RS 2  wraps around a spring-biased rolling element  66 M which translates vertically within a linear track or guide  66 G. The rolling element  66 M moves upwardly, against a force induced by a tension spring  67 , in response to extension of the extensible segment  62 , and downwardly, under the influence of the spring  67 , in response to retraction of the extensible segment  62 . 
     In step E, the discontinuity in the shingled stack SS is eliminated by driving the belt  52  of the extensible conveyor  50  to dispense envelopes  12  into shingled engagement with the shingled stack SS 1  of envelopes  12  disposed on the feed conveyor  40 . CPDs  112 ,  114  sense the extended and retracted positions EX, HM and issue signals CPS 1 , CPS 2  to the drive system  80 , through the processor  130 , to cycle the extensible conveyor  50 . 
     Although the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention. For example, while envelope position detectors  110 ,  116 ,  118 ,  120  employed are photocells, the EPDs may be any device capable of detecting when a mailpiece envelope is present or absent. Furthermore, while the OSO input module  10  extends fully to bring envelopes into shingled engagement with the first portion SS 1  of the shingled stack SS and employs a conveyor position detector  112  to indicate when the extensible segment  62  is fully extended, a plurality of EPDs and CPDs  110 ,  112  may be employed along the feed path FPE and between the segments  62 ,  64  such that the extensible segment  62  extends to an intermediate location, i.e., between the fully extended and fully retracted positions EX, HM. As such, the plurality of EPDs  110  may provide information concerning the instantaneous position L 1  . . . LN of the shingled envelopes along the feed conveyor  40  and the CPDs may be employed to vary the length of extension along the feed path FPE. It should, therefore be understood that the present invention is not to be considered as limited to the specific embodiments described above and shown in the accompanying drawings. The illustrations merely show the best mode presently contemplated for carrying out the invention. The invention is intended to cover all such variations, modifications and equivalents thereof as may be deemed to be within the scope of the claims appended hereto.