Patent Publication Number: US-6902162-B2

Title: Non-marking accumulator and related methods

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/356,229, filed Feb. 12, 2002; the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention is generally directed to the field of document handling and processing technology and, in particular, to improvements relating to the accumulation of material units. 
     BACKGROUND ART 
     A recurring problem in document handling operations is toner smudging or marking, which most often occurs as the result of the necessary interaction between document handling components and material units containing printed matter being handled by those components. The problem of toner smudging is especially acute and pervasive in document accumulation operations. In conventional accumulation configurations, a single-level accumulator drives material into and over entrance ramps with the use of o-rings (also known as polycords) that are continuously moving in the direction of material flow. These continuously moving o-rings contact each face (i.e., the front and/or the back side) of the material. The material is first driven, as separate pieces or a pair, into the accumulator from an upstream device. The material is then advanced to the exit end of the accumulator by the o-rings that are essentially designed to act as a slip drive and comes to rest as the lead edge of the material contacts a pair of output rollers. Subsequent pages then accumulate over or under each preceding piece until the accumulator&#39;s maximum capacity is reached (usually 10-15 sheets) or a full set is satisfied. The o-rings, however, continue to cycle as material comes to rest and as succeeding material enters the accumulator and begins to accumulate. Accordingly, toner smudge occurs as, for example, the bottom set of o-rings becomes impregnated with toner from preceding pieces and transfers this toner to the first page of the set as it rests in the static condition. 
     Examples of document handling devices such as accumulators that employ pressure-applying belts or o-rings to drive sheets are disclosed in U.S. Pat. Nos. 6,203,006; 5,915,686; 5,794,931; 5,775,689; 5,692,745; 5,655,761; 5,647,587; 5,590,873; 5,484,255; 5,244,200; 5,147,092; and 4,767,115. 
     Material removal can also be problematic in conventional accumulator devices. Material must be folded and often torn to be removed from between the fixed o-rings of the accumulator. Another problem relates to the stretching of o-rings over time due to wear and material removal. Moreover, material justification can be problematic, particularly when accumulating before a folder. To achieve a high quality fold with minimal shingling, a set of material that is square on all edges (front, back, and both sides) optimizes the fold quality. Other recurring issues include the ease with which an accumulator device can be changed from over-accumulation to under-accumulation, and can be adjusted to accommodate different material sizes, if such switching capabilities are provided at all. 
     The present invention is provided to address, in whole or in part, these and other problems associated with prior art document handling technology. 
     DISCLOSURE OF THE INVENTION 
     The invention disclosed herein provides a sheet accumulating apparatus and method for accumulating sheets. A series of single sheets, or a series of accumulated or stacked subsets of sheets, are inputted into an accumulation section. The apparatus is operable in either an over-accumulation mode or an under-accumulation mode. In the over-accumulation mode, each new sheet of subset of sheets enters the accumulation section on top of the developing stack of sheets in the accumulation section. In the under-accumulation mode, each new sheet of subset of sheets enters the accumulation section underneath the developing stack of sheets in the accumulation section. In either mode, the apparatus is constructed and its components selected and arranged so as to minimize contact or engagement between sheets and physical structure, and to enhance the control of the apparatus over the speed and flow of the sheets through the apparatus. Therefore, smudging of printed matter on the sheets and damage to the sheets are minimized. Moreover, the apparatus facilitates rapid adjustment by the user between the over-accumulation and under-accumulation modes without the need for tools. In addition, the sheets accumulating in the accumulation section are registered on all four sides, i.e., lead edge, trail edge, and lateral edges. Consequently, a predetermined number of sheets are accumulated into a fully registered stack for advancement to a location downstream of the apparatus. 
     According to one embodiment, a sheet accumulating apparatus comprises an accumulation section defining a sheet feed plane therethrough. An upper ramp is disposed upstream from the accumulation section and is movable into and out of the sheet feed plane. An upper retaining member is linked to the upper ramp and is movable into and out of the sheet feed plane in alternating relation to the upper ramp. A lower ramp is disposed below the upper ramp and is movable into and out of the sheet feed plane in alternating relation to the upper ramp. A lower retaining member is linked to the lower ramp and movable into and out of the sheet feed plane in alternating relation to the upper ramp. 
     Preferably, the upper ramp, the upper retaining member, the lower ramp, and the lower retaining member are pivotably movable into and out of the sheet feed plane, the upper ramp is pivotable in an opposite direction in relation to the pivoting of the upper retaining member, and the lower ramp is pivotable in an opposite direction in relation to the pivoting of the lower retaining member. 
     Preferably, the mechanical interface or functional couplings among the corresponding ramps and retaining members are implemented with linkages. Accordingly, in one embodiment, an upper linkage links the upper ramp to the upper retaining member and a lower linkage links the lower ramp to the lower retaining member. The upper linkage comprises a first upper linkage member pivotable with the upper ramp and a second upper linkage member pivotable with the upper retaining member in engagement with the first upper linkage member. The lower linkage comprises a first lower linkage member pivotable with the lower ramp and a second lower linkage member pivotable with the lower retaining member in engagement with the first lower linkage member. Even more preferably, the linkage members include respective toothed portions that engage each other, such that the linkage members can comprise intermeshing gears or gear segments. 
     In some embodiments, a front stop mechanism is disposed downstream from the upper and lower ramps and is movable into and out of the sheet feed plane. 
     In some embodiments, a carriage assembly is movably engaged with a frame of the accumulating apparatus and supports the front stop mechanism. Accordingly, the front stop mechanism is movable with the carriage assembly toward and away from the upper and lower ramps, thereby enabling the accumulating apparatus to accommodate different lengths of sheets. 
     Preferably, the accumulating apparatus comprises a sheet transport device. The sheet transport device comprises one or more sheet-engaging members, such as pusher fingers or lugs, that are movable through the accumulation section along the sheet feed plane. Such a sheet transport device is employed to at least begin transport of a stack of over- or under-accumulated sheets out from the accumulating section of the apparatus. The sheet-engaging members contact only the trail edge of the sheet stack and thus do not cause smudging. Hence, even with the use of the sheet transport device, sheets are still not subject to any moving components while accumulation is occurring. 
     Preferably, the accumulating apparatus comprises left and right side jogging members disposed at respective lateral sides of the accumulation section. These side jogging members are movable toward and away from each other along a direction transverse to a sheet flow path through the accumulation section. Alternating actuation or other movement of the side jogging members jogs the sheets into side-by-side registration in the accumulation section. 
     According to another embodiment, a sheet accumulating apparatus comprises an accumulation section defining a sheet feed plane therethrough, and an accumulating assembly disposed upstream from the accumulation section. The accumulating assembly is selectively adjustable to an over-accumulation position and an alternative under-accumulation position. The accumulating assembly comprises a first ramp, a first retaining member, and a first linkage interconnecting the first ramp and the first retaining member, wherein the first ramp is movable with first retaining member. The accumulating assembly also comprises a second ramp, a second retaining member, and a second linkage interconnecting the second ramp and the second retaining member, wherein the second ramp is movable with the second retaining member. At the over-accumulation position, the first ramp and the second retaining member are disposed out of the sheet feed plane, and the second ramp and the first retaining member extend in the sheet feed plane. At the alternative under-accumulation position, the first ramp and the second retaining member extend in the sheet feed plane, and the second ramp and the first retaining member are disposed out of the sheet feed plane. The sheet accumulating apparatus is thus structured so as to be adjustable to either accumulation position, and consequently is capable of either over-accumulating or under-accumulating sheets as desired by the end user. 
     According to yet another embodiment, a sheet accumulating apparatus comprises upper and lower frame sections, first and second upper rotatable members, upper and lower accumulation ramps, upper and lower sheet guide members, and first and second lower rotatable members. The upper frame section has an upper input end and the lower frame section has a lower input end, such that the upper and lower input ends define an input area and a sheet feed plane therebetween and the sheet feed plane extends through the input area. The first upper rotatable member is disposed in the upper frame section and the second upper rotatable member engages the first upper rotatable member, such that rotation of the first upper rotatable member in one direction corresponds to rotation of the second upper rotatable member in an opposite direction. The upper accumulation ramp is connected to the first upper rotatable member and is rotatable therewith into and out of the sheet feed plane. The upper sheet guide member is connected to the second upper rotatable member and is rotatable therewith into and out of the sheet feed plane. The first lower rotatable member is disposed in the lower frame section and the second lower rotatable member engages the first lower rotatable member, such that rotation of the first lower rotatable member in one direction corresponds to rotation of the second lower rotatable member in an opposite direction. The lower accumulation ramp is connected to the first lower rotatable member and is rotatable therewith into and out of the sheet feed plane. The lower sheet guide member is connected to the second lower rotatable member and is rotatable therewith into and out of the sheet feed plane. 
     According to still another embodiment, a sheet accumulating apparatus comprises upper and lower frame sections, a plurality of elongate upper and lower sheet guides, and upper and lower accumulation ramps. The upper frame section has an upper end and the lower frame section has a lower end, such that the upper and lower frame sections define an accumulation area therebetween. The upper end pivotably engages the lower end to enable the upper section to pivot away from the lower section and thus to provide access to the accumulation area. The elongate upper sheet guides are supported by the upper frame section and are pivotable therewith, and define an upper boundary of the accumulation area. The elongate lower sheet guides are supported by the lower frame section and define a lower boundary of the accumulation area. The upper accumulation ramp is supported by the upper frame section and is pivotable therewith. The lower accumulation ramp is supported by the lower frame section. 
     According to a further embodiment, a material accumulating apparatus comprises a frame assembly, an input section, a carriage assembly, and a front stop mechanism. The frame assembly comprises first and second lateral support plates. The input section is disposed at an upstream region of the frame assembly and defines a material flow path running between the first and second lateral support plates. The carriage assembly comprises a front stop support plate extending between the first and second lateral support plates, a first carriage member movably connecting the front stop support plate to the first lateral support plate, and a second carriage member movably connecting the front stop support plate to the second lateral support plate. The front stop mechanism is disposed downstream from the input section and is mounted to the front stop support plate. Translation of the front stop support plate along a general direction of the material flow path varies a distance between the front stop mechanism and the input section. 
     Preferably, the front stop mechanism comprises a front stop member and an actuator connected to the front stop member, and the front stop member is movable by the actuator into and out of the material flow path. It is also preferable that the front stop member be spring-mounted so as to provide a recoiling action upon contact with an incoming sheet and thus assist in registering sheets from lead edge to trail edge. It is further preferred that the accumulating apparatus comprise a first rack gear mounted to the first lateral support plate, a second rack gear mounted to the second lateral support plate, a first pinion gear fixedly disposed in relation to the first carriage member and engaging the first rack gear, and a second pinion gear fixedly disposed in relation to the second carriage member and engaging the second rack gear. By this configuration, rotation of the first and second pinion gears respectively along the first and second rack gears causes translation of the first and second carriage members respectively along the first and second rack gears. 
     In some embodiments, the invention comprises upper and lower output rollers fixedly mounted in relation to the front stop mechanism and translatable therewith. 
     According to a yet further embodiment, a material accumulating apparatus comprises a sheet input device, an accumulation area disposed generally downstream from the sheet input device, a front stop mechanism disposed downstream from the sheet input device, first and second output rollers disposed at a fixed distance downstream from the front stop mechanism, and a material transport device. The sheet input device comprises a first input roller and a second input roller. A material feed plane is defined between the first and second input rollers. The accumulation area comprises a plurality of upper guide rods and a plurality of lower guide rods, such that the material feed plane is disposed between the upper and lower guide rods. The front stop mechanism comprises a front stop member and an actuator connected to the front stop member. The front stop member is movable by the actuator into and out of the material feed plane. The material transport device comprises movable material-engaging lugs between the first and second input rollers and the first and second output rollers. 
     According to a still further embodiment, a material accumulating apparatus comprises a frame assembly, an input section disposed at an upstream region of the frame assembly, a side jogging mechanism disposed downstream from the input section, and a front stop mechanism disposed downstream from the input section. The frame assembly comprises first and second lateral support plates. The input section defines a material flow path running between the first and second lateral support plates. The side jogging mechanism comprises an upstream support rod extending between the first and second lateral support plates, a downstream support rod extending between the first and second lateral support plates, first and second mounting brackets, first and second side guides respectively linked to the first and second mounting brackets, and first and second actuating devices. Each mounting bracket has an upstream end slidably supported by the upstream support rod and a downstream end slidably supported by the downstream support rod. The first and second actuating devices are respectively adapted to translate the first and second side guides along a direction transverse to the material flow path. The front stop mechanism is mounted to the front stop support plate. Translation of the front stop support plate along a general direction of the material flow path varies a distance between the front stop mechanism and the input section. 
     According to other embodiments, the accumulating section comprises a plurality of upper elongate members and a plurality of lower elongate members. The sheet feed plane is defined between the upper and lower elongate members. Preferably, the upper and lower elongate members are cylindrical in cross-section so as to provide the minimum possible contact area for sheets that encounter the elongate members. 
     A method is also provided for registering one or more sheets during or after accumulation of the sheets in an accumulating apparatus, according to the following steps. An accumulation section is provided that defines a sheet feed plane. A front stop is moved into the sheet feed plane. A back stop is moved into the sheet feed plane at a position upstream from the front stop. A sheet is moved along an input path past the back stop into the accumulation section, whereby the sheet contacts the front stop and is recoiled thereby toward the back stop. The sheet is alternately translated along opposing directions transverse to the input path. Preferably, the sheet is moved past the back stop by contacting the sheet with an inclined surface of the back stop, whereby the sheet is at least temporarily diverted away from the sheet feed plane to move around the back stop. The sheet is alternately translated preferably by alternately moving left and right opposing side guides toward and away from a centerline of the accumulation section. 
     A method is also provided for adjusting an accumulating apparatus between an over-accumulating mode and an under-accumulating mode, according to the following steps. An accumulating section is provided that defines a sheet feed plane extending therethrough. An accumulating assembly is generally disposed upstream from the accumulating section and comprises an upper ramp, an upper retaining member movably linked to the upper ramp, a lower ramp, and a lower retaining member movably linked to the lower ramp. An over-accumulating mode is set by causing the upper ramp to move out of the sheet feed plane whereby the upper retaining member moves into the sheet feed plane, and causing the lower ramp to move into the sheet feed plane whereby the lower retaining member moves out of the sheet feed plane. The under-accumulating mode is an alternative setting. The under-accumulating mode is set by causing the upper ramp to move into the sheet feed plane whereby the upper retaining member moves out of the sheet feed plane, and causing the lower ramp to move out of the sheet feed plane whereby the lower retaining member moves into the sheet feed plane. 
     According to another method, sheets are over-accumulated according to the following steps. An accumulating section is provided that defines a sheet feed plane extending therethrough. An accumulating assembly is generally disposed upstream from the accumulating section and comprises an upper retaining member and a lower ramp, wherein the upper retaining member and the lower ramp extend into the sheet feed plane. An incoming sheet is moved generally along the sheet feed plane toward the lower ramp. The incoming sheet is caused to contact the lower ramp and move over the lower ramp. The incoming sheet is caused to contact the upper retaining member and be guided downwardly thereby, whereby the incoming sheet enters the accumulating section between the upper retaining member and a preceding sheet residing in the accumulating section. 
     According to yet another method, sheets are under-accumulated according to the following steps. An accumulating section is provided that defines a sheet feed plane extending therethrough. An accumulating assembly is generally disposed upstream from the accumulating section and comprises an upper ramp and a lower retaining member, wherein the upper ramp and the lower retaining member extend into the sheet feed plane. An incoming sheet is moved generally along the sheet feed plane toward the upper ramp. The incoming sheet is caused to contact the upper ramp and move below the upper ramp. The incoming sheet is caused to contact the lower retaining member and be guided upwardly thereby, whereby the incoming sheet enters the accumulating section between the lower retaining member and a preceding sheet residing in the accumulating section. 
     According to a further method, sheets are over-accumulated according to the following steps. A first sheet is inputted along a sheet feed plane toward an accumulation area. The first sheet is diverted above the sheet feed plane. The first sheet is urged downwardly as the first sheet moves into the accumulation area, and comes to rest in the accumulation area. A second sheet is inputted along the sheet feed plane toward the accumulation area. The second sheet is diverted above the sheet feed plane. The second sheet is urged downwardly as the second sheet moves into the accumulation area, and comes to rest in the accumulation area on top of the first sheet. The method can be repeated for subsequent sheets to form an accumulated stack of sheets in the accumulation area. 
     According to an additional method, sheets are under-accumulated according to the following steps. A first sheet is inputted along a sheet feed plane toward an accumulation area. The first sheet is diverted below the sheet feed plane. A trailing edge of the first sheet is urged upwardly as the first sheet moves into the accumulation area, such that the first sheet comes to rest in the accumulation area with its trailing edge elevated above the sheet feed plane. A second sheet is inputted along the sheet feed plane toward the accumulation area. The second sheet is diverted below the sheet feed plane and below the trailing edge of the first sheet. A trailing edge of the second sheet is urged upwardly as the second sheet moves into the accumulation area. The second sheet comes to rest in the accumulation area underneath the first sheet, and the trailing edge of the second sheet is elevated above the sheet feed plane. The method can be repeated for subsequent sheets to form an accumulated stack of sheets in the accumulation area. 
     It is therefore an object to provide an accumulating apparatus for collecting and advancing sheet articles, and particularly such an apparatus for use in high-speed media processing. 
     It is another object to provide an accumulating apparatus that permits selection and adjustment of either over-accumulating or under-accumulating of the sheet articles processed thereby, and can also accommodate different sheet sizes. 
     It is yet another object to provide an accumulating apparatus for improved handling of processed sheet articles that eliminates or at least greatly minimizes toner smudging of smearing of the sheet articles. 
     It is still another object to provide an accumulating apparatus for improved handling of processed sheet articles wherein the sheet articles are accumulated into a fully registered set of sheets. 
     Some of the objects having been stated hereinabove and which are achieved in whole or in part by this invention, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an accumulating apparatus provided in accordance with the present invention; 
         FIG. 2  is a side elevation view of an upstream region of the accumulating apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a perspective view of a portion of an accumulating assembly provided with the accumulating apparatus illustrated in  FIG. 1 ; 
         FIG. 4  is a side elevation view of an upstream region of the accumulating apparatus illustrated in  FIG. 1 , showing the apparatus operating in an over-accumulating mode; 
         FIG. 5  is a side elevation view of an upstream region of the accumulating apparatus illustrated in  FIG. 1 , showing the apparatus operating in an under-accumulating mode; 
         FIG. 6  is a side elevation view of a portion of the accumulating apparatus illustrated in  FIG. 1 , showing details of a transport device provided therewith; 
         FIG. 7  is a perspective view of an upstream region of the accumulating apparatus illustrated in  FIG. 1 ; 
         FIG. 8  is a side elevation view of the accumulating apparatus illustrated in  FIG. 1 ; 
         FIG. 9  is a side elevation view in partial phantom of a front stop mechanism; 
         FIG. 10  is a perspective view of the front stop mechanism illustrated in  FIG. 9 ; 
         FIG. 11  is another perspective view of the front stop mechanism illustrated in  FIG. 9 ; 
         FIG. 12  is a perspective view of a carriage assembly; 
         FIG. 13  is a perspective view of a side-to-side jogging assembly; 
         FIG. 14  is a side elevation view of one portion of the side-to-side jogging assembly illustrated in  FIG. 13 ; 
         FIG. 15  is a perspective view of the portion of the side-to-side jogging assembly illustrated in  FIG. 14 ; and 
         FIG. 16  is a perspective view of the accumulating apparatus illustrated in  FIG. 1 , wherein an upper section of the apparatus has been pivoted away from a lower section thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , an accumulating apparatus, generally designated  10 , is provided which is adapted to accumulate material without smudging or otherwise marring any printed matter contained on either side of the sheet material being processed. Accumulating apparatus  10  is also adapted to produce an accumulated set of sheets that are properly registered on all (leading, trailing, and lateral) edges. Moreover, accumulating apparatus  10  is selectively adjustable between an over-accumulating mode of operation and an under-accumulating mode of operation. These operational modes are described in detail hereinbelow. 
     In general, accumulating apparatus  10  comprises an input section, generally designated  15 ; an accumulation area, generally designated  20 ; and an output section, generally designated  25 . Arrow F in  FIG. 1  indicates the general direction of material flow through accumulating apparatus  10 . As understood by persons skilled in the art, the various components comprising input section  15 , accumulation area  20 , and output section  25  are disposed in relation to a framework assembly of accumulating apparatus  10 . The framework assembly can comprise a number of various structural members as appropriate for assembling accumulating apparatus  10  into an integrated unit. As shown in  FIG. 16 , for example, the framework assembly can include lateral support plates  30 A and  30 B. It will be further understood that accumulating apparatus  10  can be situated in-line between upstream and downstream modules as part of a larger material processing system. Non-limiting examples of upstream modules include feeders, cutters, readers, folders, stagers, and turnover devices. Non-limiting examples of downstream modules include readers, stagers, turnover devices, folders, inserts, diverters, envelope stuffers, postage meters, and finishers (e.g., stitchers, binders, shrink wrappers, or the like). 
     In operation, accumulating apparatus  10  is initially set to perform either over-accumulation or under-accumulation by manipulating outer thumb knobs or levers  41 A and  41 B and inner thumb knobs or levers  43 A and  43 B, as described in more detail hereinbelow. An upstream module or other means is used to feed either individual sheets of material or subsets of sheets sequentially into input section  15 . Hence, as used hereinafter, the term “sheet” denotes either a single sheet or a subset of sheets, it being understood that accumulating apparatus  10  is capable of producing an accumulated sheet set from either a plurality of individually in-fed sheets or a plurality of in-fed, previously accumulated subsets of sheets. As a general matter, “sheets” can constitute any form of material units capable of being processed by document handling equipment. 
     As described in more detail hereinbelow, input section  15  controls the speed of the incoming sheets according to a dynamic speed profile as the sheets are being fed into accumulation area  20 . Once a sheet enters accumulation area  20 , that sheet is held while other sheets are permitted to enter accumulation area  20  either under or over the first sheet. If accumulating apparatus  10  is set to over-accumulate sheets in accumulation area  20 , the first sheet entering accumulation area  20  becomes the bottom-most sheet in the resulting stack of accumulated sheets. If, on the other hand, accumulating apparatus  10  is set to under-accumulate sheets, the first sheet becomes the top-most sheet in the resulting stack of accumulated sheets. 
     As sheets are accumulated in the accumulation area  20 , the leading edge, trailing edge, and lateral edges of each sheet are registered or justified, so that all sides of the resulting stack are squared off in preparation for subsequent advancing of the sheet stack to a downstream site (e.g., a downstream sheet set processing module). In at least one embodiment, an adjustable front stop mechanism (described hereinbelow) is utilized to register the leading edge of each incoming sheet. In at least one other embodiment, a jogging mechanism (described hereinbelow) is used to assist in registering the lateral edges of the sheets in the accumulating stack. Once a predetermined number of sheets have accumulated in accumulation area  20 , such as by employing conventional sensing or counting means, a transport mechanism (described hereinbelow) generally situated within accumulation area  20  advances the stack into output section  25 , from which the sheet set is transported from accumulating apparatus  10  to the downstream site. 
     As shown in  FIG. 1 , a set of top elongate support (or sheet guide) members comprising rods  45  and a set of bottom elongate support (or sheet guide) members comprising rods  47  extend through accumulation area  20 , and respectively define upper and lower structural boundaries for the set of material units accumulating in accumulation area  20 . Preferably, two or more corresponding pairs of top support rods  45  and bottom support rods  47  are provided, with each pair being laterally spaced from adjacent pairs. Top and bottom support rods  45  and  47  are passive elements. As such, top and bottom support rods  45  and  47  do not impart active forces to the sheets, and thus do not smudge the sheets. In furtherance of the smudge-free operation of accumulating apparatus  10 , it is also preferable that top and bottom support rods  45  and  47  be cylindrical so as to present the smallest possible contact area for the sheets. 
     Referring to  FIG. 2 , the material flow path indicated by arrow F through accumulating apparatus  10  is directed generally along a central sheet feed plane P. Central sheet feed plane P thus also indicates the general flow path of sheets through accumulating apparatus  10 , and further provides a general demarcation between upper and lower sections of accumulating apparatus  10 . In  FIG. 2 , upper section is generally designated  10 A and lower section is generally designated  10 B. 
     Input section  15  ( FIG. 2 ) of accumulating apparatus  10  comprises an entrance area, generally designated  49 , defined at least in part by a top entrance guide  51 A disposed in upper section  10 A of accumulating apparatus  10  above central sheet feed plane P and a bottom entrance guide  51 B disposed in lower section  10 B below central sheet feed plane P. Input section  15  further comprises a dynamic in-feed mechanism, which preferably includes a pair of dynamic in-feed rollers  53 A and  53 B. Top in-feed roller  53 A is disposed in upper section  10 A of accumulating apparatus  10  above central sheet feed plane P, and bottom in-feed roller  53 B is disposed in lower section  10 B below central sheet feed plane P. Hence, a nip is formed between top and bottom in-feed rollers  53 A and  53 B that is generally situated about central sheet feed plane P. 
     The coupling of one of in-feed rollers  53 A or  53 B to a variable-speed motor (not shown) renders the rollers “dynamic” in the sense that their rotational speed is variable over a given range (for example, approximately 80 ips to approximately 180 ips, where “ips” denotes “inches per second”). For each cycle, defined for the present purpose as a sheet being fed through input section  15  and into accumulation area  20  (and accumulating over or under the pre-existing stack, if any), the dynamic speed profile is characterized by an initial input speed (preferably matched with the output speed of the upstream module) followed by a ramping down of the speed as the sheet enters accumulation area  20  and abuts the front stop mechanism provided. The ramp of deceleration that forms a part of the dynamic speed profile can be associated with a constant rate of deceleration or a non-linear rate. As one example, the initial in-feed speed can be 180 ips, which is thereafter dynamically slowed down according to a predetermined speed profile to a lower speed of 80 ips. 
     Input section  15  also comprises a switchable over/under accumulating mechanism that comprises the following components. First and second top gears or gear segments  55 A and  55 B, respectively, are mounted in upper section  10 A of accumulating apparatus  10  above central sheet feed plane P, and rotate about respective parallel axes in meshing engagement with each other. Similarly, first and second bottom gears or gear segments  57 A and  57 B, respectively, are mounted in lower section  10 B of accumulating apparatus  10  below central sheet feed plane P, and rotate about respective parallel axes in meshing engagement with each other. Thus, first and second top gear segments  55 A and  55 B rotate in opposite senses with respect to each other, and first and second bottom gear segments  57 A and  57 B rotate in opposite senses with respect to each other. In a preferred embodiment, first top gear  55 A and top in-feed roller  53 A rotate about the same axis, and first bottom gear  57 A and bottom in-feed roller  53 B rotate about the same axis. 
     The over/under accumulating mechanism further comprises one or more top accumulation ramps  59  and one or more bottom accumulation ramps  61 . Top accumulation ramps  59  are linked in mechanical relation to first top gear segment  55 A and rotate therewith, and bottom accumulation ramps  61  are linked in mechanical relation to first bottom gear segment  57 A and rotate therewith. As shown in  FIG. 2 , top and bottom accumulation ramps  59  and  61  preferably include respective inclined surfaces  59 A and  61 A and back-stop surfaces  59 B and  61 B. One or more top hold-down spring fingers  63  (see  FIG. 4 ) are linked in mechanical relation to second top gear segment  55 B and rotate therewith, and one or more bottom top hold-down spring fingers  65  (see  FIG. 4 ) are linked in mechanical relation to second bottom gear segment  57 B and rotate therewith. The top hold-down spring fingers  63  and the bottom hold-down spring fingers  65  are exemplary embodiments of upper and lower retaining members linked to the top and bottom ramps  59  and  61  via respective gear sets  55 A,  55 B, and  57 A,  57 B. 
     Preferably, top and bottom hold-down fingers  63  and  65  include respective arcuate sections  63 A and  65 A as shown in FIG.  4 . Each arcuate section  63 A and  65 A can be constructed as a continuous member or as a contiguous series of differently angled segments. Each of top and bottom hold-down fingers  63  and  65  is constructed of such physical dimensions and material composition as to be capable of storing spring energy. Hence, top and bottom hold-down fingers  63  and  65  are deflectable upon encountering a force and recoverable to an initial profile upon subsequent removal of the force. Inclined surfaces  59 A and  61 A of respective top and bottom accumulation ramps  59  and  61 , and arcuate sections  63 A and  65 A of respective top and bottom hold-down fingers  63  and  65 , selectively interact with incoming sheets as described hereinbelow. The selectivity depends on whether the over-accumulation mode or under-accumulation mode is active. As also described hereinbelow, respective back-stop surfaces  59 B and  61 B of top and bottom accumulation ramps  59  and  61  assist in selectively registering the trailing edge of the stack of sheets. 
     Referring to  FIG. 3 , the mechanical arrangement of outer knobs  41 A and  41 B, first and second bottom gear segments  57 A and  57 B, bottom accumulation ramps  61 , and bottom hold-down fingers  65  are illustrated in accordance with a preferred embodiment of the invention. Each outer knob  41 A and  41 B is connected to its corresponding first bottom gear segment  57 A by one or more suitable fasteners  67 , such that rotation of outer knobs  41 A and  41 B likewise causes first bottom gear segments  57 A to rotate. Each bottom accumulation ramp  61  is connected to a support member  69  by one or more suitable fasteners  71 . Support member  69  is connected between outer knobs  41 A and  41 B and thus rotates therewith. Each bottom hold-down finger  65  is connected to another support member  73  by one or more suitable fasteners  75 . Support member  73  is connected between second bottom gear segments  57 B and thus rotates therewith. It will be understood that the mechanical arrangement of inner knobs  43 A and  43 B (see FIG.  1 ), first and second top gear segments  55 A and  55 B (see FIG.  2 ), top accumulation ramps  59 , and top hold-down fingers  63  (see  FIG. 4 ) can be analogously provided. Thus, in  FIG. 1 , top accumulation ramps  59  are connected to a support member  77 , which is in turn connected between inner knobs  43 A and  43 B and thus rotates therewith. As shown in  FIG. 16 , a support member  79  is also employed for mounting top hold-down fingers  63  ( FIG. 4 ) in mechanical connection with second top gear segments  55 B. 
     Referring back to  FIG. 2 , the intermeshing of first and second top gear segments  55 A and  55 B operatively couples top accumulation ramps  59  and top hold-down fingers  63  together. Similarly, the intermeshing of first and second bottom gear segments  57 A and  57 B (see also  FIG. 4 ) operatively couples bottom accumulation ramps  61  and bottom hold-down fingers  65  together. As described hereinabove, inner thumb knobs  43 A and  43 B (see  FIG. 1 ) mechanically communicate with first top gear segments  55 A (see also  FIG. 4 ) and second top gear segments  55 B so as to effect adjustment of the relative positions of top accumulation ramps  59  and top hold-down fingers  63 . Similarly, outer thumb knobs  41 A and  41 B (see  FIGS. 1 and 3 ) mechanically communicate with first bottom gear segments  57 A and second bottom gear segments  57 B so as to effect adjustment of the relative positions of bottom en accumulation ramps  61  and bottom hold-down fingers  65 . 
       FIGS. 2 and 4  depict accumulating apparatus  10  in its over-accumulating mode. Inner thumb knobs  43 A and  43 B (see  FIG. 1 ) are pivoted to cause the coupling interaction of first and second top gear segments  55 A and  55 B, top accumulation ramps  59  and top hold-down fingers  63 . Outer thumb knobs  41 A and  41 B (see  FIGS. 1 and 3 ) are pivoted to cause the coupling interaction of first and second bottom gear segments  57 A and  57 B, bottom accumulation ramps  61  and bottom hold-down fingers  65 . As a result, and as shown in  FIG. 4 , top accumulation ramps  59  are disposed in a raised position out of the material flow path while, at the same time, top hold-down fingers  63  are disposed in a lowered position in the material flow path. Also at the same time, bottom accumulation ramps  61  are disposed in a raised position in the material flow path while bottom hold-down fingers  65  are disposed in a lowered position out of the material flow path. As described hereinbelow, this configuration results in an over-accumulation of sheets in accumulation area  20 . 
     Referring to  FIG. 5 , accumulating apparatus  10  has been converted to the under-accumulating mode by pivoting inner thumb knobs  43 A and  43 B and outer thumb knobs  41 A and  41 B to new positions. Top accumulation ramps  59  are now disposed in a lowered position in the material flow path, while top hold-down fingers  63  are disposed in a raised position out of the material flow path. At the same time, bottom accumulation ramps  61  are now disposed in a lowered position out of the material flow path, while bottom hold-down fingers  65  are disposed in a raised position in the material flow path. As described hereinbelow, this configuration results in an under-accumulation of sheets in accumulation area  20 . 
     Referring now to  FIGS. 6 and 7 , one or more dual-lugged transport belts  81 A and  81 B are disposed at the interfacial region of input section  15  and accumulation area  20  of accumulating apparatus  10 . Transport belts  81 A and  81 B rotate about rotatable elements such as pulleys  83  and  85  mounted to shafts  87  and  89 , with one of shafts  87  and  89  being driven by a suitable motor (not shown). In a preferred embodiment, upstream-side pulleys  83  rotate about the same axis as lower infeed rollers  53 B, and thus upstream-side shaft  87  can be a common axle engaged by both upstream-side pulleys  83  and lower infeed rollers  53 B. The inner surface of each transport belt  81 A and  81 B includes a plurality of inside lugs  91  that engage ribbed pulleys  83  and  85  in order to positively drive transport belts  81 A and  81 B. The outside surface of each transport belt  81 A and  81 B, likewise includes outside lugs  93  and  95  of suitable design (see  FIG. 6 ) for engaging the trailing edge of a sheet or sheets. Suitable designs of such outside lugs  93  and  95  are known in the art. In one exemplary embodiment, each transport belt  81 A and  81 B includes two outside lugs  93  and  95  cyclically spaced 180 degrees apart from each other, with each outside lug  93  and  95  of one transport belt  81 A being situated in phase with each corresponding outside lug  93  of the other transport belt  81 B. The upper run of each transport belt  81 A and  81 B is disposed at a high enough elevation within accumulation area  20  so as to enable outside lugs  93  to contact the trailing edge of the sheet stack residing in accumulation area  20 , thereby permitting transport belts  81 A and  81 B to advance the sheet stack through accumulation area  20  along the material flow path. In  FIG. 6 , the positions of lugs  93  and  95  are designated  93 A and  95 A, respectively, at the moment before lug  93 A contacts a sheet stack. 
     Referring now to  FIGS. 8-11 , a front stop mechanism, generally designated  110 , is disposed generally within accumulation area  20 . The longitudinal position of front stop mechanism  110  with respect to input section  15  is adjustable in order to accommodate different lengths of sheets. In  FIG. 8 , for example, front stop mechanism  110  is shown disposed at a position X at which sheets of a relatively short length (e.g., 3.50 inches) can be accommodated, and is also alternatively shown disposed at a position Y at which sheets of a relatively long length (e.g., 14.0 inches) can be accommodated. Front stop mechanism  110  in a preferred embodiment comprises spring-loaded, retractable front stop fingers  113 . Front stop fingers  113  are alternately extended across central sheet feed plane P (and thus in the material flow path) or retracted below central sheet feed plane P (and thus out of the material flow path). In  FIG. 8 , for purposes of illustration, front stop fingers  113  are shown in the extended position at position X of front stop mechanism  110  and in the retracted position at position Y of front stop mechanism  110 . It will be understood, however, that front stop fingers  113  are alternately extendable and retractable during the operation of accumulating apparatus  10  at all positions of front stop mechanism  110  available along the length of accumulation area  20 . 
     Referring to  FIGS. 9-11 , further details of the front stop mechanism  110  are shown. Each front stop finger or plate  113  is connected to a vertical slide plate  115  using shoulder bolts  117  or other suitable securing means. A compression spring  119  is interposed between each front stop finger  113  and vertical slide plate  115  to enable each front stop finger  113  to recoil to a degree sufficient to jog sheets entering into the accumulation area  20 , thereby registering the sheets along their respective lead edges. Preferably, compression springs  119  are generally axially aligned with central sheet feed plane P (see  FIG. 8 ) when front stop fingers  113  are extended. Vertical slide plate  115  is connected to a guide plate  121  through one or more guide members  123 A and  123 B. Guide plate  121  is mounted to a support plate  125  by means of one or more suitable fasteners such as bolts  127 . Guide members  123 A and  123 B are movable within respective slots  121 A and  121 B formed through guide plate  121  (see  FIG. 10 ) to enable vertical slide plate  115  to slide vertically with respect to guide plate  121 . The interaction of vertical slide plate  115  with guide plate  121  thus enables front stop fingers  113  to move into and out of the material feed path as described hereinabove. 
     A powered drive source adapted for reversible rotary power transfer, such as a rotary solenoid or reversible motor  131 , is mounted to support plate  125  through a suitable mounting bracket  133  (see  FIG. 11 ) and includes an output shaft  131 A. An actuating arm  135  having a U-slot (designated  135 A in  FIG. 9 ) is connected to output shaft  131 A, such that rotation of output shaft  131 A clockwise or counterclockwise rotates actuating arm  135  in a like manner. Actuating arm  135  is linked to vertical slide plate  115  by means of a transverse pin  137 . Transverse pin  137  is secured to vertical slide plate  115  through one or more suitable fasteners such as bolts  139 . Transverse pin  137  is situated within U-slot  135 A of actuating arm  135 , and thus is movable along the length of U-slot  135 A. Accordingly, rotation of actuating arm  135  in one direction imparts an upward force to transverse pin  137  and results in vertical slide plate  115  sliding upwardly, while rotation of actuating arm  135  in the other direction imparts a downward force to transverse pin  137  and results in vertical slide plate  115  sliding downwardly. 
     Referring back to  FIG. 8 , one or more pairs of output rollers  141 A and  141 B are associated with front stop mechanism  110 . Top output roller  141 A is disposed in upper section  10 A of accumulating apparatus  10  above central sheet feed plane P, and bottom output roller  141 B is disposed in lower section  10 B below central sheet feed plane P. Hence, a nip is formed between top and bottom output rollers  141 A and  141 B that is generally situated about central sheet feed plane P. In the case where a downstream material processing device operates in connection with accumulating apparatus  10 , the rotational speed of output rollers  141 A and  141 B is preferably matched to the speed of the downstream device, which ordinarily is a constant speed falling within the approximate range of, for example, 80 ips to 180 ips. Output rollers  141 A and  141 B are disposed at a fixed distance downstream from front stop fingers  113 , yet are longitudinally adjustable with front stop fingers  113  along the length of accumulation area  20  to accommodate different sizes of sheets. 
     Referring now to  FIG. 12 , a carriage assembly is illustrated that enables the position of front stop mechanism  110  and its associated output rollers  141 A and  141 B to be adjusted as described hereinabove. In  FIG. 12 , for purposes of clarity, only lower output rollers  141 B are shown with the understanding that upper output rollers  141 A are also provided to form one or more pairs of nip rollers (as shown in  FIGS. 4 ,  5  and  8 ). In addition to the front stop mechanism  110 , output rollers  141 A and  141 B are also mounted to support plate  125 . A carriage member  151 A and  151 B is secured to each lateral end of support member  125 . A pinion gear  153  traverses the full length of support plate  125  and has ends  153 A and  153 B mounted within corresponding carriage members  151 A and  151 B. Each pinion gear end  153 A and  153 B engages a respective rack gear  155 A and  155 B. This configuration assists in maintaining the parallel/perpendicular positioning of front stop mechanism  110 . Each rack gear  155 A and  155 B is respectively mounted to a lateral support plate  30 A and  30 B (only one of which is shown in FIG.  12 ). Lateral support plates  30 A and  30 B form a part of the main frame assembly of accumulating apparatus  10 , as shown in FIG.  16 . The meshing between pinion gear ends  153 A and  153 B and their corresponding rack gears  155 A and  155 B enable front stop mechanism  110  and output rollers  141 A and  141 B to translate back and forth together in a controlled manner, along the direction of material travel. This translational adjustment could be effected manually or by automated means. For example, the shaft position of pinion gear  153  could be made to engage an appropriate motor and transmission assembly so as to transfer power to carriage members  151 A and  151 B through the engagement of pinion gear ends  153 A and  153 B and rack gears  155 A and  155 B. 
     Output rollers  141 A and  141 B are driven by an output roller drive motor  161  and associated drive belt  163  and pulleys  165 A,  165 B and  165 C. The position of this motor  161  is also adjustable with output rollers  141 A and  141 B and front stop mechanism  110 . This is accomplished by mounting output roller drive motor  161  to a sliding motor support plate  167 . The lateral ends of sliding motor support plate  167  are connected to guide members  169  (only one of which is visible in  FIG. 12 ) that slide along the lengths of respective side rails  171 A and  171 B. Each side rail  171 A and  171 B is secured to a respective lateral support plate  30 A and  30 B of accumulating apparatus  10 . 
     Referring back to  FIGS. 1 and 8 , output section  25  of accumulating apparatus  10  comprises one or more pairs of exit rollers  181 A and  181 B. For each pair of exit rollers  181 A and  181 B provided, top exit roller  181 A is disposed in upper section  10 A of accumulating apparatus  10  above central sheet feed plane P, and bottom exit roller  181 B is disposed in lower section  10 B below central sheet feed plane P (in  FIG. 1 , only bottom exit rollers  181 B are shown for clarity). Exit rollers  181 A and  181 B form a nip that is generally situated about central sheet feed plane P. The speed of exit rollers  181 A and  181 B is matched to that of output rollers  141 A and  141 B and thus to that of the downstream device. 
       FIGS. 13-15  illustrate details of the side jogging mechanism provided in accumulating apparatus  10 . The side jogging mechanism includes two adjustable side guides  191 A and  191 B generally situated in accumulation area  20 . Side guides  191 A and  191 B function to guide sheets into and through accumulation area  20 , as well as to laterally jog the sheets as they accumulate (or after a predetermined number of sheets have accumulated) in order to register the side edges of the sheet stack. The respective lateral positions of side guides  191 A and  191 B are adjustable with respect to the longitudinal centerline of accumulation area  20 —that is, the centerline in the direction of material flow. Accordingly, as shown in  FIG. 13 , each side guide  191 A and  191 B is connected to a respective adjustable mounting bracket  193 A and  193 B. In addition, the upstream ends of each adjustable mounting bracket  193 A and  193 B are slidingly supported by a transversely disposed support rod  195 , and the downstream ends of each adjustable mounting bracket  193 A and  193 B are slidingly supported by another transversely disposed support rod  197 . The width between side guides  191 A and  191 B can thus be varied to accommodate different sheet sizes (e.g., a range of approximately 5.50 inches to approximately 12.0 inches) by sliding adjustable mounting brackets  193 A and  193 B toward or away from each other along threaded support rods  195  and  197 . The adjustment could be manual or mechanized in accordance with known methods. Preferably, side guides  191 A and  191 B are initially positioned equidistantly about the center line of accumulation area  20 , and the width between side guides  191 A and  191 B, for example, is approximately 0.25 inches greater than the actual width of the sheets to be processed to allow room for side-to-side jogging. 
     As shown in  FIGS. 14 and 15 , each side guide  191 A and  191 B is connected to its respective adjustable mounting bracket  193 A and  193 B by one or more suitable linking members such as bolts  201 A and  201 B. Preferably, as shown in  FIG. 15 , two or more spaced bolts  201 A and  201 B are employed to improve the stability of side guides  191 A and  191 B. As also shown in  FIGS. 14 and 15 , each side guide  191 A and  191 B is biased laterally outwardly from the centerline of accumulation area  20  by springs  203 A and  203 B. As shown in  FIG. 14 , each spring  203 A and  203 B is retained on its corresponding bolt  201 A and  201 B between the head of bolt  201 A and  201 B and a back plate  205 A and  205 B of its corresponding side guide  191 A and  191 B. 
     The jogging movement is effected by a suitable actuator such as a solenoid  207 A and  207 B mounted to each adjustable mounting bracket  193 A and  193 B. The moving portion of each solenoid  207 A and  207 B, for example an actuating arm  209 , is able to contact back plate  205 A and  205 B of each corresponding side guide  191 A and  191 B. Hence, activation of each solenoid  207 A and  207 B causes extension of its actuating arm  209 , and in turn causes its side guide  191 A and  191 B to translate inwardly toward the centerline of accumulation area  20  against the biasing force of springs  203 A and  203 B. Deactivation of each solenoid  207 A and  207 B causes its side guide  191 A and  191 B to return to its initial position under the influence of springs  203 A and  203 B. Alternate activation and deactivation of solenoids  207 A and  207 B produces the jogging action that results in side-to-side registration of sheets in accumulation area  20 . The sheet stack can be jogged each time a new sheet is added to the stack, or can be jogged after the predetermined number of sheets have been added to complete the stack. Preferably, the amount by which each solenoid  207 A and  207 B causes extension of its respective actuating arm  209  depends on the initial width set between side guides  191 A and  191 B. For example, if the initial width is set to approximately ¼ inches greater than the actual width of the sheets being processed, the distance by which each actuating arm  209  extends can be ⅛ inches 
     The operation of accumulating apparatus  10  when positioned in its over-accumulation mode will now be described with reference to  FIG. 4. A  stack S of over-accumulated sheets is shown disposed between upper and lower support rods  45  and  47 , resting on bottom support rods  47  and supported (i.e., retained or held down) by top hold-down fingers  63 . The leading edge of the sheet stack is registered against front stop fingers  113  of front stop mechanism  110 , while the trailing edge of the sheet stack is registered against the respective back surfaces of the bottom accumulation ramps  61 . As described hereinabove, the jogging action generated by the recoil of front stop fingers  113  as each sheet reaches sheet stack S assists in obtaining this front-to-back registration of all sheets of sheet stack S. An incoming sheet IS is shown being fed through input section  15  to be accumulated over existing sheet stack S. Top accumulation ramps  59  are in a raised position out of the material feed plane, and thus out of the way of incoming sheet IS. Similarly, bottom hold-down fingers  65  are in a lowered position out of the material feed plane, and thus out of the way of incoming sheet IS. Bottom accumulation ramps  61  are in a raised position in the material feed plane, such that the leading edge of incoming sheet IS encounters their respective inclined front surfaces and is thereby raised above the top side of the uppermost sheet in the accumulating stack S. Top hold-down fingers  63  are in a lowered position in the material feed plane. Each incoming sheet IS flows over bottom accumulation ramps  61 , is guided downwardly by top hold-down fingers  63 , is jogged by recoiling front stop fingers  113 , and comes to rest on the top of stack S in registry between front stop fingers  113  and bottom accumulation ramps  61 . 
     The operation of accumulating apparatus  10  when positioned in its under-accumulation mode will now be described with reference to FIG.  5 . Stack S of under-accumulated sheets, or at least the trailing end region thereof, is held against top support rods  45  by bottom hold-down fingers  65 . The leading edge of sheet stack S is registered against front stop fingers  113  of front stop mechanism  110 , while the trailing edge of sheet stack S is registered against the respective back surfaces of top accumulation ramps  59 . Top accumulation ramps  59  are in a lowered position in the material feed plane, such that the leading edge of incoming sheet IS encounters their respective inclined front surfaces and is thereby directed downwardly underneath the bottom side of the bottommost sheet in accumulating stack S. Bottom hold-down fingers  65  are in a raised position in the material feed plane, and thus support sheet stack S in a raised position and guide incoming sheets IS upwardly to allow incoming sheets IS to accumulate underneath sheet stack S. Bottom accumulation ramps  61  are in a lowered position out of the way of the incoming sheets IS. Similarly, top hold-down fingers  63  are in a raised position out of the material feed plane, and thus out of the way of incoming sheets IS and accumulating stack S. Each incoming sheet IS flows along the inclined front surfaces of top accumulation ramps  59  and between stack S and bottom hold-down fingers  65 , is jogged by recoiling front stop fingers  113 , and comes to rest at the bottom of stack S in registry between front stop fingers  113  and top accumulation ramps  59 . 
     Referring now to  FIG. 16 , according to an aspect of the invention, it can be seen that upper section  10 A of accumulating apparatus  10  includes an upper frame  220  that is hinged or otherwise rotatably attached to lateral support plates  30 A and  30 B of lower section  10 B about pivot points  223 A and  223 B (e.g., pins or axles with appropriate mounting hardware). As shown in  FIGS. 2 and 4 , upper section  10 A comprises top entrance guide  51 A, top accumulation ramp  59 , top hold-down finger  63 , first top gear segment  55 A, second top gear segment  55 B, and top support rods  45 . Through their supportive association with upper section  10 A of accumulating apparatus  10 , all of these components pivot away from accumulation area  20  as one assembly, thereby facilitating access into accumulation area  20  to enable removal of sheets without damage thereto. 
     Although not specifically shown in the drawings, it will be understood that an appropriately programmed electronic controller such as a microprocessor, or other conventional means for executing instructions and receiving and/or sending signals, is placed in communication with the variable speed motor driving dynamic infeed rollers  53 A and  53 B, the motor driving transport belts  81 A and  81 B, the actuator  131  driving front stop fingers  113 , the motor  161  driving output rollers  141 A and  141 B, the motor driving exit rollers  181 A and  181 B, and the solenoids  207 A and  207 B driving the side guides  191 A and  191 B. The electronic controller can thus maintain synchronization of these various components of accumulating apparatus  10 , as well as control the respective operations of specific components. It will be further understood that the electronic controller can receive feedback from upstream and downstream devices in order to determine the proper speeds of the various rollers, and can receive feedback from various sensors situated in accumulating apparatus  10  to determine the location of sheets or to count the number of sheets accumulating in accumulation area  20 . Thus, the electronic controller determines the dynamic speed profile of dynamic infeed rollers  53 A and  53 B, as described hereinabove, in order to feed sheets at an initial input speed and slow the sheets down to a reduced registration speed as the sheets approach front stop fingers  113 . In addition, the electronic controller determines the proper time to side jog the sheet stack as sheets enter accumulation area  20 . Moreover, the electronic controller determines when the proper number of sheets have accumulated, after which time the electronic controller causes front stop fingers  113  to retract out of the material flow path, transport belts  81 A and  81 B to move the stack forward into output rollers  141 A and  141 B, output rollers  141 A and  141 B to move the stack to exit rollers  181 A and  181 B, and the exit rollers  181 A and  181 B to move the stack toward an area or device downstream from accumulating apparatus  10 . The provision of independent input, transport, and output drives enables accumulating apparatus  10  to be matched with any upstream and downstream devices. 
     In one specific but non-limiting embodiment, accumulating apparatus  10  supports sheets that are 5.50 inches (140 mm) to 12.00 inches (305 mm) wide and 3.50 inches (89 mm) to 14.00 inches (356 mm) long. This accumulating apparatus  10  can accumulate 1 to 30 sheets of 18-lb. to 24-lb. paper. Conversion time related to material size and over/under accumulation mode switching is approximately two minutes or less. In addition, this accumulating apparatus  10  can accommodate material skew from 0.5 degrees to 2 degrees, depending on sheet length. Sheets are registered from lead-to-trail edge and side-to-side within a 0.008-inches (0.20-mm) offset. 
     The operation of accumulating apparatus  10  as described hereinabove will now be summarized with reference being made primarily to  FIGS. 4 ,  5  and  8 . As an incoming sheet IS enters accumulating apparatus  10  under the control of an upstream device, incoming sheet IS passes through top and bottom entrance guides  51 A and  51 B into the nip formed by top and bottom infeed rollers  53 A and  53 B. Incoming sheet IS thus enters accumulation area  20  under the control of dynamic in-feed rollers  53 A and  53 B. At this point, the rotational speed of dynamic in-feed rollers  53 A and  53 B is preferably matched to the output speed of the upstream device. Preferably, this matched speed is at or near the maximum speed of dynamic in-feed rollers  53 A and  53 B, and thus corresponds to the maximum flow rate of incoming sheets IS into input section  15  of accumulating apparatus  10 . Dynamic in-feed rollers  53 A and  53 B advance incoming sheet IS into accumulating apparatus  10  for a predetermined distance, at the top speed that is preferably matched to the output speed of the upstream material processing device. The speed of in-feed rollers  53 A and  53 B is then dynamically reduced to dynamically slow down the flow rate of incoming sheet IS, thereby allowing the lead edge of incoming sheet IS to contact spring-loaded front stop mechanism  110  without the risk of damage. 
     The recoiling reaction of front stop mechanism  110  induces a jogging action that registers incoming sheet IS with the rest of sheet stack S between front stop mechanism  110  and either top accumulation ramp  59  or bottom accumulation ramp  61  (depending on whether accumulating apparatus  10  is set for under-accumulation or over-accumulation as described hereinabove). Dynamic in-feed rollers  53 A and  53 B increase speed back up to top velocity to advance subsequent incoming sheets IS into accumulation area  20 , and the slowdown process again occurs such that the dynamic speed profile is implemented for each cycle of incoming sheets IS being fed into accumulating apparatus  10 . Each incoming sheet IS can be fed completely individually, in subsets, or in overlapping relation to other incoming sheets IS. 
     When a complete set of sheets (sheet stack S) has been over- or under-accumulated, the following exit routine transpires. Spring loaded front stop fingers  113  retract out of the sheet feed path. Side guides  191 A and  191 B (see  FIGS. 13-15 ) contact the sides of the sheet set and register the sheets from side-to-side in the manner described hereinabove. Side guides  191 A and  191 B hold the sheet set in a registered position for a predetermined time of the exit routine and then release the sheet set. Dual-lugged transport belts  81 A and  81 B start to cycle. In one example, one cycle equals 180 degrees at a fixed speed of approximately 30 ips. The low speed of dual-lugged transport belts  81 A and  81 B minimizes trail-edge damage when outside lugs contact  93  (see  FIG. 6 ) and advance the set of accumulated sheets. As dual-lugged transport belts  81 A and  81 B cycle, they contact the trail edge of the set of accumulated sheets and advance the lead edge of the accumulated set into the pair of output rollers  141 A and  141 B. As described hereinabove, output rollers  141 A and  141 B are positioned at a fixed distance downstream from front stop fingers  113 , and their speed is preferably matched with that of the downstream device, which ordinarily will be a fixed, constant speed ranging between, e.g., approximately 80 ips to approximately 180 ips. As the lead edge of sheet stack S enters output rollers  141 A and  141 B, output rollers  141 A and  141 B advance sheet stack S at a higher rate of speed than dual-lugged transport belts  81 A and  81 B. As sheet stack S advances in this manner, its lead edge enters the pair of fixed-position exit rollers  181 A and  181 B, the speed of which is preferably matched with the speed of output rollers  141 A and  141 B and that of the downstream device. Once the trail edge of this sheet stack S has passed by spring-loaded front stop fingers  113 , front stop fingers  113  extend back into the sheet path ready for the next set of sheets to accumulate. 
     It can be seen from the foregoing that no moving components of accumulating apparatus  10  contact the sheet material during accumulation thereof. Thus, the risk of toner smudging/transfer to the sheet material is significantly reduced or even eliminated. Moreover, the adjustments to accumulating apparatus  10  required to effect a change-over between under-accumulation and over-accumulation, and to effect a change in material size, is quick, easy, and tool-less. 
     It will be understood that various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation—the invention being defined by the claims.