Patent Publication Number: US-8540226-B2

Title: System and method for minimizing the conveyance feed path of a sheet material handling system

Description:
FIELD OF THE INVENTION 
     The present invention relates to a system and method for handling sheet material, and more particularly, to a system and method for minimizing the conveyance feed path to reduce the spatial requirements of a sheet handling system. 
     BACKGROUND OF THE INVENTION 
     Various apparatus are employed for arranging sheet material in a package suitable for use or sale in commerce. One such apparatus, useful for describing the teachings of the present invention, is a mailpiece inserter system employed in the fabrication of high volume mail communications, e.g., mass mailings. Such mailpiece inserter systems are typically used by organizations such as banks, insurance companies, and utility companies for producing a large volume of specific mail communications where the contents of each mailpiece are directed to a particular addressee. Also, other organizations, such as direct mailers, use mail inserters for producing mass mailings where the contents of each mail piece are substantially identical with respect to each addressee. Examples of inserter systems are the 8 series, 9 series, and APS™ inserter systems available from Pitney Bowes Inc. located in Stamford, Conn., USA. 
     In many respects, a typical inserter system resembles a manufacturing assembly line. Sheets and other raw materials (i.e., a web of paper stock, enclosures, and envelopes) enter the inserter system as inputs. Various modules or workstations in the inserter system work cooperatively to process the sheets until a finished mail piece is produced. For example, in a mailpiece inserter, an envelope is conveyed downstream to each processing module by a transport or conveyance including drive elements such as rollers or a series of belts. The processing modules may include, inter alia, (i) a web for feeding printed sheet material, i.e., material to be used as the content material for mailpiece creation, (ii) a module for cutting the printed sheet material to various lengths, (iii) a feed input assembly for accepting the printed sheet material from the cutting module, (iv) a folding module for folding mailpiece content material for subsequent insertion into the envelope, (v) a chassis module where sheet material and/or inserts, i.e., the content material, are combined to form a collation, (vi) an inserter module which opens an envelope for receipt of the content material, (vii) a moistening/sealing module for wetting the flap sealant to close the envelope, (viii) a weighing module for determining the weight of the mailpiece for postage, and (x) a metering module for printing the postage indicia based upon the weight and/or size of the envelope, i.e., applying evidence of postage on the mailpiece. While these are some of the more commonly used modules for mailpiece creation, it will be appreciated that the particular arrangement and/or need for specialty modules, are dependent upon the needs of the user/customer. 
     Inasmuch as a mailpiece inserter comprises a plurality of processing modules, it is oftentimes desirable to reduce the conveyance feed path, and, accordingly, the “foot-print” occupied by the inserter. That is, since the real-estate occupied by a mailpiece inserter translates into a “fixed expense” for an operator, it is desirable to reduce the space consumed by the inserter. As a result, savings can be achieved by reducing the length of the conveyance feed path. 
     Of the many challenges faced by designers of mailpiece inserters, one area which results in a requirement for greater space/length of the conveyance path is the transition between modules. That is, to accommodate sheets of variable length, or process certain mail run jobs, a threshold spacing must be maintained between modules to ensure that a downstream module does not prematurely begin processing/handling a sheet/collation before an upstream module has completed an operation. For example, it is common practice to lengthen the feed path, or include a buffer region between modules, to allow a larger sheet, e.g., 11×17 inch sheet, to be processed/handled by an upstream module without interference by a downstream module. 
     In the case of a print module, it will be appreciated that a blank sheet is fed past a printhead which prints from a leading to a trailing edge. As the sheet is fed and printed, the leading edge is conveyed downstream or “leads” as the sheet is printed along or near the trailing edge. No operation can be performed on the leading edge (which is now downstream of the printhead) while the trailing edge is being printed As a consequence, the conveyance feed path will typically include the full length of a sheet before a downstream module can accept and begin another operation. 
     Another example includes the transition between a cutting module and a feed input assembly of a mailpiece inserter. In this example, the length of content material can vary from a short insert, i.e., approximately four and one-half inches (4½″), to a double-length sheet, i.e., approximately seventeen inches (17″). As a result, the feed path between the cutting module and the feed input assembly can vary by more than twelve inches (12″) or one foot (1′). Stated in yet other terms, the point of entry/ingestion of the leading edge of a long sheet can lengthen the feed path of the inserter as compared to the entry point required by a short insert, e.g., the location of a nip for ingesting the leading edge of the insert. 
     Finally, the initial set-up and anticipated processing of a sheet/collation can adversely impact the length of the conveyance feed path. For example, it is common practice to include a symbol/mark/scan code on one or more sheets of a collation to provide information concerning the processing of the collation. When accumulating a collation of sheets, a scanner disposed upstream of the accumulator, reads the symbol/mark/scan code so that the inserter may know when a collation begins or ends. That is, the mailpiece processor interprets the symbol/mark/scan code such that it may determine which sheet, of the stream of sheets being fed along a conveyance path, is the first sheet of the next collation. 
     As a result, information is obtained concerning when the Beginning Of the next Collation (BOC) begins and/or when the end of the current collation ends. Depending upon the location of this symbol/mark/scan code, the length of the conveyance feed path (between an upstream singulating module, i.e., a module which singulates/feeds sheets, and a downstream accumulator), must accommodate the longest sheet anticipated to be processed. If, for example, the symbol/mark/scan code is located along a trailing edge of a sheet to be processed, then the length of the conveyance path must be at least as long as the distance between the leading edge of the sheet and the BOO plus a threshold pitch distance (i.e., the distance between the trailing edge of one sheet and the leading edge of the subsequent sheet as determined by the throughput requirements/speed of the mailpiece inserter). 
     In each of the above examples, it will be appreciated that conveyance systems of the prior art are constrained by a requirement to accommodate processing of the largest sheet, whether dictated by the length dimension of the sheet, or the location/position of a symbol/mark/scan code on the face of the sheet. As a result, the overall foot-print/size of the sheet handling system, e.g., a mailpiece inserter, is increased by the limitation to maintain a minimum spacing, or threshold distance, between modules. 
     A need, therefore, exists for a conveyance system which processes sheets without the limitations necessitated by the variations in sheet length or sheet processing requirements. 
     SUMMARY OF THE INVENTION 
     A method is provided for operating a sheet handling system which includes the processing steps of feeding singulated sheets from a stack of sheet material and accumulating select sheets into a completed collation of sheets along a conveyance feed path. The method includes the steps of: determining a location of a next collation mark on select sheets of the stack of material to be processed, selecting an operating mode based upon the proximity of the next collation mark relative to a leading or trailing edge of each of the select sheets, processing the singulated sheets in a first operating mode when the next collation mark is proximal to the leading edge of each of the select sheets, and in a second operating mode, when the next collation mark is proximal to a trailing edge of each of the select sheets. When processed each of the select sheets along the conveyance feed path is buffered to change the spatial relationship between each of the select sheet and each completed collation of sheets along the feed path. By selectively operating the sheet handling system based upon the location of the next collation mark and buffering the select sheets, the conveyance feed path is minimized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details of the present invention are provided in the accompanying drawings, detailed description, and claims. 
         FIG. 1  is a broken-away perspective view of the relevant portions of a sheet handling system, e.g., a mailpiece inserter, including a feed module in combination with an accumulator module operative to accumulate/stack sheets to produce a collation of sheets. 
         FIG. 2  depicts a broken-away schematic view of the mailpiece inserter taken substantially along line  2 - 2  of  FIG. 1  wherein the accumulator module includes a first conveyance, a second conveyance, and an auxiliary conveyance interposing the first and second conveyances to augment dispensation of a completed collation from an accumulation station when the first conveyance is inoperative. 
         FIG. 2   a  is an isolated perspective view of a vacuum roller assembly for a singulating apparatus which improves the reliability of sheet feeding while minimizing audible noise levels for improved workstation comfort. 
         FIG. 2   b  is an exploded view of the vacuum roller assembly depicted in  FIG. 2   a  including an external roller having a plurality of off-axis apertures disposed through the roller and a internal plenum in fluid communication with a vacuum pump at one end and with the roller apertures the other end. 
         FIG. 2   c  is a two-dimensional flat pattern perspective of the vacuum roller. 
         FIG. 3  is an enlarged isolated perspective view of the accumulator module shown in  FIG. 1  showing the first, second and auxiliary conveyances in greater detail. 
         FIG. 4  depicts an enlarged side sectional view of the accumulator module taken substantially along line  4 - 4  of  FIG. 3  including a scanner for detecting a Beginning of Collation/End of Collation (BOC/EOC) mark, on selected sheets and a plurality of sensors indicative of the location, or relative position, of sheets conveyed along the conveyance feed path. 
         FIGS. 5   a  though  5   e  depict schematic views of the accumulator module according to the present invention, in a first operating mode, wherein a BOC/EOC mark is printed proximal to the leading edge of selected sheets and wherein each of the  FIGS. 5   a  through  5   e  depict the operation of the accumulator at a particular moment in an accumulation cycle. 
         FIGS. 6   a  though  6   g  depict schematic views of the accumulator module according to the present invention, in a second operating mode, wherein a BOC/EOC mark is printed proximal to the leading edge of selected sheets and wherein each of the  FIGS. 6   a  through  6   g  depict the operation of the accumulator at a particular moment in an accumulation cycle. 
     
    
    
     DETAILED DESCRIPTION 
     The invention described herein is directed to an improved sheet handling system. Firstly, the invention describes a feed apparatus having an improved vacuum roller which reliably singulates sheet material for delivery to the accumulator while reducing the audible noise levels generated by the vacuum pump for increased operator comfort. Additionally, the invention describes an improved sheet material accumulator including an auxiliary conveyance which accumulator improves throughput by selectively operating one of at least two operating modes Finally, a method of operating a sheet handling system is described to reduce the conveyance feed path and decrease the overall envelope/foot-print occupied by the sheet handling system. 
     The system, apparatus and method of the present invention will be discussed in the context of a mailpiece inserter including a feed module disposed upstream of a sheet accumulating module, although, the teachings described herein are equally applicable to other sheet handling equipment and systems. Consequently, the described embodiment is merely an exemplary arrangement of the present invention and the appended claims should be broadly interpreted in view thereof. 
     In  FIGS. 1 and 2 , the relevant portions of a mailpiece inserter  10  are depicted including a feed input/singulation module  12  and sheet accumulation module  14 . More specifically, the feed input/singulation module  12  is adapted to accept a shingled stack of sheets  16 S comprising the content material for a plurality of mailpieces (not shown). For example, the shingled stack of sheets  16 S may comprise pre-printed monthly statements for a credit card company or financial institution. Typically, the statements include one or more pre-printed sheets, i.e., a transmittal page, one or more pages of the transaction activity, and a presentment page for return payment by a customer. Inasmuch as the pre-printed stack  16 S typically includes several pages for the creation of each mailpiece, the stack  16 S must be singulated and collated for insertion into a mailpiece envelope (also not shown). 
     A processor or controller  20  (see  FIG. 2 ) is operative to receive inputs from various sensors and/or data files for controlling the requisite operations to process the sheet material  16 . While the processor  20  receives input from a variety of modules to create a mailpiece, it should be appreciated that the present invention will describe only those inputs relevant to the feed input and sheet accumulation modules  12 ,  14 . 
     Feed Input/Singulating Module 
     In  FIGS. 1-2   c , the feed input/singulation module  12  includes a singulating assembly  22  disposed along the feed path operative to strip a single sheet of content material from the shingled stack  16 S. The singulating assembly  22  includes a separating guide  24 , a stationary roller/finger  26  and a vacuum roller assembly  30 . The separating guide  24  retards the motion of the upper sheets of the stack  16 S as the lowermost sheets are conveyed/drawn toward the vacuum roller assembly  30 . The stationary roller/finger  26  is disposed immediately downstream of the guide  24  and cooperates with the vacuum roller assembly  30  to strip/singulate the lowermost sheet  16 LM. 
     In the described embodiment, and referring to  FIGS. 2   a  and  2   b , the vacuum roller assembly  30  includes an inner plenum  32  which is held stationary by a hollow central shaft  34  and an outer vacuum roller  36  which rotates relative to the inner plenum  32  in the direction of arrow RR by a drive element (not shown). 
     The stationary inner plenum  32  defines a longitudinal plenum slot  38  (see  FIG. 2   b ) which is in fluid communication with a vacuum pump  40  operative to draw air from the slot  38 . In the described embodiment, the longitudinal plenum slot  38  defines an elongate opening which is substantially perpendicular to the feed path of the shingled sheet material  16 S and is disposed upwardly, i.e., toward the underside of lowermost sheet  16 LM. 
     The outer vacuum roller  36  is disposed over the inner plenum  32  and includes a plurality of apertures  44  which are in fluid communication with the plenum slot  38  for the purpose of producing a negative pressure differential, i.e., a singulating vacuum, along the surface of the roller assembly  30 . More specifically, the apertures  44  are arranged in three distinct regions of the vacuum roller  30  to facilitate the directed passage of air while maintaining low audible noise levels for operator comfort. 
     In the described embodiment, the rotating vacuum roller  36  includes a central region  44   a  having circular-shaped apertures  44 O and outboard regions  44   b ,  44   c  having substantially slot-shaped apertures  44 S to either side of the central region  44   a . With respect to the central region  44   a , the circular apertures  44 O are aligned in a plurality of cross-sectional planes which are orthogonal to the rotational axis RA of the vacuum roller  36 . Furthermore, the apertures  44 O within each plane are staggered, or rotated several degrees in a helical pattern about the axis RA. Furthermore, the central region  44   a  defines a concave surface  46   a  about the circumference of the vacuum roller  36  to facilitate singulation of sheet material  16 S. The import of these geometric features will be described in greater detail when discussing the operation of the vacuum roller assembly  30 . 
     With respect to the outboard regions  44   b ,  44   c , the slot-shaped apertures  44 S are similarly aligned, i.e., the geometric center GC of each are aligned relative to an orthogonal plane, however, the orientation of each slot-shaped aperture is off-axis relative to the rotational axis RA of the vacuum roller  36 . In the context used herein, “aligned” means that the locus of points defined by the geometric center GC of each aperture  44 O lies within a plane orthogonal to the rotational axis RA. Furthermore, in the context used herein, “off-axis” means that the elongate or major axis of each aperture  44 S defines an acute angle θ relative to the rotational axis RA. Finally, the external surface or periphery of the vacuum roller  36  in each of the outboard regions  44   b ,  44   c  is substantially cylindrical to facilitate initial separation of the lowermost sheet  16 LM from the stack  16 S of sheet material. The import of these geometric features will be also discussed when describing the operation of the vacuum roller assembly  30 . 
     The geometry of the vacuum roller  36  may be best understood by referring to a two-dimensional flat pattern perspective thereof depicted in  FIG. 2   c . Therein, the apertures  44 O define a plurality of vertical columns C and helical rows R. The vertical columns correspond to each of the orthogonal planes OP while each row extends along the length of the roller in a helical pattern. Therein, six (6) columns are defined which are “staggered” or “off-set” such that a row R slopes downwardly at an acute angle β relative to the rotational axis RA. Furthermore, each of the apertures  44 S associated with the outboard regions  44   b ,  44   c , defines a major axis MA which is off-axis with respect to the rotational axis RA of the vacuum roller  36 . The slope of an aperture  44 S associated with one of the outboard regions  44   b  is negative (i.e., slopes downwardly from an outboard edge of the roller to the central region  44   a ) while the slope associated with the other of the outboard regions  44   c  is positive (i.e., slopes upwardly to an outboard edge of the roller from the central region  44   a ). In the preferred description, the major axis MA of each aperture  44 S defines an angle θ between about five (5) to ten (10) degrees relative to the rotational axis RA. 
     As mentioned earlier, the geometry and arrangement of apertures  44  of the vacuum roller  36  serves to reliably singulate sheet material  16 S while reducing audible noise levels produced by the flow of air when drawing a pressure differential/vacuum across the sheets  16 S. These features are best understood by discussing the operation of the vacuum roller assembly  30 . 
     Operationally, the outer vacuum roller  36  rotates over the inner plenum  32  such that the apertures  44 O,  44 S rotate over the elongate slot  38 . As the sheet material  16 S is fed to the vacuum roller assembly  30 , a negative pressure differential develops along the surface of the vacuum roller  36 . More specifically, a pressure differential is first developed in the outboard regions  44   b ,  44   c  to draw the lowermost sheet  16 LM from the shingled stack  16 S. Inasmuch as the cylindrical external surface of the outboard regions  44   b ,  44   c  compliments the planar contour of the sheet material  16 S, the outboard regions  44   b ,  44   c  and the slot-shaped apertures  44 S, are principally responsible for drawing the lowermost sheets  16 LM from the stack  16 S. Inasmuch as frictional forces are developed between the sheets  16 , the upper sheets  16 U follow the lowermost sheet  16 LM, but are shingled when engaging the separating guide  24 . 
     As the sheets  16 LM is singulated/drawn from the stack  16 S, the stationary roller/finger  26  guides the lowermost sheet  16 LM into the concave curvature  46  of the central region  44   a . More specifically, the stationary roller/finger  26  includes a convex guide surface  26   a  which opposes and compliments the concave surface  46   a  of the vacuum roller  36 . As the sheet  16 LM follows the contour of the convex guide surface  26   a , additional vacuum pressure is applied across the sheet  16 LM, in the area immediately opposing the concave surface  46   a  of the roller  36 . As the lowermost sheet  16 LM is drawn into the concave surface  46   a  of vacuum roller  36 , it is also drawn away from a sheet  16 U immediately adjacent to and above the lowermost sheet. Accordingly, frictional forces developed between the lowermost and upper sheets  16 LM,  16 U are reduced in this region, i.e., in the region immediately above the concave surface  46   a . Inasmuch as the friction forces are reduced while the vacuum forces are increased, the lowermost sheet is reliably singulated from the stack  16 S. It will be appreciated, therefore, that the vacuum roller  36  of the present reliably singulates the lowermost sheet  16 LM without a “miss-feed”, i.e., without feeding a sheet from the stack  16 S, or “double-feeds”, i.e., two or more sheets being fed from the stack. 
     In addition to enhanced reliability, audible noise levels are reduced by the angular orientation of the slot-shaped apertures  44 S. More specifically, the inventors of the present invention discovered that a conventional arrangement of large apertures, i.e., three uniformly-spaced openings along the length of the vacuum roller assembly, produced audible noise levels which were highly uncomfortable to an operator. Upon further study and examination, it was determined that elongate openings provided a degree of relief, however, the level of audible noise continued to be problematic. Finally, it was discovered that the noise levels could be reduced by orienting the apertures  44 O,  44 S such that airflow was not abruptly ingested by the longitudinal slot  38  of the inner plenum  32 . To achieve this effect, the apertures  44 O in the central region  44   a  are staggered or off-set such that, at any time, a full compliment cannot flow through all of the apertures  44 O at the same time. That is, the apertures  44 O are arranged in a helical pattern, i.e., slope downwardly or upwardly, at an acute angle β relative to the rotational axis RA. Similarly, the slot-shaped apertures  44 S associated with the outboard regions  44   b ,  44   c  are disposed at an acute angle (i.e., cut across the longitudinal slot  38  of the inner plenum) such that a full compliment of air cannot flow through any one slot-shaped aperture  44 S. It was also discovered that the acute angle must within a relatively narrow range, i.e., less than ten (10) degrees, to prevent the loss of air or suction and greater than five (5) degrees to mitigate noise levels. 
     As sheets are singulated by the feed module  12 , they are conveyed in series along a conveyance path FP and dispensed downstream toward the accumulator module  14 . In the described embodiment, a sheet feed sensor  48  is disposed downstream of the singulating assembly  22  to sense whether each sheet has been successfully singulated and fed by the feed module  12 . More specifically, the sheet feed sensor  48  senses the leading edge of each sheet and provides a signal to the processor  20  for determining whether a miss-feed has occurred. In the event of a miss-feed, the processor  20  may discontinues sheet feed operations or provide a cue to an operator. 
     Accumulator Module 
     In  FIGS. 1 ,  2  and  3 , the accumulator module  14  is disposed downstream of the sheet feed module  12  and is operative to (i) receive pre-printed singulated sheets  16 , (ii) stack the sheets into a collation, and (iii) dispense a completed collation to a downstream module for insertion into a mailpiece envelope. Consequently, while the feed module  12  singulates sheets  16  from a shingled stack of sheets  16 S, the accumulator  14  re-stacks the sheets into collations, each associated with a particular mail recipient. 
     Information concerning processing of the singulated sheets  16  may be obtained by one or more optical scanners  50  operative to read scan codes/symbols disposed on the singulated sheets (generally within the margins thereof), directly from the mail run data file MRDF, or from other upstream or downstream modules IM of the mailpiece inserter  10 . Additionally, optical position detectors  48 ,  52 ,  54 ,  56  may be employed to determine the instantaneous location of a sheet  16  as the leading or trailing edge of a sheet passes one of the detectors  48 ,  52 ,  54 ,  56 , Furthermore, it should be appreciated that a number of rotary encoders (not shown) are disposed on at least one shaft of each of the conveyance rollers, (e.g., the drive shaft  60  of the vacuum roller assembly  30 , the drive shaft  60  of the feed motor FM which drives the exit rollers  64 ,  66  of the feed module  12 , etc.). This information is fed to the processor  20  such that, inter alia, the location of each sheet  16  along the feed path FP can be determined at nearly any point along the conveyance feed path FP. 
     With respect to the accumulator module  14 , an important source of information is the Beginning- or End-Of-Collation symbol or mark N n  disposed on select sheets, i.e., a next collation sheet  16 NC (see  FIGS. 1 and 3 ), in the series being fed to the accumulator module  14 . A Beginning-Of-Collation (BOC) mark denotes which sheet in the series of consecutive sheets is the “first sheet of the next collation”. An End-Of-Collation (EOC) mark denotes which sheet in the series of consecutive sheets is the “last sheet of the current collation”. Notwithstanding how the BOC/EOC marks N n  are arranged in the stack of sheets for particular mail run job, a scanner  50 , upstream of the accumulator module  14  reads the marks N n  on select sheets  16  to determine which sheets are associated with a current collation and which sheets are associated with a next collation. 
     In one operating mode, a BOC/EOC mark N n LE is located proximal to the leading edge of the next collation sheet  16 NC, and in a second operating mode, a BOC/EOC symbol N n TE is located proximal to the trailing edge of the next collation sheet  16 NC. The general position of the BOC/EOC mark, i.e., near the leading or trailing edges, may be input by an operator assist processing of the mark. Alternatively, the optical sensors  52 ,  54 ,  56  may be used in conjunction with the rotary encoders of the conveyance system, to locate the mark N n LE, N n TE on each of the select sheets  16 . 
     In the described embodiment, the scanner  50  searches for the location of, the mark N n LE, N n TE from signals acquired by the leading edge sensor  48 , upstream of the scanner  50 . The scanner  50  issues a next collation signal NCS to the processor  20  to determine which sheet, in a series of consecutively fed sheets, is the first sheet of the next collation, or the last sheet of the current collation. 
     In the broadest sense of the invention and referring to  FIGS. 2 ,  3 , and  4  the accumulator  14  according to the present invention includes: (i) a first conveyance C 1  for receiving singulated sheets  16  and conveying the sheets  16  to an accumulator station AS to produce completed collations CC (shown in phantom lines in  FIG. 4 ), (ii) a second conveyance C 2  for receiving completed collations from the first conveyance C 1 , in a first operating mode, and dispensing the completed collations from the accumulator station AS, (iii) an auxiliary conveyance AC operative to convey completed collations CC to the second conveyance C 2 , in a second operating mode, when the first conveyance C 1  is inoperative, and (iv) a processor  20 , responsive to the next collation signal NCS ( FIGS. 3 and 4 ) to operate the conveyances C 1 , C 2 , and AC, based upon a selected one of the operating modes. 
     More specifically, the processor  20  controls the conveyances C 1 , C 2 , AC such that in the second operating mode, the first conveyance C 1  feeds a first sheet of the next collation into a buffer region BR of the accumulator  14 , and, the auxiliary conveyance AC feeds the completed collation CC to the second conveyance C 2  while the first conveyance C 1  is deactivated to hold the first sheet of the next collation in the buffer region BR. As will be discussed in greater detail hereinafter, the buffering of the first sheet of the next collation, minimizes the conveyance feed path between the accumulator and an upstream module of the sheet handling system to reduce the overall size envelope of the accumulator  14 . 
     In  FIGS. 3 and 4 , the first conveyance C 1  is adapted to accept the singulated sheets  16  from the feed module  12  and convey the sheets  16  along a feed path FP to the accumulator station AS of the accumulator  14 . The first conveyance C 1  includes upper and lower transport elements and a means for driving the transport elements along the feed path FP. More specifically, the upper and lower transport elements include a series of continuous O-ring members  70 ,  72  (best seen in  FIG. 3 ) disposed around upper and lower pulley rollers  74 R,  76 R. The O-ring members  70 ,  72  of the upper and lower transport elements capture the sheet material therebetween and frictionally-engage a face surface of the sheet material  16  to transport the sheet material along the feed path. The upper transport element is defined by three (3) upper O-ring elements  70  disposed about the upper pulley rollers  74 R and the lower transport is defined by two (2) lower O-ring elements  72  disposed about the lower rollers  76 R. Furthermore, the upper pulley rollers  74 R are supported by, and rotate with, suspension shafts  74 S which are disposed across the accumulator  14 . Similarly, the lower pulley rollers  76 R are supported by, and rotate with, suspension shafts  76 S. Each of the suspension shafts  74 S,  76 S are rotatably mounted within and supported by side wall structures  14 SW of the accumulator  14 . 
     The mechanism for driving the transport elements includes a motor M 1 , a drive belt  78  for rotationally coupling the motor M 1  to a first of the drive/suspension shafts, e.g., the lower suspension shaft  76 S, and a gear drive mechanism (not shown) rotationally coupling a second of the drive shafts, e.g., the upper suspension shaft  74 S, to the first suspension/drive shaft  76 S. With respect to the latter, the gear drive mechanism drives the shafts  74 S,  76 S at the same speed and in opposite directions such that the O-ring elements  70 ,  72  are driven from an upstream to a downstream location along the conveyance feed path FP. 
     Accordingly, sheets are accepted between the upper and lower transport elements, i.e., between the O-ring elements  70 ,  72  and are conveyed to the accumulator station AS (described in greater detail in subsequent paragraphs) along the feed path FP. The operation of the first conveyance C 1  is discussed in greater detail below when discussing the operation of the accumulator and method for minimizing the conveyance feed path of a mailpiece inserter. 
     The second conveyance C 2  is adapted to accept a completed collation CC from the accumulator station AS and dispense a completed collation CC (see  FIG. 4 ) from the accumulator station AS to a downstream module of the mailpiece inserter. Specifically, the second conveyance C 2  includes at least one pair of nip rollers  84 R,  86 R defining a nip RN i.e., a region between the cylindrical surfaces of the rollers  84 R,  86 R, which accepts a leading edge of a completed collation CC. It should be appreciated that a threshold horizontal force F (see  FIG. 4 ) must be applied to develop sufficient friction between the sheets  16 , and/or the sheets  16  and rollers  84 R,  86 R, to cause the completed collation CC to be driven downstream by the second conveyance C 2 . 
     Each of the rollers  84 R,  86 R of the second conveyance C 2  are rotationally coupled by a drive shaft  86 S to a drive motor M 2 . In the described embodiment, the motor M 2  is rotationally coupled to the drive shaft  86 S by a drive belt  88 . Furthermore, the nip rollers  84 R,  86 R of the second conveyance C 2  are co-axially aligned with the rotational axis of the downstream pulley rollers  74 R,  76 R of the first conveyance C 1 , however, the nip rollers  84 R,  86 R may be independently, and differentially, driven relative to the pulley rollers  74 R,  76 R. For example, the downstream pulley rollers  74 R,  76 R may rotate while the nip rollers  84 R,  86 R are motionless. Conversely, the nip rollers  84 R,  86 R of the second conveyance C 2  may be driven while the pulley rollers  74 R,  76 R of the first conveyance C 1  are stopped. Additionally, or alternatively, the nip rollers  84 R,  86 R of the second conveyance C 2  may be driven at a higher/lower rotational speed than the pulley rollers  74 R,  76 R of the first conveyance C 1 . With respect to the latter, the first and second conveyances C 1 , C 2  may be operated at different speeds to match the throughput of other modules of the sheet handling system. 
     In the described embodiment, the accumulator station AS is integrated with the first and second conveyances C 1 , C 2 , however, it should be appreciated that the accumulator station AS may be an independent module, i.e., may not share components of the conveyances C 1 , C 2 . In the broadest sense of the invention, the accumulator station AS includes a means for stacking a select group of sheets, e.g., a group intended for subsequent insertion into a mailpiece envelope, to produce a collation. In the described embodiment, the accumulator station AS includes (i) a means for changing the plane of one sheet  16  relative to another sheet  16  such that the sheets may be stacked vertically, i.e., one atop the other, (ii) a support deck for collecting the vertically stacked sheets, i.e., sheets which comprise the same collation, and (iii) a device for momentarily retarding the motion of select sheets to produce a completed collation. 
     In the described embodiment, the means for changing the plane of a sheet  16  is effected by creating a vertical step  80  in the lower transport element  72  of the first conveyance C 1 . More specifically, the vertical step  80  is produced by changing the path of the lower O-ring members  72  around several guide rollers  80   a ,  80   b ,  80   c . This same arrangement, i.e., of O-ring members  72  and guide rollers  80   a ,  80   b ,  80   c , also facilitates the creation of the deck for supporting the completed collation CC. More specifically, the deck is defined by a combination of the lower O-ring members  72  and a pair of guide elements  82 . The guide elements  82  are disposed on each side of the O-ring members and in combination with the sidewalls  14 SW of the accumulator  14 . The O-ring members  72  provide support for a center portion of a completed collation CC while the side guides elements  82  support/guide the lateral edges of a collation CC. 
     In the described embodiment, the means for changing the plane of a sheet  16  is assisted by a plurality of ramps members  83  having ramp surfaces  83 R disposed on each side of an O-ring element  72 . The illustrated embodiment depicts ten (10) ramp members  83  which are laterally aligned across the width of the accumulator  14 . 
     To accumulate sheet material, the accumulator  14  retards the motion of each sheet  16  in the accumulator station AS. Apparatus to perform this function may include any of one of a variety of know mechanisms to retain a sheet at a select location along a feed path FP. For example, a simple rotating finger, or group of fingers, may extend vertically upward into the feed path to retard the motion of one sheet while a subsequent sheet is stacked over the current sheet. In the described embodiment, this function is, however, integrated with the nip rollers  84 R,  86 R of the second conveyance C 2 . More specifically, selected sheets  16  are retained in the accumulator station AS by fixing the rotational position of the nip rollers  84 R,  86 R as the first conveyance C 1  drives additional sheets  16  into the accumulator station AS. The need to lock the rotational position of the nip rollers  84 R,  86 R is particularly evident inasmuch as the nip rollers  86 R of the second conveyance C 2  share the same rotational axis as the pulley rollers  76 R of the first conveyance C 1 , (albeit the shafts are rotationally independent from each other). 
     The auxiliary conveyance AC is adapted to convey a completed collation CC to the second conveyance C 2  by engaging and disengaging the collation based upon the selected operating mode. The auxiliary conveyance AC includes at least one upper idler roller  94 R adapted to engage and disengage an uppermost sheet  16 UM (see  FIG. 4 ) of the completed collation CC and at least one lower drive roller  96 R adapted to drive a lowermost sheet  16 LM (see  FIG. 4 ) of the completed collation CC toward the second conveyance C 2 . The upper idler roller  94 R is rotationally mounted to a pivot arm  92  disposed on the upper side of the completed collation CC and is mounted to a rotary actuator A 1 . In the described embodiment, a pair of idler rollers  94 R mount to respective pivot arms  92  which, in turn, mount to a pivot shaft  90  supported by the sidewall structure  14 SW of the accumulator  14 . The rotary actuator A 1  is connected to the shaft  90  such that each of the idler rollers  94 R pivots into an out of engagement with the completed collation about a pivot axis PA (see  FIG. 4 ) 
     In the described embodiment, a pair of lower drive rollers  96 R mount to a shaft  96 S which rotationally mounts to the sidewall structure  14 SW of the accumulator  14 . Furthermore, each of the drive rollers  96 R is aligned with an upper idler roller  94 R such that, when engaged, an auxiliary drive nip AN is created therebetween. Moreover, the same motor M 2  and drive belt  88  used to drive the lower nip roller  86 R of the second conveyance C 2 . That is, the mechanisms for driving the lower drive roller  96 R of the auxiliary conveyance AC and the lower nip roller  86 R of the second conveyance C 2  are integrated, or common to both conveyances AC, C 2 , to reduce the number of component parts and the cost associated therewith. While these drive mechanisms are integrated, it should be appreciated that each roller  86 R,  96 R may be driven independently, i.e., by separate drive motors and belts. The operation of the auxiliary conveyance AC, is discussed in greater detail in the subsequent paragraphs when discussing the operation of the accumulator. 
     System and Method for Operating a Sheet Handling System to Minimize the Conveyance Feed Path Thereof 
     The following describes the operation of the accumulator  14  and the method for controlling the sheet handling system, i.e., the mailpiece inserter  10 , for minimizing the overall conveyance path required to process sheet material, i.e., prepare the sheet material for insertion into a mailpiece envelope. 
     Returning briefly to  FIGS. 1 ,  3  and  4 , a shingled stack of pre-printed sheet material  16  is fed into the feed module  12  of the mailpiece inserter  10 . The pre-printed sheets  16  can have a BOC/EOC mark N n , i.e., a mark N n LE proximal to a leading edge or a mark N n TE proximal to a trailing edge of the next collation sheet  16 NC, i.e., the sheet representing the first sheet of the next collation or the last sheet of a current collation CC. Upon being singulated by the feed module  12 , each sheet is fed serially along the feed path FP across a scan field SF of the scanner  50 . It should be appreciated that the scan field SF may be projected from above or below the sheet material  16  depending upon the location of the BOC/EOC mark N n . 
       FIGS. 5   a  though  5   e  illustrate the operation of the sheet handling system in a first operating mode, wherein a BOC/EOC mark N n LE has been printed proximal to the leading edge of selected sheets  16 . It should be appreciated that the sheet handling system of the present invention is adapted to process sheet material irrespective the location of the BOC/EOC mark N n  while, at the same time, minimizing the length of the conveyance path, i.e., the distance between modules  12 ,  14 . Each of the  FIGS. 5   a  through  5   e  depicts a snapshot in time, i.e., as the sheets of the collation are accumulated and/or dispensed from the accumulator  14 . 
     The operation of the sheet handling system described in  FIGS. 5   a - 6   g  identify changes in state, however, it should be appreciated that the various sensors and processor operate continuously. Furthermore, it should be understood that when a signal is not issued or identified, it should be assumed that the processor  20 , or components controlled by the processor, i.e., the first, second and auxiliary conveyances C 1 , C 2  and AC continue to operate in their previously identified state. Moreover, changes in the state of operation from an active to inactive state may also be synonymous with the absence, or lack of a signal. In view of the foregoing, it may be assumed that each of the conveyances C 1 , C 2  and AC is inoperative in the absence of a control signal. 
     In  FIG. 5   a , the scanner  50  detects a first Beginning of Collation/End of Collation mark, N 1 LE on a first sheet  16 NC of a current collation. The BOC/EOC mark N 1 LE has been printed proximal to the leading edge of the first sheet  16 NC. Upon receipt of a next collation signal NCS, the processor  20  issues a first conveyance drive signal FDCS to the motor M 1  to drive the pulley rollers  74 R,  76 R and O-ring elements  70 ,  72  of the of the first conveyance C 1 . Accordingly, the first sheet  16 NC is accepted by the first conveyance C 1  of the accumulator  14 , i.e., between the O-ring members  70 ,  72  of the upper and lower transport elements, for transfer to the accumulator station AS. 
     In  FIG. 5   b , the sheets are conveyed by the first conveyance C 1  to the accumulator station AS. The leading edge of each sheet  16  is guided upwardly over the ramped surfaces  83 R of the ramp elements  83  and allowed to accumulate on the support surface of the accumulator station. As mentioned earlier, the support surface is defined by the O-ring elements  72  of the lower transport element, i.e., the portion downstream of the vertical step  80 , in combination with the side guides  82  of the accumulator  14 . Upon reaching the accumulator station AS, the motion of each sheet  16  is halted by the nip rollers  84 R,  86 R of the second conveyance C 2  which is inoperative while the sheets  16  are accumulated. That is, the nip spacing of the rollers  84 R,  86 R is sufficiently close to prevent any of the sheets  16  from passing downstream thereof. As the sheets are accumulated, a second Beginning of Collation/End of Collation mark, N 2 LE is detected by the scanner  50  on a next collation sheet  16 NC. Upon receipt of a next collation signal NCS, the processor  20  tracks the location of the last sheet  16 LS of the current collation, i.e., immediately downstream of the next collation sheet  16 NC, by the first position sensor  52 . 
     In  FIG. 5   c , the first conveyance C 1  continues to drive sheet material  16  to the accumulator station AS, and urge sheet material to the second conveyance C 2 , i.e., into the nip RN of the second conveyance nip rollers  84 R,  86 R. Furthermore, the processor  20  determines when the last sheet  16 LS of the current collation has passed a first threshold location L 1  along the conveyance feed path indicative of a completed collation CC. More specifically, the first position sensor  52  issues a completed collation signal FPS to the processor  20  when the trailing edge of the last sheet  16 LS has been accumulated. 
     In  FIG. 5   d , the first conveyance C 1  urges a completed collation CC to the second conveyance C 2 . Furthermore, in response to the first position signal FPS, the processor  20  initiates a second conveyance drive signal SDS to the motor M 2  of the second conveyance C 2 . As a consequence, both the first and second conveyances C 1 , C 2  are driven to dispense the completed collation CC from the accumulator station AS. Additionally, the first sheet  16 NC of the next collation is driven downstream toward the accumulator station AS such that a pitch distance PD is maintained between the trailing edge of the completed collation CC and the leading edge of the first sheet  16 NC. 
     In  FIG. 5   e , the completed collation CC is dispensed from the accumulator station AS to a downstream module. More specifically, the processor  20  determines when the completed collation CC has passed a second threshold location L 2  along the conveyance feed path indicative that an accumulation cycle has been completed. More specifically, the second position sensor  54  issues a cycle completed signal CCS to the processor  20  when the collation passes the second threshold location, downstream of the accumulator station AS. 
       FIGS. 6   a  though  6   g  illustrate the operation of the sheet handling system, in a second operating mode, wherein a BOC/EOC mark has been printed proximal to the trailing edge of selected sheets  16 . Each of the  FIGS. 6   a  through  6   g  depicts a snapshot in time, i.e., as the sheets of the collation are accumulated, buffered in and/or dispensed from the accumulator  14 . 
     In  FIG. 6   a , the scanner  50  detects a first Beginning of Collation/End of Collation mark, N 1 TE on a first sheet  16 NC of a current collation. The BOC/EOC mark N 1 TE has been printed proximal to the trailing edge of the first sheet  16 NC. Upon receipt of a next collation signal NCS, the processor  20  issues a first conveyance drive signal FDCS to the motor M 1  to drive the pulley rollers  74 R,  76 R and O-ring elements  70 ,  72  of the of the first conveyance C 1 . Accordingly, the first sheet  16 NC is accepted by the first conveyance C 1  of the accumulator  14 , i.e., between the O-ring members  70 ,  72  of the upper and lower transport elements, for transfer to the accumulator station AS. 
     In  FIG. 6   b , the sheets  16  are conveyed by the first conveyance C 1  to the accumulator station AS. The leading edge of each sheet  16  is guided upwardly over the ramped surfaces  83 R of the ramp elements  83  and allowed to accumulate on the support surface of the accumulator station AS. As mentioned earlier, the support surface is defined by the O-ring elements  72  of the lower transport element, i.e., the portion downstream of the vertical step  80 , in combination with the side guides  82  of the accumulator  14 . Upon reaching the accumulator station AS, the motion of each sheet  16  is halted by the nip rollers  84 R,  86 R of the second conveyance C 2  which is inoperative while the sheets  16  are accumulated. That is, the nip spacing of the rollers  84 R,  86 R is sufficiently close to prevent any of the sheets  16  from passing downstream thereof. As the sheets are accumulated, a second Beginning of Collation/End of Collation mark, N 2 TE is detected by the scanner  50  on a next collation sheet  16 NC. Upon receipt of a next collation signal NCS, the processor  20  immediately identifies the location of the last sheet  16 LS of the current collation, i.e., immediately downstream of the next collation sheet  16 NC, by the first position sensor  52 . In  FIG. 6   b , the last sheet  16 LS of the current collation has already entered into the accumulator station AS inasmuch as the accumulator  14  has already accepted a portion of the next collation sheet  16 NC. As a consequence, the trailing edge of the sheet  16 LS has past the first threshold location L 1  and a first position signal FPS has been issued by the first position sensor  52 . 
     In  FIG. 6   c , the processor  20  continues to drive the motor M 1  of the first conveyance C 1 , i.e., issues the first conveyance drive signal FCDS, until the next collation sheet  16 NC has entered the buffer region BR of the accumulator  14 . In the described embodiment, the buffer region BR may be broadly defined as a region of the conveyance feed path FP upstream of the auxiliary conveyance AC, indicated by the arrow BR. More specifically, the buffer region BR is a region wherein the next collation sheet  16 NC is momentarily paused/stopped such that is its leading edge is upstream of the auxiliary conveyance rollers  94 R,  96 R and, accordingly, cannot be driven by the auxiliary conveyance until the current collation has be dispensed from the accumulator station AS. At the instant depicted in  FIG. 6   c , the processor  20  drives the first conveyance C 1  such that at least a portion of the next collation sheet  16 NC, i.e., the first sheet of the next collation, overlaps a portion OLR of the last sheet  16 LS of the current collation CC. Moreover, the first conveyance C 1  continues to drive until the next collation sheet  16 NC has passed a third threshold location L 3 . In the described embodiment, the processor  20  is responsive to a third or buffer condition position signal BCS issued by the third position sensor  56  which indicates that the trailing edge of the next collation sheet  16 NC has passed the third threshold location L 3  along the conveyance feed path. 
     Stated in yet other terms, the first conveyance C 1  continues to drive the first sheet of the next collation to effect a change in the spatial relationship between the first sheet of the next collation  16 NC and the last sheet of the current collation  16 LS next collation sheet. In the context used herein, the “change in spatial relationship” means that the first sheet of the next collation  16 NC moves closer to the last sheet of the current collation. Additionally, the change in spatial relationship may result in a portion of the next collation sheet  16 NC overlapping a portion of the last sheet of the current collation  16 LS. 
     To better understand the potential length or breadth of the buffer region BR,  FIG. 6   d  illustrates the degree of variation that may be anticipated or contemplated with respect to the buffer region BR. Therein, the first conveyance C 1  is driven further downstream of the third threshold location L 3 . In this embodiment, the leading edge of the next collation sheet  16 NC overlaps a greater portion OLR of the last sheet  16 LS of the current collation CC. Hence, in this embodiment, the buffer condition signal BCS may be view as an indication that the next collation sheet  16 NC has passed the third location L 3  along the conveyance feed path FP, and reached a desired buffer station within the buffer region BR. The need to drive the next collation sheet  16 NC further into the buffer region may be is embodiment may arise when larger sheets  16  are handled, i.e., seventeen inch (17″) vs. eleven inch (11″), and the accumulator station AS is commensurately large to handle larger sheets. 
     In each of the embodiments illustrated in  FIGS. 6   c  and  6   d , the processor  20  is responsive to the buffer condition signal BCS signal TPS, and issues a first conveyance stop signal FCSS to the first conveyance C 1 , or changes the state of the drive signal FCDS, to momentarily stop the first conveyance C 1 . Whereas, in the first operating mode, the first conveyance C 1  urges the completed collation CC into the second conveyance C 2 , in the second mode, the auxiliary conveyance AC is activated to feed the completed collation CC into the second conveyance C 2 . 
     In  FIG. 6   e , the processor  20  is responsive to the buffer condition signal BCS, to inactive the first conveyance, actuate the rotary actuator A 1  of the auxiliary conveyance AC, and activate the second conveyance C 2 . More specifically, the processor  20  issues first conveyance stop signal FCSS to discontinue/stop the motor M 1  of the first conveyance C 1 . Furthermore, the processor  20  issues an auxiliary conveyance engage signal ACES to the rotary actuator A 1  to rotate the arm  92  and idler roller  94 R of the auxiliary conveyance AC from an inactive/disengaged position (shown in dashed lines) to an active or engaged position (shown in solid lines). As a result, the rotary actuator A 1  produces a normal force between the idler and drive rollers  94 R,  96 R to increase the friction forces between the rollers  94 R,  96 R and/or between the sheets  16  of the completed collation CC. 
     In  FIG. 6   f , the processor  20  is also responsive to the buffer condition signal BCS and issues a second conveyance drive signal SCDS to the motor M 2  of the second conveyance C 2 . Inasmuch as the drive belt  88  circumscribes and drives the shafts  86 S and  96 S of the second and auxiliary conveyances, C 2 , AC, respectively, the auxiliary drive roller  96 R is also driven to urge the completed collation into the second conveyance C 2 . Consequently, in the second operating mode, while the first conveyance C 1  is momentarily inactive, the auxiliary conveyance AC functions in the same capacity as the first conveyance C 1 , i.e., to urge a completed conveyance into the nip rollers  94 R,  96 R of the second conveyance C 2 . Stated in yet other terms, in the second operating mode, the next collation sheet  16 NC is captured by, and between the O-ring members  70 ,  72  of the first conveyance C 1  while the complete collation CC is dispensed, or moved away, from the next collation sheet  16 NC by the nip rollers  84 R,  86 R of the second conveyance C 2 . That is, the trailing edge portion of the next collation sheet  16 NC is retained while the leading edge portion of the completed collation CC is conveyed by the auxiliary conveyance AC in combination with the secondary conveyance C 2 . 
     In  FIG. 6   g , the completed collation CC is dispensed from the accumulator station AS to a downstream module. More specifically, the processor  20  determines when the completed collation CC has passed the second threshold location L 2  along the conveyance feed path FP. When the complete collation CC passes the sensed location L 2 , the second position sensor  54  issues a cycle completed signal CCS to the processor  20 . In response thereto, the processor  20  disengages/disables the auxiliary and second conveyances AC, C 2  and activates the first conveyance C 1 . More specifically, the processor  20 : (i) issues a second conveyance stop signal SCSS to the motor M 2  of the second conveyance C 2  (which disables the drive to the drive roller  96 R of the auxiliary conveyance AC, (ii) issues a disengage signal ACDS to the actuator A 1  of the auxiliary conveyance AC (rotating the arm  92  and idler roller  94 R in a counterclockwise direction away from the support deck of the accumulator station AS), and (iii) issues a first conveyance drive signal FCDS to the motor M 1  of the first conveyance C 1 . By disabling the motor M 2  of the second conveyance C 2 , the rollers  84 R,  86 R are stopped to retard the motion of the next collation sheet  16 NC, thereby initiating another accumulation cycle. 
     As mentioned previously, the timing and coordination of various actions impacts the throughput of the feed input and accumulator modules  12 ,  14  and, consequently, the overall operation mailpiece inserter  10 . While information from each of the position sensors  48 ,  52 ,  54 ,  56  can be used exclusively to operate/coordinate the modules  12 ,  14 , in the described embodiment rotary encoders are used in combination with the sensors  48 ,  52 ,  54 ,  56 , i.e., (disposed on at least one shaft rotational axis of each conveyance C 1 , C 2 , AC) to obtain additional, more accurate, sheet location information. Accordingly, the processor  20  uses both position sensors and rotary encoders to track the position of each sheet  16  and each collation CC. 
     The accumulator  14  is controlled to maximize throughput of the mailpiece inserter. In one embodiment of the invention, an operator provides the processor  20  information regarding the location of the BOC/EOC mark N n , i.e., proximal to the leading or trailing edges. Based upon this information, the accumulator  14  operates in one of the first or second operating modes to accumulate the sheets  16  of a particular mail run job. Alternatively, information regarding the location of the BOC/EOC mark N n  may be obtained from the mail run data file MRDF, i.e., an electronic file having information regarding the processing requirements of a job. 
     The sheet handling system of the present invention is also adapted to maximize throughput by the independent control of the first and second conveyances C 1 , C 2 . For example, the accumulator module  14  may obtain data input from a downstream module, e.g., the chassis module (not shown), to timely dispense a completed collation or change the pitch distance PD, i.e., the spacing between the trailing edge of the sheets or between the trailing edge of a completed collation and a next collation sheet  16 NC. 
     In summary, the sheet handling system of the present invention is adapted to minimize the conveyance feed path thereof while maximizing throughput. The conveyance feed path is reduced by a buffer region adapted to accept at least a portion of a next collation sheet, i.e., within the accumulator. More specifically, the accumulator provides a buffer region, disposed internally of the accumulator, and control algorithms for moving sheets into and out of the buffer region, to accept and overlap a portion of a sheet from an upstream module, e.g., a feed module, with the sheets of a downstream module, e.g., an accumulator module. Furthermore, the invention provides a single deck accumulator module which provides throughput levels commensurate with dual deck accumulators while maintaining a similar foot-print, i.e., without increasing the space requirements between the accumulator and an upstream module. 
     It is to 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, and which is susceptible to such changes as may be obvious to one skilled in the art. 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.