Patent Publication Number: US-8987626-B2

Title: Anti-abrasion assembly for mailpiece stacking assembly

Description:
TECHNICAL FIELD 
     This invention relates to a apparatus for sorting sheet material and more particularly to a stacking assembly for a sortation module which reliably diverts and stack mailpieces without damage to/jamming of mailpieces as they enter and accumulate in a sortation bin. 
     BACKGROUND ART 
     Automated equipment is typically employed in industry to process, print and sort sheet material for use in manufacture, fabrication and mailstream operations. One such device to which the present invention is directed is a mailpiece sorter which sorts mail into various bins or trays for delivery. 
     Mailpiece sorters are often employed by service providers, including delivery agents, e.g., the United States Postal Service USPS, entities which specialize in mailpiece fabrication, and/or companies providing sortation services in accordance with the Mailpiece Manifest System (MMS). Regarding the latter, most postal authorities offer large discounts to mailers willing to organize/group mail into batches or trays having a common destination. Typically, discounts are available for batches/trays containing a minimum of two hundred (200) or so mailpieces. 
     The sorting equipment organizes large quantities of mail destined for delivery to a multiplicity of destinations, e.g., countries, regions, states, towns and/or postal codes, into smaller, more manageable, trays or bins of mail for delivery to a common destination. For example, one sorting process may organize mail into bins corresponding to various regions of the U.S., e.g., northeast, southeast, mid-west, southwest and northwest regions, i.e., outbound mail. Subsequently, mail destined for each region may be sorted into bins corresponding to the various states of a particular region e.g., bins corresponding to New York, New Jersey, Pennsylvania, Connecticut, Massachusetts, Rhode Island. Vermont, New Hampshire and Maine, sometimes referred to as inbound mail. Yet another sort may organize the mail destined for a particular state into the various postal codes within the respective state, i.e., a sort to route or delivery sequence. 
     The efficacy and speed of a mailpiece sorter is generally a function of the number of sortation sequences or passes required to be performed. Further, the number of passes will generally depend upon the diversity/quantity of mail to be sorted and the number of sortation bins available. At one end of the spectrum, a mailpiece sorter having four thousand (4,000) sorting bins or trays can sort a batch of mail having four thousand possible destinations, e.g., postal codes, in a single pass. Of course, a mailpiece sorter of this size is purely theoretical, inasmuch as such a large number of sortation bins is not practical in view of the total space required to house such a sorter. At the other end of the spectrum, a mailpiece sorter having as few as eight (8) sortation bins (i.e., using a RADIX sorting algorithm), may require as many as five (5) passes though the sortation equipment to sort the same batch of mail i.e., mail to be delivered to four thousand (4,000) potential postal codes. The number of required passes through the sorter may be evaluated by solving for P in equation (1.0) below:
 
P (# of Bins) =# of Destinations  (1.0)
 
     In view of the foregoing, a service provider typically weighs the technical and business options in connection with the purchase and/or operation of the mailpiece sortation equipment. On one hand, a service provider may opt to employ a large mailpiece sorter, e.g., a sorter having one hundred (100) or more bins, to minimize the number of passes required by the sortation equipment. On the other hand, a service provider may opt to employ a substantially smaller mailpiece sorter e.g., a sorter having sixteen (16) or fewer bins, knowing that multiple passes and, consequently, additional time/labor will be required to sort the mail. 
     As sortation equipment has been made smaller to accommodate the physical limitations of available space, the throughput requirements must increase to enable an operator to perform multiple sortation passes, i.e., to satisfy the RADIX sorting algorithm discussed in the preceding paragraph. As the throughput requirements increase, the speed of operation increases commensurately which can increase the frequency of jams or damage to mailpieces as they are diverted from a high speed feed path to one of the sortation bins. Damage can occur when a mailpiece comes to an abrupt stop or remains in contact with a high speed belt or continuously operating roller. With respect to the latter, mailpieces can be abraded when a mailpiece sits at rest while a roller or belt of an ingestion assembly continues to drive. 
     Various attempts have been made to control the divert/stacking function and configure the sortation bin such that a jams and damage are mitigated when a mailpiece is collected/accumulated in a sortation bin. In Stephens et al. U.S. Pat. No. 4,903,956, a divert/stacking assembly includes rotating arm which is driven about an axis which is substantially orthogonal to the feed path and in-plane with sheet material at it travels, on-edge, along the feed path. Once the leading edge of the sheet material comes to rest against a registration stop, the arm is activated to urge the trailing edge of the sheet material into the bin, thereby causing the edges of the accumulated sheets to be in register and each of the sheets to be parallel. While systems such as that described in the &#39;956, patent improve the general alignment of sheets within a sortation bin, such divert/stacking assemblies do not account for variable forces which may be required to divert such sheet material or sheet material which may vary in weight or thickness. Furthermore, as the rotating arms or urge rollers continue to operate, such divert/stacking assemblies can damage the sheet material. 
     A need, therefore, exists for a stacking assembly which aligns sheet material, e.g., a mailpiece, in a sortation bin while mitigating jams and damage to the sheet material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate presently preferred embodiments of the invention and, together with the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
         FIG. 1  is a top view of a mailpiece sorter including a multi-tier stacker according to the present invention for receiving and sorting mailpieces into a plurality of sortation bins. 
         FIG. 2  is a side view of the mailpiece sorter shown in  FIG. 1  including a feeder, a scanner, and a linear distribution unit for feeding the multi-tiered stacker. 
         FIG. 3  depicts an enlarged top view of a divert/stacking assembly including a re-direct assembly and an ingestion assembly operative to divert mailpieces from a high speed feed path and stack mailpieces on-edge into each of the sortation bins of the multi-tiered stacker. 
         FIG. 4  depicts a broken away side view of the divert/stacking assembly taken substantially along line  4 - 4  of  FIG. 3  including a digital rotary positioning device and a dual-lobed cam for driving the trailing edge of a mailpiece into parallel alignment with a spring-biased support blade of the stacking assembly. 
         FIG. 5  depicts an enlarged broken away view of the sortation bin including the support blade and its mounting arrangement relative to the ingestion assembly. 
         FIG. 6  depicts the dual-lobed cam including the locus of points describing the contour of the cam surface. 
         FIG. 7  depicts the rotational position and velocity curves for driving the digital rotary positioning device as a function of time. 
         FIG. 8  depicts an alternate embodiment of the present invention wherein a second cam is operative to pivot a bellcrank arm into contact with a face surface of a stacked mailpiece to separate the mailpiece from contact with a drive belt or roller of the ingestion assembly. 
         FIG. 9  is a sectional view taken substantially along line  9 - 9  of  FIG. 8  wherein the first and second cams are disposed on, and driven by, the shaft of the stepper motor. 
     
    
    
     SUMMARY OF THE INVENTION 
     A stacking assembly is operative to protect stacked mailpieces from damage due to abrasion. The stacking assembly includes a support blade moveably mounted to a bin for accepting a stack of mailpieces and an ingestion assembly including a Leading Edge (LE) urge roller and Trailing Edge (TE) alignment device. The LE urge roller is operative to accept mailpieces from a supply of mailpieces, and urge a leading edge portion thereof toward a sidewall of the stacking bin. The TE alignment device includes a first cam driven about an axis of rotation by a digital rotary positioning device which cam defines a surface operative to urge the trailing edge portion of each mailpiece into parallel alignment with the support blade. The stacking assembly also includes an anti-abrasion linkage responsive to rotation of the digital rotary positioning device to forcibly displace a surface of the stacked mailpieces away from a moving surface of the ingestion assembly. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to a new and useful anti-abrasion assembly for a mailpiece stacking assembly. The stacking assembly is described in the context of a multi-tiered sortation device, however, the invention is equally applicable to any sheet material sorter, e.g., linear, back-to-back, or tiered. The sheet material being sorted is commonly a finished mailpiece, however other sheet material is contemplated, such as the content material used in the fabrication of mailpieces, i.e., in a mailpiece inserter. In the context used herein, “mailpiece” means any sheet material, sheet stock (postcard), envelope, magazine, folder, parcel, or package, which is substantially “flat” in two dimensions. 
     In  FIG. 1 , a plurality of mailpieces are fed, scanned and sorted by a multi-tiered sorting system  10 . Before discussing the various processing functions, it will be useful to become familiar with the physical arrangement of the various modules. The principle modules of the multi-tiered sorting system  10  include: a sheet feeding apparatus  16 , a scanner  30 , a Level Distribution Unit (LDU)  40 , a multi-tiered stacker/sorter  50 , and a controller  60 . With respect to the latter, the overall operation of the multi-tiered stacker/sorter  10  is coordinated, monitored and controlled by the system controller  60 . While the sorting system  10  is described and illustrated as being controlled by a single system processor/controller  60 , it should be appreciated that each of the modules  16 ,  30 ,  40  and  50  may be individually controlled by one or more processors. Hence, the system controller  60  may also be viewed being controlled by one or more individual microprocessors. 
     The sheet feeding apparatus  16  accepts a stack of mailpieces  14  between a plurality of singulating belts  20  at one end and a support blade  22  at the other end. The support blade  22  holds the mailpieces  14  in an on-edge, parallel relationship while a central conveyance belt  24  moves the support blade  22 , and consequently, the stack of mailpieces  14 , toward the singulation belts  24  in the direction of arrow FP. 
     Once singulated, the mailpieces  14  are conveyed on-edge, in a direction orthogonal to the original feed path FP of the mailpiece stack. That is, each mailpiece  14  is fed in an on-edge lengthwise orientation across or passed a scanner  30  which identifies and reads specific information on the mailpiece  14  for sorting each mailpiece  14  into a sortation bin  80  (discussed hereinafter when describing the multi-tiered sorter  50 ). Generally, the scanner  30  reads the postal or ZIP code information to begin the RADIX sorting algorithm discussed in the Background of the Invention section of the present application. The scanner  30  may also be used to identify the type of mailpiece/parcel, e.g. as a postcard, magazine, which may be indicative of the weight or size of the mailpiece  14  being sorted. 
     Following the scanning operation, each mailpiece  14  is conveyed to the Level Distribution Unit (LDU) wherein, each mailpiece  14  is routed via a series of diverting flaps/vanes  42 ,  44 ,  46 , to the appropriate level or tier A, B, C or D of the multi-tiered sorter. The level A. B. C or D is determined by the controller  60 , based upon the information obtained by the scanner  30 . For example, if a mailpiece is destined for bin C 3  (see  FIG. 2 ), the LDU  40  routes a mailpiece  14  to level C by diverting the input feed path FP to the lower feed path FP 2 , of two feed paths FP 1 , FP 2 . The mailpiece  14  is then routed to the upper feed path FP 5  of the two lower feed paths FP 5 , FP 6  to arrive at level C. It should be appreciated that the LDU may handle and route mailpieces  14  in a variety ways to distribute mailpieces from an input feed path FP I  to an output feed path FP O , including the use of conventional nip rollers, spiral elastomeric rollers, opposing belts, etc. Furthermore, the orientation may be inverted from an on-edge to a horizontal orientation by a conventional twisted pair of opposing belts  48  shown at the input of the LDU  40  and/or visa versa to reverse the orientation, i.e., from a horizontal to an on-edge orientation (not shown) by the same type of inverting mechanism. 
     In the described embodiment, each mailpiece  14  leaves the LDU  40  in an on-edge orientation and transported to a linear feed path LFP (see  FIG. 1 ) on each level A, B, C, or D of the multi-tiered stacker/sorter  50 . Each linear feed path LFP is defined by a plurality of back-to-back belt drive mechanisms (discussed in greater detail below when discussing the components of the divert/stacking assembly of the present invention) which convey the mailpieces  14  to one of several sortation bins A 1 -A 4 , B 1 -B 4 , C 1 -C 4 , D 1 -D 4 , on each level of the stacker/sorter  50 . While the linear feed path LFP, may be defined by dedicated belt drive mechanisms, the present invention employs elements of an inventive divert/stacking assembly  70  to convey the mailpieces along the linear feed path LFP. 
     In  FIG. 3 , the divert/stacking assembly  70  of the present invention includes a re-direct mechanism  80  and a stacking assembly  90  to accumulate and stack mailpieces  14  into sortation bin A 3 . More specifically, the re-direct mechanism  80  is operative to selectively re-direct mailpieces  14  into sortation bin A 3  by interrupting the linear motion thereof and diverting the selected mailpieces an angle α relative to the linear feed path LFP. This may be accomplished by understanding that the entire sorting system  10  is equipped with sensors, e.g., photocells, encoders, to monitor the instantaneous location of any mailpiece  14  at any time along the various feed paths, including the location of the predetermined gaps between the trailing edge TE of one mailpiece  14  and the leading edge LE of a subsequent mailpiece. 
     In the described embodiment, the re-direct mechanism  80  includes a conventional divert vane  82  and an actuator (not shown) operative to pivot the vane  82  about an axis  82 A into the feed path LPF of selected mailpieces  14 . While the re-direct mechanism  80  employs a pivotable vane  82  to divert select mailpieces  82 , any mechanism which interrupts the linear motion of the selected mailpieces  14  and diverts the same at an angle may be employed. 
     In  FIGS. 3 and 4 , the stacking assembly  90  includes a Leading Edge (LE) urge roller  84 , a support blade  86  and a Trailing Edge (TE) alignment device  88 . The LE urge roller  84  is operative to accept each of the selected mailpieces  14  and urge a leading edge portion LP thereof toward a sidewall SW of the sortation bin A 3 . In the described embodiment, the urge roller  84  includes a pair of urge rollers  84   a ,  84   b  (see  FIG. 4 ) which cooperate with a pair of drive belts  85   a ,  85   b  and a pair of upstream rollers  92   a ,  92   b  to drive selected mailpieces  14  into the bin A 3  on one side thereof. Additionally, the pair of drive belts  84   a ,  84   b  wrap around a pair of divert rollers  94   a ,  94   b  to drive other mailpieces  14 , e.g., non-selected mailpieces  14 , along the linear feed path LPF on the other side thereof. More specifically, the drive belts  85   a ,  85   b  cooperate with an opposing linear conveyance drive assembly  74  to capture and drive non-selected mailpieces  14  to another sortation bin A 4  downstream of sortation bin A 3 . 
     In  FIGS. 3 and 5 , the support blade  86  is operative to hold the selected mailpieces  14  in an on-edge parallel orientation against the urge roller  84 . More specifically, the support blade  86  is disposed in a plane which is substantially parallel to the linear feed path LFP and orthogonal to the stack direction, i.e., in the direction of arrow SD, of the selected mailpieces  14 . In the described embodiment and referring to  FIG. 5 , the stacking assembly  90  includes a guide rod assembly for mounting the support blade  86  relative to the urge roller  84 . More specifically, the guide rod assembly includes a linear bearing  96  for moveably mounting the support blade  86  along a guide rod  98  toward or away from the urge roller  84  in the direction of arrow SS. In the described embodiment, the linear bearing assembly  98  and support blade  86  are spring-biased toward the urge roller  84  such that without a stack of selected mailpieces  14 , the support blade  86  rests against the respective urge roller  84 . 
     In the preferred embodiment, the stacking assembly  90  includes a damping assembly  99  operative to damp the motion of the support blade  86  in the direction of arrow DD. That is, when the support blade moves outwardly, away from the urge roller  84 , the motion of the support blade  86  is damped. More specifically, low acceleration movement of the support blade  86  is dominated by the spring while a high acceleration motion of the support blade  86  is dominated by the damper  99 . The import of this arrangement will be discussed in greater detail hereinafter when discussing the operation of the divert/stacking assembly  70  of the present invention. 
     In  FIGS. 3 ,  4  and  6 , the trailing edge (TE) alignment device  88  includes a first or dual-lobed beater cam  100  driven about an axis of rotation by a digital rotary positioning device or stepper motor  120  (see  FIG. 6 ). With respect to the latter, the stepper motor  120  is a NEMA 17 frame motor. The inventors discovered through extensive research and inventive insight that integration of a low cost stepper motor  120  would require a precise cam profile  100 S capable of maintaining the necessary “holding torque” to urge the trailing edge TP of the selected mailpieces  14  into alignment. They determined that due to the torque limitations of conventional stepper motors a novel cam profile  100 S would be required to prevent motor stall. 
     The cam profile  100 S is best described by reference to a table which identifies the locus of points N 0 -N 31  about a common vertex 100V, each of the points N 0 -N 31  being disposed on a radial line a distance X 1 -X 31  from the vertex 100V, and at an angle θ from a line of reference RL. The table defines cam profile in terms of the radial distance X as a function of the angle θ from zero (0°) degrees to one-hundred and forty degrees (140°). The radial distance X (Column IV) is measured from the vertex 100V of each point N 0 -N 31  (Column I) on the surface of the cam. Furthermore, the radial distance X (Column IV) changes from one point to the next by the rise distance (Column III). The angle θ (Column II) is measured from a line of reference RL. 
     
       
         
           
               
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                 Point No. 
                 Angle (θ) 
                 Rise (in) 
                 Total Displacement (X - in) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 0.00 
                 0.000 
                 0.538 
               
               
                 2 
                 4.66 
                 0.002 
                 0.540 
               
               
                 3 
                 9.33 
                 0.006 
                 0.544 
               
               
                 4 
                 14.000 
                 0.014 
                 0.552 
               
               
                 5 
                 18.667 
                 0.025 
                 0.563 
               
               
                 6 
                 23.333 
                 0.039 
                 0.577 
               
               
                 7 
                 28.000 
                 0.056 
                 0.594 
               
               
                 8 
                 32.667 
                 0.076 
                 0.614 
               
               
                 9 
                 37.333 
                 0.097 
                 0.635 
               
               
                 10 
                 42.000 
                 0.121 
                 0.659 
               
               
                 11 
                 46.667 
                 0.147 
                 0.685 
               
               
                 12 
                 51.333 
                 0.174 
                 0.712 
               
               
                 13 
                 56.000 
                 0.203 
                 0.741 
               
               
                 14 
                 60.667 
                 0.233 
                 0.771 
               
               
                 15 
                 65.333 
                 0.263 
                 0.801 
               
               
                 16 
                 70.000 
                 0.294 
                 0.832 
               
               
                 17 
                 74.667 
                 0.325 
                 0.863 
               
               
                 18 
                 79.333 
                 0.355 
                 0.893 
               
               
                 19 
                 84.000 
                 0.385 
                 0.923 
               
               
                 23 
                 88.667 
                 0.414 
                 0.952 
               
               
                 21 
                 93.333 
                 0.441 
                 0.979 
               
               
                 22 
                 98.000 
                 0.467 
                 1.005 
               
               
                 23 
                 102.667 
                 0.491 
                 1.029 
               
               
                 24 
                 107.333 
                 0.512 
                 1.050 
               
               
                 25 
                 112.000 
                 0.532 
                 1.070 
               
               
                 26 
                 116.667 
                 0.549 
                 1.087 
               
               
                 27 
                 121.333 
                 0.563 
                 1.101 
               
               
                 28 
                 126.000 
                 0.574 
                 1.112 
               
               
                 29 
                 130.667 
                 0.582 
                 1.120 
               
               
                 30 
                 135.333 
                 0.586 
                 1.124 
               
               
                 31 
                 140.000 
                 0.588 
                 1.126 
               
               
                   
               
            
           
         
       
     
     The cam profile may also be defined by the relationship given in equation 1.0 below.
 
 R (θ)= R   T /2×(1−COS(π×θ/θ T )  (1.0)
 
     wherein θ is an angle from a line of reference RL, wherein R(θ) is a rise height (in inches) at each angle θ, wherein RT is a total rise height (in inches), and wherein θ T  is a total angle inscribed by the cam surface  100 S. 
     In the described embodiment, the dual-lobed cam  100  is mounted to and rotates with a shaft  125  which is driven by a digital rotary positioning device or stepper motor. In the preferred embodiment, stepper motor is a NEMA 17 Frame bi-polar motor having two-hundred (200) steps, each step corresponding to about 1.8 degrees. 
       FIG. 7  illustrates the control motion profile including a substantially linear rotational position curve  160  and a trapezoidal rotational velocity curve  170 . From the position curve  160 , it will be appreciated that the stepper motor  120  consumes about 0.0655 seconds to travel 0.5 revolutions or one-hundred eighty degrees (180°). From the rotational velocity curve  170 , it will be appreciated that a maximum rotational speed of 9.0 revolutions per second is achieved during a single cycle. The time required to accelerate from a standing position to the maximum rotational speed (i.e., the left- and right-hand sloping portions T 1 , T 3  of the curve  170 ) is about 0.010 seconds. Furthermore, the time over which a constant speed is maintained (the horizontal portion T 2  of the curve  170 ) is about 0.0456 seconds. The number of degrees travelled until the motor reaches the maximum speed is about 0.0450 revolutions which is about sixteen degrees (16.5°), the number of degrees travelled while the velocity is constant is about 0.410 revolutions or about one-hundred and forty-seven degrees (147°), and the number of degrees travelled while the velocity accelerates from its maximum speed to a stop is also about 0.0450 revolutions which is about sixteen degrees (16.5°). These values are summarized in Table II below 
     
       
         
           
               
               
               
               
             
               
                 TABLE II 
               
               
                   
               
             
            
               
                   
                 Max Speed 
                 9 
                 revolutions/second 
               
               
                   
                 Cycle Time 
                 0.0655 
                 second 
               
               
                   
                 Stoke 
                 0.5 
                 revolutions 
               
               
                   
                 T1 = T3 
                 0.010 
                 seconds 
               
               
                   
                 T2 
                 0.0456 
                 seconds 
               
               
                   
                 Acceleration Distance 
                 0.04475 
                 revolutions 
               
               
                   
                 Acceleration Rate 
                 905 
                 revolutions/second2 
               
               
                   
                 Constant Velocity Distance 
                 0.410 
                 revolutions 
               
               
                   
               
            
           
         
       
     
     In operation, and returning to  FIG. 3 , mailpieces  14  are conveyed along the linear feed path LFP between the belts  84   a ,  84   b  of the ingestion assembly, i.e., the outboard side thereof, and the belts  75   a ,  75   b  of the linear conveyance assembly  74 . When a selected mailpiece, i.e., a mailpiece  14  identified by the scanner  30  to be stacked in a particular one of the sortation bins A 1 -D 4 , the re-direct assembly  80  receives a signal from the controller  60  to divert a selected mailpiece  14  into the sortation bin, i.e., sortation bin A 3  in  FIG. 3 . The selected mailpiece  14  is initially re-directed at an angle α while the leading edge alignment device  84 , i.e., the urge rollers  84   a ,  84   b  in combination with the drive belts  85   a ,  85   b , urge the leading edge portion LP (shown in phantom lines in  FIG. 3 ) of a selected mailpiece  14  toward a sidewall portion of the sortation bin A 3 . The controller  60  then issues a signal to the trailing edge alignment device  88 , i.e., the dual-lobed cam  100  and digital rotary positioning device  120 , to rotate approximately one-hundred and forty degrees (140°) to urge the trailing edge portion TP into parallel alignment with the support blade  86  or the previously stacked mailpieces  14 . 
     As each mailpiece  14  is stacked, support blade  86  moves away from the urge roller  84  under the normal forces imposed by the stack  14 S while a spring SG retains the blade  86  in contact with the outboard end of the stack  14 S. Should a particularly heavy, i.e., large inertial mass, mailpiece  14  be stacked into the sortation bin A 3 , the damping assembly (see  FIG. 5 ) prevents the blade  86  from momentarily disengaging the stack  14 S with the attendant loss of stacking control. That is, it will be appreciated that a large impact load may be imposed on the stack  14 S by a high velocity mailpiece, or one which is larger/heavier than can be handled by the spring SG without accelerating the support blade  86  outwardly, even under the load imposed by the spring SG. The damper assembly, therefore, mitigates the propensity for disengagement and the potential for misalignment, or jamming of, mailpieces in the stack  14 S. 
     In  FIGS. 8 and 9  another embodiment of the invention is depicted wherein an anti-abrasion assembly  200  is employed in combination with the ingestion assembly  90  to protect stacked mailpieces from damage due to abrasion. More specifically, the anti-abrasion assembly  200  allows the continuous operation of the ingestion assembly  90 , i.e., the urge rollers  84   a ,  84   b  and drive belts  85   a ,  84   b , without incurring abrasion to a surface of the stacked mailpieces  14 S. That is, to the extent that the support blade  86  is spring-loaded in a direction tending to trap the stack of mailpieces  14 S against the urge rollers  84   a ,  84   b  and drive belts  85   a ,  85   b , it will be appreciated that the continuous movement thereof can result in damage to the affected mailpiece, the innermost mailpiece  14   i  being spring-loaded against the moving elements of the ingestion assembly  90 . 
     In this embodiment, the inventors recognized a synergistic use of the digital rotary positioning device  120  of the Trailing Edge alignment device  88  for control in combination with an anti-abrasion device  200 . More specifically, the inventors recognized that inasmuch as the positioning device  120  has the ability for precise positioning control, including reverse control, an opportunity arises to employ this motion to disengage the stack during certain operational modes, i.e., an idle mode when mailpieces are not being stacked or accumulated into a particular sortation bin. 
     In the broadest sense of this embodiment, the anti-abrasion assembly  200  includes anti-abrasion linkage  202  responsive to rotation of the digital rotary positioning device  120  to forcibly displace a surface  210  of the stacked mailpieces  14  away from a moving surface of the ingestion assembly  84 . 
     In the described embodiment, the anti-abrasion assembly  200  includes the anti-abrasion link  202  and a second cam  204  disposed about and rotating with the shaft  125  of the stepper motor  120 . The anti-abrasion linkage  202  is pivotally mounted about support axis  202 A which is disposed between the urge rollers  84   a ,  84   b  of the leading edge alignment assembly  84  and the drive rollers  92   a ,  92   b  of the trailing edge alignment device  88 . The linkage  202  includes an input arm  206  operative to contact a lobed cam surface  204 S of the second cam  204  and an output arm  208  a operative to contact the innermost mailpiece  14   i  of the stack of mailpieces  14 S. Upon rotating the shaft  125  of the stepper motor  120 , the input arm  204  follows the cam surface  204 S which causes the linkage  202  to rotate in the direction of arrow  212 . Furthermore, inasmuch as the linkage  202  is configured as a bellcrank or lever, rotation of the input arm  206  also effects rotation of the output arm  208  toward the innermost mailpiece  14   i  of the stack  14 S. 
     In operation, the first or dual-lobed cam  100  rotates in approximately one-hundred and eighty degree (180°) increments, and minimally one-hundred and forty degree (140°) degree increments, to urge the trailing edge portion of the selected mailpieces. While in an idle condition, i.e., when mailpieces  14  are not being diverted or selected into the sortation bin, the second cam  204  imparts a rotary motion to the anti-abrasion linkage  202 , i.e., about the rotational axis  212 , such that the output arm  208  separates, or effects a gap between, the innermost mailpiece  14   i  of the stack  14 S and the urge roller  84   a ,  84   b  and the drive belts  85   a ,  85   b . Inasmuch as it may be undesirable to cyclically move the anti-abrasion linkage  202  with each revolution of the stepper motor shaft  125 , the second cam  204  may be clutch mounted (not shown) to the drive shaft  125 . More specifically, the clutch mount may be of an overrunning-type such that when the shaft  125  rotates in one direction, i.e., the direction for rotating and activating the dual-lobed cam  100 , the second cam  204  is disengaged. However, when rotated in the opposite direction, the over-running clutch mount engages the second cam  204  to impart motion to the anti-abrasion linkage  202 . 
     In summary, divert/stacking assembly employs a low cost, controllable, and highly accurate positioning device to drive a dual lobed cam for aligning mailpieces in a sortation bin. The dual lobed cam includes an optimum surface contour or profile to minimize torque on the shaft without inducing a stall condition in the positioning device. Furthermore, the invention describes an embodiment wherein the positioning device is also used to prevent abrasion of mailpieces while sitting idle awaiting additional mailpieces to be stacked in the sortation bin. 
     Although the invention has been described with respect to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention.