Abstract:
A method for sorting mail pieces includes the steps of loading mail pieces to be sorted into individual holders, sorting the holders using an automated system that stores and reorders the holders so that the holders are ordered according to a sort scheme for the mail pieces, storing the sorted holders in a storage area during sorting, and then unloading the mail pieces from the holders in order according to the sort scheme. The storage step occurs during sorting in the sense that a series of reordered holders is gradually created in one of a variety ways by the sorting process, and a storage area is provided for this purpose. Preferably the method further includes steps of unloading the sorted holders from the storage area and transporting the holders to an unloading station at which the unloading step is carried out.

Description:
[0001]    This application claims priority of U.S. Provisional Application No. 60/781,018, filed Mar. 10, 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to mail sorting systems, in particular to systems for sorting mail pieces having an address that cannot be decoded using conventional OCR or bar code scanning, or that cannot be machine sorted due to the physical characteristics of the mail pieces. 
       BACKGROUND 
       [0003]    Residual mail is a term used to refer to postal mail remaining after most of the mail to be delivered has been sorted to delivery order by automated sorting machines. Letters are currently sorted automatically by a variety of known systems such as DBCS (delivery bar code sorter), MLOCR (multi-line optical character reader) and the like. The USPS has recently funded the development of a sorting system for flats (mail pieces between 11½ and 15 inches long, or between 6⅛ and 12 inches high, or between ¼ and ¾ inch thick), which has the aim of accomplishing automated sorting of flats to delivery groups that correspond to the groups created by automated letter sorting machines. However, even with automation of both letter sorting and flats sorting, some mail pieces will still comprise manual mail that must be sorted by hand rather than by a sorting machine. 
         [0004]    Such residual mail may include mail for which the address cannot be decoded by Optical Character Recognition (OCR) or bar code scanning, and mail which cannot be machine sorted due to its physical characteristics such as too stiff, irregular shapes, too thin and open folds. Manual casing refers to the process currently carried out by postal carriers wherein mail that has not been presorted to delivery order is manually sorted to a plurality of slots in a sorting case, where each slot represents a delivery destination. The cased mail is then removed from the slots (“pulled down”) and eventually merged with presorted mail. Where flats and letters have each been presorted, the carrier takes mail from three separate stacks, letters, flats and manual mail, when delivering the mail. The time required for the casing operation combined with the need to merge stacks of presorted mail greatly slows down the manual delivery of mail. 
         [0005]    Pitney-Boyes PCT publication WO 2006110486 describes a concept of removing multiple feeders from multiple sorters and providing a pathway from each feeder to each sorter enables fewer feeds per mail piece for conventional sorters. This system includes a plurality of feeders, and a plurality of sorters configured to receive and sort the mail pieces from the feeders. The bins are sorted mail stations, and the feeders are feeding stations. Clamps are used for holding the mail pieces during sortation to expedite the proper movement of mail pieces from the feeders to appropriate sorter bins. However, use of mechanical devices such as clamps to hold mail during sorting is likely to prove difficult. 
         [0006]    The mail handling system of the present invention has the goal of making it possible to machine-sort residual mail. The system can be used to sort mail pieces of all types from postcards up to large flats. When used in combination with letter and flats sorting processes, the need to merge mail remains, but the manual casing operation can be virtually eliminated. To further reduce merge operations, the system can be used to sort both residual flats and residual letters. 
       SUMMARY OF THE INVENTION 
       [0007]    A method for sorting mail pieces according to the invention includes the steps of loading mail pieces to be sorted into individual holders, sorting the holders using an automated system that stores and reorders the holders so that the holders are ordered according to a sort scheme for the mail pieces, storing the sorted holders in a storage area during sorting, and then unloading the mail pieces from the holders in order according to the sort scheme. The storage step occurs during sorting in the sense that a series of reordered holders is gradually created in one of a variety ways by the sorting process, and a storage area is provided for this purpose. Preferably the method further includes steps of unloading the sorted holders from the storage area and transporting the holders to an unloading station at which the unloading step is carried out. 
         [0008]    Such a method can be used as part of a larger scale sorting method which deals with both machineable and non-machineable mail. Such a process includes the steps of sorting a majority of the mail pieces using an automated sorting system such as a DBCS or MLOCR machine, sorting residual mail not sortable on the automated sorting system by the steps given above, and merging the mail pieces sorted with the automated sorting system with the sorted residual mail. In this case, the “residual mail” by definition means mail left over from the conventional automated sorting machine which, due to its physical characteristics, cannot be processed by that machine. 
         [0009]    The invention further provides an apparatus for sorting mail pieces, especially residual mail, according to the foregoing methods. Such a system includes at least one loading station at which mail pieces to be sorted are loaded into individual holders, and a conveyor system that includes conveyor sections that transport holders containing mail pieces from the loading station to a splitter that diverts each holder to one of a set of conveyor lanes based on a sort scheme, thereby dividing the holders up into subgroups based on the sort scheme. An ordering system receives the holders from the conveyor system and includes a plurality of holder reordering devices that each receive a designated subgroup of the mail pieces and reorder that subgroup according to the sort scheme. An unloader receives the holders from the reordering system and removes the mail pieces from the holders in order according to the sort scheme, after which the mail pieces may be loaded into trays or packaged for delivery. 
         [0010]    According to a further aspect of the invention, a mail sorting system according to the invention includes a control computer and a plurality of holders configured for receiving and holding mail pieces therein. At least one holder loading station is provided for loading the holders with mail pieces, the holder loading station including an input device for inputting destination data for the mail pieces to the control computer. A plurality of totes are configured to receive and transport groups of holders. A conveyor system includes a first conveyor for directly transporting holders containing mail pieces in series, and a second conveyor configured to transport the totes to different locations in the mail sorting system. At least one tote loading station is provided that includes a loading mechanism that loads holders into totes. An ordering track receives and supports the holders containing mail pieces and is provided with a mechanism for reordering holders on the track according to a sort scheme. The system further has an unloading station including an unloading mechanism that removes mail pieces from the holders and a traying device that places the unloaded mail pieces in mail trays. 
         [0011]    In a preferred form of the foregoing embodiment, the input device used at the holder loading station is typically a keyboard and video display for allowing manual input of destination data for the mail pieces to the control computer that stores the destination information for the mail piece and associates it with the identification number of the holder. The holders, each containing one mail piece, are loaded into the totes at the tote loading station. Holders are loaded into a particular tote according to sort scheme. The sort scheme is configured so as to relate each tote load station to a particular ordering tracks. The loaded totes are then conveyed by the conveying system to an induction station where the holders are transferred to an ordering track such as a carousel or linear track. The control system diverts the loaded totes to one of several ordering tracks according to the sort scheme. A robot or transfer mechanism reorders the resulting subgroups of holders according to a sort scheme for each track, after which the holders are removed from the track in order. The sorted holders may be loaded into totes and conveyed from the ordering track to a traying station. At the traying station, the holders are removed from the totes, and the mail pieces removed from the holders. The mail pieces are then loaded into mail trays in order according to the sort scheme. The timing and sequence of these operations may vary as described further below. These and other aspects of the invention are discussed further in the detailed description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the accompanying description, wherein like numerals represent like elements: 
           [0013]      FIG. 1  is a schematic diagram of a mail sorting system according to the invention; 
           [0014]      FIG. 2  is a perspective view of a tote and holders according to the invention on a conveyor section; 
           [0015]      FIGS. 3A-3C  are a series of elevation views of a splitter mechanism according to the invention; 
           [0016]      FIG. 4  is a perspective view of shifting frame section of  FIGS. 3A-3C ; 
           [0017]      FIGS. 5A to 5D  are a series of views of a multiple shifting frame mechanism according to the invention at different stages of operation; 
           [0018]      FIGS. 6A and 6B  are front views of a gate mechanism according to the invention in closed and open states respectively; 
           [0019]      FIG. 7  is a partial perspective view of a sorting carousel according to the invention whereon holders carrying mail pieces are ordered according to a sort scheme; 
           [0020]      FIG. 8  is a schematic representation of a folder opening and mail traying system according to the invention; 
           [0021]      FIG. 9  is a schematic representation of a mail packaging system as an alternative to traying in  FIG. 8 ; 
           [0022]      FIG. 10  is a schematic representation of an alternate mail sorting system according to the invention; 
           [0023]      FIG. 11  is a schematic representation of a transfer station and linear sorting lane suitable for use in connection with the mail handling system of  FIG. 10 ; 
           [0024]      FIG. 12  is a schematic diagram of a two-pass sorting embodiment of the invention; and 
           [0025]      FIG. 13  is a partial side view of the system of  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring to  FIGS. 1-2 , a system  10  according to the invention includes a number of sorting stations interconnected by conveyors such as Tricon® roller conveyor sections  11  and brush conveyor sections  12 . A series of totes  13  resembling file drawers open on one or both ends are used to transport a number of mail piece holders  14  along conveyor sections  11  during certain stages of the process, whereas at other times holders  14  are transported directly on brush conveyors  12 . This makes it possible to build system  10  in a manner consistent with factory automation principles, where components of the system may be in different locations rather than grouped together as in the embodiment shown. 
         [0027]    Holders  14  are, in the simplest embodiment, no more than light weight folders with upper end hangers similar to commercially available file folders. In a more advanced embodiment, holders  14  are double-walled devices capable of being peeled away from the mail piece inside using cancellation of relative motion comparable to that used by the H-belt disclosed in Pippin U.S. patent application Ser. No. 10/142,348, filed May 19, 2002, Publication No. 20030038065, Feb. 27, 2003, the contents of which are incorporated by reference herein. Holders  14  according to the invention could also include mechanical devices such as clamps used to hold mail. 
         [0028]    Empty holders  14  are carried past a series of manual loading stations  16  on a rail  15 . Empty folders and previously filled folders are simultaneously pushed along by a brush conveyor  12  located above and at the ends of the folders. Bar code scanners are located at each load station  16 . The scanner reads the bar code located on each holder  14  as they pass by respective load stations  16 . Holder  14  load status is determined by correlating the holder  14  bar code with a computer data base. An empty holder  14  is stopped for loading following key coding of destination information for the mail piece by the operator. Bar coded holder  14  and the system at the station  16  automatically store the bar code and associates the keyed address information with the holder. This mail piece information and now related holder bar code is used later for sorting. Station  16  may include a camera and video display for presenting the operator with an enlarged image of the mail piece to facilitate entry of destination information for the mail piece. 
         [0029]    Mail entering system  10  is directed to destinations in delivery zones served by the processing center at which system  10  is located. Holders  14 , each loaded with a single mail piece, are conveyed from each station  16  by exit brush conveyor  12  that carries the holders  14  one at a time to a three-way switch or splitter  21 . In one embodiment, splitter  21  is a three position, shifting frame mechanism that moves a holder  14  from the conveyor  12  to either right or left lanes  22 A,  22 C, or leaves it in the center lane  22 B as the brush drive moves the holder along. A bar code reader positioned at splitter  21  scans holders  14  such that the holders are diverted to one of lanes  22  in accordance with a predetermined sort scheme. 
         [0030]    As shown in  FIGS. 3A-3C  and  4 , one example of a splitter  21  comprises a row of shifting frame sections  200  including a left frame  201 , center frame  202  and right frame  203  united by connectors  204  to move in unison. In the position shown in  FIG. 3A , the center frame  202  is shown in alignment with the incoming brush conveyor  12 . Center frame  202  forms a thru-lane for holders  14  that are destined to remain in lane  22 B or which will be shifted left or right by a downstream section  200  as explained further below. Each section  200  is mounted to slide along a support bar  206 . The left and right frames  201 ,  203  are preferably provided with movable stop or gate assemblies  209 . Each stop assembly  209  includes a pair of lateral anchor tabs  211  projecting outwardly from opposite outer sides of the associated frame section  201  or  203 . Tabs  211  are connected by a pair of coil springs  212  to opposite ends of a horizontal crossbar  213 . Crossbar  213  extends all the way across frame  201 ,  203  near its lower end and through elongated grooves  214  in the sidewalls  216  of each frame. A pair of vertical bars  217  located along the insides of sidewalls  216  are connected at or near their lower ends to crossbar  213  and extend upwardly through holes in a horizontal shoulder portion  218  of sidewalls  216 . 
         [0031]    Holders  14  in this example each comprise a double-walled plastic bag suspended from a pair of parallel horizontal hanger bars  55 . The continuation of brush conveyor  12  is three such brush conveyors  12 A,  12 B,  12 C side by side, one for each sorting lane. It is most economical to run brush conveyors  12  constantly rather than using a start/stop cycle. To keep each holder  14  in place during a sideways shift, the upper ends of bars  217  engage the outer ends of hangers  55  and crossbar  213  stops the lower end of the holder  14  and prevents it from swinging or moving downstream. Between shifts, a suitable actuator (e.g., an L-shaped projection or hook actuated by a solenoid) engages bars  217  without blocking movement of holders  14  and pushes crossbar  213  down, or pulls crossbar  213  down, stretching springs  212 . In this position, holders  14  continue to move under the action of brush conveyors  12 A- 12 C to the next shifting frame section  201 ,  203 , or to the takeaway lanes  22 A- 22 C. Upon disengagement of the actuator, springs  212  contract and return crossbar  213  and bars  217  to the closed position for the next cycle. 
         [0032]    In  FIG. 3B , shifting frame  200  moves to the right so that frame section  201  receives an incoming holder from the from the brush conveyor  12 . Stop assemblies  209  are in the closed position. Frame  200  then shifts back to the left ( FIG. 3C ) and stop assemblies  209  are opened so that the holder  14  in frame section  201  moves on. The cycle can then be repeated as needed. The directions in which frame  200  shifts are reversed to load a holder  14  into frame section  203 . If the holder  14  entering frame  200  is destined to remain in the center lane beneath conveyor  12 B, then it continues moving and no shift of frame  200  occurs. 
         [0033]    The foregoing example can operate with only one shifting frame  200 . However, it can be adapted to load multiple holders at a time by permitting several holders  14  to enter a center lane formed from a series of frames  200  operating side by side. In the example of  FIGS. 5A-5D , four shifting frames  200  are mounted side by side but spaced from each other. Stop gates  209  are provided in the center lane  22 B between middle frame sections  202  as shown. Loading of holders  14  starts with the forwardmost gate  209 A in the closed position and the other gates  209  between sections  202  in the open position. A holder  14  enters from brush conveyor  12  and is conveyed by conveyor  12 B to the forwardmost gate  209 A. A sensor such as a photocell or proximity switch detects the arrival of the first holder  14 , whereon the next gate  209 B is closed. A second holder  14  then enters lane  22 B and continues moving until it contacts gate  209 B. The cycle is then repeated a third time, this time with the third gate  209 C closed. Then the entry gate  209 D is closed and a fourth holder  14  is brought into position against it as shown in  FIG. 5B . 
         [0034]    Once four holders  14  are in contact with gates  209 A- 209 D, the frames  200  are shifted in accordance with the sort scheme and the read destination information from each of the four holders  14 . For example, if the holder  14  at gate  209 A needs to go to lane  22 A, that frame  200  in front of it would shift to the right as shown in  FIGS. 2A-2C . The other three frames  200  might shift in the same or opposite direction, or might not shift if the mail piece in the holder  14  should remain in the center lane  22 B. Once the frames  200  have shifted, gates  209 A- 209 D that feed into a shifted frame  200  (i.e., into either of the outer frame sections  201 ,  203 ) open, while any of gates  209 A- 209 D that adjoin an unshifted frame  200  remain closed as shown in  FIG. 5C . The action of brush conveyors  12 A- 12 C moves holders  14  into frame sections  201 ,  203 . The gates  209  which are built into the frame sections  201 ,  203  are in the closed position at this time. Once the affected holders  14  have entered the respective frame sections  201 ,  203 , any frame  200  that was shifted is then shifted back to its original position ( FIG. 5D ). All gates  209  are then opened so that all four of the holders  14  move out of the splitter through one of the lanes  22 A- 22 C. The cycle can then be repeated by closing all gates except  209 B- 209 D and starting the loading process over again. 
         [0035]    A modified form of stop gate  209 ′ useful in the foregoing embodiment is shown in  FIGS. 6A ,  6 B. The lower ends of bars  217  extend past horizontal crossbar  213  and are secured by couplings  221  to solenoids  222 , which are actuated and deactuated to raise and lower the gate  209 ′. 
         [0036]    A batch switching process such as the foregoing provides the system with greater throughput speed and is this preferred over a simple one frame splitter. Whether a single or multiple frame embodiment is contemplated, the destination information on each frame entering the frame  200  must be known, such as by using a scanner mounted near the point of entry to the splitter  21 . The control computer then operates the shifting frame(s)  200  on the basis of the sort scheme. 
         [0037]    Each lane  22  from the first splitter  21  carries holders  14  to three associated secondary splitters  23 , which operate in the same manner as splitter  21 . In this example the secondary splitters  23  are vertically stacked such that only the top splitter  23  is visible in  FIG. 1 . Lanes from splitters  23  lead to nine associated tote loaders  26  wherein each holder  14  is again shifted left or right and then pushed into an open tote  13  positioned to receive it by a combination of a right angle transfer mechanism such as described above in connection with switch  21  and overhead brush drives, following an L-shaped path. For economy, the loaders  26  are arranged as three stacks of three each, similarly to splitters  23 . At this stage, system  10  has subgroups of sorted mail contained in holders  14  down to the level of a single tier of the carousel units described below, corresponding to a range of destination points. Thus, mail in each tote  13  is directed to a destination in a predefined range, but is not yet in delivery order. 
         [0038]    Referring to  FIGS. 1 and 7 , a fully loaded tote  13  is automatically or manually removed from loader  26  and conveyed through a series of conveyor sections  11  and elevators  35  to a destination level of one or more carousels  31 , which function to reorder holders  14 . Holders  14  from the tote  13  are unloaded one at a time at an induction mechanism  32  and begin moving along an oval-shaped track  33  under the action of a brush conveyor  34 . A control computer  40  is connected to a bar code reader positioned adjacent track  33  which scans the bar codes on holders  14  moving about carousel  31  and compares the order in which the holders appear with a sort scheme order. The sort scheme will normally require all holders  14  carrying mail pieces destined for the same destination to be grouped consecutively. 
         [0039]    To re-order holders  14 , a right angle transfer mechanism  36  positioned inside track  33  engages a shifting track section that carries a holder therein to a center position inside of the track  33 . Movement of holders  14  along track  33  continues until the control system determines that the withdrawn holder should be reinserted by mechanism  36  in a new position relative to the other holders on track  33 . Several transfer mechanisms  36  can be placed inside of track  33  so that several holders  14  can be withdrawn and reinserted at the same time, increasing the throughput of the system. 
         [0040]    The algorithm for reordering holders  14  may be one which keeps track of the current order of all holders  14  on track  33  and reinserts the withdrawn holder  14  at a position where it is grouped with a series of other holders containing mail addressed to the same destination. A sensor scans each holder  14  as it passes by on track  33 , enabling control computer  40  to keep track of the order in which the holders appear. It may be necessary to provide several sensors for this purpose, one for each transfer mechanism  36 . 
         [0041]    Once a tote  13  has been emptied at induction mechanism  32 , it is lowered by the elevator  35  and continues along the return run of conveyor  11  for reloading into a tote loader  26 . The control system keeps track of full and empty slots in tote loaders  26  and directs empty totes accordingly. Tote loaders  26  also function as a storage rack for empty totes  13  not currently in use. The number of empty totes to be stored increases as the sorting process winds to completion. 
         [0042]    At the end of the sorting process, the carousel levels are full of holders  14 , and the holders are in carrier delivery order. Empty totes  13  are then unloaded from tote loaders  26  and carried along conveyor  11  to loading elevators  39  adjacent each carousel  31 . An empty tote  13  is brought into position on elevator  39 , and holders  14  are loaded into each tote  13  by sideways transfer using an unloading mechanism  41  similar to that used at loading stations  26 , one at a time or in batches. Holders  14  are unloaded from each carousel  31  in carrier delivery order. The ID codes of totes  13  used for each carousel are tracked by the control system. Full totes  13  are returned to conveyor  11  and carried to a series of traying stations  46 . The control system reads the ID tag on the tote  13  and directs it to the station  46  assigned to that carousel  31 . Totes  13  arrive in the order in which they were unloaded, which corresponds to delivery order. 
         [0043]    Referring now to  FIGS. 1 and 8 , traying stations  46  include an opener section  47  and a tray loading area  48  downstream from it. Opener  47  takes a group of vertically positioned holders  14  out of tote  13  and loads the holders onto a pair of rails  56 . A pair of belted support paddles  51  are positioned at either end of the row of holders  14 . In this embodiment, each holder  14  is essentially a bag that has been doubled over the holder support rails  55  to form a double-walled pocket  57 . As shown in  FIG. 4 , each pocket  57  has a pair of inner and outer bars  52 ,  53  at the bottom of each layer. At the unload station each end of the pocket  57  support rails  55  are held with a spring loaded gripper. Inner bar  52  is held in place at each end with stationary end effectors. An end effector engages the outer bar  53  that joins lower ends of the double-walled holders  14  to pull the outer walls down. This causes the outer layer of pocket  57  to withdraw downwardly. The inner portion of pocket  57  is peeled away from the mail piece  58  as its sides pass over and around the rails  55 . This peeling motion of the outer walls opens the holder so that mail piece  58  does not slide relative to the adjoining walls of the pocket  57 . The bottom edge of the mail piece remains stationary or registered as the pocket  57  is peeled away. As the mail piece exits the holder  14 , paddles  51  are positioned to support the stack of mail pieces  58  from either end and sweep the mail into an adjoining tray  59 . The belts on paddles  51  are driven to lower the mail into the tray  59 . To return holder  14  to its original position, a pusher mechanism with a plurality of pushing members, one for each holder  14 , engages inner bar  52  of holder  14  and pushes it down, drawing outer bar  53  up and restoring holder  14  to its original doubled-over condition. Empty holders  14  are then returned to rail  15  by reloading them into totes  13  and transporting them to a holder induction station  71 , after which totes  13  are returned by conveyor  11  to positions in tote loader  26 . 
         [0044]    Once paddles  51  have delivered mail pieces  58  to the tray  59 , they return as shown to the opener section  47  to start opening the next set of holders  14 . As an alternative to unloading into a tray, the belts of paddles  51  are driven to lower the batch of mail  58  into a delivery point packaging system  60  ( FIG. 9 ) such as is described in commonly assigned U.S. Patent Publication 20070017855, Jan. 25, 2007, the contents of which are incorporated herein by reference. 
         [0045]    Referring now to  FIGS. 10 and 11 , in an alternate embodiment, a mail handling system  110  according to the invention utilizes a plurality of sort lanes  86  each with a sled or robot  94  to order holders  14 . Mail pieces are manually loaded into holders  14  at loading stations  16  as described above. Holders  14  are conveyed from manual loading stations  16  to an induction station  112  without being loaded in totes  13 . Holders  14  are conveyed from manual loading stations  16  to a splitter  114  which transfers the holders to one of six vertically stacked lanes  116 . Each of lanes  116  is provided with a brush conveyor  118  which carries holders  14  to the associated level of one of eight induction stations  112  where the holders  14  are loaded onto a transfer station  120 . For this purpose, each lane  116  has eight adjoining branch conveyors  119  each provided with right angle transfer mechanisms  121  to divert holders  14  to the correct induction station  112 . 
         [0046]    Each of sort lanes  86  is similar to an elongated file cabinet drawer including elongated support rails  92  made of a low friction material and configured to support a large number of holders  14 . Holders  14  are picked from the end of the queue at transfer station  120  by a sled or robot  94  suspended by an overhead suspension system and equipped with one or more extendable arms  96  configured to engage and lift the holders  14 . Sled  94  is equipped to travel back and forth along the length of the sort lane  84  to place holders  14  in order according to the predetermined sort scheme. Sled  94  is provided with one or more bar code readers  98  for reading the bar codes picked from holders picked from the queue at transfer station  120  and the bar codes of holders  14  in place in sort lane  86 . Sled  94  may also be equipped with a sensor to determine its position along the sort lane  86 . 
         [0047]    In order to place the holders in order according to the predetermined sort scheme, sled  94  picks up a holder  14  from the end of the queue and reads the bar code of the holder. Sled  94  then travels along sort lane  86 , reading the bar codes of individual holders  14  already in place in the lane. In a simple version, when sled  94  passes two consecutive holders  14  having bar codes between which the holder  14  carried by sled  94  should be inserted, the sled stops and inserts the holder. Thus, by way of example, if the sort scheme is carrier delivery order and sled  94  is carrying a holder with a mail piece addressed to 2915 Maple St., when sled  94  passes consecutive holders in sort lane  86  having mail pieces addressed to 2909 Maple St. and 2919 Maple St., sled  94  will stop and place the carried holder between the two holders in the sort lane. In an alternate embodiment, lane  86  is subdivided into a series of sections each associated with a range of destinations for the sort scheme. Before scanning individual holders, sled  94  moves to the start of the section where that holder will be placed based on the address of the mail piece inside it. 
         [0048]    The computer implemented logic or algorithm controlling led  94  may be stored on an onboard processor or in control computer  78 . The algorithm may record the identification number of each holder  14  placed in sort lane  86  and the holder&#39;s position in the lane by physical location along the lane and/or relative to other holders in the lane. This information may be transmitted to control computer  78 . 
         [0049]    Once sorting is completed, ordered holders  14  are then loaded onto totes  13  at loading stations  122  and conveyed to traying station  46  via roller conveyor system  124 . Sled  94  is used to push holders  14  into totes  13 . Empty totes  13  unloaded at station  46  are then transported along the return portion  127  of conveyor  124  back to loading stations  122 . Optionally, totes  13  unloaded at station  46  are reloaded with empty holders  14  and then transported along the return portion  127  to an induction station  128  wherein the empty holders  14  are unloaded onto a brush conveyor for re-use. Totes  13  can also be used to carry empty holders  14  for unloading into either of stations  112  or  122 , where empty holders  14  are then unloaded into lanes  86  for storage. 
         [0050]    The foregoing embodiment may alternatively use totes  13  for both the loading and unloading process as described in connection with  FIG. 1 . Direct loading of holders  14  into the sort lanes  86 , without first loading and unloading into totes  13 , simplifies the process and apparatus in situations where the components of the system can be deployed close to one another as shown. 
         [0051]    As is well known in the art, two and three-pass sorts can be used to obtain a greater depth of sortation. The system of the invention can be adapted to perform multi-pass sorts by providing for unloading and recirculation of the stored holders/folders through the conveyor(s) and splitter(s) using different sort logic on the second pass. The embodiment shown in  FIGS. 12-13  illustrates a system for accomplishing a two pass sort. 
         [0052]    In this embodiment, a total of forty sort lanes  136  are arranged in four rows and ten columns as shown. A bottom, eleventh level is used to provide four extraction pass through lanes  137 . Forty folder transfer conveyors  138  transport folders filled at the loading stations through one or more splitters to one of forty associated elevators  139 . Elevators  139  are configured to support each folder on rails and move it vertically to any one of the ten sort lane levels  136  or one of the bottom pass through lanes  137 . Elevators  139  and lanes  136 ,  137  are provided with pairs of bidirectional conveyor belts that are used as rails on which the hangers of the folders depend, allowing the entire contents of the lane or elevator to move in either direction. 
         [0053]    At the start of a sorting run, empty folders stored at the far end of each lane  136  are removed and circulated to the loading stations. A set of takeaway elevators  141  is provided at the opposite ends of the sort lanes  136  for removal and transfer of empty folders into the associated compartment of takeaway elevator  141  to an empty folder transfer conveyor  142 . Transfer conveyor  142  presents an empty tote  13  that receives a group of empty folders from elevator  141 . 
         [0054]    Mail in folders traveling along conveyors  138  is sorted into sort lanes  136 . Upon completion of the first sorting pass, the folders in each sort lane  136  are in this example broken down (sorted) by carrier group, but are not in carrier order. A first lane  136 A corresponds to carriers  1 - 40 , a second lane  136 B corresponds to carriers  41 - 80 , and so on until the last lane for carriers  1441  to  1600 . A second sorting pass then begins. 
         [0055]    By means of the conveyor belts associated with the sorting lanes  136 , filled folders in first lane  136 A are unloaded back out onto elevator  139 . Elevator  139  transports batches of filled folders down to a filled folder transfer conveyor  149 , which recirculates them through the sorting system. The label on the folder is re-scanned and the folder is sorted using the splitter(s) to one of the forty transfer conveyors  138 . This time, the conveyor  138  is selected by carrier. Thus, mail for carrier # 1  in the example above would be sent to conveyor  138 A, mail for carrier # 2  would be sent to conveyor  138 B, and so on to carrier # 40 . 
         [0056]    The folders containing mail pieces are allowed to accumulate in conveyors  138  until the entire sorting lane  136 A has been emptied of mail-filled folders (empty folders may remain). At that point, the folders from the first conveyor  138 A are loaded into the associated elevator  139  and transported, all at once or in groups, to the adjoining extraction pass through lane  137 . Lane  137  transports the mail to an extraction station  150  passing below elevator  141 . Upon reaching the extraction station  150 , the folders may be taken and loaded for extraction manually by a human operator or lifted using an elevator built into station  150  and automatically loaded into an extractor  151  that extracts each mail piece from the folder. Extractor  151  operates based on the same general principle as described above for opener section  47 . 
         [0057]    The operator then stacks the extracted mail into a tray for later manual casing (sorting) by the carrier into delivery order. The foregoing process is repeated for the remaining thirty nine lanes  138  until all of the mail has been sorted by carrier, extracted and trayed. Empty folders are loaded back onto the return conveyor  142  and sent to lanes  136  where they are stored until the next sorting run. A multi-pass system such as the foregoing may take longer to process the mail, but can be built more compactly than the systems of the previous embodiments. 
         [0058]    References to a control computer herein include a variety of known control strategies ranging from a single, centralized control computer that monitors and controls all aspects of the sorting process to distributed control schemes wherein a number of computers or microcontrollers monitor and control different stages of the sorting process and communicate as needed (such as through a local area network) to execute the overall sort scheme. The sort scheme is question will usually be one that takes an incoming batch of mail addressed to a common zone such as a 5-digit zip code and sorts it by destination with batches of mail to each destination in carrier delivery order. However, other sort schemes could be used as well. These batches then are eventually merged (physically matched up with) the corresponding batches of mail sorted by normal machine processing. This merging step is done manually as discussed in the background above. 
         [0059]    While certain embodiments of the invention have been illustrated for the purposes of this disclosure, numerous changes in the method and apparatus of the invention presented herein may be made by those skilled in the art. For example, tote loaders  26  could be used in the embodiment of  FIGS. 10-11  if it were necessary to transport the holders a substantial distance to reach the sorting lanes  86 . If the different components of the system can be built physically close to one another, the use of totes  13  can be omitted entirely. Such a system could resemble that described in connection with  FIGS. 10 and 11 , except that instead of unloading the holders from the sorting lanes  86  into totes, the opener  47  and tray loader  48  are located on the exit side of each sorting lane  86 . Sled  94  is used to unload batches of holders  14  directly to opener  47 , which then operates as described in connection with  FIG. 8 . These and other variations are embodied within the scope and spirit of the present invention as defined in the appended claims.