FIELD OF THE INVENTION 
   The invention relates to mail sorting machines and processes of the type currently carried out by the U.S. Postal Service (USPS). 
   BACKGROUND OF THE INVENTION 
   Barnum et al. U.S. Pat. No. 6,671,577, Dec. 30, 2003, describes a system and method for directly connecting an ISS advanced facer canceler system (IAFCS) to a DBCS/OSS. As noted in that patent, the contents of which are incorporated by reference herein, conventional mail systems now in use by the USPS process stamped mail through a plurality of separate machines, including an advanced facer canceler system/input subsystem (IAFCS), an optical character reader (OCR) machine, and a delivery bar code sorter/output subsystem (DBCS/OSS). IAFCS places incoming mail into a single file line in a pinch belt, checks for appropriate postage on mail, cancels the postage, and stacks the mail in bins. IAFCS positions the mail upright between a pair of pinch belts with either the stamp leading and the address on the front side or the stamp trailing and the address on the back side. IAFCS obtains a picture image of the stamped side of each piece of mail and prints a mail identifier (ID tag) on each mail piece on the side opposite the stamped side that is stored along with the image. The image is used to determine mail type such as printed address and script address. After canceling the postage, IAFCS sorts the mail into bins based on mail type. Each mail type has two bins, one for mail with the stamp leading and one for mail with the stamp trailing The machines that next process the mail, such as DBCS/OSS, require that all the mail be positioned with the stamp leading. An operator takes the stamp trailing mail from a bin of the IAFCS and places it in a stamp leading position to combine with the stamp leading mail before feeding into the DBCS/OSS. Based on the mail type, the operator then moves the mail to the next processing point. Mail that has been imprinted by the IAFCS with a UV bar code, ID tag, is taken directly to the DBCS/OSS. DBCS/OSS prints a bar code onto the mail by querying the IPSS system for the result of computer OCR or operator video coding associated with the ID tag of the mail. DBCS/OSS sorts the mail into a plurality of stackers based on the bar code data which reflects the mail destination. 
   A processing method according to the &#39;577 patent processes mail through a postage verifier having an optical character reader, mail interface system, and a mail sorter. The mail interface system includes an upward module carrying mail up to an overhead transport positioned at a height above an output of the postage verifier, and a downward module carrying mail down from the overhead transport to the mail sorter. The method includes verifying and canceling postage, positioning mail pieces in a same configuration in a single file line, directing mail pieces up the upward module, directing mail pieces through the overhead transport, directing mail pieces down the downward module to a mail sorter, and sorting the mail based on destination. The interface module referred to directly connects the IAFCS machine to the DBCS/OSS sorter, eliminating the need for manual transfer of mail between these machines. 
   Difficulties remain notwithstanding the potential improvement such a Direct Connect between the IAFCS machine and the sorter could provide. One such problem arises in connection with FIM (facing identification mark) mail. Facing identification marks are ⅝ inch tall vertical bars beginning at the top of the envelope near the stamp. There are 4 types of FIM: 
   FIM A: Courtesy reply and metered reply, Postnet bar code required 
   FIM B: Business reply mail, Postnet bar code not required 
   FIM C: Business reply mail, Postnet bar code required 
   FIM D: Non fluorescent IBI and PC postage, Postnet bar code not required 
   The most common usage is for “remittance” mail, FIM A and C that consists of bills being paid by customers of a utility company, for example. 
   Currently, FIM A and C are detected on the IAFCS and sorted out for special handling to reserved bins on the IAFCS. FIM A and C mail from multiple AFCS machines within a processing and distribution center, P&amp;DC, is collected and funneled to a single DBCS machine for sorting due to the time critical nature of remittance mail. If Direct Connect is implemented and the FIM mail is passed on to the DBCS/OSS and not intercepted at the IAFCS, an additional processing step is added with respect to the existing method and a corresponding undesirable delay in processing of the FIM mail is incurred. If the FIM is pulled out at the IAFCS, this causes a loss of as much as 25% of the mail from the IAFCS machines. If the Direct Connect of the &#39;577 patent is implemented under these circumstances, the DBCS/OSS sorting machine linked to the IAFCS machine becomes “starved”, that is, does not receive enough mail from the IAFCS machine to operate efficiently The present invention addresses this problem and opens up new sorting possibilities by providing a sorting machine that is in effect several sorting machines with the capability of passing mail to be sorted between them automatically. Consolidation of inputs from multiple front ends eliminates the need for secondary sorting operations to alleviate partial trays of mail. 
   Edmonds U.S. Patent Publication 20030208298, Nov. 6, 2003, describes a method and system for single pass letter and flat processing. As part of the process, the &#39;298 publication notes that use of two interconnected OCR sorting machines expands the capacity of such machines over the two machines used separately. However, this publication provides no specific guidance as to how such capability should be implemented. 
   SUMMARY OF THE INVENTION 
   The present invention provides a sorting system using multiple sorters operating as part of a single, multi-sorting machine unified system or “supercell”. A sorting system according to the invention includes a plurality of input sections capable of operating in parallel, each including a feeder that takes in mail pieces one at a time and a scanner that scans each mail piece for destination indicia, a plurality of stackers each comprising at least one row of pockets, a control system that determines a destination pocket in the stacker for each mail piece based on a predetermined sort scheme and the destination indicia, and a routing system effective to route mail in accordance with the sort scheme from any input section to any pocket of a stacker. For purposes of the invention, “destination indicia” refers to an ID tag which is associated with stored address information, a bar code which gives the information, or a written address read using OCR. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, where like numerals denote like elements and letters (A, B, C, etc.) denote multiples of a component: 
       FIG. 1  is a perspective view of a known mail sorting machine; 
       FIG. 2  is a schematic diagram of a mail sorting machine according to the invention; 
       FIG. 3  is a three-dimensional representation of the machine of  FIG. 2 ; 
       FIG. 4  is a plan view of the machine of  FIG. 2 ; 
       FIG. 5  is a schematic diagram of a (2:4) merge used in the invention; 
       FIG. 6  is a schematic diagram of four (2:1) merges used in the invention; 
       FIG. 7  is a schematic diagram of a control system for the machine of the invention as shown in  FIGS. 2-6 . 
   


   DETAILED DESCRIPTION 
   In a typical postal sorting machine as shown in  FIG. 1 , the machine  10  includes a feeder/singulator  12  where an unordered stack  14  of mail pieces are loaded for sorting. Feeder  12  singulates and transfers or conveys the mail pieces to a scanner  18  such as a bar code scanner or an optical character recognition (OCR) apparatus. Scanner  18  reads destination information from the mail pieces and transmits the information to a control computer  20  which stores the destination information and identifies the bin  22  where the mail piece is to be directed. One or more conveyors  16  convey the mail pieces to a plurality of diverters in a stacker section  24  which contains bins  22 . This type of sorting machine is well known in the art and comes in a variety of types, such as Delivery Bar Code Sorter (DBCS) and DIOSS. A DIOSS machine is a Delivery bar code sorter (DBCS) with an optical character reader Input/Output SubSystem (IOSS). The present invention involves physically separating the stacker  24  of each sorter from its upstream components, referred to herein as an input section that includes at least feeder  12  and scanner  18 . 
   The present invention exploits an aspect of the existing multi-level stacker designs in that any single level is capable of sorting mail at a rate equal to the feed rate of the front end. Thus, a stacker line with four stacker levels is theoretically capable of sorting mail at four times the rate of the feeder of an OSS or DIOSS front-end with randomly distributed mail. Statistically, a four times advantage is not achievable due to normal distributions, but a two times advantage is. 
   Referring to  FIGS. 2 ,  3  and  4 , a mail sorting system  30  according to the invention receives mail from several (e.g. 2 to 4) IAFCS machines  31  that operate in parallel on incoming collection mail. Each IAFCS  31  is an Integrated Automated Facer-canceler System of a type now in use by the U.S. Postal Service that culls, faces, cancels, prints an ID tag and lifts a video image of the mail. Output from these machines  31  is transported to an associated input section  32 . Each input section  32  preferably includes both an OSS  33  and a DIOSS  34  which operate at the same time. OSS  33  receives canceled mail from IAFCS  31  either by means of a direct conveyor connection as described in Barnum et al. U.S. Pat. No. 6,671,577, Dec. 30, 2003, the contents of which are incorporated by reference herein, or by manual loading of an associated feeder. OSS  33  reads an ID tag put on by IAFCS  31  and sprays the corresponding Postnet bar code onto each mail piece, which is then sorted according to the sort scheme as explained further below. DIOSS  34  receives mail that does not require cancellation, primarily metered and permit mail, through its feeder  36 . DIOSS  34  prints an ID tag on each mail piece and, if resolved by the online encoding system, prints a Postnet bar code on the mail piece. The destination for each mail piece leaving each input section  32  is provided to a computerized control system  37 . 
   Mail from either source exits input section  32  and enters a routing section  40  that is interposed between input sections  32  and a series of stackers  41 . The specific design of routing section  40  will vary to some extent depending on the number of input sections and stackers associated with it. In this example, eight input machines  33 ,  34  are linked to four 254 pocket stacker lines each having four rows of pockets at different elevations, but the number of components on each side of routing section  40  does not necessarily have to be 2:1 as discussed further below. Control system  37  operates the diverts of routing section  40  in a manner effective to direct each mail piece to any one of the stackers  41 , depending on the sort scheme. 
   While a variety of vertical and horizontal conveyor systems are known in the art, to create routing system  40  successfully, certain principles should be observed. First, the average volume of mail on any one section of transport cannot exceed the average output of one DIOSS or OSS input, assuming a random distribution at input. This may require adjustment of the pinch belt transport speeds, for example, using a faster belt speed at the takeaway portion of a merge. Second, mail held in pinch belts vertical to the earth may be turned or diverted along a horizontal plane, whereas this is difficult to do with mail held horizontally. Third, mail held in pinch belts horizontal to the earth may be turned or diverted in a vertical direction, i.e. can readily change elevation. The following description of routing section  40  illustrates these principles. 
   Mail entering routing section  40  from one of the input sections  32  first enters a 2 to 4 (2:4) merge section  42 .  FIG. 5  illustrates one of the (2:4) merges  42 . Mail from a first OSS  33  travels along a vertical pinch belt conveyor to a first vertical divert  51 A where it is routed either straight ahead to a first merge  52 A or diverted to a second merge  52 B, depending on the ultimate destination. A vertical divert for purposes of the invention is one that diverts the mail while it is in a vertical position, and a horizontal divert is one which diverts the mail while the mail is in a horizontal position. 
   Mail from a first DIOSS  34  travels along a vertical belt conveyor to a divert  51 B where it is routed either straight ahead to second merge  52 B or diverted to first merge  52 A, again depending on the ultimate destination. For this purpose, although it could be avoided by designing OSS  33  and DIOSS  34  pairs at different elevations, the mail pieces pass through an intersection  53  where the conveyor paths pass through one another. For this purpose, (2:4) merges  42  are preferably each provided with input buffers  36 A,  36 B, which may for example be a feeder capable of holding 1 to 3 mail pieces in a vertical stack, taking them in on an input side and ejecting them on a output side after a short delay in first-in, first-out order. Buffers  36 A,  36 B are controlled as described hereafter to ensure that collisions between mail pieces passing through intersection  53  are avoided and each mail piece is diverted to its correct destination. Diverts  51  and merges  52  may be of types known in the mail sorting art. Shifting wedge-type diverts  51  may be used. 
   Mail conveyed from each merge  52 A,  52 B enters a pair of twist sections  56 A,  56 B wherein the belt path changes from vertical to horizontal as illustrated in the three-dimensional  FIG. 3 . Twist sections as described herein are pinch (dual) belt conveyors wherein the orientation of the belts gradually changes due to the layout of the supporting rollers as the belts move along. Once horizontal, the mail stream from merge  52 A is taken to a different (in this case, higher) elevation than the mail stream from merge  52 B. A pair of horizontal diverts  57 A,  57 B then further divide the mail streams from twist sections  56 A,  56 B into four mail streams carried by horizontal pinch belt conveyors  58 A 1 ,  58 A 2 ,  58 B 1  and  58 B 2 , each at a different elevation. Conveyors  58 A 1 , A 2 , B 1 , B 2  then each enter a second twist section  59  wherein each conveyor assumes a vertical orientation. 
   In the embodiment shown, the inputs for the entire system  30  are divided into two sections  59 A,  59 B each receiving input from 2 OSS and 2 DIOSS machines. Sections  59 A,  59 B each have two 2:4 merges  42 A,  42 B and  42 C,  42 D which are essentially identical as shown in  FIGS. 2-4 . The mail streams from left and right merges  42 A,  42 B and  42 C,  42 D must next be merged such that all mail from any one of the OSS or DIOSS machines in that section  59 A or  59 B intended for a specific sorter  41 A-D is brought together. Four (2:1) vertical merges  60 A- 60 D per section are provided for this purpose as shown in  FIGS. 4 and 6 . 
   Each (2:1) merge section  60 A- 60 D receives one mail stream from section  42 A and a matching mail stream merge  42 B destined for the same stacker  41 . For this purpose, each merge  60  includes a pair of buffers  61 A- 61 D which feed mail pieces to path merges  62 A- 62 D, respectively. The conveyors leading away from path merges  62  then comprise a 4-level vertical transport section  63  of the routing system. In transport section  63 , mail pieces from each section  59 A,  59 B destined for the same stacker  41  are brought together at four (2:4) merges  71 A-D. This requires, in the case of mail pieces needing to cross the system from one side to the other, relatively long lateral conveyor spans  66  that are spaced apart vertically as shown in  FIG. 3 . For this purpose, “crossing the system” means, for example, a mail piece entering from leftmost input section  32  that must be routed to rightmost stacker  41 . 
   Merges  71 A-D may be functionally the same as merges (2:4) merges  42  shown in  FIG. 5 , but with differences in the layout of the conveyor pathways as shown in  FIG. 3 . The output from merges  71 A-D is at four different elevations corresponding to each level of the associated stacker  41 A- 41 D. Preferably, each (2:4) merge  71 A- 71 D has associated buffers  72 A,  72 B capable of holding from 1 to 3 mail pieces at a time. Buffers  72  are operated by control system  37  to ensure that jams do not occur at (2:4) merges  71 A- 71 D. 
   Mail entering one of stackers  41 A-D enters at one of the four levels and is sorted to the pocket assigned by the sort scheme. The system of the invention is intended for use at postal P&amp;DC&#39;s for sorting according to high level sort schemes, e.g. by 3 or 5 digit zip codes. However, with a larger number of pockets available, more refined sort schemes become possible wherein fewer sorts to the 3-digit level need to be made. As such, mail sorted using the system of the invention is well suited for use with a single pass sorting system that sorts to carrier sequence order, such as the one disclosed in Pippin et al. U.S. Patent Application 20030038065, published Feb. 27, 2003, the contents of which are incorporated by reference herein. 
   FIM mail from all eight input machines is preferably funneled to one stacker or stacker row(s), where some of the pockets are assigned to specific high volume FIM recipients, some national and some local. As a result, FIM mail is handled in a manner which causes no delay in operations and does not “starve” a sorter directly connected to an IAFCS machine, as may happen in the system described Barnum et al. U.S. Pat. No. 6,671,577. 
   Stackers  41  may be of the conventional type which must be swept manually by postal workers during and after sorting. The stacks of mail are then loaded into trays for transport at a nearby traying station. In the alternative, the stackers may use cartridges in the manner described in U.S. Pat. Nos. 6,390,756, 6,183,191, 6,135,697, 6,026,967, 5,993,132, 5,947,468, 5,857,830 and 5,833,076, the contents of which patents are incorporated by reference herein. The mail cartridges are not used for two pass sorting, but instead are removed by a robot  91  and transported to a storage rack  92  and ultimately to an unloading table or machine which unloads the mail into a postal tray. Such an unloading machine is described in Isaacs U.S. Pat. No. 6,238,164, May 29, 2001, the contents of which are incorporated by reference herein. 
   Control system  37  according to the invention could comprise a single computer that reads all the incoming mail pieces and determines respective sorting destinations, as well as controls all buffers, sorting gates and diverts in order to conducting each mail piece through the routing system to the correct stacker pocket. However, referring to  FIG. 7 , it is preferable that such a system comprise several computers, including a set of processors  81  for each OSS or DIOSS machine that are programmed to determine the sorting destination and transmit that information to a master control computer  82 . In lieu of attempting to track the movements of the entire mail stream moving through the routing system at any given time, it is preferred that each mail piece be tracked by its ID tag at certain strategic locations in the system. Each IAFCS and DIOSS machine applies an ID tag, such as an ultraviolet-detectable bar code, onto all mail pieces passing through, and computer  82  maintains a table of ID numbers and associated destination pockets according to the sort scheme. 
   Each buffer  36 ,  72  has associated therewith a local controller  83  which controls the operation of the buffer and the immediately downstream diverters,  51 A-B and  57 C-D, that act in coordination with the buffer to ensure that each mail piece is diverted in the correct direction. Each buffer  36 ,  72  also has a tag reader  84  that reads the ID tag on each mail piece entering the buffer, sends the number to master computer  82 , and receives back instructions on how to divert that mail piece. By this means, it does not matter in what order mail pieces arrive at each buffer  72 , as long as each piece is diverted to the correct destination. A mail piece that reaches a buffer  72  in error is directed by master computer  82  to a special reject pocket on that stacker for later re-processing. Buffers  61 A- 61 D, which are not associated with any diverts, need not have a tag reader or computerized controller beyond what is needed to avoid jams in the downstream merges  62 . 
   In variations of the system according to the invention, the number of input feeders and stackers may be varied to some extent. For purposes of designing the routing system, it is much preferred that the number of input sorters be twice the number of stackers, and that this number be an even number, 2, 4, or 8 being most likely for practical purposes. In a system with only 2 input sorters, e.g., one OSS and one DIOSS operating in parallel, the routing system can be simplified to include only the first 2:4 merge which feeds directly to each level of a single stacker. A system twice the size of the illustrated embodiment would be possible, but the routing system would become much more complex, with sufficient diverts and merges to take a mail piece to any one of 32 levels in eight stackers. A system missing one input, i.e. 7 inputs for 8 stackers, or where one of eight inputs is out of service, could operate using the same routing system as described above or simplified for the portion of the routing system connected to the single input. For practical purposes, the preferred number of input sorters is between 6 and 8, with a corresponding number of stackers. These and other variations will occur to those skilled in the art and are within the scope of the claims presented hereafter.
A sorting system using multiple sorters operating as part of a single, multi-sorting machine unified system. The system according to the invention includes a plurality of input sections capable of operating in parallel, each including a feeder that takes in mail pieces one at a time and a scanner that scans each mail piece for destination indicia, a plurality of stackers each comprising at least one row of pockets, a control system that determines a destination pocket in the stacker for each mail piece based on a predetermined sort scheme and the destination indicia, and a routing system effective to route mail in accordance with the sort scheme from any input section to any pocket of a stacker.