Abstract:
A method of singulating and feeding a random mix of thick and thin flat articles includes: (a) sensing whether a flat article is positioned on a feed conveyor in a position for removal from the feeder conveyor with a sensor, (b) advancing the feed conveyor with a first motor an incremental step to place a series of flat articles positioned on edge in a position for removal from the feed conveyor each time the sensor detects the absence of a flat article for removal from the feed conveyor, (c) counting each incremental advance of the feed conveyor, (d) incrementally advancing the stack of flat articles with a jogger driven by a second motor after the feed conveyor has moved a predetermined number of incremental steps to load additional flat articles on the feed conveyor, the jogger tending to edge the flat articles for removal from the feed conveyor; and (e) repeating steps (a)-(d) while sequentially removing flat articles from the feed conveyor on a one-by-one basis as the feed conveyor is advanced. The method is implemented with a feeder comprising a belt type feeder conveyor, a chain driven, finger type jogger and a belt type entry conveyor where the flat articles and/or mail pieces are loaded edgewise.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus, system and method of feeding flat articles to a sorter, and in particular, feeding mail items to an automated mail processing machine such as a mail sorter. 
     BACKGROUND OF THE INVENTION 
     Modern postal services, for example, the U.S. Postal Service, handle massive volumes of mail pieces on a daily basis. Machines for receiving and sorting these massive volumes of letter mail are known. Typically, such machines are adapted to receive large volumes of flat articles and sort the articles into a plurality of pockets or bins based upon selected criteria. In the case of letter mail, the criteria is associated with the destination of the individual mail pieces which may be an indicia such as a Zip+4 destination code. Typically, such sorting machines have a feeding station, sensing and detecting equipment for determining the appropriate output compartment or pocket for the article to be sorted and diverting gates or other mechanisms for selectively diverting articles to selected ones of an array of output compartments or pockets for the sorted articles. An example of an advanced sorting machine is the DBCS sorting device, available from Siemens ElectroCom, L.P., Arlington, Tex. 
     Devices for singulating and feeding mail pieces to a sorting machine are known. One such apparatus is disclosed in U.S. Pat. No. 5,947,468, the disclosure of which is incorporated by reference for all purposes. Such devices however, do not meet all the existing needs in terms of processing different types of flat articles. Ideally, the feeder/singulator of a mail sorting machine as described above would have the capability of handling stacks of flat articles of varying thickness while maximizing throughput. However, feeding and singulating a stack of flat articles including thin flat items such as letters, and thicker packages such as packaged catalogues, for example up to ½ inch, presents a number of difficulties. For example, when thick flat articles are fed one-by-one from a stack of flat articles, the volume of the stack is reduced rapidly. Conversely, when thin, flat articles are fed, the volume of the stack is reduced at a much slower rate. Existing feeder/singulation methods and apparatus do not provide for feeding a stack of flat articles having varying thicknesses, such as mail pieces, while simultaneously maximizing throughput. The present invention addresses this drawback. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention comprises a method of singulating and feeding a random mix of thick and thin flat articles including: (a) sensing whether a flat article is positioned on a feed conveyor in a position for removal from the feeder conveyor with a sensor, (b) advancing the feed conveyor an incremental step with a first motor to place a series of flat articles positioned on edge in a position for removal from the feed conveyor each time the sensor detects the absence of a flat article for removal from the feed conveyor, (c) counting each incremental advance of the feed conveyor, (d) incrementally advancing the stack of flat articles with a jogger driven by a second motor after the feed conveyor has moved a predetermined number of incremental steps to load additional flat articles on the feed conveyor, the jogger tending to edge the flat articles for removal from the feed conveyor; and (e) repeating steps (a)-(d) while sequentially removing flat articles from the feed conveyor on a one-by-one basis as the feed conveyor is advanced. The method is implemented with a feeder comprising a belt type feeder conveyor, a chain driven, finger type jogger and a belt type staging conveyor where the flat articles and/or mail pieces are loaded edgewise. The stack of mail pieces is advanced from the staging conveyor to the jogger and then to the feed conveyor from which the flat articles are removed with a take off device, such as a vacuum assisted belt conveyor oriented perpendicular to the feed conveyor. The staging conveyor, jogger and feed conveyor are each provided with a separate drive motor, allowing each to be controlled independently and operated at a different speed, which in turn allows dynamic control of the feeder system. The jogger motor is energized after the feed conveyor motor turns a predetermined number, for example 6-8 “ticks” i.e., rotations or fractional rotations of the motor that are registered and counted with an internal clock like sensor. The number of ticks required to activate the jogger will depend upon the particular design of the feeder system, including the relative linear velocities of feeder conveyor  16  and jogger  16 , the spacing of the jogger fingers and other criteria specific to a particular application. After the jogger is activated, it advances until a jogger finger sensor detects a jogger finger moving into proximity to a jogger finger sensor at which time the jogger motor is deactivated, stopping the jogger. 
     In this aspect, the method includes loading the staging conveyor with flat articles and incrementally advancing the stack with the staging conveyor to load additional flat articles on the jogger after the feed conveyor has moved a predetermined number of incremental steps. When the staging conveyor is loaded, a paddle is placed at the end of the stack to hold the stack as it is carried to the jogger. The staging conveyor is preferably provided with a series of centrally positioned perforations or holes that extend the length of the conveyor into which a tab or projection of the paddle is inserted so the staging conveyor carries the paddle as it advances. The feeder is also equipped with one or more paddle sensors which detect the paddle as it moves to different locations such as a staging paddle sensor that senses the paddle as it approaches the end of the staging conveyor and signals the feeder controller to deactivate the unit until the staging is reloaded with addition flat articles. 
     In another aspect, the jogger imparts a bouncing motion to the stack of articles as it carries the articles to the feed conveyor. The bouncing motion is imparted with one or more shafts having at least one flattened surface that rotate between the fingers of the jogger. The bouncing motion of the jogger tends to separate and edge or align the flat articles vertically and horizontally as the articles are conveyed. Stack separation fingers, driven by the jogger create temporary gaps in the stack as the stack is conveyed from the staging conveyor to the jogger. The separation fingers are preferably actuated with a rotary cam driven by the jogger, however, the operation of the separation fingers could be initiated with a sensor or timer depending upon the particular design and application. 
     In yet another aspect, according to the invention, a feeder for a mail sorter includes a controller, a horizontal entry belt conveyor, a jogger which receives a stack of mail from the entry conveyor on edge and aligns the stack as it passes through the jogger and a horizontal feeder belt conveyor that receives the stack in increments from the jogger. An upright take off mechanism at an end of the feeder conveyor opposite the jogger sequentially removes the frontmost mail piece from the stack, conveying each piece sideways and feeding a singulated stream of mail pieces to the mail sorter. A repositionable paddle mounted on a rail above the conveyors and jogger supports a rear end of the stack of mail pieces as it moves through the feeder. A plurality of paddle sensors each signal the controller when the paddle is in proximity of the sensor. In particular a paddle sensor positioned adjacent to the end of the entry conveyor signals the controller to shut the feeder down when the paddle reaches the sensor. 
     Operation of the feed conveyor is controlled with a switch positioned adjacent to the take off device that determines when a frontmost mail piece is in sufficient engagement with the take off mechanism for the take off mechanism to remove the frontmost mail piece from a stack of mail. When a mail piece is not present, the feed conveyor motor is cyclically advanced in increments until the foremost mail piece is detected. A sensor or switch associated with the feeder conveyor motor signals the controller that counts each incremental advance of the feeder conveyor and incrementally advances the jogger to feed additional mail pieces onto the feeder conveyor when a predetermined number of incremental advances of the feeder conveyor has occurred. In a preferred embodiment, the take off mechanism comprises a vertical belt type conveyor and a jogger sensor is provided for detecting an incremental movement of the jogger. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects of the invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements, and: 
     FIG. 1 is a perspective view of a mail feeder in accordance with the invention; 
     FIG. 2 is partial top view of the feeder of FIG. 1; 
     FIG. 3 is a second side view of the feeder of FIG. 1 illustrating the process of loading the feeder; 
     FIG. 4 is a third side view of the feeder of FIG. 1 wherein the feeder is fully loaded and operational; 
     FIG. 5 is a partial cut away perspective view of a jogger suitable for use in a feeder in accordance with the invention; and 
     FIG. 6 is partial perspective view of the jogger of FIG. 5; 
     FIG. 7 is a partial side view of the jogger of FIG. 5; and 
     FIGS. 8-10 are schematic representations of the feeder of FIGS. 1-4 at different stages of operation. 
    
    
     DETAILED DESCRIPTION 
     While the invention is described below with reference to one or more preferred embodiments, the description is not intended to be construed in a limiting sense. Various rearrangements of parts, modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. 
     Referring to FIGS. 1-4, a feeder system  10  for implementing the method of the invention includes an entry or staging conveyor  12  where an operator loads a stack  14  (FIG. 3) of flat articles, such as mail pieces, for feeding to a sorting or similar processing machine, such as the DBCS sorting device referred to above. Preferably, staging conveyor  12  is a horizontal belt-type conveyor, including a plurality of spaced apart perforations or holes  13  running centrally along the length of the belt. Staging conveyor feeds stacked mail pieces to a horizontal jogger type conveyor  16  including a plurality of fingers  18 . Jogger  16  in turn feeds the stack of mail pieces to a horizontal feeder conveyor  20  which, similar to staging conveyor  12 , is a belt type conveyor including spaced apart perforations or holes  13  spaced along the length of the belt. Staging conveyor  12 , jogger  16  and feed conveyor  20  are each individually driven with motors  24 ,  26  and  28 , each using a conventional belt or chain drive (not shown). Feeder  10  is also provided with covers  38 ,  36  that span the gaps between jogger  16  and staging conveyor  12  and feed conveyor  20  and jogger  16  to prevent mail pieces from falling between the conveyors. 
     In operation, feed conveyor  20  advances the stack  14  of flat articles as an upright takeoff conveyor  30  pulls articles from the stack on a one-by-one basis and feeds the flat articles to a second set of upright, opposed belt conveyors  31 ,  31 ′. Preferably, takeoff conveyor  30  is a perforated belt type conveyor wherein a vacuum is applied through the perforations to hold flat articles against the belt. As best shown in FIG. 2, takeoff conveyor  30  is mounted perpendicular to feed conveyor  20  for receiving a flat side of articles advanced against the belt by feeder conveyor  16 . A spring loaded slide  32 , biased toward conveyor  31 , is positioned next to take off conveyor  30  guides and includes a guide  33  that holds mail pieces against conveyors  30  and  31  as the mail pieces are conveyed from the feeder. Guide  33  is preferably formed from a plastic material having a higher coefficient of friction than take off conveyor  30 . Thus, if a pair of flat articles double up or overlap as the articles are picked off of stack  14  by take off conveyor  30 , guide  33  will retard the overlapping article, while the article abutting take off conveyor  30  is advanced, separating the overlapping articles. After the article in contact with take off conveyor  30  is moved past the overlapping article, the overlapping article is then advanced. Slide  32  is moveable between a closed, engaged position with guide  33  positioned against take off conveyor  30 , an open, non-engaged position in which guide  33  is retracted from take off conveyor  30 . Slide  32  includes a micro switch  34  which de-energizes feeder  10  when the slide is in the open position. Since slide  32  is spring loaded, when engaged with guide  33  positioned against conveyors  30  and  31 , the slide may move a limited distance away from take off conveyor  30  to accommodate the passage of thick articles conveyed by the take off conveyor. 
     Turning to FIGS. 1, and  5 - 7 , jogger  16  conveys flat articles from staging conveyor  12  to feed conveyor  20  with a plurality of fingers  18  mounted on finger brackets  19  that engage stack  14  at the transition from the staging conveyor  12 , carry the stack along length of jogger  16  and disengage from the stack as it approaches the feed conveyor  20 . As shown, each bracket carries a row of three fingers mounted in spaced apart relationship on the bracket. It will be appreciated that a row of fingers  18  may be integrally formed with a bracket  19  by means of, for example, injection molding of an appropriate plastic or similar material. Fingers  18  move between and along a plurality of rotating shafts  42  that contact the bottom of stack  14  and are driven in clockwise direction as viewed from staging conveyor  12 . Each of shafts  42  includes at least one flattened surface  43  that provides a bouncing or jostling movement to the stack  14  as the stack is conveyed along the length of jogger  16 . 
     As best shown in FIGS. 5-7, brackets  19  are mounted on and carried by one or more chains  44  passing around a plurality of sprockets  46  in conjunction with guide slots  48  formed in sidewalls  49  of jogger  16 . As chains  44  carry brackets  19  and fingers  18 , guide pins  51  carried by brackets  19  engage guide slots  48 , guiding the fingers  18  through an elongated closed path. As the chain passes over sprocket  46 ′ at the entry end of jogger  16 , fingers  18  are carried upwardly between shafts  42  to engage the stack  14  of mail pieces. As shafts  42  rotate, the flat sections  43  of the shaft impart a small jostling or bouncing motion to mail pieces and urge the mail pieces against wall  49  as the fingers carry the mail pieces along the jogger  16 . It will be appreciated that the same bouncing or jostling effect may be imparted with an eccentrically formed shaft. An additional edging shaft  45 , also having at least one flattened surface  47 , is mounted in the back wall  52  of jogger  16 . Shaft  45  rotates counterclockwise as viewed from staging conveyor  12  to urge mail pieces fed by jogger  16  down against shafts  42  as the mail pieces travel along the jogger. In addition to edging the mail, the bouncing action provided by flattened surfaces  43  and  47  of shafts  42  and  45  tends to separate the mail pieces and cause any mail pieces that are held in an elevated position by pressure from abutting mail pieces to move down so that the bottom edge of such mail pieces are aligned with the rest of the stack of mail being carried by jogger  16 . 
     Referring to FIGS. 1,  5 ,  7  and  7 A in order to allow jogger  16  to engage and smoothly separate stack  14  into increments corresponding to the distance between fingers  18 , a cover  38  is positioned between staging conveyor  12  and jogger  16 . Cover  38  includes a plurality of extensions  41  separated by a first set of slots  37  through which fingers  18  rise up into stack  14 . Timing belts  39  are positioned in a second slot  40  in one or more of extensions  41  and urge stack  14  across the cover  38 , facilitating the transfer of the stack onto the jogger. As fingers  18  are advanced, jogger motor  26  simultaneously drives a cam  58  connected to a set of stack separating fingers  54 . As motor  26  advances the jogger, cam  58  drives stack separating fingers  54  upward, lifting the fingers  54  upwardly in slots  37  in cover  38  to engage the bottom of mail stack  14  (FIG.  6 ). Separating fingers  54  slip between adjacent mail pieces and hold back the bottom edges of mail pieces behind the separating fingers creating a temporary gap. Timing belts  39  aid in the process, urging the bottom of the stack  14  forward as fingers  54  are lifted by cam  58  to create the temporary separation in stack  14 . As jogger  16  advances, a set of fingers  18  rise up into the temporary gap, sliding into stack  14  without lifting mail pieces out of the stack. After fingers  18  have engaged the stack, cam  58  lowers separating fingers  54 , releasing the stack and allowing it to continue to advance. 
     Referring again to FIGS. 1-4, a paddle rail  60  is positioned adjacent to and extending along conveyor  12 , jogger  16  and feed conveyor  20  for mounting one or more slidable paddles  62 . Paddle  62  is configured slide on rail  60  along feeder  10  immediately above conveyors  12 ,  16  and  20 . In operation, the operator positions paddle  62  to engage a tab  63  extending downwardly from the bottom edge of paddle  62  with a hole  13  in one of belt conveyors  12 ,  16  so that the paddle is pulled by the conveyor along rail  60  as the conveyor advances. To engage paddle  62  with jogger  16 , the operator positions the paddle between adjacent sets of fingers  18 . In this manner paddle  62  may be carried by conveyors  12  and  20  or jogger  16  in a manner so as to hold a stack of mail pieces together as the stack travels along feeder  10 . 
     Feeder system  10  includes a staging paddle sensor  64 , a jogger paddle sensor  66  and an end position sensor  68  for detecting the presence of the paddle at various locations along feeder  10 . Feeder system  10  also includes a jogger finger sensor  72  which detects a finger  18  of jogger  16  as it passes the sensor. Feeder  10  further includes “feeder empty” switches  70   a ,  70   b ,  70   c  and  73  for detecting the absence of mail pieces on the feeder. Sensors  64 - 70   a ,  70   b ,  72  and  73  may be proximity sensors, pressure sensors, micro switches, optical sensors or similar known devices or a combination thereof, depending upon the particular design and application. For example, as illustrated in FIG. 6, each of fingers  18  may be equipped with a permanent magnet  74  and finger sensor  72  may be a magnetic proximity switch that registers each time a finger passes the sensor. In one embodiment, sensor  70   c  (FIG. 10) comprises an optical sensor positioned to scan in the direction of jogger  16  to detect the first mail piece in a stack of mail pieces. Output signals from sensors  64 - 70   a ,  70   b ,  70   c ,  72  and  73  along with slide switch  34  are fed to a control unit  76  that controls the operation of motors  24 - 28  and take off conveyor  30  as set forth below. Control unit  76  may be a microprocessor including preprogrammed instructions or a board with hardwired control logic for controlling the operation of feeder  10 . 
     Referring to FIG. 8, feeder  10  is schematically represented in an empty state. To fill feeder  10  with mail pieces, an operator initially opens slide  32  which in turn opens slide switch  34 , de-energizing motors  24 - 28 . Feeder system  10 , including motors  24 - 28  and take off conveyor  30  remain de-energized so long as slide switch  34  remains open. After opening slide  32 , the operator positions paddle  62  between two adjacent fingers  18  of jogger  16 . After positioning paddle  62  between fingers  18 , the operator loads staging conveyor  12  with a stack  14  of mail pieces positioned on edge as shown in FIGS. 3 and 9, holding the end of the stack in position manually or with a second paddle (not shown). The operator then closes slide  32 , which in turn closes slide switch  34 , activating feeder system  10  and starting motors  24 - 28 . 
     Conveyor  12  and jogger  16  advance the stack  14  to the end of jogger  16  at which time the operator lifts the paddle to clear cover  36 , re-engages paddle  62  with feed conveyor  20 . When feeder conveyor advances the paddle to a position adjacent to end position sensor  68  the operator opens slide  32 , which deactivates or shuts down feeder system  10 , including motors  24 - 28  and take off conveyor  30 . The operator then refills staging belt  12  with additional mail and positions paddle  62  to the end of mail stack  14  as illustrated in FIGS. 4 and 10. The operator then starts feeder  10  by closing slide  32 , after which feed conveyor  20  advances the mail stack  14  to take off conveyor  30 . Feeder  10  then switches to a normal operating mode in which conveyor  30  conveys mail pieces from stack  14  on a one-by-one basis to form a singulated stream of mail pieces suitable for input to a downstream processing device such as an automated mail sorting machine  80  (FIG.  1 ). In the normal mode, feeder  10  operates automatically, without operator intervention, until it becomes necessary to re-fill staging conveyor  12  with additional mail as described below. 
     During the feeder fill process, controller  76  operates in a prime mode. In the prime mode, motors  24 - 28  will not stop if staging paddle sensor  64  or jogger paddle sensor  66  senses paddle  62 , allowing feeder  10  to fill without stopping. During the fill process, the operator must lift paddle  62  as required to clear covers  36  and  38  and reposition the paddle is conveyed by staging conveyor  12  to jogger  16  and then to feed conveyor  20 . In the prime mode, staging belt  12  is advanced in small increments to allow jogger  16  and feed conveyor  20  to smoothly fill with mail pieces. At the end of the fill process, when end position sensor  68  detects the presence of paddle  62 , controller  76  switches from the prime mode to its normal mode. 
     In the normal mode, feed conveyor  20  is dynamically controlled with feeder empty switches  70   a  and  70   b  which are spring loaded micro switches with arms  71   a ,  71   b  extending through longitudinal slots in take off conveyor  30 . When arms  71   a  and  71   b  are depressed by stack  14 , closing switches  70   a  and  70   b , motor  28  that drives feed conveyor  20  is deactivated. If the foremost mail piece in the stack is tilted so as to depress only one of arms  71   a ,  71   b , the conveyor continues to advance, forcing the mail piece into an upright position such that both arms  71   a ,  71   b  are depressed. This feature prevents take off conveyor  30  from conveying a mail piece from the stack in a misaligned orientation which could result in jamming the feeder. Alternatively, if a back up switch  73  is depressed, feeder conveyor  20  is deactivated. Back up empty switch  73  includes a spring loaded arm  75  and provides a functional redundancy to switches  70   a ,  70   b . If a mail piece in a stack is too small or positioned too far to the outside of stack  14  to engage and depress arms  71   a ,  71   b , it will depress switch  73 , deactivating feed conveyor  20 . 
     As mail pieces are removed from stack  14 , allowing either arm  71   a ,  71   b  or  75  of switches  70   a ,  70   b  and  73 , respectively, to extend, motor  28  is activated, driving feed conveyor  20  until the arms are again depressed by the stack  14 . Switches  70   a ,  70   b ,  70   c  and  73  also control take off conveyor  30 , and in particular, optical sensor  70   c  which detects the absence of mail pieces on conveyor  30 , deactivating the conveyor when feed conveyor  20  is empty. Thus, in the normal mode, operation, feed conveyor  20  feeds stack  14  of mail pieces to take off conveyor  30  which removes the mail pieces from the stack on a one-by-one basis, producing a singulated stream of mail pieces that are directed to a mail sorting machine  80  for scanning and sorting into individual bins based upon the scanned information. 
     In order to maximize the throughput of feeder system  10  as a stack comprising a random mix of thick and thin mail pieces is singulated and conveyed by the feeder, feed conveyor  20  is dynamically controlled to operate in a rapid cyclic manner. In order to provide such a rapid cyclic or incremental operation, motor  28  is equipped with an internal or external clock that registers rotation of the motor with “ticks,” each corresponding to a whole or fractional rotation of the motor. Motor  28  advances feed conveyor  20  in increments corresponding to these “ticks” whenever empty sensor or switches  70   a-b  indicates that no mail piece is positioned against take off conveyor  30 . If arms  71   a-b  of switches  70   a-b  are not depressed by a mail piece, motor  28  is energized to advance one “tick.” If arm  71  is still not depressed, motor  28  is again energized to advance another “tick.” Motor  28  cycles in this manner until arms  71   a-b  are depressed, indicating that the foremost mail piece is in sufficient engagement with take off conveyer  30  to be conveyed. 
     In order to facilitate this rapid cyclic on-off operation while simultaneously maintaining a throughput approximating the capacity of jogger  16 , feed conveyor  20  is configured so as to be operated at a faster rate than jogger  16 , for example at a maximum linear velocity two to six times greater than jogger  16 . In a preferred embodiment, feed conveyor  20  advances at a linear velocity four times faster than jogger  16 . 
     Dynamic control and incremental or cyclic operation of feed conveyor  20  with empty sensors or switches  70   a ,  70   b  and  73  allows the conveyor to advance at a rate proportional to the rate at which take off conveyor  30  is removing mail pieces from stack  14 , irrespective of whether relatively thick or thin articles are conveyed at a given moment. As used herein the term “thin” is used to characterize flat articles or mail pieces having a thickness corresponding to a typical letter or even a post card having a thickness of {fraction (1/16)} inch or less. Alternatively, “thick” flat articles or mail pieces may comprise packaged catalogs or similar items having a thickness from {fraction (1/16)} inch up to ½ inch. As will be appreciated, on a volume basis, a stack of thick articles can be processed through a singulator such as feeder  10  more rapidly than a stack of thin articles. Thus, when a stack of mixed thin and thick articles are processed through a conventional feeder, the feeder must be operated at a rate low enough to process a stack comprising only thin articles. However, in a method and apparatus according to the invention, dynamic control of the feed conveyor allows feeding of a stack of mail pieces or flat articles comprising both thick and thin articles at a variable rate, allowing a high rate of throughput. 
     For example, when one or more thick mail pieces are removed from feed conveyor  20  leaving a temporary gap in stack  14 , sensors  70   a ,  70  or  73  will cause motor  28  to rapidly increment the feed conveyor until the next mail piece in stack  14  is positioned against empty switches  70   a ,  70   b  or  73 . Alternatively, when take off conveyor  30  removes a series of thin mail pieces, such as letters, postcards or single sheet forms from feed conveyor  20 , the conveyor will advance only when a sufficient number of the thin mail pieces have been removed to release one of switches  70   a ,  70   b  or  73 , which in turn causes conveyor  16  to incrementally advance. As will be appreciated, dynamic control of feed conveyor  20  thus provides for greater throughput as opposed to a single, or constant speed control, that would necessarily be set to operate at a rate low enough to accommodate a stack  14  comprising only thin mail pieces. 
     In order to keep feed conveyor full, jogger  16  is controlled to advance stack  14  at a rate proportional to the rate at which take off conveyor  30  removes mail pieces from the feeder conveyor. To accomplish this task, each tick of take off conveyor motor  28  is registered with or counted by controller  76 . After a predetermined number of ticks, controller  76  activates jogger motor  26 , advancing fingers  18  and feeding additional mail onto feed conveyor  20 . Jogger motor  26  remains activated until finger sensor  72  detects a jogger finger  18  adjacent to sensor  72  and signals controller  76  that de-energizes jogger motor  26 . As will be appreciated, during this process jogger  16  is advanced a distance corresponding to the gap or spacing between fingers  18 , for example 2-3 inches which defines an incremental volume of mail pieces. This incremental volume of mail pieces corresponds to the predetermined number of ticks advanced by motor  28  and registered by controller  76  in order to activate jogger  16 . 
     In the normal mode, motor  24  that drives staging conveyor  12  is also controlled with feeder empty switches  70   a ,  70   b ,  70   c  and  73 , advancing staging conveyor  12  as mail pieces are removed from feed conveyor  20  with take off conveyor  30 . To insure that the correct volume of mail pieces needed to fill the space between two adjacent sets of jogger fingers  18 , staging conveyor motor  24  is also equipped with an internal or external clock as described above in connection with take off conveyor motor  28 . The movement of staging conveyor  12  is controlled by registering the number of ticks advanced by staging conveyor motor  24 . When motor  24  has advanced a predetermined number of ticks corresponding to the distance between a pair of adjacent jogger fingers  18 , controller  76  deactivates the motor. 
     As staging conveyor  12  advances and stack  14  is depleted, staging conveyor  12  carries paddle  62  until the paddle activates staging paddle sensor  64 . When sensor  64  detects paddle  62 , the sensor signals controller  76  to deactivate motors  24 - 28  and take off conveyor  30 , shutting down feeder  10  until an operator reloads staging conveyor  12  with additional mail pieces and repositions the paddle behind the newly added stack of mail pieces, after which feeder  10  resumes operation in its normal mode. Staging sensor  64  may also activate an audio alarm or other signaling system to alert the operator that the staging conveyor  12  is empty. 
     In order to empty feeder  10 , the feeder is operated until paddle  62  activates staging paddle sensor  64 , deactivating feeder  10 . The operator lifts paddle  62  allowing the feeder to restart and places the paddle between two adjacent jogger fingers  18 . When jogger  16  has advanced paddle  62  sufficiently to activate jogger paddle sensor  66 , controller  76  again deactivates feeder  10  until the operator lifts the paddle, allowing feeder  10  to restart, and lowers the paddle onto feed conveyor  20 , engaging the conveyor with the paddle. When paddle  62  reaches end position sensor  68 , controller  76  deactivates motors  24 - 28 . When the last mail piece has been removed from feed conveyor  20 , optical empty switch  70   c  signals an empty condition to controller  76  which then deactivates take off conveyor  30 . 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.