Abstract:
A method and an apparatus are provided for singulating articles received in a slug and/or manipulating such articles to create a controlled gap between a trailing edge of a leading article and a leading edge of a successive article, while targeting a desired throughput. For singulation, a plurality of belts are mounted adjacent to each other with a slide chute between each pair of adjacent belts, articles moving from an infeed belt and passing from one belt to another through the chute therebetween. A plurality of sensors are positioned such that there is a single control sensor for at least selected ones of the belts, each control sensor sensing article position on a corresponding belt. Controls are provided for operating each belt in response to a corresponding control sensor, an operative state of a downstream belt and/or a difference between the desired throughput and detected throughput. For creating controlled gaps between successive articles, a plurality of belts are provided, mounted adjacent each other, articles being received on a first of the belts and passing from one belt to an adjacent belt. A plurality of control sensors are sensing article position relative to each belt and controls are provided which operate each belt in response to a corresponding control sensor, an operative state of a downstream belt and/or the difference between the desired throughput and the detected throughput. The controls are also operative to initiate stopping of a belt if a detected trailing-edge to leading-edge gap is smaller than the desired minimum gap.

Description:
This application is a Divisional of prior application Ser. No. 09/716,071, filed on Nov. 17, 2000, entitled PARCEL SINGULATION SOFTWARE CONTROL LOGIC and now pending. 
    
    
     FIELD OF INVENTION 
     This invention relates to article handling systems, and, more particularly, to a method and apparatus for singulating articles and establishing a controlled inter-article gap. 
     BACKGROUND OF THE INVENTION 
     In mail processing, airport baggage claim service, assembly line operations and other applications involving transport and processing of various articles, it is often necessary to separate articles randomly received, sometimes enmass as a slug, stack or pile, into a stream of successive articles. This process of separating articles is generally referred to as “singulation”. In a post office or delivery service, for example, packages may arrive at a conveyor system in randomly occurring slugs, the packages in each slug varying significantly in quantity, size and shape within allowed ranges. Singulating such packages or other articles is an essential preliminary step in performing sortation or most other operations on such articles. For the articles to be sorted or otherwise processed, they also must, in most cases, be separated by a gap of sufficient length. However, while at least a minimum gap between succeeding articles is required, spacing larger than the required minimum gap decreases throughput. 
     Automation apparatus is normally employed for article singulation and establishing proper article separations, such prior art apparatus using belt and chute systems, cameras and/or arrays of photo sensors for each belt to determine positioning of articles on the belts, and mechanisms ranging from robotic arms, to mechanical guides, to complicated control logic for slowing down and speeding up the belts in order to separate the articles to achieve singulation. Gapping apparatus involve various sensors for determining existing leading-edge to leading-edge or trailing-edge to leading-edge distance; gaps are adjusted to desired sizes via mechanical means. 
     While, combined, a singulation and a gapping apparatus would accomplish the task of singulating and gapping articles, such apparatus has heretofore been expensive and hard to operate, requiring the use of sophisticated technology. There exists a need for an apparatus that is capable of achieving either one or both goals without the use of cameras, computers to analyze digital images, or other expensive equipment. 
     SUMMARY OF THE INVENTION 
     In accordance with the above, this invention provides a method and an apparatus for singulating articles received in a slug and/or manipulating such articles, particularly articles of various size, to create a controlled gap between the trailing-edge of a leading article and a leading-edge of a successive article. For singulation, a plurality of belts are provided, mounted adjacent to each other, with a slide chute between each pair of adjacent belts, articles being received on a first of the belts and passing from one belt to an adjacent belt through the chute therebetween. A plurality of sensors are positioned such that there is a single control sensor for at least selected ones of the belts, each control sensor sensing article position relative to a corresponding belt. Controls are provided for operating each belt in response to a corresponding control sensor and an operative state of a downstream belt. 
     The control sensor may be located at an end of a corresponding belt, for example, the exit end of the corresponding belt. The controls may be operative to initiate stopping of a belt if a downstream belt is not running and a corresponding control sensor has been blocked for a configurable period of time. Similarly, the controls are operative to start or re-start a belt when the downstream belt is running. For preferred embodiments, the configurable time period is such that the belt has not completely stopped when a run signal is sent. The configurable time period may also be adjustable to achieve a desired apparatus throughput, such adjustment, for example, being according to an adjustment schedule. The controls may, for example, include at least one subroutine for each belt which is run on an appropriate processor. 
     The invention also includes apparatus for receiving articles in a stream and creating a controlled gap between a trailing-edge of a leading article and a leading-edge of a successive article. This apparatus includes a plurality of belts mounted adjacent each other, articles being received on a first of the belts and passing from one belt to an adjacent belt. A plurality of control sensors are positioned such that there is a single control sensor sensing article position relative to each belt and controls are provided which operate each belt in response to a corresponding control sensor and an operative state of a downstream belt. The control sensor may be located at an end of a corresponding belt, for example, the exit end of such belt. 
     The plurality of belts may be logically divided into a first section which minimizes a gap time and a second section which establishes at least a minimum gap time between successive articles. The controls are operative to initiate stopping of a belt in the first section if a downstream belt is not running and a corresponding control sensor is blocked and to send a run signal when the downstream belt is running again. The controls are also operative to initiate stopping of a belt in the second section if a detected trailing-edge to leading-edge gap time is smaller than the desired minimum gap time, and a run signal is sent to the belt after a calculated time period, the calculated time period being a function of a difference between the detected gap time and the minimum gap time. More specifically, calculation of the above function includes: (a) setting the calculated time period to be equal to the difference between the detected gap time and the minimum gap time if the difference is larger than a determined fraction of the minimum gap time; and (b) setting the calculated time period to be equal to a fraction of the minimum gap time if the difference between the detected gap time and the minimum gap time is smaller or equal to a determined fraction of the minimum gap time. The controls are also operative to initiate stopping of a belt, or at least a subset of the plurality of belts, if a corresponding control sensor has been blocked for more than a predetermined time period, which time period may be adjusted to target the desired throughput. For some embodiments, the predetermined time period is smaller than, or at most equal to a time it would take for a longest article to move past the corresponding control sensor. The controls preferably consist of at least one subroutine for each belt. 
     The invention further includes a method usable with an apparatus for manipulating articles of various size which includes stages of belts carrying the articles and belt controls for stopping and starting the belts, the method maintaining a desired article throughput and including the steps of: (a) monitoring throughput for the article manipulation; and (b) controlling stop time intervals for at least selected ones of the belts to maintain the desired throughput. The step of controlling stop time intervals, step (b) above, may include: (c) adjusting at least selected stop time intervals upward by a selected amount if current throughput is greater than the desired throughput; and (d) adjusting at least selected stop time intervals downward by selected amounts if current throughput is less than the desired throughput. The stop time intervals in steps (c) and (d) above may be adjusted according to at least one adjustment schedule which adjustment schedule is stored in a computer on which control subroutines are run. 
     The invention further includes apparatus for manipulating articles while maintaining a desired throughput, which apparatus includes stages of belts carrying the articles, and controls operating each belt, the controls being operative to stop and start the belts, and including subroutines for monitoring throughput for the article manipulation and for controlling stop time intervals for at least selected ones of the belts to maintain the desired throughput. The subroutines for controlling stop time intervals may include (a) a subroutine for adjusting at least selected intervals upward by a selected amount if current throughput is larger than the desired throughput; and (b) a subroutine for adjusting at least selected intervals downward by a selected amount if current throughput is smaller than the desired throughput. The adjustments by subroutines (a) and (b) above may be according to an adjustment schedule. 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings, the same reference numerals being used for common elements in the various figures. 
     Finally, the invention includes apparatus for receiving articles in a slug, singulating the articles and creating a controlled gap between a trailing-edge of a leading article and a leading-edge of a successive article. This apparatus includes a plurality of belts mounted adjacent each other, articles being received on a first of the belts and passing from one belt to an adjacent belt. A plurality of control sensors are positioned such that there is a single control sensor sensing article position relative to each belt and controls are provided which operate each belt in response to a corresponding sensor and an operative state of a downstream belt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagramatic top view of a combined singulation and gapping system for an illustrative embodiment. 
     FIG. 2 is a control flow diagram for the infeed chute belt of the FIG. 1 embodiment. FIG. 3 is a control flow diagram for the first belt of the singulator section of the FIG. 1 embodiment. 
     FIG. 4 is a control flow diagram for the remaining belts of a singulator section of the FIG. 1 embodiment. 
     FIG. 5 is a control flow diagram for the first three belts of a gapping section of the FIG. 1 embodiment. 
     FIG. 6 is a control flow diagram for the remaining belts of the gapping section of the FIG. 1 embodiment. 
     FIG. 7 is a timing diagram for the last six belts of the gapping section of the FIG. 1 embodiment. 
     FIG. 8 is a timing diagram for all belts of the gapping section of the FIG. 1 embodiment illustrating minimum gap time logic. 
     FIG. 9 is a timing diagram for two of the belts of the gapping section of the FIG. 1 embodiment illustrating clump eliminator logic. 
     FIG. 10 is a timing schedule for changing configurable time periods. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an illustrative apparatus in accordance with the teachings of this invention is shown for randomly receiving articles of variable size within selected limits in slugs having varying numbers of articles with varying orientations and for delivering the articles one at a time with a controlled trailing-edge to leading-edge spacing between successive articles. Articles arrive and are singulated in section  40 , proceed to section  42  where any remaining doubles are eliminated and large gaps between articles are reduced; and then proceed to section  44  where at least a minimum trailing-edge to leading-edge spacing between successive articles is established. Sections  42  and  44  together comprise a gapping section and may also be referred to as a gapping apparatus. From there, articles proceed to a sortation or other appropriate stations for further manipulation or processing. 
     For the illustrative embodiment, articles arrive at singulation section  40  from an infeed chute belt  60  through a large spiral slide chute  58 . The singulation section is comprised of multiple belts  62   a  through  62   d,  which are collectively referred to as surge belts  62  because they carry forward some unsingulated slugs. Surge belts  62  are interconnected by slide chutes  64   a - 64   d,  with slide chute  64   d  leading to section  42 . Sensors  48   a - 48   d  are positioned so that there is at least one sensor  48   x  per each surge belt  62   x.  Articles proceed from the infeed chute belt  60  onto the spiral slide chute  58 , where they are sensed by photosensor  48   a,  onto a surge belt  62   a,  then through slide chute  64   a,  and to a surge belt  62   b,  and so on: from a surge belt  62   x  to a slide chute  64   x  to a downstream surge belt  62 ( x+ 1). Sensors  48   x  are typically located at the ends of the corresponding surge belts  62   x.  They are preferably placed at the belt elevation, looking across the belt. There is belt guarding (not shown) on each side of each surge belt  62   x  in order to prevent articles from falling off, holes being formed in each guarding where sensors  48  are located. Sensors  48  are each located within one quarter inch from a top of the corresponding belt  62  because, in the environment of the illustrative embodiment, articles may be as small as half an inch in one dimension—for example, music CDs, etc. Placing sensors  48   x  at the ends of the corresponding belts  62   x  means that they detect the articles as the articles are about to move off to the corresponding slide chute  64   x,  which, combined with proper control settings, assists singulation while minimizing possible gaps without closing them completely. Each belt is run by a motor controlled by control logic. For the illustrative embodiment, surge belts  62  are located at ninety degree angles to each other, and slide chutes  64  separating them each have a different angle and slope, with each successive slide chute  64  being narrower than the previous one. In addition, surge belts  62  are inclined up, with slopes ranging approximately from thirty to forty degrees, while the slide chutes are angled down at angles which may be steeper, but extend for a shorter distance. These inclines are not required, but further assist singulation. Surge belts  62  are wider and longer than belts at later stages, but each belt  62   x  is narrower than the preceding belt  62 ( x −1), so that articles are forced into a stream. 
     Infeed chute belt  60  and each of the surge belts is controlled by controls operating each belt  62   x  in response to a corresponding sensor  48   x  and/or an operative state for a downstream surge belt. In a preferred embodiment, the surge belts  62  run at different speeds—each belt is faster than the belt preceding it, which further assists singulation because faster downstream belts carry articles away and prevent clump creation. The controls can turn each surge belt  62  on or off, depending on its current state, the state of at least one downstream belt, whether the corresponding sensor is sensing any articles, and the throughput of the whole apparatus. That is, the articles are singulated through selective, coordinated control of the on and off states for the belts. The infeed chute belt  60  is operated by a control subroutine shown in FIG.  2 . The surge belt  62   a  is operated by a control subroutine shown in FIG. 3, and the remaining surge belts  62   b - 62   d  are operated by the control subroutines shown in FIG.  4 . 
     Section  42  consists of a set of belts  66   e - 66   g,  which are collectively referred to as buffer belts  66  because they carry mostly singulated articles. Buffer belts  66  run at a faster speed than surge belts  62  in singulation section  40  and function as high speed takeaway belts. For an illustrative embodiment, belts  62  run at about 50-150 feet per minute, while belts  66   e - 66   g  run anywhere from 250 to 350 feet per minute. Each buffer belt  66  runs at a higher speed than the belt preceding it. 
     An article arrives at section  42  from section  40  at a buffer belt  66   e  and leaves photosensor  48   e - 48   g  sensing articles at that belt. Each buffer belt  66  is operated by controls  76  according to a control flow diagram (see FIG.  5 ), buffer belt  66   x  being turned on or off in response to its current state, a corresponding sensor  48   x,  the on/off state of at least one downstream belt, for example belt  66 ( x+ 1) and, for a preferred embodiment, the throughput of the entire apparatus shown in FIG.  1 . 
     Gapping section  44  consists of a set of belts  68   h - 68   n,  which are buffer belts for an illustrative embodiment and are collectively referred to as buffer belts  68 . Buffer belts  68  run incrementally faster than each other, with speeds ranging from 200 to 500 feet per minute. Buffer belt  68 h runs slower than the buffer belt  66   g.  Above each belt  68   x  there is a corresponding photosensor  48   x.  Gapping is achieved through controls turning each buffer belt  68   x  on or off according to a control subroutine (FIG.  6 ), each buffer belt  68   x  being turned on/off in response to a corresponding sensor  48   x  and/or the state of at least one downstream belt, for example belt  68 ( x+ 1). Articles arrive at the gapping section  44  from section  42  at the buffer belt  68   h  and leave the apparatus at a buffer belt  68   x,  for example buffer belt  68   n  for the embodiment of FIG. 1, from where they proceed to their next destination, for example a sortation station. 
     Additional fail-safes are available in the apparatus. Above surge belts  62 , buffer belts  66  and buffer belts  68 , additional photosensors  46  are located (shown for the surge belt  62   d;  not shown, but present above other belts  62 ,  66  and  68 ). These photosensors are generally for detection of jams that cannot be solved through cycling belts on and off and require human intervention. When articles exit at buffer belt  68   n,  any remaining doubled articles, which should be minimal, if any, are detected and re-routed back to the infeed chute  60  through a return path (not shown), so that they will go through the singulation process again. Belt controls  76  are implemented using a control computer capable of concurrently executing several subroutines, inputs to which are the states of sensors and belts, as described below, and outputs from which control motors (not shown) for each of the belts in the apparatus. The subroutines may be implemented in any computer language, and may consist of additional subroutines. 
     Although the preferred embodiment uses a single computer to execute all subroutines that comprise controls  76  in parallel, alternative embodiments may use a separate computer for each set of subroutines or bypass software and implement the subroutines in hardware or hybrid circuits. A number of the subroutines at some point refer to a configurable time  5  period, which is a variable setting, configured according to a table in FIG.  10 . An additional feedback loop (not shown)continuously monitors the apparatus output through a throughput-monitoring subroutine and, based upon a target throughput, adjusts variable time parameters to speed up or slow down the apparatus through changing the configurable time periods. 
     FIG. 2 is a flow diagram of an illustrative control subroutine for operating the infeed chute belt  60  (FIG. 1) A default state for this subroutine is state- 80 , system on, no faults, where the infeed belt is turned on and is running. When the system is in this state, the subroutine monitors a photosensor  48   a  and continuously runs a query  82  to see if the photosensor  48   a  has been blocked for more than a configurable time period  89  (FIG.  10 ). If an answer to this query is negative, the system proceeds as previously, running the belt in step  85  and returning to state  80 . If, however, photosensor  48   a  has been blocked for a time greater than the configurable time  89 , it means that several articles are passing together, which is undesirable. In that case, the motor for the infeed belt is turned off (step  84 ) to delay trailing articles, which are still on the infeed chute belt  60  and to allow articles which are already on the surge belt  62   a  to proceed. When the infeed chute belt is stopped, a query  86  is continuously run to check if the photosensor  48   a  is still blocked (i.e. if articles blocking the sensor have cleared). If the sensor is clear, the subroutine returns to query  82  to determine whether to restart the infeed chute belt  60 . In this way, the control subroutine begins singulation by separating the slug of articles into separate articles or small clumps of articles. The singulation process continues with control! subroutines shown in FIGS. 3 and 4. 
     FIG. 3 is a flow diagram of a control subroutine for the surge belt  62   a.  A default state for this subroutine is state  90 —system on, no faults, where the surge belt  62   a  is running. While the system is in this state, a query  92  is continuously run to check if the downstream belt—surge belt  62   b —is turned on. If the downstream belt is stopped, a query  93  is run to check if a photosensor  48 ( a− 1) is indicating an article at the beginning of the surge belt  62   b.  If the photosensor  48 ( a− 1) is indicating an article and the downstream belt is not running, surge belt  62   a  needs to be stopped (step  94 ) in order to avoid creating more doubles by bumping articles that are currently on the surge belt  62   a  into those that are currently on the surge belt  62   b.  If, however, there are no articles at the beginning of the downstream belt, then it is safe to continue running surge belt  62   a  (step  96 ) and system returns to the default state  90 . 
     If the query  92  indicates that downstream belt  62   b  is running, a query  95  is run to check if the photosensor  48 ( a− 1) has been blocked for a period longer than a configurable time period  99  (FIG.  10 ). If the answer is negative, belt  62   a  continues to run (step  96 ) and system returns to default state  90 . A positive answer to query  95  is a sign that an article double is coming through which needs to be singulated. In order to achieve singulation, surge belt  62   a  is stopped (step  97 ) to allow surge belt  62   b  to take away a front article of the double. Once the surge belt  62   a  is stopped, a query  98  is continuously run to check if the photosensor  48 ( a− 1) has cleared. When photosensor  48 ( a− 1) indicates that there are no articles present at the beginning of belt  62   b,  the system proceeds to run query  92  and repeats the steps thereafter as indicated above. This subroutine thus creates gaps between at least some consecutive articles by not running the belt  62   a  when photosensor  48 ( a− 1) indicates that there are articles at the beginning of the downstream belt, but running belt  62   a  when this condition does not exist. This subroutine does not attempt to properly size or minimize such gaps, leaving that for the later stages  42  and  44 . 
     FIG. 4 is a flow diagram of a control subroutine for operating belts  62   b,    62   c  and  62   d.  For each of those surge belts, referred to as surge belt  62   x,  a separate instance of the subroutine is run. A default state for this subroutine is state  100 , where surge belt  62   x  is running and there are no faults. When the system is in state  100 , a query  102  is continuously run to check if downstream surge belt  62 ( x+ 1) is running. If the answer query  102  is negative the downstream belt is not running a query  103  is run to check if a photosensor  48   x  is indicating presence of an article. If no article is detected, the subrouting continues running belt  62   x  (step  104 ) and returns to the default state  100 . If, however, an article is detected, belt  62   x  is stopped (step  105 ) to avoid creating new doubles, and the subroutine returns to query  102 . If the answer to query  102  is positive (i.e. the downstream belt is running), a query  106  is run to check whether the photosensor  48   x  has been blocked for a period of time longer than a configurable time period  107  (FIG.  10 ). A positive answer to the query  106  indicates that there is still an article double, and surge belt  62   x  is turned off for a configurable time period  109 (FIG. 10) to facilitate separation of the double, and then turned back on, with the system returning to default state  100 . The fact that the downstream belt  62   x  is running is sufficient to assure that a gap is created during the stopping for the configurable time period  109 . A negative answer to the query  106  indicates that there is no double currently passing through belt  62   x,  surge belt  62   x  thus continuing to run (step  104 ) and the subroutine returning to default state  100 . 
     FIG. 5 is a diagram of control subroutine for controlling each of the buffer belts  66   e - 66   g  in the section  42 . Belts  66   x  are high speed takeaway belts and the main goal for this section is to minimize gaps between the articles, so that the next section  44  can increase them to the desired minimum size. For each of the buffer belts  66   x,  a separate instance of the subroutine is run. A default state for this subroutine is state  110 —system on, no faults—where a belt  66   x  is running. When the subroutine is in this state, a query  112  is continuously run to check if the downstream belt  66 ( x+ 1) is running. If the downstream belt is running, there is no danger of creating additional doubles; the subroutine therefore permits belt  66   x  to continue running (step  113 ) and returns to default state  110 . 
     If the downstream belt is not running, a query  114  is run to check if photosensor  48   x  is indicating the presence of an article at the end of the belt  66   x.  If there is an article, buffer belt  66   x  is stopped (step  115 ) and the subroutine returns to query  112 . If there is no article present, the subroutine continues to run buffer belt  66   x  (step  113 ), returning to the default state  110  despite the fact that downstream belt  66 ( x+ 1) is not running. This is done in order to minimize the gap between the articles; no additional doubles will be created, because, by the time the next article moves to the end of buffer belt  66   x,  either the downstream belt will be running, or both queries  112  and  114  will return negative results and belt  66   x  will be stopped, avoiding combining two articles into a double. 
     FIG. 6 is a flow diagram of a control subroutine responsible for operation of belts  68  in the section  44 . The main goal for this section is to establish at least a minimum required gap between each pair of successive articles. In order to do that, gap time is increased to at least minimum gap time in all cases where a detected gap is not long enough. A separate instance of the subroutine is run for each buffer belt  68   x.  A default state for this subroutine is state  120 —system on, no faults, where belt  68   x  is running. When the subroutine is in that state, a query  122  is continuously run to check if the trailing-edge to leading-edge gap for successive articles passing sensor  48   x  is larger than a required minimum gap  127  (see FIG. 7 a ). The check is made according to the timing principles described later in conjunction with FIGS. 7-9. A negative answer to query  122  indicates that the detected gap is not of sufficient duration, and buffer belt  68   x  is stopped for a time period  129  described to be in conjunction with FIGS. 7-9 (step  128 ). After the belt has been stopped for the time period  129 , the subroutine returns to query  122 . However, if during the time period  129  when buffer belt  68   x  was stopped, downstream buffer belt  68 ( x+ 1) was also not running, the detected gap was not increased or increased by an insufficient amount. The illustrative apparatus includes seven buffer belts  68  running at different speeds, which increases the probability that, if the detected gap is not sufficient, the downstream belt  68 ( x+ 1) will be running during the whole time period  129 , thus creating at least the minimum required gap. 
     A positive answer to query  122  indicates that the detected gap is of sufficient duration. Query  123  is then made to determine if downstream belt  68 ( x+ 1) is running. If an answer is positive, there is no danger of decreasing the detected gap, and the subroutine proceeds to run belt  68   x  (step  124 ), returning to default state  120 . If, however, the downstream belt is not running, a query  125  is run to determine if photosensor  48   x  indicates the presence of an article at the end of belt  68   x.  If there is no article present, the subroutine continues running buffer belt  68   x  and returns to query  122 , which monitors the detected gap. If photosensor  48   x  is not clear—the article is present—the subroutine sends a stop signal to a motor for belt  68   x  (step  126 ) and returns to query  122 , which ensures that the detected gap is not reduced below the minimum required gap. 
     FIGS. 7 a  and  7   b  are timing diagrams that further illustrate behavior of queries  122  and  128  (FIG.  6 ). FIG. 7 a  shows how the existing trailing-edge to leading-edge gap is detected. Sensor  48   x  is “on” when there is no article passing, and “off” when there is an article at the end of the belt  68   x  (FIG.  1 ). If the minimum gap time  127  is shorter than detected gap time  131  and both belts  68   x  and  68 ( x+ 1) are on, then the query  122  returns “yes”, the query  123  (FIG. 6) returns “yes” and belt  68   x  continues to run. 
     FIG. 7 b  illustrates behavior according to the control flow diagram of FIG. 6 when the detected gap time  131  is shorter than the minimum required gap time, as indicated by sensor  48   x.  In that case, a “stop” signal is sent to belt  68   x  in order to increase the gap. After a calculated period of time  132  (shown in FIG.  8 ), a “run” signal is sent to belt  68   x,  restarting the belt. 
     When the “stop” signal is sent, belt  68   x  does not stop immediately—as every mechanical element, it has inertia and requires some time to slow down and stop. Since the electronics are thus faster than the mechanical parts, the stop period needs to be lengthened to take this difference into account. A timing diagram for determination of the calculated time period  132  is shown in FIG.  8 . If a difference between the detected gap time and the minimum required gap time is less than one third of the minimum required gap time, the calculated stop period is set to be one half of the minimum required gap time. This is done in order to slow down the belts enough to create at least a minimum required gap. For example, if the minimum gap between trailing and leading of successive articles is T, and the detected gap is 4T/5, the calculated stop period  132  is set to T/2. The appropriate times T are calculated based on belt speeds, application, field-testing results, etc. If the difference between the detected gap time and the minimum required gap time is equal to or greater than one third of the minimum required gap time, the calculated stop time period is set to be the difference between the detected gap time and the minimum gap time. 
     FIG. 9 illustrates timing logic employed in a subset of belts  68   x  (in the illustrative embodiment this subset consists of belts  68   m  and  68   k ) that facilitates eliminating doubles that were not eliminated in the previous stages, where a double is a set of articles following so closely one after another that there is no gap to detect. In order to create gaps between the articles in the doubles, additional “clump eliminator” logic is employed. According to this timing logic, if sensor  48   x  is off for longer than a preset time period  134 , belt  68   x  is turned off for a configurable time period  133  in order to allow a front article in the double to pass in order to create a gap. The preset time period  134  is generally set to equal to or less than an approximate time it would take for a largest article to pass (in the illustrative embodiment, the length of the largest possible article is known). 
     FIG. 10 is an illustrative timing schedule for changing the configurable time periods discussed in conjunction with FIGS. 2,  3  and  4 . At any given time, all configurable time periods are set to be equal to the values in one of the columns of FIG.  10 . For example, column  140   b  indicates that the configurable time period  89  for the infeed chute belt  60  should be set to 1 second, a configurable time period  99  for the belt  62   a  should be set to 0.5 seconds, a configurable time period  107  for the belt  62   b  on-time should be set to 0.31 seconds, and a configurable time period  109  for the belt  62   b  off-time should be set to 0.57 seconds. When the throughput-monitoring subroutine indicates that the detected throughput differs from a desired throughput, the configurable time periods are adjusted by changing all values to those in an adjacent column. When the detected throughput is greater than the target throughput, a left column is picked, and when the current throughput is less than the desired throughput, a right column is picked. The configurable time periods are thus adjusted to target the desired throughput. Although in the illustrative embodiment the timing schedule of FIG. 10 is used to determine the configurable time periods, depending on application and other factors, algorithms, different timing schedules or other techniques may be utilized to calculate configurable time periods to achieve the desired throughput. In addition, configurable time periods may be adjusted based on feedback from apparatus located after the apparatus of the FIG. 1 illustrative embodiment. For example, the required minimum gap time period may be dynamically adjusted, based on selected factors both from the present apparatus and from other apparatus used with it, such as size of the articles, desired throughput, accuracy of processing at the downstream stations, etc. 
     Although the illustrative embodiment of the invention has been shown in the accompanying drawings and described in the Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed. The number and kinds of belts employed, slide chute angles and sizes, as well as positioning of sensors and the corresponding control subroutines can each be modified. The present invention is capable of rearrangements and modifications of parts and elements by one skilled in the art without departing from the spirit and scope of the invention, which is to be defined only by the appended claims.