Abstract:
An accumulation conveyor with individually controllable zones may be controlled in a manner which efficiently reduces the gaps between accumulated articles, accomplished by control logic which determines the existence of conditions conducive to reducing the gaps and implements the control logic as appropriate. The accumulation conveyor may be controlled in a coast to stop mode. The accumulation conveyor may be controlled in manner to detect and clear jams.

Description:
[0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/210,750, filed on Mar. 19, 2009, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to conveyors, and more particularly to accumulation conveyors. The invention will be disclosed in connection with, but not necessarily limited to, zoned accumulation conveyors comprising control modules configured to control two zones which monitor and control product flow on the accumulation conveyor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention. 
           [0004]      FIG. 1  is a plan view of an accumulation conveyor embodying one or more teachings of the present invention. 
           [0005]      FIGS. 2-5  are diagrammatic side views illustrating different arrangements of zone control modules and interface modules. 
           [0006]      FIGS. 6A ,  6 B,  6 C illustrate control logic for coast to stop accumulation mode. 
           [0007]      FIGS. 7A-7V  are diagrammatic zones illustrating operation of an accumulation conveyor in coast to stop accumulation mode. 
           [0008]      FIGS. 8A ,  8 B,  8 C illustrate control logic for coast to stop with sensor coupled accumulation mode 
           [0009]      FIGS. 9A-9L   6  are diagrammatic zones illustrating operation of an accumulation conveyor in coast to stop with sensor coupled accumulation mode. 
           [0010]      FIGS. 10A ,  10 B,  10 C illustrate control logic for run up once accumulation mode. 
           [0011]      FIGS. 11A-11I  are diagrammatic zones illustrating operation of an accumulation conveyor in run up once accumulation mode. 
           [0012]      FIGS. 12A ,  12 B,  12 C illustrate control logic for run up once with sensor coupled accumulation mode. 
           [0013]      FIGS. 13A-13G  are diagrammatic zones illustrating operation of an accumulation conveyor in run up once with sensor coupled accumulation mode. 
           [0014]      FIG. 14  illustrates control logic for crowding. 
           [0015]      FIG. 15  illustrates control logic steps of the control logic illustrated in  FIG. 14 . 
           [0016]      FIG. 16  illustrates an alternate embodiment of a portion of the control logic illustrated in  FIGS. 14 and 15 . 
           [0017]      FIG. 17  illustrates control logic related to “waking” a snoozing zone. 
           [0018]      FIG. 18  illustrates the flow and jam detect control logic. 
       
    
    
       [0019]    Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. 
       DETAILED DESCRIPTION 
       [0020]    In the following description, like reference characters designate like or corresponding parts throughout the several views. Also, in the following description, it is to be understood that terms such as front, back, inside, outside, and the like are words of convenience and are not to be construed as limiting terms. Terminology used in this patent is not meant to be limiting insofar as devices described herein, or portions thereof, may be attached or utilized in other orientations. Referring in more detail to the drawings, an embodiment of the invention will now be described. 
         [0021]    Referring to  FIG. 1 , there is shown a plan view of an accumulation conveyor embodying one or more teachings of the present invention. Accumulation conveyor, generally indicated at  2 , includes a plurality of individually controllable zones  4   a ,  4   b ,  6   a ,  6   b ,  8   a ,  8   b ,  10   a ,  10   b  and  12   a . Although in the embodiment depicted in  FIG. 1  there are nine zones, the present invention is not limited to nine zones. In the embodiment depicted, zones are generally six feet long, twice as long as a typical accumulation conveyor zone, resulting in reduced manufacturing cost. As will be appreciated, the present invention provides for efficient accumulation of packages even though the zones are longer than as is typical. However, the present invention is not limited to long zones nor six feet long zones. 
         [0022]    Each zone is selectively driven in any suitable manner as is known in the art, such as the drive arrangement shown in U.S. Pat. No. 6,889,822, the disclosure of which is incorporated herein by reference. In the embodiment depicted, each zone of accumulation conveyor  2  comprises a plurality of conveyor rollers (diagrammatically illustrated) which may be selectively driven by urging an underlying drive belt (not shown) against the conveyor rollers using pneumatic actuators (not shown). In the embodiment depicted, each module  4   c ,  6   c ,  8   c ,  10   c  and  12   c  is configured to control the pneumatic actuators (not shown) of their associated zones, and is therefore connected to a pneumatic source. The modules  4   c ,  6   c ,  8   c ,  10   c  and  12   c  may be pneumatically daisy chained together. Other drive arrangements include motorized drive rollers, with modules  4   c ,  6   c ,  8   c ,  10   c  and  12   c  configured appropriately therefor. 
         [0023]    In the embodiment depicted, each pair of zones has respective zone control modules  4   c ,  6   c ,  8   c  and  10   c . Zone control modules  4   c ,  6   c ,  8   c  and  10   c  each control two zones, while zone interface module  12   c  controls zone  12   a , the discharge zone which discharges to take-away conveyor  14  illustrated as a declined belt in the embodiment depicted. 
         [0024]    Each zone  4   a ,  4   b ,  6   a ,  6   b ,  8   a ,  8   b ,  10   a ,  10   b  and  12   a  includes respective sensors  4   d ,  4   e ,  6   d ,  6   e ,  8   d ,  8   e ,  10   d  and  10   e  and  12   d  connected to the respective zones&#39; modules. In the embodiment depicted, the sensors are photo eyes with respective reflectors, although any suitable sensor may be used, such as roller sensors or diffused scan sensors. The positions and orientations of the sensors, also referred to herein as photo eyes, within the zones are selected based on the system parameters, such as length or type of packages. 
         [0025]      FIGS. 2-5  diagrammatically illustrate different arrangements of zone control modules and interface modules. Referring to  FIG. 2 , there is illustrated an arrangement similar to accumulation conveyor  2  of  FIG. 1 , in which there are Z(n+2) zones, represented by diagrammatically illustrated conveyors  16   a ,  16   b ,  18   a ,  18   b  and  20   a . Zone control modules  16   c  and  18   c  are disposed to control the pairs of conveyors that form the respective zones. Zone interface module  20   c  is disposed to control conveyor  20   a , the discharge zone, making zone interface module  20   c  the discharge interface module. 
         [0026]    The system operates on RS232 communication between zone control modules  16   c ,  18   c  and interface module  20   c , as illustrated by the lines therebetween in  FIG. 2 . Zone control modules  16   c  and  18   c  are each configured to receive information from respective sensors (not shown in  FIGS. 2-4 ) of each of the two zones respectively controlled by a single control module so as to detect product in the respective zone, are configured to control the movement of product (pneumatically in the embodiment depicted) within each of the two zones, and configured to allow zone information to be distributed among the modules. 
         [0027]    Interface module  20   c  is configured to control a single zone in the manner discussed above with respect to zone control modules, the only difference in this regard being limited to controlling a single zone. Interface module  20   c  also controls the direction of travel of the conveyor, through the use of DIP switches. (Zone controls  16   c  and  18   c  do have a default direction of travel.) Interface module  20   c  is also configured to use discrete I/O to allow control of the movement of product on the accumulation conveyor, allow external systems to monitor the fill state of a conveyor and allow external systems to monitor fault conditions. I/O from/to an external device is indicated at  22 . 
         [0028]      FIG. 2  illustrates the use of interface module  20   c  as a discharge interface module, by virtue of controlling the single zone which is at the discharge.  FIG. 3  differs from  FIG. 2  in that interface module  30   c  is disposed to control infeed conveyor  24   a  instead of a discharge conveyor. Interface module  30   c  is designated as the infeed interface module, performing the same functions as discharge interface module  20   c.    
         [0029]    Although it is possible to configure the accumulation conveyor without an interface module, the embodiments depicted herein have an interface module. Determination whether to have an infeed or discharge interface module depends mostly on practical consideration based, for example, in convenience, minimizing wiring, which end of the conveyor is desirable to have interface with the line, etc. 
         [0030]      FIGS. 2 and 3  illustrate accumulation conveyors with an odd number of zones, each with one interface module  20   c  or  30   c .  FIG. 4  illustrates an accumulation conveyor with an even number of zones, for which two interface modules are used, infeed interface module  38   c  and discharge interface module  44   c , each of which is configured as previously described. 
         [0031]      FIG. 5  illustrates an accumulation conveyor in which the direction of product flow is not restricted based on the physical configuration. The system includes intermediate module  58 , which controls no conveyor or zones, being configured to use discrete I/O to allow control of the movement of product on the accumulation conveyor, allow external systems to monitor the fill state of a conveyor and allow external systems to monitor fault conditions. Intermediate module  58  is simply an I/O handler for external system requirements. It is not considered an upstream or downstream device, but when information is passed to it, it will adjust the message per its local I/O settings and send the adjusted message on to its neighbor in the required direction of communication flow. Any number of intermediate modules may be used in any position within the zone control module string. 
         [0032]    There are also shown in  FIG. 5  optional infeed interface module  50   c  and optional discharge interface module  52   c , although it is preferred that each accumulation conveyor have at least one of either. 
         [0033]    An accumulation conveyor constructed in accordance with the teachings of the present invention present invention operates in accumulation mode unless there is a release signal from an external source, such as a PLC. The present invention contemplates four basic accumulation modes: coast to stop; coast to stop—sensor coupled; run up once; and run up once—sensor coupled. The accumulation mode is determined by the position of DIP switches on an interface module or intermediate module. 
         [0034]    Within the teachings of the present inventions, typical infeed configurations for six feet long nominal zones include:
       3′ Infeed idler with only an interface module   3′ Infeed idler without any control module (slave)   6′ Infeed idler with only an interface module   6′ Infeed idler with a zone control module (two 3′ zones)   9′ Infeed idler with a zone control module (one 6′ zone and one infeed 3′ zone)   9′ Infeed idler with a zone control module and an interface module (three 3′ zones, with interface on the infeed)   12′ Infeed idler with a zone control module (two 6′ zones)   12′ Infeed idler with a zone control module and an interface module (two 3′ zones, with the interface on the infeed, then a 6′ zone)       
 
         [0043]    Within the teachings of the present inventions, typical discharge configurations for six feet long nominal zones include:
       3′ Discharge idler with only an interface module   3′ Discharge idler without any control module (slave)   6′ Discharge idler with only an interface module (6′ release zone)   6′ Discharge idler with zone control module (3′ release zone)       
 
         [0048]    Referring to  FIGS. 6A ,  6 B and  6 C, each shows identical control logic representative of coast to stop accumulation mode, which is the least aggressive accumulation mode. The most downstream zone of the system, i.e., the discharge zone, will be inactive in the coast to stop mode unless there is a release command. The control logic is independently executed by each module for each zone controlled thereby. The differences between  FIGS. 6A ,  6 B and  6 C lie in the illustrated path followed in execution of the control logic. At step  62 , it is determined whether the accumulation conveyor is in the coast to stop mode. If no, then the logic proceeds to step  64  whereat other accumulation modes are checked for. If the coast to stop mode is active, then the logic proceeds to step  66  which determines whether the downstream sensor is occupied. 
         [0049]    As used herein, a sensor is considered occupied when the sensor has been blocked and a time delay period has expired. A sensor is considered not occupied when the sensor is clear (not blocked) and the time delay period has expired. The sensor time delay period is set by DIP switch position on the most downstream interface module. The time delay period set by DIP switches is applied to all modules in the string and their corresponding sensors. Although the time delay period for determining occupied could be different than the time delay period for determining clear, in one embodiment it is not. In one embodiment, DIP switches allowed the delay to be set at zero, 0.75 seconds, 1.0 seconds or 1.5 seconds. 
         [0050]    If the downstream zone is not occupied, the control logic proceeds to step  68 , as indicated by the heavy line in  FIG. 6A . At step  68 , the local zone (i.e., the zone being examined) is set to active, and the control logic proceeds to step  70  whereat the local zone is set to non accumulated. From there the control logic returns to step  62 . As used herein, active means the conveyor or zone is moving. 
         [0051]    If the downstream zone is occupied at step  66 , the control logic proceeds to step  72  where the local zone is set to inactive. As used herein, inactive means the conveyor or zone is not moving. The control logic proceeds to step  74  where it is determined whether the local zone sensor is occupied. If it is not, then the logic proceeds to step  70 , setting the local zone to not accumulated, a path indicated by the heavy line of  FIG. 6B . As used herein, not accumulated means the particular zone is not active or it&#39;s zone sensor is clear. As used herein, a sensor is clear when the sensor&#39;s output is in a state consistent with seeing the reflector, meaning product is not being detected by the local zone sensor directly (without time delay—it is actual sensor state). If the local zone sensor is occupied at step  74 , the control logic proceeds to step  76  whereat the local zone is set to accumulated, a path indicated by the heavy line of  FIG. 6C . As used herein, accumulated means the local zone is inactive and the local zone sensor is blocked. As used herein, a sensor is blocked when the sensor&#39;s output is in a state consistent with not seeing the reflector meaning product is being detected by the local zone sensor directly (without time delay—it is actual sensor state). 
         [0052]    Referring to  FIGS. 7A-7V , an example of the operation of the coast to stop accumulation control logic is illustrated in the series of figures. Each of  FIGS. 7A-7V  depicts zones  1 - 6  labeled in  FIG. 7A  only as  78 ,  80 ,  82 ,  84 ,  86  and  88 , with sensors  78   a ,  80   a ,  82   a ,  84   a ,  86   a  and  88   a  respectively. Zone  1  is controlled by infeed interface module  90 , zones  2  and  3  are controlled by zone control module  92 , zones  4  and  5  are controlled by zone control module  94  and zone  6  is controlled by discharge interface module  96 . As mentioned above, in the coast to stop accumulation mode, zone  6  is inactive until such time as a release command is received from an external system. 
         [0053]      FIGS. 7A and 7B  illustrate package  1  entering zone  1  and passing sensor  78   a .  FIG. 7C  illustrates package  1  transferring to zone  2 . In  FIG. 7D , sensor  80   a  becomes occupied by package  1 , stopping zone  1 , while zone  2  remains active. At  FIG. 7E , package  1  is transferring to zone  3 , and zone  1  has become active again. At  FIG. 7F , sensor  82   a  is occupied and zone  2  is stopped.  FIG. 7G  illustrates package  1  transferring to zone  4 , with zone  2  active since sensor  82   a  is not occupied. At  FIG. 7H , sensor  84   a  is occupied by package  1 , stopping zone  3 .  FIG. 7I  shows package  1  transferring to zone  5 , with sensor  84   a  becoming unoccupied, and zone  3  starting.  FIG. 7J  illustrates sensor  86   a  becoming occupied by package  1 , stopping zone  4 .  FIG. 7K  shows package  1  transferring to zone  6 , unoccupying sensor  86   a  and zone  4  starting.  FIG. 7L  illustrates package  1  coasting to a stop, since zone  6  is inactive, and causing sensor  88   a  to become occupied, thereby stopping zone  5 . 
         [0054]      FIG. 7M  illustrates package  2  progressed down the conveyor much the same as did package  1 , having coasted to a stop to block photo eye  86   a  of zone  5 , thereby deactivating zone  3 .  FIG. 7N  show packages  3  and  4  entering the accumulation conveyor pressing against each other. Referring to  FIG. 7O , sensor  78   a  of zone  1  becomes occupied but no conveyor zones are thereby affected.  FIG. 7P  illustrates sensor  80   a  of zone  2  just becoming occupied by package  3 , causing zone  1  to stop being driven, holding up package  4 .  FIG. 7Q  illustrated a gap formed between packages  3  and  4  as package  3  continues to move past sensor  80   a . In  FIG. 7R , sensor  80   a  has become unoccupied, with zone  1  starting up and moving package  4 . AT  FIG. 7S , sensor  82   a  of zone  3  is occupied by package  3 , stopping zone  2 , making the gap between packages  3  and  4  bigger.  FIG. 7T  illustrates package  3  transferred to zone  4 , which is stopped as a result of sensor  86   a  of zone  5  being blocked by package  2 . In  FIG. 7T , sensor  82   a  is unoccupied, restarting zone  2  and moving package  4  forward. 
         [0055]      FIG. 7U  illustrates that package  3  has coasted to a stop, occupying sensor  84   a , resulting in zone  3  becoming inactive. Thus, when package  4  reaches zone  3  as shown in  FIG. 7V , package  4  coasts to stop blocking photo eye  82   a  and causing zone  2  to be inactive. 
         [0056]    Referring to  FIGS. 8A ,  8 B and  8 C, each shows identical control logic representative of coast to stop with sensor coupled accumulation mode. The most downstream zone of the system, i.e., the discharge zone, will be inactive unless there is a release command. The second most downstream zone will use simple coast to stop logic. The control logic is independently executed by each module for each zone controlled thereby. The differences between  FIGS. 8A ,  8 B and  8 C lie in the illustrated path followed in execution of the control logic. 
         [0057]    At step  98 , it is determined whether the accumulation conveyor is in the coast to stop with sensor coupled mode. If no, then the logic proceeds to step  100  whereat other accumulation modes are checked for. If the coast to stop with sensor coupled mode is active, then the logic proceeds to step  102  which determines whether sensors of the two downstream zones are both occupied. If the two downstream zone sensors are not both occupied, the control logic proceeds to step  104 , as indicated by the heavy line in  FIG. 8A . At step  104 , the local zone (i.e., the zone being examined) is set to active, and the control logic proceeds to step  106  whereat the local zone is set to non accumulated. From there the control logic returns to step  98 . 
         [0058]    If the two downstream zones sensors are occupied at step  102 , the control logic proceeds to step  108  where the local zone is set to inactive. The control logic proceeds to step  110  where it is determined whether the local zone sensor is occupied. If it is not, then the logic proceeds to step  106 , setting the local zone to not accumulated, a path indicated by the heavy line of  FIG. 8B . If the local zone sensor is occupied at step  110 , the control logic proceeds to step  112  whereat the local zone is set to accumulated, a path indicated by the heavy line of  FIG. 8C . 
         [0059]    Referring to  FIGS. 9A-9L , an example of the operation of the coast to stop sensor coupled accumulation mode control logic is illustrated in the series of figures. Each of  FIGS. 9A-9L  depicts zones  1 - 6  labeled in  FIG. 9A  only as  114 ,  116 ,  118 ,  120 ,  122  and  124 , with sensors  114   a ,  116   a ,  118   a ,  120   a ,  122   a  and  124   a  respectively. Zone  1  is controlled by infeed interface module  126 , zones  2  and  3  are controlled by zone control module  128 , zones  4  and  5  are controlled by zone control module  130  and zone  6  is controlled by discharge interface module  132 . As mentioned above, in the coast to stop—sensor coupled accumulation mode, zones  5  and  6  are inactive until such time as a release command is received from an external system. 
         [0060]    In  FIG. 9A , package  1  has progressed and coasted to a stop occupying sensor  124   a . Packages  2  and  3  are arriving with a gap therebetween. In  FIG. 9B , package  2  is occupying sensor  114   a , but no zones are made inactive. At  FIG. 9C , package  2  is transferring to zone  2  as package  3  enters zone  1 . At  FIG. 9D , package  2  is occupying sensor  116   a , but zone  1  remains active since sensor  118   a  of zone  3  is not occupied. Package  3  is occupying sensor  114   a .  FIG. 9E  illustrates packages  2  and  3  transferring to the next sequential zone. In  FIG. 9F , package  2  is occupying sensor  118   a  of zone  3 , and package  3  is occupying sensor  116   a  of zone  2 , which results in zone  1  being stopped, with no effect in the example illustrated.  FIG. 9G  illustrates packages  2  and  3  transferring to zones  4  and  3  respectively, unoccupying the sensors, and resulting in zone  1  becoming active. 
         [0061]      FIG. 9H  illustrates package  2  occupying sensor  120   a  with no affect on accumulation.  FIG. 9I  illustrates packages  2  and  3  occupying sensors  120   a  and  118   a , respectively, deactivating zone  2 . Package  2  is transferring to zone  5  which is inactive.  FIG. 9J  illustrates package  2  having progressed far enough to unoccupy sensor  120   a  of zone  4  as it transfers to inactive zone  5 , allowing zone  2  to become active.  FIG. 9K  illustrates package  2  coasted to a stop in zone  5 , occupying sensor  122   a . With photo eye  124   a  blocked by package  1  and photo eye  122   a  blocked by package  2 , zone  3  is made inactive, causing package  3  to coast in zone  4 .  FIG. 9L  illustrates no further movement of packages  1  and  2 , and package  3  having coasted to a stop occupying sensor  120   a , thereby resulting in unoccupied zone  3  being active. 
         [0062]    The run up once accumulation mode compensates for the longer coast-to-stop buffers between sensors when using zones longer than three feet operated in a cost to stop manner where there is no braking force applied to stop cartons. This control strategy is implemented by allowing packages in a local zone to be driven all the way to the sensor in that zone, i.e., run up to the local zone sensor, before canceling the drive in that zone. Referring to  FIGS. 10A ,  10 B and  10 C, each shows identical control logic representative of run up once accumulation mode. The most downstream zone of the system, i.e., the discharge zone, will be inactive in the run up once mode unless there is a release command is received from an external system. The control logic is independently executed by each module for each zone controlled thereby. The differences between  FIGS. 10A ,  10 B and  10 C lie in the illustrated path followed in execution of the control logic. 
         [0063]    At step  134 , it is determined whether the accumulation conveyor is in the run up once mode. If no, then the logic proceeds to step  136  whereat other accumulation modes are checked for. If the run up once mode is active, then the logic proceeds to step  138  which determines whether the sensor of the immediately downstream zone is occupied. If the downstream zone sensor is not occupied, the control logic proceeds to step  140 , as indicated by the heavy line in  FIG. 10A . At step  140 , the local zone (i.e., the zone being examined) is set to active, and the control logic proceeds to step  142  whereat the local zone is set to non accumulated. From there the control logic returns to step  134 . 
         [0064]    If the downstream zone sensor is occupied at step  138 , the control logic proceeds to step  144 , as indicated by the heavy lines in  FIG. 10C , where it is determined whether the local zone sensor is occupied. If it is not, the logic proceeds to step  146  whereat the state of the local zone is latched, i.e., maintained in its current inactive or active state. The control logic proceeds to step  142 , setting the local zone to not accumulated, and proceeds back to step  134 . If the local zone sensor is occupied at step  144 , the logic proceeds to step  148  whereat the local zone is set to inactive and then to step  150  whereat the local zone is set to accumulated. 
         [0065]    Referring to  FIGS. 11A-11I , an example of the operation of the run up once accumulation mode control logic is illustrated in the series of figures. Each of  FIGS. 11A-11I  depicts zones  1 - 6  labeled in  FIG. 11A  only as  152 ,  154 ,  156 ,  158 ,  160  and  162 , with sensors  152   a ,  154   a ,  156   a ,  158   a ,  160   a  and  162   a  respectively. Zone  1  is controlled by infeed interface module  164 , zones  2  and  3  are controlled by zone control module  166 , zones  4  and  5  are controlled by zone control module  168  and zone  6  is controlled by discharge interface module  170 . As mentioned above, in the run up once accumulation mode, zone  6  is inactive until such time as a release command is received from an external system. 
         [0066]      FIGS. 11A and 11B  illustrate package  1  entering zone  1  and occupying sensor  152   a .  FIG. 11C  illustrates package  1  occupying sensor  154   a  of zone  2 , as package  2  enters zone  1 , with zone  1  still active.  FIG. 11D  illustrates package  1  advanced a little further than shown in  FIG. 11C , but still occupying sensor  154   a . Package  2  is occupying sensor  152   a . Under the run up once control logic, zone  2 , the downstream zone to zone  1 , is occupied so the state of the local zone sensor  152   a  is checked. Since it is occupied by Package  2 , the control logic sets the local zone, zone  1  to inactive and accumulated. In  FIG. 11E , package  1  has passed sensor  154   a , so zone  1  goes active. In  FIG. 11F , package  2  is occupying sensor  152   a  and package  3  is occupying sensor  152   a , resulting in zone  1  being deactivated, keeping package  3  in zone  1  until package  2  clears sensor  154   a .  FIG. 11G  illustrates package  1  as reaching zone  6 , occupying sensor  162   a , and package  2  reaching zone  5  occupying sensor  160   a . With zone  5 &#39;s downstream sensor (sensor  162   a  of zone  6 ) and zone  5 &#39;s sensor  160   a  occupied, zone  5  is deactivated. Zone  5  will remain deactivated (latched) until sensor  162   a  of zone  6  clears. 
         [0067]    In  FIG. 11H , package  3  is occupying sensor  158   a  of zone  4 , which with sensor  160   a  of zone  5  being blocked, zone  4  is latched off until sensor  160   a  of zone  5  is cleared. Package  4  is occupying sensor  154   a .  FIG. 11I  illustrates the removal of package  2  from the conveyor. Zone  5  will remain latched until zone  6  becomes clear. However, zone  4  will become active (unlatched) since sensor  160   a  of zone  5  became unoccupied, moving package  3  into zone  5 . In doing so, photo eye  158   a  of zone  4  will become clear, unlatching zone  3  thereby advancing package  4 . 
         [0068]    Referring to  FIGS. 12A ,  12 B and  12 C, each shows identical control logic representative of run up once with sensor coupled accumulation mode. The most downstream zone of the system, i.e., the discharge zone, will be inactive in the run up once with sensor coupled mode unless there is a release command. The second most downstream zone will use simple coast to stop logic. The control logic is independently executed by each module for each zone controlled thereby. The differences between  FIGS. 12A ,  12 B and  12 C lie in the illustrated path followed in execution of the control logic. 
         [0069]    At step  172 , it is determined whether the accumulation conveyor is in the run up once with sensor coupled mode. If no, then the logic proceeds to step  174  whereat other accumulation modes are checked for. If the run up once with sensor coupled mode is active, then the logic proceeds to step  176  which determines whether sensors of the two downstream zones are both occupied. If the two downstream zone sensors are not occupied, the control logic proceeds to step  178 , as indicated by the heavy line in  FIG. 12A . At step  178 , the local zone (i.e., the zone being examined) is set to active, and the control logic proceeds to step  180  whereat the local zone is set to non accumulated. From there the control logic returns to step  172 . 
         [0070]    If the two downstream zone sensors are occupied at step  176 , the control logic proceeds to step  182 , where it is determined whether the local zone sensor is occupied. If it is not, the logic proceeds to step  184 , as indicated by the heavy line in  FIG. 12C , whereat the state of the local zone is latched, i.e., maintained in its current inactive or active state. The control logic proceeds to step  180 , setting the local zone to not accumulated, and proceeds back to step  172 . If the local zone sensor is occupied at step  182 , the logic proceeds to step  186  whereat the local zone is set to inactive and then proceeds to step  188  whereat the local zone is set to accumulated. 
         [0071]    Referring to  FIGS. 13A-13G , an example of the operation of the run up once with sensor coupled accumulation mode control logic is illustrated in the series of figures. Each of  FIGS. 13A-13G  depicts zones  1 - 6  labeled in  FIG. 13A  only as  190 ,  192 ,  194 ,  196 ,  198  and  200 , with sensors  190   a ,  192   a ,  194   a ,  196   a ,  198   a  and  200   a  respectively. Zone  1  is controlled by infeed interface module  202 , zones  2  and  3  are controlled by zone control module  204 , zones  4  and  5  are controlled by zone control module  206  and zone  6  is controlled by discharge interface module  208 . As mentioned above, in the run up once accumulation mode, zone  6  is inactive until such time as a release command is received from an external system. 
         [0072]      FIG. 13A  illustrates packages  1 ,  2  and  3  on the accumulation conveyor. Package  1  is occupying sensor  198   a  of zone  5 , and zones  1 - 5  are active, with zone  6  being inactive. At  FIG. 13B , package  1  is transferring onto inactive zone  6 , and packages  2  and  3  are occupying sensors  194   a  and  192   a  of zones  3  and  2  respectively. With package  4  occupying sensor  190   a , zone  1  is set to inactive. In  FIG. 13C , package  2  is no longer occupying sensor  194   a , so zone  1  has been set to active.  FIG. 13D  illustrates package  2  occupying sensor  198   a  of zone  5 . Zone  5  being the second most downstream zone following the run up once control logic, with the immediate downstream sensor  200   a  occupied, and the zone  5  sensor occupied, zone  5  is set to inactive. In  FIG. 13E , zones  3  and  4  are inactive as a result of those zones being occupied and their respective downstream two zones being occupied. 
         [0073]      FIG. 13F  depicts the removal of package  3  from the accumulation conveyor. Zone  4  remains inactive even though sensor  196   a  is clear because zone  4  is latched as a result of the two downstream sensors  198   a  and  200   a  being occupied. Zone  3  has became active as a result of sensor  196   a  not being occupied.  FIG. 13G  illustrates package  4  advanced to occupy sensor  196   a  of zone  4 , resulting in zone  4  becoming inactive and latched because sensors  198   a  and  200   a  are occupied, and package  5  advanced to occupy sensor  194   a  of zone  3 , resulting in zone  3  becoming inactive and latched because sensors  196   a  and  198   a  are occupied. 
         [0074]    An aspect of the present invention that may be incorporated is zone crowding which is a control strategy designed to optimize usage of an accumulation conveyor. It is common for an accumulated conveyor to still have significant gaps between packages. This is especially true when using extended length zones. The zone crowding control logic functions to reduce gaps between packages after a local zone has been determined to be accumulated. 
         [0075]    Physical crowding is effected through conveyor pulsations implemented through a crowding control algorithm, such as that shown in  FIG. 14 . The crowding control logic is executed for each local zone, being initiated if the immediate downstream zone has been crowded for a period of time and the local zone has been accumulated for a period of time. In one embodiment the period of time is five seconds. 
         [0076]    Referring to  FIG. 14 , the crowding logic determines at step  210  whether the local sensor is clear. If it is clear, the zone is not accumulated, and the crowding routine and five second delay are reset at step  212 . If the local sensor is not clear, the control proceeds to step  214  to determine whether the local zone is already designated as crowded. If it is, the control logic returns to the program housekeeping. If the local zone is not yet crowded, the logic proceeds to step  216  and determines whether the local zone has been designated as accumulated for more than five seconds. If it has not, the crowding program will return to the program housekeeping. If the local zone has been accumulated for more than five seconds, the control logic determines whether the downstream zone is crowded at step  218 . If it is not, the control logic will return to the program housekeeping. If the downstream zone is crowded, then the control logic will initiate the physical crowding of the routine at step  220 . Referring to  FIG. 15 , there is shown the steps of step  220 , starting at  222  with activating the zone for a crowd-on-time period as determined by DIP switch settings. The local zone is next deactivated at step  224  for a crowd-off-time, also determined by DIP switch settings. Steps  226  and  228  increment and compare the number of iterations executed and once the number of iterations meet a desired or defined number, the control logic returns to step  230  shown in  FIG. 14  where the logic determines whether the local sensor is clear. If it is, the crowding routine and time delay is reset at  212 . If not, the control continues to step  232  and checks if crowding is complete. If it is not, the control returns to the crowding in progress step  220 . If crowding is complete the local zone crowded flag is set at step  234 . 
         [0077]    Referring to  FIG. 16 , there is shown an alternate embodiment of a portion of the control logic illustrated in  FIGS. 14 and 15 . The numbering of the steps in  FIG. 16  correspond to the numbering of the corresponding steps in  FIGS. 14 and 15 , with the addition of ′ to each number. The steps in  FIG. 16  that have truncated lead lines connect to the corresponding steps found in  FIGS. 14 and 15 . 
         [0078]    In one embodiment, the DIP switch settings were configured to select between the following crowd-on-time/crowd-off-time/number of iterations: 0/not applicable/0; 0.400 secs/2.0 secs/3 iterations; 0.550 secs/2.5 secs/3 iterations; and 0.700 secs/3.0 secs/3 iterations. The crowd-on-time must be long enough to be effective—it must be long enough to achieve the conveyor speed sufficient to deliver the desired surge. Other considerations include desired carton density and collision tolerance of the cartons. The crowd-off-time is selected to be long enough to allow the conveyor to stop. A high crowd-off-time would be required in conjunction with a high crowd-on-time. 
         [0079]    Crowding does not have to be implemented on a global basis, and some zones may have the crowding routine disabled, set by the position of a DIP switch. Any zone or control module with crowding disabled will not run the crowding routine and will report to it&#39;s upstream neighbor that it is crowded. The discharge zone may always have crowding disabled. 
         [0080]    One aspect that may be included in embodiments of the present invention is a zone snooze feature with a two zone advance restart. The snooze function temporarily suspends operation of an active zone that has not sensed any product movement for a period of time. Snooze may be a global setting and may be turned on and off at the interface module. The snooze logic monitors the status of the local zone sensor and the status of the first and second upstream sensors. If all three zones have been clear for a period of time, tracked by the snooze timer, set at twenty seconds in one embodiment, the local zone will enter snooze mode. While the zone is in snooze mode, the zone is inactive. 
         [0081]      FIG. 17  illustrates control logic steps related to “waking” a snoozing zone which is repeatedly executed for each zone sensor of the accumulation conveyor, regardless whether the associated zone is snoozing. Step  236  verifies that snooze is enabled for the particular zone. At step  238 , the logic determines whether the local zone sensor is blocked. If it is not, no action is taken and the program returns to the beginning. If, at  238 , the local zone sensor is blocked, the logic proceeds to step  240  where the snooze timer and snooze state (if set) is reset for all zones controlled by the particular module. This means that if the snooze state of the zone is snoozing, its state is reset and the zone is wakened. The control then proceeds to step  242  and resets the snooze timer and snooze state (if set) for the nearest downstream zone. The control then proceeds to step  244  and resets the snooze timer and snooze state (if set) for the second nearest downstream zone. Essentially, a zone will exit snooze mode when its local zone sensor or the two immediate upstream zone sensors are blocked. If the sensor of a snoozing zone becomes blocked, the next two downstream zones will be woken up. 
         [0082]    Another feature that may be included in embodiments of the present invention is flow and jam detection. If the local zone sensor is blocked and the local zone is active, and the sensor of the downstream zone has been clear for more than a period of time, such as ten seconds, and the upstream zone sensor is blocked, a warning flag is set. The system tries to push through any package in the upstream zone, by coupling the local zone to the downstream zone&#39;s logic states. In effect the local zone reports the same logic state (blocked, clear, occupied, not occupied) to the upstream zone that it is receiving from the downstream zone. The causes the upstream zone to be active. If the upstream zone sensor remains blocked for more than a period of time, such as for example, 30 seconds, and the downstream zone sensor has not been blocked during the same time period, then a jam has been detected and the local zone is decoupled from the downstream zone and reports occupied upstream, starting the accumulation process upstream of the jam. If during this 30 second time period, the “push through”, the downstream zone sensor becomes blocked, it indicates that product can move through the local zone and the local zone stays coupled to the downstream zone. The system stays in either the jam state or the coupled state until the local zone sensor becomes clear at which time all error and warning flags related to the local zone are canceled. While in such a jam condition, global slug release will function as normal downstream of the jam. The local zone release function is disabled for the jammed zone, with release being subject to the jam detect and push-through logic functionality described herein. 
         [0083]    Referring to  FIG. 18  which illustrates the flow and jam detect control logic, at  246  the control determines whether the local zone sensor is blocked and if the local zone is active. If either the local zone sensor is not blocked or the local zone is inactive, the control moves to  248 , at which it is determined whether the local zone sensor is clear the control logic resets the flags and decouples the local zone if it is coupled. If the local zone sensor is blocked, the control logic exits. If at  246  the local zone sensor is blocked and the local zone is active, the control moves to step  252  where it determines whether the JAM flag is set, indicating that the zone has been flagged as jammed. If the JAM flag is set, the control logic will return to the beginning at step  246 . If the JAM flag is not set, the control will proceed to step  254 . If at  254  the downstream zone is clear and active, and the upstream zone is occupied, for greater than a time period, in the embodiment depicted, 10 seconds, the control will proceed to step  256  at which the downstream zone is coupled to the local zone, that is the logic stats of the downstream zone are sent to the local zone. From there, the control goes to step  258  and sets the flag Zone Flow warning and flashes the local zone LED. The control proceeds to step  260  and it tests whether the downstream zone is clear and active an the upstream zone is blocked for greater than a time period, in the embodiment, 30 seconds. If it has been, then the attempt to push through the jam is terminated and at step  262  the local zone is uncoupled from the downstream zone. If it has been less than 30 seconds, the control logic loops back to  246  and continues to attempt to push through the jam. From step  262 , the control sets the JAM flag at  264  and then returns to  246 . With the JAM flag set, the control will loop out at step  252 , avoiding additional attempts at pushing through the jam. 
         [0084]    In some of the FIGS. used herein, abbreviations are used. The following chart sets forth some of them:
       DZCM—Dual Zone Control Module   DZIM—Dual Zone Interface Module   DZCS—Dual Zone Control System   LZ—Local Zone   DSZ—Downstream Zone   USZ—Upstream Zone   DSS—Downstream Sensor   LSS—Local Zone Sensor       
 
         [0093]    The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims submitted herewith.