Abstract:
Contiguous independently-controllable conveyor system zones are controlled by zone control modules executing a program element associated with each module. Each module is coupled with an object detector and a conveyor zone actuator. A two-way zone control module communication port is coupled with two adjacent upstream zone control module communication ports and two adjacent downstream zone control module communication ports. An object detector port is coupled with an object detector, an actuator control port is coupled with an actuator, and a conveyor zone actuator is thereby controlled. Memory allocation in a module includes an event logic element responsive to inputs from adjacent upstream and downstream module communication ports. A program element associated with each module identifies the position of the module in a series of modules. The actuator is controlled by an event logic element, and by communication from an object detector and an adjacent upstream and downstream module.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 10/383,890, filed Mar. 7, 2003, now U.S. Pat. No. 7,280,889, issued Oct. 9, 2007, which claims the benefit of U.S. provisional application Ser. No. 60/319,140, filed Mar. 8, 2002, which are incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a conveyor system having zone control modules which can detect product on an attached conveyor. More specifically, the invention relates to a zone control module which can be programmed with specific features and operational criteria by various hard wired or wireless devices. Additionally, the invention relates to a conveyor control system that can have several interconnected zone control modules which can pass operational information to one another using a simplified communications protocol, and to an interface which translates the simplified protocol to a standard communications network protocol that can communicate with a standard PC-based or networked computer environment. 
     DESCRIPTION OF THE RELATED ART 
     Conveyor control systems typically include one or more “zone” control modules which let a controller for the conveyor system detect the status (i.e. location) of objects being conveyed on the system. An example of such a system is disclosed in U.S. Pat. No. 6,302,266, issued Oct. 16, 2001, which discloses a conveyor system comprising a series of rollers rotatably mounted to a frame. The rollers are organized into roller “zones” in which the rollers in a zone operate in concert. A continuous-loop drive belt passes beneath the rollers, and is selectively brought into contact with a selected roller zone by a pneumatic actuator which, when actuated, extends to abut the belt with a selected number of rollers, and, when retracted, removes the abutment of the belt with the rollers. A plurality of interconnected zone control modules and photo-electric sensing devices (often referred to as “photo-eyes”) are mounted in a suitable fashion at regular intervals to the frame, with each zone control module and photo-eye operably associated with a specific zone. Each zone control module incorporates a solenoid-driven pneumatic valve for delivering pressurized air to the pneumatic actuator serving that module. A signal from the photo-eye, indicating the presence or absence of a package on the associated zone, will activate the zone control module and the pneumatic actuator for a specific zone. 
     One problem with the prior art network or PC-based conveyor systems is that they are typically server-based systems, where every zone control module must be separately connected to the server. Furthermore, each zone control module must have a unique ID, which must be reprogrammed into the system contol program when the zone control module is replaced, or new modules added. Wiring must typically be run to each zone control module, and then bussed to a controller which must decipher which zone the information came from. 
     This problem has been addressed by providing conveyor control modules with microprocessors which can deliver additional information via standard networking/communication protocols (i.e. RS-232). However, there remain problems with the prior art conveyor systems. These prior art devices require accurate positioning information to determine the zone control module&#39;s location in a series of modules. Often, standard networking protocols require a unique zone control module ID for each module, making replacement and repair to conveyor control systems difficult. 
     SUMMARY OF THE INVENTION 
     Controlling at least one of a plurality of contiguous independently-controllable zones in a conveyor system includes providing a zone control module for each one of the plurality of contiguous independently-controllable zones, providing a position-sensitive program element associated with each zone control module, coupling each zone control module with at least one object detector port, coupling each zone control module with at least one actuator control port, coupling at least one two-way zone control module communication port with at least one of at least two adjacent upstream zone control module communication ports and at least two adjacent downstream zone control module communication ports, coupling an object detector port with an object detector, coupling an actuator control port with an actuator, and controlling the state of a conveyor zone actuator. 
     The zone control module has a signal processor/generator, an object detector port, an actuator control port, at least one two-way zone control module communication port, and memory allocation having at least one event logic element responsive to inputs from at least two adjacent upstream zone control module communication ports and at least two adjacent downstream zone control module communication ports. A position-sensitive program element associated with each zone control module identifies the position of the zone control module in a series of zone control modules. Each zone control module is coupled with at least one object detector port adapted for coupling with at least one object detector. Each zone control module is coupled with at least one actuator control port adapted for coupling with at least one conveyor zone actuator. The state of a conveyor zone actuator is controlled by at least one event logic element, and by response of a signal processor/generator to communication from an object detector and from at least one adjacent upstream and downstream zone control module. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a perspective view of an embodiment comprising a portion of a conveyor system comprising microprocessor-based networkable zone control modules according to the invention. 
         FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a close-up perspective view of a networkable zone control module as shown in  FIG. 1 . 
         FIG. 4  is a configuration drawing of a control system for the conveyor system shown in  FIG. 1  showing a series of networked zone control modules according to the invention interconnected to a prior art server-based system via an interpreter also according to the invention via conventional interconnections. 
         FIG. 5  is a configuration drawing of a first alternative control system for the conveyor system shown in  FIG. 1  showing simply a series of interconnected zone control modules according to the invention terminated at upstream and downstream ends by terminators. 
         FIG. 6  is a configuration drawing of a second alternative control system for the conveyor system shown in  FIG. 1  including a master configuration module having mode-select switches. 
         FIG. 7  is a representation of the master configuration module shown in  FIG. 6  illustrating the position of the mode-select switches for selected configuration functions. 
         FIG. 8  is a drawing of a portion of the conveyor system shown in  FIG. 1  illustrating an identification convention for a series of interconnected zone control modules according to the invention. 
         FIG. 9  is a flow chart drawing of a portion of a microprocessor-based collection of event logic elements for evaluating information received by a zone control module in the system shown in  FIG. 1 . 
         FIG. 10  is a flow chart drawing of a first event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a local photo-eye event. 
         FIG. 11  is a flow chart drawing of a second event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a photo-eye delay timer event. 
         FIG. 12  is a flow chart drawing of a third event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating an auto-slug initiation event. 
         FIG. 13  is a flow chart drawing of a fourth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating an auto-slug termination event. 
         FIG. 14  is a flow chart drawing of a fifth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating an auto-slug delay timer event. 
         FIG. 15  is a flow chart drawing of a sixth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a second upstream photo-eye event. 
         FIG. 16  is a flow chart drawing of a seventh event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a first upstream photo-eye event. 
         FIG. 17  is a flow chart drawing of an eighth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a first downstream photo-eye event. 
         FIG. 18  is a flow chart drawing of a ninth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a smart photo-eye event. 
         FIG. 19  is a flow chart drawing of a tenth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a release message event. 
         FIG. 20  is a flow chart drawing of an eleventh event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating an upstream slug message event. 
         FIG. 21  is a flow chart drawing of a twelfth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a second downstream photo-eye event. 
         FIG. 22  is a flow chart drawing of a thirteenth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a downstream slug message event. 
         FIG. 23  is a flow chart drawing of a fourteenth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating an external jam event. 
         FIG. 24  is a flow chart drawing of a fifteenth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a sleep timer event. 
         FIG. 25  is a flow chart drawing of a sixteenth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a jam timer event. 
         FIG. 26  is a flow chart drawing of a seventeenth event logic element of the microprocessor-based collection of event logic elements shown in  FIG. 9  for evaluating a fourth photo-eye pin event. 
         FIG. 27A  is a flow chart of a first portion of a hierarchy logicprocess of the microprocessor-based collection of event logic elements shown in  FIG. 9 . 
         FIG. 27B  is a continued flow chart of a second portion of a hierarchy logic process of the microprocessor-based collection of event logic elements shown in  FIG. 9 . 
         FIG. 28  is a drawing of an organizational arrangement of configurations, timers, and variables for processing by the microprocessor shown in  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, and to  FIGS. 1-3  in particular, a preferred embodiment of the invention comprises a conveyor system  10  comprising a series of rollers  12  rotatably mounted between a back rail  14  and a front rail  16  in a conventional manner. The rollers  12  can be operably organized into roller units  13 , or “zones,” comprising a selected number of rollers  12  in which the rollers  12  in a zone  13  will operate in concert. A continuous-loop drive belt  18  moves beneath the rollers  12 , and is selectively brought into contact with a selected zone  13  by a drive plate  36  which is raised against an overlying zone  13  by a pneumatic actuator  38 . A plurality of interconnected zone control modules  20  are mounted in a suitable fashion, such as by a clip integrated into the zone control module  20  or a threaded fastener, at regular intervals to the front rail  16 , with each zone control module  20  operably associated with a specific zone  13 . It will be understood that the particular mounting arrangement of the modules  20  to the rails  14 ,  16  is not critical to the invention, and any suitable arrangement will be apparent to one skilled in the art. 
     Each zone control module  20  is interconnected with an associated photo-electric sensing device  22 , such as an optical sensor or a photo-eye, in a peer-to-peer network according to the invention. The optical sensors  22  are mounted to the front rail  16  through a suitable sensor mount, such as a bracket, and are adapted to detect the physical presence of an object, such as a carton (shown by example by reference numerals  30 ,  32 ,  34 ) being conveyed along the conveyor system  10 . Each optical sensor  22  is provided with a mating receiver  24  mounted to the back rail  14  so that an optical signal or photoelectric beam, shown in  FIG. 1  as a sensor beam  26 , is transmitted between the optical sensor  22  and the receiver  24 . The optical sensor  22  and the receiver  24  are shown operating in a direction perpendicular to the direction of travel of the conveyor system  10 , but the operation direction shown in  FIG. 1  shall not be construed as limiting on the invention and can be skewed relative to the direction of travel of the conveyor system  10  without departing from the scope of the invention. The zone control modules  20  are communicably interconnected by control cables  28  adapted for the transmission of digital information, including information from the optical sensors  22 , among the zone control modules  20 . The control cables  28  also supply power to the optical sensors  22  and the zone control modules  20 . 
     Selected optical sensors  22  can be programmed as “smart photo-eyes” for reporting package movement conditions along the conveyor system  10  to an installation computer system  68 . Whenever the photoelectric beam from the smart photo-eye is interrupted, the zone control module associated with the smart photo-eye sends a signal to the main computer or server  68 . This information, combined with similar information from the other smart photo-eyes provides real-time reporting on the available capacity of the conveyor system  10 . Alternatively, the computer  68  can periodically request information from each smart photo-eye according to a preselected schedule. 
     In the preferred embodiment, the zone control module  20  comprises a housing  40  adapted to enclose a solenoid-operated pneumatic valve (not shown) and a digital microprocessor (not shown). The housing  40  is provided with suitable fittings for fluid connection of a common air line  29  interconnecting adjoining zone control modules  20  as shown in  FIG. 1 , and fluidly connecting the zone control modules  20  to a source of pressurized air (not shown). The pneumatic valve is fluidly connected to the air line  29  and to the pneumatic actuator  38  via a pneumatic actuator outlet  50 . The pneumatic valve fluidly interconnects the air line  29  with the pneumatic actuator  38  for selectively activating and deactivating the pneumatic actuator  38 . A pneumatic actuator exhaust port  52  is also fluidly connected to the pneumatic valve for selectively exhausting air from the pneumatic actuator  38  when the pneumatic actuator  38  is deactivated. 
     There are several terms used herein which may have a further definition beyond their ordinary meaning and, thus, are set forth below in Table 1. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 TERM 
                 DEFINITION 
               
               
                   
               
             
             
               
                 ACCUMU- 
                 A condition wherein, if a LOCAL MODULE receives an 
               
               
                 LATION 
                 accumulation signal from DS1, the pneumatic valve 
               
               
                   
                 is turned OFF. 
               
               
                 AUTO- 
                 An operational mode in which a zone control module 
               
               
                 SLUG 
                 which is pre-configured to accept/generate an 
               
               
                   
                 AUTO-SLUG signal will activate a LOCAL pneumatic 
               
               
                   
                 valve when the LOCAL MODULE generates or receives 
               
               
                   
                 an AUTO-SLUG signal from a downstream zone 
               
               
                   
                 control module. 
               
               
                 DS1 
                 First zone control module removed from the LOCAL 
               
               
                   
                 MODULE in the direction of conveyor travel. 
               
               
                 DS2 
                 Second zone control module removed from the LOCAL 
               
               
                   
                 MODULE in the direction of conveyor travel. 
               
               
                 EXTREME 
                 A zone control module which can be configured for 
               
               
                 DOWN- 
                 an auto detection condition or an installation 
               
               
                 STREAM 
                 system-configured condition. For auto detection, a 
               
               
                 MODULE 
                 termination plug is placed on the uncoupled cable 
               
               
                 (EDM) 
                 end. This protects the connectors and attaches the 
               
               
                   
                 signal wires to ground. By grounding the signal 
               
               
                   
                 wires, the EDM module automatically detects its 
               
               
                   
                 unique location and responds to events appropriately. 
               
               
                   
                 For an installation system configuration, the EDM 
               
               
                   
                 module is mapped in the system software. During 
               
               
                   
                 initial start up, the EDM module is configured for 
               
               
                   
                 its unique location and responds to events 
               
               
                   
                 appropriately. The EDM module also releases and 
               
               
                   
                 accumulates as dictated by signals transmitted 
               
               
                   
                 from the installation computer system. 
               
               
                 JAM 
                 An operational mode reflecting one or more jammed 
               
               
                   
                 packages so that a LOCAL P.E. remains in a 
               
               
                   
                 “blocked” state, the DSI and DS2 P.E.s remained 
               
               
                   
                 “unblocked,” and the LOCAL VALVE is in an 
               
               
                   
                 “on” state after a predetermined amount of 
               
               
                   
                 time, i.e. the JAM TIMER. If the JAM TIMER is allowed 
               
               
                   
                 to expire, the LOCAL VALVE is left turned “on” 
               
               
                   
                 in an attempt to “clear” the jam, and the 
               
               
                   
                 LOCAL MODULE passes a JAM “ON” signal to US1, 
               
               
                   
                 terminating any slug or auto-slug operations upstream, 
               
               
                   
                 stopping moving product. Normal operation begins when 
               
               
                   
                 the LOCAL P.E. is clear. If the LOCAL MODULE is the 
               
               
                   
                 recipient of a JAM signal from DS1, the LOCAL 
               
               
                   
                 MODULE turns the LOCAL VALVE “off” and begins 
               
               
                   
                 accumulation. This accumulation propagates upstream. 
               
               
                   
                 If a LOCAL P.E. change in state does not occur 
               
               
                   
                 within the JAM TIMER, any slug or auto-slug 
               
               
                   
                 operations are terminated, and a JAM signal is 
               
               
                   
                 transmitted to US1 and the interpreter. If the 
               
               
                   
                 LOCAL P.E. clears, then a JAM CLEARED signal is 
               
               
                   
                 transmitted to US1 and the interpreter. 
               
               
                   
                 If a JAM signal is received from DS1, then the 
               
               
                   
                 LOCAL MODULE enters an accumulation condition. If 
               
               
                   
                 a JAM CLEARED signal is received from US1, then 
               
               
                   
                 the LOCAL MODULE enters a release condition. 
               
               
                 JAM 
                 A predetermined amount of time, T j , to detect a 
               
               
                 TIMER 
                 JAM by monitoring the LOCAL P.E., and the DS1 
               
               
                   
                 and DS2 P.E.s. 
               
               
                 LOCAL 
                 A zone control module under the influence of 
               
               
                   
                 selected zone control modules located 
               
               
                   
                 immediately upstream and downstream, i.e. 
               
               
                   
                 US1, US2, DS1, DS2. 
               
               
                 P.E. 
                 Photo-eye; a photo-electric, product sensing 
               
               
                   
                 device. 
               
               
                 RELEASE 
                 A condition of the Extreme Downstream Module 
               
               
                   
                 (EDM) wherein, if a RELEASE signal is received 
               
               
                   
                 from US1, the LOCAL VALVE is turned “on.” 
               
               
                 SLEEP 
                 An operational mode in which, after a 
               
               
                 MODE 
                 predetermined amount of time, i.e. the 
               
               
                   
                 SLEEP TIMER, the LOCAL VALVE is turned 
               
               
                   
                 “off” until a WAKE-UP signal is 
               
               
                   
                 received. The SLEEP TIMER is started when the 
               
               
                   
                 LOCAL, US1, and US2 P.E.s are cleared. If the 
               
               
                   
                 P.E.s change state, the SLEEP TIMER is 
               
               
                   
                 reset. If the SLEEP TIMER expires prior 
               
               
                   
                 to a change in the P.E. state, 
               
               
                   
                 the LOCAL VALVE is turned “off.” 
               
               
                 SLEEP 
                 A predetermined amount of time, T s , to wait 
               
               
                 TIMER 
                 before turning the LOCAL VALVE “off.” 
               
               
                 SLUG 
                 An operational mode in which a plurality of 
               
               
                   
                 zone control modules are signaled to 
               
               
                   
                 activate their VALVES to convey moving 
               
               
                   
                 product irrespective of P.E. inputs. 
               
               
                 SMART 
                 An operational mode in which, if a zone control 
               
               
                 SENSOR 
                 module is designated as a SMART SENSOR, 
               
               
                 (P.E.) 
                 the LOCAL P.E. status is transmitted to 
               
               
                   
                 the interpreter for diagnostic purposes. 
               
               
                 US1 
                 The first zone control module removed from 
               
               
                   
                 the LOCAL MODULE in the direction opposite 
               
               
                   
                 to the direction of conveyor travel. 
               
               
                 US2 
                 The second zone control module removed from 
               
               
                   
                 the LOCAL MODULE in the direction opposite 
               
               
                   
                 to the direction of conveyor travel. 
               
               
                 VALVE 
                 A solenoid valve incorporated into each zone 
               
               
                   
                 control module. The circuit board logic 
               
               
                   
                 turns the VALVE “on” or “off” 
               
               
                   
                 based on external inputs. 
               
               
                 WAKE-UP 
                 A signal that is transmitted to the LOCAL MODULE 
               
               
                   
                 from US1 or US2 when the US1 or US2 P.E.s become 
               
               
                   
                 blocked. This signal “wakes up” the 
               
               
                   
                 LOCAL MODULE and returns the LOCAL MODULE 
               
               
                   
                 to normal operation. A LOCAL MODULE P.E. can 
               
               
                   
                 also create a WAKE-UP signal when it indicates 
               
               
                   
                 a “blocked” condition. 
               
               
                   
               
             
          
         
       
     
     A microprocessor comprises a programmable digital processor in the zone control module  20  operatively connected to a downstream control cable  42  and an upstream control cable  46  for operably interconnecting adjacent zone control modules  20  in series, as shown in  FIG. 1 . The microprocessor can process information in a conventional manner, such as in 8-bit bytes, each byte conveying information as to the type of information processed, the message or command processed, and a counter. For example, a first byte can identify the type of message being sent. A second byte can contain the actual message content. The third byte is simply a counter that is initiated at some predetermined value (such as 0 or 1) and incremented by each zone control module  20  that passes the message along through the number of interconnected zone control modules  20  in a contiguous series. The microprocessor is preferably pre-programmed to perform a logic process, shown in  FIGS. 9-26 , and a hierarchy process shown in  FIGS. 27A and 27B . Further description of the messaging protocol employed by peer-to-peer networked zone control modules  20  will be provided in greater detail below. 
     There are various communications protocols employed during operable interconnection of the zone control modules  20 , the interpreter  60  and a master/server computer  68  (such as that typically used in a Field Bus environment), as shown in  FIG. 4 . 
     A master/slave concept is used to control communications between the various system elements:
         master/server installation computer  68  or temporarily installed computers  74  to the interpreters  60 ,   interpreters  60  to zone control modules  20 , or   zone control module  20  to zone control module  20 ,
 
with the master/server installation computer  68  serving as the ultimate “master” in the above listed combinations. The master in this master/slave concept is always upstream of the slave. For example, the interpreter  60  is a slave to either the master/server installation computer  68  or the temporarily installed computer  74  while the most upstream zone control module  20  is a slave to the interpreter  60 . Additionally, a downstream zone control module  20  is the slave to an upstream zone control module  20 .
       

     A baud clock can be generated by the master and sent to the slave to send or retrieve data/status information. The data signal level is changed by the master or slave during the logic “low” level of the baud clock and read by the master or slave during the logic “high” level of the baud clock. 
     With respect to the zone control modules  20  and the master/slave implementation, an upstream end point of a series of interconnected zone control modules  20  can be determined by the absence of the baud clock. To determine a downstream endpoint, an upstream master control module polls the downstream zone control module (slave) for acknowledgment (ACK) as is further described below. If no ACK signal is received from the downstream endpoint zone control module (a slave), the master upstream zone control module determines that zone control module to be the downstream endpoint. If an ACK is received from a particular polled zone control module, the endpoint determination is passed to the next successive downstream zone control module via the master/slave concept. 
     The upstream master zone control module can send any size data packets, and terminates with an end-of-signal marker (e.g., such as an ACK signal). The ACK signals the slave zone control module that the master zone control module has finished transmitting and has set the data line as an input and that it is available for the slave zone control module to transmit its data/status. A slave zone control module can send any size data packet to the master zone control module ending with an end-of-message marker (e.g., the last data item being an ACK). The ACK signal not only signals the upstream master zone control module that a downstream zone control module is present, it also signals that the downstream slave zone control module is no longer driving the data line and the upstream master zone control module can now have output drive access of it. If no ACK is received from a zone control module, it is assumed that a downstream zone control module is not present and the master zone control module is at a downstream endpoint. 
     Several examples of data protocols will now be described with the understanding that they are by example only, and that other communications protocols or methods can be used without departing from the scope of this invention. 
     With respect to the data protocol used in these examples, data is transmitted in the following example format. There is an initial start bit followed by eight data bits (bit  7  is used to determine a packet type, e.g., if bit  7 =1 it is a control byte, if bit  7 =0, it is a data byte), and is terminated with one stop bit. The following table identifies some example codes used in the protocol: 
     
       
         
               
               
               
             
           
               
                   
               
               
                   
                 Data 
                 Definition 
               
               
                   
               
             
             
               
                   
                 FF 
                 Packet Start 
               
               
                   
                 AA 
                 ACK 
               
               
                   
                 00-7F 
                 Data 
               
               
                   
               
             
          
         
       
     
     Using the above-described communication codes, several example message formats will now be described for communication between a computer  68 ,  74 , the interpreter  60  and the various zone control modules  20 . 
     The following table describes communication from the interpreter  60  to the various zone control modules  20 . 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration Packet: From Interpreter 
               
               
                 60 to Zone Control Modules 20 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Byte 1 
                 Header(0x81) 
               
               
                   
                 Byte 2 
                 Length 
               
               
                   
                   
                 # bytes in packet not including header or length 
               
               
                   
                   
                 but including checksum. 
               
               
                   
                 Byte 3 
                 Node Number (ADDRESS). If MSB is set then 
               
               
                   
                   
                 address is “ALL” nodes. 
               
               
                   
                 Byte 4 
                 Bit0 Sleep Enabled (Y/N) 
               
               
                   
                   
                 Bit1 Jam Enabled (Y/N) 
               
               
                   
                   
                 Bit2 External Slug Enabled (Y/N) 
               
               
                   
                   
                 Bit3 Auto Slug Enabled (Y/N) 
               
               
                   
                   
                 Bit4 Smart Eye (Y/N) 
               
               
                   
                   
                 Bit5 Sleep Timer Length to Follow (Y/N) 
               
               
                   
                   
                 Bit6 Jam Timer Length to Follow (Y/N) 
               
               
                   
                   
                 Bit7 Slug Line (Y/N) 
               
               
                   
                 Byte 5 
                 Sleep OR Jam timer value if at least 1 timer selected. 
               
               
                   
                   
                 If neither selected, no data byte. 
               
               
                   
                 Byte 6 
                 Jam timer value if both selected. 
               
               
                   
                   
                 If only one or neither, no data byte. 
               
               
                   
                 Byte N 
                 Checksum. 1 byte sum of all bytes excluding 
               
               
                   
                   
                 header and checksum. 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Status Packet: From Nodes to Int. Controller 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Byte 1 
                 Header (0x80) 
               
               
                   
                 Byte 2 
                 Length. No. of bytes in packet not including header 
               
               
                   
                   
                 or length but including checksum. 
               
               
                   
                 Byte 3 
                 Node no (e.g., “Address”). 
               
               
                   
                 Byte 4 
                 Data. 
               
               
                   
                   
                 Byte1 
               
               
                   
                   
                 Bit0 PhotoEye (0 = off, 1 = on) 
               
               
                   
                   
                 Bit1 Solenoid (0 = off, 1 = on) 
               
               
                   
                   
                 Bit2-7 Available for use (all 0&#39;s by default) 
               
               
                   
                 Byte 5 
                 Checksum. 1 byte sum of all bytes excluding header 
               
               
                   
                   
                 and checksum. 
               
               
                   
               
             
          
         
       
     
     The following table describes a configuration communication between an external computer  68 ,  74  and the various zone control modules  20 . 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration Packet: From External Computer 
               
               
                 68, 74 to Zone Control Modules 20 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Byte 1 
                 Header(0x81) 
               
               
                   
                 Byte 2 
                 Length. No. of bytes in packet not including header 
               
               
                   
                   
                 or length but including checksum. 
               
               
                   
                 Byte 3 
                 Node number (e.g., “Address”). If MSB is set 
               
               
                   
                   
                 then address is “ALL” nodes. 
               
               
                   
                 Byte 4 
                 Data. 
               
               
                   
                   
                 Bit0 Sleep Enabled (Y/N) 
               
               
                   
                   
                 Bit1 Jam Enabled (Y/N) 
               
               
                   
                   
                 Bit2 External Slug Enabled (Y/N) 
               
               
                   
                   
                 Bit3 Auto Slug Enabled (Y/N) 
               
               
                   
                   
                 Bit4 Smart Eye (Y/N) 
               
               
                   
                   
                 Bit5 Slug Line (Y/N) 
               
               
                   
                   
                 Bit6 Available (defaults to 0) 
               
               
                   
                   
                 Bit7 Available (defaults to 0) 
               
               
                   
                 Byte 5 
                 Sleep OR Jam timer value if at least 1 timer 
               
               
                   
                   
                 selected. If neither selected, no data byte. 
               
               
                   
                 Byte 6 
                 Jam timer value if both selected. If only one or 
               
               
                   
                   
                 neither, no data byte. 
               
               
                   
                 Byte N 
                 Checksum. 1 byte sum of all bytes excluding header 
               
               
                   
                   
                 and checksum. 
               
               
                   
               
             
          
         
       
     
     The following table describes a configuration request communication between an external computer  68 ,  74  and the various zone control modules  20 . 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Configuration Request Packet: From External 
               
               
                 Computer 68, 74 to Zone Control Modules 20 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Byte 1 
                 Header (0x81) 
               
               
                   
                 Byte 2 
                 Length. No. of bytes in packet not 
               
               
                   
                   
                 including header or length but including checksum. 
               
               
                   
                 Byte 3 
                 Node number (e.g., “Address”). If MSB is 
               
               
                   
                   
                 set then address is “ALL” nodes. 
               
               
                   
                 Byte 4 
                 Data. 
               
               
                   
                   
                 Bit0 0 
               
               
                   
                   
                 Bit1 0 
               
               
                   
                   
                 Bit2 0 
               
               
                   
                   
                 Bit3 0 
               
               
                   
                   
                 Bit4 0 
               
               
                   
                   
                 Bit5 0 
               
               
                   
                   
                 Bit6 1 
               
               
                   
                   
                 Bit7 1 
               
               
                   
                 Byte 5 
                 Checksum. 1 byte sum of all bytes 
               
               
                   
                   
                 excluding header and checksum. 
               
               
                   
               
             
          
         
       
     
     The following table describes a configuration request communication between an the various zone control modules  20  and an external computer  68 ,  74  to indicate the status of a particular zone control module  20 . 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Status Packet: From Zone Control Modules 
               
               
                 20 to External Computer 68, 74 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Byte 1 
                 Header (0x80) 
               
               
                   
                 Byte 2 
                 Length. No. of bytes in packet not 
               
               
                   
                   
                 including header or length but including checksum. 
               
               
                   
                 Byte 3 
                 Node no. (e.g., “Address”). 
               
               
                   
                 Byte 4 
                 Data. 
               
               
                   
                   
                 Bit0 PhotoEye (0 = off, 1 = on) 
               
               
                   
                   
                 Bit1 Solenoid (0 = off, 1 = on) 
               
               
                   
                   
                 Bit2 Sleep Enabled (Y/N) 
               
               
                   
                   
                 Bit3 Jam Enabled (Y/N) 
               
               
                   
                   
                 Bit4 External Slug Enabled (Y/N) 
               
               
                   
                   
                 Bit5 Auto Slug Enabled (Y/N) 
               
               
                   
                   
                 Bit6 Smart Eye (Y/N) 
               
               
                   
                   
                 Bit7 Slug Line (Y/N) 
               
               
                   
                 Byte 5 
                 Checksum. 1 byte sum of all bytes 
               
               
                   
                   
                 excluding header and checksum 
               
               
                   
               
             
          
         
       
     
     The zone control module  20  also comprises a data and memory structure comprising configuration settings  340 , timers  342 , and variables  344  illustrated by example in  FIG. 28 . The configuration settings  340  can comprise a sleep setting  346 , a jam setting  348 , an external slug setting  350 , an auto-slug setting  352 , and a smart photo-eye setting  354 . These settings are comprised of binary data (0, 1) either pre-programmed into the microprocessor or transferred to the microprocessor via the installation computer system  68 , a temporarily installed computer  74 , or a wireless device (e.g. a PDA) via an infrared port with the use of the interpreter  60 . A set of configuration setting switches may also be used to input the desired settings to the microprocessor as shown in  FIG. 6  as  82 . The timers  342  can comprise a sleep timer  356  and a jam timer  358 . The timers operate in a conventional manner and need not be described in great detail beyond the events which trigger the timers&#39; initiation and events triggered by the expiration of the timers. The variables  344  can comprise a local photo-eye register  360 , a first downstream photo-eye register  362 , a second downstream photo-eye register  364 , a sleep register  366 , a jam register  368 , a local auto-slug register  370 , an external auto-slug register  372 , and a (controller) slug register  374 . These registers preferably comprise simple on-off devices or standard RAM locations for storing “activated-deactivated” or “enabled-disabled” information. 
     The zone control modules  20  can also be provided with additional timers, including a photo-eye delay timer, and auto-slug delay timer, a sleep timer, and a jam timer. The photo-eye delay timer is initiated when an optical sensor  22  detects the presence of a package. Depending upon whether the optical sensor  22  continues to detect the presence of a package or not before the delay timer expires, the zone control module  20  communicates one or more messages to the upstream and/or downstream zone control modules  20  based upon a collection of event logic elements hereinafter described. The auto-slug delay timer is initiated when a zone control module  20  receives a message from the immediately following downstream zone control module to initiate an auto-slug function. The sleep timer is initiated when the zone control module  20  activates the pneumatic actuator  38 , which activates a zone  13 . If the zone control module  20  has not received a message from another zone control module, or has not detected the presence of a package, before the expiration of the sleep timer, the zone control module  20  enters sleep mode and deactivates the zone  13 . The jam timer is initiated when the zone control module  20  detects the presence of a package and the downstream zone control modules do not detect the presence of packages. If the jam timer expires without a change in this condition, the zone control module  20  communicates a message to upstream zone control modules to prevent the further transfer of packages from upstream. 
     The downstream control cable  42  can be terminated in a downstream connector  44 . The upstream control cable  46  can be terminated in an upstream connector  48  adapted to connect to the downstream connector  44  of an adjacent zone control module  20 , such as through mating male and female connectors, to communicatively connect the zone control modules  20  in series when it no form of the interpreter  60  is used ( FIG. 5 ). The connectors  44 ,  48  comprise conventional 4-pin connectors. 
     An optical sensor input  54  on the zone control module  20  is used to electrically interconnect the zone control module  20  with its associated optical sensor  22 . 
     The operational control configuration of the conveyor system  10  can be modified to provide different levels of operational control. Referring to  FIG. 4 , the zone control modules  20  can be connected in series to terminate at the downstream end of the conveyor system  10  in a downstream cable terminator  62 . At the upstream end, the zone control modules  20  terminate in an interpreter module  60 , which is adapted to communicate with a wireless personal digital assistant (PDA)  64 , or one or more networked computer stations  68  through a field bus  72  connected to a gateway module  66  which is connected to the interpreter module  60  through a field bus  70  using standard network protocols, such as RS-232 or a field bus protocol (as is commonly known in the material handling industry). Alternatively, the interpreter  60  can be connected to a laptop computer  74  using standard network protocols  76 , such as RS-232. This system enables selected zone control modules  20  to be individually programmed by the PDA  64 , the installation computer stations  68 , or the laptop computer  74 . 
     As shown in  FIG. 5 , an alternate configuration utilizes an upstream cable terminator  80  at the upstream termination of the zone control modules  20 , and a logic controller  78  interconnected with the downstream zone control module  20  for controlling the discharge zone as packages leave the zone shown in  FIG. 5  to another handling area in the conveyor system. As shown in  FIG. 6 , in yet another configuration, the upstream cable terminator  80  is replaced with a master configuration module  82  comprising a plurality of mode-select switches  84 . Configuration settings on the master configuration module  82  are propagated to the networked zone control modules  20  through a configuration message in the protocol described herein. 
     Referring now to  FIG. 7 , the master configuration module  82  can comprise a plurality of mode-select switches controlling a selected function. It is to be understood that the master configuration module  82  comprises a portion of the interpreter  60  logic for propagating settings to the zone control modules  20 , without departing from the scope of this invention. For example, the first sleep switch  90  and the second sleep switch  92  control four sleep operations. With both switches  90 ,  92  in the “off” position (up as viewed in  FIG. 7 ), the sleep function will be deactivated. With the first sleep switch  90  in the off position and the second sleep switch  92  in the “on” position, the sleep function will be activated after the expiration of a first interval, such as 2 seconds. With the first sleep switch  90  in the on position and the second sleep switch  92  in the off position, the sleep function will be activated after the expiration of a second interval, such as 5 seconds. Finally, with both switches  90 ,  92  in the on position, the sleep function will be activated after the expiration of a third interval, such as 8 seconds. 
     The jam switch  94  controls a hereinafter-described jam detection operation. With the jam switch  94  in the off position, the jam detection function is deactivated. With the jam switch  94  in the on position, the jam detection function is activated. Similarly, the external slug switch  96  controls a hereinafter-described external slug operation. With the external slug switch  96  in the off position, the external slug function is deactivated. Conversely, with the external slug switch  96  in the on position, the external slug function is activated. Finally, the auto-slug switch  98  controls a hereinafter described auto-slug operation. With the auto-slug switch  98  in the off position, the auto-slug function will be deactivated. With the auto-slug switch  98  in the on position, the auto-slug function will be activated. Activating a switch in the master configuration module  82  sets all zone control module  20  to perform the same function. The jam, external slug, and auto-slug functions will be further described herein with respect to  FIGS. 9-28 . 
       FIG. 8  is a drawing depicting a portion of the conveyor system  10  comprising rollers  12  organized into zones  13  controlled by associated zone control modules  20  and optical sensors  22 . Five zone control modules  20  are shown interconnected as previously described. However, it should be understood that the typical conveyor system  10  will comprise a plurality of zones  13 , corresponding zone control modules  20 , and optical sensors  22 . Nevertheless, the logic for the conveyor control system is structured around an exemplary plurality of zone control modules, or “neighborhood,” comprising five zone control modules  20  comprising a local zone control module  110 , a first downstream zone control module  112  (DS 1 ), a second downstream zone control module  114  (DS 2 ), a first upstream zone control module  116  (US 1 ), and a second upstream zone control module  118  (US 2 ). The five zone control modules  110 - 118  communicate with each other through the control cables  28  as packages travel along the conveyor system  10 . 
     As shown in  FIG. 8A , each zone control module  20  is a local zone control module  110  within a neighborhood of five zone control modules. Each zone control module  110  processes one or more of the event logic elements according to a collection of event logic elements shown in  FIG. 9  and described hereinafter. With respect to an event logic element being processed by a particular zone control module  110 , referred to as the “local” zone control module (L), the two immediately downstream zone control modules  20  and the two immediately upstream zone control modules  20  comprise a particular zone control module&#39;s “neighborhood,” and are identified as the first downstream zone control module  112  (DS 1 ), the second downstream zone control module  114  (DS 2 ), the first upstream zone control module  116  (US 1 ), and the second upstream zone control module  118  (US 2 ). However, each of the two downstream zone control modules  112  (DS 1 ),  114  (DS 2 ) and the two upstream zone control modules  116  (US 1 ),  118  (US 2 ) is also a local zone control module  110  with respect to an event logic element being processed by that zone control module, with its own neighborhood of downstream and upstream zone control modules  112 - 118 . Thus, as shown in  FIGS. 8 and 8A , a particular zone control module  20  can simultaneously comprise a local zone control module  110  (L), a first downstream zone control module  112  (DS 1 ), a second downstream zone control module  114  (DS 2 ), a first upstream zone control module  116  (US 1 ), and a second upstream zone control module  118  (US 2 ) as determined by its processing of an event logic element, or the processing of an event logic element by either of the two downstream zone control modules  112  (DS 1 ),  114  (DS 2 ) or the two upstream zone control modules  116  (US 1 ),  118  (US 2 ). 
     For convenience, the optical sensor  22  associated with a specific zone control module  20  will be referred to by the designation of that zone control module. For example, the optical sensor  22  associated with a local zone control module  110  will be referred to as the local optical sensor or photo-eye, and the optical sensor  22  associated with the second downstream zone control module  114  (DS 2 ) will be referred to as the second downstream optical sensor or photo-eye. 
     The conveyor system  10  can operate in one of several modes, referred to herein as accumulation, slug, auto-slug, jam, and sleep modes. Other modes are conceivable to those skilled in the operation of conveyors and are technically feasible in the embodiment of this invention. 
     In accumulation mode, the local zone control valve is activated if the DS 1  photo-eye indicates that the DS 1  zone is “clear.” Conversely, the local zone control valve is deactivated if the DS 1  photo-eye indicates that the DS 1  zone is “not cleared.” 
     In slug mode, all zones  13  are activated to transfer packages along the conveyor regardless of inputs from the photo-eye  22  (typically used to rapidly advance one or more objects along a conveyor system having a length of unoccupied space). 
     In auto-slug mode, a zone control module  20  which is configured to accept or generate an auto-slug signal will turn a local zone control valve on, thereby activating the zone  13  associated with the local zone control valve, when the local zone control module generates its own auto-slug signal or receives an auto-slug signal from a downstream zone control module. 
     Jam detection mode responds to the condition that occurs when a package is unable to travel down the conveyor system  10 , such as when packages are jammed in such a way as to prevent their further movement. In such a condition, the photo-eye associated with a local zone control module signals the presence of a package, the downstream photo-eyes fail to detect a package, and the local zone control valve remains in an activated state after a predetermined amount of time has expired, referred to as the jam timer. If the jam timer expires, the local zone control valve is left activated to possibly “clear” the jam condition, and the local zone control module passes a “jam on” signal to the first upstream zone control module, disabling any previously enabled slug or auto-slug condition, thereby stopping additional packages from traveling down the conveyor into the jammed zone. Normal conveyor operation resumes when the local photo-eye no longer detects the presence of a package. 
     In sleep mode, the zone control module deactivates the local zone control valve after a predetermined amount of time has expired (sleep timer), during which the local photo-eye  110  and its associated upstream photo-eyes (US 1 , US 2 )  116 ,  118  are “cleared.” The local zone control valve remains deactivated until a change in photo-eye status is received by the local zone control module  110  (L) from the second upstream zone control module  118  (US 2 ), triggering the performance of the hierarchy process, consistent with the event logic element  128  shown in  FIG. 15 , and causing the local zone control module  110  (L) to “wake up” pursuant to hierarchy process steps  258  and  260  shown in  FIG. 27A . A “wake-up” signal is also generated pursuant to the heirarchy process steps  258 ,  260  if a package is placed in the path of a local photo-eye  110 . 
       FIG. 9  illustrates a collection of event logic elements which each zone control module  20  performs whenever it undergoes an event, such as a signal from the photo-eye, or a signal from an upstream or downstream zone control module. Each event initiates the performance of event logic elements associated with that event. 
     For example, an event may comprise a change in the local photo-eye condition, identified in  FIG. 9  as the event  120 , or the expiration of a delay timer, identified in  FIG. 9  as the event  126 . An event may also comprise the receipt of a signal from a remote zone control module correlating to a change in the photo-eye condition associated with that zone control module, such as a change in the photo-eye condition of the first upstream zone control module, identified in  FIG. 9  as the event  130 . Each of these events initiates the performance of event logic elements which are illustrated in  FIGS. 10-26 . The event logic elements associated with events  120 ,  122 ,  124 ,  126 ,  128 ,  130 ,  132 ,  140 ,  142 ,  144 ,  146 ,  148 , and  150  can further initiate the performance of a hierarchy process, shown in  FIGS. 27A and 27B . For purposes of description, the numbering of the event logic elements corresponds with the numbering of the events in  FIG. 9  as shown below in Table 2. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 REFERENCE 
                 FIG. 
               
               
                 EVENT 
                 FUNCTION 
                 NO. 
                 NO. 
               
               
                   
               
             
             
               
                 Local P.E. 
                 Process local photo- 
                 120 
                 10 
               
               
                   
                 eye event 
                   
                   
               
               
                 P.E. DELAY 
                 Process photo-eye 
                 122 
                 11 
               
               
                 TIMER expired 
                 delay timer event 
                   
                   
               
               
                 Start A-SLUG 
                 Process auto-slug 
                 124 
                 12 
               
               
                 received from DS1 
                 initiation event 
                   
                   
               
               
                 Stop A-SLUG 
                 Process auto-slug 
                 125 
                 13 
               
               
                 received from DS1 
                 termination event 
                   
                   
               
               
                 A-SLUG DELAY 
                 Process auto-slug 
                 126 
                 14 
               
               
                 TIMER expired 
                 delay timer event 
                   
                   
               
               
                 Δ US2 P.E. 
                 Process second 
                 128 
                 15 
               
               
                   
                 upstream photo-eye 
                   
                   
               
               
                   
                 status change event 
                   
                   
               
               
                 Δ US1 P.E. 
                 Process first 
                 130 
                 16 
               
               
                   
                 upstream photo-eye 
                   
                   
               
               
                   
                 status change event 
                   
                   
               
               
                 Δ DS1 P.E. 
                 Process first 
                 132 
                 17 
               
               
                   
                 downstream photo- 
                   
                   
               
               
                   
                 eye status change 
                   
                   
               
               
                   
                 event 
                   
                   
               
               
                 Smart P.E. (x) 
                 Process smart 
                 134 
                 18 
               
               
                 received from DS1 
                 photo-eye event 
                   
                   
               
               
                 Release message 
                 Process release 
                 136 
                 19 
               
               
                 (ON/OFF) received 
                 message event 
                   
                   
               
               
                 from US1 
                   
                   
                   
               
               
                 SLUG message 
                 Process upstream 
                 138 
                 20 
               
               
                 (ON/OFF) received 
                 slug message event 
                   
                   
               
               
                 from US1 
                   
                   
                   
               
               
                 Δ DS2 P.E. 
                 Process second 
                 140 
                 21 
               
               
                   
                 downstream photo- 
                   
                   
               
               
                   
                 eye status change 
                   
                   
               
               
                   
                 event 
                   
                   
               
               
                 SLUG message 
                 Process downstream 
                 142 
                 22 
               
               
                 (ON/OFF) received 
                 slug message event 
                   
                   
               
               
                 from DS1 
                   
                   
                   
               
               
                 External JAM (x) 
                 Process external jam 
                 144 
                 23 
               
               
                 (ON/OFF) received 
                 event 
                   
                   
               
               
                 from DS1 
                   
                   
                   
               
               
                 SLEEP TIMER 
                 Process sleep timer 
                 146 
                 24 
               
               
                 expires 
                 event 
                   
                   
               
               
                 JAM TIMER 
                 Process jam timer 
                 148 
                 25 
               
               
                 expires 
                 event 
                   
                   
               
               
                 4th P.E. PIN 
                 Process fourth 
                 150 
                 26 
               
               
                   
                 photo-eye pin event 
               
               
                   
               
             
          
         
       
     
     Referring now to  FIGS. 9 and 10 , the first event logic element  120  evaluates the status of the local photo-eye associated with the local zone control module  110  (i.e. the zone control module responding to an event). The event logic element  120  first evaluates whether the local photo-eye is blocked (decision node  152 ) by a package. If it is, a photo-eye delay timer is started (step  154 ), the event logic element terminates, and the next event (event  122  in this example) is evaluated. A slight delay in the recognition of a blocked local photo-eye accomplishes two functions: 1) it increases the efficiency of the system by decreasing the gap between packages, and 2) it decreases the number of cycles of the local zone control module valve, thereby increasing the longevity of the entire system. If the photo-eye is not blocked, the photo-eye delay timer is stopped (step  155 ), and the local photo-eye condition, i.e. unblocked ( 0 ) or blocked ( 1 ), is stored in the zone control module&#39;s memory (local photo-eye register  360 ) (step  156 ) in order to serve as a baseline for comparison of future photo-eye conditions. The event logic element then evaluates whether the smart photo-eye function is enabled (decision node  158 ) for the local photo-eye in order to control the flow of information from the local photo-eye back to the PDA  64 , the networked computer stations  68 , or the laptop computer  74 . If it is, that information is transmitted to the first upstream zone control module  116  (US 1 ) (step  160 ) as a unique photo-eye location (x) with photo-eye status to be propagated upstream to the interpreter  60 . Additionally, the local photo-eye status is transmitted to the first upstream zone control module  116  (US 1 ) as information from a first downstream photo-eye (DS 1 ) (step  162 ). If it is not, the local photo-eye status is transmitted solely to the first upstream zone control module  116  (US 1 ) as information from a first downstream photo-eye (DS 1 ) (step  162 ). The event logic element terminates with the performance of a hierarchy process (step  164 ), described hereinafter, which determines whether the actuator  38  will be activated or deactivated based on the configuration hierarchy of the system. After the performance of the hierarchy process in  FIGS. 27A-B , the next event (event logic element  122 ) in the collection of event logic elements is evaluated. 
     Referring now to  FIGS. 9 and 11 , the second event logic element  122  evaluates whether the photo-eye delay timer has expired. The expiration of the photo-eye delay timer indicates that a package has been conveyed into the local zone for a preselected length of time, to be treated as a blocked photo-eye condition. This condition is conveyed upstream in order to control the conveying of packages to the subject zone. The local photo-eye status is first stored in memory (local photo-eye register  360 ) (step  166 ) in order to serve as a baseline for comparison of future photo-eye conditions, and the event logic element evaluates whether the smart photo-eye function is enabled as indicated by the smart photo-eye setting  354  (decision node  168 ) for possible propagation upstream to the interpreter  60  in order to control the flow of information from the local photo-eye back to the PDA  64 , the networked computer stations  68 , or the laptop computer  74 . If it is, that information is transmitted to the first upstream zone control module  116  (US 1 ) as a message in the protocol described herein (step  170 ), and the local photo-eye status is transmitted to the first upstream zone control module  116  (US 1 ) as information from a first downstream photo-eye (DS 1 ) (step  172 ). If it is not, the local photo-eye status is transmitted to the first upstream zone control module  116  (US 1 ) as information from a first downstream photo-eye (DS 1 ) (step  172 ). The event logic element terminates with the performance of a hierarchy process (step  174 ), described hereinafter. After the performance of the hierarchy process, the next event (event logic element  124 ) in the collection of event logic elements is evaluated. 
     Referring now to  FIGS. 9 and 12 , the third event logic element  124  evaluates a message received from the first downstream zone control module  112  (DS 1 ) to initiate an auto-slug condition. This message will have been generated by the auto-slug mode process  328  of the hierarchy process wherein a start auto-slug message is transmitted to the first upstream zone control module  116  (US 1 ) (step  310 ). The event logic element  124  evaluates whether a jam condition exists (decision node  178 ). If it does, the auto-slug message cannot be propagated further upstream and corrective measures must be undertaken. Thus, continuance of the hierarchy process (step  182 ) is initiated. If a jam condition does not exist, the auto-slug delay timer is initiated (step  180 ) followed by performance of the hierarchy process (step  182 ). The auto-slug delay timer allows for a certain amount of time before the “start auto-slug” message is transmitted upstream to ensure that the system is stable, and that a countervailing message or condition does not exist that would militate against an auto-slug condition. After performance of the hierarchy process, the next event (event logic element  125 ) in the collection of event logic elements is evaluated. 
     Referring now to  FIGS. 9 and 13 , the fourth event logic element  125  evaluates a message received from the first downstream zone control module  112  (DS 1 ) to terminate an auto-slug condition. The message to terminate the auto-slug condition is first stored in memory as indicated by the auto-slug setting  352  (step  183 ), and the auto-slug delay timer is cleared (step  184 ). The local zone control module  110  then delivers a message to terminate the auto-slug condition to the first upstream zone control module  116  (US 1 ) (step  185 ) for further propagation upstream. This step is followed by evaluation of the next event (event logic element  126 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 14 , the fifth event logic element  126  is initiated when the auto-slug delay timer has expired, indicating that it is “safe” to enter an auto-slug condition and to propagate the “start auto-slug” message upstream. When this event occurs, the local zone control module  110  stores a command to start the auto-slug function (local auto-slug register  370 ) (step  186 ), followed by performance of the hierarchy process (step  187 ). The next event (event logic element  128 ) in the collection of event logic elements is then evaluated. 
     Referring to  FIGS. 9 and 15 , the sixth event logic element  128  is initiated when a change in the photo-eye status of the second upstream photo-eye  118  (US 2 ) is transmitted to the local zone control module  110 . This event is relevant to the sleep mode process  320  of the hierarchy process in which the status of the second upstream photo-eye  118  (US 2 ) is evaluated (step  254 ). The local zone control module  110  stores the status of the second upstream photo-eye  118  (US 2 ) (step  188 ) in order to serve as a baseline for comparison of future photo-eye conditions, followed by performance of the hierarchy process (step  189 ). After the performance of the hierarchy process, the next event (event logic element  130 ) in the collection of event logic elements is evaluated. 
     Referring now to  FIGS. 9 and 16 , the seventh event logic element  130  is initiated when a change in the photo-eye status of the first upstream photo-eye  116  (US 1 ) is transmitted to the local zone control module  110 . This event is relevant to the sleep mode process  320  of the hierarchy process in which the status of the first upstream photo-eye  116  (US 1 ) is evaluated (step  254 ). The local zone control module  110  stores the status of the first upstream photo-eye  116  US 1  (step  190 ) in order to serve as a baseline for comparison of future photo-eye conditions, passes this information to the first downstream zone control module  112  (DS 1 ) as photo-eye information from the second upstream zone control module US 2  (step  192 ) (thereby initiating the event logic element  128  as to the first downstream zone control module  112  (DS 1 )), followed by performance of the hierarchy process (step  194 ). After the performance of the hierarchy process, the next event (event logic element  132 ) in the collection of event logic elements is evaluated. 
     Referring now to  FIGS. 9 and 17 , the eighth event logic element  132  is initiated when the local zone control module  110  receives a message concerning a change in the photo-eye status of the first downstream photo-eye  112  (DS 1 ). This event is relevant to the jam mode process  324 , the auto-slug mode process  328 , and the valve operation process  330 , wherein the status of the first downstream photo-eye  112  (DS 1 ) is evaluated (steps  272 ,  300 , and  314 , respectively). The local zone control module  110  stores the information regarding the status of the first downstream photo-eye  112  (DS 1 ) (first downstream photo-eye register  362 ) (step  196 ) in order to serve as a baseline for comparison of future photo-eye conditions, transmits this information to the first upstream zone control module  116  (US 1 ) as information from the second downstream photo-eye (step  198 ) (thereby initiating the event logic element  140  as to the first upstream zone control module  116  (US 1 )), followed by performance of the hierarchy process (step  200 ). After the performance of the hierarchy process, the next event (event logic element  134 ) in the collection of event logic elements is evaluated. 
     Referring now to  FIGS. 9 and 18 , the ninth event logic element  134  is initiated when the local zone control module  110  receives a smart photo-eye signal from the first downstream zone control module  112  (DS 1 ) for propagation upstream to the interpreter  60 . The local zone control module  110  transmits this information to the first upstream zone control module  116  (US 1 ) (step  202 ), followed by evaluation of the next event (event logic element  136 ) in the collection of event logic elements. 
     Referring to  FIGS. 9 and 19 , the tenth event logic element  136  is initiated when a release message is received from the first upstream zone control module  116  (US 1 ). This message will indicate whether the local zone control module  110  should activate its zone  13  in order to release packages off the conveyor, or should deactivate its zone  13  in order to prevent the transfer of packages downstream. The event logic element first evaluates whether the local zone control module  110  is at the downstream end of the conveyor system  10  (decision node  204 ). If the local zone control module  110  is at the downstream end of the conveyor system  10 , its pneumatic valve is activated or deactivated (step  208 ) based on an input from the installation computer system  68 , followed by evaluation of the next event in the collection of event logic elements. If it is not, the release message is transmitted to the first downstream zone control module  112  (DS 1 ) (step  206 ) in search of the downstream end local zone control module, followed by evaluation of the next event (event logic element  138 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 20 , the eleventh event logic element  138  is initiated when the local zone control module  110  receives a slug message from the first upstream zone control module  116  (US 1 ). This message will indicate whether the local zone control module  110  should activate or deactivate a slug condition. The event logic element first evaluates whether the local zone control module  110  is at the downstream end of the conveyor system  10  (decision node  210 ). If it is not, the slug message is transmitted to the first downstream zone control module (step  212 ), followed by evaluation of the next event (event logic element  140 ) in the collection of event logic elements. If the local zone control module  110  is at the downstream end of the conveyor system  10 , the local zone control module activates/deactivates its slug mode (step  214 ) based on an input from the installation computer system  68 , and transmits this information to the first upstream zone control module  116  (US 1 ) (step  216 ) for further propagation back upstream. This is followed by evaluation of the next event (event logic element  140 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 21 , the twelfth event logic element  140  is initiated when the local zone control module  110  receives status information from the second downstream zone control module  114  (DS 2 ) concerning the photo-eye associated with that module. This event is relevant to the jam mode process  324 , and the auto-slug mode process  328 , wherein the status of the second downstream photo-eye  114  (DS 2 ) is evaluated (steps  272  and  300 , respectively). The local zone control module  110  stores the information received (second downstream photo-eye register  364 ) (step  218 ) in order to serve as a baseline for comparison of future photo-eye conditions, followed by performance of the hierarchy process (step  220 ). This is followed by evaluation of the next event (event logic element  142 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 22 , the thirteenth event logic element  142  is initiated when the local zone control module  110  receives a slug message from the first downstream zone control module  112  (DS 1 ). This message will indicate whether the local zone control module  110  should activate or deactivate a slug condition. The local zone control module  110  first stores the received information (step  222 ), and then evaluates whether a jam condition exists (decision node  224 ), since a slug condition must not be inititated if a jam exists. If a jam exists, the hierarchy process is performed (step  228 ), followed by evaluation of the next event (event logic element  144 ) in the collection of event logic elements. If a jam does not exist, the slug message is passed upstream (step  226 ), and the hierarchy process is performed (step  228 ), followed by evaluation of the next event (event logic element  144 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 23 , the fourteenth event logic element  144  is initiated when the local zone control module  110  receives an external jam message from the first downstream zone control module  112  (DS 1 ) indicating that a jam condition exists downstream at “x.” The local zone control module  110  transmits the jam message to the first upstream zone control module  116  (US 1 ) (step  230 ), followed by performance of the hierarchy process (step  231 ), and evaluation of the next event (event logic element  146 ). 
     Referring now to  FIGS. 9 and 24 , the fifteenth event logic element  146  is initiated when the sleep timer of the local zone control module  110  expires, thereby activating the local zone control module  110  sleep mode and deactivating its associated zone  13 . Information that the local zone control module  110  is in sleep mode is stored in the local zone control module  110  memory (sleeve register  366 ) that (step  232 ), followed by performance of the hierarchy process (step  234 ). This is followed by evaluation of the next event (event logic element  148 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 25 , the sixteenth event logic element  148  is initiated when the local zone control module  110  jam timer has expired, indicating that the local zone is experiencing a jam condition. This information is stored in the local zone control module  110  memory (jam register  368 ) (step  236 ), followed by performance of the hierarchy process (step  238 ). This is followed by evaluation of the next event (event logic element  150 ) in the collection of event logic elements. 
     Referring now to  FIGS. 9 and 26 , the seventeenth event logic element  150  is initiated when the local zone control module  110  is the last downstream zone control module, i.e. there are no further downstream zone control modules, and the zone control module  110  is connected directly to the installation computer  68  or a logic controller (LC)  78 . In this case, the fourth pin of the 4-pin photo-eye connector is used for connection to and communication with the installation computer  68  or the logic controller (LC)  70  for control of certain customer-defined modes for handling packages at the end of the conveyor system  10 . The seventeenth event logic element  150  evaluates whether the fourth pin of the photo-eye connector is utilized. The event logic element first evaluates whether this fourth pin is grounded (decision node  240 ). If it is, indicating that the zone control module is not the last downstream zone control module, a slug condition is activated (step  242 ), followed by performance of the hierarchy process (step  246 ). If the fourth pin is not grounded, indicating that the zone control module is the last downstream zone control module, the slug condition is deactivated (step  244 ), followed by performance of the hierarchy process (step  246 ). 
     When the seventeenth event logic element  150  and the hierarchy process have been completed, the collection of event logic elements returns to the first event  120  to repeat the collection of event logic elements. 
     The hierarchy process is illustrated in  FIGS. 27A and 27B . The hierarchy process is segregated into six processes: a sleep mode process  320 , a downstream end module process  322 , a jam mode process  324 , a slug mode process  326 , an auto-slug mode process  328 , and a valve operation process  330 . 
     The sleep mode process  320  first evaluates whether sleep mode is enabled (decision node  250 ). If sleep mode is not enabled, the downstream end module process  322  is performed. If sleep mode is enabled, the process then evaluates whether the zone control module is the first upstream zone control module at the beginning of the conveyor system  10  (decision node  252 ). If it is, the downstream end module process  322  is performed. If it is not, the process then evaluates whether the first upstream photo-eye, the second upstream photo-eye, and the the local photo-eye are clear (decision node  254 ). If they are not, sleep mode is deactivated (step  258 ), the sleep timer is deactivated (step  260 ), and the downstream end module process  322  is performed. If they are, the process then evaluates whether sleep mode is activated (decision node  256 ). If it is, the local zone control module valve is deactivated (step  266 ), and the hierarchy process returns to the collection of event logic elements. If sleep mode is not activated, the process then evaluates whether the sleep timer is running (decision node  262 ). If it is not, the sleep timer is reset and activated (step  264 ), and the downstream end module process  322  is performed. If it is, the downstream end module process  322  is performed. 
     The downstream end module process  322  evaluates whether the local zone control module  110  is a downstream end module, i.e. the last module in the conveyor system  10  (decision node  268 ). If it is, the hierarchy process returns to the collection of event logic elements. If it is not, the jam mode process  324  is performed. 
     The jam mode process  324  first evaluates whether the jam mode is enabled (decision node  270 ). If it is not, the jam mode process  324  proceeds to the slug mode process  326 . If it is, the process then evaluates whether the local photo-eye is blocked, and the first and second downstream photo-eyes are clear (decision node  272 ). If they are, the process then evaluates whether jam mode is activated (decision node  274 ). If they are not, the process evaluates whether the local zone control module  110  has received a message from the first downstream zone control module  112  (DS 1 ) to activate jam mode (decision node  275 ). If such a message has not been received, jam mode is deactivated (step  276 ), a message is sent to the first upstream zone control module  116  (US 1 ) to deactivate jam mode (step  278 ), and the jam timer is deactivated (step  280 ). The slug mode process  326  is then performed. If such a message has been received, the local zone control module  110  sends a message to the first upstream zone control module  116  (US 1 ) to deactivate slug mode, deactivate auto-slug mode, and activate jam mode (step  286 ). The slug mode process  326  is then performed. If jam mode is activated (decision node  274 ), the local zone control module  110  sends a message to the first upstream zone control module  112  (DS 1 ) to deactivate slug mode, deactivate auto-slug mode, and activate jam mode (step  286 ). The slug mode process  326  is then performed. If jam mode is deactivated, the process evaluates whether the jam timer is running (decision node  282 ). If it is not, the jam timer is activated and the slug mode process  326  is performed. If the jam timer is running, the slug mode process  326  is then performed. 
     The slug mode process  326  first evaluates whether slug mode is enabled (decision node  288 ). If it is not, the auto-slug mode process  328  is performed. If slug mode is enabled, the process evaluates whether slug mode is activated for the local zone control module  110  (decision node  290 ). If it is not, the auto-slug mode process  328  is performed. If it is, the pneumatic valve is activated (step  292 ), and the hierarchy process returns to the collection of event logic elements. 
     The auto-slug mode process  328  first evaluates whether the auto-slug mode is enabled (decision node  294 ). If it is not, valve operation process  330  is performed. If it is, the process then evaluates whether the auto-slug delay timer is activated (decision node  296 ). If the auto-slug delay timer is not activated, the process then evaluates whether the first downstream zone control module  112  (DS 1 ) photo-eye and the second downstream zone control module  114  (DS 2 ) photo-eye are clear (decision node  300 ). If they are not, the local zone control module  110  transmits a message to the first upstream zone control module  116  (US 1 ) to terminate auto-slug mode (step  306 ). The valve operation process  330  is then performed. If the photo-eyes for the first and second downstream zone control modules  112  (DS 1 ),  114  (DS 2 ) are clear, the pneumatic valve for the local zone control module  110  is activated (step  302 ), the local zone control module  110  transmits a message to the first upstream zone control module  116  (US 1 ) to initiate auto-slug mode (step  310 ), and the hierarchy process returns to the collection of event logic elements. If the auto-slug delay timer is activated (decision node  296 ), the process then evaluates whether the auto-slug delay timer has expired (decision node  298 ). If it has not, the hierarchy process returns to the collection of event logic elements. If the auto-slug delay timer has expired, the pneumatic valve for the local zone control module  110  is activated (step  302 ), the local zone control module  110  transmits a message to the first upstream zone control module  116  (US 1 ) to initiate auto-slug mode (step  310 ), and the hierarchy process returns to the event logic elements as shown in  FIG. 9 . 
     The valve operation process  330  first evaluates whether the photo-eye for the first downstream zone control module  112  (DS 1 ) is clear (decision node  314 ). If it is not, the pneumatic valve for the local zone control module  110  is deactivated (step  318 ) and the hierarchy process returns to the collection of event logic elements. If it is, the pneumatic valve for the local zone control module  110  is activated (step  316 ) and the hierarchy process returns to the collection of event logic elements. 
     Referring again to  FIG. 1 , several examples of the operation of the conveyor system  10  will now be described. These include normal operation, a jam condition, and an auto-slug condition. 
     Normal Operation 
     During normal operation, the cartons  30 - 34  are traveling down the conveyor (from left to right as viewed in  FIG. 1 ). As the carton  30  passes in front of the photo-eye  22 , the photo-eye registers a change from a “clear” condition to a “blocked” condition. The zone control module  20  associated with that photo-eye, considered for purposes of this example as the local zone control module  110 , has a neighborhood of upstream zone control modules  116  (US 1 ),  118  (US 2 ) and downstream zone control modules  112  (DS 1 ),  114  (DS 2 ), as previously described. The change in the photo-eye condition is an event that initiates the logic process shown in  FIG. 9 . The local photo-eye event logic element, shown in  FIG. 10 , is triggered. Since the local photo-eye  110  is blocked by the carton  30  (decision node  152 ), the delay timer is activated (step  154 ), and the logic process continues with subsequent event logic elements and the hierarchy process. If the local photo-eye  22  becomes unblocked by the downstream movement of the carton  30  before the delay timer expires, this again triggers the event logic element  120 . The delay timer is then stopped (step  155 ) and the unblocked status of the local photo-eye  110  is stored. After an evaluation of whether “smart photo-eye” is enabled, the local photo-eye unblocked status is transmitted to the first upstream zone control module  116  (US 1 ). The hierarchy process is then performed for the local zone control module  110 . 
     Starting with the sleep mode process  320 , the hierarchy process first evaluates at the decision node  250  whether sleep mode is enabled. If it is not, the hierarchy process proceeds to the downstream end module process  322 . If sleep mode is enabled, the hierarchy process evaluates whether the local zone control module  110  is the furthest upstream zone control module (decision node  250 ). If it is, the hierarchy process proceeds to the downstream end module process  322 , since the furthest upstream zone control module, as the first module in the conveyor system  10  to receive cartons, cannot be placed in sleep mode. If the local zone control module  110  is not the furthest upstream zone control module, the hierarchy process evaluates whether the first and second upstream photo-eyes and the local photo-eye are clear (decision node  254 ). If all three photo-eyes are clear, indicating that no cartons are within the local and two immediately upstream zones (US 1  and US 2 ), the local zone control module  110  may be placed in a sleep condition. If one of the three photo-eyes is not clear, indicating that a carton is within the local or two immediately upstream zones, then the sleep condition is turned off (if the local zone control module were in the sleep condition to begin with) (step  258 ) and the sleep timer is turned off (step  260 ), followed by performance of the downstream end module process  322 . If the three photo-eyes are clear, the hierarchy subroutine evaluates whether the local zone control module  110  is in a sleep condition (decision node  256 ). If it is, the pneumatic valve is turned off, and the hierarchy process returns to the logic process for further evaluation of events. If the local zone control module  110  is not in a sleep condition but it is appropriate for the local zone control module  110  to be in a sleep condition, the hierarchy process evaluates whether the sleep timer is running (decision node  262 ). If it is, the hierarchy process proceeds to the downstream end module process  322 . If it is not running, the sleep timer is reset and turned on, and the hierarchy process proceeds to the downstream end module process  322 . In either case, when the sleep timer expires, the event logic element  146  will be triggered, the local zone control module  110  will be placed in a sleep condition (step  232 ), and the sleep mode process  320  will be repeated, this time resulting in the pneumatic valve being turned off (step  266 ) (assuming that the two upstream photo-eyes and the local photo-eye have not become blocked in the meantime). 
     If one of the three photo-eyes is not clear (decision node  254 ), resulting in performance of the downstream end module process  322 , the hierarchy process evaluates whether the local zone control module  110  is the furthest downstream zone control module (decision node  268 ). If it is, the hierarchy process returns to the logic process for further evaluation of events. If it is not, the hierarchy process proceeds to the jam mode process  324 , for evaluation of whether the local photo-eye  22  is blocked and if the blockage is the result of a jam condition. If jam mode is not enabled (decision node  270 ), the hierarchy process proceeds to the slug mode process  326 . If jam mode is enabled, the hierarchy process evaluates whether the blockage is at the local photo-eye and the two immediately downstream photo-eyes are clear, indicating that a jam condition is at the local zone (decision node  272 ). If the local photo-eye is the only photo-eye that is blocked, the hierarchy process evaluates whether the status of the local zone control module  110  already reflects a jam condition (decision node  274 ). If it does, the local zone control module  110  transmits a “slug off” and an “auto-slug off” message to the first upstream zone control module  116  (US 1 ) in order to prevent a slug-type conveyance of cartons downstream toward the jammed local zone control module  110 . The local zone control module  110  also transmits a “jam on” message to the first upstream zone control module  116  (US 1 ), thereby triggering the performance of the event logic element  144  by the first upstream zone control module  116  (US 1 ). The first upstream zone control module  116  (US 1 ) transmits the “jam on” message to its first upstream zone control module (step  230  shown in  FIG. 23 ), thereby triggering the performance of the event logic element  144  by that zone control module, with the process being repeated upstream. The first upstream zone control module  116  (US 1 ) will also perform the hierarchy process pursuant to the event logic element  144 . Since one of the downstream photo-eyes will be blocked, the hierarchy subroutine will evaluate whether a “jam on” message has been received from the first downstream zone control module  112  (DS 1 ) (decision node  275 ). Since a “jam on” message will have been received from the first downstream zone control module  112  (DS 1 ), “slug off” and “auto-slug off” messages will be transmitted to the next upstream zone control module, and a “jam on” condition will be initiated for the subject zone control module (step  286 ). 
     If, pursuant to decision node  274 , the status of the local zone control module  110  is not reflect a jam condition, the hierarchy process evaluates whether the jam timer is running (decision node  282 ) in order to evaluate whether the blockage of the photo-eye is reflective of a jam condition, or simply reflective of the normal carton movement down the conveyor line. If the jam timer is not running, the jam timer is turned on (step  284 ), and the slug mode process  326  is performed. If the jam timer is running, the slug mode process  326  is performed. 
     Pursuant to the slug mode process  326 , if slug mode is not enabled (decision node  288 ), the hierarchy process proceeds to the auto-slug mode process  328 . If slug mode is enabled, and the local zone control module is in a slug condition (decision node  290 ), the pneumatic valve is turned on (step  292 ) (if it has not already been turned on), thereby ensuring that cartons continue to be conveyed downstream, and the hierarchy process returns to the logic process for further evaluation of events. If the local zone control module is not in a slug condition, the hierarchy process proceeds to the auto-slug mode process  328 . 
     Pursuant to the auto-slug mode process  328 , the hierarchy process first evaluates whether the auto-slug mode is enabled (decision node  294 ). If it is not, the hierarchy process proceeds to the valve operation process  330 . If auto-slug mode is enabled, the hierarchy process evaluates whether an auto-slug delay timer has been started (decision node  296 ). If it has been started, the hierarchy process evaluates whether the auto-slug delay timer has expired (decision node  298 ). If it has not expired, the hierarchy process returns to the logic process for further evaluation of events. If it has expired, indicating that it is appropriate for an auto slug condition to exist so that cartons can be quickly conveyed downstream, the local pneumatic valve is turned on (step  302 ) and the local zone control module  110  transmits a “start auto-slug” message to the first upstream zone control module  116  (US 1 ) (step  310 ), thereby triggering the performance of the event logic element  124  ( FIG. 12 ) in the first upstream zone control module  116  (US 1 ). If the auto-slug delay timer has not been started, the hierarchy process evaluates whether the first and second downstream photo-eyes are clear (decision node  300 ), thereby indicating that the first and second downstream zones are available to receive cartons. If they are clear, the local pneumatic valve is turned on, and the local zone control module  110  transmits a “start auto-slug” message to the first upstream zone control module  116 . If one of them is not clear, the local zone control module transmits a “stop auto-slug” message to the first upstream zone control module  116  (US 1 ) (step  306 ), thereby triggering the event logic element  125  in the first upstream zone control module  116 . This is followed by performance of the valve operation process  330 . 
     Pursuant to the valve operation process  330 , the hierarchy process first evaluates whether the first downstream photo-eye is clear (decision node  314 ). If it is not, the local pneumatic valve is turned off (step  318 ), thereby preventing further conveyance of cartons downstream, and the hierarchy process returns to the logic process for further evaluation of events. If it is clear, the local valve is turned on (step  316 ), thereby enabling further conveyance of cartons downstream, and the hierarchy process returns to the logic process for further evaluation of events. 
     Jam Condition 
     In this example, it is assumed that the carton  30  of  FIG. 1  has become jammed and unable to move further downstream. With respect to this example, the local zone control module  110  (L) in  FIG. 8  is the zone control module associated with the jammed carton. It is also assumed that the system configuration has a sleep timer interval of five seconds, sleep mode and jam mode are enabled, but auto-slug mode is not enabled. Since the local photo-eye remains blocked by the jammed carton  30  (decision node  152 ), the photo-eye delay timer is started (step  154 ), and will eventually expire, thereby triggering event logic element  122 . The local photo-eye status is stored (step  166 ) and, assuming that the local photo-eye has not been designated a smart photo-eye, the first upstream zone control module  116  (US 1 ) receives a message from the local zone control module  110  which it interprets as a message from a first downstream zone control module concerning the local photo-eye status (step  172 ). The hierarchy process is then performed, beginning with the sleep mode process  320 . Since sleep mode is enabled (decision node  250 ), the process proceeds to decision node  252  for evaluation of whether the local zone control module  110  is the first upstream zone control module. Assuming that it is not, the process evaluates whether the two upstream and local photo-eyes are clear (decision node  254 ). Since the local photo-eye is not clear due to the jam condition, the sleep condition is turned off (step  258 ) and the sleep timer is turned off (step  260 ). The downstream end module process  322  is then evaluated (decision node  268 ). Assuming that the local zone control module  110  is not the furthest downstream zone control module, the jam mode process  324  is performed. Since jam mode is enabled (decision node  270 ), the process evaluates whether the local photo-eye is blocked (which it is, because of the jam condition) and whether the first two downstream photo-eyes are clear (decision node  272 ). If the two downstream photo-eyes are clear, the process evaluates whether a jam condition exists at the local zone control module  110  (decision node  274 ). Since it does, the local zone control module  110  transmits “slug off” and “auto-slug off” messages to the first upstream zone control module  116  (US 1 ), and transmits a “jam on” message to the first upstream zone control module  116  (US 1 ), thereby triggering the event logic element  144  to the first upstream zone control module  116  (US 1 ). The “jam on” message will be propagated upstream pursuant to the event logic element  144 . At some upstream zone control module, the local and first two downstream photo-eyes will be clear since the jam condition will exist further downstream (decision node  272 ). Since a “jam on” message will have been received from the first downstream zone control module  112  (DS 1 ) (decision node  275 ), the zone control module will transmit “slug off” and “auto-slug off” messages to the next upstream zone control module, and will transmit a “jam on” message to the next upstream zone control module, thereby triggering the event logic element  144  to the next upstream zone control module. 
     Auto-Slug Condition 
     With respect to this example, it is assumed that the system configuration has a sleep timer interval of five seconds, and that sleep mode, jam mode, and auto-slug mode are enabled, and the slug mode is disabled. Referring to  FIG. 1 , it is also assumed that the local zone control module  110  is associated with one of the optical sensors  22  between the cartons  30 ,  32  and, thus, is clear, that the second upstream photo-eye is blocked by the carton  32 , and that the local zone control module  110  has received a message from the first downstream zone control module  112  (DS 1 ) to activate the auto-slug feature (event  124 ). Since the jam mode is not activated (decision node  178 ), the auto-slug delay timer for the local zone control module  110  is activated (step  180 ), and the hierarchy process is initiated. 
     Since, pursuant to the above assumptions, sleep mode is enabled (decision node  250 ), the local zone control module  110  is not an upstream end zone control module (decision node  252 ), and the second upstream photo-eye is not clear (decision node  254 ), the sleep condition is turned off (step  258 ) and the sleep timer is turned off (step  260 ), and the downstream end module process  322  is performed. 
     Pursuant to the above assumptions, the local zone control module  110  is not a downstream end zone control module (decision node  268 ), and jam mode is enabled (decision node  270 ). Since the local photo-eye is not blocked, the conditions of decision node  272  are not satisfied. The local zone control module  110  has not received a “jam on” message from the first downstream zone control module  112  (DS 1 ) (decision node  275 ), so the local zone control module  110  sets the jam condition to “off” (step  276 ), indicating the absence of a jam condition, sends a “jam off” message to the first upstream zone control module  116  (US 1 ) (step  278 ), and turns the jam timer off (step  280 ). The slug mode process  326  is then performed. 
     Slug mode is not enabled (decision node  288 ) pursuant to the above assumptions, but auto-slug mode is enabled (decision node  294 ). The auto-slug mode process  328  first evaluates whether the auto-slug delay timer has been started (decision node  296 ). If the auto-slug delay timer has not been started, and the first and second downstream photo-eyes are clear (decision node  300 ), or if the auto-slug delay timer has been started (decision node  296 ) and has expired (decision node  298 ), the pneumatic valve is activated (step  302 ) and the local zone control module  110  transmits a message to the first upstream zone control module  116  (US 1 ) to initiate an auto-slug condition (step  310 ), thereby triggering event logic element  124  in the first upstream zone control module  116  (US 1 ). This process is propagated upstream so that the cartons  32 ,  34  are quickly transferred along the conveyor system  10 . If the auto-slug delay timer has not expired (decision node  298 ), the hierarchy process returns to the logic process for further evaluation of events. If the auto-slug delay timer has not been started, and one of the first and second downstream photo-eyes are not clear (decision node  300 ), the local zone control module  110  transmits a message to the first upstream zone control module  116  (US 1 ) to stop the auto-slug condition (step  306 ). The valve operation process  330  is then performed. 
     Pursuant to the valve operation process  330 , if the first downstream photo-eye is clear (decision node  314 ), the local pneumatic valve is turned on (step  316 ) to convey cartons downstream. If the first downstream photo-eye is not clear, the local pneumatic valve is turned off (step  318 ), to prevent further conveyance of cartons through the local zone. In either case, the hierarchy process returns to the logic process for continued performance of event logic elements. 
     The conveyor system  10  described herein provides a high degree of control and flexibility. The collection of event logic elements and hierarchy process described herein provide a superior means of controlling and monitoring the performance of the conveyor system and providing appropriate responses to different performance conditions, such as package jams or excessive capacity. The ability to select different mode of operation, such as jam mode or auto-slug mode, and to place selected zones of the conveyor system  10  in sleep mode, provide a degree of flexibility precisely tailored to the conditions associated with a specific run of packages. Energy savings can be realized by employing sleep mode, and, because the location of a jam condition can be precisely identified and its location propagated to the installation computer system  68  through the interpreter  60 , package jams can be quickly corrected, thereby saving operator time and resources. Because zone control modules are identified by position in the conveyor system  10  rather than by a unique identification number, a zone control module can be quickly replaced without the necessity of reprogramming a computer with a new module identification number. Similarly, the conveyor system  10  can be readily expanded with additional zone control modules without the necessity of reprogramming the new module identification numbers. 
     The zone control modules, interpreter, PDA, server and all other components can be operably interconnected to one another in a manner which would be apparent to one skilled in the art and the exemplary embodiments of such operable interconnection described herein shall not be construed as limiting on the invention since any communications-enabled interconnection between zone control modules and the other components referred to above can be employed, such as typical wire-based connections (Ethernet, coaxial, connecter-based conduit, etc.) or wireless communications in any of the accepted network protocols, without departing from the scope of this invention. 
     The collection of event logic events  120 - 150  and the processes  320 - 330  comprising the hierarchy process have been arranged in exemplary sequences in the preferred embodiment described herein. However, the event logic events  120 - 150  and the processes  320 - 330  may be arranged in other sequences which would be apparent to one skilled in the art without departing from the scope of the invention, and the exemplary sequences described herein shall not be construed as limiting on the invention. 
     While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the foregoing disclosure and drawings without departing from the scope of the invention.