Patent Publication Number: US-6660953-B2

Title: Multi-fire and variable fire diverter conveyor system and method

Description:
PRIOR APPLICATION INFORMATION 
     This is a divisional application of U.S. Pat. application Ser. No. 09/347,765, filed Jul. 6, 1999, now U.S. Pat. No. 6,359,247. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to conveyor systems and conveying methods and, in particular, to such systems and methods having a multi-fire mode of operation involving multiple diversion points on a single diverter, and a variable fire mode of operation involving a variable diversion point on a single diverter. 
     BACKGROUND OF THE INVENTION 
     Conveyor sorting systems and methods for sorting items (e.g., packages) are common in the prior art. Conventional sorting is accomplished by providing a reader to read a preprinted code on an item to be sorted that has been placed onto the conveyor system, and thereafter activating an appropriate diverter in the proximity of the reader to cause the item to be diverted film the conveyor to an adjacent station. An exemplary prior art sorting system is described in U.S. Pat. No. 4,249,661 (the &#39;661 patent). Other examples of high-speed sorting apparatus are disclosed in U.S. Pat. No. 6,085,892 (the &#39;892 patent) and U.S. Pat. No. 5,984,498 (the &#39;498 patent), which patents are hereby incorporated by reference. 
     It is often desirable to sort items traveling on a conveyor into different bins, stackers, conveyors or other devices, referred to generically herein as “stations,” off to the side of the conveyer, depending on the nature of the item. Presently, this type of sorting is accomplished using a separate diverter for each station, such as illustrated in FIG. 3 of the &#39;661 patent. However, the need for multiple diverters for such sorting increases the complexity and expense of the conveyer system. 
     It is also often desirable to sort items of various size based on their position relative to the diverter. For example, for relatively long items it is often desirable to divert the item from the conveyor when its center in the long dimension reaches a mid-point of the diverter. Similarly, for relatively short items it is often preferable to activate (“fire”) the diverter when a different portion of the package (e.g., its leading edge) reaches the beginning of the diverter. 
     As described in U.S. Pat. Nos. 3,242,342, 3,515,254 and 3,512,624, it is known to divert packages from a conveyor when the center of the package reaches the mid-point of the diverter. It is also known to take various actions in a conveyor system as a function of the length of a package being conveyed. See U.S. Pat. No. 3,680,692. Unfortunately, it is believed no conveyor systems exist that determine the length of a package and then fire a diverter when a selected position on the package reaches a selected position on the diverter as a function of the length of the package. As such, known conveyor systems are not particularly well adapted to conveying packages of widely varying lengths, with the result that packages are often mis-diverted, turned in an undesirable orientation or not diverted at all. 
     SUMMARY OF THE INVENTION 
     The present invention relates to conveyor systems and methods, and in particular such systems and methods having a multi-fire operation involving multiple diversion points on a single diverter, and a combined multi-fire and variable fire operation involving a variable diversion point on one of multiple diversion points of a diverter. The invention also relates to a modular conveyor system. 
     A first aspect of the invention is a diverter system for diverting items to one of a plurality of stations on either side of a conveyor. The diverter system is designed for use with a conveyor for transporting items in a first direction. The conveyor includes at least one diverter region in which the diverter system is positionable. The diverter system comprises a diverter for diverting items transported by the conveyor in the first direction to one of a plurality of stations adjacent the diverter that are spaced from one another in the first direction, when positioned in a diverter region of the conveyor, in response to a fire signal. The diverter system also includes a source of destination information identifying one of the plurality of stations to which items transported by the conveyor are to be diverted, and a controller system connected to the diverter and the source for generating, and providing to the diverter, a fire signal for each item transported by the conveyor based on destination information from the source regarding the one of the plurality of stations to which the item is to be diverted. 
     A second aspect of the invention is a conveyor system including a conveyor having at least one diverter region. In addition, the conveyor system includes the diverter system described above, with a diverter being arranged in the diverter region of the conveyor. 
     A third aspect of the invention is a diverter system for diverting items having first and second item tracking points to one of a plurality of stations, each station having a central axis and a divert axis. The diverter system is designed for use with a conveyor for transporting items in a first direction, the conveyor having at least one diverter region in which the diverter system is positionable. The diverter system comprises a diverter for diverting items transported by the conveyor in the first direction to one of a plurality of stations adjacent the diverter that are spaced from one another in the first direction, when positioned in a diverter region of the conveyor, in response to a fire signal. The diverter system also includes a source of destination information identifying one of the plurality of stations to which items transported by the conveyor are to be diverted. It also includes an item measuring system for generating information representative of the length of items transported by the conveyor and for providing a length signal based on such information for each item indicating the length of the item. In addition, the diverter system includes a controller system connected to the diverter, the source and the item measuring system, for generating a fire signal for each item to be diverted and providing the fire signal to said diverter. The controller system contains information representing a first length, and the fire signal is generated for each item to be diverted based on destination information from the source regarding one of the plurality of stations to which the item is to be diverted and as a function of the length signal for such item so that the fire signal causes the diverter to divert items that are less than the first length substantially when the first item tracking point of the item arrives at the divert axis for the one of the plurality of stations and for diverting items that are greater than the first length substantially when the second item tracking point of the item arrives at the central axis for the one of the plurality of stations. 
     A fourth aspect of the invention is a conveyor system including a conveyor having at least one diverter region. In addition, the conveyor system includes the diverter system described in the immediately preceding paragraph, with a diverter being arranged in the diverter region of the conveyor. 
     A fifth aspect of the invention is a method of diverting items moving along a conveyor having a diverter to one of a plurality of stations adjacent the diverter. The method comprises, as a first step, providing destination information for each item transported by the conveyor identifying the one of the plurality of stations adjacent the diverter to which said each item is to be diverted. The method also includes the step of diverting said each item from the conveyor to said one of the plurality of stations based on said destination information for said each item. 
     A sixth aspect of the invention is a modular conveyor system comprising a plurality of modular conveyor sections. Each section includes (1) a conveyor for transporting items in a first direction, wherein the conveyor is connectable to conveyors in other ones of the modular conveyor sections so as to form a continuous conveyor assembly, (2) a diverter for diverting items transported by the conveyor in the first direction to one of a plurality of stations adjacent the diverter that are spaced from one another in the first direction in response to a fire signal, and (3) a controller system connected to the at least one diverter for providing a fire signal to the at least one diverter for each item to be diverted, wherein the controller system is connectable to the controller systems in other ones of the modular conveyor sections so as to permit fire signals to be communicated between the controller systems. The modular conveyor system also includes a source of destination information identifying a one of the plurality of stations in the modular conveyor system to which each item transported by the modular conveyor system is to be diverted. Also, the modular conveyor system has a host controller connected to the source and to the controller systems, wherein the host controller generates the fire signal for each item transported by the modular conveyor system based on the destination information from the source, and provides the fire signal to at least one of the controller systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, the drawings show a form of the invention that is presently preferred. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
     FIG. 1 is a schematic plan view of a conveyer system according to the present invention; 
     FIG. 2 is a schematic diagram of the controller unit for the conveyor system of FIG. 1; 
     FIG. 3 is a flow diagram setting forth the initial steps for controlling the operation of the conveyor system of FIG. 1; 
     FIG. 4 is a flow diagram setting forth the steps for determining the length of an item conveyed by the conveyor system of FIG. 1, and the position of its leading edge, trailing edge and mid-point; 
     FIG. 5 is a flow diagram setting forth the steps for implementing the multi-fire mode of operation with the conveyor system illustrated in FIG. 1; 
     FIG. 6 is a flow diagram setting forth the steps for implementing the variable fire mode of operation with the conveyor system illustrated in FIG. 1; 
     FIG. 7 is a schematic diagram of the conveyor system illustrating the diversion of an item in accordance with the variable fire mode of operation; 
     FIG. 8 is a flow diagram setting forth the steps for performing the enhanced diverting method according to the present invention, which involves both variable fire and multi-fire modes; and 
     FIG. 9 is a schematic diagram of a conveyor system of the present invention comprising multiple conveyor sections. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to conveyor systems and conveying methods and, in particular, to such systems and methods having a multi-fire mode of operation involving multiple diversion points on a single diverter, a variable fire mode of operation involving a variable diversion point on a single diverter and a combination of both. 
     With reference to FIG. 1, a first aspect of the invention is a conveyer system  10  comprising a frame  12  which supports a plurality of parallel conveyor belts  14  that move from left to right over the frame at a speed determined by a conveyor belt drive controller  15  operatively connected to the conveyor belts. System  10  further includes one or more diverter regions DR with a front edge DRF, a back edge DRB and a center DRC, in which is located a diverter  16  for diverting items  18 , such as items  18   a - 18   e,  from the direction of travel of conveyor belts  14 , as indicated by arrow  17 . Diverter  16  includes a plurality of rollers  20  located between and parallel to belts  14 . Rollers  20  are preferably disposed below the level of belts  14  and are capable of being raised to the level of belts  14  or slightly above, so as to engage one or more of items  18   a - 18   e  when one or more of the items needs to be diverted from conveyor  10 , as described in more detail below. A suitable diverter  16  is disclosed in U.S. Pat. No. 6,085,892. 
     System  10  also includes a photodetector system PD arranged upstream of diverter  16  at or near an input end  34  of conveyor system  10  at a predetermined distance film diverter region DR. Photodetector system PD comprises a photodetector  30  on one side of frame  12  and a “tick” generator  32 , shown located on the opposite side of the frame. Photodetector  30  may be, for example, a diffuse photoeye. Tick generator  32  is in electrical communication with controller  15  and controller unit  40  (discussed below) and generates ticks corresponding to the speed of conveyor belts  14 . Tick generator  32  may include, for example, a light source and a detector with a beam chopper disposed therebetween, with the beam chopper driven in proportion to the speed of conveyor belts  14 . An exemplary tick generator  32  is made by Telemechanique (a division of Square D), model no. XUB-JO83135D. An exemplary photodetector  30  is a transmissive opto schmitt sensor made by Honeywell, model no. HOA0973-N55. 
     Tick generator  32  emits ticks, the timing of which is related to the speed of conveyor belts  14 . Thus, each tick interval P corresponds to a distance of travel x of conveyor belts  14 , e.g., one tick for each inch of travel, and hence the distance of travel of an item carried thereon. Thus, for n ticks, the distance of travel of an item down the conveyor is nx. 
     System  10  further includes a controller unit  40  in electrical communication with photodetector system PD, conveyer belt drive unit  15 , diverter  16  and tick generator  32 . A suitable controller unit  40  for the present invention may be the controller described in U.S. Pat. Nos. 6,085,892 and 5,984,498. Controller unit  40  controls the functions and operation of conveyor apparatus  10  of the present invention, including diverter  16 , as described in more detail below. 
     System  10  also includes destination information source  46 , which is in electrical communication with control unit  40 . Destination information source  46  contains information regarding which diverter  16  in system  10  will be used to divert a given item  18  and, optionally, which station  50  and  52  (described below) adjacent the diverter will receive the item. Destination information source  46  may comprise a conventional bar code reader system for detecting and decoding information contained in a bar code (not shown) applied to an item  18 . Suitable known bar code reader systems are described in U.S. Pat. Nos. 5,323,878, 5,412,196 and 5,412,197, which are incorporated herein by reference. Bar codes applied to items  18  may contain a unique identification code for the item, its final destination (e.g., shipping address of the party receiving the item), the diverter  16  to be used to divert the item and, optionally, the station  50  or  52  within a given diverter to which the item is to be diverted. 
     Alternatively, destination information source  46  may include computer memory (not shown) for storing a sequence table that assigns a destination based on the order of arrival of items at photodetector system PD. For example, if there is a conveyor system, such as multiple conveyor system  400  described below, where there are n diverters  16   a,    16   b  . . .  16   n,  the sequence table could be configured to send a first item to diverter  16   a,  a second item to diverter  16   b,  a third item to diverter  16   c,  a fourth item to diverter  16   a,  a fifth item to diverter  16   b,  etc. Alternatively, the sequence table could also be configured to send the first three items to diverter  16   a,  the next three to diverter  16   c,  the next three to diverter  16   c,  the next three to diverter  16   a,  etc. In any event, destination information source  46  preferably comprises a lookup table that contains the above-described destination information for each item  18  being conveyed, or that will be conveyed, by system  10 . 
     Located adjacent conveyor system  10  on either side of diverter  16  are a plurality of stations  50  and  52 , illustrated in FIG. 1 as including stations  50 - 1 ,  50 - 2 ,  50 - 3  and  52 - 1 ,  52 - 2 ,  52 - 3 , respectively, arranged along the direction of travel on either side of the conveyor system, for receiving one or more items  18   a - 18   e  that are diverted from the conveyor system. Stations  50  and  52  may comprise, for example, a stacker, one or more bins, a conveyor or other known devices for receiving an item  18 . While stations  50  and  52  have been illustrated in FIG. 1 to each have three stations, it is to be appreciated greater and lesser numbers of stations may be used. 
     With reference now to FIG. 2, controller unit  40  is now described in more detail. Controller unit  40  comprises a processor  60 , a read-write memory  61 , status lights  62 , a signal generator  63 , a battery  64 , input/output (I/O) port  66  and an amplifier  67 . Also included is at least one inflow bi-directional communications port  68  ( 68   a,    68   b ) and corresponding outflow bi-directional communications port  70  ( 70   a,    70   b ). The bi-directional communication ports  68  and  70  are preferably RS485 connectors with two RJ31X modular connections. Below is described in detail a conveyor system  400  made up of a plurality of conveyor systems  10 . In this conveyor system  400 , individual controller units  40  are interconnected to each other for bi-directional communication therebetween. 
     Controller unit  40  is powered in any of a number of ways. In one embodiment, electrical power is supplied to the controller via a cable interconnecting communication ports  68  and  70  of each controller unit. Thus, each controller unit  40  may be powered from a central source. The central power supply provides power in the range of from about 20 Vac to about 52 Vac and preferably is about 24 Vac or about 48 Vac. Alternatively, each controller unit  40  or a group of such controller units is connected to a power supply in the above voltage ranges. 
     Battery  64  is preferably a 3V Lithium coin cell or any long-life type battery known in the art. Battery  64  supplies backup power to read/write memory  61  in the event of a power failure, so that data is retained until power is restored. For a conveying or sorting system application, the information retained includes item tracking information and configuration parameters for conveyor system  10 . Also included is information concerning items  18  traversing the section of conveyor system  10  under the control of the controller unit  40 , and any sorting or routing instructions for these items. Alternatively, or in addition to battery  64 , controller  40  may use non-volatile memory of the type that retains information when there is a power failure. 
     Additionally, one or more external input devices  74  can be disposed along conveyor system  10  to sense the item being diverted or sorted. In this way, processor  60  can determine if a proper diversion was made or whether conveyor system  10  performed an incorrect diverting operation. 
     Processor  60  can thus evaluate these and other inputs to determine if conveyor system  10  is in a failed or faulted condition, and can provide an output indicating this failed condition to prevent further operation or action by the failed/faulted conveyor system. 
     Processor  60  preferably includes a non-volatile random access memory (NVRAM)  76 , an EEPROM  78 , and a central processing unit (CPU)  80 . The applications program or software routines for operating conveyor system  10  are preferably stored in EEPROM  78 , which is easily removed in the field for replacement. The configuration parameters preferably are stored in NVRAM  76  so they are easily changed in the field, particularly by the user. 
     NVRAM  76  stores data and any parameters required for the operation and/or configuration of each controller unit  40 . For example, the data regarding items in an area or section under the control of a given controller unit  40 , and any related tracking and routing data for each of these items is stored in the NVRAM. Further, the configuration parameters required to enable the control routines for a given section type of a conveying system are also stored therein. 
     A suitable CPU  80  is a PIC17C43 by MicroChip Corp., and alternatively may be PIC17C44 by MicroChip Corp. The software routines stored in EEPROM  78  are loaded into CPU  80  and specific routines are enabled by means of the configuration parameters retrieved from NVRAM  76 . 
     With reference to FIGS. 1-3, the operation of conveyor system  10  according to a first aspect of the present invention is now described. The operation steps described below are implemented via a software program preferably stored in EEPROM  78  which is executed by CPU  80  in combination with NVRAM  76 . As those skilled in the art will appreciate, the operational steps described below may be implemented with one of a variety of programming languages. In the first step  102 , one of items  18   a - 18   e  is placed onto the conveyor belts  14  at input end  34 . Next, in step  104 , photodetector system PD detects the presence of item  18  as it passes therethrough. Based on information provided by photodetector system PD, controller unit  40  determines the length L I  of item  18  in the direction of travel of conveyor belts  14 , represented by arrow  17 , and the relative positions of the item&#39;s leading edge  18   L , trailing edge  18   T , and/or mid-point MP (see item  18   a  in FIG.  1 ). 
     Referring now to also to FIG. 4, step  104  itself includes a number of steps  104   a - 104   e  pertaining to how the length L I  of items  18  and the item&#39;s leading edge  18   L , trailing edge  18   T , and/or in mid-point MP are determined. The position of item  18  relative to a point on conveyor system  10  (e.g., input end  34 ) is continuously updated as the item travels down the conveyor system, as described below. 
     In step  104   a,  as item  18  passes photodetector PD a light signal is reflected from the item and received by the photodetector  30 , causing the signal to go high for N ticks (alternatively, the signal could go low). Next, in step  104   b,  photodetector  30  transmits an electrical signal to controller unit  40  indicating the presence of item  18 , i.e., a high signal, while tick generator  32  continuously transmits a pulse train of ticks to controller  40 . Then, in step  104   c,  based on the signals transmitted in step  104   b,  controller unit  40  calculates the length L I  of the item  18  along its direction of travel by multiplying the number of ticks, during the time the output of photodetector  30  indicates the presence of an item, by the distance of travel per tick x, i.e., L I =Nx. For example, controller unit  40  may be programmed to interpret one tick as equivalent to one inch of travel, plus or minus ten percent. The actual conversion factor may vary because of mechanical tolerance build-up. In practice, the conversion factor may be measured via observation after the conveyor system is assembled. 
     Also, it will be apparent to one skilled in the art that either a time-based or distance-based calculation may be used in implementing the present invention. It may be preferable in some instances to use a distance-based calculation, because the conveyor belts  14  could stop for periods of time. In this case, tick generator  32  would stop generating ticks. On the other hand, the time-based calculation can be suspended when there is no movement of items  18  down conveyor system  10 . Accordingly, the present invention is not limited to either a time-based or a distance-based calculation in its implementation. 
     Next, in step  104   d,  controller unit  40  also calculates the position of leading edge  18   L , trailing edge  18   T , and/or mid-point MP of item  18 , as selected, passing through photodetector system PD relative to the photodetector system. This is accomplished by noting the arrival of the leading edge  18   L  and counting the number of ticks until trailing edge  18   T  or mid-point MP of the item passes through photodetector system PD. This number is N, as discussed above. The distance the leading edge  18   L  of item  18  has traveled down conveyor system  10  is equal to the length L I =Nx when the moment the leading edge of the item passes photodetector system PD. The position of the leading edge and trailing edge of item  18  is continuously updated as the item travels down conveyor system  10  at a fixed rate of speed s. Thus, tick generator  32  (or signal generator  63 ) provides a signal at an interval t that is used in calculating the distance an item  18  travels. Controller unit  40  determines the distance X an item  18  has traveled at any instant by counting the number of ticks emitted from tick generator  32 , so that X=s(nt). Controller unit  40  maintains an array of data records for each item  18  under its control. These records correlate an item  18  identification with the item&#39;s position. Further, controller unit  40  is programmed with the number of ticks between a reference point on conveyor system  10  and various points along the direction of travel of an item, such as back edge DR B , front edge DR F , or points therebetween. 
     Finally, in step  104   e,  the position X MP  of the mid-point of item  18  is calculated and tracked as the item travels down the conveyor. Position X MP  of the mid-point is simply half-way between the leading and trailing edge locations of item  18 , as ascertained above. If the leading and trailing edge positions as a function often relative to a reference point on conveyor system  10  are X LE (t) and X TE (t), respectively, then the location of the item&#39;s mid-point as a function of time is X TE (t)+L I /2 or X LE (t)−L I /2. If the variable fire functionality of conveyor system  10 , described below, is not used, step  104   e  may be omitted. 
     With reference again to FIG. 3, at step  106 , destination information is acquired by control unit  40  for an item  18  from destination information source  46 . As noted above, this information includes the diverter  16  to be used to divert the item and, optionally, the station  50  or  52  to which the item is to be diverted. 
     Multi-fire Mode 
     With continuing reference to FIG.  3  and flow diagram  100 , at query step  110 , a determination is made whether system  10  is to be operated in a multi-fire mode, a variable fire mode or both. The multi-fire mode is used when it is desired to divert items  18  to different stations within stations  50  or  52  in a given diverter  16 , such as stations  50 - 1  to  50 - 3  and/or stations  52 - 1  to  52 - 3 . The multi-fire mode of operation provides greatest benefit when length L I  of items  18  is significantly less that the length L D  of diverter  16 . 
     The multi-fire mode of operation is described with reference again to FIG.  1  and also to flow diagram  120  of FIG. 5, which is a continuation of flow diagram  100  of FIG.  3 . In step  122 , a station and station destination is retrieved for the item (e.g., item  18   d  to station  50 - 1 ) based on information contained in destination information source  46 . This information is provided to controller unit  40 . Controller unit  40  also includes information pertaining to the distance from input end  34  of conveyor system  10  (or any other fixed location on the conveyor system) to positions along the length of each diverter  16  (in the direction of arrow  17 ) where a corresponding respective station  50  or  52  is located. This information may be in the form of the number of ticks, which represent a given distance as discussed above. 
     Next, at step  124 , controller unit  40  calculates the amount of time or distance (number of ticks) it takes either the leading edge  18   L , mid-point MP, trailing edge  18   T  or other point (such points are hereinafter referred to generally as item tracking point  125 , e.g., trailing edge  18   T  of item  18   a ) after passing through photodetector system PD to reach alignment with the selected station  50  or  52  to which the item  18  is to be diverted. This calculation may be made by controller unit  40  in absolute time units or in terms of distance based on the number of ticks emitted by tick generator  32  during the period when item tracking point  125  of item  18  travels from a given reference point, e.g., leading edge  34 , on conveyor system  10  to the position in diverter  16  adjacent a selected station  50  or  52 . Controller unit  40  then generates a diverter fire signal based on this calculation which is provided to diverter  16 . This diverter fire signal contains information that directs diverter  16  when to fire. 
     In practice, calculation of a diverter fire signal may simply consist of controller unit  40  referencing predetermined distances or ticks between stations  50  and  52  stored in destination information source  46  or EEPROM  78 . For example, a diverter  16  may be spaced the distance represented by 300 ticks provided by tick generator  32  from leading edge  34  of conveyor system  10 . Each station  50  or  52  may be spaced from adjacent stations by the distance represented by 12 ticks. Controller unit 40 counts down such tick amount beginning when an item tracking point passes a reference point on conveyor system  10 , e.g., photodetector  30  or a station  50  or  52 . When such tick count is completed this defines when the item tracking point has arrived at a location where it is intended diverter  16  should fire. At such location, controller unit  40  queries destination information Source  46  to assess if controller unit  40  should provide a diverter fire signal to diverter  16 . If so, a fire signal is provided. If not, a new tick count is retrieved and a new tick countdown commences. 
     In step  126 , pursuant to information in the diverter fire signal provided by controller unit  40 , the diverter fires. This diverts the item  18  into its assigned station  50  or  52 . This firing step involves diverter  16  operating, e.g., by initiating rotation of rollers  20  in the appropriate direction, and raising the rollers above the level of belts  14 , so as to divert the item  18 . For example, in FIG. 1, item  18   d  is shown being diverted into its assigned station  50 - 1  on one side of the conveyor, and item  18   e  is shown being diverted into its assigned station  52 - 3  on the other side of the conveyor at a location downstream from station  50 - 1 . 
     Variable Fire Mode 
     With reference again to FIG.  3  and flow diagram  100 , if at query step  110  the variable fire mode is selected, then the operation of conveyor system  10  is controlled in accordance with flow diagram  140  illustrated in FIG.  6 . The variable fire mode of operation involves diverting an item  18  from conveyor system  10  when item tracking point  125  reaches a selected position along the length of diverter  16  as a function of the item length L I . 
     Accordingly, with reference to FIGS. 1,  3 ,  6  and  7 , to facilitate description of the variable fire mode of operation there is shown a conveyor system  130  which is identical to conveyor system  10  of FIG. 1, described above, except that stations  50  and  52  have been replaced with a station  137  having a central axis A, the station being arranged adjacent frame  12  next to diverter region DR. 
     Assuming the query at step  110  results in selection of the variable fire option, operation of conveyor system  10  proceeds in accordance with the steps of flow diagram  140 . At step  141 , a determination is made whether length L I  of item  18  is greater than a predetermined reference length L R . The latter may be equal to the length L D  of diverter region D R , or may be of greater or lesser length, as those of ordinary skill in the art may readily determine by routine testing. If item  18 , e.g., item  18 ′ in FIG. 7, has a length L I  greater than L R , then in step  142  controller unit  40  sets a selected item tracking point  125  as the point of item  18 ′ to be aligned with central axis A when the diverter  18  is fired. In the immediately following discussion item tracking point  125  is assumed to be mid-point MP, for the sake of simplicity. 
     Next, in step  144 , based on the speed of travel of item  18 , controller unit  40  calculates the distance to be traveled (in ticks), or time it takes, for mid-point MP of item  18 , determined at step  104 , to align with central axis A of station  137 . Central axis A is at or near the mid-point of diverter  16 , as measured in the direction of arrow  17 . Based on this determination, controller unit  40  generates a diverter fire signal provided to diverter  16  in response to this timing information. More specifically, the timing of the diverter fire signal may be calculated by determining the number of ticks generated by tick generator  32  it takes for item mid-point MP to travel to central axis A. In step  146 , when such alignment occurs, diverter  16  fires, thereby diverting item  18  to station  137 . This allows a large package to be diverted to a station  137  without being twisted or spun. 
     While it is often preferred to fire diverter  16  when an item  18  having a length L I  that is &gt;L R  is positioned so that its mid-point MP is aligned with central axis A, the present invention is not so limited. At step  142 , the item tracking point  125  may be set at any point between leading edge  18   L  and trailing edge  18   T  of item  18 ′. This is accomplished by controller unit  40  performing a calculation, in accordance with user input, that sets the item tracking point  125  at any selected location between leading edge  18   L  and trailing edge  81   T . For example, to establish an item tracking point  125  that is directly in between leading edge  18   L  and mid-point MP, controller unit  40  takes the average of the position of leading edge  18   L  and mid-point MP. 
     In the next step  144 , controller unit  40  calculates the distance to be traveled (in ticks) or time for the selected item tracking point  125  to align with the station central axis A. In step  146 , when such alignment occurs, diverter  16  fires in response to a fire signal generated by controller unit  40 , thereby diverting item  18 ′ to station  137 . 
     With continuing reference to FIG. 6, if at step  141  it is determined that item  18  has a length L I  that is not &gt;L R , then operation of conveyor system  130  proceeds to step  152 . There, item tracking point  125  is set, preferably at or near leading edge  18   L . Next, at step  154 , controller unit  40  calculates the distance to be traveled (in ticks) or the time required for the item tracking point  125  to align with divert axis B, as described above in connection with the description of such time calculation with respect to central axis A. Typically, but not necessarily, divert axis B is not coincident with central axis A, and is usually positioned closer to back edge DR B  of diverter  16  than central axis A. The exact position of divert axis B will vary as a function of the speed of conveyor system  130 , the weight and size of item  18 ″ and other factors, and may be readily determined by those of ordinary skill in the art through routine experimentation. Finally, at step  156 , diverter  16  is fired in accordance with a fire signal received from controller unit  40 , which such un it generates based on the distance or time calculation described above. 
     The concept of variable diversion is of particular importance for high-speed conveyors. For example, when a relatively small item  18 , such as item  18 ′, travels on a high-speed conveyor, it acquires a momentum P=mv, where m is the mass of the package and v is its velocity. Because of this momentum, item  18  may follow a curved path when it is diverted from the conveyor system  10  or  130 . Accordingly, it is necessary to fire diverter  16  so that the curved path along which item  18  travels when diverted results in the items being appropriately positioned on station  137 . 
     Enhanced Diverting Method 
     The multi-fire and variable modes of operation were described above as separate operations to facilitate description of the invention. However, these two methods are combinable in a single enhanced diverting method. With reference again to FIGS. 1-3 and  8 , if at step  110  (FIG. 3) a determination is made to select both multi-fire and variable fire modes of operation, then the operation of controller system  10  proceeds in accordance with the steps of flow diagram  300 . The steps of flow diagram  300  comprise a combination of various steps of the flow diagrams earlier described. 
     First, in step  302 , the item length L I  is determined, as described above in connection with step  104 . Next, in query step  304 , the item length L I  is compared to reference length L R , as described above in connection with step  141 . For example, the latter may be set to be substantially equal to length L D ) of diverter  16 , to L D /2 or to another value. If the item length L I  is longer than reference length L R , then the method proceeds to step  306 , where item tracking point  125  is set at a selected point on item  18  between its leading edge  18   L  and trailing edge  18   T , often adjacent mid-point MP, as described above in connection with step  142 . If at step  304  item length L 1  is not &gt;L R , then the process continues to step  308 . There, item tracking point  125  is set, typically proximate leading edge  18   L , as described above in connection with step  152 . After both steps  306  and  308 , the process proceeds to step  310  where one of stations  50  and  52  and associated stations on diverter  16  is retrieved, as described above in connection with step  122 . Then, at step  312 , the distance to be traveled or amount of time required for the selected item tracking point  125  to become aligned with the assigned station  50  or  52  is calculated, as described above in connection with step  124 . Finally, at step  312 , diverter  16  fires when the selected item tracking point  125  is aligned, pursuant to a diverter fire signal provided by controller unit  40 . 
     Multiple Conveyor System 
     With reference now to FIG. 9, a conveyer system  400  according to a second aspect of the invention is now described. Conveyor system  400  includes n conveyer sections  10   a,    10   b,  . . .  10   n  arranged in series, with each equivalent to a single conveyor system  10 , described above. Each section  10   a,    10   b,  . . .  10   n  also includes a photodetector system PDa, PDb, . . . PDn, respectively, and a diverter  16   a,    16   b,  . . .  16   n,  respectively, and controller units  40   a,    40   b,  . . .  40   n,  respectively. In conveyor sections  10   a - 10   n,  destination information source  46  is not required, but is included in conveyor system  400 , as discussed below. In addition, controller units  40   a,    40   b,  . . .  40   n  are connected to form what is effectively a single controller unit  410  for system  400 . Controller units  40   a,    40   b,  . . .  40   n  are in electrical communication with a host controller  412 . Associated with sections  10   a,    10   b,  . . .  10   n  are stations  50   a,    50   b,  . . .  50   n,  and stations  52   a,    52   b,  . . .  52   m,  respectively. Thus, conveyor system  400  is a modular conveyor system. 
     During set-up of conveyor system  400 , the relative distances between diverters  16   a,    16   b,  . . .  16   n  is programmed into each controller unit  40   a,    40   b,  . . .  40   n.  This information is generated by determining the distance from the beginning of a conveyor section, e.g.,  10   a,  to the location of a diverter  16   a,    16   b,  . . .  16   n,  and the distance between conveyor sections. The distance between diverter  16   a,    16   b,  . . .  16   n  is used to time the firing of the diverters. This distance may be represented in the form, the number of ticks, or timing signals generated by signal generator  63  in host controller  412 . In any event, a signal representative of distance between diverters is sent to all controller units  40   a,    40   b,  . . .  40   n  so that a universal reference is established. 
     For a more detailed description of conveyor system  400 , attention is directed to U.S. Pat. Nos. 6,085,892 and 5,984,498, which contain a description of suitable modular conveyor controller systems. 
     In operation, an item  18  enters conveyor section  10   a  at input and  34 . As described above, as item  404  passes photodetector system PDa, it is assigned a station to which it is to be diverted from information obtained by host controller  412  from destination information source  46  in electrical communication therewith. This diversion might involve the multi-fire mode of operation, the variable fire mode of operation, or both. This information is passed from host controller  412  to first control unit  40   a.  If item  18  is to be diverted to, for example, to station  52   n,  then item  18  needs to be conveyed from section  10   a  to section  10   n  without being diverted. To accomplish this, controller unit  40   a  passes the diverting information pertaining to item  18  to controller unit  40   b,  which in turn passes this information to the next controller unit, until the information reaches controller unit  40   n.  In other words, the responsibility for diverting item  18  is transferred in daisy chain fashion until it reaches the controller unit  40   n  for the section  10   n  in which the item  18  is to be diverted. 
     Controller units  40   a - 40   n  are preferably interconnected to each other for communication by appropriately interconnecting the inflow and outflow bi-directional communications ports  68  and  70  of adjacent controller units. Controllers  40   a - 40   n  are preferably connected to each other using a “daisy chain” topology, e.g., by interconnecting to an outflow bi-directional communications port  70   a  of controller unit  40   a  and into an inflow bi-directional communications port  68   b  of second controller unit  40   b.  Thus, a bi-directional communications link is established between all controller units  40   a  to  40   n  for the communication of data and information therebetween. Such interconnection and bi-directional communication is also described in more detail in connection with the controller system described in U.S. Pat. Nos. 6,085,892 and 5,984,498. 
     While the present invention has been described in connection with preferred embodiments, it will be understood that it is not so limited to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the scope of the invention as defined in the appended claims