Patent Publication Number: US-7224913-B2

Title: Printing system and scheduling method

Description:
BACKGROUND 
   The present exemplary embodiment relates generally to a printing system comprising at least two marking engines and, more particularly, to a scheduling system and method for use in conjunction with a printing system comprising at least two marking engines. It finds particular application in conjunction with scheduling sheets of print jobs in a multi-marking engine printing system for maximizing output of the printing system and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications. 
   In a typical xerographic marking engine, such as a copier, printer, combination copier/printer, etc., a photoconductive insulating member is charged to a substantially uniform potential and thereafter exposed to a light image representative of a document to be produced. This exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, corresponding to image areas of the document to be produced. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. This developed image may be subsequently transferred to a print medium, such as a sheet of copy paper, to which it may be permanently affixed by heating and/or by the application of pressure, i.e., fusing. 
   Electronic printing systems, including those that employ one or more xerographic marking engines as generally described above, can sometimes employ a scanner for scanning image-bearing documents, i.e., source documents, and conversion electronics for converting an image scanned from a source document to image signals or pixels. Alternatively, image signals or pixels representative of an image or document to be printed can be generated directly on a computer or like device, without the need for a source document. In either case, the signals are typically stored and read out successively to the printing system for formation of the images on photoconductive output media, such as a photoreceptor, and ultimately transfer to a support substrate, such as described above. 
   A common trend in the maintenance of office equipment, particularly copiers and printers, is to organize the printing system on a modular basis, wherein certain distinct subsystems of the printing system are bundled together into modules which can be readily removed and replaced with new modules, often of the same type. For example, the printing system could comprise two or more marking engine modules and a finisher module. Modular designed printing systems facilitate greater flexibility in terms of replacement and repair, and can even allow repairs of individual modules to take place at remote locations without necessitating disabling of the entire printing system. 
   Incorporated by reference, by way of background and where appropriate, are the following references relating to what have been variously called “tandem engine” printers, “cluster printing,” “output merger” and the like: U.S. Pat. No. 4,579,446; U.S. Pat. No. 4,587,532; U.S. Pat. No. 5,272,511; U.S. Pat. No. 5,568,246; U.S. Pat. No. 5,570,172; U.S. Pat. No. 5,995,721; U.S. Pat. No. 5,596,416; U.S. Pat. No. 6,402,136; U.S. patent application Ser. No. 10/785,211 by Lofthus, et al., filed Feb. 24, 2004 and entitled UNIVERSAL FLEXIBLE PLURAL PRINTER TO PLURAL FINISHER SHEET INTEGRATION SYSTEM; U.S. patent application Ser. No. 10/860,915 by Lofthus, et al., filed Jun. 3, 2004 and entitled UNIVERSAL FLEXIBLE PLURAL PRINTER TO PLURAL FINISHER SHEET INTEGRATION SYSTEM; a 1991 “Xerox Disclosure Journal” publication of November-December 1991, Vol. 16, No. 6, pp. 381-383; and the Xerox Aug. 3, 2001 “TAX” publication product announcement entitled “Cluster Printing Solution Announced.” 
   Printing systems employing multiple print engines often enable higher print speeds or print rates than heretofore realized by grouping a plurality of print engines together. These systems have been found to be very cost competitive and provide an additional advantage over single engine systems as a result of their inherent redundancy. For example, if one print engine fails or is unusable, the printing system is still able to function, possible at a reduced output rate, by using the remaining print engine or engines. One challenge in these systems is scheduling of print jobs and, more particularly, scheduling of individual sheets of print jobs through the various modules, including multiple modules each including a print engine, in an organized and efficient manner. 
   Various methods of scheduling print jobs and print media sheets of print jobs in a printing system employing multiple print engines are known. For example, U.S. Pat. No. 5,095,342 to Rarrell et al.; U.S. Pat. No 5,095,369 to Ortiz; U.S. Pat. No. 5,159,395 to Farrell; U.S. Pat. No. 5,557,367 to Yang et al.; U.S. Pat. No. 6,097,500 to Fromherz; U.S. Pat. No. 6,618,167 to Shah; 6,836,339 to Purvis et al.; and U.S. Pat. No. 6,850,336 to Purvis et al.; U.S. patent application Ser. No. 10/924,458 to Lofthus et al.; and U.S. patent application Ser. Nos. 20/384,514; 10/248,560; 10/284,561; and 10/424,322, all to Fromherz, all of which are incorporated herein in their entireties by reference., disclose exemplary scheduling systems. In particular, the &#39;339 patent and the &#39;336 patent disclose a scheduler for a printing machine to schedule the processing of sheets through the several modules of the printing machine. 
   CROSS-REFERENCE TO RELATED APPLICATION(S) 
   The following applications, the disclosures of each being totally incorporated herein by reference are mentioned: 
   U.S. Provisional Application Ser. No. 60/631,651 filed Nov. 30, 2004, entitled “TIGHTLY INTEGRATED PARALLEL PRINTING ARCHITECTURE MAKING USE OF COMBINED COLOR AND MONOCHROME ENGINES,” by David G. Anderson, et al.; 
   U.S. Provisional Patent Application Ser. No. 60/631,918 filed Nov. 30, 2004, entitled “PRINTING SYSTEM WITH MULTIPLE OPERATIONS FOR FINAL APPEARANCE AND PERMANENCE,” by David G. Anderson et al.; 
   U.S. Provisional Patent Application Ser. No. 60/631,921 filed Nov. 30, 2004, entitled “PRINTING SYSTEM WITH MULTIPLE OPERATIONS FOR FINAL APPEARANCE AND PERMANENCE,” by David G. Anderson et al.; 
   U.S. application Ser. No. 10/761,522 filed Jan. 21, 2004, entitled “HIGH RATE PRINT MERGING AND FINISHING SYSTEM FOR PARALLEL PRINTING,” by Barry P. Mandel, et al.; 
   U.S. application Ser. No. 10/785,211 filed Feb. 24, 2004, entitled “UNIVERSAL FLEXIBLE PLURAL PRINTER TO PLURAL FINISHER SHEET INTEGRATION SYSTEM,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 10/881,619 filed Jun. 30, 2004, entitled “FLEXIBLE PAPER PATH USING MULTIDIRECTIONAL PATH MODULES,” by Daniel G. Bobrow.; 
   U.S. application Ser. No. 10/917,676 filed Aug. 13, 2004, entitled “MULTIPLE OBJECT SOURCES CONTROLLED AND/OR SELECTED BASED ON A COMMON SENSOR,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 10/917,768 filed Aug. 13, 2004, entitled “PARALLEL PRINTING ARCHITECTURE CONSISTING OF CONTAINERIZED IMAGE MARKING ENGINES AND MEDIA FEEDER MODULES,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 10/924,106 filed Aug. 23, 2004, entitled “PRINTING SYSTEM WITH HORIZONTAL HIGHWAY AND SINGLE PASS DUPLEX,” by Lofthus, et al.; 
   U.S. application Ser. No. 10/924,113 filed Aug. 23, 2004, entitled “PRINTING SYSTEM WITH INVERTER DISPOSED FOR MEDIA VELOCITY BUFFERING AND REGISTRATION,” by Joannes N. M. deJong, et al.; 
   U.S. application Ser. No. 10/924,458 filed Aug. 23, 2004, entitled “PRINT SEQUENCE SCHEDULING FOR RELIABILITY,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 10/924,459 filed Aug. 23, 2004, entitled “PARALLEL PRINTING ARCHITECTURE USING IMAGE MARKING ENGINE MODULES (as amended),” by Barry P. Mandel, et al; 
   U.S. application Ser. No. 10/933,556 filed Sep. 3, 2004, entitled “SUBSTRATE INVERTER SYSTEMS AND METHODS,” by Stan A. Spencer, et al.; 
   U.S. application Ser. No. 10/953,953 filed Sep. 29, 2004, entitled “CUSTOMIZED SET POINT CONTROL FOR OUTPUT STABILITY IN A TIPP ARCHITECTURE,” by Charles A. Radulski et al.; 
   U.S. application Ser. No. 10/999,326 filed Nov. 30, 2004, entitled “SEMI-AUTOMATIC IMAGE QUALITY ADJUSTMENT FOR MULTIPLE MARKING ENGINE SYSTEMS,” by Robert E. Grace, et al.; 
   U.S. application Ser. No. 10/999,450 filed Nov. 30, 2004, entitled “ADDRESSABLE FUSING FOR AN INTEGRATED PRINTING SYSTEM,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 11/000,158 filed Nov. 30, 2004, entitled “GLOSSING SYSTEM FOR USE IN A TIPP ARCHITECTURE,” by Bryan J. Roof; 
   U.S. application Ser. No. 11/000,168 filed Nov. 30, 2004, entitled “ADDRESSABLE FUSING AND HEATING METHODS AND APPARATUS,” by David K. Biegelsen, et al.; 
   U.S. application Ser. No. 11/000,258 filed Nov. 30, 2004, entitled “GLOSSING SYSTEM FOR USE IN A TIPP ARCHITECTURE,” by Bryan J. Roof; 
   U.S. application Ser. No. 11/001,890 filed Dec. 2, 2004, entitled “HIGH RATE PRINT MERGING AND FINISHING SYSTEM FOR PARALLEL PRINTING,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 11/002,528 filed Dec. 2, 2004, entitled “HIGH RATE PRINT MERGING AND FINISHING SYSTEM FOR PARALLEL PRINTING,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 11/051,817 filed Feb. 4, 2005, entitled “PRINTING SYSTEMS,” by Steven R. Moore, et al.; 
   U.S. application Ser. No. 11/069,020 filed Feb. 28, 2004, entitled “PRINTING SYSTEMS,” by Robert M. Lofthus, et al.; 
   U.S. application Ser. No. 11/070,681 filed Mar. 2, 2005, entitled “GRAY BALANCE FOR A PRINTING SYSTEM OF MULTIPLE MARKING ENGINES,” by R. Enrique Viturro, et al.; 
   U.S. application Ser. No. 11/081,473 filed Mar. 16, 2005, entitled “PRINTING SYSTEM,” by Steven R. Moore; 
   U.S. application Ser. No. 11/084,280 filed Mar. 18, 2005, entitled “SYSTEMS AND METHODS FOR MEASURING UNIFORMITY IN IMAGES,” by Howard Mizes; 
   U.S. application Ser. No. 11/089,854 filed Mar. 25, 2005, entitled “SHEET REGISTRATION WITHIN A MEDIA INVERTER,” by Robert A. Clark et al.; 
   U.S. application Ser. No. 11/090,498 filed Mar. 25, 2005, entitled “INVERTER WITH RETURN/BYPASS PAPER PATH,” by Robert A. Clark; 
   U.S. application Ser. No. 11/090,502 filed Mar. 25, 2005, entitled IMAGE QUALITY CONTROL METHOD AND APPARATUS FOR MULTIPLE MARKING ENGINE SYSTEMS,” by Michael C. Mongeon; 
   U.S. application Ser. No. 11/093,229 filed Mar. 29, 2005, entitled “PRINTING SYSTEM,” by Paul C. Julien; 
   U.S. application Ser. No. 11/095,872 filed Mar. 31, 2005, entitled “PRINTING SYSTEM,” by Paul C. Julien; 
   U.S. application Ser. No. 11/094,864 filed Mar. 31, 2005, entitled “PRINTING SYSTEM,” by Jeremy C. deJong, et al.; 
   U.S. application Ser. No. 11/095,378 filed Mar. 31, 2005, entitled “IMAGE ON PAPER REGISTRATION ALIGNMENT,” by Steven R. Moore, et al.; 
   U.S. application Ser. No. 11/094,998 filed Mar. 31, 2005, entitled “PARALLEL PRINTING ARCHITECTURE WITH PARALLEL HORIZONTAL PRINTING MODULES,” by Steven R. Moore, et al.; 
   U.S. application Ser. No. 11/102,899 filed Apr. 8, 2005, entitled “SYNCHRONIZATION IN A DISTRIBUTED SYSTEM,” by Lara S. Crawford, et al.; 
   U.S. application Ser. No. 11/102,910 filed Apr. 8, 2005, entitled “COORDINATION IN A DISTRIBUTED SYSTEM,” by Lara S. Crawford, et al.; 
   U.S. application Ser. No. 11/102,355 filed Apr. 8, 2005, entitled “COMMUNICATION IN A DISTRIBUTED SYSTEM,” by Markus P. J. Fromherz, et al.; 
   U.S. application Ser. No. 11/102,332 filed Apr. 8, 2005, entitled “ON-THE-FLY STATE SYNCHRONIZATION IN A DISTRIBUTED SYSTEM,” by Haitham A. Hlndi; 
   U.S. application Ser. No. 11/109,558 filed Apr. 19, 2005, entitled “SYSTEMS AND METHODS FOR REDUCING IMAGE REGISTRATION ERRORS,” by Furst et al.; 
   U.S. application Ser. No. 11/109,566 filed Apr. 19, 2005, entitled “MEDIA TRANSPORT SYSTEM,” by Mandel et al.; 
   U.S. application Ser. No. 11/109,996 filed Apr. 20, 2005, entitled “PRINTING SYSTEMS,” by Mongeon et al.; and 
   U.S. application Ser. No. 11/115,766 Filed Apr. 27, 2005, entitled “IMAGE QUALITY ADJUSTMENT METHOD AND SYSTEM,” by Grace. 
   BRIEF DESCRIPTION 
   In one exemplary embodiment, a method is provided for scheduling in a printing system comprising a plurality of modules. In the method, a print job comprising one or more sheet to be printed is submitted to the printing system. Available paths are determined for one of the one or more sheets of the print job. A preferred available path for said one of the one or more sheets of the print job is determined from the available paths. The preferred available path for said one of the one or more sheets of the print job is submitted to one or more of the plurality of modules. A reservation matrix representative of said one of the one or more sheets being scheduled on the preferred available path is updated. The steps of determining the available paths, determining a preferred available path, submitted the preferred available path and updating the reservation matrix are repeated for each subsequent sheet of the one or more sheets of the print job. 
   In another exemplary embodiment, a printing system is provided. The printing system includes at least two modules, including at least one marking engine module. The printing system also includes a data source having image data which is to be printed on one or more print media sheets and a scheduler which is linked to the data source and linked to the at least two modules for scheduling processing of the one or more print media sheets through the at least two modules. 
   In still another exemplary embodiment, a xerographic system is provided. The xerographic system includes a first marking engine module which applies images to print media sheets and a second marking engine module which also applies images to print media sheets. A scheduler is linked to the first and second marking engine modules for receiving a print job and scheduling sheets of said print job through the first and second marking engine modules to minimize time of the sheets passing through the first and second marking engine modules. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of an image marking engine module. 
       FIG. 2  is a schematic view of a printing system comprising a plurality of image marking engine modules, including the marking engine module of  FIG. 1 . 
       FIG. 3  is a schematic view of the printing system of  FIG. 2 , showing interconnected print media paths of the printing system. 
       FIG. 4  is a block diagram illustrating a method for scheduling in the printing system of  FIGS. 2 and 3 . 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings wherein the showings are for purposes of illustrating one or more exemplary embodiments, a marking engine module is schematically depicted in  FIG. 1  and generally indicated by reference numeral  10 . In one application, as will be described in more detail below, the marking engine module  10  can serve as a replaceable xerographic module in a printing system. The term “marking engine” is used in connection with the one or more exemplary embodiments discussed herein to generally refer to a device for applying an image to print media. The marking engine module  10  of  FIG. 1  includes many of the hardware elements or components-employed in the creation of desired images by electrophotographical processes, as will be known and understood by those skilled in the art. In the illustrated embodiment, the marking engine module  10  includes a charge retentive surface member, such as rotating photoreceptor  12  in the form of a drum (alternatively, the rotating photoreceptor could be a belt or other rotating device having a charge retentive surface). 
   As also known and understood by those skilled in the art, images can be created on the photoreceptor  12  and ultimately transferred from the photoreceptor  12  to print media, such as a sheet of paper. The term “print media” is used in connection with the one or more exemplary embodiments discussed herein to generally refer to a usually flimsy physical sheet of paper, plastic, or other suitable physical print media substrate for images, whether precut or web fed. Disposed about the photoreceptor  12  are various xerographic subsystems, including a cleaning device or station  14 , a charging station  16 , an exposure station  18 , which forms a latent image on the photoreceptor  12 , a developer  20  for developing the latent image by applying a toner thereto to form a toner image, a transferring unit, such as a transfer corotron  22 , which transfers the toner image thus formed to the print media, and a fuser  24 , which fuses the transferred image to the print media. In the illustrated embodiment, the fuser  24  is adapted to apply at least one of heat and pressure to the print media to physically and permanently attach the toner and optionally to provide a level of gloss to the printed media. In any particular embodiment of an electrophotographic marking engine module, there can be variations to that described above, such as, for example, additional corotrons, cleaning devices, or, in the case of a color printer, multiple developers. 
   The xerographic subsystems  14 , 16 , 18 , 20 , 22 , 24  of the illustrated embodiment are controlled by a marking engine controller  26 , such as a CPU. Though the controller  26  of the illustrated embodiment is schematically shown as a single unit, it is to be appreciated that the controller can be distributed throughout the marking engine module  10  and formed of multiple remotely positioned components. For example, actuators forming the controller  26  can be located in or on the xerographic subsystems and thus the controller is not necessarily physically removed from or separate from other elements of the module  10 . In the illustrated embodiment, the marking engine controller  26  is linked to an input/output interface  28  and a memory  30 , and may also be linked to other components known by those skilled in the art to be provided with a marking engine module, such as, for example, a marking cartridge platform, a marking driver, a function switch, sensors (such as an “out of paper” indicator), a self-diagnostic unit, all of which can be interconnected by a data/control bus. 
   While the illustrated embodiment shows an electrophotographic printer marking engine module and particular reference herein is made to module  10  which includes an electrophotographic marking engine, suitable marking engines/modules can alternatively include ink-jet printers, including solid ink printers, thermal head printers that are used in conjunction with heat sensitive paper, and other devices capable of marking an image on a substrate. It is to be appreciated that such alternative marking engines/modules can, like module  10 , also include an input/output interface, a memory, a marking cartridge platform, a marking driver, a function switch, sensors, a controller and a self-diagnostic unit, all of which can be interconnected by a data/control bus. Additionally, it is to be appreciated that a single marking engine module, such as module  10 , could include multiple marking engines, in alternate embodiments. 
   The illustrated marking engine module  10  further includes a print media tray  32  suitable for holding print media, such as a stack  34  of precut print media sheets. As is known and understood by those skilled in the art, print media sheets are fed, typically from the top of the stack  34 , along sheet path  36  to the transfer station  22  for receiving the toner image and through the fuser  24  for having the toner image permanently attached thereto. Although not illustrated, it is to be appreciated that the marking engine module  10  could be configured to employ duplex operations on a print media sheet, wherein the sheet could be inverted and then fed for recirculation back through the transfer station  22  and the fuser  24  for receiving and permanently fixing a side two image to the backside of that duplex sheet. It should also be appreciated that module  10  need not be limited to a single print media tray, and could alternatively have no tray wherein the module  10  could be fed by a separate feeder module or could have two or more trays, such as trays for holding print media sheets of varying types (e.g., sizes, material, etc.). In one exemplary example, module  10  and any other marking modules associated with module  10  in a particular printing system can be fed with print media from a single and/or separate print media source, such as a high speed paper feeder, having any number of print media trays, or the multiple marking engine modules could be fed from several print media sources, in lieu of or in addition to the print media tray  32 . 
   With additional reference to  FIG. 2 , an exemplary printing system  40  is shown including an input/output interface  42 , a plurality of marking engine modules, including first marking engine module  10  and second marking engine module  44  in the illustrated embodiment, a transport module  46 , a finisher module  48  and a common control system  50 , all interconnected by links  52 . These links  52  can be wired or wireless links or other means or devices capable of supplying electronic data to and/or from the interconnected elements. For example, the links  52  can be telephone lines, computer cables, ISDN lines, wireless communication means or links (e.g., employing Bluetooth® wireless technology) and the like. While  FIG. 2  illustrates an embodiment employing two marking engine modules  10 , 44 , both of which can be similarly configured (i.e., the marking engine module  44  can be like the marking engine module  10 ), it is to be appreciated that the printing system  40  could include only a single marking engine module or could include more than two modules, such as three, four, five, six, or eight marking engine modules. Like marking module  10 , the second marking module  44  includes a second module input/output interface  54  linked to a second module controller  56  and a second module memory  58 , as well as a print media tray  60  for holding a stack  62  of print media sheets to be delivered along sheet path  64  to printer drum  66 . 
   As will be described in more detail below, the transport module  46  links or connects the sheet paths  36 , 64  of the marking engine modules  10 , 44  to the finisher module  48 . In an exemplary embodiment, the transport module  46  is a transport system including a network of flexible print media pathways that collect print media from each of the print modules  10 , 44  and deliver the collected print media to the finisher module  48 . The transport module  46  can include an input/output interface  68  linked to a transport module controller  70  and a transport module memory  72 . The transport system of the transport module  46  can comprise drive members or rollers, spherical nips, air jets, or the like (not shown) for moving print media sheets received from the marking engine modules  10 , 44  to the finisher module  48 . The transport system can further include associated motors for the drive members, belts, guide rods, frames, etc. (not shown), which, in combination with the drive members, serve to convey the print media along selected pathways at selected speeds. 
   As described in more detail below, the paths or pathways  74 , 78  (see  FIG. 3 ) of the transport module  46  allow print media sheets marked by two or more marking engine modules, such as modules  10 , 44 , to be assembled in a common stream and delivered to a finisher module, such as module  48 . It will be appreciated that the marking engine modules employed in the printing system  40 , including modules  10 , 44 , can be configured for duplex or simplex printing and that a single sheet of print media can be marked by two or more of the marking engine modules or marked a plurality of times by the same marking engine module, for example, by providing internal duplex pathways. The details of practicing parallel simplex printing and duplex printing through tandemly arranged marking engine modules are known and can be generally appreciated with reference to the foregoing cited U.S. Pat. No. 5,568,246. 
   The finisher module  48  receives pint media sheets passing through the transport module  46 , typically already assembled in a common stream by the transport module  46 . The term “finisher” or “finishing module” as broadly used herein in connection with the exemplary embodiment or embodiments disclosed herein, is any post-printing accessory device such as an inverter, reverter, sorter, mailbox, inserter, interposer, folder, stapler, collator, stitcher, binder, over-printer, envelope stuffer, postage machine, output tray, or the like. In the illustrated embodiment, the finisher module  48  includes an output tray  80  ( FIG. 3 ) to which received print media sheets can be delivered along path  82 , as well as an input/output interface  84  linked to a finisher controller  86  and a finisher memory  88 . The finisher module  48  can provide various finishes to the print media sheets of a print job or jobs, or even a portion of a print job. Finishes can include, for example, patterns of collation, binding or stapling available by the finisher module. Additional, advanced finishes can include, for example, other binding techniques, shrink wrapping, various folding formats, etc. The finisher module  48  can also be provided with multiple output trays (not shown) and the ability to deliver specified print media sheets to a selected output tray or trays. 
   With continued reference to  FIG. 2 , a data source  90 , such as a computer, network device or scanner can serve as an image input device for the printer system  40  in the illustrated embodiment. In one example, the data source  90  can be a computer network which is used to generate or acquire image signals or pixels and create print jobs therefrom. In another example, such as when on-site image input is desirable, the data source  90  could be or include a scanner which can be used by a user of the printer system  40  to scan image-bearing documents, i.e., source documents. The scanner can include or be used in conjunction with conversion electronics for converting an image scanned from a source document or documents to image signals or pixels and ultimately create print jobs therefrom. 
   Other sources of image data, each capable of serving as the data source  90 , are also contemplated, including floppy discs, hard discs, transportable memory devices, such as flash memory and the like, or any electronic storage medium or device capable of supplying image data. Of course, as will be understood and appreciated by those skilled in the art, the data source  90  need not be limited to a single data source, but could be a plurality of image input devices. For example, the data source could be or include both a network and a scanner. As is known by those skilled in art, the data source  90 , whatever its configuration, can additionally be connected or linked to other networks and/or computers (not shown), or other data sources. For example, the data source  90  can be a network server connected or linked to one or more workstations, such as personal computers. 
   A print job, including the image data of the data source  90 , is created, either upstream of the printing system  40  or in the printing system  40  itself. Typically, the print job includes the image data in the form of a plurality of electronic pages and a set of processing instructions. The term “print job” is used in connection with the one or more exemplary embodiments discussed herein to generally refer to a set of related sheets to be printed, usually one or more collated copy sets copied from a set of original document sheets or electronic document page images, from a particular user, or which are otherwise related. Each print job can, for example, include the number of print media sheets to be printed on, the size and type of each print media sheet to be printed on, whether simplex or duplex printing is required, etc. U.S. Pat. No. 5,710,635 to Webster, incorporated herein by reference, describes a representation of an example print job or document and how that representation can be transformed into something the printing system  40  can use to print the job. U.S. Pat. No. 5,604,600 to Webster and U.S. Pat. No. 5,129,639 to DeHority, both incorporated herein by reference, further describe example print job processing. 
   The control system  50  further includes a scheduling system  92  and a print media path controller  94 . The scheduling system  92  schedules the printing of a print job including selection of the marking engine modules to be used ( 10  or  44  in the illustrated embodiment) and the route of each sheet of the print job through the system  40 . As will be described in more detail below, the scheduling system  92  receives one or more print jobs, such as described above and including the image data of the data source  90 , or at least the scheduling system  92  receives information corresponding to the one or more print jobs, and therefrom schedules sheets of the one or more print jobs through the modules  10 , 44 , 46 , 48  of the printing system  40  based on various constraints, such as optimizing the output of the printing system  40 . While the operations of the scheduling system  92  are herein described with reference to a single job, it will be appreciated that the scheduling system can consider several print jobs in a queue and can schedule printing of print jobs from the queue contemporaneously or in an optimum sequence to optimize throughput of the printing system  40  or other variables, such as image quality. 
   The print media path controller  94  routes the sheets through the system, as well as controls the switch positions through the modules in order to execute a print job stream. Specifically, as will be described in more detail below, the print media path controller  94  routes sheets of print media through the system  40  as instructed by the scheduling system  92 . A user or operator of the system  40  can communicate with the control system  50  by means of a communication station  96 , which can be a touch screen, keypad and display screen, keyboard and monitor or the like. 
     FIG. 3  schematically illustrates the printing system  40  of  FIG. 2  to show the interconnected print media paths  36 , 64 , 74 , 78 , 82  through and between the assembled modules  10 , 44 , 46 , 48 . In the exemplary printing system  40  of  FIG. 3 , the marking engine modules  10 , 44  are shown linked for parallel printing of print media sheets within the system and the transport module  46  is shown connected to the marking modules  10 , 44  for receiving printed on print media sheets and delivering these to the finisher module  48 . Specifically, transport module path  74  connects first marking module path  36  to the finisher path  82  and transport module path  78  connects second marking module path  64  to the finisher path  82 . 
   In operation, with additional reference to  FIG. 4 , each of one or more modules reports its availability to the control system  50  and, more specifically, the scheduling system  92 , also referred to herein as a scheduler  92  (step S 100 ). In the illustrated embodiment, all of the modules  10 , 44 , 46 , 48  individually report whether they are available to the scheduler  92 . Reporting of availability could occur when the printing system  40  is first switched on (i.e., powered up) and/or could occur on a continuing basis as the printing system  40  is operated. For example, controller  26  of print engine module  10  could report that module  10  is switched off, out of paper, jammed, etc. to indicate that module  10  is unavailable. 
   Each of the one or more modules also reports its print media processing parameters to the control system  50  and, more specifically, the scheduler  92  (step S 102 ). Processing parameters can relate to print media sheet processing parameters, including, for example, process speed (i.e., the transit speed, such as mm/s, of sheets traveling in a particular module), sheet transit time (i.e., the elapsed or overall time for a sheet to travel in a module), and pitch period (i.e., the minimum delay or amount of time required between sheets traveling in a module, such as may be needed for sheet tracking sensors to function properly). One or more of the processing parameters can be dependent upon the print media sheet traveling in a module. For example, print media sheets of varying lengths will likely have varying sheet transit times in a particular module. Like step S 100 , step S 102  can occur at any time, such as during initial boot-up or on a continuing basis. When a processing parameter is sheet type specific, step S 102  may not be able to occur prior to the module determining what sheet is being used. The processing parameters of each module can be stored in the module&#39;s memory (e.g., memory  30  of module  10 ) and/or derived from the module&#39;s controller (e.g., controller  26  of module  10 ). 
   At some point, a user will submit a print job, or information that will form or correspond to a print job, to the printing system  40  and the scheduler  92  will receive the print job, or said information forming or corresponding to the print job (step S 104 ). The step of the scheduler  92  receiving the print job need not occur after steps S 100  and/or S 102 , but could occur at any time. As described above, the print job indicates the number of sheets to be printed and possibly specified types of sheets on which the printing system  40  is to print. Alternatively, this information can be derived from the print job or information corresponding to the print job. 
   Once a print job is received, the scheduler  92  establishes the available paths through the printing system  40  for sheet or sheets of the print job (step S 106 ). In the illustrated method, the scheduler  92  initially establishes the available paths through the printing system  40  of a selected sheet of the print job, such as the first sheet of the print job. Establishing the available paths can be dependent upon which modules are available (reported in step S 100 ), the particular print media processing parameters of each module (reported in step S 102 ), and/or the requirements or instructions associated with each sheet to be printed in the print job. For example, if the print job specifies that a particular sheet is to printed on a particular size of paper, only paths stemming from a tray capable of delivering the desired paper size will be established as being available. In another example, if the print job specifies that a particular sheet is to be printed on two sides, only paths passing through print engine modules which have reported two-sided printing capabilities will be established as being available. 
   After determining or establishing the available paths, the scheduler  92  determines or calculates the most appropriate or preferred path of the available paths (step S 108 ). In one exemplary embodiment, the preferred path is the path which gets a particular sheet of print media to the finisher module  48  in the least amount of time, i.e., the fastest available path. As described in more detail below, calculating the preferred path of the available paths (step S 108 ) can require the scheduler  92  to consult or lookup a reservation matrix which indicates when particular modules or paths will be available based on previously scheduled print media sheets. Calculating the preferred path can be dependent upon the particular print media processing parameters of each module (reported to the scheduler  92  in step S 102 ). For example, the transit time and the pitch period of a first module through which a first available path passes may be shorter than the transit time and pitch period of a second module through which a second available path passes, in which case the first available path might be preferred where speed is desirable. 
   After calculating the preferred path of the available paths, the scheduler  92  submits the calculated path to the modules (step S 110 ) and updates the reservation matrix (step S 112 ). More particularly, upon calculation of the preferred path, an itinerary is generated for the print media sheet to be processed along the preferred path. The sheet&#39;s itinerary, which is information representative of the path calculated as the preferred path and the time at which the print media sheet is to be sent along the preferred path, is submitted to the modules. In one exemplary embodiment, the sheet&#39;s itinerary is sent only to modules tasked with processing the print media sheet and/or the print media path controller  94  sends the itinerary to the modules. In any case, the modules receiving the itinerary are able to use it to determine when the print media corresponding to the itinerary is to be processed. For example, a module, such as module  44 , could receive a sheet itinerary and store it in its memory, such as memory  58 , or the itinerary could be first directed to the controller, such as controller  56 . 
   The step of updating the reservation matrix (S 112 ) occurs so that subsequently processed sheets, i.e., sheets that are to be scheduled through the printing system  40 , can be scheduled in view of the already scheduled print media sheet. For example, if a first of two available paths is determined to be the preferred or fastest path for a first print media sheet, the first path may not be the preferred or fastest path for a second, subsequent print media sheet because the first path may be occupied with processing the first print media sheet. Accordingly, a reservation matrix is stored by the scheduler  92 , which details when each module or path will be open for a subsequently processed print media sheet. The reservation matrix can be reviewed or consulted by the scheduler  92  when processing (i.e., calculating a preferred path in step S 108 ) for subsequently processed print media sheets. 
   After updating the reservation matrix, in step S 114 , if more sheets remain in a print job being processed or in a subsequently submitted print job, steps S 106  through S 114  are repeated for subsequent sheet or sheets. More specifically, step S 106  is returned to and the available paths are again established for the additional sheets to be processed. After establishing the available paths for the subsequent sheet, the scheduler  92  again determines the preferred available path (S 108 ), but for the subsequent sheet. Determining the preferred available path for the subsequent sheet takes into account the already scheduled itinerary of the already scheduled sheet. More specifically, the scheduler  92  consults the reservation matrix, which indicates when certain paths and/or modules will be available in view of the already scheduled sheet. Thus, when the preferred path is determined for the subsequent sheet, the preferred path is calculated while taking account for the processing of the earlier scheduled sheet. Upon determining the preferred path for the subsequent sheet, the scheduler  92  submits this path to the modules (S 110 ) and updates the reservation matrix to reflect scheduling of the subsequent sheet (S 112 ). The steps (S 106 -S 114 ) repeat until all sheets are processed. 
   The scheduling system or scheduler  92  herein described can be implemented either on a single program general purpose computer or a separate program general purpose computer. However, the scheduling system  92  can also be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit element, an ASIC, or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA, PAL, or the like. In general, any device, capable of implementing a finite state machine that is in turn capable of implementing the scheduler-related steps in the flowchart of  FIG. 4  can be used to implement the scheduling system  92 . 
   The disclosed method can be readily implemented in software using object or object-oriented software development environments. Alternatively, the disclosed scheduling system  92  can be implemented partially or fully in a hardware using standard logic circuits or VLSI design. Whether software or hardware is used to implement the system  92  in accordance with the exemplary embodiments is dependent, at least in part, on the speed and/or efficiency requirements of the system, the particular function, and the particular software or hardware systems or microprocessors or microcomputer systems being utilized. The scheduling system  92  and methods described herein, however, can be readily implemented in hardware or software using any suitable systems or structures, devices and/or software known by those skilled in the applicable art without undue experimentation from the functional description provided herein together with a general knowledge of the computer arts. 
   An example application of the method of  FIG. 4  will now be described in connection with the illustrated print system  40  of  FIGS. 2 and 3 . As shown in  FIGS. 2 and 3 , the printing system  40  includes four modules  10 , 44 , 46 , 48 . In step S 100 , according to the example, each module  10 , 44 , 46 , 48  reports that it is available. In step S 102 , according to the example, each module  10 , 44 , 46 , 48  reports its print media processing parameters. More specifically, in this example, each module  10 , 44 , 46 , 48  reports that it has a path or paths and reports the transit time (t) and pitch period (p) associated with each reported path. 
   More specifically, the marking engine modules  10 , 44  each report that they have a path available, path  36  on module  10  and path  64  on module  44 , and report transit times and pitch periods associated, respectively, with paths  36 , 64 . Likewise, the finisher module  48  reports that it has path  82  and reports a transit time and pitch period associated therewith. Transport module  46  reports that it has paths  74  and  78  and reports a transit time and pitch period associated with each path  74  and  78 . In one exemplary example, the reported print media processing parameters are as in TABLE 1. 
   
     
       
         
             
             
             
             
           
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
               Transit Time 
               Pitch Period 
             
             
                 
               Path 
               (seconds) 
               (seconds) 
             
             
                 
                 
             
           
          
             
                 
               first marking module path 36 
               1.8 
               0.9 
             
             
                 
               second marking module path 64 
               1.7 
               0.9 
             
             
                 
               transport module path 74 
               3.2 
               0.5 
             
             
                 
               transport module path 78 
               1.6 
               0.5 
             
             
                 
               finisher module path 82 
               1.9 
               0.5 
             
             
                 
                 
             
          
         
       
     
   
   When a print job is submitted, the print job is received by the scheduler  92  (S 104 ). In the exemplary example, the print job indicates that three (3) sheets are to printed in simplex form (i.e., one side only). Next, the scheduler establishes the available paths through the printing system  40 , based on the print media processing parameters and the print job being processed. In the exemplary example, the three (3) sheets of the print job are available from either print media tray  34  or  62  and can be printed on by either marking engine module  10  or  44 . Thus, the total count of available paths through the print system  40  is two (2), including a first print system path, comprising module paths  36 , 74  and  82 , and a second print system path, comprising module paths  64 , 78  and  82 . 
   Next, the scheduler  92  determines the preferred available path (S 106 ). In the example herein discussed, the preferred path is that which can deliver a print media sheet to the output tray  80  faster. Thus, the scheduler  92  determines the preferred available path, either first print system path  36 , 74 , 82  or second print system path  64 , 78 , 82 , is the one that can deliver the first sheet of the submitted three-sheet print job to the output tray  80  of the finisher module  48  faster. When determining the preferred path, the scheduler  92  first consults the reservation matrix to determine when specific modules will be available and thereby determines the earliest time a sheet could be released from its tray or trays, first module tray  32  or second module tray  60  in the printing system  40 . In this example, the first sheet of the print job is the first sheet submitted to the scheduler  92 , so no other sheets have yet been scheduled (alternatively, any previously scheduled sheets have already been processed or printed, so no sheet itineraries remain in the scheduler  92 ). Accordingly, since no preexisting sheet itineraries remain, the reservation matrix could be as indicated in TABLE 2. 
                               TABLE 2                           Path Available           Path   (seconds)                          first marking module path 36   T 0             second marking module path 64   T 0             transport module path 74   T 0             transport module path 78   T 0             finisher module path 82   T 0                          
wherein T 0  is approximately the time in which the print job was received by the scheduler  92 . Thus, according to the reservation matrix of this example, all of the paths are immediately available, as no reservations/itineraries have yet been made and/or remain in the printing system  40 .
 
   Next, still in step S 106 , the scheduler calculates when the first sheet of the print job would be delivered to the finisher module  48  along each of the available paths taking into consideration the earliest available release times based on the reservation matrix, compares the calculations for each available path and selects the path which will result in the sheet arriving at the finisher module  48  the earliest (i.e., selects the preferred path). In this example, the first printer system path  36 , 74 , 82  would deliver the first sheet of the print job to the finisher module  48  in 5 seconds (1.8 second transit time in module  10  and 3.2 second transit time in the transport module  46 ). The second printer system path  64 , 78 , 82  would deliver the first sheet of the print job to the finisher module  48  in 3.3 seconds (1.7 second transit time in module  44  and 1.6 second transit time in transport module  46 ). No previous sheets have been scheduled so both paths, as indicated above, are available at T 0 . Accordingly, the scheduler  92  would select the second path  64 , 76 , 82  for the first sheet of the print job. 
   Next, the scheduler  92  would submit the preferred available path to the modules (S 110 ), including the arrival time and exit times for the first sheet. For example, the first sheet would start in module  44  at T 0 , enter the transport module at T 0 +1.7 seconds (transit time through module  44 ), and enter the finisher at T 0 +1.7 seconds+1.6 seconds (transit time through module  46 ). In one exemplary embodiment, only the modules  44 , 46 , 48  that are to process the print job receive information from the scheduler  92 . The scheduler  92  also updates the reservation matrix (S 112 ). After processing the first sheet of the print job, the reservation matrix could be as indicated in TABLE 3. 
   
     
       
         
             
             
           
             
               TABLE 3 
             
             
                 
             
             
               Path 
               Path Available (seconds) 
             
             
                 
             
           
          
             
               first marking module path 36 
               T 0   
             
             
               second marking module path 64 
               T 0  + 0.9 
             
             
               transport module path 74 
               T 0   
             
             
               transport module path 78 
               T 0  + 1.7 + 0.5 = T 0  + 2.2 
             
             
               finisher module path 82 
               T 0  + 1.7 + 1.6 + 0.5 = T 0  + 3.8 
             
             
                 
             
          
         
       
     
   
   In other words, the second marking module  44  will be able to take another sheet in T 0 +0.9 (wherein 0.9 second is the pitch period for the second module  44 ). The first marking module  10 , since it still does not have a sheet schedule, can take a sheet as soon as the print job arrives, likewise with the first transport module path  74 . The second transport module path  78  can take another sheet after 2.2 seconds (includes 1.7 seconds transit time through second module  44  and 0.5 seconds pitch period for the transport module). The finisher module  48  can take a second sheet in 3.8 seconds, which includes transit times through the second module  44  and the second path  78  of the transport module  46  (1.7 seconds for second module  44  and 1.6 seconds for path  78 ), and a pitch period of 0.5 seconds for the finisher. 
   Because two more sheets remain to be processed in the example, step S 114  directs back to step S 106 , wherein the scheduler  92  determines all available paths for the second sheet of the three sheet print job. As indicated above, both paths  36 , 74 , 82  and  64 , 78 , 82  are available for all sheets of the example print job. Next, the scheduler determines the preferred available path for the second sheet of the print job (S 108 ). Again, the earliest the second sheet could be released for each path is calculated. Since the first path  36 , 74 , 82  has no sheets scheduled, a sheet could be released from tray  32  in the first path at T 0 . As with the first sheet, the first path could deliver a sheet to the finisher module  48  in 5 seconds. 
   The second path  64 , 78 , 82  already has a sheet scheduled. Accordingly, the earliest the second sheet could be released from the tray  60  is the maximum of (1) when the second module path is free (0.9 seconds from reservation matrix), (2) when the transport module second path  78  is free less the transit time through the second module  44  (2.2 seconds from the reservation matrix−1.7 seconds transit time through second module  44 =0.5 seconds), and (3) when the finisher path  82  is free less the transit time through the modules  44 , 46  (3.8 seconds from reservation matrix−1.6 seconds−1.7 seconds=0.5 seconds), or 0.9 seconds. Including the 0.9 second delay, the second sheet could be to the finisher in 4.2 seconds, which is still less than the 5 seconds required to get the second sheet through the first path  36 , 74 , 82 . Accordingly, the second path  64 , 78 , 82  is also selected for the second sheet of the print job. 
   Next, the scheduler  92  would submit the preferred available path for the second sheet to the modules (S 110 ), including the arrival time and exit times for the second sheet. The scheduler  92  also again updates the reservation matrix (S 112 ). After processing the second sheet of the print job, the reservation matrix could be as indicated in TABLE 4. 
                               TABLE 4                       Path   Path Available (seconds)                          first marking module path 36   T 0             second marking module path 64   T 0  + 1.8           transport module path 74   T 0             transport module path 78   T 0  + 3.1           finisher module path 82   T 0  + 4.7                        
Specifically, the second module  44  would have another 0.9 second pitch period added increasing the previous value, T 0 +0.9 seconds, to T 0 +1.8 seconds. Likewise, the transport module path  78  and the finisher module path  82  each have another 0.9 seconds pitch period added, respectively. The first module  10  and the first transport module path  74  are both still available at T 0 . For the third sheet of the print job, the steps (S 106 -S 112 ) are again repeated. This time, however, the first path  36 , 74 , 82  is faster for delivering the third sheet to the finisher module  48  and is selected as the preferred available path.
 
   The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.