Patent Publication Number: US-6985250-B2

Title: Alternate imaging mode for multipass direct marking

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an “alternate imaging mode” for processing print jobs. It finds particular application in conjunction with multipitch, multipass marking architectures that accumulate composite page images on an intermediate substrate and subsequently transfer the full page image to a target substrate, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications 
     The terminology “copiers,” and “copies,” as well as “printers” and “prints,” is used alternatively herein The terminology “imaging” and “marking” is used alternatively herein and refers to the entire process of putting an image, film a digital or analog source, onto a target substrate (e.g., paper). The image can then be permanently fixed to the target substrate by fusing, drying, or other means. It will be appreciated that the invention applies to multipass, multipitch marking architectures in any type of digital print system, including, but not limited to systems in the fields of incremental printing of symbolic information, photocopying, facsimile, and electrophotography. Digital print systems are also referred to by many technical and commercial names within these fields, including: electrophotographic (e.g., xerographic) printers, copiers, and multifunction peripherals; digital presses; laser printers; and ink-jet printers 
     Digital print systems include paths through which sheets of a target substrate that are to receive an image are conveyed and imaged (ie., the paper path) The process of inserting sheets of the target substrate into the paper path and controlling the movement of the sheets through the paper path to receive an image is referred to as “scheduling” 
     One type of a multipass marking architecture is used to accumulate composite page images from multiple color separations. On each pass of the intermediate substrate, marking material for one of the color separations is deposited on the surface of the intermediate substrate until the last color separations is deposited to complete the composite image. Another type of multipass marking architecture is used to accumulate composite page images from multiple swaths of a print head On each pass of the intermediate substrate, marking material for one of the swaths is applied to the surface of the intermediate substrate until the last swath is applied to complete the composite image Both of these examples of multipass marking architectures perform what is commonly known as “page printing” once the composite page image is completed by transferring the full page image from the intermediate substrate to the target substrate. 
     Multipass printing may be scheduled in what may be referred to as “burst mode.” When scheduling in “burst mode,” sheets are inserted into, imaged, and output from the paper path at the maximum throughout capacity of the print system without any “skipped pitches” or delays between each consecutive sheet A “pitch” is the portion (or length) of the paper path in the process direction which is occupied by a sheet of the target substrate as it moves through the paper path. A “skipped pitch” occurs when there is a space between two consecutively output sheets which is long enough to hold another sheet. Various methods for scheduling in “burst mode” are disclosed in U.S. Pat. No. 5,095,342 to Farrell et al. and other patents. However, these patents are directed toward scheduling problems regarding duplex printing and integration of print engines with finishing devices, rather than the problems described herein and others which the present invention overcomes 
     In a multipitch marking architecture, the surface of the intermediate substrate (e.g., intermediate transfer drum or belt) is partitioned into multiple segments, each segment including a full page image (i.e., a single pitch) and an inter-document zone For example, a two pitch drum is capable of printing two pages during a pass or revolution of the drum. Likewise, a three pitch belt is capable of printing three pages during a pass or revolution of the belt In a multipitch, multipass marking architecture, traditional “burst mode” scheduling starts accumulating images for each pitch of the intermediate substrate at the beginning of a print job and on the final pass of the multipass cycle each composite image is transferred to a target substrate 
     However, problems can arise when attempting to transfer multiple composite images from the intermediate substrate (e.g., intermediate transfer drum or belt) to the target substrate (e.g., paper) during the same pass These problems are primarily associated with integration of the intermediate substrate/transfer station with adjacent stations (e.g., preheating or other type of pre-conditioning stations and fusing stations) in the paper path. This is particularly a problem in a high-speed print system. For example: i) preceding stations (e.g, preheating or pre-conditioning stations) may not be able to operate properly if the target substrate is advanced at the same speed as in the transfer station, ii) likewise, successive stations (e.g., fusing stations) may not be able to receive the transferred sheets as fast as the transfer station can output them, iii) alternatively, to make the adjacent stations capable of such operation they may become unacceptably large and/or economically cost prohibitive. Furthermore, registration of sheets in the paper path to the composite page images on the intermediate substrate may not be sufficiently reliable if it is performed at the same speed as sheets advancing through the transfer station. 
     Accordingly, there is a need for an alternative to traditional “burst mode” scheduling for multipitch, multipass marking architectures that accumulate full page images on an intermediate substrate. The present invention contemplates an “alternate imaging mode” that overcomes the above-referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a method for scheduling print operations in a print system is provided The method comprises the steps of: a) partitioning an intermediate substrate into multiple pitch areas, b) scheduling the marking of multiple page images by a marking material applicator on the multiple pitch areas, the marking of each page image being accumulated and completed during multiple passes of an assigned pitch area past the applicator; c) beginning the marking of a first page image on a first pitch area during a first revolution of the intermediate substrate; and d) beginning the marking of subsequent page images on available pitch areas during subsequent revolutions of the intermediate substrate, such marking being delayed from the marking of the prior page image so that the marking of two or more page images are not completed during the same revolution of said intermediate substrate. 
     In accordance with another aspect of the present invention, a method for scheduling multipass, multipitch print operations in a print system is provided The method comprises the steps of: a) beginning the marking of a first page image by a marking material applicator on a first pitch area of an intermediate substrate during a first revolution of the intermediate substrate; and b) beginning the marking of subsequent page images by the applicator on available pitch areas of the intermediate substrate during subsequent revolutions of the intermediate substrate, such marking being delayed from the marking of the prior page image so that the marking of two or more page images are not completed during the same revolution of the intermediate substrate. 
     In accordance with another aspect of the present invention, a print system for processing print jobs is provided The print system comprises an intermediate substrate for receiving marking materials, being selectively partitionable into multiple pitch areas, a marking material applicator disposed to selectively apply marking material to the pitch areas on the intermediate substrate, and a controller operationally coupled to said intermediate substrate and said applicator for controlling said intermediate substrate and for scheduling the application of marking material by said applicator, wherein the controlling includes partitioning the intermediate substrate into multiple pitch areas and wherein the scheduling includes: a) scheduling the marking of multiple page images by said applicator on the multiple pitch areas, the marking of each page image being accumulated and completed during multiple passes of an assigned pitch area past said applicator, b) beginning the marking of a first page image on a first pitch area during a first revolution of said intermediate substrate, and c) beginning the marking of subsequent page images on available pitch areas of the intermediate substrate during subsequent revolutions of the intermediate substrate, such marking being delayed from the marking of the prior page image so that the marking of two or more page images are not completed during the same revolution of said intermediate substrate 
     In accordance with another aspect of the present invention, a print system for processing print jobs using a multipitch, multipass architecture is provided The print system comprises: an intermediate substrate for receiving marking materials, a marking material applicator disposed to selectively apply marking material on the intermediate substrate, and a controller operationally coupled to said applicator for scheduling the application of marking material by said applicator, wherein the scheduling includes: a) beginning the marking of a first page image on a first pitch area during a first revolution of said intermediate substrate and b) beginning the marking of subsequent page images by said applicator on available pitch areas of the intermediate substrate during subsequent revolutions of the intermediate substrate, such marking being delayed from the marking of the prior page image so that the marking of two or more page images are not completed during the same revolution of said intermediate substrate 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention 
         FIG. 1  is a diagram of the typical marking material and paper handling components of a print system related to the present invention, 
         FIG. 2  is a diagram of pitches on the intermediate substrate and along the paper path of  FIG. 1 ; 
         FIG. 3  is a timing diagram for a two-pitch, four-pass pass marking architecture that schedules print jobs in “burst mode,” 
         FIG. 4  is a timing diagram for a two-pitch, four-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention, 
         FIG. 5  is a timing diagram for a two-pitch, four-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention, 
         FIG. 6  is a timing diagram for a two-pitch, six-pass marking architecture that schedules print jobs in “burst mode,” 
         FIG. 7  is a timing diagram for a two-pitch, six-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention; and 
         FIG. 8  is a timing diagram for a two-pitch, six-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , the typical marking material and paper handling components of a print system  100  related to the present invention are shown More specifically, a marking material applicator  102 , an intermediate substrate  104 , a feeding bin  106 , a pre-conditioning station  108 , a transfer station  110 , a fusing station  112 , a collection bin  114 , and a controller  115  are shown. The paper path  116  shows sheets of target substrate  118  advancing from the feeding bin  106 , through the pre-conditioning station  108 , transfer station  110 , and fusing station  112  to the collection bin  114 . The controller  115  is operationally coupled to each station along the paper path  116  and controls advancement of the target substrate from the feeding bin  106  through each station ( 108 – 112 ) to the collection bin  114 . Likewise, the controller  115  is also operationally coupled to the intermediate substrate  104  and marking material applicator  102  The controller  115  controls movement of the intermediate substrate  104  in a process direction  120  during the processing of a print job The marking material applicator  102 , under control of the controller  115 , deposits marking material on the intermediate substrate  104  as the intermediate substrate  104  moves in the process direction  120  The marking material deposited on the intermediate substrate  104  is based on image processing of the page to be printed. Advancement of the target substrate  118  is coordinated with movement of the intermediate substrate  104  by the controller  115  so that the page image (ie, the deposited marking material) and a target substrate sheet  118  meet at the transfer station  110  The marking material is transferred from the intermediate substrate  104  to the target substrate  118  at the transfer station  110  The target substrate sheet  118  continues advancing to the fusing station  112 . At the fusing station  112 , the marking material is permanently affixed to the target substrate sheet  118 , the target substrate sheet  118  continues advancing to the collection bin  114   
     The print system  100  is preferably an ink-jet printer based on ink marking technology. Alternatively, the print system  100  can be a xerographic printer based on toner marking technology or another type of printer based on marking technology similar to toner or ink marking. The marking material applicator  102  is preferably a print head based on solid ink and piezoelectric technologies Alternatively, the print head can be based on other ink marking technologies capable of performing the desired function in a similar manner In still another alternative, in the color REaD (Recharge, Expose and Development)-type xerographic printer system, the marking material applicator  102  can be a charging, image exposure, and developer station or another assembly capable of performing the desired function in a similar manner In this case the intermediate substrate is a photoconductive medium. In still another alternative, in the color tandem-type xerographic printer system, the marking material applicator  102  can be a charging, image exposure, development station with a rotating photoconductive substrate that transfers marking materials onto the intermediate substrate  104  Additional alternatives that incorporate multiple marking material applicators  102  are also contemplated. The intermediate substrate  104  is preferably a rotating drum Alternatively, the intermediate substrate  104  can be a moving belt or another assembly capable of performing the desired function in a similar manner to the drum or belt 
     The pre-conditioning station  108  is preferably a pre-heater for heating the target substrate  118  to a predetermined temperature prior to transferring the marking material from the intermediate substrate  104  to the target substrate  118  Alternatively, the pre-conditioning station  108  can be another type of conditioning station used in conjunction with ink or toner marking technologies. For example, in toner marking technology, a charging station may be used to apply a predetermined electrical charge to the target substrate  118  prior to transferring toner from the intermediate substrate  104   
     With reference to  FIG. 2 , shown are pitches  218  on the intermediate substrate  104  and along the paper path  116  of  FIG. 1  A pitch  218  is the dimension of the target substrate  118  in the process direction  120  The print system  200  implements two-pitch marking architecture using the marking material and paper handling components of  FIG. 1  Alternatively, the print system  200  can be comprised of other components capable of implementing the two-pitch marking architecture. 
     The intermediate substrate  104  must be of a sufficient circumference or other exterior dimension to permit two-pitch printing of the desired target substrate  118  Knowing the dimensions of the surface of the intermediate substrate  104  and the dimensions of the target substrate  118 , the controller partitions the surface into four areas two pitch areas  218  and two inter-document areas  222  The two pitch areas  218  are based on the dimension of target substrate  118  in the process direction  120  While the two inter-document areas  222  are based on the remaining area on the surface of the intermediate substrate  104 . For example, a drum with a circumference of 565.5 mm (22.25 in) can implement two-pitch printing of standard “A-size” (215.9 mm (8.5 in.) by 279.4 mm (11 in.)) paper. In doing so, the drum is partitioned into two pitch areas  218  of 215.9 mm (8.5 in ) and two inter-document areas  222  of 66.85 mm (2.625 in) Variations of multipitch marking (eg, three-pitch, four-pitch, etc) may be implemented when the size of the target substrate  118  is reduced or if the size of the intermediate substrate  104  is increased. 
     Similar to partitioning the intermediate substrate  104 , the controller  115  also divides the paper path  116  into pitch areas  218  and inter-document areas  222  However, the dimensions of any given pitch area  218  and inter-document area  222  in the paper path  116  is based on the speed at which the target substrate  118  is advanced through that portion of the paper path  116  If the target substrate  118  is advanced at the same speed as the surface of the intermediate substrate  104 , the pitch area  218  and the inter-document area  222  in the paper path is the same dimension as those on the surface of the intermediate substrate  104 . However, if the target substrate  118  is advanced more slowly, the pitch area  218  and the inter-document area  222  in the paper path are larger than those on the surface of the intermediate substrate  104   
     With reference to  FIG. 3 , a timing diagram for a two-pitch, four-pass marking architecture that schedules print jobs in “burst mode” is shown More specifically,  FIG. 3  includes a periodic sawtooth waveform  302 , a square pulse train  304 , a repeating dual square pulse sequence  306 , and a repeating dual sawtooth pulse sequence  308  The periodic sawtooth waveform  302  represents passes (ie, revolutions) of the intermediate substrate  104 . The square pulse train  304  represents activation of the marking material applicator  102  by the controller  115  The repeating dual square pulse sequence  306  represents activation of the transfer station  110  by the controller  115 . The repeating dual sawtooth pulse sequence  308  represents target substrate  118  demand at the transfer station  110   
     The intermediate substrate  104  begins moving in the process direction  120  at the beginning of a print job in order to begin imaging the first page Each cycle of the sawtooth waveform (“P”)  310  represents a revolution or pass of the intermediate substrate  104 . The diagram reflects eight passes (8P), numbered sequentially P1–P8. In actuality, the intermediate substrate  104  continues to move until the print job is complete A pass (P) is a useful reference for timing operations and will be used in the following discussion for relative and proportional comparisons (e.g., 0.5P, 3.5P) 
     Returning to  FIGS. 1 and 2 , the two-pitch, four-pass marking architecture is based on requiring four passes of the marking material applicator  102  over each of the pitch areas  218  to completely mark the composite image The four passes can either apply four swaths or four color separations of the composite image. Where it is based on four swaths, the desired composite resolution and the resolution of each swath of the applicator  102  are considered. For example, if the desired resolution is 600 dots per inch (dpi), in the four-pass architecture the resolution of the marking material applicator  102  is 150 dpi. After each pass, the applicator  102  is moved in the X (i.e, cross-process) direction by the controller  115  and the resolution of the composite image is 600 dpi from the accumulation of the four 150 dpi swaths Alternatively, where the four passes apply four color separations, each color separation is applied in successive passes. For example, the applicator  102  may deposit cyan, magenta, yellow, and black color separations in successive passes. Other techniques that complete the composite image in four passes are also contemplated, including print systems with multiple marking material applicators  102 . 
     With continued reference to  FIG. 3 , each pulse  312  in the square pulse train  304  represents activation of the marking material applicator  102  by the controller  115  In the two-pitch, four-pass marking architecture, the applicator  102  is activated twice during each pass P of the intermediate substrate  104 , one activation for each pitch area  218 . For clarity, the two pitch areas  218  on the intermediate substrate  104  are referred to as “pitch A” and “pitch B” in the following discussion Furthermore, it is assumed that the applicator  102  encounters pitch A and then pitch B during each pass P In other words, pitch A represents the first page and subsequent odd pages of a print job and pitch B represents the second page and subsequent even pages 
     In “burst mode,” the applicator  102  begins depositing marking material on both pitch A and pitch B during pass P1 This is reflected by applicator activation pulses A1  314  and B1  316 . As first and second page imaging continues, pulses A2  318  and B2  320  represent activation of the applicator  102  during pass P2 Likewise, pulses A3  322  and B3  324  represent activation during pass P3 and pulses A4  326  and B4  328  represent activation during pass P4. After the fourth pass, the applicator  102  begins another identical four-pass cycle for the third and fourth pages of the print job The applicator  102  continues to be activated in like fashion until the print job is complete 
     Each pulse (e.g,  330 ) in the dual square pulse sequence  306  represents activation of the transfer station  110  by the controller  115 . After the start of A4  326 , transfer of the pitch A composite image to a target substrate  118  can begin Accordingly, a target substrate sheet  118  advancing along the paper path  116  is coordinated to meet with the composite image as it reaches the transfer station  110  Transfer of the composite image is performed during transfer station activation pulse TA1  330  Note that the duration of pulse TA1  330  is substantially the same as an applicator activation pulse  312  because the target substrate  118  and the surface of the intermediate substrate  104  are moving at substantially the same speed during the transfer operation Also note, that in actuality the transfer station activation pulse TA1  330  lags the fourth applicator activation pulse A4. The amount of lag depends on the actual positions of the applicator  102  and the transfer station  110 . For example, in the print system  100  of  FIG. 1  the applicator  104  is shown at 2 o&#39;clock and the transfer station  110  at 6 o&#39;clock with respect to the intermediate substrate  104 . This would result in an approximate delay of 0.67P from pulse A4  326  to pulse TA1  330 . Each transfer station activation pulse would lag its corresponding fourth applicator application pulse in like fashion Nevertheless, the present invention is not effected by the delay 
     Likewise, after the start of B4  328 , transfer of the pitch B composite image to a target substrate  118  can begin. Accordingly, a second target substrate sheet  118  advancing along the paper path  116  is coordinated to meet the composite image as it reaches the transfer station  110 . Transfer of the composite image is performed during the transfer station activation pulse TB1  332  Presuming the print job includes third and fourth pages, the transfer station is activated again in identical fashion after the start of A4  326  and B4  328  in pass P8 Transfer station activation for the third and fourth page images are represented by pulses TA2  334  and TB2  336 , respectively 
     Each pulse (e.g.,  338 ) in the dual sawtooth pulse sequence  308  represents target substrate  118  demand at the transfer station  110 . In “burst mode,” it is important to note that the second target substrate sheet  118  is demanded approximately 0.5P revolutions of the intermediate substrate  104  after the first target substrate sheet  118  was demanded This is reflected by sawtooth pulses  338  and  340 , which align with the beginning of transfer station activation pulses TA1  330  and TB1  332 , respectively. In contrast, the third target substrate sheet  118  is demanded approximately 3.5P revolutions after the second target substrate sheet  118 . This is reflected by sawtooth pulses  340  and  342 , which align with the beginning of transfer station activation pulses TB1  332  and TA2  334 , respectively. This pattern of odd numbered sheets demanded approximately 0.5P revolutions after even numbered sheets and even number sheets demanded approximately 3.5P revolutions after odd numbered sheets continues until the print job is complete 
     The disparity between alternating demands of 0.5P and 3.5P revolutions of the intermediate substrate  104  is perhaps emphasized by the following example. If the intermediate substrate is a drum with a circumference of 565.5 mm (22.25 in) and the drum is rotated at 1400 mm/sec. (55 in./sec.), each pass (P) is 0.4 sec. in duration and the transfer station  110  alternates between demanding target substrate sheets  118  in 0.2 sec (0.5P) and 1.4 sec (3.5P). 
     With reference to  FIG. 4 , a timing diagram for a two-pitch, four-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention is shown. Like  FIG. 3 ,  FIG. 4  includes a periodic sawtooth waveform  302 , a square pulse train  404 , a repeating dual square pulse sequence  406 , and a repeating dual sawtooth pulse sequence  408  The diagrams (ie,  302 ,  404 ,  406 , and  408 ) represent the same type of information as the diagrams of  FIG. 3   
     The intermediate substrate  104  moves in the same manner for  FIG. 4  as described for  FIG. 3 . Accordingly, the periodic sawtooth waveform  302  and a pass P  310  of the intermediate substrate  104  in  FIG. 4  are identical to that of  FIG. 3   
     As shown in  FIG. 3 , each pulse  312  in the square pulse train  404  of  FIG. 4  represents activation of the marking material applicator  102  by the controller  115  Since  FIG. 4 , like  FIG. 3 , shows timing sequences for a two-pitch, four-pass marking architecture, the marking material applicator  102  is activated in basically the same manner as described in  FIG. 3 . Accordingly,  FIG. 4  also refers to the two pitch areas  218  on the intermediate substrate  104  as “pitch A” and “pitch B.” The distinction between  FIG. 4  and  FIG. 3  is that  FIG. 4  employs “alternate imaging mode” rather than “burst mode” scheduling 
     In this embodiment of “alternate imaging mode,” the applicator  102  begins depositing marking material on pitch A during pass P1 and delays beginning pitch B imaging until pass P3. This is reflected by applicator activation pulses A1  314  during pass P1. During pass P2, first page imaging continues with pulse A2  318 . During pass P3, first page imaging continues and the applicator  102  begins depositing marking material on pitch B This is reflected by pulses A3  322  and B1  416  During pass P4, first page and second page imaging continues with pulses A4  326  and B2  420  During pass P5, second page imaging continues on pitch B and the applicator  102  begins another identical four-pass cycle for the third page of the print job on pitch A. This is reflected by pulses B3  424  and A1  314 . During pass P6, second and third page imaging continues with pulses B4  428  and A2  318 . The applicator  102  continues to be activated in like fashion until the print job is complete 
     Like in  FIG. 3 , each pulse (e.g.,  330 ) in the dual square pulse sequence  406  of  FIG. 4  represents activation of the transfer station  110  by the controller  115  After the start of A4  326 , transfer of the pitch A composite image to a target substrate  118  can begin. Transfer of the pitch A composite image is performed the same in  FIG. 4  as in  FIG. 3 . This is reflected by transfer station activation pulse TA1  330 , which occurs at the same point in  FIG. 4  as in  FIG. 3  Transfer of the pitch B composite image to a target substrate  118  can begin after the start of B4  428 . This is reflected by transfer station activation pulse TB1  432 . However, note that in  FIG. 4  the applicator activation pulse B4 begins during pass P6, rather than during pass P4 as it did in  FIG. 3  Presuming the print job includes third and fourth pages, the transfer station is activated again in identical fashion after the start of A4  326  in pass P8 and after the start of the fourth marking pass over pitch B in pass P10 (not shown) Transfer station activation for the third page image is represented by pulse TA2  334   
     As shown in  FIG. 3 , each pulse (e.g.,  338 ) in the dual sawtooth pulse sequence  408  in  FIG. 4  represents target substrate  118  demand at the transfer station  110  In this embodiment of “alternate imaging mode,” it is important to note that the second target substrate sheet  118  is demanded approximately 2.5P revolutions of the intermediate substrate  104  after the first target substrate sheet  118  was demanded This is reflected by sawtooth pulses  338  and  440 , which align with the beginning of transfer station activation pulses TA1  330  and TB1  432 , respectively Similarly, the third target substrate sheet  118  is demanded approximately 1.5P revolutions after the second target substrate sheet  118 . This is reflected by sawtooth pulses  440  and  442 , which align with the beginning of transfer station activation pulses TB1  432  and TA2  334 , respectively This pattern of odd numbered sheets demanded approximately 2.5P revolutions after even numbered sheets and even number sheets demanded approximately 1.5P revolutions after odd numbered sheets continues until the print job is complete 
     Where average demand would be 2P revolutions of the intermediate substrate  104 , the alternating demands of 2.5P and 1.5P revolutions in  FIG. 4  produces less deviation about the average than the alternating demands of 0.5P and 3.5P in  FIG. 3  This is perhaps emphasized by applying the example of the drum with a circumference of 565.5 mm (22.25 in), rotated at 1400 mm/sec (55 in/sec) used above Recall that each pass (P) of the drum is 0.4 sec. in duration Also recall that under “burst mode” scheduling ( FIG. 3 ) the transfer station  110  alternates between demanding target substrate sheets  118  in 0.2 sec. (0.5P) and 1.4 sec. (3.5P). Here, under the  FIG. 4  embodiment of “alternate imaging mode” scheduling, the transfer station  110  alternates between demanding target substrate sheets  118  in 1.0 sec (2.5P) and 0.6 sec (1.5P) 
     With reference to  FIG. 5 , a timing diagram for a two-pitch, four-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention is shown Like  FIG. 3 ,  FIG. 5  includes a periodic sawtooth waveform  302 , a square pulse train  504 , a repeating dual square pulse sequence  506 , and a repeating dual sawtooth pulse sequence  508 . The diagrams (ie.,  302 ,  504 ,  506 , and  508 ) represent the same type of information as the diagrams of  FIG. 3   
     The intermediate substrate  104  moves in the same manner for  FIG. 5  as described for  FIG. 3  Accordingly, the periodic sawtooth waveform  302  and a pass P  310  of the intermediate substrate  104  in  FIG. 5  are identical to that of  FIG. 3 . 
     As depicted in  FIG. 3 , each pulse  312  in the square pulse train  504  of  FIG. 5  represents activation of the marking material applicator  102  by the controller  115  Since  FIG. 5 , like  FIG. 3 , shows timing sequences for a two-pitch, four-pass marking architecture, the marking material applicator  102  is activated in basically the same manner as described in  FIG. 3 . Accordingly,  FIG. 5  also refers to the two pitch areas  218  on the intermediate substrate  104  as “pitch A” and “pitch B” The distinction between  FIG. 5  and  FIG. 3  is that  FIG. 5  employs “alternate imaging mode” rather than “burst mode” scheduling. 
     In this embodiment of “alternate imaging mode,” the applicator  102  begins depositing marking material on pitch A during pass P1 and delays beginning pitch B imaging until pass P2 This is reflected by applicator activation pulses A1  314  during pass P1. During pass P2, first page imaging continues and the applicator  102  begins depositing marking material on pitch B. This is reflected by pulses A2  318  and B1  516 . During pass P3, first page and second page imaging continues with pulses A3  322  and B2  520  During pass P4, first page and second page imaging continues with pulses A4  326  and B3  524  During pass P5, second page imaging continues on pitch B and the applicator  102  begins another identical four-pass cycle for the third page of the print job on pitch A. This is reflected by pulses B4  528  and A1  314 . The applicator  102  continues to be activated in like fashion until the print job is complete 
     Like in  FIG. 3 , each pulse (e.g,  330 ) in the dual square pulse sequence  506  of  FIG. 5  represents activation of the transfer station  110  by the controller  115  After the start of A4  326 , transfer of the pitch A composite image to a target substrate  118  can begin. Transfer of the pitch A composite image is performed the same in  FIG. 5  as in  FIG. 3 . This is reflected by transfer station activation pulse TA1  330 , which occurs at the same point in  FIG. 5  as in  FIG. 3 . Transfer of the pitch B composite image to a target substrate  118  can begin after the start of B4  528 . This is reflected by transfer station activation pulse TB1  532 . However, note that in  FIG. 5  the applicator activation pulse B4 begins during pass P5, rather than during pass P4 as it did in  FIG. 3  Presuming the print job includes third and fourth pages, the transfer station is activated again in identical fashion after the start of A4  326  in pass P8 and after the start of the fourth marking pass over pitch B in pass P9 (not shown). Transfer station activation for the third page image is represented by pulse TA2  334   
     As shown in  FIG. 3  each pulse (eg,  338 ) in the dual sawtooth pulse sequence  508  in  FIG. 5  represents target substrate  118  demand at the transfer station  110  In this embodiment of “alternate imaging mode,” it is important to note that the second target substrate sheet  118  is demanded approximately 1.5P revolutions of the intermediate substrate  104  after the first target substrate sheet  118  was demanded. This is reflected by sawtooth pulses  338  and  540 , which align with the beginning of transfer station activation pulses TA1  330  and TB1  532 , respectively Similarly, the third target substrate sheet  118  is demanded approximately 2.5P revolutions after the second target substrate sheet  118  This is reflected by sawtooth pulses  540  and  542 , which align with the beginning of transfer station activation pulses TB1  532  and TA2  334 , respectively This pattern of odd numbered sheets demanded approximately 1.5P revolutions after even numbered sheets and even number sheets demanded approximately 2.5P revolutions after odd numbered sheets continues until the print job is complete 
     Where average demand would be 2P revolutions of the intermediate substrate  104 , the alternating demands of 1.5P and 2.5P revolutions in  FIG. 5  produce less deviation about the average than the alternating demands of 0.5P and 3.5P in  FIG. 3 . This is perhaps emphasized by applying the example of the drum with a circumference of 565.5 mm (22.25 in.), rotated at 1400 mm/sec. (55 in./sec.) used above. Recall that each pass (P) of the drum is 0.4 sec. in duration. Also recall that under “burst mode” scheduling ( FIG. 3 ) the transfer station  110  alternates between demanding target substrate sheets  118  in 0.2 sec. (0.5P) and 1.4 sec (3.5P) Here, under the  FIG. 5  embodiment of “alternate imaging mode” scheduling, the transfer station  110  alternates between demanding target substrate sheets  118  in 0.6 sec. (1.5P) and 1.0 sec. (2.5P) 
     With reference to  FIG. 6 , a timing diagram for a two-pitch, six-pass marking architecture that schedules print jobs in “burst mode” is shown More specifically,  FIG. 6  includes a periodic sawtooth waveform  602 , a square pulse train  604 , a repeating dual square pulse sequence  606 , and a repeating dual sawtooth pulse sequence  608 . The periodic sawtooth waveform  602  represents passes (ie., revolutions) of the intermediate substrate  104 . The square pulse train  604  represents activation of the marking material applicator  102  by the controller  115 . The repeating dual square pulse sequence  606  represents activation of the transfer station  110  by the controller  115  The repeating dual sawtooth pulse sequence  608  represents target substrate  118  demand at the transfer station  110   
     The intermediate substrate  104  begins moving in the process direction  120  at the beginning of a print job in order to begin imaging the first page Each cycle of the sawtooth waveform (“P”)  610  represents a revolution or pass of the intermediate substrate  104 . The diagram reflects twelve passes (12P), numbered sequentially P1–P12 In actuality, the intermediate substrate  104  continues to move until the print job is complete. A pass (P) is a useful reference for timing operations and will be used in the following discussion for relative and proportional comparisons (e.g, 0.5P, 5.5P) 
     Returning to  FIGS. 1 and 2 , the two-pitch, six-pass marking architecture is based on requiring six passes of the marking material applicator  102  over each of the pitch areas  218  to completely mark the composite image. The six passes can either apply six swaths or six color separations of the composite image Where it is based on six swaths, the desired composite resolution and the resolution of each swath of the applicator  102  are considered For example, if the desired resolution is 600 dots per inch (dpi), in the six-pass architecture the resolution of the marking material applicator  102  is 100 dpi. After each pass, the applicator  102  is moved in the X (i.e., cross-process) direction by the controller  115  and the resolution of the composite image is 600 dpi from the accumulation of the six 100 dpi swaths Alternatively, where the six passes apply six color separations, each color separation is applied in successive passes. For example, the applicator  102  may deposit cyan, magenta, yellow, red, green, and blue color separations in successive passes. Other techniques that complete the composite image in six passes are also contemplated, including print systems with multiple marking material applicators  102 . 
     With continued reference to  FIG. 6 , each pulse  612  in the square pulse train  604  represents activation of the marking material applicator  102  by the controller  115  In the two-pitch, six-pass marking architecture, the applicator  102  is activated twice during each pass P of the intermediate substrate  104 ; one activation for each pitch area  218 . For clarity, the two pitch areas  218  on the intermediate substrate  104  are referred to as “pitch A” and “pitch B” in the following discussion. Furthermore, it is assumed that the applicator  102  encounters pitch A and then pitch B during each pass P. In other words, pitch A represents the first page and subsequent odd pages of a print job and pitch B represents the second page and subsequent even pages 
     In “burst mode,” the applicator  102  begins depositing marking material on both pitch A and pitch B during pass P1. This is reflected by applicator activation pulses A1  614  and B1  616 . As first and second page imaging continues, pulses A2  618  and B2  620  represent activation of the applicator  102  during pass P2 Likewise, pulses A3  622  and B3  624  represent activation during pass P3, pulses A4  626  and B4  628  represent activation during pass P4, pulses A5  630  and B5  632  represent activation during pass P5, and pulses A6  634  and B6  636  represent activation during pass P6 After the sixth pass, the applicator  102  begins another identical six-pass cycle for the third and fourth pages of the print job. The applicator  102  continues to be activated in like fashion until the print job is complete 
     Each pulse (e.g.,  638 ) in the dual square pulse sequence  606  represents activation of the transfer station  110  by the controller  115  After the start of A6  634 , transfer of the pitch A composite image to a target substrate  118  can begin. Accordingly, a target substrate sheet  118  advancing along the paper path  116  is coordinated to meet with the composite image as it reaches the transfer station  110  Transfer of the composite image is performed during transfer station activation pulse TA1  638  Note that the duration of pulse TA1  638  is the substantially the same as an applicator activation pulse  612  because the target substrate  118  and the surface of the intermediate substrate  104  are moving at substantially the same speed during the transfer operation. Also note, that in actuality the transfer station activation pulse TA1  638  lags the sixth applicator activation pulse A6. The amount of lag depends on the actual positions of the applicator  102  and the transfer station  110 . For example, in the print system  100  of  FIG. 1  the applicator  104  is shown at 2 o&#39;clock and the transfer station  110  at 6 o&#39;clock with respect to the intermediate substrate  104 . This would result in an approximate delay of 0.67P from pulse A6  634  to pulse TA1  638 . Each transfer station activation pulse would lag its corresponding sixth applicator application pulse in like fashion Nevertheless, the present invention is not effected by the delay. 
     Likewise, after the start of B6  636 , transfer of the pitch B composite image to a target substrate  118  can begin. Accordingly, a second target substrate sheet  118  advancing along the paper path  116  is coordinated to meet the composite image as it reaches the transfer station  110 . Transfer of the composite image is performed during the transfer station activation pulse TB1  640 . Presuming the print job includes third and fourth pages, the transfer station is activated again in identical fashion after the start of A6  634  and B6  636  in pass P12. Transfer station activation for the third and fourth page images are represented by pulses TA2  642  and TB2  644 , respectively 
     Each pulse (eg,  646 ) in the dual sawtooth pulse sequence  608  represents target substrate  118  demand at the transfer station  110 . In “burst mode,” it is important to note that the second target substrate sheet  118  is demanded approximately 0.5P revolutions of the intermediate substrate  104  after the first target substrate sheet  118  was demanded. This is reflected by sawtooth pulses  646  and  648 , which align with the beginning of transfer station activation pulses TA1  638  and TB1  640 , respectively In contrast, the third target substrate sheet  118  is demanded approximately 5.5P revolutions after the second target substrate sheet  118 . This is reflected by sawtooth pulses  648  and  650 , which align with the beginning of transfer station activation pulses TB1  640  and TA 2 642, respectively. This pattern of odd numbered sheets demanded approximately 0.5P revolutions after even numbered sheets and even number sheets demanded approximately 5.5P revolutions after odd numbered sheets continues until the print job is complete 
     The disparity between alternating demands of 0.5P and 5.5P revolutions of the intermediate substrate  104  is perhaps emphasized by the following example If the intermediate substrate is a drum with a circumference of 565.5 mm (22.25 in.) and the drum is rotated at 1400 mm/sec. (55 in./sec.), each pass (P) is 0.4 sec. in duration and the transfer station  110  alternates between demanding target substrate sheets  118  in 0.2 sec (0.5P) and 2.2 sec (5.5P). 
     With reference to  FIG. 7 , a timing diagram for a two-pitch, six-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention is shown Like  FIG. 6 ,  FIG. 7  includes a periodic sawtooth waveform  602 , a square pulse train  704 , a repeating dual square pulse sequence  706 , and a repeating dual sawtooth pulse sequence  708  The diagrams (ie,  602 ,  704 ,  706 , and  708 ) represent the same type of information as the diagrams of  FIG. 6   
     The intermediate substrate  104  moves in the same manner for  FIG. 7  as described for  FIG. 6 . Accordingly, the periodic sawtooth waveform  602  and a pass P  610  of the intermediate substrate  104  in  FIG. 7  are identical to that of  FIG. 6   
     Like in  FIG. 6 , each pulse  612  in the square pulse train  704  of  FIG. 7  represents activation of the marking material applicator  102  by the controller  115  Since  FIG. 7 , like  FIG. 6 , shows timing sequences for a two-pitch, six-pass marking architecture, the marking material applicator  102  is activated in basically the same manner as described in  FIG. 6 . Accordingly,  FIG. 7  also refers to the two pitch areas  218  on the intermediate substrate  104  as “pitch A” and “pitch B” The distinction between  FIG. 7  and  FIG. 6  is that  FIG. 7  employs “alternate imaging mode” rather than “burst mode” scheduling 
     In this embodiment of “alternate imaging mode,” the applicator  102  begins depositing marking material on pitch A during pass P1 and delays beginning pitch B imaging until pass P4. This is reflected by applicator activation pulses A1  614  during pass P1. During passes P2 and P3, first page imaging continues with pulses A2  618  and A3  622 , respectively During pass P4, first page imaging continues and the applicator  102  begins depositing marking material on pitch B This is reflected by pulses A4  626  and B1  716  During pass P5, first page and second page imaging continues with pulses A5  630  and B2  720 . During pass P6, first page and second page imaging continues with pulses A6  634  and B3  724 . During pass P7, second page imaging continues on pitch B and the applicator  102  begins another identical six-pass cycle for the third page of the print job on pitch A This is reflected by pulses B4  728  and A1  614 . During pass P8, second and third page imaging continues with pulses B5  732  and A2  618  During pass P9, second and third page imaging continues with pulses B6  736  and A3  622  The applicator  102  continues to be activated in like fashion until the print job is complete 
     Like in  FIG. 6 , each pulse (e.g.,  638 ) in the dual square pulse sequence  706  of  FIG. 7  represents activation of the transfer station  110  by the controller  115 . After the start of A6  634 , transfer of the pitch A composite image to a target substrate  118  can begin. Transfer of the pitch A composite image is performed the same in  FIG. 7  as in  FIG. 6  This is reflected by transfer station activation pulse TA1  638 , which occurs at the same point in  FIG. 7  as in  FIG. 6  Transfer of the pitch B composite image to a target substrate  118  can begin after the start of B6  736  This is reflected by transfer station activation pulse TB1  740 . However, note that in  FIG. 7  the applicator activation pulse B6 begins during pass P9, rather than during pass P6 as it did in  FIG. 6 . Presuming the print job includes third and fourth pages, the transfer station is activated again in identical fashion after the start of A6  634  in pass P12 and after the start of the sixth marking pass over pitch B in pass P15 (not shown). Transfer station activation for the third page image is represented by pulse TA2  642 . 
     Like in  FIG. 6 , each pulse (e.g.,  646 ) in the dual sawtooth pulse sequence  708  in  FIG. 7  represents target substrate  118  demand at the transfer station  110  In this embodiment of “alternate imaging mode,” it is important to note that the second target substrate sheet  118  is demanded approximately 3.5P revolutions of the intermediate substrate  104  after the first target substrate sheet  118  was demanded. This is reflected by sawtooth pulses  646  and  748 , which align with the beginning of transfer station activation pulses TA1  638  and TB1  740 , respectively. Similarly, the third target substrate sheet  118  is demanded approximately 2.5P revolutions after the second target substrate sheet  118 . This is reflected by sawtooth pulses  748  and  750 , which align with the beginning of transfer station activation pulses TB1  740  and TA2  642 , respectively. This pattern of odd numbered sheets demanded approximately 3.5P revolutions after even numbered sheets and even number sheets demanded approximately 2.5P revolutions after odd numbered sheets continues until the print job is complete. 
     Where average demand would be 3P revolutions of the intermediate substrate  104 , the alternating demands of 3.5P and 2.5P revolutions in  FIG. 7  produces less deviation about the average than the alternating demands of 0.5P and 5.5P in  FIG. 6  This is perhaps emphasized by applying the example of the drum with a circumference of 565.5 mm (22.25 in.), rotated at 1400 mm/sec (55 in/sec) used above. Recall that each pass (P) of the drum is 0.4 sec. in duration. Also recall that under “burst mode” scheduling ( FIG. 6 ) the transfer station  110  alternates between demanding target substrate sheets  118  in 0.2 sec. (0.5P) and 2.2 sec. (5.5P). Here, under the  FIG. 7  embodiment of “alternate imaging mode” scheduling, the transfer station  110  alternates between demanding target substrate sheets  118  in 1.4 sec (3.5P) and 1.0 sec. (2.5P) 
     With reference to  FIG. 8 , a timing diagram for a two-pitch, six-pass marking architecture that schedules print jobs in an “alternate imaging mode” in accordance with an embodiment of the present invention is shown. Like  FIG. 6 ,  FIG. 8  includes a periodic sawtooth waveform  602 , a square pulse train  804 , a repeating dual square pulse sequence  806 , and a repeating dual sawtooth pulse sequence  808  The diagrams (i.e.,  602 ,  804 ,  806 , and  808 ) represent the same type of information as the diagrams of  FIG. 6 . 
     The intermediate substrate  104  moves in the same manner for  FIG. 8  as described for  FIG. 6 . Accordingly, the periodic sawtooth waveform  602  and a pass P  610  of the intermediate substrate  104  in  FIG. 8  are identical to that of  FIG. 6   
     Like in  FIG. 6 , each pulse  612  in the square pulse train  804  of  FIG. 8  represents activation of the marking material applicator  102  by the controller  115  Since  FIG. 8 , like  FIG. 6 , shows timing sequences for a two-pitch, six-pass marking architecture, the marking material applicator  102  is activated in basically the same manner as described in  FIG. 6 . Accordingly,  FIG. 8  also refers to the two pitch areas  218  on the intermediate substrate  104  as “pitch A” and “pitch B” The distinction between  FIG. 8  and  FIG. 6  is that  FIG. 8  employs “alternate imaging mode” rather than “burst mode” scheduling. 
     In this embodiment of “alternate imaging mode,” the applicator  102  begins depositing marking material on pitch A during pass P1 and delays beginning pitch B imaging until pass P3. This is reflected by applicator activation pulses A1  614  during pass P1. During pass P2, first page imaging continues with pulse A2  618  During pass P3, first page imaging continues and the applicator  102  begins depositing marking material on pitch B This is reflected by pulses A3  626  and B1  816  During pass P4, first page and second page imaging continues with pulses A4  626  and B2  820  During pass P5, first page and second page imaging continues with pulses A5  630  and B3  824  During pass P6, first page and second page imaging continues with pulses A6  634  and B4  828  During pass P7, second page imaging continues on pitch B and the applicator  102  begins another identical six-pass cycle for the third page of the print job on pitch A This is reflected by pulses B5  832  and A1  614  During pass P8, second and third page imaging continues with pulses B6  836  and A2  618  The applicator  102  continues to be activated in like fashion until the print job is complete. 
     Like in  FIG. 6 , each pulse (e.g.,  638 ) in the dual square pulse sequence  806  of  FIG. 8  represents activation of the transfer station  110  by the controller  115 . After the start of A6  634 , transfer of the pitch A composite image to a target substrate  118  can begin Transfer of the pitch A composite image is performed the same in  FIG. 8  as in  FIG. 6 . This is reflected by transfer station activation pulse TA1  638 , which occurs at the same point in  FIG. 8  as in  FIG. 6 . Transfer of the pitch B composite image to a target substrate  118  can begin after the start of B6  836  This is reflected by transfer station activation pulse TB1  840 . However, note that in  FIG. 8  the applicator activation pulse B6 begins during pass P8, rather than during pass P6 as it did in  FIG. 6 . Presuming the print job includes third and fourth pages, the transfer station is activated again in identical fashion after the start of A6  634  in pass P12 and after the start of the sixth marking pass over pitch B in pass P14 (not shown). Transfer station activation for the third page image is represented by pulse TA2  642 . 
     Like in  FIG. 6 , each pulse (e.g.,  646 ) in the dual sawtooth pulse sequence  808  in  FIG. 8  represents target substrate  118  demand at the transfer station  110  In this embodiment of “alternate imaging mode,” it is important to note that the second target substrate sheet  118  is demanded approximately 2.5P revolutions of the intermediate substrate  104  after the first target substrate sheet  118  was demanded This is reflected by sawtooth pulses  646  and  848 , which align with the beginning of transfer station activation pulses TA1  638  and TB1  840 , respectively. Similarly, the third target substrate sheet  118  is demanded approximately 3.5P revolutions after the second target substrate sheet  118 . This is reflected by sawtooth pulses  848  and  850 , which align with the beginning of transfer station activation pulses TB1  840  and TA2  642 , respectively This pattern of odd numbered sheets demanded approximately 2.5P revolutions after even numbered sheets and even number sheets demanded approximately 3.5P revolutions after odd numbered sheets continues until the print job is complete. 
     Where average demand would be 3P revolutions of the intermediate substrate  104 , the alternating demands of 2.5P and 3.5P revolutions in  FIG. 8  produces less deviation about the average than the alternating demands of 0.5P and 5.5P in  FIG. 6  This is perhaps emphasized by applying the example of the drum with a circumference of 565.5 mm (22.25 in.), rotated at 1400 mm/sec (55 in./sec.) used above Recall that each pass (P) of the drum is 0.4 sec. in duration. Also recall that under “burst mode” scheduling ( FIG. 6 ) the transfer station  110  alternates between demanding target substrate sheets  118  in 0.2 sec (0.5P) and 2.2 sec (5.5P) Here, under the  FIG. 8  embodiment of “alternate imaging mode” scheduling, the transfer station  110  alternates between demanding target substrate sheets  118  in 1.0 sec. (2.5P) and 1.4 sec (3.5P) 
     The invention 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 invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof