Abstract:
A method for printer stability enhancement in a multiple printer printing system includes determining a first printer stress state of a first printer in a printing system, wherein the first printer is assigned a first printing role. A second printer stress state of a second printer in the printing system is also determined, wherein the second printer is assigned a second printing role that is different from the first printing role. The first printer stress state is compared to the second printer stress state, and the first printing role is reassigned to the second printer and the second printing role is reassigned to the first printer if the first printer stress state is different than the second printer stress state. A printing system implementing the method is also provided.

Description:
BACKGROUND 
     Currently, two or more printers (or “print engines”) are combined in a Tightly Integrated Serial Printing (TISP) system or a Tightly Integrated Parallel Printing (TIPP) system to provide a single print system of higher capacity and with other advantages. In such known systems, each printer is assigned a specific dedicated printing role. For example, a first printer of a TISP/TIPP printing system is assigned a first printing role of “side one printing” of pages and a second printer of the TISP/TIPP printing system is assigned a second printing role of “side two printing” of pages. Such dedication of printing roles provides advantages, but can also lead to problems. In particular, the first and second printers often migrate to different overall states of relative print quality, performance, and efficiency (referred to herein as “stress states”) due to differences in the printing roles performed thereby. In the above example, the side one printing duties defining the first printing role can be more demanding in terms of amount of printed output generated as compared to the side two printing duties defining the second printing role. This variation in the amount of printed output often causes the first and second printers to diverge from each other in terms of quality, replenishment of colorant (ink or toner), remaining useful life of wear parts, etc., which can be thought of as a lack of stability in the TISP/TIPP system. Any variation in quality is highly objectionable to the user, and the divergence in terms of consumption of colorant, useful life of wear components, and the like leads to inefficiencies in connection with supply usage and maintenance requirements. As such, a need has been identified for a new and improved method and system for controlling multiple printers in a TISP or TIPP system for increased stability. 
     SUMMARY 
     In accordance with a first aspect of the present development, a method for printer stability enhancement in a multiple printer printing system includes determining a first printer stress state of a first printer in a printing system, wherein the first printer is assigned a first printing role. The method further includes determining a second printer stress state of a second printer in the printing system, wherein the second printer is assigned a second printing role that is different from the first printing role. The first printer stress state is compared to the second printer stress state, and the first printing role is reassigned to the second printer and the second printing role is reassigned to the first printer if the first printer stress state is different than the second printer stress state. 
     In accordance with another aspect of the present development, a system for printer stability enhancement in a multiple printer printing system includes a first printer assigned a first printing role and a second printer assigned a second printing role that is different from the first printing role. The system further includes means for reassigning the first printing role to the second printer and for reassigning the second printing role to the first printer after completion of a printing cycle. 
     In accordance with a further aspect of the present development, a system for printer stability enhancement in a multiple printer printing system includes means for determining a first printer stress state of a first printer in a printing system, wherein the first printer is assigned a first printing role. The system further includes means for determining a second printer stress state of a second printer in the printing system, wherein the second printer is assigned a second printing role that is different from the first printing role. The system also includes means for comparing the first printer stress state to the second printer stress state, and means for reassigning the first printing role to the second printer and reassigning the second printing role to the first printer if the first printer stress state is different than the second printer stress state. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a conventional TISP/TIPP printing system; 
         FIG. 2  illustrates a TISP/TIPP printing system provided in accordance with the present development; 
         FIG. 3  is chart that illustrates examples of printer stress parameters used in the system and method according to the present development; 
         FIG. 4  illustrates a method for multiple printer stability enhancement according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a print job  20  is input to a multiple printer printing system  22  that is provided as a Tightly Integrated Serial Printing (TISP) printing system  30  and/or a Tightly Integrated Parallel Printing (TIPP) printing system  40 . The print job  20  includes first and second printing roles, e.g., with the first printing role being defined as printing side one of each page and the second printing role being defined as printing side two of each page, or the first printing role being defined as printing text and the second printing role being defined as printing images and graphics, or any other divisional of roles in a multiple printer printing system. 
     The TISP printing system  30  is configured such that a first printing role of the print job  20  is performed by a first printer  32  (Printer # 1 ) that is located upstream from a second printer  34  (Printer # 2 ) that performs a second printing role of the print job  20  after the first printing role performed by the first printer  32  is completed. The second printer  34  outputs the print job to a printed output module  36  for assembling the hard copy paper printed output into the desired physical arrangement or package. The TISP printing system  30  also includes a paper path control system  38  comprising gates, inverters, cross-overs and the like, for controlling the flow of paper (or other print recording media) to and from the first and second printers  32 , 34 . 
     Similarly, in the TIPP printing system  40 , a first printing role of the print job  20  is performed by a first printer  42  (Printer # 1 ) that is arranged and operates in parallel with a second printer  44  (Printer # 2 ) that performs a second printing role of the print job  20  simultaneously with the first printing role performed by the first printer  42 . The first and second printers  42 , 44  output their respective print jobs to a printed output module  46  for assembling the hard copy paper printed output into the desired physical arrangement or package. The TIPP printing system  40  also includes a paper path control system  48  comprising gates, inverters, cross-overs and the like, for controlling the flow of paper (or other print recording media) to and from the first and second printers  42 , 44 . 
     As noted above, the stress states of the first and second printers  32 , 34  or  42 , 44  will often undesirably diverge relative to each other over time.  FIG. 2  illustrates either a TISP or a TIPP printing system  50  provided in accordance with the present development including a first printer  52  (Printer # 1 ) and a second printer  54  (Printer # 2 ) arranged in a TISP or TIPP arrangement (the relative location of the first and second printers  52 , 54  in  FIG. 2  is not intended to be limited to either a TISP or TIPP system). Unlike the TISP and TIPP systems  30 , 40  of  FIG. 1 , the multiple-printer system  50  shown in  FIG. 2  is structured and configured to enhance stability and reduce stress state variation between the first and second printers  52 , 54 . As such, the system  50  comprises a printer variation control module  60  that receives the data defining the print job  20 . The printer variation control module  60  divides the print job  20  into at least a first printing role  62  (Printing Role # 1 ) and a second printing role  64  (Printing Role # 2 ). As indicated by the solid-line arrows R 1  and R 2 , in a first or default state, the printer variation control module  60  outputs the data associated with and defining the first printing role  62  to the first printer  52  and outputs the data associated with and defining the second printing role  64  to the second printer  54 . As indicated by the broken-line arrows R 1 ′ and R 2 ′, in a second or default state, the printer variation control module  60  outputs the data associated with and defining the first printing role  62  to the second printer  54  and outputs the data associated with and defining the second printing role  64  to the first printer  52 . The system  50  comprises a printer control system  70  that is operably connected to the printer variation control module  60  (e.g., the printer variation control module  60  can be provided by software and/or hardware implemented in the control system  70 , itself, or it can be a separate hardware and/or software module). The printer control system  70  and the printer variation control module  60  are provided by electronic circuitry and/or other hardware and/or software that is dedicated to digital image processing and/or can comprise a general purpose computer programmed to implement the image processing operations disclosed herein. 
     In response to input received by the printer control system  70 , or according to an arbitrary or pre-defined schedule, the printer control system  70  provides input to the printer variation control module  60  to cause the printer variation control module  60  to select either its first state as indicated by the solid-line arrows R 1 ,R 2  or its second state as indicated by the broken-line arrows R 1 ′,R 2 ′. In other words, the printer control system  70  periodically causes the printer variation control module  60  to reassign the first printing role  62  to the second printer  54  and to reassign the second printing role  64  to the first printer  52 , and vice versa. The printer control system  70  also receives some or all of the data defining the print job  20  for reasons described below. 
     As shown in  FIG. 2 , the system  50  also comprises a paper path control system  58  comprising gates, inverters, cross-overs and the like, for controlling the flow of paper (or other print recording media) to and from the first and second printers  52 , 54 . The paper path control system  58  is controlled by the printer control system  70  and also provides feedback to the control system  70 . The system  50  further comprises multiple sensors  59  associated with the first and second printers  52 , 54  for providing sensor data to the printer control system  70 . In particular, the sensors  59  associated with the first printer  52  provide first printer stress data input to the printer control system  70 . The first printer stress data describe and relate to the stress state of the first printer. The sensors  59  associated with the second printer  54  provide second printer stress data input to the printer control system  70 . The second printer stress data describe and relate to the stress state of the second printer. Examples of sensors  59  and the printer stress data output thereby include: (i) environmental sensors (temperature, humidity, etc.); (ii) toner usage, toner concentration, toner reservoir data sensors; (iii) streak sensors for detecting streaks on the photoreceptor; (iv) electrical sensors for measuring the development field, laser power, charge level, and the like that provide information to the printer control system concerning the printing operation being performed by the first and second printers  52 , 54  and the stress states of the first and second printers  52 , 54 . The sensors also include paper sensors and other sensors in the paper path; and other known sensors. 
     The printer control system  70  receives data from the sensors  59  and also uses the data defining and describing the print job  20  to calculate or otherwise derive first printer stress parameters that describe or indicate a stress state of the first printer  52  and to calculate or otherwise derive second printer stress parameters that describe or indicate a stress state of the second printer  54 .  FIG. 3  is chart that illustrates examples of the first printer stress parameters FP 1 -FP 7  and the corresponding second printer stress parameters SP 1 -SP 7 . Each first printer stress parameter FP 1 -FP 7  respectively relates to a corresponding second printer stress parameter SP 1 -SP 7 . As such, the printer control system  70  calculates or otherwise determines a respective stress parameter difference or “delta” Δ 1 -Δ 7  between each corresponding pair of the first and second printer stress parameters FP 1 -FP 7  and SP 1 -SP 7 . It is not intended that the present development be limited to the first and second printer stress parameters listed in  FIG. 3 . Those of ordinary skill in the art will recognize that the present development is intended to encompass these and/or other printer stress parameters and is not to be limited to the particular stress parameters disclosed herein. 
     A description of each printer stress parameter FP 1 -FP 7 , SP 1 -SP 7  is provided below: 
     Toner Age (FP 1 ,SP 1 ) 
     This parameter describes the age of the toner (or other colorant) in terms of the time it has been residing in the development housing/sump, typically described in terms of a “mean residence time.” The printer control system  70  uses the fixed size of the development housing, the amount of toner input to the development housing and the amount of toner consumed from the development housing over a known time period to calculate the toner age parameter. A variation in toner age between the first and second printers  52 , 54  indicates a variation in printer stress levels. 
     Toner Concentration (FP 2 ,SP 2 ) 
     This parameter describes the concentration of toner relative to carrier beads or other carrier material in the two-component development housing or sump. The toner concentration is measured by one of the sensors  59  and is controlled by the printer control system  70  in real-time to adjust the image density of the printed output. A variation in toner concentration between the first and second printers  52 , 54  indicates a variation in printer stress levels due to variations in printed output. 
     Area Coverage (FP 3 ,SP 3 ) 
     This parameter describes the quantity of toner being output by each printer  52 , 54  in terms of the area covered by the toner or other colorant. The printer control system  70  derives the area coverage parameter from the data defining the print job  20 . Variation in area coverage between the first and second printers  52 , 54  indicates a variation in printer stress levels. 
     Streaks (FP 4 ,SP 4 ) 
     This parameter describes the detection of streaks on the photoreceptor of the printer as detected by full-width array sensors. Detection of streaks associated with one of the printers  52 , 54  but not the other indicates a variation in printer stress levels. 
     Development Field (FP 5 ,SP 5 ) 
     This parameter describes the voltages and other electrical characteristics of the xerographic field including the magnetic roller. The development field is measured by sensors  59  and/or is known and controlled by the printer control system  70 . Differences in the development field between the first and second printers  52 , 54  indicates a variation in printer stress. 
     Laser Power/ROS (FP 6 ,SP 6 ) 
     The laser (Raster Output Scanner (ROS)) power consumed is known by the printer control system  70 . An increase in laser power consumption indicates that greater power is required to maintain the desired image density. As such, a variation in laser power between the first and second printers  52 , 54  indicates different levels of printer stress. 
     Charge Level (FP 7 ,SP 7 ) 
     The charge level on the photoreceptor is known by the printer control system  70  and/or is measured by sensors  59 . Variation in charge levels between the first and second printers  52 , 54  indicates different levels of printer stress due to component wear or other reasons. 
       FIG. 4  illustrates a method for multiple printer stability enhancement according to an exemplary embodiment, using the TISP/TIPP system  50  of  FIG. 2  or another multiple-printer printing system. In a step S 1 , the printer control system  70  receives the first and second printer stress data, i.e., the first and second printer stress parameters and/or the data required to derive the first and second printer stress parameters. In a step S 2 , the control system  70  uses the printer stress data received in step S 1 , data from the input print job  20 , and other printer stress parameters available to it as described above to calculate a first printer stress state for the first printer  52  and a second printer stress state for the second printer  54 . In a step S 3 , the control system  70  compares the first printer stress state and the second printer stress state. In a step S 4 , the control system  70  controls the printer variation control module  60  to swap the printing roles for the first and second printers  52 , 54  as described above if the difference between the first and second stress states is greater than a select threshold. As such, if the difference between the first and second stress states is greater than the select threshold then:
         if the first printing role is being performed by the first printer  52  and the second printing role is being performed by the second printer  54 , the step S 4  will cause the first printing role to be performed by the second printer  54  and the second printing role to be performed by the first printer  52 ; and   if the first printing role is being performed by the second printer  54  and the second printing role is being performed by the first printer  52 , the step S 4  will cause the first printing role to be performed by the first printer  52  and the second printing role to be performed by the second printer  54 .
 
The steps S 1 -S 4  are then repeated continuously while the printing system  50  is active.
       

     In one embodiment, the select threshold used in step S 4  is exceeded if any one of the stress parameter deltas Δ 1 -Δ 7  does not equal zero. In another embodiment, the select threshold used in step S 4  is exceeded if any one of the stress parameter deltas Δ 1 -Δ 7  varies by 10% or more from either of the respectively corresponding first and second printer stress parameters FP 1 -FP 7 , SP 1 -SP 7  used to calculate the stress parameter delta Δ 1 -Δ 7 , i.e., if the second printer stress parameter varies from the first stress parameter by 10% or more of the first stress parameter or vice versa. In other words, a tolerance range of plus or minus 10% is assigned to each of the stress parameter deltas Δ 1 -Δ 7 , and each stress parameter delta Δ 1 -Δ 7  is deemed to indicate printer stress variation only if it falls outside the tolerance range. Also, the threshold used in step S 4  can be deemed to be exceeded if one, greater than one, or all available stress parameter deltas Δ 1 -Δ 7  fall outside the tolerance range. As such, printer stress variation indicated by any one or more of the of the stress parameter deltas Δ 1 -Δ 7  can be ignored until a select minimum number of the available stress parameter deltas Δ 1 -Δ 7  fall outside the tolerance range as would indicate printer stress variation outside an acceptable range. 
     Those of ordinary skill in the art will recognize that the above-described swapping of the first and second printing roles between the first and second printers  52 , 54  according to the step S 4  will ensure that the variation between the respective stress states of the first and second printers  52 , 54  is maintained within acceptable limits. 
       FIG. 4  also illustrates an alternative embodiment for a multiple printer stability enhancement method in accordance with the present development. The method comprises a step T 1  in which the control system  70  controls the printer variation control module  60  to swap the printing roles for the first and second printers  52 , 54  as described above after completion of a predetermined fixed or arbitrarily variable printing cycle. The printing cycle is defined in terms of time, number of sheets, toner usage, data printed, and/or any other parameter related to time and/or printing activity of the system  50 . According to the present development, the print cycle can be defined in any desired manner as noted such that the first and second printers  52 , 54  swap roles periodically as controlled by the printer control system  70  in a manner that is seamless to the user in order to reduce stress variations between the printers. A printing cycle can be defined as a select number of print jobs, pages, time (minutes, hours, days, etc.) or other criteria related to the activity of the printing system  50 . As indicated by the step T 2 , the process is repeated while the printing system  50  is active. As such, according to the step T 1 :
         if the first printing role is being performed by the first printer  52  and the second printing role is being performed by the second printer  54 , the step T 1  will cause the first printing role to be performed by the second printer  54  and the second printing role to be performed by the first printer  52 ; and   if the first printing role is being performed by the second printer  54  and the second printing role is being performed by the first printer  52 , the step T 1  will cause the first printing role to be performed by the first printer  52  and the second printing role to be performed by the second printer  54 .
 
This periodic swapping of the first and second printing roles between the first and second printers  52 , 54  will ensure that variation of between the respective printer stress states of the first and second printers  52 , 54  is controlled so as to be maintained within a required range.
       

     The present development will reduce toner consumption by reducing the likelihood that the toner age FP 1 ,SP 1  of either printer  52 , 54  becomes elevated. In known systems  30 , 40 , when the toner age reaches a maximum acceptable level, the system will perform a MAC (Minimum Area Coverage) Patch and/or Toner Purge routine to use toner for waste purposes by printing colorant patches on the photoreceptor and then wiping the patches into the waste toner hopper in order to drive the toner age down to an acceptable level. The system  50  and method of the present development reduces the chance that the toner age in either printer will reach the maximum acceptable level, because both printers will be used in a uniform manner relative to each other. 
     The claims, as originally presented and as they may be amended, are intended to encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein.