Abstract:
An imaging system includes a plurality of imaging engines each comprising a photoreceptor belt having a belt seam. A sensor determines a relative position of a first photoreceptor belt of a first one of the imaging engines relative to a second photoreceptor belt seam of a second one of the imaging engines. A controller controls a motor speed of one or more motors driving the photoreceptor belts, wherein an output of the sensor comprises a basis for adjustment of the motor by the controller for relative synchronizing of the first and second belts to avoid skipping pitches in one of the imaging engines due to relative belt seam positions.

Description:
BACKGROUND  
       [0001]     The subject embodiment pertains to the art of printing systems and more particularly printing systems including a plurality of printing engines capable of operating in parallel for parallel or sequential printing of job portions. The preferred embodiments especially relate to a system and method for synchronizing relative operating positions of photoreceptor belts within the printing assembly to avoid undesirable belt seam positioning that can diminish system throughput efficiency.  
         [0002]     Printing engines utilizing photoreceptor belts, as opposed to drums, must avoid using the portion of the belt comprising the seam because the seam, if used to store any image data, can mar the output image. In most engine printing systems, paper feeding systems will detect seam position to avoid lining up the paper with the seam. When such avoidance requires delaying the printing operation for the time period of printing a single page, such a wait is referred to as “skipping a pitch” and has a noticeable negative consequence on printing systems throughput efficiency. Adjusting the feed of the paper to assure avoidance of the seam is normally all that is needed in single print engine systems and is usually successful enough so that a pitch is hardly ever skipped.  
         [0003]     A special problem exists in multiple print engine systems where a first printing engine (image output terminal or “IOT”) can be a presequential feeder to a second IOT. Of importance is that the second IOT be synchronized to the first IOT, i.e., that the second photoreceptor belt seam is synchronized to the first photoreceptor belt seam, to avoid the pitch skipping problems.  
         [0004]     When such parallel printing assemblies are initially constructed, it is intended that the respective photoreceptor belts be of the same size (length) and that the motor speed for operating the belts of the IOTs are identical. In such cases, initial calibration is intended to avoid having to adjust the relative positions or operating speeds of the respective engines during operation, or that the feeding system can adjust positions of the documents during input to each engine to accommodate any throughput problems that may arise.  
         [0005]     It is an operational objective that there is no delay in paper feed through the system so that throughput can always be maximized. Unfortunately the practical reality is that no two photoreceptor belts are exactly the same size, nor are their respective motors capable of running at exactly the same speed. The respective differences may be quite small, but over time, and the production of many print documents, the respective belts can become so out of synchronization that the conventional paper feed adjustment systems may not be capable of accommodating the phase feed differences and a pitch may have to be skipped.  
         [0006]     Accordingly, there is a need for a system capable of monitoring position and phase relationships between respectively associated IOTs, their belts and their seams, so that whatever differences do exist, may be maintained within acceptable ranges to avoid the problems of skipping pitches and throughput delays.  
       SUMMARY  
       [0007]     According to aspects illustrated herein, one disclosed feature of the embodiments is an imaging system including a plurality of imaging engines (IOTs), each comprising a photoreceptor belt having a belt seam. A sensor is provided for determining a relative position of a first photoreceptor belt seam of a first one of the imaging engines relative to a second photoreceptor belt seam of a second one of the imaging engines. A controller controls a motor speed of a motor driving one of the belts, wherein an output of the sensor comprises a basis for an adjustment of the motor speed by the controller for relative synchronizing of the first and second belts for avoiding skipping pitches in an imaging engine due to relatively misaligned belt seam positions.  
         [0008]     According to another aspect illustrated herein, a method is provided for selective synchronizing photoreceptor belt seams of a multi-engine printing system to enhance throughput. The method comprises sensing a first position of a first photoreceptor belt of a first imaging engine and sensing a relative position of a second photoreceptor belt to the first position. A difference is determined between the first and second relative positions. Adjustment is selectively made of a motor speed of a motor driving one of the first and second photoreceptor belts to adjust the difference to within an acceptable range to maintain desired throughput efficiency. The difference is preferably determined by measuring a time difference per belt revolution representative of a relative difference in seam position for the belts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is an elevated schematic view of a multi-engine printing system;  
         [0010]      FIG. 2  is an enlarged view of the printing engine itself particularly showing a photoreceptor belt assembly;  
         [0011]      FIG. 3  is an alternative partial view of the photoreceptor belt assembly, showing a seam;  
         [0012]      FIG. 4  is a timing diagram showing measurements representative of belt seam relative positions; and  
         [0013]      FIG. 5  is a flowchart illustrating process steps of one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]     With reference to  FIG. 1 , a printing assembly  10  comprises first and second imaging engines or image output terminals  12 , 14 . The engines are associated in an order to effect sequential or parallel printing of documents through the assembly  10 . By “parallel” is meant that while engine  12  is printing one sheet, downstream of the paper path, engine  14  can be concurrently printing another sheet. Sheet feed trays  18  supply sheets to feeder module  19 , which in turn feeds marking engine  20  via paper paths  22 ,  23 . After output from the IOT  12 , a sheet is received by intermediate transport module  26  where the sheet can be directed to bypass module  28  or through second IOT  14  for further marking. Such an assembly is convenient for marking a first side of a sheet with the first marking engine  12  and the second side of a sheet by second engine  14 . The user interface/controller  30  permits the operator to control the job and functions of the IOTs.  
         [0015]     It can be appreciated that a document output by the first IOT  12  can be handled by the intermediate transport module  26  to be fed to the second IOT via paper path  32 . The sheet would then be directed along second IOT paper path  34  for marking at second marking engine  40 . Output transfer module  42  would then handle such a sheet for operator pickup or further transport to a finishing module  44 .  
         [0016]     In the assembly illustrated in  FIG. 1 , it is noteworthy that the output of the first IOT  12  comprises a document feeder system to the second IOT  14 .  
         [0017]     With reference to  FIGS. 2 and 3 , exemplary embodiments of a marking engine  20  of the kind that may be implemented in either first or second IOTs  12 ,  14 , show a photoreceptor belt  60  having a photoconductive surface deposited on a conductive ground layer. The construction of the subject photoreceptor belt is well known to one of ordinary skill in the art and essentially comprises a photoresponsive material, for example, one comprising a charge generation layer and a transport layer. The conductive layer is typically made from a thin metal layer or metalized polymerfilm. The belt  60  moves in the direction of the arrow  62  to advance successive portions of the photoconductive surface sequentially through the various processing stations disposed about the path of movement thereof. Belt  60  is entrained about stripping roller  64 , tensioning roller  66  and drive roller  68 . Drive roller  68  is mounted rotatably in engagement with the belt  60 . Motor  70  rotates roller  68  to advance the belt  60  in the direction of the arrow  62 . Roller  68  is coupled to motor  70  by suitable means, such as a drive belt or gear assembly (not shown). A toner particle dispenser  72  dispenses toner particles into developer housing  74  where magnetic brushed developer rollers  76  advance developer material into contact with a latent image on the belt  60 . Fusing station  90  permanently affixes the transferred powder image to a sheet  82  passing through the assembly. Sensor  86  is disposed to identify some indicia on the belt representative of the position of the belt seam  87 . Although many forms of indicia can be used, i.e., markings, reflectors, etc., in one embodiment a belt hole  89  is employed. In addition, sensor  88  can identify a position of the sheet  82  as it passes through the system, typically by identifying its leading edge.  
         [0018]     Sensor  86  identifies the position of the photoreceptor belt seam once per revolution and by measurement of the time of passage of the seam past the sensor  86  in both the first IOT  12  and the second IOT  14 , and the time that it takes a sheet  82  to be communicated from the first IOT to the second IOT for marking at the second IOT, it is possible to determine a timing window in which there will be no pitch skipping and maximum throughput for the assembly can be, maintained. As noted above, it is conventional to slightly adjust the paper feeding operation. However, over time, differences in dimensions between the belts and operating drives between the two IOTs can relatively arrange the photoreceptor seams  87  of the belts  60  of both IOTs to a position where pitch skipping can occur. By adjusting the speed of either one or both of the photoreceptor belts in the IOTs  12 ,  14  via adjusting the drive motor  70 , an acceptable difference in relative photoreceptor belt seam positioning can be maintained.  
         [0019]     With particular references to  FIGS. 4 and 5 , it can be seen that a belt hole position representative of the first belt seam position is identified  120  by pulse  100 , 102 . Window  104  comprises a timing range representing an acceptable relative difference in position (“phase difference”) between the photoreceptor belt  12  seam and the photoreceptor belt  14  seam. In otherwords, there is a precise time when the belt hole  1  representing the seam position on the first photoreceptor belt is sensed  120  and the belt hole  2  indicating the photoreceptor belt seam for the second IOT  14  is sensed  122  and represented by pulses  106 ,  110 . The measured time difference between these two sensings is indicative of the relative positions of the first and second seams, respectively of the first and second IOTs. If the difference is determined  124  to be on the low side, as is seen with respect to the measured difference between timings  100  and  106 , motor  70  is decreased in speed to correspondingly decrease the speed of the photoreceptor belt in the second IOT  14 . The speed adjustment would tend to move the timing difference more to the middle of window  104 . If the time difference is measured to be on the high side as is shown between timing measurements  102  and  110 , the motor  70  is increased in speed to correspondingly increase the speed of the belt within the second IOT  14  so that the measured time difference would again move towards the middle of window  104 . If the relative positioning is acceptably within the window  104 , then no adjustment is necessary.  
         [0020]     The measured time differences are calculated and the motor speed is adjusted in a program stored in GUI/controller  30 . Adjustment in speed can be made to either one of the motors in the IOTs or both motors, to best maintain an acceptable relative position.  
         [0021]     The embodied distributed controls system is based on programmability and adjustability. The photoreceptor seam synchronization can be accomplished by exploiting the adjustability of the photoreceptor and the raster output scanner (ROS). The photoreceptor belt velocity can be adjusted  126  to be increased or decreased on one or both of the photoreceptors such that the time between belt seams (as indicated by belt holes) on both photoreceptors can be matched within a small tolerance, i.e., window  104 .  
         [0022]     The control algorithm for the synchronization updates and compensates once per belt revolution. The algorithm will make a small adjustment to the velocity of one or both of the photoreceptors. There will be a few predefined velocities for each photoreceptor with corresponding ROS polygon velocities that have been setup by a customer service engineer for correct magnification. The change in velocity will be so small that there should not be any image quality defects.  
         [0023]     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.  
         [0024]     The subject embodiments have been illustrated as printing systems encompassing embodiments in hardware, software, or a combination thereof. By “printing system” as used herein, it is intended to encompass any apparatus, such as digital copier, bookmaking machine, facsimile machine, multifunction machine, etc. which performs a print outputting function for any purpose. The claims are intended to encompass embodiments that print in monochrome or color or handle color image data.