Abstract:
Method and devices for reducing printing artifacts. In one embodiment, a method includes directing ink onto a medium, the medium having a trailing edge; tracking the position of the medium in relation to a nip roller; adjusting the direction of ink onto the medium a first time when the trailing edge of the medium is in close proximity to the nip roller; and adjusting the direction of ink onto the medium a second time.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     None.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     None.  
       REFERENCE TO SEQUENTIAL LISTING, ETC.  
       [0003]     None.  
       BACKGROUND  
       [0004]     1. Field of the Invention  
         [0005]     Embodiments of the invention relate to methods and systems of printing to reduce print artifacts due to media movement error at the bottom of the page.  
         [0006]     2. Description of the Related Art  
         [0007]     A common problem in printers is the occurrence of print artifacts at the bottom of the page due to unintended movement of the media during and after feedroll-to-exit-roller transfer. The feedroll is a transport mechanism that initiates the movement of a piece of print media through the printing apparatus. The feedroll may include two rollers turning in opposite directions that are configured to grip the edge of a piece of print media and send it through the printing apparatus. The exit roller mechanism, on the other hand, is the opposite of the feedroll and is configured to guide print media out of the printing apparatus. A large error (predominately in the Y or sub-scan direction) occurs when the trailing edge of the media (e.g., a sheet of paper) leaves the nip of the feedroll, commonly referred to as a “nip jump,” and is under the sole guidance of the exit-roll. Printing artifacts are created due to changes in feed rate resulting from changes in the number and type of transport mechanisms controlling the print media, specifically at the time the media enters or exits one of the transport mechanisms. Printing artifacts can be more prevalent in high quality edge-to-edge print modes on glossy media. Often, these are the modes where the desire for defect-free printing is the highest.  
       SUMMARY OF THE INVENTION  
       [0008]     Embodiments of the invention provide a method of reducing printing artifacts. One method includes printing on print media using a first set of nozzles; controlling movement of the print media out of a feedroll nip; and printing on the print media using a second set of nozzles. Another method includes printing on print media using a first set of nozzles; detecting a nip jump; and printing on the print media using a second set of nozzles.  
         [0009]     Another embodiment provides a system for reducing printing artifacts. The system includes a printing apparatus that includes a feedroll configured to feed print media to the printing apparatus, a nip roller configured to feed print media to the printing apparatus, an exit roller configured to feed print media out of the printing apparatus, and a printhead including a plurality of nozzles, where each on of the plurality of nozzles applies a printing substance to the print media. The system further includes a driver configured to provide directions to move the print media between the feedroll, the nip roller, and the exit roller, to instruct a first set of the plurality of nozzles to apply a printing substance to the print media before a nip jump, and to instruct a second set of the plurality of nozzles to apply a printing substance to the print media after the nip jump.  
         [0010]     Yet another embodiment provides a printing apparatus. The printing apparatus includes a feedroll configured to feed print media to the printing apparatus; a nip roller configured to feed print media to the printing apparatus; an exit roller configured to feed print media out of the printing apparatus; a printhead including a plurality of nozzles, where each one of the plurality of nozzles applies a printing substance to the print media; and a processor configured to provide directions to move the print media between the feedroll, the nip roller, and the exit roller in a longitudinal direction, to instruct a first set of the plurality of nozzles to apply a printing substance to the print media before a nip jump, and to instruct a second set of the plurality of nozzles to apply a printing substance to the print media after the nip jump.  
         [0011]     Another embodiment provides a printhead configured to print an image on a print media. The printhead includes a plurality of nozzles configured to apply a printing substance to a print media; and a controller configured to instruct the printhead to use a first set of the plurality of nozzles to apply a print substance to the print media before a nip jump and to use a second set of the plurality of nozzles to apply a print substance to the print media after the nip jump.  
         [0012]     Yet another embodiment provides computer-readable media containing instructions for determining a first set of nozzles, printing on the print media with the first set of nozzles before a nip jump, determining a second set of nozzles, and printing on the print media with the second set of nozzles after the nip jump.  
         [0013]     Additional embodiments provide a method for reducing printing artifacts. The method includes directing ink onto a medium, the medium having a trailing edge; tracking the position of the medium in relation to a nip roller; adjusting the direction of ink onto the medium a first time when the trailing edge of the medium is in close proximity to the nip roller; and adjusting the direction of ink on to the medium a second time.  
         [0014]     Other features and advantages of embodiments of the invention will become apparent to those skilled in the art upon review of the following detailed description and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     In the drawings:  
         [0016]      FIG. 1  is a schematic illustration of an exemplary printer mechanism for transporting print media;  
         [0017]      FIG. 2  is a bottom, perspective view of a printhead;  
         [0018]      FIG. 3  is a portion of an exemplary printed image without a print defect;  
         [0019]      FIG. 4  is a portion of an exemplary printed image with a print defect;  
         [0020]      FIG. 5  is a flow chart illustrating an exemplary method for avoiding print defects;  
         [0021]      FIG. 6  graphically illustrates exemplary print media movement and corresponding printhead operation for the method shown in  FIG. 5 ;  
         [0022]      FIG. 7  is a flow chart illustrating another exemplary method for avoiding print defects; and  
         [0023]      FIG. 8  graphically illustrates exemplary print media movement and corresponding printhead operation for the method shown in  FIG. 7 . 
     
    
       [0024]     It is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted,” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. In addition, the terms “connected” and “coupled” and variations thereof are not restricted to physical or mechanical connections or couplings.  
       DETAILED DESCRIPTION  
       [0025]      FIG. 1  illustrates schematically an exemplary printer mechanism  50  for transporting print media in and out of a printer. The mechanism  50  includes a nip roller  52 , a feedroll  54 , an encoder  55 , a midframe  56 , an edge-to-edge trough  58 , two exit rollers  59  including two top exit rollers  59   a  and bottom exit rollers  59   b , one or more motors  61  (shown schematically), a motor bus  62 , a printhead  63 , a processor  64 , a memory module  65 , and a sensor  66 . The mechanism  50  transports print media  68 , also seen in  FIG. 1 , in a sub-scan or y-axis direction  70  while the printhead  64  moves in a scan or x-axis direction  72  as it directs ink onto the print media  68 . The print media  68  has a leading edge  68   a  and a trailing edge  68   b.    
         [0026]     In some embodiments, the nip roller  52  and feedroll  54  turn in opposite directions under the operation of the motor  61  and the counter rotations push the print media  68  between the nip roller  52  and feedroll  54  and forward or into the printer mechanism  50 .  
         [0027]     After being fed by the nip roller  52  and feedroll  54 , the print media  68  moves to the midframe  56 . The midframe supports the print media  68  while the printhead  64  directs printing substance, such as ink, to the media  68  while moving in the X direction (i.e., into and out of the page as shown in  FIG. 1 ). In the case of edge-to-edge printing, the printhead  64  directs ink beyond the edge of the print media  68  in order to ensure the edge of the print media  68  is fully covered. For example, as the print media  68  moves through the mechanism  50 , the printhead  64  may continue to direct ink out of the nozzles after the trailing edge  68   b  of print media  68  passes the printhead  64 . The edge-to-edge trough  58  provides a reservoir to collect excess ink supplied by the printhead  64  when print media  68  is not present.  
         [0028]     In some embodiments, the printhead  64  includes one or more nozzles  73  that direct ink to the print media  68  (see  FIG. 2 ). For example, a typical CMY (Cyan, Magenta, and Yellow) printhead can have 160 nozzles per color, spaced at 1/600 inch intervals in the sub-scan direction. Different colors of ink directed by the printhead  64  such as cyan, magenta, yellow, or black, may be directed through different nozzles  73 . The nozzles  73  may be positioned in columns. The printhead  64  illustrated in  FIG. 2  includes five columns of nozzles  73  (illustrated horizontally) each containing eight nozzles  73 . In some embodiments, the printhead  64  controls the nozzles  73  that are “active” and the nozzles  73  that are “turned off.” Only the nozzles  73  activated by the printhead  64  direct ink to the print media. For example, the nozzles  73  may be controlled based on where they are located. Nozzles  73  in a top half  74  of the nozzles  73 , which are the rows containing the half of the nozzles  73  that are closest to the exit rollers  59 , and a bottom half  75  of the nozzles  73 , which are the rows containing the half of the nozzles  73  that are closest to the nip roller  52  and feedroll  54 , may be activated differently. The printhead  64  may turn off the top half  74  and activate the bottom half  75 , turn off the bottom half  75  and activate the top half  74 , or activate or turn off both the top half  74  and the bottom half  75 . The printhead  64  may also create other regions of nozzles  73  and activate and turn off particular regions such as the top three fourths (¾) of the nozzles  73  and the bottom three fourths (¾) of the nozzles  73 , every other row, every second row, every third nozzle  73  of every row, every third nozzle  73  of every other row, and the like.  
         [0029]     After the printhead  64  applies ink to the print media  68 , the print media  68  travels through the exit rollers  59 . The top exit rollers  59   a  in the mechanism  50  are optional. Because the top exit rollers  59   a  contact the printed surface of the print media shortly after the ink has been applied, they are designed to have minimum contact with the printed surface when gripping the print media. Typically, rowel spurs, also called starwheels, are used to minimize contact. However, when used, the top exit rollers  59   a  and bottom exit rollers  59   b  can rotate under the direction of one or more motors  61  in a similar manner as the nip roller  52  and feedroll  54 . It should be noted that a single exit roller  59  may also be used instead of multiple exit rollers  59 . It should also be apparent that additional components may be used in the mechanism  50  such as ink dryers, multiple printheads, multiple nip rollers, feedrolls, exit rollers, and the like. The components may also be arranged in a variety of configurations. For example, the nip roller  52 , feedroll  54 , and exit rollers may be positioned to flip the print media and return it to the direction it came from or send the print media past the printhead  64  twice, in order to print both sides of the print media  68  or apply multiple ink layers.  
         [0030]     In some embodiments, the motors  61  control the movement of the print media  68  by operating the nip roll  52 , the feedroll  54 , and the exit rollers  59 . In some embodiments, the printer mechanism  50  includes a separate motor  61  for each roller and the processor  65  supplies control instructions to the motor bus  62 , which forwards signals to the individual motors  61 . The processor  65  may also directly supply control signals to each individual motor  61  without using the motor bus  62 . The printer mechanism  50  may also include a single motor  61  that controls all of the rollers.  
         [0031]     The processor  64  may be a microprocessor, programmable logic control, application specific integrated circuit, or the like configured to receive input (e.g., instructions and feedback signals) and provide output (e.g., control signals). The input to the processor  64  may come from the memory module  64 , the encoder  55 , the motors  61 , the printhead  64 , and/or the sensor  66 . The memory module  64  may contain non-volatile memory such as one or more forms of ROM, one or more disk drives, RAM, other memory, or combinations of the foregoing. In some embodiments, the memory module  64  stores program code or instructions, and the processor  64  fetches the instructions and outputs control instructions based on the execution of the fetched instructions to components of the printer mechanism  50 . The encoder  55  attached to the feedroll  54  may be a sensor that tracks the movement of the feedroll  54  and, as a result, the movement of the print media  68 . The encoder may supply movement parameters of the feedroll  54  to the processor  64 , and the processor  64  may adjust the operation of the printer mechanism  50  based on the provided movement parameters. For example, if the data provided by the encoder  55  indicates that the feedroll  54  is rotating too fast and transporting the print media  68  into the printer mechanism  50  too quickly, the processor  64  may generate and send a control signal to the motor  61  and/or the printhead  64  to adjust the rotation of the feedroll  54  or the movement of the printhead  64 , respectively.  
         [0032]     In some embodiments, the sensor  66  provides tracking of the print media  68  as it moves through the printer mechanism  50 . The sensor  66  can provide positional information to the processor  64  regarding the movement of the print media  68 . The sensor  66  can provide information as to the position of an approaching leading edge  68   a  or trailing edge  68   b  of print media  68 , a print media  68  jam, a speed of the moving print media  68 , the dimensions of the print media  68 , and the like. As described for the encoder, the processor  64  may use the information obtained and provided by the sensor  66  to adjust the operation of the printer mechanism  50 .  
         [0033]     As print media  68  moves through the mechanism  50 , one or more of the rollers (e.g., the nip roller  52 , the feedroll  54 , and/or the exit rollers  59 ) controls its movement. For example, when the print media  68  is first fed into the printer mechanism  50 , the nip roller  52  and feedroll  54  control the movement of the print media  68 . Eventually, however, the leading edge  68   a  of the print media  68  moves past the midframe and moves between one of the exit rollers  59 . After the leading edge  68   a  reaches one of the exit rollers  59 , and depending on the length of the print media  68  and the position of the rollers, the print media&#39;s movement is controlled by the nip roller  52 , the feedroll  54 , and one of the exit rollers  59 .  
         [0034]     The nip roller  52 , the feedroll  54 , and one or more of the exit rollers  59  continue to direct the movement of the print media  68  until the trailing edge  68   b  of the print media  68  moves out of and past the nip roller  52  and feedroll  54 . The release of the trailing edge  68   b  of the print media from the nip roller  52  and the feedroll  54  (“the feedroll nip”) can cause the print media  68  to jump ahead in the sub-scan direction  70  more than necessary as one or more exit rollers  59  become the sole controllers of the print media. This movement is often called a “nip jump” and can cause what are referred to as “bottom of the page artifacts” or defects. The extra movement of the print media  68  can cause misalignment of the printhead  64  and the print media  68  since the print media moved more than the printhead  64  is aware of or configured to operate according to. The printhead  64  is configured to direct ink to the print media  68  as the print media  68  moves through the mechanism  50  incrementally, at “normal” indexes. An “abnormal index,” such as occurs during the nip jump, can cause portions of the print media to move past the printhead  64  where they do not receive ink. The skipped portions can appear lighter or discolored in comparison to the surrounding printed image since the skipped portions either do not receive an application of ink, or receive a misaligned application of ink. A portion of an exemplary printed image  76  without a nip jump defect is illustrated in  FIG. 3 . The image  76  with a nip jump defect  78  is illustrated in  FIG. 4 . The defect  78  appears lighter and less continuous and smooth than the surrounding printed image because of a misaligned application of ink is directed by the printhead  64  due to the abnormal movement or jump of the print media  68  as the trailing edge  68   b  leaves the nip roller  52  and feedroll  54 .  
         [0035]      FIG. 5  is a flow chart illustrating an exemplary method of reducing or eliminating nip jump defects  78 . The first step of the method presented in  FIG. 5  involves the printer mechanism  50  performing “normal” printing (block  80 ). As the print media  68  passes through the mechanism  50 , the print media&#39;s movement and the printhead&#39;s movement are configured to keep both components aligned. For example, during “normal” printing, the print media  68  may be moved forward through the mechanism  50  at regular increments and times, and the printhead  64  may direct ink toward the print media  68  at regular locations and times governed by the incremental movement of the print media  68 . Any imprecise movement of the print media  68  can cause improper operation of the printhead  64  since the components are no longer aligned. “Normal” printing as referred to in block  80 , may include operating the printer mechanism  50  as configured without adjusting for past misalignments or preparing for possible future misalignments.  
         [0036]     At block  82 , the printer mechanism  50  determines if the trailing edge  68   b  of the print media  68  is approaching the nip roller  52 . In some embodiments, the trailing edge  68   b  is considered to be approaching the nip roller  52  if the trailing edge  68   b  is within approximately 0.75 inch from the nip roller  52 . The position of the trailing edge  68   b  may also be determined with reference to the printhead  64 . In some embodiments, the printhead  64  is located 0.5 inch ahead (toward the exit rollers  59 ) of the nip roller  52 , and the trailing edge  68   b  is considered approaching the nip roller  52  when the trailing edge  68   b  is approximately 1.25 inches from the printhead  64 . The distance between the nip roller  52  and the trailing edge  68   b  may also be varied to account paper size, the size of the nip roller  52 , the size and position of the printhead  64 , and the like. The printer mechanism  50  can include sensors or tracking devices, such as the sensor  66 , that indicate the position of the print media  68 . The printer mechanism  50  can also calculate the position by knowing the length of the print media  68  and how far the print media  68  has already been transported through the mechanism  50 . If the trailing edge  68   b  of the print media is not approaching the nip roller  52 , the printer mechanism  50  continues to print normally. If, however, the trailing edge  68   b  is nearing the nip roller  52 , the printer mechanism adjusts the nozzles  73  of the printhead  64  that are directing ink to the print media  68  (block  84 ). In some embodiments, the printer mechanism  50  reduces the number of nozzles  73  used by the printhead  64  to half the total available nozzles  73 . For example, as noted above, since a typical CMY printhead can have a total of 160 nozzles per color, the printer mechanism  50  may “turn off” half of the nozzles  73  so that only 80 nozzles  73  are directing ink to the print media  68 . The printer mechanism  50  can also specify the nozzles  73  of the printhead  64  that should remain “on” or active and those that should be turned off. In some embodiments, the nozzles  73  of the printhead  64  are arranged in rows and specific nozzles  73  within certain rows or specific entire rows may be turned off or left active. The printer mechanism  50  can turn off half of the rows of nozzles  73  and can leave half of the rows active. In some embodiments, the printer mechanism  50  turns off the top half  74  of the nozzles  73  and leaves on or activates the bottom half  75  of the nozzles  73  to prepare for any misalignment that may occur during a nip jump (see  FIG. 2 ). For example, utilizing the illustrated printhead of  FIG. 2 , which has a total of 40 nozzles distributed among 8 rows, the printer mechanism  50  turns off the top four rows of nozzles (the rows closest to the exit rollers  59 ) and leaves the bottom four rows of nozzles (the rows closest to the nip roller  52 ) active.  
         [0037]     At block  86 , the printer mechanism  50  determines if a nip jump is imminent. As described above, the printer mechanism  50  can include sensors or tracking devices that indicate the position of the trailing edge  68   b  of the print media  68  or the printer mechanism  50  can calculate the position since it knows the length of the print media  68  and how far the print media  68  has already been transported through the mechanism  50 . When it is determined that a nip jump is imminent, the printer mechanism  50  makes an adjusting index move to bring the print media  68  out of the feedroll nip (block  88 ). The adjusting index move aligns the region of print media  68  previously addressed by the first set of nozzles  73  to now be addressed by the second set of nozzles  73 . The adjusting index move is made through the rollers (e.g., the nip roller  52 , the feedroll  54 , or one or more of the exit rollers  59 ). The printer mechanism adjusts the operation of the motor  61  to modify the speed of one or more of the rollers to move the print media  68  through the nip jump. In some embodiments, the adjusting index move is equal to half the height of the printhead  64  plus the normal index move. For example, using a typical CMY printhead with 160 nozzles spaced at 1/600″ and therefore a height of 320/1200″ and a normal index of 7/1200″, an adjusting index move equal to the normal index ( 7/1200″) plus half the printhead height ( 160/1200″) would be made ( 167/1200″) to bring the print media  68  out of the feedroll nip. The adjusting index move avoids an unmanaged “jump” of the media  68  that can occur when the feedroll nip is trying to hold the edge of the media  68 , and provides regulated movement of the print media that can be managed and accounted for by the printer mechanism  50 . The adjusting index move aligns the region of the print media  68  previously addressed by the bottom half  75  of the nozzles  73  to now be addressed by the top half  74  of the nozzles  73  of the printhead  64 .  
         [0038]     Once the adjusting index move has been made, the printer mechanism  50  readjusts the nozzles  73  of the printhead  64  that are directing ink to the print media  68  (block  90 ). In some embodiments, the print media  68  moved past the bottom half  75  of the nozzles  73  of printhead  64  without receiving the proper application of ink, and is now aligned such that the top half  74  of the nozzles  73  of the printhead  64  can provide proper application of ink. The printer mechanism  50  activates the top half  74  of the nozzles  73  and turns off the bottom half  75  of the nozzles.  
         [0039]     At block  92 , the printer mechanism  50  determines if an image on the print media  68  has finished printing. Once an image is printed on the print media  68 , the printer mechanism  50  can return to normal printing (block  80 ) in order to print another image on another piece of print media  68 . In some embodiments, returning to normal printing may involve activating all of the nozzles  73  of the printhead  64  instead of using only half.  
         [0040]      FIG. 6  provides a graphical representation of the method described in  FIG. 5  for a four-pass print mode. In a four-pass print mode, the printhead  64  moves in the x-axis or main scan direction  72  across the print media  68  four times per region of the print media  68 , such that each region of the print media  68  will be addressed four times by the nozzles  73  of the printhead  64 . In between each main scan the print media  68  moves in the y-axis or sub-scan direction  70  through the mechanism  50 . The print media  68  may move at regular indexes or increments and each increment aligns the print media  68  with the nozzles  73  of the printhead  64  to receive the next print swath. Exemplary print swaths  100 - 129  are also illustrated in  FIG. 6 . Each swath  100  through  129  represents the direction of ink by the printhead  64 . The rows of nozzles  73  of the printhead  64  are also illustrated in each swath  100  through  129 . For example, each swath  100  through  129  is divided into eight sections, which illustrate eight rows or groups of rows of nozzles  73  on the printhead  64 . The active nozzles  73  or rows are also illustrated in each swath  100  through  129 , indicated by the encompassing rectangle. Swaths  104  through  109  represent swaths generated during normal printing. At swath  110 , as the trailing edge  68   b  of the print media  68  approaches the nip roller  52 , the printer mechanism  50  begins to transition to a reduced nozzle usage. In particular, the printer mechanism  50  shifts to using the bottom half  75  of the nozzles  73  located in the rows of the printhead  64  closest to the trailing edge  68   b  of the print media  68 . At swath  113  the transition is complete and only half of the nozzles  73  are active.  
         [0041]     Between swaths  116  and  117 , the printer mechanism  50  determines that a nip jump is imminent and the normal index move that would occur between swath  116  and swath  117  is adjusted or increased to bring the print media  68  out of the feedroll nip. As illustrated in  FIG. 6 , the print media  68  is shown to make a large move relative to the printhead  64  prior to printing swath  117 .  
         [0042]     After swath  116 , nozzle usage is again adjusted. As seen in  FIG. 6 , the active nozzles  73  switch from the bottom half  75  for swath  116  to the top half  74  for swath  117 . The top half  74  of the nozzles  73  located closest to the leading edge  68   a  of the print media  68  is used to print the rest of an image on the print media  68 .  
         [0043]      FIG. 7  is a flow chart illustrating another exemplary method of reducing nip jump defects  78 . The first step of the method presented in  FIG. 7  again involves the printer mechanism  50  performing normal printing (block  160 ). As previously described, normal printing can involve operating the components of the printer mechanism  50  as configured without adjusting for past misalignments or preparing for future misalignments.  
         [0044]     At block  162 , the printer mechanism  50  determines if the trailing edge  68   b  of the print media  68  is approaching the nip roller  52 . As described in the previous method, in some embodiments, the trailing edge  68   b  is considered to be approaching the nip roller  52  if the trailing edge  68   b  is within approximately 0.75 inch from the nip roller  52  or within approximately 1.25 inches from the printhead  64 . It should be noted that other distances can be used. As also described in the previous method, the printer mechanism  50  can include sensors or tracking devices that indicate the position of the trailing edge  68   b  of the print media  68  or may calculate the position based on the length of the print media  68  and how far the print media  68  has already been transported through the mechanism  50 . If the trailing edge  68   b  of the print media is not approaching the nip roller  52 , the printer mechanism  50  continues to print normally. If, however, the trailing edge  68   b  is nearing the nip roller  52 , the printer mechanism  50  adjusts the nozzles  73  of the printhead  64  that are applying ink to the print media  68  (block  164 ). As noted above for the previous method, in some embodiments, the printer mechanism  50  transitions the printhead  64  to use half of the nozzles  73  that are closest to the trailing edge  68   b  of the print media  68 .  
         [0045]     At block  166 , the printer mechanism  50  determines if a nip jump has occurred. To determine if a nip jump has occurred, the printer mechanism  50  can include sensors or tracking devices that indicate the position of the trailing edge  68   b  of the print media  68 . When it is determined that a nip jump has occurred, the printer mechanism  50  determines a magnitude of the nip jump (block  168 ). When a nip jump occurs, the feedroll  54  typically moves with the print media  68  and an encoder on the feedroll  54  reveals the magnitude or skipped distance of the nip jump. The printer mechanism  50  detects this magnitude and adjusts the nozzle usage of the printhead  64 . In some embodiments, the printer mechanism can shift the active nozzles  73  from the half of nozzles  73  closest to the trailing edge  68   b  of the print media  68  by the magnitude of nip jump to realign the active nozzles with the print media.  
         [0046]     In some embodiments, in order to compensate for the nip jump, an adjusting index move may be necessary before printing the next print swath to have the print media  68  positioned correctly for the leading half of the nozzles  73 : The printer mechanism  50  can determine if an adjusting index move is needed at block  170  by analyzing the magnitude of the detected nip jump and/or the operating parameters of the printer mechanism  50 . For example, if the magnitude of the nip jump is above a set threshold, the printer mechanism  50  can decide to adjust for the relatively large jump. In addition, if the print mode set on the printer mechanism  50  requires high resolution or error-free prints, such as photo modes, the printer mechanism  50  can decide to adjust the nip jump in order to create a substantially defect-free print.  
         [0047]     If the printer mechanism  50  determines that an adjustment is necessary, the printer mechanism  50  calculates and performs an adjusting index move (block  172 ). The adjusting index move can be calculated by subtracting the magnitude of the nip jump (as measured by the encoder) from the height of half of the printhead  64 . For example, using a typical CMY printhead with 160 nozzles and a height of 320/1200″, if the magnitude of the nip jump is 3/1200″, an adjusting index move of 160-3 or 157/1200″ is made to adjust for the nip jump. Note that while the above uses half the printhead, other proportions may be utilized such as ¾, where the nozzle usage would shift from the bottom three fourths of the nozzles to the top three fourths of the nozzles. In this case, the adjusting index move would be 80-3 or 77/1200″.  
         [0048]     Once an adjusting index move is made, if necessary, the printer mechanism  50  adjusts the nozzles  73  of the printhead  64  used to direct ink to the print media  68  (block  174 ). In some embodiments, the printer mechanism  50  turns off the half of the nozzles  73  closest to the trailing edge  68   b  of the print media  68  and activates the half of the nozzles  73  that are closest to the leading edge  68   a  of the print media  68 .  
         [0049]     At block  176 , the printer mechanism  50  determines if there is any more printing to be performed on the print media  68 . Once printing is complete, the printer mechanism  50  returns to normal printing (block  160 ) in order to print another image on another piece of print media  68 .  
         [0050]      FIG. 8  provides a graphical representation of the method described in  FIG. 7  for a four-pass print mode. As previously noted, in a four-pass print mode the printhead  64  moves in the x-axis or main scan direction  72  across the print media  68  four times per region of the print media  68 , such that each region of the print media  68  will be addressed four times by the nozzles of the printhead  64 . In between each main scan the print media  68  moves in the y-axis or sub-scan direction  70  through the mechanism  50 . The print media  68  may move at regular indexes or increments and each increment aligns the print media  68  with the nozzles  73  of the printhead  64  to receive the next print swaths. Exemplary print swaths  200 - 229  are also illustrated in  FIG. 8 . Swaths  204 - 209  illustrate swaths generated during normal printing. At swath  210 , as the trailing edge  68   b  of the print media  68  approaches the nip roller  52 , the printer mechanism  50  begins to transition to a reduced nozzle usage. In particular, the printer mechanism  50  shifts to using the bottom half  75  of the nozzles  73 . At swath  213  the transition is complete and only half of the nozzles  73  are active or in use.  
         [0051]     Between swaths  216  and  217 , the printer mechanism  50  detects a nip jump and makes an adjusting index move to the print media  68  to adjust for the magnitude of the nip jump. As illustrated in  FIG. 8 , the print media  68  is shown to make a large move relative to the printhead  64  prior to printing swath  217 .  
         [0052]     After making the adjusting index move, the printer mechanism  50  adjusts the nozzles  73  of the printhead  64  that are turned off or active. As seen in  FIG. 8 , the active nozzles  73  switch from the bottom half  74  to the top half  73  for swath  217 . The top half  74  of the nozzles  73  is used to print the rest of an image on the print media  68 .  
         [0053]     One or both of the above two methods can be implemented in program code or instructions stored in the memory module  65  and may be executed by the processor  64  of the printer mechanism  50 . The program code can also be stored external to the printer mechanism  50  such as on a client workstation and can be provided to the processor  64  over a communication line or network. As the processor  64  executes the instructions, it can supply control information, such as movement directions, speed directions, and nozzle usage directions, to the printhead  64 , the nip roller  52 , the feedroll  54 , and the exit rollers  59 . The processor  64  of the printer mechanism  50  can also be configured to modify or choose from instructions provided from an external or separate computing device such as a client workstation or driver.  
         [0054]     The above methods can also be performed in a printer driver. The printer driver can be installed and executed on a client computer or workstation and can provide operational instructions to the printer mechanism  50  to perform the steps of the method. The printhead  64  of the printer mechanism  50  can also include a processor that controls the movement of the printhead  64  and the rollers.  
         [0055]     Various features and advantages of the invention are set forth in the following claims.