Abstract:
Methods and systems for an ink printing system with a printhead system comprising at least two printheads with one printhead adjacent to a second printhead, the two printheads spaced such that the media can advance a full swath distance between each scan, and the swath printed by each print head system will overlap the stitch points created by each of the printheads.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a fluid ejection system. 
     2. Description of Related Art 
     Ink jet printers have at least one printhead that directs droplets of ink towards a recording medium. Within the printhead, the ink may be contained in a plurality of channels. Energy pulses are used to expel the droplets of ink, as required, from orifices at the ends of the channels. 
     In a thermal ink jet printer, the energy pulses are usually produced by resistors. Each resistor is located in a respective one of the channels, and is individually addressable by current pulses to heat and vaporize ink in the channels. As a vapor bubble grows in any one of the channels, ink bulges from the channel orifice until the current pulse has ceased and the bubble begins to collapse. At that stage, the ink within the channel retracts and separates from the bulging ink to form a droplet moving in a direction away from the channel and towards the recording medium. The channel is then re-filled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774. 
     A carriage-type thermal ink jet printer is described in U.S. Pat. No. 4,638,337. That printer has a plurality of printheads, each with its own ink tank cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage. A swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to the width of the printed swath. The carriage is then moved in the reverse direction to print another swath of information. 
     SUMMARY OF THE INVENTION 
     As described above, inkjet printing systems usually use a single printhead, or array of colored printheads, that print a swath of information. Thus, the ink jet printer&#39;s productivity is limited to the size of the printheads used. During printing, the printheads print a swath of information. In order to increase productivity after printing a swath of information, the printheads move a full swath width relative to the printed swath of information. Thereafter, the printheads print an additional swath of information. However, the quality of printing when using this process is reduced as the opportunity to place ink drops in a given location is limited to one pass of the printhead. Another problem occurs in that stitch errors occur between each swath as the printhead fails to align with the previous swath. 
     One technique for dealing with this problem is to overlap adjacently produced swaths. However, overlapping the swaths reduces the productivity of the ink jet printer system, as the printhead moves in smaller increments based on the amount of desired overlap. Another technique used to improve productivity adds additional printheads by staggering the multiple printheads together or placing the additional printheads in line with the first printhead along the lines of carriage movement. However, this increases the scanning distance required to print each swath, which has a negative affect on system productivity. 
     This invention provides multiple pass printing with relatively small printheads and with high productivity. 
     This invention separately provides a fluid ejection system that can efficiently mask image quality defects that occur at the stitch point between swaths formed by individual printheads. 
     This invention separately provides a fluid ejection system that can advance a full swath distance between printhead scans. 
     In various exemplary embodiments of a fluid ejection system and methods according to this invention, the fluid ejection system includes a printhead system with at least two printheads. One printhead is located adjacent to a second printhead such that the printhead system can advance a full swath distance between each scan. 
     In various exemplary embodiments, a first printhead is placed less than one swath distance away from a second printhead. In other various exemplary embodiments, the first printhead is placed more than one swath distance away from the second printhead. 
     In various exemplary embodiments, the distance between the swaths printed by the first and second printheads is less than the swath width of at least the second printhead. In other various exemplary embodiments, the distance between the swaths printed by the first and second printheads is more than the swath width of at least the second printhead. 
     These and other features and advantages of this invention are described in or are apparent from the detailed description of various exemplary embodiments of the systems and methods according to this invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various exemplary embodiments of this invention will be described in detail with reference to the following figures, wherein like numerals represent like elements, and wherein: 
     FIG. 1 is a schematic view of a printing system usable with the ink jet printing systems and methods according to this invention; 
     FIG. 2 is a schematic diagram of a conventional single printhead after printing a single swath of information; 
     FIG. 3 is a schematic diagram of a printhead system according to this invention and a first set of swaths printed by the printhead system; 
     FIG. 4 is a schematic diagram of a printhead system according to this invention and a second set of swaths printed by the printhead system; and 
     FIGS. 5-7 are exemplary embodiments of swath patterns printed by the printhead system. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows an exemplary carriage-type fluid ejection system device  100 . In various exemplary embodiments, the fluid ejection system  100  is an ink jet printing device. A linear array of droplet-producing channels is housed in a printhead  140  mounted on a reciprocal carriage assembly  143 . The array extends along a first direction, indicated by the arrow C, i.e., the printing direction. In the exemplary carriage-type ink jet printing device  100  shown in FIG. 1, the printhead  140  includes two or more heads. The specific relationship between each of the heads forming the printhead  140  is discussed below with respect to FIG.  3 . Ink droplets  141  are propelled onto a recording medium  122 , such as a sheet of paper, that is stepped a preselected distance, which is less than or equal to the size of the array by a motor  134  in the printing direction, as indicated by the arrow C, each time the printhead  140  traverses across the recording medium  122  along the swath axis, as indicated by the arrow D. The recording medium  122  can be either cut sheets or a continuous medium, and can be stored on a supply roll  136  and stepped onto takeup roll  132  by the stepper motor  134 , or can be stored in and/or advanced using other structures, apparatuses or devices well known to those of skill in the art. 
     The printhead  140  is fixedly mounted on a support base  152 , which reciprocally moves in the swath axis D using any well known structure, apparatus or device, such as two parallel guide rails  154 . A cable  158  and a pair of pulleys  156  can be used to reciprocally move the printhead  140 . One of the pulleys  156  can be powered by a reversible motor  159 . The printhead  140  is generally moved across the recording medium  122  perpendicularly to the direction the recording member  122  is moved by the motor  134 . Of course, other structures for reciprocating the carriage assembly  143  are possible. 
     The fluid ejection system  100  is operated under the control of a print controller  110 . The print controller  110  transmits commands to the motors  134  and  159  and to the printhead  140  to produce an image on the image recording medium  122 . Furthermore, the printhead controller  110  can control the ejection of ink from the printhead  140 . 
     FIG. 2 shows a conventional single printhead printing a single swath  52  of ink on the recording medium  122  by ejecting ink while the printhead travels across the recording medium  122 . The printhead  50  can print a swath as the printhead  50  moves in one direction along the swath axis D and thereafter in the opposite direction along the swath axis D. Alternatively, the printhead  50  could exclusively print a swath as the printhead  50  moves in one direction along the swath axis D. As should be appreciated the printhead  50  can include a plurality of printheads within the printhead  50  so as to print a plurality of colors onto a recording medium  50 . 
     In general, as the advance distance of the recording medium  122  increases, the higher the system productivity increases. Correspondingly however, stitch errors between each swath become more visible if the printhead fails to perfectly align with the previous swath. The quality of printing with printing systems that are only a single printhead  50  is reduced as the opportunity to place ink drops in a given location is limited to one pass of the printhead. 
     A stitch error occurs whenever a subsequent drop ejected by the printhead  50  in one swath is displaced in any direction relative to the position that drop should occupy on the recording medium  122  relative to a previous drop ejected by the printhead  50  in a previous swath. In general, stitch errors are most noticeable when the subsequent drop is spaced too far from the previous drop along the printing direction C, such that the background color of the recording medium  122  can be seen between the two drops. 
     One solution to reduce stitch errors is to use a printhead  50  that can make multi-passes over a single swath before the printhead  50  advances to another swath. Alternatively, the printhead  50  could advance in increments smaller than a swath in order to obtain a greater number of passes in a given area. It should also be appreciated that the printhead  50  can advance in any number of passes in order to achieve the desired print quality. However, the conventional printing system that uses only the single printhead  50  suffers from the disadvantages discussed earlier with regards to a single printhead as the productivity of the printhead  50  is reduced in making multiple passes over a single swath, or in advancing less than a full swath in the printing direction. 
     FIG. 3 shows one exemplary embodiment of a printhead according to this invention. As shown in FIG. 3, the printhead system  140  includes two printheads  144  and  146  for printing a swath of information. It should be appreciated that printheads  144  and  146  can eject ink of only one color, such as black, or could eject as a plurality of differently colored dies for full color printing. Furthermore, each of the first and second printheads  144  and  146  can scan as described above with respect to the conventional printhead  50 . 
     The printhead system  140  moves along the swath axis D across the image recording medium  122 . In a first pass, only the first printhead  144  prints a swath of the image as the printhead system  140  moves along the swath axis D. Once the first printhead  144  prints a swath  160  of the image along the swath axis D, the recording medium  122  and the printing system  140  moves relative to each other a full swath length  180  of the first printhead  144  in the printing direction C. Then, in a second pass, again only the first printhead  144  prints a second swath  162  of the image as the printhead system  140  moves along the swath axis D. The recording medium 122  and the printing system  140  then again moves relative to each other a full swath length  180  of the printhead system  144  in the printing direction C. However, it should be appreciated that the printhead system  140  can advance a full swath length  180  rather than the recording medium  122 . 
     At this time, for the third pass, and for each subsequent pass, of the printhead system  140 , the second printhead system  146  is positioned at least partially over the first set of swaths  160  and  162  printed by the first printhead  144 . During the third and subsequent passes, the second printhead system  146  prints swaths  170 , etc. of the image that overlap the swaths  160 ,  162 , etc. of the image printed by the first printhead  144 . 
     As shown in FIG. 3, the swath  170  printed by the second printhead  146  overlaps the second swath  162  as well as the first swath  160  printed by the first printhead  144 . This masks any stitch errors between the first and second swaths  160  and  162 . As a result, stitch errors become less noticeable without having to reduce the amount the recording medium  122  and the printhead system  140  advances relative to each other in the printing direction C and without having to use the first printhead  144  to go over the same swath  160  more than once. The second printhead system  146  prints a first swath  170  of the image, such as the swath  170 , along the swath axis D, as the first printhead  144  prints the third swath of the image  164 . The recording medium  122  and the printhead system  140  then moves relative to each other in the full swath length  180  of the first printhead  144  in the printing direction C. As shown in FIG. 3, the first printhead  144  prints a swath of the image with the swath length  180 . The second printhead  146  prints a swath of the image with a swath length  184 . In various exemplary embodiments, the swath length  180  of the first printhead  144  is approximately the same as swath length  184  of the second printhead  146 . However, as should be appreciated, the swath length  180  of the first printhead  144  can be larger than the swath length  184  of the second printhead  146 , or vice-versa. The first and second printhead  144  and  146  are located relative to each other spaced apart by a gap  182 . The gap  82  smaller than at least the swath length  184  of the second printhead  146 . 
     As shown in FIGS. 3 and 4 in one exemplary embodiment, the printhead system  140  moves across the image recording medium  122  along the swath axis D. As the printhead system  140  moves, the printhead  144  prints the first-fourth swath  160 ,  162 ,  164  and  166 , respectively. At the same time, the second printhead  146  prints the first and second swaths  170  and  172 . As shown in FIG. 3, as the first printhead  144  prints the third swath  164 , the printhead  146  prints the first swath  170 . Since the gap  182  has a length that is smaller than the swath width  184 , the first swath  170  overlaps both of the previously printed first and second swaths  160  and  162 . 
     The recording medium  122  and the printing system  140  then moves relative to each other a distance in the printing distance equal to the swath length  180  of the first printhead  144 . Thereafter, the first and second printhead  144  and  146  print the first swaths  166  and the second  172 , respectively. Since the gap  182  has a length that is smaller than the swath length  184 , the second swath  172  overlaps both of the previously printed second and third swaths  162  and  164 . 
     A similar overlapping effect could also be achieved with a gap  182  that is larger than the swath length  184  of the printhead system  146 . However a slight decrease in productivity would result. The swaths printed by the printheads  144  and  146  can be greater than the swath length  184 , so long as the swaths printed by the printhead  146  overlaps the swaths printed by the printhead  144 . Thus, for example, as the printhead  144  prints the swath  168 , the printhead  146  prints the swath  170  which overlaps the swaths  160  and  162 . 
     FIGS. 5-7 show exemplary embodiments of different types of gaps between the printheads  144  and  146 , which can be used as well as swath advances by the printheads  144  and  146  of the printhead system  140 . Swaths printed by the printheads  144  and  146  are shown incrementally advancing along the swath axis D for illustrative purposes only, as it should be appreciated that the swaths  202  and  200  can start at any location along the swath axis D. Also for illustrative purposes, the swath widths of the printheads  144  and  146  will be described as having the same width. 
     FIG. 5 illustrates a first exemplary embodiment having the gap  182  between the printheads  144  and  146  at 0.9 (or 90%) times the swath width, with both of the printheads  144  and  146  advancing a full swath length. After the printheads  144  and  146  print the swaths  202  and  200  along the swath axis D, the printheads  144  and  146  advance along the swath axis C by a full swath length. Thereafter, the printheads  144  and  146  print the swaths  212  and  210  along the swath axis D. This procedure is repeated until the swaths  222 ,  232 ,  242 ,  252 , and  262  is printed by the printhead  144  and the swaths  220 ,  230 ,  240 ,  250 , and  260  are printed by the printhead  146 , as shown in FIG.  5 . 
     It should be appreciated the two pass printing occurs as swaths printed by the printheads  144  and  146  overlap each other twice across the recording medium  122 . As shown in column  300 , the swath  222  is printed by the printhead  144 . Additionally, approximately 0.1 (or 10%) of the swath  230  and 0.9 (or 90%) of the swath  240  printed by the printhead  146  extend into the column  300 . It should also be appreciated that approximately 0.1 (or 10%) of the swath  230  and 0.9 (or 90%) of the swath  240  appear in the column  300 , as the gap  182  is approximately  0 . 9  (or  90 %) of the swath widths of the printheads  144  and  146 . 
     FIG. 6 illustrates a second exemplary embodiment having the gap  182  between the printheads  144  and  146  equal to one and one third of the swath width, with both of the printheads  144  and  146  advancing two-thirds of the swath length. After the printheads  144  and  146  print the swaths  202  and  200  along the swath axis D, the printheads  144  and  146  advance along the swath axis C by two-thirds of the swath length. Thereafter, the printheads  144  and  146  print the swaths  212  and  210  along the swath axis D. This procedure is repeated until the swaths  222 ,  232 ,  242 ,  252 , and  262  are printed by the printhead  144  and the swaths  220 ,  230 ,  240 ,  250 , and  260  are printed by the printhead  146  as shown in FIG.  6 . 
     It should be appreciated that this exemplary embodiment uses three-pass printing, as the swaths printed by the printheads  144  and  146  overlap each other three times across the recording medium  122 . As shown in column  300 , swath  212  is printed by printhead  144 . Also, one-third of swath  202  and  222  is printed as the printhead  144  only advances two-thirds of the swath width. Additionally, two-thirds of the swath  240  and  250  is printed by the printhead  146  is printed in the column  300 . As should be appreciated, approximately two-thirds of swaths  240  and  250  appear in column  300  as the gap  182  is approximately one and one-thirds that of the swath widths of the printheads  144  and  146  with the printhead  146  only advancing two-thirds of the swath width. 
     FIG. 7 illustrates a third exemplary embodiment with the gap  182  between the printheads  144  and  146  at 0.9 (or 90%) times the swath width with both of the printheads  144  and  146  advancing one-half of the swath length. After the printheads  144  and  146  print the swaths  202  and  200  along the swath axis D, the printheads  144  and  146  advance along the swath axis C by one-half of the swath length. Thereafter, the printheads  144  and  146  print the swaths  212  and  210  along the swath axis D. This procedure is repeated until the swaths  222 ,  232 ,  242 ,  252 , and  262  are printed by printhead  144  and the swaths  220 ,  230 ,  240 ,  250 , and  260  are printed by printhead  146  as shown in FIG.  7 . 
     It should be appreciated that this exemplary embodiment uses four-pass printing as the swaths printed by the printheads  144  and  146  overlap each other four times across the recording medium  122  or at twice the rate in the exemplary embodiment shown in FIG.  5 . As shown in column  300 , swath  212  is printed by printhead  144 . Half of the swaths  202  and  222  is also printed as the printhead  144  only advances half of a swath width. Additionally, approximately 0.1 (or 10%) of the swath  230  and 0.9 (or 90%) of the swath  250  printed by the printhead  146  appear in the column  300 . Also, since the printhead  146  only advances half a swath width, 0.6 (or 60%) of the swath  240  and 0.4 (or 40%) of the swath  260  is printed in the column  300 . 
     Thus, it should be appreciated that the first and second printheads  144  and  146  can be advanced a full swath length  180  of the first printhead  144  while reducing quality defects that occur at the stitch point between the swaths printed by each of the first and second printheads  144  and  146  respectively. Furthermore, it should also be appreciated that the first and second printheads  144  and  146  can advance a full swath length  180  of the first printhead  144  between swaths while maintaining the image quality advantages of multipass printing. 
     Increasing productivity using multiple small printheads is desirable when building larger build volumes of printheads already in production. This reduces part cost and enables faster design cycles with less tooling expense than would be incurred during the development of larger printheads. 
     While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.