Abstract:
A printer includes at least one controller having first mode configured to control printing of an image including a sequence of columns by controlling printing a first column in the sequence and a fourth column in the sequence with a first printhead, a second column in the sequence and a fifth column in the sequence with a second printhead, and a third column in the sequence and a sixth column in the sequence with a third printhead.

Description:
BACKGROUND 
   A conventional inkjet printing system includes a printhead, an ink supply that supplies liquid ink to the printhead, and an electronic controller that controls the printhead. The printhead ejects ink drops through a plurality of orifices or nozzles toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other. 
   One type of inkjet printing system is an inline printing system in which one or more printheads are fixed and the print medium is moved relative to the printhead(s). The speed of the print medium relative to the printhead(s) is measured by an encoder. In addition, the encoder tracks the position of the print medium relative to the fixed printheads with a resolution typically indicated in dots per inch (dpi). Typically, for multiple printhead inline printing systems, the image to be printed is divided between two or more printheads by a multiple of the encoder resolution. By dividing the image to be printed into multiple images, the firing frequency of each printhead is reduced. Therefore, the print medium can be moved faster relative to the printheads while having the same final number of drops ejected onto the print medium. For example, in an inline printing system having four printheads and a 150 dots per inch (dpi) encoder, a 600 dpi image to be printed can be divided into four 150 dpi images or two 300 dpi images that are printed interlaced to provide the final desired 600 dpi image. 
   The printheads have a firing frequency that ranges from zero to a maximum value, such as 36 kHz. In one embodiment, the firing frequency in kHz is defined by the following Equation I: 
   
     
       
         
           
             
               
                 kHz 
                 = 
                 
                   
                     fpm 
                     5 
                   
                   × 
                   
                     hRes 
                     1000 
                   
                 
               
             
             
               
                 Equation 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 I 
               
             
           
         
       
     
   
   where:
         fpm=feet per minute of the print medium relative to the printheads; and   hRes=the horizontal resolution of the image.       

   Typically, in inline printing systems, an encoder is used to measure the speed of the print medium relative to the printhead(s) to set the firing frequency of the printhead(s) needed to obtain the desired resolution. For example, in a 600 dpi printing system having a 150 dpi encoder, one printhead can be used to print at 600 dpi to obtain a final resolution of 600 dpi. The maximum speed of the print medium to print a 600 dpi image using one printhead at a firing frequency of 36 kHz is 300 fpm. The maximum speed of the print medium to print a 600 dpi image using two printheads printing interlaced 300 dpi images at a firing frequency of 36 kHz is 600 fpm. The maximum speed of the print medium to print a 600 dpi image using four printheads printing interlaced 150 dpi images at a firing frequency of 36 kHz is 1200 fpm. 
   Typically, printheads have a range of values in the middle of the firing frequency range, such as 12 kHz to 24 kHz, where the printheads do not provide a good quality image. The firing frequency interval where the printheads do not provide a good quality image is called the “puddling zone” and should be avoided to obtain good image quality and printhead reliability. Therefore, to avoid the puddling zone, typically certain speeds of the print medium that would require the printheads to fire at a firing frequency within the puddling zone are avoided. In some circumstances, however, it is undesirable to avoid printing at certain speeds, such as where another system controls the print medium speed. 
   For these and other reasons, there is a need for the present invention. 
   SUMMARY 
   One aspect of the present invention provides a printer. The printer includes at least one controller having first mode configured to control printing of an image including a sequence of columns by controlling printing a first column in the sequence and a fourth column in the sequence with a first printhead, a second column in the sequence and a fifth column in the sequence with a second printhead, and a third column in the sequence and a sixth column in the sequence with a third printhead. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating one embodiment of an inkjet printing system. 
       FIG. 2  is a diagram illustrating one embodiment of an inline printing system. 
       FIG. 3  is a table illustrating one embodiment of processing print data for printing on a printing system. 
       FIG. 4  is a table illustrating another embodiment of processing print data for printing on a printing system. 
       FIG. 5  is a table illustrating one embodiment of modes for printing on a printing system. 
       FIG. 6  is a graph illustrating one embodiment of selecting a mode to avoid the puddling zone when printing on a printing system while printing at any speed up to a maximum speed. 
   

   DETAILED DESCRIPTION 
   In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     FIG. 1  illustrates one embodiment of an inkjet printing system  10 . In one embodiment, inkjet printing system  10  is an inline inkjet printing system configured to print images at any speed up to a maximum speed without using a firing frequency within the puddling zone. Inkjet printing system  10  includes an inkjet printhead assembly  12 , an ink supply assembly  14 , a mounting assembly  16 , a media transport assembly  18 , and an electronic controller  20 . At least one power supply  22  provides power to the various electrical components of inkjet printing system  10 . Inkjet printhead assembly  12  includes at least one printhead or printhead die  24  which ejects drops of ink through a plurality of orifices or nozzles  13  toward a print medium  19  so as to print onto print medium  19 . Print medium  19  is any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, and the like. Typically, nozzles  13  are arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  13  causes characters, symbols, and/or other graphics or images to be printed upon print medium  19  as inkjet printhead assembly  12  and print medium  19  are moved relative to each other. 
   Ink supply assembly  14  supplies ink to printhead assembly  12  and includes a reservoir  15  for storing ink. As such, ink flows from reservoir  15  to inkjet printhead assembly  12 . Ink supply assembly  14  and inkjet printhead assembly  12  can form either a one-way ink delivery system or a recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to inkjet printhead assembly  12  is consumed during printing. In a recirculating ink delivery system, however, only a portion of the ink supplied to printhead assembly  12  is consumed during printing. As such, ink not consumed during printing is returned to ink supply assembly  14 . 
   In one embodiment, inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet cartridge or pen. In another embodiment, ink supply assembly  14  is separate from inkjet printhead assembly  12  and supplies ink to inkjet printhead assembly  12  through an interface connection, such as a supply tube. In either embodiment, reservoir  15  of ink supply assembly  14  may be removed, replaced, and/or refilled. In one embodiment, where inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet cartridge, reservoir  15  includes a local reservoir located within the cartridge as well as a larger reservoir located separately from the cartridge. As such, the separate, larger reservoir serves to refill the local reservoir. Accordingly, the separate, larger reservoir and/or the local reservoir may be removed, replaced, and/or refilled. 
   Mounting assembly  16  positions inkjet printhead assembly  12  relative to media transport assembly  18  and media transport assembly  18  positions print medium  19  relative to inkjet printhead assembly  12 . Thus, a print zone  17  is defined adjacent to nozzles  13  in an area between inkjet printhead assembly  12  and print medium  19 . In one embodiment, inkjet printhead assembly  12  is a scanning type printhead assembly. As such, mounting assembly  16  includes a carriage for moving inkjet printhead assembly  12  relative to media transport assembly  18  to scan print medium  19 . In another embodiment, inkjet printhead assembly  12  is a non-scanning type printhead assembly. As such, mounting assembly  16  fixes inkjet printhead assembly  12  at a prescribed position relative to media transport assembly  18 . Thus, media transport assembly  18  positions print medium  19  relative to inkjet printhead assembly  12 . 
   Electronic controller or printer controller  20  typically includes a processor, firmware, and other printer electronics for communicating with and controlling inkjet printhead assembly  12 , mounting assembly  16 , and media transport assembly  18 . Electronic controller  20  receives data  21  from a host system, such as a computer, and includes memory for temporarily storing data  21 . Typically, data  21  is sent to inkjet printing system  10  along an electronic, infrared, optical, or other information transfer path. Data  21  represents, for example, a document and/or file to be printed. As such, data  21  forms a print job for inkjet printing system  10  and includes one or more print job commands and/or command parameters. 
   In one embodiment, electronic controller  20  includes one or more application-specific integrated circuits (ASICs) for controlling each printhead  24  of inkjet printhead assembly  12 . In one embodiment, electronic controller  20  controls inkjet printhead assembly  12  for ejection of ink drops from nozzles  13 . As such, electronic controller  20  defines a pattern of ejected ink drops that form characters, symbols, and/or other graphics or images on print medium  19 . The pattern of ejected ink drops is determined by the print job commands and/or command parameters. 
   In one embodiment, inkjet printhead assembly  12  includes one printhead  24 . In another embodiment, inkjet printhead assembly  12  is a wide-array or multi-head printhead assembly. In one wide-array embodiment, inkjet printhead assembly  12  includes a carrier, which carries printheads  24 , provides electrical communication between printheads  24  and electronic controller  20 , and provides fluidic communication between printheads  24  and ink supply assembly  14 . In one embodiment, each printhead  24  has its own ink supply assembly  14 , which are housed together in an inkjet cartridge or pen. 
     FIG. 2  is a diagram illustrating one embodiment of inline printing system  10 . In this embodiment, printhead assembly  12  includes four printheads  24   a - 24   d , which are fixed with respect to media transport assembly  18 . In one embodiment, printing system  10  includes four ASICs  26   a - 26   d  for controlling corresponding printheads  24   a - 24   d . In one embodiment, each printhead  24   a - 24   d  has its own ink supply assembly  14 , with each printhead and ink supply assembly housed together in an inkjet cartridge or pen. Print medium  19  is moved relative to printhead assembly  12  in the direction indicated by arrow  30  to print image  36 . Electronic controller  20  divides data  21  to be printed between printheads  24   a - 24   d  such that printheads  24   a - 24   d  print interlaced images to obtain the final desired image. In one embodiment, the movement of print medium  19  is measured by an encoder  25 . In one form of the invention, encoder  25  is a 150 dots per inch (dpi) encoder. 
   In one embodiment, 600 dpi image data is printed on print medium  19  by dividing the image data into four 150 dpi images, each of which is printed by a separate printhead  24   a - 24   d . Therefore, the 600 dpi image data, one column of which is indicated at  32  as 1/600 of an inch, is divided into four 150 dpi images, one column of which is indicated at  32  as 1/150 of an inch, which when interlaced provide the printed overlap area as indicated at  38 . In another embodiment, 600 dpi image data is printed on print medium  19  by dividing the image data into three 200 dpi images, each of which is printed by a separate printhead. In yet another embodiment, 600 dpi image data is printed on print medium  19  by dividing the image data into two 300 dpi images, each of which is printed by a separate printhead. 
     FIG. 3  is a table  50  illustrating one embodiment of processing print data for printing on printing system  10 . In this embodiment, the image data to be printed is divided into four images to be printed interlaced by four printheads to obtain the desired image. The image data is divided by a multiple of the encoder resolution. In one embodiment, electronic controller  20  receives image data  52 . In one embodiment, image data  52  is 600 dpi image data, such that each ‘I’  58  is 1/600 of an inch. Image data  52  is divided into columns I 0 -I 15 , where each column I 0 -I 15  is passed to a different printhead, as indicated at  54 . In one embodiment, each indicated column I 0 -I 15  is passed to the ASIC  26   a - 26   d  associated with each corresponding printhead  24   a - 24   d . As indicated at  54 , printhead  24   a  receives the I 0  column data, printhead  24   b  receives the I 1  column data, printhead  24   c  receives the I 2  column data, and printhead  24   d  receives the I 3  column data. The division of image data  52  continues with printhead  24   a  receiving the I 4  column data, etc. 
   Therefore, as indicated at  56 , printhead  24   a  receives the I 0 , I 4 , I 8 , and I 12  column data. Printhead  24   b  receives the I 1 , I 5 , I 9 , and I 13  column data. Printhead  24   c  receives the I 2 , I 6 , I 10 , and I 14  column data, and printhead  24   d  receives the I 3 , I 7 , I 11 , and I 15  column data. In this embodiment, printhead  24   a  prints every 1/150 of an inch as indicated at  60  to print the I 0 , I 4 , I 8 , and I 12  column data to produce a 150 dpi image. Likewise, printhead  24   b  prints the I 1 , I 5 , I 9 , and I 13  column data to produce a 150 dpi image, printhead  24   c  prints the I 2 , I 6 , I 10 , and I 14  column data to produce a 150 dpi image, and printhead  24   d  prints the I 3 , I 7 , I 11 , and I 15  column data to produce a 150 dpi image. The four 150 dpi images of printhead  24   a  through printhead  24   d  are printed interlaced on print medium  19  to provide the desired 600 dpi image of image data  52 . 
   In another embodiment, two printheads are used to print image data  52 . Once again, the image data is divided by a multiple of the encoder resolution. In this embodiment, one of the printheads receives the even numbered columns and the other of the printheads receives the odd numbered columns. The even numbered column data produces a 300 dpi image and the odd numbered column data also produces a 300 dpi image. The two 300 dpi images of the two printheads are printed interlaced on print medium  19  to provide the desired 600 dpi image of image data  52 . These embodiments have a disadvantage in that they cannot operate at all speeds up to a maximum speed without printing in the puddling zone since each printhead  24   a  through  24   d  prints at a resolution that is a multiple of the encoder resolution of 150 dpi. Therefore using this process, a 600 dpi image cannot be divided by a multiple of the 150 dpi resolution of the encoder to print using three printheads. 
     FIG. 4  is a table  80  illustrating another embodiment of processing print data for printing on printing system  10 . In this embodiment, printing system  10  can print at any speed up to the maximum speed without printing in the puddling zone. In this embodiment, image data  52  is received in electronic controller  20 , however, each ASIC  26   a - 26   d  associated with each printhead  24   a - 24   d  receives all the column data and not just the column data to be printed by the associated printhead. ASIC  26   a  receives the I 0 -I 15  column data, ASIC  26   b  receives the I 0 -I 15  column data, ASIC  26   c  receives the I 0 -I 15  column data, and ASIC  26   d  receives the I 0 -I 15  column data. Therefore, each ASIC/printhead combination is capable of printing any column of data and not just the data provided to the printhead by the process illustrated in  FIG. 3 . 
     FIG. 5  is a table  90  illustrating one embodiment of modes for printing on printing system  10  using the column data passed to ASICs  26   a - 26   d  as illustrated in table  80  of  FIG. 4  or using the column data in electronic controller  20 . Table  90  illustrates which printheads print the column data I 0 -I 15  based on the mode selected. The columns of table  90  correspond to the column data I 0 -I 15 . The column data I 0 -I 15  is printed by the corresponding printhead  24   a  through printhead  24   d  indicated by the printhead numbers in each column of table  90 . In one embodiment, the printhead numbers for each mode are stored in arrays within electronic controller  20  or within the ASIC  26   a - 26   d  associated with each printhead. 
   In this embodiment, the image data to be printed is 600 dpi. A first mode uses four printheads printing at 150 dpi. In this mode, the indicated printheads  24   a  through  24   d  print the column data as indicated in row  92 . In this mode, printhead  24   a  prints the I 0  column data, printhead  24   b  prints the I 1  column data, printhead  24   c  prints the I 2  column data, and printhead  24   d  prints the I 3  column data. This mode is similar to table  50  illustrated in  FIG. 3 . The process repeats with the I 4 -I 7  column data printed by printheads  24   a  through  24   d , respectively. 
   A second mode uses three printheads printing at 200 dpi. In this mode, the indicated printheads  24   a  through  24   c  print the column data as indicated in row  94 . In this mode, printhead  24   a  prints the I 0  column data, printhead  24   b  prints the I 1  column data, and printhead  24   c  prints the I 2  column data. The process repeats with the I 3 -I 5  column data printed by printheads  24   a  through  24   c , respectively. This second mode is not possible using the process of  FIG. 3 , since 200 dpi is not a multiple of the 150 dpi encoder. 
   A third mode uses two printheads printing at 300 dpi. In this mode, the indicated printheads  24   a  and  24   b  print the column data as indicated in row  96 . In this mode, printhead  24   a  prints the even numbered column data I 0 , I 2 , I 4  etc., and printhead  24   b  prints the odd numbered column data I 1 , I 3 , I 5 , etc. 
     FIG. 6  is a graph  100  illustrating one embodiment of selecting a mode to avoid the puddling zone when printing on printing system  10  while printing at any speed up to the maximum speed. The puddling zone is indicated at  102  and in this embodiment includes a firing frequency within the range of 12 kHz to 24 kHz. The printhead firing frequency (kHz) versus print medium speed (fpm) for printing with one printhead is indicated by line  104 , with two printheads is indicated by line  106 , with three printheads is indicated by line  108 , and with four printheads is indicated by line  110 . 
   In one embodiment, the puddling zone is avoided between speeds 0 and 400 fpm by using four printheads with each printhead printing at 150 dpi to obtain a 600 dpi image as indicated by line  110 . The puddling zone is avoided between speeds 400 and 600 fpm by using two printheads with each printhead printing at 300 dpi to obtain a 600 dpi image as indicated by line  106 . The puddling zone is avoided between speeds 600 and 900 fpm by using three printheads with each printhead printing at 200 dpi to obtain a 600 dpi image as indicated by line  108 . The puddling zone is avoided between 900 and 1200 fpm by using four printheads with each printhead printing at 150 dpi to obtain a 600 dpi image as indicated by line  110 . 
   Using this method, printer  10  can print 600 dpi images with three inline printheads firing at 200 dpi while using a 150 dpi encoder. At 600 fpm, the firing frequency is 24 kH and at 800 fpm, the firing frequency is 32 kH, avoiding the puddling zone. Therefore, putting the possible resolutions together as described with reference to  FIG. 6 , in one embodiment, printer  10  can print up to 1200 fpm with a resolution of 600 dpi without printing in the puddling zone and by using the same 150 dpi encoder. 
   Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.