Abstract:
A method for printing color images with an ink jet printer. The ink jet printer includes a printhead having printing nozzles arranged in first, second, and third columns. The first, second, and third columns each have a length approximately equal to 3*H, where H represents a length of first, second, and third sections of the second column. The method includes ejecting ink from the nozzles of the first, second, or third sections of the second column during each pass of the printhead over a printing medium as necessitated by characteristics of the color image, advancing the printing medium in the first direction by the length H, and ejecting ink from the nozzles of the first and third columns during every third pass that the printhead makes over the printing medium as necessitated by the characteristics of the color image.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink jet printer, and more specifically, to a method for printing color images with the ink jet printer. 
     2. Description of the Prior Art 
     Please refer to FIG.  1 . FIG. 1 is a schematic diagram showing a related art color printhead  450 . The printhead  450  includes three central ink flow channels  462  formed on a substrate  461 . A plurality of nozzles  464  are arranged in six columns, with each of the six columns of nozzles  464  being located on a side of one of the three central ink flow channels  462 . Each of the three central ink flow channels  462  is connected with an associated ink reservoir for providing ink of up to three different colors such as dark cyan, dark magenta, and yellow. 
     When the printhead  450  prints color images onto a printing medium, the nozzles  464  eject drops of ink during successive passes of the printhead  450  over the medium. For example, a first pass would be when the printhead  450  moves from left to right across the medium. A second pass would be when the printhead  450  moves back from right to left. Unfortunately, the color printhead  450  shown in FIG. 1 can only eject three colors of ink. For example, if a dark cyan dot were to be printed on the medium, the printhead  450  would only need one pass over the medium to eject dark cyan ink on the correct position. In addition, if one of the nozzles  464  of the related art printhead  450  were defective or stopped working, the printhead  450  would need additional passes over the medium in order for other nozzles  464  to compensate for the defective nozzle  464 . 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a method for printing a color image with an ink jet printer in order to solve the above-mentioned problems. 
     According to the claimed invention, a method for printing a color image with an ink jet printer is disclosed. The ink jet printer includes a printhead having printing nozzles arranged in first, second, and third columns extending in a first direction. Nozzles in the first column are supplied with light magenta ink. Nozzles in the second column are divided into first, second, and third sections. Nozzles of the first section are supplied with dark magenta ink, nozzles of the second section are supplied with dark cyan ink, and nozzles of the third section are supplied with yellow ink. Nozzles in the third column are supplied with light cyan ink. The first, second, and third columns each have a length approximately equal to 3*H, where H represents a length of each of the first, second, and third sections of the second column. The method includes ejecting ink from the nozzles of the first, second, or third sections of the second column during each pass of the printhead over a printing medium as necessitated by characteristics of the color image, advancing the printing medium in the first direction by the length H, and ejecting ink from the nozzles of the first and third columns during every third pass that the printhead makes over the printing medium as necessitated by the characteristics of the color image. 
     It is another objective of the claimed invention to provide a method for compensating for a defective nozzle in the second column by printing ink with compensating nozzles in the first or third column. 
     The method for compensating for a defective nozzle includes detecting a defective nozzle in the first or second section of the second column, and ejecting ink from the nozzles of the first, second, or third sections the second column during each pass of the printhead over a printing medium as necessitated by characteristics of the color image. The method also includes compensating for the defective nozzle in the first or second section of the second column by ejecting ink two times from compensating nozzles in the first or third column, respectively, and advancing the printing medium in the first direction by the length H. 
     It is an advantage of the claimed invention that the printer contains both light colored and dark colored cyan and magenta ink for reducing the number of passes that the printhead must make over a printing medium. In addition, the printer can use light colored ink to compensate for defective nozzles that eject dark colored ink, thereby requiring no extra passes of the printhead over the printing medium for compensating a defective nozzle that ejects dark cyan or magenta ink. 
     These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic diagram showing a related art color printhead. 
     FIG. 2 is a schematic diagram showing an ink jet printhead according to the present invention. 
     FIG. 3 shows a printhead that is a simplified version of the printhead shown in FIG.  2 . 
     FIG. 4 is a timing diagram showing passes of the printhead over the medium according to the present invention. 
     FIG. 5 illustrates the printhead having a defective nozzle. 
     FIG. 6 is a timing diagram showing compensation for the defective nozzle of the printhead according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     Please refer to FIG.  2 . FIG. 2 is a schematic diagram showing an ink jet printhead  100  according to the present invention. The printhead is divided into four columns and three rows of nozzles  112 , although more or less columns could be used according to the wishes of the designer. Two central columns of nozzles  112  eject yellow ink, dark magenta ink, and dark cyan ink respectively provided by three central ink flow channels  104 Y,  104 M, and  104 C formed in a substrate  101  of the printhead  100 . A yellow set  122 Y, a dark magenta set  122 M, and a dark cyan set  122 C of nozzles  112  are respectively formed on either side of the central ink flow channels  104 Y,  104 M, and  104 C. 
     The printhead  100  also contains first and second outer columns of nozzles  112 . The first outer column contains a light magenta set  128   m  of nozzles  112  that eject ink provided by a first periphery ink flow channel  108   m  formed in the substrate  101  of the printhead  100 . Similarly, the second outer column contains a light cyan set  126   c  of nozzles  112  that eject ink provided by a second periphery ink flow channel  106   c . Both the light magenta set  128   m  and the light cyan set  126   c  of nozzles  112  extend along the first through third rows of the printhead  100 . Each row and each column of the printhead  100  preferably contain the same number of nozzles  112 . 
     Please refer to FIG.  3 . For ease of explanation, FIG. 3 illustrates a printhead  10  that is a simplified version of the printhead  100  shown in FIG.  2 . The printhead  10  contains a first column  20 , a second column  30 , and a third column  40  of nozzles  112 . The first column  20  contains a first section  22 , a second section  24 , and a third section  26  of nozzles  112 , each being used to eject light magenta ink. The second column  30  contains a fourth section  32  of nozzles  112  used for ejecting yellow ink, a fifth section  34  of nozzles  112  used for ejecting dark magenta ink, and a sixth section  36  of nozzles  112  used for ejecting dark cyan ink. The third column  40  contains a seventh section  42 , an eighth section  44 , and a ninth section  46 , each being used to eject light cyan ink. 
     Each section of the first, second, and third columns  20 ,  30 , and  40  preferably contains the same number of nozzles  112 , and the height of each section is defined as H. Although each section shown in FIG. 3 contains four nozzles  112 , this is only used as an example, and any number of nozzles  112  can be used. Therefore, each of the first, second, and third columns  20 ,  30 , and  40  have a height approximately equal to 3*H. As will be shown below, since the nozzles  112  of the printhead  10  are divided into sections having a height of H, a printing medium can be advanced by a distance approximately equal to H between each pass that the printhead  10  makes over the medium. Moreover, since the nozzles  112  in the first column  20  and the third column  40  all print the same respective color ink, the nozzles  112  in the first and third columns  20  and  40  will only print ink on every third pass that the printhead  10  makes over the medium. 
     Please refer to FIG. 4 with reference to FIG.  3 . FIG. 4 is a timing diagram  200  showing passes of the printhead  10  over the medium according to the present invention. The image to be printed on the medium has a top boundary pointed to by arrow A 1  and a bottom boundary pointed to by arrow A 6 . To explain the operation of the printhead  10  during normal conditions, each row of the image will be printed with light cyan, light magenta, dark cyan, dark magenta, and yellow ink. In order to print each of the three colors located in the second column  30  of the printhead  10  on the same row of the image, three different passes of the printhead  10  are required, and the medium is advanced by the distance H between each of the passes. The number of nozzles  112  ejecting light magenta ink in the first column  20  and ejecting light cyan ink in the third column  40  is three times greater than the length of nozzles  112  ejecting yellow, dark magenta, and dark cyan in the second column  30 . Therefore, the second column  30  is used to eject ink during every pass of the printhead  10  over the medium whereas the first column  20  and third column  40  are used only once every three passes. 
     At time t 0 , the printhead  10  makes its first pass over the medium, and line  204  of dots is printed onto the medium. In the first pass, only the second column  30  is used to eject ink onto the medium. Because only the bottom third of the printhead  10  is below the top boundary of the image pointed to by arrow A 1 , only dark cyan ink from the sixth section  36  of nozzles  112  is ejected in line  204  between arrows A 1  and A 2 . By time t 1 , the printhead  10  has finished the first pass over the medium and the medium is advanced by the distance H. 
     At time t 1 , the printhead  10  makes a second pass over the medium, printing lines  208  and  212 . In the second pass, ink from both the first column  20  and the second column  30  will be printed. Only the bottom two-thirds of the printhead  10  are below arrow A 1 , and ink will be printed between arrows A 1  and A 3  by the eighth section  44 , ninth section  46 , fifth section  34 , and sixth section  36  of nozzles  112 . By time t 2 , the printhead  10  has finished the second pass, and the medium is advanced by the distance H. 
     Starting with the third pass at time t 2 , the printhead  10  is completely below arrow A 1 , and the full length of the printhead  10  is used for printing. In the third pass, ink from both the second column  30  and the third column  40  will be printed between arrows A 1  and A 4  in lines  216  and  220 . 
     At time t 3 , a fourth pass is made, printing ink from all nozzles  112  of the second column  30  between arrows A 2  and A 5  in line  224 . Similarly, at time t 4 , a fifth pass is made, printing ink from printing ink from all nozzles  112  of the first column  20  and second column  30  between arrows A 3  and A 6  in lines  228  and  232 . 
     Once the sixth pass is reached at time t 5 , only the top two-thirds of the printhead  10  is above arrow A 6 , which is the bottom of the image to be printed. Since the second column  30  and the third column  40  are to print ink during the sixth pass, only the fourth section  32 , fifth section  34 , seventh section  42 , and eighth section  44  of nozzles  112  eject ink. 
     Finally, a seventh pass is made, and only the top third of the printhead  10  is above arrow A 6 . Since only the second column  30  is to print ink, only the fourth section  32  of nozzles  112  ejects ink. 
     Notice that the second column  30  is used to eject ink during each of the seven passes illustrated in FIG. 4 since the second column  30  ejects ink of three different colors. On the other hand, the first column  20  is only used to eject ink on the second and fifth passes, and the third column  40  is only used to eject ink on the third and sixth passes. Therefore, the first column  20  and the third column  40  eject ink once every three passes and the second column  30  ejects ink during every pass. Although the example given in FIG. 4 shows the first column  20  and the third column  40  ejecting ink during separate passes, they could also eject ink during a same pass. 
     For efficiency, the printhead  10  preferably ejects ink from all three sections of the first column  20  and the third column  40  during a single pass whenever possible. However, it is also possible to eject ink from only two of the three sections during a single pass. In this case, the first column  20  and the third column  40  would be used to eject ink during every second pass or even every single pass of the printhead  10  over the medium. 
     Please refer to FIG.  5 . FIG. 5 illustrates the printhead  10  having a defective nozzle  35 . Because there is a degree of redundancy in the colors supplied to the printhead  10 , this redundancy can be taken advantage of to compensate for the defective nozzle  35 . An ink jet printer containing the printhead  10  could either detect the defective nozzle  35  automatically or a user of the ink jet printer could input this information manually. As an example, FIG. 5 shows the defective nozzle  35  being in the fifth section  34 , which is used for ejecting dark magenta ink. In the first column  20 , the first section  22 , second section  24 , and third section  26  each have a compensating nozzle  25  corresponding to the position of the defective nozzle  35  in the fifth section  34  of the second column  30 . The defective nozzle  35  was originally supposed to eject dark magenta ink, and the compensating nozzles  25  are used to eject light magenta ink. Therefore, the compensating nozzles  25  are utilized to eject ink twice on a position corresponding to the position of the defective nozzle  35 . 
     Please refer to FIG. 6 with reference to FIG.  5 . FIG. 6 is a timing diagram  300  showing compensation for the defective nozzle  35  of the printhead  10  according to the present invention. Like the timing diagram  200  shown in FIG. 4, the timing diagram  300  uses seven passes to print an image between arrows A 1  and A 6 . The major difference of FIG. 6 is compensating lines  302 ,  314 ,  322 ,  334 , and  342  need to be printed in order to compensate for the defective nozzle  35  in the fifth section  34  of the second column  30 . Since the first column  20  is used to normally print ink on every third pass, the pass immediately before and immediately after are available for compensating the defective nozzle  35 . 
     In the first pass, no dark magenta ink is printed from the fifth section  34  of the second column  30 . However, since the fifth section  34  will print ink between arrows A 1  and A 2  during the second pass, compensating line  302  must be printed during the first pass. The compensating nozzle  25  in the third section  26  ejects ink in the compensating line  302  since the third section  26  is between arrows A 1  and A 2 . Line  304  is also printed in the first pass, according to normal operation of the printhead  10 . 
     In the second pass, line  308  is printed normally and defective line  312  is also printed. In the third pass, compensating line  314  is printed along with a defective line  316  and normal line  320 . The compensating line  314  compensates for the defective line  312  between arrows A 1  and A 2 , for defective line  316  between arrows A 2  and A 3 , and for defective line  324  between arrows A 3  and A 4 . 
     In the fourth pass, compensating line  322  is printed along with a defective line  324 . The compensating line  322  compensates for the defective line  316  between arrows A 2  and A 3 , for defective line  324  between arrows A 3  and A 4 , and for defective line  332  between arrows A 4  and A 5 . 
     In the fifth pass, line  328  is printed normally and defective line  332  is also printed. In the sixth pass, compensating line  334  is printed along with a defective line  336  and normal line  340 . The compensating line  334  compensates for the defective line  332  between arrows A 4  and A 5  and for defective line  336  between arrows A 5  and A 6 . In the seventh pass, compensating line  342  is printed along with a normal line  344 . The compensating line  342  compensates for the defective line  336  between arrows A 5  and A 6 . 
     As can be seen, the first column  20  prints normal lines  308  and  328  in the second and fifth passes, respectively. That means all other passes can utilize the first column  20  to print compensating lines. The compensating lines  302 ,  314 ,  322 ,  334 , and  342  are respectively printed in the first, third, fourth, sixth, and seventh passes. 
     Instead of disposing the nozzles of the first, second, and third columns  20 , 30 , and  40  on the single printhead  10 , two or more printheads can also be used with the present invention. For example, the first column  20  and the third column  40  of nozzles can be disposed on a first printhead and the second column  30  of nozzles can be disposed on a second printhead. This arrangement utilizes simpler printhead structures while still achieving the goals of the present invention. 
     In summary, the structure of the printhead  10  allows the printhead  10  to compensate for the defective nozzle  35  without needing any additional passes of the printhead  10  over the medium. Each dot of dark magenta ink that was supposed to be printed by the defective nozzle  35  is instead replaced with two dots of light magenta ink printed by the compensating nozzles  25 . This compensation scheme works best when a color saturation and lightness level value for dark magenta ink is approximately two times a color saturation level value for light magenta ink. Although light magenta and dark magenta ink are used in this example, the same applies to light cyan and dark cyan ink. Best results will also occur when a color saturation and lightness level value for dark cyan ink is approximately two times a color saturation level value for light cyan ink. In addition, the first, second, and third columns  20 , 30 , and  40  can be positioned in different arrangements. Likewise, positions of the fourth section  32 , fifth section  34 , and sixth section  36  can all be changed. The present invention will work as long as one column ejects light magenta ink, one column ejects light cyan ink, and another column ejects yellow, dark magenta, and dark cyan ink. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.