Patent Publication Number: US-7914113-B2

Title: Print head having nozzles with varied spacing and inkjet printer including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2007-0015062, filed on Feb. 13, 2007 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to a print head and an inkjet printer including the same, and more particularly, to a print head improved in an ink drying quality and an inkjet printer including the same. 
     2. Description of the Related Art 
     In general, an ink jet printer jets a fine droplet of a printing ink onto a predetermined position to form an ink image on a printing medium. 
     As illustrated in  FIG. 1 , a conventional ink jet printer has a head unit  20  jetting an ink onto a printing medium S, and a controller (not shown) controlling an ink jet speed of the head unit  20 . 
     The head unit  20  includes a base plate  21  and a plurality of print heads  23  supported by the base plate  21  and manufactured as a unit chip by a semiconductor process. The print heads  23  are disposed in a zigzag manner in the base plate  21  along a transverse direction Z to a feeding direction X of the printing medium S. 
     As illustrated in  FIG. 2 , each print head  23  has first through fourth nozzles N 1  through N 4  jetting a black K, cyan C, magenta M, and yellow Y inks, respectively. The plurality of first nozzles N 1  through fourth nozzles N 4  are linearly arranged in the transverse direction Z and form first through fourth nozzle groups L 1  through L 4 , respectively. 
       FIG. 3  is an enlarged schematic view illustrating a pixel formed by an ink dot when a predetermined color image is formed on the printing medium S at a resolution of 1200 dpi. In  FIG. 3 , the ink dots Y, M, C and K are illustrated as if they are shifted by a short distance in the transverse direction Z to help understanding. However, the ink dots Y, M, C, and K are supposed to be formed in a pixel center point F. 
     As shown in  FIG. 3 , the yellow, magenta, cyan, and black inks are jetted during feeding the printing medium S in the feeding direction X, thereby forming ink dots Y, M, C, and K. Also, the controller (not shown) considers a transmitting speed of the printing medium S and controls the ink jet speed of the print head  23  so that the ink dots Y, M, C, and K can be formed on the same pixel centerline X 1  in the feeding direction X. 
     However, the ink is jetted so that the ink dots Y, M, C, and K can be formed on the same pixel centerline X 1  in the feeding direction X. Thus, the ink of different color is jetted before the previously jetted ink is dried, so that an ink drying performance is deteriorated and the color expression becomes unstable. 
     Also, an ink dot region for four colors has the same size with that for one color. Therefore, the ink dot region occupies a small area of a unit pixel on the printing medium S. 
     Meanwhile, to solve these problems, the controller needs to be redesigned to control an ink jet timing of each nozzle N 1 , N 2 , N 3 , and N 4  of the print head  123  so that the ink dot regions can have centers E 1 , E 2 , E 3 , and E 4 . 
     SUMMARY OF THE INVENTION 
     The present general inventive concept provides a print head and an ink jet printer including the same, which are improved in an ink drying quality by structural change. 
     Additional aspects and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     The foregoing and/or other aspects of the present general inventive concept can be achieved by providing a print head comprising a first nozzle group which comprises a plurality of first nozzles arranged linearly, and a second nozzle group and a third nozzle group which comprise a plurality of second nozzles and a plurality of third nozzles arranged linearly, and are disposed in parallel with each other and spaced from the first nozzle group by a first interval and a second interval at opposite sides of the first nozzle group, respectively. 
     The print head may further include a fourth nozzle group arranged in parallel with and spaced apart from one of the second and third nozzle groups by a third interval equal to one of the first and second intervals. 
     The print head may further includes a fourth nozzle group arranged in parallel with and spaced apart from one of the second nozzle group and the third nozzle group by a third interval different from at least one of the first and second intervals. 
     The foregoing and/or other aspects of the present invention can also be achieved by providing an ink jet printer comprising a print head, an ink tank, and a base plate which provides an ink of the ink tank to the print head, and supports the print head so that a lengthwise direction of each nozzle group can be crossed to a feeding direction of a printing medium. 
     The print head may be provided in plurality and disposed in the base plate along a transverse direction to the feeding direction. 
     The ink jet printer may further include a feeding unit which feeds the printing medium to the print head, and a controller which controls the print head and the feeding unit so that at least one of the ink dots generated on the printing medium by each nozzle group cannot be aligned with the other ink dots in the feeding direction. 
     The foregoing and/or other aspects of the present invention can also be achieved by providing a print head usable with an image forming apparatus, the print head including a first nozzle group having a plurality of first nozzles disposed on a first line, a second nozzle group having a plurality of second nozzles disposed on a second line parallel to the first line and spaced apart from the first line by a first distance, and a third nozzle group having a plurality of third nozzles disposed on a third line parallel to one of the first line and the second line and spaced apart from one of the first line and the second line by a second distance. 
     The foregoing and/or other aspects of the present invention can also be achieved by providing a print head usable with an image forming apparatus, the print head including a first nozzle group having a plurality of first nozzles disposed on a first line to eject ink of a first color, a second nozzle group having a plurality of second nozzles disposed on a second line parallel to the first line and spaced apart from the first line by a first distance to eject ink of a second color, a third nozzle group having a plurality of third nozzles disposed on a third line parallel to the second line and spaced apart from the second line by a second distance to eject ink of a third color, and a fourth nozzle group having a plurality of fourth nozzles disposed on a fourth line parallel to the third line and spaced apart from the third by a second distance to eject ink of a fourth color. 
     The foregoing and/or other aspects of the present invention can also be achieved by providing a print head usable with an image forming apparatus, the print head including a base plate, and a plurality of print heads disposed on the base plate and spaced apart from each other, each print head having a first nozzle group having a plurality of first nozzles disposed on a first line, a second nozzle group having a plurality of second nozzles disposed on a second line parallel to the first line and spaced apart from the first line by a first distance, and a third nozzle group having a plurality of third nozzles disposed on a third line parallel to one of the first line and the second line and spaced apart from one of the first line and the second line by a second distance. 
     The foregoing and/or other aspects of the present invention can also be achieved by providing an image forming apparatus including a print head comprising a first nozzle group having a plurality of first nozzles disposed on a first line, a second nozzle group having a plurality of second nozzles disposed on a second line parallel to the first line and spaced apart from the first line by a first distance, and a third nozzle group having a plurality of third nozzles disposed on a third line parallel to one of the first line and the second line and spaced apart from one of the first line and the second line by a second distance, and a controller to make a relative movement of a printing medium and the print head to form first, second, and third ink dots in a corresponding pixel of the printing medium at different regions of a pixel of the printing medium. 
     At least one of the different regions of the pixel may be disposed on an upper side or a lower side of a center line of the pixel. 
     The foregoing and/or other aspects of the present invention can also be achieved by providing an image forming apparatus including a print head comprising a first nozzle group having a plurality of first nozzles disposed on a first line to eject ink of a first color, a second nozzle group having a plurality of second nozzles disposed on a second line parallel to the first line and spaced apart from the first line by a first distance to eject ink of a second color, a third nozzle group having a plurality of third nozzles disposed on a third line parallel to the second line and spaced apart from the second line by a second distance to eject ink of a third color, and a fourth nozzle group having a plurality of fourth nozzles disposed on a fourth line parallel to the third line and spaced apart from the third by a second distance to eject ink of a fourth color, and a controller to make a relative movement of a printing medium and the print head to form first, second, third, and fourth ink dots in a corresponding pixel of the printing medium at first, second, third, and fourth regions of a pixel of the printing medium using the first, second, third, and fourth nozzles of the first, second, third, and fourth nozzle groups, respectively. 
     The first, second, third, and fourth ink dots may be disposed in the different regions disposed in a direction within the pixel. 
     At least one of the first, second, third, and fourth ink dots may not overlap another one of the first, second, third, and fourth ink dots. 
     At least one of the first, second, third, and fourth ink dots may not overlap at least the other one of the first, second, third, and fourth ink dots. 
     At least two of the first, second, third, and fourth ink dots may overlap each other. 
     At least two of the first, second, third, and fourth ink dots may be disposed in a feeding direction of the printing medium. 
     The first, second, third, and fourth ink dots may be disposed to overlap the adjacent ones of the first, second, third, and fourth ink dots. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a partial plan view illustrating a conventional inkjet printer; 
         FIG. 2  is an enlarged plan view illustrating a print head in  FIG. 1 ; 
         FIG. 3  is an enlarged view illustrating an ink dot formed on a printing medium by the print head in  FIG. 2 ; 
         FIG. 4  is a schematic sectional view illustrating an inkjet printer according to an embodiment of the present general inventive concept; 
         FIG. 5  is an enlarged plan view illustrating a print head in the inkjet printer of  FIG. 4 ; 
         FIG. 6  is an enlarged view of a pixel being formed on a printing medium by the print head of  FIG. 5 ; 
         FIG. 7  is a view illustrating a pixel being formed on a printing medium by the print head of  FIG. 5 ; 
         FIG. 8  is a view illustrating a pixel being formed on a printing medium by the print head of  FIG. 5 ; 
         FIG. 9  is a view illustrating a pixel being formed on a printing medium by the print head of  FIG. 5 ; and 
         FIG. 10  is a view illustrating a pixel being formed on a printing medium by the print head of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
     As illustrated in  FIG. 4 , an image forming apparatus, such as an inkjet printer  100 , according to an embodiment of the present general inventive concept includes a feeding unit  110 , a head unit  120 , a discharging unit  130 , and a controller  100   a.    
     The feeding unit  110  may include a feeding cassette  111 , a pickup roller  113 , an intermediate roller  115 , a feed roller  117 , and an idle roller  119 . Printing media S filed in the feeding cassette  111  are separated as a sheet by the pickup roller  113 , and advanced between the feed roller  117  and the idle roller  119  through the intermediate roller  115 . Also, the feed roller  117  is driven by the controller  100   a  at an appropriate timing, and feeds the printing medium S to the head unit  120 . The controller  100   a  can control at least one of the print unit  120  and the feeding unit  110  to make a relative movement of the printing medium S. Here, a print head of the printing unit  120  may be stationary with respect to a feeding path, and the controller  110   a  controls the feeding unit  110  to feed the printing medium S with respect to the print unit  120 . 
     The discharging unit  130  has a discharging roller  131  and an idle roller  133 , and discharges the printing medium S printed by the head unit  120 . 
     As illustrated in  FIGS. 4 and 5 , the head unit  120  has a base plate  121 , a plurality of print heads  123 , and an ink tank  125  to provide an ink to the base plate  121 . Here, the plurality of print heads  123  are formed in and supported by the base plate  121 . 
     The ink tank  125  stores the ink having a color corresponding to an ink color to be jetted from the print head  123 . The ink tank  124  may have sub-ink tanks to stores ink of different colors to correspond to different nozzles of the print heads  123 . 
     The base plate  121  includes ink channels (not illustrated) therein disposed between the ink tank  125  and the print heads  123  to provide the ink having the different colors to a plurality of nozzle groups L 5 , L 6 , L 7 , and L 8  of the print head  123 , respectively. 
     The ink channel allows ink outlets (not illustrated) of the ink tanks  125  (described later) different in color to communicate with a plurality of nozzles N 5 , N 6 , N 7 , and N 8  of the nozzle groups L 5 , L 6 , L 7 , and L 8 , respectively. 
     Referring to  FIG. 5 , the print head  123  includes a yellow nozzle group L 8 , a magenta nozzle group L 7 , a cyan nozzle group L 6 , and a black nozzle group L 5  along a feeding direction X of the printing medium S in  FIG. 1  in order. 
     The nozzle groups L 8 , L 7 , L 6  and L 5  have the nozzles N 8 , N 7 , N 6  and N 5  to jet or eject the ink having the yellow, magenta, cyan, and black colors, respectively. The nozzles N 8 , N 7 , N 6 , and N 5  may be linearly arranged. 
     Also, the nozzle groups L 8 , L 7 , L 6 , and L 5  are disposed in parallel with each other. That is, the yellow nozzle group L 8  and the magenta nozzle group L 7  are arranged in parallel while being spaced by a first interval H 1 , the magenta nozzle group L 7  and the cyan nozzle group L 6  are arranged in parallel while being spaced by a second interval H 2 , and the cyan nozzle group L 6  and the black nozzle group L 5  are arranged in parallel while being spaced by a third interval H 3 . Also, at least one of the first through third intervals H 1  through H 3  is different from another one. 
     In the meantime, the print head  123  may include a plurality of ink chambers (not illustrating) having a driving unit (for example, a piezoelectric element for a piezoelectric type, or a heater for a thermal driving type) to control a corresponding one of the ink chambers and independently communicating with each of the nozzles N 8 , N 7 , N 6  and N 5 , to provide a pressure to jet the ink, a manifold used as a common channel to provide the ink accommodated in the ink tank  125  to the ink chamber, and a restrictor used as an individual channel to provide the ink from the manifold to the ink chamber. The detailed description for the ink chamber, the manifold, and the restrictor, etc. is omitted because it has been known by those skilled in the art. 
     The print head  123  having above described configuration is manufactured by semiconductor processes such as deposition, lithography, and plating. The detailed description of the manufacture process is omitted because it has been known by those skilled in the art. 
       FIG. 6  illustrates a pixel formed by ink dots Y 1 , M 1 , C 1 , and K 1  jetted by the yellow, magenta, cyan, and black nozzles N 8 , N 7 , N 6 , and N 5  as a predetermined resolution R (the unit is dpi). The pixel has a printing region having a length of 1/R inch and a width of 1/R inch. The ink dots Y 1 , M 1 , C 1 , and K 1  may be formed within a region defining the pixel of the printing medium S with respect to a reference center line X 1  using the yellow, magenta, cyan, and black nozzles N 8 , N 7 , N 6 , and N 5  of the print head  123  disposed in the feeding direction X. 
     The pixel illustrated in  FIG. 6  is formed according to the following process. The controller  100   a  drives the feed roller  117  to feed the printing medium S in  FIG. 4  in the feeding direction X. Accordingly, if the printing medium S in  FIG. 4  is fed to a position to form the image, the yellow nozzle group L 8  is controlled to form the yellow ink dot Y 1 . Also, the magenta, cyan, and black nozzle groups L 7 , L 6 , and L 5  are sequentially controlled to form the magenta, cyan, and black ink dots M 1 , C 1 , and K 1 . The driving unit can be provided to correspond to each ink chamber and each nozzle of the head unit  120 . 
     Here, the same controller of a conventional ink jet printer can be used as the controller  110   a . That is, each nozzle group L 5 , L 6 , L 7 , and L 8  is controlled at the same ink jet timing with the conventional timing. By this, ink drying quality is enhanced and a dot coverage increases by changing the structure of the print head  123 . 
     That is, a conventional print head  23  has a constant interval G between the nozzle groups illustrated in  FIGS. 2 and 3 . However, the print head  123  according to an exemplary embodiment of the present general inventive concept is used so that jetting center points E 1 , E 2 , E 3 , and E 4  of the ink dots Y 1 , M 1 , C 1 , and K 1  can be formed on different regions of the pixel of the printing medium S along the feeding direction X. 
     For example, the printing medium S can be fed at a constant speed with respect to the head unit  120 , and the controller  100   a  controls the drivers of the head unit  120  to eject ink droplets from corresponding nozzles to form ink dots on, before, and/or after a centerline X 1  of the pixel of the printing medium S in different regions of the pixel of the printing medium S. When intervals between the nozzles in the feeding direction X or the nozzle groups in the feeding direction X are same, the ink dots can be formed on the same regions on the center line X 1  of the pixel of the printing medium S fed at the constant speed with respect to the head unit  120 . Since at least one of intervals between the nozzles in the feeding direction X or the nozzle groups in the feeding direction X is not the same as the other intervals, the ink dots can be formed on different regions on the corresponding ones of the jetting center points E 1 , E 2 , E 3 , and E 4  within the pixel of the printing medium S fed at the constant speed with respect to the head unit  120 . 
     It is possible that the controller  100   a  can control at least one of the head unit  120  and the feeding unit  110  to make a relative movement between the print head  123  and the printing medium S so that the ink dots can be formed in different regions of the pixel. 
     Hereinbelow, methods to determine the first, second, and third intervals H 1 , H 2 , and H 3  of the print head  123  will be described in detail so that the pixel may be formed according to patterns of  FIGS. 6 through 10 . 
     Referring to  FIGS. 7 to 10 , the ink dots are shifted by a short distance in the transverse direction Z for illustration purposes. 
     As illustrated in  FIG. 6 , the magenta ink dot M 1  is shifted with respect to the yellow ink dot Y 1  to the feeding direction X by a first interval deviation ΔH 1 =G−H 1  which is obtained by subtracting the first interval H 1  from an interval G between conventional nozzle groups of  FIG. 2 . At that time, if the first interval deviation ΔH 1  has a plus (or positive) value, i.e., if the first interval H 1  is narrower than the conventional interval G, the magenta ink dot M 1  is formed so that the jetting center point E 2  of the magenta ink dot M 1  can be placed in back of the jetting center point E 1  of the yellow ink dot Y 1  with respect to the feeding direction X on the contrary to  FIG. 6 . 
     That is, the jetting center point E 2  of the magenta ink dot M 1  can be placed at a lower side with respect to the jetting center point E 1  of the yellow ink dot Y 1 . 
     On the other hand, if the first interval deviation ΔH 1  has a minus (or negative) value, i.e., if the first interval H 1  is wider than the conventional interval G, as illustrated in  FIG. 6 , the magenta ink dot M 1  is formed so that the jetting center point E 2  of the magenta ink dot M 1  can be placed in front of the jetting center point E 1  of the yellow ink dot Y 1  with respect to the feeding direction X. 
     That is, the jetting center point E 2  of the magenta ink dot M 1  can be placed at an upper side with respect to the jetting center point E 1  of the yellow ink dot Y 1  as illustrated in  FIG. 6 . 
     Meanwhile, the cyan ink dot C 1  is shifted with respect to the magenta ink dot M 1  in the feeding direction X by a second interval deviation ΔH 2 =G−H 2  which is obtained by subtracting the second interval H 2  from the interval G between the conventional nozzle groups. The jetting center point E 3  of the cyan ink dot C 1  is shifted in a counter direction of the feeding direction X or in the feeding direction X with respect to the jetting center point E 2  of the magenta ink dot M 1  respectively according to the plus and minus signs (values) of the second interval deviation ΔH 2  like as the position of the jetting center point E 2  of the magenta ink dot M 1  is changed according to the sign changes of the first interval deviation ΔH 1 . 
     The black ink dot K 1  is shifted with respect to the cyan ink dot C 1  to the feeding direction X by a third interval deviation ΔH 3 =G−H 3  which is obtained by subtracting the third interval H 3  from the interval G between the conventional nozzle groups. Here, the relative position of the jetting center point E 4  of the black ink dot K 1  varies with regard to the jetting center point E 3  in the cyan ink dot C 1  according to the value of the third interval deviation ΔH 3 =G−H 3 . 
     In the meantime, if diameters of the nozzles N 1 , N 2 , N 3 , and N 4  are equal to one another under the same condition, the diameter may be approximately D. 
     Here, it is possible that the value which is obtained by adding the sum of an absolute value of the first through third interval deviations ΔH 1  through ΔH 3  and the diameter D of the ink dot can be equal to or smaller than the length of the pixel 1/R if the first through third interval deviations ΔH 1  through Δ 3  have the same sign, i.e., if each of the jetting center point E 1 , E 2 , E 3 , and E 4  of each ink dot Y, M, C, or K along the feeding direction X is aligned as illustrated in  FIG. 6 . 
     For example, if the resolution R is 1200 dpi and the interval G of the conventional print head  23  in  FIG. 2  is, for example, 67/1200 inch, the jetting point of the ink dot of  FIG. 6  is formed without the change of the controller. 
     
       
         
           
             
               
                 
                   
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                   [ 
                   
                     Formula 
                     ⁢ 
                     
                         
                     
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     Here, if H 1 &gt;G, H 2 &gt;G, and H 3 &gt;G, [formula 2] is given as follows. 
     
       
         
           
             
               
                 
                   
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     The values of H 1 , H 2 , and H 3  which satisfy [formula 2] and of which at least one interval is different from another one may be selected as follows. 
     
       
         
           
             
               H 
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               1 
             
             = 
             
               
                 
                   135 
                   4800 
                 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
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                 ⁢ 
                 
                     
                 
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     The first through third intervals H 1  through H 3  may be selected as other values satisfying [formula 2]. 
     Meanwhile, in  FIG. 7 , one color pixel is formed as a pattern where the magenta ink dot M 2  and the black ink dot K 2  are overlapped with each other and the yellow ink dot Y 2  and the cyan ink dot C 2  are overlapped each other. The jetting center point E 2  is disposed on the same line of the jetting center point E 4 , and the jetting center point E 1  is disposed on the same line of the jetting center point E 3 . 
     The first through third intervals H 1  via H 3  of the print head  123  may be determined to form the ink dots Y 2 , M 2 , C 2 , and K 2  as the same pattern as illustrated in  FIG. 7 . 
     For convenience, the resolution is 1200 dpi in  FIGS. 7 through 10 , and the interval G between the nozzle groups of the conventional print head  23  in  FIG. 2  is assumed to, for example, 67/1200 inch. Also, ΔH 4  is selected to, for example, 1/2400 inch. 
     As shown in  FIG. 7 , the first interval deviation ΔH 1  is (−)ΔH 4 , i.e., (−) 1/2400 inch because the jetting center point E 2  of the magenta ink dot M 2  is disposed in front of the jetting center point E 1  of the yellow ink dot Y 2  with respect to the feeding direction X. 
     
       
         
           
             
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                             2400 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             ( 
                             inch 
                             ) 
                           
                         
                         = 
                         
                           1428.7 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               ( 
                               µm 
                               ) 
                             
                             . 
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     On the other hand, the second interval deviation ΔH 2  is plus (+) 1/2400 inch because the jetting center point E 3  of the cyan ink dot C 2  is disposed in back of the jetting center point E 2  of the magenta ink dot M 2  with respect to the feeding direction X. 
     Accordingly, the second interval H 2  is calculated from the second interval deviation ΔH 2  as follows. 
     
       
         
           
             
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                           ( 
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                         133 
                         2400 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         ( 
                         inch 
                         ) 
                       
                     
                     = 
                     
                       1407.5 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         ( 
                         µm 
                         ) 
                       
                     
                   
                 
               
             
           
         
       
     
     Also, the third interval deviation ΔH 3  equals to the first interval deviation ΔH 1  because the jetting center point E 4  of the black ink dot K 2  is placed in front of the jetting center point E 3  of the cyan ink dot C 2  in the feeding direction X. That is, the third interval H 3  is also 1428.7 μm like the first interval H 1   
     Referring to  FIG. 8 , a color pixel is formed as a pattern that the cyan ink dot C 3  and the black ink dot K 3  overlap each other, and the yellow ink dot Y 3  and the magenta ink dot M 3  overlap each other. The jetting center point E 1  is disposed on the same line of the jetting center point E 2 , and the jetting center point E 3  is disposed on the same line of the jetting center point E 4 . 
     The first through third intervals H 1  through H 3  of the print head  123  may be calculated as follows so as to form the ink dot Y 3 , M 3 , C 3 , and K 3  as the same pattern of  FIG. 8 . 
     At that time, the first interval deviation ΔH 1  becomes zero because the jetting center point E 2  of the ink dot M 3  equals the jetting center point E 1  of the yellow ink dot Y 3 . 
     Thus, H 1 =G= 67/1200 inch=1418 μm. 
     Also, the second interval deviation ΔH 2  is equal to minus 1/2400 inch because the jetting center point E 3  of the cyan ink dot C 3  is placed in front of the jetting center point E 3  of the magenta ink dot M 3  in the feeding direction X. 
     Thus, the second interval H 2  is 133/2400 inch, i.e., 1407.5 μm. 
     The third interval deviation ΔH 3  becomes zero because the jetting center point E 4  of the black ink dot K 3  equals the jetting center point E 3  of the cyan ink dot C 3 . 
     Thus, H 3 =G= 67/1200 inch=1418 μm. 
     Referring to  FIG. 9 , a color pixel is formed as a pattern that the magenta ink dot M 4  and the cyan ink dot K 4 , and the yellow ink dot Y 4  and the black ink dot K 4  are overlapped with each other. The jetting center point E 1  is disposed on the same line of the jetting center point E 4 , and the jetting center point E 2  is disposed on the same line of the jetting center point E 3 . 
     The first through third intervals H 1  through H 3  of the print head  123  may be determined as follows to form the ink dot Y 4 , M 4 , C 4 , and K 4  as the same pattern of  FIG. 9 . 
     The first interval deviation ΔH 1  is equal to minus ΔH 4 , i.e., minus 1/2400 inch because the jetting center point E 2  of the magenta ink dot M 4  is placed in back of the jetting center point E 1  of the yellow ink dot Y 4  with respect to the feeding direction Z. 
     Thus, the first interval H 1  is 135/2400 inch, i.e., 1428.7 μm. 
     Also, the second interval deviation ΔH 2  is zero because the jetting center point E 3  of the cyan ink dot C 4  equals the jetting center point E 2  of the magenta ink dot M 4 . 
     Accordingly, the second interval H 2 =G= 67/1200 inch=1418 μm. 
     In the meantime, the third interval deviation ΔH 3  is equal to plus ΔH 4 , i.e., plus 1/2400 inch because the jetting center point E 4  of the black ink dot K 4  is placed in back of the jetting center point E 3  of the cyan ink dot C 4  in the feeding direction X. 
     Thus, the third interval H 3  is 133/2400 inch, i.e., 1407.5 μm. 
     Herein, the first through third intervals H 1  through H 3  have different value from each other. 
     Hence, the ink dots are jetted two by two in different printing region so that the ink drying quality can be more improved than that of when four ink dots are jetted on the same region. Also, the dot coverage which is a region covered with the ink dot within one pixel. 
     In the foregoing description, it is described that the ink dots are overlapped two by two to form one pixel, but not limited thereto. Alternatively, three ink dots are overlapped on the same printing region and one ink dot may be formed on another printing region, thereby forming one pixel as illustrating in  FIG. 10 . 
     Referring to  FIG. 10 , the jetting center point E 3  of the cyan ink dot C 5 , the jetting center point E 2  of the magenta ink dot M 5 , and the jetting center point E 1  of the yellow ink dot Y 5  are on the same position in the feeding direction X and/or disposed on a line parallel to the direction Z. Accordingly, the first interval deviation ΔH 1  and the second interval deviation ΔH 2  are both zero. 
     Accordingly, the first interval H 1  and the second interval H 2  are 63/1200 inch, i.e., 1418 μm. 
     Also, the third interval deviation ΔH 3  is plus ΔH 4 , i.e., plus 1/2400 inch, because the jetting center point E 4  of the black ink dot K 5  is placed in back of the jetting center point E 3  of the cyan ink dot C 5  with respect to the feeding direction X. 
     Accordingly, the third interval H 3  is 133/2400 inch, i.e., 1407.5 μm. 
     The following table shows values of the first through third intervals H 1  through H 3  of the print head  123  to have the ink dot patterns illustrated in  FIGS. 7 through 10 . 
     
       
         
           
               
               
               
               
             
               
                 TABLE 
               
               
                   
               
               
                   
                 FIRST 
                 SECOND 
                 THIRD 
               
               
                 PIXEL 
                 INTERVAL H1 
                 INTERVAL H2 
                 INTERVAL H3 
               
               
                 PATTERN 
                 (μM) 
                 (μM) 
                 (μM) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 FIG. 7 
                 1428.7 
                 1407.5 
                 1428.7 
               
               
                 FIG. 8 
                 1418 
                 1407.5 
                 1418 
               
               
                 FIG. 9 
                 1428.7 
                 1418 
                 1407.5 
               
               
                 FIG. 10 
                 1418 
                 1418 
                 1407.5 
               
               
                   
               
            
           
         
       
     
     The values of the first through third intervals H 1  through H 3  may be varied according to the interval G between the nozzle groups of the conventional print head  23  in  FIG. 2 , the value of ΔH 4 , the number of overlapped ink dots, etc. Accordingly, claim scope of the present invention is not limited to the foregoing table data. 
     In the foregoing description, it is illustrated that the print head  123  has four nozzle groups. However, the present invention may be applied as long as the print head  123  has three or more nozzle groups. 
     Also, in the foregoing description, the plurality of print head  123  arranged in zigzag along the transverse direction Z, so called, an array type print head  123 , is described in detail, but not limited thereto. Alternatively, a page-width-print-head which has a length corresponding to the width of the printing medium in the transverse direction to the feeding direction of the printing medium and is capable of high speed printing like the array type print head may be also applied. 
     As described above, the print head and the inkjet printer including the same according to the present general inventive concept has an effect as follows. 
     First, the ink dry quality may be improved. 
     Second, the dot coverage which is a region covered with the jetted ink may occupy much area of one pixel. 
     Third, the present general inventive concept may be mechanically realized without changing the controller, thereby reducing a manufacturing cost. 
     Fourth, the ink dots may be determined to be overlapped with each other by various combinations, thereby enhancing an expression of the color in the pixel unit. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.