Abstract:
A fluid discharging device includes: a head having a predetermined number of nozzle arrays in which n (n is an integral number equal to or more than 2) nozzles capable of discharging a predetermined fluid are arranged, the respective nozzle arrays formed to allow the fluid discharged from the kth (k=1, 2, . . . , n) nozzles belonging to the respective nozzle arrays to land on the same position on a target; a supply path that supplies the predetermined fluid to the respective nozzle arrays; a moving unit that relatively moves the head and the target; and a control unit that controls the moving unit to relatively move the head and the target and controls the head in such a manner that, regarding all nozzles belonging to the predetermined number of nozzle arrays, the nozzles are divided into plural groups so that the nozzles belonging to at least two or more nozzle arrays are combined to incorporate first to nth nozzles, the respective groups are as the group for use with predetermined timing, and the nozzles belonging to the set group for use are allowed to discharge the fluid to form dot rows on the target.

Description:
BACKGROUND 
   1. Technical Field 
   The present invention relates to a fluid discharging device and a control method therefor. 
   2. Related Art 
   In the related art, a fluid discharging device for discharging a fluid from a nozzle is known. For example, in a fluid discharging device in JP-A-2003-118149 (paragraphs 0037, 0038), in order to recover a defective nozzle, spare nozzle arrays respectively corresponding to cyan and magenta are formed. In this fluid discharging device, from the standpoint that it is not desirable that the disuse condition of spare nozzle arrays is continued for a long period, main nozzle arrays (not spare nozzle arrays) and the spare nozzle arrays are usually switched for use with respect to each paper of printing or a predetermined number of jobs. As a result, the life of each nozzle becomes longer. 
   However, in such a fluid discharging device, although the main nozzle arrays and the spare nozzle arrays are switched for use, there are following problems. Since a fluid is typically supplied to the plural nozzles arranged in the main nozzle array in one fluid supply path, when the main nozzle array is used for solid printing, for example, the fluid is discharged from all nozzles arranged in the main nozzle array. Accordingly, crosstalk that the discharging operations of the respective nozzles affect one another via the fluid supply path may occur, the amounts of discharged fluid may change, and landing positions may change. The same occurs with the spare nozzle array. 
   SUMMARY 
   An advantage of some aspects of the invention is to extend the life of each nozzle and suppress the crosstalk among nozzles. 
   A fluid discharging device according to an aspect of the invention includes: a head having a predetermined number of nozzle arrays in which n (n is an integral number equal to or more than 2) nozzles capable of discharging a predetermined fluid are arranged, the respective nozzle arrays formed to allow the fluid discharged from the kth (k=1, 2, . . . , n) nozzles belonging to the respective nozzle arrays to land on the same position on a target; a supply path that supplies the predetermined fluid to the respective nozzle arrays; a moving unit that relatively moves the head and the target; and a control unit that controls the moving unit to relatively move the head and the target and controls the head in such a manner that, regarding all nozzles belonging to the predetermined number of nozzle arrays, the nozzles are divided into plural groups so that the nozzles belonging to at least two or more nozzle arrays are combined to incorporate first to nth nozzles, the respective groups are switched to be set as the group for use with predetermined timing, and the nozzles belonging to the set group for use are allowed to discharge the fluid to form dot rows on the target. 
   In the fluid discharging device, the moving unit is controlled to relatively move the head and the target and the head is controlled in such a manner that, regarding all nozzles belonging to the predetermined number of nozzle arrays, the nozzles are divided into plural groups so that the nozzles belonging to at least two or more nozzle arrays are combined to incorporate first to nth nozzles, the respective groups are switched to be set as the group for use with predetermined timing, and the nozzles belonging to the set group for use are controlled to discharge the fluid to form dot rows on the target. Thus, the plural nozzles having different fluid supply paths are combined and used for forming one dot row, and the discharge operations of the respective nozzles hardly affect one another via the fluid supply paths. Further, the frequency in use of the respective nozzles becomes lower. Therefore, the life of each nozzle can be extended and the crosstalk among nozzles can be suppressed. 
   The fluid may be any fluid as long as it can be discharged from a nozzle, for example, an ink used for printing, a liquid agent used for semiconductor manufacturing process, or the like. The target may be any target as long as the fluid can attach to it, for example, paper, fabric, resin plate, metal plate, or the like. The moving unit may be a unit for moving the target relative to the fixed head or moving the head relative to the fixed target, or moving the head in a predetermined direction and moving the target in a direction perpendicular to the predetermined direction. Furthermore, the numeric number n is not specifically limited as long as it is an integral number equal to or more than 2, but determined to be on the order of several tens to several thousands based on the resolution of dots and lengths of nozzle arrays, for example. 
   In the fluid discharging device according to the aspect of the invention, the head may have two of the nozzle arrays. Three of more nozzle arrays in which nozzles capable of discharging the same fluid are arranged may be formed, but, in this case, the head is likely to be upsized and the cost may be increased. Therefore, it is preferable to provide two, i.e., the minimum number of nozzle arrays for downsizing of the head and cost reduction. In this case, the control unit may make one group of the odd-numbered nozzles belonging to one of the two nozzle arrays and the even-numbered nozzles belonging to the other of the two nozzle arrays, and the other group of the even-numbered nozzles belonging to the one of the two nozzle arrays and the odd-numbered nozzles belonging to the other of the two nozzle arrays. Thus, grouping can be easily performed. 
   In the fluid discharging device of the aspect of the invention, the nozzles may be arranged in a staggered manner in the respective nozzle arrays. Thus, higher density of nozzles can be realized because the nozzles are arranged in the staggered manner compared to the case where the nozzles are linearly arranged. 
   In the fluid discharging device of the aspect of the invention, the control unit may switch and set the respective groups as the group for use with respect to each one of the target. The respective groups may be switched with respect to each job, but, in this case, the period for continuously using the same nozzles becomes longer and heat may be stayed around the head. On the other hand, when the groups are switched with respect to each target, the period for continuously using the same nozzles becomes shorter and heat hardly stays around the head. 
   In the fluid discharging device of the aspect of the invention, the head may be a line head formed to have the nozzle arrays in length equal to or more than a width of the target. When such a line head is adopted, the head is upsized and the discharge operations of the respective nozzles are more likely to affect one another via the fluid supply paths. Therefore, it is of great significance to apply the aspect of the invention. 
   A control method for a fluid discharging device according to another aspect of the invention is a control method for a fluid discharging device including a head having a predetermined number of nozzle arrays in which n (n is an integral number equal to or more than 2) nozzles capable of discharging a predetermined fluid are arranged, the respective nozzle arrays formed to allow the fluid discharged from the kth (k=1, 2, . . . , n) nozzles belonging to the respective nozzle arrays to land on the same position on a target, a supply path that supplies the predetermined fluid to the respective nozzle arrays, a moving unit that relatively moves the head and the target, and the method includes controlling the moving unit to relatively move the head and the target and controlling the head in such a manner that, regarding all nozzles belonging to the predetermined number of nozzle arrays, the nozzles are divided into plural groups so that the nozzles belonging to at least two or more nozzle arrays are combined to incorporate first to nth nozzles, the respective groups are switched to be set as the group for use with predetermined timing, and the nozzles belonging to the set group for use are allowed to discharge the fluid to form dot rows on the target. 
   In the control method for a fluid discharging device, the moving unit is controlled to relatively move the head and the target and the head is controlled in such a manner that, regarding all nozzles belonging to the predetermined number of nozzle arrays, the nozzles are divided into plural groups so that the nozzles belonging to at least two or more nozzle arrays are combined to incorporate first to nth nozzles, the respective groups are switched to be set as the group for use with predetermined timing, and the nozzles belonging to the set group for use are controlled to discharge the fluid to form dot rows on the target. Thus, the plural nozzles having different fluid supply paths are combined and used for forming one dot row, and the discharge operations of the respective nozzles hardly affect one another via the fluid supply paths. Further, the frequency in use of the respective nozzles becomes lower. Therefore, the life of each nozzle can be extended and the crosstalk among nozzles can be suppressed. Note that, in the control method, some steps may be added for realizing actions and functions exerted by the various configurations of the above described fluid discharging device of the embodiment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
       FIG. 1  is a sectional view showing a schematic configuration of an inkjet printer  20 . 
       FIG. 2  is an explanatory diagram showing a schematic configuration of a line head  22 . 
       FIG. 3  is an explanatory diagram showing electric connection of the inkjet printer  20 . 
       FIG. 4  is a partially exploded perspective view of a cyan nozzle plate  28 C and surrounding members. 
       FIG. 5  is a flowchart of a print control routine. 
       FIGS. 6A to 6I  are explanatory diagrams showing relationships between elapsed time and dots formed on recording paper S. 
       FIGS. 7A to 7G  are explanatory diagrams showing relationships between elapsed time and dots formed on recording paper S. 
   

   DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Now, one embodiment embodying the invention will be described.  FIG. 1  is a sectional view showing a schematic configuration of an inkjet printer  20  as the embodiment,  FIG. 2  is an explanatory diagram showing a schematic configuration of a line head  22 , and  FIG. 3  is an explanatory diagram showing electric connection of the inkjet printer  20 . 
   As shown in  FIG. 1 , the inkjet printer  20  of the embodiment has the line head  22  that performs printing by discharging ink droplets onto recording paper S to be transported from a paper feed tray  52 , a paper feed mechanism  50  including a belt  60  hung around a pair of transport rollers  58 ,  58  driven by a drive motor  62  for transportation, and a controller  70  (see  FIG. 3 ) that controls the entire of the inkjet printer  20 . 
   The line head  22  is formed in a nearly rectangle parallelepiped shape and fixed to the printer main body with the longitudinal direction perpendicular to the transport direction. The line head  22  is connected via an ink cartridge  24  separately containing inks of the respective colors of cyan (C), magenta (M), and yellow (Y). The line head  22  has a nozzle plate  28  at the bottom as shown in  FIG. 2 . On the nozzle plate  28 , a first cyan nozzle array C 1  in which n first cyan nozzles NC 1  capable of discharging a cyan (C) ink are arranged, a second cyan nozzle array C 2  in which n second cyan nozzles NC 2  also capable of discharging a cyan (C) ink are arranged, a first magenta nozzle array M 1  in which n first magenta nozzles NM 1  capable of discharging a magenta (M) ink are arranged, a second magenta nozzle array M 2  in which n second magenta nozzles NM 2  also capable of discharging a magenta (M) ink are arranged, a first yellow nozzle array Y 1  in which n first yellow nozzles NY 1  capable of discharging a yellow (Y) ink are arranged, a second yellow nozzle array Y 2  in which n second yellow nozzles NY 2  also capable of discharging a yellow (Y) ink are arranged are respectively formed. The lengths of the respective nozzle arrays C 1 , C 2 , M 1 , M 2 , Y 1 , and Y 2  are equal to or more than paper width of recording paper in the maximum size of printable paper. Further, the numeric value n is a value determined based on the resolution of dots and the lengths of the nozzle arrays, about several tens to several thousands (here, several hundreds). The line head  22  and the ink cartridge  24  are connected by six tubes  26 C 1 ,  26 C 2 ,  26 M 1 ,  26 M 2 ,  26 Y 1 , and  26 Y 2  as shown in  FIG. 1 . In the line head  22 , the ink is supplied to the first cyan nozzle array C 1  via the first cyan tube  26 C 1 , and the ink is supplied to the second cyan nozzle array C 2  via the second cyan tube  26 C 2 . Further, the ink is supplied to the first magenta nozzle array M 1  via the first magenta tube  26 M 1 , the ink is supplied to the second magenta nozzle array M 2  via the second magenta tube  26 M 2 , the ink is supplied to the first yellow nozzle array Y 1  via the first yellow tube  26 Y 1 , and the ink is supplied to the second yellow nozzle array Y 2  via the second yellow tube  26 Y 2 . In the embodiment, black (K) is formed by mixing cyan (C), magenta (M), and yellow (Y), however, a black (K) ink array may be separately provided. 
   Here, the first cyan nozzle array C 1  will be described as an example. When the first cyan nozzle array C 1  is seen along the longitudinal direction, plural first cyan nozzles NC 1  forming the first cyan nozzle array C 1  are arranged in a staggered manner. Specifically, the odd-numbered (#1, 3, 5, . . . ) first cyan nozzles NC 1  are linearly arranged at a pitch of a predetermined length L along the longitudinal direction, and the even-numbered (#2, 4, 6, . . . ) first cyan nozzles NC 1  are linearly arranged in parallel with the arrangement direction of the odd-numbered first cyan nozzles NC 1  at a pitch of the predetermined length L. The adjacent odd-numbered first cyan nozzle NC 1  and even-numbered first cyan nozzle NC 1  are arranged at a pitch of a half of the predetermined length L (L/2) In the embodiment, the predetermined length L is determined so that dots may provide resolution of 180 dpi, the resolution of printed matter to be obtained is 360 dpi because printing is performed with the recording paper S transported so that the dots formed by the ink discharged from the odd-numbered first cyan nozzles NC 1  and the dots formed by the ink discharged from the even-numbered first cyan nozzle NC 1  may be arranged in a line. The resolution can be made higher by appropriately shortening the predetermined length L. The first cyan nozzles NC 1  are communicated with an ink chamber  34 C 1  provided inside the line head  22 . In the ink chamber  34 C 1 , when a voltage is applied to a piezoelectric element  38 C 1  attached to a vibrating plate  36  forming an upper wall of the ink chamber  34 C 1 , the piezoelectric element  38 C 1  deforms and compresses the volume inside the chamber (see the dotted line within the lower circle in  FIG. 2 ), and, when the application of the voltage is canceled, the piezoelectric element  38 C 1  is restored and the volume inside the chamber returns. Thereby, the ink is discharged from the first cyan nozzles NC 1 . The second cyan nozzle array C 2  is formed adjacently to the first cyan nozzle array C 1  completely in the same fashion as that of the first cyan nozzle array C 1 . That is, the first and second cyan nozzle arrays C 1  and C 2  are formed so that the position on the recording paper S where the ink discharged from the kth (k=1, 2, . . . , n) first cyan nozzle NC 1  of the first cyan nozzle array C 1  lands and the position on the recording paper S where the ink discharged from the kth second cyan nozzle NC 2  of the second cyan nozzle array C 2  lands may be the same. 
     FIG. 4  is a partially exploded perspective view showing internal structures of the first and second cyan nozzles NC 1 , NC 2 . As shown in  FIG. 4 , the line head  22  includes a cyan nozzle plate  28 C as a part of the nozzle plate  28 , and a cyan cavity plate  30 C stacked on the cyan nozzle plate  28 C. On the cyan nozzle plate  28 C, the first cyan nozzles NC 1  are sequentially formed from the #1 nozzle in the staggered manner, and the second cyan nozzles NC 2  are sequentially formed from the #1 nozzle in the staggered manner. On the cyan cavity plate  30 C, cavities  31 C 1  as the ink chambers  34 C 1  (see  FIG. 2 ) are formed correspondingly to the respective first cyan nozzles NC 1 , and the similar cavities  31 C 2  are formed correspondingly to the respective second cyan nozzles NC 2 . Of the cavities  31 C 1  formed on the cyan cavity plate  30 C, the cavities  31 C 1  corresponding to the odd-numbered first cyan nozzles NC 1  are communicated by a longitudinal groove  32 C 1 , and the cavities  31 C 1  corresponding to the even-numbered first cyan nozzles NC 1  are communicated by a longitudinal groove  33 C 1 . Further, of the cavities  31 C 2 , the cavities  31 C 2  corresponding to the odd-numbered second cyan nozzles NC 2  are communicated by a longitudinal groove  32 C 2 , and the cavities  31 C 2  corresponding to the even-numbered second cyan nozzles NC 2  are communicated by a longitudinal groove  33 C 2 . A cyan tank containing the cyan ink of the ink cartridge  24  and the line head  22  are connected by the first and second cyan tubes  26 C 1 ,  26 C 2 , the first cyan tube  26 C 1  can supply the cyan ink to the respective longitudinal grooves  32 C 1 ,  33 C 1  via a pump (not shown), and the second cyan tube  26 C 2  can supply the cyan ink to the respective longitudinal grooves  32 C 2 ,  33 C 2  via a pump (not shown). On the cyan cavity plate  30 C, the vibrating plate  36  (see  FIG. 2 ) is further stacked and the piezoelectric elements  38 C 1  (see  FIGS. 1 and 2 ) corresponding to the respective first cyan nozzles NC 1  and the piezoelectric elements  38 C 2  (see  FIG. 2 ) corresponding to the respective second cyan nozzles NC 2  are stacked on the vibrating plate  36 , however, they are omitted in  FIG. 4 . The first and second magenta nozzle arrays M 1 , M 2 , and the first and second yellow nozzle arrays Y 1 , Y 2  are formed in the same manner as the first and second cyan arrays C 1 , C 2 , and their detailed description is omitted here. 
   As shown in  FIG. 1 , the paper feed mechanism  50  includes a recording paper insertion opening  54  into which recording paper S mounted on the paper feed tray  52  is inserted, a paper feed roller  56  that feeds the recording paper S mounted on the paper feed tray  52  to the line head  22 , the endless belt  60  hung around the pair of transport rollers  58 ,  58  for electrostatistically attracting or vacuum-attracting and transporting the recording paper S. The paper feed mechanism  50  transports the recording paper S in a direction perpendicular to the arrangement direction of the ink nozzle arrays formed on the line head  22 . One of the pair of transport rollers  58 ,  58  is a driving roller driven by the drive motor  62  and the other is a driven roller that rotates according to the rotation of the driving roller. The paper feed roller  56  and the driving roller of the pair of transport rollers  58 ,  58  are driven by the drive motor  62  for transportation via a gear mechanism (not shown). 
   As shown in  FIG. 3 , the controller  70  is configured as a microprocessor centering on a CPU  72 , and includes a ROM  74  that stores various kinds of processing programs, a RAM  76  that temporarily stores or saves data, a flash memory  77  that can freely delete and write data and hold contents after the power is turned off, an interface (I/F)  78  that exchanges information between an external device and itself, and an input/output port (not shown). To the controller  70 , signals on the position of the recording paper S from a rotary encoder  64  attached to the drive motor  62  for transportation are input via an input port (not shown), and further, print jobs output from a user PC  110  or the like are input via the I/F  78 . From the controller  70 , drive signals to piezoelectric element drive circuits  39 C 1 ,  39 C 2 ,  39 M 1 ,  39 M 2 ,  39 Y 1 , and  39 Y 2  for driving the piezoelectric elements  38 C 1 ,  38 C 2 ,  38 M 1 ,  38 M 2 ,  38 Y 1 , and  38 Y 2  of the line head  22  and control signals to the drive motor  62  for transportation are output via an output port (not shown), and further, print status information to the user PC  110  and the like are output via the I/F  78 . In the ROM  74 , the respective processing programs such as a print control routine, which will be described later, are stored. Further, a buffer space for printing is provided in the RAM  76 . In the buffer space for printing, print data sent from the user PC  110  via the I/F  78  is temporarily stored. 
   In the embodiment, ink nozzles are divided into two groups A, B. The group A includes the odd-numbered first cyan nozzles NC 1  connected to the first cyan tube  26 C 1  and the even-numbered second cyan nozzles NC 2  connected to the second cyan tube  26 C 2 , the odd-numbered first magenta nozzles NM 1  connected to the first magenta tube  26 M 1  and the even-numbered second magenta nozzles NM 2  connected to the second magenta tube  26 M 2 , and the odd-numbered first yellow nozzles NY 1  connected to the first yellow tube  26 Y 1  and the even-numbered second yellow nozzles NY 2  connected to the second yellow tube  26 Y 2 . Further, the group B includes the even-numbered first cyan nozzles NC 1  connected to the first cyan tube  26 C 1  and the odd-numbered second cyan nozzles NC 2  connected to the second cyan tube  26 C 2 , the even-numbered first magenta nozzles NM 1  connected to the first magenta tube  26 M 1  and the odd-numbered second magenta nozzles NM 2  connected to the second magenta tube  26 M 2 , and the even-numbered first yellow nozzles NY 1  connected to the first yellow tube  26 Y 1  and the odd-numbered second yellow nozzles NY 2  connected to the second yellow tube  26 Y 2 . The ink nozzles are divided into the two groups A, B in this manner, and thereby, there are sequentially from first to nth ink nozzles of the same color belonging to the same group. Further, the half of the ink nozzles of the same color belonging to the same group are supplied with ink from the same ink tube, while the rest of the ink nozzles are supplied with ink from another tube. The information on which of the groups A, B includes which ink nozzle is stored in the ROM  74  in advance. 
   Next, an operation of the inkjet printer  20  of the embodiment having the above described configuration will be explained.  FIG. 5  is a flowchart of the print control routine. When a print job is input from the user PC  110 , the CPU  72  of the controller  70  loads the print control routine program from the ROM  74  and executes the program. When the print control routine is started, the CPU  72  first sets a group of ink nozzles to be used (step S 100 ) If the print control routine is first executed after factory shipment, the group A is set. If the print control routine has been executed in the past, the group different from the last group set in the previous printing is set. Subsequently, paper feed processing is executed (step S 110 ). The paper feed processing is processing of rotationally driving the paper feed roller  56  and the pair of transport rollers  58 ,  58  by driving the drive motor  62 , and transporting the recording paper S until the print starting point of the recording paper S mounted on the paper feed tray  52  comes to a predetermined position facing to the line head  22 . Then, the CPU  72  selects nozzles to discharge ink (discharge-designated nozzles) based on the print data contained in the print job from the nozzles included in the set group (step S 120 ). For example, if the set group is the group A, the discharge-designated nozzles are selected from the odd-numbered first cyan nozzles NC 1  and the even-numbered second cyan nozzles NC 2 , the odd-numbered first magenta nozzles NM 1  and the even-numbered second magenta nozzles NM 2 , and the odd-numbered first yellow nozzles NY 1  and the even-numbered second yellow nozzles NY 2 . Further, if the set group is the group B, the discharge-designated nozzles are selected from the even-numbered first cyan nozzles NC 1  and the odd-numbered second cyan nozzles NC 2 , the even-numbered first magenta nozzles NM 1  and the odd-numbered second magenta nozzles NM 2 , and the even-numbered first yellow nozzles NY 1  and the odd-numbered second yellow nozzles NY 2 . 
   Subsequently, in order that the inks are discharged from the selected discharge-designated nozzles, the control signals are sent to the piezoelectric element drive circuits  39 C 1 ,  39 C 2 ,  39 M 1 ,  39 M 2 ,  39 Y 1 , and  39 Y 2  (step S 130 ). Then, whether printing for one page has been finished or not is determined (step S 140 ), and if the printing for one page has been not finished, the processing at steps S 120  to S 140  is executed again. While the processing at steps S 120  to S 140  is repeated, the pair of transport rollers  58 ,  58  are rotated by driving the drive motor  62  to transport the recording paper S at a predetermined speed. The predetermined speed for transportation of the recording paper S is determined so that dots formed on the recording paper S provide resolution of 360 dpi. Such processing is repeatedly executed, and if determined that the printing for one page has been finished at step S 140 , paper eject processing is executed (step S 150 ). The paper eject processing is processing of rotationally driving the pair of transport rollers  58 ,  58  by driving the drive motor  62  to eject the printed recording paper S onto a receiving tray (not shown). Subsequently, whether there is the next page to be printed or not is determined (step S 160 ), and, if there is the next page, the group of the ink nozzles for use is changed to the group different from the currently set group (step S 170 ). Then, the process returns to step S 110  again, and, if there is no next page, this routine is ended. 
   Next, the dots formed in the print control routine will be described.  FIGS. 6A to 6I  are explanatory diagrams showing relationships between elapsed time and dots formed on the recording paper S when dots of cyan ink are solidly formed on the entire surface of the recording paper S in the case where the group of ink nozzles for use is set to the group A. Here, the dot rows to be formed on the recording paper S are dot rows of total six rows from the first row to the sixth row, and total nine dots from first dot to the ninth dot are arranged in each dot row. Further, the piezoelectric elements  38 C 1  of the first cyan nozzles NC 1  of the first cyan nozzle array C 1  are driven when the odd-numbered dot arrays are formed, and the piezoelectric elements  38 C 2  of the second cyan nozzles NC 2  of the second cyan nozzle array C 2  are driven when the odd-numbered dot rows are formed. The times T 1  to T 9  represent times at which the recording paper S is transported by one dot. 
   At time T 1 , as shown in  FIG. 6A , the first dot row on the recording paper S faces the odd-numbered first cyan nozzles NC 1  of the first cyan nozzle array C 1 . Then, ink is discharged from the odd-numbered first cyan nozzles NC 1 , and dots are formed in the first dot row of the recording paper S at double intervals. At times T 2 , T 3 , the ink is discharged in the same manner. That is, in  FIG. 6B  at time T 2 , dots are formed in the second dot row of the recording paper S at double intervals, and, in  FIG. 6C  at time T 3 , dots are formed in the third dot row of the recording paper S at double intervals. At time T 4 , as shown in  FIG. 6D , the fourth dot row on the recording paper S faces the odd-numbered first cyan nozzles NC 1  of the first cyan nozzle array C 1 , and the first dot row on the recording paper S faces the even-numbered second cyan nozzles NC 2  of the second cyan nozzle array C 2 . Then, the ink is discharged from the odd-numbered first cyan nozzles NC 1  of the first cyan nozzle array C 1 , and dots are formed in the fourth dot row of the recording paper S at double intervals. Simultaneously, the ink is discharged from the even-numbered second cyan nozzles NC 2  of the second cyan nozzle array C 2 , and dots are formed to fill the gaps between dots formed at double intervals in the first dot row of the recording paper S. Thereby, the first dot row is entirely filled with the dots. At times T 5 , T 6 , the ink is discharged in the same manner. That is, in  FIG. 6E  at time T 5 , the second dot row of the recording paper S is filled with dots and dots are formed in the fifth dot row at double intervals, and, in  FIG. 6F  at time T 6 , the third dot row of the recording paper S is filled with dots and dots are formed in the sixth dot row at double intervals. At time T 7 , as shown in  FIG. 6G , the fourth dot row of the recording paper S faces the even-numbered second cyan nozzles NC 2  of the second cyan nozzle array C 2 . Then, the ink is discharged from the even-numbered second cyan nozzles NC 2 , and dots are formed to fill the fourth dot row of the recording paper S. At times T 8 , T 9 , the ink is discharged in the same manner. That is, in  FIG. 6H  at time T 8 , the fifth dot row of the recording paper S is filled with dots, and, in  FIG. 6I  at time T 9 , the sixth dot row of the recording paper S is filled with dots. Thus, the first to sixth dot rows of the recording paper S are completely filled with the dots formed by the cyan ink. 
     FIGS. 7A to 7G  are explanatory diagrams showing relationships between elapsed time and dots formed on the recording paper S when dots of cyan ink are solidly formed on the entire surface of the recording paper S in the case where the group of ink nozzles for use is set to the group B. 
   At time T 1 , as shown in  FIG. 7A , the first dot row on the recording paper S faces the even-numbered first cyan nozzles NC 1  of the first cyan nozzle array C 1 . Then, the ink is discharged from the even-numbered first cyan nozzles NC 1 , and dots are formed in the first dot row of the recording paper S at double intervals. At time T 2 , as shown in  FIG. 7B , the second dot row on the recording paper S faces the even-numbered first cyan nozzles NC 1  of the first cyan nozzle array C 1 , and the first dot row faces the odd-numbered second cyan nozzles NC 2  of the second cyan nozzle array C 2 . Then, the ink is discharged from the even-numbered first cyan nozzles NC 1  of the first cyan nozzle array C 1 , and dots are formed in the second dot row of the recording paper S at double intervals. Simultaneously, the ink is discharged from the odd-numbered second cyan nozzles NC 2  of the second cyan nozzle array C 2 , and dots are formed to fill the gaps between dots formed at double intervals in the first dot row of the recording paper S. Thereby, the first dot row is entirely filled with the dots. At times T 3  to T 6 , the ink is discharged in the same manner. That is, in  FIG. 7C  at time T 3 , the second dot row of the recording paper S is filled with dots and dots are formed in the third dot row at double intervals, in  FIG. 7D  at time T 4 , the third dot row of the recording paper S is filled with dots and dots are formed in the fourth dot row at double intervals, in  FIG. 7E  at time T 5 , the fourth dot row of the recording paper S is filled with dots and dots are formed in the fifth dot row at double intervals, and, in  FIG. 7F  at time T 6 , the fifth dot row of the recording paper S is filled with dots and dots are formed in the sixth dot row at double intervals. At time T 7 , as shown in  FIG. 7G , the sixth dot row on the recording paper S faces the odd-numbered second cyan nozzles NC 2  of the second cyan nozzle array C 2 . Then, the ink is discharged from the odd-numbered second cyan nozzles NC 2 , and the sixth dot row of the recording paper S is filled with dots. Thus, the first to sixth dot rows on the recording paper S are completely filled with the dots formed by the cyan ink. 
   The correspondences between the component elements of the embodiment and the component elements of the invention are as follows. The inkjet printer  20  of the embodiment corresponds to a fluid discharging device of the invention, the line head  2  corresponds to a head, the first and second cyan tubes  26 C 1 ,  26 C 2 , the first and second magenta tubes  26 M 1 ,  26 M 2 , and the first and second yellow tubes  26 Y 1 ,  26 Y 2  correspond to a supply path, the paper feed mechanism  50  corresponds to a moving unit, and the controller  70  corresponds to a control unit. Further, when a predetermined fluid is a cyan ink, the first and second cyan nozzle arrays C 1 , C 2  correspond to a nozzle array in which n nozzles capable of discharging the predetermined fluid are arranged, when predetermined fluid is a magenta ink, the first and second magenta nozzle arrays M 1 , M 2  correspond to a nozzle array in which n nozzles capable of discharging the predetermined fluid are arranged, and, when the first and second yellow nozzle arrays Y 1 , Y 2  correspond to a nozzle array in which n nozzles capable of discharging the predetermined fluid are arranged. The embodiment makes an example of the control method for the fluid discharging device of the invention clear by describing the operation of the inkjet printer  20 . 
   According to the above specifically described inkjet printer  20  of the embodiment, taking cyan as an example, for forming the first dot row, the combination of the odd-numbered first cyan nozzles NC 1  supplied with ink by the first cyan tube  26 C 1  and the even-numbered second cyan nozzles NC 2  supplied with ink by the second cyan tube  26 C 2  or the combination of the even-numbered first cyan nozzles NC 1  supplied with ink by the first cyan tube  26 C 1  and the odd-numbered second cyan nozzles NC 2  supplied with ink by the second cyan tube  26 C 2  is used. Accordingly, the chances that the discharging operations of the respective first cyan nozzles NCI affect one another via the first cyan tube  26 C 1  and the discharging operations of the respective second cyan nozzles NC 2  affect one another via the second cyan tube  26 C 2  are reduced. The same is true for the other colors. Therefore, crosstalk among nozzles can be suppressed. Further, the respective nozzles repeat ink discharge and discharge pause with respect to each page, and the drive frequency becomes ½ compared to the case where ink discharge is performed at every time. Therefore, the life of each nozzle is extended and heat hardly stay around the line head  22 . 
   The invention is not limited to the above described embodiment and can be put into practice in various embodiments within the technical scope of the invention. 
   For example, in the above described embodiment, the line head  22  for color printing has been illustrated, however, the invention may be applied to a line head for monochrome printing including the respective ink nozzle arrays of only black nozzles that discharge a black (K) ink. 
   In the above described embodiment, the nozzles contained in the respective nozzle arrays are arranged in the staggered manner, however, they may be linearly arranged. Also, in this case, ink discharge and discharge pause are repeated after each sheet of recording paper S is printed, and the durability of nozzles is improved. 
   In the above described embodiment, the system of discharging ink by deforming the piezoelectric element to press the ink in the ink chamber has been adopted, however, a system of discharging ink by heating the ink in the ink chamber with a heating resistor (e.g., a heater) to produce air bubbles for pressing the ink may be adopted. 
   In the above described embodiment, two nozzle arrays are formed for the respective color inks, however, three or more arrays may be formed. For example, when three nozzle arrays are formed for the respective color inks, regarding all nozzles belonging to the three nozzle arrays, the nozzles may be divided into plural groups so that the nozzles belonging to at least two or more nozzle arrays may be combined to provide sequentially from first to nth nozzles, the respective groups may be switched and set as the group for use at each time when one page is printed, and the fluid may be discharged from the nozzles belonging to the set group for use to form dot rows on the recording paper S. 
   In the above described embodiment, the line head  22  fixed to the printer main body is used, however, the respective ink nozzle arrays may be formed on a head mounted on a carriage movable in a direction perpendicular to the transport direction of the recording paper S may be adopted. 
   In the above described embodiment, the inkjet printer  20  has been illustrated, however, the invention may be applied to a multifunction printer having both a scanner and a printer, or a facsimile machine. 
   The entire disclosure of Japanese Patent Application No. 2007-177489, filed Jul. 5, 2007 is expressly incorporated by reference herein.