Patent Publication Number: US-11020962-B2

Title: Liquid ejection apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2019-086069 filed on Apr. 26, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field of the Invention 
     The present disclosure relates to a liquid ejection apparatus for ejecting a liquid from nozzles. 
     Description of the Related Art 
     A printer, which performs the recording by ejecting an ink from nozzles, is known as an example of the liquid ejection apparatus for ejecting the liquid from the nozzles. In the case of the certain known printer, a head is driven so that the ink is ejected from the nozzles. It is judged whether or not the ink is ejected from the nozzles on the basis of the change in the electric potential brought about on a detecting electrode in this situation. 
     SUMMARY 
     In the case of the known printer described above, the head is driven so that the ink is ejected from the nozzles individually for each of the plurality of nozzles of the head in order to distinguish whether or not the ink is ejected in relation to each of the plurality of nozzles of the head. Then, the following operation is performed. That is, it is judged whether or not the ink is ejected from the nozzle on the basis of the change in the electric potential brought about on the detecting electrode in this situation. On this account, if the number of the nozzles of the head is large, then the head is driven a large number of times in order to judge whether or not the ink is ejected from all of the nozzles, and a long time is consequently required to perform the judgment. 
     An object of the present disclosure is to provide a liquid ejection apparatus which makes it possible to maximally shorten the time required to judge whether or not a nozzle is a ejection-defective nozzle that involves any abnormality to eject a liquid, in relation to each of a plurality of nozzles of a liquid ejection head. 
     According to an aspect of the present disclosure, there is provided a liquid ejection apparatus including: a liquid ejection head including a plurality of nozzles forming a plurality of first nozzle groups, each of the first nozzle groups including two or more nozzles of the plurality of nozzles; a signal output circuit configured to output a signal in response to a discharge of a liquid from a nozzle of the plurality of the nozzles, a signal in response to a normal discharge of the liquid being different from a signal in response to a defective discharge of the liquid, and in a case that the liquid is simultaneously ejected from two or more nozzles of the plurality of nozzles, the signal output circuit being configured to output different signals depending on the number of ejection-defective nozzles that undergo occurrence of the defective discharge of the liquid; and a controller. The controller is configured to: drive the liquid ejection head such that the liquid is simultaneously ejected from the two or more nozzles in each of the first nozzle groups, and; judge, based on the signal output from the signal output circuit, whether a first condition, a second condition or a third condition is satisfied, the first condition being a condition in which the ejection-defective nozzles are absent in the two or more nozzles of each of the first nozzle groups, the second condition being a condition in which all of the two or more nozzles of each of the first nozzle groups are the ejection-defective nozzles, and the third condition being the condition in which a part of the two or more nozzles of each of the first nozzle groups are the ejection-defective nozzles. In a case that the controller judges that two or more first nozzle groups in the first nozzle groups satisfy the third condition, the controller is configured to: classify at least some of the nozzles in the two or more first nozzle groups that satisfy the third condition, into at least one second nozzle group, each of the at least one second nozzle group including two or more nozzles and having a different combination of the nozzles as compared with the plurality of first nozzle groups; drive the liquid ejection head such that the liquid is simultaneously ejected from the two or more nozzles of each of the at least one second nozzle group; and judge, based on the signal output from the signal output circuit, whether the first condition is satisfied, the second condition is satisfied, or the third condition is satisfied. 
     It is understood that all of the nozzles, which constitute the first nozzle group that satisfies the first condition, are not the ejection-defective nozzles. Further, it is understood that all of the nozzles, which constitute the first nozzle group that satisfies the second condition, are the ejection-defective nozzles. Then, as for the first nozzle group which satisfies the first condition or the second condition, it is possible to decrease the number of times of the driving the liquid ejection head required to judge whether or not the nozzle is the ejection-defective nozzle, as compared with a case in which it is judged whether or not the nozzle is the ejection-defective nozzle by driving the liquid ejection head so that the liquid is ejected individually from each of the nozzles. 
     Further, if the plurality of nozzle groups, which satisfy the third condition, are present, the nozzles, each of which is obtained by excluding one of the two or more nozzles in relation to each of the plurality of first nozzle groups that satisfy the third condition, are classified into the plurality of second nozzle groups, while changing the combinations of the nozzles as compared with the plurality of first nozzle groups. It is understood that all of the nozzles, which constitute the second nozzle group that satisfies the first condition, are not the ejection-defective nozzles. Further, it is understood that all of the nozzles, which constitute the second nozzle group that satisfies the second condition, are the ejection-defective nozzles. 
     Then, as for the second nozzle group which satisfies the first condition or the second condition, it is possible to decrease the number of times of the driving of the liquid ejection head required to judge whether or not the nozzle is the ejection-defective nozzle, as compared with a case in which it is judged whether or not the nozzle is the ejection-defective nozzle by driving the liquid ejection head so that the liquid is ejected individually from each of the nozzles. 
     Note that if only one first nozzle group that satisfies the third condition and/or if only one second nozzle group that satisfies the third condition is/are present, it is possible to judge whether or not the nozzle is the ejection-defective nozzle by ejecting the liquid from at least a part or parts of the nozzle or nozzles for constructing the nozzle groups. 
     According to the fact as described above, the present disclosure makes it possible to maximally decrease the number of times of the driving of the liquid ejection head required to judge whether or not the nozzles are the ejection-defective nozzles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a schematic arrangement of a printer according to a first embodiment. 
         FIG. 2  depicts a plan view illustrating an ink-jet head depicted in  FIG. 1 . 
         FIG. 3  depicts a sectional view taken along a line III-III depicted in  FIG. 2 . 
         FIG. 4  explains a detecting conducting unit arranged in a cap and a connection relationship among the detecting conducting unit, a high voltage power source circuit, and a judging circuit. 
         FIG. 5A  depicts a signal outputted from the detecting conducting unit when the ink is ejected from the nozzle, and  FIG. 5B  depicts a relationship between the number of nozzles from which the ink is simultaneously ejected and a maximum voltage value of the signal depicted in  FIG. 5A . 
         FIG. 6  depicts a block diagram illustrating the electric configuration of the printer. 
         FIG. 7  depicts a flow chart illustrating a flow of the process when the viscosity of the ink contained in the nozzle is estimated at a timing other than a timing provided immediately before the recording on the recording paper. 
         FIGS. 8A and 8B  depict flow charts illustrating a flow of the nozzle judging process depicted in  FIG. 7 . 
         FIG. 9  depicts a flow chart illustrating a flow of the Nth group grouping process depicted in  FIG. 8B . 
         FIG. 10A  explains first nozzle groups and judgment results thereof in an example,  FIG. 10B  explains second nozzle groups and judgment results thereof in the example,  FIG. 10C  explains a third nozzle group and a judgment result thereof in the example,  FIG. 10D  explains a judgment result obtained when the ink is ejected from one nozzle of the third nozzle group in the example, and  FIG. 10E  explains judgment results to indicate whether or not each of the nozzles is the ejection-defective nozzle, as obtained from the judgment results depicted in  FIGS. 10A to 10D . 
         FIG. 11A  explains first nozzle groups and judgment results thereof in another example,  FIG. 11B  explains second nozzle groups and judgment results thereof in the another example,  FIG. 11C  explains a third nozzle group and a judgment result thereof in the another example,  FIG. 11D  explains a judgment result obtained when the ink is ejected from a remainder nozzle left over in the third group grouping process in the another example,  FIG. 11E  explains judgment results obtained when the ink is individually ejected from two nozzles of the third nozzle group in the another example, and  FIG. 11F  explains judgment results to indicate whether or not each of the nozzles is the ejection-defective nozzle, as obtained from the judgment results depicted in  FIGS. 11A to 11E . 
         FIG. 12  depicts a flow chart illustrating a flow of the process when a recording instruction is inputted. 
         FIGS. 13A and 13B  depict flow chart illustrating a flow of the nozzle judging process of a second embodiment. 
         FIG. 14A  explains first nozzle groups and judgment results thereof in an example of the second embodiment,  FIG. 14B  explains second nozzle groups and judgment results thereof in the example of the second embodiment,  FIG. 14C  explains a judgment result obtained when the ink is ejected from a remainder nozzle left over in the second group grouping process in the example of the second embodiment,  FIG. 14D  explains a third nozzle group and a judgment result thereof in the example of the second embodiment,  FIG. 14E  explains a judgment result obtained when the ink is ejected from one nozzle of the third nozzle group in the example of the second embodiment, and  FIG. 14F  explains judgment results to indicate whether or not each of the nozzles is the ejection-defective nozzle, as obtained from the judgment results depicted in  FIGS. 14A to 14E . 
         FIG. 15  depicts a flow chart illustrating a flow of the process when the viscosity of the ink contained in the nozzle is estimated at a timing other than a timing provided immediately before the recording on the recording paper in a modified embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present disclosure will be explained below. 
     &lt;Overall Configuration of Printer&gt; 
     As depicted in  FIG. 1 , a printer  1  according to the first embodiment (“liquid ejection apparatus” of the present disclosure) comprises, for example, a carriage  2 , a subtank  3 , an ink-jet head  4  (“liquid ejection head” of the present disclosure), a platen  5 , conveying rollers  6 ,  7 , and a maintenance unit  8 . 
     The carriage  2  is supported by two guide rails  11 ,  12  which extend in the scanning direction. The carriage  2  is connected to a carriage motor  86  (see  FIG. 6 ), for example, by the aid of an unillustrated belt. When the carriage motor  86  is driven, the carriage  2  is moved in the scanning direction along the guide rails  11 ,  12 . Note that in the following description, an explanation will be made while defining the right side and the left side in the scanning direction as depicted in  FIG. 1 . 
     The subtank  3  is carried on the carriage  2 . In this case, the printer  1  is provided with a cartridge holder  14 . Four ink cartridges  15  are removably installed to the cartridge holder  14 . Black, yellow, cyan, and magenta inks (“liquids” of the present disclosure) are stored in the four ink cartridges  15  as referred to in an order starting from one arranged on the right side in the scanning direction. The subtank  3  is connected to the four ink cartridges  15  installed to the cartridge holder  14  by the aid of four tubes  13 . Accordingly, the four color inks are supplied from the four ink cartridges  15  to the subtank  3 . 
     The ink-jet head  4  is carried on the carriage  2 , and the ink-jet head  4  is connected to a lower end portion of the subtank  3 . The four color inks are supplied from the subtank  3  to the ink-jet head  4 . Further, the ink-jet head  4  discharges the inks from a plurality of nozzles  10  which are formed on a nozzle surface  4   a  as the lower surface thereof. This structure will be explained in more detail below. That is, the plurality of nozzles  10  form nozzle arrays  9  by being arranged in the conveyance direction (“one direction” of the present disclosure) orthogonal to the scanning direction. The ink-jet head  4  has four arrays of the nozzle arrays  9  which are aligned in the scanning direction. Black, yellow, cyan, and magenta inks are ejected from the plurality of nozzles  10  as referred to starting from those for constructing the nozzle array  9  disposed on the right side in the scanning direction. 
     The platen  5  is arranged under or below the ink-jet head  4 , and the platen  5  is opposed to the plurality of nozzles  10 . The platen  5  extends over the entire length of the recording paper P (“medium” of the present disclosure) in the scanning direction, and the platen  5  supports the recording paper P from the lower position. The conveying roller  6  is arranged on the upstream side in the conveyance direction as compared with the ink-jet head  4  and the platen  5 . The conveying roller  7  is arranged on the downstream side in the conveyance direction as compared with the ink-jet head  4  and the platen  5 . The conveying rollers  6 ,  7  are connected to a conveying motor  87  (see  FIG. 6 ), for example, by the aid of unillustrated gears. When the conveying motor  87  is driven, then the conveying rollers  6 ,  7  are rotated, and the recording paper P is conveyed in the conveyance direction. 
     The maintenance unit  8  is provided in order that the inks contained in the ink-jet head  4  are ejected from the plurality of nozzles  10  by performing the suction purge as described later on. The maintenance unit  8  will be explained later on. 
     &lt;Ink-Jet Head&gt; 
     Next, the ink-jet head  4  will be explained. As depicted in  FIGS. 2 and 3 , the ink-jet head  4  is provided with a channel unit  21  and a piezoelectric actuator  22 . 
     &lt;Channel Unit&gt; 
     The channel unit  21  is formed by stacking four plates  31  to  34  in an order as referred to from the top. Each of the plates  31  to  33  is formed of a metal material such as stainless steel or the like. The plate  34  is formed of a synthetic resin material such as polyimide or the like. 
     The plate  34  is formed with four nozzle arrays  9  which are disposed adjacently in the scanning direction. Each of the nozzle arrays  9  includes the plurality of nozzles  10  which are arranged in the conveyance direction. The lower surface of the plate  34  serves as the nozzle surface  4   a  of the ink-jet head  4 . The plate  31  is formed with four pressure chamber arrays  29  which are disposed adjacently in the scanning direction. Each of the pressure chamber arrays  29  includes a plurality of pressure chambers  40  which are arranged in the conveyance direction. Each of the pressure chambers  40  has an elliptic planar shape in which the scanning direction is the longitudinal direction. Further, the plurality of pressure chambers  40  correspond to the plurality of nozzles  10  respectively. A left end portion in the scanning direction of each of the pressure chambers  40  is overlapped with corresponding one of the nozzles  10  in the upward-downward direction. 
     The plate  32  is formed with circular through-holes  42  which are provided at portions thereof overlapped in the upward-downward direction with the right end portions in the scanning direction of the plurality of pressure chambers  40  respectively. Further, the plate  32  is formed with circular through-holes  43  which are provided at portions thereof overlapped in the upward-downward direction with the nozzles  10  and the left end portions in the scanning direction of the plurality of pressure chambers  40  respectively. 
     The plate  33  is formed with four manifold channels  41  (“common channels” of the present disclosure). The four manifold channels  41  correspond to the four pressure chamber arrays  29 . The manifold channel  41  extends in the conveyance direction, and the manifold channel  41  is overlapped in the upward-downward direction with the right portions in the scanning direction of the plurality of pressure chambers  40  for constructing the corresponding pressure chamber array  29 . Accordingly, each of the pressure chambers  40  is communicated with the manifold channel  41  via the through-hole  42 . Further, a supply port  39  is provided at the end portion on the upstream side in the conveyance direction of each of the manifold channels  41 . The ink-jet head  4  is connected to channels formed in the subtank  3 , at the supply ports  39 . Accordingly, the inks are supplied from the supply ports  39  to the manifold channels  41 . Further, the plate  33  is formed with circular through-holes  44  which are provided at portions thereof overlapped in the upward-downward direction with the plurality of through-holes  43  and the plurality of nozzles  10  respectively. Accordingly, the respective nozzles  10  are communicated with the corresponding pressure chambers  40  via the through-holes  43 ,  44 . 
     Then, in the channel unit  21 , one individual channel  46  is formed by one nozzle  10 , the pressure chamber  40  corresponding to the nozzle  10 , and the through-holes  42  to  44 . 
     &lt;Piezoelectric Actuator&gt; 
     The piezoelectric actuator  22  is provided with a vibration plate  51 , a piezoelectric layer  52 , a common electrode  53 , and a plurality of individual electrodes  54 . The vibration plate  51  is formed of a piezoelectric material containing a main component of lead zirconate titanate which is mixed crystal of lead titanate and lead zirconate. The vibration plate  51  is arranged on the upper surface of the channel unit  21  to cover the plurality of pressure chambers  40 . Note that the vibration plate  51  may be formed of an insulative material other than the piezoelectric material, unlike the piezoelectric layer  52  explained below. 
     The piezoelectric layer  52  is formed of the piezoelectric material described above. The piezoelectric layer  52  is arranged on the upper surface of the vibration plate  51 , and the piezoelectric layer  52  continuously extends over the plurality of pressure chambers  40 . The common electrode  53  is arranged between the vibration plate  51  and the piezoelectric layer  52 , and the common electrode  53  continuously extends over the plurality of pressure chambers  40 . The common electrode  52  is connected to an unillustrated power source circuit, for example, by the aid of an unillustrated wiring member, and the common electrode  53  is retained at the ground electric potential. 
     The plurality of individual electrodes  54  correspond to the plurality of pressure chambers  40 . The individual electrode  54  has an elliptic planar shape which is one size smaller than the pressure chamber  40 . The plurality of individual electrodes  54  are arranged on the upper surface of the piezoelectric layer  52 . Each of the individual electrodes  54  is overlapped in the upward-downward direction with a central portion of the corresponding pressure chamber  40 . Further, the right end portion of each of the individual electrodes  54  in the scanning direction extends to the right side in the scanning direction until arrival at a position at which the individual electrode  54  is not overlapped in the upward-downward direction with the corresponding pressure chamber  40 . The right forward end in the scanning direction of each of the individual electrodes  54  serves as a connecting terminal  54   a . An unillustrated wiring member is connected to the connecting terminal  54   a . The individual electrode  54  is connected to driver IC  59  (see  FIG. 6 ) by the aid of the wiring member. Then, the driver IC  59  selectively applies any one of the ground electric potential and a predetermined driving electric potential (for example, about 20 V) individually to the plurality of individual electrodes  54 . 
     Further, each of the portions of the piezoelectric layer  52 , which is interposed by the common electrode  53  and each of the individual electrodes  54 , is polarized in the thickness direction, corresponding to the common electrode  53  and the plurality of individual electrodes  54  arranged as described above. Then, in the piezoelectric actuator  22  having the structure as described above, each of the portions, which is formed by the individual electrode  54  and the portions of the vibration plate  51 , the piezoelectric layer  52 , and the common electrode  53  overlapped in the upward-downward direction with each of the pressure chambers  40 , forms a driving element  50  for applying the pressure to the ink contained in the pressure chamber  40 . 
     In this case, in each of the driving elements  50  of the piezoelectric actuator  22 , when the electric potential of the individual electrode  54  is switched from the ground electric potential to the driving electric potential, the difference in the electric potential arises between the individual electrode  54  and the common electrode  53 . Accordingly, the electric field, which is provided in the thickness direction parallel to the polarization direction, is generated at the portion of the piezoelectric layer  52  interposed by the individual electrode  54  and the common electrode  53 . The portion of the piezoelectric layer  52  is shrunk in the horizontal direction by the electric field. The portions of the vibration plate  51  and the piezoelectric layer  52 , which are overlapped in the upward-downward direction with the pressure chamber  40 , are deformed as a whole so that the portions protrude toward the pressure chamber  40 . On the other hand, when the electric potential of the individual electrode  54  is switched from the driving electric potential to the ground electric potential, then the individual electrode  54  and the common electrode  53  have the same electric potential, and the portions of the vibration plate  51  and the piezoelectric layer  52 , which are overlapped in the upward-downward direction with the pressure chamber  40 , return to the state having been provided before the deformation. Then, the volume in the pressure chamber  40  is changed in accordance with the deformation of the portions of the vibration plate  51  and the piezoelectric layer  52  overlapped in the upward-downward direction with the pressure chamber  40  when the electric potential of the individual electrode  54  is switched between the ground electric potential and the driving electric potential. The pressure is applied to the ink contained in the pressure chamber  40 , and the ink is ejected from the nozzle  10  communicated with the pressure chamber  40 . 
     &lt;Maintenance Unit&gt; 
     Next, the maintenance unit  8  will be explained. As depicted in  FIG. 1 , the maintenance unit  8  is provided with a cap  61 , a suction pump  62 , and a waste liquid tank  63 . The cap  61  is arranged on the right side in the scanning direction as compared with the platen  5 . Then, when the carriage  2  is positioned at the maintenance position disposed on the right side in the scanning direction as compared with the platen  5 , the plurality of nozzles  10  are opposed to the cap  61 . 
     Further, the cap  61  is capable of ascending/descending by means of a cap ascending/descending mechanism  88  (see  FIG. 6 ). Then, when the cap  61  is moved upwardly by means of the cap ascending/descending mechanism  88  in a state in which the plurality of nozzles  10  are opposed to the cap  61  while positioning the carriage  2  at the maintenance position, the upper end portion of the cap  61  makes tight contact with the nozzle surface  4   a . Accordingly, the plurality of nozzles  10  are covered with the cap  61 . Note that the cap  61  of the present disclosure is not limited to one which covers the plurality of nozzles  10  by making tight contact with the nozzle surface  4   a . The cap  61  may cover the plurality of nozzles  10 , for example, by making tight contact with an unillustrated frame arranged around the nozzle surface  4   a  of the ink-jet head  4 . 
     The suction pump  62  is, for example, a tube pump. The suction pump  62  is connected to the cap  61  and the waste liquid tank  63 . Then, in the maintenance unit  8 , when the suction pump  62  is driven in the state in which the plurality of nozzles  10  are covered with the cap  61  as described above, it is possible to perform the so-called suction purge in which the inks contained in the ink-jet head  4  are ejected from the plurality of nozzles  10 . The inks, which are ejected from the ink-jet head  4 , are stored in the waste liquid tank  63 . Note that in this embodiment, the maintenance unit  8 , which performs the suction purge, corresponds to the “purge unit” of the present disclosure. 
     Note that in this section, for the purpose of convenience, the explanation has been made assuming that the cap  61  collectively covers all of the nozzles  10 , and the inks contained in the ink-jet head  4  are ejected from all of the nozzles  10  in the suction purge. However, the present disclosure is not limited thereto. For example, the cap  61  may be separately provided with a portion which covers the plurality of nozzles  10  for constructing the nozzle array  9  disposed on the rightmost side for ejecting the black ink and a portion which covers the plurality of nozzles  10  for constructing the three arrays of the nozzle arrays  9  disposed on the left side for ejecting the color inks (inks of yellow, cyan, and magenta), wherein any one of the black ink and the color inks contained in the ink-jet head  4  can be selectively ejected in the suction purge. 
     Further, as depicted in  FIG. 4 , a detecting conducting unit  66  (an example of a detecting conductor), which has a rectangular planar shape, is arranged in the cap  61 . The detecting conducting unit  66  is connected to a high voltage power source circuit  67  via a resistor  69 . Then, a predetermined positive electric potential (for example, about 300 V) is applied to the detecting conducting unit  66  by the high voltage power source circuit  67 . On the other hand, the channel unit  21  of the ink-jet head  4  is retained at the ground electric potential. Accordingly, a predetermined difference in electric potential is generated between the ink-jet head  4  and the detecting conducting unit  66 . A judging circuit  68  is connected to the detecting conducting unit  66 . The judging circuit  68  outputs a signal in accordance with a maximum voltage value Vm of a signal outputted from the detecting conducting unit  66 . 
     An explanation will be made in more detail below. For example, the voltage value of the detecting conducting unit  66  is V 0  in a state in which the ink is not ejected from the nozzle  10 . The difference in electric potential is generated between the ink-jet head  4  and the detecting conducting unit  66 . Therefore, the ink ejected from the nozzle  10  is charged or electrified. Therefore, when the ink is ejected from the nozzle  10  toward the detecting conducting unit  66  in the state in which the carriage  2  is positioned at the maintenance position, the electrified ink approaches the detecting conducting unit  66 . As depicted in  FIG. 5A , the voltage value of the detecting conducting unit  66  is raised until the ink is landed on the detecting conducting unit  66 . The voltage value arrives at a maximum voltage value Vm which is higher than the voltage value V 0 . Then, the voltage value of the detecting conducting unit  66  is gradually lowered to the voltage value V 0  after the electrified ink is landed on the detecting conducting unit  66 . That is, the voltage value of the detecting conducting unit  66  is changed in the driving period Td of the ink-jet head  4 . On the other hand, when the ink is not ejected from the nozzle  10 , then the voltage value is scarcely changed from V 0  as depicted by a broken line in  FIG. 5A , and the maximum voltage value Vm is V 0  in the driving period Td. 
     Further, as depicted in  FIG. 5B , the larger the number of the nozzles  10  from which the ink is simultaneously ejected is, the higher the maximum voltage value Vm is. The judging circuit  68  compares the relationship of magnitude between the maximum voltage value Vm and each of a plurality of threshold values set individually for the number of the nozzles  10  from which the ink is ejected simultaneously. The judging circuit  68  outputs a signal having a voltage value (output value) corresponding to the relationship of magnitude. 
     According to the fact as described above, the judging circuit  68  outputs the different signals between when the ink is ejected from the nozzle  10  and the maximum voltage value Vm is higher than V 0  and when the ink is not ejected from the nozzle  10  and the maximum voltage value Vm is V 0 . Further, when the ink is ejected from two or more nozzles  10 , the judging circuit  68  outputs a signal having a voltage value which is proportional to the number of nozzles from which the ink is actually ejected. In this situation, the number of ejection-defective nozzles from which the ink is not ejected is obtained by subtracting the number of the nozzles  10  from which the ink is actually ejected from the number of the nozzles  10  from which the ink is simultaneously ejected. The number of ejection-defective nozzles from which the ink is not ejected corresponds one-to-one to the number of the nozzles  10  from which the ink is ejected. Therefore, it is affirmed that the signal, which is outputted from the judging circuit  68 , is the signal which has the voltage value that differs in proportion to the number of ejection-defective nozzles. Note that in the first embodiment, the combination of the detecting conducting unit  66 , the high voltage power source circuit  67 , the resistor  69 , and the judging circuit  68  corresponds to the “signal output circuit” of the present disclosure. 
     Further, in this case, the positive electric potential is applied to the detecting conducting unit  66  by the high voltage power source circuit  67 . However, any negative electric potential (for example, about −300 V) may be applied to the detecting conducting unit  66  by the high voltage power source circuit  67 . In this case, conversely to the above, when the ink is ejected from the nozzle  10  toward the detecting conducting unit  66  in a state in which the carriage  2  is positioned at the maintenance position, then the electrified ink approaches the detecting conducting unit  66 , and the voltage value of the detecting conducting unit  66  is lowered until the ink is landed on the detecting conducting unit  66 . 
     &lt;Electric Configuration of Printer&gt; 
     Next, the electric configuration of the printer  1  will be explained. The operation of the printer  1  is controlled by the controller  80 . As depicted in  FIG. 6 , the controller  80  has, for example, CPU (Central Processing Unit)  81 , ROM (Read Only Memory)  82 , RAM (Random Access Memory)  83 , a flash memory  84 , and ASIC (Application Specific Integrated Circuit)  85 . The controller  80  controls the operations of, for example, the carriage motor  86 , the conveying motor  87 , the cap ascending/descending mechanism  88 , the high voltage power source circuit  67 , and the suction pump  62 . Further, the controller  80  controls the ink-jet head  4  by controlling the driver IC  59 . Further, the signal as described above is inputted from the judging circuit  68  into the controller  80 . 
     Note that as for the controller  80 , only CPU  81  may perform the various processes, only ASIC  85  may perform the various processes, or CPU  81  and ASIC  85  may cooperate to perform the various processes. Further, as for the controller  80 , one CPU  81  may perform the processes singly, or a plurality of CPU&#39;s  81  may perform the processes in a shared manner. Further, as for the controller  80 , one ASIC  85  may perform the processes singly, or a plurality of ASIC&#39;s  85  may perform the processes in a shared manner. 
     &lt;Process of Judgment of Ejection-Defective Nozzle or the Like&gt; 
     Next, an explanation will be made about the flow of the process when it is judged in the printer  1 , for example, whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle. In the printer  1 , it is judged, for example, whether or not the nozzle is the ejection-defective nozzle at a timing (for example, a regular or periodic timing) at which the recording is not performed on the recording paper P and a timing which is provided immediately before the recording on the recording paper P. 
     At the timing at which the recording is not performed on the recording paper P, it is judged, for example, whether or not the nozzle is the ejection-defective nozzle by performing the process in accordance with the flow depicted in  FIG. 7 . An explanation will be made in more detail below. At first, the controller  80  executes a nozzle judgment process (S 101 ) to judge whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle. The nozzle judgment process will be explained later on. 
     Subsequently, the controller  80  drives the ink-jet head  4  on the basis of the result of the nozzle judgment process of S 101  to perform the flashing for discharging the ink from the ejection-defective nozzle (S 102 ). Subsequently, the controller  80  drives the ink-jet head  4  so that the ink is individually discharged toward the detecting conducting unit  66  from each of the ejection-defective nozzles. It is judged whether or not the ejection-defective nozzle is recovered on the basis of the signal outputted from the judging circuit  68  in this situation (S 103 ). 
     Then, if all of the ejection-defective nozzles are recovered (S 104 : YES), the process is terminated as it is. If any unrecovered ejection-defective nozzle is present (S 104 : NO), then the controller  80  controls, for example, the carriage motor  86 , the cap ascending/descending mechanism  88 , and the suction pump  62  to perform the suction purge (S 105 ), and then the process is terminated. 
     &lt;Nozzle Judgment Process&gt; 
     Next, the nozzle judgment process of S 101  will be explained in detail. In the nozzle judgment process, as depicted in  FIG. 8A , the controller  80  firstly resets a natural number variable N to 1 (S 201 ). The first group grouping process is executed (S 202 ), and the routine proceeds to the process of S 203 . In the first group grouping process of S 202 , the controller  80  classifies the plurality of nozzles  10  of the ink-jet head  4  into a plurality of first nozzle groups each of which is composed of two or more nozzles  10 . In this procedure, the two or more nozzles  10 , which constitute each of the first nozzle groups, are selected and set from the plurality of nozzles  10  of the ink-jet head  4  so that the two or more nozzles  10 , which constitute each of the first nozzle groups, are the nozzles  10  which form the same nozzle array  9  and which are aligned adjacently in the conveyance direction. 
     In S 203 , the controller  80  drives the ink-jet head  4  so that the ink is simultaneously ejected from all of the two or more nozzles  10  for constructing the Nth nozzle group in relation to each of the plurality of Nth nozzle groups. In this procedure, the operation, in which the ink-jet head  4  is driven so that the ink is simultaneously ejected from all of the two or more nozzles  10  for constructing the Nth nozzle group, resides in such an operation that the driving elements  50 , which correspond to the two or more nozzles  10  for constructing the Nth nozzle group, are driven at the same timing. 
     Then, the controller  80  judges which condition of the first to third conditions is satisfied in relation to each of the plurality of Nth nozzle groups on the basis of the signal outputted from the judging circuit  68  in this situation (S 204 ). The first condition is such a condition that any ejection-defective nozzle is absent in the two or more nozzles  10  for constructing the Nth nozzle group. The second condition is such a condition that all of the two or more nozzles  10  for constructing the Nth nozzle group are the ejection-defective nozzles. The third condition is such a condition that only some nozzles  10  of the two or more nozzles  10  for constructing the Nth nozzle group are the ejection-defective nozzles. 
     Subsequently, the controller  80  judges that the nozzles  10 , which constitute the Nth nozzle group that satisfies the first condition, are not the ejection-defective nozzles, and the controller  80  judges that the nozzles  10 , which constitute the Nth nozzle group that satisfies the second condition, are the ejection-defective nozzles (S 205 ). 
     Subsequently, the controller  80  judges whether or not remainder nozzles are present (S 206 ), for which it has not been judged whether or not the remainder nozzles are the ejection-defective nozzles, the remainder nozzles being not classified into any nozzle group in the first group grouping process of S 202  or the Nth group grouping process of S 215  described later on. For example, if the number of the nozzles  10  which are the objects of the classification into the Nth nozzle group is indivisible by the number of the nozzles  10  for constructing each of the Nth nozzle groups, the remainder nozzles  10  are present. Then, if the remainder nozzles  10  are present (S 206 : YES), the ink-jet head  4  is driven so that the ink is ejected from each of the remainder nozzles  10 . It is judged whether or not each of the remainder nozzles  10  is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  in this situation (S 207 ), and the routine proceeds to S 208 . If the remainder nozzles  10  are not present (S 206 : NO), the routine proceeds to S 208  as it is. 
     In S 208 , it is judged whether or not all of the Nth nozzle groups satisfy the first condition or the second condition. Then, if all of the Nth nozzle groups satisfy the first condition or the second condition (S 208 : YES), the routine returns to the flow depicted in  FIG. 7 . 
     If only one Nth nozzle group, which satisfies the third condition, is present (S 208 : NO, S 209 : YES), the ink-jet head  4  is driven so that the ink is individually ejected from each of the remaining nozzles  10  obtained by excluding one nozzle  10  from the two or more nozzles  10  for constructing one Nth nozzle group which satisfies the third condition (S 210 ). Then, it is judged whether or not each of the two or more nozzles  10  for constructing one Nth nozzle group is the ejection-defective nozzle on the basis of the signal which is outputted from the judging circuit  68  in this situation and the signal which is outputted from the judging circuit  68  when the ink is simultaneously ejected from the two or more nozzles  10  in S 203  in relation to the one Nth nozzle group (S 211 ). The routine returns to the flow depicted in  FIG. 7 . 
     Specifically, in S 211 , it is judged whether or not each of the remaining nozzles  10  is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68 . Further, it is judged whether or not the one nozzle  10 , which is excluded from the Nth nozzle group as described above, is the ejection-defective nozzle on the basis of the result of the above and the number of ejection-defective nozzles obtained from the value of the signal outputted from the judging circuit  68  when the ink-jet head  4  is driven in S 203  in relation to the one Nth nozzle group. 
     Then, if the variable N is 1 (S 212 : YES), the routine returns to the flow depicted in  FIG. 7 . If the variable N is not less than 2 (S 212 : NO), the controller  80  successively judges whether or not the respective nozzles  10  of the first to [N−1]th nozzle groups, which satisfy the third condition, are the ejection-defective nozzles on the basis of the judgment result obtained in the process of S 211  and the number of ejection-defective nozzles obtained from the signal outputted from the judging circuit  68  when the ink is simultaneously ejected from the two or more nozzles in S 203  in relation to each of the first to [N−1]th nozzle groups which satisfy the third condition (S 213 ). 
     On the other hand, if a plurality of the Nth nozzle groups, which satisfy the third condition, are present (S 208 : NO, S 209 : NO), then the controller  80  increases the variable N by 1 (S 214 ), and the Nth group grouping process is executed (S 215 ). 
     In the Nth group grouping process of S 215 , the controller  80  classifies the remaining nozzles  10  obtained by excluding one nozzle  10  from each of the plurality of [N−1]th nozzle groups which satisfy the third condition, into one or a plurality of Nth nozzle group or nozzle groups each of which is composed of two or more nozzles  10  and each of which has the combination of the nozzles  10  different from those of the first to [N−1]th nozzle groups. In this procedure, the controller  80  sets the combination of the nozzles  10  in each of the Nth nozzle groups in accordance with a flow depicted in  FIG. 9 . 
     This procedure will be explained in detail. At first, the controller  80  sets the candidate for the nozzle  10  for constructing each of the Nth nozzle groups on the basis of the nozzle array  9  to which the nozzle  10  belongs (color of the ink to be ejected, i.e., manifold channel  41  to be communicated) (S 301 ). Specifically, the candidate for the combination of the nozzles  10  for constructing the Nth nozzle group is set so that the number of the Nth nozzle groups constructed by the two or more nozzles  10  for constructing the same nozzle array  9  is maximized. 
     Subsequently, if only one candidate as described above is set in the process of S 301  (S 302 : NO), the controller  80  sets the combination of the nozzles  10  for constructing the Nth nozzle group on the basis of the one candidate (S 303 ). The routine returns to the flow depicted in  FIGS. 8A and 8B . 
     If a plurality of candidates as described above, which are set in the process of S 301 , are present (S 302 : YES), the plurality of candidates are refined on the basis of the distance between the nozzles  10  in each of the Nth nozzle groups (S 304 ). Specifically, the candidates are refined to minimize the average value of the distance between the nozzles  10  in each of the Nth nozzle groups, from the plurality of candidates set in the process of S 301 . 
     If only one candidate as described above is present after the refinement in the process of S 304  (S 305 : NO), the combination of the nozzles  10  for constructing the Nth nozzle group is set on the basis of the one candidate (S 303 ). The routine returns to the flow depicted in  FIGS. 8A and 8B . 
     If a plurality of candidates as described above are present after the refinement in the process of S 304  (S 305 : YES), the plurality of candidates are refined on the basis of the number of the nozzles  10  which are adjacent in the conveyance direction in the Nth nozzle group (S 306 ). Specifically, the candidates are refined to maximize the number of the Nth nozzle groups constructed by the nozzles  10  which are adjacent in the conveyance direction, from the plurality of candidates after the refinement in the process of S 304 . 
     If only one candidate as described above is present after the refinement in the process of S 306  (S 307 : NO), the combination of the nozzles  10  for constructing the Nth nozzle group is set on the basis of the one candidate (S 303 ). The routine returns to the flow depicted in  FIGS. 8A and 8B . 
     If a plurality of candidates as described above are present after the refinement in the process of S 306  (S 307 : YES), the plurality of candidates are refined on the basis of the elapsed time after the last time discharge (S 308 ). Specifically, the candidate is refined to minimize the average value of the difference in the elapsed time after the point in time at which the ink was ejected last time, in relation to the two or more nozzles  10  for constructing the Nth nozzle group, from the plurality of candidates after the refinement in the process of S 306 . 
     If only one candidate as described above is present after the refinement in the process of S 308  (S 309 : NO), the combination of the nozzles  10  for constructing the Nth nozzle group is set on the basis of the one candidate (S 303 ). The routine returns to the flow depicted in  FIGS. 8A and 8B . 
     If a plurality of candidates as described above are present after the refinement in the process of S 308  (S 309 : YES), the combination of the nozzles  10  for constructing the Nth nozzle group is set on the basis of any candidate of the plurality of candidates (S 310 ). The routine returns to the flow depicted in  FIGS. 8A and 8B . 
     With reference to  FIGS. 8A and 8B  again, the controller  80  returns to the process of S 203  after the Nth group grouping process in S 215 . Accordingly, the Nth group grouping process is executed (S 215 ), and the processes of S 203  to S 207  are repeated until all of the Nth nozzle groups satisfy the first condition or the second condition, or only one Nth nozzle group, which satisfies the third condition, is present. Then, if all of the Nth nozzle groups satisfy the first condition or the second condition (S 208 : YES), the routine returns to the flow depicted in  FIG. 7  as described above. Further, if only one Nth nozzle group, which satisfies the third condition, is present (S 209 : YES), the routine returns to the flow depicted in  FIG. 7  after executing the processes of S 210  to S 213  as described above. Then, it is judged whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle in accordance with the nozzle judgment process explained above. 
     &lt;Judgment to Judge Whether or not Nozzle is Ejection-Defective Nozzle by Nozzle Judgment Process&gt; 
     Next, an explanation will be made while referring to specified examples about the judgment to judge whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle in accordance with the nozzle judgment process described above. 
     At first, an example will be explained with reference to  FIGS. 10A to 10E  about a case in which the number of the nozzles  10  for constructing the Nth nozzle group is two. In this case, the number of the nozzles  10  of the ink-jet head  4  is actually, for example, about several hundreds. However, in order to simplify the explanation, in the example depicted in  FIGS. 10A to 10E , it is assumed that the number of the nozzles  10  of the ink-jet head  4  is 18. n 1  to n 18  depicted in  FIGS. 10A to 10E  correspond to eighteen nozzles  10 . 
     In the nozzle judgment process, in the first group grouping process of S 202 , as depicted in  FIG. 10A , the eighteen nozzles n 1  to n 18  are classified into nine first nozzle groups G 11  to G 19  each of which is composed of two nozzles  10 . 
     Then, as depicted in  FIG. 10A , it is judged that the nozzles n 1 , n 2 , n 13 , n 14 , which constitute the first nozzle groups G 11 , G 17  that satisfy the first condition, are not the ejection-defective nozzles, and it is judged that the nozzles  10  of n 5 , n 6 , which constitute the first nozzle group G 13  that satisfies the second condition, are the ejection-defective nozzles (S 205 ). In this case, in the judgment result depicted in  FIG. 10A , “O” indicates that the first condition is satisfied. “X” indicates that the second condition is satisfied, and “Δ” indicates that the third condition is satisfied. 
     Further, according to the result depicted in  FIG. 10A , the six first nozzle groups G 12 , G 14  to G 16 , G 18 , G 19  satisfy the third condition (S 209 : NO). Therefore, in accordance with the second group grouping process (S 215 ), for example, as depicted in  FIG. 10B , the remaining nozzles  10  of n 3 , n 7 , n 9 , n 11 , n 15 , n 17 , which are obtained by excluding one nozzle  10  from each of the first nozzle groups G 12 , G 14  to G 16 , G 18 , G 19  that satisfy the third condition, are classified into three second nozzle groups G 21  to G 23  each of which is composed of two nozzles  10 . Then, it is judged that the nozzles n 3 , n 7 , which constitute the second nozzle group G 21  that satisfies the first condition, are not the ejection-defective nozzles. 
     Further, the two second nozzle groups G 22 , G 23  satisfy the third condition (S 209 : NO). Therefore, in accordance with the third groove grouping process (S 215 ), for example, as depicted in  FIG. 10C , the third nozzle group G 31  is formed by the nozzles  10  of n 9 , n 15  which are obtained by excluding one nozzle  10  from each of the second nozzle groups G 22 , G 23  that satisfy the third condition. In this case, only one third nozzle group G 31  satisfies the third condition (S 209 : YES). Therefore, for example, as depicted in  FIG. 10D , the ink-jet head  4  is driven so that the ink is ejected from the nozzle  10  of n 9  which is one of the two nozzles  10  of n 9 , n 15  for constructing the third nozzle group G 31  (S 210 ). Then, according to this result, it is judged that the nozzle  10  of n 9  is the ejection-defective nozzle. In this case, “abnormal” of the judgment result depicted in  FIG. 10D  indicates that the nozzle is the ejection-defective nozzle. Further, according to this result and the result depicted in  FIG. 10C , it is judged that the nozzle  10  of n 15  is not the ejection-defective nozzle. 
     Then, in the following procedure, the remaining nozzles  10 , for which it has not been judged whether or not the nozzles  10  are the ejection-defective nozzles, are successively judged whether or not the nozzles  10  are the ejection-defective nozzles, in accordance with the information of the nozzles  10  for which it has been judged whether or not the nozzles  10  are the ejection-defective nozzles and the results depicted in  FIGS. 10A to 10C . Accordingly, as depicted in  FIG. 10E , it is possible to judge whether or not the nozzles  10  of n 1  to n 18  are the ejection-defective nozzles. Note that in  FIG. 10E , “normal” indicates that the nozzle is not the ejection-defective nozzle, and “defective discharge” indicates that the nozzle is the ejection-defective nozzle. 
     Next, an example will be explained with reference to  FIGS. 11A to 11F  about a case in which the number of the nozzles  10  for constructing the Nth nozzle group is three. 
     In this example, in the first nozzle group grouping process of S 202 , as depicted in  FIG. 11A , the eighteen nozzles n 1  to n 18  are classified into six first nozzle groups G 11  to G 16  each of which is composed of three nozzles  10 . 
     Then, it is judged that the nozzles  10  of n 1  to n 3 , n 16  to n 18 , which constitute the first nozzle groups G 11 , G 16  that satisfy the first condition, are not the ejection-defective nozzles, and it is judged that the nozzles  10  of n 7  to n 9 , which constitute the first nozzle group G 13  that satisfies the second condition, are the ejection-defective nozzles (S 205 ). Further, in this procedure, according to the result of the process of S 203 , the numbers of the ejection-defective nozzles are acquired for the respective nozzles of the first nozzle groups G 12 , G 14 , G 15  which satisfy the third condition. In this case, parenthesized numerical values described in the judgment result depicted in  FIG. 11A  indicate the numbers of the ejection-defective nozzles. 
     Further, in this example, the three first nozzle groups G 12 , G 14 , G 15  satisfy the third condition. Therefore, in accordance with the second group grouping process (S 215 ), for example, as depicted in  FIG. 11B , the remaining nozzles  10  of n 4 , n 5 , n 10 , n 11 , n 13 , n 14 , which are obtained by excluding one nozzle  10  from each of the first nozzle groups G 12 , G 14 , G 15  that satisfy the third condition, are classified into two second nozzle groups G 21 , G 22  each of which is composed of three nozzles  10 . Then, it is judged that the second nozzle groups G 21 . G 22  satisfy the third condition, and the results are acquired such that the numbers of the ejection-defective nozzles in the second nozzle groups G 21 , G 22  are one and two respectively. 
     Then, the two second nozzle groups G 21 , G 22  satisfy the third condition. Therefore, in accordance with the third group grouping process (S 215 ), for example, as depicted in  FIG. 11C , the third nozzle group G 31  is formed by the three nozzles  10  of n 5 , n 10 , n 14  of the nozzles  10  of n 5 , n 10 , n 13 , n 14  which are obtained by excluding one nozzle from each of the two second nozzle groups G 21 , G 22 . Then, it is judged that the third nozzle group G 31  satisfies the third condition, and the result is acquired such that the number of the ejection-defective nozzle is one in the third nozzle group G 31 . Further, as depicted in  FIG. 11D , the ink-jet head  4  is driven so that the ink is ejected from the nozzle  10  of n 13  (remainder nozzle) which is left over in the third group grouping process. It is judged that the nozzle is not the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  (S 207 ). 
     Then, only one third nozzle group G 31  satisfies the third condition. Therefore, as depicted in  FIG. 11E , the ink-jet head  4  is driven so that the ink is individually ejected from each of the remaining nozzles  10  of n 5 , n 10  obtained by excluding one nozzle  10  from the three nozzles  10  of n 5 , n 10 , n 14  for constructing the third nozzle group G 31 . Then, it is judged that each of the nozzles  10  of n 5 , n 10  is not the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  in this procedure. Further, it is judged that the nozzle  10  of n 14  is the ejection-defective nozzle according to this result and the result depicted in  FIG. 11C . 
     Then, in the following procedure, the remaining nozzles  10 , for which it has not been judged whether or not the nozzles  10  are the ejection-defective nozzles, are successively judged whether or not the nozzles  10  are the ejection-defective nozzles, in accordance with the information of the nozzles  10  for which it has been judged whether or not the nozzles  10  are the ejection-defective nozzles and the results depicted in  FIGS. 11A to 11D . Accordingly, as depicted in  FIG. 11F , it is possible to judge whether or not the nozzles  10  of n 1  to n 18  are the ejection-defective nozzles. 
     &lt;Control During Recording&gt; 
     Further, in the printer  1 , when the recording instruction to instruct the recording of the image on the recording paper P is inputted, the controller  80  performs the process in accordance with the flow depicted in  FIG. 12 . 
     This process will be explained in detail below. That is, the controller  80  executes the first group grouping process in the same manner as S 202  (S 401 ). Subsequently, the controller  80  drives the ink-jet head  4  so that the ink is simultaneously ejected from all of the two or more nozzles  10  for constructing the first nozzle group in relation to each of the plurality of first nozzle groups (S 402 ). Then, the controller  80  judges which condition of the first to third conditions is satisfied by each of the plurality of first nozzle groups in the same manner as S 204  on the basis of the signal outputted from the judging circuit  68  (S 403 ). 
     Subsequently, the controller  80  drives the ink-jet head  4  on the basis of the result of the judgment in S 403 , and the flashing is performed to discharge the ink from the two or more nozzles  10  for constructing the first nozzle group which satisfies the second condition and the first nozzle group which satisfies the third condition (S 404 ). Then, after the flashing in S 404 , the recording process is executed (S 405 ). In the recording process of S 405 , the controller  80  performs the recording of the image on the recording paper P by alternately performing the recording pass in which the ink-jet head  4  is controlled to eject the ink from the plurality of nozzles  10  while moving the carriage  2  in the scanning direction by controlling the carriage motor  86  and the conveying operation in which the conveying motor  87  is controlled so that the recording paper P is conveyed by a predetermined distance by means of the conveying rollers  6 ,  7 . 
     Note that in this case, for example, in the example depicted in  FIG. 10A , the ink is discharged from the nozzles  10  of n 3  to n 12 , n 15  to n 18  for constructing the first nozzle groups G 12  to G 16 , G 18 , G 19  in the flashing of S 404 . As a result, the ink is also discharged from the nozzles  10  of n 3 , n 7 , n 10 , n 11 , n 15 , n 18  which are not the ejection-defective nozzles. Further, in the example depicted in  FIG. 11A , the ink is discharged from the nozzles  10  of n 3  to n 12 , n 4  to n 15  for constructing the first nozzle groups G 12  to G 15  in the flashing of S 404 . As a result, the ink is also discharged from the nozzles  10  of n 5 , n 10 , n 12 , n 13  which are not the ejection-defective nozzles. 
     &lt;Effect of Embodiment&gt; 
     In the first embodiment, the plurality of nozzles  10  of the ink-jet head  4  are classified into the plurality of first nozzle groups each of which is composed of the two or more nozzles  10 . Then, the ink-jet head  4  is driven so that the ink is simultaneously ejected from the two or more nozzles in relation to each of the plurality of first nozzle groups. It is judged which condition of the first to third conditions is satisfied by each of the plurality of first nozzle groups on the basis of the signal outputted from the judging circuit  68  in this situation. 
     Then, the following operation is repeated until all of the Nth nozzle groups satisfy the first condition or the second condition, or only one Nth nozzle group satisfies the third condition. That is, the nozzles, which are obtained by excluding one of the two or more nozzles in relation to each of the plurality of [N−1]th nozzle groups which satisfy the third condition, are classified into the Nth nozzle groups while changing the combination of the nozzles  10  as compared with the first to [N−1]th nozzle groups, and it is judged which condition of the first to third conditions is satisfied by each of the Nth nozzle groups. 
     It is understood that all of the nozzles for constructing the Nth nozzle group which satisfies the first condition are not the ejection-defective nozzles. Further, it is understood that all of the nozzles for constructing the Nth nozzle group which satisfies the second condition are the ejection-defective nozzles. Then, as for the Nth nozzle group which satisfies the first condition or the second condition, it is possible to decrease the number of times of the driving the ink-jet head  4  required to judge whether or not the nozzles are the ejection-defective nozzles, as compared with a case in which it is judged whether or not the nozzles are the ejection-defective nozzles by driving the ink-jet head  4  so that the liquid is individually ejected from each of the nozzles  10 . 
     Further, if only one Nth nozzle group, which satisfies the third condition, is present, the ink-jet head  4  is driven so that the ink is individually ejected from the remaining nozzles  10  obtained by excluding one nozzle  10  from the one Nth nozzle group. Accordingly, it is possible to judge whether or not each of the two or more nozzles  10  for constructing the one Nth nozzle group is the ejection-defective nozzle, on the basis of signal (signal corresponding to the number of the ejection-defective nozzles) outputted from the judging circuit  68  when the ink-jet head  4  is driven so that the ink is simultaneously ejected from the two or more nozzles  10  for constructing the one Nth nozzle group and the signal (signal to determine whether or not each of the remaining nozzles  10  is the ejection-defective nozzle) outputted from the judging circuit  68  when the ink-jet head  4  is driven so that the ink is individually ejected from the remaining nozzles  10  of the one Nth nozzle group. 
     Further, it is possible to judge whether or not each of the nozzles  10  for constructing the first to [N−1]th nozzle groups which satisfy the third condition is the ejection-defective nozzle, on the basis of the result obtained as described above and the signal outputted from the judging circuit  68  when the ink is simultaneously ejected from the two or more nozzles  10  for constructing the nozzle group, in relation to each of the first to [N−1]th nozzle groups which satisfy the third condition. 
     Then, according to the fact as described above, it is possible to maximally decrease the number of times of the driving of the ink-jet head  4  required to judge whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle. In the case of the first embodiment, if all of the first to Nth nozzle groups satisfy the third condition, the number of times of the driving of the ink-jet head  4  is the same as the number of the plurality of nozzles  10  of the ink-jet head  4 . However, in the first embodiment, as described later on, the combination of the nozzles  10  for constructing the Nth nozzle group is set so that the possibility is raised for the nozzles to have the same result of the judgment to judge whether or not the nozzles are the ejection-defective nozzles. Therefore, there is such a high possibility that at least one nozzle group of the first to Nth nozzle groups satisfies the first condition or the second condition. Then, if at least one nozzle group, which satisfies the first condition or the second condition, is present in the first to Nth nozzle groups, the number of times of the driving of the ink-jet head  4  is smaller than the number of the plurality of nozzles  10  of the ink-jet head  4 . 
     Further, in the first embodiment, the signal, which is outputted from the judging circuit  68  on the basis of the signal of the electric change of the detecting conducting unit  66  caused by the ink ejected from the nozzle  10 , differs between when the ink is ejected from the nozzle  10  and when the ink is not ejected from the nozzle  10 . Further, the signal of the electric change of the detecting conducting unit  66  caused by the ink ejected from the nozzle  10  and the signal outputted from the judging circuit  68  on the basis thereof have the voltage values which are proportional to the number of the ejection-defective nozzles. 
     Further, the nozzles  10 , which are mutually aligned adjacently in the conveyance direction and which are included in the plurality of nozzles  10  for constructing the same nozzle array  9 , have the short distance therebetween, and such nozzles  10  have the high possibility to have the same result of the judgment to judge whether or not the nozzles are the ejection-defective nozzles. Therefore, in the first embodiment, the two or more nozzles  10  for constructing the first nozzle group are set by selecting the nozzles  10  which are disposed adjacently in the conveyance direction, from the plurality of nozzles  10  of the ink-jet head  4 . Accordingly, the possibility is raised to increase the first nozzle groups which satisfy the first condition or the second condition. Then, in this case, the effect is enhanced to successfully decrease the number of times of the driving of the ink-jet head  4  in order to judge whether or not each of the plurality of nozzles  10  is the ejection-defective nozzle. 
     Further, the possibility is high for the nozzles  10  which mutually constitute the same nozzle array  9  (nozzles  10  which are communicated with the same manifold channel  41  and which have the same color of the ink to be ejected) to have the same result of the judgment to judge whether or not the nozzles  10  are the ejection-defective nozzles. Further, when the distance between the nozzles  10  is small, the possibility is high for the nozzles  10  to have the same result of the judgment to judge whether or not the nozzles  10  are the ejection-defective nozzles. Further, the possibility is especially high to have the same result of the judgment to judge whether or not the nozzles  10  are the ejection-defective nozzles, in relation to the nozzles  10  which are disposed adjacently in the conveyance direction and which are included in the nozzles  10  for constructing the same nozzle array  9 . Further, the possibility is high to have the same result of the judgment to judge whether or not the nozzles are the ejection-defective nozzles, in relation to the nozzles which have similar elapsed times after the liquid ejection head is driven last time so that the liquid is discharge. 
     In view of the above, in the first embodiment, in the Nth group grouping process performed if the variable N is not less than 2, as described above, the candidates of the combination of the nozzles  10  for the Nth nozzle group are set on the basis of the nozzle array  9  (concerning the color of the ink to be ejected and the communicated manifold channel  41 ). Then, if the plurality of candidates are present, in the following procedure, the plurality of candidates are refined respectively on the basis of distance between the nozzles  10  in each of the Nth nozzle groups, the number of the Nth nozzle groups constructed by the nozzles  10  which are disposed adjacently in the conveyance direction, and the elapsed time after the discharge performed last time in relation to the nozzles  10  for constructing the Nth nozzle group. Accordingly, the possibility is raised to increase the number of the Nth nozzle groups which satisfy the first condition or the second condition. As a result, the effect is enhanced to successfully decrease the number of times of the driving of the ink-jet head  4  required to judge whether or not each of the plurality of nozzles  10  is the ejection-defective nozzle. 
     Further, in the first embodiment, the ejection-defective nozzle can be recovered by performing the flashing in which the ink is discharged from the ejection-defective nozzle after the nozzle judgment process. 
     Further, in the first embodiment, the ink-jet head  4  is driven so that the ink is individually ejected from each of the ejection-defective nozzles after the flashing, and it is judged whether or not the ejection-defective nozzle is recovered on the basis of the signal outputted from the judging circuit in this situation. Then, if any ejection-defective nozzle, which is not recovered, is present, the suction purge is performed. Accordingly, the suction purge, in which the discharge amount of the ink is large as compared with the flashing, is performed only when any ejection-defective nozzle, which cannot be recovered by the flashing, is present. It is possible to maximally decrease the amount of the ink discharged in order to recover the ejection-defective nozzle. 
     Further, in the first embodiment, the nozzle judgment process is executed as described above at any timing other than the timing at which the recording is performed on the recording paper P, and it is judged whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle. On the contrary, the plurality of nozzles  10  of the ink-jet head  4  are classified into the plurality of first nozzle groups, immediately before the recording is performed on the recording paper P. After that, unlike the above, the flashing is performed so that the ink is discharged from the nozzles  10  for constructing the first nozzle group which satisfies the second condition and the first nozzle group which satisfies the third condition. 
     In this case, as for the first nozzle group which satisfies the third condition, the ink is also discharged by the flashing from some of the nozzles  10  which are not the ejection-defective nozzles. The discharge amount of the ink is increased. However, in this procedure, it is possible to maximally shorten the time until the recording is started on the recording paper P after the recording instruction for instructing the recording on the recording paper P is inputted. 
     Second Embodiment 
     Next, an explanation will be made about a second embodiment of the present disclosure. In the second embodiment, the judging circuit  68  compares the maximum voltage value Vm of the signal outputted from the detecting conducting unit  66  with a threshold value which corresponds to a case in which the ink is not ejected from any nozzle  10  (all nozzles  10  are the ejection-defective nozzles) when the ink is simultaneously ejected from the two or more nozzles  10  and a threshold value which corresponds to a case in which the ink is ejected from all nozzles  10  (all nozzles  10  are not the ejection-defective nozzles), and a signal, which has a voltage value corresponding to the result of the comparison, is outputted. That is, if the ink is simultaneously ejected from the two or more nozzles  10 , the judging circuit  68  outputs the signal which differs among when all of the nozzles  10  of the two or more nozzles are not the ejection-defective nozzles, when all of the nozzles  10  are the ejection-defective nozzles, and when only some of the nozzles  10  are the ejection-defective nozzles. Therefore, in the second embodiment, unlike the first embodiment, when the ink is ejected from the three or more nozzles  10 , if only some of the nozzles  10  are the ejection-defective nozzles, then it is impossible to acquire the number of the ejection-defective nozzles from the signal outputted from the judging circuit  68 . 
     &lt;Nozzle Judgment Process&gt; 
     Then, in the second embodiment, the controller  80  executes the process in accordance with a flow depicted in  FIGS. 13A and 13B  in the nozzle judgment process. The process will be explained in detail. The controller  80  executes the processes of S 501  to S 509  which are the same as or equivalent to the processes of S 201  to S 209  of the first embodiment. However, in the second embodiment, in the first group grouping process of S 502 , the plurality of nozzles  10  of the ink-jet head  4  are classified into a plurality of first nozzle groups each of which is composed of three or more nozzles  10 . 
     Further, if a plurality of Nth nozzle groups, which satisfy the third condition, are present (S 509 : NO), the controller  80  executes the processes of S 510 , S 511  which are the same as or equivalent to S 214 , S 215  of the first embodiment. However, in the second embodiment, in the Nth group grouping process of S 511 , the remaining nozzles  10 , which are obtained by excluding one nozzle  10  from each of the plurality of [N−1]th nozzle groups that satisfy the third condition, are classified into Nth nozzle groups each of which is composed of two nozzles  10  and which have combinations of the nozzles  10  different from those of the first to [N−1]th nozzle groups. 
     Further, if only one Nth nozzle group, which satisfies the third condition, is present (S 509 : YES), and N is 1 (S 512 : YES), then the controller  80  drives the ink-jet head  4  so that the ink is individually ejected from each of the three or more nozzles  10  for constructing the first nozzle group which satisfies the third condition (S 513 ). Then, it is judged whether or not each of the three or more nozzles  10  for constructing the first nozzle group which satisfies the third condition is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  in this situation (S 514 ). 
     On the other hand, if only one Nth nozzle group, which satisfies the third condition, is present (S 509 : YES), and N is not less than 2 (S 512 : NO), then the controller  80  executes the processes of S 515  to S 517  which are the same as or equivalent to S 210 , S 211 , S 213  of the first embodiment. Then, in the second embodiment, it is judged whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle in accordance with the nozzle judgment process explained above. 
     &lt;Judgment to Judge Whether or not Nozzle is Ejection-Defective Nozzle by Nozzle Judgment Process&gt; 
     Next, an explanation will be made while referring to specified examples about the judgment to judge whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle in accordance with the nozzle judgment process of the second embodiment. In this section, an example will be explained with reference to  FIGS. 14A to 14F , when the number of the nozzles  10  for constructing the first nozzle group is three. 
     In this example, in the first nozzle group grouping process of S 502 , eighteen nozzles n 1  to n 18  are classified into six first nozzle groups G 11  to G 16  each of which is composed of three nozzles  10  as depicted in  FIG. 14A . Then, it is judged that the nozzles n 1  to n 3 , n 16  to n 8 , which constitute the first nozzle groups G 11 , G 16  that satisfy the first condition, are not the ejection-defective nozzles, and it is judged that the nozzles  10  of n 7  to n 9 , which constitute the first nozzle group G 13  that satisfies the second condition, are the ejection-defective nozzles (S 505 ). 
     Further, the three first nozzle groups G 12 , G 14 , G 15  satisfy the third condition (S 509 : NO). Therefore, in the second group grouping process (S 511 ), for example, as depicted in  FIG. 14B , the nozzles  10  of n 4  to n 6 , n 10  to n 12 , n 13 , n 14 , which are included in the nozzles  10  of n 4  to n 6 , n 10  to n 12 , n 13  to n 15  for constructing the first nozzle groups G 12 , G 14 , G 15 , are classified into four second nozzle groups G 21  to G 24  each of which is composed of two nozzles  10 . Then, it is judged that the nozzles n 5 , n 13 , which constitute the second nozzle group G 22  that satisfies the first condition, are not the ejection-defective nozzles, and it is judged that the nozzles  10  of n 6 , n 11 , which constitute the second nozzle group G 23  that satisfies the second condition, are the ejection-defective nozzles (S 505 ). Further, as depicted in  FIG. 14C , the ink-jet head  4  is driven so that the ink is ejected from the nozzle  10  of n 5  which is the remainder nozzle that was leftover in the second group grouping process. It is judged that the nozzle  10  of n 15  is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  in this situation (S 507 ). 
     Further, in this example, the two nozzle groups G 21 , G 24  satisfy the third condition (S 509 : NO). Therefore, in accordance with the third group grouping process (S 511 ), for example, as depicted in  FIG. 14D , a third nozzle group G 31  is formed by n 4 , n 12  which are obtained by excluding one nozzle from each of the two second nozzle groups G 21 , G 24  that satisfy the third condition (S 511 ). Then, the one third nozzle group G 31  satisfies the third condition. Therefore, for example, as depicted in  FIG. 14E , the ink-jet head  4  is driven so that the ink is ejected from the remaining nozzle  10  of n 4  obtained by excluding one nozzle from n 4 , n 12  for constructing the third nozzle group G 31  (S 515 ). It is judged that the nozzle  40  of n 4  is the ejection-defective nozzle from the signal outputted from the judging circuit  68  in this situation (S 516 ). Further, according to this result and the result depicted in  FIG. 14D , it is judged that the nozzle  10  of n 12  is not the ejection-defective nozzle. 
     Then, in the following procedure, it is successively judged whether or not the remaining nozzles  10 , for which it has not been judged whether or not the nozzles  10  are the ejection-defective nozzles, are the ejection-defective nozzles, according to the information of the nozzle  10  for which it has been judged whether or not the nozzle  10  is the ejection-defective nozzle and the results depicted in  FIGS. 14A to 14E  (S 517 ). Accordingly, as depicted in  FIG. 14F , it is possible to judge whether or not the nozzles  10  of n 1  to n 18  are the ejection-defective nozzles. 
     In this example, the plurality of first nozzle groups, which satisfy the third condition, are present. However, only one first nozzle group, which satisfies the third condition, may be present. In this case, for example, if only the first nozzle group G 12  satisfies the third condition, the ink-jet head is driven so that the ink is individually ejected from each of the nozzles  10  of n 4  to n 6  (S 513 ). Then, it is judged whether or not each of the nozzles  10  of n 4  to n 6  is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  when the ink is ejected from each of the nozzles  10  (S 514 ). 
     &lt;Effect of Second Embodiment&gt; 
     In the second embodiment, the plurality of nozzles  10  of the ink-jet head  4  are classified into the plurality of first nozzle groups each of which is composed of the three or more nozzles  10 . Then, the ink-jet head  4  is driven so that the ink is simultaneously ejected from the three or more nozzles  10  in relation to each of the plurality of first nozzle groups. It is judged which condition of the first to third conditions is satisfied by each of the plurality of first nozzle groups on the basis of the signal outputted from the judging circuit  68  in this situation. 
     Then, if the plurality of first nozzle groups, which satisfy the third condition, are present, the two or more nozzles  10  of each of the plurality of first nozzle groups which satisfy the third condition are classified into the second nozzle groups each of which is composed of the two nozzles  10 , while changing the combination of the nozzles as compared with the plurality of first nozzle groups. It is judged which condition of the first to third conditions is satisfied by each of the second nozzle groups. 
     Further, the following operation is repeated for the case in which the variable N is not less than 3 until all of the Nth nozzle groups satisfy the first condition or the second condition or only one Nth nozzle group satisfies the third condition. That is, the nozzles, which are obtained by excluding one nozzle of the two nozzles in relation to each of the plurality of [N−1]th nozzle groups that satisfy the third condition, are classified into the Nth nozzle groups each of which is composed of the two nozzles  10 , while changing the combination of the nozzles as compared with the plurality of first to [N−1]th nozzle groups, and it is judged which condition of the first to third conditions is satisfied by each of the Nth nozzle groups. 
     It is understood that all of the nozzles  10 , which constitute the Nth nozzle group that satisfies the first condition, are not the ejection-defective nozzles. Further, it is understood that all of the nozzles  10 , which constitute the Nth nozzle group that satisfies the second condition, are the ejection-defective nozzles. Then, as for the Nth nozzle group which satisfies the first condition or the second condition, it is possible to decrease the number of times of the driving of the ink-jet head  4  required to judge whether or not the nozzle is the ejection-defective nozzle, as compared with a case in which it is judged whether or not the nozzle is the ejection-defective nozzle by driving the ink-jet head  4  so that the liquid is individually ejected from each of the nozzles. 
     Further, if only one first nozzle group, which satisfies the third condition, is present, the ink-jet head  4  is driven so that the ink is individually ejected from the three or more nozzles  10  for constructing the one first nozzle group. Accordingly, it is possible to judge whether or not each of the three or more nozzles  10  for constructing the one Nth nozzle group is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  when the ink is ejected from each of the three or more nozzles  10  for constructing the one Nth nozzle group. 
     Further, when the variable N is not less than 2, if only one Nth nozzle group, which satisfies the third condition, is present, then the ink-jet head  4  is driven so that the ink is ejected from the remaining nozzle  10  obtained by excluding one nozzle  10  from the one Nth nozzle group. Accordingly, it is possible to judge whether or not each of the two nozzles  10  for constructing the one Nth nozzle group is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  when the ink-jet head  4  is driven so that the ink is individually ejected from the remaining nozzle  10  of the one Nth nozzle group. 
     Further, it is possible to judge whether or not each of the nozzles  10  for constructing the first to [N−1]th nozzle groups which satisfy the third condition is the ejection-defective nozzle on the basis of the result obtained as described above and the signal outputted from the judging circuit  68  when the ink is simultaneously ejected from the two or more nozzles  10  for constructing the nozzle group in relation to each of the first to [N−1]th nozzle groups which satisfy the third condition. 
     Then, according to the fact as described above, it is possible to maximally decrease the number of times of the driving of the ink-jet head  4  required to judge whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle. In the case of the second embodiment, the larger the number of the first nozzle groups which satisfy the first condition or the second condition is, the smaller the number of times of the driving of the ink-jet head  4  is. Note that in the case of the second embodiment, for example, when the number of the first nozzle group or nozzle groups which satisfy(s) the first condition or the second condition is zero or small, the number of times of the driving of the ink-jet head  4  may be possibly larger than the number of the nozzles  10  of the ink-jet head  4 . However, also in the second embodiment, the combination of the nozzles  10  for constructing the Nth nozzle group is set so that the possibility is raised for the nozzles to have the same result of the judgment to judge whether or not the nozzles are the ejection-defective nozzles. Therefore, there is such a high possibility that the number of the first nozzle groups which satisfy the first condition or the second condition is increased. Then, in this case, the number of times of the driving of the ink-jet head  4  can be smaller than the number of the plurality of nozzles  10  of the ink-jet head  4 . 
     Modified Embodiment 
     The first and second embodiments of the present disclosure have been explained. However, the present disclosure is not limited to the first and second embodiments, and the present disclosure can be variously changed or modified as long as within the range defined in claims. 
     In the first embodiment, the number of the nozzles  10  for constructing the Nth nozzle group is the same irrelevant to the variable N. However, the present disclosure is not limited thereto. In the first embodiment, the number of the nozzles  10  for constructing the Nth nozzle group may differ depending on the variable N. 
     Further, in the first and second embodiments, the following operation is repeated until all of the Nth nozzle groups satisfy the first condition or the second condition, or only one Nth nozzle group satisfies the third condition. That is, the remaining nozzles  10 , which are obtained by excluding one nozzle  10  from each of the plurality of [N−1]th nozzle groups which satisfy the third condition, are classified into the Nth nozzle groups, and it is judged whether each of the Nth nozzle groups satisfies the first condition, satisfies the second condition, or satisfies the third condition. However, the present disclosure is not limited thereto. 
     For example, the following procedure is also available. That is, when the variable N is not less than 2 in the first and second embodiments, if a plurality of Nth nozzle groups, which satisfy the third condition, are present, then the ink-jet head  4  is driven so that the ink is individually ejected from each of the remaining nozzles  10  obtained by excluding one nozzle  10  in relation to each of the plurality of Nth nozzle groups which satisfy the third condition, and it is judged whether or not each of the nozzles  10  is the ejection-defective nozzle. 
     Further, in the processes of S 210 , S 211  of the first embodiment and S 515 , S 516  of the second embodiment, the ink-jet head  4  is driven so that the ink is individually ejected from each of the remaining nozzles  10  obtained by excluding one nozzle  10  from the nozzles  10  for constructing the Nth nozzle group which satisfies the third condition. Then, it is judged whether or not each of the nozzles  10  for constructing the Nth nozzle group which satisfies the third condition is the ejection-defective nozzle, on the basis of the signal outputted from the judging circuit  68  when the ink-jet head  4  is driven so that the ink is ejected from each of the nozzles  10  and the number of the ejection-defective nozzles obtained from the signal outputted from the judging circuit  68  when the ink-jet head  4  is driven so that the ink is simultaneously ejected from all of the nozzles  10  for constructing the Nth nozzle group which satisfies the third condition. However, the present disclosure is not limited thereto. For example, the following procedure is also available. That is, the ink-jet head  4  is driven so that the ink is individually ejected from each of the nozzles  10  for constructing the Nth nozzle group which satisfies the third condition, and it is judged whether or not each of the nozzles  10  for constructing the Nth nozzle group which satisfies the third condition is the ejection-defective nozzle on the basis of the signal outputted from the judging circuit  68  when the ink-jet head  4  is driven so that the ink is ejected from each of the nozzles  10 . 
     Further, in the first embodiment, the value of the signal outputted from the judging circuit  68  is proportional to the number of the ejection-defective nozzles. However, the present disclosure is not limited thereto. For example, in the first embodiment, the value of the signal outputted from the judging circuit  68  may be inversely proportional to the number of the ejection-defective nozzles. Also in this case, it is possible to acquire the number of the ejection-defective nozzles on the basis of the signal outputted from the judging circuit  68 . 
     Further, in the first and second embodiments, when the remaining nozzles  10 , which are obtained by excluding one nozzle  10  from each of the plurality of [N−1]th nozzle groups that satisfy the third condition, are classified into the Nth nozzle groups in the Nth group grouping process if the variable N is not less than 2, the candidate of the combination of the nozzles  10  in the Nth nozzle group is set on the basis of the nozzle array  9  (color of the ink to be ejected, communicated manifold channel  41 ). Then, if the plurality of candidates are present, in the following procedure, the plurality of candidates are refined respectively on the basis of the distance between the nozzles  10  in each of the Nth nozzle groups, the number of the Nth nozzle groups constructed by the nozzles  10  disposed adjacently in the conveyance direction, and the elapsed time elapsed after the discharge performed last time. However, the present disclosure is not limited thereto. 
     For example, the candidate of the combination of the nozzles  10  in the Nth nozzle group may be set on the basis of the any criterion other than the color of the ink to be ejected, of the four criteria of the color of the ink to be ejected, the distance between the nozzles  10  in each of the Nth nozzle groups, the number of the Nth nozzle groups constructed by the nozzles  10  disposed adjacently in the conveyance direction, and the elapsed time elapsed after the discharge performed last time. Then, if the plurality of candidates are present, the candidates may be refined by using the remaining three criteria in an arbitrary order. Further, the candidate may be set and refined on the basis of only some of the criteria of the four criteria. Further, the candidate may be set on the basis of only one criterion of the four criteria. If the plurality of candidates are present, the combination of the nozzles  10  for constructing the Nth nozzle group may be set on the basis of any one of the candidates. 
     Further, in the first and second embodiments, the nozzles  10 , which constitute each of the plurality of first nozzle groups, are set by selecting the nozzles  10  which are disposed adjacently in the conveyance direction, from the plurality of nozzles  10  of the ink-jet head  4 . However, the present disclosure is not limited thereto. The nozzles  10 , which constitute at least some of the first nozzle groups of the plurality of first nozzle groups, may be, for example, the nozzles  10  which are not disposed adjacently in the conveyance direction of the same nozzle array  9  or the nozzles  10  which constitute any different nozzle array  9 . 
     Further, in the first and second embodiments, it is judged whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle in accordance with the nozzle judgment process as described above at the timing immediately before the execution of the recording on the recording paper P. On the other hand, at the timing immediately before the execution of the recording on the recording paper P, the plurality of nozzles  10  of the ink-jet head  4  are classified into the plurality of first nozzle groups, and the flashing is performed so that the ink is discharged from each of the nozzles  10  for constructing the first nozzle group which satisfies the second and third conditions. However, the present disclosure is not limited thereto. For example, even at the timing immediately before the execution of the recording on the recording paper P, it may be judged whether or not each of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle in accordance with the nozzle judgment process as described above, and the flashing may be performed to discharge the ink from the ejection-defective nozzle. 
     Further, in the first and second embodiments, the flashing is performed so that the ink is discharged from the ejection-defective nozzle after the nozzle judgment process. If the ejection-defective nozzle, which is not recovered by the flashing, is present, the suction purge is performed. However, the present disclosure is not limited thereto. 
     In one modified embodiment, the ink-jet head  4  can selectively perform, as the flashing, any one of the first flashing and the second flashing in which the discharge amount of the ink is larger than that of the first flashing. Then, in this modified embodiment, as depicted in  FIG. 15 , the first flashing is performed so that the ink is discharged from the ejection-defective nozzle (S 602 ) after the nozzle judgment process (S 601 ). Subsequently, the ink-jet head  4  is driven so that the ink is individually discharged from the ejection-defective nozzle toward the detecting conducting unit  66  (S 603 ). Then, it is judged whether or not any unrecovered ejection-defective nozzle is present on the basis of the signal outputted from the judging circuit  68  in this situation (S 604 ). If any unrecovered ejection-defective nozzle is not present (S 604 : NO), the process is terminated as it is. If any unrecovered ejection-defective nozzle is present (S 604 : YES), then the second flashing is performed so that the ink is discharged from the unrecovered ejection-defective nozzle (S 605 ), and the process is terminated. 
     In this modified embodiment, the ink is discharged from the ejection-defective nozzle by means of the first flashing in which the discharge amount of the ink is small, and it is judged whether or not the ejection-defective nozzle is recovered. Then, only when the ejection-defective nozzle, which is not recovered by the first flashing, is present, the ink is discharged from the ejection-defective nozzle which is not recovered by the first flashing, by means of the second flashing in which the discharge amount of the ink is large. Accordingly, it is possible to maximally decrease the amount of the ink discharged to recover the ejection-defective nozzle. 
     Further, in the first and second embodiments, the ejection-defective nozzle is recovered by discharging the ink from the ejection-defective nozzle. However, the present disclosure is not limited thereto. For example, the conveyance amount may be changed in at least a part of the conveyance operation during the recording on the basis of what nozzle  10  of the plurality of nozzles  10  of the ink-jet head  4  is the ejection-defective nozzle, and the dot of the image to be recorded, which corresponds to the ejection-defective nozzle, may be allotted to another nozzle  10  which is not the ejection-defective nozzle to perform the recording pass. 
     Further, in the first and second embodiments, the ink contained in the ink-jet head  4  is discharged from the plurality of nozzles  10  by means of the suction purge. However, the present disclosure is not limited thereto. For example, a pressurizing pump may be provided at an intermediate portion of the tube  13  which connects the subtank  3  and the ink cartridge  15 . Alternatively, the printer may be provided with a pressurizing pump which is connected to the ink cartridge. Then, it is also allowable to perform the so-called suction purge in which the ink contained in the ink-jet head  4  is pressurized to discharge the ink contained in the ink-jet head  4  from the nozzles  10  by driving the pressurizing pump in a state in which the plurality of nozzles  10  are covered with the cap  61 . Note that in this case, the combination of the cap  61  and the pressurizing pump corresponds to the “purge unit” of the present disclosure. 
     Further, in the purge, it is also allowable to perform both of the suction with the suction pump  62  and the pressurization with the pressurizing pump. In this case, the combination of the maintenance unit  8  and the pressurizing pump corresponds to the “purge unit” of the present disclosure. 
     Further, in the first embodiment, the ink is ejected from the nozzle  10  by applying the pressure to the ink contained in the pressure chamber  40  by means of the driving element  50 . However, the present disclosure is not limited thereto. For example, the ink may be ejected from the nozzle by heating the ink to generate bubbles in the ink channel. 
     Further, in the embodiment described above, the signal is outputted from the judging circuit  68  in order to judge whether or not the nozzle is the ejection-defective nozzle and/or acquire the number of the ejection-defective nozzles, depending on the maximum voltage value Vm of the detecting conducting unit  66  as obtained when the ink is ejected from the nozzle  10  toward the detecting conducting unit  66 . However, the present disclosure is not limited thereto. 
     For example, a detecting electrode, which extends in the upward-downward direction, may be arranged. It is also allowable to output, from the judging circuit, the signal in order to judge whether or not the nozzle is the ejection-defective nozzle and/or acquire the number of the ejection-defective nozzles, depending on the voltage value of the detecting electrode as obtained when the ink is ejected so that the ink passes from the nozzle  10  through an area opposed to the detecting electrode. Alternatively, an optical sensor may be provided, which detects the ink ejected from the nozzle  10  and which distinguishes and detects the number of the inks ejected simultaneously. It is also allowable to output, from the optical sensor, the signal in order to judge whether or not the nozzle is the ejection-defective nozzle and/or acquire the number of the ejection-defective nozzles. 
     Alternatively, for example, in the same manner as described in US2007/0139461, a voltage detecting circuit (“signal output circuit” of the present disclosure), which detects the voltage change when the ink is ejected from the nozzle, may be connected to the plate on which the nozzles of the ink-jet head are formed. The signal, which depends on whether or not the nozzle  10  is the ejection-defective nozzle and which depends on the number of the ejection-defective nozzles, may be outputted from the voltage detecting circuit to the controller  80 . 
     Alternatively, for example, in the same manner as described in US2014/0300657, the ink-jet head may have a substrate which is provided with a temperature detecting element. Then, a first applied voltage may be applied to drive a heater in order to discharge the ink. After that, a second applied voltage may be applied to drive the heater so that the ink is not ejected. The signal, which corresponds to whether or not the nozzle  10  is the ejection-defective nozzle and which corresponds to the number of the ejection-defective nozzles, may be outputted on the basis of the temperature change detected by the temperature detecting element during a period until a predetermined time elapses after applying the second applied voltage. The disclosures of US2007/0139461 and US2014/0300657 are incorporated herein by reference. 
     Further, in the embodiment described above, the ink-jet head  4  is the so-called serial type head in which the ink-jet head  4  is carried on the carriage  2  and the ink is ejected from the plurality of nozzles  10  while being moved in the scanning direction. However, the present disclosure is not limited thereto. For example, the ink-jet head may be a so-called line head in which the ink-jet head extends over the entire length of the recording paper P in the scanning direction. In the embodiment described above, the controller  80  classifies the plurality of nozzles  10  of the ink-jet head  4  into a plurality of first nozzle groups each of which is composed of two or more nozzles  10  in the first group grouping process of S 202 . However, the present disclosure is not limited thereto. For example, the plurality of nozzles  10  of the ink-jet head  4  may be preliminary classified into a plurality of first nozzle groups. 
     In the foregoing description, the example has been explained, in which the present disclosure is applied to the printer for performing the recording on the recording paper P by ejecting the ink from the nozzles. However, the present disclosure is not limited thereto. The present disclosure is also applicable to any image recording apparatus for recording the image on any recording medium other than the recording paper, including, for example, T-shirts, sheets for outdoor advertisements, cases for mobile phone terminals such as smartphones or the like, corrugated cardboards, and resin members. Further, the present disclosure is also applicable to any liquid ejection apparatus for ejecting any liquid other than the ink, including, for example, metals and resins in liquid states.