Patent Publication Number: US-9403368-B2

Title: Printing apparatus and printing method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to printing apparatuses and printing methods. 
     2. Description of the Related Art 
     To date, image printing apparatuses are known which form an image on a print medium by ejecting ink to the print medium while moving a print head having a plurality of nozzles for ejecting ink arrayed therein relative to the print medium. In such image printing apparatuses, a so-called multipass method is employed through which a unit area of the print medium is scanned a plurality of times. 
     In such printing apparatuses, in a case in which the frequency at which ink is ejected is high, the following phenomenon is known to occur. Ink ejected through the nozzles drags in the air around the surface of the nozzles when moving toward the print medium, and thus the vicinity of the surface of a member in which the nozzles are formed (hereinafter, also referred to as a face) becomes depressurized. It is known that, in order to compensate for such a depressurized state, the air around the surface of the print medium moves toward the surface of the nozzles, and an air current is thus generated. Such an ascending air current toward the nozzles from the print medium tends to be greater as the amount of ink ejected at once is greater. A phenomenon in which an ink droplet generated as ejected ink splashes at the print medium or a so-called satellite ink droplet generated from a tail of ejected ink is dragged in by the ascending air current so as to travel in an opposite direction to adhere to the surface of the nozzles (hereinafter, referred to as face wetting) occurs. If ink is ejected through the nozzles after face wetting has occurred, the wet surface affects the ink at the time of ejecting the ink, and thus the ejection performance such as the direction in which the ink is ejected or the speed of the ejected ink varies. Therefore, the ink might not land on the print medium at a desired position. 
     Japanese Patent Laid-Open No. 1-71758 discloses a technique for suppressing a deterioration of printing quality due to face wetting, in which the number of dots formed in a unit area when the unit area is scanned by a print head is obtained and the surface of the nozzles is wiped on the basis of the obtained number of dots. According to the disclosed technique, the surface of the nozzles is wiped in a case in which the obtained number of dots exceeds a first value, and the surface of the nozzles is also wiped in a case in which a cumulative number of dots formed through scans spanning from a scan carried out immediately after the last time the surface is wiped to a scan to be carried out on a given unit area exceeds a second value. 
     However, according to the technique disclosed in Japanese Patent Laid-Open No. 1-71758, the face is wiped to remove the ink that has adhered to the face each time it is detected that face wetting has occurred at a notable level, and thus it takes a long time to completely form an image on the print medium. For example, in a case in which an image that is completely formed by ejecting ink on substantially the entire area of a single sheet of the print medium (hereinafter, referred to as a solid image) is to be printed, it is speculated that face wetting occurs fairly frequently, and thus an influence on the throughput of printing increases. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described problem, and the present invention is directed to providing a printing apparatus and a printing method that can suppress a deterioration of printing quality caused by face wetting and also suppress a decrease in the throughput. 
     According to an aspect of the present invention, a printing apparatus prints an image on a plurality of unit areas of a print medium by ejecting ink from a print head having at least one nozzle array in which a plurality of nozzles for ejecting ink are arrayed in an array direction while scanning the print head in a scan direction crossing the array direction, and each of the plurality of unit areas has a length in the array direction corresponding to a length of the nozzle array in the array direction. The printing apparatus includes a selecting unit configured to select either a first print mode or a second print mode with respect to each of the plurality of unit areas. The first print mode is a print mode for printing an image on the unit area by scanning the print head a first number of times, and the second print mode is a print mode for printing an image on the unit area by scanning of the print head a second number, which is greater than the first number, of times while a number of the nozzles ejecting ink each time the print head is scanned the second number of times is restricted. The printing apparatus further includes a wiping unit configured to wipe a surface of a nozzle member provided with the plurality of nozzles, an obtaining unit configured to obtain first information regarding a sum of ink ejection amounts in scans between a scan that is performed immediately after the surface of the nozzle member is wiped by the wiping unit and another scan in which ink is ejected to one of the unit areas, and a controlling unit configured to control printing according to either the first print mode or the second print mode selected by the selecting unit. In the printing apparatus, the selecting unit selects (i) the first print mode in a case in which a value indicated by the first information obtained by the obtaining unit is a first value, and (ii) the second print mode in a case in which the value indicated by the first information obtained by the obtaining unit is a second value that is greater than the first value. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an image printing apparatus according to an exemplary embodiment. 
         FIGS. 2A and 2B  are perspective views of a printing unit according to the exemplary embodiment. 
         FIG. 3  is a schematic diagram of a print head according to the exemplary embodiment. 
         FIG. 4  is a perspective view of a recovery unit according to the exemplary embodiment. 
         FIG. 5  is a block diagram illustrating a print controlling system according to the exemplary embodiment. 
         FIG. 6  is a flowchart illustrating a wetting coefficient calculation sequence according to the exemplary embodiment. 
         FIGS. 7A to 7D  are diagrams for describing the wetting coefficient calculation sequence according to the exemplary embodiment. 
         FIGS. 8A to 8C  are tables to be used to calculate the wetting coefficient according to the exemplary embodiment. 
         FIG. 9  is a flowchart for describing a printing method according to a first exemplary embodiment. 
         FIG. 10  is a diagram for describing a first print mode according to the exemplary embodiment. 
         FIGS. 11A to 11D  are diagrams for describing a second print mode according to the exemplary embodiment. 
         FIG. 12  is a flowchart for describing a printing method according to a second exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Exemplary Embodiment 
     Hereinafter, a first exemplary embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG. 1  is a perspective view illustrating an internal configuration of part of a printing apparatus  1000  according to the first exemplary embodiment of the present invention. 
     As illustrated in  FIG. 1 , the printing apparatus  1000  includes a sheet feeding unit  101 , a conveying unit  102 , a printing unit  103 , and a recovery unit  104 . The sheet feeding unit  101  feeds a print medium into the printing apparatus  1000 . The conveying unit  102  conveys the print medium, fed by the sheet feeding unit  101 , in a Y direction (conveying direction). The printing unit  103  prints an image on the print medium in accordance with image information. The recovery unit  104  carries out a recovery operation so as to maintain the ink ejection performance of a print head to thus maintain the quality of images to be printed. 
     The sheet feeding unit  101  feeds a print medium into the printing apparatus  1000 . The print media stacked on the sheet feeding unit  101  are separated by a sheet feeding roller (not illustrated) driven by a sheet feeding motor (not illustrated) and are fed, one by one, to the conveying unit  102 . 
     The conveying unit  102  conveys the print medium fed by the sheet feeding unit  101 . The print medium fed to the conveying unit  102  is pinched by a conveying roller  121 , driven by a conveying motor (not illustrated) and a pinching roller (not illustrated), and is conveyed through the printing unit  103 . 
     The printing unit  103  ejects ink on the print medium through the print head, which will be described later, in accordance with image data to thus print an image. The printing unit  103  includes a carriage  6 , which can reciprocate in an X direction (scan direction) crossing the Y direction, and print cartridges  3   a  and  3   b , which will be described later, mounted in the carriage  6 . 
     The carriage  6  is supported so as to be capable of reciprocating in the X direction along a guide rail disposed in the printing apparatus  1000 . The carriage  6 , when printing on the print medium, reciprocates over a print area along with a carriage belt  124  driven by a carriage motor (not illustrated). The position and the speed of the carriage  6  are detected by an encoder sensor (not illustrated) mounted on the carriage  6  and an encoder scale  125  that extends in the printing apparatus  1000 , and the movement of the carriage  6  is controlled in accordance with the detected position and speed. Ink is ejected from the print cartridges  3   a  and  3   b  while the carriage  6  is moved, and thus the print medium can be printed. The print medium printed by the printing unit  103  is pinched by a discharging roller (not illustrated) driven synchronously with the conveying roller  121  by the conveying unit  102  and a spurring roller (not illustrated) pressurized by the discharging roller and is then discharged to the outside of the printing apparatus  1000 . 
     The recovery unit  104  wipes ink droplets that have adhered to the surface of the nozzles so as to restore the surface of the nozzles to a normal state. The recovery unit  104  includes a capping mechanism, which will be described later, for covering the nozzles after printing is carried out, and a wiping mechanism, which will be described later, for wiping the surface of the nozzles. The recovery unit  104  further includes a slider  7  (see  FIG. 4 ) capable of sliding within a predetermined area so as to follow the movement of the carriage  6  while the carriage  6  is moving toward the recovery unit  104 . 
       FIG. 2A  is a diagram for describing, in detail, the print cartridges  3   a  and  3   b  according to the present exemplary embodiment. The print cartridge  3   a  includes a print head  5   a , which is part of a print head  5 , for ejecting chromatic color inks, namely, a cyan ink, a magenta ink, and a yellow ink. The print cartridge  3   a  includes three ink tanks (not illustrated) for storing the respective chromatic color inks, and the print head  5   a  that is formed integrally with the ink tanks and serves to eject the inks supplied from the ink tanks. Meanwhile, the print cartridge  3   b  includes a print head  5   b , which is part of the print head  5 , for ejecting a black ink. The print cartridge  3   b  includes an ink tank (not illustrated) for storing the black ink, and the print head  5   b , which will be described later, that is formed integrally with the ink tank and serves to eject the ink supplied from the ink tank. The print head  5   a  includes a nozzle array  512  for ejecting a cyan ink, a nozzle array  513  for ejecting a magenta ink, and a nozzle array  514  for ejecting a yellow ink; and the print head  5   b  includes a nozzle array  522  for ejecting a black ink. The nozzle arrays  512 ,  513 ,  514 , and  522  are provided in the surface of nozzle members  530 . The nozzle arrays  512  to  514  for the chromatic color inks may be formed in a common nozzle member  530  or may be formed separately in separate nozzle members  530 . 
     Although a mode in which the print cartridge  3   a  for the chromatic color inks and the print cartridge  3   b  for the black ink, as illustrated in  FIG. 2A , are used has been described in the present exemplary embodiment, the present exemplary embodiment may employ a different mode. For example, a print cartridge  3  that includes the print head  5  may instead be used, and the print head  5  may include the nozzle array  512  for the cyan ink, the nozzle array  513  for the magenta ink, the nozzle array  514  for the yellow ink, and the nozzle array  522  for the black ink, as illustrated in  FIG. 2B . In the print cartridge  3 , ink tanks  4  for the respective colors are provided so as to be removable from the print head  5  and can thus be replaced. 
       FIG. 3  is a diagram for describing, in detail, a surface of the print head  5  at which the nozzle face is provided according to the present exemplary embodiment. 
     The nozzle array  512  for the cyan ink, the nozzle array  513  for the magenta ink, and the nozzle array  514  for the yellow ink each include 64 nozzles, namely, a nozzle N 0  to a nozzle N 63 , formed in the surface of the nozzle member  530 , and the 64 nozzles are arrayed in the Y direction (predetermined direction) at a density of 600 nozzles per inch (i.e., 600 dpi). Meanwhile, the nozzle array  522  for ejecting the black ink includes 80 nozzles, namely, a nozzle N 0  to a nozzle N 79 , formed in the surface of the nozzle member  530 , and the 80 nozzles are arrayed in the Y direction at a density of 600 dpi. It should be noted that “the surface of the nozzles” as used in the present exemplary embodiment refers substantially to the surface of the nozzle member  530 . The nozzle array  512  for the cyan ink, the nozzle array  513  for the magenta ink, and the nozzle array  514  for the yellow ink are disposed in the X direction with a distance d provided between mutually adjacent nozzle arrays among the nozzle arrays  512 ,  513 , and  514 . Meanwhile, the nozzle array  522  for the black ink is disposed so as to be spaced apart from the nozzle array  514  for the yellow ink by a distance D, which is greater than the distance d, in the X direction with the center of the nozzle array  522  in the Y direction being flush with the center of the nozzle array  514  for the yellow ink in the Y direction along the X direction. 
       FIG. 4  is a diagram for describing, in detail, the recovery unit  104  according to the present exemplary embodiment. 
     The slider  7  serving as a wiper holder includes caps  1 A and  1 B. The cap  1 A is configured to cover the nozzles arrayed in the nozzle arrays  512 ,  513 , and  514 ; and the cap  1 B is configured to cover the nozzles arrayed in the nozzle array  522 . In addition, wipers  8  and  9  are provided in the slider  7 . The wiper  8  is configured to wipe the surface of the nozzles arrayed in the nozzle arrays  512 ,  513 , and  514 ; and the wiper  9  is configured to wipe the surface of the nozzles arrayed in the nozzle array  522 . 
     Upon the recovery unit  104  being moved through the slider  7  to a wiping position at which the wipers  8  and  9  can wipe the surface of the nozzle member  530  (the surface of the nozzles), the recovery unit  104  is moved in the X direction relative to the printing unit  103  so as to wipe the surface of the nozzles while allowing the wipers  8  and  9  to make contact with the surface of the nozzles. 
     The slider  7  is capable of moving in a Z direction between the aforementioned wiping position and a wiper standby position at which the wipers  8  and  9  are spaced apart from the print head  5 . The slider  7  is also capable of moving in a predetermined area so as to follow the movement of the carriage  6  while the carriage  6  moves toward the recovery unit  104 . The slider  7  moves along cam surfaces of slider cams  13   a  and  13   b  provided in a slider base unit  13 . Through this configuration, the height of the slider  7  in the Z direction relative to the surface of the nozzles is controlled to a predetermined height at each position along the moving direction of the carriage  6 . 
       FIG. 5  is a block diagram illustrating a configuration of a print controlling system according to the present exemplary embodiment. 
     A central processing unit (CPU)  600  controls each of the components to be described below and carries out data processing through a main pass line  605 . Specifically, the CPU  600  carries out head driving control, carriage driving control, and data processing while using the components described below in accordance with a program stored in a read only memory (ROM)  601 . 
     A random access memory (RAM)  602  is used as a work area for the data processing and so on by the CPU  600 , and a hard disk or the like may be used in place of the RAM  602  in some cases. An image input unit  603  includes an interface with a host apparatus (not illustrated), and temporarily stores an image inputted from the host apparatus. An image signal processing unit  604  carries out data processing, such as color conversion processing of converting RGB data, which is the inputted image data, to CMYK data and binarization processing of expressing the CMYK data, which has been expressed as multiple values, as binary data. 
     A CPU  630  for controlling a reading unit, such as a scanner, includes an input image processing unit  631 , and is connected to a CCD sensor  632 , a CCD sensor driving unit  633 , an image output unit  634 , and the main pass line  605 . The CCD sensor driving unit  633  controls input driving of the CCD sensor  632 . The input image processing unit  631  subjects a signal from the CCD sensor  632  to processing such as A/D conversion and shading correction. The image processed in the input image processing unit  631  is transmitted to the image input unit  603  through the image output unit  634 . 
     An operating unit  606  includes a start key and so on, which allows a user to carry out control. A recovery system controlling circuit  607  controls a recovery operation, such as auxiliary ejection, in accordance with a recovery processing program stored in the RAM  602 . Specifically, the recovery system controlling circuit  607  drives the print head  5 , the wipers  8  and  9 , and the caps  1 A and  1 B. 
     A head drive controlling circuit  615  controls driving of an electrothermal converter provided for ejecting ink from the print head  5 , and causes the print head  5  to eject ink for auxiliary ejection and printing. A carriage drive controlling circuit  616  and a conveyance controlling circuit  617  control the movement of the carriage  6  and the conveyance of the print medium, respectively, in accordance with programs. 
     A warming heater is provided on a substrate on which the electrothermal converter for ejecting ink from the print head  5  is provided, and the ink inside the print head  5  can be heated to a desired temperature. A thermistor  612  is also provided on the stated substrate so as to measure the temperature of the ink inside the print head  5 . The thermistor  612  does not need to be provided on the substrate but may be provided outside the print head  5 , such as in the vicinity of the print head  5 . 
       FIG. 6  is a flowchart for describing a method for calculating a wetting coefficient that indicates the degree of face wetting according to the present exemplary embodiment.  FIGS. 7A to 7D  are schematic diagrams for describing the process of calculating the wetting coefficient according to the present exemplary embodiment. 
     In S 601 , the number of printing dots of each of the cyan ink, the magenta ink, and the yellow ink is counted for each of a plurality of determination areas  30  each having a size of 40 dots at 600 dpi in the X direction by 64 dots at 600 dpi in the Y direction (dot counting). Here, since the nozzle array  522  for the black ink is spaced apart from the other nozzle arrays  512 ,  513 , and  514 , ejection of the black ink has little influence on the occurrence of the ascending air current. Therefore, the dot counting is carried out only for the cyan ink, the magenta ink, and the yellow ink in the present exemplary embodiment. 
     In S 602 , the number Q of printing dots of each of the cyan ink, the magenta ink, and the yellow ink in each of the plurality of determination areas  30  obtained in S 601  is divided by a scan number N of a given print mode among print modes that can be set by the printing apparatus  1000 , in which the given print mode allows a unit area to be printed at the minimum scan number. In the present exemplary embodiment, an image can be printed on the print medium through a single scan, and thus the number Q of the printing dots is divided by N=1. 
     In S 603 , the ratio of the number of printing dots of each of the inks obtained in S 602  to the maximum number of dots that can be formed by one of the inks in a single determination area  30  (hereinafter, referred to as a printing duty) is calculated. Here, the maximum number of dots that can be formed by one of the inks is 40×64. Consequently, as illustrated in  FIG. 7B , the printing duty of each of the inks in each of the plurality of determination areas  30 , which corresponds to the image illustrated in  FIG. 7A , can be obtained. For example, with reference to  FIG. 7A , a cyan ink component is at the maximum in the third and fourth columns of the sixth and seventh bands. Therefore, as illustrated in  FIG. 7B , the printing duties in the third and fourth columns of the sixth and seventh bands take high values of 80% to 98%. 
     In S 604 , a wetting coefficient is calculated on the basis of two of the printing duties, obtained in S 603 , corresponding to two of the cyan ink, the magenta ink, and the yellow ink and a table, stored in advance in the ROM  601  of the printing apparatus  1000 , indicating how likely face wetting is to occur when two of the inks are ejected, which will be described later. The wetting coefficient indicates the wettability in each of the determination areas  30 , and a weighting coefficient is defined for the wettability corresponding to each of the two printing duties. 
       FIGS. 8A to 8C  are diagrams for describing tables that are used to calculate the wetting coefficient for each of the printing duties described above and that define the weighting coefficients defined for each of the printing duties of the two inks. 
       FIG. 8A  illustrates a table that defines the weighting coefficient that indicates how likely face wetting is to occur as the magenta ink and the yellow ink are ejected and that is defined for each of the printing duties of the magenta ink and the yellow ink. The weighting coefficient has been calculated with the intensity of the ascending air current to be generated between the ejected magenta ink and yellow ink taken into consideration. Meanwhile,  FIG. 8B  illustrates a table that defines the weighting coefficient that indicates how likely face wetting is to occur as the cyan ink and the yellow ink are ejected and that is defined for each of the printing duties.  FIG. 8C  illustrates a table that defines the weighting coefficient that indicates how likely face wetting is to occur as the cyan ink and the magenta ink are ejected and that is defined for each of the printing duties. 
     These wetting coefficients differ depending on parameters such as the positional relationship of the nozzle arrays ejecting the two inks, the ejection characteristics of the nozzles, and physical properties of the inks. Thus, the tables illustrated in  FIGS. 8A, 8B, and 8C  are preferably set as appropriate in accordance with the above-described device characteristics of the printing apparatus  1000 . 
     In the present exemplary embodiment, it has been found through experimentation that ejection of inks from a pair of the nozzle array  512  for the cyan ink disposed at one end in the X direction and the nozzle array  514  for the yellow ink disposed at the other end in the X direction has the largest influence on occurrence of an ascending air current. Therefore, in the present exemplary embodiment, the weighting coefficient in each of the tables is set such that the weighting coefficient in the table corresponding to the cyan ink and the yellow ink illustrated in  FIG. 8B  is greater than the weighting coefficient in the table corresponding to the magenta ink and the yellow ink illustrated in  FIG. 8A  and the weighting coefficient in the table corresponding to the cyan ink and the magenta ink illustrated in  FIG. 8C . 
       FIG. 7C  illustrates the wetting coefficients calculated for the entire determination areas  30  on the basis of the printing duties illustrated in  FIG. 7B  and the tables illustrated in  FIGS. 8A, 8B, and 8C  of the weighting coefficients indicating how likely face wetting is to occur as two given inks are ejected. 
     For example, with reference to the printing duty illustrated in  FIG. 7B , in a determination area  30  located on the fourth column of the sixth band, the printing duty of the cyan ink is 90%, and the printing duty of the yellow ink is 90%. With reference to the table illustrated in  FIG. 8B , the weighting coefficient that indicates how likely face wetting is to occur as the cyan ink and the yellow ink are ejected in accordance with the stated printing duties is found to be 25. Thus, it can be determined that the wetting coefficient of the cyan ink and the yellow ink in the aforementioned determination area  30  is 25. In a similar manner, the wetting coefficient that indicates how likely face wetting is to occur as illustrated in  FIG. 7C  can be calculated for all of the determination areas  30  through the processing in S 604 . 
     In S 605 , the maximum wetting coefficient among the plurality of wetting coefficients in each of the determination areas  30  obtained in S 604  is selected, and this maximum wetting coefficient is obtained as a wetting coefficient XNure (second information) in each of the determination areas  30 . Through this, data indicating the wetting coefficients XNure in all of the determination areas  30  as illustrated in  FIG. 7D  can be obtained. In addition, by calculating a sum Total_XNure of the wetting coefficients in the determination areas  30  within a single band, how likely face wetting is to occur through a scan of the stated band can be determined. 
       FIG. 9  is a flowchart for describing a printing method according to the present exemplary embodiment. 
     In S 901 , binary data is obtained through binarization for each of the inks, and in S 902 , the wetting coefficient calculation sequence described above is carried out. 
     In  5903 , it is determined whether or not the wetting coefficients XNure in the plurality of determination areas  30  within a single unit area to be scanned have been calculated. Here, a unit area corresponds to an area on the print medium that can be printed through a scan performed by the print head  5 . The length of the unit area in the X direction corresponds to the entire width of the print medium, and the length in the Y direction corresponds to the length of the nozzle arrays. In the present exemplary embodiment, the unit area has a size of 240 dots at 600 dpi in the X direction by 64 dots at 600 dpi in the Y direction. It should be noted that a single unit area includes six determination areas  30 . Hereinafter, an image formed within a unit area may be referred to as a band in some cases. If it is determined that the wetting coefficients XNure have been calculated, the processing proceeds to S 904 . 
     In S 904 , as illustrated in  FIG. 7D , the sum Total_XNure of the wetting coefficients XNure in the plurality of determination areas  30  within the single unit area is calculated. Thereafter, the processing proceeds to S 905 . 
     In S 905 , the obtained sum Total_XNure corresponding to the scan of the single unit area is added to a cumulative value of the sum Total_XNure of the scans from a scan carried out immediately after the last time the surface of the nozzles has been wiped so as to obtain a cumulative value ΣNure (first information). Thereafter, the processing proceeds to S 906 . 
     In S 906 , it is determined whether or not the cumulative value ΣNure calculated in S 905  is less than a wetting threshold value THNure. Here, the wetting threshold value THNure corresponds to a value at which it is estimated that the ejection performance of the nozzles deteriorates notably if any additional ink droplet adheres to the surface of the nozzles. The wetting threshold value THNure can be set to an appropriate value in accordance with the physical properties of the nozzles and the inks. In the present exemplary embodiment, the wetting threshold value THNure is set to 100. 
     If the cumulative value ΣNure is less than the wetting threshold value THNure, the processing proceeds to S 908 . In S 908 , a first print mode, which will be described later, is set for the scan of the single unit area, and printing is then carried out. Meanwhile, if the cumulative value ΣNure is equal to or greater than the wetting threshold value THNure, the processing proceeds to S 907 . In S 907 , a second print mode, which will be described later, is set for the scan of the single unit area and printing is then carried out. After the processing in either of S 907  and S 908  is carried out, the processing proceeds to S 909 . 
     In S 909 , it is determined whether or not all of the received print data has been rasterized. If it is determined that not all of the received print data has been rasterized, the processing returns to S 902 , and in S 902 , the wetting coefficient XNure of a unit area corresponding to a subsequent scan is calculated. If it is determined that all of the received print data has been rasterized, it is determined that printing on a single sheet of the print medium has been completed. The processing then proceeds to S 910 , and in S 910 , the print medium is discharged. 
     After the print medium has been discharged, in S 911 , it is determined whether or not the cumulative value ΣNure is less than a wiping threshold value THWipe. Here, the wiping threshold value THWipe corresponds to a value for estimating as to whether or not face wetting occurs to such an extent that the ejection performance deteriorates notably due to face wetting when printing is carried out on a subsequent sheet of the print medium. As in the wetting threshold value THNure, the wiping threshold value THWipe can be set to an appropriate value in accordance with the physical properties of the nozzles and the inks. In the present exemplary embodiment, the wiping threshold value THWipe is set to 90. 
     If the cumulative value ΣNure is less than the wiping threshold value THWipe, it is determined that the possibility of a deterioration of the ejection performance occurring due to face wetting is low when a subsequent sheet of the print medium is printed, and the printing is thus terminated. 
     Meanwhile, if the cumulative value ΣNure is greater than the wiping threshold value THWipe, the processing proceeds to S 912 , and in S 912 , the surface of the nozzles is wiped by the wipers  8  and  9 . Thereafter, the processing proceeds to S 913 . In S 913 , the cumulative value ΣNure is initialized to ΣNure=0, and the printing is then terminated. 
     In the present exemplary embodiment, as illustrated in  FIG. 7D , the cumulative value ΣNure is 106 when all of the received data has been rasterized, and the cumulative value ΣNure is thus greater than the wiping threshold value THWipe of 90. Therefore, the surface of the nozzles is wiped by the wipers  8  and  9  after the print medium is discharged. The stored cumulative value ΣNure is then initialized to ΣNure=0, and the printing is terminated. 
     Hereinafter, the first print mode and the second print mode mentioned above will be described in detail. 
       FIG. 10  is a schematic diagram for describing, in detail, the first print mode according to the present exemplary embodiment. 
     With the first print mode according to the present exemplary embodiment, an image is printed in a unit area  100  of the print medium through a single scan. Specifically, in a case in which the first print mode is set in the unit area  100 , the ink is ejected through the nozzles N 0  to N 63  of each of the nozzle array  512  for the cyan ink, the nozzle array  513  for the magenta ink, and the nozzle array  514  for the yellow ink while the print head  5  is moved in the X direction so as to print an image. 
     With the first print mode, the image can be completed in the unit area  100  through a single scan, and thus printing can be finished in a short period of time. 
       FIGS. 11A to 11D  are schematic diagrams for describing, in detail, the second print mode according to the present exemplary embodiment. 
     Unlike the first print mode, with the second print mode according to the present exemplary embodiment, an image is printed in the unit area  100  of the print medium through four instances of the scan. 
     With the second print mode, the nozzles N 0  to N 63  of each of the nozzle array  512  for the cyan ink, the nozzle array  513  for the magenta ink, and the nozzle array  514  for the yellow ink are divided into four nozzle groups, namely, a first nozzle group that includes 16 nozzles including the nozzle N 0  through the nozzle N 15 , a second nozzle group that includes 16 nozzles including the nozzle N 16  through the nozzle N 31 , a third nozzle group that includes 16 nozzles including the nozzle N 32  through the nozzle N 47 , and a fourth nozzle group that includes 16 nozzles including the nozzle N 48  through the nozzle N 63 . 
     When the second print mode is set in the unit area  100 , first, as illustrated in  FIG. 11A , the inks are ejected from the first nozzle group while the print head  5  is moved in the X direction so as to print the image in an area  100   a  located at the upstream side end of the unit area  100  in the Y direction. Then, without the print medium being conveyed, as illustrated in  FIG. 11B , the image is printed in an area  100   b  of the unit area  100  which is adjacent to the area  100   a  in the Y direction by ejecting the inks from the second nozzle group while the print head  5  is moved in the X direction. Thereafter, in a similar manner, without the print medium being conveyed, the image is printed in an area  100   c  by ejecting the inks from the third nozzle group as illustrated in  FIG. 11C , and the image is printed in an area  100   d  by ejecting the inks from the fourth nozzle group as illustrated in  FIG. 11D . When the printing by the fourth nozzle group is finished, it is determined that the printing on the unit area  100  has been completed, and the print medium is then conveyed in the Y direction. 
     With the second print mode, each of the areas  100   a ,  100   b ,  100   c , and  100   d  is printed through a single scan. Therefore, even in a case in which an image printed through the first print mode and an image printed through the second print mode are adjacent to each other in the Y direction, color unevenness between the images, which could be generated due to a difference in the number of instances of the printing scan between areas, can be suppressed, and an image in which unevenness between areas is not noticeable can be printed. 
     With the second print mode, the amount of ink ejected from the print head  5  in a single scan can be reduced, and thus occurrence of the ascending air current can be suppressed. Therefore, occurrence of face wetting can be suppressed as compared with the first print mode. 
     Meanwhile, the scan number on a unit area is greater with the second print mode than with the first print mode, and thus the throughput decreases as compared to the first print mode. However, while the time it takes for a single scan to finish is approximately 0.3 second to 1 second, the time it takes to restore a state that allows printing to be carried out again after the surface of the nozzles is wiped once is 10 seconds to 30 seconds. Thus, the decrease in the throughput caused by the increase in the scan number is smaller than the decrease in the throughput caused by wiping the surface of the nozzles. In this manner, the second print mode makes it possible to suppress the decrease in the throughput to a certain extent. 
     According to the present exemplary embodiment, the image is printed in a unit area through a single scan if the cumulative value ΣNure is less than the wetting threshold value THNure, and the image is printed in a unit area through four instances of the scan when the cumulative value ΣNure has reached or exceeded the wetting threshold value THNure. In the present exemplary embodiment, the wetting threshold value THNure is set to 100, and the cumulative value ΣNure in each of the unit areas is the value indicated in  FIG. 7D , as described above. Therefore, each of the first unit area (the first band) through the sixth unit area (the sixth band) is printed through a single scan as illustrated in  FIG. 10 , and the seventh and eighth unit areas (the seventh and eighth bands) are each printed through four instance of the scan as illustrated in  FIGS. 11A to 11D . 
     With the configuration described above, printing is carried out through a print mode that focuses more on improving the throughput while face wetting has not occurred to such an extent that affects the ejection performance, and printing is carried out through a print mode that focuses more on suppressing a decrease in the ejection performance caused by face wetting in a case in which the ejection performance may decrease due to face wetting. Accordingly, printing can be carried out while suppressing the decrease in the throughput and suppressing the decrease in the ejection performance caused by face wetting at the same time. 
     Second Exemplary Embodiment 
     In the first exemplary embodiment, a mode in which printing is carried with the first print mode if the cumulative value ΣNure is less than the wetting threshold value THNure and with the second print mode if the cumulative value ΣNure is equal to or greater than the wetting threshold value THNure has been described. 
     In the meantime, in the present exemplary embodiment, a mode in which the print mode to be set is determined with the wetting coefficient XNure in each of a plurality of determination areas  30  within a unit area taken into consideration, in addition to the relationship between the cumulative value ΣNure and the wetting threshold value THNure. 
     It should be noted that descriptions of configurations that are identical to those of the first exemplary embodiment described above will be omitted. 
       FIG. 12  is a flowchart for describing a printing method according to the present exemplary embodiment. 
     In the present exemplary embodiment, in S 1206 - 1 , processing similar to that in S 906  of the first exemplary embodiment is carried out. If the cumulative value ΣNure obtained when printing is to be carried out in a single unit area is less than the wetting threshold value THNure, the processing proceeds to S 1208 , and printing is carried out through the first print mode through which an image is completed in a unit area through a single scan. Meanwhile, if the cumulative value ΣNure is equal to or greater than the wetting threshold value THNure, the processing proceeds to S 1206 - 2 . 
     In S 1206 - 2 , it is determined whether or not there is a determination area  30 , among a plurality of determination areas  30  forming the single unit area, for which the wetting coefficient XNure is greater than a second wetting threshold value THNure2. Here, the second wetting threshold value THNure2 is a value that indicates how likely face wetting is to occur, and, as in the wetting threshold value THNure, can be set to an appropriate value in accordance with the physical properties of the nozzles and the inks. In the present exemplary embodiment, it is estimated that face wetting occurs if there is at least one determination area  30  for which the wetting coefficient XNure is equal to or greater than 1, and the second wetting threshold value THNure2 is thus set to 1. 
     If the cumulative value ΣNure is equal to or greater than the wetting threshold value THNure and if there is no determination area  30  within the single unit area for which the wetting coefficient XNure is equal to or greater than the second wetting threshold value THNure2, the processing proceeds to S 1208 . In S 1208 , the first print mode is set, and printing is carried out accordingly. Meanwhile, if the cumulative value ΣNure is equal to or greater than the wetting threshold value THNure and if there is at least one determination area  30  for which the wetting coefficient XNure is equal to or greater than the second wetting threshold value THNure2, the processing proceeds to S 1207 . In S 1207 , the second print mode through which the image is completed in a unit area through four instances of the scan is set, and printing is carried out accordingly. 
     In other words, in the present exemplary embodiment, the wetting threshold value THNure is set to 100, and the second wetting threshold value THNure2 is set to 1. The cumulative value ΣNure in each of the unit areas and the wetting coefficient XNure of the plurality of determination areas  30  forming each of the unit areas take the values indicated in  FIG. 7D , as described above. 
     Therefore, the cumulative value ΣNure is less than  100  in the unit areas including the first unit area (the first band) through the sixth unit area (the sixth band); thus, the first print mode is set, and printing is carried out in each of the stated unit areas through a single scan as illustrated in  FIG. 10 . 
     In the seventh unit area (the seventh band), the cumulative value ΣNure is equal to or greater than 100, and the wetting coefficient XNure is equal to or greater than 1 in the determination areas  30  of the third column and the fourth column; therefore, it is determined that face wetting is likely to occur. Thus, the second print mode is set in S 1207 , and the printing is carried out through four instances of the scan as illustrated in  FIGS. 11A to 11D . 
     In addition, in the eighth unit area (the eighth band), the cumulative value ΣNure is equal to or greater than  100 , and the wetting coefficient XNure is equal to or greater than 0 in each of the determination areas  30 . Therefore, although face wetting has occurred at the surface of the print head  5  to a certain extent, it is determined that face wetting does not progress further when the eighth unit area is printed. Thus, the first print mode is set in S 1208 , and the printing is carried out through a single scan as illustrated in  FIG. 10 . 
     Thereafter, processes in S 1209  to S 1213  are the same as those in S 909  to S 913  described with reference to  FIG. 9  in the first exemplary embodiment. 
     According to the configuration described above, even in a case in which face wetting has already occurred to a certain extent, if it is not likely that face wetting progresses further through a subsequent instance of the scan, printing is carried out through a print mode with a smaller scan number. Through this, the decrease in the throughput can be further suppressed while suppressing the deterioration of the ejection performance caused by face wetting. 
     Other Embodiments 
     Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     Although an assumption in each of the exemplary embodiments described above is that a primary factor for causing the ascending air current leading to the occurrence of face wetting to occur is ejection of inks from two nozzle arrays among the three nozzle arrays for ejecting the chromatic color inks and a mode in which the wetting coefficient is calculated on the basis of the ejection amount from the two nozzle arrays has been described, a different mode can be employed. The primary factor for causing the ascending air current to occur varies depending on various factors such as the placement of the nozzle arrays and the physical properties of the inks. For example, the wetting coefficient may be calculated on the basis of an amount of ink ejected from only one nozzle array that has the largest ink ejection amount among the three nozzle arrays for ejecting the chromatic color inks, or the wetting coefficient may be calculated on the basis of the sum of the amounts of inks ejected from the three nozzle arrays. In addition, although an amount of ink ejected from the nozzle array for the black ink is considered to have little influence on the occurrence of the ascending air current and is thus not used to calculate the wetting coefficient, the amount of ink ejected from the nozzle array for the black ink can also be used. 
     In addition, an assumption in each of the exemplary embodiments described above is that the ejection of ink from a pair of the nozzle array  512  for the cyan ink disposed at one end in the X direction and the nozzle array  514  for the yellow ink disposed at the other end in the X direction among the three nozzle arrays for ejecting the chromatic color inks has the greatest influence on the occurrence of the ascending air current. Therefore, a plurality of tables among which a table corresponding to the printing duties of the cyan ink and the yellow ink is the most dominant have been used to calculate the wetting coefficient as illustrated in  FIGS. 8A to 8C . Alternatively, such a mode as described below can also be employed. For example, such tables may be used that the wetting threshold value XNure for each printing duty is identical among a table corresponding to the printing duties of the cyan ink and the yellow ink, a table corresponding to the printing duties of the cyan ink and the magenta ink, and a table corresponding to the printing duties of the magenta ink and the yellow ink. 
     In addition, in each of the exemplary embodiments described above, a print mode through which an image is completed in a unit area through a single scan is employed as the first print mode, and a print mode through which an image is completed in a unit area through four instances of the scan is employed as the second print mode. Alternatively, a different mode can be employed. The effect described in each of the exemplary embodiments can be obtained as long as the second print mode is such a print mode that the permissible amount of ink to be ejected in a single scan is set to an amount with which the occurrence of the ascending air current can be suppressed as compared to the first print mode and that an image is printed through a larger number of instances of the scan as compared to the first print mode. For example, a print mode through which an image is completed in a unit area through two instances of the scan may be employed as the first print mode, and a print mode through which an image is completed in a unit area through eight instances of the scan may be employed as the second print mode. 
     In addition, although a mode in which, with the second print mode, an image is printed in such a manner that each of the nozzle arrays is divided into a plurality of nozzle groups so as to limit the number of nozzles that eject ink in a single scan and the inks are ejected successively through the nozzle groups without conveying the print medium between successive instances of the scan has been employed in each of the exemplary embodiments described above, a different mode can be employed. For example, an effect similar to the effect described in each of the exemplary embodiments can be obtained even with a mode in which while all of the nozzles, namely the nozzle NO to the nozzle N 63 , are used in a single scan, a scan in which ink is ejected to only one of the four adjacent columns within a unit area is carried out four times on the unit area. 
     In addition, although a mode in which the distance between the print medium and the surface of the nozzles stays constant and the wetting coefficient is calculated by using a table of a single pattern for each of the inks has been described in each of the exemplary embodiments described above, a different mode can be employed. For example, when the distance between the print medium and the surface of the nozzles varies, the degree of occurrence of the ascending air current or the distance in which an ink droplet rises by being taken into the ascending air current varies as well. Thus, it is preferable to calculate the wetting coefficient by using a plurality of tables that differ in accordance with the distance between the print medium and the surface of the nozzles. 
     According to the printing apparatus and the printing method of an example of the present invention, printing can be carried out while the deterioration of the printing quality caused by face wetting is suppressed and the throughput is improved at the same time. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-149874, filed Jul. 18, 2013, which is hereby incorporated by reference herein in its entirety.