Patent Publication Number: US-7909431-B2

Title: Image recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2007-194078, which was filed on Jul. 26, 2007, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image recording apparatus having a liquid ejection head which ejects liquid. 
     2. Description of Related Art 
     Japanese Unexamined Patent Publication No. 2006-247844 discloses an ink-jet printer including four ink-jet heads and a maintenance unit. The four ink-jet heads, each of which is elongated in a direction perpendicular to a paper conveyance direction, are arranged side by side in the paper conveyance direction. The maintenance unit performs maintenance on the four ink-jet heads. In the ink-jet printer, the maintenance unit has a support member, a blade (wiper), a wipe roller, and an ink receiver. The support member is horizontally movable in the direction perpendicular to the paper conveyance direction. The blade (wiper), the wipe roller, and the ink receiver are mounted on the support member. While the support member is located in a maintenance position opposed to the four ink-jet heads, a purge operation is performed to eject ink from nozzles of the ink-jet heads onto the support member. Then, while the ink receiver, the wipe roller, and the blade is moving together with the support member from the maintenance position to the withdrawal position, they sequentially get opposed to ink ejection faces to absorb and wipe off ink. In this way, maintenance is performed on the four ink-jet heads. 
     In a case where wipe-off of ink is ended in the middle of the ink ejection face, ink collected by the blade is accumulated to form an ink pool at a point of ending. If ink droplets accidentally drop from the ink pool, ink adheres to a conveyor belt or a paper being conveyed on the conveyor belt, to contaminate the conveyor belt or the paper. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image recording apparatus which can suppress contamination of a recording medium and/or a recording medium conveyance mechanism. 
     According to an aspect of the present invention, there is provided an image recording apparatus comprising: a plurality of liquid ejection heads respectively having ejection faces which are arranged in such a manner that the ejection faces form two rows extending in one direction and in addition two of the ejection faces included in different rows do not overlap each other along a direction perpendicular to the one direction with respect to an in-plane direction of the ejection faces, the plurality of liquid ejection heads being divided into one or more head groups each including two of the liquid ejection heads corresponding to the different rows; a recording medium conveyance mechanism which conveys a recording medium in the one direction while making the recording medium opposed to the ejection faces; a plurality of wipers which wipe the ejection faces of the liquid ejection heads; and a movement means which moves two of the wipers for wiping two ejection faces of the two liquid ejection heads belonging to each head group, in opposite directions along the perpendicular direction while keeping the two wipers in contact with the ejection faces, in such a manner that each of the wipers moves outward from an inner end portion of the ejection face located in a region where no droplet is ejected and which is close to a center with respect to the perpendicular direction, to a position which overlaps, along the vertical direction, at least either one of an outside region of a conveyance region where the recording medium is conveyed by the recording medium conveyance mechanism and an outside region of the recording medium conveyance mechanism. 
     In this aspect, a plurality of liquid ejection heads are arranged in such a manner that a plurality of ejection faces of the plurality of liquid ejection heads form two rows along one direction and two ejection faces included in different rows do not overlap each other along the perpendicular direction. When two wipers associated with two ejection faces included in different rows wipe the ejection faces, each of the wipers moves along the perpendicular direction from the inner end portion of the ejection face to a position which overlaps, along the vertical direction, at least either one of an outside region of a conveyance region where the recording medium is conveyed by the recording medium conveyance mechanism and an outside region of the recording medium conveyance mechanism. Accordingly, even if liquid drops from a liquid pool which is formed of liquid collected by the wipers, contamination of the recording medium conveyance mechanism and/or the recording medium can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a plan view of an essential part of an ink-jet printer according to a first embodiment of the present invention; 
         FIG. 2  is a sectional view as taken along line II-II illustrated in  FIG. 1 ; 
         FIG. 3  shows two head groups illustrated in  FIG. 1 , as seen from a bottom side thereof; 
         FIG. 4  is a block diagram schematically showing a controller; 
         FIGS. 5A ,  5 B, and  5 C show, over time, a purge operation on ink-jet heads and a wiping operation on ink ejection faces; 
         FIGS. 6A ,  6 B, and  6 C show, over time, a capping operation for covering the ink ejection faces with caps; 
         FIG. 7  is a plan view of an essential part of an ink-jet printer according to a second embodiment of the present invention; 
         FIG. 8  is a plan view of an essential part of an ink-jet printer according to a third embodiment of the present invention; and 
         FIG. 9  is a plan view of an essential part of an ink-jet printer according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a plan view of an essential part of an ink-jet printer according to a first embodiment of the present invention.  FIG. 2  is a sectional view as taken along line II-II illustrated in  FIG. 1 .  FIG. 3  shows two head groups illustrated in  FIG. 1 , as seen from a bottom side thereof. 
     As shown in  FIG. 1 , an ink-jet printer  1 , which is an image recording apparatus of this embodiment, is a color ink-jet printer of line type including two head groups  3   a  and  3   b  each of which is made up of four ink-jet heads  2  or liquid ejection heads. The ink-jet printer  1  has a paper feed unit (not shown) and a paper discharge unit (not shown) at upper and lower parts of  FIG. 1 , respectively. 
     In the ink-jet printer  1 , a paper conveyance mechanism  10  which is a recording medium conveyance mechanism is provided between the paper feed unit and the paper discharge unit, at a position opposed to the two head groups  3   a  and  3   b . The paper conveyance mechanism  10  conveys a paper as a recording medium to a position opposed to ink ejection faces  4  which are ejection faces of the eight ink-jet heads  2 . As shown in  FIG. 1 , the paper conveyance mechanism  10  has a pair of belt rollers  6  and  7  which are disposed so as to sandwich the two head groups  3   a  and  3   b  with respect to the sub scanning direction (i.e., an up-and-down direction in  FIG. 1 ), and an endless conveyor belt  8  which is wound on the pair of belt rollers  6  and  7  to be stretched therebetween. A conveyor motor  97  (see  FIG. 4 ) applies driving force to the belt roller  7  which is thereby rotated in a predetermined direction. As the belt roller  7  rotates in the predetermined direction, the conveyor belt  8  travels so as to convey the paper in a paper conveyance direction A (i.e., in a direction from up to down in  FIG. 1 ). 
     The conveyor belt  8  has a two-layer structure made up of a base material and urethane rubber. An outer surface of the conveyor belt  8 , that is, a conveyor face  9  has adhesiveness. A paper fed out from the paper feed unit is maintained due to the adhesiveness of the conveyor face  9 , and in this condition conveyed in the conveyance direction A. 
     Each ink-jet head  2  has a rectangular parallelepiped shape elongated in a main scanning direction (which is a direction perpendicular to the paper conveyance direction A: a perpendicular direction), as shown in  FIGS. 1 and 2 . Each ink-jet head  2  has a head main body  5  at its lower end. 
     A reservoir unit which temporarily stores ink therein is fixed to an upper face of the head main body  5 . The reservoir unit is partially covered with a cover  14 . Referring to  FIG. 1 , a tube joint  11  is connected to a left end of the reservoir unit. Ink supplied through the tube joint  11  is stored in an ink reservoir which is formed within the reservoir unit. The reservoir unit is longer than the head main body  5  with respect to the main scanning direction. Portions  12  of the reservoir unit extend out on both sides of the reservoir unit with respect to the main scanning direction. The portions  12  serve as a fixing portion to be fixed to an elevation frame (not shown). All of the ink-jet heads  2  are fixed to the elevation frame via the fixing portion. The elevation frame can be moved up and down by a head elevation mechanism  98  (see  FIG. 4 ). 
     Normally, the eight ink-jet heads  2  are disposed in a printing position (i.e., a position of the ink-jet head  2  shown in  FIG. 2 ). When the ink-jet heads  2  are in the printing position, each ink ejection face  4  and the conveyor face  9  of the conveyor belt  8  extend in parallel with each other and at a predetermined interval therebetween. With this structure, while a paper conveyed by the conveyor belt  8  is passing immediately below the eight head main bodies  5  sequentially, a desired image is formed on the paper. For a maintenance operation on the ink-jet head  2 , on the other hand, the head elevation mechanism  98  moves up the elevation frame. This brings the eight ink-jet heads  2  fixed to the elevation frame into a head maintenance position (see  FIG. 5A ) which is above and away from the printing position. 
     As shown in  FIG. 3 , small-diameter nozzles  4   a  which eject ink, an ink ejection region  4   b  which is formed by a collection of the nozzles  4   a , and an outside region  4   c  which surrounds the ink ejection region  4   b  are provided on a bottom face of the head main body  5 , that is, on the ink ejection face  4  of the ink-jet head  2 . 
     As shown in  FIGS. 1 and 3 , the eight ink-jet heads  2  are arranged in a zigzag pattern in such a manner that the ink ejection faces  4  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces  4  included in different rows do not overlap each other with respect to the main scanning direction. The eight ink-jet heads  2  are divided into two head groups  3   a  and  3   b  each of which includes four ink-jet heads  2 . Neighboring ink ejection faces  4  of the four ink-jet heads  2  are adjacent to each other with respect to the sub scanning direction (a direction parallel to the conveyance direction A: one direction) without misalignment in the main scanning direction. 
     The two head groups  3   a  and  3   b  are arranged in a zigzag pattern with their positions staggered. The ink ejection faces  4  in one of the two head groups  3   a  and  3   b  and the ink ejection faces  4  in the other of the two head groups  3   a  and  3   b  overlap each other along the sub scanning direction, so that print regions (i.e., ink ejection regions  4   b ) in the respective head groups  3   a  and  3   b  for making printing on a paper continue in the main scanning direction. 
     More specifically, the ink-jet heads  2  are arranged in such a manner that an interval in the main scanning direction between neighboring nozzles  4   a  existing in one ink ejection region is the same as an interval in the main scanning direction between an innermost (i.e., rightmost in  FIG. 3 ) one of the nozzles  4   a  formed in the ink ejection face  4  in the head group  3   a  and an innermost (i.e., leftmost in  FIG. 3 ) one of the nozzles  4   a  formed in the ink ejection face  4  in the head group  3   b.    
     The four ink-jet heads  2  belonging to each of the head groups  3   a  and  3   b  eject ink of four different colors (magenta, yellow, cyan, and black). 
     Next, a maintenance unit  60  which performs maintenance on the ink-jet heads  2  will be described. As shown in  FIGS. 1 and 2 , the maintenance unit  60  has four caps  61  and four wipers  63 , four caps  62  and four wipers  64 , a movement mechanism  70 , and a tray  69 . The four caps  61  and four wipers  63  are associated with four ink-jet heads  2  which belong to the head group  3   a . The four caps  62  and four wipers  64  are associated with four ink-jet heads  2  which belong to the head group  3   b . The movement mechanism  70  is a part of a movement means which moves the four caps  61  and wipers  63 , and four caps  62  and wipers  64  in opposite directions along the main scanning direction. The tray  69  contains therein the eight caps  61  and  62 , the eight wipers  63  and  64 , and the movement mechanism  70 . 
     The tray  69  has pass throughs  68   a  and  68   b  which extend through the tray  69  in a vertical direction. The pass throughs  68   a  and  68   b  are at positions opposed to the respective head groups  3   a  and  3   b . Each of the pass throughs  68   a  and  68   b  has a rectangular shape in a plan view, and has such a size that the four ink ejection faces  4  in each of the head groups  3   a  and  3   b  can entirely be opposed to the conveyor face  9 . 
     The caps  61  and  62  have the same shape and the same size, and each of them is made up of a base material  65  and an annular protrusion  66 . A shape of the base material  65  is similar to but slightly larger than the ink ejection region  4   b . The annular protrusion  66  stands at a periphery of the base material  65 . This structure allows the caps  61  and  62  to cover the ink ejection regions  4   b  with distal ends of the annular protrusions  66  being in contact with the outside regions  4   c  of the ink ejection faces  4 . Thereby, drying of ink existing within the nozzles  4   a  can be suppressed. 
     Two recesses  65   a  which open upward in the vertical direction are formed in the base material  65 . The two recesses  65   a  are disposed side by side along the main scanning direction. A through hole  65   b  is formed at a bottom of the recess  65   a . Since the through holes  65   b  are formed, ink ejected into the caps  61 ,  62  in a purge operation and collected within the recess  65   a  can be discarded through the through holes  65   b  into a not-shown waste ink reservoir. 
     As shown in  FIG. 2 , each of the caps  61 ,  62  is supported from below by three springs  67 . Since each of the caps  61 ,  62  is supported by the three springs  67 , impact caused when the annular protrusion  66  comes into contact with the ink ejection face  4  can be softened, so that the ink ejection face  4  is not easily damaged by the annular protrusion  66 . 
     The maintenance unit  60  also has a cap level adjusting mechanism  99  (see  FIG. 4 ) which moves down the caps  61 ,  62  when the wipers  63 ,  64  wipe the ink ejection faces  4 . As the cap level adjusting mechanism  99  moves down the caps  61 ,  62 , distal ends of the wipers  63 ,  64  come higher than the caps  61 ,  62 , and the caps  61 ,  62  no longer come into contact with the ink ejection faces  4  during a wiping operation. 
     As shown in  FIG. 1 , each of the wipers  63  and  64  is disposed between a corresponding ink-jet head  2  and a cap  61 ,  62  associated with this ink-jet head  2 . The wipers  63 ,  64  are made of an elastic material such as rubber. The wipers  63 ,  64  stand on later-described support plates  71 ,  72  which support the caps  61 ,  62  via the springs  67 . In a case where the caps  61 ,  62  are not moved down by the cap level adjusting mechanism  99 , the distal ends of the wipers  63 ,  64  are substantially at the same level as the base materials of the caps  61 ,  62 . 
     Each of the four wipers  63  for the head group  3   a  extends up to a length substantially equal to a width with respect to the sub scanning direction of the ink ejection face  4  in the head group  3   a . The four wipers  63  are separated from each other with respect to the sub scanning direction. Like the four wipers  63 , each of the four wipers  64  for the head group  3   b  also extends up to a length substantially equal to a width of the ink ejection face  4  in the head group  3   b . The four wipers  64  are separated from each other with respect to the sub scanning direction. As a result, even though the ink-jet heads  2  belonging to the head groups  3   a  and  3   b  eject ink of different colors, it can be prevented that, when the ink ejection faces  4  are wiped, ink collected by the wipers  63 ,  64  transfers to other ink ejection faces  4  adjacent thereto to cause ink colors to be mixed on the ink ejection faces  4 . 
     As shown in  FIGS. 1 and 2 , the movement mechanism  70  has two support plates  71  and  72 , one belt  73 , and a pair of belt rollers  74  and  75 . The two support plates  71  and  72  support the four caps  61  and the four caps  62 , respectively. The one belt  73  is coupled with inner end portions of the respective support plates  71  and  72  with respect to the sub scanning direction. The pair of belt rollers  74  and  75  are disposed on outer sides of the head groups  3   a  and  3   b  with respect to the main scanning direction. The belt  73  spans the pair of belt rollers  74  and  75 . 
     The support plate  71  supports the four caps  61  and the four wipers  63  associated with the four ink-jet heads  2  belonging to the head group  3   a . At this time, the four caps  61  are located in the same position with respect to the main scanning direction, and the four wipers  63  are located in the same position with respect to the main scanning direction. The cap  61  and the wiper  63  are positioned in such a manner that, in a plan view, they overlap the corresponding ink-jet head  2  along the main scanning direction and also overlap the ink-jet head  2  belonging to the head group  3   b  along the sub scanning direction. 
     The support plate  72  supports the four caps  62  and the four wipers  64  associated with the four ink-jet heads  2  belonging to the head group  3   b . At this time, the four caps  62  are located in the same position with respect to the main scanning direction, and the four wipers  64  are located in the same position with respect to the main scanning direction. The cap  62  and the wiper  64  are positioned in such a manner that, in a plan view, they overlap the corresponding ink-jet head  2  along the main scanning direction and also overlap the ink-jet head  2  belonging to the head group  3   a  along the sub scanning direction. 
     The pair of belt rollers  74  and  75  are rotatably supported on the tray  69  so as to position the belt  73  between the two head groups  3   a  and  3   b  within the tray  69 . As shown in  FIG. 2 , the pair of belt rollers  74  and  75  are disposed in such a manner that their diameter direction includes the vertical direction. The pair of belt rollers  74  and  75  are supported so as to be rotatable in clockwise and counterclockwise directions in  FIG. 2 . The belt  73  is disposed such that its portions extending in the main scanning direction are opposed to each other with respect to the vertical direction. This enables a space formed between the head groups  3   a  and  3   b  to be made small even when the belt  73  is disposed between the head groups  3   a  and  3   b . In addition, a length of the belt can be made relatively short, which can improve accuracy in conveyance of the caps  61  and  62 . 
     The belt  73  of this embodiment is a rubber-made flat belt having a very narrow width. However, a rubber belt having a circular section, or a metal-made wire may be adopted for the belt  73 . In short, any member may be adopted as long as it functions as a belt. 
     The support plate  71  is coupled with vertically-upper one of the portions of the belt  73  extending in the main scanning direction. The support plate  72  is coupled with vertically-lower one of the portions of the belt  73  extending in the main scanning direction. As shown in  FIG. 1 , four guide rails  68   c  extending in the main scanning direction are formed on the tray  69 . Each of the pass throughs  68   a  and  68   b  is sandwiched between the guide rails  68   c  with respect to the sub scanning direction. Among the four guide rails  68   c , upper two guide rails  68   c  shown in  FIG. 1  are opposed to both ends of the support plates  71  with respect to the sub scanning direction. The two guide rails  68   c  are fitted with recesses which are formed at the both ends of the support plates  71  so as to extend in the main scanning direction. Thereby, the two guide rails  68   c  are slidable along the recesses. The lower two guide rails  68   c  shown in  FIG. 1  are opposed to both ends of the support plates  72  with respect to the sub scanning direction. The two guide rails  68   c  are fitted with recesses which are formed at the both ends of the support plates  72  so as to extend in the main scanning direction. Thereby, the two guide rails  68   c  are slidable along the recesses. 
     With the maintenance unit  60  having the above-described structure, when a rotation motor  95  (see  FIG. 4 ) rotates the belt roller  74  in the counterclockwise direction in  FIG. 2 , the four caps  61  and the four wipers  63  mounted on the support plate  71  are moved together with the support plate  71 , leftward in  FIG. 1  from a withdrawal position (as shown in  FIG. 1 ) which is not opposed to the corresponding ink ejection faces  4 , while the four caps  62  and the four wipers  64  mounted on the support plate  72  are moved together with the support plate  72 , rightward in  FIG. 1  from a withdrawal position (as shown in  FIG. 1 ) which is not opposed to the corresponding ink ejection faces  4 . Thus, all the caps  61 ,  62 , and all the wipers  63 ,  64  can be moved to a position (maintenance position) opposed to the ink ejection faces  4 . 
     At this time, each of the wipers  63 ,  64  moves from an inner end portion of the ink ejection face  4  of the corresponding ink-jet head  2  with respect to the main scanning direction (which inner end portion is near one end of the outside region  4   c ) toward an outer end portion thereof with respect to the main scanning direction, and stops at the outer end portion of the ink ejection face  4  (which outer end portion is near the other end of the outside region  4   c ). As shown in  FIG. 3 , in a case where a width of a paper, as exemplified by a paper P 1 , with respect to the main scanning direction is smaller than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  63 ,  64  stops is in a position which overlaps an outside region of the belt  8  with respect to the vertical direction. In a case where a width of a paper, as exemplified by a paper P 2 , with respect to the main scanning direction is larger than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  63 ,  64  stops is in a position which overlaps, with respect to the vertical direction, an outside region of a conveyance region where the paper is conveyed (i.e., a region outside the width of the paper P 2  with respect to the main scanning direction). This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  63  and  64 . 
     On the other hand, when the rotation motor  95  rotates the belt roller  74  in the clockwise direction in  FIG. 2 , the four caps  61  and the four wipers  63  mounted on the support plate  71  are moved together with the support plate  71 , rightward in  FIG. 1  from the maintenance position which is opposed to the corresponding ink ejection faces  4 , while the four caps  62  and the four wipers  64  mounted on the support plate  72  are moved together with the support plate  72 , leftward in  FIG. 1  from the maintenance position which is opposed to the corresponding ink ejection faces  4 . Thus, all the caps  61 ,  62 , and all the wipers  63 ,  64  can be moved to the withdrawal position not opposed to the ink ejection faces  4 . 
     Next, a controller  100  which controls an operation of the ink-jet printer  1  will be described with reference to FIG.  4 .  FIG. 4  is a block diagram schematically showing a controller. The controller  100  is made up of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, which work as a print controller  101 , a conveyance controller  102 , and a maintenance controller  103  as shown in  FIG. 4 . 
     When the controller  100  receives print data from an external device such as a PC (personal computer)  120 , the print controller  101  controls a head drive circuit  111  to eject ink from the corresponding ink-jet head  2 . 
     When the controller  100  receives print data from an external device such as the PC  120 , the conveyance controller  102  controls a motor driver  112  so as to drive a conveyor motor  97  thereby conveying a paper on the conveyor belt  8 . 
     The maintenance controller  103  has a head elevation controller  104 , a pump controller  105 , and a maintenance unit movement controller  106 . 
     The head elevation controller  104  controls the head elevation mechanism  98  in accordance with a maintenance operation, to move up and down the ink-jet head  2  together with the elevation frame. 
     When a purge is needed, such as when ink is initially introduced into the ink-jet heads  2  or when printing is started after a rest condition where a printing operation is kept unperformed for a long time, the pump controller  105  controls a pump driver  114  so as to drive an ink supply pump  96  to forcibly feed ink into the ink-jet heads  2 . 
     The maintenance unit movement controller  106 , which is a part of the movement means, controls a motor driver  115  to thereby drive the drive motor  95 , so as to make the belt  73  travel in a predetermined direction in accordance with a maintenance operation so that the caps  61 ,  62  and the wipers  63 ,  64  move together with the support plates  71 ,  72 . Moreover, the maintenance controller  106  controls a motor driver  116  in such a manner that the cap level adjusting mechanism  99  moves down the caps  61 ,  62  to a lower level, in order that the wipers  63 ,  64  can wipe the ink ejection faces  4 . The motor drivers  115  and  116 , the drive motor  95 , and the cap level adjusting mechanism  99  also form a part of the movement means. 
     Next, a maintenance operation performed by the maintenance unit  60  will be described with reference to  FIGS. 5A to 5C  and  FIGS. 6A to 6C .  FIGS. 5A ,  5 B, and  5 C show, over time, a purge operation on ink-jet heads and a wiping operation on ink ejection faces.  FIGS. 6A ,  6 B, and  6 C show, over time, a capping operation for covering the ink ejection faces with caps. 
     For performing a purge operation in order to restore the ink-jet head  2  which is showing ejection failure or the like, the head elevation controller  104  controls the head elevation mechanism  98  so that all of the ink-jet heads  2  belonging to the two head groups  3   a  and  3   b  are moved up from the printing position to the head maintenance position, as shown in  FIG. 5A . Then, the maintenance unit movement controller  106  controls the drive motor  95  so as to rotate the belt roller  74  in the counterclockwise direction in  FIG. 4  and thereby make the belt  73  travel along the main scanning direction, so that all of the caps  61  and  62  move from the withdrawal position to the maintenance position. 
     At this time, the caps  61  associated with the head group  3   a  move leftward in  FIG. 1  along the main scanning direction, and the caps  62  associated with the head group  3   b  move rightward in  FIG. 1  (rightward in  FIG. 4 ) along the main scanning direction. In other words, the cap  61  and the cap  62  move in opposite directions with respect to the main scanning direction. At this time, the wipers  63 ,  64  mounted on the same support plates  71 ,  72  also move together with the caps  61 ,  62 , respectively. 
     Then, the pump controller  105  supplies ink from a supply pump  96  to the ink-jet heads  2 , to thereby perform a purge operation for ejecting ink from the nozzles  4   a  of the ink-jet heads  2  toward the caps  61 ,  62 . After ink is purged into the caps  61 ,  62 , the maintenance unit movement controller  106  controls the drive motor  95  so as to rotate the belt roller  74  in the clockwise direction in  FIG. 4  and thereby make the belt  73  travel along the main scanning direction, so that all of the caps  61  and  62  move from the maintenance position to the withdrawal position. 
     At this time, the cap  61  associated with the head group  3   a  moves rightward in  FIG. 1  along the main scanning direction, and the cap  62  associated with the head group  3   b  moves leftward in  FIG. 1  (leftward in  FIG. 5A ) along the main scanning direction. Then, the motor driver  116  controls the cap level adjusting mechanism  99  to move down all of the caps  61 ,  62 , as shown in  FIG. 5B . At this time, the caps  61 ,  62  are moved down to such a degree that the distal ends (upper ends) of the wipers  63 ,  64  come higher than upper ends of the caps  61 ,  62  are. 
     Then, the head elevation controller  104  controls the head elevation mechanism  98  to move down all of the ink-jet heads  2  to such a degree that the ink ejection faces  4  come slightly lower than the distal ends of the wipers  63 ,  64  and higher than the upper ends of the caps  61 ,  62 , as shown in  FIG. 5C . Then, the maintenance unit movement controller  106  controls the drive motor  95  so as to rotate the belt roller  74  in the counterclockwise direction in  FIG. 4  and thereby make the belt  73  travel along the main scanning direction, so that all of the wipers  63  and  64  move from the withdrawal position to a position which allows the caps  61  and  62  to reach the maintenance position. 
     At this time, the distal ends of the wipers  63  and  64 , which locate higher than the ink ejection faces  4 , come into contact with the ink ejection faces  4  while bending, so that ink adhering to the ink ejection faces  4  as a result of the purge is wiped off. At this time, in addition, while being in contact with the ink ejection face  4  to be wiped, the wiper  63 ,  64  moves from an inner end portion of the ink ejection face  4  to be wiped (one end of the outside region  4   c ) toward an outer end portion thereof with respect to the main scanning direction. At a position where the wiper  63 ,  64  reaches the outer end portion of the ink ejection face  4  (the other end of the outside region  4   c ), the wiper  63 ,  64  stops its wiping operation. Since the wiping operation is ended at a time when the wiper  63 ,  64  reaches the outer end portion of the ink ejection face  4 , the wiper  63 ,  64  moving from the inner end portion of the ink ejection face  4  in the main scanning direction does not go beyond the outer end portion of the ink ejection face  4  during the wiping operation. This can suppress splashing of collected ink which is caused when the wipers  63  and  64  move in the main scanning direction beyond the outer end portion of the ink ejection face  4 . 
     Then, the head elevation controller  104  controls the head elevation mechanism  98  to move up all of the ink-jet heads  2  so as to separate the wipers  63  and  64  from the ink ejection faces  4 . Then, all of the wipers  63  and  64  are moved to the withdrawal position. In this way, the maintenance operation is completed in which the ink-jet head  2  showing ink ejection failure is restored by the purge and ink adhering to the ink ejection face  4  as a result of the purge is wiped off. 
     In the following, a description will be given to a capping operation for covering the ink ejection face  4  with the cap  61 ,  62  during a rest time in which the printer  1  does not perform printing on a paper or the like for a long time. In this case as well as in the above-described case, the head elevation controller  104  controls the head elevation mechanism  98  to move up all of the ink-jet heads  2  belonging to the two head groups  3   a  and  3   b  from the printing position to the head maintenance position (see  FIG. 6A ). Then, the maintenance unit movement controller  106  controls the drive motor  95  so as to rotate the belt roller  74  in the counterclockwise direction in  FIG. 6A  and thereby make the portions of the belt  73  extending in the main scanning direction travel along the main scanning direction, so that all of the caps  61  and  62  move from the withdrawal position to the maintenance position, as shown in  FIG. 6B . 
     Then, the head elevation controller  104  controls the head elevation mechanism  98  to move down all of the ink-jet heads  2  to such a degree that the ink ejection faces  4  come into contact with the upper ends of the caps  61 ,  62 , as shown in  FIG. 6C . In this way, an enclosed space is formed between the ink ejection face  4  and the cap  61 ,  62 , which can prevent ink existing within the nozzles  4   a  from drying up. 
     In the above-described ink-jet printer  1  of this embodiment, the eight ink-jet heads  2  are arranged in such a manner that the ink ejection faces  4  of the eight ink-jet heads  2  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces  4  included in different rows do not overlap each other with respect to the main scanning direction. When wiping the ink ejection faces  4 , the two wipers  63 ,  64  for the two ink ejection faces  4  included in different rows move along the main scanning direction from the inner end portions of the ink ejection faces  4  to positions at which the wipers  63 ,  64  overlap, with respect to the vertical direction, the outside region of the conveyance region where the paper is conveyed by the paper conveyance mechanism  10  and the outside region of the paper conveyance mechanism  10 . As a result, contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8  can be suppressed, even when ink drops from the ink pool which is formed of ink collected by the wipers  63  and  64 . 
     When the eight wipers  63  and  64  are located in the withdrawal position not opposed to the ink ejection faces  4 , the wiper  63  associated with the ink-jet head  2  included in one row is located in a position overlapping the ink-jet head  2  included in the one row with respect to the main scanning direction and also overlapping the ink-jet head  2  included in the other row with respect to the sub scanning direction, while the wiper  64  associated with the ink-jet head  2  included in the other row is located in a position overlapping the ink-jet head  2  included in the other row with respect to the main scanning direction and also overlapping the ink-jet head  2  included in the one row with respect to the sub scanning direction. As a result, even though free spaces are formed in regions neighboring the eight ink-jet heads  2  with respect to the main scanning direction, the eight wipers  63 ,  64  associated with the respective ink-jet heads  2  are positioned in these spaces. Positioning the wipers  63 ,  64  in the free spaces in this way makes it unnecessary to provide another space which is special for the eight wipers  63 ,  64  to be positioned therein. Therefore, the ink-jet printer  1  can be downsized. 
     Moreover, the eight ink-jet heads  2  are divided into two head groups  3   a  and  3   b  which correspond to different rows. Each of the two head groups  3   a  and  3   b  is made up of four ink-jet heads  2  which are located in the same position with respect to the main scanning direction and whose ink ejection faces  4  are adjacent to each other. Accordingly, even though free spaces are formed in regions neighboring the two head groups  3   a  and  3   b  with respect to the main scanning direction, the eight wipers  63 ,  64  associated with the ink-jet heads  2  belonging to the respective head groups are positioned in these spaces. Therefore, the ink-jet printer  1  can be downsized. 
     In addition, there are the pair of belt rollers  74  and  75 , and the belt  73  which spans the pair of belt rollers  74  and  75  and is coupled with all of the wipers  63  and  64  so that as the belt  73  travels the wipers  63  and  64  can be moved from the withdrawal position along the main scanning direction. Therefore, as the drive motor  95  which is a single drive source is used to make the belt  73  travel, all of the ink ejection faces  4  can be wiped by the wipers  63  and  64 . 
     Next, an ink-jet printer  301  according to a second embodiment of the present invention will be described below with reference to  FIG. 7 .  FIG. 7  is a plan view of an essential part of an ink-jet printer according to a second embodiment of the present invention. 
     The ink-jet printer  301  which is an image recording apparatus of this embodiment differs from that of the first embodiment, in that arrangement of eight ink-jet heads  302  which are liquid ejection heads is different from the arrangement of the eight ink-jet heads  2  of the first embodiment. Accordingly, arrangements of the eight caps  361  and  362  and eight wipers  363  and  364  are also different from the arrangements of the eight caps  61  and  62  and the eight wipers  63  and  64  of the first embodiment. In addition, a maintenance unit  360  of the ink-jet printer  301  has a movement mechanism  370  which is different in structure from the movement mechanism  70  of the first embodiment. In other points, the second embodiment is the same as the first embodiment. Structures of the ink-jet heads  302 , the caps  361  and  362 , and the wipers  363  and  364  are the same as in the first embodiment. Only an arrangement pattern thereof is different from in the first embodiment. The same members as of the first embodiment will be denoted by the same reference signs without specific descriptions thereof. 
     As shown in  FIG. 7 , the eight ink-jet heads  302  of this embodiment are arranged in such a manner that the ink ejection faces  4  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces included in different rows do not overlap each other with respect to the main scanning direction. The eight ink-jet heads  302  are divided into four head groups  303   a ,  303   b ,  303   c , and  303   d  each of which includes two ink-jet heads  302 . Ink ejection faces  4  of the two ink-jet heads  302  are adjacent to each other with respect to the sub scanning direction and belong to different rows. The four head groups  303   a ,  303   b ,  303   c , and  303   d  are arranged side by side along the sub scanning direction, so as to arrange the eight ink-jet heads  302  in a zigzag pattern with respect to the sub scanning direction. 
     Two ink-jet heads  302  included in each of the head groups  303   a ,  303   b ,  303   c , and  303   d  have their ink ejection faces  4  overlap each other in the sub scanning direction, so that a print region for making printing on a paper continue in the main scanning direction. More specifically, the ink-jet heads  302  are arranged in such a manner that an interval in the main scanning direction between neighboring nozzles  4   a  in an ink ejection region of one ink-jet head  302  is the same as an interval in the main scanning direction between an innermost (i.e., leftmost in  FIG. 7 ) one of the nozzles  4   a  formed in the ink ejection face  4  of the right-side ink-jet head  302  in  FIG. 7  which is included in the head group  303   a  and an innermost (i.e., rightmost in  FIG. 7 ) one of the nozzles  4   a  formed in the ink ejection face  4  of the left-side ink-jet head  302  in  FIG. 7  which is included in the head group  303   a . Each of the other head groups  303   b ,  303   c , and  303   d  includes two ink-jet heads  302  arranged in the same manner as in the head group  303   a.    
     The four head groups  303   a ,  303   b ,  303   c , and  303   d  eject ink of different colors. In this embodiment, the two ink-jet heads  302  belonging to the head group  303   a  eject magenta ink, the two ink-jet heads  302  belonging to the head group  303   a  eject magenta ink, the two ink-jet heads  302  belonging to the head group  303   c  eject cyan ink, and the two ink-jet heads  302  belonging to the head group  303   d  eject black ink. 
     The maintenance unit  360  has eight caps  361  and  362 , eight wipers  363  and  364 , and a movement mechanism  370 . The eight caps  361  and  362 , and the eight wipers  363  and  364  correspond to the eight ink-jet heads  302 , respectively. The movement mechanism  370  moves the respective caps  361 ,  362  and the respective wipers  363 ,  364  in the main scanning direction. 
     The movement mechanism  370  has fourteen rollers  375 , two rollers  376 , one belt  373 , four support plates  371 , and four support plates  372 . Each of the two rollers  376  has a diameter slightly larger than the roller  375 . The one belt  373  spans the sixteen rollers  375  and  376 . Each of the four support plates  371  is, at its one end (upper end in  FIG. 7 ) with respect to the sub scanning direction, coupled with the belt  373 , and each support plate  371  supports the cap  361  and the wiper  363  associated with the ink-jet head  302  belonging to one (left one in  FIG. 7 ) of the rows. Each of the four support plates  372  is, at its one end (upper end in  FIG. 7 ) with respect to the sub scanning direction, coupled with the belt  373 , and each support plate  372  supports the cap  362  and the wiper  364  associated with the ink-jet head  302  belonging to the other (right one in  FIG. 7 ) of the rows. 
     The four support plates  371  are positioned so as to overlap the ink-jet heads  302  belonging to the left row in  FIG. 7  along the main scanning direction, and in addition so as to overlap the ink-jet heads  302  belonging to the right row in  FIG. 7  along the sub scanning direction. Thus, the caps  361  and the wipers  363  supported on the support plates  371  are arranged in the same manner. 
     The four support plates  372  are positioned so as to overlap the ink-jet heads  302  belonging to the right row in  FIG. 7  along the main scanning direction, and in addition so as to overlap the ink-jet heads  302  belonging to the left row in  FIG. 7  along the sub scanning direction. Thus, the caps  362  and the wipers  364  supported on the support plates  372  are arranged in the same manner. 
     In other words, the eight support plates  371  and  372  are arranged in a zigzag pattern inverse to the zigzag arrangement pattern of the eight ink-jet heads  302 , with respect to the sub scanning direction. Such a zigzag arrangement of the support plates  371 ,  372 , the caps  361 ,  362 , and the wipers  363 ,  364  inverse to the zigzag arrangement of the ink-jet heads  302  contributes to downsizing of the ink-jet printer  301 . 
     The fourteen rollers  375  are arranged in such a manner that they neighbor outer end portion corners, with respect to the main scanning direction, of the seven support plates  371  and  372  other than the lowermost support plate  372  in  FIG. 7 , and in addition the belt  373  which spans the fourteen rollers  375  is, in its portions extending in the main scanning direction, disposed in parallel with each other between neighboring ink-jet heads  302 . The two rollers  376  are arranged in such a manner that the portions of the belt  373  extending in the main scanning direction and spanning the two rollers  376  and the two of the rollers  375  located outermost with respect to the sub scanning direction are disposed in parallel with each other, in a position outside the upper head group  303   a  with respect to the sub scanning direction in  FIG. 7  and in a position between two ink-jet heads  302  belonging to the lowermost head group  303   d  with respect to the sub scanning direction in  FIG. 7 . 
     Since the rollers  375  and  376 , and the belt  373  are arranged like this, all of the caps  361  and  362  and all of the wipers  363  and  364  can be moved from the withdrawal position not opposed to the ink ejection faces  4  to the position (maintenance position) opposed to the ink ejection faces  4 , simply by making the belt  373  travel, even though the eight ink-jet heads  302  are arranged in a zigzag pattern. 
     With the maintenance unit  360  having the above-described structure, when the drive motor  95  rotates one (upper left one in  FIG. 7 ) roller  376  in the counterclockwise direction in  FIG. 7 , the caps  361  and the wipers  363  mounted on the respective support plate  371  move together with the support plates  371  from the withdrawal position (as shown in  FIG. 7 ), leftward in  FIG. 7  along the main scanning direction, while the caps  362  and the wipers  364  mounted on the respective support plate  372  move together with the support plates  372  from the withdrawal position, rightward in  FIG. 7  along the main scanning direction. Thus, all the caps  361 ,  362 , and all the wipers  363 ,  364  can be moved to a position (maintenance position) opposed to the ink ejection faces  4 . 
     At this time, each of the wipers  363 ,  364  moves from an inner end portion of the ink ejection face  4  of the corresponding ink-jet head  302  with respect to the main scanning direction (one end of the outside region  4   c ) toward an outer end portion thereof with respect to the main scanning direction, and stops at the outer end portion of the ink ejection face  4  (the other end of the outside region  4   c ). Like in the first embodiment, in a case where a width of a paper with respect to the main scanning direction is smaller than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  363 ,  364  stops is in a position which overlaps an outside region of the belt  8  with respect to the vertical direction. In a case where a width of a paper with respect to the main scanning direction is larger than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  363 ,  364  stops is in a position which overlaps, with respect to the vertical direction, an outside region of a conveyance region where the paper is conveyed (i.e., a region outside the width of the paper with respect to the main scanning direction). This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  363  and  364 . 
     On the other hand, when the drive motor  95  rotates one roller  376  in the clockwise direction in  FIG. 7 , the caps  361  and the wipers  363  move together with the respective support plates  371  from the position opposed to the ink ejection faces  4 , rightward in  FIG. 7  along the main scanning direction, while the caps  362  and the wipers  364  move together with the respective support plates  372  from the maintenance position opposed to the ink ejection faces  4 , leftward in  FIG. 7  along the main scanning direction. Thus, all the caps  361 ,  362 , and all the wipers  363 ,  364  can be moved to the withdrawal position not opposed to the ink ejection faces  4 . 
     In this embodiment, like this, the caps  361 ,  362  and the wipers  363 ,  364  associated with two ink-jet heads  302  belonging to each of the head groups  303   a ,  303   b ,  303   c , and  303   d  are movable in opposite directions with respect to the main scanning direction. Therefore, the same maintenance operation as in the first embodiment can be performed by the maintenance unit  360  of this embodiment. 
     In the ink-jet printer  301  of this embodiment, the eight ink-jet heads  302  are arranged in such a manner that the ink ejection faces  4  of the eight ink-jet heads  302  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces  4  included in different rows do not overlap each other with respect to the main scanning direction. However, when wiping the ink ejection faces  4 , two wipers  363  and  364  associated with two ink ejection faces  4  belonging to different rows move along the main scanning direction from the inner end portions of the ink ejection faces  4  to positions at which the wipers  363 ,  364  overlap, with respect to the vertical direction, the outside region of the paper conveyance region of the paper conveyance mechanism  10  and the outside region of the paper conveyance mechanism  10 . This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  363  and  364 . 
     Moreover, even though free spaces are formed in regions neighboring the ink-jet heads  302  belonging to the respective head groups  303   a ,  303   b ,  303   c , and  303   d  with respect to the main scanning direction, the eight caps  361 ,  362  and the eight wipers  363 ,  364  are positioned in these spaces. Therefore, the ink-jet printer  301  can be downsized. 
     Next, an ink-jet printer  401  according to a third embodiment of the present invention will be described below with reference to  FIG. 8 .  FIG. 8  is a plan view of an essential part of an ink-jet printer according to a third embodiment of the present invention. 
     In the ink-jet printer  401  of this embodiment, neighboring ones of head groups  403   a ,  403   b ,  403   c , and  403   d  with respect to the sub scanning direction are oriented in opposite directions, which is different from the arrangement of the head groups  303   a ,  303   b ,  303   c , and  303   d  of the second embodiment. Accordingly, arrangement of eight caps  461 ,  62  and eight wipers  463 ,  64  is also different from the arrangement of the eight caps  361 ,  362  and the eight wipers  363 ,  364  of the second embodiment. In addition, a maintenance unit  460  of the ink-jet printer  401  has a movement mechanism  470  which is slightly different from the movement mechanism  370  of the second embodiment. Except for the above, the third embodiment is the same as the second embodiment. Structures of ink-jet heads  402 , caps  461 ,  462 , and wipers  463 ,  464  are the same as in the second embodiment, but only arrangements thereof are different from in the second embodiment. The same members as of the second embodiment will be denoted by the same reference signs without specific descriptions thereof. 
     As shown in  FIG. 8 , the eight ink-jet heads  402  of this embodiment are arranged in such a manner that the ink ejection faces  4  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces included in different rows do not overlap each other with respect to the main scanning direction. The eight ink-jet heads  402  are divided into four head groups  403   a ,  403   b ,  403   c , and  403   d  each of which includes two ink-jet heads  402 . Ink ejection faces  4  of the two ink-jet heads  402  are adjacent each other with respect to the sub scanning direction and belong to different rows. 
     The four head groups  403   a ,  403   b ,  403   c , and  403   d  are arranged side by side along the sub scanning direction. One (left one in  FIG. 8 ) of the two ink-jet heads  402  in the head group  403   a  and one of the two ink-jet heads  402  in the head group  403   b  are located in positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. The other (right one in  FIG. 8 ) of the two ink-jet heads  402  in the head group  403   b  and the other of the two ink-jet heads  402  in the head group  403   c  are located in positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. One of the two ink-jet heads  402  in the head group  403   c  and one of the two ink-jet heads  402  in the head group  403   d  are located in positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. 
     Consequently, two caps  461 ,  462  and two wipers  463 ,  464  associated with two adjacent ink-jet heads  402  which belong to neighboring two of the head groups  403   a ,  403   b ,  403   c , and  403   d  can be disposed at positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. 
     The two ink-jet heads  402  belonging to each of the head groups  403   a ,  403   b ,  403   c , and  403   d  have their ink ejection faces  4  overlap each other with respect to the sub scanning direction, which is the same structure as that of the head groups  303   a ,  303   b ,  303   c , and  303   d  of the second embodiment. The four head groups  403   a ,  403   b ,  403   c , and  403   d  eject ink of different colors like in the second embodiment. Therefore, the same effect can be obtained. 
     The maintenance unit  460  has eight caps  461  and  462 , eight wipers  463  and  464 , and a movement mechanism  470 . The eight caps  461  and  462 , and the eight wipers  463  and  464  correspond to the eight ink-jet heads, respectively. The movement mechanism  470  moves the respective caps  461 ,  462  and the respective wipers  463 ,  464  in the main scanning direction. 
     The movement mechanism  470  has eleven rollers  477 , one belt  476  which spans the rollers  477 , and five support plates  471  to  475  coupled with the belt  476 . The eleven rollers  477  are arranged in such a manner that portions of the belt  476  extending in the main scanning direction are disposed in parallel with each other, in positions between the respective head groups and in positions outside the four head groups  403   a ,  403   b ,  403   c , and  403   d , with respect to the sub scanning direction. 
     The support plate  471  is positioned so as to overlap, with respect to the main scanning direction, the other ink-jet head  402  (in the right row in  FIG. 8 ) belonging to the head group  403   a , and in addition so as to overlap, with respect to the sub scanning direction, one ink-jet head  402  (in the left row in  FIG. 8 ) belonging to the head group  403   a . The support plate  471  supports the cap  462  and the wiper  464  associated with the other ink-jet head  402  belonging to the head group  403   a . The support plate  471  is coupled with the portion of the belt  476  extending in the main scanning direction. 
     The support plate  475  is positioned so as to overlap, with respect to the main scanning direction, the other ink-jet head  402  belonging to the head group  403   d , and in addition so as to overlap, with respect to the sub scanning direction, one ink-jet head  402  belonging to the head group  403   d . The support plate  475  supports the cap  462  and the wiper  464  associated with the other ink-jet head  402  belonging to the head group  403   d . The support plate  475  is coupled with the portion of the belt  476  extending in the main scanning direction. 
     The support plate  472  is positioned so as to overlap, with respect to the main scanning direction, one ink-jet head  402  belonging to each of the head groups  403   a  and  403   b , and in addition so as to overlap, with respect to the sub scanning direction, the other ink-jet head  402  belonging to each of the head groups  403   a  and  403   b . The support plate  473  is positioned so as to overlap, with respect to the main scanning direction, the other ink-jet head  402  belonging to each of the head groups  403   b  and  403   c , and in addition so as to overlap, with respect to the sub scanning direction, one ink-jet head  402  belonging to each of the head groups  403   b  and  403   c . The support plate  474  is positioned so as to overlap, with respect to the main scanning direction, one ink-jet head  402  belonging to each of the head groups  403   c  and  403   d , and in addition so as to overlap, with respect to the sub scanning direction, the other ink-jet head  402  belonging to each of the head groups  403   c  and  403   d.    
     Each of the three support plates  472  to  474  supports two caps and two wipers associated with two ink-jet heads  402  which are, with respect to the sub scanning direction, sandwiched between other two ink-jet heads  402 . The other two ink-jet heads  402  are outermost ones of the ink-jet heads  402  belonging to the neighboring two head groups. To be more specific, the support plate  472  supports two caps  461  and two wipers  463  each associated with the one (left one in  FIG. 8 ) ink-jet head  402  belonging to each of the two head groups  403   a  and  403   b . The support plate  473  supports two caps  462  and two wipers  464  each associated with the other ink-jet head  402  belonging to each of the two head groups  403   b  and  403   c . The support plate  474  supports two caps  461  and two wipers  463  each associated with the one ink-jet head  402  belonging to each of the two head groups  403   c  and  403   d.    
     In this way, it is possible to move the three support plates  472  to  474  each of which supports two caps  461  (or  462 ) and two wipers  463  (or  464 ) associated with two ink-jet heads  402 . In addition, as compared with in the second embodiment, a less number of portions of the belt  476  extending in the main scanning direction are positioned between neighboring ink-jet heads  402 , which can simplify the structure of the movement mechanism  470 . 
     With the maintenance unit  460  having the above-described structure, when the drive motor  95  rotates one (upper left one in  FIG. 8 ) roller  477  in the clockwise direction in  FIG. 8 , the four caps  461  and the four wipers  463  mounted on the two support plates  472  and  474  move together with the support plates  472  and  474  from the withdrawal position (as shown in  FIG. 8 ), leftward in  FIG. 8  along the main scanning direction, while the four caps  462  and the four wipers  464  mounted on the three support plates  471 ,  473 , and  475  move together with the support plates  471 ,  473 , and  475  from the withdrawal position, rightward in  FIG. 8  along the main scanning direction. Thus, all the caps  461 ,  462 , and all the wipers  463 ,  464  can be moved to a position (maintenance position) opposed to the ink ejection faces  4 . 
     At this time, each of the wipers  463 ,  464  moves from an inner end portion of the ink ejection face  4  of the corresponding ink-jet head  402  with respect to the main scanning direction (one end of the outside region  4   c ) toward an outer end portion thereof with respect to the main scanning direction, and stops at the outer end portion of the ink ejection face  4  (the other end of the outside region  4   c ). Like in the first embodiment, in a case where a width of a paper with respect to the main scanning direction is smaller than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  463 ,  464  stops is in a position which overlaps an outside region of the belt  8  with respect to the vertical direction. In a case where a width of a paper with respect to the main scanning direction is larger than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  463 ,  464  stops is in a position which overlaps, with respect to the vertical direction, an outside region of a conveyance region where the paper is conveyed (i.e., a region outside the width of the paper with respect to the main scanning direction). This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  463  and  464 . 
     On the other hand, when the drive motor  95  rotates one roller  477  in the counterclockwise direction in  FIG. 8 , the four caps  461  and the four wipers  463  move together with the two support plates  472  and  474  from the maintenance position opposed to the corresponding ink ejection faces  4 , rightward in  FIG. 8  along the main scanning direction, while the four caps  462  and the four wipers  464  move together with the three support plates  471 ,  473 , and  475  from the maintenance position opposed to the corresponding ink ejection faces  4 , leftward in  FIG. 8  along the main scanning direction. Thus, all the caps  461 ,  462 , and all the wipers  463 ,  464  can be moved to the withdrawal position not opposed to the ink ejection faces  4 . 
     In this embodiment, like this, the caps  461 ,  462  and the wipers  463 ,  464  associated with two ink-jet heads  402  belonging to each of the head groups  403   a ,  403   b ,  403   c , and  403   d  are movable in opposite directions with respect to the main scanning direction. Therefore, the same maintenance operation as in the first embodiment can be performed by the maintenance unit  460  of this embodiment. 
     In the ink-jet printer  401  of this embodiment, the eight ink-jet heads  402  are arranged in such a manner that the ink ejection faces  4  of the eight ink-jet heads  402  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces  4  included in different rows do not overlap each other with respect to the main scanning direction. When wiping the ink ejection faces  4 , two wipers  463  and  464  associated with two ink ejection faces  4  belonging to different rows move along the main scanning direction from the inner end portions of the ink ejection faces  4  to positions at which the wipers  463 ,  464  overlap, with respect to the vertical direction, the outside region of the paper conveyance region of the paper conveyance mechanism  10  and the outside region of the paper conveyance mechanism  10 . This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  463  and  464 . 
     Moreover, even though free spaces are formed in regions neighboring the ink-jet heads  402  belonging to the respective head groups  403   a ,  403   b ,  403   c , and  403   d  with respect to the main scanning direction, the eight caps  461 ,  462  and the eight wipers  463 ,  464  are positioned in these spaces. Therefore, the ink-jet printer  401  can be downsized. In addition, by making one belt  476  travel, all of the caps  461 ,  462 , and all of the wipers  463 ,  464  can be moved from the withdrawal position to the maintenance position and from the maintenance position to the withdrawal position. Therefore, a structure of the movement mechanism  470  can be simplified. 
     Next, an ink-jet printer  401  according to a third embodiment of the present invention will be described below with reference to  FIG. 8 .  FIG. 9  is a plan view of an essential part of an ink-jet printer according to a fourth embodiment of the present invention. 
     In the ink-jet printer  501  of this embodiment, arrangement of eight ink-jet heads  502  is slightly different from the arrangement of the eight ink-jet heads  402  of the third embodiment. Accordingly, arrangement of eight caps  561 ,  562  and eight wipers  563 ,  564  is also different from the arrangement of the eight caps  461 ,  462  and the eight wipers  463 ,  464  of the third embodiment. In addition, a maintenance unit  560  of the ink-jet printer  501  has a movement mechanism  570  which is slightly different from the movement mechanism  470  of the third embodiment. Except for the above, the fourth embodiment is the same as the third embodiment. Structures of ink-jet heads  502 , caps  561 ,  562 , and wipers  563 ,  564  are the same as in the third embodiment, but only arrangements thereof are different from in the third embodiment. The same members as of the third embodiment will be denoted by the same reference signs without specific descriptions thereof. 
     As shown in  FIG. 9 , the eight ink-jet heads  502  of this embodiment are arranged in such a manner that the ink ejection faces  4  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces included in different rows do not overlap each other with respect to the main scanning direction. The eight ink-jet heads  502  are divided into three head groups  503   a ,  503   b , and  503   c , and a head group  503   d . Each of the three head groups  503   a ,  503   b , and  503   c  includes two ink-jet heads  502  whose ink ejection faces  4  are adjacent to each other with respect to the sub scanning direction and belong to different rows. The head group  503   d  includes two ink-jet heads  502  which sandwich therebetween the three head groups  503   a ,  503   b , and  503   c  with respect to the sub scanning direction. 
     The three head groups  503   a ,  503   b , and  503   c  are arranged side by side along the sub scanning direction. One (included in the left row in  FIG. 9 ) of the two ink-jet heads  502  in the head group  503   a  and one of the two ink-jet heads  502  in the head group  503   b  are located in positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. The other (included in the right row in  FIG. 9 ) of the two ink-jet heads  502  in the head group  503   b  and the other of the two ink-jet heads  502  in the head group  503   c  are located in positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. 
     Consequently, two caps  561 ,  562  and two wipers  563 ,  564  associated with two adjacent ink-jet heads  502  which belong to neighboring two of the head groups  503   a ,  503   b , and  503   c  can be disposed at positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. 
     Among all the ink-jet heads  502  belonging to the head groups  503   a ,  503   b , and  503   c , the two ink-jet heads  502  which are located outermost with respect to the sub scanning direction, and the two ink-jet heads  502  neighboring these ink-jet heads  502  and belonging to the head group  502   d , are disposed at positions which are the same with respect to the main scanning direction. 
     Consequently, two caps  562  and two wipers  564  associated with the other (included in the right row in  FIG. 9 ) one of the ink-jet heads  502  in the head group  503   d , and the ink-jet head  502  in the head group  503   a  neighboring the above-mentioned ink-jet head  502 , can be disposed at positions which are the same with respect to the main scanning direction and adjacent to each other with respect to the sub scanning direction. The same is applied to two caps  561  and two wipers  563  associated with one (included in the left row in  FIG. 9 ) of the ink-jet heads  502  in the head group  503   d , and the ink-jet head  502  in the head group  503   c  neighboring the above-mentioned ink-jet head  502 . 
     The two ink-jet heads  502  belonging to each of the head groups  503   a ,  503   b ,  503   c , and  503   d  have their ink ejection faces  4  overlap each other along the sub scanning direction, which is the same in the fourth embodiment. The four head groups  503   a ,  503   b ,  503   c , and  503   d  eject ink of different colors. In this embodiment, the three head groups  503   a ,  503   b , and  503   c  eject black ink, magenta ink, and cyan ink, while the head group  503   d  ejects yellow ink. 
     The maintenance unit  560  has eight caps  561  and  562 , eight wipers  563  and  564 , and a movement mechanism  570 . The eight caps  561  and  562 , and the eight wipers  563  and  564  correspond to the eight ink-jet heads  502 , respectively. The movement mechanism  570  moves the respective caps  561 ,  562  and the respective wipers  563 ,  564  in the main scanning direction. 
     The movement mechanism  570  has eight rollers  577 , one belt  576  which spans the rollers  577 , and four support plates  571  to  574  coupled with the belt  576 . The eight rollers  577  are arranged in such a manner that portions of the belt  576  extending in the main scanning direction are disposed in parallel with each other, in positions among the three head groups  503   a ,  503   b , a position between the head group  503   a  and the other ink-jet head  502  in the head group  503   d , and at a position between the head group  503   c  and the one ink-jet head  502  in the head group  503   d , with respect to the sub scanning direction. 
     The support plate  571  is positioned so as to overlap, with respect to the main scanning direction, two of the other ink-jet heads  502  (included in the right row in  FIG. 9 ) belonging to the two head groups  503   a  and  503   d , and in addition so as to overlap, with respect to the sub scanning direction, two of the one ink-jet heads  502  (included in the left row in  FIG. 9 ) belonging to the two head groups  503   a  and  503   d . The support plate  571  supports caps  562  and wipers  564  associated with two of the other ink-jet heads  502  belonging to the two head groups  503   a  and  503   d . The support plate  571  is coupled with a portion of the belt  576  extending in the main scanning direction. 
     The support plate  572  is positioned so as to overlap, with respect to the main scanning direction, two of the one ink-jet heads  502  belonging to the two head groups  503   a  and  503   b , and in addition so as to overlap, with respect to the sub scanning direction, two of the other ink-jet heads  502  belonging to the two head groups  503   a  and  503   b . The support plate  572  supports caps  561  and wipers  563  associated with two of the one ink-jet heads  502  belonging to the two head groups  503   a  and  503   b . The support plate  572  is coupled with a portion of the belt  576  extending in the main scanning direction. 
     The support plate  573  is positioned so as to overlap, with respect to the main scanning direction, two of the other ink-jet heads  502  belonging to the two head groups  503   b  and  503   c , and in addition so as to overlap, with respect to the sub scanning direction, two of the one ink-jet heads  502  belonging to the two head groups  503   b  and  503   c . The support plate  573  supports caps  562  and wipers  564  associated with two of the other ink-jet heads  502  belonging to the two head groups  503   b  and  503   c . The support plate  573  is coupled with a portion of the belt  576  extending in the main scanning direction. 
     The support plate  574  is positioned so as to overlap, with respect to the main scanning direction, two of the one ink-jet heads  502  belonging to the two head groups  503   c  and  503   d , and in addition so as to overlap, with respect to the sub scanning direction, two of the other ink-jet heads  502  belonging to the two head groups  503   c  and  503   d . The support plate  573  supports caps  561  and wipers  563  associated with two of the one ink-jet heads  502  belonging to the two head groups  503   c  and  503   d . The support plate  573  is coupled with a portion of the belt  576  extending in the main scanning direction. 
     In this way, it is possible to move the four support plates  571  to  574  each of which supports two caps  561  (or  562 ) and two wipers  563  (or  564 ) associated with two ink-jet heads  502 . In addition, as compared with in the second embodiment, a less number of portions of the belt  576  extending in the main scanning direction are positioned between neighboring ink-jet heads  502 , which can simplify the structure of the movement mechanism  570 . 
     With the maintenance unit  560  having the above-described structure, when the drive motor  95  rotates one (upper left one in  FIG. 9 ) roller  577  in the clockwise direction in  FIG. 9 , the four caps  561  and the four wipers  563  mounted on the two support plates  572  and  574  move together with the support plates  572  and  574  from the withdrawal position (as shown in  FIG. 9 ), leftward in  FIG. 9  along the main scanning direction, while the four caps  562  and the four wipers  564  mounted on the two support plates  571  and  573  move together with the support plates  571  and  573  from the withdrawal position, rightward in  FIG. 9  along the main scanning direction. Thus, all the caps  561 ,  562 , and all the wipers  563 ,  564  can be moved to a maintenance position opposed to the ink ejection faces  4 . 
     At this time, each of the wipers  563 ,  564  moves from an inner end portion of the ink ejection face  4  of the corresponding ink-jet head  502  with respect to the main scanning direction (one end of the outside region  4   c ) toward an outer end portion thereof with respect to the main scanning direction, and stops at the outer end portion of the ink ejection face  4  (the other end of the outside region  4   c ). Like in the first embodiment, in a case where a width of a paper with respect to the main scanning direction is smaller than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  563 ,  564  stops is in a position which overlaps an outside region of the belt  8  with respect to the vertical direction. In a case where a width of a paper with respect to the main scanning direction is larger than a width of the belt  8  with respect to the main scanning direction, the outer end portion of the ink ejection face  4  at which the wiper  563 ,  564  stops is in a position which overlaps, with respect to the vertical direction, an outside region of a conveyance region where the paper is conveyed (i.e., a region outside the width of the paper with respect to the main scanning direction). This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  563  and  564 . 
     On the other hand, when one roller  577  is rotated in the counterclockwise direction in  FIG. 9 , the four caps  561  and the four wipers  563  move together with the two support plates  572  and  574  from the maintenance position opposed to the corresponding ink ejection faces  4 , rightward in  FIG. 9  along the main scanning direction, while the four caps  562  and the four wipers  564  move together with the two support plates  571  and  573  from the maintenance position opposed to the corresponding ink ejection faces  4 , leftward in  FIG. 9  along the main scanning direction. Thus, all the caps  561 ,  562 , and all the wipers  563 ,  564  can be moved to the withdrawal position not opposed to the ink ejection faces  4 . 
     In this embodiment, like this, the caps  561 ,  562  and the wipers  563 ,  564  associated with two ink-jet heads  502  belonging to each of the head groups  503   a ,  503   b ,  503   c , and  503   d  are movable in opposite directions with respect to the main scanning direction. Therefore, the same maintenance operation as in the first embodiment can be performed by the maintenance unit  560  of this embodiment. 
     In the ink-jet printer  501  of this embodiment, the eight ink-jet heads  502  are arranged in such a manner that the ink ejection faces  4  of the eight ink-jet heads  502  form two rows each including four ink ejection faces  4  which are arranged side by side along the sub scanning direction and in addition the ink ejection faces  4  included in different rows do not overlap each other with respect to the main scanning direction. However, when the wipers  563  and  564  wipe the ink ejection faces  4 , two wipers  563  and  564  associated with two ink ejection faces  4  belonging to different rows move along the main scanning direction from the inner end portions of the ink ejection faces  4  to positions at which the wipers  563 ,  564  overlap, with respect to the vertical direction, the outside region of the paper conveyance region of the paper conveyance mechanism  10  and the outside region of the paper conveyance mechanism  10 . This can suppress contamination of the paper and the paper conveyance mechanism  10 , and more particularly the belt  8 , even when ink drops from an ink pool which is formed of ink collected by the wipers  563  and  564 . 
     Moreover, even though free spaces are formed in regions neighboring the ink-jet heads  502  belonging to the respective head groups  503   a ,  503   b ,  503   c , and  503   d  with respect to the main scanning direction, the eight caps  561 ,  562  and the eight wipers  563 ,  564  are positioned in these spaces. Therefore, the ink-jet printer  501  can be downsized. In addition, by making one belt  576  travel, all of the caps  561 ,  562 , and all of the wipers  563 ,  564  can be moved from the withdrawal position to the maintenance position and from the maintenance position to the withdrawal position. Therefore, a structure of the movement mechanism  570  can be simplified. 
     While some preferred embodiments of the present invention have been described above, the present invention should not be construed to be limited to the above-described embodiments. Various modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. For example, in the above-described embodiments, two ink-jet heads which eject ink of the same color are arranged in such a manner that when they eject ink to form an image, continuous printing can be made without a break with respect to the main scanning direction. However, it may also be possible that the two ink-jet heads do not overlap each other with respect to the sub scanning direction so that, when an image is formed, printing does not continue but has a break with respect to the main scanning direction. In addition, in the respective embodiments, the movement mechanism may move the cap in a direction different from the main scanning direction with respect to the in-plane direction of the ink ejection face, between the maintenance position opposed to the ink ejection face and the withdrawal position not opposed to the ink ejection face. Moreover, in the respective embodiments, the ink-jet printer may not have the caps. Further, in the second and third embodiments, the two ink-jet heads forming the head group eject ink of the same color, but they may eject different types of ink. Still further, in the respective embodiments, it may be possible that the movement mechanism has a plurality of support members which independently support wipers and caps so that the wipers and the caps are moved separately and/or together. 
     Still further, in the respective embodiments, in a case where a width of a paper with respect to the main scanning direction is smaller than a width of the belt  8  with respect to the main scanning direction, a point for the wiper to end its wiping operation on the ink ejection face is in a position which overlaps an outside region of the belt  8  with respect to the vertical direction. In a case where a width of a paper with respect to the main scanning direction is larger than a width of the belt  8  with respect to the main scanning direction, a point for the wiper to end its wiping operation on the ink ejection face is in a position which overlaps an outside region of the conveyance region where the paper is conveyed, with respect to the vertical direction. However, in a case where a width of a paper with respect to the main scanning direction is smaller than a width of the belt  8  with respect to the main scanning direction, a point for the wiper to end its wiping operation on the ink ejection face may be in a position which overlaps only the outside region of the conveyance region where the paper is conveyed, with respect to the vertical direction. In such a case, contamination of the paper alone can be suppressed. Moreover, in a case where a width of a paper with respect to the main scanning direction is larger than a width of the belt  8  with respect to the main scanning direction, a point for the wiper to end its wiping operation on the ink ejection face may be in a position which overlaps only the outside region of the belt  8  with respect to the vertical direction. In such a case, contamination of the belt  8  alone can be suppressed. 
     Still further, in the respective embodiments, one belt is used to move caps and wipers associated with two ink-jet heads belonging to each head group in opposite directions with respect to the main scanning direction. However, it may be possible to use a plurality of belts to move caps and wipers on a head group basis or on an ink-jet head basis. 
     Still further, in the respective embodiments, the paper conveyance mechanism  10  conveys a paper on the belt  8 . However, it may be possible that a plurality of rollers elongated in the main scanning direction are arranged side by side along the sub scanning direction and a paper is conveyed thereon. 
     Still further, in the respective embodiments, the maintenance unit movement controller  106  makes a control to drive the movement mechanism  70  so that the wiper  63 ,  64  is moved from the inner end portion to the outer end portion of the ink ejection face  4  of the corresponding ink-jet head  2  with respect to the main scanning direction. However, in a case where a whole extent of movement of the wiper  63 ,  64  which can be made by the movement mechanism  70  is from the inner end portion to the outer end portion of the ink ejection face  4  of the corresponding ink-jet head  2  with respect to the main scanning direction, it may be possible to provide, instead of the maintenance unit movement controller  106 , only a switch which moves the movement mechanism  70  to either one of the inner end portion and the outer end portion. 
     Still further, the above-described embodiments are examples of application of the present invention to an ink-jet printer including a plurality of ink-jet heads which eject ink from nozzles. However, such an ink-jet head is not the only thing to which the present invention is applicable. For example, the present invention may be applied to various liquid ejection apparatus including a plurality of liquid ejection heads for ejecting a conductive paste to form a fine wiring pattern on a substrate, for ejecting an organic luminescent material to a substrate to form a high-resolution display, and for ejecting optical plastics to a substrate to form a very small electronic device such as an optical waveguide. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.