Abstract:
A head cap may comprise a cap body comprising a circular projection which is configured to surround a liquid droplet ejection area formed on an ejection surface of a liquid droplet ejection head by contacting with the ejection surface, and a bottom plate portion which is configured to define a depressed portion in corporation with the circular projection and to which the circular projection is connected. The head cap may also comprise a holder which is configured to hold the bottom plate portion. The head cap may further comprise a fixing member which is configured to fix the cap body to the holder by being fitted to the holder via the bottom plate portion and disposed on a bottom surface of the depressed portion. The fixing member and the holder may clamp the bottom plate portion in the direction intersecting the direction of projection of the circular projection.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2008-302754, filed Nov. 27, 2008, the entire subject matter and disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    1. Field of the Disclosure 
         [0003]    The features herein relate to a head cap configured to cover an ejection surface of a liquid droplet ejection head for ejecting a liquid droplet, and an ink-jet printer comprising the head cap. 
         [0004]    2. Description of the Related Art 
         [0005]    A known ink-jet printer includes an ink-jet head and a maintenance unit configured to perform the maintenance of the ink-jet head. The maintenance unit includes a cap formed of an elastic member such as rubber for covering a nozzle surface of the ink-jet head. By the cap covering the nozzle surface, ink in nozzles is prevented from being dried. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In the ink-jet printer described above, a circular projection for defining a depressed portion is disposed on the cap. The maintenance unit brings the circular projection of the cap into contact with the nozzle surface such that the nozzle surface of the ink-jet head is covered by the depressed portion of the cap. When the circular projection of the cap is in contact with the nozzle surface for a long time, the circular projection may be adhered to the nozzle surface with ink remaining on the nozzle surface. When the cap is forcedly separated from the nozzle surface in this state, the cap may drop out from a holder. In order to prevent this event, it is considered to fit a projection formed on a side surface of the cap to the holder. However, since the projection is projected to the outside of the cap, the cap is upsized. 
         [0007]    A need has arisen for a head cap which is downsized while fixing the cap reliably, and an ink-jet printer comprising the head cap. 
         [0008]    According to one embodiment herein, a head cap may comprise a cap body comprising a circular projection which is configured to surround a liquid droplet ejection area formed on an ejection surface of a liquid droplet ejection head by contacting with the ejection surface, and a bottom plate portion which is configured to define a depressed portion in corporation with the circular projection and to which the circular projection is connected. The head cap may also comprise a holder which is configured to hold the bottom plate portion. The head cap may further comprise a fixing member which is configured to fix the cap body to the holder by being fitted to the holder via the bottom plate portion and disposed on a bottom surface of the depressed portion. The fixing member and the holder may clamp the bottom plate portion in the direction intersecting the direction of projection of the circular projection. 
         [0009]    Other objects, features, and advantages will be apparent to those skilled in the art from the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments are described with reference to the accompanying drawings, which are given by way of example only, and are not intended to limit the present patent. 
           [0011]      FIG. 1  is a schematic side cross-sectional view of an ink-jet printer according to an embodiment. 
           [0012]      FIG. 2  is a schematic plan view of a principal portion of the ink-jet printer shown in  FIG. 1 . 
           [0013]      FIG. 3  is a cross-sectional view taken along the line in  FIG. 2 . 
           [0014]      FIG. 4  is a bottom plan view of ink-jet heads shown in  FIG. 2  when viewing the same from below. 
           [0015]      FIG. 5A  is a plan view of a head cap shown in  FIG. 2 . 
           [0016]      FIG. 5B  is a cross-sectional view of the head cap shown in  FIG. 2 . 
           [0017]      FIG. 6A  is a plan view of the cap shown in  FIG. 5A  and  FIG. 5B . 
           [0018]      FIG. 6B  is a cross-sectional view of the cap in  FIG. 5A  and  FIG. 5B . 
           [0019]      FIG. 7A  is a plan view of a cap tip shown in  FIG. 5B . 
           [0020]      FIG. 7B  is a cross-sectional view of the cap tip shown in  FIG. 5B . 
           [0021]      FIG. 8A  is a plan view of a holder shown in  FIG. 5B . 
           [0022]      FIG. 8B  is a cross-sectional view of the holder shown in  FIG. 5B . 
           [0023]      FIG. 9  is a partially enlarged cross-sectional view of the head cap shown in  FIG. 5A  and  FIG. 5B . 
           [0024]      FIG. 10  shows a state in which a circular projection of the cap shown in  FIG. 5A  and  FIG. 5B  and an ejection surface are in contact with each other. 
           [0025]      FIG. 11A  shows a state where the ink-jet head shown in  FIG. 2  is moved from a “printing position” to a “head maintenance position” and a tray of a maintenance unit is moved to a “maintenance position”. 
           [0026]      FIG. 11B  shows a state in which ink attached to the ejection surface is wiped off by a wiper shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0027]    Various embodiments, and their features and advantages, may be understood by referring to  FIGS. 1-11 , like numerals being used for corresponding parts in the various drawings. 
         [0028]    Referring to  FIG. 1  to  FIG. 3 , an ink-jet printer  1  includes a housing  1   a  of a parallelepiped shape. A paper discharging portion  31  is positioned on an upper portion of the housing  1   a . The interior of the housing  1   a  is divided into three spaces A, B, and C in sequence from the top. A plurality of, e.g., four, ink-jet heads  2  which eject inks in magenta, cyan, yellow, and black respectively, a transporting unit  20 , and a maintenance unit  70  (inner side of the transporting unit  20  in terms of the paper plane of  FIG. 1 ) are arranged in the space A. The spaces B and C are spaces in which a paper feeding unit  1   b  and an ink tank unit  1   c  which are demountably mounted on the housing  1   a  are arranged respectively. In this embodiment, the secondary scanning direction is a direction parallel to the transporting direction when transporting a paper P by the transporting unit  20 , and the primary scanning direction is a direction orthogonal to the secondary scanning direction and is a direction along the horizontal plane. 
         [0029]    In the interior of the ink-jet printer  1 , a paper transporting path in which the paper P is transported is formed from the paper feeding unit  1   b  toward the paper discharging portion  31  (thick arrow in  FIG. 1 ). The paper feeding unit  1   b  includes a paper feed tray  23  in which a plurality of pieces of paper P can be stored, and a paper feed roller  25  mounted on the paper feed tray  23 . The paper feed roller  25  feeds the uppermost paper P from among the plurality of pieces of paper P stored in the paper feed tray  23  in stack. The paper P fed by the paper feed roller  25  is guided by guides  27   a  and  27   b , and is fed to the transporting unit  20  while being pinched by a feed roller pair  26 . 
         [0030]    The transporting unit  20  includes a plurality of, e.g., two, belt rollers  6  and  7 , an endless transporting belt  8  wound between the both rollers  6  and  7  so as to run therebetween, and a tension roller  10 . The tension roller  10  is urged downward while being in contact with an inner peripheral surface of a lower loop of the transporting belt  8 , and applies a tension to the transporting belt  8 . The belt roller  7  is a driving roller which rotates clockwise in  FIG. 1  by a drive force applied from a transporting motor M via two gears. The belt roller  6  is a driven roller which is rotated clockwise in  FIG. 1  by the transporting belt  8  being traveled by the rotation of the belt roller  7 . 
         [0031]    A peripheral surface  8   a  of the transporting belt  8  is siliconized, thereby having an adhesive characteristic. A nip roller  5  is arranged at a position opposing the belt roller  6  on the paper transporting path with the intermediary of the transporting belt  8 . The nip roller  5  presses the paper P fed from the paper feed unit  1   b  against the peripheral surface  8   a  of the transporting belt  8 . The paper P pressed against the peripheral surface  8   a  is transported rightward in  FIG. 1  while being held on the peripheral surface  8   a  by its adhesive characteristic. 
         [0032]    A separating plate  13  is disposed at a position opposing the belt roller  7  on the paper transporting path with the intermediary of the transporting belt  8 . The separating plate  13  separates the paper P held on the peripheral surface  8   a  of the transporting belt  8  from the peripheral surface  8   a . The paper P separated by the separating plate  13  is guided by guides  29   a  and  29   b  and is transported while being pinched by a plurality of, e.g., two, pairs of feed roller pair  28 , and is discharged from an opening  30  formed on the upper portion of the housing  1   a  to the paper discharging portion  31 . 
         [0033]    Referring to  FIG. 2  to  FIG. 4 , the plurality of, e.g., four, ink-jet heads  2  are fixed to a frame-shaped frame  4  in a state of extending along the primary scanning direction and being arranged adjacently to each other along a paper transporting direction B respectively. The frame  4  includes supporting portions  4   a  projecting to a position opposing a lower surface of both end portions in terms of the longitudinal direction of the ink-jet heads  2 . Then, the supporting portions  4   a  and the both end portions of the ink-jet heads  2  are fixed by screws  50 . Lower surfaces of the respective ink-jet heads  2  correspond to ejection surfaces  3   a  from which ink droplets are ejected. In other words, the ink-jet printer  1  is a line-type color ink-jet printer in which an ejection area extending in the primary scanning direction is formed. 
         [0034]    Referring to  FIG. 1 , a platen  9  is positioned in a loop of the transporting belt  8  so as to oppose the plurality of, e.g., four, ink-jet heads  2 . An upper surface of the platen  9  comes into contact with an inner peripheral surface of an upper loop of the transporting belt  8 , and supports the same from the inner peripheral side of the transporting belt  8 . Accordingly, the peripheral surface  8   a  of the upper loop of the transporting belt  8  and the lower surface of the ink-jet head  2 , that is, the ejection surface  3   a  oppose in parallel to each other, and a small gap is formed between the peripheral surface  8   a  of the transporting belt  8  and the ejection surface  3   a . The gap configures part of the paper transporting path. When the paper P transported while being held on the peripheral surface  8   a  of the transporting belt  8  passes immediately below the plurality of, e.g., four, ink-jet heads  2 , inks in the respective colors are discharged toward an upper surface of the paper P in sequence from the respective ink-jet heads  2 , such that a desired color image is formed on the paper P. 
         [0035]    Referring to  FIG. 2  and  FIG. 3 , the frame  4  is supported by frame moving mechanisms  51  provided on the ink-jet printer  1  so as to be movable in the vertical direction. The frame moving mechanisms  51  are disposed outside of the arrangement of the plurality of, e.g., four, ink-jet heads  2  (upper side and lower side in  FIG. 2 ). The frame moving mechanisms  51  each include a driving motor  52  as a drive source for moving the frame  4  upward and downward, a pinion gear  53  fixed to a shaft of the each driving motor  52 , a rack gear  54  provided upright on the frame  4  so as to mesh the each pinion gear  53 , and a guide  56  arranged at a position sandwiching the rack gear  54  with the pinion gear  53 . 
         [0036]    The plurality of, e.g., two, driving motors  52  are fixed to a body frame  1   d  of the ink-jet printer  1 , and is arranged so as to oppose to each other in terms of the paper transporting direction B. The plurality of, e.g., two, rack gears  54  extend in the vertical direction, and lower end portions thereof are fixed to side surfaces of the frame  4  respectively. Side surfaces of the rack gear  54  opposite from the pinion gears  53  are in slidable contact with the guides  56 . The guides  56  are fixed to the body frame  1   d.    
         [0037]    In this configuration, when the plurality of, e.g., two, driving motors  52  are synchronized and the respective pinion gears  53  are rotated in the normal and reverse directions, the rack gears  54  move in the vertical direction. The frame  4  and the plurality of, e.g., four, ink-jet heads  2  are moved in the vertical direction in association with the vertical movement of the rack gears  54 . 
         [0038]    Guide portions  59  are disposed on both sides of the ink-jet heads  2  in terms of the longitudinal direction. The each guide portion  59  includes a rod-shaped member  58  and a pair of guides  57  which sandwich the same therebetween. From among these members, the pair of guides  57  extend in the vertical direction as shown in  FIG. 3 , and are fixed to a body frames  1   e  opposing to each other in terms of the direction orthogonal to the paper transporting direction B respectively. In contrast, the rod-shaped members  58  extend in the vertical direction in the same manner as the guides  57  and are fixed to the side surfaces of the frame  4  in parallel to the body frames  1   e  so as to oppose to each other. In addition, the each rod-shaped member  58  is slidably sandwiched between the pair of guides  57 . These guide portions  59  are capable of preventing the ejection surfaces  3   a  of the ink-jet heads  2  from inclining with respect to the peripheral surface  8   a  when the frame  4  is moved in the vertical direction by the frame moving mechanisms  51 . 
         [0039]    In general, the frame  4  is arranged to a “printing position” where the plurality of, e.g., four, ink-jet heads  2  discharge ink on the paper for printing (the position shown in  FIG. 3 ). At the time of the maintenance of the ink-jet heads  2 , the frame  4  is moved by the frame moving mechanisms  51  and the plurality of, e.g., four, ink-jet heads  2  are arranged at a level higher than the “printing position” (for example, a “head maintenance position” described later”). 
         [0040]    The respective ink-jet heads  2  are connected to ink tanks  49  in the ink tank unit  1   c  mounted in the space C. In other words, in the plurality of, e.g., four, ink tanks  49 , the inks which are ejected by the ink-jet heads  2  corresponding thereto are stored. The inks are supplied from the respective ink tanks  49  to the ink-jet heads  2  via tubes (not shown) or the like. 
         [0041]    The ink-jet printer  1  includes the maintenance unit  70  configured to perform the maintenance for the ink-jet heads  2  and arranged on the left side of the ink-jet heads  2  in  FIG. 2  as shown in  FIG. 2  and  FIG. 3 . The maintenance unit  70  includes plurality of, e.g., two, trays  71  and  75  which are movable in the horizontal direction. The tray  71  has a substantially rectangular box shape opening upward, and is capable of containing the tray  75  therein. The tray  71  and the tray  75  are detachably connected by engaging devices described later. The both are detachably attached according to a work to be performed in the maintenance process. 
         [0042]    A holding member  74  in which a wiper  72  is held is fixed to the ink-jet heads  2  side of the tray  71 . The holding member  74  has a U-shape in plan view, and the wiper  72  is held at a portion of the holding member  74  extended along the paper transporting direction B. In contrast, depressed portions  74   a  which configure the engaging devices are formed at end portions of the holding members  74  extending in the direction orthogonal to the paper transporting direction B. 
         [0043]    The engaging devices are disposed in the vicinity of the respective sides of the trays  71  and  75  on the upper sides and the lower sides in  FIG. 2 , and each are mainly configured of the depressed portion  74   a  provided on the holding member  74  and a hooking member  83  supported by the tray  75 . The hooking members  83  extend in the direction orthogonal to the paper transporting direction B, and each are rotatably supported at a center thereof. The hooking members  83  each are formed with a hooking portion  83   a  which engages the depressed portion  74   a  at an end portion on the side of the ink-jet heads  2 . Abutment members  84  which are capable of coming into abutment with end portions  83   b  at positions of the respective hooking members  83  farthest from the ink-jet heads  2  are rotatably supported above the maintenance unit  70  respectively. When the abutment members  84  are rotated and comes into abutment with the end portions  83   b , the engagement between the hooking portions  83   a  and the depressed portions  74   a  is released. In contrast, when the abutment members  84  are moved away from the end portion  83   b , the hooking portions  83   a  engage the depressed portions  74   a  and a state shown in  FIG. 3  is restored. 
         [0044]    The tray  71  is released on a side surface opposite from the ink-jet heads  2  and, for example, when the engagement therebetween is released as during the wiping operation, only the tray  71  is movable except for the tray  75 . Irrespective of the state of engagement of the engaging devices, when the maintenance unit  70  is moved horizontally as described later, the frame  4  is moved to the “head maintenance position” which is upward (in the direction indicated by an arrow C in  FIG. 3 ) of the “printing position” in advance, and a space for the maintenance unit  70  is secured between the four ejection surfaces  3   a  and the peripheral surface  8   a . Thereafter, the maintenance unit  70  is moved horizontally in the direction indicated by an arrow D in  FIG. 3 . 
         [0045]    A waste ink receiving tray  77  is positioned immediately below the maintenance unit  70 . The waste ink receiving tray  77  has a size which contains the tray  71  in plan view, and has a shape in which a side edge portion on the side of the tray  71  opposite from the ink-jet heads  2  is overlapped even when the tray  71  is moved to the right end in  FIG. 2 . An ink discharge hole  77   a  penetrated in the vertical direction is formed at an end portion of the waste ink receiving tray  77  on the side of the ink-jet heads  2 . The ink discharge hole  77   a  allows the ink flowed into the waste ink receiving tray  77  to flow to a waste ink trap, not shown. 
         [0046]    The wiper  72  and the tray  75  are positioned in the tray  71  in sequence from the side closer to the ink-jet heads  2 . The wiper  72  is formed of a flat plate-shaped elastic material for wiping the ejection surfaces  3   a  in a wiping operation, and is disposed so as to extend in parallel to the paper transporting direction B. In the tray  75 , the plurality of, e.g., four, head caps  90  having a rectangular shape in plan view are arranged corresponding to the ejection surfaces  3   a  of the respective ink-jet heads  2  as shown in  FIG. 2 . The respective head caps  90  are arranged such that the longitudinal directions thereof extend in parallel to the longitudinal direction of the ink-jet heads  2 , and are arranged in the paper transporting direction B at the same pitches as the ink-jet heads  2 . 
         [0047]    Referring to  FIGS. 5A and 5B , the head caps  90  each have a cap  76 , a cap tip  78 , and a holder  89 . Referring to  FIGS. 5A ,  5 B,  FIGS. 6A ,  6 B, and  FIG. 9 , the cap  76  includes a substantially rectangular-shaped circular projection  76   a  projecting upward, and a bottom plate portion  76   b  being connected to a proximal end portion of the circular projection  76   a  and having a substantially elongated rectangular shape. The circular projection  76   a  and the bottom plate portion  76   b  are formed of elastic materials such as rubber or resin, and define a depressed portion  76   c  opening upward integrally with each other. In a capping operation described later, the depressed portion  76   c  seals nozzles  3   b  while surrounding an ejection area having the nozzles  3   b  opened through the ejection surface  3   a  by a distal end of the circular projection  76   a  coming into contact with the ejection surface  3   a . On a bottom surface of the depressed portion  76   c  (an upper surface of the bottom plate portion  76   b ) is provided upright with a hollow outer cylindrical portion  76   d . The outer cylindrical portion  76   d  is divided into a plurality of, e.g., four, parts by slits  76   e  extending in the axial direction. The slit  76   e  is formed from a distal end portion to a proximal end (the upper surface of the bottom plate portion  76   b ) of the outer cylindrical portion  76   d . In  FIG. 9 , a cross-sectional view on which slits  78   b  and  89   b  do not appear is illustrated. 
         [0048]    Referring to  FIGS. 5A ,  5 B,  FIGS. 7A ,  7 B, and  FIG. 9 , the cap tip  78  is a plate-shaped member arranged on the bottom surface of the depressed portion  76   c  of the cap  76 . The thickness of the cap tip  78  is set to be ½ the projecting height of the circular projection  76   a  or smaller. Three fixing members  79  arranged along the longitudinal direction are configured integrally with the cap tip  78  on a lower surface of the cap tip  78  (the surface on the side of the bottom surface of the depressed portion  76   c ). At this time, the cap tip  78  covers the plurality of, e.g., three, fixing members  79 . The fixing members  79  each include a fitting hole  78   a  opening downward, and a projecting portion  78   b  having a cylindrical shape projecting from centers of bottom surfaces of the respective fitting holes  78   a . The plurality of, e.g., three, fixing members  79  are arranged on the bottom surface of the depressed portion  76   c , and are arranged equidistantly in terms of the longitudinal direction of the cap tip  78 . The fixing member  79  arranged at the center from among the three fixing members  79  is positioned at the center of the bottom surface of the depressed portion  76   c . The height from an opening end portion of the fitting hole  78   a  to the bottom surface is the height of projection of the outer cylindrical portion  76   d  described above or higher. 
         [0049]    The lower surface of the cap tip  78  is configured with a grid like narrow groove  78   c  extending in the vertical and lateral directions in  FIG. 7A , and circular grooves  78   d  connected to the narrow groove  78   c  while extending along peripheral edges of the respective fitting holes  78   a . The narrow groove  78   c  and the circular grooves  78   d  define an introduction flow channel  81  in cooperation with the bottom surface of the depressed portion  76   c . The cap tip  78  is configured with a plurality of communicating flow channels  78   e  penetrating through the cap tip  78  in the thickness direction, and an upper surface of the cap tip  78  and the respective intersections of the narrow groove  78   c  are in communication with each other. In this manner, the communicating flow channel  78   e  and the introduction flow channel  81  are in communication with each other. 
         [0050]    Referring to  FIGS. 5A ,  5 B,  FIGS. 8A ,  8 B, and  FIG. 9 , the holder  89  is a plate-shaped member for holding the bottom plate portion  76   b  of the cap  76  from below. The holder  89  is formed with hollow inner cylindrical portions  89   a  provided upright so as to project from an upper surface (a surface on the side of the bottom plate portion  76   b ) and a lower surface. A portion near a distal end of the each inner cylindrical portion  89   a  projecting from an upper surface thereof is divided into a plurality of, e.g., four, parts by the slits  89   b  extending in the axial direction of the inner cylindrical portions  89   a . The slits  89   b  extend from the distal end of the inner cylindrical portion  89   a  to a midsection of the inner cylindrical portion  89   a , and leave from the midsection to a proximal end by a thickness of the bottom plate portion  76   b  of the cap  76  or smaller. Accordingly, the communication with the slit  76   e  of the outer cylindrical portion  76   d  is ensured. 
         [0051]    The holder  89  is supported by the tray  75  via plurality of, e.g., two, springs  88 , and is urged upward. Accordingly, when the circular projection  76   a  and the ejection surfaces  3   a  abut against each other, the springs  88  alleviate its impact force. Furthermore, even when an error is generated in parallelism of the circular projection  76   a  with respect to the ejection surfaces  3   a  to some extent, the circular projection  76   a  can follow the inclination with respect to the ejection surfaces  3   a.    
         [0052]    Referring to  FIG. 9 , the outer cylindrical portion  76   d  of the cap  76  is fitted to the fitting hole  78   a  by being inserted into the fitting hole  78   a  of the cap tip  78 . The inner cylindrical portion  89   a  of the holder  89  is fitted to the outer cylindrical portion  76   d  by being inserted into the outer cylindrical portion  76   d  of the cap  76 . At this time, the slit  76   e  of the outer cylindrical portion  76   d  and the slit  89   b  of the inner cylindrical portion  89   a  communicate with each other. The outer cylindrical portion  76   d  is clamped between an inner wall surface of the fitting hole  78   a  and an peripheral surface of the inner cylindrical portion  89   a  in terms of the radial direction (in the direction intersecting with the direction of projection of the circular projection  76   a ). Here, the inner diameter of the fitting hole  78   a  is narrowed as it goes toward an opening edge, and the outer cylindrical portion  76   d  and the inner cylindrical portion  89   a  are slightly tapered. Accordingly, the outer cylindrical portion  76   d  is tightly clamped between the inner wall surface of the fitting hole  78   a  and the peripheral surface of the inner cylindrical portion  89   a  in a water-tight manner. In addition, the projecting portion  78   b  of the cap tip  78  is fitted to the inner cylindrical portion  89   a  by being inserted into the inner cylindrical portion  89   a  of the holder  89 . 
         [0053]    In this manner, by the fixing members  79  fitted to the holder  89  via the bottom plate portion  76   b  of the cap  76 , the cap  76  is fixed to the holder  89 . Also, since the projecting portions  78   b  of the fixing members  79  are inserted into the inner cylindrical portions  89   a  of the holder  89 , wall surfaces of the inner cylindrical portions  89   a  are prevented from falling inward by a pressure generated when the fitting holes  78   a , the outer cylindrical portions  76   d , and the inner cylindrical portions  89   a  are fitted. 
         [0054]    The slits  76   e  of the outer cylindrical portions  76   d  and the slits  89   b  and internal spaces  89   c  of the inner cylindrical portions  89   a  define discharging flow channels  82 . Also, the slits  76   e  of the outer cylindrical portions  76   d  communicate with the circular grooves  78   d  of the cap tip  78 . In other words, the discharging flow channels  82  communicate with the depressed portions  76   c  via the communicating flow channels  78   e  and the introduction flow channels  81 , and communicate with the outside via openings at lower ends of the inner cylindrical portions  89   a . Ink ejected into the depressed portion  76   c  passes from the communicating flow channels  78   e  opening on an upper surface of the cap tip  78  through the introduction flow channels  81 , and is guided into the discharging flow channels  82 . The ink introduced into the discharging flow channels  82  is discharged to the outside from the openings at the lower ends of the inner cylindrical portions  89   a . Ink tubes, not shown, are connected to the lower ends of the inner cylindrical portions  89   a  and the discharged ink is discharged to a waste ink trap, not shown, via the ink tubes. 
         [0055]    Referring back to  FIG. 2  and  FIG. 3 , the maintenance unit  70  is kept standstill at a “retracted position” (a left side position which is not opposed to the ink-jet heads  2  in  FIG. 2 ) apart from the ink-jet heads  2  as shown in  FIG. 3  when a maintenance described later is not performed. Then, when the maintenance is performed, the maintenance unit  70  is moved from the “retracted position” horizontally to a “maintenance position” opposed to the ejection surfaces  3   a  of the ink-jet heads  2 . At this time, since the ink-jet heads  2  are arranged at the “head maintenance position”, the wiper  72  or the distal ends of the circular projections  76   a  does not come into contact with the ejection surfaces  3   a.    
         [0056]    At the time of wiping operation, the tray  75  is left at the position and only the tray  71  is moved from the “retracted position” to a position below the head, and receives inks wiped by the wiper  72 . When covering the ejection surfaces  3   a  with the caps  76  at the time of waiting and the purging operation, the tray  71  and the tray  75  are joined by the engaging devices, and are moved to the “maintenance position”. 
         [0057]    Referring to  FIG. 2 , the respective trays  71  and  75  are movably supported by a pair of guide shafts  96   a  and  96   b  extending in the direction orthogonal to the paper transporting direction B. The tray  71  is provided with a plurality of, e.g., two, bearing members  97   a  and  97   b , which are projected from both upper and lower surfaces of the holding member  74 . The tray  75  is provided with a plurality of, e.g., two, bearing members  98   a  and  98   b , which are projected from both upper and lower surfaces of the tray  75 . Also, the pair of guide shafts  96   a  and  96   b  are fixed at both ends thereof to the body frames  1   e  and  1   g  respectively, and are arranged in parallel to each other between the both frames  1   e  and  1   g . Here, the guide shafts  96   a  and  96   b  are fixed with screws, respectively. In this configuration, the respective trays  71  and  75  are moved in the lateral direction in the drawing (the direction indicated by an arrow D) along the guide shafts  96   a  and  96   b.    
         [0058]    A horizontal movement mechanism  91  moves the trays  71  and  75  in the horizontal direction. The horizontal movement mechanism  91  includes a motor  92 , a motor pulley  93 , an idle pulley  94 , a timing belt  95 , and the guide shafts  96   a  and  96   b , as shown in  FIG. 2 . The motor  92  is fixed to a mounting portion  1   f  formed at an end portion of the body frame  1   e  extending in parallel with the paper transporting direction B with a screw or the like. The motor pulley  93  is connected to the motor  92 , and is rotated in association with the drive of the motor  92 . The idle pulley  94  is rotatably supported by the body frame  1   g  located at the leftmost position in  FIG. 2 . The timing belt  95  is disposed in parallel with the guide shaft  96   a  and is wound around a pair of the motor pulley  93  and the idle pulley  94  so as to run therebetween. The bearing portion  97   a  provided on the holding member  74  is connected to the timing belt  95 . 
         [0059]    In this configuration, when the motor  92  is driven, the timing belt  95  runs in association with the normal or reverse rotation of the motor pulley  93 . With the traveling of the timing belt  95 , the tray  71  connected to the timing belt  95  via the bearing member  97   a  is moved in the direction toward the “retracted position” or the “maintenance position” leftward or rightward in  FIG. 2 . When the depressed portions  74   a  of the holding member  74  and the hooking portions  83   a  are engaged, the wiper  72  in the tray  71  and the caps  76  in the tray  75  move together, and when the hooking portions  83   a  are apart from the depressed portions  74   a , only the wiper  72  in the tray  71  is moved. 
         [0060]    Referring to  FIG. 10  and  FIG. 11 , the operation of the maintenance unit  70  will be described. When performing the purging operation for restoring the ink-jet head  2  which is suffering from ejection failure or the like, the capping operation for sealing the ejection surfaces  3   a  with the caps  76  is performed. The frame  4  is moved upward by the frame moving mechanisms  51  to arrange the ink-jet heads  2  to a “head maintenance position”. Accordingly, a space in which the maintenance unit  70  can be arranged is formed between the ejection surfaces  3   a  and the transporting belt  8 . 
         [0061]    Referring to  FIG. 10 , the tray  71  and the tray  75  are moved from the “retracted position” to the “maintenance position” in a state in which the tray  71  and the tray  75  are connected by the hooking member  83  by the horizontal movement mechanism  91 . At this time, the depressed portions  76   c  of the caps  76  are arranged at a position opposing the periphery of the ink ejection areas where the nozzles  3   b  are opened. In addition, the ink-jet heads  2  are moved to a “capping position” located below by the frame moving mechanisms  51  to bring the circular projections  76   a  into contact with the ejection surfaces  3   a . In this manner, the ink ejection areas of the ejection surfaces  3   a  are covered by the depressed portions  76   c  of the caps  76 , such that the nozzles  3   b  are sealed. In this procedure, the capping operation is completed. Accordingly, the nozzles  3   b  are prevented from being dried even though the waiting state continues. 
         [0062]    When performing the purging operation, in this state, a pump configured to forcedly deliver the ink in the ink tank  49  (not shown) to the ink-jet heads  2  is driven to perform the purging operation for discharging ink from the nozzles  3   b  of the ink-jet head  2  to the interiors of the caps  76 . With this purging operation, clogging of the nozzles  3   b  which are suffering from the ejection failure or increase in viscosity of ink in the nozzles  3   b  is solved. 
         [0063]    At this time, the inks ejected into the caps  76  pass from the communicating flow channels  78   e  opening on upper surfaces of the cap tips  78  through the introduction flow channels  81 , and are guided into the discharging flow channels  82 . The inks introduced into the discharging flow channels  82  are discharged to the outside from the openings at the lower ends of the inner cylindrical portions  89   a . Ink tubes, not shown, are connected to the lower ends of the inner cylindrical portions  89   a  and the discharged inks are discharged to a waste ink trap, not shown, via the ink tube. However, part of the ink remains on the ejection surfaces  3   a  as ink drops. 
         [0064]    In order to perform the wiping operation, the frame  4  is moved upward by the frame moving mechanisms  51  again to arrange the ink-jet heads  2  to the “head maintenance position”. Subsequently, the tray  71  and the tray  75  are moved from the “maintenance position” to the “retracted position” by the horizontal movement mechanism  91 . Then, the abutment members  84  are brought into abutment with the end portions  83   b  of the hooking members  83  to move the hooking portions  83   a  apart from the depressed portions  74   a , such that the engagement between the depressed portions  74   a  and the hooking portions  83   a  are released. In other words, the connection between the tray  71  and the tray  75  is released. In this state, the tray  71  is moved from the “retracted position” to the “maintenance position” by the horizontal movement mechanism  91  as shown in  FIG. 11A . 
         [0065]    The ink-jet heads  2  are moved downward by the frame moving mechanisms  51 . At this time, when the tray  71  is moved leftward in  FIG. 11  (that is, the direction from the “maintenance position” to the “retracted position”), the ink-jet heads  2  are arranged at the “wiping position” where a distal end of the wiper  72  comes into contact with the ejection surfaces  3   a . Then, as shown in  FIG. 11B , the tray  71  is moved from the “maintenance position” to the “retracted position” by the horizontal movement mechanism  91 . 
         [0066]    In this wiping operation, since an upper end of the wiper  72  is located above the level of the ejection surfaces  3   a , it comes into contact with the ejection surfaces  3   a  while being deflected, such that the ink adhered to the ejection surfaces  3   a  is wiped by the purging operation. The ink wiped by the wiper  72  runs over a surface of the wiper  72  and flows into the waste ink receiving tray  77 . Then, the ink is discharged from the discharge hole  77   a  of the waste ink receiving tray  77 . 
         [0067]    In this manner, the maintenance operation in which the ink-jet heads  2  being suffering from the ink ejection failure are restored by the capping operation and the purging operation, and the inks adhered to the ejection surfaces  3   a  are wiped by the wiping operation is ended. 
         [0068]    Subsequently, in the waiting state, or when the ink-jet printer  1  is brought into an OFF state, the ink-jet heads  2  are arranged at the “head maintenance position”, the tray  71  is moved again to the “maintenance position” in association with the tray  75 , and the ink-jet heads  2  are moved downward to the “capping position”. Alternatively, when restarting the image formation, the ink-jet heads  2  are moved downward to the “printing position” with the plurality of, e.g., two, trays  71  and  75  left at the “retracted position”. 
         [0069]    According to the ink-jet printer  1  in the embodiment as described above, the caps  76  are fixed to the holder  89  by the fixing members  79  arranged on the bottom surface of the depressed portion  76   c  of the cap  76  fitted to the holder  89  via the bottom plate portion  76   b  of the caps  76 . Here, the thickness of the fixing members  79  is a fraction of the height of the circular projection  76   a  or smaller. Therefore, the fitting portion between the cap  76  and the holder  89  do not project outward by the circular projection  76   a , such that downsizing of the head cap  90  is achieved. 
         [0070]    Since the fixing members  79  are arranged at the center of the bottom surface of the depressed portion  76   c , the cap  76  can be fixed to the holder  89  in a balanced state. 
         [0071]    Since the plurality of, e.g., three, fixing members  79  are arranged equidistantly in terms of the longitudinal direction of the cap tip  78 , the cap  76  is fixed to the holder  89  at three positions, such that the elongated cap  76  is reliably fixed to the holder  89 . Also, warp of the cap  76  in terms of the longitudinal direction is restrained. 
         [0072]    Since the cap tip  78  is accurately fixed to the bottom surface of the depressed portion  76   c  by the fixing members  79 , contact of the narrow groove  78   c  and the circular grooves  78   d  with respect to the bottom surface of the depressed portion  76   c  is ensured. Accordingly, the introduction flow channel is reliably formed, and the liquid discharged to the depressed portion  76   c  of the cap  76  can be discharged reliably to the outside via the introduction flow channel  81  and the discharging flow channel  82  communicating thereto. 
         [0073]    The cap tip  78  and the holder  89  can be fitted via the bottom plate portion  76   b  in a simple structure in which the inner cylindrical portions  89   a  are inserted to the outer cylindrical portions  76   d  while inserting the outer cylindrical portions  76   d  into the fitting holes  78   a  such that the outer cylindrical portions  76   d  are clamped between the inner wall surfaces of the fitting holes  78   a  and the peripheral surfaces of the inner cylindrical portions  89   a  in the radial direction thereof. 
         [0074]    Since the projecting portions  78   b  of the cap chip  78  are inserted into the inner cylindrical portions  89   a  of the holder  89 , the wall surfaces of the inner cylindrical portions  89   a  are prevented from falling inward by the pressure generated when the fitting holes  78   a , the outer cylindrical portions  76   d , and the inner cylindrical portions  89   a  are fitted. Accordingly, the outer cylindrical portions  76   d  are clamped between the inner wall surfaces of the fitting holes  78   a  and the peripheral surfaces of the inner cylindrical portion  89   a  at a predetermined pressure in terms of the radial direction, such that the cap  76  can be fixed to the holder  89  tightly. 
         [0075]    At this time, a portion near a distal end of the each inner cylindrical portion  89   a  projecting from the upper surface is divided into a plurality of, e.g., four, parts by the slits  89   b  extending in the axial direction of the inner cylindrical portion  89   a . Accordingly, the distal end of the inner cylindrical portion  89   a  is opened in the radial direction when the inner cylindrical portion  89   a  is fitted to the projecting portion  78   b , such that the outer cylindrical portion  76   d  is tightly clamped between the fitting hole  78   a  and the inner cylindrical portion  89   a.    
         [0076]    At this time, since the outer cylindrical portion  76   d  is divided into a plurality of, e.g., four, parts by the slits  76   e  and the slits  76   e  and the slits  89   b  of the inner cylindrical portion  89   a  are communicated with each other, the outer cylindrical portion  76   d  can be easily deformed in terms of the radial direction, and the outer cylindrical portion  76   d  and the inner cylindrical portion  89   a  can be opposed to each other efficiently. Therefore, the outer cylindrical portion  76   d  can be clamped efficiently between the fitting hole  78   a  and the inner cylindrical portion  89   a.    
         [0077]    In addition, at this time, since the discharging flow channel  82  includes the slits  76   e  of the outer cylindrical portion  76   d  and the slits  89   b  of the inner cylindrical portion  89   a , and the slits  76   e  communicate with the introduction flow channels  81 , the ink introduced by the introduction flow channels  81  passes from the slits  76   e  through the discharging flow channels  82  and is discharged efficiently to the outside. 
         [0078]    The cap tip  78  covers the fixing members  79  integrally. Accordingly, the ink in the depressed portion  76   c  is prevented from leaking out to the outside from the fitted positions (between the fitting holes  78   a  and the outer cylindrical portions  76   d , and between the outer cylindrical portions  76   d  and the inner cylindrical portions  89   a ). 
         [0079]    Although the description of the embodiments has been described above, the invention is not limited to the embodiments, and various modifications are possible. For example, the three fixing members  79  of the cap tip  78  are arranged at the center of the bottom surface of the depressed portion  76   c  in the embodiment described above, the number and the position of the fixing members  79  may be arbitrary. For example, the fixing member  79  may be arranged solely at the center of the bottom surface of the depressed portion  76   c , or the two fixing members  79  may be arranged near the both ends of the bottom surface of the depressed portion  76   c.    
         [0080]    Although the fixing members  79  are integrally formed with the cap tip  78  in the embodiment described above, the fixing members  79  may be formed as independent members. For example, the respective fixing members  79  may be formed independently, or a plurality of the fixing members  79  may be formed integrally. In this case, a configuration in which the head cap does not have the cap tip is also applicable. 
         [0081]    In this case, although the head cap  90  has a configuration in which the ink ejected into the depressed portion  76   c  of the cap  76  is discharged to the outside via the communicating flow channels  78   e , the introduction flow channels  81  and the discharging flow channels  82 , a configuration in which the head cap does not have the communicating flow channel  78   e , the introduction flow channel  81 , and the discharging flow channel  82 , and the ink in the depressed portion  76   c  is not discharged to the outside is also applicable if the ink is not ejected into the depressed portion  76   c  in the purging operation. 
         [0082]    Although the portions projecting from the upper surfaces of the inner cylindrical portions  89   a  of the holders  89  each are divided into four parts near the distal ends thereof by the slits  89   b  in the embodiment described above, the portions near the distal ends of the inner cylindrical portions  89   a  may each be divided into two parts or five parts or more. 
         [0083]    Although the outer cylindrical portions  76   d  of the cap  76  are each divided into four parts by the slits  89   b  in the embodiment described above, the outer cylindrical portions  76   d  may be divided into two parts or five parts or more. 
         [0084]    Although the fitting holes  78   a  are fitted to the holders  89  via the bottom plate portion  76   b  by inserting the inner cylindrical portions  89   a  into the outer cylindrical portions  76   d  while inserting the outer cylindrical portions  76   d  into the fitting holes  78   a  in the embodiment described above, the fixing members may be fitted to the holders via the bottom plate portion in other configuration as long as at least the bottom plate portion is clamped in the direction intersecting the projecting direction of the circular projections  76   a . For example, column-shaped projecting portions may be provided upright on the upper surface of the holders instead of the inner cylindrical portions  89   a  of the holder. 
         [0085]    Although the example in which the invention is applied to the ink-jet printer  1  has been described in the embodiment described above, the invention is also applicable to the apparatus having a liquid droplet head for discharging other types of liquid. Although the ink-jet printer  1  has the plurality of, e.g., four, head caps  90  in the embodiment described above, a configuration in which only the head cap  90  is independent is also applicable.