Patent Publication Number: US-9409430-B2

Title: Inkjet printer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2014-265089, filed on Dec. 26, 2014, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to an inkjet printer configured to perform printing by ejecting inks from inkjet heads. 
     2. Related Art 
     When inkjet heads are driven in an inkjet printer, piezoelectric elements, a drive circuit, and the like generate heat. A temperature increase due to this generated heat causes failures of the inkjet heads and the like. Accordingly, the inkjet heads need to be cooled. 
     Japanese Patent Application Publication No. 2010-264752 proposes an inkjet printer in which two fans are arranged across head arrays each including inkjet heads aligned. In the inkjet printer, one of the fans blows a cooling wind to the inkjet heads, while the other fan sucks the cooling wind. The inkjet heads are thereby cooled. 
     SUMMARY 
     In the inkjet printer of Japanese Patent Application Publication No. 2010-264752, when the number of head arrays is increased, the number of fans also needs to be increased in order to evenly cool the head arrays and prevent uneven cooling of the inkjet heads. However, this leads to an increase in an apparatus size. 
     An object of the disclosure is to provide an inkjet printer which can reduce unevenness in cooling of inkjet heads while suppressing an increase in an apparatus size. 
     An inkjet printer in accordance with some embodiments includes: a plurality of inkjet heads arranged in a plurality of head arrays; a first chamber having a plurality of first ventilation holes of a same size arranged on extended lines of the plurality of head arrays respectively, the first chamber extending in a direction orthogonal to the extended lines; a blow fan configured to send air into the first chamber from a first end of the first chamber; a second chamber facing the first chamber across the plurality of head arrays and having a plurality of second ventilation holes of a same size facing the plurality of first ventilation holes, the second chamber extending in the direction orthogonal to the extended lines; and a suction fan configured to suck air from a second end of the second chamber on a same side as a side of the first end of the first chamber. The first chamber has a shape with cross-sectional areas of an internal air flow passage in the first chamber at positions of the first ventilation holes decreasing with an increase in a distance of the first ventilation holes from the first end. The second chamber has a shape with cross-sectional areas of an internal air flow passage in the second chamber at positions of the second ventilation holes decreasing with an increase in a distance of the second ventilation holes from the second end. 
     In the configuration described above, the first chamber has such a shape that the internal air flow passage has cross-sectional areas at the positions of the first ventilation holes decreasing with the increase in the distance of the first ventilation holes from the first end (the blow fan). Moreover, the second chamber has such a shape that the internal air flow passage has cross-sectional areas at the positions of the second ventilation holes decreasing with the increase in the distance of the second ventilation holes from the second end (the suction fan). This can reduce unevenness in an air speed of a cooling wind among the head arrays. As a result, unevenness in cooling of the inkjet heads can be reduced. Moreover, since the inkjet heads are cooled only by one fan and one chamber on each of the blow side and the suction side, an increase in an apparatus size can be suppressed. Thus, the configuration described above can reduce the unevenness in the cooling of the inkjet heads while suppressing the increase in the apparatus size. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration of an inkjet printer in a first embodiment. 
         FIG. 2  is a schematic configuration diagram of a conveyer and a printing unit of the inkjet printer illustrated in  FIG. 1 . 
         FIG. 3  is a plan view of the printing unit in the inkjet printer illustrated in  FIG. 1 . 
         FIG. 4  is an exploded perspective view of the printing unit in the inkjet printer illustrated in  FIG. 1 . 
         FIG. 5  is a view illustrating a cooling wind generated by a cooler. 
         FIG. 6  is an exploded perspective view of a printing unit in a modified example of the first embodiment. 
         FIG. 7  is an exploded perspective view of a printing unit in a second embodiment. 
         FIG. 8  is a front view of the printing unit in the second embodiment. 
         FIG. 9  is a rear view of the printing unit in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     Description will be hereinbelow provided for embodiments of the present invention by referring to the drawings. It should be noted that the same or similar parts and components throughout the drawings will be denoted by the same or similar reference signs, and that descriptions for such parts and components will be omitted or simplified. In addition, it should be noted that the drawings are schematic and therefore different from the actual ones. 
     First Embodiment 
       FIG. 1  is a block diagram illustrating a configuration of an inkjet printer in a first embodiment.  FIG. 2  is a schematic configuration diagram of a conveyer and a printing unit in the inkjet printer illustrated in  FIG. 1 .  FIG. 3  is a plan view of the printing unit in the inkjet printer illustrated in  FIG. 1 .  FIG. 4  is an exploded perspective view of the printing unit in the inkjet printer illustrated in  FIG. 1 . 
     In  FIGS. 2 to 9 , directions of right, left, up, down, front and rear are denoted by RT, LT, UP, DN, FT, and RR, respectively. In  FIGS. 2 to 9 , a direction from left to right is a conveying direction of sheets P which are printing media. 
     As illustrated in  FIG. 1 , the inkjet printer  1  in the first embodiment includes a conveyer  2 , a printing unit  3 , and a controller  4 . 
     The conveyer  2  conveys the sheets P. As illustrated in  FIGS. 1 and 2 , the conveyer  2  includes a transfer belt  11 , a drive roller  12 , driven rollers  13 ,  14 , and  15 , a belt motor  16 , and a sheet suction fan  17 . 
     The transfer belt  11  conveys the sheets P while sucking and holding the sheets P thereon. The transfer belt  11  is an annular belt wound around the drive roller  12  and the driven rollers  13  to  15 . The transfer belt  11  is flexible and is made of a material such as rubber or resin which generates an appropriate degree of friction force between the sheets P and the belt. Multiple belt holes (not illustrated) are also formed in the transfer belt  11 . The transfer belt  11  sucks and holds the sheets P on the top surface by means of suction force generated at the belt holes by drive of the sheet suction fan  17 . The transfer belt  11  rotates clockwise in  FIG. 2  to convey the sucked and held sheets P to the right. 
     The drive roller  12  rotates the transfer belt  11  clockwise in  FIG. 2 . 
     The driven rollers  13  to  15  support the transfer belt  11  together with the drive roller  12 . The driven rollers  13  to  15  are driven by the drive roller  12  via the transfer belt  11 . The driven roller  13  is arranged on the left side of the drive roller  12  at the same height as the drive roller  12 . The driven rollers  14  and  15  are arranged at substantially the same height below the drive roller  12  and the driven roller  13  while being spaced away from each other in a left-right direction. 
     The belt motor  16  rotationally drives the drive roller  12 . 
     The sheet suction fan  17  generates a downward air flow. The sheet suction fan  17  thus sucks air through the belt holes of the transfer belt  11  and generates negative pressure at the belt holes to suck the sheets P such that the sheets P are held on the transfer belt  11 . The sheet suction fan  17  is arranged in a region surrounded by the annular transfer belt  11 . 
     The printing unit  3  prints images on the sheets P conveyed by the conveyer  2 . The printing unit  3  is arranged above the conveyer  2 . As illustrated in  FIGS. 1 to 4 , the printing unit  3  includes a head unit  21  and a cooler  22 . 
     The head unit  21  ejects inks to the sheets P conveyed by the conveyer  2  to print images. The head unit  21  includes multiple inkjet heads  31  and a head holder  32 . 
     Each of the inkjet heads  31  has a nozzle surface  31   a  in which nozzles (not illustrated) are opened. The nozzle surface  31   a  is a bottom surface of the inkjet head  31  which faces the sheets P conveyed by the transfer belt  11 . The multiple nozzles are formed in the nozzle surface  31   a  to be arranged in a front-rear direction (scanning direction). The inkjet heads  31  eject the inks supplied through ink supply routes (not illustrated), from the nozzles. 
     The multiple inkjet heads  31  are arranged to form multiple head arrays. In the embodiment, as illustrated in  FIG. 3 , twelve inkjet heads  31  form four head arrays L 1  to L 4  arranged in a left-right direction in parallel to one another. 
     Each of the head arrays L 1  to L 4  include three inkjet heads  31  which are arranged at equal intervals in the front-rear direction (scanning direction). Each of the inkjet heads  31  in the head arrays L 1  to L 4  is arranged to be shifted in the front-rear direction by half a pitch relative to the corresponding inkjet head  31  in the adjacent head array. The twelve inkjet heads  31  are thereby arranged in a zigzag pattern. The inkjet heads  31  in the head arrays L 1  and L 2  eject the same color of ink. The inkjet heads  31  in the head arrays L 3  and L 4  eject the same color of ink. 
     The head holder  32  holds the inkjet heads  31 . The head holder  32  is a box formed in a hollow rectangular-solid shape. As illustrated in  FIG. 4 , the head holder  32  has a bottom plate  41 , side plates  42  to  45 , and a top plate  46 . 
     The bottom plate  41  holds the inkjet heads  31  such that the inkjet heads  31  are fixed. The bottom plate  41  is formed in a rectangular shape. Attachment openings  41   a  for attaching the inkjet heads  31  are formed as many as the inkjet heads  31 . The inkjet heads  31  are inserted into and fixed to the attachment openings  41   a  such that the nozzle surfaces  31   a  protrude downward from a bottom surface of the bottom plate  41 . 
     The side plates  42 ,  43 ,  44 , and  45  form front, right, rear, and left side walls of the head holder  32 , respectively. The side plates  42  to  45  are integrally formed and stand upright at a periphery of the bottom plate  41 . 
     Four ventilation holes  42   a  are formed in the front side plate  42 . The ventilation holes  42   a  are air inlets to the head holder  32  used when air is blown from a blow chamber  51  to be described later, to the inkjet heads  31 . The four ventilation holes  42   a  are formed respectively on extend lines of the head arrays L 1  to L 4 . The four ventilation holes  42   a  all have the same size. 
     Four ventilation holes  44   a  are formed in the rear side plate  44 . The ventilation holes  44   a  are air outlets used when air is sucked out from the head holder  32  through a suction chamber  53  to be described later. The four ventilation holes  44   a  are arranged at positions facing the four ventilation holes  42   a  of the front side plate  42 , respectively. In other words, the four ventilation holes  44   a  are formed respectively on the extend lines of the head arrays L 1  to L 4 . The four ventilation holes  44   a  all have the same size. 
     The top plate  46  is a lid which closes an opening at upper ends of side walls formed by the side plates  42  to  45 . The top plate  46  is formed in a rectangular shape. 
     The cooler  22  cools the inkjet heads  31 . The cooler  22  includes the blow chamber (first chamber)  51 , a blow fan  52 , the suction chamber (second chamber)  53 , and a suction fan  54 . 
     The blow chamber  51  forms an air flow passage between the blow fan  52  and the head holder  32 . The blow chamber  51  has an elongated shape extending in the left-right direction which is a direction orthogonal to the head arrays L 1  to L 4 , and is formed to be hollow. The blow chamber  51  is arranged on the front side plate  42  of the head holder  32 . Four ventilation holes  51   a  are formed on a surface of the blow chamber  51  which comes into contact with the side plate  42 . 
     The ventilation holes  51   a  are air outlets from the blow chamber  51  used when air is blown to the inkjet heads  31 . The ventilation holes  51   a  are arranged at positions corresponding to the ventilation holes  42   a  of the side plate  42 . In other words, the four ventilation holes  51   a  are formed respectively on the extend lines of the head arrays L 1  to L 4 . The four ventilation holes  51   a  all have the same size. 
     The blow chamber  51  has such a shape that the internal air flow passage has cross-sectional areas at the positions of the ventilation holes  51   a  decreasing with an increase in the distance of the ventilation hole  51   a  from the blow fan  52 . Specifically, as illustrated in  FIGS. 3 and 4 , the blow chamber  51  is formed in such a shape that the depth of the blow chamber  51  in the front-rear direction at the position of each ventilation hole  51   a  decreases toward the left side. The depth of the blow chamber  51  in the front-rear direction at the position of each of the ventilation holes  51   a  is designed such that speeds of air flows from the respective ventilation holes  51   a  to the head arrays L 1  to L 4  are even. 
     The blow fan  52  sends air into the blow chamber  51  from a right end of the blow chamber  51 . The blow fan  52  thereby blows air to the inkjet heads  31  via the blow chamber  51 . 
     The suction chamber  53  forms an air flow passage between the head holder  32  and the suction fan  54 . The suction chamber  53  has an elongated shape extending in the left-right direction, and is formed to be hollow. The suction chamber  53  is arranged on the rear side plate  44  of the head holder  32 . In other words, the suction chamber  53  is arranged to face the blow chamber  51  across the head arrays L 1  to L 4  and the head holder  32 . Four ventilation holes  53   a  are formed on a surface of the suction chamber  53  which comes into contact with the side plate  44 . 
     The ventilation holes  53   a  are air inlets to the suction chamber  53  used when air is sucked out from the head holder  32 . The ventilation holes  53   a  are arranged at positions corresponding to the ventilation holes  44   a  of the side plate  44 . In other words, the four ventilation holes  53   a  are formed respectively on the extended lines of the head arrays L 1  to L 4 . To put it differently, the ventilation holes  53   a  are arranged to face the ventilation holes  51   a  of the blow chamber  51 . 
     The suction chamber  53  has such a shape that the internal air flow passage has cross-sectional areas at positions of the ventilation holes  53   a  decreasing with an increase in the distance of the ventilation holes  53   a  from the suction fan  54 . Specifically, as illustrated in  FIGS. 3 and 4 , the suction chamber  53  is formed in such a shape that the depth of the suction chamber  53  in the front-rear direction at the position of each ventilation hole  53   a  decreases toward the left side. The depth of the suction chamber  53  in the front-rear direction at the position of each of the ventilation holes  53   a  is designed such that speeds of air flows sucked in from the respective ventilation holes  53   a  are even. 
     The suction fan  54  sucks air from the right end of the suction chamber  53  which is an end on the same side as the side of the blow chamber  51  on which the blow fan  52  is arranged. The suction fan  54  thereby sucks air from the head holder  32  via the suction chamber  53 . 
     The controller  4  controls operations of various units in the inkjet printer  1 . The controller  4  includes a CPU, a RAM, a ROM, a hard disk drive, and the like. 
     Specifically, in printing, the controller  4  causes the inkjet heads  31  to eject the inks while causing the conveyer  2  to convey the sheets P, and also performs control such that the cooler  22  cools the inkjet heads  31 . 
     Next, operations of the inkjet printer  1  are described. 
     When receiving a print job, the controller  4  causes the belt motor  16  to activate the drive roller  12 . Rotation drive of the transfer belt  11  is thereby started. 
     Moreover, the controller  4  activates the sheet suction fan  17 . The sheet suction fan  17  thereby sucks air through the belt holes in the transfer belt  11  and the suction force is generated at the belt holes. 
     Moreover, the controller  4  activates the blow fan  52  and the suction fan  54 . The drive of the blow fan  52  causes air to be blown to the head arrays L 1  to L 4  through the ventilation holes  51   a  of the blow chamber  51  and the ventilation holes  42   a  of the side plate  42  of the head holder  32 . Meanwhile, the drive of the suction fan  54  causes air to be sucked out from the head holder  32  through the ventilation holes  44   a  of the side plate  44  of the head holder  32  and the ventilation holes  53   a  of the suction chamber  53 . As illustrated in  FIG. 5 , a cooling wind W flowing from the front side to the rear side is thus generated in the head holder  32 . 
     As described above, the blow chamber  51  has such a shape that the cross-sectional area of the internal air flow passage decreases toward the left side. The air speed is inversely proportional to the cross-sectional area of the flow passage. The wind generated by the blow fan  52  becomes weaker as the distance from the blow fan  52  increases. However, in a design in which the cross-sectional area of the flow passage decreases as the distance from the blow fan  52  increases as in the blow chamber  51 , the air speed can be maintained even at a position far from the blow fan  52 . Moreover, as described above, the shape of the blow chamber  51  is designed such that the speeds of the air flows from the respective ventilation holes  51   a  to the head arrays L 1  to L 4  are even. 
     Similarly, on the suction side, in a design in which the cross-sectional area of the flow passage decreases as the distance from the suction fan  54  increase as in the suction chamber  53 , the air speed can be maintained even at a position where the distance from the suction fan  54  is great. Moreover, as described above, the shape of the suction chamber  53  is designed such that the speeds of the air flows sucked in from the respective ventilation holes  53   a  are even. 
     Accordingly, the air speed of the cooling wind W generated by the drive of the blow fan  52  and the suction fan  54  is the same among the head arrays L 1  to L 4 . 
     When the sheets P are fed from a not-illustrated paper feeder to the conveyer  2 , the sheets P are conveyed while being sucked and held by the transfer belt  11 . The controller  4  prints images on the sheets P conveyed below the head unit  21  by ejecting the inks from the inkjet heads  31 . When the specified number of sheets to be printed is two or more, the controller  4  prints images by causing the inks to be ejected from the inkjet heads  31  to each of the sheets P sequentially fed and conveyed on the transfer belt  11 . 
     When the inkjet heads  31  are driven, the inkjet heads  31  generate heat but are cooled by the cooling wind W. As described above, since the cooling wind W flows to the head arrays L 1  to L 4  at the same air speed, the inkjet heads  31  are evenly cooled. 
     When the blow chamber  51  and the suction chamber  53  have such shapes that the internal air passage has a uniform cross-sectional area unlike the embodiment, the cooling wind becomes weaker as the distance from the blow fan  52  and the suction fan  54  to each of the head arrays increases. Accordingly, the inkjet heads  31  are unevenly cooled. 
     When the inkjet heads  31  are unevenly cooled, failures may occur. For example, there is a risk that the viscosity of the ink varies among the inkjet heads  31  and an ejection speed thereby varies among the inkjet heads  31 , which causes disturbance in printed images. Moreover, for example, there is a risk that some of the inkjet heads  31  become too hot and break. Furthermore, for example, there is a risk that some of the inkjet head  31  are cooled too much and ink mist increases. 
     Meanwhile, in the inkjet printer  1 , since the inkjet heads  31  are evenly cooled, failures like the ones described above are prevented. 
     After exiting the conveyer  2 , the printed sheets P are conveyed to a not-illustrated paper discharger and are discharged. When the last sheet P is discharged, the controller  4  stops the drive roller  12  and also stops the sheet suction fan  17 . Moreover, the controller  4  stops the blow fan  52  and the suction fan  54 . The printing operation is thereby completed. 
     As described above, in the inkjet printer  1 , the blow chamber  51  has such a shape that the internal air flow passage has cross-sectional areas at the positions of the ventilation holes  51   a  decreasing with the increase in the distance of the ventilation holes  51   a  from the blow fan  52 . Moreover, the suction chamber  53  has such a shape that the internal air flow passage has cross-sectional areas at the positions of the ventilation holes  53   a  decreasing with the increase in the distance of the ventilation holes  53   a  from the suction fan  54 . This can reduce unevenness in the air speed of the cooling wind W among the head arrays L 1  to L 4 . As a result, unevenness in the cooling of the inkjet heads  31  can be reduced. 
     Moreover, in the inkjet printer  1 , since the cooler  22  cools the inkjet heads  31  by using only one fan and one chamber on each of the blow side and the suction side, an increase in an apparatus size can be suppressed. 
     Accordingly, the inkjet printer  1  can reduce the unevenness in the cooling of the inkjet heads  31  while suppressing the increase in the apparatus size. 
     Modified Example of First Embodiment 
     Next, description is given of a modified example in which the blow chamber and the suction chamber in the aforementioned first embodiment are modified.  FIG. 6  is an exploded perspective view of a printing unit in the modified example. 
     As illustrated in  FIG. 6 , the printing unit  3 A in the modified example has a configuration in which the cooler  22  of the printing unit  3  in the aforementioned first embodiment is replaced by a cooler  22 A. The cooler  22 A has a configuration in which the blow chamber  51  is replaced by a blow chamber  51 A and the suction chamber  53  is replaced by a suction chamber  53 A in the cooler  22  in the first embodiment. 
     The blow chamber  51 A includes a blow chamber main body  61  and a frame  62 . 
     The blow chamber main body  61  has a configuration in which most of the surface of the blow chamber  51  in the first embodiment facing the side plate  42  of the head holder  32  is opened to form an opening  61   a . The blow chamber main body  61  is attached to the side plate  42  of the head holder  32  via the frame  62 . 
     The frame  62  is a frame for attaching the blow chamber main body  61  to the side plate  42  of the head holder  32 . The frame  62  covers the opening  61   a  of the blow chamber main body  61  and is arranged on the side plate  42 . Four ventilation holes  62   a  are formed in the frame  62 . 
     The ventilation holes  62   a  are air outlets from the blow chamber  51 A used when air is blown to the inkjet heads  31 . The ventilation holes  62   a  are arranged at positions corresponding to the ventilation holes  42   a  of the side plate  42 . In other words, the four ventilation holes  62   a  are formed respectively on the extend lines of the head arrays L 1  to L 4 . The four ventilation holes  62   a  all have the same size. 
     Moreover, the ventilation holes  62   a  are arranged at such positions that the depth of the blow chamber main body  61  at the position of each of the ventilation holes  62   a  decreases toward the left side. The depth of the blow chamber main body  61  in the front-rear direction at the position of each of the ventilation holes  62   a  is designed such that speeds of air flows from the respective ventilation holes  62   a  to the head arrays L 1  to L 4  are even. 
     The suction chamber  53 A includes a suction chamber main body  66  and a frame  67 . 
     The suction chamber main body  66  has a configuration in which most of the surface of the suction chamber  53  in the first embodiment facing the side plate  44  of the head holder  32  is opened to form an opening  66   a . The suction chamber main body  66  is attached to the side plate  44  of the head holder  32  via the frame  67 . 
     The frame  67  is a frame for attaching the suction chamber main body  66  to the side plate  44  of the head holder  32 . The frame  67  covers the opening  66   a  of the suction chamber main body  66  and is arranged on the side plate  44 . Four ventilation holes  67   a  are formed in the frame  67 . 
     The ventilation holes  67   a  are air inlets to the suction chamber  53 A used when air is sucked out from the head holder  32 . The ventilation holes  67   a  are arranged at positions corresponding to the ventilation holes  44   a  of the side plate  44 . In other words, the four ventilation holes  67   a  are formed respectively on the extended lines of the head arrays L 1  to L 4 . To put it differently, the ventilation holes  67   a  are arranged to face the ventilation holes  62   a  of the blow chamber  51 A. 
     Moreover, the ventilation holes  67   a  are arranged at such positions that the depth of the suction chamber main body  66  at the position of each of the ventilation holes  67   a  decreases toward the left side. The depth of the suction chamber main body  66  in the front-rear direction at the position of each of the ventilation holes  67   a  is designed such that speeds of air flows sucked from the ventilation holes  67   a  are even. 
     The unevenness in the air speed of the cooling wind W among the head arrays L 1  to L 4  can be reduced also by the cooler  22 A having the blow chamber  51 A and the suction chamber  53 A as described above. 
     Note that it is possible to employ a configuration in which the frames  62  and  67  are omitted and the blow chamber main body  61  and the suction chamber main body  66  are directly attached to the side plates  42  and  44 , respectively. In this case, the blow chamber main body  61  and the side plate  42  form the blow chamber. Meanwhile, the suction chamber main body  66  and the side plate  44  form the suction chamber. 
     Second Embodiment 
     Next, description is given of a second embodiment in which the printing unit of the aforementioned first embodiment is modified.  FIG. 7  is an exploded perspective view of the printing unit in the second embodiment.  FIG. 8  is a front view of the printing unit in the second embodiment.  FIG. 9  is a rear view of the printing unit in the second embodiment. 
     As illustrated in  FIG. 7 , the printing unit  3 B in the second embodiment has a configuration in which the cooler  22  of the printing unit  3  in the aforementioned first embodiment is replaced by a cooler  22 B. The cooler  22 B has a configuration in which the blow chamber  51  is replaced by a blow chamber  51 B and the suction chamber  53  is replaced by a suction chamber  53 B in the cooler  22  in the first embodiment. 
     As illustrated in  FIGS. 7 and 8 , the blow chamber  51 B is formed in such a shape that the width of the blow chamber  51 B in an up-down direction at the position of each of the ventilation holes  51   a  decreases toward the left side. The blow chamber  51 B thus has such a shape that the internal air flow passage has cross-sectional areas at the positions of the ventilation holes  51   a  decreasing with the increase in the distance of the ventilation hole  51   a  from the blow fan  52 . The width of the blow chamber  51 B in the up-down direction at the position of each of the ventilation holes  51   a  is designed such that the speeds of the air flows from the respective ventilation holes  51   a  to the head arrays L 1  to L 4  are even. 
     As shown in  FIGS. 7 and 9 , the suction chamber  53 B is formed in such a shape that the width of the suction chamber  53 B in the up-down direction at the position of each of the ventilation holes  53   a  decreases toward the left. The suction chamber  53 B thus has such a shape that the internal air flow passage has cross-sectional areas at positions of the ventilation holes  53   a  decreasing with the increase in the distance of the ventilation holes  53   a  from the suction fan  54 . The width of the blow chamber  53 B in the up-down direction at the position of each of the ventilation holes  53   a  are designed such that the speeds of the air flows sucked from the respective ventilation holes  53   a  are even. 
     The unevenness in the air speed of the cooling wind W among the head arrays L 1  to L 4  can be reduced also by the cooler  22 B having the blow chamber  51 B and the suction chamber  53 B as described above. 
     Accordingly, the second embodiment can reduce the unevenness in the cooling of the inkjet heads  31  while suppressing the increase in the apparatus size as in the first embodiment. 
     As in the modified example of the first embodiment, it is possible to use a blow chamber including: a blow chamber main body in which most of a surface of the blow chamber  51 B facing the side plate  42  is opened to form an opening: and a frame in which four ventilation holes are formed. Moreover, it is possible to use a suction chamber including: a suction chamber main body in which most of a surface of the suction chamber  53 B facing the side plate  44  is opened to form an opening; and a frame in which four ventilation holes are formed. Moreover, a blow chamber main body and a suction chamber main body like those described above may be directly attached to the side plates  42  and  44 , respectively. 
     OTHER EMBODIMENTS 
     In the first and second embodiments described above, each of the head arrays L 1  to L 4  includes three inkjet heads  31 . However, the number of inkjet heads included in each head array is not limited to this. Each head array may include one long inkjet head. 
     In the first embodiment and its modified example described above, the blow chambers  51  and  51 A and the suction chambers  53  and  53 A have such shapes that the depth in the front-rear direction decreases toward the left side. Moreover, in the second embodiment, the blow chamber  51 B and the suction chamber  53 B have such shapes that the width in the up-down direction decreases toward the left side. However, the shapes of the blow chamber and the suction chamber are not limited to the shapes described above. The blow chamber can have any shape as long as the internal air flow passage has cross-sectional areas at positions of the ventilation holes decreasing with the increase in the distance of the ventilation holes from the blow fan. Moreover, the suction chamber can have any shape as long as the internal air flow passage has cross-sectional areas at positions of the ventilation holes decreasing with the increase in the distance of the ventilation holes  53   a  from the suction fan. 
     Embodiments of the present invention have been described above. However, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     Moreover, the effects described in the embodiments of the present invention are only a list of optimum effects achieved by the present invention. Hence, the effects of the present invention are not limited to those described in the embodiment of the present invention.