Patent Publication Number: US-2021178783-A1

Title: Image recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2019-226106 filed on Dec. 16, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to an image recording apparatus provided with an endless belt for conveying a medium. 
     A certain image recording apparatus has an endless type suction belt and a suction mechanism with which a medium is conveyed to a position opposed to a recording head. A large number of through-holes are formed through the suction belt over its whole circumference. The suction mechanism sucks the air by the aid of the through-holes of the suction belt positioned on a conveying surface opposed to the recording head. Accordingly, the medium is sucked to the suction belt. Further, the image recording apparatus has a printing stage which is formed with suction holes and which is positioned on both sides of the suction belt. When a sheet, which has a width wider than that of the suction belt, is conveyed, the sheet is sucked to the printing stage (see, for example, Japanese Patent Application Laid-open No. 2003-104600). 
     SUMMARY 
     When the suction belt is adopted, it is necessary to provide the suction mechanism in the space surrounded by the inner circumferential surface of the suction belt. Therefore, the image recording apparatus is consequently large-sized. In order to miniaturize the image recording apparatus, it is conceived to adopt a conveying belt which has no suction hole, in place of the suction belt. However, in this case, the printing stage and the sheet are brought in surface-to-surface contact with each other. The rotating conveying belt easily slips with respect to the sheet. On this account, it is necessary to take, for example, such a countermeasure that the conveying surface of the conveying belt is allowed to protrude from the upper surface of the printing stage. As a result, it is feared that the distance may be dispersed or varied between the nozzles of the recording head and the medium 
     The present disclosure has been made taking the foregoing circumstances into consideration, an object of which is to provide an image recording apparatus which makes it possible to suppress the dispersion of the distance between a recording unit and a medium. 
     An image recording apparatus according to the present disclosure includes: 
     an endless belt which extends in a conveying direction and which has a conveying surface configured to convey a medium: 
     a driver configured to rotate the endless belt along the conveying direction; 
     a support which is aligned with the endless belt in an orthogonal direction being parallel to the conveying surface and orthogonal to the conveying direction, the support having a pair of support walls extending in the conveying direction, and arranged at an interval in the orthogonal direction so as to define between each other a space opened in an orientation in which the conveying surface faces; 
     an air flow generator configured to generate an air flow allowed to flow along the conveying direction in the space between the pair of support walls; and 
     a recorder configured to record an image on the medium supported by the endless belt and the support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically depicts an image recording apparatus  30 , wherein  FIG. 1A  depicts a perspective view schematically illustrating the appearance of the image recording apparatus  30 , and  FIG. 1B  depicts a sectional view in which a vertical cross section taken along a two-dot chain line Ib-Ib shown in  FIG. 1A  is viewed from a right position. 
         FIG. 2  depicts a sectional view in which a lateral cross section taken along a two-dot chain line l-II shown in  FIG. 1A  and  FIG. 1B  is viewed from an upper position. 
         FIG. 3A  depicts a perspective view illustrating the configuration of a support unit  46  according to an embodiment,  FIG. 3B  depicts a perspective view illustrating the configuration of a support unit  46  according to another embodiment, and  FIG. 3C  depicts a perspective view illustrating the configuration of a support unit  46  according to a first modified embodiment. 
         FIG. 4  depicts a block diagram illustrating the image recording apparatus  30 . 
         FIG. 5A  schematically depicts a support unit  46  according to a second modified embodiment, and  FIG. 5B  schematically depicts partition walls  37 L,  37 R according to a third modified embodiment. 
         FIG. 6A  schematically depicts a support unit  46  according to a fourth modified embodiment, and  FIG. 6B  schematically depicts a support unit  46 A and conveying belts  37 F,  37 G according to a fifth modified embodiment. 
     
    
    
     EMBODIMENTS 
     An explanation will be made below about an image recording apparatus  30  according to an embodiment of the present invention. Note that the embodiment explained below is merely an example of the present disclosure, and it goes without saying that the embodiment can be appropriately changed within a range without changing the gist or essential characteristics of the present invention. Further, in the following explanation, the advance, which is directed from the start point to the end point of the arrow, is expressed as “orientation”, and the displacement (coming and going) on a line to connect the start point and the end point of the arrow, is expressed as “direction”. Further, in the following explanation, the upward-downward direction  7  is defined on the basis of a state (state shown in  FIG. 1A ) in which the image recording apparatus  30  is usably installed. The front-back (front-rear) direction  8  is defined assuming that the side, on which a discharge port (outlet)  33  is provided, is designated as the front side (front surface). The left-right direction  9  is defined while the image recording apparatus  30  is viewed from the front side (front surface). 
     &lt;Appearance Configuration of Image Recording Apparatus  30 &gt; 
     In the image recording apparatus  30  depicted in  FIG. 1 , an image is recorded in accordance with the ink-jet recording system on a sheet S which forms a roll member  31  (see  FIG. 1B ). The sheet S is an example of the medium. With reference to  FIGS. 1A and 1B , a casing  32  of the image recording apparatus  30  generally has a rectangular parallelepiped shape, which has a size capable of being placed on a desk or table. That is, the image recording apparatus  30  is suitable for the use of being placed on a desk or table. Of course, the image recording apparatus  30  may be used while being placed on a floor surface or a rack. 
     The casing  32  has a right surface  32 R and a left surface  32 L, an upper surface  32 U and a lower surface  32 D, and a front surface  32 F and a back surface  32 B. Accordingly, an internal space  32 A of the casing  32  (see  FIG. 1B ) is comparted from the outside. The right surface  32 R and the left surface  32 L are positioned while being separated from each other in the left-right direction  9 . The upper surface  32 U and the lower surface  32 D are positioned while being separated from each other in the upward-downward direction  7 , and they connect the right surface  32 R and the left surface  32 L. The front surface  32 F and the back surface  32 B are positioned while being separated from each other in the front-back direction  8 , and they connect the upper surface  32 U and the lower surface  32 D. 
     As shown in  FIG. 1A , a slit-shaped discharge port  33 , which is long in the left-right direction  9 , is positioned at an upper right portion of the front surface  32 F. The sheet S (see  FIG. 1B ), on which the image has been recorded, is discharged from the discharge port  33 . 
     Other than the above, an operation panel  44  and a front cover  34 A may be provided on the front surface  32 F. With the operation panel  44 , a user performs the input in order that the image recording apparatus  30  is operated and/or various settings are decided. The front cover  34 A is positioned at a lower portion of the front surface  32 F. When the front cover  34 A is opened/closed, a tank  34  (see  FIG. 1B ) or the like, which is positioned in the internal space  32 A, is exposed or shielded. 
     &lt;Internal Structure of Image Recording Apparatus  30 &gt; 
     As shown in  FIG. 1B , a holder  35 , a tensioner  45 , a conveying roller pair  36 , a guide unit  50 , a conveying belt  37 , a recording head  38 , a support unit  46 , a fixing unit  39 , a conveying roller pair  40 , and a tank  34  are arranged in the internal space  32 A. Note that those arranged in the internal space of the casing  32  are, for example, a power source circuit and a maintenance unit including, for example, a cap for covering a nozzle surface of the recording head  38  and a wiper for wiping out the nozzle surface. However, the maintenance unit and the power source circuit are not principal parts of this embodiment. Therefore, they are omitted from the drawings, and any explanation thereof is avoided. 
     A partition wall  41  is provided in the internal space  32 A. The partition wall  41  partitions the back lower portion of the internal space  32 A to compart a sheet accommodating space  32 C. The sheet accommodating space  32 C is the space which is surrounded by the partition wall  41  and the casing  32  (specifically, the back surface  32 B, the lower surface  32 D, and the right surface  32 R) and which is isolated, for example, from the recording head  38 . 
     &lt;Roll Member  31 &gt; 
     A roll member  31  is accommodated in the sheet accommodating space  32 C. The roll member  31  has a core tube and the lengthy sheet S. The sheet S is wound around the core tube in a roll form in the circumferential direction of the axial center of the core tube. The sheet S has a sheet width A (see  FIG. 2 ) in the widthwise direction extending along the axial center of the core tube. In this case, the sheet width A may have a value which is within a range ranging from a minimum sheet width A 1  to a maximum sheet width A 2  (see  FIG. 2 ). The minimum sheet width A 1  and the maximum sheet width A 2  are the minimum width and the maximum width of the sheet S with which the image recording apparatus  30  can record the image. That is, a plurality of types of roll members  31 , which have different sheet widths A, can be accommodated in the sheet accommodating space  32 C. Note that it is also allowable that the roll member  31  does not have the core tube, and the sheet S is wound in a roll form so that the sheet S can be installed to the holder  35 . Further, it is also allowable that fan-fold paper can be accommodated in the sheet accommodating space  32 C. 
     &lt;Holder  35 &gt; 
     As depicted in  FIG. 1B , the holder  35 , which extends in the left-right direction  9 , is positioned in the sheet accommodating space  32 C. One type of the roll member  31 , which is selected from the plurality of types, can be installed to the holder  35 . Upon the installation, the holder  35  supports the roll member  31  so that the axial center of the core tube of the roll member  31  extends in the left-right direction  9  and the roll member  31  is rotatable in the circumferential direction about the axial center. Further, the center of the sheet S in the widthwise direction is positioned at the center in the left-right direction  9  of the conveying passage  43  (hereinafter referred to as “passing paper center C” (see  FIG. 2 ) as well). The holder  35  is rotated in accordance with the transmission of the rotation from an unillustrated motor. The roll member  31 , which is supported by the holder  35 , is also rotated in accordance with the rotation of the holder  35 . Note that a right cover  35 A (see  FIG. 1A ) is positioned on the right surface  32 R of the casing  32 . When the right cover  35 A is opened/closed, for example, the holder  35 , which is positioned in the sheet accommodating space  32 C, is exposed or shielded. 
     As depicted in  FIG. 1B , the sheet accommodating space  32 C is open toward the upward at a back portion. In particular, a gap  42  is formed between the partition wall  41  and the back surface  32 B, i.e., over or above the back end of the roll member  31 . When the conveying roller pairs  36 ,  40  are rotated, then the sheet S is pulled out upwardly from the back end of the roll member  31 , and the sheet S is guided to the tensioner  45 . 
     &lt;Tensioner  45 &gt; 
     The tensioner  45  is positioned over or above the partition wall  41  at the back portion of the internal space  32 A. The tensioner  45  has an outer circumferential surface  45 A which faces or is directed to the outside of the casing  32 . Specifically, the outer circumferential surface  45 A faces the upper surface  32 U and the back surface  32 B respectively. As depicted in  FIG. 2 , the outer circumferential surface  45 A has a size which is not less than the maximum sheet width A 2  in the left-right direction  9 , and the outer circumferential surface  45 A has a shape which is mutually symmetrical with respect to the passing paper center C. As depicted in  FIG. 1B , the upper end of the outer circumferential surface  45 A is disposed at the vertical position which is approximately the same as the vertical position of the nip D of the conveying roller pair  36  in the upward-downward direction  7 . 
     The sheet S, which is pulled out from the roll member  31 , is applied to the outer circumferential surface  45 A, and the sheet S abuts against the outer circumferential surface  45 A. The sheet S is curved frontwardly along the outer circumferential surface  45 A to extend in the conveying orientation  8 A, and the sheet S is guided by the conveying roller pair  36 . The conveying orientation  8 A is the frontward orientation extending in the front-back direction  8 . The tensioner  45  gives the tension to the sheet S by means of any well-known technique. 
     Note that as for the tensioner  45 , the present disclosure is not limited to the configuration depicted in  FIG. 1B , i.e., the configuration in which the urging force, which is directed backwardly, is given to the roller by means of any urging member such as a spring or the like. It is also allowable to apply any other well-known technique. 
     &lt;Conveying Roller Pairs  36 ,  40 &gt; 
     The conveying roller pair  36  is positioned in front of the tensioner  45 . The conveying roller pair  36  has a conveying roller  36 A and a pinch roller  36 B. The conveying roller  36 A and the pinch roller  36 B mutually make abutment at approximately the same vertical position as that of the upper end of the outer circumferential surface  45 A to form the nip D. 
     The conveying roller pair  40  is positioned in front of the conveying roller pair  36 . The conveying roller pair  40  has a conveying roller  40 A and the pinch roller  40 B. The conveying roller  40 A and the pinch roller  40 B mutually make abutment at approximately the same vertical position as that of the upper end of the outer circumferential surface  45 A to form the nip. Each of the conveying rollers  36 A,  40 A is rotated by the driving force transmitted from the driving unit  47  (see  FIG. 4 ). The conveying roller pair  36  is rotated while nipping the sheet S extending in the conveying orientation  8 A from the tensioner  45 , and thus the sheet S is fed in the conveying orientation  8 A along the conveying surface  43 A. The conveying roller pair  40  is rotated while nipping the sheet S fed from the conveying roller pair  36 , and thus the sheet is fed in the conveying orientation  8 A. Further, in accordance with the rotation of the conveying roller pairs  36 ,  40 , the sheet S passes through the gap  42  from the sheet accommodating space  32 C, and the sheet S is pulled out toward the tensioner  45 . 
     As depicted in  FIG. 1B , the conveying passage  43 , which extends from the upper end of the outer circumferential surface  45 A to arrive at the discharge port  33 , is formed in the internal space  32 A. The conveying passage  43  is the space which extends substantially linearly in the conveying orientation  8 A, and the sheet S can pass through the space. In particular, the conveying passage  43  extends along the conveying surface  43 A which expands in the conveying orientation  8 A and in the left-right direction  9  and which is long in the conveying orientation  8 A. Note that in  FIG. 1B , the conveying surface  43 A is depicted by a two-dot chain line which indicates the conveying passage  43 . The conveying passage  43  is defined, for example, by the guide unit  50 , the recording head  38 , the conveying belt  37 , and the fixing unit  39 . That is, the guide unit  50 , the recording head  38 , the conveying belt  37 , and the fixing unit  39  are positioned along the conveying passage  43 . 
     &lt;Guide Unit  50 &gt; 
     As depicted in  FIGS. 1A and 1B , the guide unit  50  is positioned between the conveying roller pair  36  and the recording head  38  and the conveying belt  37  in the conveying orientation  8 A. The guide unit  50  has an upper guide member  501  and a lower guide member  502  (shown in  FIG. 2  as well). The lower surface of the upper guide member  501  and the upper surface of the lower guide member  502  are positioned slightly upwardly and downwardly respectively as compared with the conveying passage  43  in the upward-downward direction  7 , and they are separated from each other in the upward-downward direction  7 . The lower surface of the upper guide member  501  and the upper surface of the lower guide member  502  are larger than the width of the sheet S in the left-right direction  9  respectively, and they have the shapes of left-to-right symmetry with respect to the passing paper center C. The lower surface of the upper guide member  501  and the upper surface of the lower guide member  502  guide, to the conveying belt  37 , the sheet S fed from the conveying roller pair  36 . The sheet S is reliably guided by the guide unit  50  from the conveying roller pair  36  to the conveying belt  37 . Note that the guide unit  50  is depicted in only  FIGS. 1A and 1B  and  FIG. 2 , and the guide unit  50  is omitted in  FIG. 3A  and the followings. 
     &lt;Recording Head  38 &gt; 
     The recording head  38  (an example of the recorder) is positioned on the just downstream side from the conveying roller pair  36  over or above the conveying passage  43 . The recording head  38  is provided with a discharge module  38 A. The discharge module  38 A has a plurality of nozzles  38 B which are arranged while being aligned in one array in the left-right direction  9 . Ink droplets are discharged downwardly from the plurality of nozzles  38 B toward the sheet S conveyed by the conveying belt  37 . Accordingly, the image is recorded on the sheet S supported by the conveying belt  37  and the support unit  46 . Note that in  FIGS. 1A and 1B , only one nozzle  38 B is depicted. Alternatively, the nozzles  38 B, which are disposed in two or more arrays separated in the front-back direction  8 , may be aligned. 
     The tank  34  stores an ink. The ink is a liquid containing a pigment or the like. The ink has a viscosity which is appropriate to uniformly disperse the pigment. The pigment forms the color of the ink. Although not depicted in the drawing, the ink is supplied from the tank  34  via a tube to the recording head  38 . 
     &lt;Conveying Belt  37 &gt; 
     The conveying belt  37 , a driving roller  37 A, and a following roller  37 B are positioned under or below the recording head  38 . The driving roller  37 A and the following roller  37 B are separated from each other in the front-back direction  8 . The conveying belt  37  is an endless belt, which has no through-hole unlike the suction belt. The conveying belt  37  is applied and stretched under tension between the driving roller  37 A and the following roller  37 B. Accordingly, the space  37 D is comparted or defined by the inner circumferential surface of the conveying belt  37 , the outer circumferential surface of the driving roller  37 A, and the outer circumferential surface of the following roller  37 B. The driving roller  37 A is rotated by the driving force given by the driving unit  47  (see  FIG. 4 ) including a motor, and the driving roller  37 A rotates the conveying belt  37 . The following roller  37 B is rotated in accordance with the rotation of the conveying belt  37 . The conveying belt  37  has the conveying surface  37 C. The conveying surface  37 C is the upper end portion of the outer circumferential surface of the conveying belt  37 , and the conveying surface  37 C extends in the conveying orientation  8 A. The conveying surface  37 C is opposed to the nozzles  38 B of the recording head  38  with the conveying passage  43  intervening therebetween. The coefficient of friction of the conveying surface  37 C is larger than the coefficients of friction of the extending ends (i.e., the upper ends) of the back wall  52 L and the respective left walls  53 L and the back wall  52 R and the respective right walls  53 R. The driving roller  37 A is rotated so that the conveying surface  37 C is moved in the conveying orientation  8 A. Further, the conveying surface  37 C gives the conveying force to the sheet S while supporting, from the lower position, the sheet S conveyed between the conveying roller pairs  36 ,  40 . Accordingly, the sheet S, which is positioned on the conveying passage  43 , is conveyed by the conveying belt  37  in the conveying orientation  8 A along with the conveying surface  37 C. 
     As depicted in  FIG. 2 , the outer circumferential surface of the conveying belt  37  including the conveying surface  37 C is smaller than the minimum sheet width A 1  in the left-right direction  9 , and has the mutually symmetrical shape with respect to the passing paper center C. Further, as depicted in  FIG. 1B , the conveying surface  37 C is disposed at approximately the same vertical position as that of the nip D in the upward-downward direction  7 . 
     &lt;Support Unit  46 &gt; 
     As shown in  FIG. 2 , the support unit  46  includes a left support unit  46 L and a right support unit  46 R. Each of the left support unit  46 L and the right support unit  46 R is produced by integrally molding a material such as a resin or the like. The left support unit  46 L and the right support unit  46 R are positioned respectively on the leftward and the rightward from the conveying belt  37 , and the left support unit  46 L and the right support unit  46 R are aligned with the conveying belt  37 . The leftward and the rightward are examples of the orthogonal direction which is parallel to the conveying surface  37 C and which is orthogonal to the conveying orientation  8 A. 
     As depicted in  FIG. 3A , the left support unit  46 L has a bottom portion  51 L and a back wall  52 L. The left support unit  46 L further has five left walls  53 L, i.e., left walls  53 L 1  to  53 L 5 . 
     The bottom portion  51 L has a rectangular upper surface  54 L. The upper surface  54 L is adjacent to the conveying surface  37 C at the left of the conveying surface  37 C as viewed in a plan view from an upper position. The upper surface  54 L expands in the front-back direction  8  and the left-right direction  9  at the position (height) lower than the position (height) of the conveying surface  37 C. The both front and back ends of the upper surface  54 L extend in the left-right direction  9  at the positions separated from each other in the front-back direction  8 . The front end of the upper surface  54 L is positioned while being separated backwardly from the following roller  37 B, and the back end of the upper surface  54 L is positioned while being separated frontwardly from the driving roller  37 A (see  FIG. 2 ). 
     The back wall  52 L has a plate-shaped form which expands in the upward-downward direction  7  and the left-right direction  9  and which is thin in the front-back direction  8 . The back wall  52 L extends upwardly from the entire region of the back end of the upper surface  54 L. The extending end of the back wall  52 L has substantially the same vertical position as that of the conveying surface  37 C over the entire region. 
     Each of the left walls  53 L has a plate-shaped form which expands in the upward-downward direction  7  and the front-back direction  8  and which is thin in the left-right direction  9 . The respective left walls  53 L extend upwardly from the positions on the upper surface  54 L which are different from each other in the left-right direction  9 . The extending end of each of the left walls  53 L has substantially the same vertical position as that of the conveying surface  37 C over the entire region. Each of the left walls  53 L extends from the front end of the upper surface  54 L along the front-back direction  8  (conveying direction, i.e., the conveying orientation  8 A and the orientation opposite to the conveying orientation  8 A), and each of the left walls  53 L arrives at the back wall  52 L. 
     The left wall  53 L 1  is positioned along the right end of the upper surface  54 L, and the left wall  53 L 1  closes the greater part of the left opening  373  of the space  37 D. That is, the left wall  53 L 1  is the partition wall which partitions the space  37 D. Note that the vertical position of the extending end of the left wall  53 L 1  is not limited to the above, which may be disposed slightly downwardly from the conveying surface  37 C. Further, the left wall  53 L 1  may close the entire region of the opening  37 J. Further, the left wall  53 L 1  may be positioned while being slightly separated leftwardly from the conveying belt  37 . 
     The left walls  53 L 2  to  53 L 5  is positioned while being separated by a predetermined distance D leftwardly from each of the left walls  53 L 1  to  53 L 4 , respectively. The left wall  53 L 5  is positioned along the left end of the upper surface  54 L. 
     In particular, as depicted in  FIG. 2 , the left side surface of the left wall  53 L 3  is separated leftwardly from the passing paper center C by a distance which is a half of the minimum sheet width A 1 . As depicted in  FIG. 2 , the left side surface of the left wall  53 L 5  is separated leftwardly from the passing paper center C by a distance which is a half of the maximum sheet width A 2 . However, the present disclosure is not limited thereto. The left side surface of the left wall  53 L 3  may be separated leftwardly from the passing paper center C by a distance which is slightly smaller than the half of the minimum sheet width A 1 . Further, the left side surface of the left wall  53 L 5  may be separated leftwardly from the passing paper center C by a distance which is slightly smaller than the half of the maximum sheet width A 2 . Accordingly, during the period in which the conveying belt  37  conveys the sheet S having the minimum sheet width A 1 , the left walls  53 L 1  to  53 L 3  support the portion left of center of the sheet S being conveyed, from the back surface side of the sheet S. During the period in which the conveying belt  37  conveys the sheet S having the maximum sheet width A 2 , the left walls  53 L 1  to  53 L 5  support the portion left of center of the sheet S being conveyed, from the back surface side of the sheet S which is conveyed by the conveying belt  37  and which has the maximum sheet width A 2 . 
     Further, according to the configuration described above, the two left walls  53 L, which are adjacent to one another in the left-right direction  9 , are examples of the pair of support walls. The two left walls  53 L surround the space together with the upper surface  54 L and the back wall  52 L to form four air flow passages  55 L. As for each of the flow passages  55 L in a state in which the conveying belt  37  does not convey the sheet S, the front end and the upper end of the flow passage  55 L are open toward the frontward and the upward respectively. That is, each of the flow passages  55 L is open in the direction in which the conveying surface  37 C faces or is directed. 
     Further, the bottom portion  51 L has air discharge ports  56 L which are disposed at positions near to the back ends of the respective flow passages  55 L and which are open toward the upward. 
     Note that in the following description, the four flow passages  55 L are also referred to as “flow passages  55 L 1 ,  55 L 2 ,  55 L 3 ,  55 L 4 ” in an order starting from those disposed nearer to the conveying belt  37 . The four air discharge ports  56 L are also referred to as “air discharge ports  56 L 1 ,  56 L 2 ,  56 L 3 ,  56 L 4 ” in an order starting from those disposed nearer to the conveying belt  37 . 
     The right support unit  46 R has a bottom portion  51 R and a back wall  52 R. The right support unit  46 R further has five right walls  53 R. i.e., right walls  53 R 1  to  53 R 5 . The bottom portion  51 R, the back wall  52 R, and the five right walls  53 R have symmetrical shapes respectively in relation to the passing paper center C with respect to the bottom portion  51 L, the back wall  52 L, and the five left walls  53 L. Therefore, any detailed explanation is avoided for the bottom portion  51 R, the back wall  52 R, and the right walls  53 R. Further, the four flow passages  55 R, i.e., the flow passages  55 R 1 ,  55 R 2 ,  55 R 3 ,  55 R 4  are formed by the bottom portion  51 R, the back wall  52 R, and the right walls  53 R. Further, the bottom portion  51 R has four air discharge ports  56 R, i.e., air discharge ports  56 R 1  to  56 R 4  which are open toward the upward and which are disposed at the positions near to the back ends of the respective flow passages  55 R. 
     As depicted in  FIG. 4 , the image recording apparatus  30  has a driving unit  47 , two pumps  48 A,  48 B, and a controller  49  in the casing  32 . Note that only the principal components of the configuration depicted in  FIGS. 1A and 1B  are depicted in  FIG. 4 . 
     The driving unit  47  includes, for example, a motor and gears. The driving unit  47  generates the driving force in order to rotate the driving roller  37 A under the control of the controller  49 . Note that the driving force may be transmitted to the conveying rollers  36 A,  40 A by a driving force transmitting unit including gears and the like. 
     The pump  48 A is connected to the air discharge ports  56 R 1 ,  56 R 2 ,  56 L 1 ,  56 L 2  via a piping  48 C so that the fluid communication can be performed. The pump  48 A sucks the air from the insides of the flow passages  55 L 1 ,  55 L 2 ,  55 R 1 ,  55 R 2  (hereinafter referred to as “inner flow passages” as well) under the control of the controller  49 . Accordingly, the air flow, which flows in the orientation opposite to the conveying orientation  8 A, is generated in each of the inner flow passages. 
     The pump  48 B is connected to the air discharge ports  56 R 3 ,  56 R 4 ,  56 L 3 ,  56 L 4  via a piping  48 D so that the fluid communication can be performed. The pump  48 B sucks the air from the insides of the flow passages  55 L 3 ,  55 L 4 ,  55 R 3 ,  55 R 4  (hereinafter referred to as “outer flow passages” as well) under the control of the controller  49 . Accordingly, the air flow, which flows in the orientation opposite to the conveying orientation  8 A, is generated in each of the outer flow passages. 
     The controller  49  is provided with CPU, ROM, RAM, EEPROM, and ASIC which are connected to one another by an internal bus or the like. The controller  49  controls the respective components of the configuration of the image recording apparatus  30 . 
     &lt;Operation of Image Recording Apparatus  30 &gt; 
     An operator installs the roll member  31  to the holder  35  as depicted in  FIG. 2 . After that, the sheet S is pulled out from the roll member  31 , and the sheet S is applied to the outer circumferential surface  45 A of the tensioner  45 . After that, the operator allows the forward end of the sheet S to be nipped by the conveying roller pair  36 . In this situation, the center of the sheet S in the widthwise direction is adjusted to the passing paper center C. 
     After that, the controller  49  acquires the information to indicate the sheet width A (hereinafter referred to as “sheet width information” as well) in the image recording apparatus  30 . The roll member  31  is provided with a memory for previously storing the sheet width information in some cases. In such a situation, when the roll member  31  is installed to the holder  35 , the controller  49  acquires the sheet width information from the memory of the roll member  31 . The operator can also input the sheet width information by operating the operation panel  44 . In this case, the controller  49  acquires the sheet width information from the operation panel  44 . 
     If the sheet width information indicates the minimum sheet width A 1 , the controller  49  decides that the pump  48 A is used when the sheet S is conveyed. On the contrary, if the sheet width information indicates the maximum sheet width A 2 , the controller  49  decides that both of the pumps  48 A,  48 B are used when the sheet S is conveyed. 
     The controller  49  outputs a predetermined driving signal to the driving unit  47  to drive the driving unit  47  irrelevant to the sheet width A of the sheet S. The driving unit  47  gives the driving forces to the driving roller  37 A and the conveying rollers  36 A,  40 A, and thus the conveying roller pairs  36 ,  40  and the driving roller  37 A are rotated. As a result, the sheet S is conveyed toward the discharge port  33  in the conveying orientation  8 A along the conveying passage  43  from the conveying roller pair  36 . In this process, the sheet S is conveyed by the conveying surface  37 C which is moved in the conveying orientation  8 A, while being supported by the conveying surface  37 C of the conveying belt  37 . The conveying surface  37 C is smaller than the minimum sheet width A 1  in the left-right direction  9 . Therefore, the portion left of center of the sheet S abuts against the upper end of the left support unit  46 L. The portion right of center of the sheet S abuts against the upper end of the right support unit  46 R. 
     If the sheet width information indicates the minimum sheet width A 1 , the controller  49  outputs a control signal to the pump  48 A to drive the pump  48 A. Accordingly, the air flows, which flow in the orientation opposite to the conveying orientation  8 A, are generated in the respective inner flow passages. When the air flows flow through the inner flow passages, the air pressures in the inner flow passages are lowered as compared with the air pressure provided over or above the sheet S. As a result, the portions left and right of center of the sheet S make tight contact with the extending ends of the left walls  53 L 1  to  53 L 3  and the right walls  53 R 1  to  53 R 3  respectively. However, the coefficients of friction of the respective extending ends are smaller than the coefficient of friction of the conveying surface  37 C. Therefore, the sheet S slides in the conveying orientation  8 A on the respective extending ends. 
     If the sheet width information indicates the maximum sheet width A 2 , the controller  49  outputs a control signal to the pumps  48 A,  48 B to drive the pumps  48 A,  48 B. Accordingly, the air flows, which flow in the orientation opposite to the conveying orientation  8 A, are generated in the respective inner flow passages and the respective outer flow passages. Accordingly, the portions left and right of center of the sheet S make tight contact with the extending ends of the left walls  53 L 1  to  53 L 5  and the right walls  53 R 1  to  53 R 5  respectively. In this case, the sucking abilities of the pumps  48 A,  48 B are controlled by the controller  49  so that the flow rate(s) of the air in the inner flow passages is/are faster than the flow rate(s) of the air in the outer flow passages. Alternatively, the flow passage resistances of the inner flow passages and the outer flow passages are previously set so that the flow rate(s) of the air in the inner flow passages is/are faster than the flow rate(s) of the air in the outer flow passages. 
     Specifically, as depicted in  FIG. 3B , the left walls  53 L 2 ,  53 L 3  may be positioned while being separated leftwardly from the left walls  53 L 1 ,  53 L 2 , respectively, by a first distance D 1  (that is, the same distance to each other). The left walls  53 L 4 ,  53 L 5  may be positioned while being separated leftwardly from the left walls  53 L 3 ,  53 L 4 , respectively, by a second distance D 2  (that is, the same distance to each other). The first distance D 1  may be smaller than the second distance D 2 . The same configuration can be applied to the right walls  53 R 2  to  53 R 5 . In this case, even when the pumps  48 A,  48 B are driven to provide the mutually identical sucking ability, the flow rate of the air in the inner flow passages can be made faster than the flow rate of the air in the outer flow passages. Note that in  FIG. 3B , the first distance D 1  is indicated only between the right walls  53 R 2 ,  53 R 3 , and the second distance D 2  is indicated only between the right walls  53 R 3 ,  53 R 4 . 
     &lt;Function and Effect of Image Recording Apparatus  30 &gt; 
     According to the image recording apparatus  30 , when the sheet S is conveyed in the conveying orientation  8 A in accordance with the rotation of the conveying belt  37 , the sheet S is sucked by the left support unit  46 L and the right support unit  46 R owing to the air flows allowed to flow through the respective flow passages  55 L,  55 R. Specifically, the sheet S is supported by the at least two right walls  53 R adjacent to one another in the left-right direction  9  and the at least two left walls  53 L adjacent to one another in the left-right direction  9 . Accordingly, it is possible to decrease the contact area between the sheet S and the left support unit  46 L and the contact area between the sheet S the right support unit  46 R Therefore, the conveying belt  37  hardly slips with respect to the sheet S. On this account, the conveying surface  37 C and the left support unit  46 L and the right support unit  46 R (more specifically, the upper ends of the left support unit  46 L and the right support unit  46 R) can be mutually disposed at the same vertical position (i.e., flush with each other). Accordingly, it is possible to provide the image recording apparatus  30  which can suppress the dispersion of the distance between the sheet S and the nozzles of the recording unit. 
     Further, the left support unit  46 L and the right support unit  46 R are positioned with the conveying belt  37  intervening therebetween. Further, when the sheet S is conveyed, the air flows, in which the flow rate distribution is in left-right symmetry (bilateral symmetry), are generated in the left support unit  46 L and the right support unit  46 R by means of only the pump  48 A or both of the pumps  48 A,  48 B. Therefore, the sheet S hardly travels obliquely on the conveying surface  37 C. 
     Further, the distance between the left side surface of the left wall  53 L 3  and the right side surface of the right wall  53 R 3  can be slightly smaller than the minimum sheet width A 1 . Further, the left wall  53 L 2  is positioned on the side nearer to the conveying belt  37  as compared with the left wall  53 L 3 , and the right wall  53 R 2  is positioned on the side nearer to the conveying belt  37  as compared with the right wall  53 R 3 . Accordingly, the support unit  46  can reliably support the sheet S having the minimum sheet width A 1 . Similarly, the distance between the left side surface of the left wall  53 L 5  and the right side surface of the right wall  53 R 5  is slightly smaller than the maximum sheet width A 2 . The left walls  53 L 2  to  53 L 4  and the right walls  53 R 2  to  53 R 4  are positioned on the sides nearer to the conveying belt  37  as compared with the left wall  53 L 5  and the right wall  53 R 5 . Accordingly, the support unit  46  can reliably support the sheet S having the maximum sheet width A 2 . 
     Further, the left support unit  46 L has the plurality of left walls  53 L which are aligned in parallel in the left-right direction  9 , and the right support unit  46 R has the plurality of right walls  53 R which are aligned in parallel in the left-right direction  9 . Therefore, the support unit  46  can stably support a plurality of types of the sheets S having different sheet widths A. Further, a plurality of types of the sheets S can stably make tight contact with the upper ends of the left support unit  46 L and the right support unit  46 R. 
     Further, the respective left walls  53 L 2  to  53 L 4  compart the two flow passages  55 L which mutually adjoin in the left-right direction  9 , and the respective right walls  53 R 2  to  53 R 4  compart the two flow passages  55 R which mutually adjoin in the left-right direction  9 . Accordingly, a plurality of types of the sheets S can stably make tight contact with the upper ends of the left support unit  46 L and the right support unit  46 R as well. 
     Further, for example, when the sheet S having the maximum sheet width A 2  is conveyed, the flow rate of the air in the inner flow passage is faster than the flow rate of the air in the outer flow passage. As a result, the force to suck the sheet S is weaker at the portions farther from the conveying belt  37  as compared with the portions nearer to the conveying belt  37  in each of the left support unit  46 L and the right support unit  46 R. Therefore, the conveying force, which is applied to the sheet S by the conveying belt  37 , is suppressed from being lost. 
     Further, each of the left wall  53 L 1  and the right wall  53 R 1  functions as the partition wall for partitioning the space  37 D. Therefore, any air flow is hardly generated in the space  37 D during the driving of the pumps  48 A,  48 B. Accordingly, the sheet S is stably conveyed by the conveying belt  37 . Further, the suction force for sucking the sheet S is hardly lowered on the left wall  53 L 2  and the right wall  53 R 2 . 
     Further, the upper ends of each of the left walls  53 L and each of the right walls  53 R are disposed at the same vertical position as that of the conveying surface  37 C. Therefore, the sheet S easily abuts against the conveying surface  37 C, and the conveying force, which is applied to the sheet S by the conveying belt  37 , is suppressed from being lost. 
     Further, the coefficient of friction of the conveying surface  37 C is larger than the coefficients of friction of the upper ends of each of the left walls  53 L and each of the right walls  53 R. Accordingly, the sheet S hardly slides on the conveying surface  37 C. Therefore, the conveyance of the sheet S is stabilized. 
     Modified Embodiments 
     Next, first to fifth modified embodiments will be explained. 
     In the embodiment, the left walls  53 L 2  to  53 L 5  are positioned while being separated leftwardly from the left walls  53 L 1  to  53 L 4 , respectively, by the identical (constant) predetermined distance D. However, the present disclosure is not limited thereto. As in a first modified embodiment depicted in  FIG. 3C , the left walls  53 L 2 ,  53 L 3  may be positioned while being separated leftwardly from the left walls  53 L 1 ,  53 L 2 , respectively, by a first distance D 1  (that is, the same distance to each other). The left walls  53 L 4 ,  53 L 5  may be positioned while being separated leftwardly from the left walls  53 L 3 ,  53 L 4 , respectively, by a second distance D 2  (that is, the same distance to each other). The first distance D 1  is larger than the second distance D 2 . The same modification can be applied to the right walls  53 R 2  to  53 R 5 . In this case, even when the pumps  48 A,  48 B are driven to provide the mutually identical sucking ability, the flow rate of the air in the outer flow passages can be made faster than the flow rate of the air in the inner flow passages. Note that in  FIG. 3C , the first distance D 1  is indicated only between the left walls  53 L 2 ,  53 L 3 , and the second distance D 2  is indicated only between the left walls  53 L 4 ,  53 L 5 . 
     In a second modified embodiment depicted in  FIG. 5A , the support unit  46  has a connecting portion  57  which mutually connects the left support unit  46 L and the right support unit  46 R at a position disposed under or below the conveying belt  37 . The connecting portion  57  is produced by means of the integral molding with the same material as that of the left support unit  46 L and the right support unit  46 R. Accordingly, the left support unit  46 L and the right support unit  46 R are easily attached to the casing  32 . 
     In a third modified embodiment depicted in  FIG. 5B , partition walls  37 L,  37 R are positioned between the driving roller  37 A and the following roller  37 B. In particular, the partition wall  37 L has a plate-shaped form which is long in the front-back direction  8  and which expands in the front-back direction  8  and the upward-downward direction  7  between the left end of the driving roller  37 A and the left end of the following roller  37 B. The partition wall  37 L comparts the space  37 D from the outside. The partition wall  37 R has a shape which is symmetrical with respect to the partition wall  37 L in relation to the passing paper center C. In this case, the left wall  53 L 1  and the right wall  53 R 1 , which function as the partition walls, can be omitted. 
     Further, as in a fourth modified embodiment depicted in  FIG. 6A , the conveying surface  37 C may have a shape which slightly expands upwardly as viewed in a plan view in the front-back direction  8 . In this case, extending ends of the left walls  53 L 1  to  53 L 5  and extending ends of the right walls  53 R 1  to  53 R 5  are positioned more downwardly at positions separated farther from the conveying belt  37 . Accordingly, the sheet S easily abuts against the conveying surface  37 C, the left walls  53 L 1  to  53 L 5 , and the right walls  53 R 1  to  53 R 5 . 
     In the embodiment, the left support unit  46 L and the right support unit  46 R are positioned on the left side and the right side of one conveying belt  37 . However, the present disclosure is not limited thereto. As in a fifth modified embodiment depicted in  FIG. 6B , it is also allowable that a support unit  46 A, which has the same or equivalent function as that of the support unit  46 , is positioned between two conveying belts  37 F,  37 G. 
     Other Modified Embodiments 
     In the embodiment, the sheet S is conveyed by the conveying roller pair  36 . However, the present disclosure is not limited thereto. The image recording apparatus  30  may convey the sheet S by means of any other conveying member such as a conveying belt or the like. 
     The tank  34  is not limited to the storage of one color ink of black. The tank  34  may store a plurality of color inks respectively. The plurality of colors are, for example, black, yellow, cyan, and magenta. Further, as for the ink, it is also allowable to use an ink containing a resin which is curable by ultraviolet light. In this case, the fixing unit  39  is an ultraviolet light radiating unit in place of the halogen heater. 
     The image recording apparatus  30  records the image on the sheet in accordance with the ink-jet system. However, in place thereof, it is also allowable to adopt a thermal head or adopt a printing system of the electrophotographic system. In this case, it is also allowable to omit the fixing unit  39  if the fixing unit  39  is not necessary. 
     It is not necessarily indispensable that the discharge port  33  is formed on the front surface  32 F of the casing  32 . For example, the discharge port  33  may be formed on the upper surface  32 U of the casing  32 , and the sheet S passing through the discharge port  33 , on which the image has been recorded, may be discharged upwardly or obliquely upwardly. 
     Further, the image recording apparatus  30  is used in the state in which the front surface  32 F and the back surface  32 B of the casing  32  are disposed in the upward-downward direction and the left-right direction. However, the attitude or posture of the use of the image recording apparatus  30  is not limited thereto. 
     According to the present disclosure, the image recording apparatus is provided, which makes it possible to suppress the dispersion of the distance between the recording unit and the medium.