Patent Publication Number: US-9421774-B2

Title: Inkjet recording apparatus and recording head maintenance method

Description:
INCORPORATION BY REFERENCE 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2015-013302, filed on Jan. 27, 2015. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The present disclosure relates to inkjet recording apparatuses and recording head maintenance methods. 
     Inkjet recording apparatuses are widely used in printers, copiers, multifunction peripherals, etc. An inkjet recording apparatus discharges ink droplets from nozzle orifices in a recording head to record an image on a recording medium. Specifically, the inkjet recording apparatus conveys a recording medium such as a sheet of paper so that the recording medium passes over a location opposite to the recording head. The recording head discharges ink droplets toward the recording medium while the recording medium is conveyed. Thus, the image is recorded on the recording medium. 
     In the inkjet recording apparatus, foreign matter on a recording medium may be attached to the nozzle orifices of the recording head. The nozzle orifices to which the foreign matter is attached may be disabled to discharge ink droplets. The foreign matter may be paper dust, for example. A phenomenon in which a nozzle orifice is disabled to discharge ink droplets is referred to as discharge disablement. In a situation in which discharge disablement occurs, an image including a white line may be formed, resulting in reduction in image quality. 
     An inkjet recording apparatus including a scraping member is proposed in order to obviate the above problem. The scraping member is disposed in a sheet feed passage that guides a recording medium from a feed section (sheet feed section) to a recording performing region (conveyance section). The scraping member comes in contact with a recording surface of the recording medium while the recording medium is fed, thereby removing foreign matter such as paper dust attached to the recording surface. The above configuration can reduce an amount of foreign matter conveyed below a recording head to reduce occurrence of discharge disablement. Thus, reduction in image quality can be prevented. 
     SUMMARY 
     An inkjet recording apparatus according to the present disclosure performs image recording on a recording medium by discharging ink droplets. The inkjet recording apparatus includes a conveyance section, a recording head, a maintenance mechanism, and a control section. The conveyance section conveys a recording medium in a first direction. The recording head discharges ink droplets toward the recording medium while the conveyance section conveys the recording medium. The maintenance mechanism performs maintenance on the recording head. The control section controls the maintenance mechanism. The control section causes the maintenance mechanism to operate upon determination that a width of a next recording target recording medium in a second direction perpendicular to the first direction is greater than a width of a recording medium subjected to image recording prior to the next recording target recording medium in the second direction. 
     A first recording head maintenance method according to the present disclosure is a method for performing maintenance on a recording head that discharges ink droplets toward a recording medium being conveyed in a first direction. The method includes: determining whether or not a width of a next recording target recording medium in a second direction perpendicular to the first direction is greater than a width of a recording medium in the second direction subjected to image recording prior to the next recording target recording medium; and upon determination that the width of the next recording target recording medium is greater than the width of the recording medium subjected to image recording prior to the next recording target recording medium, performing maintenance on the recording head. 
     A second recording head maintenance method according to the present disclosure is a method for performing maintenance on a recording head that discharges ink droplets toward a recording medium being conveyed in a first direction. The method includes: determining whether or not a width of a next recording target recording medium in a second direction perpendicular to the first direction is greater than a width of a recording medium in the second direction subjected to image recording prior to the next recording target recording medium; upon determination that the width of the next recording target recording medium is greater than the width of the recording medium in the second direction subjected to image recording prior to the next recording target recording medium, determining whether or not image recording has been performed on a predetermined number or more of recording mediums having a width smaller than the width of the next recording target recording medium in the second direction prior to the next recording target recording medium; and upon determination that image recording has been performed on the predetermined number or more of recording mediums having the width smaller than the width of the next recording target recording medium prior to the next recording target recording medium, performing maintenance on the recording head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates structure of an inkjet recording apparatus according to a first embodiment. 
         FIG. 2  is a plan view of a first conveyance section and a recording section illustrated in  FIG. 1  as viewed from above. 
         FIG. 3  is a plan view of a first conveyor belt illustrated in  FIG. 1  as viewed from above. 
         FIG. 4  illustrates structure of the first conveyance section and the recording section illustrated in  FIG. 1 . 
         FIG. 5  is a plan view of a conveyance plate illustrated in  FIG. 4  as viewed from above. 
         FIG. 6A  is a plan view illustrating a groove and a through hole in the conveyance plate according to the first embodiment. 
         FIG. 6B  is a cross sectional view of the groove and the through hole taken along the line VIB-VIB in  FIG. 6A . 
         FIG. 7  illustrates structure of an ink supplying mechanism according to the first embodiment. 
         FIG. 8  illustrates a first state of a wiping unit illustrated in  FIG. 1 . 
         FIG. 9  illustrates a second state of the wiping unit illustrated in  FIG. 1 . 
         FIG. 10  illustrates operation of the inkjet recording apparatus according to the first embodiment. 
         FIG. 11  illustrates the operation of the inkjet recording apparatus according to the first embodiment. 
         FIG. 12  illustrates operation of the wiping unit according to the first embodiment. 
         FIG. 13  illustrates the operation of the wiping unit according to the first embodiment. 
         FIGS. 14A-14C  each illustrate operation of a wiper blade according to the first embodiment. 
         FIG. 15  is a flowchart depicting a process flow of a control section included in the inkjet recording apparatus according to the first embodiment. 
         FIG. 16  illustrates a region on which maintenance is performed in a second embodiment. 
         FIG. 17  illustrates structure of an ink supplying mechanism according to the second embodiment. 
         FIGS. 18A and 18B  each illustrate operation of a wiper blade according to the second embodiment. 
         FIGS. 19A and 19B  each illustrate the operation of the wiper blade according to the second embodiment. 
         FIGS. 20A and 20B  each illustrate the operation of the wiper blade according to the second embodiment. 
         FIGS. 21A and 21B  each illustrate the operation of the wiper blade according to the second embodiment. 
         FIGS. 22A and 22B  each illustrate the operation of the wiper blade according to the second embodiment. 
         FIGS. 23A and 23B  each illustrate the operation of the wiper blade according to the second embodiment. 
         FIGS. 24A and 24B  each illustrate the operation of the wiper blade according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below with reference to the accompanying drawings. Like numerals denote like elements or corresponding elements in the drawings, and description thereof is not repeated. The drawings are schematic illustrations that emphasize elements of configuration in order to facilitate understanding thereof. Also note that material properties, shapes, dimensions, and the like, described for each of the elements of configuration in the following embodiments, are only examples and are not intended to impose any particular limitations on the elements. 
     First Embodiment 
     With reference to  FIG. 1 , description will be made first about an inkjet recording apparatus  1  according to the present embodiment.  FIG. 1  illustrates structure of the inkjet recording apparatus  1 . Specifically,  FIG. 1  illustrates a state in which the inkjet recording apparatus  1  performs image recording on a sheet P that is an example of a recording medium. The inkjet recording apparatus  1  discharges ink droplets to record an image on a sheet P. 
     The inkjet recording apparatus  1  includes an apparatus housing  100 , a sheet feed section  2 , a sheet conveyance path  3 , a first conveyance section  4 , a recording section  5 , a second conveyance section  6 , a sheet ejecting section  7 , a wiping unit  8 , a control section  9 , a first conveyance guide  101 , and a second conveyance guide  102 . 
     The sheet feed section  2  feeds a sheet P to the sheet conveyance path  3 . The sheet feed section  2  includes a sheet feed roller  22  and a sheet feed cassette  21  attachable to and detachable from the apparatus housing  100 . The sheet feed roller  22  is disposed above one end (right end in  FIG. 1 ) of the sheet feed cassette  21 . 
     The sheet feed cassette  21  is capable of being loaded with a plurality of sheets P. The sheet feed roller  22  (pickup roller) picks up a sheet P from the sheet feed cassette  21  one at a time and feeds the sheet P toward the sheet conveyance path  3 . 
     The sheet conveyance path  3  guides the sheet P to the first conveyance section  4 . The sheet conveyance path  3  is constituted by guide plates  31 . The sheet conveyance path  3  includes a first pair of conveyance rollers  32 , a second pair of conveyance rollers  33 , and a pair of registration rollers  34 . The first pair of conveyance rollers  32  is disposed around an inlet of the sheet conveyance path  3 . The second pair of conveyance rollers  33  is disposed partway along the sheet conveyance path  3 . The pair of registration rollers  34  is disposed around an outlet of the sheet conveyance path  3 . 
     The first pair of conveyance rollers  32  sandwiches the sheet P fed from the sheet feed section  2  and forwards the sheet P toward the second pair of conveyance rollers  33 . The second pair of conveyance rollers  33  sandwiches the sheet P forwarded from the first pair of conveyance rollers  32  and forwards the sheet P toward the pair of registration rollers  34 . 
     The pair of registration rollers  34  performs skew correction on the sheet P having been forwarded by the second pair of conveyance rollers  33 . The pair of registration rollers  34  synchronizes image recording on the sheet P with conveyance of the sheet P toward the first conveyance section  4 . Specifically, the pair of registration rollers  34  temporarily holds the sheet P and then feeds the sheet P toward the first conveyance section  4  according to timing of the image recording on the sheet P. More specifically, the sheet P comes in contact with the pair of registration rollers  34  and stops. Through the contact, skew correction is performed on the sheet P. The pair of registration rollers  34  then feeds the sheet P toward the first conveyance section  4  according to timing of the image recording on the sheet P. 
     The first conveyance section  4  is located directly below the recording section  5  in image recording on the sheet P. The first conveyance section  4  conveys the sheet P forwarded from the pair of registration rollers  34  toward the first conveyance guide  101 . 
     The first conveyance section  4  includes a first conveyor belt  410 . The first conveyor belt  410  is an endless belt. The sheet P fed by the pair of registration rollers  34  is guided onto the first conveyor belt  410 . The first conveyance section  4  causes the sheet P to be sucked on the first conveyor belt  410 . Through the suction, the sheet P is held on the first conveyor belt  410 . The first conveyance section  4  circulates the first conveyor belt  410  in a predetermined rotation direction (anticlockwise direction in  FIG. 1 ). Circulation of the first conveyor belt  410  conveys the sheet P in a direction indicated by an arrow X 1  (sub-scanning direction). The first conveyance section  4  accordingly conveys the sheet P in a predetermined direction that is an example of a first direction. Hereinafter, the direction in which the sheet P is conveyed by the first conveyance section  4  (first conveyor belt  410 ) is referred to as a sheet conveyance direction X 1 . 
     The recording section  5  discharges ink droplets toward the sheet P while the first conveyance section  4  conveys the sheet P, thereby recording an image on the sheet P. The recording section  5  includes line heads  51 Bk,  51 C,  51 M, and  51 Y. The recording section  5  further includes a head base  52 . The line head  51 Bk discharges droplets of black ink. The line head  51 C discharges droplets of cyan ink. The line head  51 M discharges droplets of magenta ink. The line head  51 Y discharges droplets of yellow ink. The line heads  51 Bk,  51 C,  51 M, and  51 Y have the same configuration and therefore may be referred to as line heads  51 . 
     The line heads  51  are supported by the head base  52 . The line heads  51  discharge ink droplets toward the sheet P while the first conveyance section  4  (first conveyor belt  410 ) conveys the sheet P. As a result, an image is recorded on the sheet P. Specifically, the line heads  51  discharge ink droplets toward the sheet P passing over a location opposite to the line heads  51 . As a result, an image including a character or a figure is recorded on the sheet P. 
     The first conveyance guide  101  is disposed between the first conveyance section  4  and the second conveyance section  6 . The first conveyance guide  101  guides the sheet P forwarded from the first conveyance section  4  to the second conveyance section  6 . 
     The second conveyance section  6  conveys the sheet P forwarded from the first conveyance section  4  toward the second conveyance guide  102 . The second conveyance section  6  includes a second conveyor belt  610 . The second conveyor belt  610  is an endless belt. The sheet P forwarded from the first conveyance section  4  is guided onto the second conveyor belt  610 . The second conveyance section  6  causes the sheet P to be sucked on the second conveyor belt  610 . Through the suction, the sheet P is held on the second conveyor belt  610 . The second conveyance section  6  circulates the second conveyor belt  610  in a predetermined rotation direction (anticlockwise direction in  FIG. 1 ). Circulation of the second conveyor belt  610  conveys the sheet P toward the second conveyance guide  102 . 
     The second conveyance guide  102  is disposed between the second conveyance section  6  and the sheet ejecting section  7 . The second conveyance guide  102  guides the sheet P forwarded from the second conveyance section  6  to the sheet ejecting section  7 . 
     The sheet ejecting section  7  ejects the sheet P outside the apparatus housing  100 . The sheet ejecting section  7  includes a pair of ejection rollers  71  and an exit tray  72 . The exit tray  72  is secured to the apparatus housing  100  so as to protrude outward from an exit port  11  formed in the apparatus housing  100 . The exit port  11  is formed in one side surface of the apparatus housing  100  (left side surface in  FIG. 1 ). 
     The pair of ejection rollers  71  forwards the sheet P having passed through the second conveyance guide  102  in a direction toward the exit port  11 . The sheet P forwarded by the pair of ejection rollers  71  is guided by the exit tray  72  to be ejected outside the apparatus housing  100  through the exit port  11 . The sheet P ejected outside the apparatus housing  100  is placed on the exit tray  72 . In a situation in which image recording is performed successively on a plurality of sheets P, the sheets P are stacked on the exit tray  72 . 
     The wiping unit  8  is located below the second conveyance section  6  in image recording on the sheet P. The wiping unit  8  includes a plurality of wiper blades  81 . The wiper blades  81  are cleaning members for cleaning respective nozzle surfaces  51   a  of the line heads  51 . The nozzle surfaces  51   a  of the line heads  51  face the first conveyance section  4  (first conveyor belt  410 ) in image recording on the sheet P. The nozzle surfaces  51   a  each have a plurality of nozzle orifices (not illustrated) from which ink droplets are discharged. The wiping unit  8  moves directly below the recording section  5  in maintenance on the line heads  51  and wipes the nozzle surfaces  51   a  using the wiper blades  81 . 
     The control section  9  has a storage region. The storage region stores therein programs, setting information, etc. The storage region is constituted by a magnetic disk of a hard disk drive (HDD), a random access memory (RAM), a read only memory (ROM), etc. The control section  9  executes programs stored in advance in the storage region to control respective elements in the inkjet recording apparatus  1 . 
     Various air flows are created in the interior of the apparatus housing  100  of the inkjet recording apparatus  1  in image recording on a sheet P. For example, the first conveyance section  4  sucks the sheet P onto the first conveyor belt  410 . This creates an air flow from above the first conveyor belt  410  toward the inner side of the first conveyor belt  410 . Conveyance of the sheet P creates an air flow in the sheet conveyance direction X 1 . As a result, the sheet P passes below the line heads  51  while receiving wind. A space between the line heads  51  and the first conveyor belt  410  is narrow. Therefore, comparative strong wind is likely to be created between the line heads  51  and the first conveyor belt  410 . In the above configuration, foreign matter such as paper dust attached to the sheet P tends to be blown away (flying up) by the wind below the line heads  51 . For this reason, the foreign matter blown away from the sheet P may be attached to the nozzle orifices of the line heads  51 . Foreign matter such as paper dust attached to the nozzle orifices may cause discharge disablement. The discharge disablement may cause an image including a white line to be formed, thereby reducing image quality. 
     Foreign matter such as paper dust may be charged. For this reason, in a situation in which an electric field is generated between an element of the first conveyance section  4  and the line heads  51 , the foreign matter may fly due to the presence of the electric field to be attracted to the line heads  51 . As a result, foreign matter such as paper dust may be attached to the nozzle orifices in the line heads  51 . 
     The inkjet recording apparatus  1  in the present embodiment performs maintenance on the line heads  51  after image recording on a predetermined number of sheets P (3000 sheets in the present embodiment). The inkjet recording apparatus  1  in the present embodiment performs maintenance on the line heads  51  also at initiation of the inkjet recording apparatus  1  (at power-up and return from a sleep state). Hereinafter, the maintenance performed at the above timing is referred to as regular maintenance. 
     In a situation in which image recording is performed successively on multiple sheets P having the same size, discharge disablement may occur before execution of the regular maintenance. Specifically, much paper dust is present on the end part (edge) of a sheet P, and therefore, discharge disablement may occur in a region outside a region through which multiple sheets P having the same size have passed. For the reason as above, an image formed on a next recording target sheet P may include a white line in a situation in which the next recording target sheet P has a width in a direction perpendicular to the sheet conveyance direction X 1  (direction perpendicular to the drawing surface in  FIG. 1 ) greater than a width of the multiple sheets P previously subjected to image recording in the direction perpendicular to the sheet conveyance direction X 1 . Hereinafter, the width in the direction (an example of a second direction) perpendicular to the sheet conveyance direction X 1  is referred simply to a “width”. The reason why much paper dust is present on the end part (edge) of a sheet P is that chips (paper dust) are attached to the end part of the sheet P through a production process of the sheet P (sheet making process). Chips are generated at a section of a sheet P in sheet cutting. 
     In order to tackle the above problem, the inkjet recording apparatus  1  in the present embodiment performs maintenance on the line heads  51  upon receiving a request for image recording on a next recording target sheet P. Specifically, maintenance is performed on the line heads  51  in a situation in which the number of sheets P having a width smaller than that of the next recording target sheet P is no less than a predetermined value ( 100  in the present embodiment) among sheets P subjected to image recording before image recording on the next recording target sheet P is requested. Hereinafter, maintenance performed at the above timing is referred to as sheet width dependent maintenance. The number of sheets P having a width smaller than that of the next recording target sheet P is referred to as a total number of small sheets P. The small sheets P are included among sheets P subjected to image recording before image recording on the next recording target sheet P is requested. The sheet width dependent maintenance is performed before image recording on the next recording target sheet P. 
     According to the present embodiment, in a situation in which the width of the next recording target sheet P is greater than that of a sheet P previously subjected to image recording, the sheet width dependent maintenance (maintenance on the line head  51 ) is performed. Thus, an image formed on the next recording target sheet P is unlikely to include a white line. Reduction in image quality can be accordingly prevented. 
     The control section  9  controls execution timing of the sheet width dependent maintenance based on information contained in a print request requesting image printing on a sheet P or information contained in a print job. Specifically, the control section  9  determines the width of a sheet P based on information on sheet size, orientation, etc. of a recording target sheet P. The control section  9  also determines whether or not the total number of small sheets P is no less than the predetermined number based on information on the number of pages of an original document that is a printing target, the number of printing copies, etc. 
     The total number of small sheets P may amount to no less than the predetermined number through execution of a single print job. Alternatively, the total number of small sheets P may amount to no less than the predetermined number through execution of a plurality of print jobs. In view of the foregoing, the control section  9  in the present embodiment calculates the total number of small sheets P each time a print job is executed. The calculated total number is stored in the storage region. When maintenance is performed on the line heads  51 , the control section  9  resets the total number of small sheets P stored in the storage region. Note that the predetermined number is not limited to 100. It is only required that the predetermined number is an integer equal to or greater than one. The predetermined number may be a parameter value optionally settable by a user. 
     Specifically, maintenance on the line heads  51  is executed through purge and wipe. The purge and wipe is a process of purging followed by wiping. The purging is an operation to supply ink to the line heads  51  and forcedly extrude (purge) ink from the nozzle orifices of the line heads  51 . The wiping is an operation to wipe the nozzle surfaces  51   a  of the line heads  51  by the wiper blades  81  to clean the nozzle surfaces  51   a.    
     Referring to  FIG. 2 , structure of the line heads  51  will be described next.  FIG. 2  is a plan view of the first conveyance section  4  and the recording section  5  illustrated in  FIG. 1  as viewed from above. As illustrated in  FIG. 2 , the line heads  51 Bk,  51 C,  51 M, and  51 Y are arranged side by side from upstream to downstream in the sheet conveyance direction X 1  (leftward in  FIG. 2 ). 
     The line heads  51 Bk,  51 C,  51 M, and  51 Y each include a first recording head  55   a , a second recording head  55   b , and a third recording head  55   c . The first, second, and third recording heads  55   a ,  55   b , and  55   c  are arranged in a staggered formation in a direction X 2  perpendicular to the sheet conveyance direction X 1 . Hereinafter, the direction X 2  perpendicular to the sheet conveyance direction X 1  is referred to a width direction X 2 . The first, second, and third recording heads  55   a ,  55   b , and  55   c  have the same structure and may be accordingly referred to as recording heads  55 . 
     The recording heads  55  each have the nozzle surface  51   a  described with reference to  FIG. 1 . The recording heads  55  discharge ink droplets from nozzle orifices located in correspondence with to-be-printed points on the sheet P conveyed by the first conveyor belt  410 . Thus, an image including a character or a figure is recorded on the sheet P. 
     With reference to  FIG. 3 , description will be made next about the first conveyor belt  410 .  FIG. 3  is a plan view of the first conveyor belt  410  illustrated in  FIG. 1  as viewed from above. As illustrated in  FIG. 3 , a plurality of suction holes  411  are perforated in the first conveyor belt  410 . Each of the suction holes  411  may have a diameter of 2 mm. Adjacent suction holes  411  may be spaced 8 mm from each other. The suction holes  411  are arranged in the sheet conveyance direction X 1  and the width direction X 2 . The suction holes  411  may be arranged in a staggered formation as illustrated in  FIG. 3 . 
     With reference to  FIGS. 1-4 , a description will be made next about the first conveyance section  4  and the recording section  5 .  FIG. 4  illustrates structure of the first conveyance section  4  and the recording section  5  illustrated in  FIG. 1 . For the sake of easy understanding,  FIG. 4  illustrates a section of a part of the first conveyance section  4 . 
     The first conveyance section  4  is disposed opposite to the line heads  51  in the interior of the apparatus housing  100  (see  FIG. 1 ). The first conveyance section  4  includes a drive roller  412 , a belt speed detecting roller  413 , a tension roller  414 , and a pair of guide rollers  415 . The drive roller  412 , the belt speed detecting roller  413 , the tension roller  414 , and the pair of guide rollers  415  are disposed on the internal side of the first conveyor belt  410 . The first conveyance section  4  further includes a placement roller  416  disposed on the external side of the first conveyor belt  410 . The first conveyance section  4  further includes a suction section  43  and a conveyance plate  42  that is an example of a guide member. 
     The first conveyor belt  410  is wound around the drive roller  412 , the belt speed detecting roller  413 , the tension roller  414 , and the pair of guide rollers  415 . The conveyance plate  42  and the suction section  43  are disposed on the internal side of the wound first conveyor belt  410 . The conveyance plate  42  is disposed opposite to the line heads  51  with the first conveyor belt  410  therebetween. The suction section  43  is disposed below the conveyance plate  42  on the internal side of the first conveyor belt  410 . 
     The drive roller  412  is disposed downstream of the conveyance plate  42  in the sheet conveyance direction X 1  (left side in  FIG. 4 ). The drive roller  412  is driven to rotate by a motor (not illustrated). As a result, the first conveyor belt  410  is circulated in a predetermined rotation direction (anticlockwise direction in  FIG. 4 ). Circulation of the first conveyor belt  410  conveys a sheet P in the sheet conveyance direction X 1 . 
     The belt speed detecting roller  413  is disposed upstream of the conveyance plate  42  in the sheet conveyance direction X 1  (right side in  FIG. 4 ). The belt speed detecting roller  413  rotates by friction generated between the belt speed detecting roller  413  and the first conveyor belt  410 . Preferably, the belt speed detecting roller  413  is located in cooperating relation with the drive roller  412  so as to ensure the flatness of the first conveyor belt  410  at regions opposite to the line heads  51 . 
     The belt speed detecting roller  413  includes a pulse plate (not illustrated) that integrally rotates with the belt speed detecting roller  413 . The rotational speed of the first conveyor belt  410  is measured by measuring the rotational speed of the pulse plate. 
     The tension roller  414  applies tensile force to the first conveyor belt  410  to ensure that the first conveyor belt  410  does not sag. The pair of guide rollers  415  guides the first conveyor belt  410  so that the first conveyor belt  410  passes below the suction section  43 . 
     The placement roller  416  is a driven roller. The placement roller  416  is located opposite to an upstream end of the conveyance plate  42  in the sheet conveyance direction X 1  with the first conveyor belt  410  therebetween. The placement roller  416  guides the sheet P forwarded by the pair of registration rollers  34  (see  FIG. 1 ) onto the first conveyor belt  410  to cause the sheet P to be sucked on the first conveyor belt  410 . 
     The conveyance plate  42  supports the first conveyor belt  410  while supporting the sheet P with the first conveyor belt  410  therebetween. The conveyance plate  42  guides the sheet P in the sheet conveyance direction X 1  while the first conveyance section  4  (first conveyor belt  410 ) conveys the sheet P. The conveyance plate  42  has a plurality of grooves  421  arranged in the sheet conveyance direction X 1 . The grooves  421  each extend in the sheet conveyance direction X 1 . The grooves  421  are each open toward a side of the recording section  5  (toward a side of the first conveyor belt  410 ). In the above configuration, the grooves  421  are in communication with the respective suction holes  411  (see  FIG. 3 ) in the first conveyor belt  410 . 
     The conveyance plate  42  has a plurality of through holes  422  arranged in the sheet conveyance direction X 1 . The through holes  422  are located in one-to-one correspondence with the grooves  421 . A mouth of each of the through holes  422  on the side of the recording section  5  (side of the first conveyor belt  410 ) is open at an inner surface (bottom surface) of a corresponding one of the grooves  421 . In the above configuration, the through holes  422  are in communication with the respective suction holes  411  in the first conveyor belt  410  through a corresponding one of the grooves  421 . By contrast, a mouth of each of the through holes  422  on the side of the suction section  43  is open at the lower surface of the conveyance plate  42 . 
     The suction section  43  sucks the sheet P onto the first conveyor belt  410  with the conveyance plate  42  and the first conveyor belt  410  therebetween. As a result, the sheet P is sucked onto the first conveyor belt  410 . Specifically, the suction section  43  sucks air in the space above the first conveyor belt  410  through the grooves  421  and the through holes  422  in the conveyance plate  42  and the suction holes  411  in the first conveyor belt  410 . Such suction creates wind toward the suction section  43  in the space above the conveyance plate  42 . When the sheet P guided onto the first conveyor belt  410  covers a portion of the first conveyor belt  410 , suction force (negative pressure) acts on the sheet P. As a result, the sheet P is sucked onto the first conveyor belt  410 . 
     The suction section  43  includes a suction device  432 , a duct  433 , and a box member  431  having an open top. The conveyance plate  42  is disposed so as to cover the open top of the box member  431 . The conveyance plate  42  and the box member  431  define a pressure chamber  434 . The pressure chamber  434  is in communication with the suction holes  411  in the first conveyor belt  410  through the through holes  422  and the grooves  421  in the conveyance plate  42 . 
     The suction device  432  is secured on the lower surface of the box member  431 . Specifically, the box member  431  has a bottom wall having an opening  435 . The suction device  432  is disposed in correspondence with the opening  435 . The suction device  432  is connected to the duct  433 . The suction device  432  is a fan. However, the suction device  432  is not limited to being a fan and may for example be a vacuum pump instead. 
     The suction device  432  is driven to generate negative pressure in the pressure chamber  434 . The negative pressure generates suction force in the grooves  421  through the through holes  422  to generate suction force in the suction holes  411  in the first conveyor belt  410  through the grooves  421 . As a result, air is sucked into the pressure chamber  434  through the suction holes  411  in the first conveyor belt  410  and the grooves  421  and the through holes  422  in the conveyance plate  42 . The air sucked into the pressure chamber  434  is exhausted through the suction device  432  and the duct  433 . When the sheet P guided onto the first conveyor belt  410  covers a portion of the suction holes  411 , the suction force (negative pressure) acts on the sheet P through the suction holes  411  covered with the sheet P, thereby causing the sheet P to be sucked onto the first conveyor belt  410 . 
     The line heads  51  are held on the head base  52 . Accordingly, the line heads  51  may be supported at a height at which a predetermined distance (1 mm in the present embodiment) is spaced between the first conveyor belt  410  and the line heads  51 . The inkjet recording apparatus  1  may include a raising and lowering mechanism that raises and lowers the head base  52  according to the thickness of a sheet P conveyed by the first conveyor belt  410 . The raising and lowering mechanism enables the line heads  51  to be support at a height at which a predetermined distance (1 mm in the present embodiment) is spaced between a sheet P and the line heads  51 . 
     With reference to  FIGS. 5, 6A, and 6B , a description will be made about the conveyance plate  42 .  FIG. 5  is a plan view of the conveyance plate  42  illustrated in  FIG. 4  as viewed from above. Specifically,  FIG. 5  illustrates a part of a surface  420  of the conveyance plate  42  on the side of the line heads  51 . Hereinafter, the surface  420  of the conveyance plate  42  on the side of the line heads  51  is referred to as a support surface  420 . The conveyance plate  42  supports the sheet P on the support surface  420  with the first conveyor belt  410  therebetween. 
     The conveyance plate  42  is made from a metal material. Specifically, for example, the conveyance plate  42  may be made from die-cast aluminum or a pressed metal plate. Alternatively, the conveyance plate  42  may be made from resin having excellent slidability against the first conveyor belt  410 . In a situation in which the conveyance plate  42  is made from a metal material, the conveyance plate  42  may be earthed. 
     As illustrated in  FIG. 5 , the support surface  420  has the plurality of grooves  421 . The grooves  421  are elongated grooves open toward the line heads  51 . Specifically, each of the grooves  421  is shaped in an elongated circular shape extending in the sheet conveyance direction X 1 . 
     The grooves  421  are arranged in the sheet conveyance direction X 1  and the width direction X 2 . The grooves  421  may be arranged in a staggered formation, as illustrated in  FIG. 5 . Specifically, the grooves  421  are arranged so as to be able to be opposite to the respective suction holes  411  in the first conveyor belt  410  (see  FIG. 3 ). In other words, the grooves  421  are in communication with the respective suction holes  411 . In the above arrangement, the suction holes  411  that are opposite to the grooves  421  change one-by-one as the first conveyor belt  410  advances (circulates). The grooves  421  each are located so as to be able to be opposite to at least two suction hoes  411 . 
     The grooves  421  each has one through hole  422 . The through holes  422  each are in communication with a corresponding one of the grooves  421 . The through holes  422  each have a circular shape in section. The through holes  422  may be arranged in a staggered formation, as illustrated in  FIG. 5 . 
       FIG. 6A  is a plan view of a groove  421  and a through hole  422  in the conveyance plate  42 .  FIG. 6B  is a cross sectional view (vertical cross sectional view) of the groove  421  and the through hole  422  taken along the line VIB-VIB in  FIG. 6A . As illustrated in  FIGS. 6A and 6B , the through hole  422  passes through the conveyance plate  42  in the thickness direction thereof and one end of the through hole  422  is open in the groove  421 . 
     With reference to  FIG. 7 , a description will be made next about an ink supplying mechanism  500  that supplies ink to the recording heads  55  of a corresponding one of the line heads  51 .  FIG. 7  illustrates structure of the ink supplying mechanism  500  according to the first embodiment. Specifically,  FIG. 7  illustrates the ink supplying mechanism  500  for supplying an ink of any one of the colors. The inkjet recording apparatus  1  illustrated in  FIG. 1  includes the ink supplying mechanism  500  illustrated in  FIG. 7  for each color of black, cyan, magenta, and yellow. 
     As illustrated in  FIG. 7 , the ink supplying mechanism  500  includes an ink tank  501  and a pump mechanism  502 . The ink supplying mechanism  500  further includes a first flow channel  503  and a second flow channel  504 . The first flow channel  503  connects the ink tank  501  to the pump mechanism  502 . The second flow channel  504  connects the pump mechanism  502  to the recording heads  55 . The ink supplying mechanism  500  further includes a first solenoid valve  505  and a second solenoid valve  506 . The first solenoid valve  505  that is an example of an inflow side switching valve is disposed in the first flow channel  503 . The second solenoid valve  506  that is an example of an outflow side switching valve is disposed in the second flow channel  504 . 
     The second flow channel  504  connects the pump mechanism  502  to each of the first, second, and third recording heads  55   a ,  55   b , and  55   c , which are described with reference to  FIG. 2 . However, only any one of the first, second, and third recording heads  55   a ,  55   b , and  55   c  is illustrated in  FIG. 7  for the sake of easy understanding. 
     The ink tank  501  contains an ink  511  of any one of the colors. The pump mechanism  502  includes a hollow cylinder  521  and a piston  522 . The cylinder  521  receives in the hollow space thereof a part of the piston  522 . The piston  522  is movable in the longitudinal direction of the cylinder  521  by a driving device (not illustrated). 
     The first flow channel  503  has one end connected to the ink tank  501  and the other end connected to an ink inlet formed in the bottom of the cylinder  521 . The second flow channel  504  has one end connected to an ink outlet formed in the bottom of the cylinder  521  and the other end connected to an inlet of a micro flow channel  551 . The micro flow channel  551  is located inside the recording head  55 . 
     The recording head  55  has the nozzle surface  51   a  having the nozzle orifices  51   b  arranged in the width direction X 2 . The nozzle orifices  51   b  are each in communication with the micro flow channel  551 . 
     In image recording on a sheet P, the ink  511  is contained in the cylinder  521 . The first and second solenoid valves  505  and  506  are both opened, and the piston  522  stays at a predetermined position. When ink droplets are discharged from the recording head  55  (nozzle orifices  51   b ), the ink  511  is supplied from the cylinder  521  to the micro flow channel  551  of the recording head  55  due to capillarity. In introducing the ink  511  into the cylinder  521 , the piston  522  of the pump mechanism  502  performs pulling in a state in which the first solenoid valve  505  is opened and the second solenoid valve  506  is closed. This draws the ink  511  in the ink tank  501  into the cylinder  521  of the pump mechanism  502  through the first flow channel  503 . 
     The ink supplying mechanism  500  operates in maintenance of the line heads  51  (recording heads  55 ), specifically, in purging. The ink supplying mechanism  500  is controlled by the control section  9  illustrated in  FIG. 1 . In purging, the ink  511  is contained in the cylinder  521 . The first solenoid valve  505  is closed and the second solenoid valve  506  is opened. The piston performs pushing. As a result, the ink  511  in the cylinder  521  is supplied to the micro flow channel  551  through the second flow channel  504 . The ink  511  present in the micro flow channel  551  is forcedly extruded out (purged) from the nozzle orifices  51   b . By the above purging, air babbles, thickened ink  511 , foreign matter such as paper dust are extruded outside the recording head  55 . Air babbles, thickened ink  511 , foreign matter such as paper dust are factors of causing discharge disablement. 
     The wiping unit  8  will be described next with reference to  FIGS. 8 and 9 .  FIG. 8  illustrates a first state of the wiping unit  8  illustrate in  FIG. 1 .  FIG. 9  illustrates a second state of the wiping unit  8  illustrated in  FIG. 1 . The wiping unit  8  is in the second state in maintenance on the line heads  51  (recording heads  55 ). The wiping unit  8  is controlled by the control section  9  illustrated in  FIG. 1 . 
       FIGS. 8 and 9  each illustrate three wiper blades  81  for any one of the line heads  51 Bk,  51 C,  51 M, and  51 Y for the four colors for the sake of easy understanding. The wiping unit  8  includes three wiper blades  81  for each of the line heads  51 Bk,  51 C,  51 M, and  51 Y. The three wiper blades  81  are disposed in correspondence with the first, second, and third recording heads  55   a ,  55   b , and  55   c , which are described with reference to  FIG. 2 . 
     As illustrated in  FIG. 8 , the wiping unit  8  includes a movement mechanism  82  in addition to the wiper blades  81 . The movement mechanism  82  moves the wiper blades  81  in a direction indicated by an arrow D 1  (leftward in  FIG. 8 ) and a direction indicated by an arrow D 2  (rightward in  FIG. 8 ). Hereinafter, the direction indicated by the arrow D 1  is referred to as a main scanning direction D 1  and the direction indicated by the arrow D 2  is referred to as a return direction D 2 . The main scanning direction D 1  is a direction toward one end from the other end of each of the recording heads  55  in the width direction X 2 . The return direction D 2  is a direction opposite to the main scanning direction D 1 . 
     The movement mechanism  82  includes a carriage  83  and a supporting frame  84  that supports the carriage  83 . The movement mechanism  82  further includes rolls  85 , gap rolls  86 , raising and lowering members  87 , and a bottom portion  88 . 
     The raising and lowering members  87  are each constituted by a lifting member  87   a  and a shaft  87   b . When the wiping unit  8  is in the first state, the lifting member  87   a  of each of the raising and lowering members  87  lies down on the bottom portion  88 . 
     In transition of the wiping unit  8  from the first state to the second state, the shaft  87   b  of each of the raising and lowering member  87  rotates. Specifically, the shaft  87   b  of the raising and lowering member  87  of the raising and lowering members  87  disposed upstream in the main scanning direction D 1  (right side in  FIG. 8 ) rotates in the clockwise direction in  FIG. 8 . On the other hand, the shaft  87   b  of the other raising and lowering member  87  disposed downstream in the main scanning direction D 1  (left side in  FIG. 8 ) rotates in the anticlockwise direction in  FIG. 8 . As a result, the lying lifting members  87   a  stand up from the bottom portion  88 , as illustrated in  FIG. 9 . The lifting members  87   a  stand up to raise the carriage  83 , the rolls  85 , the gap rolls  86 , and the wiper blades  81  together with the supporting frame  84 , thereby setting the wiping unit  8  into the second state. The wiping unit  8  becomes in the second state before performing purging. 
     The wiping unit  8  transitions from the second state to the first state after the wiper blades  81  clean the nozzle surfaces  51   a  illustrated in  FIG. 1 . In transition of the wiping unit  8  from the second state to the first state, the shafts  87   b  of the raising and lowering members  87  rotate in directions opposite to the directions in which the shafts  87   b  of the raising and lowering members  87  rotate in transition of the wiping unit  8  from the first state to the second state. Specifically, the shaft  87   b  of the raising and lowering member  87  of the raising and lowering members  87  disposed upstream in the main scanning direction D 1  (right side in  FIG. 9 ) rotates in the anticlockwise direction in  FIG. 9 . On the other hand, the shaft  87   b  of the other raising and lowering member  87  disposed downstream in the main scanning direction D 1  (left side in  FIG. 9 ) rotates in the clockwise direction in  FIG. 9 . As a result, the standing lifting members  87   a  lie down on the bottom portion  88 , as illustrated in  FIG. 8 . The lifting members  87   a  lie down to lower the carriage  83 , the rolls  85 , the gap rolls  86 , and the wiper blades  81  together with the supporting frame  84 , thereby setting the wiping unit  8  into the first state. 
     The carriage  83  movably engages with the supporting frame  84  through the rolls  85 . Specifically, the carriage  83  engages with the supporting frame  84  in a movable manner in the main scanning direction D 1  and the return direction D 2 . The wiper blades  81  are mounted on the carriage  83 . Movement of the carriage  83  in the main scanning direction D 1  or the return direction D 2  moves the wiper blades  81  in the main scanning direction D 1  or the return direction D 2 . 
     The carriage  83  moves in the main scanning direction D 1  in wiping. Movement of the carriage  83  in the main scanning direction D 1  moves the wiper blades  81  in the main scanning direction D 1 . Through the movement of the wiper blades  81 , the nozzle surfaces  51   a  are wiped by the wiper blades  81 . Wiping by the wiper blades  81  cleans the nozzle surfaces  51   a . When cleaning on the nozzle surfaces  51   a  ends and the wiping unit  8  transitions from the second state to the first state, the carriage  83  moves in the return direction D 2 . This movement of the carriage  83  causes the wiper blades  81  to return to the original positions. 
     The respective groups of the three wiper blades  81  of the corresponding line heads  51 Bk,  51 C,  51 M, and  51 Y for the four colors perform the same operation according to rotation of the shafts  87   b  and movement of the carriage  83 . 
     With reference to  FIGS. 10-14C , a description will be made next about operation of the inkjet recording apparatus  1  for maintenance on the line heads  51  (recording heads  55 ). In the inkjet recording apparatus  1  in the present embodiment, the maintenance mechanism for the line heads  51  includes the ink supplying mechanisms  500  described with reference to  FIG. 7  and the wiping unit  8  described with reference to  FIGS. 8 and 9 . 
     As described with reference to  FIG. 1 , the maintenance on the line heads  51  in the present embodiment means both the regular maintenance and the sheet width dependent maintenance. The operation of the inkjet recording apparatus  1  in the sheet width dependent maintenance is the same as the operation of the inkjet recording apparatus  1  in the regular maintenance. The sheet width dependent maintenance is different from the regular maintenance in a condition for initiation. 
       FIGS. 10 and 11  each illustrate the operation of the inkjet recording apparatus  1 . Specifically,  FIGS. 10 and 11  each illustrate the operation of the inkjet recording apparatus  1  in maintenance on the line heads  51 . In maintenance on the line heads  51  (recording heads  55 ), as illustrated in  FIG. 10 , the first conveyance section  4  first moves away from the line heads  51  in a direction indicated by an arrow D 11  (downward direction). The wiping unit  8  then moves in a direction indicated by an arrow D 12  (rightward in  FIG. 10 ) and stops at a location between the recording section  5  (line heads  51 ) and the first conveyance section  4 . 
     Subsequently, as illustrated in  FIG. 11 , the first conveyance section  4  moves in a direction indicated by an arrow D 13  (upward) to raise the wiping unit  8 . As a result, the wiping unit  8  is moved directly below the recording section  5  (line heads  51 ). 
       FIGS. 12 and 13  each illustrate operation of the wiping unit  8 . Specifically,  FIGS. 12 and 13  each illustrate the operation of the wiping unit  8  in maintenance on the line heads  51 . As illustrated in  FIG. 12 , the wiping unit  8  is in the first state described with reference to  FIG. 8  in moving directly below the line heads  51 . Note that  FIGS. 12 and 13  illustrate, likewise  FIGS. 8 and 9 , three wiper blades  81  for any one of the line heads  51 Bk,  51 C,  51 M, and  51 Y for the four colors for the sake of easy understanding. 
     When the wiping unit  8  moves directly below the line heads  51 , the wiping unit  8  transitions from the first state to the second state as described with reference to  FIGS. 8 and 9 .  FIG. 13  illustrates the wiping unit  8  having transitioned from the first state to the second state directly below the line heads  51 . When the wiping unit  8  transitions from the first state to the second state directly below the line heads  51 , the wiper blades  81  are each pushed against the nozzle surface  51   a  of a corresponding one of the recording heads  55 . Specifically, the wiper blades  81  are each pushed against one end of corresponding one of the nozzle surfaces  51   a  in the main scanning direction D 1  (right end in  FIG. 13 ). The gap rolls  86  come in contact with the head base  52 . Contact of the gap rolls  86  with the head base  52  causes the wiper blades  81  pushed against the nozzle surfaces  51   a  to be held constant at a given location in the vertical direction. 
     When the wiping unit  8  transitions from the first state to the second state, the ink supplying mechanisms  500  perform purging as described with reference to  FIG. 7 . Through the purging, ink is extruded from the line heads  51  (recording heads  55 ) and falls onto the supporting frame  84 . The supporting frame  84  has an upper surface that forms an ink collection tray (not illustrated). The falling purged ink is collected into the ink collection tray. Part of the purged ink remains on the nozzle surfaces  51   a.    
     After purging, the wiping unit  8  performs wiping as described with reference to  FIG. 9 . That is, the carriage  83  moves in the main scanning direction D 1  to move the wiper blades  81  in the main scanning direction D 1 . The movement of the wiper blades  81  causes the wiper blades  81  to wipe the nozzle surfaces  51   a . As a result, the purged ink remaining on the nozzle surfaces  51   a  flows down along the wiper blades  81  from the nozzle surfaces  51   a  to be collected onto the supporting frame  84  (into the ink collection tray). 
       FIGS. 14A-14C  each illustrate operation of a wiper blade  81 . Specifically,  FIGS. 14A-14C  each illustrate the operation of the wiper blade  81  in maintenance (wiping) on a recording head  55 . As illustrated in  FIG. 14A , when the ink supplying mechanism  500  described with reference to  FIG. 7  performs purging, part of purged ink  511   a  extruded through the nozzle orifices  51   b  of the recording head  55  remains on a nozzle surface  51   a . In wiping, as illustrated in  FIGS. 14A and 14B , the wiper blade  81  moves in the main scanning direction D 1  while being pushed against the nozzle surface  51   a . Movement of the wiper blade  81  causes the wiper blade  81  to wipe the purged ink  511   a  remaining on the nozzle surface  51   a . As a result, the purged ink  511   a  falls down along the wiper blade  81  from the nozzle surface  51   a.    
     When wiping ends, the wiping unit  8  transitions from the second state to the first state, as described with reference to  FIGS. 8 and 9 . As a result, as illustrated in  FIG. 14C , the wiper blade  81  is lowered from the nozzle surface  51   a  to be separate from the nozzle surface  51   a . Then, the carriage  83  described with reference to  FIGS. 8 and 9  moves in the return direction D 2 . The wiper blade  81  accordingly moves in the return direction D 2  to be located at the original position illustrated in  FIG. 8 . 
     With reference to  FIG. 15 , a description will be made next about a maintenance method for the line heads  51  (recording heads  55 ) in the present embodiment. Specifically, a description will be made about execution timing of the sheet width dependent maintenance.  FIG. 15  is a flowchart depicting a process flow of the control section  9  (see  FIG. 1 ) included in the inkjet recording apparatus  1  according to the present embodiment. Specifically,  FIG. 15  depicts a process flow for determining whether or not to perform the sheet width dependent maintenance. 
     The control section  9  executes processing of Steps S 1 -S 4  indicated in  FIG. 15  in execution of a new print job. 
     In execution of a new print job, the control section  9  first determines whether or not the width of a next recording target sheet P is greater than the width of a sheet P subjected to image recording (Step S 1 ) prior to the next recording target sheet P. 
     Upon determining that the width of the next recording target sheet P is greater than the width of the sheet P previously subjected to image recording (Yes at Step S 1 ), the control section  9  determines whether or not the total number of small sheets P is no less than a predetermined number (Step S 2 ). That is, the control section  9  determines whether or not image recording has been performed on the predetermined number or more of sheets P having a width smaller than the width of the next recording target sheet P. 
     Upon determining that the total number of small sheets P is no less than the predetermined number (Yes at Step S 2 ), the control section  9  causes the maintenance mechanism to operate. The sheet width dependent maintenance is accordingly performed on the line heads  51  (recording heads  55 ) (Step S 3 ). 
     When the sheet width dependent maintenance ends, the control section  9  controls the inkjet recording apparatus  1  to perform image recording on the next recording target sheet P (Step S 4 ). 
     By contrast, upon determination at Step S 1  that the width of the next recording target sheet P is no greater than the width of the sheet P previously subjected to image recording (No at Step S 1 ), processing by the control section  9  proceeds to Step S 4 . Upon determination at Step S 2  that the total number of small sheets P is less than the predetermined number (No at Step S 2 ), processing by the control section  9  proceeds to Step S 4 . 
     Note that in a situation in which the predetermined number referenced in the processing at Step S 2  is 1, the processing at Step S 2  may be omitted. 
     As described above, in the present embodiment, the control section  9  controls the operation timing of the maintenance mechanism (the wiping unit  8  and the ink supplying mechanisms  500 ). Specifically, upon determining that the width of the next recording target sheet P is greater than the width of the sheet P previously subjected to image recording, the control section  9  causes the maintenance mechanism to operate. In the above configuration, even in a situation in which the width of the next recording target sheet P is greater than the width of a sheet P previously subjected to image recording, an image formed on the next recording target sheet P is unlikely to include a white line. In consequence, reduction in image quality can be prevented in the present embodiment. 
     Further, in the present embodiment, the sheet width dependent maintenance can be performed using the maintenance mechanism that performs the regular maintenance. In consequence, reduction in image quality can be reduced by a simple configuration. 
     Furthermore, in the present embodiment, the control section  9  causes the maintenance mechanism to operate upon determining that image recording has been performed on the predetermined number or more of sheets P having a width smaller than the width of the next recording target sheet P. In the above configuration, when the predetermined number is set to be small, an interval of execution of the sheet width dependent maintenance can be shortened to enhance image quality. Alternatively, when the predetermined number is set to be great, the amount of ink consumed in purging can be reduced. 
     Image recording on a sheet P cannot be performed during execution of maintenance on the line heads  51 . For this reason, the shorter the interval of execution of the sheet width dependent maintenance, that is, the higher the frequency of execution of the sheet width dependent maintenance, the lower the processing speed (operation efficiency). To tackle this problem, in the present embodiment, the interval of execution of the sheet width dependent maintenance is increased by setting the predetermined number to be great for preventing lowering of the processing speed (operation efficiency). 
     Second Embodiment 
     A second embodiment will be described next with reference to the accompanying drawings. Note that a description about only matter different from that in the first embodiment is given and a description of the same matter as that in the first embodiment is omitted. The inkjet recording apparatus  1  according to the second embodiment is different from that according to the first embodiment in purging and wiping in the sheet width dependent maintenance. Specifically, in the second embodiment, the sheet width dependent maintenance is performed on respective parts of the line heads  51 . 
       FIG. 16  illustrates regions on which the maintenance is performed in the second embodiment. Specifically,  FIG. 16  illustrates regions on which the sheet width dependent maintenance is performed. As illustrated in  FIG. 16 , the inkjet recording apparatus  1  according to the present embodiment performs image recording on a sheet P having a width W 1 . In addition, the inkjet recording apparatus  1  in the present embodiment performs image recording on a sheet P having a width W 2  greater than the width W 1 . In the above configuration, in a situation in which image recording is performed on multiple sheets P having the width W 1 , discharge disablement may occur in regions A beside a region where the multiple sheets P have passed before execution of the regular maintenance. 
     The inkjet recording apparatus  1  in the present embodiment performs the sheet width dependent maintenance (purging and wiping) only on respective parts of the line heads  51  (recording heads  55 ) that corresponds to the regions A. Such partial maintenance is executed through control on the maintenance mechanism by the control section  9  described with reference to  FIG. 1 . Specifically, among the first, second, and third recording heads  55   a ,  55   b , and  55   c  of each of the line heads  51 , the first and third recording heads  55   a  and  55   c  are targets for the sheet width dependent maintenance. More specifically, the sheet width dependent maintenance is performed on a part of each first recording head  55   a  that corresponds to one of the regions A and a part of each third recording head  55   c  that corresponds to the other of the regions A. 
     The sheet width dependent maintenance is executed in a situation in which image recording is to be performed on a sheet P (next recording target sheet) having the width W 2  after image recording is performed on a predetermined number or more ( 100  in the present embodiment) of sheets P having the width W 1 , similarly to the configuration in the first embodiment. The sheet width dependent maintenance is performed prior to image recording on the sheet P having the width W 2 . 
       FIG. 17  illustrates structure of an ink supplying mechanism  500  according to the second embodiment. Specifically,  FIG. 17  illustrates the ink supplying mechanism  500  for supplying an ink of any one of the colors. The inkjet recording apparatus  1  in the second embodiment includes the ink supplying mechanism  500  illustrated in  FIG. 17  for each of the colors of black, cyan, magenta, and yellow. The control section  9  illustrated in  FIG. 1  controls the ink supplying mechanisms  500 . 
     As illustrated in  FIG. 17 , in the present embodiment, micro flow channel in the interior of each of the first and third recording heads  55   a  and  55   c  is divided into a first micro flow channel  551   a  and a second micro flow channel  551   b . In the above configuration, the first and third recording heads  55   a  and  55   c  each have the first micro flow channel  551   a  and the second micro flow channel  551   b . The second micro flow channel  551   b  is in communication with the nozzle orifices  51   b  located in a corresponding one of the regions A described with reference to  FIG. 16 . 
     The ink supplying mechanism  500  includes the ink tank  501  and the pump mechanism  502 . The ink supplying mechanism  500  further includes the first flow channel  503  and the second flow channel  504 . The first flow channel  503  connects the ink tank  501  to the pump mechanism  502 . The second flow channel  504  connects each of the first, second, and third recording heads  55   a ,  55   b , and  55   c  to the pump mechanism  502 . The ink supplying mechanism  500  includes one first solenoid valve  505  and five second solenoid valves  506 . The first solenoid valve  505  that is an example of an inflow switching valve is disposed in the first flow channel  503 . The five second solenoid valves  506  that are examples of outflow switching valves are disposed in the second flow channel  504 . 
     Specifically, a portion of the second flow channel  504  that is connected to the first recording head  55   a  branches into a portion connected to the inflow port of the first micro flow channel  551   a  and a portion connected to the inflow port of the second micro flow channel  551   b . Similarly, a portion of the second flow channel  504  that is connected to the third recording head  55   c  branches into a portion connected to the inflow port of the first micro flow channel  551   a  and a portion connected to the inflow port of the second micro flow channel  551   b . The five second solenoid valves  506  includes two second solenoid valves  506   a  and two second solenoid valves  506   b . The two second solenoid valves  506   a  are arranged for the respective first micro flow channels  551   a  of the first and third recording heads  55   a  and  55   c . The two second solenoid valves  506   b  are arranged for the respective second micro flow channels  551   b  of the first and third recording heads  55   a  and  55   c.    
     In the sheet width dependent maintenance (purging), the ink  511  is contained in the cylinder  521 . The first solenoid valve  505  is closed, and the two second solenoid valves  506   b  are opened among the five second solenoid valves  506 . In other words, the cylinder  521  is in communication with the inflow ports of the two second micro flow channels  551   b . The piston  522  performs pushing in this state. As a result, the ink  511  contained in the cylinder  521  is supplied to each of the second micro flow channels  551   b  through the second flow channel  504 . In the above configuration, at least the ink  511  present in each of the micro flow channels  551   b  is forcedly extruded out (purged) from nozzle orifices  51   b  located in the regions A. 
       FIGS. 18A-24B  each illustrate operation of a wiper blade  81  according to the second embodiment. Specifically,  FIGS. 18A-24B  each illustrate the wiper blade  81  in the sheet width dependent maintenance (wiping). More specifically,  FIGS. 18A, 19A, 20A, 21A, 22A, 23A, and 24A  each illustrate the operation of a wiper blade  81  that corresponds to a first recording head  55   a .  FIGS. 18B, 19B, 20B, 21B, 22B, 23B, and 24B  each illustrate the operation of a wiper blade  81  that corresponds to a third recording head  55   c . A wiper blade  81  that corresponds to a second recording head  55   b  performs the same operation as the respective wiper blades  81  that correspond to the first and third recording heads  55   a  and  55   c . The operation of each of the wiper blades  81  illustrated in  FIGS. 18A-24B  are performed through control on the wiping unit  8  by the control section  9  illustrated in  FIG. 1 . 
     When purging is performed in the sheet width dependent maintenance, in the second embodiment, the ink  511   a  is extruded from portions of the respective nozzle surfaces  51   a  of the first and third recording heads  55   a  and  55   c  that correspond to the regions A. In the above configuration, as illustrated in  FIGS. 18A and 18B , part of the purged ink  511   a  remains at a part of each nozzle surface  51   a  of the first and third recording heads  55   a  and  55   c.    
     In wiping, as illustrated in  FIGS. 18A and 18B , the wiper blades  81  are first pushed against the corresponding nozzle surfaces  51   a  of the first and third recording heads  55   a  and  55   c  so that the wiper blade  81  corresponding to the first recording head  55   a  wipes a part of the nozzle surface  51   a  that corresponds to one of the regions A. Then, as illustrated in  FIGS. 19A and 19B , the wiper blades  81  move in the main scanning direction D 1  while being pushed against the corresponding nozzle surfaces  51   a  so that the wiper blade  81  corresponding to the first recording head  55   a  wipes the part of the nozzle surface  51   a  that corresponds to the region A. Through the movement of the wiper blades  81 , the purged ink  511   a  remaining on the nozzle surface  51   a  of the first recording head  55   a  is wiped off by the wiper blade  81 . As a result, the purged ink  511   a  flows down along the wiper blade  81  from the nozzle surface  51   a  of the first recording head  55   a.    
     As described with reference to  FIGS. 8 and 9 , the wiping unit  8  then transitions from the second state to the first state. As a result, as illustrated in  FIGS. 20A and 20B , the wiper blades  81  are lowered from the corresponding nozzle surfaces  51   a . In other words, the wiper blades  81  are separate from the respective nozzle surfaces  51   a.    
     As illustrated in  FIGS. 21A and 21B , the wiper blades  81  next move in the main scanning direction D 1  so that the wiper blade  81  corresponding to the third recording head  55   c  moves to a location before a part of the nozzle surface  51   a  of the third recording head  55   c  that corresponds to the other region A. 
     The wiping unit  8  then transitions from the first state to the second state, as described with reference to  FIGS. 8 and 9 . As a result, as illustrated in  FIGS. 22A and 22B , the wiper blades  81  are raised and pushed against the respective nozzle surfaces  51   a.    
     Then, as illustrated in  FIGS. 23A and 23B , the wiper blades  81  move in the main scanning direction D 1  while being pushed against the corresponding nozzle surfaces  51   a  so that the wiper blade  81  corresponding to the third recording head  55   c  wipes a part of the nozzle surface  51   a  of the third recording head  55   c  that corresponds to the other region A. Through the movement of the wiper blades  81 , the purged ink  511   a  remaining on the nozzle surface  51   a  of the third recording head  55   c  is wiped off by the wiper blade  81 . As a result, the purged ink  511   a  flows down along the wiper blade  81  from the nozzle surface  51   a  of the third recording head  55   c.    
     When wiping ends, the wiping unit  8  transitions from the second state to the first state, as described with reference to  FIGS. 8 and 9 . As a result, as illustrated in  FIGS. 24A and 24B , the wiper blades  81  are lowered from the corresponding nozzle surfaces  51   a . In other words, the wiper blades  81  are separate from the respective nozzle surfaces  51   a . The wiper blades  81  then move in the return direction D 2  to return to the original positions indicated in  FIG. 8 . 
     The present embodiment describes, but is not limited to, a configuration in which each of the micro flow channels of the first and third recording heads  55   a  and  55   c  is divided into two micro flow channels  551   a  and  551   b  according to the two width types (W 1  and W 2 ) of sheets P. The present disclosure is applicable to a configuration using sheets P of three or more width types. In a situation in which the present disclosure is applied to a configuration using sheets P of three or more width types, each of the micro flow channels of the first and third recording heads  55   a  and  55   c  is divided into three or more micro flow channels according to the number of the width types of the sheets P. A second solenoid valve  506  is provided in each of the divided flow channels. 
     As has been described so far, in the present embodiment, the sheet width dependent maintenance is performed on respective parts of the line heads  51  (recording heads  55 ) in correspondence with the difference in width between the next recording target sheet P and a sheet P subjected to image recording prior to the next recording target sheet P. In the above configuration, even in a situation in which the width of the next recording target sheet P is greater than the width of the sheet P previously subjected to image recording, an image formed on the next recording target sheet P is unlikely to include a white line, similarly to the configuration in the first embodiment. Thus, reduction in image quality can be prevented. 
     Further in the present embodiment, ink is extruded from a portion of the nozzle orifices  51   b  in the line heads  51  (recording heads  55 ) in correspondence with the difference in width between the next recording target sheet P and the sheet P subjected to image recording prior to the next recording target sheet P. In the above configuration, the amount of the ink  511  consumed in the sheet width dependent maintenance can be reduced. 
     Yet in the present embodiment, the wiper blades  81  wipe respective parts of the nozzle surfaces  51   a  of the line heads  51  (recording heads  55 ) in correspondence with the difference in width between the next recording target sheet P and the sheet P subjected to image recording prior to the next recording target sheet P. In the above configuration, the amount of movement of the wiper blades  81  in a state being pushed against the respective nozzle surfaces  51   a  can be reduced in the sheet width dependent maintenance. Thus, abrasion of the wiper blades  81  can be reduced. The lifetime of the wiper blades  81  can be accordingly extended. 
     The present embodiment describes, but is not limited to, a configuration in which the wiper blades  81  wipe (clean) respective parts of the nozzle surfaces  51   a  in the sheet width dependent maintenance. Alternatively, the wiper blades  81  may wipe the entire parts of the respective nozzle surfaces  51   a  in the sheet width dependent maintenance. 
     The embodiments of the present disclosure have been described so far with reference to the drawings. The present disclosure is not limited to the above embodiments, and various alterations may be made without departing from the spirit and the scope of the present disclosure. 
     The embodiments of the present embodiment describe, but are not limited to, a configuration in which the line heads  51  is constituted by the three recording heads  55 . Alternatively, the line heads  51  may be constituted by one, two, or four or more recording heads. 
     The embodiments of the present disclosure are applied to an inkjet recording apparatus capable of performing full-color image recording. However, the present disclosure may be applicable to inkjet recording apparatuses that perform monochrome image recording. 
     Respective matter described in the embodiments of the present disclosure may be appropriately combined together.