Abstract:
An inkjet recording apparatus may include a corrugate mechanism configured to form a sheet into a corrugated shape. The inkjet recording apparatus may be configured to receive sheets of various sizes and shapes. Accordingly, in some examples, the inkjet recording apparatus may include differently configured portions to handle sheets of different sizes or shapes. According to one arrangement, the inkjet recording apparatus may be configured to receive passage of sheets of a first size through multiple ones of the differently configured portions while receiving passage of sheets of a second size though limited ones of the differently configured portions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 13/628,668 filed on Sep. 27, 2012, which claims priority from Japanese Patent Application No. 2011-259493 filed on Nov. 28, 2011 and Japanese Patent Application No. 2012-104095 filed on Apr. 27, 2012, the entire disclosures of the prior U.S. and Japanese patent applications being incorporated herein by reference. This application also claims priority from Japanese Patent Application No. 2013-016491 filed on Jan. 31, 2013 and Japanese Patent Application No. 2013-059483 filed on Mar. 22, 2013, the entire disclosures of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Aspects described herein relate to an inkjet recording apparatus that records an image onto a sheet while conveying the sheet maintained in a specified shape. 
       BACKGROUND 
       [0003]    A known inkjet recording apparatus is configured to convey a sheet by a conveyor roller pair while holding the sheet by a platen, record an image onto the sheet held by the platen by ejecting ink droplets from a recording head, and discharge the sheet having the recorded image by a discharge roller pair. The known inkjet recording apparatus further comprises a corrugate mechanism configured to form the sheet into a corrugated shape having alternating ridge portions and groove portions so as to prevent the sheet on the platen from curling during the image recording. 
       SUMMARY 
       [0004]    In the known inkjet recording apparatus, because the conveyor roller pair and the discharge roller pair are partially used to convey a smaller size sheet, a sheet conveying force of the conveyor roller pair and/or the discharge roller pair when conveying a smaller size sheet may decrease as compared with when conveying a larger size sheet. Consequently, load applied to the smaller size sheet by the corrugate mechanism may increase relatively. This may adversely affect the conveying accuracy of the smaller size sheet. 
         [0005]    According to one or more aspects, an inkjet recording apparatus may be configured to convey a sheet formed into a corrugated shape while ensuring the sheet conveying accuracy. 
         [0006]    In one or more example, an inkjet recording apparatus may comprise a first conveyor configured to selectively nip and convey a first sheet and a second sheet in a conveying direction, the second sheet having a shorter length in a first direction than the first sheet, the first direction being perpendicular to the conveying direction and a vertical direction; a recording head comprising nozzles configured to eject ink droplets onto a sheet conveyed by the first conveyor; a corrugate mechanism disposed upstream of the nozzles in the conveying direction and configured to form the sheet into a corrugated shape having alternating ridge portions and groove portions arranged in the first direction; a plurality of second conveyors disposed downstream of the nozzles in the conveying direction and spaced from each other in the first direction, each of the plurality of second conveyors being spaced, in the conveying direction, from a corresponding first portion of the corrugate mechanism, the corresponding first portion configured to form one of the ridge portions in the sheet, the plurality of second conveyors being configured to nip the sheet at nip points and convey the sheet; and a plurality of first pressing portions disposed downstream of the nozzles in the conveying direction and spaced from each other in the first direction, each of the plurality of first pressing portions being spaced, in the conveying direction, from a corresponding second portion of the corrugate mechanism, the corresponding second portion configured to form one of the groove portions in the sheet, the plurality of first pressing portions being configured to contact, at lower ends thererof, an upper surface of the sheet, and the lower ends being positioned lower than the nip points of the plurality of second conveyors. The inkjet recording apparatus defines a first zone configured to receive passage of the first sheet but not passage of the second sheet, and a second zone configured to receive passage of the first sheet and the second sheet. The plurality of first pressing portions comprise first pressing portions positioned in the first zone and first pressing portions positioned in the second zone, and a pressing force per unit area configured to be applied to the sheet by the first pressing portions positioned in the second zone is less than a pressing force per unit area configured to be applied to the sheet by the first pressing portions positioned in the first zone. 
         [0007]    In some example, an inkjet recording apparatus may comprise a first conveyor configured to selectively nip and convey a first sheet and a second sheet in a conveying direction, the second sheet having a shorter length in a first direction than the first sheet, the first direction being perpendicular to the conveying direction and a vertical direction; a recording head comprising nozzles configured to eject ink droplets onto a sheet conveyed by the first conveyor; a corrugate mechanism disposed upstream of the nozzles in the conveying direction and configured to form the sheet into a corrugated shape having alternating ridge portions and groove portions arranged in the first direction; a plurality of second conveyors disposed downstream of the nozzles in the conveying direction and spaced from each other in the first direction, each of the plurality of second conveyors being spaced, in the conveying direction, from a corresponding first portion of the corrugate mechanism, the corresponding first portion configured to form one of the ridge portions in the sheet, the plurality of second conveyors being configured to nip the sheet at nip points and convey the sheet; and a plurality of first pressing portions disposed downstream of the nozzles in the conveying direction and spaced from each other in the first direction, each of the plurality of first pressing portions being spaced, in the conveying direction, from a corresponding second portion of the corrugate mechanism, the corresponding second portion configured to form one of the groove portions in the sheet respectively, the plurality of first pressing portions being configured to contact, at lower ends thererof, an upper surface of the sheet, and the lower ends being positioned lower than the nip points of the plurality of second conveyors. The inkjet recording apparatus defines, in the first direction, a first zone configured to receive passage of the first sheet but not passage of the second sheet, and a second zone configured to receive passage of the first sheet and the second sheet. The first pressing portions comprise upstream pressing portions positioned in the first zone and the second zone and arranged in the first direction, and downstream pressing portions positioned in the first zone but not in the second zone and arranged in the first direction at positions downstream of the upstream pressing portions in the conveying direction. 
         [0008]    In some example, an inkjet recording apparatus may comprise a first conveyor configured to selectively nip and convey a first sheet and a second sheet in a conveying direction, the second sheet having a shorter length in a first direction than the first sheet, the first direction being perpendicular to the conveying direction and a vertical direction; a recording head comprising nozzles configured to eject ink droplets onto a sheet conveyed by the first conveyor; a platen configured to move up and down between a first position and a second position and comprising a plurality of ribs disposed downstream of the first conveyor in the conveying direction and extending in the conveying direction, the plurality of ribs being spaced from each other in the first direction and configured to support, at upper edges thereof, the sheet conveyed by the first conveyor; a plurality of pressing portions spaced from each other in the first direction and each interposed between a corresponding pair of the plurality of ribs, the plurality of pressing portions being configured to contact, at lower ends thereof, the upper surface of the sheet held by the plurality of ribs; a support member configured to support the platen when the platen moves down into the second position; and a plurality of urging members, each of the urging members being sandwiched between the platen and the support member and configured to urge the platen upward toward the first position. The inkjet recording apparatus define a first zone configured to receive passage of the first sheet but not passage of the second sheet, and a second zone configured to receive passage of the first sheet and the second sheet. The platen further comprises a plurality of protrusions protruding toward the support member, and a portion of the platen positioned in the second zone is deformable toward the support member when the support member receives the plurality of protrusions of the platen in the second position. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]    For a more complete understanding of the present disclosure, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
           [0010]      FIG. 1  is a perspective view depicting an inkjet recording apparatus in a first illustrative embodiment according to one or more aspects of the disclosure. 
           [0011]      FIG. 2  is a schematic vertical sectional view depicting a main body of the inkjet recording apparatus of  FIG. 1  in the first illustrative embodiment. 
           [0012]      FIG. 3  is a bottom view depicting a recording head in the first illustrative embodiment. 
           [0013]      FIG. 4  is a partial perspective view depicting the main body in the first illustrative embodiment. 
           [0014]      FIG. 5A  is a sectional view depicting a platen and contact members, taken along a line extending in a right-left direction, in the first illustrative embodiment. 
           [0015]      FIG. 5B  is a sectional view depicting the platen and the contact members when a sheet having relatively lower stiffness is conveyed, taken along the line extending in the right-left direction, in the first illustrative embodiment. 
           [0016]      FIG. 5C  is a sectional view depicting the platen and the contact members when a sheet having relatively higher stiffness is conveyed, taken along the line extending in the right-left direction, in the first illustrative embodiment. 
           [0017]      FIG. 6  is a perspective view depicting the platen and a support member, in the first illustrative embodiment. 
           [0018]      FIG. 7  is a vertical sectional view depicting the support member and a holder in the first illustrative embodiment. 
           [0019]      FIG. 8A  is a vertical sectional view depicting the support member, taken along a line passing one of second ribs and one of fifth ribs, in the first illustrative embodiment. 
           [0020]      FIG. 8B  is a vertical sectional view depicting the support member, taken along a line passing one of fourth ribs, in the first illustrative embodiment. 
           [0021]      FIG. 8C  is a partial perspective view of the support member in a third variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
           [0022]      FIG. 9A  is a partial schematic vertical sectional view depicting a main body in a first variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
           [0023]      FIG. 9B  is a partial schematic vertical sectional view of a main body in a second variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
           [0024]      FIG. 10A  is partial perspective view depicting a support member in a fourth variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
           [0025]      FIG. 10B  is a partial perspective view depicting a support member in a fifth variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
           [0026]      FIG. 11A  is schematic plan view depicting positions of a discharge roller pair, second spurs, and third spurs in the first illustrative embodiment. 
           [0027]      FIG. 11B  is a schematic plan view depicting positions of a discharge roller pair and second spurs in another embodiment according to one or more aspects of the disclosure. 
           [0028]      FIG. 12  is a schematic plan view depicting positions of a discharge roller pair, second spurs, third spurs, a roller pair, fourth spurs, and fifth spurs in the first variation of the first illustrative embodiment. 
           [0029]      FIG. 13  is a schematic back view of the platen in the first illustrative embodiment. 
           [0030]      FIG. 14A  is a schematic front view of the platen and its surroundings when no sheet is conveyed in the first illustrative embodiment. 
           [0031]      FIG. 14B  is a schematic front view of the platen and its surroundings when a sheet of smaller size is conveyed in the first illustrative embodiment. 
           [0032]      FIG. 14C  is a schematic front view of the platen and its surroundings when a sheet having relatively lower stiffness is conveyed in the first illustrative embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0033]    Illustrative embodiments according to one or more aspects are described below with reference to the accompanying drawings. The illustrative embodiments described below are only examples. Various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure. As depicted in  FIG. 1 , an up-down direction  7  may be defined with reference to an inkjet recording apparatus  10  disposed in an orientation in which it is intended to be used. A side of the inkjet recording apparatus  10 , in which a control panel  16  may be provided, may be defined as the front of the inkjet recording apparatus  10 . A front-rear direction  8  may be defined with reference to the front of the inkjet recording apparatus  10 . A right-left direction  9  may be defined with respect to the inkjet recording apparatus  10  as viewed from its front. Hereinafter, a first illustrative embodiment according to the one or more aspects of the disclosure is described. 
         [0034]    As depicted in  FIG. 1 , the inkjet recording apparatus  10  may comprise a printer unit  11  and a scanner unit  12 . The printer unit  11  may be configured to record an image onto a sheet  6  (see  FIG. 2 ). The sheet  6  may be, for example, recording paper, glossy paper, a postcard and/or other types of printing/recording media. The scanner unit  12  may be configured to read an image recorded on a document (not depicted). The inkjet recording apparatus  10  may be configured to perform one or more of printing, scanning, and copying. The inkjet recording apparatus  10  may not necessarily comprise the scanner unit  12 , whose detailed description is omitted. 
         [0035]    As further depicted in  FIG. 1 , the printer unit  11  may comprise a main body  13  and a sheet feed cassette  20 . The sheet feed cassette  20  may be disposed in a lower portion of the main body  13 . As depicted in  FIG. 2 , the sheet feed cassette  20  may be configured to accommodate one or more sheets  6  that may be loaded therein by a user. The main body  13  may comprise a housing  14  (see  FIG. 1 ) that may comprise therein a feeding portion  40 , a conveying path  31 , a conveyor roller pair  34 , a discharge roller pair  37 , contact members  60 , a recording portion  45 , second spurs  82  and third spurs  83 . The main body  13  may be configured to feed the sheet  6  into the conveying path  31  by the feeding portion  40  and convey the fed sheet  6  by the conveyor roller pair  34 . The main body  13  may be further configured to form the sheet  6  being conveyed into a shape of alternating ridge portions and groove portions (hereinafter, also referred to as a “corrugated shape”) to provide a corrugation pattern. For example, the corrugated shape of the sheet  6  may be formed by the contact members  60 . Consequently, the main body  13  may record an image onto the sheet  6  having a corrugation pattern by ejecting ink droplets from the recording portion  45 . A sheet having a corrugation pattern may also be referred to as a “corrugated sheet”. The main body  13  may be further configured to maintain the sheet  6  in the corrugated shape by the discharge roller pair  37 , the second spurs  82  and the third spurs  83  and to discharge the sheet  6  onto a sheet discharge tray  29  of the sheet feed cassette  20  by the discharge roller pair  37 . Hereinafter, components of the printer unit  11  are described. 
         [0036]    The housing  14  may have an opening  15  in the front of the housing  14  in the front-rear direction  8 . The sheet feed cassette  20  may be inserted into or removed from the inkjet recording apparatus  10  via the opening  15 . The housing  14  may comprise rails (not depicted) at a back portion of the housing  14  behind the opening  15 . The rails may be configured to support the sheet feed cassette  20  slidably along the front-rear direction  8 . 
         [0037]    The sheet feed cassette  20  may be configured to be accommodated in the lower portion of the housing  14 . The sheet feed cassette  20  may be supported by the rails (not depicted) disposed at the housing  14  and configured to be slidable along the front-rear direction  8  via the rails. As depicted in  FIG. 2 , the sheet feed cassette  20  may comprise a main tray  21  and the sheet discharge tray  29 . The main tray  21  may be configured to hold one or more sheets  6  on which an image is to be recorded. The sheet discharge tray  29  may be configured to receive one or more sheets  6  on which an image has been recorded. The sheet discharge tray  29  may be disposed above the main tray  21  and supported by the main tray  21 . 
         [0038]    The main tray  21  may comprise a lower surface  22  and an inclined wall  26 . One or more sheets  6  may be received on the lower surface  22  of the main tray  21 . The inclined wall  26  may extend obliquely upward from a rear end of the lower surface  22  in the front-rear direction  8 . The inclined wall  26  may be configured to allow the one or more sheets  6  to move obliquely upward into the conveying path  31  from the feeding portion  40 . A side guide mechanism  27  may be disposed on the lower surface  22 . The side guide mechanism  27  may be configured to center the one or more sheets  6  received on the lower surface  22  (center alignment). In the center alignment, one or more sheets  6  of any size may be positioned on the lower surface  22  while the center line of the one or more sheets  6  with respect to the right-left direction  9  may be aligned with the center line of the main tray  21  with respect to the right-left direction  9 . Sheets from L size (equivalent to 3R size) to A4 size may be loaded on the lower surface  22  of the main tray  21 . L-size sheets, postcards, 2L-size sheets, and A5 sheets may be loaded on the lower surface  22  with their long sides oriented parallel to the front-rear direction  8  such that the side guide mechanism  27  contacts and positions the long sides of the sheets. The long side of an A5 sheet may be a maximum dimension in the front-rear direction  8  loadable on the lower surface  22 . A4 sheets  6  may be loaded on the lower surface  22  with their short sides oriented parallel to the front-rear direction  8 . An A4 sheet may be a maximum size sheet loadable on the lower surface  22 . In the first illustrative embodiment, the inkjet recording apparatus  10  defines a first zone configured to receive passage of an A4 sheet (as an example of a first sheet) but not passage of an A5 sheet (as an example of a second sheet), and a second zone configured to receive passage of an A5 sheet and an A4 sheet. As depicted in  FIGS. 11A and 11B , the second zone is defined in the central portion in the right-left direction  9  while the first zone is defined in outer portions than the second zone in the right-left direction  9 . In other words, the second zone is defined between a first part and a second part of the first zone in the right-left direction  9 . 
         [0039]    The feeding portion  40  may comprise a support shaft  41 , an arm  42 , and a feed roller  43 . The support shaft  41  may be rotatably supported by a frame (not depicted). The arm  42  may extend obliquely downward from the support shaft  41 . One end of the arm  42  may be rotatably supported by the support shaft  41  and the other end of the arm  42  may rotatably support the feed roller  43 . The arm  42  may comprise a plurality of gears  44  for transmitting the rotation of the support shaft  41  to the feed roller  43 . 
         [0040]    The feed roller  43  may be configured to be rotatable by a force generated by the rotation of the support shaft  41  and transmitted through the plurality of gears  44 . The feed roller  23  may be configured to feed the one or more sheets  6 , one by one, from the main tray  21  toward the rear with respect to the front-rear direction  8  with the rotation of the feed roller  43 . The fed sheet  6  may be allowed to move into the conveying path  31  by the inclined wall  26  of the main tray  21 . 
         [0041]    As depicted in  FIG. 2 , the conveying path  31  may be defined by a plurality of guide members, including a support member  70 , and a platen  50 . The guide members other than the support member  70  are omitted from the drawings. The conveying path  31  may comprise a curved section  32 , which is indicated by a dotted and dashed line, and a straight section  33 , which is indicated by a double-dotted and dashed line. The curved section  32  may extend upward from an upper end of the inclined wall  26  of the main tray  21  and be curved toward the front in the front-rear direction  8 . The straight section  33  may extend from an end of the curved section  32  toward the front in the front-rear direction  8 . The support member  70  is described in further detail below. 
         [0042]    The platen  50  may have a plate-like shape having a thickness in the up-down direction  7 . The platen  50  may be disposed above the sheet feed cassette  20 . As depicted in  FIG. 5A , the platen  50  may comprise a plurality of first ribs  51  (as an example of a rib), a plurality of eighth ribs  56 , and a plurality of other ribs  57  that may upwardly protrude from an upper surface of the platen  50 . 
         [0043]    The first ribs  51  may be provided and configured to hold the sheet  6  to form ridge portions in the sheet  6 . As depicted in  FIG. 6 , the first ribs  51  may extend along the front-rear direction  8  from a rear end of the platen  50  to the vicinity of a front end of the platen  50 . With this configuration, the first ribs  51  may hold the ridge portions of the corrugated sheet  6  to the vicinity of the front end of the platen  50 . 
         [0044]    The first ribs  51  may be spaced apart from each other in the right-left direction  9  (as an example of a first direction) and disposed at diametrically opposed positions about the center line of the platen  50  in the right-left direction  9 . This configuration may provide a symmetric corrugation pattern in the sheet  6  of any size, which may be centered by the side guide mechanism  27 , with respect to the center line of the sheet  6 . The symmetric pattern may reduce a tendency of the corrugation pattern in the sheet  6  to be deformed and improve image-recording accuracy. A recording head  46  may be configured to eject ink droplets onto the sheet  6  based on a distance between the sheet  6  and each nozzle  47  (see  FIG. 3 ) that may be changeable due to the corrugation pattern formed in the sheet  6 . Therefore, the image-recording accuracy may be improved when the corrugation pattern of the sheet  6  is maintained. 
         [0045]    The eighth ribs  56  may be provided for adjusting the shape of respective curves (curvature radiuses) of the corrugation pattern formed in the sheet  6 . As depicted in  FIG. 5A , each of the eighth ribs  56  may be disposed between each of the first ribs  51  and each of the contact members  60  in the right-left direction  9 . The eighth ribs  56  may extend along a conveying direction  19  of the sheet  6  (see  FIG. 2 ). Each of the contact members  60  may be disposed at a middle position between two adjacent ribs of the first ribs  51  in the right-left direction  9 . 
         [0046]    The eighth ribs  56  may be shorter in height than the first ribs  51  such that portions of the sheet  6  held by the respective eighth ribs  56  do not become the tops or crests of the ridge portions in the corrugation pattern. Each of the eighth ribs  56  may hold a portion of the sheet  6  between a ridge portion and a groove portion of each curve in the corrugation pattern to adjust and/or maintain the curvature radius of each curve in the corrugation pattern of the sheet  6 . 
         [0047]    The ribs  57  may be provided and configured to hold or support the groove portions of the corrugated sheet  6 . Upper edges of the ribs  57  may be located lower than upper edges of the eighth ribs  56  (e.g., the height of ribs  57  may be smaller than the height of eighth ribs  56 ). Each of the ribs  57  may extend from a position under a downstream end of a contact portion  63  of a corresponding one of the contact members  60  with respect to the conveying direction  19  (see  FIG. 2 ) to the front end of the platen  50  in the front-rear direction  8 . 
         [0048]    Some of the ribs  57  may be disposed at a middle position under a corresponding one of the contact members  60  in the right-left direction  9 . These ribs  57  may hold bottoms of the groove portions (e.g., the troughs), respectively, of the corrugated sheet  6 . Pairs of ribs of the rest of the ribs  57  may be spaced apart from each other under a corresponding one of the contact portions  63  in the right-left direction  9 . These ribs  57  may be configured to hold the right and left portions of the bottom of each of the groove portions of the corrugated sheet  6 . The corrugated sheet  6  may be conveyed over the platen  50  while the ridge portions are held by the first ribs  51  and the groove portions are held by the ribs  57 . Therefore, the tendency of the corrugation pattern of the sheet  6  to be deformed may be reduced. 
         [0049]    The platen  50  may be pivotably supported by a rotating shaft  38 A of discharge rollers  38  (see  FIG. 2 ) at the front end of the platen  50  with respect to the front-rear direction  8 . With this configuration, the platen  50  may allow a sheet  6  having relatively higher stiffness to pass therethrough without forming a corrugated shape in the sheet  6  (see  FIG. 5C ). The platen  50  may be configured to pivot between a first position depicted in  FIG. 5A  and a second position depicted in  FIG. 5C . As depicted in  FIGS. 6 and 13 , in the first illustrative embodiment, the platen  50  may include projections  550  projecting rearward from a rear end thereof. One of the projections  550  may be disposed at a center of the platen  50  in the right-left direction  9 , and other projections  550  may be arranged symmetrically relative to the projection  550  at the center. Each of the projection  550  at the center and opposite ends in the right-left direction  9  may include a protrusion  557  formed, on a lower surface thereof, for receiving an urging spring  55  as an elastic member. The other end of the urging spring  55  may be supported by a frame  553  (depicted in  FIG. 2 ). With this configuration, the platen  50  may be urged toward the first position (upward). When the sheet  6  having relatively higher stiffness is conveyed, the platen  50  may be pivoted from the first position to the second position by the sheet  6  against urging force of the urging springs  55 . The two projections  550  at the opposite ends may be positioned outer than the second zone in the right-left direction  9  and within the first zone. Sheets  6  of smaller sizes (e.g. L-size sheet, postcard, and 2L-size sheet) may pass through the second zone. A sheet  6  of A4 size, which may be a maximum size for the first zone, may pass through the first zone. Thus, when a smaller size sheet  6  having a relatively higher stiffness  6  is conveyed, an urging force of the urging spring  555  at the center may only act on the smaller size sheet  6  through the platen  50 . This may prevent skewing of the smaller size sheet  6 . 
         [0050]    Referring again to  FIG. 2 , the recording portion  45  may comprise a carriage  48  disposed above the platen  50 , and the recording head  46  mounted on the carriage  48 . Referring to  FIG. 4 , the carriage  48  may be supported by a pair of front and rear guide rails  92 ,  93  disposed above the platen  50  and may be configured to reciprocate along the right-left direction  9 . The guide rails  92 ,  93  may be supported by the frame (not depicted) at both ends, respectively, with respect to the right-left direction  9 . The guide rail  93  may be provided with a belt (not depicted) to which the carriage  48  may be fixed. The belt may be configured to be rotated by a drive motor (not depicted) to allow the carriage  48  to reciprocate along the right-left direction  9 . 
         [0051]    As depicted in  FIG. 2 , the recording head  46  may be mounted on the carriage  48 , and disposed above the platen  50  while leaving a gap G between the recording head  46  and the platen  50 . In  FIG. 3 , the recording head  46  is shown with the plurality of nozzles  47  in a lower surface of the recording head  46  to eject ink droplets therefrom. The recording head  46  may be configured to record an image onto a sheet  6  by ejecting ink droplets from the nozzles  47  onto the sheet  6  held by the platen  50 . 
         [0052]    As depicted in  FIG. 2 , a conveyor roller pair  34  (as an example of a first conveyor) may be disposed upstream of the platen  50  with respect to the conveying direction  19  (behind the platen  50  in the front-rear direction  8 ). The conveyor roller pair  34  may be configured to nip the sheet  6  fed from the feeding portion  40  and convey the sheet  6  along the conveying direction  19 . 
         [0053]    The conveyor roller pair  34  may comprise a rotating shaft  35 A, a conveyor roller  35 , and following rollers  36 . The rotating shaft  35 A may extend along the right-left direction  9  (a direction perpendicular to the drawing sheet of  FIG. 2 ). The conveyor roller  35  may be disposed on the rotating shaft  35 A and may be configured to rotate integrally with the rotating shaft  35 A. The following rollers  36  may be disposed below the conveyor roller  35 . The rotating shaft  35 A may be supported by the frame (not depicted) at both ends of the rotating shaft  35 A with respect to the right-left direction  9  and configured to be rotated by a drive motor (not depicted). 
         [0054]    The following rollers  36  may be rotatably supported by a holding member (not depicted). The holding member may be urged upward by one or more elastic members (not depicted). The following rollers  36  may be in pressure contact with the conveyor roller  35 , which may be disposed above the following rollers  36 , by the one or more elastic members. The conveyor roller pair  34  may be configured to nip the sheet  6  by the conveyor roller  35  and the following rollers  36  and convey the sheet  6  along the conveying direction  19 . The sheet  6  being conveyed may be formed into a corrugated shape by the first ribs  51  of the platen  50  and the contact members  60 . 
         [0055]    As depicted in  FIG. 4 , the contact members  60  (as an example of a corrugate mechanism, a pressing portion, and a third pressing portion) may be attached to the guide rail  92  and spaced apart from each other in the right-left direction  9 . Each of the contact members  60  may be disposed at the middle position between ribs of the first ribs  51  adjacent in the right-left direction  9 . This configuration may form ridge portions and groove portions alternately at regular intervals in the sheet  6 . Accordingly, the tendency of the corrugation pattern in the sheet  6  to be deformed may be reduced and the image-recording accuracy may be improved. 
         [0056]    A structure of the contact members  60  is now described with reference to  FIG. 2 . In one or more examples, all of the contact members  60  may have the same configuration, and therefore, the description of one of the contact member  60  may apply to a remainder of the contact members  60 . The contact member  60  may comprise a fixing portion  61 , a curved portion  62 , and the contact portion  63 . The fixing portion  61  may be configured to be attached to the guide rail  92  (see  FIG. 4 ). The curved portion  62  may curvedly extend downward from the fixing portion  61  such that the curved portion  62  does not come into contact with the conveyor roller  35 . The contact portion  63  may extend from a lower end of the curved portion  62  such that the contact portion  63  may extend toward the gap G. 
         [0057]    The fixing portion  61  may comprise protrusions (not depicted) to be inserted from below into respective insertion openings  97  (see  FIG. 4 ) provided in the guide rail  92 . As depicted in  FIG. 4 , each of the protrusions may comprises a pawl  66  at its upper end. The pawls  66  may engage an upper surface of the guide rail  92 . The fixing portion  61  may be fixed to the guide rail  92  by sandwiching the guide rail  92  from above and below by an upper end surface of the fixing portion  61  and the pawls  66 . 
         [0058]    The contact portion  63  may have a plate-like shape that may extend obliquely downward from a tip end, e.g., a front end of the curved portion  62 . A forward part of the contact portion  63 , with respect to the conveying direction, may be located closer to the upper surface of the platen  50  than a back part of the contact portion  63 . In one example, the contact portion  63  becomes gradually closer to the upper surface of the platen  50  from a back part to a forward part of the contact portion  63 . A lower end of the contact portion  63  (e.g., a front end of the contact portion  63  in the front-rear direction  8 ) may be located in the gap G and adjacent to the nozzles  47  (see  FIG. 3 ). 
         [0059]    As depicted in  FIG. 5A , the lower end of the contact portion  63  may be located lower than the upper edges of the first ribs  51  of the platen  50  located in the first position. The sheet  6  to be conveyed over the platen  50  may be formed into a corrugated shape by the first ribs  51  and the contact portions  63 . For example, the sheet  6  may have ridge portions that may be held by the first ribs  51  and groove portions that may be depressed by the contact portions  63 . The corrugated sheet  6  may be conveyed over the platen  50  without curling, and an image may be recorded on the sheet  6  by the recording head  46 . The sheet  6  on which the image has been recorded may then reach the discharge roller pair  37  and be further conveyed by the discharge roller pair  37 . 
         [0060]    As depicted in  FIG. 2 , the discharge roller pair  37  (as an example of a second conveyor) may comprise the rotating shaft  38 A, the plurality of discharge rollers  38 , and a plurality of first spurs  39 . The rotating shaft  38 A may be disposed downstream of the platen  50  with respect to the conveying direction  19  (in front of the platen  50  with respect to the front-rear direction  8 ). The plurality of discharge rollers  38  may be disposed on the rotating shaft  38 A. The plurality of first spurs  39  may be disposed above the respective discharge rollers  38 . The discharge rollers  38  may be spaced from each other in an axial direction of the rotating shaft  38 A. In the first illustrative embodiment, eight discharge rollers  38  and eight first spurs  39  may be disposed in the right-left direction  9 . Six discharge rollers  38  and six first spurs  39  may be positioned in the first zone, while two discharge rollers  38  and two first spurs  39  may be positioned in the second zone. 
         [0061]    The rotating shaft  38 A may extend along the right-left direction  9  (the direction perpendicular to the drawing sheet of  FIG. 2 ). The rotating shaft  38 A may be rotatably supported by the frame (not depicted) at both ends. The rotating shaft  38 A may be configured to be rotated by the drive motor (not depicted). As depicted in  FIG. 7 , the rotating shaft  38 A may be located such that nip points of the discharge roller pair  37  may be located slightly higher than upper edges of fifth ribs  75  (described later). This configuration may allow the sheet  6  to move such that the tops of the ridge portions of the corrugated sheet  6  held by the fifth ribs  75  may fall on and contact the respective nip points of the discharge roller pair  37 . 
         [0062]    As depicted in  FIGS. 6 and 11A , the first spurs  39  may be rotatably disposed on elastic shafts  101 , respectively. The elastic shafts  101  may each have elasticity with respect to a diameter direction. More specifically, each of the first spurs  39  may include a pair of spurs  39 A fixed to a spacer  102  so as to be spaced from each other in the right-left direction  9 . The pair of spurs  39 A and the spacer  102  have a hole penetrating a center thereof. The elastic shaft  101 , which may be a coil spring extending in the right-left direction  9 , may be inserted into the hole so as to rotatably support the first spur  39 . Both ends of the elastic shaft  101  in the right-left direction  9  may be held by a holder  103  (see  FIG. 7 ). The elastic shaft  101  may be configured to be deformed such that a middle part of the elastic shaft  101  in the right-left direction  9  may be located higher than both ends of the elastic shaft  101  when the pair of spurs  39 A is in contact with the corresponding discharge roller  38 . In this state, the elastic shaft  101  may urge the pair of spurs  39 A downward. The first spur  39  may be in pressure contact with the corresponding discharge roller  38  by an urging force of the elastic shaft  101 . Accordingly, a lower end of each first spur  39  and an upper end of each discharge roller  38  may nip the sheet  6 . In some arrangements, all of the pairs of spurs  39 A and the elastic shafts  101  may have the same configuration. 
         [0063]    As depicted in  FIG. 6 , the discharge roller pair  37  may be disposed such that the nip points of the discharge roller pair  37  may be disposed on extensions of the first ribs  51 , respectively, along the conveying direction  19  (see  FIG. 2 ) (in front of the respective first ribs  51  in the front-rear direction  8 ). After the first ribs  51  hold/contact the tops of the ridge portions of the corrugated sheet  6 , respectively, the discharge roller pair  37  may nip the tops of the ridge portions of the corrugated sheet  6  as the tops of the ridge portions reach the nip points of the discharge roller pair  37 . In other words, the discharge rollers  38  and the first spurs  39  of the discharge roller pair  37  may be spaced, in the front-rear direction  8 , from the respective first ribs  51  configured to form the ridge portions of the corrugated sheet  6 . 
         [0064]    As depicted with a dashed line in  FIG. 2 , a distance L 1  between the nip points of the conveyor roller pair  34  and the respective nip points of the discharge roller pair  37  in the conveying direction  19  may be shorter than a length of a longer side of a sheet  6  having the shortest length, in the conveying direction  19 , useable by the image forming apparatus. Therefore, a downstream edge of a sheet  6  of any size may be nipped by the discharge roller pair  37  before an upstream edge of the sheet  6  passes the nip points of the conveyor roller pair  34  with respect to the conveying direction  19 . 
         [0065]    As depicted in  FIG. 7 , the holder  103  may be disposed above the discharge rollers  38  and may extend along the conveying direction  19  (see  FIG. 2 ). The holder  103  may be fixed to an upper plate  94  (see  FIG. 4 ). The upper plate  94  may be supported by the frame (not depicted) at its both ends with respect to the right-left direction  9 . 
         [0066]    As depicted in  FIG. 7 , the holder  103  may comprise a plurality of first fixing portions (not depicted), a plurality of second fixing portions  104 , and a plurality of third fixing portions  105 . The plurality of first fixing portions may be configured to fix both ends of the elastic shafts  101  (see  FIG. 6 ) of the first spurs  39 , respectively, with respect to the right-left direction  9 . The plurality of second fixing portions  104  may be configured to fix both ends of elastic shafts  201  of second spurs  82 , respectively, with respect to the right-left direction  9 . The plurality of third fixing portions  105  may be configured to fix both ends of elastic shafts  301  of third spurs  83 , respectively, with respect to the right-left direction  9 . In one or more examples, the first fixing portions, the second fixing portions  104 , and the third fixing portions  105  may have the same configuration, and therefore, description will be made regarding the second fixing portions  104 . Each of the second fixing portions  104  may be formed into such a groove as to sandwich a corresponding one of the elastic shafts  201  in the front-rear direction  8  and to support the elastic shaft  201  from below. The second fixing portion  104  may include a pressing portion (not depicted) for pressing the elastic shaft  201  from above. The second fixing portion  104  may include a wall portion (not depicted) for restricting the elastic shaft  201  from moving in the right-left direction  9 . Accordingly, the second spurs  82  may be held in position by the respective second fixing portions  104  of the holder  103 . 
         [0067]    The first fixing portions may be disposed above the respective discharge rollers  38  and spaced apart from each other in the right-left direction  9 . The second fixing portions  104  may be disposed on extensions of the contact portions  63 , respectively, and downstream of the first fixing portions in the conveying direction  19  (in front of the first fixing portions with respect to the front-rear direction  8 ). The second fixing portions  104  may be spaced apart from each other in the right-left direction  9 . The third fixing portions  105  may be disposed on extensions of the second fixing portions  104 , respectively, and downstream of the second fixing portions  104  in the conveying direction  19 . The third fixing portions  105  may also be spaced apart from each other in the right-left direction  9 . The third fixing portions  105  may be disposed downstream of some of the second fixing portions  104  in the conveying direction  19 , respectively. 
         [0068]    As depicted in  FIG. 7 , the holder  103  may comprise first guide surfaces  111  for guiding the groove portions of the corrugated sheet  6  to the second spurs  82 . The first guide surfaces  111  may be disposed on extensions of the contact members  60 , respectively, along the conveying direction  19  (see  FIG. 2 ) such that the first guide surfaces  111  contact respective groove portions formed in the leading edge of the corrugated sheet  6 . Each of the first guide surfaces  111  may be located between a corresponding one of the nip points of the discharge roller pair  37  and a lower end of a corresponding one of the second spurs  82  with respect to the conveying direction  19 . The first guide surfaces  111  may extend obliquely downward along the front-rear direction  8  from above the nip points of the discharge roller pair  37 , respectively. Front ends (lower ends) of the first guide surfaces  111  with respect to the front-rear direction  8  may be located at the same or substantially the same level as the nip points of the discharge roller pair  37  in the up-down direction  7 . The leading edge of the sheet  6  being conveyed may come into contact with the first guide surfaces  111  to move obliquely downward. This movement of the sheet  6  will be described in detail later. In other embodiments, for example, the holder  103  may comprise one or more inclined surfaces that may extend obliquely downward along the front-rear direction  8  from a position upstream of the nip points of the discharge roller pair  37  with respect to the conveying direction  19 . 
         [0069]    The second spurs  82  (as an example of a first pressing portion and an upstream pressing portion) and the third spurs  83  (as an example of a first pressing portion and a downstream pressing portion) may be provided for maintaining the corrugation pattern of the sheet  6  by pressing the bottoms of the groove portions of the corrugated sheet  6  from above. In other words, the second spurs  82  and the third spurs  83  may be spaced, in the front-rear direction  8 , from the respective contact portions  63  configured to form the groove portions of the corrugated sheet  6 . In some examples, and as depicted in  FIG. 6 , the second spurs  82  and the third spurs  83  may have the same configuration as the first spurs  39  and may be rotatably disposed on the elastic shafts  201 ,  301 , respectively. Therefore, the second spurs  82  and the third spurs  83  may be allowed to retract upward when a sheet  6  having higher stiffness, e.g., glossy paper, is conveyed. The elastic shafts  301  may each have the same spring constant. The elastic shafts  201  may each have the same spring constant that is greater than that of the elastic shaft  301 . 
         [0070]    Each of the second spurs  82  may include a pair of spurs  82 A, and each of the third spurs  83  may include a pair of spurs  83 A. The pair of spurs  82 A may be fixed to a spacer  202  so as to be spaced from each other in the right-left direction  9 . The pair of spurs  83 A may be fixed to a spacer  302  so as to be spaced from each other in the right-left direction  9 . 
         [0071]    The pair of spurs  82 A and the spacer  202  have a hole penetrating a center thereof. The elastic shaft  201 , which may be a coil spring extending in the right-left direction  9 , may be inserted into the hole so as to rotatably support the pair of spurs  82 A and the spacer  202 . Similarly, the pair of spurs  83 A and the spacer  302  have a hole penetrating a center thereof. The elastic shaft  301 , which may be a coil spring extending in the right-left direction  9 , may be inserted into the hole so as to rotatably support the pair of spurs  83 A and the spacer  302 . A middle part in the right-left direction  9  between the pair of spurs  82 A coupled by the spacer  202  may coincide with a bottom of a corresponding one of the groove portions of the corrugated sheet  6 . The pair of spurs  82 A and the pair of spurs  83 A may scatter or distribute a sheet pressing force of the second spur  82  and a sheet pressing force of the third spur  83 , respectively. 
         [0072]    As depicted in  FIG. 6 , the second spurs  82 , e.g., nine second spurs  82 , may be arranged in the right-left direction  9 . The second spurs  82  may be held by the second fixing portions so as be located at the same positions with respect to the right-left direction  9  as the contact portions  63 , respectively. In other words, the second spurs  82  may be disposed downstream of the contact portions  63  in the conveying direction  19 , respectively. The second spurs  82  may be configured to press from above the bottoms of the groove portions of the corrugated sheet  6  formed by the contact portions  63  to maintain the sheet  6  in the corrugated shape. As depicted in  FIG. 11 , the second spurs  82  may be positioned both in the first zone and the second zone. In the first illustrative embodiment, six second spurs  82  may be positioned in the first zone, and three second spurs  82  may be positioned in the second zone. 
         [0073]    As depicted in  FIG. 6 , the third spurs  83 , e.g., six third spurs  83  may be arranged in the right-left direction  9 . The third spurs  83  may be held by the third fixing portions  105  so as to be located at the same positions with respect to the right-left direction  9  as the second spurs  82  positioned in right and left end portions. In other words, the third spurs  83  may be positioned downstream in the conveying direction  19  of the second spurs  82  positioned in outer (non-central) portions. The third spurs  83 , along with the second spurs  82 , may be configured to press from above the bottoms of the groove portions of the corrugated sheet  6  formed by the contact portions  63  to maintain the sheet  6  in the corrugated shape. As depicted in  FIG. 11A , none of the third spurs  83  may be positioned in the second zone, and six third spurs  83  may be positioned in the first zone. 
         [0074]    The second spurs  82  and the third spurs  83  may press from above the bottoms of the groove portions of the corrugated sheet  6  formed by the contact portions  63 . Thus, the second spurs  82  and the third spurs  83  may each be disposed at the same position with reference to the right-left direction  9  as the corresponding rib  57  of the platen  50  or as a middle position between the corresponding two adjacent ribs  57 . The second spurs  82  and the third spurs  83  may have the same height in the up-down direction  7 . 
         [0075]    A distance in the right-left direction  9  between two third spurs  831  positioned near the central portion (second zone) may be longer than the short sides of small size sheets  6  (e.g., L-size sheet, postcard, and 2L-size sheet) and shorter than the long side of an A4 sheet  6 . Accordingly, the third spurs  83  may not contact the small size sheets  6 . A distance in the right-left direction  9  between two spurs  82  positioned in the central portion (second zone) may be shorter than the short sides of the small size sheets  6  (e.g., L-size sheet, postcard, and 2L-size sheet). Accordingly, the second spurs  82  may contact the sheet  6  of any size, but the third spurs  83  may not contact the sheets  6  of predetermined sizes. 
         [0076]    The second spurs  82  and the third spurs  83 , which are arranged in two rows in the first-rear direction  8  in the first zone, may press the sheet  6  in the first zone, and only the second spurs  82  may press the sheet  6  in the second zone. Accordingly, a pressing force applied to the sheet  6  by the second spurs  82  and the third spurs  83  may be smaller in the second zone than in the first zone. In other words, a pressing force (more specifically, a pressing force per unit area) applied to the sheet  6  by the second spurs  82  and/or the third spurs  83  may be smaller in the second zone than in the first zone. 
         [0077]    As depicted in  FIG. 7 , both ends of the elastic shafts  201  of the second spurs  82  in the right-left direction  9  may be fixed to the second fixing portions  104  of the holder  103 , respectively. The lower ends of the second spurs  82  may be located below the nip points of the discharge roller pair  37 , respectively, and at the same or substantially the same level as the front ends (the lower ends) of the contact portions  63 , respectively, in the front-rear direction  8 . Therefore, the second spurs  82  may be configured to press the bottoms of the groove portions of the corrugated sheet  6 , respectively, from above. 
         [0078]    As depicted by the dashed line in  FIG. 2 , the second spurs  82  may be disposed such that a distance L 2  between the lower ends of the second spurs  82  and the respective nip points of the discharge roller pair  37  in the conveying direction  19  may be shorter than a distance L 3  between the nip points of the conveyor roller pair  34  and the respective front ends of the contact portions  63  in the conveying direction  19  (the respective downstream ends of the contact portions  63  with respect to the conveying direction  19 ). With this configuration, the leading edge of the sheet  6  may reach the second spurs  82  while the upstream edge of the sheet  6 , in the conveying direction  19  (hereinafter, simply referred to as the trailing edge of the sheet  6 ), may be nipped between the first ribs  51  and the contact portions  63  from above and below. Therefore, the upstream part and the downstream part of the sheet  6  with respect to the conveying direction  19  may be maintained in the corrugated shape. 
         [0079]    As depicted in  FIG. 7 , both ends of the elastic shafts  301  of the third spurs  83  with respect to the right-left direction  9  may be fixed to the third fixing portions  105  of the holder  103 , respectively. The lower ends of the third spurs  83  may be located below the nip points of the discharge roller pair  37  and at the same or substantially the same level as the lower ends of the contact portions  63 , respectively. Therefore, the third spurs  83  may be configured to press the bottoms of the groove portions of the corrugated sheet  6 , respectively. 
         [0080]    The third spurs  83  may be disposed downstream of the second spurs  82  in the conveying direction  19  (see  FIG. 2 ) and spaced apart from the second spurs  82 , respectively. With this configuration, the second spurs  82  and the third spurs  83  may press the respective groove portions of the corrugated sheet  6  at the two points spaced apart from each other in the conveying direction  19 . Therefore, the curling of the trailing edge of the sheet  6  on the platen  50  may be reduced after the trailing edge of the sheet  6  passes the contact portions  63 . When the distance between the second spurs  82  and the third spurs  83  is too long, the trailing edge of the sheet  6  may pass the contact portions  63  before the leading edge of the sheet  6  reaches the third spurs  83  and thus the sheet  6  may be rotated about the second spurs  82 . Therefore, the third spurs  83  may be disposed at the appropriate positions apart from the second spurs  82  such that the leading edge of the sheet  6  having a shortest length in the conveying direction  19  may reach the third spurs  83  before the trailing edge of the sheet  6  passes the contact portions  63 . 
         [0081]    As depicted in  FIG. 2 , the support member  70  may be disposed below the holder  103  and configured to hold the sheet  6  to be pressed by the second spurs  82  and the third spurs  83 . The sheet  6  may be discharged onto the sheet discharge tray  29  from a discharge port  18  provided downstream of the support member  70  with respect to the conveying direction  19 . 
         [0082]    As depicted in  FIG. 7 , the support member  70  may comprise a plate-shaped base  71 , a plurality of second ribs  72 , a plurality of third ribs  73 , a plurality of fourth ribs  74 , and a plurality fifth ribs  75 . The base  71  may be disposed between the rotating shaft  38 A and the holder  103  and fixed to the frame (not depicted). The second ribs  72 , the third ribs  73 , the fourth ribs  74  and the fifth ribs  75  may protrude from an upper surface of the base  71 . As depicted in  FIG. 6 , the base  71  may have a plurality of openings  78 . The discharge rollers  38  may stick out from the upper surface of the base  71  via the openings  78 , respectively. 
         [0083]    The fifth ribs  75  may be provided for guiding the tops of the ridge portions of the corrugated sheet  6  to the nip points of the discharge roller pair  37 . Each of the fifth ribs  75  may extend from the midpoint (with respect to the right-left direction  9 ) of an upstream edge (with respect to the conveying direction  19  (see  FIG. 2 )) of a corresponding one of the openings  78  (e.g., a rear edge of the opening  78  with respect to the front-rear direction  8 ) to an upstream end of the base  71  with respect to the conveying direction  19  (the rear end of the base  71  with respect to the front-rear direction  8 ). Therefore, the fifth ribs  75  may be disposed on extensions of the first ribs  51 , respectively, with respect to the conveying direction  19 . Upper edges of the fifth ribs  75  may be located at the substantially same level as the upper edges of the first ribs  51 . Therefore, the fifth ribs  75  may hold the tops of the ridge portions of the corrugated sheet  6 , respectively. The platen  50  may have the pivotable configuration. Thus, the first ribs  51  of the platen  50  may not be able to extend to the nip points of the discharge roller pair  37 . Accordingly, the holder  103  may need to be provided with the fifth ribs  75 . 
         [0084]    As depicted in  FIG. 8A , each of the fifth ribs  75  may comprise a fifth guide surface  115  at an upstream end of each of the fifth ribs  75  with respect to the conveying direction  19  (see  FIG. 2 ). In each of the fifth ribs  75 , the fifth guide surface  115  may extend obliquely upward from an upstream end of the upper surface of the base  71  to an upper edge of the fifth rib  75  with respect to the conveying direction  19 . The fifth guide surfaces  115  may come into contact with the leading edge of the sheet  6  to allow the sheet  6  to move to the upper edges of the fifth ribs  75 . This configuration may reduce catching of the sheet  6  on the upstream ends of the fifth ribs  75  with respect to the conveying direction  19 . 
         [0085]    As depicted in  FIG. 6 , the second ribs  72  may be provided for holding the tops of the ridge portions of the corrugated sheet  6 . The second ribs  72  may be disposed on the extensions of the first ribs  51 , respectively, with respect to the conveying direction  19  (see  FIG. 2 ). Upper edges of the second ribs  72  may be located at the same or substantially the same level as the upper edges of the first ribs  51 . Therefore, the second ribs  72  may hold the tops of the ridge portions of the corrugated sheet  6 , respectively. Each of the second ribs  72  may extend along the conveying direction  19  from the midpoint (with respect to the right-left direction  9 ) of a downstream edge (with respect to the conveying direction  19 ) of a corresponding one of the openings  78  (a front edge of the opening  78  with respect to the front-rear direction  8 ). Upstream ends of the second ribs  72  may be located upstream of the lower ends of the second spurs  82 , respectively, with respect to the conveying direction  19  (front ends of the second ribs  72  with respect to the front-rear direction  8 ). Therefore, the upstream ends of the second ribs  72  with respect to the conveying direction  19  may be located upstream of the lower ends of the second spurs  82 . This configuration may allow the second ribs  72  to hold the ridge portions of the corrugated sheet  6  when the second spurs  82  press the groove portions of the corrugated sheet  6  from above. Each of the second ribs  72  may extend from the downstream edge of a corresponding one of the openings  78  to a position between the second spurs  82  and the third spurs  83  along the conveying direction  19  because the third ribs  73  may be provided on the platen  50 . 
         [0086]    As depicted in  FIG. 8A , each of the second ribs  72  may comprise a second guide surface  112  at an upstream end of each of the second ribs  72  with respect to the conveying direction  19  (see  FIG. 2 ). In each of the second ribs  72 , the second guide surface  112  may extend obliquely upward from a downstream edge of a corresponding one of the openings  78  to an upper edge of the second rib  72 . The second guide surfaces  112  may come into contact with the leading edge of the sheet  6  that has passed the nip points of the discharge roller pair  37 , and allow the sheet  6  to move to the upper edges of the second ribs  72 . This configuration may reduce catching of the sheet  6  on the upstream ends of the second ribs  72  with respect to the conveying direction  19 . 
         [0087]    The third ribs  73  may be provided and configured to hold the ridge portions of the corrugated sheet  6  by taking over from the second ribs  72 . As depicted in  FIG. 6 , the third rib  73  may be disposed on both sides of each of the second ribs  72  in the right-left direction  9  such that each pair of third ribs  73  may hold the right and left portions of the top of a corresponding ridge portion of the corrugated sheet  6 . The third ribs  73  may extend from respective positions upstream of the downstream ends of the second ribs  72  to respective positions downstream of the second spurs  82  in the conveying direction  19  (see  FIG. 2 ). With this configuration, the third ribs  73  may take over holding the sheet  6  from the second ribs  72 . Upper edges of the third ribs  73  may be located lower than the upper edges of the second ribs  72 . While the sheet  6  is conveyed, the third ribs  73  may hold the right and left portions of the tops of the ridge portions of the sheet  6 , respectively, after the second ribs  72  held the tops of the ridge portions of the sheet  6 , respectively. For example, the holding of the right and left portions of the ridge portion tops may transfer from the second ribs  72  to the third ribs  73 . 
         [0088]    As depicted in  FIG. 8A , each of the third ribs  73  may comprise a third guide surface  113  at an upstream end thereof in the conveying direction  19  (see  FIG. 2 ). In each of the third ribs  73 , the third guide surface  113  may extend obliquely upward from the upper surface of the base  71  to an upper edge of the third rib  73 . The third guide surfaces  113  may come into contact with the leading edge of the sheet  6  to allow the sheet  6  to move to the upper edges of the third ribs  73 . This configuration may reduce catching of the sheet  6  on the upstream ends of the third ribs  73  with respect to the conveying direction  19 . 
         [0089]    The fourth ribs  74  may be provided and configured to hold the right and left portions of the bottoms of the groove portions of the corrugated sheet  6  being pressed by the second spurs  82  and the third spurs  83 . As depicted in  FIG. 6 , the fourth ribs  74  may extend from respective positions upstream of the second spurs  82  to respective positions downstream of the third spurs  83  with respect to the conveying direction  19  (see  FIG. 2 ). The fourth rib  74  may be disposed between each third rib  73  and each second spur  82  that may be adjacent to each other with respect to the right-left direction  9 . With this configuration, the fourth ribs  74  may hold the right and left portions of the bottoms of the groove portions of the corrugated sheet  6 . Upper edges of the fourth ribs  74  may be located lower than the upper edges of the second ribs  72  and the third ribs  73  to hold the groove portions of the corrugated sheet  6 . 
         [0090]    As depicted in  FIG. 8B , each of the fourth ribs  74  may comprise a fourth guide surface  114  at an upstream end of each of the fourth ribs  74  in the conveying direction  19  (see  FIG. 2 ). In each of the fourth ribs  74 , the fourth guide surface  114  may extend obliquely upward from the upper surface of the base  71  to an upper edge of the fourth rib  74 . The fourth guide surfaces  114  may come into contact with the leading edge of the sheet  6  to allow the sheet  6  to move to the upper edges of the fourth ribs  74 . This configuration may reduce catching of the sheet  6  on the upstream ends of the fourth ribs  74  with respect to the conveying direction  19 . While the sheet  6  is conveyed, the fourth ribs  74  may hold the right and left portions of the groove portions of the corrugated sheet  6 , respectively. 
         [0091]    An operation of the inkjet recording apparatus  10  is now described with reference to  FIG. 2 . First, the feed roller  43  may feed, one by one, one or more sheets  6  placed on the main tray  21  into the conveying path  31 . Then, the conveyor roller pair  34  may convey the one or more fed sheets  6  successively. While the sheet  6  passes the contact portions  63  of the contact members  60 , the first ribs  51  may hold the sheet  6  and the contact portions  63  of the contact members  60  may press an upper surface of the sheet  6  to form the sheet  6  into a corrugated shape. More specifically, the sheet  6  may be formed into the corrugated shape, in which the sheet  6  may have ridge portions that may be held by the first ribs  51  and groove portions that may be depressed by the contact portions  63 . 
         [0092]    The conveyor roller pair  34  may further convey the corrugated sheet  6  over the platen  50  without the sheet  6  curling. When a leading edge of the sheet  6  reaches under the nozzles  47  (see  FIG. 3 ) of the recording head  46 , the conveyor roller  35  may be allowed to stop rotating (e.g., the conveyor roller  35  may be stopped from rotating). After that, while the carriage  48  reciprocates along the right-left direction  9 , the recording head  47  may eject ink droplets from the nozzles  47  onto the sheet  6  to perform a single line of printing. After performing the single line of printing, the conveyor roller  35  may be allowed to start rotating to convey the sheet  6  by a single line to start next single line of printing in a new line. The inkjet recording apparatus  10  may record an image on the sheet  6  by alternately performing a single line of printing and a line feed. 
         [0093]    The conveyor roller pair  34  may convey the sheet  6  while the first ribs  61  of the platen  50  may hold the tops of the ridge portions of the corrugated sheet  6  and then the fifth ribs  75  of the support member  70  may hold the tops of the ridge portions of the corrugated sheet  6 . After that, the tops of the ridge portions of the corrugated sheet  6  held by the fifth ribs  75  may reach the nip points of the discharge roller pair  37 . The discharge roller pair  37  may nip the tops of the ridge portions of the corrugated sheet  6  and convey the sheet  6  further along the conveying direction  19 . 
         [0094]    The second ribs  72  may hold the tops of the ridge portions of the sheet  6  that has passed the nip points of the discharge roller pair  37 . At this time, the first guide surfaces  111  and the fourth guide surfaces  114  may guide the groove portions of the sheet  6  to the lower ends of the second spurs  82  and the second spurs  82  may press the sheet  6  from above. Additionally, the trailing edge of the sheet  6  has not passed the contact portions  63  yet. Therefore, the forward part and the rearward part of the sheet  6  may be maintained in the corrugated shape. Thus, the sheet  6  may be reliably maintained in the corrugated shape. 
         [0095]    After the leading edge of the sheet  6  passes the second spurs  82 , the leading edge of the sheet  6  may reach the third ribs  73  and the fourth ribs  74 . The discharge roller pair  37  may further convey the sheet  6  along the conveying direction  19  while the third ribs  73  hold the right and left portions of the ridge portions of the corrugated sheet  6 , respectively, and the fourth ribs  74  hold the right and left portions of the groove portions of the corrugated sheet  6 , respectively. The sheet  6  conveyed as described above may then reach the third spurs  83 . The third spurs  83  may press the bottoms of the groove portions of the corrugated sheet  6 , respectively. With this configuration, each second spur  82  and the corresponding third spur  3  may press the sheet  6  at two points spaced apart from each other in the conveying direction  19 . Therefore, the sheet  6  may be conveyed without rotating about the second spurs  82  after passing the contact portions  63 . None of the third spurs  83  may be disposed in the second zone. Each second spur  82  and the corresponding third spur  83  may press the sheet  6  at two points in the first zone. 
         [0096]    When a sheet  6  having relatively higher stiffness is conveyed, the platen  50  may be pivotally moved from the first position depicted in  FIG. 5A  to the second position depicted in  FIG. 5C  against the urging force of the urging springs  555 . Therefore, the sheet  6  may be conveyed without being formed into a corrugated shape as depicted in  FIG. 5C . After performing image recording by the recording portion  45 , the discharge roller pair  37  may nip and convey the sheet  6  further. While the sheet  6  passes under the second spurs  82  and the third spurs  83 , the elastic shafts  201  of the second spurs  82  and the elastic shafts  301  of the third spurs  83  may be deformed by the sheet  6  such that the second spurs  82  and the third spurs  83  are upwardly moved. The discharge roller pair  37  may convey the sheet  6  to discharge the sheet  6  onto the sheet discharge tray  29  while maintaining the sheet  6  in the flat shape (e.g., without forming a corrugated shape/pattern) by which the sheet  6  may move the second spurs  82  and the third spurs  83  upward. 
         [0097]    A case where a sheet  6  of smaller size is conveyed is now described. The length in the right-left direction  9  of the sheet  6  of smaller size may be less than a length between two third spurs  831  near the central portion (second zone). The sheets  6  of smaller sizes (e.g. postcard, and L-size sheet) are likely to have a higher stiffness than A4 plain paper. An A5 sheet may be placed with its long side oriented parallel to the front-rear direction  8 . In this case, its paper fibers are directed parallel to the front-rear direction  8  and the A5 sheet, when conveyed, is unlikely to curl. When the sheet  6 , which is a postcard, is conveyed, the platen  50  may pivot into the second position and the sheet  6  may not be formed into a corrugated shape. When the sheet  6 , which is an A5 sheet, is conveyed, the sheet  6  may be formed into a corrugated shape. The discharge roller pair  37  may nip and convey further the sheet  6  having an image recorded thereon. 
         [0098]    The discharge rollers  38  of the discharge roller pair  37  may be spaced from each other in the right-left direction  9 , and so may be the first spurs  3  of the discharge roller pair  37 . The sheet  6  of smaller size may be nipped by the discharge roller pair  37  at less nip points than a sheet of larger size. As depicted in  FIGS. 11A and 11B , in the first illustrative embodiment, two discharge rollers  38  and two first spurs  39  of the discharge roller pair  37  may be disposed in the second zone. Thus, a conveying force applied by the discharge roller pair  37  to the sheet  6  of smaller size may be smaller than that applied to a sheet of larger size. 
         [0099]    The sheet  6  of smaller size nipped and conveyed by the discharge roller pair  37  may contact and move up the second spurs  82  only. The sheet  6  may be conveyed further in a flat shape without contacting the third spurs  83  and discharged onto the discharge tray  29 . 
         [0100]    In a zone where the second spurs  82  and the third spurs  83  are positioned, only the second spurs  82  may apply their loads on the sheet  6  of smaller size. On the other hand, in that zone, the second spurs  82  and the third spurs  83  may apply their loads on a sheet  6  of larger size. Thus, downstream of the discharge roller pair  37  in the conveying direction  19 , the sheet  6  of smaller size may receive less load than the sheet of larger size. Although the conveying force for the sheet  6  of smaller size may decrease, a pressing force, i.e., a conveyance resistance, to the sheet  6  of smaller size may be set less than to the sheet  6  of larger size. Consequently, the sheet conveying accuracy may be prevented from degrading. 
         [0101]    In the first illustrative embodiment, the discharge roller pair  37  may nip the tops of the ridge portions of the corrugated sheet  6  and the second spurs  82  may press the bottoms of the groove portions of the corrugated sheet  6  from above. This configuration may maintain the sheet  6  in the corrugated shape. The second spurs  82  may be disposed downstream of the nip points of the discharge roller pair  37  in the conveying direction  19 . Therefore, the second spurs  82  may press the bottoms of the groove portions of the corrugated sheet  6  after the discharge roller pair  37  nipped the tops of the ridge portions of the corrugated sheet  6 . With this configuration, the depths of the groove portions may become stable (e.g., consistency in shape, depth, size, etc. may be maintained) when the second spurs  82  press the sheet  6 . The second spurs  82  may be disposed downstream of the nip points of the discharge roller pair  37  in the conveying direction  19 . Therefore, the discharge roller pair  37  may be disposed closer to the platen  50  as compared with a case where the second spurs  82  may be disposed upstream of the nip points of the discharge roller pair  37  with respect to the conveying direction  19 . With this configuration, the sheet  6  that may tend to become flat due to the ink droplets adhered to the sheet  6  may be nipped by the discharge roller pair  37  before the sheet  6  becomes flat. Therefore, the change of the depths of the groove portions may be reduced/minimized and the depths of the groove portions may be stably maintained when the second spurs  82  press the sheet  6 . Thus, a conveyance resistance to the sheet  6  may be reduced when the second spurs  82  press the sheet  6 . As a result, in the first illustrative embodiment, the sheet  6  may be maintained in the corrugated shape and an occurrence of a paper jam or the degradation of the image-recording accuracy may be reduced. 
         [0102]    In the first illustrative embodiment, the first guide surfaces  111  provided on the holder  103  may guide the bottoms of the groove portions of the corrugated sheet  6  to the lower ends of the second spurs  82  although the depth of one or more of the groove portions of the corrugated sheet  6  may become slightly shallower. As a result, the conveyance resistance to the sheet  6  may be further reduced. 
         [0103]    In the first illustrative embodiment, the fourth ribs  74  may comprise the fourth guide surfaces  114 , respectively, that may allow the leading edge of the sheet  6 , which is moving obliquely downward by the first guide surfaces  111 , to move to the lower ends of the second spurs  82 . Therefore, an occurrence of a paper jam at the second spurs  82  may be reduced. 
         [0104]    In the first illustrative embodiment, the second ribs  72  may hold the ridge portions of the corrugated sheet  6  when the second spurs  82  press the bottoms of the groove portions of the corrugated sheet  6 . Therefore, the sheet  6  may be reliably maintained in the corrugated shape. 
         [0105]    Additionally, the third spurs  83  may be disposed downstream of the second spurs  82  in the conveying direction  19  and the second spurs  82  and the third spurs  83  may press the sheet  6  at the two points spaced apart from each other in the conveying direction  19 . This configuration may reduce the curling of the sheet  6  on the platen  50  after the trailing edge of the sheet  6  passes the contact portions  63 . 
         [0106]    In the first illustrative embodiment, the second spurs  82  may be rotatably disposed in pairs on respective elastic shafts  201  while each pair of spurs  82 A may be spaced from each other in the right-left direction  9  by the spacer  202 . The third spurs  83  may also be rotatably disposed in pairs on respective elastic shafts  301  while each pair of third spurs  83 A may be spaced from each other in the right-left direction  9  by the spacer  302 . Therefore, the force that may act on the sheet  6  may be scattered when the second spurs  82  and the third spurs  83  press the sheet  6 . Accordingly, the conveyance resistance to the sheet  6  may be further reduced. 
         [0107]    In the first illustrative embodiment, the third spurs  83  may be less in number than the second spurs  82  and no third spurs  83  may be positioned in the second zone through which the sheet  6  of smaller size passes. Thus, the load applied, as the conveyance resistance, to the sheet  6  of smaller size may relatively decrease, and the sheet conveying accuracy may be prevented from degrading. The third spurs  83  disposed in the first zone, which is defined at outer portions than the second zone in the right-left direction  9 , may maintain a larger size sheet  6  having a relatively low stiffness in the corrugated shape and prevent the sheet  6  from curling. 
         [0108]    In another embodiment, third spurs  83  may be disposed in the second zone through which the sheet  6  of smaller size passes as long as the pressing force or load (more specifically the pressing force or load per unit area) applied to the sheet  6  by the third spurs  83  positioned in the second zone is less than that applied by the second spurs  82  positioned in the second zone. For example, the spring constant of the elastic shaft  301  for supporting each third spur  83  disposed in the second zone may be less than that of the elastic shaft  201  for supporting each second spur  82 . In this case, the spring constant of the elastic shaft  301  of each third spur  83  disposed in the first zone is preferably equal to that of the elastic shaft  201  of each second spur  82 . 
         [0109]    In another embodiment, as depicted in  FIG. 11B , only second spurs  82  may be disposed downstream of the discharge roller pair  37  in the conveying direction  19 . A plurality of second spurs  82  may be arranged in the right-left direction  9 . The second spurs  821  positioned in the central portion (second zone) in the right-left direction  9  may be configured to apply less load (more specifically, less load per unit area) to the sheet  6  than the second spurs  822  positioned in the outer portions (first zone) in the right-left direction  9 . 
         [0110]    More specifically, the second spurs  821  may be positioned in the second zone through which the sheet  6  of smaller size (L-size sheet, postcard, and 2L-size sheet) may pass. The second spurs  822  may be positioned in the first zone which is defined at outer portions than the second zone in the right-left direction  9 . The spring constant of an elastic shaft  821 A of each second spur  821  may be set less than that of an elastic shaft  822 A of each second spur  822 . 
         [0111]    In this case, when the discharge roller pair  37  nips and further conveys the sheet  6  of smaller size, the sheet  6  may contact the second spurs  821 . The second spurs  821  may apply a relatively small load, i.e., a relatively small conveyance resistance, to the sheet  6 . Thus, the sheet conveying accuracy may be prevented from degrading. Because the spring constant of the elastic shaft  822 A of each second spur  822  may be greater than that of the elastic shaft  821 A of each second spur  821 , the second spurs  822  may maintain a larger size sheet  6  having a relatively low stiffness in the corrugated shape and prevent the sheet  6  from curling. 
         [0112]    The above-described configuration may be modified as long as the pressing force (more specifically, the pressing force per unit area) applied by the second spurs  821  to the sheet  6  is less than that applied by the second spurs  822 . For example, the contact position at which each second spur  821  contacts the sheet  6  may be set higher than the contact position at which each second spur  822  contacts the sheet  6 . 
         [0113]    A first variation of the first illustrative embodiment is now described. As depicted in  FIG. 9A , for example, a roller pair  120  (as an example of a third conveyor) may be further disposed downstream of the third spurs  83  with respect to the conveying direction  19  (see  FIG. 2 ). As depicted in  FIG. 12 , the roller pair  120  may comprise rollers  121  having the same configuration as the discharge rollers  38 , and fourth spurs  122  having the same configuration as the first spurs  39 . The roller pair  120  may be disposed at the same position as the discharge roller pair  37  with respect to the up-down direction  7  and the right-left direction  9 . Each of fourth spurs  122  may include a pair of spurs  122 A fixed to a spacer  402  so as to be spaced from each other in the right-left direction  9 . The pair of spurs  122 A and the spacer  402  have a hole penetrating a center thereof. An elastic shaft  401 , which may be a coil spring extending in the right-left direction  9 , may be inserted into the hole so as to rotatably support the pair of spurs  122 A and the spacer  402 . The support member  70  may have openings  79 . The rollers  121  may stick out (e.g., extend) from the upper surface of the support member  70  via the openings  79 , respectively. Both end portions of each of the elastic shafts  401  of the fourth spurs  122  in the right-left direction  9  may be fixed to the holder  103 . 
         [0114]    Each of fifth spurs  84  (as an example of a second pressing portion) may be disposed between corresponding adjacent two fourth spurs  122  or next to a corresponding fourth spur  122 . The fifth spurs  84  may be arranged in a row with the roller pair  120 . The fifth spurs  84  may be disposed at the same positions with respect to the right-left direction  9  as the third spurs  83 . In other words, the fifth spurs  84  may be disposed in the first zone at positions downstream of the third spurs  83  in the conveying direction  19 , respectively. Each of fifth spurs  84  may include a pair of spurs  84 A fixed to a spacer  842  so as to be spaced from each other in the right-left direction  9 . The pair of spurs  84 A and the spacer  842  has a hole penetrating a center thereof. An elastic shaft  841 , which may be a coil spring extending in the right-left direction  9 , may be inserted into the hole so as to rotatably support the pair of spurs  84 A and the spacer  842 . The other configuration of the inkjet recording apparatus  10  according to the first variation may be the same as the inkjet recording apparatus  10  according to the first illustrative embodiment described above. 
         [0115]    The roller pair  120  may be configured to convey the sheet  6  to discharge the sheet  6  onto the sheet discharge tray  29  by nipping the tops of the ridge portions of the corrugated sheet  6 . As described above, one or more aspects described herein may be adopted to the inkjet recording apparatus  10  that may further comprise the roller pair  120  disposed downstream of the third spurs  83  with respect to the conveying direction  19 . The fifth spurs  84 , in cooperation with the second spurs  82  and the third spurs  83 , may press the bottoms of the groove portions of the corrugated sheet  6  from above to maintain the corrugation pattern of the sheet  6 . Neither fifth spurs  84  nor third spurs  83  may be disposed in the second zone. Thus, the pressing force (load) applied, as the conveyance resistance, to the sheet  6  of smaller size may relatively decrease, and the sheet conveying accuracy may be prevented from degrading. 
         [0116]    A second variation of the first illustrative embodiment is now described. As depicted in  FIG. 9B , for example, the inkjet recording apparatus  10  may have a double-sided printing function. The inkjet recording apparatus  10  may comprise the roller pair  120 , a sheet reversing path  123 , and a support member  124 . 
         [0117]    The support member  124  may be disposed downstream of the support member  70  in the conveying direction  19  (see  FIG. 2 ). The support member  124  may have openings  125 . The roller pair  120  may comprise the plurality of rollers  121 . The rollers  121  of the roller pair  120  may stick out from an upper surface of the support member  124  via the openings  125 , respectively. Sixth ribs  126  having the same configuration as the second ribs  72  may protrude from the upper surface of the support member  124 . The sixth ribs  126  may be disposed at the same positions, in the up-down direction  7  and the right-left direction  9 , as the second ribs  72 . The sixth ribs  126  may also be configured to hold the tops of the ridge portions of the sheet  6 , respectively. 
         [0118]    The sheet reversing path  123  may extend from a position between the support member  70  and the support member  124  with respect to the conveying direction  19  to the curved section  32  by passing under the platen  50 . The sheet reversing path  123  may be defined by one or more guide members (not depicted). The other configuration of the inkjet recording apparatus  10  according to the second variation may be the same as the inkjet recording apparatus  10  according to the first illustrative embodiment described above. 
         [0119]    When the inkjet recording apparatus  10  performs the single-sided printing, the roller pair  120  may convey the sheet  6  on which an image has been recorded, along the conveying direction  19 , to discharge the sheet  6  onto the sheet discharge tray  29 . When the inkjet recording apparatus  10  performs double-sided printing, the roller pair  120  may rotate in the reverse direction after the trailing edge of the sheet  6  in which an image may be recorded on its one side passes the support member  70 . Thus, the trailing edge of the sheet  6  with respect to the conveying direction  19  may enter the sheet reversing path  123 . The inkjet recording apparatus  10  may convey the sheet  6  onto the platen  50  via the sheet reversing path  123  and the curved section  32  while the sheet  6  is turned upside down. Then, the inkjet recording apparatus  10  may record an image on the other side of the sheet  6  on the platen  50 , and discharge the sheet  6  onto the sheet discharge tray  29  by the roller pair  120 . As described above, the one or more aspects may be adopted to the inkjet recording apparatus  10  having the double-sided printing function. 
         [0120]    A third variation of the first illustrative embodiment is now described. In the above-described first illustrative embodiment, as depicted in the enlarged view of  FIG. 6 , the upstream ends of the second ribs  72  with respect to the conveying direction  19  (see  FIG. 2 ) may be disposed upstream of the lower ends of the second spurs  82  with respect to the conveying direction  19 . In some arrangements, only the second ribs  72  might be needed to hold the ridge portions of the corrugated sheet  6  when the second spurs  82  press the groove portions of the corrugated sheet  6  from above. Therefore, in the third variation, for example, as depicted in  FIG. 8C , the second ribs  72  may be disposed apart from the edges of the respective openings  78 . More specifically, the second ribs  72  may be disposed such that the upstream ends of the second ribs  72  may extend along the conveying direction  19  from the same respective positions as the lower ends of the second spurs  82  with respect to the conveying direction  19 . Accordingly, the second ribs  72  disposed as described above may hold the ridge portions of the corrugated sheet  6  when the second spurs  82  press the groove portions of the corrugated sheet  6 , and the sheet  6  may be maintained in the corrugated shape. 
         [0121]    A fourth variation of the first illustrative embodiment is now described. In the above-described first illustrative embodiment, as depicted in  FIG. 6 , the second rib portions may comprise the second ribs  72  and the third ribs  73 . Nevertheless, in the fourth variation, for example, as depicted in  FIG. 10A , the second ribs  72  may extend to respective positions downstream of the third spurs  83  with respect to the conveying direction  19 , instead of providing the third ribs  73 . The second ribs  72  may hold the ridge portions of the sheet  6 , respectively, when the second spurs  82  and the third spurs  83  press the groove portions of the sheet  6 , respectively, from above. Therefore, the sheet  6  may be reliably maintained in the corrugated shape. All or one or more of the second ribs  72  may be configured like the second ribs  72  according to the fourth variation. In addition to the third ribs  73  (see  FIG. 6 ), the second ribs  72  may extend to the respective positions downstream of the third spurs  83  with respect to the conveying direction  19 . 
         [0122]    A fifth variation of the first illustrative embodiment is now described. In the fourth variation, as depicted in  FIG. 10A , the second ribs  72  may extend to the respective positions downstream of the third spurs  83  with respect to the conveying direction  19 , instead of providing the third ribs  73 . Nevertheless, in the fifth variation, for example, as depicted in  FIG. 10B , seventh ribs  77  may be disposed instead of providing the third ribs  73 . The seventh ribs  77  may be disposed as the same respective positions, in the right-left direction  9 , as the second ribs  72 . The seventh ribs  72  may extend to respective positions downstream of the second ribs  72  in the conveying direction  19 . Upstream ends of the seventh ribs  77  may be disposed upstream of the third spurs  83  in the conveying direction  19 . Downstream ends of the seventh ribs  77  may be disposed downstream of the third spurs  83  with respect to the conveying direction  19 . Upper edges of the seventh ribs  77  may be located at the same level as the upper edges of the second ribs  72 . Each of the seventh ribs  77  may comprise a seventh guide surface  117  at the upstream end of the seventh rib  77  with respect to the conveying direction  19 . In each of the seventh ribs  77 , the seventh guide surface  117  may extend obliquely upward from the upper surface of the support member  70  to the upper edge of the seventh rib  77 . The seventh guide surfaces  117  may come into contact with the ridge portions of the corrugated sheet  6  to allow the ridge portions of the corrugated sheet  6  to move to the upper edges of the seventh ribs  77 . This configuration may reduce catching of the sheet  6  on the upstream ends of the seventh ribs  77 . 
         [0123]    The seventh ribs  77  may hold the ridge portions of the sheet  6  when the third spurs  83  press the groove portions of the sheet  6 . With this configuration, the sheet  6  may be further reliably maintained in the corrugated shape. One or more of the second ribs  72  according to the first illustrative embodiment may be configured like the second ribs  72  according to the fifth variation. In other embodiments, for example, one or more of the second ribs  72  may be configured like the second ribs  72  according to the fifth variation and one or more of the rest of the second ribs  72  may be configured like the second ribs  72  according to the fourth variation. 
         [0124]    In the first illustrative embodiment, the pressing force (more specifically, the pressing force per unit area) applied to the sheet  6 , which is conveyed downstream of the recording head  46  in the conveying direction  19 , may set smaller in the second zone than in the first zoned zone. Similarly, the pressing force (more specifically, the pressing force per unit area) applied to the sheet  6 , which is conveyed from an upstream point toward the recording head  46  in the conveying direction  19 , may be set smaller in the second zone than in the first zone. In a sixth variation of the first illustrative embodiment, a platen  50  may be rotatably supported by the rotating shaft  38 A of the discharge rollers  38  (see  FIG. 2 ), as in the first illustrative embodiment, so as to pivot against the urging force of the urging springs  555  when a sheet  6  having a relatively higher stiffness, such as a cardboard sheet, is conveyed. In addition, the platen  50  may be configured such that the central portion thereof deforms or sags downward further than the outer portions thereof in the right-left direction  9 . 
         [0125]    As depicted in  FIG. 14A , protrusions  559  may be formed in the outer portions, in the right-left direction  9 , of the platen  50  so as to protrude downward from a lower surface of the platen  50 . The protrusions  559  may be positioned outer than the first zone and near right and left ends of the platen  50 . The platen  50  may be urged by the urging springs  555  in a direction away from the frame  553  of the printer unit  11 . One of the urging springs  555  may be disposed at the center of the second zone through which sheets  6  of smaller sizes (e.g., L-size sheet, postcard, and 2L-size sheet) pass. Two of the urging springs  555  may be disposed in the first zone which is made up of the outer portions than the second zone in the right-left direction  9  and through which a sheet of maximum size (e.g., A4 sheet) passes. The urging forces of the three urging springs  555  may be set equal to each other. 
         [0126]    As depicted in  FIG. 14C , when a sheet  6  having a relatively low stiffness (e.g. A4 plain paper) is conveyed, the sheet  6  may be formed into a corrugated shape by the contact members  60 , and the platen  50  may move down by the sheet thickness against the urging force of the urging springs  555 . The entire sheet holding portion of the platen  50  in the right-left direction  9  may move down uniformly. At this time, the protrusions  559  may contact the frame  553 . The sheet  6  may extend over the first zone and the second zone. The pressing force of the contact members  60  may be applied through the sheet  6  to the platen  50 . Once the protrusions  559  contact the frame  553 , the platen  50  may not be allowed to move down further. Thus, the sheet  6  may be conveyed in a space between the platen  50  and the contact members  60  which may be elastically deformed. The discharge rollers  38  and the first spurs  39  of the discharge roller pair  37 , which are arranged in the right-left direction  9 , may convey the sheet  6  against the pressing force of the contact members  60 . 
         [0127]    As depicted in  FIG. 14B , when a smaller size sheet having a relatively higher stiffness (e.g. glossy paper) is conveyed through the second zone, the platen  50  may move down against the urging force of the urging springs  555 . When the platen  50  moves down by the pressing force of the contact members  60  till the protrusions  559  contact the frame  553 , the platen  50  may deform such that the central portion thereof sags downward further than the outer portions thereof in the right-left direction  9 . The pressing force applied from above by the contact members  60  to the smaller size sheet  6  may be less when the platen  50  is deformable than when the platen  50  is not deformable. Thus, even when the smaller size sheet  6  is conveyed with a relatively small conveying force of the discharge roller pair  37 , the load applied, as the conveyance resistance, to the sheet  6  may relatively decrease. Consequently, the sheet conveying accuracy may be prevented from degrading. 
         [0128]    By providing the protrusions  50  to the platen  50 , the pressing force (more specifically, the pressing force per unit area) applied to a sheet  6  conveyed, on the upstream side of the recording head  46 , through the second zone may be set smaller than the pressing force (more specifically, the pressing force per unit area) applied to a sheet  6  conveyed, on the upstream side of the recording head  46 , through the first zone. At least two of the protrusions  559  may be positioned within the first zone in the right-left direction  9 , at such positions that allow the central portion of the platen  50  to sag enough for sheet conveyance. 
         [0129]    Other variations of the first illustrative embodiment are now described. In the above-described first illustrative embodiment, the third spurs  83  may be disposed in pairs on respective elastic shafts  101  to press the respective groove portions of the corrugated sheet  6 . Nevertheless, in other variations, for example, one each of the third spurs  82  may be disposed on each of the elastic shafts  101 . The third spurs  83  may be configured to press the respective groove portions that are being pressed by the corresponding second spurs  82 . Accordingly, it may be unnecessary for the third spurs  83  to press the sheet  6  with the same force as that applied by the second spurs  82 . In some cases, it may be unnecessary to scatter or distribute the sheet pressing force of the third spurs  83 . In this case, one each of the third spurs  83  may be disposed on each of the elastic shafts  101 . 
         [0130]    According to one or more aspects, when the force of the second spurs  82  that press the sheet  6  is smaller, one each of the second spurs  82  may also be disposed on each of the elastic shafts  101 . 
         [0131]    In the above-described first illustrative embodiment, the third spurs  83  may be provided in the inkjet recording apparatus  10 . Nevertheless, in other embodiments or variations, for example, the inkjet recording apparatus  10  might not comprise the third spurs  83 . Instead, the second spurs  82  may maintain the sheet  6  in the corrugated shape appropriately by pressing the groove portions of the corrugated sheet  6  without providing/using the third spurs  83 . 
         [0132]    In the above-described first illustrative embodiment, the contact portions  60  and the first ribs  51  may be provided in the inkjet recording apparatus  10  to form the corrugated shape in the sheet  6 . Nevertheless, in other embodiments or variations, for example, other mechanisms may be provided upstream of the nozzles  47  in the conveying direction  19  to form the corrugated shape in the sheet  6 . 
         [0133]    In the above-described first illustrative embodiment, the support member  70  may be provided in the inkjet recording apparatus  10 . Nevertheless, in other embodiments or variations, for example, the inkjet recording apparatus might not comprise the support member  70 . In this case, the second spurs  82  may be disposed downstream of the nip points of the discharge roller pair  37  in the conveying direction  19  and close to the nip points of the discharge roller pair  37 . With this configuration, the discharge roller pair  37  and the second spurs  82  may maintain the sheet  6  in the corrugated shape appropriately even though the second ribs  72  of the support member  70  do not hold the ridge portions of the corrugated sheet  6 . 
         [0134]    In the above-described first illustrative embodiment, the holder  103  may comprise the first guide surfaces  111 . However, in other embodiments or variations, for example, the holder  103  might not comprise the first guide surfaces  111 . In this case, the discharge roller pair  37  may be disposed as close to the nozzles  47  of the recording head  46 , in the conveying direction  19 , as possible. With this configuration, the discharge roller pair  37  may nip the sheet  6  therebetween immediately after the sheet  6  becomes flat due to the ink droplets adhered to the sheet  6 . Therefore, it may become unnecessary to guide the groove portions of the corrugated sheet  6  to the second spurs  82 . 
         [0135]    In the above-described first illustrative embodiment, the first to seventh guide surfaces  111 - 117  may be provided. Nevertheless, in other embodiments or variations, for example, the first to seventh guide surfaces  111 - 117  might not be provided. The sheet  6  may be maintained in the corrugated shape appropriately and the risk of a paper jam may be reduced without the provision of the first to seventh guide surfaces  111 - 117 . 
         [0136]    In the above-described first illustrative embodiment, the first to seventh guide surfaces  111 - 117  may be the inclined surfaces (flat surfaces). Nevertheless, in other embodiments or variations, for example, the first to seventh guide surfaces  111 - 117  may be spherical surfaces or curved surfaces. 
         [0137]    The features as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the inventions as defined in the following claims.