Patent Publication Number: US-7896459-B2

Title: Image recording device and method for correcting deformation of printed sheet

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application Publication No. JP-2008-051318, which was filed on Feb. 29, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device and a method for ejecting ink droplets to record an image on a recording medium. 
     2. Description of Related Art 
     A known image recording device, e.g., an inkjet printer, records an image on a sheet of recording medium while the sheet is conveyed intermittently. In a known inkjet printer, a sheet is conveyed onto a platen while being pinched between a pair of opposed rollers. After the sheet reaches the platen, the pair of rollers are driven intermittently. Each time the sheet is conveyed by a predetermined sheet feed distance and stopped, a recording head moves in a direction orthogonal to a sheet conveying direction and ejects ink droplets onto the sheet. As sheet feed and ink ejection are repeated, a desired image is formed on the sheet from a leading edge to a trailing edge thereof. 
     In the known inkjet printer, sheet cockling may occur. Sheet cockling is a phenomenon where ink permeates fibers of the sheet and expands the fibers such that the sheet is curled and undulated. If sheet cockling occurs, a distance between the sheet and the recording head may fluctuate during image recording, and the accuracy in image recording may deteriorate. The deformed sheet may contact the recording head or cause a leading edge of the sheet to deviate from the conveying path and may cause a sheet jam. 
     A known inkjet printer, e.g., the printer described in Japanese Laid-Open Patent No. 2004-237506, comprises a recording head, a platen opposed to the recording head, a pair of rollers disposed upstream of the platen, and a pair of rollers disposed downstream of the platen. When an amount of ink which causes deformation of a sheet is ejected from the recording head onto the sheet while the sheet is pinched by the upstream rollers, the sheet is conveyed till a leading edge of the sheet is pinched by the downstream rollers. Then, the sheet is held by the upstream rollers and the downstream rollers for a predetermined amount of time to reduce deformation of a leading edge side of the sheet. 
     In the known inkjet printer, the leading edge of the sheet is pinched by the downstream rollers. However, when the sheet, e.g., a sheet having fibers running widthwise, is prone to suffer from cockling, the leading edge may be deformed greatly before the leading edge reaches the downstream rollers, and the deformed leading edge may collide with the downstream rollers and cause a sheet jam. When the distance between the recording head and the sheet is relatively small, the deformed sheet may contact the recording head and cause deterioration of the recorded image or damage to the sheet. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the invention is to provide an image recording device and method which overcome these and other shortcomings of the related art by restricting and/or correcting deformation of a sheet. Technical advantages of the invention are that sheet jams are reduced by restricting and/or correcting deformation of a sheet, and image quality is improved by maintaining a constant gap between a recording head and a sheet being conveyed. 
     According to an embodiment of the invention, an image recording device comprises a recording unit configured to eject ink onto a sheet of recording medium, a platen disposed opposite to the recording unit and configured to support the sheet, a pair of upstream rollers disposed upstream of the recording unit and the platen in a sheet conveying direction and configured to convey the sheet in the sheet conveying direction when rotating in a forward direction, and a controller. When the sheet is supported on the platen and pinched between the pair of upstream rollers, the controller is configured to control the recording unit to eject the ink onto a particular portion of the sheet. The controller is configured to selectively rotate the pair of upstream rollers in a reverse direction opposite the forward direction to convey the sheet in a direction opposite the sheet conveying direction, and is configured to subsequently stop rotating the pair of upstream rollers in the reverse direction, such that the pair of upstream rollers pinch the sheet for a particular amount of time. The upstream rollers are configured to hold the sheet in a predetermined shape that restricts deformation of the particular portion of the sheet during the particular amount of time. 
     According to another embodiment of the invention, a method for conveying a sheet of recording medium in an image recording device, the method comprises rotating a pair of upstream rollers in a forward direction to convey the sheet in a sheet conveying direction, pinching the sheet between the pair of upstream rollers, performing image recording by ejecting ink onto a portion of the sheet, rotating the pair of upstream rollers in reverse to convey the sheet in a direction opposite the sheet conveying direction, stopping the reverse rotation of the pair of upstream rollers such that the pair of upstream rollers pinch the sheet between the pair of upstream rollers for a particular amount of time, and holding the sheet in a predetermined shape to restrict deformation of the portion of the sheet with the pair of upstream rollers. 
     Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention, the needs satisfied thereby, and the features and technical advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
         FIG. 1  is a perspective view of an image recording device, e.g., a multi-function device, according to an embodiment of the invention. 
         FIG. 2  is a vertical cross-sectional view illustrating an internal structure of the image recording device according to an embodiment of the invention. 
         FIG. 3  is a partial cross-sectional view illustrating structures of a pinch roller and its surroundings according to an embodiment of the invention. 
         FIG. 4A  is an enlarged cross-sectional view of a pinch roller holder located at a retracted position according to an embodiment of the invention. 
         FIG. 4B  is an enlarged cross-sectional view of the pinch roller holder located at an advanced position according to an embodiment of the invention. 
         FIG. 5  is a schematic view illustrating structures of a recording unit and its surroundings according to an embodiment of the invention. 
         FIG. 6  is a block diagram illustrating a structure of a controller of the image recording device according to an embodiment of the invention. 
         FIG. 7  is a flowchart illustrating an image recording method employed by a printer of the image recording device according to an embodiment of the invention. 
         FIG. 8  is a flowchart illustrating an image recording method employed by a printer of the image recording device according to the embodiment of the invention. 
         FIG. 9  is a flowchart illustrating an image recording method employed by a printer of the image recording device according to another embodiment of the invention. 
         FIG. 10  a flowchart illustrating an image recording method employed by a printer of the image recording device according to the another embodiment of the invention. 
         FIG. 11  is a schematic illustrating a printer in which a leading edge of a sheet is at a recording start position on a platen according to an embodiment of the invention. 
         FIG. 12  is a schematic illustrating a printer in which an amount of ink exceeding a threshold value is ejected onto the sheet. 
         FIG. 13  is a schematic illustrating a printer in which a sheet is held in a predetermined shape according to an embodiment of the invention. 
         FIG. 14  is a schematic illustrating a printer in which a sheet is held in a predetermined shape according to another embodiment of the invention. 
         FIG. 15  is a schematic illustrating a printer in which a sheet is held in a predetermined shape according to still another embodiment of the invention. 
         FIG. 16  is a schematic illustrating a printer in which a sheet is held in a predetermined shape according to yet another embodiment of the invention. 
         FIG. 17  is a table containing a set of stopping times for various temperature ranges according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the invention and their features and technical advantages may be understood by referring to  FIGS. 1-17 , like numerals being used for like corresponding parts in the various drawings. 
     Referring to  FIG. 1 , an image recording device, e.g., a multi-function device  10 , may comprise a printer  11  at a lower portion thereof, and a scanner  12  at an upper portion thereof. The multi-function device  10  may perform one or more functions, e.g., printing, copying, scanning, facsimile functions, or any combination thereof. 
     The printer  11  may be connected to an external device, e.g., a computer, and may be configured to record an image, e.g., text or the like, on a recording medium based on image data transmitted from the external device. The scanner  12  may be a flatbed scanner. 
     The multi-function device  10  may have a substantially box shape, and may have a width and a depth which are greater than a height of the multi-function device  10 . The printer  11  may have an opening  13  at a front of the multi-function device  10 . A sheet tray  20  and an output tray  21  may be disposed inside the opening  13 . A sheet on the sheet tray  20  is conveyed to the printer  1 , and the sheet on which an image has been recorded may be discharged onto the output tray  21 . 
     An operation panel  14  for the printer  11  and the scanner  12  may be disposed at an upper, front portion of the multi-function device  10 . The operation panel  14  may comprise operation buttons and a liquid crystal display. The multi-function device  10  may operate based on instructions received via the operation panel  10 , or instructions received from a computer connected to the multi-function device  10  via a printer driver or a scanner driver. 
     Referring to  FIG. 2 , the sheet tray  20  may be disposed at a bottom portion of the multi-function device  10 . The sheet tray  20  may be an upwardly opened container configured to store sheets of paper, e.g., A4 size paper, B5 size paper, postcard size paper, or the like therein. The output tray  21  may be positioned above the sheet tray  20 . A conveying path  23  may extend from the sheet tray  20  to the output tray  21 . A sheet of recording medium on the sheet tray  20  may be guided upward, turned around along the conveying path  23  to reach a recording unit  24 . The recording unit  24  then records an image onto the sheet, and the sheet may be discharged onto the output tray  21 . 
     A feed roller  25  may be disposed at an inner portion of the sheet tray  20 . As shown in  FIG. 6 , the feed roller  25  may be driven by a line feed motor (“LF motor”)  77  and may feed a sheet from the sheet tray  20  to the conveying path  23 . The feed roller  25  may be rotatably supported at an end of an arm  26 . The arm  26  may be configured to pivot about a base end thereof and may selectively move toward and away from the sheet tray  20 . The arm  26  may be biased by the weight of the feed roller  25  or by a spring, or by both, and may pivot downward such that the feed roller  25  contacts an uppermost one of the sheets on the sheet tray  20 . 
     The conveying path  23  may extend upward from an inner portion of the sheet tray  20 , bend toward the front of the multi-function device  10 , pass the recording unit  24 , and reach the output tray  21 . A bent portion of the conveying path  23  at the inner portion of the sheet tray  20  may be defined by an outer guide member  18  and an inner guide member  19 . 
     Referring to  FIGS. 2 and 3 , a convey roller  60  and a pinch roller  61  may be disposed upstream of the recording unit  24  in the sheet conveying direction  104 . The pinch roller  61  may be disposed on a lower side of the convey roller  60 . The convey roller  60  may be driven by the line feed motor  77 , as shown in  FIG. 6 . 
     Referring to  FIG. 5 , a rotary encoder  65  may be disposed at the convey roller  60 . The rotary encoder  65  may comprise an encoder disk  66 , which is coaxial with the convey roller  60  and rotates with the convey roller  60 , and an optical sensor  67 . Light-passing portions and light-blocking portions may be arranged alternatively at regular intervals in a circumferential direction of the encoder disk  66 . The optical sensor  67  may comprise a light emitter and a light receiver which are opposite to each other with the encoder disk  66  disposed therebetween. When the encoder disk  66  rotates with the convey roller  60 , light emitted by the light emitter may be blocked by the light blocking portions at regular intervals. The light receiver may generate pulse signals based on the intensity of received light. The amount of rotation of the convey roller  60  is detected based on the pulse signals. 
     A sheet  90  may be conveyed by the convey roller  60  in a sheet conveying direction  104  while being pinched by the convey roller  60  and the pinch roller  61 . The pinch roller  61  may be rotated by the sheet  90 , which is being conveyed. 
     A discharge roller  62  and a spur  63  may be disposed downstream of the recording unit  24  in the sheet conveying direction  104 . The spur  63  may be on an upper side of the discharge roller  62 . The spur  63  may be urged by an elastic member, e.g., a spring, to contact the discharge roller  62 . The discharge roller  62  may be driven by the line feed motor  77 , as shown in  FIG. 6 . The discharge roller  62  and the convey roller  60  may rotate synchronously. The sheet  90  having an image recoded thereon may be discharged onto the output tray  21  while being pinched by the discharge roller  62  and the spur  63 . 
     The convey roller  60  and the discharge roller  62  may be driven intermittently during image recording. The convey roller  60  and the discharge roller  62  may rotate by a rotation amount corresponding to a sheet feed amount F, and may stop after the sheet  90  has been conveyed by the sheet feed amount F. The sheet feed amount F may be a predetermined amount based on the recording resolution of an image. The sheet feed amount F may be smaller for image recording in fine interlaced mode, e.g., high resolution, than for image recording in normal mode, e.g., medium resolution. When the sheet is being fed before image recording or when the sheet is being discharged after image recording, the convey roller  60  and the discharged roller  62  may rotate continuously. 
     Referring to  FIG. 5 , a registration sensor  44  may be disposed upstream of the convey roller  60  in the sheet conveying path  23 . The registration sensor  44  may detect the sheet  90  passing in the sheet conveying path  23 . A detection portion of the sensor  44 , which is projecting into the sheet conveying path  23 , may retract upon contact with the sheet  90  passing in the sheet conveying path  23 . The sensor  44  optically may detect whether the detection portion is projecting or retracted and may output an on/off signal based on the detection result. Whether a leading edge or a trailing edge of the sheet  90  reaches the position of the sensor  44  may be determined based on an on/off signal from the sensor  44 . 
     Referring to  FIG. 5 , the recording unit  24  may comprise a carriage  38 , recording head  39  and a platen  42 . The carriage  38  and the platen  42  may be disposed between the convey roller  60  and the discharge roller  62 , and may be opposite to each other vertically with the sheet conveying path  23  positioned therebetween. The carriage  38  may comprise the recording head  39 . The carriage may be driven by a carriage motor, e.g., CR motor  79 , as shown in  FIG. 6 , to travel back and forward horizontally in a direction orthogonal to the sheet conveying direction  104 . Cyan, magenta, yellow, and black inks may be supplied from ink cartridges (not shown) to the recording head  34  through ink tubes (not shown). The ink cartridges may be disposed separately from the recording head  39 . 
     The platen  42  may be disposed on a lower side of the sheet conveying path  23  and may extend along a sheet passing zone which is within the traveling range of the carriage  38 . The platen  42  may be wide enough to accommodate a width of a sheet of maximum size in the printer  11 . A distance between the recording head  39  and the sheet  90  supported on an upper surface  45  of the platen  42  may be maintained at a predetermined distance. 
     A guide surface  43  may be formed at an upstream end of the platen  42  in the sheet conveying direction  104 . The guide surface  43  may incline downward from the upper surface  45  of the platen  42  to an upstream end of the guide surface  43 . The guide surface  43  may comprise a rib projecting from the platen  42  toward the upstream side. 
     The guide surface  43  may guide a leading edge of the sheet  90  toward the upper surface  45  of the platen  42 . The carriage  38  may move in a direction orthogonal to the sheet conveying direction  104  when the convey roller  60  and the discharge roller  62  are stopped. When the carriage  38  is moving, droplets of ink of various colors selectively may be ejected from nozzles of the recording head  39  and reach the sheet  90  which is held stationary on the platen  42 . 
     Referring to  FIG. 3 , the pinch roller  61  may be rotatably supported by a pinch roller holder  51 . The pinch roller holder  51  may support the pinch roller  61  such that a shaft of the pinch roller  61  may selectively move toward and away from the convey roller  60 . The pinch roller holder  51  may comprise a spring (not shown) that urges the shaft of the pinch roller  61  toward the convey roller  60  such that the pinch roller  61  is pressed against the convey roller  60 . When the sheet  90  travels between the convey roller  60  and the pinch roller  61 , the shaft of the pinch roller  61  may move away from the convey roller  60 . With the pinch roller  61  urged by the spring toward the convey roller  60 , a rotating force of the convey roller  60  may be applied to the sheet  90 . 
     The pinch roller holder  51  may be supported by a holder base  52  so as to move along the sheet conveying direction  104 . The holder base  52  may comprise an upper surface  53 , which is a circumferential surface substantially about the shaft of the convey roller  60 . The pinch roller holder  51  may be supported on the upper surface  53  via two cylindrical rollers  54  such that the pinch roller holder  61  is movable along the upper surface  53 . 
     As shown in  FIG. 4A , when there is no sheet between the convey roller  60  and the pinch roller  61 , the pinch roller holder  51  may be at a retracted position which is furthest from the platen  42 . As shown in  FIG. 4B , as the sheet  90  may travel between the convey roller  60  and the pinch roller  61  in the sheet conveying direction, the pinch roller  61  may move from the retracted position to an advanced position which is closest to the platen  42 . After a trailing edge of the sheet  90  passes the convey roller  60  and the pinch roller  61 , the pinch roller holder  51  may move from the advanced position to the retracted position. 
     The sheet  90  pinched by the convey roller  60  and the pinch roller  61  may slant downwardly as sheet  90  is conveyed onto the platen  42 , that is sheet  90  may be conveyed from a higher position than the position of the platen, such that the sheet  90  is pressed against the platen  42 . The convey roller  60  and the pinch roller  61  may be positioned such that a nip portion therebetween is higher than the upper surface  45  of the platen  42 . Referring to  FIG. 6 , the controller  70  may control the printer  11 , the scanner  12  or both. The controller  70  may comprise a CPU (“central processing unit”)  72 , a ROM (“read only memory”)  72 , and a RAM (“random access memory”)  73 . The controller  70  may be connected to one or more sensors, scanner  12 , operation panel  14 , and others, via a bus  75  and an ASIC (“application specific integrated circuit”)  76 , such that data may be transmitted between components. 
     The ROM  72  may store programs for controlling operations of the multi-function device  10 . Using one or more of the programs stored in the ROM  72 , the controller  70  may control the printer  11  such that the sheet  90  having an image thereon may selectively be conveyed in reverse and stopped for a particular amount of time, e.g., a predetermined time. The ROM  72  may store a threshold value, e.g., an amount of ink ejected from the recording head  39 , which is a criteria for determining whether to convey the sheet  90  in reverse. The ROM  72  may store a lookup table for setting the stopping time T for which the sheet  90  is stopped. The stopping time T may be set stepwise depending on a predetermined condition, e.g., a temperature in the printer  11 . As shown in  FIG. 17 , the stopping time T may be set variably for temperature ranges A-E. 
     The RAM  73  may be a memory area or a work area in which various data used by the CPU  71  to execute the programs stored in the ROM  72  is temporarily recorded. The ASIC  76  may generate a phase signal for energizing the line feed motor  77  in response to a command from the CPU  71 . The ASIC  76  may apply the phase signal to a drive circuit  78  of the line feed motor  77 . The controller  70  may control the rotation of the line feed motor  77  by a drive signal applied to the line feed motor  77  via the drive circuit  78 . 
     The drive circuit  78  may be used to drive the line feed motor  77  connected to the feed roller  25 , the convey roller  60 , and the discharge roller  62 . The drive circuit  78  may generate an electrical signal for rotating the line feed motor  77  based on an output signal from the ASIC  76 . The rotation of the line feed motor  77  may be transmitted to the feed roller  25 , the convey roller  60 , and the discharge roller  62  via a drive mechanism comprising a gear and a drive shaft. 
     The ASIC  76  also may generate a phase signal for energizing the carriage motor  79  in response to a command from the CPU  71 , and may apply the phase signal to a drive circuit  80  of the line feed motor  79 . The controller  70  may control rotation of the carriage motor  79  by a drive signal applied to the carriage motor  79  via the drive circuit  80 . The drive circuit  80  may drive the carriage motor  79  coupled to the carriage  38 . The drive circuit  80  may generate an electrical signal for rotating the carriage motor  79  based on an output signal from the ASIC  76 . The rotation of the carriage motor  79  may be transmitted to the carriage  38  via a belt driving mechanism to move the carriage  38 . 
     The drive circuit  81  may drive the recording head  39  to eject ink of various colors onto the sheet  90  at predetermined timings. The ASIC  76  may generate an output signal for driving the recording head  39  based on a command from the CPU  71 . The controller  70  may calculate, via the drive circuit  81 , the amount of ink droplets ejected from the nozzles of the recording head  39 . 
     The registration sensor  44  may be connected to the ASIC  76 . Detection signals of the registration sensor  44  may be stored in the RAM  63  via the ASIC  76  and the bus  75 . The CPU  71  may analyze the detection signals based on a program stored in the ROM  72 , and may determine the positions of a leading edge  91 , or a trailing edge  92 , or both, of the sheet  90 . The CPU  71  may determine the positions of the sheet  90  based on the timings at which the registration sensor  44  detects the leading edge  91 , or the trailing edge  92 , or both and the sheet feed amount of the convey roller  60 . 
     The operation panel  14  may be connected to the ASIC  76 . Instructions for operating the printer  11  and various settings for printing, e.g., sheet type, sheet size, recording resolution, margins of sheet, printing with/without margin, may be stored as setting information in the RAM  73  via the ASIC  76  and the bus  75 . An interface (“I/F”)  82  may be connected to the ASIC  76 . The controller  70  may transmit data to and receive data from an external device, e.g., a computer, in which a printer driver is installed, via the interface  82 . The various settings for printing may be entered either from the operation panel  14  or the printer driver. A temperature sensor  83  may be connected to the ASIC  76 . The temperature sensor  83  may be disposed in the printer  11  and may measure the temperature in the printer  11 . The controller  70  may determine the temperature in the printer  11  based on an output signal from the temperature sensor  83 . Referring to  FIG. 7 , a user may enter various settings for printing, e.g., the sheet type, sheet size, recording resolution, margins of sheet, at the operation panel  14  or the external device before entering an instruction for staring printing. The setting information may be stored in the RAM  73  or in a RAM of the external device. The sheet type may be set by selecting the applicable items displayed on the operation panel  14  according to the sheets  90  staked on the sheet tray  20 . For example, A3, A4, or B5 may be set as the sheet size, and 600 dpi (“dots per inch”), 1200 dpi, or 2400 dpi may be set as the printing resolution. The margins for the leading edge, trailing edge, and side edges of the sheet  90  may be set in units of millimeters. 
     When the user enters an instruction to start printing at the operation panel  14  or the external device, the controller  70  may receive print data. When the multi-function device  10  performs a copy function, the print data may be generated based on image data scanned by the scanner  12 . When the multi-function device  10  performs printing image data prepared by application software in the external device, print data may be transmitted to the multi-function device  10  via the printer driver of the external device. 
     Upon receiving print data, the controller  70  may initialize the ink amount C stored in the RAM  73  to zero, as shown in step S 1  in  FIG. 7 . In step S 2 , the controller  70  may set the stopping time T for correcting deformation of the sheet  90  according to a predetermined condition, e.g., the temperature in the printer  11 . In an embodiment of the invention, the controller  70  may calculate the temperature in the printer  11  based on a detection signal of the temperature sensor  83 , determine which of the temperature ranges A-E the calculated temperature belongs to, and set the stopping time T corresponding to the applicable temperature range. 
     In step S 3 , sheet feeding may start. The line feed motor  77  may rotate the feed roller  25 , and an uppermost one of the sheets on the sheet tray  20  may be fed into the sheet conveying path  23 . The sheet  90  may be conveyed along the sheet conveying path  90  in the conveying direction  104 , and the leading edge  91  of the sheet  90  may reach the registration sensor  44 . When the registration sensor  44  detects the leading edge  91  of the sheet  90 , the signal outputted from the registration sensor  44  may change, e.g., from off to on. When a particular amount of time, e.g., a predetermined time, has elapsed after the change of the signal, the leading edge  91  may reach the nip portion between the convey roller  60  and the pinch roller  61 . The controller  70  may determine whether the leading edge  91  has reached the nip portion based on the signal of the registration sensor  44  and the elapsed time. 
     When leading edge  91  reaches the nip portion, the convey roller  60  may not rotate. Thus, the leading edge  91  may push against an outer surface of the convey roller  60 . As such, the leading edge  91  may be aligned against the outer surface of the convey roller  60 . Subsequently, when the controller  70  rotates the convey roller  60 , the leading edge  91  may be pinched between the convey roller  60  and the pinch roller  61 , and the pinch roller holder  51  may move toward the advanced position. 
     After convey roller  60  starts rotating, the controller  70  may calculate the rotation amount of the convey roller  60  based on the pulse signals from the rotary encoder  6  to determine the position of the leading edge  91 . The controller  70  may rotate the convey roller  60  to convey the sheet  90  by a predetermined amount, and may stop rotating the convey roller when the sheet  90  reaches a print starting position. As shown in  FIG. 11 , the print starting position may be a position in which the leading edge  91  of the sheet  90  is positioned below a first nozzle  40  of the recording head  39 . 
     As shown in  FIG. 11 , when the sheet  90  is conveyed by the convey roller  60  and the pinch roller  61 , the sheet  90  may be pressed against the upper surface  45  of the platen  42 , and the pinch roller holder  51  may be positioned at the advanced position and the pinch roller  61  may be positioned closest to the platen  42 . When the pinch roller holder  51  is at the retracted position, the pinch roller  61  may be positioned upstream of the lowest surface point of the convey roller  60 . Thus, as the pinch roller  61  moves along the outer surface of the convey roller  60  toward the platen  42 , the pinch roller  61  may move downward. As such, the sheet  90  conveyed by the convey roller  60  and the pinch roller  61  in a direction  105  may form a first angle  111  with respect to the upper surface  45  of the platen  42 . 
     When the sheet  90  is at the printing start position, the controller may drive the carriage motor  79  to move the carriage  38  in a direction orthogonal to the sheet conveying direction  104  and may cause the recording head  39  to eject ink droplets onto the sheet  90  based on the print data. In step S 4 , an image may begin to be recorded from the printing start position of the sheet  90 , as shown in  FIG. 7 . When the carriage  38  moves in a direction orthogonal to the sheet conveying direction  104 , a recording head  39  may move and pass across the sheet  90  and may eject ink droplets onto the sheet  90 . 
     In step S 5 , each time the recording head  39  passes across the sheet  90 , the controller  70  may add an amount of ink A ejected from the recording head  39  during each pass to the ink amount C stored in the RAM  73 . 
     In step S 6 , the controller  70  may determine whether the leading edge  91  of the sheet  90  has reached the nip portion between the discharge roller  62  and the spur  63  based on the on/off signals from the registration sensor  44  and pulse signals from the rotary encoder  65 . If the controller  70  determines that the leading edge  91  has not reached the nip portion, the controller  70  may determine whether the ink amount C stored in the RAM  73  has exceeded the threshold value in step S 7 . The threshold value may correspond to an ink amount which causes the sheet  90  to deform beyond a permissible degree. 
     If the controller  70  determines that the ink amount C is not greater than the threshold value in step S 7 , the controller  70  may rotate the convey roller  60  in step S 8  to feed the sheet  90  for a distance of the predetermined sheet feed amount F for image recording for the next pass. 
     After another pass of the recording head  39  in step S 4 , the controller  70  may add another amount of ink A ejected during the another pass to the ink amount C stored in the RAM  73  in step S 5 . Subsequently, the controller  70  may determine whether the leading edge  91  of the sheet  90  has reached the nip portion between the discharge roller  62  and the spur  63  in step S 6 . Steps S 4  through S 8  may be repeated until the leading edge  91  reaches the nip portion between discharge roller  62  and spur  63 . 
     After the controller  70  determines that the leading edge  91  has reached the nip portion, non-reversing printing may begin in step S 9 , non-reversing printing is a printing process without a determination by the controller whether the ink amount C exceeds the threshold value. 
     Non-reversing printing may continue until the printing process for one page is finished. After printing for one page is finished in step S 10 , the sheet  90  may be discharged onto the output tray  21  in step S 11 . If the print data includes data for another page in step S 12 , the controller may reset the ink amount C to zero in step S 1 , set the stopping time T based on the temperature in the printer  11  in step S 2 , and cause the printer  11  to perform printing for another page. If the print data does not include data for another page in step S 12 , the controller  70  may stop the printer from printing. 
     Deformation may occur in the sheet  90  due to absorption of ink. For example, as shown in  FIG. 12 , a portion  93  of the sheet  90  which receives ink may bow and protrude toward the recording head  39 . The degree of such deformation may generally depend on the amount of ink C received by the portion  93  of the sheet  90 . 
     If the ink amount C exceeds the threshold value in step S 7  after the recording head  39  makes a pass, the controller  70  may rotate the convey roller  60  in reverse to convey the sheet  90  in reverse, e.g., against the sheet conveying direction  104 , by a predetermined distance in step S 21 . When the sheet  90  is conveyed in reverse, the pinch roller holder  51  may move from the advanced position to the retracted position. The sheet  90  may be conveyed in reverse within a distance such that the portion  93  of the sheet  90  does not reach the nip portion between the convey roller  60  and the pinch roller  61 . As shown in  FIG. 13 , the sheet  90  may be conveyed in reverse until the portion  93  is in the vicinity of the guide surface  43  of the platen  42 . 
     When the portion  93  reaches a vicinity of the guide surface  43 , the controller  70  may stop rotating the convey roller  60 . The sheet  90  being conveyed in reverse in a direction  106  while being pinched by the convey roller  60  and the pinch roller  61  may form a second angle  112  with respect to the upper surface  45  of the platen  42 . As the pinch roller holder  51  moves from the advanced position toward the retracted position, the pinch roller  61  may move upward along the surface of the convey roller  60 , and the nip portion between the convey roller  60  and the pinch roller  61  may move upward. Thus, the inclination of the direction  106  with respect to the upper surface  45 , e.g., the second angle  112 , may become greater than the first angle  111 . 
     After being conveyed in reverse, the sheet  90  may be bent into a predetermined shape in which the portion  93  bows and protrudes toward the platen  42 . The portion  93 , which was deformed by sheet cockling and was protruding upward may now bow and protrude downward. A correcting downward force  120  may be applied to the portion  93 , and the deformation of the portion  93  may be restricted and/or corrected. 
     When the controller  70  stops rotating the convey roller  60 , the controller  70  may start a timer in step S 22 . When the controller  70  determines that the stopping time counted by the timer exceeds the stopping time T in step S 23 , the controller  70  may stop the timer in step S 24  and may reset the ink amount C stored in the RAM  73  to zero in step S 25 . 
     Subsequently, the controller  70  may start rotating the convey roller  60  in a forward direction to convey the sheet  90  in the sheet conveying direction  104  in step S 26 . As such, the sheet  90  may be conveyed forward by a distance of the sheet feed amount F plus a distance which the sheet  90  was conveyed in reverse. Thus, image recording may be performed on the sheet  90  by the recording head  39  during the next pass. When the sheet  90  is conveyed in the sheet conveying direction  104 , the pinch roller holder  51  may move from the retracted position to the advanced position. 
     When the sheet  90  reaches an image recording position for the next pass, the controller  70  may stop rotating the convey roller  60  and execute image recording for the next pass in step S 4 . When printing for the next pass by the recording head  39  is finished, the controller  70  may add an ink amount A ejected from the recording head  39  during the pass to the ink amount C stored in the RAM  73  in step S 5 . Because the ink amount C has been reset to zero in step S 25 , the ink amount A is stored as the ink amount C in the RAM  73 . As shown in  FIG. 7 , step S 8  and step S 4  are repeated until the controller  70  determines that the leading edge  91  of the sheet  90  has reached the nip portion between the discharge roller  62  and the spur  63  or unless the ink amount C exceeds the threshold value. If the ink amount C exceeds the threshold value before the leading edge  91  reaches the nip portion between the discharge roller  62  and the spur  63 , the sheet  90  may be conveyed in reverse in steps S 21  through S 26  to invert a deformed portion  93 . 
     According to an embodiment of the invention, the sheet  90  having an image recorded thereon is conveyed in reverse such that the deformed portion  93  which protrudes toward the recording head  39  may be bent to protrude toward the platen  42 . This may restrict and correct the deformation of the sheet  90 . Accordingly, sheet jams due to deformation of the sheet  90  may be reduced, and the deformed portion  93  may be prevented from contacting the recording head  39  and from being stained by the recording head  39 . Image recording quality may be improved because a constant distance between the sheet  90  and the recording head  39  may be maintained. 
     The controller  70  may set the stopping time T, for which the sheet  90  is stopped, based on predetermined conditions, e.g., the temperature in the printer  11 . Accordingly, the deformed portion  93  of the sheet  90  may be corrected efficiently, and printing may be performed quickly. 
     The sheet  90  may be conveyed by the convey roller  60  and the pinch roller  61  onto the platen  42  in the conveying direction  105 , which forms the first angle  111  with respect to the upper surface  45  of the platen  42 . The sheet  90  may be held by the convey roller  60  and the pinch roller  61  in the reverse conveying direction  106 , which forms the second angle with respect to the upper surface  45 . The first angle  111  may be an angle which allows the sheet  90  to contact the upper surface  45 , and the second angle  112  may be an angle which allows the deformed sheet  90  to be corrected. The deformation of the sheet  90  may be corrected effectively by setting the second angle  112  greater than the first angle  111 . 
     In an embodiment, the first angle  111  and the second angle  112  may be defined by the pinch roller  61  which moves with the pinch roller holder  51 . In another embodiment, the first angle  111  and the second angle  112  may be defined by the pinch roller  61  whose shaft is moved by a motor, or may be defined by the convey roller  81  and the pinch roller  61 , which both may be movable. 
     In an embodiment, the controller  70  may calculate the ink amount C and convey the sheet  90  in reverse when the controller  70  determines that a predetermined condition relating to the ink amount C is satisfied, e.g., when the controller  70  determines that the ink amount C exceeds the threshold value. In another embodiment, the controller  70  may measure a printing time taken by the recording head  39  and convey the sheet  90  in reverse when the controller  70  determines that the printing time exceeds a threshold value. This is because as the printing time increases, the ink amount ejected from the recording head  39  also may increase. 
     In another embodiment, the controller  70  may count the number of passes made by the recording head  39  for ejecting ink onto the sheet  90  and convey the sheet  90  in reverse when the controller  70  determines that the number of passes exceeds a threshold value. This is because as the number of passes increases, the ink amount ejected from the recording head  39  also may increase. 
     In another embodiment, the stopping time T may be set based on other conditions which influence the degree of deformation of the sheet  90 , e.g., a humidity, an ink amount ejected from the recording head  39 , a number of passes made by the recording head  39 , a time elapsed from the start of printing, and a type of sheet. 
     In an embodiment, correction of the portion  93  of the sheet  90  may be performed based on the type of the sheet  90 . For example, a sheet having fibers running widthwise may be more likely to be deformed than a sheet having fibers running lengthwise. Correction may be performed for the former and may not be performed for the latter. In another embodiment, the stopping time T may vary based on the type of sheet used. Further, the threshold value, e.g., the ink amount C, which may be used as a criteria to determine whether to convey the sheet  90  in reverse, may vary based on the type of sheet used. 
     As shown in  FIG. 7 , a printing process with a determination by the controller  70  whether the ink amount C exceeds the threshold value may be stopped when the leading edge  91  of the sheet  90  has reached the nip portion between the discharge roller  62  and the spur  63  because a sheet jam is unlikely to occur once the leading edge  91  reaches the nip portion. In another embodiment, a contact member, e.g., a spur, may be disposed downstream of the recording unit  24  and the platen  42  and upstream of the discharge roller  62  and the spur  63  in the sheet conveying direction  104 . The contact member may be configured to contact the sheet  90  conveyed in the sheet conveying direction  104  and to restrict the sheet  90  from deviating from the conveying path  23 . In this case, a printing process with such determination by the controller  70  may be stopped when the leading edge  91  has reached the contact member because a sheet jam is unlikely to occur once the leading edge  91  reaches the contact member. 
     In another embodiment, the controller  70  may determine whether the ink amount C exceeds the threshold value while resetting the ink amount C to zero each time the print head  39  makes a predetermined number of passes, and the controller  70  may make such determination from the start of printing until the trailing edge  92  of the sheet  90  is released from the nip portion between the covey roller  60  and the pinch roller  61 . 
     As shown in  FIGS. 9 and 10 , when the user enters an instruction to start printing, the controller  70  may set the ink amount C to zero, and may set the number of passes N made by print head  39  to zero in step S 1 ′. After updating the ink amount C by adding the amount of ink A ejected during the first pass in step S 5 , the controller  70  may determine whether the trailing edge  92  of the sheet  90  is released from the nip portion between the convey roller  60  and the pinch roller  61  in step S 6 ′. If the controller  70  determines that the trailing edge  92  of the sheet  90  is not released from the nip portion between the convey roller  60  and the pinch roller  61  in step S 6 ′, the controller  70  may increment the number of passes N by 1 in step S 61 , and may determine whether the ink amount C exceeds the threshold value in step S 62 . 
     If the controller  70  determines that that the ink amount C does not exceed the threshold value in step S 62 , the controller may determine whether the number of passes N is equal to a predetermined value a in step S 63 . For example, when the ink amount C is reset to zero each time the recording head  39  makes three passes, the controller may determine whether the number of passes N is equal to 3 (N=3) in step S 63 . If the controller determines that the number of passes N is not equal to 3 in step S 63 , the controller  70  may rotate the convey roller  60  to feed the sheet  90  by a distance of the predetermined sheet feed amount F for image recording in the next pass in step S 65 . If the controller determines that the number of passes N is equal to 3, the controller may reset the ink amount C and the number of passes N to zero in step S 64  and then feed the sheet  90  by the predetermined sheet feed amount F for image recording for the next pass in step S 65 . 
     If the controller  70  determines that the ink amount C exceeds the threshold value in step S 62 , the controller  70  may convey the sheet  90  in reverse by a predetermined distance and stops the sheet  90  by the stopping time T in steps S 21  through S 24 . The controller  70  then may reset the amount of ink C and the number of passes N to zero, and may feed the sheet  90  by a distance of the predetermined sheet feed amount F plus the distance the sheet  90  was reversely conveyed for image recording for the next pass. Thus, deformation of the sheet may be restricted or corrected over a longer range. 
       FIG. 14  illustrates a structure for holding the sheet  90  in the predetermined shape according to another embodiment of the invention. A nip portion between a convey roller  160  and a pinch roller  161  and a guide surface  15  of an inner guide member  119  may be flush with the upper surface  45  of the platen  42 . The pinch roller  161  may be fixed at a predetermined position. 
     The controller  70  may rotate the convey roller  160  in reverse to convey the sheet  90  in reverse and stop rotating the convey roller  160  when the deformed portion  93 , which protrudes upward, reaches a vicinity of the nip portion between the convey roller  160  and the pinch roller  161 , as shown in  FIG. 14 . A leading edge  91  of the sheet  90  may be supported on the upper surface of the platen  42  when a trailing edge side of the portion  93  is pinched between the convey roller  160  and the pinch roller  161 . A trailing edge side  92  of the sheet  90  exiting the nip portion may be supported on the guide surface  15  of the inner guide member  119 . A leading edge side of the sheet  90  exiting the nip portion may bend downward. However, because the leading edge  91  is supported on the upper surface  45  of the platen  45  and the trailing edge side  92  of the sheet  90  exiting the nip portion is supported on the guide surface  15 , the leading edge side of the sheet  90  may be prevented from bending downward by the upper surface  45  due to the rigidity of the sheet  90 . Thus, the portion  93  of the sheet  90  may be bent to protrude downward. A downward force  120  may be applied to the portion  93  to restrict and/or correct the deformation of the portion  93 . 
     In another embodiment, a guide surface  17  of an inner guide member  219  may protrude more upward than a nip portion between a convey roller  260  and a pinch roller  261 , as shown in  FIG. 15 . The pinch roller  261  may be fixed at a predetermined position. The controller  70  may rotate the convey roller  260  in reverse to convey the sheet  90  in reverse, and may stop the convey roller  260  when the deformed portion  93 , which protrudes upward, reaches the guide surface  17  of the inner guide member  219  after passing a nip portion between the convey roller  260  and the pinch roller  261 . A portion of the sheet  90  at the leading edge side from the portion  93  may be pinched between the convey roller  260  and the pinch roller  261 , and the portion  93  may be raised by the guide surface  17  higher than the nip portion. Thus, the portion  93  may be bent to protrude downward. A downward force  120  may be applied to the portion  93  to restrict or correct the deformation of the portion  93 . The inner guide member  219  may be configured such that the angle of the guide surface thereof is changeable so as to apply the force  120  to the portion  93  when the sheet  90  is reversely conveyed and stopped. 
     In yet another embodiment, a guide surface  16  of an outer guide member  318  may protrude downward with respect to a nip portion between a convey roller  360  and a pinch roller  361 , as shown in  FIG. 16 . The pinch roller  361  may be fixed at a predetermined position. The controller  70  may rotate the convey roller  360  in reverse to convey the sheet  90  in reverse, and may stop rotating the convey roller  360  when a deformed portion  93 , which protrudes upward, reaches the guide surface  16  of the outer guide member  218  after passing a nip portion between the convey roller  360  and the pinch roller  361 . A leading edge end of the portion  93  may be pinched between the convey roller  360  and the pinch roller  361 , and the portion  93  may be bent to protrude downward by the guide surface  16 . A downward force  120  may be applied to the portion  93  to restrict and/or correct the deformation of the portion  93 . The outer guide member  318  may be configured such that the angle of the guide surface thereof is changeable so as to apply the force  120  to the portion  93  when the sheet  90  is reversely conveyed and stopped. 
     While the invention has been described in connection with exemplary embodiments, it will be understood by those skilled in the art that other variations and modifications of the exemplary embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are considered merely as exemplary of the invention, with the true scope of the invention being indicated by the following claims.