Patent Publication Number: US-7591467-B2

Title: Sheet detecting device for image recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from Japanese Patent Application No. 2005-286595 filed Sep. 30, 2005. The entire content of the priority application is incorporated herein by reference. 
   TECHNICAL FIELD 
   The disclosure relates to a sheet detecting device for detecting the position of a sheet-like recording medium conveyed along a conveying path in a conveying direction, and an image recording apparatus having the sheet detecting device. 
   BACKGROUND 
   Japanese Patent Application Publication No. HEI-10-175751 discloses a conventional image recording apparatus having a paper sensor for detecting the position of recording paper that is conveyed along a conveying path in a predetermined conveying direction. The paper sensor includes a detection member pivotally supported between a position protruding from a paper-conveying guide into the conveying path and a position retracted from the conveying path; and a paper detecting sensor for detecting pivotal movement of the detection member. When the leading edge of the recording paper contacts the detection member, the detection member is pivotally moved and the recording paper is detected. 
   SUMMARY 
     FIGS. 1A through 1C  show a portion of the internal structure in an inkjet type image recording apparatus having a platen  102  for supporting a recording paper S at an image-recording position, and a pair of conveying rollers  103  for conveying the recording paper S fed from a paper cassette (not shown) toward the platen  102 . This image recording apparatus also includes a carriage  101  that can be moved by sliding in a direction (a direction perpendicular to the surface of the drawings of  FIGS. 1A through 1C ; hereinafter referred to as the “main scanning direction”) orthogonal to a conveying direction for conveying the recording paper S (left-and-right direction in  FIGS. 1A through 1C ; hereinafter referred to as the “sub-scanning direction”) , and a recording head  100  mounted in the carriage  101  so as to confront the platen  102 . In the image recording apparatus having this construction, the conveying rollers  103  convey the recording paper S intermittently by predetermined steps, while the carriage  101  conveys the recording head  100  and the recording head  100  ejects ink from nozzles therein onto the recording paper S at times that the recording paper S is halted between intermittent conveying steps, thereby recording an image by predetermined regions. 
   In the image recording apparatus having this construction, the recording paper S undergoes a registration process prior to the image-recording process described above. Specifically, as a feeding roller (not shown) disposed upstream of the conveying rollers  103  feeds a sheet of the recording paper S onto a conveying path  116 , a paper sensor  110  disposed on the conveying path  116  detects the conveyed position of the recording paper S (see  FIGS. 1A and 1B ). As the recording paper S is conveyed farther and reaches the nip point in the conveying rollers  103  (see  Fig. 1B , the recording paper S comes to a halt with the leading edge in a state of contact with the nip part between the conveying rollers  103 , which are driven in a reverse rotation. At this time, the feeding roller continues to feed the recording paper S so that the leading edge of the recording paper S presses against the nip part of the conveying rollers  103  and flexes within the conveying path  116 . Consequently, the entire leading edge of the recording paper S is pushed evenly against the conveying rollers  103 , correcting any skew in the recording paper S. When a predetermined time has elapsed after the paper sensor  110  detects the recording paper S, the drive roller  105 , which is driven in reverse, is temporarily halted and subsequently driven in a forward rotation a predetermined step for continuously conveying the recording paper S toward the platen  102  until the starting edge of an image-recording region on the recording paper S is aligned with an image-recording position P at which the recording head  100  ejects ink. For example, when the image-recording region begins from the leading edge of the recording paper S, the recording paper S is conveyed continuously until the leading edge of the recording paper S arrives at the position P, as shown in  FIG. 1C . Thereafter, the recording head  100  records images while the conveying rollers  103  convey the recording paper S intermittently. A controller (not shown) determines whether the leading edge of the recording paper S has arrived on the upstream side of the conveying rollers  103  and whether the leading edge has arrived at the position P based on detection signals from the paper sensor  110 . 
   The paper sensor  110  is disposed on the conveying path  116  formed of an upper guide  118  and a lower guide  117 . More specifically, the paper sensor  110  is disposed directly upstream of the conveying rollers  103 . As shown in  FIG. 2 , the paper sensor  110  is configured of a detection member  111  pivotally supported between a position protruding from the lower guide  117  into the conveying path  116  (represented by the solid line) and a position retracted from the conveying path  116  (represented by the dotted line); and an optical sensor  112 , such as a photointerrupter, for detecting the pivotal movement of the detection member  111 . The detection member  111  is divided about a support point  113  into a contact part  114  that is contacted by the recording paper S, and a shielding part  115  for blocking light emitted by the optical sensor  112 . A spring or other urging means (not shown) elastically urges the detection member  111  in the clockwise direction in  FIG. 2  so that the detection member  111  is protruding into the conveying path  116 . 
   While an external force is not applied to the detection member  111 , the contact part  114  of the detection member  111  protrudes into the conveying path  116 , as indicated by the solid line in  FIG. 2 , and the shielding part  115  is positioned between a light-emitting element and a light-receiving element of the optical sensor  112 . Consequently, the shielding part  115  blocks the optical path in the optical sensor  112 , effectively turning off the paper sensor  110 . When the leading edge of a sheet of recording paper S conveyed along the conveying path  116  contacts the contact part  114 , the detection member  111  pivotally moves counterclockwise so as to retract from the conveying path  116 . At this time, the shielding part  115  pivotally moves together with the detection member  111  and moves out of the optical path between the light-emitting element and light-receiving element of the optical sensor  112 . Accordingly, the light transmission in the optical sensor  112  is no longer interrupted, effectively turning on the paper sensor  110 . 
   However, in the paper sensor  110  described above, the portion on the leading edge of the recording paper S that collides with the contact part  114  of the probe  111  often curls up or down due to the contact. The amount of deformation in the leading edge depends on the stiffness of the recording paper S. For example, while thick paper may deform very little, thin paper will deform considerably more than the thick paper and, in some cases, may fold over completely. This difference in amount of deformation among different thicknesses of paper produces a different timing for detecting the recording paper S. As a result, the position of the recorded image varies among recording paper of different stiffness. 
   Further, when the degree or direction of warpage in the leading edge of the recording paper S differs among different sheets of recording paper, the path followed by the leading edge also differs. For example, if the leading edge of the recording paper S curls upward, the recording paper S is conveyed along the upper guide  118 . If the leading edge curls downward, the recording paper S is conveyed along the lower guide  117 . If the leading edge has no warpage, the recording paper S is conveyed straight through the conveying path  116 . The variations in the conveying path lead to fluctuations in the timing at which the recording paper S arrives at the probe  111  so that the recording paper S is detected at different timings. This problem is magnified when performing borderless printing. 
   In view of the foregoing, it is an object of one aspect of the invention to provide a sheet detecting device capable of improving the precision in detection timing for detecting the position of a conveyed recording medium, and an image recording apparatus equipped with the sheet detecting device. 
   In order to attain the above and other objects, according to one aspect, the invention provides a sheet detecting device for detecting a position of a recording medium. The sheet detecting device includes a follow roller, an urging member, a first support member, a second support member, and a detecting unit. The follow roller is disposed on a conveying path along which a recording medium is conveyed in a conveying direction. The follow roller receives a rotational force of a drive roller and follows rotation of the drive roller. The urging member applies an urging force to the follow roller for urging the follow roller toward the drive roller. The second support member rotatably supports the follow roller and supports the urging member. The second support member is supported on the first support member, allowing the second support member to move to a first position when the drive roller and the follow roller nippingly convey the recording medium, and allowing the second support member to move to a second position upstream of the first position in the conveying direction when the recording medium is separated from the drive roller and the follow roller. The second support member is provided with a detection member that moves with the second support member when the second support member moves between the first position and the second position. The detecting unit detects the detection member, thereby detecting the position of the recording medium. 
   According to another aspect, the invention provides an image recording apparatus. The image recording apparatus includes a casing, an image recording unit, and a sheet detecting device for detecting a position of a recording medium, The image recording unit is disposed in the casing for recording an image on a recording medium that is conveyed along a conveying path in a conveying direction. The sheet detecting device includes a follow roller, an urging member, a first support member, a second support member, and a detecting unit. The follow roller is disposed on the conveying path. The follow roller receives a rotational force of a drive roller and follows rotation of the drive roller. The urging member applies an urging force to the follow roller for urging the follow roller toward the drive roller. The first support member is supported by the casing. The second support member rotatably supports the follow roller and supports the urging member. The second support member is supported on the first support member, allowing the second support member to move to a first position when the drive roller and the follow roller nippingly convey the recording medium, and allowing the second support member to move to a second position upstream of the first position in the conveying direction when the recording medium is separated from the drive roller and the follow roller. The second support member is provided with a detection member that moves with the second support member when the second support member moves between the first position and the second position. The detecting unit detects the detection member, thereby detecting the position of the recording medium. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative aspects in accordance with the invention will be described in detail with reference to the following figures wherein: 
       FIGS. 1A through 1C  are explanatory diagrams illustrating an example of an image recording apparatus; 
       FIG. 2  is an enlarged view of a paper sensor provided in the image recording apparatus shown in  FIGS. 1A through 1C ; 
       FIG. 3  is a perspective view showing the outer appearance of a multifunction device according to illustrative aspects of the invention; 
       FIG. 4  is a side cross-sectional view of a printing unit provided in the multifunction device of  FIG. 3 ; 
       FIG. 5  is a plan view of the printing unit when a scanning unit has been removed; 
       FIG. 6  is a perspective view illustrating the structure around an image-recording unit; 
       FIG. 7  is a plan view illustrating the structure around the image-recording unit; 
       FIG. 8  is a perspective view showing the state of a pinch roller holder supported on a holder support member: 
       FIG. 9  is an exploded view of the holder support member and pinch roller holder; 
       FIG. 10  is a perspective view showing the structure of a rolling bearing; 
       FIG. 11  is an enlarged view illustrating the moving range of the pinch roller holder; 
       FIG. 12  is an explanatory diagram illustrating a cross section of a drive roller and pinch roller in an XY coordinate system having a center of revolution O as the point of origin; 
       FIG. 13  is an explanatory diagram showing the state of the recording paper interposed in the structure of  FIG. 12 ; 
       FIG. 14  is a partial cross-sectional view showing the state of the pinch roller holder in a retracted position; and 
       FIG. 15  is a partial cross-sectional view showing the state of the pinch roller holder in a conveying position. 
   

   DETAILED DESCRIPTION 
   A sheet detecting device and an image recording apparatus according to some aspects of the invention will be described while referring to  FIGS. 3 through 15 . In the following description, the expressions “front”, “rear”, “upper”, “lower”, “right”, and “left” are used to define the various parts when the image recording apparatus is disposed in an orientation in which it is intended to be used. 
     FIG. 3  is a perspective view showing the outer appearance of a multifunction device  1 , serving as the image recording apparatus according to the illustrative aspects. As shown in  FIG. 3 , the multifunction device  1  is integrally configured of a printing unit  2  disposed in the bottom of the multifunction device  1 , a scanning unit  3  disposed in the top of the multifunction device  1 , an original cover  7  provided on top of the scanning unit  3 , a control panel  9  disposed on the front side and top surface of the multifunction device  1 , and a slot section  8  disposed on the front surface of the multifunction device  1 . The multifunction device  1  has a printer function, scanner function, copier function, facsimile function, and the like. However, the invention can be realized with any arbitrary combination of functions, such as a scanner function and facsimile function. Hence, the invention may be applied to a standalone printer having only a printer function. 
   The multifunction device  1  is primarily connected to a computer (not shown) and records images and text on recording paper in the printing unit  2  based on print data including image data and text data that is transferred from the computer. Further, by connecting a digital camera or other external device to the multifunction device  1 , the multifunction device  1  can record image data outputted from the external device on recording paper. Similarly, by inserting a memory card or other storage medium in the multifunction device  1 , the multifunction device  1  can record image data or the like stored in the storage medium onto recording paper. The multifunction device  1  has a single-sided printing function for recording images and text on only one side of the paper based on the print data, and a duplex printing function for recording both sides of the paper. The structure of the multifunction device  1  in the following description is merely one example of an image recording apparatus according to the invention, and it should be apparent that the structure can be appropriately modified within the scope of the invention. 
   The control panel  9  is provided on the top front surface of the scanning unit  3 , which is also the top surface on the front side of the multifunction device  1 , for enabling the user to operate the printing unit  2  and scanning unit  3 . The control panel  9  is configured of various operating buttons, and a liquid crystal display unit  11 . Hence, the user can operate the multifunction device  1  by inputting instructions via the control panel  9 . The operating buttons may be configured of a Start button for initiating operations on the printing unit  2  and scanning unit  3 ; a Stop button for halting operations or canceling settings; a Mode Selection button for selecting the facsimile function, numerical buttons for inputting the number of copies, the scanning resolution of the scanning unit  3 , and the like; a Setting button for setting either single-sided printing (one-sided copying) or duplex printing (double-sided copying); and other input keys. A controller operates the multifunction device  1  based on input from the control panel  9 . Of course, when the multifunction device  1  is connected to a computer, as described above, the multifunction device  1  may be operated based on commands received from the computer via a printer driver or a scanner driver. 
   The slot section  8  is provided on the front surface of the multifunction device  1  near the left side thereof. Various small memory cards can be inserted into the slot section B. The multifunction device  1  reads image data stored on the memory cards inserted into the slot section  8  and displays data related to this image data on the liquid crystal display unit  11 , enabling the user to print desired images on recording paper using the scanning unit  3 . The user inputs a selection via the control panel  9 . 
   As shown in  FIG. 3 , the scanning unit  3  includes an original scanning base  5  functioning as a flatbed scanner. The original cover  7  is attached to the original scanning base  5  via hinges (not shown) provided on the rear side surface so as to be capable of opening and closing via the hinges. The original scanning base  5  has a structure that is well known in the art, such as a structure having a contact glass disposed on the top surface, and an image-scanning unit disposed below the contact glass and housing a contact image sensor (CIS). The original cover  7  also includes an automatic document feeder (ADF)  6 . When functioning as a flatbed scanner, the scanning unit  3  reads images from an original document placed on the contact glass by exposing and scanning the document as the image-scanning unit is moved under the contact glass. When reading an original image using the ADF  6 , the original conveyed by the ADF  6  passes over a scanning surface of the contact glass while the image-scanning unit fixed in a position below the scanning surface reads images from the original. It should also be apparent that the invention may be applied to an image-scanning unit configured of an image sensor, such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). Since the structure of the scanning unit  3  in the invention is arbitrary, a detailed description of the image-scanning unit will not be included in the present aspect. 
   Next, the structure of the printing unit  2  will be described in detail with reference to  FIGS. 3 through 7 .  FIG. 4  is a side cross-sectional view of the printing unit  2  provided in the multifunction device  1 .  FIG. 5  is a plan view of the printing unit  2  when the scanning unit  3  has been removed.  FIG. 6  is a perspective view illustrating the structure around an image recording unit described later.  FIG. 7  is a plan view illustrating the structure around the image recording unit. For convenience, a recording head, belt driving mechanism, guide rail, and purging mechanism described later have been omitted from  FIG. 7 . 
   As shown in  FIGS. 3 and 4 , an opening  4  is formed in the front surface side of the printing unit  2 . A paper tray  20  and a discharge tray  21  are mounted in the multifunction device  1  via the opening  4 . The paper tray  20  and discharge tray  21  have been omitted from  FIG. 3 . The paper tray  20  can accommodate a recording paper of a desired size, such as the A 4  size or the B 5  size. As shown in  FIG. 4 , the longitudinal direction of paper accommodated in the paper tray  20  extends in the depth direction (the front-to-rear direction) of the multifunction device  1  when the paper tray  20  is mounted in the multifunction device  1 . The discharge tray  21  is supported on the paper tray  20  and disposed thereabove. Hence, the paper tray  20  and discharge tray  21  are stacked in two vertical levels when mounted in the multifunction device  1 . The recording paper may be normal paper, glossy paper, or the like and corresponds to the recording medium of the invention. A transparency or other non-paper medium also corresponds to the recording medium of the invention. 
   A separating sloped surface  22  is provided on the far side (rear side) of the paper tray  20  when the paper tray  20  is mounted in the multifunction device  1 . The separating sloped surface  22  functions to separate paper fed from the paper tray  20  and to guide the paper upward. 
   A conveying path  23  is formed above the separating sloped surface  22 . The conveying path  23  extends upward from the top side of the separating sloped surface  22  and curves toward the front surface side of the multifunction device  1 . The conveying path  23  extends from the rear side of the multifunction device  1  to the front side, passing through the nip part of a conveying device  54  and below an image recording unit  24  described later and leads to the discharge tray  21 . Hence, paper fed from the paper tray  20  is guided to the image recording unit  24  along a U-shaped path from the bottom to the top of the conveying path  23 . After the image recording unit  24  records an image on the paper, the paper is discharged onto the discharge tray  21 . 
   A feeding roller  25  is disposed above the paper tray  20 . The feeding roller  25  is supported on the rear end of a feed arm  26 . The feed arm  26  is capable of moving up and down so that the feeding roller  25  can contact or separate from the paper tray  20 . A drive transmission mechanism  27  configured of a plurality of engaged gears transmits a driving force from a motor (not shown) to rotate the feeding roller  25 . The feeding roller  25  functions to separate and feed paper stacked on the paper tray  20  to the conveying path  23  one sheet at a time. More specifically, the feeding roller  25  contacts the topmost sheet of recording paper stacked on the paper tray  20  with pressure. By rotating, the feeding roller  25  generates a frictional force between the roller surface of the feeding roller  25  and the recording paper that conveys the topmost sheet of paper to the separating sloped surface  22 . The leading edge of the paper fed by the feeding roller  25  contacts the separating sloped surface  22  and is guided upward into the conveying path  23 . If a sheet of paper below the topmost sheet is conveyed together with the topmost sheet due to frictional force or static electricity acting between the sheets, the sheet beneath the topmost sheet is halted when contacting the separating sloped surface  22  so that only the topmost sheet is conveyed. 
   Except for the region occupied by the image recording unit  24  and the like, the conveying path  23  is configured of an outer guide surface and an inner guide surface that confront each other over a predetermined distance. For example, the section of the conveying path  23  formed on the rear side of the multifunction device  1  has an outer guide surface  1 A formed integrally with the frame of the multifunction device  1 , and an inner guide surface  28 A configured of a guide member  28  fixed to the inside of the frame. Conveying rollers  29  are provided at predetermined locations along the conveying path  23  and particularly along the curved region of the conveying path  23 . The conveying rollers  29  are disposed so that the surfaces thereof are exposed from the outer guide surface  1 A or inner guide surface  28 A, and are capable of rotating about axes parallel to the width direction of the conveying path  23 . The conveying rollers  29  enable the recording paper to be smoothly conveyed when contacting the guide surfaces  1 A and  28 A in the curved region of the conveying path  23 . 
   The image recording unit  24  includes a carriage  31  that reciprocates in a main scanning direction (a direction orthogonal to the surface of the drawing in  FIG. 4 ). A recording head  30  is mounted in the carriage  31 . Ink in the colors cyan (C), magenta (M), yellow (Y), and black (Bk) is supplied to the recording head  30  from ink tanks  32  via ink tubes  33  (see  FIG. 5 ). The recording head  30  ejects ink of each color as microdroplets through nozzles formed in the bottom surface thereof. The recording head  30  records images on a recording paper conveyed over a platen  34  as the carriage  31  reciprocates in the main scanning direction to scan the recording head  30  over the recording paper. 
   As shown in  FIGS. 5 and 6 , a pair of guide rails  35  and  36  is provided on the image recording unit  24  above the conveying path  23 . The guide rails  35  and  36  extend in the width direction of the conveying path  23  and are separated from each other in the conveying direction of the recording paper. The carriage  31  is disposed so as to straddle the guide rails  35  and  36  and is capable of sliding over the guide rails  35  and  36  in the width direction of the conveying path  23 . The guide rail  35  is disposed on the upstream side in the paper-conveying direction (the rear side) and has a plate shape that is longer in the width direction of the conveying path  23  than the scanning range of the carriage  31 . The top surface of the guide rail  35  slidably supports the upstream end of the carriage  31 . 
   The guide rail  36  disposed on the downstream side in the paper-conveying direction (the front side) is plate-shaped and has a length in the width direction of the conveying path  23  that is substantially the same as the guide rail  35 . The top surface of the guide rail  36  is bent at substantially a right angle to form an end part  37  angled upward on the upstream side of the guide rail  36  in the paper-conveying direction. An engaging member (not shown) is provided on the carriage  31  for engaging with the end part  37  of the guide rail  36  by gripping both sides of the end part  37 . In this way, the carriage  31  is slidably supported on the guide rails  35  and  36  and is capable of reciprocating in the width direction of the conveying path  23  along the end part  37  of the guide rail  36 . A pair of rollers or the like may also be used in place of the engaging member for gripping the end part  37 . Further, sliding members may also be provided on portions of the surfaces of the guide rails  35  and  36  contacted by the carriage  31  to reduce friction. 
   A belt-driving mechanism  38  is provided on the top surface of the guide rail  36 . The belt-driving mechanism  38  includes a drive pulley  39  and a follow pulley  40  disposed near both widthwise ends of the conveying path  23 , and an endless timing belt  41  disposed around the drive pulley  39  and follow pulley  40 . The timing belt  41  has teeth formed on the inner side surface thereof. A motor (not shown) is coupled to the shaft of the drive pulley  39  for inputting a driving force into the shaft of the drive pulley  39 . When the drive pulley  39  rotates, the timing belt  41  moves in a circuitous motion. The timing belt  41  may also be configured of a belt having ends, both of which ends are fixed to the carriage  31 . 
   The carriage  31  is fixed to the timing belt  41 . By moving the timing belt  41  circuitously, the carriage  31  reciprocates over the guide rails  35  and  36  in a position based on the end part  37 . Since the recording head  30  is mounted in the carriage  31 , the recording head  30  also reciprocates together with the carriage  31  along the width direction of the conveying path  23 , which is the main scanning direction. An encoder strip  42  of a linear encoder is provided on the guide rail  36  along the end part  37 . The linear encoder detects the encoder strip  42  with a photointerrupter, and a controller (not shown) controls the reciprocating motion of the carriage  31  based on detection signals from the linear encoder. 
   As shown in  FIGS. 4 ,  6 , and  7 , the platen  34  is disposed on the bottom of the conveying path  23  in confrontation with the recording head  30 , The platen  34  extends over the center region within the reciprocating range of the carriage  31  through which the recording paper passes. The width of the platen  34  is sufficiently larger than the maximum width of recording paper that can be conveyed in the multifunction device  1  so that both edges of the paper pass over the platen  34 . 
   As shown in  FIG. 5 , a purging mechanism  43  and a waste ink tray  44  are disposed outside the image recording range of the recording head  30  and, more specifically, in regions on both sides of the platen  34  through which the recording paper does not pass. The purging mechanism  43  functions to draw out air bubbles and foreign matter along with ink from nozzles and the like formed in the recording head  30 . The purging mechanism  43  includes a cap  45  for covering the nozzle surface of the recording head  30 . A pump mechanism is connected to the cap  45 . A moving mechanism is also provided for moving the cap  45  to contact or separate from the nozzle surface of the recording head  30 . When an operation is performed to remove air bubbles and the like from the recording head  30 , the carriage  31  is moved so that the recording head  30  is positioned above the cap  45 . Subsequently, the moving mechanism moves the cap  45  upward to form a hermetic seal over the nozzles formed in the bottom surface of the recording head  30 . The pump mechanism coupled to the cap  45  then draws out ink from the nozzles. 
   The waste ink tray  44  is disposed on the opposite side from the purging mechanism  43  in the width direction in a position outside the image-forming range of the carriage  31 . The waste ink tray  44  receives ink that has been flushed out of the recording head  30  (this operation is called “flushing”). The purging mechanism  43  and waste ink tray  44  constitute a maintenance unit that can perform such maintenance as removing air bubbles and mixed ink of different colors from the recording head  30 . 
   As shown in  FIG. 5 , the ink tanks  32  are accommodated in an ink tank accommodating section  46  disposed in the front right side of the printing unit  2 . The ink tanks  32  are provided separately from the carriage  31  and recording head  30  in the printing unit  2 . The ink tanks  32  include four ink tanks  32 C,  32 M,  32 Y, and  32 K accommodating ink of the respective colors cyan (C), magenta (M), yellow (Y), and black (Bk). The ink tanks  32  supply ink to the carriage  31  via the ink tubes  33 . 
   Ink from the ink tanks  32 C,  32 M,  32 Y, and  32 K accommodated in the ink tank accommodating section  46  is supplied through the ink tubes  33 , which are provided independently for each color. The ink tubes  33  are tubes formed of synthetic resin and are flexible so as to be able to bend when the carriage  31  moves in a scanning motion. Openings formed at one end of the ink tubes  33  are connected to respective joints provided at ink tank accommodating positions in the ink tank accommodating section  46 , The ink tube  33 C corresponds to the ink tank  32 C and supplies cyan ink therefrom. Similarly, the ink tubes  33 M,  33 Y, and  33 K correspond to the ink tanks  32 M,  32 Y, and  32 K and supply the corresponding ink colors magenta, yellow, and black therefrom. 
   From the ink tank accommodating section  46 , the ink tubes  33  are led along the width direction of the multifunction device  1  to a position near the center thereof, at which position the ink tubes  33  are fixed to an appropriate member on the device frame or the like. The section of the ink tubes  33  from the fixed part to the carriage  31  is a U-shaped curved portion that is not fixed to the device frame or the like and that changes in shape as the carriage  31  reciprocates. Hence, as the carriage  31  moves toward one end (the left side in  FIG. 5 ) in the reciprocating direction, the ink tubes  33  move in the same direction as the carriage  31  while flexing so that a curved radius of the U-shaped curved portion grows smaller. When the carriage  31  moves to the other end (the right side in  FIG. 5 ) in the reciprocating direction, the ink tubes  33  move in the same direction while flexing so that the curved radius of the U-shaped curved portion grows larger. 
   As shown in  FIGS. 4 ,  6 , and  7 , a pair of conveying rollers  54  having a drive roller  47  and pinch rollers  48  disposed below the drive roller  47  is provided on the upstream side of the image recording unit  24 . The drive roller  47  and pinch rollers  48  pinch a recording paper conveyed along the conveying path  23  and convey the recording paper over the platen  34 . Springs  61  (see  FIG. 8 ) apply a predetermined urging force to the pinch rollers  48  to press the pinch rollers  48  against the drive roller  47 . The pinch rollers  48  are rotatably supported in a pinch roller holder  56  with the springs  61  in a compressed state. A detection member  74  described later is provided on the pinch roller holder  56 . The pinch roller holder  56  is supported by a holder support member  57  provided on an internal frame  58  constituting part of the casing in the multifunction device  1  so as to be capable of rolling in the conveying direction of the paper. With this construction, the pinch roller holder  56  rollingly moves to a conveying position on the downstream side, shown in  FIG. 15 , when the conveying rollers  54  are conveying the recording paper and rollingly moves to a retracted position on the upstream side, shown in  FIG. 14 , when the trailing edge of the recording paper leaves the conveying rollers  54 . As shown in  FIGS. 14 and 15 , the detection member  74  moves along with movement of the pinch roller holder  56 . A detailed description of the structures of the holder support member  57  and pinch roller holder  56  and the supporting structure for supporting the pinch roller holder  56  on the holder support member  57  is given below. The pinch rollers  48 , springs  61 , pinch roller holder  56 , holder support member  57 , and restricting part  75  are one example of components constituting the sheet detecting device of the invention. 
   A photointerrupter  75  is disposed below the holder support member  57  in substantially the longitudinal center thereof. The photointerrupter  75  is attached to the internal frame  58  in a position covered by the holder support member  57 . The photointerrupter  75  is a photocoupler integrally provided with a light-emitting element for emitting light and a light-receiving element for receiving the light emitted from the light-emitting element. A slit (not shown) is formed in the photointerrupter  75  for allowing the detection member  74  to pass between the light-emitting element and light-receiving element. There is no particular restriction on the position of the photointerrupter  75 , provided that the detection member  74  can pass between the light-emitting element and light-receiving element. The photointerrupter  75  may be disposed on the holder support member  57 , for example, to simplify the assembly process. 
   The photointerrupter  75  is connected by signal lines to a control circuit board  52  described later. The control circuit board  52  monitors an electric signal (voltage or current, for example) generated in the light-receiving element based on the amount of light received. The control circuit board  52  determines that the photointerrupter  75  is on or off based on the intensity of the electric signal. For example, the control circuit board  52  determines that the photointerrupter  75  is on when a voltage signal greater than a predetermined threshold is produced in the light-receiving element, and determines that the photointerrupter  75  is off when the voltage signal is less than the threshold value. An on determination signifies paper is detected, while an off determination signifies paper is not detected. In the illustrative aspects, the invention is applied to the photointerrupter  75  as one example of the detecting unit. However, the invention may be applied to an electric sensor or the like in place of an optical sensor, such as the photointerrupter  75 , for detecting the detection member  74  based on fluctuations in electric resistance or in a magnetic field or electric field, for example. 
   A pair of discharge rollers  55  is provided on the downstream side of the image recording unit  24  and includes a drive roller  49 , and spur rollers  50  disposed above the drive roller  49 . The drive roller  49  and spur rollers  50  grip and convey the recording paper after an image has been recorded thereon. The surfaces of the spur rollers  50  are formed irregularly in a spur-like configuration so as not to degrade the image recorded on the paper. 
   As shown in  FIGS. 6 and 7 , a motor  59  is coupled to one axial end of the drive roller  47 . A driving force transmitted from the motor  59  drives the drive rollers  47  and  49  to rotate intermittently at predetermined linefeed widths. The drive roller  47  and drive roller  49  rotate in synchronization. As shown in  FIG. 6 , a rotary encoder includes an encoder disc  51  provided on the drive roller  47 , and a photointerrupter  60  for detecting the encoder disc  51 . The rotations of the drive rollers  47  and  49  are detected based on detection signals from the rotary encoder. 
   Hence, paper interposed between the drive roller  47  and pinch roller  48  is conveyed intermittently over the platen  34  at predetermined linefeed widths. The recording head  30  scans the paper after each linefeed to record an image beginning from the leading edge side of the paper. After an image has been recorded on the paper, the leading edge side becomes interposed between the drive roller  49  and spur rollers  50 . At this time, the paper is conveyed intermittently at the predetermined linefeed widths, while the leading edge side of the paper is interposed between the drive roller  49  and spur rollers  50 , and the trailing edge side is interposed between the drive roller  47  and pinch roller  48 , during which time the recording head  30  continues recording an image on the paper. After the paper is conveyed farther, the trailing edge of the paper passes through and separates from the drive roller  47  and pinch roller  48 . Hence, the paper is conveyed intermittently at the predetermined linefeed widths while interposed only between the drive roller  49  and spur rollers  50  as the recording head  30  continues to record an image after each linefeed. When the trailing edge of the recording paper comes out of the drive roller  47  and pinch roller  48 , the pinch roller holder  56  simultaneously rolls to the retracted position downstream, shown in  FIG. 14 . After the recording head  30  has completed recording an image in the predetermined region of the paper, the drive roller  49  is driven to rotate continuously so that the paper interposed between the drive roller  49  and spur rollers  50  is discharged onto the discharge tray  21 . 
   As shown in  FIG. 5 , the control circuit board  52  is disposed on the front surface side of the multifunction device  1 . Recording signals are transmitted from the control circuit board  52  to the recording head  30  via a flat cable  53 . The flat cable  53  is an insulated ribbon cable configured of conductors for transmitting electric signals coated in a synthetic resin film, such as a polyester film. The flat cable  53  electrically connects the control circuit board  52  to a control circuit board (not shown) in the recording head  30 . The flat cable  53  extends in the reciprocating direction from the carriage  31  and is folded back to form substantially a U-shaped portion. The U-shaped portion is not fixed to any other member and changes in shape as the carriage  31  reciprocates. 
   Next, the structures of the holder support member  57  and pinch roller holder  56  will be described in detail with reference to  FIGS. 8 through 11 ,  FIG. 8  is a perspective view showing the state of the pinch roller holder  56  supported on the holder support member  57 .  FIG. 9  is an exploded view of the holder support member  57  and pinch roller holder  56 .  FIG. 10  is a perspective view showing the structure of a roller bearing  80 .  FIG. 11  is an explanatory diagram illustrating a detection state and non-detection state of the detection member  74 . 
   As shown in  FIGS. 8 and 9 , the pinch roller holder  56  has an elongated shape and is oriented so that the longitudinal direction matches the width direction of the recording paper. Four roller-accommodating compartments  64 , and eight spring-accommodating compartments  62  are provided on the top surface of the pinch roller holder  56  confronting the drive roller  47 . The roller-accommodating compartments  64  are formed at predetermined intervals along the longitudinal direction of the pinch roller holder  56 . The spring-accommodating compartments  62  are formed adjacent to and on both ends of the roller-accommodating compartments  64 . The pinch rollers  48  are accommodated in the roller-accommodating compartments  64  and have rotational shafts  65  aligned with the longitudinal direction of the pinch roller holder  56 . The springs  61  are accommodated in the spring-accommodating compartments  62  in a compressed state. This structure is one example, but it should be apparent that the number of pinch rollers  48  and springs  61  and the accommodating method may be modified as appropriate. The springs  61  are not limited to the coil springs shown in the drawings. 
   The spring-accommodating compartments  62  are defined by partitioning plates  66  erected on both longitudinal sides of the spring-accommodating compartments  62 . A bearing  63  is formed in each partitioning plate  66  for supporting the rotational shaft  65  of the respective pinch roller  48 . The bearings  63  are formed as long vertical grooves in the partitioning plates  66 . The upper ends of the bearings  63  are formed slightly smaller than the diameter of the rotational shafts  65 . When the rotational shafts  65  are pressed into the bearings  63 , the upper ends of the grooves elastically expand so that the bearings  63  can receive the rotational shafts  65 . The upper ends of the grooves return to their original shape after the rotational shafts  65  are completely inserted, preventing the rotational shafts  65  from easily coming out of the bearings  63 . With this construction, the bearings  63  support the rotational shafts  65  so that the rotational shafts  65  can move vertically. 
   By housing the springs  61  in the spring-accommodating compartments  62  and inserting the rotational shafts  65  of the pinch rollers  48  into the bearings  63 , the springs  61  are mounted in the spring-accommodating compartments  62  in a compressed state. The elastic force of the compressed springs  61  urges the pinch rollers  48  upward. In other words, an urging force toward the drive roller  47  is applied is to the pinch rollers  48 . Hence, the pinch rollers  48  are urged by the springs  61  and rotatably supported by the bearings  63 . Accordingly, when a thick sheet of recording paper is conveyed through the multifunction device  1 , the paper pushes the pinch rollers  48  downward against the urging force of the springs  61  by a distance corresponding to the paper thickness. 
   Four protruding pieces  68  are formed on the bottom surface of the pinch roller holder  56 . The protruding pieces  68  are designed to engage with four engaging grooves  67  (see  FIG. 9 ) formed in the holder support member  57 . The protruding pieces  68  are provided at both ends of the pinch roller holder  56  in the longitudinal direction. The protruding pieces  68  are also provided at positions separated from each of the both ends toward the longitudinal center position by the length of one pinch roller  48 . The protruding pieces  68  are plate-shaped members protruding downward from the bottom surface of the pinch roller holder  56  and extend along the short dimension of the pinch roller holder  56 . By inserting the protruding pieces  68  into the engaging grooves  67 , the protruding pieces  68  fit into the engaging grooves  67  with a predetermined amount of play. With this construction, the pinch roller holder  56  is supported on the holder support member  57  so as to be capable of moving in the short dimension of the holder support member  57 , that is, in the conveying direction of the recording paper, while the amount of movement is restricted to a predetermined range. 
   The detection member  74  is disposed on the bottom surface of the pinch roller holder  56  and in the approximate center thereof. The detection member  74  is inserted through a through-hole  76  (see  FIG. 9 ) formed in the holder support member  57 . The detection member  74  is a plate-shaped member that protrudes downward from the bottom surface of the pinch roller holder  56 , A distal end of the detection member  74  enters or recedes from the optical path between the light-emitting emitting element and light-receiving element of the photointerrupter  75 . Hence, the detection member  74  is formed at a length sufficient to reach the optical path of the photointerrupter  75 . The positioning and shape of the detection member  74  may be modified as appropriate in accordance with the positioning of the photointerrupter  75  and the like. 
   The holder support member  57  is formed in an elongated shape similar to the pinch roller holder  56  and is disposed on the internal frame  58  so that the longitudinal dimension of the holder support member  57  matches the width dimension of the recording paper. More specifically, as shown in  FIG. 5 , the holder support member  57  is positioned on the internal frame  58  by fitting protrusions  71  formed on the bottom surface of the holder support member  57  into holes (not shown) formed in the internal frame  58 . As shown in  FIG. 12 , a curved surface  69  (supporting surface) is formed on the top surface of the holder support member  57 . The top surface  69  supports the bottom surface (support part) of the pinch roller holder  56  via roller bearings  80  interposed therebetween. 
   As shown in  FIG. 11 , the top surface  69  of the holder support member  57  slopes downward from the upstream side to the downstream side in the conveying direction. The top surface  69  has an arc shape that substantially conforms to the outer periphery of a cylindrical path about the center of revolution O, where the center of revolution O is parallel to a rotational center A of the drive roller  47  and exists in a vertical plane passing through the rotational center A. Hence, the pinch roller holder  56  moves along a path about the center of revolution O by rolling over the top surface  69 . Since the springs  61  urge the pinch rollers  48  at this time, the pinch rollers  48  move over the peripheral surface of the drive roller  47  while constantly pressing against the drive roller  47 . The center of revolution O does not necessarily have to exist in a vertical plane passing through the rotational center A, provided that the center of revolution O is positioned so that the distance between the center of revolution O and the curved top surface  69  is greater than the distance between the rotational center B and the curved top surface  69  of the holder support member  57 . 
   As shown in  FIGS. 9 and 10 , the roller bearing  80  is configured of two rollers  81  juxtaposed in parallel along the short dimension of the holder support member  57 , and a roller support member  82  for rotatably supporting the two rollers  81  together. The roller support member  82  is mounted on the top surface  69  of the holder support member  57  with the rollers  81  supported therein. Specifically, engaging pawls  83  having a substantially L-shaped cross section are formed one on each longitudinal end of the roller support member  82 . The roller bearing  80  is mounted by engaging the engaging pawls  83  in engagement parts  72  formed in the top surface  69 . As shown in the drawings, four of the roller bearings  80  are mounted at predetermined intervals along the longitudinal direction of the holder support member  57 . By interposing roller bearings  80  having this structure between the pinch roller holder  56  and the top surface  69  of the holder support member  57 , the pinch roller holder  56  is rollingly supported on the top surface  69 . However, while the illustrative aspects give one example of using the roller bearings  80  as a support structure for rollingly supporting the pinch roller holder  56 , it is possible to employ another structure that integrally provides freely rotatably rotary members on the top surface  69  of the holder support member  57  or the bottom surface of the pinch roller holder  56 . For example, it is conceivable to incorporate roller bearings or ball bearings well known in the art in the top surface  69  or the bottom surface of the pinch roller holder  56 . Instead of employing rotary bodies such as the rollers  81 , it is possible to vary the structure so that the pinch roller holder  56  slidingly moves over the holder support member  57 , for example. 
   Four of the engaging grooves  67  are formed in the top surface  69  of the holder support member  57  for engaging with the protruding pieces  68  described above. The engaging grooves  67  are formed sufficiently longer in the short dimension of the pinch roller holder  56  than the length of the protruding pieces  68  in the same direction. Ribs  73  extending upward from the top surface  69  of the holder support member  57  are formed on the rear ends of the engaging grooves  67 , continuing upward from the inner wall and rear side of the engaging grooves  67 . The ribs  73  function to restrict rearward movement of the pinch roller holder  56 . When the pinch roller holder  56  is supported on the holder support member  57  so as to be capable of moving in the short dimension of the holder support member  57  while the protruding pieces  68  are engaged with the engaging grooves  67 , forward movement of the pinch roller holder  56  is restricted when the front ends of the protruding pieces  68  contact inner walls  67 A on the front sides of the engaging grooves  67 , and rearward movement of the pinch roller holder  56  is restricted by the rear ends of the protruding pieces  68  contacting the ribs  73 . In the illustrative aspects, the movable range of the pinch roller holder  56  in the short dimension of the holder support member  57  is restricted between a conveying position and a retracted position. As shown in  FIG. 11 , the conveying position is the position of the pinch roller holder  56  when a line connecting the center of revolution O and the rotational center B of the pinch roller  48  on the rear side of the drive roller  47  forms an angle θ 1  with a vertical plane passing through the center of revolution O, and the retracted position is the position of the pinch roller holder  56  when a line connecting the center of revolution O and the rotational center B of the pinch roller  48  forms an angle θ 2  (&gt;θ 1 ) with the same vertical plane. With this configuration of the pinch roller holder  56  and holder support member  57 , the pinch roller holder  56  moves to the conveying position when the conveying rollers  54  are pinching and conveying a recording paper, and moves to the retracted position when the trailing edge of the recording paper comes out of the conveying rollers  54 . 
   The through-hole  76  is formed in the top surface  69  of the holder support member  57  for inserting the detection member  74 . The through-hole  76  is formed through the bottom surface of the holder support member  57  and is elongated in the short dimension (the front-to-rear direction) of the holder support member  57 . The length of the through-hole  76  in the short dimension of the holder support member  57  is sufficiently longer than the length of the detection member  74  in the same direction so that the detection member  74  can move in a range at least equal to the movable range of the pinch roller holder  56  supported on the holder support member  57 . 
   With this construction of the pinch roller holder  56  and holder support member  57 , the pinch roller holder  56  rollingly moves toward the conveying position when the recording paper is interposed in the conveying rollers  54 . As the pinch roller holder  56  rollingly moves, the detection member  74  retracts from the optical path in the photointerrupter  75 . Further, the pinch roller holder  56  rollingly moves toward the retracted position when the trailing edge of the recording paper leaves (separates from) the conveying rollers  54 . As the pinch roller holder  56  rollingly moves, the detection member  74  moves into the optical path of the photointerrupter  75 , blocking the transmission of light therein. 
   In this way, the multifunction device  1  detects the timing at which the recording paper becomes interposed between the conveying rollers  54  based on the movement of the pinch roller holder  56 . Since the conveying rollers  54  (more specifically, the pinch rollers  48 ) immediately move in the paper-conveying direction when the paper becomes interposed between the conveying rollers  54 , the leading edge of the paper is not bent backward or otherwise deformed. Therefore, this construction improves detection accuracy by preventing irregular detection timings caused by differences in the types of sheets, such as between thick paper and thin paper. Further, since the conveying position of the recording paper is detected based on the timing in which the paper is gripped by the conveying rollers  54 , there are no irregularities in detection timing, even when different sheets of paper follow different paths due to differing degrees and directions of warpage in the leading edge of the paper. 
   Next, the rolling principle of the pinch roller holder  56  will be described with reference to  FIGS. 12 and 13 .  FIG. 12  is an explanatory diagram illustrating a cross section of the drive roller  47  and pinch roller  48  in an XY coordinate system having the center of revolution O as the point of origin. Fig,  13  is an explanatory diagram showing the state of the recording paper interposed in the structure of  FIG. 12 . In these drawings, the drive roller  47  has a rotational center A and a radius r 1 , and the pinch roller  48  has a rotational center B and a radius r 2 . The rotational center A is positioned on the X-axis, with the point of origin O at a position separated a distance greater than the radius r 1  of the drive roller  47  in the −X direction from the rotational center A. The point of origin O conforms to the center of a cylindrical path including the top surface  69 , that is, the center of revolution O. The pinch roller holder  56  can rollingly move about the point of origin O between a position D rotated the angle θ 1  from the X-axis in the counterclockwise direction, and a position E rotated an angle θ 2  (&gt;θ 1 ) from the X-axis in the same direction. Here, the position D corresponds to the conveying position, while the position E corresponds to the retracted position. In other words, an imaginary plane (a plane including the X-axis and perpendicular to the surface of  FIG. 13 ) including the rotational axis A of the drive roller  47  and the center of revolution O is defined, and the pinch roller holder  56  is rollingly movable about the center of revolution O between: the position D that is rotated the angle θ 1  (θ 1 ≧0 in the illustrative aspects) from the X-axis toward upstream in the conveying direction; and the position E, that is rotated the angle θ 2  (θ 2 &gt;θ 1 ) from the X-axis toward upstream in the conveying direction. For explanatory purposes, the centers O, A, and B shown in  FIGS. 12 and 13  have been defined in the illustrative aspects, but it should be apparent that the center positions of the drive roller  47 , pinch roller  48 , and the curved top surface  69  are not limited to these positions. 
   In this description, an angle formed by line segments OA and OB when the pinch rollers  48  are moved to an arbitrary position will be referred to as θ, where the angle θ may fall within the range θ 1 ≦θ≦θ 2 . The springs  61  accommodated in the pinch roller holder  56  in a compressed state urge the pinch rollers  48  toward the drive roller  47  (along the line segment AB). 
   As shown in the drawings, when θ&gt; 0 , the center O of the arc DE does not match the center A of the drive roller  47  about which the pinch roller  48  moves. Therefore, as θ grows larger, the pinch roller holder  56  gradually separates from the drive roller  47 , allowing the springs  61  to extend. Hence, an elastic energy E of the springs  61  decreases as θ grows larger. At this time, a moment M 1  acts on the pinch rollers  48  in the counterclockwise direction about the center of rotation A, that is, a direction orthogonal to the line segment AB. The magnitude of the moment M 1  is proportional to a decrease dE/dθ in the elastic energy E. 
   At the same time, a frictional force (frictional moment) M 2 ′ is produced in the pinch rollers  48  in the direction opposite this rotational direction about the rotational center B as the pinch rollers  48  follow the rotation of the drive roller  47 . Here, M 2  is defined as a moment found by converting the frictional force M 2 ′ to a force about the center of rotation A, that is, a direction orthogonal to the line segment AB. The frictional force M 2 ′ generated at this time is a static frictional force produced on the sliding surfaces of the pinch rollers  48  and rotational shafts  65  as the pinch rollers  48  rotate. The moment M 2  is not indicated in  FIG. 12 . 
   Further, a rolling frictional force (frictional moment) M 3 ′ is generated when the pinch roller holder  56  rolls over the top surface  69  of the holder support member  57 . The rolling frictional force M 3 ′ acts about the center O, that is, in a direction orthogonal to the line segment OB. M 3  is defined as a moment obtained by converting the frictional force M 3 ′ to a force about the rotational center A, that is, in a direction orthogonal to the line segment AB. The moment M 3  is not shown in  FIG. 12 . 
   As shown in  FIG. 13 , a force W produced by the weight of the recording paper, an elastic force caused by flexing in the recording paper, and the like acts toward the center of the pinch rollers  48  when the drive roller  47  and pinch roller  48  convey the recording paper. This force W generates a moment M 4  in a direction where θ becomes smaller. As shown in  FIG. 13 , since the recording paper is conveyed toward the platen  34  at an angle θ above the platen  34  so as to press the paper against the platen  34 , the moment M 4  produced by the force W cannot be ignored. In this example, EI signifies the stiffness of the recording paper. 
   Further, the length of the springs  61  change by a thickness h of the recording paper when the leading edge of the paper becomes interposed between the drive roller  47  and pinch roller  48  or when the trailing edge comes out from the drive roller  47  and pinch roller  4 B. Specifically, when the leading edge becomes interposed between the drive roller  47  and pinch roller  48 , the springs  61  are contracted by the thickness h, and when the trailing edge leaves the drive roller  47  and pinch roller  48 , the springs  61  expand by the thickness h. Consequently, the elastic energy of the spring  61  also fluctuates at this time, producing a moment M 5  about the rotational center A of a magnitude proportional to dE/dθ, similar to the moment M 1  described above. 
   Since the angle θ (θ 1 ≦θ≦θ 2 ), the thickness h of the recording paper, and the stiffness EI of the recording paper are variables, the moment M 1  can be expressed by a function of θ and h, the moment M 4  by a function of θ and EI, and the moment M 5  as a function of h. While the moments M 2  and M 3  are also strictly speaking a function of θ and h, these values are much smaller than the moments M 1 , M 4 , and M 5  and will be treated as constants here. Hereinafter, functions of the angle θ will be expressed as M 1 (θ) and M 4  (θ). 
   In the illustrative aspects, the moments M 1  through M 5  must satisfy the following equations, assuming that no slippage occurs between the drive roller  47  and pinch roller  48  and that the frictional force between the drive roller  47  and pinch roller  48  and the frictional force between the pinch roller  48  and recording paper are sufficiently large. 
   Equation (1) applies when the drive roller  47  and pinch roller  48  are not conveying the recording paper. Here, the moment M 2  acts in the clockwise direction around the rotational center A, while the moment M 3  acts counterclockwise around the rotational center A.
 
 M 1(θ)+ M 3 &gt;M 2  (1)
 
   In this case, the pinch roller holder  56  retracts rearward while rolling upstream in the paper-conveying direction, and is maintained in the retracted position of θ=θ 2 . 
   When the recording paper arrives at the nip part between the drive roller  47  and pinch roller  48  and the leading edge of the recording paper is gripped by the rotating drive roller  47 , the function of equation (2) below applies. At this time, the moment M 3  acts counterclockwise around the rotational center A, while the moment M 5  acts clockwise around the rotational center A.
 
 M 1(θ)+ M 3 &lt;M 4(θ)+ M 5  (2)
 
   At this time, the pinch roller holder  56  rolls downstream in the paper-conveying direction and is maintained in the conveying position of θ=θ 1 . 
   The function in equation (3) below applies when the recording paper is being conveyed. At this time, the moment M 2  acts clockwise around the rotational center A, while the moment M 3  also acts clockwise around the rotational center A.
 
 M 1(θ)&lt; M 2 +M 3 +M 4(θ)  (3)
 
   Hence, the pinch roller holder  56  continues to be maintained in the conveying position of θ=θ 1 . 
   When the trailing edge of the recording paper comes out of the nip part between the drive roller  47  and pinch roller  48 , the following equation (4) applies. At this time, the moment M 3  acts clockwise around the rotational center A, while the moment M 5  acts counterclockwise around the rotational center A, as with the moment M 1 .
 
 M 1(θ)+ M 5 &gt;M 3  (4)
 
   As can be seen from equation (4), only a moment M 3  (right-hand side) acts as a frictional force in response to the moment M 1 (θ)+M 5  (left-hand side) produced when the trailing edge of the paper leaves the nip part between the drive roller  47  and pinch roller  48 . However, since the moment M 1 (θ)+M 5  for rolling toward the upstream side in the paper-conveying direction is greater than the moment M 3  for preventing this movement, the pinch roller holder  56  rollingly moves toward the upstream side. Here, the moment M 3  is a slight frictional force generated by the roller bearing  80 . In other words, the moment M 3  is very small compared to the moment M 1 (θ)+M 5 . Therefore, nearly all of the moment M 1 (θ)+M 5  acts to move the pinch roller holder  56  toward the upstream side. Hence, the pinch roller holder  56  is rollingly moved quickly. Once the pinch roller holder  56  is retracted to the retracted position, the pinch roller holder  56  is maintained in the retracted position of θ=θ 2 . 
   The following equation (5) applies when rotating the drive roller  47  in reverse after the trailing edge of the recording paper has left the drive roller  47  and pinch roller  48 , and even during abnormal cases in which the pinch roller holder  56  does not return to the retracted position of θ=θ 2 , thereby enabling the pinch roller holder  56  to roll to the retracted position of θ=θ 2 .
 
 M 1(θ)+ M 2 &gt;M 3  (5)
 
   In this case, the moment M 2  acts counterclockwise around the rotational center A, and the moment M 3  acts clockwise around the center O. 
   In the multifunction device  1  described above, the pinch roller holder  56  is rollingly supported via the roller bearing  80 . By providing the pinch rollers  48 , pinch roller holder  56 , the holder support member  57 , springs  61 , and the like, the pinch roller holder  56  immediately rollingly moves downstream in the conveying direction when the recording paper is gripped by the conveying rollers  54 , as established by the above equations (1)-(5). When the recording paper leaves the grip of the conveying rollers  54 , the pinch roller holder  56  immediately rollingly moves upstream in the conveying direction. Consequently, the detection member  74  immediately retracts from the photointerrupter  60 , enabling the conveyed position of the recording paper to be detected quickly and accurately. 
   While the invention has been described in detail with reference to the above aspects thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. For example, if a drive roller and follow roller designed for another purpose than to convey the recording paper are provided on the conveying path  23  in addition to the conveying rollers  54 , the invention can be applied to this follow roller. It should also be apparent that the invention may be applied to a pair of conveying rollers provided on an original conveying path formed in the ADF  6  and is not limited to the conveying path in the multifunction device  1 .