Patent Publication Number: US-8973913-B2

Title: Media conveyance device and printer

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a media conveyance device with a media separation roller that separates multifed sheet media, and to a printer having the media conveyance device. 
     2. Related Art 
     Devices having a media separation roller as a media separation mechanism to prevent multifeeding sheet media such as printing paper are known from the literature. The media separation roller is generally called a retard roller, and a mechanism having this roller is called a retard separation mechanism. When recording media are fed to the nipping point between the feed roller and the retard roller in this retard separation mechanism, the medium is advanced by the paper feed roller while a heavy feed load is applied to the media by friction from the retard roller. The retard roller deteriorates over time, including a drop in the media separation force due to wear. As a result, the retard roller is installed in the printer or other apparatus so that the retard roller can be replaced. 
     JP-A-H06-191670 and JP-A-2012-071918 disclose a sheet feeding device and a recording mechanism that have a replaceable retard roller. The sheet feeding device taught in JP-A-H06-191670 fastens the retard roller installation member to the device with screws, and the retard roller can be replaced by removing the screws. The recording device taught in JP-A-2012-071918 enables sliding the retard roller along the roller axis. To remove the retard roller from the paper path, the retard roller is slid from a fixed operating position to a replacement position. 
     Examples of apparatuses having a media conveyance device with a retard roller include printers with an automatic two-sided printing capability, scanners and facsimile machines with an automatic two-sided scanning function, and other electronic devices. Devices such as these may also have a reversing conveyance path for reversing the media. For example, after the front (first) side of the paper is printed in a printer with an automatic two-sided printing function, the front and back sides of the recording paper are reversed as the paper travels through a reversing paper path, the back (second) side is then printed. 
     The reversing paper path may be integrally assembled to the printer frame. A reversing unit having the reversing paper path may also be removably attached to the printer frame. JP-A-2010-280454 and JP-A-2010-274580 disclose an electronic device and a recording device having a removable reversing unit. 
     The retard roller replacement mechanism taught in JP-A-H06-191670 requires using a tool such as a screwdriver to replace the retard roller. Replacing the retard roller is therefore not simple. The retard roller replacement mechanism taught in JP-A-JP-A-2012-071918 requires sliding the retard roller along the roller shaft in order to replace the retard roller. This requires providing a slide mechanism for sliding the retard roller from the fixed position to the replacement position, and space sufficient to slide the retard roller, inside the paper path. This inhibits reducing the overall size of the apparatus. 
     The retard roller is also assembled so that it is pushed with a specific amount of pressure to the conveyance roller or the paper feed roller by a spring or other urging member. To replace the retard roller, the retard roller must be separated from the conveyance roller or paper feed roller in resistance to this pressure, and the retard roller removed while this pressure is relieved. Replacing the retard roller is therefore not easy because the retard roller must be removed and installed while pressure is applied. 
     SUMMARY 
     A media conveyance device and a printer with a media conveyance device according to the invention enable easily replacing the media separation roller without requiring much space. 
     A media conveyance device according to one aspect of the invention has a first media conveyance path that conveys a sheet medium; a second media conveyance path that conveys the medium and can change to an open state; a media conveyance roller and a media separation roller disposed in opposition with the first media conveyance path therebetween; and a roller installation unit to which the media separation roller is installed in a state enabling removing and installing the media separation roller from the second media conveyance path side. 
     The media conveyance device according to the invention enables replacing the media separation roller disposed to the first media conveyance path from the opened second media conveyance path. Compared with a configuration having an opening in the outside case for replacing the media separation roller, a large space can be easily provided in the opened conveyance path, and replacing the media separation roller is simplified. Providing a space such as an opening for replacing the media separation roller in the first media conveyance path is also not necessary. The first media conveyance path to which the media separation roller is disposed can therefore be compactly configured. 
     When the media conveyance device has a media guide surface defining the second media conveyance path, an opening is formed in the media guide surface, a media conveyance guide that covers the opening can be opened and closed, and the media separation roller can be removably installed through the opening to the roller installation unit. 
     A media conveyance device according to another aspect of the invention also has a roller holder unit supporting the media separation roller; and the roller holder unit is removably installed in the roller installation unit. 
     When directly replacing the media separation roller, the surface of the media separation roller can strike the roller installation unit and be damaged. Handling the media separation roller is also not easy when the size of the media separation roller is small. Because the unit to which the media separation roller is assembled is replaced in this aspect of the invention, there is little chance of damaging the media separation roller and replacing the roller is simplified. 
     Further preferably, the roller holder unit includes the media separation roller, an urging member that applies pressure urging the media separation roller toward the media conveyance roller, and a holder that supports the media separation roller and the urging member; and the roller installation unit includes a holder installation unit that removably supports the holder. 
     In a media conveyance device according to another aspect of the invention, the roller holder unit can be configured with the holder including a first holder and a second holder; the first holder supporting the media separation roller; the second holder connected to the first holder pivotably on an axis of holder rotation parallel to the axis of rotation of the media separation roller; and the urging member urging the first holder to the second holder in one direction of rotation around the axis of holder rotation. The roller installation unit can be configured with the holder installation unit including a first holder installation unit and a second holder installation unit; the first holder installation unit supporting the first holder rotatably around the axis of holder rotation and removably from a direction intersecting the axis of rotation of the media separation roller (such as perpendicular); and the second holder installation unit removably holding the second holder at a specific position of rotation on the axis of holder rotation. 
     The first holder supporting the media separation roller is urged by the urging member to pivot on the axis of holder rotation. When the roller holder unit is installed in the unit installation part, the first holder is attached to the unit installation part pivotably on the axis of holder rotation, and is urged in the direction of rotation by the urging force of the urging member. The media separation roller supported by the first holder is therefore held against the media conveyance roller with the specific pressure applied by the urging force. 
     An urging member for applying pressure pressing the media separation roller to the media conveyance roller is included in the roller holder unit. Installing and removing the media separation roller in resistance to pressure is therefore not necessary. Installing and removing the urging member that applies pressure to the roller is also not necessary when replacing the media separation roller. Installing and removing (replacing) the media separation roller is therefore simple. 
     Further preferably, the first holder in a media conveyance device according to another aspect of the invention has an engaging part that engages the second holder from the direction of rotation due to the urging force of the urging member. 
     Before installation to the unit installation part, the roller holder unit is held with the first holder and the second holder engaged by the urging force of the urging member. Handling the roller holder unit is therefore simple because the first and second holders will not rock independently and hit each other. Furthermore, because the first and second holders are rendered in unison, the roller holder unit can be easily positioned in the unit installation part. 
     In a media conveyance device according to another aspect of the invention, the first holder has a support shaft that defines the axis of holder rotation; the first holder installation unit has a channel that rotatably supports the support shaft, and a channel opening that is formed in the channel and opens in a direction intersecting the axis of rotation of the media separation roller (such as perpendicularly); the shape of the support shaft in a section perpendicular to the axis is a shape of which one side of the perpendicular direction is a wide part and the other side is a narrow part that is narrower than the wide part; and the width of the channel opening is a width that enables the narrow part of the support shaft to pass through and the wide part to not pass through. 
     The narrow part of the support shaft of the first holder in the roller holder unit can be positioned to the opening in the channel of the first holder installation unit in the unit installation part, and the support shaft can then be inserted to the channel. The first holder of the roller holder unit can therefore be easily attached to the first holder support unit of the unit installation part. 
     Further preferably, the second holder installation unit has an installation unit-side engaging part; the second holder has a holder-side engaging part that can engage the installation unit-side engaging part from the opposite direction as the direction of rotation around the axis of holder rotation; and the holder-side engaging part is elastically deformable in the direction releasing engagement with the installation unit-side engaging part. 
     When the support shaft of the first holder is inserted to the channel in the first holder support part, the first and second holders can rotate on the support shaft inserted to the channel (on the axis of holder rotation). The second holder is then rotated until the holder-side engaging part of the second holder passes the installation unit-side engaging part. As a result, the holder-side engaging part of the second holder can be engaged with the installation unit-side engaging part. The roller holder unit can thus be installed to the unit installation part by inserting the support shaft of the first holder to the channel in the first holder installation unit and then rotating the second holder after the support shaft is in the channel. To remove the roller holder unit from the unit installation part, the holder-side engaging part of the second holder is elastically deformed and removed from the installation unit-side engaging part, and the support shaft of the first holder is then removed from the channel. 
     The roller holder unit can be easily installed and removed from the unit installation part without using a screwdriver or other tools. To install and remove the roller holder unit from the unit installation part, the support shaft of the first holder is moved perpendicularly to the axis of holder rotation, and the second holder is rotated on the axis of holder rotation. Unlike when the media separation roller must be slid along the axis of the media separation roller, a large space for installing and removing the media separation roller is therefore not required in the part of the conveyance path where the media separation roller is located. 
     In a media conveyance device according to another aspect of the invention, the first holder has a holder-side contact part; and the unit installation part has an installation unit-side contact part that contacts the holder-side contact part of the first holder supported by the first holder installation unit, and can rotate the first holder in the opposite direction as the direction of rotation. 
     In some instances the media conveyance operation does not convey the media through a path passing the nipping part of the media conveyance roller and the media separation roller. In this event, the media separation roller is preferably removed from the media conveyance roller so that the feed load of the media separation roller does not act on the media conveyance roller. The media separation roller can be easily retraced by disposing a holder-side contact part to the first holder supporting the media separation roller, and retracting the first holder from the media conveyance roller side. 
     The invention can also be applied to a media conveyance device having a reversing unit with a reversing conveyance path that reverses the front and back sides of the media. The media conveyance device according to this aspect of the invention has a device unit; and a reversing unit attached to the device unit removably or pivotably on a predetermined opening and closing axis. The device unit includes a unit-side conveyance path that conveys the medium, a media storage unit that stores the media in a stack, and a media supply path that supplies the media from the media storage unit to the unit-side conveyance path. The reversing unit includes a reversing conveyance path that reverses the front and back of media conveyed from the unit-side conveyance path and returns the media to the unit-side conveyance path. The media supply path is the first media conveyance path; and part of the reversing conveyance path is the second media conveyance path. 
     Another aspect of the invention is a printer having the media conveyance device of the invention; and a print unit that prints on the media conveyed through the unit-side conveyance path of the media conveyance device. 
     Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an oblique front view of a printer according to the invention. 
         FIG. 2  is an oblique rear view of a printer according to the invention. 
         FIGS. 3A and 3B  are a vertical section view and a partial section view respectively of the printer shown in  FIG. 1 . 
         FIG. 4  is an oblique rear view of the printer in  FIG. 1  with the reversing unit open. 
         FIG. 5  shows the opening for replacing the retard roller. 
         FIGS. 6A and 6B  show the roller installation unit where the retard roller is installed. 
         FIG. 7  shows the roller installation unit with the retard roller installed. 
         FIGS. 8A ,  8 B,  8 C and  8 D show a roller holder unit. 
         FIGS. 9A ,  9 B and  9 C show a first holder. 
         FIGS. 10A ,  10 B and  10 C a second holder. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of the present invention is described below with reference to the accompanying figures. The following embodiment describes the invention applied to a printer having a reversing unit enabling two-sided (duplex) printing. The invention can obviously also be applied to devices other than printers, including scanners and facsimile machines having a reversing unit. The invention can also be applied to media conveyance devices that supply media to devices such as printers and scanners. 
     General Configuration of a Printer 
       FIG. 1  is an external oblique view from the front of an inkjet printer (“printer” below) according to this embodiment of the invention, and  FIG. 2  is an external oblique view of the printer from the back.  FIG. 3  ( a ) is a vertical section view and  FIG. 3  ( b ) is a partial section view of the internal configuration of the printer. 
     The general configuration of the printer  1  is described referring primarily to  FIG. 1  and  FIG. 2 . The printer  1  has a printer cabinet  2  and a reversing unit  3 . The printer cabinet  2  has a basically rectangular box-like shape that is long on the transverse axis X widthwise to the printer, and has a recess  4  in the middle of the back where the reversing unit  3  is installed. The reversing unit  3  is a unit for reversing the front and back sides of the printing paper (“paper” below), which is a form of sheet media, and then returning the reversed paper to the printer cabinet  2 . The reversing unit  3  is a reversing unit that can open and close as further described below, and can pivot on the bottom part on the vertical axis Z of the printer to open to the back of the printer on the longitudinal axis Y. 
     A paper cassette loading unit  5  is disposed to the front of the printer cabinet  2 . The paper cassette loading unit  5  opens to the front on the longitudinal axis Y at a position toward the bottom on the vertical axis Z in the front of the printer cabinet  2 . A paper cassette  6  can be loaded from the front into the paper cassette loading unit  5 . A paper discharge tray  7  is attached at the top of the paper cassette loading unit  5 . The paper discharge tray  7  extends substantially horizontally to the front. A rectangular paper exit  8  extending toward the back of the printer is formed at the top of the paper discharge tray  7 . 
     An operating panel  9  is at the front of the printer above the paper exit  8 . The operating panel  9  includes a power switch  9   a  and a plurality of state indicators  9   b . Rectangular access doors  10   a ,  10   b  are attached to the front of the printer on opposite sides of the paper discharge tray  7  and paper exit  8 . When the access doors  10   a ,  10   b  are open, the ink cartridge loading unit (not shown in the figure) opens and the ink cartridges (not shown in the figure) can be replaced. 
     The top of the printer is flat, and has an access cover  11  attached in the middle for maintenance. 
     Internal Configuration of the Printer 
     The internal configuration of the printer  1 , and particularly the paper conveyance path, is described next with reference to  FIG. 3 . A paper supply path  12 , main conveyance path  13 , and reversing conveyance path  14  are formed inside the printer  1 . The paper supply path  12  and main conveyance path  13  are formed inside the printer cabinet  2 , and the reversing conveyance path  14  is formed inside the reversing unit  3 . 
     The paper supply path  12  is a conveyance path that conveys paper P of a specific size stored in a stack in the paper cassette  6  to the main conveyance path  13 . The paper supply path  12  extends diagonally up from the back end of the paper cassette loading unit  5  on the longitudinal axis Y, curves toward the front, and connects to the main conveyance path  13 . Paper P stored in the paper cassette  6  is fed by a paper feed roller  15  to the paper supply path  12 . The supplied paper is fed one sheet at a time through the nipping part of a conveyance roller  17  and a retard roller  16 , which is a media separation roller. The paper supply path  12  is a first media conveyance path where the conveyance roller  17  and retard roller  16  are disposed with the paper supply path  12  therebetween. The paper P conveyed through the nipping part of the retard roller  16  and conveyance roller  17  is conveyed through the nipping part of the conveyance roller  17  and a follower roller  18  to the main conveyance path  13 . 
     The main conveyance path  13  is the conveyance path extending substantially horizontally along the longitudinal axis Y to the paper exit  8 . Disposed along the main conveyance path  13  from the upstream side in the paper conveyance direction are a paper detection lever  20 , a paper feed roller pair  21 , a printhead  22 , a first discharge roller pair  23 , and a second discharge roller pair  24 . The printhead  22  is an inkjet head, and a platen  25  is disposed opposite the nozzle face with a specific gap therebetween. 
     Paper fed from the paper supply path  12  to the main conveyance path  13  is conveyed by the conveyance roller  17  to the paper feed roller pair  21  while pushing up on the paper detection lever  20 . The paper fed into the paper feed roller pair  21  is conveyed past the printing position of the printhead  22  by the paper feed roller pair  21  toward the first discharge roller pair  23 . The paper fed to the first discharge roller pair  23  passes the first discharge roller pair  23  and second discharge roller pair  24 , and is discharged from the paper exit  8  onto the paper discharge tray  7 . 
     The reversing conveyance path  14  formed inside the reversing unit  3  is located below the main conveyance path  13  on the vertical axis Z, and is a conveyance path that generally forms a loop. The reversing conveyance path  14  includes an upstream path  26  that connects to the upstream end of the main conveyance path  13  and extends substantially horizontally to the back on the longitudinal axis Y, a descending path  27  that curves and extends down in a straight line on the vertical axis Z from the upstream path  26 , a bottom path  28  that connects to the descending path  27  and curves to the front on the longitudinal axis Y, and an ascending path  29  that curves and extends upward from the bottom path  28 . 
     The top part of the ascending path  29  curves at an angle to the printer front, and merges with the paper supply path  12  in the middle. More specifically, ascending path  29  and the downstream part of the paper supply path  12  form a common path  30 . This common path  30  is a curved path extending along the outside of the conveyance roller  17 . 
     A first conveyance roller  31  and a follower roller  32  are disposed between the upstream path  26  and the descending path  27 , and a second conveyance roller  33  and a follower roller  34  are disposed between the bottom path  28  and the ascending path  29 . Paper conveyed from the main conveyance path  13  to the reversing conveyance path  14  is nipped by the first conveyance roller  31  and follower roller  32 , then conveyed by the first conveyance roller  31  to the nipping part of the second conveyance roller  33  and follower roller  34 , and then conveyed by the second conveyance roller  33  to the nipping part of the conveyance roller  17  and follower roller  18 . The paper is then fed by the conveyance roller  17  to the main conveyance path  13  again. 
     By passing through the loop of this reversing conveyance path  14 , the paper is reversed front and back and returned to the main conveyance path  13 . Printing on both sides of the paper is therefore enabled by conveying the paper through the reversing conveyance path  14 . 
     A path-changing flapper  36  is disposed at the junction  35  of the upstream end of the main conveyance path  13 , the upstream end of the reversing conveyance path  14 , and the downstream end of the common path  30 . The path-changing flapper  36  can pivot up and down on the vertical axis Z at the back end of the flapper  36  on the longitudinal axis Y. The path-changing flapper  36  is normally held by its own weight in a first position with the main part of the flat at the front on the longitudinal axis Y resting on the outside of the conveyance roller  17 . 
     Paper reversed from the main conveyance path  13  side in this position is guided by the path-changing flapper  36  to the reversing conveyance path  14  side. The paper then passes through the reversing conveyance path  14  and returns to the junction  35 . The path-changing flapper  36  is pushed up by the paper returned to the junction  35 , and can move from the first position to a second position. When the path-changing flapper  36  is pushed up to the second position, the common path  30  at the downstream end of the reversing conveyance path  14  communicates with the main conveyance path  13 . The paper is therefore conveyed to the main conveyance path  13  while pushing the path-changing flapper  36  up. After the paper has past, the path-changing flapper  36  returns by its own weight to the first position. 
     The path-changing flapper  36  is also pushed up by the paper fed from the paper supply path  12  to the main conveyance path  13  when paper is supplied from the paper cassette  6 . After the paper passes, the path-changing flapper  36  returns of its own weight to the first position. Paper reversed from the main conveyance path  13  will therefore not go through the common path  30  into the reversing conveyance path  14  or the paper supply path  12 . The paper path can also be changed by a simple configuration without using a separate drive power source or urging member. 
     Openable Reversing Unit 
       FIG. 4  is an external oblique view from the back of the printer  1  when the reversing unit  3  is open. 
     As will be understood from  FIG. 2  and  FIG. 4 , the reversing unit  3  can open and close pivoting on a pivot axis  40  located at the bottom on the vertical axis Z of the printer. When in the closed position  3 A shown in  FIG. 2 , the reversing unit  3  is standing upright on the vertical axis Z, and the back cover  42  of the reversing unit case  41  is positioned substantially flush with the back left and right sides of the printer cabinet  2 . In the open position  3 B shown in  FIG. 4 , the reversing unit  3  is dropped to the back on the longitudinal axis Y to a substantially level position. In the open position  3 B, the ascending path  29  on the downstream side of the reversing conveyance path  14 , and the common path  30 , are open as will be understood from  FIG. 4 . Paper jams and other problems occurring on these conveyance paths can be easily handled by opening the reversing unit  3 . The common path  30  and the ascending path  29  portion of the reversing conveyance path  14  are an openable second media conveyance path. 
     As shown in  FIG. 2 , the reversing unit  3  has an opening  42   a  in the middle at the top of the back cover  42  on the vertical axis Z. A pair of lever operators  43  are exposed through this opening  42   a . When the pair of lever operators  43  is operated so that they close together, left and right lock pins  44  ( FIG. 4 ) protruding to the side from the left and right sides of the reversing unit  3  disengage matching catches  45  ( FIG. 4 ) formed in the left and right sides  4   a ,  4   b  of the recess  4  in the printer cabinet  2 . The reversing unit  3  is thus unlocked and can be opened. 
     Opening for Replacing the Retard Roller 
       FIG. 5  describes an opening for replacing the retard roller  16 . As shown in  FIG. 5 , the ascending path  29 , which is part of the reversing conveyance path  14 , and the common path  30  open when the reversing unit  3  is opened. Part of the outside surface of the conveyance roller  17 , which constitutes the conveyance path surface on the printer cabinet  2  side of the common path  30 , is also exposed. 
     The ascending path  29  is formed between a conveyance guide panel  61  disposed on the printer cabinet  2  side, and a conveyance guide panel  62  disposed on the reversing unit  3  side. Plural ribs  61   a ,  62   a  are formed extending parallel to the media conveyance direction on the surface of the conveyance guide panels  61 ,  62 . The conveyance guide surface on the printer side and the conveyance guide surface on the reversing unit side of the ascending path  29  are determined by the exposed outside surfaces of the ribs  61   a ,  62   a.    
     The conveyance guide panel  61  on the printer cabinet  2  side includes conveyance guide panels  63 ,  64  on opposite sides of the transverse axis X, and a conveyance guide panel  65  located therebetween. The conveyance guide panel  65  is positioned in the middle on the transverse axis X between the side conveyance guide panels  63 ,  64  and can be removed from the top on the vertical axis Z as shown in  FIG. 5 . In this example, a slide rail  65   a  is formed on both sides of the conveyance guide panel  65 , and plural guide tabs  67   a ,  67   b ,  67   c  that guide the slide rail  65   a  are formed on the inside faces of the conveyance guide panels  63 ,  64 . 
     Sliding the conveyance guide panel  65  up as indicated by the arrow in the figure and removing both conveyance guide panels  63 ,  64  opens the retard roller replacement opening  68  formed between the conveyance guide panels  63 ,  64 . The retard roller installation unit  70  that is installed in the printer cabinet  2  is accessible from the retard roller replacement opening  68 . A roller holder unit  90  that holds the retard roller  16  ( FIG. 3 ) is removably installed to the retard roller installation unit  70 . The roller holder unit  90  is installed in the retard roller installation unit  70  so that the roller holder unit  90  can be removed through the retard roller replacement opening  68  from the open reversing conveyance path  14  (ascending path  29 ) side. Because the retard roller  16  is installed as a unit in the retard roller installation unit  70  in this embodiment, the retard roller installation unit  70  is also referred to as a unit installation part  70  below. The roller holder unit  90  is also referred to as simply unit  90 . 
       FIG. 6A  and  FIG. 6B  describe removing the roller holder unit  90  from the retard roller installation unit  70 . The operation of removing the unit  90  from the unit installation part  70  is described below with reference to  FIG. 4 ,  FIG. 5 , and  FIG. 6A  and  FIG. 6B  before describing the specific configuration of the unit installation part  70  and unit  90 . 
     To remove the unit  90  from the unit installation part  70 , the user first opens the reversing unit  3  as shown in  FIG. 4 . Next, the conveyance guide panel  65  is pulled up as indicated by the arrow in  FIG. 5 , and removed from the printer cabinet  2 . Next, as indicated by the arrow in  FIG. 6A , the engaging plate  123  (holder-side engaging part) of the unit  90  is elastically deformed as indicated by the arrow in  FIG. 6A , and the engaging plate  123  is raised and removed from the engaging channel  77  (installation unit-side engaging part) of the unit installation part  70 . When the engaging plate  123  is lifted up and removed from the engaging channel  77 , the unit  90  can rotate upward as indicated in  FIG. 6B  pivoting on pivot pins  104  formed on opposite sides at the top. When the roller holder unit  90  rotates up a specific distance, the pivot pins  104  can be pulled out to the back from channels  73  on the unit installation part  70  side. When the pivot pins  104  of the roller holder unit  90  are removed from the channels  73  in the retard roller installation unit  70 , the unit  90  can be completely removed from the retard roller installation unit  70  and removed from the printer cabinet  2  through the retard roller replacement opening  68 . 
     Roller Holder Unit and Retard Roller Installation Unit 
     The roller holder unit  90  and retard roller installation unit  70  are further described below with reference to  FIG. 7 ,  FIG. 8 ,  FIG. 9 , and  FIG. 10 .  FIG. 7  shows the retard roller installation unit  70  to which the roller holder unit  90  is installed on the printer cabinet  2  side.  FIG. 8A  to  FIG. 8D  are, respectively, a front oblique view, rear oblique view, side view, and section view of the roller holder unit  90 .  FIG. 9A  to  FIG. 9C  are, respectively, a front oblique view, rear oblique view, and side view of a first holder, which is a part of the roller holder unit  90 .  FIG. 10A  to  FIG. 10C  are, respectively, a front oblique view, rear oblique view, and side view of a second holder that is also part of the roller holder unit  90 . 
     The longitudinal axis, transverse axis, and vertical axis of the roller holder unit  90  when installed in the printer cabinet  2  are the same as the longitudinal axis Y, transverse axis X, and vertical axis Z of the printer. The unit  90  in this example is symmetrically shaped left and right on the transverse axis, and made from parts that are symmetrical left and right. Left and right parts are therefore identified by the same reference numerals. 
     The general configuration of the roller holder unit  90  is described below with reference to  FIG. 8 . The roller holder unit  90  includes the retard roller  16 , a first holder  100 , a second holder  110 , and a tension spring  130 . The first holder  100  supports the retard roller  16 . The first holder  100  is connected to the second holder  110  and can rotate on an axis of holder rotation  100   a  that is parallel to the axis of rotation  16   a  of the retard roller  16 . The tension spring  130  spans between the first holder  100  and the second holder  110 . The first holder  100  is urged to pivot relative to the second holder  110  in a first direction of rotation A, which is clockwise in the figure, on the axis of holder rotation  100   a . An engaging pin  105  is disposed on each side of the first holder  100 . The engaging pins  105  are engaged with the engaging surfaces  118   a  on each side of the second holder  110  from the first direction of rotation A by the tension of the tension spring  130 . 
     The configuration of the first holder  100  is described next with reference to  FIG. 8  and  FIG. 9 . The first holder  100  has end plates  101  extending parallel to the longitudinal axis of the holder with a specific gap therebetween. Each end plate  101  has a header  102  with a basically triangular contour that increases in width from the top to the bottom on the vertical axis. A through-shaft  103  extends on the transverse axis perpendicularly to the header  102  between the top corners of the headers  102 . The pivot pins  104  protrude to the outside from the outside surfaces of the end plates  101  coaxially to the through-shaft  103 . The part of the pivot pin  104  connected to the end plate  101  is a round shaft portion  104   a , and the distal end of the round shaft portion  104   a  is a flat  104   b  that is flat and bends to one side when seen in section. More specifically, the shape of the flat  104   b  when seen in section perpendicularly to the axis of the pivot pin  104  is wide on one side and narrow on the other side in the direction perpendicular to the axis. The sides of the flat  104   b  are curved surfaces with the same outside diameter as the round shaft portion  104   a.    
     The retard roller  16  (see  FIG. 8 ) is disposed on the transverse axis perpendicularly to and between the corners of the headers  102  protruding at the front of the end plates  101 . An engaging pin  105  is formed parallel to the axis of holder rotation  100   a  at a position at the back of the header  102  of the end plate  101 . 
     A rectangular leg  106  extends down from the back bottom part of the header  102  of the end plate  101 . A holder-side contact pin  107  is formed extending parallel to the axis of holder rotation  100   a  on the outside surface of the leg  106 . The front outside surface of the holder-side contact pin  107  is a curved contact surface  107   a . The tops of the legs  106  of the left and right end plates  101  are connected by a connection plate  108  extending perpendicularly to the endplates  101 . A rear spring catch  109  is formed extending down from the middle of the width of the connection plate  108 . The back end  132  on the longitudinal axis of the tension spring  130  is mounted from the back on the rear spring catch  109 . 
     The configuration of the second holder  110  is described next with reference to  FIG. 8  and  FIG. 10 . The second holder  110  is a holder of a width enabling it to be placed between the left and right end plates  101  of the first holder  100 . The second holder  110  has a back panel  111  that curves in the middle on the vertical axis. The access cover  11  has a rectangular bottom back portion  112 , a horizontal portion  113  that bends perpendicularly to the front from the top end of the bottom back portion  112 , and a top back portion  114  that bends perpendicularly up from the front edge of the horizontal portion  113 . A top ceiling member  115  bends perpendicularly to the front from the top edge of the top back portion  114 . A rectangular opening  112   a  is formed in the middle of the width of the bottom back portion  112 . A rectangular opening  113   a  is also formed in the middle of the width from the horizontal portion  113  to the bottom of the top back portion  114 . The top back portion  114  is wider at the top than the bottom. A triangular reinforcing rib  116  is formed on the front of the back panel  111  extending vertically between the top ceiling member  115  and the top back portion  114 . Another triangular reinforcing rib  117  is formed on the back of the back panel  111  extending vertically between the horizontal portion  113  and the top back portion  114 . 
     An end panel  118  is formed on each side of the width of the back panel  111 . The end panels  118  are formed to connect the bottom part of the top back portion  114  to the corresponding ends of the top ceiling member  115 . A shaft connector  119  formed to each end panel  118  projects up from the top ceiling member  115 . Each shaft connector  119  forks to the front and back, and has a round channel  120  that is open to the top formed at the top end. The through-shaft  103  of the first holder  100  is rotatably inserted from above into the channels  120 . The through-shaft  103  inserted to the channels  120  is held in the channel  120  by the elastic restoring force of the shaft connector  119 . As a result, the first holder  100  and second holder  110  are held together and can pivot relative to each other on the axis of holder rotation  100   a.    
     The engaging surfaces  118   a  are formed to the part of the end panels  118  corresponding to the narrow top part of the top back portion  114 . The engaging surfaces  118   a  are end surfaces that face the back, and can be engaged by the matching engaging pin  105  of the first holder  100  from the back. 
     A spring mount  121  extending straight to the front is formed to the front of the bottom back portion  112  of the back panel  111 . The spring mount  121  is a rectangular channel that is open at the top. A front spring catch  122  is formed protruding up at the front end of the spring mount  121 . The opening  112   a  in the bottom back portion  112  is positioned at the back end of the spring mount  121 . As will be understood from  FIG. 8 , the tension spring  130  is mounted in the spring mount  121 , and the front end  131  of the tension spring  130  is held by the front spring catch  122  from the front. 
     The engaging plate  123  is formed extending at a downward angle to the back at a position near the longitudinal center of the bottom  121   a  of the spring mount  121 . The distal end of the engaging plate  123  is notched on both sides, forming a narrow engaging part  123   a . The engaging plate  123  can elastically deform in the direction approaching the bottom  121   a  of the spring mount  121 . 
     Assembling the first holder  100 , second holder  110 , and tension spring  130  is described next with reference to  FIG. 8 . The second holder  110  is first inserted between the end plates  101  of the first holder  100  from the back of the first holder  100 . The through-shaft  103  of the first holder  100  is pressed from above into the channel  120  of the second holder  110 , and the first and second holders  100 ,  110  are thereby connected pivotably relative to each other around the axis of holder rotation  100   a . The engaging pins  105  of the first holder  100  are positioned behind the engaging surfaces  118   a  of the second holder  110 . The rear spring catch  109  formed to the connection plate  108  of the first holder  100  is positioned near the back end of the spring mount  121  of the second holder  110 . 
     The front end  131  of the tension spring  130  is mounted on the front spring catch  122  of the second holder  110 , and the back end  132  is mounted on the rear spring catch  109  of the first holder  100 . The tension spring  130  is held in a specifically tensioned state by the front and back spring catches  122 ,  109 . The first holder  100  is urged to pivot on the axis of holder rotation  100   a  to the second holder  110  in the first direction of rotation A by the spring tension of the tension spring  130 . In other words, the second holder  110  is pressed to the first holder  100  from the front. As a result, the engaging pins  105  of the first holder  100  contact and engage the engaging surfaces  118   a  of the second holder  110  from the back. The first holder  100  and second holder  110  are thus assembled together with no play therebetween in the roller holder unit  90 . 
     The configuration of the retard roller installation unit  70  disposed on the printer cabinet  2  side is described next with reference to  FIG. 5  to  FIG. 8 . As will be understood from  FIG. 5  and  FIG. 6 , the unit installation part  70  is disposed between the conveyance guide  71  on the printer cabinet  2  side opposite the conveyance roller  17 , and the conveyance guide panel  61  on the reversing unit  3  side. Conveyance guide  71  defines one paper conveyance surface of the paper supply path  12 , and conveyance guide panel  61  defines one paper conveyance surface of the ascending path  29  part of the reversing conveyance path  14 . A wide roller  17   b  that is wider than the rollers  17   a  on either side is disposed to the middle of the conveyance roller  17  in the transverse direction. An opening is formed in the part of the conveyance guide  71  opposite the wide roller  17   b . When the unit  90  is installed in the unit installation part  70  through the opening  68  formed in the conveyance guide panel  61  positioned on the back side of the conveyance guide  71 , the retard roller  16  is opposite the wide roller  17   b  part of the conveyance roller  17 . 
     As will be understood from  FIG. 7 , channel  73  is formed as a first holder installation unit in the top on both sides of the width of the unit installation part  70 . The channels  73  pivotably and removably support the pivot pins  104  of the first holder  100  of the unit  90 . The channels  73  are formed on both sides of the opening  68 , and are open to the back of the printer. The inside diameter of the channels  73  is sized to support the pivot pins  104  rotatably. The opening to the channels  73  facing the back of the printer includes a wide shaft opening  73   a  to which the round shaft portion  104   a  of the pivot pins  104  can be inserted, and a narrow shaft opening  73   b  to which the narrow part of the flat  104   b  of the pivot pins  104  can be inserted. As will be understood from  FIG. 8A , the flats  104   b  of the pivot pins  104  are shaped to rise at an angle to the front when seen in section view perpendicularly to the axis of the pivot pin  104 . Therefore, as shown in  FIG. 6B , if the roller holder unit  90  is tilted so that the flats  104   b  of the pivot pins  104  are substantially horizontal, the pivot pins  104  can be inserted to the channels  73 . If the unit  90  is then rotated around the pivot pins  104  as shown in  FIG. 6A  to the vertical position after inserting the pivot pins  104  to the channels  73 , the pivot pins  104  are prevented from exiting the channels  73 . 
     A second holder engaging part  74  is disposed as a second holder installation unit to the bottom of the unit installation part  70 . The second holder engaging part  74  has a rectangular engaging channel  77  formed by a bottom plate  75  and a pair of end panels  76 . The bottom plate  75  is a flat panel extending in the longitudinal axis of the printer, and the end panels  76  extend vertically upward from both back end sides of the bottom plate  75 . The engaging channel  77  is open along the longitudinal axis of the printer, and the width of this opening is narrower than the engaging plate  123  of the second holder  110  and wider than the engaging part  123   a  formed at the distal end of the engaging plate  123 . 
     The vertical distance from the channels  73  in the unit installation part  70  to the top edge of the engaging channel  77  (the top edge of the end panels  76 ) is shorter than the vertical distance from the channel  120  in the second holder  110  to the engaging part  123   a . When the pivot pins  104  of the unit  90  are inserted to the channels  73  of the retard roller installation unit  70 , and the unit  90  is rotated on the pivot pins  104  toward the front of the printer, the engaging plate  123  of the unit  90  contacts the end panels  76  of the unit installation part  70 . Because the engaging plate  123  can deform elastically, the unit  90  can be pivoted to the vertical installation position to the unit installation part  70  as shown in  FIG. 7  by elastically deforming the engaging plate  123  upward. When the engaging plate  123  returns elastically to the original position, the engaging part  123   a  on the distal end thereof can engage the engaging channel  77  from the front. 
     The retard roller  16  of the installed unit  90  is pressed by the spring force of the tension spring  130  to the wide roller  17   b  of the conveyance roller  17 . More specifically, because the tension of the tension spring  130  is applied between the first and second holders  100 ,  110 , the first holder  100  is urged toward the front of the printer. The retard roller  16  of the unit  90  installed in the unit installation part  70  is held in a position pressed to the wide roller  17   b  of the conveyance roller  17  by the urging force of the tension spring  130 . As a result, the engaging plate  123  of the second holder  110  receiving the spring force is engaged from the front by the engaging channel  77 , and is held stationary in the unit installation part  70 . The first holder  100  supporting the retard roller  16  can pivot relative to the unit installation part  70  around the axis of holder rotation  100   a  in resistance to the spring force. 
     The printer  1  according to this embodiment of the invention also has a retraction mechanism  140  for separating the retard roller  16  from the conveyance roller  17 . As shown in  FIG. 7 , the retraction mechanism  140  has a pivot arm  141  on each side of the unit installation part  70 , a pivot shaft  142  to which the pivot arms  141  are attached, and a drive mechanism  143  that causes the pivot shaft  142  to turn. The pivot arm  141  has contact surfaces  141   a  facing the back of the printer. The first holder  100  of the unit  90  has a contact pin  107  on both sides. When the unit  90  is installed to the unit installation part  70 , the contact pins  107  of the first holder  100  oppose the contact surfaces  141   a  from the back. 
     When the retraction mechanism  140  is driven and the pivot arms  141  rotate to the back, the contact surfaces  141   a  contact the contact surfaces  107   a  of the contact pins  107  of the first holder  100 . As the pivot arms  141  continue turning, the first holder  100  is rotated to the back on the axis of holder rotation  100   a  in resistance to the urging force of the tension spring  130 . As a result, the retard roller  16  supported by the first holder  100  moves to the back away from the conveyance roller  17 . The retard roller  16  is thus retracted so that the retarding load of the retard roller  16  does not act on the conveyance roller  17  when the paper P is conveyed through the reversing conveyance path  14  and returned to the main conveyance path  13 , for example. 
     As described above, the printer  1  according to the invention has an opening  68  for replacing a retard roller disposed to a reversing conveyance path  14  that opens when the reversing unit  3  is opened. This opening  68  is covered by a conveyance guide panel  65  that defines a conveyance guide surface. To replace the retard roller  16 , the reversing unit  3  is opened, the conveyance guide panel  65  removed, and the opening  68  opened. The unit  90  installed in the unit installation part  70  is thus exposed (see  FIG. 5 ). 
     When the engaging part  123   a  of the unit  90  is elastically deformed upward, the engaging part  123   a  separates from the engaging channel of the unit installation part  70 . By holding the engaging part  123   a  and rotating the unit  90  up, the pivot pins  104  of the unit  90  can be removed to the back from the channels  73  of the unit installation part  70  (perpendicularly to the axis of holder rotation). By then pulling the unit  90  out to the back, the unit  90  can be removed from the unit installation part  70  (see  FIG. 6 ). 
     Apart of the conveyance path that opens can thus be used to replace a retard roller  16  that is disposed to the paper supply path  12  near this part of the conveyance path. Because the open part of the conveyance path is used to replace the retard roller, replacing the retard roller is simple. There is also no need to provide space for replacing the retard roller in the part of the conveyance path where the retard roller  16  is located. The size of the printer  1  can therefore be reduced because more space is not needed at the part of the conveyance path where the retard roller  16  is located. Retard roller replacement is further simplified because a large opening can be provided more easily than when space for replacing the retard roller is provided in the outside case of the printer  1 . Yet further, because this opening can be covered by a conveyance guide panel, the configuration for opening and closing the opening can be simplified compared with when the opening is provided in the outside case. 
     The roller holder unit  90  in this example includes first and second holders  100 ,  110  that are connected to rotate relative to each other around pivot pins  104 , and a tension spring  130  disposed in tension between the first and second holders. The engaging plate  123  also has an engaging part  123   a , and the unit  90  can be installed to and removed from the unit installation part  70  by elastically deforming the engaging part  123   a . When the unit  90  is installed in the unit installation part  70 , the second holder  110  is held stationary, and the first holder  100  can rotate on the axis of holder rotation  100   a . Furthermore, because the first holder  100  is urged toward the conveyance roller  17  by the tension spring  130 , the retard roller  16  supported by the first holder  100  is urged toward the conveyance roller  17 . 
     The unit  90  can thus be easily installed to and removed from the unit installation part  70  by using the engaging part  123   a . A tension spring  130  that exerts an urging force pushing the retard roller  16  toward the conveyance roller  17  is included in the unit  90 . The unit  90  can be easily installed and removed because installing and removing the unit  90  does not require overcoming this urging force. In addition, the urging force of the tension spring  130  holds the engaging pins  105  of the first holder  100  in contact with the engaging surfaces  118   a  of the second holder  110  when the unit  90  is not installed. The first and second holders  100 ,  110  are thus held together with no play therebetween, and the unit  90  is easier to handled when not installed. 
     The invention being thus described, it will be obvious that it may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.