Abstract:
A simple configuration avoids exposure of a star wheel that prevents the media from lifting up when the media conveyance path opens. A platen top unit  20  that supports first and second star wheels  25 A,  25 B is separated from an opening and closing platen unit  8 , and is supported movably vertically. when the platen unit  8  is moved to the open position  8 B to open the third conveyance path section  10   c  of the conveyance path  10  when a paper jam occurs, for example, the head elevator  17  is controlled to raise the platen top unit  20  and retract the first and second star wheels  25 A,  25 B supported by the platen top unit  20  to a position removed from easy contact with the user&#39;s hands.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a printer having a star wheel to prevent sheet media from lifting up. 
         [0003]    2. Related Art 
         [0004]    A star wheel having protrusions formed at a regular pitch around the outside is commonly used in printers to prevent sheet media from separating from the platen surface and other parts of the media conveyance path (such as the conveyor belt). JP-A-H04-164766 describes such a printer. The image forming device (printer) described in claim JP-A-H04-164766 has a star wheel rotatably attached to a movable shaft that spans the gap between lever-shaped support brackets. When the top of the device closes, the protrusions on the star wheel contact the paper (media) on the conveyance surface of the paper conveyor belt, and prevent the media from lifting away from the surface. 
         [0005]    The conveyance path of the printer opens and closes to remove paper jams or for other maintenance. In a printer that holds media down with a star wheel, the star wheel may be exposed to the space that is opened when the conveyance path is opened. When the star wheel is exposed, the operator&#39;s hand or the jammed paper may contact the star wheel, the star wheel may be damaged, and ease of maintenance may drop. 
         [0006]    The star wheel in the printer described in JP-A-H04-164766 is covered by the support brackets when the conveyance path is opened. More specifically, the movable shaft on which the star wheel is mounted can move inside a slot formed in the support brackets, and when the top unit is opened, the support brackets descend of their own weight and move to a position below the star wheel. As a result, the star wheel is covered by the support brackets so that it won&#39;t be touched by the operator&#39;s hand. 
         [0007]    The construction described in JP-A-H04-164766, however, requires a member (the support brackets) to cover the star wheel to prevent exposing the star wheel, the parts count therefore increases, and construction is complicated. 
         [0008]    The present invention provides a printer with a simple configuration that prevents a star wheel used to prevent media from lifting up from being exposed to the conveyance path when the conveyance path is opened. 
       SUMMARY 
       [0009]    A printer according to the invention has: a printhead; a platen unit that has a platen surface that supports sheet media, and moves between a head-opposing position where the platen surface is opposite the printhead with a specific gap therebetween, and an open position separated from the printhead more than at the head-opposing position; and a star wheel support member that is located above the platen unit at the head-opposing position and supports a star wheel that suppresses the media. The star wheel support member is movable between a first position in contact with the platen unit, and a second position separated from the platen surface more than at the first position. 
         [0010]    In this aspect of the invention, the star wheel support member can move in the direction away from the platen surface, and can retract the star wheel from the media conveyance path between the printhead and platen surface. Thus comprised, exposure of the star wheel to the media conveyance path can be prevented when the platen unit is moved to the open position and the media conveyance path is opened. Damage to the star wheel and a drop in ease of use can be avoided. The parts configuration can also be simplified because there is no need for a member to cover the star wheel or a mechanism to move such member. 
         [0011]    Preferably, the printer has a support frame that supports the star wheel support member movably to the first position and the second position; and a spring disposed between the support frame and the star wheel support member, and urging the star wheel support member to the second position. 
         [0012]    Thus comprised, the star wheel support member can be supported retractably from the media conveyance path by a simple configuration. 
         [0013]    Further preferably, the support frame has a first frame disposed on one side of the platen unit, and the first frame has a first opening extending in the direction of movement of the star wheel support member; a first protrusion disposed in the first opening is formed in one end of the star wheel support member; and the spring includes a first spring that urges the first protrusion from the first position toward the second position. 
         [0014]    Thus comprised, the star wheel support member can be supported movably to a first position and a second position by a simple configuration. 
         [0015]    Further preferably, the support frame has a second frame disposed on the other side of the platen unit, and the second frame has a second opening extending in the direction of movement of the star wheel support member; a second protrusion disposed in the second opening is formed on the other end of the star wheel support member; and the spring includes a second spring that urges the second protrusion from the first position toward the second position. 
         [0016]    Thus comprised, the star wheel support member can be moved to the first position and second position by moving the star wheel support member parallel. 
         [0017]    Further alternatively, the support frame has a second frame disposed on the other side of the platen unit; and the second frame pivotably supports the other end of the star wheel support member. 
         [0018]    Thus comprised, the star wheel support member can be moved to the first position and second position by a simple support configuration that causes the star wheel support member to pivot on one end. 
         [0019]    Further preferably, the direction of movement of the star wheel support member is perpendicular to the platen surface. 
         [0020]    Because it is sufficient with this configuration to provide a retraction space for the star wheel support member above the platen unit, the space emptied by retracting the printhead can be used as the retraction space of the star wheel support member. Space efficiency is therefore good, which is useful for making the printer smaller. 
         [0021]    Further preferably, the printer has a head moving mechanism configured to move the printhead in the directions toward and away from the platen surface; and the star wheel support member is pressed against the platen unit and positioned to the first position by the printhead approaching the platen surface. 
         [0022]    Thus comprised, operation of the printhead can be used to move the star wheel support member to the position (first position) pushing against the media with the star wheel. There is, therefore, no need for an independent drive source to move the star wheel support member. The parts configuration can therefore be simplified. 
         [0023]    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 
         [0024]      FIG. 1  is an external oblique view of a printer according to an embodiment of the invention. 
           [0025]      FIG. 2  is a vertical section view showing the internal configuration of the printer in  FIG. 1 . 
           [0026]      FIGS. 3A and 3B  are an oblique view and a bottom view of the carriage that carries the printhead. 
           [0027]      FIG. 4  is an oblique view of the platen unit. 
           [0028]      FIG. 5  schematically illustrates the media conveyance mechanism and printhead. 
           [0029]      FIG. 6  is an oblique view showing part of the internal mechanism of the printer. 
           [0030]      FIGS. 7A and 7B  are an oblique view and a bottom view of the platen top unit. 
           [0031]      FIGS. 8A to 8C  schematically illustrate the support structure of the platen top unit. 
           [0032]      FIGS. 9A to 9E  describe operating the platen top unit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    A preferred embodiment of a printer according to the present invention is described below with reference to the accompanying figures. 
       General Configuration 
       [0034]      FIG. 1  is an external oblique view of a printer according to the invention.  FIG. 2  is a vertical section view showing the internal configuration of the printer. As shown in  FIG. 1 , the printer  1  has a printer cabinet  2  that is basically box-shaped and is long from front to back. An operating panel  3  is disposed at the top of the front  2   a  of the printer cabinet  2  on one side of the width, and a paper exit  4 A is formed on the other side. An opening  4 B that opens and closes during maintenance is disposed below the paper exit  4 A, and an access cover  5  is disposed to this opening  4 B. 
         [0035]    The invention is described below with reference a transverse axis X across the device width, the longitudinal axis Y between the front and back of the device, and a vertical axis Z. The three directional axes X, Y, and Z are mutually perpendicular. Note also that Y 1  denotes the front of the printer, and Y 2  denotes the back of the printer. 
         [0036]    As shown in  FIG. 2 , a roll paper compartment  6  is formed inside the printer cabinet  2  at the bottom at the printer back Y 2 . A printhead  7  is disposed at the top of the printer front Y 1 , and a platen unit  8  is disposed at the bottom at the printer front Y 1 . The printhead  7  is disposed with the nozzle face facing down. The platen unit  8  has a horizontal platen surface  8   a  opposite the nozzle face of the printhead  7  with a specific gap therebetween. The platen surface  8   a  includes the horizontal belt portion  81   a  of the conveyor belt  81  described below. 
         [0037]    Inside the printer cabinet  2 , the continuous paper P pulled from the paper roll  9  in the roll paper compartment  6  is conveyed through the conveyance path  10  indicated by the imaginary line. The recording paper P passes the printing position of the printhead  7 , is conveyed toward the paper exit  4 A opened in the front  2   a  of the printer cabinet  2 , and is discharged from the paper exit  4 A. 
         [0038]    The conveyance path  10  includes a first conveyance path section  10   a , second conveyance path section  10   b , and a third conveyance path section  10   c . The first conveyance path section  10   a  that extends diagonally upward toward the back Y 2  from the roll paper compartment  6 . The second conveyance path section  10   b  continues from the top end of the first conveyance path section  10   a  toward the front Y 1  and descends gradually to the platen surface  8   a . The third conveyance path section  10   c  extends horizontally from the front Y 1  end of the second conveyance path section  10   b , that is, from the back Y 2  end of the platen surface  8   a , to the front Y 1  of the printer. 
         [0039]    A roll spindle  31  on which the paper roll  9  is installed is disposed in the roll paper compartment  6 . The roll spindle  31  extends on the transverse axis X, and is driven rotationally by drive power from a media supply motor  31   a  disposed near the bottom of the printer cabinet  2 . When installed to the roll spindle  31 , the paper roll  9  does not rotate relative to the roll spindle  31 . When the roll spindle  31  turns, the recording paper P is delivered from the paper roll  9  to the first conveyance path section  10   a  of the conveyance path  10 . 
         [0040]    A tension lever  32  that applies tension to the recording paper P is disposed to the conveyance path  10  near the top end of the first conveyance path section  10   a  and the back Y 2  end of the second conveyance path section  10   b  where the conveyance path curves. The distal end of the tension lever  32  has a curved outside surface where the tension lever  32  contacts the media, and the recording paper P travels along this curved surface. The tension lever  32  pivots on an axis of rotation  32   a  on the transverse axis X. The tension lever  32  is urged by a spring member (not shown in the figure) to the back Y 2 . 
         [0041]    A paper guide  33  is disposed on the front Y 1  side of the tension lever  32 . The paper guide  33  is included in the second conveyance path section  10   b  of the conveyance path  10 . The paper guide  33  is shaped to descend gently to the front Y 1 , and guides the recording paper P from the tension lever  32  toward the platen surface  8   a.    
       Printhead Support Mechanism 
       [0042]    The printhead  7  is an inkjet line head, and includes four heads, first head  71   a , second head  71   b , third head  71   c , and fourth head  71   d . These four heads are narrow and long on the transverse axis X, and are disposed at a regular interval on the longitudinal axis Y. Rows of ink nozzles that eject ink droplets are formed in the nozzle face of each head. The length of each ink nozzle row is greater than the maximum width of the recording paper P that can be used. The printhead  7  is mounted on a carriage  11 . The carriage  11  includes a head frame  12  that holds the printhead  7 , and a carriage frame  13  that supports the head frame  12 . The head frame  12  moves on the vertical axis Z relative to the carriage frame  13 . 
         [0043]      FIGS. 3A and 3B  illustrate the carriage  11  that carries the printhead  7 .  FIG. 3A  is an oblique view from diagonally above the top, and  FIG. 3B  is a bottom view from the platen unit  8  side. The head frame  12  includes a rectangular bottom  41 , a rectangular cylinder  42  rising from the outside edges of the bottom  41 , and a operator  43  rising from the middle of the bottom  41 . The top end of the operator  43  is above the top of the printhead  7 . The four line heads (first head  71   a  to fourth head  71   d ) of the printhead  7  are inserted from above to the rectangular cylinder  42 , and are held by the head frame  12 . The bottom ends of the line heads (first head  71   a  to fourth head  71   d ) held by the head frame  12  are below the bottom  41 . Head-side stops  44   a ,  44   b ,  44   c  are formed on the bottom  41  at positions where they can contact three balls  24  held by the platen top unit  20  described below. The three balls  24  held by the platen top unit  20  described below contact the head-side stops  44   a ,  44   b ,  44   c.    
         [0044]    The carriage frame  13  is a frame-like member disposed on the inside circumference side of the head frame  12 . A pair of guide channels  47  that extend on the vertical axis Z are formed on the side of the carriage frame  13  facing the transverse axis X. When the head frame  12  is inside the carriage frame  13 , each of a pair of guide rollers  46  disposed on the side facing the head frame  12  are inserted to the guide channels  47 . As a result, the head frame  12  is supported by the carriage frame  13  on the vertical axis Z. The head frame  12  is urged upward by the urging force of four coil springs  48  disposed between the head frame  12  and carriage frame  13 . 
         [0045]    A pair of parallel carriage guide rails  14  is disposed extending on the transverse axis X on the opposite sides of the carriage  11  on the longitudinal axis Y. The carriage  11  is supported movably on the transverse axis X by this pair of carriage guide rails  14 . As shown in  FIG. 2 , a carriage moving mechanism  15  is disposed on the front Y 1  side of the carriage  11 . The carriage moving mechanism  15  moves the carriage  11  along the pair of carriage guide rails  14  bidirectionally on the transverse axis X. 
         [0046]    The carriage  11  moves between the opposing position  11 A indicated by the dotted line in  FIG. 1 , and the standby position  11 B indicated by the double-dotted line in  FIG. 1 . 
         [0047]    When the carriage  11  is at the opposing position  11 A, the printhead  7  mounted on the carriage  11  is opposite the platen unit  8 . When the carriage  11  is at the standby position  11 B, the printhead  7  mounted on the carriage  11  is not opposite the platen unit  8 . A head maintenance unit  16  is disposed below the standby position  11 B, and when the carriage  11  moves to the standby position  11 B, the printhead  7  is opposite the head maintenance unit  16 . A head elevator  17  (see  FIG. 2 ) that lowers the head frame  12  when the carriage  11  is at the opposing position  11 A is disposed above the carriage  11 . 
         [0048]    As shown in  FIG. 2 , the head elevator  17  includes an operating lever  17   a  supported pivotably up and down, an eccentric cam  17   b  that causes the operating lever  17   a  to pivot vertically, a cam drive motor  17   c  that drives the eccentric cam  17   b , and a coil spring (not shown in the figures) that urges the operating lever  17   a  vertically. The operating lever  17   a  rotates down with rotation of the eccentric cam  17   b , and pushes the head frame  12  down through the operator  43  disposed to the head frame  12 . As a result, the head frame  12  and printhead  7  move down in unison. When the operating lever  17   a  rotates up, the urging force of the four coil springs  48  disposed between the head frame  12  and the carriage frame  13  cause the head frame  12  and the printhead  7  supported thereon to move up. 
         [0049]    As shown in  FIG. 2 , the platen top unit  20  is disposed between the platen unit  8  and the printhead  7  and head frame  12 . The platen top unit  20  holds the three balls  24  ( FIGS. 7A and 7B ) between the head frame  12  and the platen unit  8 . The head frame  12  is lowered by the head elevator  17  to a position touching these three balls  24  from above. The position of the head frame  12  to the platen unit  8  is determined by the balls  24 , and a specific predetermined gap (platen gap) is held between the printhead  7  and platen unit  8 . The platen top unit  20  also holds multiple first star wheels  25 A and second star wheels  25 B ( FIGS. 7A and 7B ). The recording paper P passing between the platen surface  8   a  and the printhead  7  is set passing below the platen top unit  20 . The recording paper P conveyed over the platen surface  8   a  is held down and prevented from lifting away from the platen surface  8   a  by the first star wheels  25 A and second star wheels  25 B. 
       Platen Unit 
       [0050]      FIG. 4  is an oblique view of the platen unit  8 . The platen unit  8  has a main body  83  made of sheet metal, for example. The main body  83  supports a plurality of guide rollers  82   a  to  82   e  ( FIG. 5 ) along the transverse axis X by a pair of side frames  83   a ,  83   b . The conveyor belt  81  is mounted on the guide rollers  82   a  to  82   e . A conveyance motor  84  is disposed inside the main body  83 , and these comprise the media conveyance mechanism  18  described below. 
         [0051]    Platen stops  89   a ,  89   b  are formed at two places at the lengthwise ends of the top of side frame  83   a . A platen stops  89   c  is formed at one place in the lengthwise center of the top of side frame  83   b . Platen stops  89   a  to  89   c  are flat horizontal stops bent substantially perpendicularly from the top ends of the side frames  83   a ,  83   b . The platen stops  89   a ,  89   b ,  89   c  are the parts that each contact one of the three balls  24  held in the platen top unit  20  from above. 
         [0052]    The platen unit  8  includes a conveyor-belt-type media conveyance mechanism  18  in.  FIG. 5  schematically illustrates the media conveyance mechanism  18  and the printhead  7 . The media conveyance mechanism  18  includes a conveyor belt  81 , which is an endless belt located below the third conveyance path section  10   c ; multiple guide rollers  82   a  to  82   e  on which the conveyor belt  81  is mounted; a belt drive roller  82   f  that drives the conveyor belt  81 ; and a conveyance motor  84  that rotates the belt drive roller  82   f . The conveyor belt  81  is pushed against the belt drive roller  82   f  by guide roller  82   a . By rotating the belt drive roller  82   f , the conveyor belt  81  moves along the path around guide rollers  82   a  to  82   e.    
         [0053]    The portion of the conveyor belt  81  between guide rollers  82   b  and  82   c  is the horizontal belt portion  81   a  extending horizontally over the third conveyance path section  10   c . Pinch rollers  19   a ,  19   b  are pushed from above the platen unit  8  to the downstream and upstream (that is, the longitudinal axis Y) ends of the horizontal belt portion  81   a  in the conveyance direction. The media conveyance mechanism  18  conveys the recording paper P held between the pinch rollers  19   a ,  19   b  and the horizontal belt portion  81   a.    
         [0054]    As shown in  FIG. 2 , the recording paper P is pulled from the paper roll  9  loaded in the roll paper compartment  6  to the first conveyance path section  10   a  of the conveyance path  10 , wraps around the tension lever  32 , and the leader is set passing through the second conveyance path section  10   b  and third conveyance path section  10   c . Drive power from the media supply motor  31   a  then causes the roll spindle  31  to turn and supply the recording paper P, and executes the conveyance operation of the media conveyance mechanism  18  to index the leading end of the recording paper P to the printing position of the printhead  7 . Next, the media conveyance mechanism  18  continues the conveyance operating conveying the recording paper P continuously at a constant speed in the forward direction from the printing position to the paper exit  4 A. The printhead  7  is also driven synchronously to the conveyance operation to print on the surface of the recording paper P. 
         [0055]      FIG. 6  is an oblique view showing part of the internal configuration of the printer  1 . As shown in  FIG. 2  and  FIG. 6 , a sheet metal printer frame  50  is disposed inside the printer cabinet  2 , and various components are assembled on the printer frame  50 . The printer frame  50  has a base frame  51  located below the platen unit  8 , and side frames  52 ,  53  that rise perpendicularly from the base frame  51  from the sides of the platen unit  8  on the transverse axis X. A front frame  54  and rear frame  55  spanning the transverse axis X above the platen unit  8  are formed at the top ends of the side frames  52 ,  53 . The platen top unit  20  is disposed between the front frame  54  and rear frame  55 . The platen unit  8  can move between a head-opposing position  8 A below the platen top unit  20 , and an open position  8 B pulled to the front Y 1  below the head-opposing position  8 A. 
         [0056]    The platen unit  8  is supported by a platen operating mechanism  60  ( FIG. 2 ), and is connected to the access cover  5  that opens and closes the opening  4 B formed below the paper exit  4 A in the front  2   a  of the printer cabinet  2 . When the platen unit  8  is at the head-opposing position  8 A, the access cover  5  is upright along the front  2   a  of the printer cabinet  2  ( FIG. 1 ). When the platen unit  8  is pulled to the open position  8 B, the access cover  5  pivots at the bottom end thereof and drops forward. 
         [0057]    As shown in  FIG. 2 , the platen operating mechanism  60  has a linkage mechanism  60 A that supports the platen unit  8  at a position on the front Y 1  side, and a guide mechanism  60 B that supports the back Y 2  side of the platen unit  8 . The linkage mechanism  60 A has top support shafts  61 ,  62  that are parallel to the transverse axis X the front Y 1  side of the platen  8 , and bottom support shafts  63 ,  64  that are parallel to the transverse axis X at the bottom of the printer cabinet  2 . These four support shafts  61  to  64  are connected by two links  65 ,  66  that connect matching top and bottom shafts, embodying a parallel linkage mechanism. One set of two links  65 ,  66  is disposed to each end of the four support shafts  61  to  64 . 
         [0058]    The guide mechanism  60 B includes a pair of curved guide channels  67  ( FIG. 2 ) formed in the pair of side frames  52 ,  53  ( FIG. 6 ) rising on opposite sides of the platen unit  8  on the transverse axis X, and a guide shaft  68  ( FIG. 2 ) attached to a position on the back Y 2  side of the platen unit  8 . The left and right ends of the guide shaft  68  are inserted to the pair of curved guide channels  67 . 
         [0059]    As shown in  FIG. 2 , when the platen unit  8  is at the head-opposing position  8 A, the links  65 ,  66  of the linkage mechanism  60 A are upright on the vertical axis Z. The ends of the guide shaft  68  of the guide mechanism  60 B are also positioned at the back Y 2  ends of the opposing curved guide channels  67 . When the platen unit  8  is pulled to the front Y 1  side, the links  65 ,  66  of the linkage mechanism  60 A pivot down at the bottom ends thereof to the front Y 1 . As a result, the platen unit  8  moves along the curved path of travel to the open position  8 B ( FIG. 6 ) while the platen surface  8   a  remains facing the top of the printer. At this time, the guide mechanism  60 B follows the movement of the linkage mechanism  60 A, the guide shaft  68  travels along the curved guide channels  67 , and the back end part of the platen unit  8  moves along the curved path of travel. 
         [0060]    When the platen unit  8  moves to the open position  8 B, a large gap is formed between the platen unit  8  and the platen top unit  20 , and the third conveyance path section  10   c  of the conveyance path  10  opens greatly to the front Y 1  side. As a result, the user can insert his hand and remove paper jams between the printhead  7  and the platen top unit  20  and platen unit  8 . 
       Platen Top Unit Support Mechanism 
       [0061]    As shown in  FIG. 2  and  FIG. 6 , the platen top unit  20  is a thin unit disposed above the platen unit  8 , and is separated from the platen unit  8 . The platen top unit  20  is supported movably on the vertical axis Z by the front frame  54  and rear frame  55  at the longitudinal axis Y ends of the platen top unit  20 . The platen top unit  20  can move to a first position  20 A ( FIG. 2 ,  FIG. 8B ) where it contacts the platen unit  8  from above, and a second position  20 B ( FIG. 8C ) separated from the platen unit  8  more than at the first position  20 A. 
         [0062]      FIG. 7A  is an oblique view from diagonally above the top of the platen top unit  20 , and  FIG. 7B  is a bottom view thereof from the platen unit  8  side. The platen top unit  20  includes a pair of longitudinal frame members  21   a ,  21   b  extended parallel to the longitudinal axis Y, and five transverse frame members  22   a - 22   e  extending parallel to the transverse axis X. The ends of the transverse frame members  22   a - 22   e  are connected to the longitudinal frame members  21   a ,  21   b . Ball receivers  23   a ,  23   b  are disposed to the longitudinal frame member  21   a  at two locations, on one side and the other side, on the longitudinal axis Y. Another ball receiver  23   c  is disposed to the longitudinal frame member  21   b  near the center on the longitudinal axis Y. The three balls  24  that function as spacers to hold a constant platen gap are supported movably in the ball receivers  23   a  to  23   c . The ball receiver  23   a  is a construction having a wire support member that supports a ball  24  movably inside a through-hole in the longitudinal frame member  21   a , and the other ball receivers  23   b  and  23   c  are identically constructed. 
         [0063]    The platen top unit  20  includes multiple first star wheels  25 A attached to the transverse frame members  22   a - 22   e , and multiple second star wheels  25 B attached to the transverse frame members  22   a - 22   e . Each of the first and second star wheels  25 A,  25 B has protrusions formed at a constant angular pitch around the outside. The first and second star wheels  25 A,  25 B are supported rollably by the transverse frame members  22   a - 22   e , and the outside surfaces are below the transverse frame members  22   a - 22   e  on the vertical axis Z. The first and second star wheels  25 A,  25 B are also supported movably on the vertical axis Z, and are urged down by an urging member not shown. As a result, if recording paper P is set with the platen unit  8  set to the head-opposing position  8 A, and the platen top unit  20  is positioned to the first position  20 A ( FIG. 2 ,  FIG. 8B ) touching the platen unit  8 , the first and second star wheels  25 A,  25 B flexibly contact the recording paper P on the platen surface  8   a.    
         [0064]    Two tabs  26  that protrude to the front Y 1  from the transverse frame member  22   a  are formed on the front Y 1  end of the platen top unit  20 . Two arms  27  that protrude to the back Y 2  side from the opposite side of the transverse frame member  22   e  on the transverse axis X are also formed on the back Y 2  end of the platen top unit  20 . 
         [0065]    As shown in  FIG. 6 , the platen top unit  20  is disposed above the platen unit  8  and between the front frame  54  and rear frame  55 . The rear frame  55  located on the back Y 2  side of the platen top unit  20  has a notch  55   a  that is long on the transverse axis X, and two connectors  57  are formed protruding to the front Y 1  from the transverse axis X ends of the notch  55   a . The arms  27  formed on the back end of the platen top unit  20  are connected to the connectors  57  pivotably on an axis of rotation L extending on the transverse axis X. 
         [0066]    The front frame  54  located on the front Y 1  side of the platen top unit  20  has two openings  56  formed opposite the tabs  26 . The openings  56  are disposed so that the tabs  26  can move on the vertical axis Z. The front part of the platen top unit  20  is therefore supported movably on the vertical axis Z. 
         [0067]      FIGS. 8A to 8C  schematically describe a support structure of the platen top unit  20 ,  FIG. 8A  being a view from the front Y 1 , and (b) and (c) being side views from one side on the transverse axis X. As shown in  FIG. 8A , tension springs  58  that urge the tabs  26  up are attached between the top edge of the opening  56  and the tabs  26 . The platen top unit  20  is urged by the urging force of the tension springs  58  to pivot up on the back end thereof connected to the connectors  57  of the rear frame  55 . 
         [0068]    The first position  20 A shown in  FIG. 8B  is the bottom end of the range of platen top unit  20  movement. The platen top unit  20  holds the three positioning balls  24  as described above, and is set to the first position  20 A by the head-side stops  44   a ,  44   b ,  44   c  of the head frame  12  that holds the printhead  7  contacting the balls  24  from above, and the platen stops  89   a ,  89   b ,  89   c  of the platen unit  8  contacting the balls  24  from below. In the first position  20 A, the tabs  26  are near the bottom end of the openings  56 , and the platen top unit  20  is substantially parallel to the platen surface  8   a.    
         [0069]    The second position  20 B shown in  FIG. 8C  is a position at the top end of the range of platen top unit  20  movement where the urging force of the tension spring  58  and the weight of the platen top unit  20  are balanced. When an escape space is formed above the platen top unit  20  by the carriage  11  moving to the standby position  11 B ( FIG. 1 ), for example, the platen top unit  20  is lifted up at the tabs  26  by the urging force of the tension spring  58 , and the platen top unit  20  swings up pivoting on the axis of rotation L passing through the back end connected to the connectors  57  of the rear frame  55 . As a result, the tabs  26  are positioned at an upward angle when at the second position  20 B. 
       Operation of the Platen Top Unit 
       [0070]      FIGS. 9A to 9E  describe operations of platen top unit  20 , and shows the platen top unit  20  from the Y 1  side.  FIGS. 9A to 9C  describe the operation whereby the carriage  11  moves from the standby position  11 B to the opposing position  11 A, and creates a specific platen gap between the printhead  7  and platen unit  8 .  FIGS. 9D and 9E  describe the operation of pulling the platen unit  8  to the front of the device and opening the third conveyance path section  10   c  of the conveyance path  10 . 
         [0071]    As described above, the carriage  11  carrying the printhead  7  can be moved by the carriage moving mechanism  15  along the carriage guide rails  14 , and move between the opposing position  11 A ( FIG. 1 ,  FIG. 9B , and  FIG. 9C ) opposite the platen unit  8 , and the standby position  11 B ( FIG. 1 ,  FIG. 9A ) retracted from the platen unit  8 . In addition, when the carriage  11  is at the opposing position  11 A, the part of the head frame  12  holding the printhead  7  can be moved on the vertical axis Z relative to the carriage frame  13  by means of the head elevator  17 . The head frame  12  moves between the platen gap holding position  12 A ( FIG. 9C ) pushing the balls  24  of the platen top unit  20  against the platen unit  8 , and a raised position  12 B ( FIGS. 9A and 9B ) not touching the balls  24 . 
         [0072]    To avoid interference between the carriage  11  and the printhead  7  and platen top unit  20 , the operation of moving the carriage  11  between the opposing position  11 A and standby position  11 B is executed when the head frame  12  holding the printhead  7  is moved to the raised position  12 B as shown in  FIGS. 9A and 9B . When not depressed by the head frame  12 , the platen top unit  20  pivots up and moves to the second position  20 B. The raised position  12 B is set to a position where there is no interference between the platen top unit  20  moved to the second position  20 B and the head frame  12 . 
         [0073]    As shown in  FIG. 9C , to print on the recording paper P with the printhead  7 , the head elevator  17  is driven to lower the head frame  12  and the printhead  7  to the carriage frame  13 . As a result, the balls  24  held by the platen top unit  20  function as spacers between the head frame  12  and platen unit  8 , the head frame  12  is positioned to the platen gap holding position  12 A, and a specific gap (platen gap) is held between the nozzle face of the printhead  7  and the platen surface  8   a . Furthermore, because the platen top unit  20  is set to the first position  20 A in contact with the platen unit  8 , the first and second star wheels  25 A,  25 B flexibly contact the recording paper P set on the platen surface  8   a.    
         [0074]    To restore the printer  1  to printing condition when a printer  1  error such as a paper jam occurs, for example, the user opens the access cover  5  and pulls the platen unit  8  from the head-opposing position  8 A through the opening  4 B in the front  2   a  to the open position  8 B. At this time, as shown in  FIG. 9D , the platen unit  8  descends, a large gap to the platen top unit  20  opens, and the third conveyance path section  10   c  of the conveyance path  10  opens wide. As a result, recording paper P stuck in the third conveyance path section  10   c  can be removed from the opening  4 B in the front  2   a.    
         [0075]    Because the platen top unit  20  is at the first position  20 A when the head frame  12  is at the platen gap holding position  12 A, the first and second star wheels  25 A,  25 B will be exposed from the opening  4 B in the front  2   a  ( FIG. 9D ) if the platen unit  8  is moved to the open position  8 B without moving the head frame  12 . The control unit of the printer  1  therefore controls the head elevator  17  to move the head frame  12  to the raised position  12 B ( FIG. 9E ) if movement of the platen unit  8  to the open position  8 B is detected. Because this moves the platen top unit  20  to the second position  20 B, the first and second star wheels  25 A,  25 B move up away from the opening  4 B in the front  2   a , and are not exposed from the opening  4 B. 
         [0076]    In addition to driving the head elevator  17  to raise the head frame  12  based on the operation of opening the platen unit  8 , moving the platen top unit  20  to the second position  20 B when the platen unit  8  opens may alternatively be controlled by driving the head elevator  17  based on detection of a paper jam to move the platen top unit  20  to the second position  20 B before opening the platen unit  8 . 
         [0077]    As described above, the platen top unit  20  that supports the first and second star wheels  25 A,  25 B in the printer  1  according to this embodiment is separate from the openable platen unit  8 , and is supported movably vertically. Therefore, when the platen unit  8  is moved to the open position  8 B to open the third conveyance path section  10   c  of the conveyance path  10  when a paper jam occurs, for example, the platen top unit  20  can be raised by controlling the head elevator  17 . Therefore, the first and second star wheels  25 A,  25 B supported by the platen top unit  20  can be retracted from the position where they may be easily be touched by the user. The chance of damaging the first and second star wheels  25 A,  25 B and a drop in ease of maintenance can therefore be avoided. Furthermore, because a member for covering the first and second star wheels  25 A,  25 B and a mechanism for moving such a member, are not needed, damage to the first and second star wheels  25 A,  25 B and a drop in ease of use can be avoided by a simple configuration. 
         [0078]    The platen top unit  20  is supported by the front frame  54  and rear frame  55  movably on the vertical axis Z. More specifically, the platen top unit  20  is supported with the tabs  26  of the platen top unit  20  urged up inside the openings  56  in the front frame  54 , and the rear end of the platen top unit  20  is supported pivotably up and down by the connectors  57  of the rear frame  55 . The platen top unit  20  is therefore supported movably vertically by a simple configuration. 
         [0079]    Furthermore, because the platen top unit  20  is retracted in the direction above and away from the platen surface  8   a  (vertically relative to the platen surface  8   a ), the space from which the printhead  7  and head frame  12  are retracted can be used as the retraction space for the platen top unit  20 . Space can therefore be used efficiently to make the printer  1  smaller. 
         [0080]    Furthermore, the head elevator  17  in this embodiment can be used to move the platen top unit  20  by means of the head frame  12 , and the urging force of the tension springs  58  can be used to raise the platen top unit  20 . A separate drive source is therefore not needed to move the platen top unit  20 . The configuration of parts can therefore be simplified. 
       Other Embodiments 
       [0081]    The rear end of the platen top unit  20  is pivotably attached to the rear frame  55 , but the support structure at the back end of the platen top unit  20  may be configured identically to the front end. For example, the arms  27  at the back end of the platen top unit  20  may be disposed inside openings formed in the rear frame  55 , and the platen top unit  20  urged up by springs, for example. In this event, the platen top unit  20  can move vertically while held horizontally. 
         [0082]    This embodiment applies the invention to an inkjet line printer, but the invention is not so limited and may be applied to a serial printer. 
         [0083]    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.