Patent Publication Number: US-6981810-B2

Title: Printer apparatus having platen roller with sheet feed guide

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to printer apparatus in which a printing operation is performed by winding a paper sheet around a platen roller, and more particularly, to thermal sublimation-type printers. 
   2. Description of Related Art 
     FIG. 18  is a schematic side view of a portion of a conventional printer apparatus. (See Japanese Laid-Open Pat. App. Pub. No. 2001-88396.) This apparatus comprises a cartridge  34  disposed detachably/reattachably above a platen roller  2  around which a paper sheet S winds. Provided on one end of the platen roller  2  is a sandwiching member  35  for sandwiching the paper sheet S. The circumference of the platen roller  2  is slightly longer than the length of the paper sheet S. 
   A pair of winding shafts  36 ,  36  is disposed inside the cartridge  34 , and an ink sheet  33  is suspended between the winding shafts  36 ,  36 . 
     FIG. 19  is an oblique view illustrating the winding shafts  36 ,  36 . On the ink sheet  33 , three colors of ink, yellow (Y), magenta (M), and cyan (C) are coated separately along the winding direction. Above the ink sheet  33 , a thermal head  31  for heating the ink sheet  33  is arranged so that it can freely goes up and down. The thermal head  31  is connected to an image processing circuit  37 , and respective image information corresponding to respective colors, yellow, magenta, and cyan, is sent from the image processing circuit  37  to the thermal head  31 . 
   In printing, the platen roller  2 , sandwiching a paper sheet S with the sandwiching member  35 , is rotated so that the thermal head  31  opposes a position on the paper sheet S that is to be recorded first. The winding shafts  36 ,  36  are rotated so that the thermal head  31  is drawn near to the first position for yellow, and the thermal head  31  is heated. 
   The image information corresponding to yellow is sent first to the thermal head  31 . The thermal head  31  heats the ink sheet  33 , causing yellow ink thereon to sublimate. With rotating the winding shafts  36 ,  36  and the platen roller  2  in a direction such that the ink sheet  33  is fed, the yellow component of the image information is printed on the paper sheet S. Upon completing the printing operation for yellow component, the thermal head  31  is separated from the platen roller  2 . The platen roller  2  rotates, and the paper sheet S returns to the original position. Next, image information corresponding to magenta is sent to the thermal head  31 , and the winding shafts  36 ,  36  and the platen roller  2  are rotated to print the image information of the magenta component on the paper sheet S. Likewise, image information corresponding to cyan is printed on the paper sheet S in a similar manner. Upon completing the printing operation, the thermal head  31  is separated from the platen roller  2 , and the platen roller  2  is rotated to eject the paper sheet S. 
   In the above-described configuration, however, it is necessary to provide a cam and a link mechanism (not shown) for parting the sandwiching member  35  away from the platen roller  2 . This creates a problem in that the size of the apparatus tends to increase. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to reduce the size of printer apparatus and stabilize the operation of the sheet feed guide  4  for guiding the feeding of paper sheets S. 
   A printer apparatus of the present invention includes: a platen roller  2  around which paper sheets S wind; a printing means  3  arranged for being drawn near to and away from the platen roller  2 ; a plurality of winding support members  21 ,  22 ,  23 , and  24  circumferentially disposed around the platen roller  2 , for guiding a paper sheet S to wrap around the roller  2 ; a sheet feed guide  4  disposed in proximity to the printing means  3  and being pivotable substantially along the circumference of the roller  2 ; and a diverting mechanism  40  for letting the sheet feed guide  4  escape to a position such that it does not interfere the printing means  3  in a print mode. 
   The sheet feed guide  4  is linked with a lever  6  that pivots in a plane substantially perpendicular to the rotation axis of the platen roller  2 , the lever having a fore-end protuberance  61 . 
   The diverting mechanism  40  comprises rotative plates  7  disposed opposing each end of the platen roller  2  and each having a cam portion  73  for guiding the protuberance  61  on the lever  6 , and a rotation-restricting part  8  for controlling movement of the lever  6  in cooperation with the cam portions  73  to let the sheet feed guide  4  escape during the print mode. Cam pieces  72  provided on the rotative plates  7  control an approach/retreat operation of the winding support members  21 ,  22 ,  23 , and  24  with respect to the platen roller  2 . 
   A plurality of winding support members  21 ,  22 ,  23 , and  24  that guide the paper sheet S to be wound around the roller  2  are disposed circumferentially around the platen roller  2 , and their approach/retreat operation with respect to the platen roller  2  is controlled by cam pieces  72  of rotative plates  7  opposing each end of the platen roller  2 . Consequently, the size of printer apparatus can be reduced in comparison with conventional apparatus. 
   Moreover, even if the sheet feed guide  4  and the printing means  3  are arranged close to each other, the diverting mechanism  40  lets the sheet feed guide  4  escape in a position at which the sheet feed guide  4  does not interfere with the printing means  3  during the print mode. This also serves to reduce the size of the printer apparatus. 
   The operation of the sheet feed guide  4  is controlled by the rotative plates  7  and rotation-restricting part  8 , which constitute the diverting mechanism  40 , and therefore, the operation of the sheet feed guide  4  becomes stable, thereby improving reliability. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an oblique view of a thermal printer, which is a printer apparatus; 
       FIG. 2  is a front cross-sectional view of  FIG. 1 ; 
       FIG. 3  is an oblique perspective view of winding support members; 
       FIG. 4  is an oblique view of a platen roller to which a sheet feed guide is attached; 
       FIG. 5  is an exploded oblique view of the sheet feed guide; 
       FIG. 6  is an oblique view of a rotative plate and the sheet feed guide in an initial mode; 
       FIG. 7  is an oblique view of the rotative plate and the sheet feed guide in a sheet feed mode; 
       FIG. 8  is an oblique view of the rotative plate and the sheet feed guide in a print mode; 
       FIG. 9  is an oblique view of the rotative plate and the sheet feed guide in an ink-sheet feed mode; 
       FIG. 10  is an oblique view of the rotative plate and the sheet feed guide in a sheet ejecting mode; 
       FIG. 11  is a front view of the rotative plate and the sheet feed guide in the initial mode; 
       FIG. 12  is a front view of the rotative plate and the sheet feed guide in the sheet feed mode; 
       FIG. 13  is a front view of the rotative plate and the sheet feed guide in the print mode; 
       FIG. 14  is a front view of the rotative plate and the sheet feed guide in the ink-sheet feed mode; 
       FIG. 15  is a front view of the rotative plate and the sheet feed guide in the sheet ejecting mode; 
       FIG. 16  illustrates the sequence of the modes that change when the rotative plate rotates in a forward direction; 
       FIG. 17  is an exploded oblique view of an adjusting mechanism; 
       FIG. 18  is a schematic side view illustrating a portion of a conventional printer apparatus; and 
       FIG. 19  is an oblique view illustrating winding shafts of the cartridge. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Outline of Overall Configuration 
     FIG. 1  is an oblique view of a thermal printer, which is a printer apparatus, and  FIG. 2  is a front cross-sectional view of  FIG. 1 . 
   A chassis  1  of the printer is formed by left and right side plates  11  and  12  that are connected with a connecting plate  13 , a stay  14 , and a rear plate  15 . A cartridge  34  can be inserted into or removed from the interior of the chassis  1  through an opening  11   a  formed on the side plate  12 . Although a long hole  10   a  and a hole  10   b  are formed in the side plate  11  as will be described later, they are not shown in  FIG. 1  for convenience in illustration. 
   The connecting plate  13  is positioned between the side plates  11  and  12  at their lower portions, and a sheet feed tray  17  is disposed below the connecting plate  13  so that it can be taken out in the direction away from the rear plate  15  (arrow F). 
   A platen roller  2 , supported by the side plates  11  and  12 , is disposed rotatably above the connecting plate  13 . The outer layer of the platen roller  2  is formed of hard rubber. 
   A printing means  3  equipped with a thermal head  31  is disposed above the platen roller  2 . Hereinafter, the term “front” is intended to mean the side from which the sheet feed tray  17  is taken out, and the term “rear” is intended to mean the rear plate  15  side. 
   As shown in  FIG. 2 , the printing means  3  can pivot upward and downward with the support shaft  32  being the pivotal axis, and the thermal head  31  is positioned at the frontward of the support shaft  32  so as to approach the platen roller  2  or retreat therefrom. 
   Four winding support members  21 ,  22 ,  23 , and  24 , disposed circumferentially of the platen roller  2  and supported by the side plates  11  and  12 , cover the platen roller  2 . (See  FIG. 3 ). Each of the winding support members  21 ,  22 ,  23 , and  24  has small rollers  25 ,  25  at both ends thereof, and pivots with the support shaft  26  about a pivotal axis. 
   Each of the winding support members  21 ,  22 ,  23 , and  24  pushes and urges the platen roller  2  by a spring (not shown). The platen roller  2  is released from the winding support members  21 ,  22 ,  23 , and  24  in the vicinity of the thermal head  31 , and at the released zone, a sheet feed guide  4  that can pivot back and forth (in the directions indicated by arrows C and D) is disposed over the platen roller  2 . 
   A sheet guide wall  16  is formed on the inner surface of the rear plate  15 . The guide wall  16  has a peak  16   c  that protrudes toward the center of rotation of the platen roller  2 . The surface of the sheet guide wall that is downward of the peak  16   c  forms a winding guide surface  16   a  for a paper sheet S, and the surface that is upward of the peak  16   c  forms a sheet-ejecting guide surface  16   b.    
   A paper sheet S, accommodated in the sheet feed tray  17 , is drawn out from the rear end of the sheet feed tray  17  by a sheet feed roller  18 . The paper sheet S slides on the winding guide surface  16   a , and is guided between the first winding support member  21  and the platen roller  2 , as indicated by arrow X. The paper sheet S passes under the sheet feed guide  4 , the second winding support member  22 , the third winding support member  23 , and the fourth winding support member  24 , and wraps around the platen roller  2 . While the platen roller  2  rotates by one revolution, a printing operation for one color is performed, and the paper sheet S is drawn near towards the original position. When the platen roller  2  by rotates three revolutions, a printing operation for three colors finishes. 
   A guiding plate  19  is disposed pivotably between the first winding support member  21  and the fourth winding support member  24 . During the time in which the platen roller  2  rotates by three revolutions, the guiding plate  19  forcibly guides the paper sheet S that passes under the fourth winding support member  24  toward the first winding support member  21  side. 
   After the platen roller  2  has rotated three revolutions, the guiding plate  19  pivots downward, as indicated by arrow Y, releasing the transfer path from the fourth winding support member  24  to the sheet-ejecting guide surface  16   b  of the guide wall  16  so that the paper sheet S travels toward the sheet-ejecting guide surface  16   b . Upon finishing sheet ejection, the guiding plate  19  returns to the original position. 
   Details of Sheet Feed Guide  4   
     FIG. 4  is an oblique view of the platen roller  2  to which the sheet feed guide  4  is attached, and  FIG. 5  is an exploded oblique view of the sheet feed guide  4 . The sheet feed guide  4  includes: a guide plate  41  for guiding the paper sheet S that has passed under the first winding support member  21  between the second winding support member  22  and the platen roller  2 ; support plates  44 ,  44  furnished at both ends of the guide plate  41 ; and a mounting member  5  and a lever  6  that are provided on each of the support plates  44 . The guide plate  41  and the support plates  44 ,  44  are formed by bending a sheet of metal plate. 
   The guide plate  41  is formed slightly longer than the platen roller  2 , and it has a smaller wing piece  43  facing frontward at its center, and larger wing pieces  42 ,  42  facing rearward on both sides of the smaller wing piece  43 . 
   The support plates  44 ,  44  oppose each other, and each of the support plates  44  has two positioning holes  45 ,  45  and a screw hole  46 . 
   The mounting member  5  is positioned on the outer surface of the support plate  44 , and is fastened on the support plate  44  by fitting positioning rods  51  and  52  protruding from the inner side into the positioning holes  45 ,  45  in the support plate  44 , and screwing a screw  53  into a screw hole  46 . 
   The outer surface of the mounting member  5  is furnished with two shorter and longer guide rods  54  and  55  that slidably fit into a guide groove  71  of a later-described rotative plate  7  or  7   a.    
   The base end of the lever  6  fits onto the positioning rod  52  of the mounting member  5  pivotably. A round-rod-like protuberance  61  protrudes outwardly from the free end of the lever  6  along the length of the guide plate  41  (along the length of the platen roller  2 ). 
   Referring to  FIG. 5 , the lever  6  is urged by a spring  62  anticlockwise (in the direction in which a cam portion  73  of the later-described rotative plate  7  or  7   a  is pressed). 
   Rotative Plate  7   
   As illustrated in  FIG. 4 , rotative plates  7  and  7   a  are attached onto each end of a rotation shaft  20  of the platen roller  2  freely-pivotably with respect to the shaft  20 . 
   Gears  77 ,  77  mesh with gear-tooth faces  70 ,  70  formed on a portion of the outer periphery of both rotative plates  7  and  7   a , and both gears  77 ,  77  are linked together by a shaft  78 . 
   A rotation drive device  79  is connected to one of the gears  77 . The rotation drive device  79  turns the rotative plates  7  and  7   a  in a forward or reverse direction corresponding to each of later-described respective modes of the printer apparatus in response to the signal from a control section (not shown). 
   An arcuate guide groove  71  into which the guide rods  54  and  55  on the sheet feed guide  4  are fitted slidably is formed in each of the rotative plates  7  and  7   a.    
   With the guide groove  71  and the guide rods  54  and  55 , the sheet feed guide  4  is guided so as to shift back and forth over the platen roller  2  while keeping a clearance between the guide plate  41  and the platen roller  2 , through which a paper sheet passes. The center of curvature of the guide groove  71  matches the center of rotation of the rotative plates  7  and  7   a.    
   A cam portion  73  that comes in contact with the protuberance  61  of the lever  6  is formed on the outer peripheral surface of each of the rotative plates  7  and  7   a.    
   The cam portion  73  includes an arcuate face  74  the center of curvature of which 5 matches the guide groove  71 , a pocket  75  recessed from the front end of the arcuate face  74 , and a pressure cam face  76  that connects to the pocket  75  and extends radially of the rotative plates  7  and  7   a.    
   The protuberance  61  of the lever  6  fits into the pocket  75  with a slight clearance. The pocket  75  is positioned slightly forward of the front end of the guide groove  71 . 
   In addition, as shown in  FIG. 4 , four cam pieces  72 ,  72  protrude from the outer peripheral surface of each of the rotative plates  7  and  7   a , for separating the winding support members  21 ,  22 ,  23 , and  24  from the platen roller  2  against the spring (not shown). 
   A rotation-restricting part  8  that restricts the rearward shifting of the sheet feed guide  4  according to switching of the modes is provided on the outer side of each of the rotative plates  7  and  7   a . The rotation-restricting part  8  employed in the present example is a punched-out hole  80  formed in each of the side plates  11  and  12  of the chassis  1 . 
   The punch-through hole  80  includes a first contact portion  81  that prevents the rearward shift of the sheet feed guide  4  by coming into contact with the protuberance  61  during the time in which the rotative plates  7  and  7   a  rotates in the forward direction (anticlockwise) and the protuberance  61  falls into the pocket  75 , a second contact portion  82  that prevents the rearward shift of the sheet feed guide  4  by coming into contact with the guide rod  55  on the sheet feed guide  4 , and a guiding surface  83  that guides the protuberance  61  that has fallen into the pocket  75  in the rotative plates  7  and  7   a  in a direction in which it comes out of the pocket  75  when the rotative plates  7  and  7   a  rotates in a reverse direction. 
   Operation Modes of Thermal Printer 
   The printer of the present example has five operation modes: an initial mode, a sheet feed mode, a print mode, an ink-sheet feed mode, and a sheet ejecting mode.  FIGS. 6 and 11  illustrate the operation of the initial mode,  FIGS. 7 and 12  the sheet feed mode,  FIGS. 8 and 13  the print mode,  FIGS. 9 and 14  the ink-sheet feed mode, and  FIGS. 10 and 15  the sheet ejecting mode. 
   In each of  FIGS. 11 through 15 , the drawing labels (a) represents the positional relationship between the rotative plate  7  and the sheet feed guide  4 , the drawing labeled (b) represents the positional relationship between the rotative plate  7  and the lever  6 , and the drawing labeled (c) represents the positional relationship between the rotative plate  7  and the rotation-restricting part  8 . 
   The initial mode is a mode in which the winding support members  21 ,  22 ,  23 , and  24  are separated from the platen roller  2  and stand by for winding a paper sheet S on the platen roller  2 . The printer apparatus automatically returns to the initial mode after use. 
   The sheet feed mode is a mode in which a paper sheet is drawn out from the sheet feed tray  17  and wound around the platen roller  2 . 
   The print mode is a mode in which the thermal head  31  pivots toward the platen roller  2  side and presses the ink ribbon  33  against the paper sheet S to perform printing. 
   The ink-sheet feed mode is a mode in which, in order to finish the printing operation for one or two colors and print the next color, the ink sheet is transferred by 1 pitch, and the platen roller  2  is slightly rotated to transfer the paper sheet S on the platen roller  2  to a print initial position. 
   The sheet ejecting mode is a mode in which the printing operation for three colors has been finished and the paper sheet is taken out from the platen roller  2 . 
   The rotative plates  7  and  7   a  rotates in the forward or reverse direction according to switching of the modes. The platen roller  2  rotates only clockwise. The rotative plates  7  and  7   a  are rotated in the forward direction (anticlockwise) from the initial mode until the sheet feed mode. The sheet ejecting mode and the ink-sheet feed mode are passed during the transition, as shown in  FIG. 16 . When the rotative plates  7  and  7   a  further rotate in the forward direction from the sheet feed mode, the print mode is reached. 
   A feature of the present example is a diverting mechanism  40  that shifts the sheet feed guide  4  to prevent the interference between the thermal head  31  and the sheet feed guide  4  immediately before reaching the print mode. The diverting mechanism  40  is constituted by the rotative plate  7  and the rotation-restricting part  8 . 
   Transition from Initial Mode to Sheet Feed Mode 
   In the initial mode the winding support members  21 ,  22 ,  23 , and  24  are separated from the platen roller  2  by the cam pieces  72 ,  72 . 
   In order to perform a printing operation, first, a paper sheet S is wound around the platen roller  2 . This requires that the rotative plates  7  and  7   a  are rotated in the forward direction (anticlockwise, indicated by arrow G) from the initial mode illustrated in  FIG. 6  and  FIG. 11  until the sheet feed mode is reached. During the sheet ejecting mode and the ink-sheet feed mode, which are performed in the transition, the protuberance  61  of the lever  6  is pressurized against the arcuate face  74  of the cam portion  73  by a spring  62 . In addition, the fore-end of the protuberance  61  is in contact with the first contact portion  81  of the rotation-restricting part  8 , as illustrated in  FIG. 11(   c ), thus preventing its rearward shifting. 
   The center of curvature of the guide groove  71  into which the guide rods  54  and  55  fit and the center of curvature of the arcuate face  74  along which the protuberance  61  slides both match the center of rotation of the rotative plates  7  and  7   a , and the first contact portion  81  prevents the lever  6  from shifting rearward. That is, the shift of the sheet feed guide  4  in the escape direction is prevented. Therefore, the sheet feed guide  4  does not follow the rotation of the rotative plates  7  and  7   a  but stays still even when the rotative plates  7  and  7   a  rotate in the forward direction, i.e., in the direction indicated by arrow G, from the initial mode shown in  FIG. 6  until the ink-sheet feed mode shown in  FIG. 9 , which is halfway, is reached. 
   As illustrated in  FIGS. 7 and 12 , when the rotative plates  7  and  7   a  rotate in the forward direction until the sheet feed mode is reached, the protuberance  61  of the lever  6  falls into the pocket  75  of the cam portion  73 , thereby making contact with the guiding surface  83  of the rotation-restricting part  8 . At the same time, the protuberance  61  comes off from the first contact portion  81  of the rotation-restricting part  8 , as illustrated in  FIG. 12(   c ). 
   The protuberance  61  that has fallen into the pocket  75  also comes into contact with a pressure cam face  76  of the cam portion  73 , thereby slightly shifting the sheet feed guide  4  in the escape direction (rearward). 
   By the time the rotative plates  7  and  7   a  reach the sheet ejecting mode, which is halfway, from the initial mode, the cam pieces  72  on the outer periphery of the rotative plates  7  and  7   a  come off from the winding support members  21 ,  22 ,  23 , and  24 . The winding support members  21 ,  22 ,  23 , and  24  press the platen roller  2 . 
   As previously described, a paper sheet S is drawn out from the rear end of the sheet feed tray  17  by the sheet feed roller  18 , as illustrated in  FIG. 2 , and the platen roller  2  rotates in the sheet winding direction, which is indicated by arrow E. The paper sheet S, sliding on the winding guide surface  16   a , is guided between the first winding support member  21  and the platen roller  2 , as indicated by arrow X. Then, the paper sheet passes under the sheet feed guide  4 , the second winding support member  22 , the third winding support member  23 , and the fourth winding support member  24 , thus wrapping around the platen roller  2 . 
   By detecting the fore-end of the paper sheet S by a sensor (not shown) provided at an appropriate position, the rotation of the platen roller  2  is stopped when the fore-end reaches a print reference position. 
   The thermal head  31  is lowered and drawn towards near the ink sheet  33 . Still, there is a clearance between the head and the platen roller  2 , and the head does not interfere with the sheet feed guide  4 . 
   Transition from Sheet Feed Mode to Print Mode 
   Upon the sensor&#39;s detection the completion of sheet feeding, the rotative plates  7  and  7   a  further rotate in the forward direction. The pressure cam face  76  of the cam portion  73  pushes the protuberance  61  on the lever  6 , letting the sheet feed guide  4  escape rearward ( FIGS. 8 and 13 ). Since the protuberance  61  has already come off from the first contact portion  81  of the rotation-restricting part  8 , there is no obstacle for the sheet feed guide  4  to shift rearward. 
   When the guide rod  55  on the sheet feed guide  4  hits the second contact portion  82  of the rotation-restricting part  8 , the rearward movement of the sheet feed guide  4  stops. 
   Since the sheet feed guide  4  has shifted rearward, the thermal head  31  can pivot around the support shaft  32  and descend. The thermal head  31  presses the ink sheet  33  against the paper sheet S on the platen roller  2 . In this state, the platen roller  2  rotates by the length of the paper sheet, thus completing a printing operation for one color. 
   Transition from Print Mode to Ink-Sheet Feed Mode 
   Upon completing the printing operation for one color, the thermal head  31  returns to the original position, and the ink sheet  33  is wound by 1 pitch (a width for one color). 
   As indicated by arrow H in  FIGS. 8 and 13 , the rotative plates  7  and  7   a  rotate in the reverse direction, undergo the sheet feed mode shown in  FIGS. 7 and 12 , and move to the ink-sheet feed mode shown in  FIGS. 9 and 14 . By the reverse rotation of the rotative plates  7  and  7   a , the protuberance  61  falls into the pocket  75  one time in the sheet feed mode, coming into contact with the guiding surface  83  of the rotation-restricting part  8  ( FIGS. 7 and 12(   c )). With a further reverse rotation of the rotative plates  7  and  7   a , the wall of the pocket  75  of the cam portion  73  pushes the protuberance  61  forward. The protuberance  61  slides on the guiding surface  83  and reaches the position at which it comes in contact with the first contact portion  81  of the rotation-restricting part  8  ( FIG. 14(   c )), arriving at the ink-sheet feed mode. 
   The platen roller  2  rotates until the fore-end of the paper sheet S reaches the print reference position. 
   From the ink-sheet feed mode the rotative plates  7  and  7   a  rotates in the forward direction, returning to the print mode to perform a printing operation for the second color. The printing operation for the third color is carried out in a similar manner to the operation for the second color. 
   Transition from Print Mode to Sheet-Ejecting Mode 
   Upon completing the printing operation for the third color, the rotative plates  7  and  7   a  rotate in the reverse direction, undergo the sheet feed mode and the ink-sheet feed mode, and moves to the sheet ejecting mode. (See  FIG. 16 .) 
   Even when the rotative plates  7  and  7   a  further rotate in the reverse direction from the state of the ink-sheet feed mode, the protuberance  61  on the lever  6  still remains on the arcuate face  74  of the cam portion  73 . The posture of the sheet feed guide  4  is the same as that in the ink-sheet feed mode. 
   As indicated by arrow Y in  FIG. 2 , the guiding plate  19  pivots downward to release the shifting path between the fourth winding support member  24  and the sheet-ejecting guide surface  16   b  of the guide wall  16 . The platen roller  2  rotates clockwise, whereby the sheet is elevated upward along the sheet-ejecting guide surface  16   b  of the guide wall  16  and is thus ejected. 
   When completing the paper sheet ejection, the guiding plate  19  returns to the original position to get ready for winding of the next paper sheet S. 
   Advantageous Effects of the Present Example 
   A plurality of winding support members  21 ,  22 ,  23 , and  24  for guiding the paper sheet S to wrap around the roller  2  are provided circumferentially around the platen roller  2 , and the approach/retreat operation thereof with the platen roller  2  is controlled by the cam pieces  72  of the rotative plates  7  disposed opposing both ends of the platen roller  2 . This makes the size of the printer apparatus smaller than conventional printer apparatus. 
   Moreover, even if the sheet feed guide  4  and the printing means  3  are arranged close to each other, the diverting mechanism  40  lets the sheet feed guide  4  escape to a position at which it does not interfere printing operations in the print mode. This also serves to reduce the size of the printer apparatus. 
   Since the operation of the sheet feed guide  4  is controlled by the rotative plate  7  and the rotation-restricting part  8 , which constitute the diverting mechanism  40 , the operation of the sheet feed guide  4  becomes stable, thereby improving reliability. 
   It should be noted that it is not absolutely necessary to match the pivotal axis of the sheet feed guide  4  with the center of rotation of the rotative plates  7  and  7   a . It is sufficient that a paper sheet can be guided between the second winding support member  22  and the platen roller  2  when the sheet feed guide  4  pivots frontward, and that the sheet feed guide  4  does not interfere with the thermal head  31  when it pivots rearward. 
   The present invention is not limited to thermal printers. The invention may be applied to, for example, printers that are capable of printing images, which include printing of characters, and to photocopiers. Further, the printing means may be of an ink-jet type. 
   Adjusting Mechanism  9   
   It should be noted that, as seen from  FIGS. 1 ,  2 , and  17 , the thermal head  31  is linked to an adjusting mechanism  9 , and its pressurizing position on the platen roller  2  is adjusted to-and-fro. 
   Both ends of the support shaft  32  of the thermal head  31  pass through arcuate long holes  10   a  formed in the side plates  11  and  12  of the chassis  1 . The adjusting mechanism  9  shifts the support shaft  32  to-and-fro by pivoting the pivot plates  95  disposed on the side plates  11  and  12 . 
   An adjustment shaft  91  arranged parallel to the support shaft  32  is fitted freely-pivotably into holes  10   b  formed in the side plates  11  and  12 . The pivot plate  95  is supported rotatably on each of the side plates  11  and  12  by the protruding rod  93  provided between the long hole  10   a  and the hole  10   b.    
   The pivot plate  95  has two larger and smaller notches  90  and  94 , with the center of rotation interposed therebetween, and one end of the support shaft  32  of the thermal head  31  fits into the smaller notch  94 , which is at the lower portion, whereas an eccentric circular portion  92  formed on the adjustment shaft  91  fits into the larger notch  90 , which is at the upper portion. 
   An arcuate hole  96 , the center of curvature of which matches the protruding rod  93 , is formed in the pivot plate  95 . When an angular shaft portion  91   a  on one end of the adjustment shaft  91  is turned with a rotating tool (such as, a spanner), the eccentric circular portion  92  rotates, thus pivoting the pivot plate  95 . As a result, the support shaft  32  can be shifted back and forth along the long hole  10   a  so that the position of the thermal head  31  can be optimally adjusted. 
   After adjusting the position of the thermal head  31 , a screw  97  fitted into the arcuate hole  96  of the pivot plate  95  is screwed to each of the side plates  11  and  12  to secure the pivot plate  95  on each of the side plates  11  and  12 . 
   Only selected embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.