Abstract:
A printer apparatus for printing data on paper traveling through the printer apparatus in a paper conveying direction. The printer apparatus includes a paper conveying portion including a driving roller and a driven roller, the driving roller and driven roller being moveable with respect to one another between an engaged position at which the driving roller and the driven roller are pressed together and a disengaged position at which the driving roller and the driven roller are separated; wherein the paper conveying portion is situated downstream, with respect to the paper conveying direction, from the location at which the data is printed on the paper; and wherein the driving roller and the driven roller are operative to pressingly sandwich the paper therebetween when the driving roller and the driven roller are in the engaged position.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a printer apparatus, and more particularly to a portable thermal printer apparatus having a first module detachably attached to a second module. 
   2. Description of the Related Art 
   In recent years, there is a growing demand for portable thermal printers that can print, for example, barcodes and meter readouts. Compared to a general printer, a higher printing precision with respect to a paper conveying direction is required since barcodes and meter readouts are read by OCR (Optical Character Recognition). 
   With a conventional portable thermal printer of a clamshell type, when a cover of the printer is closed, a platen roller formed of rubber, holding a sheet of paper, presses against a thermal head. The platen roller is rotated by a motor, and the paper is fed by the frictional force of the platen roller. A conventional example is shown in Japanese Laid-Open Patent Application No.2002-120389. 
   Owing that the platen roller presses against the thermal head, the platen roller is generally formed of rubber. Although a satisfactory performance may be obtained in the early periods of using the rubber platen rollers, it is difficult to maintain such performance for a long period due to such factors as, for example, expansion/contraction caused from heat, deterioration with age, or wear. 
   SUMMARY OF THE INVENTION 
   It is a general object of the present invention to provide a printer apparatus that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art. 
   Features and advantages of the present invention will be set forth in the description which follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by a printer particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention. 
   To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a printer apparatus for printing data on paper traveling through the printer apparatus in a paper conveying direction, the printer apparatus including: a paper conveying portion including a driving roller and a driven roller, the driving roller and driven roller being moveable with respect to one another between an engaged position at which the driving roller and the driven roller are pressed together and a disengaged position at which the driving roller and the driven roller are separated; wherein the paper conveying portion is situated downstream, with respect to the paper conveying direction, from the location at which the data is printed on the paper; and wherein the driving roller and the driven roller are operative to pressingly sandwich the paper therebetween when the driving roller and the driven roller are in the engaged position. 
   According to an embodiment of the present invention, the driving roller may include a roller part that has a plurality of fine protrusions disposed on a surface thereof, which fine protrusions protrude to dig into the paper when the paper is pressingly sandwiched between the driving roller and driven roller. 
   According to an embodiment of the present invention, the driving roller may include a roller part disposed at each end thereof. 
   According to an embodiment of the present invention, the driving roller may include a roller part disposed at the center thereof. 
   According to an embodiment of the present invention, the driving roller may include a roller part disposed over substantially the entire surface of the driving roller. 
   According to an embodiment of the present invention, the printer apparatus may further include a printing portion for printing the data on the paper, the printing portion being situated upstream of the paper conveying portion. 
   Furthermore, the present invention provides a printer apparatus for printing data on paper travelling through the printer apparatus in a paper conveying direction, the printer apparatus including: a thermal head; a platen roller; a paper conveying portion including a driving roller and a driven roller, the driving roller and driven roller being moveable with respect to one another between an engaged position at which the driving roller and the driven roller are pressed together and a disengaged position at which the driving roller and the driven roller are separated; wherein the thermal head and the platen roller are moveable relative to one another between an engaged position at which the thermal head and the platen roller are pressed together and a disengaged position at which the thermal head and the platen roller are separated; wherein the paper conveying portion is situated downstream, with respect to the paper conveying direction, from the thermal head; and wherein the driving roller and the driven roller are operative to pressingly sandwich the paper therebetween when the driving roller and the driven roller are in the engaged position. 
   According to an embodiment of the present invention, the platen roller may deliver a front-end of the paper by rotation thereof, wherein the driving roller and the driven roller may be disposed in the paper conveying portion so that the front-end of the paper, delivered from the thermal head by the rotation of the platen roller, is received between the driving roller and the driven roller, wherein the paper conveying portion may convey the delivered paper once the delivered paper is transferred to the paper conveying portion. 
   According to an embodiment of the present invention, the printer apparatus may further include: a motor; and a gear mechanism moved by the motor, the gear mechanism being coupled to the driving roller and the platen roller to rotate the driving roller and the platen roller in the same direction. 
   According to an embodiment of the present invention, the peripheral velocity of the driving roller may be faster than the peripheral velocity of the platen roller. 
   According to an embodiment of the present invention, the printer apparatus may further include: a one-way clutch for transmitting rotating motion of the gear mechanism to the platen roller, whereby the platen roller is rotated to thereby move the paper in the paper conveying direction. 
   According to an embodiment of the present invention, the printer apparatus may further include: a motor for rotating the driving roller; a gear disposed at an end of the driving roller; an oscillatory arm member disposed at an end of the driving roller, and including first and second arm parts pivoting in the same direction as the rotation of the driving roller; and first and second gears disposed on the respective first and second arm parts, which first and second gears engage said gear disposed at the end of the driving roller; wherein the oscillatory arm member rotates according to the rotation of the driving roller so that the gear of the arm portion engages with the gear disposed on the end of the driving roller. 
   According to an embodiment of the present invention, the driving roller and the platen roller may form a first module; the driven roller and the thermal head may form a second module; and the first module and second module may be detachably attached, whereby when attached the driving roller and the driven roller are pressed together and the platen roller and the thermal head are pressed together, and when detached the driving roller and the driven roller are separated and the platen roller and the thermal head are separated. 
   According to an embodiment of the present invention, the driven roller and the platen roller may form a first module; the driving roller and the thermal head may form a second module; and the first module and second module may be detachably attached, whereby when attached the driving roller and the driven roller are pressed together and the platen roller and the thermal head are pressed together, and when detached the driving roller and the driven roller are separated and the platen roller and the thermal head are separated. 
   Furthermore, the present invention provides a printer apparatus for printing data on paper travelling through the printer apparatus in a paper conveying direction, the printer apparatus including: a non-rotating platen pressing against a thermal head; an upstream paper conveying portion being situated upstream, with respect to the paper conveying direction, from the thermal head; a downstream paper conveying portion being situated downstream, with respect to the paper conveying direction, from the thermal head, the downstream paper conveying portion including a driving roller and a driven roller, the driving roller and driven roller being moveable with respect to one another between an engaged position at which the driving roller and the driven roller are pressed together and a disengaged position at which the driving roller and the driven roller are separated; wherein the driving roller and the driven roller are operative to pressingly sandwich the paper therebetween when the driving roller and the driven roller are in the engaged position. 
   It is another and more specific object of the present invention, for example, to provide a portable printer of a clamshell type that improves printing precision in a paper conveying direction without having to change the structure of a portion of a thermal head to which a rubber platen roller abuts. 
   Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view showing an internal structure of a thermal printer according to a first embodiment of the present invention; 
       FIG. 2  is a front view showing a thermal printer according to a first embodiment of the present invention; 
       FIG. 3  is a diagram showing a grip roller according to an embodiment of the present invention; 
       FIG. 4  is an enlarged view showing a main paper conveying portion according to an embodiment of the present invention; 
       FIGS. 5A through 5H  are views for explaining an operation of a thermal printer according to an embodiment of the present invention; 
       FIG. 6  is a diagram showing a slant prevention conveying mechanism according to an embodiment of the present invention; 
       FIGS. 7A and 7B  are diagrams for explaining procedures of printing and conveying an uncut type paper provided with a perforation; 
       FIGS. 8A and 8B  are diagrams for explaining procedures of printing and conveying a cut type paper; 
       FIG. 9  is a diagram showing a first variation of the thermal printer shown in  FIG. 1 ; 
       FIG. 10  is a diagram showing a second variation of the thermal printer shown in  FIG. 1 ; 
       FIG. 11  is a schematic view showing a thermal printer according to a second embodiment of the present invention; 
       FIGS. 12A and 12B  are schematic views showing a thermal printer according to a third embodiment of the present invention; 
       FIG. 13  is a schematic view showing a thermal printer according to a fourth embodiment of the present invention; 
       FIG. 14  is a schematic view showing a thermal printer according to a fifth embodiment of the present invention; 
       FIG. 15  is a schematic view showing a thermal printer according to a sixth embodiment of the present invention; 
       FIGS. 16A and 16B  are schematic views showing a thermal printer according to a seventh embodiment of the present invention; 
       FIG. 17  is a schematic view showing a thermal printer according to an eighth embodiment of the present invention; 
       FIG. 18  is a schematic view showing a thermal printer according to a ninth embodiment of the present invention; and 
       FIGS. 19A and 19B  are diagrams showing variations of the grip roller according to an embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
   [First Embodiment] 
     FIGS. 1 and 2  are drawings showing a thermal printer  10  according to a first embodiment of the present invention. The thermal printer  10  is a printer of a line printing type and is also of a clamshell type. X 1 -X 2  indicates a longitudinal direction of the thermal printer  10 , Y 1 -Y 2  indicates a width direction of the thermal printer  10 , and Z 1 -Z 2  indicates a height direction of the thermal printer  10 . A 1  indicates a paper conveying direction, and A 2  indicates a paper reversing direction. 
   The thermal printer  10  is assembled to a portable terminal apparatus  20 . The portable terminal apparatus  20  includes a casing  21  and a cover  23  that is openably supported by an axial member  22  of the casing  21  at the X 1  side. A paper roll installment portion  25  is disposed at the X 1  side of the casing  21 . 
   The thermal printer  10  has a main paper conveying portion  12  including a grip roller  40  serving as a driving roller and a pressing roller  64  serving as a driven roller. The main conveying portion  12  is situated more downstream in a paper conveying direction A 1  than a sub-paper conveying portion  11  including a thermal head  61  and a platen roller  31 , which is made of rubber in the illustrated exemplary embodiment. 
   Numeral  30  indicates a first module that is assembled inside the casing  21 . Numeral  60  indicates a second module that is assembled inside the cover  23 . When the cover  23  is open, the second module  60  is separated, that is detached, from the first module  30 . When the cover  23  is closed and locked, the second module  60  is detachably attached to the first module  30 . 
   The first module  30  includes the rubber-made platen roller  31 , the grip roller  40 , a pulse motor  50 , a speed deceleration gear alignment  51 , and first and second paper detecting sensors  32 ,  33 , for example reflection type sensors, in which the components are supported by a frame (not shown). In an order of the second paper detection sensor  33 , the platen roller  31 , the first paper detecting sensor  32 , and the grip roller  40 , said components are aligned in direction A 1 . 
   The grip roller  40  is disposed more downstream in the paper conveying direction A 1  than the platen roller  31 . The grip roller  40  is made of metal material and is manufactured by rolling. As shown in  FIG. 3 , grip roller parts  42 ,  43  are disposed on both ends of a shaft  41  of the grip roller  40 . The grip roller parts  42 ,  43  are situated at respective outer side portions of an area of a paper  81  on which printing is performed, that is, at a position corresponding to the rim portions on both sides of the paper  81 . The grip roller parts  42 ,  43  have a diameter Dg wider than that of the shaft  41 . As shown in  FIG. 3 , the grip roller parts  42 ,  43  have numerous fine protrusions  44  provided on a surface of the grip roller parts  42 ,  43 . The fine protrusions  44  have sharp tips that form spikes. In an exemplary embodiment, the height h of the fine protrusions  44  is approximately 0.04 mm, and is smaller than the thickness t ( FIG. 4 ) of the paper  81  on which printing is performed. 
   The speed deceleration gear alignment  51  includes a gear  52  situated on a shaft of the pulse motor  50 , a double-step gear  53 , a double-step gear  54 , a gear  55  situated on an end of the platen roller  31 , and a gear  56  situated on an end of the grip roller  40 . The double-step gear  54  engages gears  55 ,  56 . 
   The platen roller  31 , the grip roller  40 , the pulse motor  50 , and the speed deceleration gear alignment  51  are arranged so that, when the pulse motor  50  is driven under a condition where the peripheral velocity Vg of the grip roller parts  42 ,  43  match with a paper conveying velocity V, the platen roller  31  rotates in the same direction as the grip roller  40 , and the peripheral velocity Vg of the grip roller parts  42 ,  43  is slightly greater than a peripheral velocity Vp of the platen roller  31  (e.g. approximately 0.1% faster), that is, Vg&gt;Vp. In order to satisfy the relation of Vg&gt;Vp, the diameter Dg of the grip roller parts  42 ,  43  is slightly larger than a diameter Dp of the platen roller  31  (e.g. approximately 0.1% larger) ( FIG. 2 ). 
   The pulse motor  50  and the first and second paper detecting sensors  32 ,  33  are electrically connected to a control circuit  70  which, in the exemplary embodiment, is a microcomputer. 
   The second module  60  includes a head supporting board member  62  having the thermal head  61  fixed thereto, a spring board member  63 , the pressing roller  64 , and a cutter blade  68 , in which the components are supported by a frame (not shown). 
   The thermal head  61  has a heating part  61   a  arranged in direction Y 1 -Y 2 . The head supporting board member  62  is supported at its end portion on the X 1  side. The spring board member  63  biases the thermal head  61  substantially towards direction Z 2 . The pressing roller  64  has pressing roller parts  64   b ,  64   c , made of rubber in the illustrated exemplary embodiment, disposed on respective ends of a shaft  64   a  of the pressing roller  64 . Spring members  65 ,  66  bias said both ends of the shaft  64   a  substantially towards direction Z 2 . In an order of the thermal head  61 , the pressing roller  64 , and the cutter blade  68 , said components are aligned in the paper conveying direction A 1 . 
   It is to be noted that the platen roller  31 , the grip roller  40 , the thermal head  61 , and the pressing roller  64  are arranged so that, when the second module  60  is attached to the first module  30 , the heating part  61   a  of the thermal head  60  abuts the platen roller  31 , and the pressing roller parts  64   b ,  64   c  abut the respective grip roller parts  42 ,  43 . 
   The paper  81  is fed by the sub-paper conveying portion  11  in a case where the paper  81  is not held by the main paper conveying portion  12 , and is fed by the main paper conveying portion  12  in a case where the paper  81  is held by the main paper conveying portion  12 . In the main paper conveying portion  12 , the fine protrusions  44  of the grip roller parts  42 ,  43  dig into the bottom surface of the paper  81 , to thereby provide a conveying force to the paper  81 . Accordingly, paper can be conveyed with high precision, printing upon the conveyed paper can be performed with excellent precision, and the paper can be conveyed without encountering any slippage. 
   Next, an exemplary operation of the thermal printer  10  is described. 
   Referring to  FIGS. 5A through 5H , and initially to  FIG. 5A , first, the paper  81  is set (Step S 90 ). Here, the operator opens the cover  23 , installs a thermal paper roll  80  into the paper roll installment portion  25 , pulls out the paper  81 , and then closes the cover  23 . Thereby, as shown in  FIG. 5B , the paper  81  is sandwiched at the sub-paper conveying portion  11  between the thermal head  61  (via the heating part  61   a  of the thermal head  61 ) and the platen roller  31 , which presses against the thermal head  61 , and at the main paper conveying portion  12  (situated downstream of the sub-paper conveying portion  11  with respect to the paper conveying direction A 1 ) between the pressing roller  64  (via the pressing roller parts  64   b ,  64   c  of the pressing roller  64 ) and the grip roller  40 , which presses against the pressing roller  64 . 
   The main paper conveying portion  12  is disposed in a manner allowing a front-end part  81   a  of the paper  81  to be received at the abutting portion between the grip roller  40  and the pressing roller  64 . 
   After the paper  81  is detected by the first paper detecting sensor  32  in a state where the cover  23  is closed, for example, the thermal printer  10  is further controlled and operated according to the control circuit  70 . 
   Then, in step S 91 , a paper position is obtained in response to a printing command. First, as shown in  FIG. 5B , the pulse motor  50  ( FIGS. 1 and 2 ) is reversely driven, and the platen roller  31  and the grip roller  40  are rotated in a clockwise direction, to thereby reversely move the paper  81  toward direction A 2 . 
   As shown in  FIGS. 5C and 5D , the paper  81  is reversely moved such that the front-end part  81   a  deviates from the grip roller parts  42 ,  43 . The paper  81  is reversely moved until the first paper detecting sensor  32  detects the front-end part  81   a  and is switched to an OFF state. As a result, the position of the front-end part  81   a  of the paper  81  is obtained, and the procedure of obtaining the paper position is completed. 
   Next, a printing procedure is started (Step S 92 ). The pulse motor  50  is forwardly driven, and the platen roller  31  and the grip roller  40  are rotated in a counterclockwise direction, to thereby move the paper  81  toward direction A 1 . After the first paper detecting sensor  32  is switched to an ON state, the thermal head  61  is activated, to thereby start printing upon the paper  81 . 
   After the front-end part  81   a  of the paper  81  is inserted between the grip roller parts  42 ,  43  and the respective pressing roller parts  64   b ,  64   c  (as shown in  FIG. 5E ), the grip roller parts  42 ,  43  and the pressing roller parts  64   b ,  64   c , together with the platen roller  31 , convey the paper  81  toward direction A 1 . Accordingly, the paper  81  is smoothly transferred from the sub-paper conveying portion  11  to the main paper conveying portion  12 , and is conveyed further on by the main paper conveying portion  12 . Numeral  82  indicates an area on which printing is performed, for example. 
   Here, the paper  81  is in a state abutting the rubber-made platen roller  31  at the sub-paper conveying portion  11  while the fine protrusions  44  are dug into the bottom surface of the paper  81  at the main paper conveying portion  12 . Accordingly, the conveying force applied to the paper  81  at the main paper conveying portion  12  is greater compared to that at the sub-paper conveying portion  11 . The main paper conveying portion  12 , therefore, conveys the paper  81  at a prescribed speed corresponding to the peripheral velocity Vg of the grip roller parts  42 ,  43 . Since the fine protrusions  44  of the grip roller parts  42 ,  43  are dug into the bottom surface of the paper  81 , no slippage will occur between the paper  81  and the grip roller parts  42 ,  43 . Accordingly, the paper  81  can be conveyed with high precision. As a result, printing can be performed with higher precision. It is to be noted that, owing to the relation of Vg&gt;Vp, a slight slippage of the paper  81  may occur at the platen roller  31 . 
   By the time when the paper  81  is fed out from the sub-paper conveying portion  11 , the grip roller  40  will be rotating and the main paper conveying portion  12  will be in a state ready to convey the paper  81 . Therefore, the transition of conveying the paper  81  at the sub-paper conveying portion  11  to conveying the paper  81  at the main paper conveying portion  12  can be conducted smoothly. 
   After a command to end the printing procedure, the pulse motor  50  comes to a stop after performing step movements of a prescribed count. The portion of the paper  81  at which printing ends is situated slightly beyond the cutter blade  68  toward direction A 1 . This state is illustrated in  FIG. 5G . 
   Then, a procedure of cutting the printed part  82  of the paper  81  is executed in step S 93 . The operator pulls out the printed part  82 , which is fed out from the portable terminal apparatus, and the cutter blade  68  cuts the printed part  82  as shown in  FIG. 5H . 
   When another printing command is transmitted, the above-described operation is performed likewise. 
   As described above, the grip roller parts  42 ,  43  are made of metal material, and therefore, have a greater dimensional accuracy and wear-resistance compared to a rubber-made roller. Since the fine protrusions  44  of the grip roller parts  42 ,  43  dig into the bottom surface of the paper  81 , as shown in  FIG. 4 , no slippage occurs between the paper  81  and the grip roller parts  42 ,  43  regardless of factors such as temperature and/or humidity. This allows the thermal printer  10  to maintain a highly precise paper conveying velocity for a long period. As a result, a high printing precision in the paper conveying direction can be maintained for a long period. This allows the thermal printer to satisfactorily print out, for example, barcodes and meter readouts. 
     FIG. 6  shows the platen roller  31  disposed in a manner slightly tilting in an angle θ with respect to line YA that perpendicularly intersects with center line XA of a paper conveying path, and a paper guide member  75  disposed on a side toward Y 2 . 
   The tilting of the platen roller  31  causes the conveyed paper  81  to be drawn toward the side of Y 2 , and the paper guide member  75  guides a rim part  81   b  (on the side of Y 2 ) of the conveyed paper  81  to prevent the conveyed paper  81  from being slantingly conveyed. 
   The control circuit  70  controls the operation of the thermal printer  10  differently according to the type of paper being used. 
   In a case of using an uncut type of paper  81 A provided with a perforation  83 , the pulse motor  50  reversely moves for a prescribed number of steps, and consequently the platen roller  31  moves clockwise, from a state shown in  FIG. 5G , and then comes to a stop in a manner shown in  FIG. 7A . 
   In the reverse movement of the pulse motor  50 , and the consequent clockwise movement of the platen roller  31 , the uncut type of paper  81 A is conveyed in direction A 2 . When the reverse movement of the pulse motor  50  comes to a stop, the perforation  83  of the uncut type paper  81 A is positioned between the grip roller  40  and the platen roller  31 , and a portion of the printed part  82  situated proximal to the edge of the printed part  82  on the side of A 2  is clamped and supported by the grip roller  40  and the pressing roller  64 . 
   The printed part  82  is then pulled, for example, by the operator, in direction A 1  to separate (cut) the uncut type paper  81 A along the perforation  83 , and draw out the printed part  82  from the clamped position. Then, another printing procedure may be started after the paper position is obtained by the first paper detecting sensor  32 . 
   In a case of using a cut type of paper  81 B ( FIGS. 8A and 8B ), a printing operation is commenced when the second paper detecting sensor  33  detects a rear-end part  81 Bc of the cut type paper  81 B. After performing a prescribed amount of printing, the printing operation is completed. This operation is shown in  FIG. 8A . When printing of the cut type paper  81 B is completed, a portion of the printed part  82  ( FIG. 8B ) situated proximal to the edge of the printed part  82  on the side of A 2  is clamped and supported by the grip roller  40  and the pressing roller  64 . 
   The printed part  82  is then pulled, for example, by the operator, in direction A 1  to draw out the printed part  82  from the clamped position. 
   Next, exemplary variations of the thermal printer  10  are described. 
     FIG. 9  shows a first variation of the thermal printer  10 , in which a one-way clutch  76  is assembled to a gear  55  disposed on an end of the platen roller  31 . The one-way clutch  76  operates so that the counterclockwise rotation of the gear  55  is transmitted to the platen roller  31 . From an aspect where the platen roller  31  serves as a driving part, the one-way clutch  76  operates so that the counter clockwise rotation of the platen roller  31  is not transmitted to the gear  55 . 
   The platen roller  31 , being rotated counterclockwise by the one-way clutch  76 , delivers an end part of the paper  81  in direction A 1  from the sub-paper conveying portion  11 . When the end part of the paper  81  is received between the grip roller  40  and the pressing roller  64  of the main paper conveying portion  12 , the paper  81  is then conveyed in the main paper conveying portion  12  at a rate faster than the sub-paper conveying portion  11 . Accordingly, the platen roller  31 , now being tangentially pulled by the paper  81 , is rotated at a faster rate, whereby the speed of rotation of the platen roller  31  exceeds that which is provided by the gear  55  that is rotated by the motor  50 . This creates a state where the one-way clutch  76  no longer transmits rotation from the gear  55  to the platen roller  31 , and where the platen roller  31  is thus rotated independently from the gear  55 , and thus in accordance with the movement of the conveyed paper  81 . As a result, no slippage occurs between the platen roller  31  and the paper  81 . Therefore, the braking force that works on the paper  81  conveyed in direction A 1  can be reduced and conveyance precision of the paper  81  can be improved. 
   Furthermore, as the period for using a printer becomes longer, the platen roller  31  wears away and the diameter thereof becomes smaller. This causes the rotation speed of the platen roller  31  rotating in accordance with the movement of the conveyed paper  81  to increase, and the speed difference between the rotation of the platen roller  31  and the rotation of the gear  55  (rotated by the motor  50 ) to become larger. In this situation, the one-way clutch  76  transmits no rotation from the gear  55  to the platen roller  31  and maintains a state of not transmitting the rotation, and the platen roller  31  is thus rotated independently from the gear  55 . 
     FIG. 10  shows a second variation of the thermal printer  10 , in which a platen roller  31 A is formed of a rubber material having a relatively lower degree of hardness than, for example, the platen roller  31 . In this variation, a pressing force of the thermal head  61 , which is less than, for example, that which was previously described, will suffice since the platen roller  31 A is formed of a rubber material having a relatively lower degree of hardness. Accordingly, a board spring portion  24  is formed at a portion of the cover  23  that is made from synthetic resin for biasing the thermal head  61 . In this case, a spring board member, which is a separate component, is not required. 
   [Second Embodiment] 
     FIG. 11  is a schematic diagram showing a thermal printer  10 A according to a second embodiment of the present invention. The thermal printer  10 A has a structure where the sub-paper conveying portion  11  shown in  FIG. 2  is separated into a sub-paper conveying part  11 A- 1  and a printing part  11 A- 2 . 
   In an order of the sub-paper conveying part  11 A- 1 , the printing part  11 A- 2 , and the main paper conveying portion  12 , said components are aligned in direction A 1 . 
   A first module  30 A includes the platen roller  31 , the grip roller  40 , the pulse motor  50 , and a speed deceleration gear alignment  51 A, and the first and second paper (for example, reflection type) detecting sensors  32 ,  33 , in which the components are supported by a frame (not shown). In an order of the second paper detecting sensor  33 , the platen roller  31 , a flat-shaped platen  90 , the first paper detecting sensor  32 , the grip roller  40 , said components are aligned in direction A 1 . The speed deceleration gear alignment  51 A has a structure where the speed deceleration gear alignment  51  shown in  FIG. 2  is added with gears  57  and  58 . 
   A second module  60 A includes the head supporting board member  62  having the thermal head  61  fixed thereto, the spring board member  63 , the pressing roller  64 , and the cutter blade  68 , and a pressing roller  91 , in which the components are supported by a frame (not shown). 
   The sub-paper conveying part  11 A- 1  is formed of the platen roller  31  and the pressing roller  91 . The printing part  11 A- 2  is formed of the thermal head  61  and the flat-shaped platen  90 . 
   Since the platen  90  has a flat shape, a strict precision in the position between the thermal head  60  and the platen  90  is not required. 
   The sub-paper conveying part  11 A- 1  and the main paper conveying part  12  operate in the same manner as described with the thermal printer  10 . 
   [Third Embodiment] 
     FIG. 12  is a schematic diagram showing a thermal printer  10 B according to a third embodiment of the present invention. The thermal printer  10 B has a structure where the speed deceleration gear alignment  51  shown in  FIG. 1  is replaced by an oscillating gear mechanism  100 . 
   The oscillatory gear mechanism  100  includes a gear  101  fixed to a shaft of the grip roller  40 , a V-shaped oscillatory arm member  102  (shaded gray) with the shaft of the grip roller  40  serving as its center for oscillation, and gears  103 ,  104  engaged with the gear  101 , and supported by respective arm parts  102   a ,  102   b  of the oscillatory arm member  102 . The arm member  102  and the grip roller  40  have a sliding clutch (not shown) disposed therebetween. By the rotation of the grip roller  40 , the oscillatory arm member  102  is rotated via the frictional force of the sliding clutch until the gears are engaged in a direction same as the rotating direction of the grip roller  40 . 
   The pulse motor  50 B rotates the grip roller  40  via a speed deceleration gear alignment  51 B. 
   As shown in  FIG. 12A , when the pulse motor  50 B is forwardly (i.e. counterclockwise) rotated, the grip roller  40  is rotated in a counterclockwise direction via the speed deceleration gear alignment  51 B. The oscillatory arm member  102  is also rotated in a counterclockwise direction. Then, the gear  103 , urged by the oscillatory arm member  102 , engages with the gear  55  situated on an end of the platen roller  31  to rotate the platen roller  31  in a counterclockwise direction. 
   As shown in  FIG. 12B , when the pulse motor  50  is reversely rotated (i.e. clockwise) the grip roller  40  is rotated in a clockwise direction via the speed deceleration gear alignment  51 B. The oscillatory arm member  102  is also rotated in a clockwise direction. Then, the gear  104 , urged by the oscillatory arm member  102 , engages with the gear  55  to rotate the platen roller  31  in a clockwise direction. 
   [Fourth Embodiment] 
   The thermal printer described in the fourth through ninth embodiments below is provided in a manner such that the length L between the position at which the heating part  61   a  of the thermal head  61  presses against the paper  81  and the position at which the paper  81  is sandwiched by the grip roller  40  and the pressing roller  64  is short. 
     FIG. 13  is a schematic diagram showing a thermal printer  10 C according to the fourth embodiment of the present invention. A first module  30 C includes the platen roller  31  and the grip roller  40 . A second module  60 C includes the thermal head  61 , the head supporting board member  62 , and the pressing roller  64 . 
   The grip roller  40  is disposed lower than and proximal to the platen roller  31  such that the grip roller  40  and the platen roller  31  are situated at a different level. The pressing roller  64 , abutting the grip roller  40 , is disposed lower than the thermal head  61  and distal to the platen roller  31 . Accordingly, the length L is short. 
   [Fifth Embodiment] 
     FIG. 14  is a schematic diagram showing a thermal printer  10 D according to the fifth embodiment of the present invention. A first module  30 D includes the platen roller  31  and the grip roller  40 . A second module  60 D includes the thermal head  61 , a head supporting board member  62 D, and the pressing roller  64 . 
   The head supporting board member  62 D has a notch part  62 Da formed on an upper surface of an end part thereof (toward the side of A 1 ). A portion of the pressing roller  64  is fitted into the notch part  62 Da, and is disposed proximal to the platen roller  31 . The grip roller  40  is disposed in a position abutting the pressing roller  64 . Accordingly, the length L is short. 
   [Sixth Embodiment] 
     FIG. 15  is a schematic diagram showing a thermal printer  10 E according to the sixth embodiment of the present invention. The thermal printer  10 E has a structure where the positions of the pressing roller  64  and the grip roller  40  described in the thermal printer  10 D are switched. A first module  30 E includes the platen roller  31  and the pressing roller  64 . A second module  60 E includes the thermal head  61 , a head supporting board member  62 E, and the grip roller  40 . 
   A portion of the pressing roller  40  is fitted into the notch part  62 Ea, and is disposed proximal to the platen roller  31 . Accordingly, the length L is short. 
   [Seventh Embodiment] 
     FIGS. 16A and 16B  are schematic diagrams showing a thermal printer  10 F according to the seventh embodiment of the present invention. A first module  30 F includes the platen roller  31  and the grip roller  40 . A second module  60 F includes the thermal head  61 , a head supporting board member  62 F, and the pressing roller  64 . 
   The grip roller  40  and the platen roller  31  are disposed in a manner where a portion of the platen roller  31  is fitted between the grip roller part  42  and the grip roller part  43 . Accordingly, the length L is short. 
   [Eighth Embodiment] 
     FIG. 17  is a schematic diagram showing a thermal printer  10 G according to the eighth embodiment of the present invention. A first module  30 G includes the platen roller  31 . A second module  60 G includes the thermal head  61 , a head supporting board member  62 G, and the grip roller  40 . The thermal printer  10 G is not provided with the pressing roller  64 . The grip roller  40 , serving as a part of the second module  60 G, is disposed on the same side as the thermal head  61 . The platen roller  31 , pressing against the thermal head  61 , has a part disposed more toward the side A 1  compared to the edge (edge toward side A 1 ) of the thermal head  61 . The grip roller  40  presses against the part of the platen roller  31  disposed more toward the side A 1  compared to the edge (edge toward side A 1 ) of the thermal head  61 . The paper  81  is disposed on the peripheral surface of the platen roller  31 . Accordingly, the length L is short. In this embodiment, the main paper conveying portion  12  is formed of the grip roller  40  and the platen roller  31 . 
   [Ninth Embodiment] 
     FIG. 18  is a schematic diagram showing a thermal printer  10 H according to the ninth embodiment of the present invention. A first module  30 H includes the platen roller  31  and the pressing roller  64 . A second module  60 H includes the thermal head  61 , a head supporting board member  62 H, and the grip roller  40 . 
   The thermal printer  10 H has a structure where the thermal printer  10 G shown in  FIG. 17  is added with the pressing roller  64 . The pressing roller  64 , serving as a part of the first module  30 H, is disposed on the same side as the platen roller  31 . The pressing roller  64  is disposed in a manner abutting a lower side of the grip roller  40 . The grip roller  40  is separated from the platen roller  31 . Accordingly, the length L is short. 
     FIGS. 19A and 19B  are diagrams showing other exemplary variations of the grip roller  40 . 
     FIG. 19A  shows a grip roller  40 I in which a grip roller part  42 I is disposed across approximately the entire length of the grip roller  40 I. 
     FIG. 19B  shows a grip roller  40 J in which a grip roller part  42 J is disposed at a center of the grip roller  40 J. 
   The grip roller parts  42 I,  42 J may be formed, for example, by employing a metal mold or by applying paint technology. 
   In consequence, the printer apparatus according to an exemplary embodiment of the present invention is able to provide a more accurate paper conveying precision and, thereby a more accurate printing precision, in comparison to, for example, a conventional portable printer apparatus conveying paper with a platen roller. 
   Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority application No.2003-369318 filed on Oct. 29, 2003, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.