Abstract:
A read/write processing device including: a transport path, adapted to transport a medium therethrough; a read/write unit, adapted to read or write data on the medium and provided at a part of the transport path; a transport mechanism, provided with a first feeding roller and a pressing member adapted to transport the medium to the read/write unit while the pressing member presses the medium toward the first feeding roller; a gap adjusting mechanism, operable to adjust a gap between the read/write unit and the medium in the trasnsport path; a medium release mechanism, operable to release the mdium from the first feeding roller and the pressing member; a detector, operable to detect a jam of the medium in the transport path; and a controller, operable to control the gap adjusting mechanism to wide the gap, when the detector detects the jam.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     Embodiments of the present invention relate to a read/write processing device which transports a paper along a predetermined transport path and performs an information process on the paper carried onto a process reference surface in the transport path, such as a process of forming desired information on the paper or reading the information of the paper.  
       BACKGROUND OF THE INVENTION  
       [0002]     A printer connected to a personal computer or the like is an example of a read/write processing device which transports a paper along a predetermined transport path and performs an information process on the paper carried onto a process reference surface in the transport path.  
         [0003]     In such a printer, a paper feed unit for laminating the papers therein, a transport mechanism for transporting the sheet from the paper feed unit along a predetermined transport path one by one, a print head (process mechanism) which prints an image such as a character or a figure on the surface of the sheet carried onto a platen surface (process reference surface) disposed in the transport path, and various operating mechanisms such as a carriage for applying a predetermined moving force to the print head are mounted in an outer case.  
         [0004]     In another printer, in order to reduce the size of the read/write processing device or save space, a front feed/ejection type, in which any one of a paper feed unit and a unit of ejecting a printed sheet is disposed at the front side of the apparatus, is variously suggested (for example, see Japanese Patent No. 3520469).  
         [0005]     In such a front feed/ejection type printer, a sheet cassette laminating the sheets therein is disposed at the lower side of the front surface of the apparatus, an ejection tray for ejecting a printed sheet is disposed above the sheet cassette, a U-shaped transport path for connecting the sheet cassette with the ejection tray is formed in the outer case, a platen surface is disposed in a linear transport path configuring the U-shaped transport path, and a print head is disposed above the platen surface.  
         [0006]     In addition, in the U-shaped transport path of the front feed/ejection type printer, a paper feed roller and a driven roller which sandwich and transport a sheet for transporting the sheet to the platen surface disposed at the downstream side of the transport path, an intermediate roller and an assist roller for sandwiching and transporting the sheet fed into the transport path to the paper feed roller and the driven roller, a print head for printing the sheet carried onto the platen surface, and a ejection roller and a star wheel for ejecting the sheet printed by the print head onto the ejection tray located at the outlet of the transport path are provided.  
         [0007]     Furthermore, in another printer, a gap between the rollers sandwiching the sheet can be adjusted by, for example, a gap adjusting mechanism for adjusting a gap between the platen surface and the print head, or the paper feed roller and the driven roller on the transport path, such that a stable print is performed with respect to various media such as general paper, thick paper such as a postcard, or CD-R (for example, see JP-A-2003-266856, JP-A-2002-356036, and JP-A-5-309909).  
         [0008]     However, in a case of the front feed/ejection type printer, in order to remove the paper jam in the transport path, a transport path opening/closing mechanism for opening and closing a portion of the transport mechanism configuring the U-shaped transport path is provided, and, when the paper jam is generated, at least a portion of the jammed sheet is externally exposed by opening the transport path opening/closing mechanism.  
         [0009]     However, in a case where the transport path opening/closing mechanism for externally exposing a portion of the jammed sheet is provided as a solution for removing the paper jam in the printer, the jammed sheet may not be easily removed and thus another problem may be generated.  
         [0010]     In other words, since a portion of the jammed sheet is sandwiched between a pair of rollers in the transport path, it may be difficult to pull out the sheet with a small force. Furthermore, if the jammed sheet is forcibly pulled out, a portion of the sheet sandwiched between the pair of rollers tears, a piece of sheet remains in the transport path, and thus another problem is caused in a next transporting process.  
         [0011]     In addition, in a case where a portion of the jammed sheet is disposed between the print reference surface and the print head, when the jammed sheet is pulled out, the sheet rubs against the print head and thus the print head may be damaged or contaminated.  
         [0012]     Furthermore, when the jammed sheet is pulled out, if a driving roller of the pair of rollers rotates by a friction force with the sheet, the rotation of the driving roller reversely drives a power transmission system, a rotation force is applied to a driving motor, and a power generation phenomenon of the driving motor is generated. Thus, circuits may be damaged by the power generation of the driving motor.  
         [0013]     Meanwhile, when a mechanism for removing the paper jam is newly provided in order to prevent the above-mentioned problems from being generated, the cost increases due to the complexity of the configuration.  
       SUMMARY OF THE INVENTION  
       [0014]     Accordingly, in order to solve the above-mentioned problems, an object of at least one embodiment of the present invention is to provide a read/write processing device, which can easily remove a jammed paper when a paper jam is generated in the device, although a mechanism for removing the jam is not further provided. The embodiments of the present invention is as follows:  
         [0015]     A read/write processing device comprising:  
         [0016]     a transport path, adapted to transport a medium therethrough;  
         [0017]     a read/write unit, adapted to read or write data on the medium and provided at a part of the transport path;  
         [0018]     a transport mechanism, provided with a first feeding roller and a pressing member adapted to transport the medium to the read/write unit while the pressing member presses the medium toward the first feeding roller;  
         [0019]     a gap adjusting mechanism, operable to adjust a gap between the read/write unit and the medium in the trasnsport path;  
         [0020]     a medium release mechanism, operable to release the mdium from the first feeding roller and the pressing member;  
         [0021]     a detector, operable to detect a jam of the medium in the transport path; and 
        a controller, operable to control the gap adjusting mechanism to wide the gap, when the detector detects the jam. According to the read/write processing device having the above-mentioned configuration, when the paper jam is generated in the device, the gap adjusting mechanism automatically operates to widen the gap between the process reference surface and the read/write unit.        
 
         [0023]     Furthermore, since the gap adjusting mechanism, which automatically operates when the paper jam is generated, can process the papers having different thicknesses as well as remove the paper jam, a mechanism for removing the paper jam need not be further provided and thus the protection of the read/write unit at the time of removing the jammed paper can be realized with low cost.  
         [0024]     A read/write processing device comprising:  
         [0025]     a transport path, adapted to transport a medium therethrough;  
         [0026]     a read/write unit, adapted to read or write data on the medium and provided at a part of the transport path;  
         [0027]     a transport mechanism, provided with a first feeding roller and a pressing member adapted to transport the medium to the read/write unit while the pressing member presses the medium toward the first feeding roller;  
         [0028]     a medium release mechanism, operable to release the medium from the first feeding roller and the pressing member;  
         [0029]     a detector; operable to control the medium release mechanism to release the medium, when the detector detects the jam.  
         [0030]     According to the read/write processing device having the above-mentioned configuration, when the paper jam is generated in the device, the roller release mechanism automatically operates to release the medium from the driven roller and the paper feed roller such that the sandwiching of the paper is opened.  
         [0031]     According to read/write processing device according to the present invention, when a paper jam is generated in the device, the gap adjusting mechanism or the roller release mechanism automatically operate, and thus the gap between the process reference surface and the process mechanism widens or the driven roller is separated from the paper feed roller such that the sandwiching of the paper is opened. Accordingly, when a transport path opening/closing mechanism is opened and the jammed paper is pulled out, the contamination of the read/write unit generated when the jammed paper rubs against the process mechanism is not generated, or a piece of sheet does not remain in the apparatus when a portion of the jammed paper is pulled out. In addition, it is possible to easily remove the jammed paper with a small operation force.  
         [0032]     Thus, it is possible to provide a read/write processing device having excellent treatment and repairability, which can easily remove the jammed paper when the paper jam is generated in the device, although a mechanism for removing the paper jam is not further provided. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]      FIG. 1  is a perspective view of an inkjet printer according to a first embodiment of the present invention.  
         [0034]      FIG. 2  is a perspective view of the inkjet printer illustrated in  FIG. 1  in which an ejection tray and an upper case are removed.  
         [0035]      FIG. 3  is a perspective view of the inkjet printer illustrated in  FIG. 2  when viewed at the upper rear side thereof.  
         [0036]      FIG. 4  is a side cross-sectional view illustrating a sheet transport path in the inkjet printer illustrated in  FIG. 1 .  
         [0037]      FIG. 5  is a side cross-sectional view illustrating a feed state of the inkjet printer illustrated in  FIG. 1 .  
         [0038]      FIG. 6  is a side cross-sectional view illustrating a state of transporting the sheet in the inkjet printer illustrated in  FIG. 1 .  
         [0039]      FIG. 7  is a side cross-sectional view of main portions of the sheet transport path in the inkjet printer illustrated in  FIG. 1 .  
         [0040]      FIG. 8  is a side cross-sectional view explaining a state of normally transporting the sheet in the transport path illustrated in  FIG. 7 .  
         [0041]      FIG. 9  is a side cross-sectional view explaining an operation of a gap adjusting mechanism when a paper jam is generated in the transport path illustrated in  FIG. 8 .  
         [0042]      FIG. 10  is a side cross-sectional view explaining a state of blocking power transmission between a driving motor and an intermediate roller in the transport path illustrated in  FIG. 9 .  
         [0043]      FIG. 11  is a flowchart illustrating an operation of the inkjet printer illustrated in  FIG. 1  when a paper jam is generated. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0044]     Hereinafter, a read/write processing device according to a first embodiment of the present invention will be described with reference to the accompanying drawings. In the present embodiment, although, for example, an inkjet printer  1  illustrated in  FIG. 1  is described as a paper processing device, as the read/write processing device according to the present invention, for example, printers including a wire dot printer, a copier, a facsimile, a paper money changing machine or the like may be used, in addition to the printer.  
         [0045]      FIG. 1  is a perspective view of an inkjet printer according to a first embodiment of the present invention.  FIGS. 2 and 3  are perspective views of the inkjet printer illustrated in  FIG. 1  in which an ejection tray and an upper case are removed.  FIGS. 4 through 6  are side cross-sectional views illustrating a sheet transport path in the inkjet printer illustrated in  FIG. 1 .  FIGS. 7 through 10  are side cross-sectional views of main portions of the sheet transport path in the inkjet printer illustrated in  FIG. 1 , and  FIG. 11  is a flowchart illustrating an operation of the inkjet printer illustrated in  FIG. 1  when a paper jam is generated.  
         [0046]     The inkjet printer  1  according to the present embodiment is a front feed/ejection type printer. As illustrated in  FIG. 1 , a box-shaped sheet cassette  5  for laminating papers P therein is detachably inserted into the center of the front surface of an outer case  4  including an upper case  2  and a lower case  3 .  
         [0047]     In addition, an ejection tray  6  for receiving a printed sheet is provided to cover an upper opening portion of the sheet cassette  5 .  
         [0048]     Furthermore, a display unit  7  such as an indicator and an operational unit  8  such as a power supply switch are disposed at the left and right sides of the front surface of the outer case  4 . A black ink cartridge mounting unit and a color ink cartridge mounting unit, which are disposed at the left and right sides of the front surface of the outer case  4 , are covered by a black ink cover  9  and a color ink cover  10  which are freely opened or closed, respectively.  
         [0049]     In the outer case  4 , as illustrated in FIGS.  2  to  4 , a transport mechanism  11  which transports a sheet of paper P which is introduced from the sheet cassette  5  one by one by a pickup roller (feed roller)  21  of a below-described feed unit  22  along a U-shaped transport path, a carriage  13  which is disposed to be reciprocally moved by the transport mechanism  11  in a direction perpendicular to a transporting direction of the sheet P in the U-shaped transport path, a print head (read/write unit)  44  which is mounted in the carriage  13  and performs print (information process) by injecting particles of a recording ink onto the sheet P, ink tanks  15  and  16  for storing the recording inks which are supplied to the print head  44 , and a control unit CPU (not illustrated) which controls a transporting speed of the sheet P due to the transport mechanism, a movement speed of the carriage  13 , or an ink injecting operation of the print head  44  are provided.  
         [0050]     The carriage  13 , as illustrated in  FIGS. 2 and 3 , is supported to be moved in a width direction of the sheet by a pair of carriage shafts  53  which extend in the width direction of the sheet, and fixed to a timing belt  54  which is driven by a carriage motor  14 , such that the carriage can be reciprocally moved in the width direction of the sheet in accordance with the travel of the timing belt  54 .  
         [0051]     In the inkjet printer  1 , ink discharge from the print head  44  mounted in the carriage  13  is controlled to record (print) an image such as a character or a figure on the sheet P, in the state that the transporting direction of the sheet P is set to a sub scan direction and the movement direction of the carriage  13  is set to a main scan direction.  
         [0052]     In the inkjet printer  1  according to the present embodiment, the U-shaped transport path in which the sheet P is transported by the transport mechanism  11 , as illustrated in  FIG. 4 , includes an arc-shaped transport path A for transporting the sheet P introduced from the sheet cassette  5  and a linear transport path B connected from the arc-shaped transport path A to an ejection tray  6 .  
         [0053]     In addition, a guide unit  34  which configures an outer diameter side of the arc-shaped transport path A of the U-shaped transport path is assembled in a rear opening/closing cover  17  illustrated in  FIG. 3 , and the rear opening/closing cover  17  configures a transport path opening/closing mechanism for externally exposing a portion of the jammed sheet P in the arc-shaped transport path A since the rear opening/closing cover  17  is mounted in an openable and closable manner.  
         [0054]     Furthermore, the transport mechanism  11  has an auto sheet feeder (ASF) and a paper feed unit.  
         [0055]     The auto sheet feeder, as shown in  FIG. 5 , includes a feed unit  22  for feeding one of the several sheets P laminated in the sheet cassette  5  into an inlet of the arc-shaped transport path A disposed at the rear side of the device, an intermediate roller  31  and an assist roller  33  mounted in the arc-shaped transport path A for transporting the sheet P introduced by the feed unit  22  to a paper feed roller  41  and a driven roller  42  which are disposed at a proximal position of the print head  44 , and the guide unit  34  for controlling the transporting direction of the sheet P transported along the outer circumferential of the intermediate roller  31  configuring the inner diameter side of the arc-shaped transport path A with a predetermined gap to an arc-shape which reaches an outlet of the arc-shaped transport path A.  
         [0056]     By inserting the sheet P between the intermediate roller  31  which is the driving roller and the assist roller  33  which is the driven roller, the sheet P is transported. At the upstream side of the assist roller  33 , a retard roller  32  for preventing the several sheets P from being introduced into the arc-shaped transport path A is provided.  
         [0057]     The paper feed unit, as shown in  FIG. 6 , transports the sheet P, which is transported from the arc-shaped transport path A, to a platen  91  including a platen surface (process reference surface)  91   a  disposed at the downstream side thereof, by the paper feed roller  41  and the driven roller  42  disposed on the linear transport path B (see  FIG. 7 ).  
         [0058]     In the present embodiment, the driven roller  42  presses and biases the upper surface of the sheet P onto the paper feed roller  41  which is the driving roller contacting the lower surface of the sheet P, thereby transporting the sheet P.  
         [0059]     In addition, in the outer case  4  as shown in  FIG. 7 , a print process mechanism  43  including the print head  44  is mounted as a process mechanism for printing an image such as a character or a figure onto the sheet P which is transported onto the platen surface  91   a  of the platen  91 . The sheet P which is printed by the print process mechanism  43  is sandwiched and transported by an ejection roller  48  which is the driving roller and a star wheel  48   b  which is the driven roller and is ejected to the ejection tray  6  at the outlet of the transport path.  
         [0060]     The feed unit  22 , as illustrated in  FIGS. 4 and 5 , is configured such that the rear end of a feed lever  25  including a pickup roller  21  at the front end thereof can rotate in a vertical direction in the figures by a support pin  24 . This feed unit  22  allows the pickup roller  21  to contact the sheet P which is disposed at a highest side in the sheet cassette  5  by the vertical rotation of the feed lever  25 .  
         [0061]     When the inkjet printer  1  stops, the feed unit  22 , as illustrated in  FIG. 4 , allows the feed lever  25  to be substantially maintained in a horizontal direction such that the pickup roller  21  is maintained to be separated from the sheet P in the sheet cassette  5 .  
         [0062]     In addition, at the time of feeding the sheet, as illustrated in  FIG. 5 , the pickup roller  21  presses the sheet P at the highest side in the sheet cassette  5  by the downward rotation of the feed lever  25  about the support pin  24 , and the sheet P in the sheet cassette  5  contacts a sloped friction pad  23  by the rotation of the pickup roller  21  and separated by a friction force and the strength of the intermediate portion of the sheet P to be introduced into the arc-shaped transport path A one by one.  
         [0063]     At this time, the retard roller  32  rotates in a counterclockwise direction in  FIG. 5  and applies power to the sheet P toward the sheet cassette  5 . By this configuration, for example, even if a lower sheet P is fed together, the retard roller  32  returns the lower sheet to the sheet cassette  5  by a friction force between the retard roller  32  and the lower sheet P. As a result, each sheet is separated and transported to the arc-shaped transport path, and then fed to the processor after transported while sandwiched between the intermediate roller and the assist roller.  
         [0064]     When the print starts by the print process mechanism  43 , as illustrated in  FIG. 6 , the feed lever  25  returns to an original horizontal state.  
         [0065]     At the upper side of the guide unit  34 , an auxiliary guide member  35  is provided together with the assist roller  33  for sending the transported sheet P toward the linear transport path B.  
         [0066]     The rear end of the auxiliary guide member  35  is rotatably supported to the guide unit  34  and the front end thereof freely rotates.  
         [0067]     Moreover, as illustrated in  FIG. 6 , the auxiliary guide member  35  presses the sheet P, which is transported from the arc-shaped transport path A to the linear transport path B, downward by its own weight, and guides the sheet P to the front side of the inkjet printer  1  along the linear transport path B.  
         [0068]     The paper feed roller  41  and the driven roller  42  are disposed at the front side of the device separated from the outlet of the arc-shaped transport path A (downstream end of the guide unit  34 ) by a predetermined distance, and, as illustrated in  FIG. 6 , sandwiches the sheet P which is transported from the arc-shaped transport path A to the linear transport path B to transport the sheet P to the lower side of the print process mechanism  43  which is a print position. Furthermore, by controlling the rotation amount of the paper feed roller  41 , the sheet P can be positioned with respect to the print process mechanism  43 .  
         [0069]     As illustrated in  FIG. 4 , the print head  44  of the print process mechanism  43  has an ejection nozzle  46  for ejecting ink toward the sheet P. At the upstream side of the ejection nozzle  46  in the inkjet printer  1 , a PW sensor  47  for detecting the sheet P and detecting the width of the sheet P is provided.  
         [0070]     The PW sensor  47  detects the existence of the sheet P by irradiating light to the sheet P and detecting light reflected from the sheet P and detects the width of the sheet P by moving the carriage  13 .  
         [0071]     Furthermore, in the inkjet printer  1  according to the present embodiment, sheet detecting sensors for detecting the existence of the sheet P are provided at several places in the transport path. In this case, these sensors may be transmission sensors.  
         [0072]     In addition, the inkjet printer  1  according to the present embodiment includes a gap adjusting mechanism (APG: auto platen gap mechanism)  51  for adjusting a gap between the platen surface  91   a  and the print head  44 , in order to perform a printing process on the sheets P having different thicknesses or the like.  
         [0073]     The gap adjusting mechanism  51 , as illustrated in  FIGS. 7 through 10 , includes transmission gears  55  provided on the ends of the pair of carriage shafts  53  and  53  for movably supporting the carriage  13  in the width direction of the sheet P, a cam  57  which includes a cam surface  57   b  protruded from a portion of the outer circumferential surface of a cylindrical portion  57   a  and is integrally formed with the transmission gear  55 , a ring-shaped cam receiver  59  which is supported at the side of the printer main body to contact the outer circumferential surface of the cam  57 , a gap adjustment wheel train  61  (see  FIG. 2 ) for inputting a rotation force to the transmission gear  55 , and a gap adjustment motor  63  for rotating the gap adjustment wheel train  61 . On the other hand, the carriage shafts  53  and  53  are supported movably up and down and biased to the side of the cam receiver  59 .  
         [0074]     In the gap adjusting mechanism  51  having the above-mentioned configuration, when the rotation force output from the gap adjustment motor  63  is input to the transmission gear  55  through the gap adjustment wheel train  61  and the transmission gear  55  rotates by a predetermined angle in a direction indicated by an arrow X of  FIG. 7 , as illustrated in  FIG. 8 , by putting the cam surface  57   b  of the cam  57  on the cam receiver  59 , the carriage shafts  53  move upward. By the upward movement of the carriage shafts  53 , the print head  44  of the print process mechanism  43  integrally rises with the carriage  13  and thus the gap PG between the platen surface  91   a  of the platen  91  and the print head  44  of the print process mechanism  43  widens.  
         [0075]     The cylindrical portion  57   a  of the cam  57  adjusts the gap PG between the platen  91  and the print head  44  to a minimum by the contact with the cam receiver  59  and is used when printing a thinnest sheet P among the sheets which can be printed.  
         [0076]     As illustrated in  FIG. 9 , the cam surface  57   b  of the cam  57  includes a slope portion  58   a  of which the protrusion amount is gradually changed from the rotation center and an arc portion  58   b  having a maximum protrusion amount of the slope portion  58   a . The slope portion  58   a  is used for adjusting the gap when printing the sheet P having a different thickness, such as a postcard, or a CD-ROM, and the arc portion  58   b  is used when the gap PG between the platen  91  and the print head  44  is adjusted to a maximum when the paper jam is generated.  
         [0077]     In addition, in the inkjet printer  1  according to the present embodiment, the paper feed roller  41  is attached to a sheet feed shaft  71  illustrated in  FIG. 3 , and rotationally driven by the wheel train (gear train) which is connected with the end of the paper feed shaft and perfoms rotation transmission.  
         [0078]     The outer circumferential surface of the sheet feed shaft  71  is fixed with a pulley  72  having a large diameter. Furthermore, a pulley  74  having a small diameter is provided at the output shaft of a paper feed motor (PF motor)  73  which is disposed below the left side of the inkjet printer  1 , and a timing belt  75  is stretched over the pulley  74  and the pulley  72  having the large diameter. In order words, the paper feed roller  41  rotates by the paper feed motor  73 .  
         [0079]     As illustrated in  FIG. 8 , the driven roller  42  paired with the paper feed roller  41  is rotatably mounted on the front end (fluctuation end) of a fluctuation arm  77  which is rotatably supported by a support shaft  76 , and usually biased to maintain a contact state in which the driven roller  42  presses and contacts the paper feed roller  41 .  
         [0080]     Moreover, in the present embodiment, as illustrated in  FIG. 8 , a roller release mechanism  78  is provided which fluctuates and displaces the front end of the fluctuation arm  77  upward and retreats the driven roller  42  in a direction separated from the paper feed roller  41  in cooperation with the gap adjustment mechanism when the gap between the print head  44  and the platen  91  is adjusted by driving the gap adjustment motor  63 .  
         [0081]     The roller release mechanism  78  is constructed by forming a release protrusion  82  for pushing down the rear end of the fluctuation arm  77  and fluctuating the front end of the fluctuation arm  77  upward when the rotation amount of a rotation axis  81  reaches a predetermined angle, on the outer circumferential surface of the rotation axis  81  which rotates in a direction indicated by an arrow Y of  FIG. 8  by the rotation of the gap adjustment motor  63 .  
         [0082]     Accordingly, when the release protrusion  82  pushes down the rear end of the fluctuation arm  77  by the rotation of the rotation axis  81 , as illustrated by an arrow Z of  FIG. 9 , the front end of the fluctuation arm  77  is fluctuated and displaced upward and the driven roller  42  is released from the paper feed roller  41 .  
         [0083]     In addition, in the inkjet printer  1  according to the present embodiment, the rotation force input from the paper feed motor  73  which also functions as a driving source of the paper feed roller  41  to the sheet feed shaft  71  through the pulley  74 , the timing belt  75 , and the pulley  72  having the large diameter is transmitted to the intermediate roller  31  and an ejection roller  48   a  through a wheel train (now illustrated) connected to the sheet feed shaft  71 .  
         [0084]     Here, a one-direction clutch mechanism  84  for transmitting the power only when the paper feed motor  73  positively rotates is interposed between the wheel train connected to the sheet feed shaft  71  and the intermediate roller  31 .  
         [0085]     As illustrated in FIGS.  7  to  10 , the one-direction clutch mechanism  84  according to the present embodiment includes a relay gear  85  which is rotatably supported to a pivot  83  and receives the rotation force of the paper feed roller  41 , a fluctuation lever  87  of which the middle portion is rotatably supported by a pivot  86  disposed between the relay gear  85  and the intermediate roller  31 , a planet gear  88  which is rotatably supported to one end of the fluctuation lever  87  through a torque limiter and is engaged with a gear  31   a  fixed to the intermediate roller  31 , and a transmission gear  89  which is disposed on the pivot  86  such that their center axes are identical to each other, fluctuates the engaged planet gear  88  in a direction which is engaged with or released from the gear  31   a  of the intermediate roller  31  along the direction of the rotation force received from the relay gear  85 , and transmits the rotation force to the gear  31   a  of the intermediate roller  31 .  
         [0086]     When the paper feed roller  41  rotates in a direction in which the sheet P is normally transported (that is, when the paper feed motor  73  positively rotates), the transmission gear  89  transmits the rotation force to the gear  31   a  of the intermediate roller  31  through the planet gear  88 , while the engaged state is maintained by biasing the planet gear  88  in a direction which is engaged with the gear  31   a  of the intermediate roller  31 .  
         [0087]     When the paper feed roller  41  is negatively driven by negatively driving the paper feed motor  73  as illustrated by an arrow E of  FIGS. 7 and 10 , the transmission gear  89  biases the planet gear  88  in a direction which is separated from the gear  31   a  of the intermediate roller  31  (a direction indicated by an arrow D illustrated in  FIG. 10 ) to release the engaged state, the planet gear  88  idles and the rotation force cannot be transmitted to the gear  31   a  of the intermediate roller  31 . Accordingly, the power transmission to the intermediate roller  31  through the one-direction clutch mechanism  84  is blocked.  
         [0088]     Furthermore, the paper feed motor  73  positively rotates and the planet gear  88  may be biased through the transmission gear  89  in a direction which is engaged with the gear  31   a  of the intermediate roller  31 , such that the one-direction clutch mechanism  84  returns to an original state which can transmit the power to the intermediate roller  31 .  
         [0089]     In addition, the fluctuation range of the planet gear  88  is defined by locking a pair of engagement units  87   a  and  87   b  which is provided at the other end of the fluctuation lever  87  to the pivot  83 .  
         [0090]     Moreover, in the inkjet printer  1  according to the present embodiment, a control unit (not illustrated) for controlling the operations of the units monitors the signal of the PW sensor  47  provided in the print head  44  or the sheet detecting sensor provided in the transport path at the time of the feed operation and the print process.  
         [0091]     In addition, in the control unit, a detecting unit for detecting the existence of the sheet P in the transport path and detecting the paper jam of the sheet P in the transport path based on these detected signals detects the operation stop during the carriage  13  moves. When the detecting unit detects the paper jam, the control unit determines that the paper jam is generated and performs the process according to the flowchart illustrated in  FIG. 11 .  
         [0092]     Furthermore, the detecting unit according to the present embodiment detects the paper jam of the sheet P in the transport path by detecting the operation stop during the carriage  13  movement. However, the paper jam may be detected, for example, by detecting the movement amount of the sheet P.  
         [0093]     In other words, each one pass of the carriage  13  which is during a print process, it is determined whether the carriage (CR)  13  stops (step S 101 ), and, when the stop of the carriage  13  is not detected, it is determined that one-pass print is normally completed by the movement of the carriage  13  in the width direction of the sheet and the process returns to the step S 101 . A sensor for detecting whether a paper is existed or not may be provided in the transport path and it may be determined that the paper jam is generated when the sensor does not detect a change from a state with paper to a state without paper within a predetermined period. Further, if a paper feeding motor or a carriage motor is a DC motor, it may be determined that the paper jam is generated when the current value becomes high unusually.  
         [0094]     In the step S 101 , when the stop of the carriage  13  is detected, it is determined that the paper jam is generated and thus the process progresses to the step S 102 . In the step S 102 , the gap adjusting mechanism (APG)  51  operates such that the cam surface  57   b  of the cam  57  is put on the cam receiver  59 , as illustrated in  FIG. 7 , and the gap PG between the platen surface  91   a  of the platen  91  and the print head  44  of the print process mechanism  43  is set to a maximum position.  
         [0095]     Furthermore, since the roller release mechanism  78  operates in cooperation with the gap adjusting mechanism  51 , in the step S 102 , in addition to the gap adjustment due to the gap adjusting mechanism  51 , the driven roller  42  is separated from the paper feed roller  41  by the operation of the roller release mechanism  78  and thus the operation of releasing the sandwiching of the sheet P is performed.  
         [0096]     Next, in the step S 103 , since the paper feed motor (PF motor)  73  negatively rotates and thus the planet gear  88  of the one-direction clutch mechanism  84  illustrated in  FIG. 10  is fluctuated in a direction indicated by an arrow D, which is separated from the gear  31   a  of the intermediate roller  31 , to release the engaged state, the power transmission between the paper feed roller  41  and the intermediate roller  31  is blocked.  
         [0097]     Next, the display process, such as a process of switching on an indicator for notifying a user that paper jam error is generated, is performed and thus the printer stops (step S 104 ).  
         [0098]     In other words, when the paper jam is generated in the device, the gap adjusting mechanism  51  and the roller release mechanism  78  automatically operate, and the power transmission between the paper feed motor  73  and the intermediate roller  31  is blocked by negatively driving the paper feed motor  73  and the generation of the paper jam error is then notified.  
         [0099]     As described above, according to the inkjet printer  1  according to the present embodiment, when the paper jam is generated in the device, the gap adjusting mechanism  51  automatically operates and the gap PG between the platen surface  91   a  and the print head  44  widens to a maximum.  
         [0100]     Accordingly, when the rear opening/closing cover  17  which is the transport path opening/closing mechanism is opened and the sheet P is pulled out, the print head  44  is not contaminated by a problem that the jammed sheet P rubs against the print head  44  of the print process mechanism  43  and thus the jammed sheet P can be stably removed.  
         [0101]     Furthermore, in the inkjet printer  1  according to the present embodiment, the gap adjusting mechanism  51 , which is automatically operated by the control unit when the paper jam is generated, can process the sheets P having different thicknesses as well as remove the paper jam. Accordingly, since a new mechanism for removing the paper jam need not be further provided, the configuration of the device is not complicated and the jammed sheet P can be easily removed with the low cost.  
         [0102]     In addition, when the jammed sheet P is pulled out, since the driven roller  42  is separated from the jammed sheet P by the roller release mechanism  78  which operates in conjunction with the gap adjusting mechanism  51  and thus the sandwiching of the sheet P is opened, the jammed sheet P can be easily pulled out with a small operation force. Furthermore, when the jammed sheet P is pulled out, a piece of sheet does not remain in the device.  
         [0103]     Accordingly, it is possible to easily remove the jammed sheet P and thus the treatment and repairability of the inkjet printer  1  can be improved when the paper jam is generated.  
         [0104]     Moreover, in the inkjet printer  1  according to the present embodiment, even when the intermediate roller  31  contacts the jammed sheet P, after it is determined that the paper jam is generated, the negative rotation of the paper feed motor  73  is automatically performed and the power transmission between the paper feed motor  73  and the intermediate roller  31  is blocked by the one-direction clutch mechanism  84  so that it becomes easy to rotate. Accordingly, when the jammed sheet P is pulled out, a load is not applied to the paper feed motor  73  and thus the sheet P is pulled out with a small operation force.  
         [0105]     In addition, in the state that the power transmission is blocked by the one-direction clutch mechanism  84 , the rotation force applied to the intermediate roller  31  by a friction force with the sheet P which is pulled out is not reversely transmitted to the paper feed motor  73  and thus it is possible to avoid a problem that the circuits in the device are damaged by the power generation of the paper feed motor  73 . Thus, the reliability and durability of the inkjet printer  1  can be improved.  
         [0106]     Moreover, the read/write processing device according to the present invention is not limited to the inkjet printer described in the above-mentioned embodiment. For example, the present invention may be applied to various devices having the transport path for transporting the paper, such as a copier, a facsimile, a scanner, a magnetic information reading device, a magnetic information recording device, and a paper money changing machine. The read/write unit may be a magnetic head for reading magnetic information.