Patent Publication Number: US-9895914-B2

Title: Media transporting device and inkjet printer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 371 application of the international PCT application serial no. PCT/JP2015/064038, filed on May 15, 2015, which claims the priority benefit of Japan application No. 2014-102905, filed on May 16, 2014. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
     TECHNICAL FIELD 
     The present invention relates to a media transporting device for transporting a band-shaped medium, and an inkjet printer. 
     BACKGROUND ART 
     A conventional media transporting device including a winding mechanism that winds a band-shaped medium into a roll, a tension applying member that can apply tension on the medium by pressing a portion of the medium that is not wound by the winding mechanism by its own weight in a rotating direction having a specific axis line as a center; and a transport controller that controls the transportation of the medium is known (see e.g., Patent Literature 1). The winding mechanism includes a motor that generates power for rotating the wound medium. The tension applying member can also apply tension on the medium when an angle having the specific axis line as the center is at least within a specific range. The transport controller causes the motor to stop the generation of the power for winding the medium with the winding mechanism when the angle of the tension applying member having the specific axis line as the center is within the specific range. The transport controller causes the motor to generate the power for winding the medium with the winding mechanism when the angle of the tension applying member having the specific axis line as the center is outside the specific range. In other words, the media transporting device can continue to apply tension on the medium with the tension applying member by controlling the motor so that the angle of the tension applying member having the specific axis line as the center falls within the specific range. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Unexamined Japanese Patent Publication No. 2013-22744 
     SUMMARY OF INVENTION 
     Technical Problems 
     When a diameter of the medium wound by the winding mechanism becomes large, a distance from a rotating shaft to an outer circumference of the medium wound by the winding mechanism becomes long, and furthermore, a weight of the medium itself that is wound by the winding mechanism also becomes heavy, and hence a torque required to rotate the medium wound by the winding mechanism becomes large. Therefore, even if the motor is caused to generate the power for winding the medium with the winding mechanism when the angle of the tension applying member having the specific axis line as the center is outside the specific range, it is difficult to wind the medium with the winding mechanism. If it is difficult to wind the medium with the winding mechanism, an excessive torque applies on the motor and the motor may break down when the motor is caused to generate the power for winding the medium. In the conventional media transporting device, the motor is stopped when it is difficult to wind the medium with the winding mechanism. In other words, in the conventional media transporting device, in some cases, the motor cannot be controlled so that the angle of the tension applying member having the specific axis line as the center falls within the specific range. Therefore, the conventional media transporting device has a problem in that the tension cannot be continuously applied on the medium. 
     The present invention thus provides a media transporting device and an inkjet printer capable of continuously applying tension on a band-shaped medium for a longer time than in the conventional technique. 
     Solutions to Problems 
     A media transporting device of the present invention includes: a medium winding mechanism that executes at least one of unwinding and winding a band-shaped medium which is wound into a roll; a tension applying member that applies tension on the medium by pushing a portion of the medium that is not wound by the medium winding mechanism in a specific direction; and a transport controller that controls transportation of the medium; wherein the medium winding mechanism includes a motor that generates a power for rotating the medium wound into a roll; the medium winding mechanism limits a torque generated between the motor side and the medium side with a specific magnitude as an upper limit; the transport controller causes the motor to generate the power for winding the medium when a predetermined tension is no longer applied on the medium by the tension applying member; and the medium winding mechanism limits the torque to the specific magnitude to apply the predetermined tension on the medium when the motor is caused to generate the power for winding the medium by the transport controller when the predetermined tension is no longer applied on the medium by the tension applying member. 
     According to such configuration, the media transporting device of the present invention can apply the tension on the medium with the medium winding mechanism by causing the motor to generate the power for winding the medium with the medium winding mechanism and causing the medium winding mechanism to limit the torque, so that even if the tension cannot be applied on the medium by the tension applying member, the tension can be continuously applied on the band-shaped medium for a longer time than in the conventional technique by applying the tension on the medium with the medium winding mechanism. 
     In the media transporting device of the present invention, the specific direction is a rotating direction having an axis line extending in a width direction of the medium orthogonal to a transporting direction of the medium as a center; the tension applying member can apply tension on the medium by pushing the portion of the medium that is not wound by the medium winding mechanism by its own weight in the rotating direction; the media transporting device includes an angle detector that detects an angle of the tension applying member having the axis line as a center; the tension applying member applies tension on the medium when an angle detected by the angle detector is within at least a specific range; the transport controller stops the generation of the power by the motor for winding the medium with the medium winding mechanism when the angle detected by the angle detector is within the range; and the transport controller causes the motor to generate the power for winding the medium with the medium winding mechanism when the angle detected by the angle detector is outside the range to return the angle of the tension applying member having the axis line as the center to within the range. 
     According to such configuration, the media transporting device of the present invention causes the motor to stop the generation of the power for winding the medium with the medium winding mechanism when the angle of the tension applying member having the specific axis line as the center is within the specific range, and thus can suppress the load of the motor. When the angle of the tension applying member having the specific axis line as the center is outside the specific range, the media transporting device of the present invention can recover the state of applying the tension on the medium with the tension applying member by returning the angle of the tension applying member to within the specific range. Therefore, the media transporting device of the present invention can suppress the accumulation load of the motor and extend the lifespan of the motor. 
     The media transporting device of the present invention may further include a transportation roller that transports the portion of the medium that is not wound by the medium winding mechanism toward a side opposite to the medium winding mechanism in the transporting direction of the medium. 
     According to such configuration, the media transporting device of the present invention can return the angle of the tension applying member to within the specific range even if the angle of the tension applying member having the specific axis line as the center is outside the specific range as a result of the change in the length of the medium from the transportation roller to the medium winding mechanism according to the transportation amount of the medium by the transportation roller while the tension is being applied on the medium by the tension applying member. Therefore, the media transporting device of the present invention can maintain the state of applying the tension on the medium by the tension applying member without being influenced by the transportation amount of the medium by the transportation roller. 
     The media transporting device of the present invention may further include: an unwinding mechanism that unwinds the medium wound into a roll; and a winding mechanism that winds the medium unwound by the unwinding mechanism as the medium winding mechanism. 
     According to such configuration, the media transporting device of the present invention can apply tension on the band-shaped medium by the cooperative operation of the winding mechanism and the unwinding mechanism by causing the motor to generate the power for winding the medium with the unwinding mechanism when causing the motor to generate the power for winding the medium with the winding mechanism. 
     An inkjet printer of the present invention includes the media transporting device described above; and an inkjet head that executes printing by ink on the medium applied with tension by the media transporting device. 
     According to such configuration, the inkjet printer of the present invention can continue the printing for a longer time than in the conventional technique by executing the printing on the medium in which the tension is continuously applied for a longer time than in the conventional technique. 
     Effects of the Invention 
     The media transporting device and the inkjet printer of the present invention can continuously apply tension on a band-shaped medium for a longer time than in the conventional technique. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an outer appearance of an inkjet printer according to one embodiment of the present invention when observed from an upper right side of a front surface. 
         FIG. 2  is a front view of the inkjet printer shown in  FIG. 1  with a front cover detached. 
         FIG. 3  is a side cross-sectional view of the inkjet printer shown in  FIG. 1  when a tension is applied on a printing medium by a tension applying member. 
         FIG. 4  is a perspective view of a vicinity of a roll holder shown in  FIG. 1  when observed from an upper right side of the front surface with the cover detached. 
         FIG. 5  is a perspective view of a part of the media transporting device shown in  FIG. 1  when observed from an upper left side of the front surface with a configuration of an interior of an angle detection device exposed. 
         FIG. 6  is a side cross-sectional view of the inkjet printer shown in  FIG. 1  when the tension applying member is located at an evacuating position. 
         FIG. 7  is a block diagram of the inkjet printer shown in  FIG. 1 . 
         FIG. 8  is a flowchart of an operation of a transport controller shown in  FIG. 7 . 
         FIG. 9  is a side cross-sectional view of the inkjet printer shown in  FIG. 1  when a tension bar is brought into contact with the printing medium with an angle of the tension applying member having a specific axis line as a center exceeding an upper limit of a specific range when a winding method of the printing medium on a paper core is “inner winding”. 
         FIG. 10  is a flowchart of a bar mode process shown in  FIG. 8 . 
         FIG. 11  is a side cross-sectional view of the inkjet printer shown in  FIG. 1  when the angle of the tension applying member having the specific axis line as the center is smaller than a lower limit of the specific range. 
         FIG. 12  is a flowchart of a winding mode process shown in  FIG. 8 . 
         FIG. 13  is a side cross-sectional view of the inkjet printer shown in  FIG. 1  when the angle of the tension applying member having the specific axis line as the center is smaller than the lower limit of the specific range in a state the winding diameter is large. 
         FIG. 14A  is a front view of an angle detection device in an example different from the example shown in  FIG. 5  and  FIG. 14B  is a side view of the angle detection device shown in  FIG. 14A . 
         FIG. 15A  is a front view of an angle detection device different from the examples shown in  FIGS. 5 and 14 ; and  FIG. 15B  is a side view of the angle detection device shown in  FIG. 15A . 
         FIG. 16  is a side cross-sectional view of the inkjet printer shown in  FIG. 1  in an example different from the example shown in  FIG. 3 . 
         FIG. 17  is a side cross-sectional view of a tension applying member different from the tension applying member shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be hereinafter described using the drawings. 
     First, a configuration of an inkjet printer according to the present embodiment will be described. 
       FIG. 1  is a perspective view of an outer appearance of an inkjet printer  10  according to the present embodiment when observed from an upper right side of a front surface.  FIG. 2  is a front view of the inkjet printer  10  with a front cover  81   a  (see  FIG. 1 ) detached.  FIG. 3  is a side cross-sectional view of the inkjet printer  10  when tension is applied on a printing medium  90  by a tension applying member  50 . 
     As shown in  FIGS. 1 to 3 , the inkjet printer  10  includes a media transporting device  20  that transports the printing medium  90 , which is a band-shaped medium, and a main body  80  that is installed on the media transporting device  20  to execute printing by ink. 
     The media transporting device  20  includes a leg  21  that is installed on a floor; a platen  22  that supports the printing medium  90 , on which printing is to be executed by the main body  80 ; a transportation roller  23  that transports the printing medium  90  in a sub-scanning direction, indicated with an arrow  10   b , orthogonal to a main scanning direction, indicated with an arrow  10   a ; a pinch roller  24  that sandwiches the printing medium  90  with the transportation roller  23 ; an unwinding mechanism  30  serving as a medium winding mechanism that has the printing medium  90  wound therearound into a roll and that unwinds the printing medium  90  toward the main body  80 ; a winding mechanism  40  serving as a medium winding mechanism that has the printing medium  90  wound therearound into a roll and that winds the printing medium  90 , on which printing is executed by the main body  80 ; a tension applying member  50  that is rotatable with an axis line  50   a , which extends in a width direction of the printing medium  90  orthogonal to a transporting direction of the printing medium  90 , that is, the main scanning direction as the center and that applies tension on the printing medium  90 ; and an angle detection device  60  serving as an angle detector that detects an angle θ of the tension applying member  50  having the axis line  50   a  as the center. The unwinding mechanism  30 , the winding mechanism  40 , the tension applying member  50 , and the angle detection device  60  are supported by the leg  21 . The platen  22 , the transportation roller  23 , and the pinch roller  24  are extended in the main scanning direction. 
     The main body  80  includes a case  81  with a detachable front cover  81   a  for covering the interior of the main body  80 , an operation section  82 , which is an input device, such as a button to which various operations are input, a display section  83 , which is a display device, such as an LCD (Liquid Crystal Display) for displaying various information, a plurality of ink tanks  84  containing ink, a guide rail  85  extending in the main scanning direction indicated with the arrow  10   a , a carriage  86  supported by the guide rail  85  so as to be movable in the main scanning direction, and a plurality of inkjet heads  87  mounted on the carriage  86  to discharge ink toward the printing medium  90 . 
     As shown in  FIGS. 2 and 3 , the unwinding mechanism  30  includes a rail  31  extending in the main scanning direction indicated with the arrow  10   a  and supported by the leg  21 , and a roll holder  32  and a roll holder  33  that rotatably support a paper core (not shown) around which the printing medium  90  before printing by the inkjet head  87  is wound, by sandwiching the paper core from both sides. The rail  31  supports the roll holder  32  and the roll holder  33  in a manner movable in the main scanning direction. In other words, the roll holder  32  and the roll holder  33  can change the distance between them in the main scanning direction in accordance with the width of the printing medium  90  to use. The roll holder  32  includes a rotating shaft  32   a  inserted into a hole at an end of the paper core. Similarly, the roll holder  33  includes a rotating shaft  33   a  inserted into a hole at an end of the paper core. The rotating shaft  32   a  and the rotating shaft  33   a  are rotatable with a center axis extending in the main scanning direction as the center. 
     As shown in  FIGS. 1 to 3 , the winding mechanism  40  includes a rail  41  extending in the main scanning direction indicated with the arrow  10   a  and supported by the leg  21 , and a roll holder  42  and a roll holder  43  that rotatably support a paper core (not shown) around which the printing medium  90  after printing by the inkjet head  87  is wound, by sandwiching the paper core from both sides. The rail  41  supports the roll holder  42  and the roll holder  43  in a manner movable in the main scanning direction. In other words, the roll holder  42  and the roll holder  43  can change the distance between them in the main scanning direction in accordance with the width of the printing medium  90  to use. The roll holder  42  includes a rotating shaft  42   a  inserted into a hole at an end of the paper core. Similarly, the roll holder  43  includes a rotating shaft  43   a  inserted into a hole at an end of the paper core. The rotating shaft  42   a  and the rotating shaft  43   a  are rotatable with a center axis extending in the main scanning direction as the center. 
       FIG. 4  is a perspective view of a vicinity of the roll holder  43  when observed from an upper right side of the front surface with the cover  47  (see  FIG. 1 ) detached. 
     As shown in  FIGS. 1 to 4 , the winding mechanism  40  includes a motor  44  that generates a driving force for rotating the rotation shaft  43   a  of the roll holder  43 , that is, a power for rotating the printing medium  90  wound into a roll around the paper core rotatably supported by the roll holder  43 ; a torque limiter  45  serving as a torque limiting mechanism configuring a part of a transmission mechanism of the driving force from the motor  44  to the rotation shaft  43   a  and shielding the connection when an excessive load is applied; an encoder  46  that detects the rotation of the rotating shaft  43   a ; and a cover  47  that covers the motor  44 , the torque limiter  45 , and the encoder  46 . 
     To transmit the power of the motor  44  to the paper core, around which the printing medium  90  is wound, the winding mechanism  40  includes a gear supporting shaft  44   a  included by the motor  44 , a first gear  44   b  that gears with the gear supporting shaft  44   a , a second gear  44   c  that rotates about a rotation axis same as the rotation axis of the first gear  44   b  and of which diameter is smaller than that of the first gear  44   b , and a third gear  44   d  that gears with the second gear  44   c  and that rotates about a rotation axis same as the rotation axis of the paper core around which the printing medium  90  is wound. The torque limiter  45  limits the torque generated between the first gear  44   b  and the second gear  44   c , and operates to prevent the rotation of the first gear  44   b  from being transmitted to the second gear  44   c  when a torque of a specific magnitude is generated. 
     As described above, the torque limiter  45  limits the torque generated between the motor  44  side and the printing medium  90  side with a specific magnitude as an upper limit. The torque limiter  45  can allow the upper limit of the torque generated between the motor  44  side and the printing medium  90  side to be adjusted. 
     As shown in  FIGS. 1 to 3 , the tension applying member  50  includes an arm  51  rotatably supported by the leg  21  with a shaft  51   a  extending on the axis line  50   a  as a center, an arm  52  rotatably supported by the leg  21  with a shaft  52   a  extending on the axis line  50   a  as a center, and a tension bar  53  extending in the main scanning direction and being provided to be brought into contact with the printing medium  90 . The tension bar  53  is supported by the arm  51  and the arm  52 . The tension applying member  50  can apply tension on the printing medium  90  by pushing a portion of the printing medium  90  that is not wound by the winding mechanism  40  by its own weight in a rotating direction indicated with an arrow  10   c  having the axis line  50   a  as the center. 
     The tension applying member  50  is adapted such that an angle θ does not become smaller than, for example, 52° by the action of a stopper (not shown). The tension applying member  50  is adapted such that the angle θ is maintained within a specific range (e.g., range from 62.5° to 70°) of a range in which the tension can be applied on the printing medium  90  by the winding of the printing medium  90  by the winding mechanism  40 , as will be described later. 
       FIG. 5  is a perspective view of a part of the media transporting device  20  when observed from an upper left side of the front surface with the configuration of the interior of the angle detection device  60  exposed. 
     As shown in  FIG. 5 , the angle detection device  60  includes a plate  61  fixed to the shaft  52   a  of the arm  52  (not shown in  FIG. 5 ; see  FIG. 2 ); and a photo-interrupter  62 , a photo-interrupter  63 , and a photo-interrupter  64  fixed with respect to the leg  21 . The plate  61  includes a hole  61   a , to which the shaft  52   a  is inserted, and a plurality of slits  61   b  arranged side by side in the rotating direction indicated with the arrow  10   c  and provided to be detected by the photo-interrupter  62  and the photo-interrupter  63 . The plate  61  includes a detecting portion  61   c  to be detected by the photo-interrupter  64 . In other words, the angle detection device  60  is an encoder that detects the angle θ (see  FIG. 3 ). 
       FIG. 6  is a side cross-sectional view of the inkjet printer  10  when the tension applying member  50  is located at an evacuating position. 
     As shown in  FIG. 6 , the tension applying member  50  is adapted such that the angle θ is no greater than, for example, 95° by the action of the stopper (not shown). The position of the tension applying member  50  shown in  FIG. 6  is referred to as the evacuating position. The tension applying member  50  cannot be brought into contact with the printing medium  90  when located at the evacuating position, and hence cannot apply tension on the printing medium  90 . 
       FIG. 7  is a block diagram of the inkjet printer  10 . 
     As shown in  FIG. 7 , the inkjet printer  10  includes the operation section  82  and the display section  83  described above, a communication section  11 , which is a communication device, that carries out communication with an external device such as a PC (Personal Computer), the inkjet head  87  described above, a carriage driving device  12  that moves the carriage  86  (see  FIG. 2 ) in the main scanning direction indicated with the arrow  10   a  (see  FIG. 2 ) along the guide rail  85  (see  FIG. 2 ), a transportation roller driving device  13  that rotates the transportation roller  23  (see  FIG. 3 ), an encoder  14  that detects a rotation amount of the transportation roller  23 , the motor  44 , an encoder  46  and the angle detection device  60  described above, a clock  15 , a storage section  16 , which is a storage device, such as EEPROM (Electrically Erasable Programmable Read Only Memory) that stores various data, and a control section  17  that controls the entire inkjet printer  10 . 
     The length of the printing medium  90  transported by the transportation roller  23  is the same as a length of accumulation in a circumferential direction of points in the transportation roller  23  brought into contact with the printing medium  90 , and hence can be calculated based on a diameter of the transportation roller  23  and a detection value of the encoder  14 . Specifically, assuming that the length of the printing medium  90  transported by the transportation roller  23  is L 1 , the diameter of the transportation roller  23  is R 1 , and the rotation angle obtained from the detection value of the encoder  14  is θ 1  [rad], L 1  is “θ 1 ×R 1 ”. 
     The control section  17  includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) in which programs and various types of data are stored in advance, and a RAM (Random Access Memory) used as a work region of the CPU. The CPU executes the program stored in the ROM or the storage section  16 . 
     The control section  17  has a function of a transport controller  17   a  that controls the transportation of the printing medium  90  by executing the program stored in the ROM or the storage section  16 . 
     Next, a description will be made on the operation of the inkjet printer  10 . 
     When receiving externally transmitted print data via the communication section  11 , the control section  17  of the inkjet printer  10  controls the inkjet head  87 , the carriage driving device  12 , the transportation roller driving device  13 , and the winding mechanism  40  based on the print data to execute printing by the inkjet head  87 . 
     Specifically, the control section  17  controls the carriage driving device  12  and moves the carriage  86  in the main scanning direction indicated with the arrow  10   a  along the guide rail  85 , thus relatively moving the inkjet head  87  mounted on the carriage  86  in the main scanning direction with respect to the printing medium  90 . At this time, the control section  17  executes printing in the main scanning direction by discharging ink droplets toward the printing medium  90  with the inkjet head  87 . The control section  17  then controls the transportation roller driving device  13  and rotates the transportation roller  23  each time the printing in the main scanning direction is terminated, thus moving the printing medium  90  sandwiched by the transportation roller  23  and the pinch roller  24  in the sub-scanning direction indicated with the arrow  10   b . In other words, the control section  17  changes the printing position by the inkjet head  87  in the sub-scanning direction on the printing medium  90  by relatively moving the inkjet head  87  and the printing medium  90  in the sub-scanning direction. The control section  17  then again executes printing in the main scanning direction at a new printing position in the sub-scanning direction. 
     When the printing medium  90  is transported by the transportation roller  23 , the printing medium  90  wound around the paper core rotatably supported by the roll holder  32  and the roll holder  33  of the unwinding mechanism  30  is unwound from the unwinding mechanism  30 . 
     Furthermore, when the printing medium  90  is transported by the transportation roller  23 , the printing medium  90  after the printing by the inkjet head  87  is applied with tension by at least one of the winding mechanism  40  and the tension applying member  50 , and is also wound by the winding mechanism  40 . 
       FIG. 8  is a flowchart of an operation of the transport controller  17   a.    
     The transport controller  17   a  executes the operation shown in  FIG. 8  when the operation of the control section  17  of the inkjet printer  10  is started (when power of the inkjet printer  10  is turned ON). 
     As shown in  FIG. 8 , the transport controller  17   a  determines whether or not the printing medium  90  is wound around the paper core rotatably supported by the winding mechanism  40  before the ink is discharged by the inkjet head  87  (S 101 ). When the printing medium  90  is not wound around the paper core, the transport controller  17   a  terminates the processes shown in  FIG. 8 . 
     When the printing medium  90  is wound around the paper core, the transport controller  17   a  determines a current tension applying mode for applying tension on the printing medium  90  after the process of S 101  (S 102 ). The tension applying mode includes a “bar mode” in which tension is applied on the printing medium  90  by the tension applying member  50 , and a “winding mode” in which tension is applied on the printing medium  90  by the winding mechanism  40 . The control section  17  can accept a specification of either the “bar mode” or the “winding mode” through the operation section  82 . 
     When determining that the current tension applying mode is the “winding mode” in S 102 , the transport controller  17   a  proceeds to the detection of the winding diameter (S 108 ) for a winding mode process. 
     When determining that the current tension applying mode is the “bar mode” in S 102 , the transport controller  17   a  determines a winding method of the printing medium  90  around the paper core (S 103 ). The winding method of the printing medium  90  around the paper core includes “outer winding” in which the printing medium  90  is wound around the paper core so that the tension bar  53  makes contact with a portion of the printing medium  90  that becomes an inner surface when wound around the paper core, as shown in  FIG. 3 , and “inner winding” in which the printing medium  90  is wound around the paper core so that the tension bar  53  makes contact with a portion of the printing medium  90  that becomes an outer surface when wound around the paper core, as shown in  FIG. 9 . 
     When determining that the winding method of the printing medium  90  around the paper core is the “inner winding” in S 103 , the transport controller  17   a  transports the printing medium  90  with the transportation roller  23  by a specific length, for example, greater than or equal to 300 mm (S 104 ). 
     The reason why the printing medium  90  is transported by a specific length when determined that the winding method of the printing medium  90  around the paper core is the “inner winding” will be described below. 
       FIG. 9  is a side cross-sectional view of the inkjet printer  10  when the tension bar  53  is brought into contact with the printing medium  90  with the angle θ of the tension applying member  50  having the axis line  50   a  as the center exceeding the upper limit of a specific range when the winding method of the printing medium  90  around the paper core is the “inner winding”. 
     The “specific range” and the “specific length” are set so that the angle θ falls within the specific range as shown in  FIG. 3 , when the printing medium  90  of a specific length is transported by the transportation roller  23  while the angle θ exceeds the upper limit of the specific range as shown in  FIG. 9 . Therefore, the process of S 104  is provided to have the angle θ within the specific range when the angle θ exceeds the upper limit of the specific range. 
     The transport controller  17   a  carries out a check of a bar mode control function when determining that the winding method of the printing medium  90  around the paper core is the “outer winding” in S 103  and after the printing medium  90  is transported by a specific length in S 104  (S 105 ). Specifically, in S 105 , initialization of the encoder of the angle detection device  60 , operation check of the photo-interrupters  62 ,  63 ,  64 , and the like are carried out. 
     The transport controller  17   a  determines whether the state of the bar mode control function obtained in S 105  is “OK”, which is a state where a bar mode process, to be described later, can be carried out, or “NG”, which is a state where the bar mode process cannot be carried out (S 106 ). 
     When determining that the state of the bar mode control function is “NG”, the transport controller  17   a  proceeds to the detection of the winding diameter (S 108 ) for the winding mode process. 
     On the other hand, when determining that the state of the bar mode control function is “OK”, the transport controller  17   a  proceeds to the detection of the winding diameter (S 107 ) for the bar mode process. 
     In S 107  and S 108 , the transport controller  17   a  first stops the transportation of the printing medium  90  by the transportation roller  23 , and causes the motor  44  to generate the power for winding the printing medium  90  with the winding mechanism  40 , thereby realizing a state in which the tension is applied on the printing medium  90  by the winding mechanism  40  where the torque is limited by the torque limiter  45 . Then, the transport controller  17   a  transports the printing medium  90  with the transportation roller  23  by a predetermined length. The transport controller  17   a  can determine the length of the printing medium  90  transported by the transportation roller  23  based on the rotation amount of the transportation roller  23  detected by the encoder  14 , as described above. Even while the printing medium  90  is being transported by the transportation roller  23 , the printing medium  90  is wound by the winding mechanism  40  by an amount by which the printing medium  90  is transported by the transportation roller  23  with the tension applied thereon by the winding mechanism  40  where the torque is limited by the torque limiter  45 . After the transportation of the printing medium  90  by the transportation roller  23  is terminated, the transport controller  17   a  stops the motor  44 . The transport controller  17   a  can determine a winding diameter based on the rotation amount of the rotating shaft  43   a  detected by the encoder  46  while the printing medium  90  is transported by the transportation roller  23  by the predetermined length, and the length of the printing medium  90  transported by the transportation roller  23 . Specifically, assuming that the winding diameter (diameter) is R 2 , the length of the printing medium  90  transported by the transportation roller  23  is L 2 , and the rotation angle obtained from the rotation amount of the rotating shaft  43   a  detected by the encoder  46  is θ 2  [rad], R 2  is “2×L 2 /θ 2 ”. 
     After the process of S 107  is terminated, the transport controller  17   a  executes the bar mode process, which is the process of “bar mode” (S 109 ). 
       FIG. 10  is a flowchart of the bar mode process shown in  FIG. 8 . 
     As shown in  FIG. 10 , the control section  17  carries out the start of printing (S 130 ). When determining that the printing is terminated in S 131 , the transport controller  17   a  determines the current tension applying mode (S 139 ). 
     When determining that the current tension applying mode is the “bar mode” in S 139 , the transport controller  17   a  sets a flag (S 140 ), and terminates the bar mode process shown in  FIG. 10 . 
     When determining that the current tension applying mode is the “winding mode” in S 139 , the transport controller  17   a  unsets a flag (S 138 ), and terminates the bar mode process shown in  FIG. 10 . 
     When determining that the printing is not terminated in S 131 , the transport controller  17   a  determines whether or not the angle θ detected by the angle detection device  60  is within the specific range (S 132 ). Whether or not the angle θ is within the specific range can be determined by the detection values from the photo-interrupter  62  and the photo-interrupter  63 . 
     When determining that the angle θ is within the specific range in S 132 , the transport controller  17   a  executes the process of S 131 . 
     When determining that the angle θ is not within the specific range in S 132 , the transport controller  17   a  causes the motor  44  to generate the power for winding the printing medium  90  with the winding mechanism  40  to start the operation of the winding mechanism  40  (S 133 ). 
     The transport controller  17   a  controls the rotation speed of the motor  44  according to the winding diameter to have the length of the printing medium  90  wound in a unit time by the winding mechanism  40 , that is, the winding speed constant irrespective of the winding diameter. Specifically, assuming that the target rotation speed of the motor  44  is V, the current winding diameter is R, the rotation speed set beforehand as the rotation speed in a state where the printing medium  90  is not yet wound around the paper core rotatably supported by the winding mechanism  40  is Vr, and the diameter (hereinafter referred to as “reference winding diameter”) of the paper core rotatably supported by the winding mechanism  40  is Rr, V is “Vr×(Rr/R)”. 
     Furthermore, the transport controller  17   a  controls a rotation acceleration of the motor  44  according to the winding diameter to have an acceleration of the winding speed, that is, a winding acceleration constant irrespective of the winding diameter. Specifically, assuming that the target rotation acceleration of the motor  44  is A, the current winding diameter is R, the rotation acceleration set beforehand as the rotation acceleration in a state the printing medium  90  is not yet wound around the paper core rotatably supported by the winding mechanism  40  is Ar, and the reference winding diameter is Rr, A is “Ar×(Rr/R)”. 
     Therefore, the transport controller  17   a  controls the rotation speed and the rotation acceleration of the motor  44  so that the rotation speed of the motor  44  is accelerated up to V with the rotation acceleration A, and thereafter the rotation speed of the motor  44  is maintained at V based on the detection value of the encoder  46  and the value of the clock  15 . 
     If the winding diameter detected in S 107  is not updated, the transport controller  17   a  uses the winding diameter detected in S 107  as the current winding diameter R, but if the winding diameter detected in S 107  is updated, the updated most recent winding diameter is used as the current winding diameter R. In the bar mode process, the transport controller  17   a  can update the winding diameter based on the rotation amount of the rotating shaft  43   a  detected by the encoder  46  and the length of the printing medium  90  transported by the transportation roller  23  between a time point at which the angle θ reaches an angle determined in advance and a time point at which the angle θ again returns to the angle determined in advance. In the winding mode process, to be described later, the transport controller  17   a  can update the winding diameter based on the rotation amount of the rotating shaft  43   a  detected by the encoder  46  and the length of the printing medium  90  transported by the transportation roller  23  between two time points at which the torque is limited by the torque limiter  45 . When the motor  44  is generating the power for winding the printing medium  90  with the winding mechanism  40 , the transport controller  17   a  can determine that the torque is being limited by the torque limiter  45  if the rotation amount of the rotating shaft  43   a  detected by the encoder  46  does not change. 
     After the process of S 133 , the transport controller  17   a  determines whether or not a specific time, for example, ten seconds has elapsed from the start of the operation of the winding mechanism  40  in immediately preceding S 133  based on the value of the clock  15  (S 134 ). 
     The reason for determining in S 134  whether or not the specific time has elapsed from the start of the operation of the winding mechanism  40  in immediately preceding S 133  will now be described. 
       FIG. 11  is a side cross-sectional view of the inkjet printer  10  when the angle θ of the tension applying member  50  having the axis line  50   a  as the center is smaller than the lower limit of the specific range. 
     The “specific range” and the “specific time” are set so that the angle θ falls within the specific range as shown in  FIG. 3 , when the printing medium  90  is wound by the winding mechanism  40  for the specific time while the angle θ is smaller than the lower limit of the specific range as shown in  FIG. 11 . Therefore, the process of S 134  is provided to have the angle θ within the specific range when the angle θ is smaller than the lower limit of the specific range. 
     As shown in  FIG. 10 , when determining that the specific time has not elapsed in S 134 , the transport controller  17   a  determines whether or not the angle θ detected by the angle detection device  60  is within the specific range (S 135 ). 
     When determining that the angle θ is not within the specific range in S 135 , the transport controller  17   a  carries out the process of S 134 . 
     When determining that the angle θ is within the specific range in S 135 , the transport controller  17   a  terminates the operation of the winding mechanism  40  by stopping the motor  44  (S 136 ), and carries out the process of S 131 . 
     When determining that the specific time has elapsed in S 134 , the transport controller  17   a  terminates the operation of the winding mechanism  40  by stopping the motor  44  (S 137 ), unsets the flag (S 138 ), and terminates the bar mode process shown in  FIG. 10 . 
     As shown in  FIG. 8 , after the process of S 108  is terminated, the transport controller  17   a  executes the winding mode process, which is the process of “winding mode” (S 111 ). 
       FIG. 12  is a flowchart of a winding mode process shown in  FIG. 8 . 
     As shown in  FIG. 12 , the transport controller  17   a  starts the operation of the winding mechanism  40  by causing the motor  44  to generate the power for winding the printing medium  90  with the winding mechanism  40  (S 160 ). 
     The transport controller  17   a  controls the rotation speed and the rotation acceleration of the motor  44  according to the winding diameter, as described above, to have the winding speed and the winding acceleration constant irrespective of the winding diameter. 
     The control unit  17  starts the printing after the process of S 160  (S 161 ). After the process of S 161 , the transport controller  17   a  determines the current tension applying mode (S 162 ). 
     When determining that the current tension applying mode is the “winding mode” in S 162 , the transport controller  17   a  determines whether or not the printing is terminated (S 163 ). 
     When determining that the printing is not terminated in S 163 , the transport controller  17   a  executes the process of S 162 . 
     When determining that the current tension applying mode is the “bar mode” in S 162 , the transport controller  17   a  unsets the flag (S 164 ). 
     When determining that the printing is terminated in S 163 , the transport controller  17   a  sets the flag (S 165 ). 
     After executing the process of S 164  or S 165 , the transport controller  17   a  terminates the operation of the winding mechanism  40  by stopping the motor  44  (S 166 ), and terminates the winding mode process shown in  FIG. 12 . 
     As shown in  FIG. 8 , after terminating the execution of the bar mode process in S 109 , the transport controller  17   a  determines whether or not the flag is set (S 110 ). 
     When determining that the flag is unset in S 110 , the transport controller  17   a  executes the winding mode process (S 111 ). 
     After terminating the execution of the winding mode process in S 111 , the transport controller  17   a  determines whether or not the flag is set (S 112 ). 
     When determining that the flag is unset in S 112 , the transport controller  17   a  carries out the process of S 103 . 
     When determining that the flag is set in S 110  or S 112 , the transport controller  17   a  terminates the operation shown in  FIG. 8 . 
     In the bar mode process shown in  FIG. 10 , the transport controller  17   a  controls the winding mechanism  40  so that the angle θ is maintained within the specific range (S 131  to S 135  and S  137 ). In other words, the transport controller  17   a  remains to have the winding by the winding mechanism  40  stopped when the angle θ is within the specific range (YES in S 132 ), and executes the winding by the winding mechanism  40  when the angle θ is not within the specific range (NO in S 132 ) (S 133 ). Therefore, when the angle θ is within the specific range, the length of the printing medium  90  from the transportation roller  23  to the winding mechanism  40  becomes long by the length by which the printing medium  90  is transported by the transportation roller  23  while the tension is being applied by the tension applying member  50 . As a result, the angle θ gradually becomes small, thus becoming smaller than the lower limit of the specific range and running out of the specific range. When the angle θ is not within the specific range, the length of the printing medium  90  from the transportation roller  23  to the winding mechanism  40  becomes short by the length by which the printing medium  90  is wound by the winding mechanism  40  while the tension is being applied by the tension applying member  50  as the printing medium  90  is wound by the winding mechanism  40 . As a result, the angle θ gradually becomes large, and falls within the specific range. Thus, the printing medium  90  is wound by the winding mechanism  40  while the tension is being applied by the tension applying member  50 . 
     For example, when the winding diameter becomes large as shown in  FIG. 13 , the distance from the rotating shaft to the outer circumference of the roll-shaped printing medium  90  becomes long, and hence, even if the weight of the roll-shaped printing medium  90  is supposedly constant, the force of winding the printing medium  90  with the winding mechanism  40  becomes weak when the torque generated at the roll-shaped printing medium  90  with the winding mechanism  40  is constant. Thus, when the winding diameter becomes large, the force of winding the printing medium  90  with the winding mechanism  40  may become weak and the angle θ may not become large even if the winding mechanism  40  is controlled to wind the printing medium  90 . Actually, when the winding diameter becomes large, the weight of the roll-shaped printing medium  90  becomes heavy, and hence the possibility that the angle θ will not become large further increases even if the winding mechanism  40  is controlled to wind the printing medium  90 . When the specific time has elapsed (YES in S 134 ) without the angle θ within the specific range, the transport controller  17   a  controls the winding mechanism  40  to cause the winding mechanism  40  to wind the printing medium  90  by the winding mode process shown in  FIG. 12  (S 160 ). Therefore, the printing medium  90  is wound by the winding mechanism  40  by the amount by which the printing medium  90  is transported by the transportation roller  23  while the tension is being applied by the winding mechanism  40  where the torque is limited by the torque limiter  45 . 
     Furthermore, even when the angle θ becomes larger than the upper limit of the specific range and is no longer within the specific range, for example, when the user of the inkjet printer  10  manually moves the tension applying member  50  to change the position of the tension applying member  50  to the evacuating position shown in  FIG. 6  during the execution of the bar mode process shown in  FIG. 10 , the transport controller  17   a  controls the winding mechanism  40  to cause the winding mechanism  40  to wind the printing medium  90  by the winding mode process shown  FIG. 12  when the specific time has elapsed (YES in S 134 ) without the angle θ within the specific range (S 160 ). Therefore, the printing medium  90  is wound by the winding mechanism  40  by the amount by which the printing medium  90  is transported by the transportation roller  23  while the tension is being applied by the winding mechanism  40  where the torque is limited by the torque limiter  45 . 
     The user can shift to the winding mode process by specifying the “winding mode” through the operation section  82  (“winding mode” in S 139 ) when the bar mode process is being executed while the printing (printing operation) is stopped. Similarly, the user can shift to the bar mode process by specifying the “bar mode” through the operation section  82  (“bar mode” in S 162 ) when the winding mode process is being executed. 
     However, as the specific time elapses (YES in S 134 ) without the angle θ within the specific range if the winding diameter is large, as shown in  FIG. 13 , when shifted from the winding mode process to the bar mode process, the process returns from the bar mode process to the winding process, as described above. Therefore, if the winding diameter is large when shifting from the winding mode process to the bar mode process, for example, the user preferably removes a weight (not shown) attached to the tension applying member  50  to manually lighten the tension applying member  50  or adjusts the upper limit of the torque limited by the torque limiter  45  to be stronger by hand. 
     Furthermore, as the specific time elapses (YES in S 134 ) without the angle θ within the specific range if the tension applying member  50  is located at the evacuating position, as shown in  FIG. 6 , when shifted from the winding mode process to the bar mode process, the process returns from the bar mode process returns to the winding mode process, as described above. Therefore, if the tension applying member  50  is located at the evacuating position when shifting from the winding mode process to the bar mode process, the user preferably manually moves the tension applying member  50  to a position at which the tension applying member  50  makes contact with the printing medium  90  as shown in  FIG. 9 . 
     As described above, the inkjet printer  10  can apply the tension on the printing medium  90  with the winding mechanism  40  by causing the motor  44  to generate the power for winding the printing medium  90  with the winding mechanism  40  (S 160 ) and causing the torque limiter  45  to limit the torque, so that even if the tension cannot be applied on the printing medium  90  by the tension applying member  50  (YES in S 134 ), the tension can be continuously applied on the printing medium  90  for a longer time than in the conventional technique by applying the tension on the printing medium  90  with the winding mechanism  40 . Therefore, the inkjet printer  10  can continue the printing for a longer time than in the conventional technique by executing the printing on the printing medium  90  on which the tension is continuously applied for a longer time than in the conventional technique. 
     The magnitude of the tension applied on the printing medium  90  does not depend on the winding diameter when the tension is applied by the tension applying member  50 , but becomes smaller the larger the winding diameter when the tension is applied by the winding mechanism  40  since the torque is limited to a constant magnitude by the torque limiter  45 . In other words, the magnitude of the tension applied on the printing medium  90  by the winding mechanism  40  fluctuates in accordance with the winding diameter. In particular, if the length of the printing medium  90  is long, the fluctuation extent in the winding diameter caused by the winding of the printing medium  90  by the winding mechanism  40  is large, and hence the fluctuation extent in the magnitude of the tension applied on the printing medium  90  by the winding mechanism  40  is large. Therefore, the magnitude of the tension applied on the printing medium  90  is more stable when the tension is applied by the tension applying member  50  than when applied by the winding mechanism  40 . 
     When the tension is being applied on the printing medium  90  by the winding mechanism  40 , the printing medium  90  between the transportation roller  23  and the winding mechanism  40  slackens between when the printing medium  90  is transported by the transportation roller  23  and when the printing medium  90  is wound by the winding mechanism  40  by the amount transported by the transportation roller  23 , whereby the tension applied on the printing medium  90  temporarily lowers. In other words, when the tension is being applied on the printing medium  90  by the winding mechanism  40 , the tension applied on the printing medium  90  fluctuates when the printing medium  90  is wound by the winding mechanism  40 . On the contrary, when the tension is being applied on the printing medium  90  by the tension applying member  50 , the tension of a constant magnitude is applied on a constant basis on the printing medium  90  by the tension applying member  50  when the printing medium  90  is wound by the winding mechanism  40 . In other words, the tension applied on the printing medium  90  is more stable when the printing medium  90  is wound by the winding mechanism  40  if the tension is applied on the printing medium  90  by the tension applying member  50  than if the tension is applied on the printing medium  90  by the winding mechanism  40 . Therefore, the printing medium  90  is wound into a roll in a more aligned state by the winding mechanism  40  when the tension is applied on the printing medium  90  by the tension applying member  50  than when the tension is applied on the printing medium  90  by the winding mechanism  40 . 
     As described above, the application by the tension applying member  50  is more preferable than the application by the winding mechanism  40  for the method for applying the tension on the printing medium  90 . 
     When executing the bar mode process, the inkjet printer  10  causes the motor  44  to stop the generation of the power for winding the printing medium  90  with the winding mechanism  40  when the angle θ is within the specific range (YES in S 132 ), so that the load of the motor  44  can be suppressed. On the other hand, when the angle θ is outside the specific range (NO in S 132 ), the inkjet printer  10  can recover the state of applying the tension on the printing medium  90  by the tension applying member  50  by returning the angle θ to within the specific range. Therefore, the inkjet printer  10  can suppress the accumulation load of the motor  44  and extend the lifespan of the motor  44 . 
     The inkjet printer  10  can return the angle θ to within the specific range even if the angle θ runs out of the specific range as a result of the change in the length of the printing medium  90  from the transportation roller  23  to the unwinding mechanism  30  or the winding mechanism  40  according to the transportation amount of the printing medium  90  by the transportation roller  23  while the tension is being applied on the printing medium  90  by the tension applying member  50 . Therefore, the inkjet printer  10  can maintain the state of applying the tension on the printing medium  90  by the tension applying member  50  without being influenced by the transportation amount of the printing medium  90  by the transportation roller  23 . 
     The inkjet printer  10  increases the rotation speed and the rotation acceleration of the motor  44  when the winding diameter is small, and reduces the rotation speed and the rotation acceleration of the motor  44  when the winding diameter is large to have the winding speed and the winding acceleration constant irrespective of the winding diameter. Therefore, the inkjet printer  10  can wind the printing medium  90  transported by the transportation roller  23  with the winding mechanism  40  at a constant winding speed and winding acceleration irrespective of the winding diameter when executing the winding mode process. 
     When referring to a large winding diameter, this means that the weight (hereinafter referred to as “wound weight”) of the roll-shaped printing medium  90  wound around the paper core rotatably supported by the winding mechanism  40  is heavy. The torque of the motor  44  needs to be greater as the wound weight becomes heavier. The inkjet printer  10  controls the rotation speed and the rotation acceleration of the motor  44  in accordance with the winding diameter in the present embodiment, but may control the rotation speed and the rotation acceleration of the motor  44  in accordance with the wound weight. The wound weight is proportional to a surface area of when the roll-shaped printing medium  90  wound around the paper core rotatably supported by the winding mechanism  40  is cut along a plane orthogonal to the rotation axis of the printing medium. In other words, the wound weight is proportional to the square of the winding diameter. Therefore, the rotation speed V and the rotation acceleration A of the motor  44  controlled by the transport controller  17   a  may be “Vr×(Rr 2 /R 2 )”, “Ar×(Rr 2 /R 2 )”, respectively. When the rotation speed and the rotation acceleration of the motor  44  are controlled in accordance with the wound weight, the winding speed and the winding acceleration differ depending on the winding diameter. Therefore, when the rotation speed and the rotation acceleration of the motor  44  are controlled in accordance with the wound weight, the specific time in S 134  needs to be changed according to the winding diameter so that the winding amount of the printing medium  90  by the winding mechanism  40  becomes constant irrespective of the winding diameter. 
     The inkjet printer  10  controls the rotation speed and the rotation acceleration of the motor  44  in accordance with the winding diameter in the present embodiment, but the rotation speed and the rotation acceleration of the motor  44  may always be constant. When the rotation speed and the rotation acceleration of the motor  44  are always constant, the time which it takes for the winding amount of the printing medium  90  by the winding mechanism  40  to reach a specific amount becomes shorter the larger the winding diameter. In other words, when the rotation speed and the rotation acceleration of the motor  44  are always constant, the specific time in S 134  may be shorter the larger the winding diameter. Therefore, when the rotation speed and the rotation acceleration of the motor  44  are always constant, the inkjet printer  10  can stop the motor  44  for a longer time the larger the winding diameter, so that the lifespan of the motor  44  can be extended. 
     The configuration of the angle detection device  60  may be a configuration other than the configuration shown in  FIG. 5  as long as the angle θcan be detected. For example, the angle detection device  60  may have a configuration shown in  FIG. 14A  and  FIG. 14B  or a configuration shown in  FIG. 15A  and  FIG. 15B . 
       FIG. 14A  is a front view of an angle detection device  60  in an example different from the example shown in  FIG. 5 .  FIG. 14B  is a side view of the angle detection device  60  shown in  FIG. 14A . 
     The angle detection device  60  shown in  FIG. 14A  and  FIG. 14B  includes a photo-interrupter  65   a  fixed with respect to the leg  21  (see  FIG. 3 ) to detect the lower limit of the specific range, a photo-interrupter  65   b  fixed with respect to the leg  21  to detect the upper limit of the specific range, and a shielding plate  66  fixed to the arm  52  and detected by the photo-interrupter  65   a  and the photo-interrupter  65   b.    
       FIG. 15A  is a front view of an angle detection device  60  in an example different from the examples shown in  FIGS. 5 and 14 .  FIG. 15B  is a side view of the angle detection device  60  shown in  FIG. 15A . 
     The angle detection device  60  shown in  FIG. 15A  and  FIG. 15B  includes a photo-interrupter  67   a  fixed with respect to the leg  21  (see  FIG. 3 ) to detect the lower limit of the specific range, a photo-interrupter  67   b  fixed with respect to the leg  21  to detect the upper limit of the specific range, and a shielding plate  68  fixed to the arm  52  and detected by the photo-interrupter  67   a  and the photo-interrupter  67   b.   
     The inkjet printer  10  does not include the motor in the unwinding mechanism  30  as shown in  FIG. 3  in the present embodiment, but may include the motor  34  in the unwinding mechanism  30  as shown in  FIG. 16 . 
       FIG. 16  is a side cross-sectional view of an inkjet printer  10  in an example different from the example shown in  FIG. 3 . 
     The unwinding mechanism  30  shown in  FIG. 16  has the same configuration as the configuration of the winding mechanism  40 . In other words, the unwinding mechanism  30  shown in  FIG. 16  includes a motor  34  that generates a driving force for rotating a rotating shaft  33   a  (see  FIG. 2 ) of the roll holder  33  (see  FIG. 2 ), that is, a power for rotating the printing medium  90  wound into a roll around the paper core rotatably supported by the roll holder  33 ; a torque limiter  35  serving as a torque limiting mechanism configuring a part of a transmission mechanism of the driving force from the motor  34  to the rotating shaft  33   a  and shielding the connection when an excessive load is applied; an encoder  36  that detects the rotation of the rotating shaft  33   a ; and a cover  37  that covers the motor  34 , the torque limiter  35 , and the encoder  36 . 
     The torque limiter  35  limits the torque generated between the motor  34  side and the printing medium  90  side with a specific magnitude as an upper limit. The torque limiter  35  can allow the upper limit of the torque generated between the motor  34  side and the printing medium  90  side to be adjusted. 
     The unwinding mechanism  30  shown in  FIG. 16  can apply tension on the printing medium  90  as the torque is limited by the torque limiter  35  when the power for winding the printing medium  90  is generated in the motor  34  by the transport controller  17   a.    
     In a case of a configuration in which the sandwiching force of the printing medium  90  by the transportation roller  23  and the pinch roller  24  is weak, the inkjet printer  10  shown in  FIG. 16  can apply tension on the printing medium  90  by the cooperative operation of the unwinding mechanism  30  and the winding mechanism  40  by causing the motor  34  to generate the power for winding the printing medium  90  with the unwinding mechanism  30  when causing the motor  44  to generate the power for winding the printing medium  90  with the winding mechanism  40 . 
     If the unwinding mechanism  30  includes the motor  34  and the torque limiter  35 , the inkjet printer  10  may not include the torque limiter  45  in the winding mechanism  40 . 
     In the present embodiment, the tension applying member of the present invention can apply tension on the printing medium  90  by pushing a portion of the printing medium  90  that is not wound by the winding mechanism  40  by its own weight in the rotating direction indicated with the arrow  10   c  having the axis line  50   a  as the center. However, the tension applying member of the present invention may have other configurations. For example, the tension applying member of the present invention may have a configuration shown in  FIG. 17 . 
       FIG. 17  is a side cross-sectional view of a tension applying member  150  different from the tension applying member  50  shown in  FIG. 1 . 
     As shown in  FIG. 17 , the tension applying member  150  includes a contacting portion  151  that makes contact with the portion of the printing medium  90  that is not wound by the winding mechanism  40  (see  FIG. 1 ), a spring  152  that biases the contacting portion  151  in a direction indicated with an arrow  150   a , and an accommodating portion  153  that accommodates the spring  152 . The tension applying member  150  can apply tension on the printing medium  90  by pushing the portion of the printing medium  90  that is not wound by the winding mechanism  40  in the direction indicated with the arrow  150   a.    
     In the present embodiment, the inkjet printer  10  limits the torque with the torque limiter, which is a component different from the motor. However, the method of limiting the torque may be a method other than the torque limiter. For example, the inkjet printer  10  may adopt a method of exhibiting the function of the torque limiter by stepping out the motor such as the stepping motor, the AC motor, and the like. 
     In the present embodiment, the inkjet printer  10  has a configuration of relatively moving the inkjet head  87  and the printing medium  90  in the sub-scanning direction by transporting the printing medium  90  in the sub scanning direction indicated with the arrow  10   b , but other configurations may be adopted. For example, the inkjet printer  10  may have a configuration of relatively moving the inkjet head  87  and the printing medium  90  in the sub-scanning direction by moving the inkjet head  87  in the sub-scanning direction.