Abstract:
A medium winder, includes: a winding roller that winds a medium discharged from an image formation apparatus into a roll shape; first and second rollers that guide the medium to the winding roller; a dancer roller provided between the first and second rollers in the medium conveyance direction and movable upwardly and downwardly while contacting from above the medium between the first and second rollers; a winding driver that rotates the winding roller; a detector that detects the dancer roller; a dancer roller position recognition portion that recognizes the position of the dancer roller based on a detection result by the detector; and a winding drive controller that controls the winding driver. In an operation of unwinding the medium, the winding drive controller moves the dancer roller up and down by reducing or increasing the unwinding velocity of the medium based on a position of the dancer roller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority based on 35 USC 119 from prior Japanese Patent Application No. 2015-025545 filed on Feb. 12, 2015, entitled “MEDIUM WINDER AND MEDIUM. UNWINDING METHOD WITH THE SAME”, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The disclosure relates to a medium winder and a medium unwinding method using the medium winder. 
         [0004]    2. Description of Related Art 
         [0005]    Heretofore, paper winders have been provided as medium winders for printers capable of printing on long paper from a web as a roll medium. Paper from a web that is printed and ejected from such a printer is wound by a paper winder as a medium winder. 
         [0006]    In such a type of paper winder, the paper printed and ejected from the printer is wound around a winding roller. The paper winder includes a dancer roller. The dancer roller is moved up and down along a guide in accordance with an amount of sag generated in the paper so as to absorb the difference between the paper winding velocity in the paper winder and the paper conveyance velocity in the printer. 
         [0007]    In the above-described printer, it is necessary to warm up a printing section at the start of the printing or cool down the printing section at the end of the printing. During the warming-up and cooling-down processes, unprinted paper is wastefully ejected from the printer and is wound around the winding roller. In order not to waste paper, the printer rotates the paper feed roller and the conveyance roller in reverse directions after the warming-up and cooling-down of the printing section so as to unwind the paper which is once wound around the winding roller in the paper winder. 
         [0008]    In the process of unwinding the paper, the dancer roller also functions to absorb the difference between the paper unwinding velocity in the paper winder and the paper reverse conveyance velocity in the printer. 
         [0009]    In the process of unwinding paper, the position of the dancer roller is detected in the paper winder. When the dancer roller reaches the upper end of the guide, a driving motor to rotate the winding roller, that is, a winding roller driving motor, is driven in the reverse direction to rotate the winding roller in reverse for unwinding the paper. When the dancer roller reaches the lower end of the guide, the winding roller driving motor is halted to stop the rotation of the winding roller, thus terminating the unwinding of paper (see Japanese Patent Application Publication No. S63-51261, for example). 
       SUMMARY OF THE INVENTION 
       [0010]    In a conventional paper winder, paper is unwound by switching between activation and deactivation of the winding roller driving motor. Accordingly, tension applied to the paper significantly changes due to the weight of the dancer roller itself at the time of switching. 
         [0011]    When the tension applied to the paper changes significantly, some structure of the conveyance mechanism of the printer paper may not unwind the paper in a good condition. In this case, the paper may be damaged by meandering. 
         [0012]    An object of an embodiment of the invention is to provide a medium winder and a medium unwinding method which enable a medium to be rewound in a good condition. 
         [0013]    An aspect of the invention is a medium winder that includes: a winding roller configured to wind a medium discharged from an image formation apparatus into a roll shape; first and second rollers configured to guide the medium to the winding roller; a dancer roller provided between the first and second rollers in a medium conveyance direction, and movable upwardly and downwardly while making contact from above with the medium between the first and second rollers; a winding driver configured to rotate the winding roller; a detector configured to detect the dancer roller; a dancer roller position recognition portion configured to recognize the position of the dancer roller based on an output of the detection by the detector; and a winding drive controller configured to control the winding driver. At an operation of unwinding the medium, the winding drive controller moves the dancer roller up and down by reducing or increasing the unwinding velocity of the medium based on a position of the dancer roller. 
         [0014]    Thus according to this aspect, the winding motor controller, in the operation of unwinding the medium, reduces or increases the unwinding velocity of the medium in accordance with the position of the dancer roller to move the dancer roller up and down. Accordingly, it is unnecessary to start or stop driving the winding motor, and this prevents the tension of the medium from changing significantly. 
         [0015]    As a result, the medium can be rewound in a good condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a control block diagram of a paper winder in an embodiment of the invention. 
           [0017]      FIG. 2  is a conceptual diagram of the paper winder and a printer in the embodiment. 
           [0018]      FIG. 3  is a first diagram for explaining a winding operation in the embodiment. 
           [0019]      FIG. 4  is a second diagram for explaining the winding operation in the embodiment. 
           [0020]      FIG. 5  is a third diagram for explaining the winding operation in the embodiment. 
           [0021]      FIG. 6  is a fourth diagram for explaining the winding operation in the embodiment. 
           [0022]      FIG. 7  is a first flowchart illustrating an unwinding operation in the embodiment. 
           [0023]      FIG. 8  is a second flowchart illustrating the unwinding operation in the embodiment. 
           [0024]      FIG. 9  is a first diagram for explaining the unwinding operation in the embodiment. 
           [0025]      FIG. 10  is a second diagram for explaining the unwinding operation in the embodiment. 
           [0026]      FIG. 11  is a third diagram for explaining the unwinding operation in the embodiment. 
           [0027]      FIG. 12  is a fourth diagram for explaining the unwinding operation in the embodiment. 
           [0028]      FIG. 13  is a fifth diagram for explaining the unwinding operation in the embodiment. 
           [0029]      FIG. 14  is a sixth diagram for explaining the unwinding operation in the embodiment. 
           [0030]      FIG. 15  is a seventh diagram for explaining the unwinding operation in the embodiment. 
           [0031]      FIG. 16  is an eighth diagram for explaining the unwinding operation in the embodiment. 
           [0032]      FIG. 17  is a ninth diagram for explaining the unwinding operation in the embodiment. 
           [0033]      FIG. 18  is a tenth diagram for explaining the unwinding operation in the embodiment. 
           [0034]      FIG. 19  is an eleventh diagram for explaining the unwinding operation in the embodiment. 
           [0035]      FIG. 20  is a twelfth diagram for explaining the unwinding operation in the embodiment. 
           [0036]      FIG. 21  is a thirteenth diagram for explaining the unwinding operation in the embodiment. 
           [0037]      FIG. 22  is a fourteenth diagram for explaining the unwinding operation in the embodiment. 
           [0038]      FIG. 23  is a fifteenth diagram for explaining the unwinding operation in the embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0039]    Descriptions are provided hereinbelow for embodiments based on the drawings. In the respective drawings referenced herein, the same constituents are designated by the same reference numerals and duplicate explanation concerning the same constituents is omitted. All of the drawings are provided to illustrate the respective examples only. 
         [0040]    The description is given of a paper winder as a medium winder and a printer as an image formation apparatus that incorporates the paper winder. 
         [0041]      FIG. 2  is a conceptual diagram of the paper winder and printer in the embodiment of the invention. 
         [0042]    In  FIG. 2 , reference numeral  10  denotes the printer, and reference numeral  11  denotes the paper winder connected to printer  10 . 
         [0043]    Printer  10  includes: feeder  13  in which web  12  as a roll medium is set; conveyance roller pair  21  as a conveyance mechanism configured to convey paper P as a long-length medium fed from feeder  13 ; printing section  23  configured to form an image on paper P for printing; and conveyance motor  26  as a conveyance driver which is configured to rotate the conveyance roller pair  21 . Feeder  13  is provided with a feeding roller  14  configured to feed paper P from web  12 ; paper feeding motor  27  is a driver for feeding paper and is configured to rotate feeding roller  14 ; and the like. 
         [0044]    In the embodiment, printing section  23  includes an electrophotographic printing mechanism. The electrophotographic printing mechanism of printing section  23  includes a photoreceptor drum as an image carrier; a charging roller as a charging device configured to uniformly charge the surface of the photoreceptor drum; an LED head as an exposure device configured to form an electrostatic latent image as a latent image on the photoreceptor drum with the surface charged; a development roller as a developer carrier configured to develop the electrostatic latent image to forma toner image as a developer image; a transfer roller as a transfer member configured to transfer the toner image onto paper; and a fixing unit as a fixing device configured to fix the toner image to the paper. 
         [0045]    Paper winder  11  includes: idle rollers  15  and  16  as first and second rollers provided rotatably and configured to guide paper P ejected from printer  10 ; dancer roller  17  as an elevating roller which is provided rotatably so as to freely move up and down between idle rollers  15  and  16  in the conveyance direction of paper P and come into contact with the upper surface of paper P; winding roller  18  which is provided downstream of idle roller  16  in the conveyance direction of paper P and is configured to wind paper P ejected from printer  10  into a roll; and winding motor  35  as a winding driver which is configured to rotate winding roller  18 . 
         [0046]    Dancer roller  17  is configured to move up and down along guide  41  extended in the vertical direction and apply tension to paper P by the weight thereof. 
         [0047]    The leading edge of paper P is attached to winding roller  18 , and paper P is wound around winding roller  18  into a roll by winding motor  35  being driven. 
         [0048]    Within the range in which dancer roller  17  moves, sensors a to c as plural detectors (three detectors in this embodiment) are arranged from the bottom to the top to detect the position of dancer roller  17 . Winding motor  35  is driven by a later-described controller  30  ( FIG. 1 ) in accordance with the position of dancer roller  17  which is detected by sensors a to c, whereby winding roller  18  is rotated. A first detector includes sensor b; a second detector, sensor c; and a third detector, sensor a. The distance between sensors b and c is shorter than the distance between sensors a and b. 
         [0049]    Next, a description is given of the controller for paper winder  11 . 
         [0050]      FIG. 1  is a control block diagram of the paper winder in the embodiment of the invention. 
         [0051]    In  FIG. 1 , reference characters a to c denote sensors; reference numeral  30  denotes a controller configured to entirely control paper winder  11  ( FIG. 2 ); reference numeral  34  denotes a winding motor driver; and reference numeral  35  denotes a winding motor. 
         [0052]    Controller  30  includes sensor output detector  31  as a detection output detector, dancer roller position recognition portion  32 , and winding motor controller  33  as a winding drive controller. 
         [0053]    Sensors a to c detect dancer roller  17  and send sensor outputs as detection outputs to controller  30 . Sensor output detector  31  then reads the received sensor outputs. Each sensor output has on and off states. Sensor output detector  31  then determines whether each sensor a to c is on or off and sends the result of the determination to dancer roller position recognition portion  32 . Based on the result of the determination by sensor output detector  31 , dancer roller position recognition portion  32  recognizes the position of dancer roller  17  and sends the position information to winding motor controller  33 . 
         [0054]    Winding motor controller  33  controls winding motor driver  34  based on the position information sent to drive winding motor  35 . 
         [0055]    Next, a description is given of the operation of the winding of paper P in paper winder  11 . 
         [0056]      FIG. 3  is a first diagram for explaining a winding operation in the embodiment of the invention.  FIG. 4  is a second diagram for explaining the winding operation in the embodiment of the invention.  FIG. 5  is a third diagram for explaining the winding operation in the embodiment of the invention.  FIG. 6  is a fourth diagram for explaining the winding operation in the embodiment of the invention. 
         [0057]    In  FIGS. 3 to 6 , reference character P denotes paper; reference numerals  15  and  16  denote idle rollers; reference numeral  17  denotes dancer roller; and reference characters a to c denote sensors. 
         [0058]    In the initial state of the operation of the winding of paper P in the paper winder  11 , paper P is stopped on the upstream side (the printer  10  side) of dancer roller  17  in the winding direction of paper P and on the downstream side (the winding roller  18  side) of dancer roller  17 , as illustrated in  FIG. 3 . At this time, dancer roller  17  is stopped at a stopping position between sensors a and b, and the rotation of idle rollers  15  and  16  is also stopped. 
         [0059]    When printing starts in printer  10 , paper feed motor  27  and conveyance motor  26  are driven to rotate paper feed roller  14  and conveyance roller pair  21 . Paper P is therefore fed from paper roll  12  and is conveyed at conveyance velocity v 1  on the upstream side of dancer roller  17  in the winding direction of paper P, as illustrated in  FIG. 4 . 
         [0060]    In this process, dancer roller  17  is moved downward from the stopping position. Idle roller  15  is rotated while the rotation of idle roller  16  remains stopped. 
         [0061]    When sensor a detects dancer roller  17  and sends the sensor output to controller  30 , sensor output detector  31  reads the sensor output and determines that sensor a is “on”, as described above. Sensor output detector  31  then sends the result of this determination to dancer roller position recognition portion  32 . Dancer roller position recognition portion  32  recognizes the position of dancer roller  17 , that is, the position information thereof based on the result of the determination by sensor output detector  31 . Dancer roller position recognition portion  32  then sends the position information to winding motor controller  33 . Winding motor controller  33  controls winding motor driver  34  based on the position information to drive winding motor  35 . 
         [0062]    Winding roller  18  is thereby rotated, so that paper P is wound around winding roller  18  at a winding velocity v 2  on the downstream side of dancer roller  17  in the winding direction of paper P, as illustrated in  FIG. 5 . 
         [0063]    In this process, the relationship between conveyance velocity v 1  and winding velocity v 2  of paper P is set to:
       v 2 &gt;v 1 
 
Dancer roller  17  is moved upward from the position of sensor a. Idle rollers  15  and  16  are rotated.
       
 
         [0065]    As illustrated in  FIG. 6 , when dancer roller  17  reaches the position of sensor b, sensor b detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor b is “on”, and winding motor controller  33  stops driving winding motor  35 . The rotation of winding roller  18  is thereby stopped, and paper P is stopped on the downstream side of dancer roller  17  in the winding direction of paper P. 
         [0066]    In this process, dancer roller  17  is moved downward from the position of sensor b. The rotation of idle roller  16  remains stopped while idle roller  15  is rotated. 
         [0067]    Dancer roller  17  is moved between sensors a and b in the operation of winding paper P as described above. 
         [0068]    Next, a description is given of an operation of unwinding paper P in the paper winder  11 . 
         [0069]      FIG. 7  is a first flowchart illustrating an unwinding operation in the embodiment of the invention.  FIG. 8  is a second flowchart illustrating the unwinding operation in the embodiment of the invention.  FIG. 9  is a first diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 10  is a second diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 11  is a third diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 12  is a fourth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 13  is a fifth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 14  is a sixth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 15  is a seventh diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 16  is an eighth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 17  is a ninth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 18  is a tenth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 19  is an eleventh diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 20  is a twelfth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 21  is a thirteenth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 22  is a fourteenth diagram for explaining the unwinding operation in the embodiment of the invention.  FIG. 23  is a fifteenth diagram for explaining the unwinding operation in the embodiment of the invention. 
         [0070]    In the state where paper P is wound around winding roller  18  in a roll in the paper winder  11 , that is, in the initial state of the operation of unwinding paper P, as illustrated in  FIG. 9 , paper P is stopped on the upstream side (winding roller  18  side) and on the downstream side (printer  10  side) of dancer roller  17  in the unwinding direction of paper P. In this process, dancer roller  17  is stopped at the stopping position between sensors a and b, and the rotation of idle rollers  15  and  16  is stopped. 
         [0071]    In printer  10 , paper feed motor  27  and conveyance motor  26  are driven in the reverse direction to rotate paper feed roller  14  and conveyance roller pair  21  in reverse. As illustrated in  FIG. 10 , paper P is conveyed at a reverse conveyance velocity v 3  on the downstream side of dancer roller  17  in the unwinding direction of paper P. 
         [0072]    In this process, dancer roller  17  is moved upward from the stopping position. The rotation of idle roller  16  remains stopped while the idle roller  15  is rotated. 
         [0073]    As illustrated in  FIG. 11 , when dancer roller  17  reaches the position of sensor b, sensor b detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor b is “on”. Subsequently, as illustrated in  FIG. 12 , when dancer roller  17  reaches the position of sensor c, sensor c detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor c is “on”. Controller  30  thereby recognizes that paper P is conveyed in the reverse direction in printer  10  and sets paper winder  11  to an unwinding mode. 
         [0074]    Next, dancer roller position recognition portion  32  recognizes that dancer roller  17  is located at the position of sensor c, and winding motor controller  33  then sets unwinding velocity V of paper P to initial unwinding velocity vd. The relationship between initial unwinding velocity vd and conveyance velocity v 3  of paper P is set to:
       vd&gt;v 3 
 
Initial unwinding velocity vd is set in advance in accordance with conveyance velocity v 3  of paper P.
       
 
         [0076]    Winding motor controller  33  controls winding motor driver  34  and drives winding motor  35  in the reverse direction to start the unwinding of paper P. At this time, dancer roller  17  is located at a position higher than sensor c, as illustrated in  FIG. 13 . 
         [0077]    Winding roller  18  is thereby rotated in reverse, and paper P is unwound at an initial unwinding velocity vd in the upstream side of dancer roller  17  in the unwinding direction of paper P. Dancer roller  17  is therefore moved downward from the position higher than sensor c. Idle rollers  15  and  16  are rotated. 
         [0078]    Subsequently, when dancer roller  17  reaches the position of sensor c as illustrated in  FIG. 14  and then reaches the position of sensor b as illustrated in  FIG. 15 , sensor b detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  determined that sensor b is “on”. Winding motor controller  33  sets unwinding velocity V of paper P to the reduced unwinding velocity vd− as illustrated in  FIG. 16 , to reduce the unwinding velocity V of paper P. The relationship between reduced unwinding velocity vd− and conveyance velocity v 3  of paper P is set to:
       vd−&lt;v 3         
 
         [0080]    Winding motor controller  33  controls winding motor driver  34  to drive winding motor  35  in the reverse direction and to rotate winding roller  18  in reverse continuously, so that paper P is unwound at reduced unwinding velocity vd− on the upstream side of dancer roller  17  in the unwinding direction of paper P. 
         [0081]    At this time, dancer roller  17  is located at a position lower than sensor b. Dancer roller  17  is therefore moved upward from the position lower than sensor b. Idle rollers  15  and  16  are rotated. 
         [0082]    When winding motor controller  33  sets unwinding velocity V of paper P to reduced unwinding velocity vd−, sensor output detector  31  determines whether sensor a is “on”. When sensor a is “on”, dancer roller  17  is determined to be at the position of sensor a. Winding motor controller  33  controls winding motor driver  34  to stop driving winding motor  35  and stop the rotation of winding roller  18 , thus terminating the unwinding of paper P. 
         [0083]    When dancer roller  17  is therefore moved upward from a position lower than sensor b as described above and reaches the position of sensor b as illustrated in  FIG. 17 , sensor b detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor b is “on”, and winding motor controller  33  keeps unwinding velocity V of paper P set to reduced unwinding velocity vd−. 
         [0084]    Subsequently, sensor output detector  31  determines whether sensor a is “on”. When sensor a is “on”, dancer roller  17  is determined to be at the position of sensor a, and winding motor controller  33  controls winding motor driver  34  to stop driving winding motor  35  and stop the rotation of winding roller  18 , thus terminating the unwinding of paper P. 
         [0085]    When dancer roller  17  then reaches the position of sensor c as illustrated in  FIG. 18 , sensor c detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor c is “on”, and winding motor controller  33  sets unwinding velocity V of paper P to increased unwinding velocity vd+ to increase unwinding velocity V of paper P as illustrated in  FIG. 19 . The relationship between increased unwinding velocity vd+ and conveyance velocity v 3  of paper P is set to:
       Vd+&gt;v 3         
 
         [0087]    Winding motor controller  33  controls winding motor driver  34  to drive winding motor  35  in the reverse direction and to rotate winding roller  18  in reverse continuously, so that paper P is unwound at increased unwinding velocity vd+ in the upstream side of dancer roller  17  in the unwinding direction of paper P. 
         [0088]    Dancer roller  17  is located at a position higher than sensor c at this time. Dancer roller  17  is therefore moved downward from the position higher than sensor c. Idle rollers  15  and  16  are rotated. 
         [0089]    When dancer roller  17  is moved downward from the position higher than sensor c to reach the position of sensor c as illustrated in  FIG. 20 , sensor c detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor c is “on”, and winding motor controller  33  keeps unwinding velocity V of paper P set to increased unwinding velocity vd+. 
         [0090]    When dancer roller  17  then reaches the position of sensor b as illustrated in  FIG. 21 , sensor b detects dancer roller  17  and sends the sensor output to the controller  30 . Sensor output detector  31  then determines that sensor b is “on”, and winding motor controller  33  sets unwinding velocity V of paper P again to reduced unwinding velocity vd−. 
         [0091]    Paper P is therefore unwound at reduced unwinding velocity vd− again on the upstream side of dancer roller  17  in the unwinding direction of paper P, and dancer roller  17  is again moved upward from the position lower than sensor b. 
         [0092]    Thereafter, the aforementioned unwinding operation is repeated until paper feed motor  27  and conveyance motor  26  in the reverse direction are halted in printer  10 . To be specific, unwinding velocity V of paper P is alternately set to reduced and increased unwinding velocities vd− and vd+, so that unwinding velocity V of paper P is increased and reduced repeatedly. 
         [0093]    When the operation of paper feed motor  27  and conveyance motor  26  in the reverse direction is halted in printer  10  and paper P is stopped on the downstream side of dancer roller  17  in the unwinding direction of paper P as illustrated in  FIG. 22 , winding motor controller  33  controls winding motor driver  34  to keep winding motor  35  operating in the reverse direction and continue the unwinding of paper P. 
         [0094]    Winding roller  18  is rotated in reverse, and paper P is unwound at initial unwinding velocity vd on the upstream side of dancer roller  17  in the unwinding direction of paper P. When dancer roller  17  is then moved downward from the position of sensor b and reaches the position of sensor a as illustrated in  FIG. 23 , sensor a detects dancer roller  17  and sends the sensor output to controller  30 . Sensor output detector  31  then determines that sensor a is “on”, and winding motor controller  33  controls winding motor driver  34  to stop driving winding motor  35 , thus terminating the unwinding of paper P. 
         [0095]    At this time, paper P is stopped on the upstream side and downstream side of dancer roller  17  in the unwinding direction of paper P. Dancer roller  17  is stopped at the position of sensor a, and the rotation of idle rollers  15  and  16  is stopped. 
         [0096]    In the operation of unwinding paper P according to this embodiment, winding motor controller  33  reduces or increases unwinding velocity V of paper P in accordance with the position of dancer roller  17  to move dancer roller  17  up and down. Accordingly, it is unnecessary to start or stop driving winding motor  35 . 
         [0097]    Accordingly, the weight of dancer roller  17  is not applied to paper P when dancer roller  17  is moved up and down, which prevents the tension of paper P from changing significantly. 
         [0098]    In the process of unwinding paper P, paper P can be rewound in a good condition and can be prevented from being damaged by meandering. 
         [0099]    Moreover, the distance between sensors b and c is shorter than the distance between a and b. Accordingly, the distance that dancer roller  17  is moved between the time to increase winding velocity V of paper P and the time to reduce winding velocity V can be short. This can reduce the inertia of dancer roller  17  being moved, further preventing the tension of paper P from changing significantly. 
         [0100]    Since the distance that dancer roller  17  moves between the time to increase winding velocity V of paper P and the time to reduce winding velocity V can be made short, it is possible to reduce deceleration amount Δm, which is the difference between initial unwinding velocity Vd and reduced unwinding velocity vd−, and acceleration amount Δp, which is the difference between increased unwinding velocity vd+ and initial unwinding velocity Vd. 
         [0101]    Next, a description is given of the flowchart. 
         [0102]    Step S 1 : Sensor output detector  31  waits for sensor b to be turned “on”. 
         [0103]    Step S 2 : Sensor output detector  31  waits for sensor b to be turned “on”. 
         [0104]    Step S 3 : controller  30  sets paper winder  11  to the unwinding mode. 
         [0105]    Step S 4 : Winding motor controller  33  sets unwinding velocity of paper P to initial unwinding velocity vd. 
         [0106]    Step S 5 : Winding motor controller  33  starts the unwinding of paper P. 
         [0107]    Step S 6 : Sensor output detector  31  waits for sensor b to be turned “on”. 
         [0108]    Step S 7 : Winding motor controller  33  sets unwinding velocity of paper P to reduced unwinding velocity vd−. 
         [0109]    Step S 8 : Sensor output detector  31  determines whether sensor a is “on”. When sensor a is “on”, the procedure goes to step S 12 . When sensor a is not “on”, the procedure goes to step S 9 . 
         [0110]    Step S 9 : Sensor output detector  31  determines whether sensor b is “on”. When sensor b is “on”, the procedure goes to step S 10 . When sensor b is not “on”, the procedure returns to step S 7 . 
         [0111]    Step S 10 : Winding motor controller  33  keeps unwinding velocity of paper P set to reduced unwinding velocity vd−. 
         [0112]    Step S 11 : Sensor output detector  31  determines whether sensor a is “on”. When sensor a is “on”, the procedure goes to step S 12 . When sensor a is not “on”, the procedure goes to step S 13 . 
         [0113]    Step S 12 : Winding motor controller  33  terminates the unwinding of paper P. 
         [0114]    Step S 13 : Sensor output detector  31  determines whether sensor c is “on”. When sensor c is “on”, the procedure goes to step S 14 . When sensor c is not “on”, the procedure returns to step S 10 . 
         [0115]    Step S 14 : Winding motor controller  33  sets unwinding velocity of paper P to increased unwinding velocity vd+. 
         [0116]    Step S 15 : Sensor output detector  31  determines whether sensor c is “on”. When sensor c is “on”, the procedure goes to step S 16 . When sensor c is not “on”, the procedure returns to step S 14 . 
         [0117]    Step S 16 : Winding motor controller  33  keeps unwinding velocity V of paper P set to increased unwinding velocity vd+. 
         [0118]    Step S 17 : Sensor output detector  31  waits for sensor b to be turned “on”. 
         [0119]    In this embodiment, printer  10  is used as the image formation apparatus. However, the invention is applicable to copiers, facsimiles, and multifunction printers. 
         [0120]    The invention includes other embodiments in addition to the above-described embodiments without departing from the spirit of the invention. The embodiments are to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. Hence, all configurations including the meaning and range within equivalent arrangements of the claims are intended to be embraced in the invention.