Patent Publication Number: US-8967891-B2

Title: Methods and devices for transporting a medium in a printing apparatus

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a printing apparatus. 
     2. Related Art 
     For example, among ink jet type printers, there is a printer of a type which uses large-sized paper having a paper size of A2 or more. In the ink jet printer for such a large-sized-paper, besides single sheets of paper, so-called roll paper is often used. In addition, in the following, the so-called roll paper which is wound around a roll body, and a portion which is drawn from the roll body is referred to as paper. 
     At present, the drawing of the paper from the roll body is performed by rotationally driving a transport roller by a paper feed motor (hereinafter also referred to as a PF motor). In addition, the PF motor is controlled and driven by PID control. 
     As a printer which uses such a roll body, there is a printer which is disclosed in JP-A-2007-290866. Also, as printers which perform the PID control, there are printers which are disclosed in JP-A-2006-240212, JP-A-2003-79177, and JP-A-2003-48351. 
     Usually, the transport roller is provided spaced a certain distance in a direction in which the paper is supplied from the roll body mounted on a printer main body. Therefore, there is also a case where it is difficult to transport the paper only by the transport roller. Therefore, there is also proposed a printing apparatus in which a roll motor (hereinafter also referred to as an RR motor) which rotationally drives the roll body is provided and rotates the roll body, thereby transporting the paper. 
     However, in the printing apparatus as described above, in the case of using slippery paper (medium), there is a problem that if the diameter of the medium that is wound around the roll body is reduced, transport precision falls at the time of the start of the feeding of the paper, so that image quality may deteriorate. 
     SUMMARY 
     An advantage of some aspects of the invention is that it prevents deterioration of image quality. 
     According to an aspect of the invention, there is provided a printing apparatus including: a motor which drives a shaft of a roll body around which a medium is wound, in the feeding direction of the medium; a transport roller which transports the medium fed from the roll body; and a control section which supplies electric power for rotating the roll body to the motor, wherein the electric power that the control section supplies to the motor at the time of the start of the feeding of the medium is larger when the diameter of the medium that is wound around the roll body is R 2  (&lt;R 1 ) than when the diameter of the medium that is wound around the roll body is R 1 . 
     Other aspects of the invention will become apparent from the description of this specification and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a diagram showing a configuration example of the appearance of a printer. 
         FIG. 2  is a diagram showing the relationship between a drive system which uses a DC motor and a control system in the printer. 
         FIG. 3  is a diagram showing a configuration example of the appearance of a rotating holder and an RR motor. 
         FIG. 4A  is a timing chart of a waveform of an output signal when the RR motor performs normal rotation, and  FIG. 4B  is a timing chart of a waveform of an output signal when the RR motor performs reverse rotation. 
         FIG. 5  is a diagram showing the positional relationship among a roll body, a transport roller pair, and a printing head. 
         FIG. 6  is a block diagram showing a functional configuration example of a control section. 
         FIG. 7  is a flow chart showing the schematic flow of the overall processing which a printer of an embodiment executes. 
         FIG. 8  is a flow chart showing the flow of a measurement processing. 
         FIG. 9  is a diagram showing one example of an output of a rotary sensor. 
         FIG. 10  is a diagram showing one example of the relationship between a transport velocity V and a roll static-load N. 
         FIG. 11  is a flow chart showing the flow of an estimation processing. 
         FIG. 12  is a diagram showing an example of the correspondence relationship between a diameter D and a remaining amount L. 
         FIGS. 13A and 13B  are diagrams showing the correspondence relationship between the roll static-load N and the diameter D of the medium that is wound around the roll body. 
         FIG. 14  is a diagram showing the flow of a print processing. 
         FIG. 15  is a diagram showing the relationship between a velocity profile of a PF motor and a velocity profile of the RR motor. 
         FIG. 16  is a diagram showing the relationship between the velocity profile and an applied voltage to the RR motor. 
         FIG. 17  is an explanatory diagram of assistance in the embodiment. 
         FIGS. 18A and 18B  are conceptual diagrams for explaining the relationship between the diameter of the medium that is wound around the roll body and slippage. 
         FIG. 19  is a flow chart showing the flow of a roll control processing in the embodiment. 
         FIG. 20  is a diagram showing the relationship between the diameter of the medium that is wound around the roll body and correction assistance, and the effects of the correction assistance. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     At least the following matters will become apparent from the description of this specification and the accompanying drawings. 
     A printing apparatus will become apparent which includes: a motor which drives a shaft of a roll body around which a medium is wound, in the feeding direction of the medium; a transport roller which transports the medium fed from the roll body; and a control section which supplies electric power for rotating the roll body to the motor, wherein the electric power that the control section supplies to the motor at the time of the start of the feeding of the medium is larger when the diameter of the medium that is wound around the roll body is R 2  (&lt;R 1 ) than when the diameter of the medium that is wound around the roll body is R 1 . 
     According to such a printing apparatus, it is possible to transport the medium with high precision regardless of the diameter of the medium that is wound around the roll body. Accordingly, it is possible to prevent deterioration of image quality. 
     In such a printing apparatus, it is preferable that the electric power that the control section supplies to the motor at the time of the start of the feeding of the medium include first assistance power which assists the driving of the motor without depending on the diameter of the medium that is wound around the roll body and second assistance power which assists the driving of the motor in accordance with the diameter of the medium that is wound around the roll body. 
     According to such a printing apparatus, it is possible to make the motor be easily driven at the time of the start of the feeding of the medium. 
     In such a printing apparatus, it is preferable that the second assistance power be in inverse proportion to the diameter of the medium that is wound around the roll body. 
     According to such a printing apparatus, it is possible to reduce a slippage amount regardless of the diameter of the medium that is wound around the roll body. 
     In such a printing apparatus, it is preferable that the control section adjust the electric power which is supplied to the motor, by changing a duty value in PWM control. 
     According to such a printing apparatus, it is possible to accurately and easily control the electric power which is supplied to the motor. 
     In such a printing apparatus, it is preferable that the medium be a medium more slippery than plain paper upon transportation by the transport roller. 
     In this case, the effect of further prevention in deterioration of image quality can be obtained. 
     In the following embodiment, as one example of a printing apparatus, the case of a printer will be explained. 
     Concerning the Configuration of the Printer 
       FIG. 1  is a diagram showing a configuration example of the appearance of a printer  10  related to this embodiment.  FIG. 2  is a diagram showing the relationship between a drive system which uses a DC motor and a control system in the printer  10  of  FIG. 1 .  FIG. 3  is a diagram showing a configuration example of the appearance of a rotating holder  31  and an RR motor (roll motor)  33 . 
     In the case of this example, the printer  10  has a pair of leg portions  11  and a main body portion  20  which is supported by the leg portions  11 . A support post  12  is provided at the leg portion  11 , and rotatable casters  13  are mounted on a caster support portion  14 . 
     A variety of internal devices are mounted on the main body portion  20  in a state where they are supported by a chassis (not shown), and are covered by an outer case  21 . Also, as shown in  FIG. 2 , as a drive system which uses a DC motor, a roll driving mechanism  30 , a carriage driving mechanism  40 , and a paper transport mechanism  50  are mounted in the main body portion  20 . 
     The roll driving mechanism  30  is provided at a roll mounting portion  22  which exists on the main body portion  20 . The roll mounting portion  22  is provided on the upper side of the rear face side of the main body portion  20 , as shown in  FIG. 1 , so that a roll body RP is mounted in the inside of the roll mounting portion by opening an opening and closing lid  23  which is one element that constitutes the above-mentioned outer case  21 , and the roll body RP can be rotationally driven by the roll driving mechanism  30 . 
     Also, the roll driving mechanism  30  for rotating the roll body RP has the rotating holders  31 , a gear wheel train  32 , the RR motor  33 , and a rotation detection section  34 , as shown in  FIGS. 2 and 3 . 
     The rotating holders  31  are inserted at both end sides of a hollow hole RP 1  which is provided at the roll body RP, and a pair of rotating holders is provided in order to support the roll body RP from both end sides. 
     The RR motor  33  provides a driving force (a turning force) to a rotating holder  31   a  which is located on one end side, among a pair of rotating holders  31 , through the gear wheel train  32 . 
     In this embodiment, the rotation detection section  34  uses a rotary encoder. Therefore, the rotation detection section  34  is provided with a disc-shaped scale  34   a  and a rotary sensor  34   b . The disc-shaped scale  34   a  has light transmitting portions which allow light penetration and light shielding portions which block the penetration of light, at constant intervals along the circumferential direction thereof. Also, the rotary sensor  34   b  has a light emitting element (not shown), a light receiving element (not shown), and a signal processing circuit (not shown), as main components. 
       FIG. 4A  is a timing chart of a waveform of an output signal when the RR motor  33  performs normal rotation.  FIG. 4B  is a timing chart of a waveform of an output signal when the RR motor  33  performs reverse rotation. In this embodiment, using outputs from the rotary sensor  34   b , pulse signals (an ENC signal of A phase and an ENC signal of B phase) which are out of phase from each other by 90 degrees, as shown in  FIGS. 4A and 4B , are input to a control section  100 . Therefore, whether the RR motor  33  is in a normal rotation state or in a reverse rotation state can be detected using the lead/retardation in phase. 
     The carriage driving mechanism  40  is provided with a carriage  41  which is also a portion of a component of an ink supply/ejection mechanism, a carriage shaft  42 , a carriage motor (not shown), a belt, and so on. 
     The carriage  41  is provided with an ink tank  43  for storing ink of each color, and ink can be supplied from an ink cartridge (not shown), which is provided fixed on the front face side of the main body portion  20 , to the ink tank  43  through a tube (not shown). Also, as shown in  FIG. 2 , a printing head  44  which can eject ink droplets is provided at the lower surface of the carriage  41 . A nozzle row (not shown) correlated with each ink is provided at the printing head  44  and a piezo element (not shown) is disposed at a nozzle which constitutes the nozzle row. The ink droplet can be ejected from the nozzle which is located at an end portion of an ink path, by an operation of the piezo element. 
     In addition, the ink supply/ejection mechanism is constituted by the carriage  41 , the ink tank  43 , the tube (not shown), the ink cartridge, and the printing head  44 . Also, the printing head  44  is not limited to a piezo driving method using the piezo element, but may also adopt, for example, a heater method which uses the force of a bubble that is generated by heating ink by a heater, a magnetostriction method which uses a magnetostriction element, a mist method which controls mist by an electric field, or the like. Also, ink which is filled in the ink cartridge/the ink tank  43  may also be any kind of ink such as dye-based ink or pigment-based ink. 
     The paper transport mechanism  50  has a transport roller pair  51 , a gear wheel train  52 , a PF motor (paper feed motor)  53 , and a rotation detection section  54 , as shown in  FIGS. 2 and 5 . In addition,  FIG. 5  is a diagram showing the positional relationship among the roll body RP, the transport roller pair  51 , and the printing head  44 . 
     The transport roller pair  51  is provided with a transport roller  51   a  and a driven transport roller  51   b , and a paper P (a roll paper) which is drawn from the roll body RP can be pinched by these rollers. 
     The PF motor  53  is to provide a driving force (a turning force) to the transport roller  51   a  through the gear wheel train  52 . 
     In this embodiment, the rotation detection section  54  uses a rotary encoder, so that the rotation detection section is provided with a disc-shaped scale  54   a  and a rotary sensor  54   b , similarly to the above-mentioned rotation detection section  34 , and can output the pulse signals as shown in  FIGS. 4A and 4B . 
     Also, a platen  55  is provided further on the downstream side (the paper discharge side) than the transport roller pair  51 , so that the paper P is guided on the platen  55 . Also, the printing head  44  is disposed so as to face the platen  55 . Suction holes  55   a  are formed in the platen  55 . On the other hand, the suction holes  55   a  are provided so as allow communication with a suction fan  56 , so that air is sucked from the printing head  44  side through the suction holes  55   a  by an operation of the suction fan  56 . By this, in a case where the paper P is present on the platen  55 , the paper P can be sucked and held. In addition, the printer  10  is provided with various other sensors such as a paper width detection sensor  57  which detects the width of the paper P, or the like. 
     Concerning the Control Section 
       FIG. 6  is a block diagram showing a functional configuration example of the control section  100 . The control section  100  is a section which performs various controls. Each of output signals of the rotary sensors  34   b  and  54   b , the paper width detection sensor  57 , a linear sensor or a gap detection sensor, which are not shown, a power switch which turns on/off an electric power supply of the printer  10 , and the like is input to the control section  100 . As shown in  FIG. 2 , the control section  100  is provided with a CPU  101 , a ROM  102 , a RAM  103 , a PROM  104 , an ASIC  105 , a motor driver  106 , etc., and they are interconnected through a transmission line  107  such as a bus, for example. Also, the control section  100  is connected to a computer COM. Then, a main control section  110 , a PF motor control section  111 , and an RR motor control section  112 , which are as shown in  FIG. 6 , are implemented by the hardware, software which is stored in the ROM  102  or the PROM  104 , and/or cooperation of data, the addition of a circuit or a component, which performs a specific processing, or the like. In addition, in this embodiment, as the PROM  104 , a flash memory (a flash type EEPROM) is provided, so that writing and reading each become possible. 
     The PF motor control section  111  of the control section  100  controls the driving of the PF motor  53  such that the transport roller  51   a  is rotated, whereby the paper P is transported in a transport direction. In addition, in the following, the rotation direction of the PF motor  53  when transporting the paper P in the transport direction is called a normal rotation direction. The RR motor control section  112  controls the driving of the RR motor  33 , thereby adjusting tension (tensile force) of the paper P. In addition, the rotation direction to wind off the paper P from the roll body is referred to as the normal rotation direction of the RR motor  33 , and conversely, the rotation direction to wind up the paper is referred to as a reverse rotation direction. The main control section  110  controls operations of the PF motor control section  111  and the RR motor control section  112 . The control section  100  executes each processing, which will be described later, in cooperation with the main control section  110 , the PF motor control section  111 , and the RR motor control section  112 . 
     Concerning Overall Processing 
       FIG. 7  is a flow chart showing the schematic flow of the overall processing which the printer  10  of this embodiment executes. First, the control section  100  detects that the roll body RP has been mounted (exchanged) on the roll mounting portion  22  (S 100 ). For example, the mounting of the roll body RP on the roll mounting portion  22  may also be detected by a sensor (not shown), or the mounting of the roll body RP may also be detected in response to the operation of an operation panel (not shown). In this embodiment, at the operation panel (not shown), the mounting of the roll body RP and the kind (for example, plain paper, glossy paper, mat paper) of the paper P wound on the roll body can be input. The information for identifying the kind of paper P received is stored in the PROM  104 . Next, the control section  100  executes a measurement processing (S 200 ). In the measurement processing, a diameter D of the paper P that is wound around the roll body RP just after the mounting of the roll body RP, and a roll static-load (torque) when the roll body RP rotates are measured. Since the roll static-load varies linearly in response to the rotating velocity of the roll body RP (a transport velocity V of the paper P), a roll static-load at the time of high-speed transport, Nhi, and a roll static-load at the time of low-speed transport, Nlo, are measured. If the measurement processing is finished, the roll static-loads Nhi and Nlo and the diameter D are stored in the PROM  104 . 
     If the measurement processing is finished, a printable state is reached, and an input of a print job from the computer COM is received (S 300 ). Then, a print processing related to the received print job is executed (S 400 ). Then, if the print processing is finished, whether or not the paper P of the mounted roll body RP is plain paper is determined (S 500 ), and in a case where the paper is plain paper, an estimation processing is executed (S 600 ). In the estimation processing, the diameter D and the roll static-loads Nhi and Nlo of the roll body RP just after the print processing are acquired, and these are updated in the PROM  104 . If the estimation processing is finished, the process returns to Step S 300 . On the other hand, in Step S 500 , in a case where the paper P of the mounted roll body RP is not plain paper, the process returns to Step S 200 , thereby executing the measurement processing. That is, by the measurement processing, the roll static-loads Nhi and Nlo and the diameter D are acquired and updated in the PROM  104 . 
     As described above, in this embodiment, in the stage where the roll body RP is mounted, the measurement processing is executed, and every time the print processing is completed, the roll static-loads Nhi and Nlo and the diameter D stored in the PROM  104  are updated. However, in a case where the paper P of the mounted roll body RP is plain paper, the roll static-loads Nhi and Nlo and the diameter D are acquired by the measurement processing the first time, and for the second time and thereafter, the roll static-loads Nhi and Nlo and the diameter D are acquired by the estimation processing. On the other hand, in a case where the paper P of the mounted roll body RP is not plain paper, the roll static-loads Nhi and Nlo and the diameter D are acquired by the measurement processing each time. In addition, there is a case where the printer  10  also transports the paper P in a processing other than the print processing. For example, a case where the paper P is transported at the time of maintenance can also be considered. Also in a case where such an operation is performed, in order to update the roll static-loads Nhi and Nlo and the diameter D, it is desirable to execute the measurement processing or the estimation processing. 
     Concerning the Measurement Processing 
     Next, the measurement processing will be explained. 
       FIG. 8  is a flow chart showing the flow of the measurement processing. First, by driving the PF motor  53  in the normal rotation direction by the PF motor control section  111 , the control section  100  acquires the outputs from the rotary sensors  34   b  and  54   b  (S 205 ). Only the PF motor  53  is driven in the normal rotation direction. However, since the paper P of the roll body RP is transported in response to the driving of the PF motor  53 , the roll body RP and the RR motor  33  also rotate in the normal rotation direction depending on the transport. 
       FIG. 9  shows one example of the outputs of the rotary sensors  34   b  and  54   b  in Step S 205 . In this drawing, a broken line represents an output of the rotary sensor  54   b  with respect to the rotation amount of the PF motor  53 , and a solid line represents an output of the rotary sensor  34   b  with respect to the rotation amount of the RR motor  33 . The horizontal axis represents time, and the vertical axis represents the numbers of counts, Err and Epf, of the rotary sensors  34   b  and  54   b . The Err and Epf are the numbers of counts of the edges of the above-mentioned ENC signals and mean the rotation amounts of the rotary sensors  34   b  and  54   b  in Step S 205 . As shown in  FIG. 9 , the PF motor  53  is driven so as to be accelerated over the period from the early period to the middle period, then, gradually decelerate, and eventually stop. Since the RR motor  33  is driven, the output of the rotary sensor  34   b  is also the same. 
     Then, after the lapse of a predetermined period of time from the driving in Step S 205 , the respective numbers of counts, Err and Epf, of the rotary sensors  34   b  and  54   b  are acquired and the diameter D is calculated on the basis of the numbers of counts (S 210 ). Here, if the stretching or the slippage of the paper P is to be nearly negligible, the amount of transport ΔLpf of the paper P which is transported by the rotation of the PF motor  53  in Step S 205  and the amount of transport ΔLrr of the paper P which is transported by the rotation of the RR motor  33  can be considered to be equal to each other. Further, the amounts of transport, ΔLpf and ΔLrr, of the paper P are proportional to the respective numbers of counts, Err and Epf, of the rotary sensors  34   b  and  54   b . If these proportionality coefficients are respectively defined as k 1  and k 2 , the following expressions (1) to (3) are established.
 
Δ Lpf=k 1 ×Epf   (1)
 
Δ Lrr=k 2 ×Err   (2)
 
Δ Lpf=ΔLrr   (3)
 
     The proportionality coefficient k 1  related to the PF motor  53  is a constant which corresponds to a reduction gear ratio of the gear wheel train  52  or the diameter or the circumference ratio of the transport roller  51   a . On the other hand, since the diameter D is reduced in accordance with the transport of the paper P, the proportionality coefficient k 2  related to the RR motor  33  is a coefficient which is proportional to the diameter D. If the proportionality coefficient k 2  is divided into a constant k 3  (a constant corresponding to the reduction gear ratio of the gear wheel train  52  or the circumference ratio) and the diameter D, the above-mentioned expressions can be expressed as follows:
 
Δ Lrr=k 3 ×D×Err   (4)
 
 k 1 ×Epf=k 3 ×D×Err   (5)
 
     The control section  100  determines whether or not the calculated diameter D is a normal value (S 215 ), and in a case where it is normal, the diameter D is stored in the PROM  104  (S 220 ). In a case where it is not normal, Step S 205  is executed again. Also, in a case where it is not normal, the process may also be finished while issuing an error notification. 
     Then, the RR motor control section  112  drives the RR motor  33  in the normal rotation direction, thereby feeding the paper P at a certain transport velocity Vlo (S 225 ). Further, in Step S 225 , while the transport velocity V of the paper P is stable at the transport velocity Vlo, the control section  100  acquires the roll static-load Nlo by converting a Duty value of a PWM signal that the RR motor control section  112  outputs to the RR motor  33 , into torque. In this embodiment, PID control which targets the transport velocity Vlo is performed, so that the roll static-load Nlo is acquired by converting an average value of integral components of the PID control into torque. In addition, since the transport velocity V of the paper P can be obtained by dividing the above-mentioned amount of transport, ΔLrr, by time, the PID control which targets the transport velocity Vlo can be performed. 
     Thereafter, the RR motor control section  112  drives the RR motor  33  in the normal rotation direction, thereby feeding the paper P at a certain transport velocity Vhi (&gt;Vlo). Then, while the transport velocity V of the paper P is stable at the transport velocity Vhi, the control section  100  acquires the roll static-load Nhi by converting the Duty value of the PWM signal that the RR motor control section  112  outputs to the RR motor  33 , into torque, similarly to Step S 225 , (S 230 ). Here, the roll static-loads Nlo and Nhi can be considered to be values corresponding to loads required to rotate the roll body RP at the rotating velocities corresponding to the transport velocities Vlo and Vhi against rotational resistance (mainly frictional resistance). 
       FIG. 10  shows one example of the relationship between an arbitrary transport velocity V and a roll static-load N. As shown in this drawing, the roll static-load N can be expressed by a linear function of the transport velocity V, and if at least the roll static-loads Nlo and Nhi for the transport velocities Vlo and Vhi are known, the roll static-load corresponding to an arbitrary transport velocity V can be calculated by the following expression (6). 
     
       
         
           
             
               
                 
                   N 
                   = 
                   
                     
                       
                         
                           ( 
                           
                             Nhi 
                             - 
                             Nlo 
                           
                           ) 
                         
                         
                           ( 
                           
                             Vhi 
                             - 
                             Vlo 
                           
                           ) 
                         
                       
                       ⁢ 
                       V 
                     
                     + 
                     
                       { 
                       
                         Nlo 
                         - 
                         
                           
                             
                               ( 
                               
                                 Nhi 
                                 - 
                                 Nlo 
                               
                               ) 
                             
                             
                               ( 
                               
                                 Vhi 
                                 - 
                                 Vlo 
                               
                               ) 
                             
                           
                           ⁢ 
                           Vlo 
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     The control section  100  determines whether or not the values of the roll static-loads Nlo and Nhi are normal (S 235 ), and in a case where they are normal, the roll static-loads Nlo and Nhi are stored in the PROM  104  (S 240 ), and then the measurement processing is completed. In a case where they are not normal, the process is executed again from Step S 225 . According to the measurement processing described above, the diameter D and the roll static-loads Nlo and Nhi can be measured and stored in the PROM  104 . In addition, as described above, in a case where the paper P of the roll body RP is not plain paper, the measurement processing is executed for every execution of the print processing, so that the diameter D and the roll static-loads Nlo and Nhi are sequentially updated. 
     Concerning the Estimation Processing 
     Next, the estimation processing will be explained. 
       FIG. 11  is a flow chart showing the flow of the estimation processing. 
     First, the control section  100  acquires the diameter D, which is currently stored in the PROM  104  (S 605 ). In addition, the diameter D, which is currently stored in the PROM  104 , means the diameter D (hereinafter referred to as a reference diameter D 0 ) of the paper P that is wound around the roll body RP before the execution of the last print processing. In addition, as shown in  FIG. 7 , the condition of the execution of the estimation processing is based on the premise that the paper P of the roll body RP is plain paper. 
     Thereafter, the control section  100  acquires the amount of transport ΔL (ΔLpf) of the paper P transported in the last print processing (S 610 ). Since in each printing job, a print size in the transport direction is designated, the amount of transport ΔL actually transported in the print processing can be acquired. Of course, a cumulative total value of the number of counts of the rotary sensor  54   b  in the print processing may also be converted into the amount of transport ΔLpf by the above-mentioned expression (1). Then, on the basis of the correspondence relationship between the diameter D and the remaining amount L of the paper P which is wound on the roll body RP, the current diameter D is estimated (S 615 ). 
       FIG. 12  is a diagram showing an example of the correspondence relationship between the above-mentioned diameter D and the remaining amount L. In this drawing, the vertical axis represents the remaining amount L of the paper P which is wound on the roll body RP, and the horizontal axis represents the diameter D. As shown in this drawing, the remaining amount L can be expressed by a parabola (quadratic function) of the diameter D. In the estimation of the current diameter D, first, the remaining amount L (hereinafter referred to as a reference remaining amount L 1 ) of the paper P, which corresponds to the reference diameter D 0  before the execution of the last print processing, which has been acquired in Step S 605 , is calculated on the basis of the correspondence relationship in the drawing. Then, the remaining amount L (hereinafter referred to as a remaining amount L 2 ) of the current paper P is calculated by subtracting the amount of transport ΔL acquired in Step S 610 , from the reference remaining amount L 1 . Further, the diameter D corresponding to the remaining amount L 2  of the current paper P is calculated on the basis of the correspondence relationship in the drawing. By this, the current diameter D can be estimated. In addition, function parameters which define the correspondence relationship (quadratic function) in the drawing are stored in advance in the ROM  102 , and the parameters are read and used in Step S 615 . 
     The control section  100  updates and stores the diameter D estimated in this manner, in the PROM  104  (S 620 ). 
     Next, the control section  100  acquires a measured value w of the paper width by the paper width detection sensor  57  (S 625 ). Then, on the basis of the correspondence relationship between the diameter D and the roll static-loads Nlo and Nhi, the roll static-loads Nlo and Nhi in a case where the current roll body RP is rotated at the rotating velocities corresponding to the transport velocities Vlo and Vhi are estimated (S 630 ). 
       FIGS. 13A and 13B  are diagrams showing the correspondence relationship between the roll static-load N and the diameter D. In these drawings, the vertical axis represents the roll static-loads N (Nlo and Nhi), and the horizontal axis represents the diameter D. In these drawings, the roll static-loads Nlo and Nhi in a case where the roll body RP in which the paper P of a reference paper width w 0  is wound is driven at the transport velocities Vlo and Vhi, respectively, are shown by a sold line. As shown in these drawings, the roll static-load N can be expressed by a parabola (quadratic function) of the diameter D. This is because the weight of the roll body RP is reduced in accordance with a reduction in the diameter D, so that a frictional resistance is relieved. 
     Also, the roll static-loads Nlo and Nhi can be considered to be proportional to the paper width w. For example, in the case of a paper width W twice the reference paper width w 0 , there is a static load of twice the magnitude as shown by a broken line in the roll static-load Nlo. In the case of seeking out the roll static-loads Nlo and Nhi of an arbitrary paper width w, it is preferable if a paper width ratio w/w 0  is multiplied by the roll static-loads Nlo and Nhi which are shown by a solid line. Since the current diameter D has been acquired in Step S 615 , in Step S 630 , in the correspondence relationship in the drawings, the roll static-loads Nlo and Nhi (the solid lines) which correspond to the diameter D are respectively calculated. Further, by multiplying by the above-mentioned paper width ratio w/w 0 , the roll static-loads Nlo and Nhi related to the actual paper width w can be estimated. The control section  100  updates and stores the roll static-loads Nlo and Nhi estimated as above, in the PROM  104  (S 640 ). 
     The above-mentioned correspondence relationships ( FIGS. 12 ,  13 A, and  13 B) are prepared on the basis of a logical expression or a preliminary experiment. However, in this embodiment, the preparation is made only with respect to plain paper. Therefore, only in a case where the paper P of the mounted roll body RP is plain paper, is the estimation by the estimation processing possible. In the case of performing the printing on plain paper, since demand to shorten the time for printing is great, in this embodiment, by performing the estimation processing with respect to plain paper, the shortening of the time required for printing is attained. Of course, a configuration may also be made such that with respect to glossy paper or mat paper, the above-mentioned correspondence relationships are prepared and the estimation processing is performed by using the correspondence relationship according to the kind of mounted paper P. 
     Also in the case where the measurement processing has been performed, or also in the case where the estimation processing has been performed, the diameter D and the roll static-loads Nhi and Nlo of the current roll body RP after the execution of the print processing can be obtained. Also, the diameter D and the roll static-loads Nhi and Nlo of the current (latest) roll body RP can be stored in the PROM  104 , and the print processing which will be described later is executed by using these. 
     Concerning the Print Processing 
     Next, the print processing will be explained. 
       FIG. 14  is a diagram showing the flow of the print processing. As shown in this drawing, the print processing is performed by alternately repeating a paper transport processing (S 410 ) and a head driving processing (S 420 ). 
     In the paper transport processing (S 410 ), the PF motor control section  111  of the control section  100  controls the driving of the PF motor  53  so as to rotate the transport roller  51   a , thereby transporting the paper P in the transport direction. In each paper transport processing, the length (corresponding to the above-mentioned amount of transport ΔL; hereinafter referred to as a target amount of transport ΔLt) of the paper P to be transported is designated, and the driving control for transporting the paper by the target amount of transport ΔLt is performed with respect to the PF motor  53 . 
     On the other hand, in the head driving processing (S 420 ), ink droplets are discharged from a plurality of nozzles provided at the printing head  44  while scanning the printing head  44  in the direction perpendicular to the transport direction of the paper P in a state where the paper P is at rest. By this, ink dots can be formed on the paper P. 
     By alternately performing the paper transport processing the head driving processing, ink dots can be disposed in a two-dimensional direction, so that a planar image can be printed on the paper P. If all the paper transport processing and the head driving processing is finished, the process returns to the main flow shown in  FIG. 7 , and then the measurement processing (in the case of paper other than plain paper) or the estimation processing (in the case of plain paper) is executed. Incidentally, in this embodiment, a roll control processing is executed along with each paper transport processing (Step S 410 ). The roll control processing (Step S 430 ) is described below. 
     Concerning the Roll Control Processing 
     As described above, since the paper transport processing is performed alternating with the head driving processing, the driving of the PF motor  53  is intermittently performed. The above-mentioned roll control processing is executed in synchronization with each driving (the stopping—the driving—the stopping) of the PF motor  53 . That is, the RR motor  33  is also intermittently driven, similarly to the PF motor  53 . 
       FIG. 15  is a diagram showing the relationship between a velocity profile of the PF motor  53  and a velocity profile of the RR motor  33 . In addition,  FIG. 15  shows the velocity profiles when transporting the paper P by ΔLt in each paper transport processing. In  FIG. 15 , the vertical axis represents a velocity, and the horizontal axis represents time. As shown in  FIG. 15 , the PF motor  53  and the RR motor  33  are driven so as to be varied in the order of acceleration, constant velocity, and deceleration. However, the RR motor  33  is made to be driven somewhat behind the driving of the PF motor  53 . By doing so, a tensile force (tension) of the paper P between the transport roller  51   a  and the roll body RP is adjusted. 
     In the roll control processing, the RR motor control section  112  changes the Duty value of the PWM signal in PWM control, thereby applying a voltage (effective voltage) corresponding to the Duty value to the RR motor  33 . In this way, the RR motor  33  is driven on the basis of a roll profile. By performing the PWM control in this manner, electric power which is supplied to the RR motor  33  can be accurately and easily controlled. 
     In addition, before the explanation of the roll control processing; first, a processing (assistance) which is performed at the time of the start of the driving of the RR motor  33  will be explained. 
     Concerning the Assistance 
       FIG. 16  is a diagram showing the relationship between the velocity profiles and an applied voltage to the RR motor  33 . In addition,  FIG. 16  is an enlarged view of the first place of the acceleration portion of  FIG. 15 . In  FIG. 16 , the vertical axis on the left represents a velocity, and the vertical axis on the right represents a voltage (effective voltage). Also, the horizontal axis represents time. Also, in this drawing, a broken line shows the applied voltage to the RR motor  33 . 
     As shown in the drawing, at time t 0 , the application of a voltage to the RR motor  33  is started nearly simultaneously with the start of a PF profile (that is, the application of a voltage to the PF motor  53 ). This is because the roll body RP has its own weight, so that the roll body cannot be rotated immediately from a rest state. In addition, in order to move the roll body RP from a rest state, a force larger than that at the time of the rotation of the roil body RP is required. Therefore, in this embodiment, as shown in the drawing, electric power which is supplied at the time of the start of the driving of the RR motor  33  is set to be larger, thereby aiding (assisting) the driving of the RR motor  33 . By this assistance, the RR motor  33  can be easily driven when moving the roll body RP from a rest state (when starting the feeding of the paper P). 
     Thereafter, if the RR motor  33  starts moving (if the motor has some velocity) at time ta, the assistance is lost, and the applied voltage to the RR motor  33  is gradually increased. By this, the rotating velocity of the RR motor  33  is increased (accelerated). 
       FIG. 17  is an explanatory diagram of the assistance in this embodiment. In addition,  FIG. 17  shows in detail a rising edge portion of the broken line of  FIG. 16 . In  FIG. 17 , the horizontal axis represents time, and the vertical axis represents the applied voltage (effective voltage) to the RR motor  33 . Also, the time ta in the drawing is the time when the RR motor  33  starts moving (when the motor is rotated at some velocity). 
     As shown in the drawing, initial assistance and correction assistance are added to the applied voltage to the RR motor  33  until the time to when the RR motor  33  starts moving. 
     The initial assistance is to add a certain voltage to the applied voltage to the RR motor  33  regardless of the diameter of the paper P that is wound around the roll body RP at the time of the driving of the RR motor  33 . In other words, it is to add certain electric power to electric power which is supplied to the RR motor  33 . In addition, the electric power by the initial assistance is equivalent to first assistance power. 
     However, in a case where the paper P of the roll body RP is a slippery medium (for example, a film-like member), as will be described later, the smaller the diameter of the paper P that is wound around the roll body RP, the more easily slippage (slip) is generated. In this case, the slippage cannot be prevented only by the initial assistance. 
       FIGS. 18A and 18B  are conceptual diagrams for explaining the relationship between the diameter of the paper P that is wound around the roll body RP and the slippage.  FIG. 18A  shows when the radius of the paper P that is wound around the roll body RP is R 1 , and  FIG. 18B  shows when the radius of the paper P that is wound around the roll body is R 2  (&lt;R 1 ). In addition, a mechanical load is a rotational resistance or the like of the rotating holder  31 , for example, and a, load of a value which is not related to the diameter of the paper P that is wound around the roll body RP. 
     In a case where the paper P of the roll body RP is drawn in an arrow direction by a force of F, a force (hereinafter referred to as Fbt) of the opposite direction to F is generated. When the radius of the paper P that is wound around the roll body RP is R (=D/2), the Fbt is as follows:
 
 Fbt =mechanical load/ R  
 
Since the mechanical load is constant regardless of the diameter of the paper P that is wound around the roll body RP, the smaller the radius R, the larger the Fbt becomes. For example, in the case shown in  FIGS. 18A and 18B , the Fbt is larger when the radius is R 2  than when the radius is R 1 . Therefore, the slippage is easily generated when the radius is R 2  (that is, when the radius is smaller).
 
     Therefore, in this embodiment, the magnitude of the assistance is corrected in accordance with the diameter of the paper P that is wound around the roll body RP by applying correction assistance. Specifically, an output voltage (Ma shown in  FIG. 17 ) of the correction assistance is set to be in inverse proportion to the diameter (the radius R or the diameter D) of the paper P that is wound around the roll body RP. That is, when the diameter of the paper P that is wound around the roll body RP is larger, the Ma is set to be smaller, and when the diameter of the paper P that is wound around the roll body RP is smaller, the Ma is set to be larger. In the case of using a slippery medium, by applying the correction assistance in addition to the initial assistance, a slippage amount can be reduced, so that transport precision can be increased. Accordingly, deterioration of image quality can be prevented. In addition, electric power by the correction assistance is equivalent to second assistance power. 
       FIG. 19  is a flow chart showing the flow of the roll control processing in the embodiment. 
     If the roll control processing is started, first, the RR motor control section  112  reads the diameter D of the roll body RP, the roll static-loads Nlo and Nhi, and the kind of the paper P from the PROM  104  (S 431 ). That is, the RR motor control section acquires the diameter D of the paper P that is wound around the roll body RP just before the print processing which is being currently executed, the roll static-loads Nlo and Nhi, and the kind of the paper P. Also, the RR motor control section  112  acquires designation tension F corresponding to the kind of the paper P which has been acquired in Step S 431  (S 432 ). Strictly, unit designation tension f per a unit width is acquired, and by multiplying the unit designation tension f by a paper width w, the designation tension F(=f×w) is acquired. 
     The RR motor control section  112  determines whether or not the PF motor  53  has been driven (S 433 ), and if it is determined that the PF motor  53  has been driven, the RR motor control section determines whether or not the kind of the paper P which has been acquired in the above-mentioned Step S 431  is a slippery paper (S 434 ). In this embodiment, plain paper is set to be a reference, and a paper (for example, a film-like member) more slippery than the plain paper is defined as a slippery paper. 
     If it is determined that the kind of the paper P which has been acquired is not a slippery paper (NO in S 434 ), the RR motor control section  112  starts the driving of the RR motor  33  by adding the initial assistance to the electric power for driving the RR motor  33  according to a normal velocity profile (roll profile) (S 435 ). 
     On the other hand, in Step S 434 , if it is determined that the kind of the paper P which has been acquired is a slippery paper (YES in S 434 ), the RR motor control section  112  drives the RR motor  33  by adding the initial assistance and the correction assistance to the electric power for driving the RR motor  33  according to a normal velocity profile (roll profile) (S 436 ). By this, the smaller the diameter of the paper P that is wound around the roll body RP, the larger the electric power which is supplied to the RR motor  33  becomes. 
     After Step S 435  and Step S 436 , the RR motor control section  112  determines whether or not the roll body RP has started moving (S 437 ). If it is determined that the roll body RP has started moving, the RR motor control section drives the RR motor  33  on the basis of the velocity profile (the roll profile) without the assistance (S 438 ). 
       FIG. 20  is a diagram showing the relationship between the diameter of the paper P that is wound around the roll body RP and the correction assistance, and the effects of the correction assistance. In  FIG. 20 , the vertical axis on the left represents a voltage, and the vertical axis on the right represents transport precision. In addition, the closer the precision is to 1, the better (the transport precision is high). Also, in  FIG. 20 , the horizontal axis represents the diameter (here, the radius) of the paper P that is wound around the roll body RP. 
     Also, a dashed-dotted line in the drawing shows an output voltage (equivalent to Ma of  FIG. 17 ) of the correction assistance, a dotted line shows the transport precision when there is no correction assistance, and a solid line shows the transport precision in a case where there is the correction assistance. In addition,  FIG. 20  is one example of the results when the printing has been performed by using the slippery paper (for example, a film-like member). 
     As shown in the drawing, the magnitude of the correction assistance (the dashed-dotted line) is in inverse proportion to the diameter of the paper P that is wound around the roll body RP. For example, the output voltage of the correction assistance is larger when the radius of the paper P that is wound around the roll body RP is 70 mm than when the radius is 90 mm. Therefore, the smaller the diameter of the paper P that is wound around the roll body RP, the larger the electric power which is supplied at the time of the driving of the RR motor  33  (at the time of the start of the feeding of the paper P of the roll body RP) becomes. 
     In a case where the correction assistance is not applied (the case of only the initial assistance), as the diameter of the paper P that is wound around the roll body RP becomes smaller, the transport precision deteriorates. That is, the slippage amount increases. Therefore, it is not possible to place ink at a target position of a medium, which results in image quality deterioration. In particular, in a case where the number of ink colors which is used is small (for example, the case of four colors), deterioration of image quality becomes prominent. 
     On the other hand, if the correction assistance is applied, as shown by the solid line in the drawing, nearly constant and high transport precision can be obtained regardless of the diameter of the paper P that is wound around the roll body RP. In this manner, by applying the correction assistance, even if the slippery paper P is used, it is possible to increase the transport precision regardless of the diameter of the paper P that is wound around the roll body RP. 
     As explained above, the printer  10  of this embodiment is provided with the RR motor  33  which drives the shaft of the roll body RP in which the paper P is wound, in the feeding direction of the paper P, the transport roller  51   a  which transports the paper P fed from the roll body RP, and the control section  100  (the RR motor control section  112 ) which supplies the electric power for rotating the roll body RP to the RR motor  33 . Then, at the time of the start of the feeding of the paper P, the RR motor control section  112  acts so as to increase the electric power which is supplied to the RR motor  33 , in accordance with a reduction in the diameter of the paper P that is wound around the roll body RP. By this, even in the case of using a slippery medium, it is possible to improve the transport precision regardless of the diameter of the paper P that is wound around the roll body RP, so that deterioration of image quality can be prevented. 
     Other Embodiments 
     The printer as one embodiment, or the like has been described. However, the above-described embodiment is for facilitating the understanding of the invention, but is not intended to mean the invention as being limited thereto. The invention can be modified or improved without departing from the purpose thereof, and it is also needless to say that the equivalents thereto are included in the invention. In particular, embodiments which are described below are also included in the invention. 
     In the above-described embodiment, the case of the printer is explained. However, this embodiment is not limited to the printer, but may also be applied to a facsimile or the like, which uses a roll body (roll paper). Also, it may also be applied to a portion of a multi-function apparatus such as a scanner apparatus or a copy apparatus. Also, in the above-described embodiment, the ink jet type printer is described. However, if the printer is a type capable of ejecting fluid, it is not limited to the ink jet type printer. It is possible to apply this embodiment to various printers such as a gel jet type printer, a toner type printer, and a dot impact type printer, for example. 
     Also, the control section  100  is not limited to that in the above-described embodiment, but may also be configured so as to perform the control of the RR motor  33  and the PF motor  53  only by the ASIC  105 , for example, and besides these, the control section  100  may also be constituted by combining a single-chip microcomputer in which various peripheral devices are incorporated, or the like. 
     Also, in the above-described embodiment, the paper P is not limited to paper or a film-like member, but a sheet made of resin, aluminum foil, or the like may also be used. Also, in this embodiment, the correction assistance is applied to the case of a slippery medium. However, also with a medium (for example, plain paper) other than the slippery medium, the correction assistance may be applied. In addition, if the correction assistance is applied to the slippery medium like this embodiment, the effect of further increasing the transport precision can be obtained.