Patent Publication Number: US-2009219552-A1

Title: Apparatus for carrying a printing medium, printer that has the apparatus, method for carrying a printing medium and printer

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priorities from Japanese Patent Application No. 2007-318757 filed on Dec. 10, 2007 and Japanese Patent Application No. 2008-296385 filed on Nov. 20, 2008, and the applications are incorporated in this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for carrying a printing medium, a printer that has the apparatus, a method for carrying a printing medium, and a printer. 
     2. Description of Related Applications 
     There is a printing apparatus that forms an image by discharging liquid droplets while transporting the paper. In such a printing apparatus, it is necessary to transport the paper to the desired position precisely in order to raise the quality of an image. Accordingly, the paper is precisely transported by fixing a rotary encoder or the like to a transport roller for transporting the paper and calculating the transport amount of the paper on the basis of an output of the encoder. For example, Japanese Unexamined Patent Publication No. 2001-251878 discloses performing a PID control on the basis of information from an encoder in transport of a printing medium. 
     However, since slip and the like may occur between the transport roller and the paper, the amount of transport by the transport roller that was detected by the rotary encoder does not necessarily match the actual transport amount of the paper. Therefore, there was a case where a printing medium could not be transported to the target position with high precision. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in order to solve at least some of the above-described problems and may be realized as the following embodiments or application examples. 
     As one embodiment to which the present invention is applied, an apparatus for carrying a printing medium includes: (A) a transport roller that transports the printing medium, (B) a motor for rotating the transport roller, (C) a detector that detects a transport amount of the printing medium transported by rotation of the transport roller, and (D) a controller that has a first control mode, in which a control of the motor is not performed on the basis of a detection result of the detector, and a second control mode, in which a control of the motor is performed on the basis of the detection result of the detector, and that uses the first control mode in a state where the printing medium stops and uses the second control mode after the printing medium starts to move. 
     Other features and objects of the present invention will be apparent by reading description of this specification referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of the entire configuration of a printer  1 . 
         FIG. 2A  is a schematic view of the entire configuration of the printer  1 , and  FIG. 2B  is a cross-sectional view of the entire configuration of the printer  1 . 
         FIG. 3  is a view for explaining an encoder  52  for a transport roller. 
         FIG. 4  is a view illustrating the configuration of a first detection unit  526  of the encoder  52  for a transport roller. 
         FIG. 5A  is a timing chart showing output waveforms at the time of normal rotation of the encoder  52  for a transport roller, and  FIG. 5B  is a timing chart showing output waveforms at the time of reverse rotation of the encoder  52  for a transport roller. 
         FIG. 6  is a view for explaining an encoder  54  for direct detection. 
         FIG. 7  is a view for explaining the relationship of a controller  60 , a transport unit  20 , and each encoder in a first embodiment. 
         FIG. 8  is a view for explaining the speed profile. 
         FIG. 9  is a view for explaining speed reference and position reference. 
         FIG. 10  is a flow chart of a transport control in the first embodiment. 
         FIG. 11  is a view for explaining a controller  60 ′ in a second embodiment. 
         FIG. 12A  is a graph of a temporal change of a duty signal, and  FIG. 12B  is a graph of a speed change of a transport motor. 
         FIG. 13  is a flow chart of a transport control in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED MODES 
     At least the following things will be apparent by description of this specification and description of the accompanying drawings. 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     At least the following matters will be apparent by description of this specification and accompanying drawings. An apparatus for carrying a printing medium including: (A) a transport roller that transports the printing medium, (B) a motor for rotating the transport roller, (C) a detector that detects a transport amount of the printing medium transported by rotation of the transport roller, and (D) a controller that has a first control mode, in which a control of the motor is not performed on the basis of a detection result of the detector, and a second control mode, in which a control of the motor is performed on the basis of the detection result of the detector, and that uses the first control mode in a state where the printing medium stops and uses the second control mode after the printing medium starts to move. 
     In this way, since the detection result of the detector is not used immediately after start of transport of the printing medium, transport of the printing medium can be stably started. In addition, since the printing medium is transported by using the detection result of the detector after the printing medium starts to move surely, the printing medium can be transported to the target position with high precision. 
     In the apparatus for carrying a printing medium, it is preferable that a first encoder for detecting a rotation amount of the transport roller be further included and the controller control the motor on the basis of a detection result of the first encoder in the first control mode. In addition, it is preferable that the controller control the motor in the second control mode after the transport amount of the printing medium is calculated on the basis of the detection result of the detector and the transport amount exceeds a predetermined amount. In addition, it is preferable that in the first control mode, the controller control the motor by increasing the electric power, which is supplied to the motor, by a predetermined amount for every predetermined time. In addition, it is preferable that the detector be a second encoder that detects a rotation amount of a roller that is driven to rotate with transport of the printing medium. 
     In this way, since the detection result of the detector is not used immediately after start of transport of the printing medium, transport of the printing medium can be stably started. In addition, since the printing medium is transported by using the detection result of the detector after the printing medium starts to move surely, the printing medium can be transported to the target position with high precision. 
     A method for carrying a printing medium including: a step of controlling a motor, which rotates a transport roller that transports the printing medium, on the basis of a rotation amount of the transport roller, until the rotation amount of the transport roller reaches a predetermined amount from a state where the printing medium stops; and a step of controlling the motor on the basis of a rotation amount of a roller, which is driven to rotate with transport of the printing medium, after the rotation amount of the transport roller exceeds the predetermined amount. 
     In this way, since the detection result of the detector is not used immediately after start of transport of the printing medium, transport of the printing medium can be stably started. In addition, since the printing medium is transported by using the detection result of the detector after the printing medium starts to move surely, the printing medium can be transported to the target position with high precision. 
     A program for operating an apparatus for carrying a printing medium that causes the apparatus for carrying a printing medium to perform: a step of controlling a motor, which rotates a transport roller that transports the printing medium, on the basis of a rotation amount of the transport roller, until the rotation amount of the transport roller reaches a predetermined amount from a state where the printing medium stops; and a step of controlling the motor on the basis of a rotation amount of a roller, which is driven to rotate with transport of the printing medium, after the rotation amount of the transport roller exceeds the predetermined amount. 
     In this way, since the detection result of the detector is not used immediately after start of transport of the printing medium, transport of the printing medium can be stably started. In addition, since the printing medium is transported by using the detection result of the detector after the printing medium starts to move surely, the printing medium can be transported to the target position with high precision. 
     A printer characterized in that (A) a motor that rotates a first roller that transports a printing medium, (B) a first detection unit that detects a rotation amount of a first rotating circular plate that rotates with rotation of the first roller, (C) a second roller that rotates with transport of the printing medium, (D) a second detection unit that detects a rotation amount of a second rotating circular plate that rotates with rotation of the second roller, and (E) a controller that controls the motor are included and the controller controls the motor using a first control mode, in which a control of the motor is performed on the basis of a detection result of the first detection unit, and a second control mode, in which a control of the motor is performed on the basis of a detection result of the second detection unit. 
     In this way, since the controller can use the first and second control modes properly, transport of the printing medium can be performed more stably compared with a case where a motor is controlled in a single control mode on the basis of an output of a single detection unit (encoder). 
     Furthermore, in the printer, it is preferable that the controller control the motor in the second control mode when the rotation amount of the second rotating circular plate detected by the second detection unit exceeds a predetermined amount after controlling the motor in the first control mode and control the motor only in the first control mode when the second detection unit does not detect the rotation amount of the second rotating circular plate. 
     In this way, also in the case where the second detection unit did not detect the rotation amount of the second rotating circular plate even though the printing medium is transported, the controller can control the motor on the basis of the first control mode. Also in the case where the second detection unit did not detect the rotation amount of the second rotating circular plate, it can be prevented that the controller cannot control the motor. 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In addition, embodiments described below are described as examples of the present invention, and all configurations described are not essential components of the present invention. 
     PREFERRED EMBODIMENTS 
     Hereinafter, embodiments will be described on the basis of the drawings. 
     First Embodiment 
       FIG. 1  is a block diagram of the entire configuration of a printer  1 . In addition,  FIG. 2A  is a schematic view of the entire configuration of the printer  1 . In addition,  FIG. 2B  is a transverse sectional view of the entire configuration of the printer  1 . Hereinafter, the basic configuration of the printer will be described. 
     The printer  1  includes a transport unit  20 , a carriage unit  30 , a head unit  40 , a detector group  50 , and a controller  60 . The printer  1  that has received print data from a computer  110 , which is an external apparatus, controls each of the units (the transport unit  20 , the carriage unit  30 , and the head unit  40 ) by using the controller  60 . The controller  60  controls each unit on the basis of the print data received from the computer  110  and prints an image on paper. The situation in the printer  1  is monitored by the detector group  50 , and the detector group  50  outputs a detection result to the controller  60 . The controller  60  controls each unit on the basis of the detection result output from the detector group  50 . 
     The transport unit  20  serves to transport a printing medium (for example, paper S) in a predetermined direction (hereinafter, called a transport direction). The transport unit  20  has a paper feed roller  21 , a transport motor  22  (also called a PF motor), a transport roller  23 , a platen  24 , and a paper discharge roller  25 . The paper feed roller  21  is a roller for feeding the paper inserted in a paper insert hole into the printer. The transport roller  23  is a roller that is driven by the transport motor  22  and transports the paper S fed by the paper feed roller  21  up to a printable region together with a driven roller. The platen  24  supports the paper S being printed. The paper discharge roller  25  is a roller that discharges the paper S to the outside of the printer together with driven rollers  26  and  27  and is provided at a downstream side of the transport direction with respect to the printable region. The paper discharge roller  25  rotates in synchronization with the transport roller  23 . 
     In the printer  1  in the present embodiment, the paper S is supplied from a roll paper  211 . The roll paper  211  is provided on a cylindrical member  212  that is rotatably fixed to a roll paper supporting portion  213 . Due to the inertia that the roll paper  211  and the cylindrical member  212  have and the frictional force of each portion being in contact with the roll paper  211 , the paper S is pulled by the transport roller  23  to be transported inside the printer  1 . 
     The carriage unit  30  serves to move (also called ‘scan’) a head in a predetermined direction (hereinafter, called a moving direction). The carriage unit  30  has a carriage  31  and a carriage motor  32  (also called a CR motor). The carriage  31  can reciprocate in the moving direction and is driven by the carriage motor  32 . 
     The head unit  40  serves to discharge ink onto the paper. The head unit  40  includes a head  41  having a plurality of nozzles. Since the head  41  is provided on the carriage  31 , the head  41  also moves in the moving direction when the carriage  31  moves in the moving direction. In addition, a dot line (raster line) along the moving direction is formed on the paper by discharging ink intermittently while the head  41  is moving in the moving direction. 
     An encoder  52  for a transport roller and an encoder  54  for direct detection are included in the detector group  50 . The encoder  52  for a transport roller, which will be described later, is fixed to one end of a shaft of the transport roller  23  and detects the rotation amount of the transport roller  23 . In addition, the encoder  54  for direct detection, which will be described later, is provided at a more upstream side than the transport roller  23  in the transport direction of the paper. 
     In the drawing, a driven rotation member  541  included in the encoder  54  for direct detection is shown. The driven rotation member  541  is in contact with an upper surface of the paper and is driven to rotate with transport of the paper S. The encoder  54  for direct detection detects the rotation amount of the driven rotation member  541 . In addition, a linear encoder that detects the movement amount in the moving direction of the carriage  31 , a paper detecting sensor that detects whether or not there is paper, and the like are included in the detector group  50 . 
     The controller  60  is a control unit for controlling the printer  1 . The controller  60  includes an interface portion (not shown), a CPU, and a memory. An interface portion performs transmission and reception of data between the printer  1  and the computer  110  that is an external apparatus. The CPU is a processing unit for making an overall control of the printer. The memory serves to secure a region for storing a program of the CPU, a working area, and the like and has memory devices, such as a RAM and an EEPROM. The CPU controls each unit according to the program stored in the memory. 
       FIG. 3  is a view for explaining the encoder  52  for a transport roller. The transport motor  22  is shown in the drawing. A pinion  282  is integrally fixed to an output shaft of the transport motor  22 . In addition, a main wheel  281  is shown in the drawing. In addition, a belt  283  is stretched over the main wheel  281  and the pinion  282 , and the power is transmitted to the main wheel  281  when the output shaft of the transport motor  22  is made to rotate. The main wheel  281  is integrally fixed to one end of the transport roller  23 . Accordingly, the transport roller  23  rotates with rotation of the main wheel  281 . In addition, a first rotating circular plate  524  is integrally fixed to the shaft of the transport roller  23  so as to be adjacent to the main wheel  281 . Small slits are formed at predetermined distances therebetween on the first rotating circular plate  524 . 
     A first detection unit  526  of the encoder  52  for a transport roller is provided to interpose a portion of the slits of the first rotating circular plate  524 . The rotation amount of the transport roller  23  can be calculated since the first detection unit  526  monitors the slits of the first rotating circular plate  524 . 
     In addition, even though the pitch of the gear is largely shown in the drawing so as to be easily understood, a finer pitch may be set to improve a transport system. 
       FIG. 4  is a view illustrating the configuration of the first detection unit  526  of the encoder  52  for a transport roller. The encoder  52  for a transport roller has the first rotating circular plate  524  and the first detection unit  526  as described above. The first detection unit  526  has a light-emitting diode  5264 , a collimator lens  5262 , and a detection processing portion  5268 , and the detection processing portion  5268  includes a plurality of (for example, four) photodiodes  5266 , a signal processing circuit  5267 , and two comparators  5269 A and  5269 B. 
     The light-emitting diode  5264  emits light when a voltage Vcc is applied through a resistor of both ends, and the light is incident on the collimator lens  5262 . The collimator lens  5262  makes light emitted from the light-emitting diode  5264  become parallel beams and irradiates the parallel beams onto the first rotating circular plate  524 . The parallel beam that passed the slit provided on the first rotating circular plate  524  passes a fixed slit (not shown) to be incident on each photodiode  5266 . The photodiode  5266  converts the incident light into an electrical signal. The electrical signals output from the respective photodiodes are compared in the comparators  5269 A and  5269 B, and the comparison result is output as a pulse. In addition, a first pulse ENC_A and a second pulse ENC_B output from the comparators  5269 A and  5269 B become outputs of the encoder  52  for a transport roller. 
       FIG. 5A  is a timing chart showing output waveforms at the time of normal rotation of the encoder  52  for a transport roller, and  FIG. 5B  is a timing chart that supports output waveforms of the encoder at the time of reverse rotation of the encoder  52  for a transport roller. As shown in the drawing, in any case of the normal rotation and reverse rotation of the transport roller  23 , the first pulse ENC_A and the second pulse ENC_B, the phase is shifted by 90°. While the transport roller  23  is performing normal rotation, the phase of the first pulse ENC_A leads that of the second pulse ENC_B by 90° as shown in  FIG. 5A . On the other hand, while the transport roller  23  is performing reverse rotation, the phase of the first pulse ENC_A lags behind the second pulse ENC_B by 90° as shown in  FIG. 5B . A period T of each pulse is equal to a time for which one distance of the slits of the first rotating circular plate  524  moves through the first detection unit  526 . 
     In addition, the first pulse ENC_A and the second pulse ENC_B of the encoder  52  for a transport roller are input to the controller  60 . The controller  60  can calculate the rotation speed and the rotation amount on the basis of the pulse distance that is input. 
       FIG. 6  is a view for explaining the encoder  54  for direct detection. In the drawing, the paper S and the driven rotation member  541  that is in direct contact with the upper surface of the paper S are shown. On a portion of the driven rotation member  541  being in contact with the paper S, surface treatment for increasing the coefficient of friction is performed to secure the frictional force with the paper. 
     Two bearings  545  for rotatably supporting the driven rotation member  541  are fixed to the driven rotation member  541 . In addition, a second rotating circular plate  544  is disposed between the two bearings  545 . The second rotating circular plate  544  is integrally fixed to the driven rotation member  541 , and the second rotating circular plate  544  also rotates when the driven rotation member  541  rotates. Similar to the first rotating circular plate  524 , slits are formed on the second rotating circular plate  544 . 
     A second detection unit  546  of the encoder  54  for direct detection (referred to as a second detection unit) is provided to interpose the slits of the second rotating circular plate  544 . The second detection unit  546  monitors the slits of the second rotating circular plate  544  and transmits a pulse to the controller  60 . The controller  60  can calculate the rotation speed and the rotation amount on the basis of the pulse distance that is input. The rotation amount of the driven rotation member  541  can be calculated. Since the configuration of the second detection unit  546  is the same as the configuration of the first detection unit  526 , an explanation thereof will be omitted. 
     The two bearings  545  and the second detection unit  546  are integrally supported by a support member  542 . In addition, the support member  542  is fixed to the inside of the printer  1  through two springs  548 . The support member  542  can move slidably only in the up and down direction of the printer  1  since the movable direction is limited by a member (not shown). The support member  542  is pressed in the lower direction of the printer  1  by the two springs  548 . In addition, the driven rotation member  541  is necessarily in contact with the paper S by predetermined pressure. In this way, the driven rotation member  541  is driven to rotate with transport of the paper S. 
       FIG. 7  is a block diagram for explaining the relationship of the controller  60 , the transport unit  20 , and each encoder in the first embodiment. The controller  60 , the transport unit  20 , the encoder  52  for a transport roller, and the encoder  54  for direct detection are shown in the drawing. The controller  60  includes a PID control element portion  61 , a target speed output portion  62 , a speed calculating portion  63 , and a position calculating portion  64 . In addition, the controller  60  includes a subtracter  65  and a first switch  681 . 
     The speed calculating portion  63  includes a first speed calculating portion  631  and a second speed calculating portion  632 . The first speed calculating portion  631  measures the period of an output pulse of the encoder  52  for a transport roller and calculates the rotation speed of the transport roller  23  on the basis of the period. In addition, a transport speed when ideal transport is performed by the transport roller  23  is calculated to be output on the basis of the rotation speed of the transport roller  23  and the external diameter of the transport roller  23 . 
     In addition, the second speed calculating portion  632  measures the period of an output pulse of the encoder  54  for direct detection and calculates the rotation speed of the driven rotation member  541  on the basis of the period. In addition, the transport speed of the paper S detected by the driven rotation member  541  is calculated to be output on the basis of the rotation speed of the driven rotation member  541  and the external diameter of the driven rotation member  541 . 
     The first switch  681  switches a connection with the subtracter  65 , which will be described later, between the first speed calculating portion  631  and the second speed calculating portion  632 . When the first switch  681  is connected to a connection end ‘ 1 ’, an output of the first speed calculating portion  631  is transmitted to the subtracter  65 . In addition, when the first switch  681  is connected to a connection end ‘ 2 ’, an output of the second speed calculating portion  632  is transmitted to the subtracter  65 . 
     The output of the first speed calculating portion  631  is connected to a first position calculating portion  641 . In addition, the output of the second speed calculating portion  632  is connected to a second position calculating portion  642 . 
     The position calculating portion  64  includes the first position calculating portion  641  and the second position calculating portion  642 . The first position calculating portion  641  integrates the speed transmitted from the first speed calculating portion  631  and calculates the transport amount when ideal transport is performed by the transport roller  23 . Then, the current position of the paper S is calculated from the transport amount and is output to a first target speed output portion  621 . In addition, the second position calculating portion  642  integrates the speed transmitted from the second speed calculating portion  632  and calculates the transport amount of the paper S detected by the driven rotation member  541 . Then, the current position of the paper S is calculated from the transport amount and is output to a second target speed output portion  622 . 
     The target speed output portion  62  includes the first target speed output portion  621 , the second target speed output portion  622 , and a second switch  682 . An output (position of the paper S calculated on the basis of the output of the encoder  52  for a transport roller) of the first position calculating portion  641  is input to the first target speed output portion  621 . The first target speed output portion  621  has a first speed profile which will be described later. In addition, the first target speed output portion  621  can output the target transport speed on the basis of a distance from the current position of the paper S, which was calculated on the basis of the output of the encoder  52  for a transport roller, to the target transport position. 
     In addition, an output (position of the paper S calculated on the basis of the output of the encoder  54  for direct detection) of the second position calculating portion  642  is input to the second target speed output portion  622 . The second target speed output portion  622  has a second speed profile which will be described later. In addition, the second target speed output portion  622  can output the target transport speed on the basis of a distance from the current position of the paper S, which was calculated on the basis of the output of the encoder  54  for direct detection, to the target transport position. 
     The second switch  682  operates in conjunction with the first switch  681 , and the second switch  682  is connected to the connection end ‘ 1 ’ when the first switch  681  is connected to the connection end ‘ 1 ’. In addition, when the first switch  681  is connected to the connection end ‘ 2 ’, the second switch  682  is also connected to the connection end ‘ 2 ’. In addition, the other end of the second switch is connected to the subtracter  65 . In addition, the target transport speed output from the first target speed output portion  621  or the second target speed output portion  622  is transmitted to the subtracter  65 . 
     The subtracter  65  subtracts the transport speed, which is output from the first speed calculating portion  631  or the second speed calculating portion  632 , from the target transport speed output from the target speed output portion  62  and outputs the deviation, which is a subtraction result, to the PID control element portion  61 . 
     The PID control element portion  61  includes a proportional element  612 , an integral element  614 , and a differential element  616 . In addition, the PID control element portion  61  includes an adder  618 . The proportional element  612  multiplies a speed error ΔV by a gain Gp and outputs a proportional component QP. The integral element  614  integrates that obtained by multiplying the speed error ΔV by the gain Gi to a calculation result QI(j−1) before one and outputs an integral component QI. The differential element  616  multiplies a difference between a current speed error ΔV(j) (here, j indicates time) and a speed error ΔV(j−1) before one by a gain Gd and outputs a differential component QD. 
     Here, the calculation outputs of the proportional element  612 , the integral element  614 , and the differential element  616 , that is, the proportional component QP, the integral component QI, and the differential component QD can be given by the following expressions (1) to (3). 
         QP ( j )=Δ V ( j )× Gp   (1) 
         QI ( j )= QI ( j− 1)+Δ V ( j )× Gi   (2) 
         QD ( j )={Δ V ( j )−Δ V ( j− 1)}× Gd   (3) 
     The adder  618  adds the proportional component QP of the proportional element  612 , the integral component QI of the integral element  614 , and the differential component QD of the differential element  616 . An addition result ΣQ of the three components, that is, the proportional component QP, the integral component QI, and the differential component QD is output as a duty signal to a PWM circuit  202 , which will be described later. 
     The addition result ΣQ can be obtained by the following expression (4). 
       Σ Q ( j )= QP ( j )+ QI ( j )+ QD ( j )  (4) 
     The PWM circuit  202 , a driver  204 , and the transport motor  22  are included in the transport unit  20 . The PWM circuit  202  generates a control signal corresponding to the addition result ΣQ of the adder  618 . The driver  204  drives the transport motor  22  on the basis of the control signal. The driver  204  has a plurality of transistors, for example, and applies a voltage to the transport motor  22  by turning on and off the transistors on the basis of the control signal from the PWM circuit  202 . 
       FIG. 8  is a view for explaining the speed profile. In the speed profile, a suitable target speed at the current position of the paper S is calculated beforehand when transporting the paper S up to a target transport position D. 
     A graph of the speed profile in which the horizontal axis indicates a distance and a vertical axis indicates a target transport speed is shown in the drawing. In the drawing, the position of ‘D’ is assumed to be the target transport position. In addition, a target transport speed corresponding to the current position in the range from a position  0  to the target transport position D is expressed in the vertical axis. 
     A first speed profile for calculating the target transport speed from the position of the paper S calculated on the basis of the output of the encoder  52  for a transport roller and a second speed profile for calculating the target transport speed from the position of the paper S calculated on the basis of the output of the encoder  54  for direct detection are prepared for the speed profile. The first speed profile is stored in the first target speed output portion  621 , and the second speed profile is stored in the second target speed output portion  622 . 
     When the first switch  681  and the second switch  682  are connected to the connection end ‘ 1 ’, the first position calculating portion  641  calculates the target transport speed corresponding to the current position of the paper S calculated on the basis of the output of the encoder  52  for a transport roller referring to the first speed profile and outputs the target transport speed. Similarly, when the first switch  681  and the second switch  682  are connected to the connection end ‘ 2 ’, the second position calculating portion  642  calculates the target transport speed corresponding to the current position of the paper S calculated on the basis of the output of the encoder  54  for direct detection referring to the second speed profile and outputs the target transport speed. 
     In addition, here, although the explanation has been made assuming that the first speed profile and the second speed profile are different, one speed profile may be used in common. 
       FIG. 9  is a view for explaining speed reference and position reference. A graph of a transport speed with respect to a position d(d 1 , d 2 ) is shown in the drawing. In this graph, a portion drawn by a solid line is a transport speed that the first speed calculating portion  631  outputs on the basis of the output of the encoder  52  for a transport roller. 
     Moreover, in this graph, a portion drawn by a broken line is a transport speed that the second speed calculating portion  632  outputs on the basis of the output of the encoder  54  for direct detection. In addition, since there is a portion where the speed that the second speed calculating portion  632  outputs matches the speed that the first speed calculating portion  631  outputs, solid lines overlap at this time. 
     In addition, the ‘speed reference’ of whether to make a control on the basis of the transport speed, which was calculated on the basis of the output of either encoder at the position of the paper S, is shown below the graph. In addition, the ‘position reference’ of whether to output the target transport speed on the basis of the position, which was calculated on the basis of the output of either encoder at the position of the paper S, is shown below the graph. 
     Referring to the graph of the speed immediately after start of the movement, the transport speed that the first speed calculating portion  631  outputs rises almost linearly, while the transport speed that the second speed calculating portion  632  outputs rises with some delay. This is thought that actual transport of the paper S was delayed due to slip occurring between the transport roller  23  and the paper S even though the transport of the paper S was started by the transport roller  23 . Furthermore, it may also be considered that the movement of the paper S at the position of the driven rotation member  541  was delayed since the paper S deformed due to a force in the transport direction momentarily applied to the paper S even though the transport of the paper S was started by the transport roller  23 . 
     However, at the position d 1  after start of rotation of the transport roller  23 , the speed that the first speed calculating portion  631  outputs almost matches the speed of the second speed calculating portion  632 . In addition, the actual position d 1  is a position which is very close to the position ‘ 0 ’. Here, in order to show the situation where detection of transport performed by the encoder  54  for direct detection is delayed, the delay is shown with some emphasis. 
     In the present embodiment, information on the transport speed to be referred is changed with a position d 2  after the movement up to the position d 1  as a reference. In addition, information on the position to be referred is changed with the position d 2  as a reference. First, until the movement range of the paper S calculated from the output of the encoder  52  for a transport roller reaches the position d 2  from ‘ 0 ’, a control to the target transport speed is performed on the basis of the output from the first speed calculating portion  631 . In addition, until the movement range of the paper S calculated from the output of the encoder  52  for a transport roller reaches the position d 2  from ‘ 0 ’, output of the target transport speed is performed on the basis of the output from the first position calculating portion  641 . 
     It is determined whether or not the position of the paper has reached the position d 2  on the basis of the output of the second position calculating portion  642 . That is, the determination is performed on the basis of the position that was calculated on the basis of the output of the encoder  54  for direct detection. This is because it is thought that the second position calculating portion  642  calculates the position of the paper S more precisely than the first position calculating portion  641  since the encoder  54  for direct detection detects the transport amount of the paper S directly. 
     When the position d 2  of the paper is exceeded, the connection between the first switch  681  and the second switch  682  changes from the connection end ‘ 1 ’ to the connection end ‘ 2 ’. Then, transport from the position d 2  to the target transport position D is performed. At this time, a control of the transport speed is performed on the basis of the output of the second speed calculating portion  632 . That is, the control of the transport motor  22  is performed on the basis of the output of the encoder  54  for direct detection. Moreover, at this time, output of the target transport speed is performed on the basis of the output of the second position calculating portion  642 . That is, the output of the target transport speed is performed on the basis of the position based on the output of the encoder  54  for direct detection. 
     In addition, it is assumed that a suitable position calculated beforehand by an experiment is used as the position d 2  as the trigger of switching of the first switch  681  and the second switch  682 . 
     In this way, a control of the transport motor  22  is performed (corresponding to a first control mode) on the basis of the output of the encoder  52  for a transport roller when the paper S is in a stop state, and a control (corresponding to a second control mode) using the encoder  54  for direct detection is performed while the paper S is moving surely (after the paper S starts moving surely). In this way, also in the case where the movement of the paper S is not detected by the encoder  54  for direct detection even though the transport roller  23  rotates immediately after start of transport of the paper S, the transport motor  22  can be controlled without feeding back the speed based on the output from the encoder  54  for direct detection. In addition, a control immediately after the start of transport of the paper S can be performed stably. 
     In addition, although the determination on whether or not the position of the paper S exceeds the position d 2  was performed on the basis of the position of the paper S calculated on the basis of the output of the encoder  54  for direct detection, the determination may also be made on the basis of the position of the paper S calculated on the basis of the output of the encoder  52  for a transport roller. 
       FIG. 10  is a flow chart of the transport control in the first embodiment. Hereinafter, transport of the paper S to the target transport position will be described according to the flow chart. In the printer  1 , printing is performed while the paper S is being transported intermittently. For example, a transport control according to the flow chart is performed for each of such intermittent movement of the paper S. 
     A transport command including information on the target transport position is generated for every transport operation of the paper. When the transport command is received (step S 102 ), the controller  60  starts transport by the PID control to the target transport position on the basis of the output of the encoder  52  for a transport roller. The PID control based on the output of this encoder  52  for a transport roller is performed in transport to a predetermined position (position d 2  calculated on the basis of the output of the encoder  54  for direct detection). 
     The controller  60  determines whether or not the transport to the predetermined position was performed (step S 106 ). This determination may be performed for every rising and falling of the edge that is the output of the encoder  52  for a transport roller. Here, when the transport to the predetermined position d 2  is not performed, the PID control based on the output of the encoder  52  for a transport roller is performed subsequently (step S 104 ). On the other hand, when the transport to the predetermined position is completed, the PID control based on the output of the encoder  54  for direct detection is started (step S 108 ). Then, up to the target transport position D, a control of the transport motor  22  that performed the PID control on the basis of the output of the encoder  54  for direct detection is performed. When movement to the target transport position D is completed, the transport operation ends. 
     In the first embodiment described above, the first control mode and the second control mode were switched according to switching of the first switch  681  and the second switch  682  based on the determination on whether or not the position of the paper S exceeded the position d 2 . However, the first control mode and the second control mode may also be switched on the basis of whether or not the second detection unit  546  can detect rotation of the driven rotation member  541  as the second rotating circular plate. That is, when the position of the paper S does not exceed the position d 2 , the transport motor  22  is controlled in the first control mode. When the second detection unit  546  can detect the rotation of the driven rotation member  541  and the position of the paper S exceeds the position d 2 , the transport motor  22  is controlled in the second control mode. When the second detection unit  546  cannot detect the rotation of the driven rotation member  541 , the transport motor  22  is controlled only in the first control mode without switching the first control mode and the second control mode. 
     In this way, also in the case where the movement of the paper S is not detected by the second detection unit  546  even though the transport roller  23  rotates to transport the paper S, the control of the transport motor  22  based on the output of the first detection unit  526  can be performed. 
     As the case where the movement of the paper S is not detected by the second detection unit  546  even though the transport roller  23  rotates to transport the paper S, for example, a case where the second detection unit  546  or the encoder  54  for direct detection is poor or a case where the paper S is cut paper may be considered. In the case where the paper S is cut paper, since the length of the paper S in the paper transport direction may be shorter than the length between the transport roller  23  and the driven rotation member  541 , a case where the movement of the paper S is not detected by the second detection unit  546  even though the paper S is transported may occur. 
     Second Embodiment 
       FIG. 11  is a view for explaining a controller  60 ′ in a second embodiment. In the second embodiment, a timer  693 , an acceleration control portion  692 , and a third switch  683  are included in the controller  60 ′ in addition to each portion within the controller  60  in the first embodiment. Accordingly, the same reference numeral is given to each portion included in the controller  60  in the first embodiment and an explanation thereof will be omitted. 
     An output of the timer  693  is connected to the acceleration control portion  692 . An output of the acceleration control portion  692  is connected to the third switch  683 . In addition, the other end of the third switch  683  is connected to the PWM circuit  202 . In addition, the acceleration control portion  692  and the timer  693  are used at the time of acceleration control of the transport motor  22 . The timer  693  generates a timer interruption signal for every predetermined time on the basis of a clock signal generated in the controller  60 ′. The acceleration control portion  692  integrates a predetermined duty DXP whenever the timer interruption signal is received, generates a duty signal as the integration result, and outputs the duty signal to the PWM circuit  202 . 
     The third switch  683  operates in conjunction with the above-described first and second switches  681  and  682 . For example, when the first switch  681  is connected to the connection end ‘ 1 ’, the third switch  683  is also connected to the connection end ‘ 1 ’. Moreover, when the first switch  681  is connected to the connection end ‘ 2 ’, the connection with the connection end ‘ 1 ’ is cut so that the third switch  683  also becomes a position of the connection end ‘ 2 ’. 
       FIG. 12A  is a graph of a temporal change of a duty signal, and  FIG. 12B  is a graph of a speed change of a transport motor. When the transport motor  22  is started while the transport motor  22  stops, an initial duty signal whose signal value is a signal value DX 0  is transmitted from the acceleration control portion  692  to the PWM circuit  202 . This initial duty signal is generated in the acceleration control portion  692  together with a start command signal. Then, the initial duty signal is converted into a control signal corresponding to the signal value DX 0  by the PWM circuit  202 , such that the transport motor  22  starts to operate. 
     After the controller  60 ′ generates a start command signal, a timer interruption signal is generated from the timer  693  for every predetermined time. Whenever the timer interruption signal is received, the acceleration control portion  692  integrates the signal value DX 0  of the initial duty signal with the predetermined duty DXP and transmits to the PWM circuit  202  a duty signal having the integrated duty as a signal value. This duty signal is converted into a control signal corresponding to the signal value by the PWM circuit  202 , and the rotation speed of the transport motor  22  increases. For this reason, the value of the duty signal transmitted from the acceleration control portion  692  to the PWM circuit  202  rises in a stepwise manner. 
     The second position calculating portion  642  calculates the transport amount of the paper S on the basis of the output of the encoder  54  for direct detection. Then, the current position of the paper S is calculated from the transport amount and is outputs to the second target speed output portion  622 . In addition, when the position of the paper S calculated on the basis of the output of the encoder  54  for direct detection exceeds the position d 2 , the connection of the first to third switches  681  to  683  is switched from the connection end ‘ 1 ’ to the connection end ‘ 2 ’. A control after the connection of the first to third switches  681  to  683  was switched to the connection end ‘ 2 ’ is the same as the control after the connection of the first and second switches  681  and  682  was switched to the connection end ‘ 2 ’ in the first embodiment described above and accordingly, the explanation will be omitted. 
     In addition, although the determination on whether or not the position of the paper S exceeds the position d 2  was also performed herein on the basis of the position of the paper S calculated on the basis of the output of the encoder  54  for direct detection, the determination may also be performed on the basis of the position of the paper S calculated on the basis of the output of the encoder  52  for a transport roller. 
       FIG. 13  is a flow chart of the transport control in the second embodiment. Hereinafter, transport of the paper S to the target transport position will be described according to the flow chart. 
     A transport command including information on the target transport position is transmitted for every transport operation of the paper. When the transport command is received (step S 202 ), the controller  60 ′ performs an acceleration control using the acceleration control portion  692  and the timer  693  described above. Then, the rotation speed of the transport motor  22  increases. Accordingly, movement of the paper S is started. 
     The controller  60 ′ determines whether or not transport to the predetermined position d 2  was performed on the basis of the position of the paper S that was calculated on the basis of the output of the encoder  54  for direct detection (step S 206 ). This determination may be performed for every rising and falling of the edge that is the output of the encoder  52  for a transport roller. Here, when the transport to the predetermined position d 2  is not performed, an acceleration control is performed subsequently (step S 204 ). On the other hand, when the transport to the predetermined position d 2  is completed, the PID control based on the output of the encoder  54  for direct detection is started (step S 208 ). Then, up to the target transport position D, a control of the transport motor  22  that performed the PID control on the basis of the output of the encoder  54  for direct detection is performed. When movement to the target transport position D is completed, the transport operation ends. 
     In this way, a control of the transport motor  22  is performed (corresponding to a first control mode) by the acceleration control when the paper S is in a stop state, and a control (corresponding to a second control mode) using the encoder  54  for direct detection is performed while the paper S is moving surely (after the paper S starts moving surely). In this way, also in the case where the movement of the paper S is not detected by the encoder  54  for direct detection even though the transport roller  23  rotates immediately after start of transport of the paper S, the transport motor  22  can be controlled without feeding back the speed based on the output from the encoder  54  for direct detection. In addition, a control immediately after the start of transport of the paper S can be performed stably. 
     Control of the Position of the Paper S 
     In the above-described embodiment, the transport amount of the paper S can be precisely grasped by providing the encoder  54  for direct detection. Therefore, the position of the paper S in a range where the paper S is in contact with the driven rotation member  541  of the encoder  54  for direct detection can be precisely controlled on the basis of the position calculated by using the output of the encoder  54  for direct detection. 
     When feed of a sheet of paper S is performed by a plural number of transports, the target stop position can be corrected, for example, by adding a stop error occurred in transport in this path to transport in the next path. Then, the transport of the paper can be performed by removing the stop error that occurred in the next transport. Also in this case, the position control of the paper S with respect to the printer  1  can be performed more precisely by acquiring the position of the paper S while using the output of the encoder  54  for direct detection consistently. 
     In addition, in case of controlling the position of the paper S without using a result of the output of the encoder  54  for direct detection, the absolute position of the paper S can be controlled by using a result of the output of the encoder  52  for a transport roller consistently. 
     Other Embodiments 
     Although the printer  1  is described as a liquid discharging apparatus in the above-described embodiment, embodiment as a liquid discharging apparatus that ejects or discharges other fluids (liquid, a liquid-like body in which particles of a functional material are dispersed, or a fluid-like body such as gel) other than ink may also be made without being limited to the printer. For example, the same technique as the above-described embodiment may also be applied to various apparatuses applying the ink jet technique, such as a color filter manufacturing apparatus, a dyeing apparatus, a micro-machining apparatus, a semiconductor manufacturing apparatus, a surface treatment apparatus, a three-dimensional modeling device, a gas vaporizer, an organic EL manufacturing apparatus (particularly a polymer EL manufacturing apparatus), a display manufacturing apparatus, a film forming apparatus, and a DNA chip manufacturing apparatus. Moreover, these methods or manufacturing methods are also in the category of an application range. 
     The above embodiments are to make the present invention easily understood and are not interpreted to limit the present invention. The present invention may be changed and modified without departing from the object, and it is needless to say that the equivalents are included in the present invention. Particularly embodiments described below are also included in the present invention. 
     Regarding a Head 
     In the above-described embodiment, ink was discharged by using a piezoelectric element. However, a method of discharging the liquid is not limited thereto. Other methods, for example, a method of generating bubbles within a nozzle with heat may also be used. 
     Moreover, in the above-described embodiment, the head was provided on the carriage. However, the head may also be provided on an ink cartridge which can be attached to or detached from the carriage.