Patent Publication Number: US-8540443-B2

Title: Printer and printing method which prevents a decurling unit from deteriorating a print quality

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a printer and a printing method that decurl a recording medium. 
     2. Description of the Related Art 
     A printer that prints data onto a roll recording medium includes a decurling mechanism that decurls a recording medium. The decurling mechanism decurls the recording medium to inversely curl the recording medium by moving and pressing a raised member to the recording medium or pressing the recording medium to the raised member. 
     However, when the raised member keeps in contact with the same portion of the recording medium for a longtime, a crease is produced at the portion. Since there is a high possibility that ink does not normally adhere to the portion of the crease production, a problem of deterioration in print quality can arise. Japanese Patent Publication No. 3190489 discusses an apparatus that solves the problem. A decurling apparatus discussed in Japanese Patent Publication No. 3190489 includes a mechanism driven with power of a roller that conveys a recording sheet. When the roller rotates in the winding direction of the recording sheet, the mechanism has a decurling function, and when the roller rotates (inversely rotates) in the rewinding direction of the recording sheet, the mechanism moves to a specific position, thereby cancelling the decurling. 
     Japanese Patent Application Laid-Open No. 2002-104688 discusses a recording apparatus having a function of preventing the aging deformation of a recording sheet. It is assumed that printing is performed in the recording apparatus while the recording sheet passes through space between a grip roller having a large number of projections on the surface thereof and a pinch roller. Before the printing, a contact portion of the recording medium with the grip roller changes as predetermined time passes. 
     In printing on a roll recording medium with a dye-sublimation printer as a thermal transfer printer, heat generated by a thermal head is advantageous to decurl the recording medium. In this case, as the number of print colors (number of inks) increases, the heating time of the recording medium is prolonged. Therefore, by actively pressing the portion heated by the thermal head to the raised member, excessive decurling can produce a crease at the portion. If the crease is made in a print area (area in which a large part of an image is printed) on the recording medium, a problem of deterioration in print quality can occur. 
     The problems can be solved by additionally installing the mechanism discussed in Japanese Patent Publication No. 3190489 in the printer because the mechanism has a function of cancelling the decurling. However, to add the mechanism, the installing space of the mechanism needs to be secured, and the size of printer therefore increases and product costs rise. Since it is assumed that the recording apparatus discussed in Japanese Patent Application Laid-Open No. 2002-104688 records data on an unroll recording medium, the problems are not solved only by periodically changing the contact position between the recording medium and the grip roller. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to provide a printer and a printing method that prevent the deterioration in print quality without adding a mechanism in a case of printing in which a plurality of inks thermally adheres to a roll recording medium with heat. 
     According to the present invention, all the problems or at least one is solved. 
     According to an aspect of the present invention, a printer that divides a roll recording medium in a length direction to set one printing target range, includes a conveyance unit configured to nip and simultaneously convey the roll recording medium, a print unit configured to print an image by sequentially transferring a plurality of color inks on the recording medium while nipping the recording medium conveyed by the conveyance unit, a decurling unit disposed between the conveyance unit and the print unit, and configured to include a raised portion that decurls the recording medium by contacting the recording medium conveyed by the conveyance unit, and a control unit configured to control the conveyance unit to convey the recording medium to a waiting position after ending the transfer of one color ink. The waiting position is a position where an area on the leading edge side of the recording medium is in contact with the raised portion. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  illustrates a configuration of a printer according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating components connected to control unit in the printer according to the first exemplary embodiment. 
         FIG. 3  is a flowchart illustrating an operating procedure of the printer according to the first exemplary embodiment. 
         FIG. 4  is a flowchart illustrating another operating procedure of the printer according to the first exemplary embodiment. 
         FIGS. 5A to 5D  illustrate conveyance states of a recording medium in Y color printing operation according to the first exemplary embodiment. 
         FIGS. 6A to 6D  illustrate conveyance states of the recording medium in M color printing operation according to the first exemplary embodiment. 
         FIGS. 7A to 7D  illustrate conveyance states of the recording medium in C color printing operation according to the first exemplary embodiment. 
         FIGS. 8A to 8D  illustrate conveyance states of the recording medium in OC color printing operation according to the first exemplary embodiment. 
         FIGS. 9A to 9C  illustrate conveyance states of the recording medium in cutting operation according to the first exemplary embodiment. 
         FIG. 10  is a flowchart illustrating a procedure of cutting operation according to a modification of the first exemplary embodiment. 
         FIGS. 11A to 11E  illustrate conveyance states of the recording medium in the cutting operation according to the modification of the first exemplary embodiment. 
         FIG. 12  is a flowchart illustrating an operating procedure of a printer according to a second exemplary embodiment of the present invention. 
         FIG. 13  is a flowchart illustrating another operating procedure of the printer according to the second exemplary embodiment. 
         FIGS. 14A to 14D  illustrate conveyance states of a recording medium in Y color printing operation according to the second exemplary embodiment. 
         FIGS. 15A to 15D  illustrate conveyance states of the recording medium in M color printing operation, C color printing operation, and OC printing operation according to the second exemplary embodiment. 
         FIGS. 16A to 16E  illustrate conveyance states of the recording medium in cutting operation according to the second exemplary embodiment. 
         FIG. 17  is a flowchart illustrating an operating procedure of a printer according to a third exemplary embodiment of the present invention. 
         FIG. 18  is a flowchart illustrating another operating procedure of the printer according to the third exemplary embodiment. 
         FIGS. 19A to 19D  illustrate conveyance states of a recording medium in Y color printing operation according to the third exemplary embodiment. 
         FIGS. 20A to 20D  illustrate conveyance states of the recording medium in M color printing operation according to the third exemplary embodiment. 
         FIGS. 21A to 21D  illustrate conveyance states of the recording medium in C color printing operation according to the third exemplary embodiment. 
         FIGS. 22A to 22D  illustrate conveyance states of the recording medium in OC printing operation according to the third exemplary embodiment. 
         FIGS. 23A to 23E  illustrate conveyance states of the recording medium in cutting operation according to the third exemplary embodiment. 
         FIG. 24  illustrates a configuration of a printer according to a fourth exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
       FIG. 1  illustrates a configuration of a printer according to a first exemplary embodiment. Referring to  FIG. 1 , a printer  100  according to the first exemplary embodiment has one printing target range by separating a roll recording medium  1  in the length direction, and includes: conveyance unit  2 ; decurling unit  3 ; print unit  4 ; and control unit  5 . In the printer  100 , the control unit  5  controls operation of the conveyance unit  2  and the print unit  4 , thereby printing the data in the printing target range of the recording medium  1  that has passed through the decurling unit  3 . Hereinbelow, a description is given of a specific configuration of the conveyance unit  2 , the decurling unit  3 , the print unit  4 , and the control unit  5 . 
     In the conveyance unit  2 , the recording medium  1  is wound like a roll to a core portion  21  (refer to  FIG. 1 ). Near the core portion  21 , a grip roller  22  and a pinch roller  23  are arranged. The grip roller  22  has a plurality of projections on the surface thereof, and the pinch roller  23  is pressed to the grip roller  22  by a spring  24 . In the conveyance unit  2 , a motor  25  rotates under the control of the control unit  5 , thereby transmitting power generated by the rotation to the core portion  21  and the grip roller  22  via power transmission unit (not illustrated). As a consequence, the recording medium  1  wound to the core portion  21  is wound out, thereby passing through the space between the grip roller  22  and the pinch roller  23 . The recording medium  1  is rewound to the core portion  21  by inversely rotating the motor  25 . 
     The recording medium  1  passing through the space between the grip roller  22  and the pinch roller  23  is fed to the decurling unit  3  adjacent to the conveyance unit  2 . The decurling unit  3  includes: a first decurling member  32 ; a second decurling member  33  disposed facing the first decurling member  32 ; and a recording medium detection sensor  34  disposed in the second decurling member  33 . A raised portion  31  is set to the first decurling member  32 . A conveyance passage at the raised portion  31  is curving in the inverse direction of the curling of the recording medium. The conveyance passage that curls the recording medium  1  in the inverse direction of the curling is formed to a space between a surface provided with the raised portion  31  in the first decurling member  32  and the second decurling member  33 . 
     In the decurling unit  3 , when the recording medium  1  passes through the conveyance passage, the recording medium  1  comes into contact with the raised portion  31 . Thus, the winding the recording medium  1  to the core portion  21  results in curling the recording medium  1  that curls inward in the inverse direction (outward), thereby decurling the recording medium  1 . In the decurling unit  3 , the second decurling member  33  is disposed, thereby preventing the recording medium  1  from completely separating from the raised portion  31 . More specifically, the recording medium  1  is decurled without continuously applying specific power or elastic load to the recording medium  1 . The recording medium detection sensor  34  detects whether the leading edge of the recording medium  1  passes through the exit side of the conveyance passage. 
     The recording medium  1  passing through the decurling unit  3  is fed to the print unit  4  adjacent to the decurling unit  3 . The print unit  4  includes a platen roller  41  that supports the recording medium  1 . The platen roller  41  does not have drive force, and is rotatably supported to a shaft (not illustrated). At a position facing the platen roller  41 , a thermal head  43  is disposed to individually attach a plurality of inks coated on an ink ribbon  42  to the recording medium  1  with heat. The thermal head  43  is movable up and down between a print position and a retreating position driven by power of the motor  44  and power transmission unit (not illustrated) that transmits the power to the thermal head  43 . At the print position, the thermal head  43  can attach the ink to the recording medium  1 . At the retreating position, the thermal head  43  is apart from the platen roller  41 . As illustrated in  FIG. 1 , the ink ribbon  42  is in contact with an under portion of the thermal head  43 , and is movable from a bobbin  45  on the supply side to a bobbin  46  on the winding side. Specifically, the ink ribbon  42  wound to the bobbin  45  on the supply side is wound to the bobbin  46  on the winding side via the under portion of the thermal head  43  with power of a motor  47  and power transmission unit (not illustrated) that transmits the power to the bobbin  46  on the winding side. The ink ribbon  42  is coated with a plurality of inks including yellow (Y) color, magenta (M) color, cyan (C) color, overcoat (OC), and a black stripe marker for determining the ink position. A ribbon marker sensor  48  that detects the black stripe marker is disposed between the thermal head  43  and the bobbin  46  on the winding side. 
     Near the platen roller  41  and the thermal head  43 , a cutter  49  is disposed to cut the recording medium  1 . The cutter  49  cuts the recording medium  1  with the power of the motor  44  and power transmission unit (not illustrated) that transmits the power to the cutter  49 . 
       FIG. 2  is a block diagram illustrating components connected to the control unit  5  in the printer  100 . A main switch  71 , a print switch  72 , and an image selection switch  73  operate the printer  100 . An input/output terminal  75  is used for reading image information stored in a storage medium  76  as a nonvolatile recording medium, e.g., secure digital (SD) card. Image processing unit  77  performs image processing under the control of the control unit  5 . Display unit  78  is, e.g., a liquid crystal display (LCD), and displays data under the control of the control unit  5 . A temperature sensor  79  detects the temperature of the thermal head  43 . Driver circuits  81 ,  82 , and  83  individually control the operation of the motors  25 ,  47 , and  44 . A driver circuit  84  controls heating operation of the thermal head  43 . 
     Storage unit  6  stores control information indicating operation contents of the conveyance unit  2  and the print unit  4  corresponding to each of inks coated on the ink ribbon  42 . The control information indicates the conveyance amount of the recording medium  1  and the history of print contents. 
     Next, the operation of the printer  100  is described. 
       FIGS. 3 and 4  are flowcharts illustrating operating procedures of the printer  100 . The control unit  5  is operable with power supplied form a power source. 
     In step S 1 , the main switch  71  is pressed. In step S 2 , the control unit  5  detects whether the storage medium  76  is connected to the input/output terminal  75 . When the storage medium  76  is connected to the input/output terminal  75  (Yes in step S 2 ) and the storage medium  76  stores the image information, the control unit  5  reads the image information. In step S 3 , the control unit  5  controls the image processing unit  77  to convert the read image information into image information suitable to display, and thereafter controls the display unit  78  to display the image. A user of the printer  100  selects an image to be printed from the images displayed on the display unit  78  by operating the image selection switch  73 . In step S 4 , the control unit  5  checks that the image selection switch  73  is pressed. Then, the printer  100  enters a print standby mode. 
       FIGS. 5A to 5D  illustrate conveyance states of the recording medium  1  in Y color printing operation according to the first exemplary embodiment. 
     Referring to  FIG. 5A , in step S 5 , the user presses the print switch  72  when the printer  100  is in the print standby mode. In step S 6 , the control unit  5  controls the image processing unit  77  to convert the image selected by the user into printable image information. When the processing ends, in step S 7 , the control unit  5  rotates the motor  25 , thereby conveying the recording medium  1  to the decurling unit  3 . Referring to  5 A, when the printer  100  is in the print standby mode, the thermal head  43  is at the retreating position and the cutter  49  is opened at a passage position of the recording medium  1 . In step S 7 , the control unit  5  conveys the recording medium  1  nipped between the grip roller  22  and the pinch roller  23  to the decurling unit  3 , as illustrated in  FIG. 5B . 
     In step S 8 , the recording medium detection sensor  34  detects the leading edge of the recording medium  1  conveyed to the decurling unit  3 . The recording medium detection sensor  34  then outputs a detection signal indicating the detection to the control unit  5 . In step S 9 , the control unit  5  reads an amount of the control information stored in the storage unit  6  when inputting the detection signal, and conveys the recording medium  1  to the print start position. According to the first exemplary embodiment, referring to  FIG. 5C , the print start position is located where a length from the leading edge of the recording medium  1  to the platen roller  41  is L. The recording medium  1  is conveyed to the print start position, and the control unit  5  stops the rotation of the motor  25 . 
     In step S 10 , the control unit  5  rotates the motor  47 , thereby starting to wind the ink ribbon  42  from the bobbin  45  on the supply side to the bobbin  46  on the winding side. In step S 11 , the ribbon marker sensor  48  detects the black stripe ribbon marker coated on the ink ribbon  42 . The ribbon marker sensor  48  outputs a detection signal indicating the detection to the control unit  5 . In step S 12 , the control unit  5  stops the rotation of the motor  47  in response to an input of the detection signal, thereby stopping the winding of the ink ribbon  42 . In step S 13 , the control unit  5  rotates the motor  44 , thereby moving the thermal head  43  from the retreating position to the print position as illustrated in  FIG. 5D . 
     The thermal head  43  moves to the print position. In step S 14 , the control unit  5  inversely rotates the motor  25  based on the control information, thereby starting to convey the recording medium  1  toward the decurling unit  3 . In step S 15 , the control unit  5  performs control to heat the thermal head  43  via the driver circuit  84 , and rotates the motor  47 , thereby starting the Y color printing operation. According to the first exemplary embodiment, the Y color printing operation starts at the position apart the length L from the leading edge of the recording medium  1 , i.e., at the print start position, and steps S 14  and S 15  are actually simultaneously executed. In the Y color printing operation, the recording medium  1  is rewound together with the ink ribbon  42 , nipped between the thermal head  43  and the platen roller  41 . At this time, the thermal head  43  is heated while winding the ink ribbon  42  from the bobbin  45  on the supply side to the bobbin  46  on the winding side, thereby attaching the Y color ink coated on the ink ribbon  42  to the recording medium  1 . 
     When the attaching of the Y color ink to the recording medium  1  ends, in step S 16 , the control unit  5  inversely rotates the motor  44  to prevent unnecessary heating of the ink ribbon  42 , thereby moving the thermal head  43  from the print position to the retreating position. In step S 17 , the Y color printing operation ends. When the control unit  5  receives a detection signal indicating that the leading edge of the recording medium  1  passes through the outlet side of the conveyance passage disposed in the decurling unit  3 , from the recording medium detection sensor  34 , the control unit  5  conveys the recording medium  1  with a predetermined conveyance amount, thereby stopping the rotation of the motor  25 . In step S 18 , the control unit  5  stops the conveyance of the recording medium  1 . 
     When the conveyance of the recording medium  1  stops, in step S 19 , the control unit  5  measures temperature of the thermal head  43  based on a detection value of the temperature sensor  79 . In step S 20 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in a standby mode. When the measurement value becomes lower than the threshold, the control unit  5  executes the M color printing operation. 
       FIGS. 6A to 6D  illustrate conveyance states of the recording medium  1  in M color printing operation. 
     After ending the Y color printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at a waiting position  91  set in an area  11  on the leading edge side within the printing target range (refer to  FIGS. 6A and 6B ). When the recording medium  1  is in the standby mode as illustrated in  FIG. 6A , if the measurement value of the control unit  5  becomes lower than the threshold, the control unit  5  executes steps S 21  to S 30  as the M color printing operation. The operation in steps S 21  to S 30  is similar to that in steps S 9  to S 18 . More specifically, after conveying the recording medium  1  to the same print start position as that in the Y color printing operation, the recording medium  1  is returned toward the decurling unit  3  and the M color ink is attached to the recording medium  1  (refer to  FIGS. 6B to 6D ). In step S 30 , the contact position of the recording medium  1  with the raised portion  31  at the stop time of conveyance is set nearer to the leading edge than the waiting position  91  in the M color printing operation. In other words, the conveyance amount of the recording medium  1  in step S 30  is larger than that in step S 18 . 
     When the conveyance of the recording medium  1  stops, in step S 31 , the control unit  5  measures the temperature of the thermal head  43  from the detection value of the temperature sensor  79 . In step S 32 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode. When the measurement value becomes lower than the threshold, the control unit  5  executes the C color printing operation. 
       FIGS. 7A to 7D  illustrate conveyance states of the recording medium  1  in the C color printing operation. 
     After ending the M color printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at a waiting position  92  nearer to the leading edge than the waiting position  91 , within the area  11  on the leading edge side (refer to  FIG. 7A ). The waiting position  92  is nearer to the leading edge of the recording medium  1  than the waiting position  91 , and the leading edge of the recording medium  1  thus floats up. Thus, the decurling effect of the waiting position  92  is smaller than that of the waiting position  91 . When the measurement value of the control unit  5  becomes lower than the threshold while the recording medium  1  is in the standby mode as illustrated in  FIG. 7A , the control unit  5  executes the operation in steps S 33  to S 42 . The operation in steps S 33  to S 42  is similar to that in steps S 9  to S 18 . In other words, after conveying the recording medium  1  to the same print start position as those of the Y color printing operation and M color printing operation, the C color ink is attached to the recording medium  1  by returning the recording medium  1  toward the decurling unit  3  (refer to  FIGS. 7B to 7D ). A flowchart subsequent to step S 36  is illustrated in  FIG. 4 . 
     In the C color printing operation, the waiting position  92  of the recording medium  1  after the M color printing operation is different from the waiting position  91  after the Y color printing operation. In step S 33 , the control unit  5  thus adjusts the print start position of the C color printing operation to be similar to those in the Y color printing operation and the M color printing operation based on the control information. In step S 42 , the contact position of the recording medium  1  with the raised portion  31  at the stop time of conveyance is set to the position nearer to the leading edge of the recording medium  1  than the waiting position  92  in the C color printing operation. More specifically, the conveyance amount of the recording medium  1  in step S 42  is larger than that in step S 30 . 
     When the conveyance of the recording medium  1  stops, in step S 43 , the control unit  5  measures the temperature of the thermal head  43  from the detection value of the temperature sensor  79 . In step S 44 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode. When the measurement value becomes lower than the threshold, the control unit  5  executes the OC printing operation. 
       FIGS. 8A to 8D  illustrate conveyance states of the recording medium  1  in the OC printing operation. 
     After ending the operation of the C color printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at a waiting position  93  nearer to the leading edge of the recording medium  1  than the waiting position  92 , within the area  11  on the leading edge side (refer to  FIG. 8A ). Since the waiting position  93  is nearer to the leading edge of the recording medium  1  than the waiting position  92 , the leading edge of the recording medium  1  floats up. As a consequence, the decurling effect of the waiting position  93  is smaller than that of the waiting position  92 . When the measurement value of the control unit  5  becomes lower than the threshold while the recording medium  1  is in the standby mode as illustrated in  FIG. 8A , the control unit  5  executes the operation in steps S 45  to S 54 . The operation in steps S 45  to S 54  is similar to that in steps S 9  to S 18 . More specifically, after conveying the recording medium  1  to the same print start position as those in the Y color printing operation, the M color printing operation, and the C color printing operation, the control unit  5  attaches the OC ink to the recording medium  1  while returning the recording medium  1  toward the decurling unit  3  (refer to  FIGS. 8B to 8D ). 
     In the OC printing operation, the waiting position  93  of the recording medium  1  after the C color printing operation is different from the waiting position  92 . In step S 45 , the control unit  5  thus adjusts the print start position of the OC printing operation to be similar to those in each color operation based on the control information. In step S 54 , the control unit  5  stops the conveyance of the recording medium  1  at the position where the recording medium  1  is not in contact with the raised portion  31  based on the control information in the OC printing operation. Consequently, after ending the OC printing operation, the recording medium  1  is in the standby mode at the position without the decurling effect. After ending the OC printing operation, the control unit  5  executes the cutting operation. 
       FIGS. 9A to 9C  illustrate conveyance states of the recording medium  1  in the cutting operation according to the first exemplary embodiment. 
     After ending the OC printing operation, the recording medium  1  is in the standby mode in noncontact with the raised portion  31  (refer to  FIG. 9A ). In step S 55 , the control unit  5  rotates the motor  25  based on the control information, thereby conveying the recording medium  1  so that a length from the leading edge of the recording medium  1  to the cutter  49  becomes L as illustrated in  FIG. 9B . In step S 56 , the control unit  5  rotates the motor  44 , thereby causing the cutter  49  to cut the recording medium  1 . In step S 57 , the control unit  5  inversely rotates the motor  25 , thereby rewinding the recording medium  1  with the core portion  21  and the grip roller  22 . Then, the cutting operation ends. 
     According to the first exemplary embodiment, the recording medium  1  is in the standby mode at the decurling unit  3  each time the printing of one color ends. The waiting positions  91 ,  92 , and  93  are set within the area  11  on the leading edge side which has relatively small influence on the print quality in the printing target range. Thus, the deterioration in print quality is prevented without adding a new mechanism such as a mechanism for resetting the decurling. 
     According to the first exemplary embodiment, the waiting positions  91 ,  92 , and  93  are differently set within the area  11  on the leading edge side, thereby preventing the concentration of the decurling of the raised portion  31  at the same position in the area  11  on the leading edge side. As a consequence, the crease is more certainly prevented in the area  11  on the leading edge side. Further, the waiting positions are set nearer to the leading edge of the printing target range as the ink is attached later according to the first exemplary embodiment. Accordingly, the higher the decurling effect, the smaller the number of print colors, and the lower the decurling effect, the larger the number of print colors. Thus, even if the heating time of the recording medium is prolonged together with the increase in print colors, the creation of crease is suppressed. 
     According to the present exemplary embodiment, the decurling unit  3  is provided between the thermal head  43  and the grip roller  22 . The recording medium  1  is tensioned by the grip roller  22  conveying the recording medium  1  while nipping the recording medium  1  between the thermal head  43  and the platen roller  41 , so that the recording medium  1  is efficiently decurled. However, the leading edge of the recording medium  1  passes through the decurling unit  3  without nipping the recording medium  1  between the thermal head  43  and the platen roller  41 , and is not easily decurled as compared with another portion. The recording medium  1  is therefore in the standby mode so that the leading edge thereof is set within the decurling unit  3 , so that the recording medium  1  is uniformly decurled. 
     According to the above-described exemplary embodiment, after ending the printing with each color, the recording medium is conveyed to the waiting position. However, if the measurement value of the temperature of the thermal head is lower than a predetermined threshold, the printing with the next color immediately starts without conveyance to the waiting position and the recording medium may be thus conveyed to the print start position. 
     (Modification) 
     A printer is described according to a modification of the first exemplary embodiment. A configuration of the printer is similar to that of the printer  100 . The operation of the printer in steps S 1  to S 54  is similar to that of the printer  100 . In other words, the cutting operation is different from the first exemplary embodiment. 
       FIG. 10  is a flowchart illustrating the cutting operation of the printer according to the modification of the first exemplary embodiment.  FIGS. 11A to 11E  illustrate conveyance states of the recording medium  1  in the cutting operation according to the modification of the first exemplary embodiment. 
     After the OC printing operation, the recording medium  1  is in the standby mode in noncontact with the raised portion  31  (refer to  FIG. 11A ). In step S 65 , the control unit  5  controls the conveyance of the recording medium  1  so that a length from the leading edge of the recording medium  1  to the cutter  49  becomes λ 1  based on the control information. Only the area  11  on the leading edge side of the recording medium  1  thus passes through the cutter  49  (refer to  FIG. 11B ). In step S 66 , the control unit  5  rotates the motor  44 , thereby causing the cutter  49  to cut the recording medium  1 . As a consequence, the area  11  on the leading edge side is cut (refer to  FIG. 11C ). In step S 67 , the control unit  5  conveys the recording medium  1  to the position where the recording medium  1  passes through the cutter  49  with a length (L-λ 1 ). The portion which passes through the cutter  49  in step S 67  is a print area  13  adjacent to the area  11  on the leading edge side, on which a large part of the image is printed (refer to  FIG. 11D ). Since the print area  13  is not in contact with the raised portion  31  in the standby mode, the print area  13  is not influenced so much and little deterioration in print quality due to the decurling occurs. In step S 68 , the control unit  5  rotates the motor  44  after step S 67 , thereby causing the cutter  49  to cut the recording medium  1 . As a consequence, the print area  13  is cut (refer to  FIG. 11E ). In step S 69 , the control unit  5  inversely rotates the motor  25 , thereby rewinding the recording medium  1  with the core portion  21  and the grip roller  22 . Thus, the cutting operation ends. 
     Since the area  11  on the leading edge side in which the print quality may deteriorate, is cut from the print area  13  according to modification of the first exemplary embodiment, only a portion showing no deterioration in print quality is printed out. 
     A configuration of a printer according to a second exemplary embodiment is similar to that of the printer  100  according to the first exemplary embodiment. The operation of the printer is described below. 
       FIGS. 12 and 13  are flowcharts illustrating operating procedures of the printer according to the second exemplary embodiment. 
     Referring to  FIG. 12 , the operation in steps S 101  to S 108  is similar to that in steps S 1  to S 8  and is not specifically described. 
       FIGS. 14A to 14D  illustrate conveyance states of the recording medium  1  in the Y color printing operation according to the second exemplary embodiment. 
     The operation in step S 108  ends. Steps S 109  to S 118  are executed as the Y color printing operation. The operation in steps S 109  to S 118  is similar to that in steps S 9  to S 18 . Referring to  FIGS. 14A to 14D , the operation of the conveyance unit  2  under the control of the control unit  5  causes the recording medium  1  to pass through the decurling unit  3 , the conveyance unit  2  conveys the recording medium  1  to the print start position at which a length from the leading edge to the platen roller  41  is L, and the Y color printing operation is executed. 
     The conveyance of the recording medium  1  stops in step S 118 . In step S 119 , the control unit  5  measures the temperature of the thermal head  43  from the detection value of the temperature sensor  79 . In step S 120 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode. When the measurement value becomes lower than the threshold, the M color printing operation is executed. 
       FIGS. 15A to 15D  illustrate conveyance states of the recording medium  1  in the M color printing operation, the C color printing operation, and the OC printing operation according to the second exemplary embodiment. 
     After ending the Y color printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at the waiting position  91  set within the area  11  on the leading edge side (refer to  FIGS. 15A and 15B ). When the recording medium  1  is in the standby mode as illustrated in  FIG. 15A , if the measurement value of the control unit  5  is lower than the threshold, the operation in steps S 121  to S 130  is executed. The operation in steps S 121  to  130  is similar to that in steps S 109  to S 118 . More specifically, after conveying the recording medium  1  to the same print start position as that of the Y color printing operation, the recording medium  1  is returned toward the decurling unit  3  and the M color ink is simultaneously attached to the recording medium  1  (refer to  FIGS. 15B to 15D ). In step S 130 , the waiting position  91  is set as the contact position of the recording medium  1  with the raised portion  31 , at the end time of conveyance in the M color printing operation, similar to the end time of the Y color printing operation. 
     In step S 130 , the conveyance of the recording medium  1  stops. In step S 131 , the control unit  5  measures the temperature of the thermal head  43  from the detected value of the temperature sensor  79 . In step S 132 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode. When the measurement value becomes lower than the threshold, steps S 133  to S 142  are executed as the C color printing operation. 
     The operation insteps S 133  to S 142  is similar to that in steps S 109  to S 118 . After conveying the recording medium  1  to the same print start position as those of the Y color printing operation and the M color printing operation, the recording medium  1  is returned toward the decurling unit  3  and the C color ink is simultaneously attached to the recording medium  1  (refer to  FIGS. 15A to 15D ). In step S 142 , the waiting position  91  is set as the contact position of the recording medium  1  with the raised portion  31 , at the end time of conveyance in the C color printing operation, similar to that at the end time of the Y color printing operation and the M color printing operation. A flowchart subsequent to step S 136  is illustrated in  FIG. 13 . 
     In step S 142 , the conveyance of the recording medium  1  stops. In step S 143 , the control unit  5  measures the temperature of the thermal head  43  from the detected value of the temperature sensor  79 . In step S 144 , the control unit  5  checks whether the measurement value becomes lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode. When the measurement value becomes lower than the threshold, steps S 145  to S 154  are executed as the OC printing operation. 
     The operation insteps S 145  to S 154  is similar to that in steps S 109  to S 118 . After conveying the recording medium  1  to the same print start position as the printing with the colors, the recording medium  1  is returned toward the decurling unit  3  and the OC ink is simultaneously attached to the recording medium  1  (refer to  FIGS. 15A to 15D ). In step S 154 , the waiting position  91  is set as the contact position of the recording medium  1  with the raised portion  31 , at the end time of conveyance in the OC printing operation, similar to that at the end time of the printing operation with the colors. After ending the OC printing operation, the cutting operation is executed. 
       FIGS. 16A to 18E  illustrate conveyance states of the recording medium  1  in the cutting operation according to the second exemplary embodiment. 
     After the OC printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at the waiting position  91  (refer to  FIG. 16A ). In step S 155 , the control unit  5  conveys the recording medium  1  so that based on the control information, a length from the leading edge of the recording medium  1  to the cutter  49  becomes λ 1 . As a consequence, only the area  11  on the leading edge side of the recording medium  1  passes through the cutter  49  (refer to  FIG. 16B ). In step S 156 , the control unit  5  rotates the motor  44 , thereby causing the cutter  49  to cut the recording medium  1 . Thus, the area  11  on the leading edge side is cut (refer to  FIG. 16C ). In step S 157 , the control unit  5  conveys the recording medium  1  to the passage position of the recording medium  1  through the cutter  49  by a length (L-λ 1 ). The passage portion through the cutter  49  in step S 157  is the print area  13  (refer to  FIG. 16D ). The print area  13  is not in contact with the raised portion  31  in the standby mode of the recording medium  1 , and the influence from the deterioration in print quality due to the decurling is therefore small. In step S 158 , the control unit  5  rotates the motor  44  subsequent to step S 157 , thereby causing the cutter  49  to cut the recording medium  1 . Thus, the print area  13  is cut (refer to  FIG. 16E ). In step S 159 , the control unit  5  inversely rotates the motor  25 , thereby rewinding the recording medium  1  with the core portion  21  and the grip roller  22 . Then, the cutting operation ends. 
     According to the second exemplary embodiment, the waiting positions after the individual printing operation are identical within the area  11  on the leading edge side, thereby simplifying the conveyance control of the recording medium  1  as compared with the first exemplary embodiment. The waiting positions are identical, and the area  11  on the leading edge side that may deteriorate the print quality is thus cut from the print area  13 , so that only a portion with no deterioration in print quality is printed out. 
     A configuration of a printer according to a third exemplary embodiment is similar to that of the printer  100  according to the first exemplary embodiment. The operation of the printer is described below. 
       FIGS. 17 and 18  are flowcharts illustrating operating procedures of the printer according to the second exemplary embodiment. 
     Referring to  FIG. 17 , the operation in steps S 201  to S 208  is similar to that in steps S 1  to S 8  and is not described in detail. 
       FIGS. 19A to 19D  illustrate conveyance states of the recording medium  1  in the Y color printing operation according to the third exemplary embodiment. 
     When the operation in step S 208  ends, the Y color printing operation is executed in steps S 209  to S 218 . The operation in steps S 209  to S 218  is similar to that in steps S 9  to S 18 . Referring to  FIGS. 19A to 19D , after conveying the recording medium  1  to the print start position, the Y color printing operation is executed while returning the recording medium  1  toward the decurling unit  3  according to the second exemplary embodiment. In step S 209 , the print start position is located where a length from the leading edge of the recording medium  1  to the recording medium detection sensor  34  is M, as illustrated in  FIGS. 19C and 19D . 
       FIGS. 20A to 20D  illustrate conveyance states of the recording medium  1  in the M color printing operation according to the third exemplary embodiment. After ending the Y color printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at a waiting position  94   a  (refer to  FIG. 20A ). In step S 219 , the control unit  5  conveys the recording medium  1  to the print waiting position of the M color printing operation after a predetermined time has elapsed. Specifically, the control unit  5  rotates the motor  25  based on the control information, thereby pulling out the recording medium  1  from the decurling unit  3  by a length obtained by adding a length N from the leading edge of the recording medium  1  to the waiting position  94   a , to the length M (refer to  FIG. 20B ). In step S 220 , the control unit  5  measures the temperature of the thermal head  43  from the detected value of the temperature sensor  79 . In step S 221 , the control unit  5  checks whether the measurement value becomes lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode. When the measurement value becomes lower than the threshold, the control unit  5  is in the standby mode while the waiting position  94   b  is in contact with the raised portion  31 . 
     When the measurement value of the control unit  5  becomes lower than the threshold, the M color printing operation is executed in steps S 222  to S 230 . The operation in steps S 222  to S 230  is similar to that in steps S 210  to S 218 . In step S 227 , the control unit  5  adjusts the print start position of the M color printing operation to be similar to that of the Y color printing operation based on the control information with the conveyance unit  2 , and thereafter heats the thermal head  43 . More specifically, when the length from the leading edge of the recording medium  1  to the recording medium detection sensor  34  becomes M, the control unit  5  heats the thermal head  43  (refer to  FIG. 20C ). After the attachment of the M color ink ends, the recording medium  1  is returned toward the decurling unit  3  (refer to  FIG. 20D ). 
       FIGS. 21A to 21D  illustrate conveyance states of the recording medium  1  in the C color printing operation according to the third exemplary embodiment. 
     After ending the M color printing operation, the recording medium  1  is in the standby mode in contact with the raised portion  31  at the waiting position  94   a  (refer to  FIG. 21A ). In step S 231 , the control unit  5  conveys the recording medium  1  to the print waiting position of the C color printing operation after a predetermined time has elapsed. Specifically, the control unit  5  rotates the motor  25  based on the control information, thereby pulling out the recording medium  1  from the decurling unit  3  by a length obtained by adding a length 2N/3 to the length M (refer to  FIG. 21B ). As a result of the operation, the contact position of the recording medium  1  with the raised portion  31  becomes a waiting position  95   b , which is nearer to the leading edge of the recording medium  1  than the waiting position  94   b . In step S 232 , the control unit  5  measures the temperature of the thermal head  43  from the detected value of the temperature sensor  79 . In step S 233 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode, being in a state in which the waiting position  95   b  is in contact with the raised portion  31 . 
     When the measurement value of the control unit  5  becomes lower than the threshold, the C color printing is executed in the operation insteps S 234  to S 242 . The operation in steps S 234  to S 242  is similar to the operation in steps S 210  to S 218 . A flowchart subsequent to step S 236  is illustrated in  FIG. 18 . In step S 239 , the control unit  5  adjusts the print start position in the C color printing operation to be similar to those of the Y color printing operation and the M color printing operation based on the control information with the conveyance unit  2 , and thereafter heats the thermal head  43 . More specifically, when the length from the leading edge of the recording medium  1  to the recording medium detection sensor  34  becomes M, the control unit  5  heats the thermal head  43  (refer to  FIG. 21C ). After the attachment of the C color ink ends, the recording medium  1  is returned toward the decurling unit  3  (refer to  FIG. 21D ). 
       FIGS. 22A to 22D  illustrate conveyance states of the recording medium  1  in the OC printing operation according to the third exemplary embodiment. 
     After the C color printing operation ends, the recording medium  1  is in the standby mode in contact with the raised portion  31  at the waiting position  94   a  (refer to  FIG. 22A ). In step S 243 , the control unit  5  conveys the recording medium  1  to the print waiting position of the OC color printing operation after a predetermined time has elapsed. Specifically, the control unit  5  rotates the motor  25  based on the control information, thereby pulling out the recording medium  1  from the decurling unit  3  by a length obtained by adding a length N/3 to the length M (refer to  FIG. 22B ). As a result of the operation, the contact position of the recording medium  1  with the raised portion  31  becomes a waiting position  96   b , which is nearer to the leading edge of the recording medium  1  than the waiting position  95   b . In step S 244 , the control unit  5  measures the temperature of the thermal head  43  from the detected value of the temperature sensor  79 . In step S 245 , the control unit  5  checks whether the measurement value is lower than a predetermined threshold. Until the measurement value becomes lower than the threshold, the recording medium  1  is in the standby mode, being in a state in which the waiting position  96  is in contact with the raised portion  31 . 
     When the measurement value of the control unit  5  becomes lower than the threshold, the OC printing operation is executed in steps S 246  to S 254 . The operation in steps S 246  to S 254  is similar to that in steps S 210  to  218 . In step S 251 , the control unit  5  adjusts the print start position of the OC printing operation to be similar to those of the printing with the colors based on the control information with the conveyance unit  2 , and thereafter heats the thermal head  43 . More specifically, when the length from the leading edge of the recording medium  1  to the recording medium detection sensor  34  becomes M, the control unit  5  heats the thermal head  43  (refer to  FIG. 22C ). After the attachment of the OC ink ends, the recording medium  1  is returned toward the decurling unit  3  (refer to  FIG. 22D ). The cutting operation is subsequently executed. 
       FIGS. 23A to 23E  illustrate conveyance states of the recording medium  1  in the cutting operation according to the third exemplary embodiment. 
     After the OC printing operation ends, the recording medium  1  is in the standby mode, being in contact with the raised portion  31  at the waiting position  94   a  (refer to  FIG. 23A ). In step S 255 , the control unit  5  conveys the recording medium  1  so that based on the control information, a length from the leading edge of the recording medium  1  to the cutter  49  is λ 2 , as illustrated in  FIG. 23B . In step S 256 , the control unit  5  rotates the motor  44 , thereby causing the cutter  49  to cut the recording medium  1  as illustrated in  FIG. 23C . The cutting portion in step S 256  is an area  12  on the rear edge side of the printing target range of the recording medium  1  corresponding to the previous printing operation. In other words, at the waiting positions  94   a ,  95   a , and  96   a  in  FIG. 23B , the recording medium  1  is in contact with the raised portion  31  in the standby mode thereof in the previous printing operation. 
     Subsequent to step S 255 , in step S 257 , the control unit  5  conveys the recording medium  1  so that only the print area  13  passes through the cutter  49  based on the control information, as illustrated in  FIG. 23D . In step S 258 , the control unit  5  rotates the motor  44 , thereby causing the cutter  49  to cut the recording medium  1 . Thus, the print area  13  is cut from the area  12  on the rear end side set as the waiting position when the ink is attached to the print area  13  (refer to  FIG. 23E ). In step S 259 , the control unit  5  rotates the motor  25 , thereby rewinding the recording medium  1  with the core portion  21  and the grip roller  22 . Then, the cutting operation ends. 
     According to the third exemplary embodiment, the recording medium  1  waits with the decurling unit  3  each time the printing with one color ends. At this time, the waiting position is set within the area  12  on the rear edge side where the influence on the print quality is a relatively small in the printing target range. Thus, the deterioration in print quality is prevented without adding a new mechanism such as a mechanism for resetting the decurling. 
     According to the third exemplary embodiment, the waiting positions are differently set within the area  12  on the rear edge side, thereby preventing the concentration of the decurling of the raised portion  31  at the same position in the area  12  on the rear edge side. As a consequence, the crease is certainly prevented in the area  12  on the rear edge side. The later the ink is attached, the nearer the waiting positions are set to the leading edge of the printing target range of the recording medium  1  according to the third exemplary embodiment. As a consequence, the smaller the number of print colors, the higher the decurling effect and, the larger the number of print colors, the lower the decurling effect. Even if the heating time of the recording medium is prolonged together with the increase in print colors, the creation of crease is suppressed. 
       FIG. 24  illustrates a configuration of a printer according to a fourth exemplary embodiment. The same reference numerals denote the same components as those in the printer  100  according to the first exemplary embodiment, and are not described in detail. 
     Referring to  FIG. 24 , in a printer  200  according to the fourth exemplary embodiment, the grip roller  22  is disposed in the first decurling member  32 . The pinch roller  23  is arranged, facing the grip roller  22  in the second decurling member  33 . The printer  200  executes any of the operations according to the first to third exemplary embodiments. When executing the printing operation according to the first exemplary embodiment, at the waiting position after the OC printing operation, the recording medium  1  remains nipped between the grip roller  22  and the pinch roller  23 . 
     According to the fourth exemplary embodiment, the grip roller  22  functions as the raised portion  31  to decurl the recording medium  1  with a cylindrical surface of the grip roller  22 . Consequently, the grip roller  22  is housed within the decurling unit  3  and the scale of apparatus is reduced. Regarding conveyance resistance of the recording medium  1 , the rotatable grip roller  22  is smaller than the raised portion  31 . Hence, the recording medium  1  is smoothly conveyed. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2009-231451 filed Oct. 5, 2009, which is hereby incorporated by reference herein in its entirety.