Patent Publication Number: US-11376876-B2

Title: Printing apparatus and method of printing

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-069696, filed Apr. 1, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a printing apparatus and a printing method. 
     2. Related Art 
     Hitherto, a roll-to-roll type printing apparatus has a specification for stopping a conveyance operation before a foreign object is conveyed at a position of a printing head and damages the printing head in a case where a sensor detects the foreign object in a base material during conveyance (hereinafter, such stop is referred to as an emergency stop). In this case, the printing apparatus controls a tension, which is imposed on a stopped base material, to be a predetermined tension (JP-A-2017-170817). 
     However, in recent years, a printing apparatus has increased a printing speed. When an emergency stop is performed in such printing apparatus, it is required to stop the base material with a conveyance distance equivalent to that in the related art. In order to achieve this, it is required to increase deceleration more than that in the related art. Further, when tension control similar to that in the related art is performed for an emergency stop while increasing a printing speed, there arises a problem in that slack or tension is caused to a base material at a feeding shaft or a winding shaft more than that in the related art and sudden tension fluctuation is caused. 
     SUMMARY 
     A printing apparatus according to the present application is a printing apparatus in which a base material is conveyed by a roll-to-roll method and feedback control is performed on a tension imposed on the base material, the printing apparatus includes a control unit, a first drive motor configured to control a speed of conveyance of conveying the base material, and a second drive motor configured to control the tension imposed on the base material, wherein, in a case where a conveyance operation for conveying the base material is stopped based on detection of a foreign object, and when a speed of the first drive motor is at a predetermined value or less, the control unit stops the tension control performed by the second drive motor. 
     In the printing device described above, in a case where the conveyance operation is stopped based on the detection of a foreign object, and the control unit may start the tension control performed by the second drive motor after a passage of a predetermined time period. 
     The printing device described above may include a roll diameter sensor configured to detect a roll diameter of the base material wound in a roll shape, and the control unit may vary an inertia of the base material in accordance with a detection value of the roll diameter sensor, and control the first drive motor in a case where the conveyance operation is stopped based on the detection of a foreign object. 
     A printing method according to the present application is a printing method of a printing apparatus in which a base material is conveyed by a roll-to-roll method and feedback control is performed on a tension imposed on the base material, and which includes a control unit, a first drive motor configured to control a speed of conveyance of conveying the base material, and a second drive motor configured to control the tension imposed on the base material. The printing method includes a tension control stopping step for, in a case where a conveyance operation for conveying the base material is stopped based on detection of a foreign object, and when a speed of the first drive motor is at a predetermined value or less, stopping, by the control unit, the tension control performed by the second drive motor. 
     The printing method described above may include a tension control step for, after completing the tension control stopping step based on the detection of a foreign object, starting, by the control unit, the tension control performed by the second drive motor after a passage of a predetermined time period. 
     In the printing method described above, a roll diameter sensor configured to detect a roll diameter of the base material wound in a roll shape may be provided, and the method may include an inertia control step for, by the control unit, varing an inertia of the base material in accordance with a detection value of the roll diameter sensor, and controlling the first drive motor in a case where the conveyance operation is stopped based on the detection of a foreign object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view schematically illustrating a device configuration of a printer according to a first exemplary embodiment. 
         FIG. 2  is a schematic block diagram illustrating an electrical configuration for controlling the printer according to the exemplary embodiment. 
         FIG. 3  is a diagram illustrating a change of a tension at the time of an emergency stop in a printer using related-art tension control. 
         FIG. 4  is a flowchart illustrating one example of control at the time of an emergency stop of in the printer according to the exemplary embodiment. 
         FIG. 5  is a diagram illustrating a change of a tension at the time of an emergency stop in the printer according to the exemplary embodiment. 
         FIG. 6  is a schematic block diagram illustrating an electrical configuration for controlling a printer according to a second exemplary embodiment. 
         FIG. 7  is a flowchart illustrating one example of control at the time of an emergency stop in the printer according to the exemplary embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Exemplary Embodiment 
     An outline of a printing apparatus according to an exemplary embodiment of the present disclosure will be described with reference to the drawings. In the exemplary embodiment, the printing apparatus is a printing apparatus that conveys a base material in a roll-to-roll method. As one example of this, description is given with a line type ink jet printer  1  (hereinafter, simply referred to as a printer  1 ). 
     A device configuration of the printer  1  according to the exemplary embodiment will be described. 
       FIG. 1  is a front view schematically illustrating a configuration of the printer  1  according to the first exemplary embodiment. 
     As illustrated in  FIG. 1 , in the printer  1 , one base material S is stretched along a conveyance path R, and has both edges wound around a feeding shaft  20  and a winding shaft  40  in a roll shape. The base material S is subjected to printing while being conveyed in a conveyance direction D directed from the feeding shaft  20  to the winding shaft  40 . Note that the base material S sequentially passes through rollers described later, and thus the conveyance path R for conveying the base material S is formed. 
     Types of the base material S are broadly divided into a paper-based type and a film-based type. Specific examples of the paper type include high-quality paper, cast paper, art paper, coated paper, and the like, and specific examples of the film type include synthetic paper, polyethylene terephthalate (PET), polypropylene (PP), and the like. 
     As a schematic configuration, the printer  1  includes a feeding section  2  (feeding area) for feeding the base material S from the feeding shaft  20 , a process section  3  (process area) for recording an image on the base material S fed from the feeding section  2 , and a winding section  4  (winding area) for winding, around the winding shaft  40 , the base material S on which the image has been recorded in the process section  3 . Note that, in the following description, of both surfaces of the base material S, the surface on which the image is recorded will be referred to as a front surface, and the reverse side surface will be referred to as a back surface. 
     The feeding section  2  includes the feeding shaft  20  around which the edge of the base material S is wound, a corona treatment machine  21  being a pre-process unit that performs processing for modifying the front surface of the base material S drawn from the feeding shaft  20 , and a tension roller  22  (driven roller). Note that the corona treatment machine  21  being a pre-process unit is arranged upstream of printing units (printing heads  51  and  52 ) described later in the conveyance path R for the base material S. 
     The feeding shaft  20  supports the base material S by winding the edge thereof with the front surface of the base material S facing outward. In addition, when the feeding shaft  20  is rotated clockwise in  FIG. 1 , the base material S wound around the feeding shaft  20  is fed to the process section  3  via the pre-process unit (corona treatment machine  21 ) and the tension roller  22 . 
     The base material S is wound around the feeding shaft  20  through intermediation of a core pipe  23  that is detachable from the feeding shaft  20 . Thus, when the base material S around the feeding shaft  20  is used up, it is possible to attach, to the feeding shaft  20 , a new core pipe  23  around which the rolled base material S has been wound and replace the base material S around the feeding shaft  20 . 
     The corona treatment machine  21  being a pre-process unit subjects the front surface being a printing surface of the base material S to be conveyed to corona discharge irradiation. With this, front surface processing for modifying the front surface is performed, and wettability of ink at the time pf printing is improved. This is performed mainly when the base material S is a film type. Hereinafter, performing corona discharge irradiation is referred to as corona treatment. Note that, in the feeding section  2 , the corona treatment machine  21  includes a conveying shaft  24  for conveying the base material S. 
     The feeding shaft  20 , the conveying shaft  24 , and the tension roller  22  are configured so as to be movable in a width direction (a direction vertical to the drawing sheet of  FIG. 1 ) orthogonal to the conveyance direction D. The feeding section  2  adjusts positions of the feeding shaft  20 , the conveying shaft  24 , and the tension roller  22  in the width direction (shaft direction), and thus forms a steering mechanism  25  for suppressing meandering of the base material S. 
     The steering mechanism  25  includes an edge sensor  251  and a width-direction drive unit  252 . The edge sensor  251  is provided downstream of the tension roller  22  in the conveyance direction D so as to face an edge portion of the base material S in the width direction, and detects a position of an edge of the base material S in the width direction. Further, the width-direction drive unit  252  moves the feeding shaft  20 , the conveying shaft  24 , and the tension roller  22  in the width direction in accordance with a detection result of the edge sensor  251 . In this manner, meandering of the base material S is suppressed. 
     Note that, in the exemplary embodiment, in order to form the steering mechanism  25 , the feeding shaft  20 , the conveying shaft  24 , and the tension roller  22  are formed as an integrated block through use of a fixing member (not shown), and are incorporated in the printer  1 . In this block, with the fixing member as a reference, the feeding shaft  20  and the tension roller  22  are subjected to alignment adjustment by screw fastening to be fixed. 
     While supporting the base material S, which is fed from the feeding section  2 , with a platen drum  30 , the process section  3  performs printing an image on the base material S by performing processing as appropriate with function units  51 ,  52 ,  61 ,  62 , and  63  arranged along an outer circumference surface of the platen drum  30 . In the process section  3 , a front drive roller  31  and a rear drive roller  32  are provided upstream and downstream of the platen drum  30 , respectively. Further, from the front drive roller  31  to the rear drive roller  32  along the conveyance direction D, the base material S to be conveyed is supported by the platen drum  30 , and is subjected to printing. 
     The front drive roller  31  has a plurality of minute protrusions, which are formed by thermal spraying on the outer circumferential surface of the front drive roller  31 , and the base material S fed from the feeding section  2  is wound from the back surface side of the base material S. In addition, by being rotated clockwise in  FIG. 1 , the front drive roller  31  conveys the base material S fed from the feeding section  2  downstream in the conveyance direction D. Note that a nip roller  31   n  is provided with respect to the front drive roller  31 . This nip roller  31   n  is held in contact with the front surface of the base material S while being biased toward the front drive roller  31 , and the base material S is sandwiched between the nip roller  31   n  and the front drive roller  31 . With this, a frictional force between the front drive roller  31  and the base material S is secured, and the front drive roller  31  can securely convey the base material S. 
     The platen drum  30  is, for example, a cylindrical drum having a diameter of 400 mm, which is rotatably supported in both the conveyance direction D and the reverse direction by a support mechanism (not shown). Further, the platen drum  30  wounds the base material S conveyed from the front drive roller  31  to the rear drive roller  32 . The platen drum  30  supports the base material S from the back surface side of the base material S while being driven to rotate in the conveyance direction D of the base material S by receiving a frictional force between the platen drum  30  and the base material S. 
     The process section  3  is provided with a driven roller  33  and a tension roller  34  (driven rollers) that fold back the base material S on both sides of the part at which the base material S is wound on the platen drum  30 . The front surface of the base material S is wound on the driven roller  33  between the front drive roller  31  and the platen drum  30  to fold back the base material S. Meanwhile, the front surface of the base material S is wound on the driven roller  34  between the platen drum  30  and the rear drive roller  32  to fold back the base material S. In this manner, by folding back the base material S respectively upstream and downstream of the platen drum  30  in the conveyance direction D, a long length of the part at which the base material S is wound on the platen drum  30  can be secured. 
     The rear drive roller  32  has a plurality of minute protrusions, which are formed by thermal spraying on the outer circumferential surface of the rear drive roller  32 , and the base material S conveyed from the platen drum  30  via the driven roller  34  is wound from the back surface side of the base material S. In addition, by being rotated clockwise in  FIG. 1 , the rear drive roller  32  conveys the base material S to the winding section  4 . 
     Note that a nip roller  32   n  is provided with respect to the rear drive roller  32 . This nip roller  32   n  is held in contact with the front surface of the base material S while being biased toward the rear drive roller  32 , and the base material S is sandwiched between the nip roller  32   n  and the rear drive roller  32 . With this, a frictional force between the rear drive roller  32  and the base material S is secured, and the rear drive roller  32  can securely convey the base material S. 
     In this manner, the base material S conveyed from the front drive roller  31  to the rear drive roller  32  is supported by the outer circumferential surface of the platen drum  30 . In addition, in the process section  3 , in order to print a color image on the front surface of the base material S supported by the platen drum  30 , a plurality of line type printing heads  51  corresponding to colors different from one another are provided. Note that the printing heads  51  and a printing head  52  described later form a printing unit together. 
     As the printing heads  51 , in the exemplary embodiment, the five printing heads  51  ( 51 W,  51 Y,  51 C,  51 K, and  51 M) corresponding to white, yellow, cyan, black, and magenta are provided in the conveyance direction D in the stated color order. The printing heads  51  faces the front surface of the base material S wound on the platen drum  30  with slight clearance between the printing head  51  and the front surface, and ejects an ink having a corresponding color (colored ink) from a nozzle by an ink jet method. Further, the printing head  51  ejects the ink onto the base material S to be conveyed in the conveyance direction D, and thus a color image is formed on the front surface of the base material S. 
     Further, as the ink, an ultraviolet (UV) ink (photocurable ink) that is cured by being irradiated with ultraviolet rays (light) is used. Thus, in order to cure and fix the ink onto the base material S, the process section  3  is provided with UV irradiators  61 ,  62 , and  63 . Note that this ink curing is performed by separately using two stages of temporary curing and final curing. 
     The UV irradiator  61  for final curing is arranged downstream of the printing head  51 W for white and upstream of the printing head  51 Y for yellow. The UV irradiator  61  for final curing performs irradiation with ultraviolet light having high intensity, and cures the ink to such degree that wetting extendability of the ink is stopped (final curing). Meanwhile, the UV irradiator  62  for temporary curing is arranged downstream of the printing head  51 Y for yellow, the printing head  51 C for cyan, the printing head  51 K for black, and the printing head  51 M for magenta. The UV irradiator  62  for temporary curing performs irradiation with ultraviolet light having intensity lower than that of the UV irradiator  61 , and cures the ink to such extent that wetting extendability of the ink is sufficiently slower than that in a case without irradiation with the ultraviolet light (temporary curing). 
     The UV irradiator  61  arranged downstream of the printing head  51 W for white finally cures the ink for white as described above, and thus wetting extendability of the ink is stopped. Further, the UV irradiator  62  arranged downstream of the printing head  51 M for magenta performs temporal curing before the colored ink ejected from the printing heads  51 Y,  51 C,  51 K, and  51 M are mixed, and thus color mixing is suppressed. In this manner, a color image is formed on the base material S. 
     Furthermore, the printing head  52  is provided downstream of the UV irradiator  62  in the conveyance direction D. The printing head  52  faces the front surface of the base material S wound on the platen drum  30  with slight clearance between the printing head  52  and the front surface, and ejects a clear UV ink onto the front surface of the base material S by an ink jet method. With this, the clear ink is further ejected onto the color image formed by the printing heads  51  in five colors. The clear ink is ejected onto the entire color image, and applies texture such as shiny appearance and mat tone appearance to the color image. 
     Further, the UV irradiator  63  is provided downstream of the printing head  52  in the conveyance direction D. The UV irradiator  63  performs irradiation with intense ultraviolet light, and thus cures the clear ink ejected from the printing head  52  together with the four colored inks, which are ejected from the printing heads  51 Y,  51 C,  51 K, and  51 M and temporarily cured. With this, the four colored ink and the clear ink can be fixed onto the front surface of the base material S. 
     As described above, in the process section  3 , ejection and curing of the inks are appropriately performed onto the base material S wound around the outer circumferential portion of the platen drum  30 , and thus the color image coated with the clear ink is formed. Further, the base material S on which the color image is formed is conveyed to the winding section  4  by the rear drive roller  32 . 
     In addition to the winding shaft  40  around which the edge of the base material S has been wound, the winding section  4  includes a tension roller  41  (driven roller) for winding the base material S between the winding shaft  40  and the rear drive roller  32  from the back surface side of the base material S. The winding shaft  40  supports the base material S by winding the edge thereof with the front surface of the base material S facing outward. That is, when the winding shaft  40  is rotated clockwise in  FIG. 1 , the base material S conveyed from the rear drive roller  32  is wound around the winding shaft  40  via the tension roller  41 . In this regard, the base material S is wound around the winding shaft  40  via a core pipe  42  that is detachable from the winding shaft  40 . Thus, when the base material S wound around the winding shaft  40  becomes full, the base material S can be detached together with the core pipe  42 . 
     Next, an electrical configuration for controlling the printer  1  will be described. 
       FIG. 2  is a schematic block diagram illustrating an electrical configuration for controlling the printer  1  according to the exemplary embodiment. 
     As illustrated in  FIG. 2 , the printer  1  includes a control unit  100  that comprehensively controls the respective device units in the apparatus. The control unit  100  is a computer including a Central Processing Unit (CPU) and a Random Access Memory (RAM). 
     The printer  1  includes the control unit  100  and a user interface  200  that functions as an interface for a user. The user interface  200  is formed of an input device such as a mouse and a keyboard and an output device such as a display device. Therefore, a user can input a desired instruction to the control unit  100  by operating the input device of the user interface  200 , and can check an operation state of the printer  1  by checking the output device of the user interface  200 . Note that the input device and the output device are necessarily formed as separate bodies, and may be formed integrally as a touch panel display or the like. 
     Based on an instruction input by a user via the user interface  200  and an instruction received from other external devices, the control unit  100  controls the printing heads  51  and  52 , the UV irradiators  61 ,  62 , and  63 , the corona treatment machine  21 , and the respective device units for conveying the base material. 
     The control unit  100  controls ink ejection timings of the printing heads  51  for forming a color image in accordance with the conveyance of the base material S. Specifically, the control of the ink ejection timings is performed based on an output (detection value) of a drum encoder E 30  that is mounted to a rotary shaft of the platen drum  30  and detects a rotary position of the platen drum  30 . 
     The platen drum  30  is driven to rotate along with conveyance of the base material S, and hence the conveyance position of the base material S can be grasped by referring to the output of the drum encoder E 30  that detects the rotary position of the platen drum  30 . In view of this, the control unit  100  generates a print timing signal (PTS) from the output of the drum encoder E 30 , and controls the ink ejection timings of the printing heads  51 , based on the PTS signal. With this, the inks ejected from the printing heads  51  are caused to land on target positions on the base material S to be conveyed, and thus a color image is formed. 
     Further, a timing at which the printing head  52  ejects the clear ink is similarly controlled by the control unit  100 , based on the output of the drum encoder E 30 . With this, the clear ink can be ejected accurately onto the color image formed by the plurality of printing heads  51 . 
     Moreover, the control unit  100  controls timings of on/off states of the UV irradiators  61 ,  62 , and  63  and an irradiation light amount. Further, the control unit  100  controls on/off states and an irradiation light amount of corona irradiation with respect to the corona treatment machine  21 , based on an input operation from the user interface  200  by a user. 
     The control unit  100  has a function of controlling conveyance of the base material S. The control of conveyance of the base material S is achieved mainly with steering control, tension control, and the like of the base material S. The steering control is performed through use of the steering mechanism  25  provided to the feeding section  2 . Specifically, the control unit  100  causes the width-direction drive unit  252  to adjust the positions of the feeding shaft  20 , the conveying shaft  24 , and the tension roller  22  in the width direction in accordance with a detection result of the edge sensor  251 , and thus performs feedback control of the position of the base material S in the width direction. Further, the tension control is performed though use of motors describer later, which are connected to the feeding shaft  20 , the front drive roller  31 , the rear drive roller  32 , and the winding shaft  40 , among the members for conveying the base material. 
     With regard to the tension control of the base material S, the control unit  100  rotates a feed motor M 20  that drives the feeding shaft  20  by a direct drive method, and thus feeds the base material S from the feeding shaft  20  to the front drive roller  31 . In this case, the control unit  100  controls a torque of the feed motor M 20 , and adjusts a tension (feed tension Ta) of the base material S from the feeding shaft  20  to the front drive roller  31 . In other words, the control unit  100  controls a torque of the feed motor M 20 , and adjusts the feed tension Ta in an area being the feeding section  2 . 
     A tension sensor S 22  that detects a magnitude of the feed tension Ta is mounted to the tension roller  22  arranged between the feeding shaft  20  and the front drive roller  31 . The tension sensor S 22  may be formed of, for example, a load cell that detects a magnitude of a force received from the base material S. Further, the control unit  100  performs feedback control of a torque of the feed motor M 20 , based on a detection result (detection value) of the tension sensor S 22 , and adjusts the feed tension Ta of the base material S. 
     Further, the control unit  100  rotates a front drive motor M 31  that drives the front drive roller  31  and a rear drive motor M 32  that drives the rear drive roller  32 . With this, the base material S fed from the feeding section  2  passes through the process section  3 . In this case, speed control is performed to the front drive motor M 31  whereas torque control is performed to the rear drive motor M 32 . Specifically, the control unit  100  performs feedback control of a rotational speed of the front drive motor M 31 , based on the encoder of the front drive motor M 31 , and thus adjusts a conveyance speed of the base material S. With this, the base material S is conveyed by the front drive roller  31  at a printing speed set as a conveyance speed of the base material S while performing printing. 
     Meanwhile, the control unit  100  controls a torque of the rear drive motor M 32 , and thus adjusts a tension (process tension Tb) of the base material S from the front drive roller  31  to the rear drive roller  32 . In other words, the control unit  100  controls a torque of the rear drive motor M 32 , and adjusts the process tension Tb in an area being the process section  3 . 
     The tension sensor S 34  that detects a magnitude of the process tension Tb is mounted to a tension roller  34  arranged between the platen drum  30  and the rear drive roller  32 . The tension sensor S 34  may be formed of, for example, a load cell that detects a magnitude of a force received from the base material S. Further, the control unit  100  performs feedback control of a torque of the rear drive motor M 32 , based on a detection result (detection value) of the tension sensor S 34 , and adjusts the process tension Tb of the base material S. 
     Further, the control unit  100  rotates a winding motor M 40  that drives the winding shaft  40  by a direct drive method, and thus the base material S, which is conveyed by the rear drive roller  32 , is wound round the winding shaft  40 . In this case, the control unit  100  controls a torque of the winding motor M 40 , and adjusts a tension (winding tension Tc) of the base material S from the rear drive roller  32  to the winding shaft  40 . In other words, the control unit  100  controls a torque of the winding motor M 40 , and adjusts the winding tension Tc in an area being the winding section  4 . 
     A tension sensor S 41  that detects a magnitude of the winding tension Tc is mounted to the tension roller  41  arranged between the rear drive roller  32  and the winding shaft  40 . The tension sensor S 41  may be formed of, for example, a load cell that detects a magnitude of a force received from the base material S. Further, the control unit  100  performs feedback control of a torque of the winding motor M 40 , based on a detection result (detection value) of the tension sensor S 41 , and adjusts the winding tension Tc of the base material S. 
     Particularly, the control unit  100  adjusts the tensions Ta, Tb. and Tc to printing tensions Ta 1 , Tb 1 , and Tc 1 , respectively, during a conveyance period in which the base material S is conveyed along with a printing operation. Further, the control unit  100  adjusts the tensions Ta, Tb. and Tc to standby tensions Ta 2 , Tb 2 , and Tc 2 , respectively during a standby period in which conveyance of the base material S is stopped without a printing operation. 
     Here, the standby tensions Ta 2 , Tb 2 , and Tc 2  are lower than the printing tensions Ta 1 , Tb 1 , and Tc 1 , respectively (Ta 2 &lt;Ta 1 , Tb 2 &lt;Tb 1 , Tc 2 &lt;Tc 1 ). Further, the printing tensions Ta 1 , Tb 1 , and Tc 1  may also be referred to as conveyance tensions required for conveying the base material S appropriately. 
     As described above, in the exemplary embodiment, feedback control is performed form a rotational speed of the front drive motor M 31 , and thus a conveyance speed at which the front drive roller  31  conveys the base material S is adjusted. Note that the exemplary embodiment has four types of printing speeds, and the control unit  100  as well as an input instruction by a user can perform setting to any of the printing speeds. In the exemplary embodiment, as the printing speeds, for example, the four types including 7.6 m/min, 15 m/min, 30 m/min, and 50 m/min can be set. Note that the printing speed can also be referred to as a conveyance speed of the base material S while performing printing. 
     Note that the printer  1  includes a storage unit  101  that stores various pieces of information. The storage unit  101  stores programs describing control procedures for performing the various types of control describe above. Therefore, the control unit  100  reads a required program from the storage unit  101 , and performs each of the various types of control described above. 
     When a sensor for detecting a foreign object (not shown) detects that a foreign object adheres to the front surface of the base material S to be conveyed, the printer  1  is required to perform an emergency stop of the printing operation before the foreign object is conveyed to the positions of the printing heads  51  and damages the printing heads  51 . Note that, in the exemplary embodiment, an emergency stop of the printing operation can also be referred to as an emergency stop of the conveyance operation. The exemplary embodiment solves a defect of the printer  1  at the time of an emergency stop of the conveyance operation. 
       FIG. 3  is a diagram illustrating a change of a tension at the time of an emergency stop in a printer using related-art tension control. Further,  FIG. 3  is a diagram illustrating a result of a test conducted by the inventors. 
     Note that an upper part of  FIG. 3  illustrates a time change of a tension imposed on the base material S, and a lower part illustrates a time change of a conveyance speed of the base material S. Note that the conveyance speed is a speed of the front drive roller  31  that is driven to rotate by the front drive motor M 31 . 
     The upper part of  FIG. 3  illustrates a case with the conveyance speed higher than that in the related art, and the tension control indicates a change of a tension with adaptation of the related-art control. In detail,  FIG. 3  illustrates a change of a tension with adaptation of the related control as the tension control in a case where the related-art conveyance speed (printing speed) at, for example, 7.6 m/min, is increased to 50 m/min. 
     Further, when an emergency stop is performed with the conveyance speed higher than that in the related art, it is required to stop the base material S so that a conveyance distance before a foreign object is convened to the positions of the printing heads  51  is equivalent to a conveyance direction to that in the related art (before increase of the speed). Thus, at the time of an emergency stop, it is required to increase deceleration more than that in the related art. In other words, at the time of an emergency stop, it is required to perform stopping with acceleration higher than that in the related art. As illustrated in the lower part of  FIG. 3 , in the test, an emergency stop of the conveyance operation is started at a time t 1 , and a conveyance speed of the base material S is at 0 m/min (conveyance stop) at the time t 2 . In this case, a deceleration time Δt 12  required for an emergency stop is shorter than that in the related art, and hence deceleration is increased. 
     As described above, in a case where the conveyance operation is stopped in emergency, when a predetermined tension (approximately 100N in  FIG. 3 ) is maintained as shown in the upper part of  FIG. 3 , the tension fluctuates once between the time t 1  and the time t 2  (during the deceleration time period Δt 12 ). Further, at a time t 3  when a several seconds passes after the conveyance speed is at 0 m/min (in the exemplary embodiment, approximately two seconds later), a sudden fluctuation of the tension (sudden rise of the tension) is caused. After that, the tension is controlled to return to the predetermined tension. Note that during the sudden fluctuation of the tension, as in the upper part of  FIG. 3 , the tension is changed from 100N to 300N. From this, it can be understood that the predetermined tension rises approximately three times. 
     In a case where the conveyance operation is stopped in emergency, when the feed motor M 20  being a second motor for controlling the tension, the rear drive motor M 32 , and the winding motor M 40  respectively performs control of the tension imposed on the base material S similarly to the related art, the motors are to rotate reversely to loosen the increased tension. Further, when slack is caused, the motors are to perform winding to eliminate the slack. Moreover, at the time of emergency stop, the stop is performed with acceleration higher than that in the related art so that the stop is performed with the same distance as that in the related art. With this, a motion due to the tension control described above stands out, which causes the tension to fluctuate suddenly.  FIG. 3  is a diagram illustrating the result. 
     As described above, when a sudden tension fluctuation is caused at the time of emergency stop, for example, a defect is caused to the steering mechanism  25 . The steering mechanism  25  is obtained by forming the feeding shaft  20 , the conveying shaft  24 , and the tension roller  22  as an integrated block through use of a fixing member (not shown), and is incorporated in the printer  1 . In this block, with the fixing member as a reference, the feeding shaft  20  and the tension roller  22  are subjected to alignment adjustment by screw fastening to be fixed. When a sudden tension fluctuation is caused at the time of emergency stop, a force stronger than a fastening force of the screw fastening part is imposed on the steering mechanism  25 , which deviates the alignment. When the alignment is deviated, the steering mechanism  25  is not operated normally. Thus, conveyance accuracy of the base material S is unstable, and a defect such as degradation of printing accuracy is caused. 
       FIG. 4  is a flowchart illustrating one example of control at the time of an emergency stop of in the printer  1  according to the exemplary embodiment.  FIG. 5  is a diagram illustrating a change of a tension at the time of an emergency stop in the printer  1  according to the exemplary embodiment. Note that  FIG. 5  is a diagram illustrating a result of a test conducted by the inventors. 
     An upper part of  FIG. 5  illustrates a time change of a tension imposed on the base material S, and a lower part illustrates a time change of a conveyance speed of the base material S. Note that the conveyance speed is a speed of the front drive roller  31 . Further, the upper part of  FIG. 5  illustrates change of a tension when the control in the exemplary embodiment is adapted in a case where the conveyance speed is at 50 m/min. With reference to  FIG. 4  and  FIG. 5 , control for stopping the conveyance operation in emergency in the exemplary embodiment will be described. 
     The flowchart in the exemplary embodiment is executed by the control unit  100 . 
     In Step S 101 , the control unit  100  issues an instruction of an emergency stop to the front drive motor M 31 . In other words, the control unit  100  issues an instruction of an emergency stop to the front drive motor M 31  being a first motor, which has a function of controlling the conveyance speed for conveying the base material S. In Step S 102 , it is determined whether the front drive motor M 31  is at 0 m/min being a conveyance speed for an emergency stop. Note that the determination is performed based on an output of the encode of the front drive motor M 31 . 
     When it is determined that the conveyance speed of the front drive motor M 31  is at 0 m/min in Step S 102  (“YES” in Step S 102 ), the process proceeds to Step S 103 . In contrast, when it is not determined that the conveyance speed of the front drive motor M 31  is at 0 m/min in the Step S 102  (“NO” in Step S 102 ), Step S 102  is repeated. 
     In Step S 103 , the control unit  100  stops the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors and have a function of controlling a tension imposed on the base material S (torque control). As described above, the tension control of the second motors having a function of controlling a tension is stopped at the time of an emergency stop, and thus a sudden rise of the tension can be suppressed. 
     Herein, Step S 102  and Step S 103  correspond to a tension control stop process in the printing method. Specifically, in the tension control stop process, when the control unit  100  stops the conveyance operation in emergency, the second drive motors (the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 ) stops control of the tension in a case where the speed of the first drive motor (the front drive motor M 31 ) is equal to or less than a predetermined value (in the exemplary embodiment, 0 m/min). 
     Note that as illustrated in the lower part of  FIG. 5 , in the test, an emergency stop of the conveyance operation is started at a time t 5 , and a conveyance speed of the base material S is at 0 m/min (conveyance stop) at the time t 6 . In this case, a deceleration time period Δt 56  required for an emergency stop is shorter than that in the related art with the conveyance speed of 7.6 m/min, and hence deceleration is increased. 
     As described above, in a case where the conveyance operation is stopped in emergency, when a predetermined tension (approximately 100N in  FIG. 5 ) is maintained as shown in the upper part of  FIG. 5 , a tension fluctuation due to decrease of the conveyance speed is caused between the time t 5  and the time t 6  (the deceleration time period Δt 56 ). Note that the fluctuation in this case is a fluctuation by 100N or less. 
     However, when the conveyance speed is at 0 m/min (conveyance stop), control performed by the second drive motors having a function of controlling a torque is stopped. With this, before causing a sudden tension fluctuation due to slack or tension under a state of performing the related-art tension control (see  FIG. 3 ), control performed by the second drive motors is stopped. Thus, a sudden rise of the tension can be prevented, and a tension fluctuation can be suppressed to a minimum degree. With such operation, even when the deceleration time period Δt 56  required for an emergency stop is shorter, and deceleration is increased as compared to the related art, a sudden tension fluctuation in a case where the conveyance operation is stopped in emergency can be suppressed. 
     Referring back to the flowchart of  FIG. 4 , in Step S 103 , the control unit  100  stops the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors and have a function of controlling a torque (turns off the tension control). After that, the process proceeds to Step S 104 . In Step S 104 , in order to count an elapsed time from the stop of the tension control, the control unit  100  starts measurement with a timer. 
     In Step S 105 , it is determined whether a measurement value is equal to or more than a predetermined measurement value, that is, whether a predetermined time period (for example, 180 seconds) has elapsed from the stop operation of the drive motors having a function of controlling a torque (tension control). When the measurement value is equal to or more than the predetermined measurement value (“YES” in Step S 105 ), the process proceeds to Step S 106 . In contrast, when the measurement value is less than the predetermined measurement value (“NO” in Step S 105 ), Step S 105  is repeated. 
     In Step S 106 , the control unit  100  starts the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors and have a function of controlling a torque, (turns on the tension control). The control unit  100  drives the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40  to start the tension control. With this, in the exemplary embodiment, the tensions Ta, Tb. and Tc are adjusted to the standby tensions Ta 2 , Tb 2 , and Tc 2 , respectively. 
     Here, Step S 104 , Step S 105 , and Step S 106  correspond to a tension control process in the printing method. Specifically, in the tension control process, when a predetermined time period passes after the control unit  100  stops the conveyance operation in emergency (when the tension control stop process is completed), the tension control performed by the second drive motors (the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 ) is started. 
     Note that, when the tensions Ta, Tb. and Tc are adjusted to the standby tensions Ta 2 , Tb 2 , and Tc 2 , respectively, the control unit  100  performs display indicating that a foreign object is required to be removed via a touch panel display or the like. A user recognizes the display, opens an exterior cover (not shown) of the printer  1 , and removes a foreign object adhering to the front surface of the base material S. In this case, the tensions are adjusted to the standby tensions Ta 2 , Tb 2 , and Tc 2 , and hence slack of the base material S is prevented. Thus, the foreign object can be removed easily from the base material S. 
     After the foreign object is removed, a user issues an instruction of starting printing with the input means. With this, the control unit  100  reads, from the storage unit  101 , a program for starting a conveyance operation (printing operation) after an emergency stop, and starts the conveyance operation (printing operation) by following the program. 
     As described above, according to the printer  1  and the printing method of the printer  1  according to the present exemplary embodiment, the following advantages can be achieved. 
     With the printer  1  according to the exemplary embodiment, in a case where the conveyance operation is stopped in emergency, when the speed of the front drive motor M 31  being a first motor, which has a function of controlling the conveyance speed for conveying the base material S is at 0 m/min, the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors and have a function of controlling a tension imposed on the base material S, is stopped. 
     With this, at the time of an emergency stop of a conveyance operation, a sudden tension fluctuation can be suppressed. Particularly, at the time of an emergency stop, a sudden rise of the tension can be suppressed. Note that a sudden tension fluctuation can be suppressed, and hence the alignment of the feeding shaft  20  and the tension roller  22  in the steering mechanism  25  is prevented from being deviated. With this, feeding accuracy of the base material S can be secured, and printing accuracy can be maintained. 
     Further, particularly, in a case where the printing speed (conveyance speed) of the printer  1  is increased, a sudden tension fluctuation can be suppressed at the time of an emergency stop, which is largely effective in maintaining printing quality. 
     With the printer  1  according to the exemplary embodiment, in a case where the conveyance operation is stopped in emergency, when a predetermined time period passes (in the exemplary embodiment, 180 seconds), the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors, is started. With this, the tension control is performed, and the base material S is adjusted to have the standby tensions Ta 2 , Tb 2 , and Tc 2 . 
     With this, in a case where a foreign object is detected and an emergency stop is performed, when a predetermined time period passes, the base material S is adjusted to have the predetermined tension. Thus, slack of the base material S can be prevented, and the foreign object can be removed easily. Further, when the foreign object is removed, the base material S is prevented from moving. Thus, a conveyance operation (printing operation) after removal of the foreign object can be started smoothly. 
     With the printing method of the printer  1  according to the exemplary embodiment, the control unit  100  performs the tension control stop process. Thus, in a case where the conveyance operation is stopped in emergency, when the speed of the front drive motor M 31  being a first motor, which has a function of controlling the conveyance speed for conveying the base material S is at 0 m/min, the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors and have a function of controlling a tension imposed on the base material S, is stopped. 
     With this, at the time of an emergency stop of a conveyance operation, a sudden tension fluctuation can be suppressed. Particularly, at the time of an emergency stop, a sudden rise of the tension can be suppressed. Further, a sudden tension fluctuation can be suppressed, and hence a defect of the conveyance mechanism system of the base material S can be suppressed. 
     Particularly, in a case where the printing speed (conveyance speed) of the printer  1  is increased, a sudden tension fluctuation can be suppressed at the time of an emergency stop, which is largely effective in maintaining printing quality. 
     With the printing method of the printer  1  according to the exemplary embodiment, the control unit  100  performs the tension control process. Thus, in a case where the tension control stop process is completed (a case where the conveyance operation is stopped in emergency), when the predetermined time period passes, the tension control performed by the feed motor M 20 , the rear drive motor M 32 , and the winding motor M 40 , which are the second motors, is started. With this, the tension control is performed, and the base material S is adjusted to have the standby tensions Ta 2 , Tb 2 , and Tc 2 . 
     With this, in a case where a foreign object is detected and an emergency stop is performed, when a predetermined time period passes, the base material S is adjusted to have the predetermined tension. Thus, slack of the base material S can be prevented, and the foreign object can be removed easily. Further, when the foreign object is removed, the base material S is prevented from moving. Thus, a conveyance operation (printing operation) after removal of the foreign object can be started smoothly. 
     Second Exemplary Embodiment 
       FIG. 6  is a schematic block diagram illustrating an electrical configuration for controlling a printer  1 A according to a second exemplary embodiment. 
     Similarly to the printer  1  according to the first exemplary embodiment, the printer  1 A according to the exemplary embodiment is a printing apparatus that conveys the base material S by a roll-to-roll method, and the base material S is wound in a roll shape around the feeding shaft  20  through intermediation of the core pipe  23  that is detachable from the feeding shaft  20 . Further, the base material S after completion of printing is wound around the winding shaft  40  via the core pipe  42  that is detachable from the winding shaft  40 . 
     Normally, a roll body having a large roll diameter (obtained by winding the base material S around the core pipe  23  or  42  in a roll shape) is rotated, and thus large inertia is generated. Further, when the inertia generated by the roll body is imposed on the front drive roller  31  via the base material S, responsiveness of the front drive motor M 31  at the time of acceleration and deceleration is degraded, and control accuracy is degraded. Thus, in the exemplary embodiment, the inertia due to a rotation of the roll body is considered at the time of an emergency stop, and thus a sudden tension fluctuation is suppressed. 
     As illustrated in  FIG. 6 , the printer  1 A according to the exemplary embodiment includes a roll diameter sensor S 20  provided to the feeding shaft  20  and a roll diameter sensor S 40  provided to the winding shaft  40 . The other matters are the same as the electrical configuration in the first exemplary embodiment. 
     Note that the roll diameter sensor S 20  detects a roll diameter of a roll body provided to the feeding shaft  20 . Similarly, the roll diameter sensor S 40  detects a roll diameter of a roll body provided to the winding shaft  40 . Further, in the exemplary embodiment, in a case where the conveyance operation is stopped in emergency, when an inertia mass equivalent to the base material S is changed in accordance with the detection values detected by the roll diameter sensors S 20  and S 40 , deceleration of the front drive motor M 31  being a first motor is controlled. 
     When the conveyance operation is stopped in emergency, the printer  1  according to the first exemplary embodiment controls deceleration of the front drive motor M 31  with inertia having a fixed value both on the feeding side and the winding side. However, the printer  1 A according to the exemplary embodiment performs feedback control with inertia having a variable value in accordance with the rolls diameters on the feeding side and the winding side (weight of the base material S in a roll shape). 
       FIG. 7  is a flowchart illustrating one example of control at the time of an emergency stop of in the printer  1 A. Specifically,  FIG. 7  is a flowchart for further developing Step S 101  in the flowchart (see  FIG. 4 ) described in the first exemplary embodiment. 
     As illustrated in  FIG. 7 , in Step S 201 , the control unit  100  detects the roll diameters with the roll diameter sensors S 20  and S 40 . Note that, in the exemplary embodiment, the control unit  100  uses the detection values detected by the roll diameter sensors S 20  and S 40  directly before the time of an emergency stop. 
     In the exemplary embodiment, specifically, a time period required for an emergency stop is set to less than one second. Further, feedback of the inertia is performed every one second. Therefore, the time period required for feedback of the inertia is longer than the time period required for an emergency stop. Thus, in the exemplary embodiment, the value of the inertia directly before the emergency stop is fed back at the time of the emergency stop. 
     Subsequently, in Step S 202 , the control unit  100  calculates the value of inertia in accordance of the roll diameters (weight of the base material S in a roll shape), based on the detection value detected in Step S 201 . Further, in Step S 203 , the control unit  100  calculates deceleration for driving the front drive motor M 31 , based on the inertial value calculated in Step S 202 . 
     With the deceleration calculated from the flowchart described above, the control unit  100  adjusts a torque of the front drive motor M 31  and performs an emergency stop. After that, the process proceeds to Step S 102  in the flowchart illustrated in  FIG. 4 , and a series of operation for an emergency stop is perform. 
     As described above, with the operations in Step S 201 , Step S 202 , and Step S 203 , at the time of an emergency stop, the inertia value is changed and fed back in accordance with the roll diameters (weight of the base material S in a roll shape) at that time, and thus deceleration of the front drive motor M 31  is controlled. 
     Note that Step S 201 , Step S 202 , and Step S 203  correspond to an inertia control process in the printing method. Specifically, in the inertia control process, the control unit  100  changes an inertia mass equivalent to the base material S at the time of an emergency stop, based on the detection values of the roll diameter sensors S 20  and S 40 , and controls the first drive motor (the front drive motor M 31 ) at the time of an emergency stop. 
     As described above, according to the printer  1 A and the printing method of the printer  1 A according to the present exemplary embodiment, the following advantages can be achieved. 
     The printer  1 A according to the exemplary embodiment includes the roll diameter sensors S 20  and S 40  that detect the roll diameters of the base material S in a roll shape. Further, the control unit  100  calculates an inertia amount equivalent to the base material S accordance with the detection values of the roll diameter sensors S 20  and S 40  directly before the emergency stop, and control deceleration of the front drive motor M 31  at the time of the emergency stop. 
     With this, at the time of the emergency stop, the inertia value is fed back in accordance with weight of the base material S in a roll shape (roll diameters) directly before the emergency stop, and deceleration of the front drive motor M 31  is controlled. Thus, as compared to the printer  1  according to the first exemplary embodiment, the inertia value can be optimized, and hence a sudden tension rise can further be suppressed efficiently. 
     With the printing method of the printer  1 A according to the exemplary embodiment, the control unit  100  performs the inertia control process. Thus, an inertia mass equivalent to the base material S is determined in accordance with the detection values of the roll diameter sensors S 20  and S 40 , and deceleration of the front drive motor M 31  at the time of an emergency stop is controlled. 
     With this, at the time of the emergency stop, the inertia value is fed back in accordance with weight of the base material S in a roll shape (roll diameters) directly before the emergency stop, and deceleration of the front drive motor M 31  is controlled. Thus, as compared to the printer  1  according to the first exemplary embodiment, the inertia value can be optimized, and hence a sudden tension rise can further be suppressed efficiently. 
     Note that, the present disclosure is not limited to the embodiments described above, and various modifications and improvements can be added to the above-described embodiments. Modifications are described below. 
     Modification 1 
     In the printer  1  and the printer  1 A according to the exemplary embodiments, in a case where the conveyance speed of the first drive motor (the front drive motor M 31 ), which has a function of controlling the conveyance speed, is at 0 m/min at the time of an emergency stop, the tension control performed by the second drive motors is stopped. However, the present disclosure is not limited thereto. In a case where the conveyance speed of the front drive motor M 31  is at a set speed or less (a predetermined value or less), the tension control performed by the second drive motors may be stopped. 
     Modification 2 
     In the flow chart of the exemplary embodiment, in Step S 105 , it is determined whether a predetermined time period (in the exemplary embodiment, 180 seconds) passes from the stop operation of the front drive motor M 31  having a function of controlling a torque. However, the predetermined time period may be freely changed. 
     Modification 3 
     In the printer  1 A according to the exemplary embodiment, the time period required for an emergency stop is less than one second, and the feedback of inertia is performed every one second. Therefore, the time period required for feedback of the inertia is longer than the time period required for an emergency stop. Thus, the value of the inertia directly before the emergency stop is fed back at the time of the emergency stop. However, the present disclosure is not limited thereto. In a case where the time period required for feedback of the inertia can be shorter than the time period required for an emergency stop, deceleration of the front drive motor M 31  can be adjusted by switching the inertia value during the process of the emergency stop in a stepwise manner or a smooth manner. With this, a tension rise can further be suppressed efficiently. 
     Contents derived from the exemplary embodiments and the modifications that are described above are described below. 
     A printing apparatus according to the present application configured to convey a base material by a roll-to-roll method and perform feedback control to a tension imposed on the base material, the printing apparatus includes a control unit, a first drive motor configured to control a conveyance speed for conveying the base material, and a second drive motor configured to control the tension imposed on the base material, wherein, in a case where a conveyance operation for conveying the base material is stopped in emergency, when a speed of the first drive motor is less than a predetermined value, the control unit stops control of the tension performed by the second drive motor. 
     With this configuration, in a case where the conveyance operation is stopped in emergency, when the speed of the first drive motor having a function of controlling the conveyance speed for conveying the base material is predetermined value or less, the tension control performed by the second drive motor having a function of controlling a tension imposed on the base material is stopped. Thus, at the time of an emergency stop, a sudden tension fluctuation can be suppressed. Particularly, at the time of an emergency stop, a sudden rise of the tension can be suppressed. 
     Further, a sudden tension fluctuation can be suppressed, and hence a defect of the conveyance mechanism system of the base material can be suppressed. 
     Particularly, in a case where the printing speed (conveyance speed) of the printing apparatus is increased, a sudden tension fluctuation can be suppressed at the time of an emergency stop, which is largely effective in maintaining printing quality. 
     In the printing apparatus described above, in a case where the conveyance operation is stopped in emergency, when a predetermined time period passes, the control unit may start control of the tension performed by the second drive motor. 
     With this configuration, in a case where the conveyance operation is stopped in emergency, when a predetermined time period passes, the tension control performed by the second drive motor is started. Thus, the base material is adjusted to have a predetermined tension. With this, slack of the base material is prevented, and the foreign object can be removed easily. Further, when the foreign object is removed, the base material is prevented from moving. Thus, a printing operation after removal of the foreign object can be started smoothly. 
     The printing apparatus described above may further include a roll diameter sensor configured to detect a roll diameter of the base material in a roll shape, and the control unit may change an inertia mass equivalent to the base material in accordance with a detection value of the roll diameter sensor, and control the first drive motor at the time of an emergency stop. 
     With this configuration, an inertia mass equivalent to the base material is changed in accordance with the detection value of the roll diameter sensor at the time of an emergency stop, and the first drive motor at the time of an emergency stop is controlled. Thus, with the optimized inertia value, deceleration of the first drive motor having a function of controlling the conveyance speed for conveying the base material can be controlled, and a sudden tension rise can further be suppressed efficiently. 
     A printing method according to the present application is a printing method of a printing apparatus being configured to convey a base material by a roll-to-roll method and perform feedback control to a tension imposed on the base material and including a control unit, a first drive motor configured to control a conveyance speed for conveying the base material, and a second drive motor configured to control the tension imposed on the base material. The printing method includes stopping control of the tension performed by the second drive motor in a case where a conveyance operation for conveying the base material is stopped in emergency, when a speed of the first drive motor is less than a predetermined value. 
     With this method, the control unit performs the tension control stop process. In a case where the conveyance operation is stopped in emergency, when the speed of the first drive motor is the predetermined value or less, the tension control performed by the second drive motor is stopped. Thus, at the time of an emergency stop, a sudden tension fluctuation can be suppressed. Particularly, at the time of an emergency stop, a sudden rise of the tension can be suppressed. 
     Further, a sudden tension fluctuation can be suppressed, and hence a defect of the conveyance mechanism system of the base material can be suppressed. 
     Particularly, in a case where the printing speed (conveyance speed) of the printing apparatus is increased, a sudden tension fluctuation can be suppressed at the time of an emergency stop, which is largely effective in maintaining printing quality. 
     In the printing method described above, after stopping control the control, the control unit may start control of the tension performed by the second drive motor when a predetermined time period passes. 
     With this method, the control unit performs the tension control process, in a case where the tension control stop process is completed, when a predetermined time period passes, the tension control performed by the second drive motor is started. Thus, the base material is adjusted to a predetermined tension. With this, slack of the base material can be prevented, and the foreign object can be removed easily. Further, when the foreign object is removed, the base material is prevented from moving. Thus, a printing operation after removal of the foreign object can be started smoothly. 
     In the printing method described above, the printing apparatus described above may further include a roll diameter sensor configured to detect a roll diameter of the base material in a roll shape, and the control unit may change an inertia mass equivalent to the base material in accordance with a detection value of the roll diameter sensor, and control the first drive motor at the time of an emergency stop. 
     With this method, the control unit performs the inertia control, and hence an inertia mass equivalent to the base material is changed in accordance with the detection value of the roll diameter sensor at the time of an emergency stop, and the first drive motor at the time of an emergency stop is controlled. Thus, with the optimized inertia value, deceleration of the first drive motor having a function of controlling the conveyance speed for conveying the base material can be controlled, and a sudden tension rise can further be suppressed efficiently.