Patent Publication Number: US-11040552-B2

Title: Heating device and drying method

Description:
BACKGROUND 
     The present disclosure relates to a heating device and a drying method. 
     JP-A-2000-135785 discloses a printing apparatus including a printing unit that executes printing by attaching a liquid such as ink to a medium, and a heating device that heats the medium on which the printing has been executed by the printing unit. The heating device includes a heating element that heats the medium and a control unit that controls the heating element. The heating element is disposed to face a processing surface, which is one of both front and rear surfaces of the medium and onto which the liquid is discharged. The processing surface of the medium is heated by the heating element, and the medium is dried. 
     SUMMARY 
     The medium has a temperature at which medium damage occurs. The medium damage refers to deformation or damage of the medium, and examples thereof include heat shrinkage of the medium. The temperature at which the medium damage occurs differs depending on the type of the medium. The control unit can suppress the occurrence of the medium damage by decreasing the output of the heating element for a medium in which the medium damage occurs at a lower temperature. However, when the output of the heating element is decreased to suppress the occurrence of the medium damage, the temperature of the processing surface decreases. Accordingly, a liquid evaporation amount decreases, thus decreasing the drying efficiency of the medium. 
     An advantage of the disclosure is to provide a heating device and a drying method that make it possible to suppress a decrease in the drying efficiency of a medium. 
     Hereinafter, measures for the above-described issues and advantages of the measures will be described. 
     According to one embodiment, a heating device configured to heat a medium on which a liquid is impinged, the heating device including a heating element configured to face a processing surface, the processing surface being a surface on which the liquid is impinged, a blower configured to blow gas to a heating region between the heating element and the processing surface from the heating element side of the medium, and a control unit configured to control an output of the heating element and a driving amount of the blower. The control unit changes the driving amount of the blower in accordance with a type of the medium while maintaining the output of the heating element constant regardless of the type of the medium. 
     In the above embodiment, the control unit changes the driving amount of the blower in accordance with the type of the medium. The wind speed of the gas blown by the blower increases as the driving amount of the blower increases. When the wind speed of the gas increases, it is possible to decrease the temperature of the processing surface. Since the control unit causes the output of the heating element to be constant regardless of the type of the medium, the temperature of the processing surface is controlled in accordance with the driving amount of the blower. Since the temperature at which the medium damage occurs differs depending on the type of the medium, it is possible to control the temperature of the processing surface in accordance with the type of the medium by changing the wind speed of the gas in accordance with the type of the medium. This makes it possible to suppress the occurrence of the medium damage in the medium. Further, when the wind speed of the gas increases, the temperature of the processing surface decreases, and liquid evaporation is accelerated accordingly. Therefore, it is possible to suppress the decrease in drying efficiency compared with a case where the temperature of the processing surface is controlled by changing the output of the heating element. 
     In another embodiment, the heating device further including a flow path. And in the heating device, the blower is provided in the flow path, and an outlet of the flow path through which gas is blown out by driving the blower is configured to face the processing surface. 
     In the above embodiment, it is possible to define a gas flowing direction by means of the flow path. It is possible to induce the gas toward the processing surface and improve drying efficiency. 
     In the heating device according to another embodiment, an inlet of the flow path through which gas flows into the flow path is configured to face the processing surface, and a part of the gas blown out of the outlet flows into the flow path from the inlet. 
     In the above embodiment, a part of the gas blown out of the outlet returns to the flow path from the inlet. That is, a part of the gas circulates. The gas blown out of the outlet is heated by passing through the heating region between the heating element and the processing surface. By circulating the heated gas, it is possible to improve drying efficiency. 
     In the heating device according to another embodiment, the control unit is configured to change the driving amount of the blower in accordance with an amount of the liquid impinged on the medium. 
     In the above embodiment, the wind speed of the gas blown on the processing surface changes in accordance with the amount of the liquid attached to the medium. The liquid evaporation amount required to dry the medium differs depending on the amount of the liquid attached to the medium. By changing the driving amount of the blower in accordance with the amount of the liquid attached to the medium, it is possible to appropriately dry the medium. 
     The heating device according to another embodiment is configured to heat the medium on which the liquid discharged from a head is impinged, the head being configured to discharge the liquid, and that the control unit is configured to change the driving amount of the blower in accordance with the number of passes of the head. 
     In the above embodiment, the wind speed of the gas blown on the processing surface changes in accordance with the number of passes of the head. In a case where the amount of liquid discharged onto the medium increases as the number of passes of the head increases, it is possible to change the driving amount of the blower in accordance with the amount of liquid discharged onto the medium by changing the driving amount of the blower in accordance with the number of passes of the head. This makes it possible to appropriately dry the medium. 
     In another embodiment, a drying method for drying a medium on which a liquid is impinged by heating the medium, the drying method including heating a processing surface on which the liquid is impinged by a heating element, the heating element having an output maintained constant, and blowing gas to the medium being heated, from the heating element side of the medium, at a wind speed corresponding to a type of the medium. According to this method, it is possible to suppress the decrease in the drying efficiency of the medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a side view schematically illustrating an exemplary embodiment of a printing apparatus. 
         FIG. 2  is an electric block diagram illustrating an electrical configuration of a printing apparatus. 
         FIG. 3  is a table in which each type of medium is associated with a medium damage upper limit temperature and the like. 
         FIG. 4  is a table in which each type of medium is associated with a wind speed of gas blown on a processing surface. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     One exemplary embodiment of a heating device included in a printing apparatus will be described below. 
     As illustrated in  FIG. 1 , a printing apparatus  11  includes a support unit  12  capable of supporting a medium  90 , a transport unit  13  that transports the medium  90  along the support unit  12 , a printing unit  14  that executes printing on the medium  90 , and a heating device  15  that heats the medium  90  after printing. The printing apparatus  11  is, for example, an ink jet-type printer that prints an image such as characters and photographs on the medium  90  by impinging ink, which is an example of a liquid, to the medium  90 . The medium  90  is, for example, a long medium such as continuous paper. 
     The support unit  12  includes a first support plate  16 , a second support plate  17 , and a third support plate  18 . The first support plate  16  includes a support surface  19  for supporting the medium  90  transported by the transport unit  13 . The second support plate  17  includes a support surface  20  for supporting the medium  90  transported by the transport unit  13 . The third support plate  18  includes a support surface  21  for supporting the medium  90  transported by the transport unit  13 . The first support plate  16 , the second support plate  17 , and the third support plate  18  are arranged in this order in a transport direction of the medium  90 . Note that, in the following descriptions, descriptions will be made assuming that the transport direction of the medium  90  is a transport direction Y. The second support plate  17  faces the printing unit  14  and the third support plate  18  faces the heating device  15 . 
     The transport unit  13  includes a first rotation shaft  22  located upstream of the first support plate  16  in the transport direction Y of the medium  90 , and a second rotation shaft  23  located downstream of the third support plate  18  in the transport direction Y of the medium  90 . The first rotation shaft  22  rotatably supports a roll body R 1  around which the medium  90  before printing is wound and rolled into a cylindrical shape. The second rotation shaft  23  rotatably supports a roll body R 2  around which the medium  90  after printing is rolled into a cylindrical shape. Transport rollers  24  are disposed between the first support plate  16  and the second support plate  17 , and between the second support plate  17  and the third support plate  18 . The transport rollers  24  transport the medium  90  by rotating while in contact with the medium  90 . 
     The printing unit  14  includes a head  25  that discharges a liquid such as ink, a carriage  26  that holds the head  25 , and a guide shaft  27  that guides the movement of the carriage  26 . The head  25  is disposed to face the second support plate  17 , and is capable of discharging the liquid onto the medium  90  supported by the second support plate  17 . That is, the head  25  is capable of discharging the liquid while reciprocally moving along the guide shaft  27  extending in a direction intersecting the transport direction Y. Further, the printing unit  14  prints an image such as characters and graphics on the medium  90  by impinging the liquid discharged from the head  25  on the medium  90 . 
     Of both front and rear surfaces of the medium  90 , the surface on which the liquid discharged from the head  25  is impinged is a processing surface  91 . The processing surface  91  of the present exemplary embodiment is a surface, of both front and rear surfaces of the medium  90 , facing the head  25  when the medium  90  is supported by the support surface  20  of the second support plate  17 . 
     The heating device  15  heats the medium  90  printed with the image by the printing unit  14  and transported by the transport unit  13 . Specifically, the heating device  15  heats the processing surface  91  of the medium  90  supported by the third support plate  18 , evaporates the liquid impinged on the medium  90  by the heating, and dries the medium  90 . 
     The heating device  15  faces the support surface  21  of the third support plate  18 . The heating device  15  is disposed apart from the support surface  21 . A space between the support surface  21  and the heating device  15  is a heating region  30  that is heated by the heating device  15 . The medium  90  transported by the transport unit  13  passes through the heating region  30 . 
     The heating device  15  will be described in detail below. 
     i. The heating device  15  includes a heating unit  41  for heating the medium  90 , a housing  42  that accommodates the heating unit  41 , and a blower  43  for blowing gas. The heating unit  41  heats the medium  90  supported by the support surface  21  of the third support plate  18 . The heating unit  41  is disposed at a position facing the support surface  21 . The heating unit  41  includes heater tubes  45 , which is an example of a heating element capable of generating heat. The two heater tubes  45  of the present exemplary embodiment are arranged side by side in the transport direction Y. The heater tubes  45  are capable of facing the processing surface  91  of the medium  90  supported by the third support plate  18 . 
     The heating unit  41  may include reflection plates  46  for reflecting infrared rays of the heater tubes  45 . In this case, the reflection plates  46  are preferably disposed to surround a portion of the circumferential surface of the heater tubes  45  not facing the support surface  21 . The reflection plates  46  reflect infrared rays generated by the heater tubes  45  toward the support surface  21 . Note that, in a case where the reflection plates  46  are included, the range of the heating region  30  changes in accordance with the positions of the heater tubes  45  and the reflection plates  46 . 
     The housing  42  includes an inner wall  51  surrounding the heating unit  41 , and an outer wall  52  surrounding the inner wall  51 . The outer wall  52  is disposed outside the inner wall  51 . A flow path  44  in which gas flows is sectioned between the inner wall  51  and the outer wall  52 . It is considered that the housing  42  includes the flow path  44 . Both ends of the flow path  44  open toward the support surface  21 . 
     The flow path  44  is sectioned to surround the heating unit  41 . The flow path  44  includes an inlet  53  for causing gas to flow into the flow path  44 , and an outlet  54  for blowing out the gas from the flow path  44 . In the other words, the flow path  44  includes the inlet  53  through which the gas flow into the flow path  44 , and the outlet  54  through which the gas blowing out from the flow path  44 . The inlet  53  and the outlet  54  open toward the heating region  30 . This causes the flow path  44  of the gas to communicate with the heating region  30  for heating the medium  90 . 
     The blower  43  is disposed in the flow path  44 . The blower  43  causes the gas in the flow path  44  to flow toward the outlet  54 . Further, by the blower  43  causing the gas in the flow path  44  to flow, the gas flows into the flow path  44  from the inlet  53 . The gas in the flow path  44  is, for example, air. 
     The inlet  53  is located at a position that is in a first direction from the heating unit  41 , the first direction is along the transport direction Y and the first direction is opposite to a direction, along the transport direction Y, from the heating unit  41  to the printing unit  14 . That is, the inlet  53  is located downstream from the heating unit  41  in the transport direction Y. The outlet  54  is located on a side of the heating unit  41  in the transport direction Y, on which the printing unit  14  is located. That is, the outlet  54  is located upstream from the heating unit  41  in the transport direction Y. 
     The outlet  54  opens downstream from the outlet  54  in the transport direction Y. In other words, the outlet  54  opens such that the gas blown out of the outlet  54  flows to a position downstream from the outlet  54 , at which the inlet  53  is located. 
     After being blown onto the medium  90  supported by the support surface  21 , the gas blown out of the outlet  54  flows in the transport direction Y along the processing surface  91  as indicated by an arrow A in  FIG. 1 . The inlet  53  and the outlet  54  open at positions at which it is possible to face the processing surface  91  of the medium  90 . Thus, the gas blown out of the outlet  54  is blown out toward the processing surface  91 . It is considered that the blower  43  is capable of blowing the gas from the heater tube side of the medium, on which the heater tube  45  is disposed, toward the heating region  30 . 
     A part of the gas blown out of the outlet  54  and flowing along the processing surface  91  flows into the inlet  53  as indicated by an arrow B. That is, a part of the gas circulates in the flow path  44  and the heating region  30 . It is considered that the flow path  44  and the heating region  30  constitute a circulation path  55  of the gas. A part of the gas blown out of the outlet  54  and flowing along the processing surface  91  is discharged from between the inlet  53  and the support surface  21  to the outside of the circulation path  55  as indicated by an arrow C. 
     The gas circulating in the circulation path  55  is heated by the heating unit  41 . This causes the temperature of the gas blown out of the outlet  54  to be higher than that in a case where the gas is not caused to circulate. That is, since the gas heated by the heating unit  41  is contained in the gas flowing along the processing surface  91 , the temperature of the gas flowing along the processing surface  91  becomes higher than that in a case where the gas is not caused to circulate. Further, the flow path  44  is located to surround the heating unit  41 , and thus, the temperature in the flow path  44  increases due to the heat generated by the heating unit  41 . By the circulating gas passing through the flow path  44 , the heat generated by the heater tubes  45  can be collected and reused for drying. 
     When the heating unit  41  heats the medium  90 , vapor is generated by the evaporation of the liquid impinged on the medium  90 . When the humidity of the circulation path  55  is increased due to the vapor, the medium  90  is hard to dry. Therefore, the heating device  15  discharges the vapor with a part of the gas blown out of the outlet  54  to the outside of the circulation path  55  from between the inlet  53  and the support surface  21 . Thus, the increase in humidity in the circulation path  55  is suppressed. 
     The heating device  15  dries the medium  90  by blowing gas onto the medium  90  while heating the medium  90  supported by the support surface  21 . That is, when the medium  90  after printing is transported along the support unit  12  and reaches the heating region  30  between the heating device  15  and the support surface  21 , the evaporation of the liquid impinged on the medium  90  is promoted by the heat generated by the heater tubes  45  and the gas blown out of the outlet  54 . It is considered that the heating device  15  dries the processing surface  91  by the radiant heat from the heater tubes  45  and the gas blown by the blower  43 . 
     Next, an electrical configuration of the printing apparatus  11  will be described. 
     As illustrated in  FIG. 1  and  FIG. 2 , the printing apparatus  11  includes a control unit  60 . The control unit  60  includes a CPU  61  and a storage unit  62  constituted of a RAM, a ROM, etc. Various programs for controlling the printing apparatus  11  are stored in the storage unit  62 . The control unit  60  may include dedicated hardware (Application Specific Integrated Circuit: ASIC) that executes at least a part of processing among the various types of processing. 
     That is, the control unit  60  can be configured as one or more processors that operate in accordance with a computer program (software), one or more dedicated hardware circuits such as an ASIC, etc., or a circuit including a combination of the processors and the dedicated hardware circuits. The processors include a CPU and a memory such as a RAM, a ROM, etc. The memory stores a program code or a command configured to cause the CPU to execute processing. The memory, i.e., a computer-readable medium includes anything that can be accessed by a general-purpose or dedicated computer. 
     The heating device  15  includes a motor  71  for driving the blower  43 , and a driving circuit  72  for driving the motor  71 . The driving circuit  72  is a motor driver that controls the driving amount of the blower  43  by controlling the voltage applied to the motor  71 . Note that, as the driving circuit  72 , a driving circuit that controls the driving amount of the blower  43  by executing PWM control may be used. That is, the driving circuit  72  may be a driving circuit capable of controlling the driving amount of the blower  43  by controlling the motor  71 . 
     The heater tubes  45 , the driving circuit  72 , the transport unit  13 , and the printing unit  14  are electrically connected to the control unit  60 . The control unit  60  operates the printing apparatus  11  by controlling the heater tubes  45 , the driving circuit  72 , the transport unit  13 , and the printing unit  14 . The control unit  60  controls the heater tubes  45  and the driving circuit  72 , which are a part of the heating device  15 , and thus, it is considered that the control unit  60  is a part of the heating device  15 . 
     The printing apparatus  11  includes an input unit  63  connected to the control unit  60 . The input unit  63  is for inputting, to the control unit  60 , the type of the medium  90  on which printing is executed by the printing unit  14 . The input unit  63  is, for example, an operation panel operated by the user of the printing apparatus  11 . The control unit  60  controls the driving circuit  72  in accordance with the type of the medium  90  input by the input unit  63 . Thus, the voltage applied to the motor  71  changes in accordance with the type of the medium  90 , and the driving amount of the blower  43  is changed in accordance with the type of the medium  90 . The wind speed of the gas blown by the blower  43  changes in accordance with the driving amount of the blower  43 . The wind speed of the gas blown by the blower  43  increases as the driving amount of the blower  43  increases. The control of the heating device  15  executed by the control unit  60  when drying the medium  90  will be described in detail below. 
     The control unit  60  controls the output of the heater tubes  45 . The control unit  60  keeps the output of the heater tubes  45  constant regardless of the type of the medium  90 . In the present exemplary embodiment, the output of the heater tubes  45  is kept at the maximum output, i.e., 100%. Note that “constant” here includes the fluctuation of the output to such an extent that there is no effect on the temperature generated by the heater tubes  45  or that the effect on the temperature generated by the heater tubes  45  can be ignored. That is, “constant” includes the fluctuation of the output to such an extent that there is no effect on the drying of the medium  90 . 
     The control unit  60  changes the wind speed of the gas flowing in the heating region  30  in accordance with the type of the medium  90  by changing the driving amount of the blower  43  in accordance with the type of the medium  90 . Further, the control unit  60  changes the driving amount of the blower  43  in accordance with the amount of liquid discharged onto the medium  90  in addition to the type of the medium  90 . The control unit  60  controls the surface temperature of the medium  90 , i.e., the temperature of the processing surface  91  by changing the wind speed of the gas while keeping the output of the heater tubes  45  constant. The control unit  60  controls the driving amount of the blower  43  such that the temperature of the processing surface  91  does not exceed an acceptable temperature and a liquid evaporation amount required to dry the medium  90  can be secured. 
     The liquid evaporation amount required to dry the medium  90  differs depending on the amount of liquid discharged onto the medium  90  and the type of the medium  90 .  FIG. 3  illustrates, as an example, liquid evaporation amounts required to dry the medium  90  in a case where ink is used as a liquid in association with the types of the medium  90  and liquid amounts. Further,  FIG. 3  illustrates, in association with the types of the medium  90 , medium damage upper limit temperatures, the relationship between wind speeds and the temperatures of the processing surface  91 , the relationship between wind speeds and the temperatures of the gas circulating in the circulation path  55 , the relationship between wind speeds and liquid evaporation amounts, etc. Note that the numerical values in the table illustrated in  FIG. 3  are examples, and each numerical value can change depending on various elements, such as an environment temperature, the blowing amount of the blower  43 , and the size of the heating region  30  in the transport direction Y. 
     As illustrated in  FIG. 3 , the liquid evaporation amount required to dry the medium  90  differs depending on the amount of liquid discharged onto the medium  90  and the type of the medium  90 . The amount of liquid discharged onto the medium  90  differs depending on the number of passes of the head  25 , an image resolution, etc. The number of passes of the head  25  refers to the number of printing operations executed by the head  25  for one printing area. That is, it is also considered that the number of passes is the number of times of scanning executed by the head  25  for printing the one printing area. There is a case where the amount of liquid discharged onto the medium  90  increases as the number of passes increases. The liquid evaporation amount required to dry the medium  90  increases as the amount of liquid increases. 
     Further, the medium damage upper limit temperature differs depending on the type of the medium  90 . In  FIG. 3 , as examples of the medium  90 , polyvinyl chloride, banner (banner flag), backlit (backlight film), textile, coated paper, and wallpaper are listed. Note that each type of the medium  90  illustrated in  FIG. 3  is a generic type including a plurality of media  90 . For example, in a case of polyvinyl chloride, a polyvinyl chloride A and a polyvinyl chloride B have different specifications, and can be considered as different media  90 . In the following descriptions, as appropriate, descriptions will be made by referring to categories each including a plurality of media  90 , such as polyvinyl chloride, banner, backlit material, textile, coated paper, and wall paper as large categories, and by referring to categories for individual media  90  of each medium  90  included in the large categories, such as the polyvinyl chloride A and the polyvinyl chloride B as small categories. 
     Medium damage refers to the deformation or damage of the medium  90 , and the examples of the medium damage include the heat shrinkage of the medium  90 . The medium  90  has a temperature at which the medium damage occurs. The temperature at which the medium damage occurs is determined by the temperature characteristics of a material constituting the medium  90 . Since the material differs depending on the type of the medium  90 , the temperature at which the medium damage occurs differs depending on the type of the medium  90 . Further, even the media  90  belonging to the same large category have different specifications. For example, as illustrated in  FIG. 3 , in the case of polyvinyl chloride, the polyvinyl chloride A and the polyvinyl chloride B have different specifications, and temperatures at which the medium damage occurs are also different. 
     For the medium  90 , a medium damage upper limit temperature is set considering the above-described temperature at which the medium damage occurs. The medium damage upper limit temperature is an upper limit of a temperature at which the medium damage occurring in the medium  90  is acceptable. For example, an acceptable temperature of the processing surface  91  is the medium damage upper limit temperature. Note that, considering a margin, etc., the acceptable temperature of the processing surface  91  may be a temperature lower than the medium damage upper limit temperature. That is, the acceptable temperature of the processing surface  91  can be set, as appropriate, within a range from a temperature at which the medium damage starts to occur to the medium damage upper limit temperature. Further, the control unit  60  controls the temperature of the processing surface  91  such that the temperature of the processing surface  91  does not exceed the acceptable temperature. 
     As illustrated in  FIG. 3 , the temperature rise of the processing surface  91  can be suppressed by increasing the wind speed of the gas blown by the blower  43 . This is because a heat amount removed from the heater tubes  45  increases by increasing the wind speed, and because a gas temperature decreases as the ventilation rate of the circulation path  55  increases. The control unit  60  is capable of controlling the temperature of the processing surface  91  by changing the wind speed. 
     As illustrated in  FIG. 4 , the control unit  60  changes the wind speed of the gas, i.e., the driving amount of the blower  43  in accordance with the type of the medium  90  belonging to the large category. The storage unit  62  stores voltage information in association with the type of the medium  90  belonging to the large category. The control unit  60  controls the driving circuit  72  such that a voltage corresponding to the type of the medium  90  set by the input unit  63  is applied to the blower  43 . By doing so, the blower  43  is controlled to have a wind speed corresponding to the type of the medium  90 . In the present exemplary embodiment, the control unit  60  controls the driving circuit  72  to provide, among wind speeds at which the liquid evaporation amount required to dry the medium  90  can be secured, a wind speed at which the temperature of the processing surface  91  becomes the lowest. 
     Further, even in a case where the same medium  90  is dried, the control unit  60  changes the wind speed of the gas, i.e., the driving amount of the blower  43  in accordance with the amount of liquid discharged onto the medium  90 . For example, as illustrated in  FIG. 4 , in a case where printing on a polyvinyl chloride is executed, the amount of liquid becomes less in a case of a seven-pass printing mode than in a case of a nine-pass printing mode (the number of passes of the head  25  is set to nine) and the liquid evaporation amount required to dry the medium  90  also becomes less in the case of the seven-pass printing mode than in the case of the nine-pass printing mode. In the example illustrated in  FIG. 4 , the printing speed in the nine-pass printing mode is slower than the printing speed in the seven-pass printing mode. Drying in the nine-pass printing mode takes longer than in the seven-pass printing mode, and thus, the temperature of the processing surface  91  is easier to rise in the nine-pass printing mode. The control unit  60  suppresses the temperature rise of the processing surface  91  by causing the wind speed in the nine-pass printing mode to be faster than the wind speed in the seven-pass printing mode, thus suppressing the occurrence of the medium damage. It is considered that the control unit  60  changes the driving amount of the blower  43  in accordance with the number of passes of the head  25 . 
     Here, it is also possible to control the temperature of the processing surface  91  by causing the driving amount of the blower  43  to be constant and changing the output of the heater tubes  45  in accordance with the type of the medium  90 . However, in a case where the temperature of the processing surface  91  is controlled by changing the output of the heater tubes  45 , the occurrence of the medium damage can be suppressed, but drying ability tends to be insufficient. For example, in the part indicated by frame F 1  in  FIG. 3 , examples are provided for cases that the surface temperature of the banner is made 90° C. by changing the output of the heater tubes  45  and that the surface temperature of the banner is made 90° C. by changing the driving amount of the blower  43 . It can be seen that the drying ability is higher and the liquid evaporation amount is greater in the case where the output of the heater tubes  45  is changed than in the case where the driving amount of the blower  43  is changed even if the surface temperatures of the processing surface  91  of the banner are the same temperature. This is because the volatilization effect caused by the blown gas increases by increasing the wind speed to decrease the temperature of the processing surface  91 , and because the humidity around the processing surface  91  decreases as the ventilation rate of the circulation path  55  increases. 
     Further, as indicated in frame F 2  and frame F 3  in  FIG. 3 , a similar issue can occur in the case where the temperature of the processing surface  91  is controlled by changing the output of the heater tubes  45  even in a case where the medium  90  is made of a backlit material or textile. 
     As described above, in the case where the output of the heater tubes  45  is changed while causing the wind speed of the gas to be constant, it is difficult to suppress the occurrence of the medium damage and provide high drying efficiency. As a result, in order to secure the liquid evaporation amount required to dry the processing surface  91 , printing needs to be executed at a slower speed than the printing speed indicated in  FIG. 3 , and productivity decreases accordingly. 
     Meanwhile, in the case where the driving amount of the blower  43  is changed while maintaining the output of the heater tubes  45  constant, it is possible to suppress the temperature rise of the processing surface  91 , and suppress the decrease in drying efficiency caused by the suppression of the temperature rise of the processing surface  91 . That is, it is possible to suppress the occurrence of the medium damage and suppress the insufficiency of drying ability. As a result, it is possible to cause the printing speed to be faster than the printing speed in the case where the output of the heater tubes  45  is changed while causing the wind speed of the gas to be constant. 
     Next, the operation of the heating device  15  and a drying method using the heating device  15  will be described. 
     i. In a case where printing on the medium  90  is executed by means of the printing apparatus  11 , a user of the printing apparatus  11  selects the type of the medium  90  by means of the input unit  63 . When the printing apparatus  11  executes the printing, the control unit  60  controls driving circuit  72  to provide a wind speed corresponding to the type of the medium  90  input by the input unit  63  and a liquid amount. Further, the control unit  60  keeps the output of the heater tubes  45  constant. 
     By doing so, in the drying method using the heating device  15 , the processing surface  91  of the medium  90  is heated by the radiant heat from the heater tubes  45  the output of which is kept constant. Further, the gas blown out of the outlet  54  to the medium  90  being heated is blown from the heater tube side of the medium  90 . 
     i. By changing the driving amount of the blower  43  in accordance with the type of the medium  90 , the wind speed of the gas blown on the processing surface  91  becomes a wind speed corresponding to the type of the medium  90 . 
     According to the exemplary embodiment described above, the following advantages can be obtained. 
     (1) The control unit  60  changes the driving amount of the blower  43  in accordance with the type of the medium  90 . The wind speed of the gas blown by the blower  43  increases as the driving amount of the blower  43  increases. When the wind speed of the gas increases, it is possible to decrease the temperature of the processing surface  91 . The control unit  60  causes the output of the heater tubes  45  to be constant regardless of the type of the medium  90 , and thus, the temperature of the processing surface  91  is controlled in accordance with the driving amount of the blower  43 . Since the temperature at which the medium damage occurs differs depending on the type of the medium  90 , it is possible to control the temperature of the processing surface  91  in accordance with the type of the medium  90  by changing the wind speed of the gas in accordance with the type of the medium  90 . This makes it possible to suppress the occurrence of the medium damage in the medium  90 . Further, when the wind speed of the gas increases, the humidity around the processing surface  91  decreases, and liquid evaporation is accelerated accordingly. Therefore, it is possible to suppress the decrease in drying efficiency compared with the case where the temperature of the processing surface  91  is controlled by changing the output of the heater tubes  45 . 
     (2) It is possible to define a gas flowing direction by means of the flow path  44 . It is possible to induce the gas toward the processing surface  91  and improve drying efficiency. 
     (3) A part of the gas blown out of the outlet  54  returns to the flow path  44  from the inlet  53 . That is, a part of the gas circulates. The gas blown out of the outlet  54  is heated by passing through the heating region  30  between the heater tubes  45  and the processing surface  91 . By circulating the heated gas, it is possible to improve drying efficiency. 
     (4) The wind speed of the gas blown on the processing surface  91  changes in accordance with the amount of liquid discharged onto the medium  90 . The liquid evaporation amount required to dry the medium  90  differs depending on the amount of liquid discharged onto the medium  90 . By changing the driving amount of the blower  43  in accordance with the amount of liquid discharged onto the medium  90 , it is possible to appropriately dry the medium  90 . 
     (5) The wind speed of the gas blown on the processing surface  91  changes in accordance with the number of passes of the head  25 . 
     In a case where the amount of liquid discharged onto the medium  90  increases as the number of passes of the head  25  increases, it is possible to change the driving amount of the blower  43  in accordance with the amount of liquid discharged onto the medium  90  by changing the driving amount of the blower  43  in accordance with the number of passes of the head  25 . This makes it possible to appropriately dry the medium  90 . 
     The exemplary embodiment described above may be modified as follows. Modifications described below may be appropriately combined.
         As described in the exemplary embodiment, the amount of liquid discharged onto the medium  90  differs depending on a resolution. Thus, the control unit  60  may cause the driving amount of the blower  43  to be different in accordance with the resolution.   The control unit  60  may control the driving amount of the blower  43  in accordance with the type of the medium  90  regardless of the amount of liquid discharged onto the medium  90 . That is, the control unit  60  may control the driving amount of the blower  43  in accordance with at least the type of the medium  90 .   The inlet  53  may not open at a position capable of facing the processing surface  91 . For example, the inlet  53  may open to take in the gas from the outside of the heating region  30 . In this case, the gas blown by the blower  43  may not circulate.   The blower  43  may blow the gas to the processing surface  91  without the intervention of the flow path  44 . For example, the blower  43  may be disposed to face the processing surface  91  such that the gas is blown on the processing surface  91  when the blower  43  is driven. In this case, the housing  42  may not include the flow path  44 .   The gas may be blown by means of a pump instead of the blower  43 . That is, the printing apparatus  11  may include a generation device that generates air flow.       

     The type of the medium  90  may be specified by a host device communicably connected to the printing apparatus  11  through wire or radio wave. By operating the host device, a print job is instructed to the printing apparatus  11 . The print job includes various commands required for the print control, print condition information of printing conditions such as a print mode designated by the user, and print image data. By including the type of the medium  90  in the printing condition information, it is possible for the host device to specify the type of the medium  90 .
         The printing apparatus  11  may include a recognition unit that recognizes the type of the medium  90 . The recognition unit may recognize the type of the medium  90  by reading, for example, a mark such as a bar code or a QR code (registered trademark) attached to the medium  90 . Further, the recognition unit may recognize the type of the medium  90  from imaging data obtained by imaging the medium  90 . The control unit  60  controls the driving amount of the blower  43  in accordance with the type of the medium  90  recognized by the recognition unit.   The control unit  60  may change the driving amount of the blower  43  in accordance with the medium  90  belonging to the small category such as the polyvinyl chloride A or the polyvinyl chloride B. For example, the control unit  60  may cause the driving amount of the blower  43  to be greater in a case where the polyvinyl chloride A is dried than in a case where the polyvinyl chloride B is dried. By doing so, it is possible to set the driving amount of the blower  43  appropriate for the medium  90  more finely.       

     Note that the driving amount of the blower  43  corresponding to the medium  90  belonging to the small category may be obtained through a network. For example, as initial settings, the medium  90  belonging to the large category and the driving amount of the blower  43  associated with the medium  90  belonging to the large category are stored in the storage unit  62 . When a user obtains the medium  90  by purchasing the medium  90 , etc., the user obtains the driving amount of the blower  43  corresponding to the medium  90  through a network. By doing so, the driving amount of the blower  43  corresponding to the medium  90  possessed by the user is stored in the storage unit  62 .
         In a case where the heating device  15  includes a plurality of blowers  43 , the control unit  60  may control the driving amount of each of the blowers  43  in accordance with the type of the medium  90 . That is, the control unit  60  may be capable of causing the wind speed of the gas flowing in the heating region  30  to be a speed corresponding to the type of the medium  90 , and in a case where there are a plurality of blowers  43  that affect the wind speed of the gas flowing in the heating region  30 , the wind speed may be changed by changing the driving amounts of the plurality of blowers  43 .   As described in the exemplary embodiment, when the liquid evaporation amount required to dry the medium  90  decreases, the medium  90  can be dried even when the temperature of the processing surface  91  is decreased. Thus, in a case where the printing speed of the seven-pass printing mode and the printing speed of the nine-pass printing mode are the same, the control unit  60  may cause the driving amount of the blower  43  to be greater in the seven-pass printing mode than in the nine-pass printing mode. The control unit  60  can suppress the temperature rise of the processing surface  91  by increasing the wind speed as the number of passes decreases, i.e., as the amount of liquid discharged onto the medium  90  decreases.   The output of the heater tubes  45  may be constant and may be kept at, for example, 90%.   The driving amount of the blower  43  corresponding to the type of the medium  90  may be changed, as appropriate, within a range in which the temperature of the processing surface  91  does not exceed an acceptable temperature, and in which the liquid evaporation amount required to dry the medium  90  can be secured.   A control unit that controls the heating device  15  and a control unit that controls the printing unit  14  or the transport unit  13  may be provided separately.   The heating device  15  may be detachably mounted to the printing apparatus  11 .   The printing apparatus  11  may execute printing on the medium  90  by using other methods than the method in which the liquid discharged from the head  25  is supplied to the medium  90 , such as a method in which liquid on a stencil is transferred onto the medium  90 .   The heating element included in the heating unit  41  is not limited to the heater tubes  45 , and may be a heating wire, a heat source lamp, and the like.   The liquid discharged by the printing unit  14  is not limited to ink, and may be, for example, a liquid material in which particles of a functional material are dispersed or mixed in a liquid. For example, the printing unit  14  may discharge a liquid material containing a material such as an electrode material or a color material (pixel material) used in the manufacture of liquid crystal displays, electroluminescent (EL) displays, surface emitting displays, and the like in a dispersed or dissolved form.   The printing apparatus  11  may be a page printer that executes printing page-by-page.   The heating device  15  may be used to promote drying of objects other than a printed medium.       

     This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-042971, filed Mar. 9, 2018. The entire disclosure of Japanese Patent Application No. 2018-042971 is hereby incorporated herein by reference.