Patent Publication Number: US-2021166919-A1

Title: Plasma generation device and plasma head cooling method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a plasma generation device and a plasma head cooling method for cooling a plasma head. 
     BACKGROUND ART 
     In the conventional art, regarding a plasma generation device and a plasma head cooling method, various techniques for cooling a plasma head have been proposed. 
     For example, in an atmospheric-pressure plasma generation device disclosed in Patent Literature 1, the supply of an inert gas to a reaction chamber is stopped on the condition that a set time has elapsed after application of a voltage to electrodes is stopped. In other words, even after the application of the voltage to the electrodes is stopped and discharging disappears, the inert gas is supplied to the reaction chamber for the set time. Consequently, it is possible to prevent oxidation of the electrodes. 
     PATENT LITERATURE 
     
         
         Patent Literature 1: International Publication No. WO 2014/188592 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     Thereafter, when a body including the electrodes and the reaction chamber is cooled, the maintenance by a user becomes possible, but it is desirable that the body is cooled more preferably. 
     Therefore, the present disclosure has been made in light of the circumstances, and an object thereof is to provide a plasma generation device and a plasma head cooling method capable of appropriately cooling a plasma head. 
     Solution to Problem 
     The present specification discloses a plasma generation device including a plasma head configured to eject plasma gas that is plasmatized; a gas supply device configured to supply gas serving as the plasma gas to the plasma head; a pair of electrodes, being provided in the plasma head, which is configured to perform discharging to a part of the gas supplied from the gas supply device so as to generate the plasma gas; a temperature sensor, being provided in the plasma head, which is configured to measure a temperature of the plasma head; and a control device, wherein the control device executes a cooling process of cooling the plasma head by causing the gas supply device to continue supply of the gas until the temperature sensor measures a temperature equal to or less than a predetermined value after the discharging of the pair of electrodes is stopped. 
     Advantageous Effect of the Invention 
     According to the present disclosure, the plasma generation device can appropriately cool the plasma head. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view illustrating a plasma head of an atmospheric-pressure plasma generation device. 
         FIG. 2  is a perspective view illustrating a lower end of a plasma head of the atmospheric-pressure plasma generation device. 
         FIG. 3  is a sectional view illustrating a main section of the plasma head of the atmospheric-pressure plasma generation device. 
         FIG. 4  is a block diagram illustrating a control system of the atmospheric-pressure plasma generation device. 
         FIG. 5  is a flowchart illustrating a control program for a heater warming-up method. 
         FIG. 6  is a diagram illustrating an example of a temperature rise process of the heater during a warming-up operation. 
         FIG. 7  is a diagram illustrating an example of a correspondence relationship between a first temperature and a lower limit temperature of the heater. 
         FIG. 8  is a flowchart illustrating a control program for a plasma head cooling method. 
         FIG. 9  is a diagram illustrating a schematic configuration of the atmospheric-pressure plasma generation device attached to an industrial robot. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Overall Configuration 
     An atmospheric-pressure plasma generation device is a device generating plasma under the atmospheric pressure. As illustrated in  FIG. 9 , atmospheric-pressure plasma generation device  10  includes plasma head  18 , control device  16 , power cable  140 , gas pipe  180 , and the like. Atmospheric-pressure plasma generation device  10  transmits power from control device  16  to plasma head  18  via power cable  140 , and supplies a treatment gas or the like via gas pipe  180  to apply plasma gas from plasma head  18 . Plasma head  18  is attached to a tip of robot arm  201  of industrial robot  200 . Power cable  140  and gas pipe  180  are attached to robot arm  201 . Robot arm  201  is an articulated robot in which two arm sections  205  and  205  are connected in one direction. Industrial robot  200  moves plasma head  18  by driving robot arm  201 , and performs work of irradiating workpiece W supported by work table  5  with a plasma gas. Control device  16  includes treatment gas supply device  74  and heating gas supply device  86 . Treatment gas supply device  74  supplies at least one of an inert gas such as nitrogen and an active gas such as oxygen as a treatment gas. Heating gas supply device  86  supplies an active gas such as oxygen or an inert gas such as nitrogen. Control device  16  includes display device  115 . Display device  115  has a screen on which various types of information and the like are displayed. 
     Configuration of Plasma Head  18   
     As illustrated in  FIG. 1 , plasma head  18  includes plasma gas ejection device  12  and heated gas ejection device  14 . In the following description, a width direction of plasma head  18  is set to an X direction, a depth direction of plasma head  18  is set to a Y direction, and a direction perpendicular to the X direction and the Y direction, that is, a vertical direction is set to a Z direction. 
     Plasma gas ejection device  12  includes housing  20 , cover  22 , and pair of electrodes (refer to  FIGS. 3 and 4 )  24  and  26 . As illustrated in  FIG. 3 , housing  20  includes main housing  30 , heat sink  31 , ground plate  32 , lower housing  34 , and nozzle block  36 . Main housing  30  generally has a block shape, and reaction chamber  38  is formed inside main housing  30 . Main housing  30  is provided with multiple first gas flow paths (in  FIG. 3 , only one first gas flow path is illustrated)  50  extending in the vertical direction, and multiple first gas flow paths  50  are arranged at predetermined intervals in the X direction (in  FIG. 3 , a direction perpendicular to the drawing surface). An upper end of each of first gas flow paths  50  is open to reaction chamber  38 , and a lower end thereof is open to a bottom surface of main housing  30 . 
     Heat sink  31  is disposed on one side surface of main housing  30  in the Y direction. Heat sink  31  has multiple fins (not illustrated), to radiate heat of main housing  30 . Ground plate  32  functions as a lightning rod and is fixed to the lower surface of main housing  30 . Ground plate  32  is provided with multiple through-holes  56 , corresponding to multiple first gas flow paths  50 , penetrating in the vertical direction, and each through-hole  56  is connected to corresponding first gas flow path  50 . 
     Lower housing  34  has a block shape and is fixed to the lower surface of ground plate  32 . Lower housing  34  is provided with multiple second gas flow paths  62  extending in the vertical direction, corresponding to multiple through-holes  56 . An upper end of each second gas flow path  62  is connected to corresponding through-hole  56 , and a lower end thereof is open to the bottom surface of lower housing  34 . 
     As illustrated in  FIG. 2 , nozzle block  36  is fixed to the lower surface of lower housing  34 , and is provided with multiple third gas flow paths  66  extending in the vertical direction, corresponding to multiple second gas flow paths  62  of lower housing  34 . An upper end of each third gas flow path  66  is connected to corresponding second gas flow path  62 , and a lower end thereof is open to the bottom surface of nozzle block  36 . 
     Referring to  FIG. 3  again, cover  22  has generally a square shape and is disposed on the lower surface of ground plate  32  to cover lower housing  34  and nozzle block  36 . Through-hole  70  is formed in the lower surface of cover  22 . Through-hole  70  is larger than the lower surface of nozzle block  36 , and the lower surface of nozzle block  36  is located in through-hole  70 . Through-hole  72  extending in the Y direction is formed on the side surface of cover  22  on heated gas ejection device  14  side. 
     Pair of electrodes  24  and  26  are disposed to face each other inside reaction chamber  38  of main housing  30 . Reaction chamber  38  is connected to treatment gas supply device (refer to  FIG. 4 )  74  via gas pipe  180  illustrated in  FIG. 9 . As described above, treatment gas supply device  74  is a device supplying at least one of an inert gas such as nitrogen and an active gas such as oxygen as a treatment gas. Consequently, the treatment gas is supplied to reaction chamber  38  The treatment gas may be a dry air. 
     Heated gas ejection device  14  includes protection cover  80 , gas pipe  82 , heater  83 , connection block  84 . Protection cover  80  is disposed to cover heat sink  31  of plasma gas ejection device  12 . Gas pipe  82  is disposed to extend in the vertical direction inside protection cover  80 , and gas pipe  82  is connected to heating gas supply device (refer to  FIG. 4 )  86  via gas pipe  180  illustrated in  FIG. 9 . However, gas pipe  180  is formed of two different tubes, and includes a tube connected to reaction chamber  38  and treatment gas supply device  74 , and a tube connected to gas pipe  82  and heating gas supply device  86 . As described above, heating gas supply device  86  is a device supplying an active gas such as oxygen or an inert gas (hereinafter, referred to as a gas) such as nitrogen. Consequently, gas is supplied into gas pipe  82  from heating gas supply device  86 , and the gas flows downward. For example, a generally coiled heater  83  is suspended in gas pipe  82 . Consequently, the gas supplied from heating gas supply device  86  to gas pipe  82  is heated. As illustrated in  FIG. 1 , generally cylindrical thermo-couple cover  91  is provided in gas pipe  82  in a longitudinal direction (that is, the vertical direction) of gas pipe  82 . 
     Thermo-couple  92  is inserted into thermo-couple cover  91 . Temperature measurement contact  92 A of therm o-couple  92  is inserted into gas pipe  82  from the lower end of thermo-couple cover  91  is disposed under heater  83 . Arrow AR illustrated in  FIG. 1  indicates a direction in which the gas flows in gas pipe  82 . Therefore, thermo-couple  92  measures the temperature of the gas flowing through gas pipe  82  at a position close to heater  83  from the downstream side of the gas in gas pipe  82 . In atmospheric-pressure plasma generation device  10 , the temperature measured by thermo-couple  92  is handled as the temperature of heater  83  or the temperature of plasma head  18 . 
     Referring to  FIG. 3  again, connection block  84  is connected to the lower end of gas pipe  82  and is also fixed to the side surface of cover  22  on heated gas ejection device  14  side in the Y direction. Connection block  84  is provided with communication passage  88  that is bent in a generally L-shaped, and one end of communication passage  88  is open to the upper surface of connection block  84  and the other end of communication passage  88  is open to the side surface of connection block  84  on plasma gas ejection device  12  side. One end of communication passage  88  communicates with gas pipe  82 , and the other end of communication passage  88  communicates with through-hole  72  of cover  22 . Plasma gas ejection device  12  may not include ground plate  32 . 
     Control System of Atmospheric-Pressure Plasma Generation Device 
     Next, a control system of atmospheric-pressure plasma generation device  10  will be described. Atmospheric-pressure plasma generation device  10  includes control device  16  as illustrated in  FIG. 9  described above. As illustrated in  FIG. 4 , control device  16  includes not only above-described treatment gas supply device  74 , heating gas supply device  86 , and display device  115  but also controller  100 , high-frequency power source  102 , drive circuit  105 , flow rate controllers  103  and  104 , control circuit  106 , communication section  107 , power supply device  108 , and input device  116 . Controller  100  is implemented by a computer or the like including CPU  120 , ROM  122 , RAM  124 , and the like. Controller  100  controls plasma gas ejection device  12  and heated gas ejection device  14  by controlling high-frequency power source  102 , drive circuit  105 , and flow rate controllers  103  and  104 . Controller  100  is connected to display device  115  via control circuit  106 . Consequently, an image is displayed on display device  115  in response to a command from controller  100 . Controller  100  is connected to input device  116 . Input device  116  includes operation buttons and the like, and outputs operation information corresponding to an operation on the operation buttons. Thus, the operation information corresponding to the operation on the operation buttons is input to controller  100 . Communication section  107  performs communication with a communication apparatus connected to a network (not illustrated). A communication form is not particularly limited and is, for example, a LAN or serial communication. 
     High-frequency power source  102  generates high-frequency AC power to be supplied to electrodes  24  and  26  by using a commercial power source (not illustrated), and supplies the generated AC power to electrodes  24  and  26 . 
     Flow rate controller  103  is implemented by, for example, a mass flow controller or the like. Flow rate controller  103  controls a flow rate of the treatment gas supplied from treatment gas supply device  74  to reaction chamber  38 . Flow rate controller  103  outputs a value of the flow rate of the supplied treatment gas to controller  100 . 
     In the same manner as flow rate controller  103 , flow rate controller  104  controls a flow rate of gas supplied from heating gas supply device  86  to gas pipe  82 . Flow rate controller  103  outputs a value of the flow rate of the supplied gas to controller  100 . 
     Power supply device  108  and thermo-couple  92  that is attached near the lower end of heater  83  are electrically connected to drive circuit  105 . Power supply device  108  supplies AC power generated by using the commercial power source (not illustrated) to heater  83 . Drive circuit  105  heats heater  83  and performs temperature adjustment on heater  83  by controlling power supply device  108  based on an output value from thermo-couple  92  such that a target temperature for which an instruction is given from controller  100  is obtained. Drive circuit  105  outputs a temperature corresponding to the output value from thermo-couple  92  to controller  100 . 
     Plasma Treatment Using Atmospheric-Pressure Plasma Generation Device 
     In atmospheric-pressure plasma generation device  10 , in plasma gas ejection device  12 , a treatment gas is plasmatized in reaction chamber  38  by the above-described configuration, and the plasma gas is ejected from the lower end of third gas flow path  66  of nozzle block  36 . Gas heated by heated gas ejection device  14  is supplied to the inside of cover  22 . The plasma gas is ejected from through-hole  70  of cover  22  together with the heated gas, and thus workpiece W is subjected to plasma treatment. 
     Specifically, in plasma gas ejection device  12 , the treatment gas is supplied to reaction chamber  38  by treatment gas supply device  74 . In this case, in reaction chamber  38 , power is supplied to pair of electrodes  24  and  26 , and thus a current flows between pair of electrodes  24  and  26 . Consequently, discharging occurs between pair of electrodes  24  and  26 , and thus the treatment gas is plasmatized due to the discharging, so that plasma gas is generated. The plasma gas generated in reaction chamber  38  flows downward in first gas flow path  50 , and flows into second gas flow path  62  via through-hole  56 . The plasma gas flows downward in second gas flow path  62  and third gas flow path  66 . Consequently, the plasma gas passes through through-hole  70  of cover  22  to be ejected from the lower end of third gas flow path  66 . 
     In heated gas ejection device  14 , gas is supplied to gas pipe  82  by heating gas supply device  86 , and the gas supplied to gas pipe  82  is heated by heater  83 . Consequently, the gas supplied to gas pipe  82  is heated to 600° C. to 800° C. The gas that has been heated (hereinafter, referred to as a heated gas) flows into cover  22  from through-hole  72  of cover  22  via communication passage  88  of connection block  84 . The heated gas flowing into cover  22  is ejected from through-hole  70  of cover  22 . In this case, the plasma gas ejected from the lower end of third gas flow path  66  of nozzle block  36  is protected by the heated gas. Consequently, the plasma gas surrounded by the heated gas is discharged from plasma head  18 , and plasma treatment can be performed appropriately. 
     Specifically, during plasma treatment, workpiece W is placed at a position by a predetermined distance from through-hole  70  ejecting the plasma gas, and the plasma gas is ejected onto workpiece W from through-hole  70 . That is, during the plasma treatment, the plasma gas is ejected into the air, and workpiece W is irradiated with the plasma gas ejected into the air. 
     When an instruction for starting plasma generation is received via input device  116 , controller  100  starts plasma generation control. In the plasma generation control, controller  100  causes high-frequency power source  102  to start control for supplying predetermined power to electrodes  24  and  26 , and thus flow rate controllers  103  and  104  start to respectively supply a treatment gas and gas at predetermined gas flow rates. Controller  100  causes drive circuit  105  to start control of heater  83  such that a predetermined temperature is obtained. 
     Warming-Up Operation of Heater in Atmospheric-Pressure Plasma Generation Device 
     as described above, in atmospheric-pressure plasma generation device  10 , when the plasma treatment is performed on workpiece W, the gas supplied to gas pipe  82  is heated to 600° C. to 800° C. by heater  83 . Therefore, at the time of starting of atmospheric-pressure plasma generation device  10 , the warming-up operation of heater  83  is performed. During the warming-up operation of heater  83 , for example, in a case where thermo-couple  92  fails due to a short circuit or disconnection or the like, a measured temperature of thermo-couple  92  indicates a room temperature at all times or indicates a constant temperature without increasing from a predetermined temperature, and thus an accurate temperature of heater  83  cannot be measured by thermo-couple  92 . Thus, there is concern that the temperature of heater  83  is not adjustable, and thus heater  83  fails. Therefore, atmospheric-pressure plasma generation device  10  monitors a temperature rise process of heater  83  during the warming-up operation of heater  83 . Next, details thereof will be described. 
       FIG. 5  is a flowchart illustrating a heater warming-up method  110  for monitoring the temperature rise process of heater  83 . The control programs illustrated in the flowchart of  FIG. 5  are stored in ROM 122  of controller  100 , and are executed by CPU 120  of controller  100  when the user performs predetermined operations with input device  116  at the time of starting atmospheric-pressure plasma generation device  10  or the like. 
     Hereinafter, each process illustrated in a flowchart of  FIG. 5  will be described with reference to  FIG. 6  and  FIG. 7  along with  FIG. 4  described above. Curve L 1  in  FIG. 6  indicates an example of a temperature change of heater  83  during a warming-up operation. Data table DT in  FIG. 7  is stored in ROM  122  of controller  100 . 
     When heater warming-up method  110  is executed, first, warming-up start process S 110  is performed. In this process, the warming-up operation of heater  83  is started due to starting of the supply of power from power supply device  108  to heater  83 . 
     Next, first temperature acquisition process S 112  is performed. In this process, temperature MT 1  is acquired as a first temperature by thermo-couple  92 . 
     Next, calculation process S 114  is performed. In this process, lower limit temperature LM 1  of heater  83  is calculated. Lower limit temperature LM 1  of heater  83  is a temperature of heater  83  during the temperature rise due to the warming-up operation, and refers to the minimum temperature of heater  83  which is supposed by considering an allowable variation range of power supply device  108  at a point in time at which first predetermined time DP (for example, 10 seconds) has elapsed from a point in time at which temperature MT 1  is acquired as the first temperature. In the following description, the point in time at which first predetermined time DP has elapsed from the point in time at which the first temperature is acquired may be referred to as a reference point in time. 
     Lower limit temperature LM 1  of heater  83  is calculated based on the first temperature and data table DT. 
     According to data table DT, for the first temperature that is equal to or higher than 0° C. and lower than 400° C., a temperature obtained by adding 50° C. to the first temperature is calculated as the lower limit temperature of heater  83 . Hereinafter, as the lower limit temperature of heater  83 , a temperature obtained by adding 20° C. to the first temperature is calculated for the first temperature that is equal to or higher than 400° C. and lower than 500° C., a temperature obtained by adding 5° C. to the first temperature is calculated for the first temperature that is equal to or higher than 500° and lower than 600° C., and a temperature obtained by adding 3° C. to the first temperature is calculated for the first temperature that is equal to or higher than 600° C. and lower than 650° C. Therefore, data table DT is a data table in which a temperature range that classifies the first temperature (in  FIG. 7 , 0° C. or higher to lower than 400° C., 400° C. or higher to lower than 500° C., 500° C. or higher to lower than 600° C., and 600° C. or higher to lower than 650° C.) is correlated with a temperature difference from the first temperature to the lower limit temperature (in  FIG. 7 , 50° C., 20° C., 5° C., and 3° C.). 
     In the above-described way, lower limit temperatures LM 1  of heater  83  is calculated based on the data stored in data table DT. When lower limit temperature LM 1  of heater  83  is calculated, the flow waits until first predetermined time DP has elapsed from point in time at which temperature MT 1  is acquired as the first temperature, that is, until the reference point in time is reached (S 116 : NO). When first predetermined time DP has elapsed from the point in time at which temperature MT 1  is acquired as the first temperature (S 116 : YES), that is, when the reference point in time is reached, second temperature acquisition process S 118  is performed. In this process, temperature MT 2  is acquired as a second temperature by thermo-couple  92 . 
     Next, it is determined whether temperature MT 2  acquired as the second temperature is equal to or higher than lower limit temperature LM 1  (S 120 ). Here, in a case where temperature MT 2  acquired as the second temperature is lower than lower limit temperature LM 1  (S 120 : NO), it can be said that temperature MT 2  (that is, the temperature of heater  83 ) acquired as the second temperature does not rise to lower limit temperature LM 1  when first predetermined time DP has elapsed from the point in time at which temperature MT 1  is acquired as the first temperature, that is, when the reference point in time is reached. Therefore, it is determined that there is an abnormality, and warming-up stop process S 122  is performed. In this process, the warming-up operation of heater  83  is stopped by stopping the supply of power from power supply device  108  to heater  83 . On the screen of display device  115 , for example, the entire region is displayed red, and a message indicating that the warming-up operation has been stopped is displayed. The message indicating that the warming-up operation has been stopped is transmitted to a terminal of an administrator who manages atmospheric-pressure plasma generation device  10  or a terminal of a support desk operated by a supplier of atmospheric-pressure plasma generation device  10  through network communication of communication section  107 . Thereafter, heater warming-up method  110  is finished. 
     On the other hand, in a case where temperature MT 2  acquired as the second temperature is equal to or higher than lower limit temperature LM 1  (S 120 : YES), deeming process S 124  is performed. In this process, temperature MT 2  acquired as the second temperature is handled as the first temperature instead of temperature MT 1 . 
     Thereafter, the processes of the above S 114 , S 116 , S 118 , and S 120  are repeatedly performed. Thus, in calculation process S 114  described above, lower limit temperature LM 2  of heater  83  is calculated based on temperature MT 2  handled as the first temperature and data table DT. Lower limit temperature LM 2  of heater  83  calculated in the above-described way is the same as lower limit temperature LM 1  described above. That is, lower limit temperature LM 2  of heater  83  is a temperature of heater  83  during the temperature rise due to the warming-up operation, and is the minimum temperature of heater  83  which is supposed by considering an allowable variation range of power supply device  108  at the reference point in time at which first predetermined time DP has elapsed from the point in time at which temperature MT 2  handled as the first temperature is acquired. 
     Then, when first predetermined time DP has elapsed from the point in time at which temperature MT 2  handled as the first temperature is acquired (S 116 : YES), that is, when the reference point in time is reached, second temperature acquisition process S 118  described above is performed, and thus temperature MT 3  is acquired as the second temperature. 
     In a case where temperature MT 3  acquired as the second temperature is lower than lower limit temperature LM 2  (S 120 : NO), it is determined that there is an abnormality, and the warming-up operation of heater  83  is stopped (S 122 ). In contrast, in a case where temperature MT 3  acquired as the second temperature is equal to or higher than lower limit temperature LM 2  (S 120 : YES), deeming process S 124  is performed again, and temperature MT 3  acquired as the second temperature is handled as the first temperature instead of temperature MT 2  (S 124 ). 
     In the same manner as follows, lower limit temperature LM 3  of heater  83  is calculated based on temperature MT 3  handled as the first temperature and data table DT (S 114 ), further, when first predetermined time DP has elapsed from the point in time at which temperature MT 3  handled as the first temperature is acquired (S 116 : YES), that is, when the reference point in time is reached, temperature MT 4  is acquired as the second temperature (S 118 ). Then, in a case where temperature MT 4  acquired as the second temperature is lower than lower limit temperature LM 3  (S 120 : NO), it is determined that there is an abnormality, and the warming-up operation of heater  83  is stopped (S 122 ). In contrast, in a case where temperature MT 4  acquired as the second temperature is equal to or higher than lower limit temperature LM 3  (S 120 : YES), temperature MT 4  acquired as the second temperature is handled as the first temperature instead of temperature MT 3  (S 124 ). 
     In above-described way, heater warming-up method  110  is continued as long as the second temperature is equal to or higher than a lower limit temperature calculated based on the first temperature. 
     From the above description, heater warming-up method  110  is executed, and thus atmospheric-pressure plasma generation device  10  can monitor the temperature rise process during the warming-up operation of heater  83  provided in plasma head  18 . 
     Lower limit temperatures LM 1 , LM 2 , and LM 3  of heater  83  may be calculated from an approximate expression representing a relationship with an elapsed time from a point in time at which the supply of power to heater  83  is started (that is, a warming-up time of heater  83 ). In  FIG. 6 , such an approximate expression is represented by curve L 2  indicated by a two-dot chain line. A formula representing curved L 2  is stored in ROM  122  of controller  100 . 
     In this case, lower limit temperatures LM 1 , LM 2 , and LM 3  of heater  83  are calculated by assigning the reference point in time at which first predetermined time DP has elapsed from the point in time at which temperatures MT 1 , MT 2 , and MT 3  acquired or handled as the first temperature are acquired, the reference point in time being a point in time at which an elapsed time from the point in time at which the supply of power to heater  83  is started is measured, to the formula (approximate expression) represented by curved line L 2  in  FIG. 6 . 
     Even in a case where heater  83  is not provided in plasma head  18 , as long as heater  83  warms the plasma applied from plasma head  18 , heater  83  may be a target of heater warming-up method  110 . 
     Cooling Operation of Heater in Atmospheric-Pressure Plasma Generation Device 
     When atmospheric-pressure plasma generation device  10  is stopped after workpiece W is subjected to plasma treatment in atmospheric-pressure plasma generation device  10 , controller  100  cools plasma head  18  by continuing the supply of a treatment gas using treatment gas supply device  74  and the supply of gas using heating gas supply device  86 . After plasma head  18  is cooled, there is a case where a user touches plasma head  18  for maintenance. Therefore, the cooling of plasma head  18  is continued on the assumption that a surface temperature of plasma head  18  drops to, for example, about 40° C., but in a case where the cooling is performed while the temperature of plasma head  18  is measured again, it is possible to perform the cooling more preferably. Therefore, atmospheric-pressure plasma generation device  10  performs cooling of plasma head  18  while measuring the temperature of plasma head  18 . Next, details thereof will be described. 
       FIG. 8  is a flowchart illustrating plasma head cooling method  210  for cooling plasma head  18  while measuring the temperature of plasma head  18 . A control program illustrated in the flowchart of  FIG. 8  is stored in ROM  122  of controller  100 , and is executed by CPU  120  of controller  100  when workpiece W is subjected to plasma treatment by atmospheric-pressure plasma generation device  10 . Therefore, when plasma head cooling method  210  is executed, the supply of a treatment gas using treatment gas supply device  74  and the supply of gas using heating gas supply device  86  are performed. Hereinafter, each process illustrated in the flowchart of  FIG. 8  will be described. 
     CPU  120  of controller  100  performs each process illustrated in the flowchart of  FIG. 8  by using the temperature of heater  83  measured by thermo-couple  92 . The surface of plasma head  18  varies in temperature depending on a position thereof while workpiece W is being subjected to plasma treatment. However, the entire surface region of plasma head  18  tends to converge to the same temperature after a certain time has elapsed since its start of cooling. Therefore, in plasma head cooling method  210  illustrated in the flowchart of  FIG. 8 , the temperature of heater  83  measured by thermo-couple  92  is used as the temperature of plasma head  18 . 
     When plasma head cooling method  210  is executed, it is determined whether discharging between pair of electrodes  24 ,  26  and heating of heater  83  have been stopped (S 210 ). This determination is performed based on a signal from high-frequency power source  102 , a signal from drive circuit  105 , and the like. Here, in a case where discharging between pair of electrodes  24  and  26  or heating of heater  83  is not stopped (S 210 : NO), plasma head cooling method  210  is finished. 
     In contrast, in a case where discharging between pair of electrodes  24  and  26  or heating of heater  83  is stopped (S 210 : YES), it is determined whether the temperature of heater  83  measured by thermo-couple  92  is equal to or lower than a predetermined temperature (S 212 ). Here, the predetermined temperature is a temperature at which there is no problem even when the user touches the surface of plasma head  18  (for example, a temperature around 40° C.). Here, in a case where the temperature of heater  83  measured by thermo-couple  92  is equal to or lower than the predetermined temperature (S 212 : YES), plasma head cooling method  210  is finished. 
     In contrast, in a case where the temperature of heater  83  measured by thermo-couple  92  is higher than the predetermined temperature (S 212 : NO), cooling process S 214  is performed. In this process, the supply of the treatment gas using treatment gas supply device  74  and the supply of the gas using heating gas supply device  86  are continued. 
     Next, first notification process S 216  is performed. In this process, a message indicating that plasma head  18  is being cooled is displayed on the screen of display device  115 . The message indicating that plasma head  18  is being cooled is transmitted to the terminal of the administrator who manages atmospheric-pressure plasma generation device  10  or the terminal of the support desk operated by the supplier of atmospheric-pressure plasma generation device  10  through network communication of communication section  107 . 
     Thereafter, it is determined whether the supply of the treatment gas using treatment gas supply device  74  or the supply of the gas using heating gas supply device  86  is abnormally stopped. This determination is performed based on signals or the like from flow rate controllers  103  and  104 . Here, in a case where the supply of the treatment gas using treatment gas supply device  74  or the supply of the gas using heating gas supply device  86  is abnormally stopped (S 218 : YES), second notification process S 220  is performed. 
     In second notification process S 220 , a message indicating that the cooling of plasma head  18  is abnormal due to an abnormality in the gas supply is displayed on the screen of display device  115 . The message indicating that the cooling of plasma head  18  is abnormal due to the abnormality in the gas supply is transmitted to the terminal of the administrator who manages atmospheric-pressure plasma generation device  10  or the terminal of the support desk operated by the supplier of atmospheric-pressure plasma generation device  10  through network communication of communication section  107 . Thereafter, plasma head cooling method  210  is finished. 
     In contrast, in a case where the supply of the treatment gas using treatment gas supply device  74  or the supply of the gas using heating gas supply device  86  is not abnormally stopped (S 218 : NO), it is determined whether thermo-couple  92  shows an abnormality such as disconnection (S 222 ). This determination is performed based on an output voltage or the like of thermo-couple  92 . Here, in a case where thermo-couple  92  shows an abnormality such as disconnection (S 222 : YES), third notification process S 224  is performed. 
     In third notification process S 224 , a message indicating that the cooling of plasma head  18  is abnormal due to an abnormality of thermo-couple  92  is displayed on the screen of display device  115 . The message indicating that the cooling of plasma head  18  is abnormal due to an abnormality of thermo-couple is transmitted to the terminal of the administrator who manages atmospheric-pressure plasma generation device  10  or the terminal of the support desk operated by the supplier of atmospheric-pressure plasma generation device  10  through network communication of communication section  107 . Thereafter, plasma head cooling method  210  is finished. 
     On the other hand, when thermo-couple  92  does not show an abnormality such as disconnection (S 222 : NO), it is determined whether a second predetermined time has elapsed from stoppage of the discharging between pair of electrodes  24  and  26  and the heating of heater  83  (S 226 ). This determination is performed based on an elapsed time measured with reception of a signal from drive circuit  105 , a signal from high-frequency power source  102 , and the like as a trigger. The second predetermined time is a time (for example, 20 minutes) required for the entire surface of plasma head  18  to be cooled to a temperature (for example, a temperature around 40° C.) at which there is no problem even when the user touches the surface of plasma head  18 . 
     Here, in a case where the second predetermined time has elapsed from stoppage of the discharging between pair of electrodes  24  and  26  and the heating of heater  83  (S 226 : YES), fourth notification process S 228  is performed. In this process, a message indicating that the cooling of plasma head  18  is abnormal is displayed on the screen of display device  115 . The message indicating that the cooling of plasma head  18  is abnormal is transmitted to the terminal of the administrator who manages atmospheric-pressure plasma generation device  10  or the terminal of the support desk operated by the supplier of atmospheric-pressure plasma generation device  10  through network communication of communication section  107 . The message also includes information indicating that, even when the second predetermined time has elapsed from stoppage of the discharging between pair of electrodes  24  and  26  and the heating of heater  83 , the surface temperature of plasma head  18  (more precisely, the temperature of heater  83 ) is not equal to or lower than the predetermined temperature. Thereafter, plasma head cooling method  210  is finished. 
     In contrast, in a case where the second predetermined time has not elapsed from stoppage of the discharging between pair of electrodes  24  and  26  and the heating of heater  83  (S 226 : NO), the flow returns to determination process S 212  described above. 
     Thereafter, as described above, in a case where the temperature of heater  83  measured by thermo-couple  92  is higher than a predetermined temperature (S 212 : NO), the supply of the treatment gas using treatment gas supply device  74  and the supply of the gas using heating gas supply device  86  are continued (S 214 ), and in a case where the temperature of heater  83  measured by thermo-couple  92  is equal to or lower than the predetermined temperature (S 212 : YES), plasma head cooling method  210  is finished. 
     In the above-described way, in plasma head cooling method  210 , cooling of plasma head  18  is finished assuming that the surface temperature of plasma head  18  is reduced to a temperature (for example, a temperature around 40° C.) at which there is no problem even when the user touches the surface of plasma head  18  based on the temperature (the temperature measured by thermo-couple  92 ) of heater  83  used as the temperature of plasma head  18 . 
     As described above, plasma head cooling method  210  is executed, and thus atmospheric-pressure plasma generation device  10  can perform appropriate cooling of plasma head  18  while improving maintenance. 
     The present disclosure is not limited to the above-described embodiments, and various modifications may occur without departing from the spirit thereof. For example, atmospheric-pressure plasma generation device  10  may be provided with, instead of thermo-couple  92 , other sensors capable of measuring the temperature of heater  83  or the temperature of gas flowing in gas pipe  82 , for example, a thermistor or an infrared sensor. 
     Atmospheric-pressure plasma generation device  10  may be provided with a heater heated by a high temperature fluid such as a liquid or gas instead of heater  83  heated by power supply device  108 . In this case, the temperature of the heater is adjusted by controlling the temperature or a flow rate of the high temperature fluid. 
     When plasma head cooling method  210  is finished, the supply of the treatment gas using treatment gas supply device  74  and the supply of the gas using heating gas supply device  86  may be or need not be continued. 
     Plasma head cooling method  210  may also be executed in a state in which temperature measurement contact  92 A of thermo-couple  92  is embedded in, for example, main housing  30  of plasma head  18 . In this case, plasma head cooling method  210  may be applied to a case where heated gas ejection device  14  including heater  83  is not provided in plasma head  18 . 
     In the present embodiment, atmospheric-pressure plasma generation device  10  is an example of a plasma generation device. Treatment gas supply device  74  and heating gas supply device  86  are an example of a gas supply device. Thermo-couple  92  is an example of a temperature sensor. Display device  115  is an example of a notification device. The cooling process S 214  is an example of a cooling step. First notification process S 216 , second notification process S 220 , third notification process S 224 , and fourth notification process S 228  are an example of a notification process. The second predetermined time used in the determination of S 226  is an example of a predetermined time. 
     REFERENCE SIGNS LIST 
     
         
           10  Atmospheric-pressure plasma generation device,  16  Control device,  18  Plasma head,  24  Electrode,  26  Electrode,  74  Treatment gas supply device,  83  Heater,  86  Heating gas supply device,  92  Thermo-couple,  115  Display device,  210  Plasma head cooling method, S 214  Cooling process, S 216  First notification process, S 220  Second notification process, S 224  Third notification process, S 228  Fourth notification process