Abstract:
To provide an electron beam irradiation device capable of reducing quantity of inert gas consumed while maintaining oxygen concentration in an irradiation chamber in appropriate level. An electron beam irradiation device to irradiate an electron beam to an irradiated object passing through an irradiation chamber while introducing inert gas into the irradiation chamber comprising an oxygen concentration detection device to detect oxygen concentration in the irradiation chamber; a main controlling valve to regulate flow rate of inert gas introduced in the irradiation chamber; a control unit to control valve travel of the main controlling valve so that the flow rate of the inert gas decreases when the oxygen concentration becomes low on the basis of the oxygen concentration detected by the oxygen concentration detection device.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electron beam irradiation device to irradiate an electron beam to an irradiated object which passing an irradiation chamber while introducing inert gas in the irradiation chamber. 
   2. Description of the Related Art 
   There is known an electron beam irradiation device to irradiate an electron beam to a belt-shaped irradiated object such as a resin film and to conduct a processing such as bridging, hardening or reforming to the irradiated object. In this kind of irradiation device, when the electron beam is irradiated under the environment in which oxygen is exist, the inconvenience which the oxygen reacts to the electron beam and the irradiation energy of the electron beam is used sometimes occur. Therefore, as described in JP-B 63-8440, JP-A 5-60899 and JP-U 6-80200 for example, inert gas such as nitrogen is introduced in the irradiation chamber of the electron beam, and the oxygen is substituted for the inert gas, thereby the oxygen concentration in the irradiation chamber is restrained in a low level (less than 100 ppm, for example). 
   However, in the above-described electron beam irradiation device, the inert gas is continuously supplied in a constant flow rate, thus the quantity of the inert gas consumed is grate, and sometimes excess inert gas is introduced. For example, in the electron beam irradiation device of the type which irradiates an electron beam while making the irradiated object travel, the air which is going to enter the irradiation chamber accompanying the irradiated object is need to be removed out of the irradiation chamber by stripping it off with the inert gas, for that purpose, at the entrance of the irradiation chamber, a large quantity of the inert gas must be bowed to the irradiated object continuously. However, when the irradiated object is stopped or when the irradiated object is traveled for an arranging operation at a speed lower than when the electron beam is irradiated, the involving of the accompanying air does not exist or even if it exists the influence is small, therefore, if the inert gas is continuously introduced at the same flow rate as when the electron beam is irradiated, the inert gas is consumed vainly. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide an electron beam irradiation device capable of reducing quantity of inert gas consumed while maintaining oxygen concentration in an irradiation chamber in appropriate level. 
   To achieve the above-described object, an electron beam irradiation device according to one embodiment of the present invention is an electron beam irradiation device to irradiate an electron beam to an irradiated object passing through an irradiation chamber while introducing inert gas into the irradiation chamber, comprising: an oxygen concentration detection device to detect oxygen concentration in the irradiation chamber; a flow regulating valve to regulate flow rate of the inert gas introducing in the irradiation chamber; and a valve travel control device to control valve travel of the flow regulating valve on the basis of the oxygen concentration detected by the oxygen concentration detection device so that the flow rate of the inert gas decreases when the oxygen concentration becomes low. 
   According to the electron beam irradiation device, by controlling the valve travel of the flow regulating valve on the basis of the oxygen concentration in the irradiation chamber, the flow rate of the inert gas introduced into the irradiation chamber may be changed adequately depending on the oxygen concentration in the irradiation chamber. That is, when the oxygen concentration is in an upward tendency, by making the valve travel of the flow regulating valve bigger to increase the flow rate of the inert gas, the rising which exceeds an allowable limit of the oxygen concentration can be prevented. On the other hand, when the oxygen concentration is lower than required, by reducing the valve travel of the flow regulating valve to decrease a flow rate of the inert gas, the state that the inert gas is introduced excessively is overcome. Thereby, wasteful consumption of the inert gas is suppressed while the oxygen concentration in the irradiation chamber is maintained in a permissible level, and the quantity of the inert gas consumed can be reduced. 
   In one embodiment of the present invention, the valve travel control device may change the relation between the oxygen concentration and the valve travel of the flow regulating valve corresponding to the traveling speed so that flow rate of the inert gas for the same oxygen concentration when traveling speed of the irradiated object is high becomes relatively bigger than the flow rate when the traveling speed is low. When the traveling speed of the irradiated object is low, the flow rate of the air which is going to enter the irradiation chamber accompanying the irradiated object is small and the change in the oxygen concentration is also comparatively gentle, but if the traveling speed of the irradiated object becomes high, the flow rate of the air accompanying the irradiated object increases, and the change in the oxygen concentration occurs comparatively suddenly. In this case, even if the rise of the oxygen concentration is detected and the valve travel of the flow regulating valve is increased, there is risk that the control will be late. To the contrary, even in the same oxygen concentration, when the traveling speed of the irradiated object is high, if the flow rate of the inert gas is made to be relatively increased compared to when the speed is low, the extra flow rate of the inert gas is generated, a sudden rise of the oxygen concentration can be suppressed. In this embodiment, the case when the traveling speed is low is a concept including the state when traveling speed is 0, that is the case which the irradiated object stops. 
   In one embodiment of the present invention, a plurality of gas intake openings may be provided in the irradiation chamber, sampling pipe lines may be connected to each of the plurality of gas intake openings, the oxygen concentration detection device may be provided on each of the sampling pipe lines, the valve travel control device may judge oxygen concentration in the irradiation chamber on the basis of the detected value of the oxygen concentration in the gas taken in each sampling pipe line, and a valve travel of the flow regulating valve may be controlled on the basis of the judged oxygen concentration. According to this embodiment, because the gas in the irradiation chamber is taken from each of a plurality of gas intake openings and the oxygen concentration is detected, comparing to the case when the oxygen concentration is detected at one place of the irradiation chamber, the oxygen concentration in the irradiation chamber can be detected in high precise. In this case, a plurality of gas intake openings may line in the width direction of the irradiated object. Thereby, a partial rise of the oxygen concentration about the width direction of the irradiated object is reflected to flow control of the inert gas, and dispersion in the irradiation quality of the electron beam in the width direction can be controlled surely. Further, the plurality of gas intake openings may be arranged adjacent to a transmission window of the electron beam on the irradiation chamber. By arranging the gas intake openings in this way, the oxygen concentration in the electron beam in the neighbor of the irradiation position can be reflected to the flow rate of the inert gas, and then the flow rate of the inert gas can be controlled optimally. 
   In one embodiment of the present invention, each sampling pipe line is provided with a filter and the oxygen concentration detection device may be arranged at the downstream of the filter. By arranging the oxygen concentration detection device at the downstream of the filter, even the environment that dust such as paper powder is generated from the irradiated object come along with the irradiation of the electron beam, the dust can be removed by the filter and the oxygen concentration in the irradiation chamber can be detected precisely. 
   Further, a pressure detection devices is provided at the down stream of the filter of each sampling pipe line, and a filter monitoring device to judge the presence of a clogging of each filter on the basis of the pressure detected by the pressure detection device is further provided, the valve travel control device excludes the detected value of the oxygen concentration detected by the oxygen concentration detection device of the sampling pipe line judged as the filter is clogged from an object for judging oxygen concentration in the irradiation chamber, and the oxygen concentration in the irradiation chamber may be judged on the basis of the detected value of the oxygen concentration detected by remaining oxygen concentration detection devices. According to this embodiment, when an error occurs in the detected value of the oxygen concentration due to the clogging of the filter, the influence which the error impart to the flow control of the inert gas can be removed. 
   In one embodiment of the present invention, a pressure detection device can be provided at the downstream of the filter of each sampling pipe line and, and further, a filter monitoring device to judge presence of a clogging of each filter on the basis of the pressure detected by the pressure detection device, and an alarm device outputs a predetermined alarm when it is judged that a clogging occurs in the filter may be provided. According to the embodiment, the clogging of the filter is warned to the operator of the electron beam irradiation device and the maintenance of the filter can be promoted. 
   In one embodiment of the present invention: an introduction portion continued to the feed-in opening of the irradiated object and a processing portion in which width of the passage thereof is made wider than the introduction portion and comprises a transmission window of the electron beam may be provided on the irradiation chamber; blowing openings of the inert gas may be provided on the introduction portion and the processing portion respectively; the flow regulating valve may be provided to a main pipe line connecting a supplying source of the inert gas and each blowing opening, a control valve for branch pipe line to regulate flow rate of the inert gas may be provided on the branch pipe line which distributes inert gas from the main line to the blowing opening of the introduction portion; and as well as valve travel control of the flow regulating valve on the basis of the oxygen concentration, the valve travel control device may decrease the valve travel of the control valve for branch pipe line when the irradiated object is stopped. Blowing opening of the introduction portion generates the effect which strip the air going to enter the irradiation chamber accompanying the irradiated object and push it out of the chamber by the inert gas blowing from that, but the accompanying air does not enter when the irradiated object is stopped, thus it is not necessary to make such an effect occur. Therefore, by decreasing the valve travel of the control valve for branch pipe line corresponding to the blowing opening of the introduction portion when the irradiated object is stopped, wasteful consumption of the inert gas can be suppressed and the quantity of consumed can be further reduced. In this case, the decreasing of the valve travel of the control valve for the branch pipe line may be generated by controlling the control valve for branch pipe line to the fully-closed state of or may be generated by decreasing the valve travel to the extent not to reach the fully-closed state in comparison with when it is not stopped. 
   An electron beam irradiation device according to another aspect of the present invention is an electron beam irradiation device to irradiate electron beam to the irradiated object passing through an irradiation chamber while introducing inert gas in irradiation chamber comprising: a sampling pipe line connected to a gas intake opening provided on the irradiation chamber and to take gas of the irradiation chamber; a filter provided on the sampling pipe line; a pressure detecting device to detect pressure at the downstream of the filter; an oxygen concentration detecting device to detect oxygen concentration in the gas led to the downstream of the filter; a filter monitoring device to judge presence of a clogging of each filter on the basis of the pressure detected by the pressure detection device; and an alarm device to output a predetermined alarm when it is judged that a clogging occurs in the filter. 
   According to the electron beam irradiation device of this aspect, the oxygen concentration in the irradiation chamber can be monitored by utilizing the oxygen concentration detection device. As the oxygen concentration detection device is provided at the downstream of the filter, even in the environment in which the dust such as paper powder occur from the irradiated object come along with the irradiation of the electron beam, the filter can remove the dust and the oxygen concentration in the irradiation chamber can be detected precisely. Further, because the clogging of the filter can be judged from detected value of the pressure detection device and an alarm can be output, the maintenance of the filter is promoted to the operator, and the risk that the state which an error is generated in the detected value of the oxygen concentration by clogging of the filter is left can be removed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings attached, 
       FIG. 1  is a view showing a main portion of an electron beam irradiation device according to one embodiment of the present invention; 
       FIG. 2  is a sectional view showing a configuration of the irradiation chamber; 
       FIG. 3  is a functional block diagram of a control unit provided on the electron beam irradiation device; 
       FIG. 4  is a flow chart showing a procedure of the flow control that the controlling part of a control unit executes; 
       FIG. 5  is a view for describing the decision of the valve travel of the main control valve in the flow control. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a view showing a main portion of an electron beam irradiation device according to one embodiment of the present invention. An electron beam irradiation device  1  comprises a fixed unit  2  installed on factory floors, and a movable unit  3  installed on the fixed unit  2 . It is provided a rigid wall  2   a  at one end of the fixed unit  2 , and it is provided a pair of rails  2   b  in front of the rigid wall  2   a . The movable unit  3  is provided along the rails  2   b  movably, and a movable wall  3   a  facing to the rigid wall  2   a  is provided at one end thereof. The movable unit  3  advances toward the rigid wall  2   a , and the movable wall  3   a  is made to be combined with the rigid wall  2   a , then the irradiation chamber  4  of the electron beam is formed between both walls  2   a ,  3   a  (cf.  FIG. 2 ).  FIG. 1  shows the state that the movable unit  3  is moved back from the rigid wall  2   a , and the irradiation chamber  4  is opened. It is provided an electron beam generator  5  to generate electron beam at the rear of the movable wall  3   a  of the movable unit  3 . The electron beam emitted from the electron beam generator  5  is incident to the irradiation chamber  4  through a transmission window  6  provided on the movable wall  3   a , and is caught by an electron beam capture device  7  of the rigid wall  2   a.    
   As show in the  FIG. 2 , it is provided a feed-in opening  8  to which film F as an irradiated object is fed in at one end (an upper end) of the irradiation chamber  4 , and a feed-out opening  9  from which film F is fed out at another end (a bottom end) of the irradiation chamber  4 . In the state that the rigid wall  2   a  and the movable wall  3   a  are made to be combined together, the irradiation chamber  4  is constructed as a closed space which the perimeter thereof is closed except both openings  8 ,  9 . An introduction portion  10 , the width of the passage thereof is narrowed, is provided in a predetermined area continued from the feed-in opening  8  of the irradiation chamber  4 , and a derivation portion  11 , the width of the passage thereof is narrowed, is provided in a predetermined area continued to the feed-out opening  9 . A processing portion  12 , the width of the passage thereof is made wider than that of the introduction portion  10  and the derivation portion  11  is provided Between the introduction portion  10  and the derivation portion  11 , and above-described transmission window  6  is provided on the processing portion  12 . The film F is wound-off from a wound-off roll  13 , and fed to the introduction portion  10  of the irradiation chamber  4  from the feed-in opening  8  while guided by suitable number of feeding rollers  14 . The film F fed to the irradiation chamber  4  is led to the processing portion  12 , and the electron beam EB passed through the transmission window  6  at the processing portion  12  is irradiated to the surface of the film F. The film F after electron-beam irradiated passes the derivation portion  11  and is fed out from the feed-out opening  9 , further is wound up by the wound up roll  16  while guided by appropriate number of feeding rollers  15 . In the following, as the basis for the traveling direction V of the film F, the direction toward the wind-up roll  13  is sometimes called as the upstream about the film traveling direction, and the direction toward the wind-off roll  16  is sometimes called as the downstream about the film traveling direction. The irradiated object F may be the thing to which some processing is conducted by the irradiation of the electron beam EB, however, the description is continued assuming that the film of paper base material used as a wall paper. 
   On the movable wall  3   a  composing the irradiation chamber  4 , it is provided blowing openings at the appropriate positions to introduce inert gas such as nitrogen into the interior of the room. For example, a first slit  20 A and lot of gas supplying holes  20 B are provided as blowing openings at the introduction portion  10 , further, a second slit  20 C as a blowing opening is provided at the vicinity of boundary between the introduction portion  10  and the processing portion  12 . At the processing portion  12 , a third slit  20 D and a fourth slit  20 E as blowing openings are provided so as to stride the transmission window  6  at the front and back direction. Further it is provided a lot of gas supplying holes  20 F as blowing openings at the vicinity of the boundary between the derivation portion  11  and the processing portion  12 . The first slit  20 A and the second slit  20 C are respectively provided so as to blow the inert gas to the film F over all width. By the inert gas blown from these slits  20 A,  20 C, the air accompanying the film F drawn into the introduction portion  10  is stripped off and forced to outside of the chamber from the feed-in opening  8 . The gas supplying holes  20 B is provided between the film F and the movable wall  3   a  to restrain a flapping of the film F by forming the support layer of the inert gas for pressing down the film F. In the following, when the slits  20 A,  20 C to  20  E, the gas supplying hole  20 B,  20 F do not have be judged each other, they sometimes be described as blowing openings  20 A- 20 F. 
   Return to  FIG. 1 , on the electron beam irradiation device  1 , it is provided a supply line  22  for supplying the inert gas from tank  21  as a source of supply of the inert gas to the blowing openings  20 A- 20 F. The supply line  22  comprises a main line  23  used in common for all blowing openings  20 A- 20 F and branch pipe lines  24 A- 24 F to connect the main line  23  and the blowing openings  20 A- 20 F respectively. Subscripts A-F of the branch pipe lines  24 A- 24 F corresponds to subscripts A-F of the blowing openings  20 A- 20 F. It is provided a control valve  25  on the main line  23  as a flow regulating valve controlling flow rate of the inert gas led to each branch pipe lines  24 A- 24 F from the tank  21 . It is provided assistant control valves  26 A- 26 F as control valves for branch pipe lines controlling flow rate of each branch pipe lines  24 A- 24 F on each of the branch pipe lines  24 A- 24 F. It is provided the electromagnetic proportional controlling valve capable of regulating the flow rate by changing the valve travel proportionally on the main control valve  25 . Each of the assistant control valve  26 A- 26 F may be an opening-and-shutting valve switchable between two positions of an opened position and a closed position or electromagnetic proportional controlling valve. 
   Further, in vicinity of the third slit  20 D, in other words, adjacent to the transmission window  6 , a plurality of (three in figures) gas intake openings  30 L,  30 C and  30 R are provided along the width direction of the film F. The gas intake opening  30 C is located in the center of the width direction of the film F, the gas intake openings  30 L,  30 R of the right and the left are located in the vicinity of both ends of the width direction of the film F. In the following, when it is not necessary to judge the gas intake openings  30 L,  30 C and  30 R, these are described as gas intake openings  30 . 
   An oxygen concentration observation system  31  is connected to each of the gas intake opening  30 . In  FIG. 1 , only an oxygen concentration observation system  31  for the gas intake opening  30 R of the right side is shown, however, the oxygen concentration observation systems  31  of the same configuration are connected to each of other gas intake openings  30 C,  30 L respectively. The oxygen concentration observation system  31  comprises, sampling pipe line  32  for taking gas of the irradiation chamber  4  from the gas intake opening  30 , a filter  33  for removing dust in the gas taken to the sampling pipe line  32 , a pressure sensor  34  for detecting the pressure (filter second pressure) of the gas at the downstream (secondary side) of the filter  33 , a oxygen concentration meter  35  for detecting the oxygen concentration in the gas at the downstream of the filter  33 , a pump  36  for drawing the gas in the irradiation chamber  4  into the sampling pipe line  32 , and a flow meter  37  for detecting the flow rate of the gas discharged from the pump  36 . A cartridge type filter is used for the filter  33  so as to be changed easily. A flow meter  37  is provided so that an operator can confirm whether the gas of flow rate within the range that the oxygen concentration meter  35  can work normally flows through the sampling pipe line  32 . 
   The pressure signal and the oxygen concentration signal which the pressure sensor  34  and the oxygen concentration meter  35  output respectively are input into a control unit  40  of the electron beam irradiation device  1 . The control unit  40  conducts such as irradiation control of the electron beam by the electron beam generator  5 , traveling control of the film F, flow control of the inert gas introducing from the blowing openings  20 A- 20 F so that the electron beam is irradiated to the film F under a predetermined condition. 
     FIG. 3  is a functional block diagram of the control unit  40 . The control unit  40  has a control section  41  executing various processing which is necessary for an irradiation of the electron beam to the film F. The control section  41  is constructed as a control device which utilizing a microprocessor or a logical circuit such as LSI. The pressure sensors  34  and the oxygen concentration meters  35  of the above-described oxygen concentration observation systems  31  are connected to the control section  41 , and a control panel  42  is connected as the device which the operator of the electron beam irradiation device  1  inputs the operating condition such as traveling speed of the film F. The electron beam generator  5 , a film traveling device  43  and a valve drive circuit  44  are connected to the control section  41  as control object devices. The control section  41  provides instructions to the electron beam generator  5  and the valve driving circuit  44  according to the operating condition instructed from the control panel  42 . The electron beam generator  5  generates an electron beam according to an indication from the control section  41 . The film traveling device  43  make the film F travel by rotating and driving such as wind-up roll  16  according to the indication from the control section  41 . The valve drive circuit  44  controls the main control valve  25  and the assistant control valves  26 A- 26 F to switch according to the indication from the control section  41 . 
   In the control panel  42 , as a mode of an operation of the electron beam irradiation device  1 , a standby mode, an arranging operation mode and a continuous operation mode are selectable. When the standby mode is instructed from the control panel  42 , the control section  41  stops the electron beam irradiation from the electron beam generator  5  and stops the traveling of the film F by the film traveling device  43 . On the other hand, when a continuous traveling mode from the control panel  42  is instructed, the control section  41  make the film F travel in a predetermined production rapidity (200 m/min., for example) which is set by the control panel  42  beforehand, and the electron beam of a predetermined energy quantity is irradiated from the electron beam generator  5  continually. The arranging operation mode is chosen when the preparation operation such as design matching, a color matching or cut &amp; paste of the film F is conducted. In the arranging operation mode, the operator can instruct such as an irradiation condition of the electron beam or the traveling speed of the film F through the control panel  42  appropriately, the control section  41  controls the irradiation of the electron beam by the electron beam generator  5  and the traveling of the film F by the film traveling device  43  according to those indications. 
   The control section  41  decides the valve travel of the main control valve  25  and the assistant control valves  26 A- 26 C on the basis of the pressure and the oxygen concentration which the pressure sensor  34  and the oxygen concentration meter  35  detects respectively in any mode of the standby mode, the arranging operation mode or the continuous operation mode, and sends the decided valve travel to the valve drive circuit  44  and controls the valve travel of these control valves  25 ,  26 A- 26 C. However, in the decision of the valve travel, the traveling speed of the film F by the film traveling device  43  is also considered, but the details are mentioned later. 
   Further, a process monitoring device  45  is connected to the control section  41 . The process monitoring device  45  is provided for monitoring the irradiation quality of the electron beam. The control section  41  acquires the state quantity which is necessary for monitoring the manufacturing process, such as the acceleration voltage of the electron beam generator  5 , the beam current, the traveling speed of the film F by the film travel device  43 , the oxygen concentration detected by the oxygen concentration meter  35  from the electron beam generator  5  and the film travel device  43 , and output these state quantity to the process monitoring device  45 . The process monitoring device  45  records a temporal change of the state quantity which received from the control section  41 , and displays the record content to a display unit (not shown) such as a monitor. 
     FIG. 4  is a flow chart showing a procedure of the flow control processing which the control section  41  executes in appropriate cycle repeatedly for controlling the flow rate of the inert gas by operating the control valves  25 ,  26 A- 26 C. In the flow control processing in the figure, at first, in the step S 1 , the control section  41  takes the output signal of the pressure sensor  34  and detects the filter second pressure of each sampling pipe line  32 , and in the next step S 2 , judges whether each pressure is insufficient. This is the processing to judge whether the filter  33  functions normally. When the second pressure in either filters  33  is insufficient in the step S 2 , the control section  41  judges that the clogging occurs in the filter  33  and advances to the step S 3 , send a warning to the operator of the clogging of the filter  33  by the predetermined alarm device (for an example, a process monitoring device  45 , or a buzzer and a lamp attached thereof), and in the following step S 4 , excludes the sampling pipe line  32  judged as the filter  33  is clogged from the estimating object of the oxygen concentration. Due to the processing of the step S 2 , the control section  41  functions as the filter monitor of the present invention, and due to the processing of step S 3 , the control section  41  functions as an alarm device of the present invention. On the other hand, when all the second pressures of the filters  33  are judged as a normal in the step S 2 , steps S 3  and S 4  are skipped. 
   In the next step S 5 , the control section  41  takes the output of the oxygen concentration meter  35  of the sampling pipe line  32  judged as the second pressure of the filter  33  is normal and detects the oxygen concentration. In this case, when there are detected values of a plurality of oxygen concentration meters  35 , the mean value of those is acquired as oxygen concentration in the irradiation chamber  4 . However, the maximal value may be used, and when there are lots of oxygen concentration meters  35 , the oxygen concentration in the irradiation chamber  4  may be judged by various values such as a median value or a mode value which are determined by the statistical technique. 
   In the following step S 6 , the control section  41  decides the throttle amount ΔVO from the fully-opened position of the main control valve  25  on the basis of the detected value of the oxygen concentration. That is, as shown in  FIG. 5 , the correspondence between the oxygen concentration and the appropriate valve travel of the main control valve  25  is obtained beforehand, utilizing this correspondence, the valve travel which the oxygen concentration detected in the step S 5  is corresponding to OXC1 is determined as a basis valve travel VObase. And, the difference between the valve travel VOfull at the fully-opened state and the basic valve travel VObase of the main control valve  25  (=VOfull−VObase) is decided as the throttle amount ΔVO. As shown in  FIG. 5 , the relation between the oxygen concentration and the basic valve travel VObase of the main control valve  25  is determined so that the valve travel decrease when the oxygen concentration deteriorates, however, the changing manner may be set appropriately in consideration of the responsibility of the oxygen concentration for the flow control. 
   Next, the control section  41  acquires the traveling speed V of the film F in the step S 7 , further in the step S 8 , whether traveling speed V is zero is judged. When the traveling speed is zero, that is the film F stops or the film F is not introduced, go to the step S 9 , and the control section  41  controls only assistant control valves  26 A- 26 C corresponding to the blowing openings  20 A- 20 C of the introduction portion  10  to fully-opened state. Thereby, the introductions of the inert gas from the first slit  20 A, the second slit  20 C and the gas supplying hole  20 B are stopped. Because there is no risk that the air is break in accompanying the film F when the film F does not travel. Other assistant control valves  26 D- 26  F are controlled to the fully-opened state, and the inert gas is introduced into the irradiation chamber  4  from the third slit  20 D, the fourth slit  20 E and the gas supplying hole  20 F. 
   In the following step S 10 , the control section  41  sets the target valve travel VOtgt of the main control valve  25  to the value travel which are obtained by subtracting the throttle amount ΔVO from the valve travel VOfull of fully-opened state. In this case, the target valve travel VOtgt of the main control valve  25  corresponds to the basic valve travel VObase shown in the  FIG. 5 . On the other hand, when the traveling speed V is not zero in the step S 8 , the control section  41  goes to the step S 11  and all the assistant control valves  26 A- 26 F are controlled to fully-opened state. In the following step S 12 , the control section  41  judges whether the traveling speed V of the film F is bigger than zero and lower than the threshold Vth. The threshold Vth is given as the reference value judging whether the flow rate of the inert gas is decreased corresponding to the lowering of the oxygen concentration. The threshold Vth is set to the value lower than the lower limit of the production velocity when the film F traveling in the above-described continuous irradiation mode and higher than the upper limit of the traveling speed instructed in the arranging operation mode. 
   When the step S 12  is affirmed, the control section  41  advances to the step S 13 , and the target valve travel VOtgt of the main control valve  25  is set to the value provided in the next equation. VOtgt=VOfull−ΔVO×C Wherein C is a correction-ratio for restricting the throttle amount ΔVO into the width smaller than that when the film is stopped, 0&lt;C&lt;1. That is to say, in the step S 13 , the target valve travel VOtgt is set grater than the basic valve travel VObase given as the target valve travel VOtgt of when the film is stopped. When the film F travels, the oxygen concentration is easy to rise by entering of the accompanying air in comparison with when the film F is stopped, on the other hand, the response delay of the flow control corresponding to the detected value of the oxygen concentration occurs, therefore, when the speed of the film F in low, it is preferable to restrain the decreasing width of the flow rate smaller than that when the film F is stopped for keeping the oxygen concentration in acceptable limit. 
   On the other hand, when the step S 12  is negatively judged, the control section  41  advances to the step S 14 , and the target valve travel VOtgt of the main control valve  25  is set to the valve travel VOfull of the fully-opened state. When the step S 12  is negatively judged, because the film F travels at the production speed and the irradiation of the electron beam is conducted, in this case it is preferable to give priority to the prevention of the rise of the oxygen concentration over the reduction of the quantity of inert gas used, therefore, regardless of the oxygen concentration, the main control valve  25  is maintained in fully-opened state. When the film F consists of the paper backing, because the paper powder occurs by the irradiation of electron beam and the irradiation chamber  4  is polluted, it is preferable to set the flow rate of the inert gas greatly as much as possible. As described above, after having set the target valve travel VOtgt of the main control valve  25 , the control section  41  controls the main control valve  25  to the target valve travel VOtgt in the step S 15 , afterwards, the processing of  FIG. 4  is finished. In the step S 15 , in addition to the proportional control on the basis of the deviation of the given target valve travel VOtgt and the current valve travel, the derivation control and the integral control may be conducted. By executing above-described steps S 5 -S 15 , the control section  41  functions as a valve travel control device of the present invention. 
   According to the above-described processing, if the oxygen concentration drops when the film F is stopped or traveled low speed (V&lt;Vth), the target valve travel VOtgt of the main control valve  25  decreases, and the flow rate of the inert gas introduced into the irradiation chamber  4  is throttled. Thereby, the oxygen concentration is maintained in an acceptable limit while wasteful consumption of the inert gas is suppressed, and amount thereof can be reduced. In particular, when the film F is stopped, because the blowing of the inert gas in the introduction portion  10  is stopped, the reduction effect of quantity of the inert gas consumed is small. When the film F travels at low speed, in comparison with the speed when it is stopped, because the target valve travel VOtgt of the main control valve  25  for the same oxygen concentration is set to the higher value, it can be prevented that a rise of the oxygen concentration caused by the response delay of the control while suppressing the wasteful consumption of the inert gas. Further, when the film F traveling in the production velocity and the electron beam is irradiated, even if the oxygen concentration drops, the target valve travel VOtgt of the main control valve  25  is maintained in the valve travel VOfull of the fully-opened state and the oxygen concentration in the irradiation chamber  4  is controlled in minimum, therefore, there is no risk that the irradiation quality of the electron beam deteriorates. 
   In above-described embodiment, a plurality of gas intake openings  30 C,  30 L,  30 R are arranged in the width direction of the film F and the oxygen concentrations in the middle and the both ends of the width direction portion of the film F are detected, therefore comparing to the case in which an oxygen concentration is detected only one place, the detection accuracy of the oxygen concentration in the irradiation chamber  4  improved, and the flow rate of the inert gas can be controlled more adequately. In addition, the pressure at the downstream of the filter  33  is detected and the clogging of the filter  33  is judged, then the sampling pipe line  32  in which a clogging is generated is excluded from the estimating object of the oxygen concentration, therefore, there is no risk that the error is generated in the flow control of the inert gas caused by the clogging of the filter  33 . By the way, when the filter  33  is clogged, the oxygen concentration at the downstream of the filter  33  rises, in the case that the flow rate of the inert gas is controlled in response to the oxygen concentration, the inert gas is introduced more than required and a waste occurs to the quantity consumed. According to the embodiment, there is no risk that such a waste generates. Further, because an alarm is output when a clogging of the filter  33  is detected, maintenance of the filter  33  can be promoted to the operator. Therefore, the risk that the operator does not realize the state in which an error is generated in the detected value of the oxygen concentration because of the clogging of the filter  33  and that he/she does not ignored can be removed. 
   The present invention is not limited to above described embodiment and can be carried out in various kinds of embodiment. The variations of above-described embodiment are explained in the following. 
   In the above-described embodiment, as far as the clogging is not generated in the filter  33 , all the sampling pipe lines  32  connected to each gas intake openings  30 C,  30 L,  30 R at the three places are intended to be the objects for estimate, but the number of the object for estimating may be changed in response to the width of the film F. For example, when the width of the film F is small and the gas intake openings  30 L,  30 R of both ends are positioned outside of the film F, flow control is conducted on the basis of only the oxygen concentration in the gas taken to the sampling pipe line  32  from the central gas intake opening  30 C, on the other hand, when all the gas intake openings  30 C,  30 L,  30 R face to the film F, the oxygen concentration in the gas taken into all the sampling pipe lines  32  may be detected and the flow control on the basis of mean value may be conducted. In this case, the width of the film F is input from the control panel  42 , in response to the input value, the control section  41  may choose the sampling pipe line  32  of the object for estimating. 
   In above-described embodiment, the main control valve  25  is maintained in fully-opening state during continuous irradiation, however, the present invention is not a limited to this, during the electron beam is irradiated while the film F is traveling, the flow control of the inert gas in response to the oxygen concentration may be conducted. For example, in case that the film F consisting of the materials which does not generate a dust such as a paper powder (for example, a film of a resin backing), even in the continuous irradiation, the flow rate of the inert gas may be throttled in response to the decreasing of the oxygen concentration. 
   In above-described embodiment, the setting of the target valve travel VOtgt of the main control valve  25  is changed corresponding to three phases of the stopped phase, the low speed transit-phase, and the continuous irradiation phase of the film F, however, the present invention is not limited to this, the target valve travel VOtgt may be controlled more finely. For example, as traveling speed of the film F rises, by decreasing the correction-ratio C, the target valve travel VOtgt under the same oxygen concentration may be continuously changed according to the change of the traveling speed V. When the responsibility of the flow control of the inert gas for the change of the oxygen concentration is secured enough, the flow control in consideration of the traveling speed is omitted, regardless of the traveling speed, the flow rate of the main control valve  25  may be controlled according to the relation between the oxygen concentration and the basic valve travel VObase which illustrated in  FIG. 5 . 
   The control of the flow rate of the inert gas does not limit to the one realized by the main control valve  25 . For example, by omitting the main control valve  25  and by changing the valve travel of the assistant control valves  26 A- 26 F individually on the basis of the oxygen concentration, the flow rate of the inert gas introduced into each place of the irradiation chamber  4  may be controlled. The layout of the gas intake opening does not limit to the example in which it is arranged in the width direction of the film F in the position adjacent to the transmission window  6 . For example, the gas intake openings are provided on a plurality of positions as for the traveling direction of the film F, and the oxygen concentration distribution in the irradiation chamber  4  are judged more finely, then in response to the discriminate result, each valve travel of the assistant control valves  26 A- 26 F may be controlled individually. 
   In above-described embodiment, when the film F is stopped, the introductions of the inert gas from the first slit  20 A, the second slit  20 C and gas supplying hole  20 B are stopped, however by throttling the valve travel of the assistant control valves  26 A- 26 C to the extent not get to the fully-closed state, an amount of the inert gas less than that of in the low speed traveling or in the continuous irradiating may be supplied from those blowing openings  20 A- 20 C. However, the flow control of the inert gas utilizing the assistant control valve  26 A- 6 C may be omitted, and the position and number of blowing opening which becomes the object for controlling can be changed depending on the configuration of the irradiation chamber  4  appropriately. Further, for a plurality of blowing openings in the introduction portion  10 , an assistant control valve can be used commonly and the valve travel may be controlled.