JP2009289527A - Ultraviolet ray irradiation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a suitable light-emitting spectrum upon dimming without damaging life of a magnetron for discharging an electrodeless lamp. <P>SOLUTION: The electrodeless lamp 12, wherein a discharge medium is enclosed, capable of light-emitting ultraviolet rays is formed in a lamp house 11 on the basis of microwaves via the magnetrons 131, 132 for generating microwaves and waveguides 151, 152. The magnetrons 131, 132, and the electrodeless lamp 12 in the lamp house 11 perform cooling by sending air from an air inlet 17 and by exhausting heat from an exhaust port 214 of a duct 21. An amount of ventilation for cooling by bringing into contact with the electrodeless lamp 12 is set up to be a small amount when an output of a power supply 14 for driving the magnetrons 131, 132 is decreased. Thus, a suitable spectrum upon dimming can be obtained by preventing overcooling of the electrodeless lamp 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ultraviolet irradiation apparatus that uses an electrodeless ultraviolet lamp of a microwave feeding type and is mainly used for applications such as ink drying for printing, fine exposure for semiconductors, and curing of adhesives for liquid crystals.

  A conventional ultraviolet irradiation apparatus using an electrodeless ultraviolet lamp of a microwave feeding type emits light by exciting encapsulated chemicals with microwaves. As an application, it emits ultraviolet rays and visible light, and is used in processes such as surface hardening treatment of a surface coated with paint, ink, resin, coating, etc., and synthesis and treatment of chemical substances by photochemical reaction. A magnetron is used to generate microwaves to excite the encapsulated chemicals of the electrodeless lamp.

Excitation of an electrodeless lamp by transmitting microwaves is performed from a magnetron to an electrodeless lamp through a waveguide. In order to generate heat from the magnetron and the electrodeless lamp, the magnetron and the electrodeless lamp are simultaneously cooled by supplying cooling air from the blower to the magnetron and the electrodeless lamp. (For example, Patent Document 1)
Special table 2003-518728 gazette

  The technology of Patent Document 1 described above has a function of cooling the magnetron and the electrodeless lamp at the same time. When the air flow is reduced in order to optimize the electrodeless lamp temperature during dimming, the temperature of the magnetron is reduced. Ascends and affects the life of the magnetron. For this reason, it is common to make the air volume at the time of all-light lighting and the light control the same state.

  However, if the airflow during lighting and dimming is constant, the electrodeless metal halide lamp encapsulated with iron and mercury is overcooled and the lamp is overcooled and iron and mercury are not cooled. It was found that the emission ratio changed and caused a spectrum change.

  For this purpose, a dimming system is conceivable in which the amount of microwave irradiation to the electrodeless lamp is varied by controlling the amount of power to the magnetron and the emission intensity of the electrodeless lamp is varied. In this case, a protection system using a temperature sensor is mounted to detect an abnormal temperature in a lamp house that houses an electrodeless lamp or the like. Therefore, there is a problem that the system becomes complicated because different detection mechanisms such as a temperature sensor and an optical sensor must be used.

  An object of the present invention is to provide an ultraviolet irradiation device capable of obtaining a desired emission spectrum at the time of dimming while not impairing the life of a magnetron for discharging an electrodeless lamp.

  In order to solve the above-described problems, an ultraviolet irradiation device of the present invention includes an electrodeless lamp in which a discharge medium capable of emitting ultraviolet rays by microwaves is enclosed, a magnetron for supplying microwaves to the electrodeless lamp, A waveguide for supplying microwaves generated from the magnetron to the electrodeless lamp, a reflector for condensing or diffusing the ultraviolet light of the electrodeless lamp, and at least the magnetron and the electrodeless lamp. A cooling mechanism that cools with a cooling medium to be blown, wherein the cooling mechanism changes an amount of air blown to cool the electrodeless lamp based on an output of a power source that drives the magnetron. It is characterized by having.

  According to the present invention, a good emission spectrum can be obtained regardless of the total light state or the dimming state without impairing the life of the magnetron.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  1 to 3 are diagrams for explaining a first embodiment of the ultraviolet irradiation apparatus according to the present invention. FIG. 1 is a system configuration diagram, FIG. 2 is a cross-sectional view taken along the line II ′ of FIG. It is a block diagram for demonstrating an example of the electrodeless lamp used for FIG.

  First, in FIGS. 1 and 2, reference numeral 11 denotes a lamp house made of, for example, stainless steel having a function of shielding microwaves. A so-called electrodeless lamp 12 having no electrode is disposed at the lower center of the lamp house 11. It is attached. Reference numeral 13 denotes a magnetron that generates a microwave of 2.45 GHz, for example, and power is supplied to the magnetron 13 from a power supply 14. Reference numeral 15 denotes a waveguide that transmits the microwave generated by the magnetron 13 from the antenna 16 and transmits it to the electrodeless lamp 12.

  Here, a configuration example of the electrodeless lamp 12 will be described with reference to FIG. Reference numeral 121 denotes a cylindrical bulb having a length of about 240 mm made of quartz glass that transmits ultraviolet light. The valve 121 has a taper formed so that the central portion 122 is thinner than both end portions 123 and 124. The outer diameter of both end portions 123 and 124 is, for example, about 17 mm, and the outer diameter of the central portion 122 is 10 mm. Degree. An inert gas and a discharge medium such as mercury or iron are sealed in the light emission space 125 of the bulb 121. Support portions 126 and 127 for supporting the valve 121 are formed integrally with the valve 121 at both ends of the valve 121. The electrodeless lamp 12 can emit light from the discharge medium by irradiating microwaves.

  1 and 2 again, an air inlet 17 is provided on the upper surface of the lamp house 11, and air that is a cooling medium blown from the blower 18 is taken into the lamp house 11. A duct (not shown) is provided between the blower 18 and the intake port 17 so as to take in air sent from the blower 18.

  On the back side of the electrodeless lamp 12, a reflecting plate 19 for condensing or diffusing the irradiated ultraviolet light is installed. Further, an RF screen 20 constituting an irradiation window is provided on a part of the lamp house 11 on the front surface of the reflection plate 19. The RF screen 20 is made of metal and has an opening, blocks microwaves, and allows ultraviolet light and air to pass through. For example, the RF screen 20 is formed by knitting metal wires into a mesh shape or by punching a metal plate to have an opening.

  Reference numeral 21 denotes an exhaust duct disposed in close contact with the lower portion of the lamp house 11. The duct 21 has a box shape, and openings 211 and 212 having the same shape and the same size as the RF screen 20 are formed on the upper surface plate and the lower surface plate on which the RF screen 20 is located, respectively. Further, the duct 21 has an exhaust port 214 formed through a vent hole 213. The opening 212 is attached with a filter 22 made of, for example, quartz glass that blocks air flow and allows ultraviolet light to pass therethrough.

  The magnetron 13 and the electrodeless lamp 12 blow air from the blower 18 for blowing into the air inlet 17 and the lamp house 11, exhaust the air from the air outlet 214 of the duct 21, and cool the cooling air. Is configured.

  An electromagnetic valve 23 is attached to the side surface of the lamp house 11 facing the vicinity of the junction between the magnetron 13 and the waveguide 15. When the electromagnetic valve 23 is opened, the inside and outside of the lamp house 11 pass through the electromagnetic valve 23. It becomes a communication state. The electromagnetic valve 23 requires means such as attaching an RF filter for preventing microwave leakage.

  Reference numeral 24 denotes a control unit that controls the output voltage of the power source 14 to change the power supplied to the magnetron 13 and change the output of the microwave to adjust the light of the electrodeless lamp 12. That is, the control unit 24 operates the magnetron 13 with all light power when the input control signal is 100%, and operates with 50% of the total light of the magnetron 13 when the control signal is 50%. 14 is controlled.

  At the same time, the control unit 24 also performs control to close the electromagnetic valve 23 when the control signal is 100% and open the electromagnetic valve 23 when the control signal is 50%.

  Here, when the magnetron 13 is being driven, air is blown from the blower 18 and taken into the lamp house 11 through the air inlet 17. The taken-in air is exhausted to the magnetron 13, the electrodeless lamp 12, the RF screen 20, the duct 21, and further through the exhaust port 214 of the duct 21 as indicated by the arrow in the shoreline.

  At this time, the electrodeless lamp 12 excited by the microwave of the magnetron 13 emits ultraviolet light and can irradiate an irradiation object (not shown) via the RF screen 20 and the filter 22.

  Next, cooling when the control signal input to the control unit 24 is 50% will be described with reference to FIG. The thickness of the broken-line arrow in FIG. 4 conceptually indicates the blown amount, and the thick arrow means that the blown amount is large.

  When the control signal of 50% is supplied, the control unit 24 lowers the output of the magnetron 14 and opens the electromagnetic valve 23. The amount of blown air to the magnetron 13 is the same as when a 100% control signal is supplied. After passing through the magnetron 13, a part is exhausted through the electrodeless lamp 12, the RF screen 20, the duct 21, and the exhaust port 214. The other part is exhausted through the electromagnetic valve 23.

  For this reason, as shown by the arrow, the amount of air blown to cool the electrodeless lamp 12 in contact with the electrodeless lamp 12 is smaller than that of 100%, and the overcooling of the electrodeless lamp when the microwave output is weak. Can be prevented.

  In this embodiment, when it is possible to irradiate ultraviolet light at the time of all light and dimming, the supercooling of the electrodeless lamp at the time of dimming is suppressed, and the change in the emission ratio of iron and mercury due to the supercooling By suppressing, changes in the emission spectrum can be suppressed.

  FIG. 5 is a system configuration diagram for explaining a second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part of the same function as the said embodiment, and a different part is demonstrated here.

  In this embodiment, an exhaust hole 51 is formed in the side surface of the lamp house 11 facing the vicinity of the boundary between the magnetron 13 and the waveguide 15, and the exhaust hole 51 and the exhaust blower 52 are connected via an exhaust duct 53. Is.

  In this case, when a 100% control signal is supplied to the control unit 24, the control unit 24 turns off the exhaust blower 52, air is blown from the blower 18, and the inside of the lamp house 11 through the intake port 17. Almost all of the air taken in is exhausted from the exhaust outlet 214 along the path of the broken-line arrow shown in FIG. When 100% of the control signal is supplied to the control unit 24, the exhaust blower 52 is turned on, and the air taken into the lamp house 11 is branched, and the route indicated by the broken arrow shown in FIG. Heat is exhausted from the exhaust port 214 and the exhaust blower 52.

  As described above, when the electrodeless lamp 12 is dimmed based on the control signal of 50%, the amount of air blown to cool the electrodeless lamp 12 in contact with the electrodeless lamp 12 is controlled smaller than that in the case of 100%. By doing so, it is possible to prevent overcooling of the electrodeless lamp 12 when the output of the microwave is weak.

  Therefore, also in this embodiment, when it is possible to irradiate ultraviolet light at the time of all light and light control, the supercooling of the electrodeless lamp at the time of light control is suppressed, and the light emission of iron and mercury by the supercooling By suppressing the change in the ratio, it is possible to suppress the change in the emission spectrum.

  FIGS. 6-8 is a system block diagram for demonstrating the 3rd-5th embodiment regarding the ultraviolet irradiation device of this invention. In addition, the same code | symbol is attached | subjected to the same function part as above-described embodiment, and a different part is demonstrated here.

  In the third embodiment of FIG. 6, a microwave sensor 61 is installed in the waveguide 15, and the electromagnetic valve 23 is opened and closed based on the strength of the microwave of the magnetron 13.

  In the fourth embodiment of FIG. 7, a UV sensor 71 is installed in the duct 21 in front of the RF screen 20 irradiated with ultraviolet light, and the electromagnetic valve 23 is opened and closed based on the intensity of the ultraviolet light. It is.

  In the fifth embodiment of FIG. 8, a temperature sensor 81 for measuring the temperature in the lamp house 11 near the magnetron 13 is installed, and the electromagnetic valve 23 is opened and closed based on the strength of the temperature.

  In the third to fifth embodiments of the present invention, the electrodeless lamp 12 is turned on based on the amount of power supplied from the control unit 24 to the magnetron 13 by detecting microwaves, ultraviolet light, and temperature. It is determined whether the dimming is on or not, and the solenoid valve 23 is opened and closed.

  Therefore, even when any one of microwave, ultraviolet light, and temperature is detected, if it is possible to irradiate ultraviolet light during all light and dimming, the electrodeless lamp can be overcooled during dimming. It is possible to suppress the change in the emission spectrum by suppressing the change in the emission ratio of iron and mercury due to overcooling.

  In the first and third to fifth embodiments described above, the electromagnetic valve 23 is simply opened and closed, and in the second embodiment, the exhaust blower 52 is simply turned on and off. However, in the first embodiment, the control signal supplied to the control unit 24 is not only 100% and 50%, but also the opening / closing amount of the electromagnetic valve 23 corresponding to the control amount of an arbitrary control signal is realized. It is possible to suppress the change in the emission spectrum. Also in the second embodiment, the change in the emission spectrum can be further suppressed by adjusting the exhaust amount by the exhaust blower 52 corresponding to the control amount of an arbitrary control signal.

  In the third to fifth embodiments, it is possible to further suppress the change in the emission spectrum by setting the opening / closing amount of the electromagnetic valve 23 according to the detected amounts of microwave, ultraviolet light, and temperature. Become.

  9 and 10 are diagrams for explaining a sixth embodiment related to the ultraviolet irradiation apparatus of the present invention, FIG. 9 is a system configuration diagram, and FIG. 10 is an explanatory diagram for explaining the control of FIG. The same parts as those in the embodiment of FIG.

  In FIG. 9, reference numeral 91 denotes a temperature sensor as temperature detecting means, and the temperature sensor 91 supports the reflector 17 and the like that are outside the microwave cavity 92 in which the electrodeless lamp 12 is surrounded by the reflector 17. 93. At this position, there is no substantial influence from ultraviolet light irradiated from the electrodeless lamp 12 or microwaves transmitted from the magnetron 13.

  The output of the temperature sensor 91 is supplied to the control unit 24. The control unit 24 is configured by, for example, a microcomputer provided with a program for comparing temperature values and a program for switching the temperature reference. The set values of these programs are compared with the output value of the temperature sensor 91, and output control of the power source 14 for driving the magnetron 13 is performed based on the comparison result. Further, the control unit 24 is linked to the power source 14 and can switch the reference value of the program in the memory 241 to be compared based on the output state of the power source 14.

  Here, a control example based on the set temperature value in the lamp house 11 stored in advance in the memory 241 and the program of the control unit 24 will be described with reference to FIG. FIG. 10 is for explaining the output value of the temperature sensor 91, which is the temperature in the lamp house 11, and the lighting state of the electrodeless lamp while following the passage of time.

  First, the electrodeless lamp 12 is turned on and then turned off, and after a cooling time, it is turned on again with, for example, 50% dimming. In addition, after stabilization with dimming lighting, switching to all-light lighting (100%), at some point in time when all-light lighting occurs, some abnormality occurs, the temperature in the lamp house 11 rises more than when all-light lighting is doing. As a result, control for stopping the power supply 14 for temperature protection is shown.

  When such operation control is performed, various detection conditions of the following temperatures (1) to (4) are stored in advance in the memory 241, and various temperature management is performed to compare with the temperature sensor 91. The state can be detected.

  Here, temperature detection conditions will be described.

  (1) Let the 1st detected temperature (a) be that the inside of the lamp house 11 is cooled enough and can be turned on.

  (2) The fact that the electrodeless lamp 11 is turned on is defined as a second detected temperature (b). This is set to a value obtained by adding a predetermined numerical value to the value of the temperature sensor 91 at the start of lighting in consideration that the temperature in the lamp house 11 is higher than that at the start of lighting.

  (3) Let the detection temperature at the time of light control of the electrodeless lamp 11 be (c1), the lighting temperature at the time of all lights is (c2), and these lighting states are the third detection temperature (c). This is because the set value is switched based on a signal transmitted from the power supply 14 of the magnetron 13 according to the output state of the power supply 14, and the predetermined value has a range of upper and lower limits. At the third detection temperature (c), the output of the power supply 14 is 50% dimming lighting and 100% all-light lighting. As a matter of course, the output value of the power supply 14 can be set to a setting value corresponding to 60%, 70%, or the like.

  (4) The case where the temperature in the lamp house 11 has reached the abnormal temperature is defined as a fourth detected temperature (d).

  In FIG. 10, the reference value at the time of turn-off is the first detected temperature (a). When the output value of the temperature sensor 91 is lower than the first detected temperature (a), the output of the power source 14 is not present. The electrode lamp 12 can be turned on.

  Then, when the lighting operation of the electrodeless lamp 12 is performed, the control unit 24 switches to the value of the second detected temperature (b) as a reference for comparison in response to the output from the power supply 14. When the electrodeless lamp 12 is lit, the temperature in the lamp house 11 rises. The control unit 24 when the output value of the temperature sensor 91 exceeds the second detected temperature (b) recognizes that the electrodeless lamp 12 is lit.

  Furthermore, when the reference for comparison is switched to the third detected temperature (c) and the output value of the temperature sensor 91 reaches the lower limit of the temperature (c1) of the third detected temperature (c), the control unit 24 performs the electrodeless lamp. 12 is recognized as being lit in the dimming state. When the output of the power supply 14 is switched to all-light lighting, the value of the third detection temperature (c) is raised to the temperature (c2), and when the lower limit of the temperature (c2) of the third detection temperature (c) is reached, It is recognized that the electrodeless lamp 12 is lit in the all-light state.

  In the case of returning from dimming lighting to dimming lighting, when the upper limit of the temperature (c1) of the third detection temperature (c) is reached, it is recognized that the lighting is being performed due to the dimming state. Here, once the dimming lighting or the all-lighting lighting is recognized, and an error is detected when the lower limit is exceeded, it is possible to detect turning off or overcooling.

  Furthermore, when some abnormality occurs and the temperature in the lamp house 11 rises higher than when all the lights are lit and reaches the fourth detection temperature (d), the power supply is stopped. When the power supply 14 is stopped, the comparison target in the memory 241 returns to the first detected temperature (a), and can be turned on again when the temperature in the lamp house 11 is lowered to the third detected temperature (a).

  Thus, by comparing the temperature in the lamp house 11 monitored by the temperature sensor 91 with a plurality of temperature values stored in the memory 241, the lighting state, the stable lighting state, and the abnormal state of the electrodeless lamp 12. Etc. can be detected.

  In such a state detection, when a 100% control signal indicating that all light is lit is supplied to the control unit 24, the control unit 24 turns the electrodeless lamp 12 from the power source 14 to all light. Electric power for outputting a microwave to be lit is supplied to the magnetron 13. At the same time, the power supply 14 supplies power for blowing air suitable for all-light lighting to the blower 18 for intake air.

  Next, when the control signal for 50% dimming is supplied, the control unit 24 supplies the magnetron 13 with electric power for outputting a microwave for lighting the electrodeless lamp 12 by 50% dimming. At this time, the power supply 14 supplies the blower 18 with electric power that weakens the blowing.

  The electrodeless lamp 12 can be cooled according to all-light lighting and dimming lighting. Therefore, it is possible to suppress the change in the emission spectrum by suppressing the overcooling of the electrodeless lamp during dimming and suppressing the change in the emission ratio of iron and mercury due to the overcooling.

  In this embodiment, when power control is performed on the magnetron by comparison with data stored in advance based on the output of the temperature sensor, the power supplied to the blower is adapted to the lighting state of the electrodeless lamp. By setting, it becomes possible to suppress a change in the emission spectrum.

  The present invention is not limited to the above-described embodiment. For example, the electrodeless lamp has a diameter in the center portion in the longitudinal direction smaller than the diameters at both ends, but the center portion and both ends may have the same diameter. Although the case where there is one magnetron in the casing has been described, two or more magnetrons may be used.

  Moreover, although the control part of 6th Embodiment demonstrated the case where a microcomputer was used, it is possible to use a microcomputer also in the control part of 1st-5th embodiment.

  Furthermore, the power adjustment of the magnetron during all-light lighting and dimming lighting in the first to sixth embodiments supplies control information to the control unit, but the output voltage of the power supply itself can be varied. However, the same power adjustment is possible.

The system block diagram for demonstrating 1st Embodiment regarding the ultraviolet irradiation device of this invention. Sectional drawing of the I-I 'line | wire of FIG. The block diagram for demonstrating an example of the electrodeless lamp used for FIG. The system block diagram for demonstrating the operation | movement regarding 1st Embodiment of this invention with FIG. The system block diagram for demonstrating 2nd Embodiment of this invention. The system block diagram for demonstrating 3rd Embodiment of this invention. The system block diagram for demonstrating 4th Embodiment of this invention. The system block diagram for demonstrating 5th Embodiment of this invention. The system block diagram for demonstrating the 6th Embodiment of this invention. Explanatory drawing for demonstrating the example of control of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Lamphouse 12 Electrodeless lamp 13 Magnetron 14 Power supply 15 Waveguide 16 Antenna 17 Intake port 18 Blower 19 Reflecting plate 20 RF screen 21 Duct 213 Vent hole 214 Exhaust port 22 Filter 23 Electromagnetic valve 24 Control part 51 Exhaust hole 52 For exhaust Blower 53 Exhaust duct 61 Microwave sensor 71 UV sensor 81, 91 Temperature sensor 92 Microwave cavity 93 Frame 241 Memory

Claims (10)

An electrodeless lamp in which a discharge medium capable of emitting ultraviolet rays by microwaves is enclosed;
A magnetron for supplying microwaves to the electrodeless lamp;
A waveguide for supplying microwaves generated from the magnetron to the electrodeless lamp;
A reflector for condensing or diffusing the ultraviolet light of the electrodeless lamp;
A cooling mechanism that cools at least the magnetron and the electrodeless lamp with a cooling medium that is blown,
The ultraviolet irradiation apparatus, wherein the cooling mechanism is configured to change an air blowing amount for cooling the electrodeless lamp based on an output of a power source for driving the magnetron.   The ultraviolet irradiation device according to claim 1, wherein the cooling mechanism adjusts an amount of the cooling medium in contact with the electrodeless lamp based on an amount of power supplied from the power source to the magnetron.   2. The ultraviolet irradiation according to claim 1, wherein the cooling mechanism adjusts an amount of the cooling medium in contact with the electrodeless lamp based on a microwave amount supplied from the magnetron to the electrodeless lamp. apparatus.   The ultraviolet irradiation device according to claim 1, wherein the cooling mechanism adjusts an amount of the cooling medium in contact with the electrodeless lamp based on an amount of light emitted from the electrodeless lamp.   The ultraviolet irradiation device according to claim 1, wherein the cooling mechanism adjusts an amount of the cooling medium in contact with the electrodeless lamp based on a temperature in the electrodeless lamp house.   The amount of the cooling medium in contact with the electrodeless lamp is adjusted by opening and closing through a valve installed on a side surface of the lamp house. UV irradiation equipment.   The amount of the cooling medium in contact with the electrodeless lamp is adjusted by blowing the cooling medium into the lamp house with an intake blower and discharging a part of the cooling medium from the valve with an exhaust blower. The ultraviolet irradiation device according to any one of claims 1 to 6, wherein the ultraviolet irradiation device is exhausted.   The cooling medium after contacting the electrodeless lamp is exhausted to the outside of the lamp house through a duct so that the irradiated object is not irradiated with ultraviolet light emitted from the electrodeless lamp. The ultraviolet irradiation device according to any one of claims 1 to 7. A lamp house having an opening on at least one surface;
An RF filter that is disposed in the opening, transmits ultraviolet light, and shields microwaves;
A microwave cavity disposed in the lamp house and having at least one surface identical to the opening;
An electrodeless lamp in which a discharge medium held in the microwave cavity and capable of emitting ultraviolet rays by microwaves is enclosed;
A reflector that reflects the ultraviolet light emitted from the electrodeless lamp toward the opening;
A magnetron for lighting the electrodeless lamp;
A waveguide for supplying microwaves from the magnetron to the electrodeless lamp;
A power source for driving the magnetron;
A cooling mechanism for supplying a cooling medium from the outside into the lamp house;
A temperature sensor disposed in a position not affected by substantially ultraviolet light or microwaves in the lamp house;
Storage means for storing a plurality of temperature values in the lamp house;
A control unit that controls an output voltage value of the power source based on a temperature value detected by the temperature sensor and a temperature value stored in the storage unit;
The ultraviolet ray irradiation apparatus, wherein the power source changes an amount of the cooling medium of the cooling mechanism based on a set voltage value.   The ultraviolet irradiation apparatus according to claim 1, wherein the power supplied to the magnetron is adjusted by directly adjusting the output voltage of the power source.

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