U.S. patent application number 10/084513 was filed with the patent office on 2002-06-27 for microwave excitation gas laser oscillating apparatus.
This patent application is currently assigned to Matsushita Electric Ind. Co., Ltd.. Invention is credited to Iwasaki, Yutaka, Kubo, Masahiko.
Application Number | 20020080839 10/084513 |
Document ID | / |
Family ID | 16501561 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020080839 |
Kind Code |
A1 |
Iwasaki, Yutaka ; et
al. |
June 27, 2002 |
Microwave excitation gas laser oscillating apparatus
Abstract
Based on an oscillation ON/OFF signal and an output state
instruction signal output to a high-voltage generating circuit
(101) from a power supply control apparatus (301), heater voltage
applied from a heater circuit (201) to a heater of a magnetron (2)
is controlled depending on whether the magnetron (2) is stopped
from oscillating or is continuously or intermittently operating.
The heater voltage of the magnetron (2) measured during the
intermittent operation is controlled to be higher than that
measured during the continuous output and to be lower than that
measured while the oscillation is stopped, thereby reducing the
change in temperature of the heater and providing a lower limit
temperature at which the magnetron (2) can oscillate stably. This
configuration increases the service life of the magnetron (2) used
for a microwave excitation laser.
Inventors: |
Iwasaki, Yutaka; (Mino-shi,
JP) ; Kubo, Masahiko; (Takarazuka-shi, JP) |
Correspondence
Address: |
PARKHURST & WENDEL, L.L.P.
1421 PRINCE STREET
SUITE 210
ALEXANDRIA
VA
22314-2805
US
|
Assignee: |
Matsushita Electric Ind. Co.,
Ltd.
1006, Oaza Kadoma
Kadoma-shi
JP
|
Family ID: |
16501561 |
Appl. No.: |
10/084513 |
Filed: |
February 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10084513 |
Feb 28, 2002 |
|
|
|
09121597 |
Jul 24, 1998 |
|
|
|
6373873 |
|
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Current U.S.
Class: |
372/55 ;
372/38.02 |
Current CPC
Class: |
H03B 9/10 20130101; H01S
3/0975 20130101 |
Class at
Publication: |
372/55 ;
372/38.02 |
International
Class: |
H01S 003/00; H01S
003/22; H01S 003/223 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 1997 |
JP |
9-205108 |
Claims
1. A microwave excitation gas laser oscillating apparatus
comprising a discharge tube that excites a gas by means of
discharge to generate a laser light; a magnetron that supplies
microwaves to said discharge tube; and a microwave power supply
apparatus for supplying power to said magnetron, wherein said
microwave power supply apparatus has a heater circuit for applying
heater voltage to the heater of said magnetron; and a high-voltage
generating circuit for applying a high voltage between the anode
and cathode of said magnetron, and said heater circuit controls the
heater voltage output to said magnetron from the heater circuit
depending on whether the magnetron is stopped from oscillating or
providing a continuous output or an intermittent output.
2. A microwave excitation gas laser oscillating apparatus according
to claim 1, wherein said heater circuit is configured so that the
heater voltage measured while the magnetron is providing a
continuous output is lower than that measured while the oscillation
of the magnetron is stopped.
3. A microwave excitation gas laser oscillating apparatus according
to claim 1, wherein said heater circuit is configured so that the
heater voltage measured while the magnetron is providing an
intermittent output is lower than that measured while the
oscillation of the magnetron is stopped.
4. A microwave excitation gas laser oscillating apparatus according
to claim 1, wherein said heater circuit is configured so that the
heater voltage measured while the magnetron is providing an
intermittent output is higher than that measured while the
magnetron is providing a continuous output and is lower than that
measured while the oscillation of the magnetron is stopped.
5. A microwave excitation gas laser oscillating apparatus
comprising a discharge tube that excites a gas by means of
discharge to generate a laser light; a magnetron that supplies
microwaves to said discharge tube; and a microwave power supply
apparatus for supplying power to said magnetron, wherein said
microwave power supply apparatus comprises: a heater circuit for
applying heater voltage to the heater of said magnetron; a
high-voltage generating circuit for applying a high voltage between
the anode and cathode of said magnetron; and an abnormal-voltage
detecting circuit for detecting abnormal oscillation of the
magnetron through abnormal voltage generated in an
abnormal-voltage-detecting winding provided in a step-up
transformer constituting the high-voltage generating circuit.
6. A microwave excitation gas laser oscillating apparatus according
to claim 5, wherein the abnormal-voltage detecting circuit has a
display function for generating an abnormality alarm signal if
abnormal voltage lasts over a set period of time.
7. A microwave excitation gas laser oscillating apparatus
comprising a discharge tube that excites a gas by means of
discharge to generate a laser light; a magnetron that supplies
microwaves to said discharge tube; and a microwave power supply
apparatus for supplying power to said magnetron, wherein said
microwave power supply apparatus comprises: a heater circuit for
applying heater voltage to the heater of said magnetron; a
high-voltage generating circuit for applying high voltage between
the anode and cathode of said magnetron; and an abnormal-voltage
detecting circuit for detecting a defect in the heater section of
the magnetron by detecting abnormal voltage through a
heater-voltage-detectin- g monitor winding provided in a heater
transformer constituting said heater circuit.
8. A microwave excitation gas laser oscillating apparatus
comprising a discharge tube that excites a gas by means of
discharge to generate a laser light; a magnetron that supplies
microwaves to said discharge tube; and a microwave power supply
apparatus for supplying power to said magnetron, wherein said
microwave power supply apparatus comprises: a heater circuit for
applying heater voltage to the heater of said magnetron; a
high-voltage generating circuit for applying high voltage between
the anode and cathode of said magnetron; a current detecting
element that detects current flowing between the anode and cathode
of the magnetron; and an abnormal-current detecting circuit which
operates, when detecting that the current value of the current
detecting element is abnormal, to stop the operation of only the
abnormal microwave power supply.
9. A microwave excitation gas laser oscillating apparatus according
to claim 8, further comprising a plurality of microwave power
supply apparatuses and magnetrons.
10. A microwave excitation gas laser oscillating apparatus
comprising a discharge tube that excites a gas by means of
discharge to generate a laser light; a magnetron that supplies
microwaves to said discharge tube; and a microwave power supply
apparatus for supplying power to said magnetron, wherein said
microwave power supply apparatus comprises: a heater circuit for
applying heater voltage to the heater of said magnetron; a
high-voltage generating circuit for applying high voltage between
the anode and cathode of said magnetron; abnormal-oscillation
detecting means for detecting abnormal oscillation of the
magnetron; and a heater voltage instructing circuit which operates,
when the abnormal-oscillation detecting means detects abnormal
oscillation of the magnetron, to gradually increase the heater
voltage, store in the heater circuit a heater voltage at which the
abnormal oscillation stops, and output an instruction signal for
operation at that heater voltage.
11. A microwave excitation gas laser oscillating apparatus
according to claim 10, wherein the abnormal-oscillation detecting
means comprises an abnormal-voltage detecting circuit for detecting
abnormal oscillation of the magnetron through abnormal voltage
generated in the abnormal-voltage-detecting winding provided in the
step-up transformer constituting the high-voltage generating
circuit.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a microwave gas laser
oscillating apparatus for providing microwave discharge
excitation.
BACKGROUND OF THE INVENTION
[0002] There is a recent tendency to miniaturize gas laser
oscillating apparatuses, and to do this, attempts are made to
increase the excitation frequency. Conventional power supplies for
gas laser oscillators use DC and a high frequency between several
100 kHz and several 10 MHZ but have problems in costs and
controllability.
[0003] Various microwave excitation gas laser oscillators are now
examined, and an example is explained with reference to FIG. 12.
This figure shows a configuration of a microwave power supply
apparatus for a conventional microwave excitation laser oscillating
apparatus.
[0004] In FIG. 12, reference numeral 3 is a heater transformer in a
heater circuit 1 for applying a heater voltage to a heater section
of a magnetron 2 that generates microwaves; 4 is a high-voltage
generating circuit for applying a high voltage to a cathode and an
anode of the magnetron 2 and to which a high voltage is applied
from a switching circuit 5 via a step-up transformer 6 and a
high-voltage rectifying circuit 7.
[0005] In a microwave power supply apparatus of this configuration,
the switching circuit 5 applies about 20 kHz of switching operation
to an input DC voltage, which is then applied to the step-up
transformer 6. The step-up transformer 6 has its voltage increased
up to a value required for oscillate the magnetron 2, rectified by
the high-voltage rectifying circuit 7, and then applied to the
cathode and anode of the magnetron 2. The heater transformer 3
reduces a commercial 200 VAC or 100 VAC and directly applies it to
the heater section of the magnetron 2.
[0006] In this configuration, the variation of the commercial
voltage is directly reflected in the variation of the heater
voltage, but the output from the magnetron 2 does not vary if the
heater voltage is within a specified variation range. In addition,
the specified value of the variation of the heater voltage is
within the variation range of the commercial voltage, and no effect
appears in the output from the magnetron 2.
[0007] However, no microwave power supply apparatuses of the
conventional configuration have means for detecting abnormal
oscillation caused by the degradation of the magnetron 2, so the
decrease in laser optical output during the abnormal oscillation of
the magnetron 2 is a problem. In addition, the magnetron 2 may be
degraded in a short time, resulting in short maintenance
cycles.
DISCLOSURE OF THE INVENTION
[0008] It is thus an object of this invention to prevent abnormal
oscillation of the magnetron and to detect degradation of the
magnetron in order to increase its service life.
[0009] To achieve this object, an invention according to claim 1
comprises a discharge tube that excites a gas by means of discharge
to generate a laser light, a magnetron that supplies microwaves to
the discharge tube, and a microwave power supply apparatus for
supplying power to the magnetron, wherein the microwave power
supply apparatus has a heater circuit for applying heater voltage
to the heater of the magnetron, and a high-voltage generating
circuit for applying a high voltage between the anode and cathode
of the magnetron, and wherein the heater circuit controls the
heater voltage output to the magnetron from the heater circuit
depending on whether the magnetron is stopped from oscillating or
is providing a continuous output or an intermittent output.
[0010] According to this configuration, the heater temperature
varies to a small extent and the heater voltage is controlled at a
lower limit value at which the magnetron can oscillate stably, so
that the magnetron can oscillate stably and its service life can be
increased.
[0011] An invention according to claim 5 comprises a discharge tube
that excites a gas by means of discharge to generate a laser light,
a magnetron that supplies microwaves to the discharge tube, and a
microwave power supply apparatus for supplying power to the
magnetron, wherein the microwave power supply apparatus comprises a
heater circuit for applying heater voltage to the heater of the
magnetron, a high-voltage generating circuit for applying a high
voltage between the anode and cathode of the magnetron, and an
abnormal-voltage detecting circuit for detecting abnormal
oscillation of the magnetron through an abnormal voltage generated
in an abnormal-voltage-detecting winding provided in a step-up
transformer constituting the high-voltage generating circuit.
[0012] According this configuration, abnormal voltage generated
during abnormal oscillation is detected through the winding of the
step-up transformer in order to detect the abnormal oscillation of
the magnetron by means of the abnormal-voltage detecting
circuit.
[0013] An invention according to claim 7 comprises a discharge tube
that excites a gas by means of discharge to generate a laser light,
a magnetron that supplies microwaves to the discharge tube, and a
microwave power supply apparatus for supplying power to the
magnetron, wherein the microwave power supply apparatus comprises a
heater circuit for applying heater voltage to the heater of the
magnetron, a high-voltage generating circuit for applying a high
voltage between the anode and cathode of the magnetron, and an
abnormal-voltage detecting circuit for detecting a defect in the
heater section of the magnetron by detecting an abnormal voltage
through a heater-voltage-detecting monitor winding provided in a
heater transformer constituting the heater circuit.
[0014] This configuration allows it to accurately detect a defect
in the heater circuit of the magnetron by detecting a decrease in
the heater voltage of the magnetron caused by the lack of the
oscillation of the magnetron caused by a short or an open circuit
in the heater of the magnetron.
[0015] An invention according to claim 8 comprises a discharge tube
that excites a gas by means of discharge to generate a laser light,
a magnetron that supplies microwaves to the discharge tube, and a
microwave power supply apparatus for supplying power to the
magnetron, wherein the microwave power supply apparatus comprises a
heater circuit for applying heater voltage to the heater of the
magnetron, a high-voltage generating circuit for applying high
voltage between the anode and cathode of the magnetron, a current
detecting element that detects current flowing between the anode
and cathode of the magnetron, and an abnormal-current detecting
circuit which operates, when detecting that the current value of
the current detecting element is abnormal, to stop the operation of
only the abnormal microwave power supply.
[0016] According to this configuration, the current detecting
element detects the current flowing between the anode and the
cathode in order that the abnormal-current detecting circuit can
stop the operation of the abnormal microwave power supply.
[0017] An invention according to claim 10 comprises a discharge
tube that excites a gas by means of discharge to generate a laser
light, a magnetron that supplies microwaves to the discharge tube,
and a microwave power supply apparatus for supplying power to the
magnetron, wherein the microwave power supply apparatus comprises a
heater circuit for applying a heater voltage to the heater of the
magnetron, a high-voltage generating circuit for applying a high
voltage between the anode and cathode of the magnetron,
abnormal-oscillation detecting means for detecting the abnormal
oscillation of the magnetron, and a heater voltage instructing
circuit which operates, when the abnormal-oscillation detecting
means detects abnormal oscillation of the magnetron, to gradually
increase the heater voltage, to store in the heater circuit a
heater voltage at which the abnormal oscillation stops, and to
output an instruction signal for operation at that heater
voltage.
[0018] According to this configuration, when abnormal oscillation
occurs, the abnormal oscillation is stopped in a short time by
increasing the heater voltage and at this heater voltage at which
the oscillation is stopped, operation is carried out, so that
stable oscillation can be secured even though the magnetron
degrades.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a block diagram showing a microwave power supply
apparatus for a gas laser oscillating apparatus according to
Embodiment 1 of this invention;
[0020] FIG. 2 is a waveform diagram showing changes in heater
temperature when the heater voltage of the microwave power supply
apparatus is constant;
[0021] FIG. 3 is a waveform diagram showing that the heater voltage
of the microwave power supply apparatus is controlled to maintain a
constant heater temperature;
[0022] FIG. 4 is a block diagram showing a microwave power supply
apparatus for a gas laser oscillating apparatus according to
Embodiment 2 of this invention;
[0023] FIG. 5 is a waveform diagram showing the voltage between the
cathode and anode of the microwave power supply apparatus, a
current, and an output waveform from a tertiary winding in a
step-up transformer;
[0024] FIG. 6 is a characteristic diagram showing Efm and
abnormal-oscillation duration of the microwave power supply
apparatus;
[0025] FIG. 7 is a waveform diagram showing the definition of an
abnormal-oscillation duration during each switching cycle of the
microwave power supply apparatus;
[0026] FIG. 8 is a heater circuit block diagram showing a microwave
power supply apparatus according to Embodiment 3 of this
invention;
[0027] FIG. 9 is a heater circuit block diagram showing a microwave
power supply apparatus according to Embodiment 4 of this
invention;
[0028] FIG. 10 is a heater circuit block diagram showing a
microwave power supply apparatus according to Embodiment 5 of this
invention;
[0029] FIG. 11 is a characteristic diagram showing an
abnormal-oscillation duration vs. the heater voltage of the
microwave power supply apparatus; and
[0030] FIG. 12 is block diagram showing a conventional microwave
power supply apparatus for a microwave gas laser oscillating
apparatus.
DESCRIPTION OF THE EMBODIMENTS
[0031] (Embodiment 1)
[0032] Embodiment 1 according to this invention is described with
reference to FIGS. 1 to 3. Embodiment 1 relates to claims 1 to
4.
[0033] A microwave power supply apparatus 10 has a heater circuit
201 for applying a heater voltage to a heater section of the
magnetron 2; and a high-voltage generating circuit 101 for applying
a high voltage between an anode and a cathode of the magnetron 2.
The high-voltage generating circuit 101 has input thereto an
oscillation ON/OFF signal that determines whether to turn the
oscillation of the magnetron 2 on or off and an output state
instruction signal that determines the output state (continuous and
intermittent outputs) of the magnetron 2. The high-voltage
generating circuit 101 generates a high voltage only when both the
oscillation ON/OFF signal and the output state instruction signal
are at a high level, and applies it to the magnetron 2 for
oscillation. In addition, the oscillation ON/OFF signal and the
output state instruction signal are input to the heater circuit 201
from a power supply control device 301, and the heater circuit 201
varies the heater voltage based on the oscillation ON/OFF signal
and the output state instruction signal.
[0034] Whether the magnetron 2 oscillates stably depends on whether
the a sufficient heater voltage has been applied to allow the
heater temperature to reach a value at which the magnetron can
oscillate, provided a load state is constant. To reduce the
degradation of the magnetron 2, operation must be performed at a
possibly minimum heater temperature and with a possibly minimum
change in heater temperature caused by the activation or
deactivation of oscillation.
[0035] FIG. 2 shows the heater temperature when the heater voltage
is constant. While the oscillation of the magnetron 2 is stopped,
the heater temperature corresponds to a set heater voltage. In
addition, when the magnetron 2 is continuously oscillating, the
oscillation causes the heater to be heated to increase the heater
temperature. In addition, the thermal constant of the heater is
generally about three seconds, and the time required for the heater
temperature to stabilize depends on the thermal constant. Then, the
magnetron 2 is intermittently oscillated, the heater temperature
increases as in the continuous oscillation. The magnetron 2,
however, is subjected to a repetition of the activation and
deactivation of oscillation, so the heater temperature depends on
the time ratio of the activation and deactivation of
oscillation.
[0036] FIG. 3 shows that the output state of the magnetron 2 is
used to control the heater voltage so that the heater temperature
remains constant. If the heater voltage is constant, the heater
temperature increases when the oscillation of the magnetron 2 is
turned on, but by reducing the heater voltage, the increase in
heater temperature caused by the oscillation is canceled to allow
the heater temperature to become the same as that measured while
the magnetron 2 is not oscillating. In addition, while the
magnetron 2 is providing an intermittent output, the heater
temperature is maintained at a constant value regardless of the
operational state of the magnetron 2 by reducing the heater voltage
below the value measured while the magnetron 2 is not oscillating
and above the value measured during the continuous output of the
magnetron 2.
[0037] According to Embodiment 1, based on an oscillation ON/OFF
signal and an output state instruction signal from the power supply
control apparatus 301, the heater circuit 201 controls the heater
voltage so as to correspond to the operational state of the
magnetron 2 in order to reduce the change in heater temperature,
thereby increasing the service life of the magnetron 2. In
addition, since the heater voltage is set so that the heater
temperature has a lower limit value at which the magnetron 2
oscillates stably, the magnetron 2 can be oscillated stably to
increase its service life.
[0038] Furthermore, during the continuous oscillation of the
magnetron 2, the heater circuit 201 reduces the heater voltage
based on the oscillation ON/OFF signal and output state instruction
signal output from the power supply control apparatus 301. Thus, a
large increase in heater temperature can be restrained to reduce
the change in temperature, thereby allowing the magnetron 2 to
oscillate stably and increasing its service life.
[0039] Furthermore, during the intermittent oscillation of the
magnetron 2, the heater circuit 201 reduces the heater voltage
based on the oscillation ON/OFF signal and output state instruction
signal output from the power supply control apparatus 301. Thus,
the heater temperature, which becomes higher than when oscillation
is stopped, can be reduced to reduce the change in temperature,
thereby allowing the magnetron 2 to oscillate stably and increasing
its service life.
[0040] In addition, by setting the heater voltage in such a way
that it is high during continuous output, that it has an
intermediate value during intermittent output, and that it is
lowest during a stop, the change in the heater temperature can be
reduced and the magnetron 2 can be stably oscillated to increase
the service life of the magnetron 2.
[0041] (Embodiment 2)
[0042] Embodiment 2 of this invention is described below with
reference to FIGS. 4 to 7. Embodiment 2 relates to claims 5 and 6.
The same members as in the preceding embodiment have the same
reference numerals and their description is omitted.
[0043] A microwave power supply apparatus 20 has a heater circuit
201 for applying a heater voltage to the heater section of the
magnetron 2; and a high-voltage generating circuit 105 for applying
a high voltage between the anode and cathode of the magnetron 2.
The high-voltage generating circuit 105 has a step-up transformer
103 that increases a voltage switched by a switching circuit 102,
up to a value at which oscillation can occur. The voltage that has
been increased by the step-up transformer 103 is rectified by a
high-voltage rectifying circuit 104 and then applied between the
anode and cathode of the magnetron 2.
[0044] The step-up transformer 103 has a tertiary winding 103a that
is an abnormal-voltage-detecting winding for detecting an abnormal
voltage caused by the abnormal oscillation of the magnetron 2; and
an abnormal-voltage detecting circuit 401 for determining the
degradation of the magnetron 2 from an abnormal voltage of the
tertiary winding 103a to activate a display device such as a
built-in alarm. Reference numeral 302 designates a control circuit
that can stop the microwave power supply apparatus 20 based on a
signal from the display device.
[0045] FIG. 5 shows a magnetron current flowing between the anode
and cathode of the magnetron 2, the waveform of a voltage between
the anode and cathode of the magnetron 2, and the waveform of an
output voltage from the tertiary winding 103a. The magnetron
current performs a pulsating operation corresponding to the
switching cycle of the switching circuit 102 and has an off period
of time during which no current flows. When the magnetron 2
oscillates abnormally, an abnormal voltage is generated that is 1.5
times to twice as large as the normal value. At this point, an
abnormal voltage is generated in the tertiary winding 103a. The
abnormal voltage can be detected by the abnormal-voltage detecting
circuit 401 to detect the abnormal oscillation of the magnetron 2.
In addition, FIG. 6 shows Efm, which is a parameter indicating the
service life of the magnetron 2, and an abnormal-oscillation
duration upon the activation of the magnetron 2. The
abnormal-oscillation duration refers to a period of time over which
an abnormal voltage lasts that is generated between the anode and
cathode of the magnetron 2 during each switching cycle as shown in
FIG. 7. A larger Efm indicates that the magnetron 2 is degraded. In
addition, the magnetron 2 is most likely to undergo abnormal
oscillation upon activation, and if the abnormal oscillation lasts,
the internal loss of the magnetron causes the heater temperature to
increase, thereby allowing the magnetron to return to normal
oscillation.
[0046] The abnormal-voltage detecting circuit 401 assumes that the
magnetron 2 is degraded, based on the duration of the abnormal
oscillation. If the abnormal oscillation continues over a set
period of time, the circuit 401 displays an alarm to inform that
the magnetron 2 is degraded. When this alarm is provided, the
control circuit 302 stops the microwave power supply apparatus
20.
[0047] According to Embodiment 2, the tertiary winding 103a
provided in the step-up transformer 2 can detect the abnormal
oscillation of the magnetron 2, and the abnormal-voltage detecting
circuit 401 can accurately assume the degradation of the magnetron
2 to allow efficient maintenance.
[0048] In addition, since the abnormal-voltage detecting circuit
401 has the display device for generating an abnormality alarm
signal if the abnormal voltage lasts over a set period of time; and
the control circuit 302 that can stop the microwave power supply
apparatus 20, the lifetime service life of the magnetron 2 can be
automatically detected.
[0049] (Embodiment 3)
[0050] Embodiment 3 of this invention is described below with
reference to FIG. 8. Embodiment 3 relates to claim 7. The same
members as in the previous embodiments have the same reference
numerals and their description is omitted.
[0051] A microwave power supply apparatus 30 has a heater circuit
204 for applying a heater voltage to the heater section of the
magnetron 2; and the high-voltage generating circuit 101 for
applying a high voltage between the anode and cathode of the
magnetron 2.
[0052] A single-phase 200 VAC is input to a heater control circuit
202 in the heater circuit 204, which then provides a constant
output of 170 VAC. The output voltage from the heater control
circuit 202 is reduced by a step-down transformer 203 down to about
3 VAC, which is then applied to the heater section of the magnetron
2.
[0053] The heater circuit of the magnetron 2 may be short- or
open-circuited, and if the heater circuit is short- or
open-circuited, the magnetron 2 does not oscillate. According to
Embodiment 3, the step-down transformer 203 has a monitor winding
203a that is a winding used to monitor and detect the heater
voltage so that the abnormal-voltage detecting circuit 402 detects
a decrease in detected voltage during the shorting of the heater
circuit and an increase in detected voltage during its opening. As
a result, a defect in the heater section of the magnetron 2 can be
promptly detected.
[0054] According to Embodiment 3, the abnormal-voltage detecting
circuit 402 detects an abnormal voltage via the
heater-voltage-detecting monitor winding 203a provided in the
heater transformer 203 of the heater circuit 204 in order to enable
a defect in the heater circuit of the magnetron 2 to be
detected.
[0055] (Embodiment 4)
[0056] Embodiment 4 of this invention is described below with
reference to FIG. 9. Embodiment 4 relates to claims 8 and 9. The
same members as in the previous embodiments have the same reference
numerals and their description is omitted.
[0057] Several sets of a microwave power supply apparatus 40 and
the magnetron 2 are provided, and the microwave power supply
apparatus 40 has the heater circuit 201 for applying a heater
voltage to the heater section of the magnetron 2; and the
high-voltage generating circuit 105 for applying a high voltage
between the anode and cathode of the magnetron 2. The high-voltage
generating circuit 105 has the step-up transformer 103 that
increases a voltage switched by the switching circuit 102, up to a
large value at which the magnetron 2 can oscillate, and the voltage
that has been increased by the step-up transformer 103 is rectified
by the high-voltage rectifying circuit 104 and then applied between
the anode and cathode of the magnetron 2.
[0058] Reference numeral 403 denotes a current detecting element
that detects a magnetron current flowing between the anode and
cathode of the magnetron 2. The internal temperature of the
magnetron 2 may become abnormally high due to insufficient cooling
or a mismatch with a load, and the intermediate portion between the
anode and cathode is melted to cause a short circuit. At this
point, an excessive magnetron current flows. Thus, when the current
detecting element 403 is provided for each magnetron 2 and if the
abnormal-current detecting circuit 404 detects an abnormal current,
the control circuit 302 stops the operation of only that microwave
power supply apparatus 40.
[0059] According to Embodiment 4, the abnormal-current detecting
circuit 404 detects an abnormal value of the magnetron current via
the current detecting element 403 to enable a defect between the
anode and cathode of the magnetron 2 to be detected. Thus, if the
intermediate portion between the anode and cathode of one magnetron
2 within the several sets of the microwave power supply apparatus
40 and magnetron 2 is short-circuited, the control circuit 302 can
stop the operation of that microwave power supply apparatus 40,
thereby preventing damage or spread to other microwave power supply
apparatuses 40. Even when the only microwave power supply apparatus
40 for the defective magnetron 2 for which an abnormal current is
detected by the abnormal-current detecting circuit 404 is stopped,
the other microwave power supply apparatuses 40 serve to compensate
for the loss to allow laser light to be output without changes.
[0060] (Embodiment 5)
[0061] Embodiment 5 of this invention is described below with
reference to FIGS. 10 and 11. Embodiment 5 relates to claims 10 and
11. The same members as in the preceding embodiment have the same
reference numerals and their description is omitted.
[0062] A microwave power supply apparatus 50 has the heater circuit
204 for applying a heater voltage to the heater section of the
magnetron 2; and the high-voltage generating circuit 106 for
applying a high voltage between the anode and cathode of the
magnetron 2.
[0063] An input from an AC power supply is provided to the heater
control circuit 205 of the heater circuit 204, which then outputs a
constant AC voltage. The voltage of this output is reduced by the
step-down transformer 206 and then applied to the heater section of
the magnetron 2.
[0064] In addition, the high-voltage generating circuit 106 has the
step-up transformer 103 that increases a voltage switched by the
switching circuit 102, up to a large value at which the magnetron 2
can oscillate. The voltage that has been increased by the step-up
transformer 103 is rectified by a high-voltage rectifying circuit
104 and then applied between the anode and cathode of the magnetron
2.
[0065] In this configuration, if the magnetron 2 is degraded and if
the same heater voltage is applied, then the abnormal-oscillation
duration increases. Then, however, increasing the heater voltage
reduces the abnormal-oscillation duration and a further increase
eliminates the abnormal oscillation.
[0066] Thus, according to Embodiment 5, an abnormal voltage caused
by the abnormal oscillation of the magnetron 2 is detected by the
abnormal-voltage detecting circuit 402 and the tertiary winding
103a that is an abnormal-voltage-detecting winding provided in the
step-up transformer 103, which both constitute an
abnormal-oscillation detecting means, thereby enabling the abnormal
oscillation of the magnetron 2 to be detected, as in Embodiment 2.
Furthermore, in Embodiment 5, when the abnormal-oscillation signal
is transmitted to a heater voltage instructing circuit 501 in the
heater circuit 204, the circuit 501 outputs a heater voltage
instruction signal to the heater control circuit 205 to gradually
increase the heater voltage. The heater circuit 204 uses a storage
circuit provided in the heater voltage instructing circuit 501 to
hold the heater voltage instruction signal obtained when the
abnormal oscillation is stopped, that is, when the
abnormal-oscillation signal disappears. Subsequently, the magnetron
2 is operated at that heater voltage to prevent abnormal
oscillation. If the operation time has passed to degrade the
magnetron 2 and abnormal oscillation occurs again, the heater
voltage instructing circuit 501 further increases the heater
voltage to allow operation at a heater voltage at which no abnormal
oscillation occurs.
[0067] According to Embodiment 5, the abnormal-voltage detecting
circuit 402 can detect via the tertiary winding 103a the abnormal
voltage caused by the abnormal oscillation of the magnetron 2, and
the heater voltage instructing circuit 501 can gradually increase
the heater voltage. Consequently, the magnetron can be stopped with
a short abnormal-oscillation duration and then operated at the
heater voltage at which the abnormal oscillation is stopped, so the
abnormal oscillation of the magnetron 2 can be prevented and stable
oscillation can be ensured despite the degradation of the magnetron
2, thereby enabling the magnetron 2 to be used over a long period
of time.
* * * * *