Note: Descriptions are shown in the official language in which they were submitted.
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"MICROWAVE HEATING APPARATUS"
The invention relates to a microwave heating apparatus
and, more particularly, to a microwave heating apparatus with
a function to heat food or foodstuff by a heater.
One of the known microwave heating apparatuses cooks
through two cooking modes; a microwave cooking mode in which
food placed within a heating chamber, or a cooking chamber,
is internally heated using microwave energy supplied from a
micro wave wave generator including a magnetron, and a resis-
tor heating mode in which the food is externally heated by a
plurality of heaters. In this type of heating apparatus, the
microwave heating mode and the resistor heating mode occur
independently or the resistor heating mode follows the micro-
wave convection heating mode. The heating apparatus thus
designed is unsatisfactory for the increasingly popular, var-
iable and complicated cooking sequences.
Accordingly, an object of the invention is to provide a
microwave heating apparatus which is operable lndependently
or simultaneously in a microwave heating mode and in a resis-
tor heating mode.
The present invention provides a microwave heating ap-
paratus comprising: a heating chamber for heating food; a
microwave generator having an output varying circuit for sup-
plying microwave energy to said heating chamber, said output
varying circuit including a first means for causing said
microwave generator to provide within said heating chamber a
first power level and a second means for causing said micro-
; wave generator to provide within said heating chamber a second
power level lower than said first power level; resistive heat-
ing means for heating food within said chamber, said resistive
heating means including a first resistor having a first char-
acteristic power consumption and a second resistor having a
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second characteristic power consumption lower -than said first
power consumption; a control circuit having first to seventh
control means for obtaining first to seventh heating modes,
respectively, wherein said first control means causes said
microwave generator to provide said first power level; said
second control means causes said microwave generator to pro-
vide said second power level; said third control means causes
said first and second resistors to be connected to a power
supply; said fourth control means causes said first resistor
to be connected to said power supply; said fifth control means
causes said second resistor to be connected to said power sup-
ply; said sixth control means causes said microwave generator
; to provide said second power level and said first hea-ter to be
connected to said power supply; and said seventh control means
causes said microwave generator to provide said first power
level and said second resistor to be connected to said power
supply, the power consumption of each heating mode being pre-
determined and smaller than a rated power consumption of said
microwave heating apparatus.
The microwave heating apparatus according to the inven-
tion is capable of cooking food in a variety of heating con-
ditions with an extremely reduced heating time.
Other objects and features of the invention will be
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apparent from the following description taken in connection
with the accompanying drawings, in which:
Fig. 1 is an outside view of an embodiment of a
microwave heating apparatus according to the invention;
Fig. 2 is a vertical cross sectional view taken
along line II-II in Fig. l;
Fig. 3 is a circuit diagram of a control circuit
of the heating apparatus shown in Fig. l; and
Fig. 4 is a graph plotting operation modes shown in
Fig. 1 against power consumption.
In Figs. 1 and 2, on the front of a casing 1 of a micro-
wave heating apparatus is provided a door 2 and an operation
panel 3. A heating chamber or a cooking chamber 4 is provided
within the casing 1, of which the front opening is opened and
closed by the door 2. A space la defined between the outer
wall 4a of the heating chamber 4 and the casing 1 is provided.
A supporting member 5 horizontally fixed to the rear wall of
the heating chamber 4 has food placed thereon for cooking
within heating chamber 4. One end of a waveguide 6, being
disposed within the space la, communicates with the heating
chamber 4 through the upper wall of the heating chamber 4
while the other end is coupled with a magnetron 7, leading to
an antenna 7a for detecting microwave energy from the magne-
tron therefrom. With this connection, a microwave wave is
introduced from ...
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the magnetron 7 into the heating chamber 4. Provided within
the heating chamber 4 are an upper heater 8 (800 W) and a
lower heater 9 (400 W), disposed horizontally and fixed to
the rear wall of the heating chamber 4. The operation panel
3 includes: a cooking mode indicator 10 including light
emitting sections for visually indicating various cooking
modes; a lever 11 for switching cooking modes; a temperature
adjusting knob 12 for setting the air temperature within the
heating chamber 4 when the upper and lower heaters 8 and 9
are used; a timer 13 for set~ing a desired cooking time; a
start switch 14 for starting a cooking; and a power switch
15. Contacts of switches (not shown) are provided on the
rear side of the operation panel corresponding to the lever
11. Movement of the lever 11 to the right as viewed in the
drawing sets the following cooking modes: a 1st mode for
cooking by an oscillation output 400 W of the magnetron
- (microwave heating mode); a 2nd mode for cooking of ragout
or defrost by an oscillation output 200 W (microwave heating
mode); a 3rd mode for cooking by using the upper and lower
heaters 8 and 9 (resistor heating mode); a 4th mode for
cooking by the upper heater 8 only (resistor heating mode);
a 5th mode for cooking by the lower heater 9 only (resistor
: heating mode); a 6th mode for cooking by the oscillation
output 200 W and the upper heater 8 (microwave and resistor
heating mode); a 7th mode for cooking by an oscillation
output ...
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400 W and the lower heater 9 (microwave and resistor heating
mode). Those modes set are indieated by eorresponding light
emitting sections of the eooking mode indieator 10, respect-
ively.
Turning now to Fig. 3, there is shown a eontrol eircuit
used in the eooking apparatus shown in Figs. 1 and 2. One
end of an AC power source 20 is connected to one end of the
upper heater 8, through a power switch 15, a normally opened
contact 24al of a relay 24, and a normally opened switch llal
under control of the lever 11. The other end of the upper
heater 8 is connected to the other end of the power source 20
- through a normally opened contaet 24a2 of the relay 24. A
node between the contacts 24al and the switch llal is connec-
ted to one end of the lower heater 9, through a normally
opened switeh lla2 under eontrol of the operation of the
~ lever 11. The other end of the heater 9 is conneeted to the
7 other end of the upper heater 8. The node between the switch
llal and the switeh lla2 is eonneeted through a normally
; closed switch llbl under control of the lever 11 to one end
of a primary winding 21a of a high voltage transformer 21
included in a microwave wave generator 17. The other end of
the primary winding 21a is connected to the other end of the
lower heater 9. A rectifier circuit eomprising a capaeitor
C1 and a diode D eonnected witll the polarity as shown is
connected aeross the seeondary ...
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winding 21b of the transformer 21. The anode of the magne-
tron 7 is connected to the cathode of the diode D and the
cathode thereof is connected to the anode of the diode D.
The magnetron 7 is grounded at the anode and connected at
the cathode across the secondary winding 21c of the trans-
former 21. A normally closed switch llb2, which operates
in response to the operation of the lever 11, is connected
across the capacitor Cl through a capacitor C2. The capa-
citors Cl and C2 and the switch llb2 form an output vary- -
ing circuit 22 for the magnetron 7. When the switch llb2
is closed, the magnetron produces an output of 400 W. When
the switch llb2 is opened, it produces an output 200 W.
Connected between the connection point of the power switch
15 and the normally opened contact 24al and the other end
of the power source 20 are a door switch 23, a start switch,
or a normally opened contact 14 of an automatic releasing
type, a timer switch 13a, and a relay 24 which are arranged
in series. The timer 13 is connected in parallel with the
` relay 24 and, when the timer is set at a given time, the
timer switch 13a is closed. When the relay 24 is energized,
the normally opened contacts 24al, 24a2 and 24a3 are closed.
When the time set at the timer elapses, the switch 13a is
opened. When the relay 24 is deenergized, the contacts 24al,
24a2 and 24a3 are opened.
The rated power consumption of the microwave
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heating apparatus is set up at 1220 W, when considering
the current capacity of home use power, and is the sum
of the power consumption consumed when the upper and
lower heaters 8 and 9 are operated simultaneously and
the power consumptions of a lighting lamp tnot shown) in
the heating chamber 4, a motor and the like.
The operation of the microwave heating apparatus as
mentioned above will be described. Relations between
operations of the switches llal, l-la2, llbl and llb2 and
the respective cooking modes are tabulated in the
; following table.
T A B L E
MODE NO. CONTENTS SWITCHES
llal lla2 llbl llb2
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l MAGNETRON OUTPUT OFF OFF ON ON
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2 200 W OFE' OFF ON OFF
~_ _ AND HEATER 9 (400 W) ON ON OFF ON
4 HEATER 8 (800 W) ON OFF OFF ON
HEATER 9 (400 W) OFF ON OFF ON
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MAGNETRON OUTPUT
6 200 W AND HEATER ON OFF ON OFF
8 (800 W) __
MAGNETRON OUTPUT
7 400 W AND HEATER OFF ON ON ON
9 (400 W)
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The operation of the microwave heating apparatus in the
6th mode will be described. The power switch 15 is turned on
and food is placed on the supporting member 5 in the heating
chamber 4. Then, the door 2 is closed. And the lever 11 is
moved to set the cooking mode to the 6th mode. In this con-
dition, the normally opened switch llal is turned on by the
lever 11 while the normally closed switch llb2 is turned off.
The normally opened switch lla2 is left OFF while the normally
closed switch llbl is left ON. At the next step, a time
necessary for the cooking is set by the timer 13 to turn on the
start switch 14. Upon the ON of the start switch 14, the
timer switch 13a is turned ON to energize the relay 24. As a
result, the normally opened contact 24a3 is turned ON and thus
the relay 24 is left energized. Accordingly, the upper heater
8 of 800 W is connected to the power source and the magnetron
17 oscillates. Since the switch llb2 is turned off, the out
put power of the magnetron 7 is 200 W. The food (not shown)
on the shelf 5 is heated externally by heat emanating from the
upper heater 8 while at the time it is heated internally by a
microwave wave generated from the magnetron 7. With the elapse
of the set time of the timer 13, the timer switch 13a is turned
off. Accordingly, the relay 24 is deenergized and tne contacts
24al and 24a2 are turned off. At this time, the cooking of the
6th mode is completed.
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The power consumption of the heater is the same as the
capacity of the heater. The power consumption of the magne-
tron 7 is approximately two times the oscillation output
thereof. Accordingly, the power consumed in the 6th mode
cooking is 1200 W, the sum of the power consumption 800 W of
the upper heater 8 and that 400 W of the magnetron 7. The
sum is below the rated power consumption 1220 W of the high
frequency heating apparatus.
The operation of the microwave heating apparatus in the
7th mode will be described. In the operation the power
switch 15 is turned on, food is placed on the shelf 5, and
the door 2 is closed, as in the 6th mode. The cooking mode
is set to the 7th mode by means of the lever 11. Upon the
setting, the normally opened switch lla2 is closed. The
normally opened switch llal remains OFF, the normally closed
switch llbl remains ON, and the normally closed switch llb2
remains ON. Then, the timer 13 is set to a given time and
the start switch 14 is turned on, so that the lower heater g
and the magnetron 7 are energized. Since the switch llb2 is
turned on, the magnetron 7 oscillates at the output 400 W.
The food is externally heated by the heater 9 of 400 W while
at the same time it is internally heated by the high fre-
quency wave from the magnetron 7. With the elapse of the
set time of the timer 13, the timer switch 13a, the switch
25 24al and the switch 24a2 are turned off.
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At this time, the 7th mode cooking is completed. In the
7th mode, the lower heater has 400 W of the consumption power
and the magnetron 7 has 800 W. Therefore, the total power
consumption in this mode is below the rated power consumption
1220 W.
As described above, by selectively switching the ener-
gizations of the heaters 8 and 9 and the output of the magne-
tron, it is possible to perform the microwave heating and the
resistive heating simultaneously within the rated power con-
sumption of the apparatus. In addition to the cooking modes
6 and 7, the remaining cooking modes may be performed in sim-
ilar ways, selectively. The concurrence of the microwave
heating mode and the resistor heating mode indicates that it
; is possible to variously cook food and to reduce the cooking
time greatly.
The output varying circuit of the magnetron 7 is not
limited to that as described above. An alternative circuit,
for example, is such that a motor for defrosting is provided
together with a switch to intermittently interrupt a current 20 passage to the magnetron in accordance with the rotation of
the motor.
While the invention has been described in connection
with what is presently considered to be the most practical
and preferred embodiments, it is to be understood that the
invention is not to be limited to the disclosed embodiments
but on the contrary, is intended to cover various modifi-
cation and equivalent arrangements included within the
spirit and scope of the appended claims wllich scope is to be
accorded the broadest interpretation so as to encompass all
such modifications and equivalent structures.
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