CA1131712A

CA1131712A - Microwave heating apparatus with a variable power load control device

Info

Publication number: CA1131712A
Application number: CA350,468A
Authority: CA
Inventors: Kazufumi Matsushima
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1979-04-24
Filing date: 1980-04-23
Publication date: 1982-09-14
Also published as: GB2048028B; MY8500545A; AU528965B2; AU5752880A; GB2048028A; JPS55143791A; FR2455247A1; DE3015436A1; FR2455247B1

Abstract

Abstract of the Disclosure A microwave heating apparatus includes a heating chamber for heating food, a microwave generator for supplying a micro-wave into the heating chamber for internally heating the food, heating resistors for externally heating the food, and a con-trol circuit for controlling the connection of the microwave generator and the heating resistors to a power source. The control circuit effects a control that power is supplied to the microwave generator or the heating resistor, or is simul-taneously supplied to them. With such a construction, the food may be cooked in a desired manner and the cooking time is reduced.

Description

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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 i ~

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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 ' -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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~13~712 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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'; ~ ' ~3~'7~2 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 " ~13~71Z

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 '.- _ 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

8 (800 W) __ MAGNETRON OUTPUT

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.

, 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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g 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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A microwave heating apparatus comprising:
a heating chamber for heating food;
a microwave generator having an output varying cir-cuit for supplying microwave energy to said heating chamber, said output varying circuit including a first means for caus-ing said microwave generator to provide within said heating chamber a first power level and a second means for causing said microwave generator to provide within said heating cham-ber a second power level lower than said first power level;
resistive heating means for heating food within said chamber, said resistive heating means including a first resis-tor having a first characteristic power consumption and a sec-ond resistor having a 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, respect-ively, wherein said first control means causes said microwave generator to provide said first power level; said second con-trol means causes said microwave generator to provide 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 connec-ted to said power supply; said fifth control means causes said second resistor to be connected to said power supply; said sixth control means causes said microwave generator to provide said second power level and said first heater 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 predetermined and smaller than a rated power consumption of said microwave heat-ing apparatus.

2. A microwave heating apparatus according to claim 1, where-in said control circuit comprises:
a first power switch for switching power from a power source;
a second switch coupled to said first switch for switching power received therefrom;
a third switch coupled to said second switch for switching power received therefrom;
a first series circuit including said first resistor and a fourth switch coupled in series between a node joining said first and second switches and a return for said power source;
a second series circuit including said second resis-tor and a fifth switch coupled in series between said node joining said first and second switches and a return for said power source; and wherein said output varying circuit of said micro-wave generator comprises a sixth switch which is closed to provide said first power level and opened to provide said sec-ond power level, said first through sixth switches controlling said seven heating modes as follows:
in each of said heating modes, said first and second switches are closed;
in said first heating mode, said fourth and fifth switches are open and said third and sixth switches are closed;
in said second heating mode, said fourth, fifth and sixth switches are open and said third switch is closed;
in said third heating mode, said third switch is open and said fourth, fifth and sixth switches are closed;
in said fourth heating mode, said fifth and third switches are open and said fourth and sixth switches are closed;

in said fifth heating mode, said fourth and third switches are open and said fifth and sixth switches are closed;
in said sixth heating mode, said fifth and sixth switches are open and said fourth and third switches are closed; and in said seventh heating mode, said fourth switch is open and said third, fifth and sixth switches are closed.

3. A microwave heating apparatus according to claim 1, where-in said first resistor is disposed in an upper portion of said heating chamber and said second resistor is disposed in a lower portion of said heating chamber.