GB2255205A

GB2255205A - Method of cooking rice using a microwave oven.

Info

Publication number: GB2255205A
Application number: GB9208399A
Authority: GB
Inventors: Eun Sik Chae
Original assignee: Gold Star Co Ltd
Current assignee: LG Electronics Inc
Priority date: 1991-04-19
Filing date: 1992-04-16
Publication date: 1992-10-28
Anticipated expiration: 2012-04-16
Also published as: PH30311A; JPH05123251A; MY108401A; JPH07112457B2; KR920020136A; GB9208399D0; KR930010264B1; GB2255205B

Abstract

In a rice cooking method using a microwave oven, when a rice cooking start signal is inputted, a weight of a mixture of rice and water within a heating chamber is sensed. According to the sensed weight of the mixture, a heating time period T1, T2 of a moisture absorbing process for soaking the rice is computed, and during this heating time period, a preset microwave heating signal P1, P2 is supplied to the heating chamber to avoid premature boiling. Successively, when a heating process for boiling the rice and the water is executed, a preset microwave heating signal P3, P4 is supplied to the heating chamber, and the supply of this heating signal is continued only up to a time T3, T4 that the sensed humidity within the heating chamber reaches a preset humidity limit value G1, G2. A heating time period T5, T6 of a thorough cooking process is calculated in dependence on the heating time periods of the moisture absorbing process and the heating process, and during this heating time period, a preset microwave heating signal P5, P6 is supplied to the heating chamber. According to this method, good rice cooking is automatically executed even if the mixing ratio of the rice and water is not optimum, and a separate weight signal need not be inputted from a keyboard. <IMAGE>

Description

METHOD OF COOKING RICE USING A MICROWAVE OVEN The present invention relates to a method of controlling a microwave oven, and more particularly to a rice cooking method using a microwave oven.

The conventional rice cooking method using a microwave oven is explained with reference to FIG. 1 of the accompanying drawings.

As shown in FIG. 1, the complete rice cooking time is divided into a first heating period T1 and a second heating period T2.

Firstly, a full power microwave signal P1 is applied so that the temperature within a heating chamber rises rapidly to approximately 1000C in the first period T1. Then a microwave signal corresponding to 60% of full power is applied to cook the rice during the second heating period T2.

However, the following problems arise with this conventional method.

Moisture absorption of the rice and heating of the rice occur simultaneously during the first heating period T1. Accordingly, the rice is heated without sufficiently absorbing moisture because the temperature is rapidly raised. Therefore, the rice may not be cooked through.

Subsequently, in the second heating period T2, remaining water which has not been absorbed by the rice in the first heating period of T1 may boil and overflow. As a result, insufficient moisture may remain and the rice is either half-cooked or spoiled.

A rice cooking method for a microwave oven which solves such conventional problem is described in Korean Patent Application No. 17629/1990 by Gold Star Co. Ltd..

In accordance with this method, a special cooker is provided having a container in which a user puts a predetermined quantity (eg. corresponding to between 1 and 5 servings) of rice and water. The cooker has a key pad and the user presses a key(s) corresponding to the predetermined quantity and thereafter presses a start key. A microcomputer then controls operations in accordance with a predetermined program stored in an internal memory.

The computer firstly computes heating periods T1 T5 for respective rice cooking stages STI - ST5 and, when the door of the microwave oven is closed by the user, a plurality of relays are operated which together with the door switch energise an indicating lamp and a fan. The operation of the microwave oven is then controlled by executing sequentially each of the rice cooking stages ST1 - ST5. Thus, microwave energy for heating the rice and water to a temperature of approximately 60 0C is output so as to cause moisture to be absorbed by the rice during the heating periods T1 - T2 corresponding to a moisture absorbing period.

Subsequently, microwave energy for heating the rice and water to a temperature of approximately from 1000C to 120 C is output during heating period T3 corresponding to a heating period.

And thereafter, microwave energy for maintaining the rice and water at a temperature substantially the-same as that reached during the heating process is output during the heating periods T4 - T5 corresponding to a main cooking period.

When the main cooking period is finished, the rice cooking process is terminated.

However, in accordance with this method, the following problems have been found.

Firstly, according to this method, optimum rice cooking is carried out only when the quantity of rice and water in relation to the desired number of servings selected by a user is correctly kept. If the actual quantities differ from those preset (eg. amounts of 1.2 person, 2.5 person etc.), satisfactory rice cooking is not achieved. Secondly, according to this method, if the mixing rate of rice and water differs a little from the preset mixing rate, satisfactory rice cooking is again not achieved. Thirdly, according to this method, it has proved to be inconvenient to input the necessary key signals corresponding to the desired number of servings.

Therefore, the present invention seeks to reduce the above-described disadvantages, and it is an object of examples of the present invention to provide a rice cooking method for a microwave oven capable of executing optimum rice cooking by automatically controlling the time periods and power output of the microwave generator during successive moisture absorbing, heating and main cooking periods even without keying in the specific quantity of rice and water to be cooked.

Examples of the present invention also provide a rice cooking method for a microwave oven capable of executing optimum rice cooking even if the mixing rate of rice and water for a predetermined quantity is not quite correct.

In order to accomplish these objects, according to the present invention, firstly, a weight of mixture of the rice and the water is detected through a first sensor for detecting a weight of foods by the control of a microcomputer, and each heating time period section T1, T2 of a first stage and a second stage corresponding to the moisture absorbing process in accordance with this mixture weight is computed.

Subsequently, after a remaining gas (or steam) within a heating chamber is discharged through a predetermined time period, a second sensor (eg. humidity detecting sensor) for detecting a quantity of humidity corresponding to a heating state change quantity within the heating chamber is initialized. And successively, a first heating time period section computed for the first stage corresponding to the moisture absorbing process is counted down, and a first high frequency wave heating signal is outputted in maximum value until this heating time period is terminated.

And, when the first heating time period section of the first stage is terminated, a computed second heating time period section of the second stage is counted down, and a second high frequency wave heating signal corresponding to an approximately 30% of maximum value is outputted.

When an execution of the second stage is terminated, a third heating time period section of the third stage corresponding to the heating process is counted up and simultaneously the third high frequency wave heating signal is outputted in maximum value.

This third state is executed until the humidity quantity detected by the second sensor is raised from an initial state value to a preset first humidity limit value. When the rising of the first humidity limit value becomes slower, the third heating time period section of the third stage becomes longer as much as the value.

Whe the third stage is all executed, then a fourth stage is executed.

At the fourth stage, a fourth high frequency wave heating signal corresponding to an approximately 50% of maximum value is outputted during the fourth heating time period section.

This fourth stage is executed until the humidity quantity detected by the second sensor is raised from the initial state value to more than a preset humidity value.

When this fourth stage is finished, a fifth stage corresponding to a thoroughly cooking process is executed. The fifth heating time period section of the fifth stage is obtained by multiplying a preset constant value to a value summed from the first to fourth heating time period sections.

At the fifth stage, a fifth high frequency wave heating signal corresponding to an approximately 30% of maximum value is outputted during a computed fifth heating time period section.

Here, at a stage that the fourth stage is terminated and only the fifth stage and sixth stage which are the thoroughly cooking process have become to be remained, a value added with the fifth heating time period section of the computed fifth state and a sixth heating time period section of a preset sixth stage is displayed through a time display section, so that the user becomes possible to recognise that the rice cooking is in thoroughly cooking process. And, the user becomes to know that the cooking is becoming to be finished in accordance with the displayed remaining time being counted down.

When the fifth stage is terminated, a sixth stage comes next, and the sixth high frequency wave heating signal is outputted in maximum value during a preset sixth heating time period section.

Therefore, an efficient rice cooking can be executed even if a user does not input one by one the key signals for a predetermined quantity of the rice and the water.

In the drawings, FIG. 1 is a graph showing the relationship over the heating periods of temperature and microwave power output according to a conventional method, FIG. 2 is a block diagram showing a control apparatus for a microwave oven embodying the present invention, FIG. 3 is a circuit diagram illustrating part of a microwave oven embodying the present invention, FIG. 4 is a circuit diagram illustrating part of another embodiment of microwave oven, FIG. 5(a) and FIG. 5(b) are flow charts showing a rice cooking method exemplifying the present invention, and FIG. 6 is a graph showing the relationship over the heating periods, of humidity and microwave power output according to an example of the present invention.

Referring to the drawings, FIG. 2 shows control apparatus for a microwave oven embodying the present invention.

In FIG. 2, reference numeral 1 indicates a microcomputer, in which a predetermined program for automatically controlling the rice cooking is stored in an internal memory. The microcomputer is arranged for controlling the operation of the microwave oven in accordance with this program.

Reference numeral 2 indicates a time period display for displaying the remaining time required to complete the rice cooking process as determined by a control signal from the microcomputer 1.

A key pad 3 provides predetermined input key signals to the microcomputer 1 for selection by a user to operate the microwave oven.

Load driving circuits 4 enable the activation of various loads such as a fan and a lamp.

A clock signal generator 5 provides a clock signal for the microcomputer 1.

Input/output circuits 6 provide amplification of sensor signals to a predetermined amplitude and output these to the corresponding ports of the microcomputer 1.

A weight detecting sensor 7a detects the weight of foods being put within the heating chamber, and a humidity sensor 7b detects the humidity within the heating chamber.

In FIGS. 3 and 4, a microwave generating circuit 8 generates a microwave signal under the control of the microcomputer 1. The circuit 8 includes a magnetrom MGT, fan F, lamp LP, relays RY1 - RY3, a high voltage transformer HVT, switch contact So, relay contacts S1 S3, an AC power source AC, resistors R1 - R4, transistors Q1 - Q2, diodes D1 - D4 and capacitor C1.

A rice cooking method will now be described with reference to the construction of microwave oven shown in FIG. 2 to FIG. 4 and the flow chart shown in FIG. 5(a) and FIG. 5(b).

Referring to FIG. 2 and FIG. 3, to begin rice cooking, rice and water are put into a container and put into the heating chamber of the microwave oven. The door of the microwave is then shut which automatically closes switch contacts So. In response to its program as explained below, the microcomputer 1 energizes the relays RY1 - RY3 selectively closing the relay contacts S1 - S3 to turn on the lamp LP, start the fan F, and connect alternating current power to the primary side of the high voltage transformer HVT.

At the same time, in response to a sensor cooking key signal from the key paid 3, the microcomputer 1 starts to execute a program as shown in FIG. 5(a) and FIG. 5(b).

Thus, as shown in FIG. 5(a), when a sensor cooking key signal and the start key signal are input from the key pad 3, the microcomputer starts the fan F, and while the magnetron MGT is not energised, confirms whether or not the weight sensor 7a and the humidity detecting sensor 7b are electrically connected to its corresponding ports via the input/output circuits 6 during a predetermined time period (eg. approximately four seconds). If the weight sensor 7a and the humidity detecting sensor 7b are not connected, it displays an error for this, and thereafter terminates the routine.If they are connected the microcomputer 1 detects the weight of the foods (that is, the rice and the water) which have been put on a rotary table within the heating chamber, and multiplies the detected weight Wo by preset constants K1 and K2, to compute the first and second heating periods T1 and T2 of the first and second cooking stages ST1 and ST2 (the moisture absorbing process) in accordance with the following expressions (1).

T1 = Kl.Wo, T2 = K2.Wo ............. (1) At this time, the microcomputer 1 energises the fan F for a predetermined time period (eg. approximately ten seconds) to discharge gas and humidity within the heating chamber and thereafter using the humidity detecting sensor 7b detects the humidity remaining within heating chamber and then sets this detected value to an initial state value.

At the same time, the micrcomputer 1 controls the relays RY1, RY2 by means of the switching transistors Q1, Q2 of the load driving circuits 4 and thereby controls the microwave output power during the first and second heating periods T1 and T2 of the first and second stages ST1 and ST2, to correspond to the computed moisture absorbing process.

Thus, whenever the relays RY1, RY2, RY3 of FIG. 3 are energised, the relay contacts S1, S2, S3 are closed, and since an alternating current AC is then supplied to the microwave generating circuit 8, the circuit 8 is energised and microwave energy is output to the heating chamber, so that the rice and water start to be heated.

In executing the moisture absorbing process, the microcomputer 1 checks a flag indicating the status of the first cooking stage ST1. When the flag of the first stage ST1 is not set to a high logic state (hereinafter described as "1"), the microcomputer judges that the first heating period T1 of the first cooking stage ST1 has been completed, and checks a flag indicating the status of the second cooking stage ST2. When the flag of the first stage ST1 is set to "1", the microcomputer counts down at one second intervals the remaining time of the first heating period T1 and judges whether or not the first heating period T1 of the computed first stage ST1 is terminated.

When the computed first heating period is counted down (T1 = 0), the flag of the first stage ST1 is released to a low logic state (hereinafter described as "0") and simultaneously the flag of the second stage ST2 is set to Ill".

when the flag of said second stage ST2 is set to "1", the microcomputer 1 controls the relays RY1, RY2, RY3 of FIG. 3 so that the microwave generating circuit 8 outputs at 30% of maximum power during the second heating period T2 of the second stage ST2 until the second heating period T2 of the second stage ST2 is counted down.

Hereinafter, the whole process of rice cooking will be described with reference to the accompanying drawing of FIG. 6.

In the first cooking stage ST1 of FIG. 6, microwave energy is output at full power P1 and the rice and water are heated during the first heating period T1. When the first heating period T1 elapses, the second stage ST2 is executed, and microwave energy is output at 30% of power P2 during the second heating period T2. This allows moisture to be sufficiently absorbed into the rice.

When the second heating period T2 of the second stage ST2 (the moisture absorbing process) is terminated, the microcomputer 1 checks whether or not the flag of the third stage ST3 is at "1".

Since the flag of the third stage is set to the "1" state at the second stage ST2, the microcomputer 1 executes the third stage, and counts up the third heating period T3 by units of one second. The microcomputer 1 releases the flag of the third stage ST3 from "1" state to "0" state when the humidity change A G1 detected with the humidity detecting sensor 7b (eg. which corresponds to the gas and steam within the heating chamber produced by the heating) is raised more than a preset first humidity limit value G1, and simultaneously releases also a flag for the humidity detecting sensor 7b from "1" to "0" state and thereafter sets the flag of the fourth stage ST4 to "1" state.

Thus, the third heating period T3 of the third stage ST3 is not previously computed, and it may be longer or shorter in response to the state change within the heating chamber.

During the third heating period T3, the microwave energy is again output at full power P3 corresponding to P1 of the first period T1, and heats the rice and water within the heating chamber to a temperature between 1000C and 120 0C. It is possible, as shown in FIG.

5(1), to compare the detected humidity value AGi within the heating chamber with the preset first humidity limit value G1 not only in period T3 but also during the moisture absorbing process (periods T1 and T2) as shown in FIG. 5(a).

This meets the case when the weight sensor 7a wrongly detects the weight of the rice and water. For instance, if the weight of the rice and water is detected to be more than the actual weight, since the first heating period T2 will be computed to be longer than it should, excessive heating will take place during the moisture absorbing process. Accordingly, if and when the humidity within the heating chamber increases to more than the first humidity limit value (AG1 > G1) during the second stage of the moisture absorbing process, the second stage is terminated even if the second heating period T2 has not been completely counted down. Then the fourth cooking stage is immediately executed and the third stage is deleted.

However, if the humidity within the heating chamber detected during the second state does not reach the set first humidity limit value G1 until the second heating period T2 counts down, as described above, the third stage is then executed.

Thus, when the third cooking stage ST3 is completed during the third heating period T3, a flag for the fourth cooking stage ST4 (corresponding to the heating process) is also set to the "1" state. The fourth stage ST4 is then executed so long as the flag of the fourth stage ST4 is set to the "l" state, and microwave power is output at 50% power P4 sufficient to continue heating of the rice and water within the heating chamber during the fourth heating period T4.

Thus, microwave energy is output at full power during the third heating period T3 of the third stage ST3, and the rice and water are heated, and is then output at 50% power during the fourth heating period T4 of the fourth stage ST4, and the rice and water continue to be heated. This prevents the rice and water from overflowing, as can arise through continuous high power heating. This fourth heating period T4 is also not preset, as with the third heating period T3, and it can be shortened in accordance with the state change (ie.

humidity change within the heating chamber). That is, the fourth heating period T4 is the time period from immediately after being counted up to the time when the humidity change AG2 within the heating chamber detected by the humidity detecting sensor 7b reaches a preset second humidity limit G2.

When the humidity change AG2 detected by the humidity detecting sensor 7b exceeds the preset second humidity value G2 (E G2 > G2), the humidity detecting sensor 7b and the flag for the fourth cooking stage are released from state "1" to state "0". At the same time, the fifth heating period T5 of the fifth cooking stage ST5 (corresponding to the main cooking process) is computed in accordance with expression (2) below, and successively a flag for the fifth stage ST5 is set to state "1".

T5 = Ko (T1 + T2 = T3) ............. (2) In expression (2), Ko is a preset constant. The fifth heating period T5 can alternatively be computed by including the fourth heating period T4, and/or by excluding the third heating period T3.

Thus, microwave energy at full power P3 is output during the predetermined third heating period T3 during the third cooking stage ST3, which is the heating process. However, microwave energy is output ato 50% power P4 during the predetermined heating period T4 during the fourth cooking stage ST4 after the third heating period T3 is terminated.

Before executing the fifth stage, a sixth heating period T6 (eg. three seconds) for the sixth cooking stage ST6, which is a last stage of the main cooking process, is added to the fifth heating period T5 of the fifth stage ST5, computed as above, and this is displayed on the time period display 2. Thereafter, the microcomputer 1 checks the flag state of the fifth stage ST5, and since the flag of the fifth stage ST5 has already been set to "1" on termination of the fourth stage ST4, the fifth stag ST5 is then executed. During the fifth stage ST5, microwave energy at 30% power P5 is output to heat the interior of the heating chamber. When this fifth heating period T5 has been counted down, the flag of the fifth stage ST5 is released from state "1" to state "0".

When the fifth stage ST5 is completed, the sixth stage ST6 is then executed, and the interior of the heating chamber is heated by microwave energy at full power P6 during the sixth heating period T6 as this remaining heating time is counted down. When the sixth stage ST6 corresponding to the last stage of the main cooking process is all finished, the relays RY1 - RY3 of FIG. 3 are de-energised, and the whole rice cooking process is terminated.

In the above, the moisture absorbing process, the heating process and the main cooking process are each formed of two stages, but they may be made up of more or less stages than that.

The above described embodiment of the present invention, has the following effects and advantages.

Firstly, the weight of the rice and water mixture is detected by a weight sensor, and the heating period for the moisture absorbing process is determined according to this weight, thereby ensuring the moisture is sufficiently absorbed by the rice.

Secondly, the humidity value corresponding to a state change (eg. boiling) within the heating chamber is detected by the humidity detecting sensor, and at least two heating periods for the heating process are performed with different power levels, thereby preventing the phenomenon of the water boiling over during the rice cooking process.

Thirdly, the rice cooking time is controlled in accordance with the humidity value within the heating chamber, so that optimum cooking can be executed even if the mixing rate of rice and water is not suitable, and further the unnecessary full power heating is reduced, so that the consumption of electric power can be decreased.

Claims

1. A rice cooking method using a microwave oven comprising the steps of detecting the weight of a mixture of rice and water placed in the cooking chamber of a microwave oven; computing from said detected weight the duration of a moisture absorption period, controlling the mean level of microwave power supplied to the chamber during the moisture absorption period to avoid premature boiling; monitoring the humidity level in the cooking chamber during a subsequent heating period; controlling the level of microwave power supplied to the chamber during the heating period to reduce power when the humidity level exceeds a predetermined threshold corresponding to the onset of boiling and to initiate a main cooking period, computing the duration of the main cooking period as a predetermined function of the duration of the preceding moisture absorbing and heating periods; and controlling the level of microwave power supplied to the chamber during the main cooking period to prevent excessive boiling.

2. A method as claimed in Claim 1 wherein the main cooking period includes a final sub-period of predetermined duration in which the mean microwave power is increased.

3. A method as claimed in either of Claims 1 or 2, wherein the moisture absorption period includes a plurality of sub-periods of different mean microwave power levels, the durations of the sub-periods being computed by multiplying the sensed weight by respective predetermined factors.

4. A method as claimed in any preceding claim wherein at least a first sub-period of the main cooking period is computed to be proportional to the sum of moisture absorbing and heating periods.

5. A method as claimed in any preceding claim wherein the heating period is divided into first and second sub-periods, the first sub-period terminating and the microwave power being reduced when the humidity level exceeds said predetermined threshold, and the second sub-period terminating and the microwave power being further reduced when the humidity level exceeds a further higher predetermined threshold.

6. A method as claimed in Claim 5 wherein at least a first sub-period of the main cooking period is computed by adding together the duration of at least one of said sub-periods of the heating period and at least a sub-period of the moisture absorption period and multiplying the sum by a predetermined factor.

7. A method as claimed in any preceding claim wherein the level of microwave power is controlled to be a maximum during a first sub-period of the moisture absorption period, a first sub-period of the heating period and a last sub-period of the main cooking period.

8. A method as claimed in any preceding claim wherein the humidity level in the cooking chamber is also monitored during the moisture absorption period and the moisture absorption period is terminated prematurely if the humidity level exceeds said predetermined threshold.

9. A method of rice cooking using a microwave oven substantially as hereinbefore described with reference to and as illustrated in FIGS. 2 to 6 of the accompanying drawings.

10. A microwave oven comprising a cooking chamber; a microwave generator to supply microwave energy to the chamber; a weight sensor to sense the weight of foodstuffs placed in the chamber for cooking; a humidity sensor to sense the humidity level in the chamber; and a controller to control the mean level of microwave power supplied to the chamber by the generator during a plurality of successive periods of a cooking cycle and the durations of said periods in predetermined response to the sensed weight and humidity.

11. A rice cooking control method of a microwave oven which is characterised by comprising: a step for detecting a weight of mixture of rice and the water being put within a heating chamber; a step for computing a plurality of heating time period sections for a moisture absorption of the rice in accordance with the detected weight of mixture of the rice and the water; a step for executing the moisture absorbing process for soaking the rice by outputting a high frequency wave heating signal being preset at respectively different magnitude during each heating time period section for said moisture absorption;; a step which outputs the high frequency wave heating signal being preset at respectively different magnitude until the humidity quantity within the heating chamber corresponding to the cooking state change within the heating chamber is reached to a plurality of each humidity limit value, and executes the heating process for determining a time period until the humidity quantity within the heating chamber is reached to each humidity let set value as each heating time period section; a step for computing a plurality of the heating time period sections for the thoroughly cooking by utilising the heating time period of said moisture absorbing process and the heating process; and a step for executing the thoroughly cooked process for heating the rice and the water within the heating chamber by the high frequency wave heating signal being preset at respectively different magnitude during each heating time period section for said thoroughly cooking.

12. A rice cooking control method of a microwave oven as defined in Claim 11, which is characterised in that a last one during a plurality of the heating time periods of the thoroughly cooking process is preset without being computed by utilising the heating time periods of the moisture absorbing process and the heating process.

13. A rice cooking control method of a microwave oven as defined in Claim 11, which is characterised in that each heating time period of the moisture absorbing process is obtained by multiplying the preset plurality of the constants respectively to the detected weight of mixture of the rice and the water.

14. A rice cooking control method of a microwave oven as defined in Claim 11, which is characterised in that each heating time period of the thoroughly cooking process is obtained by adding a whole part or one part of each heating time period section of the heating process and the moisture absorbing process, and by multiplying said added value to a preset constant.

15. A rice cooking control method of a microwave oven as defined in Claim 11, which is characterised in that the moisture absorbing process and the heating process of which each first heating time period section and the last heating time period section of the thoroughly cooking process output the high frequency wave heating signal of maximum value, and the high frequency wave heating signal less than the maximum value is outputted in the heating time period section other than that.

16. A rice cooking control method of a microwave oven as defined in Claim 11, which is characterised by comprising a step that the moisture absorbing process stops the moisture absorbing process when the humidity quantity within the heating chamber is reached to the preset one humidity limit value, and stops the moisture absorbing process when it is reached to the later half of the heating process and the humidity limit value and executes the later half process of the heating process.

17. A rice cooking control method of a microwave oven as defined in Claim 11, which is characterised in that: the moisture absorbing process comprises a first heating time period section, a first stage having a first high frequency wave heating signal of maximum value; and a second heating time period section, and a second stage having a second high frequency wave heating signal corresponding to 30% of maximum value: the heating process comprises a third high frequency wave heating signal, and a third stage having a third heating time period section until the humidity quantity within the heating chamber heated by this third high frequency wave heating signal is raised from an initial value to more than a preset first humidity limit value; and a fourth high frequency wave heating signal corresponding to 50% of maximum value, and a fourth stage having a fourth heating time period section until the humidity quantity within the heating chamber heated by this fourth high frequency wave heating signal is raised from an initial value to more than a preset sensed humidity limit value; and the thoroughly cooking process comprises a fifth stage having a fifth heating time period section obtained by multiplying a preset constant to a value added with the first heating time period section, the second heating time period section and the third heating time period section, and a fifth high frequency wave heating signal corresponding to 30% of maximum value; and a sixth stage having a preset heating time period section, and a sixth high frequency wave heating signal of maximum value.

18. A rice cooking control method of a microwave oven as defined in Claim 17, which is characterised by comprising a step that the second stage stops the second stage when the humidity quantity within the heating chamber is raised to more than the preset first humidity limit value and immediately executes the fourth stage.