CN1089419C - Method for controlling a microwave oven, microwave oven and its use for cooking or heating food in accordance with the method - Google Patents

Abstract

A method for controlling a microwave oven, a microwave oven and its use for automatic cooking or heating of food are disclosed. Food-category information, which is based on the type of food and its initial state, is supplied to the oven for the selection of a corresponding preprogrammed control program. The control program is divided into time periods, during which the microwave radiation source of the oven, a microwave-activable crisp plate (4) and a grill element, if any, are activated at power levels determined by the program. The implementation of the program is monitored by one or more sensors for sensing humidity emission or other substance emission from the food and/or the temperature of the food.

Description

Method of controlling microwave oven and microwave oven using the same

The present invention relates to a method of controlling a process of heating or cooking food with a microwave radiation source and a microwave wave-excitable bottom heater in a microwave oven, the bottom heater having the form of a receptacle, tray or carrier for placing the food, the microwave radiation source and the bottom heater being separate food heating sources controllable by a control unit of the microwave oven. The invention also relates to a microwave oven for implementing the method, and to the use of such a microwave oven for cooking or heating different kinds of food by means of automatically controlled steps.

The microwave radiation source and the associated microwave feeding system generate a microwave distribution in the oven cavity, which achieves a so-called body heating of the food.

The microwave oven may comprise an additional heat source for heating the food, in the form of a microwave-excitable, so-called crisping plate (crisping plate) or browning plate (browning plate). The embrittling disk may consist of an aluminium plate with a small thermal mass and good thermal conductivity, which is provided with a microwave absorbing layer on its underside, such an embrittling disk being disclosed in SE patent specification 9003104-8. The browning disk has a large thermal mass and may consist of a ceramic disk or a glass disk provided with a microwave absorbing layer. Typically, the crisping pan and browning pan are arranged to be rotatable during heating or cooking.

The microwave oven may also have other heating sources in the form of so-called grid elements or equivalent infrared radiating elements, which are arranged in the ceiling of the oven cavity (see SE patent specification 9201786-2).

A microwave oven equipped with these three types of heat sources basically employs a body heater, a bottom heater and a top heater, in which case the heat radiation from the first two heaters is controlled by adjusting the microwave supplied to the cavity, and the latter heater is directly controlled by the activation time and power value. In order to optimally heat or cook a given type of food, the three heating sources must be used in a suitable manner, i.e. activated at a regulated power value for a suitable duration of the cooking or heating step. However, the problem is that the excitation times and power values for different kinds of food vary significantly, which is too complicated for the average user. Therefore, generally, when operating in this manner, there is no need for a user to control the cooking or heating steps, and the solution adopted is to have only one power equalization structure between the different heat sources of the microwave oven, which is determined by the manufacturer.

EP- ｃA-0066637 discloses ｃA method of supplying energy to ｃA microwave generating device and an infrared heater, in which the operating time of each radiating element is automatically changed according to the cooking cycle.

In some countries the power of the equipment connected to the Single-Phase Connection is limited, which means that the microwave radiation source and the grid element cannot be activated at the same time. Thus, it imposes a special requirement for using a heat source according to the type of food, causing a trouble to the user.

It is therefore an object of the present invention to provide a microwave oven which does not suffer from any of the above-mentioned disadvantages and which enables the heat source to be used advantageously while being more suitable for the user. Microwave ovens have become more useful due to the optimal use of heat sources, and may be used to cook or heat food or plate-like food that is currently heated in conventional ovens, for example, for the purpose of not losing the crispness of the food.

According to the invention, the above-mentioned object is achieved with a method of the type described above and having the following features, the method being characterized in that it comprises the steps of:

1. providing information about the food category to the microwave oven;

2. selecting a cooking or heating program according to the provided food category information, divided into one or more time periods;

3. energizing the two different heating sources at power values according to the selected program during each time period;

4. calculating a control variable according to one or more detection parameters obtained from one or more sensors for detecting food conditions and parameter information determined by food categories during each time period;

5. after starting the program, decrementing each time period to zero the maximum time period value determined by the food category;

6. terminating each time period when the time period has been decremented to zero, or the calculated value of the control variable exceeds a value determined by the food category; and

7. the program is terminated when all time periods have run.

The method according to the invention facilitates the operation of the microwave oven very easily, since the user only has to input information about the food category, for example only by using the control panel of the microwave oven. Thereafter, the microwave oven may be automatically started or started by operating a start button. Then, an appropriate program can be selected for the microwave oven according to the food category, and the cooking and heating steps can be fully automatically monitored.

Here, the information according to the food category or the food category means: the cooking or heating program is designed specifically for the case of special kinds of foods such as potato products, pizza (pizza) and chicken, and the state of the foods when put into the oven, such as fresh, deep-frozen raw products, deep-frozen semi-processed products, etc. The food category information may be provided by inputting, for example, a numerical value indicating a food category or state, and by inputting a first value indicating a food category and a second value indicating a food state. Preferably, the food category information is inputted by manipulating a control button dedicated to the food category or manipulating a dedicated button for the food type and initial state.

The microwave oven according to the present invention comprises: -a furnace chamber, -a microwave radiation source for feeding microwaves to the furnace chamber, -a microwave-excitable bottom heater in the form of a receptacle, tray or carrier for placing food to be heated or cooked, -a control unit for controlling the bottom heater and the microwaves fed to the furnace chamber, and-one or more sensors for detecting and transmitting to the control unit one or more detection parameters indicative of the state of the food, characterized in that there are means for providing the control unit with information about the type of food, and that the microprocessor of the control unit is programmed to perform the following functions:

1. selecting a cooking or heating program based on the provided food category information, divided into one or more time periods;

2. energizing the microwave radiation source, and thereby the bottom heater, at a power value in accordance with the selected program;

3. performing a calculation of a control variable during each time period in dependence on the parameter values obtained from said one or more sensors and one or more related constants determined by the food category;

4. after starting the program, decrementing each time period to zero the maximum time period value determined by the food category;

5. terminating each time period when the time period decreases to zero or the calculated value of the control variable exceeds a value determined by the food category;

6. when all time periods have run, the program is terminated.

In a preferred embodiment of the invention, the microwave oven has a top heater, which is for example a grid element arranged in the top plate of the oven cavity, which is controlled by the selected program.

The design of the microwave oven of the present invention is based on the insight that the average user mostly cooks or heats various foods (e.g., deep frozen easy-to-cook dishes or bread and potato products) using the microwave oven, and can distinguish the foods into various food categories according to their categories and their initial states. In addition, it has been found that optimum utilization of various heat sources, i.e., microwave fields, bottom heating crisping plates and top heating grid elements within the furnace chamber, can be achieved in a modern furnace. Such utilization can improve the result of cooking and makes it possible to use the microwave oven for a wider range of foods or plate-like foods, as well as to maintain and improve the convenience of use of the microwave oven for the user.

An application of a microwave oven according to the present invention, the microwave oven comprising: a rotating crisping pan arranged in a furnace, a grating element arranged in the ceiling of the furnace chamber, and a sensor for detecting the substances emitted by the food and a temperature value indicative of the state of the food, the method being characterized in that: the food is automatically cooked or heated according to a pre-programmed heating or cooking program selected according to the category information of the kind of the food and its initial state and provided to the microwave oven.

Preferred, non-limiting embodiments of the present invention will be described in detail with reference to the accompanying drawings. Wherein,

fig. 1 shows a microwave oven of the present invention, the door of which is opened.

Fig. 2 shows a block diagram of the relevant functional units of a microwave oven when implementing the method of the invention.

Fig. 3 shows a flow chart of a pre-programmed cooking or heating program controlled by the microprocessor for the control unit.

The microwave oven shown in fig. 1 has a housing 1, an oven door 2 for closing an oven cavity 3 in which a crisping pan 4 is arranged. The embrittlement disc 4 is made of aluminium sheet of small thermal mass, the underside of which has a layer of ferrite microwave absorbing material comprising rubber, preferably the ferrite material used has a curie point at which said layer stops absorbing energy from the microwaves, which means that the temperature of the upper side of the embrittlement disc in contact with the food is stabilized in the range of 130-. The crisping pan is adapted to rotate during the cooking or heating process. SE patent specification 9003104-8 and the applicant's designs of the type VIP20 and VIP27 microwave ovens provide a simple embrittling tray structure and its pivoting mechanism.

The microwaves are fed into the oven cavity 3 through one or more feed ports (not shown) of a microwave radiation source 20, typically a magnetron, connected to the oven (see fig. 2) via a waveguide. In the illustrated oven, a magnetron, an associated waveguide system, a power unit 19 for operating the magnetron, and a control unit 15 are arranged behind the control panel 5. In a preferred embodiment of the microwave feeding system, an upper and a lower microwave feed are used, which feeds are arranged on the right side wall of the oven cavity, while the rest of the energy feeding system is designed to feed polarized microwaves through these openings. For more details on the structure of the microwave feeding system, reference is made to SE patent specification 9003012-3 and to the applicant's microwave oven mentioned above.

A grill element (not shown) is arranged in the top plate of the oven cavity, for example in the manner described in SE patent specification 9201786-2. The grid element may be a so-called "grid tube", a quartz tube or a halogen radiation source. Specific design conditions can be found in the microwave oven designed by the applicant with the model number of VIP 20.

The control panel 5 has a display 6 which is controlled by the control unit 15 (see fig. 2) and on which symbols or simple text messages for the selected program, the remaining cooking or heating time, i.e. the confirmation of the user's selections made by the control panel and the provision of other information about how to cook or heat are to be made, are also indicated.

The control knob 7 is used to select the situation in which the oven cavity is fed with microwaves for heating, and the knob 8 is used to activate the grill element of the oven, set by the knob 9, for the desired time. These basic function options have an equivalent place to a conventional microwave oven and are also supplemented with the function options of the present invention, namely the selection from a number of pre-programmed cooking or heating programs for a specific type of food, while utilizing the interaction of direct excitation microwaves, the crisping plate and the grating elements. For example, in the case where heating with directly excited microwaves is only involved, the rotatable crisping plate 4 can be replaced by a conventional rotating base plate.

Buttons 10 and 11 are used to start and stop the operation of the microwave oven, respectively. The keypad 12 is used to enter food category information and thereby select a preprogrammed cooking or heating program. Such keys, for example, from top to bottom, may involve heating deep frozen pizzas, heating deep frozen cookies, heating deep frozen potato products (e.g., potato chips), and heating portions of deep frozen chickens. When one of the buttons is operated, the complete food category information, i.e. information about the type of food and its initial state (e.g. deep-freezing) is entered at the same time. In an improved embodiment of the microwave oven, the buttons are divided into two groups, and information on the type of food is inputted by one group of buttons and information on the initial state of the food is inputted by the other group of buttons. In the simplest present microwave oven embodiment, only one food category is used, which means that only one key button is needed. All the key buttons, as well as the knobs and the display, are connected to the control unit 15.

On the upper side of the oven, there is provided an exhaust hole 13 communicating with an exhaust passage (not shown) of the oven chamber provided in a space between a ceiling of the oven chamber 3 and the outer case 1. A humidity sensor and a temperature sensor are disposed in the evacuation passageway for sensing the humidity and temperature of the exhaust air, which have a direct relationship with respect to the condition of the food being cooked in the oven cavity. Generally, the moisture sensor may be a sensor capable of detecting substances, moisture, gases, etc. emanating from the food (see SE patent specification 9201314-2). The choice of sensors and their placement in the exhaust passage is not a matter of simplicity and will not be described in detail herein.

In view of being supplied with a single-phase power supply, the microwave oven has a power cord 14 with a plug.

The block diagram of fig. 2 shows the control unit 15 and a microprocessor and its associated program memory 16. The user's information is input to the control unit via a block 17, which represents the above-mentioned control buttons and knobs. The control unit controls the display 6. The control unit 15 controls the microwave radiation source 20 via a driver 18 and a microwave power unit 19, thereby controlling the feeding of microwaves into the oven cavity 3. The control unit 15 controls the grill element 22 via a driver 21, thereby controlling the infrared radiation fed into the furnace chamber 3. From which information is transmitted to the control unit 15 by a humidity sensor 23 and a temperature sensor 24, which detect the humidity and the temperature, respectively, of the air being discharged in the exhaust channel of the oven cavity. The control of the cooking or heating step is then achieved by a complete feedback process, so that the sensitivity of the cooking or heating step with respect to variations in the food preparation, the initial temperature and the supply voltage is reduced. For more detailed information on the structure of these functional units, reference is made to the above-mentioned patents and to microwave ovens manufactured by the applicant.

In fig. 3, a flow chart of a pre-programmed cooking or heating program is shown, which comprises three successive time periods T1, T2, T3, each having a maximum duration determined by the food category. The feeding of the microwaves, and thus the activation of the crisping plate and the grating elements, is carried out at a power value determined by the food category, as each cycle is carried out. The power values for the microwave and grid elements during the relevant period are denoted PM1, PM2, PM3 and PG1, PG2, PG3, respectively. In each cycle, the control variable C is continuously calculated from the following equation based on the information obtained from the humidity sensor and the temperature sensor.

During the time period T1 in which,

c-a 1 humidity increase + b1 temperature;

during the time period T2 in which,

c-a 2 humidity increase + b2 temperature;

during the time period T3 in which,

c-a 3 humidity increase + b3 temperature. Wherein a1, a2, a3 and b1, b2, b3 are constants determined by food category.

Within each cycle, the cycle time value is gradually decreased to zero. After the time has been reduced to zero, or when the control variable exceeds a value of c1, c2, c3, respectively, determined by the food category, the cycle is terminated and the next cycle is started. At the end of the period T3, the routine is terminated.

The power levels PM1, PM2, PM3 and PG1, PG2, PG3 for each food category are optimized separately and can be changed during a time period in a microwave oven developed in a further step. Likewise, all parameters a, b, c corresponding to the respective food categories are optimized. The microwave power supplied can be distributed between different microwave feed ports so that the energy is distributed between the bottom heating given by the embrittlement disc and the internal heating of the food supplied by the microwaves. This distribution can be achieved by means of the microwave supply system described in SE patent specification 9302302-6.

The flow chart shown in fig. 3 shows a program having the following operating steps, where y represents "yes" and N represents "no" (no):

s1 begins

S2 setting time T1, T2 and T3 according to food category.

S3 microwave power is PM1, grid has power PG1, time

The decrement is T1.

S4T 1? If T1 is 0, proceed to S6;

if T1 ≠ 0, proceed to S5.

S5 calculating C, C ≧ CI?

If not, return to S3;

if so, proceed to S6.

S6 microwave power is PM2, grid has power PG2, time

The decrement is T2.

S7T 2? If T2 is 0, proceed to S9;

if T2 ≠ 0, proceed to S8.

S8 calculates c, c ≧ c 2?

If so, proceed to S9;

if not, return to S6.

S9 microwave power is PM3, grid has power PG3,

the time decrement is T3.

S10T 3? If T3 is 0, proceed to S12;

if T3 ≠ 0, proceed to S11.

S11 calculates c, c ≧ c 3?

If so, proceed to S12;

if not, return to S9.

The program 12 terminates.

In case the microwave oven is provided with means for providing information about the weight of the food to the control unit 15, step S13 relates to a control procedure which may be developed in further steps. This can be performed, for example, by arranging the knob 9 in fig. 1 to also function as a means for setting the weight of the food when using the automatic control procedure of the invention. Alternatively, the microwave oven may be provided with a weight sensor 25 (see fig. 2) therein adjacent to the rotating crisping disk, for example in the design described in SE patent specification 9300291-3.

Based on the weight information w, the microprocessor calculates the expected durations T1e, T2e, T3e for the various time periods in the program as follows:

T1e＝k1·w

T2e＝k2·w

T3e＝k3·w

where k1, k2, k3 are constants depending on the food category.

It is also possible to detect the initial temperature of the exhaust air using the temperature of the oven cavity exhaust air as a detection parameter and to introduce the resulting correction value into said parameter information.

The microprocessor 16 of the control unit 15 can also be programmed to obtain from the temperature sensor the temperature value of the exhaust air at the start of the cooking or heating program and to adjust the program according to the obtained temperature value.

The apparatus 12 for providing food category information comprises: a first means for providing parameters of the type of food and a second means for providing parameters of the state of the food, the combination of these parameters corresponding to a cooking or heating program stored in the control unit.

The microwave oven according to the invention is provided with a rotating embrittlement disc 4 made of metal of small thermal mass and good thermal conductivity, provided with a microwave absorption layer on its underside, a grid element being provided in the ceiling of the oven cavity, the microwave oven being provided with a microwave energy feed system, the feed-in of which is at the same level as the embrittlement disc 4 and is adapted to feed polarized microwaves into said microwave absorption layer, the vertical or horizontal vector of the provided polarized microwaves being oriented substantially in the plane of said layer.

It is understood that those skilled in the art can fully develop the procedure described within the scope of the invention further, for example, at the start of the procedure the temperature of the exhaust air can be detected and the parameter information used in carrying out the procedure can be corrected on the basis of the temperature detected by the sensor. Thus, the user can eliminate any influence on the microwave oven that heats at the beginning. Other possibilities for improvement would be to introduce a temperature sensor for detecting the temperature of the embrittlement disk and to use the detected temperature to control the microwave radiation source and the grid elements. In implementing this method, so-called fuzzy logic decisions may be used. Any variations derived therefrom are considered to be within the scope of the appended claims.

Claims (17)

1. A method of controlling a process of cooking or heating food in a microwave oven, wherein cooking or heating is controlled by using a microwave radiation source (20) of the oven and a microwave energizable bottom heater (4) in the form of a receptacle, tray or carrier on which the food is placed, the radiation source and bottom heater acting as separate food heating sources controllable by a control unit (15) of the microwave oven, characterized by the steps of:

providing information about the food category to the microwave oven;

selecting a cooking or heating program according to the provided information of the food category, divided into one or more time periods T1, T2 …;

energizing the two different heating sources at power values according to the selected program during each time period;

calculating a control variable c according to one or more detection parameters obtained by one or more sensors for detecting the food condition and parameter information determined by the food category in each time period;

after starting the program, decreasing the maximum value of the time period determined by the food category for each time period to zero;

terminating each time period when the time period has been decremented to zero, or the calculated value of the control variable exceeds the value c1, c2 … as determined by the food category; and

the program is terminated when all time periods have run.

2. The method of claim 1, wherein said microwave oven further comprises a top heater in the form of a grid element or some other equivalent electrical infrared radiating element as an additional controllable heat source to energize said top heater according to a selected program.

3. A method as claimed in claim 1, wherein the program is divided into time periods T1, T2, … Tn, in each of which one or more detection parameters x1, x2, … xk are detected, characterized in that, in each time period, for each detection parameter an associated constant a1, a2, … an is selected; b1, b2, … bn; k1 … kn; as the parameter information.

4. A method as claimed in claim 3, characterized in that during the time period Tn the calculation of the control variable c is carried out in accordance with the following equation:

c＝an·x1+bn·x2+…+kn·xk

5. the method of claim 4, wherein said program comprises two time periods T1, T2 during which two sensing parameters x1, x2 are sensed, characterized in that the control variable c is calculated as follows:

c ═ a1 · x1+ b1 · x2 (over time period T1);

c ═ a2 · x2+ b2 · x2 (over time period T2).

6. The method of claim 1, wherein an increase in humidity and a temperature of the exhaust air from the microwave oven are used as the detection parameters.

7. A method as claimed in claim 1, wherein the temperature of the oven cavity exhaust air is used as a sensing parameter, characterized in that the initial temperature of the exhaust air is sensed and the resulting correction value is incorporated in said parameter information.

8. Method according to claim 1, wherein the microwave oven further comprises means for inputting or detecting the weight of the food, characterized in that the expected time Tie for each time period Ti of the cooking or heating program is calculated by means of the control unit, on the basis of the information about the weight w of the food and a constant ki determined by the food category, according to the following formula:

where, i is 1, 2, 3,

tie is the expected time of the time period,

ki is a constant determined by the food category,

w is the weight of the food; and

additional monitoring of the cooking or heating process is performed using the expected time calculation values over the time period.

9. A microwave oven comprising an oven cavity (3), a source of microwave radiation (20) for feeding microwaves into the oven cavity, a microwave-excitable bottom heater (4) in the form of a receptacle, tray or carrier on which food is placed for cooking or heating, a control unit (15) for controlling the bottom heater and the microwave feeding to the oven cavity, and one or more sensors (23, 24) for detecting one or more detection parameters indicative of the state of the food and supplying them to the control unit, characterized in that there are means (12) for supplying the control unit with information about the type of food, and in that the microprocessor (16) of the control unit is programmed so as to be able to carry out the following functions:

selecting a cooking or heating program divided into one or more time periods T1, T2, … based on the provided food category information;

energizing the microwave radiation source, and thereby the bottom heater, at a power value in accordance with the selected program;

performing a calculation of the control variable c in each time period, depending on the values of the parameters obtained from said one or more sensors and on one or more related constants determined by the food category;

after starting the program, decrementing each time period to zero the maximum time period value determined by the food category;

terminating each time period when the time period is decremented to zero or the calculated value of the control variable exceeds the value c1, c2, … as determined by the food category;

when all time periods have been run, the program is terminated.

10. The microwave oven as claimed in claim 9, wherein an exhaust passage for exhausting air from the cavity is provided, and a temperature sensor (24) and a humidity sensor (23) are respectively provided in the exhaust passage to detect the temperature and humidity of the exhausted air as detection parameters, the sensors being maintained in an operation state throughout the cooking or heating process.

11. Microwave oven according to claim 10, characterized in that the microprocessor (16) of the control unit (15) is programmed to obtain from the temperature sensor the temperature value of the exhaust air at the beginning of the cooking or heating program and to adjust the program on the basis of the obtained temperature value.

12. A microwave oven as claimed in claim 9, characterized in that the means (12) for providing food-category information are adapted to provide parameters relating to the type and state of the food placed in the oven, which parameters correspond to a cooking or heating program stored in the control unit.

The microwave oven as claimed in claim 9, characterized in that the means (12) for providing food category information comprises: a first means for providing parameters of the type of food and a second means for providing parameters of the state of the food, the combination of these parameters corresponding to a cooking or heating program stored in the control unit.

14. Microwave oven according to claim 9, characterized in that a control panel (5) is provided with a display (6), which display (6) is adapted to show signs, symbols or simply text messages indicating the selected cooking or heating program.

15. Microwave oven according to claim 9, characterized in that a top heater in the form of a grid element or some other equivalent electric infrared radiating element is provided, which top heater is controlled by a control unit (15) to control the top heater according to an activation time and heating effect selection program.

16. A microwave oven as claimed in claim 15, characterized in that a rotating crisping disk (4) of metal of small thermal mass and good thermal conductivity is provided, which is provided on its underside with a microwave absorbing layer, a grill element being provided in the top plate of the oven cavity, the microwave oven being provided with a microwave energy feed system, the feed opening of which is located at the same level as the crisping disk (4) and adapted to feed polarized microwaves to said microwave absorbing layer, the vertical or horizontal vector of the provided polarized microwaves being oriented substantially in the plane of said layer.

17. A microwave oven as claimed in claim 9, characterized in that the control unit (15) is adapted to provide information about the weight of the food item, using the weight w of the food item as an additional control parameter, by means of a weight sensor (25) or means (9) for inputting a weight measurement, which weight sensor is arranged close to the receptacle, plate or carrier (4), the control unit calculating the expected time of the time period T1e, T2e, … of the selected program on the basis of the weight of the food item and the constants k1, k2, … determined by the type of the food item, the expected time Tie of each time period Ti of the cooking or heating program being calculated according to the following formula:

where i is 1, 2, 3, … …

Tie is the expected time of the time period,

ki is a constant determined by the food category,

w is the weight of the food; and

additional monitoring of the cooking or heating process is performed using the expected time calculation values over the time period.

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