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

Abstract: A method for controlling a microwave oven, a microwave oven and its use for automatic cooking or heating of food are disclosed. On the basis of supplied food-category information on the type of food and its initial state and on the basis of supplied information on the weight of the food, a corresponding preprogrammed control program is selected. The control program is divided into time periods during which the microwave radiation source (20) 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 calculation and decrementation of the expected durations of the time periods on the basis of the weight of the food and the constants determined by the food category.

Description: This invention relates to a method for controlling a procedure for cooking or heating food in a microwave oven by using the microwave radiation source of the oven and a microwave-activable bottom heater in the form of a receptacle, a plate or a carrier on which the food is placed, which act as separate heat sources for the food and are controllable via the control unit of the oven. The invention further concerns a microwave oven for implementing the method. The microwave radiation source and the associated microwave-feed system generate a microwave distribution in the oven cavity that brings about so-called volume heating of the food. The microwave oven may comprise an additional source of heat for the food in the form of a microwave-activable, so-called crisp or browning plate. A crisp plate may consist of an aluminium plate which has small thermal mass and good thermal conductivity and on whose underside is provided a microwave-absorbing layer. SE Patent Specification 9003104-8 discloses such a crisp plate. A browning plate has greater thermal mass and may consist of a plate of ceramics or glass provided with a microwave-absorbing layer. In general, both the crisp plate and the browning plate are arranged to rotate during cooking or heating. The microwave oven may have yet another source of heat in the form of a so-called grill element or an equivalent IR-radiation element, which usually is arranged in the ceiling of the cavity (see, for instance, SE Patent Specification 9201786-2). A microwave oven equipped with these three types of heat sources basically has access to a volume heater, a bottom heater and a top heater, in which case the heat emission from the two former is controlled by regulating the microwave feed to the cavity, and the latter is controlled directly as regards activation time and power level. In order to optimise the heating or cooking of a specific type of food, the three heat sources have to be used in an appropriate manner, i.e. be activated at adjusted power levels for a suitable period of the cooking or heating procedure. However, the problem is that the activation times and power levels for different sorts of food vary considerably. For the average user, this is much too complicated, and he therefore is usually not given the opportunity to control the cooking or heating procedure in this fashion. Microwave ovens are instead so constructed that there is only one power balance, determined by the manufacturer, between the different sources of heat. EP-A-359 976 discloses a microwave oven in which the weight of the foodstuff is monitored and used during the cooking program as a parameter for completing such program. In some countries, the power consumption of apparatus with single-phase connection is restricted, which among other things means that the microwave radiation source and the grill element cannot be activated at the same time. In turn, this places special requirements on the utilisation of the heat sources depending on the type of food at issue, and tends to complicate matters further for the user. One object of the invention is, therefore, to provide a microwave oven which does not suffer from any of the drawbacks mentioned above, enables advantageous utilisation of the heat sources, and at the same time is more user-friendly. By optimal utilisation of the heat sources, the microwave oven becomes more useful in general, so that it may serve to cook or heat also such food and dishes as today should be heated in conventional ovens, e.g. in order not to lose their crispiness. According to the invention, this object is achieved by a method which is of the type mentioned by way of introduction and which is characterised by the steps in the order of supplying the oven with food-category information on the food, supplying information on the weight of the food, selecting, on the basis of the food-category information supplied, a program for cooking or heating divided into one or more time periods, calculating the expected duration of each time period on the basis of the weight information as well as parameter information determined by the food category, activating, during each time period, said heat sources at power levels and for activation times in accordance with the selected program, decrementing the time periods to zero from the calculated value after starting the program, ending each time period when it has been decremented to zero, and ending the program when all the time periods have been run through. In preferred modes of implementation of the inventive method, the weight information is automatically supplied by a weight sensor disposed adjacent to the receptacle, plate or carrier, or manually by the user via the control panel of the oven. The method according to the invention drastically facilitates handling of the microwave oven, since the user merely has to supply information on the food category, possibly also on the weight, for instance via the control panel of the oven. The oven may then be started automatically or by operating a starter button. The oven then selects an appropriate program in accordance with the food category and monitors the cooking or heating procedure fully automatically. The user needs not, as is the case in conventional ovens, select any power settings and cooking times. To put it simply, the user merely indicates what he puts in the oven, for instance deep-frozen ready-cooked chicken parts, and what he wishes to take out of the oven, for instance heated chicken parts having a crispy surface. The oven indicates when the dish is ready. By food category or food-category information is here meant information corresponding to a specially-designed cooking or heating program for a specific type of food, such as potato products, pizza and chicken, and the state of the food put in the oven, such as fresh or deep-frozen raw products, and deep-frozen semi-processed products. The food-category information can be supplied by inputting e.g. a numerical value indicating the type of food and its state, or by inputting a first value indicating the type of food and a second value indicating its initial state. Preferably, the food-category information is inputted via a control button or a keyset where each key corresponds to a certain food category, or via two control buttons or keysets each corresponding to a specific type of food and a specific initial state. A microwave oven according to the invention comprises a cavity, a microwave radiation source for feeding microwaves to the cavity, a microwave-activable bottom heater in the form of a receptacle, a plate or a carrier on which food is placed for heating or cooking, a control unit for controlling the bottom heater as well as the feeding of microwaves to the cavity, the oven being characterised in that it has means for supplying the control unit with information on the food category involved, as well as means for supplying the control unit with information on the weight of the food, and that a microprocessor of the control unit is programmed to implement the following functions in the order of: selecting, on the basis of the food-category information supplied, a cooking or heating program divided into one or more time periods, calculating the expected duration of each time period on the basis of the weight information as well as parameter information determined by the food category, activating the microwave radiation source, and hence the bottom heater, at power levels and for activation times in accordance with the selected program, decrementing the time periods to zero from the calculated value after starting the program, ending each time period when it has been decremented to zero, and ending the program when all the time periods have been run through. In a preferred embodiment of the invention, the microwave oven is provided with a top heater, for instance a grill element arranged in the ceiling of the cavity, which is controlled by the program selected. In another preferred embodiment of the microwave oven according to the invention, a weight sensor is disposed adjacent to the receptacle, plate or carrier and adapted to automatically supply the information on the weight of the food. In yet another embodiment, the control panel of the oven has means for manually supplying information on the weight of the food. The design of the inventive microwave oven is based on the insight that the average user mostly employs the oven for cooking or heating certain kinds of food, e.g. deep-frozen ready-cooked dishes or bread and potato products, that this food can be divided into food categories on the basis of the type of food and its initial state, and that the combined information on the food category and the weight of the food makes it possible to adapt a program which is determined by the food category and is automatically implemented by the oven. Furthermore, it has been found that optimal utilisation of the heat sources available in a modern oven, i.e. the microwave field in the cavity, the bottom-heating crisp plate and the top-heating grill element, may improve cooking results and make it possible to use the oven for a broader range of food or dishes, the user-friendliness of the oven being maintained or even improved. Further distinctive features of the method and the microwave oven according to the invention are stated in the appended claims. The invention will be described in more detail below with reference to a preferred, non-restricting embodiment illustrated in the drawings, in which Fig. 1 shows an inventive microwave oven whose door is open; Fig. 2 is a block diagram illustrating cooperating functional units of the oven during implementation of the inventive method; and Fig. 3 is a flow chart illustrating a preprogrammed cooking or heating program for controlling the microprocessor of the control unit. The microwave oven illustrated in Fig. 1 has an external casing 1, and an oven door 2 for closing the cavity 3, in which a crisp plate 4 is arranged. The crisp plate 4 is made of sheet aluminium of small thermal mass and its underside is provided with a microwave-absorbing layer of rubber-borne ferrite. Preferably, the ferrite material employed has a Curie point at which ceases the layer's energy absorption from the microwaves, which means that the temperature of the upper side of the crisp plate that comes into contact with the food stabilises in a temperature range of 130-230°C. The crisp plate is adapted to rotate during the cooking or heating procedure. SE Patent Specification 9003104-8, as well as the applicant's microwave ovens of type designations VIP20 and VIP27, illustrates a more detailed construction of the crisp plate as well as its rotary mechanism. The microwaves are fed to the cavity 3 through one or more feed openings (not shown) which communicate with the microwave radiation source 20 (normally a magnetron) of the oven (see Fig. 2) via waveguides. In the illustrated oven, the magnetron, the associated waveguide system, the power unit 19 for operating the magnetron, and the control unit 15 are disposed behind the control panel 5. In a preferred embodiment of the microwave-feed system, use is made of an upper and a lower feed opening, which are provided in the right-hand lateral wall of the cavity, whereas the remainder of the feed system is designed to feed polarised microwaves through these openings. For more detailed information on the construction of the microwave-feed system, reference is made to SE Patent Specification 9003012-3, as well as to the applicant's microwave ovens mentioned in the foregoing. A grill element (not shown) is arranged in the ceiling of the cavity, e.g. in the manner described in SE Patent Specification 9201786-2. The grill element may be a so-called "grill tube", a quartz tube or a halogen-radiation source. Instances of concrete designs are found in the applicant's microwave oven of type designation VIP20. The control panel 5 has a display 6 which, controlled by the control unit 15, represents, among other things, symbols or plain-text messages for selected programs, and the remaining cooking or heating time, i.e. verifies the user's selections made via the control panel as well as provides other information on how the cooking or heating proceeds. The control button 7 is used for selecting heating through the feeding of microwaves to the cavity. The button 8 is used for activating the grill element of the oven, and the desired time is set by the knob 9. These basic options have their equivalence in a conventional oven and supplement the inventive option to select from a given number of preprogrammed cooking or heating programs for specific types of food while utilising the interplay of the direct-acting microwaves, the crisp plate and the grill element. The removable crisp plate may be replaced with an ordinary rotary bottom plate in the case heating involves direct-acting microwaves only. When selecting the preprogrammed programs, the knob 9 also serves for manual inputting of the weight of the food. The buttons 10 and 11 are provided for, respectively, starting and switching off the oven. The keyset 12 serves to input the food-category information and, hence, to select a preprogrammed cooking or heating program. For instance, the buttons may, from top to bottom, concern the heating of deep-frozen pizza, the heating of deep-frozen pie, the heating of deep-frozen potato products, such as chips, and the heating of deep-frozen chicken parts. The operation of a button entails simultaneous input of complete food-category information, i.e. information on the type of food and its initial state (e.g. deep-frozen). In a modified embodiment of the oven, the buttons are divided into two sets, in which case the information on the type of food is inputted via one set and the information on the initial state of the food is inputted via the other set. In the simplest embodiment of the oven, only one food category is used, which means that only one button is required. All the buttons, as well as the knob and the display, are in communication with the control unit 15. On the upper side of the oven, there are provided ventilation holes 13 communicating with the evacuation channel (not shown) of the cavity that is provided in the space between the ceiling of the cavity and the external casing 1. In view of single-phase connection to the mains, the oven has a flex 14 with a plug. The block diagram of Fig. 2 shows the control unit 15 and the microprocessor and its associated program memory 16. The user information is inputted to the control unit via the block 17, which represents the control buttons and the knob described above. The control unit controls the display 6. Via a driver 18 and a microwave power unit 19, the control unit 15 controls the microwave radiation source 20, and hence the feeding of microwaves to the cavity 3. Via a driver 21, the control unit 15 controls the grill element 22, and hence the IR radiation fed to the cavity 3. For more detailed information on the construction of these functional units, reference is made to the above-mentioned patents as well as to the microwave ovens manufactured by the applicant. Alternatively, the weight information is automatically supplied to the control unit by a weight sensor 23 (indicated by dashed lines). The weight sensor 23 is disposed adjacent to the crisp plate 3 and senses the weight of the food placed on the plate. For instance, the weight sensor may be of the design described in SE Patent Specification 9300291-3. In Fig. 3, the flow chart illustrating a preprogrammed cooking or heating program comprises three successive time periods T1, T2 and T3. For each period, the expected duration T1e, T2e and T3e is calculated on the basis of the weight w of the food and a constant k1, k2 and k3, respectively, determined by the food category, according to T1e = k1 ° w T2e = k2 ° w T3e = k3 ° w During each period, the feeding of microwaves and, hence, the crisp plate as well as the grill element are activated at power levels determined by the food category. The power levels for, respectively, the microwaves and the grill element during the associated periods are designated, respectively, PM1, PM2 and PM3 and PG1, PG2 and PG3. These power levels are optimised for each food category and may, in a further development of the oven, vary during the time periods. Also the constants k1, k2 and k3 are optimised for each food category. In a further development of the oven, the supplied microwave power may be distributed between different feed openings to enable energy to be distributed between bottom heat from the crisp plate and microwave heating of the interior of the food. Such distribution can be achieved by using a microwave-feed system of the type described in SE Patent Specification 9302302-6. The program illustrated in the flow chart of Fig. 3 runs through the following steps, where Y represents "yes" and N represents "no". s1. Start. s2. Detection of the net weight w of the food. s3. Calculation of T1e, T2e and T3e, respectively. s4. Microwaves at the power PM1. Grill on the power PG1. Decrementation of T1e. s5. T1e = 0? If Y, proceed to s6. If N, return to s4. s6. Microwaves at the power PM2. Grill on the power PG2. Decrementation of T2e. s7. T2e = 0? If Y, proceed to s8. If N, return to s6. s8. Microwaves at the power PM3. Grill on the power PG3. Decrementation of T3e. s9. T3e = 0? If Y, proceed to s10. If N, return to s8. s10. End of the program. It will be appreciated that those skilled in the art are well qualified to develop the described program within the scope of the invention. For instance, the temperature of the ventilating air may be sensed by a temperature sensor arranged in the evacuation channel of the cavity. On the basis of the initial temperature sensed, compensatory corrections are made of the constants selected through the food category and used for calculating the expected duration of the time periods of the program. One thus eliminates any effect of the oven being heated even at the start. Another conceivable further development would be to supply the control unit with information on the temperature of the crisp plate as a further control parameter. When implementing the method, use can be made of so-called fuzzy logic decisions.

Claims: A method for controlling a procedure for cooking or heating food in a microwave oven by using the microwave radiation source of the oven and a microwave-activable bottom heater (4) in the form of a receptacle, a plate or a carrier on which the food is placed, which act as separate heat sources for the food and are controllable via the control unit (15) of the oven, characterised by the steps in the order of supplying the oven with food-category information on the food, supplying information on the weight (w) of the food, selecting, on the basis of the food-category information supplied, a cooking or heating program divided into one or more time periods, calculating the expected duration (T1e, T2e, ...) of each time period on the basis of the weight information as well as parameter information (k1, k2, ...) determined by the food category, activating, during each time period, said heat sources at power levels and for activation times in accordance with the selected program, decrementing the time periods to zero from the calculated value (T1e, T2e, ...) after starting the program, ending each time period when it has been decremented to zero, and ending the program when all the time periods have been run through. A method as set forth in claim 1, in which the microwave oven further comprises a top heater in the form of a grill element or some other equivalent electric IR-radiation element as an additional controllable heat source, characterised by the further step of activating the top heater in accordance with the selected program. A method as set forth in claim 1, in which the microwave oven is equipped with a weight sensor (23) disposed adjacent to said receptacle, plate or carrier, characterised by supplying the information on the weight of the food automatically via the weight sensor when starting the cooking or heating program. A method as set forth in claim 1, in which the microwave oven has a control panel provided with means (9) for inputting information on the weight of the food, characterised by inputting the information on the weight of the food manually by the operator via said means before starting the cooking or heating program. A method as set forth in claim 1, in which the program is divided into time periods T1, T2, ... Tn with associated constants k1, k2, ... kn selected through the food category, characterised by calculating the expected duration T1e, T2e, ... Tne of each time period on the basis of the weight (w) of the food according to T1e = k1 ° w T2e = k2 ° w ... Tne = kn ° w A microwave oven comprising a cavity (3), a microwave radiation source (20) for feeding microwaves to the cavity, a microwave-activable bottom heater (4) in the form of a receptacle, a plate or a carrier on which food is placed for heating or cooking, a control unit (15) for controlling the bottom heater as well as the feeding of microwaves to the cavity, characterised in that it has means (12) for supplying the control unit with food-category information on the food, as well as means (9) for supplying the control unit with information on the weight of the food, and that a microprocessor (16) of the control unit is programmed to implement the following functions in the order of: selecting, on the basis of the food-category information supplied, a cooking or heating program divided into one or more time periods (T1, T2, ...), calculating the expected duration (T1e, T2e, ...) of each time period on the basis of the weight information (w) as well as parameter information (k1, k2, ...) determined by the food category, activating the microwave radiation source (20), and hence the bottom heater (4), at power levels and for activation times in accordance with the selected program, decrementing the time periods to zero from the calculated value (T1e, T2e, ...) after starting the program, ending each time period when it has been decremented to zero, and ending the program when all the time periods have been run through. A microwave oven as set forth in claim 6, characterised in that the means for supplying the control unit (15) with information on the weight (w) of the food comprise a weight sensor (23) disposed adjacent to said receptacle, plate or carrier in order to automatically sense the weight of the food when a program is started. A microwave oven as set forth in claim 6, characterised in that the means for supplying the control unit (15) with information on the weight of the food comprise a means forming part of a control panel (5) of the oven and adapted for manual inputting of the weight of the food. A microwave oven as set forth in claim 8, characterised in that the inputting means is in the form of a knob (9), which is used also for setting the desired cooking or heating time when the preprogrammed programs are not being used. A microwave oven as set forth in claim 6, characterised in that the means for supplying the control unit (15) with food-category information on the food are conceived as an operating means for supplying a parameter which is based on the type of food and its initial state and which corresponds to a cooking or heating program stored in the control unit. A microwave oven as set forth in claim 6, characterised in that the means for supplying the control unit (15) with food-category information on the food are conceived as first means for supplying a food-type parameter and second means for supplying a food-state parameter, the combination of these parameters corresponding to a cooking or heating program stored in the control unit. A microwave oven as set forth in claim 6, characterised in that it has a control panel (5) provided with a display (6) for showing a designation, a symbol or a plain-text message indicating the cooking or heating program selected. A microwave oven as set forth in claim 6, characterised in that it has a top heater in the form of a grill element or some other equivalent electric IR-radiation element which can be controlled via the control unit in respect of activation time and heating power in accordance with the selected program. A microwave oven as set forth in claim 6, characterised in that it has a rotary crisp plate (4) which is made of metal and has a small thermal mass, a microwave-absorbing layer being provided on the underside of the plate, that a grill element is arranged in the ceiling of the cavity, and that the oven has a microwave-feed system having a feed opening on a level with the crisp plate (4) and adapted to feed polarised microwaves whose E-vector or H-vector extends substantially in the plane of the microwave-absorbing layer.

Inventors: IDEBRO MATS GUNNAR, SANDMAN BRITTA V M, IDEBRO, MATS GUNNAR, SANDMAN, BRITTA V.M., IDEBRO, MATS GUNNAR, C/O WHIRLPOOL IT. S.R.L., SANDMAN, BRITTA V.M., C/O WHIRLPOOL IT. S.R.L.
Applicants: WHIRLPOOL CO, WHIRPOOL CORPORATION
Application year: 1995
Main classification: H05B6
IPC codes: F24C7, H05B6, H05B11