SE502886C2 - Control method for a microwave oven, microwave oven and its use for cooking / heating a food product according to the control procedure - 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

502 886 10 15 20 25 30 35 2 A microwave oven equipped with the said three types of heat sources has in principle access to a volume heater, a sub-heater and a superheater, where the heat dissipation from the first two is controlled by regulating the microwave input to the oven cavity, while the the latter is directly controllable with respect to activation time and power level. To get optimal results for a certain type of food, the three heat sources must be used properly, i.e. activated during the appropriate time by the cooking / heating process and with adapted power levels.

The problem then is that activation times and effect levels vary greatly for different types of food. For a normal user, this is too complicated and therefore the customer / user does not normally have access to these options to control the cooking / heating process. Instead, the microwave ovens are built so that only a power balance determined by the manufacturer between the various heat sources can be selected.

In some countries, the power consumption for devices with a single-phase connection is limited, which means that e.g. the microwave source and the grill element cannot be activated at the same time. This in turn places special demands on the use of heat sources depending on the type of food in question, and tends to make the handling even more complicated for the user. An object of the invention is therefore to provide a microwave oven which does not have the disadvantages involved, which makes it possible to make advantageous use of the included heat sources and at the same time makes the microwave oven more user-friendly. Optimal utilization of the microwave oven's heat sources also enables a general increase in the microwave oven's usefulness to also include cooking / heating of food and dishes that are currently intended for heating in a traditional oven, for example in order not to lose crispness. The object of the invention is achieved by a method of the kind mentioned in the introduction which is characterized by the measures: - to supply the oven with a food class information for the food, - to select a program divided into one or more time periods for cooking or heating depending on the food class information, - during each time period activating said heat sources with power levels according to the selected program, - during each time period repeatedly calculating a control variable based on one or more sensing parameters from one or more sensors for sensing the condition of the food, and based on parameter information determined by the food class, - to count the time periods to zero from a maximum value determined by the food class after starting the program, - to end each time period when it is counted down to zero or when the calculated value of the control variable exceeds a value determined by the food class, - to end the program when all time periods geno m- ran.

The method according to the invention facilitates the operation of the microwave oven drastically, in that the user only needs to enter information about the current food class, e.g. via the oven control panel. The oven can then be started automatically or by operating a start button.

The oven then selects the current program in accordance with the food class and then monitors the cooking / heating completely automatically.

In this context, food class / food class information means information that corresponds to a specially designed cooking / heating program for a certain type of food, e.g. potato products, pizza, chicken, and the condition of the food when placed in the oven, e.g. fresh or frozen raw material, frozen semi-finished products, etc.

The input of the food class information can take place by entering e.g. a numerical value, which indicates both the type of food and its condition, alternatively by entering a first value indicating the type of food, and a second value indicating its condition. Preferably, the entry takes place by operating a control button specific to the food class, or alternatively specific buttons for food type and initial condition.

A microwave oven according to the invention comprises an oven cavity, a microwave source for feeding microwaves into the cavity, a microwave-activatable underheater in the form of a vessel, a plate or carrier on which a foodstuff is applied for heating or cooking, a control unit for controlling the microwave supply the underheater, respectively, and one or more sensors for receiving and supplying the control unit one or more sensing parameters indicating the condition of the food, and characterized in that the oven comprises means for supplying the control unit with information on the food food class, and that the control unit microprocessor is programmed to perform the following functions: - select a program for one or more time periods for cooking or heating depending on the food class information, - activate the microwave source and thereby the underheater with power levels according to the selected program, - during each time period repeatedly calculate a control variable bases on parameter values from said one or more sensors, and based on one or more associated constants determined by the food class, - count down the time periods to zero from a maximum value determined by the food class after starting the program, - end each time period when it is counted down to zero or when the calculated value of the control variable exceeds a value determined by the food class, - end the program when all time periods have elapsed. A preferred embodiment of the microwave oven according to the invention is provided with a superheater, e.g. a grill element 1 of the cavity roof, which is controlled by the selected program.

The design of the microwave oven according to the invention is based on the insight that the normal user uses his oven most frequently for cooking / heating certain types of food, e.g. heating of frozen ready-made dishes, heating of bread and potato products, etc., and that these foods can be divided into food classes based on food type and initial condition. In addition, it has been realized that optimal utilization of the available heat sources in a modern furnace, i.e. the microwave field in the cavity, the underheating crisp plate and the overheating grill element, can lead to improved cooking results and make the oven useful for a wider selection of foods / dishes. All subject to maintained or improved user-friendliness.

A use according to the invention of a microwave oven with a rotating crisp plate arranged in the oven cavity and a grill element arranged in the cavity of the cavity, as well as sensors for sensing substance release from a food and temperature values indicating the condition of the food, are characterized by cooking / heating of the food. depending on pre-programmed cooking / heating programs, which are selectable through a food class information and initial condition based on food class information, which is added to the oven.

Further features of the method and the microwave oven according to the invention appear from the claims.

The invention is described in more detail in the following by means of a preferred, non-limiting exemplary embodiment with reference to the drawings: Figure 1 shows a microwave oven according to the invention with an open oven door, 502 886 10 15 20 25 30 35 Figure 2 shows a block diagram of cooperating function units in The furnace when applying the method according to the invention, Figure 3 shows a flow chart of a pre-programmed cooking / heating program for controlling the microprocessor of the control unit.

The microwave oven shown in Figure 1 has an outer casing 1, an oven door 2 for closing the cavity 3, in which a crisp plate 4 is arranged. The crisp plate 4 consists of aluminum plate with small thermal mass, the underside of which is provided with a microwave absorbent layer of rubber. - buren ferrit. The ferrite material used preferably has a Curie point, at which the energy absorption of the layer from the microwaves ceases, which means that the temperature of the upper surface of the crisp plate, which comes into contact with the food / foodstuff, is stabilized within the temperature range 130-230 ° C. The crisp plate is arranged to rotate during cooking / heating. Examples of the construction of the crisp plate and its rotation mechanism are given in patent SE 9003104-8 and the microwave ovens manufactured by the applicant with the type designations VIP20, VIP27.

The microwave feed to the cavity 3 takes place via one or more feed openings (not shown in the drawing) which are connected to the microwave source 20 of the oven (see figure 2), i.e. normally a microwave, via waveguide. In the oven shown, the magnetron, associated waveguide system, the power unit 19 for driving the magnetron, as well as the oven control unit 15, are located behind the control panel 5. In a preferred design of the feed system, an upper and a lower feed opening are used in the right side wall of the cavity. , while the input system is otherwise designed to input polarized microwaves through these openings. Regarding the more detailed structure of the feed system, reference is made to patent SE 9003012-3 and the above-mentioned microwave ovens manufactured by the applicant. 10 15 20 25 30 35 502 886 7 In the roof of the cavity a grill element is arranged (not shown), e.g. in the manner set out in patent SE 9201786-2. The grill element can consist of a so-called grill pipe, a quartz pipe or a halogen beam source. Examples of concrete designs can be found in the microwave oven manufactured by the applicant with the type designation VIP20.

The control panel 5 is provided with a display 6, which under control from the control unit 15 (see figure 2) reproduces e.g. symbols or plain text messages for selected programs, remaining cooking / heating time, etc., i.e. provides the user with verification messages on choices made via the control panel and other information about a progressive cooking / heating process.

The control button 7 selects heating by microwave input to the cavity. The button 8 activates the oven's grill element. The desired time is set with the knob 9. These options correspond to what is available in a traditionally built oven and are included as a basic range of uses in addition to the possibility, according to the invention, to choose from a given number of pre-programmed cooking / heating programs for certain types of food. goods using an interplay between direct-acting microwaves, crispy plates and grill elements. Thus, for example, the removable crisp plate 4 can be replaced with a rotating base plate of the usual kind when heated with only direct-acting microwaves.

The buttons 10 and 11 are arranged for starting and stopping the oven, respectively. The keypad 12 is used for entering a food class information and thereby selecting a pre-programmed cooking / heating program. Thus, for example, the buttons in order from above can refer to heating of frozen pizza, heating of frozen pie, heating of frozen potato products (french fries, etc.) and heating of frozen chicken parts. Operation of a button entails simultaneous entry of a complete food class information, i.e. information on both the type of food and its initial condition, frozen, etc. In a modified version of the oven, the buttons are divided into two keypads, whereby information on the type of food is entered via one keypad and information on the initial condition is entered via the second keypad. In the simplest version of the oven, only one food class is used, which means that the keypad is reduced to one button. All buttons, as well as the knob and the display are connected to the control unit 15.

On the upper side of the oven there is a ventilation hole 13 in connection with the cavity evacuation duct (not shown) which is arranged in the space between the cavity 3 roof and the outer casing 1. In the evacuation duct there is a humidity sensor and a temperature sensor arranged to detect the humidity and temperature of the ventilation air , which is directly related to the condition of the food during cooking in the cavity. With reference to the patent SE 9201314-2, the moisture sensor can generally be constituted by a sensor capable of sensing the release of substances from food, moisture, gas, etc.

The selection of sensors and their location in the evacuation duct is done in a professional manner and is therefore not described in more detail in this context.

For single-phase connection to the mains, the oven has a plug-connected connection cable 14.

The block diagram shown in Figure 2 comprises the control unit 15 with a microprocessor and its associated program memory 16. The input of user information to the control unit takes place via the block 17, which represents the control buttons and the knob described above. The control unit controls the display on the display 6. Via a drive stage 18 and a microwave power unit 19, the microwave source 20 is controlled by the control unit 15 and thereby the microwave supply to the cavity 3. Via a drive stage 21 the grill element 22 is controlled by the control unit 15 and thereby the IR radiation. the cavity, information is returned to the control unit 15 via the humidity sensor 23 and the temperature sensor 24, which senses the humidity and the temperature of the ventilation air in the cavity evacuation duct, respectively. The control of the cooking / heating process is thus completely reconnected, whereby the sensitivity of the cooking / heating process to variations in raw materials, starting temperature and mains voltage is minimized. Regarding the more detailed structure of the listed functional units, reference is made to the above-mentioned patents and types of microwave ovens manufactured by the applicant.

The example of a flow chart for a pre-programmed cooking / heating program shown in Figure 3 comprises three successive time periods T1, T2, T3. For each period, a maximum length determined by the food class is employed. During each period, the microwave input is activated and thereby the crisp plate, as well as the grill element with power levels determined by the food class. The power levels of the microwaves and the grill element during the associated periods are designated PM1, PM2, PM3 and PG1, PG2, PG3, respectively.

Based on information from the humidity sensor and the temperature sensor, a control variable c is calculated continuously during the respective periods, according to c = al - humidity increase + bl ° temperature below T1 c - a2 - humidity increase + b2 ° temperature below T2 c = a3 - humidity increase + b3 - temperature below T3 where a1, a2, a3 and bl, b2, b3 respectively are constants determined by the food class.

During the periods, the period time is counted down to zero. When the time is counted down to zero or when the control variable exceeds a value c1, c2 and c3 determined by the food class, the period ends and the next one begins. When the period T3 has been completed, the program ends.

The power levels PM1, PM2, PM3 and PG1, PG2, PG3, respectively, are optimized for each food class and can in a further development of the oven vary during the time periods. Likewise, all constants a, b, c are optimized for each food class. The applied microwave power can in turn be distributed between different feed openings in order to enable an energy distribution between underheat from the crisp plate and microwave heating of the interior of the food.

Such distribution can be achieved by an input system described in patent SE 9302302-6.

The program according to the flow chart in figure 3 goes through the following steps, where Y stands for "yes" and N stands for "no": sl Start s2 Set period times T1, T2, T3 on the basis of food class s3 Microwaves on power PM1. Grill on power PGl.

Count down Tl. s4 Tl = 0? If Y, continue to p6. If N, continue to p5. s5 Calculate c. c 2 cl? If N, return to p3. If Y, continue to p6. s6 Microwaves on power PM2. Grill on power PG2.

Count down T2. s7 T2 = 0? If Y, continue to p9. If N continue to s8. s8 Calculate c. c 2 c2? If Y, continue to p9.

If N return to Sun. s9 Microwaves on power PM3. Grill on power DG3.

Count down T3. sl0 T3 = O? If Y, proceed to sl2. If N, continue to sll. sll Calculate c. c 2 c3? If Y, proceed to sl2.

If N, return to p9. sl2 Exit the program.

Step sl3 refers to a possible further development of the control program in the case that the microwave oven is provided with means for supplying the control unit 15 with information about the weight of the food. This can be done by e.g. the knob 9 in figure 1 is arranged to also function as a means for adjusting the weight of the foodstuff when using the automatic control programs according to the invention. Alternatively, the oven may be provided with a weight sensor 25 (see Fig. 2) in connection with the rotating crisp plate, e.g. of the embodiment described in patent application 9300291-3.

Based on the weight information w, the microprocessor calculates an expected length Tle, T2e, T3e for each time period of the program, according to_ Tle = kl ° w T2e = k2 ~ w T3e = k3 - w where kl, k2, k3 are food class dependent constants.

It will be appreciated that it is within the skill of the art to bring about further developments of the described program within the scope of the invention. An example of this is to have the temperature of the ventilation air sensed at the start of the program and, on the basis of this, to introduce compensatory corrections in the parameter information used during the implementation of the program. This eliminates the effect of the oven being heated already at start-up. A further possibility is to introduce a temperature sensor for sensing the temperature of the crisp plate and use this for controlling the microwave source and grill element. When implementing the method, one can use so-called

Fuzzy-Logic decision. Modifications due thereto are professional and are considered to be within the scope of the following claims.

Claims (18)

502 886 10 15 20 25 30 35 A patent for controlling a process for cooking or heating a food in a microwave oven using the microwave source of the oven (20) and a microwave-activatable underheater (4) in the form of a vessel, a plate or the product by k 2. carriers on which the food is applied, which for food act as separate heat sources, which are controllable of the oven control unit (15), than to supply the oven with a food class information for the food, to select one for one or more time periods (T1, T2 ,. .) subdivided cooking or heating program pledged by the measures: depending on the food class information provided, activating said heat sources with power levels according to the selected program during each time period, repeatedly calculating a control variable (c) based on one or more sensing pairs during each time period; meters from one or more sensors for sensing the condition of the food, and based on parameter information determined by the food class, counting down the time periods to zero from a maximum value determined by the food class after starting the program, interrupting each time period when it is counted down to zero, or when the calculated value of the control variable exceeds ...), to end the program when all time period r completed. a value determined by the food class (c1, c2). A method according to claim 1, wherein the microwave oven also comprises a superheater in the form of a grill element or other corresponding electric IR radiation element as an additional controllable heat source, characterized by the further measure that the superheater is activated in compliance with the selected program 10 15 20 25 30 35 502 886 13 A method according to claim 1, wherein the program is divided into time periods T1, T2, .... Tn during each of which one or more sensing parameters x1, x2, .... xk are sensed, characterized in that for each sensing parameters are selected, like said parameter information, an associated constant a1, a2, ... an; bl, b2, .. respective time period. .., bn; ... under Method according to claim 3, characterized in that the control variable c during the time period Tn is calculated according to c = an 0 xl + bn ~ x2 + .... A method according to claim 4, wherein the program comprises two time periods T1, T2, and wherein two sensing parameters x1, x2 are sensed, characterized in that the control variable c is calculated according to c = a1 x1 + bl ~ x2 during the time period T1, respectively. c = a2 ~ x1 + b2 ~ x2 during the time period T2. Method according to Claim 1, characterized in that the rise in humidity and the temperature of the ventilation air from the cavity of the furnace, respectively, are used as sensing parameters. 502 886 10 15 20 25 30 35 14 A method according to claim 1, wherein the temperature of the ventilation air from the cavity of the furnace is used as a sensing parameter, characterized in that the starting temperature of the ventilation air is sensed and corrections based thereon are entered in said parameter information. A method according to claim 1, wherein the microwave oven also comprises means for feeding or sensing the weight of the food, characterized in - that an expected length of each time period Ti of the cooking / heating program is calculated by the control unit based on information about the weight w and one of the food class determined constant ki according to Tie = ki ° w where i = 1,2,3, ..., Tie is the expected length of the time period ki is a constant determined by the food class w is the weight of the food - and that the calculated value of the time period expected length is used for supplementary monitoring of the cooking / heating. A microwave oven comprising an oven cavity (3), a microwave source (20) for feeding microwaves into the cavity, a microwave activatable underheater (4) in the form of a vessel, a plate or carrier on which a foodstuff is applied for heating or cooking, a control unit (15) for controlling the microwave supply to the cavity and the underheater, respectively, and one or more sensors (23, 24) for receiving and supplying the control unit one or more sensing parameters indicating the condition of the food, 10 15 20 25 30 35 502 886 15 characterized in that the oven comprises means (12) for supplying the control unit with information on the food class of the food, and that the microprocessor (16) of the control unit is programmed to perform the following functions: - selecting one for one or more time periods (T1, T2, ...) subdivided program for cooking or heating depending on the food class information, - activate the microwave source and thereby the underheater with power levels according to the selected program, - during each time period, repeatedly calculate a control variable (c) based on parameter values from said one or more sensors, and based on the associated one or more constants determined by the food class, - count down the time periods to zero from a maximum value determined by the food class after start of the program, - interrupt each time period when it is counted down to zero or when the calculated value of the control variable exceeds a value determined by the food class (cl, c2, ...) - end the program when all time periods have elapsed. Microwave oven according to claim 9, wherein the oven is provided with an evacuation channel for ventilation of the cavity, characterized in that a temperature sensor (24) and a humidity sensor (23) are arranged in the evacuation channel for sensing the temperature and humidity of the ventilation air, respectively, as said sensing parameters, whereby the sensors are kept activated during the cooking / heating process. 11. ll. 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 (24) a value of the ventilation air temperature at the start of the cooking / heating program, and to adjust the program depending on the temperature value. 502 886 10 15 20 25 30 35 16 Microwave oven according to claim 9, characterized in that said means (12) for supplying food class information are arranged for supplying a parameter which is based on the type of food and the condition of the food when it is placed in the oven and which is corresponding to a cooking / heating program stored in the control unit. Microwave oven according to claim 9, characterized in that said means (12) for supplying food class information comprises first means for supplying a food item parameter and second means for supplying a food condition parameter, the combination of said parameters corresponding to a cooking stored in the control unit. / heating program. Microwave oven according to claim 9, characterized in that the oven has a control panel (5) provided with a display device (6), which is arranged to display a designation, symbol or a plain text message indicating the selected cooking / heating program. Microwave oven according to claim 9, characterized in that the oven is provided with a superheater in the form of a grill element or other corresponding electric IR radiation element, which is controllable through the control unit (15), characterized in that the superheater is arranged to be controlled with respect to activation time and heat output in accordance with the selected program. Microwave oven according to claim 15, characterized in that the oven is provided with a rotating crisp plate (4) of metal with small thermal mass and good thermal conductivity, wherein a microwave absorbing layer is applied to the underside of the plate, that a grill element is arranged in the roof of the oven cavity, and that the oven has a microwave input system with an input opening level with the crisp plate (4) and arranged to supply to said absorbent layer polarized microwaves whose E- or H-vector is directed essentially in the plane of the layer. Microwave oven according to claim 9, characterized in that the control unit (15) is arranged to utilize the weight of the food (w) as an additional control parameter, wherein information about the weight of the food is supplied from a weight sensor (25), which is arranged at the plate. , the vessel or carrier (4), alternatively from a means (9) for inputting a measured value for the weight, while the control unit is arranged to calculate the expected length of a time period (Tle, T2e, ...) of the selected program based on the weight of the food and a constant determined by the food class (kl, k2, ....). Use of a microwave oven with a rotating crisp plate (4) arranged in the oven cavity (3) and a grill element arranged in the cavity of the cavity, as well as sensors (23, 24) for sensing substance release from a food and temperature values indicating the state of the food, for automatic cooking / heating of the food in dependence on pre-programmed cooking / heating programs, which are selectable through a food class information based on the food type and initial state, which is supplied to the oven.