EP3756420B1 - Method for operating a food heating device, and food heating device - Google Patents

Description

The invention relates to a method for operating a food heating device. The invention also relates to a food heating device that is set up to carry out the method. The invention is particularly advantageously applicable to food heating devices with a microwave function for heating food, in particular microwave ovens and combined baking/microwave ovens.

U.S. 4,520,250 discloses a heating apparatus in which a signal wave is applied to a frozen food and the change in absorption rate of the signal wave due to dielectric loss of the food is measured to automatically control a heating process for defrosting based on the measurement result.

WO 2012001523 A2 discloses a method of processing an object. The method includes heating the object by applying radio frequency (RF) energy, monitoring a value for a rate of absorption of RF energy by the object during the heating, and adjusting the RF energy in accordance with changes in a time derivative of the monitored signal value. The documents WO 2015/052145 A1 , WO 2013/121288 A1 , WO 2014/041430 A2 and WO 2013/033330 A2 disclose similar methods.

The document U.S. 2011/168695 A1 discloses an evaluation of phase-shifted irradiated microwave radiation by quadrature phase shift keying.

It is the object of the present invention to at least partially overcome the disadvantages of the prior art and in particular to provide an improved possibility of determining the thermal state of a frozen food in a food heating appliance, in particular a cooking appliance.

This object is solved according to the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the description and the drawings.

The object is achieved by a method for operating a food heating device, in which a first microwave radiation ("microwave measuring radiation") of a first frequency ("measuring frequency") and a second microwave radiation is radiated into a treatment chamber of the food heating appliance at a second measurement frequency that differs from the first measurement frequency, microwave measurement radiation received from the cooking chamber (and thus also superimposed) is measured and a thermal state of the food in the treatment chamber is determined on the basis of an evaluation of at least one beat property of the superimposed microwave measurement radiation is determined.

This method has the advantage that a thermal condition of the food in a food heating device can be determined particularly reliably and precisely.

In this case, use is made of the fact that when the first and second microwave measuring radiation are radiated in at the same time, their superimposed signal or beat can be measured by means of a microwave measuring device and subsequently evaluated. In one development, the power of the superimposed microwave measurement radiation is measured.

A thermal state can, for example, be a thawing state (e.g. "not thawed" or "thawed", possibly also "in the process of thawing"), a boiling state (e.g. "not boiling" or "boiling") and/or a temperature state (i.e., a temperature of the food) can be understood.

A superimposed microwave measurement radiation can be understood to mean, in particular, reflected microwave radiation received from the treatment room and possibly also transmitted microwave radiation. The received microwave measurement radiation can therefore also be understood as “at least reflected superimposed” microwave measurement radiation. The treatment space can be designed in particular as a resonance chamber for the microwave radiation with electrically conductive surfaces.

The food-heating device is in particular an electrically operated food-heating device that is set up to bring or input heating power for heating food into the treatment space in a targeted manner.

It is a development that the food heating device is a household appliance. It is a further development that the food heating device is a cooking device. Of the The treatment space can then be a cooking space or be referred to as a cooking space. Another development is that the food heating device is a cooling device, in particular a freezer. The treatment room can then be a cooling or freezing room or referred to as a cooling or freezing room.

In a further development, the first microwave measurement radiation is introduced into the treatment room by means of a first microwave transmitter, while the second microwave measurement radiation is introduced into the treatment room by means of a second microwave transmitter. A microwave transmitter can contain a microwave generator such as a magnetron or a semiconductor microwave generator for generating microwave radiation and optionally a microwave guide and/or an antenna. In particular, the first microwave transmitter and the second microwave transmitter have respective antennas that are spatially separate from one another.

The superimposed microwave measuring radiation can be measured using at least one microwave measuring device of the food heating appliance. The microwave measuring device can, for example, have a (microwave) antenna and a measuring unit connected downstream of the antenna. The at least one measuring unit can be or have a bolometer or a measuring diode, for example. In general, the microwave transmitter and the microwave measuring device can be separate devices or integrated into one device.

In a further development, the antenna corresponds to at least one microwave measuring device of an antenna of a microwave transmitter, which enables a particularly simple and inexpensive construction. If both microwave transmitters have a respective antenna, each of the two antennas can be assigned a microwave measuring device. In this case, the superimposed microwave measurement radiation received from the treatment room is measured at two different points or positions in or on the treatment room, corresponding to the different positions of the two antennas. This provides two "measuring channels" for measuring a beat. The superimposed microwave measurement radiation measured at the two measurement channels usually differs from one another due to the different positions of the associated antennas. The thermal state of the food can then be based on an evaluation of at least one beat property The superimposed microwave measurement radiation (superimposed signal) measured at the two antennas can be determined, which allows an even more reliable and/or more precise determination of the thermal state.

However, the evaluation of the beat or the superimposed signal is basically also possible using only one measurement channel, i.e. only one antenna is required for this. It is therefore a development that the superimposed microwave measurement radiation is measured at only one position. This results in a particularly compact and inexpensive structure, in particular if a shared microwave guide and/or antenna is used for the different measurement frequencies that are generated.

In one configuration, the superimposed microwave measurement radiation is measured at at least two different positions and the thermal state of the food is determined by evaluating at least one beat property of the superimposed microwave measurement radiation measured at the at least two different locations or positions. The superimposed microwave measuring radiation can therefore generally also be measured and evaluated at more than two positions. This refinement has the advantage that the thermal state can be determined particularly precisely and possibly even in a spatially resolved manner.

It is generally possible to use more than two (e.g. three or more) microwave measuring devices, which, given a distributed spatial arrangement of their antennas, enables a particularly precise, possibly spatially resolved, determination of the thermal state. In this case, one or more antennas can also be used for emitting microwave radiation, while at least one antenna is connected to a microwave measuring device only for receiving microwaves.

According to the invention, the thermal state of the food is determined based on a change in a fluctuation range of the superimposed microwave measuring radiation. The evaluated at least one beat property includes or corresponds to the fluctuation range. This range of fluctuation can be detected and evaluated particularly reliably.

The range of fluctuation can be determined, for example, as the difference between a maximum and a minimum of values of the superimposed microwave measuring radiation within a predetermined period of time, e.g. as a difference between a maximum and a minimum of p values determined in succession. The number p can be between 5 and 20, for example.

It is a development that the range of fluctuation is an average range of fluctuation. The mean fluctuation range can, for example, be an average over q fluctuation ranges determined in succession. This has the advantage that a time profile of the fluctuation ranges is smoothed and the onset of a change in the fluctuation range can thus be determined even more reliably.

In a further development, the fluctuation range of the superimposed microwave measurement radiation corresponds to a fluctuation range of the measured power of the superimposed signal. In this case, the range of fluctuation can be determined using only the measured raw data of the superimposed microwave measurement radiation. The values of the superimposed microwave measurement radiation thus correspond to the measured superimposed power of the microwave measurement radiation.

It is an alternative or additional development that the fluctuation range of the superimposed microwave measuring radiation corresponds to a fluctuation range of a degree of reflection, i.e. a ratio of the measured power of the superimposed microwave measuring radiation to the associated radiated power of both microwave transmitters. This development has the advantage that fluctuations in the radiated power can also be taken into account or compensated for, for example, as a result of control processes. The values of the superimposed microwave measurement radiation thus correspond to the degree of reflection of the superimposed microwave measurement radiation.

In one configuration, a frequency difference between the first measurement frequency and the second measurement frequency is in particular between 1 Hz and 10 MHz. This results in the advantage of a sufficiently high temporal resolution of the measurement of the superimposed microwave measurement radiation or the superimposed signal, while at the same time reliably avoiding undersampling. However, smaller or larger frequency differences can also be used.

A further development is that the microwave measurement radiation or its frequency band determined by the measurement frequencies is in at least one ISM band, e.g. between 902 MHz and 928 MHz, between 2.4 GHz and 2.5 GHz and/or between 5.725 GHz and 5.875GHz.

In one configuration, the first microwave measurement radiation and the second microwave measurement radiation are radiated continuously into the treatment room. This enables a thermal state to be determined particularly precisely in terms of time, since an associated thermal state can be determined without interrupting the measurement process. The range of fluctuation can then be determined, for example, in the manner of a running measurement window, i.e. the range of fluctuation is determined from the last p measured values. From this, in turn, the course of the fluctuation range can be recorded and evaluated.

In an alternative embodiment, the microwave measurement radiation is radiated into the treatment room within the framework of a plurality of measurement sections or measurement cycles that are spaced apart in time. This results in the advantage that the food is affected particularly little by the microwave measuring radiation and, moreover, energy is saved. In one variant, the microwave measuring radiation can be introduced alternately in terms of time for the introduction of heating power. This can be implemented, for example, by a sequence of measuring cycles and heating cycles that alternate over time. In this configuration, the first microwave measurement radiation and the second microwave measurement radiation are introduced into the treatment chamber alternately with heating power for heating the food.

• Mikrowellenbestrahlung durch Mikrowellen-Nutzstrahlung;
• Einstrahlung von weiterer elektromagnetischer Energie
• Wärmestrahlung durch mindestens einen Widerstandsheizkörper;
• Wärmebehandlung durch Heißlufteinbringung und/oder Dampfeinbringung.

In one configuration, the food heating device is set up to heat food located in the treatment chamber using at least one of the following types of heating:

• Microwave irradiation by useful microwave radiation;
• Radiation of further electromagnetic energy
• Thermal radiation through at least one resistance heater;
• Heat treatment by hot air injection and/or steam injection.

This has the advantage that the method can be carried out on a large number of food heating devices. The cooking appliance can be, for example, a microwave oven, an oven or a combination thereof, a refrigerator, in particular a freezer, with a defrosting function, etc.

If the food heating appliance is set up for microwave irradiation using useful microwave radiation, the useful microwave radiation can be generated, for example, in a frequency band between 902 MHz and 928 MHz or between 2.4 GHz and 2.5 GHz.

If the food heating device is set up for microwave irradiation by useful microwave radiation or if the food in the treatment room can be heated by means of useful microwave radiation (i.e. does the food heating device have a microwave heating function, e.g. due to its design as a microwave oven or as a baking oven/microwave oven -Combination), it is an advantageous embodiment that a frequency range of the microwave measurement radiation encompassing the measurement frequencies and a frequency range of the useful microwave radiation are different. This avoids crosstalk between the useful microwave radiation and the microwave measurement radiation and in particular enables a reliable, continuous determination of the thermal state of the food by continuous irradiation of the microwave measurement radiation with simultaneous irradiation of the useful microwave radiation. In a specific example, the useful microwave radiation can be generated in a frequency band between 902 MHz and 928 MHz or between 2.4 GHz and 2.5 GHz, while the microwave measurement radiation is generated in a frequency band between 5.725 GHz and 5.875 GHz.

Another embodiment that is advantageous for heating by useful microwave radiation is that a frequency range of the microwave measurement radiation, which includes the measurement frequencies, and a frequency range of the useful microwave radiation are the same or at least overlap. The first measurement frequency and/or the second measurement frequency can then correspond to frequencies that are also used by the useful microwave radiation. In this case, in particular, the useful microwave radiation and the microwave measurement radiation are radiated alternately in time into the treatment room. This configuration allows the particular advantage that during a measurement cycle The first and/or second microwave transmitter used for irradiating the microwave measurement radiation can also be used for irradiating the useful microwave radiation during a heating cycle, which simplifies the structure.

In one embodiment, the microwave measurement radiation is also in the form of (additional) useful microwave radiation or is used as useful microwave radiation. The power of the microwave measuring radiation is then so high that it can also cause a noticeable heating of the food or the item to be treated. This has the advantage that not only is a precise determination of the thermal state achieved, but so-called “hot spots” are also smoothed out, ie an overall more homogeneous heating of the foodstuff or item to be treated is made possible. This configuration can be used independently of the type of heating, but is particularly advantageous if the food is heated by means of microwave radiation through (dedicated) useful microwave radiation.

• zu Beginn eines Behandlungsvorgangs die erste Mikrowellen-Messstrahlung und die zweite Mikrowellen-Messstrahlung mit wechselnden ersten und zweiten Messfrequenzen bei gleichem Frequenzunterschied eingestrahlt werden,
• aus dem Behandlungsraum empfangene überlagerte Mikrowellen-Messstrahlung für jedes (Frequenz-)Paar von gleichzeitig eingestrahlter erster und zweiter Mikrowellenstrahlung gemessen wird und
• aus den Paaren mindestens ein Paar als ein Messpaar zum folgenden Auswerten bzw. Bestimmen des thermischen Zustands des Lebensmittels ausgewählt wird.

It's an embodiment of that

• at the beginning of a treatment process, the first microwave measurement radiation and the second microwave measurement radiation are irradiated with alternating first and second measurement frequencies with the same frequency difference,
• superimposed microwave measurement radiation received from the treatment room is measured for each (frequency) pair of first and second microwave radiation radiated in at the same time, and
• at least one pair is selected from the pairs as a measurement pair for the subsequent evaluation or determination of the thermal state of the food.

This irradiation of the microwave measuring radiation at the beginning of the treatment process can also be referred to as an "initial scan".

This method has the advantage that a thermal condition of a food item in a food-heating device can be determined particularly quickly and precisely. This is because an initial selection of the measurement pairs based on the initial scan enables the expected course of the measured superimposed microwave measurement radiation to have sufficient dynamics (change potential) to be easy to evaluate.

The fact that the microwave radiation is radiated into the treatment room with changing or different (measurement) frequencies during an initial scan includes, in particular, that microwave radiation with different measurement frequencies is radiated into the treatment room in chronological succession. For this purpose, the first and the second microwave transmitter can be adjusted accordingly to the respective measurement frequencies. This can also be referred to as a "sweep", in particular if the microwave measurement radiation is irradiated with measurement frequencies that increase or decrease over time. For example, during an initial scan, a first microwave measurement radiation at a first measurement frequency f1 _i and a second microwave measurement radiation at a second measurement frequency f2 _i can be radiated into the treatment room. The two measuring frequencies f1 _i and f2 _i form a frequency pair P _i = f1 _i , f2 _i with a fixed frequency difference Δf = f2 _i - f1 _i . The power of the local signal or the beat is measured for this frequency pair P _i . The power of the superimposed signal is then measured analogously for a next frequency pair P _i+1 with the same Δf, etc. In one development, the first measurement frequency f1 _i and the second measurement frequency f2 _i of consecutive pairs differ by Δf. For example, the frequency pair Pi may include the measurement frequencies 5.725 GHz and 5.726 GHz, the frequency pair Pi+1 the measurement frequencies 5.726 GHz and 5.727 GHz, etc., or the frequency pair Pi may include the measurement frequencies 5.725 GHz and 5.735 GHz, the frequency pair Pi+1 the measurement frequencies 5.735 GHz and 5.745 GHz, etc.

The beginning of a treatment process can be understood to mean a period of time in which no associated heating power is or has been radiated into the treatment space, which is intended specifically for heating the food. The start of a treatment process can also be understood to mean a period of time, the start of which coincides with the start of the introduction of heating power.

• sie gehört zu einer Gruppe mit höchsten Reflexionsgraden;
• sie gehört zu einer Gruppe mit höchsten Mikrowellenleistungen;
• sie gehört zu einer Gruppe mit höchsten Schwankungsbreiten;
• sie gehört zu einer Gruppe mit niedrigsten Reflexionsgraden;
• sie gehört zu einer Gruppe mit niedrigsten Mikrowellenleistungen;
• sie gehört zu einer Gruppe mit niedrigsten Schwankungsbreiten;
• ihr Reflexionsgrad oder ihr durchschnittlicher Reflexionsgrad erreicht oder überschreitet mindestens einen vorgegebenen ersten ("oberen") Schwellwert;
• ihre Mikrowellenleistung oder ihre durchschnittliche empfangene Mikrowellenleistung erreicht oder überschreitet mindestens einen vorgegebenen oberen Schwellwert;
• ihre Schwankungsbreite erreicht oder überschreitet mindestens einen vorgegebenen oberen Schwellwert;
• ihr Reflexionsgrad oder ihr durchschnittlicher Reflexionsgrad erreicht oder unterschreitet mindestens einen vorgegebenen zweiten ("unteren") Schwellwert;
• ihre Mikrowellenleistung oder ihre durchschnittliche Mikrowellenleistung erreicht oder unterschreitet mindestens einen vorgegebenen unteren Schwellwert.

In one embodiment, the at least one measurement pair is selected from all of the pairs available or provided for selection based on the fact that the associated superimposed microwave measurement radiation or the superimposed signal meets at least one of the following selection criteria:

• it belongs to a group with the highest degrees of reflection;
• it belongs to a group with the highest microwave power;
• it belongs to a group with the highest ranges of fluctuation;
• it belongs to a group with the lowest degrees of reflection;
• it belongs to a group with the lowest microwave power levels;
• it belongs to a group with the lowest ranges of fluctuation;
• its reflectance or average reflectance meets or exceeds at least a predetermined first ("upper") threshold;
• its microwave power or its average received microwave power reaches or exceeds at least a predetermined upper threshold value;
• their range of fluctuation reaches or exceeds at least a predetermined upper threshold value;
• their degree of reflection or their average degree of reflection reaches or falls below at least a predetermined second ("lower") threshold value;
• their microwave power or their average microwave power reaches or falls below at least a predetermined lower threshold value.

These selection criteria enable the selection of measurement frequencies, with which the thermal state can be determined particularly precisely, in a manner that is particularly easy to ascertain. However, other selection criteria can also be used as an alternative or in addition, e.g. a group with "medium" fluctuation ranges, degrees of reflection, etc.

An average degree of reflection can be a degree of reflection averaged over a period of time. Analogously, an average microwave power can be a microwave power averaged over a period of time.

A group can include one item or member (ie, exactly one measurement pair) or multiple items or members (ie, multiple measurement pairs). The group with the highest degrees of reflection can only include the measurement pair with the highest (possibly averaged) degree of reflection or the measurement pairs with the highest two, three, ... degrees of reflection, etc.

In one embodiment, thawing and/or boiling of the food is determined based on a sudden change (i.e., a sudden decrease or a sudden increase) in the fluctuation range of the superimposed microwave radiation. By means of this configuration, the thermal state of the food is thus determined in the form of a thawing state and/or boiling state. The sudden change in the range of fluctuation enables a particularly precise determination of the thawing state and/or boiling state. In particular, a time profile of the range of fluctuation can be recorded or determined for this purpose. If the fluctuation range decreases or increases noticeably over a short period of time, a transition from a frozen state to a thawed state (phase transition from solid to liquid) can be inferred for a thawing process and/or boiling water for a boiling process .

In one embodiment, several measurement pairs are or have been selected and the thermal state (e.g. the thawing state or the boiling state) is determined using a sudden change in the fluctuation range per selected measurement pair determined over time. In this way, the defrosting status can be recorded particularly precisely. When evaluating several pairs of measurements, the courses of the fluctuation range can be evaluated separately for each of the selected pairs of measurements. A thermal state can then be determined from the fact that one or more of the curves associated with different pairs of measurements (in particular all curves) show a sudden change in the fluctuation range that indicates a phase transition.

The sudden change in the fluctuation range can be determined, for example, from a percentage change in an initial value and/or from a time derivative (slope) of the fluctuation range. For example, a thawing or thawed state can be concluded if a percentage change in the fluctuation range within a predetermined short period of time (e.g. 5, 10, 20 or 30 seconds) reaches a predetermined threshold value or becomes minimum or maximum and/or an increase in the fluctuation range reaches a predetermined threshold value or reaches a maximum in absolute values. This can be applied analogously to a boiling state, for example.

1. a) die Heizleistung mit einem der Sätze von Heizparametern eingestrahlt wird und ein zeitlicher Verlauf mindestens einer Schwebungseigenschaft der überlagerten Mikrowellen-Messstrahlung bestimmt wird,
2. b) dann, wenn für diesen Behandlungsabschnitt mittels des Verlaufs der mindestens einen Schwebungseigenschaft ein vorgegebener thermischer Zustand des Lebensmittels erkannt wird, folgend
3. c) die Schritte a) und b) für Heizleistung mit mindestens einem anderen der Sätze der Heizparameter wiederholt werden.

In one configuration, heating power can be introduced into the treatment chamber during a treatment process with m (m ≥ 2) different predefined sets of heating parameters, with the heating power for different sets of heating parameters heating food in the treatment chamber differently locally and in which

1. a) the heating power is irradiated with one of the sets of heating parameters and a time profile of at least one beat property of the superimposed microwave measurement radiation is determined,
2. b) if a predetermined thermal state of the foodstuff is detected for this treatment section by means of the course of the at least one beat characteristic, then
3. c) steps a) and b) are repeated for heating power with at least one other of the sets of heating parameters.

This configuration has the advantage that the food can be treated particularly evenly (e.g. can be thawed or brought to cooking or boiling), since the change in the heating parameters changes the distribution of the energy input into the food and the power is thereby input into the food in a particularly uniform manner. Large-volume food can thus be treated evenly in a particularly reliable manner. The treatment process can have or include a chronological sequence of several treatment sections with different heating parameters.

The heating power corresponds to the heating power that is intended to heat the food, while no or only a negligibly low heating power is assigned to the microwave measuring radiation. This can be implemented in such a way that the microwave measuring radiation is radiated into the treatment room with low power and/or only for a short period of time. If a measurement cycle only takes a short period of time (e.g. less than one second), this can optionally also be carried out at the power level of the heating power, since there is no significant change in the treated material due to the measurement process in this short period of time.

Depending on the design of the food heating device, the heating output can include, for example, microwave output, heating output generated by electrical resistance heaters, etc. In general, all device parameters can be found under heating parameters be understood, which influence or set a local distribution of the heating power in the treatment room. The heating parameters can therefore also be referred to as heat output localization parameters.

However, the heating parameters applied or used during a treatment section do not have to be constant until the thermal state is detected and can be determined dynamically and, for example, not repeatedly. A set of heating parameters can therefore include a group of constant or a group of non-constant heating parameters. The heating parameters of a set can be specified or dynamically adjusted.

• Frequenz,
• Phase,
• Amplitude,
• Antennenstellung,
• Wobblerfrequenz.

In the case of irradiation of useful microwave power, the heating parameters can include, for example, one or more of the following parameters:

• Frequency,
• Phase,
• Amplitude,
• antenna position,
• wobbler frequency.

If heat is introduced by irradiating further electromagnetic energy, this can involve the introduction of electromagnetic radiation with a frequency of no more than 900 MHz, in particular radiation with a frequency between 1 MHz and 900 MHz, in particular in one area between 30 and 50MHz.

• Art der Heizkörperaktivierung (Oberhitze, Unterhitze, Heißluft usw. oder eine Kombination davon),
• Aktivierung eines Umluftlüfters.

If heat is introduced by at least one resistance heater, the heating parameters can include, for example, one or more of the following parameters:

• Type of radiator activation (top heat, bottom heat, hot air, etc. or a combination thereof),
• Activation of a circulation fan.

• die Schritte a) und b) für alle m Sätze von Mikrowellen-Parametern durchgeführt worden sind; und/oder
• wenn in mindestens einem der Schritte b) bereits anfänglich ein nach oder mit einem Erwärmen vorgesehener thermischer Zustand festgestellt wird oder worden ist.

It is an embodiment that the treatment process is terminated when

• steps a) and b) have been performed for all m sets of microwave parameters; and or
• if, in at least one of steps b), a thermal state provided for after or with heating is or has already been determined initially.

The fact that in step b) a thermal state provided after or with heating is or has been initially determined, can include, for example, in the case of a thawing state as the thermal state, that in step b) in a thawing section serving the treatment initially an already thawed state is or has been established. This can be determined, for example, by the fact that the fluctuation range of the superimposed microwave measuring radiation (i.e. the measured power and/or the degree of reflection) at the beginning of the defrosting section is noticeably lower or higher than a predetermined threshold value, with values above or below this threshold value being one correspond to the frozen state. The threshold value can have been determined and specified empirically or it can have been determined at the beginning of the thawing process, e.g. during the initial measurement. This can be applied analogously to other thermal states of food. These considerations can be applied analogously to a boiling process or a boiling state.

In a further development, steps a) to c) are carried out multiple times for all m sets of microwave parameters.

It is an embodiment that in step b) if a thawed state (or a phase change from solid to liquid) is or has been recognized in the course of a thawing section, the heating power is reduced until refreezing is determined or recognized, and following step c) is carried out. Reducing the heating power allows a locally particularly heated area of the food to be refrozen due to its possibly still frozen surroundings. The change in the heating parameters together with the detection of refreezing results in particular in the advantage that many zones can be created in the food whose water content after refreezing is immediately before thawing or before a phase transition from solid to liquid. The refreezing can be done, for example, using a signal that follows the sudden change in the fluctuation range of the received microwave measurement radiation countervailing change (e.g. a renewed increase) in the range of fluctuation can be detected. The purpose of refreezing is to allow areas that are too warm that are already liquid to solidify again, so that areas that are already liquid are not heated disproportionately due to the higher absorption capacity of water compared to ice when exposed to microwave radiation. This achieves a more uniform temperature distribution in the material to be treated.

The fact that the heating output is reduced when the defrosting is detected in step b) can include that the heating output is switched off or reduced to zero.

In one configuration, the thawing process is ended when no more refreezing is detected for at least one of the thawing sections.

In one embodiment, when a thawed state or a state in the process of being thawed is detected for a thawing section, the energy of the microwave measuring radiation is reduced by the end of this thawing section. In this way, an effect of the microwave measuring radiation that delays or prevents refreezing can be suppressed.

In one embodiment, in step a) a high level of heat output is radiated during a thawing section of the thawing process. The high heating power can be a maximum heating power or a high percentage of the maximum heating power (e.g. equal to 70%, 80% or 90% of the maximum heating power). This further development has the advantage that the thawing can take place particularly quickly.

In a further development, when a thawed state has been detected, heating power is additionally introduced into the treatment room for a short time in order to be able to ensure the thawed state in a particularly reliable manner. In particular, the thawed state of the food can be brought about particularly reliably from a state just before thawing to a thawed state.

• in Schritt a) die Mikrowellen-Nutzstrahlung mit einem der Sätze von Mikrowellen-parametern eingestrahlt wird und ein zeitlicher Verlauf mindestens einer Schwankungseigenschaft, insbesondere einer Schwankungsbreite, der überlagerten Mikrowellen-Messstrahlung bestimmt wird,
• in Schritt b) dann, wenn für diesen Behandlungsabschnitt mittels des Verlaufs der mindestens einen Schwankungseigenschaft, insbesondere Schwankungsbreite, ein vorgegebener thermischer Zustand erkannt wird, folgend
• in Schritt c) die Schritte a) und b) für Mikrowellen-Nutzstrahlung mit mindestens einem anderen der Sätze von Mikrowellenparametern wiederholt wird.

One embodiment that is particularly preferred for the irradiation of useful microwave power is that useful microwave radiation with m (m≧2) different predetermined values Sets of microwave parameters can be radiated into the treatment room and that

• in step a) the useful microwave radiation is irradiated with one of the sets of microwave parameters and a time profile of at least one fluctuation property, in particular a fluctuation range, of the superimposed microwave measurement radiation is determined,
• in step b) when a predetermined thermal state is detected for this treatment section by means of the course of the at least one fluctuation property, in particular fluctuation range
• in step c) steps a) and b) are repeated for useful microwave radiation with at least one other of the sets of microwave parameters.

The object is also achieved by a food heating device which is set up to run the method according to one of the preceding claims.

• mindestens einen Mikrowellen-Sender zum Einstrahlen der ersten Mikrowellen-Messstrahlung und der zweiten Mikrowellen-Messstrahlung in den Behandlungsraum;
• mindestens eine Mikrowellen-Messvorrichtung zum Messen von aus der ersten und zweiten Mikrowellen-Messstrahlung überlagerter Mikrowellen-Messstrahlung und
• eine Datenverarbeitungsvorrichtung zum Bestimmen mindestens eines thermischen Zustands von in dem Behandlungsraum befindlichem Lebensmittel anhand einer Auswertung mindestens einer Schwebungseigenschaft der überlagerten Mikrowellen-Messstrahlung.

It is a further development that the food heating device has at least:

• at least one microwave transmitter for radiating the first microwave measurement radiation and the second microwave measurement radiation into the treatment room;
• at least one microwave measuring device for measuring microwave measuring radiation superimposed from the first and second microwave measuring radiation and
• a data processing device for determining at least one thermal state of food located in the treatment room based on an evaluation of at least one beat property of the superimposed microwave measurement radiation.

The food heating device can be designed analogously to the method and has the same advantages.

The microwave measuring radiation can be radiated into the treatment room via one or more channels. The superimposed microwave measurement radiation can also be measured via one or more channels.

In a space-saving development, the first microwave measurement radiation is introduced into the treatment room by means of a first microwave transmitter, while the second microwave measurement radiation is introduced into the treatment room by means of a second microwave transmitter and the two microwave transmitters transmit at least one section at a time have shared microwave guidance. For this purpose, the microwaves generated by the first and by the second microwave generator can be brought together by a combiner.

In a further development, the first microwave measurement radiation and the second microwave measurement radiation are introduced into the treatment room by means of a single ("combination") microwave transmitter, which has antennas that are spatially separate from one another. The advantage of a space-saving and inexpensive arrangement is thus achieved. This development can be implemented, for example, in such a way that the microwave signal of the first measurement frequency generated by the microwave generator is split into a first branch, which leads to the first antenna, and a second branch, which leads to the second antenna. While the frequency of the microwave signal routed to the first antenna is not actively changed, the microwave signal routed to the second antenna is converted to the second measurement frequency, e.g. by means of a frequency divider and/or frequency multiplier.

A further development--which can also be applied to the above-described configurations of microwave transmitter(s)--is that the first microwave measurement radiation and the second microwave measurement radiation are radiated using a single antenna.

The data processing device can be integrated into a control device of the food heating appliance or the control device can have a data processing function for carrying out the method. In this case in particular, the control device can be set up to control the microwave transmitter, e.g. with regard to its microwave power and possibly the microwave parameters used when the microwaves are irradiated.

In the event that the food heating device radiates microwave power to heat the food in the treatment room, at least one microwave transmitter for irradiation of microwave measurement radiation correspond to the microwave transmitter for irradiation of the useful microwave power, or there may be another microwave transmitter for irradiation of the useful microwave power.

• Oberhitzeheizkörper,
• Grillheizkörper,
• Unterhitzeheizkörper,
• Ringheizkörper einer Umluftheizung,
• Umluftlüfter.

If heat is introduced by at least one resistance heating element, the household appliance can contain, for example, one or more of the following components or parts:

• top heat radiator,
• grill heater,
• bottom heat radiator,
• ring heater of a circulating air heating system,
• circulation fan.

If steam is introduced to heat an item to be treated, the household appliance can have a steam generator, e.g. a steam generator present outside the treatment room, a heatable water bowl inside the treatment room, etc.

Fig.1

zeigt als Schnittdarstellung in Seitenansicht ein mögliches erfindungsgemäßes Lebensmittel-Erwärmungsgerät;

Fig.2

zeigt eine Auftragung eines zeitlichen Verlaufs eines an zwei Messkanälen gemessenen Reflexionsgrads einer überlagerten Mikrowellenmessstrahlung für einen Auftauvorgang;

Fig.3

zeigt eine Auftragung eines Verlaufs einer Schwankungsbreite gegen die Zeit des in Fig.2 gemessenen Reflexionsgrads;

Fig.4

zeigt ein Ablaufdiagramm für einen möglichen Betrieb des Lebensmittel-Erwärmungsgeräts aus Fig.1;

Fig.5

zeigt eine Auftragung eines zeitlichen Verlaufs eines an zwei Messkanälen gemessenen Reflexionsgrads einer überlagerten Mikrowellenmessstrahlung für einen Kochvorgang;

Fig.6

zeigt eine Auftragung eines Verlaufs einer Schwankungsbreite gegen die Zeit des in Fig.5 gemessenen Reflexionsgrads.

The characteristics, features and advantages of this invention described above, and the manner in which they are achieved, will become clearer and more clearly understood in connection with the following schematic description of an exemplary embodiment, which will be explained in more detail in connection with the drawings.

Fig.1

shows a possible food heating device according to the invention in a sectional side view;

Fig.2

shows a plot of a time course of a degree of reflection of a superimposed microwave measuring radiation measured on two measuring channels for a thawing process;

Fig.3

shows a plot of the course of a fluctuation range against the time of the in Fig.2 measured reflectance;

Fig.4

Figure 12 shows a flowchart for one possible operation of the food warming device Fig.1 ;

Fig.5

shows a plot of a time course of a degree of reflection of a superimposed microwave measuring radiation for a cooking process, measured at two measuring channels;

Fig.6

shows a plot of the course of a fluctuation range against the time of the in Fig.5 measured reflectance.

Fig.1 shows a sectional side view of a possible food heating device according to the invention in the form of a microwave oven 1 serving as a cooking device.

The microwave oven 1 has a first microwave transmitter 3a with a microwave generator 4 (e.g. a magnetron) and an antenna 5. FIG. First microwaves MW1 generated by the microwave generator 4 are fed into the cooking chamber 2 via the antenna 5 . The microwave oven 1 also has a second microwave transmitter 3b with a microwave generator (not shown) and an antenna (not shown). Second microwaves MW2 generated by the microwave generator 4 are fed into the cooking chamber 2 via its antenna.

A control device 6 controls the microwave transmitters 3a, 3b and can in particular instruct the microwave generators 4 to generate the first and second microwaves MW1, MW2 with specific microwave parameters, e.g. in relation to their microwave frequency, phase and/or amplitude. The control device 6 can also be set up to control a rotation of the antennas 5 .

The antenna 5 is also coupled to respective microwave measuring devices 7a, 7b, which measure the microwave radiation received from the cooking chamber 2 via the antenna 5. The microwave measuring devices 7a, 7b can each include a bolometer for this purpose.

The microwave measuring devices 7a, 7b are also coupled to the control device 6 in order to transmit measurement data generated by the microwave measuring devices 7a, 7b, which represent a measure of the power of the received microwave radiation, to the control device 6. The control device 6 is also designed as a data processing device in order to process the measurement data (e.g. to generate a To determine the degree of reflection R), to determine a thermal state such as a thawing state and/or a boiling state and to control the microwave oven 1, for example to control the microwave transmitters 3a, 3b accordingly.

In particular, the control device 6 can be set up to operate the microwave transmitters 3a, 3b alternately in a measuring cycle and in a heating cycle. During a heating cycle, the first microwave transmitter 3a and/or the second microwave transmitter 3b are operated in order to heat the food L. During a measurement cycle, the first microwave transmitter 3a is operated in such a way that it radiates a first microwave measurement radiation MW1 with a first measurement frequency f1 into the cooking chamber 2 and the second microwave transmitter 3a is operated in such a way that it emits a second microwave measurement radiation MW2 with a second measurement frequency MW2, which differs from the first measurement frequency f1 but is close to the first measurement frequency f1, radiates into the cooking chamber 2. A frequency difference Δf = f2 - f1 can be 1 MHz, for example. In the measurement cycle, the superimposed microwave measurement radiation can be measured at both measurement devices 7a, 7b.

The control device 6 is set up to determine the thermal state of the food L based on an evaluation of at least one beat property of the superimposed microwave measuring radiation, e.g. from the measured values or superimposed signals as such or from the degree of reflection. The at least one beat property can in particular be a fluctuation range.

Fig.2 shows a plot of a time profile of a degree of reflection R or a reflection coefficient (in any units) of the superimposed microwave measurement radiation versus time t in minutes for a thawing process or thawing section, specifically for the measurement channels K1 belonging to the two microwave measurement devices 7a, 7b and K2. The degrees of reflection R associated with the measuring channels K1 and K2 have respective fluctuation ranges B.

Fig.3 shows a plot of a time course of Fig.2 determined or determined range of fluctuation B of the superimposed microwave measurement radiation versus time t for both measurement channels K1 and K2.

During the thawing process, useful microwave radiation is radiated into the cooking chamber 2 in order to heat the food L. As long as the food L is still frozen or not yet thawed, a fluctuation range B of the degree of reflection R determined from the superimposed microwave measuring radiation changes only slightly. With the phase transition of the water in the food L from frozen to liquid (thawing), the fluctuation range B drops abruptly over its time course V or in a short time (e.g. within 10 or 20 seconds), as here between t = 4 min and t=5 min in the phase transition time domain PZ. This abrupt drop in the fluctuation range(s) B can be clearly seen.

If the useful microwave radiation does not evenly penetrate the food L, it can happen that the sudden drop in the fluctuation range B is caused by a local phase transition or only local thawing, so that parts of the food L are already thawed while other parts of the food L are still in a frozen (thawed) state.

In particular, at the beginning of a thawing process, an initial scan can be carried out over all frequency pairs f1, f2 of the microwave measuring radiation MW1, MW2 that are used or can be used by the microwave generator 4. The microwave measuring radiation MW1, MW2 for all possible frequency pairs f1, f2 is irradiated with a time offset and their superimposed reflection is measured by the microwave measuring devices 7a, 7b. A time window of 100 ms, for example, can be provided for each of the pairs of microwave measurement frequencies f1, f2. From this, the control device 6 selects at least one measurement pair, in particular a plurality of measurement pairs, based on at least one stored selection criterion for subsequent use as measurement pair(s).

The thawed state of the food L is then determined based on an evaluation of the range of fluctuation B of only the at least one measurement pair. For example, useful microwave radiation and microwave measurement radiation can be radiated into the cooking chamber 2 alternately during a thawing process.

In a variant in which several measurement frequencies have been selected, the microwave measurement radiation can be evaluated individually for different measurement pairs and the achievement of the phase transition can be detected by the drop in the degree of reflection R at one, several or all measurement frequencies.

Fig.4 shows a flow chart for a possible operation of the food heating device 1.

In a first step S1, controlled by the control device 6, an initial scan is carried out by using the microwave transmitter 3a, 3b to radiate microwave measuring radiation MW1, MW2 with different pairs of measuring frequencies f1, f2 into the cooking chamber 2 at the beginning of a thawing process of the microwave measuring devices 7a, 7b in each case a power of the superimposed microwave measuring radiation is measured for each of the frequency pairs radiated in.

In a second step S2, at least one measurement pair is selected by the control device 6 on the basis of the superimposed microwave measurement radiation.

In a third step S3, controlled by the control device 6, the useful microwave radiation is radiated into the cooking chamber 2 in a first defrosting section with a first set of microwave parameters from a group of m (m ≥ 2) microwave parameters until a Phase transition is detected, e.g. based on a strong change in the degree of reflection R from a time profile V of the degrees of reflection R. In this first thawing section, the irradiation of the useful microwave radiation and the microwave measurement radiation alternate several times, around the profile V of the fluctuation range B with to record with high temporal resolution. The useful microwave radiation is irradiated with high power, in particular with maximum power.

In a fourth step S4, when a phase transition or a thawed state is or has been detected based on the curve V of the fluctuation range B, the heating power is set to zero until the curve V determines refreezing, for example by a phase transition following a noticeable increase in the fluctuation range B.

Subsequently, steps S3 and S4 can be repeated for all other predetermined m sets of microwave parameters, as indicated by step S5, alternatively only for some of the sets.

• die Schritte S3 und S4 für alle m oder einige vorgegebene Sätze von Mikrowellen-Parametern durchgeführt worden sind;
• in mindestens einem der Schritte S4 kein Wiedergefrieren mehr festgestellt worden ist; und/oder
• wenn in mindestens einem der Schritte S3 anfänglich kein gefrorener Zustand festgestellt worden ist.

The thawing process can be terminated in a step S6, for example, if

• steps S3 and S4 have been performed for all m or some predetermined sets of microwave parameters;
• refreezing was no longer detected in at least one of steps S4; and or
• if no frozen condition was initially detected in at least one of steps S3.

Steps S3 to S5 can also be run through multiple times, in particular if refreezing is or has been detected in the last of the predetermined sets of microwave parameters of the useful microwave radiation.

Optionally, step S6 can be followed by a step S7, in which the food L is briefly irradiated with useful microwave radiation ("heating burst"), e.g. to eliminate the presence of small frozen areas and/or to reliably place the food L in to transition to a fully thawed state.

Fig.5 shows a plot of a time course of a degree of reflection R or a reflection coefficient (in arbitrary units) of the superimposed microwave measuring radiation versus the time t in minutes for a cooking process, specifically for the measuring channels K1 and K2 belonging to the two microwave measuring devices 7a, 7b . The degrees of reflection R associated with the measuring channels K1 and K2 have respective fluctuation ranges B. The measurement frequencies here are, for example, f1=2461 MHz and f2=2462 MHz. 200 ml of 0.8 percent salt water are heated in a plate.

Fig.6 shows a plot of a time course of Fig.2 determined or determined range of fluctuation B of the superimposed microwave measurement radiation versus time t for both measurement channels K1 and K2.

Useful microwave radiation, for example, can also be radiated into the cooking chamber 2 during the cooking process in order to heat the food L. As long as the food L is not yet boiling, a fluctuation range B of the degree of reflection R determined from the superimposed microwave measuring radiation changes rather slightly. When the water begins to boil, the range of fluctuation B of the degree of reflection R increases abruptly or in a short time (e.g. within 10 seconds) over the course of time V, as shown here shortly after t = 4 min. This sudden increase in the fluctuation range(s) B can be clearly recognized and evaluated, e.g. for a subsequent control of the heating output.

The cooking process can be designed at least partially in the same way as the thawing process, e.g. using an initial scan, by selecting one or more measurement pairs and/or by irradiating heating power with different heating parameters, etc.

Of course, the present invention is not limited to the embodiment shown.

In general, "a", "an" etc. can be understood as a singular or a plural number, in particular in the sense of "at least one" or "one or more" etc., as long as this is not explicitly excluded, e.g. by the expression "exactly a" etc.

A numerical specification can also include exactly the specified number as well as a usual tolerance range, as long as this is not explicitly excluded.

Reference List

1

microwave oven

2

cooking chamber

3

microwave transmitter

4

microwave generator

5

antenna

6

control device

7

Microwave measuring device

K1

First measurement channel

K2

Second measurement channel

L

Food

PZ

phase transition time domain

B

range of fluctuation

S1-S7

process steps

t

time

V

Course

Claims (15)

1. Method (S1-S7) for operating a food heating appliance (1) in which

   - simultaneously a first microwave measuring radiation (MW1) of a first measuring frequency (f1) and a second microwave measuring radiation (MW2) of a second measuring frequency (f2) that is different from the first measuring frequency (f1) is irradiated into a treatment compartment (2) of the food heating appliance (1)

   - heterodyned microwave measuring radiation that is received from the cooking compartment (2) is measured, characterised in that

   - a thermal state of food (L) that is located in the treatment compartment (2) is determined with reference to an evaluation of a change in a fluctuation range (B) of the heterodyned microwave measuring radiation.
2. Method (S1-S7) according to claim 1, in which

   - the heterodyned microwave measuring radiation is measured at at least two different positions and

   - the thermal state of the food (L) is determined with reference to an evaluation of the change in the fluctuation range (B) of the heterodyned microwave measuring radiation that is measured at at least two different positions.
3. Method (S1-S7) according to one of the preceding claims, in which the first microwave measuring radiation (MW1) and the second microwave measuring radiation (MW2) are continuously irradiated into the treatment compartment (2).
4. Method (S1-S7) according to one of the preceding claims, in which the first microwave measuring radiation (MW1) and the second microwave measuring radiation (MW2) are introduced into the treatment compartment (2) alternately with heating power for heating the food (L).
5. Method (S1-S7) according to one of the preceding claims, in which the food heating appliance (1) is configured so as to heat food (L) that is located in the treatment compartment (2) by means of at least one of the following heating types:

   - microwave irradiation by microwave useful beam radiation;

   - irradiation of further electromagnetic energy

   - thermal radiation by at least one resistance heating body;

   - heat treatment by introduction of hot air and/or introduction of steam.
6. Method (S1-S7) according to claim 5, in which food (L) that is located in the treatment compartment (2) can be heated by means of microwave useful beam radiation and in which a frequency range of the microwave measuring radiation (MW1, MW2), which comprises the measuring frequencies (f1, f2), and a frequency range of the microwave useful beam radiation are different or identical.
7. Method (S1-S7) according to one of the preceding claims, in which

   - at the start of a treatment procedure the first microwave measuring radiation (MW1) and the second microwave measuring radiation (MW2) are irradiated at alternating first and second measuring frequencies (f1, f2) at the same frequency difference,

   - heterodyned microwave measuring radiation that is reflected from the treatment compartment (2) is measured for each pair of simultaneously irradiated first and second microwave radiation (MW1, MW2) and

   - at least one pair is selected from the pairs as a measurement pair for the subsequent determination of the thermal state of the food (L).
8. Method (S1-S7) according to claim 7, in which the at least one measuring pair is selected according to whether the associated reflected heterodyned microwave measuring radiation meets at least one of the following selection criteria:

   - said associated heterodyned microwave measuring radiation or heterodyne signal belongs to a group with the highest reflectances;

   - said associated heterodyned microwave measuring radiation or heterodyne signal belongs to a group with the highest microwave powers;

   - said associated heterodyned microwave measuring radiation or heterodyne signal belongs to a group with the greatest fluctuation ranges (B);

   - said associated heterodyned microwave measuring radiation or heterodyne signal belongs to a group with the lowest reflectances;

   - said associated heterodyned microwave measuring radiation or heterodyne signal belongs to a group with the lowest microwave powers;

   - said associated heterodyned microwave measuring radiation or heterodyne signal belongs to a group with the smallest fluctuation ranges (B);

   - the reflectance or average reflectance of said associated heterodyned microwave measuring radiation or heterodyne signal reaches or exceeds at least one predetermined upper threshold value;

   - the reflected microwave power or average reflected microwave power of said associated heterodyned microwave measuring radiation or heterodyne signal reaches or exceeds at least one predetermined upper threshold value;

   - the fluctuation range (B) of said associated heterodyned microwave measuring radiation or heterodyne signal reaches or exceeds at least one predetermined upper threshold value;

   - the reflectance or average reflectance of said associated heterodyned microwave measuring radiation or heterodyne signal reaches or is below at least one predetermined lower threshold value;

   - the reflected microwave power or the average reflected microwave power of said associated heterodyned microwave measuring radiation or heterodyne signal reaches or is below at least one predetermined lower threshold value.
9. Method (S1-S7) according to one of the preceding claims in which a defrosting and/or boiling of the food (L) is determined with reference to an abrupt change in the fluctuation range (B) of the heterodyned microwave radiation.
10. Method (S1-S7) (S1-S7) according to one of the preceding claims in which heating power during a treatment procedure can be introduced into the treatment compartment (2) with m (m ≥ 2) different predetermined sets of heating parameters, wherein the heating power for different sets of heating parameters heats food (L), which is located in the treatment compartment (2), in a localised different manner and in said method

    a) the heating power having one of the sets of heating parameters is irradiated and a temporal progression of the fluctuation range (B) of the heterodyned microwave measuring radiation is determined,

    b) then, if for this treatment phase by means of the progression of the at least one beat characteristic, a predetermined thermal state of the food (L) is identified, subsequently

    c) the steps a) and b) are repeated for heating power having at least one other of the sets of the heating parameters.
11. Method (S1-S7) (S1-S7) according to claim 10 in which the treatment procedure is a defrosting procedure and the defrosting procedure is terminated if

    - the steps a) and b) have been performed for all m sets of microwave parameters; and/or

    - if in at least one of the steps b) initially a thermal state that is provided after or with heating is determined or has been determined.
12. Method (S1-S7) (S1-S7) according to one of claims 10 to 11 in which in step b) then if for a defrosting phase a defrosted state that is provided during the course of a defrosting phase is identified (S3), the heating power is reduced until a refreezing is identified (S4) and subsequently step c) is performed (S5).
13. Method (S1-S7) according to claim 12 in which in step a) a high heating power is irradiated.
14. Food heating appliance that is configured so as to allow the implementation of the method (S1-S7) according to one of the preceding claims, wherein the food heating appliance (1) has:

    - at least one microwave transmitter (3a, 3b) for irradiating the first microwave measuring radiation (MW1) and the second microwave measuring radiation (MW2) into the treatment compartment (2);

    - at least one microwave measuring apparatus (7a, 7b) for measuring heterodyned microwave measuring radiation from the treatment compartment (2) and

    - a data processing apparatus (6) for determining at least a thermal state of food (L) that is located in the treatment compartment (2) with reference to an evaluation of a change in a fluctuation range (B) of the heterodyned microwave measuring radiation.
15. Food heating appliance (1) according to claim 14 in which the first microwave transmitter (3a) and/or the second microwave transmitter (3b) is provided so as to irradiate microwave useful beam radiation into the treatment compartment (2).

Images