Method for estimating a cooking chamber property and cooking appliance

Abstract

A method for estimating a cooking chamber property of a cooking chamber (14) of a cooking appliance (10) is described, comprising a fan wheel (30) associated with the cooking chamber (14) and a microwave source (22). The microwave source (22) emits several measurement signals with different frequencies during a single rotation of the fan wheel (30) over a defined frequency range, thus obtaining a series of measurements with multiple measurement points. The measurement points of a measurement series differ from one another with respect to the frequency of the measurement signal and the angular position of the fan wheel (30). For each of the multiple measurement signals, at least one frequency-dependent high-frequency property is determined, based on which the cooking chamber property is estimated. Furthermore, a cooking appliance (10) is described.

Description

[0001] The invention relates to a method for estimating a cooking chamber property of a cooking appliance. The invention further relates to a cooking appliance.

[0002] Methods are known in the art for deterministically determining the cooking chamber properties of a cooking chamber, i.e., for determining an approximate quality. Reference is made, for example, to DE 10 2019 127 620 A1 and DE 10 2021 131 619 A1.

[0003] In DE 10 2019 127 620 A1, a scattering parameter measurement is performed for each frequency of a frequency band. Based on this measurement, a frequency-dependent high-frequency property is determined, from which the cooking chamber properties can be indirectly estimated. In the solution described therein, the determination of the cooking chamber properties is thus independent of a fan wheel, meaning that the measurement does not need to be synchronized with the fan wheel's rotation.

[0004] Furthermore, a method for cooking food is known from DE 10 2021 110 521 A1, in which the control of a semiconductor microwave unit is based on a determined angular position of the fan wheel in order to generate a microwave field adapted to the angular position of the fan wheel by the semiconductor microwave unit in the cooking chamber. This ensures that the semiconductor microwave unit operates at an optimal operating point when additional energy is introduced into the food via the microwave unit. In principle, the semiconductor microwave unit allows for adjustments to its control within correspondingly short timeframes. However, it is not known from this method to estimate the properties of the cooking chamber, in particular a dielectric load in the cooking chamber, i.e., a load that influences the electromagnetic properties.Therefore, the semiconductor microwave unit is operated solely on a time-controlled basis, as there is no feedback regarding electromagnetic loading in the cooking chamber of the appliance.

[0005] If feedback regarding the electromagnetic load in the cooking chamber of the cooking appliance were desired, the scattering parameter measurements would have to be taken in the same angular range over several revolutions for all frequencies, which would mean that 100 revolutions would be necessary to obtain the scattering parameters for a frequency range of 100 MHz, e.g. a frequency range from 2,400 MHz to 2,500 MHz.

[0006] However, this means that the measurement of the cooking chamber properties takes a correspondingly long time, during which no energy input from the microwave unit is possible. For example, the measurement of the cooking chamber properties would take 12 seconds assuming a fan speed of 500 revolutions per minute.

[0007] The object of the invention is to enable a rapid measurement or estimation of the cooking chamber properties.

[0008] The object of the invention is achieved by a method for estimating the cooking chamber properties of a cooking appliance, comprising a fan wheel associated with the cooking chamber and a microwave source. The microwave source emits several measurement signals with different frequencies during a single rotation of the fan wheel over a defined frequency range, thus obtaining a series of measurements with multiple measurement points. The measurement points of a measurement series differ from one another with respect to the frequency of the measurement signal and the angular position of the fan wheel. In addition, at least one frequency-dependent high-frequency property is determined for each of the multiple measurement signals, based on which the cooking chamber properties are estimated.

[0009] The basic idea of ​​the invention is to examine multiple frequencies within a single fan wheel rotation, so that different measurement signals are emitted and evaluated during a single rotation of the fan wheel. Different measurement signals are understood to mean that the measurement signals differ in their frequency. In contrast to the prior art, in which a measurement at a fixed frequency is performed for each fan wheel rotation in order to obtain all fan wheel positions or angular positions for each frequency, it is now provided that multiple frequencies are used during a single rotation of the fan wheel.

[0010] This makes it possible for the duration for a frequency range of 100 MHz, for example from 2,400 MHz to 2,500 MHz, to be only 120 ms. In the prior art, where one frequency is provided per fan wheel revolution, 100 fan wheel revolutions would have been necessary if a resolution or frequency spacing of 1 MHz had been chosen.

[0011] A measurement series is characterized by the fact that it comprises several measurement signals, each differing in frequency. Furthermore, the measurement points assigned to the signals differ in that the signals were emitted or recorded at different angular positions of the fan wheel.

[0012] Furthermore, the measurement series is not interrupted by power control of the microwave source, i.e., by a heating operation mode. Any heating operation mode therefore only occurs after the measurement series is complete, i.e., after the measurement signals for the series have been transmitted.

[0013] The different angular positions of the fan wheel during one revolution are assigned to defined time slots, so that a corresponding measurement signal with a defined frequency can be emitted and evaluated in each time slot, thus enabling the measurement of a corresponding frequency-dependent high-frequency property. The method is insensitive to a certain degree of deviation. For example, the deviation should be less than half a time slot. In each time slot, i.e., in each different angular position of the fan wheel during one revolution, an operation is performed, namely a measurement.

[0014] The cooking chamber properties can include the dielectric properties of the cooking chamber and, optionally, ohmic losses, such as ohmic losses at the cooking chamber walls. The dielectric properties of the cooking chamber are influenced, among other things, by the cooking chamber walls, an optional load within the cooking chamber (such as food being cooked or cooking accessories), and the antenna associated with the cooking chamber, through which the microwaves are fed into the cooking chamber, particularly its load impedance.

[0015] The cooking chamber properties can be determined both in an empty and a loaded state, i.e., with food or cooking accessories present in the cooking chamber. Therefore, the cooking chamber properties can also be considered a high-frequency property of the cooking chamber, i.e., an approximate quality of the cooking chamber.

[0016] As is known, the cooking chamber properties can be determined by measuring the electromagnetic waves entering the cooking chamber (also called forward-propagating electromagnetic waves) and the electromagnetic waves exiting the cooking chamber (also called backward-propagating electromagnetic waves) at their respective input points, i.e., the corresponding antennas. For this purpose, directional couplers can be assigned to each antenna, allowing for separate measurement of the incoming and outgoing electromagnetic waves. The frequency-dependent high-frequency property can then be easily determined from the incoming and outgoing electromagnetic waves measured at the antennas. In other words, the frequency-dependent high-frequency property is related to the incoming and outgoing electromagnetic waves.For example, the frequency-dependent high-frequency property is a ratio of the amplitudes of the incident and outgoing electromagnetic waves. The frequency-dependent high-frequency property can also be a ratio of the phases of the incident and outgoing electromagnetic waves. In particular, the frequency-dependent high-frequency property is a scattering parameter (S-parameter).

[0017] Based on the frequency-dependent high-frequency property, the cooking chamber property Q can be determined in a known manner, as described, among others, in DE 10 2021 131 619 A1.

[0018] The empty cooking chamber property Q can be determined and stored once. Alternatively or additionally, the empty cooking chamber property Q can be determined during operation of the cooking appliance, e.g., at regular intervals, especially each time the cooking appliance is started, for example, before loading the cooking appliance.

[0019] Based on the high-frequency property, the corresponding cooking chamber property Q can be determined for the cooking chamber in which the high-frequency property was measured, for example, in a loaded or empty state. In particular, the cooking chamber property Q can be a measure of a dielectric load in the cooking chamber, where the dielectric load depends on the food and / or cooking accessories present in the cooking chamber, and especially on the cooking state of the food.

[0020] The cooking chamber of the appliance is generally considered a so-called multi-port, in which an unknown electromagnetic field distribution exists. This electromagnetic field distribution is influenced, among other things, by the fan and the food in the cooking chamber, in particular by a property of the food in the cooking chamber.

[0021] In other words, the cooking chamber property Q of the cooking chamber in the unloaded state represents a high-frequency property of the empty cooking chamber, whereas the cooking chamber property of the cooking chamber in the loaded state represents a high-frequency property of the loaded cooking chamber. Once the cooking chamber property for the empty cooking chamber and the cooking chamber property for the loaded cooking chamber have been determined, they can be related to each other, thus obtaining a comparative value independent of the type of cooking appliance, and in particular the type of cooking chamber. This allows the cooking chamber property to be compared with that of different cooking appliances, especially different cooking chambers. In other words, normalization occurs when the cooking chamber property for the empty cooking chamber is also taken into account and related to the cooking chamber property for the loaded cooking chamber, thus obtaining the independent comparative value.

[0022] In principle, the measurement series comprises several measurement signals, for example at least ten measurement signals, in particular at least 30 measurement signals, for example at least 50 measurement signals, preferably at least 100 measurement signals. These measurement signals are emitted directly one after the other, each at a different angular position of the fan wheel.

[0023] One aspect involves determining the magnitude function of the frequency-dependent high-frequency property. This magnitude function is then differentiated with respect to the frequency of the measurement signal to obtain a gradient of the high-frequency property, based on which the cooking chamber property is estimated. Therefore, the magnitude of the high-frequency property can first be determined for the respective measurement points. This is particularly necessary if the frequency-dependent high-frequency property is a complex-valued function. Since the high-frequency property has been determined for several measurement points in the measurement series—that is, for measurement points dependent on both frequency and angular position—a corresponding magnitude function can be formed, provided the appropriate magnitude is determined for each measurement point. The magnitude function can then be differentiated with respect to the frequency.The parameters are differentiated to obtain a corresponding gradient of the high-frequency property. This gradient serves as an indicator of the cooking chamber's properties, particularly its dielectric load.

[0024] Additionally, the actual angular position at which the measurement was performed—that is, the position at which the measurement signal was emitted and evaluated at the defined frequency—can also be stored. This enables non-equidistant sampling along a revolution. The gradient along the fan wheel angle can then be obtained using the non-equidistant measurement points.

[0025] Another aspect involves determining several frequency-dependent high-frequency properties simultaneously and independently for each of the multiple measurement signals, based on which the cooking chamber properties are estimated. These multiple frequency-dependent high-frequency properties can be different scattering parameters (S-parameters), for example, S11, S12, S21, and S22.

[0026] In the case of four antennas used to feed the microwaves into the cooking chamber, the scattering parameters S11, S12, S13, S14, S21, S22, S23, S24, S31, S32, S33, S34, S41, S42, S43 and S44 result.

[0027] The different frequency-dependent high-frequency properties reflect different information content regarding the dielectric properties of the cooking chamber, which allows the cooking chamber properties to be estimated more accurately overall.

[0028] In particular, for each frequency-dependent high-frequency property, a separate gradient of the corresponding high-frequency property is determined, based on which the cooking chamber properties are estimated. Accordingly, the respective dynamic behavior is determined for each of the different high-frequency properties in order to more accurately estimate the cooking chamber properties. This applies, for example, to each of the scattering parameters, provided that the frequency-dependent high-frequency properties are indeed scattering parameters.

[0029] According to one embodiment, a sum of all determined gradients is calculated to estimate the cooking chamber properties. In other words, the individual gradients previously determined for the different high-frequency properties are summed to obtain the corresponding sum, based on which the cooking chamber properties can be determined. Thus, a numerical integration of all determined gradients is performed to estimate the cooking chamber properties.

[0030] The defined frequency range can have a frequency span of at least 10 MHz, in particular at least 30 MHz, for example at least 50 MHz, preferably at least 100 MHz. Depending on the resolution, this determines the number of different measurement signals that are transmitted sequentially. With a resolution of one degree, this would result in at least ten measurement signals, in particular at least 30 measurement signals, for example at least 50 measurement signals, preferably at least 100 measurement signals.

[0031] A frequency sweep can be performed to obtain multiple measurement signals at different frequencies. This frequency sweep involves deliberately changing the frequency while continuously transmitting measurement signals during the change.

[0032] Furthermore, the multiple measurement signals of the measurement series can exhibit monotonically increasing or monotonically decreasing frequencies, in particular where the frequencies of the multiple measurement signals are equidistant in the frequency domain. Such frequency behavior is typical for a frequency sweep.

[0033] Another aspect stipulates that the angular positions at which measurement signals are emitted in a measurement series cover an angular range corresponding to a quarter of the fan wheel's rotation, i.e., 90°. Therefore, it is possible to perform a complete measurement series with just a quarter turn of the fan wheel, since a total of 100 angular positions need to be recorded for a frequency range of 100 MHz, which can be mapped to an angular range of 90°.

[0034] Furthermore, a measurement signal with a defined frequency can be emitted multiple times, in particular twice or four times, during a single revolution of the fan wheel at different angular positions, so that several measurement series are obtained during a single revolution of the fan wheel. This can be done periodically. Since a measurement series can be completed with just a quarter revolution of the fan wheel, it is possible to record two, four, or three measurement series during a single revolution of the fan wheel. For each measurement series, at least one frequency-dependent high-frequency property can be determined, in particular several frequency-dependent high-frequency properties simultaneously. It is also possible to determine a corresponding gradient or several gradients of the high-frequency property(ies), based on which the cooking chamber properties of the cooking chamber are estimated.

[0035] Generally, when multiple measurement series are taken, they are standardized accordingly. This means that the sum of the gradients used to estimate the cooking chamber properties is divided by the number of measurement series.

[0036] As explained above, a measurement series is characterized by the fact that a frequency range under consideration has been traversed. Multiple measurement series therefore provide multiple measured values ​​for the same frequency range, which is why normalization can be, and often is, performed.

[0037] According to another aspect, each rotation of the fan wheel is divided into several angular positions, each assigned a time slot in which a measurement signal is emitted. Specifically, 400 time slots are provided, so that 400 measurement signals are emitted in a single rotation of the fan wheel. As explained above, a frequency range of 100 MHz is typically used to estimate the cooking chamber properties, so, for example, a quarter rotation of the fan wheel is sufficient, provided the measurement signals have a frequency spacing of 1 MHz.

[0038] However, a higher resolution regarding frequency can also be chosen, for example a resolution of a quarter of a MHz, so that 400 measurement signals are necessary for a frequency range of 100 MHz.

[0039] Another embodiment involves using two or more revolutions of the fan wheel to assess the cooking chamber properties. Specifically, two or more measurement points are obtained for each angular position of the fan wheel. In other words, two different frequencies are measured successively at a given angular position, as two revolutions of the fan wheel are taken into account. Thus, during the first revolution, the specific angular position is measured at a specific frequency, and during a subsequent second revolution, the same specific angular position is measured at a frequency that differs from the specified frequency. As explained above, slight deviations in the angular position are tolerable. If information about the actual angular position is available at the time of measurement, the deviation can even be corrected accordingly.

[0040] In principle, the cooking chamber properties can be estimated during one revolution of the fan wheel and / or within a maximum of 120 ms (at a speed of 500 rpm). Should the speed increase, for example, to 2,000 rpm, the cooking chamber properties can even be estimated within a maximum of 30 ms. This results in a rapid assessment of the cooking chamber properties, thus reducing the measurement time accordingly. Consequently, energy input via the microwave source can be resumed more quickly or interrupted for a shorter time, thereby increasing the efficiency of the cooking process.

[0041] For example, the frequency range extends from 2,400 MHz to 2,500 MHz, i.e., over a frequency span of 100 MHz. The individual measurement signals can each have a spacing of 1 MHz from each other; if a higher or lower frequency resolution is required, the measurement signals can have a correspondingly different frequency spacing from each other.

[0042] As explained above, at least one frequency-dependent high-frequency property can be a scattering parameter. Scattering parameters are fundamentally easy-to-determine high-frequency properties.

[0043] As is also known, the high-frequency characteristic alone can generally be used to distinguish between an empty and a loaded cooking chamber, since a distinct resonance can develop in an empty cooking chamber (provided interfering factors are disregarded), allowing the quality of the cooking chamber to be determined. However, no distinct resonance occurs in a (heavily) loaded cooking chamber, which is why the quality cannot be directly determined. Therefore, the high-frequency characteristic itself can initially only serve to differentiate between an empty and a loaded cooking chamber. However, this alone does not provide any information regarding the cooking chamber quality of the (fully) loaded cooking chamber, which is why the previously described method is used.

[0044] The high-frequency property also correlates with the cooking properties, particularly the load quantity, since a larger load quantity leads to a sluggish or slowly changing high-frequency property (along the frequency axis). Therefore, the high-frequency property can be derived (differentiated) with respect to frequency to obtain an indicator of the cooking properties of the food in the cooking chamber, whereby the cooking properties influence the cooking chamber properties, as previously explained. Simply put, this means that a function of the high-frequency property derived with respect to frequency assumes a small value if there is a large load quantity in the cooking chamber, because the high-frequency property is correspondingly sluggish.

[0045] The cooking chamber property can be an approximate indicator of the cooking chamber's quality. The cooking chamber's quality is a known quantity. This method allows for a simple and, above all, quick estimation.

[0046] Another aspect involves estimating the cooking chamber properties, particularly the approximate efficiency of the cooking chamber, while the fan is running, specifically during one revolution. Previously, determining the cooking chamber efficiency required either stopping the fan or using only a single frequency at a specific fan position for measurement—that is, one frequency per revolution. Since measuring the entire frequency range is necessary to determine the cooking chamber efficiency, this resulted in an extremely long timeframe. However, the present method allows for a rapid estimation of the cooking chamber efficiency during operation, as it utilizes a series of measurements across different frequencies.

[0047] Furthermore, the object of the invention is achieved by a cooking appliance for cooking food, comprising a cooking chamber, a fan wheel associated with the cooking chamber, a microwave source, and a control and / or evaluation unit. The cooking appliance is configured to carry out the method of the aforementioned type. In particular, the control unit is configured to control the microwave source and / or the fan wheel, i.e., to output the measurement signals (microwave signals) or to rotate the fan wheel. The evaluation unit is specifically configured to evaluate the received measurement signals in order to estimate the cooking chamber properties.

[0048] Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made. The drawings show: Figure 1 a schematic representation of a cooking appliance according to the invention, Figure 2a schematic representation of a method according to the invention, which is carried out with the cooking appliance made of Figure 1 can be carried out Figure 3 a schematic representation of the measuring points used in a method according to the invention, according to a first embodiment, Figure 4 a schematic representation of the measuring points used in a method according to the invention, according to a second embodiment, Figure 5 a schematic representation of the measuring points used in a method according to the invention, according to a third embodiment, Figure 6 a schematic representation of the measuring points used in a method according to the invention, according to a fourth embodiment, and Figure 7 a diagram showing the recorded frequency-dependent high-frequency property over a frequency range for different scenarios.

[0049] In Figure 1A cooking appliance 10 is shown schematically, which has a housing 12 that surrounds a cooking chamber 14 and a technical chamber 16.

[0050] In the cooking chamber 14, a food item 18 is placed, which is to be cooked in the cooking appliance 10.

[0051] The device 10 comprises, in addition to a schematically depicted heating device 19, several (in this case four) microwave modules 20, each of which includes a microwave source 22 designed as a semiconductor component. Alternatively, a central microwave source 22 can be provided, to which the microwave modules 20 are connected. Each microwave module 20 also includes an antenna 24 and a directional coupler 26.

[0052] Furthermore, the microwave modules can comprise 20 additional components, such as a modulator, an amplifier, a demodulator, and / or a controller. These are not shown here for the sake of clarity.

[0053] The microwave modules 20 together can be combined as a microwave assembly 28.

[0054] Furthermore, the cooking appliance 10 includes a fan wheel 30, which is assigned to the cooking chamber 14. The fan wheel 30 is driven by a drive 32 and a drive shaft 34. This ensures that the cooking chamber climate 14 is circulated to guarantee the most homogeneous possible energy input into the food 18 by means of hot air and / or steam provided by the heating element 19, resulting in uniform heating of the food 18.

[0055] A rotary encoder 36 is assigned to the fan wheel 30, which is, for example, integrated into the drive 32. The rotary encoder 36 can detect the angular position of the fan wheel 30 during operation, i.e., while the drive 32 is rotating the fan wheel 30. The rotary encoder 36 can be an incremental encoder. For example, the rotary encoder 36 is designed as an optical encoder.

[0056] Furthermore, the cooking device 10 includes a control and / or evaluation unit 38, which is connected to the microwave modules 20, in particular the microwave source(s) 22 and the directional couplers 26, the drive 32 and / or the rotary encoder 36 for signal transmission.

[0057] In principle, it is also possible to determine the angular position from a rotor characteristic map of the drive 32, i.e. by means of the control and / or evaluation unit 38, which evaluates the recorded rotor characteristic map.

[0058] In particular, a control module 40 (of the control and / or evaluation unit 38) is connected to the microwave modules 20, in particular the microwave source(s) 22, and the drive 32 via signal transmission in order to control the microwave modules 20, in particular the microwave source(s) 22, and the drive 32.

[0059] In contrast, an evaluation module 42 (of the control and / or evaluation unit 38) is connected to the rotary encoder 36 and the microwave modules 20, in particular the directional couplers 26, in order to obtain the angular position of the fan wheel 30 from the rotary encoder 36 and microwave signals (electromagnetic signals) from the microwave modules 20, in particular the directional couplers 26, on the basis of which an evaluation is carried out, as is explained below.

[0060] In this respect, the control and / or evaluation unit 38 sends corresponding control signals to the microwave modules 20, in particular the microwave source(s) 22, in order to generate microwaves in a defined manner, which are to be fed into the cooking chamber 14.

[0061] Furthermore, the control and / or evaluation unit 38 controls the rotation of the fan wheel 30, particularly depending on a (selected) cooking program, by sending corresponding control signals to the drive 32 so that the fan wheel 30 is operated at a defined angular velocity. In this respect, the control and / or evaluation unit 38 can be a higher-level control and / or evaluation unit that also serves to execute the cooking program in order to cook the food 18 as desired.

[0062] The control and / or evaluation unit 38 can control the microwave modules 20 based on the detected rotation of the fan wheel 30, for example, due to the signal output by the rotary encoder 36. In other words, the control and / or evaluation unit 38 detects the signal output by the rotary encoder 36 (passively) and controls the microwave modules 20, provided this is possible in the intended manner.

[0063] In particular, this ensures that the microwave modules 20, especially the microwave source(s) 22, and the drive 32 are controlled in a coordinated manner.

[0064] Furthermore, the control and / or evaluation unit 38 receives corresponding signals from the rotary encoder 36, thus enabling feedback regarding the actual angular position of the fan wheel 30. Deviations from the controlled target position can therefore be detected. In principle, the rotary encoder 36 can transmit a corresponding encoder signal to the control and / or evaluation unit 38, from which the control and / or evaluation unit 38 determines the angular position of the fan wheel 30.

[0065] Furthermore, the control and / or evaluation unit 38 is also connected to the respective microwave modules 20, in particular the directional coupler 26, via signal transmission in order to receive corresponding measurement signals which are then evaluated. These measurement signals can be forward-propagating electromagnetic waves and backward-propagating electromagnetic waves, which are also referred to as incoming and outgoing electromagnetic waves, respectively.

[0066] Basically, the cooking appliance 10, in particular the control and / or evaluation unit 38, is designed to determine or estimate a cooking chamber property of the cooking chamber 14, which, among other things, allows a conclusion to be drawn about the load of the cooking chamber 14 from an electromagnetic point of view, since the dielectric properties are taken into account.

[0067] For this purpose, as for example in the Figures 2 and 3 shown, several measurement signals with different frequencies are emitted over a defined frequency range during a single revolution of the fan wheel 30, i.e. fed into the cooking chamber 14, so that a series of measurements with several measurement points is obtained.

[0068] The various measurement signals are emitted at different angular positions of the fan wheel 30, since the measurement signals are emitted in time slots that are assigned to correspondingly different angular positions of the fan wheel 30.

[0069] Such a series of measurements is in Figure 3 graphically represented, where for 100 different angular ranges of the fan wheel 30 a total of 100 different measurement signals are emitted, which differ in frequency.

[0070] For example, 100 different measurement signals are transmitted over a frequency range of 100 MHz, for instance at a frequency of 2,400 MHz to 2,500 MHz, with the measurement signals having a frequency spacing of 1 MHz from each other, which is also referred to as resolution. Generally, the defined frequency range can have a frequency span of at least 10 MHz, in particular at least 30 MHz, for example at least 50 MHz, preferably at least 100 MHz.

[0071] The resulting series of measurements therefore comprises measurement points that differ from each other with respect to the frequency of the measurement signal and the angular position of the fan wheel 30, which in Figure 3graphically represented.

[0072] Out of Figure 3 It becomes clear that one revolution of the fan wheel 30 is divided into 400 time slots, so that up to 400 different measurement signals can be sent out per revolution of the fan wheel 30. In other words, 400 different angular positions of the fan wheel 30 can be considered.

[0073] The different angular positions therefore differ by 0.9° from each other, since 400 different angular positions are possible with a complete rotation of 360°, i.e. 360° / 400 = 0.9°.

[0074] With a frequency range of 100 MHz, e.g. corresponding to the frequency range of 2,400 MHz to 2,500 MHz, and a resolution of 1 MHz per measurement signal, this results in 100 different angular positions, for each of which a measurement signal is emitted, in particular a different measurement signal, since a different frequency is always used for each angular position.

[0075] The measurement signals with the different frequencies were obtained by performing a frequency sweep. This is done from Figure 3 This is evident because the frequency changes continuously. In this case, the multiple measurement signals in the measurement series have monotonically increasing frequencies, with the frequencies of the multiple measurement signals being equidistant in the frequency domain. Alternatively, it can also be provided that the multiple measurement signals in the measurement series have monotonically decreasing frequencies.

[0076] The microwave modules 20 are controlled by the control and / or evaluation unit 38, which also evaluates the signal from the rotary encoder 36 and controls the drive 32 of the fan wheel 30 to ensure that a different measurement signal can be sent for each angular position. In other words, the rotational speed of the fan wheel 30 and the control of the microwave modules 20 must be coordinated.

[0077] For each of the multiple measurement signals, at least one frequency-dependent high-frequency property is determined, for example, a scattering parameter. This is done via the control and / or evaluation unit 38.

[0078] The corresponding evaluation is possible because forward-propagating and reverse-propagating electromagnetic waves can be provided and evaluated separately via the microwave modules 20, in particular the provided directional couplers 26, on the basis of which scattering parameters can be determined as frequency-dependent high-frequency properties.

[0079] In principle, several frequency-dependent high-frequency properties can therefore be determined simultaneously and independently of each other for each of the multiple measurement signals. These can be different scattering parameters. In the embodiment shown, the Figure 1 Four antennas 24 are provided so that the scattering parameters S11, S12, S13, S14, S21, S22, S23, S24, S31, S32, S33, S34, S41, S42, S43 and S44 can be determined.

[0080] It is also possible to use only a part of the (theoretically determinable or practically determined) scattering parameters for estimating the cooking chamber properties of cooking chamber 14, for example all scattering parameters above the main diagonal of a scattering matrix, in particular including the scattering parameters of the main diagonal.

[0081] In Figure 7 The frequency-dependent high-frequency property is exemplified by the scattering parameters S11 and S21 for the aforementioned frequency range of 100 MHz and the frequency range of 2,400 MHz to 2,500 MHz, respectively (2.4 GHz to 2.5 GHz). Furthermore, it follows from Figure 7 It is evident that the respective frequency-dependent high-frequency property has been determined for two different states of the cooking chamber 14, namely for an empty cooking chamber and a loaded cooking chamber.

[0082] The in Figure 7The shown course of the frequency-dependent high-frequency property is therefore recorded within one revolution of the fan wheel 30, in particular within a quarter revolution of the fan wheel 30, since only a 90° rotation is required for 100 measuring points, as the angular positions differ from each other by 0.9°, as explained previously.

[0083] This clearly shows that the high-frequency property, i.e., the scattering parameters, behave differently across the frequency and angular range depending on whether the cooking chamber 14 is loaded or not. In particular, it has been shown that the high-frequency property becomes sluggish when the cooking chamber 14 is loaded. Therefore, it is difficult to determine a cooking chamber property of the cooking chamber 14, for example, a cooking property of the food 18 located in the cooking chamber 14, based on the behavior of the high-frequency property itself, since no clear resonance develops.

[0084] Therefore, in a further step of the process, Figure 2 The method shown further processes the high-frequency property, i.e., the scattering parameter, as explained below.

[0085] Based on at least one frequency-dependent high-frequency property, the cooking chamber property of cooking chamber 14 can then be estimated.

[0086] First, the cooking chamber property Q of cooking chamber 14 is determined, in particular that of the empty cooking chamber 14 Q empty and that of the loaded cooking chamber 14 Q loaded. Based on the cooking chamber properties Q, the dielectric load of the cooking chamber 14 can be estimated, i.e., cooking accessories present in cooking chamber 14, food 18 present in cooking chamber 14 and / or the cooking state of the food 18.

[0087] For this purpose, an absolute value function of at least one frequency-dependent high-frequency property can be determined. This absolute value function is then differentiated with respect to the frequency of the measured signal to obtain a gradient of the high-frequency property. This differentiation aims to achieve a smooth frequency response of the high-frequency property, since its frequency-dependent behavior correlates with the load in cooking chamber 14, for example, the food being cooked 18. The greater the load in cooking chamber 14, the smoother the frequency-dependent response of the high-frequency property. This smoothness is precisely described by the frequency-differentiated function of the high-frequency property.

[0088] In other words, for the measurement series, i.e., the different measurement points, the respective magnitude of the frequency-dependent high-frequency property is determined, resulting in a corresponding magnitude function that depends on the frequency of the measurement signal. This magnitude function is then differentiated with respect to frequency to obtain a gradient of the high-frequency property.

[0089] If several frequency-dependent high-frequency properties have been determined, a corresponding gradient can be calculated separately for each of these properties. The calculated gradients can then be summed to obtain a total value, which serves as the basis for estimating the cooking chamber properties of cooking chamber 14.

[0090] In Figure 3It has been shown by way of example that 100 measurement signals, each with different frequencies, are emitted at different angular positions of the fan wheel 30, whereby the angular positions together cover an angular range corresponding to a quarter of the fan wheel 30. Therefore, the measurement of a series of measurements is already completed after a quarter turn of the fan wheel 30.

[0091] This means that a measurement signal with a defined frequency can be emitted several times, in particular two, three, or four times, during a single revolution of the fan wheel 30 at different angular positions, so that several measurement series are obtained during the single revolution of the fan wheel 30. This is exemplified in the Figures 4 and 5 shown, in which two or four measurement series are shown during a single revolution of the fan wheel 30, as can be clearly seen from the Figures 4 and 5This results in a corresponding increase in resolution.

[0092] A measurement series is therefore characterized by the fact that it comprises several measurement signals, each differing in frequency. Furthermore, the measurement points assigned to the signals differ in that the signals were emitted or recorded at different angular positions of the fan wheel 30. In this respect, a measurement series is assigned to a frequency band or frequency range.

[0093] If multiple measurement series are performed, normalization can be carried out. For this purpose, the respective results of the measurement series are added together and divided by the number of measurement series.

[0094] This applies accordingly to each frequency-dependent high-frequency property, provided that several frequency-dependent high-frequency properties are determined.

[0095] In any case, it is ensured that the cooking chamber properties of the cooking chamber 14 can be estimated within one revolution of the fan wheel 30, especially in a significantly shorter time, so that the efficiency of a cooking process is correspondingly high, since a cooking operation with the microwave assembly 28 can be continued earlier or only needs to be interrupted for a shorter time.

[0096] For example, four measurement series are performed in one revolution of the fan wheel 30, so that the cooking chamber properties of the cooking chamber 14 can be determined within 120 ms, i.e., during one revolution of the fan wheel 30. A speed of 500 revolutions per minute is specified for the fan wheel 30. Due to the short duration of 120 ms for assessing the cooking chamber properties, it is ensured that the energy input (in a heating mode) is minimally affected. The energy input into the food 18 is therefore only briefly interrupted.

[0097] This is possible because the entire frequency band, i.e. the frequency range from 2,400 MHz to 2,500 MHz, is measured, whereby at least one frequency-dependent high-frequency property (scattering parameter) is measured at each frequency (for example, resolution of 1 MHz).

[0098] The cooking chamber properties can be determined at regular intervals, e.g., every 5 seconds or every second. If the cooking chamber properties are expected to change rapidly, a shorter interval can be chosen, e.g., one second.

[0099] A time-dependent profile of the cooking chamber properties can then be generated. This profile contains information about the dielectric load in the cooking chamber 14, in particular a food property, e.g., the cooking state of the food 18 (defrost detection, temperature and / or humidity) or the load quantity. Furthermore, the cooking chamber properties can also take into account ohmic losses in the cooking chamber 14. Therefore, the cooking chamber properties can represent an approximate quality factor of the cooking chamber 14.

[0100] Using the estimated cooking chamber properties, a performance estimate can be made, which thus continuously adapts to changing cooking product properties, e.g. the cooking state of the food 18 and / or the loading quantity, if food 18 is added subsequently.

[0101] In principle, it can also be provided that two or more revolutions of the fan wheel 30 are used when estimating the cooking chamber properties, as is done in Figure 6 shown.

[0102] For each angular position of the fan wheel 30, two or more measurement points would result, differing from one another in terms of the frequency used. The number of different frequencies per angular position of the fan wheel 30 depends on the number of revolutions of the fan wheel 30 used to estimate the cooking chamber properties. In the Figure 6 The example shown takes into account two revolutions of the fan wheel 30.

[0103] This is clearly illustrated by the fact that a horizontal line of the in Figure 6The diagram shown is intersected several times. The number of intersection points of the horizontal line indicates how many revolutions of the fan wheel 30 are used to estimate the cooking chamber properties.

[0104] The microwave assembly 28 and the fan wheel assembly comprising the fan wheel 30 are synchronized or coordinated with each other, which is ensured by the control and / or evaluation unit 38, which receives signals from the rotary encoder 36, among other things.

[0105] One revolution of the fan wheel 30 (at a predetermined speed) is divided into a defined number of equal time slots, in each of which a different measurement signal is emitted by the microwave assembly 28. Each time slot is thus assigned an angular position of the fan wheel 30, with the different angular positions being equidistant from each other, since the time slots are of equal length. For example, there are 400 or 404 time slots.

[0106] With each revolution of the fan wheel 30, a specific frequency from the frequency band is assigned to each angular position of the fan wheel 30, i.e., to each time slot. Therefore, a different frequency is measured for each time slot, as can be seen from the Figures 3 to 5 becomes clear.

[0107] Since the frequency-dependent high-frequency property is measured in each measurement, the following results for 100 measurement points with a resolution or frequency spacing of 1 MHz: Figure 7 The shown curve represents the frequency-dependent high-frequency property. As explained above, the corresponding curve of the frequency-dependent high-frequency property can be obtained within a quarter turn of the fan wheel 30.

[0108] Furthermore, two frequency-dependent high-frequency properties can be recorded simultaneously, as previously explained, so that, for example, the curves for the empty cooking chamber 14 of the scattering parameters S11 and S21, which represent the frequency-dependent high-frequency properties, can be measured during a single revolution of the fan wheel 30, particularly within a quarter turn of the fan wheel 30, provided that the resolution or frequency spacing is 1 MHz and the angular positions differ from each other by 0.9°. Likewise, the curves for the loaded cooking chamber 14 of the scattering parameters S11 and S21, which represent the frequency-dependent high-frequency properties, can be measured during a single revolution of the fan wheel 30, particularly within a quarter turn of the fan wheel 30.

[0109] Basically, the fan wheel 30 is used as a mode mixer for the electromagnetic field in the cooking chamber 14, so that the food 18 placed in the cooking chamber 14 is uniformly scanned electromagnetically. However, an additional mode mixer can also be provided if desired.

Claims

1. Method for estimating a cooking chamber property of a cooking chamber (14) of a cooking appliance (10) comprising a fan wheel (30) associated with the cooking chamber (14) and a microwave source (22), wherein the microwave source (22) emits several measurement signals with different frequencies during a single rotation of the fan wheel (30) over a defined frequency range, such that a series of measurements with several measurement points is obtained, wherein the measurement points of a measurement series differ from each other with respect to the frequency of the measurement signal and an angular position of the fan wheel (30), wherein at least one frequency-dependent high-frequency property is determined for each of the several measurement signals, on the basis of which the cooking chamber property is estimated.

2. Method according to claim 1, characterized by the fact thatan absolute value function of the frequency-dependent high-frequency property is determined, whereby the absolute value function is differentiated at least with respect to the frequency of the measurement signal in order to obtain a gradient of the high-frequency property on the basis of which the cooking chamber property is estimated.

3. Method according to claim 1 or 2, characterized by the fact that Several frequency-dependent high-frequency properties are determined simultaneously and independently for each of the multiple measurement signals, based on which the cooking chamber properties are estimated.

4. Method according to claim 3, characterized by the fact that For each frequency-dependent high-frequency property, a respective gradient of the corresponding high-frequency property is determined separately, based on which the cooking chamber property is estimated.

5. Method according to claim 4, characterized by the fact that A sum of all determined gradients is formed to estimate the cooking chamber properties.

6. Method according to any one of the preceding claims, characterized by the fact that the defined frequency range has a frequency span of at least 10 MHz, in particular at least 30 MHz, for example at least 50 MHz, preferably at least 100 MHz.

7. Method according to any of the preceding claims, characterized by the fact that A frequency sweep is performed to obtain the multiple measurement signals with the different frequencies.

8. Method according to any one of the preceding claims, characterized by the fact that the multiple measurement signals of the measurement series exhibit monotonically increasing frequencies or monotonically decreasing frequencies, in particular wherein the frequencies of the multiple measurement signals are equidistant in the frequency domain.

9. Method according to any one of the preceding claims, characterized by the fact that The angular positions in which measurement signals of a measurement series are emitted cover an angular range corresponding to a quarter of the fan wheel (30).

10. Method according to any one of the preceding claims, characterized by the fact that a measurement signal with a defined frequency is emitted several times, in particular twice or four times, during each revolution of the fan wheel (30) in different angular positions, so that several series of measurements are obtained during each revolution of the fan wheel (30), in particular where the series of measurements are normalized.

11. Method according to any of the preceding claims, characterized by the fact that the single revolution of the fan wheel (30) is divided into several angular positions, each of which is assigned a time slot in which a measurement signal is emitted, in particular wherein 400 time slots are provided so that 400 measurement signals are emitted in a single revolution of the fan wheel (30).

12. Method according to any one of the preceding claims, characterized by the fact thattwo or more revolutions of the fan wheel (30) are used in estimating the cooking chamber properties, in particular where two or more measuring points are obtained for an angular position of the fan wheel (30).

13. Method according to any one of the preceding claims, characterized by the fact that the cooking space property is an approximate quality of the cooking space (14).

14. Method according to any one of the preceding claims, characterized by the fact that the cooking chamber property, in particular the approximate quality of the cooking chamber (14), is estimated during the operation of the fan wheel (30), especially during one revolution of the fan wheel (30).

15. Cooking device (10) for cooking food (18), comprising a cooking chamber (14), a fan wheel (30) associated with the cooking chamber (14), a microwave source (22) and a control and / or evaluation unit (38), wherein the cooking device (10) is configured to carry out the method according to one of the preceding claims.

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