Method for determining a microwave absorption capability in a cooking chamber

Abstract

The invention relates to a method for detecting a microwave absorber in a cooking chamber (12) of a cooking appliance (10) by determining a microwave absorption capacity in the cooking chamber (12). The method comprises the following steps: - determining a first thermal load (36) of the cooking chamber (12) based on a temperature change in the cooking chamber (12) and / or a heating power (28) of a heating device (16); - feeding microwave energy into the cooking chamber (12) by means of a microwave source (18) of the cooking appliance (10); - determining a second thermal load (42) of the cooking chamber (12) while microwave energy is being fed into the cooking chamber (12) or following the feeding of microwave energy into the cooking chamber (12); and - determining a microwave absorption capacity in the cooking chamber (12) by comparing the first thermal load (36) and the second thermal load (42). The invention further relates to a cooking appliance (10).

Description

[0001] The invention relates to a method for determining microwave absorption capacity in a cooking chamber. Furthermore, the invention relates to a cooking appliance.

[0002] In professional and commercial kitchens, cooking appliances are used that can cook food in a variety of ways. In addition to traditional methods that use hot air and / or steam to cook the food, modern cooking appliances often also use microwave sources that heat the food using electromagnetic radiation. Magnetrons and semiconductor components can be used as microwave sources.

[0003] For cooking appliances with a microwave source, it is important to know how well the microwaves are absorbed in the cooking chamber in order to correctly dose the microwaves. This depends on the quantity and surface area of ​​the food in the cooking chamber. This absorption capacity for microwaves in the cooking chamber is also referred to as the microwave load, i.e., the microwave power absorbed in the cooking chamber. Direct measurement of the microwave load is usually not technically possible in conventional cooking appliances and / or involves very complex procedures.

[0004] Methods are known from the state of the art that can determine the thermal energy absorption capacity of the cooking chamber (hereinafter also referred to as thermal load). Such methods evaluate the heating activity and / or the cooking chamber temperature profile.

[0005] The thermal load correlates with the microwave load, but it is not identical to the microwave load. Differences arise from different material properties regarding microwave absorption, from different surface-to-volume ratios, from different positioning of food in connection with spatially inhomogeneous intensity of microwave radiation in the cooking chamber, or from shielding effects, for example, from cooking chamber accessories. Therefore, the result of a conventional thermal load determination can only be considered a rough estimate of the microwave load.

[0006] Another problem is that even a very small cooking chamber load can be important for microwave dosing and must be distinguished from a completely empty cooking chamber. Microwave feeding into a completely empty cooking chamber can cause damage to components such as door glass or temperature sensors and should therefore be avoided.

[0007] It is therefore the object of the invention to provide a method with which a microwave absorber in a cooking chamber can be detected in a technically simple and reliable manner based on its microwave absorption capacity or microwave load.

[0008] The object is achieved according to the invention by a method for detecting a microwave absorber in a cooking chamber of a cooking appliance by determining a microwave absorption capacity in the cooking chamber. The method comprises the following steps: Determining a first thermal load of the cooking chamber based on a temperature change in the cooking chamber and / or a heating power of a heating device; feeding microwave energy into the cooking chamber using a microwave source of the cooking appliance; determining a second thermal load of the cooking chamber while microwave energy is being fed into the cooking chamber or following the feeding of microwave energy into the cooking chamber; and determining a microwave absorption capacity in the cooking chamber by comparing the first thermal load and the second thermal load.

[0009] The invention is based on the finding that, for small load quantities, the microwave load can be determined from a change in the thermal absorption capacity in the cooking chamber caused by microwave radiation.

[0010] It is therefore possible to record and compare thermal loads with and without or with varying microwave irradiation in order to draw conclusions about the microwave load.

[0011] The thermal loads, in turn, can be determined based on the heat output of the thermal heating element and a temperature change in the cooking chamber (caused by heating or by a pause in heating). In this context, it may be advantageous to consider the temperature change following the introduction of microwave energy (in simple terms, shortly after) when determining the second thermal load, because any temperature increase caused by the microwaves typically occurs with a time delay after the introduction.

[0012] Of course, a possible time lag between the application / suspension of the heating power and the temperature change can also be taken into account when determining the first thermal load.

[0013] The heating power and the cooking chamber temperature are typically recorded anyway in conventional cooking appliances. Therefore, no additional sensor technology is required to detect the microwave absorber and / or determine the microwave load. This allows the method according to the invention to be implemented cost-effectively, since no additional components are required; existing components can be used instead.

[0014] In a preferred variant of the method, the microwave absorption capacity in the cooking chamber is determined by calculating the difference between the first thermal load and the second thermal load. This can be done without significant computational effort and has been shown to provide reliable results.

[0015] It may also be provided that the above-mentioned procedural steps are repeated continuously over a period of time or at regular intervals.

[0016] It is conceivable that the fed-in microwave power is varied. For example, the microwave power can be varied over time using a sine function. However, it is also possible for the microwave source to be switched on and off. The switching on and off can occur cyclically at fixed or variable time intervals. This creates defined conditions for determining the first thermal load and the second thermal load. The first thermal load can be determined at times when the microwave source is switched off and / or when the microwave power is minimal. The second thermal load, on the other hand, is preferably determined at times of maximum microwave power or directly after this.

[0017] Optionally, a noise suppression method can be used to determine the second thermal load, in particular Fourier analysis. It has been shown that this allows the second thermal load to be determined with greater precision. Differences between the first thermal load and the second thermal load become more apparent or can only be detected in this way. For example, the microwave power is varied sinusoidally, with a (possibly temporally shifted) sine function being sought in the second thermal load. This can be done by a Fourier transformation and subsequent evaluation of the appropriate frequency component or by forming a correlation function between the sine of the microwave power and the second thermal load. This can also be done with other functions, for example a rectangular function.

[0018] In a further variant of the method, based on the microwave absorption capacity, a distinction is made between an empty cooking chamber and a microwave absorber provided in the cooking chamber, which has an equivalent volume of a maximum of 250 ml of water.

[0019] Equivalent volume means that the microwave absorber, for example a food, absorbs as much microwave energy as the specified amount of water under the same conditions.

[0020] In particular, the method can be suitable or intended to distinguish a loading of the cooking chamber with an equivalent volume of maximum 100 ml of water, for example 50 ml of water, from an empty cooking chamber.

[0021] The process is therefore preferably designed to be particularly sensitive to small loads. This can be achieved by using appropriately precise sensors to detect the cooking chamber temperature and / or heating power, as well as through the technical effect explained below.

[0022] It has been found that with medium or high loads, almost all of the incident microwave energy is absorbed by the food and therefore cannot contribute to a temperature increase in the cooking chamber. If, on the other hand, the load is very small, the proportion of microwave energy that is not absorbed by the food can cause a temperature increase in the cooking chamber, which in turn can be detected via the second thermal load. It has been shown that the temperature increase and thus also the second thermal load for small loads correlates strongly with the load. This effect is exploited according to the invention to reliably detect very small loads and / or to distinguish them from an empty cooking chamber.

[0023] The load information can, in turn, be used to regulate the microwave energy so that it is precisely matched to the load size. This reliably prevents small quantities of food from being overcooked due to microwave overdose and / or microwave radiation from entering an empty cooking chamber, which could lead to component damage.

[0024] In particular, temperature control is suspended so that the first thermal load of the cooking chamber and / or the second thermal load of the cooking chamber are determined or are determined when the temperature control is suspended. The suspension of temperature control results in the cooking chamber temperature not being actively kept constant (for a short time). For this purpose, no thermal heating energy can be introduced into the cooking chamber to keep the cooking chamber temperature constant. This then results in a cooling or a reduction in the cooking chamber temperature, which depends on the thermal load. Alternatively, the suspension of temperature control can result in thermal heating energy being introduced into the cooking chamber, which causes the cooking chamber temperature to rise further. This, in turn, depends on the thermal load.When the temperature control is suspended, the thermal load can be determined particularly well, since a uniform input of thermal heating energy occurs through the heating device, which is also understood as no input, i.e. an input of thermal heating energy of 0.

[0025] In a further embodiment of the method, a microwave-absorbing substance, in particular water, is injected into the cooking chamber when the microwave energy is fed into the cooking chamber. This injection deliberately introduces an additional microwave absorber into the cooking chamber, which absorbs at least a portion of the fed-in microwaves. This, in turn, affects the temperature rise resulting from the microwave feed. Simply put, the microwave energy absorbed in the additional substance can no longer contribute, or only to a very limited extent, to heating the cooking chamber. The temperature in the cooking chamber therefore rises less sharply. This effect, in turn, is highly dependent on the cooking chamber load.If, for example, the cooking chamber is loaded with food that absorbs all or almost all of the input microwave energy anyway, the injection of the substance has a negligible influence. However, the influence of the injection of the substance increases as the amount of food decreases. If, for example, the cooking chamber is empty or only very lightly loaded, the additionally injected substance has a very strong influence on the temperature behavior of the cooking chamber. The amount of injected substance is preferably known and can therefore serve as a reference. This increases the precision and / or reliability of the process. In particular, a microwave-absorbing substance is used whose influence on the thermal load is known, for example, among other things, the volume and / or the thermal properties of the microwave-absorbing substance.

[0026] In a preferred embodiment of the method, the first thermal load and / or the second thermal load are determined by evaluating a change in a cooking chamber temperature gradient over time. This is particularly useful during a heating phase of the cooking appliance, during which the cooking chamber temperature rises sharply.

[0027] Alternatively or additionally, the average heating power of the heating device can also be evaluated to determine the first thermal load and / or the second thermal load. Particularly in cooking processes where the cooking chamber temperature is to be kept at least approximately constant over time, using the average heating power to determine the thermal load has proven to be useful and reliable.

[0028] The object is also achieved according to the invention by a cooking appliance for cooking food. The cooking appliance comprises a cooking chamber, a thermal heating device, a microwave source, and a control and evaluation unit. It is designed and configured to carry out a method according to the invention.

[0029] The advantages discussed for the process naturally also apply to the cooking appliance according to the invention.

[0030] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings, to which reference is made. In the drawings: Fig. 1 a schematic representation of a cooking appliance according to the invention; Fig. 2 a schematic representation of a method according to the invention for operating the cooking appliance from Figure 1 ; and Fig. 3a diagram showing the time profiles of a thermal heating power, a microwave current, a cooking chamber temperature and a thermal load during operation of the cooking appliance Figure 1 shows schematically.

[0031] In Figure 1 a cooking appliance 10 with a cooking chamber 12 is shown.

[0032] In the illustration, a food item 14 is placed in the cooking chamber 12, which is to be cooked in the cooking appliance 10.

[0033] For this purpose, the cooking appliance 10 comprises, in addition to a thermal heating device 16, a microwave source 18, which is designed and configured to feed microwaves into the cooking chamber 12. A fan wheel 20 serves to mix the cooking chamber atmosphere and thus homogenize the cooking chamber temperature in the cooking chamber 12.

[0034] Furthermore, the cooking appliance 10 comprises a humidification nozzle 22, by means of which water can be injected into the cooking chamber 12, and a temperature sensor 24 for measuring a cooking chamber temperature.

[0035] In addition, the cooking appliance 10 also comprises a control and evaluation unit 26 which is designed and configured to evaluate data from the other components and / or to control or regulate them, in particular on the basis of the evaluated data.

[0036] The cooking appliance 10 is designed and configured to carry out a method according to the invention for detecting a microwave absorber, in particular the food 14. The steps of the method are described in Figure 2 shown schematically.

[0037] When executing the method, the thermal heating device 16 introduces thermal heating energy into the cooking chamber 12 in an optional first step S1, for example, to keep the cooking chamber temperature constant. However, it can also be provided that no thermal heating energy is (any longer) introduced into the cooking chamber 12, so that the subsequent steps are carried out during a (brief) cooling period.

[0038] In principle, the optional step S1 can also suspend or deactivate the temperature control, so that thermal heating energy or no thermal heating energy is introduced into the cooking chamber 12, regardless of the actual cooking chamber temperature. With active temperature control, the heating device would be controlled, for example, in cycles or intervals, to keep the cooking chamber temperature constant. This control or regulation can be deactivated for the following steps.

[0039] In Figure 3A diagram of the thermal heating power 28 of the heating device 16 over time is shown schematically. As can be seen, the thermal heating device 16 is operated intermittently in the exemplary embodiment. In the exemplary embodiment, thermal energy is therefore not introduced into the cooking chamber 12 continuously during cooking appliance operation, but only at specific heating intervals, for example, intermittently.

[0040] As a result of thermal heating, the cooking chamber temperature rises. If no thermal heating energy is introduced into the cooking chamber 12, the cooking chamber temperature drops. The increase or decrease in the cooking chamber temperature is detected by the temperature sensor 24. The temperature data thus generated is transmitted to the control and evaluation unit 26, which evaluates it.

[0041] The temperature curve 30 measured by the temperature sensor 24, i.e. the temperature over time, is also shown in Figure 3 shown schematically.

[0042] In the exemplary embodiment, the temperature curve 30 shows two strongly pronounced local minima 32. This is due to a door opening and the associated temperature loss in the cooking chamber 12. The time intervals 34 with the cooking chamber door open are in Figure 3 also marked.

[0043] In a second step S2 of the method, the control and evaluation unit 26 determines a first thermal load 36 based on a temperature change in the cooking chamber 12 and the heating power 28 of the thermal heating device 16.

[0044] In principle, to determine thermal loads, the heating power 28 can be compared with a temperature increase caused by heating or with a temperature drop caused by the cessation of heating, in particular a temperature gradient in general, in the cooking chamber 12. In particular, it is possible to determine thermal loads by evaluating a change in a cooking chamber temperature gradient over time and / or from an average heating power 28 of the heating device 16.

[0045] The thermal load is characteristic of the absorption capacity of thermal energy in the cooking chamber 12. In simple terms, a factor is calculated which indicates how much or which proportion of supplied thermal energy is absorbed in the food 14 and / or other parts of the cooking chamber 12 without thereby increasing the cooking chamber temperature.

[0046] Of course, the determination of the thermal load in the method according to the invention is not limited to discrete points in time. The thermal load can also be recorded or determined continuously during cooking appliance operation. Figure 3 shows an experimentally determined thermal load curve 38 as a result of such continuous recording.

[0047] As shown in the experiment, Fourier analysis can be used for noise suppression to improve the accuracy of determining the thermal load profile 38.

[0048] The first thermal load(s) 36 can be considered to be, in particular, the thermal loads of the load curve 38 that are present at minimal microwave feed and / or when the microwave source 18 is switched off. In this context, determining a plurality of first thermal loads 36 can also be considered a repetition of method step S2.

[0049] In a third step S3 of the method, the microwave source 18 feeds microwave energy into the cooking chamber 12.

[0050] Figure 3 also shows the curve of the electric current 40 over time, with which the microwave source 18 is operated during feeding. This is proportional to the fed-in microwave power. In particular, the fed-in microwave power can be calculated directly from the curve of the electric current 40. As can be seen from Figure 3 As can be seen, the current 40 and thus also the microwave power are varied. The microwave source 18 is repeatedly switched on and off. This can also be interpreted as a repetition of step S3.

[0051] In the exemplary embodiment, the introduction of microwave energy leads to an increase in the cooking chamber temperature. This temperature increase is also detected by temperature sensor 24.

[0052] In a fourth step S4 of the method, the control and evaluation unit 26 determines a second thermal load 42 based on this temperature increase.

[0053] It is conceivable that the determination of the second thermal load 42 is carried out analogously to the determination of the first thermal load 36.

[0054] If, as in the exemplary embodiment, a thermal load profile 38 is determined, then, for example, those thermal loads that are present during or immediately after the microwave feed-in can be regarded as second thermal loads 42. In particular, as in Figure 3 As shown, second thermal loads 42 appear as negative peaks 44, 46, 48 in the thermal load curve 38. The determination of several second thermal loads 42 can be regarded as a repetition of method step S4.

[0055] In a fifth step S5 of the method, the control and evaluation unit 26 determines a microwave absorption capacity (also referred to as microwave load) in the cooking chamber 12 by comparing the first thermal load(s) 36 and the second thermal load(s) 42, in particular by comparing an average value of the first thermal loads 36 and an average value of the second thermal loads 42.

[0056] For example, the microwave load can be determined by calculating the difference between the first thermal load(s) 36 and the second thermal load(s) 42. Figure 3 Figuratively speaking, a depth of the peaks 44, 46, 48 is evaluated in order to determine the microwave load at different times.

[0057] The difference between the first thermal load 36 and the second thermal load 42 correlates with the microwave power not absorbed in the cooking chamber 12 and depends on the load quantity of the cooking chamber 12. When the cooking chamber 12 is empty, the difference (except for parasitic absorption) corresponds to practically the entire radiated microwave power. However, even with a small load quantity of a microwave-absorbing food 14, a large portion of the microwave energy is absorbed. In other words, the depth of the peaks 44, 46, 48 in the thermal load curve 38 is highly dependent on the load quantity.

[0058] This is also the case in Figure 3 The first very pronounced negative peak 44 in the thermal load curve 38 was measured or determined with an empty cooking chamber 12. Subsequently, approximately 200 ml of water were introduced into the cooking chamber 12. The second negative peak 46 was measured or determined with this cooking chamber load. As can be seen from Figure 3 As can be seen, peaks 44, 46 have significantly different depths. The microwave loads are also correspondingly different. In the exemplary embodiment, the method is therefore suitable for clearly distinguishing the microwave absorption capacity of an empty cooking chamber 12 from that of a cooking chamber 12 loaded with a small amount of microwave absorber (in this case, 200 ml of water). In the exemplary embodiment, even smaller equivalent volumes of, for example, 100 ml or 50 ml of water in the cooking chamber 12 can be reliably detected using the method. However, this is not shown in the figures.

[0059] In principle, it is also possible to inject a microwave-absorbing substance, in particular water, into the cooking chamber 12 during the empty measurement or in addition to the cooking chamber loading. This can be done, for example, using the humidification nozzle 22 while the microwave energy is fed into the cooking chamber 12. The additionally introduced microwave-absorbing substance can serve, in particular, as a reference value and / or to calibrate the process.

Claims

1. A method for detecting a microwave absorber in a cooking chamber (12) of a cooking appliance (10) by determining a microwave absorption capacity in the cooking chamber (12), the method comprising the following steps: - determining a first thermal load (36) of the cooking chamber (12) based on a temperature change in the cooking chamber (12) and / or a heating power (28) of a heating device (16); - feeding microwave energy into the cooking chamber (12) by means of a microwave source (18) of the cooking appliance (10); - determining a second thermal load (42) of the cooking chamber (12) while microwave energy is being fed into the cooking chamber (12) or following the feeding of microwave energy into the cooking chamber (12); and - determining a microwave absorption capacity in the cooking chamber (12) by comparing the first thermal load (36) and the second thermal load (42). ​2. The method according to claim 1, wherein the microwave absorption capacity in the cooking chamber (12) is determined by forming a difference between the first thermal load (36) and the second thermal load (42).

3. Method according to claim 1 or 2, wherein an input microwave power is varied, in particular wherein the microwave source (18) is switched on and off, for example cyclically.

4. Method according to one of the preceding claims, wherein a noise suppression method, in particular a Fourier analysis, is used in determining the second thermal load (42).

5. Method according to one of the preceding claims, wherein, based on the microwave absorption capacity, a distinction is made between an empty cooking chamber (12) and a microwave absorber provided in the cooking chamber (12) which has an equivalent volume of a maximum of 250 ml of water, in particular an equivalent volume of a maximum of 100 ml of water, for example 50 ml of water.

6. Method according to one of the preceding claims, wherein temperature control is suspended, so that the first thermal load (36) of the cooking chamber (12) and / or the second thermal load (42) of the cooking chamber (12) are determined when the temperature control is suspended.

7. Method according to one of the preceding claims, wherein a microwave-absorbing substance, in particular water, is injected into the cooking chamber (12) when the microwave energy is fed into the cooking chamber (12).

8. Method according to one of the preceding claims, wherein the first thermal load (36) and / or the second thermal load (42) are / is determined by evaluating a change in a cooking chamber temperature gradient over time.

9. Method according to one of the preceding claims, wherein an average heating power (28) of the heating device (16) is evaluated.

10. Cooking appliance for cooking food (14), comprising a cooking chamber (12), a thermal heating device (16), a microwave source (18) and a control and evaluation unit (26), wherein the cooking appliance (10) is designed and configured to carry out a method according to one of the preceding claims.​

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