EP2153698B1 - Control method for a hob and hob for carrying out said method - Google Patents

Abstract

A method and cooktop include a cooktop panel, a cooking zone, and an induction heating device disposed below the cooktop panel. First, second and third heat sensor units are disposed beneath the cooktop panel in a region of a measuring spot. The first heat sensor unit is configured to measure heat flow from substantially only the cooktop panel. The second and third heat sensor units are configured to measure heat flow from the cooktop panel and a cooking utensil disposed thereon. A light source is provided for measuring an emissivity of the bottom of the cooking utensil. An auxiliary heater heats the region of the measuring spot. An electrical control system calculates a ratio from signals of the second and third heat sensor units and determines an actual temperature of the bottom of the cooking utensil from the ratio by using a temperature of a lower surface of the cooktop panel measured by the first sensor unit and a value of the emissivity of the cooking utensil bottom.

Description

The invention relates to a method for hob control, with a hob plate, in particular of glass ceramic, with at least one cooking zone, which is heated by means of an arranged in the installed position of the hob below the hob induction heating device with an electrical control unit with processing and memory and with below the cooking field plate in the region of a limited to the surroundings measuring spot arranged heat sensor units, wherein the first heat sensor unit substantially in the cooking zone alone of the hob plate and with the second and third heat sensor unit substantially in the cooking zone of the hob plate and a parked thereon Cookware downgoing outgoing heat flow is detected, as well as with a light source for performing a reflectance measurement via at least one heat sensor for determining the emissivity ε _{cookware of} the cookware tray on the stove top off cookware and a hob for performing the method.

Such a method is for example from the DE 10 2004 002 058 B3 known. The known method controls a cooking process in a hob, with a hob plate, in particular glass ceramic, which has perpendicular to their Hauptausdehnungsrichtungen limited by a flat top and bottom material thickness s, with at least one cooking zone, by means of a in the installation position of the hob below the cooktop panel arranged heating device is heated, with an electrical control for controlling the heating power of the heater and arranged below the cooktop plate heat sensor units.

In order to be able to regulate the heating power of the heating device, taking into account the influence of a cookware placed on the cooking zone, the known method proposes that with the first heat sensor unit essentially one in the region of the cooking zone alone of the hob plate and with the second and third heat sensor unit substantially a in the range of the cooking zone from the cooktop plate and a cookware set down therefrom outgoing heat flow is detected. The heat sensor units are arranged on the underside of the hob plate in the region of a limited measuring spot, which is limited to the environment, for example by a measuring shaft or waveguide. Depending on the output signals of the heat sensor units, the cookware bottom temperature T _{cookware is} determined and evaluated in the electrical control device with processing unit and memory for controlling or regulating the heating power of the heater.

According to the known method, it is not absolutely necessary for this purpose to know the emissivity of the cooking utensil ε _cookware . However, considering the emissivity of the cookware tray would result in a more accurate measurement of the cookware tray temperature T _cookware . In the DE 10 2004 002 058 B3 Therefore, it is proposed for the determination of ε _cookware, to perform a reflection measurement. This method leads to more accurate measurement results for determining the bottom of the cooking pot when the transmission coefficient of the hot plate is known and remains constant. In the intended use of the hob plate, however, the transmission coefficient of the hob plate is changed by contamination. In a soiled hob plate, the transmission is reduced, which leads to a faulty determination of ε _cookware . This also falsifies the measurement result of the cookware bottom temperature.

The invention thus presents the problem of providing a method for hob control in which the cookware temperature, taking into account the influence of the emissivity of the cookware and the transmittance of the hob plate is determined as accurately as possible and evaluated for the hob control in terms of controlling the power of the induction heating.

The invention also raises the problem of providing a hob for carrying out the method according to the invention.

According to the invention, this problem is solved by a method having the features of patent claim 1 and a hob with the features of claim 2. Advantageous embodiments and further developments of the invention will become apparent from the following subclaims.

The achievable with the present invention consist in particular in the improved accuracy of the control of a cooking process in a hob. This is achieved by an improved accuracy of the determination of the actual on the cooker bottom and thus the cookware temperature T _cookware , taking into account the influence of the emissivity of the cookware and the modified by contamination of the cooktop plate transmission coefficient.

The emissivity of the cookware for carrying out the method according to the invention is preferably detected metrologically via the second heat sensor unit by means of a reflection measurement of the light beam emanating from a light source and directed against the cookware bottom. In principle, it is also possible to use a further heat sensor unit for this purpose.
It is also possible to determine the emissivity of the cookware or cookware tray ε specify _{cooking utensils} and thereby to a usual average, for example ε _cookware = 0.5, set and deposit as a memory value in the controller.

The transmission coefficient of the hob plate is known as a value and stored in the controller as a memory value. The influence of a possibly caused by contamination of the cooktop plate change in the transmission coefficient is also taken into account by the above-described reflection measurement and determination of the emissivity of the cookware or the cooking utensils ε _cookware .

The cookware bottom temperature T _cookware is determined in the inventive method during the cooking phase from the ratio of the two output signals of the second and the third heat sensor unit and a correction value from the output of the first heat sensor unit.

Basically, the heat sensor units on the type, arrangement and measuring range can be selected within wide suitable limits. Therefore, it is possible that with the first heat sensor unit, for example, only the part of the heat flow emanating from the cooktop plate by means of heat conduction, for example by means of a touch temperature sensor, is detected. Advantageously, it is provided that the heat sensor units, in particular the second and third heat sensor unit, are designed as a pyrometer. It when the second and third heat sensor unit are combined as a unit to a single ratio pyrometer is particularly advantageous.

A high measuring accuracy is achieved in the method according to the invention in that the hob plate is heated in the region of the measuring spot by means of the additional heater and can be controlled by the temperature measured via the first heat sensor unit to T _target . In this way, it is ensured that the temperature of the hob plate in the region of the measuring spot is kept at about T _Soll . The value for T _target corresponds to an assumed value for the temperature of the cookware or the cooking zone to be reached after the heating phase. The measuring spot is preferably provided in the center of the cooking zone. A decentralized arrangement of the measuring corner, eg in the edge area of the cooking zone, is also possible.

The additional heater for direct heating of the hob plate is arranged in the region of the measuring spot in heat-conducting contact with the underside of the hob. As a result, the heat transfer from the auxiliary heater to the hob plate is improved, so that the heating phase is not extended by the heating of the hob plate in the region of the measuring spot on T _target in an undesirable manner.

In the region of the measuring spot, a waveguide, in particular a waveguide, delimits the beam path between the hob plate and the heat sensor units designed as pyrometers to the environment. In this way, on the one hand, it is ensured that the heat radiation radiated from the hob plate and the cookware passes largely loss-free to the heat sensor units. On the other hand, interference radiation from the environment is largely shielded, so that the measurement results are not affected in an undesirable manner.

Another advantageous alternative to the aforementioned embodiment provides that a reflective half shell, in particular integrating sphere, limits the beam path between the hob plate and the heat sensor units designed as a pyrometer to the environment, wherein the reflective half shell has openings for the aforementioned heat sensor units. Compared with the aforementioned embodiment, the multiple reflection of the heat radiation radiated from the cooking plate and the cookware bottom in the direction of the aforementioned heat sensor units is further increased, so that the input signals of the heat sensor units are amplified, resulting in an improved signal quality.

Figur 1

ein erstes Ausführungsbeispiel eines erfindungsgemäßen Kochfelds in einer Seitenansicht,

Figur 2

ein Diagramm, das den Transmissiongrad T_KF-PI einer Kochfeldplatte des Koch- felds aus Fig. 1 in Abhängigkeit von der Wellenlänge λ der elektromagnetischen Strahlung zeigt,

Figur 3

ein Diagramm, das die Korrelation zwischen der berechneten und der tatsäch- lichen Kochgeschirrbodentemperatur T_KG zeigt,

Figur 4

ein zweites Ausführungsbeispiel eines erfindungsgemäßen Kochfelds in ähn- licher Darstellung wie in Fig. 1.

An embodiment of the invention is shown purely schematically in the drawings and will be described in more detail below. It shows

FIG. 1

A first embodiment of a cooking hob according to the invention in a side view,

FIG. 2

a diagram that the degree of transmission T _{KF-PI of} a cooktop plate of the hob off Fig. 1 as a function of the wavelength λ of the electromagnetic radiation,

FIG. 3

a diagram showing the correlation between the calculated and the actual cookware bottom temperature T _KG ,

FIG. 4

A second embodiment of a hob according to the invention in a similar representation as in Fig. 1 ,

Fig. 1 shows an embodiment of a hob according to the invention. The cooktop has a hob plate 1 formed as a glass ceramic plate, with a perpendicular to the Hauptausdehnungsrichtungen by a flat top and bottom 1.1 and 1.2 limited material thickness s, with at least one cooking zone 2, arranged by means of a in the installed position of the hob below the hob plate 1 Induction heater 3 is heated. In the present embodiment, it is a hob with a total of four cooking zones 2, of which only a single cooking zone 2 is shown and explained in the drawing. However, the following explanations apply equally to the other, not shown cooking zones 2 of the hob. Below the hob plate 1 is a Sensor assembly 4 arranged, which comprises a first, second and third heat sensor unit 4.1, 4.2, 4.3, wherein the three heat sensor units 4.1 to 4.3 are each formed here as a pyrometer. The second and the third heat sensor unit 4.2, 4.3 together form a known per se quotient pyrometer. The sensor assembly 4 is preferably arranged in the center of the cooking zone 2 below the hob plate 1. This area is referred to as a measuring spot 5. A decentralized arrangement of the sensor module 4 or the measuring corner, for example in the edge region of the cooking zone, is likewise possible.

The first heat sensor unit 4.1 is designed to measure the heat flow going down essentially from the cooktop plate 1 in the region of the cooking zone 2, while the second and third heat sensor units 4.2, 4.3 each measure essentially the cooktop plate 1 in the region of the cooking zone 2 and are formed by a turned-off cookware 6 downgoing outgoing heat flow, which will be explained in more detail below. In this exemplary embodiment, the measuring range of the first thermal sensor unit 4.1 is limited to the measurement of thermal radiation in a first wavelength range x, here about 5 to about 6 μm. The measuring range of the second and the third heat sensor unit 4.2, 4.3 is the measurement of heat radiation in a second and a third wavelength range y and z, here about 3 microns to about 3.6 microns and about 3.7 microns to about 4.2 microns , limited. For the function of the quotient pyrometer with the heat sensor units 4.2 and 4.3, it is important that the second and the third wavelength range y and z differ from each other and at the same time are close to each other. Furthermore, the two wavelength ranges y and z should be chosen so large that the input signals of the heat sensor units 4.2 and 4.3 are sufficiently large for further processing. Therefore, both wavelength ranges y and z not only cover wavelengths for which the transmittance of the cooktop panel 1 is as large as possible, which will be explained in more detail below Fig. 2 is clearly visible.

If, in contrast to the aforementioned embodiment, a cooking field plate 1 inhomogeneous with respect to the transmittance is used, it is sufficient that the cooking field plate 1 in the region of the cooking zone 2 at least in the detection range of the first heat sensor unit 4.1 as low as possible and in the detection range of the second and third heat sensor unit 4.2, 4.3 has the highest possible degree of transmission for heat radiation.

The heat sensor units 4.1 to 4.3 of the sensor assembly 4 and the induction heater 3 are connected to an electrical control 7, the processing unit 7.1 and has a memory 7.2, in signal transmission connection. The signal transmission connection is in Fig. 1 symbolized by a dashed double arrow 8.

In order to control or regulate the heating power of the heating device 3 of the hob according to the invention as accurately as possible, it is necessary to determine the temperature of the stopped on the cooking zone 2 cookware 6, which will be explained in more detail below. However, since the thermal radiation of the cookware tray 6.1 is also dependent on its emissivity ε _cookware , it is therefore also necessary to specify the emissivity of the cooking utensil 6.1 ε _cookware and store in the memory 7.2 or measure during the cooking process and for processing in the processing unit 7.1 to provide. In principle, it is possible to use a further heat sensor unit for this purpose. Alternatively, in the present embodiment, the second heat sensor unit 4.2 is used for this purpose. The hob according to the invention also has a light source 9 for this purpose. The determination of the emissivity ε _{cooking utensil} of the parked on the cooking zone 2 cookware 6 or cookware base 6.1 is preferably carried out by means of a reflection measurement.

In order to reduce the influence of direct and indirect interfering radiation on the output signals of the heat sensor units 4.1 to 4.3 and at the same time to amplify the radiated heat to the heat sensor units 4.1 to 4.3 by means of multiple reflection, the first embodiment of the hob according to the invention has a from the inside with a heat radiation reflecting coating , For example, a gold layer, mirrored and designed as a waveguide waveguide 10. The waveguide 10 (waveguide) delimits the beam path between the hob plate 1 and the pyrometer-designed heat sensor units 4.1 to 4.3 to the environment. The radiated from the hob plate 1 and the cookware 6 heat radiation is in Fig. 1 symbolized by arrows. It is only a symbolic representation, because the actual beam path is much more complex due to the multiple reflection occurring.

In the area of the measuring spot 5, an additional heater 11, for example a resistance heater, is arranged. The additional heater 11 is arranged for the purpose of heat-conducting contact with the hob plate 1 directly to the bottom 1.2. In this way, the direct heating of the hob plate 1 in the region of the measuring spot 5 is made particularly effective by the additional heater 11. To control the additional heater 11, this is also signal-transmitting connected to the electrical control 7. The additional heater 11 can surround the area of the measuring spot 5 as a ring-shaped component (see FIG FIG. 1 ). It is also possible to arrange the additional heating within the measuring spot 5 (not shown).

In Fig. 2 a diagram is shown which shows the transmittance T _{hob plate} , abbreviated T _KF-PI , a cooking surface according to the invention as a function of the wavelength λ of the electromagnetic radiation using the example of designed as a glass ceramic hob plate 1 of the present embodiment. As already on the basis of Fig. 1 1, the measuring ranges of the heat sensor units 4.1 to 4.3 are adjusted to the degree of transmission T _cooktop plate of the cooktop panel 1 used for the _{cooktop according} to the invention such that the measuring range of the first heat sensor unit 4.1 is limited to a first wavelength range x for which the cooktop panel 1 has a transmittance of less than 20%, in particular approximately 0%. The measuring range of the second and third heat sensor unit 4.2, 4.3 is limited to a second and third wavelength range y and z, for which the _hob plate 1 as high a degree of transmission T _Hob plate has and at the same time the conditions already explained above for the use of a quotient pyrometer are met.

• In der Verarbeitungseinheit 7.1 wird auf an sich bekannte Weise aus den Ausgangssignalen der beiden Wärmesensoreinheiten 4.2, 4.3 fortlaufend oder in vorher festgelegten zeitlichen Abständen ein Verhältniswert gebildet. Um die Genauigkeit der Steuerung oder Regelung der Heizleistung bei dem erfindungsgemäßen Kochfeld zu verbessern, ist es erforderlich, den Emissionsgrad des Kochgeschirrs 6 bzw. des Kochgeschirrbodens 6.1 ε_Kochgeschirr zu berücksichtigen.

The inventive method is described below with reference to Fig. 1 to 4 explained in more detail:

• In the processing unit 7.1, a ratio value is formed in a manner known per se from the output signals of the two heat sensor units 4.2, 4.3 continuously or at predetermined time intervals. In order to improve the accuracy of the control or regulation of the heating power in the hob according to the invention, it is necessary to take into account the emissivity of the cookware 6 and the cooking utensil 6.1 ε _cookware .

• Die von den Wärmesensoreinheiten 4.2 und 4.3, also dem Quotientenpyrometer, empfangene Wärmestrahlung M setzt sich aus drei Strahlungsanteilen zusammen, nämlich aus Anteil a, der Wärmestrahlung der Kochfeldplatte 1, Anteil b, der Wärmestrahlung vom Kochgeschirrboden 6.1 und Anteil c, der Wärmestrahlung von der Kochfeldplatte 1, die an dem Kochgeschirrboden 6.1 reflektiert und durch die Kochfeldplatte 1 in Richtung der Wärmesensoreinheiten 4.2, 4.3 transmittiert wird.

Therefore, the ratio value determined from the output signals of the heat sensor units 4.2 and 4.3 is further processed in the processing unit 7.1 as follows:

• The thermal radiation M received by the heat sensor units 4.2 and 4.3, ie the quotient pyrometer, is composed of three radiation components, namely component a, the heat radiation of the cooktop panel 1, component b, the heat radiation from the cookware tray 6.1 and component c, the heat radiation from the cooktop panel 1, which is reflected on the cookware tray 6.1 and is transmitted through the hob plate 1 in the direction of the heat sensor units 4.2, 4.3.

mit V= Verhältniswert, M= spezifische Wärmestrahlung.Accordingly, the ratio value is as follows: $$V=\frac{M_{4.2}}{M_{4.3}}=\frac{M^{\mathit{Share\; a}}4.2+M^{\mathit{Share\; b}}4.2+M^{\mathit{Share\; c}}4.2}{M^{\mathit{Share\; a}}4.3+M^{\mathit{Share\; b}}4.3+M^{\mathit{Share\; c}}4.3}$$

with V = ratio value, M = specific heat radiation.

The dependencies of the individual radiation components on the temperature of the cooktop plate 1 T _{cooktop plate} , the emissivity of the cookware 6.1 ε _cookware and the emissivity ε _{cooktop panel} and the transmittance T _{cooktop panel of} the cooktop panel 1 are shown in the following equation, where F is generally for a mathematical function. $$V=\frac{F^{\mathit{Share\; a}}4.2\left({\epsilon }_{\mathit{KF}-\mathit{pl}},T_{\mathit{KF}\mathit{-}\mathit{pl}}\right)+F^{\mathit{Share\; b}}4.2\left({\epsilon }_{\mathit{KG}},T_{\mathit{KG}},{\tau }_{\mathit{KF}-\mathit{pl}}\right)+F^{\mathit{Share\; c}}4.2\left({\epsilon }_{\mathit{KF}-\mathit{pl}},T_{\mathit{KF}\mathit{-}\mathit{pl}},{\epsilon }_{\mathit{KG}},{\tau }_{\mathit{KF}-\mathit{pl}}\right)}{F^{\mathit{Share\; a}}4.3\left({\epsilon }_{\mathit{KF}-\mathit{pl}},T_{\mathit{KF}\mathit{-}\mathit{pl}}\right)+F^{\mathit{Share\; b}}4.3\left({\epsilon }_{\mathit{KG}},T_{\mathit{KG}},{\tau }_{\mathit{KF}-\mathit{pl}}\right)+F^{\mathit{Share\; c}}4.3\left({\epsilon }_{\mathit{KF}-\mathit{pl}},T_{\mathit{KF}\mathit{-}\mathit{pl}},{\epsilon }_{\mathit{KG}},{\tau }_{\mathit{KF}-\mathit{pl}}\right)}$$

In the equation, the indexes have been abbreviated for clarity, namely cookware with KG and hob plate with KF-PI. It should be noted that in the proportion c, the reflectance = 1 emissivity, since the transmittance of the cookware can be set approximately equal to 0.

mit F*= aufgrund des Herausziehens der multiplikativen Faktoren geänderte Funktion. Hierbei ist zu beachten, dass aus der von Anteil c abhängigen Funktion F^Anteil für beide Wärmesensoreinheiten 4.2 und 4.3, Index 4.2 und 4.3, aufgrund der auftretenden Mehrfachreflexionen ε_Kochgeschirr, ε_{Kochfeldplatte} und T_{Kochfeldplatte} nicht aus der Klammer herausgezogen werden können.After a transformation of the equation (2) results $$V=\frac{{\epsilon }_{\mathit{KF}-\mathit{pl}}\cdot F^{*\mathit{Share\; a}}4.2\left(T_{\mathit{KF}\mathit{-}\mathit{pl}}\right)+{\epsilon }_{\mathit{KG}}\cdot {\tau }_{\mathit{KF}-\mathit{pl}}\cdot F^{*\mathit{Share\; b}}4.2\left(T_{\mathit{KG}}\right)+F^{\mathit{Share\; c}}4.2\left({\epsilon }_{\mathit{KF}-\mathit{pl}},T_{\mathit{KF}\mathit{-}\mathit{pl}},{\epsilon }_{\mathit{KG}},{\tau }_{\mathit{KF}-\mathit{pl}}\right)}{{\epsilon }_{\mathit{KF}-\mathit{pl}}\cdot F^{*\mathit{Share\; a}}4.3\left(T_{\mathit{KF}\mathit{-}\mathit{pl}}\right)+{\epsilon }_{\mathit{KG}}\cdot {\tau }_{\mathit{KF}-\mathit{pl}}\cdot F^{*\mathit{Share\; b}}4.3\left(T_{\mathit{KG}}\right)+F^{\mathit{Share\; c}}4.2\left({\epsilon }_{\mathit{KF}-\mathit{pl}},T_{\mathit{KF}\mathit{-}\mathit{pl}},{\epsilon }_{\mathit{KG}},{\tau }_{\mathit{KF}-\mathit{pl}}\right)}$$

with F * = changed function due to the extraction of the multiplicative factors. It should be noted that it is not possible to remove from the function F ^component dependent on component c for both heat sensor units 4.2 and 4.3, index 4.2 and 4.3 due to the multiple reflections ε _cookware , ε _{cooktop plate} and T _{cooktop panel} occurring.

The emissivity ε _{cooktop panel} and the transmittance T _{Kohfeldplatte} the cooktop _panel 1 are known and are stored in the memory 7.2 for further processing of the comparison value V. The temperature of the cooktop panel 1 T _{hob plate} is measured during the cooking process continuously or at predetermined intervals by means of the heat sensor unit 4.1 and is thus also for the further processing of the comparison value V before. The same applies to the emissivity of the cooking utensil 6.1 ε _cookware , which is determined in the manner explained above. Thus, the only unknown is the temperature of the cookware bottom 6.1 T _cookware remains and thus can be calculated.

In a clean hob plate 1, so if there are no dirt on the top 1.1, resulting in the Fig. 3 as a line k illustrated relationship between the calculated and the actual cookware bottom temperature T _cookware . Both temperatures are essentially the same. With a dirty top 1.1, which can always occur in the operating case, the determined from the known and already explained reflection measurement emissivity of the cooking plate 6.1 ε _cookware by the deviations in the properties of the cooktop plate 1, namely emissivity E _{cooktop plate} and transmittance T _cooktop , falsified and thus does not correspond to the actual value. Therefore, for most applications, ie in which the top side 1.1 of the cooktop panel 1 is contaminated in the region of the cooking zone 2, there is a certain scattering of the calculated value for the cooktop base temperature T _cookware . See the lines m, which limit the range. The influence of a falsified value for the emissivity of the cooking utensil bottom 14.1 is minimized by the heating of the hob plate in the region of the measuring spot. The deviations between the calculated value and the actual value for the cookware bottom temperature T _cookware is therefore of an acceptable order, so that the heating power of the heating device 3 of a cooktop according to the invention can be controlled or regulated with high quality and reproducibility.

In a simpler embodiment, in which an automatic determination of the emissivity of the cookware bottom 6.1 ε _{cookware is} dispensed with, it is provided according to the invention to determine this analogous to the emissivity ε _{cooktop plate} and the transmittance T _{cooktop plate of} the cooktop plate 1, store and for further processing of the ratio V in the manner explained above. For this purpose, a mean emissivity of the cooking utensil 6.1 ε _cookware , for example, 0.5, is selected. In this way, the deviations in cookware with a lower or higher emissivity ε _{cookware are} not too large. See for example the lines o in Fig. 3 ,

The following alternatives and further embodiments of the above-mentioned first embodiment are only explained so far as they differ from the first embodiment.

Fig. 4 shows a second embodiment in which instead of a waveguide formed as a waveguide 10 designed as Ulbrichtkugel, reflective half-shell 12 is used becomes. For reasons of clarity, the existing heating device 3, the auxiliary heater 11 and the electrical control 7 were not shown here, and the area of the sensor assembly 4 of the hob was greatly enlarged. The reflective half-shell 12 has openings 12.1, so that the beam path between the hob plate 1 and the cookware bottom 6.1 and the heat sensor units 4.1 to 4.3 and the light source 9 is not blocked in an undesired manner. The integrating sphere 12 used has an inner surface 12.2 with a high degree of reflection. As an alternative to the integrating sphere 12, other forms of a reflective half-shell known to the person skilled in the art, for example a paraboloid cut-out, are also conceivable.

During the heating phase in the hob formed in the above-mentioned manner, the cookware 6 is heated to the desired temperature by means of the induction heating device 3. The hob plate 1 is heated in the region of the measuring spot 5 of the cooking zone 2 by the additional heater 11 to T _soll . The value for T _target corresponds to an assumed value for the temperature of the cookware which is to be reached after the heating phase. The monitoring of T _Soll takes place via the heat sensor 4.1. At the bottom of the cookware 6 is achieved by the heating by means of induction heating 3, a temperature which is approximately in the range of T _Soll . With the method according to the invention, the hob plate 1 is thus heated and maintained in the region of the measuring spot 5 at an approximately the same temperature as that for the cookware 6. This makes it possible to treat the hob plate 1 and the cookware 6 by measurement approximately as a single radiating body.

As a result, the known per se Quotientenpyrometer temperature measurement in the hob according to the invention with a high accuracy to use, as well as the determined by reflection measurement emissivity for the cookware in the calculation for the temperature of the cooking surface 6.1 is taken into account. Thus, during the heating phase following cooking phase, is kept constant in the T _desired by means of temperature control for both the pan 6 and also for the cooking hob plate 1, essentially, the temperature of the cooking utensil bottom can be mediated 6.1 T _{cooking utensil} of the above-mentioned ratio value.

mit T_Kochgeschirr= Temperatur des Kochgeschirrbodens 6.1 und f= allgemeine Abkürzung für eine Funktion. In der Gleichung wurde der Index aus Gründen der Übersichtlichkeit abgekürzt, nämlich Kochgeschirr mit KG.After conversion of equation (1), it follows: $$T_{\mathit{KG}}=f\left(\frac{M_{4.2}}{M_{4.2}}\right)$$

with T _Cookware = temperature of the cookware tray 6.1 and f = general abbreviation for a function. In the equation, the index has been abbreviated for clarity, namely cookware with KG.

After reaching T _{cooking utensils} for the cooking zone 2 and T _setpoint in the region of the measuring spot 5, the cookware base temperature T _{cookware is determined} in a _cooking phase following the heating phase, for example a boiling phase, solely as a function of the output signals of the second and third heat sensor units 4.2 and 4.3. This is possible under the condition that the temperature in the region of the measuring spot 5 is kept at T _target = constant. In this case, the current ratio value V is compared with previously defined reference values stored in the memory 7.2 for different temperatures T _setpoint for the cookware 6. If the current ratio value V is lower than the reference value stored for T _target , ie the cookware temperature too low, the cookware 6 is further heated by means of the induction heating device 3 until T _KG = T _desired . Such a case could occur, for example, when the user fills additional, cold water in the cookware 6 during a cooking process. If the current ratio value V is greater than the reference value, ie the cookware temperature is too high, the heating power of the induction heater 3 is reduced accordingly. The hob plate 1 is meanwhile held in the region of the measuring spot 5 to T _Soll . Instead of setting desired values for the temperature of the hob plate 1 / of the cookware 6 T _setpoint and reference values in a table and storing them, it would also be conceivable to deposit a mathematical formula.

The hob according to the invention and the method according to the invention for hob control can be applied and designed in a variety of ways. Thus, many hob functions are conceivable in which the cookware temperature and / or their control / regulation is required or advantageous. For example, an overcooking protection can be realized in which boiling over is effectively prevented by the aforementioned control or regulation. The same applies to the observance of an optimum frying temperature adapted to the food to be cooked. One press of a button is enough to start the cooking or roasting process. The user is informed when reaching the Ankochzeitpunktes or when reaching the desired pan temperature, for example, by acoustic and / or optical signals and therefore can turn his attention during the cooking or frying process other things in the household. Also, by knowing the cookware temperature or dependent thereon, such as the slope or the time course, a shortening of the heating and cooking time while simultaneously improved protection of the cooking selvedge against overheating can be realized. This ensures, for example, that there is no damage to the hob plate and possibly adjacent kitchen furniture and the cookware itself. This could be the case if the cookware is empty or empty, or if excess fat is heated too much in the cookware. Thus can be realize a so-called speed function, so the ability to adjust the heating power during the heating phase on the individual cookware and the load contained therein, such as a piece of meat or water to be cooked. For cookware with a poorer heat absorption and / or with a large load, the cooking zone is then automatically heated during the heating phase with a larger average heating power than cookware with a better heat absorption and / or a smaller load. Likewise, it is possible by the control / regulation of the heating power of Kochgeschirrbeheizung, ie the heater, directly in dependence of the cookware temperature to improve protection against emptying, overcooking or the like by an automatic safety shutdown upon reaching a predetermined shutdown temperature for the cookware. Due to the direct dependence on the temperature of the cookware, the required safety is ensured, without the heating power being reduced too early and thus unnecessarily for certain cookware, for example cookware with a good heat absorption. In this way, therefore, the heating phase can be shortened without the safety being affected in an undesired manner.

Furthermore, a so-called hold function can be realized, in which the current cookware temperature for the further cooking or frying process is automatically maintained at the push of a button or the like of the user. The same applies to a so-called keep-warm function, in which, based on the input of the user, the average heating power of the relevant cooking zone is automatically reduced to a predetermined value. It is also conceivable that the cookware temperature is regulated to a predetermined, lower value, for example 30 ° C. This has the advantage over the solutions already available on the market that not the temperature at the bottom of the hob plate, but the temperature of the cookware tray is used for controlling the heating power. In this way, the known hold function and warming function with respect to the reaction time of the control, for example, in a change in the load by filling with cold water or the insertion of a large piece of meat in the cookware, can be improved. Depending on the variety of applications, there are also very different set temperatures for the hob plate and cookware T _Soll .

Claims (5)

1. A method for controlling a cooktop comprising a cooktop panel (1), in particular one made of glass-ceramic, further comprising at least one cooking zone (2) which can be heated by an induction heating device (3) that is located below the cooktop panel (1) when the cooktop is in the installed position, further comprising an electrical control system (7) provided with a processing unit (7.1) and a memory (7.2), and further comprising heat sensor units (4.1, 4.2, 4.3) located beneath the cooktop panel (1) in the region of a measuring spot (5) which is delimited from the surroundings, the first heat sensor unit (4.1) measuring substantially a heat flow emanating downward only from the cooktop panel (2) in the area of the cooking zone (2), and the second and third heat sensor units (4.2, 4.3) measuring substantially a heat flow emanating downward, in the area of the cooking zone (2), from the cooktop panel (1) and a cooking utensil (6) placed thereon, and further comprising a light source (9) for performing a reflection measurement via at least one heat sensor to determine the emissivity ε_{cooking utensil} of the bottom (6.1) of a cooking utensil (6) placed on the cooktop panel (1),
   wherein

   - during a heat-up phase during which the cooking utensil (6) is heated up by the induction heating device (3), the cooktop panel (1) is heated to a predetermined desired temperature T_{cooking utensil} in the area of the cooking zone (2);

   - the value for the emissivity ε_{cooking utensil} of the cooking utensil bottom is stored in the memory (7.2);

   - the region of the measuring spot (5) is heated by an auxiliary heater (11) to T_desired, T_desired being at least approximately equal to the desired temperature value T_{cooking utensil} for the cooking utensil; and

   after reaching T_desired for the measuring spot (5) and T_{cooking utensil} for the cooking zone (2), a ratio is calculated from the output signals of the second and third heat sensor units (4.2, 4.3) by the electrical control system (7) in a cooking phase following the heat-up phase, the actual temperature T_{cooking utensil} of the cooking utensil bottom being determined from said ratio by means of the temperature T_{cooktop panel} measured by the first heat sensor unit (4.1) at the lower surface (1.2) of the cooktop panel and the value of the emissivity ε_{cooking utensil} of the cooking utensil bottom, and the heat output of the heating device (3) being controlled as a function thereof.
2. A cooktop for carrying out a method according to claim 1, comprising a cooktop panel (1) which is made, in particular, of glass-ceramic and which has a material thickness s defined by a flat upper surface (1.1) and a flat lower surface (1.2) in a direction perpendicular to the main directions of extension of the cooktop panel, further comprising at least one cooking zone (2) that can be heated by an induction heating device (3) located beneath the cooktop panel (1) when the cooktop is in the installed position, further comprising heat sensor units (4.1, 4.2, 4.3) located beneath the cooktop panel (1) in the region of a measuring spot which is delimited from the surroundings, and further comprising a light source (9) and an electrical control system (7) which is provided with a processing unit (7.1) and a memory (7.2) and in which the temperature T_{cooking utensil} of the cooking utensil bottom can be determined based on the output signals of the heat sensor units (4.1, 4.2, 4.3) and used to control the heat output of the heating device (3),
   wherein the region of the measuring spot (5) can be heated by an auxiliary heater (11), the heat output of the auxiliary heater (11) being controllable via the electrical control system (7).
3. The cooktop as recited in claim 4,
   wherein the auxiliary heater (11) is mounted in thermally conductive contact with the lower surface (1.2) of the cooktop for direct heating of the cooktop panel (1).
4. The cooktop as recited in either claim 4 or 5,
   wherein the optical path between the cooktop panel (1) and the heat sensor units (4.1, 4.2, 4.3) in the form of pyrometers and/or a light source (9) for illuminating the lower surface (1.2) of the cooktop panel (1) is delimited from the surroundings by a waveguide (10), in particular a hollow waveguide.
5. The cooktop as recited in either claim 4 or 5,
   wherein the optical path between the cooktop panel (1) and the heat sensor units (4.1, 4.2, 4.3) in the form of pyrometers and/or a light source (9) for illuminating the lower surface (1.2) of the cooktop panel (1) is delimited from the surroundings by a reflective half shell (12), in particular an Ulbricht sphere, the reflective half shell (12) having apertures (12.1) for the heat sensor units (4.1, 4.2, 4.3) and/or the light source (9).

Images