EP2094059A2 - Induction cooking hob with at least one induction heating element and at least one temperature sensor - Google Patents

Abstract

The hob has an induction heating element (10), and a temperature sensor (12) for determining temperature. A control unit (16) identifies a cooking utensil element (18) by electrical characteristics of the element. The control unit determines cooking utensil temperature of the element by a function that depends on the sensor temperature and the thermal parameter specified for the element. The control unit executes a partially automated calibration program for determining the thermal parameters and assigns the thermal parameters to electrical characteristics of the element. An independent claim is also included for a method for operating an induction cooking hob.

Description

The invention relates to an induction hob with at least one induction heating element and at least one temperature sensor according to the preamble of claim 1 and to a method for operating such an induction hob according to the preamble of claim 15.

From the EP 1 708 545 A2 For example, an induction hob with an induction heating element and a temperature sensor is known. The induction hob also includes a control unit which uses information signals transmitted to or transmitted from the cookware element via the induction heating element via the induction heating element used as an antenna to identify the cookware element. Furthermore, it is known to determine the actual temperature of the cookware element for heating so-called system cookers having known thermal properties from the sensor temperature detected by a temperature sensor arranged under a cover plate made of glass ceramic of the induction hob and using the parameters describing the thermal properties of the cookware element and as a controlled variable to use for adjusting the cookware temperature. As a result, for example, for frying the temperature of the cooking utensil or a content of the cooking utensil element can be controlled to a dependent of a set heating level setpoint.

The invention is in particular the object of enabling a safe determination of the cookware temperature even for cookware elements with unknown thermal properties without complex sensors.

The object is achieved in particular by the features of the independent patent claims, while advantageous embodiments and further developments of the invention result from the subclaims.

The invention is based in particular on an induction hob with at least one induction heating element and with at least one temperature sensor for determining a Sensor temperature, as well as with a control unit for identifying a cooking utensil element by means of at least one electrical characteristic of the cooking utensil element. The control unit uses a function depending on the sensor temperature and at least one thermal parameter specific to the cookware element to determine a cookware temperature of the cookware element.

It is proposed that the control unit is designed to execute an at least partially automated calibration program for determining the thermal parameter and for assigning the thermal parameter to the electrical parameter. By means of the calibration program, any cookware elements with thermal properties that are initially unknown for the induction hob can be calibrated so that they can be used like known system cookers and in particular also in a temperature-controlled mode. The assignment or linkage between the thermal properties on the one hand and the electrical parameters on the other hand can be used to enable rapid and simple identification by means of the electrical properties in later uses of the calibrated cooking utensil element and the thermal parameters from a storage unit of the induction hob or the control unit read.

As electrical parameters in this context, electromagnetic or magnetic characteristics are to be referred to, for example, an induction coefficient of the cooking utensil element and / or an impedance of the cooking utensil element. The control unit may be designed by suitable software or by special hardware for executing the calibration program. As thermal parameters are in particular characteristics for thermal properties of the cooking utensil element into consideration, which describe a reaction of the cooking utensil on the induction heating element in the cookware element or in the soil heat generated and / or a coupling between the cookware element and the temperature sensor.

In a further development of the invention, it is proposed that the control unit is designed to use at least two independent electrical characteristics of the cookware element for identifying the cooking utensil element. This can be a safe and in particular unambiguous identification of the cooking utensil element can be achieved, which can be further improved by the use of three or more electrical characteristics or by detecting frequency dependencies of the electrical characteristics. A detected vector of electrical characteristics can be used like a fingerprint to identify the cooking utensil.

If the control unit executes the semi-automated calibration program at least when the electrical characteristic can not be associated with a cookware element data set stored in a storage unit, unnecessary calibration of already stored cookware elements can be avoided and uncontrolled heating operation with uncalcined cookware elements can not occur.

A sufficiently precise modeling or simulation of the thermal behavior of the cooking utensil element can be achieved if the function for determining the cooking utensil element depends on at least two thermal parameters. As thermal parameters, for example, reaction times are considered which describe a delay in the heat transfer between the induction heating element and the cookware element or between the cookware element and the temperature sensor. Further, heat capacities or the like may be used as thermal parameters.

If the controller is adapted to automatically determine in the calibration program the at least one electrical characteristic of the cookware element and to generate a sequence of predetermined heat output levels until an operator signals the attainment of a cookware temperature setpoint via a user interface, the calibration program may be performed without expensive sensor technology become. A sensor for immediately detecting the cookware temperature, which is automatically read by the control unit, can be avoided by the user interaction.

In order to allow the user to determine cookware temperature in a comfortable manner, the induction hob may be equipped with a temperature sensor element for directly determining cookware temperature in the calibration program. The temperature sensor element can be used, for example, as a thermochromic Element be formed that changes its color when it reaches the setpoint of the cookware temperature. Such thermochromic stickers, which can be brought into direct contact with a surface of the cooking utensil, are available inexpensively and easily applicable.

Uncertainties due to user intervention can be avoided if the control unit is designed to run the calibration program fully automatically. To determine the thermal parameter, the control unit can determine at least one parameter of the time profile of the sensor temperature, for example an asymptotic value of the sensor temperature and / or a gradient of the sensor temperature. The gradient may provide a measure of a rate of increase in sensor temperature. As electrical parameters are an inductance of the cooking utensil, a resistance of the cooking utensil or a composite of the inductance and the resistance power factor of the cookware element into consideration.

In a further development of the invention, it is proposed that the control unit is designed to operate the induction heating element in a safety mode with a low heat output when the electrical parameter can not be assigned to a data set stored for a cookware element in a storage unit.

A further aspect of the invention relates to a method for operating an induction hob with at least one induction heating element and at least one temperature sensor for determining a sensor temperature. For this purpose, a cookware element is identified by means of at least one electrical parameter of the cookware element. A cookware temperature of the cookware element is determined in normal operation depending on at least the sensor temperature and at least one thermal parameter specific to the cookware element.

In order to make it possible to determine the cookware temperature also for cookware elements with unknown thermal parameters, it is proposed that the method for determining the thermal parameter and for assigning the thermal parameter to the electrical parameter comprise an at least partially automated calibration program.

Further advantages emerge from the following description of the drawing. In the drawings, embodiments of the invention are shown. The drawing, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations.

Showing:

Fig. 1

an induction hob with an induction coil, a temperature sensor and a cookware element,

Fig. 2

a flowchart of a in a control unit of the induction cooktop off Fig. 1 implemented operating program,

Fig. 3

a temporal course of a heating power for the thermal calibration of the cooking utensil element,

Fig. 4

a time course of a sensor temperature and a cookware temperature during a thermal calibration,

Fig. 5

a two-dimensional coordinate system with two thermal parameters and cookware temperature isolines,

Fig. 6

a two-dimensional diagram with two thermal parameters and sensor temperature isolines,

Fig. 7

an equivalent circuit diagram of the induction hob for the electrical identification of the cooking utensil element,

Fig. 8

Temperaturverläufe a cookware temperature for various cookware elements and

Fig. 9

a two-dimensional coordinate representation for identifying a cookware element dependent on two electrical characteristics of the cookware element.

Fig. 1 shows an induction hob with an induction heating element 10, which is arranged below a cover plate 32 of the induction cooktop. The cover plate 32 is formed of glass or glass ceramic. Under the cover plate 32 is in the region of the induction heating 10 shows a temperature sensor 12 for indirectly measuring a cookware temperature 20 (FIG. Fig. 4 ) arranged. The temperature sensor 12 immediately measures a sensor temperature 14 (FIG. Fig. 4 ) of the actual temperature sensor 12, which may be different from the cookware temperature 20 due to the lack of direct thermal contact between the temperature sensor 12 and a set on the cover plate 32 of the induction cooktop cooking utensil 18, especially at rapidly varying cookware temperatures 20.

The induction heating element 10 and the temperature sensor 12 are connected to a control unit 16 of the induction hob, which operates the induction heating element 10 and can read the measured data of the temperature sensor 12. The control unit 16 can store data in a storage unit 24 of the induction hob, or read data from the storage unit 24. The user can actuate the induction hob via a user interface 28 operated by the control unit 16, which is shown here only schematically and can be designed, for example, as a touch screen or as a conventional arrangement of control knobs.

When the cookware element 18 is positioned in the region of the induction heating element 10 on the cover plate 32, the cookware element 18 influences the electrical and electromagnetic properties of the overall system composed of the induction heating element 10 and the cookware element 18. In particular, an inductance of the cooking utensil element 18 influences an inductance L of the induction heating element 10 formed as an induction coil, and the power dissipated by eddy currents in the bottom of the cooking element 18 increases a loss angle of the induction heating element 10 and an apparent resistance R of the induction heating element 10, respectively.

An electrical auto-calibration function of the control unit 16 is used to determine a pair of electrical parameters, in particular for determining the inductance L and the resistance R of the cookware element 18 or of the overall system. The control unit 16 uses the thus determined pair of electrical characteristics L, R for identifying the cookware element 18, which is placed on the cover plate 32.

If the cookware element 18 could be identified as described below, the control unit 16 reads from memory unit 24 a thermal parameter Tpot, TGlass specific to the identified cookware element 18 and uses it these thermal parameters Tpot, TGlass as parameters of a function by means of which the control unit 16 determines an estimated value for the cookware temperature 20 from the sensor temperature 14. The function is a numerical model or a simulation of the dynamic behavior of the overall system comprising the cookware element 18 and the induction heating element 10, which takes into account in particular the thermal behavior of the parts involved. The numerical model depends in particular on two parameters, namely the first parameter Tpot, which describes the energy transfer between the induction coil of the induction heating element 10 and the cookware element 18 or a delay in this energy transfer, and a second parameter TGlass, which describes a heat transfer between the cookware element 18 and the temperature sensor 12 describes. If these parameters Tpot, TGlass are known, the control unit 16 can determine the cookware temperature 20 from the course of the sensor temperature and / or from a functional value of the heating power fed by the induction heating element 10.

Fig. 2 schematically shows the sequence of an executed by the control unit 16 operating program. In a first step 34 it is checked whether the automatic calibration mode is switched on. If yes, in a step 36 an electrical calibration is started, in which first in a step 38 the values of the electrical characteristics L, R are determined from an impedance of the overall system composed of the cookware element 18 and the induction heating element 10. In a step 40, the control unit 16 checks whether the value pair of the parameters L, R within a predetermined tolerance with a corresponding value pair L _i , R _{i of} a stored in the storage unit 24 cooking utensil element coincides.

If this is the case, the cookware element 18 is identified as one of the cookware elements already stored in the storage unit 24, and the control unit 16 reads out the thermal parameter Tpot _{i associated with} that cookware element from the storage unit 24. During operation of induction heating element 10 or during heating of cooking cooking element 18, control unit 16 also determines second cooking element thermal parameter Tglass 18, which is stronger than first thermal parameter Tpot from a position of cookware element 18 relative to induction heating element 10 and a second Bombing a bottom of the cooking utensil 18 is dependent.

If no match is found between the value pair L, R and one of the stored value pairs L _i , R _i (i = 1... N) in the step 40, the control unit 16 starts a calibration program 22 in a step 42 in which the thermal parameters Tpot, as described in more detail below. After a successful determination of the thermal parameter Tpot, the first thermal parameter Tpot is stored together with the electrical characteristics L, R as a new data structure assigned to the newly calibrated cookware element 18 in the memory unit 24 in a step 44.

If the operator signals via the user interface 28 that he does not want to run the calibration program 22, the control unit 16 automatically switches to a safety mode in which the induction heating element 10 is operated at a low heat output to avoid overheating. The same applies if the calibration fails.

The FIGS. 3 and 4 show the time course of a heating power of the induction heater 10, or a sensor temperature 14, a resulting from the dynamic model for the thermal behavior of the cooking utensil element 18 value of the cookware temperature 20 and an actual value 46 of the cookware temperature. The heating power is set in the calibration program 22 in a first phase 48 by the control unit 16 to a very high value and then, after about 2 minutes, reduced to a lower heating power level 50. The high heating power in the first phase 48 results in a rapid rise in the cookware temperature 20, followed by a rise in the sensor temperature 14 with some delay. After the heating power has been reduced to the lower heating power level 50, the cookware temperature 20 approaches an asymptotic limit and adjusts to the sensor temperature 14. Quantitatively, this behavior differs for different cookware elements. In particular, the gradient of the first, rapid rise of the cookware temperature 20 is mainly dependent on the first thermal parameter Tpot, while the asymptotic value of the cookware temperature and the sensor temperature, respectively, depends mainly on the second thermal parameter TGlass.

The control unit 16 simulates the course of the sensor temperature 14 for different value pairs of thermal parameters Tpot, TGlass, compares the simulation result with the actually measured curve of the sensor temperature 14 and selects that Value pair Tpot, TGlass, in which the simulation result has the smallest deviation from the actually measured time profile of the sensor temperature 14. The determination of the optimal values for the thermal parameters Tpot, TGlass can take place in any multidimensional optimization method, for example also by evaluating pairs of values, which in a two-dimensional representation, in which the values of the individual parameters correspond to the respective coordinate axes, in a rectangular matrix are arranged, for example, 6 x 6 or 8 x 8 or 4 x 6 points (see. FIGS. 5 and 6 ).

The control unit 16 calculates for each of the models represented by a pair of values of the thermal parameters Tpot, TGlass the progression of the cookware temperature 20 and the curve of the sensor temperature 14 and compares the thus calculated profile of the sensor temperature 14 with the measured value of the temperature sensor 12. The calibration program 22 determines the one Model that allows the lowest sensor temperature error and thus the best temperature estimate.

Fig. 5 FIG. 12 shows the cook line temperature isolines 20 that are substantially horizontal while the time-varying isolines of the sensor temperature 14 are tilted during the course of the calibration program 22 and during the cooking process, respectively, with respect to the x-axis. In a stationary state, the sensor temperature isolines are therefore determined solely by the value of the parameter TGlass. The fully automated thermal calibration therefore determines the correctly discretized model depending on the time course of the measurement of the sensor temperature 14. First, the control unit 16 determines in which of the columns of the model matrix in the representations in FIG FIGS. 5 and 6 the lowest sensor temperature error is reached.

Thereafter, the control unit 16 determines the correct line depending on the timing of the sensor temperature isolines. If both the correct row and the correct column of the model matrix are known, the value of the thermal parameter Tpot can be easily determined.

In the FIGS. 5 and 6 For example, models calculated by the control unit 16 are shown as circles with thin edge lines, the characteristics of the actual cookware 18 by a filled circle, and the model with the minimum sensor temperature error as a circle with thick edge line.

Fig. 7 shows an equivalent circuit diagram of the induction cooktop with the induction heating element 10 and the cookware element 18 comprehensive overall system 52, which can be represented by a series connection of a resistor R and an inductance L. The induction cooktop control unit 16 measures various values of load current, voltage and power. These electrical parameters are specific to the cookware element heated by the induction heating element 10.

Fig. 8 shows temperature curves of a cookware temperature 20 for various cookware elements. It turns out that the smaller the parameter Tpot, which describes a thermal coupling between the cookware element and the induction heating element, the faster the cookware temperature 20 increases.

Fig. 9 shows the electrical characteristics of various cookware elements, each of which can be represented by a vector in a two-dimensional vector space. Each of the points in Fig. 9 corresponds to a value pair L, PF from the inductance L and a power factor PF, which corresponds to the ratio of the resistance R and the amount of impedance Z. $$\mathit{PF}=\frac{R}{\left|Z\right|}=\frac{R}{\sqrt{R^2+{\mathit{\omega }}^2{L}^2}}$$

Fig. 9 also shows a tolerance range 54. If the values L, R determined in step 38 are within the tolerance range 54, the cookware element is associated with the stored cookware element corresponding to the value pair described by the point in the center of the tolerance range 54. The cookware element 18 to be identified is identified as this already calibrated cookware element.

In an alternative embodiment of the invention, the calibration program 22 is partially automated and requires user intervention. The induction hob is equipped with a in Fig. 1 equipped temperature sensor element 30, which is designed as a thermochromic element or as a thermochromic sticker. After the start of the calibration program 22, the operator places or glues the temperature sensor element 30 onto a surface of the cookware element 18 and actuates a corresponding switch of the user interface 28 as soon as the temperature sensor element 30 changes color. This color change occurs when the cookware temperature 20 has reached a target value. The control unit 16 reads the signal from the user interface 28 and determines the thermal parameter Tpot depending on the elapsed time to receive the user signal time or depending on the up to the receipt of the user signal in the cookware element 18 coupled heating power.

In further alternative embodiments of the invention, the temperature sensor element 30 can be read out contactlessly by the control unit 16, for example when the temperature sensor element 30 comprises an RFID chip.

The control unit 16 implements a method for operating an induction hob with an induction heating element 10 and a temperature sensor 12 for determining the sensor temperature 14. A cookware element 18 is identified by means of at least one electrical characteristic L, R of the cookware element 18, and a cookware temperature 20 of the cookware element 18 is Normal operation depending on at least the sensor temperature 14 and a specific for the cookware element 18 thermal parameters Tpot, TGlass determined. In a partially automated calibration program 22, the thermal parameter Tpot, TGlass, if this is not already known, determined and the electrical characteristics L, R associated with the cookware 18.

When an already calibrated pot or cooking element is already set up on the induction hob, the pot can be easily detected by a quick determination of the electrical parameters L, R and the thermal parameters Tpot, TGlass can be read from the storage unit 24, so that a short heating time can be achieved. The calibration scheme allows for good cooking results that are accurate to those of a system pan. An inventive hob is inexpensive to implement and largely independent of the used cookware element used. Above the cover plate 32 arranged temperature sensors can be avoided.

reference numeral

10

induction heating

12

temperature sensor

14

sensor temperature

16

control unit

18

Cookware element

20

Cookware temperature

22

calibration program

24

storage unit

26

function

28

User interface

30

Temperature sensor element

32

cover

34

step

36

step

38

step

40

step

42

step

44

step

46

value

48

phase

50

heating power level

52

overall system

54

tolerance

Claims (15)

Induction hob with at least one induction heating element (10) and at least one temperature sensor (12) for determining a sensor temperature (14), and with a control unit (16) for identifying a cookware element (18) by means of at least one electrical parameter (R, L, RF) of the Cooking utensil elements (18), wherein the control unit (16) for determining a cookware temperature (20) of the cookware element (18) is designed by means of a function (26) which is at least determined by the sensor temperature (14) and at least one of the cookware element (18). specific thermal parameter (Tpot, TGlass), characterized in that the control unit (16) for executing an at least partially automated calibration program (22) for determining the thermal parameter (Tpot, TGlass) and for assigning the thermal parameter (Tpot, TGlass) the electrical characteristic (R, L, RF) is designed. Induction hob according to claim 1, characterized in that the control unit (16) is adapted to use at least two independent electrical characteristics (R, L, RF) of the cooking utensil element (18) for identifying the cookware element (18). Induction hob according to one of the preceding claims, characterized in that the control unit (16) carries out the partially automated calibration program (22) at least when the electrical parameter (R, L, RF) does not belong to a cookware element data set stored in a memory unit (24). 18) can be assigned. Induction hob according to one of the preceding claims, characterized in that the function (26) for identifying the cookware temperature (20) of the cookware element (18) depends on at least two thermal parameters (Tpot, TGlass). Induction hob according to claim 4, characterized in that a first thermal parameter (Tpot) describes an energy transfer between the induction heating element (10) and the cookware element (18) and that a second thermal parameter (TGlass) is an energy transfer between the cookware element (18) and the Temperature sensor (12) describes. Induction hob according to one of the preceding claims, characterized in that the control unit (16) is adapted to automatically determine in the calibration program (22) the at least one electrical parameter (R, L, RF) of the cookware element (18) and a sequence of predetermined heating power levels to produce until an operator via a user interface (28) signals the achievement of a setpoint of the cookware temperature (20). Induction hob according to one of the preceding claims, characterized by a temperature sensor element (30) for directly determining the cookware temperature (20) in the calibration program (22). Induction hob according to claim 7, characterized in that the temperature sensor element (30) is designed as a thermochromic element. Induction hob according to one of claims 1-5, characterized in that the control unit (16) is designed for fully automatic execution of the calibration program (22) and for determining the thermal parameter (Tpot, TGlass) at least one characteristic (R, L, RF) of Time course of the sensor temperature (14) determined. Induction hob according to claims 4 or 5 and 9, characterized in that the control unit (16) for determining the two thermal parameters (Tpot, TGlass) at least a first characteristic for a speed of increase of the sensor temperature (14) and an asymptotic value of the sensor temperature (14) uses at a given Heizleistungsstufe. Induction hob according to one of the preceding claims, characterized in that the electrical characteristic (L) corresponds to an inductance of the cookware element (18). Induction hob according to one of the preceding claims, characterized in that the electrical characteristic (R) corresponds to a resistance of the cookware element (18). Induction hob according to one of the preceding claims, characterized in that the electrical characteristic (RF) corresponds to a power factor of the cookware element (18). Induction hob according to one of the preceding claims, characterized in that the control unit (16) is designed, when the electrical characteristic (R, L, RF) are not assigned to a stored in a storage unit (24) data set for a cookware element (18) can operate the induction heating element (10) in a safety mode with a low heat output. Method for operating an induction hob with at least one induction heating element (10) and at least one temperature sensor (12) for determining a sensor temperature (14), wherein a cookware element (18) by means of at least one electrical characteristic (R, L, RF) of the cookware element (18) and a cookware temperature (20) of the cookware element (18) is determined depending on at least the sensor temperature (14) and at least one thermal parameter (Tpot, TGlass) specific to the cookware element (18), characterized in that for determining the thermal parameter (Tpot, TGlass) and for assigning the thermal parameter (Tpot, TGlass) to the electrical characteristic (R, L, RF) an at least partially automated calibration program (22) is executed.

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