Household microwave appliance having mode variation apparatus

Abstract

A household microwave appliance includes a cooking chamber exposable to microwaves. A mode variation apparatus modifies a field distribution of the microwaves in the cooking chamber, and a microwave leakage sensor detects a microwave leakage radiation exiting from the cooking chamber. The household microwave appliance is designed to vary setting values of the mode variation apparatus, and to set an operating point of the mode variation apparatus based on a quantity of measurement data of the detected microwave leakage radiation resulting from a variation.

Claims

1. A household microwave appliance, comprising: a cooking chamber exposable to microwaves; a mode variation apparatus designed to modify a field distribution of the microwaves in the cooking chamber; and a microwave leakage sensor designed to detect a microwave leakage radiation exiting from the cooking chamber, said household microwave appliance being designed to vary setting values of the mode variation apparatus, and to set an operating point of the mode variation apparatus based on a quantity of measurement data of the detected microwave leakage radiation resulting from a variation.

2. The household microwave appliance of claim 1, wherein the household microwave appliance is designed to pass through a setting range of the mode variation apparatus, to measure a strength of the microwave leakage radiation for respective ones of the set values of the setting range passed through; and to determine from a resulting curve profile a characteristic property for setting the operating point.

3. The household microwave appliance of claim 2, wherein the characteristic property includes switching points at which a significant modification of the field distribution occurs, said household microwave appliance being designed to set the operating point of the mode variation apparatus such as to lie outside the switching points.

4. The household microwave appliance of claim 3, wherein the household microwave appliance is designed to set the operating point centrally between adjacent ones of the switching points.

5. The household microwave appliance of claim 3, wherein the switching points are determined from turning points of the curve profile.

6. The household microwave appliance of claim 1, wherein the characteristic property includes extreme and/or terrace points of the curve profile, said household microwave device designed to set the extreme and/or terrace points as operating points of the mode variation apparatus.

7. The household microwave appliance of claim 1, wherein the mode variation apparatus comprises an apparatus selected from the group consisting of rotary antenna, turntable, mode stirrer, microwave generator, and any combination thereof.

8. The household microwave appliance of claim 1, wherein the microwave leakage sensor is designed to measure the microwave leakage radiation passing through a wall of the cooking chamber.

9. The household microwave appliance of claim 1, wherein the microwave leakage sensor is designed to measure the microwave leakage radiation passing through a door gap between a housing flange and a door that closes the cooking chamber.

10. The household microwave appliance of claim 1 wherein the microwave leakage sensor comprises a sniffer line.

11. A method for operating a household microwave appliance, said method comprising: varying setting values of a mode variation apparatus designed to modify a field distribution of microwaves in a cooking chamber of the household microwave appliance; measuring a detected microwave leakage radiation exiting from the cooking chamber for the different setting values of the mode variation apparatus; and setting operating points of the mode variation apparatus based on the detected microwave leakage radiation.

12. The method of claim 11, further comprising: determining in response to the detected microwave leakage radiation switching points at which a marked modification of the field distribution of the microwaves occurs within the cooking chamber; and setting the operating points of the mode variation apparatus to lie outside the switching points.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The properties, features and advantages of this invention as described above and the manner in which they are achieved will become clearer and more readily understandable in conjunction with the following schematic description of an exemplary embodiment, which is explained in more detail in conjunction with the drawings.

(2) TABLE-US-00001 FIG. 1 shows a sectional side view of a household microwave appliance; FIG. 2 shows a plan view of a control facility of the household microwave appliance from FIG. 1 with an evaluation circuit; FIG. 3 shows an alternative evaluation circuit for the household microwave appliance from FIG. 1; FIG. 4 shows a graph of a measurement value measured by the microwave leakage sensor of the household microwave appliance from FIG. 1, which represents a strength of the microwave leakage radiation, against a rotation angle of the rotary antenna of the household microwave appliance from FIG. 1; FIG. 5 shows a graph of a magnitude of a derivation of the curve determined from FIG. 4 and then smoothed against the rotation angle of the rotary antenna; FIG. 6 shows a graph of switching points determined from the curve from FIG. 5 against the rotation angle of the rotary antenna; and FIG. 7 shows schematically a dependency of a microwave field distribution on the rotation angle of the rotary antenna for the microwave household appliance from FIG. 1. FIG. 8 shows a so-called light board as a measurement structure indicating the field distribution in the cooking chamber as a function of the rotation angle of the rotary antenna for a microwave household appliance according to FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

(3) FIG. 1 shows a sectional side view of an outline of a household microwave appliance 1 with a cooking chamber 2. The cooking chamber 2 is enclosed by a cooking chamber wall or muffle 3, which has a front loading opening that can be closed by a door 4. The household microwave appliance 1 has at least one microwave generator 5 for treating items (not shown) present in the cooking chamber 2, and in some instances also further heating elements such as one or more resistance heating elements (not shown).

(4) The microwaves generated by the microwave generator 5 are conducted to the cooking chamber 2 by way of a microwave guide 6 and coupled there into the cooking chamber 2 by way of a rotary antenna 7 serving as a mode variation apparatus. The rotary antenna 7 here has an antenna wing 8 for example and can be rotated through 360 about a rotation axis D by means of a stepper motor (not shown). The rotary antenna 7 can therefore assume angular positions or rotation angles in a range =[0; 360], e.g. in steps of =1 or 5.

(5) The household microwave appliance 1 or its controllable components including the microwave generator 5 and the rotary antenna 7 can be activated or actuated by means of a central control facility 9 (also referred to as appliance controller).

(6) An evaluation circuit 10, which is connected to a sniffer line 11, is integrated in the control facility 9. The sniffer line 11 is designed so that alternating currents can be induced in it by microwaves. It is configured for example as a simple wire or cable. The evaluation circuit 10 is configured to determine a strength of alternating currents induced in the sniffer line 11. The evaluation circuit 10 and the sniffer line 11 form a detection device 10, 11 for detecting microwave leakage radiation outside the cooking chamber 2, in particular in an intermediate space between the cooking chamber 2 and an outer housing 12 of the household microwave appliance 1 and/or in the region of the door 4. The sniffer line 11 can have a length of at least 800 mm, in particular at least 1000 mm, in particular at least 1500 mm, in particular at least 2000 mm.

(7) FIG. 2 shows a plan view of an outline of the control facility 9 with some of the components present thereon. Multiple electrical lines 15 are routed to a circuit board 14 of the control facility 9, their other ends being connected to functional units of the household microwave appliance 1 such as electrical consumers and/or sensors and/or sniffer lines. One of the electrical lines 15 here corresponds to the sniffer line 11.

(8) The electrical lines 15 are connected to the circuit board 14 at connection points 16, such as terminals or the like, and transition there into corresponding conductor tracks 17 of the circuit board 14. In the exemplary embodiment shown purely by way of example only one sniffer line 11 is connected to an evaluation circuit 10 arranged on the circuit board 14, which in turn is connected to a processor 18, e.g. a microcontroller, ASIC or FPGA, of the control facility 9. The evaluation circuit 10 is therefore integrated in the control facility 9.

(9) In particular the evaluation circuit 10 is connected here from the conductor track 17 connected to the sniffer line 11 by way of a coupling capacitor 19, which brings about a direct current voltage separation between the evaluation circuit 10 and the sniffer line 11.

(10) As shown in the enlarged detail A, the evaluation circuit 10 has at least one ohmic resistor 20, which is connected on the one hand to the connection connected to the processor 18 and on the other hand to a predetermined reference potential or ground. The coupling capacitor 19 and the resistor 20 form a high-pass filter 19, 20 for the signal arriving from the sniffer line 11.

(11) The coupling capacitor 19 here advantageously has a capacitance value C of magnitude

(12) $C=\frac{1}{2.Math..Math.R.Math.f_u}$ where R is the resistance value of the resistor 20 and f.sub.u a desired lower limit frequency of the high-pass filter 19, 20. The lower limit frequency f.sub.u is selected so that practically only the microwave-induced voltage components are allowed through.

(13) Thee.g. analogoutput signal of the evaluation circuit 10 is forwarded to the processor 18 for evaluation (e.g. to an analog input of a microcontroller). However the evaluation circuit 10 can also have other components or parts (not shown), for example an A/D converter, operational amplifier, etc.

(14) The control facility 9 is designed to determine switching points, at which a marked modification of the field distribution occurs in the cooking chamber 2, and corresponding operating points, based on a strength of the microwave-induced alternating current in the sniffer line 11, represented by the output signal of the evaluation circuit 10.

(15) FIG. 3 shows an alternative evaluation circuit 21 to the evaluation circuit 10. The alternative evaluation circuit 10 also has a filter function, but now with an LC filter provided.

(16) Instead of the ohmic resistor 20 shown in FIG. 2, a first coil 22 with an inductance value L1 and an anode side of a diode 23 are now connected to the coupling capacitor 19 by way of a common node point. The other connection of the first coil 22 is connected to ground, while the cathode connection of the diode 23 is connected by way of a further node point to a second capacitor 24 with a capacitance value C2 and to a second coil 25 with an inductance value L2. The other connection of the second capacitor 24 is connected to ground, while the other connection of the second coil 25 is connected to the processor 18.

(17) FIG. 4 shows a graph of a measurement value (detector voltage) LMW measured by the microwave leakage sensor 10, 11 of the household microwave appliance 1 in millivolts, representing a strength of the microwave leakage radiation, against the rotation angle of the rotary antenna 7 for slightly more than a full rotation of the rotary antenna 7. The measurement value LMW can be tapped for example at the output of the evaluation circuit 10 leading to the processor 18.

(18) Due to the cyclical nature of the antenna rotation, the measurement values LMW are repeated approximately after one rotation (=360). The profile of the measurement values LMW is logarithmically proportional to the measured field strength of the microwaves. Angle ranges with a practically constant voltage profile are shown as well as jump points. One surprising finding is that this voltage profile enables direct conclusions to be drawn about modifications of the field distribution of the microwaves in the cooking chamber 2. In particular it has been found by experimentation that the jump points correspond with a very high degree of reliability to a change in the mode pattern in the cooking chamber 2. The change in the mode pattern can be determined for example by experimentation using a light board as described in US 2008/0302958 A1. Angle ranges with almost constant measurement values LMW also show a constant brightness pattern of the light board, while switching of the mode pattern can be seen directly in the voltage profile. This is described in more detail in FIG. 8 as detailed below.

(19) Within the angle ranges I to VII shown, there is only a slight change in the mode pattern. This becomes particularly clear for example for the angle range V and there between approx. =130 and =160, the angle range VI and there between approx. =190 and =250 and the angle range VII and there between approx. =290 and =335.

(20) A possible variant for the automated determination of the operating points of the rotary antenna 7 at the appliance can include the following subsequent steps: curve smoothing of the curve shown in FIG. 4, determining the curve gradient of the smoothed curve, forming the magnitude of the curve gradient, data reduction, and from it determination of the operating points of the rotary antenna 7.

(21) Optional curve smoothing advantageously reduces the influence of measurement errors. The curve gradient, expressed as LMW/ or LMW/ for example, provides information on rising and falling edges of the (smoothed) measurement value profile.

(22) Since only the absolute change in the measurement value profile or the absolute curve gradient is of interest here, an additional magnitude is optionally formed.

(23) FIG. 5 shows a first derivation of the smoothed curve shown in FIG. 4 as a graph of a magnitude of the change in measurement value |LMW/| against the rotation angle of the rotary antenna 7.

(24) In the following step the data is reduced to switching points, for example by selecting the values with local maximum gradient. The change from one mode pattern to another takes place at these for example interpolated switching points.

(25) FIG. 6 shows a graph of switching points U1 to U7 (0 not present, 1 present) determined correspondingly from the curve from FIG. 5 against the rotation angle of the rotary antenna 7, in other words the rotation angles or angular positions of the switching points U1 to U7. Operating points of the cooking appliance can be determined in a manner that is easy to implement from these: the particularly advantageous operating points are each located centrally between two adjacent switching points U1, U2; U2, U3 etc., i.e. at a rotation angle =((U2)(U1))/2; etc. In the present exemplary embodiment, these are at least approximately the rotation angles =10, 50, 75, 110, 145, 225 and 315. Possible field distributions or mode patterns are shown in more detail below in FIG. 8.

(26) This sequence for determining the operating points can be performed at the start of a microwave operating sequence and can be referred to as an initial scan.

(27) The control facility 9 can be designed to activate the rotary antenna 7 or the associated stepper motor following the initial scan so that the different mode patterns associated with the different operating points are held for the same time periods and the item being cooked is therefore exposed for time segments of equal length (and no longer in proportion to the angle portion that the mode patterns assume during one rotation). This significantly reduces the risk of any disadvantageous formation of hotspots at the same points in the item being cooked for longer periods of time without change.

(28) For advanced cooking controls it is also advantageous that it can be established practically without a time delay when a change to the setting parameters leads to a change in the resulting mode pattern and therefore in the same way to a change in the heat distribution in the item being cooked.

(29) Of course, other evaluation methods can also be used to determine the operating points. For example zeros of the derivation of the curve profile from FIG. 4 can also be selected. This allows extreme points as well as turning and terrace points to be detected.

(30) In addition the method is generally not limited to household appliances, the mode variation apparatus of which has only a single setting parameter or degree of freedom (such as the rotation angle of the rotary antenna 7) but can also be used with multiple degrees of freedom (e.g. the rotation angles of at least two rotatable antennas or other field-modifying elements such as a mode stirrer).

(31) Generally not only the leakage rate within the housing has to be examined but any microwave leakage radiation exiting from the cooking chamber can be used to determine the operating points. This also includes microwave radiation that exits in the region of the closed door (i.e., classic leakage radiation in the front region). Measurement of the microwave leakage radiation is therefore not limited to the interior of the housing.

(32) FIG. 8 shows several camera images of a light board that match the measured curve profile of the graph from FIG. 4. The associated angle range and the rotation angle of the rotary antenna 7 are shown for each image. The light sources, which can be excited to light up by microwaves and which can be fastened to a Styrofoam plate for example in the manner of a matrix, serve here as indicators for the field distribution present in the cooking chamber 2. The higher the local microwave power, the brighter a light source shines.

(33) The resulting light patterns are shown here for the rotation angles =0, 50, 75, 106, 130, 160, 190, 240, 290 and 335. Each of the associated angle ranges I-VII has an individual light pattern. In contrast the field distribution of the microwaves in the cooking chamber 2 remains practically unchanged within one of the angle ranges I-VII. This is shown by way of example for the angular degrees 130 and 160 in the angle range V, for the angular degrees 190 and 240 in the angle range VI and for the angular degrees 290 and 335 in the angle range VII.

(34) The present invention is of course not limited to the exemplary embodiment shown.

(35) Generally one can be understood to mean a singular or a plurality, in particular in the sense of at least one or one or more etc., unless this is specifically excluded, for example by the expression just one etc.

(36) Number data can also cover just the specified number as well as a standard tolerance range, unless this is specifically excluded.