Patent ID: 12256481

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

FIG.1shows a sectional side view of an outline of a household microwave appliance1with a cooking chamber2. The cooking chamber2is enclosed by a cooking chamber wall or muffle3, which has a front loading opening that can be closed by a door4. The household microwave appliance1has at least one microwave generator5for treating items (not shown) present in the cooking chamber2, and in some instances also further heating elements such as one or more resistance heating elements (not shown).

The microwaves generated by the microwave generator5are conducted to the cooking chamber2by way of a microwave guide6and coupled there into the cooking chamber2by way of a rotary antenna7serving as a mode variation apparatus. The rotary antenna7here has an antenna wing8for example and can be rotated through 360° about a rotation axis D by means of a stepper motor (not shown). The rotary antenna7can therefore assume angular positions or rotation angles in a range φ=[0°; 360°], e.g. in steps of Δφ=1° or 5°.

The household microwave appliance1or its controllable components including the microwave generator5and the rotary antenna7can be activated or actuated by means of a central control facility9(also referred to as “appliance controller”).

An evaluation circuit10, which is connected to a sniffer line11, is integrated in the control facility9. The sniffer line11is 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 circuit10is configured to determine a strength of alternating currents induced in the sniffer line11. The evaluation circuit10and the sniffer line11form a detection device10,11for detecting microwave leakage radiation outside the cooking chamber2, in particular in an intermediate space between the cooking chamber2and an outer housing12of the household microwave appliance1and/or in the region of the door4. The sniffer line11can 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.

FIG.2shows a plan view of an outline of the control facility9with some of the components present thereon. Multiple electrical lines15are routed to a circuit board14of the control facility9, their other ends being connected to functional units of the household microwave appliance1such as electrical consumers and/or sensors and/or sniffer lines. One of the electrical lines15here corresponds to the sniffer line11.

The electrical lines15are connected to the circuit board14at connection points16, such as terminals or the like, and transition there into corresponding conductor tracks17of the circuit board14. In the exemplary embodiment shown purely by way of example only one sniffer line11is connected to an evaluation circuit10arranged on the circuit board14, which in turn is connected to a processor18, e.g. a microcontroller, ASIC or FPGA, of the control facility9. The evaluation circuit10is therefore integrated in the control facility9.

In particular the evaluation circuit10is connected here from the conductor track17connected to the sniffer line11by way of a coupling capacitor19, which brings about a direct current voltage separation between the evaluation circuit10and the sniffer line11.

As shown in the enlarged detail A, the evaluation circuit10has at least one ohmic resistor20, which is connected on the one hand to the connection connected to the processor18and on the other hand to a predetermined reference potential or ground. The coupling capacitor19and the resistor20form a high-pass filter19,20for the signal arriving from the sniffer line11.

The coupling capacitor19here advantageously has a capacitance value C of magnitude

C=12·π·R·fuwhere R is the resistance value of the resistor20and fua desired lower limit frequency of the high-pass filter19,20. The lower limit frequency fuis selected so that practically only the microwave-induced voltage components are allowed through.

The—e.g. analog—output signal of the evaluation circuit10is forwarded to the processor18for evaluation (e.g. to an analog input of a microcontroller). However the evaluation circuit10can also have other components or parts (not shown), for example an A/D converter, operational amplifier, etc.

The control facility9is designed to determine switching points, at which a marked modification of the field distribution occurs in the cooking chamber2, and corresponding operating points, based on a strength of the microwave-induced alternating current in the sniffer line11, represented by the output signal of the evaluation circuit10.

FIG.3shows an alternative evaluation circuit21to the evaluation circuit10. The alternative evaluation circuit10also has a filter function, but now with an LC filter provided.

Instead of the ohmic resistor20shown inFIG.2, a first coil22with an inductance value L1and an anode side of a diode23are now connected to the coupling capacitor19by way of a common node point. The other connection of the first coil22is connected to ground, while the cathode connection of the diode23is connected by way of a further node point to a second capacitor24with a capacitance value C2and to a second coil25with an inductance value L2. The other connection of the second capacitor24is connected to ground, while the other connection of the second coil25is connected to the processor18.

FIG.4shows a graph of a measurement value (detector voltage) LMW measured by the microwave leakage sensor10,11of the household microwave appliance1in millivolts, representing a strength of the microwave leakage radiation, against the rotation angle φ of the rotary antenna7for slightly more than a full rotation of the rotary antenna7. The measurement value LMW can be tapped for example at the output of the evaluation circuit10leading to the processor18.

Due to the cyclical nature of the antenna rotation, the measurement values LMW are repeated approximately after one rotation (Δφ=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 chamber2. 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 chamber2. 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 inFIG.8as detailed below.

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. φ=130° and φ=160°, the angle range VI and there between approx. φ=190° and φ=250° and the angle range VII and there between approx. φ=290° and φ=335°.

A possible variant for the automated determination of the operating points of the rotary antenna7at the appliance can include the following subsequent steps:curve smoothing of the curve shown inFIG.4,determining the curve gradient of the smoothed curve,forming the magnitude of the curve gradient,data reduction, and from itdetermination of the operating points of the rotary antenna7.

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

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.

FIG.5shows a first derivation of the smoothed curve shown inFIG.4as a graph of a magnitude of the change in measurement value |ΔLMW/Δφ| against the rotation angle φ of the rotary antenna7.

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.

FIG.6shows a graph of switching points U1to U7(“0” not present, “1” present) determined correspondingly from the curve fromFIG.5against the rotation angle φ of the rotary antenna7, in other words the rotation angles φ or angular positions of the switching points U1to 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, U3etc., i.e. at a rotation angle φ=(φ(U2)−φ(U1))/2; etc. In the present exemplary embodiment, these are at least approximately the rotation angles φ=10°, 50°, 75°, 110°, 145°, 225° and 315°. Possible field distributions or mode patterns are shown in more detail below inFIG.8.

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.

The control facility9can be designed to activate the rotary antenna7or 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.

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.

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

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 φ of the rotary antenna7) 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).

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.

FIG.8shows several camera images of a “light board” that match the measured curve profile of the graph fromFIG.4. The associated angle range and the rotation angle φ of the rotary antenna7are 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 chamber2. The higher the local microwave power, the brighter a light source shines.

The resulting light patterns are shown here for the rotation angles φ=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 chamber2remains 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.

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

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.

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