Operation of a domestic microwave appliance as a function of a microwave generator temperature

Abstract

In a method for operating a household microwave appliance, a microwave treatment operation is controlled as a function of a temperature of a microwave generator. The household microwave appliance includes a cooking chamber, a microwave generator for routing microwaves to the cooking chamber, a temperature-determining apparatus for determining a temperature of the microwave generator, a microwave distribution device designed to change a field distribution in the cooking chamber during a microwave treatment operation, and a control device designed to control the microwave treatment operation as a function of the temperature of the microwave generator effected by a change in the field distribution.

Claims

1. A method for operating a household microwave appliance, comprising: controlling a microwave treatment operation as a function of a temperature of a microwave generator; changing a field distribution in a cooking chamber of the household microwave appliance during the microwave treatment operation, wherein the microwave treatment operation is controlled as a function of a change in temperature of the microwave generator effected by the change in the field distribution; and determining from the change in temperature an extent of a change in a portion of a microwave power radiated into the cooking chamber which portion is reflected from the cooking chamber back to the microwave generator.

2. The method of claim 1, wherein the field distribution is changed by changing a setting value of an operating parameter of a microwave distribution device changing the field distribution.

3. The method of claim 2, wherein the operating parameter is selected from the group consisting of angle of rotation of a rotary antenna, height position of a rotary antenna, angle of rotation of a mode stirrer, height position of a mode stirrer, angle of rotation of a rotary plate, microwave frequency, phase offset between different feed points, activation or deactivation of a feed of microwaves by way of a number of feed points, and change in a power distribution between a number of feed points.

4. The method of claim 2, wherein the operating parameter is an angle of rotation of a rotary antenna.

5. The method of claim 1, further comprising: recording a temperature curve during the microwave treatment operation; determining curve gradients before and after a switchover time, at which the field distribution has been changed in the cooking chamber; and determining from the change in the curve gradients whether the back-reflected portion of the microwave power is higher for the field distribution before the switchover time or for the field distribution after the switchover time.

6. The method of claim 5, wherein one of the curve gradients is determined before the switchover time until immediately before the switchover time and/or another one of the curve gradients is determined from the switchover time, plus a predetermined delay time.

7. The method of claim 2, further comprising: setting during the microwave treatment operation the operating parameter of the microwave distribution device on the basis of a strength of the back-reflected portion of the microwave power.

8. The method of claim 7, further comprising setting a setting value so that a relatively low back-reflected portion of the microwave power is produced.

9. The method of claim 7, further comprising setting a setting value so that a relatively high back-reflected portion of the microwave power is produced.

10. A household microwave appliance, comprising: a cooking chamber; a microwave generator for routing microwaves to the cooking chamber; a temperature-determining apparatus for determining a temperature of the microwave generator; a microwave distribution device designed to change a field distribution in the cooking chamber during a microwave treatment operation; and a control device designed to control the microwave treatment operation as a function of the temperature of the microwave generator effected by a change in the field distribution, wherein the microwave distribution device is designed to change the field distribution by changing a setting value of an operating parameter of the microwave distribution device, and the control device is designed to determine from the change in temperature an extent of a change in a portion of a microwave power radiated into the cooking chamber which portion is reflected from the cooking chamber back to the microwave generator.

11. The household microwave appliance of claim 10, wherein the operating parameter is selected from the group consisting of angle of rotation of a rotary antenna, height position of a rotary antenna, angle of rotation of a mode stirrer, height position of a mode stirrer, angle of rotation of a rotary plate, microwave frequency, phase offset between different feed points, activation or deactivation of a feed of microwaves by way of a number of feed points, and change in a power distribution between a number of feed points.

12. The household microwave appliance of claim 10, wherein the control device is designed to set during the microwave treatment operation the operating parameter of the microwave distribution device on the basis of a strength of the back-reflected portion of the microwave power.

13. The household microwave appliance of claim 10, wherein the control device is designed to set a setting value so that a relatively low back-reflected portion of the microwave power is produced.

14. The household microwave appliance of claim 10, wherein the control device is designed to set a set value so that a relatively high back-reflected portion of the microwave power is produced.

15. The household microwave appliance of claim 10, wherein the operating parameter is an angle of rotation of a rotary antenna.

16. A household microwave appliance, comprising: a cooking chamber; a microwave generator for routing microwaves to the cooking chamber: a temperature-determining apparatus for determining a temperature of the microwave generator; a microwave distribution device designed to change a field distribution in the cooking chamber during a microwave treatment operation; and a control device designed to control the microwave treatment operation as a function of the temperature of the microwave generator effected by a change in the field distribution, wherein the control device is designed to record a temperature curve during the microwave treatment operation, to determine curve gradients before and after a switchover time, at which the field distribution has been changed in the cooking chamber, and to determine from the change in the curve gradients whether the back-reflected portion of the microwave power is higher for the field distribution before the switchover time or for the field distribution after the switchover time.

17. The household microwave appliance of claim 8, wherein the control device is designed to determine one of the curve gradients before the switchover time until immediately before the switchover time and/or to determine another one of the curve gradients is determined from the switchover time, plus a predetermined delay time.

18. The household microwave appliance of claim 16, wherein the microwave distribution device is designed to change the field distribution by changing a setting value of an operating parameter of the microwave distribution device, and the operating parameter is an angle of rotation of a rotary antenna.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows a sectional representation in a side view of a drawing of a household microwave appliance;

(3) FIG. 2 shows courses of a temperature of a microwave generator of the household microwave appliance for different setting values of a microwave distribution device;

(4) FIG. 3 shows courses of the temperature of the microwave generator until an equilibrium temperature is reached for different setting values of the microwave distribution device;

(5) FIG. 4 shows a course of the temperature of the microwave generator when the setting value of the microwave distribution device is changed after the equilibrium temperature is reached; and

(6) FIG. 5 shows a course of the temperature of the microwave generator when the setting value of the microwave distribution device is changed repeatedly before a respective equilibrium temperature is reached.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

(7) FIG. 1 shows a household microwave appliance 1, having a cooking chamber 2, which has a loading opening 4 which can be closed by means of a door 3. The food G can be introduced into the cooking chamber 2 through the loading opening 4. The household microwave appliance 1 further has a microwave generator in the form e.g. of a magnetron 5. Microwaves radiated by the magnetron 5 are routed to the cooking chamber 2 through a microwave guide 6 embodied as a hollow conductor and injected there into the cooking chamber 2 by means of a rotary antenna 7. The rotary antenna 7 has an antenna blade 8 within the cooking chamber 2 and can be rotated about an axis of rotation D (e.g. driven by a stepper motor, not shown). The antenna blade 8 is provided to change a field distribution of the microwaves in the cooking chamber 2 when the rotary antenna 7 is rotating. The rotary antenna 7 is therefore also used as a microwave distribution device. A temperature sensor 9 is attached to the magnetron 5, in order to measure the temperature Tm of the magnetron 5 (magnetron temperature). Furthermore, the household microwave device 1 has a control device 10, which is designed inter alia to activate the magnetron 5 (e.g. to set its output power), to read out measured values of the temperature sensor 9 and to set an angular position or angle of rotation of the rotary antenna 7 about the axis of rotation D.

(8) The control device 10 is further designed (e.g. programmed) to control a microwave treatment operation with food to be cooked G located in the cooking chamber 2 and normally functioning components as a function of the magnetron temperature Tm.

(9) FIG. 2 shows two curve progressions as a plotting of the magnetron temperature Tm in C. against a time tin seconds, namely for different angles of rotation 1 and 2 of the rotary antenna 7 with the same microwave power fed into the cooking chamber 2 and an otherwise identical experimental setup. With the experimental setup, a temperature change of a liter of water as the microwave-absorbing load was determined according to a standard method for measuring the actual output power of a microwave appliance. The time range between t=20 s and t=80 s limited by the dashed vertical lines corresponds to the on time or the activation time period of the magnetron 5 of 60 s.

(10) The microwave power introduced into the water load is also determined at the same time as the temperature curve. The setting of the angle of rotation 1 as a setting value of the operating parameter results here, after a minute of treatment or cooking time, in a significantly lower magnetron temperature Tm and a greater increase in temperature of the water load (top fig.) than when the angle of rotation 2 is set. With the angle of rotation 1, less power is then reflected back to the magnetron 5, so that a larger portion of fed microwave power is made available for heating the water load.

(11) In the example shown here, a temperature rise in the water load of 11.9 C. was determined for the angle of rotation 1, which corresponds to a power input of approx. 870 W. With the angle of rotation 2, conversely, the temperature rise amounted to just 9.8 C., this corresponds to a power input of approx. 710 W (calculation according to IEC 90705). With the angle of rotation 2, the microwave power reflected back to the magnetron 5 is therefore approx. 160 W higher than at the angle of rotation 1. This brings about a higher magnetron temperature Tm at the angle of rotation 2. Therefore, the magnetron temperature Tm toward the end of the on time of the magnetron 5 at the angle of rotation 1 therefore amounts to approx. 76 C., whereas at the angle of rotation 2 it amounts to approx. 86 C. Edge effects such as a different heating of elements in the cooking chamber (wall (muffle), glass panels of the door etc.) are present, but not significant.

(12) FIG. 3 shows curve progressions of the magnetron temperature Tm until an equilibrium temperature is reached for different angles of rotation 1, 2 and mult of the rotary antenna 7 with a permanently connected magnetron 5. Here mult refers to the setting of several values of the angle of rotation during the measuring time, in particular a permanent rotation of the rotary antenna 7.

(13) With longer heating processes, the cooling of the magnetron 5 causes it to assume a thermal equilibrium, from which the magnetron temperature corresponds constantly to the respective equilibrium temperature. The equilibrium temperature is dependent upon the selected angle of rotation (generally: on the selected set of setting values). A large reflection portion of the microwaves results in a higher equilibrium temperature with a constant cooling power. If, according to the scenario referred to with mult, the angle of rotation varies continuously during the treatment procedure, e.g. by means of antenna rotation, an equilibrium temperature averaged across all angles of rotation used develops as a result of the thermal inertia of the magnetron 5.

(14) FIG. 4 shows a course of the magnetron temperature Tm when the angle of rotation of the rotary antenna 7 is changed after the equilibrium temperature is reached.

(15) If the angle of rotation is changed in the equilibrium state (here after t=215 s from the angle of rotation 1 to the angle of rotation 2), a gradient of the temperature curve which deviates from zero is produced on account of the new reflection portions. A positive gradient indicates that with the new rotary angle more power is reflected back to the magnetron 5, with a negative gradient less power is reflected than with the previous angle of rotation. In the diagram shown, a positive gradient is shown in the temperature profile. With the angle of rotation 2, more power is consequently reflected back than with the angle of rotation 1. The change in temperature on the magnetron 5 can be observed already after approx. one second after the angle of rotation is changed, in other words very quickly.

(16) A statement about the portion of reflected microwave power can generally be made either on the basis of a comparison of the respective equilibrium states and/or by considering the sum and possibly the sign of the gradient when the equilibrium state is left. In practice, the consideration of the gradient is particularly advantageous, since this can be observed far more quickly.

(17) FIG. 5 shows a course of the magnetron temperature with a repeated change of the angle of rotation of the rotary antenna 7 before a respective equilibrium temperature is reached.

(18) If the magnetron 5 is still not in its thermal equilibrium state for a currently set angle of rotation , with a change in the angle of rotation , no statement can be made on the basis of the sign of the gradient of the curve progression. For instance, in a temperature range below the lowest equilibrium temperature, each change in the angle of rotation results in an increase in the magnetron temperature Tm and thus in a positive gradient. However, in the majority of cases a change in the angle of rotation results in a sudden change in the gradient, which is expressed in a kink in the curve or in the temperature profile.

(19) In order to be able to make statements about the portion of the reflected power of the current field distribution, a gradient m1 of the curve before the change in the angle of rotation can be compared with a gradient m2 shortly after the change in the angle of rotation . If the gradient m2 is greater than the gradient m1 of the previous angle of rotation , the portion of reflected power is also greater.

(20) FIG. 5 shows in particular the course of the magnetron temperature Tm with a repeated change in the antenna position. The switchover times tp are identified with tp-1 to tp-4. A kink in the curve can be identified in each case at least for tp-2 to tp-4.

(21) In order to evaluate the temperature curve, a difference m in the gradients m1 and m2 can be determined before and after the respective switchover times tp-1 to tp-4, for instance. Since the switchovers of the angle of rotation take place in short succession by comparison with reaching an equilibrium temperature, the curve sections outside of the switchover times tp-1 to tp-4 can be considered to be approximately linear.

(22) The gradient difference m can be calculated, for instance, as
m=m2(]tp+td;tp+td+td])m1([tpt1;tp[),

(23) i.e. from a difference in the gradient m2, which has been determined from a curve section after the switchover time tp and the duration tp, wherein this curve section begins delayed by the delay time tp after tp, and a gradient m1, which has been determined from a curve section of the duration ti, which ends immediately before the switchover time tp. By means of the delay time tp, the thermal inertia of the system is taken into account. It normally amounts to just one to two seconds.

(24) m<0 applies if less power is reflected back at the new angle of rotation . m=0 applies if the same amount of power is reflected back at the new angle of rotation , and m>0 applies if more power is reflected back at the new angle of rotation .

(25) The present invention is naturally not restricted to the exemplary embodiment shown.

(26) In general, a, an etc. may be understood as meaning a singular or plural in particular in the sense of at least one or one or more etc., unless this is explicitly excluded for example by the expression exactly one etc.

(27) Unless explicitly excluded, a number can also comprise exactly the specified number as well as a usual tolerance range.