Control Apparatus for Heating, Defrosting and/or Cooking Foods With Microwave Energy

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

The single FIGURE of the drawing is a diagrammatic and schematic circuit diagram of the principal elements of a microwave oven.

Referring now in detail to the single FIGURE of the drawing, it is seen that microwave energy is supplied through a rotating antenna MA to a cooking chamber GR of the microwave oven, into which food GG which is to be heat-treated has been introduced. The rotating antenna MA receives the microwave energy from a waveguide HL which in turn receives the microwave energy from a microwave generator MG, a magnetron. An output control unit LS which is provided for the control of the magnetron, conventionally contains a high-voltage transformer as well as rectifier and condenser units. These units, as well as switching elements required for a safe microwave operation, need not be considered in detail herein.

Through the use of an indicator/operating panel AE, set values regarding the output and length of time that the microwaves are to be beamed into the cooking chamber GR are entered into a logic control circuit AL which converts these input values for the control of the output control unit. The set values can be displayed on the indicator/operating panel AE.

A microwave directional coupler RK is connected to the waveguide HL. A first output line A1 of the microwave directional coupler RK detects measurement values which correspond to the microwave energy moving through the waveguide HL from the microwave generator MG in the direction towards the cooking chamber GR, and a second output line A2 detects measurement values regarding oppositely moving microwave energy. The relationship between these microwave movements and thus the relationship between the measurement values detected by the output lines A1 and A2 of the directional coupler RK, gives a good indication of which respective microwave energy potential is present in the cooking chamber. This is due to the fact that not only is the microwave generator capable of introducing microwave energy into the wave guide HL, but the cooking chamber returns microwave energy to the wave guide HL in accordance with the microwave energy potential prevailing in the cooking chamber, which can be detected at the output line A2 by the microwave directional coupler RK. Since the microwave potential occurring in the cooking chamber when microwaves are beamed in depends on the ability of the food GG present in the cooking chamber GR to absorb microwaves, the food can be measured by means of this chain of relationships. The ability of the food to absorb microwaves and to transform them into heat depends on the type, mass (weight) and state of the food. If, for example, no food is present in the cooking chamber GR, no significant energy is absorbed in the cooking chamber GR and the returning microwave energy detected by the microwave directional coupler RK will increase to a very large degree in relation to the microwave energy supplied. However, during the implementation of cooking processes, the change in the state of the food, e.g. from the frozen to the defrosted state, becomes important for control measurements.

The output lines A1 and A2 of the directional coupler RK are sent to a comparison circuit VS, which performs a comparison between the measured and supplied measured values and as a result sends a criterion to the logic control circuit AL. The output control unit LS of the microwave generator MG is controlled in dependence on this criterion and is readjusted in regard to the energy demand inside the cooking chamber GR and the values supplied. The values for the particular cooking processes can be supplied to the logic control circuit AL through the indicator/operating panel AE or permanently set values can be stored in the logic control circuit AL for performing standard cooking processes. The continuation of the individual process steps can be controlled and modifications of these steps may be made by superimposition of the values detected by the microwave directional coupler RK, which represent the actual cooked state of the food.

In place of the directional coupler RK in the vicinity of the wave guide HL, a corresponding sensor for detecting the microwave potential may be disposed in the cooking chamber itself between a given location for the food GG and the microwave generator MG. However, it must be taken into consideration that different intensities of microwave energy build up in the cooking chamber GR. In the present exemplary embodiment these microwave intensities are additionally spatially changed through the rotating antenna MA for an even heat-treatment of the food. These circumstances must be considered from a circuit point of view, during detection by measurement of the microwave energy potential in the cooking chamber GR as well as by means of a corresponding disposition of the sensor and by evening out the results of measurement over time.

In the illustrated exemplary embodiment, the microwave energy supplied by the microwave generator is used for heat-treatment of the food GG as well as for measuring purposes. This combination is suggested, but by no means is a prerequisite for the detection performed through measurement. On the contrary, it is also possible to supply microwave energy to the cooking chamber for measurement purposes only. This microwave energy may be relatively weak and may be beamed out only in the time slots required for measuring purposes. There is a further possibility of the microwave frequency for measuring purposes varying from the microwave frequency for performing the cooking process. This has advantages for measurement purposes due to the fact that the different wave lengths of the microwaves have different penetration depths into the food. In this connection it is also possible to use solid state microwave energy generators because the required outputs may be relatively small, as already stated.

However, it is also possible to use microwave techniques only for the purpose of measuring the state of the food and to perform the heat-treatment in connection with or exclusively by means of thermal heating elements.