EP0361586A2

EP0361586A2 - Device for automatically controlling food preparation in a microwave oven

Info

Publication number: EP0361586A2
Application number: EP89202345A
Authority: EP
Inventors: Franciscus Kokkeler; Enzo Cigarini; Mario Fioroli; Carlo Montanari
Original assignee: IRE Industrie Riunite Eurodomestici SpA; Whirlpool Europe BV; Whirlpool International BV
Current assignee: IRE Industrie Riunite Eurodomestici SpA; Whirlpool Europe BV
Priority date: 1988-09-23
Filing date: 1989-09-18
Publication date: 1990-04-04
Also published as: AU4167889A; IT8821915V0; AU627497B2; JPH02223732A; IT215282Z2; EP0361586A3

Abstract

A device for automatically controlling the preparation of a food (9) in a microwave oven, comprising at least one temperature sensor means (12) connected to a microprocessor (16) arranged to act on the microwave generator (2) so as to halt it or at least vary its power during operation, the device being characterised in that the sensor means (12) is disposed in heat conducting relationship with a metal element (10) which is constructed of a good temperature-conducting but microwave-impermeable material and is housed in a support (8) for, and in contact with, the food (9).

Description

This utility model relates to a device for automatically controlling food preparation in a microwave oven.
There are various known devices for enabling the degree of preparation (thawing, heating, cooking) of a food in a microwave oven to be automatically controlled.
One of these devices uses weight sensors which measure the weight variation of the food during said preparation. These sensors feed the obtained data to a control member or microprocessor which on the basis of a preset programme and the data obtained by the sensors halts the microwave generator operation so interrupting the preparation of the food when it has reached a predetermined weight.
An an alternative to the aforesaid there are microwave ovens provided with infrared sensors which measure the surface temperature of the food. These sensors, connected to a microprocessor, cause the control member to act on the microwave generator and halt its operation when the food surface temperature has reached a predetermined value.
It is also known to use probe-type temperature sensors which are inserted into the food to enable for example its thawing to be evaluated, even of its most inner parts.
The devices currently used for controlling food preparation have various drawbacks, such as difficult and laborious installation in the oven and high manufacturing costs. Furthermore the data determined by said sensors do not always reflect the true level of preparation attained by the food.
Finally, in the case of a temperature sensor inserted into the food itself, there are obvious difficulties connected with this insertion, such as having to make a hole in the food (if this is solid) and the need to clean said sensor after every use.
An object of the present utility model is to provide a device for automatically controlling food preparation which is of low manufacturing cost, is simple to position in the oven and enables the true state of preparation of the food to be determined with good accuracy.
These and further objects which will be more apparent to the expert of the art are attained by a device for automatically controlling food preparation in a microwave oven, comprising at least one temperature sensor means connected to a microprocessor arranged to act on the microwave generator so as to halt it or at least vary its power during operation, the device being characterised in that the sensor means is dipsoed in heat conducting relationship with a metal element which is constructed of a good temperature-conducting but microwave-impermeable material and is housed in a support for, and in contact with, the food.
The present utility model will be more apparent from the accompanying drawing which is provided for the purpose of non-limiting example only and in which:

Figure 1 is a diagrammatic cross-section through a microwave oven provided with a device constructed in accordance with the utility model;
Figure 2 is a detailed view to a larger scale than Figure 1, showing a different embodiment of the device according to the utility model;
Figure 3 is a sectional view showing a further application of the device according to the utility model;
Figure 4 is a section through a further embodiment of the device according to the utility model.

In said figures, the device of the present utility model is inserted in a microwave oven 1 provided with a microwave generator or magnetron 2 disposed in the roof 3 of a cooking chamber 4 having side walls 5 and 6 and a lower wall or base 7. On this base there is positioned a support 8 for a food 9, the support being shown as a plate in Figures 1, 2 and 4 and as a pan structure in Figure 3.
The device of the present utility model comprises an element or plug 10 of good temperature-conducting but microwave-impermeable material (such as aluminium or copper) disposed in a cavity 11 in the food support 8, and a temperature sensor 12 positioned in heat-conducting relationship with the element 10.
Said element or plug 10 is positoned in the cavity 11 so that it is in contact with the food 9. Such an arrangement enables the temperature of the element 10 to rise by conduction as the food temperature increases.
The plug 10 is retained in the cavity 11 by known means such as to ensure said contact with the food 9.
As stated, the temperature sensor 12 is in heat-conducting relationship with the metal plug 10. Specifically (see Figure 1), the sensor is carried by a rod-shaped member 13 inserted through a radial cavity 14 in the food support 8 which opens at one end in the cavity 11 and at its other end in the side of the support. The rod-shaped member 13 encloses the end of electrical conductors 15 which connect the sensor 12 to a microprocessor 16 positioned in a suitable region of the oven 1. Said microprocessor is connected to the magnetron 2.
It will now be assumed that the food 9 is to be cooked, for which purpose the magnetron 2 is put into operation in known manner. The microwaves 100 from the magnetron 2 strike the food 9 and begin to heat it. When the bottom of said food finally undergoes temperature increase, the metal plug 10 begins to heat up by thermal conduction. Its increase in temperature is sensed by the sensor 12 which feeds the obtained data to the microprocessor 16. When the food temperature has reached the desired value the microprocessor, based on the data obtained by the sensor 12, acts on the magnetron 2 to halt its operation.
If the food after cooking then remains in the oven for a time such that it cools down, i.e. if the food temperature falls below a limiting value preset on the microprocessor 16, this latter on the basis of new data obtained by the sensor 12 again operates the magnetron 2 to raise this temperature above said limiting value. Continuous control of the food temperature is therefore obtained. In contrast, if the food is to be thawed or heated to a determined temperature, the suitably programmed microprocessor acts on the magnetron 2 to halt it when the sensor 12 senses that the temperature of the metal plug 10 is equal to the required thawed or heated temperature. This is because, as stated, the heating of said plug 10 is due to the heat which passes by conduction from the food 9 to said plug, and thus the temperature measured by the sensor 12 is representative of the temperature attained by said food.
Figure 2 shows a different embodiment of the device according to the utility model. In this figure, parts identical to those described in relation to Figure 1 are indicated by the same reference numerals.
In the figure under examination, the metal plug 10 occupies the entire volume of the cavity 11 in the food support 8. The plug is placed in position below the food and retained in said cavity by known means. The temperature sensor 12 is disposed in the base 7 of the cooking chamber 4 of the oven 1 and is in contact with the plug 10. This contact can be either direct or indirect, as shown in Figure 2.
In this figure the sensor 12 is secured to the underside of a small-thickness metal plate 20, also constructed of a good temperature-conducting metal (such as aluminium or copper). The metal plate 20 is constantly in contact with the plug 10 by virtue of a spring 21 disposed in a cavity 22 provided in the base 7. In this manner the heat transmitted by conduction from the metal plug 10 to the metal plate 20 is sensed by the sensor 12 and the temperature signal is fed to the microprocessor (not shown in Figure 2) through the electrical conductor 15.
Limit stops (not shown) are provided to prevent the plate 20 escaping from the cavity 22 as a result of the thrust exerted by the spring 21 when the food support 8 is removed.
The use of the device shown in Figure 2 is analogous to that of the device of Figure 1 and is therefore not further described. It should be noted that the device of Figure 2 allows the food support 8 to be easily extracted from the oven 1, for example when it is required to clean the support. In this respect, with the embodiment of the device shown in Figure 2 the user in extracting said support 8 does not have to take into account the presence of the sensor 12 during this operation, as instead he must with the device formed as shown in Figure 1. With the embodiment shown in this latter figure the user must extract the rod-shaped member 13 carrying the sensor 12 from the cavity 14 before he extracts the food support 8 from the oven 1, and this can cause problems particularly because of the small space in which the user has to work.
A further embodiment of the device according to the present utility model is shown in Figure 3. In this figure parts identical to those described in relation to Figures 1 and 2 carry the same reference numerals.
In the figure under examination, the device according to the utility model is formed as shown in Figure 1 and described heretofore. However the device is here associated with a pan-shaped structure particularly suitable for boiling or heating liquids.
As the device shown in Figure 3 is identical to that shown in Figure 1 it will not be further described.
A further embodiment of the device according to the present utility model is shown in Figure 4. In this figure parts identical to those described in relation to Figures 1, 2 and 3 carry the same reference numerals.
In said Figure 4, the metal plug 10 is associated with the food support 8 and is retained in the cavity 11 of said support by known means.
However, in the base 7 of the cooking chamber 4 of the oven 1 there is positioned an element 80 of microwave-sensitive material (ferrite) inserted into a cup-shaped element 81 constructed of a good temperature-conducting but microwave-impermeable material (sich as aluminium or copper) and in contact with the plug 10. Advantageously, the element 80 is of annular shape, and in its cavity 82 there is disposed a plug 83 of good temperature-conducting material also in contact with the plug 10. This is to improve heat transfer between the plug 10 and temperature sensor 12 which is positioned below the cup-shaped element 81 and in contact with it.
The embodiment of the device of the utility model shown in Figure 4 also enables the thawing of a food in a microwave oven to be controlled. In this embodiment, below the food but not in contact with it there is positioned an element constructed of microwave-sensitive material and inserted either in the food support 8 or below it, i.e. in the base 7. This element is in contact with a transducer which by receiving a signal operationally related to the temperature of said element controls the microwave generator by way of a suitably programmed microprocessor.
In the said embodiment of the utility model shown in Figure 4, the annular element 80 of microwave-sensitive material is screened laterally and lowerly by the cup-shaped element 81. In addition when the food support 8 containing the plug 10 is used, the element 80 is also upperly shielded from the microwave by said plug. In this manner, for example when the food is heated, the food temperature is transmitted by conduction to the plug 10, and then by conduction to the plug 83 and cup-shaped elemnt 81 and is then measured by the sensor 12. This temperature signal is then used as already described in relation to Figures 1, 2 and 3 to halt the operation of the magnetron 2 (not shown in Figure 4). If on the other hand the food 9 is to be thawed the food is placed on a microwave-permeable support 8, for example of ceramic, which is not provided with the plug 10 and therefore offers no screen (to the microwaves) above the annular element 80. This element therefore receives microwaves (its temperature thus increasing) at a rate which varies according to the degree of thawing attained by the food 9, said food becoming increasingly more impermeable to the microwave as it thaws. When the food has completely thawed, the element 80 which is now more effectively screened by the food increases in temperature at a different rate and this is detected by the microprocessor 16 (not shown in Figure 4) which then halts the magnetron operation.
The user therefore utilizes the microwave-sensitive element 80 by operating with a food support 8 in which the plug 10 of good temperature-conducting but microwave-insensitive material is either absent or present.
In this latter case the use of the device according to the utility model is therefore similar to that already described with reference to Figures 1, 2 and 3.
A device constructed as shown in the various accompanying figures enables the preparation of foods contained in particular in a microwave oven to be automatically controlled and regulated. In addition, said device is of simple construction and is easily installed in the oven.

Claims

1. A device for automatically controlling the preparation of a food (9) in a microwave oven, comprising at least one temperature sensor means (12) connected to a microprocessor (16) arranged to act on the microwave generator (2) so as to halt it or at least vary its power during operation, the device being characterised in that the sensor means (12) is disposed in heat conducting relationship with a metal element (10) which is constructed of a good temperature-conducting but microwave-impermeable material and is housed in a support (8) for, and in contact with, the food (9).

2. A device as claimed in Claim 1, characterised in that the metal element (10) is inserted in a cavity (11) provided in the food support (8).

3. A device as claimed in Claim 2, characterised in that the temperature sensor means (12) is in contact with the metal element (10) in the cavity (11), said sensor means being rigid with a rod-shaped member (13) removably inserted through a radial cavity (14) in the food support (8).

4. A device as claimed in Claims 1 and 2, characterised in that the metal element (10) occupies the entire volume of the cavity (11) in the food support (8), said metal element (10) cooperating with the temperature sensor means (12) rigid with the bottom wall (7) of the cooking chamber (4) of the oven (1).

5. A device as claimed in Claim 4, characterised in that the metal element (10) is in contact with a metal plate (20) urged by a spring (21) with which the temperature sensor means (12) is lowerly rigid, said metal plate (20) being elastically mobile axially in a cavity (22) provided in the bottom wall (7) of the cooking chamber (4).

6. A device as claimed in Claim 4, characterised in that the temperature sensor means (12) rigid with the base (7) of the cooking chamber (4) is fixed lowerly to a cup- shaped element (81) containing an element (8) of microwave-sensitive material also rigid with the base (7) of the cooking chamber (4), the food support (8) not being provided with the metal element (10).

7. A device as claimed in Claim 6, characterised in that the food support (8) is provided with the metal element (10), the cup-shaped element (81) being in contact with this latter.

8. A device as claimed in Claim 7, characterised in that the element (80) of microwave-sensitive material disposed in the cup-shaped element (81) is annular, its cavity (82) containing a plug (83) of good temperature-conducting material, said plug (83) being in contact with the metal element (10) fixed to the food support (8).