Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR CONTROLLING A MICROWAVE OVEN, MICROWAVE
OVEN AND ITS USE FOR COOKING OR HEATING FOOD
IN ACCORDANCE WITH THE METHOD
This invention relates to a method for controlling
a procedure for cooking or heating food in a microwave
oven by using the microwave radiation source of the oven
and a microwave-activable bottom heater in the form of a
receptacle, a plate or a carrier on which the food is
placed, which act as separate heat sources for the food
and are controllable via the control unit of the oven.
The invention further concerns a microwave oven for
implementing the method, as well as the use of the micro-
wave oven for cooking or heating food of different sortsby automatically-controlled procedures.
The microwave radiation sourc/e and the associated
microwave-feed system generate a microwave distribution
in the oven cavity that brings about so-called volume
heating of the food.
The microwave oven may comprise an additional source
of heat for the food in the form of a microwave-activ-
able, so-called crisp or browning plate. A crisp plate
may consist of an aluminium plate which has small thermal
mass and good thermal conductivity and on whose underside
is provided a microwave-absorbing layer. SE Patent Speci-
fication 9003104-8 discloses such a crisp plate. A brown-
ing plate has greater thermal mass and may consist of a
plate of ceramics or glass provided with a microwave-
absorbing layer. In general, both the crisp plate and thebrowning plate are arranged to rotate during cooking or
heating.
The microwave oven may have yet another source of
heat in the form of a so-called grill element or an equi-
valent IR-radiation element, which usually is arranged in
the ceiling of the cavity (see, for instance, SE Patent
Specification 920178~-2).
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A microwave oven equipped with these three types of
heat sources basically has access to a volume heater, a
bottom heater and a top heater, in which case the heat
emission from the two former is controlled by regulating
the microwave feed to the cavity, and the latter is con-
trolled directly as regards activation time and power
level. In order to optimise the heating or cooking of a
specific type of food, the three heat sources have to be
used in an appropriate manner, i.e. be activated at
adjusted power levels for a suitable period of the cook-
ing or heating procedure. However, the problem is that
the activation times and power levels for different sorts
of food vary considerably. For the average user, this is
much too complicated, and he therefore is usually not
given the opportunity to control the cooking or heating
procedure in this fashion. Microwave ovens are instead so
constructed that there is only one power balance, deter-
mined by the manufacturer, between thé different sources
of heat.
In some countries, the power consumption of appara-
tus with single-phase connection is restricted, which
among other things means that the microwave radiation
source and the grill element cannot be activated at the
same time. In turn, this places special requirements on
the utilisation of the heat sources depending on the type
of food at issue, and tends to complicate matters further
for the user.
One object of the invention is, therefore, to pro-
vide a microwave oven which does not suffer from any of
the drawbacks mentioned above, enables advantageous util-
isation of the heat sources, and at the same time is
more user-friendly. By optimal utilisation of the heat
sources, the microwave oven becomes more useful in gene-
ral, so that it may serve to cook or heat also such food
and dishes as today should be heated in conventional
ovens, e.g. in order not to lose their crispiness.
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According to the invention, this object is achieved
by a method which is of the type mentioned by way of
introduction and which is characterised by the steps of
- supplying the oven with food-category information on
the food,
- supplying information on the weight of the food,
- selecting, on the basis of the food-category informa-
tion supplied, a program for cooking or heating divided
into one or more time periods,
- calculating the expected duration of each time period
on the basis of the weight information as well as para-
meter information determined by the food category,
- activating, during each time period, said heat sources
at power levels and for activation times in accordance
with the selected program,
- decrementing the time periods to zero from the calcu-
lated value after starting the Frogram,
- ending each time period when it has been decremented
to zero, and
- ending the program when all the time periods have been
run through.
In preferred modes of implementation of the inven-
tive method, the weight information is automatically sup-
plied by a weight sensor disposed adjacent to the recep-
tacle, plate or carrier, or manually by the user via thecontrol panel of the oven.
The method according to the invention drastically
facilitates handling of the microwave oven, since the
user merely has to supply information on the food cate-
gory, possibly also on the weight, for instance via thecontrol panel of the oven. The oven may then be started
automatically or by operating a starter button. The oven
then selects an appropriate program in accordance with
the food category and monitors the cooking or heating
procedure fully automatically. The user need not, as is
the case in conventional ovens, select any power settings
and cooking times. To put it simply, the user merely
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indicates what he puts in the oven, for instance deep-
frozen ready-cooked chicken parts, and what he wishes to
take out of the oven, for instance heated chicken parts
having a crispy surface. The oven indicates when the dish
is ready.
By food category or food-category information is
here meant information corresponding to a specially-
designed cooking or heating program for a specific type
of food, such as potato products, pizza and chicken, and
the state of the food put in the oven, such as fresh or
deep-frozen raw products, and deep-frozen semi-processed
products.
The food-category information can be supplied by
inputting e.g. a numerical value indicating the type of
food and its state, or by inputting a first value indi-
cating the type of food and a second value indicating its
initial state. Preferably, the foo~d-category information
is inputted via a control button or a keyset where each
key corresponds to a certain food category, or via two
control buttons or keysets each corresponding to a spe-
cific type of food and a specific initial state.
A microwave oven according to the invention com-
prises a cavity, a microwave radiation source for feeding
microwaves to the cavity, a microwave-activable bottom
heater in the form of a receptacle, a plate or a carrier
on which food is placed for heating or cooking, a control
unit for controlling the bottom heater as well as the
feeding of microwaves to the cavity, the oven being
characterised in that it has means for supplying the con-
trol unit with information on the food category involved,as well as means for supplying the control unit with
information on the weight of the food, and that the
microprocessor of the control unit is programmed to
implement the following functions:
- selecting, on the basis of the food-category informa-
tion supplied, a cooking or heating program divided
into one or more time periods,
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- calculating the expected duration of each time period
on the basis of the weight information as well as para-
meter information determined by the food category,
- activating the microwave radiation source, and hence
the bottom heater, at power levels and for activation
times in accordance with the selected program,
- decrementing the time periods to zero from the calcu-
lated value after starting the program,
- ending each time period when it has been decremented
to zero, and
- ~nA ing the program when all the time periods have been
run through.
In a preferred embodiment of the invention, the
microwave oven is provided with a top heater, for
instance a grill element arranged in the ceiling of the
cavity, which is controlled by the program selected.
In another preferred embodiment of the microwave
oven according to the invention, a weight sensor is dis-
posed adjacent to the receptacle, plate or carrier and
adapted to automatically supply the information on the
weight of the food. In yet another embodiment, the con-
trol panel of the oven has means for manually supplying
information on the weight of the food.
The design of the inventive microwave oven is based
on the insight that the average user mostly employs the
oven for cooking or heating certain kinds of food, e.g.
deep-frozen ready-cooked dishes or bread and potato pro-
ducts, that this food can be divided into food categories
on the basis of the type of food and its initial state,
and that the combined information on the food category
and the weight of the food makes it possible to adapt a
program which is determined by the food category and is
automatically implemented by the oven. Furthermore, it
has been found that optimal utilisation of the heat
sources available in a modern oven, i.e. the microwave
field in the cavity, the bottom-heating crisp plate
and the top-heating grill element, may improve cooking
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results and make it possible to use the oven for a
broader range of food or dishes, the user-friendliness
of the oven being maintained or even improved.
According to the invention, the use of a microwave
oven, which has a rotary crisp plate arranged in the oven
cavity, as well as a grill element arranged in the ceil-
ing of the cavity, is distinguished by the fact that the
cooking or heating of food is performed automatically
according to preprogrammed cooking or heating programs
that can be selected on the basis of information on the
weight of the food as well as food-category information
based on the type of food and its initial state, which is
supplied to the oven.
Further distinctive features of the method and the
microwave oven according to the invention are stated in
the appended claims.
The invention will be described in more detail below
with reference to a preferred, non-restricting embodiment
illustrated in the drawings, in which
Fig. 1 shows an inventive microwave oven whose door
is open;
Fig. 2 is a block diagram illustrating cooperating
functional units of the oven during implementation of the
inventive method, and
Fig. 3 is a flow chart illustrating a preprogrammed
cooking or heating program for controlling the micropro-
cessor of the control unit.
The microwave oven illustrated in Fig. 1 has an
external casing 1, and an oven door 2 for closing the
cavity 3, in which a crisp plate 4 is arranged. The crisp
plate 4 is made of sheet aluminium of small thermal mass
and its underside is provided with a microwave-absorbing
layer of rubber-borne ferrite. Preferably, the ferrite
material employed has a Curie point at which ceases the
layer's energy absorption from the microwaves, which
means that the temperature of the upper side of the crisp
plate that comes into contact with the food stabilises in
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a temperature range of 130-230C. The crisp plate is
adapted to rotate during the cooking or heating proce-
dure. SE Patent Specification 9003104-8, as well as the
applicant's microwave ovens of type designations VIP20
and VIP27, illustrates a more detailed construction of
the crisp plate as well as its rotary mechanism.
The microwaves are fed to the cavity 3 through one
or more feed openings (not shown) which communicate with
the microwave radiation source 20 (normally a magnetron)
of the oven (see Fig. 2) via waveguides. In the illu-
strated oven, the magnetron, the associated waveguide
system, the power unit 19 for operating the magnetron,
and the control unit 15 are disposed behind the control
panel 5. In a preferred embodiment of the microwave-feed
system, use is made of an upper and a lower feed opening,
which are provided in the right-hand lateral wall of the
cavity, whereas the remainder of t~he feed system is
designed to feed polarised microwaves through these open-
ings. For more detailed information on the construction
of the microwave-feed system, reference is made to SE
Patent Specification 9003012-3, as well as to the
applicant's microwave ovens mentioned in the foregoing.
A grill element (not shown) is arranged in the ceil-
ing of the cavity, e.g. in the manner described in SE
Patent Specification 9201786-2. The grill element may be
a so-called "grill tube", a quartz tube or a halogen-
radiation source. Instances of concrete designs are found
in the applicant's microwave oven of type designation
VIP20.
The control panel 5 has a display 6 which, control-
led by the control unit 15, represents, among other
things, symbols or plain-text messages for selected pro-
grams, and the ro~; n; ng cooking or heating time, i.e.
verifies the user's selections made via the control panel
as well as provides other information on how the cooking
or heating proceeds.
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The control button 7 is used for selecting heating
through the feeding of microwaves to the cavity. The
button 8 is used for activating the grill element of the
oven, and the desired time is set by the knob 9. These
basic options have their equivalence in a conventional
oven and supplement the inventive option to select from a
given number of preprogrammed cooking or heating programs
for specific types of food while utilising the interplay
of the direct-acting microwaves, the crisp plate and the
grill element. The removable crisp plate may be replaced
with an ordinary rotary bottom plate in the case heating
involves direct-acting microwaves only. When selecting
the preprogrammed programs, the knob 9 also serves for
manual inputting of the weight of the food.
The buttons 10 and 11 are provided for, respec-
tively, starting and switching off the oven. The keyset
12 serves to input the food-category information and,
hence, to select a preprogrammed cooking or heating pro-
gram. For instance, the buttons may, from top to bottom,
concern the heating of deep-frozen pizza, the heating of
deep-frozen pie, the heating of deep-frozen potato pro-
ducts, such as chips, and the heating of deep-frozen
chicken parts. The operation of a button entails simulta-
neous input of complete food-category information, i.e.
information on the type of food and its initial state
(e.g. deep-frozen). In a modified embodiment of the oven,
the buttons are divided into two sets, in which case the
information on the type of food is inputted via one set
and the information on the initial state of the food is
inputted via the other set. In the simplest embodiment of
the oven, only one food category is used, which means
that only one button is required. All the buttons, as
well as the knob and the display, are in communication
with the control unit 15. On the upper side of the oven,
there are provided ventilation holes 13 communicating
with the evacuation channel (not shown) of the cavity
that is provided in the space between the ceiling of the
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cavity and the external casing 1. In view of single-phase
connection to the mains, the oven has a flex 14 with a
plug.
The block diagram of Fig. 2 shows the control unit
15 and the microprocessor and its associated program
memory 16. The user information is inputted to the con-
trol unit via the block 17, which represents the control
buttons and the knob described above. The control unit
controls the display 6. Via a driver 18 and a microwave
power unit 19, the control unit 15 controls the microwave
radiation source 20, and hence the feeding of microwaves
to the cavity 3. Via a driver 21, the control unit 15
controls the grill element 22, and hence the IR radiation
fed to the cavity 3. For more detailed information on the
construction of these functional units, reference is made
to the above-mentioned patents as well as to the
microwave ovens manufactured by the applicant.
Alternatively, the weight information is automati-
cally supplied to the control unit by a weight sensor 23
(indicated by dashed lines). The weight sensor 23 is dis-
posed adjacent to the crisp plate 3 and senses the weight
of the food placed on the plate. For instance, the weight
sensor may be of the design described in SE Patent Speci-
fication 9300291-3.
In Fig. 3, the flow chart illustrating a prepro-
grammed cooking or heating program comprises three suc-
cessive time periods Tl, T2 and T3. For each period, the
expected duration Tle, T2e and T3e is calculated on the
basis of the weight w of the food and a constant kl, k2
and k3, respectively, determined by the food category,
according to
Tle = kl o w
T2e = k2 o w
T3e = k3 o w
During each period, the feeding of microwaves and,
hence, the crisp plate as well as the grill element are
activated at power levels determined by the food cate-
214593~
gory. The power levels for, respectively, the microwaves
and the grill element during the associated periods are
designated, respectively, PM1, PM2 and PM3 and PGl, PG2
and PG3. These power levels are optimised for each food
category and may, in a further development of the oven,
vary during the time periods. Also the constants kl, k2
and k3 are optimised for each food category. In a further
development of the oven, the supplied microwave power may
be distributed between different feed openings to enable
energy to be distributed between bottom heat from the
crisp plate and microwave heating of the interior of the
food. Such distribution can be achieved by using a micro-
wave-feed system of the type described in SE Patent Spe-
cification 9302302-6.
The program illustrated in the flow chart of Fig. 3
runs through the following steps, where Y represents
"yes" and N represents "no".
sl. Start.
s2. Detection of the net weight w of the food.
s3. Calculation of Tle, T2e and T3e, respectively.
s4. Microwaves at the power PMl. Grill on the power PG1.
Decrementation of Tle.
s5. Tle = 0? If Y, proceed to s6. If N, return to s4.
s6. Microwaves at the power PM2. Grill on the power PG2.
Decrementation of T2e.
s7. T2e = 0? If Y, proceed to s8. If N, return to s6.
s8. Microwaves at the power PM3. Grill on the power PG3.
Decrementation of T3e.
s9. T3e = 0? If Y, proceed to slO. If N, return to s8.
s10. End of the program.
It will be appreciated that those skilled in the art
are well qualified to develop the described program with-
in the scope of the invention. For instance, the tempera-
ture of the ventilating air may be sensed by a tempera-
ture sensor arranged in the evacuation ~hAnn~l of thecavity. On the basis of the initial temperature sensed,
compensatory corrections are made of the constants
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,
11
selected through the food category and used for calculat-
ing the expected duration of the time periods of the pro-
gram. One thus elim;n~tes any effect of the oven being
heated even at the start. Another conceivable further
development would be to supply the control unit with
information on the temperature of the crisp plate as a
further control parameter. When implementing the method,
use can be made of so-called fuzzy logic decisions. Any
modifications derived therefrom are but measures of con-
venience to be regarded as encompassed by the scope of
the appended claims.
