EP1850642B1 - Method of reheating food, in particular a beverage, in a microwave oven - Google Patents

Abstract

The method involves acquiring a value representing a volume of drink e.g. tea, to be reheated, such as value representing a cup, and starting up of a generator of a microwave oven. A product humidity is measured by the food during the reheating, using a humidity sensor, where the sensor is placed in an upper part of the oven. The product humidity is compared with a threshold value of a predetermined humidity depending on the value representing the volume of drink. The generator of the oven is stopped when the product humidity is equal to the threshold value of the predetermined humidity. An independent claim is also included for a microwave oven comprising a humidity sensor.

Description

The present invention relates to a method for reheating a food, and in particular a beverage in a microwave oven.

It also relates to a microwave oven adapted to implement the heating method according to the invention.

In general, the present invention relates to an automatic function for reheating beverages in a microwave oven.

The invention aims in particular the reheating of drinks such as water, tea, coffee, chocolate, milk ...

When reheating a certain quantity of beverage in a microwave oven, it must be possible to reach a correct consumption temperature.

Microwave ovens offer beverage heating functions. However, these functions are not automatic. In particular, the reheating of a beverage is generally controlled by a timer, the duration of which may be dependent on a quantity of beverage to be heated selected by the user.

Thus, the reheating time is ideal only for a given volume of liquid.

In addition, this type of reheat function, based only on a predetermined duration of reheating, does not take into account the initial temperature of the beverage, so that the final temperature of the heated beverage is rarely satisfactory for the user.

The document EP 0 264 935 describes a method for heating a food in which the volume of food to be heated and the moisture produced by the food during its heating are measured to prolong, from a pre-determined moisture threshold value, the duration of heating according to the volume of food to be heated.

The present invention aims to solve the aforementioned drawbacks and to provide a method of heating a food, including a drink, to obtain a correct reheating temperature regardless of the volume and type of container.

• acquisition d'une valeur représentative d'un volume d'aliment à réchauffer ;
• mise en route d'un générateur de micro-ondes ; et
• mesure de l'humidité produite par l'aliment pendant le réchauffage.

The process for reheating a food comprises the following steps:

• acquiring a value representative of a volume of food to be heated;
• start-up of a microwave generator; and
• measuring the moisture produced by the food during reheating.

• comparaison de l'humidité produite à une valeur seuil d'humidité prédéterminée dépendante de ladite valeur représentative du volume d'aliment ; et
• arrêt du générateur de micro-ondes au moins lorsque ladite humidité produite est égale à ladite valeur seuil d'humidité prédéterminée.

According to the invention, the method further comprises the following steps:

• comparing the produced moisture with a predetermined threshold moisture value dependent on said representative value of the food volume; and
• stopping the microwave generator at least when said produced humidity is equal to said predetermined humidity threshold value.

Thus, by monitoring the moisture produced by the food during the reheating and comparing this humidity with a humidity threshold value calibrated according to the volume of food introduced into the oven, it is possible to stop the microwave generator at a time when the moisture produced corresponds to an ideal temperature of consumption of the heated beverage.

Thanks to the use of the value of the moisture produced during reheating, it is possible to obtain a temperature at the end of the reheating process close to the ideal temperature of consumption of a food, much more precisely than in the automatic reheating functions of the prior art using a timer of predetermined duration.

In particular, by monitoring the moisture produced by the heated food, it is possible to overcome the initial temperature of the product, and thus to have a heating time longer as the food has a low temperature at the time of its introduction into the microwave oven.

• enregistrement d'un signal d'un capteur adapté à mesurer une distance entre ledit capteur et un obstacle, ledit capteur étant monté dans une paroi de la cavité du four à micro-ondes ;
• analyse dudit signal enregistré sur une période de temps prédéterminée ; et
• déduction d'une valeur représentative d'un volume d'aliment à réchauffer choisie parmi un ensemble fini prédéterminé de valeurs.

According to one characteristic of the invention, the step of acquiring a value representative of a volume of food to be heated comprises the following substeps:

• recording a signal from a sensor adapted to measure a distance between said sensor and an obstacle, said sensor being mounted in a wall of the cavity of the microwave oven;
• analyzing said recorded signal over a predetermined period of time; and
• deducing a value representative of a volume of food to be heated selected from a predetermined finite set of values.

Thanks to the use of a sensor adapted to measure a distance separating this sensor from an obstacle, it is possible to deduce automatically a volume of food to be heated.

Thus, the step of acquiring a value representative of a volume of food to be heated is performed automatically during the heating process of a food and requires no further manipulation by the user.

The method for reheating a beverage can thus be implemented by the actuation of a single beverage reheating key, the steps of the reheating process then being performed automatically to determine a volume of food to be heated and a predetermined threshold humidity value dependent on this value representative of the food volume and cause the automatic shutdown of the microwave generator when the humidity produced is equal to this predetermined humidity threshold value.

In practice, the representative value of a volume of food to be heated is selected from a set comprising at least representative values of a cup, two cups or a bowl, two bowls or three cups, and a plate.

It is thus possible to classify the volumes of food to be heated in four categories corresponding to traditional containers used for beverages to be heated in a microwave oven.

• mesure de l'humidité de la cavité ;
• détermination d'une valeur minimale atteinte par la mesure d'humidité ; et
• calcul de l'humidité produite par l'aliment par différence entre la valeur de l'humidité mesurée et la valeur minimale déterminée.

According to another practical feature of the invention, the step of measuring the moisture produced by the food during heating comprises the following sub-steps:

• measuring the humidity of the cavity;
• determination of a minimum value achieved by the moisture measurement; and
• calculating the moisture produced by the food by difference between the value of the measured humidity and the minimum value determined.

Thanks to this calculation of the moisture produced by the food by difference between the value of the measured humidity and a minimum value determined during the reheating process achieved by the humidity in the cooking chamber, it is possible to to free from the residual moisture present in the cooking chamber before the start of reheating of a beverage.

Thus, the humidity value used is directly representative of the moisture produced by the food being reheated. This calculation is particularly advantageous when two successive reheating food are implemented in the microwave oven. Indeed, during the heating of a food, the start of the ventilation of the microwave oven removes moisture emitted during a previous reheat and still present in the oven cavity.

Thus, the moisture measured at the beginning of a reheating process decreases and does not correspond directly to the actual value of the moisture produced by the food being reheated.

According to a second aspect of the invention, it also relates to a microwave oven comprising at least one humidity sensor and a microprocessor. This microwave oven comprises means for acquiring a value representative of a volume of food to be heated and the microprocessor includes a processing algorithm adapted to implement route a microwave generator, to compare the moisture produced to a predetermined moisture threshold value dependent on said value representative of the food volume, and to stop the microwave generator at least when said moisture produced is equal at said predetermined humidity threshold value.

This microwave oven has advantages and features similar to those previously described for the heating process.

In particular, the microwave oven according to the invention comprises a so-called beverage heating key adapted to control the implementation of the heating method according to the invention.

Other features and advantages of the invention will become apparent in the description below.

• la figure 1 est une vue en perspective schématique d'un four à micro-ondes conforme à un mode de réalisation de l'invention ;
• les figures 2 et 3 sont des courbes illustrant des enregistrements d'un signal de capteur adapté à mesurer une distance entre le capteur et un ou des contenants placé(s) sur un plateau tournant d'un four à micro-ondes conforme à l'invention ;
• la figure 4 est une vue schématique illustrant l'exploitation des enregistrements d'un signal des figures 2 et 3 ;
• la figure 5 est une courbe illustrant la mesure de l'humidité produite par un aliment chauffé dans un four à micro-ondes en fonction du temps ; et
• la figure 6 est une courbe illustrant le suivi de l'humidité produite par un aliment lors de la mise en oeuvre du procédé de réchauffage d'un aliment conforme à un mode de réalisation de l'invention.

In the accompanying drawings, given as non-limiting examples:

• the figure 1 is a schematic perspective view of a microwave oven according to an embodiment of the invention;
• the figures 2 and 3 are curves illustrating recordings of a sensor signal adapted to measure a distance between the sensor and a container or containers placed on a turntable of a microwave oven according to the invention;
• the figure 4 is a schematic view illustrating the exploitation of the recordings of a signal of figures 2 and 3 ;
• the figure 5 is a curve illustrating the measurement of the moisture produced by a food heated in a microwave oven as a function of time; and
• the figure 6 is a curve illustrating the monitoring of the moisture produced by a food during the implementation of the method of heating a food according to an embodiment of the invention.

We will first describe with reference to the figure 1 a microwave oven adapted to implement the present invention.

We illustrated on the figure 1 and hereinafter only those elements of the microwave oven necessary for carrying out the present invention will be described.

Of course, this microwave oven includes all the elements necessary for operation, including a microwave generator.

The oven 10 conventionally comprises a cavity 11 forming a cooking chamber in which are placed food to be heated in the microwave oven.

In order to homogenize the heating by the waves in the cooking chamber 11, it generally comprises a turntable 12 rotatably mounted on the hearth of the oven.

On the front of the oven, a door 13 allows the user to introduce food into the cavity 11 for reheating. A control panel 14 disposed on the facade also allows the user to program and set various operating parameters of the microwave oven.

In this embodiment of the invention, the control panel 14 comprises in particular a control key 15, called for example, a beverage heating key 15 adapted to control the implementation of a specific heating method which will be described later.

For the implementation of this particular method of reheating beverages, the microwave oven comprises a humidity sensor 16.

In this embodiment, the humidity sensor 16 is placed in the upper part of the microwave oven 10, between the upper wall 11a of the cavity 11 and an upper wall 10a of the oven body 10.

Generally, a microwave oven comprises a ventilation system (not shown) adapted to extract air and steam from the cavity 11 of the oven to prevent the condensation of water vapor on the walls of the cavity 11.

In this embodiment, the humidity sensor 16 is preferably placed in a space forming a duct for evacuating the air extracted from the cavity 11.

Thus, this humidity sensor makes it possible to measure the humidity contained in the air extracted from the cavity 11 during the heating of a food.

A humidity sensor may consist for example of a pair of identical thermistors. One of the thermistors is placed in a housing with small openings to allow contact of the thermistor with the ambient air.

The second thermistor is placed in an airtight case. The difference in response of the two thermistors makes it possible to follow the evolution of the humidity in the air coming from the cavity 11.

Any type of humidity sensor well known to those skilled in the art can be used here.

Furthermore, in this embodiment, the microwave oven further comprises a distance sensor 17, 17 '.

In this example, the sensor 17, 17 'is mounted in a side wall 11b of the cavity 11, near the sole of the cavity. In practice, the distance sensor 17, 17 'is placed above the turntable 12 for measuring the distance between the wall 11b of the cavity 11 and a container placed on the turntable 12.

This sensor may be an ultrasonic sensor or an infrared radiation sensor.

Preferably, this sensor is ultrasonic type that can detect any type of containers, including transparent containers that are less well detected by an infrared sensor.

This distance sensor has a measurement direction in a plane parallel to the plane of the turntable 12 on which the food to be heated is placed.

In all cases, the signal measured at the output of the sensor 17, 17 'represents the distance separating this sensor from an obstacle.

For example, for an ultrasonic sensor, the sensor comprises a transmitter 17 of a frequency wave equal for example to 40 kHz and a receiver 17 'adapted to measure in response the echo. The pulse width is proportional to the distance separating the sensor from the obstacle on which the transmitted wave is reflected.

The implementation of this distance sensor and the analysis of the signal emitted by this sensor will be described later with reference to the Figures 2 to 4 .

Of course, the sensors 16, 17, 17 'are connected to an electronic control board of the microwave oven, for controlling the operation of the oven. This electronic control card comprises, in a known manner, a microprocessor making it possible, from the signals transmitted by the sensors 16, 17, 17 'and a processing algorithm which will be described below, to control the heating of a foodstuff. in the microwave oven 10.

We will now describe the method of reheating a food, including a beverage, which can be implemented in the microwave oven described above.

In practice, the start of the reheating process can be carried out by the user, when the latter has placed a food, and preferably a drink in a container on the turntable 12 of the cavity 11, and actuated the beverage reheat button 15.

This operation has the effect of triggering the start of the microwave generator and the rotation of the turntable 12 adapted to support the food to be heated.

In this embodiment of the method for reheating a beverage, the microwave generator is adapted to emit at constant power, and generally according to the maximum power, of the order of 1000 W, emitted by the microwave generator. waves.

Concomitantly, the heating method according to this embodiment comprises a step of acquiring a value representative of the volume of food to be heated.

In this embodiment, an automatic acquisition mode of the volume of food to be heated is implemented.

Note however that the present invention is not limited to an embodiment in which the determination of the volume of food to be heated is performed automatically from the beginning of the heating process. The volume of food could also be acquired through a function available on the control panel 14, allowing the user to indicate the volume of food to be heated by indicating a typical container, for example a cup, two cups, a bowl, a plate ...

We will describe with reference to Figures 2 to 4 the step of acquiring a value representative of a volume of food to be heated implemented from the distance sensor 17, 17 '.

In practice, the signal of the distance sensor 17, 17 'is recorded over a predetermined period of time during which it is analyzed.

We have shown on the figure 2 recording a signal from a sensor with a very low detection angle, and on the figure 3 recording a signal from a sensor having a greater detection angle, for example, of the order of 45 °.

Preferably, the recording and the analysis of the signal at the output of the distance sensor 17, 17 'are made over a period of time substantially corresponding to the rotation period of the turntable 12 supporting the food to be heated.

In practice, it is possible to use an ultrasonic sensor adapted to detect the distance to a closest object at a 45 ° angle.

The signal is recorded at regular intervals, for example every second, for about a rotational period of the turntable, of the order of 15 s.

The analysis of the recorded signal as shown on the figures 2 or 3 , consists in identifying the number of minima of the signal and the maximum and minimum values taken by the recorded signal.

The knowledge of these values makes it possible to deduce a representative value of a volume of food to be heated.

In practice, this deduction is made from a finite set of container classes.

As illustrated in figure 2 when the drink is placed in a single container, for example a cup or a bowl, the recorded signal has only two minima during a rotation period of a turntable, whereas when the drink is placed in two containers, for example two cups, the recorded signal has four minima.

Similarly, figure 3 , the recorded signal allows according to the number of minima and the maximum and minimum values of the curve to differentiate the type of containers and their number.

An example of an algorithm for classifying the containers into different classes will be described below, taking into account both the size of the container and the number of minima taken by the signal.

As illustrated in figure 4 in a particular example in which a single container is placed on the turntable 12, a minimum distance d separating the distance sensor 17, 17 'from the container C and a maximum distance separating the sensor 17, 17' from the container C after rotating a half turn of the turntable 12 are measured. Thanks to the knowledge of the total dimension D of the cavity 11, it is possible to calculate a dimension X of the container C by subtracting from the dimension D of the cavity 11 the value of the shortest distance d and the largest distance d measured: $$\mathrm{X}\mathrm{=}\mathrm{D}\mathrm{-}\mathrm{d}\mathrm{-}\mathrm{of}$$

In the case where only one container C is used, as illustrated in figure 4 , the calculated dimension X substantially corresponds to the size of the container. In the case where several containers are placed on the turntable 12, this dimension X corresponds to the dimension in the plane of the outer space occupied by the containers.

The following is given by way of nonlimiting examples a table allowing from the dimension X thus calculated and the number of minima taken by the recorded signal to determine the type of container placed in the cavity 11 and thus to determine the class V of a volume of food to be heated. Dimension (cm) Number of minima Type Class V 0 ≤ X <7 1 cup 1 cup 7 ≤ X <9 <2 1 cup 1 cup ≥ 2 2 cups 2 cups / 1 bowl 9 ≤ X ≤ 13 2 cups / 1 bowl 2 cups / 1 bowl 13 <X ≤ 15 <3 2 cups / 1 bowl 2 cups / 1 bowl ≥ 3 3 cups 3 cups / 2 bowls 15 <X ≤ 17 3 cups / 2 bowls 3 cups / 2 bowls 17 <X ≤ 32 <2 1 plate 1 plate ≥ 2 2 bowls 3 cups / 2 bowls

Of course, these classification examples are in no way limiting and depend in particular on the detection angle of the sensor.

Especially if the angle of detection was lower, two cups and a bowl or three cups and two bowls could be identified in separate classes.

The analysis of the recorded signal thus makes it possible to deduce a value representative of a volume of food chosen in a predetermined finite class.

Each food volume class corresponds to a set of type and / or volume of food containers for which the behavior during reheating is identical and can be enslaved in the same way.

The Applicant has empirically determined four representative classes of a volume of beverage to be heated.

Of course, this type of classification and the number of classes can be different.

• V = 1 : une tasse
• V = 2 : deux tasses ou un bol
• V = 3 : trois tasses ou deux bols
• V = 4 : une assiette.

In this embodiment, the following classes V are thus distinguished:

• V = 1: a cup
• V = 2: two cups or a bowl
• V = 3: three cups or two bowls
• V = 4: a plate.

Thus, by using the distance sensor 17, 17 ', it is possible to determine a class V corresponding to a volume of beverage to be heated, from the beginning of the process of reheating this beverage.

Note that the finer the detection angle of the sensor, the more classes V can be increased.

Furthermore, the method of heating a food simultaneously comprises a step of measuring the moisture produced by the food during heating with the moisture sensor 16 described above.

This step of measuring the humidity is carried out as soon as the microwave generator is switched on, after the user has actuated the so-called beverage heating key 15.

We illustrated at the figure 5 a typical curve representing the profile of the moisture present in the air of the cavity of the microwave oven.

In practice, the value M (t) of the measured humidity decreases at the beginning of the reheating of a food until a time t ₁ at which the value of the humidity M (t ₁ ) reaches a minimum.

This drop in moisture at the beginning of the reheating process actually corresponds to the evacuation of the moisture present in the cavity due to a previous reheating operation.

Of course, when the microwave oven has not been operating for a certain time, the minimum value of the measured humidity may correspond to the initial time so that t ₁ = 0.

In order to overcome this drop in moisture at the beginning of the reheating process, which is not representative of the moisture produced by the food being reheated, the moisture measuring step comprises a step measuring the humidity M (t) in the cooking chamber, a step of determining the minimum value M (t ₁ ) reached by the humidity measurement and a step of calculating the humidity produced H (t ) by the difference between the measured humidity value and the determined minimum value.

Thus, H (t) = M (t) - M (t ₁ ).

The monitoring of the produced moisture H (t) makes it possible to enslave the method of reheating the food.

As stated in figure 6 the process for reheating the food comprises a step of comparing the produced moisture H (t) with a predetermined humidity threshold value Hv.

This predetermined humidity threshold value Hv is dependent on the value representative of the volume of food.

In the embodiment described above, in which four classes V of food volume have been defined, the method for reheating a food is adapted to implement four predetermined humidity threshold values H1, H2, H3, H4.

Thus, as illustrated in figure 6 when the produced moisture H (t) is equal to the predetermined moisture threshold value Hv, the method of reheating a food is terminated and a stop command of the microwave generator is automatically implemented.

Typically, a sound signal may be emitted to indicate to the user the end of the heating process of a food.

In addition to associating the representative value of the feed volume V with the predetermined humidity threshold value Hv, it is also planned to associate a predetermined threshold heating time threshold value Tv.

This maximum reheating time makes it possible to prevent the food from overheating if the humidity produced remains below the predetermined humidity threshold value Hv.

The timer can have a safe function. It also helps to deal with the case where the volume to be heated is very small compared to the size of the container. Indeed, the detection of a class V is performed according to the number and / or size of the container and not the volume of beverage actually introduced into the container.

Thus, for each class V of food volume to be heated, a predetermined humidity threshold value Hv and a predetermined heating time threshold value Tv are taken into account during the heating process to stop the microwave generator as soon as possible. that the produced humidity H (t) is equal to the predetermined humidity threshold value Hv or as soon as the elapsed time t since the start of the microwave generator is equal to the predetermined heating time threshold value Tv .

Thus, for each class V, there are volumes of food to be heated, a predetermined humidity threshold value Hv and a predetermined heating time threshold value Tv.

Thus, if the volume of food to be heated is low, and this regardless of the size or type of container, the predetermined humidity threshold value Hv will be reached before the threshold value of predetermined heating time Tv.

Conversely, if the volume of food to be heated is large, the threshold value of predetermined heating time Tv will be reached before the predetermined humidity threshold value Hv.

Thus, the use of the timer can heat volumes of liquid requiring different heating times although detected in the same class of containers.

For example, when two small cups are used, the predetermined humidity threshold value Hv is reached before the predetermined heating time threshold value Tv.

Conversely, when a bowl is used, the threshold value of predetermined heating time Tv is reached before the predetermined humidity threshold value Hv.

Thus, the heating of the liquid contained in two cups and a bowl, although these containers belong to the same class V volumes, is made with different durations perfectly adapted to the volume of liquid to be heated.

However, if the bowl contains a small volume of liquid, the predetermined humidity threshold value Hv will be reached before the predetermined heating time threshold value Tv.

The use of these two threshold values is thus necessary under the various conditions of use, that is to say with a volume of liquid to be heated adapted to the size of the container, allowing the different containers to be heated to the correct temperature. belonging to the same class V of volumes, or a volume of weak liquid in the container.

Thanks to the invention, the reheating process provides a temperature suitable for the consumption of different hot drinks, regardless of the volume of beverage and the container used.

Of course, many modifications can be made to the embodiments described above without departing from the scope of the invention.

In particular, the position and type of humidity and distance sensors are not limited to the embodiments described above.

Likewise, the power emitted by the microwave generator is not necessarily constant.

Claims (10)

1. Method of heating a food, and in particular a drink, in a microwave oven, comprising the following steps:

   - acquiring a value (V) representing a volume of food to be heated;

   - starting a microwave generator; and

   - measuring the moisture (H(t)) produced by the food during heating,

   characterised in that it also comprises the following steps:

   - comparing the moisture produced (H(t)) with a predetermined moisture threshold value dependent on the said value representing the volume of food; and

   - stopping the microwave generator at least when the said moisture produced (H(t)) is equal to the said predetermined moisture threshold value (Hv).
2. Heating method according to claim 1, characterised in that the said step of acquiring a value (V) representing a volume of food to be heated comprises the following substeps:

   - recording a signal from a sensor (17, 17') for measuring a distance between the said sensor (17, 17') and an obstacle, the said sensor (17, 17') being mounted in a wall (11b) in the cavity (11) of the microwave oven;

   - analysing the said recorded signal over a predetermined period of time; and

   - deducing a value (V) representing a volume of food to be heated chosen from a predetermined finite set of values.
3. Heating method according to claim 2, characterised in that the said signal is recorded over a period of time corresponding to the period of rotation of a rotary tray (12) disposed in the cavity (11) and adapted to support the food to be heated.
4. Heating method according to one of claims 2 or 3, characterised in that, at the analysis step, the number of minima of the recorded signal and the maximum and minimum values of the recorded signal are taken into account in order to deduce the said value (V) representing a volume of food to be heated.
5. Heating method according to one of claims 1 to 4, characterised in that the said value (V) representing a volume of food to be heated is chosen from a set comprising at least values representing a cup, two cups or one bowl, two bowls or three cups, and a plate.
6. Heating method according to one of claims 1 to 5, characterised in that the step of measuring the moisture (H(t)) produced by the food during heating comprises the following substeps:

   - measuring the moisture (H(t)) in the cavity (11);

   - determining an minimum value (H(t)) reached by the moisture measurement; and

   - calculating the moisture (H(t)) produced by the food by difference between the value of the moisture measured(H(t)) and the minimum value determined (H(t)).
7. Heating method according to one of claims 1 to 6, characterised in that it comprises the following steps:

   - associating, with the said value (V) representing the volume of food to be heated, a predetermined moisture threshold value (Hv) and a predetermined heating duration threshold value (Tv); and

   - stopping the microwave generator as soon as the said moisture produced (H(t)) is equal to the said predetermined moisture threshold value (Hv) or as soon as the time elapsed (t) since the microwave generator was started is equal to the said predetermined heating duration threshold value (Tv).
8. Microwave oven comprising at least one moisture sensor (16) and a microprocessor, characterised in that it comprises means of acquiring a value (V) representing a volume of food to be heated, the microprocessor comprising a processing algorithm for starting a microwave generator, comparing the moisture produced (H(t)) with a predetermined moisture threshold value dependent on the said value representing the volume of food, and stopping the microwave generator at least when the said moisture produced (H(t)) is equal to the said predetermined moisture threshold value (Hv).
9. Microwave oven according to claim 8, characterised in that it also comprises a distance sensor (17, 17'), of the ultrasound sensor or infrared radiation sensor type, disposed in a wall (11b) of the cavity (11) and having a measurement direction in a plane parallel to the plane of a rotary tray (12) disposed in the cavity (11) and adapted to support the food to be heated.
10. Microwave oven according to one of claims 8 or 9, characterised in that it comprises a so-called drinks heating button (15) for controlling the implementation of the said heating method according to one of claims 1 to 7.

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