EP1010357A1

EP1010357A1 - Method for controlling the duration of heating and/or cooking in an oven and oven for implementing the method

Info

Publication number: EP1010357A1
Application number: EP98903071A
Authority: EP
Inventors: Mustapha Arroubi; Lionel Durand
Original assignee: Moulinex SA
Current assignee: SEB SA
Priority date: 1997-01-20
Filing date: 1998-01-15
Publication date: 2000-06-21
Anticipated expiration: 2018-01-15
Also published as: ES2258813T3; FR2758685A1; CN1143598C; JP2001509250A; CN1249894A; US6150637A; ATE318067T1; KR20000070215A; BR9806782A; DE69833481D1; FR2758685B1; EP1010357B1; WO1998032311A1

Abstract

PCT No. PCT/FR98/00074 Sec. 371 Date Sep. 2, 1999 Sec. 102(e) Date Sep. 2, 1999 PCT Filed Jan. 15, 1998 PCT Pub. No. WO98/32311 PCT Pub. Date Jul. 23, 1998The invention concerns a method for controlling the duration of heating and/or cooking an undetermined amount Z of a given food product (5) placed in an oven chamber (1) comprising a heat source (2) and a sensor (4) for picking up a signal characteristic of the heating and/or cooking state of the food product. The invention is characterised in that it consists, after (A) supplying the heat source (2) at an initial moment t0 so that it delivers a predetermined constant power P0, in (B) measuring said characteristic signal at several successive moments over a measuring interval from said initial moment t0 to a final prefixed moment tc; in (C) computing over this measuring interval the value SZc of the integral of the characteristic signal measurements of taken in absolute value; in (D) deducing the residual time tr for heating and/or cooking for said undetermined amount Z of food product according to a predetermined polynomial equation linking the residual time tr to the value SZc of the computed integral; and in (E) stopping the supply of the heat source when the residual time tr has elapsed.

Description

METHOD OF CONTROLLING THE HEATING TIME

AND / OR COOKING IN AN OVEN

AND OVEN FOR IMPLEMENTING THE PROCESS

The present invention relates to a method for controlling the duration of reheating and / or cooking of an indefinite quantity Z of a food product of a given type placed in the enclosure of an oven comprising a heating source and a sensor. a characteristic signal of the state of reheating and / or cooking of the food product.

Many automatic control methods have already been proposed with different types of sensors capable of measuring a particular signal characteristic of the state of reheating and / or cooking of the food.

It has notably been proposed to use a probe to be immersed directly in the heart of the food to measure the internal temperature of this food. Faced with the difficulties encountered in certain situations, in particular in the case of frozen food in which it is impossible to penetrate the probe, other methods have developed which recommend the use of a sensor measuring a characteristic signal without require physical contact with the food, this sensor being for example a detector measuring the exhaust atmosphere (temperature or humidity) of the cooking chamber, or an infrared sensor measuring the surface temperature of the food. Patent FR-2 437 577 in particular describes an oven in which an infrared sensor measures the surface temperature of the food and operates either according to a first control mode in which the heating is stopped as soon as a set temperature is reached, or according to a second control mode in which the power of the oven is modulated as a function of the temperature measured surface. The modulation of the power proper consists either in carrying out successive power supply cycles at a fixed power followed by a power cut, or in performing a gradual reduction in power levels.

The previous method provides 1 • energy to the food in a gentle way. However, it is not optimal when the energy source used is a microwave source, since it runs counter to the effect generally sought in microwave ovens, namely the speed of cooking.

In addition, the previous method assumes that the temperature of the food during a reheating and / or cooking operation follows an increasing monotonous temporal evolution, with little, if at all, fluctuations, as represented by curve C of FIG. 1 illustrating the theoretical variation of the temperature T of a food of the given type as a function of time t. This assumption turns out to be false in practice, as can be seen from curve C ₂ in FIG. 1 representing a real case of variation of the temperature T of said food as a function of time t. The observation of this curve shows that an instantaneous temperature measurement is not very significant, in particular in the portion of curve included in the time interval [t _a ; t} -,]. Indeed, in this interval, the time t _a can be recorded as representing 1 • instant at which the set temperature has been reached, while in the absence of signal fluctuations (curve we would record ^" time t _j; as the time necessary to reach the setpoint.

Also known from US Pat. No. 4,812,606 is another method for controlling the cooking time of a food in a microwave oven in which the temperature of the air in the cooking chamber is measured at a predetermined instant. after the start of cooking, the residual cooking time is determined from an empirically pre-established polynomial equation relating the measured temperature to said residual time, then the feeding is stopped when the residual time has elapsed.

Again, this process is only effective if we consider that the temperature undergoes little fluctuation over time, which is generally not the case in reality. It is therefore easy to see that all the methods advocating the use of an instantaneous measurement of the temperature to decide on an action on the supply of an energy source are unreliable.

The object of the present invention is a new method for controlling the duration of reheating and / or cooking of an indefinite quantity Z of food product in an oven which makes it possible to overcome the problems associated with the fluctuation of the signals characteristic of the '' heating and / or cooking state of the product measured by the sensor.

More specifically, the method according to the invention is characterized in that it consists in:

- supplying said heating source at an initial instant t ₀ so that it delivers a predetermined constant power P ₀ ;

measuring said characteristic signal T _car (t) at a plurality of successive instants t over a measurement interval going from said initial instant t ₀ to a final instant t _c prefixed, and calculating on this measurement interval the value S _Zc the integral of the characteristic signal measurements taken in absolute value;

- deduce the residual time t _r of reheating and / or cooking for said indefinite quantity Z of food product according to a predetermined and memorized polynomial equation connecting said residual time t _r to the S _Zc value of the integral calculated, as a function of said type of food product; and

- stop supplying the heating source when the remaining time t _r has elapsed.

The present invention also relates to an oven for implementing the control method, of the type comprising an enclosure supplied by a microwave energy source forming the heating source, an infrared sensor measuring the surface temperature of the food product remotely. , and means for controlling the duration of reheating and / or cooking, characterized in that said control means are connected to the infrared sensor to receive the measurements of the surface temperature over the measurement interval and comprise a calculation module of the value S _Zc of the integral over said interval of the temperature measurements taken in absolute value, and of the residual time t _r of reheating and / or cooking according to said pre-memorized polynomial equation, said control means delivering a control signal for stopping the supply of the microwave energy source when the residual time t _r has elapsed.

The invention and the advantages which it provides will be better understood in the light of the following description of an example of implementation of the method in a microwave oven described with reference to the appended figures in which: FIG. 1 illustrates, on the one hand, the theoretical evolution (curve Ci), and on the other hand, the real evolution (curve C ₂ ) of the surface temperature of a food product of given type as a function of time;

- Figure 2 illustrates the evolution over time of the surface S located between the curve C ₂ of Figure 1 and the time axis; - Figure 3 shows a block diagram of the steps of the control method according to the invention in operational phase; and

- Figure 4 schematically illustrates a front view in section of a microwave oven implementing the method according to the invention.

As explained above with reference to FIG. 1, the characteristic signal measured by the sensor, for example the temperature at the surface of the food in the case of FIG. 1, can undergo large fluctuations. The originality of the invention lies in the fact that it proposes to focus not on the evolution of the instantaneous value of the surface temperature given by the curve C ₂ , but on the evolution over time of the surface S generated by the curve C, located between this curve C ₂ and the time axis t. The curve C ₃ illustrated in FIG. 2 represents the evolution of this surface. As we can see, the surface S, which mathematically corresponds at each instant t to the integral over time of the temperature values taken in absolute value, is a strictly monotonic increasing function of time, whatever the fluctuations undergone in reality by temperature. To obtain this surface, it is necessary to take the measurements of the characteristic signal in absolute value. Indeed, in the case of reheating a frozen product, the measurements are negative at the start of the reheating cycle, then become positive. Following this observation, tests carried out by the Applicant made it possible to show that it was possible, for an unknown quantity of food product of a given type to be reheated and / or cooked, to relate the value of the area S to an instant given to the value of the residual time necessary to obtain optimal heating and / or cooking according to an equation pre-stored polynomial, depending on the type of food product.

The method according to the invention therefore consists in carrying out the following minimum steps, described with reference to FIG. 3:

. Step A: Once the quantity Z of product of given type has been placed in the oven enclosure, the heating source is supplied, at an initial instant t _0, so that it delivers a predefined fixed power P ₀ . . Step B: A plurality of successive measurements of the characteristic signal T _car (t), for example the surface temperature of the food product, are carried out up to a final instant t _c . Measurements can be made continuously. Alternatively, only a few samples are taken at a chosen frequency.

• Step C: We calculate the integral of the measured values, taken in absolute value. The integral will be referenced below by S _Zc to indicate that it is a function of the quantity Z of food product, and that it is calculated over a time interval up to t _c . If only samples are available, the integral is in fact a sum in the sense of integration on the samples taken in absolute value.

. Step D: The residual time t _r is calculated by applying the pre-memorized polynomial equation and function of the type of food product. It is noted that knowing this residual time t _r makes it possible to obtain the total time t _z necessary for cooking the quantity Z by adding the time t _c to t _r . ^' . Step E: The supply of the heating source is stopped as soon as the calculated residual time t _r has elapsed.

The operating block diagram as shown in FIG. 3 further comprises two other steps D ′ and D ″ which will be explained below. The polynomial equation used is preferably established experimentally during a preliminary phase of development of the furnace, by carrying out for example the following steps: »0n chooses two distinct quantities X and Y of the food product of given type. We will assume hereinafter that the first quantity X is less than the second quantity Y.

. For each of the quantities X and Y, a reheating and / or cooking operation is carried out by supplying the heating source so that it delivers the power PQ, we carry out, over the measurement interval going from the initial time t ₀ until time t _c , successive measurements of the characteristic signal, and the corresponding integrals S _Xc and S _Yc are _calculated .

. For each of the quantities X and Y, the total durations t _x and t _γ necessary to obtain optimal reheating and / or cooking of the food product are measured.

We then demonstrate that it is possible, for any quantity Z of food product of the same type, to calculate, at the end of time t _c from the start of the cooking and / or reheating operation, the time residual t _r by applying, during step D previously described, the linear relation:

t _χ ~ tγ t _y S _χc _t _χ Sγ _c t _{r =} s _Zc + (I) ^s Xc ~ ^s Yc ^s Xc ~ ^S Yc

The total reheating and / or cooking time for quantity Z is therefore given by the relation:

t _{z =} t _r + t _c

is ^t χ ( ^S Zc ~ ^S Yc) ~ γ ( ^S Zc- ^S Xc) ⁺ ^ c ( ^S Xc- ^S Yc) t _{z =} (II)

^S Xc ~ ^S Yc Advantageously, the final instant t _c , corresponding to the upper limit of the measurement interval over which the integration is carried out, is chosen for each type of food product capable of being reheated and / or baked in the oven. The polynomial equation for a given type of food also preferably depends on the power delivered by the heating source and chosen by the user.

In this way, during the preliminary development phase of the oven, prior to the marketing of this oven, the manufacturer establishes a library of polynomial equations depending on the type of food and the power. In the operational phase, the user chooses only the type of food and the heating power. These two data are sufficient to know the instant t _c at the end of which the integration of the measurements will be made and to choose the associated polynomial equation allowing the residual time t _r and the total duration t _z to be defined.

In a preferred variant of the method according to the invention, provision is also made to operate the heating source at the power P ₀ for a predefined minimum duration t _min , advantageously a function of the type of food product. Thus, an additional step D '(Figure 3) consists in identifying the abnormal cases where the total duration t _z calculated during step D is less than the minimum duration t _min , and in stopping the feeding only when the minimum duration is over.

The minimum duration t _min can be determined experimentally during the preliminary development phase of the oven by choosing, for the first quantity X of food product of a given type, the lowest quantity tee of product that can be cooked and / or reheated in the oven. The total time t _x necessary for reheating and / or cooking said quantity X and measured during the prior phase then corresponds to the initial cooking time t _min .

As a variant, if the quantities X and Y have been chosen in any manner, however respecting the condition that the quantity X is less than the quantity Y, an operation is carried out during the prior development phase of the oven. reheating and / or cooking on a third quantity corresponding to the smallest quantity of food product capable of being cooked and / or reheated, this integral W _Wc is calculated for the temperature measurements taken in value absolute and performed on the measurement interval [t ₀ ; t _c ], and the duration t _min is calculated by applying the relation (II), namely:

^t χ ( ^s max ~ ^S Yc) ^-t γ ( ^S max- ^s Xc) ^{+ t} c ( ^S Xc- ^s Yc) tw- min =

⁵ Xc ~ ^s Yc

with S _max -S _Wc

In addition, the method according to the invention can also provide for operating the heating source at the power P ₀ for a predefined maximum duration t _max , advantageously a function of the type of food product. Thus, an additional step D "(FIG. 3) consists in identifying the abnormal cases where the total duration t _z calculated during step D is greater than the maximum duration t _max , and in stopping the feeding as soon as the maximum duration has elapsed, even if the residual time t _r calculated in step D has not yet elapsed This guarantees operating safety for the user.

As in the case of the minimum duration, the maximum duration t _max can be determined experimentally during the preliminary phase of development of the oven by choosing, for the second quantity Y of food product of given type, the highest quantity of product capable of being cooked and / or reheated in the oven. The total time t _y necessary for reheating and / or cooking said quantity Y and measured during the prior phase then corresponds to the maximum cooking time rnax *

As a variant, if the quantities X and Y have been chosen in any way, while respecting the condition that the quantity X is less than the quantity Y, the following is carried out, during the prior development phase of the oven, a heating and / or cooking operation on a third quantity W corresponding to the highest quantity of food product capable of being cooked and / or reheated, the integral S _w is calculated for this quantity W. _c temperature measurements taken in absolute value and carried out over the measurement interval [t ₀ ; t _c ], and the duration t _max is calculated by applying the relation (II), namely:

_ ^t χ ( ^S min ~ ^S Yc) ^-t Y ( ^S min- ^S Xc) ^{+ t} c ( ^S Xc- ^S Yc)

^S Xc ^S Yc

with S _min -S _w . _vs

An example of an oven implementing the method according to the invention will now be described with reference to FIG. 4:

The microwave oven shown by way of nonlimiting example in FIG. 4 comprises a cooking enclosure 1 delimited by a vault wall 10, a hearth wall 11, two side walls 12,13 and a bottom wall 14 A heating source comprising a magnetron type microwave energy source 2 located outside the enclosure supplies the interior of the enclosure. cooking belt 1 in microwave energy. The supply of the heating source is controlled by control means 3 according to the method of the present invention. An infrared sensor 4, placed for example above the roof wall 10, makes it possible to capture, by an opening 15 in the wall 10, the infrared radiation coming from a food product 5 of any type placed inside the cooking chamber 1, for example on a plate 6 rotated by an electric motor not shown, when the control means 3 authorize the supply of the heating source 2. The sensor 4 thus performs measurements of the surface temperature of the food product.

According to the invention, the sensor 10 is controlled by the control means 3 to carry out measurements of the temperature at the surface of the food during the measurement interval [t ₀ ; t _c ]. The control means also comprise a calculation module determining the various calculations on the one hand, of the integral S _Zc , and on the other hand, of the residual times t _r and total t _z . When the residual time has elapsed, the control means 3 deliver a control signal making it possible to stop the supply of the energy source. The control means can be produced by a microprocessor comprising a memory for storing a plurality of polynomial equations, and a clock for controlling the flow of the durations.

The new control method according to the invention achieves two objectives: - Improving the results of reheating and / or cooking food products;

- Give the user, sufficiently early in the reheating and / or cooking cycle, an idea of the remaining operating time, using only the characteristic signal. In addition, in the particular application to a microwave oven, it is possible to carry out a heating and / or cooking operation at constant power.

The invention can be generalized to any type of heating energy source, and to any type of sensor capable of giving information on the state of reheating and / or cooking of the food product.

Claims

1. Method for controlling the duration of reheating and / or cooking of an indefinite quantity Z of a food product (5) of a given type placed in the enclosure (1) of an oven comprising a source (2) heating and a sensor (4) of a characteristic signal T _because (t) of the state of reheating and / or cooking of the food product, characterized in that it consists of:

- (A) supplying said heating source (2) at an initial instant t ₀ so that it delivers a predetermined constant power P ₀ ;

- (B) measure said characteristic signal T _because (t) at a plurality of successive instants t over a measurement interval ranging from said initial instant t ₀ to a final instant t _c prefixed, and (C) calculate over this measurement interval the value S _Zc of the integral of the measurements of the characteristic signal taken in absolute value; - (D) deduce therefrom the residual time t _r of reheating and / or cooking for said indefinite quantity Z of food product according to a predetermined and stored polynomial equation connecting said residual time t _r to the value S _Zc of the integral calculated in function of said type of food product; and

- (E) stop supplying the heating source when the residual time t _r has elapsed.

2. Control method according to claim 1, characterized in that the residual time t _r is calculated by applying the following polynomial equation: t _x -t _γ ^t Y ^S Xc- ^t X ^S Yc

-r = Szc + ^s Xc ~ ^S Yc ^S Xc ~ ^S Yc in which

. t _r represents said residual time; • S _Zc represents the value of the calculated integral;

• S _Xc and S _yc are the values of integrals on characteristic signal measurements taken in absolute value and carried out, in a preliminary phase of development of the oven, on said measurement interval during reheating and / or cooking at said power P ₀ respectively of a first quantity X and of a second quantity Y of said food product of given type, the second quantity Y being greater than the first quantity X; and

• t _x and t _y are the total heating and / or cooking times required, measured in said prior phase, in the case of the first quantity X and the second quantity Y respectively.

3. Control method according to any one of the preceding claims, characterized in that it provides (D ", E) for stopping the supply of the heating source before the residual time t _r has elapsed as soon as the operating time of the oven from the initial instant t ₀ becomes equal to a predetermined maximum operating time t _max .

4. Control method according to claim 3, characterized in that the maximum duration of use t _max is predetermined for each type of food product capable of being reheated and / or cooked in the oven.

5. Control method according to claims 2 and 4, characterized in that, for a given type of food product, the maximum duration t _max use of the oven is determined experimentally by choosing, for the second quantity Y of food product, the highest quantity of said product capable of being reheated and / or cooked in the oven, the total time t _y necessary for reheating and / or cooking for this second quantity and measured during said preliminary phase corresponding to said maximum duration t _max .

6. Control method according to claims 2 and 4, characterized in that, for a given type of food product, the maximum duration t _max use of the oven is determined by calculating the relationship

^fc X ( ^S min ~ ^S Yc) ^-t Y ( ^S min- ^S Xc) ^{+ t} c ( ^S Xc- ^S Yc)

^ ^• max = ^s Xc ^{_ S} Yc in which S _min is the value of the integral on measurements of the characteristic signal taken in absolute value and carried out in the preliminary phase of development of the oven over said measurement interval during reheating and / or cooking at said power P ₀ the largest quantity of food product of the given type capable of being reheated and / or cooked in the oven.

7. Control method according to any one of the preceding claims, characterized in that the final instant t _c corresponding to the upper limit of the measurement interval is chosen for each type of food product capable of being reheated and / or baked in the oven.

8. Control method according to any one of claims 2 to 7, characterized in that it further provides (D ', E) to make operate the supply to the heating source (2) for a minimum duration t _min for a given type of food product from said initial instant t ₀ , the minimum duration t _min being determined experimentally by choosing, for the first quantity X of food product, the smallest quantity of said product capable of being reheated and / or baked in the oven, the total time t _x necessary for reheating and / or cooking for this second quantity and measured during said prior phase corresponding to said time minimum t _min .

9. Control method according to any one of the preceding claims, characterized in that the characteristic signal T _because (t) of the state of reheating and / or cooking of the food product consists of a measurement of the surface temperature of the food product.

10. Oven for implementing the control method according to claims 1 to 9, of the type comprising an enclosure (1) supplied by a microwave energy source (2) forming the heating source, an infrared sensor ( 4) remotely measuring the surface temperature of the food product, and control means (3) for the duration of reheating and / or cooking, characterized in that said control means (3) are connected to the infrared sensor (4) to receive the measurements of the surface temperature over the measurement interval and include a module for calculating the value S _Zc of the integral over said interval of the measurements of the temperature taken in absolute value, and of the residual time t _r of reheating and / or cooking according to said pre-stored polynomial equation, said control means (3) delivering a control signal to stop supplying the microwave energy source (2) when the residual time t _r has elapsed.