WO2023062599A1

WO2023062599A1 - Heating device for kitchens and cooktops

Info

Publication number: WO2023062599A1
Application number: PCT/IB2022/059871
Authority: WO
Inventors: Antonio DE MOLINER; Luca FRIGO; Federico ZOPPAS
Original assignee: I.R.C.A. S.P.A. Industria Resistenze Corazzate E Affini
Priority date: 2021-10-15
Filing date: 2022-10-14
Publication date: 2023-04-20
Also published as: IT202100026492A1

Abstract

A control system for heating elements for cooking grills and the like, adapted to adjust the operating temperature precisely by measuring the electrical power parameters of the resistor of the heating element.

Description

HEATING DEVICE FOR KITCHENS AND COOKTOPS

FIELD OF THE INVENTION

The present invention concerns a heating device for kitchens and cooktops and a control and driving system thereof and relates to the technical field of grills for cooking food by direct contact.

BACKGROUND ART

Grills consisting of one or more heating elements comprising electrically supplied resistive filaments, used for cooking food by direct contact, are frequently employed, e.g., in professional restaurant kitchens. These devices allow grilled foods to be cooked in all those settings in which it is either not possible or convenient to employ open flames.

However, such electrically supplied grills are difficult to use when their operating temperature needs to be adjusted precisely. Indeed, on this type of device, the installation of temperature sensors is not feasible due to the geometry and structure of the heaters which form the grill.

On one hand, external temperature sensors cannot be used because they would have to be in direct contact with the food being cooked, resulting in cleanliness and food safety issues. On the other hand, internal temperature sensors cannot be used because of the particular manufacturing process to which the heaters for cooking by direct contact are subjected, a process which involves passing through presses and furnaces at temperatures of 1100 °C that the thermal sensors would not withstand.

For these reasons, the temperature of the current grills for cooking food by direct contact is controlled rather approximatively, often by using an electromechanical timer of the on/off type, which is simply capable of enabling or disabling the power supply to keep the grill heaters around a given, estimated, temperature value.

The use of grills of the type described above thus presupposes some experience of their use because, since the users cannot rely on an accurate indication of the cooking temperature of the grill itself, they often have to evaluate other factors to understand whether the cooking is taking place at the correct temperature. The problem of the absence of a temperature sensor integral to the heating element and the lack of accuracy in the evaluation of the working temperature of the heating element itself also affects the heaters used for heating liquids, such as oil or water, which can be functional both for cooking food and for other applications, e.g., such as dishwashing or clothes washing.

In this case, the heater is placed in contact with the element to be heated, in this case water, and the absence of accurate temperature detection can be a source of problems and malfunction. For example, in the case of pasta cooking apparatuses in use in the kitchens of restaurants, canteens, etc., the aforementioned heaters are placed, often superimposed, on the bottom of a tray adapted to contain the water to be heated and to house a container adapted, in turn, to house the pasta to be cooked and be immersed in the water in the tray. The user is responsible for checking the water level in the tank so that the heaters are always submerged in water and correct operation is ensured. Indeed, if the heaters were to remain out of the water, they would be damaged because their temperature would rise excessively.

The temperature control in systems of the type described, when present, is usually entrusted to a power switch, and a safety thermostat is sometimes present, usually associated with the heater placed in a higher position, adapted to cut off supply to the heater when the exceeding of an alarm temperature is detected, e.g., such as a result of the water level having dropped too low and uncovering one of the heaters used. These safety thermostats have rather low accuracy and a high intervention threshold so that they do not intervene during normal operation of the heater. Thus, these safety systems are not adapted to identify a malfunction early but only to intervene to avoid the problem which occurred from propagating further.

A similar problem to the one described above is present in professional dishwashers, in which the water heating elements often have built-in safety thermal fuses. Like in the case described above, again in this case, the failure to intervene in a timely manner in the presence of malfunctions can cause the operating temperature to rise above the intervention threshold of the thermal fusible. The intervention of the thermal fuse prevents the fault from propagating into the apparatus but still results in the interruption of its operation, leading to significant recovery time and costs.

Therefore, a need is apparent to equip the heaters - used in electrically supplied grills used for cooking food by direct contact or for heating liquids, such as oil or water - with appropriate means for reading and adjusting their working temperature to avoid the above-described problems associated with devices in use at the prior art and allow an adjustment of the working and intervention temperature in case of malfunctions, which are accurate, timely and effective.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a heating device comprising an electrical resistor equipped with means adapted to control its working temperature and to provide an alarm if an emergency threshold is exceeded.

It is another object of the present invention to provide a device for controlling the operating temperature of a heating element comprising an electrical resistor, which can be integrated into new heating elements and/or applicable to existing heating elements. It is another object of the present invention to provide an electrically powered grill for cooking food by contact, comprising an electrical resistor provided with means for controlling the working temperature and providing an alarm if an emergency threshold is exceeded.

It is a further object of the present invention to provide a device for heating water for cooking food comprising means for controlling the temperature and providing an alarm if an emergency threshold is exceeded.

The heating device according to the present invention comprises: reading means of the supply voltage and current of an electrical power resistor; processing means adapted to process the performed supply voltage and current readings of the electrical resistor, to estimate the working temperature of said electrical resistor; adjustment means of the power supply of the electrical resistor, to be connected between the electrical power source and said electrical resistor, said adjustment being based on the estimate made of the working temperature of the electrical resistor. Said adjustment means of the power supplied to an electrical resistor can be implemented, for example, by an ON/OFF switch or by an electronic regulator of the power supplied to the electrical resistor, such as a bias or PWM type regulator.

The supply voltage and current reading means of the electrical resistor and the performed reading processing means can, for example, be carried out by an electronic control circuit, which reads the current and voltage at the ends of the electrical resistor and calculates an estimate of the temperature value of the electrical resistor corresponding to the voltage and current readings.

The operation of the heating device according to the invention provides that, during normal operation, the current and operating voltage of the electrical power resistor inside the heating device is constantly monitored so that the surface temperature of the heating element itself is established with high accuracy.

In this manner, wherever the heating device is used, it is guaranteed that the set temperature will be reached, within a given tolerance, with obvious benefits in terms of both the normal operation of the heater and the detection of malfunctions and prevention of breakdowns.

In another preferred embodiment, the heating device according to the invention can be made with an additional resistive wire integrated into the same structure as the heater but electrically insulated from the electrical power resistor.

This preferred embodiment allows the temperature of the heating device to be monitored also when the power resistor is not powered; furthermore, the additional resistive wire is energized at low voltage, resulting in a simplified, less expensive measurement circuit with fewer certification problems.

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the present invention will be more apparent in the light of the detailed description of a preferred, but not exclusive embodiment of a method for detecting the quantity of limescale accumulated in the heaters of devices for heating liquids, illustrated by the way of non-limiting example, with reference to the accompanying drawings, in which: Fig. 1 shows a functional block diagram of a preferred embodiment of the heating device according to the present invention;

Fig. 2 shows an example of a heating device according to the present invention provided with additional integrated resistive wire;

Fig. 3 shows a functional block diagram of a preferred embodiment of the device according to the present invention;

Fig. 4 shows a graph comparing the temperature of the heating device detected with an external sensor, with the temperature estimated by the device according to the present invention;

The same reference numerals refer to the same elements or to elements having the same functional and/or structural features. Said elements are shown in the drawings, where appropriate, with conventional symbols, showing only those specific details which are pertinent to understanding the embodiments of the present invention, so as not to highlight details which will be immediately apparent, to those skilled in the art with reference to the description given herein.

DETAILED DESCRIPTION OF THE INVENTION

With reference to accompanying Fig. 1 , the heater device according to the present invention, in a preferred embodiment, comprises a reading module of the supply voltage 10 and current 11 of a power electrical resistor 13; a user interface 14 for setting the temperature of the heater; a control module 15 and an adjustment module 16 of the supply voltage of the electrical resistor 13, driven by said control module 15 based on the setting of the temperature of the heater and based on the reading of the supply voltage and current of the electrical resistor 13, operated by said reading module of the voltage 10 and the current 11 .

Said user interface 14 may comprise a simple indexed knob connected to an electrical circuit adapted to generate a variable electrical signal as a function of the angular position of the knob, or it may comprise screens and/or keypads through which a user can set (and read) the required temperature value in a digital manner. Said control module 15 operates a temperature estimation which exploits the phenomenon of the variation of resistivity p of a material as a function of temperature, i.e., it calculates p(T).

Indeed, for most electrical conductors, e.g., such as copper, aluminum, iron, Manganin, etc., resistivity increases as the temperature increases and vice versa. This is explained, at the atomic level, by the fact that increasing the temperature of a conductor increases the thermal agitation of the atoms in the crystal lattice that composes it. Therefore, the atoms in the crystal lattice tend to experience more collisions with conduction electrons, and this results in an overall reduction in the directional motion of electrons. Therefore, it is possible to indicate the resistance (or resistivity) of a conductor by measuring the temperature of said conductor and to have an indication of the temperature of a conductor by measuring its resistance (or resistivity).

Thus, by measuring the value of the electrical resistor R 13 of the heating element 12, the device according to the present invention can accurately estimate the temperature value of both the electrical resistor R 13 and the heating element 12. Then, by acting on the supply voltage of the resistor R 13 itself, it adjusts the temperature value of the heating element 12 according to the settings provided by the user.

To achieve this result, the control module 15 operates to process both the settings provided by the user through said user interface 14 and the voltage and current readings of the resistor R 13 to determine the setting which must be set on the supply voltage of the resistor R 13 so that the heater reaches the temperature set by the user. Thus, the control module 15 implements a feedback control loop adapted to maintain the temperature value of the heater constant by minimizing the error between the value set by the user and the value estimated by measuring and subsequently processing the supply voltage and current of the power resistor R 13 inside the heating element 12.

Said control module 15, in a preferred embodiment of the invention, will comprise at least a microcontroller and memory, on which program instructions and data tables are stored which bind pairs of supply voltage and current values of the resistor R 13 (and thus resistance values R) to temperature values of the resistance R and the outer casing of the heating element 12.

Therefore, after setting a required temperature by the user, the control module 15 will drive the control module 16 of the supply voltage of the power resistor R 13 to obtain a resistor supply current value R which corresponds to a heating element casing temperature 12 equal to the temperature set by the user.

The control loop is thus based on the temperature estimate derived starting from the voltage and current readings. The resistance value is calculated from these two quantities and the surface temperature of the grill is estimated by means of an appropriate conversion table or a mathematical formula. This temperature value is thus used in the feedback loop to increase or decrease the power supplied to the heating element to minimize the error between the temperature set by the user and the estimated temperature.

The aforementioned data tables are produced in the initial set-up step, during which a sort of thermal mapping of the heating element 12 is carried out by varying the supply voltage and current of the electrical resistor R 13 and verifying the temperature reached by means of a thermal probe applied to the casing of the heating element 12.

The collected data are then interpolated to derive, for example, a fitting polynomial which represents the thermal behavior of the heating element 12 through the trend of the instantaneous temperature value as a function of the instantaneous value of the electrical resistor R 13 inside the heating element 12.

Known techniques designed to determine the function f(x) which minimizes the error between the estimated temperature T and the temperature T measured at the surface of the heating element 12 can be used to calculate the fitting polynomial required to match a resistance value R to a temperature value T.

The goal can be achieved, for example, by calculating the coefficients of the polynomial of order X which solve the following equation:

T = minfjV)

T = C_o + C xR + C₂XR² -I - 1- C_nxRⁿ with n degree of the identified polynomial. Substantially, an attempt is made to establish the fitting polynomial which best approximates the temperature curve measured at the surface of heating element 12.

For example, available tools, such as the Matlab environment, can be used to estimate the coefficients of the sought polynomial of order X.

By creating appropriate scripts in the Matlab environment, it is possible to obtain the time-aligned vectors of T (temperature) and R (resistance) from the log files of the measurements made in empirical manner. The log files can be provided in Microsoft xlsx format, among other acceptable formats, but with the use of appropriate compatible acquisition boards, the data can also be acquired directly in the Matlab environment.

Once the data have been made available and appropriately filtered, the “Basic Fitting” tool can be used, which draws the calculated fitting curve in real-time within a graph, also showing the residuals and the equation of the curve used. The derived mathematical equation, usually a polynomial of a degree greater than prime which expresses temperature as a function of resistance, is then used to calculate T starting from the measurements of R.

Accompanying Fig. 4 shows a graph comparing the measured temperature of the heating element 12 with the temperature calculated by the device according to the present invention. The choice of an appropriate fitting polynomial allows the error to be minimized to the desired degree of approximation over the range of interest.

Accompanying Fig. 2 and 3 show another preferred embodiment of the present invention. In this preferred embodiment, the heating element 12 comprises an additional resistive wire 17 integrated in the same structure as the electrical power resistor but electrically insulated from the latter.

This embodiment makes it possible to estimate the temperature of the power resistor R 13 inside the heating element 12 and then derive the external temperature of the heating element itself by measuring the supply voltage and current - and thus the resistance - of an additional resistive wire 17 inserted appropriately inside the heating element 12. In an embodiment of the invention, this additional resistive wire 17 can also be electrically insulated and powered separately with respect to the main resistive wire 13 of the heating used for heating.

This embodiment has additional advantages. It allows the temperature to be monitored even when the power part of the heating element 12 is not powered, and, furthermore, the additional resistive wire 17 is powered at low voltage allowing the use of a simplified, less expensive measurement circuit with fewer problems regarding possible device certifications.

In further detail and with reference to accompanying Fig. 3, the device according to the invention further comprises a voltage conversion module 18 adapted to supply voltage and current to the additional resistive wire 17. This voltage conversion module 18 can be made simply with a transformer or with an electronic voltage regulator according to known modes.

Said voltage 10 and current 11 reading modules are connected to the additional resistive wire 17 and provide the readings taken to the control module 15. Based on the aforesaid current and voltage readings and the settings provided by the user through the user interface 14, said control module 15 drives the power supply control module 16 of the supply voltage of the resistor R 13 of the heating element 12 to obtain a supply current value of the resistor R 13 corresponding to a temperature of the heating element casing 12 equal to the temperature set by the user. This embodiment of the invention, which is the subject of the present description, allows the temperature of the heating element 12 to be monitored also when it is not powered; furthermore, the additional resistive wire 17 is powered at low voltage, resulting in a simplified and thus less expensive measurement circuit as well as with easier certification according to current safety standards.

The device thus described resolves the described shortcomings of the prior art and introduces a heater in which the working temperature can be precisely set during operation.

Furthermore, the device according to the present invention, by continuously monitoring the current and voltage of the resistor 13 of the heating element 12, can offer early detection of malfunctions related to, for example, deterioration of the resistor R 13 or the dielectric of the heating element 12. The control module 15 can be provided with intervention thresholds, related, for example, to the measurement of the voltage or current of resistor R 13, at which an alarm signal can be generated or the power supply to resistor R 13 can be interrupted before a more serious failure occurs.

Claims

1 . A control device for a heating element (12) which includes at least one electrical resistor comprising: a reading module (10) of the supply voltage of the at least one electrical resistor; a reading module (11 ) of the supply current of the at least one electrical resistor; a user interface (14) for setting the temperature of the heating element (12); a control module (15) and an adjustment module (16) of the supply voltage of the at least one electrical resistor, the control module (15) being adapted to drive said adjustment module (16) based on the setting of the temperature of the heating element (12) and the reading of the supply voltage and the supply current values of the at least one electrical resistor, operated by said voltage reading module (10) and said current reading module (11 ).

2. A control device according to claim 1 , characterized in that said at least one electrical resistor comprises a first electrical resistor (13) and said reading module (10) of the supply voltage, said reading module (1 1 ) of the supply current, said power supply voltage adjustment module (16) are associated with said first electrical resistor (13).

3. A control device according to claim 1 , characterized in that said at least one electrical resistor comprises a first electrical resistor (13) and a second electrical resistor (17), said reading module (10) of the supply voltage, and said reading module (11 ) of the supply current are associated with said second electrical resistor (17), said power supply voltage adjustment module (16) is associated with said first electrical resistor (13).

4. A control device according to claim 3, characterized in that it further comprises a voltage conversion module (18) adapted to supply voltage and current to said second electrical resistor (17).

5. A control device according to one or more of claims 3 to 4, characterized in that it further comprises a voltage conversion module (18) adapted to supply voltage and current to an additional resistor (17) of said heating element (12).

6. A control device according to one or more of claims 1 to 5, characterized in that said control module (15) comprises at least one microcontroller and a memory on which program instructions and data tables are stored which bind pairs of supply voltage and current values of the resistor R (13) to temperature values of the outer casing of the heating element (12). A control device according to one or more of claims 1 to 6, characterized in that said control module (15) is adapted to control intervention thresholds relative to the measurement of the voltage or current of the resistor R (13), upon the reaching of which either an alarm signal is generated, or the operation of the resistor R (13) is interrupted. A control device according to one or more of the claims from 4 to 7, characterized in that said voltage conversion module (18) comprises a transformer. A control device according to one or more of the claims from 1 to 8, characterized in that said adjustment module (16) comprises an ON/OFF switch. A control device according to one or more claims from 1 to 8, characterized in that said adjustment module (16) comprises an electronic regulator of the power supplied to the electrical resistor (13). A heater comprising a heating element (12) and a control device according to one or more of claims from 1 to 10. A grill for cooking food or heating water comprising at least one heating device according to claim 11 .