Method for managing a microwave heating device and microwave heating device

Abstract

A method for managing a microwave heating device able to operate based on a first signal having a first fundamental harmonic frequency that is within the microwave range, wherein operation of the microwave heating device (1) is interrupted or modified when, inside the microwave heating device (1), the presence of a second signal is detected, the latter having harmonic components which have frequencies that are different from a fundamental harmonic frequency and an intensity higher than a critical reference value.

Claims

1. A method for managing a microwave heating device wherein the microwave heating device comprises: a heating chamber; a signal generator, the signal generator being of the solid-state type and being able to generate sinusoidal signals with a fundamental harmonic frequency within the microwave range; one or more radiating portions positioned in the heating chamber and supplied by the signal generator via a supply circuit, for radiating microwaves in the heating chamber; the signal generator and the supply circuit being settable according to multiple operating configurations, each operating configuration having its own fundamental harmonic frequency; the method comprising: a setting step in which the signal generator and the supply circuit are set according to a first operating configuration having a first fundamental harmonic frequency; and a supply step in which the signal generator generates a first signal with the first fundamental harmonic frequency, which is transmitted by means of the supply circuit, and, according to the first operating configuration, to the one or more radiating portions according to a forward direction of propagation that goes from the signal generator to the one or more radiating portions; and wherein, during the supply step, the method also comprises: a step of monitoring a second signal that propagates in the supply circuit according to a reflected direction of propagation that goes from the one or more radiating portions to the signal generator, and/or that is generated in the heating chamber; a step of detecting the intensity of one or more harmonic components of said second signal, which have a frequency higher than the fundamental harmonic frequency; a step of comparing the intensity detected with a critical reference value; and, when the comparison step indicates that the intensity detected is higher than the critical reference value, a safety intervention step in which the supply step is interrupted or in which the operating configuration is changed.

2. The method according to claim 1, wherein the supply circuit comprises a plurality of independent branches, each of which comprises a power amplifier connected to one or more radiating portions, wherein according to the method the monitoring and detecting steps are performed at each branch with reference to the intensity of only the second signal affecting the branch.

3. The method according to claim 1, wherein the critical reference value is equal to 5-10 times the intensity of a third signal that propagates in the supply circuit according to the reflected direction of propagation and/or that is generated in the heating chamber in a reference operating condition.

4. The method according to claim 1, wherein the monitoring step and/or the detecting step are carried out with reference to a signal proportional to the second signal or to one or more harmonic components of the second signal.

5. The method according to claim 1, wherein alternatively: the detecting step comprises detection of the intensity of only a second harmonic component; the detecting step comprises detection of the overall intensity of a group of harmonic components having a frequency higher than the fundamental harmonic frequency; or the detecting step comprises detection of the overall intensity of all of the harmonic components having a frequency higher than the fundamental harmonic frequency.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and the advantages of this disclosure are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of a microwave heating device, illustrated in the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of the overall layout of the microwave heating device, showing several of the most important elements;

(3) FIG. 2 is a block diagram of the power and control electronics of the microwave heating device;

(4) FIG. 3 is a schematic view of a signal generator, a control board and several power amplifiers of the microwave heating device; and

(5) FIG. 4 is a more detailed schematic view of several components of the electronic control board of FIG. 3.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(6) Below is a description first of the microwave heating device that forms the subject matter of this disclosure, and then the management method that, although not solely intended for this device, is advantageously implemented in operation of the device.

(7) With reference to the above-mentioned figures, the microwave heating device according to this disclosure was labelled with the numeral 1 in its entirety.

(8) As visible in FIG. 1, the microwave heating device 1 comprises first a heating chamber 2 in which a product 3 can be positioned (such as a food product 3 to be cooked, heated or defrosted), if necessary positioned on a suitable tray, even made of metal. In the chamber 2 there may be one or more supporting grids 4 for the product 3. Those supporting grids 4 may be made of metal material.

(9) The microwave heating device 1 also comprises a signal generator 5 that by means of a supply circuit 6 is connected to one or more radiating portions 7 positioned in the heating chamber 2 or in waveguides in turn connected to the heating chamber (embodiment not illustrated). The supply circuit 6 comprises at least one power amplifier 8 connected downstream of the signal generator 5. In use, the one or more radiating portions 7 are supplied by the signal generator 5 by means of the supply circuit 6 for radiating microwaves in the heating chamber 2. In FIG. 1, the signal generator 5 and the supply circuit 6 are schematically illustrated with a single triangle 9.

(10) FIG. 2 shows a more detailed block diagram of all of the main electric and electronic components of a microwave heating device 1 according to this disclosure. In this figure, for simplicity, all of the radiating portions 7 and the heating chamber 2 are schematically illustrated with a single block 10 in which the power signals coming out of the power amplifiers 8 meet.

(11) Therefore, generally speaking, as can be seen, the microwave heating device 1 comprises first a supply interface 11 that in use is connected to the electric mains network 12 from which it receives the energy needed in order to operate. The supply interface 11 may comprise various sections characterized by different electric output parameters (voltage and current), intended to supply all of the different elements of the heating device 1 that require an electricity supply.

(12) A control interface 13 in use allows the user to control operation of the heating device 1. The control interface 13 is connected both to a control board 14 of the microwave heating device 1, and to any sensors or detectors 15 associated with the heating chamber 2. Whilst in the embodiment illustrated the control board 14 is separate from the signal generator 5 (to which it is only connected), in other embodiments both the control board 14 and the signal generator 5 may be integrated in a single board that performs the functions of both.

(13) The control board 14 illustrated in FIG. 4 advantageously comprises a processing integrated circuit 16, which may be a microprocessor, a FPGA (currently the preferred choice as regards the processing speed), etc. and which is connected to a first DIN connector 17, to an RJ45 interface 19, and to two memory cards 20, 21 one Flash and the other DDRAM. The first DIN connector 17, in addition to a plurality of power supply voltages, carries at least four different types of signal (SPI; UART, GPIO I2C)

(14) As illustrated in FIG. 3, the first DIN connector 17 rigidly connects the control board 14 to the signal generator 5 (equipped with a second DIN connector 27 specular to the first 17), which is of the solid-state type and can generate sinusoidal (voltage) signals with a fundamental harmonic frequency within the microwave range, that is to say, within the range from 300 MHz to 300 GHz. However, preferably, the fundamental harmonic frequency of the sinusoidal signal lies within one of the ranges of the international standards for microwave heating, that is to say, ISM ranges: 433.050-434.790 MHz, 902.000-928.000 MHz, 2.400-2.500 GHz, 5.725-5.875 GHz, 24.000-24.250 GHz, 61.000-61.500 GHz, 122.000-123.000 GHz, 244.000-246.000 GHz.

(15) Depending on requirements, the signal generator 5 may be configured to generate either just one, or more, sinusoidal signals, each of which is then sent, by means of the supply circuit 6, to one or more power amplifiers 8. In the case illustrated in FIG. 2, in particular, the signal generator 5 is able to generate four first signals that are sent (preferably with predetermined phase differences from each other) to four power amplifiers 8 (it shall be understood that what is described here and below with reference to the four signals of the case illustrated, is scalable to any number of such signals).

(16) For that purpose, as is schematically illustrated in FIG. 3 which shows the generating part of the signal generator 5, the signal generator 5 comprises four generating circuits 28, preferably identical to each other, that are controlled by the control board 14 and that in use generate four signals that are identical in frequency and intensity (low), with a suitable phase difference from one another, or in phase with each other, depending on requirements. Those signals are made available at specific signal connectors 29. To guarantee optimum control of the relative phases of the four signals, one of the four generating circuits 28 is used as the master and supplies a master oscillation to the other three which are connected to it in series and which therefore operate as slaves. In fact, the master oscillation defines both an absolute phase reference for the others, and the system frequency.

(17) Therefore, in general, an electronic control unit 43 is connected to the signal generator 5 and to the supply circuit 6 for controlling their activation and setting them according to multiple operating configurations. As already indicated, each operating configuration has its own fundamental harmonic frequency and in use causes the generation of microwaves in the heating chamber 2. In particular, the electronic control unit 43 acts on the signal generator 5 in such a way that the latter generates one or more first signals that propagate towards the one or more power amplifiers 8 of the supply circuit 6 with suitable phase differences from each other. In the embodiment illustrated in the accompanying figures, the function of the electronic control unit 43 is performed by the processing integrated circuit 16 of the control board 14.

(18) The device 1 also comprises at least one monitoring circuit 32 associated respectively with the supply circuit 6 (as illustrated in FIG. 1) and/or with the heating chamber 2 (solution not illustrated). In the former case, the monitoring circuit 32 is designed in use to monitor a second signal that propagates in the supply circuit 6 according to a reflected direction of propagation, that is to say, a direction of propagation that goes from the one or more radiating portions 7 towards the signal generator 5. In the latter case, the monitoring circuit 32 is designed to monitor a second signal that is generated in the heating chamber 2.

(19) As already indicated, in the preferred embodiments, the monitoring circuit 32 comprises a coupler 33 which, if applied to the supply circuit 6, is advantageously of the directional type so that it is able to monitor exclusively the signal that propagates according to the reflected direction of propagation.

(20) Moreover, in general, at least one detecting circuit 41 is associated with the monitoring circuit 32 for in use detecting the intensity of one or more harmonic components of said second signal, which have a frequency higher than the fundamental harmonic frequency. In several embodiments the control board 14, more precisely its processing integrated circuit 16, may even directly act as the detecting circuit 41.

(21) Furthermore, at least one trigger circuit 42 is associated with the detecting circuit 41 for comparing the intensity detected (that of one or more harmonic components which have a frequency higher than the fundamental harmonic frequency) with a critical reference value. In general, the trigger circuit 42 is connected to the electronic control unit 43 for signaling to it when the intensity detected is higher than the critical reference value. In some embodiments, the control board 14, and more precisely its processing integrated circuit 16, may also perform the functions of the trigger circuit 42. In contrast, in the case schematically illustrated in FIG. 1, both the detecting circuit 41 and the trigger circuit 42 are independent of the processing integrated circuit 16. However, the trigger circuit 42 is connected to the processing integrated circuit 16 (that is to say, to the electronic control unit 43) for sending the latter a signal every time it ascertains that the intensity detected is higher than the critical reference value.

(22) The monitoring circuit 32, the detecting circuit 41 and the trigger circuit 42 are not described in detail herein, since they are in themselves conceptually known and within the reach of experts in the field.

(23) In turn, the electronic control unit 43 is programmed to act on the signal generator 5 and/or on the supply circuit 6 to interrupt their operation or to change the operating configuration when the trigger circuit 42 signals to it that the intensity detected is higher than the critical reference value.

(24) As already indicated, at least one of either the monitoring circuit 32 or the detecting circuit 41 also comprises at least one high-pass filter or one or more band-pass filters (generically identified with the block 44 in FIG. 1) able to eliminate a fundamental harmonic component, that is to say, the harmonic component whose frequency corresponds to the fundamental harmonic frequency (however, it should be noticed that a first attenuation of this fundamental harmonic component may also be caused by the coupler 33 of the monitoring circuit 32 which may appropriately be tuned only to the frequencies of the harmonic components of interest).

(25) Operation of the heating device 1 disclosed is similar to that of the prior art devices during operation without any type of electric discharges. The signal generator 5 generates the various signals with low intensity, transmits them to the one or more power amplifiers 8 which bring their power to the required level and then transmit the power signals to the radiating portions 7.

(26) In contrast, when either in the heating chamber 2 or in any other part of the supply circuit 6 an electric discharge 45 occurs, the harmonic components different from the fundamental one that propagates according to the reflected direction, are subjected to a sudden increase in intensity (in particular the second harmonic component), such that it can be identified by the trigger circuit 42 which can therefore warn the electronic control unit 43. The latter can then act on the operating configuration and prevent the discharge 45 from continuing. It should also be noticed that, in many operating conditions, an increase in the intensity of the harmonic components different from the fundamental one to the extent that it can be identified by the trigger circuit 42 may be caused by an actual electric arc or by transitory sparks which may occur during the process of ionization of the discharge channel 45. In the latter case, the electronic control unit 43 is able to act even before the actual arc begins.

(27) As already indicated, operation of the microwave heating device 1 according to this disclosure constitutes a particular case of implementation of the management method disclosed, which will be described in more detail below.

(28) In a more general form of it, the method disclosed is usable for managing any microwave heating device 1 that can operate based on a first signal having a first fundamental harmonic frequency within the microwave range. The first signal is that which, suitably amplified and if necessary divided into two or more signals with appropriate phase differences, is radiated in the heating chamber 2.

(29) In fact, the method comprises monitoring the presence in the heating device 1 of one or more second signals which have harmonic components with frequencies that are multiples of the first fundamental harmonic frequency (and higher than it), and checking whether such harmonic components have, jointly or individually, an intensity higher than a critical reference value. When that occurs, the method comprises interruption of operation of the microwave heating device 1 or modification of the operating parameters, if possible, to prevent an electric arc from being generated, or at least to interrupt it if it has already been generated.

(30) In particular, the method comprises monitoring a second signal that propagates in the supply circuit 6 according to a reflected direction of propagation, that is to say, a direction of propagation that goes towards a signal generator 5 of the microwave heating device 1 (for example, in the case of propagation along the supply circuit 6), or a second signal that is in any case present in the heating chamber 2.

(31) Depending on the embodiments, the intensity monitored and compared with the critical reference value may be that of just one of the harmonic components after the fundamental one (advantageously the second), or that of a group of harmonic components after the fundamental one (for example, between the second and the fifth, inclusive), or that of all of the harmonic components after the fundamental one.

(32) In a more specific embodiment of it, which is also reflected in the operation of the microwave heating device 1 described above, the method disclosed is applicable to a microwave heating device 1 that comprises a heating chamber 2, a solid-state signal generator 5 able to generate sinusoidal signals with a fundamental harmonic frequency within the microwave range, and one or more radiating portions 7 positioned in the heating chamber 2 and supplied by the signal generator 5 by means of a supply circuit 6, for in use radiating microwaves in the heating chamber 2. Moreover, the signal generator 5 and the supply circuit 6 can be set according to multiple operating configurations, each operating configuration having its own fundamental harmonic frequency within the microwave range.

(33) In this embodiment, the method comprises first a setting step in which the signal generator 5 and the supply circuit 6 are set according to a first operating configuration which has its own first fundamental harmonic frequency.

(34) Then comes a supply step in which the signal generator 5 generates a first signal with the first fundamental harmonic frequency. The first signal is transmitted by means of the supply circuit 6, and in accordance with the first operating configuration (that is to say, with predetermined intensity and phase values—the latter if there are two or more radiating portions 7), to the one or more radiating portions 7 according to a forward direction of propagation that goes from the signal generator 5 to the one or more radiating portions 7. The radiating portions 7 supplied in this way cause the microwaves to be radiated in the heating chamber 2. In FIG. 1 the arrows extending straight schematically illustrate several of the infinite directions of propagation/reflection of the microwaves in the heating chamber 2.

(35) During the supply step, the method also comprises the execution of further steps with the aim of preventing or interrupting any electric arcs. In particular, it comprises first a step of monitoring a second signal that propagates in the supply circuit 6 according to a reflected direction of propagation (that is to say, that goes from the one or more radiating portions 7 to the signal generator 5), and/or that is generated in the heating chamber 2. The second signal of interest is a signal that has harmonic components after the fundamental harmonic component (that is to say, that with a frequency equal to the frequency of the first signal). To effectively monitor that second signal, it is possible either to monitor the entire signal that either propagates along the reflected direction or is present in the heating chamber 2, or to selectively monitor only the harmonic components of interest of that second signal (for example, see what is described above concerning the use of couplers 33 tuned to specific frequencies, if necessary in combination with high-pass or band-pass filters) or only part of the entire signal or of the harmonic components of interest. In FIG. 1, the undulating arrow schematically illustrates the second signal generated by the electric discharge 45 (whether this is an actual permanent arc or an isolated spark) that radiates in the heating chamber 2 (in the form of an electromagnetic field) and towards the radiating portion through which it may further radiate in the supply circuit 6 (in the form of electric voltage).

(36) Then there is a step of detecting the intensity of said one or more harmonic components of interest (which have a frequency higher than the fundamental harmonic frequency), and a step of comparing the intensity detected in that way with a critical reference value.

(37) Finally, every time the comparison step indicates that the intensity detected is higher than the critical reference value, there is a safety intervention step in which the supply step is interrupted or in which the operating configuration is changed.

(38) When the supply circuit 6 comprises a plurality of independent branches, each of which is equipped with a power amplifier 8 connected to one or more radiating portions 7, in the method the detecting step may be performed at each branch with reference to the intensity of only the second signal affecting the branch.

(39) The critical reference value to be used in the detecting step must be set in such a way that it is sufficiently but not excessively higher than the intensity detectable with reference to the system background noise (at the harmonic frequencies of interest), so as to simultaneously avoid the risk of false detections of a discharge 45 and to keep the sensitivity of the system as high as possible. In general, the intensity of the system background noise monitored in normal operating conditions depends both on the natural non-linearity of the power amplifiers 8, and on the imperfect filtering of only the harmonic components of interest. Therefore, for practical applications, the intensity of the background noise, at the harmonic frequencies of interest, may conventionally be selected as equal to the detectable intensity of a third signal that propagates in the supply circuit 6 according to the reflected direction of propagation and/or that is generated in the heating chamber 2 in a reference operating condition of the microwave heating device 1. Preferably, that reference operating condition involves the device 1 operating at maximum power.

(40) The critical reference value is therefore preferably selected as equal to 5-10 times the value of the background noise (that is to say, with a 7-10 dB margin relative to the background noise).

(41) As is evident from the above description, this disclosure brings important advantages.

(42) In fact, thanks to what is provided, it is possible to prevent the formation of electric arcs in the microwave heating device 1 or at least, at worst, to minimize their duration.

(43) Finally, it should be noticed that this disclosure is relatively easy to produce and that even the cost linked to its implementation is not very high.

(44) The disclosure described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

(45) All details may be substituted with other technically equivalent elements and the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements.