WO1989012947A1 - Four a electrode a haute frequence a commande de puissance - Google Patents

Four a electrode a haute frequence a commande de puissance Download PDF

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Publication number
WO1989012947A1
WO1989012947A1 PCT/US1989/002627 US8902627W WO8912947A1 WO 1989012947 A1 WO1989012947 A1 WO 1989012947A1 US 8902627 W US8902627 W US 8902627W WO 8912947 A1 WO8912947 A1 WO 8912947A1
Authority
WO
WIPO (PCT)
Prior art keywords
foodstuff
oscillating
electrode
electrodes
recited
Prior art date
Application number
PCT/US1989/002627
Other languages
English (en)
Inventor
Lucas A. Butot
J. W. Deruiter
Original Assignee
Ifo Kampri B.V.
Malikian, Charles, L.
Malikian, Armen
Franks, Paul
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/207,561 external-priority patent/US4978826A/en
Application filed by Ifo Kampri B.V., Malikian, Charles, L., Malikian, Armen, Franks, Paul filed Critical Ifo Kampri B.V.
Priority to EP89908335A priority Critical patent/EP0422123B1/fr
Priority to DE68928898T priority patent/DE68928898T2/de
Priority to KR1019900700343A priority patent/KR900702749A/ko
Publication of WO1989012947A1 publication Critical patent/WO1989012947A1/fr

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/46—Dielectric heating
    • H05B6/62—Apparatus for specific applications
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/46—Dielectric heating
    • H05B6/48—Circuits
    • H05B6/50—Circuits for monitoring or control

Definitions

  • This invention relates to an improved device for heating a product, and particularly for heating foodstuff, by dielectric high frequency heating utilizing a power tube and an oscillating circuit, and particularly to improvements in such a device providing for increased power transfer to the foodstuff without requiring increased power and voltage ratings for the power tube and, still further, to such devices including multiple support levels therein for heating commercial quantities of food.
  • Prior art devices for heating and cooking of foodstuff are known. However, such devices are typically limited in the volume of the foodstuff which may be heated or cooked thereby, thus precluding commercial applications of such prior art devices.
  • the known prior art devices utilize oscillating circuits requiring power tubes which are specially designed therefor.
  • the prior art oscillating circuits generally provide a substantially fixed distribution of voltage and power within the heating cavity. Thus, longer heating or cooking times are required for heating or cooking greater volumes of foodstuff. Further, the prior art devices operate at frequencies which are strongly dependent on the characteristics of the foodstuff being cooked.
  • prior art high frequency cooking cavities are known to include a vertical stacking facility, thus permitting heating of multiple levels of food within a single cavity, only a single pair of electrodes is provided for transferring the electromagnetic energy to the heating (or cooking) cavity.
  • a single pair of electrodes is provided for transferring the electromagnetic energy to the heating (or cooking) cavity.
  • Yet another object of the invention is the provision of a plurality of separate load electrodes for the foodstuff, the electrodes connected between different oscillating circuits, thus minimizing the effect of different dielectric characteristics of the foodstuff on the frequencies of the oscillating circuits .
  • An additional object of the invention is to establish the electrodes of the pair of oscillating circuits to radiate an open electromagnetic field therebetween, while connecting electrodes from different oscillating circuits as plates of a load capacitor, radiating an open electromagnetic field through the foodstuff at a power intensity determined by the dielectric characteristics of the foodstuff, thus providing differing energy levels for different foodstuffs while maintaining substantially constant power level operation of the power tube.
  • Yet another object of the invention is to structure the electrodes of the oscillating circuits as supports for trays containing the foodstuff, wherein an air gap between the electrodes and the trays is provided for controlling the energy delivered to the foodstuff.
  • Still another object of the invention is the provision of a multi-level heating structure in a high frequency dielectric oven, including therein separate pairs of electrodes to form a separate load capacitor for each of a plurality of vertically displaced heating levels within a cavity of the oven.
  • an improved high-frequency dielectric oven for cooking foodstuffs is provided.
  • a power increasing device is provided in addition to the known components of such ovens, which include a cavity for receiving the foodstuff when cooking, a high frequency oscillating circuit, including a power tube, for generating a high frequency electric signal and an electrode arrangement for introducing an electric field into the cavity to transfer power from the oscillating circuit to the foodstuff.
  • the power increasing device is broadly operable for increasing the power transferred from the oscillating circuit to the foodstuff, without increasing the operating voltage of the tube or the frequency of operation thereof .
  • the foodstuff is positioned between plates of a capacitor in the oscillating circuit.
  • the oscillating circuit is arranged to provide a voltage across the capacitor which is twice the voltage across the power tube, thus to permit doubling the distance between the plates of the capacitor without diminution of the field strength therebetween, and to increase the quantities of food which may be heated between the capacitor plates.
  • the power increasing device includes a plurality of oscillating circuits having substantially identical resonant frequencies.
  • the oscillating circuits receive power from the power tube to establish respective oscillating signals therein.
  • a phase setting structure is connected to the oscillating circuits for establishing a predetermined phase relationship between pairs of the oscillating signals .
  • the electrode arrangement includes at least first and second electrodes which are respectively connected to the two oscillating circuits. The first and second electrodes are located in the cavity and include the foodstuff therebetween.
  • the electrode arrangement includes at least first and second electrode pairs within the cavity for including the foodstuff therebetween.
  • Each oscillating circuit has two electrodes, and each electrode pair has first and second electrodes, which are respectively connected to the first and second oscillating circuits.
  • the phase setting structure includes a phase reversing configuration for establishing a 180° phase shift between oscillating signals in the first and second oscillating circuits.
  • the phase setting structure is operable for doubling a peak value of an oscillating signal voltage applied across each electrode pair, relative to a peak value of a signal voltage applied thereto by a single oscillating circuit.
  • the phase reversing configuration includes a connector between a first electrode of the first electrode pair and a second electrode of the second electrode pair, thereby establishing voltages on the two electrodes of the first electrode pair which are 180° out of phase with one another.
  • the connector further establishes a similar relationship between the voltages on the first and second electrodes of the second electrode pair.
  • the connector provides the only connection between one of the two oscillating circuits and the power tube.
  • Each of the oscillating circuits includes an inductance and a capacitance, the capacitance including a pair of capacitors respectively formed between the two electrodes of the oscillating circuit and wall portions of the cavity.
  • the two electrodes of each oscillating circuit are oriented to radiate an open electromagnetic field therebetween.
  • the electrode pairs form a pair of interconnecting load capacitors between the electrodes of the first and second oscillating circuits.
  • the dielectric of the load capacitors includes the foodstuff placed therein.
  • Such an arrangement thus radiates an open electromagnetic field between the electrodes of each of the pair of interconnecting (load) capacitors.
  • the open electromagnetic field has a power intensity distribution determined by the dielectric characteristic of the foodstuff, while permitting the power tube to operate at a substantially constant power level.
  • the use of the load capacitors as connectors between the two oscillators isolates the frequency of oscillation of the oscillating circuits from the effects of the dielectric characteristics of the foodstuff.
  • both the power intensity and the frequency of the power transferring signals are maintained more nearly constant, with reduced variations caused by the dielectric characteristics of the foodstuff being cooked.
  • a variable air capacitance is included between the electrodes of the interconnecting capacitors and the foodstuff therebetween, for controlling the cooking power applied to the foodstuff within the load capacitors.
  • the connector between the opposing electrodes of the two electrode pairs which establishes the 180° phase shift between the signals of the first and second oscillating circuits, thereby establishes a virtual ground plane between the first and second electrodes of each of the load capacitors.
  • a feedback electrode is used for providing a control voltage to a grid of the power tube.
  • the feedback electrode is located between a predetermined electrode of one of the oscillating circuits and one of the wall portions of the cavity, i.e., within one of the capacitors determining the oscillating frequency of the oscillating circuit.
  • the voltage divider may be formed of a pair of separate ceramic capacitors, placed externally of the heating cavity.
  • an improved high-frequency dielectric oven for cooking foodstuff includes a multi-level structure within the cavity, for supporting a plurality of vertical levels of foodstuffs therein.
  • the multi-level structure includes a separate pair of electrodes, each pair forming a separate load capacitor, for each vertical level in the cavity.
  • the plates of the separate load capacitors radiate separate high-frequency electromagnetic fields for each of the separate vertical levels.
  • the heat generated within the foodstuff as dielectric losses therein is also controlled.
  • the electrodes of the oscillating circuits are shaped for supporting a tray containing the foodstuff.
  • each of the electrodes includes a horizontal portion and a depending portion descending at a predetermined angle from the horizontal portion, thereby to provide support thereon for a tray having a horizontal lip and an angularly depending portion connecting the horizontal lip to a bottom portion of the tray.
  • the support configuration may particularly include first and second vertically displaced support structures for each of the capacitor plates.
  • the oven of the invention includes a subdivided multi-level structure, including a plurality of levels. Each of the levels has a separate load capacitor and each has a plurality of sub-levels, formed between the plates of the separate load capacitor thereof.
  • Figure 1 is a schematic diagram of the electrical circuit of the inventive high-frequency dielectric oven
  • Figure 2 is a front view of a structure embodying the invention showing the plural levels and sub-levels for heating food, formed by the capacitor plates thereof;
  • Figure 3 is a sectional view showing an enlarged detail of the electrode structure shown in Figure 2;
  • Figure 4a is a rear view of the structure of
  • Figure 2 showing the inductors of the two oscillating circuits and Figure 4b is a perspective view of the inventive oven, including the electrode structure shown in Figure 3;
  • Figure 5 shows a multi-level cooking arrangement for foodstuff in the inventive oven and illustrates a schematic arrangement of capacitor plates within the cooking cavity in accordance with the circuit diagram of Figure 1;
  • Figure 6 shows an arrangement of a tray, supported by the electrode structure of Figure 3, and a variable air gap capacitance used for power control for the inventive oven;
  • Figure 7 shows an alternate arrangement for the variable air gap capacitor control of Figure 6
  • Figure 8 shows an alternate embodiment of the invention including a modification of the circuit diagram of Figure 1, using a single oscillating circuit to provide an open electric field for heating food between the plates of the load capacitor;
  • Figures 9a and 9b illustrate and define closed and open electric fields, respectively;
  • Figure 10 shows the distribution of the open electric field produced by the embodiment of Figure 8.
  • Figure 11 shows the field distribution for the electric field produced by the embodiment of Figure 2.
  • Figure 1 is an electrical schematic diagram disclosing interconnection and operation of the electrical circuitry of the invention.
  • the electrical circuit illustrated in Figure 1 generates a high frequency field for penetrating the foodstuff (or other product) disposed between electrode plates of at least one load capacitor.
  • the generated field is an electromagnetic field, because the dimensions of the oven cavity are small in comparison with the wavelength (40 cm compared with 8.6 meters), the magnetic component of the field may be neglected. Accordingly, the following description refers to the energy field as an electric field, rather than an electromagnetic field.
  • the high frequency electric field generated by the heating device undergoes dielectric losses within the product, thus causing heating of the same.
  • the product, or foodstuff, being heated may be enclosed in a cooking utensil and/or tray, formed of porcelain, glass, ceramics, polycarbonate materials or the like. While the specific material of the utensil is not significant, such trays, pans and the like are known to be made of non-conducting materials having low dielectric losses.
  • the high frequency field generating portion of the circuit is generally shown at 10. As is known to those skilled in the art, high frequency signals of the type generated in the generating portion 10 may interfere with external devices.
  • an enclosure 12 (or Faraday cage) is provided, for retaining the radiated high frequency energy within the high frequency oven structure.
  • a three-phase power supply is contemplated, as indicated by the plurality of power supply leads shown at 14.
  • a high voltage, three-phase, transformer 16 is provided for converting a 380 volt input voltage to 3 kV output voltage.
  • a plurality of fuses are connected to the primary winding of transformer 16 to provide overload protection for the high voltage transformer.
  • the high voltage output provided by the secondary winding of transformer 16 is connected to a rectifying bridge, shown at 20, comprising a plurality of diodes arranged in a manner well known to those of ordinary skill in the art. Accordingly, the details of the rectifying bridge are not described herein. It will be appreciated that, although a three-phase alternating current power supply is illustrated, the invention will also operate with other numbers of multiple phases, or with a single phase AC input, upon substitution of an appropriate rectifying bridge for the three-phase rectifying bridge 20. Similarly, if a sufficiently high level DC voltage is available, transformer 16 and rectifying bridge 20 may be eliminated.
  • a general purpose, communication type, power tube 22 for use in circuit with one or more oscillating circuits.
  • the circuit structure of the present arrangement eliminates a requirement for special purpose tubes used for high frequency generation in heating and cooking devices.
  • a tube such as type YD 1170, manufactured by Philips, is preferred for use in the present arrangement.
  • a pair of oscillating circuits, shown at 24 and 26, receive current pulses from the power tube 22.
  • each of the oscillating circuits generates an oscillating electrical voltage having twice the predetermined magnitude of the voltage swing across tube 22.
  • the present invention provides a voltage swing therebetween equal to two times the predetermined magnitude.
  • the rate of heat transfer to the foodstuff is increased by the increased voltage across the capacitor.
  • the increased voltage difference between the two plates of the load capacitor permits increasing the distance between the capacitor plates, without decreasing the field intensity therebetween. Accordingly, by increasing the space between the plates of the load capacitor the quantity of foodstuff which may be heated by the inventive oven is increased to commercial levels without reducing the field intensity and thus the rate of heat transfer thereto.
  • a single oscillating circuit also increases the voltage swing between the plates of the load capacitor above the voltage swing across the power tube.
  • the advantageous increase in spacing between the plates of the load capacitor may be attained by using one or two oscillating circuits.
  • Each of the oscillating circuits of Figure 1 includes an inductor and a pair of capacitors.
  • a junction point 28, between the capacitors of each oscillating circuit, is commonly connected to ground together with a cathode connection of the tube 22.
  • a control voltage for a grid 29 of tube 22 provides a feedback connection between oscillating circuit 24 and the grid 29. As shown in Figure 1, the feedback control voltage is obtained from a capacitive voltage divider 30 within the cooking cavity. The feedback control voltage is fed back from the voltage divider to grid 29 of tube 22.
  • the triode tube 22 and the oscillating circuit 24 together operate to provide a feedback Colpitts type oscillator operating at a frequency determined by the product of the inductance and capacitance within oscillating circuit 24.
  • the capacitive voltage divider is shown as part of the electrode structure positioned within the heating cavity of the oven, it should be appreciated that such a divider may be formed by using ceramic capacitors placed outside the oven cavity.
  • the current provided from an anode 34 of tube 22 is provided both to oscillating circuit 24 and to oscillating circuit 26.
  • the natural oscillating frequencies (resonant frequencies) of the two oscillating circuits are substantially the same.
  • a connector 36 which connects the upper terminal of an inductor 37 of oscillating circuit 24 to the lower terminal of an inductor 39 of oscillating circuit 26.
  • the two end points 38 and 40 of connector 36 are forced to have the same voltage thereat.
  • the oscillating signals in oscillating circuits 24 and 26 have the same phase at points 38 and 40.
  • the phase establishing connector 36 establishes a phase differential of 180° between the voltage at the point 42 and the voltage at the point 38.
  • the present invention includes a load capacitor between points 38 and 42.
  • the load capacitor shown at 44, includes a pair of electrode plates connected to points 38 and 42 of the two separate oscillating circuits, and defines an area, within the cooking cavity of the oven, for placement of the foodstuff to be heated.
  • a second load capacitor 46 is established intermediate the oscillating circuits 24 and 26, at the opposite ends of the inductors thereof. It will be appreciated that the voltage swing across capacitor 46 is equal to the voltage swing across capacitor 44.
  • the voltage swing across either capacitor is twice the peak-to-peak voltage swing of the oscillating signal in either of oscillating circuits 24 and 26. Further, the peak-to-peak voltage swing across the inductor of either circuit is twice the voltage swing across tube 22. Thus, the voltage swing across each of the load capacitors is twice the voltage swing across the anode and cathode of tube 22.
  • the loops of the two oscillating circuits 24 and 26 are separated from one another by the load capacitors 44 and 46.
  • the capacitance of the load capacitors is made less significant in determining the oscillating frequency for each of the two circuits.
  • the frequency of oscillation is thus determined substantially independently of the dielectric characteristics of the foodstuff placed between the plates of capacitors 44 and 46.
  • the frequency of oscillation of the two circuits remains substantially constant, independently of presence or absence of the product being heated within load capacitors 44 and 46 between the two circuits and substantially independently of the dielectric characteristics of such a product.
  • the DC high voltage supplied by rectifying bridge 20 is further filtered by filtering circuits generally shown at 48, including feed through capacitors and chokes, connected to both the anode 34 and grid 29 of tube 22.
  • Negative DC grid bias is established on grid 29 by a biasing resistor 50.
  • the grid current may be measured by an ammeter 52 for display on the front panel of the inventive oven.
  • an ammeter 54 is shown for measurement and display, as desired, of the anode current.
  • a potentiometer 56 is provided for adjustment of the maximum anode current.
  • a coil winding of a relay 58 provides overload protection.
  • a contact 60 thereof opens, thus removing power from the winding of a second relay 62.
  • relay 62 controls switching of a contactor 64 which controls feeding of the power supply to the high voltage transformer 16.
  • the structure of Figure 1 further includes a filament transformer 66.
  • the filament transformer includes a plurality of secondary, or output windings.
  • a first output winding 68 provides a 5.8 output AC voltage supplied to heat the cathode of tube 22.
  • a second output winding 70 provides a 220 volt AC output voltage for the winding of a relay 72, which controls main contactor 64.
  • relay 72 is in series with a contact 74 of relay 62 as well as with a fuse 76, to provide protection for the circuit.
  • contact 60 of relay 58 disables relay 62.
  • Deenergization of relay 62 opens contact 74 to disable relay 72 and, ultimately, to open contactor 64.
  • the remaining portion of the control circuit for the inventive oven is supplied power by a third output winding 78 of the filament transformer 66.
  • the output of winding 78 is a 24 volt AC voltage, and is protected by a fuse 80.
  • relay winding 72 activates contactor 64 to turn on the oven.
  • Relay winding 62 which controls contact 74, is in turn controlled by a plurality of contacts reflecting occurrences of a number of conditions.
  • a lamp indicator 84 is energized to provide a display indicating supply of power to filament transformer 66.
  • a fuse 86 is provided to protect the filament voltage transformer as well as the cooling ventilator for the system .
  • a ventilator motor 88 in parallel with the primary winding circuit for filament transformer 66.
  • a thermal circuit breaker 90 is provided in series with the ventilator motor to provide appropriate protection therefor.
  • a relay winding 92 is also provided in series with the circuit breaker and the ventilator motor.
  • the contact controlled by relay winding 92 is shown at 94 and is in series with the winding of a further relay 96 used to control switching and activation of the high voltage transformer 16.
  • One contact of relay 96 is shown at 98 and is in series with the primary winding of the filament transformer 66.
  • main switch 82 On normal operation main switch 82 is closed to activate the filament transformer 66. With relay 96 energized, a second contact thereof, shown at 100, is closed. This contact is in series with fuse 80 and these two components, together, are in series with the remaining control circuit supplied by the third output winding 78. A further safety measure is provided in the form of a door switch contact 102 which is also in series with fuse 80 and contact 100. Thus, when the main switch 82 and the door switch 102 are closed and an overload condition does not exist on the ventilator, power is supplied to the various relays, switches and indicators connected to the third output winding of the filament transformer.
  • the following description illustrates how control of the heating function may be manually or automatically established.
  • a manually operated, normally open, ON switch 104 and a manually operated, normally closed, OFF switch 106 Upon momentary activation of ON switch 104 and of a further manually operated switch 108, power is supplied to energize the winding of a latching relay 110, thus closing contact 112 thereof and permitting switch 108 to be opened again without loss of power to the winding of relay 110. Provision of power to relay winding 110 also energizes a lamp indicator 114 to indicate that the oven is under manual control. At this time, a second contact of relay 110, labeled 116, is closed to energize relay winding 62, thus closing contact 74 thereof and energizing relay winding 72, to close main contactor 64 and energize the high voltage transformer 16. At the same time, energization of winding 72 also results in closure of a second contact thereof, labeled 118, permitting reopening of the momentary switch 104.
  • a timer switch 120 may be activated.
  • power is supplied to relay winding 62 by movement of a contact arm 122 of timer switch 120 to its lower position, rather than by closure of contact 116 of relay winding 110.
  • the lamp indicator 114 is not energized.
  • contact 74 is closed thus energizing relay winding 72 and closing contactor 64 to supply power to transformer 16, initiating operation of the oscillating circuits.
  • contact 118 will also be closed at this time, thus permitting switch 104 to be deactivated.
  • normally closed OFF switch 106 may be manually operated to remove power from the winding of relay 62.
  • contact 74 is caused to open, deenergizing relay 72 and opening contactor 64, to disconnect the primary winding of transformer 16 from the power source and turning off the oscillating circuit.
  • control circuit illustrated in Figure 1 provides either manual or timed operation of the oscillating circuits, and thus of the inventive oven.
  • manually operated switches and relays are illustrated, it should be understood that various solid state circuits, switching devices, flip flops or the like may be used instead.
  • the functions hereinabove described may be carried out by a programmed computer in response to activation of various input keys of a keyboard or other input switches, or by other semiconductor circuits similarly responding to operation of input keys or switches .
  • Figure 2 there is shown a structure incorporating the various circuits, electrodes, and controls hereinabove described with reference to Figure 1. More particularly, there is shown a front view of a housing 124 and a heating cavity 126. On a front panel of the housing, a clock display 128 shows time-of-day or the heating time associated with timer switch 120.
  • a number of contact switches 130 are provided for operator use, and provide the various switching and control functions hereinabove described.
  • the electrode plates of the load capacitors are mounted by means of respective flat mounting portions 132 thereof to an insulated back wall 131 of the cavity.
  • the capacitor plates further include portions mounted to the insulated sidewalls 133 of cavity 126.
  • Plates 134 and 136 which form the electrodes of load capacitor 44, also form the upper plates of fixed capacitors 137 and 139, shown in Figure 1, which form the oscillating circuits 24 and 26 with respective inductors 37 and 39.
  • the lower plates of capacitors 137 and 139 are commonly grounded at point 28, as shown in Figure 1. Accordingly, a grounded portion of housing 124, shown at 140, forms the common ground point 28, as well as the lower capacitor electrode plates for capacitors 137 and 139. Portion 140 may be electrically connected to the housing 124.
  • electrode plate 134 (circuit point 38) is required to be connected (via a blocking capacitor) to the anode 34 of tube 22.
  • a connector 142 is shown in Figure 2 for providing the required connection.
  • the electrode plates of load capacitor 46 are shown at 144 and 146. These electrodes, similarly to electrodes 134 and 136, form bottom capacitor plates of capacitors 147 and 149, in oscillating circuits 24 and 26, respectively. Since capacitor 149 is formed between electrode plate 146 and ground, housing portion 140 also forms the upper plate of capacitor 149 of Figure 1.
  • the upper plate of capacitor 147 is required to be connected, via a blocking capacitor, to grid 29 of tube 22, there is shown yet another connector 148 to provide the required connection.
  • connector 148 is embedded in the insulated sidewall 135 of cavity 126, to provide both the upper plate of capacitor 147 and the bottom plate of capacitor 150 of Figure 1.
  • the insulated walls 135 of the cavity form the dielectric for capacitors 137, 139, 147, 149 and 150.
  • other dielectrics may be used, separate and apart from the insulated walls 135 of the cavity.
  • individual dielectric components may be used with each capacitor.
  • connector 36 connects circuit points 38 (electrode plate 134) and 40 (electrode plate 146) in order to establish the appropriate phase relationship between the voltages across the load capacitors.
  • the inventive structure provides two sets of electrodes, for two load capacitors at two stacked heating levels. Moreover, each of the electrode plates includes a pair of sublevels, defined by the positioning and shaping thereof. This aspect of the invention will be appreciated upon reference to Figure 3, which shows a sectional view of an enlarged portion of the arrangement in Figure 2.
  • electrode plates 134 and 144 each have upper and lower elements, 133a, 133b and 144a and 144b, respectively. Each element has horizontal and inclined portions. These portions are shaped to accommodate a lipped tray 152, shown in Figure 2. As seen in Figure 2, such a tray may have an upper horizontal flange, or lip, and sloping sides. By shaping the electrode plates as shown in Figure 3, the tray may rest directly on the electrodes or may otherwise be accommodated thereby.
  • Figure 3 further shows connector 142 as providing the anode connection for circuit point 38 in Figure 1, through a blocking capacitor to the anode of tube 22.
  • connector 148 and the extension thereof are shown as being embedded within the dielectric sidewall 135.
  • the extension of connector 148 may be in the form of a flat element attached thereto, to form the appropriate capacitor 147 denoted by arrow "b" in Figure 3.
  • a teflon grommet 154 is used to mount connector 148 to the conductive, grounded, portion 140 o ⁇ housing 124 in an insulated manner.
  • the flat portion of connector 148 by being separated from grounded portion 140 by a dielectric portion 135, forms capacitor 150 therewith, and is denoted by arrow "a" in the figure.
  • the illustrated structure accordingly provides the capacitive voltage divider 30 previously described.
  • the capacitive voltage divider may be constructed by connecting in series a pair of ceramic capacitors, for example, between electrode plate 144 and ground, and by connecting the point intermediate the two capacitors to grid 29.
  • housing 124 The remaining portions of the control circuit, the transformers, ventilators, contact switches and relays of Figure 1 are enclosed within housing 124.
  • FIG 4a there is shown a rear view of housing 124, broken away to illustrate the arrangement of the load capacitors with inductors 37 and 39.
  • inductor 37 connects electrode plate 134 of load capacitor 44 to electrode plate 144 of load capacitor 46.
  • Inductor 39 connects electrode plate 136 of load capacitor 44 to electrode plate 146 of load capacitor 46.
  • the inductors are positioned externally of cavity 126, to increase the amount of space available for heating of foodstuff.
  • the inductors may be connected to the flat mounting portions 132 of each of the electrode plates by passage of a conductor therebetween, via teflon grommets of the type previously described with reference to Figure 3.
  • Electrodes 136 and 146 are seen to be mounted on insulated sidewall 135 of the cavity, providing four stacked sub-levels for heating foodstuff.
  • the sub-levels are arranged as two sets of sub-levels, each set including a separate set of electrodes therefor.
  • the grounded electrode plates of capacitors 137, 139, 149 and 150 are seen to be separate conductive plates, each grounded to the housing 124. Separate trays are shown in a vertically stacked arrangement, with trays at each separate level being located within a separately generated electric field. While the illustrated structure connects the separate capacitors of the different levels to the same power tube and to the same oscillating circuits, it should be appreciated that separate oscillating circuits may be provided for each level, whether connected to the same or different power tubes. For each such arrangement, separate power controls may be provided for each of the levels.
  • FIGs 6 and 7 there is shown a manner of controlling the dielectric losses generated within the foodstuff. More particularly, in the arrangement of Figure 6 there are provided variable air gap capacitors between each of the electrode plates and the food tray. By providing an adjustable positioning device for variably spacing the tray 152 from the electrode plate, the air gap capacitance therebetween may be varied. In Figure 7, the tray is supported by a separate support plate 160. Similarly to Figure 6, however, variable gaps are provided between the tray and the capacitor plates. In the structure of Figure 7, the position of support plate 160 may be adjusted, either vertically or horizontally, in order to effect the desired variation in air gap capacitances.
  • Vf V * Ca / (Ca + Cf), where V is the voltage drop across the entire combination, i.e., the voltage between the capacitor plates .
  • the voltage developed across the foodstuff will be substantially invariant with the dielectric constant of the foodstuff.
  • any variation in power dissipation within the foodstuff will result in variation of the relative distribution of power between the air gap control capacitor and the foodstuff capacitance, while maintaining invariant the total voltage across the load capacitor.
  • the power dissipated by the power tube 22, and the rating thereof may be fixed substantially independently of the characteristics of the product being heated by the oven of the present invention.
  • FIG 8 there is shown an alternate embodiment of the invention, wherein only a single oscillating circuit is used.
  • a circuit of the type illustrated there is advantageously provided a voltage across the load capacitance which exceeds the voltage across the power tube, and which thus permits the heating of larger quantities of food thereby.
  • the circuit of Figure 8 is substantially identical to the high frequency generating portion of the circuit of Figure 1, with the exception of the absence of oscillating circuit 26, connector 36, and second load capacitor 46.
  • the circuit illustrated in Figure 8 provides a single load capacitance 44', driven by a single oscillating circuit 24', at a frequency determined by the inductance of inductor 37' and the capacitance of capacitor 137' and voltage divider 30'. Let it be assumed that the combined capacitance of capacitors 147' and 150', forming capacitive divider 30', is equal to the capacitance of capacitor 137'. Thus, the voltage drops across capacitors 147' and 150' are equal during a portion of the oscillating period when the tube current is zero.
  • the maximum voltage drop across the inductor 37' will be twice the maximum voltage drop across the tube 22, with the two voltages oscillating sinusoidally at a frequency determined by the capacitance of the tank circuit and the inductance of inductor 37'.
  • Adding the load capacitance 44' to the circuit does not change the above relationship between the magnitude of the voltages developed across inductor 37' and tube 22.
  • the capacitance of the load capacitor is directly connected across the inductor, the oscillation frequency will be dependent thereon. Nonetheless, the parallel connection between load capacitor 44' and the series combination of capacitors 137' and 30' means that the capacitance of load capacitor 44' is added thereto. If the capacitances of capacitors 137', 150' and 147' are sufficiently large relative to 44', then the frequency of oscillation will remain stable and independent of the dielectric coefficient of the foodstuff being heated.
  • Figure 9a illustrates an arrangement wherein an electric field exists only between the plates of a capacitor 162.
  • the electric field is represented by lines 164, which are confined to the area between the capacitor plates.
  • Such a circuit does not radiate electromagnetic energy.
  • Figure 9b shows a different arrangement of components.
  • the plates of the capacitor have been opened, as shown at 166 and 168.
  • Such a circuit radiates an electromagnetic field, which is not confined to the area between the radiating surfaces 166 and 168.
  • the field distribution represented by the lines 170 is defined as an open field.
  • Figure 10 there is illustrated a top view of the distribution of the electric field generated by the single oscillating circuit embodiment of Figure 8.
  • a closed electric field exists between the plates of capacitors 137', 150' and 147', while an open field is generated between the bottom plate of capacitor 146' and the top plate of capacitor 137', i.e., within the load capacitor 44'.
  • the distribution is nominally an open field distribution and some of the field lines terminate on the grounded portions of the housing, in fact the field lines simulate a closed electric field.
  • the dimension of the plates of capacitors 137', 150' and 147' along the cavity wall are doubled, in order to double the plate area of the load capacitor, thus to maintain the same capacitance thereof in order to permit the same spacing between the plates of the load capacitor. That is, since only a single oscillating circuit is used, the voltage impressed across the single load capacitor is equal to the voltage of a load capacitor of the double oscillating circuit. In order to provide the same power dissipation in the foodstuff, the load capacitance is doubled.
  • a disadvantage of the embodiment of Figure 8 is the requirement for doubling the plate areas of the capacitors, as well as a change in the field distribution from a distribution for the two oscillating circuit embodiment, described below.
  • FIG. 11 the field distribution for the embodiment of two oscillating circuits is illustrated. As shown therein, similarly to the distribution of Figure 10, there is provided a combination of a closed field between the plates of the circuit capacitors and an open field between the plates of the load capacitor. However, the field lines are seen primarily to be curvedly directed between the plates of capacitors along the same wall of the cavity.
  • the foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed, since many modifications and variations are possible in light of the above teaching. The embodiment was chosen and described in order best to explain the principles of the invention and its practical application, thereby to enable others skilled in the art best to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated therefor.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)

Abstract

Un four (124) diélectrique à haute fréquence utilise une pluralité de circuits oscillants (24, 26) que l'on fait fonctionner dans une relation de phase prédéterminée, afin de produire une répartition de tension supérieure dans un condensateur de charge (44, 66), permettant ainsi une augmentation de l'espace entre les plaques d'électrodes (134, 136, 144, 146) de condensation de charge (44, 46) afin de permettre l'utilisation du four (124) pour chauffer des quantités commerciales de produits alimentaires. Le champ électrique produit a une répartition réduisant au minimum le nombre de noeuds d'une onde stationnaire, réduisant ainsi les apparitions de points froids dans la cavité chauffante (126). On a prévu une pluralité de niveaux de plateaux, chaque niveau comportant une paire séparée d'électrodes (134, 136, 144, 146) produisant le champ électrique pour les plateaux. On peut façonner les électrodes (134, 136, 144, 146) pour qu'elles supportent directement les plateaux. L'énergie transférée au produit alimentaire est commandée par un condensateur à espace d'air variable et le tube de puissance (22) fonctionne à un niveau sensiblement constant, quelle que soit la puissance transférée au produit alimentaire.
PCT/US1989/002627 1988-06-16 1989-06-16 Four a electrode a haute frequence a commande de puissance WO1989012947A1 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP89908335A EP0422123B1 (fr) 1988-06-16 1989-06-16 Four a electrode a haute frequence a commande de puissance
DE68928898T DE68928898T2 (de) 1988-06-16 1989-06-16 Hochfrequenz-elektrodenofen mit leistungsregelung
KR1019900700343A KR900702749A (ko) 1988-06-16 1989-06-16 전원 제어장치를 구비한 고주파 전극 오븐

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US07/207,561 US4978826A (en) 1986-11-21 1988-06-16 High frequency oven with plural heating levels and an improved efficiency of power transfer
US207,561 1988-06-16

Publications (1)

Publication Number Publication Date
WO1989012947A1 true WO1989012947A1 (fr) 1989-12-28

Family

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PCT/US1989/002627 WO1989012947A1 (fr) 1988-06-16 1989-06-16 Four a electrode a haute frequence a commande de puissance

Country Status (6)

Country Link
EP (1) EP0422123B1 (fr)
KR (1) KR900702749A (fr)
AT (1) ATE175540T1 (fr)
AU (1) AU3878689A (fr)
DE (1) DE68928898T2 (fr)
WO (1) WO1989012947A1 (fr)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2671929A1 (fr) * 1991-01-18 1992-07-24 Thomson Tubes Electroniques Generateur de chauffage par haute frequence.
EP0552598A2 (fr) * 1992-01-21 1993-07-28 NPBI Nederlands Produktielaboratorium voor Bloedtransfusieapparatuur en Infusievloeistoffen B.V. Appareil pour souder des tubes médicaux en matière plastique
US5512737A (en) * 1994-05-09 1996-04-30 Henny Penny Corporation Oven liner for dielectric oven
US5541392A (en) * 1994-05-09 1996-07-30 Henny Penny Corporation Product tray for dielectric oven
US5556567A (en) * 1994-05-09 1996-09-17 Henny Penny Corporation System and process for controlling dielectric ovens
CN107734728A (zh) * 2017-11-08 2018-02-23 扬州快乐机械有限公司 一种物品加热设备

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69915466T2 (de) 1998-05-05 2005-01-20 Massachusetts Institute Of Technology, Cambridge Lichtemittierende polymere und vorrichtungen, die diese enthalten
EP2499505B2 (fr) 2009-11-10 2021-05-05 Goji Limited Dispositif et procédé de régulation énergétique

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US2401277A (en) * 1944-04-04 1946-05-28 Compo Shoe Machinery Corp Electrostatic heating apparatus
US2567983A (en) * 1946-12-19 1951-09-18 Wood Electro Process Company Method of drying lumber
US2765388A (en) * 1953-03-30 1956-10-02 Nat Cylinder Gas Co Apparatus for controlling oscillator grid drive
US3125656A (en) 1964-03-17 High frequency heating apparatus
US4119826A (en) 1977-04-04 1978-10-10 Champion International Corporation Dielectric heat generator
US4296298A (en) * 1978-06-12 1981-10-20 Raytheon Company Dielectric cooking apparatus
US4531038A (en) 1984-06-11 1985-07-23 Champion International Corporation Radio frequency dielectric heater
US4812609A (en) * 1986-11-21 1989-03-14 I.K. International B.V. Device for heating a product by means of dielectric high frequency heating

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US3386551A (en) * 1966-11-14 1968-06-04 Litton Business Systems Inc Method of and apparatus for using radio or high frequency energy to produce printed matter

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3125656A (en) 1964-03-17 High frequency heating apparatus
US2401277A (en) * 1944-04-04 1946-05-28 Compo Shoe Machinery Corp Electrostatic heating apparatus
US2567983A (en) * 1946-12-19 1951-09-18 Wood Electro Process Company Method of drying lumber
US2765388A (en) * 1953-03-30 1956-10-02 Nat Cylinder Gas Co Apparatus for controlling oscillator grid drive
US4119826A (en) 1977-04-04 1978-10-10 Champion International Corporation Dielectric heat generator
US4296298A (en) * 1978-06-12 1981-10-20 Raytheon Company Dielectric cooking apparatus
US4531038A (en) 1984-06-11 1985-07-23 Champion International Corporation Radio frequency dielectric heater
US4812609A (en) * 1986-11-21 1989-03-14 I.K. International B.V. Device for heating a product by means of dielectric high frequency heating

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2671929A1 (fr) * 1991-01-18 1992-07-24 Thomson Tubes Electroniques Generateur de chauffage par haute frequence.
US5286941A (en) * 1991-01-18 1994-02-15 Thompson Tubes Electroniques High frequency heating generator having an improved matching network between a tetrode amplifier and a resonant circuit
EP0552598A2 (fr) * 1992-01-21 1993-07-28 NPBI Nederlands Produktielaboratorium voor Bloedtransfusieapparatuur en Infusievloeistoffen B.V. Appareil pour souder des tubes médicaux en matière plastique
EP0552598A3 (en) * 1992-01-21 1993-09-08 Npbi Nederlands Produktielaboratorium Voor Bloedtransfusieapparatuur En Infusievloeistoffen B.V. Apparatus for sealing medical plastic tubing
US5512737A (en) * 1994-05-09 1996-04-30 Henny Penny Corporation Oven liner for dielectric oven
US5541392A (en) * 1994-05-09 1996-07-30 Henny Penny Corporation Product tray for dielectric oven
US5556567A (en) * 1994-05-09 1996-09-17 Henny Penny Corporation System and process for controlling dielectric ovens
US5651907A (en) * 1994-05-09 1997-07-29 Henny Penny Corporation Product tray for dielectric oven
CN107734728A (zh) * 2017-11-08 2018-02-23 扬州快乐机械有限公司 一种物品加热设备

Also Published As

Publication number Publication date
EP0422123A1 (fr) 1991-04-17
EP0422123B1 (fr) 1999-01-07
EP0422123A4 (en) 1991-10-30
ATE175540T1 (de) 1999-01-15
DE68928898D1 (de) 1999-02-18
DE68928898T2 (de) 1999-08-12
AU3878689A (en) 1990-01-12
KR900702749A (ko) 1990-12-08

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