Automatic Cooking Cycle Control System For Microwave Ovens

Abstract

A microwave oven is shown with a pair of antenna elements in the oven cavity for radiating microwave energy throughout the cavity. In different embodiments, the cavity is thermally heated via separate heaters and via the antenna elements. Programming controls establish predetermined cycles for microwave energy and thermal heat, and a control network selectively operates the magnetron and one or both heaters in the sequence determined by the programming controls. Program input apparatus is illustrated which includes pushbuttons and a card data reader for selecting different programs, and sequence control networks with timing and relay networks are illustrated for automatically cycling the microwave energy and thermal heating on and off for each program selected.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to microwave ovens.

2. Description of the Prior Art

The prior art includes microwave ovens which have means to select different microwave cooking times for different types of foods. One type of selector is a dial which is calibrated in terms of minutes and/or seconds. Another is a series of pushbuttons which have food-type designations, e.g., one pushbutton for pastries, another for vegetables, and so on. In both types, microwave energy is continuously injected into the oven cavity for the period of time that is selected. It is not possible at any setting to provide a cycle of spaced periods of microwave energy as needed or desired for various foods.

It was early recognized that in some cases it was desirable to also be able to thermally cook foodstuffs, and electric heating elements were installed in microwave ovens to be separately heated for this purpose. Such elements are also used to thermally cook some foodstuffs in conjunction with microwave cooking. For example, many meats which are cooked solely by microwave energy have an unappetizing appearance, and it is desired to overcome this objection by heating the elements so as to brown the meat surfaces to a desired color. A separate dial is provided for controlling the heating of such elements. It is not possible at any setting to provide cycles of predetermined microwave and thermal cooking operations desired for many foods. Due to the considerable variations in time scales for microwave and thermal cooking, the typical housewife finds it very difficult to schedule and combine the different types of cooking operations for satisfactory results.

Proper scheduling or cycling of microwave cooking and of microwave and thermal cooking is important for many types of foods in various conditions. Some foods, e.g., cakes and some meats, should have their outer surfaces sealed early in the cooking process, as at a high temperature before initiating microwave cooking, and it may be desirable to continue thermal heating during and/or after a period of microwave cooking.

Proper cycling is also important for thawing and cooking frozen foods, which initially contain ice crystals throughout. In prior art ovens designed solely for microwave cooking, the controls for a particular type of frozen food are set for a longer cooking time than for such food that is already thawed. To convert the ice crystals to water at 32.degree.32.degree. F. requires as much thermal energy as is required to raise water from 32.degree. F. to 180.degree.F. Accordingly, since crystals at any given depth of the food do not melt at the same rate, the unavoidable result of continuous microwave cooking is that the food at any depth is not uniformly cooked, e.g., as meat having well done and rare portions at the same depth.

To avoid the time-consuming technique of allowing frozen food to thaw at room temperature before cooking, one can subject it to microwave energy for a short period, allow a rest period for the heat thus generated to melt all the ice crystals, and then apply microwave energy as in cooking thawed food. In a microwave oven which also has electric heating means for conventional thermal cooking, thawing can be accomplished by selective operation of the electric heating means for conventional thermal cooking, thawing can be accomplished by selective operation of the electric heating means before applying microwave energy. However, microwave ovens as heretofore known do not permit cycling of microwave energy, or of microwave energy in conjunction with thermal energy, except by setting and resetting dials and pushbuttons in accordance with charts of detailed instructions, or by trial and error.

SUMMARY OF THE INVENTION

This invention embraces a microwave oven with programming and control means for automatically controlling the sequence and durations of application of microwave energy and thermal energy to foodstuffs in the oven.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a combined schematic and block diagram of an oven and a system of our invention for automatically controlling the introduction of microwave and/or thermal energy into the oven cavity;

FIG. 2 is a perspective view of a microwave oven with pushbutton controls and time-selector dial included in the program input apparatus of the system of FIG. 1;

FIG. 3 is a combined schematic and block diagram illustrating program input apparatus and a sequence control network for the oven of FIG. 2;

FIGS. 4a--4d are graphs illustrating different cycles programmed into the oven of FIG. 2;

FIG. 5 is a block diagram of program input apparatus in the form of a card data reader, and of timing and relay networks programmed to control the times and sequences of introduction of conventional heat and microwave energy into an oven; and

FIG. 6 is a block diagram of our system wherein the same elements are used both to heat and to radiate microwave energy into an oven.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Referring to FIG. 1, an oven cavity 10 is shown in which electric heater elements 12, 14 are located, such elements being adapted for connection to a current source 16 via a switching network 18 so that one or both of the elements can be heated. Also located in the cavity 10 are antenna elements 20, 22 which are connected to output probes 24, 26 from a waveguide feed 28. A magnetron 30 is shown with its input probe positioned to introduce microwave energy into the feed 28 for driving the antenna elements 20, 22 for radiating microwave energy throughout the cavity 10.

A microwave power control network 32 is shown coupled to the magnetron, and may include level control means for selectively effecting operation of the magnetron at one or the other of two energy levels, e.g., at full power or half power. A preferred means for controlling the operating power level of a magnetron is disclosed in the copending application of Helmut Boehm, entitled "Transformer Power Supply for Microwave Generators", Ser. No. 810,671, filed Mar. 26, 1969, and includes switching means in a split primary circuit of the power transformer for connecting one or a pair of secondary circuits to the anode of the magnetron.

The heater switching network 18 and microwave power control network 32 are operated from a sequence control network 40. The sequence control network 40 includes suitable timing and relay means to operate the switching network 18 and control network 34 for selectively energizing the heater elements 12, 14 and driving the antenna elements 20, 22 in a predetermined sequence. Operation of the control network 40 is programmed in accordance with the operation of program input apparatus 42.

The program input apparatus 42 includes any suitable means for establishing within the control network 40 desired sequences for the introduction of conventional heat and microwave energy into the cavity 10 and for selecting total cycle time. For example, and referring to FIG. 2, a microwave oven 44 has a number of pushbuttons 45--49, each designated for a particular cooking operation, here illustrated as "warm," "bake," "roast," "crisp," and "broil." In this example, each pushbutton when depressed sets up a different cycle within the control network 40 for the introduction of microwave and/or thermal energy into the oven cavity for predetermined fractions of the cycle. A rotatable knob 50 is provided as a time selector, with which to select the total time for any given cycle depending upon the quantity of food placed in the oven.

FIG. 3 illustrates the sequence control network 40 as including a timing network 52, relay circuits 54 connected between the timing network 52 and the heater switching network, and relay circuits 56 connected between the timing network and the microwave power control network. Each of the pushbuttons 45--49 may, for example, operate respective timers in network 52 for controlling relay circuits 54 to operate the heater switching network so as to connect one or both of the heater elements to the current source, and for controlling relay circuits 56 to operate the microwave power control network for establishing operation of the magnetron at desired power levels. The timers may be motor driven switching devices operable through respective relay paths to effect the desired operations, and the time selector 50 may be adapted to vary the speeds of the timing motors and thereby select cycle duration for a given type or quantity of food.

FIGS. 4a--4d are graphs which are illustrative of respective programs which are set up by operation of switch buttons 45--48. The "warm" cycle illustrated in FIG. 4a is set up by pressing pushbutton 45, and is one which is suitable for warming cooked foods and for thawing frozen foods. In this connection, the sequence of operations set up in the timing network 52 and relay circuits 54 is one in which the oven temperature is initially raised to a predetermined level, illustrated as 150.degree. F., such temperature being sensed by a suitable sensor in the oven. In FIG. 1 a thermostat 58 for this purpose is shown connected to the heater switching network 18 and sequence control network 40. In FIG. 3, the thermostat may be connected to the timing network 52, which is suitably adapted, e.g., as through self-holding relay means, to switch the timing devices into operation when the oven temperature reaches 150.degree.F. For such initial heating of the oven, the heater switching network 18 is operated in one example so that only one of the heaters 12, 14 is connected to the current source 16.

Upon the temperature of the oven reaching 150.degree. F., the microwave power control network is operated so that microwave energy from the magnetron 30 is introduced into the oven for predetermined periods at spaced intervals. In FIG. 4a, each such period is shown to be two-tenths of the selected cycle time, and the intervals between such periods are shown to be two-tenths of the selected time. In one example, the associated timing devices and relay circuits operate the microwave power control network so that the magnetron operates at half power. To prolong magnetron life, the filament transformer of the magnetron power supply may be left on, or it may be disconnected during generation of microwave energy and reconnected during the intervals between such periods, whereby to insure proper cathode temperature whenever the power transformer is coupled to the anode.

Also as illustrated in FIG. 4a, thermal energy is introduced into the oven for predetermined periods at spaced intervals. Here, the heater switching network is controlled so that the heater is connected to the current source for respective periods of one-twentieth of the cycle time, with adjacent periods being spaced by an interval of one-tenth of the cycle time.

In treating frozen foods by operations of the type illustrated in FIG. 4a, each type of energy to which frozen food is subjected is applied for short periods of time spaced by "rest" periods during which there is opportunity for heat generated within the body of the food to equalize. By appropriate selection of cycle time, all ice crystals are melted so that the food is completely thawed at the end of the cycle.

A conventional alarm 58 is operated at the end of any selected cycle time to notify the operator that the cycle is terminated. For warmed foods, the alarm signifies that the food can be removed and served. For precooked frozen foods, the alarm signifies that the food has been thawed, in which case the "warm" button can again be pressed to renew the cycle, at the end of which the alarm signifies that the food can be removed and served. For uncooked frozen foods, the alarm signifies that the food is thawed, and is ready to be cooked, as by pressing the "bake" button to bake a cake, or pressing the "roast" button or "broil" button to cook meat, etc.

In connection with FIG. 4a, it should be noted that we are here employing pulsed thermal energy and pulsed microwave energy. If desired, of course, a program can be established whereby warming or thawing can be effected by either form of energy along. For example, the timing and relay means in different examples alternately and simultaneously connect both heater elements to the current source for shorter periods and with greater intervals between periods, with the cycle time selected so that the desired warming or thawing is achieved thereby. Or, the microwave power control network may be controlled so that the magnetron operates at full power for shorter periods and with greater intervals between periods to achieve the desired warming or thawing.

Warming or thawing of foods in accomplished quickly with our invention. For example, by pulsing the heater element or elements on for 10 -second periods at intervals of 20 seconds, and operating the magnetron for 5 -second periods at intervals of 25seconds, an uncooked portion of frozen meat is satisfactorily thawed in 3 minutes. For thawing with thermal energy alone, such operations of the heater element or elements are preferably at greater intervals, e.g., 2 minutes, continued for a cycle time of 15 minutes in which each heater element is energized for a 10 -second period during the interval that the other is not energized. For thawing with microwave energy along, the magnetron is operated for longer periods, e.g., 10 seconds at intervals of 50 seconds, for a cycle time of 7 minutes.

The "bake" cycle illustrated in FIG. 4b, which is initiated by presenting pushbutton 46, is one in which thermal energy is introduced into the oven cavity to raise the oven temperature to a predetermined level, indicated at a range of 320.degree.--350.degree. F., and to maintain it within such range. A separate temperature sensor for this purpose is connected to the sequence control network 40 to initiate the "bake" cycle. For this cycle, the timing network and associated relay circuits control the microwave power control network so that the magnetron operates throughout the last half of the cycle.

For the "roast" cycle (FIG. 4c), the program is one in which the oven temperature is raised to and maintained at a higher level, indicated in the range 375.degree.--400.degree. F., and wherein microwave energy is introduced into the oven during the last seven-tenths of the cycle. For the "crisp" cycle (FIG. 4b), the program is again one in which thermal energy is introduced throughout the cycle, which begins when the oven temperature reaches a still higher level, indicated in the range 450.degree.--475.degree. F., but wherein microwave energy is introduced into the oven cavity during the first seven-tenths of the cycle, i.e., immediately upon the oven temperature reaching the desired level.

For broiling, only the top heater element 12 is connected to the current source when pushbutton 49 is pressed. In such case, the food is placed on a rack immediately below the heater element 12.

Our invention embraces any suitable cooperative program input and sequencing means for automatically applying microwave and/or thermal energy to an oven cavity in any desired sequence. For example, and referring to FIG. 5, the program input apparatus may include a card data reader 42' which is adapted to supply information signals or pulses to timing and relay networks 66, 68 that are connected to the current control network and magnetron power control network. The card data reader 42' may take any of various forms, depending upon the type of card employed and the manner in which recording data is recorded on the card. Examples are magnetic card readers for magnetic cards, electrical or photoelectrical readers for punched cards, and readers for sensing embossments on a card that are positioned and dimensioned in accordance with desired microwave and/or thermal heating periods. Still further, our invention embraces, the use of any suitable means for effecting the desired time sequencing, whether electrical, electromechanical or pneumatic. For electrical time delay means, our invention extends to the use of integrated circuits and the use of digital techniques with which to obtain time interval adjustments.

While the foregoing has been described with reference to a microwave oven that employs separate means for introducing microwave and thermal energy into an oven cavity, our invention is also adapted for utilizing common elements to introduce both types of energy into the cavity. Referring to FIG. 6, the cavity 10 is shown to include folded Calrod-type elements 70, 72, the ends of which are connected to the heater switching network 18, and intermediate portions of which are connected to the output probes 24, 26 of the waveguide feed 28. These are the types of elements disclosed in U.S. Pat. No. 3,320,396 of Helmut Boehm, entitled "Electronic Oven," issued May 16, 1967, and which are adapted to function as traveling wave antennas to radiate microwave energy throughout the oven when driven via a waveguide feed, and which are also adapted to be energized from a current source to radiate thermal energy into the oven. The sequence control network 40 controls the operations of the heater switching network 18 and the magnetron 30 in the same manner as previously described in the embodiment shown in FIG. 1.

FIGS. 1 and 2 illustrate means for creating airflow in the oven cavity. A cooling air source 60, which has its motor connected to the sequence control network 40, is positioned to force cooling air over the magnetron and into the waveguide feed, and the oven 44 (FIG. 2) has a plurality of openings 62 in its top wall. As taught in U.S. Pat. 3,440,386 of Helmut Boehm, entitled "Microwave Heating Apparatus," issued Apr. 22, 1969, such an arrangement is effective not only to cool the magnetron, but to force vapors to the exterior of the oven and to prevent moisture and food particles from entering the waveguide feed.

In our invention we are able to take advantage of such flow of cool air in the oven to aid in warming and thawing foods, and to prevent deterioration of uncooked frozen foods after they have thawed. In warming or thawing as above described, air entering the oven through the waveguide arms effects rapid cooling of the heater elements when they are disconnected from the current source. Accordingly, the termination of each period of heat radiation is more pronounced, whereby the ensuing rest interval has greater effect.

In thawing uncooked frozen foods, the cooling airflow may be continued after the thawing cycle is completed. In such case, the continued airflow cools the surface portions of the food sufficiently to prevent deterioration for a reasonable time after thawing, e.g., 1 hour, during which it is expected the food will be cooked as desired, e.g., by programming the sequence control network to bake a cake. For this purpose, we prefer to have separate programs for warming and thawing, e.g., respective pushbuttons for a warm cycle and a thaw cycle, or separate cards in which data for warm and thaw cycles are recorded. In such case, the warm cycle program is one in which the sequence control network operates the cooling air source throughout the cycle, and in the thaw cycle program the control network operates the air source for a predetermined time, e.g., 1 hour, after the thaw cycle is completed.

In another application of our invention, the food cooked by microwave and/or thermal energy is referenced to the temperature of the food. For this purpose, the temperature sensors described above may be constituted of probes inserted in the foods to be cooked. Such a probe is also adapted to function as a control element in the same manner as an oven thermostat. Such temperature sensors may be merely detectors, or they may be devices capable of generating signals which serve as additional data signals for controlling the starting and stopping of infrared and microwave radiations.

It should also be noted that our invention is applicable to an oven that is adapted for microwave heating either by radiating antennas inside the oven or by means for injecting microwave energy into the oven through openings in a cavity wall. Further, our invention is suitable for use in ovens which employ any suitable mode stirring devices.

It should also be noted that power conservation is an important advantage that is realized with our invention. In cycling microwave and/or thermal energy, the power expended is but a small fraction of that required to operate the magnetron continuously or to energize the heater elements continuously. This is important in geographical areas and various situations, e.g., mobile units such as house trailers, aircraft and ships, where there is limited power available for operating electrical and electronic equipment. In such circumstances, our invention permits an oven to be operated as desired with periodically applied microwave energy alone, with periodically applied thermal energy alone, or with periodic applications of both forms of energy in such a way that they are not applied simultaneously.

Claims

We claim:

1. In combination:

an oven;

means for introducing microwave energy into the oven;

means for thermally heating the interior of the oven;

control means coupled to said energy introducing means and said thermal heating means for controlling the operations thereof;

means for programming said control means to operate so as to cause said energy introducing means to introduce microwave energy into the oven for one of a plurality of periods within a predetermined time cycle, and to cause said thermal heating means to be operated for one of a plurality of periods within a predetermined time cycles, said programming means including means for effecting operation of said control means to cause either or both said energy introducing means and said thermal heating means to be operated on and off a plurality of times within a predetermined time cycle; and

means cooperatively associated with said programming means and control means for selectively establishing the duration of the time cycle over which said control means effects operations of said energy introducing means and said thermal heating means.

2. In combination:

an oven;

means for introducing microwave energy into the oven;

means for thermally heating the interior of the oven;

control means coupled to said energy introducing means and said thermal heating means for controlling the operations thereof; and

said control means including selector means selectively settable for one of a plurality of on and off sequences for said energy introducing means,

said control means including selector means selectively settable for one of a plurality of on and off sequences for said thermal heating means,

means for programming said control means including means to simultaneously set both selector means to one of a plurality of combinations of settings thereof and effect automatic on and off sequences of said energy introducing means and thermal heating means pursuant to respective settings of the selected combination, and means cooperatively associated with said programming means and control means for selectively establishing the duration of the time cycle over which said control means effects operations of said energy introducing means and said thermal heating means at the selected combination of settings.

3. In combination:

an oven;

means for introducing microwave energy into the oven;

means for thermally heating the interior of the oven;

control means coupled to said energy introducing means for controlling operations thereof, said control means including selector means selectively settable for one of a plurality of sequences of operation of said energy introducing means wherein the level of energy introduced into said oven is varied more than twice;

means for programming said control means including means to set said selector means to one of its settings and effect automatic operations of said energy introducing means to vary levels of energy introduced into the oven in the sequence corresponding to the selected setting of said selector means; and

means cooperatively associated with said programming means and control means for selectively establishing the duration of the time cycle over which said control means effects energy level changing operations of said energy introducing means at the selected setting.

4. The combination of claim 2, wherein said heating means includes a pair of heater elements spaced to receive an article of food between them, and wherein said programming means and control means are cooperative to effect operation of either heater element alone or both heater elements.

5. The combination of claim 4, wherein said programming means and control means are cooperative to effect operation of both heater elements simultaneously or alternately.

6. The combination of claim 2, including means for creating a flow of cool air into the oven, said programming means and control means being cooperative to effect operation of said flow-creating means for a predetermined time after the end of a predetermined selectively established time cycle.

7. The combination of claim 4, wherein:

said energy-introducing means includes a magnetron;

a waveguide feed extending between said magnetron and said oven;

a microwave power control network coupled between said control network and said magnetron; and

said network being adapted to operate said magnetron at different power levels,

and said programming means and control means being cooperative to control said network for operating said magnetron at a respective power level or at each power level within selectively established time cycles.

8. The combination of claim 7, wherein:

said heater elements have intermediate portions coupled to said waveguide feed and operate as driven antennas to radiate the microwave energy throughout the oven;

a current source; and

switching means coupled between said current source and both said elements, said programming means and control means being cooperative to operate said switching means to connect either or both elements to said current source.