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Publication numberUS3824365 A
Publication typeGrant
Publication dateJul 16, 1974
Filing dateDec 7, 1972
Priority dateDec 7, 1972
Also published asCA975432A1, DE2335375A1, DE2335375B2, DE2335375C3
Publication numberUS 3824365 A, US 3824365A, US-A-3824365, US3824365 A, US3824365A
InventorsW Tapper
Original AssigneeLitton Systems Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Microwave oven control system
US 3824365 A
Abstract
A control circuit for a microwave oven is disclosed which functions to automatically control the running time of the microwave generator to enable it to run continuously, during its cooking cycle, or intermittently, during its defrosting cycle. The control circuit includes a timer control switch operatively coupled to a timer motor. The timer control switch functions to control the current flow from the source of electrical power to the microwave generator. The circuit also includes a defrost control switch which functions to cyclically open and close a series current path to the microwave generator. A bypass circuit is also provided across the defrost control switch to short-circuit the defrost switch and provide a bypass current path to the microwave generator. A "cook-defrost" switch is provided to connect the circuit to the bypass circuit for the cooking mode, or to disconnect the bypass circuit to enable the current path to be governed by the defrost control switch for the defrosting mode. In one embodiment, the defrost control switch is coupled to a second timer motor which, in turn, is adapted to be cut into and out of the circuit by the "cook-defrost" switch. In a second embodiment, the defrost control switch is coupled to the first timer motor and is continuously operated thereby.
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United States Patent [191 Tapper i 111 3,824,365 [451 July 16, 1974 MICROWAVE OVEN CONTROL SYSTEM [75] Inventor: William R. Tapper, New Brighton,

Minn.

[73] Assignee: Litton Systems, Inc., Beverly Hills,

Calif.

[22] Filed: Dec. 7, 1972 [21] Appl. N0.: 313,188

[52] US. Cl. 219/1055, 200/38 B [51] Int. Cl. H05b 9/06 [58] Field of Search 2l9/l0.55; 200/38 B, 38 BA,

200/38 C, 38 CA, 38 FA [56] References Cited UNITED STATES PATENTS 3,324,273 6/1967 Ogburn 219/1055 3,470,942 10/1969 Fukada et al. 219/1055 X 3,569,656 3/1971 White 219/1055 3,694,608 9/1972 Loubert et al. 219/1055 Primary Examiner-Elliot Goldberg Assistant ExaminerHugh D. Jaeger Attorney, Agent, or FirmRobert M. Vargo [57] ABSTRACT A control circuit for a microwave oven is disclosed which functions to automatically control the running time of the microwave generator to enable it to run continuously, during its cooking cycle, or intermittently, during its defrosting cycle. The control circuit includes a timer control switch operatively coupled to a timer motor. The timer control switch functions to control the current flow from the source of electrical power to the microwave generator. The circuit also includes a defrost control switch which functions to cyclically open and close a series current path to the microwave generator. A bypass circuit is also provided across the defrost control switch to short-circuit the defrost switch and provide a bypass current path to the microwave generator. A cook-defrost" switch is provided to connect the circuit to the bypass circuit for the cooking mode, or to disconnect the bypass circuit to enable the current path to be governed by the defrost control switch for the defrosting mode. In one embodiment, the defrost control switch is coupled to a second timer motor which, in turn, is adapted to be cut into and out of the circuit by the cook-defrost switch. In a second embodiment, the defrost control switch is coupled to the first timer motor and is continuously operated thereby.

21 Claims, 2 Drawing Figures MICROWAVE GENERATING v SYSTEM PATENIEU Juu 61974 MICROWAVE GENERATING SYSTEM MICROWAVE GENERATING SYSTEM 1 MICROWAVE OVEN CONTROL SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to microwave cooking ovens and more particularly to systems for controlling the operating cycle of the microwave generators.

2. Description of the Prior Art It has been found that in defrosting frozen products within a microwave cooking oven, the heating cannot be continuous but must be intermittent in order to enable the heat absorbed in each frozen product to be distributed throughout the body of the product. If standing times were not permitted to allow for this heat distribution, the exterior surfaces of the product would be entirely cooked, while the center would still be frozen.

Heretofore, defrosting operations conducted in microwave ovens had to be performed manually. In other words, the operator had to set the timer on the oven to a very short time (approximately one minute), then time the standing time with an independent timer, and repeat this process as many times as necessary to accomplish complete defrosting. This, of course, is very cumbersome, since it requires the constant attention of the operator. As a result, defrosting of frozen products, especially large frozen products, was highly impractical.

SUMMARY OF THE INVENTION The present invention obviates the above-mentioned short-comings by providing a microwave oven having a control system which enables both the cooking and defrosting cycles to be accomplishedautomatically.

In its broadest aspect, the present invention comprises a microwave oven control circuit having a defrost control switch for opening and closing a current path between the power supply and the microwave generator, and a bypass circuit to short-circuit the defrost control switch and provide a bypass current path to the microwave generator. A cook-defrost switch is provided to selectively connect the circuit to the bypass circuit for the continuous cooking mode, or to disconnect the bypass circuit to enable the current path to be operated intermittently by the defrost control switch for the defrosting mode.

The features of the present invention which are believed to be novel are set forth with particularity in the appended Claims. The present invention, both as to its organization and manner of operation, together with the further advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the control circuit for a microwave oven of the present invention; and

FIG. 2 is a schematic view of a second embodiment of the control circuit for a microwave oven of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, FIG. 1 illustrates a control circuit generally indicated by arrow for controlling the on-time of a microwave generating system 11. Shown schematically, the microwave generating system 11 is conventional in construction and typically includes a magnetron for emitting microwaves into an oven cavity.

The control circuit 10 includes a two-part power line 13 and 15, the two parts being connected at their one ends to a source of electric power 17. Three lines 19, 21, and 23 are connected in parallel across the lines 13 and 15. The first line 19 includes a manual cook" switch 25 which is normally biased in an open position, a timer control switch 27, and a relay coil 33. The cook switch 25 is preferably positioned to physically extend through the control panel of the oven. A bypass line 29 is connected across the cook switch 25 and includes a normally open relay switch 31.

A second normally open relay switch 35 is located on the power line 13 between the parallel lines 19 and 21. Both of the relay switches 31 and 35 are operatively coupled to the relay coil 33 to be closed thereby when energized.

The timercontrol switch 27 is mechanically coupled to a timer motor 37 which is located across the line 23.

This coupling is accomplished by means of a cam 38 mounted on the output shaft of the timer motor 37. The angular position of the timer motor 37 and its cam 38 are adapted to be manually set by an interconnected dial which is preferably adapted to extend through the control panel of the oven. The cam 38 is adapted to be circular in shape with a single projection or cut-out located on the periphery thereof. The projection is adapted to trigger the timer control switch 27 at the end of the cam travel.

The line 21 includes a defrost timer motor 39 which is mechanically coupled to a defrost control switch 41 to open and close the current path through that portion of the power line 13 extending between the parallel lines 21 and 23. As in the prior instance, this mechanical coupling is accomplished by a cam 40 mounted on the output shaft of the defrost timer motor 39. The cam 40 is irregularly shaped to have a lower and upper cam surface, each representing half of the total cam travel. The cam 40 then functions to open and close the switch once for each cam revolution. For convenience, a conventional minute-timer motor rotating a one RPM is provided to enable the defrost control switch 41 to operate in 30-second equal cycles.

A cook-defrost switch 43 is provided to operate in a first position, which closes the line 21 to energize the defrost timer motor 39, and a second position to interconnect the portion of the line 21 connected to the power line 13 with a lead 45 which, in turn, is connected to the line 23. For convenience, this current path shall be called the bypass circuit which functions to short-circuit the defrost control switch 41 and enable current to be bypassed to the timer motor 37 and the microwave generating system 11. It is preferable to have the cook-defrost switch 43 also extend through the control panel of the oven.

In operation when it is desired to operate the microwave oven in its cooking "cycle, the timer dial on the control panel is first set to a setting corresponding to the duration of oven on-time desired. This action sets the cam 38 of the timer motor 37 to a predetermined position which in turn closes the timer control switch 27. The cook switch 25 is then depressed to close the line 19 and activate the relay coil 33. Upon actuation the relay coil 33 closes the relay switches 31 and 35.

The first relay switch 31 functions to keep the line 19 closed after the cook switch 25 is released. The line 19 will remain closed until the timer control switch 27 is again opened by the timer motor 37. The second relay switch 35 functions to close the power line 13 to enable current to pass therethrough. t

In the cooking cycle, the cook-defrost switch 43 is in its second positionto enable current to pass through the bypass circuit to energize the timer motor 37 and the microwave generating system 11. Current continues to be fed to the microwave generating system .11 until the cam 38 on the timer motor 37 reaches its zerotime position to open the timer control switch 27. This action functions to open the line 19 and de-energize the relay coil 33, thereby releasing the first and second relay switches 31 and 35. As a result, the line 19 is maintained in an open position and the power line 13 is opened. The opening of the line 13 stops the current flow to the timer motor 37 and the microwave generating system 11, thereby shutting off the magnetron located therein. As can be seen, the microwave generating system 11-is dependent only upon the operation of the timer control switch 27 during the cook cycle, and the operation of the oven is continuous.

In the defrost mode, the timer dial is again set as before to close the timer control switch 27. The manual cook switch 25 is then depressed to energize the relay the cook-defrost switch 43 is opened to enable the current path to be controlled'by the defrost control switch 41. The operation of the manual cook switch 25, the timer control switch 27, and the relay switches 31 and 35 all function in the same manner as described in the first embodiment. i

In the second embodiment, the earns 38 and 40 can be coupled to the timer motor 37 through gear train in order to slow down their rotational speed with respect to the speed of the timer motor 37 In this embodiment, the speed of the defrost cam 40 is sufficiently slowed down to enable the cam 40 to be profiled with a plurality of cam projections spaced about the periphery thereof. As in the first embodiment, the defrost cam 40 is profiled to enable the defrost control switch 41 to be sequentially opened and closed at 30 second intervals.

coil 33 and close the relay switches 31 and 35. The

cook-defrost switch 43 is then manually depressed to move to its first position as shown on FIG. 1. In this position, current'is fed to the'line 19 to energize the de- In the closed position of the defrost control switch 41, current passes through the line 13 to the timer motor 37 and the microwave generating system 11. As stated previously, the cam and the speed of the defrost timer motor 39 cooperate to cause the timer motor 37 and the microwave generating system to operate intermittently; i.e., 30 seconds on and 30 seconds off. After the timer motor 37 has been on the duration predetermined by the dial setting, the cam 38 reaches its zero-time position to open the timer control switch 27, which in turn releases the relay switches 31 and 35 through the relay coil 33.

The second embodiment of the present invention is shown in FIG. 2. In this embodiment, the second timer motor 39 is eliminated and the defrost control switch 41 is mechanically coupled to the first timer motor 37. Since the timer motor 37 is continuously running during the operation of the oven, the defrost control switch 41 is continuously opening and closing. This is different than the operation of the'first embodiment in which the defrost timer motor 39 was inactivated during the cooking cycle and the defrost control switch 41 did not operate. In the second embodiment, the bypass circuit 45 is provided to again extend across the defrost'control switch 41 to short-circuit the defrost cycler switch 41. As a result, during the cooking cycle, the cookdefrost switch 43 is closed to provide a current path to the microwave generating system 11 independent of the defrost control switch 41. During the defrost cycle,

As shown in FIG. 2, the oven control system 10 further includes a third cam 47 connected to the output shaft of the timer motor 37. The third cam 47 is operatively coupled to the defrost-cook switch 43 to automatically open and close the switch'43. In its preferable mode of operation, the defrost-cook switch 43 is manually opened to initiate the defrost cycle. The angular position of the cam 47 is then set to a predetermined setting, deemed sufficient to allow the frozen product 4 within the oven to be completely defrosted. As with the timer control cam 38, the cam 47 has a single projection at its zero time position to close the defrost-cook switch 43 and enable the oven to automatically switch to the cooking mode.v

As can be seen, the present invention provides a microwave oven that functions automatically in both the cooking and defrosting modes.

It should be noted that various modifications can be made to the apparatus while still remaining within the purview of the following claims.

What is claimed is:

1. A microwave oven defrosting and cooking cycle control system comprising:

a microwave oven;

a microwave generating system for said microwave oven;

a current path coupling said microwave generating system to a source of electrical energy;

timer control switch means for opening and closing said current path;

defrost control switch means for opening and closing said current path; and

bypass circuit means extending across said defrost switch means for short-circuiting said defrost switch means to enable said current path to be selectively controlled by said timer control switch means in one mode and by both control switch means in a second mode.

2. The invention of claim 1 further comprising means for cyclically opening and closing said defrost control switch. r

3. The invention of claim 1 further comprising a defrost-cook switch means for cutting said bypass circuit into and out of said current path.

4. The invention of claim 3 further comprising means for automatically opening and closing said defrost-cook switch means.

5. Theinvention of claim 1 wherein said timer control switch is coupled to a first timer to be governed thereby.

6. The invention of claim 5 wherein said first timer comprises a motor-cam assembly operatively coupled to said timer control switch means.

7. The invention of claim 5 wherein said defrost control switch means is coupled to a second timer to be governed thereby.

8. The invention of claim 7 wherein said second timer comprises a second motor-cam assembly operatively coupled to said defrost control switch means.

9. The invention of claim 5 wherein said defrost control switch means is coupled to said first timer to be governed thereby.

10. The invention of claim 9 wherein said first timer comprises a motor coupled to a pair of cam members, each cam member being mechanically coupled to said respective switch control means.

11. The invention of claim 10 further comprising:

a defrost-cook switch means for cutting said bypass circuit into and out of said current path; and

a third cam member coupled to said first timer motor, said third cam being operatively coupled to said defrost-cook switch means for automatically opening and closing said defrost-cook switch means.

12. A control circuit for coupling a power supply to a microwave generator comprising:

a pair of power lines interconnecting the power supply to a microwave generator;

a first line connected in parallel to said pair of power lines, said first line having a timer control switch and a relay coil located thereon;

a holding contact switch serially connected to one of said power lines, said contact switch being operatively coupled to said relay coil;

a second line connected in parallel to said pair of parallel lines beyond said holding contact switch with respect to the power supply, said second line having a first timer motor coupled thereto, said first timer motor being operatively coupled to said timer control switch;

a defrost control switch serially connected to one of said power lines beyond said second line with respect to the power supply; and

a bypass circuit for selectively shortcircuiting said defrost control switch.

13. The invention of claim 12 further including a defrost-cook switch for opening and closing said bypass circuit.

14. The invention of claim 12 wherein said first timer motor is mechanically coupled to said defrost control switch.

15. The invention of claim 12 wherein said first line .further includes a switch connected across said first line, said switch being biased in the open position, and a bypass circuit having a second holding contact switch coupled thereto, said second holding contact switch being operatively coupled to said relay coil.'

16. A control circuit for coupling a power supply to a microwave generator comprising:

a pair of power lines'interconnecting the power supply to a microwave generator;

a first line connected in parallel to said pair of power lines, said first line having a timer control switch and a relay coil located thereon;

a holding contact switch serially connected to one of said power lines, said contact switch being operatively coupled to said relay coil;

a second line connected in parallel to said pair of parallel lines beyond said holding contact switch with respect to the power supply, said second line having a defrost timer motor coupled thereto;

a defrost control switch serially connected to one of said power lines beyond said second line with respect to the power supply, said defrost timer motor being operatively coupled to said defrost control switch; and

a third line connected inparallel to said pair of power lines beyond said defrost control switch with respect to the power supply, said third line having a timer motor coupled thereto, said timer motor being operatively coupled to said timer control switch.

17. The invention of claim 16 further including a defrost-cook switch for opening and closing said bypass circuit.

18. The invention of claim 17 wherein said bypass circuit comprises a lead interconnecting said second line to said third line.

19. The invention of claim 18 wherein said cookdefrost switch is adapted to interconnect in one position, the second line with said lead.

20. The invention of claim 19 wherein said cookdefrost switch is adapted to interconnect, in a second position, the power line with the defrost timer motor.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 5,53%,365 DATED July 16, 197A INVENTOR(S) William R. Tapper It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

21. A microwave oven comprising:

a source of microwave energy;

a control circuit including a cyclically operated switch for energizing the source of microwave energy in a mode of intermittent energization of the source of microwave energy;

a bypass circuit path shunting the cyclically operated switch; and

a mode selector switch in the bypass circuit path for closing the bypass circuit path to initiate and maintain continuous operation of the source of microwave energy in a mode of continuous operation.

Signed and sealed this 10th day of June 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,82 r,565 DATED July 16, 197

iN\ ENTOR(S) William R. Tapper it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

21. A microwave oven Comprising:

a source of microwave energy; 7

a controlv circuit including a cyclically operated switch for energizing the source of microwave energy in a mode of intermittent energization of the source of microwave energy;

a bypass circuit path shunting the cyclically operated switch; and

a mode selector switch in the bypass circuit path for closing the bypass circuit path to initiate and maintain continuous operation of the source of microwave energy in a mode of continuous operation.

Signed and sealed this 10th day of June 1975.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents and Trademarks RUTH C. MASON Attesting Officer

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3324273 *Aug 7, 1964Jun 6, 1967Gen ElectricControl and power supply networks for magnetrons
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US3569656 *Jul 24, 1969Mar 9, 1971Bowmar Tic IncAutomatic cooking cycle control system for microwave ovens
US3694608 *Feb 8, 1971Sep 26, 1972Pillsbury CoMethod of consistently reducing moisture loss in heating frozen foods with microwave energy and apparatus therefor
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3995133 *Dec 11, 1974Nov 30, 1976The Tappan CompanyVariable power control for microwave oven
US4025804 *Nov 13, 1975May 24, 1977The Tappan CompanyMicrowave oven control with mechanical switch lock-out
US4088862 *Apr 8, 1976May 9, 1978Roper CorporationTimer operated control circuit for a microwave oven
US4121079 *Apr 25, 1977Oct 17, 1978General Electric CompanyMinimizing lamp flicker and blower speed variation in a microwave oven employing duty cycle power level control
US4129769 *Mar 11, 1977Dec 12, 1978Sharp Kabushiki KaishaTimer arrangement in a combination microwave oven and electric heating oven
US4130749 *Mar 4, 1977Dec 19, 1978Matsushita Electric Industrial Co., Ltd.Microwave oven
US4133998 *Jun 22, 1977Jan 9, 1979Sharp Kabushiki KaishaCooking mode selector for continuously varying a mean output level of a magnetron in a microwave oven
US4177370 *May 25, 1978Dec 4, 1979Sharp Kabushiki KaishaVariable cooking mode selector in a microwave oven
US4206337 *Apr 12, 1978Jun 3, 1980Robertshaw Controls CompanyMicrowave oven having improved defrost cycle timer means
US4210824 *Oct 31, 1977Jul 1, 1980Robertshaw Controls CompanyTimer controlled control system and timer construction therefor
US4220841 *Aug 4, 1978Sep 2, 1980Hitachi, Ltd.Microwave generating device utilizing a magnetron
US4524258 *Mar 8, 1984Jun 18, 1985Tokyo Shibaura Denki Kabushiki KaishaBack-up control circuit for controlling a magnetron of a microwave oven
US4551590 *May 14, 1984Nov 5, 1985Eaton CorporationAppliance control and programmer timer therefor
US4616209 *May 18, 1983Oct 7, 1986Eaton CorporationFor an electrical cooking appliance
US4629845 *Jan 16, 1985Dec 16, 1986Eaton CorporationElectrical appliance programming
US4910370 *Apr 10, 1989Mar 20, 1990Moulinex (Societe Anonyme)Microwave oven having a pre-programmed timing device
EP0128634A1 *Feb 14, 1984Dec 19, 1984Eaton CorporationA control system for an electrical appliance
Classifications
U.S. Classification219/703, 968/815, 219/719, 219/718, 200/38.0FA
International ClassificationG04F3/06, H05B6/68
Cooperative ClassificationH05B6/68, G04F3/06, H05B6/688
European ClassificationH05B6/68, G04F3/06, H05B6/68T