Microwave heating device

ABSTRACT

The present invention relates to a microwave heating device, and in particular, a microwave heating device with a microwave heating element mounted on the surface of a heating dish on which food is placed inside a heating chamber.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing of a microwave oven according to the present invention;

FIG. 2 is a front view of an operating panel according to the present invention;

FIG. 3 is a front view of a microwave oven with its door opened according to the present invention;

FIG. 4 is a perspective view of an oven broiling dish to be installed in the microwave oven according to the present invention;

FIG. 5 is a bottom view of an oven broiling dish according to the present invention;

FIG. 6 is a front view of an oven broiling dish according to the present invention;

FIG. 7 is a cross-sectional view taken along the line VII—VII shown in FIG. 5;

FIG. 8 is a cross-sectional view taken along the line VIII—VIII shown in FIG. 1;

FIG. 9 is a schematic diagram of the electrical circuitry of a microwave oven according to the present invention;

FIG. 10 is a cross-sectional view taken along the line VIII—VIII shown in FIG. 1 of the heating chamber of the microwave oven according to an embodiment of the present invention;

FIG. 11 is a right side view of the heating chamber of the microwave oven according to an embodiment of the present invention;

FIG. 12 is a cross-sectional view of the main body of the microwave oven according to the embodiment shown in FIG. 11 taken at a height where protruding parts exist;

FIG. 13 is a cross-sectional view of the main body of the microwave oven according to the embodiment shown in FIG. 11 taken at a height where protruding parts exist;

FIG. 14 is a right side view of the inside of the heating chamber of the microwave oven shown according to an embodiment of the present invention;

FIG. 15 is a cross-sectional view of the main body of the microwave oven according to the embodiment shown in FIG. 14 taken at a height where protruding parts exist;

FIG. 16 is a cross-sectional view of the main body of the microwave oven according to the embodiment shown in FIG. 14 taken at a height where protruding parts exist;

FIG. 17 is a cross-sectional view taken along the line VIII—VIII shown in FIG. 1 of the heating chamber of the microwave oven according to an embodiment of the present invention;

FIGS. 18A and 18B are temperature distribution diagrams of the oven broiling dish according to the embodiment shown in FIG. 17;

FIG. 19 is a cross-sectional view taken along the line F—F of FIG. 17;

FIG. 20 is a perspective drawing of a reflection plate according to the embodiment shown in FIG. 17;

FIG. 21 is a cross-sectional view taken along the line F—F of FIG. 17 according to an embodiment of the present invention;

FIG. 22 is a cross-sectional view taken along the line F—F of FIG. 17 according to an embodiment of the present invention;

FIG. 23 is a cross-sectional view taken along the line F—F of FIG. 17 according to an embodiment of the present invention;

FIG. 24 is a cross-sectional view taken along the line F—F of FIG. 17 according to an embodiment of the present invention;

FIG. 25 is a cross-sectional view taken along the line VIII—VIII shown in FIG. 1 of the heating chamber of the microwave oven according to an embodiment of the present invention;

FIG. 26 is a temperature distribution diagram of the oven broiling dish according to the embodiment shown in FIG. 25;

FIG. 27 is a temperature distribution diagram of the oven broiling dish according to the embodiment shown in FIG. 25;

FIG. 28 is a plan view of the rotating antenna of the microwave oven according to the embodiment shown in FIG. 25;

FIG. 29 is an example stopping direction of the rotating antenna of the microwave oven according to the embodiment shown in FIG. 25;

FIG. 30 is an example stopping direction of the rotating antenna of the microwave oven according to the embodiment shown in FIG. 25;

FIG. 31 is a back view of the oven broiling dish of the microwave oven according to an embodiment of the present invention;

FIG. 32 is a back view of the oven broiling dish of the microwave oven according to an embodiment of the present invention;

FIG. 33 is a back view of the oven broiling dish of the microwave oven according to an embodiment of the present invention;

FIG. 34 is a cross-sectional view taken along the line E—E of FIG. 33;

FIG. 35 is a cross-sectional view where the front and back sides of the oven broiling dish of FIG. 34 are reversed;

FIG. 36 is a graph showing the relation between the specific resistance of a microwave heater and the electrical field intensity due to the reflection of an oven broiling dish and due to the transmission of microwaves supplied to the heating chamber according to the present invention;

FIG. 37 is a flowchart of the thermal cooking process in a microwave oven according to the present invention;

FIG. 38 is a flowchart of the thermal cooking process in a microwave oven according to the present invention;

FIG. 39 is a flowchart of the preheat process subroutine of FIG. 37;

FIG. 40 is a flowchart of the output setting A process subroutine of FIG. 39;

FIG. 41 is a flowchart of the temperature detection process subroutine of FIG. 39;

FIG. 42 is a diagram showing the temperature detection range of each infrared detection element of the infrared sensor according to the present invention;

FIGS. 43A, B and C are flowcharts of the preheat control A process subroutine of FIG. 39;

FIG. 44 is a flowchart of the output confirmation process subroutine of FIGS. 43A-43C;

FIGS. 45A and 45B are flowcharts of the error detection process subroutine of FIGS. 43A-43C;

FIGS. 46A and 46B are diagrams showing the field of view of the infrared sensor over the oven broiling dish depending on the height at which the oven broiling dish is installed according to the present invention;

FIG. 47 is a diagram showing the chronological change of Tcave from the starting point of preheat process in a microwave oven according to the present invention;

FIG. 48 is a flowchart of the preheat control B process subroutine of FIG. 39;

FIG. 49 is a flowchart of the output setting B process subroutine of FIG. 48;

FIG. 50 is a flowchart of the preheat control C process subroutine of FIG. 39;

FIG. 51 is a flowchart of the preheat control D process subroutine of FIG. 39;

FIG. 52 is a flowchart of the oven broiling process subroutine of FIG. 37; and

FIG. 53 is a flowchart of the double side broiling process subroutine of FIG. .

KEY

microwave oven

main body

main frame

operating panel

infrared sensor

bottom plate

heating chamber

magnetron

waveguide

detection passage member

oven thermistor

oven broiling dish

microwave heating element

, recessed area

, , , , - rail

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Structure of a Microwave Oven

FIG. 1 is a perspective view of a microwave oven according to an embodiment of the present invention. A microwave oven includes a main body and a door . The main body is covered by an outer shell , which is supported by a plurality of legs . The front of the main body has an operating panel for inputting various kinds of information to the microwave oven .

The door opens and closes by pivoting around its bottom edge. A grip A is positioned at the top of the door . FIG. 2 shows the front view of the operating panel , and FIG. 3 shows the front view of the microwave oven when the door is open.

A main body frame is provided inside the main body . A heating chamber is provided inside the main body frame . A hole A is formed on the top right side of the heating chamber . A detection passage member is connected to the hole A from the outside of the heating chamber . A bottom plate is provided at the bottom of the heating chamber .

A transparent heat-resistant glass plate B is affixed to the middle of the door so that the inside of the heat chamber can be viewed from the outside of the microwave oven when the door is closed. A plastic choke cover C is positioned inside the heat chamber and is accessible through the door . The choke cover C fills a gap between the outer circumference of a contact surface D and the door . The contact surface D contacts the main frame . The microwaves that escape through the gap between the contact surface D and the main frame are prevented from leaking out from the heating chamber by a choke structure (not shown). The choke structure is covered by the choke cover C and formed in the door .

The operation panel provides a display unit , an adjusting knob , and various keys. The display unit has a liquid crystal display panel and the like for displaying various kinds of information. The adjusting knob is used for inputting numerical values and other kinds of information.

A preheat start key is used to prepare the food for various kinds of cooking. An oven broiling key is used for heating foods using an oven broiling dish as described later. A temperature selection key is used for entering the desired temperature for cooking at a temperature selected by using the adjusting knob .

The microwave oven can automatically cook using various selections included on a cooking menu, and the cooking intensity can be adjusted by keys , so that by pressing key weakens the intensity level and pressing key strengthens the intensity level. A grilling key is used to control the degree of browning of the food in the heating chamber using a heater (not shown). A deodorizing key is used for removing odors in the heating chamber .

The microwave oven can be constructed having a plurality of trays (or oven broiling dishes ) in the heating chamber . An oven step adjusting key is used to enter whether one or two steps are to be used for oven cooking in the heating chamber . A fermentation key is used for fermenting foods such as bread dough. An oven output key is used for controlling the output of microwaves generated in the microwave oven . A defrosting key is used for defrosting frozen foods; pressing the defrosting key twice will defrost frozen sashimi (i.e., sliced raw fish fillets) in the microwave oven . A cancellation key is used for canceling the key operation before the input has been completed.

An oven broiling dish , as shown in FIG. 4, can be placed in the heating chamber of the microwave oven . Rails , , , protrude into the heating chamber to support the oven broiling dish . Rails , , , are aligned in horizontal lines, respectively. Recessed areas , are formed between rail and rail and between rail and rail , respectively. Recessed areas , protrude outward from the heating chamber . Rails , , , and recessed areas , can be made by press-forming the sheet metal that constitute the walls of the heat chamber .

FIG. 4 is a perspective view of the oven broiling dish . FIGS. 5 and 6 are a bottom view and a front view, respectively, of the oven broiling dish , and FIG. 7 is a cross-sectional view along line VII—VII of FIG. .

The oven broiling dish has a bottom B and an outer periphery D that extends outward in the horizontal direction. The outer periphery D is connected to the bottom D via a wall E. A groove A is provided on the outer edge of the bottom B that connects to the wall E.

A microwave heating element is formed by a vapor deposition process on the bottom surface of the bottom B of the oven broiling dish . The microwave heating element is formed from a material that generates heat when it absorbs microwaves, such as an electrically conductive material or, more specifically, an electrically conductive material that includes molybdenum added with tin oxide. The thickness of the deposition film is preferably on the order of 8×10−8 m, and the specific resistance is preferably 2-6 Ω/m. The hatched area in FIG. 5 shows the surface of the microwave heating element .

A leg C is formed on each corner of the oven broiling dish . In FIG. 7, Z indicates the height of the lowest part of the leg C; Y indicates the height of the lowest part of the bottom B correspond to the back of the groove A; and X indicates the height of the lowest part of the microwave heating element .

Since X is higher than Y and Z, if the oven broiling dish is taken out of heating chamber and placed on a carrying surface, such as a table, after the microwave heating element has been heated to a high temperature, then the leg C or the bottom B of the oven broiling dish contacts the carrying surface. Therefore, the microwave heating element does not contact the carrying surface directly, and the high temperature heat of the microwave heating element is prevented from being transmitted to the carrying surface.

Furthermore, if the microwave heating element is heated to a high temperature and contacts the choke cover C, the choke cover C may melt. The gap between the contact surface D and the main frame widens when the choke cover C melts and allows the microwaves to leak from the heating chamber . However, since the oven broiling dish is constructed as shown in FIG. 7, the oven broiling dish can be placed on the door when it is opened as shown in FIG. 3 without allowing the microwave heating element to contact the choke cover C.

The microwave heating element is vapor-deposited at a distance W apart from the edge of the outer periphery D of the oven broiling dish and on the inside of the groove A, as shown in FIG. . The distance W must be greater than one quarter of the wavelength λ of the microwaves supplied into the heating chamber , i.e., greater than λ/4, in order to send the microwaves efficiently above the heating dish . In order to generate the microwaves efficiently in microwave oven , the distance W must be greater than 3 cm. For example, if the distance W is 5 cm, approximately 75-80% of the microwaves generated by the magnetron will be absorbed by the microwave heating element and approximately 20-25% will be sent above and through the oven broiling dish .

FIG. 8 is a cross-sectional view of the inside of the microwave oven taken along line VIII—VIII shown in FIG. 1 with some components omitted from the drawing.

An infrared sensor is mounted on one end of the detection passage member . The infrared sensor senses infrared rays inside the heating chamber via the hole A. A magnetron is provided inside the outer shell adjacent to the right bottom corner of the heating chamber . A waveguide is provided at the bottom of the heating chamber to connect the magnetron to the bottom part of the main frame . A rotating antenna is provided between the bottom part of the main frame and the bottom plate . An antenna motor is provided below the waveguide . The rotating antenna is connected to the antenna motor by a shaft . The antenna motor drives the rotation of the rotating antenna .

The object to be heated, i.e., the food, is placed on the bottom plate , or on the oven broiling dish , in the heating chamber . The oven broiling dish is positioned inside the heating chamber with the periphery part D of the oven broiling dish being supported by rails , , , .

The microwaves generated by the magnetron are sent through the waveguide and through the bottom of the heating chamber while being agitated by the rotating antenna . Thus, the food in the heating chamber is heated.

In FIG. 8, the flow of microwaves supplied to the heating chamber is indicated by arrows. The size of the arrows graphically represents the intensity of the electric field of the microwaves. The microwaves supplied to the heating chamber are absorbed by the microwave heating element to heat the microwave heating element . The heat supplied from the microwave heating element heats the food on the oven broiling dish . The flow of microwaves to the microwave heating element is shown by large arrows below the microwave heating element in FIG. .

The microwaves supplied to the heating chamber reach areas above the oven broiling dish by passing through the outer edge of the oven broiling dish and through the gap between the oven broiling dish and the walls of recessed areas , . Thus, the food on the oven broiling dish is heated by directly supplying the microwaves to the food. The flow of microwaves directly supplied to the food is shown by large arrows above and below the outer edge of the oven broiling dish in FIG. .

In the embodiment of the present invention described above, a passage is formed for sending the microwaves that are introduced into the heating chamber from the waveguide and into the area above the heating dish, i.e., the oven broiling dish . By sending the microwaves through the passage, the microwaves bypass the microwave heating element . The passage comprises a portion of the heating chamber below the oven broiling dish , the outer edge of the oven broiling dish where the microwave heating element is not present, (i.e., an area that includes the outer edge of bottom B, the outer periphery D, and the wall E), and the recessed areas , of the heating chamber . Moreover, since the distance W shown in FIG. 5 is greater than λ/4, the dimension of the passage perpendicular to the traveling direction of the microwaves in the passage is greater than λ/4.

Furthermore, in FIG. 8, the portion of the microwaves that pass through the microwave heating element without being converted into heat are marked by small arrows above the center of the oven broiling dish . Moreover, a grilling heater (not shown in FIG. 8) is positioned above the heating chamber , and a lower heater (not shown in FIG. 8) is positioned below the heating chamber .

Rails , and rails , are provided on the right and left surfaces of heating chamber , respectively, to support the oven broiling dish from underneath. Rails , , , are a plurality of members spaced apart from each other so that rails , or rails , provide space between the inner wall of the heating chamber and the edge of the oven broiling dish . Therefore, it is easier to send microwaves to areas above the oven broiling dish compared to a microwave oven having continuous line rails extending from the proximate side to the distal side of the heating chamber .

Microwave diffusing protrusions A, A are provided in recessed areas , , respectively. Protrusions A, A diffuse the microwaves that pass through recessed areas , to areas above the oven broiling dish .

2. Electrical Circuitry of the Microwave Oven

FIG. 9 is a schematic drawing of the electrical circuitry of the microwave oven . The microwave oven has a control circuit that generally controls the operation of the microwave oven . The control circuit includes a microcomputer.

In the microwave oven , the AC voltage from an external commercial power source is rectified by a rectifying bridge and converted into a DC voltage by a choke coil and a smoothing capacitor . The rectifying bridge , the choke coil , and the smoothing capacitor comprise a rectifying device that rectifies the AC voltage of the commercial power source .

A switching device having an IGBT (insulator gate bipolar transistor) is connected in parallel to a free wheel diode and a resonance capacitor between the collector and emitter of the switching device to comprise a resonance type switching circuit. A microwave transformer has a primary winding , a secondary winding , and a heater winding . An input DC voltage is supplied to the collector of the switching device via the primary winding of the microwave transformer . The switching device is turned on and off by a drive signal from a drive circuit to create cycles in which the input DC voltage is converted into microwaves. The switching device , the free wheel diode , and the resonance capacitor comprise a frequency converter . The control circuit controls the drive timing of the switching device using the drive circuit .

The secondary winding of the microwave transformer is connected to a voltage doubler rectifying circuit comprising a voltage doubler capacitor and a voltage doubler rectifying diode . A microwave voltage generated on the secondary winding of the microwave transformer is rectified by the voltage doubler rectifying circuit to produce a DC high voltage. The voltage doubler rectifying circuit has a drive power source which supplies anode power between an anode of a magnetron and a cathode . The cathode is also a heater for heating the magnetron . The current supplied to the magnetron is detected by a current transformer which sends a detection signal to the control circuit . The side of the magnetron near the anode is grounded, and the heater voltage from the heater winding is supplied to the cathode of the magnetron .

A door switch X is located on the microwave oven . The door switch X opens the circuit shown in FIG. 9 when the door is open and closes the circuit shown in FIG. 9 when the door is closed. Thus, the power supply from the commercial power source to the magnetron stops when the door is open. The ability of the door switch X to open and close the circuit shown in FIG. 9 prevents the magnetron from generating microwaves while the door is open. Furthermore, the microwave oven has a chamber light , which illuminates the inside of the heating chamber and an oven thermistor for detecting the temperature inside the heating chamber . The control circuit receives operation commands from several key inputs -, which are the adjusting knob and other keys on the operation panel , and from detection outputs of the infrared sensor and the oven thermistor . With the operation commands, the control circuit controls the rotating motion of the rotating antenna and the display contents of the display unit . The control circuit also controls the operation of the grilling heater , the lower heater , and the chamber light by driving relays appropriately.

3. Variations of the Heating Chamber of the Microwave Oven

FIG. 10 shows the heating chamber of the microwave oven according to an embodiment of the present invention. In particular, FIG. 10 shows an embodiment of the main frame and its adjacent parts shown in FIG. . However, the main difference between this embodiment and the embodiment shown in FIG. 8 is that the embodiment in FIG. 20 has four steps of rails in the heating chamber for the oven broiling dish . Each step of rails comprise a pair of rails, i.e., rails , , rails , , rails , , and rails , , in order from top to bottom.

FIG. 10 shows four steps of rails in the heating chamber . The outer periphery D of the oven broiling dish abuts the top-level rails , , located at the highest attainable position in the heating chamber .

FIG. 10 also shows the grilling heater positioned at the top of the heating chamber . The heat emitted by the grilling heater is shown as solid-lined arrows, and microwaves generated by the magnetron are shown in broken-lined arrows. Similar to the embodiment of the present invention shown in FIG. 8, the microwaves supplied from the bottom of the heating chamber are absorbed by the microwave heating element , while a portion of the microwaves are guided to areas above the oven broiling dish through the outer edge of the oven broiling dish .

In the embodiment shown in FIG. 10, the surface of the food placed on the oven broiling dish is heated by the microwave heating element while the inside of the food is heated as it absorbs the microwaves directly and further browned by being heated by the grilling heater .

FIG. 11 shows an embodiment of the heating chamber of the microwave oven according to the present invention. FIG. 11 is a right side view of the microwave oven that shows the relation between position of the inside of the heating chamber and the position of the door . The right side of the main body is not shown in FIG. .

Rail is positioned above rails , on the wall of the heating chamber as shown in FIG. . Although it is not shown in FIG. 11, a rail , which is similar to rail of FIG. 25, is formed on the wall of the heating chamber and positioned opposite to rail . The oven broiling dish can be supported by rail and rail in the heating chamber . Also, in the embodiment shown in FIG. 11, a protruding part is positioned below and near the center of rail in the heating chamber . A protruding part , as shown in FIGS. 12 and 13, is formed on the wall of the heating chamber positioned opposite to the protruding part although it is not shown in FIG. .

Sometimes a metallic dish, such as an enameled metal dish , is used in the heating chamber. Protruding parts , stop the magnetron from generating microwaves when a metallic dish is placed at locations in the heating chamber where the oven broiling dish can be placed but where a metallic dish cannot be placed when the magnetron is generating microwaves. In the embodiment shown in FIG. 12, one of such locations is above the bottom plate and close, i.e., within 1 cm, to the bottom plate . When microwaves are supplied to the heating chamber via a rotating antenna in the heating chamber while the enameled metal dish is placed close to the bottom plate , electric discharges may occur between the rotating antenna and the enameled metal dish , which is dangerous.

The enameled metal dish is a dish that holds food for the purpose of oven cooking only with the heaters, i.e., the grilling heater and the lower heater . The enameled metal dish is made of an enameled sheet metal.

FIGS. 12 and 13 are cross-sectional drawings of the microwave oven shown in FIG. 1 taken at the height of protruding parts , .

In FIG. 12, the oven broiling dish is placed on the bottom plate in the heating chamber , and protruding parts , are located between the respective corners of the oven broiling dish and the walls of the heating chamber . In other words, the oven broiling dish can be placed in the heating chamber at the same height as the height of protruding parts , .

In contrast, if the enameled metal dish is placed on the bottom plate as shown in FIG. 13, the enameled metal dish cannot advance any further into the heating chamber since the corners of the enameled metal dish abut protruding parts , . In other words, the enameled metal dish cannot be placed in the heating chamber at the height of protruding parts , . If the enameled metal dish is placed at the height of protruding parts , , the door cannot be closed because the enameled metal dish sticks out as shown in FIG. . When the door is not closed, the door switch X opens the circuit shown in FIG. 9, thereby preventing the magnetron from generating microwaves.

In the embodiment shown in FIGS. 11-13, the protruding parts , and the shapes of the corners of the oven broiling dish and the enameled metal dish prevent the enameled metal dish from being placed in the heating chamber at the same height as protruding parts , . However, the oven broiling dish can be placed in the heating chamber at the same height as protruding parts , . Moreover, the oven broiling dish can be placed at any height in the heating chamber without being prevented by protruding parts , from being fully stored as for the enameled metal dish shown in FIG. .

Furthermore, the oven broiling dish stored in the heating chamber has a dimension L in the depth direction and a dimension L (>L) in the width direction as shown in FIG. . The oven broiling dish also leaves a gap of a distance K to the front part X of the heating chamber . Therefore, when the door is closed while the oven broiling dish is stored in the heating chamber , there is a gap between the oven broiling dish and the door which is greater than the distance K. Therefore, air and microwaves beneath the oven broiling dish can be sent to areas above the oven broiling dish when the door is closed.

In the embodiment shown in FIGS. 11-13, the formation of protruding parts , create a position in the heating chamber where the oven broiling dish can be placed but the enameled metal dish cannot be placed when microwaves are generated by the magnetron . Additionally, the heating chamber can prevent the magnetron from generating microwaves when the oven broiling dish is placed at an undesirable position, and this embodiment of the present invention is shown in FIGS. 14-16.

FIG. 14 is a right side view of the microwave oven in which some components are not shown. Protruding parts , of the embodiment shown in FIG. 12 are moved forward in the heating chamber to become protruding parts A, A as shown in FIG. . FIGS. 15 and 16 are cross-sectional drawings of the main body of the microwave oven shown in FIG. 14 taken at a height of protruding parts A, A.

In FIG. 15, as protruding parts A, A are located toward the front from protruding parts , (as shown in FIG. 12) in the heating chamber . Thus, the oven broiling dish cannot be pushed back into the full depth of the heating chamber since the movement of the oven broiling dish is blocked by the protruding parts A, A. The oven broiling dish is blocked and the door is prevented from closing, when the oven broiling dish is attempted to be installed at the height of protruding parts A, A. In the embodiment shown in FIGS. 14-16, the enameled metal dish also cannot be installed in the heating chamber since it is blocked by protruding parts A, A which prevents the door from closing, when it is attempted to be installed at the same height as protruding parts A, A

As shown in FIG. 16, the oven broiling dish can be installed in the heating chamber without abutting against protruding parts A, A by rotating the oven broiling dish 90° from the position shown in FIG. 15 since L

The depth dimension of the heating chamber is “L +K” as shown in FIG. . Therefore, protruding parts , must protrude from the back surface of the heating chamber by an amount greater than “L +K−L” in order to prevent the door from closing when the oven broiling dish is placed in the heating chamber as shown in FIG. .

Reflection plates - (see FIG. 19 for reflection plates , ) are provided on the outer periphery of the rotating antenna as shown in FIG. 17 in an embodiment of the present invention. FIG. 17 is a cross-sectional drawing comparable to the cross-sectional drawings of FIGS. 18A and 18B.

In the embodiment shown in FIG. 17, as described later in more detail, reflection plates - on the outer periphery of the rotating antenna suppress the microwaves supplied to the heating chamber via the rotating antenna from flowing near the walls of the heating chamber . Thus, the microwaves are absorbed more efficiently by the microwave heating element , thereby reducing the fluctuation of heat over the oven broiling dish as shown in FIGS. 18A and 18B.

FIGS. 18A and 18B are temperature distribution diagrams of the oven broiling dish after the magnetron has generated microwaves for three minutes. FIG. 18A shows an oven broiling dish when reflection plates - are included on the outer periphery of the rotating antenna , and FIG. 18B shows an oven broiling plate when reflection plates - are not included.

In FIG. 18B, the reflection plates - are not included on the outer periphery of the rotating antenna . Although there are areas at the four corners of the oven broiling dish where the temperatures are as high as 300° C., the areas near the center of the oven broiling dish barely reach 100° C. However, in FIG. 18A, although there are high temperature spots at the center and at the four corners of the oven broiling dish , almost all of the oven broiling dish is heated above 150° C., with many areas reaching above 175° C. Thus, the fluctuation of heat of the oven broiling dish can be eliminated by providing reflection plates -.

Next, the structure of reflection plates - is shown in FIGS. 19 and 20. FIG. 19 is a cross-sectional drawing taken along the line F—F on FIG. 17, and FIG. 20 is a perspective view of reflection plate .

A bottom plate holding area for holding the bottom plate is positioned at the bottom of the heating chamber , and an antenna enclosure housing the rotating antenna is positioned below the bottom plate holding area . The shape of walls surfaces of the antenna enclosure , which intersects the traveling direction of the microwaves, has a rectangular shape with rounded corners as shown in FIG. .

Reflection plate , as shown in FIG. 20, has a L-shaped cross section, and reflection plates - have the same structure as reflection plate . Reflection plates - are made of a material that reflects microwaves. Reflection plates - can also be made by coating a material that reflects microwaves.

Reflection plates - are placed between the rounded corner areas of the rectangular shape of the antenna enclosure and the rotating antenna . Reflection plates - can be placed where the distance between the outer edge of the rotating antenna and the walls of the antenna enclosure is the longest. One of the longest distances between the outer edge of the rotating antenna and the walls of the antenna enclosure is Q shown in FIG. 19; and one of the shortest distances is Q shown in FIG. . Placing reflection plates - as described above makes it possible to prevent the microwaves supplied to the heating chamber via the rotating antenna from diffusing into areas near the walls of the heating chamber , thereby suppressing the fluctuation of heat over the oven broiling dish by suppressing the supply of more microwaves to the areas near the walls of the heating chamber .

Reflection plates - extend further than the rotating antenna in the traveling direction of the microwaves. More specifically, in FIG. 17, the traveling direction of the microwaves is upward, the height of reflection plates - is H, and the height of the rotating antenna is H (

Alternatively, the walls of the antenna enclosure can be structured as shown in FIGS. 21 and 22 rather than including reflection plates -.

In FIG. 21, the cross section of the antenna enclosure is circular. In FIG. 22, the cross section of the antenna enclosure is polygonal, i.e., octagonal. Since the cross section of the antenna enclosure is circular or polygonal, the distance between the edge of the rotating antenna and the walls of the antenna enclosure can be minimized and more of the microwaves supplied by the rotating antenna can be prevented from moving toward the walls of the heating chamber .

FIGS. 23 and 24 show an embodiment of the present invention in which, in addition to reflection plates -, the lower heater surrounds the rotating antenna as shown in FIGS. 23 and 24. The lower heater is affixed by an affixing member A in the antenna enclosure .

As shown in FIGS. 23 and 24, reflection plates - are located outside of the rotating antenna and inside the lower heater . Thus, the microwaves supplied to the heating chamber via the rotating antenna in areas where reflection plates - are provided are sent upward by reflection plates - before being diffused by the lower heater . Therefore, the microwaves can be sent accurately to the desired direction.

The heating mode can be made dependent on the height of the oven broiling dish in heating chamber when the height of the oven broiling dish is adjustable.

FIG. 25 shows an embodiment of the present invention in which the oven broiling dish can be installed at two different heights in the heating chamber of the microwave oven .

Rails , are provided above rails , , , in order to support the oven broiling dish in the heating chamber . Rail is symmetric to rail , which is the same as rail shown in FIG. . The oven broiling dish is supported by rails , , , as indicated by solid lines in FIG. 25 when installed on the lower level, or the oven broiling dish is supported by rails , as indicated by dotted lines in FIG. 25 when installed on the upper level of the heating chamber . Dimension HC in FIG. 25 is 15 mm and is the distance from the bottom surface of the antenna enclosure to the bottom surface of the rotating antenna . Dimension HB is 10 mm and is the distance from the upper surface of the rotating antenna to the bottom surface of the bottom plate . Dimension HA is ⅛ of the wavelength of the microwaves and is the distance from the top surface of the bottom plate to the bottom surface of the oven broiling dish installed on the lower level.

When heating by microwaves, the heating mode for the oven broiling dish depends on the distance from the bottom plate , i.e., the lowest surface on which the object to be heated can be placed in the heating chamber .

The oven broiling dish carrying food can be placed at least ⅛ of the wavelength of the microwaves from the bottom plate to suppress the fluctuation of heat over the oven broiling dish .

FIG. 26 shows the temperature distribution over the oven broiling dish when it is installed on the upper level and when microwaves are supplied to the heating chamber for a specified time while the rotating antenna rotates. FIG. 27 shows the temperature distribution over the oven broiling dish when it is installed on the lower level. Everything is the same including the supply of microwaves in the cases of FIG. and FIG. 27 except for the installation position of the oven broiling dish . Different temperature bands are indicated by different styles of hatching in FIGS. 26 and 27.

While the center portion of the oven broiling dish is heated, there is a noticeable temperature difference between the center and the periphery, and although the temperature at the center is slightly higher, the fluctuation of temperature in FIG. 27 is substantially lower compared to FIG. .

When the oven broiling dish is installed on the upper level, the fluctuation of heat shown in FIG. 26 is suppressed by stopping the rotation of the rotating antenna at a predetermined position when supplying microwaves into the heating chamber . By stopping the rotation of the rotating antenna at a position corresponding to the position where the oven broiling dish is installed, the mode of supplying microwaves minimizes the fluctuation of heat over the oven broiling dish .

The mode of supplying microwave into the heating chamber changes depending on the stopping position of the rotating antenna which is dependent on the structure of the rotating antenna . FIG. 28 shows a plan view of the rotating antenna .

The rotating antenna is a circular disk made of metal having multiple areas punched out of the disk. A hole in the center of the rotating antenna is fitted on the shaft which is the center of rotation. The rotating antenna has a first portion having a rectangular shape which extends from the hole . Since the width W1 of the first portion is 35 mm, the leakage of microwaves traveling in the direction of arrow M on the first portion is minimized. The length W of the first portion is 65 mm. Consequently, microwaves are emitted with relatively strong intensities from the tip of the first portion in the M direction and from an area on the rotating antenna .

The rotating antenna has fan-shaped cutouts positioned opposite to the first portion relative to the hole . Since the distance W from the hole to the cutouts is 45 mm, microwaves are emitted from areas A, B on the rotating antenna . A second portion is positioned between the fan-shaped cutouts as a bridge connecting the center portion of the rotating antenna and the peripheral areas of the rotating antenna , thereby prompting the emission of microwaves through the periphery of the rotating antenna .

The rotating antenna constructed as described above allows the mode of supplying microwaves in the heating chamber to change according to the stopping position of the rotating antenna and allows the mode of heating the oven broiling dish to change.

The oven broiling dish can be installed on the lower level of the heating chamber . However, depending on the cooking menu, the oven broiling dish can be installed on the upper level to cook by combining heating by the grilling heater at the top of the heating chamber and by heating with microwaves. Therefore, the installation position of the oven broiling dish is indicated to the user by a display on the display unit which depends on the cooking menu. The rotating antenna stops at the stopping position which depends on the installation position of the oven broiling dish . For example, for a cooking menu which requires that the oven broiling dish be placed on the upper level, the rotating antenna stops at a stopping position shown in FIG. 29 to supply microwaves to the heating chamber . However, for a cooking menu which requires that the oven broiling dish to be placed on the lower level, the rotating antenna stops at a stopping position shown in FIG. 30 at a position rotated 90° clockwise from the position of FIG. 29 to supply microwaves to the heating chamber .

4. Variations of the Oven Broiling Dish

As described in the embodiment of the present invention shown in FIGS. 25-30, the height of the oven broiling dish in the heating chamber in the microwave oven can be changed. Also, as shown in FIGS. 26 and 27, the temperature distribution of the oven broiling dish changes as the height of the oven broiling dish is changed. The temperature distribution of the oven broiling dish can be changed by altering the area of the microwave heating element which is vapor-deposited (“the vapor deposition area”) according to the installation height of the oven broiling dish . Specifically, the vapor-deposition area of the microwave heating element on the oven broiling dish is preferably equal to the area of the rotating antenna in the horizontal direction, if the installation height (i.e., the distance from the bottom plate ) of the oven broiling dish is equal to ⅛ of the wavelength of the microwaves supplied to the heating chamber .

As the installation height of the oven broiling dish is increased greater than ⅛ of the wavelength of the microwaves, the vapor deposition area becomes increasingly larger in the horizontal direction than the area of the rotating antenna , as shown in FIG. . Additionally, as the installation height decreases below ⅛ of the wavelength, the vapor deposition area decreases in area in the horizontal direction to be smaller than the area of the rotating antenna , as shown in FIG. .

FIGS. 31 and 32 are bottom views of the oven broiling dish in this embodiment of the present invention. In FIG. 31, the rotating antenna overlaps with the microwave heating element . The rotating antenna is indicated by dashed line AN and is whited out in FIG. . Also, in FIG. 31, the vapor deposition area of the microwave heating element is greater than the area of the rotating antenna . In contrast, in FIG. 32, the position of the rotating antenna is indicated by dashed line AN, and the microwave heating element , which overlaps the rotating antenna , is indicated by a hatched. In FIG. 32, the area of the microwave heating element is smaller than the area of the rotating antenna .

FIGS. 33 and 34 show another embodiment of the present invention. FIG. 33 shows the bottom view of the oven broiling dish . FIG. 34 is a cross-section drawing taken along the line E—E of FIG. . The oven broiling dish according to this embodiment has grooves with a depth of approximately 5 mm, and the microwave heating element A is vapor-deposited along the grooved surface. On the top side of the oven broiling dish , microwave heating element coatings B-G are vapor-deposited only on the areas which align with the hills on the bottom side of the oven broiling dish . By placing food to be cooked directly on the top side of the oven broiling dish , one can cook foods that are normally cooked on steel plates such as pancakes. Although, the surface where microwave heating elements B-G are vapor-deposited looks like a grooved surface as shown in FIG. 34, the thickness of microwave heating element coatings A-G is only approximately 8×10−8 m such as for the microwave heating element . Thus, the grooves formed by microwave heating element A and coatings B-G are almost indiscernible in practical use.

FIG. 35 shows an embodiment of the present invention in which the top and bottom sides of the oven broiling dish in FIG. 34 are reversed. In FIG. 35, food is placed on the grooved surface where the microwave heating element A is deposited to provide an ideal cooking surface for foods such as steaks that produce liquids during cooking such as melted fat. The liquids are collected in the grooves to be separated from the food.

Microwave heating element coatings B-G are vapor-deposited only on the areas of the bottom of the oven broiling dish which align with the hills of the top side of the oven broiling dish in order to have high temperatures only on the hills that contact the food. This configuration not only prevents microwave heating element coatings B-G from being deposited on areas that do not need to be coated, but also prevents overheating the areas that do not need to be heated to high temperatures.

By depositing the microwave heating element A and microwave heating element coatings B-G in different configurations on the top and bottom sides of the oven broiling dish as shown in FIGS. 34 and 35, different modes of cooking can be performed on the oven broiling dish .

In the embodiment shown in FIG. 35, the specific resistance of the microwave heating element , A and coatings B-G is preferably in the range of 200-600 Ω/m by adjusting the thickness of the coating. FIG. 36 relates the electric field intensity caused by microwaves reflected from the oven broiling dish to the electric field intensity caused by microwaves passed through the oven broiling dish . The microwaves are supplied to the heating chamber using an electrically conductive material comprising tin oxide added with molybdenum in the microwave heating element , A and coatings B-G on the oven broiling dish .

FIG. 36 shows that the electric field intensity caused by microwaves reflected from the oven broiling dish balances with the electric field intensity caused by microwaves passed through the oven broiling dish when the specific resistance of the microwave heating element , A and coatings B-G is in the range of 200-600 Ω/m. Under these conditions, thermal cooking using the oven broiling dish becomes more efficient.

5. An Example of Thermal Cooking Process Using a Microwave Oven

An example of the thermal cooking process using a microwave oven according to the present invention is shown in FIGS. 37-53. FIGS. 37 and 38 show a flowchart of the cooking process.

Initial settings are received by the microwave oven in step S. Then, a control circuit decides at step S whether the cooking process is a thermal cooking process using the oven broiling dish according to a manual oven broiling method in which a preheat temperature and a cooking time are entered manually by the user. The control circuit makes this decision by deciding whether the oven broiling key has been pressed twice within a specified time period. When the control circuit decides that manual oven broiling has been selected, the control circuit sets the preheat temperature and cooking time, which was preset by the user using the adjusting knob at step S, and then, the control circuit advances to step S.

The oven broiling process has two stages when using the magnetron : the first stage and the second stage. In step S, the cooking times for the first and second stages are set by processing the preset cooking time in a predetermined manner. When advancing from the first stage to the second stage, an alarm is sounded to prompt the user to turn over the food on the oven broiling dish , as described later.

However, at step S, if it is judged that manual oven broiling is not selected, another decision is made at step S to decide whether the automatic oven broiling process has been selected. Automatic oven broiling is a cooking process in which the food on the oven broiling dish is heated at an automatically-determined preheat temperature during an automatically-determined cooking time. The control circuit decides that automatic oven broiling has been selected if the oven broiling key is pressed only once within a specified time period. If the control circuit decides that automatic oven broiling has been selected, the control circuit advances to step S. If the control circuit determines that automatic oven broiling has not been selected at step S, the control circuit advances to step S.

Step S, in which the preheat temperature and the cooking time are set, is omitted when automatic oven broiling is selected, because the preheat temperature and the cooking time for automatic oven broiling are predetermined.

In step S, the control circuit waits for the heating start operation (i.e., when the user presses the preheat key ), and then, the control circuit advances to step S.

In step S, the control circuit waits for the magnetron to start and then performs the preheat process in step S. The preheat process heats the microwave heating element , A and coatings B-G, if applicable, to preheat the oven broiling dish .

When the preheat process in step S is complete, the control circuit stops driving the magnetron in step S and notifies the user of the completion of the preheat process, for example, by sounding an alarm. In step S, the control circuit waits for the heating start operation, and after the heating start operation, the control circuit advances to step S. When the preheat process is completed in step S, the user is warned that the oven broiling dish is very hot so that the user fully understands the danger because the oven broiling dish can reach very high temperatures relatively quickly.

In step S, the control circuit executes the oven broiling process, and after the completion of the oven broiling process, the control circuit notifies the user of the completion in step S. Then, the control circuit returns to step S.

At step S, if it is decided that automatic oven broiling is not selected, the control circuit advances to step S. In step S, the control circuit decides whether manual double side broiling has been selected. Manual double side broiling is a cooking process by heating the food by both the grilling heater and the oven broiling dish , and the cooking time is manually entered by the user. This decision is made by determining whether the grilling key is pressed twice within a specified time. If the control circuit decides that manual double side broiling has been selected, the control circuit sets the cooking time, which was preset by the user using adjusting knob in step S. After step S, the control circuit advances to step S. For manual double side broiling and double side broiling to be described later, there are two stages: the first stage of microwave heating using the magnetron and the second stage of heating using the grilling heater .

However, in step S, if the control circuit decides that manual oven broiling has not been selected, another decision is made whether automatic double side broiling has been selected by the user in step S. Automatic double side broiling is a cooking process in which the cooking time is automatically determined and food is heated using the grilling heater and the oven broiling dish . This decision is made by deciding whether the grilling key is pressed only once within a specified time. If the control circuit decides that automatic double side broiling has been selected, the control circuit reads out and sets the cooking times of the first stage and second stage in step S. Then, the control circuit advances to step S. The first stage and second stage comprise a cooking course which is a course corresponding to a cooking course number that the user has selected using the adjusting knob on the operating panel after automatic double side broiling has been selected.

In step S, the control circuit waits for the user to perform the heating start operation by pressing the preheat key , and then, the control circuit advances to step S.

In step S, the control circuit calculates the preheat time from the cooking time set up in steps S and S and then advances to step S. The preheat time is calculated depending on the cooking time according to a predetermined method so that the preheat time is longer if the cooking time is longer. For example, the preheat time can be 3 minutes if the cooking time is less than 5 minutes, or the preheat time can be 5 minutes if the cooking time is over 5 minutes but less than 10 minutes. After calculating the preheat time, the control circuit advances to step S.

In step S, the control circuit starts driving the magnetron . When it determines that the preheat time is expired in step S, it stops driving the magnetron in step S and notifies the user that the preheat process is complete in step S. In step S, the control circuit waits for the user to perform the heating start operation and then advances to step S.

In step S, the control circuit executes the double broiling process, notifies the user when the process is complete in step S, and returns to step S.

If the control circuit decides in step S that automatic double side broiling has not been selected in step S, the control circuit decides whether another cooking process is selected in step S. Another cooking process can include the defrosting process which is activated when the defrosting key is pressed. When another cooking process is selected, the cooking time which is preset by the user is set up in step S, the cooking process is executed for the specified cooking time in step S, and then, the control circuit returns to step S. If the control circuit decides that another cooking step is not selected in step S, the control circuit advances directly to step S.

The preheat process is shown in FIGS. 39-50, and FIG. 39 is a subroutine flowchart of the preheat process of step S. In the preheat process, the control circuit starts the timer for counting a count value t in step S.

Next, the control circuit executes the output setting A process in step S. The output setting A process is shown in FIG. . In the output setting A process, the control circuit first detects the temperature Ti of the inverter, i.e., a frequency conversion circuit , in step S.

Next, in step S, the control circuit decides whether the timer is counting count value ta. The count value ta is a measurement of the time required for Tcave to change from Tcave to Tcave. Tcave is the average temperature measured within a scanning range by an infrared detection element, i.e., the preheat control object. Tcave is a specified temperature, and Tcave is a specified temperature higher than Tcave . If the timer is counting the count value ta, the control circuit advances to step S; if not, the control circuit advances to step S.

In step S, the control circuit decides whether Ti measured in step S is smaller than a specified value Ti. If Ti is smaller than Ti, the control circuit advances to step S; if not, the control circuit advances to step S.

In step S, the control circuit decides whether Ti detected in step S is smaller than the specified value Ti (>Ti). If Ti is smaller than Ti, the control circuit advances to step S; if not, the control circuit advances to step S.

When the output setting A process reaches step S, the control circuit sets an output P of the magnetron to P, the maximum preheat time tmax to tmax, and then returns to the preheat process in step S. The maximum preheat time is the time at which the preheat process ends regardless of the temperature detected by the infrared sensor and measured from when the preheat process began.

When the output setting A process reaches step S, the control circuit sets the output P of the magnetron to P, the maximum preheat time tmax to tmax, and then returns to the preheat process in step S.

When the output setting A process reaches step S, the control circuit sets the output P of the magnetron to P, the maximum preheat time tmax to tmax, and then returns to the preheat process in step S.

The relation of the outputs P, P, P of the magnetron is P>P>P. Therefore, as the temperature of the inverter increases, the output of the magnetron decreases. The inverter has a temperature rise which is highest when the magnetron is being driven.

If the timer is not counting the count value ta, the output P of the magnetron is set to P1 when “Ti

The maximum preheat times tmax-tmax can be selected to be different from each other. Therefore, the maximum preheat time can be determined according to the output of the magnetron .

As shown in FIG. 39, after the output setting A process in step S, the control circuit causes the open thermistor to detect a temperature Tth in the heating chamber and calculates a preheat holding output Px. The preheat holding output Px is calculated from a predetermined function f(x) as a function of a preheat temperature x determined in step S, for example. Since Px is the output of the magnetron when the temperature of the oven broiling dish is held constant, Px<

Next, the control circuit executes a dish temperature detection process in step S. The dish temperature detection process is shown in FIG. .

Each infrared detection element of the infrared sensor has an initial position. In the dish temperature detection process, the control circuit moves each infrared detection element of the infrared sensor to the initial position in step S. Each infrared detection element in the infrared sensor has a temperature detection area.

The infrared sensor according to this embodiment of the present invention is equipped with eight infrared detection elements, each designated as element n (for n=1-8). The temperature detection area ARn of infrared detection element n can be expressed as AR-AR on the oven broiling dish as shown in FIG. . FIG. 42 shows 8×16 points obtained by drawing eight lines A-H from left to right and 16 lines 0-15 in the depth direction on the oven broiling dish . Each temperature detection area AR-AR corresponding to an infrared detection element n contains 16 points. The infrared sensor scans each infrared detection element n to detect the temperatures of the 16 points sequentially as they are lined up in the depth direction on the temperature detection area AR-AR, respectively. In step S, the initial position of each infrared detection element n is the position for detecting the temperature on the points lying on the line 0 in the depth direction.

As shown in FIG. 41, the control circuit causes the infrared sensor to scan so that each infrared detection element n detects the temperatures of the 16 points in each temperature detection area AR-AR, respectively, in step S.

Next, in step S, the control circuit calculates an average temperature Tdnave and a maximum temperature Tnmax of the temperatures of the 16 points detected by the infrared detection elements n of the infrared sensor in step S.

In step S, the control circuit decides whether any of the eight infrared detection elements n is to used as the object of the preheat control, i.e., the preheat control object. This decision is made at step SA, step SA, or step SA to be described later. If the control circuit has selected a preheat control object, the control circuit calculates in step S the average value of the temperatures of the points that have been detected by the element that is the preheat control object. If the control circuit has not selected a preheat control object, the control circuit returns to the preheat process.

As shown in FIG. 39, after step S in which the control circuit detects the temperature Tdnave in the dish temperature detection process, the control circuit stores the temperature Tdnave in step S as Tdnave (for n=1-8 representing the infrared detection element n so that there exists Tdave-Tdave, where “0” stands for the first scanning).

Next, in step S, the control circuit decides whether Tth detected in step S is smaller than the specified Tth. If Tth is smaller than Tth, the control circuit advances to step S; if Tth is greater than Tth, the control circuit advances to step S.

In step S, the control circuit decides whether the maximum value of Tdnave is smaller than the specified Tdave. If Tdnave is smaller than Tdave, the control circuit advances to step S; if Tdnave is greater than Tdave, the control circuit advances to step S.

In step S, the control circuit decides whether the maximum value of Tdnave is smaller than the specified Tdave. If Tdnave is smaller than Tdave, the control circuit advances to step S; if Tdnave is greater than Tdave, the control circuit advances to step S.

Then, in step S, step S, step S, and S, as shown in FIG. 39, the control circuit executes preheat control A process, preheat control B process, preheat control C process, and preheat control D process, respectively, and then returns to the main program.

The preheat control A process is shown in FIGS. 43A-43C. In the preheat control A process, the control circuit decides in step SA if the cooking menu that is currently being executed in the microwave oven is a menu that requires the oven broiling dish to be installed on the lower level of the heating chamber , as shown in FIG. . The microwave oven can indicate to the user the required level on which the oven broiling dish is to be installed for each menu. If the menu requires the dish to be installed on the lower level, the control circuit advances to step SA; if the menu requires the dish to be installed on the upper level, the control circuit advances to step SA.

In step SA, the control circuit decides whether the maximum value of the latest Tnmax is smaller than the specified Tnmax. If Tnmax is smaller than Tnmax, the control circuit advances to step SA; if Tnmax is greater than Tnmax, the control circuit advances to step SA.

In step SA, the control circuit executes the output confirmation process, which is shown in FIG. . In the output confirmation process, the control circuit first executes the output setting A process in step SE. The output setting A process is described above and is shown in FIG. .

Next, in step SE, the control circuit decides whether the output P of the magnetron has changed in the output setting A process executed immediately before in step SE. If P has not changed, the control circuit returns to the preheat control A process; if P has changed, the control circuit advances to step SE.

In step SE, the control circuit decides whether the output P after the change equals P. If the output after the change is P, the control circuit returns to the preheat control A process; if the result of the change is not P, the control circuit advances to step SE.

In step SE, the control circuit decides whether the preheat time tn has already been determined. If tn has been determined, the control circuit advances to step SE; if tn has not been determined, the control circuit returns to the preheat control A process.

In step SE, the control circuit changes the preheat time tn depending on the change of the output of the magnetron and returns to the preheat control A process. The preheat time tn after the change (“tn after change”) is calculated according to Formula 1 using the output of the magnetron before and after the change (“output before change” and “output after change”, respectively), the preheat time tn before the change (“tn before change”), and the count value t of the timer, which began counting in step S.

As shown in FIG. 43A, after the output confirmation process is completed in step SA, the control circuit executes the dish temperature detection process in step SA. The dish temperature detection process is described above and shown in FIG. .

Next, in step SA, the control circuit executes the error detection process. The error detection process is shown in FIGS. 45A and 45B.

In the error detection process, the control circuit decides in step SF whether the count value t of the timer started in step S is the specified value te. If t is te, the control circuit advances to step SF; if not, the control circuit advances to step SF.

In step SF, the control circuit decides whether the output P of magnetron is P. If P is P, the control circuit advances to step SF; if P is not P, the control circuit advances to step SF.

In step SF, the control circuit decides whether the output P of magnetron is P. If P is P, the control circuit advances to step SF; if P is not P, the control circuit returns to the preheat control A process.

In step SF, the control circuit sets up threshold values Ta, Tb for deciding if there is an error in the temperature increase values ΔT, ΔT, respectively, of the oven broiling dish . Then, the control circuit advances to step SF. In step SF, the threshold values Tc, Td are set to the temperature increase values ΔT, ΔT, respectively. Then, the control circuit advances to step SF. The threshold values for the temperature increase values ΔT, ΔT of the oven broiling dish are used as the basis of the error judgment in correspondence with the output of magnetron and can be set differently.

In step SF, the control circuit decides whether the count value t of the timer is te. If t is te, the control circuit advances to step SF; if not, the control circuit returns to the preheat control A process.

In step SF, the control circuit decides whether the output P of the magnetron is P. If P is P, the control circuit advances to step SF; if P is not P, the control circuit advances to step SF.

In step SF, the control circuit decides whether the output P of the magnetron is P. If P is P, the control circuit advances to step SF; if P is not P, the control circuit returns to the preheat control A process.

In step SF, the control circuit sets up the threshold values Te, Tf as the temperature increase values of the oven broiling dish ΔT, ΔT, respectively, to determine if there is an error. Then, the control circuit advances to step SF. In step SF, the threshold values Tg, Th are set to the temperature increase values ΔT, ΔT, respectively, and the control circuit advances to step SF. In other words, the threshold values can be set differently to the temperature increase values on the oven broiling dish and are used as the basis for error judgment in correspondence with the output of the magnetron . In comparison to steps SF and SF, different threshold values can be set depending on the time the steps are executed, e.g., the values of te or te.

In step SF, the control circuit decides whether the maximum value of “Tnmax−Tnmax” is smaller than ΔT. “Tnmax−Tnmax ” is a value of increase of the maximum value of the temperature detected by each infrared detection element from the maximum value of the initial detection. Also, the maximum value of “Tnmax−Tnmax ” is the maximum value among the values of increase of the eight infrared detection elements.

If the maximum value of “Tnmax−Tnmax ” is smaller than ΔT, the control circuit alerts the user with an error notice and stops the preheat process in step SF. As a result, if the temperature increase of the oven broiling dish is smaller than an expected range, or if each infrared detection element of the infrared sensor cannot detect the temperature properly, the preheat process can be stopped.

However, if the maximum value of “Tnmax−Tnmax ” is greater than ΔT, the control circuit advances to step SF.

In step SF, the control circuit decides whether the menu operated in the microwave oven is a menu that requires the oven broiling dish to be installed on the lower level of the heating chamber . If the menu requires the oven broiling dish to be on the lower level, the control circuit advances to SF; if the menu requires the oven broiling dish to be on the upper level, the control circuit advances to step SF.

In step SF, the control circuit decides whether the minimum value of “Tnmax−Tnmax ” is greater than ΔT. If the minimum value of “Tnmax−Tnmax ” is greater than ΔT, the control circuit issues an error notice and cancels the preheat process in step SF; if the minimum value of “Tnmax−Tnmax ” is smaller than ΔT, the control circuit returns to the preheat control A process.

In step SF, the control circuit decides whether the minimum value of “Tnmax−Tnmax ” is greater than ΔT. If the minimum value of “Tnmax−Tnmax ” is greater than ΔT, the control circuit alerts the user with an error notice and stops the preheat process in step SF; if the minimum value of “Tnmax−Tnmax ” is smaller than ΔT, the control circuit returns to the preheat control A process.

In steps SF-SF, the method for detecting an error varies with the height at which the oven broiling dish is installed. The area included in the field of view QA of each infrared detection element of the infrared sensor varies over the oven broiling dish when the height at which the oven broiling dish is installed varies as shown in FIGS. 46A and 46B. FIG. 46A shows the field of view QA of the infrared sensor of the oven broiling dish when installed on the upper level, and FIG. 46B shows the field of view of the infrared sensor of the oven broiling dish when installed on the lower level. If the oven broiling dish is stored on the lower level as shown in FIG. 46B, almost the entire oven broiling dish is included in the field of view QA, whereas if the oven broiling dish is installed on the upper level as shown in FIG. 46A, a substantial area of the oven broiling dish is out of the field of view QA. In step SF, the control circuit decides whether the infrared detection element can detect the temperature rise on the oven broiling dish based on the decision of whether the temperature detected by the infrared detection element has risen sufficiently. If the control circuit determines that the infrared sensor cannot detect the temperature rise, the control circuit alerts the user with an error notice and terminates the preheat process.

It is also preferable for the microwave oven to change the scanning range of each infrared detection element by changing the angle of the infrared sensor by other means according to the height at which the oven broiling dish is installed in the heating chamber . When the height at which the oven broiling dish is installed in microwave oven is specified in the cooking menu, the scanning range must be changed based on the selected cooking menu. If the height at which the oven broiling dish is installed is improper for the scanning range of the infrared detection elements in the error detection process, an error notice will be issued since the infrared element cannot detect the temperature rise on the oven broiling dish . In the error detection process, an error notice can be issued when the oven broiling dish is not installed at the specified height for the particular cooking menu and also when detecting an error based on the height of the oven broiling dish through a change of the scanning range. Since an error notice can be made in this additional case, the user must be issued an error notice to understand that there is a possibility of error in the installation position of the oven broiling dish .

The error detection process issues an error notice when the temperature rise is not within the specified range. The method of the temperature rise varies with the material of the oven broiling dish installed in the heating chamber . In the error detection process, the installation position of the oven broiling dish and the material of the oven broiling dish must be proper. Therefore, an oven broiling dish made of a different material from the material of the regular oven broiling dish cannot be installed in the heating chamber by mistake.

When the microwave heating element is vapor-deposited only on a portion of the oven broiling dish , the scanning range of the infrared detection elements can be limited to the area where the microwave heating element is vapor-deposited. Therefore, the infrared sensor can detect temperatures efficiently since the infrared sensor skips area where temperature detection is not necessary.

Additionally, the scanning ranges of the infrared detection elements can depend on the cooking menu to skip areas where temperature detection is not necessary. For example, during a simmering process, only the central area of the heating chamber can be scanned or only the area where food is present can be scanned by conducting a preliminary detection of the entire heating chamber at the beginning of the heating process, thereby determining the location of the food. Alternatively, the area where the food is present can be scanned by allowing the user to enter the location of the food.

As shown in FIG. 43A, if the preheat process is not cancelled in the error detection process in step SA, the control circuit decides whether the maximum value of the latest Tnmax is greater than Tnmax in step SA. If Tnmax is greater than Tnmax, the control circuit advances to step SA; if Tnmax is smaller than Tnmax, the control circuit returns to step SA.

In step SA, the control circuit calculates “Tnmax−Tnave,” selects four infrared detection elements by discarding the two infrared detection elements with the highest “Tnmax−Tnave” and the two infrared detection elements with the lowest “Tnmax−Tnave ” as the preheat control objects, and the control circuit advances to step SA.

In step SA, the control circuit selects as the preheat control objects the infrared detection elements specified as the default A infrared detection elements among the eight infrared detection elements, and the control circuit advances to step SA. Step SA selects predetermined infrared detection elements to be the preheat control objects if it is difficult to determine the preheat control objects, such as when the oven broiling dish is already warm from the beginning of the heating process.

In step SA, the control circuit selects as the preheat control objects the infrared detection elements specified as the default A infrared detection elements among the eight infrared detection elements, and the control circuit advances to step SA. As shown in FIGS. 46A and 46B, step SA selects the infrared detection elements that are considered appropriate to become the preheat control objects when it is too difficult to place the entire oven broiling dish within the field of view QA of the infrared detection elements.

The control circuit executes the output confirmation process (as shown in FIG. 44) in step SA, executes the dish temperature detection process (as shown in FIG. 41) in step SA, and executes the error detection process (as shown in FIGS. 45A and 45B) in step SA.

If the preheat process is not canceled in the error detection process in step SA, the control circuit decides whether Tcave has reached Tcave in step SA. Tcave is the average temperature detected by the preheat control objects in the scanning range, and Tcave is the specified temperature. The control circuit repeats steps SA-SA until Tcave reaches Tcave , and then, the control circuit advances to step SA.

In step SA, the control circuit starts counting the count value ta on the timer, and then, the control circuit advances to step SA.

The control circuit executes the output confirmation process (as shown in FIG. 44) in step SA, executes the dish temperature detection process (as shown in FIG. 41) in step SA, and executes the error detection process (as shown in FIGS. 45A and 45B) in step SA.

If the preheat process is not canceled in the error detection process in step SA, the control circuit decides whether Tcave has reached the specified temperature Tcave in step SA. The control circuit repeats steps SA-SA until Tcave reaches Tcave , and then stops counting ta in step SA. Then, the control circuit determines the preheat time t and advances to step SA when Tcave reaches Tcave . The preheat time t is determined by a predetermined function f (x, ta) which is dependent on the preheat temperature x and the count value ta of the timer.

As the preheat time t is determined by the function f (x, ta) in this embodiment, there is no need for the infrared detection elements to detect temperatures up to such a high temperature as the preheat temperature x. Therefore, the cost of the microwave oven can be reduced. The reason for being able to determine t based on the preheat temperature x and the count value of the timer ta will be described below with reference to FIG. .

FIG. 47 indicates the chronological change of Tcave measured from the start of the preheat process. In FIG. 47, TM is the upper limit of the temperature that can be detected by the infrared detection elements, and x is the preheat temperature. The change in Tcave is shown by a solid line.

When the preheat process starts, Tcave rises up to TM and afterwards remains constant at Tcave, even if the temperature of the oven broiling dish continues to rise. The time t required for the oven broiling dish to reach the preheat temperature x can be estimated by considering an extension line (shown as a dashed line) extending from Tcave to Tcave . Examples of x, TM, Tcave , and Tcave are 200° C., 140° C., 110° C., and 70° C. respect

As shown in FIG. 43C, after step SA, the control circuit executes the output confirmation process (shown in FIG. 44) in step SA, decides the count value t of the timer (which was started to count in step S) in step S, repeats step SA until the count value t reaches the preheat time t or the maximum preheat time tmax, and then returns to the preheat process when the count value t reaches the preheat time t or the maximum preheat time tmax. Next, the preheat control B process (shown in FIG. 39 as step S) is shown in detail in FIG. . In the preheat control B process, the control circuit sets the preheat time t as a function of the preheat temperature x, i.e., f (x), in step SB; sets the output P of the magnetron to the preheat holding output Px (which was set in step S) in step SB; and executes the output setting B process in step SB. The output setting B process is shown in FIG. .

In the output setting B process, the control circuit detects the inverter temperature Ti in step SG and decides whether Ti is smaller than the specified temperature Ti in step SG. If Ti is smaller than Ti, the control circuit returns to the preheat control B process; if Ti is greater than Ti, the control circuit sets the output P of magnetron to P in step SG, sets the preheat time tn to tmax in step SG, and returns to the preheat control B process.

As shown in FIG. 48, after step SB, the control circuit decides whether the count value t of the timer, which began counting in step S, has reached the preheat time t. The control circuit repeats the output setting B process in step SB until the count value t of the timer reaches t in step SB, and then returns to the preheat process.

As shown in FIG. 39, since the preheat control B process is executed when the temperature of the heating chamber detected by the open thermistor is relatively low and the temperature of the oven broiling dish is relatively high, the output of the magnetron lowers and the temperature of oven broiling dish settles down automatically in the preheat process.

The preheat control C process executed in step S is shown in FIG. . The preheat control C process is executed when the temperature of the heating chamber is relatively high and the temperature of the oven broiling dish is relatively low as shown in FIG. . In the preheat control C process, the control circuit sets the preheat time t based on a function of the preheat temperature x and the temperature of the heating chamber detected by the open thermistor , i.e., f (x, Tth) in step SC. Then, the control circuit executes the output confirmation process (as shown in to FIG. 44) in step SC and repeats step SC until the count value t of the timer reaches the preheat time t in step SC, and returns to the preheat process when the count value t of the timer reaches the preheat time t.

Table 1 shows an example of the function f (x, Tth).

The function f (x, Tth) defines the preheat time for each preheat temperature zone. The function f (x, Tth) also defines two temperature zones of Tth (low) and Tth (high) using specified threshold values from the detection temperature Tth from the open thermistor and defines the preheat time for each of the temperature zones.

The preheat control D process executed in step S is shown in FIG. . In the preheat control D process, the control circuit sets the preheat time t based on a function of the preheat temperature x, i.e., f (x) in step SD; sets the output of magnetron to P; and executes the output setting B process (shown in FIG. 49) in step SD. The control circuit repeats step SD until the count value t of the timer reaches the preheat time t in step SD and returns to the preheat process when the count value t of the timer reaches the preheat time t4.

Since the maximum preheat time is determined in the preheat processes described above, the preheat process will be completed automatically even if problems develop in the infrared detection elements. Also, the number of infrared detection elements that are used as the preheat control objects is assumed to be four out of eight infrared elements, however the invention is not limited to this assumption.

In the preheat process of this embodiment, the magnetron is driven for a predetermined time during the preheat control C process or during the preheat control C process in step S, if the temperature Tth of the heating chamber detected by the open thermistor is decided by the control circuit to exceed the specified temperature Th. Also, if the control circuit decides that the temperature Tth of the heating chamber detected by the open thermistor in step S exceeds the specified temperature, the control circuit selects the infrared detection elements of the infrared sensor in step S. The temperature detected by the open thermistor is a condition to determine the branching of the preheat control A process through the preheat control D process, and the output of the magnetron is determined in each of the preheat control A process through the preheat control D process. For example, when the control circuit advances to the preheat control D process, the output of the magnetron is set to P unless the temperature of the inverter is higher than Ti. Thus, the temperature of the heating chamber is also a factor for deciding the output of the magnetron .

In the preheat processes of this embodiment, the maximum value of Tdnave (the average temperature detected by the eight infrared detection elements of the infrared sensor in the scanning range for detecting temperatures in the heating chamber for the first scanning after the start of the heating process by the magnetron ) is compared to the specified value Tdave or Tdave in steps S and S. Different preheat times are set in the preheat control A process through the preheat control D process in steps S-S. Thus, the preheat time is determined according to the temperature of the oven broiling dish at a specified time after the start of microwave generation by the magnetron . The temperature used for comparison in step S or step S can be the temperature measured just before the magnetron starts to generate microwaves instead of the maximum value of Tdnave.

Next, the oven broiling process executed in step S in FIG. 37 is shown in FIG. . In the oven broiling process, the control circuit starts driving the magnetron in step S and waits for the first stage cooking time to pass in step S. When the first stage cooking time expires, the control circuit stops driving the magnetron and notifies the user that the first stage is completed by a device such as an alarm in step S. Then, an instruction is displayed using the display unit , for example, thereby prompting the user to turn over the food on the oven broiling dish .

The control circuit then waits for the user to perform the heating start operation to start the heating process in step S and starts driving the magnetron again in step S.

The control circuit then waits for the second stage cooking time to expire in step S, stops driving the magnetron in step S, and returns to the main program.

In the oven broiling process described above, the second stage cooking time after the food is turned over can be shorter than the first stage cooking time in order to obtain better results when cooking.

After the magnetron is restarted in step S, immediately after the second stage cooking time has started, it is preferable to let the magnetron temporarily deliver a higher output since the temperatures in the heating chamber and the oven broiling dish are assumed to drop as the magnetron stops operating temporarily during steps S and S. The output of the magnetron can be lowered during the oven broiling and double side broiling processes as in the preheat process as certain times such as when the inverter temperature is too high. It is preferable to extend the second stage cooking time in order to cover the reduction of the output of the magnetron in the first stage.

Moreover, the microwave oven can reduce the output of the magnetron , for example, when the inverter temperature becomes too high, and can maintain steady output even if the conditions for reducing the output of the magnetron are satisfied but there is little cooking time remaining.

The double side broiling process, which is executed in step S in FIG. 38, is shown in FIG. . In the double side broiling process, the control circuit starts driving the magnetron in step S and decides whether manual double side broiling is selected in step S. If the control circuit decides that manual double side broiling has been selected, the control circuit determines the first stage cooking time and the second stage cooking time based on a predetermined cooking time, which was set up in step S. The control circuit uses a predetermined method for selecting the first stage and second stage cooking times in step S and then advances to step S. If the control circuit decides that manual double side broiling has not been selected in step S, the control circuit advances to step S.

Since the first stage cooking time and the second stage cooking time are automatically determined in step S, the user can execute an appropriate double side broiling process using the microwave oven by simply entering the total cooking time.

In step S, the control circuit waits for the first cooking time to expire and then, advances to step S. In step S, the control circuit stops driving the magnetron and starts driving the grill heater . In step S, the control circuit waits for the second stage cooking time to expire and then advances to step S.

In step S, the control circuit stops driving the grill heater and returns to the main program. In the double side broiling process, the top surface of the food on the oven broiling dish is browned by grill heater , and the bottom surface is browned by the microwave heating element of the oven broiling dish , and the inside of the food is cooked by microwaves, so that the entire portion of food can be cooked in a short period of time. Although it is preferable if both the magnetron and the grill heater are driven simultaneously, the maximum breaker capacity of normal houses, i.e., the no-fuse breaker capacity of 15-20 A, does not allow the simultaneous use of microwave ovens and heaters.

Therefore, the microwave oven and the heater are used separately as described above.

When the installation position of the oven broiling dish in the heating chamber of the microwave oven is selected from a plurality of levels as shown in FIGS. 10, , etc., in a cooking process where the surface of the food is browned using the grill heater such as in the double side broiling process, it is preferable to place the oven broiling dish at a location closest to the grill heater . The control circuit is capable of displaying a suggestion in the display unit for prompting the user to place the oven broiling dish in a location closest to the grill heater .

All of the embodiments disclosed herein should be construed as examples and not of a limiting nature. The scope of the invention are indicated not by the descriptions above, but by the claims shown herein, and the invention is intended to include all variations within the scope of claims and their equivalencies.

CLAIMS

1. A microwave heating device comprising: a heating chamber for holding an object to be heated; a magnetron for generating microwaves; a waveguide for supplying the microwaves generated by said magnetron through the bottom of said heating chamber; a heating dish on which said object to be heated is placed, said heating dish having a bottom surface; a microwave heating element for generating heat by absorbing the microwaves, said microwave heating element located on the bottom surface of said heating dish; and an access passage disposed between said microwave heating element and an outer edge of said heating dish for allowing the microwaves introduced by said waveguide to reach above said heating dish from underneath said heating dish.

2. A microwave heating device described in claim 1, wherein said heating chamber has recessed areas for providing gaps between an inner wall of said heating chamber and said heating dish, said recessed areas located adjacent to said heating dish installed within said heating chamber.

3. A microwave heating device described in claim 1, wherein said heating dish is provided with said microwave heating element except on the outer edge area of said heating dish.

4. A microwave heating device described in claim 1, further comprising: a heater located above said heating dish.

5. A microwave heating device described in claim 1, wherein a dimension of said access passage in the direction perpendicular to the propagating direction of said microwaves is greater than one quarter of the wavelength of said microwaves.

6. A microwave heating device described in claim 1, wherein the inner wall of said heating chamber has a first surface and a second surface that faces a direction different from that of the first surface; and rails are formed on said first surface and said second surface for supporting said heating dish, wherein said rails formed on said first surface or second surface comprise a plurality of members spaced from each other on a single plane.

7. A microwave, heating device described in claim 1 wherein a groove is formed on the outer edge of the surface of said heating dish that carries said object to be heated.

8. A microwave heating device described in claim 1, wherein the lowest part of said heating dish is located below said microwave heating element.

9. A microwave heating device described in claim 1, further comprising: a rotating antenna that rotates for spreading the microwave energy in said waveguide inside the heating chamber, and a rotation control unit for controlling the rotation of said rotating antenna, wherein said rotation control unit stops said rotating antenna at a position corresponding to the height at which said heating dish is stored when said magnetron generates the microwaves.

10. A microwave heating device described in claim 1, further comprising: a rotating antenna that rotates for spreading the microwave energy in said waveguide inside the heating chamber, wherein the area of a surface of said microwave heating element of said heating dish perpendicular to the traveling direction of said microwaves is equal to the area of said rotating antenna when the distance between said heating dish and the bottom face of said heating chamber in the traveling direction of said microwaves is ⅛ of the wavelength of said microwaves, increases in proportion to the degree said distance in said traveling direction is greater than ⅛ of the wavelength of said microwaves, and reduces in proportion to the degree said distance in said traveling direction is smaller than ⅛ of the wavelength of said microwaves.

11. A microwave heating device described in claim 1, wherein said heating dish is stored in said heating chamber at a location ⅛ of the wavelength of said microwaves apart from the bottom face of said heating chamber.

12. A microwave heating device described in claim 1, further comprising: a rotating antenna that is provided inside the heating chamber and rotates within a specified plane for spreading the microwaves in said waveguide; and metal plates provided on the circumference of said rotating antenna, wherein said heating chamber is connected to said waveguide; further comprising: an antenna enclosure provided in the vicinity of said connection between said waveguide for enclosing said rotating antenna; wherein in case when a placement span, which is a distance between the circumference of said rotating antenna and the surface of said antenna enclosure along a direction perpendicular to said specified plane, is not uniform, said metal plates are positioned in areas where said placement span is the longest.

13. A microwave heating device described in claim 12, wherein the tips of said metal plates are located ahead of said rotating antenna relative to the traveling direction of said microwaves.

14. A microwave heating device described in claim 13, further comprising: a heater provided on the outer periphery of said rotating antenna, wherein said metal plates are located between said heater and said rotating antenna.

15. A microwave heating device described in claim 1, further comprising: a door that controls an access to said heating chamber; and a first protruding part provided on the inner wall of said heating chamber, which protrudes into said heating chamber, and abuts against said heating dish when the heating dish is placed in a position undesirable for the introduction of the microwaves into the heating chamber; wherein said magnetron generates microwaves on the condition that said door is closed, and said abutting of said heating dish against said first protruding part prevents said door of said heating chamber from closing.

16. A microwave heating device described in claim 1, further comprising: a door that controls an access to said heating chamber; a heater for heating foods in said heating chamber; a metallic dish, which is held in said heating chamber and carries said object to be heated when it is heated by said heater; and a second protruding part that abuts with said metallic dish when said metallic dish is placed in a position undesirable for the introduction of the microwaves into the heating chamber; wherein said magnetron generates microwaves on the condition that said door is closed; said abutting of said heating dish against said second protruding part prevents said door of said heating chamber from closing; and said heating dish is shaped in such a way that it does not abut against said second protruding part even when said heating dish is located in every position possible in said heating chamber.

17. A microwave heating device described in claim 1, wherein said microwave heating element has a thickness that equalizes the amount of microwaves absorbed by said microwave heating element with the amount of microwaves passed through.

18. A microwave heating device described in claim 1, wherein said microwaves pass through said outer edge of said heating dish.

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