EP2348257B1

EP2348257B1 - Microwave cooking device

Info

Publication number: EP2348257B1
Application number: EP09834343.7A
Authority: EP
Inventors: Koji Yoshino; Hiroshi Kawai; Kazumi Iwasaki; Ichiro Hori; Yuji Hayakawa; Takahiko Yamasaki
Original assignee: Panasonic Corp
Current assignee: Panasonic Corp
Priority date: 2008-12-25
Filing date: 2009-12-14
Publication date: 2016-06-29
Anticipated expiration: 2029-12-14
Also published as: JPWO2010073528A1; EP2348257A1; EP2348257A4; WO2010073528A1; CN102265092A; JP5310741B2; CN102265092B

Description

TECHNICAL FIELD

The present invention relates to a microwave cooking device that dielectrically heats an object to be heated.

BACKGROUND ART

An microwave oven that represents a microwave cooking device has come to be a cooking tool essential in daily life owing to its simplicity of being able to directly heat food as an object to be heated and not requiring preparation for a pot or a pan. In recent years, a product has been put into practical use which has a heating chamber for housing food in a shape with a large width and enhanced convenience, formed by flattening a bottom surface of a space inside the heating chamber and further making a width to be not smaller than 400 mm that is relatively larger than a depth, so that a plurality of dishes can be arrayed and heated.
Further, with microwave ovens becoming multifunctional, one equipped with so-called "grilling function" and "defrosting function" has appeared in the market. The "grilling function" is a function where a so-called heating plate is used which is provided on its under face with a microwave absorber, such as ferrite, that absorbs microwaves to generate heat, and a temperature of the heating plate is raised with microwaves to cook food placed thereon. Further, the "defrosting function" is a function where frozen food is heated with microwaves, steam or a combination of these, to defrost the food.
Foregoing conventional microwave cooking device 300 is described with reference to FIG. 14. Microwave cooking device 300 includes magnetron 302, waveguide 303, heating chamber 301, placing table 306, feeding section (antenna space 310), rotary antenna 305, motor 304, heating plate 308, plate holding section 307, and heating device 309.
Magnetron 302 represents a microwave generating device. Waveguide 303 transmits microwaves radiated from magnetron 302 to heating chamber 301. Heating chamber 301 is placed on its inside with an object to be heated (not shown) such as food, and then used in a heating operation with microwaves. Placing table 306 is made up of a low-loss dielectric material, such as ceramic or glass, predisposed to facilitate microwaves to transmit therethrough, and fixed to the inside of heating chamber 301 and placed with the object to be heated.
Feeding section 310 is an antenna space formed below placing table 306 inside heating chamber 301. Rotary antenna 305 is fitted to the vicinity of the center of heating chamber 301, extending from waveguide 303 to feeding section 310, to radiate microwaves inside waveguide 303 into heating chamber 301. Motor 304 rotationally drives rotary antenna 305. Heating plate 308 is mounted inside heating chamber 301 in accordance with an application, and plate holding section 307 supports heating plate 308. Heating device 309 performs electrothermal heating.
In the case of executing a warming function to directly heat the object to be heated by microwave heating, a microwave heating treatment is started in a state where food or the like is placed on placing table 306. Microwaves radiated from magnetron 302 pass through waveguide 303 and rotary antenna 305, and are radiated from the upper surface of a radiation section of rotary antenna 305 toward heating chamber 301. At this time, rotary antenna 305 normally radiates the microwaves while rotating at a constant rate in order to uniformly stir the microwaves inside heating chamber 301 (e.g. refer to Patent Document 1).
In the case of executing a defrosting function to heat frozen food as the object to be heated by microwave heating, the frozen food is first placed on a heat-resistant tray or flat plate, and the tray or the flat plate in that state is placed on placing table 306. The defrosting function is then selected, to start an operation of the microwave cooking device. When the object to be heated reaches a predetermined temperature or the operation is performed for a set period of time, the defrosting operation is completed (e.g. refer to Patent Document 2).
In the case of executing a grilling function for cooking in a grill style, food (e.g. chicken thigh, fish, etc.) is placed on heating plate 308 placed on plate holding section 307. In this state, a surface portion of the food is thermally treated by heating device 309 located to the upper side of the food. Meanwhile, the back face of the food is heat-treated by heating plate 308 having absorbed microwaves to raise its temperature.
Further, there also is microwave cooking devices 300 different from the one configured as described above, which has a plurality of substantially rectangular slit holes as openings provided around the heating plate body, and in which a slit hole closing material formed of rubber chiefly composed of ferrite is detachably provided with respect to the slit holes (e.g. refer to Patent Document 3).
In the case of executing a defrosting function to heat frozen food as the object to be heated in the microwave cooking device provided with the slit holes, frozen food is placed on a heat-resistant tray or flat plate, and the tray or the flat plate in that state is placed on placing table 306. Further, the slit hole closing material is detached to open up the slit holes, and a menu is selected, to start an operation of the microwave cooking device. When the object to be heated reaches a predetermined temperature or the operation is performed for a set period of time, the defrosting operation is completed.
However, in the case of cooking frozen food by the grilling function in the conventional microwave cooking device as described in Patent Document 2 above, it is necessary, after execution of the foregoing defrosting function, to further set a menu so as to execute the grilling function. Hence it is necessary, after completion of defrosting, to re-set heating plate 308 with defrosted food placed thereon on predetermined plate holding section 307 so as to re-execute the grilling function, thereby forcing a user to perform a complicated operation.
Thereat, when continuous execution of the defrosting function to the grilling function on frozen food is intended in the state of heating plate 308 being mounted on heating chamber 301 from the beginning, a desired effect cannot be obtained due to the mounted heating plate 308. That is, since there is almost no gap between an outer edge of heating plate 308 and an inner wall of heating chamber 301, microwaves uniformly radiated from feeding section 310 (rotary antenna 305) to heating chamber 301 are blocked by the lower face of heating plate 308, and not apt to diffract to the upper surface side of heating plate 308.
Further, in the case of using the conventional microwave cooking device as described in Patent Document 3 for cooking frozen food, it is necessary, after execution of the defrosting function, to re-set the menu so as to execute the grilling function. Hence it is necessary, after completion of defrosting, to mount the slit hole closing material for closing the slit holes, and re-set the heating plate with defrosted food placed thereon on a predetermined plate holding section so as to re-execute the grilling function, thereby forcing a user to perform a complicated operation as in the above case.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

Patent Document 1: Unexamined Japanese Patent Publication No. 2004-071216 Patent Document 2: Unexamined Japanese Patent Publication No. H09-229372 Patent Document 3: Unexamined Japanese Patent Publication No. 2007-225186 . A further Patent Document JP 2006 196336 A is disclosing a microwave cooking device according to the preamble of claim 1

DISCLOSURE OF THE INVENTION

The present invention is to provide a microwave cooking device according to claim 1, which is capable of performing a defrosting function and a grilling function in an automatic and continuous manner without a user's operation even in the case of setting a heating plate with an object to be heated placed thereon inside a heating chamber.
The present invention has a configuration including: a heating chamber provided with a glass-fitted door at a front opening, for housing an object to be heated; a microwave-transparent placing table constituting a bottom surface inside the heating chamber; a metal heating plate, on an under face of which a microwave absorber is provided, which is detachably mounted in the heating chamber, and on which the object to be heated is placed; a microwave generating section; a waveguide for transmitting microwaves from the microwave generating section to the heating chamber; a directional feeding section having directivity, for supplying the microwaves from the waveguide to the heating chamber; a driving section for rotationally driving the directional feeding section; a control section for controlling the driving section to turn the directional feeding section to a direction of the door and supply the microwaves into a space above the heating plate, using the inside of the glass as a principal transmission channel; and a feeding section formed below the placing table, and housing the directional feeding section.
With the above configuration, it is possible to use the inside of the door as a transmission channel for microwaves without using an additional material and requiring processing on an existing material. That is, it is possible to effectively utilize a dead space without making the configuration complicated, so as to increase an amount of diffraction of microwaves to the upper side of the heating plate. It is thereby possible to obtain desired finishing of cooking suitable for the kind of the object to be heated, such as the object to be heated having been made to directly absorb microwaves and defrost, and also to improve heating efficiency. Accordingly, it is possible to perform the defrosting function and the grilling function in an automatic and continuous manner without a user's operation in a state where the heating plate with the object to be heated placed thereon is mounted inside the heating chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front sectional view showing an internal structure of a microwave oven as a microwave cooking device according to an embodiment of the present invention.
FIG. 2 is a view showing a cross section 2-2 of the microwave ven in FIG. 1.
FIG. 3A is a view of a cross section 3-3 of the microwave oven in FIG. 1 for explaining an orientation of a rotary waveguide in the present embodiment.
FIG. 3B is another view of the cross section 3-3 of FIG. 1 for explaining the orientation of the rotary waveguide in the microwave oven in the present embodiment.
FIG. 3C is still another view of the cross section 3-3 of FIG. 1 for explaining the orientation of the rotary waveguide in the microwave oven in the present embodiment.
FIG. 4 is an explanatory view of an origin detection mechanism of the rotary waveguide in the microwave oven in the present embodiment.
FIG. 5 is a constitutional view showing a configuration of a control section in the microwave oven in the present embodiment.
FIG. 6 is a flowchart showing an operation of the microwave oven in the present embodiment.
FIG. 7 is a view showing a configuration of a temperature detector used in the microwave oven in the present embodiment.
FIG. 8 is a plan view showing a modified example of the rotary waveguide in the microwave oven in the present embodiment.
FIG. 9A is a plan view for explaining a heating plate in the microwave oven in the present embodiment.
Fig. 9B is a side view for explaining the heating plate in the microwave oven in the present embodiment.
FIG. 9C is a view of a cross section 9C-9C of FIG. 9A for explaining the heating plate in the microwave oven in the present embodiment.
FIG. 10A is an explanatory view of an orientation of an opening section of the rotary waveguide with respect to the heating plate, and diffraction of microwaves to the upper surface side of the heating plate in the microwave oven in the present embodiment.
FIG. 10B is another explanatory view of the orientation of the opening section of the rotary waveguide with respect to the heating plate and diffraction of the microwaves to the upper surface side of the heating plate in the microwave oven in the present embodiment.
FIG. 11A is an explanatory view of a checking method for an amount of diffraction of the microwaves to the heating plate in the microwave oven in the present embodiment.
FIG. 11B is another explanatory view of the checking method for the amount of diffraction of the microwaves to the heating plate in the microwave oven in the present embodiment.
FIG. 11C is still another explanatory view of the checking method for the amount of diffraction of the microwaves to the heating plate in the microwave oven in the present embodiment.
FIG. 12A is an explanatory view of the relation, on the heating plate, between the orientation of the opening section of the rotary waveguide and the amount of diffraction of the microwaves in the microwave oven in the present embodiment.
FIG. 12B is another explanatory view of the relation, on the heating plate, between the orientation of the opening section of the rotary waveguide and the amount of diffraction of the microwaves in the microwave oven in the present embodiment.
FIG. 13 is a diagram representing the relation shown in FIG. 12B.
FIG. 14 is a front sectional view showing an internal structure of a conventional microwave oven.

PREFERRED EMBODIMENTS FOR CARRYING OUT OF THE INVENTION

Embodiment

Hereinafter, a microwave cooking device according to an embodiment of the present invention is described, taking a microwave oven as an example, with reference to FIGS. 1 to 13.
As shown in FIGS. 1 and 2, door 31b is fitted to body 31a in microwave oven 31. In body 31a, there are built heating chamber 34 that houses an object to be heated such as food, magnetron 32 that generates microwaves for cooking the object to be heated, and waveguide 33 connected to magnetron 32 for guiding the microwaves into heating chamber 34. Front-face opening 38 is formed on the front face of heating chamber 34.
Door 31b is fitted to body 31a, and configured so as to openably/closably cover front-face opening 38 formed in heating chamber 34. Door 31b may be fitted to body 31a via a hinge or as a sliding type such as a sliding door. When microwave oven 31 is of a built-in type, door 31b may be fitted to body 31a in such a form as to be drawn out. When fitted via the hinge, the door may be fitted to any one of the left side, the right side, and the lower side of front-face opening 38.
Door 31b includes metal plate 60, inner glass 61 and outer glass 62 that sandwich metal plate 60 in a front-back direction, and a choke cover (not shown) that covers an outer periphery of metal plate 60. In metal plate 60 of a position opposed to front-face opening 38, a plurality of through holes are formed so as to make the inside of heating chamber 34 visible. Choke structure 63 is formed on the outer periphery of metal plate 60.
FIG. 2 illustrates the case of bending metal plate 60 a plurality of times to form choke structure 63. It is to be noted that choke structure 63 is preferably formed at the end of metal plate 60 by bending the end section formed in comb shape a plurality of times with a plurality of slits provided at predetermined intervals. In the case of forming choke structure 63 in comb shape, the number of slits are not particularly limited.
Inner glass 61 functions to constitute one face of heating chamber 34 with door 31b in a closed state. Inner glass 61 makes the inside of heating chamber 34 visible with door 31b in the closed state. Outer glass 62 functions to constitute the outside surface of door 31b. As does inner glass 61, outer glass 62 also makes the inside of heating chamber 34 visible with door 31b in the closed state.
Microwave oven 31 includes placing table 35, feeding section (antenna space) 37, rotary waveguide 39, motor 41, control section 411, and photo interrupter 36. It should be noted that heating chamber 34 is connected to the top of waveguide 33, and forms a space with a size in a width direction (about 400 mm) being larger than a size in the depth direction (about 310 mm). Placing table 35 is made of a low-loss dielectric material, such as ceramic or glass, predisposed to facilitate microwaves to transmit therethrough, and is fixed to the inside of heating chamber 34 for placement of food (not shown) that represents the object to be heated.
Feeding section 37 is formed below placing table 35 inside heating chamber 34. Rotary waveguide 39 is fitted to the inside of feeding section 37 to radiate microwaves inside waveguide 33 into heating chamber 34. Motor 41 is a driving section that rotationally drives rotary waveguide 39. Control section 411 is a control section that controls motor 41 to control rotation and an orientation of rotary waveguide 39. Photo interrupter 36 constitutes an origin detection mechanism that detects an origin of each rotation of rotary waveguide 39.
It should be noted that rotary waveguide 39 is a directional feeding section having open section 58 shown in FIGS. 3A to 3C and being capable of radiating microwaves with concentration on a direction that open section 58 faces.
Returning to FIG. 1, heating device 401 capable of performing electrothermal heating is mounted on the upper surface of heating chamber 34. Further, heating chamber 34 has three stages of plate holding sections that support heating plate 402. Specifically, heating chamber 34 has upper-stage plate holding section 403, middle-stage plate holding section 404, and lower-stage plate holding section 405. It is to be noted that upper-stage plate holding section 403, middle-stage plate holding section 404 and lower-stage plate holding section 405 are generically referred to as plate holding section 400.
Heating plate 402 is described with reference to FIGS. 9A to 9C. FIG. 9A shows a plan view of heating plate 402 seen from above. Fig. 9B shows a side view of heating plate 402 seen from side. FIG. 9C shows a view of a cross section 9C-9C in FIG. 9A. Heating plate 402 is made up of frame-shaped periphery 402a, and plate 402c which is formed inside periphery 402a and in which a plurality of grooves 402b (not shown in FIG. 9C) with a predetermined depth are formed in parallel. The object to be heated is placed on this plate 402c, which is placed inside heating chamber 34. Microwave absorber 406 (e.g. ferrite) is provided on the back face side of the plate (placing table 35 side).
As shown in FIG. 5, operation section 31c is disposed in a front-face lower portion of door 31b. Operation section 31c is a device with which a variety of cooking menus are selectable by the user in accordance with food and cooking contents. For example, with operation section 31c, it is possible to set heating time, and select a previously set automatic cooking menu, such as a "warming function", a "defrosting function", a "defrosting/grilling function" or a "grilling function".
The "warming function" refers to a cooking method of radiating microwaves toward food so as to heat the food. The "defrosting function" refers to a frozen-food defrosting method performed by a method of continuously or intermittently radiating microwaves to frozen food to heat the food, a method of heating and defrosting frozen food with steam, or a method of defrosting food by combination of these.
The "defrosting/grilling function" refers to cooking such that open section 58 of rotary waveguide 39 is turned to either a direction of front-face opening 38 of heating chamber 34, being a direction in which microwaves are apt to diffract to the upper surface of the heating plate, or a direction of a gap between an outer edge of heating plate 402 and an inner wall of heating chamber 34, to allow frozen food placed on heating plate 402 to absorb microwaves and defrost, and subsequently, the defrosted food is cooked by the later-mentioned "grilling function". In the present embodiment, open section 58 of rotary waveguide 39 is turned to front-face opening 38 of heating chamber 34, a heating-plate upper surface heating mode, with which a supply of microwaves to the upper surface of heating plate 402 is large, is executed to allow frozen food placed on heating plate 402 to absorb microwaves and defrost, and subsequently, the defrosted food is cooked by the later-mentioned "grilling function".
The "grilling function" refers to concentration of microwaves on microwave absorber 406 on the back face side of heating plate 402 with food placed thereon, to generate heat at a high temperature. The function refers to a cooking method of heating food via heating plate 402, and a cooking method of heating food by combination of the above heated-up heating plate 402 and a heating device.
Based upon an output signal from operation section 31c, control section 411 controls magnetron 32 and motor 41, to execute these menus.
Microwave oven 31 according to the present embodiment controls open section 58, as a site with strong radiation directivity, of rotary waveguide 39 to a predetermined orientation, and especially in the "defrosting/grilling function", in the first half, an amount of diffraction of microwaves to the upper surface of heating plate 402 is increased, to efficiently perform defrosting. In the last half, the microwaves are concentrated on microwave absorber 406 on the back face side of the plate of heating plate 402, to efficiently generate heat. A specific control is described later.
Returning to FIG. 2, coupling section 46 is formed of a substantially cylindrical conductive material passing through a substantially circular coupling hole (not shown) provided on an interface face between waveguide 33 and heating-chamber bottom surface 42. Radiation section 48 is formed of a conductive material generally having a wider area in a horizontal direction than in a vertical direction, and electrically connected by crimping, welding, or the like, to the top end of coupling section 46 so as to be integrated. Rotary waveguide 39 includes coupling section 46 and radiation section 48.
Further, rotary waveguide 39 is fitted to shaft 50 of motor 41 such that the center of coupling section 46 matches the center of the rotational drive. Radiation section 48 is configured to have radiation directivity since having a non-uniform shape with respect to a rotating direction. The center of rotation of rotary waveguide 39 is arranged at the center of the inside of heating chamber 34.
As shown in FIGS. 3A to 3C, radiation section 48 is formed such that radiation-section upper surface 52 is formed in trapezoidal shape with open section 58 side taken as a base, as seen from above. Three sides out of the four sides of the trapezoidal shape except for the base have radiation-section bent sections 54, having been bent to heating-chamber bottom surface 42 (FIG. 1) side, and are configured so as to limit radiation of microwaves to the outside of those three sides.
With this configuration, in the case of uniformly heating general food by means of the "warming function", it is not necessary to particularly think of where to place the food as in the conventional microwave oven, and rotary waveguide 39 may be constantly rotated as has conventionally been done. Further, in the case of being able to realize more uniform heating by stopping of rotary waveguide 39 at a certain angle in the middle of rotation, stopping may be mixed with the rotation. In the present embodiment, the rotation is constantly performed.
In the case of heating frozen food placed on placing table 35 inside heating chamber 34 by means of the "defrosting function", rotary waveguide 39 may be rotated and stopped at predetermined time intervals, and in the case of being able to realize more uniform heating by constant rotation, the rotation is constantly performed. In the present embodiment, the rotation is constantly performed.
In the case of cooking frozen food by means of the "defrosting/grilling function", an operation is started in a state where heating plate 402 with the frozen food placed thereon is set on predetermined plate holding section 400, such as upper-stage plate holding section 403. Open section 58 of rotary waveguide 39 is turned to front-face opening 38 of heating chamber 34, microwaves reach the upper side of heating plate 402 via inner glass 61 of door 31b, to defrost the frozen food placed on heating plate 402, and subsequently after the defrosting, the food is cooked by means of the grilling function.
In the case of heating food placed on heating plate 402 by means of the "grilling function", the operation of rotary waveguide 39 may be stopped or rotary waveguide 39 may be constantly rotated in a state where open section 58 of rotary waveguide 39 faces a predetermined position (e.g. different direction from that of front-face opening 38).
A predetermined stopping position of rotary waveguide 39 is described with reference to FIGS. 3A to 3C. In microwave oven 31 according to the present embodiment, control section 411 stores angle information (stopping position) of rotary waveguide 39, taking as a reference an origin detected by an origin detection mechanism having photo interrupter 36. As shown in FIG. 3A, the stopping position is taken as 180 degrees in a state where open section 58 of rotary waveguide 39 faces door 31b, and is taken as an origin position (0 degrees) in a state where open section 58 faces backward.
With the orientation of FIG. 3A, microwaves are radiated with concentration on inner glass 61 of door 31b. The radiated microwaves then pass through a gap between heating plate 402 and inner glass 61, the inside of inner glass 61, a gap space between the inner glass and metal plate 60, to diffract to the upper side of heating plate 402. As for the microwaves that travel inside inner glass 61 among the above microwaves, inner glass 61 is a dielectric, and a wavelength of the microwaves that travel through the dielectric is reduced to a value multiplied by a reciprocal of a square root of a dielectric constant of the dielectric. Hence in the case of glass with a dielectric constant of 4 to 9, the glass corresponds to existence of a space gap about twice to three times as large as a thickness of the glass. This allows many of the microwaves radiated to inner glass 61 side to diffract to the upper side of heating plate 402 through use of the this wide gap. Meanwhile, although a suitable orientation of rotary waveguide 39 for the "grilling function" is not sweepingly decided, the orientation is at least different from the state where the rotary waveguide 39 faces the direction of door 31b. It is therefore considered that the suitable orientation is previously obtained by experiment, and then stored into control section 411.
For example, as shown in FIG. 3B, in the case of obtaining a result that microwaves are concentrated on heating plate 402 placed on upper-stage plate holding section 403 to efficiently raise a temperature of heating plate 402 when open section 58 of rotary waveguide 39 faces a direction of the right side face of heating chamber 34 rather than the direction of door 31b, that position (e.g. 130 degrees clockwise from the origin) is previously stored into control section 411 as a stopping position of rotary waveguide 39 in the "grilling function" at the time of heating plate 402 being placed on upper-stage plate holding section 403.
Next, as for the "grilling function" at the time of heating plate 402 being placed on middle-stage plate holding section 404, for example as shown in FIG. 3C, in the case of obtaining a result that microwaves are concentrated on heating plate 402 to efficiently raise the temperature of heating plate 402 when open section 58 of rotary waveguide 39 faces a direction of the left side face of heating chamber 34, that position (e.g. 230 degrees clockwise from the origin) is previously stored into control section 411 as a stopping position of rotary waveguide 39 in the "grilling function" at the time of heating plate 402 being placed on middle-stage plate holding section 404.
As described above, microwave oven 31 controls the orientation of rotary waveguide 39 in accordance with the position of heating plate 402. For turning rotary waveguide 39 to a predetermined direction, there is considered a method of using a stepping motor as motor 41, a method of detecting a reference position to control conducting time even when a constantly rotated motor is used, or some other method.
The origin detection mechanism is described with reference to FIG. 4. In the present embodiment, the origin detection mechanism is provided in shaft 50 of the stepping motor used as motor 41. The origin detection mechanism is made up of disc 36a with shaft 50 taken as a central shaft and photo interrupter 36. Disc 36a is provided with a rectangular slit 36b.
Disc 36a is fitted to shaft 50 of motor 41 that rotates rotary waveguide 39, and rotates so as to block an optical path of photo interrupter 36 including a light-emitting device and a light-receiving device.
With this configuration, when slit 36b passes through the optical path of photo interrupter 36, nothing blocks the optical path, and hence a time point of passage of slit 36b can be detected. Therefore, previously setting the position of slit 36b as the origin of rotary waveguide 39 allows detection of the origin of rotary waveguide 39 by means of photo interrupter 36 fitted to each motor 41.
Next, control section 411 is described with reference to FIG. 5. Control section 411 includes antenna controlling section 412 and storing section 413. Antenna controlling section 412 controls an operation of motor 41, to control an operation of rotary waveguide 39. Storing section 413 stores positional information (angle information) of rotary waveguide 39. Antenna controlling section 412 references to necessary information from storing section 413 in accordance with a command signal from operation section 31c, and controls motor 41, to control the operation of rotary waveguide 39. Storing section 413 stores positional information of rotary waveguide 39 which is suitable for defrosting and positional information of rotary waveguide 39 which is suitable for heating of heating plate 402 with respect to each of the positions (upper stage, middle stage, lower stage) where heating plate 402 is placed inside heating chamber 34. Specifically, positional information 414 (180 degrees clockwise from the origin) for defrosting on the upper stage, positional information 415 (130 degrees clockwise from the origin) for grilling on the upper stage, positional information 416 (230 degrees clockwise from the origin) for grilling on the middle stage, and some other information are stored.
Next, an operation of microwave oven 31 according to the present embodiment is described with reference to FIG. 6. First, microwave oven 31 is powered on, to come into a standby state in step S102.
In step S102, the state is a menu selection accepting state made by the user using operation section 31c. Specifically, operation section 31c outputs to control section 411 menu signal Sm in accordance with menu selection made by the user. In the present embodiment, the user selects the "warming function", the "defrosting/grilling function", the "grilling function", or some other menu in accordance with contents of an object to be heated (kind of food) which is wished to be heated. It is to be noted that the menu includes the position (upper stage, middle stage or lower stage) where heating plate 402 is placed.
When it is determined that the "warming function" has been selected, operation section 31c outputs to antenna controlling section 412 menu signal SmA representing the "warming function". The control then goes to next step S103.
In step S103, antenna controlling section 412 responses to menu signal SmA, and rotates motor 41 at a constant rate so as to rotate rotary waveguide 39 at a constant rate. The control then goes to next step S104.
In step S104, control section 411 makes magnetron 32 operated so as to start a heating treatment. The control then goes to next step S105.
In step S105, a timer starts counting time. After the lapse of a first predetermined period P1 has been confirmed, the control goes to next step S106.
In step S106, operations of magnetron 32 and the like are stopped, to complete the heating treatment by means of the "warming function".
In step S102, when the "defrosting/grilling function" is selected, operation section 31c outputs to antenna controlling section 412 menu signal SmB representing that the "defrosting/grilling function" has been selected. The control then goes to next step S107.
In step S107, based upon menu signal SmB, antenna controlling section 412 determines whether or not the position where heating plate 402 is placed is the upper stage. It should be noted that with the "defrosting/grilling function", the kind such as meat, fish or pizza is selectable. The control then goes to next step S108.
In step S108, based upon the positional information determined in step S107, antenna controlling section 412 controls the operation of motor 41 with reference to the corresponding positional information from storing section 413. Specifically, based upon the positional information in menu signal Sm determined in step S107, antenna controlling section 412 references to positional information 416 in storing section 413. Thereby, antenna controlling section 412 controls the operation of motor 41 such that rotary waveguide 39 rotates to a direction in which microwaves are apt to diffract to the upper surface of heating plate 402, for example to the direction of front-face opening 38 (180 degrees) and is then stopped. The control then goes to next step S109.
In step S109, in the state where rotary waveguide 39 is stopped in the predetermined position controlled in step S108, control section 411 makes magnetron 32 operated, to start a heating treatment. The control then goes to next step S110.
In step S110, after the lapse of predetermined stopping time, rotary waveguide 39 is again rotated to make one turn, and stopped again at 180 degrees for predetermined time. In this manner, the rotation and stopping at 180 degrees are repeated. The control then goes to next step S111.
In step S111, the timer starts counting time. After the lapse of a second predetermined period P2 has been confirmed, the control goes to next step S112. During this time, the state of microwaves being apt to diffract to the upper side of the heating plate is kept, thereby enabling efficient defrosting of the food.
In step S112, it is determined whether or not defrosting has been completed. When defrosting has not been completed (No in S112), defrosting is continued, and it is determined in step S112 whether or not defrosting has been completed. This is repeated until completion of defrosting. When defrosting has been completed (Yes in S112), the control goes to next step S113 for shifting to the "grilling function", with completion of defrosting. Thereafter, the control should shift to the "grilling function" for grilling food, in which the food may be grilled in a similar manner to the case of the "grilling function" being selected in foregoing step S102 (namely, the case of grilling originally non-frozen food).
In step S102, when the "grilling function" is selected, operation section 31c outputs to antenna controlling section 412 menu signal SmC representing that the "grilling function" has been selected. The control then goes to next step S113. It is to be noted that the foregoing menu signals SmA and Smb, together with this menu signal SmC, are generically referred to as menu signal Sm.
In step S113, based upon menu signal SmC, antenna controlling section 412 determines whether the position where heating plate 402 is placed is the upper stage, the middle stage or the lower stage. It should be noted that with the "grilling function", the kind of an object to be grill-cooked, such as fish, chicken thigh, roast beef, roast chicken, pizza or paella is selectable. The position of the placing plate being the upper stage, the middle state or the lower stage corresponding to each kind of objects to be grill-cooked is stored, and the position of the placing plate is determined by selection of the kind of the object to be grill-cooked by means of the "grilling function". However, the present invention is not limited thereto, and for example, a detector may be provided in each of plate holding sections 403 to 405, and the plate position may be determined by means of a signal from this detector. The control then goes to next step S114.
In step S114, based upon menu signal SmC, antenna controlling section 412 references corresponding positional information from storing section 413, to control the operation of motor 41. For example, when the grilling function on the upper stage is selected by operation section 31c, antenna controlling section 412 references to upper-stage positional information 415, and controls the operation of motor 41 such that rotary waveguide 39 rotates to a position at 130 degrees clockwise from the origin, and is stopped at that position. The control then goes to next step S115.
In step S115, while making rotary waveguide 39 remain stopped, control section 411 makes magnetron 32 operated to start a heating treatment. The control then goes to next step S116. In step S116, after the lapse of predetermined stopping time for rotary waveguide 39, rotary waveguide 39 is again rotated to make one turn, and stopped again at 130 degrees for predetermined time. In this manner, the rotation and stopping at 130 degrees are repeated. The control then goes to step S117.
In step S117, the timer starts counting time, and after the lapse of a third predetermined period P3 has been confirmed, the control goes to next step S118. During this time, the state of microwaves being apt to concentrate on the ferrite provided on the back face of the heating plate is kept, thereby raising a temperature of the heating plate to enable efficient grilling of the under face of food.
In step S118, magnetron 32 is stopped, and in next step S119, heating device 401 is driven. In subsequent step S120, the timer starts counting time, and after the lapse of a fourth predetermined period P4 has been confirmed, the control goes to next step S106. During this time, heating device 401 enables efficient grilling of the upper surface of food.
In step S106, after stopping of operations of rotary waveguide 39, heating device 401, magnetron 32 and the like, the heating treatment by means of the "grilling function" is completed.
With the above configuration, microwave oven 31 according to the present embodiment has plate holding sections 403 to 405 being three stages (upper stage, middle stage, lower stage) in heating chamber 34, and it is thereby possible to select a cooking menu in accordance with the position of the plate holding section, so as to cook a variety of food by means of the "grilling function".
For example, in the case of the upper stage (plate holding section 403), this is used at the time of cooking a food with a small thickness which has hitherto been grill-cooked, such as fish or chicken thigh. In the case of the middle stage (plate holding section 404), this is used at the time of cooking a large food such as roast beef or roast chicken. In the case of the lower stage (plate holding section 405), since a food such as pizza or paella requires thermal power on its back face whereas requiring just soft thermal power on its upper surface, keeping a distance from the upper surface heating device can lead to improvement in cooking performance.
Further, by making the ferrite as microwave absorber 406, stuck on the under face of heating plate 402, absorb microwaves to generate heat, it becomes possible to grill the under face of an object to be cooked. Moreover, by heating the upper surface of the object to be cooked with heating device 401 disposed on the upper surface of heating chamber 34, it becomes possible to perform upper surface cooking. Furthermore, in order to efficiently heat the back face of heating plate 402, the stopping position of rotary waveguide 39 of the microwave cooking device is controlled by the position of the plate holding section.
The temporary stopping position of rotary waveguide 39 varies since a distribution of microwaves changes depending upon the position where heating plate 402 is placed, but the stopping position is previously obtained by an experiment as described above and stored into storing section 413. Adding the origin detection mechanism to motor 41 can lead to accurately control of the stopping position of rotary waveguide 39, thereby to realize heating with maximal efficiencies on the respective positions of the plate holding sections 403 to 405. In the "grilling function" as thus described, fewer microwaves propagate through a space above heating plate 402 (space where food is placed), thereby allowing prevention of moisture inside the food from excessively evaporating.
It should to be noted that, although the example was described where rotary waveguide 39 is stopped at the time of selecting the" defrosting/grilling function" or the "grilling function", the operation control of rotary waveguide 39 is not limited thereto.
For example, antenna controlling section 412 of control section 411 may reciprocate rotary waveguide 39 by the order of a predetermined angle (e.g. ±5 degrees) with a target angle (stopping position) taken as a center. This can lead to not a little unification of the distribution without affecting the heating efficiency of the heating plate. Although this reciprocating operation may be performed from the start of the heating, the configuration may be formed such that the operation is started after the lapse of predetermined time (e.g. after 30 seconds to 1 minute) from the start of the heating.
In order to execute this reciprocating operation, control section 411 is configured to have: a stopping upper limit time storing section that previously stores upper limit time for allowing stopping of rotary waveguide 39; a stopping time counting section that counts the time during stopping of rotary waveguide; and a reciprocation angle storing section that stores an angle by which rotary waveguide 39 is reciprocated.
Further, the configuration may be formed so as to rotate rotary waveguide 39 only by a predetermined angle (e.g. 5 degrees) after the lapse of predetermined time (e.g. after 30 seconds to 1 minute) from the start of the heating in execution of the grilling function.
Moreover, for a similar purpose, the configuration may be formed to control a rotational rate of rotary waveguide 39. The configuration may be formed, for example such that rotary waveguide 39 is rotated slowly in the vicinity of a predetermined position, and rotated at a constant rate in the other positions, thereby to concentrate microwaves on heating plate 402. Also in this case, at which rate in the vicinity of which position rotary waveguide is controlled so as to allow concentration of microwaves on the heating plate is previously obtained by experiment.
Furthermore, control section 411 stores a predetermined stopping position (angle) as an origin when rotary waveguide 39 is located in the predetermined stopping position (angle). Then, control section 411, for example, executes an origin detecting mode for confirming the origin of rotary waveguide 39, along with the "warming function" and the "grilling function", before or after execution of the heating treatment.
On the origin detecting mode, the angle of rotary waveguide 39 cannot be specified, and continuously oscillating microwaves might bring about an unwilling heating state, to cause a failure. Therefore, control section 411 performs control of stopping the operation of the magnetron during driving of rotary waveguide 39 on the origin detecting mode.
Moreover, control section 411 performs the operation on the origin detecting mode after completion of the heating treatment, and stands by with the origin in a detected state by at the time of non-heating. This can prevent generation of standby time for detecting the origin before the start of the heating treatment.
FIG. 7 shows an example of temperature detectors for detecting a temperature distribution. Temperature detector 10 includes infrared detecting elements 13, case 18, and stepping motor 11. Infrared detecting elements 13 are arrayed in a row on substrate 19, and case 18 houses the whole of substrate 19, and stepping motor 11 moves case 18 in a direction vertically intersecting with a direction in which infrared detecting elements 13 are arrayed.
The top of substrate 19 is provided with metal can 15 in which infrared detecting elements 13 are sealed, and electronic circuit 20 that processes operations of infrared detecting elements 13. Can 15 is provided with lens 14 through which infrared rays pass. Case 18 is provided with infrared passage hole 16 that allows passage of infrared rays and hole 17 that allows passage of a lead from electronic circuit 20.
With this configuration, the rotational operation of stepping motor 11 allows movement of case 18 in the direction vertical to the direction in which infrared detecting elements 13 are arrayed in a row. The reciprocal rotational operation of stepping motor 11 of the temperature detector allows detection of a temperature distribution of almost all areas inside heating chamber 34.
Although the case where the number of rotary waveguides is one has been described, the number of rotary waveguides 39 is not limited thereto, and may be two or more. For example, as shown in FIG. 8, the configuration may be formed to have two rotary waveguides 90, 91 in a width direction of heating chamber 34.
In FIG. 8, the respective opening sections 92, 93 of rotary waveguides 90, 91 are disposed as facing the vicinity of the center inside heating chamber 34. Also in this case, how two rotary waveguides 90, 91 are positionally related to each other when microwaves are apt to diffract to the upper side of heating plate 402 or when microwaves are concentrated on heating plate 402 may be previously obtained by experiment.
Forming a plurality of rotary waveguides 39 increases the number of combinations of the stopping positions of rotary waveguides 90, 91 (e.g. one rotary waveguide 90 being at an original position while the other rotary waveguide 91 being at 90 degrees counterclockwise from the origin, etc.), to increase a variable width of the control of microwaves. This further allows, with efficiency, diffraction of microwaves to the upper side of heating plate 402 and concentration of microwaves on heating plate 402. It is therefore possible to improve heating efficiency of defrosting and heating efficiency of grilling in the "defrosting/grilling function". Meanwhile, it becomes possible to heat with concentration on a right half or left half area, or an upper half or lower half area, of heating plate 402, expanding a range of variations of cooking procedures.
Although microwaves are radiated from the lower side of heating chamber 34 into heating chamber 34 in the present embodiment, feeding section 37 may be provided above heating chamber 34, and microwaves are radiated from above heating chamber 34, so as to be made to diffract to the lower face of heating plate 402.
Next, with reference to FIGS. 10A,10B, 11A to 11C, 12A and 12B, a relation is described between an orientation of open section 58 of rotary waveguide 39 with respect to heating plate 402 and an amount of microwaves to be supplied to the upper surface of heating plate 402. FIG. 10A shows a state where heating plate 402 (FIG. 9) set on plate holding section 400 of heating chamber 34 is seen from above. FIG. 10B shows a state where food placed on heating plate 402 being heated with microwaves is seen from a direction of inner glass 61 of door 31b. It is to be noted that as indicated by a broken line in FIG. 10A, rotary waveguide 39 is oriented in a lateral direction of microwave oven 31, namely a direction parallel to door 31b.
As shown in FIG. 10A, there is almost no gap between heating plate 402 and each of the right and left walls of heating chamber 34 in microwave oven 31. For this reason, microwaves MW radiated from magnetron 32 are radiated to the right and left inner walls of heating chamber 34 in a roughly vertical direction and to door 31b and back wall projecting section 420 (circulating fan unit storing section) in a roughly parallel direction, via open section 58 of rotary waveguide 39. Therefore, most of the microwaves radiated inside heating chamber 34 are reflected on the right and left side walls of heating chamber 34, plate holding section 400 and the like, and most of them are ultimately absorbed into microwave absorber 406. Those are then converted into heat by microwave absorber 406 to directly heat food F from the lower side.
It should be noted that, although there are a few microwaves that diffract to the upper side of heating chamber 34 from gaps between heating plate 402 and door 31b/back wall projecting section 420 (circulating fan unit storing section), those are not sufficient for heating the food placed on heating plate 402 from above. That is, such a state is not suitable for heating for defrosting of frozen food. Thereat in the present embodiment, in the defrosting function, open section 58 of rotary waveguide 39 is located with an orientation in the roughly vertical direction to door 31b, to radiate microwaves to door 31b or back wall projecting section 420. As described above, there are gaps between heating plate 402 and door 31b, and between heating plate 402 and the side wall on the back wall projecting section 420 side.
Most of microwaves radiated from open section 58 of rotary waveguide 39 travels over heating plate 402 via the gap between heating plate 402 and door 31b and the gap between heating plate 402 and the side wall on back wall projecting section 420 side, to reach the upper side of heating chamber 34. These microwaves are reflected on the inner wall of heating chamber 34, to be used for heating the object to be heated (food) placed on upper-stage plate holding section 403. That is, a space between heating plate 402 and the inner wall of heating chamber 34, generated due to door 31b and back wall projecting section 420 is utilized as a principal transmission channel to supply microwaves to the upper surface of heating plate 402.
Although there are some microwaves that are reflected on the right or left side wall of heating chamber 34, plate holding section 400, and placing table 35, to be absorbed into microwave absorber 406, an amount thereof is far small as compared with the case of open section 58 being oriented in the direction parallel to door 31b. As described above, since door 31b is fitted with inner glass 61 that functions as the transmission channel corresponding to a space gap about twice to three times as large as a plate thickness of its own, it is possible to effectively supply microwaves to the upper side of heating plate 402.
Therefore, in the present invention, when the "defrosting/grilling function" is selected, rotary waveguide 39 is located so as to make open section 58 face door 31b in order to construct the foregoing principal transmission channel. In that state, microwaves are supplied just for predetermined first heating time T1, to supply the microwaves to the upper surface side of heating plate 402 of heating chamber 34 so as to defrost frozen food or the like. Then, if need be, rotary waveguide 39 is moved (rotated) to make open section 58 oriented in the direction parallel to door 31b, so as to supply microwaves just for predetermined second heating time T2. It is thereby possible to make microwave absorber 406 generate heat, thereby to warm or grill the frozen food from the lower side.
It should be noted that in the foregoing method, microwaves are supplied together to the upper side of heating plate 402 (for first predetermined time T1), to defrost frozen food from above, and thereafter the microwaves are supplied together to microwave absorber 406 (for second predetermined time T2), to heat the defrosted food from below. In this case, the lower side of the frozen food is heated after the upper side thereof has been heated (defrosted), and there may be a case of a heat distribution of the food becoming non-uniform. In consideration of such a case, the position of open section 58 may be intermittently changed.
Specifically, instead of open section 58 first being stopped with the orientation parallel to door 31b continuously just for first heating time T1, open section 58 is stopped for the time shorter than the first heating time, to lightly defrost the frozen food. Next, open section 58 is located with the orientation vertical to door 31b, and heating (grilling) is performed by microwave absorber 406 for the time shorter than second heating time T2. This operation is repeatedly performed. In this method, total time for direct heating (defrosting) with microwaves and a total time for heating (grilling) by microwave absorber 406 are not necessarily the same as first and second heating time T1, T2, and are decided as appropriate.
Further, other than the foregoing two methods, open section 58 may not be stopped with a predetermined orientation, but rotary waveguide 39 may be rotated at a constant rate. In this case, in accordance with the orientation of open section 58, heating (defrosting function) with microwaves supplied to the upper surface of heating plate 402 and heating (grilling function) by microwave absorber 406 on the under face of heating plate 402 are performed in a continuous and alternate manner.
Next, with reference to FIGS. 11A to 11C, 12A and 12B, a relation is described between the orientation of open section 58 of rotary waveguide 39 in heating chamber 34 and the amount of microwaves to be supplied to the upper surface of heating plate 402. The amount of microwaves that are radiated on the lower face side of heating plate 402 and diffract to the upper surface side of heating plate 402 via the gap (principally inner glass 61) between heating plate 402 and (door 31b including) the inner wall of heating chamber 34 can be confirmed by a method shown in FIGS. 11A to 11C.
Heating plates 402 shown in FIGS. 11A to 11C respectively correspond to those in FIGS. 9A to 9C. The amount of the microwaves can be confirmed by means of a temperature of water placed on the upper surface of heating plate 402. First, an insulator is placed as insulation spacer S on the upper surface of heating plate 402. Thereon, resin-made container V with 150-cc water W kept therein is placed. It is to be noted that insulation spacer S is used for preventing heat from heating plate 402 from being conducted to water W via resin-made container V, to measure a temperature rise of water W only with the diffracted microwaves.
When an amount of water W is referred to as m[g], specific heat of water W as C, a temperature rise of water W as ΔT, and heating time as t[s], electric power P[W] absorbed by water W can be expressed as Equation (1): $P = 4.19 \times m \times C \times ΔT / t$
where C = 1 and m = 150 g in the present embodiment.
Specifically, when heating is performed in microwave oven 31 for t = 180[s], in the case of water W with an initial temperature of 20°C being changed to 60°C, Equation (2) can be obtained from above Equation (1): $P = 4.19 \times 150 \times 1 \times (60 - 20) / 180 = 140 [W]$
Next, with reference to FIGS. 12A and 12B, a relation is described between the orientation of open section 58 of rotary waveguide 39 in heating chamber 34 and the amount of diffraction of microwaves (directivity of microwaves with respect to the orientation of open section 58). FIG. 12A is a plan view of heating plate 402 placed inside heating chamber 34, as shown in FIG. 10A. In the figure, the front side is door 31b side, the back side is the back wall projecting section 420 (circulating fan unit storing section) side, the right is the right inner wall side of heating chamber 34, and the left is the left inner wall side of heating chamber 34. Directions of these seen from open section 58 of rotary waveguide 39 are respectively regarded as 180, 0, 90 and 270 degrees.
FIG. 12B represents the orientation of rotary waveguide 39 (open section 58) with strong directivity by means of angles. With the orientation of back wall projecting section 420 (circulating fan unit storing section) side taken as a reference (0 degrees), angles clockwise therefrom seen from above are taken as the plus side. With the amount of diffraction in the case of rotation taken as the reference, differences from the reference are plotted in increments of 15 degrees. It is found from the figure that the directivity is maximal with rotary waveguide facing forward (door 31b side) at 180 degrees, the directivity is next maximal with rotary waveguide facing backward (back wall projecting section 420 side), and the directivity is small with rotary waveguide facing the right or left.
FIG. 13 shows the orientation of open section 58, the amount of diffracted microwaves, and the difference from the rotation. That is, in the case of holding rotary waveguide 39 in the position where open section 58 faces door 31b (inner glass 61) side, microwaves radiated from rotary waveguide 39 can be efficiently supplied to the direction of heating plate 402. It is to be noted that also in the case of making open section 58 face back wall projecting section 420 (circulating fan unit storing section) side, the amount of diffraction of microwaves is large as compared with the case of making open section 58 face the right or left inner wall side.
Based upon the relation (FIG. 12) as thus obtained between the orientation of open section 58 of rotary waveguide 39 and the amount of diffraction of microwaves (directivity of microwaves), it is possible to decide as appropriate a position (angle) in which, and the time for which, rotary waveguide 39 is stopped at the time of defrosting.
From the above, in microwave oven 31, control section 411 makes open section 58 radiate microwaves MW just for first predetermined time T1 in first position D1 where a large number of microwaves MW diffract, while making open section 58 radiate microwaves MW just for second predetermined time T2 in second position D2 where a small number of microwaves MW diffract, and hence it is possible to continuously defrost and cook frozen food while keeping the food placed on heating plate 402. It should be noted that first position D1 is the position at 180 degrees or 0 degrees in FIG. 12B, and second position D2 is the position at 90 degrees or 270 degrees in FIG. 12B. In addition, first position D1 and second position D2 can be decided as appropriate with respect to each microwave oven 31.
Further, control section 411 may make microwaves MW continuously radiated in first position D1 just for first predetermined time T1, and thereafter makes microwaves MW continuously radiated in second position D2 just for second predetermined time T2. Further, control section 411 may repeat continuous radiation of microwaves MW in first position D1 for first small heating time ΔT1 which is smaller than first predetermined time T1, and subsequent continuous radiation of microwaves MW in second position D2 for second small heating time ΔT2 which is smaller than second predetermined time T2, until respective totals of first small heating time ΔT1 and second small heating time ΔT2 become not shorter than first predetermined time T1 and second predetermined time T2.
It is to be noted that in the present embodiment, the aspect of using heating plate 402 provided with microwave absorber 406 has been described. As another embodiment, there can be considered a case of using a heat-resistant tray, where microwave absorber 406 cannot be placed, in place of heating plate 402. Also in this case, a similar effect can be obtained to the effect of the present invention that the inside of the door is used as the transmission channel for microwaves and the orientation of rotary waveguide 39 is controlled to adjust the amount of diffraction of microwaves to the upper side of the tray.
It is to be noted that a temperature detecting section for detecting a temperature of the object to be heated may be provided, and only in the case of determining the object to be heated as frozen food due to its temperature being low, control section 411 may make rotary waveguide 39 as the directional feeding section face the direction of door 31b and stopped. It is thereby possible to make use of the defrosting function and increase the amount of diffraction of microwaves to the upper side of heating plate 402, so as to efficiently perform defrosting.
In the case of determining the object to be heated as a refrigerated object or an object at room temperature due to its temperature being high, the amount of diffraction may be small because of no need for defrosting. For this reason, rotary waveguide 39 may not be made to face the direction of door 31b and stopped, but the object to be heated may be efficiently grilled by making use of the grilling function.
In the case of increasing the amount of diffraction, stopping rotary waveguide 39 from the beginning to the end is not necessary. An operation of rotation after stopping for predetermined time may be repeated. At this time, it is considered that the stopping time may change depending upon the temperature of the object to be heated. The lower the temperature is, the longer the stopping time is made, and the higher the temperature is, the shorter the stopping time is made, whereby the amount of diffraction can be subjected to multistage control in accordance with the temperature of the object to be heated.
Further, a weight detecting section for detecting a weight of the object to be heated may be provided, and especially in the case of determining that the weight of the object to be heated is large, control section 411 may make rotary waveguide 39 face the direction of door 31b and stopped. It can be considered that, when the weight of the object is large, its size is also roughly large, and there is a tendency that an object of a large size is resistant to heating into its central portion only by heat conduction. In this case, the object is considered to be easy to heat when heated with microwaves. It is therefore possible to make rotary waveguide 39 face the direction of the door and stopped, and increase an amount of diffraction of microwaves to the upper side of heating plate, so as to efficiently heat the large object into its center.
In the case of determining that the weight of the object to be heated is small, it can be considered that its size is also roughly small, and there is a tendency that the object of a small size can be heated into its central portion only by heat conduction, whereby the amount of diffraction may be small. Hence rotary waveguide 39 may not be made to face the direction of door and stopped, but the object may be grilled by making use of the grilling function.
In the case of increasing the amount of diffraction, stopping rotary waveguide 39 from the beginning to the end is not necessary. An operation of rotation after stopping for predetermined time may be repeated. At this time, it is considered that the stopping time may change depending upon the weight of the object to be heated. The larger the weight is, the longer the stopping time is made, and the smaller the weight is, the shorter the stopping time is made, whereby the amount of diffraction can be subjected to multistage control in accordance with the weight of the object to be heated.
Further, as a safety measure in the case of misuse such as use of a plate other than heating plate 402 despite the menu of the "defrosting/grilling function" being selected, the configuration can be formed to have a misuse determining section. In this case, when the misuse determining section determines misuse of heating plate 402, control section 411 may make rotary waveguide 39 continue to rotate without being stopped.
Normally, in the case of using regular heating plate 402, control section 411 makes rotary waveguide 39 face the direction of the door and stopped, to allow microwaves to diffract to the upper side of the heating plate and be efficiently absorbed into food. On top of that, since microwave absorber 406 for absorbing microwaves is provided on the lower face of the heating plate, all the microwaves inside the heating chamber can be safely consumed.
In the case of not using regular heating plate 402, it is considered that misuse may occur, such as putting food alone on the placing table without placement of heating plate 402, placing a metal plate different from heating plate 402, and forgetting to place both heating plate 402 and food and making a start on a completely no-load condition. Especially in the case of placing a metal plate different from heating plate 402, there is nothing to be able to absorb microwaves on the lower face of the metal plate, and further in the case of the no-load condition, there is nothing at all to be able to absorb microwaves. At this time, an electric field inside heating chamber 34 becomes strong, and further when rotary waveguide 39 is stopped, the strong electric field might be concentrated on one part. Thereat, when misuse of heating plate 402 is determined, making rotary waveguide 39 continuously rotated without being stopped can prevent the strong electric field from being concentrated on one part.
It is to be noted that in the case of determining misuse, it is considered that the output of microwaves will be reduced or stopped. As a specific misuse determining section, heating plate 402 may be provided so as press a switch when mounted in heating chamber 34. When the switch is disposed in a mounted position of the end of heating plate 402 and the switch is not pressed, it is possible to determine misuse in that regular heating plate 402 is not in use.
As another misuse determining section, a temperature detecting section, which detects a temperature of at least either heating plate 402 or the object to be heated, may be provided. When a temperature different from a predetermined temperature is detected, it is possible to determine misuse in that regular heating plate 402 is not in use.
Further, as another misuse determining section, a weight detecting section, which detects a weight of at least either heating plate 402 or the object to be heated, may be provided. When a weight different from a predetermined weight is detected, it is possible to determine misuse in that regular heating plate 402 is not in use.
Although the present invention has been described in detail or with reference to the specific embodiments, it is obvious for a person skilled in the art to be able to make a variety of alterations and modifications without deviating from the content of the claims.

INDUSTRIAL APPLICABILITY

Since being capable of performing heating continuously from defrosting, the present invention is applicable to a microwave heating device such as a microwave oven.

REFERENCE MARKS IN THE DRAWINGS

31: microwave oven (microwave heating device)
31a: body
31b: door
31c: operation section
32: magnetron (microwave generator)
33: waveguide
34: heating chamber
35: placing table
37: feeding section
38: front-face opening
39: rotary waveguide (directional feeding section)
41: motor
42: heating-chamber bottom surface (placing table)
58: opening section
60: metal plate
61: inner glass (glass)
62: outer glass
90: rotary waveguide
91: rotary waveguide
92: opening section
93: opening section
400: plate holding section
402: heating plate (tray)
402a: periphery
402b: groove
402c: plate
403: upper-stage plate holding section
404: middle-stage plate holding section
405: lower-stage plate holding section
406: microwaves absorber
411: control section
412: circulating fan unit storing section
420: back wall projecting section

Claims

A microwave cooking device (31), comprising:
a heating chamber (34) provided with a glass-fitted door (31b) at a front opening (38), for housing an object to be heated;

a microwave-transparent placing table (35) constituting a bottom surface inside the heating chamber (34);

a tray (402) detachably mounted in the heating chamber (34), for carrying the object to be heated;

a microwave generating section (32);

a waveguide (33) for transmitting microwaves from the microwave generating section (32) to the heating chamber (34);

a directional feeding section (39) having directivity, for supplying the microwaves from the waveguide (33) to the heating chamber (34);

a driving section (41) for rotationally driving the directional feeding section (39);

a control section (411) for controlling the driving section (41) to rotate the directional feeding section (39);

and a feeding section (37) formed below the placing table (35), for housing the directional feeding section (39),
characterized in that
the control section (411) turns the directional feeding section (39) to concentrate the microwave radiation on a direction of the door (31b) in the case of the object to be heated being in a frozen state, and supplies the microwaves into a space above the tray (402), using the inside of the glass of the door (31b) as a principal transmission channel.
The microwave cooking device (31) according to claim 1, wherein the tray (402) is a heating plate, provided on an underside thereof with a microwave absorber (406).
The microwave cooking device (31) according to claim 3, wherein the control section (411) stops the directional feeding section (39) at a position where the directional feeding section (39) faces a predetermined direction.
The microwave cooking device (31) according to claim 3, wherein the control section (411) rocks the directional feeding section (39) in the vicinity of a position where the directional feeding section (39) faces a predetermined direction.
The microwave cooking device (31) according to claim 3, wherein during heating with the microwaves, the control section (411) decelerates the directional feeding section (39) in the vicinity of a position where the directional feeding section (39) faces a predetermined direction, while rotating the directional feeding section (39).
The microwave cooking device (31) according to claim 1, further comprising
a temperature detecting section (10) for detecting a temperature of the object to be heated, wherein
the control section (411) determines whether or not the object to be heated is in the frozen state based upon an output of the temperature detecting section (10), while controlling the driving section (41) to turn the directional feeding section (39) to concentrate the microwave radiation on the direction of the door (31b) in the case of determining that the object to be heated is in the frozen state, and controlling the driving section (41) to turn the directional feeding section (39) to a direction other than the door (31b) in the case of determining that the object to be heated is not in the frozen state, for controlling supplies of the microwaves to spaces above and below the tray (402).
The microwave cooking device (31) according to claim 1, further comprising a weight detecting section for detecting a weight of the object to be heated, wherein
the control section (411) controls the driving section (41) to change an orientation of the directional feeding section (39) based upon the weight of the object to be heated for controlling supplies of the microwaves to spaces above and below the tray (402).
The microwave cooking device (31) according to claim 1, further comprising a misuse determining section for determining the tray (402) being misused, wherein
the control section (411) rotates the directional feeding section (39) when the misuse determining section determines the tray (402) being misused.
The microwave cooking device (31) according to claim 8, wherein the misuse determining section has a switch pressed by the tray (402) when the tray (402) is mounted in the heating chamber (34), and determines the tray (402) being misused indicating the tray (402) not in use when the switch is not pressed.
The microwave cooking device (31) according to claim 8, wherein the misuse determining section has a temperature detecting section for detecting at least one of a temperature of the tray (402) and a temperature of the object to be heated, and determines the tray (402) being misused indicating the tray (402) not when a detected temperature is different from a predetermined temperature.
The microwave cooking device (31) according to claim 8, wherein the misuse determining section has a weight detecting section for detecting at least one of a weight of the tray (402) and weight of the object to be heated, and determines the tray (402) being misused indicating the tray (402) not in use when detected weight is different from a predetermined weight.