microwave oven

Abstract

To provide a microwave oven capable of compatibly suppressing excessive heating and insufficient heating of a cooked object.SOLUTION: A microwave oven 1 includes: a heating chamber 12; a microwave source 30; a sensor 35 for detecting steam generated from a cooked object C; and a control part 45 for performing heating treatment of the cooked object C. The heating treatment includes a normal completion step (a step S5) and preventive completion steps (steps S6-S8). The preventive completion steps include a first step (the step S6) to be completed when showing that a steam amount per unit time obtained from a detection result of the sensor 35 reaches a set steam amount which is smaller than a first maximum steam amount as a maximum steam amount per unit time generated from a first cooked object C1 and is greater than a second maximum steam amount as a maximum steam amount per unit time generated from a second cooked object C2.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a microwave oven. [Background technology]

[0002] The microwave oven disclosed in Patent Document 1 has a function for preventing overheating of food due to erroneous operation in a manual heating process in which the heating time is manually set by the user. This overheating prevention function is configured so that when the manually set first heating time does not match the weight of the food detected by the weight sensor, a second heating time corresponding to the weight is automatically set without following the first heating time, and the heating process ends when the second heating time has elapsed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-213472 Summary of the Invention [Problem to be solved by the invention]

[0004] The microwave oven in Patent Document 1 only changes the heating time depending on the weight of the food, without taking into consideration the actual heating state of the food. As a result, some food may be overheated or underheated, and there is room for improvement in the microwave oven in Patent Document 1 in terms of preventing food from being overheated or underheated.

[0005] An object of the present invention is to provide a microwave oven that can prevent food from being overheated and underheated at the same time. [Means for solving the problem]

[0006] One aspect of the present invention provides a microwave oven comprising: a heating chamber for heating an object to be cooked; a microwave source that outputs microwaves to heat the object to be cooked; a sensor for detecting steam generated from the object to be cooked; and a control unit that outputs microwaves from the microwave source to heat the object to be cooked based on a manually set heating time, wherein the object to be cooked includes a first object to be cooked and a second object to be cooked that is larger in volume and has more moisture than the first object to be cooked; the heating process by the control unit has a normal termination step that terminates when the heating time has elapsed and a preventive termination step that terminates before the heating time has elapsed, and the preventive termination step includes a first step that terminates when the amount of steam per unit time obtained from the detection result of the sensor indicates that the amount of steam per unit time has reached a set steam amount that is less than a first maximum steam amount, which is the maximum amount of steam generated per unit time from the first object to be cooked, and is greater than a second maximum steam amount, which is the maximum amount of steam generated per unit time from the second object to be cooked.

[0007] The first cooking item includes foodstuffs such as potatoes and sweet potatoes that contain a lot of water and have a small volume. The temperature of the first cooking item (e.g., potatoes) rises rapidly when heated, and the amount of steam generated from the first cooking item per unit time changes from a small amount that gradually seeps out like steam to a maximum amount that suddenly erupts (first maximum steam amount). However, the first cooking item may be overheated when it reaches the first maximum steam amount, and in an overheated state, it is not suitable as a foodstuff.

[0008] The second cooking item includes dishes such as curry and stews that contain more water and are larger in volume than the first cooking item. The temperature of the second cooking item (e.g., curry) rises more slowly when heated than the first cooking item, and the amount of steam generated per unit time from the second cooking item is always gradually seeping out (second maximum steam amount). However, the second cooking item may be undercooked by the time the second maximum steam amount is reached, and an undercooked state is not suitable for cooking.

[0009] In contrast, the heating process of this embodiment includes a normal termination step that terminates when a manually set heating time has elapsed and a preventive termination step that terminates before the heating time has elapsed. The preventive termination step includes a first step that terminates when the amount of steam per unit time obtained from the sensor indicates that the set amount of steam has been reached. Thus, the preventive termination step is performed based on the sensor's detection results for detecting steam generated from the food, i.e., the heated state of the food, rather than the weight of the food. Furthermore, the set amount of steam compared to the amount of steam obtained from the sensor's detection results is less than the first maximum amount of steam generated per unit time by the first food. This allows the system to detect the heating state before a large amount of steam is generated from the first food (resulting in overheating), i.e., the small amount of steam exuded from the first food, thereby preventing overheating of the first food. Furthermore, the set amount of steam is greater than the second maximum amount of steam generated per unit time by the second food. This prevents the system from transitioning to the preventive termination step even when steam is generated from the second food, and the food continues to be heated for the manually set heating time. This prevents the second food from being undercooked. In other words, in this embodiment, it is possible to prevent the food from being overheated and underheated at the same time.

[0010] Specifically, the control unit determines the amount of steam based on the input voltage from the sensor, and the first step ends when the input voltage from the sensor indicates that it has reached a set voltage that is lower than a first equivalent voltage corresponding to a first maximum rising gradient due to steam generated from the first cooking item, has a gentler gradient than the first maximum rising gradient, and is higher than a second equivalent voltage corresponding to a second maximum rising gradient due to steam generated from the second cooking item.

[0011] The rising gradient (slope) of the input voltage from the sensor due to steam generated from the first cooking item is greater when a large amount of steam is emitted than when a small amount of steam is seeped out, and is greatest in the latter state (first maximum rising gradient). On the other hand, the rising gradient (slope) of the input voltage from the sensor due to steam generated from the second cooking item is roughly constant, and is greatest when steam begins to be generated (second maximum rising gradient). The set voltage compared to the input voltage from the sensor is lower than the first equivalent voltage, which corresponds to the first maximum rising gradient due to steam generated from the first cooking item, and higher than the second equivalent voltage, which corresponds to the second maximum rising gradient due to steam generated from the second cooking item, so overheating and underheating of the cooking items can be reliably prevented.

[0012] The preventive termination process includes an additional heating time obtained by multiplying the execution time from the start of heating by the microwave source to the end of the first step by a predetermined coefficient, or a second step of terminating heating by the microwave source after the heating time has elapsed.

[0013] The preventive termination step includes a second step in which the additional heating time is set based on the execution time until the first step is completed, and the step terminates when the additional heating time or a manually set heating time has elapsed. This prevents the user from feeling uncomfortable when the food is heated for longer than the manually set heating time. On the other hand, if the additional heating time for a small-volume first food item is excessively long, the food may become overheated and unusable as an ingredient, while if the additional heating time is excessively short, the food may become undercooked. Therefore, by setting the additional heating time by multiplying the execution time until the first step is completed by an appropriate coefficient, overheating and undercooking of the first food item can be effectively prevented, and an appropriate heating state can be achieved.

[0014] The sensor is a steam temperature sensor that detects the temperature of the steam, and is disposed on the ceiling wall of the heating chamber.

[0015] The sensor is a steam temperature sensor that detects the temperature of steam and is located on the ceiling wall of the heating chamber, so that the temperature of the steam generated from the food and flowing upward can be reliably detected. [Effects of the Invention]

[0016] The microwave oven of the present invention can prevent food from being overheated and underheated at the same time. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view of a microwave oven according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view of the microwave oven with the tray placed and the door closed, taken along line II-II of FIG. 1. [Figure 3] Cross-sectional view of line III-III in Figure 2. [Figure 4] Front view of a microwave oven. [Figure 5] 10 is a flowchart of a manual range process. [Figure 6] A continuation of Figure 5. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] 1 to 4 show a microwave oven 1 according to an embodiment of the present invention. In the accompanying drawings, the X direction is the front-to-rear direction of the microwave oven 1, with the direction indicated by the arrow being the rear side and the direction opposite the arrow being the front side. The Y direction is the width direction of the microwave oven 1, with the direction indicated by the arrow being the left side and the direction opposite the arrow being the right side. The Z direction is the height direction of the microwave oven 1, with the direction indicated by the arrow being the top side and the direction opposite the arrow being the bottom side.

[0020] 1 to 4, microwave oven 1 includes microwave oven main body 10, door 20 attached to microwave oven main body 10 so as to be able to open and close, and a dedicated tray 28 removably placed in heating chamber 12. As shown most clearly in FIG. 2, microwave oven 1 also includes magnetron (microwave source) 30, heater 32, infrared sensor 34, thermistor (sensor) 35, operation panel 40, and control unit 45. Control unit 45 executes the heating process set by operating operation panel 40, and heats food C (see FIG. 2) in heating chamber 12.

[0021] 1 to 3, microwave oven body 10 includes heating chamber 12 within housing 11. Heating chamber 12 is a rectangular parallelepiped space with opening 17 on the front side. Heating chamber 12 is defined by bottom wall 13, top wall 14, a pair of side walls 15, a rear wall 16, and a door 20, all of which are rectangular. Of these, bottom wall 13 is made of a microwave-transmitting material such as ceramic, glass, or resin. Top wall 14, a pair of side walls 15, and rear wall 16 are all made of a microwave-reflecting material such as a metal plate.

[0022] Guide rails 18, 19 for positioning trays 28 are provided on the pair of side walls 15. Of these, the upper guide rail 18 is provided in an area above the center of the overall height of the heating chamber 12, and the lower guide rail 19 is provided in an area below the center of the overall height of the heating chamber 12. Both guide rails 18, 19 are provided so as to extend in the front-to-rear direction by bulging a portion of the side wall 15 into the heating chamber 12 by press working so as to form a right-angled triangle shape.

[0023] Door 20 is attached to the front side of housing 11 and releasably closes opening 17 of heating chamber 12. Door 20 is rotatable about a rotation axis (not shown) extending in the width direction between an open position shown in Fig. 1 and a closed position shown in Fig. 3. However, door 20 may also be rotatable about a rotation axis extending in the height direction, as long as it is configured to be able to open and close opening 17 of heating chamber 12.

[0024] Door 20 comprises an opaque metal frame 21 that is a microwave reflector, and a window 22 that allows visibility into the heating chamber 12. As shown most clearly in Figure 3, window 22 comprises an inner window 23 that faces the heating chamber 12, and an outer window 24 that is spaced apart on the outside of inner window 23. Both inner window 23 and outer window 24 are made of transparent glass or resin that is microwave-transparent. A reflective layer 25 that is made of perforated metal with a large number of holes to ensure visibility and that is capable of reflecting microwaves is provided between inner window 23 and outer window 24.

[0025] 1 , the tray 28 is a rectangular plate that is rectangular when viewed in the height direction, and is selectively and detachably mounted on either the upper guide rail 18 or the lower guide rail 19. By placing an item C on the tray 28, the item C can be placed above the bottom wall 13 of the heating chamber 12 with a gap therebetween. The tray 28 of this embodiment is made of a microwave-transparent material such as ceramic, glass, or resin. The width of the tray 28 is smaller than the distance between the pair of side walls 15 of the heating chamber 12, and the front-to-rear dimension of the tray 28 is smaller than the distance between the rear wall 16 and the door 20 of the heating chamber 12, with both dimensions being as large as possible without interfering with placement in the heating chamber 12.

[0026] 2, magnetron 30 is disposed between housing 11 and heating chamber 12 and microwave-heats food C in heating chamber 12 with microwaves. More specifically, a metal duct (waveguide) 31 is disposed on the underside of bottom wall 13 of heating chamber 12, and magnetron 30 is disposed at the end of this duct 31. An expanded portion 31a that generally covers the underside of bottom wall 13 of heating chamber 12 is provided at the end of duct 31 opposite magnetron 30. The area of ​​bottom wall 13 surrounded by expanded portion 31a constitutes output portion 13a that outputs microwaves into heating chamber 12.

[0027] 2 and 3, the heater 32 is disposed adjacent to the top wall 14 and heats the food C in the heating chamber 12 by radiant heat. In this embodiment, two heaters 32 are disposed at an interval in the front-to-rear direction, and each heater extends in the width direction from one of the pair of side walls 15 to the other. However, only one heater 32 may be provided at the center in the front-to-rear direction, or three or more heaters 32 may be provided.

[0028] The infrared sensor 34 is a monocular thermopile type that has one infrared detection element and detects the temperature of the food C1 on the bottom wall 13 inside the heating chamber 12. The infrared sensor 34 is disposed so as to be located outside the heating chamber 12 with respect to the upper guide rail 18 formed on the right side wall 15. More specifically, the infrared sensor 34 is disposed below the tray placement portion, which is the upper end of the upper guide rail 18, and is attached so as to face the inside of the heating chamber 12 through a through-hole provided in the center of the upper guide rail 18 in the front-to-rear direction.

[0029] The thermistor 35 is a steam temperature sensor that detects the temperature of steam inside the heating chamber 12, and is disposed above the top wall 14 outside the heating chamber 12. The thermistor 35 has a detection unit 35a that penetrates the top wall 14 and is disposed inside the heating chamber 12. More specifically, the detection unit 35a is disposed in a corner of the heating chamber 12 that is defined by the top wall 14, the rear wall 16, and the right-hand side wall 15 in FIG. 2 .

[0030] Referring to FIG. 4, operation panel 40 includes three operation sections (input sections) 41 to 43 and one liquid crystal panel 44, and is provided below window section 22 of door 20.

[0031] Operation unit 41 is, for example, a rotary switch, and is provided for manually setting one of a plurality of heating treatments. Operation unit 42 is, for example, a rotary push switch, and is provided for manually setting the details of the heating treatment set by operating operation unit 41, and for starting the heating treatment. Operation unit 43 is, for example, a push switch, and is provided for canceling (cancelling) the manual setting made by operating operation units 41 and 42.

[0032] The liquid crystal panel 44 is of a segment display type and is provided with a numeric display section 44a capable of displaying three-digit numbers. The liquid crystal panel 44 is also capable of displaying letters, arrows, etc. in addition to numbers, and displays the setting status set by the operation sections 41 and 42 and the execution status of the heating process. However, the liquid crystal panel 44 may be of a dot matrix display type as long as it is provided with a numeric display section 44a capable of displaying two or more digits of numbers.

[0033] Referring to FIG. 2, the control unit 45 is made up of, for example, one microcomputer, and is electrically connected to the magnetron 30, the heater 32, the infrared sensor , the thermistor , and the operation panel . The control unit 45 executes the heating process set by operating the operation panel 40 according to a pre-stored program. The heating process is performed in one of a microwave heating mode in which only the magnetron 30 is controlled until heating is completed, a heater heating mode in which only the heater 32 is controlled until heating is completed, and a combined heating mode in which both the magnetron 30 and the heater 32 are controlled.

[0034] More specifically, the control unit 45 executes one of "oven," "grill," "microwave," "automatic," "regris grill," "tray microwave," and "defrost" that are set by operating the operation unit 41 shown in Fig. 4. For heating processes other than "automatic," the heating time and input power can be set by operating the operation unit 42 to change the value on the number display unit 44a of the liquid crystal panel 44. For "automatic," one of multiple menus (not shown) can be set by operating the operation unit 42.

[0035] Microwave (microwave heating process), tray microwave (tray microwave heating process), and defrosting (defrosting heating process) are performed in microwave heating mode. As shown in FIG. 2, "microwave" is performed with the food C placed on the bottom wall 13 of the heating chamber 12, and the magnetron 30 is controlled based on the detection results of the infrared sensor 34 and the thermistor 35, respectively, to heat the food C with microwaves. "Tray microwave" is performed with the food C placed on a tray 28 (see FIG. 1) in the heating chamber 12, and the magnetron 30 is controlled based only on the detection result of the thermistor 35, without using the infrared sensor 34, to heat the food C with microwaves. "Defrosting" is performed with the food C placed on the bottom wall 13 of the heating chamber 12, and the magnetron 30 is controlled based only on the detection result of the infrared sensor 34 to heat the food C with microwaves.

[0036] The oven (oven heating process) and grill (grill heating process) are performed in heater heating mode. The "oven" and "grill" processes are performed with the food C placed on the tray 28 in the heating chamber 12, and the heater 32 is controlled based only on the detection result of the thermistor 35, without using the infrared sensor 34, to heat the food C by radiant heat.

[0037] Resigli (resigli heating process) is performed in the combined heating mode. Resigli is performed with the food C placed on the tray 28 in the heating chamber 12, and the magnetron 30 and heater 32 are controlled based solely on the detection results of the thermistor 35, without using the infrared sensor 34, to heat the food C using microwaves and radiant heat. For example, the magnetron 30 is first activated to cook the food C to the center, then the magnetron 30 is stopped and the heater 32 is activated to brown the surface of the food C, and the heater 32 is stopped after a specified heater heating time has elapsed.

[0038] The automatic (automatic heating process) is performed in a heating mode determined according to the manually set cooking menu. Whether the food item C is placed on the bottom wall 13 or on the tray 28 is determined by the cooking menu. For example, the cooking menu includes "reheating refrigerated rice" performed in the microwave heating mode, "toast (inside out)" performed in the heater heating mode, and "fried food 'scrape'" performed in the combined heating mode.

[0039] Next, the manual microwave heating process in which the heating time tt is manually set by operating the operation units 41 and 42 will be specifically described.

[0040] First, the cooking item C to be heated by the manual microwave heating process includes a first cooking item C1 that contains a lot of water and has a small volume, and a second cooking item C2 that contains more water and has a larger volume than the first cooking item C1. Examples of the first cooking item C1 include ingredients such as potatoes and sweet potatoes, and examples of the second cooking item C2 include dishes such as curry and simmered dishes.

[0041] Generally, in a manual microwave heating process, the power (amount of heat) input by the magnetron 30 is set manually, and therefore may be set to the same regardless of the volume of the food item C. In this case, the amount of heat per unit volume of the first food item C1, which has a smaller volume, is greater than the amount of heat per unit volume of the second food item C2, which has a larger volume. Furthermore, the gradient of temperature rise of the first food item C1 due to heating is greater than the gradient of temperature rise of the second food item C2.

[0042] More specifically, the temperature of the first food item (e.g., potatoes) C1 rises rapidly due to heating, and the amount of steam generated per unit time from the first food item C1 gradually seeps out in small amounts like steam, changing to a state in which a large amount is suddenly ejected (first maximum steam amount). The gradient (slope) of the input voltage Vt(n) from the thermistor 35 due to the steam generated from the first food item C1 is greater when a large amount of steam is ejected than when a small amount of steam is ejected. For example, when a small amount of steam is exuding from the food item C1, the input voltage Vt(n) from thermistor 35 reaches a third equivalent voltage Vt(n-10)+Vc, which corresponds to the third temperature rise gradient. Furthermore, when a large amount of steam is emitted from the food C1, the input voltage Vt(n) from the thermistor 35 reaches a first equivalent voltage Vt(n-10)+Va, which corresponds to a first temperature rise gradient that is steeper than the third temperature rise gradient, and then generally follows the gradient of the first temperature rise gradient. In other words, when a large amount of steam is emitted from the food C1, the gradient of the temperature rise gradient due to the input voltage Vt(n) from the thermistor 35 becomes the greatest (first maximum rise gradient).

[0043] On the other hand, the temperature of the second cooking item (e.g., curry) C2 rises more slowly when heated than the first cooking item C1, and the amount of steam generated per unit time from the second cooking item C2 is always gradually exuded compared to the first cooking item C1 (second maximum steam amount). The rising gradient (slope) of the input voltage Vt(n) from the thermistor 35 due to the steam generated from the second cooking item C2 is generally constant. For example, when 1.5 liters of curry, an example of the second cooking item C2, is heated, the input voltage Vt(n) from thermistor 35 reaches a second equivalent voltage Vt(n-10)+Vb corresponding to a second temperature rising gradient that is smaller than the first temperature rising gradient when steam is generated, and then generally follows the gradient of the second temperature rising gradient. In other words, in the case of the second cooking item C2, the gradient of the temperature rising gradient of the input voltage Vt(n) from thermistor 35 reaches its greatest value (second maximum rising gradient) when steam begins to be generated (second maximum rising gradient).

[0044] Here, among the first equivalent voltage Vt(n-10)+Va, the second equivalent voltage Vt(n-10)+Vb, and the third equivalent voltage Vt(n-10)+Vc, Vt(n-10) means the voltage input from the thermistor 35 10 times earlier. Va is a constant term corresponding to the magnitude of fluctuation according to the first temperature rise gradient, Vb is a constant term corresponding to the magnitude of fluctuation according to the second temperature rise gradient, and Vc is a constant term corresponding to the magnitude of fluctuation according to the third temperature rise gradient. The constant term Va of the first cooking item C1 is greater than the constant term Vb of the second cooking item C2, and the constant term Vc of the first cooking item C1 is equal to or greater than the constant term Vb of the second cooking item C2; for example, the constant term Va is 0.2, the constant term Vb is 0.1, and the constant term Vc is 0.1 (Vb≦Vc <Va)。

[0045] When the first cooking item C1 is in the first temperature rise gradient state where a large amount of steam is emitted from the first cooking item C1, the first cooking item C1 is not underheated but may be overheated. When the third temperature rise gradient state where a small amount of steam is exuded from the first cooking item C1 or the second temperature rise gradient state where steam is exuded from the second cooking item C2 is in the third temperature rise gradient state where a small amount of steam is exuded from the first cooking item C1 or the second temperature rise gradient state where steam is exuded from the second cooking item C2, the first cooking item C1 and the second cooking item C2 are not overheated but may be underheated. On the other hand, the overheated first cooking item C1 is not suitable as an ingredient, and the underheated first cooking item C1 and the second cooking item C2 are not suitable as ingredients or as dishes. Therefore, in this embodiment, based on the above knowledge, the manual microwave heating process by the control unit 45 is configured as follows.

[0046] The manual microwave heating process includes a normal termination process (steps S5, S10 to S12 shown in Figures 5 and 6) that ends when the manually set heating time tt has elapsed, and a preventive termination process (steps S6 to S12 shown in Figures 5 and 6) that prevents the food C from being overheated or underheated.

[0047] The prevention end process sets the heating end time of the cooked food C by the magnetron 30 based on the detection result of the thermistor 35 corresponding to the actual temperature of the heated cooked food C, and ends before the elapse of the heating time tt. More specifically, the prevention end process includes a first step (step S6 in FIG. 5) that ends when the input voltage Vt(n) from the thermistor 35 reaches a determined set voltage Vt(n - 10)+Vs, and a second step (step S8 in FIG. 5) that ends when the automatically set additional heating time tc1×α elapses. That is, the first step ends when it indicates that the amount of steam per unit time obtained from the detection result of the thermistor 35 has reached the determined set steam amount. However, in the second step, when the total heating time tc obtained by adding the additional heating time tc1×α to the execution time tc1 before the setting of the additional heating time tc1×α is longer than the manually set heating time tt, it ends when the heating time tt elapses (step S9 in FIG. 5).

[0048] Among the set voltages Vt(n - 10)+Vs in the first step, Vt(n - 10) means the input voltage Vt ten times before input from the thermistor 35, and Vs is a constant term corresponding to the magnitude of the variation according to the determined set temperature rise gradient. The constant term Vs is smaller than the constant term Va of the first temperature rise gradient (the first maximum rise gradient) of the first cooked food C1, and larger than the constant term Vc of the third temperature rise gradient of the first cooked food C1 and the constant term Vb of the second temperature rise gradient (the second maximum rise gradient) of the second cooked food C2 (Vb≦Vc<Vs<Va). That is, the set voltage in the first step is lower than the first equivalent voltage of the first cooked food C1, and higher than the third equivalent voltage of the first cooked food C1 and the second equivalent voltage of the second cooked food C2. In other words, the set steam amount is less than the first maximum steam amount, which is the maximum amount of steam per unit time generated from the first cooked food C1, and more than the second maximum steam amount, which is the maximum amount of steam per unit time generated from the second cooked food C2. Also, the set temperature rise gradient in the first step is gentler than the first temperature rise gradient of the first cooked food C1, and steeper than the third temperature rise gradient of the first cooked food C1 and the second temperature rise gradient of the second cooked food C2.

[0049] An excessively large value for the constant term Vs may result in overheating when the first cooking item C1 is being heated, while an excessively small value for the constant term Vs may result in underheating when the first cooking item C1 or the second cooking item C2 is being heated. Therefore, the value of the constant term Vs is preferably set to a value greater than the constant term Vb for the second cooking item C2 and greater than the constant term Vc for the first cooking item C1, for example, greater than (but not including) 0.1 V and less than 0.20 V; in this embodiment, it is set to 0.12 V. Alternatively, the current input voltage Vt(n) may be compared to the set voltage Vt(n-10) × k, which is the input voltage Vt(n-10) from 10 times earlier multiplied by a coefficient k corresponding to the set temperature rise gradient. The current input voltage Vt(n) may also be compared to the input voltage Vt(n-5) from 5 times earlier, and the comparison target can be changed as needed.

[0050] In the additional heating time tc1 × α of the second step, tc1 is the execution time from the start of heating by the magnetron 30 to the end of the first step, and α is a predetermined coefficient. When the heating target is the first cooking item C1, an excessively large coefficient α results in overheating, while an excessively small coefficient α results in underheating. Therefore, the coefficient α is preferably set in the range of 4.0 to 8.0, inclusive, and is set to 6.0 in this embodiment.

[0051] Next, the manual microwave heating process performed by the control unit 45 will be described in more detail with reference to FIGS.

[0052] 5, in the manual microwave heating process, the control unit 45 reads the manually set heating time tt in step S1, and then activates the magnetron 30 in step S2. Next, in step S3, the thermistor 35 starts intermittent detection (e.g., every second) of the voltage Vt(n), and then in step S4, the counter starts measuring the total heating time tc by the magnetron 30.

[0053] Next, in step S5, it is determined whether the total heating time tc has reached the set heating time tt. If the total heating time tc has not reached the heating time tt, the process proceeds to step S6, and if the total heating time tc has reached the heating time tt, the process proceeds to step S10.

[0054] In step S6, it is determined whether the input voltage Vt(n) from the thermistor 35 is equal to or greater than the set voltage Vt(n-10)+Vs. If the input voltage Vt(n) is less than the set voltage Vt(n-10)+Vs, the process returns to step S5. If the input voltage Vt(n) is equal to or greater than the set voltage Vt(n-10)+Vs, the process proceeds to step S7. Here, the constant term Vs is smaller than the constant term Va of the first temperature rise gradient of the first cooking item C1 and larger than the constant term Vb of the second temperature rise gradient of the second cooking item C2. Therefore, if the cooking item C is a first cooking item C1 such as potato, the process proceeds to step S7, where the prevention termination step is executed. On the other hand, if the cooking item C is a second cooking item C2 such as curry, the process does not proceed to step S7, and steps S5 and S6 are repeated until the heating time tt has elapsed.

[0055] In step S7, the execution time tc1 until the condition of step S6 is met is stored, and then in step S8, it is determined whether the total heating time tc is equal to or greater than the execution time tc1 plus the additional heating time tc1×α, that is, whether the additional heating time tc1×α has elapsed since the condition of step S6 was met. If the additional heating time tc1×α has not elapsed, the process proceeds to step S9, and if the additional heating time tc1×α has elapsed, the process proceeds to step S10.

[0056] In step S9, it is determined whether the total heating time tc has reached the set heating time tt. If the total heating time tc has not reached the heating time tt, the process returns to step S8, and if the total heating time tc has reached the heating time tt, the process proceeds to step S10.

[0057] If the total heating time tc reaches the heating time tt in steps S5 and S9, and if the additional heating time tc1×α has elapsed in step 8, the operation of the magnetron 30 is stopped in step S10, as shown in Fig. 6. Subsequently, the intermittent detection of the voltage Vt by the thermistor 35 is stopped in step S11, and then the measurement of the total heating time tc by the counter is stopped in step S12, and the process returns.

[0058] The microwave oven 1 configured in this manner has the following features.

[0059] The manual microwave heating process includes a normal termination step (step S5) that terminates when the manually set heating time tt has elapsed, and a preventive termination step (steps S6-S9) that terminates before the heating time tt has elapsed. The preventive termination step includes a first step (step S6) that terminates when the amount of steam per unit time obtained from the detection result of the thermistor 35 indicates that it has reached the set steam amount. As such, the preventive termination step is performed based on the detection result of the thermistor 35 that detects steam generated from the cooking item C, i.e., the actual heating state of the cooking item C, rather than the weight of the cooking item C. Furthermore, the set steam amount that is compared with the amount of steam obtained from the detection result of the thermistor 35 is lower than the first maximum steam amount, which is the maximum amount of steam generated per unit time from the first cooking item C1. Therefore, the heating state before a large amount of steam is generated from the first cooking item C1 (which would result in overheating), i.e., the small amount of steam seeping out from the first cooking item C1, can be detected, thereby preventing overheating of the first cooking item C1. Furthermore, since the set steam volume is higher than the second maximum steam volume, which is the maximum volume of steam generated per unit time from the second food item C2, the food item C2 does not enter the prevention end step even if steam is generated from the second food item C2, and the food item C2 continues to be heated for the manually set heating time tt, thereby preventing the second food item C2 from being undercooked. In other words, the food item C2 can be prevented from being both overheated and undercooked.

[0060] More specifically, the gradient (slope) of the input voltage Vt(n) from the thermistor 35 due to steam generated from the first food item C1 is greater when a large amount of steam is emitted (first temperature gradient) than when a small amount of steam is exuded (third temperature gradient), and is greatest in the latter state (first maximum gradient). On the other hand, the gradient (slope) of the input voltage Vt(n) from thermistor 35 due to steam generated from the second food item C2 is roughly constant, and is greatest when steam begins to be generated (second maximum gradient). Furthermore, the set voltage Vt(n-10)+Vs, which is compared with the input voltage Vt(n) from thermistor 35, is lower than the first equivalent voltage Vt(n-10)+Va, which corresponds to the first temperature rise gradient (first maximum rise gradient) due to steam generated from the first food item C1, and is higher than the second equivalent voltage Vt(n-10)+Vb, which corresponds to the second temperature rise gradient (second maximum rise gradient) due to steam generated from the second food item C2, so overheating and underheating of the food items can be reliably prevented.

[0061] The preventive termination step includes a second step (steps S7 and S8) that sets an additional heating time tc1×α based on the execution time tc1 until the first step (step S6) is completed, and terminates when the additional heating time tc1×α or a manually set heating time tt has elapsed. This prevents the user from feeling uncomfortable when the food item C is heated for longer than the manually set heating time tt. On the other hand, if the additional heating time tc1×α for the small-volume first food item C1 is set too long, it may become overheated and unusable as an ingredient, while if the additional heating time tc1×α is set too short, it may become undercooked and unsuitable as an ingredient. Therefore, by setting the additional heating time tc1×α by multiplying the execution time tc1 of the first step by an appropriate coefficient α, it is possible to effectively prevent the first food item C1 from being overheated or undercooked, and to obtain an appropriate heating state.

[0062] The thermistor 35 for detecting the temperature of steam is disposed on the ceiling wall of the heating chamber 12. Therefore, the temperature of the steam generated from the food C and flowing upward can be reliably detected.

[0063] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible.

[0064] For example, the sensor may be a humidity sensor, and may be modified as needed as long as it is capable of detecting steam generated from the food item C. The sensor's detection result may be a current value or a digital value, and may have a reversed sign. The first step of the prevention termination process may be terminated when the amount of steam per unit time obtained from the sensor's detection result indicates that the set amount of steam has been reached. The set amount of steam may be set to a value that is less than a first maximum amount of steam, which is the maximum amount of steam generated per unit time from the first food item C1, and greater than a second maximum amount of steam, which is the maximum amount of steam generated per unit time from the second food item C2.

[0065] The additional heating time tc1×α may be set to be equal to or shorter than the manually set heating time tt, and the manual microwave heating process by the control unit 45 may be configured to omit step S9 shown in FIG.

[0066] The microwave oven 1 does not necessarily have to include the infrared sensor 34 for detecting the temperature of the food C.

[0067] The microwave oven 1 may not be provided with the heater 32 and may be capable of operating only in the microwave heating mode. [Explanation of symbols]

[0068] 1 microwave 10 Microwave oven body 11. Housing 12 Heating chamber 13 Bottom wall 13a Output section 14 Ceiling wall 15 Side wall 15a Ventilation hole 16 Back wall 17 Aperture 18 Upper guide rail 19 Lower guide rail 20 Doors 21 Frame 22 Window 23 Interior window 24 Exterior window 25 Reflective layer 28 trays 30 Magnetron (microwave source) 31 Duct 31a Expansion section 32 Heater 35 Thermistor (sensor) 35a Detector 40 Operation Panel 41~43 Operation section 44 LCD panel 44a Number display section 45 Control Unit C Cooked food

Claims

1. a heating chamber for heating food; a microwave source that outputs microwaves for heating the food; a sensor for detecting steam generated from the food; a control unit that outputs microwaves from the microwave source based on a manually set heating time and heats the food; Equipped with The food includes a first food and a second food having a larger volume and a larger amount of water than the first food, The heating process by the control unit includes a normal termination step that terminates when the heating time has elapsed and a preventive termination step that terminates before the heating time has elapsed, The prevention termination process includes a first step of terminating the microwave oven when the amount of steam per unit time obtained from the detection result of the sensor indicates that the amount of steam has reached a set steam amount that is less than a first maximum steam amount, which is the maximum amount of steam per unit time generated from the first food, and greater than a second maximum steam amount, which is the maximum amount of steam per unit time generated from the second food.

2. The control unit determines the amount of steam based on an input voltage from the sensor, 2. The microwave oven of claim 1, wherein the first step is terminated when the input voltage from the sensor indicates that the input voltage has reached a set voltage that is lower than a first equivalent voltage corresponding to a first maximum rising gradient due to steam generated from the first food, has a gentler rising gradient than the first maximum rising gradient, and is higher than a second equivalent voltage corresponding to a second maximum rising gradient due to steam generated from the second food.

3. 3. The microwave oven according to claim 1, wherein the preventive termination step includes an additional heating time obtained by multiplying an execution time from the start of heating by the microwave source to the end of the first step by a predetermined coefficient, or a second step of terminating heating by the microwave source when the heating time has elapsed.

4. 3. The microwave oven according to claim 1, wherein the sensor is a steam temperature sensor for detecting the temperature of the steam, and is disposed on a ceiling wall of the heating chamber.

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