microwave oven

Abstract

To provide a microwave oven capable of appropriately detecting a heating state of a cooked object in both cases of using a tray and not using it.SOLUTION: A microwave oven 1 includes: a heating chamber 12; an output part 13a provided on a bottom wall 13 of the heating chamber 12; a first sensor 34 for detecting temperatures of cooked objects C1, C2; a second sensor 35 for detecting steam generated from the cooked objects C1, C2; a tray 28 arranged detachably in the heating chamber 12; and a control part 45 for outputting microwaves from the output part 13a to perform heating treatment of the cooked objects C1, C2. The heating treatment by the control part 45 includes: first treatment to be executed when the tray 28 is not used, for heating the cooked objects C1, C2 on the basis of detection results of both the first sensor 34 and the second sensor 35; and second treatment to be executed when the tray 28 is used, for heating the cooked objects C1, C2 on the basis of a detection result of the second sensor 35 only.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a microwave oven that uses an infrared sensor to detect the temperature of the food to prevent it from being underheated or overheated, and a thermistor to detect the temperature of the steam generated from the food, and heats the food based on the results of these detections. This microwave oven can also heat food placed on a dedicated tray placed in the heating chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-167686 Summary of the Invention [Problem to be solved by the invention]

[0004] If the food is placed on the bottom wall of the heating chamber without using a tray, the food is close to the microwave output unit, which can result in uneven heating, with some parts of the food being heated and others not. On the other hand, if the food is placed on a tray inside the heating chamber, the food is far from the microwave output unit, so the food can be heated evenly without uneven heating by microwaves that are evenly distributed throughout the heating chamber. In other words, the heating progress (how the food cooks) differs depending on whether a tray is used or not. However, the microwave oven in Patent Document 1 does not take into consideration the appropriate detection of the heating state of the food, whether a tray is used or not.

[0005] An object of the present invention is to provide a microwave oven that can appropriately detect the heating state of food whether or not a tray is used. [Means for solving the problem]

[0006] One aspect of the present invention provides a microwave oven comprising: a heating chamber for heating an item to be cooked; a microwave output unit provided in the bottom wall of the heating chamber; a first sensor for detecting the temperature of the item to be cooked; a second sensor for detecting steam generated from the item to be cooked; a tray removably arranged in the heating chamber above the bottom wall at a distance; and a control unit that outputs microwaves from the output unit to perform a heating process on the item to be cooked, wherein the heating process by the control unit includes a first process that is performed when the tray is not in use and heats the item to be cooked based on the detection results of both the first sensor and the second sensor, and a second process that is performed when the tray is in use and heats the item to be cooked based on the detection result of only the second sensor.

[0007] The heating process by the control unit includes a first process that is performed when a tray is not used, and a second process that is performed when a tray is used. In the first process, since uneven heating of the food placed on the bottom wall of the heating chamber tends to occur, the control unit can appropriately detect the heating state of the food by using the detection results of both the first sensor and the second sensor. In the second process, since the food placed on the tray in the heating chamber tends to be heated evenly, the control unit can appropriately detect the heating state of the food by using the detection result of only the second sensor. In this way, the microwave oven of this embodiment can appropriately detect the heating state of the food whether a tray is used or not, and can heat the food to a good state.

[0008] The first processing by the control unit is terminated when either a first condition indicating that the input voltage from the first sensor has reached a set voltage corresponding to a predetermined set temperature or a second condition indicating that the input voltage from the second sensor has reached a first equivalent voltage corresponding to a predetermined first rising gradient is met, and the second processing by the control unit is terminated when the input voltage from the second sensor has reached a second equivalent voltage corresponding to a predetermined second rising gradient, and the second equivalent voltage is lower than the first equivalent voltage.

[0009] In the case of the first process where uneven heating occurs and unheated areas are present, the food is still not heated enough when steam is generated from the food, whereas in the case of the second process where there is no uneven heating and unheated areas are unlikely to exist, the food is heated sufficiently when steam is generated from the food. Therefore, in this embodiment, the second equivalent voltage determined in the second process is lower than the first equivalent voltage determined in the first process, and the state in which steam is generated from the food is detected with high sensitivity. As a result, compared to the first process, the second process detects the heating state of the food using only the second sensor, thereby preventing overheating of the food and allowing the food to be heated appropriately.

[0010] The tray is made of a microwave-transparent material, so that food can be heated evenly and reliably.

[0011] The heating chamber is provided with a guide rail for placing the tray, and the first sensor is an infrared sensor that is placed below the upper end of the guide rail. As a result, even when the tray is placed on the guide rail, nothing is interposed between the food placed on the bottom wall of the heating chamber and the first sensor, so the temperature of the food can be detected reliably and accurately by the first sensor.

[0012] The infrared sensor has only one infrared detection element with a field of view centered toward the bottom wall of the heating chamber. Because the infrared sensor is a monocular type with a single infrared detection element, it can be implemented at a lower cost than infrared sensors with multiple infrared detection elements. Moreover, because the field of view center of the infrared sensor extends toward the bottom wall of the heating chamber, it can reliably detect the temperature of the food on the bottom wall of the heating chamber.

[0013] The second sensor is a steam temperature sensor that detects the temperature of steam and is located on the ceiling wall of the heating chamber. Therefore, whether the food is placed on the bottom wall of the heating chamber or on a tray on the guide rail, the temperature of the steam generated from the food and flowing upward can be detected reliably and accurately. As a result, the food can be appropriately heated based on the detection result of only the second sensor, which is a steam temperature sensor, especially when the food is placed on a tray on the guide rail. [Effects of the Invention]

[0014] The microwave oven of the present invention can appropriately detect the heating state of the food being cooked whether or not a tray is used. [Brief explanation of the drawings]

[0015] [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 microwave heating process without using a tray. [Figure 6] 10 is a flowchart of a tray microwave heating process using a tray. [Figure 7] 10 is a flowchart of a resist heating process. [Figure 8] A continuation of Figure 7. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] 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.

[0018] 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 detachably disposed in heating chamber 12. As shown most clearly in FIG. 2, microwave oven 1 also includes magnetron (microwave source) 30, heater 32, infrared sensor (first sensor) 34, thermistor (second sensor) 35, fan 36, operation panel 40, and control unit 45. Control unit 45 executes the heating process set by operating operation panel 40, and heats food C1 or C2 (see FIG. 2) in heating chamber 12.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] Tray 28 is a rectangular plate that is rectangular when viewed in the height direction, and is selectively and detachably disposed on either upper guide rail 18 or lower guide rail 19. As shown most clearly in Figure 2, by placing food C2 on tray 28, food C2 can be placed above bottom wall 13 of heating chamber 12 with a gap therebetween.

[0024] 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 dimension between the pair of side walls 15 of the heating chamber 12, and is formed to be as large as possible without interfering with placement in the heating chamber 12. The front-to-rear dimension of the tray 28 is smaller than the dimension between the rear wall 16 and door 20 of the heating chamber 12, and is formed to be as large as possible without interfering with placement in the heating chamber 12.

[0025] 2, magnetron 30 is disposed between housing 11 and heating chamber 12 and uses microwaves to heat foods C1 and C2 inside heating chamber 12. 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 one end of 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.

[0026] 2 and 3, the heater 32 is disposed adjacent to the top wall 14 and heats the foods C1 and C2 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.

[0027] 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.

[0028] The infrared sensor 34 is a monocular thermopile type equipped with one infrared detection element that detects the temperature of the food C1 placed on the bottom wall 13 of the heating chamber 12. The infrared sensor 34 has a conical field of view 34a, which is the range within which it can detect infrared rays. The angle of the field of view 34a of the monocular infrared sensor 34 is, for example, 12 degrees. In order to detect the temperature of the food C1 placed on the bottom wall 13 of the heating chamber 12, the field of view center 34b, which is the axis of the field of view 34a, is positioned so that it passes 2 cm above the center of the bottom wall 13 of the heating chamber 12.

[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] The fan 36 is disposed between the housing 11 and the heating chamber 12, and cools electrical components such as the magnetron 30 and a control board (not shown) on which the control unit 45 is disposed by blowing air. The fan 36 of this embodiment can also cool the inside of the heating chamber 12 by blowing air through a large number of vents 15a provided in the side wall 15.

[0031] Referring to FIG. 4, the operation panel 40 includes three operation sections 41 to 43 and one liquid crystal panel 44, and is provided below the window section 22 of the door 20.

[0032] 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.

[0033] 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.

[0034] 2, the control unit 45 is composed of, for example, a microcomputer, and is electrically connected to the magnetron 30, heater 32, infrared sensor 34, thermistor 35, fan 36, and operation panel 40. 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 heater 32 are controlled.

[0035] 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 (heating temperature) can be set by operating the operation unit 42 to change the numerical value on the numeric 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.

[0036] 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 food C1 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 C1 with microwaves. "Tray microwave" is performed with food C2 placed on a tray 28 placed in the heating chamber 12, and the magnetron 30 is controlled based solely on the detection result of the thermistor 35, without using the infrared sensor 34, to heat the food C2 with microwaves. "Defrosting" is performed with food C1 placed on the bottom wall 13 of the heating chamber 12, and the magnetron 30 is controlled based solely on the detection result of the infrared sensor 34 to heat the food C1 with microwaves.

[0037] 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 C2 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 C2 by radiant heat.

[0038] Resigli (resigli heating process) is performed in the combined heating mode. Resigli is performed with the food C2 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 C1 using microwaves and radiant heat. For example, the magnetron 30 is first activated to cook the food C1 to the center, then the magnetron 30 is stopped and the heater 32 is activated to brown the surface of the food C1, and the heater 32 is stopped after a set heater heating time has elapsed.

[0039] The automatic (automatic heating process) is performed in a heating mode determined according to the manually set cooking menu. The cooking menu determines whether the food is placed on the bottom wall 13 or on the tray 28. 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 'Sacred'" performed in the combined heating mode.

[0040] Next, a microwave heating process (first process) in which the tray 28 is not used and a tray microwave heating process (second process) in which the tray 28 is used will be described.

[0041] The control unit 45 determines whether the tray 28 is being used by manually setting the heating process through the operation of the operation unit 41. However, the determination of whether the tray 28 is being used may also be performed by an ultrasonic sensor, a weight sensor, or the like, as long as it is configured to be able to determine whether the tray 28 is being used or not.

[0042] In the microwave heating process, uneven heating of the food item C1 tends to occur because the food item C1 placed on the bottom wall 13 of the heating chamber 12 is close to the output unit 13a. If there are unheated portions of the food item C1, the food item C1 is not yet sufficiently heated when steam is generated from the food item C1. Therefore, in the microwave heating process, a first condition based on the detection result of the infrared sensor 34 and a second condition based on the detection result of the thermistor 35 are set, by which it can be determined that the food item C1 has been sufficiently heated, and the food item C1 is heated by the magnetron 30 until either of these conditions is met.

[0043] The first condition is that the input voltage Vi from the infrared sensor 34 indicates that it has reached a set voltage Vs corresponding to a predetermined set temperature Ts (Vi≧Vs). The set temperature Ts is set in a temperature range of 60°C or higher and 80°C or lower, and is set to 70°C in this embodiment. The set voltage Vs is a voltage value output by the infrared sensor 34 when the food C1 reaches the set temperature Ts, and is set to a voltage equivalent to 70°C in this embodiment.

[0044] The second condition is that the input voltage Vt from the thermistor 35 has reached a first equivalent voltage Vt(n-10)+Va, which corresponds to a predetermined first temperature rise gradient (Vt(n)≧Vt(n-10)+Va). Here, Vt(n-10) refers to the voltage input from the thermistor 35 10 times earlier, and Va is a constant term corresponding to the magnitude of fluctuation according to the first temperature rise gradient. The constant term Va is set to a value range of 0.06 V to 0.10 V based on the temperature rise gradient when a specific food item C1 (e.g., one cup of cooked rice) is heated to 70°C, and is set to 0.08 V in this embodiment. However, the establishment of the second condition may also be determined by comparing the current input voltage Vt(n) with a first equivalent voltage Vt(n-10)×k1, which is obtained by multiplying the 10th previous input voltage Vt(n-10) by a coefficient k1 corresponding to the first temperature rise gradient. Furthermore, the current input voltage Vt(n) may be compared with the input voltage Vt(n-5) five times earlier, and the comparison target can be changed as necessary.

[0045] In tray microwave heating, because the distance between the food item C2 placed on the tray 28 and the output unit 13a is great, the food item C2 tends to be heated evenly by microwaves that are evenly distributed throughout the heating chamber 12. If there are no unheated portions of the food item C2, the food item C2 is sufficiently heated for cooking when steam is generated from the food item C2. Therefore, in tray microwave heating, a condition is set based on the detection result of the thermistor 35 that determines that the food item C2 has been sufficiently heated, in other words, that steam is generated from the food item C2, without detection by the infrared sensor 34, and the food item C2 is heated by the magnetron 30 until this condition is met.

[0046] The condition for determining whether the tray microwave heating process has ended is whether the input voltage Vt from thermistor 35 has reached a second equivalent voltage Vt(n-10)+Vb, which corresponds to a predetermined second temperature rise gradient (Vt(n)≧Vt(n-10)+Vb). As with the microwave heating process, Vt(n-10) represents the voltage input from thermistor 35 10 times earlier, and Vb is a constant term corresponding to the magnitude of fluctuation according to the second temperature rise gradient. However, the current input voltage Vt(n) may also be compared to the second equivalent voltage Vt(n-10)×k2, which is obtained by multiplying the 10th previous input voltage Vt(n-10) by a coefficient k2 corresponding to the second temperature rise gradient, to determine whether the condition is met. Alternatively, the current input voltage Vt(n) may be compared to the 5th previous input voltage Vt(n-5), and the comparison target can be changed as needed.

[0047] In the tray microwave heating process, unheated portions of the food item C2 are less likely to occur, and the accuracy of determining the heating state of the food item C2 based on the detection results of the thermistor 35 is higher than in the microwave heating process. Therefore, the value of the constant term Vb in the tray microwave heating process is set to a value in the range of 0.03 V to 0.05 V, which is lower than the value of the constant term Va in the microwave heating process, and is set to 0.04 V in this embodiment. In other words, the second temperature rise gradient in the tray microwave heating process is gentler than the first temperature rise gradient in the microwave heating process, and the value of the second equivalent voltage Vt(n-10)+Vb is lower than the value of the first equivalent voltage Vt(n-10)+Vb. This enables highly sensitive detection of the state in which steam is generated from the food item C2.

[0048] Next, a resilience heating process using both the magnetron 30 and the heater 32 will be described.

[0049] In the resistivity heat treatment, heating is performed by the magnetron 30 followed by heating by the heater 32, so the temperature inside the heating chamber 12 after cooking is completed is higher than in a heating process that uses only the magnetron 30. If the resistivity heat treatment is performed when the inside of the heating chamber 12 is at a high temperature, the accuracy of detecting the steam temperature by the thermistor 35 decreases. Therefore, the resistivity heat treatment of this embodiment is configured as follows.

[0050] At the start of the resi-grilling heating process, if the temperature inside the heating chamber 12 obtained from the detection result of the thermistor 35 indicates that it is equal to or higher than the first set temperature Ts1, or if it is equal to or higher than the second set temperature Ts2, the fan 36 is operated to cool the inside of the heating chamber 12, and then heating is started. On the other hand, if the temperature inside the heating chamber 12 is lower than the second set temperature Ts2, heating is started immediately without operating the fan 36. In this embodiment, the first set temperature Ts1 is set to 70°C, and the second set temperature Ts1 is set to 45°C.

[0051] When the input voltage Vt from the thermistor 35 is equal to or higher than a first set voltage Vc corresponding to a predetermined first set temperature Ts1, the control unit 45 operates the fan 36 until the input voltage Vt falls below the first set voltage Vc. Furthermore, when the input voltage Vt is equal to or higher than a second set voltage Vd corresponding to a predetermined second set temperature Ts2, the control unit 45 operates the fan 36 for a predetermined set time ts1 (e.g., 1 minute 30 seconds). Regardless of whether the fan 36 is operated, the control unit 45 adjusts a predetermined heating time ts2 (e.g., 4 minutes) by the heater 32 based on the operation times tc and ts1 of the fan 36 to keep the total execution time of the registration re-heating process constant.

[0052] Next, the microwave heating process, tray microwave heating process, and register reheating process performed by the control unit 45 will be described in more detail with reference to FIGS.

[0053] Referring to FIG. 5, in the microwave heating process, the control unit 45 activates the magnetron 30 in step S11, and then starts intermittent detection of the voltage Vi (e.g., every second) by the infrared sensor 34 in step S12, and starts intermittent detection of the voltage Vt (e.g., every second) by the thermistor 35 in step S13.

[0054] Next, in step S14, it is determined whether the input voltage Vi from the infrared sensor 34 is equal to or greater than the set voltage Vs. If the input voltage Vi is less than the set voltage Vs, the process proceeds to step S15, and if the input voltage Vi is equal to or greater than the set voltage Vs, the process proceeds to step S16.

[0055] In step S15, it is determined whether the input voltage Vt(n) from the thermistor 35 is equal to or greater than the first equivalent voltage Vt(n-10)+Va. If the input voltage Vt(n) is less than the first equivalent voltage Vt(n-10)+Va, the process returns to step S14, and if the input voltage Vt(n) is equal to or greater than the first equivalent voltage Vt(n-10)+Va, the process proceeds to step S16. In other words, if either the first condition shown in step S14 or the second condition shown in step S15 is met, the process proceeds to step S16.

[0056] In step S16, the operation of magnetron 30 is stopped, and then in step S17, the intermittent detection of voltage Vi by infrared sensor 34 is stopped, and in step S18, the intermittent detection of voltage Vt by thermistor 35 is stopped, and the process returns.

[0057] Referring to FIG. 6, in the tray microwave heating process, the control unit 45 activates the magnetron 30 in step S21, and then starts intermittent detection of the voltage Vt by the thermistor 35 (for example, every second) in step S22.

[0058] Next, in step S23, the process waits until the input voltage Vt(n) from the thermistor 35 indicates a value equal to or greater than the second equivalent voltage Vt(n-10)+Vb. When the input voltage Vt(n) becomes equal to or greater than the second equivalent voltage Vt(n-10)+Vb, the process stops operation of the magnetron 30 in step S24, and then stops intermittent detection of the voltage Vt by the thermistor 35 in step S25, and returns.

[0059] 7, in the registration reheating process, the control unit 45 performs detection using the thermistor 35 in step S31, and then determines in step S32 whether the input voltage Vt from the thermistor 35 is equal to or greater than a first set voltage Vc corresponding to a first set temperature Ts1. If the input voltage Vt is equal to or greater than the first set voltage Vc, the process proceeds to step S33, and if the input voltage Vt is less than the first set voltage Vc, the process proceeds to step S38.

[0060] In step S33, the fan 36 is operated, and then in step S34, measurement of the operation time tc of the fan 36 is started using the counter tc. Subsequently, in step S35, detection is performed by the thermistor 35, and in step S36, it is determined whether the input voltage Vt from the thermistor 35 indicates that it is less than the first set voltage Vc. If the input voltage Vt is equal to or greater than the first set voltage Vc, the process returns to step S35 and waits until the input voltage Vt becomes less than the first set voltage Vc. If the input voltage Vt becomes less than the first set voltage Vc, measurement of the operation time tc is stopped in step S37, and then operation of the fan 36 is stopped in step S41, and the process proceeds to step S42.

[0061] On the other hand, if the input voltage Vt is less than the first set voltage Vc in step S32, it is determined in step S38 whether the input voltage Vt from thermistor 35 is equal to or greater than the second set voltage Vd corresponding to the second set temperature Ts2. If the input voltage Vt is equal to or greater than the second set voltage Vd, the process proceeds to step S39, where the fan 36 is operated. After waiting until the set time ts1 has elapsed in step S40, the process stops the operation of the fan 36 in step S41 and proceeds to step S42. On the other hand, if the input voltage Vt is less than the first set voltage Vc in step S38, the process proceeds to step S42 without performing any of steps S33 to S37 or S39 to S41.

[0062] 8, in step S42, the magnetron 30 is operated, and then in step S43, intermittent detection of the voltage Vt by the thermistor 35 is started (for example, every second). Next, in step S44, the process waits until the input voltage Vt(n) from the thermistor 35 indicates an equivalent voltage Vt(n-10)+Vb or higher, and when the input voltage Vt(n) becomes equal to or higher than the equivalent voltage Vt(n-10)+Vb, the process proceeds to step S45. Note that the equivalent voltage Vt(n-10)+Vb is set to be the same as the second equivalent voltage Vt(n-10)+Vb in the tray microwave heating process, but they may be different.

[0063] In step S45, operation of magnetron 30 is stopped, and then in step S46, intermittent detection of voltage Vt by the thermistor 35 is stopped. Then, in step S47, heater 32 is operated, and the process waits until the time obtained by subtracting the operation time of fan 36 from the set heating time ts2 has elapsed. That is, if the process proceeds from step 32 in FIG. 7 via steps S33 to S37, S41, and S42 to step S47, the process waits until the time obtained by subtracting operation time tc from heating time ts2 has elapsed. If the process proceeds from step 32 in FIG. 7 via steps S38 to S42 to step S47, the process waits until the time obtained by subtracting operation time ts1 from heating time ts2 has elapsed. If the process proceeds from step 32 in FIG. 7 via steps S38 and S42 to step S47, the process waits until the heating time ts2 has elapsed. When the heating time has elapsed, the operation of the heater 32 is stopped in step S49, and the process returns.

[0064] The microwave oven 1 configured in this manner has the following features.

[0065] The heating process performed by control unit 45 includes a microwave heating process that is performed when tray 28 is not used, and a tray microwave heating process that is performed when tray 28 is used. In the microwave heating process, uneven heating of food item C1 placed on bottom wall 13 of heating chamber 12 tends to occur, so control unit 45 can appropriately detect the heating state of food item C1 by using the detection results of both infrared sensor 34 and thermistor 35. In the tray microwave heating process, food item C2 placed on tray 28 in heating chamber 12 tends to be heated evenly, so control unit 45 can appropriately detect the heating state of food item C2 by using the detection result of only thermistor 35. In this way, microwave oven 1 of this embodiment can appropriately detect the heating state of food items C1 and C2 whether tray 28 is used or not, and can heat food items C1 and C2 to a good state.

[0066] In the case of microwave heating, when uneven heating occurs and unheated areas are present, the heating is still insufficient when steam is generated from the food item C1. However, in the case of tray microwave heating, when uneven heating is not present and unheated areas are unlikely to exist, the heating is sufficient when steam is generated from the food item C2. Therefore, the second equivalent voltage Vt(n-10)+Vb determined for the tray microwave heating process is set lower than the first equivalent voltage Vt(n-10)+Va determined for the microwave heating process, and the state in which steam is generated from the food item C2 is detected with high sensitivity. Therefore, compared to microwave heating, the tray microwave heating process detects the heating state of the food item C2 using only the thermistor 35, preventing overheating of the food item C2 and allowing the food item C2 to be heated appropriately.

[0067] Since the tray 28 is made of a microwave-transparent material, the food C2 can be heated evenly without fail.

[0068] The infrared sensor 34 is disposed below the upper end of the guide rail 18 of the heating chamber 12. As a result, even when the tray 28 is placed on the guide rail 18, nothing is interposed between the food C1 placed on the bottom wall 13 of the heating chamber 12 and the infrared sensor 34, so that the temperature of the food C1 can be detected reliably and with high accuracy by the infrared sensor 34.

[0069] Because infrared sensor 34 is a monocular type equipped with one infrared detection element, it can be implemented at a lower cost than infrared sensors equipped with multiple infrared detection elements. Moreover, because the center of view 34b of infrared sensor 34 extends toward bottom wall 13 of heating chamber 12, it can reliably detect the temperature of food C1 on bottom wall 13 of heating chamber 12.

[0070] A thermistor 35, which is a steam temperature sensor that detects the temperature of steam, is disposed on the top wall 14 of the heating chamber 12. Therefore, whether the food is placed on the bottom wall 13 of the heating chamber 12 or on the tray 28 on the guide rail 18, the temperature of the steam generated from the food C1, C2 and flowing upward can be detected reliably and with high accuracy. As a result, particularly when the food is placed on the tray 28 on the guide rail 18, the food can be appropriately heated based on the detection result of the thermistor 35, which is a steam temperature sensor, alone.

[0071] In the registration reheating process, which operates the magnetron 30 and heater 32, the fan 36 is operated based on the temperature inside the heating chamber 12 at the start of the process. This allows the thermistor 35 to detect the temperature of the food C1 with high accuracy, allowing the food C1 to be heated appropriately. Meanwhile, the heating time by the heater 32 is adjusted based on the operation time of the fan 36. This allows the total execution time of the registration reheating process to be kept constant, preventing the user from feeling uncomfortable due to a longer execution time.

[0072] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible.

[0073] For example, the tray 28 may be made of a microwave reflector such as metal, and the front-to-rear dimension of the tray 28 may be made smaller than the dimension between the rear wall 16 of the heating chamber 12 and the door 20, so that microwaves can pass through the gap between the tray 28 and the rear wall 16.

[0074] The first sensor can be changed as needed as long as it is capable of detecting the temperature of the food item C1. The second sensor may be a humidity sensor, and can be changed as needed as long as it is capable of detecting steam generated from the food items C1 and C2.

[0075] The infrared sensor 34 may include multiple infrared detection elements.

[0076] 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]

[0077] 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 31 Duct 31a Expansion section 32 Heater 34 Infrared sensor (first sensor) 34a field of view 34b Center of visual field 35 Thermistor (second sensor) 35a Detector 36 Fans 40 Operation Panel 41~43 Operation section 44 LCD panel 44a Number display section 45 Control Unit C1,C2 Cooked food

Claims

1. a heating chamber for heating food; a microwave output section provided on a bottom wall of the heating chamber; a first sensor for detecting the temperature of the food; a second sensor for detecting steam generated from the food; a tray that is detachably disposed within the heating chamber above the bottom wall with a space therebetween; a control unit that outputs microwaves from the output unit to heat the food; Equipped with The heating process by the control unit is a first process that is executed when the tray is not in use and heats the food based on detection results of both the first sensor and the second sensor; a second process that is executed when the tray is used and heats the food based on the detection result of only the second sensor; Including microwave ovens.

2. the first process by the control unit is terminated when either a first condition indicating that the input voltage from the first sensor has reached a set voltage corresponding to a predetermined set temperature or a second condition indicating that the input voltage from the second sensor has reached a first equivalent voltage corresponding to a predetermined first rising gradient is satisfied; the second process by the control unit is terminated when it indicates that the input voltage from the second sensor has reached a second equivalent voltage corresponding to a predetermined second rising gradient; 2. The microwave oven according to claim 1, wherein the second equivalent voltage is lower than the first equivalent voltage.

3. 3. The microwave oven according to claim 1, wherein the tray is made of a microwave-transparent material.

4. the heating chamber includes a guide rail for arranging the tray; 3. The microwave oven according to claim 1, wherein the first sensor is an infrared sensor and is disposed below an upper end of the guide rail.

5. 5. The microwave oven according to claim 4, wherein said infrared sensor comprises only one infrared detection element having a center of view extending toward said bottom wall of said heating chamber.

6. 3. The microwave oven according to claim 1, wherein the second sensor is a steam temperature sensor that detects the temperature of the steam and is disposed on a ceiling wall of the heating chamber.

Images