JPH09213473A - Microwave oven - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect abnormal oven heating caused by the disconnection of a heater or the like by a simple structure. SOLUTION: A temperature increase ΔT in a cooking box during a specified time is obtained based on the detected temperature of a thermister 8 and compared with an abnormality detection level ΔS. If the temperature increase ΔT is larger than the level ΔS, heating by a heater is continued until a predetermined heating time is reached. If the temperature increase ΔT is smaller than the level ΔS, abnormal heating is determined and by turning OFF relays RL3 and RL4, the supplying of currents to heaters 9a and 9b is stopped. Thus, since the heating abnormality of the heater is detected based on the detected temperature of the thermister 8 for controlling a temperature in the cooking box, a structure is simplified and a cost increase is prevented.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a microwave oven,
In particular, it relates to a so-called microwave oven provided with a heater.

[0002]

2. Description of the Related Art In the so-called microwave oven, in addition to heating by microwaves generated by a magnetron, the surface of an object to be heated is burnt or colored by radiation and hot air from a heater.

[0003]

In the microwave oven of this type, a current detecting transformer has been conventionally used to detect a heating failure due to a break in the heater or the like. Therefore, the circuit configuration is complicated and the cost is high.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a microwave oven capable of detecting a wire break of a heater with a simple structure. .

[0005]

MEANS FOR SOLVING THE PROBLEMS AND BEST MODE FOR CARRYING OUT THE INVENTION A microwave oven according to the present invention made to solve the above problems heats an object to be heated contained in a cooking cabinet by infrared radiation. In a microwave oven equipped with a heater for a), a) temperature detecting means for detecting the temperature inside the cooking cabinet, and b) calculating the temperature rise during a predetermined time based on the temperature detected by the temperature detecting means. And c) a judging means for judging by comparing the temperature rise value calculated by the calculating means with a predetermined value, and d) a current supplied to the heater when the temperature rise value is below a predetermined value. And a heating control means for shutting off.

In the microwave oven of the present invention, a temperature detecting means is provided to control the heating temperature inside the cooking cabinet. Since the heater directly heats the air inside the cooking cabinet, the temperature inside the cooking cabinet rises significantly when the heater is heated. Therefore, the calculation means calculates the temperature increase during a predetermined time from the start of heating or after a lapse of a certain time after the start of heating, based on the detection signal from the temperature detection means, and the determination means determines that this temperature increase is the heater operation. When it is normal, determine whether it is valid. That is, when the temperature rise is less than the predetermined value, it is determined that the heater heating is abnormal, the current supplied to the heater is cut off, and the heater heating operation is stopped.

Further, when the heating control means stops heating the heater, the cook is informed that the cooking has not ended and stopped due to an abnormality detection in the middle, and further that the abnormality is an abnormality of the heater heating. Is desirable. Therefore, the microwave oven according to the present invention is further provided with an abnormality notifying unit for notifying an abnormality, and is configured to drive the abnormality notifying unit when the heating control unit cuts off the current supplied to the heater. Is preferred.

In the microwave oven according to the present invention, a heating operation in which an electric current is intermittently supplied to the heater may be performed depending on the type of object to be heated or the type of cooking. In such an operating state, naturally, the temperature rise inside the cooking cabinet is also different from that during the continuous heating operation. Therefore, in order to prevent the accuracy of the abnormality detection from being impaired by the heating output condition, it is more preferable that the determining means is configured to change the predetermined value according to the operating condition of the heater. For example, depending on the ON / OFF control cycle of the heater, the predetermined value may be reduced as the OFF time becomes longer.

[0009]

According to the microwave oven of the present invention, the heating abnormality of the heater is detected based on the temperature detected by the temperature detecting means installed for controlling the temperature in the cooking cabinet. Anomaly detection can be performed simply by adding a program, the configuration is simple, and cost increase is almost unnecessary.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a microwave oven according to the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of this microwave oven, and FIG. 2 is an electrical system configuration diagram of this microwave oven. In FIG. 1, a magnetron 3 is attached to the upper rear portion of a cooking cabinet 2 formed inside a housing 1, and microwaves are radiated into the cooking cabinet 2 via a waveguide 4. A turntable 5 for placing an object 6 to be heated is provided in the lower part of the cooking cabinet 2 and is rotationally driven by a turntable motor 7. A thermistor 8 for detecting the temperature is attached to the top of the cooking cabinet 2.
Further, an upper heater 9a and a lower heater 9b are provided outside the top and bottom of the cooking cabinet 2, respectively, so that so-called oven heating can be performed. A transformer 10 for oscillating the magnetron 3 is provided in the lower rear part of the housing 1.

Further, in FIG. 2, a fuse 12 for preventing overcurrent and a temperature fuse 13 for preventing heating are connected to the wiring from the power source 11. Further, it is connected to a circuit described later via a door switch 14 which is conductive when the door of the cooking cabinet 2 is completely closed, and a first relay RL1. Door switch 14 and first relay R
When L1 is closed, the power supply 11 includes a lighting lamp 15 that illuminates the interior of the cooking cabinet 2, a blower motor 16 for blowing air to cool the magnetron 3, and a turntable for which energization is controlled by opening and closing the second relay RL2. Motor 7, third
Heater 9 whose energization is controlled by opening and closing the relay RL3 of
a, a lower heater 9b whose energization is controlled by opening / closing the fourth relay RL4, and a primary coil 10a of a transformer 10 whose energization is controlled by opening / closing the fifth relay RL5. Secondary side low voltage coil 10 of transformer 10
b is a power source for heating the heater of the magnetron 3, and the secondary side high-voltage coil 10c is a capacitor 1 for voltage rectification.
7 and a diode 18 and serves to apply a high voltage to the magnetron 3.

The first to fifth relays RL1 to RL5 are on / off controlled by a control unit 19 including a microcomputer or the like. Further, the control unit 19 is input with a signal from the operation unit 20 according to the selection of range heating / oven heating, the heating time, the heating temperature, and the like according to the operation of the cook. In addition, the detection signal is input from the thermistor 8. Further, the control unit 19 outputs a signal to the display unit 21 to perform a display according to the input from the operation unit 20 or a display for notifying the progress of the cooking operation.

Hereinafter, the heating control operation when the oven heating is selected in the microwave oven having the above configuration will be described with reference to FIGS.
A description will be given according to the flowchart in FIG. In the initial state, all of the first to fifth relays RL1 to RL5 are in the off state. First, the control unit 19 performs a key scan on the operation unit 20 to determine whether or not there is a key input (step S1). If there is a key input, it is then determined whether or not the heating selected by the key input is heater heating (step S2).
That is, in case of range heating, the process other than this flowchart is performed. If the heater heating is performed in step S2, it is subsequently determined whether or not there is a timer operation for inputting the heating time (step S3), and the determination is repeated until the timer operation is performed.

When the timer is operated in step S3, the input value by the operation is stored in the internal register of the control unit 19 as the heating time TM (step S4). Next, it is determined whether or not the heating temperature is input (step S5), and the input value is used as the heating temperature OM in the control unit 1.
It is stored in the internal register 9 (step S6). Then, it is determined whether or not the heating start key has been operated (step S7). If the start key has not been operated, the process returns to step S3 and the timer operation determination is performed again. If there is a start key input in step S7, the process proceeds to step S8. First, the first relay RL1 is turned on, whereby the illumination lamp 15 is turned on and the blower motor 16 is driven.

Next, the data in the memory for storing the temperature detected by the thermistor 8 is reset (step S
9), the flags F0, F1, F2, F3 are reset to 0 (step S10). Further, the level ΔS for abnormality detection is determined according to the value of the heating temperature OM set in the internal register (step S11).

When the above internal setting is completed, the third relay RL3 is turned on to start energizing the upper heater 9a (step S12). Further, the fourth relay RL4 is turned on to start energizing the lower heater 9b (step 1
3). Then, a flag F0 indicating that the heater is turned on
Is set to 1 (step S14).

Next, the process proceeds to S23 of FIG. 4, and the internal timer of the control unit 19 starts counting down from the heating time TM set in the internal register. And
It is determined whether the internal timer has become 0 (step S24). Immediately after the heating is started, the internal timer has not become 0, so the step proceeds to S15, the temperature T0 of the thermistor 8 is detected, and it is judged whether or not the temperature T0 is equal to or higher than the set temperature OM (step S16). Immediately after the heating is started, the temperature T0 has not reached the set temperature OM, so the step proceeds to S27.

Here, it is determined whether or not the flags F2 and F3 are 0 (steps S27, S).
28), initially, since both of the flags F2 and F3 are reset in step S10, step S10
At 29, it is determined whether one minute has elapsed from the start of heating. Until 1 minute has elapsed, the step returns to S23, and the steps S23, S24, S15, S16 and S2 described above are performed.
Monitoring of the temperature in the cooking cabinet 2 is continued by the routine of S7 and S28. When 1 minute has elapsed in step S29, the process proceeds to step S30, and after the flag F3 is set, the detected temperature T1 of the thermistor 8 at this time is stored in the memory (step S31).

Next, it is determined whether or not 4 minutes have elapsed from the start of heating (step S32). Until 4 minutes have passed, the process returns to step S23, and the same routine as in the case of returning from step S29 is performed. However, in step S28, the flag F3 has already been set by the process of the previous step S30. Step S28
To S32. When 4 minutes have passed in step S32, the process proceeds to step S33, and the detected temperature T4 of the thermistor 8 at this time is stored in the memory. Then, the temperature difference ΔT between the detected temperature T1 at the time of 1 minute stored previously in the memory and the detected temperature T4 at the time of 4 minutes newly stored in the memory is calculated (step S34).

FIG. 6 is a diagram showing an example of a state in which the temperature inside the cooking cabinet 2 rises when the heater heating is normal and abnormal. When the heater heating is normal, the temperature is controlled so as to rise steadily from the start of heating and be maintained near that temperature after reaching the set temperature OM. At this time, the temperature difference ΔT becomes ΔT1 shown in the figure. On the other hand, when the upper heater 9a is not operating due to a disconnection or the like, the temperature detected by the thermistor 8 rises very slowly because it is heated only by the lower heater 9b, and the temperature difference ΔT at this time is ΔT shown in the figure.
It becomes T2. Therefore, the abnormality detection level ΔS is set to ΔT1 and ΔT
If it is set between 2 and 2, the above heating abnormality can be detected.

However, the degree of temperature rise when the heating is normal varies depending on the heating output. That is,
When the heater is intermittently turned on / off, or when it is driven at a low output by inverter control, the temperature rise rate of the temperature detected by the thermistor 8 is higher than that at the time of high output heating even in a normal heating state. Get loose. Therefore, in order to accurately detect the abnormality, the abnormality detection level ΔS is appropriately corrected according to the heating output. Specifically, the abnormality detection level Δ predetermined according to a plurality of different heating outputs
S is stored in the memory, and an appropriate value is selected from this.

In step S35, the temperature difference ΔT is compared with the abnormality detection level ΔS. If the temperature difference ΔT is equal to or higher than the abnormality detection level ΔS, the process proceeds to step S36, and the flag F2 indicating that the abnormality detection is executed is set. (Step S36). If the flag F1 is set, it is reset (step S37). Further, it is determined whether the flag F0 is 0 (step S38), and if the heater is in the on state, the flag F0 is determined.
Is 1, the process proceeds to step S23, and it is determined whether or not a preset heating time has elapsed after the internal timer countdown.

If the temperature difference ΔT is smaller than the abnormality detection level ΔS in step S35, it can be determined that the temperature rise is small and the heating is abnormal. In this case, step S in FIG.
39, turn off the third relay RL3, and turn on the upper heater 9
The current supplied to a is cut off and the fourth relay R
L4 is turned off to cut off the current supplied to the lower heater 9b (step S40). That is, the heating of the heater is stopped (step S41), the error display is lit on the display section 21, and the buzzer of the notification section 22 is driven to give a warning to the cook (step S42).

When the heaters 9a and 9b are operating normally, the temperature inside the cooking cabinet 2 rises with the passage of time as shown in FIG. 6, so that the temperature T0 detected by the thermistor 8 at a certain point The set temperature OM is reached. In this case, the process proceeds from step S16 to S17, and it is determined whether or not the flag F1 indicating the heater OFF operation is 0 (step S17). If F1 is 0, that is, the heater is in the on state, the process proceeds to step S18. . At this time, the third relay RL3 and the fourth relay RL4 are turned off to cut off the current supplied to the upper heater 9a and the lower heater 9b (steps S18 and S19). Then, the flag F1 is set to indicate that the heater is turned off (step S20), and if the flag F2 is reset, it is set (step S21). If the flag F2 is reset at the time of step S21, it means that the temperature in the cooking cabinet 2 has reached the set temperature OM before the processing of step S36, that is, before the lapse of 4 minutes from the start of heating. Therefore, it is not necessary to detect the abnormality, and the flag F2 is set. Further, the flag F0 is reset (step S22), and the process proceeds to step S23.

If the time from the start of heating has not reached the input heating time TM, step S23,
Proceed to S24 and S15, and detect temperature T in step S16.
When 0 is lower than the set temperature OM, the process proceeds to S27, and since the flag F2 is 1 here, the process proceeds to step S37. After resetting the flag F1, the flag F0 is determined and the process proceeds to step S12. And the third relay R
L3 and the fourth relay RL4 are turned on to supply current to the upper heater 9a and the lower heater 9b. As a result, heating by the heater is restarted (steps S12 and S1).
3). Then, a flag F0 indicating that the heater is turned on
Is set (step S14), and step S23 is set again.
Return to

Before or after the abnormal heating is detected, if the internal timer reaches 0 in step S24, it means that the set heating time TM has ended, so that the process goes to step S25. Go on, the third relay R
L3 and the fourth relay RL4 are turned off to cut off the current supplied to the upper heater 9a and the lower heater 9b,
The heating and cooking is finished (steps S25 and S26).

The numerical values in the above embodiment are examples and can be changed as appropriate.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an embodiment of a microwave oven according to the present invention.

FIG. 2 is an electrical configuration diagram of an embodiment of a microwave oven according to the present invention.

FIG. 3 is a control flowchart of a heating operation in the embodiment of FIG.

FIG. 4 is a control flowchart of a heating operation in the embodiment of FIG.

5 is a control flowchart of a heating operation in the embodiment of FIG.

FIG. 6 is a schematic diagram showing a state in which the temperature inside the cooking cabinet rises.

[Explanation of symbols]

 2 ... Cookhouse 3 ... Magnetron 8 ... Thermistor 9a ... Upper heater 9b ... Lower heater 19 ... Control part 20 ... Operation part RL3 ... Third relay RL4 ... Fourth relay

Claims (3)

[Claims] 1. A microwave oven provided with a heater for heating an object to be heated housed in a cooking cabinet by infrared radiation, comprising: a) temperature detecting means for detecting the temperature inside the cooking cabinet; and b). Calculating means for calculating a temperature rise during a predetermined time based on the temperature detected by the temperature detecting means; and c) judging means for judging the temperature rise value calculated by the calculating means by comparing it with a predetermined value. And d) heating control means for shutting off the current supplied to the heater when the temperature rise value is equal to or lower than a predetermined value. 2. The microwave oven according to claim 1, wherein
A microwave oven further comprising an abnormality notifying unit for notifying an abnormality, and driving the abnormality notifying unit when the heating control unit cuts off the current supplied to the heater. 3. The microwave oven according to claim 1, wherein the determination unit changes the predetermined value according to an operating condition of the heater.