JP2020092757A - rice cooker - Google Patents

Abstract

To make it easy to identify an external element causing failure of a switching element.SOLUTION: A rice cooker comprises: a resonant circuit 9 consisting of an inner pot 8, a heating coil 6 and a smoothing capacitor 4 connected in parallel with the heating coil 6; a switching element 10 for supplying a high-frequency current to the resonant circuit 9; current detection means 14 for detecting a current value flowing in the heating coil 6; and a microcomputer 18 for performing variable control on the ON time of the switching element 10 on the basis of the current value detected by the current detection means 14 so that the inner pot 8 is heated with the prescribed electric power. The microcomputer 18 stores the maximum value and the minimum value of the ON time of the switching element 10 in advance during induction heating of the inner pot 8 with the prescribed electric power. When the microcomputer performs variable control on the ON time of the switching element 10 to obtain the prescribed electric power during cooking rice, the microcomputer updates the stored ON time if it is larger than the maximum value of the ON time stored in advance or smaller than the minimum value of the ON time stored in advance.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rice cooker, and more particularly to a rice cooker suitable for improving the maintainability of an electromagnetic induction heating type rice cooker.

Patent Document 1 detects the temperature of a switching element, determines that the cooling state is abnormal when a temperature above a certain level is detected, and cooks the rice when the number of cooked rice with the detection exceeds a predetermined number. The rice cooker that indicates that is abnormal is described.

JP, 2010-88648, A

The device disclosed in Patent Document 1 detects the temperature of the switching element and judges that the cooling state is abnormal when the temperature rise above a certain level is detected. However, the reason why the temperature rise of the switching element further rises from the normal time and becomes high is that the heat generation temperature is higher than the normal value due to abnormal operation of the switching element due to external factors in addition to the abnormal cooling state. The switching element may fail. In that case, there is a problem that recurrence cannot be prevented unless the external factors are removed.

In order to solve the above-mentioned conventional problems, in the present invention, an inner pot for containing rice and water, a heating coil located below the inner pot for inductively heating the inner pot, and a resonance connected in parallel with the heating coil A resonance circuit composed of a capacitor, a switching element for flowing a high-frequency current through the resonance circuit, a current detection means for detecting a value of a current flowing through the heating coil, and the current detection means for heating the inner pot with a predetermined electric power. And controlling the ON time of the switching element by varying the ON time of the switching element based on the detected current value. The ON time of the switching element when the inner pot is induction-heated with the predetermined electric power. The maximum value and the minimum value of are stored in advance, and when the ON time of the switching element is variably controlled to obtain the predetermined power during rice cooking, the maximum value of the ON time stored in advance is stored. If it is greater than or less than the minimum value of the ON time stored in advance, the stored ON time is updated.

According to the present invention, by storing the operating state of the switching element at the time of abnormality, it is possible to easily identify the external factor causing the failure and improve the maintainability.

Circuit block of an inverter control circuit showing an embodiment of the present invention Example of current voltage waveform of switching element Example of rice temperature and output power during rice cooking operation Memory flow of microcomputer when cooking rice

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit block diagram of an embodiment of an inverter control circuit of the present invention.

In the figure, 1 is an AC commercial power source. Reference numeral 2 denotes a rectifier circuit, which is composed of a plurality of rectifiers, whose input is connected to an AC commercial power source 1, rectifies the commercial power source 1 and converts it into a DC power source, and outputs it. One end of the choke coil 3 is connected to the plus terminal of the rectifier circuit 2 via the current detection circuit 14, the other end is connected to one end (high voltage side terminal) of the smoothing capacitor 4, and the other end of the smoothing capacitor 4 is grounded. . A smoothing circuit 5 is formed by the choke coil 3 and the smoothing capacitor 4, and smoothes the DC power output from the rectifying circuit 2. Reference numeral 6 is a heating coil, which is connected in parallel to the resonance capacitor 7, and one end of which is connected to the high voltage side terminal of the smoothing capacitor 4. Reference numeral 8 denotes an inner pot of an IH jar rice cooker, which is arranged in the vicinity of the heating coil 6 and is induction-heated by the magnetic flux generated by the heating coil 6 to heat rice and water contained therein to cook rice. Reference numeral 9 is a resonance circuit including a heating coil 6, a resonance capacitor 7, and an inner pot 8. Reference numeral 10 is a switching element, the collector terminal is connected to one end of the heating coil 6 different from the connection point with the smoothing circuit 5, the emitter terminal is grounded, and the resonance circuit 9, that is, the heating coil 6 is subjected to high-frequency current by high-speed switching. Is something that flows. Reference numeral 11 is a diode, and the cathode terminal and the anode terminal are connected to the collector terminal and the emitter terminal of the switching element 10, respectively. Reference numeral 12 is an inverter unit, which is formed of a switching element 10 and a diode 11. Reference numeral 13 denotes a drive circuit, the output of which is connected to the base terminal of the switching element 10 to convert the input signal into a drive voltage suitable for driving and drive the switching element 10. Reference numeral 18 denotes a microcomputer, and the output terminal OUT1 outputs a pulse signal for setting electric power and is connected to the drive circuit 13. The input terminal IN1 is connected to the current detection means 14 described later, the input terminal IN2 is connected to the voltage detection means 15 described later, the input terminal IN3 is connected to the power supply frequency detection means (power supply waveform 0V detection means) 16 described later, and the input terminal IN4. Is connected to the output terminal of the trigger circuit. Further, the microcomputer 18 has a plurality of heating modes. Reference numeral 15 is a voltage detecting means for detecting the voltage of the commercial power supply 1. Further, it is possible to detect an arbitrary voltage within the waveform of one cycle obtained by rectifying the commercial power supply. Reference numeral 16 is a power supply frequency detection means (power supply waveform 0V detection means) which can detect the frequency of the commercial power supply. Reference numeral 14 denotes a current detecting means, the detecting portion of which is connected between the power supply 1 and the rectifier circuit 2, and the output portion of which is connected to the input terminal IN1 of the microcomputer 18, which detects the current flowing through the heating coil 6 to detect the current. The microcomputer 18 grasps the output power of the inverter unit 12 and detects the inner pot from the current value.

Next, the operation for heating the inner pot 8 will be described.

First, the state of the circuit and the operation of the microcomputer 18 before the start of heating will be described.

AC power is supplied from the commercial power supply 1 to the rectifier circuit 2, rectified by the rectifier circuit 2, smoothed by the smoothing circuit 5, and converted to DC power. This DC power supply is in a ready state for supplying a current to the inner pot 8 selected by the microcomputer 18 when the resonance circuit 9 and the switching element 10 in the inverter section 12 connected thereto are driven. .. The microcomputer 18 is energized and stands by until a heating start signal from a user (not shown) is input without outputting an active signal from the output terminal OUT1.

Next, the operation of the circuit and the microcomputer 18 after the start of heating will be described. When the user's signal to start heating is input to the microcomputer 18, the microcomputer 18 understands the fact and starts the heating operation as follows. In response to the heating start signal, the microcomputer 18 outputs a power setting pulse signal suitable for the inner pot 8 from the output terminal OUT1, and this signal is transmitted to the base of the switching element 10 in the inverter unit 12 via the drive circuit 13. Then, the switching element 10 is driven. When the switching element 10 is driven, a current is supplied from the DC power supply to the resonance circuit 9, and the current starts to flow in the heating coil 6, the switching element 10, and the like. The current flows through the switching element 10 only during the ON time of the pulse signal determined by the predetermined power output from the output terminal OUT1 of the microcomputer 18, and the collector terminal and the emitter terminal of the switching element 10 after the pulse signal becomes OFF. The trigger circuit 17 for detecting the voltage generated during the period, that is, 0 V of the resonance voltage, starts operating, and its output is transmitted to the input terminal IN4 of the microcomputer 18. When the signal of the trigger circuit 17 is transmitted to the microcomputer 18, the microcomputer 18 outputs a pulse signal at a frequency synchronized with the signal from the output terminal OUT1. After that, while the inner pot 8 is selected, the signal is output terminal OUT1 of the microcomputer 18 →drive circuit 13 →switching element 10 →trigger circuit 17 →input terminal IN4 of the microcomputer 18 → And transmitted in a loop. As a result, the switching element 10 is periodically driven by the microcomputer 18 at the ON timing, so that the high-frequency current continuously flows through the heating coil 6 to heat the inner pot 8. The current detecting means 20 detects the current flowing between the commercial power source 1 and the rectifier circuit 2 in response to this high frequency current and inputs it to the input terminal IN1 of the microcomputer 18, and the microcomputer 18 inputs the input primary current. Appropriate processing is performed to grasp output power.

FIG. 2 shows a voltage/current waveform example of the switching element 10 when the resonance circuit 9 is driven at a high frequency. The operation of the switching element 10 produces a current waveform 19 of the switching element 10 and a voltage waveform 20 of the switching element 10. FIG. 3 shows an example of a rice temperature and a predetermined output power during the rice cooking operation. By the operation of the switching element 10 indicated by the predetermined power operation 22 during the rice cooking operation, the inner pot 8 becomes the temperature 21 shown in the rice temperature example during the rice cooking operation. The ON time t of the switching element 10 is determined by the ON time of the pulse signal determined by the predetermined power output from the output terminal OUT1 of the microcomputer 18. In a plurality of heating modes, predetermined power is output and rice cooking operation is performed.

The electrical characteristics of the induction heating type rice cooker are determined by the relationship between the inner pot 8 and the heating coil 6 and the gap between the inner pot 8 and the heating coil 6. However, since there is a dimensional error of the inner pot 8 of the rice cooker, a dimensional error of the gap, and a dimensional error of the heating coil 6, the combination of the inner pot 8 and the heating coil 6 and the gap between the inner pot 8 and the heating coil 6 are different. Due to the difference, the maximum value and the minimum value of the ON time t of the switching element 10 are different for each rice cooker. Therefore, the ON time t of the switching element 10 which operates at the predetermined output after the adjustment of the predetermined output is adjusted using the inner pot 8 (a standard inner pot for setting, etc.) packed in the manufacturing process of the rice cooker is normal. The maximum value and the minimum value which are the range are stored in the microcomputer 18.

FIG. 4 shows a flow of storing the maximum value and the minimum value in the microcomputer 18 when a predetermined power operation is performed during the rice cooking operation.

After the rice cooking is started (S1), when the rice is operated at a predetermined electric power in the course of the rice cooking (S2), that is, when the switching element 10 is operated so that the electric power generated by the switching element 10 becomes a predetermined electric power, switching is performed. The ON time t of the element 10 is compared with the maximum value of the ON time t of the switching element 10 stored in the microcomputer 18 (S3), and if it is larger than the stored maximum value, the stored value is updated (S4). If the ON time t of the switching element 10 is less than the minimum value of the stored ON time t, the minimum value of the ON time t of the switching element 10 stored in the micro computer 18 is compared (S5). Updates the stored value (S6) and holds the stored value if it is greater than or equal to the minimum value and less than or equal to the maximum value. This operation is performed every predetermined power operation in a plurality of heating modes.

The minimum value and the maximum value updated as the stored values can be displayed on the display device (not shown) by the micro computer 18 by the user's instruction input. Similarly, the maximum value and the minimum value, which are normal ranges when the inner pot 8 (a standard inner pot for setting or the like) packed in the manufacturing process of the rice cooker is used, can be displayed on the display device.

When the above-mentioned electrical characteristics change, the ON/OFF time (cycle) of the inverter waveform when outputting a predetermined electric power fluctuates, the frequency changes, and the ON time t of the switching element 10 fluctuates. By storing the value (maximum thermal power) and the minimum value (minimum thermal power), it is possible to estimate the cause related to the electrical characteristics described above, which facilitates failure and failure analysis.

For example, when the ON time of the switching element 10 is larger than the maximum value in the normal range, it is considered that the structural gap between the inner pot 8 and the heating coil 6 is wide, and the possible causes in actual use conditions are: When rice is cooked with the bottom of the inner pot 8 recessed inward, or when rice is cooked with foreign substances such as rice on the bottom of the inner pot 8, the bottom of the inner pot 8 is physically The gap between the heating coil 6 and the heating coil 6 becomes large, and when the rice is cooked and the inverter operates in this state, a malfunction such as damage due to overcurrent/overvoltage applied to the switching element 10 can be assumed.

Further, when the ON time of the switching element 10 is less than the minimum value in the normal range, it is considered that the structural gap between the inner pot 8 and the heating coil 6 is narrowed. It is possible to assume a problem that the bottom surface of the inner pot 8 is deformed in a convex shape in the outward direction. When the rice is cooked in that state and the inverter is operated, an overcurrent/overvoltage may be applied to the switching element and damage may be assumed.

According to the present embodiment described above, by storing the operating state of the switching element at the time of abnormality, it is possible to easily identify the external factor causing the failure and improve maintainability. Further, if the external factors can be estimated, the user can be advised of usability, and the recurrence of similar failures can be prevented.

2: Rectifier circuit 3: Choke coil 4: Smoothing capacitor 5: Smoothing circuit 6: Heating coil 7: Capacitor 8: Inner pot 9: Resonance circuit 10: Switching element 12: Inverter section 13: Drive circuit 14: Current detection means 17: Trigger circuit 18: Microcomputer

Claims (1)

An inner pot for containing rice and water, a heating coil located below the inner pot for inductively heating the inner pot, and a resonance circuit including a resonance capacitor connected in parallel with the heating coil,
A switching element for passing a high-frequency current through the resonance circuit,
A current detection means for detecting the value of the current flowing through the heating coil,
A microcomputer for varying and controlling the ON time of the switching element based on the current value detected by the current detecting means so as to heat the inner pot with a predetermined electric power,
The microcomputer is
The maximum value and the minimum value of the ON time of the switching element when the inner pot is induction-heated with the predetermined power are stored in advance, and the switching element is turned ON to obtain the predetermined power during rice cooking. When the time is variable and controlled, if it is larger than the maximum value of ON time stored in advance or less than the minimum value of ON time stored in advance, the stored ON time is updated. Rice cooker characterized by doing.

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