JP2003308960A - High frequency heating cooker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency heating cooker in which oscillation detection of a magnetron can be surely performed and failure of the magnetron can be detected at an early stage. <P>SOLUTION: The high frequency heating cooker is provided with the magnetron 17 which supplies a microwave to a heat chamber in which food is contained and heats the above food a control circuit 28 by which this magnetron 17 is driven to generate the above microwave, an oscillation detection section 30 for detecting whether the microwave is generated or not by the above magnetron 17 after driving the above magnetron 17, and a microcomputer 29 which carries out heating of the above food by directing a drive, a stop, or the like to the above control circuit 28. The above microcomputer 29 sets up the time until it issues a direction of the stop after directing the drive to the above control circuit 28 to more than the time in which it can be surely checked in at least the above oscillation detection section that the microwave has been generated by the above magnetron. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency cooker for driving a magnetron to heat food with microwaves.

[0002]

2. Description of the Related Art Conventionally, a high-frequency heating cooker of this kind is described in, for example, Japanese Patent Laid-Open No. 62-71190.

This is equipped with an inverter circuit for rectifying an AC voltage, converting the AC voltage into an AC power of a predetermined frequency and applying the AC power to a magnetron, which enables continuous output adjustment. It is described that a means for turning on / off the operation of the inverter circuit and a low output adjusting means for varying the on / off duty are provided.

By providing a means for turning on / off the operation of the inverter circuit, the minimum heating output, which was about 200 W in the operation of the conventional inverter circuit, can be set below that output, from 0% to 100%. It is possible to set the heating output of%.

[0005]

In general, a magnetron has a structure in which a microwave is generated after power is supplied.
For example, there is a delay time such as 5 seconds.

Further, in order to safely operate the high frequency heating cooker, various sensors are provided on the cooker.
As one of them, there is an oscillation detector for detecting whether the magnetron normally oscillates.

The oscillation detector detects changes before and after microwave output from the magnetron, for example, changes in the value of current flowing through the magnetron, and determines whether the magnetron is operating normally. is there. Therefore, a microwave is actually output from the magnetron, and then a detection time is required to confirm oscillation.

However, if the time for driving the magnetron is shorter than the time obtained by adding the above-mentioned delay time and detection time, the oscillation detection unit cannot determine whether the magnetron is operating normally.

Therefore, the failure of the magnetron cannot be detected early. Due to this failure, the inverter circuit and other parts of the high-frequency cooker may be burdened, and these parts may unnecessarily fail.

The present invention has been made to solve the above problems.

[0011]

A high frequency heating cooker according to a first aspect of the present invention includes a heating chamber for storing food, a magnetron for supplying microwaves to the heating chamber to heat the food, and a magnetron for driving the magnetron. And a magnetron drive unit for generating the microwave, and after driving the magnetron,
An oscillation detection unit that detects whether the magnetron has generated microwaves, and a control unit that instructs the magnetron drive unit to drive and stop the heating of the food, and the control unit, The time from when the magnetron drive unit is instructed to drive to when the magnetron drive unit is instructed to stop is set to be at least the time at which it is possible to confirm that the magnetron has generated microwaves in the oscillation detection unit.

A heating cooker according to a second aspect of the present invention is a heating chamber for storing food, a magnetron for supplying microwaves into the heating chamber to heat the food, and an inverter for converting a commercial power supply into a high frequency power supply. A magnetron drive unit that includes a circuit and supplies electric power from the inverter circuit to the magnetron to generate the microwave; and an oscillation detection unit that detects whether the magnetron has generated the microwave after driving the magnetron, A control unit that controls the operation of the inverter circuit to adjust the heating output of the food by the magnetron, and executes heating of the food,
When driving with a heating output lower than the low heating output obtained by the control of the inverter circuit, the control unit performs duty driving of the inverter circuit, and at the time of the duty driving, at least the first magnetron driving time. Is a configuration in which the oscillation detection unit is set to a time longer than that at which it is possible to confirm that the magnetron has generated microwaves.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 is a high-frequency heating cooker body of the present invention, 2 is a heating chamber for storing food,
3 is a frame that covers the outer periphery of the heating chamber 2, 4 is a door that opens and closes the front opening of the heating chamber 2, and 5 is a display unit 6 and a key input unit 7.
Is an operation unit having.

In FIG. 2, 8 is a commercial AC power source, 9 is a diode bridge for full-wave rectifying the commercial AC power source 1,
0 is a choke coil connected to the + terminal of the diode bridge 9 to suppress noise, 11 is a choke coil 10
Is connected in series between the + terminal and the-terminal of the diode bridge 9, and the smoothing capacitor for smoothing the pulsating current power source rectified by the diode bridge 9, 12 is connected in parallel to the smoothing capacitor 11. Inverter circuit that has been created.

The inverter circuit 12 comprises a resonance capacitor 13, a switching element 14 composed of an IGBT or the like including a diode connected in antiparallel, and a high voltage transformer 15. Specifically, the resonance capacitor 13 and the switching element 14 are connected in series, the series connection circuit is connected in parallel to the smoothing capacitor 11, and the resonance capacitor 13 is connected in parallel with the primary winding 15a of the high-voltage transformer 15. To be done.

Reference numeral 16 is a secondary winding 15 of the high voltage capacitor 15.
A high-voltage rectifier circuit connected to b for rectification, and 17 is a magnetron which is supplied with rectified electric power from the high-voltage rectifier circuit 16 and generates microwaves. The magnetron 17 has an anode 17a and a cathode 17b. The cathode 17b is connected to the high voltage rectifier circuit 16 and also to the heater winding 15c of the high voltage transformer 15 so that microwaves can be generated. , The cathode 17b is being heated.

The high-voltage rectifier circuit 16 is composed of high-voltage diodes 18 and 19, high-voltage capacitors 21 and 22, and a discharging high-voltage resistor 23.

Specifically, the high voltage diode 18 and the high voltage capacitor 20 are connected in series, and the series connection circuit is connected in parallel to the secondary winding 15b of the high voltage transformer 15. The high voltage diode 18 is connected so that a current flows in the direction of the secondary winding 15b.

The series circuit of the high voltage diode 19 and the high voltage capacitor 21 is connected in parallel to the series circuit of the high voltage diode 18 and the high voltage capacitor 20. This high-voltage diode 19 allows the current to flow from the secondary winding 15b, that is, the high-voltage diode 18
Is connected in the opposite direction to. And the high voltage diode 18
And the connection point between the high voltage capacitor 20 and the high voltage diode 1
A discharge high-voltage resistor 23 is connected between the connection point of 9 and the high-voltage capacitor 21.

Furthermore, the connection point between the high voltage diode 18 and the high voltage capacitor 20 is the cathode 17 of the magnetron 17.
b, and the connection point between the high voltage diode 19 and the high voltage capacitor 21 is the anode 17a of the magnetron 17.
Connected to.

The inverter circuit 12 gives an ON signal having a predetermined period length to the switching element 14, and when the ON signal ends, the primary winding 15a of the high voltage transformer 15 is turned on.
And the resonance capacitor 13 starts a resonance operation. By detecting the voltage at the connection point between the switching element 14 and the resonance capacitor 13 that the predetermined resonance operation has been completed, the control circuit 28 described later obtains the on-timing of the switching element 14 and turns on the switching element 14. . Then, the ON signal having the predetermined ON period length is again given to the switching element 14.

By repeating the above operation repeatedly, the inverter circuit is operated, the commercial power supply is converted into the high frequency power supply, and the magnetron 17 is supplied.

If the ON period of the ON signal given to the switching element 14 is lengthened, the oscillation frequency of the inverter circuit 12 is lowered to increase the output, and if the ON period is shortened, the oscillation frequency of the inverter circuit 12 is decreased. Rises and the output drops. Therefore, the output of the inverter circuit 12, that is, the electric power supplied to the magnetron 17 is adjusted by adjusting the ON period length of the switching element 14.

The operating frequency of the inverter circuit 12 is limited due to various factors. If the lower limit of the oscillating frequency is lower than 20 KHz, it falls within the audible range for humans, and therefore cannot be lower than that.

The upper limit of the oscillating frequency of the inverter circuit 12 is higher than the operating frequency of the switching element 14, so the inverter circuit 12 has a higher frequency than that frequency.
Can not work. Actually, it is lower than the upper limit of the operating frequency of the switching element 14, and the cathode 1 of the magnetron 17 is
The frequency of the heater current flowing through 7b is such that the lowest current value at which the magnetron 17 can operate can be secured. Therefore, the minimum output that can be set by varying the oscillation frequency of the inverter circuit 12 is about 200W.

Reference numeral 24 is a drive circuit which outputs an ON signal and an OFF signal to the switching element 14 and serves as an inverter drive section for operating the inverter circuit 12 at a predetermined frequency, and 25 is a current flowing from the commercial power supply 8 to the diode bridge 9.
That is, a current transformer for detecting the input current to the high-frequency heating cooker, and 27 is a control unit for controlling the drive of the drive circuit 24 to perform microwave heating of food.

The control section 27 is connected to the display section 6, the key input section 7, and the current transformer 25, outputs an ON / OFF signal of the switching element 14 to the drive circuit 24, and detects an abnormality in the inverter circuit 12 or the like. At this time, the control circuit 28 that stops the output of the ON signal to the drive circuit 24 to stop the operation of the inverter circuit 12, and the microcomputer 29 that instructs the control circuit 28 to drive and stop the inverter circuit 12, set output, and the like. It consists of and.

The display unit 6 and the key input unit 7 are connected to the microcomputer 29, and the control circuit 28 is instructed based on the operation contents of the key input 7, and the display unit 6 displays the result and the remaining heating time. Is displayed.

The control circuit 28 includes the current transformer 2
It also has a current determination unit 30 that is connected to the current transformer 5 and determines whether or not the current detected by the current transformer 25 has exceeded a predetermined value. The current transformer 25 and the current determination unit 30
Corresponds to the oscillation detector of the present invention.

As shown in FIG. 3, the current judging section 30 inputs the setting level section 31 for outputting the judging level VSH, the judging level VSH of the setting level section 31 to the + input terminal, and the detection signal of the current transformer 25. By inputting the signal obtained by smoothing to the-terminal, the two signals are compared. As a result, if the signal at the-input terminal is smaller than the signal at the + input terminal, the High signal is output, and the signal at the + input terminal is input. It has a comparator 32 that outputs a Low signal if the signal at the negative input terminal is larger, and a buffer circuit 33 that includes a resistor and a transistor for buffering the output signal of the comparator 32 and inverting the signal. .

Specifically, as shown in FIG. 4, time t0
Even if the power supply to the magnetron 17 is started at
No current flows immediately between the anode 17a and the cathode 17b of the magnetron 17, and only the current consumed by the inverter circuit 12 or the like is detected by the canned transformer 25. At this time, the signal input to the comparator 32 is lower than the determination level VSH. Therefore, the Low signal is output from the comparator 32 and is output to the microcomputer 29 via the buffer circuit 33.

Thereafter, at time t1, the cathode 17
When the temperature of b rises and a current starts to flow between the anode 17a and the cathode 17b, the magnetron 17 generates microwaves, and the consumed power rises accordingly, and the current value detected by the current transformer 25 increases. Also rises.

At this time, the comparator 32 determines that the signal from the current transformer 25 has risen above the determination level VSH and outputs a Low signal. This Low signal is output at time t2 which is slightly delayed from time t1 due to the calculation time of the comparator 32 and the like. Then, it is inverted through the buffer circuit 33 and output as a High signal to the microcomputer 29. The signal output from the buffer circuit 33 to the microcomputer 29 is hereinafter referred to as the B signal.

The operation of the microcomputer 29 having such a configuration will be described with reference to FIG.

First, in step S1, it is recognized that the heating conditions such as the heating time and the heating output are input from the key input unit 7. In step S2, it is determined whether or not the heating input operation, that is, the start key is operated by the key input unit 7. In this step, the operation waits until the start key is operated.

When it is determined in step S2 that the start key has been operated, the process proceeds to step S3, and it is determined whether the heating output input in step S1 is not more than a low output that can be set by varying the oscillation frequency of the inverter circuit 12.

If it is determined in step S3 that the output is lower than or equal to the low output, the process proceeds to step S4. In step S4, the heating output set in step S1 and the drive start instruction are output to the control circuit 28. By this instruction, the drive circuit 24 starts driving, and the oscillation operation of the inverter circuit 12 starts. Then, the countdown of the heating time set in step S5 is started, and the remaining heating time is output and displayed on the display unit 6.

In step S6, the current determination unit 30 detects whether the magnetron 17 is oscillating.
This detection confirms the oscillation of the magnetron 17 by continuously receiving the B signal from the current determination unit 30 for a certain period of time. In step S7, it is determined whether or not the outgoing call is detected in step S6. If it is determined that it is detected, the process proceeds to step S8.

FIG. 6 shows the specific operation in this step.
It will be explained based on. First, at time t0, the signal A is output from the microcomputer 29 to the control circuit 28, and driving of the inverter circuit 12 is started. At this time,
The signal level detected by the current transformer 25 and input to the-input terminal of the comparator 32 is lower than the determination level VSH input to the + input terminal. That is, it means that the input current input to the diode bridge 9 is small.

Thereafter, at time t1, magnetron 1
When a microwave is generated at 7, the above-mentioned input current rapidly increases, and at time t2, the signal magnitudes of the − input terminal and the + input terminal of the comparator 32 are reversed, and the output of the comparator 32 is inverted. This signal is the B signal and is input to the microcomputer 29 as the detection result of the current detection unit 30.

Upon receiving the B signal input, the microcomputer 29 determines that the magnetron 17 has oscillated at time t3 when the signal is continuously received for a certain period of time.

In step S8, it is determined whether or not the countdown in step S5 is completed, and if completed, the process proceeds to step S9. In step S9, an instruction to stop driving is output to the control circuit 28, a buzzer (not shown) is driven to notify the end, and the food heating operation is ended. After that, it is in a standby state until the next use by the user.

If it is determined in step S7 that the oscillation of the magnetron 17 has not been detected, the magnetron 1
Since the failure of 7 may be considered, the process proceeds to step S10, the control circuit 28 is instructed to stop the heating operation, and the display unit 6 displays that the oscillation is abnormal in step S11. It should be noted that, in this step S11, the occurrence of the abnormality is stored in a non-volatile memory or the like without displaying the oscillation abnormality, and then in step S8.
Alternatively, the heating operation may be continued by returning to.

If it is determined in step S3 that the heating output set in step S1 is less than or equal to the low output that can be set by changing the oscillation frequency of the inverter circuit 12, the process proceeds to step S12. In step S12,
The heating output set in step S1 and the drive start instruction are output to the control circuit 28. By this instruction, the drive circuit 24 starts driving, and the oscillation operation of the inverter circuit 12 starts. This heating output is the lowest output that can be handled by the oscillation frequency of the inverter circuit 12.

In step S13, the first driving time W1 and the second and subsequent driving times W2 for the duty operation for driving and stopping the magnetron at a predetermined cycle are set. This driving time W1 is the driving time W2
Magnetron 1 that is longer and through the current detector 30
The length is such that the oscillation of No. 7 can be detected.

In step S14, the countdown of the set heating time is started, and the remaining heating time is output to the display unit 6 and displayed. In step S15, the operation of the inverter circuit 12 in the duty operation set in step S13 is started. Specifically, in the driving in a constant cycle, the driving time of the first inverter circuit 12 is set to W1, and the driving time and the stop instruction to the control circuit 28 are continued during heating so that the driving time is W2 after the second time. To instruct.

In step S16, it is determined whether or not it is the first drive. If it is determined to be the first drive, step S1
Move to 7. In step S17, it is detected whether the magnetron 17 is oscillating by the same operation as in step S6. Note that this detection confirms the oscillation of the magnetron 17 by continuously receiving the B signal from the current determination unit 30 for a certain period of time, as in step S6. In step S18, it is determined whether or not the outgoing call is detected in step S17. If it is determined that it is detected, the process proceeds to step S19.

In step S19, it is determined whether or not the countdown in step S14 is completed, and if completed, the process proceeds to step S20. In step S20, an instruction to stop driving is output to the control circuit 28, a buzzer (not shown) is driven to notify the end, and the food heating operation is ended. After that, it is in a standby state until the next use by the user.

Incidentally, steps S17 to S18
Is omitted by the determination in step S16 after the second heating of the switching element 14 and thereafter.

In step S18 described above, the magnetron 17
If it is determined that the oscillation is not detected, the magnetron 17 may be faulty. Therefore, the process proceeds to step S10, the control circuit 28 is instructed to stop the heating operation, and the oscillation abnormality is displayed on the display unit 6 in step S11. Is displayed. It should be noted that, in this step S11, the occurrence of the abnormality is stored in a non-volatile memory or the like without displaying the oscillation abnormality, and then the step S11 is performed.
The heating operation may be continued by returning to 19.

By repeating the above steps S1 to S20, the high-frequency heating cooker performs the food heating operation.

[0052]

According to the present invention, the oscillation of the magnetron can be surely detected, and the failure of the magnetron can be detected at an early stage.

[Brief description of drawings]

FIG. 1 is an external view of a microwave oven of the present invention.

FIG. 2 is a control block diagram of the microwave oven shown in FIG.

FIG. 3 is a detailed view of a current detection unit in FIG.

FIG. 4 is a diagram showing signals input to a negative input terminal and a positive input terminal of a comparator.

5 is a diagram showing an operation flowchart of the microcomputer in FIG.

FIG. 6 is a diagram showing a relationship between a duty operation signal (A signal) output from a microcomputer to a control circuit, a magnetron drive state, and an output signal (B signal) of a current detection unit.

[Explanation of symbols]

12 Inverter circuit 14 Switching element 17 magnetron 25 Current Transformer 27 Control unit 28 Chopper 29 Microcomputer 30 Current detector

Claims (2)

[Claims] 1. A heating chamber for containing food, a magnetron for supplying microwaves to the heating chamber to heat the food, a magnetron drive unit for driving the magnetron to generate the microwaves, the magnetron After driving, an oscillation detection unit that detects whether the magnetron has generated microwaves, and a control unit that instructs the magnetron drive unit to drive and stop the heating of the food, and the control. The section sets the time until the stop instruction is issued after the magnetron drive section is instructed to drive the magnetron drive section at least at a time at which it is possible to confirm that the magnetron has generated microwaves. High frequency cooker to do. 2. A heating chamber for containing food, a magnetron for supplying microwaves into the heating chamber to heat the food, and an inverter circuit for converting a commercial power source into a high frequency power source. A magnetron driving unit that supplies electric power to the generator to generate the microwave; an oscillation detection unit that detects whether the magnetron generates microwave after driving the magnetron; and an operation of the inverter circuit to control the magnetron. By adjusting the heating output of the food according to, comprising a control unit for executing the heating of the food, the control unit, when driven by a heating output lower than the low heating output obtained by the control of the inverter circuit, The inverter circuit is duty driven, and at the time of the duty driving, at least first. The magnetron driving time is set to be longer than a time at which it is possible to confirm that the magnetron has generated microwaves in the oscillation detection unit.