JP2565946B2 - Combined cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a composite cooker capable of high-frequency dielectric heating as a microwave oven and electromagnetic induction heating as an electromagnetic cooker.

(Prior Art) Recently, a composite cooker equipped with an inverter circuit and capable of high-frequency dielectric heating as a microwave oven and electromagnetic induction heating as an electromagnetic cooker has been developed and put into practical use.

In such a composite cooker, it is necessary to determine whether or not the pot, which is a load, is appropriate during electromagnetic induction heating, and immediately stop the operation of the inverter circuit to ensure safety if the pot is incorrect.

(Problems to be solved by the invention) Therefore, it is conceivable to provide a load detection circuit like a general electromagnetic cooker. However, the load detection circuit has a large number of parts and is high in cost, and further, adjustment is difficult. There's a problem.

The present invention has been made in view of the above circumstances, and an object thereof is to ensure sufficient safety at the time of electromagnetic induction heating without causing an increase in cost and without requiring difficult adjustment. It is to provide a compound cooker having excellent reliability that can be achieved.

[Configuration of the Invention] (Means for Solving Problems) Input current detecting means for detecting an input current to the inverter circuit, and calculating means for calculating an input current calculated value based on a signal from the input current detecting means. , Output control means for controlling the heating output by the inverter circuit to a set output based on the input current calculated value from the calculating means, and automatically during electromagnetic induction heating according to the input current calculated value and the input current calculated value Load determining means for determining whether or not the load is proper by comparing with the load detecting set value that changes, and stopping means for stopping the operation of the inverter circuit when the result of the determination is incorrect.

(Operation) During electromagnetic induction heating, if the calculated value of the input current to the inverter circuit is less than or equal to the load detection set value, the load is determined to be inappropriate and the operation of the inverter circuit is stopped.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, reference numeral 1 denotes a main body of the compound cooker, which has a door 2 pivotably supported on the front surface thereof and a top plate 3 provided on the upper surface thereof.

A heating chamber (not shown) is provided in the main body 1 corresponding to the door 2.
The magnetron 44, which will be described later, is installed in the heating chamber.
High frequency radio waves are supplied from. Furthermore, a turntable (not shown) for placing food is provided in the heating chamber.

In the main body 1 corresponding to the top plate 3, a heating coil 50, which will be described later, faces the lower surface of the top plate 3 so as to be spaced apart from and face each other.
Is provided.

The corner portion where the front surface and the upper surface of the main body 1 are connected is the operation portion 4
Has become. The operating portion 4 is inclined so that it is easy to see and operate, and there are a cook plate key 5 for setting electromagnetic induction heating, a range key 6 for setting high frequency dielectric heating, and an up setting for output setting. Key 7, output setting down key 8, start key 9, cancel key 10,
A time setting knob 11 and a display 12 are provided.

 The control circuit is shown in FIG.

20 is a commercial AC power supply, and the power supply 20 includes a fuse 21, a door switch 22a, a door switch 22b, and a magnetron thermal.
Door monitor switch (short switch) 22 through 23
c is connected.

A heating room illumination lamp (in-compartment lamp) 24 is connected to the power source 20 via a fuse 21, a door switch 22a, a relay contact 72a, a main relay contact 71a, a door switch 22b, and a magnetron thermal 23. A turntable drive motor 25 is connected in parallel to the heating room illumination lamp 24.

Power supply 20, fuse 21, door switch 22a, main relay contact 71a, door switch 22b, magnetron thermal
A blower motor 26 for cooling the magnetron and cooling the heating coil is connected via 23.

Further, the power source 20, the fuse 21, the door switch 22a,
The inverter circuit 30 is connected via the main relay contact 71a, the door switch 22b, and the magnetron thermal 23.

The inverter circuit 30 has a rectifier circuit including a diode bridge 31, a choke coil 32, and a smoothing capacitor 33, and the output coil of the rectifier circuit is connected to one end of each of the primary coil 40a and the heating coil 50 of the high-voltage transformer 40. . The other end of the primary coil 40 is connected to one end of the resonance capacitor 34 through the normally closed side of the relay contact (bidirectional contact) 73a, and the other end of the resonance capacitor 34 is connected to the other end of the rectifier circuit. ing. Further, the other end of the heating coil 50 is connected to one end of the resonance capacitor 34 via the normally open side of the relay contact 73a.

That is, when the relay contact 73a is inactive, the primary coil 40a
And the resonance capacitor 34 form a series resonance circuit. When the relay contact 73a is activated, the heating coil 50 and the resonance capacitor 34 form a series resonance circuit.

The resonance capacitor 34 has a switching element such as NPN.
Type power transistor 35 is connected in parallel between the collector and emitter, and a damper diode (flywheel) 36 is connected in parallel. The power transistor 35 and the damper diode 36 are packaged in one package.

The power transistor 35 excites the resonance circuit by turning it on and off, whereby a high-frequency current flows through the primary coil 40a or the heating coil 50.

In the secondary coil 40b of the high voltage transformer 40, a high voltage capacitor 4
The anode and cathode of the magnetron 44 are connected via a voltage doubler rectifier circuit composed of 1 and high voltage diodes 42 and 43. Then, the anode of the magnetron 44 is grounded,
The heater (cathode) is the secondary coil 40c of the high-voltage transformer 40.
Connected to.

On the other hand, the primary coil of the step-down transformer 27 is connected to the power source 20 via the fuse 21 and the magnetron thermal 23, and the control unit 60 is connected to the secondary coil thereof.

The control unit 60 controls the entire cooking device, and includes a power supply circuit 61, a microcomputer 62, a relay drive circuit 63, a D / A (digital / analog) converter 64,
Timing circuit 65, oscillator circuit 66, pulse width modulation circuit (PW
Comparator 67, base drive circuit 6
Have eight.

The relay drive circuit 63 includes a main relay 71 and a relay 7
It drives 2,73.

The D / A converter 64 issues an output setting signal of a voltage level corresponding to the output setting command from the microcomputer 62.

The timing circuit 65 uses the voltage of the smoothing capacitor 33 and the power transistor of the inverter circuit 30 in order to minimize the loss due to the switching of the inverter circuit 30.
The collector voltage of 35 is taken in, and the oscillation timing of the oscillation circuit 66 is determined accordingly.

 The oscillator circuit 66 generates a sawtooth wave signal.

The comparator 67 pulse width modulates the sawtooth wave signal emitted from the oscillation circuit 66 by the output setting signal from the D / A converter 64.

The base drive circuit 68 turns on and off the transistor 35 of the inverter circuit 30 by the output of the comparator 67.

Then, the operation unit 4 is connected to the microcomputer 62.

Further, a current transformer 80 is provided on the input line to the inverter circuit 30. The current transformer 80 constitutes an input current detecting means together with a bridge rectifier 81 that rectifies its output, and the output of the bridge rectifier 81 is supplied to the microcomputer 62.

Next, the operation of the above structure will be described with reference to FIG.

The pan 51 is placed on the top plate 3 and the cook plate key 5 of the operation unit 4 is pressed. Further, a desired cooking time is set by the time setting knob 11, and a desired output is set by the up key 7 or the down key 8.

At this time, the character "Cook plate" is displayed on the display 4 and the set cooking time is displayed numerically. Further, in the display device 4, the number of light emitting elements corresponding to the set output is turned on.

When the start key 9 is pressed, the microcomputer
62 operates relays 71 and 72. When the relay 71 operates, the contact 71a is turned on, and an energization path to the inverter circuit 30 and the blower motor 26 is formed. When the relay 73 operates, the normally open side of the contact 73a is closed, and the heating coil 50 is selected.

Further, the microcomputer 62 issues an output setting command based on the setting output. This output setting command is D / A
Converted to an analog output setting signal by the converter 64,
It is supplied to the comparator 67.

Further, a sawtooth wave signal is emitted from the oscillator circuit 66, and the comparator 67 pulse-width modulates it.

That is, when the voltage of the output setting signal is higher than the voltage of the sawtooth wave signal, the output voltage of the comparator 67 becomes high level.
When the voltage of the output setting signal is lower than the voltage of the sawtooth wave signal, the output voltage of the comparator 67 becomes low level.

The output of the comparator 67 is amplified by the base drive circuit 68,
It is applied between the base and emitter of the power transistor 35.

When the power transistor 35 is turned on, a heating coil is passed between the collector and emitter of the power transistor 35.
Current flows to 50. When the power transistor 35 is turned off, the current flowing through the heating coil 50 charges the resonance capacitor 34. Then, a current flows from the resonance capacitor 34 to the heating coil 50 this time.

Thus, the high frequency current flows through the heating coil 50 when the power transistor 35 is turned on and off, and the heating coil 50
Generates a high-frequency magnetic field. The high frequency magnetic field is applied to the pan 51 through the top plate 3 to cause an eddy current in the pan 51. When the eddy current is generated, the pot 51 self-heats due to the eddy current loss, and the food inside is heated. That is, cooking is started.

The timing circuit 65 generates a trigger pulse at the intersection of the voltage of the smoothing capacitor 33 (rectified voltage) and the collector voltage of the power transistor 35, and triggers the oscillation circuit 66. As a result, the power transistor 35 turns on when its own collector voltage is low, and the switching loss of the power transistor 35 can be reduced.

When the set cooking time elapses, the microcomputer 62
Stops the operation of relays 71 and 73. When the operation of the relay 71 is stopped, the contact 71a is turned off and the energization path to the inverter circuit 30 is cut off. That is, cooking is completed.

On the other hand, food is stored in the turntable in the heating chamber to close the door 2, and the range key 6 of the operation unit 4 is pressed. Further, a desired cooking time is set by the time setting knob 11, and a desired output is set by the up key 7 or the down key 8.

At this time, the character "range" is displayed on the display 4 and the set cooking time is displayed numerically. Further, in the display device 4, the number of light emitting elements corresponding to the set output is turned on.

When the start key 9 is pressed, the microcomputer
62 operates relays 71 and 72.

When the relays 71, 72 are operated, the contacts 71a, 72a are turned on, and an energizing path to the inverter circuit 30, the heating room lighting lamp 24, the turntable drive motor 25, and the blower motor 26 is formed.

Since the relay 73 does not operate, the normally closed side of the contact 73a is closed, and the primary coil 40a of the high voltage transformer 40 is selected.

Then, the inverter circuit 30 operates similarly to the electromagnetic induction heating, and the high frequency current flows through the primary coil 40a. Then, the voltage generated in the secondary coil 40b is double-voltage rectified and applied to the magnetron 44, so that the magnetron 44
Oscillates. When the magnetron 44 oscillates, high-frequency radio waves are supplied into the heating chamber, and high-frequency dielectric heating starts.

When the set cooking time elapses, the microcomputer 62
Stops the operation of relays 71 and 72. When the operation of the relay 71 is stopped, the contact 71a is turned off and the energization path to the inverter circuit 30 is cut off. That is, cooking is completed.

By the way, when the inverter circuit 30 is operating, an input current to the inverter circuit 30 is detected by the current transformer 80, and a DC voltage of a level corresponding to the detected current is supplied from the bridge rectifier 81 to the microcomputer 62.

The microcomputer 62 calculates the average value or the execution value of the input current to the inverter circuit 30 from the output of the bridge rectifier 81 (corresponding to a calculation means), and the calculated input current value is the output control set value (set output). If it becomes smaller than (corresponding), the level of the output setting signal is increased and the ON period of the power transistor 35 is lengthened. On the contrary, when the input current calculated value becomes larger than the output control setting value, the level of the output setting signal is lowered and the ON period of the power transistor 35 is shortened (corresponding to the output control means).

When the ON period of the power transistor 35 becomes long, the high frequency current flowing through the heating coil 50 or the primary coil 40a becomes large and the output rises. When the ON period becomes short, the high frequency current flowing through the heating coil 50 or the primary coil 40a becomes small, and the output drops.

Therefore, at the time of electromagnetic induction heating, the output can be maintained at the set output regardless of whether the pan 51 is different from the standard pan. That is, the element of the inverter circuit 30 is not overloaded, and the life of the element is improved. Furthermore, proper heating is possible and reliability can be improved.

Also, during high frequency induction heating, the output can be maintained at the set output regardless of the temperature change of the magnetron 44,
Appropriate heating can be performed.

Since the heating coil 50 is connected to the normally open side of the relay contact 73a, if the coil of the relay 73 has a disconnection failure, the heating coil 50 is immediately disconnected from the power supply, which is safe. .

By the way, during electromagnetic induction heating, the microcomputer 62
Compares the calculated value (average value or input value of input current) based on the output of the bridge rectifier 81 with the load detection set value Vs to determine whether the load is appropriate.

That is, as shown in FIG. 4, the weak output operation for load detection is performed for t det time from t ₁ to t ₂ when the start key 9 is pressed. At this time, if there is no pot 51 on the top plate 3, the input current to the inverter circuit 30 is small and the output voltage of the bridge rectifier 81 becomes low level as shown in FIG. When an improper pan made of aluminum is placed on the top plate 3 or a small metal object such as a fork or knife is placed on the top plate 3, the input current to the inverter circuit 30 is still small and the bridge rectifier is too small.
The output voltage of 81 becomes low level as shown in FIG.

The microcomputer 62 has a load detection setting value Vs, and initially maintains the setting value Vs at a low level. Then, the input current calculation value and the load detection setting value Vs are compared at time t ₂ , and if the input current calculation value is lower than the load detection setting value Vs, it is determined that the load is inappropriate (corresponding to load determining means. ) After that, from t ₄ to t ₅ after the time t off, the same t det
The weak output operation for load detection is repeated for the time. In addition,
This weak output is set to a value such that small objects such as forks and knives do not generate heat.

However, it is assumed that the proper pot has already been placed at t ₃ hours on the way from t ₂ hours to t ₄ hours. At this time, the input current to the inverter circuit 30 increases in accordance with the weak output operation at time t _{2 and} the output voltage of the bridge rectifier 81 becomes high level as shown in FIG.

Thus, the input current calculated value at t ₅ hours exceeds the load detection setting value Vs, microcomputer 62 will successively increased to the target value corresponding to the set output level of the output setting signal, substantial electromagnetic Induction heating is started.

Note that the non-moving toff time is set to about 1.5 seconds to 2 seconds so that the user does not feel unnatural. Further, the ratio between the t off time of non-operation and the t det time of weak output operation is set so that small objects such as forks and knives cannot be heated.

At the start of heating, the inverter circuit 30
The input current to is increased. At this time, the microcomputer 62 uses the load detection setting value Vs to increase the input current calculation value.
To follow. When the output reaches the set output and stabilizes (t ₆ hours), the load detection set value Vs at that time is held as it is.

When the user shifts the pot on the top plate 3 at t ₇ hours during cooking, the state without the pot approaches, and the input current to the inverter circuit 30 decreases.

When the input current becomes smaller (when the input current calculated value becomes smaller), the microcomputer 62 operates the original output control to increase the level of the output setting signal. However, it is an attempt to forcibly increase the output while being in a state close to no load, and stress (overvoltage) is applied to the power transistor 35 of the inverter circuit 30.

At this time, however, since the load detection set value Vs is kept high, the input current calculated value immediately becomes less than or equal to the load detection set value Vs as the input current becomes smaller. When the input current calculated value becomes equal to or lower than the load detection set value Vs, the microcomputer 62 determines that the load is improper, and immediately stops the operation of the inverter circuit 30 (corresponding to a stop means). Therefore, it is possible to prevent the malfunction such that the transistor 35 is stressed.

Thus, when there is no pan 51 on the top plate 3,
If a small metal object such as a fork or knife is placed, or if an aluminum improper pot is placed, it is automatically detected and electromagnetic induction heating is not performed. It is safe without overloading the elements of the circuit 30. Moreover, it is possible to prevent unnecessary heating of the forks, knives, empty cans, etc., so that the user is not burned.

In particular, the microcomputer 62, which controls the cooking device as a whole, determines whether or not the load is appropriate. Therefore, only the current transformer 80 and the bridge rectifier 81 need be provided as components for load detection. It has low points and low cost. Moreover, no difficult adjustments are necessary.

Substantially, the current transformer 80 and the bridge rectifier 81, which are the input current detection means for output control, are also used, so that the cost is very low.

Further, the load detection set value Vs is made to follow the increase of the input current after the heating is started, and the operation of the inverter circuit 30 is immediately stopped when the pan 51 is moved, so that the power transistor 35 of the inverter circuit 30 is stressed. It is possible to prevent the power transistor 35 from being broken without being applied.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention.

As described above, according to the present invention, the input current detection means for detecting the input current to the inverter circuit is provided, and the input current calculation value is calculated based on the signal from the input current detection means. Means is provided, and output control means for controlling the heating output by the inverter circuit to a set output based on the input current calculated value from the calculating means is provided. A load discriminating means for discriminating whether or not the load is proper is provided by comparing with a load detection set value which automatically changes according to the set value. Therefore, it does not increase the cost and does not require difficult adjustment, and it is possible to secure sufficient safety during electromagnetic induction heating. We can provide a scientific instrument.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a control circuit in an embodiment of the present invention, FIG. 2 is an external perspective view of the same embodiment, and FIG.
The figure which shows the voltage waveform of each part in the figure, FIGS.
Each of the figures is a view for explaining the operation of the same embodiment. 1 ... Main body, 2 ... Door, 3 ... Top plate, 4 ...
… Operation part, 30 …… Inverter circuit, 40 …… High voltage transformer, 44 …… Magntron, 50 …… Heating coil, 60 …… Control part, 62 …… Microcomputer (calculation means, output control means, load discrimination means, Stopping means), 80 …… Current transformer.

Claims (3)

(57) [Claims] 1. A composite cooker comprising an inverter circuit and capable of high-frequency induction heating and electromagnetic induction heating, wherein an input current detecting means for detecting an input current to the inverter circuit, and a signal from the input current detecting means. Calculating means for calculating the input current calculated value based on the above, output control means for controlling the heating output by the inverter circuit to a set output based on the input current calculated value from the calculating means, and the input current calculation during electromagnetic induction heating A load discriminating means for discriminating whether or not the load is proper by comparing the value with a set value for load detection which automatically changes according to the calculated input current, and the operation of the inverter circuit when the discriminating result is improper. A composite cooker comprising: a stopping means for stopping. 2. The load discriminating means increases the heating output toward the set output when the load is discriminated to be appropriate, and the load detecting set value increases as the input current calculated value increases accordingly. The composite cooker according to claim 1, wherein the load detection set value is held as it is when the heating output reaches the set output and stabilizes. 3. A relay for switching between high frequency induction heating and electromagnetic induction heating, a primary coil of the high frequency induction heating high voltage transformer is connected to the normally closed side of the relay contact, and an electromagnetic induction heating heating coil is connected to the normally open side. The compound cooker according to claim 1 or 2, characterized in that: