JPS592156B2 - High frequency heating device - Google Patents

Description

Detailed Description of the Invention The present invention provides a high-frequency heating device that controls the output of a high-frequency oscillator for heating by receiving radio waves emitted by a heat-sensitive device, and receives the high-frequency radio waves for heating as a power source for the heat-sensitive device. Regarding.

Generally, when heating an object inside a heating chamber to a certain temperature using high-frequency energy, if the quantity and quality of the object are constant, the time required to heat it to a certain temperature is measured in advance. It is only necessary to irradiate the high-frequency energy for the time obtained at that time. In this case, this purpose can be achieved by adjusting the set time of the time setting device as much as necessary for the operation of the high-frequency heating device.

However, in most cases, the quantity and quality of the material to be heated are unspecified, and in this case it is necessary to change the setting time for each item. This is impossible, and conversely, it is extremely difficult to heat most objects to the desired temperature just by setting the time once.

Therefore, traditionally, a heat-sensitive element is brought into contact with the object to be heated, and high-frequency energy is irradiated while directly measuring the temperature of the object, and the signal output from the heat-sensitive element is received by a high-frequency energy irradiation control device to control the high-frequency energy. .

In other words, methods such as stopping heating at a desired temperature have been used, but in this case, the heat-sensitive element installed inside the heating chamber and the high-frequency energy irradiation control device installed outside are connected by wire. However, when actually used, various problems arose regarding the convenience of use. That is, the object to be heated is generally placed in a container and heated, but in this case, depending on the object to be heated, it may be necessary to cover the container to prevent water vapor from evaporating from the object. At that time, the wired heat-sensitive device cannot directly contact the object to be heated. Therefore, for these objects to be heated, it has not been possible to control the output by the heat-sensitive device, that is, to control the degree of heating. Furthermore, in recent years, a so-called turntable system in which the object to be heated is rotated has become mainstream in order to prevent uneven heating, but the above-mentioned heat-sensitive device cannot be used with this system. In other words, the heat-sensitive device rotates in the heating chamber together with the object to be heated, but the high-frequency energy irradiation control device is fixed, so the connected lead wires etc. gradually become twisted and the heat-sensitive device becomes detached from the object to be heated. The disadvantage is that the wires may break. Another disadvantage was that the heat-sensitive device required a battery, making it inconvenient to handle. This invention eliminates the drawbacks of the prior art and eliminates kinks in the control connection lines.
To provide a high-frequency heating device that does not have a built-in power source in the heat-sensitive device, can set the heating time without relying on sensation, and can accurately control the heating time without setting mistakes. This invention will be explained based on the drawings.

FIG. 1 shows the configuration of this invention.

A heating chamber 2 is provided inside the main body 1, and a container 3 and an object to be heated 5 wrapped in a lid 4 are placed in the heating chamber 2 by opening and closing a door 6. The object to be heated 5 is provided with a heat sensing device 8 into which a heat sensing portion 7 is inserted. The upper part of the heating chamber 2 is partitioned by a partition plate 9 made of a dielectric material, and an antenna All of a magnetron 10 that emits high frequency energy projects into this space. Around the antenna All, a starrer blade 13 that rotates due to wind power is attached to a starrer shaft 13-1.
It is supported by a screw. On the other hand, on a part of the heating chamber wall 12 to which the magnetron 10 is attached, there is provided an antenna B14 which can protrude into the heating chamber 2 via a chiyoke tuned to the wavelength of the high frequency energy emitted from the magnetron 10. The output of this antenna Bl4 is the receiving device 15
The signal is amplified and detected from 11C. The output of the receiving device 15 is connected to an irradiation control device 16 that controls the amount of high-frequency energy emitted from the magnetron 10. The irradiation control device 16 operates to change the input power of the magnetron 10 in response to the output of the receiving device 15. Further, an operation panel 17 is provided above the door 6 of the main body 1, and a part of this operation panel 17 includes a temperature setting knob 18 and a variable resistor 19 whose resistance value changes depending on the rotation angle of this knob 18.
(VRl to be described later) is attached. A power cable 20 is provided at the rear of the main body 1 to take in electric power to drive the device. FIG. 2 is a detailed view of the main parts of the heat-sensitive device 8 including the heat-sensitive section 7. As shown in FIG. The figure A shows a sectional view, and the figure A shows a circuit diagram. In the figure, the outer shell 21 is made of metal and prevents high frequency energy from irradiating the interior. Hollow protrusions 22 and 23 are provided on the top and bottom of this outer shell 21. Inside one of the projections 22, there is provided a chiyoke part 24 that matches the wavelength of the high frequency energy emitted from the antenna All of the magnetron 10, and the antenna C2 is passed through the chiyoke part 24.
5 protrudes from the outer shell 21 to the outside. Further, the other hollow protrusion 23 is provided with a heat sensitive section 7. In this device, a thermistor 26 whose resistance value has a negative relationship with temperature and which changes almost linearly is used as a heat-sensitive element. On the other hand, inside the outer shell 21, a high frequency oscillation circuit 27 and a low frequency modulation circuit 28 for frequency modulating the high frequency oscillation circuit 27 in accordance with the resistance value of the thermistor 26 are provided.

In this embodiment, as a driving power source for the high frequency oscillation circuit 27 and the low frequency modulation circuit 28, an antenna D3l with a rectifier 30 interposed in series is provided outside the outer shell 21, and one end of the rectifier 30 is connected to the outer shell. The voltage generated by the heating high-frequency magnetron 10 that is applied to the other terminal side is transferred to the antenna C.
The DC voltage was introduced into the outer shell 21 through the same chain yoke 24 as 25, and was obtained through a stabilizing circuit. This circuit operates as follows. First, the heat sensitive device 8 is installed in the heating chamber 2, and the antennas of the magnetron 10 are all connected to each other.
At the same time, a current is generated in the antenna D3l. This current is limited in one direction by the interposition of the rectifier 30 and charges the capacitor C. This charge is controlled by a stabilizing circuit 29 to reduce the large fluctuation voltage generated in the capacitor C by the current of the antenna D3l, which changes depending on the quantity and quality of the heated object 5, the position stirrer of the heat sensitive device, the state of the spring 13, etc. The voltage is always stabilized at a constant level, and consists of a smoothing (integration) circuit 32 made up of a capacitor and a resistor, and a zener diode ZD. In this way, a constant voltage is always generated at the output end, that is, at both ends of the Zener diode ZD, while the magnetron 10 is firing. This voltage was connected to the power terminals of the high frequency oscillation circuit 27 and the low frequency modulation circuit 28 to serve as a power source.
It should be noted that this stabilizing circuit 29 is effective even when the heat sensitive section is operated by a battery.

That is, the battery voltage gradually decreases as the battery is used. This is because the operating points of the high frequency oscillation circuit 27 and the low frequency modulation circuit 28 change accordingly, causing their respective oscillation frequencies to change, causing malfunctions. The operation of arbitrarily performing wireless heating control on the object to be heated 5 according to the present invention will be explained with reference to the circuit shown in FIG. 2.

Since the heat sensitive device 8 is equipped with the stabilizing circuit 29 as described above, it is installed in the heating chamber, and at the same time the magnetron 10 emits radio waves and starts heating the object 5 to be heated, TRl and P
A voltage is applied to UTl (N-gate thyristor).

A resonant circuit including antenna C25 is connected to the collector of TRl as a load, and the lower part is connected to the emitter via the C-E capacitance of C1 and TRl, so positive feedback is applied. Oscillation starts at a frequency of (Hz) 2πV] (here, CO=C1+C2+C3C3-TRl's C-E capacitance).

(If antenna C25 is adjusted by C4 to a value that has no reactance.) This output is
radiated into the air. At the same time, the low frequency modulation circuit 28 including PUT1 also starts operating. PUTl has the characteristic that when the anode voltage becomes higher than the gate voltage set by the N-gate thyristor, the anode and cathode become conductive instantly.If a capacitor C5 is connected between this anode and cathode, the following will occur. It starts to oscillate like this. First, the capacitor C5 is charged via the thermistor 26 and the sensitivity correction resistor R1, and when the charging voltage becomes slightly higher than the gate voltage, PUT1 becomes conductive and the charge in the capacitor C5 is discharged at the same time. Therefore PUTl is 0 again
The state becomes FF. Capacitor C5 starts charging again. That is, the anode voltage of PUT1 causes oscillation exhibiting a positive sawtooth waveform to the anode terminal of the Zener diode ZD. At the same time, the gate voltage also generates a pulse that is approximately equal to the anode terminal voltage of the Zener diode ZD only when PUT1 is in a conductive state. The repetition period of this pulse, that is, the oscillation frequency, changes depending on the temperature change of the thermistor 26. In other words, if the resistance of the thermistor 26 is large, the current charging C5 will be small and it will take a long time for the charging voltage of capacitor C5 to exceed the gate voltage. Conversely, if the resistance of the thermistor 26 is small, the charging current of capacitor C5 will be As the voltage increases, the gate voltage is quickly exceeded, and the repetition period becomes faster. The period of the pulse generated at the gate is also similar. From the above, when the heat sensitive part 7 is inserted into the object to be heated 5, the resistance value of the thermistor 26 changes in accordance with the temperature of the object to be heated, and the period of the pulse generated at the gate changes as long as the temperature of the object to be heated is low. When the temperature becomes high, pulses are generated repeatedly at a slow cycle. The low frequency modulation circuit 28 was set to have a frequency of 1 KHz when the temperature of the object to be heated was 20° C. and 8 KHz when the temperature of the object to be heated was 90° C. The above-mentioned high frequency oscillation circuit 27 is set so that f1=70 MHz with the antenna attached. This gate voltage is connected to TRl by capacitor C6.
is applied to the emitter of via resistor R2. This way, TR
The emitter voltage of PUTl is excited in response to the gate voltage of PUTl. At this time, the D operating point of TRl changes due to the change in its bias voltage. When the operating point changes, the capacitance C3 between the collector and emitter changes accordingly. That is, in f1 of the high frequency oscillation circuit 27 described above, CO changes, causing a frequency transition and frequency modulation. As a result of the above, this heat sensitive section emits radio waves frequency modulated by a low frequency of several kHz with a center frequency of 70 MHz corresponding to the temperature of the object to be heated 5 into the heating chamber.

Of course, as mentioned above, the heat-sensitive device 8 operates in the microwave electric field emitted from the magnetron 10, so in order to prevent the heating of the internal elements themselves by the microwaves and the resulting malfunction, the heat-sensitive device 8 is placed outside the outer shell 21 of the antenna C25. A cheese yoke 24 tuned to microwaves is provided on the protrusion to prevent microwaves from flowing into the interior. On the other hand, the high frequency of the high frequency oscillation circuit 27 emitted into the heating chamber 2 is transmitted by the antenna Bl.
4, the receiving device 1 is
5.

The receiving device 15 is tuned to the center frequency of the high frequency of the high frequency oscillation circuit 27. The high-frequency amplification and detection circuit of the receiving device 15 is a well-known circuit that is already commercially available, so a description thereof will be omitted. The ratio detection wave output of the receiving device 15 is transmitted to the low frequency modulation circuit 28.
A gate voltage waveform of is generated.

This low frequency wave is used to eliminate variations in the strength of the low frequency component of the radio waves output from the thermal device 8 by the TR2 shown in FIG. 3, and also for waveform shaping, and is a saturation type amplifier circuit. This collector output waveform of TR2 has the polarity reversed for the change in the PUTl gate voltage, and its peak value is constant. Therefore, the output voltage of the integrating circuit formed by R4 and C7 provided in parallel with collector resistor R3 is proportional to the frequency of the low frequency oscillated by the low frequency modulation circuit 28.
In other words, it is added. When the temperature of the hot object 5 is high, the voltage across the capacitor C7 becomes high, and when the temperature is low, the voltage across the capacitor C7 becomes low. The output of this integrating circuit is input to the TR3 base of one of the comparison circuits consisting of TR3 and TR4. The circuit consisting of TR3 and TR4 is a differential amplifier A. Now set TR4 to a constant operating point and repeat. T.R.
When the input of 3 becomes large and the pace voltage of TR3 becomes higher than the emitter voltage, TR3 becomes forward biased and the TR
A current is generated in 3. This current increases the voltage across emitter resistor R5. Since the base voltage of TR4 does not change during the process, it eventually becomes reverse biased and becomes 0FF. Further TR
When the base voltage of TR 3 increases, the collector voltage of TR 4 increases to the power supply voltage. By changing the base voltage of TR4, the voltage at which TR4 becomes 0FF can be arbitrarily selected. That is, when the input voltage of TR3 reaches any desired value, TR4 can be set to 0FF. The variable resistor VRl makes this TR4 base voltage variable. The collector output of this TR4 is T
It is connected to a Schmitt circuit S consisting of R5 and TR6. Therefore, when TR4 becomes 0FF, TR5 becomes 0N.
, TR6 becomes 0FF. This Schmitt circuit S prevents the chatter of the relay 33, which will be described later, and makes it clear whether the coil current of the relay 33 is 0N or 0FF, and also allows TR5 to change from 0FF to 0 when the input level fluctuates.
Due to the so-called hysteresis characteristic, which has a difference in the voltage level when changing to N and when changing from 0N to 0FF, TR4's output constantly fluctuates, but once TR5 becomes 0N at a certain voltage, TR4 The voltage of TR5
Even if the voltage drops slightly below the 0N voltage of TR5, the voltage from 0N to 0 of TR5
If the value is equal to or higher than the FF voltage level, TR5 continues to be 0N. Therefore, the current flowing through the coil of the relay 31 does not directly correspond to the constantly fluctuating output of the TR4, and chattering is eliminated. By the way, the collector output of TR6 is amplified by TR7, and the current flowing through the coil of relay 33 is interrupted. The normally open contact Rb of this relay 33 constitutes a high-frequency irradiation control device for the magnetron 10, and a voltage doubler rectifier capacitor C8 is provided in the secondary circuit of the step-up transformer 34 to switch the input of the magnetron 10. , C9, C8 is intermittent by the circuit. And these capacitors +)'C8 and C9 are set so that the rated first high frequency output can be output when this contact is closed.
C9, which operates even when this contact is open, has a smaller capacity than C8 so that the high frequency of the magnetron 10 outputs a low output that has almost no effect on the heated object. The operation of the high frequency heating device of this invention is as follows.

As mentioned above, a low voltage is generated at the base of the TR 3 when the temperature of the object to be heated 5 is low, and a high voltage is generated when the temperature of the heated object 5 is high. Let variable resistor VRl be the variable resistor 19.
Now, by rotating the knob 18 and changing the angle of the variable resistor 19, the base voltage of TR4 is set. When the power switch SW is turned on, the receiving device 15 and the irradiation control device 16 start operating, and TR4, TR6, and TR7 become 0N, current flows through the coil of the relay 33, and its normally open contact Rb closes and is rated for the magnetron 10. Power is supplied to magnetron 1
0 heating high frequency waves, ie microwaves, are emitted. The temperature of the object to be heated 5 gradually rises. At this time, the modulation frequency gradually increases as the resistance of the heat sensitive section 7 decreases as the temperature of the object to be heated increases. This low frequency appearing in the detection output of the receiver 15 charges C7 of the integrating circuit (R4, C7) and biases TR3 in the forward direction. When the temperature of the heated object 5 rises and the voltage across C7 becomes higher than the base voltage of TR4, the operating point of TR4 moves from 0N to 0FF, and the base voltage of TR3 does not become 1V higher than the base voltage of TR4. In the meantime, TR4 becomes 0FF. During this time, TR6 and TR7 become 0FF, and the coil current of the relay 33 becomes O, and its contact Rb opens. At this time, as described above, the power supplied to the magnetron 10 is set to a value that provides a low output that does not heat the object to be heated, and the amount of heating high frequency waves emitted from the magnetron 10 is reduced. Here, we will discuss why the heating high frequency of the magnetron 10 is not completely set to 0FF.

As mentioned above, the heat sensitive device 8 uses the high frequency heating wave of the magnetron 10 as one driving source.

The power required for this heat-sensitive device 8 is about 10 mW, and the total power consumption of the power receiving device, that is, the antenna 31 with the diode 30, and the stabilizing circuit is on the order of several percent. This means that a high frequency wave of about 200 m has to be emitted into the heating chamber 2. However, this high frequency output of several watts does not cause much heating of the object to be heated. From these points, in this embodiment, even if the contact Rb of the relay 33 is opened, an output that does not affect heating is always emitted. As a result of the above, the temperature of the object to be heated simultaneously begins to decrease.

By providing the Schmitt circuit S as described above, the relay 33 does not repeat intermittent connections during this time and the modulation frequency also decreases at the same time, so the charging voltage of C7 also decreases and when it becomes below the base voltage of TR3, TR3 becomes 0FF, . TR4 is 0N, . T.R.
6. TR7 becomes 0N, and contact Rb of relay 33 becomes 0N.
Then, the magnetron 10 emits high frequency energy. Repeat this cycle. As described above, according to the present invention, once the correspondence between the resistance value of the variable resistor VRl and the temperature of the heated object 5 is set, the temperature of the heated object can be adjusted to the desired temperature regardless of the quantity or quality. Now I can keep it. In this embodiment, frequency modulation is used as the modulation method of the thermosensitive device, but it goes without saying that even if a modulation method such as AM or PWM is used, it is only necessary to appropriately select a detection circuit for the modulation method.

The present invention produces the following effects based on the above configuration. 1) Whether the heated object is on a turntable or wrapped in a container, it is not connected to the main body with lead wires, etc., so there is no twisting of the lead wires, and the temperature can be controlled as desired. It can be heated up to temperature and maintained at that temperature.

2) It is no longer necessary to set the heating time for each object to be heated based on feeling, and errors in setting the heating time are eliminated.

3) Since a magnetron heating high-frequency oscillation device is used as a power source for the heat-sensitive device, it is possible to eliminate the safety and inconvenience that occur when batteries are used.

In other words, (1) the thermal device does not operate due to battery consumption;
Even if the heated object reaches a certain temperature, no voltage is generated in the receiver's integrating circuit, and the magnetron is operated at its rated output to avoid the danger of overheating the heated object or causing a fire due to bending damage. (2) The trouble of replacing batteries and the need for a structure for storing and taking out the device itself are eliminated. 4) Accurate temperature control is possible.

5) When cooking by stewing, there are young fruits.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the high-frequency heating device of the present invention, Figure 2 is a detailed view of the heat-sensitive device and the main parts of the heat-sensitive part, Figure A is a cross-sectional view, and Figure 3 is a circuit diagram, and Figure 3 is a receiving device and irradiation device. A circuit diagram of a high-frequency heating device of the present invention including a control device, a high-frequency oscillation device for heating, and a power supply circuit is shown. 1...Heating chamber main body, 2...Heating chamber, 5
... Heated object, 7 ... Heat sensitive part, 8 ...
...Thermal device, 10... Magnetron, which is a high frequency oscillation device for heating, 11... Antenna A
ll4... Antenna Bll5... Receiving device, 16... Irradiation control device, 19...
・Variable resistor, 20... Cable, 21...
...Metallic outer shell, 24...Chiyoke part, 25
...Antenna Cl26...Thermistor, 27...High frequency oscillation circuit, 28...
Low frequency modulation circuit, ZD... Zener diode,
PUTl...N gate thyristor, TRl~T
R7...Transistor, R3-R5...
・Resistance, C7~C, ... Capacitor, S...
...Schmitt circuit, 33...Relay, Rb
...Contact, 34...Step-up transformer.

Claims (1)

[Claims] 1 The main body is divided into a heating chamber and an outside of the heating chamber, a heat sensitive part detects the temperature of the object to be heated inside the heating chamber, a low frequency modulation circuit that oscillates at a frequency corresponding to the detected temperature, and a heat sensitive part that is modulated by the low frequency modulation circuit. A heat-sensitive device consisting of a high-frequency oscillation circuit that emits high-frequency waves is provided outside the heating chamber, and a high-frequency oscillator for heating and a receiving device that receives the high-frequency waves emitted by the heat-sensitive device are installed outside the heating chamber. A high-frequency heating device is provided with an irradiation control device that controls the high-frequency output of the high-frequency oscillation device for heating using a modulation signal, the heat-sensitive device is a heat-sensitive element whose resistance changes depending on the temperature, and the frequency changes with the heat-sensitive element whose resistance changes. a high-frequency oscillation circuit that is modulated by the output of the low-frequency modulation circuit; and a circuit that receives radio waves emitted from the heating high-frequency oscillation device and serves as a power source for the low-frequency modulation circuit and the high-frequency oscillation circuit. An impedance circuit is connected between the heating high-frequency oscillation device and the power source, and during the heating operation of the heated object, the modulated signal emitted by the high-frequency oscillation circuit is constantly received, and the temperature of the heated object is controlled. The irradiation control device is configured to switch the impedance circuit according to the modulation signal to an impedance value at which the heating high frequency output amount does not produce a heating effect on the object to be heated, when the set heating temperature is reached.