JPH02278690A - Microwave oven - Google Patents

Abstract

PURPOSE:To prevent any functional deterioration in a long-time operation or at a repetitive or continuous usage by disposing a pyroelectric element near a cooling fan, and introducing high temperature gas such as steam in a heating chamber toward the pyroelectric element through a vent passage. CONSTITUTION:In a microwave oven, a pyroelectric element 5 for detecting the completion of heating is disposed near a cooling fan 11. Meanwhile, high temperature gas such as steam in a heating chamber 7 is exhausted from vent holes 8 pored at a part of the wall surface of the heating chamber 7 toward the pyroelectric element 5 through a vent passage 9 connected to the vent holes 8. Consequently, at the repetitive usage, a temperature at the pyroelectric element 5 can be restrained from rising up, and at the same time, the vent holes 8 for drawing the steam out of the heating chamber 7 can be selectively positioned in the optimum position where the steam is easily drawn out irrespective of an increase in temperature at the pyroelectric element 5. Therefore, it is possible to obtain an electronic range having small deterioration in sensitivity even at the repetitive or continuous heating and provided with a completion detecting system having a high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oven equipped with a finish detection system that automatically detects the heating state of an object to be heated and controls the heating.

Conventional technology High-temperature gas, such as water vapor, generated as the object to be heated is heated is extracted through a vent provided on the wall of the heating chamber, and this gas is applied to a pyroelectric element installed outside the heating chamber. A microwave oven that detects the completion (progress) of heating based on changes in the generated voltage is being considered. Although this method of finish detection uses a pyroelectric element, it does not require a complicated configuration such as a chopper, and since it does not use an optical system, it is resistant to lη distortion, and the viewing angle is It has many advantages, such as being very easy to use, without any problems, and being able to be constructed at low cost.

On the other hand, the detection principle of this method uses the temperature change of the pyroelectric element caused by the steam generated from the food, so there were many issues such as a decrease in sensitivity when the temperature of the pyroelectric element itself increased. .

A conventional example will be explained below with reference to FIG.

As shown in the figure, an object to be heated 6 (food) placed in a heating chamber 7 is dielectrically heated by microwaves (high frequency) of 2450 M]Iz generated by a magnetron IO.

The temperature of the heated object 6 increases by 1, and the temperature of the heated object 6 (
When the temperature of water, which is contained in large amounts in foods (food), reaches a temperature close to the boiling point,
A large amount of high-temperature steam is generated, and this steam rises toward the ceiling of the heating chamber 7. Roughly, this steam passes through the vent 3 provided on the ceiling of the heating chamber 7, hits the pyroelectric element I attached to the cover 2 provided loosely to cover the vent 3, and is released on the surface of the pyroelectric element 1. The condensation gives the pyroelectric element 1 a large amount of thermal energy mainly consisting of latent heat. As a result, the temperature of the pyroelectric element 1 rises and a voltage is generated due to the pyroelectric effect, so that the finished state of the object to be heated 6 (food) can be determined by detecting this.

Problems to be Solved by the Invention However, in this configuration, since the pyroelectric element 1 is provided near the vent 3 provided in the ceiling of the heating chamber 7, if heating is continued for a long time, the heating will occur. Room 7
The temperature of the pyroelectric element 1 rises by 1, and the temperature of the pyroelectric element 1 also becomes considerably high. However, the basic principle of this detection system is to provide the pyroelectric element 1 with a large amount of thermal energy generated when steam generated from food or the like touches the pyroelectric element 1 and condenses. Therefore, the temperature of the pyroelectric element 1 must be lower than that of the steam, but the generated steam is necessarily 100°C.
It is as follows. Therefore, when the pyroelectric element 1 reaches a high temperature close to 100° C., its detection ability is lost, and if it is operated for a long time or used repeatedly, it will no longer function as a detection system.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a microwave oven equipped with a finish detection system using a pyroelectric element that does not easily deteriorate in function even after long-term operation or continuous repeated use.

Means for Solving the Problems In order to achieve the above objects, the present invention provides a pyroelectric element in the vicinity of a cooling fan that cools a microwave generating means, and at the same time, a pyroelectric element is provided in the vicinity of a cooling fan that cools a microwave generating means. The pyroelectric element is guided through a vent hole provided in a portion and a vent passage provided in conjunction with the vent hole.

Function The microwave oven of the present invention has a pyroelectric element for detecting the completion of heating near the cooling fan, and high-temperature gas such as steam in the heating chamber is taken out from a vent provided in a part of the wall of the heating chamber. The structure is such that it is applied to the pyroelectric element through a ventilation path connected to a ventilation hole. For this reason, the temperature rise of the pyroelectric element can be kept low even during repeated use, and the position of the vent for extracting steam from the heating chamber can be selected at the optimal position that is not directly related to the temperature rise of the pyroelectric element and that makes it easy to extract the steam. Therefore, the microwave oven is equipped with a high-sensitivity finish detection system with little loss of sensitivity even during repeated or continuous heating.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. FIG. 1 is a schematic sectional view showing the structure of a microwave oven according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the basic circuit structure of the automatic finish detection system.

In FIG. 1, the object to be heated 6 (food) placed in the heating chamber 7 is 2450 M]lz generated by the magnetron 10.
dielectrically heated by microwaves. When the temperature of the object to be heated 6 increases with heating and reaches a temperature close to the boiling point of water contained in the object to be heated 6 (food), a large amount of high-temperature steam is generated.
This steam rises toward the ceiling of the heating chamber 7. Furthermore, this steam passes through a vent 8 provided in the ceiling of the heating chamber 7, is guided to a cylindrical first vent passage 9, and hits the pyroelectric element 5.

The steam that hits the pyroelectric element 5 condenses on the surface of the pyroelectric element 5 and gives a large amount of thermal energy, mainly latent heat, to the pyroelectric element 5, so the temperature of the pyroelectric element 5 rises and a pyroelectric voltage is generated. occurs. At this time, the steam generated from the object to be heated 6 (food) moves while fluctuating in the air, which is cooler than the steam, so the amount of steam hitting the pyroelectric element 5 also fluctuates temporally and spatially. Therefore, even if the heated object 6 (food) reaches a constant temperature and steam is generated steadily,
At one moment, the temperature of the pyroelectric element 5 rises due to a large amount of steam, but at the next moment, the amount of steam that hits it decreases and the temperature drops, and at the next moment, it receives a large amount of steam again and the temperature rises. Sustains irregular temperature fluctuations. As a result,
The pyroelectric element 5 continues to generate irregular alternating current voltage in response to the temperature fluctuations described above while the object to be heated 6 (food) continues to generate high-temperature steam. FIG. 3 shows the state of the voltage generated by the pyroelectric element 5, and the heating time is t.
Steam is rapidly generated from the object to be heated 6 near the point a, and this steam continues to generate a large-amplitude AC voltage V (several tens of mV) between the electrodes of the pyroelectric element 5.

FIG. 2 shows the basic circuit configuration of a detection system including the pyroelectric element 5.

In FIG. 2, the voltage generated by the pyroelectric element 5 is applied to a DC (direct current) cant circuit 17. The signal is passed through L, P, F (low bus filter) 18 and amplified by an amplifier (amplification circuit) 19, and then read by a microcomputer 20.

For example, the item to be heated 6 is a reheating menu (reheating food)
If so, the temperature at the ta point (Figure 3), where a large amount of steam begins to be generated, is almost sufficient for heating, so the microcomputer 20
When the voltage reaches a predetermined reference voltage Va, it is determined that the magnetron 10 and the cooling fan 11 should be stopped. Since the pyroelectric element 5 has a very high impedance, a resistor 22 of about IMΩ and a capacitor 23 of about 0.05 μF are coupled in parallel with the pyroelectric element 5 to alleviate this impedance. Further, the control sequence of the microcomputer 20 is selected through the operation panel 21.

FIG. 4 is a detailed explanatory diagram of the pyroelectric element 5, showing a flat ceramic plate 24 having a pyroelectric effect, electrodes 25 and 26 formed on both sides of the plate, and a metal such as stainless steel bonded to one side of the plate. It consists of a plate 27.

High-temperature gas such as steam is applied to the metal plate 27, heat is transferred to the ceramic plate 24 via the metal plate 27, and the ceramic plate 24 generates a voltage due to the pyroelectric effect. or,
In the case of the pyroelectric element 5 shown in FIG. 4, the electrode 26 on the side bonded to the metal plate 27 passes through a part of the circumferential edge of the ceramic plate 24 and extends partially to the opposite surface. 25.2
The structure allows the lead cotton 28 to be drawn out from the metal plate 6 only from the surface that is not bonded to the metal plate 27.

As mentioned earlier, the metal plate 27 functions as a sensing surface of the pyroelectric element 5, and also functions as a mechanical reinforcement for the ceramic plate 24, which generally has a thickness of only about 0.2 mm. Electrode 2, which easily deteriorates when exposed to direct contact with steam, etc.
It also serves as a protective cover for 6.

Now, in the case of the present invention whose embodiment is shown in FIG.
A magnetron 1 which is a microwave generating means coupled to
The cooling fan 11 that cools the 0 is a propeller fan, and the pyroelectric element 5 is connected to the blade 11 of this propeller fan 11.
Near the upper or lower extension of the plane of rotation of a,
In this example, it is arranged almost above the blade 11a. Unlike other sirocco fans, the propeller fan 11 generates a large amount of wind in directions other than the direction of the blowing axis (rotation axis), and in particular, a large amount of air is also generated in the direction of the rotation plane of the blades 11a. This wind cools the pyroelectric element 5 and keeps the temperature of the pyroelectric element 5 sufficiently low.

Further, a part of this wind is taken into the second ventilation path 15,
The air is discharged to the outside of the aircraft from an exhaust port 13 provided at the upper part of the back surface of the body 31. The metal plate 27, which is the sensing surface of the pyroelectric element 5, is placed on the inner wall side of the second ventilation path 15,
At a position substantially opposite to this metal plate 27, the first air passage 9
are connected to each other through a part of the wall surface of the second air passage 15.

A portion of the cold air sucked from outside the aircraft through the intake port 14 by the cooling fan 11 passes through the second air passage 15 toward the exhaust port 13 with a constant wind pressure (wind speed). .

As a result, negative pressure is generated at the joint with the first air passage 9 (
Hernoulli's theorem), the steam in the first air passage 9 is forcibly sucked into the second air passage 15, mixed with the cold air that was originally flowing inside the second air passage 15, and the pyroelectric element 5 After being hit, it is guided out of the aircraft through the exhaust port 13. The steam hitting the metal plate 27, which is the sensitive surface of the pyroelectric element 5, is thus forcibly mixed with the cold air, so the above-mentioned fluctuation effect is large, and as mentioned earlier, the steam itself is absorbed from inside the heating chamber 7. Since it is forcibly sucked out, the steam generated from the heated object 6 is quickly and in large quantities guided to the pyroelectric element 5, resulting in high detection speed and high sensitivity.

What should be noted here is that the blade tH11a, on which the pyroelectric element 5 is arranged, is located in the direction of the road on the rotational plane or in the GJ approximately vertical direction, and in this case, the position approximately at the top of the blade 11a is on the blowing side of the cooling fan. The air passage is closest to the body 31, which is the outermost wall of the microwave oven, and is the second air passage from the cooling fan 11 to the body 31 (in the case of Fig. 1, the air passage 15
and exhaust port 13) can be configured in the shortest possible time, reducing wind pressure (
Therefore, the function as the above-mentioned second ventilation path is maximized.

Furthermore, the wind taken into the second ventilation path 15 in this configuration is
They are not used to cool the other magnetrons 15 or the power source (not shown), and these air passages 15 and the pyroelectric element 5 are obstacles to the wind that cools the magnetron 10 and the power source (not shown). Therefore, the function originally performed by the cooling fan 11 is not impaired at all.

Next, another embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 5, this microwave oven has a ceramic heater 29 on the ceiling of the heating chamber 7 and a flat heater 30 on the bottom of the heating chamber 7.
These heaters can be used to function as an oven.

When used as an oven, the heating chamber 7 has a temperature of 200 to 30
However, since the pyroelectric element 5 is arranged at a certain distance from the heating chamber 7 due to the structure of the present invention, the temperature rise can be kept at about 100°C, so the temperature rise is kept at about 100°C. The electronic element 5 will not be damaged.

The position where the pyroelectric element 5 is arranged is forcibly cooled by the cooling fan 11, so if the cooling fan 11 is activated after use as an oven, the pyroelectric element 5 can be removed in a short time. The effects of the present invention are even greater, such as being able to cool down to a detectable temperature. It goes without saying that even if a gas heater is used as the second heating source, the same effect can be obtained.

Effects of the Invention As described above, in the microwave oven of the present invention, since the pyroelectric element is placed near the cooling fan, the electronic Even if the heating chamber becomes high in temperature when the microwave is used repeatedly and continuously, the temperature of the pyroelectric element does not rise much, and there is almost no deterioration in finish detection ability.

Furthermore, when the cooling fan is a propeller fan, a large amount of the air generated by the propeller fan exists in areas other than the blowing shaft, so the cooling effect is large, and it is inevitable that the air will flow upward or downward from the plane of rotation of the propeller fan's blades. By placing a pyroelectric element on or near the extension, a part of the cooling air is used to suck out the steam from the heating chamber, and the air itself is mixed with the steam to create a fluctuation effect. can be increased to significantly improve detection performance.

In addition, if the microwave oven has a lid as in the second embodiment, the temperature of the heating chamber when heating the heater is 200 to 300°.
Since the temperature reaches a high temperature of C, arranging the pyroelectric element at a certain distance from the heating chamber using the method of the present invention not only maintains detection performance but also prevents damage to the pyroelectric element itself. It can be prevented. Furthermore, the position where the pyroelectric element is placed is forcibly cooled by a cooling fan, so if the cooling fan is activated after the oven is used, the temperature at which the pyroelectric element can be detected can be detected in a short time. The effect is very great, such as cooling down to a maximum temperature.

[Brief explanation of drawings]

Fig. 1 is a schematic cross-sectional view of a microwave oven according to an embodiment of the present invention, Fig. 2 is a block diagram showing the basic circuit configuration of the automatic finish detection system part of the microwave oven, and Fig. 3 is an automatic finish detection system of the microwave oven. This is to explain the operation of the detection system part, and shows a change diagram of the output voltage of the pyroelectric element, Figure 4 (
a) and (b) are a plan view and a cross-sectional view of the pyroelectric element in the same microwave oven, FIG. 5 is a schematic cross-sectional view of a microwave oven in another embodiment of the present invention, and FIG. 6 is a schematic diagram of a conventional microwave oven. FIG. 4...Pyroelectric element, 7...Heating chamber, 8.
...Vent, 9...Vent passage, IO...
... Magne 1-ron, 11... Cooling fan. Name of agent: Patent attorney Shigetaka Awano Idiot 1 Figure

Claims (2)

[Claims] (1) A heating chamber, a microwave generating means coupled to the heating chamber, a cooling fan for cooling the microwave generating means, a pyroelectric element provided near the cooling fan, and a pyroelectric element provided in the vicinity of the cooling fan. A microwave oven comprising a vent provided in a part of a wall surface of the heating chamber to guide gas in the heating chamber, and a first vent path coupled to the vent. (2) The cooling fan is a propeller fan, a pyroelectric element is arranged on or near the upper or lower extension of the plane of rotation of the blades of the propeller fan, and the cool air of the cooling fan is guided to the pyroelectric element. The microwave oven according to claim (1), further comprising a second ventilation path.