JPH0475290A - High frequency heating apparatus - Google Patents

Abstract

PURPOSE:To suppress excessive input to a wave detection circuit and eliminate effects on a human being and prevent error operation due to leakage power returning by suppressing the leakage power in the vicinity of the wave detection circuit to below the prescribed level of a rated power for parts composing the wave detection circuit. CONSTITUTION:An earth face of a printed board 9 having an antenna 6 and a detection circuit 10 comprised of parts for 1/10W rated power in front and back sides is soldered at four points of extruded parts 15 formed in a metal board 14 for soldering. A metal cover 16 for electromagnetic wave shielding is put on them for covering and fastened by machine screws 18 to metal supporting fittings 17. In this case, when the electric power leaked to the surroundings is measured by a leakage meter (leaked wave measuring apparatus) under practical cooking conditions or worst use conditions, it is <=10mW/cm<2> and is <=1/10 of the 1/10W rated parts and thus excessive input to the wave inspection circuit does not occur and leakage power which affects human body and causes a malformation is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-frequency heating device that automatically detects the presence or absence of food, the thawing state, etc.

BACKGROUND OF THE INVENTION In recent years, there has been a growing movement to automate the thawing of foods using high-frequency heating devices.

Conventionally, the mainstream method is to know the weight of food using a time auto that manually calculates the weight of the food, or a weight sensor that automatically detects the weight of the food, and then heats it to the optimal heating time that is preset for each food weight. Met. moreover,
A microwave detection element (i.e., an antenna) is placed in the heating chamber, and the microwave power detected by the element without being absorbed by the food is inversely proportional to the weight of the food (published in Japanese Patent Publication No. 52-2133). was there. The configuration will be explained below using FIG. 8.

A frozen food 2 is placed in a heating chamber 1, and a radio wave 4 is applied from a radio wave emitting section 3. At this time, a part 5 of the radio waves not absorbed by the food 2 is transmitted to an antenna 6 installed in the heating chamber 1.
However, since this detected amount is inversely proportional to the weight of the food 2, the weight of the food 2 can be determined conversely, and the optimum heating time can be set.

Problems to be Solved by the Invention In such conventional high-frequency heating devices, the antenna is configured inside the heating chamber, and the detection signal (
In order to transmit high-frequency waves, a detection circuit must be constructed near the antenna, and there is a problem in that heat from the heating chamber and the walls of the heating chamber is transmitted to the detection circuit, causing thermal damage to the components of the detection circuit.

Furthermore, regarding where to install the antenna in the heating chamber, due to the shape of the heating chamber, high-frequency radio waves have a complicated distribution within the heating chamber, and there are places where the electric field is concentrated and places where it is not. Therefore, there was a problem that it was difficult to know where to attach it. In particular, if configured in an area where electric fields are extremely concentrated, there is a risk of destroying the detection circuit due to excessive input, and there is a problem that it may affect the human body.Also, even if it is not so extreme, there is a problem that the circuit may malfunction due to the wraparound of leaked radio waves. was there.

The present invention solves the above problems, and aims to provide a high-frequency heating device with high reliability, safety, and simple configuration.

Means for solving the problem High frequency heating bag of the present invention! In order to achieve the above purpose,
A heating chamber that stores food, a radio wave radiation section that radiates magnetic waves to the food to heat it, an antenna provided near an opening made on the heating chamber wall surface, and a detection circuit that detects the electric power detected by the antenna. , and a controller that controls the operation of various devices using the detection output, and is configured so that the leakage power in the vicinity of the opening, the antenna, and the detection circuit is 1/10 or less of the rated power of the components constituting the detection circuit. are doing.

Effect of the Invention With the above-described configuration, the present invention provides the antenna near the opening made in the wall of the heating chamber, which suppresses heat conduction from the heating chamber and the wall of the heating chamber, and prevents leakage near the opening, antenna, and detection circuit. /! i.Since the power is configured to be 1/10 or less of the rated power of the components that make up the detection circuit, excessive input to the detection circuit can be suppressed, and malfunctions due to leakage power can be prevented without affecting the human body. It doesn't happen.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a sectional view of a high-frequency heating device showing an embodiment of the present invention. Radio waves 4 are radiated from a radio wave radiator 3 to a food 2 placed in a heating chamber 1. At this time, some of the radio waves 5 that were not absorbed by the food 2 pass through the resin hole cover, pass through the hole 8 made in the wall of the heating chamber 1, and pass through the copper foil on the printed circuit board 9. detected by antenna 6,
After being transmitted to the detection circuit 10 on the back side of the printed circuit board 9 and detected, the signal is sent to the controller 12 via a lead 11 as the output of the detection circuit. According to the detected amount, the controller 12 knows the condition of the food, determines the optimum thawing time, and controls the operation of the radio wave emitting section 3 and the fan 13 for cooling the radio wave emitting section.

Further, the configuration around the antenna will be described in more detail in FIG. 2.

FIG. 2 is a perspective view of essential parts showing an example of how the detection circuit 7 and antenna 6 are attached to the wall surface of the heating chamber l. The ground plane of the printed circuit board 9, which has the antenna 6 and the detection circuit 10 composed of components with a 1/Low rated power on the front and back sides, is soldered to four locations on the protrusions 15 of the metal plate 14. It is covered with a metal cover 16 for blocking radio waves, and is fastened with screws 18 to a metal support 17 attached to the wall surface of the heating chamber 1 by spot welding. In this configuration, the printed circuit board 9 (detection circuit 10) can be reliably grounded by soldering to the metal plate 14 and the metal support 17.
The metal support 17 and the wall of the heating chamber 1 are surely short-circuited by welding, so the mounting has good positional accuracy, the grounding is reliable, and the metal plate 14 absorbs the stress caused by tightening the screws. Therefore, it can be seen that stress on the detection circuit can be suppressed.

In the case of this configuration example, when the surrounding leakage power is measured with a leakage meter (leakage measuring device) even during actual cooking or in the worst usage condition, it is less than 10 mw/cffl, which is 1/Lo
It is less than 1/10 of the W-rated components, does not cause excessive input to the detection circuit, and does not generate leakage power that may affect the human body or cause malfunction.

FIG. 3 is a diagram of an example of the printed circuit board 9 viewed from the detection circuit 10 side. The broken line in the figure indicates the pattern on the back side of the board.
- The dotted chain line is the part on the back side where there is a pattern but no resist (that is, the ground for soldering to the metal plate 14 described in FIG. 2). The radio waves transmitted from the antenna 6 are guided to the detection circuit IO through the through hole 19, and the 250 mW
Rated Nyonotoki Harrier diode 20 or 1/10
The signal is detected by a detection diagram 10 composed of a W-rated chip component 21 and a microstrip line, and the signal is transmitted from the lead wire 11 in a state of direct current. Generally, chip components have a rated power of 100 mw to 500 n+iv, and have a characteristic that the rated value decreases as the temperature rises.

In high-frequency heating equipment, even if the leakage is less than 1/10 of the rated value in the mounted state, the actual temperature conditions and power consumption of each chip component must be investigated.

4 to 7 are characteristic diagrams showing the principle of thawing detection in the high-frequency heating device of the present invention. Here we will add an explanation of the detection principle.

The product of the dielectric constant Er and the dielectric loss tan δ of the food is, if the food is heated uniformly and the temperature of the whole food increases at the same time,
It changes as shown in Figure 4. The horizontal axis is the temperature of the food, and the vertical axis is Er.
-tan δ. Er-jan δ is an index that shows how easily food absorbs radio waves, and indicates that it is difficult to absorb radio waves when frozen, and it is easy to absorb radio waves at around 0°C.

In other words, the amount of radio waves that are not absorbed by the food and detected by the food antenna increases when the food is frozen, and decreases around 0°C. From this, FIG. 5 is obtained. The horizontal axis shows the temperature of the food, and the vertical axis shows the detection circuit output. As you can see from this figure, if the food shows a uniform temperature rise,
It is thought that decompression can be detected at the inflection point of the detection output.

However, in reality, heating by a high-frequency heating device is non-uniform, resulting in a combination of areas where radio waves are concentrated and areas where they are not, resulting in a waveform in which many of the curves in Figure 5 overlap, and - generally, an inflection. Decompression is not complete at this point.

What really matters is the initial value and initial rate of change of the output of the detection circuit. The initial value is approximately inversely proportional to the weight of the food; for example, for a small amount of food, the absorption of radio waves is low and the output of the initial detection circuit is large, whereas for a large amount of food, the absorption of radio waves is large and the output of the initial detection circuit is small. . Also,
In the case of low-temperature (-20°C) food, the initial rate of change in the output of the detection circuit is large, but it is medium! In the case of food at (-1°C), the initial rate of change in the output of the detection circuit is small.

A typical example is shown in Figure 6. The horizontal axis is time and the vertical axis is the detection circuit output. In the figure, a indicates a small amount of low-temperature food, and b indicates a large amount of medium-temperature food.

Based on the above principle, the correlation between the weight and the initial output is determined using the initial output change rate shown in FIG. 7 as a parameter, and the weight and initial temperature of the food are determined. (However, in the figure, C is a low-temperature food with a significant change, and d is a medium-temperature food with a small change rate.) Of course, by setting the optimum heating time for each weight and initial point in the controller 12, you can adjust the weight of the plate etc. Compared to other weight sensors, etc., which make false judgments, this product achieves extremely stable thawing detection.

The following points can be mentioned as effects of this embodiment.

The antenna 6 and the detection circuit 10 are connected to a metal plate 14. metal cover 1
6. Since it is covered with the metal support 17 and the wall surface of the heating chamber 1, it is difficult for waves to leak to the outside and it is difficult to receive noise from the outside world.

Since the antenna 6 is installed near the opening 8 and protected by the opening hole, there is no direct hit of flying objects from the food 2 to the antenna 6, and error factors such as changes in permittivity near the antenna 6 due to food debris are eliminated. can.

Effect of the invention According to the present invention, there are the following effects.

(1) Since the antenna 6 is installed near the opening 8 in the wall of the heating chamber 1, heat conduction from the inside of the heating chamber 1 and the wall of the heating chamber 1 is suppressed, and the temperature of the components of the detection circuit can be lowered. It has high reliability and can achieve extremely stable detection.

(2) Opening 8. The leakage power near the antenna 6 and the detection circuit 10 is 1/10 of the rated power of the components that make up the detection circuit.
Since it is configured as follows, it is possible to prevent excessive input to the detection circuit, so it is difficult to cause damage and has no effect on the human body, making it completely safe.

(3) Similar to (2), the leakage power does not cause noise to the operation of external equipment and cause malfunction, and stable equipment operation can be provided.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a high-frequency heating device according to embodiments of the present invention, FIG. 2 is an exploded perspective view of the device, FIG. 3 is a front view of the detection circuit of the device, and FIG. 4 is an Er -tan δ temperature characteristic diagram, Figure 5 is the ideal temperature characteristic diagram of the detection circuit output, Figure 6 is the ideal temperature characteristic diagram of the output of the detection circuit.
Fig. 7 is a characteristic diagram showing the change in the detection circuit output over time, and Fig. 7 is a characteristic diagram showing the change in the initial value of the detection circuit output with respect to the weight.
FIG. 8 is a cross-sectional view showing the configuration of a conventional high-frequency heating device. 1... Heating chamber, 2... Food, 3...
...Radio wave emitting section, 6...Antenna, 8...
...Open hole, lO...Detection circuit, 12...
...Controller. Name of agent: Patent attorney Shigetaka Awano (1 person) Figure 1 Figure Heats up! ... - 4 items for 7 minutes T 1%F'! Konfusuma Wave circuit 15'l A

Claims (1)

[Claims] a heating chamber for storing food; a radio wave radiating section for heating the food by emitting electromagnetic waves; an antenna provided near an opening formed in the heating wall; and a detection circuit for detecting the electric power detected by the antenna. and a controller that controls various equipment operations based on the output of the detection circuit, and when the antenna and the detection circuit are mounted, leakage power near the opening, the antenna, and the detection circuit is controlled by the detection circuit. A high-frequency heating device configured to have a power consumption of 1/10 or less of the rated power of the components constituting the device.