JPH0475283A - High frequency heating apparatus - Google Patents

Abstract

PURPOSE:To accelerate heat radiation of a wave-detector circuit to suppress the temperature increase of the circuit by forming an empty space in a metal cover on the wave-detection circuit and blowing a part of cooling wind from a fan. CONSTITUTION:A part 5 of radio waves which are not adsorbed by a food 2 are permeated through a slit cover 8 of resin, pass a slit 9 formed in the side wall of a heating chamber 1, are detected by an antenna 6 in a printed circuit board10, transmitted to a wave detection circuit 7 formed on the back side of the board10, inspected there, and then sent to a controller 12 as wave inspected output. A large quantity 14 of a cooling wind from a fan 13 is sent to a radio wave radiating part 3 but a part 15 of the cooling wind is sent to a metal cover 16 covering the wave detection circuit 7 to assist it for heat radiation. An empty space with the length at longest 1/4 of the radio waves is formed in each side of the metal cover 16 and a part 15 of the cooling wind cools not only the metal cover 16 itself but the printed board 10 through the space while passing it.

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 (Japanese Patent Publication No. 52-2133). there were. 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 controller 7a and a radio wave radiator 3. At this time, some of the radio waves 5 that are not absorbed by the food 2 are detected by an antenna 6 installed in the heating chamber 1 and detected by a detection circuit 7.
This detected amount is inversely proportional to the weight of food 2, so
The weight of the product can be determined and the optimal heating time can be set.

Problems to be Solved by the Invention In such conventional systems, the detection circuit was sealed with a metal cover in order to completely block radio wave leakage to the outside world and at the same time block noise from the outside world. However, in the case of a high-frequency heating device, if you repeatedly cook or cook for a long time, the temperature of the heating chamber and the walls of the heating chamber rises, and the metal cover becomes hot due to conduction heat, and there is no place for the heat to escape, so the detection circuit Excessive heat may also be applied, causing destruction of component parts. Therefore, a major issue was how to suppress the temperature rise in the detection circuit.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a high-frequency heating device configured to suppress a rise in temperature of a detection circuit.

Means for Solving the Problems In order to achieve the above objects, the high frequency heating device of the present invention has the following features:
A heating chamber that stores food, a radio wave radiator that radiates electromagnetic waves to heat the food, a fan that cools the radio wave radiator, an antenna that detects some of the electromagnetic waves in the heating chamber, and an antenna that detects the electric power detected by the antenna. It has a detection circuit that detects waves and a controller that controls various equipment operations using the output of the detection circuit.The detection circuit is covered with a metal cover, and the cover is not completely sealed, but has a gap that allows some of the wind from the fan to pass through. It is configured so that it can pass through.

According to the above-described structure, the present invention provides a gap in the metal cover covering the detection circuit to allow a portion of the cooling air from the fan to pass through, thereby promoting heat dissipation from the detection circuit and suppressing temperature rise.

Example Embodiments of the present invention will be described below 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, a part of the radio waves 5 that was not absorbed by the food 2 passes through the resin slit cover 8, passes through the slit 9 made in the wall of the heating chamber 1, and is transmitted to the copper foil on the printed circuit board 10. The signal is detected by the antenna 6 and transmitted to the detection circuit 7 on the back side of the printed circuit board 10 for detection, and then sent to the controller 12 via the lead 11 as the output of the detection circuit. According to the detected amount, the controller 12 knows the condition of the food and determines the optimal thawing time.
It controls the operation of the radio wave emitting section 3 and the fan 13 for cooling the radio wave emitting section.

On the other hand, most of the cooling air 14 from the fan 13 is sent to the radio wave radiating section 3, but a portion 15 of the cooling air is sent to the metal cover 16 covering the detection circuit 7 to help dissipate heat.

The gap between the metal cover 16 will be explained using 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 1. Connect the ground plane of the printed circuit board 10, which has the antenna 6 and the detection circuit 7 on the front and back sides, to the protrusion 1 for soldering the metal plate 17.
Solder at the 4 locations marked 8.

It is covered with a metal cover 16 for blocking radio waves, and is fastened with screws 20 to a metal support 19 attached to the wall of the heating chamber 1 by spot welding. Here, the metal cover 16 is provided with a gap 21 on each surface having a length of 174 wavelengths of electromagnetic waves at its longest distance, so that a portion of the cooling air 15 described in FIG.
However, not only the metal cover 16 itself but also enters the gap 21 and passes through the printed circuit board 10 while cooling it. The gap 21 prevents heat from accumulating inside the metal cover 16.
The detection circuit 7 is always kept at a low temperature. Further, since the gap 21 has a length of 174 or less of the wavelength of electromagnetic waves, there is no leakage of waves to the outside, no radio waves enter from the outside world, and the detection accuracy is good.

FIG. 3 is a diagram of an example of the printed circuit board 10 viewed from the detection circuit 7 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 17 described in FIG. 2). The radio waves transmitted from the antenna 6 are guided through the through hole 22 to the detection circuit 7, and are detected by the detection circuit 7, which is composed of chip components such as a Schottky barrier diode 23 and a microstrip line.
A signal is transmitted in a direct current state after the lead wire 11. FIGS. 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-tan δ is an index that shows how easily food absorbs radio waves, and indicates that it is difficult to absorb radio waves when frozen, but it is easy to absorb radio waves at around 0°C. In other words, more radio waves are detected by the antenna without being absorbed by the food when it is frozen, and O″CC
There will be fewer nearby. 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 can be seen from this figure, if the food shows a uniform temperature rise, thawing 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.

Therefore, what is actually effective 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,
For foods at low temperatures (-20°C), the initial rate of change in the output of the detection circuit is large, while for foods at medium temperatures (-10"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 as a parameter, as shown in FIG. 7, and the weight and initial temperature of the food are determined. (However, in the figure, C is a low-temperature food with a large rate of change, and d is a medium-temperature food with a small rate of change.) Of course, by setting the optimum heating time for each weight and initial layer in the controller 12, the weight of the plate can be adjusted. Compared to other weight sensors, etc., which make false judgments, this technology achieves extremely stable thawing detection.

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

Since the antenna 6 is constructed with a pattern, the dimensional accuracy is extremely high and the matching to the detection circuit 7 is stable.
Excellent detection accuracy.

A gap 24 is also provided in the metal support 19 to provide good ventilation, thereby further suppressing the temperature rise of the detection circuit.

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

(1) A gap is provided in the metal cover that covers the detection circuit to allow some of the cold air from the fan to pass through. This cools the metal cover, which tends to heat up due to conduction heat from the heating chamber wall, and prevents the temperature from rising. Since the detection circuit itself is also cooled, the detection circuit is always kept at a low temperature, preventing thermal damage to component parts, and providing extremely stable detection performance even when automating cooking.

(2) When cold air is constantly passed through, steam (water vapor) is less likely to accumulate and condensation does not occur on the detection circuit, which has the effect of preventing malfunctions.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of a high-frequency heating device according to an embodiment 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・Temperature characteristic diagram of tan δ, 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.
The figure is a characteristic diagram showing the time change of the output of the detection circuit, and Fig. 7 is a characteristic diagram showing the change of the initial value of the output of the detection circuit 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, 7...Detection circuit, 12...
...Controller, 13...Fan, 16...
...Metal cover, 21...Gap. Name of agent: Patent attorney Shigetaka Awano. Inspecting the food by the Antenna of the Antenna [Il M Collection-1 #p Ofan Taru A Cover 'T-sama ['0] Fig. T ['5] 2θ Carp figure

Claims (2)

[Claims] (1) a heating chamber that stores food; a radio wave radiator that radiates electromagnetic waves to the food to heat the food; a fan that cools the radio wave radiator; and an antenna that detects part of the electromagnetic waves in the heating chamber; It has a detection circuit that detects the power detected by the antenna, and a controller that controls various equipment operations based on the output of the detection circuit, and the detection circuit is covered with a cover made of metal, and the cover is not completely sealed but has a gap. A high-frequency heating device having a configuration in which a part of the air from the fan passes through. (2) The high-frequency heating device according to claim 1, wherein the length of the gap in the cover is 1/4 or less of the wavelength of the electromagnetic wave.