JPH03250578A - High frequency heating device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 A conventional thawing detection method for a high-frequency heating device will be described.

With Time Auto, the heating time is set in advance for each weight of food, and by manually inputting the weight of the food, the food will be heated for a time corresponding to that weight.

In addition, the weight sensor automatically detects the weight of the food, so compared to Time Auto, there is no need to manually operate the weight keys, but after detecting the weight, it heats up until the preset time like Time Auto. It has become.

Furthermore, the concept of detecting changes in the state of food by the amount of reflected power from the heating chamber has been considered for some time, as shown in Japanese Patent Application Laid-Open No. 159087/1987, but it has never been realized. .

Problems to be Solved by the Invention When thawing is detected using methods such as time auto or weight sensors, thawing is completed after heating for a certain amount of time regardless of the initial temperature, shape, placement, ingredients, etc. of the food, so the finished product is Conditions vary widely. If you perform thawing detection on items with a high initial temperature (for example, a frozen item that has just been brought home from shopping), the item may boil or the item with a low initial temperature (for example,
When thawing detection was performed on food that had been stored for a long time in a freezer with strong cooling capacity, it was found that the food had not been thawed at all.
From the user's point of view, it was extremely inconvenient to use.

Next, by using the amount of reflected power, it is theoretically possible not only to determine the weight based on the amount of initial reflected power, but also to estimate the initial temperature of the food and how it is placed by using changes in the amount of reflected power over time. However, in reality, the configuration of the antenna that captures the reflected power, the configuration of the detection circuit, or the matching between the two was poor, and the result was that only data with a large amount of variation could be obtained as a detection output, making it extremely difficult to put it into practical use. In particular, various configurations of the antenna 8 have been considered, in which the conductor is bent and the circuit 9 is attached as shown in Figure 8.
There have been problems in that it is very difficult to suppress variations in size (length), mounting angle, and matching degree, and it is not easy to maintain matching accuracy with the detection circuit.

The present invention solves these conventional problems,
The purpose is to accurately extract reflected power with a simple configuration and defrost food with high precision.

Means for Solving the Problems In order to solve the above problems, the high frequency heating device of the present invention has the following features:
a heating chamber for storing food; a radio wave radiating section for heating the food by emitting electromagnetic waves; an antenna for detecting part of the magnetic waves in the heating chamber; and a detection circuit for detecting the electric power detected by the antenna. , and a controller for controlling various equipment operations, and the antenna is formed of copper foil on a printed circuit board.

Function: The high-frequency heating device of the present invention uses an antenna made of copper foil on a printed circuit board to detect and control the reflected power, which changes depending on the state of the food placed in the heating chamber, so it can detect thawing with high accuracy. is realized.

Embodiment Hereinafter, one embodiment of the present invention will be described based on 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, depending on the condition of the food 2, a portion of the radio waves including reflected waves 5
passes through a slit 6 made in the wall of the heating chamber 1, and is detected by an antenna 8 fixed with a metal fitting 7. The antenna 8 is constructed on the same double-sided substrate 10 and connected to the detection circuit 9, and the radio waves detected by the antenna 8 are detected by the detection circuit 9 and sent to the controller 11. The controller 11 knows the state of the food according to the detected amount, determines the optimum thawing time, and controls the operation of the radio wave emitting section 3 (that is, stops oscillation when the optimum thawing time comes).

FIGS. 2 and 3 are views rotated by 180'' around the AA' axis, showing the configuration of the front and back sides of the double-sided substrate 10, in which the antenna 8 and the detection circuit 9 are arranged. The antenna 8 is surrounded by a w4WM ground plane 12, and the antenna 8
It is also made of copper foil.

The antenna 8 and the detection circuit 9 are connected through a through hole 13, and the back surface of the antenna 8 has no copper foil except for the connecting portion of the through hole 13. The detection circuit 9 is arranged on the back side of the ground plane 12 so as not to overlap the back side of the antenna 8 . Here, the antenna 8 is a copper foil antenna whose detection amount is considered to be determined approximately by the length of the long side l, unlike a strip antenna with a grounded back surface.

FIG. 4 is a sectional view of the main part of the installation. The fitting 7 is fixed so as to cover the slit 6 in the wall of the heating chamber 1, and is connected to the ground plane 12 of the double-sided board 10. The antenna 8 is surrounded by a ground plane 12 and has a through hole 13.
It is connected to the detection circuit 9 on the back side.

Here, as an effect of the embodiment, since the antenna and the detection circuit are constructed on the front and back sides of the same double-sided board and are connected through through holes, matching accuracy is improved.

Additionally, since the antenna is surrounded by a ground plane and fixed to the heating chamber wall using metal fittings, leakage of waves to the outside is suppressed and noise from the outside world is difficult to detect.

FIG. 5 is a circuit configuration diagram showing an example of the detection circuit 9. As shown in FIG.

The power PIN obtained from the antenna is detected by a surface-mounted detection diode 14, and then passed through an LPF (low pass filter) 1.
After filtering with 6, the detection output ■. Sent to the controller as u7. When a detection circuit is configured on a double-sided substrate as described above, the inductance and capacitance components of the LPFs 15 and 16 are often configured with microstrip lines.

FIG. 6 is a characteristic diagram showing temporal changes in the detected output VOt17. An example of a control method within the controller will be explained. The time required for one rotation of the turntable of the high-frequency heating device tty+ is divided into several sections tl+Lx,...
・The maximum value V t l +vL in each section
Find t, etc. At this time, since Vt+ changes in accordance with the weight of the food, the weight m can be calculated from Vtl in reverse, as shown in FIG. Also, since VLI vtg roughly corresponds to the initial temperature of the food, conversely VL vtg corresponds to the initial temperature of the food.
The initial state of the food can be known and the optimal thawing time can be determined by using a method of 0 or more that can estimate the initial temperature T from I Vt□.

Effects of the Invention As described above, according to the high frequency heating device of the present invention, the following effects can be obtained.

Since the antenna is formed of W4M on a printed circuit board, dimensional accuracy is good. In the case of thawing detection using high-frequency heating equipment like this one, the radio wave distribution changes in a complex manner due to differences in the heating chamber shape, radio wave emitting part, etc., so the dimensional accuracy of the antenna is one of the management points that requires the most attention. According to this invention,
Since the dimensional accuracy is extremely high, the effect in actual use is great when considering the variations during mass production.

Also, the board with the antenna is installed near the oven wall, but compared to the type of antenna that bends the conductor and attaches it to the detection circuit, as shown in Figure 9, it is easier to match the distance between the coupling hole on the oven and the antenna. The condition is extremely stable.

Similarly, compared to the antenna shown in FIG. 9, the distance between the oven and the antenna substrate can be made smaller, the antenna can be made smaller, it does not take up much space, and there is no effect on the size or appearance of the high-frequency heating device.

Furthermore, the connection of the input stage of the antenna and the detection circuit to the transmission line is extremely easy since both are made of copper foil, and the matching accuracy between the antenna and the detection circuit is also very high.

Furthermore, if there is no copper foil on the back side of the antenna, there is a gap between the copper foil antenna and the copper foil ground plane that surrounds it (i.e., there is no copper foil and the board material is exposed). The matching condition can be changed depending on the width of the area), and the sensitivity can be changed freely. The optimum range of circuit input is determined by considering the performance and reliability of the detection circuit, but by setting the gap width accordingly,
You can easily give the desired circuit input.

In addition, if there is no copper foil on the back side of the antenna, there is no need to connect it to the pile wave circuit via a transmission line such as a 50Ω line after the antenna is completed, as is the case with micro-strinb antennas that have copper foil on the back side. The antenna can be connected directly to the detection circuit. Especially when configuring the antenna and detection circuit on opposite sides of the board, they can be connected only with through holes.
The transmission line can be omitted and it can be made more compact.

Furthermore, although high-frequency materials are expensive as substrate materials, if the present invention allows for miniaturization, significant cost reductions can be achieved.

Furthermore, unlike the antenna shown in FIG. 9, it can be made into a planar structure, so it is easy to coat with resist, etc., and has the effect of increasing work efficiency.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a high-frequency heating device according to the first embodiment of the present invention, Figs. 2 and 3 are block diagrams showing an example of the structure of an antenna and a detection circuit, and Fig. 4 is a block diagram showing an example of the structure of an antenna and a detection circuit. FIG. 5 is a circuit diagram showing an example of a detection circuit.
Figure 6 shows the detection circuit output■. Fig. 7 is a characteristic diagram showing the relationship between the detection circuit output ■□ and the food weight m, and Fig. 8 is a characteristic diagram showing the relationship between the detection circuit output VL, -V, and the initial temperature T of the food. A characteristic diagram showing the relationship, FIG. 9 is a configuration diagram showing an example of the configuration of a conventional antenna and a detection circuit. 1... Heating chamber, 2... Food, 3...
...Radio wave emitting part, 7...Mounting metal fittings, 8...
...Antenna, 9...Detection circuit, 10...
...Double-sided board, 11...Controller.

Claims (2)

[Claims] (1) A heating chamber that stores food, a radio wave radiator that radiates electromagnetic waves to heat the food, an antenna that detects a part of the electromagnetic waves in the heating chamber, and a detector that detects the electric power detected by the antenna. A high-frequency heating device that has a circuit and a controller that controls various device operations, and the antenna is formed of copper foil on a printed circuit board. (2) A claim characterized in that the antenna is formed of copper foil applied to one side of the substrate material, and there is no copper foil on the other side of the antenna other than the connection area between the antenna and the detection circuit, which is directly behind the antenna. (1) The high frequency heating device described.