JP2893804B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating device that automatically detects the presence or absence of food, the state of thawing, and the like.

2. Description of the Related Art A conventional thawing detection method of a high-frequency heating device will be described.

In the time auto, a heating time is set in advance for each food weight, and heating is performed up to a time corresponding to the weight by inputting the weight of the food as a key.

In addition, the weight sensor automatically detects the weight of food, so there is no need for key input operation of the weight compared to time auto.However, after weight detection, the weight sensor heats up to a preset time like time auto. Has become.

Furthermore, the concept of detecting a change in the state of food by the amount of reflected power from the heating chamber has been considered for a long time, as shown in Japanese Patent Application Laid-Open No. 56-159087, but has not been realized. .

Problems to be solved by the invention When thawing is detected by a method such as time auto or weight sensor, thawing is completed by heating for a certain period of time regardless of the initial temperature, shape, placement, components, etc. of the food, so the finish is completed. The state varies greatly. If thawing is detected on a product with a high initial temperature (for example, a frozen product as brought back from shopping), it may boil or a product with a low initial temperature (for example, food that has been stored for a long time in a freezer with a high cooling capacity). )
When the detection of the thawing was performed, the thawing was not completed at all, which was extremely inconvenient for the user.

Next, if the reflected power is used, it is theoretically possible not only to determine the weight based on the initial reflected power, but also to estimate the initial temperature of the food and how to put it by using the time change of the reflected power. However, in practice, the configuration of the antenna that captures the reflected power, the configuration of the detection circuit, or the matching between the two are poor, and only data with a large variation as the detection output can be obtained. In particular, although various configurations of the antenna 8 of the type in which the conductor is bent and attached to the circuit 9 as shown in FIG. 8 have been considered, it is very difficult to suppress variations in size (length), mounting angle and matching degree. In addition, there is a problem that it is not easy to maintain the matching accuracy with the detection circuit.

An object of the present invention is to solve such a conventional problem, and to accurately extract reflected power with a simple configuration and to accurately defrost food.

Means for Solving the Problems In order to solve the above problems, a high-frequency heating device of the present invention includes a heating chamber for storing food, a radio wave radiating section for radiating and heating electromagnetic waves to the food, and an electromagnetic wave in the heating chamber. An antenna for detecting a part of the antenna, a detection circuit for detecting the power detected by the antenna, and a controller for controlling the operation of various devices, the antenna is formed of copper foil on a printed circuit board, the printed circuit board A ground plane formed of another copper foil above surrounds the antenna.

The high-frequency heating device of the present invention detects reflected power, which varies depending on the state of food placed in the heating chamber, with an antenna formed of copper foil on a printed circuit board, detects and detects the reflected power, and controls the reflected power. Since the ground plane formed of another copper foil surrounds the periphery of the antenna, the matching state changes depending on the width of the gap between the antenna and the ground plane, and has the effect of changing the sensitivity. Similarly, the ground plane can suppress radio wave leakage from around the antenna to the outside and noise from the outside to the antenna.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the configuration of a high-frequency heating apparatus according to an embodiment of the present invention. A radio wave 4 is radiated from the radio wave radiating unit 3 to the food 2 arranged in the heating chamber 1. At this time, depending on the state of the food 2, a part 5 of a radio wave including a reflected wave passes through a slit 6 opened in the wall of the heating chamber 1 and is detected by an antenna 8 fixed by a mounting bracket 7. The antenna 8 is a detection circuit 9
Are configured and connected on the same double-sided substrate 10,
The radio wave detected by the antenna 8 is detected by the detection circuit 9 and sent to the controller 11. The controller 11 knows the state of the food according to the amount of detection, determines the optimal thawing time, and controls the operation of the radio wave radiating unit 3 (that is, stops the oscillation when the optimal thawing time comes).

FIGS. 2 and 3 are diagrams rotated 180 degrees around the AA 'axis, showing the front and back configuration of the double-sided board 10, in which the antenna 8 and the detection circuit 9 are arranged. The antenna 8 is surrounded by a copper foil ground plane 12, and the antenna 8 itself is also made of copper foil. The antenna 8 and the detection circuit 9 are connected by a through hole 13, and the back surface of the antenna 8 is a through hole.
Except for the 13 connection parts, there is no copper foil. The detection circuit 9 is arranged behind the ground plane 12 so as not to overlap with the back surface of the antenna 8. Here, the antenna 8 is a copper foil antenna, which is different from a general strip antenna with a ground on the back side, and the amount of detection is considered to be substantially determined by the length of the long side l.

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

Here, as an effect of the embodiment, since the antenna and the detection circuit are formed on the front and back of the same double-sided board and connected by through holes, matching accuracy is obtained. In addition, since the antenna is surrounded by the ground plane and fixed to the wall of the heating chamber by the mounting bracket, it is possible to suppress leakage to the outside and hardly detect noise from the outside.

FIG. 5 is a circuit diagram showing an example of the detection circuit 9. The power P _IN obtained from the antenna is detected by a surface-mounted detection diode 14, filtered by an LPF (low-pass filter) 16, and sent to a controller as a detection output V _OUT . As described above, when a detection circuit is configured on a double-sided board, the inductance and capacitance components of the LPFs 15 and 16 are often configured by microstrip lines.

FIG. 6 is a characteristic diagram showing a time change of the detection output _VOUT . An example of a control method in the controller will be described. Time t required for one turn of the turntable of the high-frequency heating device
Some between _TT1 interval t _1, t _2, is divided into ..., the maximum value V _t1, V _t2, etc. at each interval. At this time, since _Vt1 changes in accordance with the weight of the food, the weight m can be obtained from _Vt1 on the contrary as shown in FIG. Also, since V _t1 −V _t2 roughly corresponds to the initial temperature of the food, V _t1 −V _t2 conversely changes as shown in FIG.
_t1 from -V _t2 can estimate the initial temperature T. In the above way,
The initial state of the food can be known, and the optimum thawing time can be determined.

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 copper foil on a printed circuit board, dimensional accuracy is good. In the case of thawing detection of a high-frequency heating device as in this case, the radio wave distribution changes in a complicated manner due to differences in the shape of the heating chamber, the radio wave radiating portion, and the like. According to the present invention,
Since the dimensional accuracy is extremely good, the effect in practical use is great, considering variations during mass production.

In addition, the board with the antenna is mounted near the oven wall, but as shown in Fig. 9, the distance between the coupling hole on the oven and the antenna is more accurate than that of the antenna in which the conductor is bent and attached to the detection circuit. The state is extremely stable.

Similarly, as compared with the antenna of FIG. 9, the distance between the oven and the antenna substrate can be reduced, the size can be reduced, the space is not required, and the size and appearance of the high-frequency heating device are not affected.

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

Further, the matching state is changed by the width of the gap between the copper foil antenna and the ground plane of the copper foil formed so as to surround the antenna (that is, the area where the copper foil is not present and the board material is exposed). And the sensitivity can be changed freely. The optimum range of the circuit input is determined in consideration of the performance and reliability of the detection circuit. However, by setting the width of the gap in accordance with the optimum range, the desired circuit input can be easily provided.

Similarly, the ground plane can suppress radio wave leakage from the surroundings of the antenna to the outside and noise from the outside to the antenna, so that detection and control can be stabilized.

Also, when there is no copper foil on the back of the antenna, there is no need to connect to the detection circuit via a transmission line such as a 50Ω line after the antenna is completed, such as a microstrip antenna with copper foil on the back, and Can be directly connected to the detection circuit. Especially when the antenna and the detection circuit are configured on opposite sides of the board, they can be connected only with through holes.
The transmission line can be omitted, and compactness is possible.

Furthermore, high-frequency materials are expensive as substrate materials, but if the present invention enables downsizing, significant cost reduction can be achieved.

Further, unlike the antenna shown in FIG. 9, since the antenna can have a planar configuration, coating with a resist or the like can be easily performed, and there are effects such as an increase in work efficiency.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a high-frequency heating apparatus according to a first embodiment of the present invention, FIGS. 2 and 3 are configuration diagrams showing an example of the configuration of an antenna and a detection circuit, and FIG. FIG. 5 is a circuit diagram showing an example of a detection circuit;
FIG. 6 is a characteristic diagram showing a time change of the detection circuit output V _OUT , FIG. 7 is a characteristic diagram showing a relationship between the detection circuit output V _t1 and the food weight m, and FIG. 8 is a graph showing the detection circuit output V _t1 −V _t2 . Food initial temperature T
FIG. 9 is a configuration diagram showing an example of a configuration of a conventional antenna and a detection circuit. 1 ... heating room, 2 ... food, 3 ... radio wave radiator, 7 ...
Mounting bracket, 8 Antenna, 9 Detection circuit, 10
Double-sided board, 11 ... Controller.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masato Kajita 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-company (72) Inventor Tomomi Moriyama 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A 1-286285 (JP, A) JP-A 62-178001 (JP, A) JP-A-62-236420 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05B 6/68

Claims (2)

(57) [Claims] 1. A heating chamber for storing food, a radio wave radiating section for radiating and heating an electromagnetic wave to the food, an antenna for detecting a part of the electromagnetic wave in the heating chamber, and detecting power detected by the antenna. And a controller for controlling the operation of various devices, the antenna is formed of copper foil on a printed circuit board, and the antenna is formed around a ground plane formed of another copper foil on the printed circuit board. A high-frequency heating device configured to surround. 2. An antenna is formed of copper foil applied to one surface of a substrate material, and there is no copper foil in a portion directly behind the antenna other than a connection portion between the antenna and a detection circuit on the other surface. The high-frequency heating device according to claim 1, wherein