JPH01286285A - High frequency heating device - Google Patents

Abstract

PURPOSE:To eliminate the abnormal exothermic of each part of a device and improve the reliability by detecting a reflection amount of high frequency within a heating chamber and stopping the oscillation movement when the output signal is out of a determined time and a determined range. CONSTITUTION:When a heated material 6 is heated within a heating chamber 6, the reflected wave quantity of high frequency is detected as a voltage signal Vs by a wave detecting means 15. As the reflected wave is reduced when the food 6 is increased, and increased when it is reduced, it is possible to judge whether the condition is closed to empty baking or not. When the voltage signal Vs exceeding a determined value VO continues for a determined time, a control means 18 makes a power switch 19 turned off to stop the movement.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a high-frequency heating device that performs dielectric heating using high-frequency waves.

2. Description of the Related Art Conventionally, in high-frequency heating devices such as microwave ovens, a magnetron is generally used as a high-frequency oscillator for generating high-frequency waves. Since the magnetron is driven by a DC voltage of approximately 3 kV to 4 kV and oscillates at a high frequency, it is necessary to boost the commercial power source as its power source, and a high voltage transformer is used as its power source. The power conversion efficiency of the magnetron and high-voltage transformer used is approximately 70% to 80%, and the heat generated by the loss is forcedly cooled by a fan, thereby realizing a compact high-voltage transformer and magnetron.

Problems to be Solved by the Invention These conventional high-frequency heating devices have the following problems.

As shown in FIG. 5, in a method in which food 2, etc. in a heating chamber 1 is heated by high frequency waves from a magnetron 4 which receives the output of a high voltage transformer 3, the capacity of the cooling fan 5 is the maximum when the high voltage transformer 3 and magnetron 4 are heated. It was designed to be able to be cooled without causing damage even under conditions of rising temperatures. The maximum temperature rise condition is when the variation in commercial power supply voltage is maximum and the input is maximum due to variation in each component.
The room temperature is high and the installation location is a place where it is difficult to blow cooling air. Furthermore, the fact that the heating chamber is in an empty firing state with no object to be heated at all is a major factor in increasing the temperature rise. Even when the object to be heated, such as the food 2, is small and is close to dry baking, the temperature rise of the magnetron 4 becomes extremely high. this is,
This is because the radio waves emitted from the magnetron 4 are not consumed within the heating chamber 1 but are reflected back to the magnetron 4.

This caused the magnetron to heat up abnormally, shortening its lifespan. Furthermore, under conditions close to dry firing, parts placed on the walls of the heating chamber and near the magnetron also experienced a large temperature rise, leading to a drop in reliability.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a high-frequency oscillator, a heating chamber into which the high-frequency waves radiated by the high-frequency oscillator is fed and stores an object to be heated such as food; an antenna shorter than a quarter wavelength of the radiation frequency of the high-frequency oscillator; an attenuator that attenuates the power input from the antenna; a detection means for detecting the oscillation state of the high-frequency oscillator via the antenna; and the detection means The configuration includes a control means for stopping the operation if the output signal of the controller is outside a predetermined range for a predetermined period of time.

Function According to the present invention, the frequency band of the high frequency means for heating food etc. (for example, 2.450 MHz in the case of a general microwave oven)
z), it is possible to detect the amount of reflected radio waves emitted into the heating chamber and not absorbed by the food or the like. This reflected radio wave is small when there is a lot of food in the heating chamber, and increases when there is little food in the heating chamber, so it can be determined whether the state is close to dry baking. In conditions close to dry firing, the high-frequency oscillation operation is automatically stopped by the control means after it has been operated for a predetermined period of time, so there is no abnormal heat generation of each component, etc., and the cooling means can be simplified. The reliability of each component such as an oscillator can be improved.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a block diagram of the main body of a high-frequency heating device according to an embodiment of the present invention. In Figure 1, 6 is an object to be heated such as food, 7
8 is a heating chamber, and 8 is a high frequency oscillator (magnetron).

9 is a high voltage transformer; 10 and 11 are a high voltage capacitor and a high voltage diode, respectively; the output of the high voltage transformer 9 is voltage doubled and rectified by a high voltage capacitor 10 and a high voltage diode 11, and is applied to the magnetron 8. The high frequency waves emitted from the magnetron 8 are radiated into the heating chamber 7 through the waveguide 12 . An antenna 13 is shorter than 1/4 wavelength of the oscillation frequency of the magnetron 8.

(3 to 5 mm in the present invention) 14 is an attenuator, 15 is a detection means, 16 is an amplifier for amplifying the detected signal, 17 is a cooling fan, 18 is also used for the amplified detected signal, and the main This control means includes a timer circuit that controls the power switch 19.

FIG. 2 is a circuit diagram of the detection means 15 for detecting the signal received by the antenna 13. 2o is a 50 ohm resistance, 21
is a detection diode, 22, 23 is a resistor, and 24 is a bypass capacitor. Through these, the reflected radio wave component of the radio wave radiated by the magnetron 8 received by the antenna 13 is converted into a voltage signal V.
Detected as s. Note that 14 is an attenuator, and the power radiated by the magnetron 8 into the heating chamber 7 is several hundreds of watts, so that the detection means 14 does not receive an excessive input.

FIG. 3 is a diagram in which the detection means 15 is composed of a microstrip line.

Copper foil patterns 26 and 27 are etched onto a dielectric substrate 25 having a certain dielectric constant E'.

The copper foil section 26 has a characteristic impedance of 50 ohms, and the section 27 is grounded. By configuring the detection means 15 on the microstrip line, it is easy to optimally design the length of the line according to the frequency band to be detected, and since etching is performed, the detection accuracy is improved. .

FIG. 4 shows the relationship between the signal voltage Vs detected by the detection means 15 when the object to be heated 6 is heated in the heating chamber 7 and the weight of the object to be heated. Even if the weight of the object to be heated is the same, the dielectric constant changes depending on the type of the object, such as meat or soup, or depending on the state of the object, such as whether it is frozen, and the detection signal voltage Vs changes.

However, below a certain level, that is, in a state where the number of objects to be heated is small and is close to dry firing, a signal exceeding Vo is detected as a detection signal voltage. When there is no object to be heated and there is no object to be heated, in a dry firing state or in a state close to dry firing, the step-up transformer 9 and the magnetron 8 generate more heat as described above, shortening the life of the parts and reducing the reliability of the product. For this reason, in FIG. 1, the detection signal voltage is transmitted to the control means 18, and when a signal equal to or higher than vo is generated, the power switch 19 is turned off and the operation is controlled to be stopped. However, if the detection signal is stopped as soon as it exceeds vo, there is a problem that if the object to be heated is small, it will not operate at all. is the time required to heat up sufficiently (for example, the radio wave output is 500
(about 10 minutes if using a W microwave), then turn the power switch 1.
9 is turned off to stop the operation.

By employing the above configuration, the dry firing state does not continue for a long time, so that the maximum temperature rise value of each component including the magnetron 8 can be suppressed to a low value. Therefore, parts with low heat resistance can be used, and costs can be reduced. Furthermore, since the cooling configuration can be made simpler, the degree of freedom is increased, which is advantageous in terms of cost.

If the control means is such that when the dry firing detection function is activated and the operation stops, the switch will not be turned on again until each part has cooled down (approximately 30 minutes), further increasing reliability.

Effects of the Invention As described above, the high frequency heating device of the present invention provides the following effects.

(1) Since the dry firing state is detected by utilizing the fact that the detection signal becomes large when the number of objects to be heated is small, and the operation is stopped after a predetermined time, there is no abnormal temperature rise in each component of the device.

Therefore, a high-frequency heating device with long durability and high reliability can be realized.

(2) Since the temperature rise during dry baking is reduced, parts with low heat resistance grade can be used, and the cooling configuration can be simplified, so the cost of the high frequency heating device can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a high-frequency heating device according to an embodiment of the present invention;
Fig. 2 is a circuit diagram of the detection means of the same device, Fig. 3 is a plan view of the detection means of the same device configured on a microstrip line, Fig. 4 is a diagram of the weight of the heated object and the signal characteristics of the detection means,
FIG. 5 is a sectional view of a conventional high frequency heating device. 6...Object to be heated, 7...Heating chamber, 8.
...High frequency oscillator, 13...Antenna,
14... Attenuator, 15... Detection means,
18... Control means. Name of agent: Patent attorney Toshio Nakao and 1 other person6-
--Double wide curtains, Hg chamber δ--High M spear J each uu section (Magnetron 21 δ--P
J Keiji I Fig. 1 Fig. 12 Fig. 3 Fig. 4 θ d1M dream arm! Quantity Figure 5

Claims (1)

[Claims] a high-frequency oscillator; a heating chamber in which the high-frequency waves radiated by the high-frequency oscillator are supplied with power and house objects to be heated such as food;
an antenna shorter than a quarter wavelength of the radiation frequency of the high-frequency oscillator; an attenuator that attenuates the power input from the antenna; a detection means that detects the oscillation state of the high-frequency oscillator via the antenna; A high-frequency heating device comprising control means for stopping operation if an output signal of the means is outside a predetermined range for a predetermined period of time.