JPH0124355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a microwave oven that can determine the type of food and determine the appropriate cooking time for the food.

<Conventional technology> Conventionally, a device has a function of determining the type of food and determining the appropriate cooking time according to the type of food.
Microwave ovens with the so-called "automatic heating method" do not require individual heating command keys for each type of food.
Gas sensors or humidity sensors are used to detect changes in the concentration of exhaust gas generated from heated foods or water vapor generated from foods, and the type of food is determined from the rate of change in the output signals of these gas sensors. ing.

<Problems to be Solved by the Invention> By the way, gases such as exhaust gas and water vapor generated from food do not change easily until the temperature of the food exceeds approximately 60°C. It is necessary for the exhaust gas or water vapor to be generated to a certain extent.

Therefore, when trying to thaw frozen food using a conventional "automatic heating method" microwave oven using such a sensor, even if the temperature of the food rises to 0 to 5 degrees Celsius and thawing is completed, the food will not be completely thawed. Sensors that respond to the generation of exhaust gas or the evaporation of moisture cannot detect the completion of defrosting. Therefore, in this type of microwave oven that uses the automatic heating method, it is not possible to defrost frozen foods, and the microwave oven is turned on manually after an appropriate heating time judged by the cook based on experience. If you don't cut the
Even after thawing is completed, heating of the frozen food continues until cooking is completed. However, since frozen foods are continuously heated using microwaves with the same power as when heating non-frozen foods, the food is not thawed evenly throughout the food, causing local temperature differences and uneven thawing. There are problems that arise.

The present invention has been made in view of these conventional problems, and is an improvement over the existing "automatic heating method"
It is a technical problem to provide a microwave oven that has an automatic thawing function for frozen foods in addition to the functions of the above microwave ovens, and that can uniformly thaw frozen foods.

<Means for Solving the Problems> In the present invention, as a technical means for achieving the above-mentioned problems, a microwave oven is configured as follows. In other words, a heating instruction switch commonly used for different types of food, a gas sensor installed in the exhaust passage of the heating chamber to detect gas or water vapor generated from heated food, and an input signal from this gas sensor as well as a built-in a microcomputer that issues a drive control command for the microwave generator according to the program, and a food discriminating means for discriminating the type of food in the heating chamber based on the rate of change of the gas sensor output signal; A microwave oven comprising a level setting means for setting a detection level for stopping heating of the gas sensor according to the determined type of food,
The microcomputer is equipped with an infrared sensor disposed above the heating chamber to detect the temperature of the food, and a drive switching means for switching the microwave generator between a continuous energization state and an intermittent energization state. frozen food discriminating means for discriminating whether or not the food in the heating chamber is a frozen food based on the rate of change of the output signal of the sensor; and the food discriminating means when the frozen food discriminating means determines that the food is a non-frozen food. a drive command means that issues a continuous energization command to the drive switching means and issues an intermittent energization command to the drive switching means when it is determined that the food is a frozen food; The apparatus is characterized in that it is further provided with thawing level setting means for setting a detection level for stopping heating of the infrared sensor.

<Function> With the above configuration, when the food to be cooked is inserted into the heating chamber and the heating instruction switch is turned on, the microwave generator is driven and heating is started.
The infrared sensor detects the rising temperature of the food, and the frozen food determining means determines whether the food is a frozen food based on the rate of change in the output signal of the infrared sensor. If it is determined that the food is frozen, the microcomputer controls the microwave generator to be energized intermittently via the drive switching means, and the food is thawed evenly by intermittent microwave output. When the defrosting occurs and the output of the infrared sensor reaches the heating stop detection level set by the defrosting level setting means, the driving of the microwave generator is stopped.

On the other hand, if the frozen food discriminating means determines that the food is a non-frozen food, the food discriminating means determines the type of food in the heating chamber from the rate of change in the output signal of the gas sensor, and the level setting means determines the type of food. A detection level for heating stop corresponding to the food is set, and the microwave generator is driven to continue heating the food until the output of the gas sensor reaches the set level.

<Example> Hereinafter, a preferred example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic cross section of an embodiment of the present invention,
A magnetron 9 that generates microwaves, an infrared sensor 8 that detects the temperature of food, a rotary chopper 10, and a thermistor 11 that corrects the temperature of the infrared sensor 8 are provided on the upper surface of the heating chamber 4. At the exhaust port 6 of the heating chamber 4, a humidity sensor is provided as the gas sensor 4 in this embodiment for detecting changes in water vapor generated from food. In addition, fan 5 and turntable 12
is set in place. The infrared sensor 8 is configured as an analog thermometer using a pyroelectric infrared detection element, and is disposed corresponding to a small hole in the heating chamber 4, and a chopper 10 is disposed on the front part to detect food. The chopper 10 intermittents the infrared rays emitted from the chopper 10 to obtain an electric signal corresponding to the constant rotation of the chopper 10. Further, the pyroelectric infrared detection element has a temperature between food and ambient temperature (chopper 1).
To measure the absolute temperature, it is necessary to measure the reference ambient temperature.In order to measure this ambient temperature, a thermistor 11 is placed near the infrared sensor 8. As shown in FIG. 2, it outputs a voltage corresponding to the temperature of the food with reference to the ambient temperature Ta.

FIG. 3 shows the electric circuit of the embodiment, in which the output of the infrared sensor 8 is input to the amplifier via the FET source follower, where it is amplified and smoothed, and then converted into a digital signal by the A-D converter 15. Ru. The outputs of the gas sensor 7 and thermistor 11 are also converted into digital signals by A-D converters 13 and 14, respectively. Each output of these A-D converters 13, 14, 15 and an output from a heating command keyboard, which will be described later, are input to the microcomputer 16 via an input/output interface 17. Power to the magnetron 9 is supplied from an AC power source via a door switch 20 and a relay switch. controlled. In addition, the heating command keyboard 1 has an automatic heating key 2 and a heating key 3.
As shown in FIG. 4, these are arranged on the front panel of the microwave oven body on the side of the heating chamber 4.

Next, the operation of the embodiment described above will be explained based on FIG. 5, which shows a program stored in the ROM of the microcomputer 16. First, when food is placed in the heating chamber 4 and the automatic heating key 2 is pressed, the relay switch 19 closes and power is supplied to the magnetron 9, which oscillates and outputs microwaves to start heating the food. (Step 51). Immediately after that, at time t=t ₀ , the initial value V ₀ of the output voltage of the infrared sensor 8 and the gas sensor (a humidity sensor is shown in this embodiment) 7
The initial value _U0 of the output voltage of is stored in the RAM (step 52). Furthermore, as long as it is possible to detect changes in the output voltage of the infrared sensor 8 over time, the time t= after a predetermined time has elapsed from time t=t ₀ .
The output voltage V ₁ of the infrared sensor ₈ and the output voltage U ₁ of the gas sensor 7 at t 1 are detected and stored in the RAM (step 53). Then, the above-mentioned infrared sensor 8
_The predetermined time ₍ t ₁
-t ₀ ) of the output voltage of the infrared sensor 8 is determined, and it is determined whether this change rate is positive or negative (step 54).

Here, if the food inserted into the heating chamber 4 is a non-frozen food and the food temperature T ₀ at time t=t ₀ is higher than the ambient temperature Ta, the second
As is clear from the correspondence between the output voltage of the infrared sensor 8 and the food temperature indicated by the dotted line in the figure,
Since V ₁ -V ₀ >0, the food is determined to be a non-frozen food, and the process proceeds to step 61 where it is heated in the same manner as the existing "automatic heating method".

This "automatic heating method" will be explained with reference to Figure 6. Figure 6 shows how the terminal voltage of the gas sensor 7 changes over time depending on the type of food being cooked. ,
Depending on the ingredients contained in the food, the boiling point varies, for example, ethyl alcohol at 78.3°C, acetic acid at 118°C, and acetaldehyde at 20.8°C, so food exhibits unique characteristics depending on the type of food, as shown in the figure. Therefore,
Each output voltage of the gas sensor 7 at time t= _t0 and time t= _t1 memorized in steps 52 and 53, respectively
The ratio U ₁ /U ₀ of U ₀ and U ₁ is calculated (step 61),
The type of food can be determined from the magnitude of this value U ₁ /U ₀ . For example, when t ₀ = 30 seconds and t ₁ = 40 seconds, if the sake sake is represented by the curve S, then U ₁ /U ₀ =U _S1 /U _S0 <0.9,
For side dishes and rice bowls, U ₁ / U ₀ = U _D1 / U _D0 = 0.9~
0.95, since the preparation is usually wrapped in wrap film, gas does not come out until a certain vapor pressure is reached, so U ₁ /U ₀ = U _H1 /U _H0 = 0.95 to 1.0 (However, in Figure 7, U _H0 = U (displayed as _H1 = U _H ). In this way, the type of food is determined from the magnitude of the value of the rate of change U ₁ /U ₀ of the output voltage of the gas sensor 7, and if this value is between 0.95 and 1.0, the
The detection level V _HS shown in the figure, if it is 0.9 or less, the detection level V _SS , and if it is 0.9 to 0.95, the detection level V _DS.
are set respectively. These levels are set so that each of the identified food products can have a good finish. Once this setting has been made, the output voltage of the gas sensor 7 is continuously checked, and when it is determined that this output voltage has reached the detection setting level (step 62), the microwave output is stopped (step 60). , heating and cooking is completed.

On the other hand, regardless of whether the food is a frozen food, the food temperature T _{0 at time t = t 0 is} lower than the ambient temperature Ta, and the food temperature T ₁ at time t = t ₁ is still lower than the ambient temperature Ta. For example, as is clear from the correspondence between the output voltage of the infrared sensor 8 and the food temperature shown by the solid line in FIG. 2, V ₁ -V ₀ <0. Note that even if T ₀ < Ta, if the output voltage T ₁ becomes higher than the ambient temperature Ta, there is a possibility that V ₁ - _{V 0} ≧ 0, but in the case of V ₁ - _{V 0} > 0. for,
Steps from step 54 as in the case of T ₀ > Ta
Of course it will go on to 61. In any case, step
If it is determined in step 54 that V ₁ -V ₀ ≦0, the process proceeds to step 55, where the thermistor 11 sets the chopper 1.
0, that is, the ambient temperature Ta, and based on this value, the microcomputer 16 calculates the output voltage Vr of the infrared sensor 8 corresponding to a temperature of -1°C (step 56). Next, the output voltage V ₁ of the infrared sensor 8 at time t=t ₁ and the output voltage
It is determined whether the difference with Vr is positive or negative (step 57),
If V ₁ −Vr≧0, the food is determined to be frozen food,
Thereafter, thawing is performed while the microwave output is intermittent (step 58) in order to thaw the frozen food evenly. When it is detected by the output voltage of the infrared sensor 8 that the frozen food has risen to a predetermined temperature (several degrees Celsius) (step 59), the microwave output is stopped (step 60) and the thawing of the frozen food is started. Complete. Note that in step 57, V ₁ −Vr<0
If it is determined that the temperature of the food is over -1℃, in this case, the food is considered not to be frozen even if the temperature is below 0℃, and the process goes to step 61.
Then, the above-mentioned "automatic heating cooking" is performed.

<Effects of the Invention> As detailed above, according to the microwave oven of the present invention, by simply operating a single heating instruction key, the microwave oven of the existing "automatic heating method" can be heated according to the type of food. In addition to being able to heat the food by automatically setting an appropriate cooking time, it is also possible to identify the frozen food and automatically defrost it, which has the advantage of uniformly defrosting the frozen food.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of the present invention, and FIG.
The figure shows an output characteristic diagram of an infrared sensor, which is a part of its components, FIG. 3 is its electrical circuit diagram, FIG. 4 is its front view, FIG. 5 is a flowchart explaining its operation, and FIG. 6 is FIG. 3 is a characteristic diagram illustrating the operation of food discrimination means. 2... Automatic heating key (heating instruction switch),
4... Heating chamber, 7... Gas sensor, 8... Infrared sensor, 9... Magnetron (microwave generator), 16... Microcomputer.

Claims (1)

[Claims] 1. A heating instruction switch commonly used for different types of food, a gas sensor installed in the exhaust passage of the heating chamber to detect gas or water vapor generated from heated food, and an input signal from this gas sensor as well as a built-in a microcomputer that issues drive control commands for the microwave generator according to a programmed program; and a food discriminating means for discriminating the type of food in the heating chamber based on the rate of change of the gas sensor output signal; a level setting means for setting a detection level for stopping heating of the gas sensor according to the type of food being heated, an infrared sensor disposed above the heating chamber and detecting the temperature of the food; drive switching means for switching the microwave generator between a continuous energization state and an intermittent energization state;
Frozen food discriminating means for discriminating whether or not the food in the heating chamber is a frozen food based on the rate of change of the output signal of the infrared sensor; drive command means for driving the determining means and issuing a continuous energization command to the drive switching means, and issuing an intermittent energization command to the drive switching means when it is determined that the food is a frozen food; A microwave oven characterized in that the microwave oven is further equipped with a defrosting level setting means for setting a detection level for stopping heating of the infrared sensor when the infrared sensor is activated.