JPH0641815B2 - Microwave oven with ultrasonic microphone - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven with an ultrasonic microphone that detects and controls the state of gas generated from food in response to heating of the food.

2. Description of the Related Art As shown in FIG. 9, a conventional microwave oven with a sensor controls a device by detecting a change in the resistance value of a humidity sensor 28 by dividing the voltage of a reference voltage power supply 29 with a resistor 39. There is. (For example, Japanese Laid-Open Patent Publication No. 53-77365) Problems to be Solved by the Invention Since such a conventional method uses the voltage across the resistor 39 as a control signal, each configuration is required when a large number of products are produced. Variations in the resistance of the element humidity sensor 28, the resistance 39, and the voltage of the power supply 29 lead to variations in the control voltage signal, making management difficult. The present invention has been made in view of the above point, and an object thereof is to provide a means for detecting the heating state of food with a simple configuration.

Means for Solving the Problems In order to solve the above problems, the present invention uses an ultrasonic microphone that uses a ceramic piezoelectric element having a resonance frequency in the ultrasonic region as a sensor, and a low level that occurs as heating progresses. The change of the frequency signal is detected as the change of the voltage signal of the microphone, the voltage is increased by the amplifier and the control output is obtained by the voltage comparator.

Effect The present invention, which has the above-described configuration, can be used as a cooking sensor having stable characteristics only by managing changes in the microphone voltage. That is, it is possible to perform control with a simple configuration, which does not require a reference voltage or a resistor for voltage division in the conventional example.

Embodiment FIG. 1 shows an embodiment of a microwave oven with an ultrasonic microphone according to the present invention. In FIG. 1, the ultrasonic microphone 1
Is connected to the amplifier 2 for voltage amplification and the comparator 3 for voltage comparison, and the output of the comparator 3 is controlled by the controller 4 in this case to control the oscillation of the magnetron 5.

Food 7 is arranged in the heating chamber 6. A part of the cooling air is guided to the heating chamber 6 via the duct 9 by the magnetron cooling fan 8.

A part of the cooling air is shown by a solid arrow line 10 and a gas such as moisture generated from food is shown by a dotted line 11. Gas such as water generated from the cooling air and food is sent from the inside of the heating chamber 6 to the outside through the exhaust unit 12.

An ultrasonic microphone is attached to the exhaust unit 12.

Using Fig. 2 to Fig. 5, Fig. 6 shows an example of actual measurement configuration, and Fig. 7 shows the change in the result depending on the type of ultrasonic microphone, and Fig. 7 shows the drip-proof type 41KH.
z The results when using an ultrasonic microphone are shown.

FIG. 2 shows the structure of the microwave oven used in the experiment. The microwave oven has a radio wave output of 500 W, and the radio wave of the magnetron 5 is
The food tray 14 is provided to the heating chamber via the waveguide 13 and the food plate 14 is rotated by the motor 15. FIG. 3 shows a state in which the ultrasonic microphone 1 is attached to the exhaust unit 12. Figure 4 shows various ultrasonic microphones tested under the same conditions.
The structure of a drip-proof 41 KHz ultrasonic microphone having the largest output signal is shown. Piezoelectric element 16, silicon rubber spacer 17, terminal 18, vibrating portion 19, vibrating case 2
0, lead wire 21, inner ring 22, terminal plate 23, and silicone rubber 24.

(National Technica Reporter
t 504 to 514 Vo29.NO.3 JAN 1983) Fig. 5 shows a block diagram of the measuring circuit. Ultrasonic microphone 1
The output of the piezoelectric element 16 in the amplifier 25 with a gain of 40 dB
(YHP model 65A) was connected to an AC voltmeter 26 (manufactured by NF Circuit, model M-177, 300 mV range), and the DC output terminal of the voltmeter 26 was connected to the input of the recorder 27 to perform an experiment. .

Examples of results are shown in FIGS. 6 to 8, where the horizontal axis represents time,
The vertical axis shows the relative value of the magnitude of the output signal, and the relative ratio of the signal output is constant in each graph. FIG. 6 shows an example of the result of an experiment in which the type of ultrasonic microphone and the resonance frequency are changed when 500 cc of water is heated as a load. (a) 20KHz, (b) 35KHz, (c) 40KHz, (d) 40KH
z, (e) 60 KHz, and open type except the drip-proof type (d). In the figure, the arrows indicate the boiling tow points visually confirmed and entered. It can be seen that the output changes with boiling tow in the 40 KHz band of (c) and (d).

Fig. 7 shows a drip-proof microphone with a water content of 200cc, 40
Output examples when the output is changed to ₀ cc and 1000 cc and continuously recorded from the heating start time T ₀ are shown in (a), (b) and (c), respectively. It can be understood that the timing of boiling tow of water can be understood from the change in output voltage by the steam generated from water. These are the phenomena that the output of the piezoelectric element 16 is generated at a low frequency due to the boiling tow, as is clear from the time scale of FIG. As a mechanism, it is presumed that the state of the exhaust airflow changes before and after the boiling tow, and the state change causes some low-frequency physical change to the piezoelectric element 16 through the thin plate 20 to generate a low-frequency signal. it can.

FIG. 8 shows an example of output signals when 225 g of frozen shimai and 300 g of sliced carrots are frozen and wrapped in wrap and continuously heated as a load under the same measurement conditions. As can be understood from the above measurement example, the threshold voltage ΔV in the comparator 3 of FIG.
_With the configuration in which the signal output voltage from the piezoelectric element 16 in the ultrasonic microphone 1 is compared with _T , the output of the comparator 3 can be correlated with the heating progress degree of the food 7. Especially, the boiling point can be detected. If the magnetron output 5 is stopped by the controller 4 using this detection signal, automatic cooking becomes possible. It is also possible to use a controller 4 to notify the completion of cooking with a buzzer or a lamp. Furthermore, increasing the amplification of the amplifier and devising the installation method of the ultrasonic microphone, and increasing the detection sensitivity, it is possible to detect not only at the boiling toe point but also at a water temperature of 60 ° C where the water vapor pressure increases rapidly. Yes, in this case, if the threshold voltage can be manually variably set, many effects can be expected such as adjustment of cooking completion.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to realize a microwave oven with a function of detecting the heating state of food with an extremely simple structure.

That is, when using a humidity sensor or gas sensor,
It essentially utilizes the grain boundary phenomenon of the sensing element. Therefore, in order to prevent clogging of grain boundaries, there are many complicated measures for maintenance such as keeping the temperature warm by a heater and periodically burning away dirt with a heater, but the present invention requires such a measure. Since it does not, the detection function can be configured at low cost with low power consumption. When a condenser microphone or the like provided on the side surface of the heating chamber is used, the condenser microphone or the like generally uses a signal in the 10 KHz band, and the heating chamber has a motor or transformer for a microwave oven. A lot of noise is generated in the audible band such as electromagnetic noise and wind noise caused by a fan. Therefore, although it is difficult to perform stable control under the influence of such noise, the present invention is based on the configuration using the ultrasonic microphone including the piezoelectric element having the resonance frequency of 20 KHz to 60 KHz. Since it is not affected, stable control can be performed. Further, if a drip-proof type sensor configuration is adopted in which the vibration case 20 is interposed between the exhaust unit 12 and the piezoelectric element 16, stable sensor performance can be secured for a long period of time. In addition, in the embodiment, one heating chamber is provided with an exhaust portion, but two or more portions that are exhausted from the heating chamber are provided, and an ultrasonic microphone is provided in either one of the heating chambers. It is included.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a microwave oven with an ultrasonic microphone according to an embodiment of the present invention, FIGS. 2 to 4 are cross-sectional views of main parts of the microwave oven, and FIG. 5 is a block diagram of the microwave oven. Sixth
FIG. 8 to FIG. 8 are waveform charts showing the measurement results of the microwave oven, and FIG. 9 is a block diagram of a conventional example. 1 ... Ultrasonic microphone, 2 ... Amplifier, 3 ... Comparator, 4
...... controller, 6 ...... heating chamber, 12 ...... exhaust unit, △ _{V T} ...
... Threshold voltage, 16 ... Piezoelectric element, 20 ...
… Vibration case (thin plate).

Claims (2)

[Claims] 1. An ultrasonic microphone composed of a piezoelectric element is fixed to an exhaust portion of a heating chamber where a gas such as moisture generated by heating from a food placed in the heating chamber is discharged, and an output of the ultrasonic microphone is provided. A microwave oven with an ultrasonic microphone in which the output of the magnetron is controlled by the controller based on the output obtained by comparing the voltage amplified by the amplifier with the voltage of the preset threshold voltage by the comparator. 2. The microwave oven with an ultrasonic microphone according to claim 1, wherein the ultrasonic microphone has a piezoelectric element having a resonance frequency in the range of more than 20 KHz and less than 60 KHz.