JPH01219424A - Microwave oven with piezoelectric element sensor - Google Patents

Abstract

PURPOSE:To enable always tables finished state of a worked product to be attained even under a repetitive use by a method wherein a temperature compensating element for use in detecting an atmosphere temperature of a piezoelectric element is applied and a gain of an amplifier is made variable in response to a signal thereof. CONSTITUTION:When a cooking start button 34 is depressed and water vapor is started to generate from a heated object 12, a differential signal pulse of a piezoelectric element sensor 1 is generated. If its value exceeds a set voltage, an energization of a magnetron 13 is terminated. Subsequently, when the same amount of heated objects 12 is heated, water vapor is similarly generated and a differential signal pulse is generated. Then, as a temperature of a discharging part 8 is increased, a signal level of the differential signal pulse is decreased. However, since as a resistance of a thermistor 6 is varied, an amplification gain of an amplifier 18 is also varied, a heating operation is terminated at the same heating time even if the same amount of heated objects 12 are repeatedly heated without depending upon an atmosphere temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oven, which detects and controls the state of gas generated from food as the food is heated, and uses a piezoelectric sensor as a detection element. This is related to the microwave oven used.

Conventional technology As a conventional sensor for detecting the cooking status of a microwave oven,
As shown in FIG. 9, the microwave oven is controlled by detecting a change in the resistance value of the humidity sensor 36 by dividing the voltage of the reference voltage power source a7 with a resistor 38 and comparing the voltage. (For example, Japanese Unexamined Patent Publication No. 53-77365) As shown in FIG. 10, as a simple means of detecting a heating state, a polarization current is generated due to thermal change of water vapor to the piezoelectric element sensor 1. However, there is a means to detect the polarization current.

(For example, Japanese Unexamined Patent Publication No. 61-269890) Problems to be Solved by the Invention When using such a conventional humidity sensor 36,
Since the voltage across the resistor is used as a control signal, if a large number of units are produced, variations in the resistance of each component, the humidity sensor 36, and the voltage of the power supply will lead to variations in the control voltage signal, making management difficult. there were.

Furthermore, when the piezoelectric element sensor 1 is used, due to the temperature characteristics of the piezoelectric element sensor, if the object to be heated 12 is repeatedly heated in a microwave oven, the temperature of the exhaust section 8 to which the piezoelectric element sensor 1 is attached will rise. Since the detected polarization current of the piezoelectric element sensor 1 also decreases, the same amount of heated object 12
When heated, there was a problem that the heating end time was not constant.

Means for Solving the Problems In order to solve the above problems, the present invention uses a temperature compensation element that detects the ambient temperature of a piezoelectric element sensor, and is configured to vary the gain of an amplifier based on the signal. be.

According to the present invention, the decrease in polarization current caused by the temperature characteristics of the piezoelectric element sensor due to the temperature rise in the exhaust path is corrected by the signal of the compensation element, and a stable output signal of the piezoelectric element sensor is generated regardless of the ambient temperature. However, the cooking state of the heated object can be detected with a simple configuration.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIGS. 1(a) and 1(b) are perspective views of a piezoelectric sensor 1 according to an embodiment of the present invention, and a piezoelectric sensor 1 and a temperature correction element 6.
The figure shows the installation state. In FIG. 1 (at), a piezoelectric ceramic element 1 made of lead titanate or the like is provided with electrodes 2.3 on both sides, and each electrode 2.3 has a lead wire 4.
5 is wired. Further, as shown in FIG. 1(b), the piezoelectric element sensor 1 and the temperature correction element 6 (a thermistor in one embodiment of the present invention) are installed in the exhaust part 8 of the heating chamber 7 through holes 9. is arranged adjacent to the screw 10.1.
1 is attached to the exhaust wall.

FIG. 2 is a block diagram of the main body of a microwave oven having the piezoelectric element sensor 1 of the present invention. A heating chamber 7 into which the object to be heated 12 is taken in and taken out, and a magnetron 1 which heats the object to be heated 12 at high frequency.
3. A piezoelectric element sensor 1 provided in the heating chamber exhaust section 8, a thermistor 6 as a correction element for temperature compensation, and a magnetron 13
A cooling fan 14 that cools the air, a duct 15 that blows part of the air from the cooling fan 14 into the heating chamber, a door switch 16, and a filter 17 that filters the output signal of the piezoelectric sensor 1 (
(hereinafter referred to as a filter), an amplifier 1B that amplifies the signal of the filter 17, a setting means 21 that determines the completion of cooking of the object to be heated 12, a comparator 22 that compares the signal of the amplifier 18 and the signal of the setting means 21, and the comparator 22 of the comparator 22. It is comprised of a control means 23 that detects a signal and controls the main body, and a biasing means 24 that biases the magnetron 13. Further, a heated object 12 is placed in the heating chamber 7, and a portion of the cooling air from the magnetron 1a is guided into the heating chamber T via a duct 15 by a cooling fan 14. Actual arrow line 25 shows part of the cooling air.
Gas such as moisture generated from the object to be heated 12 is indicated by the dotted arrow line 26.
It is shown in The cooling air and the gas containing moisture generated from the object to be heated 12 are discharged to the outside of the heating chamber 7 through the exhaust section 8 . Here, in Figure 3, 400 cc of water
An example of the output voltage waveform regarding the signal and noise of the piezoelectric element sensor 1 when heated is shown. Heat shows an example of a signal waveform when the water in the heating chamber 7 boils. Panel b shows the results of spectrum analysis of this waveform.

It can be seen that a large signal is generated in the 0 to 50 Hz band due to the hot air containing warm water vapor hitting the piezoelectric element sensor 1. A. When the water in the heating chamber 7 boils,
"A" is before boiling, "C" is when the microwave oven is not energized, and the difference between "A" and "A" is about 30 dB, and the signal level is a voltage of several mV. Further, even when dirt was attached to the piezoelectric element sensor 1, the output waveform shown in FIG. 3 did not change. This is because the piezoelectric element sensor 1 generates a signal in response to thermal changes. Therefore, as shown in FIG. 4, in order to filter the output signal of the piezoelectric element sensor 1 into a filter having a pass band from 0 to 50 Hz, a band-pass filter is created using a bypass filter 27 and a low-pass filter 28. . FIG. 5 is a diagram showing the relationship between the output voltage of the piezoelectric element sensor 1 in the 0 to 50 Hz band and the ambient temperature, and the output voltage of the piezoelectric element sensor 1 decreases as the ambient temperature rises. This is explained as follows. The piezoelectric element sensor generates a polarization current depending on the differential amount of the above-mentioned thermal sonication containing warm moisture. This is because if the ambient temperature around the piezoelectric element sensor 1 is high at this time, even if warm water vapor collides with the piezoelectric element sensor 1 and exchanges heat, the change in thermal temperature will be small. FIG. 6 is a system block diagram of an embodiment of the present invention, in which the amplifier gain of the amplifier 18 is made variable in accordance with the ambient temperature in order to perform the above correction, and the piezoelectric The output voltage of the element sensor 1 is expressed by equation (1).

The value in parentheses is the amplifier gain.

Therefore, if an optimal constant is set so that the resistance value of the thermistor 6 decreases as the ambient temperature rises, a stable output regardless of the ambient temperature can be obtained, as shown in FIG.

Reference numeral 21 denotes a setting means consisting of a control means, a ladder resistor and an operational amplifier, and determining the termination of the heating means. The voltage level of the setting means 21 and the signal level of the amplifier 18 are compared by the comparator 22, and when the control means 23 detects that the voltage level of the setting means 21 has been exceeded, the energizing means energizes the magnetron 1G. 24, the relay 32 of the cooling fan 14, and the lamp 31 for lighting inside the heating chamber 7.
The contact point of the magnetron 13, the cooling fan 14, etc. is stopped.

Note that 33 is a power supply that supplies the control means 23 and the like;
is the cooking start button. Start button 34
When steam starts to be generated from the object to be heated 12 after pressing , a differential signal pulse of the piezoelectric sensor 1 is generated, and when the set voltage is exceeded, the magnetron 13 is de-energized. When the same amount of the heated object 12 is subsequently heated, water vapor is similarly generated and a differential signal pulse is generated. However, the signal level of the differential signal pulse decreases as the temperature of the exhaust section 8 rises, but the amplifier gain changes as the resistance of the thermistor 6 changes, so the same amount of object 12 can be repeatedly heated regardless of the ambient temperature. In both cases, the heating ends in the same heating time T. In one embodiment of the present invention, a microcomputer is used as the control means 23, and it configures a complicated control sequence such as detecting differential signal pulses, setting an arbitrary level of the setting means 21, and setting the reheating time. suitable for.

In addition, as shown in FIG. 7, the piezoelectric sensor 1 and the correction element 6 are integrally molded with resin 35. Therefore, the temperature of the piezoelectric sensor 1 and the thermistor 6 of the correction element are the same, and the correction element 6 provides accurate In addition, it is possible to make various corrections.
This has the effect of preventing deterioration of the element due to the gas of the heated object 12.

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

(1) The relative signal drop in the detection ability of the differential signal pulse at the end of heating due to the ambient temperature of the piezoelectric element sensor is corrected by the gain of the amplifier using the temperature correction element, so it can be reliably used even if the microwave oven is used repeatedly. There is no difference in the heating completion time, and the heated object can always be finished in a stable manner.

(2) Humidity sensors require a heater to refresh the oil or gas from the heated object that adheres to the sensor, and a power source for the heater, making maintenance of the sensor complicated; however, piezoelectric sensors are , such a special circuit is not required at all, and the end of the heating state can be automatically detected at low cost and with a simple configuration.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of a piezoelectric element sensor according to an embodiment of the present invention, FIG. 1(b) is a cross-sectional view showing the installation state of the same piezoelectric element sensor and a temperature correction element, and FIG. A block diagram of the main body configuration of a microwave oven using the same piezoelectric element sensor, Fig. 3 is a frequency spectrum waveform diagram of the same piezoelectric element sensor, Fig. 4 is a circuit configuration diagram of the same filter, and Fig. 5 is a diagram of the same piezoelectric element sensor. A characteristic diagram showing the relationship between the output voltage and the ambient temperature, FIG. 6 is a system block diagram of the same, and FIG. 7 is a characteristic diagram showing the relationship between the output voltage of the piezoelectric sensor and the ambient temperature when the same correction is applied.
FIG. 8 is a sectional view of a piezoelectric element sensor and a temperature correction element according to another embodiment of the present invention, FIG. 9 is a block diagram of the main body configuration using a conventional humidity sensor, and FIG. 10 is a piezoelectric element sensor of another example of the prior art. FIG. 2 is a block diagram of a main body configuration using an element sensor. 1...Piezoelectric element sensor, 6...Temperature correction element (thermistor), 7...Heating chamber, 8...
... Exhaust section, 12 ... Heated object, 13 ...
... Heating means, 17 ... Filter, 18 ...
...Amplifier, 19,20...Resistor, 21.
... Setting means, 22 ... Comparison section, 23.
... Control means, 24 ... Urging means, 35
······resin. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2- Piezoelectric element balance a4
, 5- Sea￥Job 6- Temperature correction element! Fig. 2 rlA Fig. 3 Shoulder line* Oh) Fig. 4 Fig. 5 20 60 90° Figure 10

Claims (3)

[Claims] (1) A heating chamber into which a heated object is taken in and taken out, a heating means for heating the heated object, a piezoelectric element sensor that detects the cooking state of the heated object, and a correction element for temperature compensation of the piezoelectric element sensor. a filter for appropriately filtering the signal of the piezoelectric element sensor; and an amplifier; a setting means for determining the end of cooking of the object to be heated; and a comparison for comparing the signal after the amplifier with the signal from the setting means. a piezoelectric element, comprising a device, an energizing means for energizing the heating means, and a control means for stopping the energizing of the energizing means in response to a signal from the comparator, and for varying the gain of the amplifier with the correction element. Microwave oven with sensor. (2) A microwave oven with a piezoelectric element sensor according to claim 1, wherein the control means is constituted by a microcomputer. (3) A microwave oven with a piezoelectric sensor according to claim 1, wherein the piezoelectric sensor and the correction element are integrally molded with resin.