JPH02147827A - Piezoelectric element applying sensor - Google Patents

Abstract

PURPOSE:To simplify the constitution of a piezoelectric element applying sensor and, at the same time, to make the signal processing easier and to detect the cooked state of foods accurately by constituting the sensor in such a way that, when a positive temperature change is applied to the sensor, a positive high voltage can be outputted. CONSTITUTION:A pair of electrodes 3 having different polarities are vapor deposited on a piezoelectric element 2 and one end of the electrodes 3 is stuck onto a metallic plate 5 with a bonding agent 4. Lead wires 6 and 7 of an output section are extended from the electrodes 3. A molded resin body 8 encloses the element 2, electrodes 3, the bonding agent 4, load-out sections of the lead wires 6 and 7, and the surface of the plate 5 in the vicinity of the sticking surface of the element 2 in a united state. Since one of the electrodes 3 is connected with the reference potential of a single power source amplifier circuit which processes the signal of the element 2, with the polarity being selected so that a positive voltage can be outputted to the other electrode 3 when a positive temperature change is applied to the element 2, the cooked state of foods can be detected accurately with such simple constitution. Moreover since the metallic plate body is used for the reference potential as ground, etc., the output of this sensor can be processed easily and a high reliability can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sensor using a piezoelectric element that utilizes the pyroelectric effect of a piezoelectric element, and in particular to a humidity sensor for cooking appliances such as electronic I/O. be.

2. Description of the Related Art Conventionally, a humidity sensor uses a sensor chip 22. as shown in FIG. Heater 23. Resin base 24. Mesh cover 25. It is composed of a terminal 26. Sensor chip 2
Since the resistance value of No. 2 changes depending on humidity, the cooking state of the microwave oven is detected by comparing a reference voltage with a voltage determined by the resistance value. The heater 23 is used to refresh the sensor chip 22 as it gets dirty due to food gas, oil, etc. when the humidity sensor is used in a microwave oven. It is used for this purpose. (Nasigonal Technical Report VOL, 29 No. 3 JAN
19B3) Problems to be Solved by the Invention However, when using a humidity sensor as described above, gas or oil in the food adheres to the sensor chip 22 during cooking, reducing detection sensitivity. It is necessary to evaporate deposits on the sensor chip 22 using the heater 23 for refresh heat treatment each time, which generates extra power and cost.In addition, since the voltage across the resistor is used as a control signal, it is difficult to produce a large number. In this case, the resistance of the sensor chip 22 which is each component, other resistances, variations in power supply voltage, etc. may lead to variations in the control voltage signal.
It was difficult to manage.

There is also a method of using a piezoelectric element instead of a conventional humidity sensor, but the polarized current that is the output of the piezoelectric element is minute and requires an amplifier to control it, and the output may vary depending on its polarity. In some cases, the value appears largely in the positive direction, while in others it appears largely in the negative direction.

Furthermore, a metal plate is used to prevent dirt and insulation deterioration of the piezoelectric element, but when used in cooking equipment, there is a problem that the metal plate can short-circuit with the case of the cooking equipment, oven, etc. due to moisture or water vapor. .

Therefore, the first object of the present invention is to increase the output of the piezoelectric element and match it with the circuit.

The second purpose is to be able to accurately and safely process the output of the piezoelectric element.

Means for Solving the Problems In order to achieve the above-mentioned first object, the piezoelectric element applied sensor of the present invention has the polarity of the piezoelectric element changed, and one of the electrodes connected to a single power supply amplification circuit that processes the signal of the piezoelectric element. The other electrode is connected in such a way that a positive voltage is generated at the other electrode when a positive temperature change is applied to the piezoelectric element as a reference potential.

In order to achieve the second objective, a metal plate or a conductive plate is used as a reference potential such as a ground.

According to the present invention, a piezoelectric element is used, and when used in a cooking appliance such as a microwave oven, the polarity is selected and connected so that a positive voltage is output when a positive temperature change is applied. With a simple configuration, the cooking finish state of food can be accurately detected.

Further, since a metal or conductive plate is used as a reference potential such as a ground, sensor output can be easily processed and high reliability can be achieved.

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings. FIG. 1 shows the configuration of a piezoelectric element applied sensor 1. As shown in FIG. (a) is a cross-sectional view, and (b) is a view from above. A pair of vapor-deposited polarities 3 are applied to a lead titanate-based piezoelectric element 2, and one end of the electrode 3 is electrically contacted and bonded onto a metal plate 5 with an adhesive 4. Output leads 6 and 7 are led out from the electrode 3, and each lead is electrically insulated. The resin 8 is applied to the piezoelectric element 2 to prevent the influence of environmental humidity.
Electrode 3. Adhesive 4. The lead-out portion of the lead 6.7, the vicinity of the bonding surface of the piezoelectric element 2 made of metal 5, etc. are integrally sealed with a non-moisture permeable molding material. Which of the leads 6 and 7 is at the reference potential will be explained with reference to FIG.

In FIG. 2(a), the vertical axis represents the temperature change applied to the piezoelectric element applied sensor, and the horizontal axis represents time. If a positive temperature change is applied to the piezoelectric element-applied sensor when it is turned on as shown in (a), the sensor output (2) as shown in (b) or (C) will be obtained depending on the polarity of the piezoelectric element. In this invention, the reference potential is selected so as to obtain the output shown in FIG. 3(b). (
b) From the figure, it can be seen that when a positive temperature change is applied to the piezoelectric element applied sensor, a positive voltage is generated as the sensor output, and matching can be achieved with the subsequent single power supply amplification circuit.

FIG. 3 shows the mechanism of polarization of a piezoelectric element.

Piezoelectric element 2. In a normal state, the electrode 3 has a balance of positive and negative charges due to polarization. However, temperature changes from outside△
When T is applied, this polarization is broken by the pyroelectric effect of the piezoelectric element, and a polarization current is generated in the lead portion. If the lead portion is short-circuited with a resistor 8, a voltage 2 can be obtained at both ends of the resistor. In the figure, the side on which negative charges are generated is set as the reference potential, which corresponds to the first claim of the present invention.

FIG. 4 shows a specific configuration example when the piezoelectric element applied sensor of the present invention is used in a microwave oven. A heating chamber 10 into which the food 9 is placed, and a magnetron 11 which heats the food 9 with high frequency. Piezoelectric element applied sensor attached to the heating chamber exhaust part 12 1. Cooling fan 13 for cooling Magne-Lon 11. A duct 14 that blows part of the air from the cooling fan 13 to the heating chamber 10. It is composed of a controller 15 and the like that controls various R device movements based on the output signals of the piezoelectric element application sensor 1.

Detection of the completion of heating the food 9 is performed as follows. Food 9 is placed in heating chamber 10 , and a portion of the cooling air from magnetron 11 is guided into heating chamber 10 via duct 14 by cooling fan 13 . A part of the cooling air is made of real arrow cotton 16,
Gas such as moisture generated from the food 9 is indicated by a dotted arrow line 17. A portion of the cooling air 16 and gas 17 such as moisture generated from the food 9 are discharged to the outside of the heating chamber 10 through the exhaust section 12 . At this time, there is a time T in the exchange of heat between the piezoelectric element applied sensor 1 and the gas 17 such as moisture generated from the food 9, and the piezoelectric element applied sensor 1 generates an output signal accordingly.

The controller 15 controls the operation of the magnetron 11 and the cooling fan 13 based on this output signal. The following is an overview of heating end detection. Since microwave ovens are originally grounded, the heating chamber 10, body cover 18. The potential of other parts is the ground potential.

As shown in FIG. 1, the piezoelectric element applied sensor 1 has a metal plate 5 in electrical contact with one electrode, and is configured to receive water vapor directly. The problem here is a short circuit between the metal plate 5 and the microwave oven body. Even if the metal plate 5 and the main body of the electronic cash register are normally electrically open, there is a risk of short-circuiting due to water droplets adhering to them. Therefore, setting the metal plate 5 to ground potential in advance corresponds to the second claim of the present invention. In the figure, a part 6 of the same potential as the metal plate is set to the ground potential.

FIG. 5 shows a specific example of the configuration of the controller 15. As shown in FIG.

When the output of the piezoelectric element application sensor 1 enters the controller 15,
A low-pass filter 19 eliminates 60 Hz noise, a single power supply amplifier 20 raises the signal to a level that is easy to control, and the signal is A/D inputted to a microcomputer 21. The microcomputer 21 knows the cooking status of the food based on the signal size, pulse l], etc., and provides control signals to the Magnelon 11 and the cooling fan 13.

As described in ``Effects of the Invention'', the present invention has a configuration in which a large positive voltage is output when a positive temperature change is applied to the piezoelectric element applied sensor. For this reason, it has a simple configuration, easy signal processing, and can accurately detect the finished cooking state of food.

In addition, since the metal plate of the piezoelectric sensor of the present invention is at ground potential, abnormalities such as failure to output due to a short circuit with the cooking equipment case, oven, etc. do not occur, and food can be cooked safely and accurately. It is possible to detect the state.

[Brief explanation of the drawing]

Figure 3 is a schematic diagram showing the polarization state of a piezoelectric element, Figure 4 is a configuration diagram when a piezoelectric element sensor is used in a microwave oven, 1...Piezoelectric Element application sensor, 2...Piezoelectric element, 3...
...Electrode, 5...Metal, 6.7...
Lead. Name of agent: Patent attorney Shigetaka Awano To one person: Temperature change applied to piezoelectric element applied sensor/-11 Piezoelectric element applied sensor 2- Piezoelectric element 3-Electrode S-m-Metal 6.7-11 sword

Claims (2)

[Claims] (1) A metal plate or a conductive plate, a piezoelectric element having a pair of electrodes, and a lead wire for taking out the sensor output, and one electrode of the piezoelectric element is connected to the metal plate or the conductive plate. electrically connected to the body, and the polarity of the piezoelectric element is determined by connecting one of the electrodes to a reference potential of a single power supply amplifier circuit that processes the signal of the piezoelectric element, and applying a positive temperature change to the piezoelectric element. A piezoelectric element applied sensor configured to be connected so that a positive voltage is generated at the other electrode when the other electrode is turned. (2) A metal plate or conductive plate, a piezoelectric element having a pair of electrodes, and a lead wire for taking out the sensor output, and one electrode of the piezoelectric element is connected to the metal plate or the conductive plate. A piezoelectric element-applied sensor configured to be electrically connected on a body and to set one of the electrodes, a metal plate, or a conductive plate to a ground potential.