JPH0823536B2 - Piezoelectric element applied sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element application sensor that uses the pyroelectric effect of a piezoelectric element, and more particularly to a sensor for automation of cooking appliances such as microwave ovens. .

2. Description of the Related Art Conventionally, a humidity sensor, which is a typical automation sensor for warming a microwave oven, includes a sensor chip 22, a heater 23, a resin base 24, a mesh cover 25, and a terminal 26 as shown in FIG. ing. Since the resistance value of the sensor chip 22 changes depending on humidity, the temperature of the microwave oven is detected by comparing the reference voltage with the voltage determined by the resistance value.
If there was a sudden change in humidity, it was judged that water vapor had begun to come out from the food, and the end was judged. The heater 23 is for refreshing when the humidity sensor is used in a microwave oven because the sensor chip 22 is contaminated by food gas, oil, etc.
It is used for power saving of 23. (National Technical Report VOL.29 No.3 JAN 1983) Problems to be Solved by the Invention However, when the humidity sensor is used as described above, gas or oil in food adheres to the sensor chip 22 and is detected during cooking. Since the sensitivity decreases, the deposit 23 on the sensor chip 22 must be evaporated by the heater 23 for the refresh heating process each time cooking is performed, resulting in extra power and cost and the voltage across the resistor. Since it is used as a control signal, the resistance of the sensor chip 22 that is each component, other resistances, variations in the power supply voltage, etc. will lead to variations in the control voltage signal when it is produced in large numbers, making management difficult. Met.

There is also a method of using a piezoelectric element instead of the conventional humidity sensor, but the polarization current that is the output of the piezoelectric element is very small, and an amplifier is required to control it, and depending on its polarity, the output may vary. There is a large positive output and a large negative output. Furthermore, although a metal plate is used to prevent the piezoelectric element from becoming dirty and the insulation deteriorates, when used in cooking equipment, there is a problem that the metal plate is short-circuited with the case of the cooking equipment, the oven, etc. due to moisture or water vapor. .

Further, when the piezoelectric element itself is exposed to moisture or water vapor, there is a problem that a leak current increases and a fiery fire occurs.

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

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

 The third purpose is to protect the piezoelectric element.

Means for Solving the Problems At least two electrodes on the piezoelectric element, electrically connected to the first electrode of the electrodes, thermally connected to the piezoelectric element, infrared does not pass, conductive And a lead wire connected to at least a second electrode among the electrodes, and when a positive temperature change is applied to the piezoelectric element through the plate body, A positive voltage is generated in the second electrode by using the first electrode as a reference potential. In order to achieve the second object, a piezoelectric element application sensor of the present invention is electrically connected to a piezoelectric element, at least two electrodes on the piezoelectric element, and a first electrode of the electrodes. A plate body that is thermally connected to the piezoelectric element, does not transmit infrared rays, and is made of a conductive material; and a lead wire that is connected to at least a second electrode of the electrodes, One electrode is set to the ground potential. In order to achieve the third object, the piezoelectric element application sensor of the present invention is electrically connected to a piezoelectric element, at least two electrodes on the piezoelectric element, and a first electrode of the electrodes. , A plate which is thermally connected to the piezoelectric element, does not transmit infrared rays, and is made of a conductive material, and a lead wire connected to at least a second electrode of the electrodes, The piezoelectric element, the electrode, and the lead-out portion of the lead wire are integrally molded with resin on one side surface of the body.

Effect According to the present invention, when a positive temperature change is applied to the piezoelectric element through the plate body which does not transmit infrared rays and has conductivity, the first electrode electrically connected to the plate body is used as the reference potential to generate the second Since a positive voltage is generated at the electrode of, when heating food with cooking equipment, if heating progresses and the food begins to generate steam, high temperature steam hits the plate and positive voltage is applied to the piezoelectric element through the plate. Since the temperature is changed, the output from the piezoelectric element can be obtained as a positive voltage accordingly. Further, according to the present invention, since the first electrode electrically connected to the plate body having the property of not transmitting infrared rays and having conductivity is set to the ground potential, the plate body is set to the ground potential like the case of the cooking appliance, the oven, or the like. can do. Further, according to the present invention, the piezoelectric element, the electrode, and the lead-out portion of the lead wire are integrally molded with resin on one side surface of the plate body that transmits infrared rays and has conductivity, so that the entire other surface of the plate body is effective. You can use it to apply steam. If the other surface of the plate receives water vapor or food debris, the molded surface is protected from the water vapor or food debris.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the configuration of the piezoelectric element application sensor 1. (A) is sectional drawing, (b) is the figure which looked at (a) from the top. A lead titanate-based piezoelectric element 2 is provided with a pair of vapor-deposited electrodes 3, and one end of the electrode 3 is electrically contacted and adhered to a metal plate 5 with an adhesive 4.

Here, the piezoelectric element 2 and the metal plate 5 are configured to easily transfer heat via the electrode 3 and the adhesive 4. Leads 6 and 7 of the output section are led out from the electrode 3, and each lead is electrically insulated. Resin 8 is used to prevent the influence of environmental humidity.
The piezoelectric element 2, the electrode 3, the adhesive 4, the lead-out portions of the leads 6 and 7, and the vicinity of the bonding surface of the piezoelectric element 2 on one side surface of the metal plate 5 are integrally sealed with a non-moisture permeable molding material. There is. When such a piezoelectric element applied sensor 1 is used as an automation sensor because it is a microwave oven, water vapor generated from food hits the metal plate 5 from the bottom of FIG. 1 (a), and the metal plate 5, the adhesive 4, the electrode The change in humidity is transmitted to the piezoelectric element 2 via 3. Which of the leads 6 and 7 becomes the reference potential will be described with reference to FIG.

In FIG. 2 (a), the vertical axis represents the temperature change applied to the piezoelectric element application sensor, and the horizontal axis represents time. (A) The figure shows
When a positive temperature change is applied to the piezoelectric element application sensor, the sensor output Vs as shown in FIG. 6B or FIG. 6C is obtained depending on the polarity of the piezoelectric element. In the present invention, the reference potential is selected so that the output shown in FIG.
In the case of the diagram (b), when a positive temperature change is applied to the piezoelectric element applied sensor, a positive voltage is generated as the sensor output, and an inexpensive single power supply amplification circuit is used as the subsequent processing circuit. It turns out that matching is possible.

FIG. 3 shows the mechanism of polarization of the piezoelectric element. In a normal state, the piezoelectric element 2 and the electrode 3 are balanced by positive and negative charges due to polarization. However, when a temperature change ΔT is applied from the outside, this polarization is destroyed by the pyroelectric effect of the piezoelectric element, and a polarization current is generated in the lead portion. Here, if the lead portion is shorted by the resistor 8, the voltage Vs can be taken out across the resistor 8. The fact that the side generating negative charges in the figure is the reference potential corresponds to the first claim of the present invention.

FIG. 4 is a specific configuration example when the piezoelectric element application sensor of the present invention is used in a microwave oven. A heating chamber 10 in which the food 9 is placed, a magnetron 11 for heating the food 9 at a high frequency, a piezoelectric element applied sensor 1 attached to the heated chamber exhaust part 12, a cooling fan 13 for cooling the magnetron 11, and a part of the wind of the cooling fan 13. It is composed of a duct 14 that blows air to the heating chamber 10, a controller 15 that controls the operation of various devices according to the output signals of the piezoelectric element application sensor 1.

The detection of heating completion of the food 9 is performed as follows. The food 9 is placed in the heating chamber 10, and a part of the cooling air of the magnetron 11 is guided into the heating chamber 10 by the cooling fan 13 via the duct 14. A part of the cooling air is shown by a solid arrow line 16 and a gas such as moisture generated from the food 9 is shown by a dotted arrow line 17. A part 16 of the cooling air and a gas 17 such as water generated from the food 9 are discharged to the outside of the heating chamber 10 through the exhaust unit 12. At this time, the piezoelectric element applied sensor 1 has a metal plate (not shown) as an exhaust part.
It is configured to face upward so that heat is transferred between the gas 17 such as moisture generated from the food 9 and the metal plate.
The temperature change of ΔT is applied to the piezoelectric element via the metal plate, the adhesive, and the electrode, and the piezoelectric element application sensor 1 generates an output signal in response to the temperature change. The controller 15 controls the operations of the magnetron 11 and the cooling fan 13 by this output signal. The above is the outline of the end of heating detection. Since the microwave oven is essentially grounded, the potential of the heating chamber 10, the body cover 18, and other parts is the ground potential. As shown in FIG. 1, the piezoelectric element application sensor 1 has a structure in which the metal plate 5 is in electrical contact with one of the electrodes, and receives the water vapor properly. The problem here is the short circuit between the metal plate 5 and the microwave oven body. Normally, even if the metal plate 5 and the microwave oven main body are electrically open, there is a risk of a short circuit due to the attachment of water droplets. For this reason, to set the metal plate 5 to the ground potential in advance corresponds to the second claim of the present invention. In FIG. 4, the lead 6 having the same potential as the metal plate is set to the ground potential, and even if the metal and the microwave oven main body are electrically short-circuited, there is no influence on the performance of the piezoelectric element application sensor.

FIG. 5 is a specific example showing the configuration of the controller 15. When the output of the piezoelectric element applied sensor 1 enters the controller 15, the low-pass filter 19 eliminates noise of 60 Hz, and the single power supply amplifier 20 raises the signal to a level at which it is easy to control the signal. D
input. The microcomputer 21 knows the cooking state of the food from the magnitude of the signal, the pulse width, etc., and gives a control signal to the magnetron 11 and the cooling fan 13.

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

(1) Since the piezoelectric element generates a voltage when a rapid temperature change is applied through the plate body, there is an effect that it is possible to detect, for example, a rapid generation of water vapor due to heating of food.

Therefore, there is an effect that the end of heating of food can be detected like a humidity sensor of a cooking device.

Further, even if it is exposed to water vapor or food scraps, it is only necessary to be able to detect a rapid temperature change, so that it is easy to handle, and good detection performance can be maintained, resulting in a highly reliable effect.

Furthermore, the material of the electrode does not need to be limited to be transparent or non-transparent to infrared rays, and has an effect of high versatility.

(2) When a positive temperature change is applied to the piezoelectric element through the plate body, a positive voltage is generated at the second electrode with the first electrode electrically connected to the plate body as a reference potential. Therefore, it is easy to obtain the output as a positive voltage, and there is an effect that the configuration of the subsequent processing circuit can be simplified. For example, when it is used as a sensor for a cooking device, a positive temperature change is always given to the plate due to the generation of water vapor due to the heating of food, so it is sufficient to always process the signal as a positive voltage, eliminating the need for a control component for output inversion. Therefore, there is an effect that the number of amplifiers can be reduced by one step. Further, if the number of parts can be reduced, it is possible to suppress the influence of variations in parts and improve the reliability. Therefore, the detection performance is stable, and there is an effect of improving performance as a sensor. Further, if it is used as a sensor for automating cooking, it has the effect of improving the quality of cooking.

(3) Since the first electrode electrically connected to the conductive plate member that does not transmit infrared rays is set to the ground potential, the plate member is set to the same ground potential as the case of the cooking appliance or the oven. can do. Therefore, even if the plate body is exposed to water vapor and the cooking equipment case or oven is short-circuited, the plate body, the case, and the oven are originally at the ground potential, and the output can always be accurately output based on the first electrode. There is. Therefore, there is an effect that safety and reliability can be improved.

(4) The piezoelectric element, the electrode, and the lead-out portion of the lead wire are integrally molded with resin on one side surface of the plate body that does not transmit infrared rays and has conductivity, and the entire other surface of the plate body is effectively made. You can use it to apply steam. Therefore, the temperature change due to water vapor can be accurately detected, which has the effect of improving the detection performance of the sensor.

If the other surface of the plate receives water vapor or food debris, the molded surface is protected from the water vapor or food debris. There is an effect that the deterioration of the piezoelectric element and the electrode due to water vapor and food scraps can be prevented, and safety and reliability can be enhanced.

Further, there is an effect that a small amount of resin material for molding is required.

[Brief description of drawings]

1A and 1B are a cross-sectional view and a plan view of a piezoelectric element application sensor showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing a temperature change applied to the piezoelectric element application sensor and a sensor output corresponding to the temperature change. FIG. 3 is a schematic diagram showing the polarization state of the piezoelectric element, FIG. 4 is a configuration diagram when the piezoelectric element sensor is used in a microwave oven, and FIG. 5 is a block diagram showing the inside of the controller, FIG.
The figure is a partially cutaway perspective view of a conventional humidity sensor. 1 ... Piezoelectric element applied sensor, 2 ... Piezoelectric element, 3 ... Electrode, 5 ... Metal plate, 6, 7 ... Lead.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Kasai 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-1-253644 (JP, A)

Claims (4)

[Claims] 1. A piezoelectric element, at least two electrodes on the piezoelectric element, and a first electrode of the electrodes are electrically connected to the piezoelectric element and are thermally connected to the piezoelectric element, and infrared rays are not transmitted. A plate having a conductive material and a lead wire connected to at least a second electrode of the electrodes, and when a positive temperature change is applied to the piezoelectric element through the plate. A piezoelectric element application sensor configured such that a positive voltage is generated at the second electrode with the first electrode as a reference potential. 2. A piezoelectric element, at least two electrodes on the piezoelectric element, and a first electrode of the electrodes are electrically connected to the piezoelectric element and are thermally connected to the piezoelectric element, and infrared rays are not transmitted. A piezoelectric element application sensor having a plate body made of a conductive material and a lead wire connected to at least a second electrode of the electrodes, and having the first electrode at a ground potential. 3. A piezoelectric element, at least two electrodes on the piezoelectric element, and a first electrode of the electrodes are electrically connected to the piezoelectric element and are thermally connected to the piezoelectric element, and infrared rays are not transmitted. A plate body made of a conductive material and a lead wire connected to at least a second electrode of the electrodes, and the piezoelectric element, the electrode, and the lead wire on one side surface of the plate body. Piezoelectric element applied sensor in which the lead-out part is integrally molded with resin. 4. The structure according to claim 1, wherein the first electrode is electrically connected to a reference potential of a single power supply amplifier circuit that processes a signal of the piezoelectric element. The piezoelectric element application sensor described.