JPH0439552Y2 - - Google Patents

Description

[Detailed explanation of the idea]

<<Industrial Application Field>> This invention relates to a piezoelectric sensor using an element in which a piezoelectric element is attached to a support plate, and more specifically relates to a piezoelectric sensor that measures the load applied to the sensor. <Prior art> Conventionally, sensors that measure loads such as weight using this type of piezoelectric effect have typically used a single element with a piezoelectric element attached to a support plate, and the load was applied from the piezoelectric element side. However, there was one that measured the load (weight) by measuring the amount of charge (voltage) generated according to the deflection of the element at that time. <<Problems to be solved by the invention>> However, the piezoelectric element has a limit in its resistance to load, and there is a problem in that the piezoelectric element breaks when a load exceeding a certain level is applied. Since the yield strength of the piezoelectric element is determined by the thickness of the element, it is necessary to manufacture elements having various thicknesses depending on the weight of the object to be measured. In other words, it is necessary to prepare a thin element for small weight measurement and a thick element for large weight measurement, and because the same element cannot be used, the manufacturing work and process are complicated and mass production is difficult. Various problems arose, including an increase in manufacturing costs. 《Purpose of the invention》 This invention was made in view of the above-mentioned problems, and its purpose is to expand the limit of the load that can be measured with the same element with a simple structure, and to By making it possible to measure any weight using an element, it is possible to mass-produce the element, reduce costs, and provide a piezoelectric sensor that is easy to use because the load-output voltage characteristic always has linearity. There is something to do. <<Means for solving the problem>> In order to achieve the above-mentioned object, the piezoelectric sensor according to the present invention uses an element in which a piezoelectric element is attached to a first support plate, and when a load is applied to the piezoelectric element, In a piezoelectric sensor that measures the load based on the magnitude of the electric charge generated in the piezoelectric sensor, the element is arranged so as to be freely put in and taken out of the inner case so that the piezoelectric element faces the load application side, and the A second support plate is provided on the first support plate side of the element.
A support plate is inserted into the inner case, and a means for pressurizing the element, which includes a pressurizing part and a flexible support member, applies one end of the pressurizing part to the piezoelectric element of the element. The inner case is mounted so as to come into contact with the element, and an outer case surrounds the outer periphery of the inner case, and the outer case is provided with a through hole through which the other end of the pressurizing part projects. A bias applying means is formed for bringing the element disposed in the inner case into close contact with the second support plate. <<Operation>> An appropriate bias load is applied from the piezoelectric element side to the element disposed inside the inner case by the bias load applying means provided in the outer case. Then, due to the bias load, the element becomes horizontal, the gap between the element and the second support plate disappears, and the element and the second support plate come into close contact with each other. When the load to be measured is applied, the element (piezoelectric element) is subjected to the resistance of the second support plate from the beginning. Then, when a load is applied to the element from the piezoelectric element side using a pressure means provided in the inner case in this state, the piezoelectric element is deflected in accordance with the magnitude of the applied load, and the charge ( voltage) is generated. At this time, the second support plate serves as a resistance plate, and the amount of deflection of the piezoelectric element is smaller than the amount of deflection of the piezoelectric element when the same load is applied to the element alone. Therefore, the maximum permissible load (measurable range) is expanded compared to when the element is used alone. <<Examples>> Hereinafter, preferred embodiments of the piezoelectric sensor according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 3 are cross-sectional views showing one embodiment of this invention. As shown in the figure, 10 is a first support plate, and in this embodiment, a metal plate is used. A piezoelectric element 12 is thermally bonded to the upper surface of this first support plate, and constitutes an element 14. In this embodiment, piezoelectric ceramics are used for the piezoelectric element 12. In addition, the first support plate 10 and the piezoelectric element 12
A lead wire 15 is attached to the upper surface of each element 12, so that the amount of charge (voltage) generated by the piezoelectric element 12 when a load is applied to the element 12 can be measured using, for example, a voltmeter. The element 14 is inserted into the inner case 16 so that the piezoelectric element 12 side faces upward. That is, the inner case 16 has the receiving part 1 inside the lower part.
8 is formed integrally protruding inward in the radial direction,
The element 14 is arranged on this receiving part 18. Further, a pressurizing means 20 for applying pressure to the element 14 is detachably screwed into the upper opening of the inner case 16. This pressurizing means 20 is composed of a flexible support member 22 and a rod-shaped pressurizing part 24 that protrudes upward at the center thereof, and both are integrally formed. Furthermore, a side wall 25 that requires a thread on the outer surface is formed hanging from the outer peripheral edge of the support member 22, and is threadedly engaged with a thread formed on the upper inner side of the inner case 16 here. By rotating the pressure section 24, the pressure means 20 is moved up and down. In the present invention, a second support plate 2 is provided between the element 14 and the receiving portion 18 provided in the inner case 16.
8 has been inserted. This second support plate 28 needs to have spring properties, and in this embodiment a metal plate is used. Preferably, a plurality of support plates having different thicknesses are prepared, and a second support plate 28 having an optimum thickness is inserted and arranged according to the load to be applied. Moreover, this element 14
Due to the difference in thermal expansion coefficient between the support plate 10 and the piezoelectric element 12, the piezoelectric element 12 side is always slightly curved due to the heat during thermal bonding, so that the element 14 and the second support plate 28 There is a small gap Δd between them. A space is formed between the lower part of the second support plate 28 and the bottom of the inner case 16, so that the element 14 and the second support plate 28 can be bent downward. . Furthermore, in the present invention, an outer case 30 is provided to surround the inner case 16. The outer case 30 has an openable bottom 32,
The bottom portion 32 is screwed into the lower opening of the outer case 30 so as to be vertically movable. In addition, a through hole 34 is bored in the center of the top surface of the outer case 30, and the upper end of the pressurizing part 24 formed in the pressurizing means 24 of the inner case 16 passes through the through hole 34 and is connected to the outer case. It is designed to protrude upwards from the top surface of 30. Further, an actuating portion 36 is integrally formed to hang down from the lower peripheral edge of the through hole 34 . This operating portion 36 and the bottom portion 32 constitute a bias load applying means. Note that in this embodiment, the first support plate 12
Although a metal plate is used in this example, the present invention is not limited to this, and for example, a non-conductive member may be used. However, in that case, the lead wire 15 is of course attached to the lower surface side of the piezoelectric element 12.
Similarly, the second support plate is not limited to a metal plate as long as it is a member having spring properties. Further, although the bottom portion 32 is formed to be vertically movable as a bias load applying means, for example, the upper end portion of the outer case 30 may be vertically movable. Next, the operation of this embodiment will be explained. First, the second support plate 28 is placed on the receiving part 18 of the inner case 16, and the element 14 is placed on it so that the piezoelectric element 12 is placed upward. place Then, the pressurizing means 20 is attached to the inner case 16, and the pressurizing means 20 is rotated in the direction in which the screw is tightened, and moved downward until the lower end surface of the pressurizing part 24 comes into contact with the piezoelectric element 12 (see Fig. 1). ). Next, a bias load BW is applied to eliminate the gap d occurring between the element 14 and the second support plate 28. That is, outer case 3
0 in the direction in which the screw on the bottom part 32 is tightened.
Then, the bottom portion 32 moves upward, and the inner case 16 also moves upward. Then, when the bottom part 32 is further rotated and raised, the pressurizing means 2
The support member 22 at the peripheral edge of the pressure unit 24 of No.
0 is bent, and the flexible peripheral edge of the pressurizing means 20 and the inner case 16 are moved upward. Therefore, a downward reaction force is applied from the actuating part 36 to the pressurizing part 24, and this force becomes a bias load BW and is applied to the element 14, causing the element 14 to bend slightly and become horizontal, eliminating the gap Δd. This brings the element 14 and the second support plate 28 into close contact (FIG. 2). When the object to be measured is placed on the upper end surface of the pressurizing section 24 with the bias load BW always being applied in this way, the pressurizing section 24 moves downward due to the biasing force due to its own weight, and the element 14 and second
The support plate 28 of the device is deflected downward, and a charge corresponding to the amount of deflection is generated from the piezoelectric element 12. This charge amount is taken out as a voltage via the lead wire 15, and the voltage is measured. You can measure your own weight (Figure 3). In other words, if a constant load is continued to be applied to a piezoelectric element, the electric charge that has been generated will leak inside the element and the output voltage will become zero, and the amount of electric charge generated from the piezoelectric element will change from the state in which the piezoelectric element is present. This occurs in response to changes when the piezoelectric element changes to a different state after being pressurized, and if a load is applied in advance to bend the piezoelectric element, and then a new load is applied to that state, the piezoelectric element will bend. A corresponding amount of charge is generated. Therefore, the voltage generated here is nothing but the weight of the object to be measured. In order to apply an appropriate bias load BW, for example, the load-output voltage characteristics may be investigated, and the load at the starting point when linearity of the characteristics can be obtained is applied. FIG. 4 is a graph showing the load-output voltage characteristics of the piezoelectric sensor when no bias load is applied. The characteristics shown by the solid line in the figure are the characteristics of the pressurizing part 24
That is, the characteristics are when a load is applied to the element 14 and the second support plate 28, and the characteristics shown by the broken line are the characteristics when a load is applied to the element 14 alone. As is clear from the figure, the solid line characteristic first exhibits linearity with a relatively steep slope (corresponding to the broken line characteristic), and then shows linearity with a gentle slope. In other words, since the element is initially bent to create a gap Δd, it is not affected by the second support plate, so the initial characteristics are the same as those obtained when a load is applied to the element 14 alone.
However, when a larger load is applied, element 1
4 and the second support plate 28, the amount of deflection of the piezoelectric element under the same load becomes smaller due to the resistance of the second support plate 28, so that the inclination becomes smaller. Therefore, the load when this characteristic changes is the bias load.
It becomes BW. In this embodiment, the thickness of both the first support plate 10 and the piezoelectric element 12 is 200 mm.

[μm] was used, but the bias load BW in this case was 500

It was [g]. Therefore, 500

If the bias load BW of [g] is continued to be applied, a voltage corresponding to the bias load BW is generated once, but after a while the output voltage becomes zero, but the element 14 and the second support plate 28 remain in close contact with each other. Therefore, when a load W is applied from this state, the piezoelectric element is influenced by the second support plate 28 which is a resistance plate from the beginning, and the generated output voltage corresponds to the load W. In other words, the vertical and horizontal axes in Figure 4 move in parallel, and A in the figure
The point becomes the origin of the bias output voltage characteristics. In this example, the device was oriented upward in order to measure the weight of the object to be measured (weight sensor), but the present invention is not limited to this, and can be used to measure various loads and pressures. In that case, it is also possible to use the device by tilting it sideways. <<Effect of the invention>> As described above, according to the load sensor according to the present invention, the second support plate is inserted into the support plate side of the element in which the piezoelectric element is attached to the support plate. becomes a resistance plate, and even if the same load is applied, the amount of deflection of the piezoelectric element becomes smaller, and the load required to achieve the amount of deflection that causes damage to the piezoelectric element becomes larger. Therefore, a load larger than the load that can be measured by the element alone can be applied, and the measurable range can be expanded. Further, since the resistance force of the second support plate changes simply by changing the thickness of the second support plate inserted into the element, the measurement range can be arbitrarily set while using the same element. That is, there is no need to manufacture various elements according to the weight of the object to be measured, and if the same element is manufactured, the weight will be constant, so mass production can be achieved, and costs can be reduced. Furthermore, since the outer case is provided with a bias load applying means that brings the element and the second support plate into close contact with each other from above the piezoelectric element of the element, the starting point of the load-output voltage characteristic moves, and the piezoelectric element Therefore, only the characteristic of linearity can be used, the load can be easily measured, and the usability of the piezoelectric sensor is improved, and various other effects can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the piezoelectric sensor according to the present invention, Fig. 2 is a sectional view showing a state in which a bias load is applied to the element, and Fig. 3 is a sectional view showing a state in which a load to be measured is applied to the element. The cross-sectional view shown in FIG. 4 is a graph showing the load-output voltage characteristics in a state where no bias load is applied. 10...First support plate, 12...Piezoelectric element, 1
4...Element, 16...Inner case, 20...
Pressure means, 24...pressure section, 28...second support plate, 30...outer case.

Claims (1)

[Scope of utility model registration request] In a piezoelectric sensor that uses an element in which a piezoelectric element is attached to a first support plate and measures a load based on the magnitude of electric charge generated when a load is applied to the piezoelectric element, the piezoelectric element is placed on the load application side. The element is arranged in and out of the inner case so as to face the element, and a second support plate is inserted into the first support plate side of the element in the inner case. A means for applying pressure to the element, which includes a pressurizing section and a flexible support member, is attached such that one end of the pressurizing section is in contact with the piezoelectric element of the element; The outer periphery of the inner case is surrounded by an outer case, and the outer case is provided with a through hole through which the other end of the pressurizing part protrudes, and the element arranged in the inner case and the A piezoelectric sensor characterized in that a bias applying means is formed for bringing the second support plate into close contact with the piezoelectric sensor.