JPS5847012B2 - stress detector - Google Patents

Description

[Detailed description of the invention] The present invention relates to a force detector for detecting stress.

More specifically, the present invention relates to a force detector that converts force into an electrical signal using a piezoelectric element.

Generally, force is divided into dynamic force and static force.

Examples of devices that measure dynamic force include vibrometers, accelerometers, wave height meters, impact testers, vortex flowmeters, and gyros.

On the other hand, there are pressure gauges, differential pressure gauges, load cells (scales), etc. that measure static force.

The present invention relates to a force detector suitable for use in these sensors.

An example in which the force detector of the present invention is used as a pressure gauge sensor will be described below.

FIG. 1 is a diagram illustrating the configuration of an example of a pressure sensor using a piezoelectric element that has been commonly used in the past.

In the figure, 1 is a cylindrical container with a bottom surface 11, and 2 is a flexible, thin-walled circular shape that covers the opening of the container 1 and whose circumferential end is fixed to the container 1, and which measures the pressure to be measured. It is a pressure receiving plate.

3 is a disc-shaped piezoelectric element, and a bonding surface 31 of the piezoelectric element 3 is bonded to the pressure receiving plate 2 with an adhesive.

In such a configuration, when the measurement pressure P is applied, the pressure receiving plate 2
When the pressure receiving plate 2 is deflected, a force is applied to the piezoelectric element 3 in the direction of the arrow X shown in the figure, and an electrical output corresponding to the amount of deflection of the pressure receiving plate 2 is obtained from the piezoelectric element 3.

In such a device, in order to increase the sensitivity, the pressure receiving plate 2 must be made wider and the amount of deflection must be increased.

However, in this way it is not possible to construct an inherently robust sensor.

FIG. 2 is a diagram illustrating the configuration of another example of a conventionally commonly used pressure sensor.

In this example, a push screw 12 made of an electrically insulating material is provided on the bottom surface 11 of the container 1 to press and support the piezoelectric element 3 in the direction of the arrow Y shown in the figure.

In such a configuration, since the piezoelectric element 3 is supported by the push screw 12, the measured pressure P is
can be directly received as a force in the same direction as the acting direction of the force.

However, with such a support method using the push screw 12, the characteristics of the electrical output of the piezoelectric element 3 change significantly due to changes in the state of the support point, loosening of the push screw, etc.

In the conventional example described above, for example, an epoxy adhesive is used for the bonding surface 31 between the pressure receiving plate 2 and the piezoelectric element 3, but when used in a high temperature atmosphere, such adhesive is used. Adhesives cannot be used.

Further, the joint surface 31 between the pressure receiving plate 2 and the piezoelectric element 3 must be a dense layer in order to transmit force.

For high temperature applications, for example, it is common practice to braze the piezoelectric element 3 to the pressure receiving plate 2.

In this case, since it is not possible to directly braze the piezoelectric element, a method is used in which a platinum layer is formed on the adhesive surface of the piezoelectric element 3, which also serves as an electrode, and this platinum layer is used to fix it to the pressure receiving plate 2. There is.

It is difficult to form a platinum layer by vapor deposition because platinum is inert.
Generally, the bonding surface of the piezoelectric element 3 is formed by sputtering platinum, which requires complicated work and is very expensive.

However, since electrical insulation between the pressure receiving plate 2 and the pressure receiving plate 2 is not possible,
If insulation is required, additional measures are required.

The present invention solves these problems.

An object of the present invention is to provide a small force detector with good sensitivity and stable characteristics.

FIG. 3 is an explanatory diagram of the configuration of an embodiment of the present invention.

In the figures, the same symbols as in Figures 1 and 2 have the same functions.

Below, only the parts different from those in FIGS. 1 and 2 will be explained.

3 is a piezoelectric element part, in this case lithium niobate (L
A piezoelectric element made of iN b Os ) is used.

4 is made of an insulating material, and the piezoelectric element part 3 is connected to a container 1 and a pressure receiving plate 2.
This is a sealed body that is electrically insulated from the inside of the container 1 and sealed inside the container 1, and is made of a glass material.

In the above configuration, when the measurement pressure P is applied to the pressure receiving plate 2,
Stress is generated within the container 1 depending on the measured pressure P.

Since the piezoelectric element part 3 is integrally and highly rigidly sealed inside the container 1 by the sealing body 4, stress is also generated in the piezoelectric element part 3.

Due to this stress, the piezoelectric element part 3 has the following effects due to the piezoelectric effect:
A charge or voltage is generated corresponding to the measured pressure.

If this electrical signal is measured by a measuring device with high input impedance, the pressure value of the pressure to be measured can be detected.

In this case, since the entire piezoelectric element part 3 is fixed to the container 1 and the pressure receiving plate 2 by the sealing body 4, (1) stress transmission characteristics are excellent, and measured pressure is reliably transmitted to the piezoelectric element with high sensitivity.

(2) There is no instability such as peeling due to deterioration of adhesive function due to aging of the adhesive, and a stable product can be obtained over a long period of time.

(3) Since there is little air permeability, there is no deterioration in insulation due to moisture.

Since a piezoelectric element is originally an insulating material, even a slight drop in insulation due to moisture or the like can have a large effect on the output electrical signal.

(4) In particular, glass with a melting temperature of 500°C or higher is selected and has high heat resistance.

(5) Since the dielectric strength is sufficiently high, even if the piezoelectric element exceeds the Curi point during the sealing process and the piezoelectric effect disappears, the piezoelectric effect can be restored by performing a polarization (or repolarization) process after the sealing process.

(6) The sealing state is reproducible and consistent, and does not affect the characteristics of the piezoelectric element.

(7) Insulation and sealing can be performed at the same time.

(8) The bonding portion between the electrode of the piezoelectric element and the lead wire can be reinforced.

(9) Low cost.

It has the following advantages.

Note that even if a slight gap is partially formed between the sealed body 4 and the pressure receiving plate 2 or the piezoelectric element portion 3, the transmission efficiency decreases.

Therefore, in the case of glass in particular, each component has a circular piezoelectric element to prevent uneven stress from occurring during thermal contraction when the molten glass cools and solidifies during the sealing process, and to prevent cracks from forming in the glass. It is desirable to form concentric circles around the center.

In addition, mutual dimensions are carefully determined so that stress due to overcurrent is not applied to each component and the bonding surfaces of the components do not separate due to differences in thermal expansion coefficients.

It is preferable that the joint surfaces be in a sealed state where compressive force is applied to each other.

Note that when the piezoelectric element part 3 is insulated and sealed in the container 1 with the sealing body 4, the lead wire 3 drawn out from the piezoelectric element part 3
2, the piezoelectric element part 3 is suspended and supported so that the piezoelectric element part 3 is placed in the center of the container 1, the position of the piezoelectric element part at the time of sealing can be determined almost accurately by a simple method. I can do it.

FIG. 4 is a configuration explanatory diagram of another embodiment of the present invention.

In this embodiment, the pressure receiving plate 2 in the shape of a thin disk is constructed from a metal block with a large mass, and is designed to be used as an accelerometer sensor or the like.

In the above embodiment, the piezoelectric element part 3 was explained to be made of lithium niobate, but it may also be made of piezoelectric crystal such as lithium niobate or crystal, or ceramic piezoelectric ceramic such as zircon or lead titanate. It may be a pressure-sensitive element, in short, any element that converts pressure into an electrical signal is fine.

Furthermore, the sealing body 4 is not made of glass, but may be made of a sealing material such as epoxy, cement, ceramic, or mica. It is sufficient that the insulated tag is chemically stable.

As explained above, in the present invention, the piezoelectric element portion is configured to be integrated with the container using a sealing material inside the container.

As a result, the piezoelectric element portion can be reliably fixed in the container with uniform force, so that force can be transmitted to the piezoelectric element more efficiently than in the past, and high sensitivity can be obtained.

Therefore, according to the present invention, it is possible to realize a force detector that is small, highly sensitive, and has stable characteristics.

[Brief explanation of drawings]

1 and 2 are explanatory diagrams of the configuration of a conventional example, FIG. 3 is an explanatory diagram of the configuration of one embodiment of the present invention, and FIG. 4 is an explanatory diagram of the configuration of another embodiment of the present invention. 1...Container, 2...Pressure plate, 3...
. . . Piezoelectric element portion, 4 . . . Sealing body.

Claims (1)

[Claims] 1 a piezoelectric element section that detects stress as a charge or voltage;
A force detector that detects force as stress, comprising a container with one side fixed and the piezoelectric element section provided therein, and a highly rigid sealed body that seals and fixes the piezoelectric element section inside the container. .