JPS5829859B2 - force 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 detects stress and converts it into an electrical signal.

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 embodiment of a pressure sensor using a piezoelectric element, which has been commonly used in the past.

In the figure, 1 is a cylindrical container with a bottom surface 11, 2 is a flexible thin disc-shaped container that covers the opening of the container 1, and whose circumferential end is fixed to the container 1, and the pressure to be measured is It is a pressure receiving plate that receives

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.

With this configuration, when the measuring 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 cases, 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 conventional example of a pressure sensor that has been commonly used.

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 a button with such a configuration, the piezoelectric element 3 is supported by the push screw 12, so that 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, an epoxy adhesive, for example, is used for the bonding surface 31 between the pressure receiving plate 2 and the piezoelectric element 3. However, when used in a high temperature atmosphere, such adhesive is agents cannot be used.

Further, the bonding surface 31 between the pressure receiving plate 2 and the piezoelectric element 3 must be in close contact with each other 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. .

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 diagrams, buttons that are the same as those in Figures 1 and 2 have the same functions.

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

2' is a cylindrical force receiving body having a flange 21' and fixed to the container 1 on the flange 21' side.

Reference numeral 3 denotes a piezoelectric element part, which is disk-shaped and placed inside the container 1. In this case, two piezoelectric elements are placed facing each other across the center axis of the force receiving body 2'. Piezoelectric elements are used.

4 is made of an insulating material, and the piezoelectric element part 3 is connected to the container 1 and the force receiving body 2.
A sealing body that is electrically insulated from ′ and sealed inside the container 1,
Glass material is used.

With the above configuration, the measurement pressure P applied to the force receiving body 2' as shown in FIG. 3 is transmitted to the piezoelectric element portion 3 via the sealing body 4.

In this case, as shown in FIG. 3, stresses in opposite directions are generated across the central axis of the force receiving body 2.

Thus, an electric signal corresponding to this stress is generated in each piezoelectric element portion 3a, 3b.

The measured pressure P can be detected by processing this electrical signal using an electrical circuit with high input impedance.

In this embodiment, twice as many electrical signals can be obtained by differentially processing the outputs of the piezoelectric element sections 3a and 3b.

Further, since the measured pressure P is amplified by the length l of the force receiving body 2' and applied to the piezoelectric element section 3, the piezoelectric element section 3 can detect it with high sensitivity.

Furthermore, by configuring the force receiving body 2' to have two lengths, the container portion can be separated from the measurement location, so that it can be used, for example, at a measurement location in a high temperature atmosphere.

In this case, the entire piezoelectric element portion 3 is covered with the container 1 by the sealing body 4.
Since it is integrally fixed to the force-receiving body 2', (1) the stress transmission characteristics are excellent and the 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 portion 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 in the glass. It is preferable to configure the structure concentrically around Must be decided carefully.

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

Furthermore, 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. Can be done.

FIG. 4 is an explanatory diagram of the configuration of another embodiment of the present invention, and FIG. 5 is an explanatory diagram of the configuration of the main part of FIG. 4.

In FIGS. 4 and 5, 3' is a piezoelectric element portion, which has a disk shape as shown in FIG. 5, and its center is located on the central axis of the force-receiving body 2'.

The piezoelectric element portion 3' consists of a disk-shaped element body 31' and electrodes 32', 33', and 34'.

The electrode 32' has a thin disk shape and is provided on one side of the element body 31'.

On the other hand, the electrode 33'. 34' has a substantially arcuate shape and is symmetrically provided on the other side of the element body 31' with the center of the element body 31' being narrowed.

With this configuration, the signals detected between the electrodes 32' and 33' and between the electrodes 32' and 34' are as shown in FIGS. 6A and 6B.
As shown in FIG. 6, the phase is opposite, and when this output is taken out differentially, an output twice as large as that in FIG. 6A and H is obtained, as shown in FIG. 6C.

Since only one detection element is required, the cost can be reduced, and since one detection element can be installed in a small space, a compact device can be obtained.

The piezoelectric element portion 3' shown in FIG. 5 has a cylindrical shape as shown in FIG. 7A, a rectangular shape as shown in FIG. 1B, or a rectangular shape as shown in FIG. 7C.
It may also be configured in a donut shape such as.

FIG. 8 is an explanatory diagram when the present invention is applied to a flow rate measuring device using a Karman vortex.

In the figure, A is a pipe through which the fluid to be measured flows, B is a columnar vortex generator inserted at right angles to the pipe 1, and C is the device of the present invention.

Conventionally, in this type of device, the pressure of the vortex flowing downstream of the vortex generator bends a pressure receiving plate or diaphragm with one end fixed, and this is detected by a strain gauge attached near the fixed part. There is a device that has been

However, with such devices, the amount of strain must be increased in order to obtain sufficient detection sensitivity, and the rigidity of the strain gauge mounting section must be reduced, which inherently requires a robust structure. The drawback was that it was difficult to do so.

In this embodiment, the pressure received by the force receiving body 2' is transferred via the sealing body 4 by the piezoelectric element part 3' which is sealed and fixed in the container 1 near the part fixed to the pipe A. It is now possible to directly detect stress as stress.

Moreover, since the pressure to be measured is magnified and detected by the length l in the diameter direction of the conduit A of the force receiving body 2', high detection sensitivity can be obtained.

Therefore, the device of the present invention can be made more robust.

Furthermore, since the natural frequency can be increased, a wide range of flow velocities or flow rates can be detected with high sensitivity.

Although the container 1 and the force-receiving body 2' are constructed as separate bodies in the above-mentioned embodiments, it goes without saying that they may be constructed as one body.

Moreover, although it has been described that two piezoelectric element parts 3 are arranged, it is of course possible to arrange one piezoelectric element part 3 on one side of the central axis of the force receiving body 2'.

In the above-mentioned embodiments, it was explained that the piezoelectric element part 3 is made of lithium niobate, but it may also be made of piezoelectric crystal such as lithium niobate or crystal, or zircon lead titanate (P
It may be a ceramic piezoelectric ceramic such as ZT) or lead titanate, or a pressure sensitive element, as long as it converts pressure into an electrical signal.

Furthermore, the sealing body 4 may be made of epoxy, cement, ceramic, mica, or other sealing materials instead of glass, and in short, the force acting on the force receiving body 2 can be reliably sensitive to the piezoelectric element portion 3. Any material that conducts well, electrically insulates, and is chemically stable is sufficient.

As explained above, in the present invention, the piezoelectric element portion is integrally sealed inside the container with a sealing material.

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 conventional example.

Further, since the force receiving body is provided, the force to be measured is expanded, and detection can be performed with high sensitivity. Furthermore, since the container portion can be separated from the measurement location, high temperature locations can also be measured.

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 the conventional example, FIG. 3 is an explanatory diagram of the configuration of one embodiment of the present invention, FIG. 5 is an explanatory diagram of the configuration of another embodiment of the present invention, and FIG. 6 is an explanatory diagram of the differential output. FIG. 7 is an explanatory diagram of the essential part of another embodiment of the present invention. FIG. 8 is an explanatory diagram of the main part of the present invention using Karman vortex FIG. 2 is an explanatory diagram when applied to a flow rate measuring device. 1... Container, 2... Receptive body, 3...
. . . Piezoelectric element portion, 4 . . . Sealing body.

Claims (1)

[Claims] 1 A piezoelectric element section for detecting stress, a container whose negative side is fixed and the piezoelectric element section is provided inside, and one end of the container has the same pressure on the other side and a measuring force acts on the other end side. A force detector comprising a columnar force receiving body and a sealing body that seals and fixes the piezoelectric element part to the container so that stress generated by a measurement force on the force receiving body is transmitted to the piezoelectric element part. .