JPS6228843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric membrane vibration sensor for measuring natural or artificial vibrations of, for example, the ground, buildings, machines, etc., and particularly relates to a membrane vibration sensor using a polymer piezoelectric film as a piezoelectric body.

Conventional piezoelectric vibration sensors are mostly seismo-type piezoelectric sensors in which a piezoelectric material itself is used as the main spring, and a weight is connected to a case via a piezoelectric spring. Inorganic piezoelectric materials such as lead titanium zirconate are used.

On the other hand, examples of piezoelectric materials include monopolymers such as polyvinylidene fluoride, polyvinyl fluoride, and polyvinyl chloride, vinylidene fluoride and other monomers such as vinyl fluoride, trifluoroethylene, tetrafluoroethylene, fluorochlorovinylidene, etc. A polymer piezoelectric material obtained by polarizing a copolymer with It has been proposed to apply it to vessels.

A membrane vibration sensor using a polymeric piezoelectric film includes a polymeric piezoelectric film stretched over a frame, and an approximately center portion of the polymeric piezoelectric film in order to apply a tensile force to the polymeric piezoelectric film. A vibration measuring device consisting of a weight attached to a part has been proposed, but this vibration measuring device is not necessarily satisfactory in terms of sensitivity.

An object of the present invention is to provide a membrane vibration sensor with higher detection sensitivity using a polymer piezoelectric film.

According to the present invention, the object is to respond to external vibrations by having at least two ends supported by a plate spring fixed to a base body and given a curved strain, and tensioned by the elastic force of the plate spring. A weight is directly or indirectly coupled to a freely vibrating portion of the polymer piezoelectric film so that most of the weight of the weight is retained by the polymer piezoelectric film that vibrates. Achieved by a membrane vibration sensor.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

In the vibration sensor shown in FIG.
2' is attached. This piezoelectric film is stretched across both ends of a bent plate spring 4 (for example, an arcuate plate spring) fixed to a base 3, and a weight 5 is fixed to the center of the piezoelectric film 1. ing. One electrode, for example the electrode 2, is connected to an ammeter, a voltmeter, an
The other electrode 2' is coupled to the ground side of the instrument circuit 7 via wiring from electrode 2'.

In Fig. 1, 8 is a screw for attaching the leaf spring to the base body 3.
Reference numeral 9 indicates a screw for attaching the film, and reference numeral 10 indicates a screw for attaching the board to an object subject to vibration detection, such as the ground, a building, or a machine.

The vibration sensor shown in FIG. 1 is a seismic type vibration sensor that uses a polymer piezoelectric film 1 as a spring. However, the polymer piezoelectric film 1 has a low Young's modulus and therefore has a high mechanical-electrical constant g. It is natural that extremely good sensitivity can be obtained because the long sides can be made longer than that of the film 1, but since it is a polymer film, it has extremely high elongation, so it is difficult to stretch the film by fixing both ends of the film. Therefore, the strength of the spring can be freely changed by changing the tension. Therefore, in this system, the natural frequency of the spring can be freely changed not only by changing the mass of the weight but also by changing the tension of the film. Furthermore, since the vibrations of a stretched film are greatly attenuated by air resistance, the damping ratio can be easily changed by, for example, providing a case if necessary and changing the gap with the case and the size of the air holes provided in the case. be able to.

As is known, the characteristics of a seismic vibration sensor are expressed by the natural frequency fn and the damping ratio h. When the dimensions of the film are constant, vibration can be changed by changing the tension of the film and the mass of the weight, as well as the thickness and area of the film. Therefore, in the vibration sensor of the present invention, the size of the device , any natural vibration can be obtained regardless of the shape, the size can be freely selected, and the damping ratio can be easily set so as to obtain appropriate damping.

Therefore, the membrane vibration sensor of the present invention is not limited to an acceleration sensor, but can be freely configured as a vibration displacement sensor or a vibration velocity sensor. In addition, for example, by changing the film tension,
Distortion of leaf springs (curvature, width, thickness, length, shape, etc.)
This allows the user to easily change the distance between the film and the case or the size of the air holes in the case using the same device. It is also possible to measure the displacement, velocity and acceleration of the vibration with the same device.

In the present invention, the curved leaf spring is preferably an elastic metal body such as a phosphor bronze plate or steel material. Since the polymeric piezoelectric film is fixed at least to both ends of this leaf spring, an appropriate tension is always applied to it and it can respond sensitively even to very minute vibrations. If both ends of the piezoelectric film are stretched on a rigid body instead of being supported by curved leaf springs as in the present invention, when the polymer piezoelectric film is relaxed by the weight of the weight, the polymer piezoelectric When the force to pull the weight back to the initial position of the weight supported together with the piezoelectric film does not act, and a force due to vibration is applied to the weight, the tension applied to the piezoelectric film is:
This is smaller than the case where a polymeric piezoelectric film is supported by a plate spring that has been given a bending strain, and cannot exhibit acute sensitivity to the force caused by vibration.

The tension of the film can be adjusted by adjusting the degree of curvature of the curved leaf spring. It is desirable that the elasticity of the spring in vertical vibration is sufficiently greater than the elasticity of the piezoelectric film.

In FIG. 1, both ends of the piezoelectric film are supported by plate springs and stretched, but the piezoelectric film may be Y-shaped or cross-shaped and supported by plate springs at three or four points.

The membrane vibration sensor of the present invention (1) can detect vibrations without being affected by acceleration; (2) It can also respond to low frequency vibrations. (3) Can detect vibrations in a wide range of frequencies. (4) It has the excellent effect of being able to respond to minute vibrations.

Example 1 Thickness 30μ with aluminum vapor deposited film on both sides
A piezoelectric vinylidene polyfluoride film with a width of 10 mm and a piezoelectric constant of d ₃₁ 7×10 ⁻⁷ cgsesu was used. This film 1 is stretched between both ends of a plate spring 4 made of phosphor bronze (PBSP, 0.25 mm thick, 10 mm wide, with small notches on both ends in front of the film holding part) fixed on a substrate 3. 3.16 in the center of film 1.
I made a vibration sensor as shown in Figure 1 with a fixed weight 5 of g. The length of the free vibrating part of this piezoelectric film 1 (including the part where the weight is fixed) was 50 mm.

The phosphor bronze plate spring 4 of this vibration sensor is used to apply tension to the piezoelectric film 1 by stretching it, and the elasticity of the spring when vertically vibrating is made sufficiently larger than that of the piezoelectric film 1. Since the influence of the elastic vibration of the spring 4 can be ignored during vibration measurement in the vibration range close to the natural vibration of the film 1, it may be considered as a part of the base body.

This vibration sensor was fixed on a vibration table as the base 3, and the vibration frequency was varied while keeping the amplitude of the vibration table constant at 10 μm, and the electrode output voltage was measured. As the instrument circuit 8, an oscilloscope was used.

As a result of the measurement, it was confirmed that this vibration sensor is a vibration displacement type pickup having a film resonance frequency of 25 Hz and an output voltage of 10 V/1 mm of vibration amplitude sensitivity.

Example 2 A vibration sensor similar to that of Example 1 was manufactured by changing the configuration of the phosphor bronze plate spring. In other words, PBSPS with a width of 10 mm and a thickness without notches as a phosphor bronze plate spring.
When a vibration sensor of 0.3 mm was used and the rest was the same as in Example 1, the resonance frequency was 51 Hz,
The output sensitivity was 1.8V/1mm.

Next, change the weight of this vibration sensor's weight.
When the weight is 7.16g, the resonance frequency is 39Hz and the output sensitivity is 2.5V/1mm, and when the weight is 11.96g, the resonance frequency is 28Hz and the output sensitivity is 3.2V/1.
It became mm.

In the membrane vibration sensor of the present invention, at least two ends of the polymer piezoelectric film are supported by a plate spring fixed to a base body and given a bending strain, and tensioned by the elastic force of the plate spring. Since the polymer piezoelectric film is stretched, when the weight of the polymeric piezoelectric film is relaxed by the weight of the weight and the position of the weight moves downward, the weight is It is constantly pulled back to the initial position where it was stretched together with the polymeric piezoelectric film. On the other hand, if a polymer piezoelectric film is stretched together with a weight on the fixed end of a rigid body instead of a leaf spring that has been given a bending strain, the polymer piezoelectric film will relax under the weight of the weight. However, since the fixed end is a rigid body, no force is applied to pull the weight back to its initial position, which is suspended together with the polymeric piezoelectric film.

In this way, in the case of a sensor consisting of a polymer piezoelectric film supported by a plate spring that is given a bending strain and a weight, the weight is placed on a horizontal plane that includes the fixed positions of both ends of the polymer piezoelectric film. It vibrates around a position extremely close to . On the other hand, in the case of a sensor consisting of a weight and a polymeric piezoelectric film supported on the fixed end of a rigid body, instead of a leaf spring that is given a bending strain, the weight is formed by fixing both ends of the polymeric piezoelectric film. It vibrates around a position far from the horizontal plane that contains the position.

In the sensor configured as described above, when a force F due to vibration is applied to the weight, the polymer piezoelectric film is pulled in its length direction,
Tension T is applied to the polymer piezoelectric film. Force F
When the angle between the direction in which T is applied (vibration direction) and the polymer piezoelectric film is θ, the tension T is expressed by the following equation.

T=F/2cosθ The magnitude of the electrical signal generated by this tension T is proportional to the tension T.

Here, in the case of a sensor consisting of a polymer piezoelectric film supported by a plate spring subjected to a bending strain and a weight (hereinafter referred to as system 1), θ is θ ₁ , and both ends are connected to a rigid body. If θ is θ ₂ in the case of a sensor consisting of a supported polymeric piezoelectric film and a weight (hereinafter referred to as system 2), the relationship θ ₁ >θ ₂ always holds true from the above. If the same force F due to vibration acts on these two systems, the weight of system 1 will vibrate around θ 1, and the mass of system 2 will vibrate around θ ₁ .
The weight of oscillates around θ ₂ . At this time,
The rate of change of the tension T generated in the polymeric piezoelectric film near θ ₁ and θ ₂ is expressed as [dt/dθ] ₌ = ₁ and [dt/dθ] ₌ = ₂ . For example, θ ₁ = 80°,
When θ ₂ = 60°, [dt/dθ] _{= 80} ° = 16.6F, [dt/dθ] _{= 60}
゜ = 1.73F, and _{the following} relationship is obtained: [dt/dθ] _{= 1} > [dt/dθ] ₌ 2.

This relationship holds that θ ₁ > θ ₂ in the range 0°<θ≦90°
always holds as long as the relationship holds. In this way, when the same vibration-based force is applied, the system 1 sensor always obtains a larger electrical signal compared to the system 2 sensor.

As described above, the membrane vibration sensor of the present invention is composed of a weight and a polymer piezoelectric film supported by a plate spring subjected to a bending strain. It has the advantage of being able to respond more sensitively to vibrations than membrane vibration sensors.

The membrane vibration sensor of the present invention can be used not only as an acceleration sensor, but also as a speed sensor and a displacement sensor, and can also be used as a vibration acceleration sensor, as well as a vibration speed sensor and a vibration displacement sensor. Can be applied.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a preferred embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Polymer piezoelectric film, 2, 2'... Thin film electrode, 3... Substrate, 4... Arcuate plate spring, 6... Weight.

Claims (1)

[Claims] 1. A polymeric piezoelectric film that vibrates in response to external vibrations, with at least two ends supported by a plate spring fixed to a base and given a bending strain, and tensioned by the elastic force of the spring. A membrane vibration sensor characterized in that a weight is directly or indirectly coupled to a freely vibrating portion of the polymer piezoelectric film so that most of the weight of the weight is retained.