JPS61213635A - Curved piezoelectric oscillator type level sensor - Google Patents

Abstract

PURPOSE:To obtain a level sensor which has stable resonance characteristics and is manufactured at a high yield by curving a piezoelectric element plate. CONSTITUTION:When an AC voltage is applied between electrodes 5 and 6 from lead lines 8 and 9, the piezoelectric oscillator 1 expands and contracts repeatedly in oscillation mode shown by arrows according to a change in the polarity of the input voltage. The periphery of the oscillator 1, however, is fixed by a ring member 2 and curved, so the oscillator 1 oscillates in the leftward direction of an arrow B when expanding or the rightward direction of the arrow B when contracting. Namely, the oscillation of the oscillator 1 is converted form the mode A to the mode B. When, however, the oscillator 1 is flat, a force required to convert oscillation in the mode A into flexural oscillation in the mode B is large, so the sensor becomes lower in sensitivity. On the other hand, the oscillator 1 is curved, so the sensitivity is extremely high and the Q value of resonance is large.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a level sensor that detects whether the amount of liquid or powder in a container is sufficient, and in particular has stable detection characteristics and reliability. The present invention relates to a level sensor with high production yield.

[Conventional technology and problems]

Conventionally, various types of level sensors have been proposed for detecting whether the amount of liquid or powder in a container is sufficient, but piezoelectric level sensors have recently been attracting attention from a practical standpoint.

Japanese Patent Publication No. 5B-1371 provides electrodes on both sides of a piezoelectric ceramic plate, divides the electrode on one side into two, uses this divided electrode as an input electrode, and places a piezoelectric ceramic plate between it and the electrode on the opposite side. A piezoelectric element configured to apply a mechanically vibrating alternating current voltage or pulse voltage, use the other divided electrode as an output electrode, and extract a level detection signal from between the electrodes on the opposing surface is pasted on a diaphragm. attachment, fluid, powder,
A level in which the piezoelectric element is driven to vibrate almost parallel to the direction in which the level of the object to be detected, such as particles, changes, and the level detection signal voltage changes depending on the level of the object to be detected. )★Discloses the detector. In a level detector having such a structure, among the vibration modes of the piezoelectric element, a vibration mode parallel to the electrodes is utilized. Since the piezoelectric element is bonded to the diaphragm, the vibration mode is converted into a vibration shade (bending) in a direction perpendicular to the diaphragm. Therefore, when an alternating current electric signal is applied to the piezoelectric element, the diaphragm vibrates in a curved manner, but when the frequency of the electric signal matches the natural frequency of this curved vibration, it resonates and the amplitude reaches its maximum. At this time, electrically, the admittance is at its maximum, but the admittance near the resonance frequency is extremely sensitive to the state of the field element, and changes significantly when powder, liquid, etc. come into contact with it. This phenomenon is used to detect the level of liquids, powders, etc.

However, the resonance characteristics of the piezoelectric element are extremely sensitive to the condition of the diaphragm, and if the bonding condition changes due to air bubbles, foreign matter, etc. entering the adhesive layer between the diaphragm and the piezoelectric element, the resonance characteristics will also vary significantly. Therefore, when attempting to manufacture a level sensor having desired resonance characteristics using the above structure, there is a problem in that the yield is extremely low. Also, the temperature
There is also the problem that the adhesion state between the piezoelectric element and the imaging plate changes slightly due to changes in environmental conditions such as humidity, resulting in a reduction in resonance characteristics.

JP-A-57-80898 discloses a piezoelectric ceramic thin film and an i
Holding the electrodes formed on both main surfaces of the i-film and the periphery of the thin film 1
The present invention discloses a piezoelectric ceramic transducer comprising a frame, and an electric signal applying means for applying an electric signal to the electrode, and the piezoelectric ceramic thin film is fitted into the frame and has a curved surface.

However, this piezoelectric ceramic transducer is used for speakers and microphones, and is not a level sensor for powder, liquid, or the like.

[Means for solving problems]

Therefore, an object of the present invention is to provide a piezoelectric vibrator type level sensor that has stable resonance characteristics and can be manufactured with a high yield.

As a result of intensive research in view of the above purpose, the present inventors came to the conclusion that the structure in which the piezoelectric element is attached to the diaphragm is the cause of the above problem, and the inventors realized that the piezoelectric element plate was curved to attach the diaphragm. The present invention was completed based on the discovery that a level sensor with sufficiently stable resonance characteristics can be obtained without the need for additional steps.

The piezoelectric vibrator type level sensor of the present invention, which detects the level of an object to be detected in a container, includes a curved plate-shaped piezoelectric element, a common electrode provided on one side of the piezoelectric element, and a common electrode provided on the other side of the piezoelectric element. When an excitation input voltage is applied to the common electrode and one of the divided electrodes, an object to be detected is emitted from the common electrode and the other divided electrode. It is characterized by being able to obtain an output voltage according to the level.

[Examples and effects]

FIG. 1 shows the appearance of an embodiment of the level sensor of the present invention. The level sensor has an outwardly convex curved piezoelectric vibrator 1, a ring member 2 and a support frame 3 that fix the periphery of the vibrator.

This level sensor detects the level of the object to be detected, as shown by 4, for example.

2(a) and 2(b) show the main parts of the level sensor. In this embodiment, the curved piezoelectric vibrator has a common electrode 5 on a convex curved surface and a divided electrode on a concave curved surface. 6.7. A lead wire 8 connected to the common electrode 5 is grounded to the metal ring member 2. Further, lead wires 9 and 10 are connected to the divided electrodes 6 and 7, respectively. Since the common electrode 5 is on the side of the object to be detected, it is covered with a protective film 11. Note that it is preferable to extend a part of the common electrode 5 to the concave curved surface side and draw out the lead wire from there so that the lead wire does not come out.

FIG. 3 shows the vibration principle of the curved piezoelectric vibrator 1.

Generally, when electrodes are provided on both sides of a piezoelectric body and an alternating current voltage is applied, the piezoelectric body vibrates perpendicularly and parallel to the electrodes.

The vibration frequencies of both are generally different.

In the piezoelectric vibrator 1 of the present invention, vibration parallel to the electrodes is utilized. Now, when an alternating current voltage is applied between the electrodes 5.6 through the lead wire 8.9, the piezoelectric vibrator 1 repeats expansion and contraction in response to positive and negative fluctuations in the input voltage.

This vibration mode is indicated by arrow A. However, the circumference of the piezoelectric vibrator 1 is fixed by the ring member 2 and is curved, so when the piezoelectric vibrator l tries to expand, the vibration mode becomes a leftward vibration of arrow B, and vice versa. , when trying to reduce the size, it vibrates in the right direction of arrow B. That is, in the structure of the present invention, the vibration of the piezoelectric vibrator l is converted from mode A to mode B. However, if the piezoelectric vibrator 1 is flat, the force required to convert mode A vibration to mode B curved vibration is large, making it insensitive as a sensor and unsatisfactory. On the other hand, since the piezoelectric vibrator of the present invention is curved, it has very good sensitivity and a high resonance Q value.

When the vibration of the piezoelectric vibrator 1 is restrained by an object to be detected such as powder, a corresponding output voltage is obtained from the electrode 5.7 through the lead wire 8.10. Thereby, the level of the object to be detected is detected.

It is desirable that the curved piezoelectric vibrator be thin so that it can sensitively detect the level of the object to be detected, but if it is too thin, there is a problem of breakage, so it is generally desirable that the piezoelectric vibrator be about 0.1 to 0.5 +u+. Also, the radius of curvature of the piezoelectric vibrator is 200
~500 am. If the radius of curvature is smaller than 200II11, it is likely to be damaged (if it is larger than 500+w+m, a large force will be required to convert the vibration mode to the vertical direction of the vibrator, reducing the sensitivity as a sensor.The piezoelectric vibrator as a whole It does not need to be curved, and may have a partially flat shape, for example, a shape with a curved periphery and a flat central part.

The diameter of the piezoelectric vibrator may generally be 10 to 30 m+s.

The electrodes are preferably formed of conductive paint in order not to interfere with the vibration of the piezoelectric vibrator, and have a thickness of 0.1-0.
It is about 3 arms. The protective film formed on the common electrode can be formed using a urethane adhesive or the like, and its thickness is about 0.1=0.2++v+.

The ring member 2 firmly fixes the piezoelectric vibrator, and has an inner circumference that matches the outer circumference of the piezoelectric vibrator.

Also, since the lead wire is grounded, it is made of metal. If necessary, it can be bonded to the outer periphery of the piezoelectric vibrator using an adhesive. The ring member 2 is also fixed to the support frame 3.

Although the objects to be detected include liquids, powders, and granules, it exhibits an excellent function particularly in detecting the level of powders such as toner in copying machines. The input for excitation of the piezoelectric vibrator may be either an alternating current voltage or a pulse voltage.

FIG. 4 shows a level sensor according to another embodiment of the invention. The curved piezoelectric vibrator 20 itself is the same as that of the embodiment shown in FIGS. 1 and 2, but is arranged so that the concave curved surface side is in contact with the object to be detected. The outer periphery of the piezoelectric vibrator 20 is fixed to a rim 22 of a rimmed disc 21. A common electrode is provided on the concave curved surface of the piezoelectric vibrator, and divided electrodes are provided on the convex curved surface of the piezoelectric vibrator, and appropriate lead wires (not shown) are connected to each electrode. Since the piezoelectric vibrator is provided very close to the disk 21, when the piezoelectric vibrator is strongly pressed by a foreign object, the disk 21 acts as a backup and prevents damage to the piezoelectric vibrator. .

The present invention will be explained in more detail by the following examples.

EXAMPLE A level sensor having the structure shown in FIGS. 1 and 2 was manufactured. The curved piezoelectric vibrator 1 is made of Pb (Zr-Ti)03
Made of piezoelectric ceramics, thickness 0.1tm, diameter 1
The diameter was 6 mm, and the radius of curvature was 300 III. Each of the electrodes 5 to 7 was formed using conductive paint, and the protective film was formed using an ultraviolet curing urethane adhesive.

When a sine wave voltage of 5cm was applied to the lead wire 5.7 and the frequency was swept, a steep peak of admittance appeared at 5.62K11z, and a high Q resonance state was obtained. When the sensor was gently put into the toner in the container with its vibrating surface vertical, the admittance of the vibrator decreased as the toner surface 4 became higher, and when it was completely submerged, it became close to a non-resonant state. Therefore, it can be seen that this level sensor is effective as a toner level detection device.

〔Effect of the invention〕

As described above, the piezoelectric level sensor of the present invention has high sensitivity because it uses a vibrator made of a curved piezoelectric element itself, and has stable resonance characteristics because it does not have a structure in which the piezoelectric element and the diaphragm are bonded. and can be manufactured with high yield.

Furthermore, since there is no adhesive part, it is stable against fluctuations in environmental conditions such as temperature and humidity, and is highly reliable.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the external appearance of a curved piezoelectric vibrator type level sensor according to an embodiment of the present invention, and FIG. 2(b) is a rear view of the main parts shown in FIG. 2(a), FIG. 3 is a partially omitted enlarged view of FIG. 2(a), and FIG.
The figure is a longitudinal cross-sectional view of a main part of a curved piezoelectric vibrator type level sensor according to another embodiment of the present invention. l, 20 ...... Curved piezoelectric vibrator 2 ...... Ring member 5.6.7 Old... Electrode 8.9, lO... Lead wire 11... Protective film Figure 1

Claims (2)

[Claims] (1) A piezoelectric vibrator type level sensor that detects the level of an object to be detected in a container includes a curved plate-shaped piezoelectric element, a common electrode provided on one side of the piezoelectric element, and a common electrode provided on the other side of the piezoelectric element. It has a divided electrode provided and a member that fixes the periphery of the piezoelectric element, and when an excitation input voltage is applied to the common electrode and the one divided electrode, the common electrode and the other divided electrode A piezoelectric vibrator type level sensor characterized in that an output voltage corresponding to the level of the object to be detected is obtained from an electrode. (2) In the piezoelectric vibrator type level sensor according to claim 1, the common electrode is provided on a convex curved surface of the piezoelectric element, and the divided electrode is provided on a concave curved surface of the piezoelectric element. A piezoelectric vibrator type level sensor, wherein a protective film is formed on the surface of the common electrode, and the protective film side is in contact with the object to be detected.