JPH07209071A - Piezoelectric vibration sensor - Google Patents

Abstract

PURPOSE:To provide a piezoelectric vibration sensor, which can be easily manufactured and of which output can be remarkably reduced by pyroelectricity and which can be downsized. CONSTITUTION:A detecting part 5, which is formed by providing electrodes on both surfaces of a piezoelectric body 7, is rigidly fitted onto a base 3. One electrode of the detecting part 5 is formed out of two divided electrodes a1, a2, and shape of these divided electrodes a1, a2 are formed into a linear symmetrical shape arranged in both sides of a line for dividing these divided electrodes. The other electrode of the detecting part 5 is a common electrode (b), which is not divided, and the two divided electrodes a1, a2 are electrically connected in series to each other through the common electrode (b). Shape of a load body 9 is formed into a linear symmetrical shape arranged in both sides of the described line when it is projected to the described line from over. A detecting axis is in parallel with the electrode surface of the detecting unit 5 and vertical to the described line, and the output of a sensor is obtained as a sum of quantity of charge or potential difference generated between the two divided electrode a1, a2 and the common electrode (b).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric vibration sensor, which has improved sensitivity and reduced malfunction due to pyroelectric noise.

[0002]

2. Description of the Related Art In general, a vibration sensor is used for facility diagnosis for measuring vibration of machinery and equipment and monitoring and diagnosing abnormality of machinery. It is also used in consumer products that perform various controls depending on the presence or absence of vibration and the size of the device, such as a camera shake prevention mechanism for video cameras and a mechanism for preventing data reading and writing errors due to vibration and shock in hard disk drives, floppy disk drives, etc. Has been. There is a piezoelectric type vibration sensor as a kind of such a vibration sensor, and the piezoelectric type vibration sensor is classified into several types such as a cantilever type, a diaphragm type, a shearing type, a compression type and the like depending on a vibration detecting method.

By the way, in a compression type piezoelectric vibration sensor (hereinafter abbreviated as piezoelectric type vibration sensor), electrodes for signal extraction are provided on both sides of a plate-shaped or film-shaped piezoelectric body as a detection section, Further, a lead wire or the like is connected to this electrode so that a sensor signal can be output. Then, one surface of the detection unit is rigidly fixed to a pedestal such as a substrate or a sensor package on which a processing circuit for processing the output from the detection unit is mounted, and the load body is rigidly fixed to the other surface. In the piezoelectric vibration sensor having such a configuration, when the piezoelectric body is subjected to vibration in a direction perpendicular to the electrode surface provided on the piezoelectric body, the piezoelectric body is compressed and stretched in proportion to the force, that is, acceleration, due to the inertial force of the load body. Under the stress of, a charge proportional to the magnitude of the stress is induced on the electrode provided on the piezoelectric body, a potential difference occurs between the pair of electrodes, a sensor output is obtained, and the magnitude of vibration (acceleration) is known. You can Further, in the Cartesian coordinate system, for vibrations in the other two directions orthogonal to the vibration detection direction, by forming the detection portion in point symmetry with respect to the detection axis, the induced charges generated on the electrodes are mutually Canceled and no output is obtained. Therefore, a piezoelectric vibration sensor having excellent directivity can be obtained (Japanese Patent Application No. 1-273111).

Therefore, the conventional piezoelectric vibration sensor is often used as a vibration sensor because of its relatively simple structure and excellent directivity as described above. However, the following drawbacks have been pointed out due to its simple structure and the characteristics that the piezoelectric body originally has. First of all, the first point is due to its structure. As described above, in the compression type, since electrodes are provided on both sides of the piezoelectric body, it is necessary to connect lead wires for extracting output to both sides thereof. As a result, the work for manufacturing the piezoelectric vibration sensor becomes complicated, and the cost increases due to the time and labor, and the price also rises because it is not suitable for mass production.

The second point is due to the property that the piezoelectric body originally has. That is, since the piezoelectric body has piezoelectricity and pyroelectricity at the same time, it is resistant to ambient temperature changes. Also, electric charges are induced in the electrodes on the piezoelectric body, and the piezoelectric vibration sensor malfunctions to generate an output. This output is large as the ambient temperature changes rapidly, and there is a problem that the piezoelectric body itself has a very high pyroelectric sensitivity. In order to solve such problems, the structure of the piezoelectric vibration sensor body has been thickened in the past, and materials with poor heat conduction have been used to make it difficult for heat to transfer, thereby reducing pyroelectric noise to a low level. However, these also contribute to the cost increase. Further, the one in which a lead wire is connected to each of the electrodes on both sides of the piezoelectric body has a drawback that it is difficult to realize because of a limitation in miniaturization in consideration of mounting in a precision instrument.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is a piezoelectric type that is easy to manufacture, can significantly reduce the output due to pyroelectricity, and can be miniaturized. To obtain a vibration sensor.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a piezoelectric type vibration is obtained by rigidly mounting a sensing section having electrodes on both sides of a piezoelectric body on a pedestal, and rigidly mounting a load body on the sensing section. In the sensor, one electrode of the detection unit is a divided electrode divided into two, and the shape of these two divided electrodes is line symmetric with the line segment dividing these divided electrodes as the center of symmetry, and the other electrode Is a non-divided common electrode, the two divided electrodes are electrically connected in series through the common electrode, and the shape of the load body is such that the load body is connected to the line segment from above. When projected, it is line-symmetrical with the line segment as the center of symmetry, the detection axis is parallel to the electrode surface of the detection unit, and is in a direction perpendicular to the line segment, and the output of the sensor is of the two divided electrodes. The amount of charge generated between each and the common electrode Characterized in that it is obtained as the sum of the position difference. The line segment that divides the split electrode is preferably an electrode gap and has a linear shape.

[0008]

1 is a perspective view showing an embodiment of a piezoelectric vibration sensor of the present invention. This piezoelectric vibration sensor has a base 3
The detection unit 5 is rigidly mounted on the pedestal 3, and the load body 9 is rigidly mounted on the detection unit 5.

The pedestal 3 has a sufficient rigidity, and examples thereof include a substrate on which a processing circuit for processing an electrical output from the detection section 5 is mounted, a package for housing a piezoelectric vibration sensor, and the like.

The detecting section 5 is formed by sandwiching a piezoelectric body 7 made of a material having piezoelectricity with a first electrode 11 and a second electrode 12 made of a metal foil. As the material having piezoelectricity, an inorganic piezoelectric material such as lead zirconate titanate, lead titanate, barium titanate, or a ferroelectric polymer material such as polyvinylidene fluoride is used.

The first electrode 11 is between the pedestal 3 and the piezoelectric body 7, and is divided into two by an electrode gap (line segment) 13 as shown in FIG. a
₁ and the second divided electrode a ₂ . The shapes of the first divided electrode a ₁ and the second divided electrode a ₂ are the electrode gap 1
It has line symmetry with 3 as the center of symmetry. It is desirable that the electrode gap (line segment) 13 be linear.

The second electrode 12 is located between the piezoelectric body 7 and the load body 9 and is not divided (hereinafter, this second electrode 12 is referred to as a common electrode b). Then, the first divided electrode a ₁ and the second split electrodes a _2, are electrically connected in series via a common electrode b as shown in FIG. 3, also, the first divided electrode a ₁ second One end of a lead wire (not shown) for extracting an output is connected to each of the two-divided electrodes a ₂ . The other ends of these lead wires are connected to a connection terminal (not shown) of a processing circuit that processes an electrical output. Then, when the piezoelectric vibration sensor detects vibration, the magnitude of the vibration can be evaluated by the magnitude of the output (V), and at this time, the output (V) is the first divided electrode a _{1 as} shown in FIG. Of the charge amount or potential difference (V _a1-b ) between the common electrode b and the common electrode b and the charge amount or potential difference (V _b-a2 ) between the common electrode b and the second divided electrode a ₂ (V _{a1- b} + V
_b-a2 ).

The load body 9 is composed of a rigid body that functions as an inertial mass portion, is displaced by receiving vibration (acceleration), and causes the piezoelectric body 7 of the detection portion 5 to be distorted or stressed. When the load body 9 is projected onto the electrode gap 13 from above, it has line symmetry with the electrode gap 13 as the center of symmetry.

In the piezoelectric type vibration sensor having such a configuration, the direction parallel to the electrode surface of the detection portion 5 and perpendicular to the electrode gap 13 is the detection axis G, and the vibration component in this direction is detected, It becomes insensitive to vibration components in other directions.

Next, the principle of detecting vibration in the piezoelectric vibration sensor shown in FIG. 1 will be described. When the piezoelectric type vibration sensor of FIG. 1 receives a vibration from a direction parallel to the electrode surface of the detection unit 5 and perpendicular to the electrode gap 13, the detection unit 5 causes the inertia force of the load body 9 to move the pedestal 3 of the pedestal 3. When the piezoelectric body 7 is projected onto the electrode gap 13 from above by generating a rotational moment force with the fixed surface as a fulcrum, the piezoelectric body 7
On both sides of which the electrode gap 13 is a symmetry line, stresses of the same absolute value are applied in the opposite directions of compression and tension, and at positions symmetrical with respect to the electrode gap 13. Then, as shown in FIG. 3, the charge amount or the potential difference (V _a1-b ) between the first divided electrode a ₁ and the common electrode b and the common electrode b.
When the charge amount or potential difference between the second divided electrode a ₂ (V
_b-a2 ) becomes equal, and the sum ( _Va1-b + _Vb-a2 ) is obtained as the output (V), and the magnitude of vibration can be known.

When the piezoelectric type vibration sensor of FIG. 1 receives vibration from a direction parallel to the electrode surface of the detection portion 5 and perpendicular to the detection axis G, the first divided electrode a ₁ and the second divided electrode a ₁ Electrode a ₂
, And the electric charges induced between the common electrode b and each other are canceled out, no potential difference occurs, and no output is obtained. When the piezoelectric vibration sensor of FIG. 1 receives a vibration from a direction perpendicular to the surface of the piezoelectric body 7, the inertial force of the load body 9 causes a stress to be generated in the piezoelectric body 7 substantially uniformly. Split electrode a ₁ and common electrode b
_Potential difference (V _a1-b ) between the common electrode b and the second divided electrode a
_The relationship as shown in the following formula (I) is established between the potential difference (V _b-a2 ) between the _two . V _a1-b = −V _b-a2 (I) Therefore, the potential difference between the first divided electrode a ₁ and the common electrode b (V
_a1-b) and the sum becomes zero between the common electrode b and the potential difference between the second divided electrode _{a 2 (V b-a2)} , the output is not obtained. As described above, the piezoelectric vibration sensor of the embodiment has an excellent directivity in the vibration detection direction, like the conventional piezoelectric vibration sensor.

Next, in the piezoelectric type vibration sensor shown in FIG. 1, the principle that the output due to pyroelectricity is greatly reduced will be described. In the piezoelectric type vibration sensor of FIG. 1, when a sudden temperature change is applied, electric charges are induced by the pyroelectric effect between each of the first divided electrode _a1 and the second divided electrode _a2 and the common electrode b, and the potential difference is Occurs. The electric charge induced by the pyroelectric effect is due to the direction of temperature change, that is, as the temperature rises or falls,
Since it depends on the polarization direction of the piezoelectric body 7, the first split electrode
Charges having different signs are induced between the _a1 surface, the second divided electrode _a2 surface, and the common electrode b surface, but the magnitude of the charges is different from that of the piezoelectric body 7.
Are almost equal in the same plane. Therefore, at this time, a potential difference (V _a1-b ) due to the pyroelectric output generated between the first divided electrode a ₁ and the common electrode b and a potential difference (V a due to the pyroelectric output generated between the common electrode b and the second divided electrode a ₂ sum with _b-a2 ) (V _a1-b + V
_b-a2 ) becomes 0, and no output due to the pyroelectric effect can be obtained.

In the piezoelectric vibration sensor of FIG. 1, the first divided electrode a ₁ and the second divided electrode a ₂ provided on one surface of the piezoelectric body 7 are electrically connected in series via the common electrode b. Since it is connected, the lead wire for extracting the output may be connected to one side of the piezoelectric body, so unlike the conventional piezoelectric vibration sensor in which the lead wire was connected to the electrodes on both sides of the piezoelectric body, An apparatus used in semiconductor manufacturing or the like such as wire bonding can be used for connecting lead wires. Further, when the split electrode side of the detection unit 5 is fixed to the pedestal 3, since it can be directly placed on a processing circuit that processes an electrical output, the wire boding does not take time. Therefore, the piezoelectric vibration sensor of the embodiment is easy to manufacture and can be mass-produced, so that the cost can be reduced. Further, since it is sufficient to connect a lead wire for taking out an output to one side of the piezoelectric body 7, the size can be reduced accordingly, and mounting on a precision device becomes possible. Further, noise due to the pyroelectric effect is significantly reduced, so that the cost can be reduced, and the reliability of the vibration detection value is further improved. Further, the sum (V _a1 ) of the potential difference (V _a1-b ) generated between the first divided electrode a ₁ and the common electrode b and the potential difference (V _b-a2 ) generated between the common electrode b and the second divided electrode a _{2 Since -b} + _Vb-a2 ) is obtained as an output, the sensitivity to vibration in the detection axis G direction is high.

Specific examples will be shown below. (Example) A piezoelectric vibration sensor as shown in FIG. 1 was produced as follows. First, a piezoelectric body 7 made of lead zirconate titanate having a thickness of 450 μm, a length of 3 mm and a width of 3 mm.
Two pieces of split electrodes made of copper foil having a thickness of 30 μm, a length of 1.3 mm, and a width of 3 mm are attached to one surface of the piezoelectric body with an epoxy adhesive so that the electrode gap becomes 400 μm, and then the piezoelectric body 7 On the surface opposite to the surface where the divided electrodes of
A common electrode b made of copper foil having a length of 0 μm, a length of 3 mm, and a width of 3 mm was attached using an epoxy adhesive to fabricate the detection unit 5. Next, an alumina substrate on which the divided electrode surface of the produced sensing unit 5 is mounted with an impedance exchanging circuit for processing the electrical output from the sensing unit 5, an amplifying circuit, and an electrical circuit including these connecting terminal portions. The upper connection terminal portion was fixed by using a conductive adhesive. Then, on the upper surface of the common electrode of the detection unit 5, a mass of 1 g, a thickness of 1 mm, a length of 6 mm,
A brass load element 9 having a width of 3 mm was fixed using an epoxy adhesive to obtain a piezoelectric vibration sensor. This was used as the piezoelectric vibration sensor of the example. In this piezoelectric vibration sensor, the direction parallel to the electrode surface of the detection unit 5 and perpendicular to the electrode gap 13 is the detection axis.

(Comparative Example) A piezoelectric vibration sensor (Japanese Patent Application No. 3-139638) as shown in FIG. 4 was produced as follows. First, a copper foil electrode 21 having a thickness of 30 μm, a length of 3 mm, and a width of 3 mm was attached to both surfaces of a piezoelectric body 7 similar to that used in the above-mentioned embodiment using an epoxy adhesive,
The detector 5 was produced. Then, on the upper surface of the one electrode 21 of the manufactured detection unit 5, a thickness of 1 mm, a length of 3 mm, and a width of 3 m.
An FRP support 22 of m was provided, a notch was made in a part of the support to expose the electrode 21, and one end of a lead wire was connected to this. In addition, the other electrode 21 surface of the detection unit 5 is
Directly conductive bonding to one connection terminal portion on the alumina substrate 23 on which an impedance exchange circuit for processing the electric output from the detection unit 5, an amplification circuit, and an electric circuit including these connection terminal portions are mounted. Then, the other end of the lead wire was connected to another connecting terminal portion. Then, on the upper surface of the support 22 of the detection unit 5, a mass of 1 g,
A brass load element 9 having a thickness of 1 mm, a length of 4.25 mm and a width of 4.25 mm was fixed using an epoxy adhesive to obtain a piezoelectric vibration sensor. This was used as a piezoelectric vibration sensor of a comparative example. In this piezoelectric type vibration sensor, the detection axis is in the same direction as in the above embodiment.

Then, regarding the piezoelectric type vibration sensor of the above-described embodiment and the piezoelectric type vibration sensor of the comparative example, the respective detection axis directions and two directions orthogonal to the detection axis direction (the orthogonal direction 1 and the orthogonal direction 2). The sensitivities when a sine acceleration of 80 Hz and 1 G was applied were measured. The results are shown in Table 1 below.

[0022]

[Table 1]

As is clear from the results shown in Table 1 above,
It can be seen that the piezoelectric vibration sensor of the example has about three times the sensitivity in the detection axis direction as compared with the piezoelectric vibration sensor of the comparative example.
Further, it can be seen that the directivity is excellent in both the piezoelectric vibration sensors of the example and the comparative example, and the sensitivities in the two directions orthogonal to the detection axis direction are each less than 5%.

Next, the pyroelectric output was measured when the piezoelectric vibration sensor of the example and the piezoelectric vibration sensor of the comparative example were transferred from room temperature to a constant temperature bath at 60 ° C. The measurement here is how many times the maximum pyroelectric output can be obtained (pyroelectric sensitivity) with respect to the sensitivity per 1 G obtained in the result of the sensitivity measurement previously performed, and the sensitivity of the sensor. Two points of time (convergence time) required to fall within the output range of ± 10% were evaluated. The results are shown in Table 2 below.

[0025]

[Table 2]

As is clear from the results shown in Table 2 above, the piezoelectric vibration sensor of the embodiment has significantly less output due to the pyroelectric effect and lower pyroelectric sensitivity than the piezoelectric vibration sensor of the comparative example. I understand.

[0027]

As described above, in the piezoelectric vibration sensor of the present invention, the two divided electrodes provided on one surface of the piezoelectric body are electrically connected in series via the common electrode. Since the lead wire for extracting the output may be connected to one side of the piezoelectric body, unlike the conventional piezoelectric vibration sensor in which the lead wire is connected to the electrodes on both sides of the piezoelectric body, the semiconductor device such as wire bonding is used for connecting the lead wire. The equipment used for manufacturing can be used, and when fixing the split electrode side of the detection part to the pedestal, it can be placed directly on the processing circuit that processes the electrical output. It doesn't take. Therefore, the piezoelectric vibration sensor of the present invention,
It is easy to manufacture and can be mass-produced, so the cost can be reduced. Further, since it is sufficient to connect a lead wire for taking out the output to one side of the piezoelectric body, it is possible to make the size smaller and mount it on a precision instrument. Further, noise due to the pyroelectric effect is significantly reduced, so that the cost can be reduced, and the reliability of the vibration detection value is further improved. Further, since the sum of the potential differences generated between each of the two divided electrodes and the common electrode is obtained as an output, the sensitivity to vibration in the detection axis direction is high.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a piezoelectric vibration sensor of the present invention.

FIG. 2 is a cross-sectional view of the piezoelectric vibration sensor shown in FIG. 1, taken along line XX.

3 is a diagram showing an equivalent circuit in which two divided electrodes of the piezoelectric vibration sensor shown in FIG. 1 are electrically connected in series via a common electrode.

FIG. 4 is a perspective view showing a piezoelectric vibration sensor of a comparative example.

[Explanation of symbols]

3 ... Pedestal, 5 ... Detection part, 7 ... Piezoelectric body, 9 ... Load body,
11 ... 1st electrode, a ₁ ... 1st division electrode, a ₂ ... 2nd division electrode, 12 ... 2nd electrode, b ... Common electrode, 13 ...
・ Electrode gap, G ... Detection axis

Claims (2)

[Claims] 1. A piezoelectric vibration sensor comprising a pedestal, to which a detection unit having electrodes provided on both sides of a piezoelectric body is rigidly attached, and a load body is rigidly attached to the detection unit. The electrode is a divided electrode divided into two, and the shape of these two divided electrodes is line symmetry with the line segment dividing these divided electrodes as the center of symmetry, and the other electrode of the detection unit is not divided. A common electrode, the two divided electrodes are electrically connected in series via the common electrode, and the shape of the load body is the line when the load body is projected onto the line segment from above. Is a line symmetry with the center of the symmetry as the center of symmetry, the detection axis is parallel to the electrode surface of the detection unit and is in a direction perpendicular to the line segment, and the output of the sensor is that of the two divided electrodes and the common electrode. As the sum of the amount of charge or the potential difference that occurs between The piezoelectric vibration sensor, characterized in that it is. 2. The piezoelectric vibration sensor according to claim 1, wherein the line segment that divides the split electrode is an electrode gap, and the shape of the electrode gap is linear.