JPH06207869A - Piezoelectric vibration sensor - Google Patents

Abstract

PURPOSE:To enable correct detection of vibration without being affected by pyroelectric noise, by short-circuiting electrodes in one pair out of pairs of electrodes which are in contact with the side charged positively or negatively and by detecting an output between the electrodes in the other set. CONSTITUTION:The output generated by a stress in a first piezoelectric body 3 is denoted by V, for instance. Moreover, the amplitude of pyroelectric noise generated in this piezoelectric body 3 is denoted by Vs1. Then the output generated on the opposite sides of the piezoelectric body 3, that is between electrodes 5 and 6, is V+Vs1. Besides, the pyroelectric noise generated in a second piezoelectric body 4, that is, an output between electrodes 7 and 8, is -Vs2. Accordingly, the output of the whole of a sensor constructed of these components connected in series, i.e., an output between the electrodes 5 and 8, is expressed by V+(Vs1-Vs2). When the amplitudes of the noise generated in the piezoelectric bodies 3 and 4 are assumed to be equal herein, Vs1-Vs2 is offset and the output of the sensor is only based on the vibration of arm object to be measured. Thus, the vibration can be detected correctly.

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, and more particularly to a piezoelectric vibration sensor that is not affected by pyroelectric noise and can be miniaturized.

[0002]

2. Description of the Related Art Conventionally, as a piezoelectric vibration sensor for measuring the vibration of an object to be measured, a cantilever type, a diaphragm type,
Various types such as a compression type and a shearing type are known, but a compression type that is highly reliable and can be downsized is often used. Generally, this compression type sensor is composed of a pedestal, a pedestal side electrode, a piezoelectric body, a load body side electrode, and a load body which are sequentially laminated, and the lower surface of the pedestal is rigidly attached to an object to be measured for use. When the measured object vibrates, the pedestal side vibrates together with the measured object, but a delay occurs due to inertial force on the load side, and the delay causes a compressive or tensile stress to act on the piezoelectric body in proportion to the vibration acceleration. . At that time, electric charge or voltage is generated on both sides of the piezoelectric body in proportion to the stress. Therefore, the magnitude of vibration of the object to be measured can be detected by measuring the electric output from the electrodes arranged on both sides of the piezoelectric body. It is a thing.

However, in this compression type sensor, due to the effect of pyroelectricity, which is the property of the piezoelectric body to generate an electric charge due to the inherent temperature change, the output generated by the stress change due to the vibration is added to the pyroelectricity. What is superposed with the characteristic noise is detected as the sensor output. Therefore, in order to accurately detect the vibration of the object to be measured, it is necessary to reduce this pyroelectric noise as much as possible. As an attempt to reduce this pyroelectric noise, two piezoelectric bodies are arranged side by side on one pedestal, and piezoelectric vibrations are electrically connected so as to cancel out the pyroelectric noise similarly generated in the two piezoelectric bodies. Sensors have been proposed.

FIG. 2 is a diagram showing an example of such a piezoelectric vibration sensor. In FIG. 2, 11 is a first piezoelectric body, 12 is a second piezoelectric body, and electrodes a14 and c16 respectively.
It is bonded to the pedestal 2 via. Further, on the surfaces of the first piezoelectric body 11 and the second piezoelectric body 12 opposite to the pedestal,
The electrode b15 and the electrode d17 are bonded to each other, and the load body 13 is further bonded to the electrode b15 of the first piezoelectric body 11 to form the detection unit 1. Of the above four electrodes, the electrode a14 and the electrode c1 arranged on the pedestal side.
6 is connected by a conductive wire 9 and is short-circuited. On the other hand, the electrode b1
5 and the electrode d17 are connected to separate conductive lines 19 and 20, and these conductive lines 19 and 20 are connected to a measuring device (not shown) to detect the output between the electrode b15 and the electrode d17. . Here, the first piezoelectric body 11 and the second piezoelectric body 12 are both positively charged on the pedestal side so that the directions of generation of electric charges due to temperature change are the same, for example, when the temperature rises, It is assumed that the opposite side is arranged to be negatively charged.

According to such a sensor, the sum of the output and the pyroelectric noise due to the stress change due to the vibration is generated at both ends of the first piezoelectric body 11 forming the detecting portion 1, and
Only pyroelectric noise is generated at both ends of the piezoelectric body 12.
Then, from the output of the first piezoelectric body 11 to the second piezoelectric body 12
Since they are electrically connected so as to subtract the output of P, the pyroelectric noises cancel each other out, and only the output due to the stress change due to vibration is obtained.

[0006]

However, in the sensor in which the two piezoelectric bodies are arranged side by side, the pyroelectric noise is significantly reduced, but since the two piezoelectric bodies are arranged side by side,
The lateral size of the sensor will be at least twice as large. On the other hand, this vibration sensor is often mounted on a curved surface such as a rotating body, and it is desirable to make the bottom surface as small as possible in order to reliably mount it on these curved surfaces and detect vibration accurately. Therefore, an object of the present invention is to provide a piezoelectric vibration sensor that is not affected by pyroelectric noise and can be downsized.

[0007]

This problem is formed by sequentially laminating an electrode, a first piezoelectric body, an electrode, a load body, an electrode, a second piezoelectric body and an electrode. When the second piezoelectric body generates an electric charge due to a temperature change, one of the pair of electrodes contacting the positively charged side and the pair of electrodes contacting the negatively charged side of each piezoelectric body This can be solved by a piezoelectric vibration sensor characterized by short-circuiting the electrodes of the pair of electrodes and detecting the output between the electrodes of the other pair.

The piezoelectric vibration sensor of the present invention will be described in detail below. FIG. 1 is a diagram showing an embodiment of a piezoelectric vibration sensor of the present invention. In the figure, reference numeral 1 denotes a detection unit, which is adhered to a pedestal 2 which is a flat aluminum block. The detection unit 1 includes an electrode A5, a first piezoelectric body 3, an electrode B6, a weight body 10 which is a brass block having a predetermined mass, an electrode C7, and a second piezoelectric body 4, from the side of the pedestal 2. And the electrode D8 are sequentially laminated and adhered. The electrode B6 and the electrode C7 are electrically short-circuited by being connected by a conductive wire 9, and the conductive wires 19 and 20 are respectively connected to the electrode A5 and the electrode D8.

The detector 1 and the pedestal 2 are housed in a hollow package (not shown) so that the bottom surface of the pedestal 2 and the bottom surface of the package are in close contact with each other. It is glued. In addition,
Although not shown, an impedance conversion circuit is provided inside the package, and the conductive wire 1 connected to the electrodes A5 and D8 is provided in the impedance conversion circuit.
9 and 20 have been entered. Further, the impedance conversion circuit is provided with a cable for taking out the output whose impedance has been lowered to the outside, and the cable extends through the side surface of the package to the outside. Here, in the first piezoelectric body and the second piezoelectric body, when a temperature change occurs, the load body side, that is, the side in contact with the electrode B6 and the electrode C7 respectively, is charged with the same sign, and the electrode A5, the electrode It is assumed that the side in contact with D8 is arranged so as to be charged with the same sign of the opposite polarity.

The piezoelectric vibration sensor is rigidly attached to the object to be measured by screwing or the like so that the bottom surface of the package is brought into close contact with the object to be measured. Then, the cable extending from the sensor is connected to the measuring device, and the magnitude of the vibration of the object to be measured is detected by measuring the charge amount or the voltage fluctuation generated according to the vibration acceleration of the object to be measured.

According to such a piezoelectric vibration sensor, when vibration is generated in the object to be measured, the pedestal side of the first piezoelectric body 3 similarly vibrates, but the load body 10 and the second piezoelectric body 3 on the load body side. A delay due to an inertial force based on the mass of the piezoelectric body 4 or the like occurs, and the delay causes stress to act on both surfaces of the first piezoelectric body 3. On the other hand, such stress does not act on the second piezoelectric body 4, and only pyroelectric noise is generated.

In the present invention, the pyroelectric noises generated in these two piezoelectric bodies are canceled by connecting them in series with opposite polarities to reduce the noises. For example, let V be the output generated by the stress in the first piezoelectric body 3,
Further, when the magnitude of the pyroelectric noise generated in the first piezoelectric element 3 and V _S1, both sides of the first piezoelectric element 3, i.e., the output generated between electrodes A5 and the electrode B6 becomes V + V _S1 .
The pyroelectric noise generated in the second piezoelectric body 4, that is, the output between the electrodes C7 and D8 can be expressed as -V _S2 in consideration of the polarity. Therefore, the output of the whole sensor in which they are connected in series, that is, the output between the electrode A5 and the electrode D8 is V + (V _S1
-V _S2 ). Here, if the magnitudes of pyroelectric noises generated in the first and second piezoelectric bodies are the same, (V _S1 −V _S2 ) is canceled out, and the sensor output is only that based on the vibration of the measured object. , It becomes possible to detect vibration accurately.

Further, in such a piezoelectric vibration sensor,
Since the piezoelectric body, the load body, and the electrodes A, B, C, and D are all stacked in the vertical direction, the size in the horizontal direction can be made as small as the conventional piezoelectric vibration sensor, and rotation is possible. Can be securely attached to curved surfaces such as the body. Also, the size in the vertical direction is at most 1
The increase is less than or equal to mm, which is not a practical problem.

In the above description, one embodiment of the present invention has been described. The shape and material of the piezoelectric vibration sensor of the present invention are as follows.
It is not limited to this. In the above description, the electrode B6
Although the electrode C7 and the electrode C7 are short-circuited, the electrode A5 and the electrode D8 may be short-circuited to detect the output between the electrode B6 and the electrode C7. In addition, the arrangement direction of the piezoelectric body is not limited to the above, and in the direction of charge generation of pyroelectric noise, one of the pairs of electrodes on the side charged with the same sign is short-circuited, and the output is detected between the other electrodes. If the conductive wires are connected as described above, any arrangement direction may be adopted.

The first and second piezoelectric bodies used in the piezoelectric vibration sensor of the present invention are lead zirconate titanate (PZ).
T), a ceramic piezoelectric material such as lead titanate (PT), a polyvinylidene fluoride (PVDF), a vinylidene cyanide / vinyl acetate copolymer, a plastic piezoelectric material such as nylon 7 or nylon 11, or a mixture thereof. can do. However, it is preferable to use the same material for the first piezoelectric body and the second piezoelectric body so that the pyroelectric noises of both have the same characteristics.

As the pedestal, various materials such as the above-mentioned metal materials such as the aluminum block and plastic materials are used, but it is preferable to use a rigid body in order to efficiently transmit the vibration of the object to be measured. Further, the load body may be made of any material as long as it has a predetermined mass, but in consideration of downsizing of the whole sensor, a material having a large specific gravity is selected so that the volume is small even with the same weight. Is preferred.

The piezoelectric body and the electrode, the electrode and the pedestal or the load body, and the pedestal and the package may be connected by any means as long as they can be firmly connected, but the connection by adhesion suitable for mass production is preferable. In addition, a means for keeping these connections strong may be provided separately. The package may be made of a metal material such as stainless steel or may be a plastic material, but it is preferable to use an electromagnetically shielded package in order to eliminate the influence of disturbance noise.

Further, in the above description, the impedance conversion circuit is housed in the package, but the present invention is not limited to this. For example, an amplifier circuit may be incorporated to improve the sensor output. Further, the substrate on which those circuits are formed may be used as the pedestal to reduce the size of the entire sensor.

The piezoelectric vibration sensor of the present invention will be described below with reference to specific examples. Example 1 A vibration sensor having a structure as shown in FIG. 1 was manufactured by the method described below. A PVDF piezoelectric film having a size of 5 mm × 5 mm and a thickness of 0.1 mm is prepared, and epoxy adhesive is used on both upper and lower surfaces thereof to form a thickness of 30 μm.
A copper foil was bonded to obtain a sensor chip in which three layers were laminated. One copper foil of those sensor chips is used as an electrode A, and the other copper foil is used as an electrode B, and the electrode A is 10 mm × 10 mm ×
A 10 mm aluminum block was adhered to form a pedestal. Also,
A brass block having a size of 6 mm × 6 mm × 1 mm was adhered to the electrode B to form a load body. Further, another sensor chip was bonded to the opposite surface of the load body, the electrode on the load body side was designated as electrode C, and the electrode on the opposite side was designated as electrode D. The electrode B and the electrode C were short-circuited with a conductive wire to form a detection unit. Further, the electrode A and the electrode D were each connected to an impedance conversion circuit.

However, the first and second sensor chips
Both of the piezoelectric bodies are arranged so that the load body side is positively charged when the temperature rises. 20 mm x 20 mm
In a brass hollow package with a size of 20 mm,
The detection unit and the impedance conversion circuit were housed. At that time, attach the pedestal so that it closely adheres to the bottom of the package,
Completed the vibration sensor.

The sensor thus produced was attached to a vibration generator, the output cable was connected to a voltage measuring device, and the sensor output (V) when the vibration of frequency 80 Hz and acceleration 1 G was applied, and the vibration The peak value (V of the output change that occurs when the sensor is immersed in hot water at 60 ° C.
_S ) was measured. The results are shown in Table 1. However, the results were expressed as the percentage of V _S for V (%).

(Embodiment 2) A piezoelectric body having a thickness of 0.5 m
The same sensor as in Example 1 was prepared except that the PZT plate of m was used, and the same measurement was performed. The results are shown in Table 1.
However, the results were expressed as the percentage of V _S for V (%).

(Comparative Example 1) A PVDF piezoelectric film having a size of 5 mm x 5 mm and a thickness of 0.1 mm was prepared, and epoxy adhesives were used on both upper and lower surfaces thereof to obtain a thickness of 30 μm.
A copper foil was bonded to obtain a sensor chip in which three layers were laminated. One of the copper foils of the sensor chips is used as a base electrode, the other copper foil is used as a load body electrode, and the base electrode is 10 mm ×
An aluminum block of 10 mm × 10 mm was adhered to form a pedestal. Further, a brass block having a size of 6 mm × 6 mm × 1 mm was adhered to the electrode on the load body side to form a load body and a detection unit was manufactured. The pedestal side electrode and the load body side electrode were each connected to an impedance conversion circuit. 20 mm x 20 mm x 20 m
The detector and the impedance conversion circuit were housed in a brass hollow package having a size of m. At that time, the pedestal-side electrode of the detection portion was adhered to the bottom surface of the package so as to be in close contact, and the vibration sensor was completed. The same measurement as in Example 1 was performed using the sensor thus manufactured. The results are shown in Table 1. However, the results were expressed as the percentage of V _S for V (%).

(Comparative Example 2) A piezoelectric body having a thickness of 0.5 m
A sensor similar to Comparative Example 1 was prepared except that the PZT plate of m was used, and the same measurement as in Example 1 was performed. The results are shown in Table 1. However, the result is the ratio of V _S to V (%)
Displayed in.

[0025]

[Table 1]

As is clear from these results, in the sensor made up of only one piezoelectric body as in the comparative example, the pyroelectric noise under the present measurement conditions is larger than the output based on the vibration. On the other hand, in the case where the two piezoelectric bodies are laminated as in the example, the magnitude of the pyroelectric noise is significantly reduced to 5% of the output.

[0027]

As described above, according to the piezoelectric type vibration sensor of the present invention, not only can the influence of pyroelectric noise, which has been a problem in the past, be greatly reduced, but the entire sensor can be made compact. Since it is maintained, it can be reliably attached to a curved surface such as a rotating body, and the magnitude of vibration can be accurately detected.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing an example of a conventional piezoelectric vibration sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Detection part, 2 ... Pedestal, 3 ... 1st piezoelectric body, 4 ... 2nd piezoelectric body, 5 ... Electrode A, 6 ... Electrode B, 7 ... Electrode C, 8 ... Electrode D, 9 ... Conductive wire, 10 ... Load body, 19 ... Conductive wire, 20
… Conductive wire

Claims (1)

[Claims] 1. An electrode, a first piezoelectric body, an electrode, a load body, an electrode, a second piezoelectric body, and an electrode are sequentially laminated, and the first piezoelectric body and the second piezoelectric body change in temperature. When a charge is generated by, a short circuit is made between the electrodes of one of the pair of electrodes in contact with the positively charged side and the pair of electrodes in contact with the negatively charged side of each piezoelectric body. , A piezoelectric vibration sensor characterized by detecting an output between electrodes of the other set.