JPH08201420A - Impact sensor - Google Patents

Abstract

PURPOSE: To provide an impact sensor which can be manufactured at a low cost, is improved in acceleration outputting voltage characteristic and frequency characteristic, and has high sensitivity and high quality. CONSTITUTION: An impact sensor is constituted of a case 4 having a rectangular recessed section 10 and is equipped with an upper lid 9, bimorph-structure element 3 formed by sticking two piezoelectric ceramic plates 1 and 2 respectively carrying Ni-plated internal and external electrodes 7 and 8 to each other, internal terminal 5, and external terminal 6. A pair of recessed supporting sections 12 is formed at the central side edges of the case in the direction perpendicular to the direction of the long axis of the case 4 and the internal terminal 5 is integrally formed with the external terminal 6 on the inner side face of the sections 12 and the element 3 is mounted by inserting both ends of the element 3 into the supporting sections 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock sensor using a bimorph structure element composed of two piezoelectric ceramics.

[0002]

2. Description of the Related Art Various types of conventional acceleration detection methods have been put into practical use. Among them, the impact sensor using the piezoelectric ceramic has a simple structure and can be used at a high temperature, and is therefore widely used for detecting vibrations of various machines and knocking detection of automobile engines.

FIG. 3 is a perspective view showing a conventional impact sensor. The conventional impact sensor includes an upper lid 9, a case 4 having a rectangular parallelepiped concave portion 10, a bimorph structure element 3 in which two piezoelectric ceramics 1 and 2 having an external electrode 8 and an internal electrode 7 are bonded together, and an internal terminal. 5 and an external terminal 6 formed integrally.

The bimorph structure element 3 has a size of 1 to 2 μm on a surface of the rectangular plate-shaped piezoelectric ceramics 1 and 2 orthogonal to the thickness direction.
The external electrode 8 and the internal electrode 7 are formed by applying a degree of Ni plating, and two sheets are bonded together by using an adhesive agent. Both ends of the bimorph structure element 3 are connected to the internal terminals 5 exposed in the recess 10 of the case 4.

The recess 10 of the case 4 is provided so as to have a uniform clearance of about 0.15 mm from both ends of the bimorph structure element 3.

The internal terminal 5 is connected to an external terminal 6 provided in the longitudinal direction of the case 4 and protruding. External terminal 6
Is a structure that is surface-mounted on a substrate.

When an external force is applied to the above-mentioned impact sensor in the thickness direction of the rectangular plate-shaped bimorph structural element, for example, acceleration of impact or the like causes the bimorph structural element to vibrate in the thickness direction. The impact sensor detects the amount of electric charge generated by the displacement due to the external force.

The sensitivity at this time is determined by dimensions such as the length, width and thickness of the rectangular plate of the piezoelectric ceramic, and its frequency characteristic is determined by its capacitance and the impedance of the amplifier circuit.

[0009]

However, in the conventional impact sensor, the internal terminal 5 and the external terminal 6 formed by punching and bending the metal plate 13 as shown in FIG. 4 are used.
When and are molded into a case, they are integrally molded. That is, the punched product of the metal plate 13 is placed in a mold, and a resin of liquid crystal polymer is press-fitted to integrally mold the case and the internal and external terminals. However, the stamped product of the metal plate is expensive, and the dimension and accuracy of the stamped product are poor. Therefore, the dimension and accuracy of the bimorph structure element must be suppressed to 2 to 3 μm. There was a drawback that it took man hours. In addition, there are drawbacks such that the acceleration output voltage characteristic and the operating frequency characteristic are deteriorated and variations occur.

Further, in order to obtain an impact sensor having good frequency characteristics, it is sufficient to make the length of the piezoelectric ceramic large, but this is contrary to the demand for shortness, lightness and thinness. On the other hand, when the size is reduced and the impedance of the amplifier circuit is increased, the S / N ratio is deteriorated, so that there is a problem that a shock sensor having high sensitivity in a low frequency region cannot be obtained.

[0011] Therefore, the object of the present invention is inexpensive and
An object of the present invention is to provide a high-sensitivity impact sensor having improved acceleration output voltage characteristics, high detectability, and improved frequency characteristics.

[0012]

SUMMARY OF THE INVENTION The present invention comprises a bimorph structural element having two piezoelectric ceramics bonded together, a case having an internal terminal, an external terminal and an upper lid.
In a shock sensor in which the bimorph structural element is housed in the case and the electrodes of the bimorph structural element are connected to the internal terminals, a long axis of the bimorph structural element is provided in a central portion of opposite side surfaces inside the case. A shock sensor characterized in that a groove for supporting an end portion in a direction is provided, and further, the internal terminal integrated with the external terminal is provided in the groove, wherein the case is made of liquid crystal polymer resin, The impact sensor is characterized in that the internal terminal and the external terminal are made of a conductive resin.

[0013]

Function: The case and the upper lid are made of liquid crystal polymer.
When molding the case, a recess is provided inside the case,
A groove serving as a pair of supporting portions is provided on a central edge of the case that is orthogonal to the long axis direction. At this time, a conductive resin is injected into the inner peripheral side surface of the supporting portion and the bottom surface and outer peripheral side surface of the case to simultaneously form terminals in which internal and external terminals are integrated in advance. By fitting and mounting both ends of the bimorph structural element in which two piezoelectric ceramics are bonded to each other in the longitudinal direction to the supporting part, only the ends are closely attached and fitted with a predetermined clearance evenly with the case. . As a result, variation is reduced, resolution of acceleration output voltage characteristics and frequency characteristics is resolved, acceleration output voltage characteristics are improved, and frequency characteristics are improved. Therefore, the detectability is increased. Moreover, since resin is cheaper than metal, the price can be reduced.

[0014]

Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view and a perspective view showing an impact sensor of the present invention. FIG. 1A is a perspective view of a bimorph structural element used in the impact sensor of the present invention. FIG.
(B) is an assembled perspective view of the impact sensor of the present invention.
FIG. 1C is a cross-sectional view taken along the line AA of FIG. FIG.
(D) is a perspective view of the impact sensor of the present invention.

As shown in FIG. 1A, the impact sensor of the present invention has a length of 3.5 mm, a width of 0.7 mm and a thickness of 0.15 m.
A rectangular plate-shaped piezoelectric ceramics 1 and 2 having a thickness of m are plated with Ni having a thickness of 1 to 2 μm to form a positive (+) external electrode 8 and a negative (-) internal electrode. The bimorph structure element 3 formed by adhering them with the adhesive 11 is used as a passive element.

As shown in FIG. 1B, the bimorph structure element 3 has a thickness of 0.35 mm. The case 4 has a pair of supporting portions 12 for fitting and mounting the above bimorph structural element in a rectangular parallelepiped block made of a liquid crystal polymer and having a length of 5.4 mm, a width of 1.3 mm and a height of 1.3 mm. The length is 3.6mm, the width is 0.65mm, and the height is 0.6mm.
A 9 mm recess 10 is provided.

Further, as shown in FIG. 1C, the external terminal 6 made of a conductive resin provided on the case 4 is integral with the internal terminal 5 and passes through the bottom surface of the case 4 to support the support portion 12. It is exposed flatly on the inner surface and is in close contact with and connected to the external electrodes 8 at both ends of the bimorph structure element 3 attached to the support portion 12. In addition, a length of 5.4 mm, width of 1.3 mm, and thickness of 0.2 m made of the liquid crystal polymer shown in FIG.
The upper lid 9 made of m is covered with an adhesive and fixed, and then, as shown in FIG.
A surface mount type impact sensor as shown in (3) is completed.

The output voltage was measured by applying vibration to the impact sensor of the present invention in the thickness direction of the bimorph structure element with a vibrator.

As a comparative example, as shown in FIG. 3, a bimorph structure element 3 made of a rectangular plate-shaped piezoelectric ceramic with Ni-plated electrodes is used as in the case 4 as in the case of the conventional example as in the above-described embodiment. The sample was attached to the concave portion 10, covered with the upper lid 9, fixed with an adhesive, and provided as a sample. This conventional product was vibrated in the thickness direction of the bimorph structure element 3 by a vibrator to measure the output voltage.

The results are shown in FIGS. 2 (a) and 2 (b). FIG. 2A is a diagram showing frequency characteristics. Figure 2
(B) is a diagram showing an acceleration output voltage characteristic.

As shown in FIG. 2 (a), in the product of the present invention,
The frequency characteristic of 50 Hz to 10 KHz becomes a graph like B, and a constant output voltage of 5 dB was obtained in the region of 100 Hz to 10 KHz.

On the other hand, in the conventional product, 50 Hz to 10 KHz
The frequency characteristic of becomes a graph like C, and 100-70
Although the output voltage is 0 dB at 0 Hz, at 900 Hz or higher, the resonances indicated by X, Y, and Z occur at both ends of the bimorph structure element, the output voltage is disturbed, and the frequency characteristic is deteriorated.

Further, as shown in FIG. 2 (b), 0 to 15G
The acceleration output voltage is D
On the other hand, the conventional product has a graph like E, and the acceleration output voltage of the product of the present invention is higher than that of the conventional product. Therefore, it can be seen that the detectability of the impact sensor is improved.

[0025]

As described above, by using the conductive resin for the integrally molded internal terminal and external terminal,
The adhesion between the case and the internal and external terminals increased, and the terminal resonance disappeared. Therefore, the frequency characteristics are improved,
Moreover, the variation is reduced and the acceleration output voltage characteristic is improved. Therefore, it is possible to provide an inexpensive and highly sensitive impact sensor of high quality.

[Brief description of drawings]

FIG. 1 is a sectional view and a perspective view showing an impact sensor according to an embodiment of the present invention. FIG. 1A is a perspective view of a bimorph structure element used in an impact sensor according to an embodiment of the present invention. Figure 1 (b)
FIG. 3 is an assembled perspective view of an impact sensor according to an embodiment of the present invention. FIG.
1C is a cross-sectional view taken along the line AA of FIG. Figure 1 (d)
The perspective view of the impact sensor of the Example of this invention.

FIG. 2 is a diagram showing frequency characteristics and acceleration output voltage characteristics of the impact sensor according to the embodiment of the present invention. FIG. 2A is a diagram showing frequency characteristics. FIG. 2B is a diagram showing an acceleration output voltage characteristic.

FIG. 3 is an assembled perspective view of a conventional impact sensor.

FIG. 4 is a perspective view showing an internal terminal and an external terminal formed by punching out and integrally bending a metal plate used in a conventional impact sensor.

[Explanation of symbols]

 1, 2 Piezoelectric ceramic 3 Bimorph structural element 4 Case 5 Internal terminal 6 External terminal 7 Internal electrode 8 External electrode 9 Upper lid 10 Recess 11 Adhesive 12 Supporting part 13 Metal plate B, D Conventional product C, E Conventional product C, E Conventional product X, Y , Z resonance point

Claims (2)

[Claims] 1. A bimorph structure element formed by laminating two piezoelectric ceramics together, a case having an internal terminal, an external terminal and an upper lid, the bimorph structure element being housed inside the case, and an electrode of the bimorph structure element. In the impact sensor formed by connecting the internal terminal to the internal terminal, a groove for supporting a longitudinal end of the bimorph structural element is provided in a central portion of opposite side surfaces inside the case, and the external groove is provided in the groove. An impact sensor comprising the internal terminal integrated with a terminal. 2. The impact sensor according to claim 1, wherein the case is made of a liquid crystal polymer resin, and the integrated internal terminal and external terminal are made of a conductive resin.