JPH08201421A - Cantilever type impact sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a high-sensitivity impact sensor with improved frequency characteristics in a low frequency range. [Structure] A bimorph structural element 2 in which two rectangular and plate-shaped piezoelectric ceramics 5 provided with external electrodes 8 and internal electrodes 9 plated with Ni are bonded together, and a concave portion of a liquid crystal polymer case 1 having an upper lid 6 A cantilever type impact sensor attached to the support portion 4 at one end of the weight sensor 10, wherein a weight 12 such as solder is provided on the plate surface on the side where the bimorph structural element 2 is not fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock sensor having a piezoelectric ceramic cantilever structure, and more particularly to a shock sensor for low frequency vibration.

[0002]

2. Description of the Related Art Conventionally, impact sensors based on various principles have been used as sensors for detecting impact, vibration and the like. Among them, piezoelectric ceramics are widely used because of their simple structure, small size, light weight, and robustness.

By the way, the impact sensor using the piezoelectric ceramic utilizes the fact that an electric force is generated by applying an external force to the piezoelectric ceramic to cause distortion, and the amount of this electric charge is proportional to the magnitude of the external force. Is. In this case, compression type, shearing type,
It is roughly divided into three types of bending type. Generally, a bent type is often used as a low frequency impact sensor. This bend-type impact sensor generates electric charge by bending a piezoelectric ceramic element. It has a unimorph structure or a bimorph structure in which two piezoelectric ceramic elements are laminated together to form a rectangular shape or a disk shape. is there.

For example, as shown in FIG. 2, a conventional impact sensor comprises a case 1 having an upper lid 6 and a bimorph structural element 2 in which two rectangular and plate-shaped piezoelectric ceramics 5 are bonded together. One end of the ceramic is fixed to the supporting portion 4 formed on the case 1 with an adhesive or the like to form a cantilever structure.

When an external force is applied to the above-mentioned shock sensor in a direction orthogonal to the plate surface of a rectangular and plate-shaped piezoelectric ceramic due to a shock, for example, the piezoelectric ceramic moves in the thickness direction with the supporting portion of the cantilever as a fulcrum. Swing to. A displacement is caused by this external force, and a sensor is obtained by detecting the amount of electric charge generated by the displacement.

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

[0007]

In order to obtain the above impact sensor in the low frequency region, the piezoelectric ceramic may be made large in size, but there is a demand for shortness, smallness, lightness and thinness, and there is a limitation in size. 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.

In order to eliminate these drawbacks, the object of the present invention is to add weight to the tip portion of a cantilever type piezoelectric ceramic with solder or the like so as not to increase the size of the piezoelectric ceramic and to reduce the size in the low frequency range. It is to provide a high-sensitivity impact sensor with improved frequency characteristics.

[0009]

According to the present invention, in a cantilever structure impact sensor using a plate-shaped bimorph structural element, a weight is added to the plate surface of the non-fixed side of the bimorph structural element. Is a shock sensor.

[0010]

The relationship between the external force applied to the impact sensor and the amount of electric charge generated accordingly is as follows. When polarization is applied by applying a voltage between the external electrodes, the relationship between the stress of the piezoelectric ceramic and the amount of charge per unit area with the electrode surface is q = dx
It is represented by. Where x = stress of the piezoelectric ceramic, q =
The charge amount per unit area of the electrode surface, d = piezoelectric strain constant. At this time, if Q = generated charge amount and S = electrode area, then q = Q / S holds. If F = external force,
x = F / S. Therefore, Q = dF.

As described above, the amount of electric charge generated by the impact sensor is proportional to the external force.

Since the weight is added to the longitudinal end of the rectangular and plate-shaped piezoelectric ceramic with solder or the like, an external force such as acceleration is received more in the thickness direction than when the weight is not added. Therefore, the amount of electric charge Q generated by the sensor becomes larger than that when the weight is not added. For this reason,
Since the amount of generated charges can be increased, the sensitivity of the sensor can be increased.

[0013]

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

FIG. 1 is an explanatory diagram of each component of the shock sensor according to the embodiment of the present invention and the frequency characteristic of its output voltage. FIG. 1A is a perspective view of a piezoelectric ceramic used in the impact sensor of the present invention, and FIG. 1B is a bimorph structural element used in the impact sensor of the present invention, in which a weight such as solder is added to the tip of the piezoelectric ceramic. 1 is a perspective view showing FIG.
FIG. 1C is an assembled perspective view of the impact sensor of the present invention, FIG.
1A shows a metal terminal of the impact sensor of the present invention.
FIG. 1E is a perspective view of the impact sensor of the present invention, and FIG. 1F is a graph of frequency characteristics showing the relationship between the frequency and the output voltage of the impact sensor of the present invention and the related art.

In the impact sensor of the present invention, as shown in FIG. 1A, the length is 18 mm, the width is 3.5 mm, and the thickness is 0.35.
In the thickness direction of the rectangular piezoelectric ceramic plate 5 mm,
An external electrode 8 and an internal electrode 9 made of Ni plating having a thickness of 2 to 3 μm are applied, and these are bonded with an adhesive 7 to form a bimorph structure element 2 which is used as a passive element.

As shown in FIG. 1B, one end of the bimorph structure element 2 is attached to the end of the fixing base 13. At this time, there is also a type in which the output terminal 3 for taking out is provided in the vicinity of the base fixed to the pedestal 13. Since the shock sensor described here is provided with a metal terminal for mounting on a substrate, the output terminal 3 shown in FIG. 1B is not necessary. Then, a solder weight 12 having a diameter of about 1.5 mm was attached to the outer end surface of the bimorph structure element 2 which was not fixed.

As shown in FIG. 1C, the case 1 used in the impact sensor of the present invention has a length 2 made of liquid crystal polymer.
A rectangular block having a width of 4 mm, a width of 5 mm, and a height of 5 mm is provided with a support portion 4 for a bimorph structural element, and has a recess 10 having a length of 20 mm, a width of 3.5 mm, and a height of 3.7 mm.

After that, the bimorph structural element 2 is mounted in the recess 10 of the case 1. At this time, one end of the bimorph structural element 2 is tightly adhered and fixed to the support portion 4.

FIG. 1D is a sectional view taken along the line AA of FIG. As shown in FIG. 1 (d), the metal terminal 11 provided on the case 1 is exposed so as to pass through the bottom surface of the case 1 and to be flat on the inner surface of the support portion 4, and the bimorph structure element 2 is When attached to the support portion 4, the external electrode 8 of the bimorph structure element 2 is closely attached and connected.

Further, as shown in FIG. 1C, an upper lid 6 made of a liquid crystal polymer having a length of 24 mm, a width of 5 mm and a thickness of 1.5 mm is prepared and placed on the case 1.

As described above, the case 1 and the upper lid 6
Then, the piezoelectric ceramic bimorph structure element 2 provided with the external electrode and the internal electrode is assembled to complete a surface mount type impact sensor as shown in FIG.

Vibration was applied to the impact sensor in the thickness direction of the bimorph structure element by a vibrator to measure the output voltage.

In the same manner as in the above-mentioned embodiment, a bimorph structure element without a weight, which is made of the rectangular plate-shaped piezoelectric ceramic with Ni-plated electrodes, is inserted into the recess of the case via a support portion. The sample was attached, covered with an upper lid, and fixed with an adhesive to prepare a sample as a comparative example of a conventional product. The output voltage was measured by applying vibration to this conventional product in the thickness direction of the bimorph structure element with a vibrator.

The results are shown in FIG. 1 (f).

In the embodiment of the present invention, 50 Hz to 5 KHz
1 has a frequency characteristic as shown by a graph B in FIG. 1 (f), and an output voltage of about 1 Vpp was obtained at 700 Hz / 5 G.

In the comparative example of the conventional product, 50 Hz to 5 KHz
The frequency characteristic of is as shown by the graph of C shown in FIG. 1 (f), and only an output voltage of about 510 mVpp was obtained at 700 Hz / 5 G.

[0027]

As described above, the output voltage of the product of the present invention is about double that of the conventional product. Therefore, according to the present invention, it was possible to provide a high-sensitivity impact sensor having improved frequency characteristics in a low frequency range.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing each component of an impact sensor according to an embodiment of the present invention and frequency characteristics of its output voltage. FIG. 1A is a perspective view of a piezoelectric ceramic used in the impact sensor of the present invention. FIG. 1B is a perspective view of a bimorph structural element used in the impact sensor of the present invention, in which a weight such as solder is added to the tip of the piezoelectric ceramic. FIG. 1C is an assembled perspective view of the impact sensor of the present invention. FIG. 1D is a sectional view taken along the line AA of FIG. 1C showing a metal terminal of the impact sensor of the present invention. FIG.
(E) is a perspective view of the impact sensor of this invention. FIG. 1F is a frequency characteristic graph showing the relationship between the frequency and the output voltage of the shock sensor of the present invention and the related art.

FIG. 2 is a perspective view showing a conventional impact sensor.

[Explanation of symbols]

 1 Case 2 Bimorph Structural Element 3 Output Terminal 4 Support 5 Piezoelectric Ceramic 6 Top Lid 7 Adhesive 8 External Electrode 9 Internal Electrode 10 Recess 11 Metal Terminal 12 Weight 13 (For Fixing) Stand B B Example (Invention Product) C Comparative Example (Conventional product)

Claims (1)

[Claims] 1. A shock sensor having a cantilever structure using a plate-shaped bimorph structure element, wherein a weight is added to the plate surface of the non-fixed side of the bimorph structure element.