JPH0526895A - Piezoelectric acceleration sensor - Google Patents

Abstract

PURPOSE:To remove the dispersion of output per sensor caused by the thickness of an adhesive agent layer and improve impact resistance, by joining directly a supporting plate made up of conductive plastics and a piezoelectric film with ultrasonic waves. CONSTITUTION:Supporting plates 2 made up of conductive plastics are directly joined to both inside and outside surfaces of a piezoelectric film 1. The supporting plate 2 can be joined with the piezoelectric film 1 by applying ultrasonic waves, because the plate 2 are made of plastics. Therefore, the dispersion of sensor output caused by the thickness of an adhesive agent layer 3 does not occur because the piezoelectric film 1 and the supporting plate 2 can directly be joined without putting the adhesive agent layer 3 between the film 1 and the plate 2. Both are incorporated in one and very firmly joined because joined directly with the ultrasonic waves. Therefore, it does not occur that the both scale off, and consequently the impact resistance is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
In particular, the present invention relates to an acceleration sensor in which there is little variation in the output of each sensor due to the adhesive and the impact resistance is improved.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view showing a conventional acceleration sensor. This is generally a pedestal 5 made of a material having sufficient rigidity, on which a detection unit 4 and a load body 7 made of a rigid body functioning as an inertial mass unit are provided.

The detector 4 is fixed to a measurement surface of the pedestal 5 which is perpendicular to the detection axis. Detection unit 4 of this acceleration sensor
3 has a sandwich structure in which the electrode 6 and the support plate 2 are fixed to both front and back sides of the piezoelectric film 1 by an adhesive such as an epoxy-based adhesive, as shown in FIG. The planar shape of the piezoelectric film 1 is formed point-symmetrically with respect to the detection axis G. In the detection unit 4 of this acceleration sensor,
The support plate 2 and the piezoelectric film 1 have the same planar shape. The shape of the contact surface of the load body 7 with the detection unit 4 is point-symmetrical about the detection axis G. This load body 7 is point-symmetric with respect to the detection axis G of the measurement surface, and as shown in FIG. 4, when the cross section M of the load body 7 is taken on a plane including the detection axis G, for example, plane S. The cross section M is always line-symmetric with respect to the detection axis G. In this way, the load body 7
Is formed in a three-dimensional shape symmetrical with respect to the detection axis G, the crosstalk of the sensor output can be reduced.

[0004]

The conventional acceleration sensor as described above has the following problems. When manufacturing the detection unit 4 industrially, first, the large piezoelectric film 1, the support plate 2, and the electrode 6 are bonded to each other with an adhesive to manufacture the detection unit 4, which is cut to fit the acceleration sensor. Manufacture the size. However, at this time, since the thickness of the adhesive layer 3 provided between the respective layers is very difficult to control, the thickness naturally varies when viewed macroscopically. Therefore, in the conventional acceleration sensor, the sensor output varies due to the thickness of the adhesive layer 3 for each sensor. Further, since the respective components of the detection section are fixed by the adhesive, the adhesive is easily peeled off particularly when a strong impact is applied from the lateral direction. For example, the piezoelectric film 1 and the support plate 2
And peel off.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has solved the above problems by directly bonding a support plate made of a conductive plastic and a piezoelectric film by ultrasonic waves. The piezoelectric film may be made of polyvinyl fluoride, polyvinyl chloride, nylon 11 or the like. When melted, these materials lose their piezoelectricity. However, since the ultrasonic bonding occurs only in the very vicinity of the interface, no problem occurs in the piezoelectricity of the piezoelectric film of the acceleration sensor of the present invention. The material of the conductive plastic forming the support plate is not particularly limited, and may contain a filler. The conductive plastic used preferably has a volume resistivity of 500 Ω · cm or less. Further, it is desired that the conductive plastic preferably has a high elastic modulus.

[0006]

In the piezoelectric acceleration sensor of the present invention, since the support plate made of conductive plastic is used, it can also serve as an electrode, and the support plate can be provided so as to be in direct contact with the piezoelectric film. it can. Furthermore, since the support plate is made of plastic, it can be bonded to the piezoelectric film by applying ultrasonic waves. Therefore, in the piezoelectric acceleration sensor of the present invention, the piezoelectric film and the support plate can be directly bonded without the adhesive layer. Also,
Since the piezoelectric film of the piezoelectric acceleration sensor of the present invention and the supporting plate are directly bonded by ultrasonic waves, they are integrated and bonded extremely firmly. Therefore, the both are not separated, and as a result, the impact resistance is improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wire connecting method of the present invention will be described in detail below with reference to the drawings. The same components as those of the conventional example are designated by the same reference numerals to simplify the description.

The difference between the piezoelectric acceleration sensor of the present embodiment and the conventional one is in the structure of the detection section 4. As shown in FIG. 1, the detection unit 4 of the present embodiment is one in which a support plate 2 made of a conductive plastic is directly bonded to both front and back surfaces of a piezoelectric film 1. The piezoelectric film 1 and the support plate 2 are ultrasonically bonded to the interface by applying ultrasonic waves for 5 seconds. As the piezoelectric film 1, a square film made of polyvinylidene fluoride having a thickness of 110 μm and a side of 5 mm was used. As the support plate 2, a material obtained by spreading polybutylene terephthalate into which carbon fiber was kneaded as a filler to a thickness of 1.5 mm and further forming a square shape having a side of 5 mm was used. The volume resistivity of this product is 10 Ω · cm.

Fifty samples having the above-mentioned structure were prepared, and variations in sensor output and impact resistance were measured for this sample. Impact resistance measurement is made of aluminum 10
A sensor having the above structure was fixed on a block of cm ³ , and dropped on a concrete block so that the impact direction was orthogonal to the detection axis G. The impact resistance was determined by examining the number of sensors destroyed at this time. Further, the variation of the sensor output is shown by the value of the maximum output / minimum output among the 50 samples.

For comparison, the output and impact resistance of the conventionally used sensor were measured. The sensor prepared as a comparative example uses the same piezoelectric film 1 as described above, and the electrodes 6 are provided on both sides of the piezoelectric film 1.
A copper foil having a thickness of 30 μm and a side shape of 5 mm is adhered to both sides of the piezoelectric film 1 with an epoxy adhesive, and glass epoxy is provided on both sides of the copper foil having a thickness of 1.5 nm and a side shape of 5 mm. Support plate 2
As well as glued. Fifty comparison samples were manufactured.

The measurement results are as shown below.

As can be seen from Table 1, the acceleration sensor of this embodiment has smaller variation in the output from each sensor and improved impact resistance as compared with the conventional one.

Detection unit 4 of the piezoelectric acceleration sensor of this embodiment
Since the support plate 2 made of conductive plastic is used, it can also serve as the electrode 6, and the support plate 2 can be provided so as to be in direct contact with the piezoelectric film 1. Further, since the support plate 2 is made of plastic, it can be bonded to the piezoelectric film 1 by applying ultrasonic waves. Therefore, in the piezoelectric acceleration sensor according to the present embodiment, the piezoelectric film 1 and the support plate 2 can be directly bonded without the adhesive layer 3, so that the output of each sensor due to the thickness of the adhesive layer. The variability disappeared. Moreover, since the piezoelectric film 1 and the support plate 2 are directly ultrasonically bonded, they are integrated and firmly bonded. Therefore, both were not separated and the impact resistance was improved.

[0014]

In the detecting portion of the piezoelectric acceleration sensor of the present invention, since the supporting plate made of conductive plastic is used, it can also serve as an electrode and is supported so as to be in direct contact with the piezoelectric film. A plate can be provided.
Furthermore, since the support plate is made of plastic, it can be bonded to the piezoelectric film by applying ultrasonic waves.
Therefore, in the piezoelectric acceleration sensor of the present invention, since the piezoelectric film and the support plate can be directly bonded without the adhesive layer interposed, there is no variation in the output from sensor to sensor due to the thickness of the adhesive layer. It was Further, since the piezoelectric film and the supporting plate are directly ultrasonically bonded, they are integrated and firmly bonded. Therefore, both were not separated and the impact resistance was improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an acceleration sensor according to a first embodiment.

FIG. 2 is a sectional view showing a conventional acceleration sensor.

FIG. 3 is a cross-sectional view showing a detection unit of a conventional acceleration sensor.

FIG. 4 is a perspective view for explaining a load body of a conventional acceleration sensor.

[Explanation of symbols]

1 ... Piezoelectric film 2 ... Support plate 4 ... Detection part 5 ... Pedestal 7 ... Load body

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takayuki Imai 1-5-1 Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd.

Claims (1)

Claims: 1. A pedestal rigidly attached to an object to be measured,
The pedestal has a detection unit fixed to a measurement surface perpendicular to the detection axis, and a load body made of a rigid body fixed on the detection unit and acting as an inertial mass unit. The detection unit has a piezoelectric film and the piezoelectric film. In the piezoelectric acceleration sensor including a support plate provided on both front and back sides, the support plate is made of conductive plastic, and the piezoelectric film and the support plate are directly fixed by ultrasonic bonding. ..