JP2689799B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor having a piezoelectric element incorporated therein, and more particularly to the structure of the piezoelectric element itself.

[0002]

2. Description of the Related Art Conventionally, the structure of an acceleration sensor is generally classified according to the direction of acceleration applied to a piezoelectric element. Among these acceleration sensors, the direction in which strain occurs is parallel to the electric axis. There is a so-called vertical effect type (compression type) and a so-called lateral effect type (bending type) because the direction of strain is perpendicular to the electric axis. As an example of the compression type acceleration sensor 20, as shown in FIG. 7, each of the piezoelectric ceramics member 21 and the weight 22 polarized along the thickness direction is formed into an annular shape, and then these are formed. There is a structure which is attached to the base plate 24 by a shaft 23 which penetrates coaxially. Note that such an acceleration sensor 20 is usually configured by using a plurality (two in the figure) or one of the piezoelectric ceramic members 21, and electrodes (not shown) on both end faces. Each of the piezoelectric ceramic members 21a and 21b formed with is polarized along the directions opposite to each other.

Further, a bending type acceleration sensor 25 is also known.
Then, a principle structure as shown in FIG. 8 in which only a main part is simplified, that is, a unimorph type in which a flat plate-shaped piezoelectric ceramic member 26 and a metal plate 27, which are polarized along the thickness direction, are laminated one by one, The vibrating member 28 is attached to the base plate 2
The structure that cantilevered by 9 is adopted,
The vibration member 28 receives the acceleration and bends to detect the acceleration. In this case, it goes without saying that electrodes are formed on both main surfaces of the piezoelectric ceramic member 26, and a weight 30 is attached to the free end of the vibrating member 28 in order to improve the sensitivity. Good. Further, although not shown, a bimorph type vibrating member formed by laminating two piezoelectric ceramic members and a metal plate interposed therebetween is also used.

[0004]

By the way, in the acceleration sensors 20 and 25 having the above-mentioned conventional structure, the following disadvantages occur. That is, the compression type acceleration sensor 20 not only has a complicated structure and is relatively large, but also deteriorates the SN ratio due to pyroelectric noise. Then, in this acceleration sensor 20,
There is also a disadvantage that the sensitivity in the other axis direction different from the acting direction of acceleration, that is, the so-called other axis sensitivity is large.

An acceleration sensor 25 called a bending type is also used.
So, using a bimorph type vibration member has the advantage that pyroelectric noise is less likely to occur due to the cancellation of the piezoelectric ceramic members, but because the resonance frequency is low, it is difficult to detect high-frequency acceleration, and the vibration member is also used. Since 28 is supported as a cantilever, inconvenience will occur in terms of mechanical strength. Furthermore, in these acceleration sensors 20 and 25, the electrodes formed on the piezoelectric ceramic members 21 and 26 and the wiring patterns on the circuit board can be connected by lead wires (neither is shown). However, in such a case, soldering failure or disconnection of the lead wire may occur, and the acceleration sensor 20,
25, the reliability is lowered.

The present invention was devised in view of such inconvenience, and it is possible to reduce the sensitivity of another axis while suppressing the occurrence of pyroelectric noise, and to simplify and downsize the structure. It is an object of the present invention to provide an acceleration sensor that can improve reliability by increasing mechanical strength while aiming.

[0007]

In order to achieve such an object, an acceleration sensor according to the present invention is an acceleration detection device in which at least a pair of piezoelectric ceramic members are joined in parallel in a direction different from the acting direction of acceleration. The piezoelectric ceramic member is characterized in that each of the piezoelectric ceramic members is polarized in a direction along the acting direction of acceleration and in opposite directions.

[0008]

According to the above, the piezoelectric element is configured as a so-called shear type piezoelectric element in which the direction of strain due to the action of acceleration is displaced in a plane parallel to the electric axis. Therefore, it becomes possible to construct an acceleration sensor by mounting this piezoelectric element as a single unit.

[0009]

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

FIG. 1 is a perspective view showing a schematic structure of an acceleration sensor according to this embodiment, and reference numeral 1 in this figure is an acceleration sensor. The acceleration sensor 1 includes a piezoelectric element 2 for acceleration detection that outputs a signal corresponding to the acting direction and magnitude of acceleration, and various electronic components 3 including a signal processing circuit for processing the signal output from the piezoelectric element 2. 、…
And a circuit board 4 that supports them in a positioned state, and a required wiring pattern (not shown) is formed on the circuit board 4 by a technique such as thick film printing. That is, the electrodes of the piezoelectric element 2 and the electronic components 3, ... Are attached to the wiring pattern formed on the circuit board 4 by soldering or adhesion using a conductive adhesive.

Piezoelectric element 2 in this acceleration sensor 1
As shown in FIG. 2, is composed of a pair of piezoelectric ceramic members 6 and 7 that are joined in parallel along a direction different from the acting direction of acceleration, for example, a direction orthogonal to the acting direction. Each of the members 6 and 7 is
It is polarized along the directions in which the acceleration acts, but in opposite directions (indicated by arrows A and B in the figure). Reference numeral 8 in the figure denotes an electrode formed on each end face of each piezoelectric ceramic member 6, 7, and one electrode 8 of each of these piezoelectric ceramic members 6, 7 uses an adhesive or the like. They are joined by being bonded together.

Therefore, the piezoelectric element 2 functions as a so-called shear type piezoelectric element in which the direction in which strain due to acceleration occurs occurs in a plane parallel to the electric axis, and this piezoelectric element 2 is subject to acceleration. When they act, the voltage signals proportional to the acting direction and the magnitude of the acceleration are output from the electrodes 8 located at both ends thereof. Then, the output signal flows through the wiring pattern (not shown) provided on the circuit board 4 to the electronic components 3, ... And is processed. At this time,
Since the electrodes 8 located at both ends of the piezoelectric element 2 are supported by the wiring pattern, there is a gap between the lower surface of the main body portion and the upper surface of the circuit board 4, and the gap causes the piezoelectric element 2 to move. The vibration space is secured.

By the way, the structure and shape of the piezoelectric element 2 are not limited to those shown in FIG. 2, and as modifications thereof, piezoelectric elements having various structures and shapes as shown in FIGS. Can be considered. That is, the piezoelectric element 2 shown in FIG. 3 is polarized along the direction along which the acceleration acts and is polarized in opposite directions, and is joined in parallel along a direction different from the direction along which the acceleration acts. The structure is such that an additional mass member 9 having conductivity is interposed between the joining surfaces of the members 6 and 7, and when the piezoelectric element 2 having such a structure is used, the piezoelectric ceramic members 6 and 7 are mutually connected. The amount of deviation is increased, and the sensitivity of the acceleration sensor 1 is increased. Then, at this time, in the piezoelectric element 2 shown in FIGS. 2 and 3, as shown in FIG. 4, both ends 2a and the intermediate portion 2b of the piezoelectric element 2 are displaced along the direction along the acting direction of the acceleration. Alternatively, the vibration space of the piezoelectric element 2 can be surely secured in such a case. Reference numeral 8 in FIGS. 3 and 4 also indicates an electrode.

As another modified example, as shown in FIG. 5, output terminals 10 may be attached to both end surfaces of the piezoelectric element 2, respectively. Furthermore, in the piezoelectric element 2 to which such an output terminal 10 is attached, as shown in FIG.
It goes without saying that the output terminals 10 and the piezoelectric element 2 may be displaced from each other along the direction along the acting direction of the acceleration, as shown in FIG.

[0015]

As described above, the acceleration sensor according to the present invention is provided with the piezoelectric element for acceleration detection, which is formed by joining at least a pair of piezoelectric ceramic members in parallel in a direction different from the acting direction of acceleration. , Each of the piezoelectric ceramic members is in a direction along the acting direction of acceleration,
And because they are polarized in opposite directions,
This piezoelectric element is configured and functions as a shear-type piezoelectric element, and an acceleration sensor can be configured by attaching this piezoelectric element as a single unit. Therefore, according to the present invention, the occurrence of pyroelectric noise is reduced, and the sensitivity of other axes can be reduced, and
The effect that the mechanical strength can be increased while the structure is simplified and the size is reduced is obtained.

Further, according to the present invention, since it is not necessary to connect the piezoelectric element and the wiring pattern of the circuit board by the lead wire, there is no inconvenience associated with the lead wire connection, and the reliability of the acceleration sensor is improved. Can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic structure of an acceleration sensor according to an embodiment.

FIG. 2 is a perspective view showing a simplified piezoelectric element according to the first embodiment.

FIG. 3 is a simplified perspective view showing a piezoelectric element according to a second embodiment.

FIG. 4 is a perspective view showing a simplified piezoelectric element according to a third embodiment.

FIG. 5 is a simplified perspective view showing a piezoelectric element according to a fourth embodiment.

FIG. 6 is a simplified perspective view showing a piezoelectric element according to a fifth embodiment.

FIG. 7 is a perspective view showing a schematic structure of an acceleration sensor according to a conventional example.

FIG. 8 is a perspective view showing a schematic structure of another acceleration sensor according to the conventional example.

[Explanation of symbols]

 1 Acceleration Sensor 2 Piezoelectric Element 6 Piezoelectric Ceramics Member 7 Piezoelectric Ceramics Member

Claims (5)

(57) [Claims] 1. A piezoelectric ceramic member (6) comprising a piezoelectric element (2) for acceleration detection, which is formed by bonding at least a pair of piezoelectric ceramic members (6, 7) in parallel in a direction different from the acting direction of acceleration. , 7) are polarized in directions opposite to each other, and in directions opposite to each other. 2. The acceleration sensor according to claim 1, wherein an additional mass member (9) having conductivity is attached between the joint surfaces of the piezoelectric ceramic members (6, 7). 3. A piezoelectric element (2), wherein both ends (2a) and an intermediate portion (2b) of the piezoelectric element (2) are displaced from each other in a direction along an acceleration acting direction. The acceleration sensor described. 4. A piezoelectric element (2) is provided on both end faces thereof, respectively.
The acceleration sensor according to claim 1 or 2, wherein an output terminal (10) is attached. 5. The acceleration sensor according to claim 4, wherein the output terminal (10) and the piezoelectric element (2) are displaced from each other in a direction along the acting direction of the acceleration.