GB2299861A

GB2299861A - Piezoelectric vibrator unit

Info

Publication number: GB2299861A
Application number: GB9607687A
Authority: GB
Inventors: Takeshi Nakamura
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 1995-04-12
Filing date: 1996-04-12
Publication date: 1996-10-16
Anticipated expiration: 2016-04-12
Also published as: GB9607687D0; JP3189620B2; DE19614369C2; DE19614369A1; JPH08285882A; GB2299861B

Description

2299861 1 PIEZOELECTRIC VIBRATOR UNIT The present invention relates to a

piezoelectric vibrator unit and more particularly to a vibrator unit that is used as an acceleration sensor.

Referring to Fig. 6 which shows one example of a conventional piezoelectric vibrator unit, the piezoelectric vibrator unit 1 includes a plate type vibrator 2 having piezoelectric elements 3a and 3b respectively mounted on upper and lower surfaces thereof. Each of the piezoelectric elements 3a and 3b comprises a piezoelectric layer provided with electrodes on both upper and lower surfaces thereof, respectively. The electrodes provided on one surface of the piezoelectric layer are adhered to both main surfaces of the vibrator 2. In other words, the electrode A provided on one surface of the piezoelectric layer B is adhered to one of main surfaces of the vibrator 2 and the electrode C provided one one surface of the piezoelectric layer D is adhered to the other of main surfaces of the vibrator 2. Further, each of the piezoelectric elements 3a and 3b is polarized in the width direction thereof extending from outside of the vibrator 2 toward the vibrator 2. Further, the piezoelectric elements 3a and 3b are connected with lead wires 4a and 4b, respectively. The lead wires 4a and 4b are used to connect the piezoelectric elements 3a and 3b to external circuits such as an oscillation circuit functioning as a drive means and a differential amplifying circuit functioning as a detecting means.

At one longitudinal side end of the vibrator 2 there are 2 provided a pair of support members 5 each of which have a substantially L-shaped cross section. These support members 5 extend from a portion near one end of the vibrator 2 in the width direction of the vibrator 2 and are integral with the vibrator 2. The piezoelectric vibrator unit 1 is supported by the support members 5 in a cantilever fashion.

Such a conventional piezoelectric vibrator unit 1 is used as an acceleration sensor, for example, and in that case, one side end of the vibrator 2 is supported by fixing the support members 5 thereto. Then, when drive signals of the same phase are applied to the two piezoelectric elements 3a and 3b through lead wires 4a and 4b, the vibrator 2 vibrates in the longitudinal direction thereof and when, in this state, an accelerating force is applied on the surface of the vibrator 2 in a vertical direction thereto, the vibrator 2 flexes together with the piezoelectric elements 3a and 3b in proportion to the magnitude of the accelerating force being applied so that voltages are generated from the piezoelectric elements 3a and 3b in proportion to the degrees of flexing thereof, respectively. The voltages thus generated are inputted, for example, to a differential amplification circuit through the lead wires 4a and 4b so that the difference between the voltages are measured to thereby obtain the accelerating force applied on the piezoelectric elements.

However, the above-described conventional piezoelectric vibrator unit requires a relatively large number of parts requiring an increased number of manhours for manufacturing and assembly.

3 Furthermore, a high degree of skill is required for handling and connection of lead wires for electrically connecting the piezoelectric vibrator and the related external circuit.

Accordingly, the preferred embodiments of the present invention provide a piezoelectric vibrator unit which is composed of fewer parts as compared to the conventional piezoelectric vibrator unit.

The preferred embodiments of the present invention also provide a piezoelectric vibrator unit which requires no lead wires for establishing electrical connections with external circuits.

The piezoelectric vibrator unit according to the preferred embodiments of the present invention comprises a piezoelectric board, a plurality of electroconductive vibrating strips of constant elasticity which are respectively attached to the upper and lower surfaces of the piezoelectric board in opposite relationship with each other in the thickness direction of the piezoelectric board and support members integrally connected with the vibrating strips for supporting the piezoelectric vibrator unit so as to establish electrical connection between the piezoelectric vibrator unit and an external circuit.

It is preferable that the support members are integral with the vibrating strips at the node portions of the vibrating strips.

Further, it is preferable that the piezoelectric board is polarized in the thickness direction thereof in such a manner that the longitudinal sides thereof are polarized in opposite directions, respectively.

4 The piezoelectric vibrator unit according to the preferred embodiments of the present invention operates such that when a voltage is applied between the conductive vibrating strips, the piezoelectric board vibrates. As a result of the vibration of the board, the vibrating strips, which are constant-elastic, also vibrate. In this state, when an accelerating force is applied on the surface of the piezoelectric vibrator unit in a vertical direction thereto, the piezoelectric board and the vibrating strips flex. As a result the resonance characteristic of the piezoelectric board changes, thereby generating a voltage between the vibrating strips. Therefore, it is possible to measure the accelerating force applied to the piezoelectric vibrator unit by measuring the voltage between the vibrating strips.

Further, because the support members for supporting the piezoelectric vibrator unit and establishing electrical connection of the piezoelectric vibrator unit with a related external circuit are integrally connected with the vibrating strips, it is possible to electrically connect the piezoelectric vibrator unit and the external circuit without using any lead wires. Further, because the support members are integral with the node portions of the vibrating strips, it is possible to support the piezoelectric vibrator unit and the vibrating strips without hindering the vibration of the vibrator unit and vibrating strips.

In addition, when the piezoelectric board is polarized in the thickness direction thereof, the piezoelectric vibrator unit vibrates expansively and contractively in the longitudinal direction thereof. Further, when the piezoelectric board is polarized in the thickness direction thereof and both longitudinal sides of the board are polarized in opposite directions, the piezoelectric vibrator unit vibrates expansively and contractively without changing the length thereof.

According to the preferred embodiments of the present invention, it is possible to obtain a piezoelectric vibrator unit comprising a small number of parts to thereby simplify the manufacturing process. Further, the piezoelectric vibrator unit and a related external circuit can be electrically connected by the electroconductive supporting members. Accordingly, it is possible to dispense with the lead wires required in conventional devices so that the number of parts is reduced, the structure of the unit is simplified and the cost and difficulty of the manufacturing process is reduced.

These and other features, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention taken in conjunction with the accompanying drawings.

Fig. 1 is a perspective view of a piezoelectric vibrator unit according to a preferred embodiment of the present invention; Fig. 2 is a perspective view of a modification of the piezoelectric vibrator unit shown in Fig. 1; Fig. 3 is a perspective view of another modification of the piezoelectric vibrator unit shown in Fig. 1; 6 Fig. 4 is a perspective view of still another modification of the piezoelectric vibrator unit shown in Fig. 1; Fig. 5 is a perspective view of a further modification of the piezoelectric vibrator unit shown in Fig. 1; and Fig. 6 is a perspective view of one example of a conventional piezoelectric vibrator unit.

Referring to Fig. 1 which is a perspective view of a piezoelectric vibrator unit according to a preferred embodiment of the present invention, a piezoelectric vibrator unit 10 includes a substantially rectangular piezoelectric board 12 which is made of, for example, a piezoelectric ceramic material. on the upper surface of the piezoelectric board 12 there is formed a sheet-like electrode 14a covering the entire area of the upper surface and on the lower surface thereof there is formed a sheet-like electrode 14b covering the entire area of the lower surface. As designated by the chain line arrows in Fig. 1, one end of the piezoelectric board 12 is polarized in the longitudinal direction thereof from the electrode 14b toward the electrode 14a while the other opposing end is polarized from the electrode 14a toward the electrode 14b. Accordingly, the direction of polarization of the piezoelectric the board 12 is reversed at substantially the central portion of the board 12 in the longitudinal direction thereof.

Further, the piezoelectric vibrator unit 10 includes a pair of sheet-like vibrating strips 16a and 16b. The vibrating strip 16a is placed over the entire exposed surface of the electrode 14a so as to 7 be electrically and mechanically connected to the electrode 14a. Likewise, the vibrating strip 16b is placed over the entire exposed surface of the electrode 14b so as to be electrically and mechanically connected to the electrode 14b. Both of the vibrating strips 16a and 16b are preferably made of a constant-elastic metal having conductivity such as nickel, iron, chromium, titanium or alloys thereof, e.g., elinvar or an iron-nickel alloy.

At a node portion located on one side end of the vibrating strip 16a in the longitudinal direction thereof, there are integrally formed a pair of elongate rod-shaped support members 18a which extend sidewardly from the strip 16a in the width direction of the strip 16a. Further, at a node portion located on the other side end of the strip 16b in the longitudinal direction thereof, there are integrally formed a pair of elongate rod-shaped support members 18b which extend sidewardly from the strip 16b. The support members 18a and 18b are preferably made of the same material as the vibrating strips 16a and 16b.

One of the pair of support members 18a and 18a is electrically connected with one end of an oscillation circuit 20 functioning as a drive means with the other end of the oscillation circuit 20 being electrically connected with one of the pair of support members 18b. Similarly, the other support member 18a is electrically connected with one end of a differential amplifying circuit (not shown) functioning as a detecting means without using any lead wires. The other end of the differential oscillation circuit is electrically 8 connected to the other support member 18b without using lead wires. In other words, the support members 18a and 18b are fixed to a support board (not shown), for example. In that case, a plurality of electrodes (not shown) are provided at portions of the support board to which the support members 19a and 18b are respectively attached. These electrodes and the support members 18a and 18b are connected together by soldering, welding or the like. Thus, the electrodes provided on the support board are connected to external circuits such as the above-mentioned oscillation circuit 20 and differential amplifying circuit, and the like. As a result, the piezoelectric vibrator unit 10 is electrically connected to the external circuits through the support members 18a and 18b and at the same time, mechanically supported by the support members 18a and 18b.

Next, a case where the piezoelectric vibrator unit 10 is used as an acceleration sensor will be described.

The piezoelectric vibrator unit 10 vibrates in the longitudinal direction thereof upon application of a drive signal to the vibrator unit 10. In that case, since the piezoelectric board 12 has been polarized in the reverse direction at substantially the central portion in the longitudinal direction thereof, when one side end of the board 12 expands, the opposite side end contracts and vice versa, repeating vibrations in an alternative fashion. Accordingly, the piezoelectric vibrator unit 10 shows almost no change in the length thereof at the time of its expansive and contractive vibrating operations. Further, the support members 18a and 18b are 9 respectively formed at the node portions of the piezoelectric vibrator unit 10. Consequently, the piezoelectric vibrator unit 10 shows only a small vibration loss and vibrates in a stabilized manner.

When an accelerating force is applied on the surface of the piezoelectric vibrator unit 10 in a vertical direction relative to that surface while the unit 10 vibrates, the piezoelectric board 12 and the vibrating strips 16a and 16b flex causing the resonance frequency of the piezoelectric board 12 to vary, which results in a voltage being generated between the vibrating strips 16a, 16b. By detecting the voltage between the vibrating strips 16a, 16b using the detecting means, it is possible to obtain the value of the accelerating force applied upon the piezoelectric vibrator unit 10.

According to this preferred embodiment, it is possible to obtain a piezoelectric vibrator unit having a small number of parts as compared to the conventional unit and to thereby simplify the manufacturing process. Further, the piezoelectric vibrator unit 10 according to the preferred embodiment can be electrically connected to an external circuit through the conductive support members 18a and 18b. Therefore, unlike the conventional piezoelectric vibrator unit, no lead wires are required, which contributes to the reduction of the number of parts, the simplification of the structure and the reduction of the cost and difficulty of the manufacturing process.

The above-described piezoelectric board 12 may comprise a couple of sheetlike piezoelectric boards which have been combined to form a unitary member. In that case, if the direction of polarization of the piezoelectric board 12 at one side end thereof in the longitudinal direction is reversed to the direction of polarization of the board at the other end thereof, the same effect as the above-described preferred embodiment can be obtained.

Fig. 2 is a perspective view of a modification of the piezoelectric vibrator unit shown in Fig. 1. The support members 18a of the piezoelectric vibrator unit 10 shown in Fig. 2 are formed so that they extend sidewardly in opposite directions from one end of the vibrating strip 16a in the longitudinal direction. Further, the support members 18b of the piezoelectric vibrator unit 10 shown in Fig. 2 are formed so that they extend sidewardly in opposite directions from the vibrating strip 16b in the longitudinal direction at a position spaced from the abovementioned one end of the vibrator unit 10 by a distance corresponding to about one-fourth of the entire length of the vibrator unit 10. When the piezoelectric vibrator unit 10 is used as, for example, an acceleration sensor, it operates in the same manner as the preferred embodiment in Fig. 1. It is also possible with the preferred embodiment of Fig. 2 to obtain a piezoelectric vibrator unit having a small number of parts as compared to the conventional piezoelectric vibrator unit. Further, it is possible with this preferred embodiment to dispense with the lead wires as required by the conventional vibrator unit so that the number of parts is reduced, the structure of the unit is simplified and the cost and difficulty of the manufacturing process is reduced.

11 Fig. 3 is a perspective view of another modification of the piezoelectric vibrator unit shown in Fig. 1. The support members 18a and 18b of the unit 10 shown in Fig. 3 are formed so that they extend sidewardly in opposite directions from substantially the central portion thereof, respectively. As shown by the chain line arrow in Fig. 3, the piezoelectric board 12 is polarized from the electrode 14b toward the electrode 14a. When the piezoelectric vibrator unit 10 shown in Fig. 3 is used as, for example, an acceleration sensor, the unit 10 expands and contracts in the longitudinal direction thereof. In this state, when an accelerating force is applied on the surface of the vibrator unit 10 in the vertical direction relative to that surface, the piezoelectric board 12 and the vibrating strips 16a and 16b flex whereupon the resonance characteristic of the piezoelectric board 12 changes, causing a voltage to be generated between the vibrating strips 16a and 16b. Therefore, by measuring this voltage with a suitable detecting means, it is possible to determine the accelerating force applied on the piezoelectric vibrator unit 10. According to the preferred embodiment shown in Fig. 3, it is also possible to make the number of parts smaller as compared to the conventional piezoelectric vibrator unit. Further, it is possible to dispense with the lead wires which have hitherto been required so that the number of parts is reduced, the structure of the device is simplified and the cost and difficulty of the manufacturing process is reduced.

12 Fig. 4 is a perspective view of a still another modification of the piezoelectric vibrator unit shown in Fig. 1. Unlike the preferred embodiment shown in Fig. 1, the piezoelectric vibrator unit 10 includes a planar square piezoelectric board 12. On the upper surface of the piezoelectric board 12, an electrode 14a is formed so as to cover the entire area of the upper surface and on the lower surface thereof, an electrode 14b is formed so as to cover the entire area of that surface. As shown by the chain line arrow in Fig. 4, the piezoelectric board 12 is polarized in a direction extending from the electrode 14b toward the electrode 14a.

Further, unlike the preferred embodiment shown in Fig. 1, the piezoelectric vibrator unit 10 includes planar square vibrating strips 16a and 16b. The vibrating strip 16a is formed on the upper surface of the piezoelectric board 12 so as to cover the electrode 14a thereby establishing electrical and mechanical connections with the electrode 14a.

The vibrating strip 16a support members 18a which are project outwardly from one of Likewise, the vibrating strip members 18b which are integral has a pair of elongate rod-shaped integral with the strip so as to the opposing two sides thereof. 16b has a pair of elongate support with the strip 16b so as to project outwardly from another of the opposing two sides thereof. Accordingly, the support members 18a extend in directions which are substantially vertical to the extending directions of the support members 18b respectively. Further, on the upper surface of the 13 vibrating strip 16a there is provided a support member 18c extending in a vertical direction relative to that surface. The support member 18c is formed by cutting a suitable portion of the upper surface of the vibrating strip 16a to form a substantially U-shape portion and then raising the cut portion. Similar to the support members 18a and 18b, the support member 18c is used to establish electrical connection between the piezoelectric vibrator unit 10 and the related external circuit and to mechanically support the vibrator unit 10. The piezoelectric vibrator unit 10 in Fig. 4 is used as, for example, a vibrator unit that is operated in a spreading vibration mode. This preferred embodiment has a smaller number of parts than the conventional piezoelectric vibrator unit. Further, this preferred embodiment eliminates the lead wires required by the conventional vibrator unit so that the number of parts is reduced, the structure of the unit is simplified and the cost and difficulty of the manufacturing process is reduced.

Further, as shown by the broken line arrows in Fig. 4, each of the support members 18a may be bent upwardly in a vertical direction with respect to the upper surface of the vibrating strip 16a while each of the support members 18b may be bent downwardly in a vertical direction with respect to the lower surface of the vibrating strip 16b and in that case, the vibrator unit 10 can be mechanically supported and electrically connected to the piezoelectric board and the related external circuit.

Fig. 5 is a perspective view of a further modification of the piezoelectric vibrator unit shown in Fig. 1. The piezoelectric vibrator unit 10 shown in Fig. 5 includes a planar circular piezoelectric board 12 in contrast to the preferred embodiment shown in Fig. 1. On the upper surface of the piezoelectric board 12, a circular electrode 14a is formed so as to cover the entire area of the upper surface and on the lower surface of the board 12 a circular electrode 14b is formed so as to cover the entire area of that surface. The board 12 is polarized in a direction extending from the electrode 14b toward the electrode 14a as shown by the chain line arrow in Fig. 5.

Further, in contrast to the preferred embodiment shown in Fig. 1, the piezoelectric vibrator unit 10 includes planar circular vibrating strips 16a and 16b. The vibrating strip 16a is formed on the upper surface of the piezoelectric board 12 so as to cover the electrode 14a to thereby establish electrical and mechanical connections with the electrode 14a. Likewise, the vibrating strip 16b is formed on the lower surface of the board 12 so as to cover the electrode 14b to thereby establish electrical and mechanical connections with the electrode 14b.

The vibrating strip 16a has a pair of elongate rod-shaped support members 18a which are integral with the strip so as to project radially and outwardly of the strip in opposite directions. Further, the vibrating strip 16b has a pair of support members 18b which are integral with the strip so as to project radially and is outwardly of the strip in opposite directions. The preferred preferred embodiment shown in Fig. 5 operates in the same manner as the preferred embodiment shown in Fig. 3. Further, this preferred embodiment has a smaller number of parts than the conventional piezoelectric vibrator unit and eliminates the lead wires which have conventionally been required so that the number of parts is reduced, the structure of the unit is simplified and the cost and difficulty of the manufacturing process is reduced. while preferred embodiments of the invention have been disclosed, various modes of carrying out the principles disclosed herein are contemplated as being within the scope of the following claims. Therefore, it is understood that the scope of the invention is not to be limited except as otherwise set forth in the claims.

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Claims

CLAIMS:

1. A piezoelectric vibrator unit comprising: a piezoelectric board; a plurality of electrodes provided on respective upper and lower surfaces of said piezoelectric board; a plurality of electroconductive vibrating strips each having a constant elasticity and extending over a respective one of said electrodes on said piezoelectric board; and a plurality of support members for supporting said piezoelectric vibrator unit and for electrically connecting said piezoelectric vibrator unit to external electronic components, each of said support members being integral with a respective one of said vibrating strips.

2. The piezoelectric vibrator unit according to Claim 1, wherein each of said support members are integral with node portions of said respective vibrating strips.

3. The piezoelectric vibrator unit according to Claim 2, wherein said piezoelectric board is polarized in a width direction thereof.

4. The piezoelectric vibrator unit according to Claim 3, wherein a first portion of said piezoelectric board is polarized in a first direction and a second portion of said piezoelectric board is polarized in a second direction which is opposite to said first direction.

5. The piezoelectric unit according to claim 1, wherein said piezoelectric board comprises a substantially rectangular member.

6. The piezoelectric unit according to claim 1, wherein said piezoelectric board comprises a substantially planar square member.

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7. The piezoelectric unit according to claim 1, wherein said piezoelectric board comprises a substantially circular member.

8. The piezoelectric unit according to claim 1, wherein a first pair of said plurality of support members are located at an end of said piezoelectric board and a second pair of said plurality of support members are spaced from said first pair of said plurality of support members by a distance equal to about one fourth of an entire length of said piezoelectric board.

9. The piezoelectric vibrator unit of claim 1, wherein said plurality of support members are provided at substantially a central portion of said piezoelectric substrate.

10. The piezoelectric vibrator unit of claim 1, wherein said plurality of support members comprise rod-shaped members.

11. The piezoelectric vibrator unit of claim 1, wherein said plurality of electroconductive vibrating strips comprise substantially planar square members.

12. The piezoelectric vibrator unit of claim 1, wherein each of said support members extend outwardly from said vibrating strips in a direction substantially parallel to a width of each of said vibrating strips to a location outside a periphery of said piezoelectric board.

13. The piezoelectric vibrator unit of claim 1, wherein at least one of said support members extends outwardly from a respective one of said vibrating strips in a direction substantially parallel to a thickness of said piezoelectric board to a point outside of said piezoelectric board.

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14. A piezoelectric vibrator unit substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.