JP2001133476A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform detection from acceleration in a constant acceleration region up to acceleration in a varying acceleration region such as vibration, etc. SOLUTION: The respective surfaces of piezoelectric substances 11a, 11b in two layers and the base end part of a beam 11 having electrodes 14, 15, 16 in its intermediate parts are fixed to a base member 12, and a weight 13 is fixed to its tip part. The piezoelectric substances 11a, 11b of two layers generate transverse vibration of a cantilever beam, by applying AC voltage V to their respective electrodes. It has been known that the resonance frequency f of the beam on this occasion changes by axial tension P acting on the beam. Accordingly, the axial tension P acting on the beam 11 is known, and the magnitude of acceleration becomes detectable, if the resonance frequency f of the beam 11 to which acceleration is applied in the axial direction is known, since the axial tension P acting on the beam 11 by the inertia force of the weight 13 of mass M changes, when the acceleration is applied to this beam in the axial direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor using a piezoelectric body for detecting vibration acceleration and the like, and more particularly to an acceleration sensor using a vibrating beam capable of detecting from a constant acceleration to a fluctuating vibration acceleration.

[0002]

2. Description of the Related Art Conventionally, an acceleration sensor for detecting acceleration such as vibration converts a distortion generated in a piezoelectric body into an electric signal. Hereinafter, the basic configuration and operation of a conventional acceleration sensor using the lateral effect of a piezoelectric body will be described with reference to FIG.

In FIG. 7, a weight 2 having a mass M is fixed to the tip of a beam 1. The piezoelectric body 3 is attached to the base end side of the beam 1 by bonding or the like. Electrodes 4 and 5 are formed on the surface of the piezoelectric body 3, and lead wires 6 and 7 for extracting electric signals are connected to the electrodes 4 and 5. Beam 1
Is fixed to the base member 8 and takes the form of a cantilever. When the vibration of the acceleration α is applied to the base member 8, the beam 1 bends under the concentrated load of the external force F = Mα at the tip. Thereby, the piezoelectric body 3 attached to the beam 1
On one surface, a compressive strain is generated along with the bending of the beam 1, and an extension strain is generated on the other surface. The compression strain and the extension strain are proportional to the external force F, and the voltage V from the electrodes 4, 5 formed on the piezoelectric body 3 via the leads 6, 7.
Can be taken out as Therefore, by measuring the voltage V generated in the piezoelectric body 3, the acceleration α of the vibration can be known.

[0004]

However, in the acceleration sensor using the lateral effect of the piezoelectric body, the electric charge generated on the surface due to the distortion of the piezoelectric body 3 is discharged by the vibration of low frequency. There is a problem that the constant acceleration and the vibration acceleration at a low frequency cannot be measured.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an acceleration sensor capable of detecting a region from a region of constant acceleration to a region of fluctuation such as vibration.

[0006]

According to the present invention, there is provided an acceleration sensor comprising a two-layer piezoelectric body, a beam having electrodes on the surface of each of the two-layer piezoelectric bodies and an electrode between the two-layer piezoelectric bodies, It has a configuration including a base member for fixing the base end of the beam and a weight fixed to the tip of the beam. The two-layer piezoelectric body has an AC voltage V applied to both sides and electrodes between the piezoelectric bodies.
, Lateral vibration of the cantilever is generated.
It is known that the resonance frequency f of the beam at this time changes depending on the axial force P acting on the beam. Therefore, when acceleration is applied to the beam in the axial direction, the axial force acting on the beam changes due to the penetrating force of the weight of the mass M. If the resonance frequency f of the beam at that time is known, the axial force acting on the beam is obtained. P is known, and the magnitude of the acceleration can be detected.

Further, the acceleration sensor of the present invention comprises two sets of beams each composed of two layers of piezoelectric bodies, each of which has electrodes on the surface of the two layers of piezoelectric bodies and electrodes between the two layers of piezoelectric bodies.
It has a configuration provided with a base member for fixing the base end of each of the two sets of beams, and a weight commonly fixed to the opposed front ends of the two sets of beams. Lateral vibrations of the secondary resonance frequency having opposite phases are applied to the piezoelectric bodies of the two sets of beams. At this time, when an acceleration in the axial direction is applied to the two sets of beams, the axial force in the tensile direction and the compressive direction acts alternately on the two sets of beams. Therefore, the change in the resonance frequency shift of the two sets of beams is detected. By inverting the changed frequency around the resonance frequency and taking the sum, the detection sensitivity of the acceleration in the axial direction can be doubled.

Further, the acceleration sensor according to the present invention is composed of two layers of piezoelectric members, and four sets of beams orthogonal to each other having electrodes on the surfaces of the two layers of piezoelectric members and electrodes between the two layers of piezoelectric members. And a base member for fixing the base end of each of the four sets of beams, and a weight commonly fixed to the opposed front ends of the four sets of beams. With the four sets of vibrating beam structures, the acceleration in the X-axis and Y-axis directions can be detected, and the angular velocity around the Z-axis can be detected by rotating about the center weight.

The acceleration sensor according to the present invention has a configuration in which the beam having the electrodes, the base member, and the weight are integrally formed of a piezoelectric material and are laminated in two layers. With this configuration, an acceleration sensor that is inexpensive and has excellent mass productivity can be realized.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows the configuration of a vibrating beam axial force sensor type acceleration sensor according to Embodiment 1 of the present invention. In FIG. 1, a beam 11 is a first
Of the bimorph piezoelectric body composed of the piezoelectric body 11a and the second piezoelectric body 11b, the base end of which is a base member 1
2, and a weight 13 having a mass M is fixed to a tip end thereof. A first electrode 14 is provided on the surface of the first piezoelectric body 11a.
However, a second electrode 15 is formed on the surface of the second piezoelectric body 11b, and an intermediate electrode 16 is formed on a portion where the second piezoelectric body 11b overlaps each other by a method such as firing, and lead wires 17, 18, and 19 are respectively formed. It is connected. Lead wire 19
Are connected to one side of an AC drive power supply 20 for generating lateral vibration in the beam 11, and the leads 17 and 18 are connected to the other side of the drive power supply 20.

The n-th resonance frequency f of the transverse vibration of the beam 11
_0n is represented by the following equation (1).

(Equation 1) Here, λ: constant determined by the beam support method and vibration mode L: beam length E: Young's modulus of the piezoelectric material constituting the beam I: secondary moment of area of the beam g: gravitational acceleration γ: constituting the beam Piezoelectric density A: Beam cross-sectional area

Next, the resonance frequency fn of the beam 11 when the axial force P acts on the beam 11 is _expressed by the following equation (2).

(Equation 2) Here, in the range where the amplitude of vibration is small, the above equation (2) is approximately as follows.

(Equation 3)

Accordingly, the axial force P can be determined by measuring the change in the impedance of the beam 11 and detecting the resonance frequency f when the axial force P acts on the beam 11. Specifically, the acceleration by the driving power source 20, for example, as shown in FIG. 3, while providing lateral vibration that vibrates in the first-order resonance frequency f ₀₁ in the beam 11, the base over scan member 12 in the axial direction of the beam 11 When α acts, the acceleration α and the weight 13 generate an axial force P due to inertial force. The resonance frequency f ₁ at this time is measured. Since the mass of the weight 13 is M, the axial force P becomes P = Mα,
The acceleration α is represented by α = P / M. Therefore, by measuring the resonance frequency f of the beam 11, the acceleration α can be detected.

When the frequency of the acceleration α is low or 0H
Even at z, the first shock absorber 11a and the second piezoelectric body 11b constituting the beam 11 vibrate around the resonance frequency, so that the discharge from the piezoelectric body surface does not matter.
Further, the lateral vibration mode of the beam 11 driven by the drive power supply 20 may be a higher-order vibration mode other than the first-order vibration mode. In addition, beam 1
1 while applying lateral vibration to the base member 1 with the driving power supply 20.
If the beam 2 is rotated around the axis of the beam 11, Coriolis force acts on the beam 11. If the deflection of the beam 11 due to this Coriolis force is measured by a known means, the angular velocity can be measured.

(Embodiment 2) FIG. 2 shows a configuration of a vibrating beam axial force sensor type acceleration sensor according to Embodiment 2 of the present invention. In FIG. 2, a beam 21 is a bimorph piezoelectric body beam composed of a first piezoelectric body 21a and a second piezoelectric body 21b which are superimposed on each other. Beam 22 is also
This is a bimorph piezoelectric body beam having the same shape and configuration as the beam 21 and composed of a first piezoelectric body 22a and a second piezoelectric body 22b superimposed on each other. Beams 21 and 2
2 is a common base member 2 whose base ends are U-shaped.
3 and a weight 24 having a mass M is
Are fixed in common. First piezoelectric body 21a of beam 21
A first electrode 25 is formed on the surface of the second piezoelectric body 21b, a second electrode 26 is formed on the surface of the second piezoelectric body 21b, and an intermediate electrode 27 is formed on a portion where the first and second piezoelectric bodies 21b overlap each other by a method such as firing. Lead wires 28, 29, 30 are connected. The lead wire 30 is connected to one side of an AC drive power supply 31 for generating lateral vibration in the beam 21, and the lead wires 28 and 29 are connected to the other side of the drive power supply 31. Similarly, a first electrode 32 is provided on the surface of the first piezoelectric body 22a of the beam 22, a second electrode 33 is provided on the surface of the second piezoelectric body 22b, and an intermediate electrode 34 is provided on a portion where the beams 22 overlap each other. Are formed by a method such as baking, and lead wires 35, 36, and 37 are connected to each. The lead 37 is connected to one side of an AC drive power supply 38 for generating lateral vibration in the beam 22, and the lead wires 35 and 36 are connected to the other side of the drive power supply 38.

Next, the operation of this embodiment will be described. From the driving power source 31 to the beam 21 provide lateral vibration of the secondary resonance frequency f _02, simultaneously with the beam 21 from the drive power source 38 to the beam 22 provide lateral vibration of the secondary resonance frequency f ₀₂ of the opposite phase. At this time, vibration is applied to the base member 23 in the axial direction of the beams 21 and 22, and the axial force P in the tensile direction and the compressive direction acts on the beams 21 and 22 alternately. ,
The resonance frequency f ₀₂ of the beams 21 and 22 is Δf = f ₀₂ −
f ₂ and −Δf = f ₂ −f ₀₂ . Therefore, if the resonance frequency detected from the impedance change and the changed frequency of either the beam 21 or the beam 22 are inverted with respect to the resonance frequency f ₀₂ and the sum is obtained, the detection sensitivity of the acceleration in the axial direction is increased. Can be doubled.

(Embodiment 3) FIG. 3 shows a configuration of a vibration beam axial force sensor type acceleration sensor according to Embodiment 3 of the present invention. The acceleration sensor according to the third embodiment is obtained by combining the acceleration sensors shown in FIG. 2 in a cross shape. In FIG. 3, beams 41, 42, 43, 44
Are two layers of piezoelectric bodies 41a, 41b, 42a,
This is a bimorph piezoelectric body beam composed of 42b, 43a, 43b, and 44a, 44b. Each beam 41, 4
2, 43 and 44 each have a base end which is a base member 45.
And fixed to the columns 46, 47, 48, 49 of
A common weight 50 is fixed to the front end portions facing each other. Electrodes are formed on the surfaces and intermediate surfaces of the respective piezoelectric bodies of the beams 41, 42, 43, and 44 by a method such as firing, and lead wires are connected to the respective electrodes. Each lead wire has an AC drive power supply 51, 52, 53, 54 for generating lateral vibration in the beams 41, 42, 43, 44.
Is connected.

Next, the operation of the third embodiment will be described. When lateral vibration of the secondary resonance frequency f ₀₂ is given to the beam 41 from the driving power supply 51 and lateral vibration of the secondary resonance frequency f _{02 having} a phase opposite to that of the beam 41 is given to the beam 42 from the driving power supply 52, the above-described embodiment is performed. It operates in the same manner as in the second embodiment, and can detect the acceleration of the beams 41 and 42 in the axial direction (X direction). Similarly, the secondary resonance frequency f
_When the lateral vibration of ₀₂ and the beam 44 are subjected to the lateral vibration of the secondary resonance frequency f _{02 having} a phase opposite to that of the beam 43 from the driving power supply 54, the beam 44 operates in the same manner as in the second embodiment.
4 can be detected in the axial direction (Y direction).

Further, while vibrating the beams 41 and 42 at the resonance frequency in the same manner as in the second embodiment and vibrating the weight 50 in the X-axis direction of the beams 41 and 42, the whole acceleration sensor When rotated about the axis, Coriolis force acts on the weight 50, and the beams 43 and 44 are deformed by vibration. Due to the deformation of the beams 43 and 44, electric charges are generated in the piezoelectric bodies 43a, 43b and 44a, 44b constituting the beams 43 and 44, and can be taken out as voltages from both ends of the driving power supplies 53 and 54. Thereby, the angular velocity about the Z axis can be detected.

(Embodiment 4) Embodiment 4 of the present invention
Is a structure in which the configuration of the acceleration sensor according to each of the first, second, and third embodiments is integrally formed by using a piezoelectric material as shown in FIGS. 4, 5, and 6, respectively. That is, in FIG. 4, the beam 111, the base 121, and the weight 13
1 is formed integrally from a piezoelectric material, and the material 101 having the electrode portions 141 formed on both surfaces of the beam portion 111 is laminated in two layers. Also, in FIG.
21, the base portion 231 and the weight portion 241 are integrally formed of a piezoelectric material, and the electrode portions 2 are formed on both surfaces of the beam portions 211 and 221.
The material 201 on which 51 is formed is laminated in two layers. Also, in FIG. 6, the beam portions 411, 421, 43
1, 441, the base portion 451, and the weight portion 501 are integrally formed of a piezoelectric material, and the beam portions 411, 421, 431,
The material 301 in which the electrode portions 601 are formed on both surfaces of
It is a laminate of layers. Such an acceleration sensor having an integral structure has advantages that the structure is simple and robust, and that it can be manufactured at low cost.

[0021]

As described above, according to the present invention, by measuring the change in the resonance frequency of the vibrating beam, the axial force acting on the vibrating beam can be determined, whereby the fluctuation from the constant acceleration region acting on the beam can be obtained. This has the effect of being able to detect up to vibration acceleration. By providing two or four sets of vibrating beams, it is possible to increase the detection sensitivity and detect vibration acceleration and angular acceleration in two directions. Further, by using a laminated vibrating beam axial force sensor having a laminated structure, an acceleration sensor which is inexpensive and excellent in mass productivity can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a configuration of an acceleration sensor according to Embodiment 1 of the present invention.

FIG. 2 is a schematic perspective view showing a configuration of an acceleration sensor according to Embodiment 2 of the present invention.

FIG. 3 is a schematic perspective view showing a configuration of an acceleration sensor according to Embodiment 3 of the present invention.

FIG. 4 is a schematic perspective view showing a configuration of an acceleration sensor according to a fourth embodiment of the present invention.

FIG. 5 is a schematic perspective view showing a configuration of another acceleration sensor according to Embodiment 4 of the present invention.

FIG. 6 is a schematic perspective view showing the configuration of another acceleration sensor according to Embodiment 4 of the present invention.

FIG. 7 is a schematic front view showing a configuration of an acceleration sensor in a conventional example.

[Explanation of symbols]

11, 21, 22, 41, 42, 43, 44 beams 11a, 11b, 21a, 21b, 22a, 22b, 4
1a, 41b, 42a, 42b, 43a, 43b, 44
a, 44b Piezoelectric body 12, 23, 45 Base member 13, 24, 50 Weight 14, 15, 16, 25, 26, 27, 32, 33, 3,
4 electrodes 101, 201, 301 Material 111, 211, 221, 411, 421, 431, 4
41 Beam part 121, 231, 451 Base part 131, 241, 501 Weight part 141, 251, 601 Electrode part

Claims (4)

[Claims] 1. A beam composed of two layers of piezoelectric bodies and having a surface having an electrode between the two layers of piezoelectric bodies and an electrode between the two layers of piezoelectric bodies, and a base member for fixing a base end of the beam. And a weight fixed to the tip of the beam. 2. Two sets of beams each composed of two layers of piezoelectric bodies and having electrodes between the surfaces of the two layers of piezoelectric bodies and electrodes between the two layers of piezoelectric bodies, and each of the two sets of beams. An acceleration sensor comprising: a base member for fixing a base end portion; and a weight commonly fixed to opposed end portions of the two sets of beams. 3. Four orthogonal beams each comprising two layers of piezoelectric bodies and having electrodes between the two layers of piezoelectric bodies and electrodes between the two layers of piezoelectric bodies, and the four sets of beams. An acceleration sensor comprising: a base member for fixing the respective base end portions; and a weight commonly fixed to the opposed end portions of the four beams. 4. The acceleration sensor according to claim 1, wherein the beam having the electrode, the base member, and the weight are integrally formed of a piezoelectric material and laminated in two layers.