JP2008304409A - Acceleration detecting unit and acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration detecting unit that has high measurement accuracy and sensitivity of acceleration and does not break even if excessive stress is applied. <P>SOLUTION: This acceleration detecting unit has a fixing member 5 that is not displaced by acceleration application, a bi-tuning fork type piezoelectric vibrating element 10 having two fixed ends connected to a stress sensitive section so as to grip the stress sensitive section, a weight member 15, and a buffer member 22. The fixing member 5 has a step section 5b and a recessed section 5a. The weight member 15 is fixed to one fixed end 10a of the bi-tuning fork type piezoelectric vibrating element 10, and the other fixed end 10b is stuck and fixed to the step section 5b of the fixing member 5 using an adhesive 20. The weight member 15 fixed to the one fixed end 10a of the bi-tuning fork type piezoelectric vibrating element 10 is supported on the bottom surface of the recessed section 5a of the fixing member 5 via the buffer member 22. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an acceleration detection unit and an acceleration sensor, in particular, a double tuning fork type piezoelectric vibration element as a stress sensitive element, and an improved acceleration detection unit that can withstand excessive stress applied to the double tuning fork type piezoelectric vibration element, And an acceleration sensor.

Conventionally, acceleration sensors have been widely used from automobiles, airplanes, rockets to monitoring abnormal vibrations of various plants. Patent Document 1 discloses a momentum sensor capable of measuring acceleration or rotational speed. FIG. 4 is a plan view of an acceleration sensor that detects one-dimensional acceleration, and is a sensor that detects applied acceleration as a change in the natural frequency of the vibrating body. The entire sensor is formed by punching a metal or piezoelectric material plate into the illustrated shape. The left end of the frame-type vibrating body 40 in the figure is integral with the fixing member 45, and the leftmost end is fixed to the base. The right end is fixed to the additional mass 47 via the connecting portion 53 and detects the acceleration component in the direction of arrow G shown in the figure. In the frame-shaped vibrating body 40 composed of the vibrating legs 51 and 52 connected at both ends, the spring axes of both are parallel, but as shown by the broken lines in the figure, they are symmetrical on both sides of the central axis in the longitudinal direction of the frame. Is excited by bending vibration.
When a tensile force or a compressive force is applied to both ends in the longitudinal direction of the frame in the free vibration state, the frequency changes according to the force, and the magnitude of the force is measured from the amount of change. The periphery of the fixing member 45 has an outer frame shape, and supports an additional mass and also serves as a guide member for linear motion in the left-right direction.

FIG. 5 is a plan view showing a two-dimensional acceleration sensor, and includes four frame-shaped vibrating bodies 41 to 44 similar to the frame-shaped vibrating body 40 shown in FIG. These have substantially the same shape and are integrally formed from a single plate-like material. 61 to 68 are vibrating legs, 53, 73, 74, and 75 are connecting portions, 47 is an additional mass, and the four frame-type vibrating bodies 41 to 44 are connected to the additional mass 47 at the center, The outer ends thereof are arranged radially at intervals of 90 °, and their outer ends are integrated with the fixing member 46.
The four frame-type vibrating bodies 41 to 44 are self-excited by an electro-mechanical converter and an oscillation circuit (not shown). For the acceleration component in the vertical direction in FIG. 5, the frequency change amount of the frame-type vibrators 41 and 43 due to the inertial force of the additional mass 47 is measured, and for the horizontal acceleration component, the frequency change amount of the frame-type vibrator members 42 and 44 is measured. Can be obtained. Further, it is described that the acceleration Gθ in an arbitrary direction in the sensor plane can be obtained by comparing the magnitude and sign of both components.
JP 2000-206141 A JP 60-39911 A

However, in the acceleration sensor described in Patent Document 1, when excessive acceleration is applied in the vertical direction with respect to the frame-type vibrating body, there is no protection device against the displacement of the frame-type vibrating body, and there is a risk of damage. There was a problem. In addition, the frequency of all the frame-type vibrating bodies changes with respect to the acceleration in the vertical direction, causing a measurement error.
The present invention has been made to solve the above problems, and it is an object of the present invention to provide an acceleration detection unit and an acceleration sensor corresponding to a case where excessive force or acceleration is applied.

In order to achieve the above object, an acceleration sensor according to the present invention has a stepped portion and a recessed portion protruding from the stepped portion so as to sandwich a fixing member that is not displaced by application of acceleration, a stress sensitive portion, and the stress sensitive portion. A double tuning fork type piezoelectric vibration element having two fixed ends connected to the stress sensitive part, a weight member fixed to one fixed end of the double tuning fork type piezoelectric vibration element, and a double tuning fork type piezoelectric vibration element And a buffer member provided between the weight member and the recessed portion in a state where the other fixed end portion is fixed to the step portion of the fixing member.
In the acceleration sensor of the present invention, the weight member is fixed so that the center of gravity is the center of the thickness of the fixed end. In the acceleration sensor of the present invention, the weight member is fixed to one surface of the fixed end portion.
When the acceleration detection unit is configured as described above, when the acceleration in the detection axis direction is applied, the buffer member is easily deformed, so that the measurement accuracy and sensitivity of the acceleration are not affected. When excessive stress or acceleration is applied, the buffer member absorbs the force, so that there is an effect that the double tuning fork type piezoelectric element as the stress sensitive element is not damaged.
The acceleration sensor of the present invention is characterized by including the acceleration detection unit of the present invention. When the acceleration sensor is configured as in the present invention, there is an effect that an acceleration sensor with good measurement accuracy and sensitivity of acceleration and withstanding excessive stress and acceleration can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A and 1B are diagrams showing an acceleration detection unit 1 according to the first embodiment. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the line Q-Q. The acceleration detection unit 1 includes a fixed member 5 that is not displaced by application of acceleration, a double tuning fork type piezoelectric vibration element 10 having two fixed ends connected to the stress sensitive part so as to sandwich the stress sensitive part, and a weight member 15. The buffer member 22 is provided. The fixing member 5 has a step portion 5b and a recessed portion 5a protruding from the step portion 5b. The weight member 15 is fixed to one fixed end portion 10a of the double tuning fork type piezoelectric vibration element 10 so that the center of gravity of the weight member 15 is at the center of the thickness of the fixed end portion 10a. The other fixed end portion 10 b is bonded and fixed to the step portion 5 b of the fixing member 5 using an adhesive 20. The weight member 15 fixed to one fixed end portion 10 a of the double tuning fork type piezoelectric vibration element 10 is supported by the bottom surface of the recessed portion 5 a of the fixed member 5 via the buffer member 22.

  In order to gain an understanding of the present invention, a double tuning fork type piezoelectric vibration element will be described briefly. Patent Document 2 discloses an electrode structure of a double tuning fork type piezoelectric vibration element. FIG. 6A is a plan view of a double tuning fork type piezoelectric vibration element. Excitation electrodes divided into three are formed on the respective vibrating arm portions 81a and 81b. The excitation electrode is divided along a line serving as a vibration node, and the electrodes are connected so that voltages of opposite polarities are applied to the excitation electrodes adjacent to each other of the division line. The dividing line of the excitation electrode is 0.255L from the ends of the fixed end portions 80a and 80b near the center, where L is the length of the vibrating arm portion 81a (81b). FIG. 6B is a cross-sectional view taken along the line AA of FIG. 6A and shows a connection method of the excitation electrodes. That is, the first, second, and third excitation electrodes are formed on the front and back surfaces of the vibrating arm portions 81a, 81b, and the fourth, fifth, and sixth excitation electrodes are formed on both side surfaces. As shown in FIG. 6B, the excitation electrodes facing each other on the front and back surfaces and both side surfaces of the vibrating arm portions 81a and 81b are connected to each other and the corresponding excitation electrodes of the vibrating arm portions 81a and 81b are oppositely polarized high frequency. A voltage is applied to excite symmetrical bending vibrations on both sides of the central axis of the double tuning fork type piezoelectric vibration element.

In particular, when a double tuning fork type piezoelectric vibration element is configured using a quartz material, an acceleration detection unit having excellent frequency temperature characteristics, frequency stability, and stress sensitivity can be configured. In the present embodiment example, a double tuning fork type crystal vibrating element having two vibrating arms is used as the stress sensitive element. The double tuning fork type quartz vibrating element has good sensitivity to tensile and compressive stress, and when used as a stress sensitive element for altimeter or depth gauge, it has excellent decomposition ability. You can know the difference.
The resonance frequency f _F when the external force F is applied to the two vibrating arms of the double tuning fork type crystal vibrating element is as follows.
f _F = f ₀ (1- (KL ² F) / (2EI)) ^1/2 (1)
Here, f ₀ is the resonance frequency of the double tuning fork type quartz vibrating element when there is no external force, K is a constant according to the fundamental mode (= 0.0458), l is the length of the vibrating beam, E is the longitudinal elastic constant, I Is the moment of inertia of the cross section. Second moment I are from I = dw ^3/12, the equation (1) can be modified as follows. Here, d is the thickness of the vibration beam, and w is the width.
f _F = f ₀ (1−S _F σ) ^1/2 (2)
However, the stress sensitivity _SF and the stress σ are respectively expressed by the following equations.
S _F = 12 (K / E) (L / w) ² (3)
σ = F / (2A) (4)

From the above, when the force F acting on the double tuning fork type vibration element is negative in the compression direction and positive in the extension direction (tensile direction), the relationship between the force F and the resonance frequency f _F is the resonance frequency f. _F decreases and increases with stretching (tensile). The stress sensitivity S _F is proportional to the square of l / w of the vibrating beam. However, the piezoelectric vibration element is not limited to a double tuning fork type crystal vibration element, and any piezoelectric vibration element whose frequency changes due to stretching / compression stress may be used.

The acceleration detection unit 1 shown in FIG. 1 is characterized in that a buffer is provided between the weight member 15 fixed to one fixed end portion 10a of the double tuning fork type piezoelectric vibration element 10 and the bottom surface of the recessed portion 5a of the fixed member 5. For example, a silicon adhesive is sandwiched between the members 22. The acceleration detection axis of the acceleration detection unit 1 is in the direction of arrow G in FIG. When acceleration is applied in the direction of the arrow, the buffer member 22 is sufficiently soft, and a force F of α × m (m is the mass including the weight member) according to the acceleration α is applied to the double tuning fork type piezoelectric vibration element 10. In addition, the frequency of the double tuning fork type piezoelectric vibration element 10 changes according to the stress F. A terminal electrode of the double tuning fork type piezoelectric vibration element 10 is connected to an oscillator, and an acceleration unit is used in a self-excited oscillation state.
In the conventional acceleration detection unit, when an excessive force or acceleration is applied in the vertical direction to the double tuning fork type piezoelectric vibration element 10, the elastic limit of the double tuning fork type piezoelectric vibration element 10 is exceeded, and there is a risk of damage. there were. On the other hand, in the acceleration detection unit 1 of the present invention, since the elastic buffer member 22 is sandwiched between the weight member 15 and the fixed member 5, buffering is performed against excessive force and acceleration. Since the member 22 absorbs the force, there is an effect that the double tuning fork type piezoelectric element as the stress sensitive element is not damaged.

FIG. 2 is a cross-sectional view showing the configuration of the second embodiment of the acceleration detection unit. A double tuning fork type piezoelectric vibration element 10 having a fixed member 5 that is not displaced by application of acceleration and two fixed end portions connected to the stress sensitive portion so as to sandwich the stress sensitive portion is provided. The weight member 15 is fixed to one surface (lower side) of one fixed end portion 10 a of the double tuning fork type piezoelectric vibration element 10, and the other fixed end portion 10 b of the double tuning fork type piezoelectric vibration element 10 is a step of the fixing member 5. The part 5b is bonded and fixed using an adhesive. The weight member 15 fixed to one fixed end portion of the double tuning fork type piezoelectric vibration element 10 is supported by the recessed portion 5 a of the fixing member 5 via the buffer member 22.
In this case as well, as in the first embodiment shown in FIG. 1B, the acceleration detection axis of the acceleration detection unit 1 is in the direction of arrow G in FIG. When acceleration is applied in the direction of the arrow, the buffer member 22 has elasticity, so that a force F due to the acceleration α is applied to the double tuning fork type piezoelectric vibration element 10. In response to the stress F, the frequency of the double tuning fork type piezoelectric vibration element 10 changes. When an excessive force is applied to the double tuning fork type piezoelectric vibration element 10 from the vertical direction, the double tuning fork type piezoelectric vibration element 10 is also slightly deformed in that direction, but the buffer member 22 absorbs the stress, so that The double tuning fork type piezoelectric element has the effect of not being damaged.

FIG. 3 is a cross-sectional view showing the configuration of the acceleration sensor of the present embodiment. The acceleration sensor includes the acceleration detection unit 1, the oscillation circuit 30, the data processing unit 32, a housing 35 that accommodates these, and a lid member 36 that seals the housing 35.
The acceleration sensor of the present invention has not only excellent acceleration sensitivity and accuracy, but also has a feature that even if excessive stress is applied, the double tuning fork type piezoelectric vibration element of the stress sensitive portion is not damaged.

It is the figure which showed the structure of the acceleration detection unit of 1st Embodiment, (a) is a top view, (b) is sectional drawing. It is sectional drawing which shows the structure of the acceleration detection unit of 2nd Embodiment. It is sectional drawing which shows the structure of the acceleration sensor of this Embodiment. It is a top view which shows the structure of the conventional one-dimensional acceleration sensor. It is a top view which shows the structure of the conventional two-dimensional acceleration sensor. It is a figure which shows the structure of the conventional double tuning fork type piezoelectric vibration element, (a) is a top view, (b) is sectional drawing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Acceleration detection unit, 5 ... Fixed member, 5a ... Recessed part, 5b ... Step part, 10 ... Double tuning fork type piezoelectric vibration element, 10a ... One end of double tuning fork type piezoelectric vibration element, 10b ... Double tuning fork One end of the piezoelectric piezoelectric element, 15 weight member, 20 ... adhesive, 22 ... buffer member, 30 ... oscillation circuit, 32 ... data processing, 35 ... housing, 36 ... lid member

Claims (2)

A fixing member having a stepped portion and a recessed portion protruding from the stepped portion, and not displaced by application of acceleration;
A double tuning fork type piezoelectric vibration element having a stress sensitive part and two fixed ends connected to the stress sensitive part so as to sandwich the stress sensitive part;
A weight member fixed to one fixed end of the double tuning fork type piezoelectric vibration element;
A buffer member provided between the weight member and the recessed portion in a state in which the other fixed end portion of the double tuning fork type piezoelectric vibration element is fixed to the step portion of the fixing member;
An acceleration detection unit comprising:   An acceleration sensor comprising the acceleration detection unit according to claim 1.

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