JP4848973B2 - Acceleration detection unit and acceleration sensor - Google Patents

Description

  The present invention relates to an acceleration detection unit and an acceleration sensor, and is particularly suitable for preventing damage to a stress sensitive element.

  Acceleration sensors have been widely used in automobiles, airplanes, rockets, and other abnormal vibration monitoring devices for various plants. Patent Document 1 discloses a pressure sensor as shown in FIG. In FIG. 3, 50 is a housing, 60 is a pressure inlet, and 70a and 70b are bellows. A force transmission member 80 is connected to the bellows 70a and 70b, and the pressure sensitive element 90 is bonded and fixed between the flexible portion 80a and the fixing portion 80b of the force transmission member 80. When pressure is applied to the bellows 70a and 70b from the pressure introduction port of the pressure sensor shown in FIG. The pressure is applied to the pressure-sensitive element 90 as a compressive force or a tensile force, and the resonance frequency of the pressure-sensitive element 90 changes according to this force, and the pressure is measured by detecting this.

Since the bellows 70a and 70b, the force transmission member 80, the pressure-sensitive element 90, and the housing 50 are made of different materials, thermal distortion occurs due to temperature changes in the usage environment, and pressure measurement accuracy is degraded. become. Therefore, the supporting portion of the pressure-sensitive element 90 is bridge-fixed between the force transmission member flexible portion 80a and the fixing member 110 of the pressure-sensitive element 90 that is spaced from the force transmission member and provided in the pressure sensor housing. Thus, the pressure sensitive element 90 is configured not to be affected by the thermal strain accompanying the change in the ambient temperature. The thermal strain analysis is performed separately for the bellows line, the force transmission member, the force transmission member support, and the pressure-sensitive element fixing part. , The respective linear expansion coefficients are applied, the dimensions of each member are set, and the linear expansion coefficient of the fixing member of the pressure-sensitive element 90 is set. It is disclosed that a pressure sensor that is not affected can be constructed.
JP-A-2-228534

However, the pressure sensor as shown in Patent Document 1 or the conventional acceleration sensor has no or no protection device when a strong pressure or a large acceleration is applied during measurement. There is a problem that the element or the stress sensitive element may be damaged.
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 in which a stress sensitive element is not damaged even when a large acceleration is applied to the acceleration sensor. .

  To achieve the above object, an acceleration detection unit according to the present invention includes a fixed member that is not displaced by application of acceleration, a movable member that is displaced by application of acceleration, a first beam that supports the movable member on the fixed member, stress A stress sensitive element having two sensitive ends connected to the stress sensitive part so as to sandwich the stress sensitive part, a weight member displaced in the acceleration detection direction, and a second member for connecting the weight member to the movable member The stress sensitive element has one fixed end supported by the fixed member and the other fixed end supported by the movable member. The first beam has an acceleration on the movable member. When applied, the movable member is flexible so as to be displaced in the direction of the acceleration detection axis. According to the present invention as described above, when the excessive acceleration is applied, the displacement amount of the weight member is limited by the limiting member, and the first beam does not bend any more, so that excessive strain is applied to the stress sensitive element. It has the effect of not causing damage without being added.

  Further, in the acceleration detection unit of the present invention, the fixing member is formed by an element supporting portion that supports one fixed end of the stress sensitive element, and the element supporting portion is extended to the side parallel to the extending direction of the stress sensitive element. An overhang portion having a first beam at the tip, and the first beam is supported orthogonally to the second beam, and the upper surface of the movable member and the upper surface of the element support portion are parallel to each other; and , Parallel to the acceleration detection axis direction. According to the present invention, since the stress sensitive element is fixed in the acceleration detection axis direction, there is an effect that the applied acceleration can be accurately measured.

  In the acceleration detection unit of the present invention, the fixing member has an element support portion that supports one of the fixed ends of the stress sensitive element, and is extended from the element support portion to a side parallel to the extension direction of the stress sensitive element. And an overhanging portion having a first beam at the portion, the first beam is supported by the movable member, the upper surface of the movable member and the upper surface of the element support portion are parallel, and the acceleration detection axis direction It is orthogonal to. According to the present invention, since the stress sensitive element is fixed in the acceleration detection axis direction, there is an effect that the applied acceleration can be accurately measured.

  In the acceleration detection unit of the present invention, the first beam has a shape that prevents displacement of the movable member in the depth direction orthogonal to the acceleration detection axis direction. According to the present invention, since the movable member is displaced only in the acceleration detection axis direction, there is an effect that acceleration components other than the acceleration detection axis direction are removed.

  In the acceleration detection unit of the present invention, the dimension in the depth direction of the first beam is longer than the dimension of the width of the first beam in the acceleration detection axis direction. According to the present invention, since the movable member is displaced only in the acceleration detection axis direction, there is an effect that acceleration components other than the acceleration detection axis direction are removed.

  In the acceleration detection unit of the present invention, the second beam includes a neck portion having a shape in which both surfaces in the depth direction are recessed in a hyperbolic shape. According to the present invention, the second beam is easily bent in the direction of the acceleration detection axis, and when excessive acceleration is applied, the weight member contacts the limiting member provided inside the housing (housing), for example. In contact therewith, the first beam does not bend any more, so that there is an effect that excessive strain is not applied to the stress sensitive element and damage is not caused.

  In the acceleration detection unit of the present invention, the stress sensitive element has two fixed ends and a stress sensitive portion including a piezoelectric substrate having two vibration beams connected between the fixed ends, and a vibration region of the piezoelectric substrate. And a double tuning fork type piezoelectric vibration element. According to the present invention, the acceleration measurement accuracy of the acceleration detection unit is improved, and the temperature characteristics and reproducibility are improved.

  The acceleration detection sensor of the present invention includes the acceleration detection unit of the present invention and a housing that has a limiting member for limiting displacement of the weight member in the acceleration detection axis direction and accommodates the acceleration detection unit in an airtight manner. And an oscillation circuit electrically connected to the excitation electrode constituting the stress sensitive element. According to the present invention, when excessive acceleration is applied, the weight member comes into contact with the limiting member provided inside the housing (housing), and the first beam is not further bent. In addition, there is an effect that excessive strain is not applied to the stress-sensitive element and damage is not caused.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a perspective view showing a configuration of an acceleration detection unit 1 according to the present invention. The acceleration detection unit 1 has a fixed member 3 that is not displaced by application of acceleration, a movable member 21, a beam (first beam) 10 that supports the movable member 21 on the fixed member 3, and a stress sensitive portion 31. A stress sensitive element 30 having two fixed ends 32 and 33 connected to each other, a weight member 22 movable in the acceleration detection direction, and a second beam 11 connecting the weight member 22 to the movable member 21 are provided. The fixing member 3 is fixed to a housing (housing) (not shown). The stress sensitive element 30 has one fixed end 32 supported by the fixed member 3 and the other fixed end 33 supported by the movable member 21. The beam 11 is arranged so as to be orthogonal to the beam 10 integrated with the fixing member 3. Further, the beam 10 has flexibility that can be bent so as to displace the movable member 21 in the acceleration detection axis direction (X-axis direction) when acceleration is applied to the movable member 21.
The weight member 22 is provided with protrusions 23 on both sides in the acceleration detection axis direction (X-axis direction).

The fixing member 3 is formed to project from the element support 4 supporting one fixed end 32 of the stress sensitive element 30 to the side parallel to the projecting direction of the stress sensitive element 30 from the element support 4, and to the tip. And an overhang portion 5 including a beam 10. The beam 10 formed at the tip of the overhang portion 5 is fixed so as to be orthogonal to the beam 11 of the movable member 21 that supports the weight member 22. The upper surface of the element support portion 4 and the upper surface of the movable member 21 are configured to be parallel to the acceleration detection axis (X axis). One fixed end 32 of the stress sensitive element 30 is fixed to the upper surface of the element support portion 4, and the other fixed end 33 is fixed to the upper surface of the movable member 21.
The beam 10 is shaped to prevent displacement of the movable member 21 in the depth direction orthogonal to the acceleration detection axis direction (X-axis direction), and the dimension of the beam 10 in the depth direction is the acceleration detection axis direction ( It is formed to have a length equal to or greater than the width of the beam 10 in the (X-axis direction). This is because the movable member 21 is prevented from being displaced in directions other than the acceleration detection axis direction, and the acceleration only in the acceleration detection axis direction is detected.

The shape between the beam 11 and the weight member 22 is formed such that both surfaces in the depth direction orthogonal to the acceleration detection axis direction (X-axis direction) are the hyperbolic dents 12. This is a structure in which when the acceleration is applied, the beam 11 bends at the center portion of the recess 12 and the bending of the beam 10 is suppressed so that an excessive force is not applied to the stress sensitive element 30. In addition to the hyperbolic dent 12, circular holes may be provided on both sides in the depth direction. In short, what is necessary is just to be comprised so that the beam 11 of the upper part of the weight member 22 may bend.
The stress sensitive element 30 includes a stress sensitive part including a piezoelectric substrate having two fixed ends 32 and 33 and two vibration beams 31 connected between the fixed ends 32 and 33, and a vibration region of the piezoelectric substrate. It is a double tuning fork type piezoelectric vibration element provided with the formed excitation electrode. The acceleration detection unit 1 shown in FIG. 1 shows an example using a double tuning fork type crystal vibrating 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. Further, the frequency temperature characteristic exhibited by the double tuning fork type crystal resonator element is an upwardly convex quadratic curve, and each parameter is set so that the apex temperature becomes room temperature (25 ° C.).

ここで、ｆ₀は外力がないときの双音叉型水晶振動素子の共振周波数、Ｋは基本波モードによる定数（＝０．０４５８）、Ｌは振動ビームの長さ、Ｅは縦弾性定数、Ｉは断面２次モーメントである。断面２次モーメントＩはＩ＝ｄｗ³／１２より、式（１）は次式のように変形することができる。ここで、ｄは振動ビームの厚さ、ｗは幅である。
［数２］

但し、応力感度Ｓ_Fと、応力σとはそれぞれ次式で表される。
［数３］

［数４］

The resonance frequency f _F when the external force F is applied to the two vibrating beams of the double tuning fork type quartz vibrating element is as follows.
[Equation 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.
[Equation 2]

However, the stress sensitivity _SF and the stress σ are respectively expressed by the following equations.
[Equation 3]

[Equation 4]

Here, A is the sectional area (= w · d) of the vibration beam. From the above, when the force F acting on the double tuning fork vibrator 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 that the force F is a compression force and the resonance frequency. f _F decreases and increases with stretching (tensile) force. The stress sensitivity S _F is proportional to the square of the vibration beam L / w. Further, the relationship between the stress and the apex temperature has a characteristic that the apex temperature shifts to the low tone side when an extensional stress is applied to the double tuning fork type crystal vibrating element and shifts to the high temperature side when compressive stress is applied.
However, the piezoelectric vibration element is not limited to a double tuning fork type crystal resonator, and any piezoelectric vibration element whose frequency changes due to stretching / compression stress may be used.

  In the acceleration detection unit 1 shown in FIG. 1, when acceleration is applied, stress (acceleration × mass) is applied to the movable member 21, and the beam 10 bends in a direction perpendicular to the acceleration detection axis (Z-axis direction). As the beam 10 bends, stress with the beam 10 as a fulcrum is applied to the stress sensitive element 30, and the resonance frequency of the stress sensitive element 30 changes according to the stress. The magnitude of acceleration is obtained from the change in resonance frequency. However, since the stress sensitive element 30 is formed using a material such as quartz, for example, there is a possibility that the stress sensitive element 30 may be damaged by a stress exceeding the elastic limit.

  A feature of the acceleration detection unit 1 shown in FIG. 1 is that a hyperbolic recess 12 is formed on both sides of the beam 11 connecting the movable member 21 and the weight member 22 in the depth direction (Y-axis direction), and a central portion of the recess 12 is formed. As a limiting member that limits the displacement of the weight member 22 when excessive acceleration is applied to the weight member 22, the projection is formed on both surfaces of the acceleration detection axis (X axis) of the weight member. An object 23 is provided, and the protrusion 23 is sandwiched inside a housing (housing) (not shown) so as to face the stoppers 40 and 41 through a slight gap. As a result, when excessive acceleration is applied to the movable member 21, the beam 10 bends in the acceleration detection axis direction (Z-axis direction) due to stress (acceleration × mass), and the depression 12 of the beam 11 is caused to be an acceleration detection axis by this bending. When bent in the direction (X axis), the weight member 22 is slightly displaced in the X axis direction. Due to this displacement, the protrusion 23 provided on the weight member 22 abuts against the stoppers 40, 41, thereby suppressing the bending of the beam 10 beyond the setting and preventing the stress sensitive element 30 from being damaged. Note that the stoppers 40 and 41 that are limiting members may be connected to the fixing member 3 instead of the housing. Further, it is not necessary to provide the protrusions 23 on both sides of the weight member 23.

FIG. 2 is a perspective view showing the configuration of the acceleration detection unit 2 of the second embodiment. The same members as those in the acceleration detection unit 1 of FIG. The acceleration detection unit 2 includes a fixed member 3 that is not displaced by application of acceleration, a movable member 21 that is supported on the fixed member 3 by a beam (first beam) 13, and a stress sensitive element 30. . In the stress sensitive element 30, one fixed end 32 is supported by the fixed member 3 and the other fixed end 33 is supported by the movable member 21. And the beam 13 has the flexibility which can be bent so that when the acceleration is applied to the movable member 21, the movable member 21 is displaced in the acceleration detection axis direction (X-axis direction).
The fixing member 3 is formed to project from the element support 4 supporting one fixed end 32 of the stress sensitive element 30 to the side parallel to the projecting direction of the stress sensitive element 30 from the element support 4, and to the tip. And an overhang portion 5 including a beam 10. The beam 10 formed at the tip of the overhang portion 5 is fixed so as to be orthogonal to the beam 11 of the movable member 21 that supports the weight member 22. The upper surface of the element support portion 4 and the upper surface of the movable member 21 are configured to be parallel to the acceleration detection axis (X axis). One fixed end 32 of the stress sensitive element 30 is fixed to the upper surface of the element support portion 4, and the other fixed end 33 is fixed to the upper surface of the movable member 21. Further, the movable member 21 has a structure in which a weight member 22 is connected by the beam 11, and has a structure in which protrusions 23 are provided on both sides of the weight member 22 in the acceleration detection axis direction (X axis).

The fixing member 3 is formed with an element support portion 4 that supports one fixed end 32 of the stress sensitive element 30, and is extended from the element support portion 4 to the side parallel to the extension direction of the stress sensitive element 30. And an overhang portion 5 having 13. The beam 13 supports the lower surface 21 b of the movable member 21.
The upper surface 21a of the movable member 21 and the element support unit upper surface 4 are parallel to each other and orthogonal to the acceleration detection axis direction (X-axis direction). Further, the dimension in the depth direction of the beam 13 is formed to be longer than the dimension of the width of the beam 13 in the direction orthogonal to the acceleration detection axis direction.

The acceleration detection unit 2 shown in FIG. 2 is different from the acceleration detection unit 1 shown in FIG. 1 in that the upper surface of the protruding portion 5 of the fixed member 3 and the lower surface 21b of the first movable member are connected. The beam 13 is provided.
In the acceleration detection unit 2 of the second embodiment shown in FIG. 2, when acceleration is applied, stress (acceleration × mass) acts on the movable member 21 and the beam 13 bends. As the beam 13 bends, stress with the beam 13 as a fulcrum acts on the stress sensitive element 30, and the resonance frequency of the stress sensitive element 30 changes according to the stress. Further, the damage preventing action of the stress sensitive element 30 is as described in FIG.
When the acceleration sensor is configured using the acceleration detection unit of the present embodiment, the acceleration detection units 1 and 2 shown in FIG. 1 or 2 and the limiting member for limiting the displacement of the weight member 22 in the acceleration detection axis direction. A projection housing 23 and stoppers 40, 41, a housing that houses the acceleration detection units 1, 2 and hermetically seals, and an oscillation circuit that is electrically connected to the excitation electrode that constitutes the stress sensitive element 30. And so on. In this case, the gap between the protrusion 23 and the stoppers 40 and 41 needs to be set within the stress limit of the strain of the stress sensitive element 30.

By configuring the acceleration sensor in this way, the stress sensitive element 30 can be prevented from being damaged even when excessive acceleration is applied to the acceleration sensor.
As a material of the fixed member and the movable member excluding the stress sensitive elements of the acceleration detection units 1 and 2 and the first and second beam portions, adjacent bronze, brass, copper, and the like are applicable.
Although the present invention has been described by taking the acceleration detection unit provided with the neck portion having the hyperbolic concave 12 as an example, the present invention is not limited to this.
For example, it may be a neck portion provided with a through hole or a recess in the intermediate portion of the beam 11 in the depth (Y-axis direction) direction, or a recess 12 formed only on one surface of the beam 11. .
When the neck portion is a hyperbola shape or a through hole, the center line of the beam 11 and the center line of the neck portion coincide with each other, so that the balance of the center of gravity between the weight member 22 and the movable member 21 is set. It is easy to set a balance for balancing these with the fixing member 3.
However, it is easier to process the case where the recess 12 is provided only on one surface of the beam 11.

The schematic perspective view which showed the structure of the acceleration detection unit which concerns on the 1st Embodiment of this invention. The schematic perspective view which showed the structure of the acceleration detection unit which concerns on 2nd Embodiment. Sectional drawing which shows the structure of the conventional pressure sensor.

Explanation of symbols

  1, 2 Acceleration detection unit, 3 fixing member, 4 element support portion, 5 overhang portion, 10, 11, 13 beam, 12 dent, 21 movable member, 22 weight member, 21a movable member upper surface, 21b movable member lower surface, 23 protrusion Part, 30 Stress sensitive element, 31 Stress sensitive part, 32, 33 Fixed end, 40, 41 Stopper

Claims (8)

A fixed member that is not displaced by application of acceleration; a movable member that is displaced by application of acceleration; a first beam that supports the movable member on the fixed member; a stress sensitive part; and the stress sensitive part sandwiching the stress sensitive part. A stress sensitive element having two fixed ends connected to the portion, a weight member that is displaced in the acceleration detection direction, and a second beam that connects the weight member to the movable member,
The stress sensitive element has one fixed end supported by the fixed member and the other fixed end supported by the movable member.
The acceleration detection unit according to claim 1, wherein the first beam has a flexibility that can be bent so as to displace the movable member in an acceleration detection axis direction when an acceleration is applied to the movable member. The fixing member includes an element support portion that supports one fixed end of the stress-sensitive element, and is formed to project from the element support portion to a side parallel to a direction in which the stress-sensitive element extends, and the first member is formed at the distal end portion. An overhang portion provided with a beam,
The first beam is supported orthogonally to the second beam, and the upper surface of the movable member and the upper surface of the element support portion are parallel to each other and parallel to the acceleration detection axis direction. The acceleration detection unit according to claim 1. The fixing member includes an element support portion that supports one fixed end of the stress sensitive element, and is formed to project from the element support portion to a side parallel to an extension direction of the stress sensitive element. An overhang portion provided with a beam,
The first beam is supported by the movable member, and an upper surface of the movable member and an upper surface of the element support portion are parallel to each other and orthogonal to the acceleration detection axis direction. Item 2. The acceleration detection unit according to item 1.   4. The first beam according to claim 1, wherein the first beam has a shape that prevents displacement of the movable member in a depth direction orthogonal to the acceleration detection axis direction. 5. Acceleration detection unit.   The dimension in the depth direction of the first beam has a length equal to or greater than the dimension of the width of the first beam in the acceleration detection axis direction. Acceleration detection unit.   The acceleration detection unit according to any one of claims 1 to 5, wherein the second beam has a shape in which both sides in the depth direction are recessed in a hyperbola shape.   The stress sensitive element includes a stress sensitive part formed of a piezoelectric substrate having two fixed ends and two vibration beams connected between the fixed ends, an excitation electrode formed on a vibration region of the piezoelectric substrate, The acceleration detecting unit according to any one of claims 1 to 6, wherein the acceleration detecting unit is a double tuning fork type piezoelectric vibrating element.   An acceleration detection unit according to any one of claims 1 to 7, and a limiting member that limits displacement of the weight member in the acceleration detection axis direction. The acceleration detection unit is housed in an airtight manner. An acceleration sensor comprising: a housing for sealing; and an oscillation circuit electrically connected to an excitation electrode constituting the stress sensitive element.

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