JP2008014744A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor which can be made compact and which is satisfactory in sensitivity with a comparatively simple configuration. <P>SOLUTION: The configuration comprises a base section 51 made of a piezo-electric material; a tuning fork type piezoelectric vibrating reed 32, which is formed integrally with the base section and includes at least a pair of vibrating arms 34, 35 extending in parallel from the base section; and an vibrating means 11 for vibrating the piezoelectric vibrating reed. The piezoelectric vibrating reed 32 is arranged, such that the direction in which each vibrating arm extends, coincides with the direction G in which an acceleration to be detected acts on. When the acceleration is applied on, variations in the frequency of the piezoelectric vibrating reed are detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an acceleration sensor that measures acceleration acting on a moving body or the like, and more particularly, to an acceleration sensor that can be formed extremely compactly with a relatively simple configuration.

A conventional acceleration sensor is known which is formed of a mass portion having a predetermined mass and a spring element such as a beam portion for supporting the mass portion.
Generally, when acceleration acts on a mass portion, the mass portion is displaced by inertia. In this case, since the spring element supports the mass portion, the mass portion is displaced until the stress generated in the spring element balances with the inertial force of the mass portion. At this time, since the stress generated in the spring element corresponds to the acceleration, the acceleration is known by detecting this stress.
In such an acceleration sensor, it has been pointed out that it is necessary to use a special detection means such as a semiconductor sensor for stress detection, and a problem of stress-voltage conversion efficiency.

  Therefore, the parallel beam vibrating body is connected to and supported by the support base, the parallel beam vibrating body is connected to the mass member, means for exciting the parallel beam vibrating body, and the frequency of the parallel beam vibrating body is detected. An acceleration sensor having a configuration provided with means is also proposed (see Patent Document 1, FIG. 1 and FIG. 2).

According to the acceleration sensor having such a configuration, the beam of the parallel beam vibrating body is bent by the inertial force of the mass portion generated by the acceleration. As a result, the shape rigidity of the parallel beam vibrator changes, and the resonance frequency thereof changes. By detecting this change in frequency, acceleration is to be detected. For this reason, since the frequency of the parallel beam vibrating body is detected by a detecting means such as a frequency counter, no special means such as a conventional semiconductor sensor is required, and there is no problem of conversion efficiency.
JP-A-9-257830

However, the acceleration sensor disclosed in Patent Document 1 requires a mass portion having a relatively large shape and mass, and it is difficult to reduce the size accordingly.
In addition, there is a problem that a vibration mode with optimal stress sensitivity corresponding to acceleration is not selected.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an acceleration sensor that can be configured in a small size, has a relatively simple configuration, and good sensitivity.

  According to the first aspect of the present invention, there is provided a piezoelectric vibrating piece including a base portion formed of a piezoelectric material, and at least a pair of vibrating arms formed integrally with the base portion and extending in parallel from the base portion, An oscillation unit that oscillates the piezoelectric vibrating piece; and a detection unit that detects a change in the oscillation frequency of the oscillation unit when acceleration is applied. The direction in which each vibrating arm extends is affected by the acceleration to be detected. This is achieved by an acceleration sensor in which the piezoelectric vibrating reed is arranged so as to coincide with the direction in which it moves.

According to the configuration of the first aspect of the invention, the base portion is a portion that does not participate in bending vibration, forms the base end of each vibrating arm, and can be used for joining and supporting the piezoelectric vibrating piece. The vibrating arms need to have a paired configuration in order to perform stable flexural vibration, and at least a pair is formed. The oscillation means is for exciting a specific mode of vibration with respect to the piezoelectric vibrating piece.
When the piezoelectric vibrating reed is arranged so that the extending direction of each vibrating arm coincides with the direction in which the acceleration to be detected acts, when the acceleration acts, the dimension in the length direction of the vibrating arm is It changes very slightly. The acceleration can be detected by detecting the frequency change.
Therefore, since a relatively large mass portion is not required, the entire structure can be made compact, and a semiconductor sensor or the like for detecting stress is not required. Since the frequency change is detected, an acceleration sensor with extremely good sensitivity can be obtained.

According to a second invention, in the configuration of the first invention, the piezoelectric vibrating piece is a tuning fork type piezoelectric vibrating piece.
According to the configuration of the second invention, the use of the tuning-fork type piezoelectric vibrating piece as the piezoelectric vibrating piece makes it possible to detect the acceleration with high accuracy and high resolution because the piezoelectric vibrating piece having extremely high stress-frequency sensitivity is used. it can.
Moreover, the tuning-fork type piezoelectric vibrating piece having the configuration of the present invention can be manufactured by using substantially the same manufacturing process as the tuning-fork type piezoelectric vibrating piece used in a clock oscillator or the like. Therefore, it is very advantageous in terms of manufacturing cost.
Conventionally, there is an example in which a sensor for detecting acceleration and angular velocity is configured using a tuning fork type piezoelectric vibrating piece. However, the acceleration is calculated using the fact that the frequency of flexural vibration changes due to the shape change of the vibrating arm due to acceleration. There is nothing to detect.

According to a third invention, in the configuration of any one of the first and second inventions, the piezoelectric vibrating piece is housed in a package and hermetically sealed by a lid.
According to the configuration of the third invention, when detecting the acceleration, the piezoelectric vibrating piece is hermetically sealed, so that the bending resistance of the vibrating arm can be eliminated, and stable vibration can be obtained. Acceleration detection can be performed.

A fourth invention is characterized in that, in the configuration of any one of the first to third inventions, the outer shape of the tip of each vibrating arm of the piezoelectric vibrating piece is formed large.
According to the configuration of the fourth aspect of the invention, it is preferable that the tip of the vibrating arm that performs flexural vibration can be enlarged so that the mass can be increased more than other portions and is easily affected by acceleration.

A fifth invention is characterized in that, in the configuration of any one of the first to fourth inventions, a weight is arranged at the tip of each vibrating arm of the piezoelectric vibrating piece.
According to the configuration of the fifth aspect of the invention, it is preferable that the tip of the vibrating arm that performs flexural vibration is made heavier so that the mass can be increased than other portions and is easily affected by acceleration.

A sixth invention is characterized in that, in the configuration of any one of the first to fifth inventions, the thickness of the arm main body excluding the tip of each vibrating arm of the piezoelectric vibrating piece is formed thin.
According to the configuration of the sixth invention, sensitivity to acceleration can be further improved by reducing the rigidity of the vibrating arm.

FIG. 1 shows a first embodiment of the acceleration sensor of the present invention.
In the figure, the acceleration sensor 10 has a piezoelectric vibrating piece 32. The piezoelectric vibrating piece 32 includes, for example, a rectangular or square base 51 formed of a piezoelectric material, and a pair of vibrating arms 34 and 35 extending in the same direction with the base as a base end.

  Here, the piezoelectric vibrating piece 32 is formed using, for example, a quartz wafer of a size capable of separating a plurality of or many piezoelectric vibrating pieces 32 as a piezoelectric substrate of the piezoelectric material. In this case, when cutting from a single crystal of crystal, in the orthogonal coordinate system consisting of the X, Y, and Z axes, the X axis is an electrical axis, the Y axis is a mechanical axis, and the Z axis is an optical axis. A crystal Z plate obtained by rotating and cutting in the clockwise direction around the axis in the range of 0 to 5 degrees to a predetermined thickness is used.

By etching such a quartz wafer, the outer shape of the piezoelectric vibrating piece 32 of FIG. 1 is formed.
Electrodes are formed on, for example, the main surfaces, that is, the upper surface and the lower surface of the vibrating arms 34 and 35 of the piezoelectric vibrating piece 32, and these electrodes are routed around the extraction electrodes 52 and 53 of the base 51.
When a drive voltage is applied to the extraction electrodes 52 and 53, a horizontal bending motion is generated so that the tip portions of the vibrating arms 34 and 35 are moved closer to and away from each other. The frequency of the alternating current generated as a piezoelectric action due to the deformation of the vibrating arms 34 and 35 due to the bending motion is as follows, where the arm width is W and the arm length is l:
(Frequency) f = W / l ² (Formula 1).

Therefore, in the present embodiment, the direction in which the vibrating arms 34 and 35 extend is aligned with the direction in which the acceleration G for detecting the piezoelectric vibrating piece 32 acts, and for example, by the method described later, 51 is fixed.
The oscillation means 11 is connected to the extraction electrodes 52 and 53 of the base 51. The oscillating means 11 is, for example, an oscillator, and applies a driving voltage having a predetermined frequency to the piezoelectric vibrating piece 32 to bend and vibrate the piezoelectric vibrating piece 32 in a specific vibration mode.

The frequency due to this vibration is detected by the detecting means 12 connected to the oscillating means 11 via the oscillating means 11.
The detection means 12 may be, for example, a frequency counter that can detect the frequency due to the bending vibration of the piezoelectric vibrating piece 32.

Thus, according to the acceleration sensor 10 of FIG. 1, when the acceleration G acts on the piezoelectric vibrating piece 32, both the vibrating arms 34 and 35 are deformed very slightly by the stress. In this deformation, the length 1 of each vibrating arm 34, 35 expands and contracts with a very small dimension.
Due to this expansion and contraction, the frequency due to the flexural vibration of the piezoelectric vibrating piece 32 changes based on the above formula 1.
That is, in FIG. 1, when the acceleration acts in the G1 direction, the vibrating arms 34 and 35 extend slightly. For this reason, the frequency by bending vibration changes low.
When the acceleration acts in the G2 direction, the vibrating arms 34 and 35 are slightly shortened, and therefore the frequency due to the bending vibration changes to be high.

Therefore, the frequency counter serving as the detection unit 12 detects whether the direction in which the acceleration G acts is the G1 direction or the G2 direction when the piezoelectric vibrating piece 32 is driven by the oscillation unit 11. The detected frequency is detected as a change to the “low” direction or a change to the “high” direction.
Alternatively, instead of a simple frequency counter, for example, a detection unit including a calculation unit using a personal computer, a predetermined storage unit, and a display unit may be used as the detection unit.
Accordingly, for example, the degree of frequency change corresponding to the degree of action of the acceleration G is stored in advance as, for example, a table value, and the acceleration based on the frequency change is immediately stored according to the detected frequency change. May be displayed.

FIG. 2 is a schematic perspective view for explaining the piezoelectric vibrating piece 13 in detail.
In the case of the present embodiment, the piezoelectric vibrating piece 32 is particularly shaped and structured as illustrated in order to obtain a required performance by forming it in a small size.
That is, the piezoelectric vibrating piece 32 includes a fixing base 51 and a pair of vibrating arms 34 and 35 that extend in parallel to be divided into two forks obliquely upward in the drawing with the base 51 as a base end. A so-called tuning fork type piezoelectric vibrating piece, which is entirely shaped like a tuning fork, is used.
The piezoelectric vibrating piece 32 as a whole is extremely small. In FIG. 2, for example, the total length is about 1300 μm, the length of the vibrating arm is about 1040 μm, and the arm width is about 40 μm to 55 μm. It is a small piezoelectric vibrating piece.

FIG. 3 is an end view taken along line AA of FIG. As shown in FIGS. 2 and 3, long bottomed long grooves 56 and 57 extending in the length direction are formed in the respective vibrating arms 34 and 35 of the piezoelectric vibrating piece 32. As shown in FIG. 3, the long grooves 56 and 57 are formed on both the front and back surfaces of the vibrating arms 34 and 35.
Further, in FIG. 3, lead electrodes 52 and 53 are formed near both ends in the width direction of the end portion (lower end portion in FIG. 2) of the base portion 51 of the piezoelectric vibrating piece 32. The lead electrodes 52 and 53 are similarly formed on the back surface (not shown) of the base 51 of the piezoelectric vibrating piece 32.

  Each of these lead electrodes 52 and 53 is a portion connected to electrode parts 31 and 31 on the package side, which will be described later, by conductive adhesives 43 and 43. As shown in FIGS. 2 and 3, the lead electrodes 52 and 53 are integrally connected to the excitation electrodes 54 and 55 provided in the long grooves 56 and 57 of the vibrating arms 34 and 35, respectively. Yes. Further, as shown in FIG. 3, the excitation electrodes 54 and 55 are also formed on both side surfaces of the vibrating arms 34 and 35. For example, with respect to the vibrating arms 34, the excitation electrodes 54 in the long groove 56. And the excitation electrode 55 of the side part is made to have a different polarity. Further, with respect to the vibrating arm 35, the excitation electrode 55 in the long groove 57 and the excitation electrode 54 on the side surface thereof have different polarities.

5 and 6 show a second embodiment.
The second embodiment includes a configuration in which the piezoelectric vibrating piece 32 used in the acceleration sensor of the first embodiment is housed in, for example, a package as a housing container, and the following description is common to the first embodiment. The same reference numerals are given to the components, and redundant description is omitted, and differences will be mainly described. 6 is an end view taken along line BB of FIG.

The acceleration sensor 10-2 has a configuration in which the piezoelectric vibrating piece 32 is accommodated in a package 36.
The package 36 is formed, for example, by laminating a plurality of substrates formed by molding an aluminum oxide ceramic green sheet as an insulating material, and then sintering. Each of the plurality of substrates is formed with a predetermined hole on the inner side thereof, so that a predetermined internal space S2 is formed on the inner side when stacked. The internal space S2 is a housing space for housing the piezoelectric vibrating piece 32.

A piezoelectric vibrating piece 32 is mounted inside the package 36 and hermetically sealed with a lid 39. Here, the lid 39 is formed by selecting a material such as ceramic, metal, or glass. Preferably, the inside of the package 36 is hermetically sealed in a vacuum state.
When the lid 39 is made of metal, for example, there is an advantage that the strength is generally higher than that of other materials. As the material of the lid 39, a material having a thermal expansion coefficient approximate to that of the package 36 is suitable, and for example, Kovar can be used.
Moreover, in order to enable frequency adjustment after sealing the lid, the lid 39 is made of a light transmitting material such as glass, for example. For example, a plate body such as borosilicate glass can be used.

In the inner space S2 of the package 36, in the vicinity of the left end portion, the laminated substrate that is exposed to the inner space S2 and constitutes the inner bottom portion has, for example, electrode portions 31, 31 formed by nickel plating and gold plating on tungsten metallization. Is provided. The electrode portions 31 are connected to the outside to supply a driving voltage.
The electrode portions 31 and 31 are electrically connected to mounting terminals 45 and 46 formed on the bottom surface of the package 36 by a conductive pattern or the like.

In addition, conductive adhesives 43 and 43 are applied on the electrode portions 31 and 31, and the base 51 of the piezoelectric vibrating piece 32 is placed on the conductive adhesives 43 and 43, so that the conductive adhesive is provided. 43 and 43 are hardened. In addition, as the conductive adhesives 43 and 43, a synthetic resin agent as an adhesive component exhibiting a bonding force and containing conductive particles such as fine silver particles can be used. A system-based or polyimide-based conductive adhesive or the like can be used.
Further, the oscillation means 11 is connected to the mounting terminals 45 and 46, and the detection means 12 is connected to the oscillation means 11.

Here, when the base 51 shown in detail in FIG. 2 is to be joined to the inside of the package 36 as shown in FIG. 5, the area of the base 51 is increased so as not to hinder the overall miniaturization, and conductive bonding is performed. As the coating amount of the agent 43 is increased, the connection is more firmly established. Accordingly, the stress due to the acceleration G acts appropriately on the piezoelectric vibrating piece 32 without escaping.
In order to do this, it is preferable to use, for example, an epoxy or polyimide adhesive as the adhesive because it can be fixed to a rigid.

According to the configuration of the second embodiment, the first embodiment can be achieved by aligning the length directions of the vibrating arms 34 and 35 of the piezoelectric vibrating piece 32 in the direction of G in FIG. Similar to the embodiment, the acceleration can be detected appropriately.
Further, if an integrated circuit (not shown) is housed in the package 36 together with the piezoelectric vibrating piece 32 and the integrated circuit has the functions of the oscillation means 11 and the detection means 12, acceleration data can be obtained immediately from the mounting terminals 45 and 46. it can.

FIG. 6 is a schematic perspective view of Modification 1 of the piezoelectric vibrating piece 32.
In the piezoelectric vibrating piece 32-1 in FIG. 6, the same reference numerals as those of the piezoelectric vibrating piece 32 in FIG. 2 are the same in configuration, and redundant description will be omitted.
In the piezoelectric vibrating piece 32-1, weight portions 58 and 59 are formed at the tip portions of the vibrating arms 34 and 35, respectively.
Specifically, in the piezoelectric vibrating piece 32-1, the outer shape of the tip portion of each vibrating arm 34, 35 is formed to be a weight portion 58, 59.

  Thereby, it is preferable that the tip portions of the vibrating arms 34 and 35 that perform flexural vibrations are enlarged so that the mass can be increased more than other portions, and it is easy to be affected by acceleration. In addition, the weight portions 58 and 59 are not formed as mass portions independent of the piezoelectric vibrating piece 32-1, but are formed integrally with the tip of the vibrating arm, so that the number of parts does not increase and the shape is increased. Is not extremely large.

7 is a partial longitudinal sectional view of the weight portion 59 of the vibrating arm 35 (the weight portion 58 of the vibrating arm 34 has the same structure), particularly the piezoelectric vibrating piece of FIG. FIG.
As shown in the drawing, regarding the thickness of the arm main body excluding the tip portion 59-1 of the vibrating arm, it is usually processed by etching or the like so as to be particularly thin as shown in FIG. Shows the configuration.
Thereby, the sensitivity with respect to acceleration can be improved more by reducing the rigidity of the vibrating arm 35-1.

FIG. 8 shows a change in frequency detected when acceleration G acts in the G2 direction on the acceleration sensor 10 of FIG. 1 of the first embodiment.
As shown in FIG. 8, since the characteristic of the change in frequency deviation with respect to the acceleration G is a characteristic close to a linear function, a complicated peripheral circuit is not required, and accurate acceleration can be obtained with a simple circuit. It can be done.

The present invention is not limited to the above-described embodiment. Each configuration of each embodiment can be appropriately combined or omitted, and can be combined with other configurations not shown.
In addition, the present invention can be applied without a container as long as the piezoelectric vibrating piece is used, and in the above-described embodiment, a box that uses ceramic for a package that is a container for the piezoelectric vibrating piece. However, the present invention is not limited to this configuration, and the piezoelectric vibrating piece may be housed in a housing container equivalent to a package such as a metal cylindrical case.

1 is a schematic configuration diagram of an acceleration sensor according to a first embodiment of the present invention. FIG. 2 is a schematic perspective view of a piezoelectric vibrating piece used in the acceleration sensor of FIG. 1. FIG. 3 is a cut end view taken along line AA of the piezoelectric vibrating piece in FIG. 2. The schematic block diagram of the acceleration sensor which concerns on the 2nd Embodiment of this invention. FIG. 5 is a cut end view taken along line BB of the acceleration sensor of FIG. 4. The schematic perspective view of the modification 1 of the piezoelectric vibrating piece used for this invention. The fragmentary sectional view of the modification 2 of the piezoelectric vibrating piece used for this invention. The acceleration sensor of FIG. 1 WHEREIN: The graph which shows a frequency change when an acceleration acts.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Acceleration sensor, 30 ... Piezoelectric device, 36 ... Package, 32 ... Piezoelectric vibrating piece, 34, 35 ... Vibrating arm, 51 ... Base, 54, 55 ... Excitation Electrode, 56, 57 ... long groove

Claims (6)

A piezoelectric vibrating piece comprising a base formed of a piezoelectric material, and at least a pair of vibrating arms formed integrally with the base and extending in parallel from the base;
Oscillating means for oscillating the piezoelectric vibrating piece;
Detecting means for detecting a change in the oscillation frequency of the oscillation means when acceleration is applied;
An acceleration sensor characterized in that the piezoelectric vibrating reed is arranged so that the extending direction of each vibrating arm coincides with the direction in which the acceleration to be detected acts.   The acceleration sensor according to claim 1, wherein the piezoelectric vibrating piece is a tuning fork type piezoelectric vibrating piece.   The acceleration sensor according to claim 1, wherein the piezoelectric vibrating piece is housed in a package and hermetically sealed with a lid.   The acceleration sensor according to any one of claims 1 to 3, wherein an outer shape of a tip portion of each vibrating arm of the piezoelectric vibrating piece is formed large.   The acceleration sensor according to any one of claims 1 to 4, wherein a weight is disposed at a tip portion of each of the vibrating arms of the piezoelectric vibrating piece.   The acceleration sensor according to any one of claims 1 to 5, wherein a thickness of an arm main body excluding a tip of each vibrating arm of the piezoelectric vibrating piece is thin.

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