JP4867865B2 - Acceleration sensor element and acceleration sensor - Google Patents

Description

  The present invention relates to a variable capacitance type acceleration sensor, and more particularly to an acceleration sensor element that detects a change in capacitance by using a vibration mode of a tuning fork type piezoelectric vibrator and an acceleration sensor using the same.

  Conventionally, various variable capacitance type acceleration sensors have been proposed. For example, the mass portion which is a weight is supported so as to be swingable between the upper and lower cover plates, and the capacitance formed between the upper and lower surface conductive members of the mass portion and the electrodes of the cover plate facing each other. A capacitance-type acceleration sensor that detects acceleration and obtains acceleration is known (see, for example, Patent Document 1). The acceleration sensor detects acceleration by detecting a change in capacitance due to the difference in capacitance between the electrodes due to a change in the distance between the electrodes due to the inclination of the mass portion receiving the acceleration.

  Further, an angular velocity / acceleration sensor using a vibration mode of a tuning fork type crystal resonator is known (see, for example, Patent Documents 2 and 3). This angular velocity / acceleration sensor sandwiches a quartz crystal plate provided with two beams that bend a tuning-type tuning fork type vibration from both the top and bottom sides, and faces the displacement detection electrodes on both the top and bottom surfaces (and side surfaces) of each beam. A bridge circuit is configured by electrostatic capacitance formed between the electrodes of the quartz plate. When the beam simply vibrates in the vertical direction due to the Coriolis force due to the angular velocity / acceleration or when the free end performs a precession motion, the angular velocity / acceleration can be detected from the change in capacitance caused thereby.

  Similarly, as an angular velocity sensor using a tuning fork type vibrator, a single crystal layer tuning fork type vibrator is integrated with a single crystal substrate, and capacitance generated at the opposing portion of the tooth profile of the tip of each transducer and the tooth profile of the single crystal substrate. And a capacitor having a capacitance generated between the tip of each vibrator and a substrate are configured to form a bridge circuit (see, for example, Patent Document 4). Also in this case, when the vibrator is displaced by receiving the Coriolis force, the change in the capacitance caused thereby is detected to detect the angular velocity.

JP-A-8-166404 JP-A-7-128355 JP 7-128356 A JP-A-8-304441

  However, in the conventional capacitive acceleration sensor described above, the beam of the mass portion that is supported so as to be swingable is sandwiched between two supporting plates interposed between the upper and lower cover plates, so that The number of points is high, the price is high, and the assembly is troublesome. Further, the distance between the conductive member and the electrode is likely to vary, and it is difficult to always assemble stably to a constant capacitance. Therefore, there is a problem that it is difficult to stably obtain a highly accurate acceleration sensor.

  In addition, conventional angular velocity / acceleration sensors using tuning fork vibrators both vibrate the vibrator vertically by Coriolis force due to acceleration or angular velocity, and detect changes in capacitance due to changes in the distance between electrodes. In addition, a separate quartz plate with electrodes is required. Therefore, the number of parts is large, the price is high, the assembly is troublesome, and the size is increased in the height direction. Therefore, it is difficult to reduce the size, and it is difficult to always obtain a constant inter-electrode distance stably.

  Therefore, the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to stably obtain high detection accuracy, to reduce the number of parts, to reduce the cost, and to assemble. It is an object of the present invention to provide a variable-capacitance type acceleration sensor element that can be simplified and miniaturized, and a high-accuracy acceleration sensor using the same.

  According to the present invention, in order to achieve the above object, a base portion made of a piezoelectric material, a pair of vibration arms extending in parallel from the base portion, a weight portion positioned ahead of the vibration arm, and the weight And three detection arms extending in parallel with and on both sides of the vibrating arm from the portion, each vibrating arm having a first excitation electrode formed on the upper and lower main surfaces thereof and a first excitation electrode formed on both side surfaces thereof. Each of the detection arms has a detection electrode formed on a side surface opposite to the side surface of the vibration arm adjacent to the two excitation electrodes, and the second excitation electrode of each vibration arm and the detection arm adjacent thereto are detected. The second excitation electrode and the detection electrode are wired so that the four capacitors formed by the electrodes form a bridge circuit, and the weight portion and the detection arm are integrally displaced by acceleration, so that the second excitation of each vibration arm Electrode and next to it Varying the gap between the detection electrode of the detection arm, the acceleration sensor element so as to vary the capacitance of each capacitor is provided.

  When acceleration is applied with an AC voltage applied and the vibrating arm is excited in the tuning fork bending vibration mode, the weight and the detection arm bend the connecting portion in accordance with the magnitude and direction of the acceleration and are displaced together. Since the gap between the capacitors fluctuates and the capacitance changes in proportion, the magnitude and direction of acceleration can be detected by synchronously detecting the output of the bridge circuit. By using the second excitation electrode on the side surface of the vibrating arm used as an oscillator for detecting the equilibrium state of the bridge circuit in this manner as one terminal of each capacitor, the acceleration sensor element with a simple configuration and wiring can be used. High detection accuracy can be obtained.

  Therefore, according to another aspect of the present invention, an acceleration sensor comprising the acceleration sensor element of the present invention, and a circuit for synchronously detecting a drive voltage for exciting a vibration arm of the acceleration sensor element and an output of the bridge circuit thereof. Is provided. Such a circuit configuration can be used as it is for a detection circuit of an angular velocity sensor so that it can be developed and manufactured at low cost.

  In one embodiment, two detection arms extending on both sides of the vibrating arm are coupled to the base by a coupling portion extending from the base, and the coupling portion is bent to be weighted when subjected to acceleration. In addition, since the detection arm is integrally displaced and the size of each gap between the vibration arm and the detection arm changes in accordance with the magnitude of acceleration, stable and high detection accuracy can be obtained.

  In another embodiment, the base and the vibrating arm, the weight, and the detection arm can be integrally formed of a piezoelectric material. As a result, the number of parts can be reduced, the assembly can be simplified, the cost can be reduced, and the size can be reduced.

  In particular, when the piezoelectric material is quartz, an acceleration sensor element can be manufactured with high dimensional accuracy by using conventional photolithography and etching techniques, and there is little variation in sensitivity. It can be realized at a low price. In addition, since the tuning fork type crystal resonator has a very stable oscillation frequency, it can be used as an oscillator for detecting the equilibrium state of the bridge circuit, thereby enabling more accurate and highly accurate acceleration detection.

  In still another embodiment, the detection arm is configured such that the thickness of the detection arm is smaller than the thickness of the vibration arm and the total thickness of the detection arm is within the thickness range of the vibration arm. However, even if it swings in a direction perpendicular to the plane, the capacitance of each capacitor formed between the vibration arm and the detection arm is kept constant, so that stable detection accuracy can be ensured.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1A and 1B show an embodiment of an acceleration sensor element according to the present invention. The acceleration sensor element 1 includes a base 2 and a pair of vibration arms 3 and 4 extending in parallel from the base. Further, the acceleration sensor element 1 has three detection arms 5 to 7 extending in parallel with both sides of the vibration arm and between them.

  The two detection arms 5 and 6 arranged on both sides of the vibrating arms 3 and 4 have narrow ends of the base 2 side extending from the base to the narrow connecting portions 8 and 9 extending in parallel with the vibrating arm. Are connected. The opposite ends of the detection arms 5 and 6 are coupled to a weight portion 10 disposed at the tip of the vibration arm. The remaining one detection arm 7 extends from the weight portion 10 to the base portion 2 between the vibrating arms 3 and 4. The four gaps defined between each of the detection arms 5 to 7 and the adjacent vibration arms 3 and 4 are constant at least in the length range in which the detection arm and the vibration arm overlap and have the same width. It is provided to become. The detection arms 5 to 7 and the weight portion 10 are integrally formed by being firmly coupled to each other at least in a plane.

  First and second main electrodes 11a, 11b, 12a and 12b extending in the longitudinal direction are respectively formed on the upper and lower main surfaces of the vibrating arms 3 and 4, and second longitudinally extending second sides are also formed on both side surfaces thereof. Excitation electrodes 13a, 13b, 14a, and 14b are respectively formed. The first excitation electrodes 11a and 11b (12a and 12b) of one vibration arm 3 (4) are respectively connected to the second excitation electrodes 14a and 14b (13a, 13a) of the other vibration arm 4 (3) through the wiring on the surface of the base 2. 13b).

  The detection arms 5 and 6 arranged on both sides of the vibration arms 3 and 4 are formed with detection electrodes 15 and 16 on one side surface facing the side surfaces of the adjacent vibration arms. The detection electrodes 15 and 16 are connected to each other by wiring on the upper surface of the weight portion 10. The center detection arm 7 has detection electrodes 17a and 17b formed on the side surfaces thereof facing the adjacent side surfaces of the vibration arms 3 and 4, respectively. The detection electrodes 17 a and 17 b are connected to each other on the lower surface of the detection arm 7.

  Four connection electrodes 18 to 21 are formed on the base portion 2 along the end sides thereof. The two connection electrodes 19 and 20 on the center side are connected to the corresponding first excitation electrode and second excitation electrode through wirings drawn from the respective vibration arms. By wiring the excitation electrodes in this way, when a predetermined AC voltage is applied to the connection electrodes 19 and 20, the vibration arms approach or separate from each other as indicated by solid and broken arrows in FIG. Vibrate in the tuning fork bending vibration mode.

  The detection electrodes 15 and 16 are connected to each other by wiring on the upper surface of the weight portion 10 and connected to one corresponding connection electrode 18 by wiring drawn to the base portion 2 through the upper surface of one connecting portion 8. The detection electrodes 17a and 17b are connected to the other connection electrode 19 corresponding to the weight portion 10, one of the detection arms 6 on the right side in the figure and the wiring drawn to the base portion 2 through the lower surface of the connecting portion 9 coupled thereto. It is connected.

  The acceleration sensor element 1 of the present embodiment can be processed into the desired outer shape described above, for example, by etching a crystal wafer, similarly to the conventional crystal resonator. Each of the electrodes and wirings can be similarly patterned using a conventional photoetching technique. Moreover, in another Example, it can form using various well-known piezoelectric materials other than quartz.

  Since the connecting portions 8 and 9 are formed narrower than the detection arm as described above, the connecting portions 8 and 9 can be bent in the plane direction by an external force, that is, in the width direction with respect to the base portion 2. The acceleration sensor element 1 is supported and fixed in a cantilever manner with a conductive adhesive or the like at the base 2 in the same manner as a conventional crystal resonator. When a force in the plane direction is applied to the acceleration sensor element 1, the detection arms 5 to 7 and the weight portion 10 are rigidly and integrally formed as described above, so that the connecting portions 8 and 9 are bent. Displaces integrally.

  2A and 2B show deformation states that occur when accelerations in different directions are applied to the acceleration sensor element 1 in the width direction. When the acceleration a acts rightward in the width direction of the acceleration sensor element 1, as shown in FIG. 2 (A), the detection arms 5 to 7 and the weight portion 10 bend the connecting portions 8 and 9 and integrally move to the left side. Displace. As a result, the gaps between the left side surface of the vibration arms 3 and 4 and the right side surface of the detection arms 5 and 7 are expanded, and the right side surface of the vibration arms 3 and 4 and the left side surface of the detection arms 6 and 7 are correspondingly expanded. The gaps become narrower. Conversely, when the acceleration a acts to the left in the width direction of the acceleration sensor element 1, as shown in FIG. 2B, the detection arms 5 to 7 and the weight portion 10 bend the connecting portions 8 and 9 to the right side. Displaces integrally. As a result, the gaps between the right side surface of the vibrating arms 3 and 4 and the left side surface of the detection arms 5 and 7 are expanded, and the left side surface of the vibrating arms 3 and 4 and the right side surface of the detection arms 6 and 7 are The gaps become narrower.

  In the acceleration sensor element 1 according to the present embodiment, a capacitor C1 is formed by one second excitation electrode 13a of the vibration arm 3 and the detection electrode 15 of the detection arm 5 that is adjacent to the second excitation electrode 13a. The capacitance of the capacitor C1 is determined by the gap between the second excitation electrode 13a and the detection electrode 15 and the electrode area where they overlap. Furthermore, a capacitor C2 is formed by the other second excitation electrode 13b of the vibration arm 3 and the detection electrode 17a of the detection arm 7 which is adjacent to the second excitation electrode 13b. The capacitance of the capacitor C2 is the gap between these electrodes and the overlapping electrode area. Determined by. Similarly, a capacitor C3 is formed by one of the second excitation electrodes 14a of the vibration arm 4 and the detection electrode 17b of the detection arm 7 facing adjacent thereto, and the capacitance of the capacitor C3 overlaps with the gap between the electrodes. It is determined by the electrode area. A capacitor C4 is formed by the other second excitation electrode 14b of the vibration arm 4 and the detection electrode 16 of the detection arm 6 that is adjacent to the second excitation electrode 14b. The capacitance of the capacitor C4 depends on the gap between the electrodes and the overlapping electrode area. It is determined.

  According to the present invention, the capacitances of the capacitors C1 to C4 are set to be equal in the state of FIG. 1A where no acceleration acts on the acceleration sensor element 1. However, in each of the capacitors C1 to C4, when the acceleration acts on the acceleration sensor element 1 as described above, the gap between the electrodes constituting them becomes wide or narrow depending on the direction, and the capacitance changes. Therefore, it is a variable capacitor.

FIG. 3 shows an equivalent circuit of the acceleration sensor element 1. In the figure, reference numeral 22 denotes a tuning fork type crystal resonator constituted by vibrating arms 3 and 4 extending from the base 2. Capacitors C1 to C4 constitute a bridge circuit connected to a crystal resonator 22 excited by an AC voltage V0 applied to input terminals D1 and D2, as shown in FIG. An output voltage V _S1S2 corresponding to the capacitance values of the capacitors C1 to C4 is generated between the output terminals S1 and S2.

When no acceleration acts on the acceleration sensor element 1, the bridge circuit is in an equilibrium state where the capacitances of the capacitors C1 to C4 are equal. Therefore, the output voltage is V _S1S2 = 0. When acceleration acts on the acceleration sensor element 1 and the gaps between the detection arms 5 to 7 adjacent to the vibration arms 3 and 4 fluctuate, the capacitances of the capacitors C1 to C4 change proportionally. The equilibrium state is lost, and the corresponding voltage V _S1S2 is output.

When the acceleration G acts to the left in the width direction of the acceleration sensor element 1 as shown in FIG. 2A, the capacitance of each capacitor is C1 <C4 and C3 <C2. As a result, a positive voltage V _S1S2 is output between the output terminals S1 and S2. Conversely, when the acceleration G acts to the right in the width direction of the acceleration sensor element 1 as shown in FIG. 2B, the capacitance of each capacitor becomes C4 <C1 and C2 <C3. As a result, a negative voltage V _S1S2 is output between the output terminals S1 and S2.

FIG. 4 shows a result of measuring the output voltage V _S1S2 of the bridge circuit related to the displacement amount of each of the detection arms 5 to 7 with respect to a constant input voltage by making the acceleration sensor element 1 of FIG. In the figure, the horizontal axis represents the amount of displacement of the arm in proportion to the position of the arm as a reference, that is, 0 when no acceleration acts, and ± 1 when the gap between the arms disappears. Yes. As shown in the figure, it can be understood that sufficiently practical linearity can be obtained at least in the range where the displacement amount is about ± 30%.

  FIG. 5 shows a modification of the acceleration sensor element 1 of FIG. In the figure, components similar to those in FIG. 1 are denoted by the same reference numerals. In the acceleration sensor element 1 of this modification, linear grooves 23 and 24 extending in the longitudinal direction are respectively provided in the upper and lower main surfaces of the vibration arms 3 and 4, and the first excitation is provided on the inner surface of each groove. Electrodes 11a, 11b, 12a, and 12b are formed. As a result, a lower CI value can be secured for the tuning fork type crystal resonator and the stability is further improved, so that the detection accuracy of the acceleration sensor is increased.

  Further, the detection arms 5 to 7 are different from the embodiment of FIG. In the present embodiment, steps 5a to 7a are provided in the vicinity of the boundary between each detection arm and the weight portion 10 in order to reduce the thickness uniformly over substantially the entire length. Steps 5 b and 6 b are provided between the connecting portions 8 and 9. For example, when the grooves 23 and 24 of the vibration arms 3 and 4 are processed by half etching of the quartz wafer, the detection arms 5 to 7 of FIG. It can be easily realized.

  In the acceleration sensor element 1, when an acceleration component in the vertical direction acts on the plane, the detection arms 5 to 7 and / or the vibration arms 3 and 4 may be displaced not only in the plane direction but also in the vertical direction. Even in that case, in this embodiment, since the total thickness of each detection arm is maintained within the thickness range of the vibration arm, the electrode area where the adjacent electrodes overlap is not changed, so that the vertical The influence of the direction acceleration component on each of the capacitors C1 to C4 can be eliminated. Therefore, there are advantages that the output of the acceleration sensor element 1 is more stable and the detection accuracy is improved.

  In another embodiment, the thickness of the vibrating arm can be smaller than the thickness of the detection arm. In this case as well, the total thickness of the vibrating arm is maintained within the thickness range of the detection arm. Therefore, even if the detection arm swings in the direction perpendicular to the plane, the electrode area where the adjacent electrodes overlap does not change, so that the capacitance of each capacitor is kept constant and stable detection accuracy is achieved. Can be secured.

  FIG. 6 illustrates a circuit configuration of the acceleration sensor 30 using the acceleration sensor element 1 of the present embodiment. In the figure, a crystal oscillation circuit 31 for driving a crystal resonator 22 is connected to input terminals D1 and D2 of the acceleration sensor element 1, and output terminals S1 and S2 are connected to q-V converters 32a and 32b. And is connected to a differential amplifier 33. The output of the differential amplifier 33 is connected to the synchronous detection circuit 34 together with the output of the crystal oscillation circuit 31 to be synchronously detected. The output of the synchronous detection circuit 34 is smoothed by the low-pass filter 35 and output as a voltage signal representing the magnitude and direction of acceleration.

  As mentioned above, although the detailed Example of this invention was described in detail, this invention can add and implement various modifications and changes to the said Example in the technical range. For example, various known tuning-fork type piezoelectric vibrator structures other than those shown in FIGS. 1 and 5 can be employed for the vibrating arm. In another embodiment, as long as the gap between the vibration arm and the detection arm is configured to change in accordance with the magnitude of acceleration, the detection arm and the weight are separated from the base to be separate parts. Can do. Further, the circuit configuration of FIG. 6 is merely an example, and it is obvious to those skilled in the art that various other circuit configurations can be considered as an acceleration sensor using the acceleration sensor element of the present invention.

(A) is a plan view showing an embodiment of the acceleration sensor element according to the present invention, (B) is an enlarged cross-sectional view taken along the line II. (A) (B) is a figure which shows a deformation | transformation state when the acceleration of a different direction acts on the acceleration sensor element of FIG. The equivalent circuit diagram of the acceleration sensor element of FIG. The diagram which shows the relationship between the deformation amount of a sensor arm, and a sensor output. (A) is a plan view showing a modification of the acceleration sensor element of FIG. 1, and (B) is an enlarged sectional view taken along the line VV. The circuit diagram of the acceleration sensor using the acceleration sensor element of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Acceleration sensor element, 2 ... Base part, 3, 4 ... Vibration arm, 5-7 ... Detection arm, 5a-7a, 5b, 6b ... Step, 8, 9 ... Connection part, 10 ... Weight part, 11a, 11b, 12a, 12b ... 1st excitation electrode, 13a, 13b, 14a, 14b ... 2nd excitation electrode, 15, 16, 17a, 17b ... detection electrode, 18-21 ... connection electrode, 22 ... crystal resonator, 23, 24 ... Groove, 30 ... acceleration sensor, 31 ... crystal oscillation circuit, 32a, 32b ... q-V converter, 33 ... differential amplifier, 34 ... synchronous detection circuit, 35 ... low-pass filter.

Claims (6)

A base portion formed of a piezoelectric material, a pair of vibration arms extending in parallel from the base portion, a weight portion positioned at the tip of the vibration arm, and both sides of the vibration arm from the weight portion and in parallel between them. Three extending detection arms,
Each of the vibrating arms has a first excitation electrode formed on the upper and lower main surfaces and a second excitation electrode formed on both side surfaces,
Each detection arm has a detection electrode formed on a side surface facing the side surface of the vibration arm adjacent to the detection arm;
The second excitation electrode and the detection electrode are wired so that four capacitors formed by the second excitation electrode of each vibration arm and the detection electrode of the detection arm adjacent thereto form a bridge circuit. ,
The weight part and the detection arm are integrally displaced by acceleration to change a gap between the second excitation electrode of each vibration arm and the detection electrode of the detection arm adjacent to the second excitation electrode. An acceleration sensor element characterized by changing the angle.   The two detection arms extending on both sides of the vibration arm are coupled to the base by a coupling portion extending from the base, and the coupling portion is bent, whereby the weight portion and the detection arm are accelerated. The acceleration sensor element according to claim 1, wherein the acceleration sensor element is integrally displaced.   The acceleration sensor element according to claim 1 or 2, wherein the base, the vibration arm, the weight, and the detection arm are integrally formed of the piezoelectric material.   4. The acceleration sensor element according to claim 1, wherein the piezoelectric material is quartz.   The thickness of the detection arm is made thinner than the thickness of the vibration arm, and the total thickness of the detection arm is located within the thickness range of the vibration arm. 5. The acceleration sensor element according to any one of 4 above.   An acceleration sensor element according to any one of claims 1 to 5, and a circuit for synchronously detecting a drive voltage for exciting the vibration arm of the acceleration sensor element and an output of the bridge circuit of the acceleration sensor element. An acceleration sensor characterized by

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