JPH0419568A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To reduce the size of the sensor and to enable accurate detection with excellent sensitivity in three right-angled directions by enabling a detecting element to detect strain and displacement when receiving acceleration in the respective direction of a diaphragm provided with a weight at the center part. CONSTITUTION:The weight 3 is provided at the center part of the diaphragm 2 which is fixed horizontally to a rigid base plate 5 at the peripheral part. A piezoelectric element 6 centering on the position of the weight 3 is provided on the surface of the diaphragm 2 on the side of a common electrode 8 across a conductive adhesive layer 10 and plural couples of divided electrodes 9 of point symmetry on the opposite side of a substrate 7 are connected to a printed wiring board 11 through leads 13. An inertial force operates on the weight through the operation of acceleration in the respective directions and the diaphragm 2 deforms according to the directions. The acceleration in each direction is detected according to the electrostatic capacity formed between the electrodes 8 and 9 corresponding to the deformation.

Description

[Detailed description of the invention] [Industrial application field]

The present invention particularly relates to an acceleration sensor that accurately detects earthquake acceleration in both horizontal and vertical directions with good sensitivity.

[Conventional technology]

Conventionally, there are three main methods for measuring acceleration electrically: electrodynamic type, piezoelectric type, and servo type. The electrodynamic type is a method that extracts a voltage according to acceleration by the movement of a coil integrated with a weight within a magnetic field. The piezoelectric type converts the inertial force exerted by a weight into voltage using the piezoelectric effect. The servo type is a method in which force and torque are applied in the opposite direction to balance the displacement of a pendulum-shaped weight due to acceleration, and the current that generates this force and torque is determined.

[Problem to be solved by the invention]

The electrodynamic type and piezoelectric type each have good sensitivity to acceleration in the horizontal direction, but poor sensitivity to acceleration in the vertical direction. Therefore, it is unsuitable for measuring accelerations associated with initial vertical and lateral vibrations, such as in earthquakes. The servo type method is superior in terms of accuracy and stability, but in order to measure in three directions perpendicular to each other, a total of three sets of sensors for each direction and a vector calculation circuit for each sensor output are required, making the device The disadvantage is that the size and cost increase. The object of this invention is to solve the problems of the conventional technology and to solve the problem in three directions perpendicular to each other, especially horizontally. It is an object of the present invention to provide a small-sized acceleration sensor capable of accurately detecting each acceleration in each vertical direction with good sensitivity.

[Means to solve the problem]

In order to solve this problem, the acceleration sensor according to the first invention includes: a diaphragm whose periphery is fixed to a rigid base member and installed horizontally; a weight provided at the center of the diaphragm; It is provided on the surface of the diaphragm with the position of the weight as the center, and consists of a common electrode and a plurality of pairs of segment electrodes that are arranged point-symmetrically with respect to the position of the weight, facing the common electrode and sandwiching a piezoelectric material between them. a piezoelectric strain sensing element; and based on the voltage induced between the common electrode and each of the partial electrodes of the strain sensing element, Detect acceleration. The acceleration sensor according to the second invention includes: a diaphragm whose peripheral portion is fixed to a rigid base member and which is installed horizontally; a weight provided at the center of the diaphragm; The opposite side of the plum,
a capacitance type displacement detection element comprising a common electrode fixed to the surface of the base member facing the base member, and a plurality of pairs of segment electrodes arranged point-symmetrically with respect to the position of the weight; , each acceleration in a direction along the surface of the diaphragm and a direction perpendicular to the surface of the diaphragm is detected based on the capacitance formed between the common electrode and each partial electrode of the displacement detection element.

[Effect]

1st. In the acceleration sensors according to each of the second inventions, when receiving acceleration in the direction along the diaphragm surface,
Due to the inertial force of the weight due to the acceleration, a bending moment about an axis included in the surface of the diaphragm and perpendicular to the acceleration direction acts on the diaphragm. This bending moment causes the maximum opposite strain and displacement to occur on the axis passing through the center of the diaphragm surface in the direction of acceleration, at points symmetrical about the center. Further, when the diaphragm is subjected to acceleration in a direction perpendicular to the diaphragm surface, the inertial force of the weight caused by the acceleration causes the diaphragm to curve and deform so that its center becomes convex in the direction opposite to the acceleration. This curved deformation causes distortion and displacement of the same magnitude in the same direction at locations on the same circumference around the center of the diaphragm surface. The distortions and displacements of the diaphragm at each of the above locations when subjected to acceleration in each of the above directions are as follows.
In each of the second inventions, the inertial force of the weight due to acceleration and the acceleration are determined based on the voltage and capacitance that are detected by the piezoelectric type and capacitance type strain and displacement detection elements and are the respective outputs. It will be done.

【Example】

An embodiment of the acceleration sensor according to the first invention (hereinafter referred to as the first embodiment) will be described below with reference to the drawings. This first embodiment is a so-called piezoelectric acceleration sensor that uses a piezoelectric element to detect distortions at various locations on a diaphragm caused by inertial force based on acceleration. This is an acceleration sensor for earthquakes that is configured to output a warning signal when the maximum value of . FIG. 1 is a side view of the first embodiment. In the figure, a piezoelectric acceleration sensor 1 mainly includes a diaphragm 2. A weight protruding from the center 3. and a main member on which the flange 4 on the lower surface of the periphery is integrally formed, a piezoelectric element 6 fixed to the center of the upper surface of the diaphragm 2, a rigid base plate 5 to which the lower end surface of the flange 4 is fixed, and a piezoelectric It is composed of a printed wiring board 11 incorporating a signal processing circuit that processes the output signal of the element 6 and outputs an alarm signal. Note that the diaphragm 2 and the base plate 5 are installed horizontally. As an outside member, it takes the form of a flexible wiring board,
Piezoelectric element6. Glue 13 between printed wiring boards 11 , airtight terminals 14 inserted into base board 5 , and printed wiring boards 1
1, a cover 16 for shielding and protecting the main components, and a base plate 5 for sealing the main components.
．． There is an O-ring 17 inserted between the covers 16. As shown in FIG. 2, the piezoelectric element 6 consists of a substrate 7 made of a piezoelectric material, a common electrode 8 sandwiching this from both sides, and four pairs of dividing electrodes 9. In addition, FIG. 2(a) is a side view of the
FIG. 5B is a surface view of the common electrode side, and FIG. 2C is a surface view of the split electrode side. The substrate 7 is a disc-shaped member with a hole in the center, and the common electrode 8 is a donut-shaped member. Each of the dividing electrodes is a fan-shaped plate member, and is equally distributed on the same circumference with respect to the center of the substrate 7. Each village of four sets of dividing electrodes 9A, 9a,
These are 9B, 9b, 9C, 9c, 9D, and 9d. As shown in FIG. 1, the piezoelectric element 6 fixes the common electrode side to the surface of the diaphragm 2 via a conductive adhesive layer IO. Each partial electrode of the piezoelectric element 6 is drawn out via a lead 13 and connected to a printed wiring board 11. The operation of the first embodiment will be explained with reference to FIG. 3, FIG. 4, and FIG. Figure 3 shows the operation of the first embodiment when vertical acceleration is applied; Figure (a) is a side view of the main part, Figure (b) is a plan view of the main part, and Figure 4. is the first
Regarding the operation when acceleration in the horizontal direction is applied in the embodiment, FIG. In Fig. 3(a), when acceleration acts vertically in the direction of the arrow, an inertial force in the opposite direction acts on the weight 3, so the diaphragm 2 is deformed in a curved manner so as to convex upward as shown by the broken line. do. Due to this curved deformation, Fig. 3(b)
A voltage of the same direction and magnitude is induced between each of the partial electrodes 9A, 9a, 9B, . . . and a common electrode (not shown). In Fig. 4(a), when acceleration acts horizontally in the direction of the arrow, a leftward inertia force acts on the weight 3, so the diaphragm 2 has a convex downward convex on the left side and a convex downward on the right side as shown by the broken line. Curved and deformed so that it becomes convex upward. Due to this curved deformation, voltages of opposite signs and of the same magnitude are induced between each of the pair of partial electrodes 9G, 9c in FIG. 4(b) and a common electrode (not shown). Also,
Each of the other pairs of electrodes 9A, 9a, 9B, 9b, 9
As for D and 9d, voltages of the same magnitude and opposite signs are induced. However, since the magnitude of the induced voltage corresponds to the distortion based on the bending deformation, the magnitude of each partial electrode 9C, 9c is the maximum, and each partial electrode 9B, 9b, 9D, 9d
is medium, and each electrode 9A, 9a is at its minimum. Therefore, in the case of acceleration in the vertical direction as shown in FIG. 3, the voltage value corresponding to the acceleration can be obtained by calculating the sum of all the induced voltages related to the respective electrodes. In addition, in the case of acceleration in the horizontal direction as shown in Figure 4, if we calculate the difference in induced voltage for each of the pair of electrodes, we can obtain the multiplied value corresponding to the acceleration in the direction connecting the electrodes. voltage value can be obtained. Furthermore, the direction connecting the pair of electrodes, which is the largest among the difference values, corresponds to the main direction of the horizontal acceleration. A signal processing circuit for outputting an alarm signal based on the output voltage of each segment electrode will be described with reference to the circuit diagram of FIG. 5. In FIG. 5, the portion below the horizontal two-dot chain line is the signal processing circuit 12, and the portion above is the circuit for each electrode of the piezoelectric element 6. 20 is a conversion circuit, 18
is a subtraction circuit that calculates the voltage difference between a pair of electrodes, 1
Reference numeral 9 denotes an adder circuit that calculates the sum of the voltages of the respective electrodes, and 21 a filter circuit, which has a bandpass filter function that allows only frequency components of 10 Hz or less, which are characteristic of seismic waves, to pass through. 22 and 23 are comparison circuits, and subtraction circuits 18. Addition circuit I9
Each output is compared with the setting value of each corresponding setting circuit 24, 25. Here, when each output of the subtraction circuit 18 and the addition circuit 19 is larger than the corresponding set value,
It is assumed that each comparison circuit 22, 23 outputs an H signal. 26 is an OR circuit which outputs an H signal as an alarm signal when either of the comparison circuits 22 and 23 outputs an H signal. An embodiment of the acceleration sensor according to the second invention (hereinafter referred to as the second embodiment) will be described below with reference to the drawings. This second embodiment is a so-called capacitive seismic acceleration sensor that uses capacitor-type detection elements to detect displacements at various locations on a diaphragm caused by inertial force based on acceleration. FIG. 6 is a side view of the second embodiment. In the figure, the capacitive acceleration sensor 31 mainly consists of a diaphragm 3.
2. A weight protruding from the center 33. and a main member integrally formed with the flange 34 on the lower surface of the periphery, and a common electrode 38 fixed to the center portion of the lower surface of the diaphragm 32;
It is composed of a rigid base plate 35. In addition, the base plate 35. A substrate 37 coated with an insulating film 41 is inserted between the lower end surfaces of the flanges 34 . As will be described in detail later, on the surface of this substrate 37, four sets of each pair of electrodes are arranged on the circumference around the weight 33, facing the common electrode 38 with an air layer interposed therebetween. Each capacitor is configured. Note that the diaphragm 32 and the base plate 35 are installed horizontally. FIG. 7 is a plan view of the dividing electrode substrate. In the figure, on the surface of the substrate 37, fan-shaped electrodes are arranged equally on the same circumference with respect to the center of the substrate 37 (the axis position of the weight 33 in FIG. 6). Each village 39A of 4 sets of dividing electrodes
, 39a , 39B, 39b , 39C, 39c, 39
D, 39d. Each of these electrodes has connection pads 40A, 40a, 40B, 40b, 40, respectively.
C, 40c, and 400.40d are correspondingly integrated including lead portions, and are arranged four on each side. In addition,
An insulating film 41 made of low-melting glass is coated on an annular region indicated by a dotted line, excluding each of the electrodes and the connection pads. Note that the lower end surface of the flange 34 is attached onto the insulating film 41. In FIG. 6, a terminal 44 inserted into a base 45 made of an insulating material, a connection pad 38A on the upper surface of the diaphragm 32, and each of the connection pads on the substrate 37 are connected by lead wires 43. Note that, in order to ground the common electrode 38, the connection pad 38A is electrically connected to the common electrode 38 via a diaphragm 32 doped with an impurity element to increase conductivity. The cover 46 covers the diaphragm 32
It is hermetically fixed to the base 45 to protect the main parts. By the way, diaphragm 328 weight 33. The flange 34 and the flange 34 are integrally formed by plasma etching using silicon, and the weight 33 of the diaphragm 32 is
A common electrode 38 is formed on the opposite side by sputtering. In this way, the main parts of the acceleration sensor are:
Since it is manufactured using a semiconductor manufacturing process, it can be made ultra-small and low-cost, and is suitable for mass production. The operation of the second embodiment is basically the same as that of the first embodiment. The displacement at each location of the diaphragm caused by the inertial force of the weight due to acceleration is detected by each capacitance formed between the common electrode and each segment electrode,
The acceleration is calculated from this detected value. perpendicular to the diaphragm,
The acceleration in each horizontal direction is also detected from the total value of each capacitance and the difference value between each pair of capacitances, as in the first embodiment. Further, an alarm signal to be issued when the acceleration exceeds a set value can also be output by a signal processing circuit according to FIG. 5 in the first embodiment.

【Effect of the invention】

This first. According to each of the second inventions, acceleration in each of the three directions can be accurately measured with good sensitivity using a single sensor with a simple structure, and cost reduction and miniaturization are achieved in common compared to the conventional technology. It has the effect of helping you achieve your goals. In particular, in the second invention, according to the embodiment, the diaphragm and the weight are integrally formed from a semiconductor material, and everything up to the formation of the common electrode is performed by a semiconductor manufacturing process, so that further cost reduction and miniaturization can be achieved. , and is suitable for mass production.

[Brief explanation of drawings]

FIG. 1 is a side view of an embodiment according to the first invention, and FIG. 2 is a strain detection element of this embodiment, where (a) is a side view thereof, and (b) is a surface thereof on the common electrode side. Figure 3 (C) is a surface view of the electrode side, Figure 3 shows the operation of this embodiment when acceleration is applied in the vertical direction, and Figure (a) is a side view of the main part. Figure (b) is a plan view of the main part, Figure 4 shows the operation of this embodiment when horizontal acceleration is applied, and Figure (a) is a side view of the main part.
b) is a plan view of the main part thereof, FIG. 5 is a circuit diagram showing the configuration of the signal processing circuit of this embodiment, FIG. 6 is a side view of the embodiment according to the second invention, and FIG. 7 is this embodiment. FIG. 3 is a surface view of the displacement detection element on the side of the dividing electrode. Code explanation 1.31: Acceleration sensor, 2, 32: Diaphragm,
3.33: Weight, 4,34: Flange, 5,35: Base plate, 6: Piezoelectric element, 7,37: Substrate, 8,38: Common electrode, 9.397 Minute electrode (general term), 11 Niblint wiring board , 12: Signal processing circuit, 13, 43: Lead, 1
8: Subtraction circuit, 19: Addition circuit, 20: Conversion circuit, 21
: Filter circuit, 22, 23 : Comparison circuit, 24.2
5: Setting circuit, 26: OR circuit, 41: Insulating film. Representative Patent Attorney Iwao Yamaguchi ＼ Meeting (Regret (b) (C) Figure 2 Question 6

Claims (1)

[Scope of Claims] 1) A diaphragm whose peripheral portion is fixed to a rigid base member and installed horizontally; A weight provided at the center of this diaphragm; A surface of the diaphragm centered around the position of this weight; a piezoelectric strain sensing element, which is provided in a piezoelectric strain sensing element and includes a common electrode, and a plurality of pairs of dividing electrodes facing the common electrode and arranged point-symmetrically with respect to the position of the weight with a piezoelectric material in between; The strain sensing element is characterized by being configured to detect each acceleration in a direction along the surface of the diaphragm and in a direction perpendicular to the surface of the diaphragm based on the voltage induced between the common electrode and each partial electrode. acceleration sensor. 2) A diaphragm whose periphery is fixed to a rigid base member and installed horizontally; a weight provided at the center of this diaphragm; a surface on the opposite side of the diaphragm centered on the position of this weight; a capacitance type displacement sensing element comprising a common electrode and a plurality of pairs of segment electrodes arranged point-symmetrically with respect to the position of the weight; The displacement detection element is configured to detect each acceleration in a direction along the surface of the diaphragm and in a direction perpendicular to the surface of the diaphragm, based on the capacitance formed between the common electrode and each partial electrode. An acceleration sensor that is characterized by: