JP4275269B2 - Piezoelectric three-axis acceleration sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric triaxial acceleration sensor that detects acceleration using piezoelectric ceramics.
[0002]
[Prior art]
A piezoelectric ceramic substrate having an electrode pattern for acceleration detection formed on one surface and a counter electrode pattern formed on the other surface is subjected to polarization treatment, and acceleration is caused by stress generated in the stress generation region of the piezoelectric ceramic substrate upon receiving acceleration. An acceleration sensor that outputs an acceleration detection signal (voltage signal or current signal) from each output electrode based on the spontaneous polarization charge generated in the detection electrode is known. In this type of acceleration sensor, in a piezoelectric triaxial acceleration sensor that detects acceleration in three axial directions orthogonal to each other, an acceleration detection electrode pattern is composed of a pair of X axis direction acceleration detection electrodes and a pair of Y axis direction acceleration detections. Electrode, a plurality of Z-axis direction acceleration detection electrodes, an X-axis output electrode, a Y-axis output electrode, and a Z-axis output electrode are electrically connected via an X-axis connection line, a Y-axis connection line, and a Z-axis connection line, respectively. Connected to and formed. The basic principle and basic technology of this piezoelectric triaxial acceleration sensor are disclosed in detail in International Publication WO 93/02342 (PCT / JP92 / 00882).
[0003]
However, since the piezoelectric ceramic substrate has a high relative dielectric constant, the piezoelectric triaxial acceleration sensor naturally generates a capacitance between the connection line and the counter electrode pattern. Spontaneous polarization charges generated between the connection line and the counter electrode pattern are also accumulated in this capacitance. Therefore, there arises a problem that the output of the acceleration detection signal taken out from the output electrode is reduced to some extent. Therefore, it has been proposed to form a low dielectric constant layer having a dielectric constant sufficiently smaller than that of the piezoelectric ceramic substrate between the connecting line and the piezoelectric ceramic substrate over the entire surface of the piezoelectric ceramic substrate. . In addition, it has also been proposed to form the counter electrode pattern in an annular shape corresponding to the electrode group of the acceleration detection electrode so that the counter electrode pattern does not easily face the connection line. However, even if the counter electrode pattern is formed in this way, the counter electrode pattern is diagonally opposed to the connection line, and thus the capacitance of the diagonally opposed portion is not eliminated. Therefore, a low dielectric constant layer is also required in this case.
[0004]
[Problems to be solved by the invention]
When the low dielectric constant layer is formed over the entire surface of the piezoelectric ceramic substrate as in the past, in the stress generation region of the piezoelectric ceramic substrate, the low dielectric constant layer inhibits the deflection of the piezoelectric ceramic substrate, and the stress generation region The amount of stress generated is uneven. Therefore, variations occur in the levels of the X-axis acceleration detection signal, Y-axis acceleration detection signal, and Z-axis acceleration detection signal output from the output electrode. Therefore, conventionally, variations in the levels of the X-axis, Y-axis, and Z-axis acceleration signals have been adjusted by a signal amplification circuit provided in the sensor. However, when the variation in the level of the X-axis, Y-axis, and Z-axis acceleration signals is adjusted by the signal amplifier circuit, there is a problem that the manufacture of the piezoelectric triaxial acceleration sensor becomes complicated.
[0005]
An object of the present invention is to provide a piezoelectric triaxial acceleration sensor that does not require adjustment of variations in the levels of X-axis, Y-axis, and Z-axis acceleration signals by a signal amplifier circuit.
[0006]
[Means for Solving the Problems]
The piezoelectric triaxial acceleration sensor to be improved by the present invention is a pair of X axis acceleration detection electrodes for detecting triaxial accelerations in the X axis direction, the Y axis direction, and the Z axis direction orthogonal to each other. The pair of Y-axis acceleration detection electrodes and the plurality of Z-axis acceleration detection electrodes, the X-axis output electrode, the Y-axis output electrode, and the Z-axis output electrode are the X-axis connection line, the Y-axis connection line, and the Z-axis connection line. Are formed on the front surface, and at least a pair of X-axis acceleration detection electrodes, a pair of Y-axis acceleration detection electrodes, and a plurality of Z-axis acceleration detection electrodes are formed on the front surface. A piezoelectric ceramic substrate in which a counter electrode pattern facing the electrode is formed and a portion between each acceleration detecting electrode and the counter electrode pattern is polarized, and a diaphragm in which the back surface of the piezoelectric ceramic substrate is bonded to the surface A weight provided in the center of the diaphragm, and a base for supporting the diaphragm so that the portion of the piezoelectric ceramic substrate around the weight is bent when acceleration acts on the weight. ing. Piezoelectric ceramic substrate is an annular stress that is located between the weight-facing area facing the weight, the base-facing area facing the base, and each acceleration detecting electrode located between the weight-facing area and the base-facing area. Generating region. A low dielectric constant layer having a dielectric constant sufficiently smaller than that of the piezoelectric ceramic substrate is formed between the X-axis connecting line, the Y-axis connecting line, and the Z-axis connecting line and the piezoelectric ceramic substrate. Yes. In the present invention, the low dielectric constant layer is not formed between the connecting wire portion located in the stress generation region and the piezoelectric ceramic substrate. Further, the shape of the counter electrode pattern is determined so as not to oppose the connecting line through the piezoelectric ceramic substrate as much as possible. If the low dielectric constant layer is not formed between the connecting line portion located in the stress generation region and the piezoelectric ceramic substrate as in the present invention, the low dielectric constant layer causes the stress generation region of the piezoelectric ceramic substrate as in the prior art. Therefore, it is possible to prevent the generation amount of stress in the stress generation region from being biased.
[0007]
However, if a low dielectric constant layer is not formed between the portion of the connection line located in the stress generation region and the piezoelectric ceramic substrate, spontaneous polarization occurs between the connection line and the counter electrode pattern in the stress generation region. There arises a problem that electric charges are generated. Therefore, in the present invention, the shape of the counter electrode pattern is determined so as not to oppose the connection line through the piezoelectric ceramic substrate as much as possible, and the spontaneous polarization charge is generated between the connection line and the counter electrode pattern in the stress generation region. Prevented. As described above, according to the present invention, it is possible to prevent variations in the levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal output from the output electrode. There is no need to adjust the variation in the level of each acceleration signal.
[0008]
In order to prevent the counter electrode pattern from facing the connection line through the piezoelectric ceramic substrate as much as possible, the counter electrode pattern may be formed in a shape that follows the outline of the electrode group formed by each acceleration detection electrode.
[0009]
The stress generation region includes an annular first stress generation portion that surrounds the weight-facing region and an annular second stress that surrounds the first stress generation portion and generates a different type of stress from the stress applied to the first stress generation portion. And a curved line portion formed by a boundary line between the first stress generation portion and the second stress generation portion. Therefore, at least one electrode of the pair of X-axis acceleration detection electrodes, the pair of Y-axis acceleration detection electrodes, and the plurality of Z-axis acceleration detection electrodes has a weight in the X-axis direction, the Y-axis direction, and the Z-axis direction. When the same magnitude of acceleration is applied, the inflection curve portion is set so that the levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal output from each output electrode are substantially equal. It is preferable to have an output adjusting extension electrode portion extending beyond the first stress generating portion to the second stress generating portion.
[0010]
As described above, when the output adjustment extension electrode portion is provided on at least one of the pair of X-axis acceleration detection electrodes, the pair of Y-axis acceleration detection electrodes, and the plurality of Z-axis acceleration detection electrodes, the output adjustment extension is performed. In the acceleration detecting electrode provided with the electrode portion, a part of the charge generated in the portion on the first stress generating portion is canceled by the reverse polarity charge generated in the output adjusting extension electrode portion, and output from the output electrode. The level of the acceleration detection signal is reduced. Therefore, by appropriately determining the amount of decrease, the levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal can be adjusted to be substantially equal. In this way, if the levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal output from the X-axis output electrode, the Y-axis output electrode, and the Z-axis output electrode are substantially equal, A piezoelectric triaxial acceleration sensor that can match the output level of the acceleration signal can be obtained without using a signal amplifier circuit. In addition, since the signal levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal can be made the same, it is necessary to change the amplification degree according to the acceleration detection signal in each direction even if an amplification circuit is used. The configuration and design of the amplifier circuit are simplified.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 are a front view, a plan view, a side view, and a rear view showing the piezoelectric triaxial acceleration sensor according to the embodiment of the present invention in a partially broken state. As shown in FIGS. 2 and 3, the acceleration detecting device is fixed on a surface opposite to the surface of the diaphragm 1, the weight 3, the base 5, and the surface on which the weight 3 of the diaphragm 1 is attached. The acceleration sensor element 7 is provided. Each of these members is housed in an insulating resin case 9, and a plurality of terminal fittings 11A to 11H are disposed inside the insulating resin case 9, and a metal cover member 13 is fitted therein. Has been.
[0012]
The diaphragm 1, the weight 3, and the base 5 are configured as a single unit 10 that is integrally formed of a metal material made of brass. The diaphragm 1 has a disk shape. The weight 3 has a cylindrical shape, and is arranged so that an extended portion of the axis passes through the center of the diaphragm 1. The base 5 has a cylindrical shape and supports the outer periphery of the diaphragm 1. Further, a V-shaped groove 5 a that is continuous in the circumferential direction is formed on the outer peripheral portion of the base 5. The single unit 10 is used as an insert when the insulating resin case 9 is molded together with the plurality of terminal fittings 11A to 11H.
[0013]
As shown in the plan view of FIG. 5 and the back view of FIG. 6, the acceleration sensor element 7 has an acceleration detection electrode pattern E1 for triaxial acceleration detection formed on the surface of the piezoelectric ceramic substrate 7a, and a counter electrode pattern E0 on the back surface. Is formed. The back surface of the piezoelectric ceramic substrate 7a and the counter electrode pattern E0 are joined to the surface of the diaphragm 1 by an adhesive layer made of a synthetic resin material such as epoxy. The piezoelectric ceramic substrate 7a has a substantially quadrangular outline. As shown in FIGS. 1 and 3, a plurality of main body portions 7b located on the diaphragm 1 and an insulating resin case 9 are formed from the main body portion 7b. And an extension 7c extending to the vicinity of the terminal fittings 11A to 11H. As shown in FIGS. 1 and 5, four semicircular recesses 7 d to 7 g and four semicircular recesses are formed on the edge of the extension 7 c located on the two opposing sides of the piezoelectric ceramic substrate 7 a. The recesses 7h to 7k are formed at equal intervals. The piezoelectric ceramic substrate 7a is subjected to polarization treatment at a portion corresponding to the electrode so that spontaneous polarization charges are generated when stress is applied to the inside thereof. The polarization process will be described later. The piezoelectric ceramic substrate 7a has a weight facing region 8A, a base facing region 8B, and a stress generation region 8C located between the weight facing region 8A and the base facing region 8B. The weight 3 is located in the portion corresponding to the weight opposing region 8A, and the base 5 is located in the portion corresponding to the base opposing region 8B. The stress generation region 8C includes an annular first stress generation portion 8C1 surrounding the weight opposing region 8A and an annular second stress generation portion 8C2 surrounding the first stress generation portion 8C1. When acceleration acts on the weight 3 in a direction parallel to the substrate surface of the piezoelectric ceramic substrate 7a (X-axis direction or Y-axis direction), the first stress generating portion 8C1 is centered on the center of gravity of the weight 3. It is deformed into a symmetrically different state (a state where tensile stress is applied and a state where compressive stress is applied). Further, when an acceleration acts on the weight 3 in a direction (Z-axis direction) orthogonal to the substrate surface of the piezoelectric ceramic substrate 7a, each portion of the first stress generating portion 8C1 is deformed to the same state. The second stress generating portion 8C2 is a region in which a different type of stress from the stress applied to the first stress generating portion 8C1 is extremely small. In FIG. 5, 8D is a boundary line (curved line portion) between the first stress generating portion 8C1 and the second stress generating portion 8C2.
[0014]
The acceleration detecting electrode pattern E1 and the counter electrode pattern E0 formed on the front and back surfaces of the piezoelectric ceramic substrate 7a are both formed by screen printing. The acceleration detection electrode pattern E1 includes an X-axis direction detection electrode pattern 15, a Y-axis direction detection electrode pattern 17, and a Z-axis direction detection electrode pattern 19, as shown in FIG. The X-axis direction detection electrode pattern 15 has a structure in which a pair of X-axis direction acceleration detection electrodes EX1, EX2 and an X-axis output electrode OX are connected in series by X-axis connection lines L1 to L3. The pair of X-axis direction acceleration detection electrodes EX1 and EX2 includes four Z-axes of a pair of Y-axis direction acceleration detection electrodes EY1 and EY2 and a Z-axis direction detection electrode pattern 19 of a Y-axis direction detection electrode pattern 17 described later. Together with the direction acceleration detection electrodes EZ1 to EZ4, an annular row surrounding the weight opposing region 8A is formed. The electrodes EX1 and EX2 of the pair of X-axis direction acceleration detection electrodes are line-symmetric with respect to the X-axis direction virtual line XL and straddle the weight opposing region 8A and the first stress generating portion 8C1. It has a shape close to a rectangle.
[0015]
The Y-axis direction acceleration detection electrode pattern 17 has a structure in which a pair of Y-axis direction acceleration detection electrodes EY1, EY2 and a Y-axis output electrode OY are connected in series by a Y-axis connection line L4. The electrodes EY1 and EY2 of the pair of Y-axis direction acceleration detection electrodes are line-symmetric with respect to the Y-axis direction virtual line YL, and the weight opposing region 8A, the first stress generating portion 8C1, and the second stress It has a shape close to a rectangle straddling the generator 8C2. These electrodes EY1 and EY2 are both of the charge generation electrode portions EY1a and EY2a located on the weight opposing region 8A and the first stress generation portion 8C1, and the first stress generation portion 8C1 beyond the curve portion 8D. Output extension electrode portions EY1b and EY2b extending on the second stress generating portion 8C2. As described above, the second stress generating portion 8C2 generates a different type of stress from the stress applied to the first stress generating portion 8C1, although the amount is small. Therefore, charges having opposite polarity to the charge generation electrode portions EY1a and EY2a are generated in the output adjustment extension electrode portions EY1b and EY2b positioned on the second stress generation portion 8C2. As a result, some of the charges generated in the charge generation electrode portions EY1a and EY2a are canceled by the reverse polarity charges generated in the output adjustment extension electrode portions EY1b and EY2b, and output from the Y-axis output electrode OY. The signal level decreases.
[0016]
The Z-axis direction acceleration detection electrode pattern 19 has a structure in which four Z-axis direction acceleration detection electrodes EZ1 to EZ4 and a Z-axis output electrode OZ are connected in series by a Z-axis connection line L5 in this order. Yes. Each of the Z-axis direction acceleration detection electrodes EZ1 to EZ4 has a shape close to a rectangle, and includes a pair of X-axis direction acceleration detection electrodes EX1 and EX2 and a pair of Y-axis direction acceleration detection electrodes EY1 and EY2. It is formed across the weight opposing region 8A and the first stress generating portion 8C1 in a state of being disposed between the electrodes. The shape and dimensions of the Z-axis direction acceleration detection electrodes EZ1 to EZ4 are the same as those of the output electrode OZ when accelerations of the same magnitude are applied to the weight 3 in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The level of the output Z-axis acceleration detection signal is set to be substantially equal to the levels of the Y-axis acceleration detection signal and the Z-axis acceleration detection signal output from the output electrodes OY and OZ.
[0017]
In the acceleration sensor of this example, assuming that the shape and dimensions of the Y-axis direction acceleration detection electrodes EY1, EY2 are the same as those of the X-axis direction acceleration detection electrodes EX1, EX2, the weight 3 has the X-axis direction, the Y-axis direction, and the Z-axis. When acceleration of the same magnitude is applied in the axial direction, the Y-axis acceleration detection signal output from the output electrode OY is output from the X-axis acceleration detection signal output from the output electrode OX or the output electrode OZ. It becomes larger than the Z-axis acceleration detection signal. This is considered to be due to the difference in length between the X-axis connection lines L1 to L3 and the Y-axis connection line L4. According to this example, by providing the output adjustment extension electrodes EY1b and EY2b on the Y-axis direction acceleration detection electrodes EY1 and EY2, the level of the Y-axis acceleration detection signal output from the Y-axis output electrode OY is reduced, and When acceleration of the same magnitude is applied to the weight 3 in the X-axis direction, the Y-axis direction, and the Z-axis direction, the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis output from the output electrodes OX to OZ. The level of the axial acceleration detection signal can be made substantially equal.
[0018]
The X-axis output electrode OX, the Y-axis output electrode OY, and the Z-axis output electrode OZ are formed so as to surround the recesses 7d, 7h, and 7k, respectively, at the three corners of the piezoelectric ceramic substrate 7a. In addition, an earth electrode OE is formed at the remaining corner of the piezoelectric ceramic substrate 7a so as to surround the recess 7g. An extension 21 extending to the edge of the piezoelectric ceramic substrate 7a adjacent to the X-axis direction acceleration detection electrode EX1 is connected to the ground electrode OE. The ground electrode OE is electrically connected to the base 5 via a conductive adhesive layer (not shown) formed on the side and back surface of the piezoelectric ceramic substrate 7a.
[0019]
Low dielectric constant layers 27 to 31 are formed in a predetermined pattern in a part of the weight opposing region 8A and the base opposing region 8B so as to be positioned between the connection lines L1 to L5 and the piezoelectric ceramic substrate 7a. The low dielectric constant layers 27 to 31 are all formed by screen printing using a thermosetting resin (relative dielectric constant: 10) made of a resin (epoxy) paste having a dielectric constant sufficiently smaller than that of the piezoelectric ceramic substrate 7a. And has a thickness of 20 μm. For the low dielectric constant layer, a dielectric material having a relative dielectric constant of 1/100 or less of that of the piezoelectric ceramic substrate 7a is preferably used. As the dielectric material, any material having a dielectric constant sufficiently smaller than that of the piezoelectric ceramic substrate 7a may be used, and glass and thermosetting resin can be used. The low dielectric constant layer 27 is formed between the connection lines L4 and L5 and the piezoelectric ceramic substrate 7a in the weight fixing region 8A, and has a circular shape. The low dielectric constant layer 29 is formed on one side of the base facing region 8B so as to be positioned between the connection lines L1, L2, L3, L5 and the extension portion 21 and the piezoelectric ceramic substrate 7a. The low dielectric constant layer 31 is formed on the other side of the base facing region 8B so as to be positioned between the connection lines L4 and L5 and the piezoelectric ceramic substrate 7a. Thus, the low dielectric constant layers 27 to 31 are not formed between the connection lines L1, L2, L4, and L5 located in the stress generation region 8C and the piezoelectric ceramic substrate 7a. If the low dielectric constant layers 27 to 31 are configured as in this example, the low dielectric constant layer does not hinder the bending in the stress generation region 8C of the piezoelectric ceramic substrate 7a, so that the stress in the stress generation region 8C is reduced. It is possible to prevent the generation amount from being biased.
[0020]
As shown in FIG. 6, the counter electrode pattern E0 formed on the back surface of the piezoelectric ceramic substrate 7a includes an annular counter electrode E0a facing the acceleration detection electrodes EX1 to EZ4 of the acceleration detection electrode pattern E1, and a counter electrode. It has the extending | stretching part E0b extended from E0a to the edge part of the piezoelectric ceramic substrate 7a, and the back surface electrode parts E0c-E0f formed in the four corners of the piezoelectric ceramic substrate 7a. The counter electrode E0a has a shape along the outline of the electrode group formed by the acceleration detection electrodes EX1 to EZ4 so as not to face the connection lines L1 to L5 through the piezoelectric ceramic substrate 7a as much as possible. As described above, in this example, since the low dielectric constant layer is not formed in the stress generation region 8C, it is possible to prevent the generation amount of stress in the stress generation region 8C from being biased. However, since the low dielectric constant layer is not formed in the stress generation region 8C, there arises a problem that spontaneous polarization charges are generated between the connection lines L1, L2, L3, and L5 and the counter electrode E0a. Therefore, in this example, the shape of the counter electrode E0a is determined so as not to face the connection lines L1 to L5 through the piezoelectric ceramic substrate 7a as much as possible, and the connection lines L1, L2, L3, L5 in the stress generation region 8C Generation of spontaneous polarization charge between the counter electrode E0a was prevented. A part of the extending portion E0b is opposed to the end portion 21a of the extension portion 21 of the acceleration detecting electrode pattern E1, and the end portion 21a of the extension portion 21 is connected to the end portion 21a extending through the side portion of the piezoelectric ceramic substrate 7a. And are electrically connected. Thereby, the counter electrode E0a included in the counter electrode pattern E0 is electrically connected to the ground electrode OE. The back surface electrode portions E0c to E0f are opposed to the ground electrode OE, the X-axis output electrode OX, the Z-axis output electrode OZ, and the Y-axis output electrode OY, and are respectively connected via connecting portions extending on the side portions of the piezoelectric ceramic substrate 7a. It is electrically connected to each facing electrode.
[0021]
In each part of the piezoelectric ceramic substrate 7a corresponding to the X-axis direction acceleration detection electrodes EX1 and EX2, when the same kind of stress is generated in each part due to the acceleration in the Z-axis direction acting on the weight 3 Polarization processing is performed so that spontaneous polarization charges having opposite polarities appear on the acceleration detection electrode EX1 located on one side of the facing region 8A and the acceleration detection electrode EX2 located on the other side. Similarly to the portions of the piezoelectric ceramic substrate 7a corresponding to the X-axis direction acceleration detection electrodes EX1 and EX2, the portions of the piezoelectric ceramic substrate 7a corresponding to the Y-axis direction acceleration detection electrodes EY1 and EY2 are also weights 3. When the same kind of stress is generated in each part due to the acceleration in the Z-axis direction, the Y-axis direction acceleration detection electrode EY1 located on one side of the weight opposing region 8A and the Y located on the other side Polarization processing is performed so that spontaneous polarization charges having opposite polarities appear on the axial acceleration detection electrode EY2. Further, each part of the piezoelectric ceramic substrate 7a corresponding to the Z-axis direction acceleration detection electrodes EZ1 to EZ4 is all when the same kind of stress is generated in each part due to the Z-axis direction acceleration acting on the weight 3. Polarization processing is performed so that spontaneous polarization charges having the same polarity appear on the Z-axis direction acceleration detection electrodes EZ1 to EZ4. For this reason, when the diaphragm 1 is deformed based on the acceleration acting on the weight 3, the piezoelectric ceramic substrate 7a is bent, and the spontaneous polarization charge generated between the acceleration detecting electrode pattern E1 and the counter electrode pattern E0 is changed. The acceleration in the direction of three axes (X axis, Y axis, Z axis) applied to the weight 3 is measured as a change in current or voltage.
[0022]
In this example, the acceleration detection electrodes EX1 to EZ4 and the counter electrode pattern E0 are screen-printed using a glass-silver paste and then baked to a thickness of 5 μm, and then a DC voltage is applied between the opposing electrodes. By applying, the piezoelectric ceramic substrate 7a was subjected to polarization treatment. Next, after the low dielectric constant layers 27 to 31 were screen-printed with a resin (epoxy) paste, the connection lines L1 to L9 were screen-printed with a silver paste to form an acceleration detection electrode pattern E1.
[0023]
As shown in FIG. 1 to FIG. 3, the insulating resin case 9 has a substantially rectangular parallelepiped shape, and includes a central cavity portion 9 a and side cavity portions 9 b communicating with the central cavity portion 9 a and the outside. Is formed inside. 2 and 3, the central hollow portion 9a passes through the insulating resin case 9 in the vertical direction of the drawing sheet. The central hollow portion 9a is provided on the inner peripheral surface of the substantially cylindrical unit housing portion 9c and the insulating resin case 9. In order to form the portion 9d, it has a substantially cylindrical gap portion 9e having a smaller diameter than the single unit storage portion 9c. The single unit 10 is stored in the single unit storage portion 9c so that the bottom surface of the base 5 of the single unit 10 and the stepped portion 9d come into contact with each other. Further, inside the single unit housing portion 9c, a resin portion enters the V-shaped groove 5a of the base 5 of the single unit 10 to form a protruding portion 9f. In this example, since the insulating resin case 9 is integrally formed by injection molding using the single unit 10 as an insert, the step portion 9d and the protrusion 9f function as a retainer from the insulating resin case 9 of the single unit 10. is doing. In addition, by forming the insulating resin case 9 using the single unit 10 as an insert in this way, a part 5 b of the outer peripheral surface of the base 5 is exposed in the side cavity 9 b of the insulating resin case 9. . The insulating resin case 9 has a surface 9g which is located on the same side as the surface of the diaphragm 1 and is flush with the surface of the diaphragm 1, and a back surface 9h which is located on the opposite side of the surface 9g. Yes. The extension portion 7c of the piezoelectric ceramic substrate 7a described above is placed on the surface 9g. On the back surface 9h, a plurality of (three in this example) a plurality of terminal fittings 11A to 11H, which will be described later, protrude in the same direction as the other end portions 11f of the insulating resin case 9 protrude from the back surface 9h. Spacers 9i are formed. If such spacers 9i are formed, a gap can be formed by the spacers 9i between the back surface 9h of the insulating resin case 9 and the circuit board when the acceleration detecting device is attached to the circuit board. Therefore, when soldering the terminal fittings 11A to 11H of the acceleration detecting device to the circuit board, it is possible to prevent the flux contained in the solder from entering the inside of the acceleration detecting device through the insulating resin case 9 or the like. Further, as shown in FIG. 2, a substantially rectangular recess 9j that opens outward is formed on the outer peripheral portion of the insulating resin case 9 at the lower portion of the side surface 9k where the side cavity 9b opens. .
[0024]
As shown in FIG. 3, the plurality of terminal fittings 11 </ b> A to 11 </ b> H all have the same substantially cylindrical shape, and are respectively in positions corresponding to the recesses 7 d to 7 k of the piezoelectric ceramic substrate 7 a in the insulating resin case 9. Has been placed. One terminal fitting of the terminal fittings 11A to 11H has annular flange portions 11c and 11d that protrude in a direction perpendicular to the longitudinal direction at one end portion 11a and a central portion in the longitudinal direction. Thereby, the area of the end surface 11e of one edge part 11a becomes larger than the cross-sectional area of the terminal metal fitting orthogonal to a longitudinal direction. Further, the flange portion 11d at the center portion in the longitudinal direction functions as a retaining member for the terminal fittings 11A to 11F from the insulating resin case 9. The plurality of terminal fittings 11 </ b> A to 11 </ b> H are insulated so that the end surface 11 e of one end portion 11 a is exposed on the surface 9 g of the insulating resin case 9 and the other end portion 11 f protrudes from the back surface of the insulating resin case 9. It is arranged in the resin case 9. Almost half (semicircle) of each end face 11e of the plurality of terminal fittings 11A to 11H is exposed to the outside from the inside of the recesses 7d to 7k of the piezoelectric ceramic substrate 7a. And as shown in FIG.1 and FIG.3, end surface 11e of each one of four terminal metal fittings 11A, 11D, 11E, 11H located in the corner | angular part of the piezoelectric ceramic board | substrate 7a among several terminal metal fittings 11A-11H ... Are electrically connected to the electrodes OX, OY, OZ, OE formed on the extension portion 7c of the piezoelectric ceramic substrate 7a by the conductive portions 25 made of a conductive adhesive. In this example, among the plurality of terminal fittings 11A to 11H, one end face 11e of the other four terminal fittings 11B, 11C, 11F, and 11G simply contacts the edge of the piezoelectric ceramic substrate 7a. However, these end faces 11e may be connected to the edge of the piezoelectric ceramic substrate 7a by an adhesive. The terminal fittings 11B, 11C, 11F, and 11G constitute dummy terminals.
[0025]
The cover member 13 has a one-side-opened box shape having a substantially rectangular upper wall portion 13a and four substantially rectangular side wall portions 13b to 13e, and is integrally formed of stainless steel. The cover member 13 is fitted to the insulating resin case 9 so that the upper wall portion 13a is located above the acceleration sensor element 7 and the side wall portions 13b to 13e are in contact with the side surfaces of the insulating resin case 9. In this state, the acceleration sensor element 7 is covered. As shown in FIGS. 2 and 3, the side wall portion 13b of the cover member 13 that contacts the side surface 9k of the insulating resin case 9 (the side surface where the side hollow portion 9b of the insulating resin case 9 is formed) is in contact with The piece 13f and the convex portion 13g are integrally formed by pressing. The contact piece 13f extends in the side cavity portion 9b of the insulating resin case 9 so that a part of the side wall portion 13b forms an opening 13h and stands on the base 5 side. It has an upright part 13f1 extending in a direction orthogonal to each other and a contact part 13f2 bent in an arc shape at the end of the upright part 13f1. The contact portion 13f2 is fitted into a fitting recess formed by a part of the V-shaped groove 5a of the base 5 (a portion exposed in the side cavity portion 9b), whereby the cover member 13 is 5 is electrically connected. As described above, since the ground electrode OE is electrically connected to the base 5 via the conductive adhesive layer (not shown), the cover member 13 is electrically connected to the ground electrode OE together with the base 5. It will be grounded. Particularly in this example, since the contact portion 13f2 is pressed against the base 5 by the spring property of the upright portion 13f1 in a state where the cover member 13 is fitted to the insulating resin case 9, the cover member 13 and the cover member 13 are simultaneously mounted. The electrical connection with the base 5 can be completed, and the contact between the base 5 and the contact piece 13f of the cover member 13 is ensured.
[0026]
The convex portion 13g is formed by bending a part of the side wall portion 13b of the cover member 13. The convex portion 13 g is fitted into a concave portion 9 j formed on the side surface 9 k of the insulating resin case 9 and serves to fix the cover member 13 to the insulating resin case 9. According to such a fixing method, the convex portion 13g of the cover member 13 is fitted to the insulating resin case 9 with springiness, so that the cover member 13 can be easily attached to the insulating resin case 9 by attaching the cover member 13. Can be fixed to.
[0027]
In this example, the output adjustment extension electrodes EY1b and EY2b are provided only on the pair of Y-axis acceleration detection electrodes EY1 and EY2. However, depending on the design of the acceleration sensor element, the output adjustment extension is applied to the other electrodes. An electrode part may be provided. In that case, by appropriately setting the shape and dimensions of the extension electrode part for output adjustment, when the same acceleration is applied in the X-axis direction, Y-axis direction and Z-axis direction, the output is output from each output electrode. The levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal may be made substantially equal.
[0028]
【The invention's effect】
According to the present invention, since the low dielectric constant layer is not formed between the connecting wire portion located in the stress generation region and the piezoelectric ceramic substrate, it is possible to prevent the generation of stress in the stress generation region from being biased. Can do. However, since the low dielectric constant layer is not formed in the stress generation region, there arises a problem that spontaneous polarization charges are generated between the connection line and the counter electrode pattern. Therefore, in the present invention, the shape of the counter electrode pattern is determined so as not to oppose each connecting line through the piezoelectric ceramic substrate as much as possible. As described above, according to the present invention, it is possible to prevent variations in the levels of the X-axis acceleration detection signal, the Y-axis acceleration detection signal, and the Z-axis acceleration detection signal output from the output electrode. There is no need to adjust the variation in the level of each acceleration signal.
[Brief description of the drawings]
FIG. 1 is a front view showing a piezoelectric triaxial acceleration sensor according to an embodiment of the present invention in a partially broken state.
FIG. 2 is a plan view showing the piezoelectric triaxial acceleration sensor according to the embodiment of the present invention in a partially broken state.
FIG. 3 is a side view showing the piezoelectric triaxial acceleration sensor according to the embodiment of the present invention in a partially broken state.
FIG. 4 is a rear view of the piezoelectric triaxial acceleration sensor according to the embodiment of the present invention.
FIG. 5 is a plan view of an acceleration sensor element used in the piezoelectric triaxial acceleration sensor according to the embodiment of the present invention.
FIG. 6 is a back view of an acceleration sensor element used in the piezoelectric triaxial acceleration sensor according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Diaphragm 3 Weight 5 Base 7 Acceleration sensor element 8A Weight opposing area 8B Base opposing area 8C Stress generating area 8C1 1st stress generating part 8C2 2nd stress generating part 27-31 Low dielectric constant layers EX1, EX2 X-axis direction acceleration detection electrodes EY1, EY2 A pair of Y-axis direction acceleration detection electrodes EZ1 to EZ4 Z-axis direction acceleration detection electrodes E0 Counter electrode pattern E0a Counter electrode

Claims (2)

A pair of X-axis acceleration detection electrodes, a pair of Y-axis acceleration detection electrodes, and a plurality of Z-axis acceleration detections for respectively detecting three-axis accelerations in the X-axis direction, Y-axis direction, and Z-axis direction orthogonal to each other Acceleration detection electrode pattern in which the electrode and the X-axis output electrode, the Y-axis output electrode, and the Z-axis output electrode are electrically connected via the X-axis connection line, the Y-axis connection line, and the Z-axis connection line, respectively, on the surface A counter electrode pattern that is formed on the back surface and faces at least the pair of X-axis acceleration detection electrodes, the pair of Y-axis acceleration detection electrodes, and the plurality of Z-axis acceleration detection electrodes; A piezoelectric ceramic substrate in which a portion between the acceleration detection electrode and the counter electrode pattern is polarized;
A diaphragm in which the back surface of the piezoelectric ceramic substrate is bonded to the front surface;
A weight provided in the center of the diaphragm;
A base that supports the diaphragm so that bending occurs in a portion of the piezoelectric ceramic substrate around the weight when the acceleration acts on the weight;
The piezoelectric ceramic substrate is located between a weight facing region facing the weight, a base facing region facing the base, and between the weight facing region and the base facing region. An annular stress generation region disposed;
The X-axis connecting line, wherein between the Y axis connecting line and the Z-axis connecting line between the piezoelectric ceramic substrate, the piezoelectric ceramic substrate dielectric constant dielectric constant than the small minimum dielectric constant layer is formed A piezoelectric triaxial acceleration sensor,
The low dielectric constant layer is not formed between the portion of each connection line located in the stress generation region and the piezoelectric ceramic substrate,
The piezoelectric triaxial acceleration sensor , wherein the counter electrode pattern has a shape along an outline of an electrode group formed by the acceleration detection electrodes . In the stress generation region, an annular first stress generation portion surrounding the weight-opposing region, and a different type of stress from the stress applied to the first stress generation portion surrounding the first stress generation portion is generated. An annular second stress generation part, and a curved line part composed of a boundary line between the first stress generation part and the second stress generation part,
At least one of the pair of X-axis acceleration detection electrodes, the pair of Y-axis acceleration detection electrodes, and the plurality of Z-axis acceleration detection electrodes is formed on the weight with the X-axis direction, the Y-axis direction, and when the acceleration of the same magnitude to each of the Z-axis direction is applied, the X-axis acceleration detection signal outputted from the respective output electrodes, the Y-axis acceleration detection signal and the level of the Z-axis acceleration detection signal is equal properly so as to, according to claim 1, characterized in that it has the inflection curve portion beyond extending the second stress portion on from the first stress portion output adjustment extension electrode portions Piezoelectric three-axis acceleration sensor.

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