JP2008051647A - Piezoelectric acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a piezoelectric acceleration sensor which has a simple structure, is small and has high performance, and can detect three-axis acceleration. <P>SOLUTION: The piezoelectric acceleration sensor 1 is formed by using piezoelectric ceramic material, and includes an external frame member 9 in a closed shape, a fixed-fixed beam member 3 connecting two points of the external frame 9, and a first and a second cantilever beam 4 and 5 connected to the fixed-fixed beam 3 perpendicularly. Moreover, in addition to the above constitution the fixed-fixed beam 3 and the first and second beams 4 and 5 are respectively polarized in directions perpendicular to each other. Furthermore, acceleration detection electrodes are formed on the fixed-fixed beam 3 and the first and second beams 4 and 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric sensor using a piezoelectric effect obtained when a piezoelectric body is subjected to compression deformation or bending deformation by an external force, and more specifically, a piezoelectric acceleration sensor capable of detecting triaxial acceleration. It is about.

  A piezoelectric acceleration sensor is a sensor that utilizes a so-called piezoelectric phenomenon that generates a voltage when a piezoelectric body is compressed or deformed by an external force. In particular, the piezoelectric phenomenon due to bending deformation is widely used as sensing for detecting the acceleration associated with dropping or running of a mobile object such as a portable electronic device or an automobile, or detecting the impact associated with a collision. Among them, with recent demands for smaller and higher performance electronic devices, piezoelectric acceleration sensors are also required to have the same smaller size and higher performance.

As a conventional piezoelectric acceleration sensor, for example, Patent Document 1 discloses a bimorph type piezoelectric acceleration sensor configured by sandwiching a both-end support beam member in which a piezoelectric ceramic plate is face-to-face bonded with an intermediate electrode sandwiched between cases. Has been. Patent Document 2 discloses a bimorph type piezoelectric acceleration sensor in which a cantilever member in which two plate-shaped piezoelectric ceramic plates are face-to-face bonded with a Si substrate interposed therebetween is sandwiched between containers. Yes.
JP-A-9-61450 Japanese Patent Laid-Open No. 9-243656

  By the way, the piezoelectric acceleration sensors described in Patent Document 1 and Patent Document 2 are different from each other in that only one of a cantilever member and a cantilever member is used as a member for detecting acceleration. Yes. Basically, both can detect only a uniaxial acceleration. In order to detect at least triaxial acceleration using a conventional piezoelectric acceleration sensor, a plurality of acceleration sensors are required. Therefore, the conventional piezoelectric acceleration sensor cannot sufficiently satisfy the demand for downsizing and high performance.

  In addition, in order to manufacture a bimorph type piezoelectric body, at least a polishing process for flattening the opposing surface of the piezoelectric body with high accuracy and a flat surface for cleaning the bonding property of the opposing piezoelectric body are cleaned. The process to do is needed. For this reason, a manufacturing process will become complicated by using a special apparatus or increasing working time. Further, even if a lamination process is adopted instead of these processes, the number of processes is remarkably increased due to the manufacturing process of the piezoelectric green sheet, the lamination process of a plurality of piezoelectric green sheets, and the like. Furthermore, since production facilities are upsized, there is a concern that the manufacturing cost will rise.

  The present invention has been made in view of the above points, and an object thereof is a piezoelectric acceleration that has a simple structure, is small in size, has high performance, and can detect triaxial acceleration. It is to provide a sensor.

The present invention relates to a piezoelectric acceleration sensor formed using a piezoelectric ceramic material, an outer frame member having a closed shape, a both-end supporting beam member connected between two points of the outer frame member, and a both-end supporting member The piezoelectric acceleration sensor includes a plurality of cantilever members connected orthogonally.
In the present invention, in addition to the above-described configuration, it is desirable that the both-supported beam member and the plurality of cantilevered members are polarized in directions orthogonal to each other.
Furthermore, in the present invention, it is desirable that an acceleration detection electrode is formed on the cantilever member and the plurality of cantilever members.

  The piezoelectric acceleration sensor of the present invention has a so-called monomorph structure in which an outer frame member, a both-end support beam member that is a part for detecting acceleration, and a plurality of cantilever members are integrally formed of piezoelectric ceramics. It is as. For this reason, the structure of a piezoelectric acceleration sensor can be made very simple. In addition, a piezoelectric acceleration sensor can be created with a processing accuracy of several tens of microns. For this reason, effects such as simplification of element design, element miniaturization, and cost reduction can be obtained. Further, since each beam member is formed in a columnar shape, it has excellent strength, and there is an effect that a highly reliable piezoelectric acceleration sensor can be obtained.

  Further, the polarization treatment is performed so that the both cantilever members and the polarization axes of the plurality of cantilever members are orthogonal to each other. From this, there is an effect that it is possible to detect accelerations of a plurality of axes by one piezoelectric acceleration sensor.

  Furthermore, when an external force is applied to the piezoelectric acceleration sensor, the most bent part of each of the cantilever members and the plurality of cantilever members, that is, the part where the stress is generated most is grasped in advance. In addition, by forming an acceleration detection electrode having a specific shape and area, a highly sensitive piezoelectric acceleration sensor can be easily obtained.

  Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. This embodiment will be described as an example applied to a piezoelectric acceleration sensor 1 having a so-called monomorph type structure integrally formed of piezoelectric ceramics. The piezoelectric acceleration sensor 1 according to the present embodiment mainly detects a fall of a portable electronic device, an acceleration when a moving body such as an automobile travels, or a shock for detecting an impact related to a collision. It is suitably adopted as.

  First, an external configuration example of the piezoelectric acceleration sensor 1 will be described with reference to a perspective view of FIG. In the piezoelectric acceleration sensor 1, among the X axis, Y axis, and Z axis in FIG. 1, the XY plane corresponds to the mounting surface. The outer frame member 9 corresponding to the outer frame of the piezoelectric acceleration sensor 1 is formed in a rectangular shape (in this example, a square) as a “closed shape”. The outer frame member 9 is not a member for detecting acceleration, but is a member for holding the cantilever member 3 on which a first cantilever member 4 and a second cantilever member 5 described later are formed.

  Inside the outer frame member 9, a both-end supported beam member 3 that detects acceleration in the Y-axis direction is formed. The both-end supporting beam member 3 is a linear member that connects two arbitrary points on two opposite sides of the outer frame member 9. The both cantilever members 3 are formed with a first cantilever member 4 and a second cantilever member 5. The first cantilever member 4 is a member that mainly detects acceleration in the Z-axis direction. One end of the first cantilever member 4 is connected in a state orthogonal to the both cantilever members 3. On the other hand, the second cantilever member 5 is a member that mainly detects acceleration in the X-axis direction. One end of the second cantilever member 5 is connected to the first cantilever member 4 while being separated from the first cantilever member 4 and orthogonal to the both cantilever members 3.

  In the piezoelectric acceleration sensor 1, an electrode for detecting an X-axis acceleration formed in the X-axis direction of the second cantilever member 5 is an X-axis acceleration detection electrode 6. An electrode for detecting the Y-axis acceleration formed in the Y-axis direction of the both-end supported beam member 3 is a Y-axis acceleration detection electrode 7. The electrode for detecting the Z-axis acceleration formed in the Z-axis direction of the first cantilever member 4 is a Z-axis acceleration detection electrode 8. In order to form an electrode for detecting acceleration, an Ag (silver) paste coating / firing method, a metal vapor deposition method, or the like can be cited as a suitable forming method. Any of the forming methods can be used for mass production.

  The X, Y, and Z-axis acceleration detection electrodes formed on the beam members are formed in a rectangular shape so as to cover substantially the entire specific surface of each beam member. However, the shape of the acceleration detection electrode is not limited to a rectangular shape and can be variously changed. For example, the distribution of distortion, displacement, generated voltage, etc. of the piezoelectric acceleration sensor 1 when subjected to an external force is grasped in advance by simulation or analysis by a finite element method, and electrodes are formed only at a site where the distribution intensity is high. It may be.

  The piezoelectric acceleration sensor 1 is provided with one common ground electrode 2 as a common ground terminal for the X, Y, and Z-axis acceleration detection electrodes. The common ground electrode 2 is formed on the both-supported beam member 3 and in a region not in contact with the Y-axis acceleration detection electrode. The common ground electrode 2 can be an electrode for the X, Y, and Z axis acceleration detection electrodes. The common ground electrode 2 is also an electrode formed by the same formation method as the acceleration detection electrode described above (for example, Ag (silver) paste coating / firing method, metal vapor deposition method).

  In the piezoelectric acceleration sensor 1, the outer frame member 9, the both cantilever members 3, the first cantilever member 4 and the second cantilever member 5 are collectively referred to as a piezoelectric body 10. Here, a configuration example of the piezoelectric body 10 will be described with reference to FIG. FIG. 2A is a front view of the piezoelectric body 10 viewed from above the Z axis. FIG. 2B shows an example of a cross-sectional view taken along the line A-A ′ of the piezoelectric body 10 shown in FIG. In the following description, the acceleration detection electrodes 6 to 8 and the common ground electrode 2 formed on the piezoelectric body 10 are omitted.

  As is clear from FIGS. 2A and 2B, the piezoelectric body 10 has a uniform Z-axis dimension (is in a flush state) at all locations. For this reason, when manufacturing the piezoelectric body 10, various methods, such as a powder metallurgy method, a casting method, or a lamination method, can be adopted, and there is an advantage that the productivity is excellent.

  Moreover, since all the parts of the piezoelectric body 10 are integrally formed, the strength of the piezoelectric body 10 can be increased. Furthermore, the conventional bimorph type piezoelectric acceleration sensor requires assembly work of components, but the piezoelectric body 10 according to the present invention does not require assembly work, and can be expected to be downsized. Further, by using the piezoelectric body 10 according to the present invention, the piezoelectric acceleration sensor 1 having high dimensional accuracy can be formed.

  Next, the respective polarization directions in the beam members 3 to 5 will be described with reference to FIG. In the piezoelectric acceleration sensor 1, polarization processing is performed so that the polarization direction (Y axis detection) 13 of the both-end supported beam member 3 is parallel to the Y axis direction. In addition, the first cantilever member 4 is polarized so that the polarization direction (Z-axis detection) 11 is parallel to the Z-axis direction. Further, the polarization process is performed such that the polarization direction (X-axis detection) 12 of the second cantilever member 5 is parallel to the X-axis direction. As a result, the polarization directions polarized by the respective beam members 3 to 5 are orthogonal to each other. Due to the different polarization directions in this way, the piezoelectric acceleration sensor 1 can detect the accelerations of the three axes of the X, Y, and Z axes with only one sensor element.

  Here, the polarization treatment of the piezoelectric ceramic and the piezoelectric body will be briefly described. Piezoelectric ceramics refer to polycrystalline ferroelectrics that are baked and hardened at high temperatures, and polycrystalline grains exist inside. The individual crystal grains of the piezoelectric ceramic in the process after the sintering is finished have a polarization direction in an arbitrary direction for each domain. For this reason, the dipole moment as a whole is zero. That is, since the polarization direction is not uniform, the piezoelectricity is not exhibited even if an external force is applied. Therefore, by forming an electrode pair for polarization processing on a surface orthogonal to a desired polarization direction and applying a high voltage to the electrode pair, the polarization direction is uniformly aligned. As a result, even if the voltage is removed, the polarization direction does not return to the initial state (a state in which any direction is directed to each domain) again. This alignment of the direction of polarization is called polarization processing. By performing the polarization process, the piezoelectric phenomenon and the inverse piezoelectric phenomenon can be used.

  Here, an example of the manufacturing process of the piezoelectric acceleration sensor 1 will be described with reference to the flowchart of FIG.

(Raw material blending process)
The molar ratio of the target material and the amount of the additive are converted into the weight ratio of the raw material, and the weighing is prepared (step S1). The piezoelectric ceramic employed in the piezoelectric acceleration sensor 1 has a basic composition of Pb (Ti, Zr) O ₃ .

(Mixing and grinding process)
Next, the weighed and mixed raw material and pure water are poured into the ball mill. Further, the material is mixed and pulverized by rotating the ball mill for a desired time while adding alumina balls and the like for mixing and pulverizing in the ball mill (step S2).

(Drying process)
After completion of the mixing and grinding step, the obtained slurry is dried using equipment such as a spray dryer (step S3).

(Preliminary firing process)
Then, in order to cause the mixed and pulverized raw material powder to undergo a solid-phase reaction, temporary baking is performed under conditions of 700 ° C. to 900 ° C. (step S4).

(Crushing process)
The raw material at the stage where the pre-baking is finished becomes a massive body by a solid phase reaction. In the subsequent molding process (step S8 described later), it is necessary to fill the mold with powder. For this reason, the same process as step S2 is performed again, and pulverization is performed so that the raw material has a desired particle size (step S5).

(Binder mixing process)
Then, a binder such as PVA (polyvinyl alcohol) is added and kneaded in the pulverization step of Step S5, and the binder is dispersed and homogenized in the raw material powder (Step S6). By dispersing and homogenizing the binder in the raw material powder, the binding power of the raw material powder is increased. For this reason, it becomes possible to hold | maintain the shape of the molded object obtained at a later shaping | molding process (after-mentioned step S8). In addition, the crushing process of step S5 and the binder mixing process of step S6 are processes performed at the same timing.

(Granulation process)
And in order to obtain the powder which has a moderate particle diameter with good fluidity, it granulates using a spray dryer etc. (Step S7).

(Molding process)
Then, the granulated powder is molded into a target shape (the shape of the piezoelectric body 10 (see FIG. 2)) (step S8).

(Binder removal process)
Generally, by using a flow sintering furnace, the binder removal step and the sintering step are performed consistently. First, binder removal is performed under conditions of 300 ° C. to 500 ° C. (step S9).

(Sintering process)
Then, sintering is performed under the condition of reaching 1100 ° C. to 1300 ° C. at a desired temperature raising speed (step S10).

(Polarization electrode formation process)
Then, an electrode for performing polarization processing of the piezoelectric ceramic is formed on the piezoelectric body 10 (step S11). In order to enable the piezoelectric acceleration sensor 1 to perform three-axis detection, the polarization axes are orthogonal to each other with respect to the cantilever member 3, the first cantilever member 4, and the second cantilever member 5. Polarization processing is performed. At this time, it is desirable to perform electrode formation by vapor deposition films, such as Ag (silver) and Al (aluminum), formed by means such as vacuum vapor deposition on the surfaces of the beam members 3 to 5 orthogonal to the polarization axis.

(Polarization process)
After electrode formation is performed to polarize the piezoelectric ceramic, a direct current electric field is applied in insulating oil at around 100 ° C. to align the direction of spontaneous polarization (step S12). Piezoelectric ceramics are imparted with piezoelectricity by the polarization treatment step. In the piezoelectric acceleration sensor 1, in order to enable three-axis detection, the polarization direction 13 of the cantilever member 3 is in the Y-axis direction, and the polarization direction 11 of the first cantilever member 4 is in the Z-axis direction. The polarization process is performed so that the polarization direction 12 of the second cantilever member 5 is in the X-axis direction, that is, the polarization axes are orthogonal to each other.

(Polarization electrode peeling process)
The electrode pair formed in the polarization electrode forming step in step S11 is used for polarizing the piezoelectric ceramic. By the way, even if it is attempted to detect the acceleration applied to the X, Y, and Z axes using this electrode pair, the piezoelectric characteristics are offset by the relationship between the bending direction of the beam member and the polarization axis, and the acceleration is detected. Therefore, it is necessary to separately form an electrode for detecting acceleration. Therefore, the electrode for polarization treatment must be peeled off, but the electrode formed by the vapor deposition film such as Ag (silver) or Al (aluminum) formed in step S11 is easy and easy by using a mixed acid of phosphoric acid and nitric acid It can be surely dissolved and removed (step S13).

(Acceleration detection electrode process and common earth electrode formation process)
After the polarization electrode pair is peeled off in step S13, the acceleration detection electrode and the common ground electrode are formed in the same process as step S11 (polarization electrode forming process) (step S14). At this time, the distribution of the distortion, displacement, and generated voltage of the piezoelectric acceleration sensor 1 when receiving an external force is grasped in advance by an analysis such as a simulation or a finite element method. And it becomes possible to obtain efficiently the piezoelectric acceleration sensor 1 with a high detection sensitivity by forming an electrode only in a site | part with high distribution intensity | strength.

  Note that the electrode formed here needs to have high reliability as a component of a product. That is, it is desirable to provide a high peel strength between the piezoelectric element body and the electrode so that no peeling failure or the like occurs during the use of the piezoelectric acceleration sensor over time. In general, a means for forming an electrode by applying an Ag paste using a method such as a screen printing method and then firing it at 500 ° C. to 650 ° C. is economical. In this case, the polarization is depolarized due to the temperature rise during electrode formation (firing), so that it is not practical in manufacturing the piezoelectric acceleration sensor of the present invention. Therefore, in the formation of the acceleration detection electrode of the piezoelectric acceleration sensor according to the present invention, a multi-layer electrode having a high bonding strength with the piezoelectric ceramic material in which a gold or silver electrode is formed on a base such as Ni or Cr is deposited. It is desirable to form by sputtering.

  After passing through the above steps, a piezoelectric acceleration sensor 1 capable of detecting triaxial acceleration is completed by performing appearance inspection and performance inspection. In addition, the manufacturing process mentioned above is only an example. If the final configuration and the obtained functions and effects are the same as those of the piezoelectric acceleration sensor 1 according to the present embodiment, various processes such as a laminating method and a casting method can be employed.

  Next, the behavior of the piezoelectric acceleration sensor 1 when the acceleration is applied to the piezoelectric body 10 in the X, Y, and Z axis directions will be described with reference to FIG. FIG. 5 schematically shows the behavior of the piezoelectric acceleration sensor 1 when acceleration is applied in the X, Y, and Z axis directions, respectively.

(When acceleration occurs in the X-axis direction)
As shown in FIG. 5A, when the piezoelectric body 10 is accelerated in the X-axis direction, the first cantilever member 4 and the second cantilever member 5 are bent in the X-axis direction. Is shown. FIG. 5D is an example of a transmission diagram when the piezoelectric body 10 is viewed from the Y-axis direction. The second cantilever member 5 is polarized in the X-axis direction, and its width dimension is set smaller than the width dimension of the first cantilever member 4. For this reason, the degree of bending of the second cantilever member 5 increases. That is, it can be positioned as a beam member suitable for detecting the acceleration with respect to the X axis.

(When acceleration occurs in the Y-axis direction)
FIG. 5B shows that when the piezoelectric body 10 is accelerated in the Y-axis direction, the both-support beam member 3 is bent in the Y-axis direction. FIG. 5E is an example of a transmission diagram when the piezoelectric body 10 is viewed from the Y-axis direction.
At this time, both the cantilever members 3 are polarized in the Y-axis direction, and the weight components of the first cantilever member 4 and the second cantilever member 5 function as a weight. Will be greatly bent. For this reason, it can be positioned as a beam member suitable for detecting the acceleration with respect to the Y axis.

(When acceleration occurs in the Z-axis direction)
As shown in FIG. 5C, when the piezoelectric body 10 is accelerated in the Z-axis direction, the both-supported beam member 3 is bent in the Z-axis direction, and the first cantilever member 4 and the second It is shown that the cantilever member 5 is bent so as to be twisted. FIG. 5F is an example of a transmission diagram when the piezoelectric body 10 is viewed from the Y-axis direction. At this time, since the first cantilever member 4 is polarized in the Z-axis direction and is set to be heavier than the second cantilever member 5, a large inertial force is generated. The degree of bending increases to work. Therefore, it can be positioned as a beam member suitable for detecting the acceleration with respect to the Z axis.

  The operation example described above shows an example where the piezoelectric body 10 is accelerated in any one of the X, Y, and Z axes. The piezoelectric acceleration sensor 1 detects acceleration in the Y-axis direction (refer to the Y-axis direction in FIG. 1) by the both-supported beam member 3 formed on the piezoelectric body 10, and the Z-axis direction by the first cantilever beam member 4. The acceleration in the X-axis direction (see the X-axis direction in FIG. 1) can be detected by the second cantilever member 5 (see the Z-axis direction in FIG. 1). Then, these three-axis accelerations are detected in a complex manner, and single-axis accelerations are calculated. By this calculation processing, not only the acceleration about a single axis of the X, Y, and Z axes can be detected, but also the acceleration in all directions can be detected. Even if acceleration occurs in the direction opposite to the X, Y, and Z axis directions described above, the beam member is similarly deformed. Further, even if the deformation amount of the beam member varies depending on the direction in which the acceleration occurs, the calculation process may be performed in consideration of the different deformation amount.

  The piezoelectric acceleration sensor 1 according to this embodiment includes an outer frame member 9, a cantilever member 3 for detecting acceleration, a first cantilever member 4, and a second cantilever member 5 including piezoelectric ceramics. As a monomorph type structure integrally formed by the above. For this reason, it can be set as a very simple structure. Moreover, the piezoelectric acceleration sensor 1 can be created with a processing accuracy of several tens of microns. For this reason, effects such as simplification of the design of the piezoelectric acceleration sensor 1, miniaturization of elements, and cost reduction can be obtained. Moreover, since each beam member 3-5 is formed in the column shape, it is excellent in intensity | strength, and there exists an effect that the highly reliable piezoelectric acceleration sensor 1 is obtained.

  In addition, polarization processing is performed so that the polarization axes of both the cantilever member 3, the first cantilever member 4, and the second cantilever member 5 are orthogonal to each other. For this reason, it is possible to detect accelerations of a plurality of axes by using only one piezoelectric acceleration sensor 1.

  Further, when an external force is applied to the piezoelectric acceleration sensor 1, the most bent portion of each of the cantilever members and the plurality of cantilever members, that is, the portion where the greatest stress is generated is grasped in advance. In addition, by forming an acceleration detection electrode having a specific shape and area, a highly sensitive piezoelectric acceleration sensor can be easily obtained.

  Next, a piezoelectric acceleration sensor 20 according to a second embodiment of the present invention will be described with reference to FIGS. This embodiment will be described as an example applied to the piezoelectric acceleration sensor 20 having a so-called monomorph type structure integrally formed of piezoelectric ceramics.

  First, an external configuration example of the piezoelectric acceleration sensor 20 will be described with reference to FIG. FIG. 6A shows a perspective view of the piezoelectric acceleration sensor 20. In the piezoelectric acceleration sensor 20, the XY plane of the X, Y, and Z axes in FIG. FIG. 6B shows an example of the piezoelectric acceleration sensor 20 viewed from the front from above the Z axis. FIG. 6C shows an example of a cross-sectional view taken along line B-B ′ of the piezoelectric acceleration sensor 20 shown in FIG. The outer frame member 29 corresponding to the outer frame of the piezoelectric acceleration sensor 20 is formed in a rectangular shape (in this example, a square) as a “closed shape”. The outer frame member 29 is not a member for detecting acceleration, but is a member that holds the both cantilever members 3 in which the first cantilever member 4 and the second cantilever member 5 (not shown) are formed. When the piezoelectric acceleration sensor 20 shown in FIG. 6A is mounted on an electronic device or the like, a lid member 21 that protects against dust or dust is attached to the upper and lower XY planes.

  Next, an external configuration example of the piezoelectric acceleration sensor 20 with the lid member 21 removed will be described with reference to FIG. Note that the common ground electrode 2, the both cantilever members 3, the first cantilever member 4, and the second cantilever member 5 of the piezoelectric acceleration sensor 20 have the same configuration as the piezoelectric acceleration sensor 1 already described. Therefore, detailed description is omitted. Further, since the X-axis acceleration detection electrode 6, the Y-axis acceleration detection electrode 7, and the Z-axis acceleration detection electrode 8 have the same configuration as that of the piezoelectric acceleration sensor 1 already described, detailed description thereof is omitted.

  FIG. 7A is a perspective view of the piezoelectric acceleration sensor 20 with the lid member 21 removed. Here, in the piezoelectric acceleration sensor 20, the outer frame member 29, the both cantilever members 3, the first cantilever member 4, and the second cantilever member 5 are collectively referred to as a piezoelectric body 30. FIG. 7B is a view of only the piezoelectric body 30 of the piezoelectric acceleration sensor 20 shown in FIG. FIG. 7C shows an example of a cross-sectional view taken along line C-C ′ in FIG. The piezoelectric acceleration sensor 20 in the present embodiment is different from the structure in the first embodiment in that the thickness dimension T1 of the outer frame member 29 is larger than the thickness dimension T2 of the beam members 3 to 5. ing. The piezoelectric acceleration sensor 20 according to the second embodiment is also different from the structure of the first embodiment in that the lid member 21 is attached to the upper and lower surfaces in the Z-axis direction.

  The relationship between the thickness dimensions T1 and T2 may be set from the amplitude value if the applied acceleration and the maximum value of the strain generated in the piezoelectric body due to the acceleration are known, for example. Therefore, the piezoelectric acceleration sensor 1 according to the first embodiment described above can be easily produced by various manufacturing processes. Further, by attaching the lid member 21, even if the lid member 21 is mounted on the mounting board in this state, it is possible to prevent each beam member from interfering with the mounting board or the like when the sensor is driven.

  In addition, since the outer frame member 29 has a “closed shape”, a highly airtight structure can be easily obtained by applying a simple operation of attaching the lid member 21 to the piezoelectric acceleration sensor 20. For this reason, it becomes possible to block the entry of dust and dust from the outside. As a result, the piezoelectric acceleration sensor 20 can be used in various environments while maintaining high reliability.

  In addition, when affixing the lid member 21 to the piezoelectric body 30, it is necessary to prevent the beam members 3 to 5 from interfering with the lid member 21 when the beam members 3 to 5 are bent by an external force. For this reason, a level | step difference is produced in the boundary part of the outer frame member 29 and each beam member 3-5. Then, by forming a minute gap between the outer frame member 29 and each of the beam members 3 to 5, problems such as contact between the lid member 21 and the beam members 3 to 5 can be reduced.

  The piezoelectric acceleration sensor 20 according to this embodiment is different from the first embodiment in that the lid member 21 is attached to the upper and lower surfaces of the piezoelectric body 30. The piezoelectric acceleration sensor 20 has the same functions and effects as the piezoelectric acceleration sensor 1 according to the first embodiment described above. Furthermore, by attaching the lid member 21, it is possible to block dust and dust from entering from the outside. For this reason, there is an effect that sensing can be performed in more detail without being affected by external dust or dust. The mounting surface of the piezoelectric body 30 may be used in place of the lid member 21 so that the lid member 21 is attached to only one surface of the piezoelectric body 30.

  The piezoelectric acceleration sensors according to the first and second embodiments described above have a monomorph structure integrally formed of piezoelectric ceramics, and have a function of detecting triaxial acceleration. The beam members 3 to 5 can detect accelerations in the X, Y, and Z axis directions, respectively. Then, by calculating the detected triaxial acceleration, it is possible to detect not only the acceleration about the single axes of the X, Y, and Z axes, but also the acceleration in all directions. For this reason, effects such as simplification of the design of the piezoelectric acceleration sensor, miniaturization of elements, and cost reduction can be obtained. Moreover, since each beam member 3-5 is excellent in intensity | strength from being formed in columnar shape, there exists an effect that a highly reliable piezoelectric acceleration sensor is obtained.

  Further, the polarization treatment is performed so that the both cantilever members and the polarization axes of the plurality of cantilever members are orthogonal to each other. For this reason, there is an effect that it is possible to detect accelerations of a plurality of axes by one piezoelectric acceleration sensor. In addition, an acceleration detection electrode having a specific shape and area is formed after grasping in advance the portion of the beam member where the stress is the greatest. This has an effect that a highly sensitive piezoelectric acceleration sensor can be easily obtained.

  The piezoelectric acceleration sensor according to the present invention is not limited to the first and second embodiments described above. Various shapes can be changed without departing from the essence. For example, the mounting direction of the piezoelectric acceleration sensor according to the present invention is such that the XY plane is the mounting plane in the X, Y, and Z axes in FIG. 1, but the XZ plane or YZ plane is the same. You may make it be a mounting surface. Even when the mounting surface is the XZ plane or the YZ plane, the polarization direction of each beam member, the formation position, shape, area, etc. of the acceleration detection electrode should be set so as to satisfy the desired conditions. Thus, functions and effects similar to those of the first and second embodiments described above can be obtained.

  In addition, at least one of the electrode pairs formed as the electrode for polarization processing needs to be peeled off, but the other electrode can be continuously used as an acceleration detection electrode. Therefore, in step S13 of FIG. 4, only one polarization processing electrode is peeled from the polarization processing electrode pair formed on each beam member. Thereafter, in step S14, only the common ground electrode may be formed without forming the acceleration detection electrode on each beam member.

  In the first and second embodiments described above, the piezoelectric body is rectangular (square). However, the piezoelectric body is not limited to this shape, and may be rectangular, polygonal, or rounded. Functions and effects similar to those of the embodiment can be obtained.

  In the first and second embodiments, the first cantilever member 4 and the second cantilever member 5 are configured to have different width dimensions, but are limited to such shapes. However, it can be appropriately modified depending on the required conditions. This is because, when uniform acceleration is applied to the X, Y and Z axes, both the dimension setting of each beam member and the electrode formation setting are set so that uniform acceleration can be detected in all beam members, or This is because setting one of them is an important requirement.

  Here, a modified example of the cantilever member formed on the both-end supported beam member constituting the piezoelectric body will be described with reference to FIG. FIG. 8A is a diagram illustrating an example of the piezoelectric body 40 in which the cantilever member is deformed. A both-end supporting beam member 43 linearly connected between two points of the outer frame member 44 formed in a rectangular shape is provided. The both cantilever members 43 are formed with a first cantilever member 41 and a second cantilever member 42 in different directions. The ends where the first cantilever member 41 and the second cantilever member 42 are connected are at different positions on the both cantilever members 43. FIG. 8B is a diagram illustrating an example of the piezoelectric body 50 in which the cantilever member is deformed. A both-end supporting beam member 53 linearly connected between two points of the outer frame member 54 formed in a rectangular shape is provided. The both cantilever members 53 are formed with a first cantilever member 51 and a second cantilever member 52 in different directions. However, the end portion to which the first cantilever member 51 and the second cantilever member 52 are connected is at the same position of the both cantilever members 53.

  As described above, the first and second embodiments described above can be performed even when the direction in which the first cantilever member and the second cantilever member are connected is changed or the connection position with respect to the both cantilever members is changed. Functions and effects similar to those of the acceleration sensor according to the example can be obtained. Further, the length dimension of the beam member may be changed, or the inertial force or the like resulting from the weight distribution may be changed by changing the volume condition of the beam member. Thus, it goes without saying that various modifications can be adopted as the shape of the beam member.

1 is a perspective view showing a configuration example of a piezoelectric acceleration sensor according to a first embodiment example of the present invention. It is explanatory drawing which showed the structural example of the piezoelectric material which concerns on the 1st Example of this invention. It is explanatory drawing which showed the example of the beam member which concerns on the 1st Example of this invention. It is the flowchart which showed the example of the manufacturing process of the piezoelectric acceleration sensor which concerns on the 1st Example of this invention. It is explanatory drawing which showed the example of the bending of the piezoelectric material which concerns on the 1st Example of this invention. It is explanatory drawing which showed the structural example of the piezoelectric acceleration sensor which concerns on the 2nd Example of this invention. It is the perspective view which showed the structural example of the piezoelectric acceleration sensor which concerns on the 2nd Example of this invention. It is explanatory drawing which showed the structural example of the piezoelectric material which concerns on the other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric acceleration sensor, 2 ... Common earth electrode, 3 ... Both-supported beam member, 4 ... 1st cantilever member, 5 ... 2nd cantilever member, 6 ... X-axis acceleration detection electrode, 7 ... Y Axis acceleration detection electrode, 8 ... Z-axis acceleration detection electrode, 9 ... outer frame member, 10 ... piezoelectric body, 11 ... polarization direction of first cantilever member (Z-axis detection), 12 ... second cantilever beam Polarization direction of member (X-axis detection), 13 ... Polarization direction of both-supported beam member (Y-axis detection), 20 ... Piezoelectric acceleration sensor, 21 ... Lid member, 29 ... Outer frame member, 30, 40, 50 ... Piezoelectric body

Claims (3)

In a piezoelectric acceleration sensor formed using a piezoelectric ceramic material,
An outer frame member having a closed shape;
A both-end supporting beam member connected between two points of the outer frame member;
A piezoelectric acceleration sensor comprising: a plurality of cantilever members connected perpendicularly to the both cantilever members. The piezoelectric acceleration sensor according to claim 1,
The piezoelectric acceleration sensor, wherein the both-supported beam member and the plurality of cantilevered members are polarized in directions orthogonal to each other. The piezoelectric acceleration sensor according to claim 1 or 2,
An acceleration detection electrode is formed on the both cantilever members and the plurality of cantilever members.

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