Vibration Sensors

Abstract

To provide a vibration sensor which hardly causes noise even when the support member of a piezoelectric element is strained.SOLUTION: A vibration sensor 10 comprises a base 20, a pole 30 and a vibrator 40. The pole 30 includes a large-diameter part 32 fixed to the base 20 and extending upward and a small-diameter part 36 extending upward from the large-diameter part 32. A support face 34 is formed between the large-diameter part 32 and the small-diameter part 36. The vibrator 40 includes a piezoelectric element 42 and a support plate 44 for supporting the piezoelectric element 42. Each of the piezoelectric element 42 and the support plate 44 has a disk shape with center holes 422, 442 formed therein. The inner circumferential part 424 of the piezoelectric element 42 and the inner circumferential part 444 of the support plate 44 are pressed against a support face 34.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a vibration sensor using a piezoelectric element. [Background technology]

[0002] For example, Patent Document 1 discloses an acceleration sensor (vibration sensor) that uses a piezoelectric element.

[0003] Referring to FIG. 10, the vibration sensor 90 of Patent Document 1 includes a piezoelectric vibrator 92 made of a piezoelectric element, a metal plate 94, a case 982, and a substrate 984. The substrate 984 is fixed on a bottom surface 988 inside the case 982 in the vertical direction, and thereby constitutes a support member 98 together with the case 982. The metal plate 94 is attached to the support member 98 so as to extend along a predetermined direction perpendicular to the vertical direction. More specifically, both ends of the metal plate 94 in the predetermined direction are fixed on the substrate 984. On the other hand, an intermediate portion of the metal plate 94 in the predetermined direction is located above the bottom surface 988 and extends along the bottom surface 988. The piezoelectric vibrator 92 is fixed to the intermediate portion of the metal plate 94 in the predetermined direction. That is, the piezoelectric vibrator 92 is supported by the support member 98 in a double-supported beam shape.

[0004] An electrode 924 is provided on the piezoelectric vibrator 92. When acceleration is applied to the support member 98, the piezoelectric vibrator 92 vibrates and bends in the vertical direction in response to the vertical component of the acceleration, and a voltage corresponding to the bending is generated between the metal plate 94 and the electrode 924. By measuring the voltage generated between the metal plate 94 and the electrode 924, the acceleration applied to the support member 98 can be detected. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2011 / 043219 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the support structure of Patent Document 1, when the support member 98 is pulled in both horizontal directions perpendicular to the vertical direction, the support member 98 may be distorted, which may cause the metal plate 94 to bend in the vertical direction. In this case, a noise voltage not caused by acceleration is generated between the metal plate 94 and the electrode 924, making it impossible to detect correct acceleration. In other words, according to the vibration sensor of Patent Document 1, there is a risk that noise may be generated in the measured voltage due to distortion of the support member of the piezoelectric element.

[0007] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a vibration sensor that is less susceptible to noise even if a support member for a piezoelectric element is distorted. [Means for solving the problem]

[0008] The present invention provides a first vibration sensor, A vibration sensor including a base, a pole, and a vibrator, The pole has a large diameter portion, a small diameter portion, and a support surface, the large diameter portion is fixed to the base and extends upward from the base in a vertical direction, the small diameter portion extends upward from an upper end of the large diameter portion, In a horizontal plane perpendicular to the up-down direction, the small diameter portion is located inside the large diameter portion, the support surface is an upper surface of the large diameter portion and is located between an outer periphery of the large diameter portion and an outer periphery of the small diameter portion in the horizontal plane, The vibrator includes a piezoelectric element and a support plate. Each of the piezoelectric element and the support plate has a circular shape with a central hole formed in the horizontal plane, The piezoelectric element is supported by the support plate, the small diameter portion passes through the central hole of the piezoelectric element and the central hole of the support plate in the vertical direction, The inner periphery of the piezoelectric element in the horizontal direction and the inner periphery of the support plate in the horizontal direction are pressed against the support surface. A vibration sensor is provided.

[0009] The present invention also provides a second vibration sensor, the first vibration sensor comprising: The vibration sensor includes a nut, the reduced diameter portion is at least partially threaded; The nut is threaded onto the small diameter portion, The inner periphery of the piezoelectric element and the inner periphery of the support plate are sandwiched between the nut and the support surface. A vibration sensor is provided.

[0010] Furthermore, the present invention provides a third vibration sensor, which is the first or second vibration sensor, The vibration sensor is a non-resonant sensor. A vibration sensor is provided.

[0011] Furthermore, the present invention provides a fourth vibration sensor, which is any one of the first to third vibration sensors, The distance in the vertical direction between the support surface and the base is 0.25 to 2 times the outer diameter of the piezoelectric element in the horizontal plane. A vibration sensor is provided.

[0012] Further, the present invention provides a fifth vibration sensor, which is any one of the first to fourth vibration sensors, The large diameter portion has a cylindrical shape. A vibration sensor is provided.

[0013] Further, the present invention provides a sixth vibration sensor, which is the fifth vibration sensor, The outer diameter of the piezoelectric element in the horizontal plane is larger than the outer diameter of the large diameter portion in the horizontal plane and is within 5 times the outer diameter of the large diameter portion. A vibration sensor is provided.

[0014] Further, the present invention provides a seventh vibration sensor as the fifth or sixth vibration sensor, The lower end surface of the nut has a ring shape in the horizontal plane, The outer diameter of the lower end surface of the nut in the horizontal plane is equal to the outer diameter of the large diameter portion in the horizontal plane. A vibration sensor is provided.

[0015] Furthermore, the present invention provides an eighth vibration sensor, which is any one of the first to seventh vibration sensors, The small diameter portion has a cylindrical shape. A vibration sensor is provided.

[0016] Furthermore, the present invention provides a ninth vibration sensor, which is any one of the first to eighth vibration sensors, The vibrator is a unimorph type piezoelectric vibrator. A vibration sensor is provided.

[0017] Further, the present invention provides a tenth vibration sensor, which is any one of the first to eighth vibration sensors, The vibrator is a bimorph type piezoelectric vibrator. A vibration sensor is provided.

[0018] Further, the present invention provides an eleventh vibration sensor, which is any one of the first to tenth vibration sensors, The vibrator includes a weight. A vibration sensor is provided.

[0019] The present invention also provides a measuring instrument including any one of the first to eleventh vibration sensors as a first measuring instrument. Effect of the Invention

[0020] According to the present invention, the vibrator having a piezoelectric element is supported by the support surface of the pole fixed to the base and extending upward, so that distortion of the base is unlikely to be transmitted to the vibrator. In addition, the vibrator of the present invention has a disk shape with a central hole, and the inner periphery of the vibrator is pressed toward the support surface. With this structure, even if the piezoelectric element is pulled in a first horizontal direction parallel to the horizontal plane due to distortion of the base, the piezoelectric element is compressed in a second horizontal direction parallel to the horizontal plane and perpendicular to the first horizontal direction. As a result, noise that may be generated due to distortion of the base is offset. As described above, according to the present invention, it is possible to provide a vibration sensor that is unlikely to generate noise even if the support member (base and pole) of the piezoelectric element is distorted. [Brief description of the drawings]

[0021] [Figure 1] 1 is a perspective view showing a vibration sensor according to an embodiment of the present invention; [Diagram 2] 2 is a top view showing the vibration sensor of FIG 1. The outlines of the hidden large diameter portion of the pole and the hidden lower surface of the nut are drawn with dashed lines. [Diagram 3] 3 is a cross-sectional view of the vibration sensor taken along line III-III in Fig. 2. The boundary between the base and the pole, the boundary between the large diameter portion and the small diameter portion of the pole, and the boundary between the small diameter portion and the upper end of the pole are drawn with dashed lines. [Figure 4] 2 is an exploded perspective view showing the vibration sensor of FIG 1. The contour between the inner periphery and the outer periphery of the piezoelectric element is drawn by a dashed line. [Diagram 5] Fig. 5(A) is a diagram showing a typical deflection caused by vibration of the vibrator of the vibration sensor of the present embodiment, and Fig. 5(B) is a diagram showing a typical deflection caused by vibration of the vibrator of the vibration sensor of the comparative example. [Figure 6] FIG. 2 is a perspective view showing a modified example of the vibration sensor of FIG. [Figure 7] 2 is a partially cutaway perspective view showing a part of a measuring device including another modified example of the vibration sensor of FIG. 1. [Figure 8] FIG. 8 is a diagram showing a measurement result by the first embodiment of the measuring device of FIG. 7. [Figure 9] FIG. 8 is a diagram showing a measurement result by the second embodiment of the measuring device of FIG. 7. [Figure 10] FIG. 1 is a cross-sectional view showing the acceleration sensor of Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 1, a vibration sensor 10 according to an embodiment of the present invention includes a metallic support member 12, a vibrator 40, and a nut 50. The vibrator 40 is supported by the support member 12 while being pressed against the support member 12 by the nut 50. However, the present invention is not limited to this. For example, as long as the vibrator 40 is supported by the support member 12, the nut 50 may be provided as necessary. Meanwhile, the vibration sensor 10 may include other members in addition to the above-mentioned members.

[0023] The vibration sensor 10 according to this embodiment can be used as a component of an electronic device such as a measuring device 80 (see FIG. 7). When an electronic device equipped with the vibration sensor 10 is subjected to vibration or impact, acceleration occurs in the electronic device, which causes the vibrator 40 of the vibration sensor 10 to bend. The vibration sensor 10 is a bending type sensor that converts the bending of the vibrator 40 into a voltage and outputs it. By measuring the voltage output by the vibration sensor 10, the acceleration occurring in the electronic device can be detected, and thus the applied vibration or impact can be detected.

[0024] 1 to 4, the support member 12 of this embodiment is made of metal and has high rigidity. That is, the support member 12 is not easily distorted when subjected to acceleration. Due to this structure, the vibrator 40 is likely to bend in response to acceleration. However, the material of the support member 12 is not limited to metal. For example, the support member 12 may be molded from resin as long as the support member 12 has sufficient rigidity.

[0025] The vibration sensor 10 includes a metal base 20 and a metal pole 30. In this embodiment, the base 20 and the pole 30 are each a part of the support member 12. In other words, the base 20 and the pole 30 are integrally formed with each other and fixed to each other. However, the present invention is not limited to this. As long as the pole 30 is fixed to the base 20, the base 20 and the pole 30 may be formed separately from each other.

[0026] The base 20 in this embodiment is a flat plate extending parallel to a horizontal plane (XY plane) perpendicular to the up-down direction (Z direction), and has a rectangular shape in the XY plane. However, the present invention is not limited to this, and the shape of the base 20 can be modified in various ways as necessary.

[0027] 3 and 4, the pole 30 of this embodiment has a large diameter portion 32, a support surface (upper surface) 34, a small diameter portion 36, and an upper end portion 38. The pole 30 extends linearly upward in the Z direction from the base 20 (along the +Z direction).

[0028] Specifically, the large diameter portion 32 has an upper end 324 and a lower end 322. The upper end 324 and the lower end 322 are located at both ends of the large diameter portion 32 in the Z direction. The large diameter portion 32 is fixed to the base 20 at the lower end 322, and extends straight upward from the base 20 to the upper end 324. The small diameter portion 36 has an upper end 364 and a lower end 362. The upper end 364 and the lower end 362 are located at both ends of the small diameter portion 36 in the Z direction. The small diameter portion 36 is fixed to the upper end 324 of the large diameter portion 32 at the lower end 362, and extends straight upward from the upper end 324 of the large diameter portion 32 to the upper end 364.

[0029] The pole 30 of this embodiment is provided with an upper end portion 38. The upper end portion 38 extends straight upward from the upper end 364 of the small diameter portion 36. However, the present invention is not limited to this, and the upper end portion 38 may be provided as necessary.

[0030] 2 to 4, large diameter section 32 has an outer periphery 326 in the XY plane, and small diameter section 36 has an outer periphery 366 in the XY plane. In this embodiment, large diameter section 32 has a cylindrical shape, and outer periphery 326 has a cylindrical shape. Small diameter section 36 has a cylindrical shape, and outer periphery 366 has a cylindrical shape. The position of the center point of large diameter section 32 in the XY plane and the position of the center point of small diameter section 36 in the XY plane coincide with each other.

[0031] With the above-described structure, the pole 30 is distorted in the same manner in the radial direction around the center points of the large diameter portion 32 and the small diameter portion 36 in the XY plane in response to the same force. However, the present invention is not limited to this. For example, the shape of each of the large diameter portion 32 and the small diameter portion 36 in the XY plane may be a polygon. Also, the size of each of the large diameter portion 32 and the small diameter portion 36 in the XY plane may differ depending on the position in the Z direction.

[0032] The size of the small diameter portion 36 in the XY plane is smaller than the size of the large diameter portion 32 in the XY plane. In addition, the small diameter portion 36 is located inside the large diameter portion 32 in the XY plane. With this structure, the upper surface 34 of the large diameter portion 32 is formed between the small diameter portion 36 and the large diameter portion 32. The upper surface 34 of the large diameter portion 32 is a plane parallel to the XY plane, and is located at the upper end 324 of the large diameter portion 32 in the Z direction. The upper surface 34 of the large diameter portion 32 functions as a support surface 34 that supports the vibrator 40. That is, the support surface 34 is the upper surface 34 of the large diameter portion 32, and is located between the outer periphery 326 of the large diameter portion 32 and the outer periphery 366 of the small diameter portion 36 in the XY plane.

[0033] 1, 3 and 4, the vibrator 40 includes a piezoelectric element 42 made of a piezoelectric material such as lead zirconate titanate (PZT), a metal support plate 44, and an electrode 48. The piezoelectric element 42 is uniformly polarized in the Z direction. The electrode 48 is formed by applying a conductive material such as silver paste to the upper surface (+Z side surface) of the piezoelectric element 42. The piezoelectric element 42 is supported by the support plate 44. According to this embodiment, the lower surface (-Z side surface) of the piezoelectric element 42 is firmly fixed and supported by the upper surface of the support plate 44 with a fixing agent such as a conductive adhesive. However, as long as the piezoelectric element 42 and the support plate 44 vibrate together as one vibrator 40, the method of supporting the piezoelectric element 42 is not limited to this embodiment.

[0034] Each of the piezoelectric element 42 and the support plate 44 has a disk shape. More specifically, the piezoelectric element 42 has a circular shape with a circular center hole 422 formed in the XY plane, and the support plate 44 has a circular shape with a circular center hole 442 formed in the XY plane. In this embodiment, the center hole 422 of the piezoelectric element 42 is located at the center of the piezoelectric element 42 in the XY plane, and the center hole 442 of the support plate 44 is located at the center of the support plate 44 in the XY plane. The size of the center hole 422 of the piezoelectric element 42 in the XY plane is equal to the size of the center hole 442 of the support plate 44 in the XY plane. In addition, in the vibrator 40, the position of the center point of the piezoelectric element 42 in the XY plane and the position of the center point of the support plate 44 in the XY plane coincide with each other.

[0035] With the above-described structure, when the vibrator 40 is subjected to acceleration in the Z direction, parts of the vibrator 40 at the same position in the radial direction around the center point in the XY plane vibrate in the same manner. However, the present invention is not limited to this. For example, the shape of each of the central hole 422 of the piezoelectric element 42 and the central hole 442 of the support plate 44 in the XY plane may be polygonal. Also, the size of the central hole 422 of the piezoelectric element 42 in the XY plane may be different from the size of the central hole 442 of the support plate 44 in the XY plane.

[0036] 3 and 4, the vibrator 40 is attached to the small diameter portion 36 of the pole 30. More specifically, the outer diameter of the small diameter portion 36 in the XY plane is equal to or smaller than the diameter of the central hole 422 of the piezoelectric element 42 and the central hole 442 of the support plate 44 in the XY plane. The small diameter portion 36 penetrates the central hole 422 of the piezoelectric element 42 and the central hole 442 of the support plate 44 in the Z direction, and protrudes upward beyond the upper surface of the piezoelectric element 42. The position of the center point of the small diameter portion 36 in the XY plane and the position of the center point of the vibrator 40 in the XY plane are coincident with each other. In addition, the lower surface of the vibrator 40 is in contact with the support surface 34 of the pole 30.

[0037] In this embodiment, the small diameter portion 36 of the pole 30 is at least partially formed with threads 368. Also, the nut 50 of this embodiment is formed with threads 58 that correspond to the threads 368 of the small diameter portion 36. The nut 50 is screwed onto the small diameter portion 36, thereby pressing the vibrator 40 against the support surface 34.

[0038] In detail, the piezoelectric element 42 has an inner peripheral portion 424 located around the central hole 422 in the XY plane, and an outer peripheral portion 426 located outside the inner peripheral portion 424 in the XY plane. The support plate 44 has an inner peripheral portion 444 located around the central hole 442 in the XY plane, and an outer peripheral portion 446 located outside the inner peripheral portion 444 in the XY plane.

[0039] The inner periphery 424 of the piezoelectric element 42 and the inner periphery 444 of the support plate 44 are located directly above the support surface 34. With this arrangement, the inner periphery 424 of the piezoelectric element 42 and the inner periphery 444 of the support plate 44 are sandwiched between the nut 50 and the support surface 34 and pressed against each other in the Z direction. plane The XY of the inner periphery 424 and the support plate 44 in plane The inner periphery 444 of the pole 30 is pressed against the support surface 34. On the other hand, the outer diameters of the piezoelectric element 42 and the support plate 44 in the XY plane are larger than the outer diameter of the large diameter portion 32 of the pole 30 in the XY plane. In other words, the piezoelectric element 42 protrudes from the large diameter portion 32 in the XY plane while being supported by the support plate 44.

[0040] 5(A), the center of the vibrator 40 in the XY plane is supported by the pole 30, while the portion of the vibrator 40 protruding from the pole 30 in the XY plane can vibrate in the Z direction. That is, the vibrator 40 is supported by the pole 30 so as to be able to bend in the Z direction (polarization direction).

[0041] In more detail, when the vibration sensor 10 is subjected to acceleration, the vibrator 40 is subjected to an inertial force proportional to the acceleration. For example, when acceleration in the polarization direction (Z direction) is applied to the vibration sensor 10, the part of the vibrator 40 that protrudes from the pole 30 in the XY plane is bent in the polarization direction. As a result, charges of opposite signs are generated in the electrode 48 and the support plate 44 of the vibrator 40. That is, a voltage (detection voltage VD) proportional to the acceleration is generated between the electrode 48 and the support plate 44. The generated detection voltage VD is input to an amplifier circuit (not shown) via a conductive wire (not shown). The acceleration applied to the vibration sensor 10 can be detected by measuring the voltage (output signal) amplified by the amplifier circuit.

[0042] When the frequency of the acceleration applied to the vibration sensor 10 coincides with or is close to the resonant frequency, the vibrator 40 bends significantly even if the magnitude of the acceleration is slight. In other words, the vibrator 40 bends significantly at or near the resonant frequency, thereby generating a large detection voltage VD. On the other hand, in a frequency band sufficiently lower than the resonant frequency, the vibrator 40 generates a detection voltage VD that is approximately proportional to the magnitude of the acceleration, regardless of the frequency of the acceleration. The vibration sensor 10 of this embodiment is a non-resonant sensor used in a frequency band sufficiently lower than the resonant frequency of the vibrator 40. The frequency band in which the vibration sensor 10 of this embodiment is used is a range in which a detection voltage VD within a predetermined range compared to the detection voltage VD at a reference frequency (e.g., 157 Hz) can be obtained.

[0043] As can be understood from the above description, from the viewpoint of widening the frequency band in which the vibration sensor 10 can be used, it is preferable that the resonant frequency of the vibrator 40 is high. For example, it is preferable that the resonant frequency of the vibrator 40 is three times or more the upper limit value of the frequency band in which the vibration sensor 10 is used. However, if the resonant frequency of the vibrator 40 becomes high, the detection voltage VD of the vibrator 40 tends to become small. Therefore, it is preferable that the resonant frequency of the vibrator 40 is within a predetermined range.

[0044] 3, according to this embodiment, the vibrator 40 having the piezoelectric element 42 is supported by the support surface 34 of the pole 30 that is fixed to the base 20 and extends upward, and distortion of the base 20 is unlikely to be transmitted to the vibrator 40. In other words, noise caused by distortion of the base 20 is unlikely to occur in the detection voltage VD.

[0045] In addition, the vibrator 40 of this embodiment has a disk shape with central holes 422, 442 formed therein, and the inner peripheral parts 424, 444 of the vibrator 40 are pressed against the support surface 34. With this structure, even if the piezoelectric element 42 is pulled in a first horizontal direction (e.g., X direction) parallel to the XY plane due to distortion of the base 20, the piezoelectric element 42 is compressed in a second horizontal direction (e.g., Y direction) parallel to the XY plane and perpendicular to the first horizontal direction. As a result, noise that may occur in the detection voltage VD due to distortion of the base 20 is cancelled out.

[0046] As described above, according to the present invention, it is possible to provide a vibration sensor 10 that is less susceptible to noise even if the support member 12 (base 20 and pole 30) of the piezoelectric element 42 is distorted.

[0047] 5(B), if the support plate 44 is sandwiched vertically but the piezoelectric element 42 is not sandwiched vertically, when the pole 30 is subjected to acceleration, the support plate 44 is likely to bend with a portion near the pole 30 as an inflection point. As a result, the piezoelectric element 42 is less likely to bend due to acceleration, and the detection voltage VD becomes smaller. On the other hand, referring to FIG. 5(A), according to the present invention, the piezoelectric element 42 is sandwiched vertically together with the support plate 44, so that the piezoelectric element 42 is more likely to bend due to acceleration, and the detection voltage VD becomes sufficiently large. In other words, the detection sensitivity of the vibration sensor 10 becomes higher.

[0048] 3, according to this embodiment, the piezoelectric element 42 and the support plate 44 are sandwiched between the nut 50 and the support surface 34, and are thereby pressed and fixed against the support surface 34. This structure makes it easy to increase the detection sensitivity of the vibration sensor 10. However, the present invention is not limited to this. For example, the piezoelectric element 42 and the support plate 44 may be pressed and fixed against the support surface 34 by a fastener (not shown) without using the nut 50.

[0049] 2 and 3, the nut 50 of this embodiment has a lower end surface 52. The lower end surface 52 of the nut 50 is a plane parallel to the XY plane and has a ring shape in the XY plane. The outer diameter of the lower end surface 52 of the nut 50 in the XY plane is equal to the outer diameter of the large diameter portion 32 of the pole 30 in the XY plane. With reference to FIG. 3, this structure allows the inner periphery 424 of the piezoelectric element 42 and the support plate 44 to be sandwiched with equal force between the support surface 34 and the lower end surface 52 of the nut 50. As a result, stable high detection sensitivity is obtained, and noise that may occur in the detection voltage VD can be reduced. However, the present invention is not limited to this. For example, the outer diameter of the lower end surface 52 of the nut 50 in the XY plane may be different from the outer diameter of the large diameter portion 32 of the pole 30 in the XY plane.

[0050] As described above, the support member 12 of the present embodiment is made of metal and has high rigidity. For example, if the support member 12 is made of elastic resin, the support surface 34 is easily elastically deformed, and the resonant frequency of the vibrator 40 is easily lowered. If the resonant frequency of the vibrator 40 is lowered, the frequency band in which the vibration sensor 10 can be used is narrowed. In addition, if the support member 12 is made of resin, the pole 30 is easily elastically deformed in the XY plane, and there is a risk of noise being generated in the detection voltage VD. That is, there is a risk of the detection accuracy of the vibration sensor 10 being deteriorated. In addition, if the support member 12 is made of elastic resin, the entire support member 12 functions as a damper, and there is a risk of the detection voltage VD being reduced. For the above reasons, it is preferable that the support member 12 is made of metal. However, if a sufficiently high rigidity can be obtained, the material of the support member 12 is not limited to metal.

[0051] The distance DS in the Z direction between the support surface 34 and the base 20 is preferably 0.25 times or more and 2 times or less than the outer diameter DL of the large diameter part 32 of the pole 30 in the XY plane. If the distance DS is smaller than 0.25 times the outer diameter DL, noise caused by distortion of the base 20 increases. On the other hand, if the distance DS is larger than twice the outer diameter DL, the pole 30 becomes more likely to be elastically deformed in the XY plane, and a vibration mode different from the bending mode in the Z direction is more likely to occur in the vibrator 40. As a result, the detection voltage VD may decrease and the detection accuracy may deteriorate.

[0052] If the outer diameter DP of the piezoelectric element 42 in the XY plane is equal to or smaller than the outer diameter DL of the large diameter portion 32 of the pole 30 in the XY plane, the piezoelectric element 42 does not bend. On the other hand, if the outer diameter DP is even slightly larger than the outer diameter DL, the piezoelectric element 42 bends. However, if the outer diameter DP is greater than five times the outer diameter DL, the pole 30 may be elastically deformed or a vibration mode different from the Z-direction bending mode may occur in the vibrator 40. Therefore, from the viewpoint of obtaining a sufficiently high detection voltage while suppressing noise, it is preferable that the outer diameter DP of the piezoelectric element 42 in the XY plane is larger than the outer diameter DL of the large diameter portion 32 in the XY plane and is within five times the outer diameter DL of the large diameter portion 32.

[0053] The resonant frequency of the vibrator 40 can be adjusted by changing the thickness (size in the Z direction) of the vibrator 40 in addition to the outer diameter DP of the piezoelectric element 42. Therefore, when designing the vibrator 40, the degree of freedom in design is improved by taking the thickness of the vibrator 40 into consideration.

[0054] The vibrator 40 in this embodiment is a unimorph type piezoelectric vibrator. However, the present invention is not limited to this. For example, the vibrator 40 may be a bimorph type piezoelectric vibrator.

[0055] In addition to the modifications already described, this embodiment can be modified in various ways as described below.

[0056] Comparing Fig. 6 with Fig. 1, the vibration sensor 10A according to the modified example includes a weight 60 in addition to the same base 20, pole 30, vibrator 40, and nut 50 as the vibration sensor 10. The weight 60 is fixed to the vibrator 40 by a fixing agent such as an adhesive. By providing the weight 60, the deflection of the vibrator 40 can be increased, thereby improving the detection sensitivity of the vibration sensor 10A. In this modified example, the weight 60 is fixed to the upper surface of the outer circumferential portion 426 of the piezoelectric element 42. However, the present invention is not limited to this, and the weight 60 may be attached to a required portion as necessary.

[0057] 7, a measuring device 80 is a measuring instrument equipped with a vibration sensor 10B. That is, the vibration sensor 10B according to another modified example is a component of the measuring device 80. In addition to the vibration sensor 10B, the measuring device 80 is equipped with a metal case 82 and a circuit board 84. The vibration sensor 10B and the circuit board 84 are attached inside the case 82. The circuit board 84 is mounted with various electronic components (not shown) such as an amplifier circuit (not shown).

[0058] Comparing FIG. 7 with FIG. 1, the vibration sensor 10B according to this modification has a structure slightly different from that of the vibration sensor 10, and functions in the same manner as the vibration sensor 10. In detail, the vibration sensor 10B has the same vibrator 40 and nut 50 as the vibration sensor 10, and has a support member 12B different from the support member 12 of the vibration sensor 10. The support member 12B is made of metal like the support member 12 of the vibration sensor 10, and has a base 20B different from the base 20 of the vibration sensor 10, and a pole 30 the same as that of the vibration sensor 10. That is, the vibration sensor 10B has a base 20B and a pole 30. The base 20B is press-fitted into the bottom of the case 82 and fixed to the case 82. The large diameter part 32 of the pole 30 is fixed to the base 20B and extends upward in the Z direction from the base 20B. The vibration sensor 10B has the same structure as the vibration sensor 10, except for the above-mentioned differences.

[0059] 7, the electrode 48 of the piezoelectric element 42 of the vibration sensor 10B and the lower surface of the support plate 44 are connected to an amplifier circuit (not shown) of a circuit board 84 via a conductive wire 88. A detection voltage VD (see FIG. 3) generated between the electrode 48 and the support plate 44 is input to the amplifier circuit (not shown) via the conductive wire 88. By measuring the voltage (output signal) amplified by the amplifier circuit, the acceleration received by the measuring device 80 can be detected, and thus vibrations and impacts applied to the measuring device 80 can be detected.

[0060] The case 82 in this modification is made of a material with high rigidity that is hardly distorted by expected acceleration. In addition, even if the case 82 is pulled in a direction parallel to the XY plane and distorted, the vibration sensor 10B is hardly affected by this distortion. According to this modification, a measuring device 80 that can be miniaturized and is resistant to noise can be obtained. EXAMPLES

[0061] The vibration sensor according to the present invention will now be described with reference to specific examples.

[0062] A first and second embodiment of the measuring device 80 shown in FIG. 7 were fabricated, and the sensitivity to noise and acceleration when the base 20B was distorted was measured. In the first and second embodiments, the outer diameter DL (see FIG. 3) of the large diameter portion 32 was 4 mm, and the distance DS (see FIG. 3) between the support surface 34 (see FIG. 3) and the base 20B was 2 mm. The outer diameter of the small diameter portion 36, the diameter of the central hole 422 (see FIG. 3) of the piezoelectric element 42, and the diameter of the central hole 442 (see FIG. 3) of the support plate 44 were all 2 mm. The thickness (size in the Z direction) of the piezoelectric element 42 was 0.2 mm, and the thickness (size in the Z direction) of the support plate 44 was 0.4 mm.

[0063] In the first embodiment, the outer diameter DP (see FIG. 3) of the piezoelectric element 42 was set to 6 mm, and the outer diameter DP of the support plate 44 was changed by 1 mm increments within a range between 6 mm and 10 mm, and the output signal of the amplifier circuit (not shown) was measured. At this time, the noise when the base 20B was pulled to both sides in the horizontal direction and distorted, and the sensitivity to the acceleration applied to the measurement device 80 were measured. The measurement results are shown in FIG. 8. Similarly, in the second embodiment, the outer diameter DP of the piezoelectric element 42 and the outer diameter DP of the support plate 44 were set to be equal, and the output signal of the amplifier circuit was measured by changing the outer diameter DP by 1 mm increments within a range between 6 mm and 10 mm. At this time, the noise when the base 20B was pulled to both sides in the horizontal direction and distorted, and the sensitivity to the acceleration applied to the measurement device 80 were measured. The measurement results are shown in FIG. 9.

[0064] As can be seen from Fig. 8 and Fig. 9, the vibration sensor 10B of the first and second embodiments has high sensitivity to acceleration and a sufficiently low noise level. In particular, by making the outer diameter DP (see Fig. 3) of the support plate 44 and the piezoelectric element 42 larger than the distance DS (see Fig. 3) between the support surface 34 (see Fig. 3) and the base 20B, it is possible to improve the sensitivity to acceleration and reduce the noise level. However, if the outer diameter DP (see Fig. 3) of the support plate 44 and the piezoelectric element 42 is increased, the resonance frequency decreases. Therefore, it is preferable that the outer diameter DP of the support plate 44 and the piezoelectric element 42 does not exceed 5 times the distance DS between the support surface 34 and the base 20B. [Explanation of symbols]

[0065] 10,10A,10B Vibration Sensor 12, 12B Support member 20,20B Base 30 Paul 32 Large diameter section 322 Bottom end 324 Top 326 Circumference 34 Support surface (top surface) 36 Small diameter section 362 bottom end 364 Top 366 Circumference 368 Screw 38 Upper end 40 Transducers 42 Piezoelectric element 422 Center hole 424 Inner circumference 426 Outer periphery 44 Support plate 442 Center hole 444 Inner circumference 446 Outer periphery 48 electrode 50 Nut 52 Lower end surface 58 Screw 60 weight 80 Measuring Equipment 82 cases 84 Circuit Board 88 Conductive Wire

Claims

1. A vibration sensor including a metal base, a metal pole, and a vibrator, the vibration sensor is a non-resonant sensor, The pole has a large diameter portion, a small diameter portion, and a support surface, the large diameter portion is fixed to the base and extends upward from the base in a vertical direction, the small diameter portion extends upward from an upper end of the large diameter portion, In a horizontal plane perpendicular to the up-down direction, the small diameter portion is located inside the large diameter portion, the support surface is an upper surface of the large diameter portion and is located between an outer periphery of the large diameter portion and an outer periphery of the small diameter portion in the horizontal plane, The vibrator includes a piezoelectric element and a support plate. Each of the piezoelectric element and the support plate has a circular shape with a central hole formed in the horizontal plane, The piezoelectric element is supported by the support plate, the small diameter portion passes through the central hole of the piezoelectric element and the central hole of the support plate in the up-down direction, an inner periphery of the piezoelectric element in the horizontal plane and an inner periphery of the support plate in the horizontal plane are positioned directly above the support surface and are pressed against the support surface, The vibration sensor includes only one piezoelectric element supported by the support plate. Vibration sensor.

2. The vibration sensor according to claim 1, The outer diameter of the piezoelectric element and the outer diameter of the support plate in the horizontal plane are equal to each other. Vibration sensor.

3. 3. The vibration sensor according to claim 1, When the base and the pole are viewed from above along the vertical direction, the pole is located inside the base. Vibration sensor.

4. A vibration sensor according to any one of claims 1 to 3, The vibration sensor includes a nut, the reduced diameter portion is at least partially threaded; The nut is threaded onto the small diameter portion, The inner periphery of the piezoelectric element and the inner periphery of the support plate are sandwiched between the nut and the support surface. Vibration sensor.

5. A vibration sensor according to any one of claims 1 to 4, The distance in the vertical direction between the support surface and the base is 0.25 to 2 times the outer diameter of the piezoelectric element in the horizontal plane. Vibration sensor.

6. 5. The vibration sensor according to claim 4, The large diameter portion has a cylindrical shape. Vibration sensor.

7. 7. The vibration sensor according to claim 6, The outer diameter of the piezoelectric element in the horizontal plane is larger than the outer diameter of the large diameter portion in the horizontal plane and is within 5 times the outer diameter of the large diameter portion. Vibration sensor.

8. The vibration sensor according to claim 6 or 7, The lower end surface of the nut has a ring shape in the horizontal plane, The outer diameter of the lower end surface of the nut in the horizontal plane is equal to the outer diameter of the large diameter portion in the horizontal plane. Vibration sensor.

9. A vibration sensor according to any one of claims 1 to 8, The small diameter portion has a cylindrical shape. Vibration sensor.

10. A vibration sensor according to any one of claims 1 to 9, The vibrator is a unimorph type piezoelectric vibrator. Vibration sensor.

11. A vibration sensor according to any one of claims 1 to 10, The vibrator includes a weight. Vibration sensor.

12. A measuring instrument comprising the vibration sensor according to any one of claims 1 to 11.

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