load sensor

Abstract

The load sensor of the present invention is a load sensor for detecting load in the thickness direction, comprising: a piezoelectric vibrator having a piezoelectric substrate and an excitation electrode, the piezoelectric substrate having a main surface extending in the thickness direction, the excitation electrode being disposed on the main surface of the piezoelectric substrate; a lower housing and an upper housing that clamp and hold the piezoelectric vibrator in the thickness direction, wherein the end of one of the lower housing and the upper housing is riveted to the end of the other housing, the lower housing being less prone to elastic deformation than the upper housing, and a preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing caused by the riveting; and an upper metal plate that contacts the surface of the piezoelectric vibrator opposite to the upper housing, the flatness of the surface of the upper metal plate opposite to the piezoelectric vibrator being smaller than the flatness of the surface of the upper housing opposite to the piezoelectric vibrator.

Description

Technical Field

[0001] This invention relates to load sensors. Background Technology

[0002] Previously, load sensors using piezoelectric vibrators were known. Such load sensors measure the frequency of strain changes in a piezoelectric vibrating element subjected to a load, and detect the load based on the frequency change. In order to improve the responsiveness of load sensors using piezoelectric vibrators to frequency changes of the load within a small load range, a predetermined load (preload) is sometimes applied to the quartz oscillator.

[0003] For example, Patent Document 1 discloses a load sensor using a quartz oscillator, which applies a preload (preload) to the quartz oscillator in the long direction by fastening a threaded component via a retainer housed in a housing, and suppresses the torsional force generated when the preload is applied by a thrust bearing.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2015-25796

[0005] However, according to the load sensor described in Patent Document 1, there are adverse effects such as damage to the quartz oscillator caused by excessive application of preload, which reduces reliability. Summary of the Invention

[0006] The present invention was made in view of the following circumstances, and its purpose is to provide a load sensor that achieves improved reliability.

[0007] One aspect of the present invention is a load sensor for detecting loads in the thickness direction, comprising: a piezoelectric vibrator having a piezoelectric substrate and an excitation electrode, the piezoelectric substrate having a main surface extending in the thickness direction, the excitation electrode being disposed on the main surface of the piezoelectric substrate; a lower housing and an upper housing that clamp and hold the piezoelectric vibrator in the thickness direction, wherein the end of one of the lower housing and the upper housing is riveted to the end of the other housing, the lower housing being less prone to elastic deformation than the upper housing, and a preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing caused by the riveting; and an upper metal plate that contacts the surface of the piezoelectric vibrator opposite to the upper housing, the flatness of the surface of the upper metal plate opposite to the piezoelectric vibrator being smaller than the flatness of the surface of the upper housing opposite to the piezoelectric vibrator.

[0008] Another aspect of the load sensor of the present invention is a load sensor for detecting load in the thickness direction, comprising: a piezoelectric vibrator having a piezoelectric substrate and an excitation electrode, the piezoelectric substrate having a main surface extending in the thickness direction, the excitation electrode being disposed on the main surface of the piezoelectric substrate; a lower housing and an upper housing that clamp and hold the piezoelectric vibrator in the thickness direction, wherein the end of one of the lower housing and the upper housing is riveted to the end of the other housing, the lower housing being less prone to elastic deformation than the upper housing, and a preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing caused by the riveting; and a lower metal plate that contacts the surface of the piezoelectric vibrator opposite to the lower housing, the flatness of the surface of the lower metal plate opposite to the piezoelectric vibrator being smaller than the flatness of the surface of the lower housing opposite to the piezoelectric vibrator.

[0009] According to the present invention, a load sensor with improved reliability can be provided. Attached Figure Description

[0010] Figure 1 This is a perspective view of the load sensor according to the first embodiment.

[0011] Figure 2 This is an exploded perspective view of the load sensor according to the first embodiment.

[0012] Figure 3 This is a cross-sectional view of the load sensor according to the first embodiment.

[0013] Figure 4 This is a three-dimensional view of the quartz oscillator of the first embodiment.

[0014] Figure 5 This is an exploded perspective view of the quartz oscillator of the first embodiment.

[0015] Figure 6 This is a flowchart illustrating a method for manufacturing a load sensor according to the first embodiment.

[0016] Figure 7 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0017] Figure 8 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0018] Figure 9 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0019] Figure 10 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0020] Figure 11 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0021] Figure 12 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0022] Figure 13 This is a diagram illustrating one step in the manufacturing process of a load sensor.

[0023] Figure 14 This is an exploded perspective view of the load sensor according to the second embodiment.

[0024] Figure 15 This is a cross-sectional view of the load sensor according to the second embodiment. Detailed Implementation

[0025] The embodiments of the present invention will be described below. In the following drawings, the same or similar reference numerals denote the same or similar constituent elements. The drawings are illustrative, and the dimensions and shapes of the parts are schematic and should not be construed as limiting the scope of the present invention to these embodiments.

[0026] In the accompanying drawings, to clarify the relationships between the drawings and aid in understanding the positional relationships of the components, an orthogonal coordinate system consisting of the X-axis, Y-axis, and Z-axis is sometimes added for convenience. Directions parallel to the X-axis, Y-axis, and Z-axis are designated as the X-axis direction, Y-axis direction, and Z-axis direction, respectively. The surface defined by the X-axis and Y-axis is designated as the XY plane. Furthermore, for convenience, the positive Z-axis direction (direction of the arrow) is designated as "up" or "above," and the negative Z-axis direction (opposite to the arrow) is designated as "down" or "below," but the orientation of the load sensor is not limited to these definitions.

[0027] <First Implementation>

[0028] [Construction of a load sensor]

[0029] First, refer to Figures 1 to 5 The structure of the load sensor in the first embodiment will be described. Figure 1 This is a perspective view of the load sensor according to the first embodiment. Figure 2 This is an exploded perspective view of the load sensor according to the first embodiment. Figure 3 This is a cross-sectional view of the load sensor according to the first embodiment. Figure 4 This is a three-dimensional view of the quartz oscillator of the first embodiment. Figure 5 This is an exploded perspective view of the quartz oscillator of the first embodiment.

[0030] Load sensor 1 is a load sensor that detects loads in the Z-axis direction. The Z-axis direction is an example of the thickness direction. Figure 2As shown, the load sensor 1 includes a quartz oscillator 10, a lower housing 20, an upper housing 30, a circuit board 40, a lower metal plate 52, and an upper metal plate 53.

[0031] The quartz oscillator 10 has a quartz vibrating element 11, a first cover plate 12, and a second cover plate 13.

[0032] The quartz vibrating element 11 is an electromechanical energy conversion element that converts electrical energy into mechanical energy through the piezoelectric effect.

[0033] The quartz vibrating element 11 is excited at a predetermined frequency based on an applied alternating voltage. Furthermore, the quartz vibrating element 11 strains according to the load applied to the load sensor 1 in the thickness direction, and its resonant frequency varies based on this strain. In other words, by measuring the resonant frequency of the quartz vibrating element 11, the load applied to the load sensor 1 can be calculated. The primary vibration of the quartz vibrating element 11 is the thickness shear vibration mode.

[0034] Furthermore, the main vibration of a quartz vibrating element is not limited to the thickness shear vibration mode; for example, it can also be the thickness longitudinal vibration mode, the profile vibration mode, the length vibration mode, or the bending vibration mode.

[0035] like Figure 4 as well as Figure 5 As shown, the quartz oscillating element 11 includes a thin-film quartz crystal element 11S, a first excitation electrode 14a and a second excitation electrode 14b constituting a pair of excitation electrodes, a first lead-out electrode 15a and a second lead-out electrode 15b constituting a pair of lead-out electrodes, and a first connection electrode 16a and a second connection electrode 16b constituting a pair of connection electrodes.

[0036] The quartz substrate 11S has a first main surface 11A and a second main surface 11B forming a pair of main surfaces. The first main surface 11A and the second main surface 11B are opposite to each other in the X-axis direction. The first main surface 11A and the second main surface 11B extend in the Y-axis direction and the Z-axis direction, respectively. The first main surface 11A is located on the side opposite to the first cover substrate 12. The second main surface 11B is located on the side opposite to the second cover substrate 13. The first main surface 11A and the second main surface 11B are configured as rectangles having a short side extending in the Y-axis direction and a long side extending in the Z-axis direction. The quartz substrate 11S is a flat plate with uniform dimensions in the X-axis direction.

[0037] Furthermore, the shapes of the first and second main surfaces of the quartz substrate are not limited to the shapes described above. For example, the first and second main surfaces of the quartz substrate can also be rectangles having a long side extending in the Z-axis direction and a short side extending in the X-axis direction, or squares having a side extending in the Z-axis direction and a side extending in the X-axis direction. The first and second main surfaces of the quartz substrate can also be rectangular shapes having sides extending along directions intersecting the Y-axis and Z-axis directions. The first and second main surfaces of the quartz substrate can also be polygons, circles, ellipses, or combinations thereof extending in the Y-axis and Z-axis directions.

[0038] Furthermore, the main surface of the quartz substrate is not limited to the shape described above, as long as it extends at least in the Z-axis direction. The first and second main surfaces of the quartz substrate can also be polygons, circles, ellipses, or combinations thereof extending in the Z-axis and X-axis directions.

[0039] Furthermore, the quartz substrate is not limited to a flat plate shape. The quartz substrate can also have a mesa-type structure or a reverse mesa-type structure with concave and convex surfaces on at least one of a pair of main surfaces. The quartz substrate can be a convex structure with a continuously varying thickness or a beveled structure with a discontinuously varying thickness.

[0040] The quartz substrate 11S is, for example, an AT-cut type quartz crystal. The AT-cut type quartz substrate 11S is a substrate cut from which the crystallographic axes of synthetic quartz crystal—namely, the crystallographic X-axis (electric axis), crystallographic Y-axis (mechanical axis), and crystallographic Z-axis (optical axis)—are rotated 35 degrees for 15 minutes ± 1 minute 30 seconds around the crystallographic X-axis from the crystallographic Y-axis to the crystallographic Z-axis. The crystallographic XZ' plane is used as the main surface. Furthermore, the crystallographic X-axis, crystallographic Y-axis, and crystallographic Z-axis are not aligned with the crystallographic X-axis. Figures 1 to 5 For convenience, the X, Y, and Z axes are attached to the figure. The X-axis, attached for convenience, corresponds to the crystallographic Y' axis; the Y-axis, attached for convenience, corresponds to the crystallographic Z' axis; and the Z-axis, attached for convenience, corresponds to the crystallographic X-axis.

[0041] The quartz resonator 11 using an AT-cut quartz substrate 11S exhibits high frequency stability over a wide temperature range. Furthermore, the AT-cut quartz resonator demonstrates excellent time-varying characteristics, enabling low-cost manufacturing. Moreover, the AT-cut quartz resonator utilizes a thickness shear vibration mode as its primary vibration.

[0042] Furthermore, the cutting angle of the quartz substrate is not limited to the aforementioned angles. The rotation angles of the Y' and Z' axes in the AT-cut quartz substrate 11S can also be tilted within a range of -5 degrees or more, or +15 degrees, from 35 degrees 15 minutes. Additionally, different cuts besides AT cutting can be used for the quartz substrate, such as BT cutting, GT cutting, and SC cutting. Furthermore, the main vibration mode of the quartz resonator is not limited to the thickness shear vibration mode; for example, it can also be thickness longitudinal vibration, contour vibration, length vibration, or bending vibration.

[0043] The first excitation electrode 14a and the second excitation electrode 14b apply an alternating voltage to the quartz substrate 11S to excite the quartz substrate 11S. For example... Figure 5 As shown, the first excitation electrode 14a is disposed at the center of the first main surface 11A of the quartz substrate 11S. The second excitation electrode 14b is disposed at the center of the second main surface 11B of the quartz substrate 11S. The first excitation electrode 14a and the second excitation electrode 14b are positioned opposite each other in the X-axis direction across the quartz substrate 11S.

[0044] like Figure 5 As shown, the first excitation electrode 14a and the second excitation electrode 14b have approximately the same shape and size. For example, the planar shape of the first excitation electrode 14a when viewed from the first main surface 11A of the quartz substrate 11S and the planar shape of the second excitation electrode 14b when viewed from the second main surface 11B of the quartz substrate 11S are both circles of the same size. The first excitation electrode 14a and the second excitation electrode 14b are configured to overlap each other entirely in the X-axis direction.

[0045] Furthermore, the planar shapes of the first excitation electrode and the second excitation electrode are not limited to the shapes described above. The planar shapes of the first excitation electrode and the second excitation electrode may also be polygonal, circular, elliptical, or a combination thereof.

[0046] like Figure 5 As shown, the first lead-out electrode 15a electrically connects the first excitation electrode 14a and the first connection electrode 16a, and the second lead-out electrode 15b electrically connects the second excitation electrode 14b and the second connection electrode 16b. The first lead-out electrode 15a is disposed on the first main surface 11A of the quartz substrate 11S, and the second lead-out electrode 15b is disposed on the second main surface 11B of the quartz substrate 11S. The first lead-out electrode 15a is led out from the first excitation electrode 14a to the end of the quartz substrate 11S on the positive Y-axis side. The second lead-out electrode 15b is led out from the second excitation electrode 14b to the end of the quartz substrate 11S on the negative Y-axis side.

[0047] The first connecting electrode 16a and the second connecting electrode 16b electrically connect the quartz resonator 11 to the circuit board 40. For example... Figure 4As shown, the first connecting electrode 16a is disposed on the side of the quartz oscillator 10 in the positive Y-axis direction. The second connecting electrode 16b is disposed on the side of the quartz oscillator 10 in the negative Y-axis direction. The first connecting electrode 16a is bonded to the connecting portion 41 of the circuit board 40 (described later) via a first solder 17a, and is electrically connected to the connecting portion 41. The second connecting electrode 16b is bonded to the connecting portion 41 via a second solder 17b, and is electrically connected to the connecting portion 41.

[0048] The first cover plate 12 and the second cover plate 13 are containers that house the excitation section of the quartz oscillator 11, which has a first excitation electrode 14a and a second excitation electrode 14b, in an excitation-capable state. The first cover plate 12 seals the first excitation electrode 14a of the quartz oscillator 10 in a cavity, and the second cover plate 13 seals the second excitation electrode 14b of the quartz oscillator 10 in a cavity. Figure 4 As shown, the first cover plate 12 is disposed on the negative X-axis side of the quartz vibrating element 11, and the second cover plate 13 is disposed on the positive X-axis side of the quartz vibrating element 11.

[0049] like Figure 5 As shown, the first cover substrate 12 has a first substrate layer 12S and a first bonding layer 12G. Similarly, the second cover substrate 13 has a second substrate layer 13S and a second bonding layer 13G.

[0050] The first substrate layer 12S and the second substrate layer 13S are, for example, quartz substrates with the same cut angle as the quartz substrate 11S. As a result, thermal stress acting on the quartz vibrating element 11 from the first cover substrate 12 and the second cover substrate 13 can be suppressed.

[0051] Furthermore, the materials of the first and second substrate layers are not limited to the materials described above, but from the viewpoint of suppressing thermal stress acting on the quartz resonator, materials having a coefficient of thermal expansion close to that of the quartz substrate of the quartz resonator are preferred. Additionally, from the viewpoint of suppressing damage to the quartz oscillator caused by deviations in the magnitude of strain of the quartz resonator, the first substrate layer, and the second substrate layer when strain occurs in the quartz oscillator due to the load applied to the load sensor, materials of the first and second substrate layers having a Young's modulus close to that of the quartz substrate of the quartz resonator are preferred. For example, the materials of the first and second substrate layers may also be glass, ceramics such as alumina, or metals such as Fe-Ni-Co alloys.

[0052] The first bonding layer 12G bonds the first substrate layer 12S to the quartz resonator 11. The second bonding layer 13G bonds the second substrate layer 13S to the quartz resonator 11. For example, the first bonding layer 12G is an organic adhesive containing a spacer filler for adjusting the spacing between the quartz resonator 11 and the first substrate layer 12S. This organic adhesive is, for example, an adhesive containing epoxy, vinyl, acrylic, polyurethane, or silicone resins. The second bonding layer 13G is an organic adhesive containing the same spacer filler as the first bonding layer 12G.

[0053] Furthermore, the materials of the first and second bonding layers are not limited to the materials described above, and can also be provided using inorganic adhesives such as silicon-based adhesives containing water glass or calcium-based adhesives containing cement. The first and second bonding layers can also be low-melting-point glasses (such as lead borate-based or tin phosphate-based glasses).

[0054] A central opening C12 is formed in the first bonding layer 12G in the region overlapping with the first excitation electrode 14a, opening toward the quartz resonator 11. Additionally, an end opening E12 is formed in the first bonding layer 12G in the region overlapping the connection portion between the first lead-out electrode 15a and the first connecting electrode 16a, opening toward the quartz resonator 11. The central opening C12 and the end opening E12 penetrate the first bonding layer 12G in the X-axis direction, exposing the first substrate layer 12S. The central opening C12 forms a cavity that opens the first excitation electrode 14a, and the end opening E12 increases the contact area between the first lead-out electrode 15a and the first connecting electrode 16a. In the second bonding layer 13G, the same as in the first bonding layer 12G, a central opening C13 and an end opening (not shown) are formed. The first bonding layer 12G liquid-tightly seals the first excitation electrode 14a, and the second bonding layer 13G liquid-tightly seals the second excitation electrode 14b.

[0055] The lower housing 20 and the upper housing 30 clamp and hold the quartz oscillator 10 in the Z-axis direction. The lower housing 20 and the upper housing 30 are containers for housing the quartz oscillator 10. The lower housing 20 is located on the negative Z-axis side of the quartz oscillator 11, and the upper housing 30 is located on the positive Z-axis side of the quartz oscillator 11. One end of the lower housing 20 and the upper housing 30 is riveted to the other end. The lower housing 20 is less prone to elastic deformation than the upper housing 30. The upper housing 30 is configured to be elastically deformable, functioning as a leaf spring. Through the riveting of the ends of the lower housing 20 and the upper housing 30, the upper housing 30 elastically deforms towards the lower housing 20, applying a preload in the Z-axis direction to the quartz oscillator 10.

[0056] The lower shell 20 and the upper shell 30 are formed of the same ferritic stainless steel SUS430, and the thickness of the lower shell 20 is greater than that of the upper shell 30. For example, the thickness of the lower shell 20 is about 1.0 mm, and the thickness of the upper shell 30 is about 0.3 mm. In other words, by forming the lower shell 20 thicker than the upper shell 30, the lower shell 20 is made less prone to elastic deformation when compared with the upper shell 30.

[0057] Furthermore, the characteristic of the lower shell being less prone to elastic deformation when compared with the upper shell can be achieved, for example, by using a material with a yield strength (yield point stress) value greater than that of the upper shell as the material of the lower shell, or by adding reinforcing ribs or other shapes to the lower shell to suppress deformation.

[0058] The lower housing 20 is circular when viewed from above in the Z-axis direction. The lower housing 20 has a central portion 21 and an end portion 22. When viewed from above in the Z-axis direction, the central portion 21 is located at the center of the lower housing 20, and the end portion 22 is frame-shaped, surrounding the central portion 21. The lower housing 20 is flat, and the central portion 21 has a planar upper surface 21A on the side opposite to the quartz oscillator 10. A cutout SL1 is formed at the end portion 22. The cutout SL1 is a through hole that opens the lower housing 20 in both the positive and negative Z-axis directions. Furthermore, the cutout SL1 opens to the outer side of the lower housing 20 when viewed from above in the Z-axis direction. The lower housing 20 is flat, and the thickness of the central portion 21 and the end portion 22 in the Z-axis direction are approximately equal. The lower surfaces of the central portion 21 and the end portion 22 are continuous in the XY plane direction.

[0059] The upper housing 30 is circular when viewed from above in the Z-axis direction. The upper housing 30 has a pressure-bearing part 31, an upper side wall part 32, a peripheral part 33, a lower side wall part 34, and an end part 35.

[0060] like Figure 1 As shown, when viewed from above in the Z-axis direction, the pressure-bearing part 31 is provided in the center of the upper housing 30, the upper side wall part 32 is frame-shaped around the pressure-bearing part 31, the peripheral part 33 is frame-shaped around the upper side wall part 32, the lower side wall part 34 is frame-shaped around the peripheral part 33, and the end part 35 is frame-shaped around the lower side wall part 34.

[0061] like Figure 3 As shown, the pressure-bearing portion 31 is the part that faces the quartz oscillator 10 in the Z-axis direction and bears the load acting on the load sensor 1. The pressure-bearing portion 31 is furthest from the lower housing 20 in the upper housing 30. The pressure-bearing portion 31 has a lower surface 31B that faces the quartz oscillator 10.

[0062] like Figure 3As shown, the upper sidewall portion 32 extends and protrudes from the outer edge of the pressure-bearing portion 31 towards the lower housing 20. The peripheral portion 33 extends and protrudes from the lower end of the upper sidewall portion 32 towards the side opposite to the pressure-bearing portion 31. The lower sidewall portion 34 extends and protrudes from the outer edge of the peripheral portion 33 towards the lower housing 20. The end portion 35 has an upper end portion 35a, a lower end portion 35b, and a folded-back portion 35c. The upper end portion 35a extends and protrudes from the lower end of the lower sidewall portion 34 towards the side opposite to the peripheral portion 33. The lower surface of the upper end portion 35a contacts the upper surface of the end portion 22 of the lower housing 20. The folded-back portion 35c extends and protrudes from the outer edge of the upper end portion 35a along the side of the lower housing 20. The lower end portion 35b extends and protrudes from the lower end of the folded-back portion 35c towards the upper end portion 35a. The upper surface of the lower end portion 35b contacts the lower surface of the end portion 22 of the lower housing 20. The upper end portion 35a and the lower end portion 35b of the upper housing 30 clamp the end portion 22 of the lower housing 20 in the Z-axis direction.

[0063] The circuit board 40 is disposed on the side of the upper housing 30 of the lower housing 20. The circuit board 40 is configured to avoid the area between the quartz oscillator 10 and the lower housing 20. The circuit board 40 is flexible, and circuits are formed on the circuit board 40. The circuit board 40 is, for example, a flexible printed circuit board (FPC) formed by bonding a conductor foil such as copper foil onto an insulating substrate film such as polyimide or polyester.

[0064] like Figure 3 As shown, the circuit board 40 has a connecting portion 41, a peripheral portion 42, and a lead-out portion 43. The connecting portion 41 is connected to the side of the quartz oscillator 10 extending in the Z-axis direction. The peripheral portion 42 is provided on the upper surface 21A of the central portion 21 of the lower housing 20, and is located in a region away from the quartz oscillator 10 when viewed from above in the Z-axis direction. The peripheral portion 42 is, for example, adhered to the upper surface 21A of the central portion 21 of the lower housing 20 by adhesive. The portion of the circuit board 40 that connects the connecting portion 41 and the peripheral portion 42 is bent. Circuit components 49, etc., constituting an oscillation circuit that converts the resonant frequency of the quartz oscillator 10 into an electrical signal are mounted on the peripheral portion 42. The lead-out portion 43 passes through the cutout SL1 of the lower housing 20 and is led out from the internal space between the lower housing 20 and the upper housing 30. Figure 1 As shown, in the lead-out section 43, the circuit board 40 is electrically connected to the external circuit 90.

[0065] The lower metal plate 52 is positioned between the quartz oscillator 10 and the lower housing 20 along the Z-axis. For example... Figure 2 as well as Figure 3As shown, the lower metal plate 52 contacts the surface of the quartz oscillator 10 that faces the lower housing 20. Furthermore, the lower metal plate 52 contacts the surface of the lower housing 20 that faces the quartz oscillator 10 without passing through the circuit board 40. In other words, when viewed from above in the Z-axis direction, the lower metal plate 52 is positioned spaced apart from the peripheral portion 42 of the circuit board 40.

[0066] like Figure 3 As shown, the lower metal plate 52 has an upper surface 52A opposite to the quartz oscillator 10 and a lower surface 52B opposite to the lower housing 20. The upper surface 52A of the lower metal plate 52 is bonded to the quartz oscillator 10, for example, by an adhesive. In other words, the upper surface 52A of the lower metal plate 52 is in indirect contact with the quartz oscillator 10 via an adhesive. The adhesive used to bond the lower metal plate 52 to the quartz oscillator 10 is not particularly limited, but is, for example, an organic adhesive with relatively high hardness, such as an epoxy adhesive. The lower surface 52B of the lower metal plate 52 is, for example, detachably abutting against the upper surface 21A of the central portion 21 of the lower housing 20. In other words, the lower surface 52B of the lower metal plate 52 is in direct contact with the upper surface 21A of the central portion 21 of the lower housing 20.

[0067] Furthermore, the contact method between the lower metal plate and the lower housing and the quartz oscillator is not limited to the methods described above. For example, the lower metal plate can be clamped and held by the lower housing and the quartz oscillator. In other words, the upper surface of the lower metal plate can be detachably abutted against the lower surface of the quartz oscillator, thereby directly contacting the lower surface of the quartz oscillator. Alternatively, the side of the lower metal plate can be bonded to the side of the quartz oscillator using an adhesive, thereby directly contacting the lower surface of the lower metal plate with the lower surface of the quartz oscillator. On the other hand, for example, the lower surface of the lower metal plate can also be bonded to the upper surface of the central portion of the lower housing using an adhesive, thereby indirectly contacting the upper surface of the central portion of the lower housing. Alternatively, the side of the lower metal plate can be bonded to the upper surface of the central portion of the lower housing using an adhesive, thereby directly contacting the lower surface of the lower metal plate with the upper surface of the central portion of the lower housing. A circuit board can also be provided between the lower housing and the lower metal plate, with the lower surface of the lower metal plate contacting the circuit board instead of the lower housing.

[0068] like Figure 3 As shown, when viewed from above along the Z-axis, the area of ​​the lower metal plate 52 is larger than the area of ​​the quartz oscillator 10, but smaller than the area of ​​the central portion 21 of the lower housing 20. The lower metal plate 52 completely overlaps with the quartz oscillator 10. In other words, the upper surface 52A of the lower metal plate 52 is in complete contact with the lower surface of the quartz oscillator 10.

[0069] The flatness of the upper surface 52A of the lower metal plate 52 is smaller than that of the upper surface 21A of the central portion 21 of the lower housing 20. In other words, the unevenness of the upper surface 52A of the lower metal plate 52 is smaller than that of the upper surface 21A of the central portion 21 of the lower housing 20, and the upper surface 52A of the lower metal plate 52 is flatter and smoother than the upper surface 21A of the central portion 21 of the lower housing 20.

[0070] The lower metal plate 52 is less prone to elastic deformation than the upper shell 30, and preferably less prone to elastic deformation than the lower shell 20. As an example, the lower metal plate 52 may be formed of the same ferritic stainless steel SUS430 as the lower shell 20 and the upper shell 30. The thickness of the lower metal plate 52 in the Z-axis direction is smaller than the thickness of the central portion 21 of the lower shell 20 in the Z-axis direction, but larger than the thickness of the pressure-bearing portion 31 of the upper shell 30 in the Z-axis direction. For example, the thickness of the lower metal plate 52 is approximately 0.5 mm. In other words, by forming the lower metal plate 52 thicker than the upper shell 30, the characteristic of the lower metal plate 52 being less prone to elastic deformation when compared to the upper shell 30 is achieved. Furthermore, even when the thickness of the lower metal plate 52 is smaller than the thickness of the lower shell 20, since the area of ​​the lower metal plate 52 when viewed from above in the Z-axis direction is smaller than the area of ​​the lower shell 20, the lower metal plate 52 can still be structured to be less prone to elastic deformation compared to the lower shell 20.

[0071] Furthermore, for example, the lower metal plate 52 can be made of a material with a higher yield strength than the material of the upper shell 30 to achieve the characteristic that the lower metal plate 52 is less prone to elastic deformation when compared with the upper shell 30. For example, it is preferable that the yield strength of the lower metal plate 52 is 600 MPa or more and 2000 MPa or less.

[0072] The upper metal plate 53 is positioned between the quartz oscillator 10 and the upper housing 30 along the Z-axis. For example... Figure 2 as well as Figure 3 As shown, the upper metal plate 53 is in contact with the surface of the quartz oscillator 10 that is opposite to the upper housing 30. Additionally, the upper metal plate 53 is in contact with the surface of the upper housing 30 that is opposite to the quartz oscillator 10.

[0073] like Figure 3As shown, the upper metal plate 53 has a lower surface 53B opposite to the quartz oscillator 10 and an upper surface 53A opposite to the upper housing 30. The lower surface 53B of the upper metal plate 53 is bonded to the quartz oscillator 10, for example, by an adhesive. In other words, the lower surface 53B of the upper metal plate 53 is in indirect contact with the quartz oscillator 10 via an adhesive. The adhesive used to bond the upper metal plate 53 to the quartz oscillator 10 is not particularly limited, but is, for example, an organic adhesive with relatively high hardness, such as an epoxy adhesive. The upper surface 53A of the upper metal plate 53 is, for example, detachably abutting against the lower surface 31B of the pressure-bearing portion 31 of the upper housing 30. In other words, the upper surface 53A of the upper metal plate 53 is in direct contact with the lower surface 31B of the pressure-bearing portion 31 of the upper housing 30.

[0074] Furthermore, the contact method between the upper metal plate and the upper housing and the quartz oscillator is not limited to the methods described above. For example, the upper metal plate can also be clamped and held by the upper housing and the quartz oscillator. In other words, the lower surface of the upper metal plate can also detachably abut against the upper surface of the quartz oscillator, thereby directly contacting the upper surface of the quartz oscillator. Alternatively, the side of the upper metal plate can be bonded to the side of the quartz oscillator using an adhesive, thereby directly contacting the lower surface of the upper metal plate with the upper surface of the quartz oscillator. On the other hand, for example, the upper surface of the upper metal plate can also be bonded to the lower surface of the pressure-bearing part of the upper housing using an adhesive, thereby indirectly contacting the lower surface of the pressure-bearing part of the upper housing. Alternatively, the side of the upper metal plate can be bonded to the lower surface of the pressure-bearing part of the upper housing using an adhesive, thereby directly contacting the upper surface of the upper metal plate with the lower surface of the pressure-bearing part of the upper housing.

[0075] like Figure 3 As shown, when viewed from above along the Z-axis, the area of ​​the upper metal plate 53 is larger than the area of ​​the quartz oscillator 10, but smaller than the area of ​​the pressure-bearing portion 31 of the upper housing 30. The upper metal plate 53 completely overlaps with the quartz oscillator 10. In other words, the lower surface 53B of the upper metal plate 53 is in complete contact with the upper surface of the quartz oscillator 10.

[0076] The flatness of the lower surface 53B of the upper metal plate 53 is smaller than that of the lower surface 31B of the pressure-bearing part 31 of the upper housing 30. In other words, the unevenness of the lower surface 53B of the upper metal plate 53 is smaller than that of the lower surface 31B of the pressure-bearing part 31 of the upper housing 30, and the upper surface 52A of the upper metal plate 53 is flatter and smoother than the upper surface 21A of the central part 21 of the lower housing 20.

[0077] The upper metal plate 53 is less prone to elastic deformation than the upper shell 30, and preferably less prone to elastic deformation than the lower shell 20. As an example, the upper metal plate 53 may be formed of the same ferritic stainless steel SUS430 as the lower shell 20 and the upper shell 30. The thickness of the upper metal plate 53 in the Z-axis direction is smaller than the thickness of the central portion 21 of the lower shell 20 in the Z-axis direction, but larger than the thickness of the pressure-bearing portion 31 of the upper shell 30 in the Z-axis direction. For example, the thickness of the upper metal plate 53 is approximately 0.5 mm. In other words, by forming the upper metal plate 53 thicker than the upper shell 30, the characteristic of the upper metal plate 53 being less prone to elastic deformation when compared to the upper shell 30 is achieved. Furthermore, even when the thickness of the upper metal plate 53 is smaller than the thickness of the lower shell 20, since the area of ​​the upper metal plate 53 when viewed from above in the Z-axis direction is smaller than the area of ​​the lower shell 20, the upper metal plate 53 can still be structured to be less prone to elastic deformation compared to the lower shell 20.

[0078] Furthermore, for example, the upper metal plate 53 can be made of a material with a higher yield strength than the material of the upper shell 30 to achieve the characteristic that the upper metal plate 53 is less prone to elastic deformation when compared with the upper shell 30. For example, it is preferable that the yield strength of the upper metal plate 53 is 600 MPa or more and 2000 MPa or less.

[0079] [Manufacturing method of load sensor]

[0080] Next, refer to Figures 6 to 13 The manufacturing method of the load sensor 1 in this embodiment will be described. Figure 6 This is a flowchart illustrating the manufacturing method of the load sensor 1 according to the first embodiment. Figures 7 to 13 This is a diagram showing one step of the manufacturing method of load sensor 1.

[0081] First, prepare the quartz oscillator 10 and the circuit board 40 (S10). For example... Figure 7 As shown, the connecting portion 41 and the peripheral portion 42 of the circuit board 40 are connected to each other by a temporary fixing portion 45. This restricts the displacement of the connecting portion 41, and prevents problems such as bending of the connecting portion 41 during the transport of the circuit board 40. The quartz oscillator 10 has a lower metal plate 52 and an upper metal plate 53 bonded to it by adhesive.

[0082] Next, the quartz oscillator 10 is mounted on the circuit board 40 (S20). For example... Figure 8As shown, with the quartz oscillator 10, which has been joined to the lower metal plate 52 and the upper metal plate 53, placed horizontally, the side of the quartz oscillator 10 is joined to the connection portion 41 of the circuit board 40, thus electrically connecting the quartz oscillator 10 to the circuit board 40. The quartz oscillator 10 is then mounted on the circuit board 40 along with other circuit components 49 via reflow soldering.

[0083] Next, the temporary fixing part 45 is cut off (S30). For example... Figure 9 As shown, the temporary fixing part 45 is cut off, so that the connecting part 41 can be bent relative to the peripheral part 42.

[0084] Next, the circuit board 40 is joined to the lower housing 20 (S40). Figure 10 As shown, the lead-out portion 43 is aligned with the cutout portion SL1, and the peripheral portion 42 is joined with the central portion 21 of the lower housing 20.

[0085] Next, erect the quartz oscillator 10 (S50). As follows... Figure 11 As shown, the quartz oscillator 10 is erected so that the lower metal plate 52 is positioned between the quartz oscillator 10 and the lower housing 20. The portion connecting the connecting part 41 and the peripheral part 42 is bent.

[0086] Next, the upper housing 30 (S60) is installed. For example... Figure 12 As shown, the pressure-bearing portion 31 of the upper housing 30 covers the upper metal plate 53, and the end portion 35 of the upper housing 30 covers the end portion 22 of the lower housing 20. This causes the lower housing 20 to abut against the lower metal plate 52, and the upper metal plate 53 to abut against the upper housing 30. The quartz oscillator 10 is clamped and temporarily fixed by the lower housing 20 and the upper housing 30.

[0087] Next, the end 35 of the upper housing 30 is riveted (S70). Figure 13 As shown, the end 35 of the upper housing 30 is folded back, and the end 22 of the lower housing 20 is riveted in the vertical direction. The upper housing 30 undergoes elastic deformation to function as a leaf spring, applying a preload to the quartz oscillator 10.

[0088] As explained above, according to this embodiment, the load sensor 1 includes a quartz oscillator 10, a lower housing 20 configured to apply a preload to the quartz oscillator 10, an upper housing 30, and an upper metal plate 53 in contact with the surface of the quartz oscillator 10 that faces the upper housing 30. The flatness of the surface of the upper metal plate 53 facing the quartz oscillator 10 is smaller than the flatness of the surface of the upper housing 30 that faces the quartz oscillator 10.

[0089] Accordingly, since the end 22 of the lower housing 20 is riveted to the end 35 of the upper housing 30, and a preload is applied to the quartz oscillator 10 through the elastic deformation of the upper housing 30, it is not easy to apply excessive preload to the quartz oscillator 10. Therefore, it is not easy to cause damage to the quartz oscillator 10 due to excessive preload, and the reliability of the load sensor 1 can be suppressed. In addition, since the unevenness of the lower surface 53B of the upper metal plate 53 is smaller than that of the lower surface 31B of the pressure-bearing part 31 of the upper housing 30, stress concentration on the upper surface of the quartz oscillator 10 caused by the unevenness of the surface pressing the upper surface of the quartz oscillator 10 can be suppressed when a load is applied to the load sensor 1. Therefore, damage to the quartz oscillator 10 from the upper housing 30 side can be suppressed, and the reliability of the load sensor 1 can be improved. In addition, since stress concentration on the upper surface of the quartz oscillator 10 can be suppressed, the load resistance of the load sensor 1 can be improved.

[0090] As one aspect of this embodiment, the upper metal plate 53 is less prone to deformation compared to the upper housing 30.

[0091] Accordingly, when a preload is applied to the quartz oscillator 10 through the elastic deformation of the upper housing 30, or when a load is applied to the load sensor 1, stress concentration at the four corners of the upper surface of the quartz oscillator 10 can be suppressed. Therefore, damage to the quartz oscillator 10 from the upper housing 30 side can be further suppressed, and the load-bearing capacity of the load sensor 1 is improved. This further improves the reliability of the load sensor 1.

[0092] In one embodiment, the yield strength of the upper metal plate 53 is 600 MPa or more and 2000 MPa or less. Furthermore, in another embodiment, the thickness of the upper metal plate 53 is greater than the thickness of the pressure-bearing portion 31 of the upper housing 30.

[0093] Accordingly, the upper metal plate 53 can be configured to be less prone to elastic deformation compared to the upper shell 30.

[0094] As one embodiment, the load sensor 1 further includes a lower metal plate 52 that contacts the surface of the quartz oscillator 10 that faces the lower housing 20. The flatness of the surface of the lower metal plate 52 facing the quartz oscillator 10 is smaller than the flatness of the surface of the lower housing 20 facing the quartz oscillator 10.

[0095] Accordingly, since the unevenness of the upper surface 52A of the lower metal plate 52 is smaller than that of the upper surface 21A of the central portion 21 of the lower housing 20, stress concentration on the lower surface of the quartz oscillator 10 caused by the unevenness of the surface pressing the lower surface of the quartz oscillator 10 can be suppressed when a load is applied to the load sensor 1. Therefore, damage to the quartz oscillator 10 from the lower housing 20 side can be suppressed, and the load capacity of the load sensor 1 is improved. This further improves the reliability of the load sensor 1. For example, the load capacity of a load sensor without a lower metal plate and an upper metal plate is about 600N, while the load capacity of the load sensor 1 is increased to about 1000N.

[0096] Furthermore, although it is preferred that the load sensor 1 includes both a lower metal plate 52 and an upper metal plate 53, it is sufficient to include at least one of the lower metal plate 52 and the upper metal plate 53. Even when the upper metal plate 53 is included and the lower metal plate 52 is omitted, damage to the quartz oscillator 10 caused by stress concentration from the upper housing 30 side can be suppressed. Conversely, even when the lower metal plate 52 is included and the upper metal plate 53 is omitted, damage to the quartz oscillator 10 caused by stress concentration from the lower housing 20 side can be suppressed.

[0097] As one embodiment of this invention, the load sensor 1 also includes a circuit board 40. The circuit board 40 is configured to avoid the area between the quartz oscillator 10 and the lower housing 20, and the circuit board 40 is connected to the side of the quartz oscillator 10 extending in the Z-axis direction.

[0098] Accordingly, when a load is applied to the load sensor 1, stress concentration on the quartz oscillator 10 caused by unevenness or deformation of the circuit board 40 is prevented. Therefore, damage to the quartz oscillator 10 from the lower housing 20 side can be suppressed, further improving the load-bearing capacity of the load sensor 1. This further improves the reliability of the load sensor 1. Furthermore, when a load is applied to the load sensor 1, no load is applied to the first solder 17a and the second solder 17b that electrically connect the quartz oscillator 10 to the circuit board 40, nor to the wiring within the circuit board 40. Therefore, the increase in contact resistance between the quartz oscillator 10 and the circuit board 40, and the occurrence of continuity-related defects such as wire breaks in the circuit board 40, which accompany the use of the load sensor 1, can be reduced. This further improves the reliability of the load sensor 1.

[0099] The following describes other embodiments. Furthermore, structures that are the same as or similar to those shown in the first embodiment will be given the same or similar reference numerals, and their descriptions will be omitted where appropriate. Also, the same effects of the same structures will not be mentioned sequentially.

[0100] <Second Implementation>

[0101] Next, refer to Figure 14 as well as Figure 15 The structure of the load sensor 2 in the second embodiment will be described. Figure 14 This is an exploded perspective view of the load sensor 2 according to the second embodiment. Figure 15 This is a cross-sectional view of the load sensor 2 according to the second embodiment.

[0102] The lower housing 220 of the load sensor 2 is disc-shaped. A step difference is formed between the central portion 221 and the end portion 222 of the lower housing 220. The end portion 222 of the lower housing 220 protrudes towards the upper housing 30 compared to the central portion 221. On the side of the lower housing 220 opposite to the upper housing 30, the central portion 221 of the lower housing 220 is concave relative to the end portion 222. On the opposite side of the side of the lower housing 220 opposite to the upper housing 30, the central portion 221 of the lower housing 220 is convex relative to the end portion 222. The central portion 221 and the end portion 222 of the lower housing 220 are flat, and the thickness of the central portion 221 of the lower housing 220 is approximately equal to the thickness of the end portion 222.

[0103] Accordingly, the lower end 35b of the upper housing 30 does not contact the mounting surface of the load sensor 2, while the lower surface of the central portion 221 of the lower housing 220 contacts the mounting surface of the load. Therefore, when a load is applied to the load sensor 2, deformation of the lower housing 220 can be suppressed, and stress concentration at the four corners of the lower surface of the quartz oscillator 10 can be suppressed. Thus, damage to the quartz oscillator 10 from the lower housing 220 side can be further suppressed, and the load-bearing capacity of the load sensor 2 is improved. Consequently, the reliability of the load sensor 2 can be further improved.

[0104] A cutout SL2 is formed in the lower housing 220 of the load sensor 2. The cutout SL2 is formed on the opposite side of the cutout SL1, separated by the quartz oscillator 10. The cutout SL2 is a through-hole that opens the lower housing 220 in both the positive and negative Z-axis directions. Furthermore, when viewed from above in the Z-axis direction, the cutout SL2 opens to the outer side of the lower housing 220. The cutout SL1 is an example of a first cutout, and the cutout SL2 is an example of a second cutout.

[0105] Therefore, when riveting the end 35 of the upper housing 30 to the end 222 of the lower housing 220, the generation of force in the XY plane direction can be suppressed, and the generation of axial offset can be suppressed.

[0106] Furthermore, as long as the cutouts are formed symmetrically about the quartz oscillator when viewed from above in the Z-axis direction, the number of cutouts formed in the lower shell is not limited to the aforementioned number. For example, in the lower shell, the first to third cutouts may be formed in a direction that divides the circumference angle centered on the quartz oscillator into three equal parts, or the first to fourth cutouts may be formed in a direction that divides the circumference angle centered on the quartz oscillator into four equal parts.

[0107] The following are some or all of the embodiments of the present invention. However, the present invention is not limited to the following descriptions.

[0108] <1> A load sensor, which detects loads in the thickness direction, comprising:

[0109] A piezoelectric vibrator has a piezoelectric substrate and an excitation electrode. The piezoelectric substrate has a main surface extending in the thickness direction, and the excitation electrode is disposed on the main surface of the piezoelectric substrate.

[0110] The lower and upper housings are used to clamp and hold the piezoelectric vibrator in the thickness direction. One end of the lower and upper housings is riveted to the end of the other. The lower housing is less prone to elastic deformation than the upper housing. A preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing caused by the riveting.

[0111] The upper metal plate is in contact with the surface of the piezoelectric vibrator opposite the upper housing.

[0112] The flatness of the surface of the upper metal plate opposite the piezoelectric vibrator is smaller than the flatness of the surface of the upper shell opposite the piezoelectric vibrator.

[0113] <2> According to the load sensor described in <1>, where,

[0114] The upper metal plate is less prone to deformation compared to the upper shell.

[0115] <3> According to the load sensor described in <1> or <2>, where,

[0116] The yield strength of the upper metal plate is above 600 MPa and below 2000 MPa.

[0117] <4> The load sensor described in any one of <1> to <3>, wherein,

[0118] The thickness of the upper metal plate is greater than the thickness of the upper shell in the region opposite the piezoelectric vibrator in the thickness direction.

[0119] <5> The load sensor described in any one of <1> to <4>, wherein,

[0120] It also has a lower metal plate that contacts the surface of the piezoelectric vibrator opposite to the lower housing.

[0121] The flatness of the surface of the lower metal plate opposite the piezoelectric vibrator is smaller than the flatness of the surface of the lower shell opposite the piezoelectric vibrator.

[0122] <6> A load sensor, which detects loads in the thickness direction, comprising:

[0123] A piezoelectric vibrator has a piezoelectric substrate and an excitation electrode. The piezoelectric substrate has a main surface extending in the thickness direction, and the excitation electrode is disposed on the main surface of the piezoelectric substrate.

[0124] The lower and upper housings are used to clamp and hold the piezoelectric vibrator in the thickness direction. One end of the lower and upper housings is riveted to the end of the other. The lower housing is less prone to elastic deformation than the upper housing. A preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing caused by the riveting.

[0125] The lower metal plate contacts the surface of the piezoelectric vibrator that is opposite to the lower housing.

[0126] The flatness of the surface of the lower metal plate opposite the piezoelectric vibrator is smaller than the flatness of the surface of the lower shell opposite the piezoelectric vibrator.

[0127] <7> The load sensor described according to any one of <1> to <6>, wherein,

[0128] It also has a circuit board located on the upper housing side of the lower housing.

[0129] The circuit board is designed to avoid the area between the piezoelectric vibrator and the lower housing.

[0130] The circuit board is connected to the side of the piezoelectric vibrator extending in the thickness direction.

[0131] <8> The load sensor described according to any one of <1> to <7>, wherein,

[0132] On the opposite side of the upper housing, the central part of the lower housing opposite the piezoelectric vibrator is convex relative to the end of the lower housing.

[0133] <9> The load sensor described in any one of <1> to <8>, wherein,

[0134] The lower housing has the following features: a first cutout for leading out wiring electrically connected to the piezoelectric vibrator to the outside; and a second cutout located on the opposite side of the first cutout, across the piezoelectric vibrator.

[0135] <10> The load sensor described according to any one of <1> to <5>, wherein,

[0136] The upper metal plate is connected to the piezoelectric vibrator.

[0137] <11> The load sensor described according to any one of <1> to <5>, wherein,

[0138] The upper metal plate is held in place by a piezoelectric vibrator clamping it to the upper housing.

[0139] <12> According to the load sensor described in <1> or <11>, wherein,

[0140] A piezoelectric vibrator is a quartz oscillator.

[0141] Furthermore, although this specification describes a quartz crystal resonator with a quartz crystal element as the piezoelectric substrate, the piezoelectric resonator is not limited to this. Examples of suitable piezoelectric substrates for use in this embodiment include piezoelectric ceramics such as lead zirconate titanate (PZT) or aluminum nitride, and piezoelectric single crystals such as lithium niobate or lithium tantalate, but these are not limited to this, and appropriate substrates can be selected.

[0142] As explained above, according to one aspect of the present invention, a load sensor capable of achieving improved reliability can be provided.

[0143] Furthermore, the embodiments described above are intended to facilitate understanding of the present invention and are not intended to limit the scope of the invention. The present invention can be modified / improved without departing from its spirit, and equivalents are also included in the present invention. That is, as long as the features of the present invention are present, embodiments with appropriate design changes made by those skilled in the art to the embodiments and / or modifications are also included within the scope of the present invention. For example, the elements, their configurations, materials, conditions, shapes, dimensions, etc., of the embodiments and / or modifications are not limited to the examples and can be appropriately modified. In addition, the embodiments and modifications are illustrative; of course, different substitutions or combinations of the structures shown in the embodiments and / or modifications are possible, and these substitutions or combinations are also included within the scope of the present invention as long as they contain the features of the present invention.

[0144] Explanation of reference numerals in the attached figures

[0145] 1…load sensor, 10…quartz oscillator, 11…quartz resonator, 11S…quartz substrate, 11A…first main surface, 11B…second main surface, 14a…first excitation electrode, 14b…second excitation electrode, 15a…first lead-out electrode, 15b…second lead-out electrode, 16a…first connecting electrode, 16b…second connecting electrode, 17a…first solder, 17b…second solder, 12…first cover plate, 12S…first substrate layer, 12G…first bonding layer, 13…second cover plate, 13S…second substrate layer, 13G…second bonding layer 20…Lower housing, 21…Central part, 21A…Upper surface, 22…End, SL1…First cut, 30…Upper housing, 31…Pressure-bearing part, 31B…Lower surface, 32…Upper side wall, 33…Peripheral part, 34…Lower side wall, 35…End, 35a…Upper end, 35b…Lower end, 35c…Fold-back part, 40…Circuit board, 41…Connecting part, 42…Peripheral part, 43…Lead-out part, 52…Lower metal plate, 52A…Upper surface, 52B…Lower surface, 53…Upper metal plate, 53A…Upper surface, 53B…Lower surface.

Claims

1. A load sensor for detecting loads in the thickness direction, comprising: A piezoelectric vibrator has a piezoelectric substrate and an excitation electrode. The piezoelectric substrate has a main surface extending in the thickness direction, and the excitation electrode is disposed on the main surface of the piezoelectric substrate. The lower housing and the upper housing are a lower housing and an upper housing that clamp and hold the piezoelectric vibrator in the aforementioned thickness direction, and are configured such that the end of one of the lower housing and the upper housing is riveted to the end of the other housing. The lower housing is less prone to elastic deformation than the upper housing, and the piezoelectric vibrator is preloaded in the aforementioned thickness direction by the elastic deformation of the upper housing caused by the riveting. The upper metal plate is in contact with the surface of the piezoelectric vibrator that is opposite to the upper housing. The flatness of the surface of the upper metal plate opposite to the piezoelectric vibrator is smaller than the flatness of the surface of the upper housing opposite to the piezoelectric vibrator.

2. The load sensor according to claim 1, wherein, The upper metal plate is less prone to deformation compared to the upper shell.

3. The load sensor according to claim 1 or 2, wherein, The yield strength of the upper metal plate is above 600 MPa and below 2000 MPa.

4. The load sensor according to any one of claims 1 to 3, wherein, The thickness of the upper metal plate is greater than the thickness of the upper housing in the region opposite the piezoelectric vibrator in the thickness direction.

5. The load sensor according to any one of claims 1 to 4, wherein, The aforementioned upper metal plate is bonded to the aforementioned piezoelectric vibrator or the aforementioned upper housing by an adhesive.

6. The load sensor according to any one of claims 1 to 4, wherein, The piezoelectric vibrator clamps and holds the upper metal plate in place with the upper housing.

7. The load sensor according to any one of claims 1 to 6, wherein, It also includes a lower metal plate, which is in contact with the surface of the piezoelectric vibrator opposite to the lower housing. The flatness of the surface of the lower metal plate opposite to the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing opposite to the piezoelectric vibrator.

8. A load sensor for detecting loads in the thickness direction, comprising: A piezoelectric vibrator has a piezoelectric substrate and an excitation electrode. The piezoelectric substrate has a main surface extending in the thickness direction, and the excitation electrode is disposed on the main surface of the piezoelectric substrate. The lower housing and the upper housing are a lower housing and an upper housing that clamp and hold the piezoelectric vibrator in the aforementioned thickness direction, and are configured such that the end of one of the lower housing and the upper housing is riveted to the end of the other housing. The lower housing is less prone to elastic deformation than the upper housing, and the piezoelectric vibrator is preloaded in the aforementioned thickness direction by the elastic deformation of the upper housing caused by the riveting. The lower metal plate is in contact with the surface of the piezoelectric vibrator that is opposite to the lower housing. The flatness of the surface of the lower metal plate opposite to the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing opposite to the piezoelectric vibrator.

9. The load sensor according to claim 7 or 8, wherein, The lower metal plate is bonded to the piezoelectric vibrator or the lower housing by an adhesive.

10. The load sensor according to claim 7 or 8, wherein, The lower metal plate is held in place by the piezoelectric vibrator clamping it to the lower housing.

11. The load sensor according to any one of claims 1 to 10, wherein, It also includes a circuit board disposed on the side of the upper housing of the lower housing. The circuit board is configured to avoid the area between the piezoelectric vibrator and the lower housing. The circuit board is connected to the side of the piezoelectric vibrator extending in the thickness direction.

12. The load sensor according to any one of claims 1 to 11, wherein, On the opposite side to the upper housing, the central portion of the lower housing opposite the piezoelectric vibrator is convex relative to the end portion of the lower housing.

13. The load sensor according to any one of claims 1 to 12, wherein, The lower housing has the following features: a first cutout for leading out wiring electrically connected to the piezoelectric vibrator to the outside; and a second cutout located on the opposite side of the first cutout, across the piezoelectric vibrator.

14. The load sensor according to any one of claims 1 to 13, wherein, The piezoelectric vibrator mentioned above is a quartz vibrator.

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