Load sensor

Abstract

A load sensor according to the present invention senses a load in a thickness direction, the load sensor comprising: a piezoelectric vibrator having a piezoelectric substrate that has a main surface extending in the thickness direction, and an excitation electrode provided on the main surface of the piezoelectric substrate; a lower casing and an upper casing sandwiching and holding the piezoelectric vibrator in the thickness direction, an end part of the lower casing or the upper casing being crimped and fixed to an end part of the other of the lower casing and upper casing, and the lower casing being less susceptible to elastic deformation than the upper casing and being configured to apply a preload in the thickness direction to the piezoelectric vibrator by elastic deformation of the upper casing due to the crimping and fixing; and an upper metal plate that contacts a surface, of the piezoelectric vibrator, facing the upper casing. The flatness of a surface, of the upper metal plate, facing the piezoelectric vibrator is less than the flatness of a surface, of the upper casing, facing the piezoelectric vibrator.

Description

Load Sensor

[0001] The present invention relates to a load sensor.

[0002] Load sensors using piezoelectric vibrators have been known. These load sensors measure the frequency that changes based on the distortion of the piezoelectric vibrator element when a load is applied, and detect the load based on the frequency change. In some load sensors using piezoelectric vibrators, a predetermined load (preload) is applied to the quartz crystal unit in advance to improve the responsiveness of the frequency change to loads in a small load range.

[0003] For example, Patent Document 1 discloses a load sensor that uses a quartz oscillator, in which a preload (preload) is applied to the quartz oscillator in the longitudinal direction via a retainer housed in a case by tightening a screw member, and a thrust bearing suppresses the torsional force acting when the preload is applied.

[0004] Japanese Patent Application Laid-Open No. 2015-25796

[0005] However, with the load sensor described in Patent Document 1, problems such as damage to the quartz crystal oscillator due to excessive preload may occur, resulting in reduced reliability.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a load sensor with improved reliability.

[0007] A load sensor according to one aspect of the present invention is a load sensor that detects a load in the thickness direction, and includes a piezoelectric substrate having a main surface extending in the thickness direction, a piezoelectric vibrator having an excitation electrode provided on the main surface of the piezoelectric substrate, a lower housing and an upper housing that sandwich and hold the piezoelectric vibrator in the thickness direction, an end of one of the lower housing and the upper housing being crimped and fixed to an end of the other housing, the lower housing being less susceptible to elastic deformation than the upper housing, and an upper housing configured so that a preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing due to the crimping fixation, and an upper metal plate in contact with the surface of the piezoelectric vibrator facing the upper housing, and the flatness of the surface of the upper metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the upper housing facing the piezoelectric vibrator.

[0008] A load sensor according to another aspect of the present invention is a load sensor that detects a load in the thickness direction, and includes a piezoelectric substrate having a main surface extending in the thickness direction, a piezoelectric vibrator having an excitation electrode provided on the main surface of the piezoelectric substrate, a lower housing and an upper housing that sandwich and hold the piezoelectric vibrator in the thickness direction, an end of one of the lower housing and the upper housing being crimped and fixed to an end of the other housing, the lower housing being less susceptible to elastic deformation than the upper housing, and configured so that a preload is applied to the piezoelectric vibrator in the thickness direction by the elastic deformation of the upper housing due to the crimping fixation, and a lower metal plate in contact with the surface of the piezoelectric vibrator facing the lower housing, and the flatness of the surface of the lower metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing facing the piezoelectric vibrator.

[0009] According to the present invention, it is possible to provide a load sensor with improved reliability.

[0010] FIG. 1 is a perspective view of a load sensor according to a first embodiment. FIG. 2 is an exploded perspective view of a load sensor according to the first embodiment. FIG. 3 is a cross-sectional view of a load sensor according to the first embodiment. FIG. 4 is a perspective view of a quartz crystal resonator according to the first embodiment. FIG. 5 is an exploded perspective view of a quartz crystal resonator according to the first embodiment. FIG. 6 is a flowchart showing a manufacturing method of a load sensor according to the first embodiment. FIG. 7 is a view showing a step of a manufacturing method of a load sensor. FIG. 8 is a view showing a step of a manufacturing method of a load sensor. FIG. 9 is a view showing a step of a manufacturing method of a load sensor. FIG. 10 is a view showing a step of a manufacturing method of a load sensor. FIG. 11 is a view showing a step of a manufacturing method of a load sensor. FIG. 12 is an exploded perspective view of a load sensor according to a second embodiment. FIG. 13 is a cross-sectional view of a load sensor according to the second embodiment.

[0011] Hereinafter, embodiments of the present invention will be described. In the following description of the drawings, the same or similar components are denoted by the same or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of each part are schematic. The technical scope of the present invention should not be interpreted as being limited to the embodiments.

[0012] For the sake of convenience, each drawing may be accompanied by an orthogonal coordinate system consisting of X, Y, and Z axes to clarify the relationships between the drawings and to aid in understanding the positional relationships of the various components. The directions parallel to the X, Y, and Z axes are referred to as the X-axis, Y-axis, and Z-axis directions, respectively. The plane defined by the X and Y axes is referred to as the XY plane. For the sake of convenience, the positive direction of the Z axis (the direction of the arrow) will be referred to as up or upward, and the negative direction of the Z axis (the direction opposite to the arrow) will be referred to as down or downward, but the orientation of the load sensor is not limited to this.

[0013] First Embodiment

[0014] [Load Sensor Structure] First, the configuration of the load sensor according to the first embodiment will be described with reference to Figs. 1 to 5. Fig. 1 is a perspective view of the load sensor according to the first embodiment. Fig. 2 is an exploded perspective view of the load sensor according to the first embodiment. Fig. 3 is a cross-sectional view of the load sensor according to the first embodiment. Fig. 4 is a perspective view of a quartz crystal resonator according to the first embodiment. Fig. 5 is an exploded perspective view of the quartz crystal resonator according to the first embodiment.

[0015] The load sensor 1 is a load sensor that detects a load in the Z-axis direction. The Z-axis direction is an example of the thickness direction. As shown in Fig. 2, the load sensor 1 includes a quartz crystal unit 10, a lower housing 20, an upper housing 30, a circuit board 40, a lower metal plate 52, and an upper metal plate 53.

[0016] The quartz crystal resonator 10 includes a quartz crystal resonator element 11 , a first lid substrate 12 , and a second lid substrate 13 .

[0017] The quartz crystal vibrating element 11 is an electromechanical energy conversion element that converts electrical energy into mechanical energy and vice versa by the piezoelectric effect.

[0018] The quartz crystal vibrating element 11 is excited at a predetermined frequency based on the applied alternating voltage. The quartz crystal vibrating element 11 is distorted in accordance with the load applied to the load sensor 1 in the thickness direction, and the resonant frequency of the quartz crystal vibrating element 11 changes based on this distortion. In other words, the load applied to the load sensor 1 can be calculated by measuring the resonant frequency of the quartz crystal vibrating element 11. The main vibration of the quartz crystal vibrating element 11 is a thickness shear vibration mode.

[0019] The main vibration of the quartz crystal vibration element is not limited to the thickness shear vibration mode, but may be, for example, a thickness extensional vibration mode, an extensional vibration mode, a length vibration mode, or a bending vibration mode.

[0020] As shown in FIGS. 4 and 5 , the quartz crystal vibrating element 11 includes a thin quartz crystal substrate (Quartz Crystal Element) 11S, a first excitation electrode 14a and a second excitation electrode 14b that constitute a pair of excitation electrodes, a first extraction electrode 15a and a second extraction electrode 15b that constitute a pair of extraction electrodes, and a first connection electrode 16a and a second connection electrode 16b that constitute a pair of connection electrodes.

[0021] The quartz crystal substrate 11S has a first major surface 11A and a second major surface 11B that constitute a pair of major surfaces. The first major surface 11A and the second major surface 11B face each other in the X-axis direction. The first major surface 11A and the second major surface 11B extend in the Y-axis direction and the Z-axis direction. The first major surface 11A is located on the side facing the first lid substrate 12. The second major surface 11B is located on the side facing the second lid substrate 13. The first major surface 11A and the second major surface 11B are each formed in a rectangular shape with a short side extending in the Y-axis direction and a long side extending in the Z-axis direction. The quartz crystal substrate 11S has a flat plate shape with a uniform dimension in the X-axis direction.

[0022] The shapes of the first and second main surfaces of the quartz substrate are not limited to those described above. For example, the shapes of the first and second main surfaces of the quartz substrate may be rectangular with long sides extending in the Z'-axis direction and short sides extending in the X-axis direction, or square with sides extending in the Z'-axis direction and sides extending in the X-axis direction. The shapes of the first and second main surfaces of the quartz substrate may be rectangular with sides extending in directions intersecting the Y-axis direction and the Z-axis direction. The shapes of the first and second main surfaces of the quartz substrate may be polygonal, circular, elliptical, or a combination thereof extending in the Y-axis direction and the Z-axis direction.

[0023] Furthermore, the principal surfaces of the quartz substrate are not limited to those described above as long as they extend at least in the Z-axis direction. The first and second principal surfaces of the quartz substrate may be polygonal, circular, elliptical, or a combination thereof, extending in the Z-axis direction and the X-axis direction.

[0024] Furthermore, the quartz crystal substrate is not limited to a flat plate. The quartz crystal substrate may have a mesa structure or an inverted mesa structure, in which at least one of the pair of main surfaces has an uneven surface. The quartz crystal substrate may have a convex structure in which the amount of change in thickness changes continuously, or a bevel structure in which the amount of change in thickness changes discontinuously.

[0025] The quartz crystal substrate 11S is, for example, an AT-cut quartz crystal. The AT-cut quartz crystal substrate 11S is cut out with the crystalline X-Z' plane as the principal surface, with the crystalline Y'-axis and crystalline Z'-axis being the crystalline X-axis (electrical axis), crystalline Y-axis (mechanical axis), and crystalline Z-axis (optical axis) of synthetic quartz crystal, respectively, being the crystalline Y'-axis and the crystalline Z'-axis, which are obtained by rotating the crystalline Y-axis and the crystalline Z-axis around the crystalline X-axis by 35 degrees 15 minutes ± 1 minute 30 seconds from the crystalline Y-axis toward the crystalline Z-axis. Note that the crystalline X-axis, the crystalline Y-axis, and the crystalline Z-axis do not coincide with the X-axis, Y-axis, and Z-axis shown for convenience in FIGS. 1 to 5 . The X-axis shown for convenience in the figures corresponds to the crystalline Y'-axis, the Y-axis shown for convenience in the figures corresponds to the crystalline Z'-axis, and the Z-axis shown for convenience in the figures corresponds to the crystalline X-axis.

[0026] The quartz crystal vibrating element 11 using the AT-cut quartz crystal substrate 11S has high frequency stability over a wide temperature range. The AT-cut quartz crystal vibrating element also has excellent aging characteristics and can be manufactured at low cost. Furthermore, the AT-cut quartz crystal vibrating element uses the thickness shear vibration mode as its primary vibration mode.

[0027] The cut angle of the quartz crystal substrate is not limited to the above. The rotation angles of the Y'-axis and Z'-axis in the AT-cut quartz crystal substrate 11S may be tilted in a range of 35°15' to -5° or more or +15° or less. The cut angle of the quartz crystal substrate may be a cut other than the AT-cut, such as a BT-cut, GT-cut, or SC-cut. The primary vibration mode of the quartz crystal vibrating element is not limited to the thickness-shear vibration mode, and may be, for example, thickness-extensional vibration, diametrical vibration, longitudinal vibration, or flexural vibration.

[0028] The first excitation electrode 14a and the second excitation electrode 14b apply an AC voltage to the quartz substrate 11S to excite the quartz substrate 11S. As shown in Fig. 5, the first excitation electrode 14a is provided in the center of the first main surface 11A of the quartz substrate 11S. The second excitation electrode 14b is provided in the center of the second main surface 11B of the quartz substrate 11S. The first excitation electrode 14a and the second excitation electrode 14b face each other in the X-axis direction, sandwiching the quartz substrate 11S therebetween.

[0029] 5, the first excitation electrode 14a and the second excitation electrode 14b have substantially the same shape and dimensions. For example, the planar shape of the first excitation electrode 14a when the first main surface 11A of the quartz crystal substrate 11S is viewed in plan, and the planar shape of the second excitation electrode 14b when the second main surface 11B of the quartz crystal substrate 11S is viewed in plan, are circular shapes of the same size. The first excitation electrode 14a and the second excitation electrode 14b are arranged so that they entirely overlap each other in the X-axis direction.

[0030] The planar shapes of the first excitation electrode and the second excitation electrode are not limited to those described above, and may be polygonal, circular, elliptical, or a combination thereof.

[0031] 5, the first extraction electrode 15a electrically connects the first excitation electrode 14a and the first connection electrode 16a, and the second extraction electrode 15b electrically connects the second excitation electrode 14b and the second connection electrode 16b. The first extraction electrode 15a is provided on the first main surface 11A of the quartz substrate 11S, and the second extraction electrode 15b is provided on the second main surface 11B of the quartz substrate 11S. The first extraction electrode 15a is extended from the first excitation electrode 14a to the end of the quartz substrate 11S on the positive side of the Y-axis. The second extraction electrode 15b is extended from the second excitation electrode 14b to the end of the quartz substrate 11S on the negative side of the Y-axis.

[0032] The first connection electrode 16a and the second connection electrode 16b electrically connect the quartz crystal vibrating element 11 to the circuit board 40. As shown in Fig. 4, the first connection electrode 16a is provided on a side surface of the quartz crystal vibrating element 10 facing the positive direction of the Y axis. The second connection electrode 16b is provided on a side surface of the quartz crystal vibrating element 10 facing the negative direction of the Y axis. The first connection electrode 16a is joined to a connection portion 41 of the circuit board 40 (described later) by a first solder 17a and is electrically connected to the connection portion 41. The second connection electrode 16b is joined to the connection portion 41 by a second solder 17b and is electrically connected to the connection portion 41.

[0033] The first lid substrate 12 and the second lid substrate 13 are containers that accommodate, in an excitable manner, the excitation portion on which the first excitation electrode 14a and the second excitation electrode 14b of the quartz crystal vibrating element 11 are formed. The first lid substrate 12 seals the first excitation electrode 14a of the quartz crystal vibrating unit 10 in a cavity, and the second lid substrate 13 seals the second excitation electrode 14b of the quartz crystal vibrating unit 10 in a cavity. As shown in Fig. 4, the first lid substrate 12 is provided on the negative side of the quartz crystal vibrating element 11 in the X-axis direction, and the second lid substrate 13 is provided on the positive side of the quartz crystal vibrating element 11 in the X-axis direction.

[0034] 5, the first lid substrate 12 has a first substrate layer 12S and a first bonding layer 12G. Similarly, the second lid substrate 13 has a second substrate layer 13S and a second bonding layer 13G.

[0035] The first substrate layer 12S and the second substrate layer 13S are, for example, quartz crystal substrates having the same cut angle as the quartz crystal substrate 11S. This reduces the thermal stress acting on the quartz crystal vibrating element 11 from the first lid substrate 12 and the second lid substrate 13.

[0036] Although the materials for the first and second substrate layers are not limited to those described above, from the viewpoint of suppressing thermal stress acting on the quartz crystal resonator element, it is desirable for the materials to have a thermal expansion coefficient close to that of the quartz crystal substrate of the quartz crystal resonator element. Furthermore, from the viewpoint of suppressing damage to the quartz crystal resonator due to differences in the magnitude of distortion between the quartz crystal resonator element, the first substrate layer, and the second substrate layer when the quartz crystal resonator is distorted by a load applied to the load sensor, it is desirable for the materials for the first and second substrate layers to have a Young's modulus close to that of the quartz crystal substrate of the quartz crystal resonator element. For example, the materials for the first and second substrate layers may be glass, ceramics such as alumina, or metals such as Fe—Ni—Co alloys.

[0037] The first bonding layer 12G bonds the first substrate layer 12S to the quartz vibrating element 11. The second bonding layer 13G bonds the second substrate layer 13S to the quartz vibrating element 11. For example, the first bonding layer 12G is an organic adhesive containing a gap spacer filler for adjusting the gap between the quartz vibrating element 11 and the first substrate layer 12S. The organic adhesive is, for example, an adhesive containing an epoxy-based, vinyl-based, acrylic-based, urethane-based, or silicone-based resin. The second bonding layer 13G is an organic adhesive containing the same gap spacer filler as the first bonding layer 12G.

[0038] The materials of the first and second bonding layers are not limited to those described above, and may be inorganic adhesives such as silicon-based adhesives containing water glass, calcium-based adhesives containing cement, etc. The first and second bonding layers may be low-melting glass (e.g., lead borate-based or tin phosphate-based).

[0039] A central opening C12 that opens toward the quartz-crystal vibrating element 11 is formed in a region of the first bonding layer 12G that overlaps with the first excitation electrode 14a. Furthermore, an end opening E12 that opens toward the quartz-crystal vibrating element 11 is formed in a region of the first bonding layer 12G that overlaps with the connection portion of the first extraction electrode 15a with the first connection electrode 16a. 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 exposes the first excitation electrode 14a, and the end opening E12 increases the contact area of ​​the first extraction electrode 15a with the first connection electrode 16a. Similar to the first bonding layer 12G, the second bonding layer 13G is formed with a central opening C13 and end openings (not shown). The first bonding layer 12G seals the first excitation electrode 14a liquid-tight, and the second bonding layer 13G seals the second excitation electrode 14b liquid-tight.

[0040] The lower housing 20 and the upper housing 30 sandwich and hold the crystal unit 10 in the Z-axis direction. The lower housing 20 and the upper housing 30 are containers that house the crystal unit 10. The lower housing 20 is located on the negative Z-axis side of the crystal unit 11, and the upper housing 30 is located on the positive Z-axis side of the crystal unit 11. One end of the lower housing 20 and the upper housing 30 is crimped to the other end. The lower housing 20 is less susceptible to elastic deformation than the upper housing 30. The upper housing 30 is configured to be elastically deformable and functions as a leaf spring. By crimping the ends of the lower housing 20 and the upper housing 30, the upper housing 30 elastically deforms toward the lower housing 20, applying a preload in the Z-axis direction to the crystal unit 10.

[0041] The lower housing 20 and the upper housing 30 are made of the same ferritic stainless steel SUS430, and the thickness of the lower housing 20 is greater than the thickness of the upper housing 30. For example, the thickness of the lower housing 20 is about 1.0 mm, and the thickness of the upper housing 30 is about 0.3 mm. In other words, the lower housing 20 is less susceptible to elastic deformation than the upper housing 30 because the lower housing 20 is made thicker than the upper housing 30.

[0042] The resistance of the lower housing to elastic deformation compared to the upper housing may be achieved, for example, by using a material for the lower housing that has a greater strength (yield point stress) value than the material for the upper housing, or by giving the lower housing a shape that suppresses deformation of ribs or the like.

[0043] The lower housing 20 has a circular shape when viewed in a plane in the Z-axis direction. The lower housing 20 has a central portion 21 and end portions 22. When viewed in a plane in the Z-axis direction, the central portion 21 is located at the center of the lower housing 20, and the end portions 22 are arranged in a frame shape surrounding the central portion 21. The lower housing 20 is flat, and the central portion 21 has a flat upper surface 21A on the side facing the quartz crystal unit 10. A notch SL1 is formed in the end portion 22. The notch SL1 is a through-hole that opens through the lower housing 20 in the positive and negative directions of the Z-axis. The notch SL1 also opens to the outside of the lower housing 20 when viewed in a plane in the Z-axis direction. The lower housing 20 is flat, and the thickness of the central portion 21 and the thickness of the end portions 22 in the Z-axis direction are approximately equal, and the lower surfaces of the central portion 21 and the end portions 22 are continuous in the XY plane.

[0044] The upper housing 30 has a circular shape when viewed in a plane in the Z-axis direction. The upper housing 30 has a pressure-receiving portion 31, an upper side wall portion 32, a peripheral portion 33, a lower side wall portion 34, and an end portion 35.

[0045] As shown in Figure 1, when viewed in a plane in the Z-axis direction, the pressure-receiving portion 31 is provided in the center of the upper housing 30, the upper side wall portion 32 is provided in a frame shape around the pressure-receiving portion 31, the peripheral portion 33 is provided in a frame shape around the upper side wall portion 32, the lower side wall portion 34 is provided in a frame shape around the peripheral portion 33, and the end portion 35 is provided in a frame shape around the lower side wall portion 34.

[0046] 3, the pressure receiving portion 31 faces the quartz crystal unit 10 in the Z-axis direction and is the portion that receives the load acting on the load sensor 1. The pressure receiving portion 31 is the portion of the upper housing 30 that is farthest from the lower housing 20. The pressure receiving portion 31 has a lower surface 31B that faces the quartz crystal unit 10.

[0047] As shown in FIG. 3 , the upper sidewall 32 extends from the outer edge of the pressure-receiving portion 31 toward the lower housing 20. The peripheral portion 33 extends from the lower end of the upper sidewall 32 in the opposite direction from the pressure-receiving portion 31. The lower sidewall 34 extends from the outer edge of the peripheral portion 33 toward the lower housing 20. The end 35 has an upper end 35a, a lower end 35b, and a folded portion 35c. The upper end 35a extends from the lower end of the lower sidewall 34 in the opposite direction from the peripheral portion 33. The lower surface of the upper end 35a is in contact with the upper surface of the end 22 of the lower housing 20. The folded portion 35c extends from the outer edge of the upper end 35a along the side of the lower housing 20. The lower end 35b extends from the lower end of the folded portion 35c toward the upper end 35a. The upper surface of the lower end portion 35b is in contact with 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 sandwich the end portion 22 of the lower housing 20 in the Z-axis direction.

[0048] The circuit board 40 is provided on the upper housing 30 side of the lower housing 20. The circuit board 40 is provided to avoid the area between the crystal unit 10 and the lower housing 20. The circuit board 40 is flexible, and an electric circuit is formed on the circuit board 40. The circuit board 40 is, for example, a flexible printed circuit (FPC) in which a conductive foil such as copper foil is bonded to an insulating base fill such as polyimide or polyester.

[0049] As shown in FIG. 3 , the circuit board 40 has a connection portion 41, a peripheral portion 42, and a lead-out portion 43. The connection portion 41 is connected to a side surface of the crystal unit 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, in an area spaced apart from the crystal unit 10 in a plan view in the Z-axis direction. The peripheral portion 42 is attached to the upper surface 21A of the central portion 21 of the lower housing 20, for example, with an adhesive. The portion connecting the connection portion 41 and the peripheral portion 42 of the circuit board 40 is bent. The peripheral portion 42 is equipped with circuit components 49 and the like that constitute an oscillation circuit that converts the resonant frequency of the crystal unit 10 into an electrical signal. The lead-out portion 43 passes through a cutout portion SL1 in the lower housing 20 and leads out of the internal space between the lower housing 20 and the upper housing 30. As shown in FIG. 1 , the circuit board 40 is electrically connected to an external circuit 90 at the lead-out portion 43.

[0050] The lower metal plate 52 is provided between the quartz crystal unit 10 and the lower housing 20 in the Z-axis direction. As shown in Figures 2 and 3, the lower metal plate 52 is in contact with the surface of the quartz crystal unit 10 facing the lower housing 20. The lower metal plate 52 is also in contact with the surface of the lower housing 20 facing the quartz crystal unit 10 without the circuit board 40 in between. In other words, in a plan view in the Z-axis direction, the lower metal plate 52 is provided at a distance from the peripheral portion 42 of the circuit board 40.

[0051] As shown in FIG. 3 , the lower metal plate 52 has an upper surface 52A facing the quartz crystal unit 10 and a lower surface 52B facing the lower housing 20. The upper surface 52A of the lower metal plate 52 is bonded to the quartz crystal unit 10, for example, with an adhesive. That is, the upper surface 52A of the lower metal plate 52 is indirectly in contact with the quartz crystal unit 10 via the adhesive. The adhesive used to bond the lower metal plate 52 and the quartz crystal unit 10 is not particularly limited, but may be, for example, a relatively hard organic adhesive such as an epoxy adhesive. The lower surface 52B of the lower metal plate 52 is in detachable contact with, for example, the upper surface 21A of the central portion 21 of the lower housing 20. That is, 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.

[0052] The manner in which the lower metal plate contacts the lower housing and the crystal unit is not limited to the above. For example, the lower metal plate may be sandwiched and held between the lower housing and the crystal unit. That is, the upper surface of the lower metal plate may be in direct contact with the lower surface of the crystal unit by detachably abutting against the lower surface of the crystal unit. The upper surface of the lower metal plate may be in direct contact with the lower surface of the crystal unit by bonding the side surfaces of the lower metal plate and the side surfaces of the crystal unit with an adhesive. On the other hand, for example, the lower surface of the lower metal plate may be in indirect contact with the upper surface of the central portion of the lower housing by bonding the side surfaces of the lower metal plate and the upper surface of the central portion of the lower housing with an adhesive. The lower surface of the lower metal plate may be in direct contact with the upper surface of the central portion of the lower housing by bonding the side surfaces of the lower metal plate and the upper surface of the central portion of the lower housing with an adhesive. A circuit board may be provided between the lower housing and the lower metal plate, and the lower surface of the lower metal plate may be in contact with the circuit board rather than the lower housing.

[0053] 3 , in a plan view in the Z-axis direction, the area of ​​the lower metal plate 52 is larger than the area of ​​the quartz crystal unit 10 and smaller than the area of ​​the central portion 21 of the lower housing 20. The lower metal plate 52 overlaps the entire quartz crystal unit 10. In other words, the upper surface 52A of the lower metal plate 52 is in contact with the entire lower surface of the quartz crystal unit 10.

[0054] The flatness of upper surface 52A of lower metal plate 52 is smaller than the flatness of upper surface 21A of central portion 21 of lower housing 20. In other words, the unevenness of upper surface 52A of lower metal plate 52 is smaller than the unevenness of upper surface 21A of central portion 21 of lower housing 20, and upper surface 52A of lower metal plate 52 is flatter and smoother than upper surface 21A of central portion 21 of lower housing 20.

[0055] The lower metal plate 52 is less susceptible to elastic deformation than the upper housing 30, and preferably less susceptible to elastic deformation than the lower housing 20. As an example, the lower metal plate 52 is formed of, for example, the same ferritic stainless steel SUS430 as the lower housing 20 and the upper housing 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 housing 20 in the Z-axis direction and larger than the thickness of the pressure-receiving portion 31 of the upper housing 30 in the Z-axis direction. For example, the thickness of the lower metal plate 52 is approximately 0.5 mm. In other words, the lower metal plate 52 is less susceptible to elastic deformation than the upper housing 30 by forming the lower metal plate 52 thicker than the upper housing 30. Incidentally, even if the thickness of the lower metal plate 52 is smaller than the thickness of the lower housing 20, the area of ​​the lower metal plate 52 is smaller than the area of ​​the lower housing 20 in a plan view in the Z-axis direction, so it is possible to configure the lower metal plate 52 to be less susceptible to elastic deformation than the lower housing 20.

[0056] The resistance of the lower metal plate 52 to elastic deformation compared to the upper housing 30 may be achieved, for example, by using a material for the lower metal plate 52 that has a higher yield strength than the material for the upper housing 30. For example, the yield strength of the lower metal plate 52 is desirably 600 MPa or more and 2,000 MPa or less.

[0057] The upper metal plate 53 is provided between the quartz crystal unit 10 and the upper housing 30 in the Z-axis direction. As shown in Figures 2 and 3, the upper metal plate 53 is in contact with the surface of the quartz crystal unit 10 that faces the upper housing 30. The upper metal plate 53 is also in contact with the surface of the upper housing 30 that faces the quartz crystal unit 10.

[0058] As shown in FIG. 3 , the upper metal plate 53 has a lower surface 53B facing the quartz crystal unit 10 and an upper surface 53A facing the upper housing 30. The lower surface 53B of the upper metal plate 53 is bonded to the quartz crystal unit 10, for example, with an adhesive. That is, the lower surface 53B of the upper metal plate 53 is indirectly in contact with the quartz crystal unit 10 via the adhesive. The adhesive used to bond the upper metal plate 53 and the quartz crystal unit 10 is not particularly limited, but may be, for example, a relatively hard organic adhesive such as an epoxy adhesive. The upper surface 53A of the upper metal plate 53 is in detachable contact with, for example, the lower surface 31B of the pressure-receiving portion 31 of the upper housing 30. That is, the upper surface 53A of the upper metal plate 53 is in direct contact with the lower surface 31B of the pressure-receiving portion 31 of the upper housing 30.

[0059] The manner in which the upper metal plate contacts the upper housing and the quartz crystal unit is not limited to the above. For example, the upper metal plate may be sandwiched and held between the upper housing and the quartz crystal unit. That is, the lower surface of the upper metal plate may be in direct contact with the upper surface of the quartz crystal unit by detachably abutting against the upper surface of the quartz crystal unit. The lower surface of the upper metal plate may be in direct contact with the upper surface of the quartz crystal unit by bonding the side surfaces of the upper metal plate and the side surfaces of the quartz crystal unit with an adhesive. On the other hand, for example, the upper surface of the upper metal plate may be in indirect contact with the lower surface of the pressure receiving portion of the upper housing by bonding the side surfaces of the upper metal plate to the lower surface of the pressure receiving portion of the upper housing with an adhesive. The upper surface of the upper metal plate may be in direct contact with the lower surface of the pressure receiving portion of the upper housing by bonding the side surfaces of the upper metal plate to the lower surface of the pressure receiving portion of the upper housing with an adhesive.

[0060] 3 , in a plan view in the Z-axis direction, the area of ​​the upper metal plate 53 is larger than the area of ​​the quartz crystal unit 10 and smaller than the area of ​​the pressure-receiving portion 31 of the upper housing 30. The upper metal plate 53 overlaps the entire quartz crystal unit 10. In other words, the lower surface 53B of the upper metal plate 53 is in contact with the entire upper surface of the quartz crystal unit 10.

[0061] The flatness of the lower surface 53B of the upper metal plate 53 is smaller than the flatness of the lower surface 31B of the pressure-receiving portion 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 the unevenness of the lower surface 31B of the pressure-receiving portion 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 portion 21 of the lower housing 20.

[0062] The upper metal plate 53 is less susceptible to elastic deformation than the upper housing 30, and preferably less susceptible to elastic deformation than the lower housing 20. As an example, the upper metal plate 53 is formed of, for example, the same ferritic stainless steel SUS430 as the lower housing 20 and the upper housing 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 housing 20 in the Z-axis direction and larger than the thickness of the pressure-receiving portion 31 of the upper housing 30 in the Z-axis direction. For example, the thickness of the upper metal plate 53 is approximately 0.5 mm. In other words, the upper metal plate 53 is less susceptible to elastic deformation than the upper housing 30 by forming the upper metal plate 53 thicker than the upper housing 30. Incidentally, even if the thickness of the upper metal plate 53 is smaller than the thickness of the lower housing 20, the area of ​​the upper metal plate 53 in a plan view in the Z-axis direction is smaller than the area of ​​the lower housing 20, so it is possible to configure the upper metal plate 53 to be less susceptible to elastic deformation than the lower housing 20.

[0063] The resistance of upper metal plate 53 to elastic deformation compared to upper housing 30 may be achieved, for example, by using a material for upper metal plate 53 that has a higher yield strength than the material for upper housing 30. For example, the yield strength of upper metal plate 53 is desirably 600 MPa or more and 2,000 MPa or less.

[0064] [Method of Manufacturing Load Sensor] Next, a method of manufacturing the load sensor 1 according to this embodiment will be described with reference to Fig. 6 to Fig. 13. Fig. 6 is a flowchart showing a method of manufacturing the load sensor 1 according to the first embodiment. Fig. 7 to Fig. 13 are views showing steps of the method of manufacturing the load sensor 1.

[0065] First, the quartz crystal unit 10 and the circuit board 40 are prepared (S10). As shown in Fig. 7, the connection portion 41 and the peripheral portion 42 of the circuit board 40 are connected to each other by temporary fastening portions 45. This limits the displacement of the connection portion 41, making it less likely that the connection portion 41 will bend or otherwise be damaged during transportation of the circuit board 40. A lower metal plate 52 and an upper metal plate 53 are bonded to the quartz crystal unit 10 with an adhesive.

[0066] Next, the quartz crystal unit 10 is mounted on the circuit board 40 (S20). As shown in Fig. 8, with the quartz crystal unit 10, to which the lower metal plate 52 and the upper metal plate 53 have already been bonded, laid flat, the sides of the quartz crystal unit 10 are bonded to the connection portions 41 of the circuit board 40, thereby electrically connecting the quartz crystal unit 10 to the circuit board 40. The quartz crystal unit 10 is mounted on the circuit board 40 by reflow soldering, together with other circuit components 49.

[0067] Next, the temporary fixing portion 45 is cut (S30). As shown in FIG. 9, the temporary fixing portion 45 is cut to make the connecting portion 41 bendable relative to the peripheral portion 42.

[0068] Next, the circuit board 40 is joined to the lower housing 20 (S40). As shown in Fig. 10, the peripheral portion 42 is joined to the central portion 21 of the lower housing 20 with the drawn-out portion 43 aligned with the cutout portion SL1.

[0069] Next, the quartz crystal unit 10 is set upright (S50). As shown in Fig. 11, the quartz crystal unit 10 is set upright so that the lower metal plate 52 is positioned between the quartz crystal unit 10 and the lower housing 20. The portion connecting the connecting portion 41 and the peripheral portion 42 is bent.

[0070] Next, the upper housing 30 is placed on top (S60). As shown in Fig. 12, the pressure-receiving portion 31 of the upper housing 30 is placed on the upper metal plate 53, and the end 35 of the upper housing 30 is placed on the end 22 of the lower housing 20. The lower housing 20 is abutted against the lower metal plate 52, and the upper metal plate 53 is abutted against the upper housing 30. The crystal unit 10 is sandwiched between the lower housing 20 and the upper housing 30 and temporarily fixed.

[0071] Next, the end 35 of the upper housing 30 is crimped (S70). As shown in Fig. 13, the end 35 of the upper housing 30 is folded back and crimped vertically to the end 22 of the lower housing 20. The upper housing 30 elastically deforms and functions as a leaf spring, applying a preload to the crystal unit 10.

[0072] As described above, according to this embodiment, the load sensor 1 includes the quartz crystal unit 10, the lower housing 20 and the upper housing 30 configured to apply a preload to the quartz crystal unit 10, and the upper metal plate 53 in contact with the surface of the quartz crystal unit 10 facing the upper housing 30. The flatness of the surface of the upper metal plate 53 facing the quartz crystal unit 10 is smaller than the flatness of the surface of the upper housing 30 facing the quartz crystal unit 10.

[0073] This configuration prevents excessive preload from being applied to the quartz crystal unit 10 by caulking the end 22 of the lower housing 20 and the end 35 of the upper housing 30, thereby applying a preload to the quartz crystal unit 10 through elastic deformation of the upper housing 30. This reduces the likelihood of damage to the quartz crystal unit 10 due to excessive preload, thereby preventing a decrease in the reliability of the load sensor 1. Furthermore, the unevenness of the lower surface 53B of the upper metal plate 53 is smaller than the unevenness of the lower surface 31B of the pressure-receiving portion 31 of the upper housing 30. This reduces stress concentration on the upper surface of the quartz crystal unit 10 due to the unevenness of the surface pressing against the upper surface of the quartz crystal unit 10 when a load is applied to the load sensor 1. This reduces damage to the quartz crystal unit 10 from the upper housing 30 side, improving the reliability of the load sensor 1. Furthermore, reducing stress concentration on the upper surface of the quartz crystal unit 10 improves the load-bearing capacity of the load sensor 1.

[0074] In one aspect of this embodiment, the upper metal plate 53 is less likely to deform than the upper housing 30 .

[0075] This makes it possible to suppress stress concentration at the four corners of the top surface of the quartz crystal unit 10 when a preload is applied to the quartz crystal unit 10 due to elastic deformation of the upper housing 30 or when a load is applied to the load sensor 1. Therefore, damage to the quartz crystal unit 10 from the upper housing 30 side can be further suppressed, improving the load resistance of the load sensor 1. This makes it possible to further improve the reliability of the load sensor 1.

[0076] In one aspect of the present embodiment, the proof stress value of the upper metal plate 53 is 600 MPa or more and 2000 MPa or less. In another aspect of the present embodiment, the thickness of the upper metal plate 53 is greater than the thickness of the pressure-receiving portion 31 of the upper housing 30.

[0077] This allows the upper metal plate 53 to be configured to be less susceptible to elastic deformation than the upper housing 30 .

[0078] In one aspect of this embodiment, the load sensor 1 further includes a lower metal plate 52 that contacts the surface of the quartz crystal unit 10 that faces the lower housing 20. The flatness of the surface of the lower metal plate 52 that faces the quartz crystal unit 10 is smaller than the flatness of the surface of the lower housing 20 that faces the quartz crystal unit 10.

[0079] According to this, the unevenness of the upper surface 52A of the lower metal plate 52 is smaller than the unevenness of the upper surface 21A of the central portion 21 of the lower housing 20, so that when a load is applied to the load sensor 1, it is possible to suppress stress concentration on the lower surface of the quartz crystal unit 10 due to the unevenness of the surface pressing against the lower surface of the quartz crystal unit 10. Therefore, it is possible to suppress damage to the quartz crystal unit 10 from the lower housing 20 side, and the load capacity of the load sensor 1 is improved. This further improves the reliability of the load sensor 1. For example, while the load capacity of a load sensor that does not have a lower metal plate and an upper metal plate is about 600 N, the load capacity of the load sensor 1 is improved to about 1000 N.

[0080] It is desirable that the load sensor 1 include both the lower metal plate 52 and the upper metal plate 53, but it is sufficient that the load sensor 1 include at least one of the lower metal plate 52 and the upper metal plate 53. Even if the upper metal plate 53 is provided and the lower metal plate 52 is omitted, it is possible to at least suppress damage caused by stress concentration on the upper housing 30 side of the quartz crystal unit 10. Conversely, even if the lower metal plate 52 is provided and the upper metal plate 53 is omitted, it is possible to at least suppress damage caused by stress concentration on the lower housing 20 side of the quartz crystal unit 10.

[0081] In one aspect of this embodiment, the load sensor 1 further includes a circuit board 40. The circuit board 40 is provided to avoid the area between the quartz crystal unit 10 and the lower housing 20, and the circuit board 40 is connected to a side surface of the quartz crystal unit 10 that extends in the Z-axis direction.

[0082] This prevents stress concentration on the quartz crystal unit 10 due to unevenness or deformation of the circuit board 40 when a load is applied to the load sensor 1. Therefore, damage to the quartz crystal unit 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, the load is not applied to the first solder 17a and the second solder 17b that electrically connect the quartz crystal unit 10 and the circuit board 40, nor is the load applied to the wiring within the circuit board 40. This reduces the occurrence of electrical continuity problems that occur during use of the load sensor 1, such as an increase in contact resistance between the quartz crystal unit 10 and the circuit board 40 and disconnection of the circuit board 40. This further improves the reliability of the load sensor 1.

[0083] Other embodiments will be described below. Note that components that are the same as or similar to those in the first embodiment are denoted by the same or similar reference numerals, and descriptions thereof will be omitted as appropriate. Furthermore, similar effects resulting from similar components will not be mentioned one after another.

[0084] Second Embodiment Next, the configuration of a load sensor 2 according to a second embodiment will be described with reference to Fig. 14 and Fig. 15. Fig. 14 is an exploded perspective view of the load sensor 2 according to the second embodiment. Fig. 15 is a cross-sectional view of the load sensor 2 according to the second embodiment.

[0085] The lower housing 220 of the load sensor 2 is formed in a dish shape. A step is formed between a central portion 221 and an end portion 222 of the lower housing 220. The end portion 222 of the lower housing 220 protrudes more toward the upper housing 30 than the central portion 221 of the lower housing 220. On the side of the lower housing 220 facing the upper housing 30, the central portion 221 of the lower housing 220 is recessed relative to the end portion 222 of the lower housing 220. On the side of the lower housing 220 opposite the side facing the upper housing 30, the central portion 221 of the lower housing 220 is protruded relative to the end portion 222 of the lower housing 220. The central portion 221 and the end portion 222 of the lower housing 220 are formed in a flat plate shape, and the thickness of the central portion 221 of the lower housing 220 is approximately equal to the thickness of the end portion 222 of the lower housing 220.

[0086] As a result, the lower end 35b of the end 35 of the upper housing 30 does not come into contact with the installation surface of the load sensor 2, and the lower surface of the central portion 221 of the lower housing 220 comes into contact with the installation 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 crystal unit 10 can be suppressed. Therefore, damage to the quartz crystal unit 10 from the lower housing 220 side can be further suppressed, and the load resistance of the load sensor 2 can be improved. This can further improve the reliability of the load sensor 2.

[0087] A cutout portion SL2 is formed in the lower housing 220 of the load sensor 2. The cutout portion SL2 is formed on the opposite side of the quartz crystal unit 10 from the cutout portion SL1. The cutout portion SL2 is a through-hole that opens in the lower housing 220 in the positive and negative directions of the Z axis. The cutout portion SL2 opens to the outside of the lower housing 220 in a plan view in the Z axis direction. The cutout portion SL1 is an example of a first cutout portion, and the cutout portion SL2 is an example of a second cutout portion.

[0088] This makes it possible to suppress the generation of force in the XY plane direction when the end 35 of the upper housing 30 is crimped to the end 222 of the lower housing 220, thereby suppressing the occurrence of axial misalignment.

[0089] The number of cutouts formed in the lower housing is not limited to the above, as long as the cutouts are formed at positions point-symmetrical about the quartz crystal unit in a plan view in the Z-axis direction. For example, the lower housing may have first to third cutouts formed in directions that divide the circumferential angle around the quartz crystal unit into three equal parts, or may have first to fourth cutouts formed in directions that divide the circumferential angle around the quartz crystal unit into four equal parts.

[0090] Some or all of the embodiments of the present invention will be described below, but the present invention is not limited to the following descriptions.

[0091] <1> A load sensor that detects a load in a thickness direction, comprising: a piezoelectric substrate having a main surface extending in the thickness direction, and a piezoelectric vibrator having an excitation electrode provided on the main surface of the piezoelectric substrate; a lower housing and an upper housing that sandwich and hold the piezoelectric vibrator in the thickness direction, an end of one of the lower housing and the upper housing being crimped and fixed to an end of the other housing, the lower housing being less susceptible to elastic deformation than the upper housing, and configured so that a preload is applied to the piezoelectric vibrator in the thickness direction by elastic deformation of the upper housing due to the crimping; and an upper metal plate in contact with a surface of the piezoelectric vibrator facing the upper housing, wherein the flatness of the surface of the upper metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the upper housing facing the piezoelectric vibrator.

[0092] <2> The load sensor according to <1>, wherein the upper metal plate is less likely to deform than the upper housing.

[0093] <3> The load sensor according to <1> or <2>, wherein the upper metal plate has a yield strength of 600 MPa or more and 2000 MPa or less.

[0094] <4> The load sensor according to any one of <1> to <3>, wherein the thickness of the upper metal plate is greater than the thickness of the upper housing in a region facing the piezoelectric vibrator in the thickness direction.

[0095] <5> The load sensor according to any one of <1> to <4>, further comprising a lower metal plate in contact with a surface of the piezoelectric vibrator facing the lower housing, wherein the flatness of the surface of the lower metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing facing the piezoelectric vibrator.

[0096] <6> A load sensor that detects a load in a thickness direction, comprising: a piezoelectric substrate having a main surface extending in the thickness direction, and a piezoelectric vibrator having an excitation electrode provided on the main surface of the piezoelectric substrate; a lower housing and an upper housing that sandwich and hold the piezoelectric vibrator in the thickness direction, an end of one of the lower housing and the upper housing being crimped and fixed to an end of the other housing, the lower housing being less susceptible to elastic deformation than the upper housing, and configured so that a preload is applied to the piezoelectric vibrator in the thickness direction by elastic deformation of the upper housing due to the crimping; and a lower metal plate in contact with a surface of the piezoelectric vibrator facing the lower housing, wherein the flatness of the surface of the lower metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing facing the piezoelectric vibrator.

[0097] <7> The load sensor according to any one of <1> to <6>, further comprising a circuit board provided on the upper housing side of the lower housing, the circuit board being provided to avoid a region between the piezoelectric vibrator and the lower housing, and the circuit board being connected to a side surface of the piezoelectric vibrator extending in a thickness direction.

[0098] <8> The load sensor according to any one of <1> to <7>, wherein, on the side opposite to the side facing the upper housing, a central portion facing the piezoelectric vibrator of the lower housing is provided in a convex shape relative to an end of the lower housing.

[0099] <9> A load sensor described in any one of <1> to <8>, wherein a first cutout portion for pulling out wiring electrically connected to the piezoelectric vibrator to the outside and a second cutout portion located on the opposite side of the first cutout portion across the piezoelectric vibrator are formed at the end of the lower housing.

[0100] <10> The load sensor according to any one of <1> to <5>, wherein the upper metal plate is joined to the piezoelectric vibrator.

[0101] <11> The load sensor according to any one of <1> to <5>, wherein the upper metal plate is held by being sandwiched between the piezoelectric vibrator and the upper housing.

[0102] <12> The load sensor according to <1> or <11>, wherein the piezoelectric vibrator is a quartz crystal vibrator.

[0103] In this specification, a quartz crystal resonator having a quartz crystal substrate (quartz crystal element) has been described as an example of a piezoelectric substrate (piezoelectric element), but the piezoelectric resonator is not limited to this. Examples of piezoelectric substrates suitable for use in the piezoelectric vibrator according to this embodiment include piezoelectric ceramics such as lead zirconate titanate (PZT) and aluminum nitride, and piezoelectric single crystals such as lithium niobate and lithium tantalate, but the substrate is not limited to these and can be selected as appropriate.

[0104] As described above, according to one aspect of the present invention, it is possible to provide a load sensor that can improve reliability.

[0105] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. The present invention may be modified or improved without departing from its spirit, and equivalents are also included within the scope of the present invention. In other words, designs modified by those skilled in the art as appropriate to the embodiments and / or modifications are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention. For example, the elements and their arrangements, materials, conditions, shapes, sizes, etc. of the embodiments and / or modifications are not limited to those illustrated and can be modified as appropriate. Furthermore, the embodiments and modifications are merely examples, and it goes without saying that partial substitutions or combinations of the components shown in different embodiments and / or modifications are possible. These are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention.

[0106] REFERENCE SIGNS LIST 1...Load sensor 10...Crystal vibrator 11...Crystal vibrating element 11S...Crystal substrate 11A...First main surface 11B...Second main surface 14a...First excitation electrode 14b...Second excitation electrode 15a...First extraction electrode 15b...Second extraction electrode 16a...First connection electrode 16b...Second connection electrode 17a...First solder 17b...Second solder 12...First lid substrate 12S...First substrate layer 12G...First bonding layer 13...Second lid substrate 13S...Second substrate layer 13G...Second bonding layer 20...Lower housing 21...Central portion 21A...Upper surface 22...End portion SL1...First notch portion 30...Upper housing 31...Pressure receiving portion 31B...Lower surface 32...Upper side wall portion 33...Peripheral portion 34...Lower side wall part 35...End part 35a...Top end part 35b...Lower end part 35c...Folded part 40...Circuit board 41...Connection part 42...Peripheral part 43...Drawer part 52...Lower metal plate 52A...Top surface 52B...Bottom surface 53...Top metal plate 53A...Top surface 53B...Bottom surface

Claims

1. A load sensor for detecting a load in a thickness direction, comprising: a piezoelectric substrate having a main surface extending in the thickness direction, and a piezoelectric vibrator having an excitation electrode provided on the main surface of the piezoelectric substrate; a lower housing and an upper housing that sandwich and hold the piezoelectric vibrator in the thickness direction, an end of one of the lower housing and the upper housing being crimped and fixed to an end of the other housing, the lower housing being less susceptible to elastic deformation than the upper housing, and configured so that a preload is applied to the piezoelectric vibrator in the thickness direction by elastic deformation of the upper housing due to the crimping; and an upper metal plate in contact with a surface of the piezoelectric vibrator facing the upper housing, wherein the flatness of the surface of the upper metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the upper housing facing the piezoelectric vibrator.

2. The load sensor according to claim 1, wherein the upper metal plate is less susceptible to deformation than the upper housing.

3. The load sensor according to claim 1 or 2, wherein the upper metal plate has a yield strength of 600 MPa or more and 2000 MPa or less.

4. A 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 a region facing the piezoelectric vibrator in the thickness direction.

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

6. The load sensor according to any one of claims 1 to 4, wherein the upper metal plate is sandwiched and held between the piezoelectric vibrator and the upper housing.

7. A load sensor as described in any one of claims 1 to 6, further comprising a lower metal plate in contact with the surface of the piezoelectric vibrator facing the lower housing, wherein the flatness of the surface of the lower metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing facing the piezoelectric vibrator.

8. A load sensor for detecting a load in a thickness direction, comprising: a piezoelectric substrate having a main surface extending in the thickness direction, and a piezoelectric vibrator having an excitation electrode provided on the main surface of the piezoelectric substrate; a lower housing and an upper housing sandwiching and holding the piezoelectric vibrator in the thickness direction, wherein an end of one of the lower housing and the upper housing is fixed to an end of the other housing by crimping, and the lower housing is less susceptible to elastic deformation than the upper housing, and the lower housing and upper housing are configured so that a preload is applied to the piezoelectric vibrator in the thickness direction by elastic deformation of the upper housing due to the crimping; and a lower metal plate in contact with a surface of the piezoelectric vibrator facing the lower housing, wherein the flatness of the surface of the lower metal plate facing the piezoelectric vibrator is smaller than the flatness of the surface of the lower housing facing 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 with an adhesive.

10. The load sensor according to claim 7 or 8, wherein the lower metal plate is sandwiched and held between the piezoelectric vibrator and the lower housing.

11. A load sensor as described in any one of claims 1 to 10, further comprising a circuit board provided on the upper housing side of the lower housing, the circuit board being provided to avoid the area between the piezoelectric vibrator and the lower housing, and the circuit board being connected to a side of the piezoelectric vibrator extending in the thickness direction.

12. A load sensor as described in any one of claims 1 to 11, wherein, on the side opposite to the side facing the upper housing, the central portion of the lower housing facing the piezoelectric vibrator is provided in a convex shape relative to the end portion of the lower housing.

13. A load sensor as described in any one of claims 1 to 12, wherein the end of the lower housing is formed with a first notch for pulling out wiring electrically connected to the piezoelectric vibrator to the outside, and a second notch located on the opposite side of the piezoelectric vibrator from the first notch.

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

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