Load sensor and method for manufacturing load sensor

Abstract

This load sensor 1 for sensing a load in the thickness direction comprises: an upper casing 30 having an upper surface part 31 and a side surface part 32 extending in the thickness direction from the outer circumference of the upper surface part 31; a lower casing 20 having a lower surface part 21 that faces the upper surface part 31 in the thickness direction, the lower casing 20 having a property of being less elastically deformable than the upper casing 30; a piezoelectric vibrator 10 accommodated in a space between the upper casing 30 and the lower casing 20, the piezoelectric vibrator 10 having a piezoelectric substrate 13 provided between the upper surface part 31 and the lower surface part 21, and a pair of excitation electrodes provided on the mutually opposing main surfaces of the piezoelectric substrate 13. The pair of excitation electrodes extend in the thickness direction. One edge from among an edge 35 of the upper casing 30 and an edge 25 of the lower casing 20 is fixed by crimping to the other edge. The elastic deformation of the upper casing 30 due to the crimping causes the upper casing 30 to apply a preload to the piezoelectric vibrator 10 in the thickness direction.

Description

Load sensor and method for manufacturing the load sensor

[0001] The present invention relates to a load sensor and a method for manufacturing a load sensor.

[0002] A load sensor using a piezoelectric vibrator is known, and when a load is applied to the piezoelectric vibrator, the resonant frequency of the piezoelectric vibrator changes in response to the load, and the load sensor measures the magnitude of the load based on this change.

[0003] Japanese Patent Application Laid-Open No. 2015-25796

[0004] For example, Patent Document 1 discloses a load sensor that uses a quartz crystal oscillator as a piezoelectric oscillator. In this load sensor, a preload (preload) is applied to the quartz crystal oscillator in the longitudinal direction by tightening a screw member through a retainer housed in a case, and a thrust bearing suppresses the torsional force acting when the preload is applied.

[0005] However, when applying a preload by tightening a screw member as in Patent Document 1, there is a risk that, for example, the crystal resonator element may be damaged due to excessive preload, or that detection may be impaired due to changes in the preload during long-term measurements. Furthermore, there is a problem in that the device cannot be made thinner due to the inclusion of a thrust bearing.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a load sensor and a method for manufacturing a load sensor that has a low profile and suppresses long-term fluctuations.

[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 comprises an upper housing having an upper surface portion and a side portion extending in the thickness direction from the outer periphery of the upper surface portion; a lower housing having a lower surface portion facing the upper surface portion in the thickness direction and having a property of being less prone to elastic deformation than the upper housing; and a piezoelectric vibrator housed in the space between the upper and lower housings, the piezoelectric vibrator having a piezoelectric substrate provided between the upper and lower surface portions and a pair of excitation electrodes provided on opposing main surfaces of the piezoelectric substrate, the pair of excitation electrodes extending along the thickness direction, and one of the ends of the upper housing and the lower housing being crimped and fixed to the other end, so that the upper housing applies a preload in the thickness direction to the piezoelectric vibrator due to elastic deformation of the upper housing caused by the crimping.

[0008] A method for manufacturing a load sensor according to another aspect of the present invention is a method for manufacturing a load sensor that detects a load in a thickness direction, the load sensor comprising: an upper housing having an upper surface portion and a side portion extending in the thickness direction from an outer periphery of the upper surface portion; a lower housing having a lower surface portion facing the upper surface portion in the thickness direction and having a property of being less prone to elastic deformation than the upper housing; and a piezoelectric vibrator housed in a space between the upper housing and the lower housing, the piezoelectric vibrator having a piezoelectric substrate provided between the upper surface portion and the lower surface portion and a pair of excitation electrodes provided on main surfaces of the piezoelectric substrate that face each other, the method comprising: mounting the piezoelectric vibrator on the lower housing; The method includes setting an upper housing on the piezoelectric vibrator, setting the upper housing on the piezoelectric vibrator, and crimping and fixing one of the ends of the upper housing and the lower housing to the other end, wherein setting the upper housing on the piezoelectric vibrator includes providing a gap for preload adjustment between the end of the upper housing and the end of the lower housing by supporting the upper housing on the piezoelectric vibrator, and crimping and fixing includes reducing the gap for preload adjustment and elastically deforming the upper housing, and causing the upper housing to apply a preload in the thickness direction to the piezoelectric vibrator due to the elastic deformation of the upper housing.

[0009] According to the present invention, it is possible to provide a load sensor and a method for manufacturing the load sensor, which has a low profile and is suppressed from fluctuating over time.

[0010] FIG. 1 is a perspective view schematically showing a load sensor according to a first embodiment; FIG. 2 is a cross-sectional view schematically showing a configuration of a load sensor according to the first embodiment; FIG. 3 is an exploded perspective view schematically showing a structure of a piezoelectric vibrator according to the first embodiment; FIG. 4 is a diagram showing load characteristics of the load sensor according to the first embodiment; FIG. 5 is a flowchart showing a manufacturing method of the load sensor according to the first embodiment; FIG. 6 is a cross-sectional view schematically showing a structure of a load sensor according to a second embodiment; FIG. 7 is a perspective view schematically showing a structure of a load sensor according to the second embodiment; FIG. 8 is a cross-sectional view schematically showing a structure of a load sensor according to a third embodiment;

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The drawings of the present embodiment are merely examples, and the dimensions and shapes of each part are schematic, so the technical scope of the present invention should not be interpreted as being limited to the embodiment.

[0012] <First embodiment> The configuration of a load sensor 1 according to a first embodiment of the present invention will be described with reference to Figures 1, 2, and 3. Figure 1 is a perspective view that schematically shows the load sensor according to this embodiment. Figure 2 is a cross-sectional view that schematically shows the configuration of the load sensor according to the first embodiment. Figure 3 is an exploded perspective view that schematically shows the structure of the load sensor according to the first embodiment.

[0013] To clarify the relationships between the drawings and to aid in understanding the positional relationships of the various components, each drawing is conveniently accompanied by a Cartesian coordinate system consisting of the X-axis, Y-axis, and Z-axis. The directions parallel to the X-axis, Y-axis, and Z-axis are called the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. For convenience, the positive direction of the Z-axis (the direction of the Z-axis arrow) is called "up," and the negative direction of the Z-axis (the direction opposite to the direction of the Z-axis arrow) is called "down." The plane defined by the X-axis and Y-axis is called the XY plane, and similar terms are used for the YZ plane and the ZX plane.

[0014] 1 and 2, the load sensor 1 includes a piezoelectric vibrator 10, a lower housing 20, an upper housing 30, and a buffer material 40. The load sensor 1 detects a load in the thickness direction.

[0015] In the following explanation, the side of the load sensor 1 on which the upper housing 30 is provided will be referred to as the top (or front), and the side on which the lower housing 20 is provided will be referred to as the bottom (or back), and the thickness direction, which is the load detection direction of the load sensor 1, will also be defined as the up-down direction.

[0016] The piezoelectric vibrator 10 excites the piezoelectric vibration element 11 in response to an applied voltage. The piezoelectric vibration element 11 is, for example, a quartz crystal vibration element in which a quartz crystal piece is used as a piezoelectric body that vibrates in response to an applied voltage, but is not limited to this.

[0017] The piezoelectric vibrator 10 includes a piezoelectric vibrating element 11 and a pair of support layers 12a and 12b. As shown in Fig. 3, the piezoelectric vibrating element 11 is sandwiched between the support layers 12a and 12b in the Y-axis direction.

[0018] The piezoelectric vibration element 11 includes a piezoelectric substrate 13, a first excitation electrode 14a, a second excitation electrode 14b, a first connection electrode 15a, and a second connection electrode 15b. The piezoelectric vibration element 11 also includes a first main surface 11a and a second main surface 11b. The first main surface 11a and the second main surface 11b extend in the XZ plane and face each other in the Y-axis direction, sandwiching the piezoelectric vibration element 11 therebetween. The first main surface 11a constitutes the Y-axis positive side of the piezoelectric vibration element 11, and the second main surface 11b constitutes the Y-axis negative side of the piezoelectric vibration element 11. The piezoelectric vibration element 11 includes a vibration portion 16 located in the center when viewed in a plan view of the XZ plane and contributing to excitation, and a peripheral portion 17 surrounding the vibration portion 16. The vibration portion 16 is circular when viewed in a plan view of the XZ plane, but the shape of the vibration portion 16 is not limited to this. The shape of the vibration part 16 when viewed in a plan view of the XZ plane may be any shape that includes the first excitation electrode 14a and the second excitation electrode 14b when viewed in a plan view of the XZ plane, and may be, for example, a polygonal shape, an elliptical shape, or a shape that is a combination of these. The peripheral edge part 17 is provided in a frame shape that is continuous in the circumferential direction around the vibration part 16. However, the shape of the peripheral edge part is not limited to the above, and it may be provided discontinuously in the circumferential direction.

[0019] The piezoelectric substrate 13 is a flat substrate made of a piezoelectric material. The piezoelectric substrate 13 has a pair of principal surfaces extending along the XZ plane, which constitute the first principal surface 11a and the second principal surface 11b of the piezoelectric vibration element 11. The pair of principal surfaces of the piezoelectric substrate 13 are rectangular, with short sides extending in the X-axis direction and long sides extending in the Z-axis direction. By setting the thickness direction in which a load is detected as the longitudinal direction of the piezoelectric substrate 13, the distortion of the vibration unit 16 when a load is applied in the thickness direction can be increased, thereby improving the detection accuracy of the load sensor 1. Note that the shape and orientation of the piezoelectric substrate 13 are not limited to those described above, as long as the piezoelectric substrate 13 can withstand a load. For example, the shape of the pair of principal surfaces of the piezoelectric substrate 13 may be square, or may be rectangular with short sides extending along the Z-axis direction. The shape of the pair of principal surfaces of the piezoelectric substrate 13 may be circular, elliptical, polygonal, or a combination thereof. Furthermore, although the piezoelectric substrate is provided in a flat plate shape, this is not limited thereto, and it may be provided in, for example, a mesa shape, an inverted mesa shape, a bevel shape, or a convex shape.

[0020] The first excitation electrode 14a and the second excitation electrode 14b are provided inside the vibrating portion 16 when viewed in a plan view of the XZ plane, and are stacked so as to sandwich the piezoelectric substrate 13 from the Y-axis direction. The first excitation electrode 14a is provided on the first principal surface 11a side. Similarly, the second excitation electrode 14b is provided on the second principal surface 11b side in a position opposite the first excitation electrode 14a. When viewed in a plan view of the XZ plane, the first excitation electrode 14a and the second excitation electrode 14b are provided inside the vibrating portion 16 and are spaced apart from the peripheral portion 17. The first excitation electrode 14a and the second excitation electrode 14b are each provided in a circular shape when the first principal surface 11a and the second principal surface 11b are viewed in a plan view. However, the shape of the first excitation electrode 14a and the second excitation electrode 14b when viewed in a plane is not limited to the above, and may be a polygonal shape, an elliptical shape, or a combination of these, for example, a rectangular shape.

[0021] The first connection electrode 15a extends from the first excitation electrode 14a to the corners of the piezoelectric vibration element 11 in the positive X-axis direction and the negative Z-axis direction, and is electrically connected to the outside of the piezoelectric vibrator 10. Specifically, one end of the first connection electrode 15a is connected to the first excitation electrode 14a, and the other end is provided at a corner of the piezoelectric vibration element 11. This corner is exposed from the retention layer 12a. The first excitation electrode 14a is electrically connected to the outside via the first connection electrode 15a provided at the exposed portion. Similar to the first connection electrode 15a, the second connection electrode 15b also extends from the second excitation electrode 14b to the corners of the piezoelectric vibration element 11 in the negative X-axis direction and the negative Z-axis direction, and is electrically connected to the outside of the piezoelectric vibrator 10. Specifically, one end of the second connection electrode 15b is connected to the second excitation electrode 14b, and the other end is provided at a corner of the piezoelectric vibration element 11. This corner is exposed from the retention layer 12b. The second excitation electrode 14b is electrically connected to the outside via the second connection electrode 15b provided on the exposed portion. In the example shown in Fig. 2, the first connection electrode 15a and the second connection electrode 15b are electrically connected to the electrodes of the buffer material 40 described later by anisotropic conductive paste 19.

[0022] The retaining layer 12a corresponds to one of a pair of retainers that accommodate the vibration portion 16 of the piezoelectric vibration element 11. The retaining layer 12a has a recess 18a at a position that overlaps the vibration portion 16 of the piezoelectric vibration element 11 when viewed in plan on the XZ plane. The recess 18a opens toward the first main surface 11a of the piezoelectric vibration element 11. When the piezoelectric vibration element 11 and the retaining layer 12a are bonded, the vibration portion 16 and the bottom wall of the recess 18a are spaced apart, forming a vibration space between them for the vibration portion 16 to vibrate. The side wall of the recess 18a in the retaining layer 12a is bonded to the first main surface 11a of the peripheral portion 17 of the piezoelectric vibration element 11. The first excitation electrode 14a is sealed in the vibration space. Like the retaining layer 12a, the retaining layer 12b corresponds to one of a pair of retainers that accommodate the vibration portion 16 of the piezoelectric vibration element 11. The retaining layer 12b is disposed opposite the retaining layer 12a across the piezoelectric vibration element 11. The retaining layer 12b has a recess 18b at a position overlapping the vibration portion 16 of the piezoelectric vibration element 11 when viewed in plan in the XZ plane. The recess 18b opens toward the second main surface 11b of the piezoelectric vibration element 11. When the piezoelectric vibration element 11 and the retaining layer 12b are bonded together, the vibration portion 16 and the bottom wall of the recess 18b are spaced apart, forming a vibration space between them for the vibration portion 16 to vibrate. The sidewall of the recess 18b in the retaining layer 12b is bonded to the second main surface 11b of the peripheral portion 17 of the piezoelectric vibration element 11. The second excitation electrode 14b is sealed in the vibration space. The shape of the retaining layer 12a is not particularly limited as long as it can excite the vibration portion 16. For example, if the piezoelectric vibration element has an inverted mesa shape, the retaining layer may be flat. The retaining layers 12a and 12b may be box-shaped, with notches provided at the corners where they come into contact with the first connection electrode 15a and the second connection electrode 15b, respectively.

[0023] The lower housing 20 is provided below the piezoelectric vibrator 10 and houses the piezoelectric vibrator 10 together with the upper housing 30. The lower housing 20 is less susceptible to elastic deformation than the upper housing 30. For example, the ease of elastic deformation of the lower housing 20 and the upper housing 30 may be differentiated by their thicknesses, materials, shapes, etc. In this embodiment, the upper housing 30 is made of stainless alloy steel SUS430 with a thickness of, for example, approximately 0.4 mm, and the lower housing 20 is made of stainless alloy steel SUS430 with a thickness of, for example, approximately 1 mm, thereby achieving a difference in rigidity.

[0024] The lower housing 20 has a lower surface portion 21 located in the center when the XY plane is viewed in plan, and an end portion 25 located on the outer periphery of the lower surface portion 21 when the XY plane is viewed in plan.

[0025] When viewed in plan on the XY plane, the shape of the lower surface portion 21 is circular, but is not limited to this and may be rectangular, for example. The lower surface portion 21 is flat and has a uniform thickness T21. The shape of the lower surface portion 21 is not limited to this and may have at least one protrusion formed by ribbing, for example. By having such a protrusion, the lower surface portion becomes even less susceptible to elastic deformation compared to a flat plate-shaped configuration. Furthermore, the lower surface portion 21 may have partially thin or thick portions.

[0026] The end portion 25 is provided in a ring shape around the lower surface portion 21. The end portion 25 sandwiches an end portion 35 of the upper housing 30 (described later) in the thickness direction by crimping. Specifically, the end portion 25 has a lower end portion 25a connected to the lower surface portion 21, an upper end portion 25b folded upward from the lower end portion 25a, and a folded portion 25c connecting the lower end portion 25a and the upper end portion 25b. The lower end portion 25a and the upper end portion 25b overlap in the thickness direction. The upper end portion 25b and the lower end portion 25a sandwich and fix the end portion 35 of the upper housing 30 in the thickness direction. The gap between the lower end portion 25a and the end portion 35 of the upper housing 30 is substantially zero, and the lower end portion 25a and the end portion 35 of the upper housing 30 are in contact. The gap between the upper end portion 25b and the end portion 35 of the upper housing 30 is substantially zero, and the upper end portion 25b and the end portion 35 of the upper housing 30 are in contact. However, the present invention is not limited to the above configuration, as long as at least the upper end of the lower housing and the end of the upper housing are in contact with each other. For example, the upper end of the lower housing may be in contact with the end of the upper housing, and the lower end of the lower housing may be spaced apart from the end of the upper housing. For example, the folded portion 25c is spaced apart from the end 35 of the upper housing 30, but this is not limiting and the folded portion may be in contact with the end 35.

[0027] The upper housing 30 has a top surface portion 31 that extends in a circular shape when viewed in a plan view of the XY plane, a side surface portion 32 that extends in the negative direction of the Z axis from the outer periphery of the top surface portion 31, and an end portion 35 that extends from the outer periphery of the lower end of the side surface portion 32 to the side opposite the top surface portion 31. Furthermore, the top surface portion 31 has a protrusion portion 31a that protrudes in the positive direction of the Z axis from its central portion when viewed in a plan view of the XY plane, a peripheral portion 31b that surrounds the protrusion portion 31a in the XY plane, and an intermediate portion 31c that connects the protrusion portion 31a and the peripheral portion 31b. A wiring hole 36 is provided in the peripheral portion 31b.

[0028] The protrusion 31a is provided in the central portion of the upper surface portion 31 and is the furthest from the lower surface portion 21 on the upper surface portion 31. The protrusion 31a is plate-shaped extending along the XY plane and is circular when the XY plane is viewed in a plane. The protrusion 31a has a thickness T31a along the Z-axis direction. The protrusion 31a has a lower surface on the negative Z-axis side and an upper surface on the positive Z-axis side. The lower surface of the protrusion 31a is in contact with the piezoelectric vibrator 10. The upper surface of the protrusion 31a receives the load detected by the load sensor 1. Note that when the XY plane is viewed in a plane, the shape of the protrusion 31a is not limited to a circular shape and may be changed as appropriate depending on the magnitude and range of the load, etc.

[0029] The peripheral portion 31b is annular in shape surrounding the central portion in a plan view, and is configured as a plate along the XY plane. The outer end of the peripheral portion 31b is connected to the upper end of the side portion 32. As the peripheral portion 31b moves away from the protrusion 31a, it approaches the lower surface portion 21, i.e., it slopes downward. The peripheral portion 31b has a thickness T31b along the Z-axis direction.

[0030] The intermediate portion 31c is cylindrical and connects the protruding portion 31a and the peripheral portion 31b, with its upper end connected to the outer end of the protruding portion 31a and its lower end connected to the inner end of the peripheral portion 31b. The intermediate portion 31c has a thickness T31c along the radial direction when viewed in plan on the XY plane.

[0031] The thickness T31a of the protrusion 31a is smaller than the thickness T21 of the lower surface portion 21. The thickness T31a of the protrusion 31a is approximately equal to the thickness T31b of the peripheral portion 31b. Furthermore, the thickness T31a of the protrusion 31a is approximately equal to the thickness T31 of the intermediate portion 31c. However, the thickness T31a of the protrusion 31a may be larger than the thickness 31b of the peripheral portion 31b. In this case, the lower surfaces of the protrusion 31a and the peripheral portion 31b may be continuous along the XY plane. Furthermore, when the upper housing 30 is formed by press working, the intermediate portion 31c is expanded, and therefore the thickness T31c of the intermediate portion 31c may be smaller than the thickness T31a of the protrusion 31a or the thickness T31b of the peripheral portion 31b.

[0032] When the height from the lower housing 20 to the connection between the outer circumferential surface of the intermediate portion 31c and the upper surface of the peripheral portion 31b is defined as h1, the height from the lower housing 20 to the upper surface of the protrusion 31a is greater than h1 by a height h2 from the connection between the outer circumferential surface of the intermediate portion 31c and the upper surface of the peripheral portion 31b to the upper surface of the protrusion 31a. The height h1 is greater than the height h2. The height h2 is also greater than the thickness T31a of the protrusion 31a. Therefore, the distance in the thickness direction between the upper surface of the peripheral portion 31b and the lower surface 21 is smaller than the distance in the thickness direction between the lower surface of the protrusion 31a and the lower surface 21.

[0033] When viewed in plan on the XY plane, the area of ​​the protrusion 31 a is larger than the area of ​​the piezoelectric vibrator 10 and smaller than the area of ​​the peripheral portion 31 b. For example, the area of ​​the protrusion 31 a is preferably 10% to 20% of the area of ​​the upper surface portion 31, more preferably 5% to 10%, and more preferably about 5%.

[0034] The buffer material 40 is disposed between the piezoelectric vibrator 10 and the lower surface 21 of the lower housing 20 and has lower rigidity than the lower housing 20. The buffer material 40 can prevent the piezoelectric vibrator 10 from cracking due to a large load applied to the load sensor 1. The piezoelectric vibrator 10 is set in the center of the buffer material 40 in a planar view. The buffer material 40 is, for example, a circuit board. As shown in FIG. 2 , the buffer material 40 is electrically connected to the first connection electrode 15a and the second connection electrode 15b of the piezoelectric vibrating element 11 via anisotropic conductive paste 19. The buffer material 40 is connected to wiring 41. The wiring 41 is led out from the buffer material 40 to the outside through wiring holes 36. In addition to the piezoelectric vibrator 10, elements such as capacitors, resistors, and inductors may be mounted on the buffer material 40, which is a circuit board. The buffer material 40 may be made of a substrate material such as glass or epoxy. The buffer material 40 may also be an adhesive that bonds the piezoelectric vibrator 10 and the lower housing 20. In this case, the adhesive may be epoxy or the like. In this case, the wiring 41 may be drawn from the piezoelectric vibrator 10 without the use of an adhesive and electrically connected to the outside through the wiring hole 36. As described above, the buffer material 40 is made of a substrate material or an adhesive material, but is not limited to this. For example, the buffer material 40 may be made of a substrate material and an adhesive material, and the adhesive may bond the piezoelectric vibrator 10 to the substrate. Furthermore, although the example shown in FIG. 2 shows a configuration in which the buffer material 40 is provided, the piezoelectric vibrator 10 may also be mounted on the lower housing 20 without the buffer material 40.

[0035] When the load sensor 1 receives a load in a direction along the XZ plane along which the first main surface 11a and the second main surface 11b of the piezoelectric vibration element 11 extend, distortion occurs in the vibration portion 16, causing a change in the vibration characteristics of the piezoelectric vibrator 10. This change in vibration characteristics is utilized to detect an external load. The load sensor 1 detects an external load by transmitting the load from the protrusion 31a to the piezoelectric vibrator 10. Furthermore, by providing the protrusion 31a on the upper surface portion 31, a load from above the load sensor 1 is received by the upper surface of the protrusion 31a and transmitted to the lower surface of the protrusion 31a, thereby suppressing deflection of the upper housing 30 and load distribution, thereby improving the detection accuracy of the load sensor 1. The load sensor 1 is configured such that the lower housing 20 and the upper housing 30 are fixed by crimping at the end 25 and end 35, causing the upper housing 30 to elastically deform toward the lower housing 20 and apply a preload to the piezoelectric vibration element 11.

[0036] Next, experimental results of loading and unloading the load sensor 1 of this embodiment to examine its load characteristics are shown. FIG. 4 is a graph showing the resonant frequency of the piezoelectric vibrator 10 relative to the applied load on the load sensor 1. In FIG. 4, the vertical axis represents the resonant frequency [Hz] of the piezoelectric vibrator 10, and the horizontal axis represents the load [N] applied to the load sensor 1. The change in the resonant frequency when the load is increased and the change in the resonant frequency when the load is decreased and unloaded are plotted. FIG. 4 shows that the resonant frequency is accurately proportional to the external force from low to high loads, demonstrating high linearity. Furthermore, the transitions in the resonant frequency when loaded and unloaded are nearly identical, indicating low hysteresis characteristics. This indicates that a load sensor with good responsiveness was obtained by applying a preload and excluding the low-load region where the frequency change to load changes is poor.

[0037] Next, a method for manufacturing the load sensor 1 according to the first embodiment of the present invention will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a flowchart showing a method for manufacturing the load sensor 1 according to an embodiment of the present invention. Fig. 6 is a cross-sectional view showing the method for manufacturing the load sensor according to the first embodiment.

[0038] First, a piezoelectric vibrator, an upper housing, and a lower housing are prepared (S10). For example, two types of metal plates made of stainless alloy steel SUS430 with different thicknesses are prepared and pressed to prepare the lower housing 20 and the upper housing 30. As shown in FIG. 6 , the lower housing 20 prepared in this step has an upper end 25 b extending from a folded portion 25 c in the positive direction of the Z axis.

[0039] Next, the piezoelectric vibrator is set on the lower housing (S20). The piezoelectric vibrator 10 prepared in S10 is mounted on a buffer material 40 that functions as a circuit board. Specifically, three layers, namely, the piezoelectric vibration element 11 and the pair of holding layers 12a and 12b, are arranged in the Y-axis direction, and the first connection electrode 15a and the second connection electrode 15b are electrically connected to the electrode pads of the buffer material 40 via anisotropic conductive paste 19. Thereafter, the buffer material 40 is set on the underside 21 of the lower housing 20 with the side on which the piezoelectric vibrator 10 is mounted facing up.

[0040] Next, the upper housing is set on the piezoelectric vibrator (S30). The upper housing 30 prepared in S10 is set on the piezoelectric vibrator 10. Specifically, the piezoelectric vibrator 10 and the protrusion 31a of the upper housing 30 are set so that they overlap when viewed in a plan view of the XY plane. At this time, as shown in FIG. 6 , the upper end 25b of the lower housing 20 extends in the positive direction of the Z axis, and a gap 50 is provided between the end 35 of the upper housing 30 and the end 25 of the lower housing 20. When the height from the bottom surface of the end 35 of the upper housing 30 to the connection between the outer circumferential surface of the middle portion 31c and the top surface of the peripheral portion 31b is defined as h11, the height from the bottom surface of the end 35 of the upper housing 30 to the top surface of the protrusion 31a is greater than h11 by the height h21 from the connection between the outer circumferential surface of the middle portion 31c and the top surface of the peripheral portion 31b to the top surface of the protrusion 31a. Furthermore, in this case, if the size of gap 50 in the thickness direction is g1, the height from the upper surface of lower surface portion 21 to the upper surface of peripheral portion 31b is g1 + h11, and the height from the upper surface of lower surface portion 21 to the upper surface of protrusion 31a is g1 + h11 + h21. Height h11 is greater than height h21. Height h21 is also greater than thickness T31a of protrusion 31a and thickness T31b of the peripheral portion. Therefore, the distance in the thickness direction between the upper surface of peripheral portion 31b and lower surface portion 21 is smaller than the distance in the thickness direction between the lower surface of protrusion 31a and lower surface portion 21.

[0041] The lower and upper housings are crimped together (S40). As shown in FIG. 2, the upper end 25b of the lower housing 20 is bent inward to contact the upper end 35. The lower end 25a and the upper end 25b are then sandwiched from above and below to reduce the gap 50 for preload adjustment, and the end 35 of the upper housing 30 and the lower end 25a of the lower housing 20 are brought into contact with each other. At this time, the gap 50 is pressed until the thicknesswise dimension g1 of the gap 50 becomes approximately zero. However, this is not limited to this, and the gap 50 may be pressed so that a certain thicknesswise dimension remains. As the thicknesswise dimension of the gap 50 decreases, the end 35 of the upper housing 30 is displaced downward. This displacement of the end 35 causes elastic deformation of the upper housing 30, applying a preload to the piezoelectric vibrator 10 in the thicknesswise direction. The preload applied to the piezoelectric vibrator 10 can be adjusted by adjusting the thicknesswise dimension g1 of the gap 50 before crimping. Furthermore, when a certain amount of the gap 50 in the thickness direction is left after the caulking, the preload may be adjusted depending on the size of the gap 50 in the thickness direction after the caulking.

[0042] The elastic deformation of the upper housing 30 due to the crimping causes a change in the dimension in the thickness direction of the upper housing 30. For example, the peripheral portion 31b of the upper housing 30 is approximately horizontal with the lower surface portion 21 before the crimping, but after the crimping, it slopes downward as it moves away from the protrusion 31a. In this case, the height h11 before the crimping is smaller than the height h1 after the crimping, and the equation h1 = h11 + g1 is satisfied.

[0043] As described above, by fixing the upper housing 30 and the lower housing 20 by crimping, a preload is applied to the piezoelectric vibrator 10 by elastic deformation of the upper housing 30 .

[0044] According to this, by applying a preload, it is possible to obtain a load sensor that can be used in a load range with good responsiveness, excluding the low load range in which the responsiveness of frequency change to load change is poor.

[0045] Furthermore, compared to a configuration in which a screw member or a thrust bearing is provided to apply a preload, the preload can be applied by the configuration of the upper housing 30 and the lower housing 20, so that the load sensor 1 can be made low-profile.

[0046] Furthermore, by crimping the lower housing 20, which is less prone to elastic deformation than the upper housing 30, the crimped portion is less likely to open, and the change over time in the preload applied to the piezoelectric vibrator 10 can be suppressed.

[0047] Furthermore, the protrusion 31 a directly transmits the load applied to the load sensor 1 to the piezoelectric vibrator 10 , suppressing deflection of the upper housing 30 and load dispersion, thereby improving the detection accuracy of the load sensor 1 .

[0048] Furthermore, by providing the buffer material 40, it is possible to prevent the piezoelectric vibration element 11 from cracking due to the load. By using the circuit board as the buffer material 40, it is possible to reduce the size of the load sensor 1.

[0049] In the above embodiment, the end 25 and the end 35 are configured in an annular shape. This allows a preload to be applied isotropically to the piezoelectric vibrator 10. However, this is not limited to this. The end of the upper housing and the end of the lower housing may be provided only on a portion of the annular circumference rather than the entire circumference. Furthermore, even when the end of the upper housing and the end of the lower housing are provided on the entire annular circumference, the crimping fixation may be limited to a portion.

[0050] Other embodiments will be described below. In each of the following embodiments, the description of the matters common to the first embodiment will be omitted, and only the differences will be described. Components with the same reference numerals as those in the first embodiment will have the same configuration and function as those in the first embodiment, and detailed description thereof will be omitted. Similar effects resulting from similar configurations will not be mentioned.

[0051] Second Embodiment Next, the structure of a load sensor 2 according to a second embodiment will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a cross-sectional view schematically showing the structure of the load sensor according to the second embodiment. Fig. 8 is a perspective view schematically showing the structure of the load sensor according to the second embodiment.

[0052] In the second embodiment, the structure of the lower housing 20 is different from that of the first embodiment. Specifically, whereas in the first embodiment, the lower surface 21 of the lower housing 20 is formed in a flat plate shape, in this embodiment, a plurality of protrusions 122 formed by ribbing are provided on the lower surface 121b of the lower surface 121 of the lower housing 120, opposite the upper housing 30. This makes the lower housing 120 even less susceptible to elastic deformation compared to a lower housing with a flat lower surface. Note that at least one protrusion is sufficient, and the number is not limited. Furthermore, the protrusions may be provided on the upper surface 121a of the lower surface 121 facing the upper housing 30, or on both the upper surface 121a and the lower surface 121b of the lower surface 121.

[0053] 7, the upper surface 121a, on which the protrusions 122 are not provided, has recesses 123 at positions corresponding to the protrusions 122. This allows the manufacturing process to be simplified by simultaneously processing the protrusions 122 and the recesses 123 by, for example, press working.

[0054] In this embodiment, the configuration in which the convex portion 122 and the concave portion 123 are integrated has been described, but the present invention is not limited to this. That is, the portion corresponding to the back surface of the convex portion 122 may be configured to be flat without providing the concave portion 123.

[0055] Furthermore, fixing portions 124 are provided on the lower surface 121b to serve as feet of the load sensor 2. When the protrusions 122 and the fixing portions 124 are provided on the lower surface 121b, the thickness dimension of the fixing portions 124 is equal to or greater than the thickness dimension of the protrusions 122. When the XY plane of the lower surface 121b is viewed in plan, the fixing portions 124 are provided on the outer periphery side of the protrusions 122. When the load sensor 2 is mounted on an external substrate, the fixing portions 124 come into contact with the external substrate, thereby stabilizing the posture of the load sensor 2 and improving the reliability of sensing. In this embodiment, four fixing portions 124 are provided, but this is not limited thereto, and three or more fixing portions are preferably provided. The number and shape of the fixing portions may be changed as appropriate as long as they function as feet.

[0056] Third Embodiment Next, the structure of a load sensor 3 according to a third embodiment will be described with reference to Fig. 9. Fig. 9 is a cross-sectional view that schematically shows the structure of the load sensor according to the third embodiment.

[0057] The third embodiment differs from the first embodiment in terms of the crimping method. Specifically, whereas in the first embodiment, the end 25 of the lower housing 20 is crimped to the upper housing 30, in this embodiment, the end 235 of the upper housing 230 is crimped to the lower housing 220. In this embodiment, the end 235 of the upper housing 230 has an upper end 235a connected to the side surface 32, a lower end 235b folded downward from the upper end 235a, and a folded portion 235c connecting the upper end 235a and the lower end 235b. The end 225 of the lower housing 220 is sandwiched between the upper end 235a and the lower end 235b in the thickness direction. By crimping the upper housing 230, which is more elastically deformable than the lower housing 220, a load sensor 3 with improved processing accuracy compared to the first embodiment can be provided. Note that if the upper housing 230 is thin, the upper housing 230 can be easily crimped.

[0058] 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.

[0059] <1> As described above, according to one aspect of the present invention, there is provided a load sensor for detecting a load in a thickness direction, the load sensor comprising: an upper housing having an upper surface portion and a side portion extending in the thickness direction from the outer periphery of the upper surface portion; a lower housing having a lower surface portion facing the upper surface portion in the thickness direction and having a property of being less prone to elastic deformation than the upper housing; and a piezoelectric vibrator housed in a space between the upper housing and the lower housing, the piezoelectric vibrator having a piezoelectric substrate provided between the upper surface portion and the lower surface portion and a pair of excitation electrodes provided on main surfaces of the piezoelectric substrate that face each other, the pair of excitation electrodes extending along the thickness direction, one end of the upper housing or the other end of the lower housing being crimped and fixed to the other end, and the upper housing being configured to apply a preload in the thickness direction to the piezoelectric vibrator due to elastic deformation of the upper housing caused by the crimping.

[0060] According to the above-described aspect, by fixing the upper and lower housings by crimping, a preload can be applied to the piezoelectric vibrator by elastic deformation of the upper housing, and a load sensor with good load characteristics due to the preload can be provided. Furthermore, a load sensor with a lower profile and reduced long-term fluctuations can be provided compared to conventional load sensors that include a configuration for applying a preload externally to the load sensor.

[0061] <2> In one aspect, there is provided the load sensor according to <1>, wherein an end portion of the upper housing is sandwiched between an end portion of the lower housing in the thickness direction.

[0062] <3> In one aspect, there is provided the load sensor according to <1>, wherein an end of the lower housing is sandwiched between ends of the upper housing in the thickness direction.

[0063] <4> In one aspect, there is provided a load sensor according to any one of <1> to <3>, wherein the upper surface portion has a protrusion portion, the protrusion portion is provided in a central portion in a plan view of the upper surface portion, and protrudes on the opposite side to the side facing the lower surface portion, and the piezoelectric vibrator is provided between the protrusion portion and the lower surface portion.

[0064] According to the above aspect, the protrusion receives the load, thereby suppressing deflection of the upper housing and load distribution, thereby improving the detection accuracy of the load sensor.

[0065] <5> In one aspect, there is provided the load sensor according to any one of <1> to <4>, wherein a buffer material that is more easily elastically deformed than the lower housing is provided between the lower surface portion and the piezoelectric vibrator.

[0066] According to the above aspect, when a large load is applied to the load sensor 1, cracking of the piezoelectric vibrator 10 due to the load can be suppressed.

[0067] <6> In one aspect, there is provided the load sensor according to <5>, wherein the buffer material is a circuit board electrically connected to the piezoelectric vibrator.

[0068] <7> In one aspect, there is provided the load sensor according to any one of <1> to <6>, wherein the lower surface portion has at least one first protrusion formed by rib processing.

[0069] According to the above aspect, the strength of the lower surface portion can be improved.

[0070] <8> In one aspect, there is provided a load sensor as described in <7>, in which the first protrusion protrudes on the side of the lower surface opposite to the side facing the upper surface, the lower surface further has a second protrusion protruding on the side opposite to the side facing the upper surface, the second protrusion protruding to an extent equal to or greater than the first protrusion, and being provided between the first protrusion and an end of the lower surface when the lower surface is viewed in a plane.

[0071] According to the above aspect, the posture of the load sensor can be stabilized, and the reliability of sensing can be improved.

[0072] <9> In one aspect, there is provided the load sensor according to any one of <1> to <8>, wherein the piezoelectric vibrator is a quartz crystal vibrator.

[0073] <10> According to another aspect of the present invention, a method for manufacturing a load sensor for detecting a load in a thickness direction includes: an upper housing having an upper surface portion and a side portion extending in a thickness direction from an outer periphery of the upper surface portion; a lower housing having a lower surface portion facing the upper surface portion in the thickness direction and being less susceptible to elastic deformation than the upper housing; and a piezoelectric vibrator accommodated in a space between the upper housing and the lower housing, the piezoelectric vibrator having a piezoelectric substrate provided between the upper surface portion and the lower surface portion and a pair of excitation electrodes provided on main surfaces of the piezoelectric substrate facing each other, the method including: setting the piezoelectric vibrator on the lower housing; a first end of the upper housing and a second end of the lower housing, the first end of the upper housing being supported by the piezoelectric vibrator, and a second end of the lower housing being crimped to the first end of the upper housing; a second end of the upper housing being supported by the piezoelectric vibrator, the second end of the lower housing being supported by the piezoelectric vibrator, and a third end of the upper housing being supported by the piezoelectric vibrator, the second end of the upper housing being supported by the piezoelectric vibrator, the third end of the lower housing being supported by the piezoelectric vibrator, and the third end of the upper housing being supported by the piezoelectric vibrator, the third end of the upper housing being supported by the piezoelectric vibrator, and the fourth end of the upper housing being supported by the piezoelectric vibrator, the fourth end of the upper housing being supported by the piezoelectric vibrator, and the fourth end of the lower housing being supported by the piezoelectric vibrator, the fourth end of the upper housing being supported by the piezoelectric vibrator, and the fourth end of the upper housing being supported by the piezoelectric vibrator, the fourth end of the upper housing being supported by the piezoelectric vibrator,

[0074] According to the above aspect, a method for manufacturing a load sensor having good load characteristics due to a preload can be provided.

[0075] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit 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 appropriately by those skilled in the art 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 of the embodiments, as well as their arrangement, materials, conditions, shape, size, etc., are not limited to those exemplified and can be modified as appropriate. Furthermore, the elements of the embodiments can be combined to the extent technically possible, and such combinations are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention.

[0076] REFERENCE SIGNS LIST 1...load sensor 10...piezoelectric vibrator 11...piezoelectric vibrating element 20...lower housing 30...upper housing 40...buffer material 50...gap

Claims

1. A load sensor that detects a load in a thickness direction, an upper housing having a top surface portion and a side surface portion extending in the thickness direction from an outer periphery of the top surface portion; a lower housing having a lower surface portion facing the upper surface portion in the thickness direction, the lower housing being less susceptible to elastic deformation than the upper housing; a piezoelectric vibrator accommodated in a space between the upper housing and the lower housing, the piezoelectric vibrator having a piezoelectric substrate provided between the upper surface portion and the lower surface portion, and a pair of excitation electrodes provided on opposing main surfaces of the piezoelectric substrate; Equipped with The pair of excitation electrodes extend along the thickness direction, A load sensor in which one of an end of the upper housing and an end of the lower housing is crimped to the other end, and the upper housing is configured to apply a preload to the piezoelectric vibrator in the thickness direction due to elastic deformation of the upper housing caused by the crimping.

2. The load sensor according to claim 1 , wherein an end portion of the upper housing is sandwiched between an end portion of the lower housing in the thickness direction.

3. The load sensor according to claim 1 , wherein an end portion of the lower housing is sandwiched between an end portion of the upper housing in the thickness direction.

4. The upper surface portion has a protrusion, The protrusion is provided in a central portion of the upper surface portion in a plan view and protrudes toward an opposite side to a side facing the lower surface portion, The load sensor according to claim 1 , wherein the piezoelectric vibrator is provided between the protrusion and the lower surface portion.

5. The load sensor according to claim 1 , further comprising a buffer material between the lower surface portion and the piezoelectric vibrator, the buffer material being more easily deformed elastically than the lower housing.

6. The load sensor according to claim 5 , wherein the buffer material is a circuit board electrically connected to the piezoelectric vibrator.

7. The load sensor according to claim 1 , wherein the lower surface portion has at least one first protrusion portion formed by rib processing.

8. the first protrusion protrudes from the lower surface portion toward an opposite side to a side facing the upper surface portion, The lower surface portion further includes a second protruding portion protruding toward an opposite side to the side facing the upper surface portion, The load sensor according to claim 7 , wherein the second protrusion protrudes equal to or greater than the first protrusion and is provided between the first protrusion and an end of the lower surface when the lower surface is viewed in a plane.

9. The load sensor according to claim 1 , wherein the piezoelectric vibrator is a quartz crystal vibrator.

10. A load sensor that detects a load in a thickness direction, an upper housing having a top surface portion and a side surface portion extending in the thickness direction from an outer periphery of the top surface portion; a lower housing having a lower surface portion facing the upper surface portion in the thickness direction, the lower housing being less prone to elastic deformation than the upper housing; a piezoelectric vibrator accommodated in a space between the upper housing and the lower housing, the piezoelectric vibrator having a piezoelectric substrate provided between the upper surface portion and the lower surface portion, and a pair of excitation electrodes provided on opposing main surfaces of the piezoelectric substrate; A method for manufacturing a load sensor comprising: setting the piezoelectric vibrator on the lower housing; placing the upper housing on the piezoelectric vibrator; caulking and fixing one of an end portion of the upper housing and an end portion of the lower housing to the other end portion; Including, Setting the upper housing on the piezoelectric vibrator includes: providing a gap for adjusting a preload between an end of the upper housing and an end of the lower housing by supporting the upper housing on the piezoelectric vibrator; The said caulking and fixing is reducing the preload adjustment gap and elastically deforming the upper housing; a preload being applied to the piezoelectric vibrator in the thickness direction by the upper housing elastically deforming the upper housing.