Electrode pad connection structure

Abstract

Provided is an electrode pad connection structure that prevents cracking and peeling of a tab portion of a strain gauge, and allows for an improvement in connection reliability between the strain gauge and a gauge lead. Provided is an electrode pad connection structure for electrically connecting an electrode pad, to which a gauge lead is connected, to a tab portion of a strain gauge, which has a gauge grid portion and the tab portion, and is disposed on a straining body, the electrode pad connection structure having an insert structure in which a portion or the entirety of one of the tab portion and the electrode pad is enclosed inside the other.

Description

[Technical Field]

[0001] The present disclosure relates to a connection structure for electrode pads of a strain gauge. [Background technology]

[0002] Load cells using strain gauges, whose resistance changes with strain caused by a load, are widely used. For example, a known load cell is configured to incorporate a strain gauge into a bridge circuit, which is a conversion circuit that converts the change in resistance of the strain gauge due to a load into an electrical signal, and output the change in resistance as an electrical signal. In such load cells, the strain gauge placed on the strain generating element has an electrode pad formed on the tab portion of the strain gauge as an extraction electrode, and the gauge lead is soldered to the electrode pad and incorporated into the bridge circuit.

[0003] Here, conventionally, foil strain gauges made of metal or alloy with a gauge factor of about 2 have often been used as strain gauges. However, for load cells with large output, such as force detection sensors attached to the axles of automobiles to detect the load applied to the wheels, or load cells that detect multiple component forces and have large differences in sensitivity to each component force, the gauge factor of the strain gauge must be large. Patent Documents 1 and 2 disclose strain gauges made primarily of chromium nitride (Cr-N) as strain gauges with large gauge factors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-074454 [Patent Document 2] Japanese Patent Application Publication No. 2019-090722 Summary of the Invention [Problem to be solved by the invention]

[0005] When using strain gauges primarily made of nitrogen and chromium, a phenomenon in which parts of the strain gauge become ceramic when the temperature rises can occur. On the other hand, metal materials are generally used for electrode pads. Therefore, when high heat is applied to the electrode pads and the tabs of the strain gauge, such as when soldering gauge leads to the strain gauge, the thermal expansion coefficients of the electrode pad material and the strain gauge material differ significantly. As a result, tensile or compressive stress is applied to the tabs as the electrode pads expand. This can result in cracks in the tabs or peeling off from the strain gauge, potentially causing damage or disconnection of parts of the electrical circuit.

[0006] The present disclosure has been made in consideration of the above problems, and an object of the present disclosure is to provide a connection structure for an electrode pad that can suppress cracking or peeling of the tab portion of a strain gauge and improve the connection reliability between the strain gauge and the gauge lead. [Means for solving the problem]

[0007] In order to solve the above problem, according to one aspect of the present disclosure, An electrode pad connection structure for electrically connecting an electrode pad to which a gauge lead is connected to a tab portion of a strain gauge, the tab portion having a gauge grid portion and a tab portion, the electrode pad connection structure comprising: There is provided a connection structure for an electrode pad, which has an insert structure in which part or all of one of the tab portion and the electrode pad is sandwiched inside the other. [Effects of the Invention]

[0008] As described above, according to the present disclosure, cracking and peeling of the tab portion of the strain gauge can be suppressed, and the reliability of the connection between the tab portion and the electrode pad can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a load cell (six-component force detector) of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the arrangement of strain gauges in the load cell of the present disclosure. [Figure 3] FIG. 2 is an explanatory diagram showing the configuration of a bridge circuit of the load cell of the present disclosure. [Figure 4] FIG. 1 is an explanatory diagram showing a connection structure of an electrode pad according to a first embodiment of the present disclosure. [Figure 5] 5 is a cross-sectional view taken along the arrow II in FIG. 4. [Figure 6] FIG. 5 is a cross-sectional view taken along the line II-II in FIG. 4. [Figure 7] FIG. 10 is an explanatory diagram showing a connection structure of an electrode pad according to a second embodiment of the present disclosure. [Figure 8] 10A and 10B are explanatory diagrams showing a configuration example of a tab portion according to the embodiment; [Figure 9] FIG. 8 is a cross-sectional view taken along the line III-III in FIG. 7. [Figure 10] FIG. 8 is a cross-sectional view taken along the line IV-IV in FIG. 7. [Figure 11] FIG. 10 is a schematic diagram showing the arrangement of strain gauges in a six-component force detector of a modified example. [Figure 12] FIG. 2 is an explanatory diagram showing the gauge pattern of a biaxial shear strain gauge. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0011] <<1. Overview of Embodiments of the Present Disclosure>> <1-1. Detailed Description of the Background of the Present Disclosure> First, the background to the creation of the technology of the present disclosure will be described. Note that the background described below merely shows one aspect of the configuration of a load cell to which the technology of the present disclosure can be applied, and load cells to which the present disclosure can be applied are not limited to load cells with the configurations exemplified below.

[0012] Six-component force detectors are known that detect loads (Fx, Fy, Fz) applied to the wheels of vehicles such as automobiles in the longitudinal direction (hereinafter also referred to as the "x-axis"), width direction (hereinafter also referred to as the "y-axis"), and height direction (hereinafter also referred to as the "z-axis") of the vehicle, as well as moments (Mx, My, Mz) about the x-axis, y-axis, and z-axis, respectively. Such six-component force detectors have a cylindrical strain element attached to the axle, but when considering the resistance to the applied loads, it is difficult for a typical foil strain gauge with a gauge factor of about 2 to obtain an output equivalent to that of a load cell that detects loads in only one axis direction.

[0013] In contrast, it is believed that the desired output can be obtained by using a thin-film strain gauge with a large element resistance and a large gauge factor, such as Cr-N (for example, the gauge factor for a Cr-N gauge is 10 to 12). However, when high heat is applied to a Cr-N gauge, some of the gauge may become ceramic-like, resulting in brittle fracture. Here, metal materials are generally used as the material for the electrode pad to which the solder is bonded, considering that alloys are unlikely to form with the solder and that the solder has high wettability with the electrode pad material.

[0014] When soldering the gauge leads to the electrode pads, high heat is transferred not only to the electrode pads but also to the tabs of the strain gauges. This results in a significant difference in the thermal expansion coefficients of the electrode pad material and the strain gauge material. When the metal electrode pad expands, tensile or compressive stress acts on the tabs, potentially causing cracking or peeling from the strain gauge body. In particular, six-component force detectors, which detect the load applied to a wheel, are prone to cracking or peeling because the strain gauges are mounted on a cylindrical strain gauge. Furthermore, six-component force detectors have numerous connection points between the tabs and electrode pads. Even a single connection failure renders the six-component force detector defective, so it is necessary to improve the reliability of each connection point.

[0015] Under these circumstances, the technology disclosed herein provides a connection structure for an electrode pad that, when using a strain gauge that has a larger gauge factor than conventional foil strain gauges and is prone to brittle fracture, can suppress cracking of the tab portion or peeling from the strain element that can occur when high heat is transmitted to the electrode pad and tab portion, such as in the case of solder connection, and can increase the connection reliability between the strain gauge and gauge lead.

[0016] <1-2. Features of the embodiment of the present disclosure> (1-2-1) An embodiment of the present disclosure is a connection structure for an electrode pad for electrically connecting an electrode pad to which a gauge lead is connected to a tab portion of a strain gauge that is disposed on a strain generating body and has a gauge grid portion and a tab portion, The connector has an insert structure in which part or all of one of the tab portion and the electrode pad is sandwiched inside the other.

[0017] This configuration increases the bonding strength between the tab portion and the electrode pad. Even if the strain gauge is made of a material prone to brittle fracture, or if high heat is applied when soldering the gauge lead to the electrode pad electrically connected to the tab portion, cracking of the tab portion or peeling from the strain element can be suppressed. Therefore, the connection reliability between the strain gauge and the gauge lead can be improved.

[0018] The "insert structure in which part or all of one of the tab portion and the electrode pad is sandwiched inside the other" refers to a state in which the other member is disposed on both sides of part or all of one of the members, the tab portion or the electrode pad, in a predetermined direction. However, this does not include a configuration in which the other member is disposed on both sides of the extending direction of the plane of one member, such as when one member is formed in a layered shape and the other member is disposed on top of the other member, with the other member having a width greater than that of the one member, to cover the other member.

[0019] (1-2-2) In addition, in the embodiment of the present disclosure, The electrode pad having a U-shaped cross section is disposed on the strain generating element so that the opening of the U-shape is positioned to the side, The tab portion may be sandwiched inside the U-shaped electrode pad.

[0020] With this configuration, the top and bottom of the tab are sandwiched between the electrode pads, and the tab and the electrode pad are firmly bonded together. Therefore, even if thermal stress occurs in the tab, the bond between the tab and the electrode pad is maintained, and the connection reliability between the strain gauge and the gauge lead can be increased.

[0021] (1-2-3) In addition, in the embodiment of the present disclosure, the gauge grid portion includes a plurality of straight line portions each extending in a predetermined first direction; Both leg portions of the U-shaped electrode pad may extend along the first direction, and the tab portion may extend into the U-shaped electrode pad from the first direction.

[0022] With this configuration, even if the linear portions of the gauge grid expand or contract due to distortion of the strain-generating body, the influence of distortion of the tab portion on changes in resistance can be reduced, thereby improving the reliability of the load cell measurements.

[0023] (1-2-4) In addition, in the embodiment of the present disclosure, the tab portions each have a longitudinal direction extending in a predetermined second direction and a plurality of elongated holes penetrating the tab portions in a thickness direction or a plurality of grooves recessed in a thickness direction of the tab portions, The electrode pad may have a comb-like cross section, and the comb-like portions may extend into the plurality of slots or the plurality of grooves.

[0024] With this configuration, the tab portion and the electrode pad are sandwiched between each other, and are firmly bonded to each other. Therefore, even if thermal stress occurs in the tab portion, the bonded state between the tab portion and the electrode pad is maintained, and the connection reliability between the strain gauge and the gauge lead can be increased.

[0025] (1-2-5) In addition, in the embodiment of the present disclosure, the gauge grid portion includes a plurality of straight line portions each extending in a predetermined first direction; The second direction extends in the same direction as the first direction. 5. The electrode pad connection structure according to claim 4.

[0026] With this configuration, even if the linear portions of the gauge grid expand or contract due to distortion of the strain-generating body, the influence of distortion of the tab portion on changes in resistance can be reduced, thereby improving the reliability of the load cell measurements.

[0027] (1-2-6) In addition, in the embodiment of the present disclosure, the strain gauge is disposed on the strain element via an insulating layer; The electrode pad may be formed in contact with the tab portion and the insulating layer.

[0028] With this configuration, the electrode pad is formed not only on the tab portion but also in an area including the insulating layer, which, combined with the increased bonding strength between the electrode pad and the insulating layer, further increases the bonding strength between the electrode pad and the tab portion.

[0029] (1-2-7) In addition, in the embodiment of the present disclosure, The strain gauge may be made of Cr—N, and the electrode pad may be made of Au.

[0030] This configuration allows a strain gauge with a large gauge factor to be used to obtain a large output from the load cell. It also prevents the formation of an alloy between the solder and the electrode pad, improves the wettability between the solder and the electrode pad, and improves the stability of the solder joint. Furthermore, the linear thermal expansion coefficient is brought closer to that of the solder, thereby reducing the thermal stress generated in the strain gauge.

[0031] <<2. Details of the Embodiments of the Present Disclosure>> Below, a configuration example of a load cell to which the electrode pad connection structure of each embodiment described later is applied will be described, and then each embodiment will be described.

[0032] <2-1. Example of load cell (6-component force detector) configuration> Next, a configuration example of a load cell according to an embodiment of the present disclosure will be described. In this embodiment, an example will be described in which the technology of the present disclosure is applied to a six-component force detector capable of detecting six-component forces (Fx, Fy, Fz, Mx, My, Mz) applied to a vehicle wheel, as one aspect of a load cell. The load cell according to this embodiment is a six-component force detector that detects six-component forces applied to a wheel, and is incorporated into a hub bearing unit that is attached to a suspension device and rotatably supports the wheel of a vehicle such as an automobile.

[0033] Figure 1 shows a cross-sectional view of a hub bearing unit including a six-component force detector, cut along a plane including the axle. In Figure 1, the right side indicates the outer side in the vehicle width direction, and the left side indicates the inner side in the vehicle width direction. Note that the configuration of the hub bearing unit shown in Figure 1 is merely an example, and is not limited to the configuration shown in Figure 1.

[0034] The hub bearing unit 100 is configured to include a hub 110, an outer cylinder 120, an inner cylinder 130, rolling elements 140, a base 150, and a six-component force detector 1. The hub 110 is a member to which a rim disc portion of a wheel (not shown) consisting of a rim and a tire is fastened. The hub 110 is configured by integrally forming a cylindrical portion 111, a flange portion 112, a collar portion 113, etc.

[0035] The cylindrical portion 111 is formed in a cylindrical shape concentric with the rotational axis (axle) of the wheel. The cylindrical portion 111 is inserted into the inner diameter side of the inner tube 130, the sensor 10, and the base portion 150. A spline hole 111a that fits with a spline shaft portion of a drive shaft (not shown) is formed in the outer region of the inner peripheral surface of the cylindrical portion 111 in the vehicle width direction. The flange portion 112 is a disk-shaped portion that protrudes outward in a flange-like shape from the outer end of the cylindrical portion 111 in the vehicle width direction. The outer surface of the flange portion 112 in the vehicle width direction functions as a base to which a rim disc is fastened. The flange portion 112 has, for example, about five openings 112a formed at equal intervals around the circumferential direction on a predetermined pitch circle diameter, into which hub bolts are inserted. The collar portion 113 is a cylindrical portion that protrudes from the outer surface of the flange portion 112 in the vehicle width direction and is concentric with the axle. The collar portion 113 fits into a center bore, which is a circular opening formed in the center of the rim disc, and improves the mounting accuracy of the wheel.

[0036] The outer cylinder 120, inner cylinder 130, and rolling elements 140 work together to form a rolling bearing (hub bearing) that rotatably supports the wheel. The outer cylinder 120 is formed by integrally forming a tubular portion 121, a flange portion 122, etc. The tubular portion 121 is a cylindrical portion that is concentric with the axle. A raceway surface that guides the rolling elements 140 is formed on the inner peripheral surface of the tubular portion 121. The inner end of the tubular portion 121 in the vehicle width direction is formed to protrude inward in the vehicle width direction relative to the inner end of the tubular portion 131 of the inner cylinder 130 in the vehicle width direction.

[0037] The flange portion 122 is formed so as to protrude radially outward from the outer end of the cylindrical portion 121 in the vehicle width direction in a brim-like shape. The flange portion 122 is the portion to which the flange portion 112 of the hub 110 is fastened. The outer surface of the flange portion 122 in the vehicle width direction abuts against the inner surface of the flange portion 112 of the hub 110 in the vehicle width direction. The flange portion 122 has a screw hole 122a formed concentrically with the opening 112a of the hub 110. A hub bolt (not shown) used to secure the wheel is fastened into the screw hole 122a.

[0038] The inner cylinder 130 is configured by integrally forming a cylindrical portion 131, a flange portion 132, etc. The cylindrical portion 131 is a cylindrical member concentric with the axle, and is inserted into the inner diameter side of the cylindrical portion 121 of the outer cylinder 120. A predetermined gap is provided between the outer peripheral surface of the cylindrical portion 131 and the inner peripheral surface of the cylindrical portion 121 of the outer cylinder 120. A raceway surface that guides the rolling elements 140 is formed on the outer peripheral surface of the cylindrical portion 131. The flange portion 132 is formed by protruding from the outer end of the cylindrical portion 131 in the vehicle width direction toward the inner diameter side. The flange portion 132 holds the outer end of the first flange 12 of the sensing body 10 in the vehicle width direction. The rolling elements 140 are bearings incorporated between the raceway surfaces of the outer cylinder 120 and the inner cylinder 130. The rolling element 140 is incorporated between the outer cylinder 120 and the inner cylinder 130 together with a retainer 141 and a retainer 142 that position the rolling element 140 between the outer cylinder 120 and the inner cylinder 130 .

[0039] The base 150 is a portion that fastens and fixes the hub bearing unit 100 to an upright (hub knuckle) (not shown) of a suspension device. The base 150 is configured by integrally forming a tubular portion 151, a flange portion 152, a recess 153, a protrusion 154, etc. The tubular portion 151 is a cylindrical member that is concentric with the axle, and the inner end of the tubular portion 111 of the hub 110 in the vehicle width direction is inserted into the tubular portion 151. The outer peripheral surface of the tubular portion 111 of the hub 110 is disposed opposite the inner peripheral surface of the tubular portion 151 at a predetermined radial distance.

[0040] The flange portion 152 is formed so as to protrude radially outward from the outer end of the cylindrical portion 151 in the vehicle width direction in a brim-like shape. The flange portion 152 is a fastening surface portion for fastening the base portion 150 to an upright (not shown). The flange portion 152 is formed with a plurality of openings 152a distributed in the circumferential direction, into which a plurality of bolts used for fastening to the upright are inserted. Inside the flange portion 152, a through-hole 152b is formed, extending from within a space in which the outer peripheral surface of the cylindrical portion 11 of the sensor 10 is disposed to the outer peripheral edge of the flange portion 152, in which wiring connected to a strain gauge and the like are disposed.

[0041] The recess 153 is a portion formed by expanding the inner diameter of a region of the inner circumferential surface of the base 150 in the axial direction, which corresponds to the flange portion 152, in a stepped manner. The recess 153 is a portion that holds the second flange 13 of the sensor 10. The protrusion 154 is a cylindrical portion formed to protrude outward in the vehicle width direction from a radially intermediate portion of the flange portion 152. The outer circumferential surface of the protrusion 154 is disposed radially opposite to and spaced apart from the inner circumferential surface of the cylindrical portion 121 of the outer cylinder 120 at the end portion on the inner side in the vehicle width direction.

[0042] The six-component force detector 1 is a load cell capable of detecting loads acting on a wheel in three orthogonal axial directions and moments around the three orthogonal axes. The six-component force detector 1 is configured with a sensing body 10 formed substantially in a cylindrical shape, a plurality of strain gauges provided on the sensing body 10, and a bridge circuit including the strain gauges.

[0043] The sensing body (sensor core) 10 is formed to have a cylindrical portion 11, a first flange 12, a second flange 13, etc. The cylindrical portion 11 is a cylindrical portion having substantially constant inner and outer diameters over a predetermined axial length, and is a portion to which a plurality of strain gauges (described later) are attached (bonded). The first flange 12 is provided at the outer end of the cylindrical portion 11 in the vehicle width direction, and is formed to protrude outward and inward from the cylindrical portion 11. The first flange 12 is fixed to the inner tube 30 with its outer peripheral surface abutting against the inner peripheral surface of the cylindrical portion 131 of the inner tube 30 near the outer end of the vehicle width direction, and its end face abutting against the inner surface of the flange portion 132 in the vehicle width direction.

[0044] The second flange 13 is provided at the inner end of the cylindrical portion 11 in the vehicle width direction, and is formed to protrude radially outward and radially inward relative to the cylindrical portion 11. The second flange 13 is fixed to the base 150 with its outer circumferential surface and end surface fitted into the recess 153 of the base 150. With this configuration, substantially all of the force acting on the wheel is transmitted to the base 150 via the sensing body 10.

[0045] The six-component force detector 1 has an Fx detection system, an Fy detection system, an Fz detection system, an Mx detection system, a My detection system, and an Mz detection system, each having a bridge circuit including strain gauges provided on the cylindrical portion 11 of the sensing body 10 described above. The Fx detection system detects a radial force Fx (x-axis direction) acting on the cylindrical portion 11 of the sensing body 10. The Fy detection system detects an axial force Fy (y-axis direction) acting on the cylindrical portion 11 of the sensing body 10. The Fz detection system detects a radial force Fz (z-axis direction) acting on the cylindrical portion 11 of the sensing body 10, which is perpendicular to the x-axis direction. The Mx detection system detects a moment Mx about the x-axis acting on the cylindrical portion 11 of the sensing body 10. The My detection system detects a moment My about the y-axis acting on the cylindrical portion 11 of the sensing body 10. The Mz detection system detects the moment Mz acting on the cylindrical portion 11 of the sensing body 10 around the z axis.

[0046] The above-mentioned Fx detection system, Fy detection system, Fz detection system, Mx detection system, My detection system, and Mz detection system are each configured with a bridge circuit including four strain gauges. Fig. 2 is a schematic diagram showing the arrangement of strain gauges in the six-component force detector 1. Fig. 3 is a diagram showing the arrangement of strain gauges and the configuration of the bridge circuit in the Fx detection system in the six-component force detector 1, and shows a representative example of the arrangement of strain gauges and the configuration of the bridge circuit in each force detection system (Fx detection system, Fy detection system, Fz detection system) and each moment detection system (Mx detection system, My detection system, Mz detection system).

[0047] As shown in FIGS. 2 and 3, the Fx detection system includes strain gauges 21 to 24. The strain gauges 21 to 24 are single-axis strain gauges and are attached to the outer peripheral surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 21 is disposed in a region on the first flange 12 side of the outer peripheral surface of the cylindrical portion 11 (a region close to the intermediate portion 14). The strain gauge 22 is disposed on a line that passes through the strain gauge 21 and is parallel to the axial direction of the cylindrical portion 11, and is disposed in a region on the second flange 13 side of the outer peripheral surface of the cylindrical portion 11 (a region close to the intermediate portion 15). The strain gauge 23 is disposed at a position shifted 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 22 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 22). The strain gauge 24 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 when viewed from the strain gauge 21 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 21).

[0048] As shown in Fig. 3, the bridge circuit of the Fx detection system is configured as a Wheatstone bridge circuit, in which strain gauges 21 to 24 are connected sequentially in a loop, and the positive and negative poles of a power supply are connected between strain gauge 22 and strain gauge 23, and between strain gauge 21 and strain gauge 24, respectively. The bridge circuit extracts as outputs the potential differences between strain gauge 21 and strain gauge 22, and between strain gauge 23 and strain gauge 24. The configuration of the bridge circuit will be explained in detail later.

[0049] The Fy detection system is configured with strain gauges 41 to 44. The strain gauges 41 to 44 are single-axis strain gauges and are attached to the outer peripheral surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis direction of the cylindrical portion 11. The strain gauge 41 is disposed midway between the strain gauges 21 and 22 of the Fx detection system. The strain gauges 42, 43, and 44 are disposed at positions that are shifted in phase around the central axis of the cylindrical portion 11 by 90 degrees, 180 degrees, and 270 degrees, respectively, relative to the strain gauge 41. The bridge circuit of the Fy detection system has the same configuration as that of the Fx detection system shown in FIG. 3, except that the strain gauges 21 to 24 are replaced with the strain gauges 41 to 44.

[0050] The Fz detection system is composed of strain gauges 31 to 34. The strain gauges 31 to 34 are single-axis strain gauges and are attached to the outer peripheral surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis of the cylindrical portion 11. The strain gauge 31 is arranged at a 90-degree angle around the central axis of the cylindrical portion 11 relative to the strain gauge 21 of the Fx detection system. The strain gauge 32 is arranged at a 90-degree angle around the central axis of the cylindrical portion 11 relative to the strain gauge 22 of the Fx detection system. The strain gauges 31 and 32 are arranged on the same line parallel to the axial direction of the cylindrical portion 11. The strain gauge 33 is arranged at a position 180 degrees away from the strain gauge 32 around the central axis of the cylindrical portion 11 (a position symmetrical to the strain gauge 32 about the central axis of the cylindrical portion 11). The strain gauge 34 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 when viewed from the strain gauge 31 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 31). The bridge circuit of the Fz detection system has the same configuration as that of the Fx detection system shown in FIG. 3, except that the strain gauges 21 to 24 are replaced with strain gauges 31 to 34.

[0051] The Mx detection system is composed of strain gauges 51 to 54. The strain gauges 51 to 54 are uniaxial strain gauges and are attached to the outer peripheral surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis of the cylindrical portion 11. The strain gauge 51 is arranged adjacent to the strain gauge 31 of the Fz detection system in the direction of the central axis of the cylindrical portion 11. The strain gauge 52 is arranged adjacent to the strain gauge 32 of the Fz detection system in the direction of the central axis of the cylindrical portion 11. The strain gauges 51 and 52 are arranged on the same straight line parallel to the axial direction of the cylindrical portion 11. The strain gauge 53 is arranged at a position shifted 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 52 (a position symmetrical to the strain gauge 52 about the central axis of the cylindrical portion 11). The strain gauge 54 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 when viewed from the strain gauge 51 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 51). The bridge circuit of the Mx detection system has the same configuration as that of the Fx detection system shown in FIG. 3, except that the strain gauges 21 to 24 are replaced with strain gauges 51 to 54.

[0052] The My detection system is composed of strain gauges 71 to 74. The strain gauges 71 to 74 are shear type strain gauges and are attached to the outer peripheral surface of the cylindrical portion 11 so that their detection direction is the circumferential direction of the cylindrical portion 11. The strain gauge 71 is arranged midway between the strain gauges 41 and 42 of the Fy detection system. The strain gauge 72 is arranged midway between the strain gauges 42 and 44 of the Fy detection system. The strain gauges 73 and 74 are arranged in positions symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauges 72 and 71, respectively. The bridge circuit of the My detection system has the same configuration as that of the Fx detection system shown in FIG. 3, except that the strain gauges 21 to 24 are replaced with strain gauges 61 to 64.

[0053] The Mz detection system is composed of strain gauges 61 to 64. The strain gauges 61 to 64 are single-axis strain gauges and are attached to the outer peripheral surface of the cylindrical portion 11 so that their detection direction is parallel to the central axis of the cylindrical portion 11. The strain gauge 61 is arranged adjacent to the strain gauge 21 of the Fx detection system in the direction of the central axis of the cylindrical portion 11. The strain gauge 62 is arranged adjacent to the strain gauge 22 of the Fx detection system in the direction of the central axis of the cylindrical portion 11. The strain gauges 61 and 62 are arranged on the same straight line parallel to the axial direction of the cylindrical portion 11. The strain gauge 63 is arranged at a position shifted 180 degrees around the central axis of the cylindrical portion 11 from the strain gauge 62 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 62). The strain gauge 64 is disposed at a position shifted by 180 degrees around the central axis of the cylindrical portion 11 when viewed from the strain gauge 61 (a position symmetrical about the central axis of the cylindrical portion 11 with respect to the strain gauge 61). The bridge circuit of the Mz detection system has the same configuration as that of the Fx detection system shown in FIG. 3, except that the strain gauges 21 to 24 are replaced with strain gauges 61 to 64.

[0054] <2-2. Bridge circuit> Next, with reference to FIG. 3, a brief description will be given of an example of the configuration of the bridge circuit of each force detection system and each moment detection system.

[0055] The bridge circuit 80 of the Fx detection system shown in FIG. 3 has four terminals, namely, a first terminal 81, a second terminal 82, a third terminal 83, and a fourth terminal 84, and four strain gauges 21, 22, 23, and 24. The strain gauge 21 is provided between the first terminal 81 and the second terminal 82, and the strain gauge 22 is provided between the second terminal 82 and the fourth terminal 84. The strain gauge 24 is provided between the first terminal 81 and the third terminal 83, and the strain gauge 23 is provided between the third terminal 83 and the fourth terminal 84. A current path passing through the first terminal 81, the strain gauge 21, the second terminal 82, the strain gauge 22, and the fourth terminal 84 constitutes a first path 86. A current path passing through the first terminal 81, the strain gauge 24, the third terminal 83, the strain gauge 23, and the fourth terminal 84 constitutes a second path 87.

[0056] The strain gauges 21, 22, 23, and 24 are resistive elements whose resistance value changes depending on the amount of strain. In this embodiment, the strain gauges are made of a material with a gauge factor of 4 or more. For example, the strain gauges may be made of a Cr-N thin film. If the strain gauge has a gauge factor of 4 or more, it is possible to obtain the output desired for a six-component force detector 1 that detects the load applied to a wheel. However, the strain gauge is not limited to a Cr-N thin film.

[0057] In addition, in bridge circuit 80, one or more of the sides on which strain gauges 21, 22, 23, and 24 are arranged may be connected with resistive elements for adjusting the initial balance of the resistance values ​​or resistive elements for compensating for the temperature characteristics of the output of bridge circuit 80 that change with temperature.

[0058] In the bridge circuit 80, when a load is applied to the strain element, strain is generated in each of the strain gauges 21, 22, 23, and 24, and the resistance value of each of the strain gauges 21, 22, 23, and 24 changes depending on the amount of strain. The bridge circuit 80 outputs an electrical signal depending on the potential difference between the second terminal 82 of the first path 86 and the third terminal 83 of the second path 87.

[0059] <2-3. Embodiments of the electrode pad connection structure> Next, each embodiment of the electrode pad connection structure of the present disclosure will be specifically described.

[0060] (2-3-1. First embodiment) 4 to 6 are explanatory diagrams showing the connection structure of an electrode pad according to a first embodiment of the present disclosure. Fig. 4 is a plan view showing one strain gauge arranged on a flexure element. Fig. 5 is a cross-sectional view taken along line II in Fig. 4, and Fig. 6 is a cross-sectional view taken along line II-II in Fig. 4.

[0061] The strain gauge 201 is disposed on the flexure element 213 via an insulating layer 215. The flexure element 213 is made of a material with a predetermined rigidity, such as iron or other metal, and corresponds to the cylindrical portion 11 in the six-component force detector 1 described above. The insulating layer 215 is made of an electrically insulating material and electrically insulates the flexure element 213 from the strain gauge 201, which is made of a Cr-N thin film or the like. When the flexure element 213 is cylindrical, for example, the material of the insulating layer 215 is preferably a substance that can conform to portions other than a perfectly flat surface, such as a curved surface. For example, the insulating layer 215 may be a thin film formed using a polyester resin film, a polyimide resin film, or the like.

[0062] The strain gauge 201 has a gauge grid portion 203 and a tab portion 205. The gauge grid portion 203 includes a plurality of straight portions 204 extending in a predetermined first direction (X direction in the drawing). The plurality of straight portions 204 are arranged along a direction (Y direction in the drawing) perpendicular to the first direction and are electrically connected in series. The tab portion 205 has a first tab portion 205a and a second tab portion 205b provided on both ends of the gauge grid portion 203 (hereinafter, collectively referred to as tab portion 205 unless a distinction is required). The tab portion 205 is located closer to the first direction (X direction) than the gauge grid portion 203.

[0063] A first electrode pad 207a and a second electrode pad 207b are electrically connected to the first tab portion 205a and the second tab portion 205b, respectively (hereinafter, they will be collectively referred to as electrode pads 207 unless a distinction is required). Gauge leads 211a and 211b are electrically connected to the first electrode pad 207a and the second electrode pad 207b, respectively, using solders 209a and 209b.

[0064] Here, the connection structure between the second tab portion 205b and the second electrode pad 207b will be described as an example. In this embodiment, the second tab portion 205b has an insert structure in which it is sandwiched inside the second electrode pad 207b. Specifically, the second electrode pad 207b has a U-shaped cross section cut along a plane extending in the first direction (X direction), and is disposed on the strain element 213 so that the opening of the U is located on the side of the gauge grid portion 203. In other words, both legs (upper leg portion 207bu and lower leg portion 207bd) of the U-shaped second electrode pad 207b extend along the first direction (X direction). The second tab portion 205b is formed in a state where it penetrates into the U-shaped second electrode pad 207b from the first direction.

[0065] As shown in FIG. 6, in this embodiment, the second electrode pad 207b has a rectangular parallelepiped shape with a recess that opens to the gauge grid portion 203 side, and the second tab portion 205b is formed in the recess.

[0066] Therefore, compared to simply stacking an electrode pad on the tab portion, the bonding area between the second tab portion 205b and the second electrode pad 207b is increased. This strengthens the connection between the second tab portion 205b and the second electrode pad 207b, reducing the risk of disconnection due to insufficient adhesion or peeling. Furthermore, since the connection between the second tab portion 205b and the second electrode pad 207b is strong, it is possible to prevent a decrease in electrical conductivity at the connection between the second tab portion 205b and the second electrode pad 207b even when the temperature of the load cell changes.

[0067] Furthermore, since the second tab portion 205b is in a state of extending into the second electrode pad 207b from the first direction (X direction) in which the straight portion 204 of the gauge grid portion 203 extends (the influence of the second tab portion 205b on distortion is reduced), the accuracy of detecting the amount of distortion by the strain gauge 201 can be improved.

[0068] Furthermore, the second electrode pad 207b is formed in contact with the second tab portion 205b and the insulating layer 215. This expands the area in which the second electrode pad 207b is formed compared to when the electrode pad is stacked on the tab portion, reducing the risk that the solder 209b will protrude from the second electrode pad 207b and come into contact with the material of the strain gauge 201. This prevents the material of the strain gauge 201 from being subjected to high heat, which would cause the characteristics to change.

[0069] The material constituting the second electrode pad 207b is preferably a material that is unlikely to form an alloy with the solder when high heat is applied, such as during soldering. This is because if an alloy is formed, the electrical resistance value changes, making it difficult to adjust the bridge balance. Furthermore, the material constituting the second electrode pad 207b is preferably a material that wets well with solder and reduces the contact angle of the solder 209b bonded to the upper leg portion 207bu. This is because the smaller the contact angle of the solder 209b, the more stable the bonding of the solder 209b.

[0070] Furthermore, it is preferable that the material constituting the second electrode pad 207b be selected taking into consideration the linear thermal expansion coefficient of the solder 209b. If the linear thermal expansion coefficient of the second electrode pad 207b is significantly larger than that of the solder 209b, high heat is transferred to the second electrode pad 207b during solder connection, generating large thermal stress, which may increase the thermal stress applied to the second tab portion 205b due to the thermal expansion of the second electrode pad 207b. The linear thermal expansion coefficient of a typical solder 209b is 20×10 -6 / K~22×10 -6 / K, the coefficient of linear thermal expansion of the material of the second electrode pad 207b is 30×10 -6 It is preferable that the temperature is in the range of 1 / K.

[0071] For example, the material of the second electrode pad 207b is Ag (coefficient of linear thermal expansion: 19×10 -6 / K), Cu (linear thermal expansion coefficient: 17×10 -6 / K) or Au (linear thermal expansion coefficient: 14 × 10-6 / K). In particular, the smaller the coefficient of linear thermal expansion of the material of the second electrode pad 207b, the smaller the tensile or compressive stress generated in the second electrode pad 207b during solder connection, and thus the smaller the tensile or compressive stress applied to the second tab portion 205b. Therefore, it is more preferable that the material of the second electrode pad 207b be Au.

[0072] In this embodiment, the insulating layer 215, the strain gauge 201, and the electrode pad 207 (first electrode pad 207a and second electrode pad 207b) that constitute the electrode pad connection structure are all made of thin films. That is, each of them is made of a thin film formed by a lamination process in which constituent materials are laminated to form a thin film, a development process in which a resist film is laminated on the formed thin film and then a desired pattern is formed by photolithography, and a patterning process in which the thin film in the area not masked by the resist film is etched to form a thin film with the desired pattern.

[0073] In particular, in this embodiment, after forming the lower leg portion (207bd) of the electrode pad 207 having a U-shaped cross section, the strain gauge 201 including the tab portion 205 is formed, and then the upper leg portion (207bu) of the electrode pad 207 is formed, thereby forming an insert structure in which the tab portion 205 is sandwiched inside the electrode pad 207.

[0074] 4, the entire tab portion 205 is sandwiched within the electrode pad 207, but only a portion of the tab portion 205 may be sandwiched within the electrode pad 207. Furthermore, after the insulating layer 215, strain gauge 201, and electrode pad 207 are formed on the strain element 213 and the gauge lead 211 is connected to the electrode pad 207 with solder 209, the structure is covered with an electrically insulating protective film, although the protective film is not shown.

[0075] As described above, the electrode pad connection structure according to this embodiment has an insert structure in which part or all of the tab portion of the strain gauge is sandwiched inside the electrode pad. This strengthens the connection between the tab portion and the electrode pad, preventing disconnection or poor electrical continuity between the strain gauge and the electrode pad. Furthermore, the electrode pad connection structure according to this embodiment reduces the risk of solder coming into contact with the strain gauge during soldering, preventing disconnection or poor electrical continuity due to changes in the strain gauge characteristics.

[0076] Furthermore, the connection structure of the electrode pad according to this embodiment improves the connection reliability between the strain gauge and the gauge lead, which increases the yield rate during the manufacture of a six-component force detector in which a large number of strain gauges (10 or more) are arranged on a strain generating body, and also increases the reliability of the measurement results.

[0077] (2-3-2. Second embodiment) 7 to 10 are explanatory diagrams showing a connection structure of an electrode pad according to a second embodiment of the present disclosure. Fig. 7 is a plan view showing one strain gauge arranged on a flexure element, and Fig. 8 is a plan view showing the planar shape of a tab portion. Fig. 9 is a cross-sectional view taken along the line III-III in Fig. 7, and Fig. 10 is a cross-sectional view taken along the line IV-IV in Fig. 7.

[0078] Similar to the strain gauge 201 of the first embodiment, the strain gauge 221 is disposed on a strain gauge 233 via an insulating layer 235. The strain gauge 221 has a gauge grid portion 223 and a tab portion 225. A first electrode pad 227a and a second electrode pad 227b are electrically connected to the first tab portion 225a and the second tab portion 225b, respectively (hereinafter, collectively referred to as electrode pads 227 unless a distinction is required). Gauge leads 231a and 231b are electrically connected to the first electrode pad 227a and the second electrode pad 227b, respectively, using solders 229a and 229b.

[0079] Here, the connection structure between the second tab portion 225b and the second electrode pad 227b will be described as an example. In this embodiment, the second tab portion 225b and the second electrode pad 227b have an insert structure in which a part of the second tab portion 225b and a part of the second electrode pad 227b are sandwiched inside each other.

[0080] As shown in Fig. 8, each second tab portion 225b has a plurality of slots 226 that extend longitudinally in a predetermined second direction (x direction in the example of Fig. 8) and penetrate through the thickness of the second tab portion 225b. Also, as shown in Fig. 10, the second electrode pad 227b has a comb-like cross section, and is formed with the comb-teeth portions inserted into the plurality of slots 226 of the second tab portion 205b. In other words, each comb-teeth portion is formed with its longitudinal direction extending in the predetermined second direction (x direction in the example of Fig. 8).

[0081] This increases the contact area between the second tab portion 225b and the second electrode pad 227b compared to simply stacking an electrode pad on the tab portion. This strengthens the connection between the second tab portion 225b and the second electrode pad 227b, reducing the risk of disconnection due to insufficient adhesion or peeling. Furthermore, because the connection between the second tab portion 225b and the second electrode pad 227b is strong, it is possible to prevent a decrease in electrical conductivity at the connection between the second tab portion 225b and the second electrode pad 227b even when the temperature of the load cell changes.

[0082] The second direction in which the slots 226 of the second tab portion 225b and the comb-tooth portions of the second electrode pad 227b extend may be different from the first direction (x direction), but extending the second direction in the same direction as the first direction (reducing the effect on the distortion of the second tab portion 225b) can improve the accuracy of detecting the amount of distortion by the strain gauge 221. The number of slots 226 and the comb-tooth portions is not limited to the example shown in the figure, and may be any number.

[0083] The material constituting the second electrode pad 227b may be selected similarly to that of the second electrode pad 227b in the first embodiment. Also in this embodiment, the insulating layer 235, the strain gauge 221, and the electrode pad 227 (first electrode pad 227a and second electrode pad 227b) constituting the electrode pad connection structure are all made of thin films. That is, the thin films are formed by a lamination process in which constituent materials are laminated to form a thin film, a development process in which a resist film is laminated on the formed thin film and then a desired pattern is formed by photolithography, and a patterning process in which the thin film in the area not masked by the resist film is etched to form a thin film of the desired pattern.

[0084] The electrode pad connection structure according to this embodiment described above can also achieve the same effects as the electrode pad connection structure according to the first embodiment. Instead of providing elongated holes in the tab portion, the tab portion may be formed in a lattice pattern, and an insert structure may be formed in which a portion of the electrode pad is sandwiched between the gaps in the lattice. Even with this insert structure, the bonding area between the tab portion and the electrode pad can be increased, thereby strengthening the connection between the tab portion and the electrode pad.

[0085] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that a person skilled in the art to which the present disclosure pertains can conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0086] For example, in the above embodiment, an example has been described in which the technology of the present disclosure is applied to a six-component force detector that detects the load applied to a wheel as a load cell, but the application of the technology of the present disclosure is not limited to six-component force detectors. The technology of the present disclosure can be applied to various force detection sensors that use strain gauges.

[0087] In the above embodiment, an example of a load cell using a single-axis strain gauge has been described, but the load cells to which the technology of the present disclosure can be applied are not limited to such an example. For example, the technology of the present disclosure can also be applied to a load cell using a biaxial shear strain gauge as shown in Figures 11 and 12.

[0088] Specifically, Fig. 11 is a schematic diagram showing the arrangement of strain gauges in a six-component force detector of a modified example, and Fig. 12 is an explanatory diagram showing the gauge pattern of biaxial shear strain gauges. The six-component force detector shown in Fig. 11 is provided with shear strain gauges 271 and 272 of the Fx detection system and shear strain gauges 275 and 277 of the Fz detection system, which will be described below, instead of the above-mentioned Fx detection system strain gauges 21-24 and Fz detection system strain gauges 31-34. Fig. 12 shows shear strain gauge 271 as an example, but shear strain gauges 272, 275, and 277 also have substantially the same gauge patterns.

[0089] The shear strain gauge 271 is configured as a so-called arrow-shaped two-axis (two-pole) shear strain gauge. The shear strain gauge 271 has a first detection unit 271a and a second detection unit 271b, each made of a Cr-N thin film or the like, formed on a common insulating layer 271c, which is a thin insulating film. The first detection unit 271a and the second detection unit 271b are each configured by connecting multiple linear sections, arranged parallel to each other along the detection direction, in series. The first detection unit 271a and the second detection unit 271b are configured so that their electrical resistance changes easily in response to strain in the direction in which the linear sections expand and contract (the detection direction). The detection directions of the first detection unit 271a and the second detection unit 271b are arranged to be substantially perpendicular to each other. The shear strain gauge 271 is attached to the outer circumferential surface of the cylindrical portion 250 so that the detection directions of the first detection unit 271a and the second detection unit 271b are inclined at 45° in opposite directions relative to the central axis of the cylindrical portion 250. The shear strain gauges 272, 275, and 277 are also attached to the outer circumferential surface of the cylindrical portion 250 in a similar manner.

[0090] 11, shear strain gauges 271, 272, 275, and 277 are attached to the outer peripheral surface of the central portion in the central axis direction of cylindrical portion 250. Fx detection system shear strain gauge 271 is disposed midway between Mx detection system strain gauges 251 and 252. Fx detection system shear strain gauge 272 is disposed midway between Mx detection system strain gauges 253 and 254 (at a position symmetrical about the central axis with shear strain gauge 271). Fz detection system shear strain gauge 275 is disposed midway between Mz detection system strain gauges 261 and 262. Fz detection system shear strain gauge 277 is disposed midway between Mz detection system strain gauges 263 and 264 (at a position symmetrical about the central axis with shear strain gauge 275).

[0091] Furthermore, strain gauges 281-284 of the Fy detection system and strain gauges 291-294 of the My detection system are arranged at offset positions around the central axis to avoid interference with strain gauges 271, 272 of the Fx detection system and strain gauges 275, 277 of the Fz detection system. For example, as shown in Fig. 11, shear strain gauge 271, strain gauge 282, strain gauge 292, shear strain gauge 277, strain gauge 284, strain gauge 294, shear strain gauge 272, strain gauge 283, strain gauge 293, shear strain gauge 275, strain gauge 281, and strain gauge 291 can be arranged sequentially at positions offset by an angle of 30° around the central axis around the circumferential direction of cylindrical portion 250.

[0092] The first and second detection units of shear strain gauges 271, 272 of the Fx detection system form a bridge circuit similar to the bridge circuit shown in Fig. 3. This bridge circuit generates an output corresponding to the Fx-direction component of force input to sensing unit 250. Similarly, the first and second detection units of shear strain gauges 275, 277 of the Fz detection system form a bridge circuit similar to the bridge circuit shown in Fig. 3. This bridge circuit generates an output corresponding to the Fz-direction component of force input to sensing unit 250.

[0093] The technology of the present disclosure can be applied to a load cell using a biaxial shear strain gauge configured in this manner, and the effects obtained by the above embodiment can be achieved. [Explanation of symbols]

[0094] 21, 22, 23, 24: strain gauge, 80: bridge circuit, 201, 221: strain gauge, 203, 223: gauge grid portion, 204, 224: straight portion, 205, 225: tab portion, 205a, 225a: first tab portion, 205b, 225b: second tab portion, 207, 227: electrode pad, 207a, 227a: first electrode pad, 207b, 227b: second electrode pad, 207bd, 207bu: foot portion, 209, 209a, 209b, 229, 229a, 229b: solder, 211, 211a, 211b, 231, 231a, 231b: gauge lead, 213, 233: strain element, 215, 235: insulating layer

Claims

1. A strain body, a strain gauge disposed on the strain generating element and having a gauge grid portion and a tab portion; an electrode pad electrically connected to the tab portion of the strain gauge; a gauge lead connected to the electrode pad; A force detector comprising: A force detector having an insert structure in which part or all of one of the tab portion and the electrode pad is sandwiched inside the other.

2. The electrode pad having a U-shaped cross section is disposed on the strain generating element so that an opening of the U-shape is positioned to the side, The tab portion is sandwiched inside the U-shaped electrode pad.

10. The force detector of claim 1.

3. the gauge grid portion includes a plurality of linear portions each extending in a predetermined first direction; Both leg portions of the U-shaped electrode pad extend along the first direction, and the tab portion enters the inside of the U-shaped electrode pad from the first direction.

3. A force detector according to claim 2.

4. the tab portions each have a longitudinal direction extending in a predetermined second direction and a plurality of elongated holes penetrating the tab portions in a thickness direction or a plurality of grooves recessed in a thickness direction of the tab portions, the electrode pad has a comb-like cross section, and the comb-like portions are inserted into the plurality of elongated holes or the plurality of grooves; 10. The force detector of claim 1.

5. the gauge grid portion includes a plurality of linear portions each extending in a predetermined first direction; The second direction extends in the same direction as the first direction.

5. A force detector according to claim 4.

6. the strain gauge is disposed on the strain element via an insulating layer; the electrode pad is formed in contact with the tab portion and the insulating layer; 10. The force detector of claim 1.

7. The strain gauge is made of Cr—N, and the electrode pad is made of Au.

10. The force detector of claim 1.

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