Small 3-axis force sensor

Abstract

To provide a noise-reduced, high-accuracy and downsizable three-axis force sensor, the size of which is smaller than conventional sensors, and with which the electric resistance value of electroconductive members constituting a full bridge circuit can be fully secured.SOLUTION: A three-axis force sensor according to the present invention comprises: a tabular substrate; a projection part which is provided so as to project from one face of the substrate; a strain part as a thin-walled part which is formed by providing a groove which is recessed in annular form so as to enclose the periphery of the base end of the protrusion part from the one face of the substrate; and a plurality of electroconductive members arranged on the other face that is opposite the one face where the protrusion part is provided, so as to extend in archwire form along the inner and outer circumferential edges of the strain region which are equivalent of the strain part, respectively, and to have a 4-turn symmetry, thus constituting four full-bridge circuits, with the plurality of electroconductive members being arranged so as to have a 4-turn symmetry.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a miniaturizable three-axis force sensor, and to a strain-generating substrate for the three-axis force sensor and an arrangement pattern of conductive members in a strain-generating area of ​​the substrate. [Background technology]

[0002] A force sensor used to measure the force applied to an object mainly comprises a strain element and a conductive member that is in contact with the strain element and converts the applied force electrically. The conductive member has an appropriate strain gauge and changes its electrical resistance in response to strain.

[0003] In particular, Patent Document 1 proposes a force sensor for detecting forces in each of the three axial directions. The force sensor in Patent Document 1 has a cylindrical section that receives forces in the three axes and a strain-generating section that generates strain due to the forces received by the cylindrical section. A conductive member made of a Cr-based thin film that is a strain gauge is used to electrically convert the strain generated in the strain-generating section. By adjusting the arrangement of the conductive member, the sensor is configured to be able to measure forces from each direction.

[0004] Furthermore, for example, Patent Document 2 proposes a force sensor array using force sensors in which a conductive member made of a Cr-based thin film is configured as a single wire and arranged in contact with a strain generator. Each force sensor used in the force sensor array is arranged so that the conductive member forms a bridge circuit on the underside of a strain generator having a groove. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-166847 [Patent Document 2] Japanese Patent Publication No. 2021-060226 Summary of the Invention [Problem to be solved by the invention]

[0006] Since force sensors are expected to be applied to the ICT industry, such as in wearable devices (e.g., JP 2021-067553 A), there is a need for force sensors that can be used in environments suitable for miniaturization, such as wearable devices.

[0007] However, miniaturizing the force sensors of Patent Documents 1 and 2 poses a problem: the conductive member itself must also be small, making it impossible to achieve a sufficiently large electrical resistance. If the electrical resistance is not sufficiently large, the sensor's thermal and electromagnetic measurement errors become large, making it unable to adequately measure force. In particular, while the electrical resistance is proportional to the length of the conductive member and inversely proportional to the cross-section, when manufacturing a strain-generating body in a three-axis force sensor with a length of 10 mm or less, the conductive member's length is insufficient, resulting in an unstable electrical resistance and reduced measurement accuracy. Therefore, there is a problem in that strain-generating bodies in existing three-axis force sensors cannot be reliably manufactured with a length of 10 mm or less.

[0008] Therefore, an object of the present invention is to provide a three-axis force sensor that is smaller than conventional sensors, yet can ensure sufficient electrical resistance of the sensors that make up the full bridge circuit, and that has reduced noise, is highly accurate, and can be made smaller. [Means for solving the problem]

[0009] (1) The three-axis force sensor of the present invention comprises a plate-shaped substrate, a protrusion protruding from one surface of the substrate, a thin-walled strain-generating portion formed by providing a groove recessed in an annular shape from the one surface of the substrate around the base end of the protrusion, and a plurality of conductive members extending in an arc shape along each of the inner and outer peripheral edges of a strain-generating region corresponding to the strain-generating portion on the other surface opposite the surface on which the protrusion is provided and arranged to have four-fold rotational symmetry, wherein each of the plurality of conductive members constitutes four full bridge circuits arranged to have four-fold rotational symmetry, and one pair of the conductive members constituting each of the full bridge circuits that forms opposite sides of the full bridge circuits is arranged on the inner peripheral edge of the strain-generating region, and another pair of the conductive members constituting each of the full bridge circuits, other than the one pair that forms opposite sides of the full bridge circuits, is arranged on the outer peripheral edge of the strain-generating region.

[0010] With this configuration, strain can be generated in the strain-generating portion by a force applied from at least one of the upper and side surfaces of the protrusion. The spatial distribution of strain generated in the strain-generating portion is measured using four full-bridge circuits, resulting in a highly accurate and sensitive three-axis force sensor. Furthermore, one set of conductive members constituting the full-bridge circuit is arranged on the inner periphery of the strain-generating region, and the other set of conductive members constituting the full-bridge circuit is arranged on the outer periphery of the strain-generating region, with each conductive member extending in an arc-like shape. Therefore, even when the three-axis force sensor is miniaturized to 10 mm or less, or even to approximately 5 mm, the electrical resistance of each conductive member is sufficiently ensured within the limited space of the board to form a full-bridge circuit. Furthermore, since the conductive members are not stacked or folded, they do not come into contact with each other, preventing short circuits and maintaining sufficient durability even when miniaturized.

[0011] (2) Furthermore, in the three-axis force sensor of the present invention, it is preferable that each of the pair of conductive members arranged on the inner peripheral edge of the strain-generating region is arranged to extend in an arc shape along different circumferences.

[0012] With this configuration, even in a strain-generating region with a small inner diameter, the length is maintained to ensure sufficient electrical resistance for the conductive members. Furthermore, because the two conductive members that make up one pair are arranged on the inner periphery of the strain-generating region, high-precision force measurement and high durability are achieved even when the sensor is small.

[0013] (3) Furthermore, in the three-axis force sensor of the present invention, it is preferable that the conductive members of the other set, which are different from the one set arranged on the outer peripheral edge of the strain-generating region, are arranged so as to extend in an arc shape along different circumferences.

[0014] With this configuration, even if the strain-generating region has a small outer diameter, the conductive member can be maintained long enough to ensure a sufficient electrical resistance. Furthermore, because the two conductive members constituting the other pair are arranged on the outer periphery of the strain-generating region, high-precision force measurement and high durability can be achieved even with a small sensor.

[0015] (4) Furthermore, in the three-axis force sensor of the present invention, it is preferable that the other surface of the substrate is provided with a connecting portion that connects the ends of the conductive members, a power supply portion that supplies power to each of the four full bridge circuits, and a grounding portion that grounds each of the four full bridge circuits.

[0016] With this configuration, the connecting part, power supply part, and ground part are integrated with the sensor, which allows for a smaller three-axis force sensor. Also, external influences can be reduced, allowing for highly accurate force measurement.

[0017] (5) Furthermore, it is preferable that the three-axis force sensor of the present invention includes a set of holder parts that mechanically fix one side and the other side of the substrate, and a sensor substrate for connecting electrical signals to the four full bridge circuits.

[0018] With this configuration, the holder and sensor substrate are integrated with the sensor, which allows for a smaller three-axis force sensor. Also, external influences can be reduced, allowing for highly accurate force measurement.

[0019] (6) Furthermore, in the three-axis force sensor of the present invention, it is preferable that the holder portion has an amplifier board equipped with an amplifier IC that amplifies the output signal of the full bridge circuit.

[0020] With this configuration, the amplifier board is integrated with the sensor, making it possible to miniaturize the three-axis force sensor. Furthermore, external influences can be reduced, enabling highly accurate force measurement. Furthermore, incorporating the amplifier board makes it possible to create a highly sensitive force sensor.

[0021] (7) In the three-axis force sensor of the present invention, it is preferable that both ends of the conductive member disposed on the substrate are connected to the sensor substrate by wire bonding.

[0022] According to this configuration, since the connection is made using wire bonding, it is possible to reduce short circuits even in a small size, and to realize a highly durable sensor.

[0023] (8) In the three-axis force sensor of the present invention, the conductive member is preferably made of a Cr-based thin film.

[0024] According to this configuration, since a conductive member made of a Cr thin film is used, it is highly sensitive and measures three-axial forces with high accuracy.

[0025] (9) Furthermore, in the three-axis force sensor of the present invention, it is preferable that, among the conductive members constituting the one set, the length of the conductive members arranged on the circumference with a shorter radius centered on the strain-flexible portion is longer than the length of the conductive members arranged on the circumference with a longer radius centered on the strain-flexible portion, and that, among the conductive members constituting the other set, the length of the conductive members arranged on the circumference with a shorter radius centered on the strain-flexible portion is shorter than the length of the conductive members arranged on the circumference with a longer radius centered on the strain-flexible portion.

[0026] With this configuration, even at the inner periphery of the strain-generating region, the length of the conductive member located closest to the inner periphery can be set to ensure a sufficient electrical resistance value. Furthermore, since there is no contact with adjacent conductive members, the effects of short circuits and other problems can be reduced, improving durability. Furthermore, since the cross-sectional area is sufficient, variations in electrical resistance values ​​during manufacturing can be suppressed, reducing noise and errors, and providing a sensor that can measure with high accuracy even in a small size. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram showing a schematic configuration of a substrate of a three-axis force sensor of the present invention. FIG. [Figure 2] 1 is a diagram showing a schematic configuration of an arrangement of conductive members in a three-axis force sensor according to a first embodiment of the present invention. FIG. [Figure 3] FIG. 3 is an enlarged view of one full-bridge circuit in FIG. 2. [Figure 4] FIG. 4 is a circuit diagram of the full-bridge circuit of FIG. 3. [Figure 5] FIG. 10 is a diagram showing a schematic configuration of the arrangement of conductive members according to a second embodiment of the three-axis force sensor of the present invention. [Figure 6] FIG. 6 is an enlarged view of one full-bridge circuit in FIG. 5. [Figure 7] FIG. 7 is a circuit diagram of the full-bridge circuit of FIG. 6. [Figure 8] FIG. 10 is a diagram showing the relationship between the normal load and the strain of the substrate obtained by simulation using the finite element method. [Figure 9] FIG. 10 is a diagram showing the relationship between horizontal load and strain of a substrate obtained by simulation using the finite element method. [Figure 10] FIG. 2 is a diagram showing a sensor head of the three-axis force sensor of the present invention. [Figure 11A] 10 is a schematic diagram showing the positional relationship between the sensor head, the sensor substrate, and some of the connecting wires of the three-axis force sensor of the present invention, as viewed from above the other surface of the substrate. FIG. [Figure 11B] 2 is a schematic diagram showing the positional relationship between the sensor head, the sensor substrate, and some of the connecting wires of the three-axis force sensor of the present invention. FIG. [Figure 12] FIG. 10 is a diagram showing the relationship between the load when a load is applied in the Z direction and the output obtained from each full bridge. [Figure 13A] 10 is a diagram showing the relationship between the load when a load is applied in the X direction and the bridge output obtained from each full bridge. FIG. [Figure 13B] 10 is a diagram showing the relationship between the load when a load is applied in the X direction and the amplifier output obtained from each full bridge. FIG. [Figure 14A] 10 is a diagram showing the relationship between the load when a Y-direction load is applied and the bridge output obtained from each full bridge. FIG. [Figure 14B] FIG. 10 is a diagram showing the relationship between the load when a Y-direction load is applied and the amplifier output obtained from each full bridge. [Figure 15A] FIG. 10 is a diagram showing the relationship between the load and the measured electrical resistance value of each conductive member. [Figure 15B] FIG. 10 is a diagram showing the relationship between the load and the simulated value of the electrical resistance of each conductive member. [Figure 16] FIG. 10 is a diagram showing sensitivity coefficient dependency of changes in electrical resistance value of each conductive member. [Figure 17A] 1A and 1B are diagrams showing a schematic configuration when the number of wire bonds is reduced in the arrangement of conductive members according to the first embodiment of the present invention. [Figure 17B] FIG. 2 is a diagram showing a schematic configuration when the number of wire bonds is further reduced in the arrangement of the conductive members according to the first embodiment of the present invention. [Figure 18A]FIG. 10 is a diagram showing a schematic configuration when the number of wire bonds is reduced in the arrangement of conductive members according to the second embodiment of the present invention. [Figure 18B] FIG. 10 is a diagram showing a schematic configuration when the number of wire bonds is further reduced in the arrangement of conductive members according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the three-axis force sensor of the present invention will be described with reference to the following description and drawings. FIG. 1A is a top view of one surface 10 of the three-axis force sensor of the present invention. The three-axis force sensor of the present invention has a substrate 1, a protrusion 2 formed to protrude from one surface 10 of the substrate 1, and a strain-flexing portion 3 formed as a thin portion by providing a circular groove in one surface 10 of the substrate 1 that surrounds the base end of the protrusion 2. As shown in FIG. 1B, which is a cross-sectional view taken along the line AA in FIG. 1A, the groove that forms the strain-flexing portion 3 is provided on one surface 10 of the substrate 1 so as to have a U-shaped cross section. To explain the positions and orientations of the components of the three-axis force sensor, a three-dimensional cylindrical coordinate system (r, θ, Z) is used, with the geometric center of gravity of the substrate 1 as its pole.

[0029] The outer shape of the substrate 1 is cylindrical, but is not limited to this. The outer shape of the substrate 1 may be any shape, such as a rectangular pillar, that is optimal for the measurement environment. The shape of the protrusion 2 is cylindrical with a convex surface on the first surface 10, but is not limited to this. The surface on the first surface 10 of the protrusion 2 may be flat or concave. The shape of the protrusion 2 may be any rectangular pillar, truncated cone, truncated pyramid, cone, pyramid, or other shape that is optimal for the location where the three-axis force sensor of the present invention will be used. The protrusion 2 is formed integrally with the substrate 1, but is not limited to this. It may also be formed by various methods, such as by screwing or press-fitting. The shape of the first surface 10 of the strain-flexing portion 3, as viewed from above, is formed as a ring, but is not limited to this. The shape of the first surface 10 of the strain-flexing portion 3, as viewed from above, may be a ring structure along the sides of any shape, such as a square or triangle. The thickness of the strain-flexing portion 3 is thinner than the thickness of the area of ​​the substrate 1 other than the strain-flexing portion 3. The thickness of the strain-flexing part 3 may be kept constant, or the thickness may vary continuously or discontinuously along the diameter. Additionally, the thickness and structure of the substrate 1 are adjusted from the viewpoint of generating a predetermined strain. A material having a predetermined elastic modulus is selected as the material for the substrate 1. A metal material having a predetermined elastic modulus and corrosion resistance is usually used as the material for the substrate 1, but it is not limited to metal materials; organic materials such as ceramics and rubber can also be used.

[0030] When force is applied to either the protrusion 2 or the substrate 1, strain is generated in the strain-flexible part 3, but if a load exceeding a certain level is applied, this will lead to damage to the strain-flexible part 3. Therefore, the thickness of the strain-flexible part 3 is adjusted so that it can withstand the maximum applied load. Preferably, it is adjusted so that a safety factor of at least three times the von Mises stress generated by the maximum applied load can be ensured.

[0031] 2, which is a top view of the other surface 11, which is the surface opposite to the surface on the side of one surface 10 of the three-axis force sensor of the present invention, a conductive member 4 is provided on the other surface 11 of the substrate 1 of the three-axis force sensor of the present invention and is arranged so as to come into contact with the strain-flexing portion 3. The conductive member 4 is used to electrically measure the strain generated in the strain-flexing portion 3.

[0032] The conductive member 4 is made of, for example, a Cr thin film made of Cr and inevitable impurities, as described in Patent Document 1, or a Cr—N thin film made of Cr, N and inevitable impurities. The Cr—N thin film is, for example, a thin film of the general formula Cr 1 0 0-x N x where the composition ratio x is 0.0001≦x≦30 in atomic percent.

[0033] The conductive member 4 is a material represented by the general formula Cr 1 0 0-x Mn x (x is atomic %, and 0.1≦x≦34) or the general formula Cr 1 0 0-x Al x The conductive member 4 may be made of a Cr thin film represented by the general formula Cr 1 0 0-x-y Al x N y (x and y are atomic percentages, and 4≦x≦25, 0.1≦y≦20.) The Cr-N thin film has an extremely small temperature coefficient of resistance (TCR) (<±50 ppm / °C), making it stable against temperature changes, so the pressure sensitivity and pressure measurement accuracy are independent of temperature.

[0034] In a preferred embodiment of the present invention, the conductive member 4 is a Cr—N film, and is sputter-deposited to a thickness of approximately 0.1 μm. The film is deposited by reactive sputtering using a Cr target and Ar gas with an appropriate amount of N2 gas added. After deposition, a predetermined pattern is formed using a positive resist, and then wet etching is performed using a Cr etching solution to remove unnecessary portions, yielding the conductive member 4 made of Cr—N.

[0035] The Cr or Cr-N thin film constituting the conductive member 4 may be formed by any suitable method, including vapor deposition using an alloy capable of forming a Cr or Cr-N thin film; sputtering using a Cr target or an alloy target capable of forming a Cr-N thin film, a composite target, or a multi-element target; and, in the case of a Cr-N thin film, reactive sputtering using a nitrogen gas-containing deposition atmosphere; vapor phase transport using a source capable of forming the above thin film; or liquid-phase deposition including plating. Furthermore, such thin films may be formed in the desired shape using a masking method or other techniques. After formation, the thin film may be processed into an optimal shape for the measuring device by etching or trimming, such as dry etching (plasma etching, sputter etching, etc.), chemical etching (etching), lift-off, or laser trimming. Furthermore, the Cr or Cr-N thin film may be used as is, but is preferably subjected to heat treatment at a temperature of 200°C to 1000°C in air, a non-oxidizing gas, a reducing gas, or a vacuum.

[0036] The conductive members 4 constitute four full bridge circuits 40, 41, 42, and 43, respectively. Each of the four full bridge circuits 40, 41, 42, and 43 has four-fold rotational symmetry with respect to the poles of the substrate 1, and is arranged so as to divide the strain-flexing part 3 into four equal parts. Each of the full bridge circuits 40, 41, 42, and 43 is constituted by four conductive members 4. In this case, conductive members 400, 401, 402, and 403 constitute full bridge circuit 40, conductive members 410, 411, 412, and 413 constitute full bridge circuit 41, conductive members 420, 421, 422, and 423 constitute full bridge circuit 42, and conductive members 430, 431, 432, and 433 constitute full bridge circuit 43. Each of the conductive members 4 is formed to extend in an arc shape.

[0037] 2 is a top view of the other surface 11 of the substrate 1 when the three-axis force sensor according to the first embodiment of the present invention is provided with conductive members 4. Of the conductive members 4 constituting the full bridge circuit 40, conductive members 403 and 401 are arranged radially adjacent to each other on the inner periphery of the strain-flexing region of the strain-flexing section 3, while conductive members 400 and 402 are arranged radially adjacent to each other on the outer periphery of the strain-flexing region of the strain-flexing section 3. Here, conductive members 403 and 401 form one pair that constitutes opposite sides of the bridge, and conductive members 400 and 402 form another pair that constitutes another pair that is different from the other pair. Conductive members 410-413, 420-423, and 430-433 that constitute the full bridge circuits 41, 42, and 43, respectively, are arranged in the same manner as in the full bridge circuit 40.

[0038] 5 is a top view of the other surface 11 of the substrate 1 when a conductive member 4 is provided in the three-axis force sensor according to the second embodiment of the present invention. Of the conductive members constituting the full bridge circuit 40, conductive member 403 and conductive member 401 are arranged radially adjacent to each other on the inner periphery of the strain-flexing region of strain-flexing section 3, while conductive member 400 and conductive member 402 are arranged circumferentially adjacent to each other on the outer periphery of the strain-flexing region of strain-flexing section 3. Here, conductive member 403 and conductive member 401 form one pair that constitutes opposite sides of the bridge, and conductive member 400 and conductive member 402 form another pair that constitutes another opposite side. Conductive members 410-413, 420-423, and 430-433 that constitute full bridge circuits 41, 42, and 43, respectively, are arranged in the same manner as full bridge circuit 40.

[0039] To avoid redundancy, only full bridge circuit 40 will be described below. However, each of full bridge circuits 41, 42, and 43 is configured similarly to full bridge circuit 40. FIG. 3 is an enlarged view of full bridge circuit 40, one of the four full bridges in a three-axis force sensor according to a first embodiment of the present invention. FIG. 4 is a circuit diagram showing full bridge circuit 40 according to the first embodiment. FIG. 6 is an enlarged view of full bridge circuit 40, one of the four full bridges in a three-axis force sensor according to a second embodiment of the present invention. FIG. 7 is a circuit diagram showing full bridge circuit 40 according to the second embodiment. In the first embodiment, one pair of conductive members 403 and 401 constituting full bridge circuit 40 are arranged so as to extend in arcs of approximately 90 degrees along different circumferences, and another pair of conductive members 400 and 402 are arranged so as to extend in arcs of approximately 90 degrees along different circumferences. In the second embodiment, one set of conductive members 403 and 401 constituting the full bridge circuit 40 are arranged so as to extend in arcs of approximately 90 degrees along different circumferences, and another set of conductive members 400 and 402 are arranged so as to extend in arcs of approximately 45 degrees along the same circumference.

[0040] In the present invention, the length and cross-sectional area of ​​each conductive member 4 are adjusted along the radial direction of the strain-flexing part 3. If the inner and outer diameters of the strain-flexing part 3 are shortened, it becomes difficult to arrange the conductive member 4 due to the size of the electrode pad 5 that electrically connects the conductive member 4. Therefore, among the conductive members that make up the full bridge circuit 40, of the conductive members 403 and conductive members 401 that make up one set, it is preferable that the length of the conductive member 403 arranged on a circumference with a shorter radius and centered on the strain-flexing part 3 is longer than the conductive member 401 arranged on a circumference with a longer radius and centered on the strain-flexing part 3, but this is not limited to this. The length of the conductive member 403 may be the same as the length of the conductive member 401, or the length of the conductive member 403 may be shorter than the length of the conductive member 401. Furthermore, among the conductive members constituting the full bridge circuit 40, it is preferable that the length of the conductive member 402 and the conductive member 400 constituting the other pair, which are arranged on a circumference with a shorter radius and centered on the strain-flexible portion 3, is longer than the length of the conductive member 400 arranged on a circumference with a longer radius and centered on the strain-flexible portion 3, but this is not a limitation. The length of the conductive member 402 may be the same as the length of the conductive member 400, or the length of the conductive member 402 may be shorter than the length of the conductive member 400. Furthermore, since the conductive member 400 and the conductive member 402 of the three-axis force sensor according to the second embodiment of the present invention are arranged on the same circumference, the lengths and cross-sectional areas of the conductive members 400 and 402 on the same circumference are made the same, but this is not a limitation, and the cross-sectional areas and lengths may be adjusted to have the same electrical resistance values.

[0041] The cross-sectional area of ​​each conductive member 4 is adjusted so that the electrical resistance of each conductive member 4 is the same. Since the electrical resistance is proportional to the length and inversely proportional to the cross-sectional area, it is preferable that the cross-sectional area of ​​conductive member 401 is smaller than that of conductive member 403 and that the cross-sectional area of ​​conductive member 400 is larger than that of conductive member 402, but this is not limitative and the cross-sectional area is adjusted according to the length of each conductive member.

[0042] Next, the electrode pads 5 are formed. In a preferred embodiment, a positive resist is applied, and the pad electrode portions are exposed and developed to form a resist pattern. Ti and Au, which are the materials for the electrode pads 5, are successively deposited by sputtering, and unnecessary portions are removed by a lift-off method, followed by final cleaning. In this way, four full-bridge circuits 40, 41, 42, and 43 are formed in their respective predetermined positions on the other surface 11.

[0043] 10 is a diagram showing the sensor head of the present invention. The three-axis force sensor of the present invention has a holder portion 7 for fixing the substrate 1. The holder portion 7 has a top holder 70 that fixes the substrate 1 from one surface 10 and a bottom holder 71 that fixes the substrate 1 from the other surface 11.

[0044] The top holder 70 has a substantially rectangular plate shape and is provided with a hole 704 penetrating from one surface 700 to the other surface 701 of the top holder 70. The shape of the hole 704 when viewed from above on the one surface 700 of the top holder is circular, but the radius of the hole 704 increases intermittently from the one surface 700 to the other surface 701 of the top holder. In this case, the hole 704 has a through portion 705 provided on the one surface 700 side of the top holder 70 and configured to have a radius longer than the outer diameter of the strain-flexing part 3 of the substrate 1 and shorter than the radius of the substrate 1, and a countersunk portion 706 provided on the other surface 701 side of the top holder 70 and configured to have a radius approximately equal to the radius of the substrate 1. The depth position of the countersunk portion 706 in the axial direction may be changed in various ways, provided that it abuts against one surface 10 of the annular portion located outside the strain-flexing part 3 of the substrate 1 when combined with the bottom holder 71 described below. The centers of the shapes of the through portion 705 and the countersunk portion 706 when viewed from above one surface 700 of the top holder 70 are arranged to coincide with the center of the shape of the strain-flexing portion 3 when viewed from above one surface 10 of the substrate 1.

[0045] The bottom holder 71 has a substantially rectangular plate 712 and four protrusions 717 formed to protrude from four corners of the plate 712 to the other surface 711 of the plate 712. The plate 712 has a hole 714 that penetrates from one surface 710 to the other surface 711 of the plate 712. The shape of the one surface 710 of the hole 714 when viewed from above is circular, but the radius of the hole 714 intermittently increases from the one surface 710 to the other surface 711 of the bottom holder 71. In this case, the hole 714 has a through portion 715 provided on the other surface 711 side of the plate 712 and configured so that the radius is longer than the outer diameter of the strain-flexing part 3 of the substrate 1 but shorter than the radius of the substrate 1, and a countersunk portion 716 provided on the one surface 710 side of the bottom holder 71 and configured so that the radius is approximately the same as the radius of the substrate 1. The depth position of the countersunk portion 716 in the axial direction may be changed in various ways, provided that it abuts against the other surface 11 of the annular portion on the outside of the strain-flexing portion 3 of the substrate 1 when combined with the top holder 70. Furthermore, the center of the shape of the through portion 715 and the countersunk portion 716 when viewed from above one surface 700 of the plate 712 is provided to coincide with the center of the shape of the strain-flexing portion 3 when viewed from above one surface 10 of the substrate 1. Furthermore, as shown in Fig. 11A, the protruding portion 717 is a substantially square prism with one corner closest to the center of the bottom holder 71 scooped outward.

[0046] The other surface 11 of the substrate 1, on which the full-bridge circuits 40, 41, 42, and 43 are formed, is inserted into the countersunk portion 716 of the bottom holder 71, and the top holder 70, which also has a countersunk portion 706, is placed over the one surface 10 of the substrate 1 on which the protrusion 2 is formed, and the substrates are sandwiched in place. Next, the top holder 70 and the bottom holder 71 are fastened together with a plurality of screws. This configuration makes it easy to adjust the insertion position of the substrate 1, and can achieve a structure that suppresses rotation and movement of the substrate 1 within the holder 7. Furthermore, because this configuration mechanically fixes the holder portion, the regions of the one surface 10 and the other surface 11 of the substrate 1 where the top holder 70 and the bottom holder 71 abut are subject to fixed boundary conditions.

[0047] Furthermore, the plate 712 of the bottom holder 71 has a through-hole 715 that opens to the other surface 711, which is different from the surface 710 that holds the substrate 1. The through-hole 715 is provided with a sensor board 72 that provides power and ground to each of the full-bridge circuits 40 to 43, an amplifier board 73 that amplifies signals obtained from each of the full-bridge circuits 40 to 43, and connection lines 75 that connect each of the full-bridge circuits 40 to 43. As shown in FIG. 11A, the amplifier board 73 and the sensor board 72 are each formed in a substantially cross shape so as to avoid four protrusions 717, and as shown in FIG. 11B, they are supported in a horizontal position by the four protrusions 717. If the axial direction in which one surface 10 of the substrate 1 faces is defined as the Z axis, the holder section is composed of the top holder 70, the substrate 1, the plate 712 of the bottom holder 71, the sensor board 72, and the amplifier board 73, in that order. To improve noise resistance, the amplifier board 73 is disposed directly below the sensor board 72, but this is not limiting, and the order of the sensor board 72 and the amplifier board 73 may be reversed.

[0048] FIG. 11 is a diagram showing an outline of the connection between each of the full bridge circuits 40 to 43 on the substrate 1 and the sensor substrate 72. The connection wires 75 are preferably Au wires connected by wire bonding, but this is not a limitation and an anisotropic conductive material (ACP, ACF, etc.) may also be used for the connection. The sensor substrate 72 has a circular opening, and a wire bonding capillary travels back and forth through the opening to connect the wiring. After the wiring of the connection wires 75 is completed, it is preferable to pot the bonding portions of the sensor substrate 72 with epoxy resin to prevent the connection wires 75 from peeling off.

[0049] After connecting the sensor board 72 to each of the full bridge circuits 40-43 on the board, an adhesive layer is provided on the sensor board 72, and then the amplifier board 73 is attached. A roughly rectangular amplifier IC for amplification is mounted on the amplifier board 73. The four bridge outputs from the sensor board are connected to the input side of the amplifier IC and are amplified at a predetermined magnification. The amplifier IC is designed so that the amplification factor can be selected. The amplifier board 73 preferably has a total of six lines connected to the outside: four amplified analog signals as output lines, a power supply line, and a ground line. These six lines are used to connect to an external data collection system or control device. It is preferable that the sensor board and amplifier board have a four-layer structure, with two layers being signal line layers and the remaining layers being power line layers and ground layers.

[0050] Furthermore, for one full bridge circuit, two power supply units 61, two ground units 62, two positive bridge output units, and two negative bridge output units are typically connected by eight bonds, for a total of 32 wire bonds, but this is not limited to this. In the pattern formation process using lithography described above, the number of wire bonds in a later process may be reduced by using a photomask that also has connecting units 63 that connect the four conductive members in a predetermined arrangement method.

[0051] For example, as shown in FIG. 17A, one full bridge circuit 40 may have six bonded wires. The positive outputs of the bridges are connected to each other, and the negative outputs are connected to each other at a connecting portion 63. Wire bonding may be performed at any position on the connecting portion 63, and in FIG. 17A, the wire bonding position is located at the center of the connecting portion 63. In this case, the number of bonded wires for the four full bridge circuits 40, 41, 42, and 43 is 24.

[0052] 18A, for example, it is also possible to have four bonded wires for one full bridge circuit. By providing one power supply unit 61, one ground unit 62, one positive bridge output unit, and one negative bridge output unit, and by providing the connecting unit 63 not only on the strain-flexing unit 3 but also outside the strain-flexing region, the total number of bonded wires for the four full bridge circuits 40, 41, 42, and 43 becomes 16.

[0053] Alternatively, for example, in the pattern formation process using lithography described above, if a power supply unit 61 and a ground unit 62 connected in common to each of the four full-bridge circuits 40, 41, 42, and 43 are formed in addition to the connecting unit 63, the number of wire bonds can be further reduced. FIG. 17B shows a case where the number of wire bonds is 18. Compared to the embodiment of FIG. 17A, the number of wire bonds in the embodiment of FIG. 17B is reduced from 24 to 18. The power supply unit 61 is provided on the outside of the conductive member 400, and the ground unit 62 is arranged in a circular ring shape with a notch in the central region of the substrate 1. To explain the breakdown of wire bonding in detail, one full bridge requires one power supply unit 61, one ground unit 62, one positive bridge output unit, and one negative bridge output unit, for a total of four, making a total of 16 for the four full bridge circuits 40, 41, 42, and 43.In addition, one each is required for the power supply unit 61 and ground unit 62, which are common patterns, making a total of 18 together with the former. Although not shown, if a wire from a common power supply unit 61 is arranged between the conductive member 400 and the conductive member 402, or between the conductive member 401 and the conductive member 403, and a connecting unit 63 connected to the electrode pad 5 on one side of the conductive member 401 is provided, the number of wire bonds required for each full bridge circuit 40, 41, 42, 43 will be three in total, including one ground unit 62, one positive bridge output unit, and one negative bridge output unit, for a total of 12 for the four bridges, which, together with one each of the power supply unit 61 and the ground unit 62 that form the common pattern, will total 14.

[0054] 18A, for example, as shown in Fig. 18B, it is also possible to arrange the common power supply unit 61 and ground unit 62 in the same manner as described above. In this case, the number of wire bonds in each of the full bridge circuits 40, 41, 42, and 43 is only two, one for the positive bridge output unit and one for the negative bridge output unit, for a total of eight for the four full bridges 40, 41, 42, and 43. It is also possible to add one each for the patterns of the power supply unit 61 and ground unit 62, which are common patterns, bringing the total number of wire bonds to 10.

[0055] It is preferable to take measures such as increasing the film thickness of the common power supply unit 61 and ground unit 62 or increasing the diameter of the bonding wire connected to this common pattern, but this is not a limitation. The layout of the patterns of the power supply unit 61 and ground unit 62 can also be such that the ground unit 62 is on the outside and the power supply unit 61 is on the inside, and this can be adjusted as long as it does not interfere with the layout of the conductive members 400, 401, 402, and 403 and insulation from the holder unit 7 is achieved. The areas of the power supply unit 61, ground unit 62, positive bridge output unit, and negative bridge output unit are not limited to being circular and may be adjusted to any shape.

[0056] The present invention is not limited to the above-described embodiments, and modifications and improvements can be made by those skilled in the art within the technical scope of the present invention. [Example]

[0057] (Formation of Substrate 1) Examples of the present invention are described below. The examples are configured in accordance with the first embodiment. A protrusion 2 with an outer diameter of 2 mm and a central height of 2.7 mm was integrally formed in the center of one surface 10 of a disk-shaped substrate 1 made of SUS316L, with a diameter of 5.4 mm and a thickness of 1.2 mm at the flat portion. A groove with an inner diameter of 2 mm, an outer diameter of 3 mm, and a depth of 0.9 mm was provided around the base end of the protrusion 2, forming a circular strain-generating portion 3 with a thickness of 0.3 mm. Meanwhile, the other surface 11 of the substrate 1 was subjected to flatness correction and mirror finishing after groove processing, and the surface roughness was finished to an arithmetic mean roughness Ra of 1 nm or less.

[0058] (Forming a full bridge circuit) On the other surface 11 of the substrate 1, four full-bridge circuits 40 to 43 are arranged to have four-fold rotational symmetry with respect to the center of the substrate 1. Full-bridge circuit 40 is made up of four conductive members 400 to 403 formed to extend in the shape of an arc of approximately 90 degrees. Similarly, full-bridge circuits 41, 42, and 43 are each made up of four conductive members 410 to 413, 420 to 423, and 430 to 433, respectively, formed to extend in the shape of an arc of approximately 90 degrees.

[0059] To avoid redundancy, only full-bridge circuit 40 will be described below, but unless otherwise specified, the same applies to the other full-bridge circuits 41 to 43. Furthermore, unless otherwise specified, the descriptions of conductive members 400, 401, 402, and 403 also apply to conductive members 410, 411, 412, and 413, conductive members 420, 421, 422, and 423, and conductive members 430, 431, 432, and 433. Conductive member 401 and conductive member 403 are disposed adjacent to each other on the other surface 11 of substrate 1, on the circumference of the inner diameter of strain-flexing portion 3, and conductive member 400 and conductive member 402 are disposed adjacent to each other on the other surface 11 of substrate 1, on the circumference of the outer diameter of strain-flexing portion 3. Here, one pair consisting of conductive member 400 and conductive member 402 constitutes the opposite side of full bridge circuit 40, and another pair consisting of conductive member 401 and conductive member 403 constitutes the other opposite side of full bridge circuit 40.

[0060] The width centers of the conductive members 400, 402, 401, and 403 are located on the circumference of a circle with a diameter of 3.0 mm (corresponding to the outer diameter of the strain-flexing unit 3), 2.84 mm, 2.16 mm, and 2.0 mm (corresponding to the inner diameter of the strain-flexing unit 3), respectively, based on the center of the disk-shaped substrate 1. The widths of the conductive members 400, 402, 401, and 403 are designed to be different and range from approximately 27 μm to 46 μm. The lengths of the conductive members 400, 402, 401, and 403 are designed to be different and range from 1.26 mm to 2.14 mm. As a result of these adjustments, the electrical resistance of all four metal conductors at the design stage is approximately 160.5 Ω. This electrical resistance is higher than 120 Ω, which is one of the standard electrical resistance values ​​for strain gauges widely used in industry, and is a practical electrical resistance value while still achieving miniaturization.

[0061] Conductive member 403 is arranged on the circumference of a circle with a diameter of 2.0 mm, based on the center of substrate 1, which is the inner diameter of strain-flexing part 3, and has a line width of 30 μm and an arc length of 1.4 mm. The circumference of a circle with a diameter of 2.0 mm is 6.28 mm, and 1 / 4 of that circumference is calculated to be 1.57 mm, but the arc length of conductive member 403 is 1.40 mm, utilizing 89% of 1 / 4 of the circumference. Because such a length can be secured, the line width can be set to 30 μm, and it is configured as an arc wire with stable manufacturing and good reproducibility.

[0062] Adjacent conductive members 401 are arranged 80 μm apart from conductive members 403, and are located on a circle with a diameter of 2.16 mm, with the center of the substrate 1 as the reference. The width of the conductive members 401 is set to 27 μm, and the length is set to 1.26 mm. In terms of the sensitivity of the force sensor, it is advantageous to place the conductive members 401 as close as possible to the conductive members 403, but the size of the electrode pads 5 provided on both ends of the conductive members 4 must be taken into consideration and determined so that the electrode pads 5 do not come into contact with the adjacent conductive members 4. In this embodiment, the electrode pads 5 are arranged 20 μm or more apart from other conductive members 4.

[0063] The relationship between conductive member 400 and conductive member 402, which are arranged on the outer periphery of the strain-flexing region of strain-flexing unit 3, is also implemented in a similar manner. Conductive member 400 is arranged on a circle with a diameter of 3.0 mm, based on the center of substrate 1, which is the outer diameter of strain-flexing unit 3, and has a line width of 46 μm and a length of 2.14 mm. Conductive member 402 is arranged on a circle with a diameter of 2.84 mm, based on the center of substrate 1, and has a width of 36 μm and a length of 1.68 mm. Because conductive members 400 and 402 are wider than conductive members 401 and 403, they are configured as arch wires with more stable manufacturing and good reproducibility.

[0064] Table 1 shows the electrical resistance values ​​of each conductive member 4 measured by the method described above. It also shows the average value, standard deviation, range (maximum value minus minimum value), and value equivalent to ±2.5% of the average value for each of the full bridge circuits 40, 41, 42, and 43.

[0065] [Table 1]

[0066] According to Table 1, the standard deviation of the electrical resistance values ​​of the conductive members 4 constituting each of the full-bridge circuits 40, 41, 42, and 43 is small, with the range well within ±2.5% of the average value. The values ​​in the column labeled "Total" in Table 1 are the average electrical resistance values ​​and their standard deviations for a total of 32 conductive members 4. An integer between 0 and 3 is substituted for X in conductive members 4X0, 4X1, 4X2, and 4X3. For full-bridge circuit 40, 0 is substituted for X in conductive members 4X0, 4X1, 4X2, and 4X3, and conductive members 4X0, 4X1, 4X2, and 4X3 become conductive members 400, 401, 402, and 403, respectively. Similarly, 1, 2, and 3 are substituted for X in full-bridge circuits 41, 42, and 43, respectively. The standard deviation of each conductive member 4 is 2.09 Ω, and there is little error in each of the full bridge circuits 40, 41, 42, and 43. Therefore, the conductive members 4 shown in the examples of the present invention maintain a large electrical resistance value even though they are conductive members 4X1 and 4X3, which are located on the inner periphery of the strain-generating region where the electrical resistance value is unstable due to their thinness, and therefore a sensor that can measure force with high precision despite its small size can be realized.

[0067] Each of the conductive members 400, 401, 402, and 403 is connected to the outside via wire bonding to the electrode pads 5 at both ends. For one full bridge, there are two power supply units 61, two ground units 62, two positive bridge output units, and two negative bridge output units, for a total of eight bonds. This is because the conductive members 4 constituting the full bridge circuit 40 formed on the substrate 1 are arranged to extend in an arc shape. Since the present invention is implemented for four full bridge circuits 40, 41, 42, and 43, a total of 32 wire bonds are formed. A voltage of 3.3 V is applied from the power supply unit 61 to each of the full bridge circuits 40, 41, 42, and 43. The resulting output is amplified 50 times using the amplifier board 73.

[0068] (result) First, we will show the results of the simulation. The strain when a vertical load of 40 N is applied to the apex of protrusion 2 was calculated using the finite element method. The distribution of the obtained strain is shown in Figure 8. The strain is symmetrical with respect to the center of substrate 1, so only one side is shown. Circles indicate circumferential strain, and squares indicate radial strain. The outside of r = -1.9 mm has a fixed boundary condition. The figure also shows the positions of conductive member 400, conductive member 402, conductive member 401, and conductive member 403.

[0069] The circumferential strain exhibits positive values ​​(tensile) throughout, with the inner diameter side exhibiting higher values ​​than the outer diameter side. On the other hand, the radial strain exhibits a large positive strain near the inner diameter, and in this vicinity, the circumferential and radial directions have the same sign and are added together, resulting in a large change in the electrical resistance values ​​of the conductive members 401 and 403. The radial strain then begins to rapidly decrease toward the outside of the strain-flexing portion 3, turns negative (compressive) near the center between the inner and outer peripheral edges of the strain-flexing region of the strain-flexing portion 3, and reaches a maximum value of compression near the outer diameter of the strain-flexing portion 3. The conductive members 400 and 402 are arranged in this vicinity. Here, the circumferential strain is positive, but the radial strain is a significantly larger negative value, so the added value has a large negative value.

[0070] In this way, one pair of conductive members 401 and 403, and another pair of conductive members 400 and 402, which form opposite sides of the full bridge, are placed at positions showing large strain. The metal conductor material used is a Cr-N thin film, which has a high ability to sense radial strain, i.e., high lateral sensitivity. Therefore, a highly sensitive bridge can be formed.

[0071] Therefore, the load in the Z direction can be calculated by using the sum of the outputs of the four full-bridge circuits 40, 41, 42, and 43. Z40 , E Z41 , E Z42 , E Z43 Then, the load in the Z direction is E Z40 , E Z41 , E Z42 , E Z43is linearly proportional to the sum of

[0072] Next, we will show the simulation results when a horizontal load is applied to the protrusion 2. We will explain the case of a horizontal unidirectional load (X-direction load) as an example. Figure 9 shows the strain distribution when horizontal unidirectional loads of 5N, 10N, and 15N are applied in the direction (+X direction) from full bridge circuit 40 to full bridge circuit 43 of full bridge circuits 40, 41, 42, and 43. Circles indicate circumferential strain, and squares indicate radial strain. Both strain distributions have two-fold rotational symmetry with respect to the center of substrate 1. The horizontal axis in the figure represents the distance from the center, and fixed boundary conditions apply from ±1.9 mm outward.

[0073] The circumferential strain takes a large negative value (compression) at the inner diameter of the strain-flexing part 3 on the side where force is applied (the full-bridge circuit 40 side), approaches zero toward the center of the substrate 1, turns positive from the center, and takes a large positive value (tension) at the inner diameter of the strain-flexing part 3 on the opposite side (the full-bridge circuit 43 side). The absolute value of the strain amount is maximum slightly outside the inner diameter of the strain-flexing part 3. The strain monotonically decreases in the strain-flexing part 3 and reaches zero at the outer fixed boundary.

[0074] On the other hand, the radial strain becomes a negative value (compression) that greatly exceeds the circumferential strain near the inner diameter on the side where the force is applied, and the strain rapidly decreases toward the center of the substrate 1, reaching zero at the center. The strain increases toward the inner diameter side of the strain-flexing part 3 where the opposite full bridge circuit 43 is located, and reaches a maximum positive value at the inner peripheral edge of the strain-flexing region of the strain-flexing part 3 where the opposite full bridge circuit 43 is located.

[0075] Unlike the circumferential strain, which shows a gradual change in the strain-causing part 3, the radial strain changes suddenly inside the strain-causing part 3, showing maximum positive and negative values ​​inside and outside the strain-causing area of ​​the strain-causing part 3. The radial strain becomes zero near the center between the inner and outer peripheral edges of the strain-causing area of ​​the strain-causing part 3.

[0076] The combined circumferential and radial strains have the same sign at the inner periphery of the strain-causing region of strain-causing section 3, resulting in a large additive value. One pair of conductive members 401 and 403, forming the opposite side of each full bridge, is located at this position. Meanwhile, at the outer periphery of the strain-causing region of strain-causing section 3, the circumferential and radial strains have different signs, but the absolute value of the radial strain is significantly greater. The other pair of conductive members 400 and 402 is located nearby. As mentioned above, the conductive member 4 is made of a Cr-N thin film, which has a high ability to sense radial strain, i.e., high lateral sensitivity. Therefore, a highly sensitive bridge can be formed even in the case of horizontal loads. The strain generated in the full bridge circuits 41 and 42 is extremely small, so it is not shown in the figure.

[0077] The X-direction load is expressed by the difference between the outputs of the full-bridge circuit 40 and the full-bridge circuit 43. That is, the bridge outputs of the full-bridge circuit 40 and the full-bridge circuit 43 are respectively expressed as E X40 , E X43 Then, the load in the X direction is E X40 -E X43 is linearly proportional to

[0078] The same argument applies to the horizontal load (Y-direction load) that intersects at right angles with the X-direction load. A load applied in the direction from the full bridge circuit 41 to the full bridge circuit 42 (+Y direction) changes the bridge outputs of the full bridge circuits 41 and 42 to E Y41 , E Y42 Then, the Y direction load is E Y41 -E Y42 is linearly proportional to

[0079] From the simulation results, the relationship between the load and each of the full-bridge circuits 40, 41, 42, and 43 was measured. The tip of a force sensor (Aiko Engineering, RZ5, 50N range) was brought into contact with the apex of the protrusion 2 on the substrate 1, and a load was applied in the vertical direction to obtain the bridge output of each of the full-bridge circuits 40, 41, 42, and 43. A gauge attachment (Aiko Engineering, 012B) was attached to the tip of the force sensor.

[0080] FIG. 12 shows the relationship between the bridge output of the full-bridge circuits 41 and 42 and the applied vertical load. The horizontal axis represents the applied load value of the force sensor, and the vertical axis represents the bridge output of the full-bridge circuits 41 and 42. Note that the bridge output in this figure was measured using a digital voltmeter (Keysight, 34972A) without using the amplifier board 73, and represents the bridge output itself. The bridge output exhibits good linearity from the low load range (5N or less) to approximately 40N. The bridge output is approximately -2.5mV at 5N, approximately -5mV at 10N, approximately -9.5mV at 20N, and approximately -19mV at 40N. Although not shown, the full-bridge circuits 40 and 43 also exhibited good linear response.

[0081] In addition, the tip of the force sensor was abutted against the protrusion 2 of the substrate 1, and a horizontal load was applied in the direction from the full bridge circuit 43 to the full bridge circuit 40 (X-direction load). A gauge attachment (015B) was attached to the tip of the force sensor.

[0082] Figure 13A shows the bridge outputs of each of the full-bridge circuits 40, 41, 42, and 43, and Figure 13B shows the amplifier outputs after the bridge outputs are amplified by the amplifier board 73. In both graphs, the horizontal axis represents the applied horizontal load (-X-direction load), plotted for two cases: approximately 4 N and approximately 8 N. Looking at the bridge outputs, the full-bridge circuits 40 and 43 show similar values ​​with opposite signs. In this case, the X-axis load is applied from the full-bridge circuit 43 side, so the full-bridge circuit 43 side is negative (compression), while the opposite full-bridge circuit 40 is positive (tension). Meanwhile, the outputs of the full-bridge circuits 41 and 42, which are positioned 90° from the full-bridge circuits 43 and 40, respectively, remain extremely small. Therefore, the bridge outputs of the full-bridge circuits 43 and 40 show a good linear relationship with the applied X-direction load.

[0083] The magnification of the amplifier board 73 was set to 50x. When the applied X-direction load was approximately 8N, the bridge output of the full-bridge circuit 43 was -8.3mV according to Figure 13A, and the corresponding amplifier output was -407mV, as shown in Figure 13B. The magnification was calculated to be approximately 49x, indicating that the amplifier IC was functioning normally. As shown in the figure, the amplifier output also exhibited good linearity.

[0084] Next, the tip of the force sensor was brought into contact with the protrusion 2 of the substrate 1, and a horizontal load was applied in the direction from the full bridge circuit 41 to the full bridge circuit 42 (Y direction load). A gauge attachment (015B) was attached to the tip of the force sensor.

[0085] Figure 14A shows the bridge outputs of each of the full-bridge circuits 40, 41, 42, and 43, and Figure 14B shows the amplifier outputs after the bridge outputs are amplified by the amplifier board 73. In both graphs, the horizontal axis represents the applied horizontal load (+Y-direction load), plotted for two cases: approximately 4 N and approximately 8 N. Looking at the bridge outputs, the full-bridge circuits 41 and 42 show similar values ​​with opposite signs. In this case, the Y-axis load is applied from the full-bridge circuit 41 side, so the full-bridge circuit 41 side is negative (compression), and the opposite full-bridge circuit 42 is positive (tension). Meanwhile, the outputs of the full-bridge circuits 40 and 43, which are positioned 90° away from the full-bridge circuits 41 and 42, respectively, remain extremely small. Therefore, the bridge outputs of the full-bridge circuits 41 and 42 show a good linear relationship with the applied Y-direction load.

[0086] The amplifier board 73 was set to a magnification of 50x again. When the applied Y-direction load was approximately 8N, the bridge output of the full-bridge circuit 41 was -8.5mV, as shown in Figure 14A, and the corresponding amplifier output was -420mV, as shown in Figure 14B. The magnification was calculated to be approximately 49.4x, indicating that the amplifier IC was functioning normally. As shown in the figure, the amplifier output also exhibited good linearity.

[0087] From the above, it can be said from the actual measurement data that the three-axis force sensor of the present invention is miniaturized and yet functions properly as a force sensor for the three axes X, Y, and Z.

[0088] FIG. 15A shows the relationship between the electrical resistance of each of the conductive members 410, 411, 412, and 413 constituting the full-bridge circuit 41 and the normal load. Here, the change in electrical resistance (ΔR) is the electrical resistance after the load is applied minus the electrical resistance before the load is applied. The horizontal axis represents the applied load. Seven loads were applied, starting with a low load of 5 N or less, with the maximum load being approximately 40 N. Each load was applied for approximately 20 seconds. Referring to FIG. 15A, each of the conductive members 410, 411, 412, and 413 exhibited good linearity with respect to the applied load. At an applied load of approximately 40 N, the change in resistance of the conductive member 411 (ΔR2) and the change in resistance of the conductive member 412 (ΔR3) were negative, approximately −0.5 Ω. Meanwhile, the change in resistance of the conductive member 410 (ΔR1) and the change in resistance of the conductive member 413 (ΔR4) were positive, exceeding approximately 1 Ω. Although not shown, these characteristics were also observed in the other full-bridge circuits 40, 42 and 43.

[0089] As described above, the change in the electrical resistance value of each conductive member 4 constituting each full bridge circuit 40, 41, 42, and 43 shows good linearity with respect to the load, which confirms that the bridge output generated based on this change also has good linearity.

[0090] Table 2 shows strain values ​​obtained by simulation when a vertical load (40 N) shown in Fig. 8 is applied. Here, the full-bridge circuit 41 will be used as an example for explanation, but the same applies to the full-bridge circuits 40, 42, and 43. The ratio of the change in electrical resistance (ΔR1, ΔR2, ΔR3, ΔR4) of each of the conductive members 410, 411, 412, and 413 to the electrical resistance in the steady state of each of the conductive members 410, 411, 412, and 413 (change in electrical resistance (ΔR) / electrical resistance in the steady state) is expressed as the sum of the product of the longitudinal sensitivity coefficient and the circumferential strain of each of the conductive members 410, 411, 412, and 413 ((longitudinal sensitivity coefficient) × (circumferential strain)) and the product of the transverse sensitivity coefficient and the radial strain of each of the conductive members 410, 411, 412, and 413 ((transverse sensitivity coefficient) × (radial strain)).

[0091] [Table 2]

[0092] FIG. 15B is a diagram showing calculated changes in electrical resistance of conductive members 410, 411, 412, and 413 of full-bridge circuit 41, using the strain values ​​obtained from the simulation shown in Table 2. The longitudinal sensitivity coefficient was determined in a separate preliminary experiment and was found to be 15. The transverse sensitivity coefficient was also assumed to be 15, the same as the longitudinal sensitivity coefficient. The measured values ​​shown in FIG. 15A and the calculated values ​​shown in FIG. 15B generally agreed at a vertical load of 40 N, although there were slight differences in the values.

[0093] 16 shows the sensitivity coefficient dependency of the change in the electrical resistance value of each of the conductive members 410, 411, 412, and 413. The values ​​(virtual values) of the longitudinal sensitivity coefficient and the transverse sensitivity coefficient were changed to calculate the change in the electrical resistance value of each of the conductive members 410, 411, 412, and 413 that make up the full bridge circuit 41. The combinations of the coefficients are shown in Table 3.

[0094] [Table 3]

[0095] Case 2 in Table 3 corresponds to the case shown in Figure 15B, and Case 6 corresponds to the case where the transverse sensitivity coefficient is assumed to be 0. From this, it is clear that the change in electrical resistance value is significantly dependent on the sensitivity coefficient. First, ΔR decreases as the transverse sensitivity coefficient decreases. In particular, ΔR of conductive member 410 and ΔR of conductive member 412 approach zero from negative values ​​when the transverse sensitivity coefficient is 5 or less. At a transverse sensitivity coefficient of approximately 3, ΔR of conductive member 410 also changes from zero to a positive value. When the transverse sensitivity coefficient is 0, ΔR of conductive member 410 and ΔR of conductive member 412 become positive values ​​close to 0.2 Ω. This indicates that even if a large radial strain occurs near strain-flexing portion 3, if the transverse sensitivity coefficient is low, this strain cannot be detected, resulting in a strain gauge that is not highly sensitive. A transverse sensitivity coefficient of 3 or more is required, and a value of 5 or more is desirable for practical use.

[0096] Meanwhile, a comparison between Case 2 and Case 1 shows the effect of the longitudinal sensitivity coefficient when the transverse sensitivity coefficient is the same. Case 1 assumes that the longitudinal sensitivity coefficient is increased from 15 to 20 compared to Case 2. At the inner periphery of the strain-causing region of strain-causing portion 3, where the circumferential strain and radial strain have the same positive sign, ΔR of conductive member 411 and ΔR of conductive member 413 are added together and increase as the longitudinal sensitivity coefficient increases. On the other hand, at the outer periphery of the strain-causing region of strain-causing portion 3, where the circumferential strain is positive and the radial strain is negative, ΔR of conductive member 410 and ΔR of conductive member 412 are added together as the longitudinal sensitivity coefficient increases, indicating that the absolute negative value decreases.

[0097] The above considerations suggest that since the value of ΔR is highly dependent on the sensitivity coefficient, it is desirable that the strain gauge used to determine the sensitivity coefficient has a pattern that allows for separation of longitudinal and transverse sensitivities. [Explanation of symbols]

[0098] 1. Substrate, 2. Projection, 3. Deformable part, 4. Conductive material, 5. Electrode pad, 7. Holder, 10. One side, 11. Other side, 40-43. Full bridge circuit, 61. Power supply, 62. Grounding part, 63. Connection part, 70. Top holder, 71. Bottom holder, 72. Sensor substrate, 73. Amplifier substrate, 75. Connection wire, 400-403, 410-413, 420-423, 430-433. Conductive material, 70 0...One surface (top holder), 701...Other surface (top holder), 704...Hole (top holder), 705...Through portion (top holder), 706...Counterbore portion (top holder), 710...One surface (bottom holder), 711...Other surface (bottom holder), 712...Plate (bottom holder), 714...Hole (bottom holder), 715...Through portion (bottom holder), 716...Counterbore portion (bottom holder), 717...Protruding portion.

Claims

1. A plate-shaped substrate; a protrusion provided so as to protrude from one surface of the substrate; a strain-generating portion as a thin portion formed by providing a groove recessed in an annular shape from one surface of the substrate so as to surround the periphery of the base end of the protrusion; a plurality of conductive members extending in an arc shape along the inner and outer peripheral edges of a strain-flexing region corresponding to the strain-flexing portion on the other surface opposite to the surface on which the protrusion is provided, and arranged to have four-fold rotational symmetry; each of the plurality of conductive members constitutes four full-bridge circuits arranged to have four-fold rotational symmetry; one pair of the conductive members constituting each of the full bridge circuits, the pair forming opposite sides of each of the full bridge circuits, is disposed on an inner peripheral edge of the strain generating region; a pair of the conductive members constituting each of the full bridge circuits other than the pair of conductive members constituting the opposite sides of each of the full bridge circuits is disposed on an outer circumferential edge of the strain generating region, A three-axis force sensor characterized in that each of the pair of conductive members arranged on the inner peripheral edge of the strain-generating region is arranged to extend in an arc shape along different circumferences.

2. A plate-shaped substrate; a protrusion provided so as to protrude from one surface of the substrate; a strain-generating portion as a thin portion formed by providing a groove recessed in an annular shape from one surface of the substrate so as to surround the periphery of the base end of the protrusion; a plurality of conductive members extending in an arc shape along the inner and outer peripheral edges of a strain-flexing region corresponding to the strain-flexing portion on the other surface opposite to the surface on which the protrusion is provided, and arranged to have four-fold rotational symmetry; each of the plurality of conductive members constitutes four full-bridge circuits arranged to have four-fold rotational symmetry; one pair of the conductive members constituting each of the full bridge circuits, the pair forming opposite sides of each of the full bridge circuits, is disposed on an inner peripheral edge of the strain generating region; a pair of the conductive members constituting each of the full bridge circuits other than the pair of conductive members constituting the opposite sides of each of the full bridge circuits is disposed on an outer circumferential edge of the strain generating region, A three-axis force sensor characterized in that the conductive members of the other set, which are different from the one set arranged on the outer peripheral edge of the strain-generating region, are arranged so as to extend in an arc shape along different circumferences.

3. A plate-shaped substrate; a protrusion provided so as to protrude from one surface of the substrate; a strain-generating portion as a thin portion formed by providing a groove recessed in an annular shape from one surface of the substrate so as to surround the periphery of the base end of the protrusion; a plurality of conductive members extending in an arc shape along the inner and outer peripheral edges of a strain-flexing region corresponding to the strain-flexing portion on the other surface opposite to the surface on which the protrusion is provided, and arranged to have four-fold rotational symmetry; each of the plurality of conductive members constitutes four full-bridge circuits arranged to have four-fold rotational symmetry; one pair of the conductive members constituting each of the full bridge circuits, the pair forming opposite sides of each of the full bridge circuits, is disposed on an inner peripheral edge of the strain generating region; a pair of the conductive members constituting each of the full bridge circuits other than the pair of conductive members constituting the opposite sides of each of the full bridge circuits is disposed on an outer circumferential edge of the strain generating region, a connecting portion that connects an end portion of the conductive member to the other surface of the substrate; a power supply unit that supplies power to each of the four full-bridge circuits; a grounding portion for grounding each of the four full bridge circuits,

4. A plate-shaped substrate; a protrusion provided so as to protrude from one surface of the substrate; a strain-generating portion as a thin portion formed by providing a groove recessed in an annular shape from one surface of the substrate so as to surround the periphery of the base end of the protrusion; a plurality of conductive members extending in an arc shape along the inner and outer peripheral edges of a strain-flexing region corresponding to the strain-flexing portion on the other surface opposite to the surface on which the protrusion is provided, and arranged to have four-fold rotational symmetry; each of the plurality of conductive members constitutes four full-bridge circuits arranged to have four-fold rotational symmetry; one pair of the conductive members constituting each of the full bridge circuits, the pair forming opposite sides of each of the full bridge circuits, is disposed on an inner peripheral edge of the strain generating region; a pair of the conductive members constituting each of the full bridge circuits other than the pair of conductive members constituting the opposite sides of each of the full bridge circuits is disposed on an outer circumferential edge of the strain generating region, a holder portion that mechanically fixes each of the one surface and the other surface of the substrate; a sensor substrate for connecting the four full-bridge circuits with electrical signals.

5. 5. The three-axis force sensor according to claim 4, The three-axis force sensor is characterized in that the holder portion has an amplifier board equipped with an amplifier IC that amplifies the output signal of the full bridge circuit.

6. A plate-shaped substrate; a protrusion provided so as to protrude from one surface of the substrate; a strain-generating portion as a thin portion formed by providing a groove recessed in an annular shape from one surface of the substrate so as to surround the periphery of the base end of the protrusion; a plurality of conductive members extending in an arc shape along the inner and outer peripheral edges of a strain-flexing region corresponding to the strain-flexing portion on the other surface opposite to the surface on which the protrusion is provided, and arranged to have four-fold rotational symmetry; each of the plurality of conductive members constitutes four full-bridge circuits arranged to have four-fold rotational symmetry; one pair of the conductive members constituting each of the full bridge circuits, the pair forming opposite sides of each of the full bridge circuits, is disposed on an inner peripheral edge of the strain generating region; a pair of the conductive members constituting each of the full bridge circuits other than the pair of conductive members constituting the opposite sides of each of the full bridge circuits is disposed on an outer circumferential edge of the strain generating region, A three-axis force sensor, characterized in that both ends of the conductive member arranged in the strain-generating region are connected to a sensor substrate by wire bonding.

7. A plate-shaped substrate; a protrusion provided so as to protrude from one surface of the substrate; a strain-generating portion as a thin portion formed by providing a groove recessed in an annular shape from one surface of the substrate so as to surround the periphery of the base end of the protrusion; a plurality of conductive members extending in an arc shape along the inner and outer peripheral edges of a strain-flexing region corresponding to the strain-flexing portion on the other surface opposite to the surface on which the protrusion is provided, and arranged to have four-fold rotational symmetry; each of the plurality of conductive members constitutes four full-bridge circuits arranged to have four-fold rotational symmetry; one pair of the conductive members constituting each of the full bridge circuits, the pair forming opposite sides of each of the full bridge circuits, is disposed on an inner peripheral edge of the strain generating region; a pair of the conductive members constituting each of the full bridge circuits other than the pair of conductive members constituting the opposite sides of each of the full bridge circuits is disposed on an outer circumferential edge of the strain generating region, Among the conductive members constituting the set, the length of the conductive member arranged on the circumference with a shorter radius centered on the strain-flexing portion is longer than the length of the conductive member arranged on the circumference with a longer radius centered on the strain-flexing portion, A three-axis force sensor characterized in that, among the conductive members constituting the other group, the length of the conductive members arranged on a circumference with a shorter radius centered on the strain-generating portion is shorter than the length of the conductive members arranged on a circumference with a longer radius centered on the strain-generating portion.

8. The three-axis force sensor according to any one of claims 1 to 7, A three-axis force sensor characterized in that the conductive member is made of a Cr thin film.

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