Strain sensor and power transmission device

Abstract

To provide a technique for improving strain detection accuracy by a plurality of resistance wires while securing sufficient strength in folding parts concerning a strain sensor.SOLUTION: A strain sensor includes an insulation layer, first conductive layers 43, and second conductive layers 44. The insulation layer is fixed to a detected body. The first conductive layers are formed on a front surface of the insulation layer. The second conductive layers are laminated on front surfaces of the first conductive layers. The first conductive layers have a detection wire pattern. The detection wire pattern includes: a plurality of resistance wires extending in a predetermined direction; and folding parts for connecting end parts of the resistance wires. The second conductive layers are laminated on front surfaces of the folding parts. Thus, the folding parts of the detection wire pattern are reinforced by the second conductive layers. Consequently, generation of cracks is suppressed in the folding parts, and also a resistance value in the folding parts is reduced by laminating the second conductive layers, thereby to improve strain detection accuracy by the plurality of resistance wires.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a strain sensor and a power transmission device. [Background technology]

[0002] In recent years, there has been a rapid increase in demand for reducers to be installed in the joints of robots and the like. A conventional reducer is described, for example, in Japanese Patent Application Laid-Open No. 2004-198400. In this publication, a strain gauge is attached to a flexible external gear that rotates at a reduced rotation speed. This makes it possible to detect the torque acting on the flexible external gear. [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-198400 Summary of the Invention [Problem to be solved by the invention]

[0003] A strain gauge has a detection line pattern including multiple resistance wires extending parallel to one another and folded portions connecting the ends of adjacent resistance wires. The strain gauge detects strain in a detection object based on changes in the resistance values ​​of the multiple resistance wires. In this type of strain gauge, it is desirable to reduce the resistance value of the folded portions to improve strain detection accuracy. To reduce the resistance value of the folded portions, for example, it is possible to increase the line width of the folded portions compared to the line width of the multiple resistance wires.

[0004] However, flexible external gears used in reducers repeatedly undergo periodic flexural deformation. Therefore, increasing the line width of the folded portion increases the rigidity of the folded portion, making it less likely to flex. As a result, the strength of the folded portion may decrease.

[0005] An object of the present invention is to provide a technology that can improve the accuracy of detecting strain using a plurality of resistance wires while ensuring sufficient strength of the folded-back portion in a strain sensor. [Means for solving the problem]

[0006] The present invention is a strain sensor comprising an insulating layer fixed to a detected object, a first conductor layer formed on the surface of the insulating layer, and a second conductor layer laminated on the surface of the first conductor layer, wherein the first conductor layer has a detection line pattern including a plurality of resistance wires extending in a predetermined direction and a folded portion connecting the ends of the resistance wires, and the second conductor layer is laminated on the surface of the folded portion. [Effects of the Invention]

[0007] According to the present invention, the folded portion of the detection line pattern is reinforced by the second conductor layer. This ensures the strength of the folded portion. Furthermore, by laminating the second conductor layer, the resistance value of the folded portion is reduced. This improves the accuracy of strain detection using multiple resistance lines. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a vertical cross-sectional view of a power transmission device. [Figure 2] FIG. 2 is a cross-sectional view of the power transmission device. [Figure 3] FIG. 3 is a plan view of the strain sensor. [Figure 4] FIG. 4 is a partial cross-sectional view of the diaphragm portion and the strain sensor. [Figure 5] FIG. 5 is a partial enlarged view of the first detection line pattern. [Figure 6] FIG. 6 is a partial enlarged view of the second detection line pattern. [Figure 7] FIG. 7 is a circuit diagram of a Wheatstone bridge circuit including a first detection line pattern and a second detection line pattern. [Figure 8] FIG. 8 is a plan view of the strain sensor according to the second embodiment. [Figure 9] FIG. 9 is a partial enlarged view of the third detection line pattern. [Figure 10] FIG. 10 is a circuit diagram of a first Wheatstone bridge circuit including four third detection line patterns. [Figure 11] FIG. 11 is a circuit diagram of a second Wheatstone bridge circuit including four fourth detection line patterns. [Figure 12] FIG. 12 is a plan view of a strain sensor according to a first modified example. [Figure 13] FIG. 13 is a partially enlarged view of a detection line pattern according to the third modified example. [Figure 14] FIG. 14 is a graph showing the relationship between the length L of the adjacent portion and the stress S. [Figure 15] FIG. 15 is a partial longitudinal sectional view of a robot equipped with a power transmission device. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings.

[0010] In this application, the direction parallel to the central axis of the power transmission device is referred to as the "axial direction," the direction perpendicular to the central axis of the power transmission device is referred to as the "radial direction," and the direction along the arc centered on the central axis of the power transmission device is referred to as the "circumferential direction." However, the above-mentioned "parallel direction" also includes a direction that is approximately parallel. Furthermore, the above-mentioned "orthogonal direction" also includes a direction that is approximately orthogonal.

[0011] In addition, in this application, the term "number of rotations" means the number of times an object rotates per unit time (rotation speed).

[0012] 1. First Embodiment <1-1. Power transmission device configuration> FIG. 1 is a longitudinal sectional view of a power transmission device 1 according to a first embodiment. FIG. 2 is a transverse sectional view of the power transmission device 1 as seen from position AA in FIG. 1. This power transmission device 1 is a device that transmits rotational motion obtained from a motor at a first rotation speed to a subsequent stage while reducing the rotation speed to a second rotation speed that is lower than the first rotation speed. The power transmission device 1 is used, for example, by being incorporated into a joint of a robot together with a motor. However, the power transmission device of the present invention may also be used in other devices such as an assist suit or an unmanned transport vehicle.

[0013] As shown in FIGS. 1 and 2, the power transmission device 1 of this embodiment includes an internal gear 10, a flex gear 20, a wave generator 30, and a strain sensor 40.

[0014] The internal gear 10 is an annular gear having a plurality of internal teeth 11 on its inner peripheral surface. The internal gear 10 is fixed, for example by screws, to the frame of the device on which the power transmission device 1 is mounted. The internal gear 10 is arranged coaxially with the central axis 9. The internal gear 10 is also located radially outward of a cylindrical portion 21 (described later) of the flex gear 20. The rigidity of the internal gear 10 is much higher than the rigidity of the cylindrical portion 21 of the flex gear 20. Therefore, the internal gear 10 can be considered to be a substantially rigid body. The internal gear 10 has a cylindrical inner peripheral surface. The plurality of internal teeth 11 are arranged circumferentially on this inner peripheral surface at a constant pitch. Each internal tooth 11 protrudes radially inward.

[0015] The flex gear 20 is a flexible, annular gear. The flex gear 20 is supported rotatably around the central axis 9. The flex gear 20 has a cylindrical portion 21 and a flat portion 22. The cylindrical portion 21 extends cylindrically in the axial direction around the central axis 9. The axial tip of the cylindrical portion 21 is located radially outside the wave generator 30 and radially inside the internal gear 10. The cylindrical portion 21 is flexible and therefore can deform radially. In particular, the tip of the cylindrical portion 21, which is located radially inside the internal gear 10, is a free end and can therefore be displaced radially more than other portions.

[0016] The flex gear 20 has a plurality of external teeth 23. The plurality of external teeth 23 are arranged at a constant pitch in the circumferential direction on the outer peripheral surface near the axial tip of the cylindrical portion 21. Each external tooth 23 protrudes radially outward. The number of internal teeth 11 of the internal gear 10 described above and the number of external teeth 23 of the flex gear 20 are slightly different.

[0017] The flat plate portion 22 has a diaphragm portion 221 and a thick portion 222. The diaphragm portion 221 extends radially outward from the axial base end of the cylindrical portion 21 in a flat plate shape, and also extends in an annular shape centered on the central axis 9. The diaphragm portion 221 is slightly flexible and deformable in the axial direction. The thick portion 222 is an annular portion located radially outward from the diaphragm portion 221. The axial thickness of the thick portion 222 is greater than the axial thickness of the diaphragm portion 221. The thick portion 222 is fixed, for example by screwing, to a component to be driven of an apparatus in which the power transmission device 1 is installed.

[0018] The wave generator 30 is a mechanism that generates periodic bending deformation in the cylindrical portion 21 of the flex gear 20. The wave generator 30 has a cam 31 and a flexible bearing 32. The cam 31 is supported rotatably about the central axis 9. The cam 31 has an outer peripheral surface that is elliptical when viewed in the axial direction. The flexible bearing 32 is interposed between the outer peripheral surface of the cam 31 and the inner peripheral surface of the cylindrical portion 21 of the flex gear 20. Therefore, the cam 31 and the cylindrical portion 21 can rotate at different rotation speeds.

[0019] The inner ring of the flexible bearing 32 contacts the outer peripheral surface of the cam 31. The outer ring of the flexible bearing 32 contacts the inner peripheral surface of the flex gear 20. As a result, the cylindrical portion 21 of the flex gear 20 is deformed into an elliptical shape that follows the outer peripheral surface of the cam 31. As a result, the external teeth 23 of the flex gear 20 and the internal teeth 11 of the internal gear 10 mesh with each other at two locations corresponding to both ends of the major axis of the ellipse. At other circumferential positions, the external teeth 23 and the internal teeth 11 do not mesh with each other.

[0020] The cam 31 is connected to the motor directly or via another power transmission mechanism. When the motor is driven, the cam 31 rotates around the central axis 9 at a first rotational speed. This causes the major axis of the ellipse of the flex gear 20 to rotate at the first rotational speed. Consequently, the meshing position between the external teeth 23 and the internal teeth 11 also moves circumferentially at the first rotational speed. As described above, the number of internal teeth 11 on the internal gear 10 is slightly different from the number of external teeth 23 on the flex gear 20. Due to this difference in the number of teeth, the meshing position between the external teeth 23 and the internal teeth 11 shifts slightly circumferentially with each rotation of the cam 31. As a result, the flex gear 20 rotates around the central axis 9 at a second rotational speed lower than the first rotational speed relative to the internal gear 10. Therefore, a rotational motion at a reduced second rotational speed can be generated from the flex gear 20.

[0021] <1-2. Strain sensor configuration> The strain sensor 40 is a sensor that detects the strain of the flex gear 20 when the power transmission device 1 is in operation. In this embodiment, the flex gear 20, which is a circular body, is the object to be detected by the strain sensor 40. As shown in FIG. 1 , the strain sensor 40 is fixed to the circular surface of the disc-shaped diaphragm portion 221.

[0022] FIG. 3 is a plan view of the strain sensor 40. FIG. 4 is a partial cross-sectional view of the diaphragm portion 221 and the strain sensor 40. As shown in FIGS. 3 and 4, the strain sensor 40 has a circuit board 41. The circuit board 41 of this embodiment has a conductor formed on the surface of a flexibly deformable insulating layer 42. As shown in FIG. 3, the circuit board 41 has an annular main body portion 411 centered on the central axis 9, and a flap portion 412 protruding radially outward from the main body portion 411.

[0023] As shown in FIG. 4, the circuit board 41 of the strain sensor 40 has an insulating layer 42, a first conductor layer 43, and a second conductor layer 44. The insulating layer 42 is made of resin, which is an insulator. The first conductor layer 43 and the second conductor layer 44 are made of metal, which is a conductor. The first conductor layer 43 is formed on the surface of the insulating layer 42. The first conductor layer 43 is made of a material such as an alloy containing copper or an alloy containing chromium. The second conductor layer 44 is laminated on the surface of the first conductor layer 43. The second conductor layer 44 is made of a material such as copper, silver, or gold.

[0024] When manufacturing the circuit board 41, first, a thin metal film constituting the first conductor layer 43 is formed on the entire surface of the insulating layer 42. Then, the formed thin metal film is partially etched to match the shapes of the torque detection pattern Pt and the wiring portion 46 (described later). This forms the first conductor layer 43. Then, a thin metal film constituting the second conductor layer 44 is formed on the surfaces of the insulating layer 42 and the first conductor layer 43. Then, the formed thin metal film is partially etched to match the shapes of the first folded portion ra and the second folded portion rb (described later). This forms the second conductor layer 44. At this time, since the second conductor layer 44 is formed of a metal material different from that of the first conductor layer 43, the second conductor layer 44 can be etched without etching the first conductor layer 43. However, the manufacturing method of the circuit board 41 is not limited to this example.

[0025] As shown in FIG. 4, the strain sensor 40 is fixed to the diaphragm portion 221 of the flex gear 20 with double-sided adhesive tape 47. Specifically, the front surface of the diaphragm portion 221 and the rear surface of the insulating layer 42 of the circuit board 41 are fixed via the double-sided adhesive tape 47. The double-sided adhesive tape 47 is made by molding an adhesive material into a tape shape and hardening it to the extent that it can maintain its shape. Using such double-sided adhesive tape 47 makes it easier to fix the strain sensor 40 to the diaphragm portion 221 than when a fluid adhesive is used. Furthermore, it reduces variation in the fixing work between workers.

[0026] In order to transmit the deformation of the diaphragm portion 221 to the strain sensor 40 with high accuracy, it is preferable that the double-sided adhesive tape 47 does not have a base film and is made of adhesive material only.

[0027] <1-3. Torque detection pattern> The circuit board 41 is mounted with a torque detection pattern Pt, a signal processing circuit 45, and a wiring portion 46. The torque detection pattern Pt is disposed in the main body portion 411. The signal processing circuit 45 is disposed in the flap portion 412. The torque detection pattern Pt and the signal processing circuit 45 are connected by the wiring portion 46. The first conductor layer 43 has the torque detection pattern Pt and the wiring portion 46.

[0028] The torque detection pattern Pt is a pattern for detecting the torque applied to the flex gear 20. As shown in Fig. 3, the torque detection pattern Pt includes a first detection line pattern R1 and a second detection line pattern R2.

[0029] The first detection line pattern R1 is an arc-shaped or annular pattern as a whole, in which a single conductor extends in a zigzag manner in the circumferential direction. In this embodiment, the first detection line pattern R1 is provided in a range of approximately 360° around the central axis 9.

[0030] FIG. 5 is a partially enlarged view of the first detection line pattern R1. As shown in FIGS. 3 and 5, the first detection line pattern R1 includes a plurality of first resistance wires r1 and a plurality of first folded portions ra. The plurality of first resistance wires r1 are arranged in the circumferential direction and substantially parallel to one another. Each first resistance wire r1 extends linearly in a direction inclined relative to the radial and circumferential directions. The first resistance wire r1 is inclined to one circumferential side relative to the radial direction of the flex gear 20. The inclination angle of the first resistance wire r1 relative to the radial direction is, for example, 45°.

[0031] The first folded portions ra are arc-shaped portions that connect the ends of adjacent first resistance wires r1 in the circumferential direction. The first folded portions ra connect the first resistance wires r1 alternately on the inside and outside in the radial direction. This allows the first resistance wires r1 to be connected in series as a whole.

[0032] The second detection line pattern R2 is an arc-shaped or annular pattern as a whole, in which a single conductor extends in a zigzag pattern in the circumferential direction. The second detection line pattern R2 is located radially inward of the first detection line pattern R1. In this embodiment, the second detection line pattern R2 is provided within a range of approximately 360° around the central axis 9.

[0033] FIG. 6 is a partially enlarged view of the second detection line pattern R2. As shown in FIGS. 3 and 6, the second detection line pattern R2 includes a plurality of second resistance wires r2 and a plurality of second folded portions rb. The plurality of second resistance wires r2 are arranged in the circumferential direction and substantially parallel to one another. Each second resistance wire r2 extends linearly in a direction inclined relative to the radial and circumferential directions. The second resistance wire r2 is inclined toward the other circumferential side relative to the radial direction of the flex gear 20. The inclination angle of the second resistance wire r2 relative to the radial direction is, for example, 45°.

[0034] The second folded portions rb are arc-shaped portions that connect the ends of adjacent second resistance wires r2 in the circumferential direction. The second folded portions rb connect the second resistance wires r2 alternately on the inside and outside in the radial direction. This allows the second resistance wires r2 to be connected in series as a whole.

[0035] 7 is a circuit diagram of a Wheatstone bridge circuit Ct including a first detection line pattern R1 and a second detection line pattern R2. As shown in FIG. 7, the Wheatstone bridge circuit Ct includes a first detection line pattern R1, a second detection line pattern R2, and two fixed resistors Rs. The first detection line pattern R1 and the second detection line pattern R2 are connected in series. The two fixed resistors Rs are also connected in series. The series of the two detection line patterns R1 and R2 and the series of the two fixed resistors Rs are connected in parallel between the positive and negative poles of the power supply voltage. A midpoint M1 between the first detection line pattern R1 and the second detection line pattern R2 and a midpoint M2 between the two fixed resistors Rs are connected to a voltmeter Vt.

[0036] The resistance values ​​of the first detection line pattern R1 and the second detection line pattern R2 change depending on the torque applied to the flex gear 20. For example, when torque is applied to the flex gear 20 in one circumferential direction about the central axis 9, the resistance value of the first detection line pattern R1 decreases, and the resistance value of the second detection line pattern R2 increases. On the other hand, when torque is applied to the flex gear 20 in the other circumferential direction about the central axis 9, the resistance value of the first detection line pattern R1 increases, and the resistance value of the second detection line pattern R2 decreases. In this way, the resistance values ​​of the first detection line pattern R1 and the second detection line pattern R2 change in opposite directions with respect to torque.

[0037] When the resistance values ​​of the first detection line pattern R1 and the second detection line pattern R2 change, the potential difference between the midpoint M1 between the first detection line pattern R1 and the second detection line pattern R2 and the midpoint M2 between the two fixed resistors Rs changes, and the measurement value vt of the voltmeter Vt changes. Therefore, the direction and magnitude of the torque applied to the flex gear 20 can be detected based on the measurement value vt of the voltmeter Vt.

[0038] As shown in Fig. 5, the first conductor layer 43 is exposed on the surface of the first resistance wire r1. In contrast, the second conductor layer 44 is laminated on the surface of the first folded portion ra. Therefore, the first folded portion ra of the first detection line pattern R1 is reinforced by the second conductor layer 44. This ensures the strength of the first folded portion ra. Even if the flex gear 20 repeatedly undergoes elliptical deformation, cracks are unlikely to occur in the first folded portion ra.

[0039] Of the resistance value of the first detection line pattern R1, the portion that contributes to torque detection is the resistance value of the multiple first resistance wires r1. Therefore, if the resistance value of the multiple first folded portions ra is large, the torque detection accuracy decreases. In this regard, by laminating the second conductor layer 44 on the first folded portions ra as in this embodiment, the resistance value of the first folded portions ra decreases. This makes it possible to increase the proportion of the resistance value of the multiple first resistance wires r1 in the resistance value of the first detection line pattern R1. Therefore, it is possible to improve the torque detection accuracy.

[0040] 5, the line width da of the first folded portion ra is approximately the same as the line width d1 of the first resistance wire r1. This reduces the rigidity of the first folded portion ra compared to when the line width da of the first folded portion ra is larger than the line width d1 of the first resistance wire r1. In other words, the flexibility of the first folded portion ra is increased. This further reduces the occurrence of cracks in the first folded portion ra.

[0041] The line width da of the first folded portion ra and the line width d1 of the first resistance wire r1 do not necessarily have to be exactly the same, and an error of about ±10% is acceptable. That is, the line width da of the first folded portion ra may be approximately 90 to 110% of the line width d1 of the first resistance wire r1. Furthermore, the line width da of the first folded portion ra may be equal to or smaller than the line width d1 of the first resistance wire r1. Setting the line width da of the first folded portion ra equal to or smaller than the line width d1 of the first resistance wire r1 increases the flexibility of the first folded portion ra. This further reduces the occurrence of cracks in the first folded portion ra.

[0042] The same is true for the second detection line pattern R2. That is, as shown in FIG. 6, the first conductor layer 43 is exposed on the surface of the second resistance wire r2. In contrast, the second conductor layer 44 is laminated on the surface of the second folded portion rb. Therefore, the second folded portion rb of the second detection line pattern R2 is reinforced by the second conductor layer 44. This ensures the strength of the second folded portion rb. Even if the flex gear 20 repeatedly undergoes elliptical deformation, cracks are unlikely to occur in the second folded portion rb.

[0043] Of the resistance value of the second detection line pattern R2, the portion that contributes to torque detection is the resistance value of the multiple second resistance wires r2. Therefore, if the resistance value of the multiple second folded portions rb is high, the torque detection accuracy will decrease. In this regard, by laminating the second conductor layer 44 on the second folded portions rb as in this embodiment, the resistance value of the second folded portions rb will decrease. This makes it possible to increase the proportion of the resistance value of the multiple second resistance wires r2 in the resistance value of the second detection line pattern R2. Therefore, it is possible to improve the torque detection accuracy.

[0044] 6, the line width db of the second folded portion rb is substantially the same as the line width d2 of the second resistance wire r2. This reduces the rigidity of the second folded portion rb compared to when the line width db of the second folded portion rb is larger than the line width d2 of the second resistance wire r2. In other words, the flexibility of the second folded portion rb is increased. Therefore, the occurrence of cracks in the second folded portion rb can be further suppressed.

[0045] The line width db of the second folded portion rb and the line width d2 of the second resistance wire r2 do not necessarily have to be exactly the same, and an error of about ±10% is acceptable. That is, the line width db of the second folded portion rb may be approximately 90 to 110% of the line width d2 of the second resistance wire r2. Furthermore, the line width db of the second folded portion rb may be equal to or smaller than the line width d2 of the second resistance wire r2. Setting the line width db of the first folded portion rb equal to or smaller than the line width d2 of the second resistance wire r2 further increases the flexibility of the second folded portion rb. This further reduces the occurrence of cracks in the second folded portion rb.

[0046] Furthermore, it is desirable to use a material for the second conductor layer 44 that has a lower resistivity or gauge factor than the first conductor layer 43. By stacking the second conductor layer 44, the resistance values ​​of the first folded portion ra and the second folded portion rb can be more effectively reduced. This further improves the torque detection accuracy of the torque detection pattern Pt. For example, the first conductor layer 43 may be made of a copper-containing material such as a Cu-Ni alloy, and the second conductor layer 44 may be made of copper. Alternatively, the first conductor layer 43 may be made of a chromium-containing material, and the second conductor layer 44 may be made of gold. However, the first conductor layer 43 may also be made of chromium, chromium nitride, chromium oxide, or the like.

[0047] 2. Second embodiment (angle detection pattern) Next, a second embodiment will be described. The second embodiment differs from the first embodiment described above only in the shape of the detection line pattern in the strain sensor 40. The other configurations are the same as those in the first embodiment, so a duplicated description will be omitted.

[0048] FIG. 8 is a plan view of a strain sensor 40 according to the second embodiment. In the example of FIG. 8, an angle detection pattern Pθ, a signal processing circuit 45, and a wiring section 46 are mounted on a circuit board 41. The angle detection pattern Pθ is disposed in a main body section 411. The signal processing circuit 45 is disposed in a flap section 412. The angle detection pattern Pθ and the signal processing circuit 45 are connected by the wiring section 46. The first conductor layer 43 has the angle detection pattern Pθ and the wiring section 46.

[0049] The angle detection pattern Pθ is a pattern for detecting the rotation angle of the rotational motion input to the flex gear 20. As shown in Fig. 8, the angle detection pattern Pθ includes four third detection line patterns R3 and four fourth detection line patterns R4.

[0050] The four third detection line patterns R3 are arranged at equal intervals in the circumferential direction around the central axis 9. In this embodiment, one third detection line pattern R3 extends over an angular range of approximately 45° around the central axis 9.

[0051] FIG. 9 is a partially enlarged view of the third detection line pattern R3. As shown in FIGS. 8 and 9, the third detection line pattern R3 includes a plurality of third resistance wires r3 and a plurality of third fold portions rc. The plurality of third resistance wires r3 are arranged parallel to one another at small radial intervals. Each third resistance wire r3 extends in an arc shape along the circumferential direction. The third fold portion rc is an arc-shaped portion that connects the circumferential ends of radially adjacent third resistance wires r3. The plurality of third resistance wires r3 are connected alternately at one end and the other end in the circumferential direction by the third fold portions rc. As a result, the plurality of third resistance wires r3 are connected in series as a whole.

[0052] The four fourth detection line patterns R4 are arranged concentrically with the first detection line pattern R1 and in an area in the circumferential direction where the third detection line pattern R3 is not arranged. In this embodiment, the third detection line patterns R3 and the fourth detection line patterns R4 are arranged alternately in the circumferential direction. The four third detection line patterns R3 and the four fourth detection line patterns R4 are arranged as a whole in an annular shape centered on the central axis 9.

[0053] A partial enlarged view of the fourth detection line pattern R4 is omitted because it is similar to the third detection line pattern R3. As shown in FIG. 8, the fourth detection line pattern R4 includes a plurality of fourth resistance wires r4 and a plurality of fourth folded portions rd. The plurality of fourth resistance wires r4 are arranged parallel to one another at small radial intervals. Each fourth resistance wire r4 extends in an arc shape along the circumferential direction. The fourth folded portion rd is an arc-shaped portion that connects the circumferential ends of radially adjacent fourth resistance wires r4. The plurality of fourth resistance wires r4 are connected alternately between one circumferential end and the other circumferential end by the fourth folded portion rd. As a result, the plurality of fourth resistance wires r4 are connected in series as a whole.

[0054] Fig. 10 is a circuit diagram of a first Wheatstone bridge circuit C1 including four third detection line patterns R3. In the example of Fig. 10, the four third detection line patterns R3 are distinguished and shown as R31, R32, R33, and R34. The third detection line patterns R31, R32, R33, and R34 are arranged counterclockwise in this order, starting with R31 in Fig. 8.

[0055] As shown in FIG. 10, four third detection line patterns R31, R32, R33, and R34 are incorporated into a first Wheatstone bridge circuit C1. The third detection line pattern R31 and the third detection line pattern R32 are connected in series in this order. The third detection line pattern R34 and the third detection line pattern R33 are connected in series in this order. Between the positive and negative poles of the power supply voltage, two rows of the third detection line patterns R31 and R32 and two rows of the third detection line patterns R34 and R33 are connected in parallel. A midpoint M11 between the third detection line patterns R31 and R32 and a midpoint M12 between the third detection line patterns R34 and R33 are connected to a first voltmeter V1.

[0056] Fig. 11 is a circuit diagram of a second Wheatstone bridge circuit C2 including four fourth detection line patterns R4. In the example of Fig. 11, the four fourth detection line patterns R4 are distinguished and shown as R41, R42, R43, and R44. The fourth detection line pattern R41 is located between the third detection line patterns R31 and R34 in Fig. 8. The fourth detection line patterns R41, R42, R43, and R44 are arranged in this order clockwise, starting with R41 in Fig. 8.

[0057] As shown in FIG. 11, four fourth detection line patterns R41, R42, R43, and R44 are incorporated into a second Wheatstone bridge circuit C2. The fourth detection line pattern R41 and the fourth detection line pattern R42 are connected in series in this order. The fourth detection line pattern R44 and the fourth detection line pattern R43 are connected in series in this order. Between the positive and negative poles of the power supply voltage, two rows of the fourth detection line patterns R41 and R42 and two rows of the fourth detection line patterns R44 and R43 are connected in parallel. A midpoint M21 between the fourth detection line patterns R41 and R42 and a midpoint M22 between the fourth detection line patterns R44 and R43 are connected to a second voltmeter V2.

[0058] When the power transmission device 1 is driven, the diaphragm portion 221 has portions that expand in the circumferential direction (hereinafter referred to as "expanded portions") and portions that contract in the circumferential direction (hereinafter referred to as "contracted portions"). Specifically, two expanded portions and two contracted portions alternate in the circumferential direction. That is, the expanded portions and contracted portions alternate at 90° intervals in the circumferential direction. The locations where these expanded portions and contracted portions occur rotate at the first rotation speed described above.

[0059] The resistance values ​​of the third detection line patterns R31, R32, R33, and R34 and the fourth detection line patterns R41, R42, R43, and R44 vary depending on the circumferential distortion of the diaphragm portion 221. For example, when the above-described expansion portion overlaps a certain detection line pattern, the resistance value of that detection line pattern increases. Conversely, when the above-described contraction portion overlaps a certain detection line pattern, the resistance value of that detection line pattern decreases.

[0060] 8, when the contracted portions overlap with the third detection line patterns R31 and R33, the extended portions overlap with the third detection line patterns R32 and R34. Furthermore, when the extended portions overlap with the third detection line patterns R31 and R33, the contracted portions overlap with the third detection line patterns R32 and R34. Therefore, in the first Wheatstone bridge circuit C1, the third detection line patterns R31 and R33 and the third detection line patterns R32 and R34 exhibit resistance value changes in opposite directions.

[0061] 8, when the contracted portions overlap with the fourth detection line patterns R41 and R43, the extended portions overlap with the fourth detection line patterns R42 and R44. When the extended portions overlap with the fourth detection line patterns R41 and R43, the contracted portions overlap with the fourth detection line patterns R42 and R44. Therefore, in the second Wheatstone bridge circuit C2, the fourth detection line patterns R41 and R43 and the fourth detection line patterns R42 and R44 exhibit resistance value changes in opposite directions.

[0062] As a result, the first voltmeter V1 and the second voltmeter V2 each output periodically changing sinusoidal measurement values ​​v1 and v2. The period T of these measurement values ​​v1 and v2 corresponds to half the period of the first rotation speed described above. Furthermore, the direction of the input rotational motion can be determined based on whether the phase of the measurement value v2 of the second voltmeter V2 leads the phase of the measurement value v1 of the first voltmeter V1 by 1 / 8 of the period of the first rotation speed (1 / 4 of the period of the measurement values ​​v1 and v2) or lags behind by 1 / 8 of the period of the first rotation speed (1 / 4 of the period of the measurement values ​​v1 and v2).

[0063] Therefore, based on the output values ​​of these two Wheatstone bridge circuits C1 and C2, it is possible to detect the rotation angle of the rotational motion input to the flex gear 20. Specifically, for example, a function table may be prepared in advance that associates the combination of the measurement values ​​v1 and v2 of the first voltmeter V1 and the second voltmeter V2 with the rotation angle, and the measurement values ​​v1 and v2 may be input into the function table to output the rotation angle.

[0064] As shown in FIG. 9, the first conductor layer 43 is exposed on the surface of the third resistance wire r3. In contrast, the second conductor layer 44 is laminated on the surface of the third folded portion rc. Therefore, the third folded portion rc of the third detection line pattern R3 is reinforced by the second conductor layer 44. This ensures the strength of the third folded portion rc. Even if the flexgear 20 repeatedly undergoes elliptical deformation, cracks are unlikely to occur in the third folded portion rc.

[0065] Of the resistance value of the third detection line pattern R3, the portion that contributes to detecting the rotation angle is the resistance value of the multiple third resistance wires r3. Therefore, if the resistance value of the multiple third folded portions rc is high, the detection accuracy of the rotation angle decreases. In this regard, by laminating the second conductor layer 44 on the third folded portion rc as in this embodiment, the resistance value of the third folded portion rc decreases. This makes it possible to increase the proportion of the resistance value of the multiple third resistance wires r3 in the resistance value of the third detection line pattern R3. Therefore, it is possible to improve the detection accuracy of the rotation angle.

[0066] 9, the line width dc of the third folded portion rc is substantially the same as the line width d3 of the third resistance wire r3. This reduces the rigidity of the third folded portion rc compared to when the line width dc of the third folded portion rc is larger than the line width d3 of the third resistance wire r3. In other words, the flexibility of the third folded portion rc is increased. This further reduces the occurrence of cracks in the third folded portion rc.

[0067] The line width dc of the third folded portion rc and the line width d3 of the third resistance wire r3 do not necessarily have to be exactly the same, and an error of about ±10% is acceptable. That is, the line width dc of the third folded portion rc may be approximately 90 to 110% of the line width d3 of the third resistance wire r3. Furthermore, the line width dc of the third folded portion rc may be equal to or smaller than the line width d3 of the third resistance wire r3. Setting the line width dc of the third folded portion rc equal to or smaller than the line width d3 of the third resistance wire r3 increases the flexibility of the third folded portion rc. Therefore, the occurrence of cracks in the third folded portion rc can be further suppressed.

[0068] The same is true for the fourth detection line pattern R4. That is, the first conductor layer 43 is exposed on the surface of the fourth resistance wire r4. In contrast, the second conductor layer 44 is laminated on the surface of the fourth folded portion rd. Therefore, the fourth folded portion rd of the fourth detection line pattern R4 is reinforced by the second conductor layer 44. This ensures the strength of the fourth folded portion rd. Even if the flex gear 20 repeatedly undergoes elliptical deformation, cracks are unlikely to occur in the fourth folded portion rd.

[0069] Of the resistance value of the fourth detection line pattern R4, the portion that contributes to detecting the rotation angle is the resistance value of the multiple fourth resistance wires r4. Therefore, if the resistance value of the multiple fourth folded portions rd is large, the detection accuracy of the rotation angle decreases. In this regard, by laminating the second conductor layer 44 on the fourth folded portion rd as in this embodiment, the resistance value of the fourth folded portion rd decreases. This makes it possible to increase the proportion of the resistance value of the multiple fourth resistance wires r4 in the resistance value of the fourth detection line pattern R4. Therefore, it is possible to improve the detection accuracy of the rotation angle.

[0070] Furthermore, the line width of the fourth folded portion rd is approximately the same as the line width of the fourth resistance wire r4. In this way, the rigidity of the fourth folded portion rd is lower than when the line width of the fourth folded portion rd is larger than the line width of the fourth resistance wire r4. In other words, the flexibility of the fourth folded portion rd is increased. Therefore, the occurrence of cracks in the fourth folded portion rd can be further suppressed.

[0071] The line width of the fourth folded portion rd and the line width of the fourth resistance wire r4 do not necessarily have to be exactly the same, and an error of about ±10% is acceptable. That is, the line width of the fourth folded portion rd may be approximately 90 to 110% of the line width of the fourth resistance wire r4. Furthermore, the line width of the fourth folded portion rd may be equal to or smaller than the line width of the fourth resistance wire r4. If the line width of the fourth folded portion rd is equal to or smaller than the line width of the fourth resistance wire r4, the flexibility of the fourth folded portion rd will be increased. Therefore, the occurrence of cracks in the fourth folded portion rd can be further suppressed.

[0072] Furthermore, it is desirable to use a material for the second conductor layer 44 that has a lower resistivity or gauge factor than the first conductor layer 43. By stacking the second conductor layer 44, the resistance values ​​of the third folded portion rc and the fourth folded portion rd can be more effectively reduced. This further improves the accuracy of detecting the rotation angle using the angle detection pattern Pθ. For example, the first conductor layer 43 may be made of a material containing copper, such as a Cu-Ni alloy, and the second conductor layer 44 may be made of copper. Alternatively, the first conductor layer 43 may be made of a material containing chromium, and the second conductor layer 44 may be made of gold. However, the first conductor layer 43 may also be made of chromium, chromium nitride, chromium oxide, or the like.

[0073] <3. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0074] <3-1. First modified example> In the second embodiment described above, in the angle detection pattern Pθ, the multiple third resistance wires r3 included in the third detection line pattern R3 and the multiple fourth resistance wires r4 included in the fourth detection line pattern R4 each extend in the circumferential direction. This is to detect periodic deformation of the diaphragm portion 221 in the circumferential direction. However, when the power transmission device 1 is driven, the diaphragm portion 221 periodically deforms not only in the circumferential direction but also in the radial direction. Therefore, as shown in FIG. 12 , the orientation of the third resistance wires r3 and the fourth resistance wires r4 may also be radial. That is, it is sufficient that the multiple third resistance wires r3 included in the third detection line pattern R3 and the multiple fourth resistance wires r4 included in the fourth detection line pattern R4 each extend in either the radial direction or the circumferential direction.

[0075] <3-2. Second modified example> In the strain sensors 40 of the first and second embodiments described above, the second conductor layer 44 may be laminated on the surface of the wiring portion 46 extending from the end of each detection line pattern. This reduces the resistance of the wiring portion 46. This allows for more accurate detection of changes in the resistance of the first resistance wire r1 and the second resistance wire r2, or changes in the resistance of the third resistance wire r3 and the fourth resistance wire r4. This further improves the accuracy of torque or rotation angle detection.

[0076] <3-3.Third modified example> In the first and second embodiments described above, the second conductor layer 44 is laminated only on the folded portion of the resistance wire and the folded portion. However, as shown in FIG. 13 , the second conductor layer 44 may also be laminated on the surface of the adjacent portion r51 of the resistance wire r5 that is adjacent to the folded portion re. In the example of FIG. 13 , the second conductor layer 44 is laminated on the surface of the folded portion re and the surface of the adjacent portion r51 of the resistance wire r5. In this way, the folded portion re and the adjacent portion r51 are reinforced by the second conductor layer 44. This makes it possible to prevent cracks from occurring near the boundary between the folded portion re and the resistance wire r5.

[0077] The graph in Fig. 14 is the result of analyzing the stress S applied to the circumferential end E, which is the most likely to have stress concentration, in the inner circumference of the folded portion re by changing the length L of the adjacent portion r51 in the structure of Fig. 13. The horizontal axis in Fig. 14 indicates the ratio L / w of the length L of the adjacent portion r51 to the line width w of the resistance line r5. The vertical axis in Fig. 14 indicates the ratio S / S0 of the stress S to the stress S0, where S0 is the stress applied to the end E when the length L of the adjacent portion r51 is 0. From the results in Fig. 14, it can be seen that by making the length L of the adjacent portion r51 where the second conductor layer 44 is laminated larger than 0 compared to the case where the length of the adjacent portion r51 is 0 or less, the stress S applied to the end E can be reduced. However, if the length L of the adjacent portion r51 is too long, the stress S applied to the end E becomes larger than when the length L of the adjacent portion r51 is 0. It is desirable that the length L of the adjacent portion r51 where the second conductor layer 44 is laminated is, for example, larger than 0 and smaller than twice the line width w of the resistance line r5 (0 < L / w < 2).

[0078] <3-4. Fourth Modified Example> Fig. 15 is a partial longitudinal sectional view of a robot 100 provided with a power transmission device 1. In the example of Fig. 15, the power transmission device 1 is incorporated in a joint of the robot 100. The cam 31 of the wave generator 30 is fixed to the output shaft 91 of the motor 90. The internal gear 10 is fixed to a motor case 92 that supports the motor 90. The flex gear 20 is fixed to an arm 93 of the robot 100. When the motor 90 is driven, the flex gear 20 rotates with respect to the internal gear 10 at a reduced second rotational speed. Thereby, the arm 93 can be rotated with respect to the motor case 92 at the second rotational speed.

[0079] <3-5. Other Modified Examples> In the first embodiment described above, the torque detection pattern Pt includes two detection line patterns R1 and R2. The Wheatstone bridge circuit Ct is a half-bridge circuit configured with the two detection line patterns R1 and R2 and two fixed resistors Rs. However, in the structure of the first embodiment, the torque detection pattern Pt may include four detection line patterns. The Wheatstone bridge circuit Ct may be a full-bridge circuit configured with the four detection line patterns.

[0080] The strain sensor 40 of the first embodiment described above has only the torque detection pattern Pt as the detection line pattern. The strain sensor 40 of the second embodiment described above has only the angle detection pattern Pθ as the detection line pattern. However, the strain sensor 40 may have both the torque detection pattern Pt and the angle detection pattern Pθ.

[0081] Furthermore, in the first and second embodiments described above, the detection line pattern is provided on only one surface of the circuit board 41. That is, in the first and second embodiments described above, the first conductor layer 43 and the second conductor layer 44 are formed on only one surface of the insulating layer 42. However, the detection line pattern may be provided on both surfaces of the circuit board 41. That is, the first conductor layer 43 and the second conductor layer 44 may be formed on both surfaces of the insulating layer 42.

[0082] Furthermore, the strain sensor 40 may have a detection line pattern other than the torque detection pattern Pt and the angle detection pattern Pθ. For example, the strain sensor 40 may have a detection line pattern for detecting temperature or a detection line pattern for detecting axial strain of the flex gear 20.

[0083] In the first and second embodiments, the signal processing circuit 45 is mounted on the circuit board 41. However, the signal processing circuit 45 may be provided outside the circuit board 41.

[0084] In the flex gear 20 of the above embodiment, the diaphragm portion 221 extends radially outward from the base end of the cylindrical portion 21. However, the diaphragm portion 221 may extend radially inward from the base end of the cylindrical portion 21.

[0085] Furthermore, in the above embodiment, the object to be detected by the strain sensor 40 was the flexgear 20. However, the object to be detected by the strain sensor 40 is not limited to the flexgear 20. For example, in a planetary reducer having a sun wheel and multiple planetary wheels that revolve around the sun wheel while rotating on their own axis, the strain sensor according to the present invention may be attached to a ring in which the multiple planetary wheels are inscribed. In this case, a circuit board may be fixed to the circular surface of the ring. In other words, the object to be detected in the present invention may be the ring of the planetary reducer.

[0086] In addition, the detailed configurations of the strain sensor and the power transmission device may be appropriately modified without departing from the spirit of the present invention. Furthermore, the elements appearing in the above-described embodiments and modifications may be appropriately combined without causing any contradiction. [Industrial Applicability]

[0087] The present application can be used in strain sensors and power transmission devices. [Explanation of symbols]

[0088] 1 Power transmission device 9 Center axis 10 Internal Gear 20 Flex Gear 21 Cylindrical part 22 Flat plate part 23 Outer teeth 30 Wave Generator 40 Strain Sensor 41 Circuit Board 42 Insulating layer 43 First conductor layer 44 Second conductor layer 45 Signal processing circuit 46 Wiring section 47 Double-sided adhesive tape 221 Diaphragm part 411 Main body 412 Flap section Ct Wheatstone bridge circuit C1 First Wheatstone bridge circuit C2 Second Wheatstone bridge circuit Pt Torque detection pattern Pθ Angle detection pattern R1 First detection line pattern R2 Second detection line pattern R3 Third detection line pattern R4 4th detection line pattern Vt voltmeter V1 First voltmeter V2 Second voltmeter r1 First resistance line r2 2nd resistance wire r3 3rd resistance wire r4 Fourth resistance line ra First fold rb Second fold rc 3rd turn rd 4th fold

Claims

1. an insulating layer fixed to the object to be detected; a first conductor layer formed on a surface of the insulating layer; a second conductor layer laminated on a surface of the first conductor layer; Equipped with The first conductor layer is A detection line pattern including a plurality of resistance lines extending in a predetermined direction and folded portions connecting the ends of the resistance lines. and the second conductor layer is laminated on a surface of the folded portion, the second conductor layer is laminated on a surface of the folded portion and a surface of an adjacent portion of the resistance wire that is adjacent to the folded portion; A strain sensor, wherein the length of the adjacent portion is less than twice the line width of the resistance wire.

2. an insulating layer fixed to the object to be detected; a first conductor layer formed on a surface of the insulating layer; a second conductor layer laminated on a surface of the first conductor layer; Equipped with The first conductor layer is A detection line pattern including a plurality of resistance lines extending in a predetermined direction and folded portions connecting the ends of the resistance lines. and the second conductor layer is laminated on a surface of the folded portion, A strain sensor, wherein the folded portion has a line width smaller than that of the resistance wire.

3. 3. The strain sensor according to claim 1, A strain sensor, wherein the material of the second conductor layer has a lower resistivity than the material of the first conductor layer.

4. an insulating layer fixed to the object to be detected; a first conductor layer formed on a surface of the insulating layer; a second conductor layer laminated on a surface of the first conductor layer; Equipped with The first conductor layer is A detection line pattern including a plurality of resistance lines extending in a predetermined direction and folded portions connecting the ends of the resistance lines. and the second conductor layer is laminated on a surface of the folded portion, A strain sensor, wherein the material of the second conductor layer has a lower gauge factor than the material of the first conductor layer.

5. The strain sensor according to claim 3 or 4, the material of the first conductor layer is a material containing copper or a material containing chromium, The strain sensor, wherein the material of the second conductor layer is copper, silver, or gold.

6. The strain sensor according to any one of claims 1 to 5, The first conductor layer is a torque detection pattern including the detection line pattern for detecting torque applied to the detection object; and The resistance wire extends in a direction inclined relative to the radial and circumferential directions.

7. an insulating layer fixed to the object to be detected; a first conductor layer formed on a surface of the insulating layer; a second conductor layer laminated on a surface of the first conductor layer; Equipped with The first conductor layer is A detection line pattern including a plurality of resistance lines extending in a predetermined direction and folded portions connecting the ends of the resistance lines. and the second conductor layer is laminated on a surface of the folded portion, The first conductor layer is An angle detection pattern including the detection line pattern for detecting the rotation angle of the rotational motion input to the detection object and The resistance wire extends in a circumferential or radial direction.

8. The strain sensor according to any one of claims 1 to 7, The first conductor layer is A wiring portion extending from an end of the detection line pattern and The second conductor layer is laminated on a surface of the wiring portion.

9. A strain sensor according to any one of claims 1 to 8; a circular body that is the object to be detected; A power transmission device comprising:

10. 10. The power transmission device according to claim 9, The circular body is a flexible cylindrical portion extending cylindrically in the axial direction; a plurality of external teeth provided on an outer peripheral surface of the cylindrical portion; a flat diaphragm portion extending radially outward or radially inward from an axial end of the cylindrical portion; and The strain sensor is fixed to the diaphragm portion.

11. The power transmission device according to claim 9 or 10; an arm that rotates at a rotational speed output from the power transmission device; A robot equipped with

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