External gears, strain wave reducers, and robots

Abstract

To provide a technology which can reduce a load applied on a strain gauge while accurately detecting torque applied on an outer tooth gear.SOLUTION: An outer tooth gear 20 has a flank part 21, a plurality of outer teeth, a diaphragm part 232, and a strain gauge 42. The flank part 21 extends in an axial direction which is parallel with a center axis. The plurality of outer teeth are arranged at one side of the flank part 21 in the axial direction. The outer teeth extend to the outside of a radial direction. The diaphragm part 232 expands in a direction intersecting with the axial direction at the other side of the flank part 21 in the axial direction. The strain gauge 42 is arranged at least at either of a face of the diaphragm part 232 at one side in the axial direction, and a face at the other side in the axial direction. The strain gauge 42 is arranged in only a region which is smaller than a half of a radial length from one end of the diaphragm part 232 in the radial direction up to the other end in the radial direction with a radial meddle point Rm between one end of the diaphragm part 232 in the radial direction at a cross section passing the center axis, and the other end in the radial direction as a center.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an external gear, a strain wave reducer, and a robot. [Background technology]

[0002] In recent years, there has been an increasing demand for wave reducers to be installed in the joints of robots, etc. In conventional wave reducers, a strain gauge is attached to the external gear that rotates at the reduced rotational speed. This makes it possible to detect the torque acting on the external gear (Patent Document 1). [Patent Document 1] JP 2000-131160 A Summary of the Invention [Problem to be solved by the invention]

[0003] A conventional external gear has a thin-walled diaphragm portion. A strain gauge is attached to the diaphragm portion. The external gear is fixed to an output member at either the radially inner side or the radially outer side of the diaphragm portion. The external gear also has a cylindrical portion extending in the axial direction from the other of the radially inner side and the radially outer side of the diaphragm portion.

[0004] Because the external gear has the above-mentioned configuration, for example, when the external gear undergoes elliptical deformation or when an axial force acts on the external gear, the distribution of strain generated in the external gear becomes non-uniform due to the geometric shape of the external gear and the boundary conditions when an external force is applied, etc. Therefore, it is difficult to place the strain gauge in an optimal region of the external gear and accurately detect the strain of the external gear caused by torque while reducing the load on the strain gauge.

[0005] In the conventional external gear structure, the strain gauges are arranged over a wide radial range of the diaphragm portion. This can result in a large load being placed on the strain gauges. Therefore, with the conventional structure, it is difficult to reduce the load on the strain gauges while accurately detecting the torque applied to the external gear.

[0006] An object of the present invention is to provide a technique capable of reducing the load on a strain gauge while accurately detecting the torque applied to an external gear. [Means for solving the problem]

[0007] Books Disclosure The external gear of the present invention has a cylindrical body portion extending in an axial direction parallel to a central axis, a plurality of external teeth disposed on one axial side of the body portion and extending radially outward, a diaphragm portion extending in a direction intersecting the axial direction on the other axial side of the body portion, and a plurality of external teeth disposed on at least one of the surfaces on the one axial side and the other axial side of the diaphragm portion. 1. A strain gauge and a first bridge circuit including the first strain gauge; having the first strain gauge comprises a first resistance wire having an overall arc-shaped pattern about the central axis, a second resistance wire having an overall arc-shaped pattern about the central axis and disposed line-symmetrically with the first resistance wire, a third resistance wire having an overall arc-shaped pattern about the central axis and positioned on the other radial side of the first resistance wire, and a fourth resistance wire having an overall arc-shaped pattern about the central axis and disposed line-symmetrically with the third resistance wire, The above 1. The strain gauges are arranged only in an area less than half the radial length from one radial end to the other radial end of the diaphragm portion, centered on the radial midpoint between one radial end and the other radial end of the diaphragm portion in a cross section passing through the central axis. Effect of the Invention

[0008] According to the present invention, the load on the strain gauge can be reduced while the torque applied to the external gear is detected with high accuracy. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of the robot. [Diagram 2] FIG. 2 is a vertical cross-sectional view of the wave reducer. [Diagram 3] FIG. 3 is a cross-sectional view of the wave reducer. [Figure 4]FIG. 4 is a plan view of the torque sensor. [Diagram 5] FIG. 5 is a partial vertical sectional view of the external gear. [Figure 6] FIG. 6 is a partial plan view of the torque sensor. [Figure 7] FIG. 7 is a circuit diagram of a bridge circuit including the first to fourth resistance wires. [Figure 8] FIG. 8 is a graph showing the distribution of strain in the diaphragm portion. [Figure 9] FIG. 9 is a partial plan view of a torque sensor according to a first modified example. [Figure 10] FIG. 10 is a partial plan view of a torque sensor according to a second modified example. [Figure 11] FIG. 11 is a partial plan view of a torque sensor according to a third modified example. [Figure 12] FIG. 12 is a partial plan view of a torque sensor according to a fourth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings.

[0011] <1.About Robots> 1 is a schematic diagram of a robot 100 equipped with a wave reducer 1 according to one embodiment. The robot 100 is a so-called industrial robot that performs tasks such as transporting, processing, and assembling parts in, for example, a manufacturing line of industrial products. As shown in FIG. 1, the robot 100 includes a base frame 101, an arm 102, a motor 103, and the wave reducer 1.

[0012] The arm 102 is rotatably supported with respect to the base frame 101. The motor 103 and the wave motion reducer 1 are incorporated in a joint between the base frame 101 and the arm 102. When a driving current is supplied to the motor 103, a rotational motion is output from the motor 103. The rotational motion output from the motor 103 is decelerated by the wave motion reducer 1 and transmitted to the arm 102. As a result, the arm 102 rotates with respect to the base frame 101 at a decelerated speed.

[0013] As described above, the robot 100 has the wave reducer 1. The external gear 20 (described later) of the wave reducer 1 has a structure that can reduce the load on the strain gauge while accurately detecting the torque acting on the external gear 20. This makes it possible to realize a high-performance robot.

[0014] <2. Structure of the wave reducer> Next, the detailed structure of the wave reducer 1 will be described.

[0015] In the following, the direction parallel to the central axis 9 of the wave reducer 1 is referred to as the "axial direction", the direction perpendicular to the central axis 9 of the wave reducer 1 is referred to as the "radial direction", and the direction along the arc centered on the central axis 9 of the wave reducer 1 is referred to as the "circumferential direction". However, the above "parallel direction" also includes a substantially parallel direction. Furthermore, the above "perpendicular direction" also includes a substantially perpendicu- lar direction.

[0016] In this embodiment, the “radial outer side” corresponds to the “one radial side”, and the “radial inner side” corresponds to the “other radial side”. Therefore, the “radial outer end” corresponds to the “one radial end”, and the “radial inner end” corresponds to the “other radial end”.

[0017] FIG. 2 is a longitudinal sectional view of the wave reducer 1 according to one embodiment. FIG. 3 is a transverse sectional view of the wave reducer 1 as seen from the position AA in FIG. 2. To avoid complicating the drawing, hatching indicating a cross section is omitted in FIG. 3. The wave reducer 1 is a device that reduces the rotational motion of a first rotational speed obtained from a motor 103 to a second rotational speed lower than the first rotational speed. As shown in FIGS. 1 and 2, the wave reducer 1 of this embodiment includes an internal gear 10, an external gear 20, and a wave generator 30. The wave reducer 1 can detect the torque acting on the external gear 20 with higher accuracy by a principle described later.

[0018] The internal gear 10 is an annular gear centered on a central axis 9. The internal gear 10 is fixed to a base frame 101 of the robot 100. The internal gear 10 is arranged coaxially with the central axis 9. The internal gear 10 is also arranged radially outward of an external tooth 22 of the external gear 20, which will be described later. The rigidity of the internal gear 10 is sufficiently higher than the rigidity of a body part 21 of the external gear 20, which will be described later. For this reason, the internal gear 10 can be considered as a substantially rigid body. The internal gear 10 has a plurality of internal teeth 11 on its inner circumferential surface. The plurality of internal teeth 11 are arranged at a constant pitch in the circumferential direction on the inner circumferential surface of the internal gear 10. Each internal tooth 11 protrudes radially inward. In other words, the internal gear 10 has a plurality of internal teeth 11 arranged radially outward from the external teeth 22 and extending radially inward.

[0019] The external gear 20 is a flexibly deformable annular gear. The external gear 20 is fixed to an arm 102 of the robot 100. The external gear 20 is supported rotatably about a central axis 9.

[0020] The external gear 20 of this embodiment has a body portion 21 and a plurality of external teeth 22. The external gear 20 further has a disk portion 23. The body portion 21 is a cylindrical portion extending in an axial direction parallel to the central axis 9. More specifically, the body portion 21 is a cylindrical portion extending in the axial direction around the central axis 9. An end portion on one axial side of the body portion 21 (hereinafter referred to as "one axial end") is located radially outside the wave generator 30 and radially inside the internal gear 10. The body portion 21 is flexible and therefore deformable in the radial direction. In particular, the one axial end of the body portion 21 is a free end and therefore can be displaced radially more than other portions.

[0021] The multiple external teeth 22 are arranged on the radially outer surface of one axial end of the body portion 21. The multiple external teeth 22 are arranged at a constant pitch in the circumferential direction. Each external tooth 22 protrudes radially outward. In other words, the multiple external teeth 22 are arranged on one axial side of the body portion 21 and extend radially outward. The number of internal teeth 11 that the internal gear 10 has and the number of external teeth 22 that the external gear 20 has are slightly different.

[0022] The disk portion 23 extends radially outward from the other axial end of the body portion 21. As shown in Fig. 2, the disk portion 23 of this embodiment has a curved portion 231, a diaphragm portion 232, and a thick portion 233. In other words, the external gear 20 has the diaphragm portion 232. In this embodiment, the disk portion 23 is a disk-shaped portion. Moreover, the disk portion 23 is an annular portion that surrounds the central axis 9.

[0023] The curved portion 231 is an annular portion that extends from the end on the other axial side of the body portion 21 (hereinafter referred to as the "axial other end") toward the other axial side and the radially outer side. As shown in FIG. 2, the curved portion 231 is curved in an arc shape in a cross section passing through the central axis 9. More specifically, the curved portion 231 is in an arc shape centered on a point located radially outside the axial other end of the body portion 21 in a cross section passing through the central axis 9. The axial other end of the body portion 21 and the radially inner end of the diaphragm portion 232 (hereinafter referred to as the "radially inner end") are smoothly connected via the curved portion 231. That is, the external gear 20 connects the body portion 21 and the diaphragm portion 232 and has the curved portion 231 that is curved in an arc shape in a cross section passing through the central axis 9. Thereby, the strength of the connection region between the body portion 21 and the diaphragm portion 232 can be improved.

[0024] The diaphragm portion 232 is an annular portion that extends radially outward from the end on the radially outer side of the curved portion 231. In the present embodiment, the diaphragm portion 232 is a disk-shaped part. The diaphragm portion 232 extends in a direction intersecting the axial direction on the other axial side of the body portion 21. The diaphragm portion 232 is flat and annular with the central axis 9 as the center. That is, the diaphragm portion 232 extends radially on one side on the other axial side of the body portion 21. In the present embodiment, the diaphragm portion 232 extends radially outward more than the body portion 21 on the other axial side of the body portion 21. Thereby, compared with the case where the diaphragm portion extends radially inward on the other axial side of the body portion, the space radially inward of the body portion 21 can be widened, so that the space can be effectively utilized. Since the diaphragm portion 232 is thin, it can be slightly bent and deformed.

[0025] The thick portion 233 is an annular portion located radially outward of the diaphragm portion 232. The thick portion 233 extends radially outward from a radially outer end (hereinafter referred to as the "radial outer end") of the diaphragm portion 232. The axial thickness of the thick portion 233 is greater than the axial thickness of the diaphragm portion 232. In other words, the external gear 20 has the thick portion 233 which extends radially outward from one radial end of the diaphragm portion 232 and has a greater axial thickness than the diaphragm portion 232. The thick portion 233 is fixed to the arm 102 of the robot 100, for example, by a bolt.

[0026] In this embodiment, the thick portion 233 protrudes further toward the other axial direction than the surface on the other axial direction side of the diaphragm portion 232. Therefore, the other axial end of the thick portion 233 is disposed on the other axial direction side than the other axial end of the diaphragm portion 232. In this manner, the thick portion 233 does not protrude to the side facing the external teeth 22. Therefore, the space on the external teeth 22 side can be made larger. As a result, the degree of freedom in designing the size, shape, arrangement, etc. of each component disposed on the external teeth 22 side is improved.

[0027] The wave generator 30 is a mechanism that generates periodic bending deformation in the body 21 of the external gear 20. The wave generator 30 is disposed radially inward of the external teeth 22. More specifically, the wave generator 30 is disposed radially inward of the external gear 20 and is rotatable around the central axis 9. The wave generator 30 has a cam 31 and a flexible bearing 32. The cam 31 is supported rotatably around the central axis 9. The radial outer surface of the cam 31 is elliptical when viewed in the axial direction. The flexible bearing 32 is interposed between the radial outer surface of the cam 31 and the radial inner surface of the body 21 of the external gear 20. Therefore, the cam 31 and the body 21 can rotate at different rotational speeds.

[0028] The inner ring of the flexible bearing 32 contacts the radially outer surface of the cam 31. The outer ring of the flexible bearing 32 contacts the radially inner surface of the body 21. As a result, the body 21 deforms into an elliptical shape along the radially outer surface of the cam 31. As a result, the external teeth 22 of the external 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 22 and the internal teeth 11 do not mesh with each other.

[0029] The cam 31 is connected to the output shaft of the motor 103. When the motor 103 is driven, the cam 31 rotates around the central axis 9 at a first rotation speed. As a result, the major axis of the ellipse of the external gear 20 also rotates at the first rotation speed. Then, the meshing position between the external teeth 22 and the internal teeth 11 also changes in the circumferential direction at the first rotation speed. Also, as described above, the number of the internal teeth 11 of the internal gear 10 and the number of the external teeth 22 of the external gear 20 are slightly different. Due to this difference in the number of teeth, the meshing position between the external teeth 22 and the internal teeth 11 changes slightly in the circumferential direction for each rotation of the cam 31. As a result, the external gear 20 rotates around the central axis 9 with respect to the internal gear 10 at a second rotation speed lower than the first rotation speed.

[0030] <3. Torque sensors> <3-1. Torque sensor configuration> The external gear 20 is equipped with a torque sensor 40. The torque sensor 40 is a sensor for detecting torque applied to the external gear 20. The torque sensor 40 is disposed on a diaphragm portion 232 of the external gear 20. Specifically, the diaphragm portion 232 has a surface 234 that intersects with the central axis 9 and spreads out in an annular shape centered on the central axis 9. The surface 234 is the surface on the other axial side of the diaphragm portion 232. The torque sensor 40 is fixed to the surface 234 of the diaphragm portion 232.

[0031] In this embodiment, the torque sensor 40 is disposed on one of both surfaces of the diaphragm portion 232 on the other axial side that does not face the external teeth 22. That is, the external gear 20 has a strain gauge 42, which will be described later. The strain gauge 42 is disposed on the other axial side of the diaphragm portion 232. In this way, even if the strain gauge 42 is disposed on the diaphragm portion 232, the space on one axial side of the diaphragm portion 232 can be widely utilized. Furthermore, when manufacturing the external gear 20, it is easy to dispose the strain gauge 42 on the diaphragm portion 232 without touching the external teeth 22. This facilitates the work of attaching the strain gauge 42 to the diaphragm portion 232.

[0032] However, the torque sensor 40 may be disposed on a surface on one axial side of the diaphragm portion 232. That is, the torque sensor 40 only needs to be disposed on at least one of the surface on one axial side and the surface on the other axial side of the diaphragm portion 232. In other words, the external gear 20 has a strain gauge 42 disposed on at least one of the surface on one axial side and the surface on the other axial side of the diaphragm portion 232.

[0033] Moreover, in this embodiment, the torque sensor 40 is located radially inside the thick portion 233. Therefore, a part of the thick portion 233 and the torque sensor 40 are arranged at the same axial position based on the axial position of the diaphragm portion 232. In this way, the thick portion 233 and the torque sensor 40 can be arranged in a narrower axial range than when the thick portion 233 and the torque sensor 40 are arranged at different axial positions. Therefore, even if the torque sensor 40 is arranged, the axial dimension of the entire external gear 20 including the torque sensor 40 can be reduced.

[0034] Fig. 4 is a plan view of the torque sensor 40. Fig. 5 is a partial vertical cross-sectional view of the external gear 20 in the vicinity of the torque sensor 40. As shown in Figs. 4 and 5, the torque sensor 40 has an insulating layer 41 and a strain gauge 42.

[0035] The insulating layer 41 is a flexibly deformable substrate. The insulating layer 41 extends in a direction intersecting the central axis 9. The insulating layer 41 is made of an insulating resin or an inorganic insulating material. The insulating layer 41 is disposed on the surface 234 of the diaphragm portion 232. The insulating layer 41 has a main body portion 411 and a flap portion 412. The main body portion 411 is an annular portion centered on the central axis 9. The flap portion 412 is a portion that protrudes radially outward from the main body portion 411.

[0036] The strain gauge 42 is formed on the surface of the insulating layer 41. The strain gauge 42 is made of a metal that is a conductor. The material of the strain gauge 42 is, for example, a copper alloy, a chromium alloy, or copper. The strain gauge 42 has a first resistance wire W1 to a fourth resistance wire W4. The first resistance wire W1 to the fourth resistance wire W4 are connected to an external electric circuit via electrodes (not shown) provided on the flap portion 412.

[0037] The first resistance wire W1 is an arc-shaped pattern as a whole, in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, the first resistance wire W1 is provided in a semicircular shape within a range of about 180° centered on the central axis 9. FIG. 6 is a partial plan view of the torque sensor 40. As shown in FIG. 6, the first resistance wire W1 includes a plurality of first detection wires w1. The plurality of first detection wires w1 are arranged in the circumferential direction in a substantially parallel posture. Each of the first detection wires w1 is inclined toward one side in the circumferential direction with respect to the radial direction. The inclination angle of the first detection wires w1 with respect to the radial direction is, for example, 45°. The ends of the first detection wires w1 adjacent to each other in the circumferential direction are alternately connected to each other on the radial inner side or the radial outer side. As a result, the plurality of first detection wires w1 are connected in series as a whole.

[0038] The second resistance wire W2 is an overall arc-shaped pattern in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, the second resistance wire W2 is provided in a semicircular shape within a range of approximately 180° centered on the central axis 9. The second resistance wire W2 includes a plurality of second detection wires (not shown). The plurality of second detection wires are arranged in the circumferential direction in a substantially parallel posture to each other. Each second detection wire is inclined toward the other circumferential side with respect to the radial direction. The inclination angle of the second detection wire with respect to the radial direction is, for example, 45°. Ends of the second detection wires adjacent to each other in the circumferential direction are alternately connected on the radial inner side or the radial outer side. As a result, the plurality of second detection wires are connected in series as a whole.

[0039] The first resistance wire W1 and the second resistance wire W2 are arranged concentrically and line-symmetrically. The radial distance from the central axis 9 to the first resistance wire W1 is approximately the same as the radial distance from the central axis 9 to the second resistance wire W2.

[0040] The third resistance wire W3 is an arc-shaped pattern as a whole, in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, the third resistance wire W3 is provided in a semicircular shape within a range of about 180° centered on the central axis 9. As shown in FIG. 6, the third resistance wire W3 includes a plurality of third detection wires w3. The plurality of third detection wires w3 are arranged in the circumferential direction in a substantially parallel posture. Each of the third detection wires w3 is inclined toward the other circumferential side with respect to the radial direction. The inclination angle of the third detection wires w3 with respect to the radial direction is, for example, 45°. The ends of the third detection wires w3 adjacent to each other in the circumferential direction are alternately connected on the radial inner side or the radial outer side. As a result, the plurality of third detection wires w3 are connected in series as a whole.

[0041] The fourth resistance wire W4 is an arc-shaped pattern as a whole, in which a single conductor extends in the circumferential direction while being bent in a zigzag pattern. In this embodiment, the fourth resistance wire W4 is provided in a semicircular shape within a range of about 180° centered on the central axis 9. The fourth resistance wire W4 also includes a plurality of fourth detection wires (not shown). The plurality of fourth detection wires are arranged in the circumferential direction in a substantially parallel posture to each other. Each of the fourth detection wires is inclined toward one circumferential side with respect to the radial direction. The inclination angle of the fourth detection wire with respect to the radial direction is, for example, 45°. The ends of the fourth detection wires adjacent to each other in the circumferential direction are alternately connected to each other on the inside or outside of the radial direction. As a result, the plurality of fourth detection wires are connected in series as a whole.

[0042] The third resistance wire W3 and the fourth resistance wire W4 are arranged concentrically and line-symmetrically. The radial distance from the central axis 9 to the third resistance wire W3 is substantially the same as the radial distance from the central axis 9 to the fourth resistance wire W4. The third resistance wire W3 and the fourth resistance wire W4 are located radially inward of the first resistance wire W1 and the second resistance wire W2.

[0043] FIG. 7 is a circuit diagram of a bridge circuit 43 including the first resistance wire W1 to the fourth resistance wire W4. As shown in FIG. 7, the first resistance wire W1 to the fourth resistance wire W4 are incorporated into the bridge circuit 43. The first resistance wire W1 and the second resistance wire W2 are connected in series in this order. The third resistance wire W3 and the fourth resistance wire W4 are connected in series in this order. Then, between the positive and negative poles of the power supply voltage, the series of the first resistance wire W1 and the second resistance wire W2 and the series of the third resistance wire W3 and the fourth resistance wire W4 are connected in parallel. In addition, a midpoint 431 of the first resistance wire W1 and the second resistance wire W2 and a midpoint 432 of the third resistance wire W3 and the fourth resistance wire W4 are connected to a voltmeter V.

[0044] The resistance value of each of the detection lines, the first resistance line W1 to the fourth resistance line W4, changes according to the torque applied to the diaphragm portion 232. For example, when a torque is applied to the diaphragm portion 232 in one circumferential direction about the central axis 9, the resistance value of each of the first detection lines w1 and the fourth detection lines decreases, and the resistance value of each of the second detection lines and the third detection lines w3 increases. On the other hand, when a torque is applied to the external gear 20 in the other circumferential direction about the central axis 9, the resistance value of each of the first detection lines w1 and the fourth detection lines increases, and the resistance value of each of the second detection lines and the third detection lines w3 decreases. In this way, the first resistance line W1 and the fourth resistance line W4 and the second resistance line W2 and the third resistance line W3 show resistance value changes in opposite directions with respect to torque.

[0045] When the resistance values ​​of the first resistance wire W1 to the fourth resistance wire W4 change, the potential difference between the midpoint 431 of the first resistance wire W1 and the second resistance wire W2 and the midpoint 432 of the third resistance wire W3 and the fourth resistance wire W4 changes, and the measurement value of the voltmeter V also changes. Therefore, based on the measurement value of the voltmeter V, the direction and magnitude of the torque applied to the diaphragm portion 232 can be detected.

[0046] <3-2. Strain gauge position> Fig. 8 is a graph showing the distribution of strain in diaphragm portion 232 when diaphragm portion 232 is elliptical deformed. Fig. 8 shows the results of a structural analysis of diaphragm portion 232. In the graph of Fig. 8, the horizontal axis indicates radial position R. Specifically, the horizontal axis indicates a value made dimensionless by dividing the distance from central axis 9 by the distance from central axis 9 to the radial outer end of diaphragm portion 232.

[0047] In the graph of FIG. 8, two types of strain are plotted: detected strain S1 and equivalent strain S2. The detected strain S1 indicates the magnitude of the shear strain (the shear strain (εrθ) in a cylindrical coordinate system with the central axis 9 as the reference axis) generated in the diaphragm portion 232 due to elliptical deformation. In the graph of FIG. 8, the detected strain S1 is normalized by dividing by the maximum absolute value. The equivalent strain S2 is a single scalar value (amount of strain corresponding to the von Mises stress) that represents the multi-directional strain at each radial position. In the graph of FIG. 8, the equivalent strain S2 is normalized by dividing by the maximum value.

[0048] 8, both the detected strain S1 and the equivalent strain S2 are large near the radial inner end of the radial range Rd of the diaphragm portion 232. Also, near the radial outer end of the radial range Rd of the diaphragm portion 232, the detected strain S1 is small but the equivalent strain S2 is large.

[0049] Therefore, in the torque sensor 40 of this embodiment, the strain gauges 42 are arranged only near the center of the diaphragm portion 232 in the radial direction, as shown in Fig. 5 and Fig. 6. Specifically, the radial region Rg in which the strain gauges 42 are arranged is set to a region that is equal to or less than half the radial length from the radial outer end to the radial inner end of the diaphragm portion 232, with the radial midpoint Rm between the radial outer end and the radial inner end of the diaphragm portion 232 in the cross section passing through the central axis 9 as the center. In other words, the strain gauges 42 are arranged only in a region that is equal to or less than half the radial length from one radial end to the other radial end of the diaphragm portion 232, with the radial midpoint Rm between one radial end and the other radial end of the diaphragm portion 232 in the cross section passing through the central axis 9 as the center. In other words, the entire radial region Rg in which the strain gauges 42 are arranged is included within the radial range Rd of the diaphragm portion 232.

[0050] In this way, if the strain gauge 42 is disposed only near the radial midpoint Rm of the diaphragm portion 232, the strain gauge 42 does not detect strain near the radial inner end and the radial outer end. As shown in the graph of FIG. 8, the amount of change in the detected strain S1 and the equivalent strain S2 are both small near the radial midpoint Rm. The strain gauge 42 detects only a stable amount of strain near the radial midpoint Rm. Therefore, the torque sensor 40 can accurately detect the torque applied to the external gear 20.

[0051] Furthermore, if the strain gauges 42 are arranged in a wide radial region of the diaphragm portion 232, large strains may occur in the diaphragm portion 232 near the radial inner end and the radial outer end of the diaphragm portion 232 due to elliptical deformation or a force in the central axis direction, and a large load may be applied to the strain gauges 42. However, in this embodiment, the strain gauges 42 are arranged only in an area equal to or less than half of the radial range Rd centered on the radial midpoint Rm, so that it is possible to prevent a large load from being applied to the strain gauges 42.

[0052] The strain gauges 42 are preferably arranged only in an area that is 40% or less of the radial length from one radial end to the other radial end of the diaphragm portion 232, with the radial midpoint Rm between one radial end and the other radial end of the diaphragm portion 232 as the center. In other words, it is more desirable that the area Rg in which the strain gauges 42 are arranged is an area that is 40% or less of the radial length from the radial outer end to the radial inner end of the diaphragm portion 232, with the radial midpoint Rm between the radial outer end and the radial inner end of the diaphragm portion 232 as the center. This enables the torque sensor 40 to detect the torque applied to the external gear 20 with higher accuracy.

[0053] Further, it is more desirable that the region Rg where the strain gauge 42 is disposed be a region that is 30% or less of the radial length from the radially outer end to the radially inner end of the diaphragm portion 232, centered on the radial midpoint Rm between the radially outer end and the radially inner end of the diaphragm portion 232. Thereby, the torque sensor 40 can detect the torque applied to the external gear 20 with higher accuracy.

[0054] As shown in FIG. 6, the strain gauge 42 of the present embodiment has a first gauge portion G1 and a second gauge portion G2. The first gauge portion G1 is composed of the first resistance wire W1 and the second resistance wire W2 described above. The second gauge portion G2 is composed of the third resistance wire W3 and the fourth resistance wire W4 described above. The first gauge portion G1 is disposed more radially outward than the second gauge portion G2. The radially outer end of the first gauge portion G1 is disposed more radially outward than the radial midpoint Rm of the diaphragm portion 232. The radially inner end of the second gauge portion G2 is disposed more radially inward than the radial midpoint Rm of the diaphragm portion 232.

[0055] In the present embodiment, the radially inner end of the first gauge portion G1 is disposed at substantially the same radial position as the radial midpoint Rm of the diaphragm portion 232. Also, the radially outer end of the second gauge portion G2 is disposed at substantially the same radial position as the radial midpoint Rm of the diaphragm portion 232. By doing so, the first gauge portion G1 and the second gauge portion G2 can be disposed in a state of being close to each other in the radial direction near the radial midpoint Rm of the diaphragm portion 232. Therefore, the entire first gauge portion G1 and the second gauge portion G2 can be disposed in a region where errors are less likely to occur. Also, compared with the case where the first gauge portion G1 and the second gauge portion G2 are disposed with a wide gap in the radial direction, the errors of the first gauge portion G1 and the second gauge portion G2 are reduced. Thus, for example, when differential output is performed by taking the difference in output between the first gauge portion G1 and the second gauge portion G2, the error of the differential output is reduced.

[0056] In particular, in this embodiment, the radial length of the first gauge section G1 and the radial length of the second gauge section G2 are approximately equal to each other, which can suppress a difference in the magnitude of error between the first gauge section G1 and the second gauge section G2.

[0057] <4. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. In the following, various modified examples will be described, focusing on the differences from the above embodiment. In addition, in the following description of the modified examples, the same reference numerals are used in the description of each part in order to facilitate understanding of the differences between the above embodiment and the modified examples.

[0058] <4-1. First modified example> Fig. 9 is a partial plan view of the torque sensor 40 according to the first modified example. In the example of Fig. 9, the radial inner end of the first gauge section G1 is disposed radially outward from the radial midpoint Rm of the diaphragm section 232. Moreover, the radial outer end of the second gauge section G2 is disposed radially inward from the radial midpoint Rm of the diaphragm section 232. In this manner, a radial gap may be provided between the radial inner end of the first gauge section G1 and the radial outer end of the second gauge section G2.

[0059] However, it is desirable that the radial distance Rs between the radial inner end of the first gauge section G1 and the radial outer end of the second gauge section G2 is shorter than both the radial length R1 of the first gauge section G1 and the radial length R2 of the second gauge section G2. In other words, it is desirable that the first gauge section G1 and the second gauge section G2 are disposed in positions close to each other in the radial direction. This allows the entire first gauge section G1 and the second gauge section G2 to be disposed in an area where errors are unlikely to occur.

[0060] <4-2. Second modified example> Fig. 10 is a partial plan view of a torque sensor 40 according to a second modification. In the example of Fig. 10, the first gauge section G1 and the second gauge section G2 are arranged so as to partially overlap in the radial direction. Specifically, the radial inner end of the first gauge section G1 is arranged radially inward from the radial midpoint Rm of the diaphragm section 232. Moreover, the radial outer end of the second gauge section G2 is arranged radially outward from the radial midpoint Rm of the diaphragm section 232.

[0061] In this way, the first gauge section G1 and the second gauge section G2 can be entirely positioned closer to the radial midpoint Rm of the diaphragm section 232. Therefore, the first gauge section G1 and the second gauge section G2 can be positioned in an area where errors are less likely to occur. In addition, the first gauge section G1 and the second gauge section G2 can be positioned in a limited radial area, and the wiring area of ​​the first gauge section G1 and the second gauge section G2 can be made large.

[0062] <4-3.Third modified example> Fig. 11 is a partial plan view of a torque sensor 40 according to a third modified example. In the example of Fig. 11, the first gauge section G1 has a first inner gauge section G11 and a first outer gauge section G12. The first outer gauge section G12 is disposed radially outward from the first inner gauge section G11. The second gauge section G2 has a second inner gauge section G21 and a second outer gauge section G22. The second outer gauge section G22 is disposed radially outward from the second inner gauge section G21. In addition, the second outer gauge section G22 is disposed radially inward from the first inner gauge section G11.

[0063] In this way, more resistance wires can be arranged on one side of the insulating layer 41 than in the above embodiment. In the above embodiment, the torque sensor 40 has only one bridge circuit 43 including four resistance wires W1 to W4. In contrast, in the example of FIG. 11, two bridge circuits including four resistance wires can be provided. Therefore, the torque sensor 40 can output detection signals from the two bridge circuits, respectively. Therefore, by comparing the two detection signals, it can be confirmed that the two torque sensors 40 are operating normally.

[0064] <4-4. Fourth modified example> FIG. 12 is a partial plan view of the torque sensor 40 according to the fourth modification. In the example of FIG. 12, both the first gauge portion G1 and the second gauge portion G2 are disposed radially outward from the radial midpoint Rm of the diaphragm portion 232. That is, in the example of FIG. 12, the strain gauge 42 is disposed only on one radial side from the radial midpoint Rm of the diaphragm portion 232. In this way, the region radially inward from the radial midpoint Rm of the diaphragm portion 232 can be effectively utilized for purposes other than disposing the strain gauge 42. In addition, by disposing the strain gauge 42 radially outward from the radial midpoint Rm of the diaphragm portion 232, the strain gauge 42 can be disposed in a longer circumferential region.

[0065] The strain gauge 42 may be disposed only on the other radial side of the radial midpoint Rm of the diaphragm portion 232. In that case, the region radially outward of the radial midpoint Rm of the diaphragm portion 232 can be effectively utilized for purposes other than disposing the strain gauge 42. Thus, a longer circumferential region of the diaphragm portion 232 can be utilized for other purposes.

[0066] <4-5. Other variations> In the above embodiment, the strain gauge 42 is disposed on the surface of the insulating layer 41, which is a flexibly deformable substrate. However, the strain gauge 42 may be disposed on the surface 234 of the diaphragm portion 232. For example, an insulating film is formed on the surface 234 of the diaphragm portion 232, and a conductor layer is formed on the surface of the insulating film by sputtering or the like. Then, unnecessary portions of the conductor layer are removed by chemical means such as etching or physical means such as a laser, to form the strain gauge 42. For the insulating film, for example, an inorganic insulating material is used.

[0067] A signal processing circuit that processes detection signals of the strain gauges 42 may be attached to the external gear 20 together with the strain gauges 42. Alternatively, the signal processing circuit may be provided at a position away from the external gear 20. In other words, the external gear 20 may be one that is equipped with at least the strain gauges 42, which are resistance wire patterns, of the torque sensor 40.

[0068] Furthermore, the external gear 20 may further include a rotation angle sensor that detects the rotation angle of the rotational motion input to the external gear 20. In this case, periodic errors in the detection signal of the torque sensor 40 can be corrected based on the detection value of the rotation angle detection sensor. Therefore, the torque applied to the external gear 20 can be detected with higher accuracy.

[0069] Furthermore, the external gear 20 may further include a temperature sensor that measures the temperature of the external gear 20. In this case, errors in the detection signal of the torque sensor 40 caused by temperature changes can be corrected based on the detection value of the temperature sensor. Therefore, the torque applied to the external gear 20 can be detected with higher accuracy.

[0070] In the above embodiment, the torque sensor 40 has four resistance wires, the first resistance wire W1 to the fourth resistance wire W4. The bridge circuit 43 is a full bridge circuit including the four resistance wires, the first resistance wire W1 to the fourth resistance wire W4. However, the torque sensor 40 may have only two resistance wires. In that case, the bridge circuit 43 may be a half bridge circuit configured with the two resistance wires and two fixed resistors.

[0071] Moreover, the external gear 20 in the above embodiment is a so-called "hat-shaped" gear in which the diaphragm portion 232 spreads radially outward from the body portion 21. The hat-shaped external gear 20 is excellent in that it can effectively utilize the space on the radial inside of the body portion 21. However, the external gear 20 may be a so-called "cup-shaped" gear in which the diaphragm portion 232 spreads radially inward from the body portion 21. In the case of the cup-shaped external gear 20, the "radial inner side" corresponds to the "one radial side", and the "radial outer side" corresponds to the "other radial side". Therefore, the "radial inner end" corresponds to the "one radial end", and the "radial outer end" corresponds to the "other radial end".

[0072] In the above embodiment, a description has been given of the wave reducer 1 mounted on the robot 100. However, a wave reducer 1 having a similar structure may be mounted on other devices such as an assist suit or an unmanned transport vehicle.

[0073] Other details of the configuration of the external gear, the strain wave reducer, and the robot may be modified as appropriate without departing from the spirit of the present invention. Furthermore, the elements appearing in each of the above embodiments and modified examples may be combined as appropriate without causing any contradiction. [Industrial Applicability]

[0074] The present application can be used in an external gear, a strain wave reducer, and a robot. [Explanation of symbols]

[0075] 1 Wave reducer 9 Center axis 10 Internal gear 11 Inner teeth 20 External gear 21 Torso 22 Outer teeth 23 Disc section 30 Wave Generator 31 Cam 32 Flexible bearings 40 Torque Sensor 41 Insulating layer 42 Strain Gauge 43 Bridge Circuit 100 Robots 231 Curved section 232 Diaphragm part 233 Thick part G1 First gauge section G2 2nd gauge section Rd Radial range of the diaphragm Rg The radial area where the strain gauge is located Rm Diaphragm part radial midpoint W1 First resistance line W2 Second resistance line W3 3rd resistance wire W4 4th resistance wire

Claims

1. A cylindrical body portion extending in an axial direction parallel to a central axis; A plurality of external teeth are disposed on one axial side of the body portion and extend radially outward; a diaphragm portion extending in a direction intersecting the axial direction on the other axial side of the body portion; a first strain gauge disposed on at least one of a surface on one axial side and a surface on the other axial side of the diaphragm portion; a first bridge circuit including the first strain gauge; having The first strain gauge comprises: A first resistance wire having an arc-shaped pattern as a whole centered on the central axis; A second resistance wire having an arc-shaped pattern as a whole about the central axis and arranged line-symmetrically with the first resistance wire; a third resistance wire having an arc-shaped pattern as a whole about the central axis and located on the other radial side of the first resistance wire; a fourth resistance wire having an overall arc-shaped pattern centered on the central axis and arranged line-symmetrically with the third resistance wire; an external gear, wherein the first strain gauge is arranged only in an area that is less than half the radial length from one radial end to the other radial end of the diaphragm portion, centered on a radial midpoint between one radial end and the other radial end of the diaphragm portion in a cross section passing through the central axis.

2. The external gear according to claim 1 , wherein the first strain gauge is disposed only on one radial side or only on the other radial side of the radial midpoint of the diaphragm portion.

3. A radial end of the first resistance wire is disposed radially on one side of the radial midpoint of the diaphragm portion, The external gear according to claim 1 , wherein the other radial end of the third resistance wire is disposed on the other radial side of the radial midpoint of the diaphragm portion.

4. An externally toothed gear as described in claim 3, wherein the radial distance between the other radial end of the first resistance wire and one radial end of the third resistance wire is shorter than either the radial length of the first resistance wire or the radial length of the third resistance wire.

5. An externally toothed gear as described in claim 3 or 4, wherein the radial length of the first resistance wire and the radial length of the third resistance wire are approximately equal.

6. The other radial end of the first resistance wire is disposed on the other radial side of the radial midpoint of the diaphragm portion, The external gear according to claim 4 or 5, wherein one radial end of the third resistance wire is disposed on one radial side of the radial midpoint of the diaphragm portion.

7. A second strain gauge arranged radially on the other side of the first strain gauge; a second bridge circuit including the second strain gauge; The second strain gauge comprises: A fifth resistance wire having an overall arc-shaped pattern centered on the central axis; A sixth resistance wire having an overall arc-shaped pattern centered on the central axis and arranged line-symmetrically with the fifth resistance wire; A seventh resistance wire having an arc-shaped pattern as a whole about the central axis and located on the other radial side of the fifth resistance wire; an eighth resistance wire having an overall arc-shaped pattern centered on the central axis and arranged line-symmetrically with the seventh resistance wire; 2. The external gear according to claim 1, wherein the second strain gauge is arranged only in an area that is equal to or less than half of the radial length from one radial end to the other radial end of the diaphragm portion, with a radial midpoint between the one radial end and the other radial end of the diaphragm portion in a cross section passing through the central axis as a center.

8. A radial end of the first strain gauge is disposed radially on one side of the radial midpoint of the diaphragm portion, the other radial end of the second strain gauge is disposed on the other radial side of the radial midpoint of the diaphragm portion, 8. The external gear according to claim 7, wherein a radial distance between the other radial end of the first strain gauge and one radial end of the second strain gauge is shorter than both of a radial length of the first strain gauge and a radial length of the second strain gauge.

9. An externally toothed gear as described in claim 8, wherein the radial length of the first strain gauge and the radial length of the second strain gauge are approximately equal.

10. The other radial end of the first strain gauge is disposed on the other radial side of the radial midpoint of the diaphragm portion, 10. The external gear according to claim 8, wherein one radial end of the second strain gauge is disposed on one radial side of the radial midpoint of the diaphragm portion.

11. An externally toothed gear as described in any one of claims 1 to 10, having at least one of: a sensor capable of outputting a detection value corresponding to the rotational angle of the rotational motion input to the externally toothed gear, for correcting the detection signal of the first bridge circuit based on the detection value, and a temperature sensor capable of measuring the temperature of the externally toothed gear, for correcting the detection signal of the bridge circuit based on the temperature.

12. An external gear according to any one of claims 1 to 11; an internal gear having a plurality of internal teeth disposed radially outward from the external teeth and extending radially inward; a wave generator disposed radially inward of the external gear and rotatable about the central axis; A wave reducer having a

13. An apparatus comprising the wave reducer according to claim 12.

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