Mechanical parts, power transmission systems, and robots

Abstract

To provide a technique of reducing errors due to missing of detection resulting from a gap region where a stain gauge is not arranged.SOLUTION: A mechanical part has a base part and a plurality of strain gauges. The base part extends in a direction intersecting the central axis. The plurality of strain gauges are arranged in the base part. The strain gauges are arranged in a circumferential direction about the central axis. A plurality of gap regions are arranged between the strain gauges next to each other in the circumferential direction. The gap regions include gap regions arranged at 90 degree-angular intervals about the central axis.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a mechanical component, a power transmission device, and a robot. [Background Art]

[0002] In recent years, demand for strain wave gearing mounted in robot joints and the like has been increasing. A conventional strain wave gearing has a plurality of strain gauges. The strain gauges are affixed to an external gear that rotates at the rotational speed after speed reduction. This enables detection of torque applied to the external gear (Patent Document 1).

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-131160 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] However, the external gear in Patent Document 1 is flexurally deformed by a wave generator having an elliptical contour. For this reason, not only torque due to external force that is originally desired to be measured, but also sinusoidal torque caused by flexural deformation from the wave generator (hereinafter referred to as "ripple torque") is generated in the external gear. The strain gauges detect this ripple torque together with torque generated in the external gear by external force.

[0005] Further, the plurality of strain gauges are arranged at intervals in the circumferential direction on the surface of the external gear. For this reason, ripple torque applied to the external gear is not detected in gap regions between adjacent strain gauges in the circumferential direction. Such undetected ripple torque due to detection deficiency becomes a cause of error in torque detection.

[0006] An object of the present invention is to provide a technology capable of reducing errors caused by detection deficiency attributable to gap regions where no strain gauges are arranged. [Means for Solving the Problem]

[0007] The first invention is a mechanical part comprising a base portion extending in a direction intersecting the central axis, and a plurality of strain gauges arranged on the base portion, wherein the plurality of strain gauges are arranged in a circumferential direction about the central axis, and a plurality of gap regions are arranged between adjacent strain gauges in the circumferential direction, and the plurality of gap regions include gap regions arranged at an angular interval of 90° about the central axis.

[0008] The second invention is a mechanical part comprising a base portion extending in a direction intersecting the central axis, and a plurality of strain gauges arranged on the base portion, wherein the plurality of strain gauges are arranged in a circumferential direction about the central axis, and a plurality of gap regions are arranged between adjacent strain gauges in the circumferential direction, and the plurality of gap regions include gap regions arranged at an angular interval of 60° about the central axis. [Effects of the Invention]

[0009] According to the first and second inventions, errors due to detection defects caused by gap areas where strain gauges are not placed can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of the robot. [Figure 2] Figure 2 is a longitudinal cross-sectional view of the power transmission device. [Figure 3] Figure 3 is a cross-sectional view of the power transmission device as seen from position AA in Figure 2. [Figure 4] Figure 4 is a partial longitudinal cross-sectional view of the external gear near the sensor substrate. [Figure 5] Figure 5 is a plan view of the sensor substrate. [Figure 6] Figure 6 is a partial plan view of the sensor substrate. [Figure 7] Figure 7 is the circuit diagram of the first bridge circuit. [Figure 8] Figure 8 is the circuit diagram of the second bridge circuit. [Figure 9]Fig. 9 is a graph showing ripple torque detected by a torque sensor. [Figure 10] Fig. 10 is an enlarged view of the gap region. [Figure 11] Fig. 11 is an enlarged view of the gap region. [Figure 12] Fig. 12 is a plan view of a sensor substrate according to a first modified example. [Figure 13] Fig. 13 is a plan view of a cam according to a second modified example. DESCRIPTION OF EMBODIMENTS

[0011] Hereinafter, exemplary embodiments of the present application will be described with reference to the drawings.

[0012] <1. Robot> Fig. 1 is a schematic diagram of a robot 100 including a power transmission device 1 according to an embodiment. The robot 100 is, for example, a so-called industrial robot that performs operations such as component conveyance, processing, and assembly on an industrial product manufacturing line. As shown in Fig. 1, the robot 100 includes a base frame 101, an arm 102, a motor 103, and the power transmission device 1.

[0013] The arm 102 is rotatably supported with respect to the base frame 101. The motor 103 and the power transmission device 1 are incorporated in a joint portion between the base frame 101 and the arm 102. When a drive current is supplied to the motor 103, rotational motion is output from the motor 103. The rotational motion output from the motor 103 is decelerated by the power transmission device 1 and transmitted to the arm 102. Thereby, the arm 102 rotates at the speed after deceleration with respect to the base frame 101.

[0014] Since the robot 100 includes the power transmission device 1, the robot 100 with small torque detection errors can be realized by the mechanism described later.

[0015] <2. Configuration of Power Transmission Device> Next, the detailed structure of the power transmission device 1 will be described.

[0016] In the following description, a direction parallel to the central axis 9 of the power transmission device 1 is referred to as an "axial direction", a direction orthogonal to the central axis 9 of the power transmission device 1 is referred to as a "radial direction", and a direction along an arc centered on the central axis 9 of the power transmission device 1 is referred to as a "circumferential direction". However, the aforementioned "parallel direction" includes substantially parallel directions. In addition, the aforementioned "orthogonal direction" includes substantially orthogonal directions.

[0017] Fig. 2 is a longitudinal sectional view of the power transmission device 1 according to an embodiment. Fig. 3 is a cross-sectional view of the power transmission device 1 taken from the position A-A in Fig. 2. To avoid complexity of the drawing, hatching indicating a cross-section is omitted in Fig. 3.

[0018] This power transmission device 1 is a wave reducer. The power transmission device 1 reduces the rotational motion at a first rotational speed obtained from the motor 103 to a second rotational speed slower than the first rotational speed. As shown in Fig. 2 and Fig. 3, the power transmission device 1 includes an internal gear 20, an external gear 30, and a wave generator 40. The power transmission device 1 of the present embodiment further includes an input shaft 10.

[0019] The input shaft 10 is a member that rotates at the first rotational speed before speed reduction. The input shaft 10 is connected to an output shaft of the motor 103. The input shaft 10 extends axially along the central axis 9. The input shaft 10 of the present embodiment has a cylindrical shape centered on the central axis 9. The input shaft 10 penetrates the power transmission device 1 in the axial direction. Note that the input shaft 10 may be the same member as the output shaft of the motor 103.

[0020] The internal gear 20 is a mechanical component that rotates at a second rotational speed lower than the first rotational speed as the input shaft 10 rotates. The internal gear 20 is fixed to an arm 102. The internal gear 20 is arranged radially outward of external teeth 32 which will be described later. The rigidity of the internal gear 20 is sufficiently higher than the rigidity of a body portion 31 of the external gear 30 which will be described later.

[0021] The internal gear 20 is annular in shape with a central axis 9. The internal gear 20 has a plurality of internal teeth 21. The plurality of internal teeth 21 protrude radially inward from the radially inner surface of the internal gear 20. The plurality of internal teeth 21 are arranged at a constant pitch in the circumferential direction on the inner circumferential surface of the internal gear 20.

[0022] The external gear 30 is a flexibly deformable annular mechanical component. The external gear 30 is fixed to the base frame 101. As shown in Figures 2 and 3, the external gear 30 has a body 31, a plurality of external teeth 32, a base portion 33, and a thick portion 34.

[0023] The body portion 31 is a cylindrical part centered on the central axis 9. One axial end of the body portion 31 is connected to the base portion 33. The body portion 31 extends from the radially inner end of the base portion 33 toward the other axial end. The other axial end of the body portion 31 is located radially outward of the wave generator 40 and radially inward of the internal gear 20. Because the body portion 31 is flexible, it can bend and deform radially.

[0024] Multiple external teeth 32 protrude radially outward from the radially outer surface of the body portion 31. Multiple external teeth 32 are arranged on the radially outer surface of the other axial end of the body portion 31. Multiple external teeth 32 are arranged at a constant pitch in the circumferential direction. Some of the multiple external teeth 32 mesh with some of the multiple internal teeth 21 described above. The number of internal teeth 21 in the internal gear 20 and the number of external teeth 32 in the external gear 30 are slightly different.

[0025] The base portion 33 surrounds the central axis 9 and extends in a direction intersecting the central axis 9. Preferably, the base portion 33 extends along a plane perpendicular to the central axis 9. The base portion 33 extends radially outward from one axial end of the body portion 31. The base portion 33 is also annular, surrounding the central axis 9. Because the base portion 33 is thin-walled, it is slightly flexible and deformable.

[0026] The thickened portion 34 is an annular portion located radially outward from the base portion 33. The axial thickness of the thickened portion 34 is greater than the axial thickness of the base portion 33. The thickened portion 34 is fixed to the base frame 101 either directly or via other components.

[0027] The wave generator 40 is a mechanism that generates periodic deflection deformation in the external gear 30. The wave generator 40 is positioned radially inward of the external teeth 32. The wave generator 40 includes a cam 41 and a flexible bearing 42. In this embodiment, the input shaft 10 and the cam 41 are formed from a single part. However, the cam 41 may be a separate part from the input shaft 10. In that case, it is sufficient that the cam 41 is fixed to the input shaft 10. The cam 41 is a part that imparts displacement to the external gear 30 with a period of 180°. The radially outer surface of the cam 41 is elliptical with respect to the central axis 9.

[0028] The flexible bearing 42 is a bearing that can be deformed by bending. The flexible bearing 42 is positioned between the radially outer surface of the cam 41 and the radially inner surface of the body 31 of the external gear 30.

[0029] The inner ring of the flexible bearing 42 contacts the radially outer surface of the cam 41. The outer ring of the flexible bearing 42 contacts the radially inner surface of the body 31. As a result, the body 31 deforms into an elliptical shape along the radially outer surface of the cam 41. Consequently, at two locations corresponding to the ends of the major axis of the ellipse, the external teeth 32 of the external gear 30 and the internal teeth 21 of the internal gear 20 mesh. At other locations in the circumferential direction, the external teeth 32 and the internal teeth 21 do not mesh.

[0030] When the motor 103 is driven, the cam 41 rotates at a first rotational speed around the central axis 9 along with the input shaft 10. As a result, the major axis of the ellipse of the external gear 30 also rotates at the first rotational speed. Consequently, the meshing position between the external teeth 32 and the internal teeth 21 also changes circumferentially at the first rotational speed. Furthermore, as mentioned above, the number of internal teeth 21 of the internal gear 20 and the number of external teeth 32 of the external gear 30 are slightly different. Due to this difference in the number of teeth, the meshing position between the external teeth 32 and the internal teeth 21 changes slightly circumferentially with each rotation of the cam 41. As a result, the internal gear 20 rotates around the central axis 9 with respect to the external gear 30 at a second rotational speed that is slower than the first rotational speed.

[0031] <3. About Torque Sensors> The power transmission device 1 has a torque sensor 50. The torque sensor 50 is a sensor for detecting the torque applied to the base portion 33 of the external gear 30 described above. As shown in Figure 2, the torque sensor 50 has a sensor substrate 51. The sensor substrate 51 is fixed to the surface of the base portion 33. Figure 4 is a partial longitudinal cross-sectional view of the external gear 30 near the sensor substrate 51. Figure 5 is a plan view of the sensor substrate 51. As shown in Figures 4 and 5, the sensor substrate 51 has an insulating layer 511 and a conductive layer 512.

[0032] The insulating layer 511 is flexibly deformable. The insulating layer 511 extends in a direction intersecting the central axis 9. The insulating layer 511 is also annular in shape with the central axis 9 at its center. The insulating layer 511 is made of an insulating resin or inorganic insulating material. The insulating layer 511 is positioned on the surface of the base portion 33.

[0033] The conductive layer 512 is formed on the surface of the insulating layer 511. A conductive metal is used as the material for the conductive layer 512. For example, copper alloys, chromium alloys, or copper can be used as the material for the conductive layer 512. As shown in Figure 5, the conductive layer 512 has a plurality of first strain gauges W1 and a plurality of second strain gauges W2. The plurality of second strain gauges W2 are positioned radially outward from the plurality of first strain gauges W1.

[0034] The multiple first strain gauges W1 include multiple internal strain gauges W11 and multiple external strain gauges W12. The multiple external strain gauges W12 are positioned radially outward from the multiple internal strain gauges W11.

[0035] The internal strain gauge W11 has four strain gauges Ra, Rb, Rc, and Rd. The four strain gauges Ra, Rb, Rc, and Rd are spaced apart in the circumferential direction. Each of the four strain gauges Ra, Rb, Rc, and Rd is provided in an arc shape within a range of approximately 90° around the central axis 9. The four strain gauges Ra, Rb, Rc, and Rd are arranged concentrically. The radial distances from the central axis 9 to the four strain gauges Ra, Rb, Rc, and Rd are approximately the same.

[0036] Figure 6 is a partial plan view of the sensor substrate 51. As is typically shown for strain gauge Ra in Figure 6, the four strain gauges Ra, Rb, Rc, and Rd each have multiple resistance wires r1. The resistance wires r1 extend in a direction having both radial and circumferential components. The multiple resistance wires r1 are arranged circumferentially in a position approximately parallel to each other. Of the four strain gauges Ra, Rb, Rc, and Rd, the resistance wires r1 of two strain gauges, Ra and Rb, are inclined to one side in the circumferential direction with respect to the radial direction. The resistance wires r1 of the other two strain gauges, Rc and Rd, are inclined to the other side in the circumferential direction with respect to the radial direction. The inclination angle of the resistance wires r1 with respect to the radial direction is, for example, 45°. The ends of adjacent resistance wires r1 in the circumferential direction are alternately connected on the radially inward or radially outward side. As a result, the multiple resistance wires r1 are connected in series as a whole.

[0037] The external strain gauge W12 has four strain gauges Re, Rf, Rg, and Rh. The four strain gauges Re, Rf, Rg, and Rh are spaced apart in the circumferential direction. Each of the four strain gauges Re, Rf, Rg, and Rh is provided in an arc shape within a range of approximately 90° around the central axis 9. The four strain gauges Re, Rf, Rg, and Rh are arranged concentrically. The radial distances from the central axis 9 to the four strain gauges Re, Rf, Rg, and Rh are approximately the same.

[0038] As shown representatively in Figure 6 for strain gauge Re, the four strain gauges Re, Rf, Rg, and Rh each have multiple resistance wires r1. The resistance wires r1 extend in directions having both radial and circumferential components. The multiple resistance wires r1 are arranged circumferentially, approximately parallel to each other. Of the four strain gauges Re, Rf, Rg, and Rh, the resistance wires r1 of two strain gauges, Rg and Rh, are inclined to one side of the circumferential direction with respect to the radial direction. The resistance wires r1 of the other two strain gauges, Re and Rf, are inclined to the other side of the circumferential direction with respect to the radial direction. The inclination angle of the resistance wires r1 with respect to the radial direction is, for example, 45°. The ends of adjacent resistance wires r1 in the circumferential direction are alternately connected on the radially inward or radially outward side. This connects the multiple resistance wires r1 in series as a whole.

[0039] The multiple second strain gauges W2 include multiple internal strain gauges W21 and multiple external strain gauges W22. The multiple external strain gauges W22 are positioned radially outward from the multiple internal strain gauges W21.

[0040] The internal strain gauge W21 has four strain gauges Ri, Rj, Rk, and Rl. The four strain gauges Ri, Rj, Rk, and Rl are spaced apart in the circumferential direction. Each of the four strain gauges Ri, Rj, Rk, and Rl is provided in an arc shape within a range of approximately 90° around the central axis 9. The four strain gauges Ri, Rj, Rk, and Rl are arranged concentrically. The radial distances from the central axis 9 to the four strain gauges Ri, Rj, Rk, and Rl are approximately the same.

[0041] As shown in Figure 6, the four strain gauges Ri, Rj, Rk, and Rl each have multiple resistance wires r2. The resistance wires r2 extend in directions having both radial and circumferential components. The multiple resistance wires r2 are arranged circumferentially, approximately parallel to each other. Of the four strain gauges Ri, Rj, Rk, and Rl, the resistance wires r2 of two strain gauges, Ri and Rj, are inclined to one side of the circumferential direction with respect to the radial direction. The resistance wires r2 of the other two strain gauges, Rk and Rl, are inclined to the other side of the circumferential direction with respect to the radial direction. The inclination angle of the resistance wires r2 with respect to the radial direction is, for example, 45°. The ends of adjacent resistance wires r2 in the circumferential direction are alternately connected radially inward or radially outward. This connects the multiple resistance wires r2 in series as a whole.

[0042] The external strain gauge W22 has four strain gauges Rm, Rn, Ro, and Rp. The four strain gauges Rm, Rn, Ro, and Rp are spaced apart in the circumferential direction. The four strain gauges Rm, Rn, Ro, and Rp are each provided in an arc shape within a range of approximately 90° around the central axis 9. The four strain gauges Rm, Rn, Ro, and Rp are arranged concentrically. The radial distances from the central axis 9 to the four strain gauges Rm, Rn, Ro, and Rp are approximately the same.

[0043] As shown in Figure 6, the four strain gauges Rm, Rn, Ro, and Rp each have multiple resistance wires r2. The resistance wires r2 extend in directions having both radial and circumferential components. The multiple resistance wires r2 are arranged circumferentially, approximately parallel to each other. Of the four strain gauges Rm, Rn, Ro, and Rp, the resistance wires r2 of two strain gauges, Ro and Rp, are inclined to one side of the circumferential direction with respect to the radial direction. The resistance wires r2 of the other two strain gauges, Rm and Rn, are inclined to the other side of the circumferential direction with respect to the radial direction. The inclination angle of the resistance wires r2 with respect to the radial direction is, for example, 45°. The ends of adjacent resistance wires r2 in the circumferential direction are alternately connected radially inward or radially outward. This connects the multiple resistance wires r2 in series as a whole.

[0044] Note that the angle of inclination of the resistance wires r1 and r2 with respect to the radial direction may be other than 45°. For example, the angle of inclination of the resistance wires r1 and r2 with respect to the radial direction may be 30° or 60°.

[0045] Multiple first strain gauges W1 constitute a first bridge circuit C1. That is, multiple internal strain gauges W11 and multiple external strain gauges W12 constitute a first bridge circuit C1. By configuring the first bridge circuit C1 with multiple internal strain gauges W11 and multiple external strain gauges W12, the torque applied to the base section 33 can be detected with high accuracy. Figure 7 is a circuit diagram of the first bridge circuit C1. As shown in Figure 7, the first bridge circuit C1 is configured by connecting eight strain gauges Ra, Rb, Rc, Rd, Re, Rf, Rg, and Rh to each other.

[0046] Four strain gauges Ra, Rb, Rc, and Rd are connected in series in this order. Four strain gauges Re, Rf, Rg, and Rh are connected in series in this order. Then, between the positive and negative terminals of the power supply voltage, the rows of four strain gauges Ra, Rb, Rc, and Rd are connected in parallel to the rows of four strain gauges Re, Rf, Rg, and Rh. In addition, the first voltmeter V1 is connected between the midpoint M11 of two strain gauges Rb and Rc and the midpoint M12 of two strain gauges Rf and Rg.

[0047] The resistance values ​​of the resistance wires r1 of the eight strain gauges Ra, Rb, Rc, Rd, Re, Rf, Rg, and Rh change according to the torque applied to the base section 33. For example, when a torque is applied to the base section 33 in one direction in the circumferential direction around the central axis 9, the resistance values ​​of the resistance wires r1 of the four strain gauges Ra, Rb, Rg, and Rh decrease, while the resistance values ​​of the resistance wires r1 of the other four strain gauges Rc, Rd, Re, and Rf increase. On the other hand, when a torque is applied to the base section 33 in the other direction in the circumferential direction around the central axis 9, the resistance values ​​of the resistance wires r1 of the four strain gauges Ra, Rb, Rg, and Rh increase, while the resistance values ​​of the resistance wires r1 of the other four strain gauges Rc, Rd, Re, and Rf decrease. Thus, the four strain gauges Ra, Rb, Rg, and Rh, and the other four strain gauges Rc, Rd, Re, and Rf, exhibit resistance changes in opposite directions with respect to torque.

[0048] When the resistance values ​​of the four strain gauges Ra, Rb, Rg, and Rh change in opposite directions, the potential difference between the midpoint M11 of the two strain gauges Rb and Rc and the midpoint M12 of the two strain gauges Rf and Rg changes, and the measured value of the first voltmeter V1 also changes. Therefore, the direction and magnitude of the torque applied to the base section 33 can be detected based on the measured value of this first voltmeter V1.

[0049] Multiple second strain gauges W2 constitute a second bridge circuit C2. That is, multiple internal strain gauges W21 and multiple external strain gauges W22 constitute a second bridge circuit C2. By configuring the second bridge circuit C2 with multiple internal strain gauges W21 and multiple external strain gauges W22, the torque applied to the base section 33 can be detected with high accuracy. Figure 8 is a circuit diagram of the second bridge circuit C2. As shown in Figure 8, the second bridge circuit C2 is configured by connecting eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp to each other.

[0050] Four strain gauges Ri, Rj, Rk, and Rl are connected in series in this order. Four strain gauges Rm, Rn, Ro, and Rp are connected in series in this order. Then, between the positive and negative terminals of the power supply voltage, the rows of four strain gauges Ri, Rj, Rk, and Rl are connected in parallel to the rows of four strain gauges Rm, Rn, Ro, and Rp. In addition, a second voltmeter V2 is connected between the midpoint M21 of two strain gauges Rj and Rk and the midpoint M22 of two strain gauges Rn and Ro.

[0051] The resistance values ​​of the resistance wires r2 of the eight strain gauges Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp change according to the torque applied to the base section 33. For example, when a torque is applied to the base section 33 in one direction in the circumferential direction around the central axis 9, the resistance values ​​of the resistance wires r2 of the four strain gauges Ri, Rj, Ro, and Rp decrease, while the resistance values ​​of the resistance wires r2 of the other four strain gauges Rk, Rl, Rm, and Rn increase. On the other hand, when a torque is applied to the base section 33 in the other direction in the circumferential direction around the central axis 9, the resistance values ​​of the resistance wires r1 of the four strain gauges Ri, Rj, Ro, and Rp increase, while the resistance values ​​of the resistance wires r1 of the other four strain gauges Rk, Rl, Rm, and Rn decrease. Thus, the four strain gauges Ri, Rj, Ro, and Rp, and the other four strain gauges Rk, Rl, Rm, and Rn, exhibit resistance changes in opposite directions with respect to torque.

[0052] When the resistance values ​​of the four strain gauges Ri, Rj, Ro, and Rp change in opposite directions, the potential difference between the midpoint M21 of the two strain gauges Rj and Rk and the midpoint M22 of the two strain gauges Rn and Ro changes, and the measured value of the second voltmeter V2 also changes. Therefore, the direction and magnitude of the torque applied to the base section 33 can be detected based on the measured value of this second voltmeter V2.

[0053] The power transmission device 1 further comprises a housing 60 and a signal processing board 70. As shown in Figure 2, the housing 60 is located on one axial side of the external gear 30. The housing 60 covers the external gear 30 from one axial side. The housing 60 is fixed to the external gear 30.

[0054] The signal processing board 70 is fixed to the surface of the housing 60. The signal processing board 70 consists of an electrical circuit equipped with a microprocessor. The signal processing board 70 is electrically connected to the first bridge circuit C1 and the second bridge circuit C2. The signal processing board 70 detects the torque applied to the base section 33 based on the output signals of the first voltmeter V1 and the second voltmeter V2.

[0055] In particular, the torque sensor 50 of this embodiment has a plurality of first strain gauges W1 constituting a first bridge circuit C1 and a plurality of second strain gauges W2 constituting a second bridge circuit C2. Therefore, even if an abnormality occurs in one of the bridge circuits, torque can be detected by the other bridge circuit.

[0056] <4. Regarding the placement of strain gauges> As described above, in this embodiment, the external gear 30, which is a mechanical component, has multiple strain gauges Ra, Rb, Rc, Rd, Re, Rf, Rg, Rh, Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp. The multiple strain gauges Ra, Rb, Rc, Rd, Re, Rf, Rg, Rh, Ri, Rj, Rk, Rl, Rm, Rn, Ro, and Rp are arranged on the base portion 33.

[0057] The four strain gauges Ra, Rb, Rc, and Rd are arranged circumferentially around the central axis 9. Gap regions A are placed between adjacent strain gauges in the circumferential direction. The four gap regions A are arranged at 90° angular intervals around the central axis 9.

[0058] The four strain gauges Re, Rf, Rg, and Rh are arranged circumferentially around the central axis 9. Gap regions A are placed between adjacent strain gauges in the circumferential direction. The four gap regions A are arranged at 90° angular intervals around the central axis 9.

[0059] The four strain gauges Ri, Rj, Rk, and Rl are arranged circumferentially around the central axis 9. Gap regions A are placed between adjacent strain gauges in the circumferential direction. The four gap regions A are arranged at 90° angular intervals around the central axis 9.

[0060] The four strain gauges Rm, Rn, Ro, and Rp are arranged circumferentially around the central axis 9. Gap regions A are placed between adjacent strain gauges in the circumferential direction. The four gap regions A are arranged at 90° angular intervals around the central axis 9.

[0061] The external gear 30 is deflected by the elliptical cam 41. As a result, the external gear 30 generates not only the torque caused by the external force that is the intended measurement, but also a torque (hereinafter referred to as "ripple torque T") caused by the deflection deformation by the cam 41. The torque sensor 50 detects this ripple torque T along with the torque generated in the external gear 30 by the external force.

[0062] Figure 9 is a graph showing the ripple torque T detected by the torque sensor 50 at a given point in time. The horizontal axis of Figure 9 represents the circumferential position around the central axis 9. The vertical axis of Figure 9 represents the value of the ripple torque T detected by the torque sensor 50. In this embodiment, since the diameter of the radial outer surface of the cam 41 changes with an angular period of 180° around the central axis 9, the ripple torque T also appears sinusoidally with an angular period of 180° around the central axis 9, as shown in Figure 9.

[0063] Then, the value obtained by integrating the ripple torque T shown in Figure 9 over the range from 0° to 180° becomes the total value of the ripple torque T detected by the torque sensor 50 at the circumferential position from 0° to 180° at that time.

[0064] However, as shown in Figure 9, the ripple torque T detected by the torque sensor 50 has a detection gap To. The detection gap To occurs at an angular position corresponding to the gap region A of the strain gauge. That is, since there is no strain gauge in gap region A, the ripple torque T cannot be detected, resulting in a detection gap To. When the cam 41 rotates, the sinusoidal waveform of the ripple torque T in Figure 9 moves in the horizontal axis direction, but the position of the detection gap To does not change. This detection gap To can become an error component of the integral value of the ripple torque T as described above.

[0065] In this embodiment, the gap regions A are arranged at 90° angular intervals. This arrangement ensures that the detection defects To caused by the gap regions A also occur at 90° angular intervals, as shown in Figure 9. Therefore, in a 180° periodic ripple torque T, the two detection defects To are in opposite phases, causing them to cancel each other out when integrated. As a result, the error due to detection defects To can be reduced in the integral value of the ripple torque T.

[0066] Figures 10 and 11 are enlarged views of gap region A. In Figures 10 and 11, gap region A is indicated by dashed hatching. As shown in Figures 10 and 11, in this embodiment, there are two types of gap region A shapes depending on the inclination of the resistance wires of adjacent strain gauges. The maximum circumferential length L1 of gap region A in Figure 10 is twice the maximum circumferential length L2 of gap region A in Figure 11. Also, the maximum central angle θ1 of gap region A in Figure 10 is twice the maximum central angle θ2 of gap region A in Figure 11.

[0067] However, regardless of the shape of gap region A, the areas of multiple gap regions A are equal to each other. In this way, the amount of loss in ripple torque T due to gap regions A can be made equal. This further reduces the error due to the detected loss To in the integral value of ripple torque T. Note that the area of ​​gap region A is the area of ​​the region that exists in the circumferential direction between adjacent strain gauges, and in the radial direction between the extension of the radially inner edge of the strain gauge and the extension of the radially outer edge of the strain gauge.

[0068] The areas of multiple gap regions A may have unavoidable errors. That is, the areas of multiple gap regions A only need to be approximately the same.

[0069] In particular, in this embodiment, the areas of the gap regions A in the multiple first strain gauges W1 are equal to each other, and the areas of the gap regions A in the multiple second strain gauges W2 are equal to each other. More specifically, the areas of the gap regions A in the multiple inner strain gauges W11 included in the multiple first strain gauges W1 are equal to each other. Also, the areas of the gap regions A in the multiple outer strain gauges W12 included in the multiple first strain gauges W1 are equal to each other. Also, the areas of the gap regions A in the multiple inner strain gauges W21 included in the multiple second strain gauges W2 are equal to each other. Also, the areas of the gap regions A in the multiple outer strain gauges W22 included in the multiple second strain gauges W2 are equal to each other.

[0070] In this way, the amount of ripple torque T lost due to gap region A can be made equal in both the first bridge circuit C1 and the second bridge circuit C2. This further reduces the error in the output value due to the detected loss To in both the first bridge circuit C1 and the second bridge circuit C2.

[0071] <5. Variation> Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. Below, various modifications will be described, focusing on the differences from the above embodiments.

[0072] <5-1. First variation> Figure 12 is a plan view of the sensor substrate 51 according to the first modified example. In the above embodiment, the circumferential positions of the multiple gap regions A in the multiple first strain gauges W1 and the circumferential positions of the multiple gap regions A in the multiple second strain gauges W2 were the same. In contrast, in the example of Figure 12, the circumferential positions of the multiple gap regions A in the multiple first strain gauges W1 and the circumferential positions of the multiple gap regions A in the multiple second strain gauges W2 are different.

[0073] Thus, the circumferential positions of the multiple gap regions A in the multiple first strain gauges W1 and the circumferential positions of the multiple gap regions A in the multiple second strain gauges W2 do not have to be the same. This makes it possible to use two bridge circuits, the first bridge circuit C1 and the second bridge circuit C2, and to improve the degree of freedom in the arrangement of the multiple strain gauges.

[0074] <5-2. Second variation> Figure 13 is a plan view of the cam 41 according to the second modified example. In the above embodiment, the radial outer surface of the cam 41 was elliptical. Therefore, the diameter of the radial outer surface of the cam 41 changed with an angular period of 180° around the central axis 9. In contrast, in the example of Figure 13, the radial outer surface of the cam 41 is roughly triangular in shape with smoothly curved corners. Therefore, the diameter of the radial outer surface of the cam 41 changes with an angular period of 120° around the central axis 9. That is, the cam 41 in Figure 13 is a component that imparts displacement to the external gear 30 with a period of 120°. The power transmission device 1 may use the cam 41 in Figure 13 instead of the cam 41 in the above embodiment.

[0075] When using the cam 41 in Figure 13, the ripple torque T changes sinusoidally with an angular period of 120° around the central axis 9. In this case, the gap regions A should be arranged at 60° angular intervals around the central axis 9. In this way, the detection loss To caused by the gap regions A will also occur at 60° angular intervals. Therefore, in the ripple torque T with a 120° period, the two detection loss Tos are in opposite phases, and when integrated, the detection loss Tos cancel each other out. As a result, the error due to detection loss To can be reduced in the integral value of the ripple torque T.

[0076] <5-3. Other variations> In the above embodiment, the torque sensor 50 had a plurality of first strain gauges W1 constituting a first bridge circuit C1 and a plurality of second strain gauges W2 constituting a second bridge circuit C2. However, the torque sensor 50 may have only one of the plurality of first strain gauges W1 constituting the first bridge circuit C1 and the plurality of second strain gauges W2 constituting the second bridge circuit C2.

[0077] In the above embodiment, multiple strain gauges were arranged on the external gear 30, which is a mechanical component. However, instead of the external gear 30, multiple strain gauges may be arranged on another mechanical component, the internal gear 20. In other words, the "mechanical component" in this invention may be either the external gear 30 or the internal gear 20. This increases the design flexibility of the power transmission device 1. That is, strain gauges can be arranged on the preferred external gear 30 or internal gear 20, according to the specifications and design of the product on which the power transmission device 1 is installed.

[0078] Furthermore, in the power transmission device 1 of the above embodiment, the external gear 30 was fixed to the base frame 101, and the internal gear 20 rotated at a second rotational speed after reduction. However, the internal gear 20 may be fixed to the base frame 101, and the external gear 30 may rotate at a second rotational speed after reduction.

[0079] Furthermore, the external gear 30 in the above embodiment was a so-called "hat-shaped" flexible external gear in which the base portion 33 widens radially outward from the body portion 31. However, the external gear 30 may also be a so-called "cup-shaped" flexible external gear in which the base portion 33 widens radially inward from the body portion 31.

[0080] Furthermore, the above embodiment described a power transmission device 1 mounted on a robot 100. However, a power transmission device 1 with a similar structure may be mounted on other devices such as an assist suit or an automated guided vehicle.

[0081] Furthermore, the configuration of mechanical parts, power transmission devices, and detailed components of the robot may be modified as appropriate without departing from the spirit of the present invention. In addition, elements appearing in the above embodiments and modifications may be combined as appropriate without creating any inconsistencies.

[0082] <6. Summary> This technology can be configured as follows:

[0083] (1) A mechanical part comprising a base portion extending in a direction intersecting the central axis, and a plurality of strain gauges arranged on the base portion, wherein the plurality of strain gauges are arranged in a circumferential direction about the central axis, and a plurality of gap regions are arranged between adjacent strain gauges in the circumferential direction, and the plurality of gap regions include gap regions arranged at 90° angular intervals about the central axis.

[0084] (2) A mechanical part having a base portion extending in a direction intersecting the central axis, and a plurality of strain gauges arranged on the base portion, wherein the plurality of strain gauges are arranged in a circumferential direction about the central axis, and a plurality of gap regions are arranged between adjacent strain gauges in the circumferential direction, and the plurality of gap regions include gap regions arranged at an angular interval of 60° about the central axis.

[0085] (3) A mechanical part according to (1) or (2), wherein the areas of the plurality of gap regions are equal to each other.

[0086] (4) A mechanical part according to any one of (1) to (3), wherein the plurality of strain gauges includes a plurality of internal strain gauges arranged in the circumferential direction and a plurality of external strain gauges arranged in the circumferential direction radially outward from the plurality of internal strain gauges, and the plurality of internal strain gauges and the plurality of external strain gauges constitute a bridge circuit.

[0087] (5) A mechanical part according to any one of (1) to (4), wherein the plurality of strain gauges includes a plurality of first strain gauges constituting a first bridge circuit and a plurality of second strain gauges positioned radially outward from the plurality of first strain gauges and constituting a second bridge circuit.

[0088] (6)(5) A mechanical part according to (5), wherein the areas of the plurality of gap regions in the plurality of first strain gauges are equal to each other, and the areas of the plurality of gap regions in the plurality of second strain gauges are equal to each other.

[0089] A mechanical part according to (7)(5) or (6), wherein the circumferential positions of the plurality of gap regions in the plurality of first strain gauges and the circumferential positions of the plurality of gap regions in the plurality of second strain gauges are different.

[0090] (8) A power transmission device comprising a mechanical component as described in any one of (1) to (7), the device comprising an internal gear, an external gear that meshes with the internal gear, and a wave generator that generates periodic deflection in the external gear, wherein either the internal gear or the external gear is the mechanical component.

[0091] A robot equipped with the power transmission device described in (9)(8). [Industrial applicability]

[0092] The present invention can be used in mechanical parts, power transmission devices, and robots. [Explanation of Symbols]

[0093] 1. Power transmission device 9 Center axis 10 Input shafts 20 Internal gear 21 Inner teeth 30 External gears 31 Torso 32 External teeth 33 Base section 34 Thick part 40 Wave Generator 41 Cam 42 Flexible bearings 50 Torque Sensor 51 Sensor board 60 Housing 70 Signal Processing Board 100 robots 101 Base Frame 102 Arm 103 Motor 511 Insulating layer 512 Conductor layer A Gap area C1 First Bridge Circuit C2 Second Bridge Circuit Ra, Rb, Rc, Rd, Re, Rf, Rg, Rh, Ri, Rj, Rk, Rl, Rm, Rn, Ro, Rp strain gauges W1 First strain gauge W11 Internal Strain Gauge W12 External Strain Gauge W2 Second strain gauge W21 Internal Strain Gauge W22 External Strain Gauge T Ripple Torque To detect missing

Claims

1. It is a machine part, A base portion that extends in a direction intersecting the central axis, Multiple strain gauges arranged in the base portion, It has, The aforementioned plurality of strain gauges are arranged on the same circumference centered on the central axis, Multiple gap regions are arranged between adjacent strain gauges in the circumferential direction. The plurality of gap regions include gap regions arranged at 90° angular intervals with respect to the central axis. The aforementioned plurality of strain gauges are, Multiple internal strain gauges arranged in the circumferential direction, A plurality of outer strain gauges arranged circumferentially, radially outward from the plurality of inner strain gauges, Includes, A mechanical component in which a bridge circuit is formed by the plurality of internal strain gauges and the plurality of external strain gauges.

2. It is a machine part, A base portion that extends in a direction intersecting the central axis, Multiple strain gauges arranged in the base portion, It has, The aforementioned plurality of strain gauges are arranged on the same circumference centered on the central axis, Multiple gap regions are arranged between adjacent strain gauges in the circumferential direction. The plurality of gap regions include gap regions arranged at 60° angular intervals with respect to the central axis. The aforementioned plurality of strain gauges are, Multiple internal strain gauges arranged in the circumferential direction, A plurality of outer strain gauges arranged circumferentially, radially outward from the plurality of inner strain gauges, Includes, A mechanical component in which a bridge circuit is formed by the plurality of internal strain gauges and the plurality of external strain gauges.

3. It is a machine part, A base portion that extends in a direction intersecting the central axis, Multiple strain gauges arranged in the base portion, It has, The aforementioned plurality of strain gauges are arranged on the same circumference centered on the central axis, Multiple gap regions are arranged between adjacent strain gauges in the circumferential direction. The plurality of gap regions include gap regions arranged at 90° angular intervals with respect to the central axis. The aforementioned plurality of strain gauges are, Multiple first strain gauges constituting the first bridge circuit, A plurality of second strain gauges are arranged radially outward from the plurality of first strain gauges and constitute a second bridge circuit, Machine parts, including those mentioned above.

4. It is a machine part, A base portion that extends in a direction intersecting the central axis, Multiple strain gauges arranged in the base portion, It has, The aforementioned plurality of strain gauges are arranged on the same circumference centered on the central axis, Multiple gap regions are arranged between adjacent strain gauges in the circumferential direction. The plurality of gap regions include gap regions arranged at 60° angular intervals with respect to the central axis. The aforementioned plurality of strain gauges are, Multiple first strain gauges constituting the first bridge circuit, A plurality of second strain gauges are arranged radially outward from the plurality of first strain gauges and constitute a second bridge circuit, Machine parts, including those mentioned above.

5. It is a machine part, A base portion that extends in a direction intersecting the central axis, Multiple strain gauges arranged in the base portion, It has, The aforementioned plurality of strain gauges are arranged on the same circumference centered on the central axis, Multiple gap regions are arranged between adjacent strain gauges in the circumferential direction. The plurality of gap regions include gap regions arranged at 90° angular intervals with respect to the central axis. The aforementioned plurality of gap regions include gap regions with different shapes from each other. A mechanical part in which the areas of the aforementioned multiple gap regions are equal to each other.

6. It is a machine part, A base portion that extends in a direction intersecting the central axis, Multiple strain gauges arranged in the base portion, It has, The aforementioned plurality of strain gauges are arranged on the same circumference centered on the central axis, Multiple gap regions are arranged between adjacent strain gauges in the circumferential direction. The plurality of gap regions include gap regions arranged at 60° angular intervals with respect to the central axis. The aforementioned plurality of gap regions include gap regions with different shapes from each other. A mechanical part in which the areas of the aforementioned multiple gap regions are equal to each other.

7. A machine part according to any one of Claims 1 to 4, A mechanical part in which the areas of the aforementioned multiple gap regions are equal to each other.

8. A machine part according to claim 3 or claim 4, The areas of the multiple gap regions in the multiple first strain gauges are equal to each other. A mechanical part in which the areas of the multiple gap regions in the multiple second strain gauges are equal to each other.

9. A machine part according to claim 3 or claim 4, A mechanical part in which the circumferential positions of the plurality of gap regions in the plurality of first strain gauges and the circumferential positions of the plurality of gap regions in the plurality of second strain gauges are different.

10. A power transmission device comprising the mechanical component described in any one of Claims 1 to 6, Internal gears and An external gear that meshes with the aforementioned internal gear, A wave generator that generates periodic deflection in the external gear, Equipped with, A power transmission device in which either the internal gear or the external gear is the mechanical component.

11. A robot equipped with the power transmission device described in claim 10.

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