Wave gear device, manufacturing method of the same, and robot joint device

Abstract

To provide a wave gear device which can easily achieve predetermined performance, and to provide a manufacturing method of the wave gear device and a robot joint device.SOLUTION: A wave gear device 1A includes: a rigid internal gear 2; a flexible external gear 3; and a wave generator 4. The wave gear device 1A deforms the flexible external gear 3 in conjunction with rotation of a cam 41, causes part of external teeth 31 to engage with parts of internal teeth 21, and rotates the flexible external gear 3 relative to the rigid internal gear 2 according to a tooth number difference between the flexible external gear 3 and the rigid internal gear 2. The wave gear device 1A has a friction pressure welding part 500 which couples a first component and a second component.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure generally relates to a wave gear device, a method for manufacturing a wave gear device, and a joint device for a robot, and more particularly to a wave gear device including a rigid internal gear, a flexible external gear, and a wave generator, a method for manufacturing a wave gear device, and a joint device for a robot. [Background technology]

[0002] Patent Document 1 discloses a top-hat type strain wave gearing device. This strain wave gearing device includes an annular rigid internal gear (circular spline) with internal teeth, a flexible external gear (flexspline) with external teeth that partially mesh with the internal teeth and that is positioned inside the rigid internal gear, and a wave generator that is positioned inside the flexible external gear and causes the flexible external gear to rotate relative to the rigid internal gear while flexing it.

[0003] This wave gear device is used, for example, with the rigid internal gear, flexible external gear, and wave generator fixed to the casing, output shaft, and input shaft of an industrial robot, respectively. In this state, when rotational motion is input to the wave generator from the input shaft, the rotational motion input to the wave generator is internally decelerated and output from the flexible external gear to the output shaft. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-97861 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-mentioned wave gear device, for example, in order to improve the concentricity between the rigid internal gear and the flexible external gear and achieve specified performance, improved assembly precision is required, but this may vary depending on the skill level of the worker, etc.

[0006] The present disclosure has been made in view of the above circumstances, and aims to provide a strain wave gear device that can easily achieve predetermined performance, a method for manufacturing a strain wave gear device, and a joint device for a robot. [Means for solving the problem]

[0007] A wave gearing device according to one aspect of the present disclosure includes a rigid internal gear, a flexible external gear, and a wave generator. The rigid internal gear is an annular component having internal teeth. The flexible external gear is an annular component having external teeth and disposed inside the rigid internal gear. The wave generator includes a non-circular cam that is driven to rotate about a rotation axis, and a bearing attached to the outside of the cam. The wave generator is disposed inside the flexible external gear and generates a deflection in the flexible external gear. The wave gearing device deforms the flexible external gear as the cam rotates, meshing a portion of the external teeth with a portion of the internal teeth, and rotating the flexible external gear relative to the rigid internal gear in accordance with the difference in the number of teeth between the flexible external gear and the rigid internal gear. The wave gearing device includes a friction weld portion that connects a first component and a second component.

[0008] A method for manufacturing a wave gear device according to one embodiment of the present disclosure is a method for manufacturing the wave gear device, and includes a joining process for joining the first part and the second part at the friction welded portion, and a centering process for setting the rotation centers of the first part and the second part after the joining process.

[0009] A robot joint device according to one aspect of the present disclosure includes the strain wave gear device, a first member fixed to the rigid internal gear, and a second member fixed to the flexible external gear. [Effects of the Invention]

[0010] The present disclosure has the advantage of being able to provide a strain wave gear device that can easily achieve predetermined performance, a method for manufacturing a strain wave gear device, and a robot joint device. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1A is a cross-sectional view showing a schematic configuration of a wave gear device according to a basic configuration. [Figure 1B] FIG. 1B is an enlarged view of region Z1 of FIG. 1A. [Figure 2A] FIG. 2A is a schematic view of the strain wave gear device as viewed from the input side of the rotary shaft. [Figure 2B] FIG. 2B is an enlarged view of region Z1 of FIG. 2A. [Figure 3A] FIG. 3A is a schematic exploded perspective view of the strain wave gear device as viewed from the output side of the rotary shaft. [Figure 3B] FIG. 3B is a schematic exploded perspective view of the strain wave gear device as viewed from the input side of the rotary shaft. [Figure 4] FIG. 4 is a cross-sectional view showing a schematic configuration of an actuator including the above strain wave gear device. [Figure 5] FIG. 5 is a cross-sectional view showing an example of a robot using the above strain wave gear device. [Figure 6] FIG. 6 is a cross-sectional view showing a schematic configuration of the strain wave gear device according to the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing a schematic configuration of the strain wave gear device. [Figure 8] FIG. 8 is a cross-sectional view showing a schematic configuration of the strain wave gear device. [Figure 9] FIG. 9 is an explanatory diagram that schematically shows a method for manufacturing the above strain wave gear device. DETAILED DESCRIPTION OF THE INVENTION

[0012] (Basic configuration) (1) Overview An overview of the wave gear device 1 according to this basic configuration will be described below with reference to Figures 1A to 4. All drawings referred to in this disclosure are schematic, and the ratios of size and thickness of each component in the drawings do not necessarily reflect the actual dimensional ratios. For example, the tooth shapes, dimensions, number of teeth, etc. of the internal teeth 21 and external teeth 31 in Figures 2A to 3B are merely shown schematically for the purpose of explanation, and are not intended to be limited to the shapes shown in the drawings.

[0013] The wave gearing 1 according to this basic configuration is a gearing comprising a rigid internal gear 2, a flexible external gear 3, and a wave generator 4. In this wave gearing 1, an annular flexible external gear 3 is disposed inside the annular rigid internal gear 2, and the wave generator 4 is disposed inside the flexible external gear 3. The wave generator 4 bends the flexible external gear 3 into a non-circular shape, thereby partially meshing the external teeth 31 of the flexible external gear 3 with the internal teeth 21 of the rigid internal gear 2. When the wave generator 4 rotates, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the rigid internal gear 2, and a relative rotation corresponding to the difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 is generated between the two gears (the rigid internal gear 2 and the flexible external gear 3). If the rigid internal gear 2 is fixed, the relative rotation of the two gears will cause the flexible external gear 3 to rotate. As a result, the flexible external gear 3 produces a rotational output that is reduced at a relatively high reduction ratio according to the difference in the number of teeth between the two gears.

[0014] The wave generator 4, which causes deflection in the flexible external gear 3, has a non-circular cam 41 that is driven to rotate about an input-side rotation axis Ax1 (see FIG. 1A ), and a bearing 42. The bearing 42 is disposed between an outer peripheral surface 411 of the cam 41 and an inner peripheral surface 301 of the flexible external gear 3. An inner ring 422 of the bearing 42 is fixed to the outer peripheral surface 411 of the cam 41, and the outer ring 421 of the bearing 42 is pressed by the cam 41 via ball-shaped rolling elements 423, causing elastic deformation. Here, the rolling of the rolling elements 423 allows the outer ring 421 to rotate relative to the inner ring 422. Therefore, when the non-circular cam 41 rotates, the rotation of the inner ring 422 is not transmitted to the outer ring 421, and a wave motion is generated in the external teeth 31 of the flexible external gear 3 that are pressed by the cam 41. As a result of the wave motion of the external teeth 31, the meshing position between the internal teeth 21 and the external teeth 31 moves in the circumferential direction of the rigid internal gear 2 as described above, and relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2.

[0015] In short, in this type of strain wave gear device 1, the wave generator 4 having the bearing 42 deflects the flexible external gear 3, and power is transmitted by the meshing of the internal teeth 21 and the external teeth 31.

[0016] 4, the wave gearing 1 according to this basic configuration, together with a drive source 101 and an output unit 102, constitutes an actuator 100. In other words, the actuator 100 according to this basic configuration includes the wave gearing 1, a drive source 101, and an output unit 102. The drive source 101 rotates the wave generator 4. The output unit 102 extracts the rotational force of either the rigid internal gear 2 or the flexible external gear 3 as an output.

[0017] 4, the strain wave gearing 1 according to this basic configuration constitutes a robot joint device 130 together with a first member 131 and a second member 132. In other words, the robot joint device 130 according to this basic configuration includes the strain wave gearing 1, a first member 131, and a second member 132. The first member 131 is fixed to the rigid internal gear 2. The second member 132 is fixed to the flexible external gear 3. As a result, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2 in the strain wave gearing 1, and this causes relative rotation between the first member 131 and the second member 132 in the robot joint device 130.

[0018] (2) Definition In this disclosure, "annular" refers to a ring-like shape that forms an enclosed space (region) at least in plan view, and is not limited to a circular shape (annular) such as a perfect circle in plan view, but may also be, for example, an elliptical shape or a polygonal shape. Furthermore, even if a shape has a bottom 322, such as a cup-shaped flexible external gear 3, if its body 321 is annular, it is called an "annular" flexible external gear 3.

[0019] In this disclosure, "rigidity" refers to the property of an object to resist deformation when an external force is applied to the object and the object attempts to deform. In other words, an object with rigidity is less likely to deform when an external force is applied to it. In addition, in this disclosure, "flexibility" refers to the property of an object to elastically deform (bend) when an external force is applied to it. In other words, an object with flexibility is more likely to elastically deform when an external force is applied to it. Therefore, "rigidity" and "flexibility" have opposing meanings.

[0020] In particular, in this disclosure, the "rigidity" of the rigid internal gear 2 and the "flexibility" of the flexible external gear 3 are used in a relative sense. In other words, the "rigidity" of the rigid internal gear 2 means that the rigid internal gear 2 has a high rigidity, at least relatively compared to the flexible external gear 3, meaning that it is less likely to deform even when an external force is applied. Similarly, the "flexibility" of the flexible external gear 3 means that the flexible external gear 3 has a high flexibility, at least relatively compared to the rigid internal gear 2, meaning that it is more likely to elastically deform when an external force is applied.

[0021] Furthermore, in this disclosure, one side of the rotation axis Ax1 (the right side in FIG. 1A) may be referred to as the "input side," and the other side of the rotation axis Ax1 (the left side in FIG. 1A) may be referred to as the "output side." In other words, in the example of FIG. 1A, the flexible external gear 3 has an opening surface 35 on the "input side" of the rotation axis Ax1. However, the "input side" and "output side" are merely labels used for the purpose of explanation, and are not intended to limit the positional relationship between the input and output when viewed from the strain wave gear device 1.

[0022] In this disclosure, the term "non-circular" refers to a shape that is not a perfect circle, and includes, for example, an elliptical shape and an oval shape. In this basic configuration, as an example, the non-circular cam 41 of the wave generator 4 is elliptical. In other words, in this basic configuration, the wave generator 4 bends the flexible external gear 3 into an elliptical shape.

[0023] In this disclosure, the term "elliptical shape" refers to any shape in which a perfect circle is compressed and the intersection of its major and minor axes, which are perpendicular to each other, is located at the center. It is not limited to a mathematical "ellipse," which is a curved line formed by a set of points whose sum of distances from two fixed points on a plane is constant. In other words, the cam 41 in this basic configuration may be a curved line formed by a set of points whose sum of distances from two fixed points on a plane is constant, like a mathematical "ellipse," or it may be an elliptical shape, such as an oval, rather than a mathematical "ellipse." As mentioned above, all drawings referenced in this disclosure are schematic, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. For example, in FIG. 2A, the shape of the cam 41 of the wave generator 4 is depicted as a somewhat exaggerated ellipse, but this is not intended to limit the actual shape of the cam 41.

[0024] In this disclosure, the term "axis of rotation" refers to a virtual axis (straight line) that serves as the center of rotational motion of a rotating body. In other words, the axis of rotation Ax1 is a virtual axis that does not have a physical entity. The wave generator 4 performs rotational motion around the axis of rotation Ax1.

[0025] In this disclosure, "internal teeth" and "external teeth" do not refer to a single "tooth," but rather to a set (group) of multiple "teeth." In other words, the internal teeth 21 of the rigid internal gear 2 are made up of a set of multiple teeth formed on the inner circumferential surface of the rigid internal gear 2. Similarly, the external teeth 31 of the flexible external gear 3 are made up of a set of multiple teeth formed on the outer circumferential surface 303 (see FIG. 1A) of the flexible external gear 3.

[0026] In this disclosure, "parallel" refers to a case where two straight lines on a plane do not intersect no matter how far they are extended, that is, a case where the angle between the two is exactly 0 degrees (or 180 degrees), as well as a case where the angle between the two is within an error range of a few degrees (for example, less than 10 degrees) from 0 degrees. Similarly, in this disclosure, "orthogonal" refers to a case where the angle between the two is exactly 90 degrees, as well as a case where the angle between the two is within an error range of a few degrees (for example, less than 10 degrees) from 90 degrees.

[0027] (3) Composition The detailed configurations of the harmonic gear device 1, the actuator 100, and the robot joint device 130 according to this basic configuration will be described below with reference to FIGS. 1A to 4. FIG.

[0028] Fig. 1A is a cross-sectional view showing the schematic configuration of the strain wave gear device 1, and Fig. 1B is an enlarged view of region Z1 in Fig. 1A. Fig. 2A is a schematic view of the strain wave gear device 1 as viewed from the input side of the rotation axis Ax1 (the right side of Fig. 1A), and Fig. 2B is an enlarged view of region Z1 in Fig. 2A. Fig. 3A is a schematic exploded perspective view of the strain wave gear device 1 as viewed from the output side of the rotation axis Ax1 (the left side of Fig. 1A). Fig. 3B is a schematic exploded perspective view of the strain wave gear device 1 as viewed from the input side of the rotation axis Ax1. Fig. 4 is a cross-sectional view showing the schematic configuration of an actuator 100 and a robot joint device 130 that include the strain wave gear device 1.

[0029] (3.1) Strain wave gearing As described above, the strain wave gearing 1 according to this basic configuration includes the rigid internal gear 2, the flexible external gear 3, and the strain wave generator 4. In this basic configuration, the materials of the rigid internal gear 2, the flexible external gear 3, and the strain wave generator 4, which are the components of the strain wave gearing 1, are metals such as stainless steel, cast iron, carbon steel for machine structures, chromium-molybdenum steel, phosphor bronze, or aluminum bronze. The term "metal" used here includes metals that have been subjected to surface treatments such as nitriding.

[0030] Furthermore, in this basic configuration, a cup-type wave gearing device is exemplified as an example of the wave gearing device 1. That is, the wave gearing device 1 according to this basic configuration uses a flexible external gear 3 formed in a cup shape. The wave generator 4 is combined with the flexible external gear 3 so as to be housed within the cup-shaped flexible external gear 3.

[0031] In addition, in this basic configuration, as an example, the wave gear device 1 is used with the rigid internal gear 2 fixed to an input side case 111 (see FIG. 4) and an output side case 112 (see FIG. 4), etc. As a result, relative rotation between the rigid internal gear 2 and the flexible external gear 3 causes the flexible external gear 3 to rotate relative to the fixed member (the input side case 111, etc.).

[0032] Furthermore, in this basic configuration, when the strain wave gearing 1 is used in the actuator 100, a rotational force is applied as an input to the wave generator 4, and a rotational force is extracted as an output from the flexible external gear 3. In other words, the strain wave gearing 1 operates with the rotation of the wave generator 4 as the input rotation and the rotation of the flexible external gear 3 as the output rotation. As a result, the strain wave gearing 1 produces an output rotation that is reduced at a relatively high reduction ratio relative to the input rotation.

[0033] Furthermore, in the wave gearing 1 according to this basic configuration, the input-side rotation axis Ax1 and the output-side rotation axis Ax2 are on the same straight line. In other words, the input-side rotation axis Ax1 and the output-side rotation axis Ax2 are coaxial. Here, the input-side rotation axis Ax1 is the center of rotation of the wave generator 4 to which the input rotation is applied, and the output-side rotation axis Ax1 is the center of rotation of the flexible external gear 3 that generates the output rotation. In other words, in the wave gearing 1, output rotation is obtained that is reduced in speed at a relatively high reduction ratio relative to the input rotation on the same axis.

[0034] The rigid internal gear 2 is also called a circular spline, and is an annular component having internal teeth 21. In this basic configuration, the rigid internal gear 2 has an annular shape, with at least the inner circumferential surface being a perfect circle in a plan view. The internal teeth 21 are formed on the inner circumferential surface of the annular rigid internal gear 2 along the circumferential direction of the rigid internal gear 2. The multiple teeth that make up the internal teeth 21 all have the same shape and are provided at equal pitch over the entire circumferential area of the inner circumferential surface of the rigid internal gear 2. In other words, the pitch circle of the internal teeth 21 is a perfect circle in a plan view. The rigid internal gear 2 also has a predetermined thickness in the direction of the rotation axis Ax1. All of the internal teeth 21 are formed over the entire length of the rigid internal gear 2 in the thickness direction. All of the tooth traces of the internal teeth 21 are parallel to the rotation axis Ax1.

[0035] As described above, the rigid internal gear 2 is fixed to the input side case 111 (see FIG. 4) and the output side case 112 (see FIG. 4), etc. Therefore, the rigid internal gear 2 has a plurality of fixing holes 22 (see FIGS. 3A and 3B) for fixing.

[0036] The flexible external gear 3, also known as a flex spline, is an annular component having external teeth 31. In this basic configuration, the flexible external gear 3 is a cup-shaped component made of a relatively thin elastic metal body (metal plate). In other words, the flexible external gear 3 is flexible due to its relatively small (thin) thickness. The flexible external gear 3 has a cup-shaped main body 32. The main body 32 has a trunk 321 and a bottom 322. The trunk 321 has a cylindrical shape, with at least the inner circumferential surface 301 being a perfect circle in a plan view, when no elastic deformation occurs in the flexible external gear 3. The central axis of the trunk 321 coincides with the rotation axis Ax1. The bottom 322 is disposed on one opening surface of the trunk 321 and has a disk shape that is a perfect circle in a plan view. The bottom 322 is disposed on the opening surface of the pair of opening surfaces of the trunk 321 on the output side of the rotation axis Ax1. As described above, the trunk 321 and the bottom 322 as a whole form the main body 32 in the form of a bottomed cylinder, i.e., a cup-like shape, that is open to the input side of the rotation axis Ax1. In other words, an opening surface 35 is formed on the end surface of the flexible external gear 3 opposite the bottom 322 in the direction of the rotation axis Ax1. In other words, the flexible external gear 3 is cylindrical, with the opening surface 35 on one side in the tooth trace direction D1 (here, on the input side of the rotation axis Ax1). In this basic configuration, the trunk 321 and the bottom 322 are integrally formed from a single metal member, thereby realizing a seamless main body 32.

[0037] Here, the wave generator 4 is combined with the flexible external gear 3 such that the non-circular (elliptical) wave generator 4 is fitted inside the body portion 321. As a result, the flexible external gear 3 is subjected to an external force from the wave generator 4 in the radial direction (direction perpendicular to the rotation axis Ax1) from the inside to the outside, and is elastically deformed into a non-circular shape. In this basic configuration, by combining the wave generator 4 with the flexible external gear 3, the body portion 321 of the flexible external gear 3 is elastically deformed into an elliptical shape. In other words, a state in which no elastic deformation occurs in the flexible external gear 3 means a state in which the wave generator 4 is not combined with the flexible external gear 3. Conversely, a state in which elastic deformation occurs in the flexible external gear 3 means a state in which the wave generator 4 is combined with the flexible external gear 3.

[0038] More specifically, the wave generator 4 is fitted into the end of the inner circumferential surface 301 of the body portion 321 opposite to the bottom portion 322 (the input side of the rotation axis Ax1). In other words, the wave generator 4 is fitted into the end of the body portion 321 of the flexible external gear 3 on the opening surface 35 side in the direction of the rotation axis Ax1. Therefore, when elastic deformation occurs in the flexible external gear 3, the end of the flexible external gear 3 on the opening surface 35 side in the direction of the rotation axis Ax1 deforms more greatly than the end on the bottom portion 322 side, and becomes closer to an elliptical shape. Due to this difference in the amount of deformation in the direction of the rotation axis Ax1, when elastic deformation occurs in the flexible external gear 3, the inner circumferential surface 301 of the body portion 321 of the flexible external gear 3 includes a tapered surface that is inclined with respect to the rotation axis Ax1.

[0039] Furthermore, the external teeth 31 are formed along the circumferential direction of the body portion 321 on at least the end of the outer peripheral surface 303 (see FIG. 1A) of the body portion 321 opposite the bottom portion 322 (the input side of the rotation axis Ax1). In other words, the external teeth 31 are provided on at least the end of the body portion 321 on the opening surface 35 side in the direction of the rotation axis Ax1 of the flexible external gear 3. The multiple teeth constituting the external teeth 31 all have the same shape and are provided at an equal pitch over the entire circumferential area of the outer peripheral surface 303 of the flexible external gear 3. In other words, the pitch circle of the external teeth 31 is a perfect circle in a plan view when no elastic deformation occurs in the flexible external gear 3. The external teeth 31 are formed only within a range of a certain width from the edge of the body portion 321 on the opening surface 35 side (the input side of the rotation axis Ax1). Specifically, at least a portion of the body 321 where the wave generator 4 is fitted in the direction of the rotation axis Ax1 (the end portion on the opening surface 35 side) has external teeth 31 formed on the outer circumferential surface 303. The tooth traces of the external teeth 31 are all parallel to the rotation axis Ax1.

[0040] In short, in the wave gearing 1 according to this basic configuration, the tooth traces of both the internal teeth 21 of the rigid internal gear 2 and the external teeth 31 of the flexible external gear 3 are parallel to the rotation axis Ax1. Therefore, in this basic configuration, the "tooth trace direction D1" is a direction parallel to the rotation axis Ax1. The dimension of the tooth trace direction D1 of the internal teeth 21 is the face width of the internal teeth 21, and similarly, the dimension of the tooth trace direction D1 of the external teeth 31 is the face width of the external teeth 31, so the tooth trace direction D1 is synonymous with the face width direction.

[0041] In this basic configuration, as described above, the rotation of the flexible external gear 3 is extracted as output rotation. For this reason, the output section 102 (see FIG. 4) of the actuator 100 is attached to the flexible external gear 3. A plurality of attachment holes 33 are formed in the bottom section 322 of the flexible external gear 3 for attaching a shaft serving as the output section 102. Furthermore, a through hole 34 is formed in the center of the bottom section 322. The area around the through hole 34 in the bottom section 322 is thicker than other parts of the bottom section 322.

[0042] The flexible external gear 3 configured in this manner is disposed inside the rigid internal gear 2. Here, the flexible external gear 3 is combined with the rigid internal gear 2 so that only the end of the outer circumferential surface 303 of the body portion 321 opposite the bottom portion 322 (the input side of the rotation axis Ax1) is inserted inside the rigid internal gear 2. In other words, the portion of the body portion 321 into which the wave generator 4 is fitted (the end on the opening surface 35 side) in the direction of the rotation axis Ax1 is inserted inside the rigid internal gear 2. Here, external teeth 31 are formed on the outer circumferential surface 303 of the flexible external gear 3, and internal teeth 21 are formed on the inner circumferential surface of the rigid internal gear 2. Therefore, when the flexible external gear 3 is disposed inside the rigid internal gear 2, the external teeth 31 and the internal teeth 21 face each other.

[0043] Here, the number of teeth of the internal teeth 21 of the rigid internal gear 2 is 2N (N is a positive integer) more than the number of teeth of the external teeth 31 of the flexible external gear 3. In this basic configuration, as an example, N is "1", and the number of teeth (of the external teeth 31) of the flexible external gear 3 is "2" more than the number of teeth (of the internal teeth 21) of the rigid internal gear 2. This difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 defines the reduction ratio of the output rotation to the input rotation in the strain wave gear device 1.

[0044] 1A and 1B, as an example of this basic configuration, the relative positions of the flexible external gear 3 and the rigid internal gear 2 in the direction of the rotation axis Ax1 are set so that the centers of the external teeth 31 in the tooth trace direction D1 and the internal teeth 21 in the tooth trace direction D1 face each other. In other words, the centers of the external teeth 31 of the flexible external gear 3 and the internal teeth 21 of the rigid internal gear 2 in the tooth trace direction D1 are aligned with each other in the direction of the rotation axis Ax1. In addition, in this basic configuration, the dimension (tooth width) of the external teeth 31 in the tooth trace direction D1 is larger than the dimension (tooth width) of the internal teeth 21 in the tooth trace direction D1. Therefore, in the direction parallel to the rotation axis Ax1, the internal teeth 21 are contained within the range of the tooth trace of the external teeth 31. In other words, the external teeth 31 protrude in at least one direction in the tooth trace direction D1 relative to the internal teeth 21. In this basic configuration, the external teeth 31 protrude relative to the internal teeth 21 in both tooth trace directions D1 (on the input side and output side of the rotation axis Ax1).

[0045] Here, when no elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is not combined with the flexible external gear 3), the pitch circle of the external teeth 31, which form a perfect circle, is set to be slightly smaller than the pitch circle of the internal teeth 21, which also form a perfect circle. In other words, when no elastic deformation occurs in the flexible external gear 3, the external teeth 31 and the internal teeth 21 face each other with a gap between them and do not mesh with each other.

[0046] On the other hand, when elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is combined with the flexible external gear 3), the body portion 321 bends into an elliptical shape (non-circular shape), so that the external teeth 31 of the flexible external gear 3 partially mesh with the internal teeth 21 of the rigid internal gear 2. In other words, the body portion 321 of the flexible external gear 3 (at least the end portion on the opening surface 35 side) elastically deforms into an elliptical shape, so that the external teeth 31 located at both ends in the major axis direction of the elliptical shape mesh with the internal teeth 21, as shown in FIG. 2A . In other words, the major axis of the pitch circle of the external teeth 31 that describe an ellipse matches the diameter of the pitch circle of the internal teeth 21 that describe a perfect circle, and the minor axis of the pitch circle of the external teeth 31 that describe an ellipse is smaller than the diameter of the pitch circle of the internal teeth 21 that describe a perfect circle. In this way, when the flexible external gear 3 elastically deforms, some of the teeth that make up the external teeth 31 mesh with some of the teeth that make up the internal teeth 21. As a result, in the wave gear device 1, it is possible to make some of the external teeth 31 mesh with some of the internal teeth 21.

[0047] The wave generator 4 is also called a wave generator, and is a component that causes deflection in the flexible external gear 3, thereby generating wave motion in the external teeth 31 of the flexible external gear 3. In this basic configuration, the wave generator 4 is a component whose outer circumferential shape is non-circular, specifically elliptical, in plan view.

[0048] The wave generator 4 has a non-circular (here, elliptical) cam 41 and a bearing 42 attached to the outer periphery of the cam 41. That is, the non-circular (elliptical) cam 41 is fitted inside an inner ring 422 of the bearing 42, and the cam 41 is assembled to the bearing 42. As a result, the bearing 42 receives an external force from the cam 41 in the radial direction (a direction perpendicular to the rotation axis Ax1) from the inside to the outside of the inner ring 422, and is thereby elastically deformed into a non-circular shape. In other words, a state in which no elastic deformation occurs in the bearing 42 means a state in which the cam 41 is not assembled to the bearing 42. Conversely, a state in which elastic deformation occurs in the bearing 42 means a state in which the cam 41 is assembled to the bearing 42.

[0049] The cam 41 is a non-circular (here, elliptical) component that is driven to rotate around the rotation axis Ax1 on the input side. The cam 41 has an outer circumferential surface 411 (see FIG. 1B), and at least the outer circumferential surface 411 is made of a metal plate that is elliptical in plan view. The cam 41 has a predetermined thickness in the direction of the rotation axis Ax1 (i.e., the tooth trace direction D1). This gives the cam 41 the same level of rigidity as the rigid internal gear 2. However, the thickness of the cam 41 is smaller (thinner) than the thickness of the rigid internal gear 2. In this basic configuration, as described above, the rotation of the wave generator 4 is considered to be the input rotation. Therefore, the input unit 103 (see FIG. 4) of the actuator 100 is attached to the wave generator 4. A cam hole 43 for attaching a shaft serving as the input unit 103 is formed in the center of the cam 41 of the wave generator 4.

[0050] Bearing 42 has an outer ring 421, an inner ring 422, and a plurality of rolling elements 423. In this basic configuration, as an example, bearing 42 is a deep groove ball bearing that uses spherical balls as rolling elements 423.

[0051] The outer ring 421 and the inner ring 422 are both annular components. The outer ring 421 and the inner ring 422 are both annular components made of a relatively thin elastic metal body (metal plate). That is, the outer ring 421 and the inner ring 422 are flexible due to their relatively small (thin) thickness. In this basic configuration, the outer ring 421 and the inner ring 422 each have an annular shape that is a perfect circle in a plan view when the bearing 42 is not elastically deformed (when the cam 41 is not assembled with the bearing 42). The inner ring 422 is slightly smaller than the outer ring 421 and is disposed inside the outer ring 421. Here, the inner diameter of the outer ring 421 is larger than the outer diameter of the inner ring 422, so a gap is generated between the inner peripheral surface 425 of the outer ring 421 and the outer peripheral surface of the inner ring 422.

[0052] The plurality of rolling elements 423 are arranged in the gap between the outer ring 421 and the inner ring 422. The plurality of rolling elements 423 are arranged side by side in the circumferential direction of the outer ring 421. The plurality of rolling elements 423 are all metal balls of the same shape, and are provided at equal pitches over the entire circumferential area of the outer ring 421. Although not specifically shown here, the bearing 42 further has a cage, and the plurality of rolling elements 423 are held between the outer ring 421 and the inner ring 422 by the cage.

[0053] In addition, in this basic configuration, as an example, the dimensions of the outer ring 421 and the inner ring 422 in the width direction (direction parallel to the rotation axis Ax1) are the same as the thickness of the cam 41. In other words, the dimensions of the outer ring 421 and the inner ring 422 in the width direction are smaller than the thickness of the rigid internal gear 2.

[0054] With this configuration of the bearing 42, when the cam 41 is assembled with the bearing 42, the inner ring 422 of the bearing 42 is fixed to the cam 41, and the inner ring 422 elastically deforms into an elliptical shape that follows the outer peripheral shape of the cam 41. At this time, the outer ring 421 of the bearing 42 is pressed by the inner ring 422 via the multiple rolling elements 423, and elastically deforms into an elliptical shape. Therefore, both the outer ring 421 and the inner ring 422 of the bearing 42 elastically deform into an elliptical shape. In this state where elastic deformation occurs in the bearing 42 (when the cam 41 is assembled with the bearing 42), the outer ring 421 and the inner ring 422 form elliptical shapes that are similar to each other.

[0055] Even when elastic deformation occurs in the bearing 42, the gap between the outer ring 421 and the inner ring 422 is maintained substantially constant around the entire circumference of the outer ring 421 due to the presence of multiple rolling elements 423 between the outer ring 421 and the inner ring 422. In this state, the multiple rolling elements 423 roll between the outer ring 421 and the inner ring 422, allowing the outer ring 421 to rotate relative to the inner ring 422. Therefore, when elastic deformation occurs in the bearing 42, if the cam 41 rotates about the rotation axis Ax1, the rotation of the cam 41 is not transmitted to the outer ring 421, but the elastic deformation of the inner ring 422 is transmitted to the outer ring 421 via the multiple rolling elements 423. In other words, in the wave generator 4, when the cam 41 rotates about the rotation axis Ax1, the outer ring 421 elastically deforms such that the major axis of the elliptical shape formed by the outer ring 421 rotates about the rotation axis Ax1. Therefore, as for the wave generator 4 as a whole, the outer peripheral shape of the elliptical wave generator 4 when viewed from the input side of the rotation axis Ax1 changes with the rotation of the cam 41 so that its major axis rotates around the rotation axis Ax1.

[0056] The wave generator 4 configured as above is disposed inside the flexible external gear 3. The flexible external gear 3 is assembled with the wave generator 4 so that only the end of the inner circumferential surface 301 of the body 321 opposite the bottom 322 (the opening surface 35 side) is fitted into the wave generator 4. In this case, the bearing 42 of the wave generator 4 is disposed between the outer circumferential surface 411 of the cam 41 and the inner circumferential surface 301 of the flexible external gear 3. The outer diameter of the outer ring 421 in a state where no elastic deformation occurs in the bearing 42 (a state where the cam 41 is not assembled with the bearing 42) is the same as the inner diameter of the flexible external gear 3 (body 321) in a state where no elastic deformation occurs. Therefore, the outer circumferential surface 424 (see FIG. 2B ) of the outer ring 421 of the wave generator 4 contacts the inner circumferential surface 301 of the flexible external gear 3 over the entire circumferential direction of the bearing 42. Therefore, when elastic deformation occurs in the flexible external gear 3 (when the wave generator 4 is combined with the flexible external gear 3), the body part 321 bends into an elliptical shape (non-circular shape). In this state, the flexible external gear 3 is fixed to the outer ring 421 of the bearing 42.

[0057] However, because the flexible external gear 3 and the wave generator 4 are merely fitted together, the flexible external gear 3 and the outer ring 421 of the bearing 42 are not completely fixed. Therefore, as described above, a small gap X1 (see FIG. 1B ) is generated between the flexible external gear 3 and the outer ring 421 fitted inside the flexible external gear 3. Strictly speaking, because the outer peripheral surface 424 of the outer ring 421 has a slightly smaller diameter than the inner peripheral surface 301 of the flexible external gear 3, the gap X1 between the outer ring 421 and the flexible external gear 3 is not completely filled, and at least a partial gap X1 is generated. Then, due to the influence of this gap X1, relative rotation can occur between the outer ring 421 and the flexible external gear 3 as the cam 41 of the wave generator 4 rotates and the outer ring 421 and the flexible external gear 3 elastically deform. This relative rotation is, for example, about one thousandth or one hundredth of the rotational speed of the cam 41, but such relative rotation causes the outer ring 421 and the flexible external gear 3 to rub against each other, which is one cause of fretting wear.

[0058] In this disclosure, the term "gap" refers to a space that can occur between the opposing surfaces of two objects, and a gap can occur between the two objects even if the two objects are not separated. In other words, even if the two objects are in contact, a small gap can occur between the two objects. Between the flexible external gear 3 and the outer ring 421 fitted inside the flexible external gear 3, a gap X1 occurs between the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3, which face each other. However, since the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3 basically come into contact with each other, no large gap X1 occurs between them. Therefore, the gap X1 between the outer ring 421 and the flexible external gear 3 is a small gap that can occur partially between the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3. As an example, a microscopic gap X1 is generated between the outer peripheral surface 424 of the outer ring 421 and the inner peripheral surface 301 of the flexible external gear 3, which allows the lubricant Lb1 to penetrate.

[0059] 2A , in the wave gear device 1 configured as described above, the body portion 321 of the flexible external gear 3 bends into an elliptical shape (non-circular shape), causing the external teeth 31 of the flexible external gear 3 to partially mesh with the internal teeth 21 of the rigid internal gear 2. In other words, (the body portion 321 of) the flexible external gear 3 elastically deforms into an elliptical shape, causing the external teeth 31 at two locations corresponding to both ends of the elliptical shape in the major axis direction to mesh with the internal teeth 21. When the cam 41 rotates around the rotation axis Ax1, the rotation of the cam 41 is not transmitted to the outer ring 421 and the flexible external gear 3, but the elastic deformation of the inner ring 422 is transmitted to the outer ring 421 and the flexible external gear 3 via multiple rolling elements 423. Therefore, the outer peripheral shape of the flexible external gear 3, which is elliptical when viewed from the input side of the rotation axis Ax1, changes with the rotation of the cam 41 so that its major axis rotates around the rotation axis Ax1.

[0060] As a result, wave motion is generated in the external teeth 31 formed on the outer peripheral surface 303 of the flexible external gear 3. The generation of wave motion in the external teeth 31 causes the meshing positions between the internal teeth 21 and the external teeth 31 to move in the circumferential direction of the rigid internal gear 2, causing relative rotation between the flexible external gear 3 and the rigid internal gear 2. In other words, the external teeth 31 mesh with the internal teeth 21 at both ends in the major axis direction of the elliptical shape formed by (the body portion 321 of) the flexible external gear 3, and therefore, as the major axis of this elliptical shape rotates about the rotation axis Ax1, the meshing positions between the internal teeth 21 and the external teeth 31 move. In this way, the wave gear device 1 according to this basic configuration deforms the flexible external gear 3 in conjunction with the rotation of the wave generator 4 about the rotation axis Ax1, meshing some of the external teeth 31 with some of the internal teeth 21, and rotating the flexible external gear 3 in accordance with the difference in the number of teeth with the rigid internal gear 2.

[0061] Incidentally, in the strain wave gearing 1, as described above, the difference in the number of teeth between the flexible external gear 3 and the rigid internal gear 2 determines the reduction ratio of the output rotation to the input rotation in the strain wave gearing 1. In other words, if the number of teeth of the rigid internal gear 2 is "V1" and the number of teeth of the flexible external gear 3 is "V2," the reduction ratio R1 is expressed by the following formula 1.

[0062] R1=V2 / (V1-V2) (Equation 1) In other words, the smaller the difference in the number of teeth (V1-V2) between the rigid internal gear 2 and the flexible external gear 3, the larger the reduction ratio R1. As an example, if the number of teeth V1 of the rigid internal gear 2 is 72, the number of teeth V2 of the flexible external gear 3 is 70, and the difference in the number of teeth (V1-V2) is 2, then the reduction ratio R1 is 35 according to the above formula 1. In this case, when viewed from the input side of the rotation axis Ax1, when the cam 41 rotates clockwise around the rotation axis Ax1 through one revolution (360 degrees), the flexible external gear 3 rotates counterclockwise around the rotation axis Ax1 by the difference in the number of teeth of 2 (i.e., 10.3 degrees).

[0063] According to the strain wave gear device 1 of this basic configuration, such a high reduction ratio R1 can be achieved with a combination of one stage of gears (rigid internal gear 2 and flexible external gear 3).

[0064] Furthermore, the wave gear device 1 only needs to include at least a rigid internal gear 2, a flexible external gear 3, and a wave generator 4, and may further include, for example, a spline bush 113, etc., as described in the section "(3.2) Actuator."

[0065] Next, the tooth trace modification of the internal teeth 21 and external teeth 31 in this basic configuration will be described.

[0066] 1B, the internal teeth 21 have tooth roots 212 and tooth tips 213. Since the internal teeth 21 are provided on the inner peripheral surface of the rigid internal gear 2, the tooth roots 212 of the internal teeth 21 correspond to the inner peripheral surface of the rigid internal gear 2, and the tooth tips 213 protrude inward from the inner peripheral surface of the rigid internal gear 2 (toward the center of the rigid internal gear 2).

[0067] 1B, the external teeth 31 have tooth bottoms 312 and tooth tips 313. The external teeth 31 are provided on the outer peripheral surface 303 of (the body part 321 of) the flexible external gear 3, so the tooth bottoms 312 of the external teeth 31 correspond to the outer peripheral surface 303 of (the body part 321 of) the flexible external gear 3, and the tooth tips 313 protrude outward from the outer peripheral surface 303 of (the body part 321 of) the flexible external gear 3.

[0068] At the meshing position between the internal teeth 21 and the external teeth 31, the internal teeth 21 mesh with the external teeth 31 such that the tooth tips 313 of the external teeth 31 are inserted between a pair of adjacent tooth tips 213 of the internal teeth 21. At this time, the tooth bottoms 212 of the internal teeth 21 face the tooth tips 313 of the external teeth 31, and the tooth bottoms 312 of the external teeth 31 face the tooth tips 213 of the internal teeth 21. Ideally, a small gap is secured between the tooth bottoms 212 of the internal teeth 21 and the tooth tips 313 of the external teeth 31, and between the tooth bottoms 312 of the external teeth 31 and the tooth tips 213 of the internal teeth 21. In this state, the tooth surfaces of the internal teeth 21 and the external teeth 31 that face each other in the tooth thickness direction come into contact with each other, and power is transmitted between the rigid internal gear 2 and the flexible external gear 3.

[0069] Furthermore, the internal teeth 21 have chamfered portions 211 at both ends in the tooth trace direction D1. The chamfered portions 211 are C-faces that reduce the amount of protrusion of the internal teeth 21 on both sides in the tooth trace direction D1, and are portions that do not generally contribute to the meshing between the internal teeth 21 and the external teeth 31. In other words, the chamfered portions 211 of the internal teeth 21 do not contact the external teeth 31 even at the meshing positions between the internal teeth 21 and the external teeth 31. Similarly, the external teeth 31 have chamfered portions 311 at both ends in the tooth trace direction D1. The chamfered portions 311 are C-faces that reduce the amount of protrusion of the internal teeth 21 on both sides in the tooth trace direction D1, and are portions that do not generally contribute to the meshing between the internal teeth 21 and the external teeth 31. In other words, the chamfered portions 311 of the external teeth 31 do not contact the internal teeth 21 even at the meshing positions between the internal teeth 21 and the external teeth 31.

[0070] Here, in this basic configuration, the internal teeth 21 of the rigid internal gear 2 have tooth trace modification portions 210. In other words, in the wave gearing 1, tooth trace modification is applied to at least the internal teeth 21. The tooth trace modification portions 210 of the internal teeth 21 are provided at least at one end in the tooth trace direction D1. In other words, the internal teeth 21 have tooth trace modification portions 210 at least at one end in the tooth trace direction D1 of the internal teeth 21. In this basic configuration, the tooth trace modification portions 210 are provided at both ends of the internal teeth 21 in the tooth trace direction D1.

[0071] Furthermore, in this basic configuration, the external teeth 31 of the flexible external gear 3 also have tooth trace modification portions 310. In other words, in the wave gearing 1, tooth trace modification is performed not only on the internal teeth 21 but also on the external teeth 31. The tooth trace modification portions 210 of the external teeth are provided on at least one end in the tooth trace direction D1. In other words, the external teeth 31 have tooth trace modification portions 310 on at least one end in the tooth trace direction D1 of the external teeth 31. In this basic configuration, the tooth trace modification portions 310 are provided on both ends of the external teeth 31 in the tooth trace direction D1.

[0072] Thus, in the wave gearing 1 according to this basic configuration, at least one of the internal teeth 21 and the external teeth 31 has the tooth lead modification portions 210, 310. The tooth lead modification portions 210, 310 make it possible to prevent stress concentration due to excessive tooth contact between the internal teeth 21 and the external teeth 31, and as a result, improve the tooth contact between the internal teeth 21 and the external teeth 31. This makes it difficult for foreign matter to be generated due to chipping or wear caused by contact between the internal teeth 21 and the external teeth 31, and makes it possible to realize a wave gearing 1 that is less susceptible to deterioration in reliability.

[0073] (3.2) Actuator Next, the configuration of the actuator 100 according to this basic configuration will be described in more detail.

[0074] As shown in Fig. 4, an actuator 100 according to this basic configuration includes a wave gearing device 1 according to this basic configuration, a drive source 101, and an output unit 102. That is, the actuator 100 includes the drive source 101 and the output unit 102 in addition to the rigid internal gear 2, flexible external gear 3, and wave generator 4 that constitute the wave gearing device 1. In addition to the wave gearing device 1, drive source 101, and output unit 102, the actuator 100 also includes an input unit 103, an input-side case 111, an output-side case 112, a spline bushing 113, a spacer 114, a first fastener 115, a second fastener 116, and a mounting plate 117. In this basic configuration, the actuator 100 also includes input-side bearings 118 and 119, an input-side oil seal 120, output-side bearings 121 and 122, and an output-side oil seal 123.

[0075] In this basic configuration, the materials of the parts of the actuator 100 other than the driving source 101, the input side oil seal 120, and the output side oil seal 123 are metals such as stainless steel, cast iron, carbon steel for mechanical structures, chromium molybdenum steel, phosphor bronze, or aluminum bronze.

[0076] The driving source 101 is a power generating source such as a motor (electric motor). The power generated by the driving source 101 is transmitted to the cam 41 of the wave generator 4 in the harm gearing 1. Specifically, the driving source 101 is connected to a shaft serving as an input unit 103, and the power generated by the driving source 101 is transmitted to the cam 41 via the input unit 103. This enables the driving source 101 to rotate the cam 41.

[0077] The output part 102 is a cylindrical shaft arranged along the rotation axis Ax2 on the output side. The central axis of the shaft serving as the output part 102 coincides with the rotation axis Ax2. The output part 102 is held by the output side case 112 so as to be rotatable about the rotation axis Ax2. The output part 102 is fixed to the bottom part 322 of the main body part 32 of the flexible external gear 3, and rotates together with the flexible external gear 3 about the rotation axis Ax2. In other words, the output part 102 extracts the rotational force of the flexible external gear 3 as an output.

[0078] The input unit 103 is a cylindrical shaft arranged along the input-side rotation axis Ax1. The central axis of the shaft serving as the input unit 103 coincides with the rotation axis Ax1. The input unit 103 is held by the input-side case 111 so as to be rotatable about the rotation axis Ax1. The input unit 103 is attached to the cam 41 of the wave generator 4 and rotates together with the cam 41 about the rotation axis Ax1. In other words, the input unit 103 transmits the power (rotational force) generated by the drive source 101 as an input to the cam 41. In this basic configuration, as described above, the input-side rotation axis Ax1 and the output-side rotation axis Ax2 are on the same straight line, and therefore the input unit 103 and the output unit 102 are positioned on the same axis.

[0079] The input side case 111 holds the input part 103 via input side bearings 118 and 119 so that the input part 103 can rotate. The pair of input side bearings 118 and 119 are arranged side by side with a gap between them along the rotation axis Ax1. In this basic configuration, the shaft serving as the input part 103 penetrates the input side case 111, and the tip of the input part 103 protrudes from the input side end face of the input side case 111 on the rotation axis Ax1 (the right end face in FIG. 4 ). The gap between the input side end face of the input side case 111 on the input side of the rotation axis Ax1 and the input part 103 is sealed by an input side oil seal 120.

[0080] The output side case 112 holds the output part 102 via output side bearings 121 and 122 so that the output part 102 can rotate. The pair of output side bearings 121 and 122 are arranged side by side with a gap between them along the rotation axis Ax2. In this basic configuration, the shaft serving as the output part 102 penetrates the output side case 112, and the tip of the output part 102 protrudes from the end face of the output side of the rotation axis Ax1 in the output side of the output side case 112 (the left end face in FIG. 4 ). The gap between the output side end face of the output side of the rotation axis Ax1 of the output side case 112 and the output part 102 is sealed by an output side oil seal 123.

[0081] As shown in FIG. 4 , the input-side case 111 and the output-side case 112 are coupled to each other with the rigid internal gear 2 of the strain wave gearing 1 sandwiched between them in a direction parallel to the rotation axis Ax1, i.e., in the tooth trace direction D1. Specifically, the input-side case 111 contacts the rigid internal gear 2 from the input side of the rotation axis Ax1, and the output-side case 112 contacts the rigid internal gear 2 from the output side of the rotation axis Ax1. In this manner, the input-side case 111 is fastened to the output-side case 112 with screws (bolts) passing through the multiple fixing holes 22, with the rigid internal gear 2 sandwiched between them. As a result, the input-side case 111, the output-side case 112, and the rigid internal gear 2 are coupled to each other and integrated. In other words, the rigid internal gear 2, together with the input-side case 111 and the output-side case 112, constitute the outer shell of the actuator 100.

[0082] The spline bushing 113 is a cylindrical component for connecting the shaft serving as the input portion 103 to the cam 41. The spline bushing 113 is inserted into a cam hole 43 formed in the cam 41, and the shaft serving as the input portion 103 is inserted into the spline bushing 113 so as to pass through the spline bushing 113. Here, movement of the spline bushing 113 relative to both the cam 41 and the input portion 103 in the rotational direction about the rotation axis Ax1 is restricted, but the spline bushing 113 is movable at least relative to the input portion 103 in a direction parallel to the rotation axis Ax1. This achieves a spline connection structure as a connection structure between the input portion 103 and the cam 41. Therefore, the cam 41 is movable along the rotation axis Ax1 relative to the input portion 103 and rotates together with the input portion 103 about the rotation axis Ax1.

[0083] The spacer 114 is a component that fills the gap between the spline bushing 113 and the cam 41. The first fastener 115 is a component that prevents the spline bushing 113 from coming off the cam 41. The first fastener 115 is made of, for example, an E-ring, and is attached to the spline bushing 113 at a position on the input side of the rotation axis Ax1 when viewed from the cam 41. The second fastener 116 is a component that prevents the input portion 103 from coming off the spline bushing 113. The second fastener 116 is made of, for example, an E-ring, and is attached to the input portion 103 so as to come into contact with the spline bushing 113 from the output side of the rotation axis Ax1.

[0084] The mounting plate 117 is a component for mounting the shaft serving as the output portion 102 to the bottom portion 322 of the flexible external gear 3. Specifically, the mounting plate 117 is fastened to the flange portion with screws (bolts) passing through the multiple mounting holes 33, with the area around the through-hole 34 in the bottom portion 322 sandwiched between the mounting plate 117 and the flange portion of the output portion 102. In this way, the shaft serving as the output portion 102 is fixed to the bottom portion 322 of the flexible external gear 3.

[0085] In this basic configuration, a lubricant Lb1 is enclosed inside the outer shell of the actuator 100, which is made up of the input case 111, the output case 112, and the rigid internal gear 2. In other words, a "lubricant reservoir" capable of storing liquid or gel-like lubricant Lb1 exists in the space surrounded by the input case 111, the output case 112, and the rigid internal gear 2.

[0086] That is, in the wave gear device 1 according to this basic configuration, for example, a liquid or gel-like lubricant Lb1 is injected into the meshing portions between the internal teeth 21 and the external teeth 31, and between the outer ring 421 and the inner ring 422 of the bearing 42. As an example, the lubricant Lb1 is liquid lubricating oil. When the wave gear device 1 is in use, the lubricant Lb1 also enters the gap X1 between the outer ring 421 (outer peripheral surface 424) of the bearing 42 and the flexible external gear 3.

[0087] As an example of this basic configuration, as shown in Fig. 4, the lubricant Lb1 is stored only in the lower part (vertical lower part) of the outer casing of the actuator 100 so that the liquid level of the lubricant Lb1 is located further below the lower ends of the output-side bearings 121, 122. Therefore, in the state shown in Fig. 4, only a portion of the external teeth 31 and the outer ring 421 of the bearing 42, etc. in the rotational direction is immersed in the lubricant Lb1. From this state, when the output part 102 rotates in conjunction with the rotation of the input part 103, the outer ring 421 and the flexible external gear 3 also rotate around the rotation axis Ax1, and as a result, the entire external teeth 31 and the outer ring 421 of the bearing 42, etc. in the rotational direction are immersed in the lubricant Lb1.

[0088] (3.3) Robot joint device Next, the configuration of the robot joint device 130 according to this basic configuration will be described in more detail.

[0089] 4, a robot joint device 130 according to this basic configuration includes the strain wave gear device 1 according to this basic configuration, a first member 131, and a second member 132. In other words, the robot joint device 130 includes the first member 131 and the second member 132 in addition to the rigid internal gear 2, flexible external gear 3, and wave generator 4 that constitute the strain wave gear device 1.

[0090] The first member 131 is a member fixed to the rigid internal gear 2, and the second member 132 is a member fixed to the flexible external gear 3. Therefore, in the strain wave gearing 1, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2, which also causes relative rotation between the first member 131 and the second member 132. In this way, the robot joint device 130 forms a connecting portion when two or more members (the first member 131 and the second member 132) are connected (movably connected) via the strain wave gearing 1 in a state where they can move relative to each other.

[0091] Here, the first member 131 and the second member 132 may be directly or indirectly fixed to the rigid internal gear 2 and the flexible external gear 3, respectively. In the example of Fig. 4, the first member 131 is coupled to the output side case 112, and thereby indirectly coupled (fixed) to the rigid internal gear 2. Similarly, the second member 132 is coupled to the output section 102, and thereby indirectly coupled (fixed) to the flexible external gear 3.

[0092] In the robot joint device 130 configured in this manner, for example, when the cam 41 of the wave generator 4 rotates due to power generated by the drive source 101, relative rotation occurs between the flexible external gear 3 and the rigid internal gear 2. Then, as the flexible external gear 3 rotates relative to the rigid internal gear 2, relative rotation occurs between the first member 131 and the second member 132 about the output-side rotation axis Ax2 (coaxial with the input-side rotation axis Ax1). As a result, the robot joint device 130 can drive the first member 131 and the second member 132, which are connected via the strain wave gear device 1, to rotate relatively about the rotation axis Ax1. This makes it possible for the robot joint device 130 to realize various robot joint mechanisms.

[0093] (4) Application examples Next, an application example of the strain wave gear device 1, the actuator 100, and the robot joint device 130 according to this basic configuration will be described with reference to FIG.

[0094] 5 is a cross-sectional view showing an example of a robot 9 using a strain wave gear device 1 according to this basic configuration. This robot 9 is a horizontally articulated robot, a so-called SCARA (Selective Compliance Assembly Robot Arm) type robot.

[0095] As shown in FIG. 5, the robot 9 includes two robot joint devices 130 (including the strain wave gear device 1) and a link 91. The two robot joint devices 130 are provided at two joint portions of the robot 9, respectively. The link 91 connects the two robot joint devices 130. In the example of FIG. 5, the strain wave gear device 1 is a top hat type strain wave gear device rather than a cup type strain wave gear device. In other words, the strain wave gear device 1 illustrated in FIG. 5 uses a flexible external gear 3 formed in a top hat shape.

[0096] (Embodiment 1) As shown in Figures 6 and 7, the wave gearing 1A according to this embodiment differs from the wave gearing 1 according to the basic configuration mainly in that it is a top-hat type wave gearing. Hereinafter, components similar to those in the basic configuration will be assigned the same reference numerals and explanations will be omitted where appropriate. Figure 6 is a schematic cross-sectional view of the wave gearing 1A. Figure 7 is a schematic cross-sectional view of the wave gearing 1A, with an enlarged view of the main parts shown in the bubbles.

[0097] As shown in FIG. 6, the wave gear device 1A according to this embodiment includes a flexible external gear 3 formed in a top hat shape. This flexible external gear 3 has a flange portion 323 instead of a bottom portion 322 (see FIG. 1A). That is, the main body portion 32 of the flexible external gear 3 has a trunk portion 321 and a flange portion 323. The trunk portion 321 has a cylindrical shape in which at least the inner circumferential surface 301 is a perfect circle in a plan view when no elastic deformation occurs in the flexible external gear 3. The flange portion 323 is formed so as to extend outward (the side opposite the rotation axis Ax1) from one opening edge of the trunk portion 321 (the left side in FIG. 6), and has an annular shape in a plan view. In this embodiment, the trunk portion 321 and the flange portion 323 are integrally formed from a single metal member, thereby realizing a seamless main body portion 32.

[0098] The strain wave gearing 1A also includes a bearing member 5. The bearing member 5 has an inner ring 51 and an outer ring 52, and is a component for extracting the output of the strain wave gearing 1A as relative rotation between the inner ring 51 and the outer ring 52. In addition to the inner ring 51 and the outer ring 52, the bearing member 5 has a plurality of rolling elements 53. The inner ring 51 and the outer ring 52 are both annular components. The inner ring 51 and the outer ring 52 both have an annular shape that is a perfect circle in a plan view. The inner ring 51 is one size smaller than the outer ring 52 and is disposed inside the outer ring 52. Here, the inner diameter of the outer ring 52 is larger than the outer diameter of the inner ring 51, so a gap is created between the inner circumferential surface of the outer ring 52 and the outer circumferential surface of the inner ring 51.

[0099] A plurality of rolling elements 53 are disposed in the gap between the inner ring 51 and the outer ring 52. The plurality of rolling elements 53 are arranged in a row in the circumferential direction of the outer ring 52. The plurality of rolling elements 53 are all metal components of the same shape, and are provided at equal intervals over the entire circumferential area of the outer ring 52. More specifically, in this embodiment, the bearing member 53 is made of a cross roller bearing. This bearing member 5 is configured to withstand all of a radial load, a thrust load (a direction along the rotation axis Ax1), and a bending force (bending moment load) relative to the rotation axis Ax1.

[0100] The outer periphery of the flange portion 323 forms a boss 36 that is thicker than other portions of the flange portion 323. The boss 36 has an annular shape centered on the center (rotation axis Ax1) of the flange portion 323. The boss 36 has a sufficiently large thickness compared to portions of the flange portion 323 other than the boss 36, and has sufficient rigidity to fix the outer ring 52 of the bearing member 5. The boss 36 has multiple mounting holes that pass through the boss 36 (bottom portion 322) along the rotation axis Ax1, and the flexible external gear 3 is fixed to the outer ring 52 of the bearing member 5 with bolts B1 that pass through the mounting holes.

[0101] On the other hand, the rigid internal gear 2 is fixed to the inner ring 51 of the bearing member 5. Here, the rigid internal gear 2 and the flexible external gear 3 are concentrically arranged so that the center of both the rigid internal gear 2 and the center of the flexible external gear 3 are located on the rotation center of the bearing member 5 (rotation axis Ax1).

[0102] As a result, when the cam 41 of the wave generator 4 rotates about the rotation axis Ax1, a wave motion is generated in the external teeth 31 formed on the outer peripheral surface 303 of the flexible external gear 3. The generation of wave motion in the external teeth 31 causes the meshing position between the internal teeth 21 and the external teeth 31 to move in the circumferential direction of the rigid internal gear 2, generating relative rotation between the flexible external gear 3 and the rigid internal gear 2. Thus, the relative rotation between the rigid internal gear 2 and the flexible external gear 3 is output from the wave gear device 1A as relative rotation between the inner ring 51 and the outer ring 52 of the bearing member 5.

[0103] In this type of strain wave gearing 1A, for example, improving the concentricity between the rigid internal gear 2 and the flexible external gear 3 to achieve predetermined performance requires improving assembly precision, but this precision can vary depending on factors such as the skill of the worker. In this disclosure, "concentricity" refers to the degree to which the centers of rotation of multiple rotating objects coincide with each other, and is synonymous with coaxiality.

[0104] The wave gear device 1A according to this embodiment employs the configuration described below to realize a wave gear device 1A that easily achieves predetermined performance.

[0105] That is, as shown in FIG. 7, the wave gear device 1A according to this embodiment has a friction-welded portion 500 that joins a first component (the rigid internal gear 2 in this embodiment) and a second component (the inner ring 51 of the bearing member 5 in this embodiment).

[0106] The friction welding portion 500 is a joint (connection) formed by friction welding. In this disclosure, "friction welding" refers to a technique for joining two objects by using the frictional force (frictional heat) generated when the two objects are rubbed together. In other words, the friction welding portion 500 is a portion formed when a first part and a second part are rubbed together, and the first part and the second part are softened by frictional heat while pressure is applied to join the first part and the second part. Such a friction welding portion 500 can firmly join, for example, objects made of different materials, different metals, or different sizes.

[0107] According to this embodiment, for example, before the gear cutting process for forming the internal teeth 21 of the rigid internal gear 2 and before the raceway surface (outer circumferential surface) of the rolling elements 53 of the inner ring 51 is performed, the rigid internal gear 2 and the inner ring 51 can be joined at the friction-welded portion 500 and handled as a single component. Therefore, for example, the internal teeth 21 of the rigid internal gear 2 and the raceway surface of the inner ring 51 can be formed based on the outer diameter of the inner ring 51, and the concentricity between the rigid internal gear 2 and the bearing member 5 does not depend on the assembly work. Therefore, it is possible to improve the concentricity between the rigid internal gear 2 and the flexible external gear 3 and achieve predetermined performance, regardless of the skill level of the worker, etc.

[0108] Furthermore, because bolt holes or a spigot structure for joining the first component (the rigid internal gear 2 in this embodiment) and the second component (the inner ring 51 of the bearing member 5 in this embodiment) are no longer necessary, there is also the advantage of increased freedom in design layout. For example, compared to when a spigot structure is provided on the rigid internal gear 2 and the inner ring 51, it is easier to increase the pitch circle diameter (PCD) of the internal teeth 21 and the raceway diameter of the rolling elements 53. This also leads to an increase in the torque capacity and improved moment rigidity of the strain wave gear device 1A.

[0109] Furthermore, the friction welding portion 500 seamlessly and firmly joins the first part (the rigid internal gear 2 in this embodiment) and the second part (the inner ring 51 of the bearing member 5 in this embodiment), making it possible to improve the joining strength compared to joining using fasteners such as bolts.

[0110] In this embodiment, the first component is the rigid internal gear 2, and the second component is the inner ring 51 of the bearing member 5. Therefore, the rigid internal gear 2 and the inner ring 51 are joined at the friction-welded portion 500. Therefore, as described above, it is possible to improve the concentricity between the rigid internal gear 2 and the flexible external gear 3 and achieve predetermined performance, regardless of the skill level of the worker.

[0111] 7 and 8, in this embodiment, the friction welding portion 500 joins together opposing surfaces 201, 501 of a first component (the rigid internal gear 2 in this embodiment) and a second component (the inner ring 51 of the bearing member 5 in this embodiment) that face each other in an axial direction parallel to the rotation axis Ax1. That is, the friction welding portion 500 joins together at least the opposing surface 201 of the rigid internal gear 2 that faces one side in the axial direction (the left side in FIG. 8) and the opposing surface 501 of the inner ring 51 that faces the other side in the axial direction (the right side in FIG. 8). In this way, joining the opposing surfaces 201, 501 that face each other in the axial direction makes it possible to firmly join the first component and the second component.

[0112] Furthermore, the friction welding portion 500 joins at least the circumferential surfaces 202, 502 of the first component (the rigid internal gear 2 in this embodiment) and the second component (the inner ring 51 of the bearing member 5 in this embodiment) that face each other in a radial direction perpendicular to the rotation axis Ax1. That is, the friction welding portion 500 joins at least the circumferential surface 202 facing one radial direction (outward in FIG. 8) of the rigid internal gear 2 and the circumferential surface 502 facing the other radial direction (inward in FIG. 8) of the inner ring 51. In this way, by joining the circumferential surfaces 202, 502 that face each other in the radial direction, the first component and the second component can be firmly joined together.

[0113] Furthermore, the friction welding portion 500 joins at least the inclined surfaces 203, 503 of the first component (the rigid internal gear 2 in this embodiment) and the second component (the inner ring 51 of the bearing member 5 in this embodiment), which are inclined with respect to the rotation axis Ax1. That is, the friction welding portion 500 joins at least the inclined surface 203 of the rigid internal gear 2 and the inclined surface 503 of the inner ring 51. In this way, by joining the inclined surfaces 203, 503 inclined with respect to the rotation axis Ax1, the first component and the second component can be firmly joined.

[0114] In this embodiment, the friction welding portion 500 joins the first component (the rigid internal gear 2 in this embodiment) and the second component (the inner ring 51 of the bearing member 5 in this embodiment) around the entire circumference of the rotation axis Ax1. In other words, the first component and the second component are joined seamlessly at the friction welding portion 500 in the circumferential direction about the rotation axis Ax1, thereby achieving a strong bond. Moreover, by joining the first component and the second component seamlessly in the circumferential direction, it is possible to prevent the lubricant Lb1 from leaking from the gap between the first component and the second component without using an oil seal or the like.

[0115] 9 is an explanatory diagram that schematically shows a method for manufacturing the strain wave gear device 1A according to this embodiment. Fig. 9 shows steps related to the manufacturing of the first component (the rigid internal gear 2 in this embodiment) and the second component (the inner ring 51 of the bearing member 5 in this embodiment) that are joined at the friction welded portion 500 of the strain wave gear device 1A.

[0116] First, in the first step, the rigid internal gear 2 is moved closer to the inner ring 51 while the inner ring 51 is rotated about the rotation axis Ax1. In this state, the gear cutting process for forming the internal teeth 21 of the rigid internal gear 2 and the processing of the raceway surface (outer peripheral surface) of the rolling elements 53 in the inner ring 51 have not been performed, and the internal teeth 21 and the raceway surface have not yet been formed.

[0117] In the next second step, while the inner ring 51 is rotated about the rotation axis Ax1, pressure is applied to the rigid internal gear 2 so as to press the rigid internal gear 2 against the inner ring 51. At this time, the pressure applied to the rigid internal gear 2 is first set to a relatively small first value, and frictional heat is generated between the rigid internal gear 2 and the inner ring 51. Thereafter, the pressure applied to the rigid internal gear 2 is set to a second value larger than the first value, and the rigid internal gear 2 is pressed against the inner ring 51, thereby performing friction welding to join the two (upset step).

[0118] In the next third step, the rigid internal gear 2 and the inner ring 51 are joined at the friction welded portion 500. This makes it possible to treat the rigid internal gear 2 and the inner ring 51 as a single component joined by friction welding. At this point, any "burrs" that have occurred at the friction welded portion 500 are removed as appropriate.

[0119] In the next fourth step, gear cutting is performed to form the internal teeth 21 of the rigid internal gear 2, and the raceway surface (outer circumferential surface) of the rolling elements 53 of the inner ring 51 is processed. At this time, for example, the internal teeth 21 of the rigid internal gear 2 and the raceway surface of the inner ring 51 can be formed based on the outer diameter of the inner ring 51, and the concentricity of the rigid internal gear 2 and the bearing member 5 does not depend on the assembly work.

[0120] As explained above, the manufacturing method of the wave gear device 1A according to this embodiment includes a joining step and a centering step (including the fourth step). The joining step is a step of joining the first part and the second part at the friction welding portion 500 (i.e., by friction welding). The centering step is a step of setting the centers of rotation of the first part and the second part after the joining step.

[0121] In this embodiment, the joining step includes the first and second steps in Fig. 9. The centering step includes gear cutting to form the internal teeth 21 of the rigid internal gear 2, and processing the raceway surfaces (outer peripheral surfaces) of the rolling elements 53 in the inner ring 51. In other words, the centering step includes the fourth step in Fig. 9.

[0122] According to this aspect, in the centering step, the first part and the second part can be treated as a single part, so concentricity does not depend on the assembly work. Moreover, by forming the first part and the second part as a single part, the number of parts in the entire strain wave gear device 1A is reduced, and the assembly work is simplified. Furthermore, because the joining step is a step in which the first part and the second part are joined by friction welding, there is no need to use adhesives or the like to join the first part and the second part, and the environmental load is small.

[0123] (Variation) Embodiment 1 is merely one of various embodiments of the present disclosure. Various modifications of Embodiment 1 are possible depending on the design, etc., as long as the object of the present disclosure can be achieved. Furthermore, all drawings referred to in this disclosure are schematic diagrams, and the ratios of the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensional ratios. Modifications of Embodiment 1 are listed below. The modifications described below can be applied in appropriate combinations.

[0124] In the first embodiment, the first part is the rigid internal gear 2 and the second part is the inner ring 51 of the bearing member 5, but this configuration is not limiting. As an example, the first part may be the flexible external gear 3 and the second part may be the outer ring 52 of the bearing member 5. In this case, the flexible external gear 3 and the outer ring 52 of the bearing member 5 are joined by a friction-welded portion 500.

[0125] In the first embodiment, the friction welding portion 500 joins the opposing surfaces 201, 501, the peripheral surfaces 202, 502, and the inclined surfaces 203, 503 of the first and second parts, but is not limited to this configuration. For example, the friction welding portion 500 may join at least one of the opposing surfaces 201, 501, the peripheral surfaces 202, 502, and the inclined surfaces 203, 503.

[0126] Furthermore, it is not an essential configuration of the wave gear device 1A that the internal teeth 21 and the external teeth 31 are subjected to tooth profile modification. For example, at least one of the internal teeth 21 and the external teeth 31 does not have to be subjected to tooth profile modification.

[0127] Furthermore, the fact that each rolling element 423 is supported at four points in the bearing 42 is not an essential configuration for the strain wave gear device 1A; for example, each rolling element 423 may be supported at two points.

[0128] Furthermore, the strain wave gear device 1A is not limited to the top hat type described in the first embodiment, but may be, for example, a cup type, a ring type, a differential type, a flat type (pancake type), or a shield type.

[0129] Furthermore, the configuration of the actuator 100 is not limited to the configuration described in the first embodiment and can be modified as appropriate. For example, the connection structure between the input portion 103 and the cam 41 is not limited to a spline connection structure, and an Oldham coupling or the like may be used. By using an Oldham coupling as the connection structure between the input portion 103 and the cam 41, misalignment between the input-side rotation axis Ax1 and the wave generator 4 (cam 41) can be offset, and further, misalignment between the rigid internal gear 2 and the flexible external gear 3 can be offset. Furthermore, the cam 41 does not have to be movable along the rotation axis Ax1 relative to the input portion 103.

[0130] Furthermore, application examples of the strain wave gearing 1A, actuator 100, and robot joint device 130 according to this embodiment are not limited to the horizontal articulated robot described above, but may also be, for example, industrial robots other than horizontal articulated robots, or non-industrial robots. Examples of industrial robots other than horizontal articulated robots include vertical articulated robots and parallel link robots. Examples of non-industrial robots include domestic robots, nursing care robots, and medical robots.

[0131] Furthermore, bearing 42 is not limited to a deep groove ball bearing, but may be, for example, an angular contact ball bearing. Furthermore, bearing 42 is not limited to a ball bearing, but may be, for example, a roller bearing, such as a cylindrical roller bearing, a needle roller bearing, or a tapered roller bearing, in which rolling elements 423 are made of "rollers" that are not ball-shaped. Even if rolling elements 423 are not ball-shaped (spherical), a pressure difference occurs when rolling elements 423 roll, and rolling elements 423 function as a pump structure.

[0132] Furthermore, the material of each component of the strain wave gear device 1A, the actuator 100, or the robot joint device 130 is not limited to metal, but may be, for example, a resin such as engineering plastic.

[0133] Furthermore, the lubricant Lb1 is not limited to a liquid substance such as lubricating oil (oil), but may be a gel substance such as grease.

[0134] (summary) As described above, the wave gearing (1, 1A) according to the first aspect includes a rigid internal gear (2), a flexible external gear (3), and a wave generator (4). The rigid internal gear (2) is an annular component having internal teeth (21). The flexible external gear (3) is an annular component having external teeth (31) and is disposed inside the rigid internal gear (2). The wave generator (4) includes a non-circular cam (41) that is driven to rotate about the rotation axis (Ax1), and a bearing (42) that is attached to the outside of the cam (41). The wave generator (4) is disposed inside the flexible external gear (3) and generates a deflection in the flexible external gear (3). The strain wave gearing (1, 1A) deforms the flexible external gear (3) in accordance with the rotation of the cam (41), meshing some of the external teeth (31) with some of the internal teeth (21), and rotating the flexible external gear (3) relative to the rigid internal gear (2) in accordance with the difference in the number of teeth between the rigid internal gear (2). The strain wave gearing (1, 1A) has a friction welded portion (500) that joins the first component and the second component.

[0135] According to this aspect, for example, before the gear cutting process for forming the internal teeth 21 of the rigid internal gear 2 and before the raceway surface (outer circumferential surface) of the rolling elements 53 of the inner ring 51 is performed, the rigid internal gear 2, which is the first component, and the inner ring 51, which is the second component, can be joined at the friction-welded portion 500 and treated as a single component. Therefore, for example, the internal teeth 21 of the rigid internal gear 2 and the raceway surface of the inner ring 51 can be formed based on the outer diameter of the inner ring 51, and the concentricity between the rigid internal gear 2 and the bearing member 5 does not depend on the assembly work. Therefore, it is possible to improve the concentricity between the rigid internal gear 2 and the flexible external gear 3 and achieve predetermined performance, regardless of the skill level of the worker.

[0136] In the wave gear device (1, 1A) according to the second aspect, the first component is the rigid internal gear (2) and the second component is the inner ring (51) of the bearing member (5) in the first aspect.

[0137] According to this embodiment, the first component, the rigid internal gear (2), and the second component, the inner ring (51), can be joined at the friction welding portion (500) and treated as a single component, thereby improving the concentricity between the rigid internal gear (2) and the flexible external gear (3) and achieving the specified performance.

[0138] In the wave gear device (1, 1A) according to the third aspect, in the first or second aspect, the friction welding portion (500) joins opposing surfaces (201, 501) of the first component and the second component that face each other in at least an axial direction parallel to the rotation axis (Ax1).

[0139] According to this aspect, the first component and the second component can be firmly joined together.

[0140] In the wave gear device (1, 1A) according to the fourth aspect, in any one of the first to third aspects, the friction-welded portion (500) joins together at least the peripheral surfaces (202, 502) of the first and second components that face each other in a radial direction perpendicular to the rotation axis (Ax1).

[0141] According to this aspect, the first component and the second component can be firmly joined together.

[0142] In the wave gear device (1, 1A) according to the fifth aspect, in any one of the first to fourth aspects, the friction-welded portion (500) joins together at least the inclined surfaces (203, 503) of the first and second components that are inclined with respect to the rotation axis (Ax1).

[0143] According to this aspect, the first component and the second component can be firmly joined together.

[0144] In the wave gear device (1, 1A) according to the sixth aspect, in any one of the first to fifth aspects, the friction welded portion (500) joins the first part and the second part over the entire circumference of the rotation shaft (Ax1).

[0145] According to this aspect, a strong connection is achieved. Moreover, since the first component and the second component are connected seamlessly in the circumferential direction, it is possible to prevent the lubricant (Lb1) from leaking from the gap between the first component and the second component without using an oil seal or the like between the first component and the second component.

[0146] The manufacturing method of the wave gear device (1, 1A) according to the seventh aspect is a manufacturing method of the wave gear device (1, 1A) according to any one of the first to sixth aspects, and includes a joining step of joining the first part and the second part at the friction-welded portion (500), and a centering step of setting the rotation centers of the first part and the second part after the joining step.

[0147] According to this embodiment, it is possible to improve the concentricity between the rigid internal gear (2) and the flexible external gear (3) and to achieve a predetermined performance.

[0148] A robot joint device (130) according to the eighth aspect includes a wave gear device (1, 1A) according to any one of the first to sixth aspects, a first member (131) fixed to the rigid internal gear (2), and a second member (132) fixed to the flexible external gear (3).

[0149] According to this embodiment, it is possible to improve the concentricity between the rigid internal gear (2) and the flexible external gear (3) and to achieve a predetermined performance.

[0150] The configurations according to the second to sixth aspects are not essential for the strain wave gear device (1, 1A) and can be omitted as appropriate. [Explanation of symbols]

[0151] 1,1A Strain Wave Gearing 2 Rigid internal gear (first part) 3 Flexible external gear 4. Wave Generator 5 Bearing materials 21 Inner teeth 31 Outer teeth 41 Cam 42 bearings 51 Inner ring (second part) 130 Robot joint device 131 First member 132 Second member 201,501 Opposite surface 202,502 circumferential surface 203,503 Slope 500 Friction welded part Ax1 Rotation axis

Claims

1. an annular rigid internal gear having internal teeth; an annular flexible external gear having external teeth and disposed inside the rigid internal gear; a wave generator that has a non-circular cam that is driven to rotate around a rotation axis and a bearing attached to the outside of the cam, and is disposed inside the flexible external gear and causes deflection in the flexible external gear, a strain wave gear device in which the flexible external gear is deformed in accordance with the rotation of the cam, a portion of the external teeth is meshed with a portion of the internal teeth, and the flexible external gear is rotated relative to the rigid internal gear in accordance with a difference in the number of teeth between the flexible external gear and the rigid internal gear, a friction welded portion that joins the first component and the second component; Wave gearing.

2. The first component is the rigid internal gear, the second component is an inner ring of a bearing member; The strain wave gear device according to claim 1 .

3. The friction welded portion joins opposing surfaces of the first component and the second component that face each other in at least an axial direction parallel to the rotation axis. The strain wave gear device according to claim 1 or 2.

4. The friction-welded portion joins at least peripheral surfaces of the first component and the second component that face each other in a radial direction perpendicular to the rotation axis. The strain wave gear device according to claim 1 or 2.

5. The friction-welded portion joins at least inclined surfaces of the first component and the second component that are inclined with respect to the rotation axis. The strain wave gear device according to claim 1 or 2.

6. the friction welded portion joins the first component and the second component over the entire circumference of the rotating shaft, The strain wave gear device according to claim 1 or 2.

7. A method for manufacturing the strain wave gear device according to claim 1 or 2, comprising the steps of: a joining step of joining the first component and the second component at the friction welded portion; a centering step of setting rotation centers of the first component and the second component after the joining step. A method for manufacturing a strain wave gear device.

8. The wave gear device according to claim 1 or 2; a first member fixed to the rigid internal gear; and a second member fixed to the flexible external gear. Robotic joint device.

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